Polyester-based resin composition, manufacturing process for the polyester-based resin composition and molded articles using the polyester-based resin composition

Abstract

Polyester-based resin composition comprising a polyester-based resin (A) and a carbodiimide compound (B) 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 8 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 residue of a compound comprising a functional group with reactivity with an isocyanate; R2 is a divalent aliphatic group with at least one alicyclic structure, provided that -N=C=N- is directly bonded to the alicyclic structure of R2; R3 is a divalent residue of a polyester diol; X is a group selected from the group consisting of groups represented by the following general formulas (2) to (4): m is a number from 1 to 20; n is a number from 1 to 20;p is a number from 1 to 5; and several R2 groups and several X groups can each be the same or different from each other; and wherein the content of the polyester-based resin (A) in the polyester-based resin composition is 80 to 99.9 wt%.;

Description

Technical field

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

[0002] Polyester resins have been widely used in applications such as films and foils 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 prevents 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 service life 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 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 PTL3, the technology is described using a carbodiimide-based compound as a hydrolysis inhibitor and an adipic acid as a plasticizer.

[0008] PTL4 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 mentioned documents Patent literature

[0009] PTL1: JP 9-249801A PTL2: JP 2000-256436A PTL3: JP 2009-256405A PTL4: JP 2013-75972A Brief description of the invention: Technical problem

[0010] Although the hydrolysis of the polyester resin can be suppressed in the technology described in PTL1, the disadvantage tends to arise that, 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 and kneading and after molding, and therefore it tends to be difficult to produce a stable molded article from the polyester resin.

[0011] 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.

[0012] In the technology described in PTL3, 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.

[0013] The technology described in PTL4 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.

[0014] It is an object of the present invention to provide a polyester-based resin composition which has excellent hydrolysis resistance and leakage resistance and is free from a significant increase in melt viscosity and solution viscosity, a method for producing the polyester-based resin composition and a molded article using the polyester-based resin composition.

[0015] 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 thus fulfilled by the above result.

[0016] Thus, according to the present invention, the following polyester-based resin composition, the following method for producing the 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) 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 8 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 residue of a compound containing a functional group with reactivity with an isocyanate; R 2 a divalent aliphatic group with at least one alicyclic structure, with the proviso that -N=C=N- is directly attached to the alicyclic structure of R 2 is bound; R 3 a divalent residue of a polyester diol; X is a group selected from the group consisting of groups represented by the following general formulas (2) to (4): m is a number from 1 to 20; n is a number from 1 to 20; p is a number from 1 to 5; and several R 2 -groups and multiple X-groups can each be the same or different from each other. [2] The polyester-based resin composition according to point [1] above, wherein the polyester diol has a number-average molecular weight of 1,000 to 40,000. [3] The polyester-based resin composition according to one of the above points [1] or [2], wherein R 2 a divalent residue of dicyclohexylmethane-4,4'-diisocyanate. [4] The polyester-based resin composition according to any of the above points [1] to [3], wherein the carbodiimide compound (B) has a carbodiimide equivalent of 100 to 1,000. [5] The polyester-based resin composition according to any of the above points [1] to [4], 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. [6] The polyester-based resin composition according to one of the above points [1] to [5], wherein the compound comprising a functional group with reactivity with an isocyanate is a monoalcohol, a monophenol, a monoisocyanate or a monoamine. [7] A method for producing the polyester-based resin composition according to any of the above points [1] to [6], comprising the step of melting and kneading the polyester-based resin (A) and the carbodiimide compound (B). [8] The method for producing the polyester-based resin composition according to point [7] above, wherein the carbodiimide compound (B) is formed into pellets. [9] A molded article obtained by molding the polyester-based resin composition according to any of the above points [1] to [6].

[0017] According to the present invention, a polyester-based composition exhibiting excellent hydrolysis resistance and leakage resistance, and free from a significant increase in melt viscosity and solution viscosity, a method for producing the polyester-based resin composition, and a molded article using the polyester-based resin composition can be provided. Description of embodiments [polyester-based resin composition]

[0018] 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) 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 8 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 residue of a compound containing a functional group with reactivity with an isocyanate; R 2 a divalent aliphatic group with at least one alicyclic structure, with the proviso that -N=C=N- is directly attached to the alicyclic structure of R 2 is bound; R 3a divalent residue of a polyester diol; X is a group selected from the group consisting of groups represented by the following general formulas (2) to (4): m is a number from 1 to 20; n is a number from 1 to 20; p is a number from 1 to 5; and several R 2 -groups and multiple X-groups can each be the same or different from each other.

[0019] 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.

[0020] That is, in the carbodiimide compound (B) represented by the general formula (1) and included in the polyester-based resin composition according to the present invention, the polyester segment is present between the polycarbodiimide groups. For this reason, it is assumed that an adequate distance between the polycarbodiimide groups is provided, thus preventing the resulting composition from undergoing a rapid increase in viscosity due to a crosslinking reaction of the resin after melting and kneading.

[0021] Since the polyester segment is also present between the polycarbodiimide groups in the carbodiimide compound (B), the solubility and dispersibility of the carbodiimide compound (B) in the polyester-based resin (A) can be improved. Therefore, it is assumed that not only is an increase in the melt viscosity and solution viscosity of the polyester-based resin composition prevented, but the molded article obtained from the polyester-based resin composition also exhibits excellent hydrolysis resistance and leakage resistance.

[0022] Furthermore, it is assumed that by using a polycarbodiimide with a specific alicyclic structure as the polycarbodiimide, even if the concentration of the carbodiimide group in the polycarbodiimide is lower than that of conventional aliphatic polycarbodiimides, the resulting polyester-based resin composition can exhibit excellent hydrolysis resistance. <Polyesterbasiertes Harz (A)>

[0023] The polyester-based resin (A) used in the present invention is not particularly restricted, provided that the resin has an ester group.

[0024] 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.

[0025] 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, from the point of view of good cost-efficiency and good processability, and a polyethylene terephthalate is further preferred.

[0026] 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% from the point of view of improving the hydrolysis resistance, melt viscosity and solution viscosity of the polyester-based resin composition. <Carbodiimidverbindung (B)>

[0027] The carbodiimide compound (B) used in the present invention is represented by the following general formula (1). where R 1 a residue of a compound containing a functional group with reactivity with an isocyanate; R 2 a divalent aliphatic group with at least one alicyclic structure, with the proviso that -N=C=N- is directly attached to the alicyclic structure of R 2 is bound; R 3 a divalent residue of a polyester diol; X is a group selected from the group consisting of groups represented by the following general formulas (2) to (4): m is a number from 1 to 20; n is a number from 1 to 20; p is a number from 1 to 5; and several R 2 -groups and multiple X-groups can each be the same or different from each other.

[0028] In the general formula (1) R 1a residue of a compound containing a functional group with reactivity with an isocyanate (hereinafter also referred to as an ‘end-capping agent (a)’ or a ‘component (a)’).

[0029] In the carbodiimide compound (B) used in the present invention, residual isocyanate end groups present therein are end-capped with component (a) as an end-capping agent in order 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. Therefore, it is assumed that 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 (a)]

[0030] Examples of the above-mentioned component (a) include a monoalcohol, a monophenol, a monoisocyanate and a monoamine.

[0031] Specific examples of monoalcohols include methanol, ethanol, cyclohexanol, polyethylene glycol monomethyl ether, and polypropylene glycol monomethyl ether.

[0032] Specific examples of monophenols include phenol, methylphenol, dimethylphenol, and naphthol.

[0033] 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, tolol isocyanate, dimethylphenyl isocyanate and 2,6-diisopropylphenyl isocyanate.

[0034] Specific examples of monoamines include primary amines such as butylamine and cyclohexylamine; and secondary amines such as diethylamine, dibutylamine, and dicyclohexylamine.

[0035] 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 from these compounds, a monoalcohol is further preferred, polyethylene glycol monomethyl ether or polypropylene glycol monomethyl ether is even more preferred, and polyethylene glycol monomethyl ether is even more preferred.

[0036] In the general formula (1) R 2 a divalent aliphatic group with at least one alicyclic structure, with the stipulation that -N=C=N- is directly attached to the alicyclic structure of R 2 is bound.

[0037] Since the carbodiimide group (-N=C=N-) in the carbodiimide compound (B) used in the present invention is directly bonded to the alicyclic structure, 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.

[0038] The divalent aliphatic group with at least one alicyclic structure can be a divalent residue of a diisocyanate with at least one alicyclic structure (hereinafter also referred to as a ‘diisocyanate (b)’ or a ‘component (b)’). [Diisocyanate; component (b)]

[0039] Examples of the aforementioned component (b) include cyclohexane-1,4-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and methylcyclohexane diisocyanate. Of these compounds, dicyclohexylmethane-4,4'-disocyanate is preferred from the perspective of improving the hydrolysis resistance, melt viscosity, and solution viscosity of the polyester-based resin composition.

[0040] In the general formula (1) R 3 a divalent residue of a polyester diol (hereinafter referred to as a ‘polyester diol (c)’ or a ‘component (c)’).

[0041] The carbodiimide compound (B) used in the present invention has the polyester segment as R 3Consequently, it is assumed that the carbodiimide compound (B) has good compatibility with the polyester-based resin (A) and that its solubility and dispersibility in the polyester-based resin (A) can be improved, so that not only can an increase in the melt viscosity and solution viscosity of the polyester-based resin composition be suppressed, but also the hydrolysis resistance and leakage resistance of the polyester-based resin composition can be improved. [Polyesterdiol; component (c)]

[0042] The component (c) mentioned above is not particularly restricted, provided it is a diol containing an ester group. Examples of component (c) include compounds with a chemical structure obtained by polycondensation between a polycarboxylic acid and a polyhydric alcohol.

[0043] Examples of the preferred polycarboxylic acid used in the present invention include at least one dibasic acid selected from the group consisting of aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, corticic acid, azelaic acid, sebacic acid, brassidic acid and dimeric acids and hydrogenated products thereof; alicyclic dibasic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid; and aromatic dibasic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and naphthalenedicarboxylic acid.

[0044] Furthermore, examples of the preferred polyhydric alcohol used in the present invention include at least one glycol selected from the group consisting of aliphatic glycols such as ethylene glycol, propylene glycol, butanediol, neopentyl glycol, methylpentanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, dodecanediol and dimeric diols; alicyclic glycols such as cyclohexanediol and hydrogenated xylene glycol; and glycols containing an aromatic ring, such as xylene glycol.

[0045] The number-average molecular weight of component (c) is preferably from 1,000 to 40,000, more preferably from 1,500 to 35,000, and even more preferably from 2,000 to 30,000, 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.

[0046] 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 m, a number from 1 to 20, preferably from 2 to 18, more preferably from 4 to 16 and even more preferably from 6 to 15.

[0047] In the general formula (1) from the perspective described above, n is a number from 1 to 20, preferably from 2 to 18, more preferably from 4 to 16 and even more preferably from 6 to 15.

[0048] In the general formula (1) from the perspective described above, p is a number from 1 to 5, preferably from 1 to 4 and more preferably from 1 to 3. (Carbodiimide equivalent)

[0049] The carbodiimide equivalent (chemical formula weight per 1 mol of a carbodiimide group) of the carbodiimide compound (B) is preferably 100 to 1,000, more preferably 150 to 850 and even more preferably 200 to 600, 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))

[0050] The content of the carbodiimide compound (B) in the polyester-based resin composition is from 0.1 to 8 parts by mass, preferably from 0.2 to 7 parts by mass, more preferably from 0.3 to 6 parts by mass and even more preferably from 0.5 to 5 parts by mass based on 100 parts by mass of a total amount of the polyester-based resin 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. <Verfahren zum Herstellen einer Carbodiimidverbindung (B)>

[0051] The carbodiimide compound (B) used in the present invention can be prepared by known methods.

[0052] Examples of the methods for preparing the carbodiimide compound (B) are as follows: (i) A process in which the diisocyanate (b) is subjected to a carbodiimidation reaction in the presence of a catalyst to obtain a polycarbodiimide (hereinafter also referred to as ‘component (d)’), after which the end-capping agent (a) and the polyester diol (c) are added to component (d) to subject these components to a copolymerization reaction and an end-capping reaction; (ii) Process in which the diisocyanate (b), the polyester diol (c) and the end-capping agent (a) are subjected to a carbodiimidation reaction, a copolymerization reaction and an end-capping reaction in the presence of a catalyst; (iii) A process in which the diisocyanate (b) and the polyester diol (c) are subjected to a copolymerization reaction and thereafter the end-capping agent (a) and a catalyst are added to the resulting copolymer to subject the copolymer to a carbodiimidation reaction and an end-capping reaction; and the like.

[0053] Of these methods, from the point of view of good productivity, the carbodiimide compound (B) is preferably produced by the above method (i). (Production of polycarbodiimide (d))

[0054] The polycarbodiimide (d) mentioned above can be synthesized by subjecting the diisocyanate (b) to a carbodiimidation reaction without solvent or in the presence of an inert solvent using an organophosphorus compound or a metal-organic compound as a carbodiimidation catalyst.

[0055] 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.

[0056] The temperature used in the carbodiimidation reaction is preferably from 70 to 250°C, more preferably from 100 to 230°C and even more preferably from 150 to 200°C from the point of view of good productivity.

[0057] The reaction time of the above-mentioned carbodiimidation reaction, as described above, is preferably from 1 to 50 hours, more preferably from 10 to 40 hours and even more preferably from 20 to 30 hours.

[0058] The amount of 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 0.2 to 1 part by mass, based on 100 parts by mass of the diisocyanate (b). (Copolymerization reaction)

[0059] The copolymerization reaction mentioned above can be carried out by reacting the polycarbodiimide (d), end-capping agent (a), and polyester diol (c) prepared above under heated conditions. The order of adding component (d), component (a), and component (c) is not particularly restricted. However, for the sake of good processability after the synthesis of the desired compound, it is preferred that component (d), component (a), and component (c) be added simultaneously. Furthermore, to suppress side reactions, it is preferred that component (d) and component (a) be added first, and after confirming the cessation of the reaction between component (d) and component (a), component (c) is then added.

[0060] From the perspective of improving the hydrolysis resistance, melt viscosity and solution viscosity of the polyester-based composition, the mixing ratio between the polycarbodiimide (d) and the polyester diol (c) is adjusted such that the ratio of the number of moles of isocyanate end groups in the polycarbodiimide (d) to the number of moles of hydroxyl groups in the polyester diol [NCO(d) / OH(c)] is preferably from 1.20 to 2, more preferably from 1.25 to 2 and even more preferably from 1.33 to 2.

[0061] The reaction temperature used after the above-mentioned copolymerization reaction is preferably from 40 to 250°C, more preferably from 90 to 220°C and even more preferably from 130 to 200°C from the point of view of good productivity.

[0062] From the same perspective as described above, the reaction time of the above-mentioned copolymerization reaction is preferably from 5 minutes to 20 hours, more preferably from 30 minutes to 10 hours, and even more preferably from 1 to 3 hours.

[0063] From the perspective of good productivity of the polyester-based composition, it is preferred that the carbodiimide compound (B) obtained in this way be melted and mixed with the polyester-based resin (A) to form a masterbatch, or that the carbodiimide compound (B) be formed into pellets, preferably only forming the carbodiimide compound (B). The pelleting of the carbodiimide compound (B) can be carried out by forming the carbodiimide compound (B) into a pellet shape using a known pelleting machine. <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. [Method for producing a polyester-based resin composition]

[0066] The process for producing the polyester-based resin composition according to the present invention comprises the step of melting and kneading the polyester-based resin (A) and the carbodiimide compound (B).

[0067] In the manufacturing process of the present invention, the use of the aforementioned carbodiimide compound (B) suppresses a significant increase in the melt viscosity of the resulting composition, thereby improving 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 loaded into the mixer and melted as the base resin, and then the carbodiimide compound (B) is loaded into the mixer together with any other optional components that may be added.

[0069] The melting and kneading time can be adjusted according to the shape and the rotational speed of the screw used, etc., and is typically from 1 to 30 minutes, preferably from 1 to 10 minutes, and more preferably from 1 to 5 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 150 to about 350°C, preferably from 200 to 320°C, and more preferably from 240 to 300°C.

[0070] The carbodiimide compound (B) used in the manufacturing process of the present invention is preferably formed into pellets.

[0071] Conventional low-melting-point polycarbodiimide additives tend to melt at the inlet section of an extruder when fed through a feeder or similar device, making loading the additives into the extruder difficult. Conversely, when powdered polycarbodiimide additives are dry-mixed with polyester-based resin pellets and the resulting dry mixture is fed into the extruder, the powdered polycarbodiimide additives tend to separate due to their different shapes compared to the pellets. Consequently, the resulting polyester-based resin composition tends to suffer from an uneven concentration of polycarbodiimide.Furthermore, since the polycarbodiimide additives exhibit somewhat impaired compatibility with the polyester-based resin (A), it may be difficult to disperse the polycarbodiimide additives uniformly in the resulting molded articles at a low concentration.

[0072] On the other hand, the carbodiimide compound (B) used in the present invention can also be pelletized and dry-mixed with the polyester-based resin (A) and then formed into molded articles. More precisely, the carbodiimide compound (B), which has a high molecular weight, can readily be formed into pellets due to its high melting point. Therefore, it is assumed that the pelletized carbodiimide compound (B) used in the present invention suffers little segregation due to its pellet form and exhibits good compatibility with the polyester-based resin (A), since the polyester segment is present in one molecule of the resin. This allows the carbodiimide compound (B) to be uniformly dispersed in a molded article formed from the polyester-based resin (A), even when compounded at a low concentration in the article.

[0073] Furthermore, it is assumed that, since the carbodiimide compound (B) can be dry-mixed directly with the polyester-based resin (A), the production of a masterbatch of any type of polyester-based resin (A) is not necessary, and therefore not only can the number of manufacturing steps for the polyester-based resin composition be reduced, but also deactivation of the composition (reaction between ester-based resin and carbodiimide) due to the heat profile after the formation of the masterbatch can be prevented. [Molded articles using polyester-based resin composition]

[0074] The molded article according to the present invention is produced by molding the polyester-based resin composition according to the present invention.

[0075] 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.

[0076] 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

[0077] 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

[0078] 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, and 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)

[0079] 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)

[0080] 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.

[0081] 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 Life Tester) testing chamber "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 chamber 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) Assessment of leakage resistance

[0082] 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 visually inspected to determine whether or not any leakage had occurred. Synthesis example 1 (synthesis of carbodiimide compound P1)

[0083] A reaction vessel equipped with a reflux condenser and stirrer was loaded with 100 parts by mass of 4,4'-dicyclohexylmethane diisocyanate and 0.5 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 185°C for 24 hours, yielding an isocyanate-terminated poly(4,4'-dicyclohexylmethanecarbodiimide).

[0084] As a result of subjecting the resulting reaction product to an infrared (IR) absorption spectrum measurement, it was confirmed that an absorption peak attributable to a carbodiimide group was present at a wavelength of approximately 2150 cm⁻¹. –1was produced. Furthermore, as a result of subjecting the reaction product to a titration to measure a residual isocyanate group concentration (hereinafter also referred to as ), it was confirmed that the residual isocyanate group concentration was 3.78% and the number of repeating component units represented by (-R2-N=C=N-) (hereinafter also referred to as a “degree of polymerization”) was 9.0.

[0085] The resulting isocyanate-terminated poly(4,4'dicyclohexylmethanecarbodiimide) was then heated to 150°C, and 7.9 parts by mass of polyethylene glycol monomethyl ether (molecular weight: 208) and 57.3 parts by mass of the polyester diol "VIRON 220" (molecular weight: 3,000), available from TOVOBO Co., Ltd., were added, and 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 P1. Synthesis examples 2 to 4 (synthesis of carbodiimide compounds P2 to P4)

[0087] 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 to P4 were obtained. Synthesis example 5 (synthesis of carbodiimide compound P5)

[0088] The same procedure as in Synthesis Example 1 was repeated, except that the reaction conditions and the type of end-sealing agent used were changed as shown in Table 1, and no polyesterdiol “VIRON 220” (molecular weight: 3,000), available from TOYOBO Co., Ltd., was added, so that a carbodiimide compound P5 was obtained. Synthesis example 6 (Synthesis of pellet-shaped carbodiimide compound P6)

[0089] A reaction vessel equipped with a reflux condenser and stirrer was loaded with 100 parts by mass of 4,4'-dicyclohexylmethane 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 28 hours, yielding an isocyanate-terminated poly(4,4'-dicyclohexylmethanecarbodiimide). 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. Measurement of NCO% in the reaction product confirmed that the NCO% was 2.92% (degree of polymerization: 12.0).

[0090] The resulting isocyanate-terminated poly(4,4'-dicyclohexylmethanecarbodiimide) was then heated to 150°C, and 6.1 parts by mass of polyethylene glycol monomethyl ether (molecular weight: 208) were added. The resulting mixture was heated to 180°C and reacted at this temperature for 1 hour with stirring. After this time, the reaction product was removed from the reaction vessel and cooled to room temperature, yielding a pale yellow, transparent, isocyanate-terminated 4,4'-dicyclohexylmethanecarbodiimide, terminated at one end by an isocyanate group.

[0091] Subsequently, 90.6 parts by mass of the isocyanate-terminated 4,4'-dicyclohexylmethanecarbodiimide prepared above and 44.0 parts by mass of the polyester diol "VIRON 220" (molecular weight: 3,000), available from TOYOBO Co., Ltd., were fed into a twin-screw extruder "Labo Plastomill", available from Toyo Seiki Seisaku-sho, Ltd., and melted and kneaded at 180°C to obtain strands. The resulting strands were pelletized using a pelletizing machine to obtain a pelletized carbodiimide compound P6.

[0092] As a result of subjecting the resulting pellet-shaped carbodiimide compound P6 to an infrared (IR) absorption spectrum measurement, it was confirmed that an IR absorption of an isocyanate group at a wavelength of 2200 to 2300 cm⁻¹ –1 was derived. Synthesis example 7 (synthesis of pellet-shaped carbodiimide compound P7)

[0093] The same procedure as in synthesis example 6 was repeated, except that the composition of raw materials and reaction conditions were changed as shown in Table 1, so that a carbodiimide compound P7 was obtained. Example 1

[0094] 99.00 parts by mass of a PET resin available from China Petrochemical Corporation was melted at 270°C using a laboratory mixer. Then, 1.00 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 viscosity properties of the polyester-based resin composition obtained in this manner are shown in Table 2. Examples 2 to 5 and comparative examples 1 to 4

[0095] The same procedure as in Example 1 was repeated, except that the formulated composition of the respective components was modified as shown in Table 2, resulting in polyester-based resin compositions. The viscosity properties of the polyester-based compositions obtained in this way are shown in Table 2. Examples 6 to 8 and comparative examples 5 to 8

[0096] The polyester-based resin compositions obtained in the respective examples and comparison examples mentioned above were subjected to the aforementioned assessment procedures to measure their hydrolysis resistance and to confirm whether or not leakage occurred. The results are presented in Table 3.

[0097] The results shown in Tables 2 and 3 confirmed that all polyester-based resin compositions produced according to the invention were free from a significant increase in melt viscosity and solution viscosity and exhibited excellent hydrolysis resistance and leakage resistance, even when the carbodiimide group concentration therein was similar to that in the respective resin compositions obtained in comparative examples.

[0098] On the other hand, the polyester-based resin composition produced in Comparative Example 1, in which the carbodiimide compound P4 containing a polycarbonate diol resin was compounded, suffered from a remarkable increase in melt viscosity.

[0099] Furthermore, the sheet structures (Comparative Examples 6 to 8) obtained from the resin compositions prepared in Comparative Examples 2 and 3, in which the carbodiimide compound P5, which did not contain a diol residue, was compounded, and the resin composition prepared in Comparative Example 4, in which the carbodiimide compound P3, which was prepared from the aliphatic diisocyanate, which did not have an alicyclic structure, was compounded, exhibited a deteriorated hydrolysis resistance compared to those sheet structures (Examples 6 to 8) obtained from the resin compositions prepared in Examples 1, 2 and 4.

Claims

[1] Polyester-based resin composition comprising a polyester-based resin (A) and a carbodiimide compound (B) 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 8 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 residue of a compound that includes a functional group with reactivity with an isocyanate; R 2 a divalent aliphatic group with at least one alicyclic structure, with the proviso that -N=C=N- is directly attached to the alicyclic structure of R 2 is bound; R 3 a divalent residue of a polyester diol; X is a group selected from the group consisting of groups represented by the following general formulas (2) to (4). m is a number from 1 to 20; n is a number from 1 to 20; p is a number from 1 to 5; and several R 2 -groups and multiple X-groups can each be the same or different from each other. [2] Polyester-based resin composition according to claim 1, wherein the polyester diol has a number-average molecular weight of 1,000 to 40,000. [3] Polyester-based resin composition according to claim 1 or 2, wherein R 2 a divalent residue of dicyclohexylmethane-4,4'-diisocyanate. [4] Polyester-based resin composition according to any one of claims 1 to 3, wherein the carbodiimide compound (B) has a carbodiimide equivalent of 100 to 1,000. [5] Polyester-based resin composition according to any one of claims 1 to 4, 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. [6] Polyester-based resin composition according to any one of claims 1 to 5, wherein the compound comprising a functional group having reactivity with an isocyanate is a monoalcohol, a monophenol, a monoisocyanate or a monoamine. [7] Method for producing the polyester-based resin composition according to any one of claims 1 to 6, comprising the step of melting and kneading the polyester-based resin (A) and the carbodiimide compound (B). [8] Method for producing the polyester-based resin composition according to claim 7, wherein the carbodiimide compound (B) is formed into pellets. [9] Molded article obtained by molding the polyester-based resin composition according to any one of claims 1 to 6.