GB1589562A - Polyurethane elastomers - Google Patents

Description

(54) POLYURETHANE ELASTOMERS (71) We, IMPERIAL CHEMICAL INDUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 3JF, a British Company. do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method for the manufacture of polyurethane elastomers.

According to the invention, there is provided a method for the manufacture of a polyurethane elastomer which comprises forming a mixture containing components which react together to form a polyurethane elastomer and an inert liquid that has a boiling-point of at least 1500C at atmospheric pressure and is immiscible with the polyurethane precursors and incompatible with the final polyurethane and allowing reaction to proceed whereby a polyurethane elastomer is formed in which the inert liquid is dispersed throughout as a discontinuous phase.

In forming the mixture containing components which react together to form a polyurethane elastomer, use may be made of the components and techniques that have been described in the prior art for this purpose. In this connection, reference is made to Chapter IX of "Polyurethanes:Chemistry and Technology" by J.H. Saunders and K.C.

Frisch, published by Interscience Publishers. In general, the essential ingredients of a reaction mixture for the preparation of a polyurethane elastomer are an organic polyisocyanate such as diphenylmethane diisocyanate, a substantially linear polymeric polyol having a hydroxyl number generally in the range 30 to 120, preferably 50 to 60, for example a polyester or polyether diol, and a chain-extender, for example a glycol, a diamine or water.

In addition to the essential constituents, the reaction mixtures may contain auxiliary agents, for example catalysts, fillers, dyes, pigments and flame-retardants. For the production of micro-cellular elastomers, small amounts of blowing agents may be included.

In performing the invention, use may be made of any of the conventional methods and equipment that have been described in the polyurethane elastomer art. Thus, one-shot and prepolymer techniques may be employed and the elastomer may be formed by a casting, millable gum or thermoplastic process. The inert liquid may be incorporated at any convenient stage, for example in the polyisocyanate, the polyol, in a prepolymer derived therefrom or even by mixing with the elastomer whilst the latter is still workable.

The inert liquid that is included in the reaction mixture is a liquid that is inert towards the other components thereof. The term "immiscible" means that under the conditions employed and in the amounts used, a major proportion of the liquid is not miscible with any of the polyurethane precursors, that is to say the polyisocyanates and polyols, as distinct from any minor auxiliary agents used. Thus, a material having a solubility of 1% by weight in one of the polyurethane precursors is regarded as immiscible when used at a concentration of 10% by weight. Miscibility with the minor auxiliary agents is not regarded as significant so long as this does not cause the liquid to be miscible with any of the polyurethane precursors. Suitable inert liquids include hydrocarbon oils.

In order to ensure that the inert liquid is uniformly dispersed throughout the final product, it is important to ensure that it is uniformly dispersed in the reaction mixture. To achieve this condition it will be necessary in some cases to include a dispersing agent in the reaction mixture. The type of dispersing agent to include will depend upon the constitution both of the inert liquid and of the other components. Thus, an inert liquid may be dispersed in one of the polyurethane precursors with the aid of a dispersing agent which is a polymeric material containing in the molecule at least one chain of a type which is soluble and non-self-associated in the inert liquid and at least one chain of another type which is soluble and non-self-associated in the polyurethane precursor.

The amount of inert liquid to be included in the reaction mixture depends upon the effect it is desired to achieve. Inclusion of the liquid can have a number of advantages compared with an elastomer formulation from which it is absent. These include usefulness of the liquid as a carrier for other additives, for example dyes and pigments; absorption of some of the heat of reaction which could otherwise adversely affect the reaction or the product; improved mould release; reduced shrinkage; improvement of the physical properties of the product, for example improved energy absorption, and the economic advantage of a relatively cheap additive. Additionally, the chemical composition of the inert liquid can be such as to improve the fire resistance of the elastomer. Depending upon the formulation and the particular inert liquid, one or more of these advantages will be present in any specific case. The amount of inert liquid can in fact be as low as 5% or as high as 60% by weight based on the weight of the elastomer.

The invention is illustrated but not limited by the following Examples in which all parts and percentages are by weight. The words "Shellflex", "Silverson", "Imprez" and "Arco" used in the Examples are registered trade marks.

Example 1 A prepolymer was prepared by reacting 1300 parts of diphenylmethane diisocyanate with 2000 parts of a poly(ethylene/tetramethylene adipate) having an ethylene/tetramethylene molar ratio of 1:1 and a hydroxyl number of 56 and molecular weight of 2000.

2 Parts of a dispersing agent were stirred into 165 parts of the prepolymer at 50-60"C using a high shear "Silverson" stirrer. 46 Parts of a hydrocarbon oil (Shellflex 273) having a boiling point exceeding 1500C at atmospheric pressure were added slowly to the prepolymer whilst maintaining the high shear stirring which was then continued for a further ten minutes. The resulting emulsion was extremely fine and quite stable.

The prepolymer emulsion was warmed to 90"C under vacuum and 18 parts of butane-1,4-diol were added. After mixing and degassing, the mixture was poured into a mould consisting of two aluminium plates coated with a release agent and separated by a rubber gasket. The resulting elastomer was cured at 1100C for 16 hours. The cured elastomer, containing 20% of liquid filler, had the following properties: Hardness, Shore A 88 Tensile strength (MNm-2) 15.2 Elongation at break (%) 440 Permanent set (%) 45 100% modulus (MNm-2) 25 Slight sweating of the oil on the surface of the sheets was apparent after storage for several days.

The dispersing agent used in this Example was prepared as follows: 6.5 Parts of hydroxyethyl methacrylate, 10 parts of an 80/20 mixture of the 2,4- and 2,6isomers of tolylene diisocyanate and 2 drops of dibutyltin dilaurate were dissolved in 20 parts of toluene and reacted at 60"C for 3 hours. 260 Parts of poly(ethylene/tetramethylene adipate) (as described above) were than added and the mixture left at 60"C for 16 hours.

700 Parts of toluene were then added followed by 80 parts of lauryl methacrylate and 0.4 part of azobisisobutyronitrile. The solution was refluxed for 3 hours, a further 0.2 part of azobisisobutyronitrile added and refluxing continued for 2 more hours. 100 Parts of butylbenzyl phthalate were added and the toluene removed under vacuum. The resulting dispersing agent was a yellow viscous liquid.

Example 2 Elastomers were prepared using the method described in Example 1 to illustrate the effect of using mixtures of Shellflex 273 and Imprez T85 (a rosin-like hydrocarbon resin).

The elastomers, again containing 20% of filler (Shellflex 273 and Imprez T85 together) having boiling points exceeding 150"C at atmospheric pressure, had the following properties: Shellflex 273/lmprez T85 weight ratio 75:25 50:50 25:75 0:100 Hardness, Shore A 90 88 90 93 Tensile Strength (MNm-2) 19.5 20.1 18.9 20.0 Elongation (%) 460 530 465 410 Permanent set (%) 2) 45 55 40 45 100% Modulus (MNm- 21 19 21 23 None of the elastomers containing Imprez T85 showed any signs of sweating after storage for several weeks.

Example 3 Elastomers were prepared using the method described in Example 1 to illustrate the effect of using various concentrations of a 50/50 blend of Shellflex 273 and Imprez T85. The elastomers had the following properties: Concentration of liquid filler (%) 0 10 20 30 Hardness, Shore A 93 93 88 83 Tensile strength (MNm-2) 35.8 29.0 20.1 14.5 Elongation (%) 505 530 530 410 Permanent set (%) 30 55 55 35 100% modulus (MNm-2) 26 36 19 16 Example 4 A prepolymer was prepared as described in Example 1 but replacing the poly(ethylene/ tetramethylene adipate) by an equal weight of poly(ethylene adipate) having the same molecular weight. Dispersions were made using various concentrations of the dispersing agent described below and using 30%, based on the eventual elastomer, of a 50/50 blend of Shellflex 273 and Imprez T85. Elastomers made as described in Example 1 had the following properties. The mean droplet diameter of the dispersed oil phase was measured using scanning electron micrographs of cut surfaces of the elastomers.

% Dispersing agent 0 1 2 5 10 20 30 (based on liquid filler) Hardness, Shore A 76 75 74 74 72 72 72 Tensile strength (MNm-2) 17.5 18.1 18.5 17.0 12.0 8.5 7.9 Elongation at break (%) 565 535 535 525 475 370 365 Permanent set (%) 19 18 16 20 10 5 5 100% modulus (MNm-2) 13 12 12 13 11 10 9 Mean droplet diameter (y) 17 8 3.5 1.25 0.75 0.5 < 0.5 The dispersing agent used in this Example was prepared as follows: 6.5 Parts of hydroxyethyl methacrylate, 10 parts of an 80/20 mixture of the 2,4- and 2,6isomers of tolylene diisocyanate, 1 drop of dibutyltin dilaurate and 20 parts of toluene were mixed and allowed to react for 3 hours at 60"C. 260 Parts of the poly(ethylene/ tetramethylene adipate) (described in Example 1) were then added and the mixture left at 60"C for 16 hours. 1000 Parts of toluene were added followed by an adduct of glycidyl methacrylate and poly(12-hydroxystearic acid) (200 parts of a 50% solution in petrol), 50 parts of methyl methacrylate and 3 parts of azobisisobutyronitrile. The solution was refluxed for 3 hours, a further 1 part of azobisisobutyronitrile added and refluxing continued for 2 more hours. 100 Parts of butyl benzyl phthalate were added and the toluene removed under vacuum. The resulting dispersing agent was a pale straw-coloured viscous liquid.

Example 5 A prepolymer was prepared by reacting 1400 parts of polypropylene glycol of molecular weight 2000 and 910 parts of diphenylmethane diisocyanate.

2 Parts of a dispersing agent were stirred into 165 parts of the prepolymer using a "Silverson" stirrer. 46 Parts of Shellflex 273 were added slowly to the stirred prepolymer and stirring was then continued for a further 10 minutes. The isocyanate value was adjusted to 8.28%.

This emulsion was cured by reaction with 18 parts of butane-1,4-diol as described in Example 1. The resulting elastomeric sheet had the following properties: Hardness, Shore A 80 Tensile Strength (MNm-2) 11.6 Elongation (%) 505 100% Modulus (MNm-2) 14 The dispersing agent used in this Example was prepared as follows: 100 Parts of a hydroxyl-ended polybutadiene (R45 HT - ARCO Chemical Co.) and 16 parts of an 80/20 mixture of the 2,4- and 2,6- isomers of tolylene diisocyanate were reacted at 80"C for 2 hours. 500 Parts of toluene and 400 parts of an ethylene oxide tipped polypropylene glycol having a molecular weight of 3750 were then added followed by 1 drop of dibutyltin dilaurate. After mixing, the solution was lift to react for 16 hours. 100 Parts of butyl benzyl phthalate were added and the toluene removed under vacuum. The resulting dispersing agent was a pale brown viscous liquid.

Example 6 Elastomers were prepared as described in Example 5 but increasing the concentration of Shellflex in the elastomer from 20% to 30% and 40%. The elastomers had the following properties: Shellflex 273 30% 40% Hardness, Shore A 72 60 Tensil strength MNm-2) 6.9 6.1 Elongation (%) 315 345 100% Modulus (MNm-2) 12 7 Example 7 Elastomers were prepared as described in Example 5 but using 30% of Shellflex 273 and various amounts of dispersing agent. The elastomers had the following properties: % Dispersing agent 0 2 5 (based on Shellflex 273) Hardness, Shore A 74 72 73 Tensile strength (MNm-2) 6.8 6.9 7.2 Elongation (%) 345 315 335 100% Modulus (MNm-2) 12 12 12 Example 8 An elastomer was prepared as described in Example 5 but replacing the 20% of Shellflex 273 by 30% of a 50/50 mixture of Shellflex 273 and Imprez T85. The elastomers had the following properties: Hardness, Shore A 74 Tensile strength (MNm-2) 9.9 Elongation (%) 435 100% Modulus (MNm-2) 15 Example 9 An emulsion was made of liquid paraffin (21% on the final elastomer) having a boiling point exceeding 1500C of atmospheric pressure in a polyoxypropylene polyol using the dispersing agent described in Example 5. The emulsion was mixed with butane-1,4-diol, triethylene diamine, trichlorofluoromethane and a trace of water to make a conventional shoe-soling formulation. This blend was reacted with a diphenylmethane diisocyanate/ glycol prepolymer and run into a 1/4 inch deep mould coated with a release agent. The mould was rapidly closed and foaming and curing were complete in four minutes. The resulting microcellular sheet had the following properties: Hardness, Shore A 66 Density (g/cc) 0.58 Tensile strength (kNm-2) 3500 Elongation at break (%) 280

Claims (6)

WHAT WE CLAIM IS:

1. A method for the manufacture of a polyurethane elastomer which comprises forming a mixture containing components which react together to form a polyurethane elastomer and an inert liquid that has a boiling-point of at least 1500C at atmospheric pressure and is immiscible with the polyurethane precursors and incompatible with the final polyurethane and allowing reaction to proceed whereby a polyurethane elastomer is formed in which the inert liquid is dispersed throughout as a discontinuous phase.

2. A method as claimed in claim 1 wherein the inert liquid is a hydrocarbon oil.

3. A method as claimed in claim 1 or claim 2 wherein the inert liquid is dispersed in one of the polyurethane precursors with the aid of a dispersing agent which is a polymeric material containing in the molecule at least one chain of a type which is soluble and non-self-associated in the inert liquid and at least one chain of another type which is soluble and non-self-associated in the polyurethane precursor.

4. A method as claimed in any of the preceding claims wherein the amount of inert liquid used is from 5% to 60% by weight based on the weight of the elastomer.

5. A method as claimed in claim 1 substantially as hereinbefore described with reference to any one of the foregoing Examples.

6. Polyurethane elastomers whenever manufactured by a method claimed in any one of the preceding claims.