Superabsorbent composition containing transitional crosslinking points

This invention relates to an absorbent composition containing transition crossing points. There are two types of cross-linking points, conventional permanent cross-linking points and transition cross-linking points. Permanent crisscrossing points are those that exist in a polymer without experiencing a significant decrease or increase in their total numbers before, during, or after saline saturation. The transition crisscrossing points may be preexisting in a polymer and experience a significant decrease in their total numbers after saline saturation, or they may be established in a use situation and experience a significant increase in their total numbers during or after the saline saturation

The superabsorbent materials used in disposable honeycombs or other current personal hygiene products are generally a crosslinked polyelectrolyte highly insoluble in water but inflatable. For example, a high molecular weight sodium polyacrylate sai (Na-PA), crosslinked by either covalent bonds, tans corno -CC-, -CO-, -CN-, or ionic bonds, taies corno Al³⁺, Zr⁴⁺Faith³⁺Cr³⁺You³⁺, or Ce⁴⁺, they can absorb more than 40 grams of 0.9% saline NaCl per gram of the polymer when no external pressure is applied, or more than 20 grams of the saline solution per gram of the polymer when a pressure of 0.3 is applied pounds per square inch. Absorbency without pressure in the polymer is the capacity of free swelling, and that with pressure in it is absorbency under load (AUL).

<img file="AR037293A1_D0001.tif" />

In general, a polyelectrolyte, when slightly crosslinked, has a high free swelling capacity but a low absorbency value under load due to a lower gel stiffness. On the other hand, a polyelectrolyte, when highly crosslinked, has a lower free swelling capacity but a higher absorbency value under load. In order to have a maximum absorbency value under load, the current superabsorbent material has to sacrifice its free swelling capacity. This is only true when permanent crisscrossing points are formed in the superabsorbent material. While a gel with high but soft free swelling is not able to absorb liquid under pressure, it is capable of retaining significant amounts of liquid under pressure if the gel is allowed to swell first and then a load is applied.

Current commercially available superabsorbent materials are usually crosslinked by permanent cross-linking points through covalent bonds. In the art the use of metal ions is known (Al³⁺ or Zr⁴⁺) either as a surface or volume crosslinking agent. Within the same art, the addition of metal ions in the superabsorbent polymers is followed by a drying process. The drying process causes the resulting ionic bonds to be permanently crosslinked instead of being crosslinked.

Because the conventional superabsorbent material is incapable of simultaneously possessing high free swelling capacity and an absorbency under high load, it can be difficult to control the fluid absorption rate of the material. In addition, the process to make the material

<img file="AR037293A1_D0002.tif" />

surface cross-linking step or other modification processes in order to adjust fluid absorption rate, fluid distribution, and fluid intake.

There is a need or desire to have an absorbent material that can simultaneously possess high absorbent capacity and high absorbency under load.

SYNTHESIS OF THE INVENTION

In response to the difficulties described and the problems encountered in the prior art, a new absorbent composition has been discovered.

The present invention relates to a water-swellable, water-insoluble absorbent material that exhibits high free swell absorbency and high load absorbency (AUL). The absorbent material is particularly suitable for use in absorbent garments, honeycombs, learning briefs, adult incontinence products and feminine hygiene products.

The absorbent material is made of superabsorbent material with permanent cross-linking points and transition cross-linking points or transition crosslinker at the same time. As a result, the absorbent material of the invention has a free swelling absorbency of at least 15

<img file="AR037293A1_D0003.tif" />

<img file="AR037293A1_D0004.tif" />

g / g and a change in absorbency (whose detailed definition refers to the section Test method, below) greater than or equal to 15% over saturation due to the increase or decrease in the numbers of transition criss-cross points, even when the Conventional superabsorbent material without transition crisscross points exhibits a similar change less than 10%.

Unlike the permanent cross-linking points that exist in a polymer without experiencing a significant decrease or increase in their total numbers before, during, or after saline saturation, the transition cross-linking points may be pre-existing in the polymer and then undergo a process of dissociation with use, or they can be recently established in a use situation. Both the increase and the decrease in numbers of transition crisscrossing points occur only in situ in an absorbent product when the absorbent composition is saturated with body fluids, such as urine. In the present invention, a superabsorbent material can be crosslinked to a first degree by means of permanent cross-linking points in which degree it does not become crosslinked and has a very high free swelling capacity. The superabsorbent material can continue to be crosslinked to a second degree by means of an in situ transition crosslinker in an absorbent product after being saturated to which degree said material is very well crosslinked and has a very high absorbency value under load. This absorbent composition contains a formable transition crosslinker. Alternatively, in a use situation, the superabsorbent material can exhibit a high load absorbency value contributed by both types of cross-linking points and then further recover a high capacity of

<img file="AR037293A1_D0005.tif" />

Free swelling after saturation due to the dissociation of said transition crisscross points by a transition crisscrossing agent. This second type of absorbent composition contains removable transition crosslinker.

Both the first and the second type of transition crosslinking agents can be used in many ways with superabsorbent materials. For example, the transition crosslinking agents can be granular powder which can be mixed with conventional superabsorbent material. As a further example, the superabsorbent material or other components of the panai can be coated with the transition crosslinking agents, such as the coating, the flow layer, the erasure, or the bottom sheet. When a transition crosslinking agent is mixed with a superabsorbent material, it is important that the transition crosslinking agent is not reacting (or crosslinking) with the superabsorbent material. The two substances mix together only physically. No intersecting points are formed between them. To prevent the transition crosslinking agent from forming crosslinking points with the superabsorbent material, it is important to avoid any presence of water in the mixture or in the mixing processes, such as coating, agglomeration, combination, encapsulation, etc. . Water is capable of dissolving (or ionizing) the transition crosslinking agent to trigger a transition crosslinking reaction. The absorbent composition comprising a superabsorbent material and a transition crosslinker forming agent or a transition crosslinker removing agent must avoid any contact with any aqueous liquid in all preparation steps of

<img file="AR037293A1_D0006.tif" />

the production of the absorbent composition as well as the production of the absorbent product.

Suitable polymers for the absorbent material of the invention include polyelectrolytes or polymers which are capable of converting into polyelectrolytes through an ion exchange process or in situ neutralization. Examples of such polymers are (1) any anionic polymers and their respective polymers in acidic forms; (2) any cationic polymers and their respective polymers in base forms;

(3) mixtures of the two types of preceding polymers.

When a water-insoluble, water-swellable, acid-based polymer is used, a basic neutralizing agent is also used in order to achieve high absorbency. The basic neutralizing agent can be a water-insoluble, water-swellable polymer or an organic or inorganic compound whose base is not a polymer. When a water-insoluble, water-swellable basic polymer is used, an acid-neutralizing agent is also used in order to achieve high absorbency. The acid-neutralizing agent can be a water-insoluble, water-swellable polymer or an organic or inorganic compound whose base is not a polymer.

The polymers mentioned above are crosslinked, using a permanent crosslinking agent, to a degree that gives the polymers a high free swelling capacity but a low absorbency value under load. The appropriate permanent crosslinking agents

<img file="AR037293A1_D0007.tif" />

such as methylene bisacrylamide; (2) reactive crosslinking agents, such as dialdehydes, or diepoxides; (3) latent crosslinking agents, such as an organic compound having at least two functional groups or functionalities capable of reacting with the carboxyl groups (COO), carboxylic acid (-COOH), amino (· ΝΗ₂), or hydroxyl (-OH). Examples include, without limitation, diamines, polyamines, diols, polyols, dicarboxylic acid, polycarboxylic acid, and polyoxides. Another suitable crosslinking agent includes a metal ion with more than two positive charges, such as AL³⁺Faith³⁺, Ce³⁺, Ce⁴⁺You⁴⁺, Zr⁴⁺, and CR³⁺. In the case of cationic polymers, polyanionic substances are suitable crosslinking agents.

The proportion of permanent cross-links to transition cross-links can range in a wide range according to the total required absorbency of the final superabsorbent material. If extremely high free swelling is required, a lower amount of permanent crosslinking is needed. If an absorbency under extremely high load and a very firm swollen gel in the final product is required, a higher amount of permanent crosslinks is needed. The appropriate proportions of permanent crosslinks to transition crosslinks range from about 1: 9 to about 9: 1.

A considerable advantage of an absorbent material that has both intersecting, permanent and transitional, is the ability to have, at the same time,

<img file="AR037293A1_D0008.tif" />

Absorption of this material allows the material to provide a controlled fluid absorption rate as well as an improved fluid intake and distribution. Additionally, different crosslink densities can be created in different areas of a panai or other absorbent garment using only a superabsorbent. The absorbent composition of the invention can also simplify the superabsorbent process and reduce production costs, for example by eliminating the surface cross-linking step or other modification process. The absorbent composition may also provide greater flexibility in the product delivery, which may result in thinner products. Other potential benefits include improvements in gel stiffness and gel bed permeability.

In view of the foregoing, particular embodiments of the invention provide a water-insoluble, water-insoluble absorbent material that exhibits high free swell absorbency and high load absorbency (AUL).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an absorbent garment containing the absorbent composition of the invention.

Figure 2 illustrates the apparatus for determining the absorbency values ​​under load of an absorbent material.

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Within the context of this specification, each term or phrase given below will induce the following meaning or meanings.

Absorbency under load refers to the absorbency of a substance when a pressure of 0.3 pounds per square inch is applied to the substance.

Free swelling absorbency or free swelling ability refers to the absorbency of a substance when no pressure is applied to the substance.

Hydrolyzable bonds refers to bonds that can break when they come into contact with water, such as anhydrous bonds.

In situ reactive agent refers to a chemical that reacts in a situation of use, such as a chemical that can be mixed with other chemicals in a dry state and which after saturation forms transition crossing points.

Latent crosslinking agent refers to a reagent that does not crosslink a superabsorbent material in the polymerization process and that will crosslink it later when it is dry and adequate conditions are provided. Such conditions include, without limitation, heat, microwave, electron beam, UV, or any radiation of high energy, high humidity, and so on.

<img file="AR037293A1_D0010.tif" />

Permanent cross-linking points refers to the cross-linking points that are present in a polymer and that do not experience a significant decrease or increase in the total number of such cross-linking points before, during, or after saline saturation.

Polymers include, without limitation, homopolymers, copolymers, such as block, graft, alternating and random copolymers, terpolymers, etc. and mixtures and modifications thereof. In addition, unless specifically limited otherwise, the term polymer should include all possible geometric configurations of the material. These configurations include, without limitation, the isotactic, syndiotactic and atactic symmetries.

Polymerizable crosslinking agent refers to a reagent that contains more than one functional group that is polymerizable. For free radical polymerization, a reagent comprising more than one carbon-carbon double bond C = C is considered a polymerizable crosslinker, for example, methylene-bis-acrylamide.

Crosslinker reagent refers to a reagent that contains at least two functional groups capable of reacting with any pending group of a superabsorbent polymer. For example, when sodium polyacrylate is used, a reactive crosslinking agent can be chosen from a diol (butanediol) or a polyol (polyethylene glycol). A diol or a polyol forms ester bonds with carboxylic acid groups of the polyacrylate

<img file="AR037293A1_D0011.tif" />

of sodium. Said reactive crosslinking agent may also be chosen from a diamine (ethylene amine) or a polyamine (chitosan). A diamine or a polyamine forms amide bonds with carboxylic acid groups of sodium polyacrylate. Another example of said reactive crosslinking agent is a metal ion having at least three positive charges, for example, Al³*, Zr⁴⁺, Ce³⁺, Ce⁴⁺Faith³⁺, to form ionic bonds with carboxyl groups (-COO ') of sodium polyacrylate.

Supersorbent or superabsorbent material refers to an organic or inorganic water insoluble material, inflatable in water capable, under the most favorable conditions, of absorbing at least 15 times its weight and, more desirably, at least about 30 times its weight in an aqueous solution containing 0.9 weight percent sodium chloride. The superabsorbent materials may be polymers and modified natural, synthetic and natural materials. Additionally, the superabsorbent materials may be inorganic materials, such as silica gels, or organic compounds such as crosslinked polymers.

Transition crisscrossing points refers to crisscrossing points that are preexisting in a polymer before saturation and experience a significant decrease in the total number of such crisscrossing points after saline saturation, or crisscrossing points that are established. in a situation of use and also experience a significant increase in the total number of such crisscross points during or after saline saturation.

<img file="AR037293A1_D0012.tif" />

Trip dissociation links refers to the bonds that dissociate when triggered by a specific change in the environment surrounding the link, such as those links sensitive to changes in pH, ionic concentration, temperature, or humidity level

Trigger bonding refers to the bonds that are formed when triggered by a specific change in the environment surrounding a polymer, such as those bonds sensitive to changes in pH, ionic concentration, temperature, or temperature. humidity level

Water insoluble refers to a material that does not dissolve when exposed to water.

Water inflatable refers to a material that swells in size when exposed to water. The water-swellable material generally retains its original identity or physical structure, but in a highly expanded state, during water absorption and, therefore, must have sufficient physical integrity to resist flow and fusion with neighboring particles.

Weak links refers to bonds that can be easily broken, such as hydrogen bonds, or macromolecular physical interaction.

These terms can be defined with additional language in the remaining parts of the specification.

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DETAILED DESCRIPTION OF THE CURRENTLY PREFERRED EMBODIMENTS

The present invention relates to a water-insoluble, water-swellable absorbent composition that includes a superabsorbent material containing permanent cross-linking points and a transition crosslinker, or a superabsorbent material containing permanent and transitional cross-linking points and an agent of crisscross removal. Due to the presence of the transition crosslinker or transition crosslinking removal agent, the absorbent material has an absorbency value under load of at least 10 g / g, or at least 15 g / g, or at least 20 g / g, and a change in absorbency greater than or equal to 15% after saturation. Alternatively, the change in absorbency can be at least 20% after saturation, or at least 30% after saturation. In addition, in addition to the high absorbency under load, the absorbent material also has a high free swelling absorbency of at least 15 g / g, or at least 20 g / g, or at least 25 g / g.

The absorbent material of the present invention is particularly suitable for use in disposable absorbent articles, honeycombs, learning briefs, incontinence products, other personal hygiene products or health care garments, including medical garments , or the like. An example of a learning brief 20 that includes the absorbent material is shown in Figure 1.

<img file="AR037293A1_D0014.tif" />

The absorbent material of the invention includes a superabsorbent material (SAM) with transition cross-linking points and permanent cross-linking points. Permanent cross-linking points exist in a polymer without experiencing a significant decrease or increase in the total number of such cross-linking points before, during or after saline saturation. Transition crisscrossing points may exist in a polymer and experience a significant decrease in the total number of such crisscrossing points after saline saturation, or they may be established in a use situation and experience a significant increase in the total number. of such crisscrossing points during or after saline saturation.

In one embodiment of the invention, the superabsorbent material can be crosslinked to a first degree by means of permanent cross-linking points in which time the superabsorbent material does not reach the crisscross and has a very high free swelling capacity. This superabsorbent material that does not reach the crosslink is then mixed with a formable transition crosslinker to form the absorbent composition of this invention. The absorbent composition can continue crosslinking to a second degree by the transition crosslinker when a body fluid, such as urine, is in contact with the absorbent composition at which time the superabsorbent material is well crosslinked and has an absorption value under load. very high.

<img file="AR037293A1_D0015.tif" />

Appropriate formable transition crosslinks in this embodiment may include, without limitation, (1) reactive agents in situ, such as metal oxides, hydroxides, salts, and combinations of any of these, more specifically inorganic salts (AI₂(SW₄) 3, Fe2CI₃, Ce (SO₄)₂), ammonium zirconium carbonate (AZC), aluminum oxide (AI₂OR₃), zirconium oxide, aluminum hydroxide (AI [OH]₃), aluminum chloride (AICI₃), citric ammonium sulfate (Ce [NH₄]₄[SW₄]₄), or organic compounds (dialdehydes, diepoxides, chimene, moisture resistant resins), these chemicals can be mixed with polyacrylate superabsorbent material in a dry state (powder) and in the form of cross-linking points in situ to saturation; (2) shot formation links, as well as the bonds that are formed when triggered by changes in pH, ionic concentration, temperature, or humidity level. The key criterion of cross-linked taies of transition is that such bonds cannot be formed before the polymer is saturated and must be capable of forming cross-linking points between the polymer chains until the chains are fully swollen. If such crisscrossing points are formed before the polymer begins to swell, the polymer cannot achieve a high free swelling capacity.

In another embodiment, the superabsorbent material can exhibit a high absorbency value under load contributed by both types of cross-linking, permanent and transition points, and then additionally add a high capacity of free swelling to saturation due to dissociation

<img file="AR037293A1_D0016.tif" />

of the transition crisscross points by a transition crosslinker removal agent.

Appropriate removable transition crosslinks in this embodiment may include, without limitation, (1) weak bonds, such as hydrogen bonds or macromolecular physical interaction; (2) hydrolysable bonds, such as anhydrous bonds; or (3) the dissociation bonds per trip, as well as the links that dissociate when triggered by changes in pH, ionic concentration, temperature, or humidity level. For example, when a metal ion (for example, Al³⁺) is used to crosslink a superabsorbent material, a chelating agent such as a phosphate (for example, sodium phosphate) can be used to remove the unique bonds of Al³⁺ between the superabsorbent polymer chains. The key criterion for cross-linked taies of transition is that the bond has to be able to function as a crosslinked point until the neighboring molecular segments are fully swollen, and it also has to be able to dissociate during use within a certain amount of time. reasonable.

Suitable polymers for the superabsorbent material of this invention may include, without limitation, any polyelectrolytes or polymers which are capable of being converted into polyelectrolytes through in situ neutralization or ion exchange process. Examples of such polymers are (1) any anionic polymers and their respective polymers in acidic forms; (2) any cationic polymers and their

<img file="AR037293A1_D0017.tif" />

respective polymers in base forms; (3) mixtures of the two types of preceding polymers.

Water insoluble, water swellable, anionic (or acidogenic) polymers include functional groups that are capable of generating or being converted to anions. Such functional groups include, without limitation, the carboxyl groups, sulfonic groups, sulfate groups, sulphite groups, and phosphate groups. Suitably, the functional groups are carboxyl groups. Generally, the functional groups are coupled to a crosslinked base polymer. Suitable base polymers include polyacrylates, polyacrylamides, polyvinyl alcohols, ethylene maleic anhydride copolymer, polyvinyl ethers, polyacrylamide methylpropane sulfonic acid, polyacrylic acids, polyvinylpyrrolinol copolymerines, copolymerines thereof. Naturally based polysaccharide polymers can also be used; these include carboxymethyl celluloses, carboxymethyl starches, acrylic grafted celluloses, hydrolyzed starch grafted polyacrylonitriles, and copolymers thereof. Synthetic polypeptides can also be used, such as polyaspartic acid and polyglutamic acid.

Water insoluble, water swellable, cationic (or basic) polymers suitable include functional groups that are capable of generating or being converted to cations. Such functional groups include, without limitation, quaternary ammonium groups, primary, secondary, or tertiary amino groups, imino groups, imido groups, and amido groups. Appropriate functional groups are quaternary ammonium groups and

<img file="AR037293A1_D0018.tif" />

a crosslinked base polymer. Suitable base polymers include polyamines, polyethyleneimines, polyacrylamides, polyvinylamines, polydiallyl dimethyl ammonium hydroxide, polyquaternary ammoniums, and copolymers thereof. Naturally based polysaccharide polymers can also be used, including chitin and chitosan. Synthetic polypeptides can also be used, such as polyaspargines, polyglutamines, and polyarginines.

When a water insoluble polymer, swellable in acidic water is used, appropriately at least about 50 mole percent, or at least about 70 mole percent, or at least about 90 mole percent, or substantially around 100 percent molar, of the acid-forming functional groups of the acid-forming polymer are in free acid form. In order to achieve high absorbency, a basic neutralization agent is used, which can be a water insoluble polymer, water swellable or an organic or inorganic compound whose base is not a polymer. Examples of suitable basic neutralization agents include, without limitation, the basic polymeric materials such as polyamines, polyamines, polyamides, polyquaternary ammoniums, chitins, chitosans, polyaspargines, polyglutamines, polylysines, and polyarginines; basic organic materials such as organic salts, for example, sodium citrate, and aromatic and aliphatic amines, imines, and amides; the inorganic bases such as metal oxides, for example calcium oxides; hydroxides, for example, barium hydroxide; The taies salts as the

<img file="AR037293A1_D0019.tif" />

sodium carbonate and sodium bicarbonate; and combinations of any of these.

When a water-insoluble, water-swellable, basic polymer is used, appropriately at least about 50 mole percent, or at least about 70 mole percent, or at least about 90 mole percent, or substantially about 100 mole percent, of the basic functional groups of the basic polymer are in free base form. In order to achieve high absorbency, an acid-neutralizing agent is used, which can be a water insoluble polymer, water swellable or an organic or inorganic compound whose base is not a polymer. Examples of suitable acid-neutralizing agents include, but are not limited to, polymeric acid-like materials such as polyacrylic acid, polymaleic acid, carboxymethyl cellulose, alginic acid, poly-aspartic acid, and polyglutamic acid; the organic acidic material such as aromatic and aliphatic acids, for example, citric acid, glutamic acid or aspiric acid; and inorganic acids such as metal oxides, for example, aluminum oxide; and salts such as iron chloride, calcium chloride and zinc chloride; and combinations of any of these.

Any of the polymers mentioned above can be crosslinked using a permanent crosslinking agent to a degree that allows the polymer to have a high free swelling capacity but a low absorption value under load. Appropriate permanent crosslinking agents include, without limitation, crosslinking agents.

<img file="AR037293A1_D0020.tif" />

crosslinked reagents, such as dialdehydes for example, glutaraldehyde, or diepoxides, for example, diglycidyl ether of polyethylene glycol; latent crosslinking agents, such as an organic compound having at least two functional groups or functionalities capable of reacting with the carboxyl groups (-COO), carboxylic acid (-COOH), amino (-NH₂), or hydroxyl (-OH). Examples of such crosslinking agents include, without limitation, diamines, polyamines, diols, polyols, polycarboxylic acids and polyoxides. Another suitable crosslinking agent includes a metal ion with at least three positive charges, such as Al³⁺Faith³⁺, Ce³⁺, Ce⁴⁺You⁴⁺, Zr⁴⁺, and CR³⁺. In the case of cationic polymers, polyanionic substances are suitable crosslinking agents. Examples are sodium polyacrylate, carboxymethyl cellulose, and -PO₄³'.

The water-insoluble, water-swellable polymer included in the absorbent composition can generally have a wide range of molecular weights. A water-insoluble, water-swellable polymer having a relatively high molecular weight may be beneficial for use in the present invention. However, a wide range of molecular weights is generally suitable for use in the present invention. Water-insoluble, water-swellable polymers suitable for use in the present invention may appropriately have an average molecular weight greater than about 100,000 and up to about 10,000,000. The methods for

<img file="AR037293A1_D0021.tif" />

Determining the molecular weight of a polymer are known to experts in the art.

Transition crosslinking agents, described above, can be used in many ways with superabsorbent materials. For example, the transition crosslinking agents can be a granular powder, or other form of particle, and mixed with conventional superabsorbent material. In this case, the superabsorbent material and the transition crosslinking agent can be mixed either homogeneously or non-homogeneously (zoning). The homogeneous mixture is intended to achieve a uniform mixture of two particles. Each substance remains in its own domain or phase. A molecular level mixture of the superabsorbent material and the transition crosslinking agent is not achieved. In order to achieve the composition of this invention, it is important that two substances remain in their own phase before in situ saturation triggers a cross-linking reaction in an absorbent product. As another example, the crosslinked transition agents can be coated, mixed, printed, or encapsulated in superabsorbent material or other components of the absorbent article, such as a coating, flow layer, erasure, or a lower sheet (see Figure 1).

The proportion of the permanent cross-linking points to the transition cross-linking points can range in a wide range according to the total required absorbency of the final superabsorbent material. If extremely high free swelling is desired, a smaller amount of permanent cross-linking points is used. If an absorbency under load is desired

<img file="AR037293A1_D0022.tif" />

use a higher amount of permanent cross-linking points. Appropriately, the ratio of the permanent cross-linking points to the transition cross-linking points is between about 1: 9 and about 9: 1, or between about 2: 8 and about 8: 2, or between about 3: 7 and around 7: 3.

As mentioned, the absorbent material of the invention appropriately has a free swelling absorbency of at least 15 g / g. The test method to determine the free swelling absorbency is described below. Additionally, the absorbent material of the invention appropriately has an absorbency under load (AUL) value of at least 15 g / g. The test method for determining absorbency under load is described below. Also previously mentioned, the absorbent material of the invention has a change in absorbency greater than or equal to 15% at saturation due to an increase or decrease in the numbers of the cross-linking points. In comparison, the conventional superabsorbent material without the transition crisscross points exhibits a similar change of less than 10%.

Conventional superabsorbent material is produced by synthesizing acrylate monomer in an aqueous solution and then drying the formed gel. The dried superabsorbent material is then ground in a particulate form for use in an absorbent product. Commercially available superabsorbent taies have little change in absorbency when they undergo a rewetting and drying process due to the lack of change in

<img file="AR037293A1_D0023.tif" />

Uæê&gt; '- A:. iWisa .. ...... 'intersecting points. On the other hand, if the absorbent composition comprising a transition crosslinking agent or a transition crosslinker removal agent contacts the water or a liquid containing water and then dries before use in the absorbent product, the Composition exhibits a large change (either an increase or a decrease) in absorbency compared to the current commercially available superabsorbent. The change occurs for two reasons: (1) an increase or decrease in total cross-linking points due to the formation or removal of transition cross-linking points; or (2) the transformation of transition crisscross points to permanent crisscross points. The effect of permanent cross-linking points on absorbency is different from that of transition cross-linking points.

In general, absorbency is reduced when any type of cross-linking points increases. However, transition crisscrossing points have a much smaller effect on absorbency than permanent crisscrossing points. For example, when using Al³⁺ As a transition crosslinker and mixed with sodium polyacrylate gel, the mixture exhibits a reasonably higher absorbency when saturated with the saline solution, but a much lower absorbency when the mixture is exposed to water, dried and then saturated with the solution. saline. This is because the Al ions³⁺ They form transition crisscrossing points with sodium polyacrylate when the mixture is saturated once, while the ions form permanent crisscrossing points when the mixture is re-saturated after completely drying the first saturation. The process

<img file="AR037293A1_D0024.tif" />

of permanent crosslinking. Therefore, it is possible to measure the change in absorbency between a first saturation and a second saturation to indicate the existence of transition crossing points. When the change in absorbency is greater than 15%, this indicates that the absorbent composition contains a transition crosslinker or a transition crosslinker removal agent.

The examples provided below demonstrate the effect of transition crosslinkers on absorbency under load and free swell absorbency values ​​(zero load absorbency - AUZL), as well as the dissociation of transition crisscross points in a use situation , the transport properties of the various superabsorbent materials within the compositions with superabsorbent placed with air / clear, and the absorbency change data for a number of absorbent materials.

The presence of both types of cross-linking, permanent and transition points in the absorbent composition of the invention results in an absorbent material having a high free swelling absorbency and at the same time a high absorbency under load. The absorbent composition also exhibits other benefits, which include a controlled fluid absorption rate, as well as an improved fluid distribution, intake, gel stiffness, and gel bed permeability. Also, by applying the transition crosslinking agent (s) at various densities between different areas of the superabsorbent material or the compound containing material

<img file="AR037293A1_D0025.tif" />

superabsorbent having a certain degree of permanent crosslinking density, various densities of the total crosslinking points within a single absorbent article can be achieved using a single superabsorbent material.

Examples

Example 1

In order to form transition crisscrossing points in use, Hoechst Celanese's superabsorbent merchant, designated as IM 1000 P, a crosslinked sodium sai grafted with polyacrylic acid starch, was mixed with various amounts of a transition crusader, the Zirconium Ammonium Carbonate (AZC) commercially available from Magnesium Elektron, Ine .. Since the ammonium zirconium carbonate was in the form of a solution, it was previously dissolved in 25 milliliters (ml) of 0.9% NaCl test saline by weight and then the absorbency of the IM 1000 P in the saline solution was evaluated. Table 1 shows the absorbent properties of IM 1000 P and IM 1000 P / AZC. Without ammonium zirconium carbonate, the IM 1000 P has a very high zero absorbency (AUZL) but a very low absorbency value at 0.3 psi. Test methods to determine absorbency under zero load and absorbency under load are described below. As can be seen from the results in Table 1, the incorporation of transition crosslinkers (ammonium zirconium carbonate) significantly increases absorbency under load to 0.3 psi and slightly reduces absorbency values ​​under zero load.

<img file="AR037293A1_D0026.tif" />

Table 1: IM 1000 P absorbent properties with various levels of ammonium zirconium carbonate

<td>Absorbency Test</td><td colspan="6">Amount of 40% AZC solution pre-dissolved in 25 ml of 0.9% NaCl Saline</td>

<td></td><td>og</td><td>0.05 g</td><td>0.10 g</td><td>0.20 g</td><td>0.50 g</td><td>1.00g</td>

<td>AUZL (g / g)</td><td> 50,4</td><td> 46,5</td><td> 42,1</td><td> 39,0</td><td> 39,7</td><td> 43,5</td>

<td>AUL at 0.3 psi (g / g)</td><td> 11,4</td><td> 18,2</td><td> 19,2</td><td> 20,1</td><td> 20,1</td><td> 21,9</td>

Example 2

In order to form the transition crisscrossing points in use, the IM 1000 P was mixed with various amounts of a solid transition crisscler, citric ammonium sulfate (CAS: Ce [NH₄]₄[SO4] 42H₂O) commercially available at Mallinckrodt located in San Louis, Missouri, United States of America. The mixtures were evaluated in absorbency tests under zero load and absorbency under load at 0.3 psi in 0.9% NaCl saline. Table 2 shows the test results. Once again, without the serum ammonium sulfate, the IM 1000 P had very high absorbency values ​​under zero load but very low absorbency values ​​under load at 0.3psi. As can be seen from the results in Table 2, the incorporation of transition crosslinkers (serum ammonium sulfate) significantly increases the absorbency values ​​under load to 0.3 psi and slightly reduces the absorbency values ​​under zero load.

Table 2: Absorbent properties of IM 1000 P with various levels of serum ammonium sulfate

<img file="AR037293A1_D0027.tif" />

<td>Absorbency Test</td><td colspan="6">Amount of Ce [NH4] 4 [SO4j42H2O per gram of IM 1000 P</td>

<td></td><td>og</td><td>0.0005 g</td><td>0.001 g</td><td>0.005 g</td><td>0.01 g</td><td>0.02g</td>

<td>AUZL (g / g)</td><td> 50,2</td><td> 45,3</td><td> 44,6</td><td> 40,2</td><td> 37,4</td><td> 34,7</td>

<td>AUL at 0.3 psi (g / g)</td><td> 11,4</td><td> 11,3</td><td> 10,9</td><td> 13,7</td><td> 19,5</td><td> 23,8</td>

Example 3

In order to demonstrate the removal of the transition crisscrossing points in use, 3.75 grams of 40% ammonium zirconium carbonate solution was dissolved in 2000 grams of distilled water and 100 grams of IM 1000 P were added. The solution was stirred and all the liquid was absorbed by the IM 1000 P within a few minutes. The swollen IM 1000 P was dried in a homo at 60 ° C overnight and the dry IM 1000 P was sieved to particles of 300 to 600 microns. The particles were heat treated at 200 ° C for 4 hours. The heat-cured IM 1000 P was tested for absorbency under zero load and absorbency under load in 0.9% NaCI saline solution containing different amounts of Na saline solution₃PO₄ 1% pre-dissolved (Na₃PO₄ it is previously dissolved in 0.9% NaCl saline solution at a weight ratio of 1 to 99). Two commercial superabsorbent materials, IM 1000 P and Favor 880, available from Stockhausen Inc., were used as controls for these tests. Table 3 summarizes the results of this study.

<img file="AR037293A1_D0028.tif" />

As can be seen from the results in the table, the transition crosslinking removal agent, Na₃PO₄, remove the Zr ionic transition crisscross points⁴⁺ to increase absorbency, while Na₃PO₄ reduces the absorbency of the conventional superabsorbent material due to the effect of high concentration of sai.

Table 3: Absorbent properties of crosslinked ammonium zirconium carbonate IM 1000 P with various levels of Na₃PO₄

<td>SAM</td><td>Interviewer of transition</td><td>Test absorbency</td><td colspan="6">Quantity (grams) of 1% NA3PO4 in 15 ml of solution saline</td>

<td></td><td></td><td></td><td> 0</td><td> 0,25</td><td> 0,50</td><td> 0,75</td><td> 1,00</td><td> 1,50</td>

<td>IM1000P</td><td>Any</td><td>AUZL</td><td> 50,2</td><td> 46,7</td><td> -</td><td> 46,3</td><td></td><td> 46,5</td>

<td></td><td></td><td>AUL</td><td> 11,4</td><td> 10,0</td><td> -</td><td> 8,6</td><td></td><td> 8,7</td>

<td>IM 1000 P</td><td>1.5% AZC</td><td>AUZL</td><td> 28,4</td><td> 28,3</td><td> 29,3</td><td> 30,7</td><td> 31,5</td><td> 32,6</td>

<td></td><td></td><td>AUL</td><td> 24,1</td><td> 23,9</td><td> 23,9</td><td> 24,9</td><td> 25,8</td><td> 26,1</td>

<td>Please 880</td><td>Any</td><td>AUZL</td><td> 31,4</td><td> 27,5</td><td> -</td><td> 28,3</td><td></td><td> 27,8</td>

<td></td><td></td><td>AUL</td><td> 29,8</td><td> 25,9</td><td> •</td><td> 24,8</td><td></td><td> 24,8</td>

Example 4

In order to dissociate the transition crisscrossing points in use, 27 grams (g) of acrylic acid, 0.065 grams of K2S₂OR₈0.108 grams of N, N'methylene bis-acrylamide (MBA) and 175 grams of distilled water were added to a 500 milliliter bottle and mixed at room temperature

<img file="AR037293A1_D0029.tif" />

to form a completely dissolved solution. The bottle was then immersed in a barium of water at 60 ° Celsius for several hours and constantly stirred inside the barium. The polyacrylic acid gel was formed and cut into _ inch cubes that were added in a previously prepared solution that has 7.5 grams of NaOH and 500 grams of water. The polyacrylic acid gel after this step had a degree of neutralization of about 50 mole percent and was then dried at 80 ° Celsius and ground in particles. The particles were heated 160² at 200 ° Celsius to induce anhydride bonds between the crosslinked carboxylic acid groups as transition. The particles were mixed with sodium bicarbonate powder at a weight ratio of 1 gram of the polymer to 0.23 or 0.46 grams of bicarbonate. The additional bicarbonate brought the total degree of neutralization to 70% or 90% and may also have provided a slightly basic condition which could have helped dissociate the anhydride bonds. The absorbent properties of the treated polymer were evaluated in 0.9% saline NaCl. Table 4 shows the results of the tests (absorbency data were measured for 10 hours).

Table 4: Absorbent properties of treated polymer

<td>Degree of neutralization of</td><td>PA / NaHCO3</td><td>T treatment with</td><td>AUZL</td><td>AUL at 0.3 psi</td>

<td>polyacrylate gel</td><td>(g / g)</td><td>heat (° C / minutes)</td><td>(g / g)</td><td>(g / g)</td>

<td> 70%</td><td> 1/0,23</td><td>Not heated</td><td> 39,2</td><td> 10,5</td>

<td></td><td></td><td> 200/60</td><td> 40,5</td><td> 13,2</td>

<td></td><td></td><td> 200/120</td><td> 40,1</td><td> 14,1</td>

<td> 90%</td><td> 1/0,46</td><td>Not heated</td><td> 50,8</td><td> 12,3</td>

<img file="AR037293A1_D0030.tif" />

<td></td><td></td><td> 1 60/240</td><td> 50,6</td><td> 17,8</td>

<td></td><td></td><td> 200/60</td><td> 51,2</td><td> 18,6</td>

<td></td><td></td><td> 200/120</td><td> 50,4</td><td> 19,2</td>

Example 5

The air-borne superabsorbent compounds, which include 37% superabsorbent powder and 63% wood pulp eraser and have a total base weight of 500 grams per square meter (g / m²), were made using both superabsorbents, the current commercial superabsorbent Favor 880, available from Stockhausen GmbH &amp; Co. located in Krefeld, Federal Republic of Germany, and the previous commercial superabsorbent IM 1000 P, and a commercially available wood pulp eraser in US Alliance, Childersburg, Alabama, United States of America, under the trade designation CR1654. The compounds were densified to a density of about 0.2 g / cm³. An inclined transport test (refer to European Patent 0 532 002 A1 for detailed information on the Inclined Transport Test) was performed on the densified compounds (inclination angle: 30 °, test time: 1 hour, 30 minutes) . Runoff distance and capacity as parameters to characterize transport properties were recorded. The results are shown in table 5.

Table 5: Runoff properties of superabsorbent compounds placed with air / clear

<img file="AR037293A1_D0031.tif" />

<td>Composition</td><td>Test fluid</td><td>Transport distance (cm)</td><td>Capacity of transport (g / g)</td>

<td>37% IM 1000 P / 63% CR1654</td><td>0.9% NaCl</td><td> 12,1</td><td> 8,3</td>

<td>37% IM 1000 P / 63% CR1654</td><td>0.9% NaCI / AZC *</td><td> 19,6</td><td> 13,5</td>

<td>37% Please 880/63% CR1654</td><td>0.9% NaCl</td><td> 21,5</td><td> 12,5</td>

* AZC is pre-dissolved in 0.9% NaCl saline solution at a rate of 0.5 g of 40% AZC to 25 ml of 0.9% NaCl saline solution

Example 6

In order to demonstrate that an absorbent composition comprising transition crisscross points exhibits a greater change in absorbency than that comprising only permanent crisscrossing points, conventional superabsorbent materials (DRYTECH 2035, commercially available from Dow Chemical Co., Midland, Michigan, United States of America) and the absorbent compositions of this invention were selected and their absorbency change values ​​were measured according to the test methods described below. The results are shown in Table 6. As can be seen from the results in Table 6, the absorbent compositions comprising removable or formable transition crisscross points exhibit a change value.

<img file="AR037293A1_D0032.tif" />

(, Μ ·;: i ''

9&gt; 3 absorbency, either absorbency under zero load or absorbency load, greater than 15%.

Table 6: Absorbency Change Data

<td>Super absorbent / Transition Interrogator / Removal agent</td><td colspan="2">Absorbency (g / g) before treatment</td><td colspan="2">Absorbency (g / g) after the treatment</td><td colspan="2">Change in absorbency (%)</td>

<td></td><td>AUZL</td><td>AUL at 0.3 psi</td><td>AUZL</td><td>AUL at 0.3 psi</td><td>AUZL</td><td>AUL at 0.3 psi</td>

<td>* Please 880</td><td> 31,4</td><td> 29,8</td><td> 33,6</td><td> 27,4</td><td> + 7,0</td><td> -8,1</td>

<td>* Drytech 2035</td><td> 29,5</td><td> 28,6</td><td> 30,2</td><td> 26,5</td><td> + 2,4</td><td> - 7,3</td>

<td>* IM 1000 P</td><td> 50,4</td><td> 11,4</td><td> 48,6</td><td> 10,9</td><td> -3,6</td><td> - 4,4</td>

<td>IM 1000 P / 40% AZC</td><td> 39,7</td><td> 20,1</td><td> 15,4</td><td> 12,8</td><td> - 61,2</td><td> - 36,3</td>

<td>IM 1000 P / 9% AICl3</td><td> 38,3</td><td> 23,2</td><td> 14,2</td><td> 13,6</td><td> - 62,9</td><td> - 41,4</td>

<td>IM 1000 P / 6% CE [NH₄] 4 [SO4] 4</td><td> 37,4</td><td> 19,5</td><td> 13,2</td><td> 10,1</td><td> - 64,7</td><td> - 48,2</td>

<td>IM 1000 P / 1.5% AZC &amp; 200 ° C for 4 hours / 6% Na3PO₄</td><td> 31,5</td><td> 25,8</td><td> 45,6</td><td> 15,2</td><td> + 44,8</td><td> -41,1</td>

<td>* PAA-NaHCC&gt; 3 / not heated</td><td> 50,8</td><td> 12,3</td><td> 50,1</td><td> 11,9</td><td> -1,4</td><td> - 3,3</td>

<td>PAA-NaHCC&gt; 3/200 ° C for 2 hours</td><td> 50,4</td><td> 19,2</td><td> 49,8</td><td> 13,2</td><td> - 1,2</td><td> - 31,3</td>

Note: * It is not an example of the invention

TEST METHOD TO DETERMINE CROSSED

TRANSITION AND CHANGE OF ABSORBENCE

<img file="AR037293A1_D0033.tif" />

Place 10 grams of an absorbent composition comprising a superabsorbent material (either conventional superabsorbent material or the superabsorbent material that has removable or formable transition crosslinks) in a 500 milliliter beaker and add 250 grams of distilled water with stirring. After the superabsorbent absorbs all the water, dry the superabsorbent in a homo at 50 ° Celsius until the superabsorbent is completely dry. Grind the dried superabsorbent into particles. The particles measuring 300 to 600 microns are used to evaluate the absorbent properties. Absorbency under zero load and absorbency under a load of 0.3 pounds per square inch are used to assess the change of absorbency before and after treatment. It is believed that the permanent cross-linking points should have little change but the transition cross-linking points should have a significant change after the previous treatment (either formed or removed).

The amount of transition crosslinks can be quantified by the absorbency change value. The change of absorbency is the change of absorbency to saturation, and can be defined by the percentage of increase or decrease in absorbency values ​​under zero load or absorbency under load of a superabsorbent before and after the treatment described herein. precedent in this test method. The higher the change in absorbency (either increase or decrease), the more transition crisscrossing points the superabsorbent has.

<img file="AR037293A1_D0034.tif" />

TEST METHOD FOR DETERMINING ABSORBENCE UNDER LOAD (AUL)

Absorbency under load (AUL) is a test that measures the ability of an absorbent material to absorb a liquid (such as a 0.9 percent by weight solution of sodium chloride in distilled water) while under a load or applied restrictive force. With reference to figure 2, the apparatus and method for determining the absorbency under load are described. A perspective view of the device in position is shown during a test. A laboratory lever 1 is shown having an adjustable pen 2 to raise and lower the platform 3. A laboratory support 4 holds a spring 5 connected to a measuring probe of modified thickness 6, which passes through the box 7 of the meter, which is strictly supported by laboratory support. A plastic sample cup 8, which contains the sample of superabsorbent material to be tested, has a liquid permeable bottom and rests inside a Petri piato 9, which contains the saline solution that will be absorbed and optionally a removal agent or A transition crusader. A weight 10 rests on top of a separator disk (not visible) placed on top of the sample of superabsorbent material (not visible).

The sample cup consists of a plastic cylinder that measures 1 inch inside diameter and an outside diameter of 1.25 inches. The bottom of the sample cup is formed by adhering a net metal screen 100 that has 150 micron openings to the end of the cylinder by heating the screen above the melting point of the plastic and pressing the plastic cylinder

<img file="AR037293A1_D0035.tif" />

against the hot screen to melt the plastic and join the screen to the plastic cylinder.

The modified thickness gauge used to measure the expansion of the sample while absorbing the saline solution is a Mitutoyo digimatic indicator, IDC series 543, model 543-180, which has a range of 0-0.5 inches and a precision of 0, 00005 inches (Mitutoyo Corporation, 31-19, Shiba 5chome, Minatoku, Tokyo 108, Japan). Such as is supplied by Mitutoyo Corporation, the thickness gauge contains a spring attached to the probe inside the measurement box. This spring is removed to provide a freely falling probe which has a downward force of about 27 grams. Additionally, the cap on the top of the probe, located above the meter housing, is also removed to allow coupling of the probe to the suspension spring 5 (available from McMasterCarr Supply Co., Chicago, Illinois, article No. 9640K41), which serves to reduce or counteract the downward force of the probe to about 1 gram. A wire hook can be attached to the top of the probe to attach to the suspension spring. The lower tip of the probe is also provided with an extension needle (Mitutoyo Corporation, No. 131279) to allow the probe to be inserted into the sample cup.

To carry out the test, a sample of 0.160 grams of the absorbent material, which has been screened at a particle size between

300 and 600 microns, it is placed in the sample cup. The sample is then covered with a plastic separator disk, which weighs 4.4 grams, which is slightly smaller than the inside diameter of the sample cup and serves

<img file="AR037293A1_D0036.tif" />

to protect the sample so that it is not altered during the test. The weight of 100 grams is then placed on top of the separator disk, so a load of about 0.3 pounds per square inch is applied. The sample cup is placed in the petri dish on the platform and the laboratory lever is raised until it makes contact with the probe tip. The meter is set to zero. A sufficient amount of saline solution is added to the Petri piato (15 to 25 milliliters) to begin the test. The probe measures the distance at which weight 10 is raised by expanding the sample as it absorbs the saline solution. This distance, multiplied by the cross-sectional area within the sample cup, is a measure of the volume of expansion of the sample due to absorption. By factoring the density of the saline solution and the weight of the sample, the amount of saline absorbed is easily calculated. The weight of the saline absorbed after 60 minutes is the absorbency value under load expressed in grams of saline absorbed per gram of absorbent. If desired, the modified thickness meter readings can be continuously entered into a computer (Mitutoyo Digimatic DP-2 DX Miniprocessor) to make the calculations and provide absorbency readings under load. As a cross-analysis, absorbency under load can also be determined by establishing the difference in weight between the sample cup before and after the test, where the difference in weight is the amount of solution absorbed by the sample.

TEST METHOD FOR DETERMINING LOW ABSORBENCE

ZERO LOAD (AUZL)

<img file="AR037293A1_D0037.tif" />

The same procedure used to determine the absorbency under load, described above, is used to determine the absorbency under zero load, except that a weight of 100 grams is not used (article 10 in Figure 2). The zero load absorbency is used in this invention to represent the free swelling capacity of an absorbent composition.

It will be appreciated that the details of the above embodiments, given for illustrative purposes, should not be considered as limiting the scope of this invention. While only a few exemplary embodiments of this invention have been described in detail in the foregoing, those skilled in the art will readily appreciate that it is possible to make many modifications to the exemplary embodiments without materially departing from the novel advantages and teachings of this invention. Therefore, said modifications are intended to be included within the scope of this invention, which is defined by the following claims and all equivalents thereof. In addition, it is recognized that many embodiments can be conceived that do not achieve all the advantages of some embodiments, particularly preferred embodiments, however, the absence of a particular advantage should not be interpreted as necessarily meaning that said embodiment is outside. of the scope of the present invention.