Note: Descriptions are shown in the official language in which they were submitted.
1;~;~3409
The present invention relates to an improved multiple
layer packaging sheet material which can be formed into closed
and sealed packages suitable for holding products containing
substantial fractions of cyanoacrylate.
Products containing cyanoacrylate are quite active
chemically. Because of the reactive nature of cyanoacrylates, it
has been difficult to find packagin~ means and material with
which the cyanoacrylate product does not interact in a way which
is detrimental to the cyanoacrylate in the package, and to
u holding it in the package.
Traditionally, cyanoacrylate adhesives have been
packaged in plastic bottles and metal tubes. The plastic
containers do not provide adequate vapor barrier, such that the
1~ shelf-life of products packaged in conventional plastic
containers is undesirably short. Metal tubes also have some
undesirable characteristics. They are relatively inflexible such
that they can be flexed only a few times as in repeated
dispensing before cracks develop in the tube sidewall. Overall,
2U though, shelf life of cyanoacrylate products is better in metal
tubes than plastic, at least untll the tube is initially opened.
nevertheless, the shelf life, even in metal tubes, is less than
desired~ Clearly, cyanoacrylates are readily identified as being
difficult to hold in a package over a desirable shelf life
2~ period.
Products have been packaged in tube-type containers of
generally three types. The first type is a metal tube. Such
tubes provide excellent barrier properties, but have undesirable
functional properties as discussed above. The second type is a
plastic tube made from either single or multiple layers of
plastics. While plastic tubes may be excellent for many
products, no plastic packaging materials are known which are
excellent for holcling cyanoacrylate-type products. The third
type is a tube macle from previously formed multiple layer sheet
-- 1 --
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~2684(~
materials containin~ a layer of metal foil and a plurality of
layers of plastic materials, generally re~erred to hereinafter as
laminated tubes.
The third type of tube container has been used
conventionally for holding hygienic-type products such as
toothpaste. Tooth paste is chemically quite active, and is
generally considered difficult to hold in a package.
Attempts to package cyanoacrylate adhesives in the
u third type of tube containers were not successful with any of the
conventionally known sheet materials used t~ make the laminated
tubes. After being packaged in conventional tubes of the third
type, the cyanoacrylate adhesive migrated through polymer layers
to the foil layer. The tube delaminated between the foil layer
1~ and the ad~acent polymer layer. The delaminated tube was not
satisfactory for the package.
Cyanoacrylate also tends to cause swelling or polymers.
In trials with some experimental multiple layer tubes, polymer
2U layers disappeared as distinct layers, presumably having been
either dissolved into the cyanoacrylate or otherwise ab~orbed
into it.
The present invention provides a packaging sheet
21 material capable of holding cyanoacrylate-type products.
The present invention also provides such a sheet
material which has excellent barrier to passage of matter through
the sheet material.
3U The invention again provides a package capable of
holding a cyanoacrylate-type product.
According t~ the present invention there is provided a
multiple layer sheet material having all the layers firmly
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adhered to each other. The sheet material has a first layer of
high density polyethylene (HDPE), a second layer which may be a
polymer or an adheslve, and a third primer layer of polyethylene
imine ( PEI ) . The third primer layer is between the first and
second layers.
Regarding the layer compositions, each of the layers
has preferred features which, while not critical to the
invention, contribute to its efficiency or optimization. Thus,
the resin density of the HDPE as determined by ASTM D-2839 is
preferably at least 0.950. It should also preferably have a
u narrow molecular weight distribution and should be substantially
free of amine components. Preferably it crystallinity is
relatively high as developed in formation of that film~like
layer.
The second layer may be any of a wide variety of
functional materials which exhibit the desired properties.
Preferred for the second layer is ethylene acrylic acid copolymer
~EAA) .
2~
The primer in the third layer is preferably applied as
a liquid solution containing a cross-linking type PEI.
Preferred embodiments of the sheet material include a
fourth layer of metal foil so positioned in the structure that
2~ the second layer is between the third and fourth layers.
Finally, in most preferred embodiments, a flfth layer
adhered a sixth layer, as of polyethylene, to the metal foil.
3~ Another aspect of the invention is seen in a package
which includes the novel packaging sheet material herein ln the
form of a package and a quantity of product therein where the
product contains cl substantial fraction of a cyanoacrylate-type
component. The package is configured such that no edge of the
-- 3 --
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126~3409
sheet material is exposed to the product.
Thus according to one aspect thereof the presentinvention provides a multiple layer sheet material, including:
(a) a first layer of high density polyethylene; tb) a second
layer, the composition of said second layer being chosen from the
group consisting of polymers and adheives; and (c) a third primer
layer, the composition of said primer layer ha~ing been made from
a primer comprising a ma~or fraction of a Lewis base and
components of a cyanoacrylate material, said third layer being
between said first and second layers.
:l.U
In a further aspect thereof the present invention
provides a multiple layer sheet material, including: (a) a first
layer of high density polyethylene; (b) a second layer; (c) a
third primer layer, the composition of said primer layer
comprising a ma~or fraction of a Lewis base, said third primer
layer being between said first and second layers; and (d) a
fourth layer of metal foil, said second layer bsing between said
third and fourth layers.
2U In a still further aspect thereof the invention
provides a multiple layer sheet material, comprising: ~a) a first
layer of high density polyethylene; (b~ a second layer, the
composition of said second layer comprising ethylene acrylic acid
~opolymer; and (c) a third primer layer, the composition of said
primer layer comprising a major fraction of a Lewis base; said
third layer being adhered in said sheet material to both said
first and second layers. Suitably said Lewis base is
polyethylene imine.
The present invention again provides a multiple layer
sheet material comprising: (a) a first layer of polyethylene
having a resin density of at least 0.950, having a narrow
molecular weight distribution, and being substantially free of
amine compone~ts; (b) a second layer, the composition of said
second layer being chosen from the group conslsting of polymers
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and adhesives; and (c) a third primer layer, said third layer
including a Lewis base and reacted components from a
cyanoacrylate-type material, said third layer being between said
first and second layers.
The present invention further provides a multiple layer
sheet material comprising, in order: ~a) a first layer of
polyethylene having a resin density of at least 0.950, having a
narrow molecular weight distribution, and being substantially
free of amine components; tb~ a second primer layer of
polyethylene imine on one surface of said first layer; (c) a
third layer of ethylene acrylic acid copolymer on said second
primer layer; and ~d) a fourth layer of metal foil on said third
layer.
1~ The invention also provides a multiple layer sheet
material including: (a) a first layer of hlgh density
polyethylene; (b) a second layer, the composition of said second
layer being selected from the group consisting of heat rPsistant
polymers and abuse resistant polymers; (c) a third primer layer,
2U the composition of said primer layer comprising a ma~or fraction
of a Lewis base, said third layer being between said first and
second layers; and (d) a fourth barrier layer bet~een said second
and third layers.
The invention also provides a package wherein the
packaging sheet material has been modified by virtue of contact
with cyanoacrylate-type components. In the modified form of the
sheet material, the primer layer includes reacted components from
the cyanoacrylate products.
3~
Thus the present invention in another aspect thereof
provides a package comprising a packaging sheet material and a
product therein, said product including a substantial fraction of
cyanoacrylate typ~ component, said packaging sheet material
including: (a) a ~irst layer of hlgh density polyethylene; (b) a
-- 5 --
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~ 9
second layer, the composltion of said second layer being chosen
from the group consisting of polymers and adhesives; and (c) a
third primer layer of polyethylene imine, sald third layer being
between said first and second layers, said first layer being
disposed toward the inside of said package, said package being
configured such that no edge of said sheet material is exposed to
said product.
The present invention again provides a package
comprising a packaging sheet material and a product enclosed
therein, said product including a substantial fraction of
cyanoacrylate-type component, said packaging sheet material
including: (a) a first layer of polyethylene having a resin
density of at least 0.950, having a narrow molecular weight
distribution, and being substantially free of amine components;
(b) a second layer of ethylene acrylic acid copolymer; (c) a
third primer layer, said third layer including polyethylene imine
and reacted components from said cyanoacrylate~type product; and
(d) a fourth layer of metal foil; said third layer being between
said first and second layers, said second layer being between aid
2U third and fourth layers, said first layer being disposed toward
the inside of said package, all the layers of said sheet material
being adhered to each other, sald package be~ng configured such
that no edge of said sheet material is exposed to said product.
The present lnvention will be further illustrated by
J way of the accompanying drawings in which:
FIGURE 1 is a cross-section of a three-layer sheet
structure of this invention.
3~ FIG~RE 2 is a cross-section of a four-layer sheet
structure of this invention.
FIGURE 3 is a cross-section of a six-layer sheet
structure of this invention.
-- 6 --
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FIGURE 3A is a cross-section of sheet structure not of
this invention. It is similar to sheet structure of FIGURE 3,
except without the primer layer of FIGURE 3.
FIGURE 3s is a cross-section of another sheet structure
not of this invention. It is similar to sheet structure of
FIGURE 3 but has the primer layer in the wrong location.
FIGURE 3C is a cross-section of a sheet structure of
the invention which has two primer layers.
FIGURE 4 is a pictorial view of an exemplary package of
this invention, and including a cyanoacrylate-type product
therein.
FIGURE 5 is a greatly enlarged cross-section taken at
5-5 of Figure 4, and showing the primer layers immediately after
filling the pac~age with product.
FIGURE 6 ls a greatly enlarged cross-section as in
2U FIGURE 5 shown after a long enough time that the primer layer has
been modified and includes reacted components from the product.
In FIGURE 1 is shown a cross-section of a simple sheet
structure 110 of the invention, inc'uding two polymeric layers
112 and 116 and a thin primer layer 114 therebetween. Layer 112
2~ is HDPE. The composition of layer 116 is usually polymeric and
may be chosen with substantial freedom. Layer 114 is a thin
- layer of primer.
In the numbering system, the first digit rep~esents the
3~ FIGURE number. The second and third digits represent the element
in the FIGURE. Common second and third digit numbers in the
various FIGURES represent common elements. Thus 14 represents
the primer layer :ln any of the FIGURES where it is shown. 114
represents the pr:Lmer layer in only FIGURE 1.
-- 7
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FIGURE 2 shows a cross-section of a sheet structure 210
of the lnvention of intermediate complexity. Layer 212 is HDPE.
Layer 214 is a thin primer layer. Layer 216 is an adhesive which
is effective to adhere to a foil layer 218. with the
introduction of the foil layer into the structure, the
composition of adhesive layer 216 is selected such that it
provides good adhesion between the foil layer 218 and the HDPE
layer 212 through the primer 214. EAA is preferred ~or layer
216.
LU FIGURE 3 shows a cross-section of a sheet structure 310 of the invention having more complexity than the structures of
FIGURES 1 and 2, and also having more-preferred functional
properties. Layers 312, 314, 316 and 318 are equivalent to the
respective ones of those layers in FIGURE 2. Layer 320 is an
1~ adhesive layer which adheres layer 322 to the foil layer 318.
Layer 322 is protective of the foil layer and its composition is
selected with that protection property as an important criteria.
As stated earlier, cyanoacrylate is highly xeactive a a
2~ chemical product. it is this strong tendency toward reaction
that makes it so difficult to s\design a packaging material to
hold it. It is ~urther important that certain layers of the
packaging material of this invention not to be permitted to come
into direct contact with the cyanoacrylate product. As it has
2~ been found that direct contact with cyanoacrylate can be
tolerated by HDPE, it is preferred, and h~ghly functional for the
cyanoacrylate-type product to be in direct contact with only the
HDPE layer in the flnished packages of this invention. An
acceptable package structure is a fin-sealed pouch 411 as seen in
3U FIGURE 4. The peripheral seals 424 are pointed out on 2 of the 4
sides of the pouch.
FIGURE 5 shows a cross-section of the pouch of FIGURE
4. Each of the layers 12, 14, 16, 18, 20, and 22 is shown in its
overall relationship to the sheet structure, the package, and the
3~
-- 8 --
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product. it is seen that the fin-sealed type of construction
ensures that the cyanoacrylate product has direct contact only
with the hdpe layer. The FIGURE 5 structure is accurately
descriptive of the package at the time the product is put into
the package.
As is illustrated in FIGURES 1, 2, 3, and 5, the primer
layer 14 is extremely thin. It is important that the primer
layer be continuous, in order to met its minimum required
functional parameter. Meeting the minimum required functional
u parameters, however, does not impose. any minimum requirements for
physical thickness of the primer layer beyond that required for
continuity. The typical quantity of a PEI present in the sheet
structure is of the order of 0.04 lbs. per 3000 square foot ream.
In practice, the presence of layer 14 as a distinct layer is not
visually detectable by normal microscopic examination of a cross-
section of the sheet structure up to the time it is brought into
contact with a cyanoacrylate-type product.
FIGURE 6 represents the cross-section as in FIGURE 5,
2~ but after the cyanoacrylate product has been in the package for a
while. The significant change is that a visible layer 614R has
developed at layer 14, which was also the interface of iayers 12
and 16 for aperance purposes when the sheet material was formed.
For example, in packages evaluated after one week of storage at
120F., the new layer as at 614R was 0,4 to 0.7 mil thick.
Packages evaluated after four weeks of storage at 1~0F. had
layers 614R which were 0.9 to 1.6 mils thick. A primary
component of the new layer 614R is reacted polymer of
cyanoacrylate. Notably, the storage conditions cited herein are
unusual in that they accelerate, in many respects, the normal
process of aging for both the packaging material and the product.
Thus, the tests iterated herein may repre~ent the entire normal
shelf life of the packaged product, or even beyond. ;~
In some experimentally-made sheet materials which were
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otherwise the same as the sheet materials 10 of the invention,
the primer layer 14 was not continuous, but unintentionally had
small discontinuities of pin-hole size. Packages made with these
sheet materials were not satisfactory. On inspection of the
filled and sealed packages after a short storage period of 1 or 2
weeks, spot delaminations were unex]pectedly observed. On detail
inspection, discontinuities were identified ad~acent each spot
delamination. The discontinuities were visible to microscopic
inspection, in the reacted layer 614R. No spot delaminations
were observed which could not be as~sociated with a dlscontlnuity.
Thus the inventors have reached the conclusion that the primer
layer 14 serves some function of the nature of lmpending the
migration of the cyanoacrylate product to the surface of the
surface of the foil 18. it appears that the cyanoacrylate does
penetrate, and pass through any discontinuity of the primer layer
14, to swell the layer 16, and react at the foil layer 18 to
cause delamination. The inventors herein have concluded that the
continuity of primer layer 14 is critical to operability of the
invention. To that end, it is desirable to treat the surface of
the HDPE layer, as necessary, such as by corona discharge, to
ensure good wetting of the HDPE layer by the PEI when it is
2U applied.
In certain cases, ~t may be desirable to have
additional layers between ~PE layer 12 and the primer 14. Such
additional layers may be used so long as any interaction they may
2~ have with, or as a result of, the product is acceptable and so
long as the primPr layer is continuous as described earl~er and
is separated from any foil layer by at least one intervening
layer.
3~ Experimentation has shown that, of the polyethylene
imines available, the cross linking types are preferable over the
non-crosslinking types. it is hypothesized that the P~I may act
as a chemically basic electron donor material, and may interact
with the product in polymerization, or other reaction of the
-- 10 --
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.
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cyanoacrylate product. Once the cyanoacrylate has reacted, the
size of the reacted molecule is apparently such that it is no
longer as mobile in the laminated sheet structure, and remains in
the vicinity of the reaction site to form a part of the visible
layer 14R. Based on the belief that the PEI acts as a catalytic
electron donor, it is believed that other Lewis bases, such as
J amines and salts of weak acids, should function in a similar
manner to impede migration of the product.
Essentially, the presence of the primer layer 14
u impedes migration of the cyanoacryliate through the structure past
the primer layer. FIGURE 3A represents a cross-section of sheet
structure similar to the six layer structure of FIGURE 3, but
without the primer layer 14. Layers 312A, 316A, 318A, 320A and
322A all represent layers equlvalent to the respective layers in
1~ the sheet structures of the invention. Without a primer layer
14, though, the sheet structure is not capable of satisfactorily
holding cyanoacrylate-type products wlthout significant
deleterious affect on the packaging sheet structure. Typical
affects are swelling of polymer layers and delaminatlon. FIGURE
2U 3B represents a cross-section of sheet structure simllar to the
structure of FIGURE 3, but with the primer layer 14 in the wrong
place. Layers 312B, 314B, 316B, 320B, and 322B all represent
layers equivalent to the respective layers in the sheet structure
of the invention. Primer layer 14, however, is at the interfacs
between the foil 18 and the EAA 16, rather than at the interface
between the HDPE 12 and the EAA 16. With the primer thus
improperly positioned, namely ad~acent the foil rather than
displaced from it, the sheet structure is not capable of
satisfactorily holding cyanoacrylate-type products. Typical
affects are swelling, especially layer 16, and delamination,
3U particularly at the foil interface. Primers may be used
elsewhere in the invention, as seen in FIGUR~ 3C, so as long as
the primary of primer between layers 12 and 16 is retained. To
that end layer 312C, 314Cl, 316C, 318Ct 320C, and 322C all
represent layers equivalent to the respective layers in FIGURE 3.
3~
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Layers 314C2 is an additional primer layer which may, for
example, be used to promote adhesion between layers 320C and
322C. This practice of using one or more additional primer
layers, in addition to the primary primer layer at the interface
of layers 12 and 16, is fully satisfactory so long as primary
primer layer 14, as described herein, is displaced from the
product and from the foll by at least one layer, and is between
the product and the foil.
In general, of the polymers usually associated with
good heat sealing capabilities, HDPE is the least affected by
cyanoacrylate-type product. Other polymers are caused, by
cyanoacrylate-type products, to swell by 50% to over 150%. As in
the case of linear low density polyethylene copolymer (LLDP~),
some polymeric materials are even absorbed into the product.
1~ While HDPE is also swelled somewhat, in the better HDPE's, the
swelling is 11mited to only about 30%, and overall strength of
the package is sustained satisfactorily. While most high density
polyethylenes are acceptable, some are more preferred. The
preferred polymers are characterized by the following properties.
z~ Resin density should be at least 0.950. The HDPE preferably has
a narrow molecular weight distribution. A high degree pf
crystallinity in the HDPE layer is desirable, and can be somewhat
controlled by the rate of cooling when the HDPE layer is formed
by some melt forming process such as extrusion.
2~
The critical elements of the invention are the HDPE
layer 12 which serves as the sealant layer without being
unacceptably affected by the cyanoacrylate product, and the
primer layer 14. the presence of the primer layer at the
disclose disclosed location causes the mobility of the
3~ cyanoacrylate product to be impeded such that it does not readily
pass through layer 14 and have harmful affect on the layers 16,
18, etc., which are beyond layers 12 and 14, a viewed from the
layer 12 surface through the sheet material. Thus, the
compositions of the various layers 16, 18, etc., beyond layer 14
- 12 -
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may not need to be selected for their resistance to
cyanoacrylate. Rather, they may be selected for their other
desirable properties. thus, layer 16 is defined rather broadly,
as a polymer or an adhesive, and may be selected for the
properties desired. in a three layer structure as in FIGURE 1,
layer 16 may, for example, conveniently be any polymer which
adheres well to the primed side of the HDPE layer. Typical layer
1~ polymers would be low density polyethylene ~LDPE~, HDPE, and
propylene ethylene copolymer (PPE). Where a fourth layer is
present in the sheet material, then the layer 16 must adhere well
u to it as well as to the interface at layers 12 and 14. In these
structures, layer 16 may be considered to be a layer serving
primarily an adhesive function. The adhesive layer may be
polymeric adhesive. Where the fourth layer is metal ~-oil, and
adhesive polymer such as EAA is known to adhere well to foil and
1~ is preferred for layer 1~. Where the fourth layer 18 is
polymeric, an adhesive polymer with graft substitutions of
carboxy moietics such as maleic anhydride may be preferred. In
some cases, adhesive emulsions may be used. In general, the
selection of material for layer 16 depends on the definition of
2~ its function in the sheet structure, whether it be of a
protective nature, as may be true in a three layer structure, or
an adhesive nature in structures having more than three layers.
The compositions, then, of layers 1~ and 14 are
2~ selected with the primary purpose - in addition to their normal
package structural functions - of controlling migration of the
cyanoacrylate product through the sheet material. When properly
selected and applied, they functionally control the migration of
the cyanoacrylate through the sheet material, such that the
compositions of all the other layers may be selected without
primary consideration of their susceptibillty to cyanoacrylate.
Thus layer 18 is a metal foil layer which would be highly
susceptible to loss of adhesion to polymers in the presence of
cyanoacrylate-type products. Rather it is selected for its
excellent properties as a barrier against passage of any matter
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through the package sheet material, into or out of the package.
Other barrier materials may be used in the invention. Along with
selection of the barrier material, if one is used, prop~r
materlals are selected from those known in the art, for the
layers ad~acent the barrier layer to ensure adhesion to, and
compatibility with, the rest of the ~sheet structure. Exemplary
of possible alternate barrier materials are vinylidene chloride
copolymPrs, ethylene vinyl alcohol copolymers, and blends
including ma;or fractions of these.
Layer 16 is preferably E~A, another material
susceptible of being greatly swelled by cyanoacrylate. But, with
the protection provided by layers 12 and 14, the EAA is not thus
disastrously affected by the product and may be selected for its
excellent adhesive properties to the metal foil. Likewise layers
1' 20 and 22 may also be selected without primary consideration of
direct interaction with the product. By the same consideration,
the layers 16 through 22, as well as additional layers may be
selected with substantial freedom as long as the layers 12 and 14
serve a protective function between the layers 16 through 22 and
2~ the product.
The most preferred structure of the sheet mater~al
herein is that illustrated by FIGURES 3, 5, and 6. The sealant
layer 12 and the primer layer 14 are narrow molecular weight HDPE
and crosslinking PEI respectively. "Narrow molecular weight" is
a relative term, used by the industry, that identifies the
sub;ect group of HDPE polymers by sub~ectively comparing their
molecular weight distributions with those of other HDPE polymers.
Layer 16 is EAA which serves as an adhesive to the metal foil
barrier layer 18. Layer 20 is preferably EAA which serves as an
adhesive between the foil layerl8 and layer 22 which is desirably
a layer of polymer which is selected for either its excellent
abuse resistance or lts heat resistance. Whlle a preferred
composition for layer 22 is HDPE, other materials may be
preferred for some uses. Exemplary of these are oriented
3~ ;
- 14 -
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polypropylene, oriented polyester, and orlented nylon. In some
preferred embodiments, the layer 22 composition is LDPE. The
composition oE the adhesive layer 20 is selected in view of the
selected compositions of both layers 18 and 22. Additional
layers may be used as dictated by the situation, such as for
printing, pigmenting, etc.
!j
In order for the combined properties of the HDPE in
layer 12 and the primer in layer 14 to provlde protection for the
other material layer in the sheet structure, namely protection
from the cyanoacrylate product, it is important that the HDPE and
PEI layers be interposed between the cyanoacrylate and the other
layers at all areas where cyanoacrylate is in contact with the
packaging sheet material. Illustratlve of this principle is a
fin-sealed package as illustrated in FIGURES 4, 5, and 6.
1~- Formation of a finished package as shown in FIGURE 4, from
multiple layer sheet materials, is conventionally known in the
industry. While the sheet structures disclosed herein are highly
unusual, forming them into a finished package is relatively
straight forward, as by means of conventionally forming heat
2U seals about the periphery as shnwn in FIGURE 4. The development
of the vl~ible layer in its role in impending penetration of
cyanoacrylate into the rest of the packaging structure.
The process of making the sheet structure of the
2' invention will now be discussed in terms of the preferred
embodiments of the more complex structure; and it will be seen
that the simplier structures are in some cases substructures
thereof. The discussion of complex structures as in FIGURE 3,
thus, also includes the general types of processes which are used
to make the simpler 3 or 4 layer structures.
3~
In the first operation, a layer of HDPE is formed, as
by an extrusion process. The process is designed for relatively
slow cooling of the extruded HDPE layer in order to encourage
development of crystallinity. A preferred process is tubular
3~
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blown extrusion. Another acceptable process is cast extrusion
where the sheet is cast onto a relatively warm roll and where the
elevated temperature are held over a perlod of time, down stream
of the extrusion, which is conducive to development of
crystallinity. The HDPE layer is then preferably corona treated
to a level of at least 38 dynes/cm. of surface energy. the
treated side of the HDPE is then primed with a PEI prlmer
solution and dried, leaving a continuous layer of PEI on the
surface of the HDPE. The primed sicle of the ~DPE layer is then
extrusion laminated to aluminum foil uslng EAA as the extrusion
laminant. The structure at this state is represented by FIGURE
2. The structure as represented by FIGURE 3 iS completed by
extrusion laminating a previously formed abuse resistant layer,
such as HD~E, to the exposed side of the foil, using EAA as the
extrusion laminant.
If desired, the sheet material may then be reacted with
cyanoacrylate moieties, to form a sheet material having a reacted
primer layer 14R, before forming it into a package structure as
in FIGURE 4. The reaction may be carried out by contacting the
HDPE layer 12 with the cyanoacrylate moieties.
2U
In making the 3-layer structure, representad by FIGURE
1, the HDPE layer is formed, treated and primed as previously
discussed. Layer 16 is then added by an appropriate process. A
typical process is extrusion coating of the appropriate material
onto the primed surface. In another exemplary process, layer 16
is formed in a separate operation and is ~oined to primer layer
14 by heat and pressure lamination at a hot nip, or may be
extrusion laminated to layer 14 by using an intervening layer of
an extrusion laminant.
3U
Thus it is seen that the invention provides a packaging
sheet material capable of holding cyanoacrylate-type products.
it further provides a sheet material which has excellent barrier
properties to passage of matter through the sheet material. Even
- 16 -
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.... - ~, ... .
more significantly, the invention provides a sheet material which
can be made into a closed and sealed package capable of holding a
cyanoacrylate-type product.
The sheet materials of this invention are also, of
course, capable of holding products which have lower chemical
activity than cyanoacrylate. In those cases, materials which are
less preferred for holding cyanoacrylate may be more desirable
because of other advantages such as economics or processing
advantages.
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