Note: Descriptions are shown in the official language in which they were submitted.
PCT/US93/09935
WO 94/08796
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~IOLTIL~YER FILM STRUCTORE
This invention relates to a multilayer packaging
or label stock film structure having excellent
printability and non-blocking characteristics.
The standard commercial approach to achieve
wetting and adhesion of printing inks on certain
packaging and label stock film is to subject the film
to a surface modifying treatment, especially with
corona discharge or a gas flame. This type of
treatment does not always provide for sufficient ink
adhesion for many applications. Excellent adhesion
can be obtained by applying a primer layer to the
film before application of the ink. While this may
provide an excellent surface for wetting and adhering
printing inks, preprimed film cannot be sold in roll
form: the primer layer will cause destructive
blocking between the primed surface and the reverse
side of the film after it is rolled up and stored for
any length of time.
The present invention seeks to provide a film
which has excellent printability and which is not
subject to destructive blocking.
The present invention provides a printable film
structure comprising a polymeric film substrate
having at least one surface adherently incompatable
with printing ink and having a primer coating thereon
of a type which can cause destructive blocking
between contacting layers of such coated films
wherein the primer coating has thereon a polyester or
coating of a water dissipatable printing ink base,
with or without pigment, to prevent blocking.
In one aspect of the present invention, the
printing ink base is a coating of a water-
dissipatable copolyester having an inherent viscosity
of at least 0.1 as measured in a 60/40 parts by
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weight solution of phenol/tetrachloroethane at 25°C
and at a concentration of 0.5 gm. of polyester in 100
ml. solvent, especially wherein the copolyester
comprises the condensation product of the following
monomers (or their polyester forming equivalents):
a) from 90 to 97 mole % isophthalic acids and,
correspondingly,
b) from 3 to 10 mole % of 5-sulfrisophthalic
acid;
c) from 70 to 85 mole % of 1,4-cyclohexane-
dimethanol; and, correspondingly,
d) from 15 to 30 mole % of diethylene glycol.
In another aspect of the present invention the
copolyester comprises the condensation product of the
following monomers (or their polyester forming
equivalents) .
a) from 60 to 75 mole % terephthalic acid:
b) from 15 to 25 mole % of at least one
dicarboxylic acid of the formula .
HOOC (CH2)n COOH
wherein n is from 1 to 11:
c) more than 6 to 15 mole % of at least one
sulfomonomer containing an alkali metal
sulfonate group attached to a dicarboxylic
aromatic nucleus; and
d) a stoichiometric quantity of about 100 mole
% of at least one copolymerisable aliphatic
or cycloaliphatic alkylene glycol having
from 2 to 11 carbon atoms.
In the film structure described above the primer
coating can be a coating of a member selected from
E
the group consisting of (A) the reaction product of
acidified aminoethylated vinyl polymer and an epoxy
resin, (B) poly(ethyleneimine), and (C) mixtures
thereof.
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The substrates contemplated herein include any
polymeric film substrate that can be employed for
packaging purposes; for a label stock film; or for
decorative purposes. Included within this class of
materials are nylon; polyethylene terephthalate;
polycarbonate; and polyolefins. The contemplated
structures also include coextrudates of the recited
materials, laminates of any two or more of these
materials or interblends of any of the materials
extruded as a single base film. A particularly
preferred class of films are the polyolefins. Within
the polyolefin class, homopolymers and copolymers of
propylene are preferred. Particularly preferred are
isotactic polypropylenes containing at least 80% by
weight of isotactic polypropylene. The preferred
base substrate layer can be homopolymer polypropylene
having a melting point from 161°C (321°F) to 169°C
(336°F). Commercially available materials of this
description include Exxon 4252 and FINA 3371. When
the preferred substrate is employed it can be
employed as is or with coextruded or laminated thin
skin layers which each amount to from 2 to 18% of the
total thickness. The skin material can be a
copolymer of propylene and another olefin, e.g.,
ethylene and/or butene-1. The other olefin can be
present in the copolymer in an amount from 1 to 7 wt.
%. White opaque, cavitated polypropylene is also a
substrate film of choice. Polyethylene film in all
of its forms and densities, oriented or unoriented is
also contemplated.
The films employed can be unaxially or biaxially
oriented. The preferred range of orientation can be
from 1.3 to 7 times in the machine direction and from
5 to 10 times in the transverse direction.
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Before primer coating any of these materials
they may be corona discharge treated to 38 to 42
dynes/cm by standard commercial techniques. They may
also be flame treated by means known in the art.
The primer coating material contemplated, as '
indicated above, is the type which inherently causes
destructive film blocking between contacting layers
of such a coated film when the film is convolutely
rolled up and store for at least a number of days.
As indicated above, the primer coating comprises a
reaction product of an acidified aminoethylated vinyl
polymer and an epoxy resin: a poly(ethyleneimine): or
a mixture thereof.
The primer coating (A) is described in U.S.
Patent 5,066,434.
As disclosed the primer materials include the
reaction product of an epoxy resin and an acidified
aminoethylated vinyl polymer. The contemplated epoxy
resins are glycidyl ethers of polyhydroxy compounds.
Typical polyhydroxy compounds which may be used
include bisphenol A, ring substituted bisphenol A,
resorcinol, hydroquinone, phenol-formaldehyde,
novolac resins, aliphatic diols, such as ethylene
glycol, propylene glycol, 1,4-butanediol, 1,6-
hexanediol, glycerol, lower alkyl hydantoins and
mixtures thereof.
The preferred epoxy resins of the present
invention are those made by the glycidation reaction
between epichlorohydrin and bisphenol A. Epoxy
resins of this type are commonly classified by their
epoxy equivalent weight (EEW) which is defined as the
weight of resin in grams which contains one gram
equivalent of epoxy groups. Resins with an EEW from
170 to 280 may be used in the present invention, but
the preferred range is from 180 to 210.
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A variation in the composition of the epoxy
resin component is one in which a hydantoin compound
is substituted for the bisphenol A. For example,
1,1-dimethyl hydantoin may be employed in a low
molecular weight epoxy resin since resins based on
this material are completely water soluble thereby
eliminating the necessity for emulsification.
Although the specific structure of the epoxy
resin is not critical to the primer employed in the
present invention, important considerations in the
selection of the epoxy resin depend upon its physical
state. For example, it must be liquid and capable of
being readily dispersed or dissolved with the second
component or curing agent as described hereinbelow.
If the epoxy resin is of low viscosity, it may be
stirred directly into the second component, i.e.,
curing agent, however, it is preferred to employ the
epoxy resin in an aqueous emulsion.
The second component in the epoxy primer
compositions of the present invention is an amino
modified acrylic polymer which is water soluble.
This polymer is a curing agent for the epoxy
compound. The preferred material is described in the
U.S. Patent No. 3,719,629 and may be generically
described as an acidified amino-ethylated
interpolymer having pendant amino alkylate groups.
This material is produced by polymerizing acrylate,
methacrylate, styrene or other suitable monomers with
sufficient methacrylic or acrylic acid to give a -
COOH content of 7.5 to 12.5. Solvent polymerization
techniques are preferred. The polymer is then
reacted with ethyleneimene monomer and acidified with
hydrochloric acid to render the polymer water
soluble.
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The primer coating may be applied to the
substrate as a dispersion or as a solution, from an
organic vehicle, for example, an alcohol or an °
aromatic hydrocarbon, such as xylene or a mixture
thereof. .. '
In one embodiment of the present invention, a
liquid epoxy resin is emulsified in a stilution of the
curing agent by rapid stirring. Thereafter, the
resultant dispersion is diluted with water to the
desired concentration for coating, which typically
includes from about 2 to about 25~ solids.
When mixing the epoxy resin with the curing
agent, it is generally preferred to use a
stoichiometric equivalent balance of epoxy and amine
groups. However, it has been found that the
stoichiometric ratio may be varied over a wide range,
for instance, from about one epoxy group to about
three amine groups through three epoxy groups to one
amine group and, preferably, from about one epoxy
group to two amine groups through about two epoxy
groups to about one amine group, without seriously
affecting the product's usefulness as a primer
coating.
It is to be understood that the solution or
dispersion of epoxy resin and curing agent can
contain small amounts of wetting agents in order to
facilitate the application of the primer material to
the surface of layer (b). Conventional non-ionic
wetting agents which can be employed include the
hexyl or benzyl ether of ethylene glycol, the hexyl
ether of diethylene glycol, butyl alcohol, hexyl
alcohol, octyl alcohol and diacetone alcohol.
Although mixtures of the epoxy resin and the ,
curing agents will cross-link or cure without the
necessary addition of a catalyst, it has been found
WO 94/08796 ~ ~ PCT/US93/09935
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advantageous, in certain instances, to use an amine
catalyst. Such catalysts include propylene diamine
and hexamethylene diamine.
The alternative primer coating material (B)
poly(ethyleneimine) is also known as PEI. The use of
PEI as a primer material for polymeric coatings on
film substrates such as cellophane or polyolefins is
well known in the art as disclosed in British Patent
Nos. 766,827 & 910,875. This material is also
described in U.S Patent No. 3,230,175. A
commercially available material of this type is known
as EPOMIN L50 a product of Nippon Shogubi. This
material can be applied from either aqueous or
organic solvent media, such as ethanol in a solution
comprising from 0.1 to 0.6% by weight of the
poly(ethyleneimine) when a mixture of A and B are
employed any ratio is contemplated.
The above described primer coating materials
when applied to any of the defined substrate film
structures have the draw back of causing destructive
blocking when such films are convolutely wound for
shipment to a converter. The essence of the present
invention involves the discovery that a certain class
of water-dispersible polyester ink bases can be
coated onto the surface of these primers and,
thereafter, the film structures can be convolutely
wound without any danger of destructive blocking. In
addition, it has been discovered that these
polyesters can withstand extremely high (93°C;
200°F.+) temperatures. Further, these polyester
surfaces permit an exceptionally strong bonding to
result when printed indicia or design is printed
thereon. As will be shown, the multilayer structure
and the printed information and/or design can
withstand water temperatures of 200°F. alone or in
WO 94/08796 ~ ~ ~ ~ ~ ~ ~ PGT/US93/09935
_g_
combination with moderate abrasive action in contact
with the printed surface. These polyesters have been
described as linear, water-dissipatable polyesters
having inherent viscosities as disclosed above and
having the equimolar proportions of acid and hydroxy
moieties referred to above. The polyesters comprise
repeating units of components (a), (b), (c) and (d),
as follows:
(a) 90 to 97 mole % isophthalic acid,
(b) 3 to 10 mole % 5-sulfoisophthalic acid,
(c) 70 to 85 mole % 1,4-cyclohexanedimethanol,
and
(d) 15 to 30 mole % diethylene glycol.
Component (b) can be in the form of a sodium salt.
These polyesters are described in detail in U.S.
Patent 5,006,598.
The following Examples illustrate the invention.
ERAMPhE 1
Biaxially oriented homopolypropylene of a
thickness of about 1.9 mils is corona discharge
treated to about 38 dynes/cm and is one-side prime
coated with the reaction product of an acidified
aminoethylated vinyl polymer and an epoxy resin as
described in Example 3 of U.S. Patent No. 4,214,039.
After drying in hot air to a weight of 0.05 gms/msi,
the film is convolutely wound and stored at 70°F for
about 7 days. On attempting to uncoil the film it
will be found to have destructive blocking and be
unusable for subsequent conversions.
EXAMPLE 2
A film as in Example 1, before being rolled up
is top-coated with the polyester composition
described in Example 13 of U.S. Patent No. 5,006,598.
This top-coat is applied to a dry weight of just less
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than 0.06 gms/msi. The film is convolutely wound and
stored at 70'F for about 7 days. This film can be
unrolled and re-rolled with no evidence of blocking.
ERAMPLE 3
The film of Example 2 is printed with a water-
based flexographic ink known as '°No. WR30007, from
Environmental Inks and Coating Corp.. Employing #610
Scotch Tape R from 3M Co. as an adherence test, the
printing can not be removed.
ERAMPLE 4
The printed film of Example 3 is coated with a
pressure sensitive adhesive on the reverse side
thereof and applied as a label to a glass container.
The label and glass are submerged in 200°F. water for
10 minutes and then scraped in an attempt to remove
the ink. The ink will be found to be firmly bonded
to the polyester coated epoxy primed oriented
polypropylene substrate. The flexographic ink will
not wet corona treated polypropylene film alone and
the ink can be easily lifted off by the tape.
ERAMPLE 5
Biaxially oriented homopolypropylene of a
thickness of about 1.9 mils is corona discharge
treated to about 38 dynes/cm and is one-side prime
coated with the reaction product of an acidified
aminoethylated vinyl polymer and an epoxy resin as
described in Example 3 of U.S. Patent No. 4,214,039.
After drying in hot air to a weight of 0.05 gms/msi,
the film is convolutely wound and stored at 70°F for
about 7 days. On attempting to uncoil the film it
will be found to have destructive blocking and be
unusable for subsequent conversions.
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ERAMPLE 6
A film as in Example 5, before being rolled up
is top-coated with the polyester composition
described in Example 28 of U.S. Patent No. 4,525,419.
This top-coat is applied to a dry weight of just less '
than 0.06 gms/msi. The film is convolutely wound and
stored at 70°F for about 7 days: This film can be
unrolled and re-rolled with no evidence of blocking.
ERAMPLE 7
The film of Example 6 is printed with a water-
based flexographic ink known as "No. WR30007, from
Environmental Inks and Coating Corp.. Employing #610
Scotch Tape R from 3M Co. as an adherence test, the
printing can not be removed.
EXAMPLE 8
The printed film of Example 7 is coated with a
pressure sensitive adhesive on the reverse side
thereof and applied as a label to a glass container.
The label and glass are submerged in 200°F. water for
10 minutes and then scraped in an attempt to remove
the ink. The ink will be found to be firmly bonded
to the polyester coated epoxy primed oriented
polypropylene substrate. The flexographic ink will
not wet corona treated polypropylene film alone and
the ink can be easily lifted off by the tape.
The foregoing examples demonstrate that oriented
polypropylene film can be prime coated with a primer
material which leads to destructive blocking between
adjacent layers. This blocking can be eliminated by
top coating the prime coating with a polyester
composition within the scope of U.S. Patent 4,525,419
or 5,006,598. This polyester coating not only
prevents the destructive blocking of the film but
also provides a surface to which conventional label
printing inks will aggressively adhere and even
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WO 94/08796 - PGT/US93/09935
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withstand the rigors of hot water applied in an
agitating manner to the film in label form applied to
a container surface. The same effect will be
experienced if the prime coating is
' S poly(ethyleneimine) alone or in combination with the
epoxy prime coating material.
The polyesters of the present invention are
fundamentally an ink without any pigment. If
commercial pigments were added to polyester, they
indeed could be employed as a printing ink
composition. When the primed substrate is coated
with the proper amount of the polyester, blocking
between films is prevented. This would be true
whether the polyester contained an ink pigment or
not. Thus, in its broadest sense the present
invention overcomes the tendency of primed substrate
films to block by applying a pigment or non-pigmented
polyester uniformly over the primed surface. As
indicated, since the polyester is fundamentally an
ink without pigment and a necessary attribute of an
ink is that it has good adhesion to itself, the
primed and polyester coated film has excellent print
characteristics. It has been found however, that the
ink base polyester compositions must not be coated to
an extent greater than 0.06 gms/msi. As a lower
limit the polyester can be coated to that extent
which effectively prevents blocking of the primed
substrate film.
