Thermoplastic elastomer composition.

0001The present invention relates to a novel thermoplastic elastomer composition, more particularly to a thermoplastic elastomer composition comprising a polyester block copolymer and a liquid diphenylmethane diisocyanate, which has a high melt viscosity and is suitable for producing hollow shaped products such as bellows or section profiles such as moldings by blow molding or extrusion molding.

Prior Art

0002It is known that thermoplastic elastomers having a high melt viscosity can be prepared by incorporating a polyester polyether block copolymer with a metal salt of a fatty acid, such as a dimeric acid salt or Surlyn A (a metal salt of ethylene-acrylic acid copolymer, manufactured by Du Pont), or by modifying a polyester polyether block copolymer with a polyisocyanate compound. The modification of a polyester polyether block copolymer with a polyisocyanate compound is disclosed, for example, in U.S. Defensive Patent Publication T-908011, Japanese Patent First Publication Nos. 121699/1977 and 78413/1982.

0003It has, however, been found that the reaction of a polyester polyether block copolymer with an isocyanate group in the polyisocyanate compound proceeds comparatively slowly even by mixing in molten state, and hence, the modification is completed only a certain period of time after melt- extrusion, and hence, when the modification is carried out by using a conventional solid type diphenylmethane diisocyanate: (abbreviated as "MDI"), it is difficult to uniformly mix it with the polyester block copolymer and to control the reaction. That is, it has been found that because of maldistribution of the solid MDI, it reacts only partially with the polyester elastomer, and hence, the products show various melt viscosity in each production lots and the shaped articles obtained therefrom have occasionally fish eye.

Brief Description of the Invention

0004The present inventors have intensively studied on uniform melt-mixing of a polyester block copolymer and a polyisocyanate compound in order to control easily the reaction and to obtain the desired compound having a high melt viscosity, and have unexpectedly found that when a liquid MDI is used as the polyisocyanate compound, it can easily uniformly be mixed with polyester block copolymers to give the desired thermoplastic elastomer composition having a high melt viscosity.

0005An object of the invention is to provide a novel thermoplastic elastomer composition having a high melt viscosity which is useful for the production of hollow shaped products and section profiles. Another object of the invention is to provide a thermoplastic elastomer composition which has less variation in the production lots. These and other objects and advantages of the invention will be apparent to the skilled persons in this field from the following description.

Detailed Description of the Invention

0006The thermoplastic elastomer composition of the invention comprises 100 parts by weight of a polyester block copolymer and 0.05 to 20 parts by weight of a liquid diphenylmethane diisocyanate (MDI). According to the present invention, the polyester block copolymer and the liquid MDI can uniformly be mixed to give a composition having a high melt viscosity with less variation of the qualities in the production lots, and further, the product has advantageously an improved water resistance.

0007The polyester block copolymer used in the present invention is a thermoplastic polyester block copolymer comprising a polyester segment having a high melting point and a polymer segment having a low melting point and having a molecular weight of 400 to 6,000 wherein a polymer produced from the polyester segment having a high melting point alone has a melting point of not lower than 150°C and the polymer segment having a low melting point alone has a melting or softenifig point of not higher than 80°C. The polymer segment having a low melting point is contained in the ratio of 5 to 80 % by weight, preferably 20 to 80 % by weight, based on the whole weight of the polyester block copolymer.

0008The polyester composing the polyester segment having a high melting point includes polyesters obtained from an aromatic dicarboxylic acid (e.g. terephthalic acid, isophthalic acid, 1,5-dinaphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, bibenzoic acid, bis(p-carboxyphenyl)methane, 4, 4'-sulfonyldibenzoic acid, etc.) and a diol having a low molecular weight (e.g. ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentamethylene glycol, 2,2-dimethyl- trimethylene glycol, 1,6-hexamethylene glycol, decamethylene glycol, p-xylylene glycol, cyclohexanedimethanol, etc.); copolyesters obtained from two or more kinds of the above aromatic dicarboxylic acids and two or more kinds of the above diols; polyesters derived from an oxyacid such as p-(S-hydroxyethoxy)benzoic acid, p-hydroxybenzoic acid; polylactones (e.g. polypivalolactone, etc.); polyetheresters obtained from an aromatic ether dicarboxylic acid (e.g. 1,2- bis(4,4^1-dicarboxymethylphenoxy)ethane, di-(4'-carboxyphenoxy)ethane, etc.) and the above-mentioned diol; and copolyesters obtained from a combination of the above-mentioned dicarboxylic acids, oxyacids and diols having a low molecular weight. The polyesters have a melting point of not lower than 150°C, preferably 150 to 230°C.

0009The polymer segment having a low melting point and having a molecular weight of 400 to 6,000 is contained in substantially amorphous state in the polyester block copolymer. The polymer segment alone show a melting or softening point of not higher than 80°C, preferably less than 40°C. Suitable examples of the polymer segment having a low melting point are polyether glycols (e.g. polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, etc.) and a mixture thereof, and polyether glycol copolymers obtained by copolymerizing the above polyethers. Moreover, the polymer segment having a low melting point includes also polyesters obtained from an aliphatic or alicyclic dicarboxylic acid having 2 to 12 carbon atoms and an aliphatic or alicyclic glycol having 2 to 10 carbon atoms, for example, aliphatic polyesters such as polyethylene adipate, polytetramethylene adipate, polyethylene sebacate, polyneopentyl sebacate, pclytetra- methylene dodecanate, polytetramethylene azelate, polyhexamethylene azelate, poly-c-caprolactone, etc.; and aliphatic copolyesters obtained from two kinds of the above-mentioned aliphatic dicarboxylic acids and two kinds of the above-mentioned glycols. The polymer segment having a low melting point includes further polyester polyether block copolymers obtained by a combination of the above-mentioned aliphatic polyesters and aliphatic polyethers.

0010In preferred thermoplastic polyester block copolymers used in the present invention, the polyester segment having a high melting point consists of a polyester obtained from an aromatic dicarboxylic acid and a glycol having a low molecular weight and the polymer segment having a low melting point consists of a polyalkylene glycol or a polylactone. In the preferred polyester block copolymers, the aromatic dicarboxylic acid composing the polyester segment having a high melting point consists, more preferably, of 65 to 100 % by mole of terephthalic acid and 35 to 0 % by mole of isophthalic acid, and the low molecular weight glycol component consists, more preferably, of 65 to 100 % by mole of 1,4-butanediol and 35 to 0 % by mole of other glycol having a molecular weight of not more than 300. The polyalkylene glycol composing the polymer segment having a low melting point consists, more preferably, of at least 70 % by mole of polytetramethylene glycol, and the lactone consists, more preferably, of at least 70 % by mole of ε-caprolactone.

0011The polyester block copolymers can be prepared by a conventional polycondensation reaction, preferably by subjecting an aromatic dicarboxylic acid or a dialkyl ester thereof, a compound forming the low melting point segment (e.g. a polyalkylene glycol) and a low molecular weight glycol to esterification or ester exchange reaction by heating at a temperature of about 150 to 260°C in the presence of a catalyst and then subjecting to a polycondensation reaction while removing excess low molecular weight diol under vacuum; or by previously preparing a prepolymer for forming the polyester segment having a high melting point and a prepolymer for forming the polymer segment having a low melting point, mixing the previously prepared prepolymers with a bifunctional chain extender which is reactive with the terminal group of the prepolymers, reacting them, and then removing the volatile components contained therein under high vacuum; or by mixing with heating a polyester having a high melting point and having a high degree of polymerization with a lactone, and subjecting them to ester exchange reaction while proceeding ring opening polymerization of the lactone.

0012The liquid MDI used in the present invention means a liquified MDI which is prepared by partial carbodi- imidation of pure MDI (said pure MDI being solid at room temperature and having a melting point of 38°C). The carbodiimide forms usually a cycloadduct with other MDI at room temperature, as is shown in Scheme-I: <chemistry id="chem0001" num="0001"><img file="EP0180973A2_D0001.tif" /></chemistry>

0013Accordingly, the liquid MDI is a mixture of pure MDI (formula A) and the cycloadduct (formula B). The liquid MDI is prepared by heating a conventional MDI (which is solid at room temperature) in an inert gas or under high vacuum (e.g. less than 1 mmHg), by which one molecule of carbon dioxide is removed from two molecules of MDI and thereby the MDI is carbodiimidated. Said carbodiimide thus produced reacts almost with another molecule of MDI at a temperature of lower than 65°C and thereby is converted into a cycloadduct which is a pale yellow, transparent liquid. In the liquid MDI, the ratio of the cycloadduct and the pure MDI may be optionally varied in any ratio. Thus, the liquid MDI used in the present inventiuon is clearly different from a mere mixture of a conventional pure MDI with a conventional polycarbodiimide (e.g. STABAXCL-P, manufactured by Mobay Chemical Co.)

0014In the liquid MDI used in the present invention, the cycloadduct (B) and pure MDI (A) are in equilibrium as is shown in the above Scheme-I, and the ratio thereof is in the range of cycloadduct/pure MDI = 0.005 mole/1 mole to 0.5 mole/1 mole. The preferred molar ratio of cycloadduct is 0.02 to 0.2. When the molar ratio of cycloadduct is less than 0.005, the mixture of the cycloadduct and pure MDI becomes solid at room temperature, and on the other hand, when the molar ratio of cycloadduct is over 0.5, the liquid MDI is hardly reactive with a polyester block copolymer and hence the reaction takes much longer time until completion, and thereby, the modification of the polyester block copolymer is less effective. Such a suitable liquid MDI is commercially available, for instance, Isonate 143 L (manufactured by Kasei Upjon K.K., Japan, molar ratio of cycloadduct/pure MDI - about 0.13).

0015The thermoplatic elastomer composition of the present invention is prepared by mixing 100 parts by weight of the polyester block copolymer as mentioned hereinbefore and 0.05 to 20 parts by weight of the liquid MDI as mentioned above. When the liquid MDI is used in an amount of less than 0.05 part by weight per 100 parts by weight of the copolymer, the composition shows little increase of melt viscosity thereof before the mixing, and on the other hand, when the amount of liquid MDI is over 20 parts by weight, the composition shows too increased melt viscosity and becomes insoluble in a solvent for measuring solution viscosity (e.g. phenol/tetrachloroethane), and such a composition can not give a sheet having a uniform thickness by extrusion molding. The melt viscosity is proportional to the solution viscosity.

0016The thermoplastic elastomer composition is conveniently produced by kneading a polyester block copolymer and a liquid MDI with a single or twin screw extruder at a temperature of 180 to 250°C to extrude in a shape of, for example, strands, cooling the extruded product with water and then forming it into the form of chips. In order to promote the reaction during the kneading, the kneading may be carried out in the presence of a catalyst such as a tertiary amine (e.g. triethylamine) or an organic tin compound (e.g. dibutyl tin laurate). Besides, depending on the conditions in the kneading, the chips obtained may be aged, for example, by heating in order to complete the reaction.

0017The composition of the present invention has various excellent properties. The composition may be incorporated by some stabilizers, such as a stabilizer for ultraviolet, a stabilizer for heat oxidation and a stabilizer for hydrolysis. Suitable examples of the stabilizer are stabilizers for ultraviolet such as substituted benzophenones (e.g. 2-hydroxy-4-methoxybenzophenone) and substituted benzotriazoles (e.g. 2-(2'-hydroxy-5'-methylphenyl)benzotriazole); stabilizers for heat oxidation such as phenol derivatives (e.g. tetrakis-[methylene-3-(3,5-di-tert-butyl-4'-hydroxyphenyl)-propionate]methane, 1,3,5-trimethyl-2,4,6-tris[3,5-di-tert-butyl-4-hydroxybenzyl]benzene, 4,4'-thiobis(3-methyl-6-tertbutylphenol), 4,4'-butylidenebis(6-tert-butyl-m-cresol, etc.), aromatic amines (e.g. N,N'-bis(β-naphthyl)para- phenylenediamine, N,N'-bis(1-methylheptyl)-paraphenylene- diamine, etc.), thiodipropionates (e.g. dilauryl dithiopropionate, distearyl dithiopropionate, etc.), or a mixture of two or more thereof; and stabilizers for hydrolysis such as carbodiimides (e.g. STABAXOL-P, manufactured by Mobay Chemical Co.). These stabilizers may be added to the mixture together with the liquid MDI or at any stage of the production of composition.

0018The reaction product of a thermoplatic polyester copolymer and a liquid MDI which is made in the form of chips in the extruder is less variation of melt viscosity in each production lots in comparison with the products produced by using a conventional solid MDI. Moreover, by using the liquid polyisocyanate containing carbodiimide bond, the resulting product contains polycarbodiimide in the main chain, and hence, shows improved hydrolysis resistance. Besides, when a polycarbodiimide is incorporated into the polyester elastomer as an agent for preventing hydrolysis, it can be formed into the desired shaped articles without occurrence of any bad smell. When a composition obtained by melt-mixing at a comparatively lower temperature (e.g. at about 200°C), forming into chips and heat treating at a temperature of 40 to 100°C for 1 to 4 hours, the remaining isocyanate group is completely reacted without occurrence of any side reaction. After the heat treatment, the composition may immediately be subjected to the subsequent drying step at 100°C.

0019The present invention is illustrated by the following Preparations, Examples and Reference Examples, but should not be construed to be limited thereto. In the Preparations, Examples and Reference Examples, "part" and mean "part by weight" and "% by weight", respectively, unless specified otherwise.

0020The properties of the products in Preparations, Examples and Reference Examples are measured by the following methods.

0021Surface hardness, tensile strength, tensile elongation, and flexural fatigue resistance are measured by the method as defined in Japan Industrial Standards (JIS) K 6301.

0022Solution viscosity is measured in a concentration of the test sample of 2g/liter in phenol/tetrachloroethane (6/4) at 30°C.

0023Boiling water resistance is measured by dipping the test sample in a boiling water at 100°C for 10 days and thereafter measuring the tensile strength and tensile elongation thereof.

Preparation 1

0024A solid MDI (Isonate 125 M, manufactured by Kasei Upjohn K.K.) is heat treated at 150°C under high vacuum (0.5 mmHg) to give liquid MDI (a) to (d) which have various ratios of cycloadduct/pure MDI. These liquid MDI have the following molar ratio of cycloadduct/pure MDI which is measured by isocyanate equivalent in the liquid MDI. <tables id="tabl0001" num="0001"><img file="EP0180973A2_D0002.tif" /></tables>

Preparation 2

0025Dimethyl terephthalate, 1,4-butanediol and polyoxytetramethylene glycol (number average molecular weight: about 1,000) (abbreviated as "PTMG") are polymerized to give polyester polyether block copolymers having PTMG units of 25 % and 50 %, respectively (Polymer A and Polymer B). Solution viscosity (nsp/c) is 1.45 in Polymer A and 1.71 in Polymer B.

Exam

D

le 1

0026To each of Polymer A and Polymer B (each 100 kg) is added liquid MDI (a) (5.0 kg), and the mixture is melt- mixed and melt-extruded with a single screw extruder. The extruded mixture is solidified in the form of strand in water bath and then cut into chips. The chips thus obtained are aged with a hot air dryer at 80°C for one hour and then dried at 110°C for one hour to give Compositions I and II.

Reference Example 1

0027Example 1 is repeated except that a solid MDI is used instead of the liquid MDI to give Compositions III and IV.

0028Various properties of Compositions I to IV, i.e. general properties, variation of solution viscosity of composition in production lots (maximum and minimum among 5 points measurement), flexural fatigue resistance, boiling water resistance, etc. were measured. The results are shown in Table 1. As is clear from the results, Compositions I and II showed excellent water resistance and extremely small variation of solution viscosity of composition in the production lots. <tables id="tabl0002" num="0002"><img file="EP0180973A2_D0003.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0180973A2_D0004.tif" /></tables>

0029Besides, Compositions II and IV were each extruded with a sheet extruder (i.e. a single screw extruder having a hanger slit die at the tip thereof) to form a sheet. Occurrence of fish eye per 100 cm² on the sheet thus prepared was counted, and further the solution viscosity (nsp/c) at said fish eye region and also at smooth surface region was also measured. The results are shown in Table 2. <tables id="tabl0004" num="0004"><img file="EP0180973A2_D0005.tif" /></tables>

0030As is clear from the above results, Composition IV showed occurrence of fish eye and partial increase of viscosity due to variation in the production lots during forming step.

Example 2

0031Example 1 is repeated except that liquid MDI (b) is used instead of liquid MDI (a) to give Composition V.

0032As to the Composition V, the general properties, variation of solution viscosity in the production lots, flexural fatigue resistance and boiling water resistance were measured. The results are shown in Table 4.

Preparation 3

0033In the same manner as described in Preparation 2, there are prepared various polyester polyether block copolymers (Polymer C, D and E). The components of these polymers are shown in Table 3. <tables id="tabl0005" num="0005"><img file="EP0180973A2_D0006.tif" /></tables>

Example 3

0034To each of these Polymers C, D and E (each 100 kg) is added liquid MDI (a) (5.0 kg), and the mixture is treated in the same manner as described in Example 1 to give Compositions VI to VIII.

0035As to these Compositions VI to VIII, the general properties, variation of solution viscosity in the production lots, flexural fatigue resistance, and boiling water resistance were measured. The results are shown in Table 4.

Preparation 4

0036To polybutylene terephthalate (solution viscosity: 1.02) (100 parts) is added c-caprolactone (50 parts), and the mixture is heated at 250°C to give an aromatic polyester - aliphatic polyester block copolymer (solution viscosity: 1.23) (Polymer J).

Example

0037To Polymer J (100 kg) is added liquid MDI (a) (5.0 kg), and the mixture is treated in the same manner as described in Example 1 to give Composition IX.

0038As to the Composition IX, the general properties, variation of solution viscosity of composition in the production lots, flexural fatigue resistance, and boiling water resistance were measured. The results are shown in Table 4. <tables id="tabl0006" num="0006"><img file="EP0180973A2_D0007.tif" /></tables>

Reference Example 2

0039Example 1- is repeated except that liquid MDI (c). and (d) are used instead of liquid MDI (a) to prepare Compositions X and XI.

Reference Example 3

0040In the same manner as described in Examples 3 and 4 except that a solid MDI is used instead of liquid MDI, Polymers C, D, E and J are each mixed with the solid MDI to prepare Compositions XII to XV.

Reference Example 4

0041In the same manner as described in Example 1 except that a liquid 2,4-tolylenediisocyanate (TDI) (melting point: 19.5 - 21.5°C) or a dimer of isophorone diisocyanate (IPDI) (which is solid at room temperature), there are prepared Compositions XVI and XVII.

0042As to the Compositions X to XVII prepared in Reference Examples 2 to 4, the general properties, variation of solution viscosity in the production lots, flexural fatigue resistance, and boiling water resistance were measured. The results are shown in Table 5. <tables id="tabl0007" num="0007"><img file="EP0180973A2_D0008.tif" /></tables>

0043As is clear from the above Examples and Reference Examples, the thermoplatic elastomer composition of the present invention which is incorporated with the specific liquid MDI shows less variation of solution viscosity of composition in the production lots and excellent flexural fatigue resistance and boiling water resistance without occurrence of fish eye and partial increase of viscosity due to variation in the production lots during the forming step, while the product obtained by using a solid diisocyanate shows large variation of solution viscosity of composition in the production lots, less flexural fatigue resistance and less boiling water resistance, and further shows occurrence of fish eye during the forming step.