Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L15/00—Chemical aspects of, or use of materials for, bandages, dressings or absorbent pads
  • A61L15/16—Bandages, dressings or absorbent pads for physiological fluids such as urine or blood, e.g. sanitary towels, tampons
  • A61L15/42—Use of materials characterised by their function or physical properties
  • A61L15/60—Liquid-swellable gel-forming materials, e.g. super-absorbents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/04—Acids; Metal salts or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F251/00—Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F261/00—Macromolecular compounds obtained by polymerising monomers on to polymers of oxygen-containing monomers as defined in group C08F16/00
  • C08F261/02—Macromolecular compounds obtained by polymerising monomers on to polymers of oxygen-containing monomers as defined in group C08F16/00 on to polymers of unsaturated alcohols
  • C08F261/04—Macromolecular compounds obtained by polymerising monomers on to polymers of oxygen-containing monomers as defined in group C08F16/00 on to polymers of unsaturated alcohols on to polymers of vinyl alcohol
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F290/00—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups
  • C08F290/02—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups on to polymers modified by introduction of unsaturated end groups
  • C08F290/06—Polymers provided for in subclass C08G
  • C08F290/062—Polyethers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes

Definitions

• the invention relates to powdery absorbents for water and aqueous liquids based on water-swellable but not water-soluble polymers.
• These crosslinked polymers based on monomers containing acid groups are obtained by using a special combination of two pre-crosslinking agents and a postcrosslinking agent and show previously unachieved property combinations of high retention, high absorption under pressure, low soluble fractions and rapid liquid absorption.
• the commercially available superabsorbent polymers are essentially crosslinked polyacrylic acids or crosslinked starch / acrylic acid graft copolymers in which the carboxyl groups are partially neutralized with sodium and / or potassium ions.
• Such polymers are used e.g. in hygiene articles that contain body fluids such as Can soak up urine or in materials used to wrap cables. There they swell and form hydrogels, taking large amounts of aqueous fluids and body fluids, e.g. Urine or blood. Furthermore, it is necessary that the amount of liquid taken up is retained under the pressure typical of the application. In the course of the technical development of the superabsorbent polymers, the requirement profile for these products has changed significantly over the years. While the development of the superabsorbent initially focused on the very high swelling capacity when in contact with liquid, it was later shown that it is not only the amount of liquid absorbed that is important, but also the strength of the swollen gel.
• Retention on the one hand and strength of the swollen gel on the other hand represent opposing properties, as is already known from US Pat. No. 3,247,171.
• This specific absorption property which is called “absorption under pressure” (AUP) in Anglo-Saxon parlance, is e.g. in US 5,314,420.
• superabsorbers In addition to a high level of retention and liquid absorption under pressure, superabsorbers must contain the smallest possible proportion of soluble polymer chains. These arise due to imperfect crosslinking during the polymerization. In use, these soluble fractions are not completely retained in the swollen polymer body. This leads to a reduction in the performance of the superabsorbent, since the liquid in the diaper is no longer evenly distributed and, in extreme cases, can also cause these soluble parts to escape from the diaper construction, combined with a slimy feeling on the skin. According to the teaching of EP 312 952, for a good stability of the swollen gel, as well as for a high absorption rate and a high water absorption, it is essential that the polymer has low soluble fractions.
• WO 94/09043 is based on the task of providing new superabsorbent polymers with an increased absorption capacity for aqueous liquids, even under pressure.
• double-crosslinked superabsorbents the preparation of which in the first stage involves pre-crosslinking during the polymerization with methylene bisacrylamide, bis (acrylamido) acetic acid, allyl acrylate, allyl methacrylate, esters or amides with terminal vinyl and allyl functions or highly ethoxylated trimers ⁇ thylolpropane triacrylate provides and in the second stage the resulting polymer particles coated on the surface with a crosslinker and then crosslinked.
• the preferred surface crosslinkers are polyhydroxy compounds which are applied together with water or water / solvent mixtures and are reacted at elevated temperatures (175-230 ° C.) after the moisture of the polymer gel has been obtained the first stage was partially removed.
• Ethoxylated trimethylolpropane triacrylate is the preferred crosslinking agent, the number of EO units per polyglycol chain being between 2 and 7. According to the statements in this document, the use of trimethylolpropane triacrylate which is not or only slightly ethoxylated leads to significantly poorer properties of the superabsorbers crosslinked therewith.
• the products described do not meet the requirements for absorption under higher pressure at 49 g / cm 4 (0.7 psi).
• Figure 13 on page 8/8 of WO 93/21237 which shows the course of liquid absorption under pressure for various pressure loads, clearly shows the weakness of the polymers described there, whose measured values of approx.
• US 5 314 420 had set itself the task of providing products that are able to absorb the liquid very quickly. This is achieved by adding a carbonate-containing blowing agent to the monomer solution and then re-crosslinking the polymer formed. This document indicates the possibility of combining a number of preferred crosslinkers, and does not provide a solution to the problem of simultaneously increasing retention, absorption under pressure and absorption speed, and reducing soluble fractions.
• Another problem in the production of superabsorbent polymers is the relatively poor solubility of many standard crosslinkers in the aqueous monomer solution at the low temperatures at which the polymerization starts, in some cases significantly below 20 ° C. At these temperatures, the aqueous monomer solution becomes cloudy when using the customary crosslinkers, such as trimethylolpropane triacrylate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate or allyl methacrylate, to name just a few examples. This cloudy solution indicates that the crosslinkers are not homogeneously dissolved, which is the case with the subsequent polymer sation leads to irregular networking and thus to an inferior product.
• customary crosslinkers such as trimethylolpropane triacrylate, diethylene glycol diacrylate, tetraethylene glycol dimethacrylate or allyl methacrylate
• DE-OS 41 38 408 proposes adding a non-polymerizable surfactant to the monomer solution in order to distribute the otherwise poorly soluble crosslinker more evenly.
• This approach has two major disadvantages.
• the surfactant-containing monomer solution foams so strongly when blowing out with nitrogen that the blowing-out process to remove the disruptive oxygen from the monomer solution takes longer than without the addition of surfactant.
• the surfactants in the polymer favor the re-emergence of the water absorbed, which leads to the undesired appearance of the rewet and disqualifies the product for use in hygiene articles, since it releases the absorbed liquid too easily.
• Rl polyvalent C2-10 alkyl
• Pre-crosslinker I a (meth) acrylic acid ester of a polyglycol mono (meth) allyl ether, contains a (meth) allyl function, a (meth) acrylic acid ester function and a hydrophilic chain inserted between these two functions, which consists of at least three, preferably 5 to 20, particularly preferably 8-12 glycol units.
• glycol units both ethylene glycol and propylene glycol units, individually or in combination, are possible, mixtures with both random and block alkoxy latex being suitable.
• the use of mixed ethylene glycol / propylene glycol chains as well as pure propylene glycol chains is possible, with pure polyethylene glycol chains being preferred.
• the type I pre-crosslinker described can be prepared, for example, by the procedure described in US Pat. No. 4,618,703 or by direct esterification with an excess of acrylic acid or methacrylic acid (Examples 4-9).
• the esters thus obtained can be crude, ie in the presence of the catalyst used and that used in excess (Meth) acrylic acid stored and processed. For higher purity requirements or for longer storage, it is also possible to wash the esters as described in US Pat. No. 4,618,703 and to clean them from low-boiling constituents by distillation.
• the degree of esterification should be above 90%, better above 95%, since free hydroxyl functions initially do nothing to improve the application properties and lead to a lowering of the retention in the case of subsequent crosslinking.
• Vorvemetzer II a (meth) acrylic acid ester of polyhydroxy compound, is a polyfunctional alcohol, the alcohol functions of which have been converted to (meth) acrylic acid esters.
• polyhydroxy compounds come e.g. Trimethylolpropane, ethylene glycol, propylene glycol, glycerin, pentaerythritol or their ethoxylated homologs such as e.g. Polyethylene glycol in question.
• (meth) acrylic acid esters such as trimethylolpropane triacrylate, trimethylolpropane-3EO-triacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, otherwise poorly soluble in the monomer solution as crosslinking agent II, since crosslinking agent I keeps them in solution.
• the type II pre-crosslinkers are commercially available.
• the Craynor CN 435 used in the examples is the triacrylic acid ester of 15-EO-trimethylolpropane
• the Craynor SR 351 used is the triacrylic acid ester of trimethylolpropane. Both are products of the Cray Valley Company.
• the pre-crosslinker I is 40-90, preferably 40-80, particularly preferably 60-80 mole percent based on the mixture of crosslinkers and the pre-crosslinker II is 10-60, preferably 20-60, particularly preferably 20-40 mole percent based on the crosslinker mixture used.
• these precrosslinker combinations are used in concentrations of 0.1-2%, preferably 0.3-1.0% by weight.
• the described pre-crosslinking combination shows the surprising advantage that even sparingly soluble crosslinking components II are solubilized by the presence of I and can thus fully develop their effectiveness without the Rewet behavior being negatively influenced by the presence of unpolymerized surfactants, as in DE 41 38 408 becomes.
• the properties of the superabsorbents according to the invention are improved by the process of subsequent surface crosslinking, in particular also in their liquid absorption under pressure, since the known phenomenon of "gel blocking" is suppressed, in which swollen polymer particles stick together and another liquid Impede absorption and fluid distribution in the diaper.
• the carboxyl groups of the polymer molecules on the surface of the superabsorbent particles are crosslinked with crosslinking agents at elevated temperature.
• 5,314,420, page 8, lines 3-45 can all be used according to the invention advantageously in combination with the pre-crosslinker combinations I and II.
• These compounds generally contain at least two functional groups. Alcohol, amine, aldehyde, glycidyl and epichloro functions are preferred, crosslinker molecules with several different functions also being conceivable.
• One of the following post-crosslinking agents is preferably 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 ester, trimethylpentol ester, ethoxylated ethoxylated sorbitan trimethyl, propyl ethoxylated sorbitan, ethoxylated sorbitan trimethyl, propylene oxide, ethoxylated sorbitan trimethylsole, ethoxylated sorbitan ethoxylated pentaerythritol, polyvinyl alcohol, sorbitol, ethylene carbonate, propylene carbonate and polyepoxides such as ethylene glycol diglycidyl ether.
• the use of ethylene carbonate as postcrosslinking agent is particularly preferred.
• the postcrosslinking agent is used in an amount of 0.01 to 30 percent by weight, preferably 0.1-10 percent by weight, particularly preferably 0.1-1 percent by weight, based on the polymer to be crosslinked.
• the polymerization process according to the invention can be initiated by various conditions, for example by irradiation with radioactive, electromagnetic or ultraviolet rays or by redox reaction of two compounds, such as sodium hydrogen sulfite with potassium persulfate or ascorbic acid with hydrogen peroxide.
• the thermally triggered decomposition of a so-called radical starter such as, for example, azobisisobutyronitrile, sodium persulfate, t-butyl hydroperoxide or dibenzoyl peroxide can also be used as the start of polymerization.
• a so-called radical starter such as, for example, azobisisobutyronitrile, sodium persulfate, t-butyl hydroperoxide or dibenzoyl peroxide
• the polymerization start is preferably triggered by the redox reaction between hydrogen peroxide and ascorbic acid and completed by the thermally initiated decomposition of sodium persulfate and / or 2,2'-azobis (2-methylpropionamide) dihydrochloride.
• the solution polymerization is preferably carried out in water as a solvent.
• the solution polymerization can be carried out continuously or batchwise.
• the patent literature has a wide range of possible variations with regard to the concentration ratios, temperatures, type and amount of the initiators and also of the post-catalysts.
• the unsaturated monomers containing acid group groups to be used according to the invention are, for example, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, vinylsulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid and their alkali metal and / or ammonium salts .
• Up to 40% by weight of further comonomers, based on the acidic monomers, such as, for example, acrylamide, methacrylamide, and or their salts can optionally be used to modify the polymer properties.
• the neutralization then taking place subsequently in the polymer gel.
• the acidic monomer constituents are neutralized to 25-95%, preferably 50-80%, before the polymerization and are then present as sodium and / or potassium and / or ammonium salts for neutralization at the start of the polymerization bases are preferably used which have no negative influence on the subsequent polymerization.
• Sodium hydroxide solution or potassium hydroxide solution or ammonia, particularly preferably sodium hydroxide solution is preferably used, the addition of sodium carbonate, potassium carbonate or sodium bicarbonate having an additional positive effect, as taught by US Pat. No. 5,314,420 and US Pat. No. 5,154,713.
• This partially neutralized monomer solution is cooled down to a temperature of below 30 ° C., preferably below 20 ° C., before the start of the polymerization in the adiabatic solution polymerization.
• a temperature of below 30 ° C. preferably below 20 ° C.
• other temperatures are known and customary in the prior art.
• the polymers according to the invention can contain water-soluble polymers as a graft base in amounts of up to 30% by weight, based on the sum of the monomers present. These include partially or fully hydrolyzed polyvinyl alcohols, starch or starch derivatives, cellulose or cellulose derivatives, polyacrylic acids, polyglycols or mixtures thereof.
• the molecular weights of the polymers added as the graft base must be adapted to the conditions of the polymerization conditions. For example, in the case of an aqueous solution polymerization, for reasons of the viscosity of the polymer solution, it may be necessary to use only low- or medium-molecular-weight polymers, whereas this factor plays a subordinate role in suspension polymerization.
• polymers which can be obtained by crosslinking polymerization of partially neutralized acrylic acid preference is given to those which contain additional proportions of graft-polymerized starch or of polyvinyl alcohol.
• the acidic monomers in the end product are neutralized at least 25 mol%, preferably at least 50 mol% and particularly preferably 50 to 80 mol%.
• the neutralization is carried out either by adding the corresponding alkali metal or ammonium hydroxides or with the corresponding carbonate or hydrogen carbonates.
• the partial neutralization can already take place during the preparation of the monomer solution the polymerization or, as described in US Pat. No. 4,654,039, can only be carried out on the finished polymer.
• the partial neutralization is preferably carried out before the polymerization.
• Post-crosslinking to be carried out according to the invention is e.g. in US 4,666,983 and DE 40 20 780.
• Post-crosslinking agents are often advantageously also added in the form of a solution in water, organic solvents or mixtures thereof, in particular when small amounts of post-crosslinking agents are used.
• Suitable mixing units for applying the post-crosslinking agent are e.g.
• the postcrosslinking reaction is heated to temperatures of 120 to 250 ° C., preferably to 135 to 200 ° C. and particularly preferably to 150 to 185 ° C.
• the duration of the reheating is limited by the point at which the desired property profile of the super absorber is destroyed again as a result of heat damage.
• different sieve fractions are used to process the superabsorbers, e.g. for diapers between 100 and 1000 mm, preferably between 150 and 850 mm.
• This fraction is generally produced by grinding and sieving before post-crosslinking.
• hydrophilic superabsorbents according to the invention are used wherever aqueous liquids have to be absorbed.
• aqueous liquids include, for example, the already known applications for these products in hygiene articles in the form of diapers for small children and incontinence products for adults, in sanitary napkins, in wound plasters, in food packaging, in the agricultural sector in plant breeding, in cable insulation, in absorbent sheet-like structures made of paper, and water-soluble Polymers and thermo- plastic plastics and foams, and as an active ingredient carrier with the task of delaying the release to the environment.
• the liquid absorption under pressure (AUP at 0.3 and 0.7 psi, corresponding to 21 g / cm.2 or 49 g / cm ⁇ ) is according to the method described in US Pat. No. 5,314,420 page 9, line 28 ff true, using 0.9% saline as the measuring liquid.
• the soluble fractions (1h and 16h) are determined as described in US Pat. No. 4,654,039, with the exception that a 0.9% sodium chloride solution is used as the test liquid instead of synthetic urine.
• the swelling speed (SG) of the polymer is determined using the following method: Twenty (20) grams of a synthetic urine solution (manufactured according to US 4,654,039) are weighed into a narrow beaker. One (1) gram of the material to be tested is weighed into a wide (5 cm diameter) cylindrical dish centrally in the middle. The powder with the superabsorbent properties is distributed evenly over the bottom of the shell by gentle shaking. The synthetic urine solution is added in one pour using a funnel ending 1 cm above the bottom of the bowl and thus the Time measurement started. The time measurement is ended as soon as no free liquid can be recognized.
• Example 7 (methacrylic acid ester of 20-EO allyl alcohol, MAA20): 445.3 g (0.42 mol) of 20-EO-allyl alcohol from Example 3, 0.8 g of p-methoxyphenol, 385 g (4.53 mol) of methacrylic acid and 4 g of conc. Sulfuric acid is reacted analogously to Example 4, the reaction time being doubled and the vacuum being tightened to 20 mbar at the end of the reaction. 555 g of solid product are obtained. Acid number 103.5 mg KOH / g; Saponification number 158.3 mg KOH / g; Degree of esterification 93.9%.
• Example 8 (methacrylic acid ester of 5 EO-allyl alcohol, MAA5):
• a monomer solution composed of 265.2 g of acrylic acid and 372.4 g of fully deionized water and the crosslinking agents used are prepared in a cylindrical plastic vessel.
• the mixture is partially neutralized with 206.1 g of 50% sodium hydroxide solution (70% degree of neutralization) with stirring and cooling.
• the solution is cooled to 7-8 ° C. and bubbled with nitrogen until the oxygen content in the monomer solution has dropped to a value of less than 0.2 ppm.
• Example 18 and comparative examples V6-V10 were polymerized according to the general preparation instructions mentioned above, but without the addition of sodium carbonate.
• 100 g of the ground and sieved to 150-800 mm polymer are wetted with vigorous mixing with a solution of 0.5 g of ethylene carbonate and 1.5 g of demineralized water in a mixer from MTI and then in an oven for 30 minutes Temperature of 180 ° C heated.
• Examples 18 to 18 of the invention provide polymers with a combination of good properties:

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• 1995
  • 1995-11-21 DE DE19543368A patent/DE19543368C2/de not_active Expired - Fee Related
• 1996
  • 1996-11-18 DK DK96939835T patent/DK0873188T3/da active
  • 1996-11-18 CA CA002235704A patent/CA2235704A1/en not_active Abandoned
  • 1996-11-18 JP JP51148197A patent/JP3900538B2/ja not_active Expired - Fee Related
  • 1996-11-18 KR KR19980703802A patent/KR100406312B1/ko not_active Expired - Fee Related
  • 1996-11-18 EP EP96939835A patent/EP0873188B1/de not_active Expired - Lifetime
  • 1996-11-18 CN CNB961996617A patent/CN1142953C/zh not_active Expired - Fee Related
  • 1996-11-18 US US09/068,560 patent/US6143821A/en not_active Expired - Lifetime
  • 1996-11-18 DE DE59603516T patent/DE59603516D1/de not_active Expired - Lifetime
  • 1996-11-18 CZ CZ981505A patent/CZ150598A3/cs unknown
  • 1996-11-18 WO PCT/EP1996/005074 patent/WO1997018890A1/de not_active Ceased
  • 1996-11-18 AT AT96939835T patent/ATE185982T1/de not_active IP Right Cessation
  • 1996-11-18 ES ES96939835T patent/ES2139394T3/es not_active Expired - Lifetime
  • 1996-11-19 TW TW085114160A patent/TW408137B/zh not_active IP Right Cessation

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