U.S. patent application number 11/810716 was filed with the patent office on 2007-10-18 for food packaging laminates.
Invention is credited to Annegret Janssen, Wolfgang Zenker.
Application Number | 20070243293 11/810716 |
Document ID | / |
Family ID | 22962168 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070243293 |
Kind Code |
A1 |
Janssen; Annegret ; et
al. |
October 18, 2007 |
Food packaging laminates
Abstract
The invention relates to a flexible packaging. Specifically,
this invention relates to a laminate, the use of the laminate in
the packaging of food, drinks, medicine and toys, and a
corresponding package. The laminate can be a film-to-film and
film-to-foil laminates, suitable for typical food packaging uses,
using hot melt laminating adhesives. Such laminates are
substantially fee from volatile contaminates, especially migratable
isocyanates and aromatic amines.
Inventors: |
Janssen; Annegret;
(Luneburg, DE) ; Zenker; Wolfgang; (Adendorf,
DE) |
Correspondence
Address: |
H.B. Fuller Company;Patent Department
1200 Willow Lake Blvd.
P.O. Box 64683
St. Paul
MN
55164-0683
US
|
Family ID: |
22962168 |
Appl. No.: |
11/810716 |
Filed: |
June 7, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10433027 |
Nov 26, 2003 |
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PCT/EP01/12879 |
Nov 7, 2001 |
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11810716 |
Jun 7, 2007 |
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60253903 |
Nov 29, 2000 |
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Current U.S.
Class: |
426/124 |
Current CPC
Class: |
B32B 2317/122 20130101;
B32B 27/32 20130101; B32B 2367/00 20130101; B32B 2307/412 20130101;
A22C 2013/0059 20130101; B32B 27/06 20130101; B32B 2307/31
20130101; B32B 15/085 20130101; B32B 2439/62 20130101; B32B 27/36
20130101; B32B 7/12 20130101; B32B 2307/75 20130101; B32B 27/18
20130101; B32B 2439/70 20130101; B32B 2439/46 20130101; B32B
2439/80 20130101; B32B 2311/00 20130101; B32B 2037/1215 20130101;
B32B 7/10 20130101; B32B 27/10 20130101; B32B 15/09 20130101; B32B
2323/00 20130101 |
Class at
Publication: |
426/124 |
International
Class: |
B65B 25/00 20060101
B65B025/00 |
Claims
1. A method of packaging a food, the method comprising: surrounding
a food with a flexible laminate, the flexible laminate being
substantially free of migratable isocyanates and migratable
aromatic amines and comprising a first flexible substrate, a
non-reactive hot-melt adhesive composition, and a second flexible
substrate bonded to the first substrate through the hot-melt
adhesive composition, the hot-melt adhesive composition comprising
thermoplastic polymer and tackifying agent, the first and second
flexible substrates being selected from the group consisting of
polymer film, metallized polymer film, foil and combinations
thereof.
2. The method of claim 1 further comprising forming the flexible
laminate into a bag-like structure.
3. The method of claim 2 further comprising sealing the bag-like
structure.
4. The method of claim 1 further comprising forming the flexible
laminate into a bag-like structure prior to surrounding the food
with the flexible laminate.
5. The method of claim 4, wherein the surrounding comprises placing
the food in the bag-like structure.
6. The method of claim 1, further comprising applying a vacuum to
the package and sealing the package.
7. The method of claim 1 further comprising heat sealing a first
surface of the flexible laminate to a second surface of the
flexible laminate.
8. The method of claim 1, wherein the laminate is free of defects
consisting of streaking and enclosed air.
9. The method of claim 1, wherein the hot melt adhesive composition
is in the form of a continuous layer having a coat weight no more
than 10 g/m.sup.2.
10. The method of claim 1, wherein the hot melt adhesive
composition is in the form of a continuous layer having a coat
weight from 3 g/m.sup.2 to 5 g/m.sup.2.
11. The method of claim 1, wherein the hot melt adhesive
composition is in the form of a continuous layer having a coat
weight less than 3 g/m.sup.2.
12. The method of claim 1, wherein the hot melt adhesive
composition further comprises at least one of wax and
plasticizer.
13. The method of claim 1, wherein the food comprises at least one
of medicine, snack foods, confectionery, aqueous foods, moist
foods, dry food stuffs, milk, coffee, tea, cheese, fresh fruits,
fresh vegetables, fresh meats and fish.
14. The method of claim 1, wherein the laminate is in the form of a
"form-fill-and-seal" package.
15. The method of claim 1, wherein the laminate is in the form of a
tube prior to surrounding the food.
16. A packaged food comprising: a food; and a flexible laminate
surrounding the food, the flexible laminate comprising a first
substrate, a non-reactive hot melt laminating adhesive, and a
second substrate laminated to the first substrate through the
adhesive, the flexible laminate being essentially free of
migratable polyisocyanates and migratable aromatic amines.
17. The packaged food of claim 16, wherein the food comprises at
least one of medicine, snack foods, confectionery, aqueous foods,
moist foods, dry food stuffs, milk, coffee, tea, cheese, fresh
fruits, fresh vegetables, fresh meats and fish.
18. The packaged food of claim 16, wherein the flexible laminate is
heat sealed to itself.
19. The packaged food of claim 16, wherein the hot-melt adhesive
composition comprises thermoplastic polymer and tackifying
agent.
20. The packaged food of claim 16, wherein the first and second
substrates are selected from the group consisting of polymer film,
metallized polymer film, foil and combinations thereof.
21. The packaged food of claim 16, wherein the food is edible.
22. The packaged food of claim 21, wherein the food is selected
from the group consisting of medicine, toys, snack foods,
confectionery, aqueous foods, moist foods, dry foodstuffs, milk,
coffee, tea, fresh fruit, fresh vegetables, fresh meats, fish, and
corresponding frozen items.
23. The packaged food of claim 16, wherein the laminate is in a
form selected from the group consisting of a bag, pouch and a
box.
24. The packaged food of claim 16, wherein the laminate is in the
form of a "form-fill-and-seal" package.
25. A packaged food comprising: a package defining an opening; a
food disposed in the package; and a flexible laminate extending
across the opening of the package and sealing the opening, the
flexible laminate being in a form selected from the group
consisting of a capseal and a heat-seal lidding, the flexible
laminate comprising a first substrate comprising a first surface, a
non-reactive hot melt laminating adhesive on the first surface of
the first substrate, and a second substrate laminated to the first
substrate through the adhesive, the flexible laminate being
essentially free of migratable polyisocyanates and migratable
aromatic amines.
26. The packaged food of claim 25, wherein the package is in the
form of a beaker, bowl, dish or a combination thereof.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/433,027, filed Nov. 26, 2003, which was the National
Stage of International Application No. PCT/EP01/12879, filed Nov.
7, 2001, which claims the benefit of U.S. Provisional Application
No. 60/253,903, filed Nov. 29, 2000, all of which are incorporated
herein.
BACKGROUND OF THE INVENTION
[0002] The invention relates to a flexible packaging. Specifically,
this invention relates to a laminate, the use of the laminate in
the packaging of food, drinks, medicine and toys, methods of
producing such laminates, methods of packaging articles and a
corresponding package.
[0003] It is well known to package food in wraps, bags, pouches
etc. made of laminates. Preferred materials for food packaging
often consist of a first substrate, such as a film, which is
generally thin and transparent, but can be printable, and a second
substrate which can be another, (often thicker) film, a metal foil,
a metalized film etc.
[0004] Whereas in the past, such film-to-film and film-to-foil
laminations were often produced using volatile organic
solvent-based laminating adhesives, environmental and regulatory
restrictions have in the more recent past caused the industry to
use waterborne adhesives, especially polyurethane dispersions and
acrylic emulsions.
[0005] Examples of polyurethane dispersions are disclosed in U.S.
Pat. Nos. 5,494,960, 5,532,058, 5,861,410, 5,907,012 and 5,834,554.
U.S. Pat. No. 5,907,012 are specially suitable for indirect food
contact and U.S. Pat. No. 5,834,554 for direct food contact
packaging.
[0006] Recently, the laminating industry has begun to investigate
into solvent-free two-component reactive adhesives. Although some
of these are applied at elevated temperatures, these are not hot
melt adhesives.
[0007] Also the food industry has begun to use similar laminates,
as food packaging materials. Such laminates are produces using
reactive, generally polyurethane-based laminating adhesives.
[0008] However, film-to-film and film-to-foil laminates using
solvent-free reactive laminating adhesives, even including
two-component polyurethane laminating adhesives, may lead to
problems specifically in food. In some cases, solvent-free reactive
laminating adhesives may retain relatively high levels of monomer,
unless they are very carefully cured. Such careful curing requires
time and energy expenditure. Whereas in many applications of
laminated materials, such monomer contamination does not present a
problem, this is not true in the food industry, since the monomers
may migrate into the food, which is not acceptable.
[0009] Specifically, the use of reactive polyurethane adhesives has
in some cases been found to lead to contamination of the packaged
food with unreacted isocyanates and carcinogenic aromatic amines
(probably formed by reaction of adhesive components with moisture
from the food).
[0010] Thus, food packaging materials may release volatile and/or
migratable contaminations which result from the adhesives used in
manufacturing such materials.
[0011] This problem is, as far as the food industry is concerned,
acerbated by the need for just-in-time production and delivery,
such restraints actually promoting the use of not fully cured
laminates.
[0012] Food as mentioned herein includes any item, whether edible
or not, that are intended to be brought into contact with the body
of a mammal, especially put into people's mouth, such as food
items, drinks, medicine and baby toys. Mammals in this context
include humans. Contact with the body means the possibility of
undesired contamination of the body by volatiles and/or migratables
as defined above.
SUMMARY OF THE INVENTION
[0013] The present inventors have invented a laminate that
overcomes these problems in the prior art.
[0014] The invention specifically provides a laminate for use in
food packing. The laminate can be based on a laminate of a
(conventional) film material and a second (conventional) substrate,
using a hot melt (solvent-free) laminating adhesive, which is
substantially free from volatile and/or migratable contaminants,
especially monomeric or oligomeric isocyanates and aromatic
amines.
[0015] Another aspect of the present invention is to identify the
use of such flexible laminating materials in food packaging and a
corresponding method of packaging food items. The laminate can be a
film-to-film and film-to-foil laminate, suitable for typical food
packaging uses, using solvent-free non-reactive hot melt laminating
adhesives. Such laminates are substantially free from volatile
contaminants, especially migratable isocyanates and aromatic
amines. They can be produced with the properties necessary for food
packaging uses, if the laminating adhesive is applied as a
pre-formed film to the first substrate, prior to laminating to a
second substrate.
[0016] Lamination can be done either in-line or off-line. For
off-line laminating, a substrate is preferably pre-coated with a
hot melt adhesive, and this pre-coated film is later laminated to a
second substrate by heat sealing. In-line lamination of the two
films can be done directly in the nip, or in a second nip (the
laminating station) using a release-roller in the first nip to
squeeze out any entrapped air between the first film and the
extruded ("pre-formed") adhesive film. Entrapped air can also be
squeezed out using this same technique for off-line lamination.
[0017] Such pre-formed adhesive films can be generated using
non-contact coating methods. Thus, film-on-film laminates using
solvent-free hot melt adhesives can be produced, by non-contact
coating of the adhesive onto one of the films and then contacting
and, in case, nipping the two films. A corresponding disclosure can
be found in Applicant's earlier application PCT/EP98/01588,
incorporated herein by reference, especially where the coating
method, the selection of film and other substrate materials and the
selection of adhesives is concerned.
[0018] The present invention further relates to a method of forming
a laminate for food packaging comprising: [0019] a) positioning a
slot nozzle at least 0.5 mm spaced away from a first substrate and
advancing said first substrate along a path; [0020] b) applying a
non-reactive hot melt adhesive to a surface of said first substrate
from said slot nozzle; [0021] and [0022] c) mating a second
substrate with the adhesive bearing surface of said first substrate
to form a laminate that has reduced contamination of packaged goods
by volatile and/or migratable organic materials.
[0023] Preferably, the adhesive is applied directly to said first
substrate surface, i.e. it does not contact anything solid between
the point in time when the adhesive leaves the slot nozzle and the
point in time when the adhesive first contacts the substrate.
However, in some applications, it may be advantageous that the
adhesive is applied from the slot nozzle to a transfer device such
as a roller or transfer tape, and is then coated onto the substrate
surface from said roller or tape. Also in such methods, the slot
nozzle will preferably not be in contact with the transfer device.
In such cases, the nozzle will be positioned spaced at least 0.5 mm
away from the surface of said transfer device, and may of course be
much more distanced from the substrate.
[0024] Lastly, the invention is concerned with methods of packaging
articles which are intended to come into contact with mammalian
bodies, especially humans, and among these specially with items for
ingestion and mouth contact, such as food, drink, medicine and toy
items such as baby toys, and with correspondingly packaged such
articles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1A shows the basic structure of a coating and
laminating equipment suitable for practicing the present
invention.
[0026] FIGS. 1B and 1C show other structures of a coating and
lamination equipment also suitable for practicing the present
invention.
[0027] FIGS. 2 through 10 show preferred equipment for practicing
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The flexible food packaging items of the invention will
often be in the form of a bag or pouch, which can be sealed, such
as heat-sealed, as is customary in the food packaging industry.
Alternatively, the invention's flexible food packaging items can be
in the form of a web or sheet material for the production of such
bags or pouches, or for wrapping purposes. It is preferred that the
pre-forming of the hot melt laminating adhesive film, e.g. by the
non-contact coating method as already mentioned, occurs during the
in-line production of the laminate material. To achieve this, the
devices as e.g. shown in already mentioned PCT/EP98/01588 can be
used. The amount of hot melt laminating adhesive used corresponds
to the typical range of area weights in this type of laminate, but
will generally be at the lower end thereof, since the non-contact
coating method employed in this invention permits the use of very
low area weights without causing problems such as streaking.
[0029] Coating weights of no more than about 20 g/m.sup.2,
preferably no more than about 10 g/m.sup.2, more preferable from
about 2 to about 6 g/m.sup.2, are realized.
[0030] It is surprising that this non-contact coating method is
particularly suitable for food packaging, Thus the food packaging
laminates of the present invention generally use the typical film
substrates known in the art. Thus, the film material will often be
a polyolefin such as LDPE, PE or PP, or a polyester such as PET;
the second substrate will often be another, often thicker
polyolefin such as PE or PP, or a PET or nylon film. Metalized
films such as metalized PP or PET can be used. The films used in
the invention are generally heat-sealable. Corresponding film and
substrate materials are e.g. disclosed by B. S. Glassbrenner,
"Third Generation Solventless Laminating Adhesives for the Flexible
Packaging Market," TAPPO 1996 Polymers, Laminations and Coatings
Conference, the contents of which are hereby incorporated by
reference.
[0031] Film-to paper laminates for the graphical industry using hot
melt laminating adhesives are e.g. described in U.S. Pat. No.
5,958,178.
[0032] It can be specifically advantageous to use biodegradable
materials, especially biodegradable hot melt adhesives and films,
in the context of this invention. Some biodegradable materials are
e.g. disclosed in applicant's PCT/US94/09666, incorporated herein
by reference.
[0033] These and more types of hot melt adhesives can be used with
this coating method to produce reduced monomers or volatile
organics without drying or solvent evaporating steps, and can
achieve low levels of adhesive coating. This is especially
important for food packaging. While reactive solvent or water-based
emulsions and solvent-less reactive adhesives have to be carefully
prepared to achieve adhesives with low levels of monomers,
oligomers as well as other impurities, it is easier to achieve such
low levels with thermoplastic materials suitable for food
packaging, especially when low amounts are used.
[0034] The preferred adhesives in the context of the present
invention comprises those disclosed in PCT/EP98/01588. It is
preferred to use non-reactive hot melt adhesives based on
copolymers of olefins and (meth-)acrylic acid; copolymers of
olefins and (meth-)acrylic acid derivatives; copolymers of olefin
and (meth-)acrylic acid esters; copolymers of olefins and vinylic
compounds; poly-.alpha.-olefins, especially atactic
poly-.alpha.-olefins (APAOs); thermoplastic synthetic rubber;
metallocen-catalysed polymers, especially based on ethylenes and/or
propylene; ionomers and especially copolymers; and mixtures of two
or more of these thermoplastic polymers.
[0035] Specifically, useful ones include EMA, EnBA, EVA, or
ethylene copolymers, blended with aliphatic hydrocarbon resins,
aromatic hydrocarbon resins, wood or colophonium resins and
polyethylene or polyethylene wax, or thermoplastic materials such
as polyolefins, especially polyethylene, polypropylene, amorphous
polyolefins such as Vestoplast 703.RTM. (Huls) and the like. One
especially useful hot melt adhesives includes Advantra.RTM., where
low monomer content, narrow molecular weight distribution, and low
viscosity for easier coating without the need for additives and
diluents are possible.
[0036] Specific advantages can be obtained where the thermoplastic
polymer has two or even three different EnBA components, which
differ in the amount of ester, in the melt flow index, or in the
melting point or softening temperature range. It is specifically
preferred that the thermoplastic polymer comprises at least two
EnBAs with differ by a factor of at least 4 and up to 10 in their
melt flow index (MFI), expressed, as usual, in grams per 10
minutes.
[0037] Uncompounded thermoplastic materials such as polyolefins,
especially polyethylene, polypropylene, amorphous polyolefins such
as Vestoplast 70.RTM. (Huls), polyesters, polyamides and the like,
may also be suitable as laminating adhesives of the present
invention.
[0038] A preferred type of polyolefin, typically described as
"metallocene polyolefins", is produced with a single-site catalyst
resulting in a homogenous distribution of comonomer branching, and
a narrow molecular weight distribution, i.e., a molecular weight
distribution, M.sub.w/M.sub.n, less than or equal to 3, preferably
less than or equal to 2.5. The connotation "metallocene" is not
meant in any way to be limiting regarding the specific catalyst
used in the process of manufacturing the copolymer, but merely an
abbreviated description of the homogenously branched linear or
substantially linear polymer structures themselves.
[0039] By the term homogenous, it is meant that any comonomer is
randomly distributed within a given interpolymer molecule and
substantially all of the interpolymer molecules have the same
ethylene/comonomer ratio within that interpolymer. The DSC melting
peak of homogenous linear and substantially linear ethylene
polymers will broaden as the density decreases and/or as the number
average molecular weight decreases. However, unlike heterogeneous
polymers, when a homogenous polymer has a melting peak greater than
115.degree. C. (such as is the case of polymers having a density
greater than 0.940 g/cm.sup.3), such polymers do not additionally
have a distinct lower temperature melting peak.
[0040] In addition or in the alternative, the homogeneity of the
polymers is typically described by the SCBDI (Short Chain Branch
Distribution Index) or CDBI (Composition Distribution Branch Index)
and is defined as the weight percent of the polymer molecules
having a comonomer content within 50 percent of the median total
molar comonomer content. The SCBDI of a polymer is readily
calculated from data obtained from techniques known in the art,
such as, for example, temperature rising elution fractionation
(abbreviated herein as "TREF") as described, for example, in Wild
et al., Journal of Polymer Science, Poly. Phys. Ed., Vol. 20, p.
441 (1982), in U.S. Pat. No. 4,798,081 (Hazlitt et al.), or in U.S.
Pat. No. 5,089,321 (Chum et al.) the disclosures of all of which
are incorporated herein by reference. The SCBDI or CDBI for the
homogenous linear and for the substantially linear
ethylene/.alpha.-olefin polymers used in the present invention is
preferably greater than 50 percent.
[0041] Heterogeneous polymers are ethylene/.alpha.-olefin
interpolymers characterized as having a linear backbone and a DSC
melting curve having a distinct melting peak greater than
115.degree. C. attributable to a high density fraction.
Heterogeneous interpolymers will typically have an M.sub.w/M.sub.n
greater than 3 (when the density of the interpolymer is less than
about 0.960 g/cc) and will typically have a CDBI less than or equal
to 50, indicating that such interpolymers are a mixture of
molecules having differing comonomer contents and differing amounts
of short chain branching.
[0042] The homogenous polyethylenes useful in this invention fall
into two broad categories, the linear homogenous polyethylenes and
the substantially linear polyethylenes. Both are known.
[0043] Homogenous linear ethylene polymers have long been
commercially available. As exemplified in U.S. Pat. No. 3,645,992
to Elston, homogenous linear ethylene polymers can be prepared in
conventional polymerisation processes using Ziegler-type catalysts
such as, for example, zirconium and vanadium catalyst systems. U.S.
Pat. No. 4,937,299 to Ewen et al. and U.S. Pat. No. 5,218,071 to
Tsutsui et al. disclose the use of metallocene catalysts, such as
catalyst systems based on hafnium, for the preparation of
homogenous linear ethylene polymers. Homogenous linear ethylene
polymers are typically characterized as having a molecular weight
distribution M.sub.w/M.sub.n, of about 2. commercially available
examples of homogenous linear ethylene polymers include those sold
by Mitsui Petrochemical Industries as Tafmer.TM. resins and by
Exxon Chemical Company as Exact.TM. resins.
[0044] The substantially linear ethylene polymers (SLEPs) are
homogenous polymers having long chain branching. They are disclosed
in U.S. Pat. Nos. 5, 272,236 and 5,272,272, the disclosures of
which are incorporated herein by reference. SLEPs are available
from The Dow Chemical Company as polymers made by the Insite.TM..
Process and Catalyst Technology, such as Affinity.TM. polyolefin
plastomers (POPs). SLEPs can be prepared via the solution, slurry,
or gas phase, preferably solution phase, polymerisation of ethylene
and one or more optional .alpha.-olefin comonomers in the presence
of a constrained geometry catalyst, such as is disclosed in
European Patent Application 416,815-A, incorporated herein by
reference. The constrained geometry catalysts are described in more
detail later.
[0045] The term "substantially linear" means that, in addition to
the short chain branches attributable to homogenous comonomer
incorporation, the ethylene polymer is further characterized as
having long chain branches in that the polymer backbone is
substituted with an average of 0.01 to 3 long chain branches/1000
carbons. Preferred substantially linear polymers for use in the
invention are substituted with from 0.01 long chain branch/1000
carbons to 1 long chain branch/1000 carbons, and more preferably
from 0.05 long chain branch/1000 carbons to 1 long chain
branch/1000 carbons. In contrast to the term "substantially
linear", the term "linear" means that the polymer lacks measurable
or demonstrable long chain branches, i.e., the polymer is
substituted with an average of less than 0.01 long chain
branch/1000 carbons.
[0046] For ethylene/.alpha.-olefin interpolymers, the long chain
branch is longer than the short chain branch that results from the
incorporation of the .alpha.-olefin(s) into the polymer backbone.
Each long chain branch has the same comonomer distribution as the
polymer backbone and can be as long as the polymer backbone to
which it is attached.
[0047] The presence of long chain branching can be determined in
ethylene polymers by using C.sup.13 nuclear magnetic resonance
(NMR) spectroscopy and is quantified using the method described by
Randall (Rev. Macromol. Chem. Phys., C.29, V.2&3, p. 285-297),
the disclosure of which is incorporated herein by reference.
[0048] As a practical matter, current C.sup.13 nuclear magnetic
resonance spectroscopy cannot determine the length of a long chain
branch in excess of six carbon atoms. However, there are other
known techniques useful for determining the presence of long chain
branches in ethylene polymers, including ethylene/1-octene
interpolymers. Two such methods are gel permeation chromatography
coupled with a low angle laser light scattering detector
(GPC-LALLS) and gel permeation chromatography coupled with a
differential viscometer detector (GPC-DV). The use of these
techniques for long chain branch detection and the underlying
theories have been well documented in the literature. See, e.g.,
Zimm, G. H. and Stockmayer, W. H., J. Chem. Phys., 17, 1301 (1949)
and Rudin, A., Modern Methods of Polymer Characterization, John
Wiley & Sons, New York (1991) pp. 103-112, both of which are
incorporated by reference. Further, and in particular, A. Willem de
Groot and P. Steve Chum, both of The Dow Chemical Company, at the
Oct. 4, 1994, conference of the Federation of Analytical Chemistry
and Spectroscopy Society (FACSS) in St. Louis, Mo., presented data
demonstrating that GPC-DV is a useful technique for quantifying the
presence of long chain branches in substantially linear ethylene
polymers.
[0049] The empirical effect of the presence of long chain branching
in the substantial linear ethylene/.alpha.-olefin interpolymers
used in the invention is manifested as enhanced theological
properties which are quantified and expressed herein in terms of
gas extrusion rheometry (GER) results and/or a melt flow
I.sub.10/I.sub.2, which may be varied independently of the
M.sub.w/M.sub.n.
[0050] Substantially linear ethylene polymers are further
characterized as having: [0051] (a) a melt flow ratio,
I.sub.10/I.sub.2.gtoreq.5.63, [0052] (b) a molecular weight
distribution, M.sub.w/M.sub.n as determined by gel permeation
chromatography and defined by equation:
(M.sub.w/M.sub.n)(I10/I.sub.2)-4.63, [0053] (c) a critical shear
stress at the onset of gross melt fracture, as determined by gas
extrusion rheometry, of greater than 4.times.10.sup.6
dynes/cm.sup.2 or a gas extrusion rheology such that the critical
shear rate at onset of surface melt fracture for the substantially
linear ethylene polymer is at least 50 percent greater than the
critical shear rate at the onset of surface melt fracture for a
linear ethylene polymer, wherein the substantially linear ethylene
polymer and the linear ethylene polymer comprise the same comonomer
or comonomers, the linear ethylene polymer has an I.sub.2,
M.sub.w/M.sub.n and density within ten percent of substantially
linear ethylene polymer and wherein the respective critical shear
rates of the SLEP and the linear ethylene polymer are measured at
the same melt temperature using a gas extrusion rheometer, and
[0054] (d) a single differential scanning calorimetry, DSC, melting
peak between -30 and 150.degree. C.
[0055] An apparent shear stress versus apparent shear rate plot is
used to identify the melt fracture phenomena and quantify the
critical shear rate and critical shear stress of ethylene
polymers.
[0056] According to Ramamurthy in the Journal of Rheology, 30 (2),
337-357, 1986, the disclosure of which is incorporated herein by
reference, above a certain critical flow rate, the observed
extrudate irregularities may be broadly classified into two main
types: surface melt fracture and gross melt fracture.
[0057] Surface melt fracture occurs under apparently steady flow
conditions and ranges in detail from loss of specular film gloss to
the more severe form of "sharkskin". Herein, as determined using
the above-described GER, the onset of surface melt fracture (OSMF)
is characterized at the beginning of losing extrudate gloss at
which the surface roughness of the extrudate can only be detected
by 40.times. magnification. The critical shear rate at the onset of
surface melt fracture for the substantially linear ethylene
polymers is at leas 50 percent greater than the critical shear rate
at the onset of surface melt fracture of a linear ethylene polymer
having essentially the same I.sub.2 and M.sub.w/M.sub.n.
[0058] Gross melt fracture occurs at unsteady extrusion flow
conditions and ranges in detail from regular (alternating rough and
smooth, helical, etc.) to random distortions. For commercial
acceptability to maximize the performance properties of films,
coatings and moldings, surface defects should be minimal, if not
absent. The critical shear stress at the onset of gross melt
fracture for the substantially linear ethylene polymers, especially
those having a density >0.910 g/cc, used in the invention is
greater than 4.times.10.sup.6 dynes/cm.sup.2. The critical shear
rate at the onset of surface melt fracture (OSMD) and the onset of
gross melt fracture (OGMF) will be used herein based on the changes
of surface roughness and configurations of the extrudates extruded
by a GER. Preferably, the substantially linear ethylene polymer
will be characterized by its critical shear rate when used as the
first ethylene polymer of the invention and by its critical shear
stress when used as the second ethylene polymer of the
invention.
[0059] The adhesive can also comprise up to 100% of at least one
EMA, EnBA or homogenous linear polymer. Preferably, the
thermoplastic polymer component comprises at least two, preferably
three, different EnBA components, wherein one EnBA component has a
melt flow index which is at least four times and up to 10 times
higher than the melt flow index of at least one other EnBA
component, said melt flow index being in units of gram per 10
minutes. If the thermoplastic polymer comprises more than one EnBA
component, said EnBA components differing in the ester content, in
the melt flow index and/or the melting point or softening
point.
[0060] Tackifying resins can be used and are selected from
aliphatic and aromatic hydrocarbon resins, especially hydrogenated
aliphatic hydrocarbon resins and .alpha.-methyl styrene resins,
colophonium resins and colophonium ester resins, especially
hydrogenated such colophonium and colophonium ester resins. The
preferred tackifying resin is hydrogenated aliphatic hydrocarbon
resin, and .alpha.-methyl styrene resin, with the amounts of from
about 10 to about 40% by weight.
[0061] The hot melt laminating adhesive can additionally comprise
at least one other polymer, especially a polyolefin such as
polyethylene or a polyethylene wax.
[0062] The amount of preferred ingredients present in the adhesive
is tabulated as follows: TABLE-US-00001 Most Preferred preferred
Thermoplastic (co-)polymer 10-100% 20-80% 35-60% Aliphatic
hydrocarbon resin 0-50% 0-45% 0-40% Aromatic hydrocarbon resin
0-20% 0-15% 0-10% Colophonium resin 0-40% 0-35% 0-30% Polyethylene
or polyethylene wax 0-20% 0-15% 0-10%
as well as, in case, small amounts of customary additives.
[0063] The adhesive film is continuous, even at low coating weights
and the laminate does not easily exfoliate or delaminate upon
sealing. The adhesive peel strength ranges from 0.5N/15 mm to film
destruction, depending on the substrates, adhesive formulation used
as well as angle and rate of peeling.
[0064] The structure of the machine can be that or similar to that
shown in FIGS. 1A-1C. FIGS. 1A and 1B show an embodiment where a
thermoplastic composition is released from a coating device (3)
onto a first substrate (1), and a second substrate (4) is then
disposed upon the free surface of the coated adhesive, by a nip
roll (5). It is to be understood that this arrangement can be
modified in other embodiments and especially that the second
substrate (4) need not be used in all cases. Then, the nip roll (5)
can be employed to nip the thermoplastic composition directly to
the first substrate. For such embodiments, the nip roll (5) will be
release-coated, e.g. may be a steel roller with a
polytetrafluorethylene surface layer.
[0065] More specifically shown in FIGS. 1A and 1B, Substrate 1 (1)
travels past a series of idle rollers (2) to ensure the web is in
proper alignment prior to approaching the coating device (3).
Substrate 2 (4) is optionally adhered to the coating surface by
means of a nip roll (5). Substrate 1 is defined as the first
substrate that is contacted with the substantially continuous
thermoplastic film. Substrate 1 may be any substrate which is
generally provided in a roll good such as non-woven, paper
including release-coated paper, and a wide variety of films, foils
and other materials. The embodiment of FIG. 1A, where the nip roll
(5) is located fairly remote from the contact point of adhesive
film and first substrate, is especially suited for the coating of
porous substrates. The embodiment of FIG. 1B is especially suitable
when Substrate 1 is nonporous meaning air does not readily pass
through the substrate. In the case of film lamination, Substrate 1
is typically a film. Substrate 2 may also be provided in a roll
good and be the same or a different material as Substrate 1.
[0066] FIG. 1C shows an embodiment where the adhesive film is first
nipped onto the first substrate (1) by nip roll (5), which is part
of a nipping station as later shown by rolls A and B in FIGS.
2-10.
[0067] A second substrate 4 is then disposed on the free surface
not in contact with the first substrate (1), at a lamination
station formed by rolls C and D. With this type of machine, it is
possible to nip the adhesive film directly onto the first substrate
(1) by means of nip roller (5) or nip a second substrate (4) onto
the first substrate and adhesive, again by means of nip roller (5).
In the tests, both methods were tried. The dispensing temperature
of the hot melt can range from about 90.degree. to about
200.degree., preferably from about 110.degree. to about 140.degree.
C. depending on the composition, thickness and speed of
coating.
[0068] Machine speeds of up to about 500 m/minute, preferably about
350 m/minute, and more preferably about 300 m/minute are suitable.
During the coating process, the adhesive film is release from the
coating slot nozzle, at various distances from a first substrate
(1) to be coated with the adhesive. Also, the distance of the slot
nozzle from the substrate can be varied between a few millimetres
and up to 500 mm and more, preferably from about 10 millimeter to
about 300 millimeter, and more preferably from about 20 millimeter
to about 100 millimeter, without materially affecting the quality
of the coating.
[0069] When the adhesive film released from the coating slot nozzle
is directly coated onto a first substrate by means of nip roller
(5) provided with a release coating, the adhesive shows no tendency
to adhere to the nip roller. The nip pressure can also be varied
and can be as high as about 10 bars, preferably about 8 bars, and
more preferably about 7 bars, when the nip roller presses against
the substrate.
[0070] It is generally found that as the adhesive coated onto the
first substrate leaves the nip station, no air is enclosed between
the adhesive and the first substrate.
[0071] In another aspect, a second substrate can be laminated onto
the adhesive layer by a second set of rollers, located in the flow
path of the substrate upstream of the nip roller (5). Also these
laminations, usually have no streaking, enclosed air, or other
lamination defects.
[0072] The coating head can be at about 0.5 mm away from the
substrate, preferably at about 2 mm, more preferably at about 10
mm, and most preferably not more than 20 mm.
[0073] The temperature at which the adhesive contacts the substrate
is preferably not more than 150.degree. C., more preferably not
more than 120.degree. C., and most preferably not more than
110.degree. C., as it is desirable to use as substrates polymeric
film that are either of low gauge, or film material that has low
melting points.
[0074] FIGS. 2-10 illustrate various preferred embodiments of the
present invention wherein an extruded thermoplastic composition
such as a hot melt adhesive is applied to a first substrate and
then laminated to a second substrate. In each of these
illustrations, Substrate 2 is optional in that the invention may
alternatively involve a single continuous nonporous film formed
from a non-contact coating method and coated onto a single
substrate. In the absence of the second substrate, FIG. 5B
represents a transfer coat application since the molten composition
is first applied to a release coated roller which then contacts a
first substrate at the nip. The first substrate may then by
laminated to the second substrate in a subsequent step. For many
food packaging laminates, the film-to-film method shown in FIGS.
2-5A is presently the most preferred lamination method.
[0075] In embodiments where the thermoplastic coating or hot melt
adhesive is contacted to a first substrate in the absence of a
second substrate, as illustrated in FIGS. 6 and 7 it is important
to have a release coating such as silicon, Teflon, or release paper
on the roller (s) in contact with the adhesive or porous substrate
to prevent adherence of the thermoplastic composition to the
roller. The nip roller presses the air out from between the
thermoplastic coating film and the substrate to insure there is no
air entrapment between the first substrate and the thermoplastic
composition. Roller A can be a steel cylinder to encourage heat
transfer whereas roller B, typically the nip roller is rubber. In
many cases it is however more preferred that roller A is rubber
whereas roller B is a steel cylinder with an external
release-coating (FIGS. 5B to 10).
[0076] FIGS. 2-10 demonstrate that the nozzle position may be
varied from perpendicular positions to parallel positions with
respect to the position of the substrate.
[0077] FIGS. 6-9 show further embodiments which are specifically
suitable for film-to-film laminations for food packaging.
[0078] FIGS. 8 and 9 illustrate a second substrate being laminated
to the first substrate at a position farther from the coating
device. In this embodiment, it is preferred that roller C be heated
to reactivate or extend the open time of the hot melt adhesive or
thermoplastic coating prior to being laminated to the second
substrate. The temperature of roller C can vary between about
30-100.degree. C. for lamination between rollers C and D.
Alternatively, roller C may be a chill roll to hasten the speed of
set of the thermoplastic coating or hot melt adhesive. This can be
useful where the coating is produced for intermediate storage. The
substrate laminated in the nip of rollers C and D can be either in
web form, or in the form of sheets (FIGS. 8 and 9). As shown in
FIG. 10, where roller C is a chill roll, the inventive method can
be used to produce substrates such as films coated on one side with
a thermoplastic composition, which can e.g. be used for heat
sealing applications. Where this is desired, a further layer of a
release paper can of course be added, as shown in FIG. 9, to
protect the heat-sealing material e.g. for intermediate
storage.
[0079] The coating device is positioned at a distance of at least
0.5 mm, preferably at least 2 mm, from the substrate (or the
release coated roller in the case of transfer coating in the
absence of a second substrate--FIG. 5B). The maximum distance the
coating device may be positioned from the substrate is only limited
by practicality, particularly when the coating device is positioned
substantially vertically. Preferably, the distance is less than
about 5 m, preferably less than about 3 m, more preferably less
than about 1 m, even more preferably less than about 500 mm, and
most preferably from about 2 to 20 mm, depending on the properties
of the thermoplastic composition being coated. It is typically
advantageous that the area between the coating device and substrate
be shielded during coating from air-borne contaminants and air
currents to prevent distortion of the coating prior to contacting
the substrate. This is particularly the case when the distance
between the coating device and substrate is greater than about 500
mm.
[0080] The distance is largely dictated by the viscosity and open
time of the thermoplastic composition being coated. In the case of
producing film coatings on fibrous substrates in this manner, it is
surmised that the thermoplastic composition cools sufficiently in
its suspended state such that it has built in viscosity and
cohesive strength to the extent that any filaments or fibers
present on the substrate surface cannot penetrate the coating, yet
the thermoplastic composition is molten enough to adequately adhere
to the substrate. The greater the distance between the coating
device and the nip roller, the more the hot melt adhesive or
coating will cool prior to contacting the first substrate. For some
adhesive compositions, this cooling will adversely affect the
adhesion (or anchorage) to the substrate. Therefore, the substrate
may be passed over a heated roller prior to being nipped, or a
heated nip roller may be employed if the distance between the nip
roller and the coating device causes the coating or adhesive to
cool to the extent that it will no longer adequately adhere or
anchor to the substrate. Also, transfer coating as shown in FIG. 5B
can be employed, where the release-coated nip roller B can be
temperature-controlled by a heating cooling system such as passing
cooling fluid through roller B.
[0081] The diameter of rolls A and B is preferably about 15 mm to
about 50 mm.
[0082] Thereafter, the sufficiently cooled coating contacts the
substrate surface and adheres to the surface without deeply
penetrating into the substrate. If the thermoplastic coating is of
such a composition that it substantially detackifies after
sufficient cooling, the laminate of the coated substrate, thus
formed, can be rolled up and stored.
[0083] Alternatively this can be achieved by placing a release
coated second substrate, such as a silicone-coated paper, on the
surface of the adhesive coating. The laminate can then be used at
some later time. The laminate can be bonded by any suitable bonding
technique including ultrasonic bonding, heat sealing, or more
commonly adhesive bonding.
[0084] Preferably, the coating is done "in-line" immediately before
any further processing. An example of an in-line process for which
the invention is particularly well suited may be found in DE 195 46
272 C1 to Billhofer Maschinenfabrik GmbH, incorporated herein by
reference. Suitable slot nozzles, made by INATEC GmbH of
Langenfeld, Germany, are shown in U.S. Pat. No. 5,958,178.
[0085] Preferably, the laminating material is a synthetic film
material, especially a clear and transparent film material as is
customarily used for such laminations.
[0086] Typically such film materials comprise plane or embossed
films, which are at least substantially made from oriented
polypropylene, polyethylene, polyesters such as Mylar.RTM.,
polyacetate, nylon, celluloseacetate, and so forth having a
thickness of about 5 microns to about 50 microns. These films are
commonly laminated or sealed to printed paper or boardstock.
Composite materials are commonly produced including film-to-film
and film-to-foil and metalized substrates are commonly used for
laminates. These types of laminates are commonly found in such
industries as graphic arts and packaging. Using the method of the
invention, such laminates can be produces using non-reactive hot
melt adhesives instead of the commonly used reactive adhesives.
[0087] Generally, the exit temperature of the thermoplastic
composition will be less than about 240.degree. C., and thus much
lower than typical polymer extrusion temperatures, which are of the
order of 300.degree. C. Although the temperature of the
thermoplastic composition as it exits the coating device may range
from about 80.degree. C. and about 180.degree. C. or more, the
non-contact coating system of the present invention allows coating
to be accomplished at extremely low temperatures. For this
embodiment it is preferred that the thermoplastic composition be
coated at a temperature less than 160.degree. C., more preferably
less than about 140.degree. C., even more preferable less than
about 120.degree. C. and even more preferable less than about
110.degree. C. As mentioned previously, heat sensitive materials
can also be coated in this manner by employing higher coating
temperatures in combination with increasing the distance between
the coating device and the substrate to be coated to allow for
sufficient cooling. Materials which are normally too sensitive
mechanically and/or thermally (e.g. very low gauge films) for
customary coating methods can therefore be coated using the method
of the present invention. Such sensitive materials include low
gauge polyethylene materials and the like.
[0088] A substantial advantage of the present invention is that a
substantially continuous coating layers can be made from hot melts
at very low coating weights. Even with customary commercially
available hot melts, continuous layers can be produced at coating
weights ranging from about 0.5 g/m.sup.2 to as much as 50-60
g/m.sup.2, preferably at coating weights of not more than about 20
g/m.sup.2, more preferably at coating weights of not more than 10
g/m.sup.2, even more preferably between 3 g/m.sup.2 and 5 g/m.sup.2
and most preferably less than 3 g/m.sup.2. However, coating weights
higher than 60 g/m.sup.2 may be useful for other applications
wherein reducing the mechanical and heat-induced stresses is of
primary importance.
[0089] The very thin coatings which can be produced according to
the invention not only contribute to the economical advantages of
the inventive method, but also makes it possible to achieve a very
much reduced stiffness of the material, which thus comes much
closer, in its properties, to uncoated substrates.
[0090] The invention also concerns foodstuff items packaged in
accordance with the invention. The use of such flexible laminating
materials as packaging material for the food, drink and drug
industries has the major advantage of avoiding contamination of the
packaged items by volatile and/or migratable packaging material
components such as monomers. This makes it possible to produce
packaging laminate materials for the food industry advantageously
from solvent-free hot melt laminate adhesives, without incurring
the danger of contaminating the food with monomers and their
reacting products. At the same time, optically very advantageous
laminates are obtained, which are not inferior, but quite often
superior, in these aspects than state-of-the-art laminates.
[0091] Specifically, the present invention is related to the use of
a flexible laminate material comprising a polymer plastics material
film laminated onto a second substrate by means of a hot melt
laminating adhesive, as a packaging material to reduce
contamination of packaged goods, especially food, by volatile
packaging material components, such as monomers or ologomers. Such
volatile and/or migratable components can include isocyanates
and/or aromatic amines.
[0092] These foodstuffs can be selected from all foodstuffs which
have been packaged, are currently packaged or may in the future be
packaged using laminated packaging material as above disclosed.
Specifically, these will be items such as medicine, snack foods and
confectionery, aqueous and moist foods, dry foodstuffs, coffee, tea
and such goods, heat-treated and steamed, as well as autoclaved
goods, but also fresh fruit, fresh vegetables, fresh meats, fish
and cheese, as well as corresponding items for deep freezing and
other low temperature preservation purposes. Vacuum preservation
packaging is included, and the packed food items of the invention
further include prepared food for reheating, as well as beverages.
Thus, the invention includes the packaging of milk in film bags, as
well as fruit and vegetable juices and alcoholic beverages such as
wine.
[0093] In addition, such laminates can be used as capseals for
various food, drink and medicine packaging, as well as aseptic
packaging of food and drink items mentioned above. Also, other
non-food uses can include packaging of toys for example, for small
children and babies, who may put such items in their mouths, are
expressly within the scope of the present invention. Also, boxes
and pouches for baked goods are contemplated.
[0094] The present invention is further illustrated by the
following non-limiting examples.
EXAMPLES
[0095] Hot melt adhesives were produced from different
thermoplastic polymers, tackifiers and plasticizers as shown in
Table 1 below:
Examples 1-10
[0096] TABLE-US-00002 TABLE 1 Ingredients Ex 1 Ex 2 Ex 3 Ex 4 Ex 5
Ex 6 Ex 7 Ex 8 Ex 9 Ex 10 Lotryl .RTM. 17 BA 07 23 40 35 10 23 --
-- -- -- -- EnBA copolymer Lotryl .RTM. 35 BA 40 15 -- -- 20 15 20
15 15 -- -- EnBA copolymer Lotryl .RTM. 35 BA 320 17 -- -- 30 17 10
16 15 20 20 EnBA copolymer Escorene .RTM. UL 150 - 19 -- -- -- --
-- 20 24 23 45 45 EVA copolymer AC-8 Polyethylene wax 5 10 -- -- 5
-- 5 -- 5 -- AC 540 Polyethylene wax -- -- -- -- -- -- -- -- -- 5
Paraflint .RTM. C 80 -- -- -- -- -- 10 -- -- -- -- Polyethylene wax
Mobil Wax 145 paraffin wax -- -- -- -- -- -- -- 5 -- -- Escorez
.RTM. 5300 28 38 38 38 -- 23 28 30 20 20 Hydrocarbon resin Foral
.RTM. AX 10 10 25 -- 28 15 10 10 -- -- rosin acid resin Kristalex
.RTM. F 85 -- -- -- 10 -- -- -- -- -- .alpha.-methyl styrene resin
Kristalex .RTM. F 100 -- -- -- -- -- -- -- -- 10 10 .alpha.-methyl
styrene resin
[0097] Hot melt adhesives corresponding to the compositions
depicted in Examples 1 and 7 were coated onto substrates, using a
modified PAK 600 laminating machine by Kroenert, Hamburg, Germany.
The structure of this machine is basically similar to that shown in
FIGS. 1A-1C. With this type of machine, it is possible to nip the
adhesive film directly onto the first substrate (1) by means of nip
roller (5) or nip a second substrate (4) onto the first substrate
and adhesive, again by means of nip roller (5). In the tests, both
methods were tried. The dispensing temperature of the hot melt was
140.degree. C. for the composition of Example 1, and 110.degree. C.
for the composition of Example 7. These compositions showed
favourable low viscosities of Examples 1 and 7.
[0098] Coatings were made on polyester film (Polyester RN 36,
produced by Putz Folien, Taunusstein-Wehen, Germany) and high
density polyethylene films (HDPE KC 3664.00, obtained from
Mildenberger & Willing, Gronau, Germany).
[0099] Coating weights were 5 to 6 g/m.sup.2 at machine speeds of
approximately 70 m/minute. (In separate tests, coating weights of 2
to 3 g/m.sup.2 were obtained.)
[0100] The adhesive film was released from the coating slot nozzle,
at various distances from the first substrate (1) to be coated with
the adhesive, in a variety of tests. In another set of experiments,
it was found that the distance of the slot nozzle from the
substrate could be varied between a few millimetres and up to 500
mm and more, without materially affecting the quality of the
coating.
[0101] Where in these experiments, the adhesive film released from
the coating slot nozzle was directly coated onto the first
substrate by means of nip roller (5) provided with a release
coating, it was found that the adhesive did not adhere to the nip
roller. The nip pressure was not measured, but the nip roller was
pressed against the substrate at a laminating pressure of 7 to 8
bar.
[0102] It was found that the adhesive coated onto the first
substrate left the nip station with no air enclosed between the
adhesive and the first substrate.
[0103] In other tests, a second substrate was laminated onto the
adhesive layer by a second set of rollers, located in the flow path
of the substrate upstream of the nip roller (5). Also these
laminations, using the same films were examined for streaking,
enclosed air, or other lamination defects.
[0104] The laminations thus made were all free of flaws. No
streaking, enclosed air or any other defects were observed.
[0105] In a similar fashion, laminations were made using the same
type of films, but the other adhesives depicted in Examples 2 to 10
of Table 1. The results were as good as those obtained with the
adhesive compositions of Examples 1 and 7.
[0106] In further tests, typical food packaging items were produces
and tested as follows:
Embodiment A
[0107] Laminates were produced on a modified Billhofer "Coat 2000"
laminating machine as mentioned above and equipped with an INATEC
slot nozzle, using 20 .mu.m OPP-Films, available under the trade
name "Propafilm RGP" from UCB Films.
[0108] For the laminating trials, one of the films was
counter-printed and the other one was metalized, i.e. the printed
surface of the one film was laminated to the metalized surface of
the other film. The hot melt composition used corresponds to
Example 7 in Table 1. In one trial the coating weight of the hot
melt was 5 g/m.sup.2, in a second trial 8 g/m.sup.2 and in yet
another example 14 g/m.sup.2 was used.
[0109] The laminates thus made were then subjected to heat-seal
tests as conventional in the packaging industry.
[0110] In all cases the laminates produced were of good quality and
showed no delaminating tendencies in heat-seal trials.
Embodiment B
[0111] Laminates were produced on a machine as in Embodiment A,
using two 20 .mu.m OPP-Films, available under the trade name
"Propafilm RGP" from UCB Films.
[0112] For the laminating trials, one of the films was
counter-printed and the other one was metalized, i.e., the printed
surface was laminated to the metalized surface. (Different printing
inks were used, which were also different from Embodiment A).
[0113] The hot melt composition used corresponds to Example 9 in
Table 1. In one trial the coating weight of the hot melt was 5
g/m.sup.2, in a second trial 10 g/m.sup.2 was used.
[0114] In both cases the laminates produced were of good quality
and showed no delaminating tendencies in heat-seal trials (as in
Embodiment A).
Embodiment C
[0115] Laminates were produced (as above) with two 20 .mu.m
OPP-Films, available under the trade name "Trespaphan GND 20" from
Trespaphan.
[0116] For the laminating trials one of the films was
counter-printed and the other one was unprinted, i.e. the printed
surface of the first film was laminated to the unprinted surface of
the second film. (The printing colours were different from
Embodiments A and B).
[0117] The hot melt composition used corresponds to Example 7 in
Table 1. In one trial the coating weight of the hot melt was 2
g/m.sup.2, in a second trial 5 g/m.sup.2 and in yet another example
10 g/m.sup.2 was used.
[0118] In all cases the laminates produced were of good quality and
showed no delaminating tendencies in heat-seal trials (as
above-described).
Embodiment D
[0119] Laminates were produced (as above) using 40 .mu.m PE-film
available from Huhtamaki and 400 .mu.m PVC from MKF. Both films
were unprinted. Such laminates are commonly used to produce
(through heat-moulding) beakers, bowls or dishes which can be
closed by heat-seal lidding. It has become rather common to use
APET (atactic polyester films) instead of PVC for food
packaging.
[0120] The laminates were formed both in-line, i.e. laminating the
PE-film, after applying the hot melt to it, in-line onto the
PVC-film. In another trial the hot melt coated PE-film was wound
onto a roll and later (thus off-line), the coated PE-film was heat
sealed onto the PVC-film.
[0121] The hot melt composition used for these trials corresponds
to Example 10 in Table 1. The coating weight used was 10
g/m.sup.2.
[0122] In both cases, i.e. with laminates produced in-line and
off-line the laminates had excellent clarity and lamination
strength and did not show any signs of delamination upon
heat--moulding the laminates and heat-lidding the moulded
dishes.
Embodiment E
[0123] Laminates were produced with conventional "direct coating"
(i.e. contact between slot nozzle and substrate) methods with 36
.mu.m PETP-films, available as Mylar RN 36 from DuPont Teijin Films
and 40 .mu.m PE-films from Transpac.
[0124] Both films were unprinted. The hot melt composition used
corresponds to Example 7 in Table 1. In one trial the coating
weight of the hot melt was 5 g/m.sup.2, in a second trial 11
g/m.sup.2 and in yet another example 20 g/m.sup.2 was used.
[0125] All laminates showed high lamination strength very good
clarity and no signs of delamination in heat sealing trials (as
above-described).
[0126] The laminates made by such direct coating methods were
however found to be streaky, i.e. the adhesive did not form a
closed, perfect layer between the two films at coating weights
below 20 g/m.sup.2.
[0127] Laminates as described in Embodiments A-C and E proved very
suitable for typical "form-fill-and-seal" applications. In these,
the laminates are supplied to a food packaging device (such as a
bagging machine) and are initially bonded to form a tube-like
structure, by a longitudinal sealing step. The food item to be
packaged is then placed into a suitable section of the film tube
and the packaging is then completed by forming transverse seals
across the tube on either side of the food items, which separate
the food items from each other and at which the packaged item can
then be cut off from the rest of the tube.
* * * * *