JP7733505B2 - Polybutylene terephthalate resin composition and molded article - Google Patents

Description

Embodiments of the present invention relate to polybutylene terephthalate resin compositions and molded articles.

As a crystalline thermoplastic resin, polybutylene terephthalate resin has excellent mechanical strength, electrical properties, and other characteristics, making it an engineering plastic that is used in a wide range of applications, including automobiles, electrical and electronic devices, etc.

When a molded article is obtained using a polybutylene terephthalate resin, a resin composition obtained by mixing the polybutylene terephthalate resin with various additives is generally used.
As such additives, for example, olefin-based elastomers are generally used for the purpose of improving the impact resistance and toughness of molded articles.

Patent Document 1 describes a resin composition containing a thermoplastic resin having an intrinsic viscosity of 0.82 dL/g or less, measured at 30°C in a mixed solvent of tetrachloroethane and phenol in a 1:1 (mass ratio), and an impact modifier such as an ethylene-alkyl acrylate copolymer having a melt flow rate (MFR) of 50 g/10 min or more, measured at 190°C using a test load of 2.16 kg.
Patent Document 2 describes that adding a thickener such as a polyolefin resin or elastomer having a melt flow rate (MFR) of 20 g/10 min or less to a polyester resin improves the drawdown phenomenon during injection molding and also improves the impact resistance of the molded product.

Japanese Patent Application Laid-Open No. 2021-66787 Japanese Patent Application Laid-Open No. 2004-300450

Olefin elastomers tend to be insufficiently compatible with polybutylene terephthalate resins, and when olefin elastomers are used, the surface of the molded article may become rough, resulting in poor appearance.
Even if a compatibilizer is used to improve compatibility, it tends to be difficult to obtain a sufficient improvement in appearance.

An object of one embodiment of the present invention is to provide a polybutylene terephthalate resin composition that can be used to mold molded articles that have excellent toughness, rigidity, and appearance.

One embodiment of the present invention relates to a polybutylene terephthalate resin composition comprising: (A) 100 parts by mass of a polybutylene terephthalate resin having an intrinsic viscosity of 0.65 to 0.90 dL/g; (B) 5 to 30 parts by mass of an ethylene-ethyl acrylate copolymer; and (C) 10 to 100 parts by mass of an inorganic filler, wherein the melt flow rate of the ethylene-ethyl acrylate copolymer (B) is 25 g/10 min or less at 190°C under a load of 2.16 kg.
Another embodiment of the present invention relates to a molded article made using the polybutylene terephthalate resin composition.

Embodiments of the present invention provide a polybutylene terephthalate resin composition capable of producing molded articles with excellent toughness, rigidity, and appearance, and a molded article made using the resin composition.

FIG. 1 is a schematic diagram showing the upper surface of a molded piece used in the evaluation of appearance, surface roughness, and alkali resistance in the examples. FIG. 2 shows photographs of reference examples corresponding to the appearance evaluation grades A, B, and C in the examples.

The following describes preferred embodiments of the present invention, but the present invention is not limited to the following embodiments.

<Polybutylene terephthalate resin composition>
A polybutylene terephthalate resin composition (hereinafter sometimes simply referred to as a "resin composition") according to one embodiment of the present invention contains at least a polybutylene terephthalate resin, an ethylene-ethyl acrylate copolymer, and an inorganic filler.

The following describes each component that can be used in the resin composition of this embodiment.

(A) Polybutylene Terephthalate Resin (A) Polybutylene terephthalate resin (hereinafter also referred to as "PBT resin") is a polybutylene terephthalate-based resin obtained by polycondensation of a dicarboxylic acid component containing at least terephthalic acid or an ester-forming derivative thereof ( _C1-6 alkyl ester, acid halide, etc.) and a glycol component containing at least an alkylene glycol having 4 carbon atoms (1,4-butanediol) or an ester-forming derivative thereof (acetylated product, etc.).
The polybutylene terephthalate resin (A) is not limited to a homopolybutylene terephthalate resin, but may be a copolymer containing 60 mol % or more (particularly 75 mol % or more and 95 mol % or less) of butylene terephthalate units.

The intrinsic viscosity (IV) of the (A) polybutylene terephthalate resin is preferably 0.65 dL/g or more and 0.90 dL/g or less, more preferably 0.70 dL/g or more and 0.90 dL/g or less, and even more preferably 0.75 dL/g or more and 0.90 dL/g or less, and may be, for example, 0.85 dL/g or more and 0.90 dL/g or less. When a polybutylene terephthalate resin having an intrinsic viscosity within this range is used, the resulting polybutylene terephthalate resin composition will have particularly excellent appearance and strength.
The intrinsic viscosity can also be adjusted by blending polybutylene terephthalate resins having different intrinsic viscosities. For example, a polybutylene terephthalate resin having an intrinsic viscosity of 0.85 dL/g can be prepared by blending a polybutylene terephthalate resin having an intrinsic viscosity of 1.0 dL/g with a polybutylene terephthalate resin having an intrinsic viscosity of 0.7 dL/g.
(A) The intrinsic viscosity (IV) of the polybutylene terephthalate resin can be measured, for example, in o-chlorophenol at a temperature of 35°C.

The amount of terminal carboxyl groups in the polybutylene terephthalate resin (A) is not particularly limited as long as it does not impede the object of the present invention.
The amount of terminal carboxyl groups in the polybutylene terephthalate resin (A) is preferably 30 meq/kg or less, more preferably 25 meq/kg or less, while the amount of terminal carboxyl groups in the polybutylene terephthalate resin (A) is preferably 5 meq/kg or more, more preferably 10 meq/kg or more.
The amount of terminal carboxyl groups in the (A) polybutylene terephthalate resin is preferably 5 meq/kg or more and 30 meq/kg or less, more preferably 10 meq/kg or more and 25 meq/kg or less. By using a polybutylene terephthalate resin having a terminal carboxyl group amount in this range, the resulting polybutylene terephthalate resin composition is less susceptible to strength reduction due to hydrolysis in a humid and hot environment.

In the (A) polybutylene terephthalate resin, examples of dicarboxylic acid components (comonomer components) other than terephthalic acid and its ester-forming derivatives include _C8-14 aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-dicarboxydiphenyl ether; _C4-16 alkanedicarboxylic acids such as succinic acid, adipic acid, azelaic acid, and sebacic acid; _C5-10 cycloalkanedicarboxylic acids such as cyclohexanedicarboxylic acid; and ester-forming derivatives of these dicarboxylic acid components ( _C1-6 alkyl ester derivatives, acid halides, etc.). These dicarboxylic acid components can be used alone or in combination of two or more.

Among these dicarboxylic acid components, _C8-12 aromatic dicarboxylic acids such as isophthalic acid, and _C6-12 alkanedicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid are more preferred.

In the (A) polybutylene terephthalate resin, examples of glycol components (comonomer components) other than 1,4-butanediol include _C2-10 alkylene glycols such as ethylene glycol, propylene glycol, trimethylene glycol, 1,3-butylene glycol, hexamethylene glycol, neopentyl glycol, and 1,3-octanediol; 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; _C2-4 alkylene oxide adducts of bisphenol A, such as an ethylene oxide 2-mol adduct of bisphenol A and a propylene oxide 3-mol adduct of bisphenol A; and ester-forming derivatives of these glycols (acetylated products, etc.). These glycol components can be used alone or in combination of two or more.

Among these glycol components, C _2-6 alkylene glycols such as ethylene glycol and trimethylene glycol, polyoxyalkylene glycols such as diethylene glycol, and alicyclic diols such as cyclohexanedimethanol are more preferred.

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; _C3-12 lactones such as propiolactone, butyrolactone, valerolactone, and caprolactone (e.g., ε-caprolactone); and ester-forming derivatives of these comonomer components (e.g., _C1-6 alkyl ester derivatives, acid halides, and acetylated products).

Any of the polybutylene terephthalate copolymers copolymerized with the comonomer components described above can be suitably used as the (A) polybutylene terephthalate resin. Furthermore, a combination of a homopolybutylene terephthalate polymer and a polybutylene terephthalate copolymer may also be used as the (A) polybutylene terephthalate resin.

(B) Ethylene ethyl acrylate copolymer Ethylene ethyl acrylate copolymer (hereinafter also referred to as "EEA" copolymer) is a copolymer containing ethylene and ethyl acrylate as copolymerization components. The copolymerization type is not particularly limited, and the copolymer may be any of random, block, or graft copolymers. For example, the copolymer may partially have two or more structures selected from the random structure, block structure, and graft structure.

The ratio of ethylene to ethyl acrylate in the copolymer is not particularly limited, but from the standpoint of ensuring compatibility with PBT resin and suppressing blocking during production, the melting point of the EEA copolymer is preferably 85°C or higher, more preferably 88°C or higher, and particularly preferably 90°C or higher.

From the perspective of improving the appearance of articles molded from EEA copolymer, it is preferable that (B) EEA copolymer have a melt flow rate of 25 g/10 min or less at 190°C under a load of 2.16 kg.

The inclusion of EEA copolymer can improve the toughness of molded articles. On the other hand, olefin-based elastomers tend to be insufficiently compatible with polybutylene terephthalate resins, and using olefin-based elastomers can result in the surface of molded articles becoming rough and resulting in poor appearance. Using a highly viscous EEA copolymer with a melt flow rate of 25 g/10 min or less at 190°C and a load of 2.16 kg can improve the appearance of molded articles.

From the viewpoint of improving the appearance of a molded article, the melt flow rate of the (B) EEA copolymer at 190°C under a load of 2.16 kg is preferably 25 g/10 min or less, more preferably 20 g/10 min or less, even more preferably 2 g/10 min or less, and particularly preferably 1 g/10 min or less. The melt flow rate of the (B) EEA copolymer at 190°C under a load of 2.16 kg may be, for example, 0.01 g/10 min or more and 25 g/10 min or less.
The melt flow rate can also be adjusted by blending EEA copolymers having different melt flow rates. For example, an EEA copolymer having a melt flow rate of 30 g/10 min at 190°C and a load of 2.16 kg can be blended with an EEA copolymer having a melt flow rate of 10 g/10 min at 190°C and a load of 2.16 kg to prepare an EEA copolymer having a melt flow rate of 15 g/10 min at 190°C and a load of 2.16 kg. The melt flow rate at 190°C and a load of 2.16 kg is a value measured under conditions of 190°C and a load of 2.16 kg according to a method in accordance with ISO 1133.

In this embodiment, an EEA copolymer that is substantially free of comonomer components other than ethylene and ethyl acrylate may be used, or an EEA copolymer that contains other comonomer components may be used.

In an EEA copolymer that is substantially free of comonomer components other than ethylene and ethyl acrylate, the amount of comonomers other than ethylene and ethyl acrylate in the copolymerized monomers is 3% by mass or less, preferably 1% by mass or less, and may be 0% by mass.

When the (B) EEA copolymer contains a comonomer component other than ethylene and ethyl acrylate, examples of the other comonomer include maleic anhydride, (meth)acrylic acid esters such as butyl acrylate, and methyl methacrylate. For example, a comonomer containing a highly reactive functional group such as a glycidyl group may also be used.
Examples of EEA copolymers containing a comonomer component other than ethylene and ethyl acrylate include graft copolymers of ethylene ethyl acrylate and butyl acrylate-methyl methacrylate (EEA-g-BAMMA copolymers).

When the (B) EEA copolymer contains a comonomer component other than ethylene and ethyl acrylate, the mass ratio of the total amount of ethylene and ethyl acrylate to the total amount of comonomers other than ethylene and ethyl acrylate is, for example, preferably 95:5 to 50:50, more preferably 85:15 to 55:45, and even more preferably 80:20 to 60:40.

(B) EEA copolymer can be produced by any method. For example, EEA copolymer can be obtained by mixing predetermined amounts of ethylene and ethyl acrylate (and other comonomer components) and carrying out radical polymerization using a radical initiator in a conventional manner. Alternatively, for example, a grafted precursor obtained by copolymerizing the monomers of the butyl acrylate-methyl methacrylate copolymer component with a radical (co)polymerizable organic peroxide can be melt-kneaded in EEA copolymer particles composed of ethylene and ethyl acrylate, and a graft copolymer of ethylene ethyl acrylate and butyl acrylate-methyl methacrylate (EEA-g-BAMMA copolymer) can be obtained by a grafting reaction between the polymers.

(B) The EEA copolymer may be used alone or in combination of two or more types.

The content of the (B) EEA copolymer is preferably 5 parts by mass or more and 30 parts by mass or less, more preferably 10 parts by mass or more and 25 parts by mass or less, and even more preferably 15 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the (A) polybutylene terephthalate resin.
From the viewpoint of impact resistance, the content of the EEA copolymer (B) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of the polybutylene terephthalate resin (A). On the other hand, from the viewpoint of rigidity, the content of the EEA copolymer is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the polybutylene terephthalate resin (A).

(C) Inorganic Filler The polybutylene terephthalate resin composition can contain (D) an inorganic filler. By containing (D) an inorganic filler, mechanical properties and heat resistance can be improved. From the viewpoint of improving the rigidity of a molded article, it is preferable that the polybutylene terephthalate resin composition contains (D) an inorganic filler. In addition, the molding shrinkage rate and linear expansion coefficient of the polybutylene terephthalate resin composition can be reduced.

(C) Examples of inorganic fillers include fibrous inorganic fillers (e.g., glass fiber, asbestos fiber, silica fiber, alumina fiber, silica-alumina fiber, zirconia fiber, boron nitride fiber, silicon nitride fiber, boron fiber, potassium titanate fiber, silicon carbide fiber, whiskers (whiskers of alumina, silicon nitride, etc.)), plate-like inorganic fillers (e.g., talc, mica, glass flakes, graphite, etc.), and powder-like inorganic fillers (e.g., glass beads, glass powder, milled fiber (milled fiber such as glass), wollastonite, etc.). Among these inorganic fillers, glass-based fillers (e.g., glass fiber, glass flakes, glass beads), talc, mica, and wollastonite are preferred, with glass fiber being particularly preferred in terms of availability, strength, and rigidity. Furthermore, plate-like and powder-like fillers are preferred in terms of suppressing the anisotropy of the molding shrinkage and linear expansion coefficient of the polybutylene terephthalate resin composition. When using these fillers, known surface treatment agents can be used as needed.

When a fibrous filler is used as the (C) inorganic filler, there are no particular limitations on its shape, but for example, the length is about 100 μm to 5 mm, more preferably about 500 μm to 3 mm, and the diameter is about 1 to 50 μm, more preferably about 3 to 30 μm. Furthermore, when a plate-like filler or powdery filler is used, there are no particular limitations on its average particle size, but for example, it is about 0.1 to 100 μm, more preferably about 0.1 to 50 μm. These (C) fillers can be used alone or in combination of two or more.

The content of (C) inorganic filler is preferably 10 parts by mass or more and 100 parts by mass or less, more preferably 20 parts by mass or more and 90 parts by mass or less, even more preferably 30 parts by mass or more and 75 parts by mass or less, and even more preferably 40 parts by mass or more and 60 parts by mass or less, per 100 parts by mass of the polybutylene terephthalate resin composition.

From the viewpoint of rigidity, the content of (C) inorganic filler is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 30 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of the polybutylene terephthalate resin composition. On the other hand, from the viewpoint of flowability, the content of (C) inorganic filler is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 75 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of the polybutylene terephthalate resin composition.

(D) Silicone-Based Compound The polybutylene terephthalate resin composition of the present embodiment preferably contains (D) a silicone-based compound.

Preferred silicone compounds include, but are not limited to, pure silicone resins such as dimethylpolysiloxane, methylphenylpolysiloxane, and diphenylpolysiloxane, which are commonly known as silicone oils, and modified silicones obtained by reacting pure silicone resins with modifying resins such as alkyd resins, polyester resins, acrylic resins, and epoxy resins.

Alternatively, a cured silicone powder having silicone oil absorbed therein (hereinafter, sometimes referred to as "silicone oil-absorbed cured silicone powder") may be used. For example, the silicone oil-absorbed cured silicone powder may be obtained by blending 0.5 to 80% by weight of silicone oil into a fine powder of cured silicone, allowing the silicone oil to absorb, and then powdering the mixture by any method.
As the silicone that absorbs silicone oil to form a hardened silicone powder, for example, conventionally known silicone rubber or silicone gel can be used.

Examples of silicone oils include those represented by the following general formula (1): In the following general formula (1), R is a substituted or unsubstituted monovalent hydrocarbon group or a hydroxyl group, and n is an integer.
R ₃ SiO[R ₂ SiO] _n SiR ₃ (1)
In the above general formula (1), R represents a substituted or unsubstituted monovalent hydrocarbon group or a hydroxyl group. Examples of the substituted or unsubstituted monovalent hydrocarbon group include alkyl groups such as a methyl group, an ethyl group, and a propyl group; alkenyl groups such as a vinyl group and an allyl group; aralkyl groups such as a cycloalkyl group and a β-phenylethyl group; a 3,3,3-trifluoropropyl group, a 3-mercaptopropyl group, a 3-aminopropyl group, and a 3-glycidoxypropyl group.

Polybutylene terephthalate resins tend to have low long-term durability against alkaline solutions. For example, when a resin molded article is used in a location where it comes into contact with chemicals containing sodium hydroxide, sodium hypochlorite, sodium percarbonate, calcium chloride, etc., such as toilet cleaners, bathtub cleaners, bleaches, and snow-melting agents, the resin molded article is exposed to an alkaline atmosphere. If a resin molded article made of polybutylene terephthalate resin is exposed to such an alkaline atmosphere for a long period of time while being subjected to excessive strain due to screwing, metal press-fitting, caulking, etc., the effects of both the strain and the alkaline components can cause so-called environmental stress cracking, resulting in cracks in the molded article.
Furthermore, polybutylene terephthalate resin is often used as an insert-molded product in which a metal or inorganic solid (hereinafter also referred to as metal, etc.) is inserted. In such insert-molded products, there is an interface, known as a weld, where the resin flows around the metal, etc. and meets during injection molding, and the above-mentioned environmental stress cracking generally occurs in the weld of the molded product.

From the viewpoint of improving the alkali resistance of the molded article, the kinematic viscosity of the (D) silicone compound at 25°C is preferably 1000 to 10,000 cSt (10 to 100 cm ² /s), more preferably 2000 to 8,000 cSt, even more preferably 3000 to 8,000 cSt, even more preferably 3000 to 6,000 cSt, and even more preferably 4,000 to 6,000 cSt. When the previously described silicone oil-absorbed cured silicone powder is used, the silicone oil to be absorbed should have a kinematic viscosity within the above range.
The kinematic viscosity at 25°C can be determined by the method described in JIS Z8803.

(D) The silicone-based compound may be used alone or in combination of two or more.

The content of the (D) silicone compound is preferably 0.5 parts by mass or more and 2 parts by mass or less, more preferably 0.6 parts by mass or more and 1.5 parts by mass or less, and even more preferably 0.7 parts by mass or more and 1.1 parts by mass or less, per 100 parts by mass of the (A) polybutylene terephthalate resin.

From the viewpoint of the effect of improving the alkali resistance of the molded article, the content of the (D) silicone-based compound is preferably 0.5 parts by mass or more, more preferably 0.6 parts by mass or more, and even more preferably 0.7 parts by mass or more, relative to 100 parts by mass of the (A) polybutylene terephthalate resin.
On the other hand, from the viewpoint of suppressing problems caused by exudation from the molded article (e.g., contact contamination, etc.), the content of the (D) silicone-based compound is preferably 2 parts by mass or less, more preferably 1.5 parts by mass or less, and even more preferably 1.1 parts by mass or less, per 100 parts by mass of the (A) polybutylene terephthalate resin.

(E) Other Components The polybutylene terephthalate resin composition of the present embodiment may optionally contain components other than the above-described (A) polybutylene terephthalate resin, (B) ethylene-ethyl acrylate copolymer, (C) inorganic filler, and (D) silicone-based compound, depending on the purpose. (E) Other components include, but are not limited to, antioxidants, stabilizers, molecular weight modifiers, ultraviolet absorbers, antistatic agents, colorants, lubricants, mold release agents, crystallization accelerators, crystal nucleating agents, infrared absorbers, flame retardants, flame retardant assistants, hydrolysis resistance improvers, flow improvers, and compatibilizers.

In the polybutylene terephthalate resin composition of the present embodiment, the total content of the components (A) to (D) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 99% by mass or more, based on the total composition.
The upper limit of the total content of the components (A) to (D) is not particularly limited and may be 100% by mass. By keeping the total content of the components (A) to (D) within the above range, it is possible to obtain a resin composition that can be used to mold molded articles with excellent toughness, rigidity, and appearance.

From the viewpoint of fluidity, the fluidity of the polybutylene terephthalate resin composition is such that the melt viscosity measured in accordance with ISO 11443 at a furnace temperature of 260°C, a capillary diameter of 1 mm x 20 mmL, and a shear rate of 1000 sec ^-1 is preferably 0.3 kPa s or less, more preferably 0.28 kPa s or less, and even more preferably 0.25 kPa s or less.

The polybutylene terephthalate resin composition can be produced by various methods known for producing thermoplastic resin compositions. A suitable method is, for example, to melt-knead the components using a melt-kneading device such as a single-screw or twin-screw extruder, and then extrude the components into pellets.

<Molded product>
A molded article made using the above-mentioned polybutylene terephthalate resin composition will now be described.

One embodiment of the present invention relates to a molded article molded using the polybutylene terephthalate resin composition described above.
This molded article may, for example, include only a resin part made of the polybutylene terephthalate resin composition, or, for example, as described below, may include a resin part made of the polybutylene terephthalate resin composition and an insert member made of a metal and/or an inorganic solid.

The method for obtaining a molded article using a polybutylene terephthalate resin composition is not particularly limited, and known methods can be used. For example, a molded article can be obtained by injection molding the polybutylene terephthalate resin composition. For example, the components of the polybutylene terephthalate resin composition can be melt-kneaded and extruded to produce pellets of the polybutylene terephthalate resin composition, which can be then injected into an injection molding machine equipped with a predetermined mold and subjected to injection molding.
The molded article of this embodiment can also be an insert-molded article obtained by injection molding the polybutylene terephthalate resin composition together with an insert member made of a metal and/or an inorganic solid.

The molded article of this embodiment has excellent toughness and rigidity, as well as an excellent appearance. From the perspective of obtaining a molded article with a good appearance in which surface roughness is suppressed, the surface roughness of the molded article, as measured by the arithmetic mean roughness Ra according to JIS B 0601-2013, is preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.7 μm or less.

The molded article of this embodiment may be applied, for example, to a molded article (more preferably, an insert-molded article) used as a part that comes into contact with an alkaline solution. When applied to a molded article (more preferably, an insert-molded article) used as a part that comes into contact with an alkaline solution, it is particularly preferable to use a polybutylene terephthalate resin composition containing 0.5 to 2 parts by mass of a silicone-based compound with a kinematic viscosity at 25°C of 1,000 to 10,000 cSt (more preferably, 2,000 to 8,000 cSt, even more preferably, 3,000 to 8,000 cSt, and even more preferably, 4,000 to 6,000 cSt) per 100 parts by mass of polybutylene terephthalate resin.

Embodiments of the present invention include, but are not limited to, the following embodiments.
<1> (A) 100 parts by mass of a polybutylene terephthalate resin having an intrinsic viscosity of 0.65 to 0.90 dL/g;
(B) 5 to 30 parts by mass of ethylene ethyl acrylate copolymer;
(C) 10 to 100 parts by mass of an inorganic filler;
The polybutylene terephthalate resin composition (B) is an ethylene ethyl acrylate copolymer having a melt flow rate of 25 g/10 min or less at 190° C. under a load of 2.16 kg.
<2> The polybutylene terephthalate resin composition according to <1>, wherein the melt flow rate of the ethylene-ethyl acrylate copolymer (B) is 5 g/10 min or less.
<3> The polybutylene terephthalate resin composition according to <1> or <2>, further comprising: (D) a silicone compound having a kinematic viscosity at 25°C of 3000 to 8000 cSt in an amount of 0.5 to 2 parts by mass per 100 parts by mass of the polybutylene terephthalate resin (A).
<4> A molded article obtained by using the polybutylene terephthalate resin composition according to any one of <1> to <3>.
<5> A molded article made using the polybutylene terephthalate resin composition according to <3>, which is used for a part that comes into contact with an alkaline solution.
<6> The molded article according to <4> or <5>, having a surface roughness of 2 μm or less as an arithmetic mean roughness Ra in accordance with JIS B 0601-2013.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

The components shown in Tables 1 to 3 were mixed in the proportions (parts by mass) shown in the tables, and then melt-kneaded and extruded using a twin-screw extruder (TEX30, manufactured by The Japan Steel Works) at a cylinder temperature of 260°C and a screw rotation of 130 rpm to obtain pellets of a polybutylene terephthalate resin composition. Details of each component used are provided below.

(1) Polybutylene terephthalate resin (PBT resin)
PBT resin A-1: PBT resin manufactured by Polyplastics Co., Ltd. (intrinsic viscosity (IV) = 0.88 dL/g)
PBT resin A-2: PBT resin manufactured by Polyplastics Co., Ltd. (intrinsic viscosity (IV) = 0.69 dL/g)

(2) Ethylene ethyl acrylate copolymer (EEA copolymer)
EEA copolymer B-1: Ethylene ethyl acrylate copolymer "NUC-6510" manufactured by ENEOS NUC Corporation (ethyl acrylate content 23% by mass, melt flow rate 0.5 g/10 min at 190°C and a load of 2.16 kg)
EEA copolymer B-2: Ethylene ethyl acrylate copolymer "NUC-6520" manufactured by ENEOS NUC Corporation (ethyl acrylate content 24% by mass, melt flow rate 1.6 g/10 min at 190°C and a load of 2.16 kg)
EEA copolymer B-3: Ethylene ethyl acrylate copolymer "DPDJ-9169" manufactured by ENEOS NUC Corporation (ethyl acrylate content 20% by mass, melt flow rate 20.0 g/10 min at 190 ° C. and a load of 2.16 kg)
EEA copolymer B-4: Ethylene ethyl acrylate copolymer "NUC-6570" manufactured by ENEOS NUC Corporation (ethyl acrylate content 25% by mass, melt flow rate 20.0 g/10 min at 190°C and a load of 2.16 kg)
EEA copolymer B-5: Ethylene ethyl acrylate copolymer "NUC-6940" manufactured by ENEOS NUC Corporation (ethyl acrylate content 35% by mass, melt flow rate 20.0 g/10 min at 190°C and a load of 2.16 kg)
EEA copolymer B-6: Ethylene ethyl acrylate copolymer "NUC-6070" manufactured by ENEOS NUC Corporation (ethyl acrylate content 25% by mass, melt flow rate 250.0 g/10 min at 190°C and a load of 2.16 kg)
EEA copolymer B-7: ethylene ethyl acrylate and butyl acrylate-methyl methacrylate graft copolymer "Modiper A5300" manufactured by NOF Corporation (melt flow rate 0.1 g/10 min at 190°C and a load of 2.16 kg)

(3) Inorganic filler/glass fiber (GF): "ECS03T-127" manufactured by Nippon Electric Glass Co., Ltd. (average fiber diameter 13 μm, average fiber length 3 mm)

(4) Silicone Compound Silicone Compound: Dimethylpolysiloxane having a kinematic viscosity of 5000 cSt at 25°C

(5) Others: Hydrolysis resistance improver (epoxy resin): bisphenol A type epoxy resin "jER1004K" manufactured by Mitsubishi Chemical Corporation
Antioxidant: "Irganox 1010" manufactured by BASF Japan Ltd.
Colorant (carbon black): "Raven UV-Ultra" manufactured by Columbian Carbon Japan Co., Ltd.
Compatibilizer: Ethylene glycidyl methacrylate "Bondfast E" manufactured by Sumitomo Chemical

<Evaluation>
(1) Appearance The obtained pellets of the polybutylene terephthalate resin composition were dried at 140°C for 3 hours, and then injection molded at a cylinder temperature of 260°C and a mold temperature of 80°C to produce a flat molded piece having a film gate, a hole, and a weld portion, with a thickness of 1 mm and a side length of 80 mm.

Figure 1 is a schematic diagram of the resulting molded piece. In Figure 1, 10 schematically indicates the molded piece, 1 the film gate, 2 the hole, and 3 the weld. 4 indicates the end of the molded piece on the film gate side, and 5 indicates the end on the opposite side of the hole 2 from end 4. In Figure 1, the line connecting X and X' indicates the measurement range for surface roughness, which will be described later.

The vicinity of the edge 5 on the upper surface of this molded piece was visually observed and evaluated according to the following criteria. The results are shown in the table. Photographs of reference examples corresponding to the following evaluation criteria A, B, and C are shown in Figure 2. In Figure 2, A shows a photograph of the surface of a molded piece of a reference example corresponding to evaluation criteria A, B shows a photograph of a reference example corresponding to evaluation criteria B, and C shows a photograph of a reference example corresponding to evaluation criteria C. In Figure 2, B and C, the areas surrounded by white frames are areas where whitening was observed.
A: No bleaching is observed. B: Some bleaching is observed. C: Overall bleaching is observed.

(2) Surface Roughness Using a surface roughness measuring device (Mitutoyo Corporation, contour measuring machine "Surftest Extreme SV-3000CNC"), the area of 4 mm connecting X and X' of the molded piece prepared for the appearance evaluation was measured, and the arithmetic mean roughness Ra was determined in accordance with JIS B 0601-2013. The results are shown in the table.

(3) Alkali Resistance Test specimens were prepared by cutting the molded specimens produced for the appearance evaluation into strips 10 mm wide and 80 mm long, with the weld located approximately in the center of the longitudinal direction. The test specimens were fixed to a jig in a bent state so that a bending strain of 1.0% was constantly applied to the weld. In this state, the jig and the specimen were immersed in a 10% by mass aqueous solution of sodium hydroxide and allowed to stand at an ambient temperature of 23°C. After 24 hours, the test specimens were observed for cracks. Evaluations were performed using three test specimens for each example and comparative example pellet. The evaluation results are shown in the table. A means that no cracks occurred in any of the three test specimens, and B means that cracks occurred in at least one of the three test specimens.

(4) Charpy impact strength (toughness)
The obtained pellets of the polybutylene terephthalate resin composition were dried at 140°C for 3 hours, and then injection molded at a molding temperature of 260°C and a mold temperature of 80°C to prepare Charpy impact test specimens, which were evaluated at 23°C in accordance with the test standards defined in ISO179/1eA. The results are shown in the table.

(5) Melt Viscosity The melt viscosity of the obtained polybutylene terephthalate resin composition pellets was measured using a Capillograph 1B (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under the conditions of a furnace temperature of 260°C, a capillary diameter of 1 mm x 20 mmL, and a shear rate of 1000 sec ^-1 in accordance with ISO 11443. The results are shown in the table.

(6) Flexural modulus (rigidity)
The resulting polybutylene terephthalate resin composition pellets were dried at 140°C for 3 hours and then injection molded at a resin temperature of 260°C and a mold temperature of 80°C to prepare bending test specimens (80mm x 10mm x 4mm) in accordance with ISO 3167. The bending modulus of the prepared test specimens was measured in accordance with ISO 178. The results are shown in the table.

As shown in Tables 1 to 3, the polybutylene terephthalate resin compositions of Examples 1 to 10 showed excellent results in terms of appearance, surface roughness, Charpy impact strength, and flexural modulus, and it is clear that molded articles excellent in appearance, toughness, and rigidity can be obtained.
On the other hand, the compositions of Comparative Examples 1 and 2, which did not contain the EEA copolymer, gave molded articles with low Charpy impact strength values. Also, the compositions of Comparative Examples 3 to 5, which used an EEA copolymer with a high melt flow rate at 190°C under a load of 2.16 kg, gave molded articles with poor appearance and high surface roughness values.

Claims (5)

(A) 100 parts by mass of a polybutylene terephthalate resin having an intrinsic viscosity of 0.65 to 0.90 dL/g;
(B) 5 to 30 parts by mass of ethylene ethyl acrylate copolymer;
(C) 10 to 100 parts by mass of an inorganic filler;
The polybutylene terephthalate resin composition (B), wherein the ethylene ethyl acrylate copolymer has a melt flow rate of 2 g/10 min or less at 190° C. under a load of 2.16 kg. 2. The polybutylene terephthalate resin composition according to claim 1 , further comprising: (D) a silicone compound having a kinematic viscosity at 25°C of 3000 to 8000 cSt in an amount of 0.5 to 2 parts by mass per 100 parts by mass of the polybutylene terephthalate resin (A). A molded article made using the polybutylene terephthalate resin composition according to claim 1 or 2 . A molded article made using the polybutylene terephthalate resin composition according to claim 2 , which is used for a part that comes into contact with an alkaline solution. The molded product according to claim 3 or 4 , wherein the surface roughness is 2 μm or less as an arithmetic mean roughness Ra in accordance with JIS B 0601-2013.