VISCOELASTIC FOAM WITH SLOW RECOVERY TIME

Abstract

Recovery times of flexible polyurethane foams are increased by treatment with a pressure sensitive adhesive. An emulsion or dispersion of the adhesive in an aqueous carrier liquid is impregnated into the foam, with subsequent removal of the carrier. This invention is of special interest when the glass transition temperature of the starting foam is 16 C. or lower.

Claims

1. A viscoelastic foam comprising a) an open-celled flexible polyurethane foam having internal surfaces coated with b) a pressure sensitive adhesive having a glass transition temperature of at most 0 C., wherein the pressure sensitive adhesive constitutes 1.5 to 35% of the combined weights of a) and b).

2. The viscoelastic foam of claim 1 wherein the pressure sensitive adhesive constitutes up to 25% of the combined weights of a) and b).

3. The viscoelastic foam of claim 2 wherein the open-celled flexible polyurethane foam has a glass transition temperature of at most 16 C.

4. The viscoelastic foam of claim 4 wherein the open-celled flexible polyurethane foam has an airflow of at least 0.944 L/s, a density of 32 to 64 kg/m.sup.3 and a resilience of no more than 20%.

5. The viscoelastic foam of claim 4 wherein the open-celled flexible polyurethane foam has a recovery time of up to 2 seconds.

6. The viscoelastic foam of claim 4 wherein the pressure sensitive adhesive is not isocyanate-based.

7. The viscoelastic foam of claim 4 wherein the pressure sensitive adhesive is an acrylic polymer having a glass transition temperature of no higher than 20 C.

8. The viscoelastic foam of claim 4 which has a recovery time at least 200% of the recovery time of the open-celled flexible polyurethane foam.

9. A method of reducing the recovery time of an open-celled polyurethane foam, comprising (1) impregnating a starting flexible polyurethane foam with a solution or emulsion of a pressure sensitive adhesive in a liquid carrier, the pressure sensitive adhesive having a glass transition temperature of no greater than 0 C., to wet internal surfaces of the foam and form an impregnated foam, and (2) removing the liquid carrier from the impregnated foam to produce a coated foam having a coating of the pressure sensitive adhesive on the internal surfaces of the flexible polyurethane foam.

10. The method of claim 9 wherein the pressure sensitive adhesive is not isocyanate-based.

11. The method of claim 10 wherein the pressure sensitive adhesive is an acrylic polymer having a glass transition temperature of no higher than 20 C.

12. The method of claim 9 wherein step (1) is performed by steps including: (1-A) immersing the starting flexible polyurethane foam into the solution or emulsion of the pressure sensitive adhesive and/or by applying the solution or emulsion of the pressure sensitive adhesive to a surface of the starting flexible polyurethane foam and allowing it to penetrate into the starting flexible polyurethane foam; and 1-B) mechanically compressing the foam while immersed or otherwise in contact with the solution or emulsion.

13. The method of claim 9 wherein the coating of the pressure sensitive adhesive constitutes 1.5 to 35% of the weight of the coated foam.

14. The method of claim 9 wherein the recovery time of the coated foam is at least 200% of the recovery time of the starting flexible polyurethane foam.

15. A flexible polyurethane foam made according to the method of claim 9.

Description

EXAMPLES 1-5 AND COMPARATIVE SAMPLES A AND B

[0057] Comparative Sample A is an untreated flexible foam that has properties as indicated in Table 1 below. This foam has a glass transition temperature of 15 C.

[0058] Comparative Sample B and Examples 1-5 each are prepared by separately coating a specimen of Comparative Sample A with a pressure sensitive adhesive emulsion sold as ROBOND PS-90 by The Dow Chemical Company. This product is a one-component alkyl acrylate polymer that does not contain a tackifier, in the form of a 53% solids emulsion in an aqueous liquid phase. The dried adhesive has a glass transition temperature of approximately 40 C.

[0059] To coat the samples, the pressure sensitive adhesive product is diluted with various amounts of water. The diluted emulsion is poured into an 800-mL open vessel. The starting foam specimen in each case has its skin removed, and is dried and weighed. The foam specimen is then immersed in the diluted emulsion, squeezed manually, immersed a second time and squeezed again to remove excess emulsion. Pressure is released to re-expand the foam and allow gas to reenter the cells. The foams are dried overnight under ambient conditions (about 22 C.), and then dried at 80 C. for at least one hour. The resulting coated foams are then weighed and conditioned (25 C./50% relative humidity) overnight for property testing according to ASTM D3574 (recovery time according to the process described hereinbefore). Results are as indicated in Table 1.

TABLE-US-00001 TABLE 1 Sample Designation Property A* B* 1 2 3 4 5 Dilution ratio.sup.1 N/A 10:1 2:1 1.5:1 1:1 0.5:1 0.2:1 Wt. % PSA.sup.2 0 0.7 2.2 8.3 10.2 17.2 23.8 Foam Density, 47.7 48.0 48.8 52.0 53.1 57.6 62.6 kg/m.sup.3 Airflow, L/s 1.7 2.1 2.2 2.15 2.2 2.1 2.1 Resiliency, % 3.0 3.0 3.0 3.0 2.8 3.0 3.0 Recovery time, s 2.2 2.1 4.0 6.0 6.2 10.1 14.6 *Not an example of the invention. .sup.1Weight ratio of water to ROBOND PS-90 emulsion product. .sup.2Calculated as (weight coated foam weight starting foam) weight coated foam. PSA is pressure sensitive adhesive.

[0060] As can be seen from the data in Table 1, above an initial threshold, recovery time increases steadily with increasing coating weight of the pressure sensitive adhesive. Resiliency is essentially unaffected. Foam density increases in proportion to the added weight of the coating, which indicates that the coating process does not result in cell collapse or other undesirable densification effect.

[0061] Airflow for the treated foams in all cases is higher than that of Comparative Sample A. This indicates that pore clogging is essentially absent and that the pressure sensitive adhesive instead forms a thin coating on the internal surfaces of the foam. The increase in airflow may be due to additional cell opening that takes place during the compression steps.