SK8932000A3 - Absorbent article containing superabsorbent material - Google Patents

Abstract

Absorbent structure in an absorbent article such as a diaper, sanitary napkin, incontinence guard, wound dressing, bed protection, etc., said structure containing a superabsorbent material possibly in combination with other absorption- or carrier materials and where the superabsorbent material has a content of renewable and/or biodegradable raw material of at least 20 % by weight, calculated on the dry weight of superabsorbent material, and has a phase angle delta </=8 DEG defined as the phase shift between deformation and strain measured at rheological measurements.

Description

Technical field

The present invention relates to an absorbent structure in an absorbent article such as a diaper, sanitary napkin, wound dressing, bed pad, etc., wherein said structure comprises a superabsorbent material, preferably in combination with other absorbent and / or carrier materials, and wherein the superabsorbent material comprises a replaceable or bio base material which constitutes at least 20% by weight, calculated on the dry weight of the superabsorbent material.

BACKGROUND OF THE INVENTION

The superabsorbent material may take a particular form, e.g. granular, granular, flaked or fibrous, or may be in the form of a fine fiber, foam or fiber coating, and has a great ability to absorb fluids such as water, body fluids, such as urine or blood, while swelling and forming a water-insoluble gel.

The so-called superabsorbents are cross-linked polymers that have the ability to absorb liquid in several times, 10 times or more of their bulk. They also have the ability to retain fluid even when subjected to external pressure. They are mostly used in sanitary articles such as baby diapers, incontinence aid, sanitary napkins and the like, and usually have a particular shape such as grains, granules, flakes or fibers and blend or layer with other absorbent material, such as cellulose fiber.

Superabsorbents are usually cross-linked polymers with different chemical compositions. Commonly occurring suberabsorbents are cross-linked polyacrylates. Acrylic acid and polyacrylates are synthetic products based on a crude oil material, for example a non-reproducible crude material. However, increasing environmental concerns call for a change to materials based on renewable and / or biodegradable raw materials. This applies in particular to disposable products which are discarded after use. Polysaccharides such as cellulose and starch are examples of materials that are both biodegradable and renewable and can be used as starting materials for

13409 superabsorbents. Other examples of useful polysaccharides are xanthan, alginate, chitosan, pectin, guar gum. Proteins and peptides are also examples of renewable polymers. The performance of a particular superabsorbent in an absorbent article depends on many factors, such as where and how the superabsorbent is mixed into the absorbent structure, particle shape, particle size, and physical and chemical properties such as absorption capacity, gel strength, and fluid acquisition capacity.

A phenomenon called gel blocking may have a negative effect on the absorption capacity, for example in a fiber structure containing superabsorbents. Gel blocking means that the superabsorbent particles upon wetting form a gel that blocks pores in the fiber structure or between the particles, thereby blocking the transport of fluid from the soaked area to the remainder of the absorbent particles and the transport of fluid to all particles. This phenomenon also involves poor utilization of the full absorbent capacity of the absorbent mass and creates the risk of fluid leakage.

High gel strength - cross-linking of the superabsorbent results in a reduced risk of a phenomenon called gel blocking. However, too high gel strength results in too low absorption capacity. By gel strength is meant the susceptibility to gel deformation. This is measured in rheometers and is calculated as the ratio between (a) the cut / deflection pressure applied to the sample and (b) the relative deflection / deflection pressure displayed by the sample. The chopping modulus, G ', is measured by the unit Pa. This is described in Example EP-B-254 476.

Another common procedure for characterizing superabsorbent and its capacity to function in an absorbent article such as a diaper, incontinence aid, sanitary napkin, and the like is to measure its ability to absorb fluid under pressure, the so-called absorbent. AUL (absorption under load). This is exemplified in EP-B 0,339,461. Here, in a special device, the ability of a superabsorbent to absorb a saline solution according to so-called &quot; requirements for the principle of absorbency under a certain load, usually 2 kPa, which is a standard load for this technical field.

Other common measurement parameters are free swelling capacity (FSC), which is measured as (g) absorbed fluid per (g) superabsorbent, while this is allowed to swell freely and the ability to retain fluid after centrifuging, centrifuge hold capacity (CRC). According to the latter method, the superabsorbent can absorb fluids freely up to the saturation point, after which the sample is centrifuged and subsequently the amount of absorbed fluid that is retained after centrifugation is measured.

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However, none of these processes characterizing the properties of the superabsorbent shows the whole truth and is not always related to the performance of the superabsorbent in concept with the product. This is particularly true of superabsorbents based wholly or partially on renewable and / or biodegradable raw materials, which typically have a low AUL value and a low gel strength and where neither AUL or any of the above measurement procedures is a good criterion for superabsorbent performance in the absorbent article.

SUMMARY OF THE INVENTION

OBJECTIVE AND MOST IMPORTANT FEATURES OF THE INVENTION. It is an object of the present invention to provide an absorbent structure for an absorbent article of the above type, wherein the absorbent structure comprises superabsorbent material entirely or partially based on renewable and / or biodegradable raw materials, and which shows very good performance in the absorbent structure measured.

According to the invention, this is achieved by the fact that the superabsorbent material has a phase angle δ <8 °, defined as the phase shift between the deformation and the strain measured in rheological measures.

The superabsorbent material preferably has a phase angle δ <6 °, preferably <4 ° and most preferably <3 °.

The superabsorbent material should preferably have a renewable and / or biodegradable raw material content of at least 40, preferably at least 60, and most preferably at least 80% by weight calculated on the dry weight of the superabsorbent material.

Alternatively, the superabsorbent material comprises a cross-linked polymer, wherein the polymer is based on a renewable and / or biodegradable raw material, and the cross-linked agent is either renewable and / or biodegradable or non-renewable / non-biodegradable.

The absorbent structure may, according to an embodiment, comprise a combination of hydrophilic fibers and a superabsorbent material, wherein the hydrophilic fibers are preferably fluff pulp, tissue or hydrophilic synthetic fibers and the absorbent structure comprises between 5 and 80% by weight of superabsorbent material calculated on the total weight of the structure.

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In another embodiment, the absorbent structure comprises a combination of absorbent foam material and superabsorbent material.

In yet another embodiment, the superabsorbent material is in the form of a foam and, in another embodiment, it is in the form of a coating on the fibrous material.

The superabsorbent material may have a relatively low absorptive capacity under load (AUL), more specifically no more than 25, preferably no more than 20, and most preferably no more than 18 ml of an aqueous solution containing 0.9% by weight sodium chloride per g of superabsorbent material under load. kPa.

The purpose of the absorbent structure of the invention is to use it in an absorbent article of the kind comprising a liquid-permeable thin skin layer, a liquid-impermeable bottom thin layer and an absorbent structure applied therebetween. The absorbent article may be a diaper, a sanitary napkin, an incontinence aid, a wound dressing, a bed liner, and the like. Of course, the shaping and construction of the absorbent article is entirely optional and the invention can be applied to all kinds of such articles.

Increasing environmental enthusiasm has resulted in efforts to replace materials in absorbent articles, e.g. baby diapers that are based on non-renewable / non-biodegradable raw materials with those materials that are wholly or partially based on renewable and / or biodegradable raw materials. The materials discussed are in the form of liquid-impermeable thin films, in the form of a plastic thin film, and in the form of liquid-permeable thin films, in the form of non-woven fabrics and superabsorbents.

Superabsorbents based on renewable and / or non-renewable raw materials such as starch, cellulose, alginate, etc. often have low gel strength and low AUL. It has been shown in tests conducted that those superabsorbents having substantially the same FSC (free swelling capacity), CRC (centrifugal holding capacity) and AUL values can have very different absorption capacity when combined with hydrophilic fibers, usually pulp fluff. , in the absorbent structure. The inventors of the present invention have therefore searched for another parameter showing a clear correlation with the absorbent capacity of supercrabsorbent when incorporated into an absorbent structure, since it is intended to incorporate it into an absorbent article such as a diaper.

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Rheology is the science of deformation and movement properties by material. The term rheology encompasses all material deformation that occurs when subjected to pressure, both normal gravity and higher pressures, if necessary. Rheology deals with the relationship between PRESSURE, DEFORMATION and TIME.

When the entire energy of deformation develops as heat in the material, it is referred to as VISCOSE and it is said that the material is moving. In the case where all the deformation energy is stored in the material, the material is referred to as elastic and there is no movement. A material in which a portion of the deformation energy is stored and a portion is decomposed as heat is termed viscous-elastic.

For measurements of viscose-elastic material, the material is stressed to a sinusoidal deformation (or deformation, depending on the type of tool to be used) and sinusoidal deformability (or stress) in the material is measured. The phase shift between deformation and stress is called the phase angle δ. This has a value of 0 ° for an ideal elastic material and 90 ° for an ideal viscous material.

When creating vector analyzes of stress / strain relationship, element G 'is obtained in the deformation phase and element G', 90 ° compensation in the deformation phase.

The higher the values of the modules G ' According to the aforementioned EP-B-254 476, it is the module G 'to be measured which, as the invention has proved, is unsuitable for the purpose of predicting the function of the superabsorbent in the absorbent structure.

Examples of a particular embodiment of the invention

Now, in accordance with the invention, we show that it is the phase angle δ, defined as the tangent δ = G'7G ', which is a parameter that shows a clear correlation with the properties of the superabsorbent in the concept of the absorbent structure. Those superabsorbents having a value of δ <8 ° exhibit particularly good product performance in the form of absorption capacity and degree of entrapment. It is particularly surprising that this also applies to superabsorbents having as low an AUL value as 10 g / g at 2 kPa, which is evident from Table 1 below.

Rheological measurements are carried out on a Carri Med CSL ²¹⁰⁰ from TA Instruments. Rcomctcr is a “regulated pressure” tool. Measurements shall be made according to

13409 established medical procedures, so the person skilled in the technology should be able to easily repeat the measurements.

For all measurements, the materials are prepared in the form of samples according to the following principle: 1 g absorbent material per 20 g synthetic urine. In order to test the materials at equilibrium during the swelling process, the mix + synthetic urine sample may stand for 2 hours before testing, but within 6 hours as the mix was prepared.

The measurement is divided into two steps. "Pressure expansion" defining the linear region of the material. A linear viscose-elastic region occurs when the deformation is so small that the material only changes insignificantly from its equilibrium position. From this linear position, the chopping pressure at which the material is tested in the upcoming frequency spread is selected. From the spreading of the frequency 01-10 Hz the quantities G ', G' and δ are obtained. All G ', G' and δ-values shown in the table below were obtained at 1.13 Hz.

The superabsorbent based on the renewable raw material to be tested was a number of test substances based on cross-linked CMC (carboxymethyl cellulose): A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, All, A12 , A13 and A14. The preparation of superabsorbents based on cross-linked CMC is described in Example EP-B-201 895. Some test substances based on cross-linked carboxymethyl starch: B1, B2, and B3 have also been tested and which can be produced analogously to cross-linked carboxymethyl starch. methyl cellulose (CMC). Furthermore, some test substances based on cross-linked polymers: C1, C2 and C3 have been tested and can be produced, for example, according to WO96 / 08523.

As a reference material, a commercially available superabsorbent from Hoechst, also called Sanwet IM 7100, which is transversely coupled to sodium polyacrylate and pure pulp fluff, has been tested without the addition of a superabsorbent mix.

The absorbent concept tested consists of 20% by weight of superabsorbent blend of chemical type pulp fluff. The basis weight of the pulp structure was 500 g / m 2.

Outside δ-values, FSC (g / g), CRC (g / g) and AUL (g / g) were measured at 2 kPa superabsorbents. The test liquid was in all cases synthetic urine according to the following instructions: 60 mmol KCl (4.5 g), 130 mmol NaCl (7.6 g), 3.5 mmol

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_MgSO4 (0.42 g), 2.0 mmol of _CaSO4 * 2 H ₂ 0 (0.34 g), 300 mmol of urine (18 g) and 1 g 0.1% triton were dissolved in 1 liter of distilled water.

The measurement procedures used to test superabsorbent function in the absorbent structure as described above were as follows:

Inclined Absorption Capacity: The sample was placed at a 30 ° slope to mimic the position of the diaper during use, and the lower portion was in contact with the fluid bath (synthetic urine) and absorbed fluid by aspiration. The sample was weighed before and after absorbing the fluid and the absorption was recorded as g absorbed fluid per g absorbent sample.

Collection time: Three additions of each 60 ml of liquid (synthetic urine) were made at a time interval of 10 minutes. The time taken to absorb the whole fluid was measured (visual observation).

The result of the measurements is shown in Table 1 below.

Table 1

material FSC (g / g) CRC (g / g) δ (°) Inclined Absorption Capacity (g / g) Collection time (s) 1.23 brash - - - - 6.5 31,87,127 IM 7100 46 28 28 1.9 13.5 20,15,22 Al 27 13 13 13.0 9.2 19,34,58 A2 29 22 11 16.0 8.8 21,73,134 A3 39 23 9 13.0 9.5 21,45,98 A4 40 20 13 15.0 9.0 19,38,81 A5 45 27 Ί 16.0 8.9 24,75,145 A6 43 25 13 15.0 9.1 22,53,123 A7 27 13.6 14 14.0 9.0 20,44,83 A8 25 13 14 15.0 9.2 20,41,97 A9 30 18 14 15.0 9.8 18,50,77 A10 54 32 11 20 9.6 21,67,210 all 32 13 16 8.8 10.0 13,23,36 A12 58 18 12 21 9.0 18,90,960 A13 37 21 14 14 10.7 16,60,131 A14 29 16 12 8.8 9.6 24,24,40 BI 26 14 15 6.0 10.7 22,28,42 B2 27 17 6 9.9 9.4 25,60,79 B3 20 12 9 - 10.2 23,40,63 Cl 31 17 8 2.9 12.1 22,30,49 C2 28 13 14 2.4 11.3 21,30,49 C3 23 10 18 2.0 9.8 21,33,54

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The correlation studies here show that the δ-value positively correlates with collection times 2 and 3, e.g. low collection time at low δ-values and negative, with absorbent capacity, e.g. high absorption capacity in combination with δ-values explains the result of absorption capacity and collection time 3.

In the above tests, the superabsorbent was in the form of particles that were mixed with lumps of pulp pulp to form an absorbent mass. However, the invention is not limited to such absorbent masses, but it would also be possible to apply superabsorbent particles in the form of a layer between the pulp layers or other optional hydrophilic fibers, natural or synthetic. The superabsorbent can also be applied between layers of fine paper (thin film), nonwoven materials or other material. The superabsorbent may also be present in the form of fibers, as a thin coating or as a coating on another material or as a foam. Instead of or outside the pulp, the absorbent mass may comprise other types of hydrophilic fibers, absorbent foam material or the like.

Μ-Ζοον

Claims (12)

PATENT CLAIMS An absorbent structure in an absorbent article such as a diaper, sanitary napkin, incontinence aid, wound dressing, bed protective layer, etc., wherein said structure comprises a superabsorbent material, preferably in combination with other absorbent or carrier materials, and wherein the content of superabsorbent material constitutes a renewable and / or biodegradable raw material of at least 20% by weight, calculated on the dry weight of the superabsorbent material, characterized in that the superabsorbent material has a phase angle δ <8 ° defined as the phase shift between deformation and strain measured rheological measurements. Absorbent structure according to claim 1, characterized in that the superabsorbent material has a phase angle δ <6 °, preferably 4 4 ° and most preferably 3 3 °. Absorbent structure according to claim 1 or 2, characterized in that the superabsorbent material has a renewable and / or biodegradable raw material content of at least 40, preferably at least 60 and most preferably at least 80% by weight, calculated on the dry weight of the superabsorbent material. Absorbent structure according to any one of the preceding claims, characterized in that the superabsorbent material comprises cross-linked polymers, wherein the polymer is based on a renewable and / or biodegradable raw material and also a cross-linked factor, either renewable and / or biodegradable or non-renewable. nonbiodegradable. Absorbent structure according to any one of the preceding claims, characterized in that it comprises a combination of hydrophilic fibers and a superabsorbent material. The absorbent structure of claim 5, wherein the hydrophilic fibers comprise pulp, tissue or hydrophilic synthetic fibers. Absorbent structure according to claims 5 or 6, characterized in that it contains between 5 and 80% by weight of superabsorbent material calculated on the total weight of the structure. 13409 Absorbent structure according to claims 1-4, characterized in that it comprises a combination of an absorbent foam material and a superabsorbent material. The absorbent structure of claims 1-4, wherein the superabsorbent material is in the form of a foam. 10. The absorbent structure of any one of claims 1-4, wherein the superabsorbent material is in the form of a coating on a fibrous material. Absorbent structure according to claims according to any preceding claim, characterized in that the superabsorbent material has an absorbent capacity under a load of 2 kPa (AUL) of not more than 25, preferably not more than 20 and most preferably not more than 18 ml, of an aqueous solution containing 0. 9% by weight of sodium chloride per g of superabsorbent material. 12. Absorbent article such as a diaper, sanitary napkin, incontinence aid, wound dressing, bed liner, etc. comprising a liquid pervious cover layer, a liquid pervious backsheet, and an absorbent structure interposed therebetween, wherein the absorbent structure is of the kind set forth in any one of claims 1-11.