Polyester resin composition and molded articles using the polyester resin composition

Abstract

Polyester-based resin composition comprising a polyester-based resin (A) and a carbodiimide compound (B) having a structure represented by the following general formula (1), wherein the content of the carbodiimide compound (B) in the polyester-based resin composition is from 0.1 to 10 parts by mass based on 100 parts by mass of a total amount of the polyester-based resin (A) and the carbodiimide compound (B): where R1 is a divalent organic group comprising at least one aromatic group, with the proviso that -N=C=N- is directly bonded to the aromatic group of R1; R2 is a divalent residue of a diol compound; x is a number from 2 to 30; and y is a number from 1 to 20.

Description

Technical field

[0001] The present invention relates to a polyester-based resin composition comprising a polyester-based resin and a carbodiimide compound, and to a molded article utilizing the polyester-based resin composition. State of the art

[0002] Polyester resins have been widely used in applications such as films and sheet materials due to their excellent transparency, mechanical strength, melt stability, solvent resistance, and recyclability. Furthermore, in recent years, polyester resins have also been used for housings of household appliances and office automation equipment.

[0003] However, polyester resins are more susceptible to hydrolysis compared to conventional general-purpose resins. Therefore, to improve the hydrolysis resistance of polyester resins, a method of adding a carbodiimide compound to the polyester resins was investigated.

[0004] By compounding a carbodiimide compound into a polyester resin and molding the resulting resin composition, a carboxyl group contained in the polyester resin, or a carboxyl group produced by the degradation of an ester group contained in the polyester resin, can be trapped by the carbodiimide compound after kneading the resin at an elevated temperature. This suppresses any deterioration of the initial properties of a molded article obtained from the composition. Furthermore, since the carbodiimide compound remains in the resulting molded article, its durability can be improved.

[0005] For example, PTL1 discloses a hydrolysis stabilizer for unsaturated polyester resins, which includes a specific aliphatic or aromatic carbodiimide compound, etc., as a major component.

[0006] PTL2 discloses a carbodiimide as a stabilizer against the cleavage of polyester-based plastics due to their hydrolysis, which has not only a carbodiimide structure, but also a urethane structure, a urea structure or both a urethane and a urea structure, and is in the form of a solid at 25°C and in which the carbodiimide structure is bonded to a non-aromatic carbon atom.

[0007] PTL3 discloses a specific polycarbodiimide compound in which the carbodiimide groups are not continuously bonded to one another, but are bonded to one another via an organic chain containing a urethane bond and / or a urea bond, to improve the strength, bonding properties and adhesion properties of resins when used as a crosslinking agent for the resins, etc., or as a thermoplastic resin.

[0008] PTL4 aims to obtain an aliphatic polyester resin composition exhibiting excellent heat aging resistance and discloses an aliphatic polyester resin composition comprising an aliphatic polyester resin, a hydrolysis inhibitor, and a non-reactive silicone. In PTL4, the technology is described using a carbodiimide-based compound as the hydrolysis inhibitor and an adipic acid as a plasticizer.

[0009] PTL5 aims to obtain a material that satisfies both hydrolysis resistance and bending processability and discloses a polyester-polycarbodiimide copolymer with a chemical structure formed by coupling a polyester segment with a number-average molecular weight of 5,000 to 30,000 and a polycarbodiimide segment via a urethane bond, as well as an adhesive composition containing the polyester-polycarbodiimide copolymer. List of oppositions patent literature

[0010] PTL1: JP 9-249801A PTL2: JP 2000-256436A PTL3: JP 2002-3564A PTL4: JP 2009-256405A PTL5: JP 2013-75972A Brief description of the invention: Technical problem

[0011] Although the hydrolysis of the polyester resin can be suppressed in the technology described in PTL1, a disadvantage tends to arise: due to a rapid reaction between a carboxyl group in the polyester resin and a carbodiimide group, the polyester resin suffers from increased viscosity and gelation after melting, kneading, and molding. Therefore, it tends to be difficult to produce a stable molded article from the polyester resin. Furthermore, if an aromatic polycarbodiimide is used as the carbodiimide compound, the crystallization of the crystalline polyester resin is inhibited due to the progression of a crosslinking reaction within the polyester resin.

[0012] Although the solid carbodiimide can be obtained in the technology described in PTL2 and the strength retention rate of polyester-based plastics at low temperature can be improved by adding the solid carbodiimide, the problem tends to arise that the resulting plastic material has poor hydrolysis resistance and therefore still exhibits a deteriorated strength retention rate after storage under high temperature and high humidity conditions.

[0013] Since, in the technology described in PTL3, the carbodiimide groups of the polycarbodiimide compound are not continuously linked to each other, but are linked to each other via the organic chain, the problem tends to arise that the concentration of the carbodiimide groups in a molecule of the polycarbodiimide compound is reduced, and thus the effect of suppressing the hydrolysis of the polyester resin in the resulting compound is worsened.

[0014] In the technology described in PTL4, the polyester resin composition can exhibit improved moldability through the use of a plasticizer. However, if a common plasticizer such as phthalate esters is used in the resin composition, a problem tends to arise: depending on the amount of plasticizer added, leaching from the resulting molded article can occur, leading to a deterioration of the article's properties, as well as environmental and human health damage due to the plasticizer leakage. Furthermore, since the plasticizer lacks reactivity with a carboxyl group, the carbodiimide compound tends to be less effective at suppressing the hydrolysis of the polyester resin composition. Therefore, there was a need for further improvement of the polyester resin composition's properties.

[0015] The technology described in PTL5 aims to obtain a coating film exhibiting excellent hydrolysis resistance and flexural workability. However, since the coating film is produced from a composition containing polyester-polycarbodiimide copolymer as a major component, the resulting products tend to have limited applications, necessitating improvements in productivity and manufacturing costs in some cases.

[0016] It is an object of the present invention to provide a polyester-based composition which has excellent hydrolysis resistance and leakage resistance and is free from a significant increase in melt viscosity and solution viscosity, and a molded article utilizing the polyester-based resin composition.

[0017] As a result of the present inventors' serious and intensive investigations to fulfill the above problem, it was found that compounding a specific amount of a specific carbodiimide compound into a polyester-based resin could solve the aforementioned conventional problems. The present invention was fulfilled by the above result.

[0018] Thus, according to the present invention, the following polyester-based resin composition and the following molded article using the polyester-based resin composition are provided. [1] A polyester-based resin composition comprising a polyester-based resin (A) and a carbodiimide compound (B) having a structure represented by the following general formula (1), wherein the content of the carbodiimide compound (B) in the polyester-based resin composition is from 0.1 to 10 parts by mass based on 100 parts by mass of a total amount of the polyester-based resin (A) and the carbodiimide compound (B): where R 1 a divalent organic group comprising at least one aromatic group, with the proviso that -N=C=N- is directly attached to the aromatic group of R 1 is bound; R 2 a divalent residue of a diol compound; x is a number not less than 2; and y is a number not less than 1. [2] The polyester-based resin composition according to point [1] above, wherein the diol compound is at least one compound selected from the group consisting of a polyether polyol, a polyester polyol, a polycarbonate polyol and an alkylene diol. [3] The polyester-based resin composition according to point [1] or [2] above, wherein the diol compound has a number-average molecular weight of 100 to 40,000. [4] The polyester-based resin composition according to one of the above points [1] to [3], wherein R 1 a divalent residue of at least one compound selected from the group consisting of toluene diisocyanate, tolide diisocyanate and diphenylmethane diisocyanate. [5] The polyester-based resin composition according to any of the above points [1] to [4], wherein the carbodiimide compound (B) has a carbodiimide equivalent of 200 to 1,500. [6] The polyester-based resin composition according to any of the above points [1] to [5], wherein the polyester-based resin (A) is at least a resin selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polybutylene succinate, a polylactic acid and a polyhydroxyalkanoic acid. [7] The polyester-based resin composition according to any of the above points [1] to [6], wherein the carbodiimide compound (B) is end-capped with a monoalcohol, a monophenol, a monoisocyanate or a monoamine. [8] A molded article obtained by molding the polyester-based resin composition according to any of the above points [1] to [7].

[0019] According to the present invention, a polyester-based resin composition, which exhibits excellent hydrolysis resistance and leakage resistance and is free from a significant increase in melt viscosity and solution viscosity, and a molded article utilizing the polyester-based resin composition can be provided. Description of embodiments [polyester-based resin composition]

[0020] The polyester-based resin composition according to the present invention is characterized in that it contains a polyester-based resin (A) and a carbodiimide compound (B) having a structure represented by the following general formula (1), wherein the content of the carbodiimide compound (B) in the polyester-based resin composition is from 0.1 to 10 parts by mass based on 100 parts by mass of a total amount of the polyester-based resin (A) and the carbodiimide compound (B): where R 1 a divalent organic group comprising at least one aromatic group, with the proviso that -N=C=N- is directly attached to the aromatic group of R 1 is bound; R 2 a divalent residue of a diol compound; x is a number not less than 2; and y is a number not less than 1.

[0021] The reason why the polyester-based resin composition according to the invention exhibits excellent hydrolysis resistance and leakage resistance and is free from a significant increase in melt viscosity and solution viscosity is explained below, although it is not clearly determined.

[0022] This means that in the carbodiimide compound (B) contained in the polyester-based resin composition according to the present invention, the remaining diol compound is present between carbodiimide segments. For this reason, it is assumed that the carbodiimide compound (B) exhibits good compatibility with the polyester-based resin (A) and can therefore be dispersed more uniformly in the polyester-based resin (A), thus preventing the resulting composition from undergoing a local crosslinking reaction after melting and kneading and consequently from increasing in viscosity.Since the carbodiimide group present in the carbodiimide compound (B) reacts with a carboxyl group present in the polyester-based resin (A) or with a carboxyl group produced by degradation of the polyester-based resin (A), leakage of the carbodiimide compound (B) from the resulting molded article is prevented. Furthermore, it is assumed that, because the carbodiimide compound (B), whose carbodiimide groups remain unreacted, also has a high affinity for the polyester-based resin (A), virtually no leakage of the carbodiimide compound (B) from the molded article occurs.

[0023] Furthermore, due to the use of a specific aromatic polycarbodiimide as the polycarbodiimide, it is assumed that even if the concentration of the carbodiimide group in the aromatic polycarbodiimide compound is lower than that of conventional aliphatic polycarbodiimides, the resulting polyester-based resin composition can exhibit excellent hydrolysis resistance. <Polyesterbasiertes Harz (A)>

[0024] The polyester-based resin (A) used in the present invention is not particularly restricted, provided that the resin has an ester group.

[0025] Examples of the polyester-based resin (A) used in the present invention include at least one resin selected from the group consisting of polyethylene terephthalate (hereinafter also referred to as “PET”), polybutylene succinate (hereinafter also referred to as “PBS”), polybutylene succinate adipate (hereinafter also referred to as “PBSA”), polybutylene adipate terephthalate (hereinafter also referred to as “PBAT”), polybutylene terephthalate (hereinafter also referred to as “PBT”), polyethylene naphthalate, a polyarylate, an ethylene terephthalate isophthalate copolymer, a polylactic acid (hereinafter also referred to as “PLA”) and a polyhydroxyalkanoic acid (hereinafter also referred to as “PHA”) such as polybutyric acid.

[0026] Of these polyester-based resins, at least one resin is preferred from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polybutylene succinate, a polylactic acid and a polyhydroxyalkanoic acid, and is more preferably a polyethylene terephthalate.

[0027] Since the carbodiimide compound (B) with a specific structure is contained in the polyester-based resin composition according to the present invention, the crosslinking reaction of the polyester-based resin (A) can be suppressed. Consequently, unlike conventional carbodiimide compounds, the carbodiimide compound (B) does not inhibit crystallization of the polyester resin and can therefore be suitably used together with the crystalline polyester-based resin.

[0028] The content of the polyester-based resin (A) in the polyester-based resin composition according to the present invention is preferably from 80 to 99.9 wt%, more preferably from 85 to 99.8 wt%, even more preferably from 90 to 99.7 wt% and even more preferably from 95 to 99.5 wt%. <Carbodiimidverbindung (B)>

[0029] The carbodiimide compound (B) used in the present invention has a structure that is represented by the following general formula (1). where R 1 a divalent organic group comprising at least one aromatic group, with the proviso that -N=C=N- is directly attached to the aromatic group of R 1 is bound; R 2 a divalent residue of a diol compound; x is a number not less than 2; and y is a number not less than 1.

[0030] The content of the structure represented by the above-mentioned general formula (1) in the carbodiimide compound (B) is, from the point of view of improving the hydrolysis resistance, melt viscosity and solution viscosity of the polyester-based resin composition, preferably not less than 50 wt%, more preferably not less than 60 wt%, even more preferably not less than 70 wt% and even more preferably not less than 80 wt%.

[0031] In the general formula (1) R 1 a divalent organic group containing at least one aromatic group, with the proviso that -N=C=N- is directly attached to the aromatic group of R 1 is bound.

[0032] Since the carbodiimide group (-N=C=N-) in the carbodiimide compound (B) used in the present invention is directly bonded to the aromatic group, the reactivity of the carbodiimide compound (B) can be enhanced with a carboxyl group. Consequently, it is expected that even if the concentration of the carbodiimide group in the carbodiimide compound (B) is lower than that of conventional aliphatic polycarbodiimides, the resulting polyester-based resin composition can exhibit excellent hydrolysis resistance.

[0033] The divalent organic group containing at least one aromatic group can be a divalent residue of a diisocyanate containing at least one aromatic group (hereinafter also referred to as a “diisocyanate (a)” or a “component (a)”). From the perspective of improving the hydrolysis resistance, melt viscosity, and solution viscosity of the polyester-based resin composition, the diisocyanate containing at least one aromatic group is preferably a diisocyanate containing one or two aromatic groups, and more preferably an aromatic diisocyanate containing one or two aromatic groups. [Diisocyanate component (a)]

[0034] Examples of the above-mentioned component (a) include phenylene diisocyanate, toluene diisocyanate, tolide diisocyanate, 1,5-naphthalene diisocyanate, diphenylmethane diisocyanate, diphenyldimethylmethane diisocyanate, diphenyl ether diisocyanate, and 3,3'-dimethylbiphenyl-4,4'-diisocyanate. Of these compounds, at least one is preferred from the group consisting of toluene diisocyanate, tolide diisocyanate, and diphenylmethane diisocyanate, with toluene diisocyanate being more preferred, for the purpose of improving the hydrolysis resistance, melt viscosity, and solution viscosity of the polyester-based resin composition.

[0035] In the general formula (1) R 2a divalent residue of a diol compound (hereinafter referred to as a “diol compound (b)” or a “component (b)”). However, as used in this specification, the diol compound refers to a compound containing two hydroxyl groups in one molecule thereof.

[0036] The carbodiimide compound (B) used in the present invention contains the aforementioned divalent diol group between polycarbodiimide groups. Therefore, it is assumed that, since the carbodiimide compound (B) exhibits good compatibility with the polyester-based resin (A) and can thus be dispersed more uniformly in the polyester-based resin (A), a local crosslinking reaction in the polyester-based resin composition can be prevented after melting and kneading, and thus an increase in the viscosity of the composition can be suppressed. [Diol compound; component (b)]

[0037] The component (b) mentioned above can be a high molecular weight compound or a low molecular weight compound containing two hydroxyl groups in one molecule thereof.

[0038] Examples of the high-molecular-weight compound containing two hydroxyl groups in one molecule include a polyether polyol, a polyester polyol, a polycarbonate polyol, a silicone diol, a polyolefin polyol, a polyurethane polyol, an alkylene-(C 21or more)-diol, etc. Of these compounds, from the point of view of improving the melt viscosity and solution viscosity of the polyester-based resin composition, at least one compound is preferred which is selected from the group consisting of a polyether polyol, a polyester polyol, a polycarbonate polyol and an alkylene diol, more preferred is at least one compound which is selected from the group consisting of a polyester polyol and a polycarbonate polyol and even more preferred is a polycarbonate polyol.

[0039] Examples of the low-molecular-weight compound containing two hydroxyl groups in one molecule include alkanediols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and an alkylene (C7 to C) 20)-diol; diols containing an alicyclic aliphatic group, such as cyclohexanediol, cyclohexanedimethyl, and hydrogenated bisphenol A; alkenediols such as 1,4-dihydroxy-2-butene; and diols containing an aromatic ring, such as bishydroxyethoxybenzene, xylene glycol, and bis(2-hydroxyethyl)terephthalic acid. Of these compounds, from the perspective of improving the melt viscosity and solution viscosity of the polyester-based resin composition, alkylenediols and diols containing an aromatic ring are preferred, diols containing an aromatic ring are more preferred, and bis(2-hydroxyethyl)terephthalic acid is even more preferred.

[0040] The number-average molecular weight of component (b) is preferably from 100 to 40,000, more preferably from 150 to 10,000, and even more preferably from 200 to 1,000, from the perspective of improving the hydrolysis resistance, melt viscosity, and solution viscosity of the polyester-based resin composition. However, the number-average molecular weight can be measured by gel chromatography using polystyrene as a reference standard, although the measurement of the number-average molecular weight of the low-molecular-weight compound is not limited to this method.

[0041] In the general formula (1) x is a number not less than 2 and y is a number not less than 1.

[0042] In the general formula (1), from the point of view of improving the hydrolysis resistance, melt viscosity and solution viscosity of the polyester-based resin composition x, preferably a number of 2 to 30, more preferably of 2 to 25 and even more preferably of 2 to 20.

[0043] In the general formula (1) from the perspective described above, y is preferably a number from 1 to 20, more preferably from 1 to 15 and even more preferably from 1 to 10.

[0044] In the carbodiimide compound (B) used in the present invention, residual isocyanate end groups are end-capped with an end-capping agent (hereinafter also referred to as an “end-capping agent (c)” or a “component (c)”) to improve the compatibility of the carbodiimide compound (B) with the polyester-based resin (A) and the storage stability of the polyester-based resin composition. Thus, when the residual isocyanate end groups in the carbodiimide compound (B) are end-capped, the quality of the resulting polyester-based resin composition can be suitably improved. [End-capping agent; component (c)]

[0045] Examples of the above-mentioned component (c) include a monoalcohol, a monophenol, a monoisocyanate, and a monoamine.

[0046] Specific examples of monoalcohols include methanol, ethanol, cyclohexanol, polyethylene glycol monomethyl ether, and polypropylene glycol monomethyl ether.

[0047] Specific examples of monophenols include phenol, methylphenol, dimethylphenol, and naphthol.

[0048] Specific examples of monoisocyanates include low alkyl monoisocyanates such as methyl isocyanate, ethyl isocyanate, propyl isocyanate and n-, sec- or tert-butyl isocyanate; alicyclic aliphatic monoisocyanates such as cyclohexyl isocyanate; and aromatic monoisocyanates such as phenyl isocyanate, toluene isocyanate, dimethylphenyl isocyanate and 2,6-diisopropylphenyl isocyanate.

[0049] Specific examples of monoamines include primary amines such as butylamines and cyclohexamine; and secondary amines such as diethylamine, dibutylamine, and dicyclohexylamine.

[0050] From the perspective of improving the compatibility of the carbodiimide compound (B) with the polyester-based resin (A) and the storage stability of the polyester-based resin composition, a monoalcohol or a monoisocyanate is preferred, a monoisocyanate is more preferred, an aromatic monoisocyanate is even more preferred, and phenyl isocyanate is even more preferred.

[0051] The end-capping means (c) can be used alone or in combination with any two or more of them. (Carbodiimide equivalent)

[0052] The carbodiimide equivalent (chemical formula weight per 1 mol of a carbodiimide group) of the carbodiimide compound (B) is preferably 200 to 1,500, more preferably 250 to 1,250 and even more preferably 300 to 1,000 from the point of view of improving the hydrolysis resistance, melt viscosity and solution viscosity of the polyester-based resin composition. (Content of carbodiimide compound (B))

[0053] The content of the carbodiimide compound (B) in the polyester-based resin composition is from 0.1 to 10 parts by mass, preferably from 0.2 to 6 parts by mass, more preferably from 0.3 to 4 parts by mass and even more preferably from 0.5 to 2 parts by mass based on 100 parts by mass of a total amount of the polyester-based resin (A) and the carbodiimide compound (B) from the point of view of improving the hydrolysis resistance, melt viscosity and solution viscosity of the polyester-based resin composition. (Numerical mean molecular weight of the carbodiimide compound (B))

[0054] The number-average molecular weight of the carbodiimide compound (B) is preferably from 250 to 50,000, more preferably from 300 to 10,000, more preferably from 400 to 5,000, and even more preferably from 500 to 3,000, from the perspective of improving the hydrolysis resistance, melt viscosity, and solution viscosity of the polyester-based resin composition. The number-average molecular weight can be measured by gel chromatography using polystyrene as a reference standard. <Verfahren zum Herstellen einer Carbodiimidverbindung (B)>

[0055] The carbodiimide compound (B) used in the present invention can be prepared by known methods.

[0056] Examples of the methods for preparing the carbodiimide compound (B) are as follows: (i) Process in which the diisocyanate (a) and the diol compound (b) are reacted together to produce an isocyanate-terminated compound containing a urethane bond terminated at both ends thereof by an isocyanate group (hereinafter also referred to as ‘component (d)’), wherein component (a), component (d) and the end-capping agent (c) are subjected to carbodiimiation and end capping in the presence of a catalyst; (ii) Process in which the diisocyanate (a) is subjected to carbodiimidation in the presence of a catalyst to obtain a polycarbodiimide (hereinafter also referred to as ‘component (e)’), after which the diol compound (b) and the end-capping agent (c) are added to component (e) to subject these components to a copolymerization reaction and an end-capping reaction; (iii) A process in which the diisocyanate (a), the diol compound (b) and the end-capping agent (c) are subjected to a urethanation reaction, a carbodiimidation reaction and an end-capping reaction in the presence of a catalyst and the like.

[0057] Of these methods, from the point of view of good productivity, the carbodiimide compound (B) is preferably produced by the above method (i).

[0058] More precisely, it is preferred that the diisocyanate (a) and the diol compound (b) are mixed together such that the amount of an isocyanate group in the diisocyanate (a) is excessively large in relation to that of a hydroxy group in the diol compound (b) in order to subject the mixture to a urethanation reaction, after which the end-capping agent (c) and an organophosphorus compound or an organometallic compound as a carbodiimidation catalyst, etc., are added to the reaction mixture in order to subject the mixture to a carbodiimidation reaction without solvent or in the presence of an inert solvent.

[0059] Specific examples of the aforementioned carbodiimidation catalyst include 3-methyl-1-phenyl-2-phospholene-1-oxide, 3-methyl-1-ethyl-2-phospholene-1-oxide, 1,3-dimethyl-2-phospholene-1-oxide, 1-phenyl-2-phospholene-1-oxide, 1-ethyl-2-phospholene-1-oxide, and 1-methyl-2-phospholene-1-oxide. Of these carbodiimidation catalysts, 3-methyl-1-phenyl-2-phospholene-1-oxide is preferred due to its good industrial availability. The carbodiimidation catalysts can be used alone or in combination with any two or more of them.

[0060] The reaction temperature used in the urethanation reaction between the above-mentioned components (a) and (b) can be appropriately determined depending on the raw materials used and, from the point of view of good productivity, is preferably from 30 to 200°C, more preferably from 35 to 120°C and even more preferably from 40 to 80°C.

[0061] The reaction temperature used in the carbodiimidation reaction is preferably from 40 to 250°C, more preferably from 60 to 200°C and even more preferably from 80 to 150°C from the point of view of good productivity.

[0062] The reaction time of the above-mentioned carbodiimidation reaction, as described above, is preferably from 10 minutes to 20 hours, more preferably from 1 to 10 hours and even more preferably from 2 to 4 hours.

[0063] The amount of carbodiimidation catalyst used can be determined according to the type of catalyst used and is preferably from 0.01 to 10 parts by mass, more preferably from 0.05 to 5 parts by mass and even more preferably from 0.1 to 3 parts by mass, based on 100 parts by mass of the diisocyanate (a). <Andere Bestandteile>

[0064] The polyester-based resin composition can, if necessary, be compounded in a suitable manner with various additives such as a pigment, a filler, a leveling agent, a surfactant, a dispersant, a UV absorber, an antioxidant, a flame retardant, a colorant, etc. <Gesamtgehalt von polyesterbasiertem Harz (A) und Carbodiimidverbindung (B)>

[0065] The total content of the polyester-based resin (A) and the carbodiimide compound (B) in the polyester-based resin composition according to the present invention is preferably 90 to 100 wt%, more preferably 92 to 100 wt% and even more preferably 95 to 100 wt% from the point of view of improving the hydrolysis resistance, melt viscosity and solution viscosity of the polyester-based resin composition. <Verfahren zum Herstellen einer polyesterbasierten Harzzusammensetzung>

[0066] The polyester-based resin composition according to the present invention can be produced, for example, by compounding the carbodiimide compound (B) together with optional other components which may be added to the polyester-based resin (A), and then melting and kneading the resulting mixture.

[0067] In the process for producing the polyester-based resin composition of the present invention, the use of the aforementioned carbodiimide compound (B) therein can suppress a significant increase in the melt viscosity of the resulting composition and thus improve its processability after melting and kneading. For this reason, the resulting polyester-based composition is expected to exhibit excellent productivity.

[0068] The melting and kneading step can be carried out using a known mixer equipped with a heating element, etc. The order in which the respective materials are added to the mixer is not particularly restricted. Preferably, however, the polyester-based resin (A) is first added to the mixer and melted as the base resin, and then the carbodiimide compound (B) is added to the mixer along with any other optional components that may be added.

[0069] The melting and kneading time can be adjusted depending on the mold and the speed of the screw used, etc., and is typically from 1 to approximately 10 minutes. The melting and kneading temperature can also vary depending on the type of polyester-based resin (A) used as the base resin and is typically from approximately 150 to approximately 350°C. [Molded articles using polyester-based resin composition]

[0070] The molded article according to the present invention is produced by molding the polyester-based resin composition according to the present invention.

[0071] Upon obtaining the shaped article from the polyester-based resin composition according to the present invention, the polyester-based resin composition can be shaped after the aforementioned melting and kneading step by an extrusion molding process, an injection molding process, a blow molding process, etc. Alternatively, the polyester-based resin composition according to the present invention can first be compounded into a masterbatch, etc., and then the resulting masterbatch, etc., can be fused and kneaded with other materials, followed by a suitable molding process of the resulting kneaded material.

[0072] The polyester-based resin composition according to the present invention is free from a significant increase in its melt viscosity, even when molded by any of the molding methods described above, and can therefore exhibit good processing efficiency. Furthermore, the molded article produced by molding the polyester-based resin composition according to the invention exhibits good hydrolysis resistance and is excellent with respect to various properties such as strength, etc. Examples

[0073] The present invention will now be described in more detail with reference to the following examples and comparative examples. However, it should be clarified that the following examples, etc., are intended only to illustrate the invention and are not meant to limit it. [Assessment criteria](1) Solution viscosity

[0074] A polyester-based resin composition was melted and kneaded, then dried for 4 hours at 130°C. Subsequently, 0.15 g of the dried resin composition was dissolved in 30 mL of a mixed solution containing phenol and tetrachloroethane in a weight ratio (phenol / tetrachloroethane) of 1:1. The viscosity of the resulting solution was measured using a Cannon-Fenske viscometer at 30°C. The unit of viscosity was (dL / g). (2) Melt flow index (MFR) (melt viscosity)

[0075] A polyester-based resin composition was melted and kneaded, then dried for 4 hours at 130°C. The melt flow rate (MFR) of the dried polyester-based resin composition was measured at a test temperature of 270°C and a test load of 2.16 kgf using the VR-4100 melt flow rate indexer, a viscosity meter available from Ueshima Seisakusho Co., Ltd. The unit of the melt flow rate index was g / 10 min. The melt flow rate index (MFR) measured in this way (g / 10 min) was used as an index of the melt viscosity of the polyester-based resin composition. It should be noted that the higher the MFR value, the lower the melt viscosity of the polyester-based resin composition. (3) Strength retention rate (hydrolysis resistance test)

[0076] A polyester-based resin composition was melted and kneaded, then pressed into a flat sheet at a temperature not less than the composition's softening point, resulting in a sheet approximately 300 μm thick. This sheet was then cut into a strip 10 mm wide and 70 mm long.

[0077] The resulting strip of sheet material was then subjected to a tensile test using a tensile strength testing machine to measure its tensile strength. Furthermore, the strip was placed in the HAST (Highly Accelerated Stress Tester) testing device "HAST CHAMBER EHS-210M," available from ESPEC Corporation, and left at 121°C and 100% RH. After 24 and 40 hours, respectively, the strip was removed from the testing device and subjected to a tensile strength measurement using a tensile strength testing machine. The tensile strengths of the five strips were measured before and after the test to calculate the respective mean values ​​of the tensile strengths measured before and after the test. The strength retention rate was determined as an assessment index of the hydrolysis resistance of the polyester-based resin composition according to the following formula. Strength retention rate (%) = [(mean tensile strengths after testing) / (mean tensile strengths before testing)]×100 (4) Crystallization assessment

[0078] A polyester-based resin composition was melted and kneaded, then allowed to cool to room temperature. This was followed by a visual inspection of the resin to determine whether or not whitening had occurred. Since the polyester resin becomes whiter as crystallization progresses, this indicates that, if whitening is detected, the resin exhibits excellent crystallizing properties. [Assessment criteria] A: Whitening has occurred; and B: No whitening occurred. (5) Assessment of leakage resistance

[0079] A polyester-based resin composition was melted and kneaded, then pressed into a fabric under the same conditions as described in point (3) above, “Strength Retention Rate”. The fabric obtained in this way was observed visually to determine whether or not any leakage had occurred. Synthesis example 1 (synthesis of carbodiimide compound P1)

[0080] A reaction vessel equipped with a reflux condenser and a stirrer was loaded with 100 parts by mass of toluene diisocyanate and 94.8 parts by mass of a polyester polyol "Kuraray Polyol P-520" (molecular weight: 500), available from Kuraray Co., Ltd., and the contents of the reaction vessel were stirred for 1 hour at 60°C in a nitrogen gas stream. Subsequently, 47.9 parts by mass of phenyl isocyanate and 2.2 parts by mass of a carbodiimidation catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide) were added to the reaction vessel, and the contents of the reaction vessel were stirred for 3 hours at 110°C. The resulting reaction mixture was subjected to an infrared (IR) absorption spectrum measurement, and after confirmation that an absorption peak attributable to a carbodiimide group was present at a wavelength of approximately 2150 cm⁻¹, the reaction was concluded that the reaction mixture was not attributable to a carbodiimide group. –1was generated and an absorption peak, attributable to an isocyanate group, was observed at a wavelength of approximately 2270 cm. –1 After the reaction product was essentially scattered, it was removed from the reaction vessel and cooled to room temperature, yielding a light yellow carbodiimide compound P1. Synthesis examples 2 and 3 (synthesis of carbodiimide compounds P2 and P3)

[0081] The same procedure as in Synthesis Example 1 was repeated, except that the composition of raw materials and reaction conditions were changed as shown in Table 1, so that the carbodiimide compounds P2 and P3 were obtained. Synthesis example 4 (synthesis of carbodiimide compound P4)

[0082] A reaction vessel equipped with a reflux condenser and stirrer was loaded with 100 parts by mass of toluene diisocyanate and 0.3 parts by mass of a carbodiimidation catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide), and the contents of the reaction vessel were stirred in a nitrogen gas stream at 110°C for 3 hours. The resulting reaction mixture was subjected to an infrared (IR) absorption spectrum measurement, and after confirmation that an absorption peak attributable to a carbodiimide group was present at a wavelength of approximately 2150 cm⁻¹, the following was determined: –1 was generated and an absorption peak, attributable to an isocyanate group, was observed at a wavelength of approximately 2270 cm. –1 After the reaction product was essentially scattered, it was removed from the reaction vessel and cooled to room temperature, yielding a light yellow carbodiimide compound P4. Synthesis example 5 (synthesis of carbodiimide compound P5)

[0083] The same procedure as in synthesis example 4 was repeated, except that the composition of raw materials was changed as shown in Table 1, so that a carbodiimide compound P5 was obtained. Synthesis example 6 (synthesis of carbodiimide compound P6)

[0084] A reaction vessel equipped with a reflux condenser and stirrer was loaded with 100 parts by mass of tetramethylxylylene diisocyanate and 0.5 parts by mass of a carbodiimidation catalyst (3-methyl-1-phenyl-2-phospholene-1-oxide). The contents of the reaction vessel were stirred in a nitrogen gas stream at 185°C for 24 hours, yielding an isocyanate-terminated tetramethylxylylene carbodiimide. Infrared (IR) absorption spectrum analysis of the resulting reaction product confirmed the presence of an absorption peak attributable to a carbodiimide group at a wavelength of approximately 2150 cm⁻¹. –1 was produced. Furthermore, as a result of subjecting the reaction product to a titration to measure a residual isocyanate group concentration (NCO%), it was confirmed that the residual isocyanate group concentration was 4.11%.

[0085] The resulting isocyanate-terminated tetramethylxylylenecarbodiimide was then heated to 150°C, and 8.5 parts by mass of polyethylene glycol monomethyl ether (molecular weight: 208) and 61.5 parts by mass of the polyester polyol “VIRON 220” (molecular weight: 3,000), available from TOYOBO Co., Ltd., were added. The resulting mixture was heated to 180°C and reacted at this temperature for 2 hours with stirring.

[0086] The resulting reaction mixture was subjected to an infrared (IR) absorption spectrum measurement, and after confirming a dissipation of the IR absorption of an isocyanate group at a wavelength of 2200 to 2300 cm⁻¹ –1 The reaction product was removed from the reaction vessel and cooled to room temperature, resulting in a light yellow transparent carbodiimide compound P6. Example 1

[0087] 99 parts by mass of a PET resin available from Sichuan EM Technology Co., Ltd., were melted at 270°C using a laboratory mixer. Then, 1 part by mass of the carbodiimide compound P1, obtained in Synthesis Example 1, was added, and the remaining mixture was blended for 3 minutes to obtain a polyester-based resin composition. The evaluation results of the polyester-based resin composition obtained in this manner are shown in Table 2. Examples 2 and 3 and comparative examples 1 to 5

[0088] The same procedure as in Example 1 was repeated, except that the formulated composition of the respective materials was modified as shown in Table 2, resulting in polyester-based resin compositions. The evaluation results of the polyester-based resin compositions obtained in this way are shown in Table 2.

[0089] The results in Table 2 confirmed that the polyester-based resin compositions obtained in Examples 1 to 3 exhibit excellent hydrolysis resistance and crystallization properties, as well as excellent viscosity properties due to their low solution viscosity and low melt viscosity. Furthermore, it was confirmed that no runout occurred in any of the sheet structures obtained from the polyester-based resin compositions obtained in Examples 1 to 3, thus demonstrating excellent runout resistance.

[0090] On the other hand, in Comparative Example 1, in which the carbodiimide compound (B) was added in an excessive amount, Comparative Example 4, in which no carbodiimide compound (B) was compounded, and Comparative Example 5, in which the prepared carbodiimide compound P6 was compounded by using the aliphatic diisocyanate as the diisocyanate, it was confirmed that the polyester-based resin compositions obtained in these Comparative Examples exhibited poorer hydrolysis resistance compared to the polyester-based resin compositions obtained in Examples 1 to 3.

[0091] Furthermore, in comparative examples 2 and 3, in which the carbodiimide compounds P4 and P5, which did not contain a diol compound residue, were compounded, it was confirmed that the polyester-based resin compositions obtained in these comparative examples suffered from a significant increase in melt viscosity.

Claims

[1] Polyester-based resin composition comprising a polyester-based resin (A) and a carbodiimide compound (B) having a structure represented by the following general formula (1), wherein the content of the carbodiimide compound (B) in the polyester-based resin composition is from 0.1 to 10 parts by mass based on 100 parts by mass of a total amount of the polyester-based resin (A) and the carbodiimide compound (B): where R 1 a divalent organic group comprising at least one aromatic group, with the proviso that -N=C=N- is directly attached to the aromatic group of R 1 is bound; R 2 a divalent residue of a diol compound; x is a number not less than 2; and y is a number not less than 1. [2] Polyester-based resin composition according to claim 1, wherein the diol compound is at least one compound selected from the group consisting of a polyether polyol, a polyester polyol, a polycarbonate polyol and an alkylene diol. [3] Polyester-based resin composition according to claim 1 or 2, wherein the diol compound has a number-averaged molecular weight of 100 to 40,000. [4] Polyester-based resin composition according to any one of claims 1 to 3, wherein R 1 a divalent residue of at least one compound selected from the group consisting of toluene diisocyanate, tolide diisocyanate and diphenylmethane diisocyanate. [5] Polyester-based resin composition according to any one of claims 1 to 4, wherein the carbodiimide compound (B) has a carbodiimide equivalent of 200 to 1,500. [6] Polyester-based resin composition according to any one of claims 1 to 5, wherein the polyester-based resin (A) is at least a resin selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polybutylene succinate, a polylactic acid and a polyhydroxyalkanoic acid. [7] Polyester-based resin composition according to any one of claims 1 to 6, wherein the carbodiimide compound (B) is end-capped with a monoalcohol, a monophenol, a monoisocyanate or a monoamine. [8] Molded article obtained by molding the polyester-based resin composition according to any one of claims 1 to 7.