U.S. patent application number 10/656179 was filed with the patent office on 2005-04-07 for absorbent inserts, method of producing them and their use.
This patent application is currently assigned to Stockhausen GmbH & Co. KG. Invention is credited to Jonas, Gerd, Klimmek, Helmut, Krause, Frank, Pfluger, Klaus.
Application Number | 20050074614 10/656179 |
Document ID | / |
Family ID | 26027300 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050074614 |
Kind Code |
A1 |
Jonas, Gerd ; et
al. |
April 7, 2005 |
Absorbent inserts, method of producing them and their use
Abstract
The invention relates to an absorbent insert for foodstuff
packagings, the liquid-absorbing component of which is a
superabsorbent polymer which, in a hitherto unrivaled fashion,
persistently absorbs and retains large quantities of liquid even
under high pressure load, protects the foodstuffs from bacterial
decay, and prevents contamination of the packagingd goods by
migrating soluble constituents of the polymer. This combination of
properties of the superabsorbers used is expressed by the Q.sub.SAP
0.3 quotient of retention according to the tea bag test+absorption
against pressure (AAP) 0.3, divided by the amount of solubles (LA),
which quotient is at least 20. Superabsorbers having such
properties are obtained by using special combinations of
crosslinkers. Furthermore, the invention relates to a process for
producing said absorbent inserts and their use in foodstuff
packagings, as ice substitute, and as leak-proofing means in
transport packagings.
Inventors: |
Jonas, Gerd; (Kempen,
DE) ; Klimmek, Helmut; (Krefeld, DE) ; Krause,
Frank; (Kleve, DE) ; Pfluger, Klaus; (Krefeld,
DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Stockhausen GmbH & Co.
KG
Krefeld
DE
|
Family ID: |
26027300 |
Appl. No.: |
10/656179 |
Filed: |
September 8, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10656179 |
Sep 8, 2003 |
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09961431 |
Sep 25, 2001 |
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09961431 |
Sep 25, 2001 |
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09147476 |
Feb 25, 1999 |
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6350710 |
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09147476 |
Feb 25, 1999 |
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PCT/EP97/03380 |
Jun 27, 1997 |
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Current U.S.
Class: |
428/411.1 |
Current CPC
Class: |
C08F 290/062 20130101;
B32B 3/30 20130101; Y10T 442/2484 20150401; Y10T 442/2525 20150401;
Y10T 442/673 20150401; B01J 20/2805 20130101; B32B 3/266 20130101;
B01J 20/28021 20130101; B32B 2439/70 20130101; C08F 281/00
20130101; Y10T 442/664 20150401; Y10T 428/237 20150115; B01J
20/28033 20130101; B32B 5/22 20130101; B32B 2307/726 20130101; Y10T
428/31504 20150401; C08F 261/04 20130101; B32B 27/00 20130101; B32B
23/00 20130101; B01J 20/28023 20130101; B32B 2264/02 20130101 |
Class at
Publication: |
428/411.1 |
International
Class: |
B32B 009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 6, 1996 |
DE |
196 27 409.5 |
Nov 2, 1996 |
DE |
196 45 240.6 |
Claims
1-21. (Canceled)
22. An absorbent insert for a packaging, comprising: a top and a
bottom covering layer; and a core which absorbs an aqueous liquid
and includes an absorbent polymer; wherein the absorbent polymer
has a quotient Q.sub.SAP 0.3 calculated from retention and
absorption under a pressure of 0,3 psi (21 g/cm.sup.2) and from an
amount of a soluble ratio of at least 20 and a retention of at
least 22 g/g.
23. The absorbent insert of claim 22, wherein the polymer has a
Q.sub.SAP 0,3 of at least 30.
24. The absorbent insert according to claim 22, wherein the
absorbent polymer has a retention of at least 25 g/g.
25. The absorbent insert according to claim 22, wherein the
absorbent polymer has an absorption under pressure of at least 15
g/g.
26. The absorbent insert according to claim 22, wherein the soluble
ratio of the absorbent polymer is 3.5 wt.-%.
27. The absorbent insert according to claim 22, wherein having a
migration value of .ltoreq.15 mg/g.
28. The absorbent insert according to claims 22, wherein the top
and bottom covering layer comprise a plastic or cellulose film, a
fabric or a fleece; and at least one part of the covering layer
film is permeable to water or an aqueous liquid as a result of a
perforation.
29. Absorbent insert according to claim 22, wherein the core
comprises fleece, a fiber, a fabric; wherein the polymer absorbing
an aqueous liquid is dispersed and optionally fixed.
30. Absorbent insert according to claim 29, wherein the core has an
arrangement in layers of the absorbent polymer part within the core
of fiber and fabric.
31. Absorbent insert according to claim 29 or 30, wherein the fiber
is a hollow fiber.
32. Absorbent insert according to claim 22, wherein the absorbent
polymer is made from a partially neutralized monoethylenically
unsaturated monomer containing an acid group and, optionally
another monomer copolymerizable therewith; wherein the absorbent
polymer is further made from crosslinker as well as a polymer
optionally serving as graft basis.
33. Absorbent insert according to claim 32, wherein said
unsaturated monomer containing an acid group is selected from the
group consisting of an acrylic acid, a methacrylic acid,
vinylacetic acid, vinyl sulfonic acid, (meth)allylsulfonic acid,
maleic acid, 2-acrylamido-2-methylpropane- sulfonic acid and a
mixture thereof.
34. A method of packaging foodstuff, comprising: packaging a
foodstuff in a package captaining the absorbent insert for a
package, comprising a top and a bottom covering layer and a core
which absorbs an aqueous liquid and includes an absorbent polymer;
wherein the absorbent polymer has a quotient Q.sub.SAP 0,3
calculated from retention and absorption under a pressure of 0,3
psi (21 g/cm.sup.2) and from the amount of soluble ratio of at
least 20 and a retention of at least 22 g/g.
35. A method of making an ice for a packaging application,
comprising: (a) providing an absorbent insert for a packaging,
comprising a top and a bottom covering layer and a core which
absorbs an aqueous liquid and includes an absorbent polymer,
wherein the absorbent polymer has a quotient Q.sub.SAP 0,3
calculated from retention and absorption under a pressure of 0,3
psi (21 g/cm.sup.2) and from the amount of soluble ratio of at
least 20 and a retention of at least 22 g/g; (b) soaking said
absorbent insert in water, thereby obtaining a soaked insert; and
(c) freezing the soaked insert.
Description
[0001] The invention relates to a new and improved absorbent insert
for foodstuff packagings, especially for meat, poultry and fish. It
consists of a flat pouch made of a water-permeable film and has a
filling which at least in part is composed of a superabsorbent
polymer having high gel stability, high retention and a low ratio
of solubles. The insert is remarkable for its rapid and sustained
absorption of liquid exuding from the foodstuff, and it extends the
preserving period by effectively preventing microbial growth. In
addition, the inserts soaked with water, when they are in the
frozen state, are excellently suited as an ice substitute for
refrigerating foodstuffs.
[0002] Foodstuffs are frequently presented in a prepacked form on
the market. Such packagings consist predominantly of flat trays,
wherein the foodstuff is covered externally by air-, water- and
odor-proof films. As a result, neither the aqueous constituents
present in the foodstuffs nor those adhering due to previous
washing can escape from the packagings. An optically quite
impressive sight is the accumulation of liquid at the contact
surface between the film and red meat. On the one hand, this makes
the packaged foodstuffs appear unappetizing as a consequence and,
because of the ingredients exuding from the foodstuffs together
with the liquids, gives rise to microbial growth affecting the
preserving period and, in addition, is a source of microbial
infections. The high contamination of poultry with bacteria of the
Salmonella class is generally familiar.
[0003] To overcome these problems, absorbent substrates for
packaged foodstuffs have been developed, which are predominantly
composed of multiple layers of cellulose. In practice, however, it
was found that these substrates do not meet the requirements with
respect to absorptive capacity and retention capability under the
weight of foodstuffs resting on them.
[0004] Thus, for example, a normally six-ply layer of cellulose
wadding with the dimensions 7.times.10 cm is capable of absorbing
only about from 8 to 10 g of liquid at maximum. Now, when a piece
of meat is packed in a packaging tray and kept for sale in a
refrigerated display case, up to 10% of the net weight may be
released as meat juice and hence, up to 50 g in the case of a 500 g
piece of meat. Such a quantity surpasses by far the absorptive
capacity of the absorbent layer made of cellulose fleece. As a
result, there is bacterial growth on these moist, non-sterile
substrates, impairing the keeping quality of the foodstuff.
[0005] Therefore, a number of efforts have been made to develop
packaging systems in order to remove the liquid exuded by foodstuff
from that foodstuff by absorption, so that no nutrients would be
available for bacterial growth.
[0006] DE 3,034,170 C2 describes a water-adsorbing insert for
foodstuff packagings, especially for meat, poultry, fish, and
sausages, which contains a mixture of diatomaceous earth and
aerosil in a flat pouch made of a water-permeable film. Because the
inorganic filling material merely adsorbs the liquid, its
absorptive capacity is low, i.e., uneconomically high amounts of
adsorbent are required for sufficient liquid binding, thereby
undesirably increasing the weight of the packaging. Another
drawback of the inorganic adsorbers is their incapability of
retaining the adsorbed liquid over a long time or under pressure
load.
[0007] DE 3,034,169 C2 suggests mixtures of diatomaceous earth and
an organic gel-forming agent as filling material for
water-adsorbing inserts of foodstuff packagings, wherein
carboxymethylcellulose, cellulose ethers, polyvinylpyrrolidone,
starch, dextrose, gelatin and/or pectins are mentioned. The ratio
of organic gel-forming agents is reported to be around 20 wt.-%. As
a result of the high ratio of solubles and the extremely slow
swelling rate of the above-mentioned compounds, the use of such
adsorbing inserts for foodstuff must be regarded as critical.
Solubles of the organic gel-forming agents reduce the swelling
capacity thereof and may migrate out of the insert and contact the
foodstuffs; slow swelling rates obstruct effective absorption of
the liquid in the packaging, so that leaking of accumulated liquid
may occur.
[0008] EP 302,504 B1 suggests an absorbent pad which may be
arranged in a packaging under foodstuff tending to exude liquid,
e.g., meat, poultry and the like. The absorbent pad is constituted
of a mat of a liquid-absorbing wood flake material enveloped by
paper. The paper-enveloped absorbent pad in turn is enveloped by a
liquid-impermeable material such as polyethylene which, however,
has a multiplicity of perforations extending in longitudinal
direction of the envelope. As a result of the relatively low
absorptive capacity and the low bulk density of wood flakes, a
practice-oriented absorption of liquid is obtained only with an
uneconomically high packaging volume.
[0009] DE 4,325,879 C2 describes molded articles made of
thermoplastic foams as packaging material for goods containing
moisture, wherein the cell structure of the hydrophobic foam
framework is partially open, thereby being capable of absorbing
liquids which, however, cannot be bound tightly. In order to absorb
polar solvents such as water, the hydrophobic foams must be
modified in addition, using up to 10 wt.-% of a surfactant wetting
agent. To prevent compressing of the foams under the weight of the
foodstuffs, foams having higher density, i.e., higher stability,
are required. However, the absorptive capacity of such
thermoplastic foams is reduced with increasing foam density, i.e.,
with increasing stability of the foam.
[0010] To improve the absorptive capacity, superabsorbent polymers
have been suggested as filling materials for absorbent pads.
Compared to cellulose, they are capable of storing larger amounts
of aqueous liquids.
[0011] DE 4,120,319 A1 and DE 4,234,632 A1, respectively, describe
tray-shaped foodstuff packaging containers having integrated a
liquid absorber system. To absorb liquid released by foodstuffs,
polyacrylate polymers having a moisture absorption capacity ranging
from 1 to 100 ml/g are preferably used; in particular, the alkali
salts of starch-modified polyacrylates are preferably used. Other
statements indicate that moisture is deposited on charged goods if
there is direct contact between the absorber and the charged goods.
Thus, it must be concluded that the absorbers used are not capable
of binding liquid from the foodstuff sufficiently tightly or
retaining same under pressure, and that solubles from the absorber
may possibly be passed onto the foodstuff in case of direct
contact. Because close contact of these absorbent polymers with the
charged goods as well as pressure load on the swollen absorber must
be avoided, an expensive construction of the packaging container in
the form of an additional perforated bottom plate with supporting
elements is required, separating the foodstuff from the
absorber.
[0012] Absorbent substrates as supporting layers in meat and
poultry meat packagings for collecting liquid exuded from these
meat products are known from EP 434,733 B1. Inside the absorbent
substrate confined externally by a partially perforated plastic
film, there are layers of cellulose and thermoplastic fibers,
wherein superabsorbent polymer grains of carboxymethylcellulose or
acrylate absorbers are fixed, thereby improving the retention
properties of the absorbent substrate, so that liquid already
absorbed not re-released even under pressure load. The
superabsorbers do not have to meet specific requirements with
respect to absorptive capacity, gel stability and solubles. To
avoid migration in case of higher load on the absorbent pad, it is
recommended not to perforate the upper film adjacent to the
foodstuff and allow the liquid to enter at the lateral edges of the
absorbent substrate, which are not completely sealed.
[0013] U.S. Pat. No. 4,449,977 describes a flexible absorbent
product containing uniformly dispersed particles of a
water-insoluble, water-swellable organic polymer in a
water-insoluble, non-swellable matrix of a thermoplastic polymer,
namely, a polyester. Preferably, the matrix is in the form of a
film. The absorbent product is produced by co-extruding said
mixture of water-insoluble matrix material (polyester) and
water-insoluble but water-swellable organic polymer used as
absorbent material. However, the absorbent material may also be
applied onto the extruded matrix layer. The absorbent product may
be used in a diaper, the matrix containing the absorbent material
being covered on one side with a liquid-impermeable layer, and on
the other side with a liquid-permeable layer. Such absorbent
products are disadvantageous in that part of the absorber particles
are prevented from swelling by the hydrophobic polyester matrix,
and that the continuously extending polyester matrix forms a
barrier type layer in the distribution of liquid to be absorbed.
The suggested superabsorbent polymers, including crosslinked
polyalkylene oxides, carboxymethylcellulose crosslinked with
epichlorohydrin, partially saponified polyacrylamide prepared from
acrylamide and N,N'-methylenebisacrylamide do not comply with the
polymers admitted for foodstuff packagings and do not meet the
requirements with respect to low solubles and gel stability under
load.
[0014] EP 320,314 B1 describes water-absorbing, non-woven layers of
partially surface-saponified polyacrylonitrile fibers optionally
provided with top and bottom protective layers. As a result of the
low water-absorbing capacity or these polyacrylonitrile fibers,
being from 3 to 5 g/g, the high amounts of liquid occurring in many
foodstuff packagings cannot be bound quantitatively. In addition,
after initial swelling, the closely adjoining fibers in the outer
region of the layer block further penetration of the aqueous liquid
into the interior region, thus producing a considerable loss in
capacity.
[0015] EP 395,223 A2 describes an absorbent pad for aqueous and
organic liquids, consisting of a core of liquid-absorbing polymeric
material, which core absorbs the liquid, and an insoluble and
flexible envelope which, however, is permeable to the liquid. The
absorbent pad is used in the fields of hygiene products, transport
and foodstuff packagings. The predominantly powdered absorbent
polymeric materials on the basis of synthetic and/or natural
polymers, including crosslinked polyacrylates, may also be
dispersed on one or between two interior water-permeable fabric
surfaces which in turn are enclosed by the exterior absorbent pad
envelope. The exterior envelope is sufficiently flexible to allow
an increase in volume caused by the swelling of the absorber
polymer. The polymer powders to be used should have a particle
distribution of between 20 and 100 mesh and a powerful absorption
of from 50 to 600 g of saline solution or from 600 to 800 g of
water/g of polymer, with a low ratio of solubles. There are no
specific requirements with Respect to the amount of solubles and
the gel stabilities of the swollen absorbers. The preferred
polymers are identical with those which also in EP 562,846 A1 cited
hereinafter, are reported to be preferred.
[0016] EP 562,846 A1 describes a flat, light-weight pad having a
filling of crosslinked superabsorbent polymers and a
liquid-impermeable envelope which, from a specific expansion on, is
capable of opening itself at a predetermined position, which pad
may also be used in foodstuff packaging, among other things. The
water-insoluble but water-swellable absorbers are slightly to
moderately crosslinked, have low solubility and preferably, are
polymerizates of acrylic acid or methacrylic acid or salts thereof.
In a particularly good embodiment with respect to retention and
absorption, an absorber is used which is copolymerized with styrene
in accordance with U.S. Pat. No. 4,677,174. Claimed therein are
polymers having from 0.001 to 0.3 wt.-%, relative to the monomers,
of bisacrylamide and polyol acrylate type crosslinkers; in the
embodiments, the crosslinker concentrations mostly are clearly
below 0.1%. As to the solubles, there are no indications in U.S.
Pat. No. 4,677,174 but, e.g., from WO 93/21237, page 17, Table 1,
it is familiar to a person skilled in the art that using polyol
acrylic ester type crosslinkers will result in soluble ratios of
from 7.9 to 19.2%, the low value of 7.9% already requiring a
crosslinker concentration of 0.9 wt.-% of monomers. However, this
concentration exceeds by far the upper limit of 0.3 wt.-%
recommended in U.S. Pat. No. 4,677,174. Consequently, while such
low crosslinker concentrations do provide high absorption, this is
achieved only with the disadvantage of very high soluble ratios and
low gel stability. For absorbers to be used in foodstuff
packagings, however, neither high solubles, nor low gel
stabilities, nor toxicologically critical bisacrylamide type
crosslinkers are suitable.
[0017] The essential problems in the construction/function of all
these well-known packaging systems using liquid absorbers are
exceedingly low absorptive capacity of the absorbent material,
insufficient absorption rate and insufficient pressure resistance
(gel strength) of the swollen absorber, respectively, and
especially, exceedingly high solubles which may remigrate into the
foodstuffs together with the liquids absorbed by the foodstuffs.
Thus, for example, perforation of the absorbent pad film adjacent
to the foodstuff is largely forsaken, in order to avoid contact
with exuding liquid. Again and again, the result of this is that
exudates may undesirably accumulate in hollows on the upper film
adjacent to the foodstuff, thus contributing to early spoilage of
the foodstuff.
[0018] Therefore, U.S. Pat. No. 4,321,997 suggests an expensive
construction of an absorbent pad having interior spacers to prevent
the absorbed liquid from being squeezed out of the absorbent
insert. If used, the superabsorber is located on or in the fluffy
ply of the absorbent pad. To avoid microbial growth, preservatives
are added, which is generally critical in the field of foodstuff
packaging.
[0019] The problem of high solubles is also present when using
superabsorbent polymers in the hygienics field of application.
Indeed, the high absorption demanded there has been achieved
together with sufficient gel stability, but it has also been
recognized that ultimately, the solubles ratio was still
exceedingly high. In particular, it has been recognized that
solubles forming only after a long exposure time of the aqueous
liquid on the absorber, impair the long-term absorptive
capacity.
[0020] Therefore, US Re. 32,649 describes a polymerization process
under acidic pH conditions for the production of polyacrylate-based
superabsorbent polymers low in solubles for sanitary use. However,
the limits for solubles delineated therein, being 17 wt.-% at
maximum, preferably 10 wt.-% at maximum after an extraction period
of 16 hours, would still be exceedingly high for use in the field
of foodstuff packaging.
[0021] Thus, the EC commission for the regulation of foodstuff
packagings and other consumer goods designates the measurement of
overall migration (global migration) with an admissible maximum
value of 10 milligrams of migrated packaging component per square
decimeter packaging surface or 60 milligrams per kilogram foodstuff
as an important marker value. This limitation is intended to
protect foodstuff from unacceptable alterations caused by the
packaging. The council directive 90/128 EEC specifically regulates
the contact of plastic materials and consumer goods with
food-stuffs.
[0022] The above-mentioned limits are determined according to
directive 85/572/EEC, using so-called simulants comprising
distilled water, 3% acetic acid in aqueous solution, 15% ethanol in
aqueous solution and rectified olive oil. Therein, for example,
distilled water is used as a simulant for fish, meat and
vegetables. The directive 82/711/EEC for determining the migration
from materials for foodstuff packagings prescribes a test period of
10 days for a contact time of >24 hours.
[0023] With respect to meat and fish, it should also be noted for
the simulant that these foodstuffs exude saline aqueous solutions
corresponding to a physiological solution, i.e., a 0.9 wt.-% saline
solution. Frequently, the washing water adhering to the foodstuff
is also to be considered. In an extreme case, the mixture of
washing water/exudate may correspond to a saline solution of about
0.2 wt.-%. However, because the absorptive behavior of the
superabsorbent polymers is crucially determined by the salt content
of the aqueous liquid, migration tests using these saline liquids
are indispensable for assessing the inserts.
[0024] It is therefore the object of the present invention to
provide inserts for foodstuff packagings, which contain new,
superabsorbent polymers and do not have the apparent drawbacks of
prior art illustrated above. In particular, it is necessary to
provide absorbers for said inserts which, under the pressure of
foodstuffs resting on them, have high absorptive capacity and
retention for exudates from these foodstuffs and, in contrast to
prior art findings, have only minor amounts of solubles despite the
high absorption under pressure. The inserts produced therefrom are
intended to absorb the exudates from foodstuffs rapidly and
persistently, have low weight and volume compared to the absorbed
liquid as well as negligibly low migration values, show sufficient
protection against bacterial growth and prevent odor production
when storing the foodstuffs.
[0025] According to the invention, said object is attained by means
of absorbent substrates produced using crosslinked polymerizates
which absorb aqueous liquids and are built up of partially
neutralized monomers bearing ethylenically mono-unsaturated acid
groups, optionally other monomers co-polymerizable therewith, and
optionally polymers suitable as basis for grafting, characterized
in that the quotient of the absorption values, i.e., of retention
(TB=tea bag test, for description see below) and absorption against
pressure (AAP) at 0.3 psi (21 g/cm.sup.2, for description see
below) and the amount of solubles (LA) of the absorbent crosslinked
polymers contained in the insert,
Retention (TB)+Absorption against pressure (AAP) at 0.3 psi
Q.sub.SAP 0.3=Solubles (LA)
[0026] is at least 20, preferably at least 30, and particularly
preferred, at least 40.
[0027] It was found for the absorbent substrates according to the
invention that the quotient of the absorption values and the
solubles ratio is of crucial significance for the functional
capability of the substrate. The higher this quotient is adjusted
by means of the crosslinkers used according to the invention, the
better the capability of the absorbent substrate of persistently
absorbing large amounts of exudate even at high pressure load, of
protecting the foodstuffs from bacterial infestation and preventing
contamination of the foodstuffs by re-migrated exudates or migrated
material from the absorbent substrate. Using the absorbent
substrates of the invention, it is also possible to stack multiple
packaging units on top of the other, with no absorbed liquid being
pressed out of the insert in the bottom packaging.
[0028] In another preferred embodiment of the invention,
superabsorbent polymers are used which also in case of AAP 0.7
(Q.sub.SAP 0.7) comply with the quotient required according to the
invention. Absorbent substrates filled with such absorbers are
particularly suited for the aforementioned applications under high
foodstuff load.
[0029] The absorbers used according to the invention have a
retention (TB) of at least 22 g/g, preferably at least 25 g/g, and
particularly preferred, of at least 28 g/g, and an absorption
against pressure (AAP 0.3) of at least 15 g/g, preferably at least
20 g/g, with at least 22 g/g being particularly preferred; the
solubles ratio (LA) is 3.5 wt.-% at maximum, preferably 2.5 wt.-%
at maximum, and particularly preferred, 1.5 wt.-% at maximum.
[0030] The inserts produced using the superabsorbent polymers of
the invention have low migration values of below 15 mg/g,
preferably below 10 mg/g and particularly preferred, below 5 mg/g
absorbent insert, and protect the foodstuffs from bacterial
infestation.
[0031] The absorbent insert of the invention consists of an
absorbent core and an envelope. The absorbent core contains the
superabsorbent polymer particles of the invention, optionally
enclosed by fibers or fabric, the polymer particles optionally
being embedded or fixed in the fibers or fabric. A layered
arrangement of the superabsorbent particles inside the absorbent
core of fibers or fabric was found to be advantageous, where it is
frequently advantageous to use absorbers in the layered arrangement
which have different particle sizes and/or different absorptive
capacities, in order to obtain optimum absorption and long-term
storage of the exudates.
[0032] Preferably, the fibers used have a length/diameter ratio of
more than or equal to 50. As fiber material, absorbent or
non-absorbent natural or synthetic, crimped or non-crimped staple
fibers may be used. Suitable fibers include cellulose fibers
(cotton, wood, among others), regenerated fibers (viscose, rayon,
among others), and synthetic fibers (including polyolefins,
polyacrylates, polyamides, polyesters, polystyrene). Staple fibers
of polypropylene (PP), polyethylene (PE) and polyethylene
terephthalate (PET) are particularly preferred.
[0033] In another preferred embodiment, fibers in the form of
hollow fibers are used, which are capable of storing and/or
conveying liquids in their cavities.
[0034] The fineness of the fibers to be used according to the
invention preferably ranges from 0.005 to 3 den (from 0.006 to 3.3
dtex), and the length may vary between 0.1 and 15 cm, preferably
between 0.5 and 7.0 cm.
[0035] The fibrous fabrics to be used according to the invention
may be produced using all the well-known methods. By way of
example, carded needled nonwovens, thermally or latex-fixed
nonwovens and meltblown nonwovens may be mentioned.
[0036] The fiber content of the insert preferably ranges from 30 to
300 g/m.sup.2, particularly preferred, between 40 and 100
g/m.sup.2.
[0037] Fibrous fabrics are capable of absorbing liquids exuded from
the foodstuffs, where both an absorption by the fibrous material
and an absorptive effect with intercalation into the space between
the fibers may take effect.
[0038] The features of the superabsorbers to be used according to
the invention are not bound to specific polymeric structures or
production processes. In principle, all the superabsorbers on
synthetic or natural basis may be used, which meet the requirements
with respect to the quotient (TB+AAP 0.3)/LA and thus, impart
sufficient functionality to the absorbent substrates according to
the invention. On the one hand, said functionality lies in their
ability to absorb the exudates completely, even under pressure, and
to prevent back-flow into the foodstuff as effectively as possible,
and on the other hand, reduce migration from the absorbent
substrate to an acceptable minimum in cases of undesired excessive
amounts of liquid.
[0039] The polymerizate absorbing aqueous liquids to be used
according to the invention may be obtained by polymerization of
ethylenically unsaturated monomers bearing acid groups, e.g.,
acrylic acid, methacrylic acid, vinylacetic acid, maleic acid,
2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid,
(meth)allylsulfonic acid and/or mixtures thereof, in the presence
of crosslinkers.
[0040] To modify the properties, the polymerizates of the invention
may optionally contain other comonomers largely soluble in the
aqueous monomer solution, if not opposed by food law regulations.
Such comonomers common in the production of synthetic
superabsorbers may be non-ionic, anionic or cationic as well; for
example, vinylpyrrolidone, vinylacetamide, hydroxyethyl acrylate,
alkylaminoalkyl (meth)acrylate may be mentioned. Likewise, mixtures
of these comonomers may be employed. The ratio of these comonomers
should not exceed 40 wt.-%, because they might impair the
swellability of the superabsorbers.
[0041] The ratio of acidic monomers in the monomer mixture is 55-99
wt.-%.
[0042] Surprisingly, it was found that a specific combination of
crosslinker mixtures, degree of neutralization and batch
concentration results in the formation of superabsorbers which have
a level of properties with respect to high retention, high
absorption against pressure, rapid liquid absorption and extremely
low solubles ratio, which has not been achieved to date and
therefore, are excellently suited for use in absorbent substrates
of foodstuff packagings for absorbing aqueous liquids. Of course,
the superabsorbers to be used according to the invention are also
excellently suited for use in the hygienics industry (diapers,
liners, etc.) and in transport packagings.
[0043] As components of crosslinker mixtures, those of the types of
di- and triallylamine (Group A crosslinkers), acrylate and
methacrylate esters of polyol (Group B crosslinkers) are possible
in an embodiment of the invention, especially esters of polyhydroxy
compounds with unsaturated carboxylic acids, which are alkoxylated
in a preferred embodiment. C.sub.3-6 polyhydroxy compounds having
2-4 hydroxyl groups are preferred as starting compounds for the
synthesis of such crosslinkers; for example, trimethylolpropane,
glycerol, pentaerythritol, 1,3-propanediol, propylene glycol, or
1,4-butanediol. If the alcohol is alkoxylated prior to
esterification, ethylene oxide is preferably used. Preferably,
alkoxylated polyhydroxy compounds are employed, having attached at
least 1 mole of ethylene oxide, preferably at least 3 moles of
ethylene oxide per mole polyhydroxy compound. Other preferred
crosslinkers are polyethylene glycol diacrylate or dimethacrylate,
which contain polyethylene glycol residues having from 3 to 20 EO
units. Likewise, acrylate or methacrylate esters of alkoxylated
allyl or methallyl alcohol (Group C crosslinkers) were found to be
excellently suited crosslinkers. Preferably, these crosslinkers
contain at least three, more preferably from 5 to 20 ethylene oxide
units between the unsaturated groups.
[0044] Depending on the degree of neutralization, the crosslinkers
have different crosslinking activity, so that in each case, certain
adaptations must be made. Thus, for example, a methacrylate ester
of an alkoxylated methallyl alcohol has better reactivity at high
degrees of neutralization than at low ones.
[0045] Some of the acrylate or methacrylate ester crosslinkers to
be used according to the invention are commercially available,
e.g., trimethylolpropane oxethylate triacrylate by the Cray Valley
Company under the designation of Sartomer SR 415 (20EO), Craynor
435 (15EO), Sartomer RO 208 (9EO), Sartomer 454 (3EO), and
pentaerythritol oxethylate tetraacrylate under the designation of
Craynor SR 494 (5EO), and Servocure RTT 192 (5EO) by the Servo
Delden BV Company, glycerol ethoxylate triacrylate (5.5EO) under
the designation of Sartomer 921, and glycerol propoxylate
triacrylate under the designation of Sartomer 9021 by the Cray
Valley Company, and polyethylene glycol-400 diacrylate as Craynor
SR 344, and polyethylene glycol-600 dimethacrylate as Craynor SR
252 by the Cray Valley Company.
[0046] It has been found that the crosslinker combination, in
addition to a Group A crosslinker, must always include at least one
additional crosslinker from the different crosslinker Groups B) and
C).
[0047] A preferred crosslinker combination I) is composed of:
[0048] from 0.05 to 0.8 wt.-%, preferably from 0.2 to 0.6 wt.-%
type A crosslinker;
[0049] from 0.05 to 1.4 wt.-%, preferably from 0.1 to 1.0 wt.-%
type B crosslinker, and optionally
[0050] from 0 to 0.5 wt.-% type C crosslinker.
[0051] Another preferred crosslinker combination II) is composed
of:
[0052] from 0.05 to 0,8, preferably from 0.3 to 0.8 wt.-% type A
crosslinker,
[0053] from 0.05 to 1.5 wt.-%, preferably from 0.4 to 0.9 wt.-%
type C crosslinker, and optionally
[0054] from 0 to 0.5 wt.-% type B crosslinker.
[0055] In each case, the mutual proportions of crosslinkers may be
determined without great expense, using a few optimization tests.
The total amount of crosslinker to be employed according to the
invention ranges from 0.7 to 2.0 wt.-%, preferably from 0.9 to 1.5
wt.-%, relative to the monomers used.
[0056] The degree of neutralization of the acidic monomers during
polymerization has great impact on the properties of the
superabsorbers formed. High properties are obtained when from 15 to
80 mole-% and preferably, from 30 to 70 mole-%, and particularly
preferred, from 40 to 70 mole-% the acidic monomers are neutralized
and, for example, are present as sodium, potassium or ammonium
salts and/or mixtures thereof. The neutralization is carried out
either by addition of alkali or ammonium hydroxides or by using the
corresponding carbonates or hydrogen carbonates. In some cases it
may be more favorable to employ the monomers in non-neutralized or
low-neutralized condition prior to polymerization, and to perform
the final neutralization only after the polymerization.
[0057] The maximum monomer concentration depends on the way in
which the polymerization heat can be removed in the polymerization
process employed. In the aqueous gel polymerization process, the
monomer concentration may be up to 35 wt.-%; however, high product
properties are achieved the range of from 23 to 29 wt.-%.
[0058] As a basis for grafting, the polymerizates of the invention
may contain water-soluble polymers in amounts of up to 30 wt.-%.
Among others, these include partially or completely saponified
polyvinyl alcohols, starch or starch derivatives, cellulose or
cellulose derivatives, polyacrylic acids, polyglycols, or mixtures
thereof. The molecular weights of the polymers added as grafting
basis must be adapted to the aspects of the polymerization
conditions. Thus, in the case of a polymerization in aqueous
solution, for example, it may be necessary due to the viscosity of
the polymerizate solution to employ only polymers of low or medium
molecular weights, whereas this factor plays a minor role in
suspension polymerization.
[0059] In addition to polymerizates to be obtained by crosslinking
polymerization of partially neutralized acrylic acid, it is
particularly preferred to use those containing additional fractions
of graft-polymerized starch or of polyvinyl alcohol.
[0060] The addition of natural and/or synthetic fibers results in a
more rapid absorption of liquid and an augmented retention of the
superabsorber of the invention.
[0061] In principle, the preferred production of the superabsorbers
to be used according to the invention is effected according to two
methods:
[0062] According to the first method, the partially neutralized
acrylic acid in aqueous solution and in the presence of the
crosslinkers of the invention and optionally, additional
crosslinkers, comonomers and graft polymers, is converted to a gel
by free-radical polymerization, which then is crushed, dried,
milled and optionally post-crosslinked, and optionally treated with
conditioning agents, and screened to the desired particle size. The
solution polymerization may be carried out continuously or
batchwise. The patent literature presents a wide spectrum of
possible variations with respect to concentration ratios,
temperatures, type and amount of initiators as well as a variety of
possible ways for post-crosslinking. Typical processes have been
described in the following patent specifications which hereby are
intended to be a constituent part of the production process
according to the invention: U.S. Pat. No. 4,076,663; U.S. Pat. No.
4,286,082; DE 2,706,135; DE 3,503,458; DE 4,020,780; DE 4,244,548;
DE 4,323,001; DE 4,333,056; DE 4,418,818.
[0063] The second method comprises the inverse suspension and
emulsion polymerization processes. In these processes, an aqueous,
partially neutralized acrylic acid solution is dispersed in a
hydrophobic, organic solvent, using protective colloids and/or
emulsifiers, and the polymerization is started using free-radical
initiators. The crosslinkers either are dissolved in the monomer
solution and metered together with same, or added separately and
optionally, afterwards. The addition of optionally present graft
basis polymers is effected via monomer solution or by directly
placing in the oil phase. After the polymerization is completed,
the water is removed azeotropically from the reaction mixture, and
the polymer product is filtrated off.
[0064] Surface crosslinking of the polymer particles is normally
used to increase the absorption of liquid under pressure. It may be
effected both in the suspension and subsequently on the isolated
polymer powder. The basic process is described in the patent
specifications U.S. Pat. No. 4,340,706, DE 3,713,601, DE 2,840,010,
for example, and is hereby intended to be considered as a
constituent part of the production process according to the
invention.
[0065] Advantageously, the post-crosslinkers are frequently added
in the form of a solution in water, organic solvents or mixtures
thereof, and especially where low quantities of post-crosslinker
are used. Suitable mixing units for applying the post-crosslinking
agent are, e.g., Patterson-Kelley mixers, DRAIS turbulence mixers,
Lodige mixers, Ruberg mixers, screw mixers, pan mixers, and
fluidbed mixers, as well as continuously operated vertical mixers
wherein the powder is mixed at a rapid frequency using rotating
knives (Schugi mixer). After the post-crosslinker has been mixed
with the pre-crosslinked polymer, heating is effected at
temperatures of from 120 to 250.degree. C., preferably from 135 to
200.degree. C., and particularly preferred, from 150 to 185.degree.
C., in order to carry out the post-crosslinking reaction. The time
period for additional heating is limited by that point where the
desired properties pattern of the superabsorber is destroyed as a
result of heat damage.
[0066] As a rule, suitable post-crosslinkers include at least two
functional groups. Here, alcohol, amine, aldehyde glycidyl and
epichloro functions are preferred and also, crosslinker molecules
having multiple different functions are possible. Preferably, one
of the following post-crosslinking agents is used: ethylene glycol,
diethylene glycol, triethylene glycol, polyethylene glycol,
glycerol, polyglycerol, propylene glycol, diethanolamine,
triethanolamine, polypropylene oxide, block copolymers of ethylene
oxide and propylene oxide, sorbitan fatty acid esters, ethoxylated
sorbitan fatty acid esters, trimethylolpropane, ethoxylated
trimethylolpropane, pentaerythritol, ethoxylated pentaerythritol,
polyvinyl alcohol, sorbitol, ethylene carbonate, propylene
carbonate, and polyepoxides such as ethylene glycol diglycidyl
ethers. It is particularly preferred to work using ethylene
carbonate as post-crosslinking agent. The cost-crosslinking agent
is used in amounts of from 0.01 to 30 weight percent, preferably
0.1-10 weight percent, and particularly preferred, 0.1-1 weight
percent relative to the polymer to be post-crosslinked.
[0067] Frequently, the superabsorbers to be used according to the
invention are added with common conditioning agents familiar to a
person skilled in the art, in order to prevent static charging or
unintended agglomeration, for example. To this end, e.g., stearates
and polyalkylene glycols are used.
[0068] The superabsorbent polymers to be used according to the
invention are preferably present within a particle size range of
from 10 to 1,000 .mu.m, and particularly preferred, between 100 and
850 .mu.m. The particles are dispersed within the insert, swelling
to a gel when absorbing liquid. In addition to the preferred
homogeneous dispersion of the particles, it may be advantageous in
many cases, for improved absorption or absorption rate, to build up
a concentration gradient and/or a particle size gradient of the
absorbers inside the core. The ratio of superabsorbent polymer is
from 30 to 150 wt.-%, preferably from 50 to 100 wt.-% relative to
the weight of the fibers. In a preferred embodiment, it was found
sufficient to use from 30 to 50 g/m.sup.2 of the superabsorbent
polymer of the invention in a fiber matrix of from 60 to 90
g/m.sup.2 in order to absorb liquid exudates from foodstuffs.
[0069] The exterior envelope of the insert consists of a bottom and
a top perforated film and/or a fleece made of plastic, through
which liquid may permeate into the absorbent core. It is quite
possible to perforate only one side of the envelope, but, due to
the extremely low migration values of the absorbent substrates of
the invention, it is advantageously possible to perforate the
envelope on the foodstuff side as well, which is advantageously
possible, since virtually no migrated materials can reach the
foodstuff. Frequently, it is also advantageous to design the
perforation density of top and bottom sides in different fashion,
in order to improve the absorption. For example, polyethylene,
polypropylene, polyamide, polyester and polyvinyl chloride having
weights per unit area of from 12 to 25 g/m.sup.2, preferably from
15 to 20 g/m.sup.2 are used as plastics. Top and bottom films are
preferably bound to each other at their edges. To this end, the
edges of the enveloping materials are welded together under
temperature and pressure, for example, or frequently as well, glued
together using hot-melt adhesives. In various cases, mechanical
binding is also possible, e.g., by sewing the edges of the
envelopes. Occasionally, adhesive and/or welded and mechanical
binding are combined. Indeed, it is ensured in any case that the
powders of the superabsorbent polymers cannot escape the envelope
and reach the foodstuffs.
[0070] Optionally, absorbent substrates may be put to use for
special packaging units where the absorbent core merely consists of
the superabsorbent polymer and does not include any additional
interior fibrous materials.
[0071] Similarly, when the absorbent substrates are used as a
substitute for ice, they preferably consist only of the enveloping
film or fleece and the superabsorbers to be used according to the
invention. After swelling with water, the substrates are frozen and
used instead of ice for refrigerating foodstuffs. In contrast to
refrigerating using ice, there is no thawed water in this case.
[0072] Among the numerous possible forms of inserts, rectangular or
quadratic ones are preferred; however, other forms, such as round
ones are also used for special packaging containers. Frequently, it
is advantageous to modify the insert in such a way that instead of
a continuous uniform structure, a honeycomb type structure is
produced, wherein basically, many individual absorbent pads are
present, neighboring each other. Such honeycomb subdivision shows
to advantage particularly in those cases where an absorbent
substrate as absorbing component, having relatively large surface,
is filled with superabsorber only, i.e., without fiber or fleece
components, because in this way, persistently good distribution of
the absorber over the surface is ensured.
[0073] Testing Methods
[0074] Retention TB (Superabsorber)
[0075] The retention is determined according to the tea bag method,
wherein 200 mg of test substance is welded in a tea bag, immersed
in a 0.9% NaCl solution for 30 minutes, drained for 10 minutes,
centrifuged in a centrifuge (23 cm in diameter, 1,400 rpm) for 5
minutes and weighed. A tea bag having no water-absorbing
polymerizate is run as a so-called blank:
TB=(final weight-blank)/initial weight (g/g)
[0076] Absorption Against Pressure AAP (SuDerabsorber)
[0077] The ability of a water-absorbing polymerizate absorb liquid
from a reservoir under a defined pressure (Absorption Against
Pressure (0.3 psi=21 g/cm.sup.2), (0.7 psi=49 g/cm.sup.2)) is
determined as follows: 900 mg of test substance is weighed in a
plastic cylinder (inner diameter=6 cm, height=5 cm) having a screen
fabric (mesh width=400 mesh) as bottom, dispersed uniformly, and
weighted using a defined weight in the form of a plastic plate
(diameter=5.98 cm), together with a metal piston (diameter=5.98
cm). The plastic plate is situated between the test substance and
the metal piston. Thereafter, the entire testing unit is placed on
a glass filter place (diameter=12 cm, porosity=0) which is covered
with a filter paper and soaked with 0.9% NaCl solution. The filter
plate is embedded in the NaCl solution up to its top edge. The test
substance is allowed to absorb liquid for 60 minutes:
[0078] AAP(0.3 or 0.7 psi)=(weight of the testing unit prior to
absorption-weight of the testing unit after absorption)/initial
weight of test substance (g/g)
[0079] Solubles LA (Superabsorber)
[0080] 100 g of a 0.9% saline solution is placed in a 250 ml
Erlenmeyer flask and stirred at 500 rpm using a magnetic stirrer.
0.2 g of superabsorber is weighed in. After complete addition,
stirring is effected for 16 hours, with the piston closed.
Subsequently, filtration is effected over a glass microfilter. The
filtrated solution is adjusted to a pH value of about 10.0, using
sodium hydroxide solution. Thereafter, titration is effected to a
pH value below 3.0, using 0.1 N hydrochloric acid. A titration
curve having two inflection points is obtained. The first
equivalence point corresponds to excess sodium hydroxide at pH 8.0
to 8.4, and the second equivalence point corresponds to displaced
acrylic acid at pH 4.0 to 4.3. The difference in the quantity of
hydrochloric acid between the inflection points indicates the total
amount of acrylates and thus, the water-soluble ratio of the
superabsorber. Calculation:
% Solubles (LA)=(V2-V1).times.C.times.Equivalent
weight*.times.100.2EW.tim- es.10.times.VF
[0081] V2=HCl consumption to reach the 2nd inflection point
[ml]
[0082] V1=HCl consumption to reach the 1st inflection point
[ml]
[0083] C.dbd.HCl normality [moles/1000 ml]
[0084] EW=Initial weight of superabsorber [g]
[0085] VF=Amount of filtrate [g]
[0086] (*)=Equivalent weight calculated from the decree or
[0087] superabsorber neutralization
[0088] Rate of Liquid Absorption (SG)
[0089] In this test, the time period is measured, in which 1 g of
superabsorber absorbs 20 g of a 0.2% saline solution at room
temperature. This test procedure is described in EP 0.443,627, page
12, "Free-Swell-Rate".
[0090] Residual Monomers (Superabsorber)
[0091] The residual monomers (RM) are determined from the filtrate
of the solubles determination using the HPLC method and evaluated
according to the internal standard method.
[0092] Migration Measurement (Absorbent Substrate)
[0093] The absorbent substrate in a 250 ml screw cap jar is
perfused with a test liquid and stored therein without agitation
for 10 days at room temperature.
[0094] The test liquid may consist of distilled water, 0.2% or 0.9%
saline solution and is employed in excess relative to the
absorptive capacity of the absorbent substrate. The excess is to
simulate that case where the substrate is exposed to an amount of
liquid higher than prescribed.
[0095] Subsequently, the test liquid not absorbed by the absorbent
pad is sucked off over a 45 .mu.m filter and examined for the
fractions migrated from the absorbent substrate. If distilled water
is used as test liquid, the migrated fractions are obtained from
the dry residue of the sucked-off aqueous phase. In contrast, if
0.2% or 0.9% aqueous salt solutions are used as test liquids, the
sodium chloride content must be subtracted from the dry residue to
obtain the migration value. The results are expressed as ma of
migrated material per dm.sup.2 or per g of absorbent substrate.
[0096] Measurement of Microbial Contamination
[0097] A Petri dish is charged with the respective absorbent pad
and a nutrient broth. The amount of nutrient broth is proportioned
in such fashion as to be completely absorbed by the absorbent pad.
Subsequently, cultivation is effected in an incubator at 30.degree.
C. for 48 hours. To visualize microbial growth, the broth is added
with triphenyltetrazolium chloride (TTC; 2 drops of a 1% TTC
solution/9 ml of broth). TTC is reduced by microbial activity from
a colorless solution to an intensively reddish coloration and thus,
may be used as a qualitative measure for microbial activity.
[0098] For the quantitative determination of microbial activity
using 1% TTC solution, tea bags with and without superabsorber are
incubated with blood and tissue water (thawed water) of a
purchased, commercially available boiling fowl (deep-frozen). The
tea bag is subsequently subjected to measurement using a thin-layer
scanner (Desaga CA 60 thin-layer scanner) at .lambda.=435 nm and
compared to a white silica gel TLC plate. The typical thawed water
contains about 10.sup.4 germs/ml. The obtained relative peak
heights are correlated and used as a measure for microbial activity
with respect to germ count increase (intensity of red coloration)
as well as areal propagation (size of red-colored area).
[0099] The following examples demonstrate the design of some
absorbent substrates of the invention, the advantageously low
migration values in water and aqueous solutions, and the
antimicrobial activity. Furthermore, the production of the
superabsorbers to be used advantageously in these absorbent
substrates, using the special combinations of crosslinkers will be
described, and the favorable combination of properties, comprising
retention, absorption against pressure, and solubles will be
illustrated.
EXAMPLE 1
[0100] An absorbent insert having the following design was
produced:
[0101] A: Top and bottom sealing films made of a perforated
polyethylene film having 16 g/m.sup.2; manufactured by Paramount
Packaging, USA;
[0102] B: Polypropylene fibers 3d, 64 mm fiber length, 79
g/m.sup.2, type 123 by the Company HERCULES INC., Wilmington,
USA;
[0103] C: Superabsorbent polymer according to Example 5, 43
g/m.sup.2, uniformly spread into the B-layer between the
polypropylene fibers.
[0104] The core of the insert of B+C has the dimensions
76.times.127 mm, the insert itself measures 89.times.140 mm and is
sealed at its edges by a welding seam.
EXAMPLE 2
[0105] Following the procedure of Example 1, an absorbent insert
was produced:
[0106] A: Top and bottom fleeces made of polypropylene, 17
g/m.sup.2, manufactured by the SCOTT PAPER Company, polypropylene
fibers by the Company HERCULES INC., Wilmington, USA;
[0107] B: Films of perforated polyethylene having 16 g/m.sup.2,
each one above and below the C-layer;
[0108] C: Polypropylene fibers 3d, 64 mm fiber length, 68
g/m.sup.2, type 123 by the Company HERCULES INC., Wilmington,
USA;
[0109] D: Superabsorbent polymer according to Example 4, 42
g/m.sup.2, uniformly spread into the polypropylene fibers of layer
C.
[0110] The core of the insert of B+C+D has the dimensions
76.times.127 mm, the insert itself measures 89.times.140 mm and is
sealed at its edge.
EXAMPLE 3
[0111] An absorbent insert was produced on a production machine at
a rate of about 5.5 to 6.5 m/min; the design is as follows:
[0112] A: Top and bottom fleeces of polyethylene terephthalate, 17
g/m.sup.2
[0113] B: Fibers of polyethylene terephthalate, 65 g/m.sup.2
[0114] C: Superabsorbent polymer according to Example 7, 50
g/m.sup.2, uniformly spread into the B fiber layer.
[0115] The individual layers were mechanically bound to each other
by needle punching.
EXAMPLES 4-13
[0116] Superabsorbent polymers to be used according to the
invention were polymerized according to the following guideline
formulation:
[0117] In a cylindrical plastic vessel, a polymerization batch of
1000 g in total is prepared. To this end, 280 g of acrylic acid for
batches with 28% WS (active substance) and 240 g of acrylic acid
for batches with 24% WS, respectively, and the employed
crosslinkers, comonomers and other components are mixed in
completely desalted water. With stirring and cooling, partial
neutralization is effected to the degree of neutralization (NG)
indicated in Table 1, using 50% sodium hydroxide solution. The
solution is cooled to 7-8.degree. C. and purged with nitrogen until
the oxygen content in the monomer solution has dropped to a value
of low 0.2 ppm. Subsequently, 100 ppm of azobis(2-amidinopropane)
dihydrochloride, dissolved in 10 g of salted water, 800 ppm of
sodium persulfate, dissolved in 6 g of VE-water (desalted water),
70 ppm of hydrogen peroxide (35%), dissolved in 1 g of VE-water
(desalted water), are added. Then, the polymerization is initiated
by adding 9 ppm of ascorbic acid, dissolved in 2 g of water, which
results in a significant temperature rise. Once polymerization is
completed, the gel-like polymer block is crushed, willowed and
dried. Thereafter, the polymer is milled and screened for the grain
fraction of 150-800 .mu.m.
1TABLE 1 AAP TB 0.3 SG RM Ex. WS NG TAA TMPTA TMP3EOTA PE5EOTA
PEG400DA AA10EOMA [g/g] [g/g] LA Q.sub.SAP 0.3 [s] [ppm] B4 28 80
0.35 0.7 28.5 19.0 1.8 26.4 B5 28 70 0.35 0.7 28.5 17.3 1 45.8 28
B6 28 75 0.45 0.7 26.5 21 1 47.5 B7 28 55 0.3 0.4 25.5 24.0 2.2
22.5 450 B8 24 50 0.3 0.8 22.9 19.2 1.4 30.1 230 B9 28 40 0.3 0.4
23.6 19.3 1.9 22.6 300 B10 28 40 0.3 0.6 25.1 19.1 1.9 23.3 470 B11
28 55 0.3 0.5 26.2 22.3 2 B12 28 50 0.3 0.15 0.6 26.6 20.2 1.9 24.6
33 490 B13 24 40 0.3 0.8 20.0 19.1 1.9 20.6 210 TAA: triallylamine,
TMPTA: trimethylolpropane triacrylate, TMP3EOTA:
trimethylolpropane(3EO) triacrylate, PE3EOTA: pentaerythritol(3EO)
tetraacrylate, PE5EOTA: pentaerythritol(5EO) tetraacrylate,
PEG400DA: polyethylene glycol(400) diacrylate, AA10EOMA: allyl
alcohol(10EO) methacrylate. The figures referring to the
crosslinkers indicate wt.- %/acrylic acid.
COMPARATIVE EXAMPLES 1-6
[0118] According to the formula of Example, polymerizates having
28% AS were produced using the crosslinkers indicated in Table 2.
V1 contains only 300 mg of sodium peroxodisulfate and, in addition,
0.4 wt.-% sodium carbonate. V2 contains no hydrogen peroxide. V3
was prepared using 600 mg of sodium peroxodisulfate. The results
demonstrate that superabsorbers, in which the employed amounts of
crosslinkers fall outside the limits of the invention or outside
the compositions of the invention do not have the required
Q.sub.SAP 0.3 values.
2TABLE 2 NG TAA TMP3EOTA PEG600DA AA-10EO-MA TB AAP 0.3 LA SG RM
Batch [mol - %] [wt.- %] [wt.- %] [wt.- %] [wt.- %] [g/g] [g/g]
[wt.- %] Q.sub.SAP 0.3 [s] [ppm] V1 70 0.1 0.2 44.6 7.5 11.1 4.7
500 V2 55 0.6 25.1 20.5 3.3 13.8 45 200 V3 40 0.25 0.3 30 8.5 6.5
5.9 42 210 V4 30 0.2 0.3 26 9.8 6.1 5.8 48 155 V5 55 1.25 26 19.7
3.4 13.4 700 V6 55 1.0 25.2 24.9 3.0 16.7 790 (PE5EOTA) TAA:
triallylamine, TMP3EOTA: trimethylolpropane(3EO) triacrylate,
PEG600DA: polyethylene glycol(600) diacrylate, AA-10EO-MA:
methacrylate ester of an allyl alcohol etherified with 10 moles of
EO; PE5EOTA: pentaerythritol(5EO) tetraacrylate.
COMPARATIVE EXAMPLE 7
[0119] In this example, a superabsorber is crosslinked using an
amount of N,N'-methylenebisacrylamide as employed in the
embodiments U.S. Pat. No. 4,677,174. Such sparingly crosslinked
absorbers are described in EP 562,846 A1 for use in absorbent
substrates for foodstuffs.
[0120] Following the procedure of Example 4 according to the
invention, 280 g of acrylic acid is 90% neutralized with equimolar
quantities of sodium hydroxide solution and ammonium hydroxide and
polymerized using 26.5 mg of N,N'-methylenebisacrylamide (0.009
wt.-% based on acrylic acid) as crosslinking component.
[0121] The polymerizate is poorly crosslinked and has an
exceptionally high solubles ratio of 74 wt.-%, which is
unacceptable for use in absorbent substrates for foodstuffs.
EXAMPLE 14
[0122] The superabsorber of the invention of Example 5 is subjected
to a post-crosslinking reaction, thereby significantly improving
the properties of the absorber in liquid absorption under pressure,
especially under high pressure (AAP 0.7).
[0123] 100 g of the polymer screened to 150 to 800 .mu.m is mixed
with a solution of 0.5 g of ethylene carbonate, 2 g of desalted
water and 4 g of acetone with vigorous intermixing and
subsequently, heated in an oven at a temperature of
[0124] 180.degree. C. for 25 minutes. Table 3 illustrates the
properties of the superabsorber before and after post-crosslinking.
The improvement of the Q.sub.SAP quotient for the post-crosslinked
superabsorber is evident. Absorbent substrates filled with such
superabsorbers are particularly suited for safe packaging of heavy
foodstuffs.
3 TABLE 3 TB AAP 0.3 AAP 0.7 LA Absorber from [g/g] [g/g] [g/g]
[wt.- %] Q.sub.SAP 0.3 Q.sub.SAP 0.7 Example Example before after
before after before after before after before after before after 14
5 28.5 26.4 17.3 28.9 7.7 23.5 1 1.2 45.8 46.1 36.2 41.5
EXAMPLE 15
[0125] Following the polymerization procedure of Examples 4-13, a
superabsorber to be used according to the invention is produced,
with the proviso that at a AS of 28 wt.-% and a neutralization
degree of 40%, 0.3 wt.-% triallylamine and 0.5 wt.-% PE5EOTA are
used and subsequently, the resulting polymer is post-crosslinked
according to Example 14 using ethylene carbonate. The properties
are as follows: TB=21.8 g/g, AAP 0.3=24.7 g/g, AAP 0.7=20.5 g/g,
LA=1.9 wt.-%, Q.sub.SAP 0.3=24.5, Q.sub.SAP 0.7=22.3.
EXAMPLE 16
[0126] Following the polymerization procedure of Examples 4-13, a
superabsorber to be used according to the invention is produced at
a AS of 28 wt.-% and a neutralization degree of 55%, with the
proviso that 5 wt.-% acrylic acid is replaced with
acrylamidopropanesulfonic acid. Subsequently, the absorber is
post-crosslinked according to the experimental specificatons of
Example 14, using ethylene carbonate. The absorber has the
following properties: TB=23 g/g, AAP 0.3=25 g/g, AAP 0.7=20.5 g/g,
LA=1.5 wt.-% Q.sub.SAP 0.3=32, Q.sub.SAP 0.7=29
EXAMPLE 17
[0127] Following the polymerization procedure of Examples 4-13, a
superabsorber to be used according to the invention is produced at
a AS of 28 wt.-% and a neutralization degree of 55%, with the
proviso that in addition, 1 wt.-% of partially saponified polyvinyl
alcohol, type Mowiol 5/88 (Hoechst AG Company, Germany), is present
as a grafting basis in the monomer mixture to be polymerized.
Subsequently, the absorber is post-crosslinked according to the
experimental specifications of Example 14, using ethylene
carbonate. The absorber has the following properties: TB=24.4 g/g,
AAP 0.3=26 g/g, AAP 0.7=22 g/g, LA=1.7 wt.-%, Q.sub.SAP 0.3=29.6,
Q.sub.SAP 0.7=27.3.
COMPARATIVE EXAMPLES 8-11
[0128] The properties of commercially available superabsorbers
offered for use in absorbent substrates for foodstuffs, were
determined. The data are presented in Table 4.
4 TABLE 4 AAP TB 0.3 LA SG Comparison Absorber [g/g] [g/g] [wt.- %]
Q.sub.SAP 0.3 [s] V8 Sanwet IM 1000 49.0 7.0 5.2 10.8 31 #1 V9
Sanwet IM 3900 33.5 13.0 5.1 9.1 32 #2 V10 Sanwet IM 5000S 31.0
20.0 6.6 7.7 #3 V11 Salsorb 90P 26.5 24.0 8.1 5.9 22 #4 #1-#3:
Superabsorbers made of starch/polyacrylate by the Company Hoechst
AG; #4: Superabsorber made of crosslinked polyacrylate by the
Company Allied Colloids Ltd.
[0129] The examined superabsorbers for commercially avail able
absorbent substrates do not meet the requirements according to the
invention with respect to the Q.sub.SAP 0.3 quotient.
EXAMPLE 18
[0130] Absorbent substrates having a total weight of 0.59 g and
consisting of tea bags (100 mm.times.100 mm=1 dm.sup.2) having a
filling of 0.2 g of superabsorber of Example 6 and Comparative
Example 1, respectively, are produced and examined in distilled
water and in 0.2% saline solution according to the method for
determining the migration. The results in Table 5 demonstrate that
only the absorbent substrate of the invention, having a
superabsorber of Example 6 with Q.sub.SAP 0.3=47.5 meets the low
migration values of mg/g absorbent substrate required according to
the invention. The absorbent substrate with the absorber of
Comparative Example V1, having a Q.sub.SAP 0.3=4.7, shows
unsatisfactorily high migration values.
5TABLE 5 Migration value Migration value Migration value Migration
value Superabsorber [mg/dm.sup.2 or mg/g Excess [mg/dm.sup.2 or
mg/g Excess [mg/dm.sup.2 or mg/g Excess [mg/dm.sup.2 or mg/g from
Excess of test absorbent of test absorbent of test absorbent of
test absorbent Example liquid substrate] liquid substrate] liquid
substrate] liquid substrate] B6 50 ml of 4.5 or 7.6 100 ml of 5.7
or 9.6 50 ml of 2.2 or 3.7 100 ml of 4.1 or 6.9 distilled distilled
0.2% NaCl 0.2% NaCl water water soln. soln. V1 50 ml of 11.3 or
19.2 100 ml of 14.9 or 25.2 50 ml of 18.2 or 30.8 100 ml of 20.0 or
33.9 distilled distilled 0.2% NaCl 0.2% NaCl water water soln.
soln.
EXAMPLE 19
[0131] Absorbent substrates having a total weight of 0.59 g and
consisting of tea bags (100 mm.times.100 mm=1 dm.sup.2) having a
filling of 0.2 g of superabsorber of Example 6 and Comparative
Example 1, respectively, are produced and examined in 80 ml of 0.9%
saline solution according to the method for determining the
migration. The results demonstrate the superiority of the absorbent
substrates of the invention with respect to lowest migration
values.
6TABLE 6 Migration value Superabsorber [mg/dm.sup.2 or mg/g
absorbent of Example Amount of test liquid substrate] B6 80 ml of
0.9% NaCl soln. 9.1 or 15.0 V1 80 ml of 0.9% NaCl soln. 20.2 or
34.2
COMPARATIVE EXAMPLE 12
[0132] Commercially available absorbent substrates for foodstuffs
were examined for their migration properties in 0.2 and 0.9% saline
solutions. The products, when compared to those of the invention,
have a significantly higher migration.
[0133] Measurement in d-stilled water was not possible because the
absorbent substrates were caused to burst by the absorber
particles.
7TABLE 7a Migration value Migration value Excess of [mg/dm.sup.2 or
mg/g Excess of [mg/dm.sup.2 or mg/g Commercial product test liquid
absorbent substrate] test liquid absorbent substrate] THERMAFREEZE#
50 ml of 0.9% 58.2 or 21.3 100 ml of 0.9% 80.6 or 29.5 NaCl soln.
NaCl soln. Sorba-Freeze Pads## 50 ml of 0.9% 142.7 or 34.9 100 ml
of 0.9% 183.5 or 44.9 NaCl soln. NaCl soln. #Commercial product of
the Company Therma Rite, Australia/Denmark ##Commercial product of
the Company Sorba-Freeze Ltd., Scotland
[0134]
8TABLE 7b Migration value Migration value Excess of [mg/dm.sup.2 or
mg/g Excess of [mg/dm.sup.2 or mg/g Commercial product test liquid
absorbent substrate] test liquid absorbent substrate] THERMAFREEZE#
50 ml of 0.2% 51.8 or 19.0 100 ml of 0.2% 61.2 or 22.4 NaCl soln.
NaCl soln. Sorba-Freeze Pads## 50 ml of 0.2% 127.7 or 31.2 100 ml
of 0.2% 146.4 or 36.9 NaCl soln. NaCl soln.
COMPARATIVE EXAMPLE 13
[0135] The Superabsorber contained in the THERMAFREEZE absorbent
substrate is isolated, and its properties are determined. TB=24.5
g/g, AAP 0.3=19.5 g/g, LA=2.4 wt.-%, Q.sub.SAP 0.3=18.3. With
respect to the requirements according to the invention, the
migration values are clearly above the limit of 15 mg/g, and the
Q.sub.SAP 0.3 of the employed superabsorber is below the limit of
20.
COMPARATIVE EXAMPLE 14
[0136] In a sterile Petri dish, a non-sterile paper plate
(commercially available as foodstuff base) is soaked with 18 ml of
sterile Caso broth and incubated for 48 hours at 30.degree. C.
Result: bacteria grow on the paper plate, recognizable by the mucus
formation and the intensive odor of bacterial decomposing
activity.
COMPARATIVE EXAMPLE 15
[0137] In a sterile Petri dish, 18 ml of sterile Caso broth is
incubated for 48 hours at 30.degree. C. Result: neither bacteria
nor fungi are detectable in the broth.
COMPARATIVE EXAMPLE 16
[0138] In a non-sterile Petri dish, 18 ml of sterile Caso broth is
incubated for 48 hours at 30.degree. C.
[0139] Result: bacteria and molds grow in the broth, recognizable
by the turbidity of the broth and the intensive odor of bacterial
decomposing activity.
EXAMPLE 20
[0140] Tea bags without and with superabsorber of Example 5 (0.5
g/dm.sup.2) were placed in a Petri dish 20 cm in diameter and
subjected to conditions according to those indicated in the
following Table under "Incubation". The incubation itself was
effected for 24 hours in an incubator at 37.degree. C. There was no
additional contamination by germs. As already illustrated in the
chapter on testing methods, the measurement of microbial activity
was performed using a thin-layer chromatographic procedure where
the specification of the relative peak heights correlates with the
germ count. It is apparent that the use of the polymer of the
invention is originally responsible for the rapid decrease of
microbial activity:
9TABLE 8 Relative Test Incubation peak height A Tea bags without
polymer 5626 Addition of 5 ml of thawed water and addition of 2
drops of TTC solution B Tea bags with polymer 745 Addition of 5 ml
of thawed water and addition of 2 drops of TTC solution C As in B,
but without incubation in the incubator; 728 instead, immediate
measurement
EXAMPLE 21
[0141] In a sterile Petri dish, a non-sterile cellulose fleece
containing superabsorber (Example 6, 0.5 g/dm.sup.2) is soaked with
18 ml of sterile casein soya meal peptone broth (Caso broth), to
which 4 drops of a 1% TTC solution have been added, and incubated
for 48 hours at 30.degree. C. Result: only two red bacteria
colonies are recognizable on the fleece. No change in odor due to
bacterial decomposing activity is perceptible.
[0142] A comparative test using absorber-free cellulose fleece
shows bacterial growth which can be recognized by an intensive red
coloration of the entire fleece and an intensive odor caused by
bacterial metabolic activity.
* * * * *