| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | December 19, 1989 |
| PATENT TITLE |
Preparation of linear, low-molecular-weight polyester-based polyols |
| PATENT ABSTRACT | This invention relates to certain linear, low-molecular-weight polyester-based polyols having at least two hydroxyl groups, low viscosity, high solids content and having the structural formula: ##STR1## wherein R is a moiety derived from a saturated aliphatic polyhydric alcohol; n is 1 or 2, and at least about 50% by weight, of n is n=1; p is 0 to 4 inclusive and m is 2 to 10 inclusive; said polyol being substantially free of any unreacted polyhydric alcohol |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | December 21, 1984 |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
We claim: 1. A process for preparing a linear, low-molecular-weight polyesterbased polyol having, (a) at least two hydroxyl groups, (b) low viscosity, (c) high solids content; comprising heat reacting at least one polyhydric alcohol having from 1 to 6 hydroxyl groups of which at least one is a primary hydroxyl group with at least one aliphatic saturated dicarboxylic acid or a lower alkyl ester thereof in a mole ratio of from about 2.2:1.0 to about 6.0:1.0 respectively until esterification or transesterification is substantially completed. stripping the thus produced product in order to remove any excess of said unreacted polyhydric alcohol by using a product stripping temperature of from about 150.degree. C. to 225.degree. C. at an absolute pressure of from about 0.05 to 200 torr for a period of time from about 10 seconds to 10 minutes whereby the resultant product is substantially free of said polyhydric alcohol, and immediately cooling the resultant product to prevent further chemical reaction. 2. The process according to claim 1 in which the stripping is accomplished using a continuous evaporator. 3. The process according to claim 1 in which the stripping is accomplished using a wiped-film evaporator. 4. The process according to claim 1 in which the stripping temperature is between about 160.degree. C. and 210.degree. C. at an absolute pressure from about 0.1 to 150 torr and for a period of time from about 20 seconds to about 2 minutes. |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION This invention is in the field of certain linear, low-molecular-weight polyester-based polyols having at least two hydroxyl groups, comparatively low viscosities and comparatively high solids contents. This invention is also in the field of coating compositions containing these polyols with a cross-linking agent such as aminotriazine compounds and resins such as melamine-formaldehyde resins, urea-formaldehyde resins, epoxy resins, isocyanates or acrylic polymers containing reactive groups, such as hydroxyl groups, carboxyl groups, amide groups, amine groups and the like. THE PRIOR ART The instant applicants are aware of the following U.S. Pat. Nos., 4,018,848; 4,119,762; 4,222,911; and British No. 1,561,076, all of which patents are incorporated herein by reference. DESCRIPTION OF THE INVENTION This invention relates to linear, low-molecular-weight, polyester-based polyols having at least two hydroxyl groups, a comparatively low viscosity, and a comparatively high solids content. The invention also relates to a process for the preparation of said polyols. The polyols of the present invention can be prepared by transesterifying a mixture of the alkyl esters of aliphatic dibasic acids, sometimes referred to herein as dicarboxylic acids, or simply esterifying a mixture of said acids with one or more of certain polyhydric alcohols. It is preferred to start with the methyl esters of dicarboxylic acids such as adipic, glutaric and/or succinic acids although other lower alkyl esters could be used, such as the ethyl, propyl and butyl esters and the like, but cost factors generally remove these higher esters from consideration since nothing of value is to be gained by their use. Furthermore, this mixture of methyl esters is available commercially and is therefore additionally preferred, for this reason. These methyl esters, as available commercially, have a mole ratio of about 0.5:1.5:0.6, dimethyl adipate, dimethyl glutarate and dimethyl succinate respectively. Variations of this mole ratio can be tolerated depending upon the desired properties of the final product. Lower viscosities are obtainable with higher levels of glutarate, for example. It is not necessarily limited, for instance, to a mixture of these three recited esters. It is also possible to use mixtures of only two dibasic acid esters or even a single dibasic ester if desired. The same would apply to the dibasic acids and their anhydrides wherever available as well, such as mixtures of the acid compounds or single compounds if desired. The dibasic acids that can be used include succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, tartaric and the like including the higher homologs or mixtures thereof. Additionally, one can use tribasic acids such as citric or tricarballylic acid. However, these tribasic acids should be used in combination with the dibasic acids and generally in less than 50 mole percent based on the total moles of acid. Additionally, one can use limited amounts of the aromatic dibasic or tribasic acids whether they are monoaromatic acids such as o-, m-, or p- phthalic acids, mellitic acid and the like including their anhydrides wherever available or their lower alkyl esters or the polyaromatic dibasic acids such as naphthalic acids and the like. When the aromatic acids are used, they must be used with one or more linear aliphatic dicarboxylic acids and in amounts less than the amount of the aliphatic acids. In fact, the aromatic acids, when used, should be present in an amount not exceeding about 30 mole percent based on the total moles of aromatic and aliphatic acids used and preferably not exceeding about 10 mole percent, same basis, for most purposes. The methyl esters of these dibasic acids, sometimes referred to as dibasic esters, are mixed with one or more polyhydric alcohols containing at least two alcoholic hydroxyl groups of which at least one hydroxyl group is a primary hydroxyl group. The preferred diol is cyclohexane dimethanol, CHDM, for brevity. Examples of other polyhydric alcohols with primary hydroxyls that could be used include neopentyl glycol; 1,4-butanediol; 1,6-hexanediol; 2,2,4-trimethyl 1,3 pentanediol; 1,2,6-hexanetriol; trimethylol ethane; trimethylol propane; pentaerythritol, dipentaerythritol, sorbitol, mannitol; dimethylolpropionic acid; and 2,2-dimethyl-3-hydroxypropyl-2, 2-dimethyl-3-hydroxypropionate and the like. Diols containing a mixture of primary and secondary hydroxyls may be used, and include propylene glycol and 1,2-hexylene glycol. Mixtures of other diols may also be used. Usually a catalyst is employed for the esterification/transesterification reaction for the purpose of lowering reaction temperatures and reducing color development in the product. Typical catalysts that may be employed are the alkoxides of titanium, soluble tin compounds such as dibutyl tin dilaurate and soluble manganese compounds such as Mn(OAc).sub.2. Catalyst levels of 0.005 to 1.0% by weight of the reactants can be used or typical levels of 0.01 to 0.5% on the same basis can be used. In the preferred embodiment, the mixed methyl esters are combined with CHDM in a suitable reaction vessel and heated in the presence of a conventional transesterification catalyst, such as a titanium alkoxide, in order to accomplish transesterification. The methanol is split off during the heating step and is easily removed as free methanol until the new reaction product is devoid of or substantially completely free of methanol. The resultant product will contain, as a general rule, some varying amounts of unreacted cyclohexane dimethanol depending on the initial mole ratio of the reactants. The initial starting mole ratios of the dimethyl esters, also referred to as dibasic esters, considered as a whole and as one entity, to the cyclohexane dimethanol can be varied between about 1.0:1.5 and 1.0:10.0 respectively, dimethyl esters to CHDM, but preferably between about 1.0:2.0 and 1.0:4.0 respectively, dimethyl esters to CHDM. The ultimately produced polyol will be devoid of or substantially completely free of any cyclohexane dimethanol. The expressions, devoid of or substantially completely free of, means less than about 12% and preferably less than about 4% by weight based on the total weight of the final polyol reaction product. The conventional technique used to remove the unreacted diol is batch distillation. The preferred technique uses continuous rapid stripping of the CHDM or other alcoholic reactant, immediately followed by cooling the product to prevent chemical reaction and equilibration. Continuous large-scale rapid stripping can be accomplished using several processes including continuous column distillation, shell-and-tube evaporators and falling-film evaporator-strippers, to name several examples. It is conceivable that other techniques could be applied to remove excess diol, including liquid-liquid extraction or crystallization. A useful laboratory technique to demonstrate the importance of rapid stripping and immediate cooling utilizes a rotary evaporator and an oil bath. The charge is a mole ratio of 1:3, dibasic acid to cyclohexane dimethanol transesterification product into the rotary evaporator at an absolute pressure of 1-2 Torr and an oil bath temperature of 180.degree.-185.degree. C. for eight minutes. 43% of the charge is volatilized and the resultant product has a viscosity of 13,800 cps, at 25.degree. and a 60 minutes solids content of 98.8%. If one were to use the batch distillation technique, one experiences high viscosity and low solids content. The reason for these adverse results may reside in the fact that the product is equilibrating chemically toward the most probable component distribution during the slow batch distillation. Actually, polyesterification reactions and transesterification reactions such as this always lead to equilibrium product distributions dictated by simple statistical considerations. Therefore, a batch distillation of a high glycol-to-acid polyol to a lower glycol/acid mole ratio may tend to give the same equilibrium product one would obtain by running the whole transesterification reaction at the final mole ratio. The expression, "Low Viscosity", as used hereinabove and as applied to the products of the present invention, means viscosities of not more than about 15,000 cps and preferably not more than about 10,000 cps when measured on a substantially 100% solids material at 25.degree. C. However, when aromatic polycarboxylic acids are used as one of the acidic compounds, these viscosities will be higher, such as 30,000 cps or even higher. The viscosities are, in fact, low when compared with the viscosities of similar polyols that are prepared by processes that are outside of the scope of the process of the present invention even though these similar polyols contain substantailly the same reactants and contain substantially the same amounts of each reactant on a mole/mole basis. Although one of the principal uses of the polyols of the present invention is in coating compositions, one may use these polyols in such areas as adhesives, foams, moldings, elastomers, and laminates with whatever modifications may be required and such further additives as fillers, layers, and the like. Surprisingly, it was found that rapid stripping of a 3:1 mole ratio CHDM: dibasic ester polyester polyol feed followed by rapid cooling removed approximately 35% of the total weight of feed as CHDM and gave products which combined both low viscosity, on the order of 10,000 cps at 25.degree. C., and high solids content, on the order of 98%. In contrast, conventional batch distillation removing the same weight of CHDM with or without rapid-cooling gives products with much higher viscosities, on the order of 19,000 cps or higher at 25.degree. C., and lower solids content, on the order of 90%. These properties are extremely important in the formulation, application, and performance of high-solids coatings, as will be shown elsewhere in this application. In principal, the same technique is applicable to other ester polyols as well. The maximum positive effect is achieved when all of the reactive groups have equal chemical reactivity. Thus, a diol with one primary and one secondary hydroxyl group will naturally yield a diester high in secondary hydroxyls, because the primaries will have reacted first to form the diester. Further, it will be much harder to get chain extension once one has diester, since the secondary hydroxyl end groups are not very reactive. In a case like this, one would be able to get a good yield of diester starting with a low diol:acid ratio, not much over 2:1. Following the same line of reasoning, one should be able to remove excess diol molecules easily without significant chain extension, so it should be possible to get extremely high solids. In one embodiment, a wiped-film evaporator is used to accomplish the rapid stripping of the CHDM. A wiped-film evaporator, such as the Artisan Rototherm.RTM. thin-film evaporator consists of a heated cylindrical chamber with a feed inlet at the top above a rotatable heated cylindrical member or rotor onto which the feed flows, maintaining the feed as a thin film on the inner wall of the cylindrical chamber. A top exit is provided for the CHDM vapor to escape. An outlet is provided at the bottom from which the desired polyol product emerges. The rotor is attached to an electric motor which provides the rotation. The temperature of the heated film is about 350.degree. F. and the absolute pressure is about 2 mm. The residence time of the material being treated varies from about 30 seconds to 2 minutes. The product leaving at the outlet passses through a heat-exchanger which cools it to approximately 200.degree. F. before it flows into the product storage vessel. The polyols of the present invention can be used as coating compositions without modification when combined with any one or more of a host of crosslinking agents, such as polyisocyanate or the aminotriazine-aldehyde such as the melamine-formaldehyde resins and the like. One can also use the acrylic co-polymers containing alcoholic hydroxy groups in conjunction with the polyols of the present invention and crosslinking agents with or without other reactive groups such as carboxy groups, amide groups, amine groups and the like as shown in the U.S. Pat. Nos. 3,663,389, 3,894,993, and 3,945,961. These patents are incorporated herein by reference. Other conventional additives may also be used such as pigments, catalysts, and the like. |
| PATENT EXAMPLES | available on request |
| PATENT PHOTOCOPY | available on request |
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