GB2083484A - Reinforced Reaction Injection Molded Elastomers - Google Patents

Abstract

Reaction injection molded polyurethane elastomers reinforced with inert fillers are made by reacting two streams with one another, one stream containing polyisocyanate and the other stream containing at least one active hydrogen-containing material, wherein all the inert filler is placed in the isocyanate-containing stream before mixing and reaction with the active hydrogen-containing stream. The products exhibit improved tensile strength and thermal dimensional stability when compared with conventional products in which the filler is present in the active hydrogen-containing component The fillers may be chopped or milled glass fibres, chopped or milled carpet fibres and/or other mineral fibres.

Description

SPECIFICATION Improved Reinforced Reaction Injection Molded Elastomers The invention concerns the field of reinforced reaction injection molded polyurethanes (RRIM).

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 comprise a high molecular weight polyhydric polyether and a low molecular weight active hydrogen containing compound. The low molecular weight active hydrogen containing compounds are ethylene glycol, 1,4butane diol or similar materials known to those skilled in the art.

Generally, the active hydrogen containing materials, both high and low molecular weight, are mixed together with catalyst and other optional materials in one tank and the polyisocyanate is contained in another tank. When these two streams are brought together in a mold, reaction is effected, and the RIM part is made. In many cases, in order to improve the strength properties of the RIM product, a reinforcing material such as chopped or milled glass or other mineral fibres is incorporated into the RIM formulation by placing the inert filler material in the unreacted components.

Prior to our invention, the filler material has been placed in the active hydrogen containing material side, that is, the polyol side or split between the polyol side and the polyisocyanate side before the polyol and the isocyanate streams are mixed together.

It has been surprisingly discovered that properties are considerably improved if all of the inert filler material is placed in the isocyanate side prior to reaction.

The invention is a method of improving certain physical properties of inert fiber reinforced reaction injection molded polyurethane elastomers (RRIM) made by the reaction of two streams, one containing polyisocyanate and one containing active hydrogen containing materials. The method involves placing all of the inert filler material in the isocyanate containing stream prior to mixing and reaction with the active hydrogen containing stream and then reacting the streams in a conventional manner.

The polyols useful in the RIM elastomers of this invention include polyether polyols, polyester diols, triols, tetrols, etc., having an equivalent weight of from about 1,000 to about 3,000. Those polyether polyols based on trihydric initiators which have hydroxyl numbers ranging from about 56 to about 24 are especially preferred. The polyethers may be prepared from lower alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide or mixtures of propylene, butylene 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.

The chain-extenders useful in the process of this invention are preferably difunctional. Mixtures of difunctional 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. Ethyiene 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, naphthalene-1 ,4-diisocyanate, bis(4isocyanatophenyl)methane, bis(3-methyl-3-isocyanatophenyl)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 avaiiable 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 uretoniminemodified 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 [ocNOocR2 NCO] $catalyst OCNOOCH2OON=c=NOOCH2 + + C02 Carbodilmide OCNCH -N-C=NCII 2 II O=C-NOO CH2DcNCo Uretonimine Examples of commercial materials of this type are Upjohn's Isonate1 25M (pure MDI) and Isonate(B)1 43L ("liquid" 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.

in one embodiment of the invention, the polyisocyanate not prereacted with any active hydrogen containing compounds such as polyols before the polyisocyanate stream and polyol streams are mixed to form the RRIM part.

In another embodiment, the polyisocyanate stream may comprise a quasi-prepolymer. A quasiprepolymer is the reaction product of a polyol with more than the stoichiometric amount of polyisocyanate.

Catalysts can be present to accelerate the reaction. Among those most frequently employed in this art are the amine catalysts and the organo methallic compounds. For example, trimethylamine, Nmethylmorpholine, N,N,N',N'-tetramethyl-1 ,3-butanediamine, 1 ,4-diazabicyclo[2.2. 1 ]octane, dibutyltin dilaurate, stannous octoate, dioctyltin diacetate, lead octoate, lead naphthenate, lead oleate, etc. Also useful are other known catalysts such as the tertiary phosphines, the alkali and alkaline earth metal hydroxides or alkoxides, the acidic metal salts of strong acids, salts of various metals, etc. These catalysts are well known in the art and are employed in catalytic quantities, for example, from 0.001 percent to about 5 percent, based on the weight of the reaction mixture.

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.

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)n-(oxyalkylene)mR]3 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.

The reinforcing materials useful in the practice of our invention are those which are useful and known to those skilled in the art. For example, chopped or milled glass fibers, chopped or milled carpet fibers and/or other mineral fibers are useful. The invention herein lies not in which pert fiber is useful but in the method of its incorporation in the reaction medium. That is, invention concerns placing all of the inert fibers or filiers in the isocyanate portion prior to reaction with the active hydrogen containing portion.

In a particularly preferred embodiment, a 5500 molecular weight polyether polyol based on a trihydric initiator (hydroxyl number of about 33), ethylene glycol, silicone fluid and catalysts are mixed and comprise the polyol stream. The polyisocyanate stream comprises a quasi-prepolymer of the 5500 molecular weight polyol described above and liquid MDI. Glass fibers are placed in the polyisocyanate stream. The polyol stream and the polyisocyanate stream are mixed and reacted in a RRIM machine resulting in a RRIM elastomer which is cured at 121 or for about 30 minutes.

The examples which follow exemplify the improvement obtained by the process of the invention.

However, these examples are not intended to limit the scope of the invention.

Glossary of Terms and Materials 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.

FOMREZ UL-29-a stannic diester of a thiol acid. The exact composition is unknown. Product of Witco Chemical Co.

ISONATE 1 43L-pure MDI isocyanate modified so that it is a liquid at temperatures where MDI crystallizes-product of the Upjohn Co.

Ouasi-prepoiymer L-55-0-a quasi-prepolymer formed by reacting weights of Isonate 1 43L and THANOL SF-5505.

Example I THANOL SF-5505 (16.0 pbw.), ethylene glycol (6.44 pbw) L-5430 silicone fluid (0.20 pbw.), THANCAT DMDEE (0.25 pbw.), FOMREZ UL-29 (0.025 pbw.), and dibutyltin dilaurate (0.015 pbw.) were premixed and charged into the polyol component working tank of an Accuratio VR-100 RRIM machine. ISONATE 143L (29.66 pbw.), L 55-0 quasi-prepolymer (5.75 pbw.) and Owens/Corning Fiberglass P 1 7B 0.16 cm milled glass fiber (14.6 pbw.) were premixed and charged into the isocyanate component working tank of the machine. The amount of glass dispersed in the isocyanate component represented 20 per cent of the resulting elastomer.The isocyanate component was adjusted to 320C and the polyol component adjusted to 49"C. The machine was adjusted so that the isocyanate/polyol ratio was 2.18 by weight at a total throughput of 60 Ib./min.

At the above conditions, the components were injected through the impingement mix head into a 45.7x45.7x0.32 cm steel mold preheated to 71 C. The parts were released in one minute. Some of the samples received no post cure while others were post cured 30 minutes at 121 OC and still others at 1 6306. The dimension of the parts post treated under the three conditions were accurately measured and compared to the dimensions of the mold. Then, after conditioning for one week, mechanical properties were obtained both parallel and perpendicular to the flow of glass fiber filled components into the mold.

Example II (Comparative) The formulation of Example I was repeated except that in this case, 20 per cent by weight OCF P1 1 7B 0.16 cm milled glass was added to each component (5.73 pbw in the polyol component and 8.85 pbw. in the isocyanate component). The filled plaques were molded under exactly the same conditions as in Example I except that in this case, the weight ratio of the isocyanate/polyol component was 1.544. These were cured and tested according to the conditions outiined in Example I.

Example lil (Comparative).

The formulation of Example I was repeated, except that in this case, all the milled glass fiber (14.6 pbw) was dispersed in the polyol component. The filled plaques were molded under exactly the same conditions as Example I except that in this case, the weight ratio of the isocyanate/polyol components was 0.944. These were cured and tested according to the condition outlined in Example I.

Thus, the composition of the three elastomers described in Example I, II and III is exactly the same. The only difference among them is in which component or components the glass was dispersed before reaction.

Table I gives the properties of the three elastomers. Note that all properties are best for the elastomer of Example I where all the glass is dispersed in the Isocyanate component. In particular, tensile strength is improved by the practice of this invention. In Table II, the shrinkage/expansion properties of the three elastomers as shown as a function of annealing temperature. Note that the elastomer of Example I is least affected by temperature. Example Ill, where all the glass is dispersed in the polyol component, displays the greatest sensitivity to temperature. In fact, when this elastomer is annealed at 1 630C for 1/2 hour (Table II), it actually expands versus the mold size. Since it is very desirable, that RRIM elastomers be insensitive to temperature changes, it is clear that the elastomer of Example I is the best.

Table I Properties as a Function of the Distribution of Glass in the Polyol and Isocyanate Liquid Components Example I* Example I* Example III* Flow Direction Parallel Perpendicular Parallel Perpendicular Parallel Perpendicular Tensile strength, Kg/m (x106) 3.586 3.164 3.164 3.094 2.848 2.672 Elongation, % 42 48 28 64 30 65 Flexural Modulus, at 25 C Kg/m (x108) 1.723. 1.090 1.652 1.055 1.617 1.055 Heat Sag., cm 15.25 cm overhang 1/2 hr.at 163 C 0.56 0.79 0.61 1.37 0.99 0.91 *Isocyanate Index=1.02, all parts annealed 1/2 hr. at 163 C.

Table II Shrinkage/Expansion as a Function of the Distribution of Glass in the Polyol and Isocyanate Components Annealing Condition Example I Example Il Example 111 No annealing -0.35 -0.35 -0.35 Annealed 1/2 hr. at 121 0C -0.57 -0.57 -0.35 Annealed 1/2 hr. at 1630C -0.24 -0.13 +0.31 *Shrinkage is reported as a negative () % and expansion is represented as a positive (+) % versus cold steel mold dimensions. Data is reported in the direction perpendicular to the flow direction since this is where differences are most exaggerated.

Claims (8)

Claims

1. A method for making reaction injection molded polyurethane elastomers reinforced with inert fillers wherein two streams are reacted with one another, one stream containing polyisocyanate and the other stream containing at least one active hydrogen containing material wherein all the inert filler is placed in the isocyanate-containing stream before mixing and reaction with the active hydrogencontaining stream.

2. A method as claimed in Claim 1 wherein the active hydrogen-containing material is a polyol.

3. A method as claimed in Claim 2 wherein the polyol is a polyether polyol based on a trihydric initiator having a hydroxyl number from 56 to 24.

4. A method as claimed in Claim 3 wherein the polyol has a molecular weight of about 5500.

5. A method as claimed in any preceding Claim wherein the polyisocyanate is methylene bis(4phenylisocyanate), in pure form or in the form of a mixture.

6. A method as claimed in any preceding Claim wherein the inert filler comprises glass.

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

8. Reaction injection molded polyurethane elastomers when made by a method as claimed in any of the preceding Claims.