| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | April 26, 1994 |
| PATENT TITLE |
Method for producing saturated polyester |
| PATENT ABSTRACT | A method for producing a high molecular weight saturated polyester comprising adding to a saturated polyester with the terminal group being substantially hydroxyl group, having a number average molecular weight of 5,000 or more and being in the molten state, diisocyanate containing isocyanate group the amount of which corresponds to 1/10 to 2 equivalents of the amount of the hydroxyl group |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | November 25, 1991 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A method for producing a high molecular weight saturated polyester having a melting point of 105.degree. to 120.degree. C. and film forming properties, comprising adding a diisocyanate to a saturated aliphatic polyester in a molten state at a temperature not lower than the melting point thereof, wherein said saturated aliphatic polyester is obtained by the reaction of (a) succinic acid and butanediol-1,4, (b) succinic acid, adipic acid and butanediol-1,4, or (c) succinic acid and ethylene glycol and has terminal groups being substantially hydroxyl groups, and a number average molecular weight of 10,000 or more, and wherein said diisocyanate has an isocyanate group the amount of which corresponds to from 1/10 to 2 equivalents of the amount of the hydroxyl group of the saturated aliphatic polyester. 2. The method claimed in claim 1, wherein the amount of diisocyanate containing isocyanate group corresponds to the amount of 0.3 to 1.5 equivalents of the hydroxyl group. 3. The method claimed in claim 1, wherein the amount of diisocyanate containing isocyanate group corresponds to the amount of 0.5 to 1.2 equivalents of the hydroxyl group. 4. The method claimed in claim 1, wherein the saturated aliphatic polyester has a number average molecular weight of from 10,200 to 16,200. 5. The method claimed in claim 1, wherein the amount of said diisocyanate is from 0.2 to 5 parts by weight per 100 parts by weight of the saturated aliphatic polyester. 6. A method claimed in claim 1, wherein said diisocyanate is hexamethylenediisocyanate. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester useful for various applications, comprising further polymerizing a polymeric saturated polyester with the terminal group being substantially a hydroxyl group. 2. Description of the Related Art It has been well known that saturated polyesters, in particular those containing terephthalate as one component, have been utilized as film, molded articles and glass fiber reinforced plastics for applications in various fields. They are also useful as base resins for adhesives and paints, so their development has also been progressing recently. The present invention relates to a method for imparting satisfactory practical properties to polyesters such as those with relatively low melting points to be used as paints and adhesives and aliphatic polyesters not sufficiently provided with film forming properties, etc. by increasing the molecular weights thereof rather than polyesters with relatively high melting points such as polyethylene terephthalate. As has been well known, the method for synthesizing a polyester of a high molecular weight (the term "high-molecular weight" means a number average molecular weight of about 10,000 or more) depends on the deglycol reaction of the terminal hydroxyl group of a low-molecular polyester. Hence, the concentration of the terminal group decreases remarkably as the molecular weight increases. Furthermore, a decomposition reaction additionally occurs due to the temperature during the ester exchange, so a limitation is imposed on the molecular weight. Such a tendency can be distinctively observed in aliphatic polyesters in particular. When a conventional deglycol reaction in reduced pressure is employed for producing a high-molecular saturated polyester as is shown in FIG. 1, for example, it is observed that the molecular weight begins to decrease once the molecular weight reaches the maximum. In such case, it is very hard to produce an aliphatic polyester with a molecular weight satisfactory for forming tough film by means of the conventional deglycol reaction. In other words, it may be concluded that a film with mechanical properties for practical use cannot be formed from the molecular weights which have been realized by aliphatic polyesters. Polyesters with aromatic structures also induce similar situations, for example, when the polyesters are to be used as a base resin of an adhesive. The unsatisfactory molecular weights thereof appear as insufficient mechanical properties. SUMMARY OF THE INVENTION Thus, the present inventors, as a result of various studies aimed at increasing the molecular weight of such polyesters with lower thermal decomposition temperatures, as much as possible, have found that a high-molecular polyester can be unexpectedly synthesized in a smooth manner without a risk of gelation, by adding to a saturated polyester with the terminal group being substantially a hydroxyl group and being in the molten state at a temperature not less than the melting point thereof, a diisocyanate containing isocyanate group the amount of which corresponds to 1/10 to 2 equivalents of the amount of the hydroxyl group to thus achieve the present invention. Although according to technical common sense, gelation cannot be avoided in the process of reacting isocyanate with polymers at higher temperatures, the present invention is significant in that the increase in the molecular weight of a polyester can be realized without the risk of gelation, by setting the molecular weight of the polyester and the amount of isocyanate, at 5,000 or more and 1/10 to 2 equivalents of the amount of the hydroxyl group, respectively. The amount of diisocyanate to be used is preferably 0.3 to 1.5 equivalents, more preferably 0.5 to 1.2 equivalents. If the amount of diisocyanate to be used is represented as the equivalent of the hydroxyl group of isocyanate group and is less than 1/10 equivalent of the hydroxyl group, the effect on the increase in the molecular weight is poor; if the amount is above 2 equivalents, the risk of gelation gets higher. Although various acid components may be used in a saturated polyester as a principal component of the present invention, the following species may be illustrated; succinic acid, terephthalic acid (including dimethyl terephthalate), isophthalic acid, adipic acid, sebacic acid, dodecanoic acid, and alicyclic polybasic acids with poor polymerizing potency although the acids have unsaturated bonds, the acids being generally regarded as saturated acids, for example, tetrahydro anhydrous phthalic acid, methyltetrahydro anhydrous phthalic acid, endomethylene tetrahydro anhydrous phthalic acid, and the like. In terms of melting point, film forming property and cost, two combinations, namely the combination of succinic acid and ethylene glycol and the combination of succinic acid and butanediol 1,4 are preferable. In this case, a part of the succinic acid can be substituted with adipic acid, sebacic acid or decamethylene dicarboxylic acid, and the substituted proportion is preferably 50 mol % or less. In view of desirable properties such as toughness, adhesive property and the like, an acid component in the polyester is a compound of a carbon number of 5 or more. Because anhydrous phthalic acid has a sublimation property, it is difficult to synthesize a high-molecular polyester by means of this acid alone. However, the concurrent use of the acid with other acids is possible. Polyhydric alcohols must be of the type in which at least a part thereof is transferred to the outside of the ester by means of the temperature and the pressure during the deglycol reaction, because polyester is polymerized through the deglycol reaction. Examples thereof include for example ethylene glycol, propylene glycol, butanediol 1,3, butanediol 1,4, pentanediol 1,5, 3-methyl-pentanediol 1,5, hexanediol 1,6, nonanediol 1,9, diethylene glycol, dipropylene glycol, neopentyl glycol and 2-methyl propanediol 1,3. A part of a polyhydric alcohol component, for example, a part of butanediol 1,4, can be substituted with hexanediol 1,6 or decamethylene glycol. The amount of high-boiling polyhydric alcohol, for example, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, bisphenol A propylene oxide adduct, polyethylene glycol, and polytetramethylene glycol, is limited to 50 mol % or less. Alkylene monoepoxide can be used under the same conditions. For polyester production, esterification is effected up to a desirable acid number (10 or less generally) in the excess of polyhydric alcohol, followed by deglycol reaction in the presence of a reaction catalyst such as a tetraalkyl titanium compound under vacuo. Said reaction catalyst may be added at the outset of esterification reaction. A desired amount of diisocyanate is added in the stage where a required molecular weight is achieved. No limitation is imposed on the types of diisocyanate to be used in the present invention, and commercially available ones may be used as they are. Their examples include 2,4-tolylenediisocyanate, a mixture of 2,4-tolylenediisocyanate and 2,6-tolylenediisocyanate, diphenylmethane diisocyanate, p,p'-diphenyl diisocyanate, 1,6-naphthylene diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. The reaction proceeds simultaneously on the addition of diisocyanate, and the reaction is then completed in a few minutes. The saturated polyester with the increased molecular weight by means of diisocyanate in accordance with the present invention can be subjected to the applications mainly as adhesives, sticking agents, molded articles, films and the like. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph representing the relation of the reaction time and the distribution of molecular weights in the process of producing a high-molecular saturate polyester according to the conventional reaction in reduced pressure. FIG. 2-A is a graph representing the results of the GPC measurement of the molecular weight of Polyester A in Example 1. FIG. 2-B is a graph representing the results of the GPC measurement of the molecular weight of Polyester B in Example 1. FIG. 3-A is a graph representing the results of the GPC measurement of the molecular weight of Polyester G in Example 4. FIG. 3-B is a graph representing the results of the GPC measurement of the molecular weight of Polyester H in Example 4. |
| PATENT EXAMPLES | available on request |
| PATENT PHOTOCOPY | available on request |
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