Method for producing reaction injection molded elastomers from amine terminated polyethers, a blend of an aromatic amine terminated chain extender, a substituted acyclic aliphatic amine terminated chain extender and an aromatic polyisocyanate

Abstract: The invention is reaction injection molded (RIM) elastomer comprising a cured reaction product of primary or secondary amine terminated polyethers of greater than 1500 molecular weight, an aromatic polyisocyanate, a combination of an unsubstituted aro­ matic diamine chain extender and a substituted acyclic aliphatic diamine chain extender. The invention is also a method of prep­ aration of a RIM polyurea elastomer as described above.

Description: This invention concerns the field of reaction injection molded elastomers. US-A- 4 254 069 and - 4 272 618 concern the curing of RIM polyurethane elastomers. In the glossary of these patents, a "polyol" is defined as a di- or greater functionality high molecular weight alcohol or an amine terminated molecule composed of ether groups. In the discussion of chain extenders in these patents, amines, including aromatic diamines, are disclosed. However, the actual examples are of polyether polyurethanes using polyols (hydroxyl terminated) of high molecular weight. The chain extender, monoethanolamine, was used as a crosslinker. US-A- 4 396 729, -4 444 910, and - 4 333 067 concern elastomers prepared using a high molecular weight amine terminated polyether, an aromatic diamine chain extender and an aromatic polyisocyanate which may merely be a polyisocyanate or a quasi-prepolymer prepared from a polyol reacted with a polyisocyanate wherein some isocyanate groups are still left unreacted. These patents and other related patents state that certain aliphatic amine chain extender materials as disclosed in US-A- 4 246 363 and - 4 269 945 (see below) may also be used. Various patents have been applied for and received using the basic combination recited above as well as various mold release agents and other additives, for example, catalysts. EP-A- 0 081 701 concerns reaction injection molded elastomers. US-A- 3 838 076 discloses foams made from amine terminated polyethers, wherein the amine termination ranges from 10 to 50 percent. US-A- 3 523 918 describes the use of amine chain extenders for the preparation of integral skin foams. Also, US-A- 4 218 543 describes the use of high molecular weight polyols, certain aromatic diamines and isocyanates for the production of RIM parts. US-A- 4 218 543 specifically claims as a chain extender 1-methyl-3,5-diethyl-2,4-diaminobenzene (diethyltoluenediamine) and its isomer. US-A- 4 523 004 discloses the substituted aromatic diamine chain extenders employed according to this application in a RIM product. US-A- 4 246 363 claims a RIM polyurethane composition derived from using at least three different polyols (some are actually amine crosslinkers, both aliphatic and aromatic having specific relationships and reactivity and solubility parameters to one another. US-A- 4 269 945 claims a process for preparing RIM polyurethanes wherein a relatively high molecular weight hydroxyl containing polyol, a chain extender and a polyisocyanate are used. The chain extender may be an aliphatic amine containing material having at least one primary amine group. US-A- 4 530 941 discloses reaction molded polyurethanes prepared from a composition comprising (a) a relatively high molecular weight polyol, (b) a chain extender, and (c) a polyisocyanate or polyisothiocyanate improved by replacing a portion of the relatively high molecular weight polyol with an aminated or partially aminated polyoxyalkylene material. US-A- 4 578 446 discloses the use of an alkyl substituted chain extender wherein the chain extender is used in a polyurethane cast elastomer process. US-A- 4 631 298 discloses blending various slower reacting chain extenders with diethyltoluene diamine in a RIM system using amine terminated polyethers. The reference to amine chain extenders disclosed in US-A- 4 246 363 and - 4 269 945 is included also. Numerous other patents or patent applications disclose and/or claim RIM plastics made with the ingredients of U. S. Patent US-A- 4 433 067 plus other ingredients. For example, US-A- 4 474 901, columns 2 and 3, disclose the use of certain low molecular weight aliphatic primary amines. Aliphatics are disclosed U. S. Patents, including 4,585,850 and 4,607,090 as crosslinkers in US-A- 4 585 850 and - 4 607 090 WO86/05795 discloses that NCO-terminated prepolymers can be prepared by reacting an excess of isocyanate with an amine-functional compound having an equivalent weight of at least 400, e.g. a polyoxyalkylene polyamine. The prepolymers react with compounds having Zerewitnoff-active hydrogen atoms, e.g. having mercaptan, hydroxyl, primary or secondary amine, or acid groups. US-A-3359243 discloses the production of elastomeric polyureas by reacting aromatic isocyanates with polyoxyalkylene diamines and with various hydrazines, diamines or piperazines. Reaction is generally carried out in solution, and fibers are formed from these solutions. This invention provides a method for producing a reaction injection molded elastomer by reacting, in a closed mold, an aromatic polyisocyanate, an amine terminated polyether of at least 1,500 molecular average weight and an amine equivalent weight from 750 to 4000, and having a functionality of 2 to 6, and having more than 50% of its active hydrogens in the form of amine hydrogens, and a chain extender, characterised in that the chain extender comprises both (i) an aromatic di-primary amine and (ii) an N,N'-dialkyl aliphatic diamine or acrylonitrile adduct of an aliphatic diamine. According to one preferred embodiment, the polyethers have greater than 50% of their active hydrogens in the form of amine hydrogens and the chain extenders comprise a blend of diethyltoluene diamine and N,N'-ditertiarybutyl ethylenediamine. The amine terminated polyethers useful in this invention include primary and secondary amine terminated polyether polyols of greater than 1500 average molecular weight having from 2 to 6 functionality, preferably from 2 to 3, and an amine equivalent weight from 750 to 4000. Mixtures of amine terminated polyethers may be used. In a preferred embodiment the amine terminated polyethers have an average molecular weight of at least 2500. The amine terminated polyether resins useful in this invention are polyether resins made from an appropriate initiator to which lower alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide or mixtures thereof are added with the resulting hydroxyl terminated polyol then being aminated. When two or more oxides are used, they may be present as random mixtures or as blocks of one or the other polyether. In the amination step it is highly desirable that the terminal hydroxyl groups in the polyol be essentially all secondary hydroxyl groups for ease of amination. Normally, the amination step does not completely replace all of the hydroxyl groups. However, the majority of hydroxyl groups are replaced by amine groups. Therefore, the amine terminated polyether resins useful in this invention have greater than 50 percent of their active hydrogens in the form of amine hydrogens. If ethylene oxide is used it is desirable to cap the hydroxyl terminated polyol with a small amount of higher alkylene oxide to ensure that the terminal hydroxyl groups are essentially all secondary hydroxyl groups. The polyols so prepared are then reductively aminated, for example, as outlined in US-A- 3 654 370. In the practice of this invention, a single high molecular weight amine terminated polyether resin may be used. Also, mixtures of high molecular weight amine terminated polyols such as mixtures of di- and trifunctional materials and/or different molecular weight or different chemical composition materials may be used. The aromatic di primary amine chain extenders useful in this invention include, for example, 1-methyl-3,5-diethyl-2,4-diaminobenzene, 1-methyl-3,5 diethyl-2-6-diaminobenzene amine (known as DETDA or diethyltoluene diamine), 1,3,5-triethyl-2,6-diaminobenzene, 3,5,3',5'-tetraethyl-4,4'-diaminodiphenylmethane and the like. Particularly preferred aromatic diamine chain extenders are 1-methyl-3,5-diethyl-2,4-diaminobenzene or a mixture of this compound with 1-methyl-3,5-diethyl-2,6-diaminobenzene. The aliphatic amine terminated chain extenders (those not containing ring structures) useful for this invention are secondary amines and include those N,N'-dialkyl aliphatic amines chain extenders picked from those having significantly lower activity than the aromatic di primary amine chain extenders mentioned above. Some of the aliphatic amines falling in this category would include N,N'-dialkylethylenediamine, N,N'-dialkylpropylenediamine, N,N'-dialkylbutylenedlamine, and the like. Acrylonitrile adducts of aliphatic diamines may also be employed in the practice of this invention. The slower N,N'-dialkyl aliphatic diamine or acrylonitrile adduct of an aliphatic diamine chain extender would be used at a concentration, for example, of 5 to 25%, of the total chain extender combination. It is especially preferred to use as the N,N'-dialkyl aliphatic diamine chain extender N,N'-ditertiarybutyl ethylenediamine. The above exemplified chain extenders are not to be construed as conclusive of all acceptable N,N'-dialkyl aliphatic diamine chain extenders falling within the scope of this invention. They are merely given as examples. Those skilled in the art will readily see that there are other N,N'-dialkyl aliphatic diamine chain extenders which will have the effect noted in the examples which follow. Therefore, it is within the ability of those skilled in the art to identify equivalent N,N'-dialkyl aliphatic diamine chain extenders without departing from the scope of this invention. Chain extenders such as DETDA react very rapidly and produce premature gelling, and consequently densification at the mold inlet. It was surprising that only a minor amount of N,N'-dialkyl aliphatic diamine chain extender blended with DETDA had a dramatic effect on the reaction speed and eliminated the premature gelling but still made RIM parts with good properties. The ratio of aromatic di primary diamine chain extenders to the N,N'-dialkyl aliphatic diamine chain extenders may vary depending on the other reactive ingredients in the formulation. Those skilled in the art will recognize that it is within their skill to blend these chain extenders to achieve a balance between speed of reaction and part properties. When a proper blend is achieved, the reaction will be fast enough to produce parts at a rapid rate but not so fast as to produce premature gelling and densification at the inlet of the mold known as the injection point. Thus, a proper balance of these two types of chain extenders will produce parts with excellent properties as well as having improved processing characteristics. A wide variety of aromatic polyisocyanates may be used here. Typical aromatic polyisocyanates include p-phenylenediisocyanate, 2,6-toluenediisocyanate, dianisidinediisocyanate, bitolylenediisocyanate, naphthalene-1,4-diisocyanate, bis(4-isocyanatophenyl) methane, bis(3-methyl-3-isocyantophenyl)methane, bis(3-methyl-4-isocyanatophenyl)methane, and 4,4'-diphenylpropanediisocyanate. Other aromatic polyisocyanates used in the practice of the invention are methylene-bridged polyphenyl polyisocyanate mixtures which have a functionality of from 2 to 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, in US-A- 2 683 730, - 2 950 263, - 3 012 008, - 3 344 162 and - 3 362 979. Usually methylene-bridged polyphenyl polyisocyanate mixtures contain 20 to 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 20 to 100 weight percent methylene diphenyldiisocyanate isomers, of which 20 to 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 2.1 to 3.5. These isocyanate mixtures are known, commercially available materials and can be prepared by the process described in US-A- 3 362 979. By far the most preferred aromatic polyisocyanate is methylene bis(4-phenylisocyanate) or MDI, which can be employed as 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 (see, e.g. US-A- 3 394 164) are often used and are included in the scope of the terms MDI or methylene bis(4-phenylisocyanate) used herein. 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 and is described in US-A- 4 433 067. Examples of commercial materials of this type are Dow's ISONATE® 125M (pure MDI) and ISONATE 143L ("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. Of course, the term polyisocyanate also includes quasi-prepolymers of polyisocyanates with active hydrogen containing materials. As mentioned above, additional catalysts are not necessary for the practice of this invention. In a preferred embodiment of our invention no added catalysts are employed. Other conventional formulation ingredients may be employed as needed such as; for example, foam stabilizers or emulsifiers. Reinforcing materials, if desired, useful in the practice of our invention are known to those skilled in the art. For example, chopped or milled glass fibers, chopped or milled carbon fibers and/or other mineral fibers are useful. Of course, internal mold release agents may be employed. Zinc stearate is known. US-A- 4 396 729 U. S. 4,396,729 discloses mold release agents in general as well as dimethyl siloxane with organic acid groups. Post curing of the elastomer of the invention is optional. Post curing will improve some properties such as heat sag. Employment of post curing depends on the desired properties of the end product. The examples which follow exemplify this invention. EXAMPLE 1 (Comparison) JEFFAMINE® T-5000 (70.5 pbw), diethyltoluene diamine (28.0 pbw), and zinc stearate (1.75 pbw) were charged into the B-component working tank of the Cincinnati Milacron RIM machine. Recirculation temperature was set at 47°C (117°F). Quasi-prepolymer A (94.4 pbw) was charged into the A-component tank and the temperature of this component was adjusted to 51°C (124°F). The components were injected into a production-type fascia tool which was preheated to 72°C (162°F). Total shot weight was 3.1 kg (6.75 lbs). At a 2.7 kg/s (6-lb/sec) injection rate, the part showed some density gradient around the point of injection. A 61 cm x 61 cm x 3 mm (2 ft. x 2 ft. x 0.125 inch) plaque was also injected at a rate of 1.4 kg/s (3-lb/sec) [1.3 kg (2.95 lb shot)]. This plaque was used to determine physical properties. EXAMPLE 2 JEFFAMINE T-5000 (70.5 pbw), diethyltoluene diamine (28.0 pbw), N,N'-di-t-butyl ethylenediamine (Di-t-BuEDA) (1.4 pbw) and zinc stearate (1.75 pbw) were charged into the B-component working tank of the Cincinnati Milacron RIM machine. Recirculation temperature was set at 48°C (119°F). Quasi-prepolymer A (98.8 pbw) was charged into the A-component tank and the temperature of this component was adjusted to 52°C (125°F). The components were injected into a production-type fascia tool which was preheated to 72°C (162°F). Total shot weight was 3.1 kg (6.75 lbs). At a 2.3 kg/s (5-lb/sec) injection rate, the part looked similar to that of Example 1, which was shot at 2.7 kg/s (6-lb/sec). A flat plaque was also prepared in a similar manner to Example 1. EXAMPLE 3 JEFFAMINE T-5000 (70.5 pbw), diethyltoluene diamine (28.0 pbw), N,N'-di-t-butyl ethylenediamine (4.2 pbw) and zinc stearate (1.75 pbw) were charged into the B-component working tank of the Cincinnati Milacron RIM machine. Recirculation temperature was set at 48°C (119°F). Quasi-prepolymer A (107.5 pbw) was charged into the A-component tank and the temperature of this component was adjusted to 44°C (112°F). The components were injected into a production-type fascia tool which was preheated to 72°C (162°F). Total shot weight was 3.1 kg (6.75 lbs). At a 2.0 kg/s (4.5-lb/sec) injection rate, the part looked similar to that of Example 1, which was shot at 2.7 kg/s (6-lb/sec). A flat plaque was also prepared in a similar manner to Example 1. The above data indicate that significantly longer injection times can be obtained by the addition of N,N'-ditertiarybutyl ethylenediamine to the B-component without seriously affecting properties. GLOSSARY OF TERMS AND MATERIALS ISONATE® 143L - Carbodiimide modified liquid MDI, a product of the Dow Chemical Co. JEFFAMINE® T-5000 - Polypropylene oxide triamine of about 5,000 molecular weight DETDA - Diethyltoluene diamine, a product of Ethyl Corp. THANOL® SF-5505 - A 5,500 molecular weight polyether triol containing approximately 80% primary hydroxyl groups. Quasi-prepolymer A - A quasi-prepolymer prepared by reacting THANOL® SF-5505 (40 pbw) with ISONATE® 143L (60 pbw).

Claims: A method for producing a reaction injection molded elastomer by reacting, in a closed mold, an aromatic polyisocyanate, an amine terminated polyether of at least 1,500 average molecular weight and an amine equivalent weight from 750 to 4000, and having a functionality of 2 to 6, and having more than 50% of its active hydrogens in the form of amine hydrogens, and a chain extender, characterised in that the chain extender comprises both (i) an aromatic di-primary amine and (ii) an N,N'-dialkyl aliphatic diamine or acrylonitrile adduct of an aliphatic diamine. A method according to claim 1 characterised in that the polyethers have a molecular weight of at least 2,500. A method according to claim 1 or claim 2 characterised in that the polyethers have a molecular weight of at least 5000. A method according to any of the preceding claims characterised in that the percent of N,N'-dialkyl aliphatic diamine or acrylonitrile adduct of aliphatic diamine chain extender to total chain extender is 5 to 25%. A method according to any of the preceding claims characterised in that the polyethers have greater than 50% of their active hydrogens in the form of amine hydrogens and the chain extenders comprise a blend of diethyltoluene diamine and N,N'-ditertiarybutyl ethylenediamine.

Inventors: DOMINGUEZ RICHARD JOSEPH GILBE, GRIGSBY ROBERT ALLISON JR, RICE DORIS MARVIN, DOMINGUEZ, RICHARD JOSEPH GILBERT, GRIGSBY, ROBERT ALLISON, JR., RICE, DORIS MARVIN
Applicants: TEXACO DEVELOPMENT CORP, TEXACO DEVELOPMENT CORPORATION
Application year: 1988
Main classification: C08G18
IPC codes: C08G18