GB2417031A

GB2417031A - Superabsorbent composition

Info

Publication number: GB2417031A
Application number: GB0415643A
Authority: GB
Inventors: Padraig Gerard Troy; Graham Emery Steer
Original assignee: SP HEALTHCARE Ltd; Craig Medical Products Ltd
Current assignee: SP HEALTHCARE LIMITED
Priority date: 2004-07-14
Filing date: 2004-07-14
Publication date: 2006-02-15
Also published as: WO2006008645A2; GB0415643D0; WO2006008645A3

Abstract

A superabsorbent composition comprises superabsorbent (100pbw), silica (3-20 pbw), water (0.5-15pbw) and glycerol (5-50pbw). The silica is or comprises porous silica. The silica substantially coats the superabsorbent particles and absorbs the water and glycerol.

Description

241 703 1

SUPERABSORBENT COMPOSITION

Field of the Invention

This invention relates to a so-called superabsorbent material, and to a method of producing the material. The invention is especially suitable for absorbing liquid matter excreted by the body (e.g. for use in the fields of ostomy, diaper, personal hygiene, incontinence or woundcare), and/or for absorbing aqueous matter, but it is not limited exclusively to these fields.

Background to the Invention

GB-A-2301350 and EP-A-0891758 describe superabsorbent formulations and methods of producing articles containing superabsorbent material. A significant aspect of the superabsorbent formulation is the inclusion of glycerol and water, which binds the superabsorbent powder granules together when compressed, to form a consolidated mass. The superabsorbent material can be formed into tablets, or compressed between upper and lower layers to e.

form a sheet-like product. e 20

The stability of the consolidated structure depends on the amount of water and glycerol in the composition. Increasing the amount of water and glycerol .

: can increase the physical stability. However, there are practical limits on the A..

amount of water and glyercol that can be mixed with the superabsorbent, because the superabsorbent begins to gel when mixed with significant amounts of water and glycerol, and thereby loses its desirable powder structure Such limitations on the amount of water and glyerocl have limited the structural stability which has been achieved hitherto, and make the conventional product vulnerable to at least some degree of shedding (particularly at the edges). Also, articles made of the material tend not to be flexible, and may shed material if bent or flexed.

It would be desirable to provide a way of increasing the amount of glycerol and water which can be incorporated in the formulation without detracting significantly from other advantageous characteristics of the superabsorbent formulation.

EP 0629411 describes a formulation containing superabsorbent and non porous silica.

Summarv of the Invention The present invention has been devised bearing the above in mind.

Broadly speaking, one aspect of the invention is to include silica in a formulation including superabsorbent material (e.g. powder or granules). The silica may act as a lubricant, enabling the superabsorbent particles to flow more easily, thus making handling of the superabsorbent particles easier, and leading to easier mixing and compressing processes; and ..

It is especially preferred that the silica be or comprise porous silica. An effect of porous silica may be that it may have an excellent absorptive capacity for pulling in water and/or a non-volatile lubricious polyhydroxy compound (e.g. glycerol) between (e.g., around, and surface) the superabsorbent granules.

This enables an increase in the amount of water and the non-volatile : lubricious polyhydroxy compound that can be mixed with the superabsorbent A..

material without gelling the superabsorbent.

Preferably, the amount of silica present (per 100 parts wt of superabsorbent material) is at least 3 parts, more preferably at least 4 parts, more preferably at least 5 parts, more preferably at least 6 parts, more preferably at least 7 parts, and in one form at least 8 parts.

Preferably, the amount of silica present (per 100 parts wt of superabsorbent material) is not greater than 20 parts, more preferably not greater than 15 parts, more preferably not greater than 10 parts and, in one form, not greater than 8 parts.

The optimum amount of silica may depend to some extent on the size and surface area of the particles of superabsorbent. Generally, it is preferred that the silica be present in such a quantity to provide a surface coating on substantially all of the superabsorbent particles. Preferably, each particle is substantially entirely coated. It will be appreciated that a smaller particle size results in a larger surface area to be coated per unit volume, thus requiring a greater quantity of silica for optimum effect.

The superabsorbent particles may comprise an alkali metal polyacrylate (e. g. sodium polyacrylate), or some other polyacrylate, or other material which provides superabsorbent properties (defined generally as the ability to absorb many times their own weight of liquid matter). Suitable materials include for example, water-swellable polymers.

Preferably, the formulation includes glycerol. Alternatively, another non . volatile lubricious polyhydroxy compound may be used which is watersoluble or water-dispersible at or below 40 C and is liquid at room temperature (15 to 20 C). Suitable other compounds include, for example: propane 1-2 dial; polyethylene glycol 200 (or 300); or sorbitol. . .

. Preferably, the amount of glycerol (or other material) is 5-50 parts per 100 parts of the superabsorbent material, more preferably 5-40 parts, more preferably 5-30 parts, more preferably 10-25 parts. In one embodiment, the amount of glycerol (or other material) is between 12 and 18 parts per 100 parts of superabsorbent.

Preferably, the formulation also includes water. Preferably, the water is present in an amount of 0.5 to 15 parts by weight per 100 parts of superabsorbent, more preferably 0.5 to 8 parts, and more preferably 0.5 to 6 parts. In one example, the amount of water is between 3 and 5 parts.

The formulation may also include additives, for example, a malodour counteractant.

In another aspect, the invention provides a method of producing an absorbent material, the method comprising: (a) mixing together superabsorbent particles and silica; and (b) adding to the mixture from step (a) a cohesive formulation to make the mixture consolidatable.

As mentioned above, it is especially preferred that the silica be or comprise porous silica.

Preferably, the silica and superabsorbent particles are mixed to provide a mixture in which substantially all of the superabsorbent particles are coated with silica. Preferably, the particles are substantially entirely coated with silica. .

Preferably, the cohesive formulation is added after the mixing in step (a) is carried out.

Preferably, the cohesive formulation includes glycerol and water. Instead of glycerol may be used another non-volatile lubricious polyhydroxy compound .

: which is water-soluble or water-dispersible at or below 40 C and is liquid at .

room temperature (15 to 20 C).

Other features and advantages of the invention will become apparent from the

following description of a preferred embodiment.

Brief Description of the Drawinas

An embodiment of the invention is now described by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic flow diagram showing a production process for producing an absorbent material; Figs. 2a and 2b are schematic drawings showing the superabsorbent granules before (a) and after (b) mixing with silica; and Fig. 3 is a schematic drawing of apparatus for consolidating the material to form shaped articles.

Description of Preferred Embodiment

An example superabsorbent formulation may comprise, in parts by weight (pbw): Superabsorbent 100 pbw Silica 6-10 pbw Glycerol 14 pbw . . Water 4 pbw. ... ..e

.....

A suitable superabsorbent material is1 for example, sodium polyacrylate . available under trade name HySorb from BASF. Sodium polyacrylate .

: superabsorbent materials are also available from Dow Chemicals and from ...

Stockhausen A suitable silica material is or comprises porous silica. Porous silica may be formed by a precipitation process. For example, a precipitated silica may be produced from a water glass solution to which sulphuric acid is added under certain conditions. The silica develops in the aqueous phase. The precipitated silica may be washed out and dried by a suitable drying process, for example, by spray drying.

Suitable porous silica materials may be available from Degussa (under trade name Sipernat), Grace Davison (under trade name Perkasil), Ineos (under trade name Gasil), PPG industries (under trade name Flo-Gard) and Rhodia (under trade name Tixosil).

Referring to Figs. 1 and 2, the formulation is prepared in first and second stages 10 and 12. The first stage is to mix together the superabsorbent granules and the silica. Fig. 2a shows the superabsorbent granules 14 prior to mixing, and Fig. 2b shows the granules 14 after mixing. As can be seen from Fig. 2b, the effect of mixing is to coat the granules 14 with a thin coating of silica 16. The silica 16 acts as a lubricant making the granules easier to flow, and therefore easier to mix.

The second stage 12 is to add a premix of glycerol and water to the silica coated superabsorbent formulation. The effect of the porous silica is generally to enable a greater quantity of glycerol/water to be mixed with the superabsorbent, without gelling the superabsorbent, than if the silica were absent. It is believed that this is as a result of the porous silica pulling in and absorbing the water/glycerol outside the superabsorbent powder granules.

Not only does this permit the glycerol/water to penetrate more extensively between the superabsorbent granules 14, it also keeps the water/glycerol in the desired position between the superabsorbent particles for binding the superabsorbent particles together when compressed, with little or no gelling of : . the superabsorbent material (at least prior to use of the material to absorb significant quantities of liquid).

The optimum quantity of silica may depend at least to some extent on the size of the superabsorbent granules 14. It is preferred that the quantity of silica be sufficient to coat substantially the entire surface of the superabsorbent particles 14. During the second stage 12, the formulation Is mixed to a powder consistency.

The superabsorbent formulation can be formed into a desired shaped article by compression, which consolidates the powder structurally, in the same manner as that described in GB-A-2301350 and EP-A-0891758 referred to hereinbefore. The presence of the glycerol/water (particularly in the higher quantity than that attainable hitherto) enables the mixture to be compressed at room temperature with only relatively mild pressure being required. In most S cases no other heat is required. Moreover, the increased quantity of glycerol/water provides greater structural stability than that achievable hitherto, so that the formed article is less prone to shedding, and can be flexible Fig. 3 illustrates, by way of example, apparatus 18 for forming a sheet of superabsorbent, suitable for use in ostomy, incontinence or woundcare applications. The powder formulation is fed from a supply 20 onto a travelling sheet 21 of tissue paper which is pulled off a supply roll 22. A second (overhead) sheet 23 of tissue paper is fed from a second supply roll 24 and these two sheets sandwich the powder between them. The product passes between a first pair of rolls 26 which form a first nip 27 and to a second pair of rolls 28 forming a second nip 29. The inter-roll spacing at the second nip 29 - may be for example 0.1 to 2.0 mm. That at the first nip 27 may be 0.75 to 4 mm. No external heat is applied. The resulting product is a flat sheet 31 which can be converted to roll-stock for later conversion or cut into suitable shapes, e.g. rectangles 32, and can be directly placed in personal hygiene, diaper, ostomy or incontinence products. It has been found to rapidly absorb a liquid such as urine. In tests, over 60 ml of synthetic urine were absorbed in under ë..

. 60 seconds, usually under 40 seconds, by a product of one square centimetre area and 2 mm thickness made by the method described above.

If desired, the sheet may be processed during production to form packetlike articles, as described in EP-A-0891758.

Reference has been made in the above specification to malodour counteractants. One example of a malodour counteractant is a bactericide, e.g. benzyl alkonium chloride. Another example is a fragrance Other examples are included in a range of bactericides manufactured by ConvaTec TM (Calgon-Vestal Div.). Yet other malodour counteractants which may be used are methylchlorosiothiazolinone, methylisothiazolinone, or denatonium benzoate.

It will be appreciated that the foregoing description is merely illustrative of preferred forms of the invention, and that many modification may be made within the scope of the invention. Aspects believed to be of particular importance are identified in the claims. However, the applicant claims protection for any novel feature or idea described and/or illustrated herein whether or not emphasis has been placed thereon.

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a....: q . . He .q I..

Claims

Claims 1. A formulation for utilisation to absorb liquid, comprising:

superabsorbent; S silica; water; and a non-volatile lubricious polyhydroxy compound which is water-soluble or water-dispersible at or below 40 C and is liquid at room temperature (i.e. at at least one temperature within the range 15 to 20 C), wherein the silica is or comprises porous silica.
2. A formulation according to claim 1, wherein the silica is precipitated silica.
3. A formulation according to claim 1 or 2, wherein the quantity of silica is at least 3 parts by weight per 100 parts by weight of the superabsorbent. -
4. A formaulation according to claim 1, 2 or 3, wherein the quantity of silica is not more than 20 parts by weight per 100 parts by weight of the . 20 superabsorbent. ease
5. A formulation according to claim 1 or 2, wherein relative quantities in the - . formulation are, in parts by weight (pbw): I superabsorbent 100 pbw silica 3-20 pbw water 0.5-15 pbw said lubricious polyhydroxy compound 5-50 pbw.
6. A formulation according to claim 5, wherein the silica is present in a quantity to provide a surface coating on at least the majority of the surface area of the superabsorbent.
7. A formulation according to claim 6, wherein the silica is present in a quantity to provide a surface coating on substantially the entire surface area of the superabsorbent.
8. A formulation according to claim 5 or any claim dependent thereon wherein S the silica is present in a quantity of at least 4 pbw.
9. A formulation according to claim 8, wherein the silica is present in a quantity of at least 5 pbw.
10. A formulation according to claim 9, wherein the silica is present in a quantity of at least 6 pbw.
11. A formulation according to claim 10, wherein the silica is present in a quantity of at least 7 pbw.
12. A formulation according to claim 11, wherein the silica is present in a quantity of at least 8 pbw. e . I.
13. A formulation according to claim 3, or any claim dependent thereon, . 20 wherein the silica is present in a quantity of not greater than 20 pbw. :
14. A formulation according to any preceding claim wherein the polyhydroxy . . : compound is glycerol. ee. e e.
15. A formulation according to claim 5, or any claim dependent thereon, wherein the poyhydroxy compound is present in an amount of 5-30 pbw.
16. A formulation according to claim 5, or any claim dependent thereon, wherein the polyhydroxy compound is present in an amount of at least 12 pbw.
17. A formulation according to claim 16, wherein the polyhydroxy compound is present in an amount of at least 13 pbw.
18. A formulation according to claim 15, wherein the polyhydroxy compound is present in an amount of at least 14 pbw.
19. A formulation according to claim 5, or any claim dependent thereon, wherein the water is present in an amount of 0.5-6 pbw.
20. A formulation according to claim 5, or any claim dependent thereon, wherein the water is present in an amount of at least 3 pbw.
21. A formulation according to claim 20, wherein the water is present in an amount of at least 4 pbw.
22. A formulation according to any preceding claim, wherein the superabsorbent comprises a water swellable polymer.
23. A formulation according to claim 22, wherein the superabsorbent comprises a polyacrylate.

- .e
24. A formulation according to claim 23, wherein the polyacrylate is an alkali metal polyacrylate. . .
25. A formulation according to claim 24, wherein the superabsorbent A..

comprises sodium polyacrylate.
26. A method of producing a superabsorbent formulation, the method comprising: (a) mixing together superabsorbent and silica to coat the superabsorbent with silica; and (b) mixing with the silica coated superabsorbent, water and a non- volatile lubricious polyhyroxy compound which is water-soluble or water- dispersible at or below 40 C and is liquid at room temperature (i.e. at at least one temperature within the range 15 to 20 C); / wherein the silica is or comprises porous silica.
27. A method according to claim 26, wherein the lubricious polyhydroxy compound is glycerol.
28. A method according to claim 26 or 27, wherein the relative quantities in the formulation are, in parts by weight (pbw): superabsorbent 100 pbw silica 3-20 pbw water 0.5-15 pbw said lubricious polyhydroxy compound 550 pbw.
29. A method according to claim 26, 27 or 28, wherein the silica is present in a quantity to provide a surface coating over substantially the majority of the surface area of the superabsorbent.
30. A method according to claim 29, wherein the silica is present in a quantity . to provide a surface coating on substantially the entire surface area of the - .e superabsorbent.
31. A method of producing a superabsorbent formulation, the method . comprising: ë : (a) providing superabsorbent particles which are substantially entirely coated 1..e with silica; and (b) mixing with the silica coated superabsorbent, water and a non- volatile lubricious polyhydroxy compound which is water-soluble or water- dispersible at or below 40 C and is liquid at room temperature (i.e. at at least one temperature in the range of 15 C-20 C) wherein the silica is or comprises porous silica.
32. An ostomy, diaper, personal hygiene, incontinence or woundcare product comprising or containing a superabsorbent formulation as defined in any of claims 1 to 24.
33. Use of a superabsorbent formulation as defined in any of claims 1 to 24 in an ostomy, diaper, personal hygiene, incontinence or woundcare product.
34. Use of porous silica with a formulation including superabsorbent, water and a non-volatile lubricious polydyroxy compound, to provide a coating on the superabsorbent particles for absorbing at least a portion of the water and the non-volatile lubricious polyhydroxy compound, wherein the non-volatile lubricious polyhydroxy compound is water-soluble or water-dispersible at or below 40 C and is liquid at room temperature (i.e. at at least one temperature within the range 15 to 20 C). ë .

I A..