BLOWING AGENT COMPOSITIONS

Abstract: The use as an activator for a chemical blowing agent, or as an accelerator or activator in the vulcanisation of rubber, of a reaction product of urea and an oxide, carbonate or hydrox­ ide of zinc, cadmium, calcium or lead, which reaction product may be optionally solvated, and certain such products per se.

Description: This invention concerns compounds which activate chemical blowing agents or activate the action of rubber curing accelerators, compositions containing them, and methods of using them. Chemical blowing agents, particularly azodicarbonamide, have been used for many years in the manufacture of foamed plastics materials, the properties of which depend largely on the decomposition characteristics of the blowing agent at the temperature employed. Consequently, it has become conventional to use so-called 'activators' for the blowing agent to modify the way in which it decomposes, the most common of such activators being zinc, cadmium and lead compounds. By judicious selection of these and the quantities employed, it has been possible to achieve a considerable range of characteristics and properties in the final foamed product. By far the most effective are mixtures of cadmium and zinc compounds. As will be appreciated however, cadmium and lead compounds are expensive and toxic, and a great need has existed for an effective activator which can eliminate or substantially reduce the use of such compounds. In the curing or vulcanisation of rubber, elemental sulphur has generally been employed as the curing agent, with organic accelerators being used to accelerate the reaction in conjunction with zinc oxide to activate the accelerator. With the increasing cost of zinc oxide, the need has constantly existed for a new activator which is more efficient and cost-effective. In Belgian Patent No 371947, there is described a process for the preparation of what are called alkaline earth cyanates which comprises heating a mixture of an alkaline earth oxide or carbonate with urea to a temperature of from 130 to 400°C. In particular, an Example is given of the preparation of calcium dicyanate, though no use is stated for any of the cyanates produced. In West German Auslegeschrift No 1258082, there is described a process for the preparation of open-celled soft polyvinyl chloride foams by the use of azodicarbonamide as a chemical blowing agent in the presence of a catalyst system which comprises zinc oxide, organic tin salts and urea. These are made into complex pastes with polyvinyl chloride and several other additives, and are heated to temperatures in excess of 200°C to produce the desired foams. Because the systems are complicated, and the chemistry is complex, it is not clear precisely what reactions are occurring, nor how exactly the azodicarbonamide is being activated. We have now found a group of compounds, some of which are novel, which have improved properties as activators for chemical blowing agents and as activators for rubber curing accelerators. The compounds may also be rubber curing accelerators themselves. Accordingly, in one aspect, this invention provides the use as an activator for a chemical blowing agent, or as an accelerator or activator in the vulcanisation of rubber, of a reaction product of urea and an oxide, carbonate or hydroxide of zinc The chemical structure of such products corresponds to the formula: ( HN₃) n Zn(NCO)₂ (I) where n, which may be fractional, is from 0.5 to 4. Where n is fractional, it is likely that a mixture of compounds is involved, in each of which n represents a whole number, though this is not certain. In another aspect, the invention provides compounds whose elemental analysis corresponds to compounds of formula I wherein n is from 1.0 to 3.0, especially 1.5 to 2.5. In a further aspect, the invention provides an activated blowing agent composition which comprises a thermally decomposable blowing agent, especially azodicarbonamide, a sulphonhydrazide or dinitrosopentamethylenetetramine, in association with a suitable amount of (NH₃) n Zn(NCO)₂ The ratio of the optionally solvated reaction product to the blowing agent is preferably from 1:20 to 1:1 by weight, especially from 1:10 to 1:2. In yet another aspect, the invention provides a rubber curing composition which comprises sulphur and a suitable amount of (NH₃) n Zn(NCO)₂ The ratio of the optionally solvated reaction product to the sulphur is preferably from 1:5 to 5:1, especially from 1:2 to 2:1. The reaction of the oxide, carbonate or hydroxide with urea is preferably carried out by heating the reactants together, optionally in the presence of a suitable solvent, to a temperature in the range of 120° to 180°C. Analysis of the products obtained at various temperatures appears to indicate that n in formula I decreases with increasing temperature, so that products having the desired value of n can be produced by controlling the reaction temperature appropriately. From 2 to 5 moles of urea are preferably employed per mole of the metal oxide, carbonate or hydroxide. Some solvents for the reaction, e.g. methanol, dimethylformamide and dimethylsulphoxide appear to be true solvents, and give the same reaction product as in the absence of any solvent. An especially preferred reaction product results when urea is reacted with zinc oxide, carbonate or hydroxide, especially zinc oxide, at a temperature of from 135° to 160°C. This product appears to be of formula I wherein n represents approximately 2. The reaction products of the invention are highly efficient activators for blowing agents, particularly azodicarbonamide, giving greater expansion at equivalent rates, or equal expansion at lower rates, than conventional zinc/cadmium compound activators. Consequently, reduced rates may normally be employed. Since the metal in the reaction product is zinc, the toxicity problems and expense of conventional cadmium compounds may be avoided. When used in the so-called inhibition method of chemical embossing, the compounds of the present invention may be inhibited by acids, e.g. safe unsaturated fatty acids, for example linolenic acid, which may consequently be employed as the inhibitor in place of the toxic and difficult to handle tri-mellitic anhydride which is used in conventional zinc oxide activation. The reaction products of the invention are also highly efficient activators for rubber curing accelerators, giving greater activation at equivalent rates, or equal activation at lower rates, than zinc oxide. The following examples are given, though only by way of illustration. Example 1 Urea (300g) and zinc oxide (100g) were heated together in an open beaker. Reaction started at 120°C, but the temperature then increased to 125-128°C and became steady. Ammonia was evolved. After 30 minutes the reaction slowed and the solution became clear. The temperature was then increased to 140°C for 15-20 minutes. A white solid formed which was washed when cold with methanol to remove unreacted urea and by-products. 220g of product were obtained. Analysis Found: NH₃ 19.4%, Zn 34.9%, NCO 42.0% (NH₃)₂Zn(NCO)₂ requires: NH₃ 18.6%, Zn 35.5%, NCO 45.9%. Example 2 Zinc carbonate (100g) and urea (250g) were heated together in an open beaker, following the method of Example 1. The white solid formed was found to be virtually identical to the product of Example 1. Example 3 In a formulation comprising, by weight: it was found to be possible to replace the zinc oxide with 1.25% of the zinc compound of Example 1 (representing over a 60% reduction in the quantity of zinc required) without affecting the rate of the vulcanisation. In addition there was good activation of the azodicarbonamide giving a high quality rubber foam.

Claims: Claims for the following Contracting States: BE, CH, LI, DE, FR, GB, IT, LU, NL, SE The zinc compounds of the formula: (NH₃) n Zn(NCO)₂ where n, which may be fractional, is from 0.5 to 4. The zinc compounds according to claim 1 where n is from 1.5 to 2.5. The zinc compound according to claim 2 where n is 2. A compound according to any of claims 1 to 3 which is at ambient temperature. The use as an accelerator or activator in the vulcanisation of rubber of one or more compounds according to any of claims 1 to 3. A composition for use in the acceleration or activation in the vulcanisation of rubber, which contains one or more compounds according to any of claims 1 to 3. A blowing agent activator composition which contains one or more compounds according to any of claims 1 to 3. An activated blowing agent composition which contains a thermally-decomposable blowing agent in association with one or more compounds according to any of claims 1 to 3, said composition being at ambient temperature. A composition according to claim 8 in which the blowing agent is azodicarbonamide. Claims for the following Contracting State: AT The use as an accelerator or activator in the vulcanisation of rubber of one or more zinc compounds of the formula: (NH₃) n Zn(NCO)₂ where n, which may be fractional, is from 0.5 to 4. The use according to claim 1 where n in the zinc compound is from 1.5 to 2.5. The use according to claim 2 where n in the zinc compound is 2. A composition for use in the acceleration or activation in the vulcanisation of rubber, which contains one or more zinc compounds of the formula: (NH₃) n Zn(NCO)₂ where n, which may be fractional, is from 0.5 to 4. A blowing agent activator composition which contains one or more zinc compounds of the formula: (NH₃) n Zn(NCO)₂ where n, which may be fractional, is from 0.5 to 4. A composition according to claim 4 or claim 5 where n in the zinc compound employed is 2.

Inventors: BATHGATE, RAYMOND JOHN
Applicants: SCHERING AGROCHEMICALS LIMITED
Application year: 1984
Main classification: C08J9
IPC codes: C08L7, C08K5, C01G9, C08L21, C07F3, C08J9