Method for suppressing generation of burrs during injection molding of polybutylene terephthalate resin composition

Abstract

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

Description

Method for suppressing flash formation during injection molding of polybutylene terephthalate resin composition

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

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

[0003] When manufacturing molded products using PBT resin, burrs may occur. In recent years, molded products have often been made thinner to reduce weight, and molding conditions such as high injection pressure, injection speed, cylinder temperature, and mold temperature are often used, or PBT resin compositions with improved fluidity are often used. However, this tends to make molded products more susceptible to burrs. Burrs not only mar the appearance but can also be the starting point for damage, so they are usually removed, but removing burrs often requires manual labor, which tends to be very labor-intensive.

[0004] As a method for reducing burrs, Patent Document 1 describes a resin composition containing a polybutylene terephthalate resin, a polyester resin other than polybutylene terephthalate resin, an inorganic reinforcing material, a glycidyl group-containing styrene copolymer, and an ethylene-glycidyl (meth)acrylate copolymer, and having a crystallization temperature of 175 to 180°C as determined by a differential scanning calorimeter (DSC). It also describes that by using a predetermined amount of the glycidyl group-containing styrene copolymer and the ethylene-glycidyl (meth)acrylate copolymer in combination, it is possible to significantly reduce the amount of burrs while maintaining the appearance of the molded product. Patent Document 2 describes a resin composition containing a polybutylene terephthalate resin, an amorphous resin, an inorganic reinforcing material, an ethylene-glycidyl (meth)acrylate copolymer, and an ester exchange inhibitor, and that the resin composition is melt-melted at 265°C and a shear rate of 10 sec. －１ It also describes a resin composition having a melt viscosity of 0.5 to 1.5 kPa·s at room temperature, and that the occurrence of flash can be significantly suppressed.

[0005] JP 2013-159732 A International Publication No. 2021 / 045124

[0006] An object of an embodiment of the present invention is to provide a method for suppressing flash generation during injection molding of a polybutylene terephthalate resin composition.

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

[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.

[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 generation of burrs during injection molding of a polybutylene terephthalate resin composition> A method for suppressing the generation of burrs during injection molding of a polybutylene terephthalate resin composition according to an embodiment of the present invention (hereinafter also simply referred to as a "burr suppression method") includes adding a cyclic carbodiimide compound (B) to a polybutylene terephthalate resin (A).

[0011] When manufacturing molded products using PBT resin, burrs may occur. Furthermore, materials with high fluidity tend to easily infiltrate gaps between mold parting surfaces, which can easily cause burrs to form on molded products. In the burr suppression method of the embodiment, burrs generated during injection molding of a PBT resin composition are suppressed by adding a cyclic carbodiimide compound (B) to a PBT resin (A). In recent years, recycled materials have become more common due to environmental considerations. When using the burr suppression method of the embodiment, good burr suppression effects can be achieved even with recycled materials.

[0012] Furthermore, 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 result in a tendency for heat resistance to decrease. 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 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 The PBT resin (A) is a resin obtained by polycondensation of a dicarboxylic acid component containing an alkylene glycol (e.g., an alkyl ester or acid halide of 1,4-butanediol) having at least 4 carbon atoms (e.g., 1,4-butanediol) or an ester-forming derivative thereof (e.g., an acetylated product thereof) with a glycol component containing an alkylene glycol (1,4-butanediol) having at least 4 carbon atoms (e.g., 1,4-butanediol) or an ester-forming derivative thereof (e.g., an acetylated product thereof). The PBT resin (A) is not limited to a homopolybutylene terephthalate resin, but may also be a copolymer containing 60 mol% or more (particularly 75 mol% to 95 mol%) of butylene terephthalate units. Furthermore, the raw materials for the PBT resin (A), 1,4-butanediol or an ester-forming derivative thereof and terephthalic acid or an ester-forming derivative thereof (e.g., an alkyl terephthalate ester), may be derived from either fossil resources or biomass resources. The PBT resin (A) may be used singly or in combination of two or more types.

[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 of C, such as succinic acid, adipic acid, azelaic acid, and sebacic acid; ４－１６ alkanedicarboxylic acids such as cyclohexanedicarboxylic acid; ５－１０ cycloalkanedicarboxylic acids of the formula (C); ester-forming derivatives of these dicarboxylic acid components (C １－６ These dicarboxylic acid components may 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 are more preferred.

[0016] In the PBT resin (A), examples of glycol components (comonomer components) other than 1,4-butanediol or its ester-forming derivatives include C glycols such as ethylene glycol, propylene glycol, trimethylene glycol, 1,3-butylene glycol, hexamethylene glycol, neopentyl glycol, and 1,3-octanediol. ２－１０ alkylene glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, and the like; alicyclic diols such as cyclohexanedimethanol and hydrogenated bisphenol A, and the like; aromatic diols such as bisphenol A and 4,4'-dihydroxybiphenyl, and the like; C-type alkylene glycols of bisphenol A such as ethylene oxide 2-mol adduct of bisphenol A and propylene oxide 3-mol adduct of bisphenol A, and the like; 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 those listed above, 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.); ３－１２lactones; ester-forming derivatives of these comonomer components (C １－６ alkyl ester derivatives, acid halides, acetylated derivatives, etc.

[0018] Any of the polybutylene terephthalate copolymers obtained by copolymerizing the comonomer components described above can be suitably used as the PBT resin (A). Also, 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 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. The intrinsic viscosity can also 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 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, it is a compound containing a cyclic structure formed by linking two nitrogen atoms of the carbodiimide group via a linking group.

[0023] The cyclic carbodiimide compound (B) can contain one or more cyclic structures containing a carbodiimide group. The number of atoms directly constituting the cyclic structure containing the 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, and more preferably 10 or more. Furthermore, 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]

[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, for example, a structure in which groups such as an aliphatic group, an alicyclic group, and / or an aromatic group 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 from among 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 the cyclic structure together with the carbodiimide group is not particularly limited. For example, in L, the number of atoms directly constituting the cyclic structure together with the carbodiimide group is preferably 5 or more, and more preferably 7 or more. Furthermore, in L, the number of atoms directly constituting the 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 the 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 divalent to tetravalent aliphatic group having 1 to 20 carbon atoms, a divalent to tetravalent alicyclic group having 3 to 20 carbon atoms, a divalent to tetravalent aromatic group having 5 to 15 carbon atoms, or a combination thereof.

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

[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 -O-X-O-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 the bonding site with the nitrogen atom of the carbodiimide group.

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

[0036]

[0037] In formula (3), * indicates a bonding site with the oxygen atom in formula (2). In formula (3), p and q are each preferably independently 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 (except when 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 atoms to which A and B are bonded. Examples of the substituent include alkyl groups having 1 to 20 carbon atoms. When A and B are bonded to each other to form a cyclic structure together with the carbon atoms to which A and B are bonded, X may be, for example, a group represented by the following formula (4):

[0038]

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

[0040] *-(CH ２ ) ｒ -O-Ar ３ -N=C=N-Ar ４ -O-(CH ２ ) ｓ -* (5) In formula (5), * represents the end of M and indicates the bonding site with the carbon atom. r and s are each independently preferably an integer of 1 to 3, more preferably 1 or 2, and may be, for example, 1. Ar ３ and Ar ４ 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.

[0041] Specific examples of the cyclic carbodiimide compound include 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 -(CH ２ ) 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, and 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. 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 flash suppression method of the embodiment, the method for adding the cyclic carbodiimide compound (B) to the PBT resin (A) is not particularly limited. Examples of the timing for adding the cyclic carbodiimide compound (B) include melt-kneading raw materials during the 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 masterbatch may be prepared using the PBT resin (A) as a matrix and the cyclic carbodiimide compound (B) at a concentration of 10 to 40%, and the masterbatch may be blended with a resin composition containing the PBT resin (A) to achieve the carbodiimide content specified in the present application prior to injection molding, followed by injection molding.

[0044] [Other Components] In the burr suppression method of the embodiment, other components may be further blended into the PBT resin as needed. Examples of other components include, but are not limited to, inorganic fillers, antioxidants, weather stabilizers, molecular weight modifiers, 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 charged into an extruder, melt-kneaded, and pelletized can be used. As described above, for example, when each component is charged into an extruder and melt-kneaded, the 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 recycled PBT resin composition may, for example, include a material obtained by processing a molded product made using a PBT resin composition containing a cyclic carbodiimide compound (B) added to a PBT resin (A). For example, a recycled PBT resin composition may be obtained by pulverizing a molded product made using a PBT resin composition containing a cyclic carbodiimide compound (B) added, and using the pulverized product as is or by further processing. The recycled product may be obtained through a single recycling process, or may be obtained through two or more recycling processes. A PBT resin composition containing a cyclic carbodiimide compound (B) added to a PBT resin (A) can exhibit good burr suppression even when recycled. Alternatively, a molded product made from a PBT resin composition not containing a cyclic carbodiimide may be pulverized, and the pulverized product and the cyclic carbodiimide compound (B) may be introduced into an extruder, melt-kneaded, and pelletized.

[0047] <Molded Article> A molded article can be obtained using the PBT resin composition according to the embodiment. The method for obtaining a molded article is not particularly limited, and known methods can be used. For example, a molded article can be produced by feeding the PBT resin composition into an extruder, melt-kneading the composition, extruding it, and pelletizing it, and then feeding the pellets into an injection molding machine equipped with a predetermined mold and injection molding it. Molded articles obtained using the PBT resin composition according to the embodiment can be suitably used for, for example, specific examples of automobile and electrical parts 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 parts, and lighting products.

[0048] Embodiments of the present invention include the following, but are not limited to the following: <1> A method for suppressing flash formation 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 <1>, in which the amount of the cyclic carbodiimide compound (B) added is 0.1 to 5 parts by mass per 100 parts by mass of the polybutylene terephthalate resin. <3> The method according to <1> or <2>, in which the polybutylene terephthalate resin composition is a recycled product.

[0049] The present invention will be explained 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> (Materials α-1 and α-3) α-1 and α-3, which are compositions containing a 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 to 250°C in the middle section, with a discharge rate of 15 kg / h and a screw rotation speed of 130 rpm, to obtain pellets of each of Materials α-1 and α-3.

[0051] (Materials 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, 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 ("Carbodista TCC-NP" manufactured by Teijin Limited) 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 ISO 3167 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 pulverized in a small pulverizer, and then the pulverized product was used to produce a 1A type ISO test piece conforming to ISO 3167 again using an injection molding machine. Thereafter, the obtained ISO test piece was further pulverized 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 FANUC injection molding machine "ROBOSHOT S-2000i 100B" was used at a cylinder temperature of 260 ° C. and a mold temperature of 80 ° C. to prepare a 1A type ISO test piece (width 10 mm, thickness 4 mmt) conforming to ISO 3167. The obtained ISO test piece was then pulverized in a small pulverizer, and the pulverized product was used again to prepare a 1A type ISO test piece conforming to ISO 3167 using an injection molding machine. Then, the obtained ISO test piece was further pulverized to obtain R-1.

[0059]

[0060] <Evaluation> The obtained materials α-1 to α-6 were evaluated as follows. The results are shown in Table 2.

[0061] (1) Melt Viscosity The pellets of materials α-1 to α-6 obtained above were melted in accordance with ISO 11443 using a Capillograph 1B (manufactured by Toyo Seiki Seisakusho Co., Ltd.) at 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) Burr Length Using the pellets of materials α-1 to α-6 obtained above, a disk-shaped cavity mold having a burr measurement section on the periphery with a mold gap of 60 μm in part was injection molded with an injection molding machine EC60 manufactured by Toshiba Machine Co., Ltd. at a cylinder temperature of 260°C, a mold temperature of 80°C, and the minimum pressure required to completely fill the cavity. The length of the burr generated in that area was then measured under magnification using an image projector (CNC image measuring machine (model: QVBHU404-PRO1F) manufactured by Mitutoyo Corporation).

[0063]

[0064] As shown in Table 2, Examples 1 and 2 had shorter burr lengths than Comparative Examples 1 to 4, in which no cyclic carbodiimide compound was used, indicating that burrs generated during injection molding were suppressed. Furthermore, Example 2, which uses R-1, which is the same material α-1 used in Example 1 recycled twice, as material α-2, also showed a good burr suppression effect. In particular, Examples 1 and 2 had the same melt viscosity values ​​as Comparative Examples 1 and 2, but had shorter burr lengths, indicating that burrs could be suppressed without sacrificing fluidity.

[0065] The disclosure of this application is related to the subject matter described in Japanese Patent Application No. 2023-138125, filed on August 28, 2023, the entire disclosure of which is incorporated herein by reference.

Claims

1. A method for suppressing flash formation 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 per 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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