GB2075023A - Synthetic rubber latex foams - Google Patents

Abstract

Char resistant rubber latex foams are prepared from a synthetic rubber latex, especially S.B.R. or polybutadiene latex, by the inclusion of 5 to 30 phr of castor oil. The product foams are capable of passing the cigarette burn test laid down in B.S. 5852 Part 1, 1979.

Description

SPECIFICATION Moulded rubber foams This invention relates to moulded rubber foams and in particular to such foams for use in cushioning and upholstery.

Much attention is being given to the problem of reducing fire risk and the hazards produced by fires. This is of particular concern to the furniture business since several fires have been traced back to the ignition of cushioning or upholstery and fatalities have been caused by noxious smoke and fumes given off during such fires. Recently strict legislation has been introduced or proposed to reduce the risk of ignition and propagation in upholstered furniture. One test is "the smouldering cigarette test", specified in British Standard No. 5852. It is important that upholstered furniture satisfy this test to be acceptable to the distributors and customers.

Rubber latex foams prepared from natural latex generally perform well in the abovementioned test, and little charring occurs. However, synthetic rubber foams generally perform badly in the test and therefore methods have been studied to increase the char resistance of the foams. Some of these methods involve dipping the finished foam in a chemical composition. However, such methods are clumsy in that they involve extra stages in the manufacturing process. The inclusion of an additive in the latex foam compound during the manufacturing stage is much to be preferred.

We have now found, and this is the basis of our invention, that castor oil is surprisingly an effective additive for rubber latex foams, causing the resultant foams to perform much better in the smouldering cigarette test, and in most cases to pass the test.

According to the present invention char resistant synthetic rubber latex foams are prepared from a latex composition containing 5 to 30 parts by weight per hundred parts by dry weight of latex of castor oil.

The mechanism by which the inclusion of castor oil in the synthetic rubber latex composition enhances the char resistance of the foam, is not clear. However, it appears to involve some sort of depolymerisation reaction which causes shrinkage and melting, resulting in foams prepared from synthetic rubber latices behaving in a very similar way to foams prepared from natural rubber latices.

Apart from the inclusion of castor oil in an amount within the range specified above, no, or only slight, modification of the foam composition is required. Typically the composition is based upon a butadiene rubber latex, for example, polybutadiene or styrene butadiene rubber latex (or a blend thereof) or a blend of one or more butadiene rubber latices with up to 50% by weight of natural rubber. The latex is compounded with vulcanising ingredients and heat sensitive or delayed action gelling agent(s), and, if desired, fillers and other ingredients.

In the absence of castor oil, up to 100 parts per hundred parts by dry weight of rubber of aluminium hydrate - a well known flame retardant -- is required for the synthetic rubber foam to pass the cigarette burn test. This forms a hard char, in no way resembling the mechanism by which natural rubber latex foams pass the same test However the addition of such large amounts of aluminium hydrate is not a practical proposition since it seriously affects the physical properties of the foam. If desired, for example, 5 to 40 phr of aluminium trihydrate may be included with, for example, 1 5 phr of castor oil. The castor oil still promotes shrinkage and melting but this is less pronounced.

The following Examples illustrate the invention: EXAMPLE 1 A moulded rubber foam was prepared by the Dunlop process using the following formulation: Dry Conc. Wet INTEX 131* 100.00 65 153.80 Potassium Oleate 0--0.50 20 0-2.50 Castor Oil 20.00 - 20.00 Sulphur 2.50 50 5.00 ZDC (Zinc diethyl carbamate) 1.00 50 2.00 ZMBT (Zinc mercaptobenzthiazole) 0.80 50 1.60 Zinc Oxide 3.00 50 6.00 DPG (Diphenyl guanadine) 0.50-0.75 40 1.25-1.875 Antioxidant 1.00 50 2.00 * An S.B.R. latex (INTEX is a Registered Trade Mark).

Total Solids = 66.5%67.2% Mix Viscosity = 900 cps-1 000 cps (approx.) GELLING Sodium silico fluoride (20%) requirement =40-70 gm wet/kg wet.

Gelling time = 12 minutes approx.

Apart from requiring the use of extra soap and DPG to adjust to the correct gelling pH, the processing characteristics of the fluid foam almost exactly resembled a similar foam not containing the castor oil. The characteristics of the solid foam products (with and without castor oil) were also virtually identical.

When subjected to the smouldering cigarette test laid down in British Standard 5852 Part 1, 1979, using a Senior Service (Trade Mark) cigarette, the foam containing the castor oil melted and shrank away from the source of heat. It thus passed the test. A chain scission reaction was also observed which was very similar to that from an all natural rubber latex foam. No propagation or heat transfer was observed in the foam or on the fabric. In contrast, a similar foam, not containing castor oil, showed no sign of melting and, left undisturbed, smouldered uncontrollably until the entire foam was consumed. The covering used in this test was an ordinary non flame retardant fabric.

EXAMPLE 2 A foam was prepared to the formulation given in Example 1 with the addition of 40 phr (dry) of aluminium hydrate. When this foam was tested in the cigarette burn test, the aluminium trihydrate acted as a heat sink and a hard char was formed which acted as insulation and absorbed the heat. The foam passed the test.

Similar foams containing varying amounts of aluminium trihydrate in combination with 20 phr of castor oil also passed the test but the melting and shrinkage phenomena were much iess pronounced.

Claims (4)

1. A char resistant synthetic rubber latex foam prepared from a latex composition containing 5 to 30 parts by weight per hundred parts by dry weight of latex of castor oil.

2. A char resistant foam according to claim 1 wherein the latex is a polybutadiene latex, a styrene butadiene rubber latex, a mixture thereof, or a blend of either latex or a mixture thereof containing up to 50% by weight of natural rubber latex.

3. A char resistant foam according to claim 1 or 2 containing 5 to 40 parts by weight per hundred parts dry weight of latex of aluminium trihydrate.

4. A char resistant foam according to claim 1 substantially as hereinbefore described with reference to the Examples.