Storage Stable Blend Comprising a Long Chain Polyol, a Short Chain Diol and a Urethane

The present invention relates to polyol blends such as are used in preparation of molded parts and more particularly to the stabilization of such polyol blends and to improved thermoset molded parts made therefrom.

Reaction Injection Moldings (RIM) are urethanes basically consisting of a polyol and a polyisocyanate, usually with an extender (e.g. a glycol or a diamine), optionally with a blowing agent (e.g. air), optional reinforcing material (e.g. glass, mica, etc.), wetting agents, and the like, which materials are high pressure injected through a mixing head into a pre-heated mold with usual post-molding baking thereafter applied. RIM urethanes can range from low modulus to very high modulus material parts, foamed on the interior but with a smooth surface. RIM urethanes are capable of being made into very large one-piece parts which are very light in weight. Typical present-day uses of RIM parts include, for example, automobile parts (e.g. bumpers, air deflectors, fenders, front ends, etc.), business machine housings, ski boots, office furniture, and a wide variety of products.

When a glycol extender is utilized in conjunction with a long chain polyol, such as a long chain polyoxyalkylene polyol, it has been reported that the blend suffers from storage stability by separating into two phases. Such phase separation creates difficulties at the plant since mixing of the phase-separated blend must precede use of the blend whether such blend is utilized in RIM part formation or is utilized for other purposes. A variety of proposals aimed at rendering the mixture of long chain polyol and short chain diol compatible have appeared in the art. For example, U.S. Pat. No. 3,929,730 proposes to compatibilize the blend of a polyol and 1,4-butanediol by the addition of thiodiglycol or phenylenediethanolamine. U.S. Pat. No. 3,993,576 proposes to compatibilize mixtures of high molecular weight polyols and low molecular weight polyols by the addition of a butylene glycol or propylene glycol such as dibutylene glycol. U.S. Pat. No. 4,220,732 proposes to compatibilize the blend of polyol and glycol by utilizing as the glycol extender a combination of 1,4-butanediol and phenyldiethanolamine. U.S. Pat. No. 4,385,133 compatibilizes the polyol/glycol blend by employing as the polyol component a mixture of specific polyoxypropylene polyoxyethylene polyols of specific molecular weight and functionality. U.S. Pat. No. 4,485,032 discloses areas or substituted ureas as compatibilizing agents for long chain polyols and up to 30% ethylene glycol. Amounts in excess of 30% resulted in gelled, unuseable products. Other proposals involve the use of salts (potassium chloride or potassium acetate) or add a small amount of isocyanate for partial reaction and compatibilization of the blend. These prior art compatibilizing agents suffer from several deficiencies, primarily low extender levels allowed, high viscosity of resulting mixtures and limited applicability.

Despite such advances in the art, need for effectively stabilizing the polyol/glycol blend while improving the final product still is a desire of the art.

The present invention is addressed to compatibilizing an incompatible blend of a long chain polyol, such as a long chain polyoxyalkylene polyol, and short chain diol, such as a glycol. Such method comprises incorporating into the blend a compatibilizing amount of a urethane.

Another aspect of the present invention is the resulting compatibilized blend of long chain polyol, short chain diol, and compatibilizing urethane. Other aspects of the present invention will readily appear to those skilled in the art based upon the disclosure contained herein.

Advantages of the present invention include the ability to effectively and efficiently compatibilize a blend of polyol and glycol for making a practical storage stable product. Yet another advantage is the increased compatibility of urethane modified polyol blend and isocyanate which is achieved. A further advantage is the ability to make tough and rigid thermosets via the simultaneous polymerization of hydroxy/isocyanate functionality and ethylenic unsaturation functionality. These and other advantages of the present invention will be readily apparent from the description which follows.

The three prime ingredients of the compatibilized blend are a long chain polyol, a short chain diol, and a compatibilizing urethane. Referring initially to the urethane, it has been found that urethanes useful in the practice of the present invention include those of: ##STR1## where R and R' independently represent an alkyl group having from 1 to 20 carbon atoms, an aryl group having from 6 to 12 carbon atoms, an alkaryl group having from 7 to 20 carbon atoms, hydroxyl, hydroxyalkyl or hydroxyaryl; and ##STR2## where R and R' independently represent an alkyl group having from 1 to 20 carbon atoms, an aryl group having from 6 to 12 carbon atoms, an alkaryl group having from 7 to 20 carbon atoms, hydroxyl, hydroxyalkyl or hydroxyaryl.

The proportion of compatibilizing urethane is an amount effective for making the blend of long chain polyol and short chain diol storage stable or phase-stable. Such effective amount typically translates into a percentage of urethane ranging from about 1 to about 20 and advantageously between about 2 and about 10. Of course, mixtures of the urethanes may be utilized as is necessary, desirable, or convenient.

The foregoing description illustrates the presently preferred embodiment of the present invention wherein a long chain polyol and short chain glycol incompatible mixture is compatibilized by a urethane. It should be realized that addition of additional long chain polyols to such three-component mixture usually will affect the amount of urethane required for compatibilizing the incompatible blend. Thus, the weight ratio noted above is illustrative only and may be required to be adjusted to a significant degree on occasion.

Referring to the incompatible blend of long chain polyol and short chain diol, RIM technology requires levels of short chain diol to be such that the solubility level of the short chain diol in the long chain polyol is exceeded; thus the lack of storage or phase stability. The short chain diols most often are alkylene glycols typically ranging from about 2 to 8 carbon atoms in length. Alternatively, the short chain diols can be polyoxyalkylene glycols resulting from the reaction of an alkylene oxide (e.g. ethylene oxide, propylene oxide, or the like) with a short chain alkylene glycol. Advantageously the short chain diols used are propylene glycol/dipropylene glycol mixtures, with minor (less than 50% of the total short chain diol) amounts of other diols such as ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, and the like. The ratio of propylene glycol to dipropylene glycol can be from about 5:1 to about 1:20. It has been found that extremely high levels of short chain glycols, not possible with prior art compatibilizing agents, can form compatible mixtures with the present invention. The ratio of short chain diol to long chain polyol can be from about 1:4 to about 3:1.

Referring to the long chain polyols, such polyols typically are polyoxyalkylene polyols with average molecular weight ranging from between about 500 and about 20,000 and include diols, triols, tetraols, graft or polymer polyols, and the like. The majority of oxyalkylene groups are oxyethylene or oxypropylene groups including mixtures thereof. Additional examples of long chain polyols can be found in U.S. Pat. Nos. 4,385,133, 3,929,730, 3,993,576, and 4,227,032.

The urethane-compatibilized blend is storage or phase stable which means that the compatibilized blend exhibits single phase characteristics when stored at, for example, room temperature, for a time period of at least three months though typically storage of up to six months may be required. Additionally, the compatibilized blend exhibits thermal stability by exhibiting no significant increase in viscosity when subjected to storage at elevated temperature of, for example, about 100.degree. C. Additionally the compatibilized blend can be subjected to multiple freeze-thaw cycles and still exhibit single phase characteristics wherein no significant increase of viscosity can be detected. The ability to exhibit single phase characteristics with no significant increase in viscosity renders the compatibilized blend "storage stable" for present purposes.

Any of the organic polyisocyanates commonly employed in the art of preparing polyurethanes can be employed in forming urethane parts from the compatibilized blend of the present invention. Such polyisocyanates often are polymeric isocyanates in order to reduce toxic vapors of isocyanate monomers. Further, alcohol-modified and other modified isocyanate compositions (e.g. thiocyanates) may be used. Polyisocyanates preferably will have from about 2-4 isocyanate groups per molecule in forming urethane parts. Suitable polyisocyanates for use in the present invention include, for example, hexamethylene diisocyanate, 4,4'-toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymethyl polyphenyl isocyanate (polymeric MDI or PAPI), m-and p-phenylene diisocyanates, bitolylene diisocyanate, triphenylmethane triisocyanate, tris-(4-isocyanatophenyl) thiophosphate, cyclohexane diisocyanate (CHDI), is-(isocyanatomethyl) cyclohexane (H.sub.6 X DI), dicyclohexylmethane diisocyanate (H.sub.12 MDI), trimethylhexane diisocyanate, dimer acid diisocyanate (DDI), dicylcohexylmethane diisocyanate, and dimethyl derivatives thereof, trimethyl hexamethylene diisocyanate, lysine diisocyanate and its methyl ester, isophorone diisocyanate, methyl cyclohexane diisocyanate, 1,5-napthalene diisocyanate, triphenyl methane triisocyanate, xylylene diisocyanate and methyl and hydrogenated derivatives thereof, polymethylene polyphenyl isocyanates, chlorophenylene-2,4-diisocyanate, and the like and mixtures thereof. Aromatic and aliphatic polyisocyanate dimers, trimers, oligomers, polymers (including biuret and isocyanurate derivatives), and isocyanate functional prepolymers often are available as preformed packages and such packages are suitable for use in the present invention also.

The proportion of isocyanate groups to hydroxyl groups in the urethane-forming composition (isocyanate index) typically will range from about 0.8:1 to about 1.2:1, though such ratio can vary as is well known in this art. The two packages or streams which are utilized in forming RIM parts comprise the compatibilized blend as one stream and the polyisocyanate as the second stream. Each stream may contain appropriate catalytic amounts of catalysts which promote the reaction between hydroxyl groups and isocyanate groups. Urethane-promoting catalysts are well known in the art and include a wide variety of organic and inorganic salts of, and organometallic derivatives of, bismuth, lead, tin, and the like, as well as organic phosphines and tertiary organic amines. The art cited above contains exemplary lists of such catalysts and should be referred to for a further description thereof.

Other commonly used additives for RIM products can be applied to the present invention provided that they are inert to the stability and reactivity of the composition. Such additives include, for example, fillers, blowing agents, reinforcing agents, dyes, pigments, moisture scavengers, diluents, surfactants, mold release agents, and the like.

The following examples show how the present invention has been practiced, but should not be construed as limiting. In this application, all units are in the metric system, and all percentages and proportions are by weight, unless otherwise expressly indicated. Also, all citations set forth herein are expressly incorporated here by reference.

Incompatible mixtures of long chain polyols and short chain diols were prepared using the compatibilizers of the present invention compared with known compatibilizers and with the absence of compatibilizers. The formulations and test results are set forth below. The indicated amounts of the various components were mixed and heated if necessary, allowed to cool to room temperature and observed. Miscibility was indicated when a clear, homogeneous solution was attained with no phase separation after setting for seven days.

The polyol/diol compatibilized mixture of Example 5 (41.5 g, 0-55 hydroxyl equivalent) was mixed by hand with 0.05 g dibutyltin dilaurate and 83.2 g (105 isocyanate index) of a modified liquid MDI product (equivalent weight=144 g). This mixture was then poured into a mold heated to 90.degree. C. After three minutes a hard, tough opaque panel had formed and was removed from the mold.