Note: Descriptions are shown in the official language in which they were submitted.
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Title: COEXTRUDED ADHESIVE CONSTRUCTIONS
Cross Reference to Related Application
This application is a continuation-in-part of copending U.S.
application serial number 09/148,365 filed September 4, 1998, the written
description and claims of which are hereby incorporated by reference in their
entirety.
Field of the fnv<:n_ lion
The prasent invention relate, to thin coextruded adhesive
constructions used for making tags, labels, signs, decals and the like and,
more
particularly, to highly-conformable, cost efficient coextruded pressure-
sensitive
adhesive constructions.
Backarnund of the Invention
Pressure-sensitive adhesive (P'SA) constructions such as labels,
tapes, decals, signs and the Like are known in the art. For example, PSA label
constructions are commonly used to apply a particular facestock having a
specific nature of printing to an object or article. PSA label constructions
typically comprise a release liner, a PSA layer disposed onto the liner, and a
facestock laminated onto the PSA layer. This lamination may be formed by first
coating or laminating the PSA to the liner, then laminating the facestock onto
the PSA-coated liner; or alternatively by coating or laminating the PSA to the
facestock, then the PSA-coated facestocb; onto the liner. The facestock is
characteristically made from a web or sheet of paper, cardboard or plastic,
which is printed on with information or other indicia either before or after
it is
laminated to the PSA and liner. In a typical process of "converting" the
facestock/PSA/liner laminate, the laminate its printed on the exposed
facestock
surface, the laminate is die-cut down to the liner surface to outline the
label
shape, and the waste material between the labels (matrix) is stripped out. The
PSA label facestock and adhesive is then adhered to a substrate surface by
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separating the label from the liner and causing the PSA layer of the label to
come into contact with the substrate surface. In the most popular labeling
process, the label is separated from the linE~r by bending the liner back over
a
peel plate, whereupon the label is sufficiently stiff to cause the label to
continue
on a straight path toward the desired substrate surface.
As used in this patent application, "separation" refers to removal
of the label from the liner, "application" refers to adhesion of the label to
the
substrate surface, and "dispensing" or "dispensability" refers to the combined
steps of separation and application. "Peel plate dispensing" denotes the use
of
a peel plate or other similar device having a small radius of curvature in the
separation of liner from label.
The term "faceless" pressure sensitive adhesive constructions is
used in the present application to refer to 'the very thin (e.g., less than 1
mil,
preferably 0.1 to 0.5 or 0.6 mils), and to contrast the manufacturing methods
disclosed herein from conventional PSA label construction manufacturing
methods. As discussed above, in conventional manufacture of PSA label
materials, a self supporting preformed wf;b or sheet is laminated to a PSA
("preforrned" means that the facestock had been formed into a self supporting
web or sheet in a previous manufacturing process, and in the case of a liquid
or
molten facestock material, that the material has been dried or hardened?.
Faceless constructions of the present invention are formed by coextrusion of a
film forming material (herein sometimes relPerred to as "FFM"y and an adhesive
whereby the facestock web or sheet and tlhe adhesive are formed in situ.
In the manufacture and production of PSA constructions, a
substantial amount of the overall cast involved is attributed to the material
costs
for the different material layers, e.g., the I'SA and the facestock, be it
paper,
cardboard, or plastic. The layer thickneases and layer materials for such
conventional PSA constructions have been selected to provide desired
properties
of convertibility, e.g., by conventional converting techniques such as by die-
cutting and matrix-stripping; dispensability, e.g., by conventional dispensing
equipment such as by peel plate; and conformability, e.g., enabling the
applied
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PCTJUS99120295
label to adhere to an irregular or deformable substrate surface without
becoming
detached or damaged.
It is known that the stiffness of a PSA construction will have an
impact on its convertibility and dispensability. The stiffness of a label of a
given
material decreases as the label is made thinner. As a rule of thumb, as the
construction stiffness is increased so is convertibility and dispensability of
the
construction. However, the conformability of a PSA construction is known to
decrease as the construction stiffness is increased. Thus, the objective
stiffness
for a PSA construction is a compromise between convertibility/dispensability
and
conformability and cost. Tao low a stiffness of the label will cause the label
to
go around the peel plate with the liner. It is one objective of this invention
to
provide a minimal material label construcaion with enough stiffness to be
dispensable using a peel plate.
Prior art PSA constructions hawing a Gurley stiffness of at least 10
and mare commonly of at least 20 or greater are known and are described in
U.S. Patent Nos. 5,186,782; 5,516,393; 4,713,273; and 5,451,283. The
'782, '393 and '283 patents exploited the idea that a proper differential
between machine direction stiffness and cross dimension stiffness, with the
latter being the lower of the two, could enable a heat-set film to be
dispensed
at high speeds, yet be suitable for flexible-film end uses. Such label film
might
exhibit acceptable overall conformability to flexible substrates even though
the
film has less inherent conformability than the then standard polymer labels
based on polyvinyl chloride fPVC?.
Specific end uses calling for highly-conforrnabte PSA constructions
include those where the label is to be adhered to a srnali-diameter contoured
surface or irregular surface. In such an end use, unnecessary construction
stiffness or rigidity could interfere with label's ability to conform and
remain
adhered to the underlying substrate surface. Additionally, these conventional
PSA constructions are not manufactured in a most economically efficient
manner.
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PCT/US99/20295
Additionally, conventional PSA, label constructions are not well
suited for specific uses such as label urea where the label and underlying
substrate are subjected to particular prcEcess conditions. For example,
conventional PSA label constructions comprising a paper facestock and/or
lacking necessary properties of conformaloility are known to be adversely
affected when used on glass beverage bottles, during the washinglrinsing,
filling
and pasteurization process, due not only the decomposition of the paper
facestock itself but also to the failure of lthe PSA to remain adhered to the
substrate surface. ft is believed that such label lifting can be attributed to
the
rigidity or stiffness of such conventional PSA labels that, once the PSA is
heated, causes the label and PSA to peek away and lift from the substrate
surface. in this instance, to avoid damage to the paper label, the paper
labels
are applied to a bottle after it has been rin:>ed, filled, and pasteurized,
i.e., the
label is "post applied". Generally, printed paper labels are post applied to
filled
1 b bottles using aqueous adhesives or hot melt adhesives.
If post-applied paper labels .are not completely adhered to the
bottle, are misaligned on the bottle, or are otherwise incorrectly applied to
the
filled bottle, then the entire bottle and contents will be unusable and must
be
discarded. Thus, it is desired that glass bottles be labeled and inspected
prior
to being filled and pasteurized to eliminate: defective bottles or labels.
It is known in the art to use certain high-performance acrylic PSA
to pre-apply plastic labels to glass bottles following bottle formation at a
bottle
manufacturing plant. Examples include tJptiflex labels available from Ffexcon,
and Primeline label films available from Polykote Corporation. While these
labels
can generally withstand the bottle washing/rinsing, filling, and
pasteurization
operations at a bottle filling plant, they make use of specialized adhesives,
such
as solvent or emulsion acrylics, that are economically undesirable from a
manufacturing perspective, making them an unattractive option when compared
to conventional gum-type labels.
it is, therefore, desired to provide a thin PSA construction for use
as a label, tag, decal, sign and the like. 1n one embodiment, it is desired
that
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any printed message or indicia on such consitruction be protected from damage
that can be caused by contact with adjacent physical objects or by exposure to
moisture, weather and the like. Also, it is desired that the PSA label
construction be convertible by die-cutting and matrix-stripping methods at
high
5 speeds, and be highly conformable. It is further desired that such PSA
construction be capable of withstanding rinsing, filling, and pasteurization
operations when applied to a glass beverage bottle to permit its use as a pre-
applied label. Such PSA constructions also are useful in labelling of fruit
and in
this application, the labels should be resistant to moisture in view of the
various
transport methods used including floating the labelled fruit in various
solutions
during sorting, cleaning, etc. 1t is also desired that the PSA Label
construction
be manufactured in an economically efficient manner when compared to
conventional PSA constructions.
Summary of the Invention
1 b A die-cuttable and matrix-strippable adhesive construction is
described which comprises a coextrudate comprising
A. a continuous polymeric film having an upper surface
and a lower surface, and a thickness of from about 0.1 mil up to about 1 mil,
and
B. an adhesive layer having an upper and lower surface
wherein the upper surface of the adhesive Ifayer is adhesively joined to the
lower
surface of the polymer film, provided thait when the adhesive of the adhesive
layer comprises a thermoplastic component and a solid tackifier resin
component, the thickness of the polymeric; film (A) may be up to 1.5 or 2
mils.
2b The invention also relates to a die-cuttable and matrix strippable
pressure sensitive adhesive label construc;tian comprising
A. a coextrudate comprising
A-1. a continuous polymeric film having an upper
surface and a lower surface, and a thickness of from about 0.1 to about 1 mil,
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PCTIUS99I20295
A-2. a pressure sensitive adhesive layer having an
upper and lower surface wherein the upper surface of the adhesive layer is
adhesively joined to the lower surface of the polymeric film, and
B, a substrate having a release surface wherein the
release surface is in contact with the lower surface of the adhesive layer of
the
coextrudate provided, however; that when the adhesive of the adhesive layer
comprises a thermoplastic elastomer component and a solid tackifier component,
the thickness of the polymer film (A) may be up to 2 mils. Far some
applications, particularly when the thickness of the continuous polymeric
films
are at the lower end of the ranges specified, the stiffness and other
properties
of the construction can be improved by overlaminating another polymer film
over
the continuous polymer film. Alternatively when the constructions do not have
the required stiffness for peel-plate dispensing, hand dispensing and other
dispensing techniques described in U.S. Patents 4;217,164, 4,303,461 and
1 b 4,896,793 can be used for dispensing the constructions onto a given
substrate.
Die-cut labels also are described which are prepared by die-cutting
the die-cuttable and matrix-strippable adhesive constructions of the
invention,
particularly, those adhesive constructions described above which contain the
coextrudate in combination with a substrate having a release surface, wherein
the release surface is in contact with a lower surface of the adhesive layer
of
the coextrudate. Generally, the substrate having a release surface is a
release
coated liner or carrier. Methods for preparing the adhesive constructions and
die-cut labels are also described.
Brief Descriation o~f the Drawinas
Fig. 1 is a schematic side elevation of a method of making an
adhesive construction of the invention;
Fig. 1 A is a cross-sectional ride view of an adhesive construction
of the invention as prepared in Fig. 1.
Fig. ~ 1 B is a cross-sectional side view of another adhesive
construction of the invention as prepared in Fig. 1.
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PCTNS99120295
Fig. 2 is a schematic side elevation of another method of making
an adhesive construction of the invention.
Fig. 3 is a cross-sectional side view of an overiaminated adhesive
construction of the invention.
Fig. 4 is a cross-sectional side view of another overlaminated
adhesive construction of the invention.
Detailed Description of the Invention
The present invention is direc;ted to thin, printable, convertible,
dispensable, and conformable coextruded adhesive constructions generally
comprising (A) a thin continuous layer of a polymeric film of from about 0.1
mil
up to about 1 or 2 mils, and (B) an adhesive: layer which is adhesively joined
to
the lower surface of the polymeric film. A significant advantage of such
coextrudates, is that there is provided a tf~chnique for forming very thin
label
construction of a low caliper printable film laminated to a hot melt PSA. Such
thin film PSA label constructions are not gE:nerally available using
conventional
manufacturing processes because of the diifficulty in handling such thin
polymer
films which may be as thin as from 0.2: to about 0.5 or 0.6 rnil. In one
embodiment, the thin continuous layer of polymer film (A) may comprise more
than one film layer. Thus, the film (A) may be a multilayer polymeric film
containing up to 9 or 10 thin polymer layer or even up to 500 or 1000 polymer
film layers.
In a first embodiment, the polymeric film of the coextrudate can be
obtained from any polymeric material that is capable of being coextruded with
a variety of adhesives, and more particularly, as described below, with
pressure
sensitive adhesives. For example, it may be desired that the polymeric film
material have a solubility parameter that is inconsistent with or incompatible
with that of the adhesive to prevent migration between the two layers when
coextruded. The polymeric film material <~Iso should, when combined with the
adhesive layer, provide a sufficiently selif-supporting construction to
facilitate
label dispensing (label separation and application.) Alternatively, when the
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polymeric film combined with the adhesive i~~ not sufficiently self-
supporting, an
averlaminate layer can be applied to the exposed face of the polymeric film to
provide additional stiffness and dispensability; as well as other properties
as
described more fully below. Preferably, the polymeric film material is chosen
to
provide the construction with the desired properties such as printability, die-
cuttability, matrix-strippability, dispensability, etc.
The polymeric film materials useful in the coextrudates of the
present invention include polystyrenes, polyoiefins, polyamides, polyesters,
polycarbonates, polyvinyl alcohol, polyethylene vinyl alcohol), polyurethanes,
polyacrylates, poiy(vinyl acetates), ionomers and mixtures thereof. In one
preferred embodiment, the polymeric film m<~terial is a polyolefin. The
polyolefin
film materials generally are characterized as having a melt index or melt flow
rate of less than 30, more often less than 20, and most often less than 10 as
determined by ASTM Test Method 1238.
The polyolefins which can be utilized as the polymeric film material
include polymers and copolymers of ethylene, propylene, 1-butane, etc., or
blends of mixtures of such polymers and copolymers. Preferably, the
polyolefins
comprise polymers and copolymers of ethylene and propylene. In another
preferred embodiment, the polyoiefins comprise propylene homopolymers, and
copolymers such as propylene-ethylene and propylene-1-butane copolymers.
Blends of polypropylene and polyethylene with each other, or blends of either
or both of them with polypropylene-polyethtylene copolymer also are useful. in
another embodiment, the poiyofefin film rnaterials are those with a very high
propylenic content, either polypropylene homopolymer or propylene-ethylene
copolymers or blends of polypropylene and polyethylene with low ethylene
content, or propylene-1-butane copolymers or blend of polypropylene and pofy-
1-butane with low butane content.
Various polyethylenes can be utilized as the polymeric film material
including low, medium, and high density polyethylenes. An example of a useful
tow density polyethylene (LDPE) is Rexene: 1017 available from Huntsman.
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The propylene homopolymer:~ which can be utilized as the
polymeric fiilm material in the constructions of the invention, either alone,
or in
combination with a propylene copolymer as described herein, include a variety
of propylene homopolymers such as those (having melt flow rates (MFR) fram
about 0.5 to about 20 as determined by ASTM Test D 1238, condition L. In
one embodiment, propylene homopoiymers having MFR's of less than 10, and
mare often from about 4 to about 10 are particularly usefiul and provide
facestocks having improved die-cuttability. Useful propylene homopolymers also
may be characterized as having densities in the range of from about 0.88 to
about 0.92 g/cm3. A number of useful propylene homopafymers are available
commercially from a variety of sources, and some useful polymers include:
5A97, available from Union Carbide and h<~ving a melt flow of 12.0 g/10 min
and a density of 0.90 g/cm3; DX5E66, also available from Union Carbide and
having an MFI of 8.8 g/10 min and a densiity of 0.90 g/cm3; and WRDS-1057
from Union Carbide having an MFI ofi 3.9 g/10 min and a density of 0.90 g/cm3.
Usefiul commercial propylene hamopolyme:rs are also available from Fina and
Montel.
Particularly useful polyamide resins include resins available from
EMS American Griton Inc., Sumter, SC. under the general tradename Grivory
such as CF6S, CR-9, XE3303 and G-21. Grivory G-21 is an amorphous nylon
copolymer having a glass transition temperature of 125°C, a melt flow
index
(DIN 53735) of 90 m1/10 .min arid an elongation at break (ASTM D638) of 15.
Grivory CF65 is a nylon 6/12 film grade reain having a melting point of 135
° C,
a melt flow index ofi 50 mU10 min, and an elongation at break in excess of
350%. Grilon CR9 is another nylon 6/12 film grade resin having a melting point
of 200°C, a melt flow index of 200 ml/ 10 min, and an elongation at
break at
250%. Grilon XE 3303 is a nylon 6.6/6.10 film grade resin having a melting
point of 200°C, a melt flow index of 60 ml/ 10 min, and an elongation
at break
of 100%. Other useful pofyamide resins include those commercially available
from, for example, Union Camp of Wa~yne, New Jersey under the Uni-Rez
product fine, and dimer-based polyamide resins available from Bostik, Emery,
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Fuller, Henkel (under the Versamid product liney. Other suitable polyamides
include those produced by condensing dimerized vegetable acids with
hexamethylene diamine. Examples of polya~mides available from Union Camp
include Uni-Rez 2665; Uni-Rez 2620; Uni-Re;z 2623; and Uni-Rez 2695. Some
5 of the physical properties of polymer films formed from the Uni-Rez
polyamides
are summarized in the following Table I.
Table
Brookfield Tensile Percent
Uni-Rez Softening Viscosity Strength Ultimate
10 Pro uct Point tC,~,(cPs at 190C~jPSI Elongation
2620 105 900 1000 50
2623 106 6500 1000 400
2665 165 11,000 2000 500
2695 128 5000 200 175
2620/2623 128 5100 1000 313
(blend at 1:31
Polystyrenes can also be utilized as the polymeric film material in
the coextruded adhesive constructions of the invention and these include
homopolymers as well as copolymers of styrene and substituted styrene such
as alpha-methyl styrene. Examples of styrene copolymers and terpolymers
include: acrylonitrile-butene-styrene (ABS); styrene-acrylonitrile copolymers
(SAN); styrene butadiene (SB); styrene-malefic anhydride (SMA); and styrene-
methyl methacrylate (SMMA); etc. An example of a useful styrene copolymer
is KR-7 0 from Phillips Petroleum Co. KR-1 CI is believed to be a copolymer of
styrene with 1,3-butadiene.
Polyurethanes also can be utilized as the polymeric film material in
the coextruded adhesive constructions of thE> invention, and the polyurethanes
may include aliphatic as well as aromatic polyurethanes.
Polyesters prepared from various glycols or polyols and one or more
aliphatic or aromatic carboxylic acids also are useful fitm materials.
Polyethylene
terephthalate (PET) and PETG (PET modified with cyclohexanedimethanol) are
useful film forming materials which are available from a variety of commercial
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sources including Eastman. For example, Kodar 6763 is a PETG available from
Eastman Chemical. Another useful polyester from duPont is Selar PT-8307
which is polyethylene terephthalate.
Acrylate polymers and copolymers and alkylene vinyl acetate resins
(e.g., EVA polymers) also are useful as the film forming materials in the
preparation of . the coextruded adhesive constructions of the invention.
Commercial examples of available polymers include Escorene UL-7520 (Exxon),
a copolymer of ethylene with 19.3% vinyl acetate; Nucrell 699 (duPont), an
ethylene copolymer containing 1 1 % of methacrylic acid, etc.
lonomers (polyolefins containing ionic bonding of molecular chains)
also are useful. Examples of ionomers include ionomeric ethylene copolymers
such as Surlyn 1706 (duPont) which is believed to contain interchain ionic
bonds
based on a zinc salt of ethylene methacrylic acid copolymer. Suriyn 1702 from
duPont also is a useful ionomer.
Polycarbonates also are useful, and these are available from the
Dow Chemical Co. (Calibre) G.E. Plastics (Lexan) and Bayer (Makrolon). Most
commercial polycarbonates are obtained by the reaction of bisphenol A and
carbonyl chloride in an interfacial process. Molecular weights of the typical
commercial polycarbonates vary from about 22,000 to about 35,000, and the
melt flow rates generally are in the range of from 4 to 22 g/10 min.
The polymeric film material may contain inorganic fillers and other
organic or inorganic additives to provide desired properties such as
appearance
properties (opaque or colored films), durability and processing
characteristics.
Nucleating agents can be added to increa:~e crystallinity and thereby increase
stiffness. Examples of useful materials include calcium carbonate, titanium
dioxide, metal particles, fibers, flame retardants, antioxidant compounds,
heat
stabilizers, light stabilizers, ultraviolet light stabilizers, antiblocking
agents,
processing aids, acid acceptors, etc.
Various nucleating agents anti pigments can be incorporated into
the films of the present invention. The amount of nucleating agent added
should be an amount sufficient to provide the desired modification of the
crystal
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structure while not having an adverse efifeci: on the desired properties of
the
films. It is generally desired to utilize a nucl~;ating agent to modify the
crystal
structure and provide a large number of considerably smaller crystals or
spherulites to improve the transparency (clarity), and stiffness, and the die-
cuttabiiity of the film. Obviously, the amount of nucleating agent added to
the
film formulation should not have a deleterious affect on the clarity of the
film.
Nucleating agents which have been used heretofore for polymer films include
mineral nucleating agents and organic nucleating agents. Examples of mineral
nucleating agents include carbon black, silica, kaolin and talc. Among the
organic nucleating agents which have been suggested as useful in polyolefin
films include salts of aliphatic mono-basic or di-basic acids or aryalkyi
acids such
as sodium succinate, sodium glutarate, sodium caproate, sodium 4-
methylvalerate, aluminum phenyl acetate, and sodium cinnamate. Alkali metal
and aluminum salts ofi aromatic and alicyclic carboxylic acids such as
aluminum
benzoate, sodium or potassium benzoate, sodium betanaphtholate, lithium
benzoate and aluminum tertiary-butyl benzoate also are useful organic
nucleating
agents. Substituted sorbitol derivatives such as bis (benzylidene) and bis
(alkylbenzilidine) sorbitols wherein the alkyl groups contain from about 2 to
about 18 carbon atoms are useful nucleating agents. More particularly,
sorbitol
derivatives such as 1,3,2,4-dibenzylidE:ne sorbitol, 1,3,2;4-di-para-
methylbenzylidene sorbitol, and 1,3,2,4-di-pare-methylbenzylidene sorbitol are
effective nucleating agents for polypropylenf;s. Useful nucleating agents are
commercially available from a number of sources. Milled 8C-41-10, (a
concentrate of 10% Miilad 3988 and 90% polypropylene), Milled 3988 and
Milled 3905 are sorbitol nucleating agents available from Milliken Chemical
Co.
The amounts of nucleating agent incorporated into the film
formulations of the present invention generally range from about 100 to about
6000 ppm of the film. In another embodiment, the amount of nucleating agent
is in the range of about 1000 to about 500() ppm, mare preferably of about
1500 to 3500 ppm, mare preferably about 2000 to 2500 ppm.
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The polymeric film material is chosen to provide a continuous
polymer film in the coextrudate with the desired properties such as improved
printability, weatherability, strength, water resistance, abrasion resistance,
gloss, die-cuttability, matrix strippability and other properties. It is
particularly
desirable that the surface of the film can be printed or adapted to be printed
with inks using printing techniques such as flexographic printing, screen
printing, offset lithography, letter press, thermal transfer, etc., and that
the
applied ink has acceptable adhesion to the surface of the film of the adhesive
constructian. The choice of polymeric film forming material also is determined
by its physical properties such as melt viscosity, high speed tensile
strength,
percent elongation etc. As will be discussed in more detail below, coextrusion
of the polymeric film material and the adhesive to form the coextrudate is
facilitated when the melt viscosities of the two materials, i.e., the
polymeric film
material of the first Dayer and the adhesive material, are similar. Thus, the
choice of polymeric film material to be utilized in the formation of the
coextruded adhesive constructions of the present invention may be dependent
upon the melt viscosity of the adhesive being coextruded with the polymeric
film
forming material. In one embodiment, the pc>lymeric film material of the first
layer has a hot melt viscosity that is within a factor of from about 0.07 to
about
15 times, more often greater than 1 to about 15 times, and preferably from 1
up to about 10 times the hot melt viscosity of the adhesive at the shear rates
incurred during the coextrusion process: Generally the shear rates range from
about 100 sec-' to about 10,000 sec-'.
The thickness of the polymer film material is from about 0.1 to
about 1.5 or even 2.0 mils. More often the thickness of the film is from about
0.2 to about 1.0 mil. A thickness of about 0.5 mils is particularly useful.
The
continuous polymeric film may comprise a single layer or the film can be a
multilayer film of two or more adjacent coextruded layers. For example the
film
can comprise one layer of a polyolefin and one layer of a blend of a
polyolefin
and a copolymer of ethylene and vinyl acetate: (EVA). In another embodiment
the film comprises three layers, a base or core layer of, for example, a
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polyolefin, and skin layers in both sides of thc: base or core layer which may
be
comprised of the same or different polymer blends.
Turning now to the adhesives, the coextrudate constructions of the
present invention also include an adhesive layer (hereinafter sometimes
referred
to as "substrate adhesive") having an upper surface and a lower surface
wherein
the upper surface of the adhesive layer is adhesively joined to the lower
surface
of the polymer film. The adhesive may be a heat-activated adhesive, a hot melt
adhesive, or a pressure sensitive adhesive (PSA). Adhesives which are tacky at
any temperature up to about 160 ° C (about 320 ° F) are
particularly useful. PSAs
which are tacky at ambient temperatures are particularly useful in the
coextruded adhesive constructions of the present invention. A variety of
conventional PSAs can be utilized provided that the viscosity is or can be
modified to be similar to the viscosity of thE; polymeric film material which
is
being coextruded with the adhesive. Useful PSA compositions are fluid or
pumpable at the temperatures used in the melt processing. Also, the adhesive
compositions should not significantly degrade or gel at the temperature
employed and over the time required for melt processing and extrusion.
Typically, the adhesive compositions have a viscosity of from 1000 poise to
1,000,000 poise at the processing ternperat~ure.
The adhesives may generally be classified into the following
categories:
Random copolymer adhesives such as those based upon acrylate
and/or methacrylate copolymers, a-olefin copolymers, silicone copolymers,
chloroprene/acryionitrile copolymers, and the like.
Block copolymer adhesives including those based upon linear block
copolymers (i.e., A-B and A-B-A type), branched block copolymers, star block
copolymers, grafted or radial block copolymers, and the like, and
Natural and synthetic rubber adhesives.
A description of useful pressure-sensitive adhesives may be found in
Encyclopedia of Polymer Science and Engineering, Vol. 13. Wiley-Interscience
Publishers (New York, 1988). Additional description of useful pressure-
sensitive
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adhesives may be found in Encyc%pedia of Polymer Science and Technology,
~/ol. 1, lnterscience Publishers (New York, 1964).
Commercially available pressure--sensitive adhesives are useful in
the invention. Examples of these adhesives include the hot melt pressure-
5 sensitive adhesives available from H.B. Fuller (:ompany, St. Paul, Minn. as
HM-
1597, HL-2207-X, HL-2115-X, HL-2193-X. Other useful commercially
available pressure-sensitive adhesives includle those available from Century
Adhesives Corporation, Columbus, Ohio.
Conventional PSAs, including silicone-based PSAs, rubber-based
10 PSAs, and acrylic-based PSAs are useful. Another commercial example of a
hot
melt adhesive is H2187-01, sold by Ato Findley, Inc., of Wauwatusa,
Wisconsin. in addition, rubber based block copolymer PSAs described in U.S.
Patent 3,239,478 (Harlan) also can be utilized in the coextruded adhesive
constructions of the present invention, and this patent is hereby incorporated
by
15 a reference for its disclosure of such hot melt adhesives.
In ane preferred embodiment, the pressure sensitive adhesive
utilized in the present invention comprise rubber based elastomer materials
such
as linear, branched, graft or radial block copolymers represented by the
diblock
structures A-B, the triblock A-B-A, the radial or coupled structures (A-B)",
and
combinations of these where A represents a hard thermoplastic phase or block
which is non-rubbery or glassy or crystalline at room temperature but fluid at
higher temperatures, and B represents a soft block which is rubbery or
elastomeric at service or room temperature. These thermoplastic elastomers
may comprise from about 75% to about 95°/~ by weight of rubbery
segments
and from about 5% to about 25% by weight of non-rubbery segments.
The non-rubbery segments or hard blocks comprise polymers of
mono- and polycyclic aromatic hydrocarbons, and more particularly vinyl-
substituted aromatic hydrocarbons which may be monocyclic or bicyclic in
nature. The preferred rubbery blocks or segments are polymer blocks of
homopolymers or copolymers of aliphatic conjugated dienes. Rubbery materials
such as polyisoprene, polybutadiene, and strrrene butadiene rubbers may be
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16
used to form the rubbery block or segment:. Particularly preferred rubbery
segments include polydienes and saturated olefin rubbers of ethylene/butylene
or ethyleneipropylene copolymers. The latter rubbers may be obtained from the
corresponding unsaturated polyalkylene moiEaies such as polybutadiene and
polyisoprene by hydrogenation thereof.
The block copolymers of vinyl aromatic hydrocarbons and
conjugated dienes which may be utilized include any of those which exhibit
elastomeric properties. The block copolymers may be diblock, triblock,
multiblock, starbiock, polyblock or graftblock copolymers. Throughout this
specification and claims, the terms diblock, trilblock, multiblock, polyblock,
and
graft or grafted-block with respect to the strucl:ural features of block
copolymers
are to be given their normal meaning as defined in the literature such as in
the
Encyclopedia of Polymer Science and Engineering, Vol. 2, ( 1985) John Wiley &
Sons, Inc., New York, pp. 325-326, and by J.E. McGrath in Block Copolymers,
Science Technology, Dale J. Meier, Ed., Harwood Academic Publishers, 1979,
at pages 1-5.
Such block copolymers may contain various ratios of conjugated
dienes to vinyl aromatic hydrocarbons including those containing up to about
40% by weight of vinyl aromatic hydrocarbon. Accordingly, mufti-block
copolymers may be utilized which are linear or radial symmetric or asymmetric
and which have structures represented by the formulae A-B, A-B-A, A-B-A-B,
B-A-B, (AByo,~,Z...BA, etc., wherein A is a polymer block of a vinyl aromatic
hydrocarbon or a conjugated diene/vinyl aromatic hydrocarbon tapered
copolymer block, and B is a rubbery polymer block of a conjugated diene.
The block copolymers may be prE;pared by any of the well-known
block polymerization or copolymerization procedures including sequential
addition of monomer, incremental addition of monomer; or coupling techniques
as illustrated in, for example, U.S. Patents 3,251,905; 3,390,207; 3,598,887;
and 4,219,627. As is well known, tapered copolymer blocks can be
incorporated in the mufti-block copolymers by copolymerizing a mixture of
conjugated diene and vinyl aromatic hydrocarbon monomers utilizing the
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17
difference in their copolymerization reactivity rates. Various patents
describe
the preparation of multi-block copolymers containing tapered copolymer blocks
including U.S. Patents 3,251,905;3,639,521; and 4,208,356, the disclosures
of which are hereby incorporated by reference.
Conjugated dienes which may bc: utilized to prepare the polymers
and copolymers are those containing from 4 to about 10 carbon atoms and more
generally, from 4 to 6 carbon atoms. Examples include from 1,3-butadiene,
2-methyl-1,3-butadiene (isoprene), 2,3-dime~thyi-1,3-butadiene, chloroprene,
1,3-pentadiene, 1,3-hexadiene, etc. Mixtures of these conjugated dienes also
may be used. The preferred conjugated dienes are isoprene and 1,3-butadiene.
Examples of vinyl aromatic hydrocarbons which may be utilized to
prepare the copolymers include styrene and the various substituted styrenes
such as o-methyistyrene, p-methylstyrene, p-t~ert-butylstyrene, 1,3-
dimethylsty-
rene, alpha-methylstyrene, beta-methylstyrene, p-isopropylstyrene, 2,3-dimeth-
ylstyrene, o-chlorostyrene, p-chlorastyrene, o-bromostyrene, 2-chloro-4-
rnethyl-
styrene, etc. The preferred vinyl aromatic hydrocarbon is styrene.
Many of the above-described copolymers of conjugated dimes and
vinyl aromatic compounds are commercially available. The number average
molecular weight of the block copolymers, prior to hydrogenation, is from
about
20,000 to about 500,000, preferably from about 40,000 to about 300;000.
The average molecular weights of the individual blocks within the
copolymers may vary within certain limits. In rnost instances, the vinyl
aromatic
block will have a number average molecular weight in the order of about 2000
to about 125,000, and preferably between about 4000 and fi0,000. The
conjugated diene blocks either before or after hydrogenation will have number
average molecular weights in the order of about 10,000 to about 450,000 and
more preferably from about 35,000 to 150,000.
Also, prior to hydrogenation, the. vinyl content of the conjugated
diene portion generally is from about 10% to aibout 80%, and the vinyl content
is preferably from 'about 25% to about 65%, particularly 35% to 55% when it
is desired that the modified block copolymer exhibit rubbery elasticity. The
vinyl
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1$
content of the block copolymer can be measured by means of nuclear magnetic
resonance.
Specific examples of diblock copolymers include styrene-
butadiene (SB), styrene-isoprene (SI), and the hydrogenated derivatives
thereof. Examples of triblock polymers include styrene-butadiene-styrene
(SBS), styrene-isoprene-styrene (SIS), alph;e-methylstyrene-butadiene-alpha-
methylstyrene, and alpha-methylstyrene-i~~oprene alpha-methylstyrene
Examples of commercially available block copolymers useful as the adhesives in
the present invention include those available from Shell Chemical Company and
listed in the following Table Il.
Table II
StyrenelRubber Melt
ICr-_a_ton Tvoe R do w In ex
D1101 Linear SBS 31/69 < 1
1 5 D1107P Linear SIS 15/85 11
D1111 Linear SIS 22/78 3
D1112P Linear SIS 15/85 23
D1113P Linear SIS 16184 24
D1117P Linear S1S 17/83 33
D1320X Mufti-arm (SI)"10/90 NA
Vector 411 1 is an SIS block copolymer available from Dexco of Houston Texas.
Upon hydrogenation of the SBS <;opolymers comprising a rubbery
segment of a mixture of 1,4 and 1,2 isomers, a styrene-ethylene-butylene
styrene (SEES) block copolymer is obtained. Similarly, hydrogenation of an SIS
polymer yields a styrene-ethylene propylene-styrene (SEPS) block copolymer.
The selective hydrogenation of the block copolymers may be
carried out by a variety of well known processes including hydrogenation in
the
presence of such catalysts as Raney nickel, noble metals such as platinum,
palladium, etc., and soluble transition metal catalysts. Suitable
hydrogenation
processes which can be used are those wherein the diene-containing polymer
or copolymer is dissolved in an inert hydrocarbon diluent such as cyclohexane
and hydrogenated by reaction with hydrogen in the presence of a soluble
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19
hydrogenation catalyst. Such procedures are described in U.S. Patents
3,1 13,986 and 4,226,952, the disclosures of which are incorporated herein by
reference. Such hydrogenation of the block copolymers which are carried out
in a manner and to extent as to produce selectively hydrogenated copolymers
having a residual unsaturation content in the polydiene block of from about
0.5°/a to about 20% of their original unsaturation content prior to
hydrogenation.
In one embodiment, the conjugiated diene portion of the block
copolymer is at least 90% saturated and more often at least 95% saturated
while the vinyl aromatic portion is not significantly hydrogenated.
Particularly
useful hydrogenated block copolymers are hydrogenated products of the block
copolymers of styrene-isoprene-styrene such as a styrene-(ethylene/propyl-
ene)-styrene block polymer. When a polysi:yrene-polybutadiene-polystyrene
block copolymer is hydrogenated, it is desirat~le that the 1,2-poiybutadiene
to
1,4-polybutadiene ratio in the polymer is froim about 30:70 to about 70:30.
When such a block copolymer is hydrogenated', the resulting product resembles
a regular copolymer block of ethylene and 1-butane (EB). As noted above, when
the conjugated diene employed as isoprene, the resulting hydrogenated product
resembles a regular copolymer block of ethylene and propylene (EP).
A number of selectively hydrogenated block copolymers are
available commercially from Shell Chemical Company under the general trade
designation "Kraton G." One example is Kraton 61652 which is a hydrogenated
SBS triblock comprising about 30% by weight of styrene end blocks and a mid-
block which is a copolymer of ethylene and 1-butane (EB). A lower molecular
weight version of G 1652 is available from Shell under the designation Kraton
G 1650. Kraton G 1651 is another SEBS block copolymer which contains about
33% by weight of styrene. Kraton 61657 is am SEBS diblock copolymer which
contains about 13%w styrene. This styrene content is lower than the styrene
content in Kraton G 1650 and Kraton G 1652.
In another erribodiment, the ;selectively hydrogenated block
copolymer is of the formula
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B~(AB)oAp
wherein n = 0 or 1;
o is 1 to 100;
pfs0or1;
5 each B prior to hydrogenation is predominantly a polymerized
conjugated diene hydrocarbon block having a number average molecular weight
of about 20,000 to about 450,000;
each A is predominantly a polymerized vinyl aromatic hydrocarbon
block having a number average molecular weiight of from about 2000 to about
10 1 15,000; the blocks of A constituting about 5~% to about 95% by weight of
the
copolymer; and the unsaturation of the bloc; B is less than about 10% of the
original unsaturation. In other embodiment,, the unsaturation of block B is
reduced upon hydrogenation to less than 5% of its original value; and the
average unsaturation of the hydrogenated block copolymer is reduced to less
15 than 20% of its original value.
The block copolymers may also iriclude functionalized polymers
such as may be obtained by reacting an alpha, beta-olefinically unsaturated
monocarboxylic or dicarboxylic acid reagent onto selectively hydrogenated
block
copolymers of vinyl aromatic hydrocarbons and conjugated dienes as described
20 above. The reaction between the carboxylic acid reagent in the graft block
copolymer can be effected in solutions or by .a melt process in the presence
of
a free radical initiator.
The preparation of various selectively hydrogenated block
copolymers of conjugated dienes and vinyl aromatic hydrocarbons which have
been grafted with a carboxylic acid reagent is described in a number of
patents
including U.S. Patents 4,578,429; 4,657,970; and 4,795,782, and the
disclosures of these patents relating to grafted selectively hydrogenated
block
copolymers of conjugated dienes and vinyl aromatic compounds, and the
preparation of such compounds are hereby .incorporated by reference. U.S.
Patent 4,795,782 describes and gives examples of the preparation of the
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21
grafted block copolymers by the solution process and the melt process. U.S.
Patent 4,578,429 contains an example of grafting of Kraton 61652 (SEBS)
polymer with malefic-anhydride with 2,5-dimethyl-2,5-di(t-butylperoxy) hexane
by a melt reaction in a twin screw extruder. (See Col. 8, lines 40-61.)
Examples of commercially available maleated selectively
hydrogenated copolymers of styrene and butadiene include Kraton FG 1901 X,
FG 1921 X, and FG 1924X from Shell, often referred to as maleated selectively
hydrogenated SEBS copolymers. FG 1901 ~; contains about 1.7%w bound
functionality as succinic anhydride and about 28%w of styrene. FG 1921 X
contains about 1 %w of bound functionality as succinic anhydride and 29%w
of styrene. FG1924X contains about 13°/~ styrene and about 1 % bound
functionality as succinic anhydride.
Useful block copolymers also are available from Nippon Zeon Co.,
2-1, Marunochi, Chiyoda-ku, Tokyo, Japan. For example, Quintac 3530 is
available from Nippon Zeon and is believed to be a linear styrene-isoprene-
styrene block copolymer.
The polymer film materials and adhesive compositions used to form
the constructions of the present invention may be neat, or they may be
emulsions or solvent-based. Emulsion and solvent-based acrylic based PSAs are
known and described in, for example, U.S. Patent No. 5,639,811 and
5,164,444, respectively, and these patents are hereby incorporated by
reference
for such disclosures. When emulsions of the film materials and/or adhesive
compositions are used, the water may be remroved in an extruder by using the
process described and claimed in U.S. Patenl: 5,716,669 (LaRose et al). It is
preferred, however, that the film materials and PSAs which are coextruded are
compositions substantially free (e.g., less than 1 %w) of water and/or
solvents.
The presence of water or solvents during the; coextrusion process can result,
and generally does result, in pinholes and bubbles in the coextruded film. The
presence of voids in the film due to steam is referred to in the art as
"moisture
slits."
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22
Since the adhesive constructions of the present invention are
formed by coextruding a film of the above described polymeric film materials
and an adhesive layer as described more fully below, the hot melt viscosity of
the polymeric film material and of the adhesive should be within a window or
range of viscosities which can produce a coextrudate of continuous and uniform
layers of the polymeric film material and thE: adhesive in order to avoid film
defects and intermingling of the polymeric film material and the adhesive
during
the coextrusion process. Intermingling of the film material and the adhesive
is
not desired because it can cause a loss of clarity in the extruded film, as
well as
a tendency to cause blocking. In general, it is preferred that the polymeric
film
material have a hot melt viscosity that is within a factor of from about 0.07
to
about 15 times the hot melt viscosity of the adhesive at the shear rates
incurred
during the coextrusion process. Generally the shear rates range from about 100
sec-'to about 10,000 sec-'. More often the factor is from about 1 to about 15.
A preferred factor is from 1 to about 10. It is also desirable for the polymer
film
material and the adhesive to have relatively similar melt viscosities at the
extrusion temperatures. for example, when the PSA is a conventional hot melt
adhesive, the extrusion temperatures of the PSA are in the range of from about
750°C to about 200°C, and preferably in the range of from about
175°C to
about 200°C. It is, therefore, desired that thE; polymeric film
material selected
for use with the PSA have an extrusion temperature below about 200°C
and
preferably in the range of from about 150 ° C to about 180 ° C.
It is desired that the corltinuoua polymeric film in the adhesive
constructions of the invention have a high speed tensile strength of at least
1
pound/inch-width and more often, a high speed tensile strength in the range of
from about 2 to about 10 pounds/inch-width. High speed tensile strength is
determined in accordance with TAPPI Test 494 modified by running the sample
at a speed of 100 ft/rnin. The high speed tensile strength of the polymer film
should be sufficient; at the given thickness, to permit matrix stripping after
die-
cutting without undue tearing of the film. It is. also desirable that the
polymeric
film material in the coextruded adhesive constructions of the present
invention
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23
have an elongation at break of less than about 200%, and more preferably, in
the range of from about 125% to about 1 ;75%. A polymeric film material
having a percent ultimate elongation at break greater than about 200% can
produce an adhesive construction that is difficult to convert by die-cutting
and
matrix-stripping, depending on the type of adhesive and polymeric film
material,
and on their respective coating weights.
In one embodiment, the key features of the coextruded adhesive
constructions of the present invention include (1 ) the use of a thin
polymeric
film and (2) an adhesive layer having a relatively low coat weight. Thus, the
adhesive constructions of the present invention are characterized as having a
polymeric film with a thickness of from about 0.1 mil up to about 1.5 or 2
mils,
and an adhesive coating weight of less than 40, and preferably Less than 20
g/m2. In one embodiment, the adhesive layer has a coat weight in the range of
from about 0.5 to about 20 g/m2. Alternatively, the thickness of the adhesive
layer may range from about 0.02 mils to about 2 mils, and more preferably,
between about 0.02 mils and about 0.8 mils. It should be understood that the
thickness and coat weight of both the polymeir film and the adhesive layer may
vary depending upon the different types of polymer film material and adhesives
that are selected, and the properties desired in the adhesive construction.
For
example, different polymers and different film thicknesses will result in
constructions having different conformabilitiea and different stiffnesses. The
constructions of the invention, in one embodiment, should have sufficient
Gurley stiffness to permit high speed dispensing such as by a peel-plate, yet
be
sufficiently flexible to be conformable to most surfaces. For applications
requiring a high degree of conformability, the adhesive constructions can be
designed to have Gurley stiffnesses in the machine direction of less than
about
10, and even less than about 5. Gurley stififness is determined according to
TAPPI Test 543 pm. Typically, the adhesive constructions of the invention have
a Gurley stiffness in the machine direction of less than 40 mg and even less
than 25 mg.
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24
It is also a feature of the coextruded adhesive construction of the
present invention that such thin polymeric films can provide the structural
properties (e.g., strength and stiffness) necessary to facilitate conversion.
The
coextruded adhesive constructions of the present invention having a polymeric
film of the given thicknesses provides an adhesive construction that is, in
combination with the adhesive layer, sufficiently self supporting to
facilitate
conversion (i.e., printing, die-cutting and matrix stripping). As hated
herein,
when the machine direction stiffness of the coextruded adhesive constructions
is too low (e.g., less than 10 Gurley) to be used satisfactorily in high speed
peel-
plate dispensing techniques, the construction can be dispensed using other
techniques or the stiffness can be increased by overlaminating a polymer film
to the thin polymer films of the coextruded adihesive construction as
described
herein. Useful dispensing techniques and dispensing equipment for adhesive
constructions of low stiffness including the VE:ntura dispenser are described
in
U.S. Patents 4,217,164, 4,303,461 and 4,896,793, and these patents are
incorporated herein for such descriptions.
As mentioned above, in one embodiment, the adhesive
compositions comprise thermoplastic elastomers comprising at least one
thermoplastic elastomeric block copolymer which include linear, branched,
graft
or radial block copolymers. In addition, the adhesive compositions which are
coextruded also contain at least one solid tac;kifier resin component. A solid
tackifier is defined herein as one having a sofi:ening point above
80°C. When
the solid tackifier resin component is present, the coextrudable pressure-
sensitive adhesive compositions generally comprise from aboufi 40 to about
80% by weight of a thermoplastic elastomer component and from about 20%
to about 60% by weight (preferably from about 55 to 65% by weight) of a solid
tackifier resin component. The solid tackifier reduces the modulus of the
mixture sufficiently to build tack or adhesion. Also, solid tackifiers
(particularly
the higher molecular weight solid tackifiers (e.g., Mw greater than 2000) and
those having a lower dispersity (Mw/Mn= les:~ than about 3)) are less
sensitive
to migration into the polymer film Payer, and this is desirable, since
migration of
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tackifier into the polymer film layer causes dimensional instability, and the
constructions can swell and/or wrinkle, and may become too soft. In addition,
the constructions may lose adhesive properties. or cause blocking, and the
ability
of the polymer film to be printed satisfactorily may be reduced by migration
of
5 the tackifier. For example, attempts to print the polymeric film layer after
migration of tackifier or other components from the adhesive layer may result
in poor anchorage of the ink and/or blurring .of the printing. Migration of
the
tackifier and other components present in the adhesive layer is a particular
problem when the polymer film comprises a polyolefin such as polyethylene.
10 Conventional solid tackifier resins include hydrocarbon resins, rosin,
hydrogenated rosin, rosin esters, poiyterpene resins, and other resins which
exhibit the proper balance of properties. A variety of useful solid tackifier
resins
are available commercially such as terpene resins which are sold under the
trademark Zonatac by Arizona Chemical Company, and petroleum hydrocarbons
15 resins such as the resins sold under the tradeyark Escorez by Exxon
Chemical
Company. One particular example of a useful solid tackifier is Escorez 2596
which is a C5-C9 (aromatic modified aliphatic) synthetic tackifier having an
Mw
of 2100 and a dispersity (Mw/Mn) of 2.69: Another useful solid tackifier is
Escorez 1310LC, identified as an aliphatic hydrocarbon resin having an Mw of
20 1350 and a dispersity of 1.$. Wingtack 95 is a synthetic tackifier resin
available from Goodyear, Akron, Ohio consisting predominantly of polymerized
structure derived from piperylene and isoprene.
The modules of the adhesive mi~aures to be coextruded also may
be lowered by the incorporation of liquid rubbers, i.e., liquid at room
25 temperature. The liquid rubbers generally will have an Mw of at least 5,000
and
more often at least 20,000. Incorporation of liquid rubbers in amounts of less
than 10%, and even less than 5% by weight teased on the overall weight of the
adhesive formulation results in adhesives which is coextrudable with the
polymeric film materials. The incorporation of a liquid rubber also produces
an
adhesive having increased tack and adhesion. Liquid block copolymers such as
liquid styrene-isoprene block copolymers are particularly useful. For example,
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26
Kraton LVSI-101, available from the Shell Chemical Company, is effective in
lowering the modulus of the adhesive, and it has been found, surprisingly,
that
this liquid styrene-isoprene block copolymer functions as a processing aid,
improving the smoothness of the flow of thE~ adhesive from the die. Kraton
LVSI-101 has a weight average molecular weight of about 40,000. Another
example of a useful liquid rubber is a liquid pofyisoprene obtained by
selectively
or partially degrading a high molecular weight polyisoprene. An example of a
commercially available partially degraded high molecular weight polyisoprene
is
Isolene D-400 from Elementis Performance Polymers, Belleville, N.J., and this
liquid rubber has an Mw of about 20,000. Other liquid rubbers which may be
incorporated into the adhesive mixture include liquid styrene-butadiene
rubbers,
liquid butadiene rubbers, ethylene-propylene rubbers, etc.
The adhesive compositions also imay include other materials such
as antioxidants, heat and light stabilizers, ultraviolet light absorbers,
viscosity
modifiers, fillers, colorants, antiblocking agenta, reinforcing agents,
processing
acids, etc. Hindered phenolic and amine antioxidant compounds may be
included in the adhesive compositions, and a wide variety of such antioxidant
compounds are known in the art. A variety of antioxidants are available from
Ciba-Geigy under the general trade designations "Irganox" and "Irgafos". For
example, the hindered phenofic antioxidant n-octadecyl 3-(3,5-di-t-butyl-4-
hydroxyphenol)- proprionate is available under the general trade designation
"Irganox 1076". irganox 1010, is identified a;s Tetrakis (methylene 3-t3',5'-
di-
tert-butyl-4'-hydroxyphenol) proprionate) methane. Irgafos 168 is another
useful
antioxidant from Ciba-Geigy.
Hydroquinone-based antioxidants also may be utilized, and one
example of such an antioxidant is 2,5-di-tertiary-amyl-hydroquinone.
Light stabilizers, heat stabilizers, and UV absorbers also may be
included in the adhesive compositions. Ultraviolet absorbers include benzo-
triazof derivatives, hydroxy benzyl phenones, esters of benzoic acids, oxalic
acid,
diamides, etc. Light stabilizers include hindered amine light stabilizers, and
the
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27
heat stabilizers include dithiocarbamate compositions such as zinc dibutyl
dithiocarbamate.
The adhesive compositions, like the polymeric films, may contain
inorganic fillers and other organic and inorg<~nic additives to provide
desired
properties. Examples of useful fillers include calcium carbonate, titanium
dioxide, metal particles, fibers; etc. An example of a useful end-block
reinforcing agent is Cumar LX509 from Neville Resins.
The following examples illustrate specific pressure sensitive
adhesive formulations which are coextrudable; with polymeric film materials as
7 0 described above. Unless otherwise indicated in the following examples, in
the
claims, and elsewhere in the written description, all parts and percentages
are
by weight, and temperatures are in degrees centigrade.
Adhesive 1 Percent By Weight
Kraton D1320X 60.0
Escorez 2596 40.0
Adhesive 2
Kraton D 1320X 57.1
Escorez 2596 38.1
Kraton LVSI-101 4.8
Adhesive 3
Kraton D 1320X 50.0
Escorez 2596 45.8
Kraton LVSI-101 4.2
Adhesive 4
Quintac 3530 50.0
Escorez 2596 45.8
Kraton LVSI-101 4.2
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28
Adhesive 5
Quintac 3530 50.0
Escorez 2596 45.8
Isolene D-400 4.2
Adhesive 6
Kraton D 1 1 12P 35.0
Escorez 131OLC 65.0
Adhesive 7
Kraton D 11 17P 35.0
Escorez 1310LC 65.0
Adhesive 8
Kraton D1112P 35.0
Escorez 2596 65.0
Adhesive 9
Kraton D 1 107 30.0
Escorez 2596 48.0
Kraton LVSI-101 22.0
Adhesive 10
Vector 41 1 1 52.6
Wingtaok 95 31.6
Cumar LX509 15.8
As noted above, the adhesive constructions of the present
invention comprise coextrudates of a polymeric film and an adhesive layer. The
polymeric film may comprise one or more layers.
A coextrusion technique useful in preparing an embodiment of the
adhesive constructions of the present invention is schematically shown in Fig.
1. The apparatus shown in Fig. 1 utilizes three extruders 10, 1 1 and 12 which
can provide three molten streams (sometimes hereinafter referred to as streams
A, B and C respectively) of material to the coextrusion die 17. Extruder 10
provides a molten stream 13 of an adhesive composition to the die 17. Extruder
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29
11 provides a molten stream 14 of polymeric film material to the die 17.
Extruder 12 is optional, and when present, provides a molten stream 15 of a
polymeric film material which may be the same as or different from the polymer
film material of molten stream 14 from extruder 11: It is of course understood
that if no third molten stream is desired, there is no need to utilize
extruder 12.
When extruder 12 is utilized, and the molten stream 15 is a polymer film
material which is the same as the polymer film material of molten stream 14,
the resulting coextrudate is a two layer construction, one layer of polymer
film
and one layer of adhesive. When the polymeric film material of molten stream
15 is different from the polymeric film material of molten stream 14, the
polymeric film of the coextrudate 23 comprises two layers (31 and 31 A in Fig.
1 B), and the coextrudate comprises three layers, the two polymer film layers
(31
and 31 A) and the adhesive layer 30. Additional extruders can be used when it
is desired to have additional streams of molten material fed to the die 17.
Two
or more extruders containing the same polymeric film material are used to
provide a coextrudate with a thicker polymeric film.
In one preferred embodiment, polfymer film material is not charged
to extruder 12, or the polymer charged to extruder 12 is the same as that
charged to extruder 1 1, and the resulting coextrudate comprises a single
layer
of polymer film, and a layer of adhesive.
The extruders 10, 11 and 12 are utilized to blend and melt the
compositions and as pumps to deliver the mohten streams to the feedblock and
the extrusion die. Alternatively, the compositions may be preblended prior to
being introduced into the extruders. The precise extruder utilized is not
critical
to the process. A number of useful extruders are known; and these include
single and twin-screw extruders, batch-off e~;truders, etc. Such extruders are
available from a variety of commercial sources including Killion Extruders,
Inc.,
C.W. Brabender Inc., American Leistritz Extruder Corp, and Davis Standard
Corp.
A variety of useful coextrusion diie systems are known. Examples
of extrusion dies useful in the invention acre the Cloeren "vane" dies, and
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multimanifold dies available commercially from the Cloeren Company of Orange,
Texas.
Although the selection of the extrusion die to be utilized in the
process of the invention is not critical, certain factors do have an influence
on
5 the performance of the extrusion process. For example, when a single
manifold
is to be utilized, the relative viscosities of the: materials, and their
ability to be
processed at a single manifold temperature must be considered. When the
relative viscosities of the materials exceed a tolerable limit, or when a
single
manifold temperature cannot be tolerated by the materials, multimanifold dies
10 are typically employed. In multimanifold die:>, each material flows in its
own
manifold to the point of confluence. Each individual manifold also can be
designed specifically for the theology of each polymer resin and/or adhesive,
and
each manifold also can be controlled at different process temperatures.
Multimanifold dies can be designed with zero common land length
15 so that the materials do not meet until the diE; lip or exit orifice.
Alternatively,
they can be designed with a short common flow channel such as, example, up
to about 10 mm, and preferably less than about 5 mm. A zero common land
would be preferred where the molten streams Have extreme viscosity differences
and/or temperature requirements. A short common land is generally beneficial
20 because the period of high temperatures and high pressure while the melts
are
in the common land can improve the bond strength between the layers of the
construction and minimize or eliminate air entrainment. In one preferred
embodiment of the present invention, the manifold dies are selected so that
the
molten streams are joined about 1 mm before; the die lip.
25 Referring again to Fig. 1, the unified molten structure 19 of two or
more layers exits the extrusion die 17 through orifice 18, and the molten
structure is deposited onto a solid substrate 21 Se.g., a release liner)
supplied
from a roll 20 so that the tower surface of the adhesive layer is in contact
with
the liner, while the upper surface of the polymeric film is in contact with
air.
30 The liner 21 is partially wrapped around the ifirst of a three chill roll
stack 22,
22A and 22B. Chill roll 22 also acts as a casting roll. The liner 21 contacts
the
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31
surface of casting roll 22 and is interposed bEaween the surface of the
casting
roll and the adhesive layer of the molten stream 19. In the embodiment
illustrated in Fig. 1, the molten structure 19 is deposited on the liner 21
and the
construction 23 which is formed in the process then passes aver chill rolls
22A
and 22B and is wound over roll 24 or wound upon itself.
The casting/cooling roll 22 and tf ~e chill rolls 22A and 22B typically
are maintained at a temperature below the temperature of the unified molten
structure 19 in order to cool the molten structure after it is deposited on
the
liner. Typically this temperature is in the range of from about 5 ° to
about
100°C, preferably from about 20° to about :30°C.
Fig. 1 A is a cross-section of the adhesive construction 23 of one
embodiment of the present invention wherein the polymeric film is a monolayer.
Thus, the adhesive construction 23 illustrated in Fig. 1 A comprises the
polymer
film layer 31, an adhesive layer 30, and a release liner 21. Fig. 1 B is a
cross-
section of an adhesive construction 23' of t:he present invention wherein an
adhesive composition is supplied to extruder 10, and different polymer film
materials are supplied to extruders 11 and 12. The resulting adhesive
construction illustrated in Fig. 1 B comprises polymer film layers 31 and 31 A
(derived from the materials supplied to extruders 1 1 and 12, respectively),
an
adhesive layer 30, and a release liner 21.
Fig. 2 illustrates another coextru;sion procedure useful in preparing
the adhesive constructions of the present invention. The apparatus shown in
Fig. 2 utilizes four extruders 41, 42, 43 and 44 which provide four molten
streams (sometimes hereinafter referred to as streams A, B, C and D,
respectively? of material. Extruders 41, 42 and 43 provide molten streams 45,
46 and 47, respectively, to a feedblock 49, and extruder 44 provides a molten
stream 48 of an adhesive composition directly to the die 50. As in the
procedure shown in Fig. 1 and described above, the molten streams of polymer
film material exiting extruders 41, 42 and 43 may be the same or different,
although it is preferred, in one embodiment, that the polymeric film materials
exiting extruders 41, 42 and 43 are the same:. Three extruders containing the
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32
same polymeric film material are used to provide a coextrudate with a thicker
polymeric film.
Feedblock 49 in Fig. 2 combines the molten streams of polymeric
film material into a single flow channel. The feedbiock 49 delivers the molten
structure to the extrusion die 50 where the molten structure is combined with
the adhesive stream 48, and thereafter the combined streams are reduced in
height and increased in width as desired so as to provide a relatively thin
and
wide construction. An example of a useful fes;dblock is the Claeren
coextrusion
feedblock available commercially from the Cloeren Company of Orange, Texas.
The discussion above, with regard to the selection of the extrusion die used
in
the process of Fig. 1 is applicable to the process of Fig. 2.
The unified molten structure 52 of two or more layers exits the
extrusion die 50 through orifice 51, and the molten structure is deposited
onto
a solid substrate 54 (e.g., a release liner) supplied from a roll 53 so that
the
lower surface of the adhesive layer is in contact with the liner, while the
upper
surface of the polymeric film is in contact with air. The liner 54 is
partially
wrapped around the first of a three chill roll shack 55; 56 and 57. Chill roll
55
also acts as a casting roll. The liner 54 contacas the surface of the casting
roll
55 and is interposed between the surface of the casting roll and the adhesive
layer of the molten stream 52. In the embodiment illustrated in Fig. 2, the
molten structure 52 is deposited on the liner 54, and the construction 58
which
is formed in the process then passes over chill rolls 56 and 57 and is wound
over roll 59 or wound upon itself.
The casting/cooting roll 55, and chill rolls 56 and 57 typically are
maintained at a temperature below the ternperature of the unified molten
structure 52 in order to cool the molten structure after it is deposited on
the
liner. Typically this temperature is in the range of from about 5°C to
about
100 ° C, preferably from about 20 ° C to about: 30 ° C.
A number of additional steps optionally can be performed an the
coextrudate if desired. Thus, for example, the: coextrudate may be uniaxially
or
biaxially oriented (e.g., by heat stretching and heat setting). If it is
desired to
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33
uniaxially or biaxially orient the coextruded adhesive constructions of the
present
invention, such orientation preferably occurs before the coextrudate is joined
with a support material such as the release liner 21 and 54 of Figs. 1 and 2
respectively. For example, if it is desired to orient the coextrudate, the
process
described with regard to Figs. 1 and 2 is modified as follows. The flow of
molten material into the die and/or feedblock is rearranged so that the
unified
molten structures 19 and 52, of Figs. 1 and 2 respectively, have the adhesive
layer on top, and the molten film layer contacts the casting/chill roll 22 or
55
where the molten material is cast into a film and cooled. Chill rolls 22A and
22B
in Fig. 1, and chill rolls 56 and 57 in Fig. 2 are omitted or rearranged so
that the
adhesive side of the cast film does not come into contact with the additional
chill roils. After the cast film has cooled, the construction may be subjected
to
orientation followed by lamination to the reie~ase surface of a release liner.
In
one preferred embodiment of the invention, the adhesive constructions are not
oriented.
Machine direction or biaxial orientation of the cooled cast films of
the invention prepared as described above free of a release liner can be
accomplished by techniques known in the arit. For example, the films can be
oriented in the machine direction by using teetering frames where the clips at
the edge of the teetering frame travel faster in the machine direction thereby
stretching the film in the machine direction. Alternatively, the clips can be
programmed to travel faster in the machine direction or to widen in the cross
direction, or to stretch in both directions thereby orienting the film in both
directions. When the film is to be stretched uaing a teeter frame, the edges
of
the film are preferably free of adhesive so that the clips will not stick to
the film.
After orientation on the teetering frame, the coextruded adhesive construction
then can be laminated to a release liner.
The adhesive constructions of the present invention such as
illustrated in Figs. 1 A and 1 B can either be collected for future printing,
overlaminating, and converting at a different time andlor geographic location,
or
these constructions can be routed to one or more other stations for printing,
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34
overlaminating; and/or converting during the same operation, In an example
process, the adhesive construction 23 of Fig. 'I is taken up on roll 24 and
saved
for future printing, overlaminating and/or conversion. Before printing, it
often
is desired that the exposed film surface of t;he adhesive construction of the
invention be treated to make the exposed surface of the polymer film more
receptive to subsequent printing or marking. In an example embodiment, the
construction is treated by conventional surface treatment methods, such as
corona treatment and the like, to increase the surface energy of the polymer
film
layer to facilitate wetting during the printing process.
An important feature of the adhesive constructions of the present
invention is the ability to deposit printing indicia or other forms of marking
on
the upper surface of the film layer. Thus, the polymer film material selected
for
the exposed or upper surface of the adhesive constructions should be one which
is receptive to printing with inks using printing techniques such as
flexographic
printing, screen printing, offset lithography, letter press, thermal transfer,
etc.,
and the applied ink has acceptable adhesion to the surface of the adhesive
construction.
In some instances, the properties of the very thin adhesive
constructions described above can be improved by lamination of another
polymeric film over the polymeric film of the c~oextrudate. In this
embodiment,
the very thin coextrudate of the invention cornprising a polymeric film and
the
adhesive is sometimes referred to herein as a "prelaminate". Prelaminates are
less than about 1 mil thick and more often from about 0.2 to 0.5 or 0.6 mil
thick. This additional film over the polymer film of the prelaminate
(coextrudate?
generally is sometimes referred to herein and in the claims as an
"overlaminate
film" or "overlaminate layer", and the adhe:~ive construction containing the
overlaminate film is sometimes referred to as the "overlaminated construction"
of the invention. The overlaminate film can provide additional properties such
stiffness and weatherability to the adhesive construction. The overlaminate
film
can also provide a transparent coating or film over printed indicia to protect
the
print from damage caused by physical conjtact with adjacent objects, and
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damage caused by exposure to moisture, waiter, or weather. The transparent
coating can also enhance the optical quantities. of the underlying printed
indicia
to pravide a glassier and richer image. The overlaminated constructions of
this
invention are uniquely suited for use as labels on substrates subjected to
5 subsequent liquid processing such as bottle washing/rinsing, filling and
pasteurization, or liquid immersion (e.g., ice bath) without displaying
adverse
consequences such as label lifting or hazing.
The overlaminated film can bE~ laminated to the coextruded
adhesive constructions by pressure when in the; form of a continuous film
having
10 a layer of adhesive material interposed between the continuous polymer film
of
the adhesive structure and the overlaminate film. The overlaminate film can be
laminated to the continuous polymer film of the adhesive construction by heat
and pressure without added adhesive when either the continuous polymer film
or the overlaminate film is formed from a material that when heat activated
15 forms its own adhesive surface for lamination. Alternatively, the
averlaminate
film can be applied to a curable (thermal ar radiation) fluid adhesive, such
as UV
curable varnish. Alternatively, the overlaminat~e film can be applied by
extrusion
or coating technique to the adhesive construction as a film-farming material
that
subsequently cures to form a continuous film. Printing indicia can be disposed
20 on the continuous polymer film surface and/or an a backside surface of the
overlaminate film layer. As a further alternative, an overlaminated adhesive
construction of the invention can be prepared by (a) separately coextruding
two
adhesive constructions, each comprising a continuous polymeric film and an
adhesive layer as described above and (b) joining the two caextrudates to form
25 a four layer structure of adhesive/film/adhesive/film. In another
embodiment, an
apparatus comprising four extruders such as shown in Fig. 2 (or an extruder
can
be added to the apparatus of Fig. 1 ) can be utilized with a polymer film
forming
material charged to the first and third extruders, and an adhesive charged to
the
second and fourth extruders. The result of such a coextrusion process is a
30 film/adhesive/film/adhesive construction.
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3fi
Fig. 3 illustrates another embodiment of an overlaminated adhesive
construction 40 prepared in accordance with the principles of this invention.
The overlaminated adhesive construction 40 comprises the adhesive
construction 23 as described above and illustrated in Fig. 1 A which comprises
the release liner 21, the adhesive layer 30 and the polymer film layer 31. The
overlaminated construction 40 of Fig. 3 also comprises printing indicia or
other
form of marking 32 disposed on the polymeric film layer 31, a second adhesive
layer 33 disposed over the printing indicia or marking 32, and an overlaminate
film layer 34 disposed over the second adhesive layer 33. The second adhesive
layer 33 can be formed from the same types. of adhesive materials discussed
above for the adhesive constructions of the invention.
Fig. 4 is a cross-sectional side view of another overlaminated
adhesive structure 40A of the present invention. This overlaminated structure
40 comprises the adhesive construction 23' described above and illustrated in
Fig. 1 B which camprises the release liner 21, tlhe adhesive layer 30, the
first film
layer 31, and the second film layer 31 A. In addition the construction of Fig.
4
comprises a layer of printing indicia 32, a sf:cond adhesive layer 33 and the
overlaminate layer 34.
It is to be understood that the overlaminated adhesive
constructions of the present invention can be configured differently depending
on the particular label end use. For example, the printed indicia can be
interposed between the second adhesive layer 33 and the overlaminate film
Layer 34 in Fig. 4 /e.g., a reversed printed overlaminate film layery. Such a
construction generally can be prepared by using an overlaminated film 34 that
is first reversed printed and subsequently has a layer of adhesive applied to
the
reverse-printed surface. The overlaminated film then is laminated to the
polymeric film layer 31 or 31 A via the adhesive layer by conventional
pressure
lamination techniques.
In another embodiment, overlaminated adhesive constructions in
accordance with the present invention can be prepared which are similar to the
constructions illustrated in Figs. 3 and 4 except that the second adhesive
layer
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37
33 is eliminated. In this embodiment, the ove;rlar~iinate film layer 34, is
formed
of a material that is heat activatable to provide its own adhesive surface for
lamination. The material should have a sufficient "open tack" time to
facilitate
lamination at a relatively low temperature so as to avoid unwanted heat
effects
in the adhesive constructions. "Open tack" refers to the amount of time that
the
just activated film material remains tacky or open to adhesive contact with an
adjacent surface.
The preparation of adhesive constructions in accordance with the
process of the present invention is illustrated in the following examples.
Example 1
The apparatus utilized in this e;cample is generally similar to the
apparatus of Fig. 1 and consists of three extruders (a Killion 1 " single
screw
extruder (stream A), a 3/4" Brabender single screw extruder (stream B), and a
27 mm Leistritz twin screw extruder in the co-rotating mode (stream C)) and a
6" Cloeren, three layer, three manifold vane die. The adhesive for the
adhesive
layer of the construction of the invention is fed to the Leistritz twin screw
extruder having 9 heated zones which area maintained at 145 °C, 155
° C,
160°C, 160°C, 160°C, 160°C, 160°C,
155°C, and 155°C. The adaptor is
also heated to 155 ° C; and the first extruder zone is unheated. Kraton
D 1320X
is dusted with 0.1 phr of stabilizers (a 2:1 Blend of lrgafos 168 and lrganox
565) and fed through the solids feed-port at tihe first zone at a rate of
447g1hr.
Kraton LVSI-101 is heated to 120°C and fed at a rate of 57g/hr, into
the fourth
zone. Escorez 1310 is heated to 135°C and fed at a rate of 407g/hr.
into the
sixth zone. The twin screw extruder is operated at 450 rpm and requires 2.$
amps. The Brabender extruder operated at 5 rpm is charged with Unirez 2623.
The temperature profile is 150°C, 155°C and 165°C in
three zones with a head
pressure of 600 kPa. Additional Unirez 2623 is charged to the Kiliion extruder
operated at 5 rpm. The third zone of the Killion extruder is heated to
165°C
and maintained at 1380 kPa head pressure. Molten streams from the three
extruders are combined inside the Cloeren diie set to a temperature of 165
° C
whereby the two molten streams (streams A ~& B) of polyamide are disposed on
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38
the molten stream of adhesive (stream C), and streams combine inside the die
in such a manner that the adhesive containing side will contact a release
liner
upon exiting the die. The release liner consist~~ of glassine paper coated
with GE
7000-series silicone release on one side. The: liner is partially wrapped
around
the bottom-most chill roll (also casting roll) of a three chill roll stack
that is
maintained in a closed nip position: The chill rolls are maintained at about
22 ° C, and the molten stream exiting the die is cast onto the liner
wrapped on
the bottom-most chili roll. The line speed is about 12 m/min. The resulting
extrudate is about 7.5 cm. wide and about 0.5 mils (12 micron) in thickness.
Example 2
The procedure of Example 1 is generally followed except that
Unirez 2623 is replaced by polypropylene 5E:66 from Union Carbide, and the
extruder temperatures and the die temperaturE; are raised to 210°C. The
Killion
extruder is operated at a 5 rpm and the hE:ad pressure is 4800 kPa. The
Brabender extruder is operated at 8 rpm with a head pressure of 4300 kPa. The
Leistritz extruder utilizes the same temperature profile as in Example 1, and
the
Kraton D1320X, LVSi 101 and Escorez 2596. are handled in the same manner
as in Example 1 except the feed rates are Ei70 g/hr, 76 glhr and 543 g/hr,
respectively. The head pressure on the Leistritz twin screw is 1310 kPa with
a melt temperature of 166°C. The adhesive construction with liner is
wound
at 12 m/min, and the adhesive construction is about 1 1.5 cm wide and about
0.5 miss (12 micron) thick.
Examples 3-Ei
In these examples, the apparatus used is similar to the apparatus
of Fig. 2. Two Klllion 1 " extruders are usedl for streams A and C. A Davis-
Standard 1.5" extruder is used for stream B. A Leistritz twin screw extruder
is
used for stream D. The Killion extruders are operated at 200°C, and the
Davis-
Standard extruder is operated at 215°C. The Leistritz extruder is
heated
according to the following profile: unheated, 145 ° C, 160 ° C,
160 ° C, 170 ° C,
170°C, 175°C, 175°C, 180°C and 180°C. The
adaptor is heated to 210°C.
The speeds of the extruders are varied according to the product desired. The
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39
streams A, B and C consists of polypropylene 5E66 from Union Carbide; and
these streams are fed through a feedblock into one manifold of an 1 1 "
Production Components dual manifold extrusion die. Stream D is a pressure
sensitive adhesive which is fed directly into tine other manifold of the
extrusion
dies. The extrudate is cast with adhesive in contact with a release liner, and
stream A in contact with the chili roll 56. The chill roll stack is maintained
at
about 90 ° C and the die gap for the ABC layer is set to about 380
microns. The
gap for the adhesive Payer is about 250 microns. Additional details regarding
these four examples, as well as the details of the product, are summarized in
the
following Table 111.
Table III
Example Example Example Example
3 4 5 6
Killion rpms 5 5 2.5 2.5
Davis-Standard 4% 4% 2% 2%
1 5 Leistritz rpms 450 450 450 450
Kraton D1320X/A0 glhr 1013 253 370 1521
Kraton LVSI g/hr 95 24 38 134
Escorez 2596 glhr 950 238 340 1426
Line speed m/min 6.1 6.1 9.1 9.1
PP film thickness tmu) 35 25 5 10
Adhesive coatweight (glm2) 23 5 .5 24
As mentioned above, the composite constructions of the present
invention may be combined with a release liner by contacting a release finer
with
the substrate adhesive layer to form label stock. The release liner which may
be utilized in the label constructions may comprise any of a variety of
materials
known to those skilled in the art to be suitable as release liners. In one
preferred
embodiment, the release liner comprises a silicone coated paper substrate.
Coated polymer film substrates also can be wised as release liners.
The label stock may then be converted to labels by procedures well
known to those skilled in the art. Thus, the label stock may be printed and
die-
cut into individual labels. The printing step may occur before or after the
combining of the adhesive constructions of the invention and the release
liner,
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but will precede the die-cutting of the facestock into individuals labels. The
film
must remain in accurate register between printing steps (for example, between
successive impressions and different colors) in order that image or text may
be
of high quality, and between printing and sulasequent die-cutting in order
that
5 the image or text be located properly on the labels. The film is under
tension
during printing, and may be subjected to some; increase in temperature, such
as,
for example, when UV inks are curred, and the film must maintain dimensional
stability in the machine-direction.
The label stock is die-cut into a series of spaced pressure-sensitive
10 labels carried by the release liner. This step may be performed by rotary
cutting
dies in a well known manner and involves a subsequent stripping of the iadder-
shaped matrix of waste or trim materials surrounding the formed labels when
they are die-cut (the "rungs" of the ladder rE:presenting the spacing between
successive labels). The labels then remain on the liner in spaced relation
with
15 each other. One failure mode in this operation involves poorly die-cut
labels
remaining with the matrix as it is stripped. In this mode, as the release
levels
decrease, poor die-cutting is more likely to cause labels to stay attached to
the
matrix material and be removed from the liner during matrix stripping along
with
the matrix. Another failure mode results when the films being die-cut are of
20 insufficient strength. As the strength of the matrix material decreases,
the
matrix tends to tear as the matrix around thf; die-cut labels is pulled from
the
finer. The films of the present invention do Name sufficient strength to avoid
or
reduce breakage of the matrix upstripping.
The composite constructions in one embodiment of the present
25 invention advantageously have sufficient stiiffness to be dispensable
utilizing
commercially available dispensable apparatus such as a peel-back edge. In a
preferred embodiment of the present inverntion, the composite constructions
are
peel-piste dispensable. Dispensability, as defined earlier, includes the steps
of
the separation of the labels from the liner, andi the successful application
of the
30 label to a substrate surface.
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41
The coextruded adhesive constructions of this invention are useful
in a variety of applications including signs, labels, tags, decals, etc. As
noted
above, the constructions are particularly useful in preparing labels. The
constructions also can be used as decals such as for pin striping of, for
example,
automobiles and trucks, especially when the constructions are very thin (e.g.,
faceless). When the thermoplastic elastomer adhesives described above are
used in faceless constructions, the constructiions exhibit reduced oozing of
the
adhesive around the edges, and the edging or the decal or pin stripe is less
evident after application. The constructions also are useful in autdoor signs
and
decals for application to, for example, glass windows. The thin constructions
of the invention can be die-cut, and the signs and decals can be removed from
the release layer by hand. High speed dispensing (and therefore stiffness) is
not
an issue in these applications. Highly conformable (flexible) films such as
medical films also can be prepared from the adhesive constructions of the
invention. Such films which are prepared using the thermoplastic elastomer
adhesives exhibit low water vapor transmission which can be further improved
by selection of particular FFMs. The adhesive constructions also are useful in
preparing tamper-evident labels or seals for containers such as bottles which
may contain printed words such as VOID. For example, when the top of a
capped bottle having a film around the top of the bottle and cap is twisted to
open, the film will be pulled down on the Ibottle rather than fracturing and
forming sharp edges.
While the invention has been explained in relation to its preferred
embodiments, it is to be understood that various modifications thereof will
become apparent to those skilled in the art upon reading the specification.
Therefore, it is to be understood that the invention disclosed herein is
intended
to cover such modifications as fall within the scope of the appended claims.
