Method for suppressing occurrence of blur in injection molding of polybutylene terephthalate resin composition

Abstract

To provide a method for suppressing occurrence of blurs generated in injection molding of a polybutylene terephthalate resin composition.SOLUTION: A method for suppressing occurrence of blurs generated in injection molding of a polybutylene terephthalate resin composition adds a cyclic carbodiimide compound (B) to a polybutylene terephthalate resin (A).SELECTED DRAWING: None

Description

[Technical field]

[0001] An embodiment of the present invention relates to a polybutylene terephthalate resin composition and a molded article. [Background technology]

[0002] Polybutylene terephthalate resin (hereinafter referred to as "PBT resin") has excellent mechanical properties, electrical properties, other physical properties, and chemical properties, and also has good processability, so it is used as an engineering plastic in a wide range of applications such as automobile parts and electrical and electronic parts.

[0003] When manufacturing molded products using PBT resin, burrs may occur. In recent years, molded products are often made thinner to reduce weight, and molding conditions such as high injection pressure, injection speed, cylinder temperature, and mold temperature are often used, and PBT resin compositions with improved fluidity are often used, but molded products tend to be more susceptible to burrs. Burrs not only spoil the appearance, but can also be the starting point of damage, so they are usually removed, but removing burrs often requires manual work and tends to be a lot of effort.

[0004] As a method for reducing burrs, Patent Document 1 describes a resin composition that contains a polybutylene terephthalate resin, a polyester resin other than polybutylene terephthalate resin, an inorganic reinforcing material, a glycidyl group-containing styrene-based copolymer, and an ethylene-glycidyl (meth)acrylate copolymer, and has a cooling crystallization temperature of 175 to 180°C as determined by differential scanning calorimetry (DSC). It describes how the amount of burrs generated can be significantly reduced while maintaining the appearance of the molded product by using a combination of predetermined amounts of the glycidyl group-containing styrene-based copolymer and the ethylene-glycidyl (meth)acrylate copolymer. Patent Document 2 describes a resin composition containing polybutylene terephthalate resin, an amorphous resin, an inorganic reinforcing material, an ethylene-glycidyl (meth)acrylate copolymer, and an ester exchange inhibitor, which is heated at 265°C and a shear rate of 10 sec -1It is also described that a resin composition having a melt viscosity of 0.5 to 1.5 kPa·s at room temperature can be used to significantly suppress the occurrence of burrs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-159732 A [Patent Document 2] International Publication No. 2021 / 045124 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of an embodiment of the present invention is to provide a method for suppressing burrs generated during injection molding of a polybutylene terephthalate resin composition. [Means for solving the problem]

[0007] One embodiment of the present invention relates to a method for suppressing the generation of burrs during injection molding of a polybutylene terephthalate resin composition, comprising adding a cyclic carbodiimide compound (B) to a polybutylene terephthalate resin (A). Effect of the Invention

[0008] According to an embodiment of the present invention, a method for suppressing the generation of burrs during injection molding of a polybutylene terephthalate resin composition can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Preferred embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments.

[0010] <Method for suppressing the occurrence of burrs during injection molding of polybutylene terephthalate resin composition> The method for suppressing burrs generated during injection molding of a polybutylene terephthalate resin composition according to an embodiment of the present invention (hereinafter, also referred to simply as the "burr suppression method") is characterized by adding a cyclic carbodiimide compound (B) to a polybutylene terephthalate resin (A).

[0011] When manufacturing molded products using PBT resin, burrs may occur. In addition, materials with high fluidity tend to easily seep into the gaps between the mold parting surfaces, which can easily cause burrs on the molded product. In the burr suppression method of the embodiment, a cyclic carbodiimide compound (B) is added to the PBT resin (A) to suppress burrs that occur during injection molding of the PBT resin composition. In recent years, recycled materials have become more common due to environmental considerations, and when the burr suppression method of the embodiment is used, a good burr suppression effect can be obtained even for recycled materials.

[0012] In addition, in the methods described in Patent Documents 1 and 2, ethylene-glycidyl (meth)acrylate (EGMA) copolymer is used to suppress burrs, which is thought to lead to a decrease in heat resistance. In the burr suppression method of the embodiment, burrs are suppressed by using a cyclic carbodiimide compound (B), and EGMA copolymer is not essential, so that a decrease in heat resistance is easily avoided and a decrease in strength and elastic modulus is also unlikely to occur.

[0013] [Polybutylene terephthalate resin (A)] The PBT resin (A) contains at least terephthalic acid or its ester-forming derivative (C 1-6 It is a resin obtained by polycondensation of a dicarboxylic acid component containing an alkylene glycol having at least 4 carbon atoms (such as an alkyl ester or acid halide of the alkylene glycol) and a glycol component containing an alkylene glycol having at least 4 carbon atoms (such as an acetylated product) or an ester-forming derivative thereof. The PBT resin (A) is not limited to a homopolybutylene terephthalate resin, and may be a copolymer containing 60 mol % or more (particularly 75 mol % to 95 mol %) of butylene terephthalate units. Furthermore, 1,4-butanediol and terephthalic acid or terephthalic acid alkyl ester, which are the raw materials for the PBT resin (A), may be derived from either fossil resources or biomass resources. The PBT resin (A) can be used alone or in combination of two or more.

[0014] In the PBT resin (A), examples of the dicarboxylic acid component (comonomer component) other than terephthalic acid and its ester-forming derivatives include C terephthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-dicarboxydiphenyl ether, etc. 8-14 Aromatic dicarboxylic acids; succinic acid, adipic acid, azelaic acid, sebacic acid, etc. 4-16 Alkanedicarboxylic acids such as cyclohexanedicarboxylic acid, etc. 5-10 Cycloalkanedicarboxylic acids; ester-forming derivatives of these dicarboxylic acid moieties (C 1-6 These dicarboxylic acid components can be used alone or in combination of two or more.

[0015] Among these dicarboxylic acid components, C 8-12 Aromatic dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid 6-12 The alkanedicarboxylic acids of the formula (I) are more preferred.

[0016] In the PBT resin (A), examples of glycol components (comonomer components) other than 1,4-butanediol include C glycols such as ethylene glycol, propylene glycol, trimethylene glycol, 1,3-butylene glycol, hexamethylene glycol, neopentyl glycol, and 1,3-octanediol. 2-10alkylene glycols; polyoxyalkylene glycols such as diethylene glycol, triethylene glycol, and dipropylene glycol; alicyclic diols such as cyclohexanedimethanol and hydrogenated bisphenol A; aromatic diols such as bisphenol A and 4,4'-dihydroxybiphenyl; C diols of bisphenol A such as 2-mol ethylene oxide adduct of bisphenol A and 3-mol propylene oxide adduct of bisphenol A 2-4 or ester-forming derivatives of these glycols (acetylated products, etc.). These glycol components can be used alone or in combination of two or more.

[0017] Among these glycol components, C ethylene glycol, trimethylene glycol, etc. 2-6 More preferred are alkylene glycols such as 1,2-dimethylphenyl, polyoxyalkylene glycols such as diethylene glycol, and alicyclic diols such as cyclohexanedimethanol. Examples of comonomer components that can be used in addition to the dicarboxylic acid component and the glycol component include aromatic hydroxycarboxylic acids such as 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and 4-carboxy-4'-hydroxybiphenyl; aliphatic hydroxycarboxylic acids such as glycolic acid and hydroxycaproic acid; C hydroxycarboxylic acids such as propiolactone, butyrolactone, valerolactone, and caprolactone (ε-caprolactone, etc.); 3-12 Lactones; ester-forming derivatives of these comonomer components (C 1-6 Examples of the alkyl ester derivatives, acid halides, acetylated derivatives, etc. of the above-mentioned compounds include the above-mentioned compounds.

[0018] Any of the polybutylene terephthalate copolymers obtained by copolymerizing the comonomer components described above can be suitably used as the PBT resin (A). In addition, a homopolybutylene terephthalate polymer and a polybutylene terephthalate copolymer may be used in combination as the PBT resin (A).

[0019] As the PBT resin (A), for example, market collected products can be used (material recycling). In addition, PBT resins produced by decomposing 1,4-butanediol, terephthalic acid, etc. from PBT resin waste to the monomer level (chemical recycling) and polycondensing the obtained raw materials can also be used.

[0020] The amount of terminal carboxyl groups in the PBT resin (A) is not particularly limited. From the viewpoint of durability, the amount of terminal carboxyl groups in the PBT resin is preferably 30 meq / kg or less, and more preferably 20 meq / kg or less. From the viewpoint of adhesion to fillers and the like and compatibility with additives, the amount of terminal carboxyl groups in the PBT resin (A) is preferably 2 meq / kg or more, and more preferably 3 meq / kg or more. The amount of terminal carboxyl groups in the PBT resin (A) is, for example, preferably 2 to 30 meq / kg, and more preferably 3 to 20 meq / kg.

[0021] The intrinsic viscosity (IV) of the PBT resin (A) is not particularly limited. From the viewpoint of fluidity during injection molding, the intrinsic viscosity (IV) of the PBT resin (A) is preferably 0.6 to 1.2 dL / g, more preferably 0.7 to 1.0 dL / g, and even more preferably 0.7 to 0.9 dL / g. In addition, the intrinsic viscosity can be adjusted by blending PBT resins having different intrinsic viscosities. For example, a PBT resin having an intrinsic viscosity of 0.85 dL / g can be prepared by blending a PBT resin having an intrinsic viscosity of 1.00 dL / g with a PBT resin having an intrinsic viscosity of 0.80 dL / g. The intrinsic viscosity (IV) of the PBT resin (A) can be measured, for example, in o-chlorophenol at a temperature of 35°C.

[0022] [Cyclic carbodiimide compound (B)] In the present disclosure, the cyclic carbodiimide compound (B) is a compound containing a carbodiimide group present in a cyclic structure, more specifically, a compound containing a cyclic structure formed by linking two nitrogen atoms of the carbodiimide group with a linking group.

[0023] The cyclic carbodiimide compound (B) may contain one or more cyclic structures containing a carbodiimide group. The number of atoms directly constituting the cyclic structure containing a carbodiimide group is not particularly limited. For example, the number of atoms directly constituting the cyclic structure, including the carbon and nitrogen atoms of the carbodiimide group, is preferably 8 or more, more preferably 10 or more. The number of atoms directly constituting the cyclic structure is preferably 50 or less, more preferably 30 or less, even more preferably 20 or less, and even more preferably 15 or less. The number of atoms directly constituting the cyclic structure may be, for example, 8 to 50, 8 to 30, 10 to 20, or 10 to 15.

[0024] The number of carbodiimide groups in the cyclic structure containing the carbodiimide group is preferably 1. The cyclic carbodiimide compound (B) may contain, for example, only one cyclic structure containing only one carbodiimide group, or may contain two or more cyclic structures containing only one carbodiimide group.

[0025] The cyclic carbodiimide compound (B) can be represented, for example, by the following formula (1).

[0026] [ka]

[0027] In formula (1), L represents a linking group. L may include, for example, an aliphatic group, an alicyclic group, and / or an aromatic group. L may include a heteroatom, and may include a structure in which, for example, aliphatic groups, alicyclic groups, and / or aromatic groups are linked by a heteroatom. Examples of heteroatoms include an oxygen atom, a nitrogen atom, a sulfur atom, and a phosphorus atom. L may be linear or may include a branched structure. L may include a cyclic structure. For example, L may further have a second cyclic structure containing one or more atoms of the atoms directly constituting the main chain of L, and for example, such a second cyclic structure may further include a carbodiimide group.

[0028] In L, the number of atoms directly constituting a cyclic structure together with the carbodiimide group is not particularly limited. For example, in L, the number of atoms directly constituting a cyclic structure together with the carbodiimide group is preferably 5 or more, more preferably 7 or more. In addition, in L, the number of atoms directly constituting a cyclic structure together with the carbodiimide group is preferably 47 or less, more preferably 27 or less, even more preferably 17 or less, and even more preferably 12 or less. In L, the number of atoms directly constituting a cyclic structure together with the carbodiimide group may be, for example, 5 to 47, 5 to 27, 7 to 17, or 7 to 12.

[0029] L may include, for example, a di- to tetravalent aliphatic group having 1 to 20 carbon atoms, a di- to tetravalent alicyclic group having 3 to 20 carbon atoms, a di- to tetravalent aromatic group having 5 to 15 carbon atoms, or a combination thereof.

[0030] Examples of the divalent to tetravalent aliphatic group having 1 to 20 carbon atoms include alkylene groups having 1 to 20 carbon atoms, such as a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, a dodecylene group, a hexadecylene group, a heptadecylene group, an octadecylene group, a nonadecylene group, and an eicosylene group; a methanetriyl group, an ethanetriyl group, a propanetriyl group, a butanetriyl group, a pentanetriyl group, a hexanetriyl group, a heptanetriyl group, an octanetriyl group, a nonanetriyl group, a decatriyl group, a cyclohex ... and alkanetriyl groups having 1 to 20 carbon atoms, such as a methanetetrayl group, an ethanetetrayl group, a propanetetrayl group, a butanetetrayl group, a pentanetetrayl group, a hexanetetrayl group, a heptanetetrayl group, an octanetetrayl group, a nonanetetrayl group, a decanetetrayl group, a dodecanetetrayl group, a hexadecanetetrayl group, and an octadecanetetrayl group. Examples of the divalent to tetravalent alicyclic group having 3 to 20 carbon atoms include a cycloalkylene group, a cycloalkanetriyl group, and a cycloalkanetetrayl group.

[0031] Examples of divalent to tetravalent aromatic groups having 5 to 15 carbon atoms include arylene groups such as a phenylene group and a naphthalenediyl group; arenetriyl groups such as a benzenetriyl group and a naphthalenetriyl group; and arenetetrayl groups such as a benzenetetrayl group and a naphthalenetetrayl group.

[0032] In formula (1), L preferably contains one or more selected from the group consisting of a substituted or unsubstituted arylene group such as a substituted or unsubstituted phenylene group, a heteroatom such as an oxygen atom, and a substituted or unsubstituted alkylene group. L may contain, for example, a substituted or unsubstituted arylene group such as a substituted or unsubstituted phenylene group, a heteroatom such as an oxygen atom, and a substituted or unsubstituted alkylene group.

[0033] For example, L may be a linking group represented by the following formula (2). *-Ar 1 -OXO-Ar 2 -* (2)

[0034] In formula (2), Ar 1 and Ar 2 are each independently an arylene group, and may be, for example, a substituted or unsubstituted phenylene group. When the phenylene group has a substituent, examples of the substituent include an alkyl group having 1 to 20 carbon atoms. X is a divalent linking group, and examples of X include a substituted or unsubstituted alkylene group. In formula (2), * indicates a bonding site with a nitrogen atom of a carbodiimide group.

[0035] When X is an unsubstituted alkylene group, X can be, for example, -(CH2) n n is preferably 1 to 6, more preferably 1 to 4, and may be 2, for example. When X is an alkylene group having a substituent, examples of X include a group represented by the following formula (3).

[0036] [ka]

[0037] In formula (3), * indicates a bonding site with the oxygen atom of formula (2). In formula (3), p and q are each preferably an integer of 1 to 3, more preferably 1 or 2, and may be, for example, 1. A and B are each independently a substituent or a hydrogen atom (excluding the case where A and B are both hydrogen atoms), or A and B may be bonded to each other to form a cyclic structure together with the carbon atom to which A and B are bonded. Examples of the substituent include an alkyl group having 1 to 20 carbon atoms. When A and B are bonded to each other to form a cyclic structure together with the carbon atom to which A and B are bonded, for example, X may be a group represented by the following formula (4), etc.

[0038] [ka]

[0039] In formula (4), * indicates a bonding site with the oxygen atom of formula (2). M is a group formed by mutual bonding of A and B of formula (3), and both ends of M form a ring structure together with the carbon atoms to which they are bonded. M may be, for example, a group represented by the following formula (5), etc.

[0040] *-(CH2) r -O-Ar 3 -N=C=N-Ar 4 -O-(CH2) s -* (5) In formula (5), * denotes an end of M and indicates a bonding site with a carbon atom. Each of r and s is preferably an integer of 1 to 3, more preferably 1 or 2, and may be, for example, 1. Ar 3 and Ar 4are each independently an arylene group, and may be, for example, a substituted or unsubstituted phenylene group. When the phenylene group has a substituent, examples of the substituent include an alkyl group having 1 to 20 carbon atoms.

[0041] A specific example of the cyclic carbodiimide compound is a compound represented by formula (1), in which L is a linking group represented by formula (2), and Ar 1 and Ar 2 are each independently a substituted or unsubstituted phenylene group, and X is -(CH2)2-; a compound represented by formula (1), in which L is a linking group represented by formula (2), and Ar 1 and Ar 2 are each independently a substituted or unsubstituted phenylene group, X is a linking group represented by formula (4), p and q are each 1, M is a group represented by formula (5), r and s are each 1, Ar 3 and Ar 4 are each independently a substituted or unsubstituted phenylene group.

[0042] The cyclic carbodiimide compound (B) may be used alone or in combination of two or more kinds. The amount of the cyclic carbodiimide compound (B) added can be appropriately selected. From the viewpoint of suppressing burrs, the amount of the cyclic carbodiimide compound (B) added is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass or more, relative to 100 parts by mass of the PBT resin. From the viewpoint of flowability, the amount of the cyclic carbodiimide compound (B) added is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the PBT resin. The amount of the cyclic carbodiimide compound (B) added is, for example, preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, and even more preferably 0.2 to 2 parts by mass, relative to 100 parts by mass of the PBT resin.

[0043] In the burr suppression method of the embodiment, the method of adding the cyclic carbodiimide compound (B) to the PBT resin (A) is not particularly limited. The timing of adding the cyclic carbodiimide compound (B) may be, for example, when melt-kneading the raw materials during preparation of the PBT resin composition. For example, the cyclic carbodiimide compound (B) may be added by feeding the PBT resin (A), the cyclic carbodiimide compound (B), and, if necessary, other components described below, into an extruder and melt-kneading them. Alternatively, a master batch may be prepared so that the cyclic carbodiimide compound (B) has a concentration of 10 to 40% with the PBT resin (A) as a matrix, and the master batch may be blended into a resin composition containing the PBT resin (A) before injection molding so that the carbodiimide amount of the present application is obtained, and then injection molding may be performed.

[0044] [Other ingredients] In the burr suppression method of the embodiment, other components may be further blended with the PBT resin as necessary, such as, but not limited to, inorganic fillers, antioxidants, weather stabilizers, molecular weight regulators, ultraviolet absorbers, antistatic agents, dyes, pigments, lubricants, crystallization accelerators, crystal nucleating agents, near-infrared absorbers, flame retardants, flame retardant assistants, organic fillers, and colorants.

[0045] [Polybutylene terephthalate resin composition] The method for producing the PBT resin composition is not particularly limited, and for example, a known method can be used. For example, a method in which each component is put into an extruder, melt-kneaded, and pelletized can be mentioned. As described above, for example, when each component is put into an extruder and melt-kneaded, a cyclic carbodiimide compound (B) can be added.

[0046] The PBT resin composition may be a recycled product. The recycled product may be a resin composition containing a material obtained by processing a molded product. The PBT resin composition as a recycled product may contain, for example, a material obtained by processing a molded product produced using a PBT resin composition in which a cyclic carbodiimide compound (B) is added to a PBT resin (A). For example, the PBT resin composition as a recycled product may be obtained by crushing a molded product produced using a PBT resin composition in which a cyclic carbodiimide compound (B) is added, and the crushed product may be used as is or further processed. The recycled product may be obtained through one recycling process, or may be obtained through two or more recycling processes. The PBT resin composition in which a cyclic carbodiimide compound (B) is added to a PBT resin (A) can exhibit good burr suppression even when it becomes a recycled product through a recycling process. Alternatively, a molded product made of a PBT resin composition not containing a cyclic carbodiimide may be pulverized, and the pulverized product and the cyclic carbodiimide compound (B) may be put into an extruder, melt-kneaded, and pelletized.

[0047] <Molded products> A molded article can be obtained by using the PBT resin composition of the embodiment. The method for obtaining the molded article is not particularly limited, and a known method can be adopted. For example, the PBT resin composition is put into an extruder, melt-kneaded, extruded, and pelletized, and the pellets are put into an injection molding machine equipped with a predetermined mold and injection molded to produce the molded article. Molded articles obtained using the PBT resin composition of the embodiment can be suitably used for, for example, automobiles and electrical parts, specific examples of which include connectors, relays, bobbins, switches, ECU cases, sensor cases, actuator cases, junction boxes, breakers, solenoid valves, air conditioner parts, copier parts, optical equipment parts, computer-related parts, telecommunication equipment-related products, and lighting products.

[0048] The embodiments of the present invention include the following, but the present invention is not limited to the following embodiments. <1> A method for suppressing burrs generated during injection molding of a polybutylene terephthalate resin composition, comprising adding a cyclic carbodiimide compound (B) to a polybutylene terephthalate resin (A). <2> The amount of the cyclic carbodiimide compound (B) added is 0.1 to 5 parts by mass relative to 100 parts by mass of the polybutylene terephthalate resin. <1> The method described above. <3> The polybutylene terephthalate resin composition is a recycled product. <1> or <2> The method described above. EXAMPLES

[0049] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0050] <Production of materials α-1 to α-6> (Material α-1 and α-3) Compositions α-1 and α-3 containing PBT resin and a cyclic or aromatic carbodiimide compound were produced as follows: The components shown in Table 1 were melt-kneaded and extruded in the ratios (parts by mass) shown in Table 1 using a 30 mmφ twin-screw extruder (TEX30C, manufactured by The Japan Steel Works, Ltd.) at 230°C in the raw material supply section and 240-250°C in between, with a discharge rate of 15 kg / h and a screw rotation speed of 130 rpm, to obtain pellets of materials α-1 and α-3, respectively.

[0051] (Material α-4 and α-5) For material α-4, pellets of PBT resin (A-3) shown in Table 1 were used as pellets of material α-4. For material α-5, pellets of PBT resin (A-1) shown in Table 1 were used as pellets of material α-5.

[0052] (Material α-2) For material α-2, R-1 shown in Table 1 was produced by the method described below and used as pellets of material α-2. (Material α-6) For material α-6, the PBT resin (A-4) shown in Table 1 was produced by the method described below and used as pellets of material α-6.

[0053] Details of each component in Table 1 are as follows.

[0054] A-1: Polybutylene terephthalate resin (intrinsic viscosity 0.73 dL / g, manufactured by Polyplastics Co., Ltd.) A-2: Polybutylene terephthalate resin (intrinsic viscosity 0.83 dL / g, manufactured by Polyplastics Co., Ltd.) A-3: Polybutylene terephthalate resin (intrinsic viscosity 0.88 dL / g, manufactured by Polyplastics Co., Ltd.) A-4: Recycled product of A-1 (intrinsic viscosity 0.69 dL / g, produced by the method described below)

[0055] B-1: Cyclic carbodiimide compound (Teijin Limited "Carbodista TCC-NP") B-2: Aromatic carbodiimide compound ("STABAXOL P100" manufactured by LANXESS KK)

[0056] R-1: Recycled material α-1 (intrinsic viscosity 0.73 dL / g, produced by the method described below)

[0057] (Production of A-4) A-1 was dried at 140°C for 3 hours, and then a 1A type ISO test piece (width 10 mm, thickness 4 mmt) conforming to ISO3167 was produced using a FANUC injection molding machine "ROBOSHOT S-2000i 100B" at a cylinder temperature of 260°C and a mold temperature of 80°C. The obtained ISO test piece was crushed in a small crusher, and the crushed product was used to produce a 1A type ISO test piece conforming to ISO3167 again using an injection molding machine. The obtained ISO test piece was then further crushed to obtain A-4.

[0058] (Production of R-1) The pellets of material α-1 produced above were dried at 140°C for 3 hours, and then a 1A type ISO test piece (width 10 mm, thickness 4 mmt) conforming to ISO3167 was produced using a FANUC injection molding machine "ROBOSHOT S-2000i 100B" at a cylinder temperature of 260°C and a mold temperature of 80°C. The obtained ISO test piece was crushed in a small crusher, and then the crushed product was used to produce a 1A type ISO test piece conforming to ISO3167 again using an injection molding machine. The obtained ISO test piece was then further crushed to obtain R-1.

[0059] [Table 1]

[0060] <Evaluation> The obtained materials α-1 to α-6 were subjected to the following evaluations. The results are shown in Table 2.

[0061] (1) Melt Viscosity The pellets of materials α-1 to α-6 obtained above were subjected to a shear rate of 1000 sec using a Capillograph 1B (manufactured by Toyo Seiki Seisakusho) in accordance with ISO 11443, with a furnace temperature of 260°C, a capillary diameter of 1 mm x 20 mmL, and a shear rate of 1000 sec. -1 The melt viscosity was measured under the condition of a residence time of 9 minutes.

[0062] (2) Length of the burr Using the pellets of materials α-1 to α-6 obtained above, a mold with a disk-shaped cavity, the outer periphery of which is provided with a burr measurement section having a mold gap of 60 μm, was used to perform injection molding at a cylinder temperature of 260° C., a mold temperature of 80° C., and the minimum pressure required to completely fill the cavity, using an injection molding machine EC60 manufactured by Toshiba Machine Co., Ltd. Then, the length of the burr generated in that portion was measured under magnification using a projection machine (CNC image measuring machine (model: QVBHU404-PRO1F) manufactured by Mitutoyo Corporation).

[0063] [Table 2]

[0064] As shown in Table 2, in Examples 1 and 2, the length of the burr was shorter than in Comparative Examples 1 to 4 in which a cyclic carbodiimide compound was not used, and it was shown that the burr generated during injection molding was suppressed. In addition, in Example 2, R-1 obtained by recycling the material α-1 used in Example 1 twice was used as material α-2, and a good burr suppression effect was shown. In particular, although Examples 1 and 2 had the same melt viscosity value as Comparative Examples 1 and 2, the length of the burr was shorter, and it was shown that the burr could be suppressed without sacrificing fluidity.

Claims

1. A method for suppressing burrs generated during injection molding of a polybutylene terephthalate resin composition, comprising adding a cyclic carbodiimide compound (B) to a polybutylene terephthalate resin (A).

2. The method according to claim 1, wherein the amount of the cyclic carbodiimide compound (B) added is 0.1 to 5 parts by mass based on 100 parts by mass of the polybutylene terephthalate resin.

3. The method according to claim 1 or 2, wherein the polybutylene terephthalate resin composition is a recycled product.

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