Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method for making a
resin coated fabric adaptable to packaging food products such as
cheese or sausage, to a method for making food wraps therefrom,
and to fabrics and wraps made by these methods.
Multiple ply composite materials have increasingly
gained acceptance for the direct contact packaging of food
products, as practiced with certain kinds of cheese and
particularly with sausage products. These materials may be
multiple ply composite synthetic resin materials in sheet form
produced by co-extrusion or by subsequent coating, for example.
Sausage casings made from film comprising regenerated cellulose
(cellophane) are used on a large scale. The permeability of such
films to water vapor can be modified by coating them and they can
be made oil-and grease-proof. Polyvinylidene chloride in
particular has proved itself as a coating material for cellophane
film used as a packaging material in the food industry, for
example as sausage casings. The coatings can be formulated to be
heat sealable by incorporating further comonomers. tSee Ulmanns
Encyklopaedie der technischen Chemie, 4th edition, vol. 11,
p.678, p. 101.~ Sausage casings for fresh and cooked sausages,
produced from a synthetic nonwoven fabric stabilized by means of
synthetic resins, are known from published German patent
application OS 21 2a 613. According to published German patent
application OS 31 41 519, which corresponds to U.S. patent
4,525,418, textile wraps for the
direct contact packaging of food products and which exhibit good
tearing behavior, are permeable to gases and water vapor, and at
the same time are practically liquid- and grease- proof and
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therefore are suitable also for use in the making of fresh,
boiled, and cooked sausages, are obtained from fabrics coated
with certain acrylic resins.
In the usual coating method, direct coating, a
spreadable resin composition is applied directly to a textile
base, as described in U.S. patent 4,525,418. The textile base
may be coated on one or both sides. To obtain a thicker coat,
coating may be repeated.
Direct coating calls for adequate strength in the
textile substrate. As a rule, only woven fabrics and closely
bonded nonwoven fabrics possess the requisite strength; knitted
fabrics and lightweight nonwovens do not.
Thus, there has been a need for a textile packaging
material for food products which is coated with acrylic resins
corresponding to those used in U.S. patent 4,525,418 and which
can be produced in particular from low strength fabrics, the
coated textile material then being sealable by the use of heat or
of an adhesive, except Eor filler openings, to form a wrap.
It has been found that food products wraps which
substantially meet actual use requirement, in particular for
artificial sausage casings, can be produced from open-mesh
fabrics if these are coated with certain acrylic resins,
as described for example in U.S. patent 4,525,418, by the
so-called transfer or counter-coat process. Suitable base
fabrics for the heat sealed wraps or for the heat sealable
acrylic resin coated fabrics of the invention, respectively,
are knitted fabrics, scrim, and lightweight nonwovens.
These may be made from natural fibers, modified natural
fibers, synthetic fibers, or mixtures thereof.
Illustrative of these are fibers of cotton, linen, wool,
regenerated cellulose, cellulose esters, polyamides,
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polypropylene, and polyacrylonitrile, among others. Of course,
woven fabrics can also be coated by the transfer process and then
used to package food products. This, however, is too expensive
in comparison with the direct coating methods used up to now in
the manufacture of food product wraps, and therefore
disadvantageous, in contrast to the coating of open textiles such
as knitted and nonwoven fabrics according to the present
invention.
The invention provides a heat-sealable fabric coated
with thermoplastic acrylic resin and adaptable to use as a food
wrap, made by depositing at least one layer of acrylate emulsion
polymer onto a release backing from an aqueous acrylic resin
dispersion, completely embedding a lightweight fabric weighing
less than 70 g/m2 in said resin layer to form a laminate, and
then drying the laminate.
The invention relates to a wrap, adaptable to be filled
with a food product and made of a fabric coated with acrylic
resin, characterized in that, in its production, the fabric is
embedded in a preformed coating layer or layers and that, after
the resulting laminate has been dried, a blank for the wrap is
cut therefrom and then sealed along its edges by heat sealing or
adhesive bonding, except for a filer opening or openings.
The wrap of the invention is advantageously produced
from low strength fabrics, such as knitted fabrics, scrim, or
open nonwovens. For the production of the acrylic resin coating,
acrylate emulsion polymers of the type described particularly in
U.S. patent 4,525,418 are used.
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The principal advantage of the wraps of the invention
is that the coating can be applied to open mesh textile bases
which, in the manufacture of textile based wraps for food
products, provide significant economic benefits over the nonwoven
fabrics used until now.
The use properties of the novel wraps meet the
mechanical and processing requirements imposed on them. Thus,
they can be used as casings not only for fresh, boiled, and
cooked sausages, but also for almost any other type of sausage.
Much like natural gut, they possess good strength, including tear
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resistance. The permeability to gases and water vapor of the
novel wraps can be adapted to their end use by varying the
composition of the acrylic resin coating within the limits
established in U.S. patent 4,525,418, as well as the coating
thickness. The wraps can be readily cut to size. The cut-to-
size blank is easily given the desired shape of the wrap by heat
sealing, that is by the application of heat and pressure to the
thermoplastic acrylic resin coating, or by high frequency sealing
of the edges. Optionally, a separate adhesive, for example a hot
melt adhesive, may be used concurrently in sealing the edges.
The acrylic resins to be used for the coating of
textile material according to the invention are copolymers of a
lipophilic monomer component comprising esters of acrylic acid
and/or of methacrylic acid with Cl to C5 alcohols for example,
and of a hydrophilic monomer component which, in addition to a
hydrophilic monomer with acid properties, such as acrylic acid,
methacrylic acid, crotonic acid, or maleic acid, may contain
further hydrophilic monomers such as hydroxyalkyl esters of
acrylic acid and/or methacrylic acid, for example 2-hydroxyethyl
acrylate or 2-hydroxyethyl methacrylate. The amount o
lipophilic monomers in the polymers to be used for the acrylic
resin coating will range approximately from 90 to 99 percent by
weight. In the preparation of the copolymer, further monomers
such as styrene, alpha-methyl styrene, or vinyl acetate may be
used concurrentLy. As a rule, their amount will then range from
0.10 to 10 percent by weight of the lipophilic monomers. They
are used to impart specific mechanical properties to the coating.
Crosslinking monomeric components may also be used, if desired.
However, the acrylic resin coating must be sufficiently
thermoplastic, that is heat sealable, to permit heat sealing of
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the resin coated textile material. That means that the coating
should not be crosslinked, or then only slightly.
Acrylic resin copolymer compositions suitable for the
coating of fabrics for food product wraps are described in the
aforementioned U.S. patent, for example. These are suitable also
for the wraps of the invention, produced by coating fabrics by
the transfer process with acrylic resins formulated to be hea~
sealable. The viscosity of the coating composition is adjusted
by the addition of a thickening agent approved for food products,
for example hydroxyethylcellulose (commercially available as
"Natrosol") or ethyl acrylate/methacrylic acid copolymers
(commercially available as "Rohagit"), so that it will be from
20000 to 80000 mPa/s.
The production of the acrylic resins suitable for the
coating is known per se. Reference is made to the aforementioned
U.S. patent 4,525,418 and the prior art discussed therein, for
instance. As disclosed in U.S. Patent 4,525,418, the resin
can comprise a binary mixture of a first and a second
acrylate emulsion polymer. The first polymer can comprise
(a) at least 90 weight percent, based on the total first
polymer, of a lipophilic monomer component comprising at
least one member selected from the group consisting of
esters of acrylic acid and of methacrylic acid with a lower
alkanol, and from 0 to 10 weight percent, based on said
lipophilic monomer, of at least one further comonomer, the
methyl methacrylate content of the first polymer not
exceeding 40 weight percent of the total first polymer; (b)
a hydrophilic monomer component having acidic properties, in
an amount from 0 to 5 weight percent, based on the total
,first polymer; and (c) a crosslinking monomer component in
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an amount from 0 to 7 weight percent, based on the total
first poly~ter. The second emulsion polymer can comprise (a)
at least 95 weight percent, based on this total second
polymer, of a lipophilic monomer component comprising more
than 60 weight percent, based on this total lipophilic
component, of methyl methacrylate, and of less than 40
weight percent, based on this lipophilic component, of at
least one further member selected from the group consisting
of esters of acrylic acid and/or of methacrylic acid with a
lower alkanol, and of from 0 to lo weight percent, based on
this lipophilic component, of a further monomer; and (b) of
less than 5 weight percent of a hydrophilic monomer
component having acidic properties.
The coated textile material may comprise one or more
acrylic resin layers. When the packaging material is built up
from more than one acrylic resin layer, the various resin layers
may be of different thicknesses and polymeric compositions.
The hardness of the coating can be predetermined by the
ratio of comonomers and particularly by the ratio of acrylic
esters, and especially of butyl acrylate, to methacrylic esters
such as methyl methacrylate, in the copolymer. However, it can
also be controlled by the use of a blend of an acrylic resin
dispersion formulated to be "soft", that is of a resin with a
predominant amount of acrylic esters, and particularly of butyl
acrylate, and of a "harder" acrylic resin dispersion containing
pre~in~ntly methyl methacrylate, for example.
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Various properties of the food product wrap, such as
its water vapor permeability, or the peelability of sausages, can
be optimized by the addition of proteinaceous or cellulosic
materials such as collagen or regenerated cellulose in amounts
from 0.1 to 20 percent by dry weight of the acrylic resin coating
compositions. These substances are admixed, for example as
solutions, with the acrylic resin dispersions before coating is
effected. However, all of the coatings will have acrylic resin
character.
~ ood product wraps according to the invention are
obtained by embedding the fabric base in a previously prepared,
as yet unsolidified, coating composition, rather than by direct
spread-coating of acrylic resin dispersions onto the fabric.
Both techniques are known to be employed in the manufacture of
artificial leather, for example. Unlike the direct spread-
transfer
coating of the fabric, the so-called ~ranac~ process permits the
use of very lightweight textile materials, sensitive to tension,
since the fabrics do not have to be pulled through a coating
machine. (See Ullmanns, op. cit., vol. 15,pp. 166-168.)
The food product wraps to be manufactured by the
process of the invention, which wraps can be used to advantage as
casings for various types of sausages, are usually provided with
more than one synthetic resin coat, mostly with two acrylic resin
coats. To this end, a first resin coat is spread onto a endless
backing web, suitably a paper web, e.g. a web of release paper.
After the first coat has dried, a second coat of resin is applied
and a fabric web is then embedded therein beEore this coat has
dried. After the laminate has been dried at temperatures of
about lOOoC to 140C, the composite is separated from the backing
~eb. Normally, the coating irst applied to the backing web is
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the outer surface when the composite acrylic resin coated fabric
is used as a packaging material for food products.
For the production of this top coat, which is the
coating first applied to the backing, of paper for example, and
which becomes the outer layer of the wrap, an acrylic composition
is used which is preferably formulated to be somewhat "harder".
This composition can be prepared by blending an acrylic resin
emulsion having a relatively "soft" character, for example a
butyl acrylate/methyl methacrylate/hydroxyethyl acrylate/
methacrylic acid copolymer containing less than 45 percent by
weight of methyl methacrylate, with a "harder" acrylic resin
emulsion containing more than 60 percent by weight of methyl
methacrylate. Usable top coats can thus be produced from blends
of such emulsion polymers in ratios from 8:2 to 6:4, and more
particularly in a ratio of 7:3, in parts by weight of copolymers
having a relatively soft character to polymers of harder resin
character, respectively.
The coating composition for the second-applied coat
(or innermost coating of the wrap) is again an acrylic resin,
formulated to be relatively soft and containing less than 45
percent by weight of methyl methacrylate and, as hydrophilic
components, particularly acrylic acid or methacrylic acid in an
amount of about 1 percent by weight, as well as hydroxyalkyl
esters of acrylic acid or methacrylic acid, for example in
amoûnts from 0 to 10 percent by weight. In the coating operation
in accordance with the presentinvention, dispersions having a
solids contents higher than 50 percent, for example of at least
55 percent by weight (see published German patent application OS
19 10 488, for example), are advantageously used.
! Depending on the nature of the embedded fabric and on
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the intended end use of the wraps produced, the amount of coating
composion used may vary within certain limits. For example, in
the coating of textile materials by the transfer process, from
about 30 g to about 90-lO0 g per square meter, and more
particularly from 40 g to 80 g per square meter, of dry polymer,
will be needed per coat to produce casings for cooked or boiled
sausages.
The thickness of the acrylic resin coating should be
from 40 to lO0 microns, and more particularly from 60 to 80
microns. In the case of a multiple layer acrylate structure, the
last-applied coat in which the fabric is embedded is normally
thicker than the preceding layer or layers.
The water vapor permeability or transmission (as
determined in conformity with German standard DIN 53 112) of food
product wraps prodeced by the method of the invention is
considerably lower than that of food packaging materials made by
direct coating with the same amount of acrylic resin substance.
In the case of the wraps of the invention, it is about
lO0/g/m2/24 hr. or less, whereas textile materials direct-coated
with comparable amounts of acrylic resin exhibit water vapor
transmission rates of over 200g/m2/24 hr. Lower water vapor
transmission rates are of advantage in the storage of many food
products. Intermediate values can be readily obtained by the
concurrent use of proteinaceous and/or cellulosic materials.
From the coated fabric web, portions in the desired
shape of the food product wrap, for example a sausage casing, are
cut or punched ou~ by known methods. During or following this
operation, the coated fabric may be subjected to a further
operation, such as the embossing of a pattern in the packaging
material.
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The open sides of the blank are placed face to face and
then heat sealed as much as possible by the use of heat and
pressure by methods commonly used with thermoplastic coatings. A
tightly sealed composite wrap is so obtained. By coating a hot
melt adhesive such as a polyamide adhesive onto the edges of the
polyacrylate coated fabric, an additional heat sealing and
bonding coat is obtained.
The hydrophilic monomers referred to earlier are
monomers whose solubility in water at 20C is greater than 6
weight percent, while the monomers referred to as hydrophobic
have a solubility of 6 weight percent or less.
In the invention, "harder" acrylic resins are acrylic
polymers formed of a relatively large amount of monomers which,
as homopolymers, each have a glass transition temperaure, Tg,
above 30C, in contrast with "softer" acrylic resins composed of
a relatively large amount of monomers which, as homopolymers,
each have a glass transition temperature less than 30C. ~See
Ullmanns, op.cit, vol. 15, pp.215-222; J. Brandrup and E. H.
Immergut, Polymer Handbook, 2nd edition, 1975, III, pp. 139-154.)
A better understanding of the present invention and of
its many advantages will be had by referring to the following
specific examples, given by way of illustration, in which the
parts are parts by weight.
EXAMPLE 1
A coating material having the ~ollowing composition
was coated with a doctor blade onto water resistant release
paper ("Stripkote ClS"~:
800 parts o a 50~ dispersion of a first
emulsion polymer,
200 parts of a 50% dispersion of a second
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emulsion polymer,
7 parts of hydroxyethylcellulose thickener
(e.g. "Natrosol 250 HR")* and
50 parts of water.
The first emulsion polymer was prepared from the
following monomer mixture:
55.5 parts of butyl acrylate,
39.0 parts of methyl methacrylate,
5.0 parts of hydroxyethyl acrylate, and
0.5 part of methacrylic acid.
The second emulsion polymer was prepared from the
following monomer mixture:
65.0 parts of methyl methacrylate,
34.0 parts of butyl acrylate, and
1.0 part of methacrylic acid.
A fixed, warp-kni.tted polyamide fabric having a weight
of 17 g/m2 was laminated under light pressure into the
aforementioned coating layer, applied in a thickness of 0.12 mm.
This laminate was dried with circulating air at a temperature
from 100C to 120C and the release paper was then removed.
The resin coating contained about 60 g of solids per square
meter. The water vapor transmission rate was 100 g/m2/24 hr.
After being filled with sausage meat, sausage casings
made from the material and heat sealed ~sealing time, 1 sec.;
sealing pressure, about 4 bar: sealing temperature, 180C-200C)
were found to have a seal that proved resistant to boiling.
~XAMPLE 2
A top coat of a coating material composed of
700 parts of a 50~ dispersion of a first
, emulsion polymer,
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300 parts of a 50% dispersion of a second
emulsion pol~ner,
80 parts of a 30% dispersion o a third
emulsion polymer, diluted with water in a weight
ratio of 1:3, and
10 parts of a 25% aqueous ammonia solution
was applied in a thickness of 0.1 mm to release paper and dried
with circulating air at 100C-120C. The resulting coating
ontained 50 g of so]ids/m2.
polymers
The first and second emulsion polymr~ were prepared as
in Example 1, which the third emulsion polymer was an ethyl
acrylate/methacrylic acid copl~neric thickener ("Rohagit SD15"~*
A coating material having the following composition was
applied thereover as a laminating coat .in a thickness of 0.15 mm
and with a solids content of 75 g/m2:
1000 parts of a 50% dispersion of the aforesaid
first emusion plymer,
80 parts of a 30% dispersion of the aforesaid
third emulsion polymer, diluted with water in a
weight ratio of 1:3, and
10 parts of a 25% aqueous ammonia solution.
A nonwover fabric having a weight of 30 g/m2, made of
polyester/rayon staple ~80/20), was embedded in this coat and the
laminate was then dried at 120~C to 130C.
The acrylic resin/~abric laminate ~rom which the paper
base had been stripped had a water vapor transmission rate of
60 g/m2/24 hr. and exhibited the good heat sealability mentioned
in Example 1.
EXAMPLE 3
, A food product wrap according to the invention was
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produced by the method used in Example 2 using an elastic,
unfixed, warp-knitted polyamide fabric weighing 25 g/m2.
EXAMPLE 4
G0 parts of CMC (Carboxymethylcellulose, Cl3nose~
72 lEL ~rom Hercules, Wilming~on, Del. jUSA) are wcll mixed
at about 20C firs-~ with 300 parts of water and then with
lOûO parts of the emulsion polymcr I (see example l).
Ten minutes lat~r thc pas~e is ready for coating.
A release pa~cr was ].ami.nated with a coat there~rom in a
thickness of 0.15 mm and into this coa~ a warp-knittcd
polyester fabri.c was embedded. This laminote was dried
with circulating air at a temperature from 100C to
120C and then the release paper was removed.
EXAMPLE 5
A:
600 parts,oE proteinaceous material inform of powder
; (Lactovi~ WBl Erom Lactovit, Dusseldorf, Germany) are
well mixed with 500 parts o~ ethanol, then diluted wlth
3575 parts oE water and 275 parts o~ a stabili.zing agent
(product Erom Lactovit) are added.
The suspension is warmed up to 6ûC witll stirring for
so]ubilizati.on.
B:
Is a mixture made from lO00 parts o~ emulsion po].ymer I
(see e~amplc l), 150 parts oE watcr, 50 parts oE the
emulsion polymer III (see cxample 2) and lO parts of
a 25 ~,' aqueous ammonia so].ution.
For the preparation of the paste for coating, lO00 parts
of B and 500 parts of A are mixed and with this mixture
a reJ.case paper was k1ll1i.l-1ated. For prevel1tin~ solidirication
on accoull~ o tl1e prote.i.llaccous m3terial, tlle coati.llg ma~s
is he]d at ~10C to 50~C.
Into the polyacrylate coat containing tl1e pro~einaceous
material a warp-knitted polyamide fabric was embedded.
The laminate was dried at a temperature from about 100C to
l20C and then the release paper was removed.
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