~" ' MM II II II Ml I Ml II I II Ml II I II J European Patent Office CO Publication number: 0 171 536 B1 Office europeen„ des brevets © EUROPEAN PATENT SPECIFICATION © Date of publication of patent specification: 12.02.92 © Int. CI.5: C08G 18/10, C08G 18/76 © Application number: 85107091.2 @ Date of filing: 08.06.85 The file contains technical information submitted after the application was filed and not included in this specification © P-TMXDI polyurethane elastomers with good compression set properties. © Priority: 30.07.84 US 634081 Proprietor: AMERICAN CYANAMID COMPANY 1937 West Main Street P.O. Box 60 @ Date of publication of application: Stamford Connecticut 06904-0060(US) 19.02.86 Bulletin 86/08 Inventor: Chang, Eugene Yue Chieh © Publication of the grant of the patent: 532 Rolling Hills Road 12.02.92 Bulletin 92/07 Bridgewater New Jersey 08807(US) © Designated Contracting States: AT BE CH DE FR GB IT LI NL SE Representative: Wachtershauser, Gunter, Dr. Tal 29 © References cited: W-8000 Munchen 2(DE) EP-A- 0 022 497 EP-A- 0 111 694 DE-A- 1 645 147 US-A- 3 428 610 US-A- 4 218 543 JOURNAL OF CELLULAR PLASTICS, vol. 18, no. 6, November - December 1982, pages 376-383, Westport, Connecticut, US; V.D. AR- ENDT et al. "M- and P-TMXDI: two new isocyanates for the polyurethane industry" 00 CO CO m Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid (Art. 99(1) European patent convention). Rank Xerox (UK) Business Services EP 0 171 536 B1 Description Field 5 This invention relates to cast polyurethane elastomers based on p-tetramethylxylene diisocyanate (p- TMXDI) having good compression set properties. In Journal of Cellular Plastics, Vol. 18 (1982), No. 6, page 376 - 383 m- and p-TMXDI are introduced as a new family of aliphatic diisocyanates to the polyurethane industry. Polyurethane elastomers are prepared by a reacting excess polyisocyanate with a polyol to form a liquid or low melting polyurethane prepolymer io having terminally reactive isocyanate groups, which can then be reacted with a diamine curing agent to form a polyurethane elastomer. Unfortunately, some of these elastomers exhibit poor "compression set", which makes them undesirable for use in molded articles which are to be used under load as in machine rolls and wheels (see Table 6 on page 380 of the above cited reference). For such load-bearing uses it is essential for the elastomer to exhibit high dimensional stability in order 75 to to retain its resilience and not form flat spots under extended use. This property is known in the art as "good compression set". Compression set is commonly determined by ASTM Method D395 and represents the amount of residual deformation that occurs when an elastomer sample is placed under load sufficient to reduce its height to a specified value, held under that load for a certain period of time at a constant temperature, and then released from the load. Thus, if the height before sample loading is 100 units and it 20 is compressed under load to a height of 90 units, but recovers to a height of 95 units when the load is removed, its compression set is 50%, i.e., 50% of the deformation was permanent. Obviously, the lower the compression set value for a given elastomer, the better it is for load bearing uses. U.S. 3,997,514 discloses a process for preparing polyurethane elastomers having a compression set of 50% or less. In the process an isocyanate terminated prepolymer is prepared and vulcanized by the steps 25 of: 1. Encapping an aromatic diisocyanate, such as 2,4-tolylene diisocyanate, with a glycol, such as poly- (tetramethylene ether)glycol (M.W. about 1,000), 2. reacting the resulting intermediate with an aliphatic diisocyanate to form a prepolymer, and 3. curing the prepolymer with a suitable diamine to form a vulcanizate having improved compression set, 30 specifically 50% or less. Examples of aromatic diisocyanates are given in the penultimate paragraph of column 1 , and examples of aromatic polyamines useful as cross-linking agents are given in the penultimate paragraph of column 2. Tolylene diamines are among the examples of polyamines enumerated in this paragraph, as well as 4,4'- methylenedianiline. 35 U.S. 3,428,610 relates to cross-linked polyurethane plastics and to a method of preparing the same. The cross-linked polyurethanes are prepared by reacting (1) one equivalent of an intermediate containing between 0.5% and 15% free NCO groups with (2) between 0.8 to 1.2 equivalents of a liquid aromatic diamine. The liquid aromatic diamine has (i) one linear alkyl substituent of 1 to 3 carbon atoms in an ortho position to one amino group and two linear alkyl substituents of one to three carbon atoms in both ortho 40 positions to the other amino groups, or (ii) two linear alkyl substituents of one to three carbon atoms in both ortho positions of both amino groups. The patent discloses that any suitable organic polyisocyanate may be used, such as an aliphatic polyisocyanate having the formula OCN-(CH2)„-NCO 45 in which n = 2 to 8 and aromatic diisocyanates. Examples of the polyisocyanates are given in the paragraph bridging columns 3 and 4. Among the examples of the suitable aromatic diamines that are set forth in the first full paragraph in column 4, are 1-methyl-3,5-diethyl-2,4-diaminobenzene and 1-methyl-3,5- diethyl-2,6-diaminobenzene. (Both of these isomers are also known as diethyltoluenediamine or DETDA.) 50 This reference, however, does not relate to the effect of the use of a particular aromatic diamine and its effect on the compression set properties of the resulting polyurethane elastomer. U.S. 4,218,543 relates to a one-step process for the production of elastomeric moldings which have a compact surface by the technique of reaction injection molding, using highly reactive systems of specific polyisocyanates, polyhydroxyl compounds and specific active aromatic polyamines. This patent also relates 55 to active hydrogen-containing blends useful in preparing elastomeric moldings, in which the blends comprise polyhydroxyl compounds, and specific active aromatic diamines. The elastomeric moldings are based on: (a) 4,4'-diisocyanatodiphenylmethane and polyisocyanates based on 4,4'-diisocyanatodiphenylmethane; 2 EP 0 171 536 B1 (b) hydroxyl group containing compounds having a molecular weight of from 1,800 to 12,000 and preferably containing at least two primary hydroxyl groups; (c) active aromatic amines as chain-lengthening agents; (d) catalysts for the reaction between hydroxyl groups and isocyanate groups; and 5 (e) optionally, blowing agents, auxiliary agents and/or additives known in polyurethane chemistry. Among the examples of the aromatic amines are 1-methyl-3,5-diethyl-2,4-diaminobenzene and 1-methyl- 3,5-diethyl-2,6-diaminobenzene. This patent (U.S. 4,218,543) is directed towards reaction injection molding of polyurethanes where the gelation times are extremely fast (approximately 1 second or less). Based on the teachings of this patent, it io would not be expected that diethyltoluenediamines (DETDA) could be utilized in polyurethane cast elastomers which require gel times of the order of several minutes. In particular, it would not be expected that good compression set properties could be obtainable with a particular polyurethane prepolymer when DETDA is used as the curing agent to produce the polyurethane elastomer. Good compression set is achievable in the known cast elastomer art, wherein, for example, toluene is diisocyanate is the diisocyanate used to prepare the prepolymer, and curing is effected with methylenbis(o- chloroaniline)[MBCA, also known as MOCA® brand of methylenebis(o-chloroaniline)]. The principal drawback of this system is the requirement for use of MBCA, which has been reported to be a cancer suspect agent based on tests with laboratory animals. A welcome contribution to the art would be a polyurethane castable elastomer which has good 20 compression set properties ~ i.e., a compression set value of less than or equal to 40%~and does not require the use of MBCA. Such a contribution is provided by this invention. Summary of the Invention 25 This invention provides a polyurethane elastomer composition, having a compression set less than or equal to about 40%, comprising the reaction product of p-TMXDI based prepolymer and an aromatic diamine selected from DETDA, 2,4-bis(p-aminobenzyl)aniline (BABA) and mixtures thereof. Detailed Description of the Invention 30 This invention provides a polyurethane elastomer composition, having a compression set of less than or equal to 40%, comprising the reaction product of: (a) a polyurethane prepolymer having terminally reactive isocyanate groups as defined in claim 1 ; with between about 75 and about 110% of the stoichiometric 35 (b) amount of a curative selected from the group consisting of DETDA, BABA and the mixtures thereof; and (c) optionally, from about 0.01 % to about 2% by weight of catalyst, based on the weight of curative. Another embodiment of this invention provides a method of making a polyurethane elastomer having a compression set of less than or equal to about 40% comprising the steps of reacting the polyurethane 40 prepolymer of (a) with a curative of (b) and optionally the catalyst of (c). In yet another embodiment of this invention, there are provided articles of manufacture made from the compositions of this invention.