KR100552032B1 - Absorbent Foam - Google Patents

Abstract

Absorbent foams that are highly absorbent while exhibiting desirable flexibility and crosslinkability are disclosed. In one embodiment, the absorbent foam is a water swellable, and include water-insoluble polymers, absorbent foam is absorbent foam g liquid of about 10 g or more free swell values, and m ² g of about 30 g flexibility in power of each party of absorbent foam per Indicates a value. In a second embodiment, the absorbent foam has a cell having an average cell size of about 10 microns to about 100 microns and an average wall thickness of about 0.1 microns to about 30 microns. Such absorbent foams can be used in disposable absorbent articles for the absorption of fluids such as body fluids. Also disclosed are methods of making absorbent foams. The process generally forms a solution of the polymer in a solvent, freezes the solution to a temperature below the freezing point of the solvent at a relatively slow cooling rate, removes the solvent from the frozen solution, and recovers the polymer to form a water swellable, water insoluble polymer foam. It includes forming a.

Absorbency, Foam, Free Swelling Value, Flexibility, Water Swellability, Water Insolubility, Polyacrylamide, Polyacrylic Acid, Absorption Capacity, Cell

Description

Absorbent Foam

The present invention relates to an absorbent foam that is highly absorbent while exhibiting desirable flexibility and flexibility. Such absorbent foams can be used in disposable absorbent articles for the absorption of fluids such as body fluids. The present invention also relates to a process for producing the absorbent foam. The process generally forms a soluble polymer solution in a solvent, freezes the solution to a temperature below the freezing point of the solvent at a relatively slow cooling rate, removes the solvent from the frozen solution, and recovers the polymer to obtain water swellable, water insoluble Forming a polymeric foam.

Disposable absorbent products are commonly used in many applications. For example, in the infant care sector, diapers and training pants have generally replaced reusable cloth absorbent products. Other typical disposable absorbent products include feminine hygiene products such as sanitary napkins or tampons, adult incontinence products, and health hygiene products such as surgical cloths or trauma bandages. Typical disposable absorbent articles generally include a topsheet, a backsheet, and a composite structure comprising an absorbent structure between the topsheet and the backsheet. Such products typically include some type of fastening system for fitting the product to the wearer.

In disposable personal care absorbent articles, it is known to use water-swellable, generally water-insoluble, absorbents, commonly known as superabsorbents. Such absorbent materials are generally used in absorbent articles to increase the absorbent capacity of the article while reducing the total volume of the absorbent article. Such absorbent materials are generally present in absorbent articles in the form of small particles in fiber substrates, such as wood pulp fuzz. Substrates of wood pulp fuzz generally have an absorption capacity of about 6 g of liquid per g of fuzz. Superabsorbents generally have an absorption capacity of about 10 times or more, preferably about 20 times, often up to 100 times their weight in water. Obviously, incorporating such absorbents in disposable absorbent products can reduce the overall volume while increasing the absorbent capacity of the product.

As an alternative to using fiber substrates containing superabsorbents, absorbent foam composites are also known. One form of absorbent foam composite is to prepare a foam material, such as polyurethane, to include granular superabsorbent material in the structure of the polyurethane foam. Alternatively, the granular superabsorbent material is placed between two or more layers of polyurethane foam material to form a laminated composite structure. Such foam structures may be useful hygroscopic materials in certain applications, but because their absorbent properties tend to be limited, they do not appear to be optimal for use in disposable absorbent products. In particular, foam materials such as polyurethanes in such structures generally do not have sufficient absorbent capacity to retain liquids. Thus, although the granular superabsorbents in the foam structure can retain the liquid, the overall capacity of the foam structure for absorbing and retaining liquid is limited. Moreover, the overall absorbent quality of the foam structure tends to be limited by the mass ratio of the granular superabsorbent portion to the foam portion of the structure, due to its relatively low surface area.

Absorbent foams are also known to comprise essentially all superabsorbent materials. Typically, blowing agents are used to form foamed, water-swellable polymer liquid absorbents. However, certain absorbent foams produced using certain blowing agents have been found to have limited use for liquid absorption or liquid distribution. This is typically due to the physical characteristics of the foam structure, which may include discontinuous grooves, too large average cell size, unacceptably wide cell size distribution, and / or capillary diameters that vary randomly over a wide range, This results in undesirable absorption and absorption capacities and undesirable liquid distribution properties. In addition, known absorbent foams made essentially of all superabsorbent materials have been found to have undesirable non-absorbent physical properties, typically lacking flexibility or being too brittle. In addition, many known foams have hydrophobic properties and require treatment with a humectant or other suitable treatment step to achieve hydrophilicity. Disposable absorbent products generally need to be flexible enough to withstand rough use by the consumer and also flexible enough to be satisfactorily pleasant to use, so this undesirable non-absorbent physical feature of the absorbent foam is a disposable absorbent article. There is a tendency to limit the usefulness of the absorbent foam in the process.

Thus, there is a continuing need for improvement of absorbent foams. In particular, there is a need for an absorbent foam that exhibits relatively high liquid absorption capacity while exhibiting desirable flexibility and flexibility. There is also a need for a method for producing such absorbent foams simply, safely and cost-effectively.

It is therefore an object of the present invention to provide an absorbent foam which exhibits a relatively high liquid absorption capacity while exhibiting desirable physical features such as flexibility and flexibility.

It is also an object of the present invention to provide a method for the production of absorbent foams simply, safely and cost-effectively.

It is also an object of the present invention to provide a disposable absorbent article comprising an absorbent foam which exhibits desirable physical properties such as flexibility and flexibility while exhibiting a relatively high liquid absorption capacity.

Summary of the Invention

The present invention relates to absorbent foams which exhibit relatively high liquid absorbing capacity while exhibiting desirable physical properties such as flexibility and flexibility.

One aspect, the absorbent foam is absorbent foam g liquid represents approximately 10 g or more of Free Swell value (Free Swell value), absorbent foam m flexibility value of about less than 30 g of force per g per ^second per (Softness value) of the invention The present invention relates to an absorbent foam containing a water swellable and water insoluble polymer.

In another aspect, the invention provides a water swellable, water insoluble polymer, wherein the cells in the absorbent foam have an average cell size of about 10 microns to about 100 microns and have an average wall thickness of about 0.1 microns to about 30 microns. It relates to an absorbent foam.

The present invention also relates to a process for producing the absorbent foam.

One embodiment of this method comprises forming a solution of soluble polymer in a solvent, freezing the solution to a temperature below the freezing point of the solvent at a relatively slow cooling rate, removing the solvent from the frozen solution, and optionally treating the polymer Forming a water swellable, water insoluble polymer.

Another embodiment of this method is to form a solution gel of crosslinked polymer in solvent, freeze the solution gel to a temperature below the freezing point of the solvent at a relatively slow cooling rate, remove the solvent from the frozen solution gel, and Obtaining an swellable, water-insoluble absorbent polymer foam.

In another aspect, the present invention relates to a disposable absorbent article comprising the absorbent foam disclosed herein.

One embodiment of such a disposable absorbent article includes a liquid permeable topsheet, a backsheet attached to a liquid permeable topsheet, and an absorbent foam of the invention located between the liquid permeable topsheet and the backsheet.

1 shows an apparatus used to determine the free swelling value and the absorbent under load value of an absorbent foam or material.

The present invention relates to an absorbent foam which exhibits a relatively high liquid absorption capacity while exhibiting desirable flexibility and flexibility. Absorbent foams include water swellable, water insoluble polymers. As used herein, water swellable, water insoluble polymers are required to a considerable extent to provide absorbent foams with liquid-absorbing capacity. As such, the water swellable, water insoluble polymer must be efficient to provide the absorbent foam with the desired degree of liquid-absorbing capacity.

The term "foam", as used herein, generally refers to a porous polymeric substrate, wherein the boundary or wall of the cell as an aggregate of hollow cells comprises a solid polymeric material. The cells may be connected to one another to form grooves or capillaries in the foam structure, which promote liquid distribution in the foam.

The term "water swellable, water insoluble" as used herein is meant to refer to a material that swells to its equilibrium volume upon exposure to excess water but does not dissolve in water. As such, the water swellable, water insoluble material generally retains its original properties or physical structure even in a very expanded state upon absorption of water, and therefore must be physically perfect enough to withstand flow and fusion with adjacent materials.

As used herein, a material is considered to be “water soluble” when it is dissolved in substantially excess water to form a solution, thereby losing its initial form and essentially being molecularly dispersed through an aqueous solution. As a general rule, since crosslinking tends to make the material water insoluble, the water soluble material does not have a substantial degree of crosslinking.

Polymers suitable for use in the present invention are generally soluble in the solvent initially so that the soluble polymer can be formed into a solution by mixing with a liquid solvent such as water, and then the polymer is treated to make the polymer water swellable and water insoluble. As a result, an absorbent foam comprising such a water swellable, water insoluble polymer is any polymer that will exhibit desirable absorbent and physical properties.

Suitable polymers for use in the present invention include various types of anionic, cationic and nonionic materials. Suitable polymers include polyacrylamide, polyvinyl alcohol, ethylene maleic anhydride copolymer, polyvinylether, polyacrylic acid, polyvinylpyrrolidone, polyvinylmorpholine, polyamine, polyethyleneimine, polyacrylamide, polyquaternary ammonium, Natural polysaccharide polymers such as carboxymethyl cellulose, carboxymethyl starch, hydroxypropyl cellulose, algin, alginate, carrageenan, acrylic graft starch, acrylic graft cellulose, chitin and chitosan, and polyaspartic acid, polyglutamic acid, polyasparagine, Synthetic polypeptides such as polyglutamine, polylysine, and polyarginine, as well as salts, copolymers, and mixtures of such polymers.

In one embodiment of the invention, the polymer used is preferably a glassy polymer. As used herein, the term “glassy” polymer refers to a polymer having a glass transition temperature (Tg) of about 23 ° C. (about room temperature) or more at a relative humidity of about 30% or less. Examples of glassy polymers include, but are not limited to, sodium polyacrylate, polyacrylic acid, carboxymethyl cellulose sodium, and chitosan salt polymers. Examples of non-glassy polymers include, but are not limited to, polyethylene oxide, polyvinyl acetate, and polyvinyl ether polymers.

In providing the absorbent foam with the desired degree of liquid-absorbing capacity, one property of the water swellable, water insoluble polymers associated with its effect is the molecular weight of the polymer. In general, water-swellable, water-insoluble polymers having high molecular weights exhibit higher liquid-absorbing capacity than water-swellable, water-insoluble polymers having low molecular weights.

Water swellable, water insoluble polymers useful in the absorbent foams of the present invention may generally have a wide range of molecular weights. Relatively high molecular weight, water swellable, water insoluble polymers are often advantageous for use in the present invention. Nevertheless, a wide range of molecular weights is generally suitable for use in the present invention. Water swellable, water insoluble polymers suitable for use in the present invention advantageously have a weight average molecular weight of at least about 10,000, more advantageously at least about 100,000, even more advantageously at least about 200,000, suitably at least about 500,000, more suitable Preferably a weight average molecular weight of at least about 1,000,000 and up to about 20,000,000. Methods for determining the molecular weight of polymers are known in the art.

In general, the polymer is preferably present in the absorbent foam in an amount effective to obtain an absorbent foam that exhibits desirable properties. The polymer may be from about 50% to 100% by weight, advantageously from about 60% to about 100% by weight, more advantageously based on the total weight of the polymer, crosslinker, any other component present in the absorbent foam. About 70% to about 100%, suitably about 80% to about 100%, more suitably about 90% to about 100%, even more suitably about 95% to about 100% Present in the absorbent foam in an amount of%. In one embodiment of the invention, the absorbent foam preferably consists essentially of the polymer and the crosslinking agent used to crosslink the polymer. As will be appreciated by those skilled in the art, these absorbent foams may also comprise traces of solvent retained in the production process and / or traces of water vapor absorbed in the air. In general, the presence of any material in the absorbent foam that is not a water swellable, water insoluble polymer tends to reduce the overall liquid absorbent capacity of the absorbent foam.

Water swellable, water insoluble polymers useful in absorbent foams are generally crosslinked. The amount of crosslinking should generally be more than the minimum amount sufficient to render the polymer water insoluble and less than the maximum amount that the polymer can be sufficiently water swellable, so that the water swellable, water insoluble polymer absorbs the desired amount of liquid.

Crosslinking of the polymer may generally occur when the polymer is in solution or after removing the solvent from the solution used to prepare the absorbent foam. Crosslinking of such polymers can generally be achieved by two different types of crosslinking agents. Such crosslinkers are soluble in commonly used solvents, for example water.

One type of crosslinker is a potential crosslinker. Suitable latent crosslinkers are generally internal latent crosslinkers or external latent crosslinkers. Internal potential crosslinking agents generally can be copolymerized to the monomer or monomers used to prepare the polymer, and therefore generally at least one vinyl group and the side groups on the base polymer, such as carboxyl groups on the sodium polyacrylate polymer (-COO ^-) Or one functional group or functionality that can be reacted with a carboxylic acid group (-COOH) on a polyacrylic acid polymer. Examples of suitable copolymerizable crosslinkers include ethylenically unsaturated monomers such as ethylene glycol vinyl ether and amino propyl vinyl ether.

External potential crosslinkers generally crosslink the polymer itself after the polymer is formed from the specific monomer or monomers used to make the polymer and / or after the polymer is mixed with a solvent to form a solution. Potential crosslinkers generally do not participate in the overall polymerization process, but instead react to the polymer at a later point in time where appropriate crosslinking conditions are provided. Suitable crosslinking conditions include the use of heat treatments such as treatment at temperatures above about 60 ° C., exposure to ultraviolet light, exposure to microwaves, steam or high humidity treatments, high pressure treatments, or treatments with organic solvents.

Suitable external potential crosslinkers are any organic compound having two or more functional groups or functionalities that can react with the carboxyl, carboxylic acid, amino or hydroxyl groups of the polymer. Such organic crosslinkers are preferably selected from the group consisting of diamines, polyamines, diols, and polyols and mixtures thereof, in particular the group consisting of primary diols, primary polyols, primary diamines and primary polyamines and mixtures thereof. Among the diols and polyols, those having four or more longer carbon chain lengths are generally advantageous. Specifically, the crosslinking agent may be selected from the group consisting of chitosan glutamate, type A gelatin, diethylenetriamine, ethylene glycol, butylene glycol, polyvinyl alcohol, hyaluronic acid, polyethylene imine and derivatives thereof and mixtures thereof. Other suitable organic crosslinking agents include amino acids such as monochloroacetic acid, sodium chloroacetic acid, citric acid, butane tetracarboxylic acid, and aspartic acid, and mixtures thereof. Other suitable potential crosslinkers include metal ions having two or more positive charges, such as Al ³⁺ , Fe ³⁺ , Ce ³⁺ , Ce ⁴⁺ , Ti ⁴⁺ , Zr ⁴⁺ and Cr ³⁺ . Suitable metal ion crosslinkers generally include crosslinkers of transition elements with empty d-orbitals. Suitable metal ion crosslinkers include AlCl ₃ , FeCl ₃ , Ce ₂ (SO ₄ ) ₃ , Zr (NH ₄ ) ₄ (CO ₃ ) ₄ and Ce (NH ₄ ) ₄ (SO ₄ ) ₄ · 2H ₂ O, other known Metal ion compounds and mixtures thereof. Such metal ion crosslinkers are believed to form ionic bonds with carboxyl, carboxylic acid, amino or hydroxyl groups on a polymer when used with a particular polymer. Metal ions with only divalent positive charges such as Zn ²⁺ , Ca ²⁺ , or Mg ²⁺ are also suitable as crosslinking agents for certain polymers.

When the polymer is a cationic polymer, suitable crosslinkers are next ion materials such as sodium polyacrylate, carboxymethyl cellulose or polyphosphate.

The second type of crosslinking mechanism that a particular polymer may experience is associated with macromolecular rearrangements of the polymer chains during the solidification process of the polymer, which results in the polymer forming a very regular structure with highly crystalline, generally water insoluble. . Suitable polymers for this crosslinking approach include, but are not limited to, polyvinyl alcohol, chitosan, and carboxymethyl cellulose with relatively low degrees of carboxymethylation. Additional strong bonds of the polymer can be formed between the polymer chains during the solidification process, as a result of which generally a water insoluble material can be obtained. An example of this behavior is that strong hydrogen bonds in the polyvinyl alcohol form an insoluble material.

Suitable crosslinkers for the polymer solution gel process are also generally two different types: internal polymerizers or external crosslinkers. The first type of crosslinking agent is a polymerizable and crosslinking agent. Suitable polymerizable crosslinkers are generally reactive toward the monomer or monomers used to prepare the polymer, ie generally comprise at least two functional groups or functionalities that can react with the monomer. Examples of suitable polymerizable crosslinkers include ethylenically unsaturated monomers such as N, N'-methylene bis-acrylamide for free radical polymerization, and polyamines or polyols for condensation polymerization. The second type of crosslinking agent is a reactive compound having at least two functional groups or functionalities that can be reacted with the carboxyl, carboxylic acid, amino or hydroxyl groups of the polymer in a solution step, wherein the crosslinking is not potential, No further conditions are necessary to initiate the crosslinking reaction. Suitable crosslinkers may be selected from the group consisting of aldehydes such as glutaraldehyde, or glycidyl ethers such as polyethylene glycol diglycidyl ether.

Another approach for forming a crosslinked polymer network in the polymer solution or on the recovered polymer is to use free energy treatment such as electron beam radiation or microwave radiation to form free radicals in the polymer, which is then used to form a crosslinking point. It is to form. This approach can be applied when, but not limited to, no crosslinking agent is used to prepare the absorbent foam.

If a crosslinking agent is used, it is advantageously from about 0.01% to about 20% by weight, more preferably from about 0.05% to about 10% by weight, suitably based on the total weight of polymer and crosslinker present in the absorbent foam It is generally preferred to use the crosslinking agent in an amount from about 0.1% to about 5% by weight.

In general, a crosslinking catalyst is not required to aid in the crosslinking of the polymer to produce the absorbent foam of the present invention, but it may be advantageous. For example, if citric acid is used as the crosslinking agent, sodium hypophosphite is advantageously used as the crosslinking catalyst. If a crosslinking catalyst is used, it is generally preferred to use the crosslinking catalyst in an amount of about 0.01 to about 3% by weight, suitably about 0.1 to about 1% by weight, based on the total weight of the polymer used.

The main components of the absorbent foam of the present invention have been described above. Such absorbent foam is not limited thereto and may include other components that do not adversely affect the desirable properties of the absorbent foam. Examples of materials that can be used as additional components include, but are not limited to, pigments, antioxidants, stabilizers, plasticizers, nucleating agents, surfactants, waxes, flow promoters, solid solutions, particulates, and added to improve processability of absorbent foams. Contains materials. If such additional components are included in the absorbent foam, these additional components are advantageously about 10 weights based on the total weight of the polymer, any crosslinker, and any other components present in the absorbent foam. It is generally preferred to be used in an amount of less than%, more advantageously less than about 5 wt%, suitably less than about 1 wt%.

Absorbent foams of the present invention suitably have the ability to absorb liquids, which are referred to herein as free swelling (FS) values. The method of determining the free swelling value is given below in connection with the following examples. The free swelling value, determined as described below and reported herein, is capable of absorbing 1 g of material for about 1 hour under negligible load of about 0.00068 atm (about 0.01 lb / in ² (psi)). , (G) of the aqueous solution containing 0.9% by weight sodium chloride. As a general rule, the absorbent foam of the present invention has a load of about 0.00068 atm (about 0.01 psi), at least about 10 g per g of absorbent foam, advantageously at least about 15 g, more advantageously at least about 20 g, suitable Preferably a free swelling value of at least about 25 g, more suitably at least about 30 g, and up to about 200 g.

In addition, the absorbent foam of the present invention suitably has the ability to absorb liquid when the absorbent composition is under external pressure or under load, i.e., the ability to be absorbed under load (AUL). Disposable absorbent products are often subjected to external pressure or load during wear and / or use to the consumer, which may adversely affect the ability of the absorbent to be used to effectively absorb liquids that attack the disposable absorbent product. Therefore, it has been found that the ability of a material to absorb liquid when the absorbent composition is under external pressure or load is an important feature of the absorbent material used in disposable absorbent articles. The method of determining the absorbency under load is given below in connection with the following examples. The load-absorbing capacity value determined as shown below and reported therein is 0.9 wt.% Chlorine, capable of absorbing 1 g of material for about 1 hour under a load of about 0.02 atm (about 0.3 lb / in ² (psi)). The amount (g) of the aqueous solution containing sodium is shown. As a general rule, the absorbent foam of the present invention has a load of about 0.02 atm (about 0.3 psi), at least about 10 g per g absorbent foam, advantageously at least about 15 g, more advantageously at least about 20 g, suitable Preferably, it has a load-absorbing capacity value of about 25 g or more, more suitably about 30 g or more and about 100 g or less.

It has been found that the conditions under which absorbent foams are stored can potentially affect the absorbent properties as the foam ages. Even ambient conditions such as relatively mild conditions, such as about 24 ° C. and at least about 30% relative humidity, suitably about 30 to about 60% relative humidity, may degrade their absorbent properties as the absorbent foam ages. Typically, storage conditions such as relatively high temperatures and / or relatively high relative humidity relative to ambient conditions may degrade the absorbent foam's absorption properties more quickly and / or more seriously as the absorbent foam ages.

In one embodiment of the present invention, the absorbent foam of the present invention tends to maintain its initial free swelling value and AUL value after aging. Specifically, the absorbent foam of the present invention may retain at least about 50%, suitably at least about 70% of its initial free swell or AUL value after about 60 days of aging. Typically, the aging conditions are ambient conditions such as about 24 ° C. and relative humidity of at least about 30%. For example, if the absorbent foam of the present invention has an initial AUL value of about 20, after aging for about 60 days at about 24 ° C. and at a relative humidity of at least about 30%, the absorbent foam has an AUL value of at least about 10, suitably It may have an AUL value of about 14. Alternatively, similar absorbent foams may not retain their initial free swelling value or AUL value after aging under similar conditions.

Suitably, the absorbent foam of the present invention retains at least about 50% and more suitably at least about 70% of its initial free swell and AUL values after aging for about 60 days at about 24 ° C. and about 100% relative humidity. do.

As used herein, the term "initial free swelling value" or "absorption capacity under initial load" refers to about after the preparation of an absorbent foam when the absorbent foam is stored at ambient conditions such as about 24 ° C. and about 30 to about 60% relative humidity. Refers to the free swelling value or AUL value indicated by the absorbent foam measured within one day.

In addition, the absorbent foam of the present invention preferably exhibits additional liquid handling properties such as a suitable liquid vertical wick material or a liquid intake rate value.

The absorbent foams of the present invention also suitably exhibit the desired flexibility characteristics, which are defined using the flexibility values. Disposable absorbent products, including absorbent foams, are flexible because the soft materials generally provide maximum compressibility and foldability in order to prevent premature liquid leakage, provide a certain level of comfort, and reduce packaging volume. It is preferred to use flexible absorbent foams, with the result that disposable absorbent articles comprising such hygroscopic foams provide good suitability for the wearer or user. The method of measuring the flexibility value is given below in connection with the examples. The flexibility values measured as described below and reported herein are related to the force values related to the stiffness of the material. Using the test methods described herein, the material's flexibility value provides the average stiffness of the material in all directions, which is a measure of the force exerted on the material at a rate of 50 cm per minute in the circular bending test. In general, the higher the force value needed to bend the material, the harder the material is. As a general rule, the absorbent foams of the present invention is advantageously about 30 g or less, more advantageously less than about 25 g, even more glass is less than about 20 g, suitably from about 15 per m per ² g of the absorbent foam It is desirable to exhibit a flexibility value of a force of less than g, more suitably less than about 10 g, and even more suitably less than about 5 g.

Typical foams include open spaces or cells within the structure of the foam. In the development of the present invention, the cell size of an absorbent foam generally affects certain liquid transport properties such as vertical liquid wick availability, but the cell size of an absorbent foam generally has minimal impact on the overall flexibility or flexibility of the absorbent foam. Figured out it's crazy. This has been found to be particularly consistent when the polymer used to make the absorbent foam is a glassy polymer. Instead, it has been found that the flexibility or flexibility of the absorbent foam generally depends on the thickness of the cell walls. In general, the thinner the wall thickness of the cells of the absorbent foam, the more flexible and / or more flexible the absorbent foam. In order to achieve the desired absorbent and physical characteristics of the absorbent foam of the present invention, it has been found that both the average cell size of the absorbent foam and the average thickness of the cell walls need to be carefully controlled, preferably optimized.

In one embodiment of the invention, it is preferred that the average cell size of the cells in the absorbent foam is advantageously from about 10 microns to about 100 microns, suitably from about 10 microns to about 50 microns. The average cell size in this range of cells in the absorbent foam has generally been found to form an effective groove system for distributing liquid within the structure of the absorbent foam. A method of determining the average cell size of voids in an absorbent foam is given below in connection with the examples.

In one embodiment of the invention, it is generally preferred that the average wall thickness of the cells in the absorbent foam is advantageously from about 0.1 micron to about 30 microns, suitably from about 0.5 microns to about 10 microns. By this range of wall thickness of the cells in the absorbent foam, it has generally been found that desirable physical properties, such as flexibility and / or flexibility, of the absorbent foam are achieved. A method of determining the average wall thickness of the pores of an absorbent foam is given below in connection with the examples.

As used herein, the term "hydrophobic" refers to a material having a contact angle of water in air of at least 90 degrees. In contrast, as used herein, "hydrophilic" refers to a material having a contact angle of water in air of less than 90 degrees. For this application, contact angle measurements are measured as described in Robert J. Good and Robert J. Stromberg, Ed., "Surface and Colloid Science-Experimental Methods", Vol. II (Plenum Press, 1979). . Absorbent foams of the present invention are generally hydrophilic at the time of manufacture and therefore generally do not require subsequent treatment to make them hydrophilic. This is different from many conventional absorbent foams known in the art, in which the polymeric material of the foam is not inherently hydrophilic but becomes hydrophilic by appropriate treatment such as the addition of surfactants.

It has been found that the absorbent foam of the present invention can be produced by a relatively simple, safe and cost-effective method. In one embodiment, the process generally forms a soluble polymer solution in a solvent, freezes the solution to a temperature below the freezing point of the solvent at a relatively slow cooling rate, removes the solvent from the frozen solution, and optionally treats the polymer. Forming a water swellable, water insoluble polymer absorbent foam.

In another embodiment, the method forms a monomer solution in a solvent, polymerizes the monomer to form a solution gel of the crosslinked polymer in the solvent, freezes the solution gel to a temperature below the freezing point of the solvent at a relatively slow cooling rate and And removing the solvent from the frozen solution gel. Optionally, before freezing the solution gel, additional solvent may be used to further swell the solution gel of the crosslinked polymer.

The absorbent foam of the present invention also forms a solution of soluble polymer in a solvent, adds a blowing agent to the solution, initiates a blowing agent, removes the solvent from the solution, and optionally treats the polymer to provide water swellable, water insoluble polymer absorbency. It is contemplated that it may be formed by a method comprising forming a foam.

The term "solvent" as used herein is intended to refer to a material, in particular in liquid form, capable of dissolving the polymer used herein to form a substantially uniformly dispersed mixture at the molecular level. In one embodiment of the invention, the solvent used to prepare the absorbent foam needs to be able to be frozen first and then sublimed, wherein the solvent is transferred directly from its frozen state into the vapor state. For that reason, the solvent used to prepare the absorbent foam should have a freezing point at which the solvent changes from liquid to solid. The freezing point of water and other solvents is generally known in the art. However, as will be appreciated by those skilled in the art, the freezing point of a particular solvent may be influenced by factors such as the relative concentrations of the particular solvent, polymer and crosslinking agent as well as the individual components in the solution.

Soluble polymers or monomers are typically dissolved in a solvent comprising at least about 30 wt% water, advantageously about 50 wt% water, suitably about 75 wt% water, more suitably 100 wt% water. . When the co-solvent is used with water, other suitable solvents include methanol, ethanol, acetone, isopropyl alcohol, ethylene glycol, glycerol and other solvents known in the art. However, when water soluble polymers are used. The use or presence of such other non-aqueous solvents may interfere with the formation of a homogeneous mixture, as a result of which the polymer does not dissolve efficiently in the solvent to form a solution.

In general, solutions of polymers, solvents, and optionally crosslinkers and / or any other components are prepared, wherein the polymers may be added to the solution as polymers or may be formed as polymers from monomers in solution. In the present invention, it has been found that controlling the concentration of polymer in solution is important for achieving absorbent foams that exhibit the desired properties. In general, if the concentration of the polymer in the solution is too high, it has been found that the absorbent foams produced due to the formation of relatively thick cell walls do not exhibit desirable properties, especially flexibility. The use of too large concentrations of polymers in solution is assumed to result in a relatively small volume of space occupied by solvent molecules relative to the total solution volume, but is not constrained by this assumption. In general, it has been found that if the concentration of the polymer in solution is too low, too thin cell walls are formed and too large cells are formed, so that the absorbent foams produced do not exhibit desirable properties, in particular absorption properties and liquid distribution capacity. . It is assumed that the use of too low a concentration of polymer in solution results in too large a volume of space occupied by solvent molecules, but is not bound by this assumption. In general, it was found that the higher the concentration of polymer in solution, the resulting absorbent foam exhibits a smaller average cell size and a thicker average cell wall compared to absorbent foams prepared from solutions with low concentrations of polymer in solution.

Thus, it is generally preferred that the solution comprises about 0.1 to about 30 weight percent, advantageously about 0.5 to about 20 weight percent, suitably about 1 to about 10 weight percent polymer, based on the total solution weight. . The solution generally comprises from about 99.99 to about 70 weight percent, advantageously from about 99.5 to about 80 weight percent, suitably about 99 to about 90 weight percent solvent.

In one embodiment of the invention, it is believed that dissolving the soluble polymers in a solvent causes the fragments of each polymer chain to be entangled with each other. This entanglement causes the polymer chains to interpenetrate with each other in the mixture, resulting in random and coiled entangled molecular arrangements, which effectively provide crosslinking points and add polymers in further processing such as, for example, heat-treatment. It is thought to help crosslinking. In order to ensure that each fragment of the polymer is effectively entangled with each other, it is appropriate to form the solution into a stable and homogeneous solution at equilibrium before further processing steps to ensure that the polymer is effectively dissolved in the solvent. It is understood that there may be relatively small amounts of non-soluble portions of the polymer that typically do not dissolve in the solvent. For example, the retained crystalline sites of the crystalline-crosslinked polymers are typically not soluble in water, while the non-crystalline sites are typically soluble in water.

In general, the order of mixing the polymers or monomers, solvents and optionally crosslinkers is not critical. For that reason, any of the polymers, monomers or crosslinking agents may be added to the solvent first, and then the remaining components may be added continuously or all the components may be added together at the same time. However, when using certain crosslinker components, it may be advantageous to first add the polymer or monomer and solvent and then add the crosslinker to the solution.

Solutions of polymers or monomers, solvents and optionally crosslinkers may generally be formed at temperatures at which the polymers or monomers are dissolved in a solvent. Generally, such temperatures are in the range of about 10 ° C to about 100 ° C.

The solution can be acidic (less than pH 7), neutral (pH 7) or basic (greater than pH 7). If desired, the solution can be acidified by addition of an aqueous solution of an inorganic acid such as hydrochloric or nitric acid or an aqueous solution of an organic acid such as acetic acid. Similarly, if it is desired to provide a solution with a basic pH, a base such as an aqueous solution of sodium hydroxide, potassium hydroxide or ammonia can be added to the solution.

The solution generally has a pH in the range of about 2 to about 12, advantageously about 4 to about 9, more advantageously about 4 to about 7.5, suitably about 6 to about 7.5. The absorbent foams obtained generally have the same pH as the solution.

When the absorbent foam of the present invention is to be used in personal care products such as diapers, training pants, and feminine hygiene products, it is preferred that the absorbent foams generally have neutral properties. For this reason, it is generally advantageous to form solutions with neutral pH. If a solution with acidic or basic pH is formed, the absorbent foam recovered may be (respectively) acidic or basic, but may be neutralized. The recovered absorbent foam that is acidic can be neutralized, for example, by contact with a gaseous base such as ammonia. Recovered absorbent foams that are basic can be neutralized, for example, by contact with an acidic gas such as carbon dioxide.

After forming a solution comprising a polymer or monomer, a solvent and optionally a crosslinking agent, it is advantageous to stir or stir the solution or otherwise blend to effectively and uniformly mix the components to form an essentially homogeneous solution.

If monomers are used, the monomers are properly treated to form the desired polymer in solution.

The solution is then cooled to a temperature below the freezing point of the solvent to freeze the solvent and bring it to solid phase in solution. Since the polymer and optionally the crosslinking agent are essentially uniformly dispersed in the solution, it is generally preferred that the polymer and optionally the crosslinking agent form an essentially continuous substrate in the frozen solution when the solvent is frozen into a solid phase. As such, the essentially continuous substrate of the polymer and optionally the crosslinker is substantially trapped by the frozen solvent to form an essentially uniform discontinuous structure. As used herein, the term “capture” and related terms means that the frozen solvent phase substantially surrounds or surrounds the essentially continuous substrate of the polymer and optionally the crosslinker.

As will be appreciated by those skilled in the art, the temperature at which the solution is cooled to freeze the solvent is typically dependent on factors such as the relative concentrations of the solvents, polymers and crosslinkers used as well as the respective components in the solution. In general, if the temperature at which the solution eventually cools is too close to the freezing point of the solvent, the frozen polymer solution may not exhibit sufficient strength and may be modified in further processing steps such as vacuum treatment to remove the frozen solvent. It turns out that. In addition, the freezing point of the solvent may be lowered due to the effect of the dissolved polymer and / or crosslinker. For that reason, if the solution is simply cooled to the freezing point of pure solvent, some of the solvent present in the solution may not be frozen at such temperatures. In general, if the temperature at which the solution eventually cools is too below the freezing point of the solvent, the molecules of the solvent in the solution may form non-uniform crystalline phases throughout the solution, which may affect the polymer substrate and the absorbent foam produced therefrom. It has been found that cracks may be formed. Such cracking tends to reduce the mechanical properties of the absorbent foam, such as tensile strength and flexibility or flexibility. In addition, the use of very low temperatures can slow down the rate of sublimation of the frozen solvent.

In one embodiment where the solvents used to make the absorbent foam are essentially all water or an aqueous solution comprising most of the water and other solvents, the temperature at which the solution eventually cools is from about −50 ° C. to about 0 ° C., glass Preferably from about -50 ° C to about -5 ° C, more advantageously about -40 ° C to about -10 ° C, suitably about -30 ° C to about -10 ° C.

The rate at which the solution cools from a temperature above the freezing point of the solvent to a temperature below the freezing point of the solvent has been found to be important in achieving absorbent foams exhibiting the desirable properties described herein. In the qualitative method, if the cooling rate used is too fast, visible cracks or visible non-uniformities begin to form in the freezing solution, so the cooling rate should not be too fast. As such, there is generally a critical cooling rate for a particular solution to achieve the desired absorbent foam of the present invention. Using fast cooling rates relative to such critical cooling rates results in undesirable absorbent foams exhibiting relatively non-uniform pore structures and cracked polymer substrates. In contrast, using slower cooling rates relative to such critical cooling rates generally yields desirable absorbent foams having a relatively uniform pore structure and without significant cracks or deformations in the polymer matrix.

For the freezing point of the solvent, the critical cooling rate used for a particular solution typically depends on the relative concentrations of the solvents, polymers and crosslinkers used, as well as the respective components in the solution. In one embodiment of the invention wherein the solvent is water or an aqueous solution which also contains most water and other solvents, more particularly the polymer is used at a concentration of about 0.5 to about 2 weight percent based on the total weight of the solvent. The critical cooling rate was found to drop to a temperature of about 0.4 ° C. to about 0.5 ° C. per minute. Thus, in this embodiment, the cooling rate used to freeze the solvent is preferably less than about 0.4 ° C. per minute, advantageously less than about 0.3 ° C. per minute, suitably less than about 0.1 ° C. per minute.

As will be appreciated by those skilled in the art, in addition to attempts to use a cooling rate slower than the critical cooling rate to achieve an essentially uniform cell structure in the absorbent foam, other methods may also be applied. Such other methods include, but are not limited to, the inclusion of small air bubbles or the use of nucleating agents. The use of the nucleating agent is assumed to increase the number of nuclei, thereby crystallizing the solvent molecules essentially uniformly during the cooling process, but are not bound by this assumption. The use of nucleating agents generally increases the critical cooling rate.

After the solution is cooled to freeze the solvent and form a solid phase in the solution, and after the solution reaches a relatively stable temperature, the frozen solvent is substantially removed from the solution. In the present invention, it has been found that using a suitable vacuum to sublimate the frozen solvent generally yields the desired absorbent foam. As will be apparent to those skilled in the art, the vacuum used for a particular freezing solution depends on factors such as the solvent, polymer and crosslinking agent typically used, the relative concentrations of the respective components in the solution, and the temperature of the frozen solution. Preferred vacuum conditions are advantageously less than about 500 millitorr, more advantageously less than about 300 millitorr, suitably less than about 200 millitorr, more suitably less than about 100 millitorr. In general, the higher the vacuum, the faster the rate of sublimation of the frozen solvent.

As used herein, sublimation of a frozen solvent from a frozen solution by the use of a vacuum refers to the removal of substantially all solvent from the frozen solution, if necessary, prior to further processing steps. However, it should be understood that even after substantially all of the solvent has been removed, a small amount of solvent may remain trapped in the structure of the residual polymer matrix. The amount of solvent remaining trapped within the structure of the polymer matrix typically depends on the method and conditions for subliming the freezing solvent. Generally, less than about 20 weight percent, advantageously less than about 15 weight percent, and suitably less than about 10 weight percent of the original amount of solvent in the solution will remain trapped in the residual polymer matrix of the absorbent foam.

After substantially subliming the frozen solvent from the frozen solution, a polymer and optionally a crosslinker remain, which polymer generally forms a polymer matrix comprising cells that are generally interconnected to achieve the foam structure. The polymer matrix forms the wall of the cell with the open cell formed by sublimation of the frozen solvent. As mentioned above, it is generally preferred that the foam structure obtained exhibits a preferred average pore size and a preferred cell wall average thickness.

The recovered foam structure may already exhibit desirable absorbent and physical properties, so that the recovered foam structure becomes the absorbent foam of the present invention and does not require additional processing steps. As will be appreciated by those skilled in the art, this generally depends on the particular polymer used in the preparation of the foam and the particular crosslinking agent if used. Processes for preparing a foam structure in which the recovered foam structure may already exhibit desirable absorbent and physical properties include polymerizing the monomer in solution to form a crosslinked insoluble polymer gel solution, and the polymer at a relatively low temperature such as about room temperature or less. The use of crosslinkers which can be reacted with, and the polymers used, such as polyvinyl alcohol or chitosan, include the ability to form highly ordered structures during the freezing and solidification process.

If the recovered foam structure does not exhibit desirable absorbent and physical properties, it may be necessary to treat the recovered polymer foam structure in further processing steps. For example, if the crosslinker used is a potential crosslinker, such crosslinker may not react with the polymer since no suitable crosslinking conditions have yet been provided in the polymer and crosslinker mixture. As such, in order to crosslink the polymer to achieve a water insoluble, water swellable polymer, it may be necessary to provide effective crosslinking conditions. Suitable post-treatment conditions include the use of heat treatment, exposure to ultraviolet light, exposure to microwave furnaces, exposure to electron beams, steam or high humidity treatments, high pressure treatments, or treatment with organic solvents.

In general, if heat-treatment is required, a combination of temperatures and times effective to achieve the desired degree of crosslinking without causing undesirable damage to the polymer is suitable for use in the present invention, resulting in polymers and absorbent foams. Represents the preferred properties described herein. As a general rule, when crosslinking agents are used, the polymer may be from about 50 ° C. to about 250 ° C., advantageously from about 80 ° C. to about 250 ° C., more advantageously from about 100 ° C. to about 200 ° C., suitably from about 100 ° C. to about Heat treatment to a temperature of 160 ° C. The higher the temperature used, the shorter the time period generally required to achieve the desired degree of crosslinking. If a high temperature is used with an effective period, such as from about 100 ° C. to about 250 ° C. for a period of from about 50 seconds to about 500 minutes, effective freedom for certain polymers such as carboxyalkyl polysaccharides without the use of crosslinking agents The swelling value and the absorbency value under load can be achieved.

In general, the heat treatment process lasts over a period in the range of about 1 minute to about 600 minutes, advantageously about 2 minutes to about 200 minutes, suitably about 5 minutes to about 100 minutes.

If a heat-treatment process or other acceptable post-recovery process is used, these processes generally crosslink or further crosslink the polymer and generally the polymer becomes water swellable and water insoluble. The post-recovery process involves the formation of crosslinks between functional groups from the polymer and the external crosslinking agent or between functional groups on the polymer when the polymer contains one or more functional groups, regardless of the presence of the crosslinking agent. It is believed that the degree of crosslinking is possible, but is not limited to this assumption. One example of a self-crosslinkable polymer is carboxymethyl cellulose that contains both carboxylic acid groups and hydroxyl groups and can form ester bonds. In addition to any crosslinking, such self-crosslinking may also be caused by the presence of a crosslinking agent. In addition, when the crosslinking agent is a diamine or a polyamine, it is considered that crosslinking occurs by amidation of the polymer carboxyl group through the formation of an ammonia salt. Esterification via a self-crosslinking process is thought to occur mainly under weakly acidic, neutral or weakly basic conditions. It is believed that esterification through a self-crosslinking process does not proceed to a significant extent under relatively basic conditions. Crosslinking due to the crosslinking agent can occur in both acidic and basic conditions. That is, the presence of the crosslinking agent allows the crosslinking to occur over a wide pH range.

In general, there is an optimum degree of crosslinking or amount of crosslinking of a particular polymer that optimizes the absorptive properties of that particular crosslinked polymer. If too little crosslinking occurs, the polymer may have relatively low absorptive properties such as absorptive load values due to lack of gel strength. If too much crosslinking occurs, the polymer may have relatively low absorbency properties, such as free swelling values, because the polymer is unable to absorb liquid.

Those skilled in the art will appreciate that the presence of crosslinks formed by esterification or amidation, ionic bonds or other types of bonds can be detected through various analytical techniques. For example, infrared spectroscopy and nuclear magnetic resonance can be used to verify the presence of ester and amide crosslinks.

Absorbent foams of the present invention include disposable products, including diapers, adult incontinence products and disposable absorbent products such as bed pads, menstrual devices such as sanitary napkins and tampons, and wipes, bibs, wound care bandages, and surgical capes or drapes. Suitable for use in other absorbent products. Thus, in another aspect, the present invention relates to a disposable absorbent article comprising the absorbent foam of the present invention.

In one embodiment of the invention, there is provided a disposable absorbent article comprising a liquid permeable topsheet, a backsheet attached to the liquid permeable topsheet, and an absorbent structure positioned between the liquid permeable topsheet and the backsheet. The structure includes the absorbent foam of the present invention.

Absorbent articles and structures according to all aspects of the present invention are generally subject to multiple attacks of body fluids during use. Thus, it is desirable that the absorbent articles and structures be able to absorb multiple attacks of the amount of body fluids to which the absorbent articles and structures are exposed during use. Attacks are usually separated from each other by some length of time.

Test Methods

Free swelling

Free swelling capacity (FS) is 0.9 weight percent sodium chloride, which can absorb 1 g of material for about 1 hour under negligible applied load or binding force, such as about 0.00068 atm (about 0.01 lb / in ² ). It is a test which measures the quantity (g) of the aqueous solution containing this.

Referring to FIG. 1, an apparatus and method for determining free swelling values and absorbency under load are shown. Perspective view of the device in place during the test. An experimental jack 1 is shown with an adjustable handle 2 for raising and lowering the work bench 3. The experimental stand 4 bears a spring 5 connected to the thickness change measuring probe 6, which penetrates the housing 7 of the instrument firmly supported by the experimental stand. The plastic sample cup 8 containing the absorbent foam material sample to be tested has a liquid permeable bottom and is placed in a petri dish 9 containing the salt solution to be absorbed. To determine the absorbency value under load only, the weight 10 is placed on a spacer disk (not shown) overlying the absorbent foam material sample (not shown).

The sample cup consists of a plastic cylinder with a 25.4 mm (1 inch) inner diameter and 31.75 mm (1.25 inch) outer diameter. The bottom of the sample cup is a 100 mesh metal sieve having a 150 micron opening in the cylinder by heating the sieve above the melting point of the plastic and pressing the plastic cylinder against the hot sieve to melt the plastic and bond the sieve to the plastic cylinder. It is formed by attaching to the end.

The thickness change meter used to measure the swelling of the sample while absorbing the salt solution is a Mitutoyo Digimatic Indicator (Mitutoyo) with a range of 0 to 12.7 mm (0 to 0.5 inches) and an accuracy of 0.00127 mm (0.00005 inches). Digimatic Indicator), IDC Series 543, Models 543-180 (Mitutoyo Corporation, Japan 108, and Minatoku Shiba 5 Chome 31-19). When supplied from Mitutoyo Corporation, the thickness gauge has a spring attached to the probe in the meter housing. This spring is removed to provide a free-fall probe with a downward force of about 27 g. In addition, remove the cap covering the tip of the probe located above the instrument housing and attach the probe to the suspension spring 5 (McMaster-Carr Supply Co., Chicago, Illinois, Item No. 9640K41). Suspension springs can be attached and used to calculate or reduce the probe's downward force to about 1 g + 0.5 g. A wire hook can be attached to the end of the probe to attach it to the suspension spring. An extension needle (Mitotoyo Corporation, part number 131279) is also provided at the bottom end of the probe so that the probe can be inserted into the sample cup.

In order to perform the test, absorbent foam material samples were cut into circular disks of about 1 inch diameter. A total of about 0.160 g of absorbent foam material sample, typically about 3 to 4 circular disk layers, is placed in the sample cup. The sample is then covered with a plastic spacer disk having a weight of 4.4 g, a diameter of about 0.995 inches, which prevents the sample from being disturbed during the test and evenly applies the load over the entire sample. The sample cup with material sample and spacer disk is weighed to obtain dry weight. Place the sample cup in a Petri dish on the workbench and raise the laboratory jack until the top of the plastic spacer disk contacts the tip of the probe. Zero the meter. A sufficient amount of salt solution is added to the Petri dish (50-100 ml) to begin the test. When the sample absorbs the salt solution, the distance the plastic spacer disk is raised by expanding the sample is measured by the probe. This distance multiplied by the cross-sectional area inside the sample cup is a measure of the expansion volume of the sample due to absorption. Factoring in the density of the salt solution and the weight of the sample, the absorption of the salt solution is easily calculated. The weight of the salt solution absorbed after 1 hour is the free swelling value expressed in g of salt solution absorbed per gram of absorbent foam sample. If desired, in order to calculate and provide a free swelling scale value, the scale value of the thickness change meter can be continuously input to a computer (Mitutoyo Digimatic Miniprocessor DP-2DX). As a cross-check, the free swelling value can be determined by determining the weight difference between the sample cups before and after the test, where the weight difference is the amount of solution absorbed by the sample.

Absorption capacity under load

Absorbency under load (AUL) is the amount of an aqueous solution containing 0.9% by weight of sodium chloride that is capable of absorbing 1 g of material for 1 hour under applied load or binding force of about 0.02 atm (about 0.3 pounds per in ² ) g) test. Method for measuring the load and absorption capacity value of the absorbent composition, onto the absorbent foam when placed a weight of 100 g on top of the plastic spacer disc foam to absorb the salt solution, the load of about 0.02 atm (about 0.3 pounds per in ²⁾ Except for this, it is substantially the same as the method for measuring the free swelling value.

flexibility

The flexibility values of the materials are determined by tests modeled following the ASTM D4032-82 circular bending procedure. This modified test is used for the purpose of the present invention, hereinafter simply referred to as "circular bending procedure". Circular bending test is a multi-directional simultaneous deformation of a material in which one side of the material is concave and the other side of the material is convex. The circular bending procedure provides a force value that relates to the stiffness of the material and at the same time averages the stiffness in all directions, and conversely to the flexibility of the material.

The apparatus required for the circular bending procedure is: a modified circular bending stiffness tester with a smoothly polished steel sheet workbench with an orifice of 102.0 mm (length) × 102.0 mm (width) × 6.35 mm (depth) and a diameter of 18.75 mm to be. The edge of the recess of the orifice shall be 45 ° angle up to a depth of 4.75 mm. Dimensions below: total length of 72.2 mm, a diameter of 6.25 mm, a ball nose with a radius of 2.97 mm, and a needle-point extending 0.88 mm from the ball nose and having a 0.33 mm base diameter, and a point with a radius of less than 0.55 mm A plunger comprising a is used. Mount the plunger about the orifice at equal intervals on all sides. Needle-points are simply used to prevent lateral movement of the sample during the test. The bottom of the plunger should be secured on top of the orifice face. From this position, the downward reciprocation of the ball nose is the actual bottom of the orifice plate.

A reverse compressive load cell with a load range of about 0.0 to about 2000.0 g was used as the force measurement gauge. The compression tester used was an Instron Model No. 1122 Reverse Compression Load Cell, available from Instron Engineering Corporation of Canton, Massachusetts.

After calibrating the load cell, the gauge length for displacement of the plunger was fixed at 25.4 mm. To perform the test, absorbent foam samples were cut into 38.1 mm × 38.1 mm square specimens using a die cutter. The sample was placed on a test bench and the plunger was pushed down onto the sample at a crosshead speed of 500 mm / min for a 25.4 mm gauge length. During the movement of the plunger, the absorbent foam sample was bent downward into the 18.75 mm hole by the plunger, and the force applied by the compression tester was measured and recorded by the load cell so that the foam sample was bent during the 25.4 mm gauge length displacement of the plunger. Dividing the force measured by the load cell as the basis weight of the sample was recorded as a unit of (g / gsm) in g per m ² of g / sample of force. This value is used as the flexibility value to obtain a quantitative measure of the flexibility of the specimen. The higher the flexibility value (g / gsm), the stronger the sample, i.e. less flexibility.

Measurement of Cell Pore Size and Cell Wall Thickness

Foam samples were cut with a sharp razor. The cut foam was attached to a piece of metal using copper tape and imaged with an environmental scanning electron microscope using a 12 kV beam voltage. The device used was an environmental scanning electron microscope model E-2020 from Electroroscan Corporation, Wilmington, Massachusetts. Sample chamber pressure was about 1.2 Torr. Images were collected using an environmental backscattered electron detector, which has the advantage of being able to recognize any change in the composition. The magnification varies depending on the size of the sample under investigation, 150 magnifications are used for the general inspection of the sample and 2500 magnifications are used to measure cell wall thickness and cell size. Cell wall thickness and cell size measurements are taken directly directly on an environmental scanning electron microscope. It was not possible to apply routine automatic phase analysis to these complex structures for cell wall thickness measurements. Manual measurement is required. The cell wall thickness and cell size of each sample were averaged from 20 or more measurements.

For use in the examples below, the following polymeric materials were obtained.

Polymer 1: Carboxymethylcellulose having a weight average molecular weight of at least 1,000,000 and having a degree of substitution of carboxymethyl groups for anhydroglucose units of cellulose materials of about 0.7 is Hercules Inc., Wilmington, Delaware, USA. .) Obtained under the trade name B313 carboxymethylcellulose from the subsidiary Aqualon. Carboxymethylcellulose is an anionic polymer.

Polymer 2: A sodium polyacrylate polymer having a weight average molecular weight of about 4,000,000 and a degree of neutralization of about 70% was obtained as catalog number 06501 from Polysciences, Warrington, PA. Sodium polyacrylate polymers are anionic polymers.

Polymer 3: A sodium polyacrylate polymer having a weight average molecular weight of about 240,000 and a degree of neutralization of about 70% was obtained from Polyscience, Warrington, PA, under catalog number 18613. Sodium polyacrylate polymers are anionic polymers.

Polymer 4: Sodium polyacrylate polymer having a weight average molecular weight of about 60,000 and a degree of neutralization of about 70% was obtained under the catalog number 18611 from Polyscience, Warrington, PA. Sodium polyacrylate polymers are anionic polymers.

Polymer 5: Chitosan acetate having a weight average molecular weight of about 11,000,000 and an acetylation degree of about 80% was obtained under the trade name VNS-608 chitosan from the Vanson Company, Seattle, WA. Chitosan acetate is a cationic polymer.

Polymer 6: Polyethylene oxide having a weight average molecular weight of about 4,000,000 was obtained under the trade name WSR-301 polyethylene oxide from Union Carbide Corporation, Danbury, Connecticut. Polyethylene oxide is a nonionic polymer.

Example 1

The weight of the various polymer samples was dissolved in each batch containing about 2000 g of distilled water at a temperature of about 23 ° C. For carboxymethylcellulose (polymer 1) and polyethylene oxide (polymer 6) solutions, about 0.2 g citric acid was added to the solution as crosslinking agent. To the sodium polyacrylate solution (polymer 2-4) solution, about 0.75 g of an aqueous solution containing about 40% by weight of ammonium zirconium carbonate was added to the solution as crosslinking agent. Various solutions were combined for about 2-3 hours to ensure that the ingredients were thoroughly mixed. About 500 g of each prepared solution was placed in a separate stainless steel pan with dimensions of 254 mm (10 inches) (width) x 508 mm (20 inches) (length) x 25.4 mm (1 inch) (depth) . Pans containing each solution were placed in a freeze dryer, available as Virtis Genesis Model 25 EL Freeze Dryer from Virtis, Inc. of Gardiner, NY, USA. In order to freeze the water in the solution, various solutions in the pan were cooled to about −15 ° C. at various cooling rates. The various solutions in the pan were kept at about -15 ° C for about 1 hour to allow the water to be substantially completely frozen. The frozen solution was placed in a lyophilizer and treated for about 15 hours with a vacuum of about 105 millitorr provided by a vacuum pump with a condenser fixed at a temperature of about -60 ° C to about -70 ° C. The resulting foam structure was treated at various temperatures for various periods of time to aid in crosslinking of the polymer. The final foam structure was then evaluated for free swell values, absorbency values under load, and flexibility values. Table 1 summarizes the evaluation results for the various process conditions and various samples. Foam samples prepared using Polymer 4 (Sample 7) were water soluble and thus did not exhibit measurable free swelling values and absorbency under load values.

A comparative foam sample (Sample 10) was prepared as follows. An aqueous solution of about 250 g of acrylic acid containing 50% by weight of acrylic acid was neutralized using 1 N sodium hydroxide solution to form a sodium acrylate solution having a degree of neutralization of 75%. Neutralization was carried out slowly using an ice bath careful to maintain a solution temperature of about 5 ° C. to avoid polymerization. Approximately 200 ml of the solution was placed in a 2-liter reaction vessel equipped with a heating jacket and a high shear mixer (Ultra-Turrax T25 mixer from Janke & Kunkel GmbH, Stauffen, Germany). Transferred to. 0.5 g of N, N'-methylenebisacrylamide, about 1.3 g of 2,2'-azobis- (2-amidopropane) hydrochloride (monomer-polymer and prolific of Pisterville, PA, USA) in a solution in the reaction vessel Rabo Ratoris Inc. (Monomer-Polymer & Dajac Laboratories, Inc.) and about 20 g of 600 weight average molecular weight polyethylene glycol (Union Carbide Company) were added and the mixture was kept at 22 ° C. About 3.5 g of sorbitan monolaurate and about 6.5 g of ethoxylated sorbitan monolaurate are mixed with about 60 g of 1,1,2-trichlorotrifluoroethane and the mixture is added to a solution in the reaction vessel. Added. Start the high shear mixer and mix the mixture at a speed of about 8000 rpm for about 10 minutes, then remove the mixer from the reaction vessel, increase the temperature to about 60 ° C. and hold for about 1 hour to form a foam. The temperature was then increased and maintained at about 80 ° C. for about 30 minutes, and finally the temperature was increased and maintained at about 120 ° C. for about 30 minutes. The reactor was cooled to about 22 ° C. A mixture consisting of about 5 g of glycerol and about 25 g of isopropyl alcohol was added to the foam in the reactor and the temperature was raised to about 180 ° C. and maintained for about 1 hour. The reactor was then cooled to ambient temperature, the foam removed from the reactor and left in the chamber at about 80% relative humidity for about 6 hours to obtain the final foam material. These foam samples were evaluated for free swelling values, absorbency under load values, and flexibility values, and the evaluation results are summarized in Table 1.

Sample Number Polymer type Polymer concentration (% by weight) Cooling rate Heat treatment condition (temperature / hour) Free swelling value (g / g) Absorption capacity under load (g / g) Flexibility value (g / gsm) Sample 1 Polymer 1 0.5 0.03 ° C / min 130 ℃ / 10 minutes 26.1 18.3 2.90 Sample 2 Polymer 1 0.5 0.2 ° C / min 130 ℃ / 10 minutes 21.8 - 6.53 Sample 3 Polymer 1 0.5 0.4 ° C / min 130 ℃ / 10 minutes 22.1 - 20.58 ^* Sample 4 Polymer 1 4.0 0.4 ° C / min 130 ℃ / 10 minutes 18.7 - 45.93 Sample 5 Polymer 2 0.5 0.03 ° C / min 200 ℃ / 40 minutes 35.0 19.5 1.36 Sample 6 Polymer 3 0.5 0.03 ° C / min 200 ℃ / 5 hours 42.8 2.5 1.09 ^* Sample 7 Polymer 4 0.5 0.03 ° C / min 200 ℃ / 72 hours 0 0 1.54 Sample 8 Polymer 5 0.5 0.03 ° C / min 100 ℃ / 10 minutes 22.5 14.3 3.26 Sample 9 Polymer 6 0.5 0.03 ° C / min 60 ℃ / 10 hours 15.3 4.1 0.46 ^* Sample 10 - - 15 10.5 > 100 * Not an embodiment of the invention

Example 2

Multiple substantially similar foam samples were prepared as follows. About 10 g of Polymer 1 (carboxymethylcellulose) was dissolved in about 2000 g of distilled water at a temperature of about 23 ° C. About 0.2 g citric acid was added to the solution as crosslinking agent. The solution was combined for about 2-3 hours to mix the ingredients thoroughly. About 500 g of the solution was placed in a stainless steel pan with dimensions of 254 mm (10 inches) (width) x 508 mm (20 inches) (length) x 25.4 mm (1 inch) (depth). The pan containing the solution was placed in a freeze dryer, commercially available from Virtis Inc. of Gardiner, NY, USA under the trade name Virtis Genesis Model 25 EL Freeze Dryer. To freeze the water in the solution, the solution in the pan was cooled to about -15 ° C at a cooling rate of about 0.04 ° C / min. The solution in the pan was kept at about −15 ° C. for about 1 hour to allow the water to substantially freeze. The frozen solution was placed in a lyophilizer and treated for about 15 hours with a vacuum of about 105 millitorr provided by a vacuum pump with a condenser fixed at a temperature of about -60 ° C to about -70 ° C.

The resulting foam structure was treated at various temperatures for various periods of time to aid in crosslinking of the polymer. The final foam structure was then evaluated for free swell values, absorbency values under load, and flexibility values. Table 2 summarizes the evaluation results for the various process conditions and various samples.

Sample number Heat treatment condition (temperature / hour) Free swelling value (g / g) Absorption capacity under load (g / g) Flexibility value (g / gsm) ^* Sample 11 none 0 0 20.58 Sample 12 150 ℃ / 5 minutes 27.9 - - Sample 13 150 ℃ / 10 minutes 25.1 14.3 - Sample 14 150 ℃ / 20 minutes 15.7 11.2 - Sample 15 150 ℃ / 30 minutes 16.6 11.3 20.58 ^* Sample 16 none 0 0 - Sample 17 130 ℃ / 5 minutes 60.1 29.9 20.58 Sample 18 130 ℃ / 10 minutes 26.1 18.3 - Sample 19 130 ℃ / 15 minutes 21.8 16.2 - Sample 20 130 ℃ / 20 minutes 18.2 14.6 - Sample 21 130 ℃ / 25 minutes 17.4 13.9 20.58 * Not an embodiment of the invention

Those skilled in the art will appreciate that various modifications and variations can be made in the present invention without departing from the scope of the invention. Accordingly, the detailed description and examples set forth above are merely given for illustration and should not be construed as limiting the scope of the invention as set forth in the claims below.

Claims (43)

A water swellable, water insoluble polymer present in the absorbent foam at a weight of 50% to 100% by weight based on the total weight of the absorbent foam, the free swelling value of at least 10 g of liquid per g of absorbent foam and the absorbent foam m ² Absorbent foam, characterized in that it exhibits a flexibility value of less than 30 g per gram sugar. The polymer according to claim 1, wherein the polymer is polyacrylamide, polyvinyl alcohol, ethylene maleic anhydride copolymer, polyvinyl ether, polyacrylic acid, polyvinylpyrrolidone, polyvinylmorpholine, polyamine, polyethyleneimine, polyacrylamide, Polyquaternary ammonium, carboxymethyl cellulose, carboxymethyl starch, hydroxypropyl cellulose, algin, alginate, carrageenan, acrylic graft starch, acrylic graft cellulose, chitin, chitosan, polyaspartic acid, polyglutamic acid, polyasparagine, poly Absorbent foam selected from the group consisting of glutamine, polylysine, polyarginine, and salts, copolymers, and mixtures of such polymers. The absorbent foam of claim 2 wherein the polymer is selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, chitin, chitosan, and salts, copolymers and mixtures of such polymers. 4. The absorbent foam of claim 3 wherein the water swellable, water insoluble polymer is selected from the group consisting of polyacrylic acid and salts thereof. The absorbent foam of claim 1 wherein the water swellable, water insoluble polymer is present in the absorbent foam at a weight of 60% to 100% by weight. The absorbent foam of claim 1 wherein the absorbent foam further comprises a crosslinking agent. 7. The absorbent foam of claim 6, wherein the crosslinking agent is selected from the group consisting of a polymer and an organic compound having at least two functional groups or functionalities capable of reacting with at least two positively charged metal ions. 7. The absorbent foam of claim 6, wherein the crosslinking agent is present in the absorbent foam at a weight of 0.01% to 20% by weight based on the total weight of the absorbent foam. The absorbent foam of claim 1 wherein the absorbent foam exhibits a free swelling value of at least 15 g of liquid per gram of absorbent foam. The method of claim 1 wherein the absorbent foam is absorbent foam absorbent foam m represents the flexibility value of the power of less than 25 g per g per ^second. The absorbent foam of claim 1, wherein the absorbent foam exhibits a load-absorbing capacity value of at least 10 g of liquid per gram of absorbent foam. The absorbent foam of claim 1 wherein the absorbent foam comprises cells in which the average cell size of the cell is between 10 microns and 100 microns. The absorbent foam of claim 1 wherein the absorbent foam comprises a cell having a thick wall, wherein the average wall thickness of the cell is between 0.1 and 30 microns. 2. The water swellable, water insoluble polymer of claim 1, wherein the water swellable, water insoluble polymer is selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, chitin, chitosan, and salts, copolymers, and mixtures of the polymer, wherein the absorbent foam has a thick wall. An absorbent foam comprising a cell, wherein the average cell size of the cell is from 10 microns to 100 microns and the average wall thickness of the cell is from 0.1 microns to 30 microns. delete delete delete delete delete delete delete delete The method of claim 1 wherein the absorbent foam is absorbent foam g absorbent foam showing the flexible value of the liquid 10 g or more free swell values, and an absorbent foam of less than 30 g per m ² Power per g sugar. A liquid permeable topsheet, a backsheet attached to the topsheet, and an absorbent core positioned between the liquid permeable topsheet and the backsheet, wherein the absorbent core comprises from 50% to 100% by weight based on the total weight of the absorbent foam; be present in the absorbent foam, by weight water-swellable, can include an absorbent foam comprising a water-insoluble polymer, the absorbent foam is absorbent foam g liquid 10 g of the above free swell values, and the absorbent foam m ² force of less than 30 g per g sugar per Disposable absorbent product, characterized by exhibiting flexibility values. delete a. To form a solution comprising a weight of water and a polymer, wherein the polymer is present in the solution at a weight of 0.1 to 30 weight percent based on the total solution weight, b. The solution is cooled to a temperature of −50 ° C. to 0 ° C. at a cooling rate of less than 0.4 ° C. per minute under conditions effective to freeze water, c. Substantially removing the frozen water from the solution, d. Characterized by comprising recovering the polymeric foam, A process for producing an absorbent foam comprising a water swellable, water insoluble polymer. 27. The method of claim 26, wherein the frozen water is removed from the solution using a vacuum of less than 500 millitorr. 28. The method of claim 27 wherein less than 20% by weight of the weight of water in the solution remains in the recovered absorbent foam. 27. The method of claim 26, further comprising treating the polymer foam under conditions effective to achieve a water swellable, water insoluble polymer. The method according to claim 29, wherein the polymer foam is treated with a treatment selected from the group consisting of heat treatment, exposure to ultraviolet light, exposure to microwaves, exposure to electron beams, steam treatment, high humidity treatment, high pressure treatment and organic solvent treatment. . 31. The method of claim 30, wherein the polymeric foam is treated at a temperature of 50 ° C to 250 ° C. 27. The method of claim 26, wherein the solution further comprises a crosslinking agent. 33. The method of claim 32, wherein the crosslinking agent is selected from the group consisting of a polymer and an organic compound having at least two functional groups or functionalities capable of reacting with at least two positively charged metal ions. 27. The method of claim 26, wherein the polymer is a water soluble polymer. 27. The polymer of claim 26 wherein the polymer is polyacrylamide, polyvinyl alcohol, ethylene maleic anhydride copolymer, polyvinylether, polyacrylic acid, polyvinylpyrrolidone, polyvinylmorpholine, polyamine, polyethyleneimine, polyacrylamide, Polyquaternary ammonium, carboxymethyl cellulose, carboxymethyl starch, hydroxypropyl cellulose, algin, alginate, carrageenan, acrylic graft starch, acrylic graft cellulose, chitin, chitosan, polyaspartic acid, polyglutamic acid, polyasparagine, poly Glutamine, polylysine, polyarginine, and salts, copolymers, and mixtures of said polymers. 36. The method of claim 35, wherein the polymer is selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, chitin, chitosan, and salts, copolymers, and mixtures of said polymers. 27. The method of claim 26, wherein the water swellable, water insoluble polymer is present in the absorbent foam at a weight of 50% to 100% by weight based on the total weight of the absorbent foam. 27. The method of claim 26 wherein the absorbent foam is shown how the value of the absorbent foam flexibility g liquid 10 g or more free swell values, and the absorbent foam m ² less than 30 g of force per g sugar per. 39. The method of claim 38, wherein the absorbent foam comprises cells having a thick wall, wherein the average cell size of the cells is between 10 microns and 100 microns, and wherein the average wall thickness of the cells is between 0.1 microns and 30 microns. . delete 27. The method of claim 26, wherein the polymer is selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, chitin, chitosan and salts, copolymers and mixtures of the polymers, the solution further comprising a crosslinking agent, wherein the vacuum is less than 500 millitorr. Used to remove the frozen water from the solution and less than 20% by weight of the weight of the water in the solution remains in the recovered absorbent foam and is subjected to heat treatment, exposure to ultraviolet light, exposure to microwaves, exposure to electron beams, steam treatment Further comprising treating the polymer foam with a treatment selected from the group consisting of high humidity treatment, high pressure treatment and organic solvent treatment, wherein the water swellable, water insoluble polymer is 50 to 100 weight percent based on the total weight of the absorbent foam Absorbent foam is present in the absorbent foam by weight of%, the absorbent foam having a free swelling value of at least 10 g of liquid per absorbent foam, absorbent FOCE g liquid 10 g or more under load absorption capacity value per, and an absorbent per m ² per foam g denotes a flexibility value of less than 30 g of force, the absorbent foam comprises a cell having a wall with a thickness, the average cell of the cell The size is from 10 microns to 100 microns and the average wall thickness of the cell is from 0.1 microns to 30 microns. Absorbent foam produced by the method of claim 26. 43. The polymer of claim 42 wherein the polymer is selected from the group consisting of polyacrylic acid, carboxymethyl cellulose, chitin, chitosan, and salts, copolymers and mixtures of said polymers, wherein water swellable, water insoluble polymers are based on the total weight of the absorbent foam So that the absorbent foam is present in the absorbent foam at a weight of 50% to 100% by weight, the absorbent foam having a free swelling value of at least 10 g of liquid per gram of absorbent foam, an absorbency value under load of at least 10 g of liquid per gram of absorbent foam, and m of absorbent foam. A softness value of less than 30 g per gram per ^two , wherein the absorbent foam comprises cells with a thick wall, the average cell size of the cells is from 10 microns to 100 microns and the average wall thickness of the cells is from 0.1 micron to Absorbent foam, characterized in that it is 30 microns.

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