Absorbent gelling material comprising a dry mixture of at least two types of hydrogel-forming particles and method for making the same

• US 5,714,156 A
• Filed: 01/06/1997
• Issued: 02/03/1998
• Est. Priority Date: 07/05/1994
• Status: Expired due to Term

• Current Assignee: The Procter & Gamble Company
• Original Assignee: The Procter & Gamble Company
• Inventors: Schmidt, Mattias, Goldman, Stephen Allen, Plischke, Manfred
• Primary Examiner(s): Page, Thurman K.
• Assistant Examiner(s): Shelborne, Kathryne E.
• Application Number:
  US08/765,503
• Time in Patent Office: 393 Days
• Field of Search: 424/404, 424/484, 424/486, 424/487, 604/358, 604/365, 604/368, 604/367, 604/372, 604/378, 604/382
• US Class Current: 424/404
• CPC Class Codes: A61F 13/53 characterised by the absorbing medium A61F13/20 takes precedence
• CPC Class Codes: A61L 15/225 Mixtures of macromolecular compounds
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents

Abstract

The invention relates to an absorbent gelling material comprising a dry mixture of at least a first type of hydrogel-forming particles and a second type of hydrogel-forming particles. The absorbent gelling material in accordance with the invention is characterized in that the first type of hydrogel-forming particles has an Absorption Against Pressure value which is higher than the Absorption Against Pressure value of the second type of hydrogel-forming particles, the weight of the second type of hydrogel-forming particles forming at least 10% of the combined weight of the first and second type of hydrogel forming particles. The invention also relates to a method for making such material.

Claims

1. Absorbent gelling material comprising a dry mixture of at least a first hydrogel-forming particles and a second hydrogel forming particles,

wherein the first hydrogel-forming particles has an Absorption Against Pressure value which is higher than the Absorption Against Pressure value of the second hydrogel-forming particles, the weight of the second hydrogel-forming particles forming at least 10% of the combined weight of the first and and second hydrogel-forming particles.

2. Absorbent gelling material according to claim 1, wherein the second hydrogel-forming particles have a mass median particle size not substantially smaller than the mass median particle size of the first hydrogel-forming particles.

3. Absorbent gelling material according to claim 1, wherein the difference in AAP-values of the first and the second material is at least 2 g/g.

4. Absorbent gelling material according to claims 1, wherein the first hydrogel-forming particles having an absorption against pressure value AAP₁, a fraction ,w, of the combined weight of the first and second hydrogel-forming particles is comprised of the first hydrogel-forming particles, a fraction p of the combined weight of the first and second hydrogel-forming particles being comprised of the second hydrogel-forming particles, than second hydrogel-forming particles having an absorption against pressure value AAP₂, wherein:

space="preserve" listing-type="equation">p+w=1,

and wherein for the absorption against pressure value of the mixture, AAP₁,2 ;

space="preserve" listing-type="equation">AAP.sub.1,2 >

w.AAP.sub.1 +p.AAP.sub.2,

the absorption against pressure values being measured at pressures between 21.1 gcm^-2 (0.3 psi) and 70.3 gcm^-2 (1 psi), preferably between 35.2 gcm^-2 (0.5 psi) and 56.2 gcm^-2 (0.8 psi).

5. Absorbent gelling material according to claim 1, wherein at a pressure of 49.2 gcm^-2 (0.7 psi), the AAP-value of the first hydrogel-forming particles is at least 15 g/g.

6. Absorbent gelling material according to claim 1, wherein at a pressure of 49.2 gcm^-2 (0.7 psi), the AAP value of the second hydrogel-forming particles is not higher than 25 g/g.

7. Absorbent gelling material according to claim 1 wherein the AAP value of the first hydrogel-forming particles is at least 1.25 times higher than the AAP value of the second hydrogel-forming particles.

8. Absorbent gelling material comprising a dry mixture of at least a first hydrogel-forming particles and a second hydrogel-forming particles, characterised in that the first hydrogel-forming particles has a Teabag Centrifuge Capacity (TCC) value which is greater than the Teabag Centrifuge Capacity value of the second hydrogel-forming particles, the amount of the second hydrogel-forming particles forming at least 10% of the combined weight of the first and second hydrogel-forming-materials, the Absorption Against Pressure value of the mixture being higher than the Absorption Against Pressure value of either one of the first hydrogel-forming particles and the second hydrogel-forming particles, wherein the absorption against pressure values are measured at pressures between 21.1 gcm^-2 (0.3 psi) and 70.3 gcm^-2 (1 psi), preferably between 35.2 gcm^-2 (0.5 psi) and 56.2 gcm^-2 (0.8 psi).

9. Absorbent gelling material according to claim 8, characterised in that the Teabag Centrifuge Capacity value of the first hydrogel-forming material is at least 19 g/g.

10. Absorbent gelling material according to claims 8, wherein the Teabag Centrifuge Capacity value of the second hydrogel-forming material is not higher than 40 g/g.

11. Absorbent gelling material according to claim 8, wherein the amount of the second hydrogel forming particles is between 10% and 75% of the combined weight of the first and and second hydrogel-forming-materials, perferably between 20% and 60% of the combined weight of the first and second hydrogel-forming particles.

12. Absorbent gelling material according to claim 8, the mass median particle size of the first type of hydrogel-forming particles being between 50 and 400 micrometer, the mass median particle size of the second hydrogel-forming particles being between 250 and 800 micrometer.

13. Absorbent article comprising an absorbent gelling material according to claim 8.

14. Method of making an absorbent gelling material comprising a dry mixture of at least a first hydrogel-forming particles and a second type of hydrogel forming particles, the first hydrogel-forming particles having an Absorption Against Pressure value or a Teabag Centrifuge Capacity value which is higher than the Absorption Against Pressure value or the Teabag Centrifuge Capacity value of the second hydrogel-forming particles, the method comprising the steps of:

providing the first hydrogel-forming material and the second hydrogel-forming material;

introducing both hydrogel-forming material in a mixing means; and

mixing both hydrogel-forming particles to form the mixture.

15. Method according to claim 14, charactericed in that the method comprises the steps of:

separating a fraction of hydrogel-forming particles from a bulk mass of hydrogel-forming particles,

physically or chemically modifying the separated fraction of hydrogel-forming particles to increase the Absorption Against Pressure-value or the Teabag Centrifuge Capacity-value, or both, of the separated fraction to form the first hydrogel-forming particles; and

mixing the modified separated fraction back into the bulk mass.

16. Method according to claim 15, wherein the separated fraction is obtained by sieving or air-separation, and wherein the separated fraction is modified by surface crosslinking.

17. Method of making an absorbent gelling material according to claim 14 characterised in that the method comprises the steps of:

polymerizing a first monomer forming the first hydrogel-forming particles

polymerising a second monomer forming the second hgf-forming particles, and

mixing the first type and second hydrogel-forming particles.

18. Method according to claim 17, wherein the first and second hydrogel-forming particles are surface cross-linked after having been mixed.