GB2116572A

GB2116572A - High density flexible polyurethane foam

Info

Publication number: GB2116572A
Application number: GB08206589A
Authority: GB
Inventors: Chang Kun-Huang
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-05
Filing date: 1982-03-05
Publication date: 1983-09-28
Also published as: HK35186A; GB2116572B; MY8600542A

Abstract

A process of making higher density flexible polyurethane foam from waste polyurethane foam is accomplished by powdering the waste polyurethane foam and mixing it with any foamable polyurethane composition and moulding the mixture in a mould. Before mixing the powdered foam is sufficiently dried and screened to get a uniform particle size.

Description

SPECIFICATION Method of producing high density flexible PU foam This invention relates to a method of producing high density and resilience flexible polyurethane foam.

Polyurethane foam is generally formed by the reaction of isocyanate with a polymer having hydroxyl group or carboxyl group This polymer can be polyester or polyether, which is generally called polyol. During the reaction, the gas such as carbon dioxide generated causes the reaction mixture to swell into the form of foam. In case of polymer with hydroxyl group, to liberate carbon dioxide some free water must be contained in the reaction mixture. In some cases, halocarbon are added as a blowing agent. In these reactions, other chemicals such as catalyst surfactant are also used. It is importent that the reaction mixture must be rapidly and sufficiently mixed.

The polyurethane foam are divided into flexible foam semirigid foam and rigid foam. The flexible foam are easy to deform under load and can recover from deformation upon removal of load.

There are generally two processes for producing flexible polyurethane foam: one shot process and prepolymer process. The former process is done by mixing the properly formulated polyol, isocyanate, catalyst, blowing agent and then poured into the mold. In prepolymer process, polyol is firstly mixed with isocyanate to form a prepolymer which has terminal isocyanate group and is stable for storage. When the prepolymer reacts with blowing agent such as water in the presence of catalyst a polyurethane foam product can be obtained.

The polyurethane foams produced by the processes as described above are flexible foam and the density thereof is 1 8-30kg"m. These are low density flexible foams and have poor resilence and load characteristic so that they are mostly used as packing and rubbing materials. However, it is found that higher density polyurethane foam has better mechanical properties, resilence, comfort and air permeability and can be used in shoesole, hat liner and others where better load characteristic is required.

The higher density flexible foam can be produced under high molding pressure. This method is costly and the formed foam has a layer of skin surface that causes poor air permeability.

Although there are other high density forms made from other polymer, their comfort characteristic are not as satisfactory as polyurethane foam.

In accordance with the invention a higher density and resilence flexible polyurethane foam is made by firstly pulverizing a cured polyurethane foam and mixing the pulverized foam powder with a foamable polyurethane composition. The cured polyurethane foam may be either unused cured polyurethane foam or waste polyurethane foam or the mixture of both made by any process. As the waste polyurethane foam can be reused by this process, this is not only economical but also can save the energy supplied for treatment of waste foam.

It is preferable that the pulverized foam powder is sufficiently dried before mixing with foamable polyurethane composition so that these powder can be completely soaked in the viscous mixture.

The most preferable particle size of the powder is 0.5mm---3mm. To obtain a uniform size distribution of powder, the pulverized powder can be screened before mixing.

The foamable polyurethane composition may includes isocyanate, polyol or polyol blend, catalyst and blowing agent. Blowing agent can water or halocarbon or the mixture of both. The mixture are formulated with proper ratio and rapidly and thoroughly mixed with the pulverized foam powder of suitable weight, and then poured into the mold. The gas such as carbon dioxide liberated from the reaction acts as a blowing gas and cause foams in the mold. The cured foam is found, upon testing, that its density, resilence and load characteristic are higher than those produced by any known process as described above.

An object of the invention is to provide a method of making a higher density flexible polyurethane foam from waste polyurethane foam.

Another object of the invention is to provide a method of reusing waste polyurethane foam, thereby saving the production cost and the energy supply for treatment of waste polyurethane foam that can cause air pollution in the environment.

The following example is presented in illustration of the process of this invention and is not intended as an undue limitation on the generally broad scope thereof.

About 100 gm of waste polyurethane foam is ground into a powder form until the particle size thereof is 0.5m/m-a.0m/m. The powder is then placed in a drying apparatus for drying. After drying the powdered substance is subjected to screening to get a uniform size distribution. The screened powder is then put into a mixer into which 25gm of Voranol 3800 polyol, 12.5gm of TDI, about 0.32gm of silicone and Tin-9 are further added.

After mixing for 30 minutes the reaction mixture is poured into the mold. At that time, the powder is completely soaked in the reaction mixture and uniformly incorporated with the formed foam which swells to a volume as large as five times. This expanded foam in the mold is then compressed mechanicaily and cooled at the room temperature for 24 hours. The cast foam is finally released from mold after cooling. This foam is a higher flexible polyurethane foam and test data for this foam are given as follows: 1. Density of PU foam 0.178g/cm3 2. Hardness (ASKER TYPE C) 37 3. Tensile strength 3.0kg/cm2 4. Elongation 65% 5. Influence of Heating No Stickiness and crack 6. Decrease in Elongation -8% 7. Decrease in tensile strength 7% 8. Air permeability 200 l/m2 sec.

9. Water vapour transmission rate 3036 (g/m2/400C, Above 90% RH/24hrs)

Claims

1. A method of making a high density and resilence flexible polyurethane foam comprising the steps of. pulverizing a cured polyurethane foam, mixing said pulverized polyurethane foam powder with a foamable polyurethane composition, and molding the mixture in a mold.

2. A method as claimed in Claim 1, wherein said cured polyurethane foam is waste polyurethane foam.

3. A method as claimed in Claim 2, wherein the foamable polyurethane composition consists essentially of, polyol, isocyanate, catalyst, blowing agent.

4. A method as claimed in Claim 3, further comprising the step of drying the pulverized powder before mixing.

5. A method as claimed in Claim 4, further comprising the step of screening the pulverized powder before mixing.

6. A method as claimed in Claim 5, wherein the particle size of pulverized powder is 0.5 mm- 3mm.

7. A method of making a high density resilient flexible polyurethane foam substantially as hereinbefore described.

8. A high density resilient flexible polyurethane foam manufactured substantially as hereinbefore described.