GB2068986A - Rim Elastomers with Improved Catalyst Efficiency - Google Patents

Abstract

A reaction injection molded polyurethane elastomer is made by reacting a polyisocyanate (the A- component) with a high molecular weight polyhydric polyether and a low molecular weight active hydrogen containing compound having a functionality of at least two (the B- component in the presence of a tin catalyst, wherein all of tin catalyst is mixed with the A-component before reaction. Reaction proceeds more quickly with the use of less catalyst than is needed with the conventional process in which the tin catalyst is incorporated in the B-component. Moreover the elastomer properties (tensile strength, tear strength, elongation, impact resistance and sag) are improved.

Description

SPECIFICATION Rim Elastomers with Improved Catalyst Efficiency The invention concerns the field of reaction injection molded polyurethanes.

Reaction Injection Molding (RIM) is a technique for the rapid mixing and molding of large, fast curing urethane parts. RIM polyurethane parts are used in a variety of exterior body applications on automobiles where their light weight contributes to energy conservation. RIM parts are generally made by rapidly mixing active hydrogen containing materials with polyisocyanate and placing the mixture into a mold where reaction proceeds. These active hydrogen containing materials usually comprise a high molecular weight polyhydric polyether (polyol) and a low molecular weight active hydrogen containing compound (chain extender). After reaction and demolding, the parts may be subjected to an additional curing step which comprises placing the parts in an ambient temperature of about 1 2O0C or greater.

Usual practice is to place all components except the isocyanate in one vessel (polyol, chain extender, tin catalysts, amine catalysts, silicone surfactants, etc. called the B-component) and the isocyanate in another vessel (called the A-component) prior to reaction. Then the A and B components are mixed together in the desired stoichiometric balance in a mold as discussed above.

It has been surprisingly discovered that significant advantages occur when all of the tin catalyst is placed in the A-component prior to reacting the A and B components in the mold.

The invention is a method for making reaction injection molded polyurethane of improved properties with reduced catalyst usage. The product comprises the reaction product of a high molecular weight polyhydric polyether, a low molecular weight active hydrogen containing a compound of at least 2 functionality and a polyisocyanate in the presence of a tin catalyst wherein two (2) components are reacted together. One component contains all of the isocyanate. In the method of this invention, all of the tin catalyst is placed with the isocyanate component prior to reaction.

The polyols useful in the process of this invention include polyether polyols, polyester diols, triols, tetrols, etc., having an equivalent weight of at least 500, and preferably at least 1000 up to about 3000. Those polyether polyols based on trihydric initiators of about 4000 molecular weight and above are especially preferred. The polyethers may be prepared from lower alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide or mixtures of propylene oxide, butylene oxide and/or ethylene oxide. In order to achieve the rapid reaction rates which are normally required for molding RIM polyurethane elastomers, it is preferable that the polyol be capped with enough ethylene oxide to increase the reaction rate of the polyurethane mixture.Normally at least 50% primary hydroxyl is preferred, although amounts of primary hydroxyl less than this are acceptable if the reaction rate is rapid enough to be useful in industrial application. Other high molecular weight polyols which may be useful in this invention are polyesters or hydroxyl terminated rubbers (such as hydroxyl terminated polybutadiene). Hydroxyl terminated quasi-prepolymers of polyols and isocyanates are also useful in this invention.

The chain-extenders useful in the process of this invention are preferably difunctional. Mixtures of di-functional and trifunctional chain-extenders are also useful in this invention. The chain-extenders useful in this invention include diols, amino alcohols, diamines or mixtures thereof. Low molecular weight linear diols such as 1 4-butanediol and ethylene glycol have been found suitable for use in this invention. Ethylene glycol is especially preferred. Other chain-extenders including cyclic diols such as 1,4-cyclohexane diol and ring containing diols such as bishydroxyethylhydroquinone, amide or ester containing diols or amino alcohols, aromatic diamines and aliphatic amines would also be suitable as chain-extenders in the practice of this invention.

A wide variety of aromatic polyisocyanates may be used here. Typical aromatic polyisocyanates include p-phenylene diisocyanate, polymethylene polyphenylisocyanate, 2,6-toluene diisocyanate, dianisidine diisocyanate, bitolylene diisocyanate, napthalene- 1 ,4-diisocyanate, bis(4isocyanatophenyl)methane, bis(3-methyl-3-isocyantophenyl)methane, bis(3-methyl-4isocyanatophenyl)methane, and 4,4'-diphenyl-propane diisocyanate.

Other aromatic polyisocyanates used in the practice of the invention are methylene-bridged polyphenyl polyisocyanate mixtures which have a functionality of from about 2 to about 4. These latter isocyanate compounds are generally produced by the phosgenation of corresponding methylene bridged polyphenyl polyamines, which are conventionally produced by the reaction of formaldehyde and primary aromatic amines, such as aniline, in the presence of hydrochloric acid and/or other acidic catalysts. Known processes for preparing polyamines and corresponding methylene-bridged polyphenyl polyisocyanates therefrom are described in the literature and in many patents, for example, U.S. Patents 2,683,730; 2,950,263; 3,012,008; 3,344,162 and 3,362,979.

Usually methylene-bridged polyphenyl polyisocyanate' mixtures contain about 20 to about 100 weight percent methylene diphenyldiisocyanate isomers, with the remainder being polymethylene polyphenyl diisocyanates having higher functionalities and higher molecular weights. Typical of these are polyphenyl polyisocyanate mixtures containing about 20 to 100 weight percent methylene diphenyldiisocyanate isomers, of which 20 to about 95 weight percent thereof is the 4,4'-isomer with the remainder being polymethylene polyphenyl polyisocyanates of higher molecular weight and functionality that have an average functionality of from about 2.1 to about 3.5. These isocyanate mixtures are known, commercially available materials and can be prepared by the process described in U.S. Patent, 3,362,979, issued January 9, 1968 to Floyd E, Bentley.

By far the most preferred aromatic polyisocyanate is methylene bis(4-phenylisocyanate) or MDI.

This can be used in the form of pure MDI, quasi-prepolymers of MDI, modified pure MDI, etc. Materials of this type may be used to prepare suitable RIM elastomers. Since pure MDI is a solid and, thus, often inconvenient to use, liquid products based on MDI are often used and are included in the scope of the terms MDI or methylene bis(4-phenylisocyanate) used herein. U.S. Patent 3,394,1 64 is an example of a liquid MDI product. More generally uretonimine modified pure MDI is included also. This product is made by heating pure distilled MDI in the presence of a catalyst.The liquid product is a mixture of pure MDI and modified MDI:

2 [OCN O CH2 O NCO ] Catalyst OCNO CH2 Q"QCH2 0NCO + + C02 -N CH2 NCO Carbodiimide

Uretonimine Examples of commercial materials of this type are Upjohn's ISONATE 1 25M (pure MDI) and ISONATE 143L(''llquid'' MDI). Preferably the amount of isocyanates used is the stoichiometric amount based on all the ingredients in the formulation or greater than the stoichiometric amount.

The RIM formulation includes a great number of other recognized ingredients such as additional cross-linkers-catalysts, extenders, blowing agents and the like. Blowing agents may include halogenated low-boiling hydrocarbons, such as trichloromonofluoromethane, and methylene chloride, carbon dioxide, nitrogen, etc., used.

Catalysts such as tertiary amines or an organic tin compounds or other polyurethane catalysts are useful. The organic tin compound may suitably be a stannous or stannic compound, such as a stannous salt of a carboxylic acid, a trialkyltin oxide, a dialkyltin dihalide, a dialkyltin oxide, etc., wherein the organic groups of the organic portion of the tin compound are hydrocarbon groups containing from 1 to 8 carbon atoms. For example, dibutyltin dilaurate, dibutyltin diacetate, diethyltin diacetate, dihexyltin diacetate, di-2-ethylhexyltin oxide, dioctyltin dioxide, stannous octoate, stannous oleate, etc., or a mixture thereof, may be used.

Tertiary amine catalysts include trialkylamines (e.g. trimethylamine, triethylamine), heterocyclic amines, such as N-alkylmorpholines (e.g., N-methylmorpholine, N-ethylmorpholine, dimethyldiaminodiethylether, etc.), 1 ,4-dimethylpiperazine, triethylenediamine, etc., and aliphatic polyamines, such as NIN,N'N'-tetramethyl-1 ,3-butanediamine.

Other conventional formulation ingredients may also be employed, such as, for example, foam stabilizers, also known as silicone oils or emulsifiers. The foam stabilizer may be an organic silane or siloxane. For example, compounds may be used having the formula: RSi[O-(R2SiO)-(oxyalkylene)Ri3 wherein R is an alkyl group containing from 1 to 4 carbon atoms; n is an integer of from 4 to 8; m is an integer of from 20 to 40; and the oxyalkylene groups are derived from propylene oxide and ethylene oxide. See, for example U.S. Patent 3,194,773.

Although not essential for the practice of this invention, the use of commonly known additives which enhance the color or properties of the polyurethane elastomer may be used as desired. For example, chopped or milled glass fibers, chopped or milled carbon fibers and/or other mineral fibers are useful.

In a particularly preferred embodiment, a high molecular weight polyether polyurethane polyol of about 5000 molecular weight or above is reacted with a polyisocyanate to form a reaction injection molded polyurethane part as follows: A B-component is prepared containing ethylene glycol chain extender, a silicone surfactant, an amine catalyst and most of the polyol. An A-component is prepared containing all of the polyisocyanate and a small portion of the polyol reacted with some of the polyisocyanate and all of a tin catalyst to be used in the formulation. The A and B components are mixed together in a RIM machine. After reaction of the A and B components, the resulting polyurethane part is post cured at a temperature of 1 630C for about one half of an hour.As will be shown in the data below, such a procedure causes a striking improvement in heat sag over procedures of hhe prior art where the tin catalyst is present in the B-component. The following examples demonstrate my invention. They are not to be construed as limiting the invention in any way, but merely to be exemplary of the improvement and manner in which the invention may be practiced.

A glossary of terms and materials used in the following examples follows the examples.

Example I A RIM elastomer was made using the following formulation. The tin catalysts (FOAMREZ UL-29 and dibutyltin dilaurate) are in the B-component in the conventional manner.

B-Component THANOL SF 5505 16 pbw Ethylene glycol 6.44 pbw L5430 Surfactant 0.2 pbw FOAMREZ UL-29 0.025 pbw THANCAT DMDEE 0.25 pbw dibutyltin dilaurate 0.015 pbw A-Component THANATE Quasi-Prepolymer L55-0 5.33 pbw ISONATE 143L 27.45 pbw The above weight ratio yields an elastomer with an Isocyanate index of 0.96. The properties are given in Table I.

Example II This example is the same as Example I except for two features a) the tin catalysts (FOAMREZ UL29 and dibutyltin dilaurate) are dissolved in the A-component rather than in the B-component (as in Example I) and b) the total amount of tin catalyst is 1/2 that in Example I for each tin catalyst. This was also molded to a weight ratio appropriate for an Isocyanate index of 0.96. The properties are also given in Table I.

Table I (Postcured at 163 OC for 1/2 hour) Tin catalysts in B Component full Tin catalysts in A- standard level Component, 1/2 level Material Example I Example l/ Tensile, kg/m2 272.4 324.9 Elongation % 167 177 Tear, kg/cm 912.65 1053.74 Impact Resistance Izod J./m notch 613.9 800.7 Heat sag, in 1/2 hour at 1630C 15.25cm overhang 7.14 3.81 Reactivity Profile Cream/Rise/Tack free time in sec. 6.0/7.0/6.5 5.0/6.0/5.5 The above comparison shows that the strength and heat properties of the elastomer made by the method of the invention (Example II) are superior to those of the elastomer made by the method of the prior art (Example I).Also, the reactivity profile of Example II is faster than Example I even though the amount of tin catalyst present in Example II is only 50% of that available in Example I. Thus, the improvements in reactivity profile and elastomer, properties are clearly the result of having the tin catalyst in the A-component.

Glossary of Terms and Materials RIM -- Reaction Injection Molding Polyol--A di or greater functionality high molecular weight alcohol composed of ether groups such as ethylene, propylene, butylene, etc., oxides.

MDI4,4' diphenyl methane diisocyanate ISONATE 1 43L - Pure MDI isocyanate modified so that it is a liquid at temperatures where MDI crystallizes -- product of the Upjohn Co.

THANATE Quasi-prepolymer L-55-0 - A quasi-prepolymer formed by reacting weights of ISONATE 1 43L and THANOL SF-5505.

THANOL SF-5505 -- a 5500 molecular weight polyether triol containing approximately 80% primary hydroxyl groups.

L5430 Silicone Oil - A silicone glycol copolymer surfactant containing reactive hydroxyl groups.

Product of Union Carbide.

THANCAT DMDEE -- Dimorpholinodiethylether FOAMREZ UL-29 - A stannic diester of a thiol acid. The exact composition is unknown. Product of Witco Chemical Co.

Claims (5)

Claims

1. A method for making a reaction injection molded polyurethane elastomer by reacting a high molecular weight polyhydric polyether, a low molecular weight active hydrogen containing compound having a functionality of at least two, and a polyisocyanate in the presence of a tin catalyst and other ingredients, these ingredients being separated into two components before reaction, one component containing all of the polyisocyanate, wherein all of the tin catalyst is mixed with the polyisocyanate component before reaction.

2. A method as claimed in Claim 1 wherein the polyol comprises a polyether having a molecular weight of above 4000.

3. A method as claimed in Claim 1 or 2 wherein the polyisocyanate comprises 4,4'diphenylmethane diisocyanate in pure or modified form.

4. A method as claimed in any preceding Claim wherein the elastomer is postcured at about 3250F.

5. A method as claimed in Claim 1 and substantially as hereinbefore described with reference to Example 2.