|Title of Invention||
"A SWELLING PASTE"
|Abstract||A swelling paste consisting of a component 1 which is an aqueous, partially neutralized solution of a polymer constituted of free-radical-polymerizable monomers of the kind as herein described, partially neutralized, free-radical-polymerizable monomers of the kind as herein described containing carboxyl groups and ccarboxylate groups, and other free-radical-polymerizable monomers of the kind as herein described copolymerizable with (a) and (b), a component 2 consisting of a crosslinker characterized in that said crosslinker is an aldehyde or an aldehyde-liberating compound as herein described, and optionally additives of the kind as herein described.|
|Full Text||The present invention relates to a swelling paste.
The present invention relates to a printable swelling paste containing a mixture of polymers having carboxyl and amide group moieties, and aldehyde crosslinkers. The swelling paste may be stored for a long period of time, with no thickening or gelling taking place. It is applied onto support materials of most various kinds and crosslinked by exposure to heat. As a result, structures are formed having high absorptive capacity for water and aqueous liquids.
Superabosrobent polymers are known for a long time and commercially available in the form of powders, e.g., under the designation of FAVOR or CABLOC. However, the processing of powders is technically expensive and, once abraded particles give rise to breathable fines, not harmless in terms of occupational medicine.
While alternatively possible polymerizations of monomer solutions on prefabricated surfaces or filaments are known, they are a domain of chemical industry factories because of the protective gas technique required and the safety regulations to be observed and cannot be transferred to factories of other industrial sectors such as the printing and textile industries.
EP 188,091 describes absorptive porous sheet materials produced by padding a mixture of an aqueous solution of a non-crosslinked prepolymer with a crosslinker onto a nonwoven and subsequent thermal crosslinking. This process is disadvantageous in that the polyhaloalkanol, haloepoxyalkane and polyglycidyl ether type crosslinkers may be added just a short time before processing due to their reactivity, because otherwise undesirable thickening of the mixture takes place during storage, and the above-described crosslinkers are critical for health reasons.
EP 357,474 describes spraying of low-viscosity aqueous solutions of non-crosslinked polyacrylic acids on sheet fabrics made of cellulose and subsequent thermal crosslinking by simultaneously applied crosslinkers to give water-swell-able gels. Multivalent metal ions, as well as epoxides, azir-idines, polyglycidyl ethers are described as crosslinkers which, due to their cancerogenic potential, are barely usable anymore, the hygienics and food packaging industrial sectors being considered as particularly problematic. In addition, they give rise to early crosslinking already at room temperature when storing the coating solutions, so that further processing of the high-viscosity and/or gelled mass is no longer possible.
DE-OS-23 27 249 describes a washing procedure wherein water-insoluble, solid cation exchangers based on polymers of (meth)acrylic acid, (meth)acrylamide and formaldehyde or formaldehyde-amine condensation products are used. Polymerization of the monomers takes place in the presence of formaldehyde, resulting directly in crosslinked water-insolu-
ble polymers. The polymer does not go through a separable water-soluble state where processing as a dissolved polymer would be possible.
Also, US-Re-32,649, page 7, mentions glyoxal as a possible crosslinking agent in the production of superabsorb-ers. However, as in DE-OS-23 27 24 9, a polymerization is involved resulting in crosslinked, water-insoluble polymers in a single step, where soluble intermediates cannot be isolated.
DE 195 21 431 Al describes a process wherein reactive crosslinkers such as polyfunctional epoxides, aziridines, polyglycid ethers, and epihalohydrines are added to an aqueous solution of a pre-crosslinked polyacrylic acid just prior to the printing process. Although, a printable paste is already described therein, these reactive crosslinkers have the crucial disadvantage that the mixture of the two components cannot be stored for long time but must be prepared freshly every hour due to thickening which already begins at room temperature.
Therefore, the invention is based on the object of providing a printable paste which may be applied on a prefabricated sheet material in a single operation and, following a thermal aftertreatment, is capable of swelling in the presence of water or aqueous solutions, thereby multiplying its original volume. The finished paste should be capable of being stored for at least one week at room temperature, with no viscosity changes of the paste or swellability decrease occurring subsequent to processing. In addition, the paste
must be free of readily inflammable or dangerous substances. Crosslinking should be possible at temperatures as low as
140°C and, due to the thermal sensitivity of the support material and/or for economic reasons, may not take longer
than 5 minutes at maximum, at temperatures from 160°C on. Thereafter, crosslinking must be completed, and the coated substrate must have sufficient swellability and swelling rate. Furthermore, the gel produced should have sufficient stability.
Surprisingly, the object of the invention was accomplished using a mixture of two components, component 1 being an aqueous solution of a copolymer made of monomers containing carboxyl groups and amide groups, component 2 being an aldehyde crosslinker, and other additives may optionally be present in said mixture.
Thus, the invention is directed to a swelling paste made of
A) a component 1, consisting of an aqueous, partially or
completely neutralized solution of a polymer produced by
free-radical polymerization of mixtures of
a) monomers containing amide groups, and
b) monomers containing carboxyl groups and/or carboxyl-ate groups, and optionally,
c) other free-radical-polymerizable monomers,
B) a component 2, consisting of a crosslinker, and optionally,
C) other additives,
Accordingly, there is provided a swelling paste consisting of (A) a component 1 which is an aqueous, partially neutralized solution of a polymer constituted of (a)
free-radical-polymerizable monomers of the kind as herein described, (b) partially neutralized, free-radical-polymerizable monomers of the kind as herein described containing carboxyl groups and ccarboxylate groups, and (c ) other free-radical-polymerizable monomers of the kind as herein described copolymerizable with (a) and (b),
(B) a component 2 consisting of a crosslinker characterized in that said crosslinker is an aldehyde or an aldehyde-liberating compound as herein described, and optionally
(C) additives of the kind as herein described.
The polymer of component 1 preferably consists of
a) 1-80, more preferably 1-60, and most preferably form 1 to 20 -mole-% of free-radical-polymerizable monomers containing amide groups, and
b) 20-99, more preferably 40-99, and most preferably 80-99 mole-% of partially neutralized, free-radical-polymerized monomers containing carboxyl groups.
For example, monomers according to a) containing amide groups are (meth) acrylic acid amides such as acryl-amide, methacrylamide, and vinyl carboxylic acid amides such as N-vinylformamide and N-vinylacetamide. Preferably, acrylamide is used.
As carboxyl group-containing monomers according to b), methacrylic acid, maleic acid, fumaric acid, itaconic acid and the salts and mixtures thereof are possible in addition to acrylic acid. For example, sodium, potassium, ammonium, alkylammonium, alkanolammonium or mixtures thereof are possible as counter ions. As monomer containing carboxyl groups, acrylic acid with sodium as counter ion is preferably used.
Among other things, the carboxyl group neutralization degree of the polymers of
the invention has crucial impact on the swelling properties and the retention of the
crosslinked swelling pastes and is preferably at least 25, more preferably at least
50 mole-%. According to the invention, the
tralization of the carboxyl groups may be carried out prior to or after polymerization, and frequently, part of the neutralizing agent is added prior to polymerization and the rest afterwards. In any event, however, care must be taken that the addition of alkali does not give rise to unintended saponification of the monomers containing amide groups. In the polymer already produced, on the other hand, it may be quite reasonable to generate amine groups by acidic saponification of the moieties formed from, e.g., vinyl carboxylic acid amides, which in turn are capable of undergoing a crosslinking reaction with crosslinker component 2.
In addition to the monomers a) and b), the polymer component 1 may have
c) 0-4 9 mole-% of other anionic or non-ionic monomers polymerized therein, such as (meth)allylsulfonic acid, vinyl-sulfonic acid, 2-acrylamido-2-methyl-l-propanesulfonic acid, mono(meth)acrylic esters of alcohols, vinyl esters, alkylox-ethylates or alkylphenoloxethylates. The comonomers are used to modify the polymer properties, e.g., to improve the adherence to the support material, increase the salt stability, or adjust the flexibility.
In the production of the swelling pastes of the invention, the polymers are mostly used in the form of from 15 to 60 wt.-%, preferably fro~ 20 to 40 wt.-% aqueous solutions. In special cases, such as the production of films, it may be necessary to add alcoholic additives to the aqueous phase, which improve film formation.
The production of the copolymers is according to prior art and is effected either by adiabatic or isothermal polymerization of the solution of monomers, where the neutralization may take place partially or completely as early as in the monomer solution or as late as in the finished polymer. Typically, the polymerization is started using a redox pair as initiator or a thermal initiator or a mixture of both. Typical redox pairs which are used particularly in the polymerization in aqueous solution are: hydrogen peroxide/ascorbic acid, sodium persulfate/sodium bisulfite; hydroxylamine hydrochloride/hydrogen peroxide; ascorbic acid/t-BHP, redox systems including metal salts, and other well-known systems. If the polymerization is carried out in organic solvents, organic peroxides are frequently used, optionally in combination with redox partners. For molecular weight control, it may be reasonable to employ chain-transferring compounds, so-called modifiers, such as mercaptoethanol, thioglycolic acid or others.
In some cases it has proven convenient to pre-cross-link the copolymers to be used according to the invention with minor amounts of free-radical crosslinking monomers during their production, with the proviso that no water-insoluble fractions are formed. The aqueous solutions of these slightly pre-crosslinked polymers may impart favorable rheological properties to the swelling paste of the invention for processing, among others, or otherwise improve the film and swelling properties of the crosslinked final product.
Component 2 acts as a crosslinker, linking the individual polymer chains in a Mannich reaction through the
acrylamide functions incorporated therein, to yield a water-insoluble yet water-swellable network. All the water-soluble or readily water-dispersible compounds having at least one aldehyde function or those compounds liberating aldehyde groups in the presence of water and upon heating are possible as crosslinkers. Examples to be mentioned herein are formaldehyde, hexamethylenetriamine, acetaldehyde, paraldehyde, glyoxal, trimeric glyoxal hydrate and glyoxylic acid.
The swelling paste is produced by mixing the aqueous polymer solution (component 1) and the crosslinker (component 2) and may be processed directly thereafter. Frequently, it has proven advantageous to add the crosslinker component in the form of a solution as well. The weight ratio of polymer to crosslinker in the swelling paste may vary within a broad range. The content of crosslinker relative to the polymer usually ranges from 1 to 15 wt.-%, preferably from 1 to 9 wt.-%. Depending on the content of amide group-bearing monomers of the polymer, more or less crosslinker is required in order to furnish the desired swelling and retention properties. Likewise, the crosslinking activity of the cross-linker in the amount to be used must be considered. A person skilled in the art may easily determine the precise amounts of crosslinker in the course of a product optimization.
To adjust the desired viscosity of the swelling pastes of the invention, dilution with water or addition of thickeners or surfactants is known to the person of average skill in the art. In contrast to the mixtures according to the teaching of the German application DE 195 21 431 Al, the swelling paste may be stored for several weeks with no loss
of quality, which clearly facilitates the production process. Moreover, the handling of highly toxic, cancerogenic or mutagenic crosslinkers by the final user frequently lacking the practice in dealing with these substances is no longer necessary, but has been required according to the state of the prior applications EP 188,091, EP 357,474 and DE 195 21 431.
The swelling paste may contain further additives having advantageous effects, which are not polymerized therein. In particular, substances for reducing the brittleness (hardness) of the dried product, those for tack reduction, for improving the printing viscosity, and for increasing the conductivity are possible. Thus, in order to improve the gel stability and to adjust the desired printing viscosity, common thickeners effective in water, such as cellulose derivatives or more highly crosslinked polyacrylates, e.g., those sold by the Stockhausen company under the designation of "Cabloc CTF" may be added. They do not swell in the polyacry-late solution as usual, yet improve significantly the viscosity behavior during the printing process.
The swelling paste thus produced may be applied on a prefabricated sheet material, fabric, fleece or on filaments according to well-known methods. Here, imprinting or knife coating on fabrics or nonwovens using a template is preferred in order to achieve a uniform pattern.
Subsequently, the polymer thus coated must be subjected to crosslinking, which may be achieved by a thermal treatment. The duration of the thermal treatment depends on the applied temperature, the concentration of the selectea
crosslinker and the molar ratio of the amide moieties incorporated in the polymer chains. The temperature may be between
100°C and 160°C, preferably 130-160°C, more preferably between 140 and 150°C. In any event, the crosslinking temperature must be above the boiling point of the solvent (water) and below the shrinking temperature of the supporting substrate. For economic reasons, the available time period is below 5 minutes, preferably below 2 minutes.
After crosslinking, the swelling paste of the invention advantageously has a retention of at least 25 g/g, preferably at least 60 g/g, and in addition, has a swelling height per 10 g/m coated dry substance - likewise after crosslinking - of at least 0.8 mm, preferably at least 1.0 mm, and more preferably at least 1.5 mm.
The production of support-free films is effected in such a way that initially, the swelling paste is coated on a support material, preferably one made of metal or plastic, optionally using release agents. After solvent removal, optionally effected below the boiling point of the solvent, and thermal crosslinking, the film is removed from the support material, often subsequent to previous conditioning.
The finished substrate may find use in various industrial fields, such as the cable industry, the hygienics industry, in food packaging, in landscaping applications, in the clothing industry, or even in the burial business.
In order to test the various swelling pastes, each of them was knife-coated on a polyester fabric on a comber table using a template and subsequently dried in a Heraeus circulating air oven. A uniform pattern of dots was constantly obtained. Here, the dried paste was subject to some laboratory-inherent fluctuations.
Measurement of swelling height and swelling rate
To measure the swelling height and the swelling rate, a circular piece (25.4 cm2) of the coated sheet material is placed in a plastic beaker having an inner diameter of 80.5 mm and a height of 30 mm. First, two thin polyester fleeces (0.5 mm in thickness) and then a round piston having a diameter of 80 mm and a weight of 100 g are placed on top of the above fleece. The piston has 60 through borings of 2 mm diameter each. During measurement, the level of the piston upper edge is observed. 75 ml of di-ionised water (conductivity: Determination of retention
In order to determine the retention, a circular piece of the printed fabric having a diameter of 3 cm is welded in a commercially available tea bag. The bag is immersed in a dish with distilled water for thirty minutes, suspended for 10 minutes and centrifuged at 1,200 rpm in a commercially available spin dryer for 5 minutes. The weight of the centrifuged tea bag is determined. To calculate the retention, the weight of the dry tea bag including the fabric is subtracted from the weight of the centrifuged tea bag and divided by the weight of the imprinted polymer.
1,000 g of a solution of a copolymer of 90 mole-% acrylic acid and 10 mole-% acrylamide, having a neutralization degree of 50%, a dry substance of 25 wt.-% and an average molecular weight of 200,000 g/mol, is stirred with 37.5 g of 40% glyoxal. The paste obtained has a viscosity of 9,700 mPa-s (determined at 20°C using a Brookfield viscosime-ter spindle 4/10 rpm) and is printed on a polyester fabric after one hour, using a template. Each of the printed substrates is heated for two minutes on a tenter in a Heraeus brand circulating air oven. The following results were obtained:
The mixture of Example 1, which was formulated ready-to-use but not used, was stored at room temperature for one
week and thereafter, had a viscosity of 10,200 mPa-s (20°C, Brookfield spindle 4/10 rprr.) . Again, the paste was processed as described in Example 1:
The paste of Example 1 was stored for a total of 4 weeks. After this storage period, the paste had a viscosity of 9,600 mPa-s. Processing was as described in Example 1:
100 g of the aqueous copolymer solution of Example 1 is mixed with 3.83 g of glyoxylic acid (50% in water) instead of glyoxal and processed as described in Example 1 after a one day storage.
100 g of a solution of a terpolymer of 94 mole-% acrylic acid, 5 mole-% acrylamide and 1 mole-% methoxypoly-ethylene glycol(1,000) methacrylate (Bisomer S 10W), neutralization degree 50%, dry substance 25%, viscosity 11,000 mPa-s, was stirred with 3.75 g of 40% glyoxal and further processed as described in Example 1.
100 g of the copolymer solution of Example 1 was mixed with 3 g of hexamethylenetetramine and processed as described in Example 1.
Example 6 was repeated, except that prior to the hexamethylenetetramine addition, the neutralization degree of the copolymer used was increased to 60 and 70 mole-%, respectively, using sodium hydroxide solution.
The swelling paste of Example 4 was diluted 1:1 with distilled water and subsequently coated onto aramide fibers. The aramide fibers thus treated were subjected to a short thermal treatment using a hot-air hairdryer. Thereby obtaining a water or water proof polymer coating of 16 wt.-% the treated aramide fibers were subjected to a swelling test as described in EP 482,703, page 5, from line 50 on. The product was immediately tight and even so until the end of testing after 6 days.
Comparative example 1;
The polymer of Example 1 was mixed with 2 wt.-% of ethylene glycol diglycidyl ether. The product mixture had an
initial viscosity of 11,000 mPa-s. After only 4 hours of storage at room temperature, the viscosity had risen to
27,000 mPa-s. After a storage period of 48 hours, the product was completely crosslinked and could only be removed piece by piece from the storage flask with massive effort, using a sharp-edged tool.
Comparative example 2:
A polymer comparable to that of Example 1, having a
viscosity of 20,200 mPa-s, was used, with the difference that this was a pure homopolymer of acrylic acid having a neutralization degree of 50%, i.e., no amide functions are bound to the polymer chain. This polymer, in the form of a 30% aqueous solution, was mixed with 3.75 wt.-% of glyoxal and printed and dried as indicated in Example 1.
An aqueous solution of a polymer consisting of 30 mole-% acrylic acid, 30 mole-% sodium acrylate and 4 0 mole-% acrylamide with a dry substance of 28% and a viscosity of 7,800 mPa-s was mixed with 0.75 wt.-% of 40% glyoxal and processed as described in Example 1. The printed
fabric was heated to 150°C in the Heraeus drying oven for 2
An aqueous solution of a polymer consisting of 20 mole-% acrylic acid, 20 mole-% sodium acrylate and 60 mole-% acrylamide with a dry substance of 27% and a
viscosity of 14,400 mPa-s, was mixed with 0.75 wt.-% of glyoxal and 0.5 wt.-% of glyoxal, respectively, and processed as described in Example 1. Drying was effected for 2 minutes at 150°C in the Heraeus circulating air oven.
1. A swelling paste consisting of
(A) a component 1 which is an aqueous, partially neutralized solution
of a polymer constituted of
(a) free-radical-polymerizable monomers of the kind as herein described,
(b) partially neutralized, free-radical-polymerizable monomers of the kind as herein described containing carboxyl groups and ccarboxylate groups, and
(c) other free-radical-polymerizable monomers of the kind as herein described copolymerizable with (a) and (b),
(B) a component 2 consisting of a crosslinker characterized in that said crosslinker is an aldehyde or an aldehyde-liberating compound as herein described, and optionally
(C) additives of the kind as herein described.
2. The swelling paste as claimed in claim 1, characterized in that the
polymer of component 1 consists of
(a) 1-80, preferably 1-60, and more preferably 1-20 mole-% of free-radical-polymerizable monomers containing amide groups and
(b) 20-99, preferably 40-99, and more preferably 80-99 mole-% of partially neutralized, free-radical-polymerizable monomers containing carboxyl groups, and
(c) 0-49 mole-%, relateive to the monomers (a) + (b), of other monomers polymerized therein, which are copolymerizable with (a) and (b),
3. The swelling paste as claimed in claim 1 and 2, wherein said monomers containing amide groups (a) comprise acrylamide and/or methacrylamide.
4. The swelling paste as claimed in claim 1 and 2, wherein said monomers containing carboxyl groups and carboxylate groups comprise acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid or mixtures of these acids.
5. The swelling paste as claimed in claims 1 to 3, wherein the content of the carboxylate groups relative to the content of the carboxyl groups is at least 25, preferably at least 50 mole-%.
6. The swelling paste as claimed in one of claims 1 to 4, wherein the crosslinker component 2 contains or consists of formaldehyde, glyoxal, glyoxylic acid or hexamethylenetetramine or mixtures thereof as aldehydes or aldehyde-liberating compounds.
7. The swelling paste as claimed in claims 1 to 6, wherein the content of crosslinker component 2 is from l-15wt-%, relative to polymer of component 1.
8. The swelling paste as claimed in the preceding claims as and when, said swelling paste being utilized for the production of absorbent fibers, fiber bundles, filaments, fleeces fabrics; production of power and communication cables, burial business and clothing industry.
9. A swelling paste substantially as herein described with reference to the foregoing examples.
|Indian Patent Application Number||980/DEL/1998|
|PG Journal Number||40/2010|
|Date of Filing||16-Apr-1998|
|Name of Patentee||EVONIK STOCKHAUSEN GMBH,|
|Applicant Address||BAKERPFAD 25, 47805 KREFELD, GERMANY|
|PCT International Classification Number||C08L 39/00|
|PCT International Application Number||N/A|
|PCT International Filing date|