JP7680831B2 - Flame-retardant polybutylene terephthalate resin composition - Google Patents

Description

The present invention relates to a flame-retardant polybutylene terephthalate resin composition that has excellent hydrolysis resistance and fluidity.

Polybutylene terephthalate resin has excellent mechanical properties, electrical properties, heat resistance, weather resistance, water resistance, chemical resistance, and solvent resistance, and is therefore widely used as an engineering plastic for a variety of applications, including automobile parts and electrical and electronic parts. In particular, flame-retardant polybutylene terephthalate resin compositions containing flame retardants are used for electrical and electronic parts such as connectors, relays, and switches.

However, polybutylene terephthalate resin has a problem with hydrolysis resistance because the main chain is made of ester bonds, and it does not necessarily have sufficient durability when used in high-temperature, high-humidity environments.

Therefore, studies are being conducted to improve the hydrolysis resistance of flame-retardant polybutylene terephthalate resin compositions from a material perspective. For example, Patent Document 1 discloses a polybutylene terephthalate resin composition in which a halogenated benzyl acrylate compound, an antimony oxide compound, and a carbodiimide compound are blended with polybutylene terephthalate resin.

According to Patent Document 1, the resin composition described therein is flame retardant, has excellent heat shock resistance, and is also excellent in tensile strength retention (hydrolysis resistance) after a pressure cooker test. However, the resin composition described in Patent Document 1 has an issue of increased viscosity due to the reaction between the polybutylene terephthalate resin and the carbodiimide compound.

In addition, according to the examples in Patent Document 1, although the use of a plasticizer in combination has some effect in improving fluidity, the effect is very small, and the hydrolysis resistance is not at a sufficient level to meet the increasingly stringent requirements of recent years.

Incidentally, it is also known to blend a flow improver into polybutylene terephthalate resin in order to improve the flowability of the resin composition during molding. For example, Patent Document 2 discloses a polybutylene terephthalate resin composition with excellent flowability, which is obtained by blending a glycerin fatty acid ester into polybutylene terephthalate resin, but this document does not disclose any technology for improving hydrolysis resistance as well.

WO2011/058992 publication WO2009/050859 publication

Conventionally, there was a limit to how much hydrolysis resistance can be improved by adding a carbodiimide compound, and even if a certain amount or more was added to the terminal carboxyl groups of the polybutylene terephthalate resin, the effect plateaued, and no further improvement could be expected.

The present invention has been made to solve these problems, and its purpose is to provide a flame-retardant polybutylene terephthalate resin composition that has excellent hydrolysis resistance and fluidity.

The inventors achieved the object of the present invention by:

1. A flame-retardant polybutylene terephthalate resin composition containing at least (A) a polybutylene terephthalate resin having a terminal carboxyl group amount of 1 to 9 meq/kg or less, (B) a carbodiimide compound, and (C) a halogen-based flame retardant, wherein the carbodiimide compound has a carbodiimide functional group amount of 5 to 40 equivalents per equivalent of the terminal carboxyl group amount, and the value obtained by subtracting the terminal carboxyl group amount of the polybutylene terephthalate resin from the carbodiimide functional group amount of the carbodiimide compound is 30 meq/PBT kg or more.
2. The flame-retardant polybutylene terephthalate resin composition according to 1 above, which has a tensile strength retention rate of 90% or more in a thermal cycle test in accordance with USCAR-2 (5.6.2 Temperature/Humidity Cycling) Class 5.
3. The flame-retardant polybutylene terephthalate resin composition according to 1 or 2 above, which has a melt viscosity of 0.2 kPa·s or less as measured at 260° C. in accordance with ISO 11443.
4. The flame-retardant polybutylene terephthalate resin composition according to any one of 1 to 3 above, further comprising (D) a polyhydric hydroxyl group-containing compound.

According to the present invention, a flame-retardant polybutylene terephthalate resin composition having excellent hydrolysis resistance and fluidity can be obtained.

The following describes in detail the embodiments of the present invention. The present invention is not limited to the following embodiments.

<Flame-retardant polybutylene terephthalate resin composition>
The flame-retardant polybutylene terephthalate resin composition of the present invention is a flame-retardant polybutylene terephthalate resin composition containing at least (A) a polybutylene terephthalate resin having a terminal carboxyl group amount of 1 to 9 meq/kg, (B) a carbodiimide compound, and (C) a halogen-based flame retardant, characterized in that the carbodiimide compound has a carbodiimide functional group amount of 5 to 40 equivalents per equivalent of the terminal carboxyl group amount.

The present invention has discovered that when the amount of terminal carboxyl groups in a polybutylene terephthalate resin is as small as 9 meq/kg or less, the improvement in hydrolysis resistance does not plateau but is significantly improved by adding a large excess of a carbodiimide compound relative to the amount of terminal carboxyl groups.

<(A) Polybutylene terephthalate resin>
The polybutylene terephthalate resin (A) of the present invention is a thermoplastic resin having, as at least polymerization components, terephthalic acid (terephthalic acid or an ester-forming derivative thereof) and an alkylene glycol having 4 carbon atoms (1,4-butanediol) or an ester-forming derivative thereof. The polybutylene terephthalate resin (A) has a terminal carboxyl group amount of 1 to 9 meq/kg.

Examples of the base resin (A) polybutylene terephthalate resin (hereinafter also referred to as PBT resin) include homopolyesters (polybutylene terephthalate) consisting of repeating units derived from butylene terephthalate, and copolyesters (butylene terephthalate copolymers or polybutylene terephthalate copolyesters) that have repeating units derived from butylene terephthalate as the main component and repeating units derived from copolymerizable monomers in the ratios described below.

The copolymerizable monomers in the copolyester (butylene terephthalate copolymer or modified PBT resin) (hereinafter sometimes simply referred to as copolymerizable monomers) include dicarboxylic acid components other than terephthalic acid, diols other than 1,4-butanediol, oxycarboxylic acid components, lactone components, etc. The copolymerizable monomers can be used alone or in combination of two or more.

Examples of the dicarboxylic acid (or dicarboxylic acid component or dicarboxylic acids) include aliphatic dicarboxylic acids (e.g., C 4-40 dicarboxylic acids, preferably C _4-14 dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, hexadecanedicarboxylic acid, and dimer acid), alicyclic dicarboxylic acid components (e.g., C _8-12 dicarboxylic acids, such as hexahydrophthalic acid, hexahydroisophthalic acid, hexahydroterephthalic acid, and himic acid), and aromatic dicarboxylic acid components other than terephthalic acid (e.g., C ₁₂ dicarboxylic acids, such as phthalic acid, isophthalic acid, naphthalenedicarboxylic acids, such as 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenoxyetherdicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylmethanedicarboxylic acid, and 4,4'-diphenylketonedicarboxylic acid). _8-16 dicarboxylic acids), or reactive derivatives thereof (for example, lower alkyl esters (C _1-4 alkyl esters of phthalic acid or isophthalic acid such as dimethylphthalic acid, dimethylisophthalic acid (DMI), etc.), acid chlorides, acid anhydrides, and other derivatives capable of forming esters).

If necessary, polycarboxylic acids such as trimellitic acid and pyromellitic acid or ester-forming derivatives thereof (alcohol esters, etc.) may be used in combination. By using such polyfunctional compounds in combination, a branched polybutylene terephthalate resin can also be obtained.

The diol (or diol component or diols) may, for example, be an aliphatic alkanediol other than 1,4-butanediol [for example, an alkanediol (for example, a lower alkanediol such as ethylene glycol, trimethylene glycol, propylene glycol, neopentyl glycol, hexanediol (1,6-hexanediol, etc.), octanediol (1,3-octanediol, 1,8-octanediol, etc.), decanediol, preferably a linear or branched C _2-12 alkanediol, more preferably a linear or branched C _2-10 alkanediol, etc.); (poly)oxyalkylene glycol (for example, a polyoxyalkylene glycol having a plurality of oxy C glycols having _{2 to 4} alkylene units (e.g., diethylene glycol, dipropylene glycol, ditetramethylene glycol, triethylene glycol, tripropylene glycol, polytetramethylene glycol, etc.), alicyclic diols (e.g., 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.), aromatic diols (e.g., dihydroxy C _6-14 arenes such as hydroquinone, resorcinol, naphthalenediol, etc.; biphenols (4,4'-dihydroxybiphenyl, etc.); bisphenols; xylylene glycol, etc.), and reactive derivatives thereof (e.g., ester-forming derivatives such as alkyl, alkoxy or halogen-substituted products).

If necessary, polyols such as glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, or ester-forming derivatives thereof may be used in combination. By using such polyfunctional compounds in combination, a branched polybutylene terephthalate resin can also be obtained.

Examples of bisphenols include bis(hydroxyaryl)C 1-6 alkanes such as bis(4-hydroxyphenyl)methane (bisphenol F), 1,1-bis(4-hydroxyphenyl)ethane (bisphenol AD), 1,1-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)-3-methylbutane, 2,2-bis(4-hydroxyphenyl)hexane, and _{2,2-bis(4-hydroxyphenyl)-4-methylpentane; and bis(hydroxyaryl)C 1-6} alkanes such as 1,1-bis(4-hydroxyphenyl)cyclopentane and 1,1-bis(4-hydroxyphenyl)cyclohexane. Examples of the alkylene oxide adducts include _4-10 cycloalkanes, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfide, 4,4'-dihydroxydiphenyl ketone, and alkylene oxide adducts thereof. Examples of the alkylene oxide adducts include _C2-3 alkylene oxide adducts of bisphenols (e.g., bisphenol A, bisphenol AD, bisphenol F), such as 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, diethoxylated bisphenol A (EBPA), 2,2-bis[4-(2-hydroxypropoxy)phenyl]propane, and dipropoxylated bisphenol A.

The number of moles of alkylene oxide ( _C2-3 alkylene oxide such as ethylene oxide or propylene oxide) added is about 1 to 10 moles, and preferably about 1 to 5 moles, per hydroxy group.

Examples of the oxycarboxylic acid (or oxycarboxylic acid component or oxycarboxylic acids) include oxycarboxylic acids such as oxybenzoic acid, oxynaphthoic acid, hydroxyphenylacetic acid, glycolic acid, oxycaproic acid, etc., and derivatives thereof. Examples of the lactone include _C3-12 lactones such as propiolactone, butyrolactone, valerolactone, caprolactone (e.g., ε-caprolactone, etc.).

Of these copolymerizable monomers, preferred are diols [ _C2-6 alkylene glycols (straight-chain or branched-chain alkylene glycols such as ethylene glycol, trimethylene glycol, propylene glycol, hexanediol, etc.), polyoxy _{C2-4 alkylene glycols having a repeating number of about 2 to} 4 oxyalkylene units (diethylene glycol, etc.), bisphenols (bisphenols or alkylene oxide adducts thereof, etc.)], dicarboxylic acids [ _C6-12 aliphatic dicarboxylic acids (adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, etc.), asymmetric aromatic dicarboxylic acids in which a carboxyl group is substituted at an asymmetric position on an arene ring, 1,4-cyclohexanedimethanol, etc.], and the like.

As the (A) polybutylene terephthalate resin, a homopolyester (polybutylene terephthalate) and/or a copolymer (polybutylene terephthalate copolyester) is preferred. The (A) polybutylene terephthalate resin may be a copolyester in which the proportion (modification amount) of copolymerizable monomer is usually 45 mol% or less (e.g., about 0 mol% or more and 45 mol% or less), preferably 35 mol% or less (e.g., about 0 mol% or more and 35 mol% or less), and more preferably 30 mol% or less (e.g., about 0 mol% or more and 30 mol% or less).

In the copolymer, the proportion of the copolymerizable monomer can be selected, for example, from the range of about 0.01 mol% to about 30 mol%, and is usually about 1 mol% to about 30 mol%, preferably about 3 mol% to about 25 mol%, and more preferably about 5 mol% to about 20 mol%.

When a homopolyester (polybutylene terephthalate) and a copolymer (copolyester) are used in combination, the ratio of the homopolyester to the copolyester is in a range in which the ratio of the copolymerizable monomer is 0.1 mol% or more and 30 mol% or less (preferably 1 mol% or more and 25 mol% or less, and more preferably 5 mol% or more and 25 mol% or less) relative to the total monomers, and can usually be selected from the range of the former/latter = 99/1 to 1/99 (mass ratio), preferably 95/5 to 5/95 (mass ratio), and more preferably 90/10 to 10/90 (mass ratio).

(A) The amount of terminal carboxyl groups in the polybutylene terephthalate resin is 1 to 9 meq/kg. A more preferred amount of terminal carboxyl groups is 2 to 8 meq/kg, and an even more preferred amount of terminal carboxyl groups is 3 to 6 meq/kg.

To achieve this range of terminal carboxyl group amount, a high molecular weight polymer with fewer terminal groups of polybutylene terephthalate resin may be used, or a melt polymerized product with an IV of about 0.1 to 0.8 dl/g may be polymerized by solid-phase polymerization. When solid-phase polymerization is used, it is desirable to treat at a low temperature for a long time because a high treatment temperature increases the number of terminal carboxyl groups, but if the temperature is too low, the polymerization rate is low and productivity is poor, so it can usually be adjusted under reduced pressure or in an inert gas atmosphere at, for example, 120 to 220°C, preferably 140 to 200°C, and more preferably 150 to 190°C.

In addition, when using batch polymerization, if the resin discharge time after polymerization is long, the number of terminal carboxyl groups will increase due to thermal decomposition, so it is better to use one that has fewer terminal carboxyl groups discharged initially.

The intrinsic viscosity (IV) of the (A) polybutylene terephthalate resin is preferably 0.6 dL/g or more, and more preferably 0.7 dL/g or more. The intrinsic viscosity is preferably 1.3 dL/g or less, and more preferably 1.2 dL/g or less. By blending (A) polybutylene terephthalate resins having different intrinsic viscosities, for example, by blending polybutylene terephthalate resins having intrinsic viscosities of 1.5 dL/g and 0.5 dL/g, an intrinsic viscosity of 0.6 to 1.3 dL/g or less may be achieved.

The intrinsic viscosity (IV) can be measured in o-chlorophenol at a temperature of 35°C. By using a polybutylene terephthalate resin with an intrinsic viscosity in this range, it is easy to efficiently impart sufficient hydrolysis resistance and reduce the melt viscosity.

The polybutylene terephthalate resin (A) may be a commercially available product, or may be produced by copolymerizing (polycondensing) terephthalic acid or a reactive derivative thereof with 1,4-butanediol and, if necessary, a copolymerizable monomer by a conventional method such as ester exchange or direct esterification.

<(B) Carbodiimide Compound>
The carbodiimide compound (B) used in the present invention is a compound having a carbodiimide group (-N=C=N-) in the molecule. As the carbodiimide compound, any of an aliphatic carbodiimide compound having an aliphatic main chain, an alicyclic carbodiimide compound having an alicyclic main chain, and an aromatic carbodiimide compound having an aromatic main chain can be used, but the use of an aromatic carbodiimide compound is preferred in terms of hydrolysis resistance.

Examples of aliphatic carbodiimide compounds include diisopropylcarbodiimide, dioctyldecylcarbodiimide, di-tert-butylcarbodiimide, 1-ethyl-3-tert-butylcarbodiimide, 1-(2-butyl)-3-ethylcarbodiimide, 1,3-di-(2-butyl)carbodiimide, poly(diisopropylcarbodiimide), etc. Examples of alicyclic carbodiimide compounds include dicyclohexylcarbodiimide, poly(diisopropylcarbodiimide), etc.

Aromatic carbodiimide compounds include diphenylcarbodiimide, di-2,6-dimethylphenylcarbodiimide, di-2,6-diethylphenylcarbodiimide, di-2,6-diisopropylphenylcarbodiimide, di-2,6-ditert-butylphenylcarbodiimide, N-triyl-N'-phenylcarbodiimide, N-(2,6-diisopropyl-4-phenoxyphenyl)-N-tert-butylcarbodiimide, N,N-bis[3-isocyanato-2,4,6-tris(1-methylethyl)phenyl] amino]carbodiimide, N-cyclohexyl-N-(4-(dimethylamino)naphthyl)carbodiimide, di-o-tolylcarbodiimide, di-p-tolylcarbodiimide, di-p-nitrophenylcarbodiimide, di-p-aminophenylcarbodiimide, di-p-hydroxyphenylcarbodiimide, di-p-chlorophenylcarbodiimide, di-p-methoxyphenylcarbodiimide, di-3,4-dichlorophenylcarbodiimide, di-2,5-dichlorophenylcarbodiimide, di-o-chlorophenylcarbodiimide Mono- or dicarbodiimide compounds such as diimide, di-2,4,6-trimethylphenylcarbodiimide, di-2,4,6-triisopropylphenylcarbodiimide, di-2,4,6-triisobutylphenylcarbodiimide, p-phenylene-bis-di-o-triylcarbodiimide, p-phenylene-bis-dicyclohexylcarbodiimide, p-phenylene-bis-di-p-chlorophenylcarbodiimide, and ethylene-bis-diphenylcarbodiimide, as well as poly(4,4'-diphenylmethanecarbodiimide), poly (p-phenylenecarbodiimide), poly(m-phenylenecarbodiimide), poly(3,3'-dimethyl-4,4'-diphenylmethanecarbodiimide), poly(naphthylenecarbodiimide), poly(1,3-diisopropylphenylenecarbodiimide), poly(1-methyl-3,5-diisopropylphenylenecarbodiimide), poly(1,3,5-triethylphenylenecarbodiimide), poly(diisopropylphenylenecarbodiimide) and poly(triisopropylphenylenecarbodiimide). Two or more of the above carbodiimide compounds can also be used in combination.

Among these, di-2,6-dimethylphenylcarbodiimide, poly(4,4'-diphenylmethanecarbodiimide), poly(phenylenecarbodiimide) and poly(triisopropylphenylenecarbodiimide) are particularly suitable.

It is preferable to use a carbodiimide compound (B) having a number average molecular weight of 2000 or more. By using a carbodiimide compound (B) having a number average molecular weight of 2000 or more, it is possible to improve the hydrolysis resistance of the flame-retardant polybutylene terephthalate resin composition over a long period of time. Furthermore, it is advantageous in that the generation of gas and odor can be reduced even when the residence time of the polybutylene terephthalate resin composition during melt-kneading or molding is long.

The amount of the carbodiimide compound (B) in the flame-retardant polybutylene terephthalate resin composition is preferably such that the amount of the carbodiimide functional group is 5 to 40 equivalents when the amount of the terminal carboxyl group of the polybutylene terephthalate resin (A) is taken as 1 equivalent.

A more preferred blending amount is when the amount of terminal carboxyl groups in (A) polybutylene terephthalate resin is taken as 1 equivalent, and the amount of carbodiimide functional groups is 6 to 35 equivalents, and most preferably 10 to 30 equivalents. Within this range, a flame-retardant polybutylene terephthalate resin composition can be obtained that has excellent flowability during molding and mechanical properties after molding.

The amount obtained by subtracting the amount of terminal carboxyl groups in the polybutylene terephthalate resin (A) from the amount of functional groups in the carbodiimide compound (B) is 30 meq/PBT kg or more, more preferably 40 meq/PBT kg or more, and even more preferably 50 meq/PBT kg or more. This value is calculated from the amount of each functional group based on 1 kg of PBT.

The amount of carbodiimide functional groups means the amount of carbodiimide functional groups in the carbodiimide compound in the resin composition, and the carbodiimide equivalent means the amount of carbodiimide functional groups in the carbodiimide compound.

<(C) Halogen-Based Flame Retardant>
The halogen-based flame retardant (C) of the present invention is preferably a brominated aromatic flame retardant containing a structure in which one or more hydrogen atoms in a benzene ring are substituted with a halogen atom.Specific examples of the flame retardant include brominated acrylate polymers, brominated epoxy compounds, brominated polycarbonates, brominated polystyrenes, brominated phthalimides, and brominated polyphenylene ethers, and more preferably a brominated acrylate polymer and/or a brominated epoxy compound.

Examples of brominated acrylate polymers include those represented by the following general formula (I):

At least one X in the formula is bromine. The number of X in one structural unit is 1 to 5, but from the perspective of flame retardancy, it is preferably 3 to 5. The average degree of polymerization m is 10 to 2000, and preferably 15 to 1000. A low average degree of polymerization leads to poor thermal stability, and a degree exceeding 2000 leads to poor moldability of the flame-retardant polybutylene terephthalate resin composition to which it is added. The above brominated acrylate polymers may be used alone or in combination of two or more.

The brominated acrylate polymer represented by the general formula (I) can be obtained by polymerizing bromine-containing benzyl acrylate alone, but it may also be copolymerized with a similarly structured benzyl methacrylate or the like. Examples of bromine-containing benzyl acrylate include pentabromobenzyl acrylate, tetrabromobenzyl acrylate, tribromobenzyl acrylate, or a mixture thereof.

Among these, pentabromobenzyl acrylate is preferred. In addition, benzyl methacrylate, which is a copolymerizable component, is a methacrylate corresponding to the above-mentioned acrylate.

Furthermore, copolymerization with vinyl monomers is also possible, and examples of such monomers include acrylic acid, acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, and benzyl acrylate, methacrylic acid, methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and benzyl methacrylate, unsaturated carboxylic acids or their anhydrides such as styrene, acrylonitrile, fumaric acid, and maleic acid, vinyl acetate, and vinyl chloride.

Crosslinkable vinyl monomers, xylylene diacrylate, xylylene dimethacrylate, tetrabromo xylylene diacrylate, tetrabromo xylylene dimethacrylate, butadiene, isoprene, and divinylbenzene can also be used. These are used in an equimolar amount relative to benzyl acrylate or benzyl methacrylate, preferably 0.5 times the molar amount.

One example of a method for producing the above brominated acrylate polymer is a method in which brominated acrylic monomers are reacted to a predetermined degree of polymerization by solution polymerization or bulk polymerization. In the case of solution polymerization, it is preferable not to use a halogenated aromatic compound such as chlorobenzene as a solvent.

In addition, as the solvent for solution polymerization, aprotic solvents such as ethylene glycol monomethyl ether, methyl ethyl ketone, ethylene glycol dimethyl ether, and dioxane are preferred. However, in the present invention, as described below, the resin composition may contain a protic compound, so that a polymerization solvent containing a protic compound can also be used.

The above brominated acrylate polymer is preferably washed with water and/or an aqueous solution containing alkaline (earth) metal ions in order to remove reaction by-products such as residual sodium polyacrylate. An aqueous solution containing alkaline (earth) metal ions can be easily obtained by adding an alkaline (earth) metal salt to water, but an alkaline (earth) metal hydroxide (e.g., calcium hydroxide) that does not contain chloride ions, phosphate ions, etc. is optimal.

When calcium hydroxide is used as the alkali (earth) metal salt, calcium hydroxide is generally soluble at about 0.126 g in 100 g of water at 20°C, and there are no particular restrictions on the aqueous solution concentration as long as it is up to the solubility. In addition, there are no particular restrictions on the method of washing with an aqueous solution containing water and/or alkali (earth) metal ions, and a method such as immersing the brominated acrylate polymer in an aqueous solution containing water and/or alkali (earth) metal ions for an appropriate period of time may be used.

After the above-mentioned washing process using water and/or an aqueous solution containing alkaline (earth) metal ions, the brominated acrylate polymer generally has a dry solid content in the hot water extract of 100 ppm or less, and when such a brominated acrylate polymer is used, there is almost no generation of foreign matter on the surface of the molded product.

As the brominated epoxy compound, an aromatic epoxy compound (such as a biphenyl type epoxy compound, a bisphenol A type epoxy compound, a phenol novolac type epoxy compound, or a cresol novolac type epoxy compound) containing one or more epoxy groups per molecule is preferably used, and those having a number average molecular weight of 1,000 or more and 20,000 or less can be preferably used. From the viewpoint of moldability of the flame-retardant polybutylene terephthalate resin composition, the number average molecular weight is more preferably 2,000 or more and 15,000 or less, and even more preferably 3,000 or more and 10,000 or less.

The epoxy equivalent of the above epoxy compound is preferably 30,000 g/equivalent (g/eq) or more, more preferably 32,000 g/eq or more, even more preferably 34,000 g/eq or more, even more preferably 36,000 g/eq or more, and particularly preferably 36,500 g/eq or more.

By setting the epoxy equivalent within this range, the flame-retardant polybutylene terephthalate resin composition of the present invention can be prevented from adhering to the screw of an extruder or molding machine during molding. This can reduce the inclusion of screw deposits in the molded product, resulting in a molded product with a good appearance.

In addition, it is preferable to use the above-mentioned brominated epoxy compound whose ends are blocked with bromophenol (e.g., tribromophenol), since this can prevent a decrease in the fluidity of the flame-retardant polybutylene terephthalate resin composition.

Specific examples of brominated polycarbonates include brominated bisphenol A, particularly brominated polycarbonates obtained from tetrabromobisphenol A. Examples of the terminal structure include phenyl groups, 4-t-butylphenyl groups, and 2,4,6-tribromophenyl groups, and it is particularly preferred that the terminal structure has a 2,4,6-tribromophenyl group.

The average number of carbonate repeat units in the brominated polycarbonate may be appropriately selected and determined, but is usually 2 to 30. If the average number of carbonate repeat units is small, this may cause a decrease in the molecular weight of the polybutylene terephthalate resin (A) during melting. Conversely, if it is too large, the melt viscosity may increase and moldability may deteriorate. Therefore, it is preferable that the average number of repeat units is 3 to 15, and especially 3 to 10.

The molecular weight of the brominated polycarbonate is arbitrary and may be selected appropriately, but the viscosity average molecular weight is preferably 1,000 to 20,000, and more preferably 2,000 to 10,000.

The brominated polycarbonate obtained from the above brominated bisphenol A can be obtained, for example, by a conventional method of reacting brominated bisphenol A with phosgene. The end-capping agent includes an aromatic monohydroxy compound, which may be substituted with a halogen or an organic group.

Brominated polystyrene can be produced by either brominating polystyrene or polymerizing brominated styrene monomers, but polymerizing brominated styrene is preferred because it has a smaller amount of free bromine atoms. The hydrogen atom of the vinyl group to which the brominated benzene is bonded may be replaced with a methyl group.

Brominated polystyrene may also be a copolymer in which other vinyl monomers are copolymerized. Examples of vinyl monomers in this case include styrene, α-methylstyrene, acrylonitrile, methyl acrylate, butadiene, and vinyl acetate. Brominated polystyrene may be used alone or as a mixture of two or more types with different structures, and may contain units derived from styrene monomers with different bromine numbers in a single molecular chain.

Specific examples of brominated polystyrene include poly(4-bromostyrene), poly(2-bromostyrene), poly(3-bromostyrene), poly(2,4-dibromostyrene), poly(2,6-dibromostyrene), poly(2,5-dibromostyrene), poly(3,5-dibromostyrene), poly(2,4,6-tribromostyrene), poly(2,4,5-tribromostyrene), poly(2,3,5-tribromostyrene), and poly(4-bromo-α-methylstyrene). Examples include poly(2,4-dibromo-α-methylstyrene), poly(2,5-dibromo-α-methylstyrene), poly(2,4,6-tribromo-α-methylstyrene) and poly(2,4,5-tribromo-α-methylstyrene), and poly(2,4,6-tribromostyrene), poly(2,4,5-tribromostyrene) and polydibromostyrene and polytribromostyrene containing an average of 2 to 3 bromine groups in the benzene ring are particularly preferred.

Examples of brominated phthalimides include N,N'-(bistetrabromophthalimide)ethane, N,N'-(bistetrabromophthalimide)propane, N,N'-(bistetrabromophthalimide)butane, N,N'-(bistetrabromophthalimide)diethyl ether, N,N'-(bistetrabromophthalimide)dipropyl ether, N,N'-(bistetrabromophthalimide)dibutyl ether, N,N'-(bistetrabromophthalimide)diphenylsulfone, N,N'-(bistetrabromophthalimide)diphenylketone, and N,N'-(bistetrabromophthalimide)diphenyl ether. Among these, N,N'-ethylenebis(tetrabromophthalimide) is preferred.

The halogenated flame retardant (C) used in the present invention may contain, in addition to the above-mentioned compounds which are the flame retardant itself, halogenated aromatic compounds derived from the solvent used during polymerization or decomposition products of the halogenated flame retardant as impurities. The content of such impurities, i.e., halogenated aromatic compounds other than the flame retardant, is preferably 100 ppm or less, more preferably 50 ppm or less, even more preferably 30 ppm or less, and particularly preferably 10 ppm or less.

The content of halogenated aromatic compounds other than flame retardants can be determined, for example, by measuring the gas generated when a crushed sample of a halogenated flame retardant is heated in the headspace using a gas chromatograph, and determining the amount of gas generated from the halogenated aromatic compounds.

In addition, in the present invention, the flame-retardant polybutylene terephthalate resin composition containing the above-mentioned (C) halogen-based flame retardant preferably has a content of halogenated aromatic compounds other than the flame retardant, which are the above-mentioned impurities, of less than 0.5 ppm, more preferably 0.3 ppm or less, and even more preferably 0.1 ppm or less.

By setting the content of halogenated aromatic compounds other than flame retardants in the flame-retardant polybutylene terephthalate resin composition within the above range, corrosion of metal terminals can be suppressed in insert molded products using the flame-retardant polybutylene terephthalate resin composition. The content of halogenated aromatic compounds other than flame retardants can be determined, for example, by measuring the amount of gas generated by heating a sample of a pulverized flame-retardant polybutylene terephthalate resin composition in headspace using a gas chromatograph, and determining the amount of gas generated from the halogenated aromatic compounds.

The halogen-based flame retardant (C) used in the present invention preferably contains 10 to 1,000 ppm of protic compounds as measured by headspace gas chromatography (heated at 180°C for 1 hour).

In the present invention, the protic compound refers to a compound having proton (hydrogen ion) donating properties. Examples of this protic compound include those derived from the polymerization solvent of the halogen-based flame retardant (C), among which alkoxy alcohols are preferred, and C ₁ -C ₂₀ alkoxy C ₁ -C ₂₀ alcohols and/or C ₁ -C ₂₀ dialkoxy C ₁ -C ₂₀ alcohols are more preferred.

As the _C1 - _C20 alkoxy _C1 - _C20 alcohol, methoxy _C1 - _C20 alcohol and _C1 - _C20 alkoxy ethanol are more preferred, and methoxy ethanol is particularly preferred. As _{the C1} - _C20 dialkoxy _C1 - _C20 alcohol, 3,3-diethoxypropanol is preferred.

In addition, examples of protic compounds in the present invention include those derived from the raw materials of the halogen-based flame retardant (C). Note that, in the present invention, protic compounds derived from the polymerization solvent are preferred over those derived from the raw materials of the halogen-based flame retardant (C).

In the present invention, the amount of the protic compound contained in the halogen-based flame retardant (C) is preferably 10 to 1000 ppm in the halogen-based flame retardant (C) as described above, more preferably 100 to 800 ppm, and even more preferably 300 to 500 ppm.

If the amount of protic compounds contained in the halogen-based flame retardant (C) is less than 10 ppm, it becomes difficult to obtain the effect of improving the flowability of the flame-retardant polybutylene terephthalate resin composition. If the amount of protic compounds contained in the halogen-based flame retardant (C) is more than 1000 ppm, the amount of gas generated during compounding increases, and strand breakage becomes more likely to occur during pelletization.

The total content of organic solvents selected from the group consisting of toluene, methyl isobutyl ketone, methyl ethyl ketone, and acetone in the halogen-based flame retardant (C) of the present invention is preferably 50 ppm or less. The total content of the organic solvents is more preferably 40 ppm or less, even more preferably 30 ppm or less, even more preferably 20 ppm or less, particularly preferably 10 ppm or less, and most preferably 8 ppm or less.

By setting the content of the organic solvent in the (C) halogen-based flame retardant within this range, it is possible to reduce the generation of deposits on the extruder or molding machine screw when molding the flame-retardant polybutylene terephthalate resin composition of the present invention, and to suppress deterioration of the appearance of the molded product due to the inclusion of such deposits.

The flame-retardant polybutylene terephthalate resin composition of the present invention preferably contains an antimony compound as a flame retardant assistant. Representative examples of antimony compounds as flame retardant assistants include antimony trioxide, antimony tetraoxide, antimony pentoxide, sodium (pyro)antimonate, and the like. Furthermore, it is also preferable to use a drip prevention agent such as polytetrafluoroethylene in combination with the composition to prevent the spread of fire due to dripping of burnt resin.

The amount of the halogen-based flame retardant (C) added to the polybutylene terephthalate resin (A) is in the range of 3 to 50 parts by mass, preferably 10 to 40 parts by mass, of the halogen-based flame retardant (C) per 100 parts by mass of the polybutylene terephthalate resin (A).

When an antimony compound is added, the amount is preferably in the range of 1 to 30 parts by mass per 100 parts by mass of (A) polybutylene terephthalate resin. If the amount of (C) halogen-based flame retardant added is too small, sufficient flame retardancy cannot be imparted, and if the amount is too large, the physical properties of the molded product may deteriorate.

<(D) Polyhydric Hydroxyl Group-Containing Compound>
In the present invention, it is also preferable to add (D) a polyhydric hydroxyl group-containing compound.
The polyhydroxyl group-containing compound (D) is a compound having two or more hydroxyl groups in one molecule. The polyhydroxyl group-containing compound (D) preferably has a hydroxyl value of 200 to 1,000.

By using (D) a polyhydric hydroxyl group-containing compound, it is possible to efficiently improve the fluidity of the polybutylene terephthalate resin composition when melted while maintaining the properties of (A) the polybutylene terephthalate resin at a high level.

Here, the fluidity of the polybutylene terephthalate resin composition is preferably 0.2 kPa·s or less, more preferably 0.19 kPa·s or less, and even more preferably 0.18 kPa·s or less (e.g., 0.17 kPa·s or less), in terms of melt viscosity measured in accordance with ^ISO11443 at a furnace temperature of 260°C, a capillary of φ1 mm×20 mmL, and a shear rate of 1000 sec-1.

(D) The polyhydric hydroxyl group-containing compound may be one produced by a conventional method or a commercially available product.

The hydroxyl value of the (D) polyhydric hydroxyl group-containing compound is preferably 100 or more. A more preferred hydroxyl value is 200 or more, and an even more preferred hydroxyl value is 250 or more. If the hydroxyl value is 100 or more, the effect of improving the fluidity tends to be enhanced, and the effect of improving hydrolysis resistance is also obtained.

On the other hand, if the hydroxyl value is too large, the reaction with (A) polybutylene terephthalate proceeds excessively, which may reduce the molecular weight of (A) polybutylene terephthalate resin and impair its excellent properties such as mechanical properties, heat resistance, and chemical resistance. The preferred hydroxyl value is 1,000 or less, and more preferably 500 or less.

The content of the polyhydric hydroxyl group-containing compound (D) in the flame-retardant polybutylene terephthalate resin composition is preferably 0.05 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the polybutylene terephthalate resin (A). More preferably, it is 0.1 parts by mass or more and 4 parts by mass or less. Even more preferably, it is 0.5 parts by mass or more and 3 parts by mass or less.

As the polyhydric hydroxyl group-containing compound (D) of the present invention, it is preferable to use an ether obtained by addition polymerization of an alkylene oxide to a glycerin fatty acid ester or diglycerin. The ethers obtained by addition polymerization of an alkylene oxide to a glycerin fatty acid ester and diglycerin are described below.

Glycerol fatty acid esters are esters composed of glycerol and/or its dehydrated condensate and fatty acid. Among glycerol fatty acid esters, those obtained using fatty acids having 12 or more carbon atoms are preferred.

Examples of fatty acids with 12 or more carbon atoms include lauric acid, oleic acid, palmitic acid, stearic acid, 12-hydroxystearic acid, behenic acid, and montanic acid. Fatty acids with 12 to 32 carbon atoms are preferred, and fatty acids with 12 to 22 carbon atoms are particularly preferred.

Specifically, lauric acid, stearic acid, 12-hydroxystearic acid, or behenic acid are particularly preferred. Fatty acids with 12 or more carbon atoms are preferred because they tend to adequately maintain the heat resistance of the resin. Fatty acids with 32 or less carbon atoms are preferred because they are more effective at improving the flowability described above.

Preferred examples of glycerin fatty acid esters include glycerin monostearate, glycerin monobehenate, diglycerin monostearate, triglycerin monostearate, triglycerin stearic acid partial ester, tetraglycerin stearic acid partial ester, decaglycerin lauric acid partial ester, and glycerin mono 12-hydroxystearate.

Examples of ethers obtained by addition polymerization of alkylene oxide to diglycerin include polyoxypropylene diglyceryl ether obtained by addition polymerization of propylene oxide to diglycerin, and polyoxyethylene diglyceryl ether obtained by addition polymerization of ethylene oxide to diglycerin. In the present invention, among these ethers, the use of polyoxyethylene diglyceryl ether is particularly preferred.

<Other ingredients>
The flame-retardant polybutylene terephthalate resin composition of the present invention may contain other resins, reinforcing fillers, antioxidants, heat stabilizers, ultraviolet absorbers, antistatic agents, colorants such as dyes and pigments, lubricants, plasticizers, crystal nucleating agents, and other conventionally known additives, within the scope of not impairing the effects of the present invention. In the present invention, it may be preferable to contain a transesterification catalyst and a transesterification terminator as other components.

When the above composition contains an ester exchange reaction catalyst, the reaction between (A) polybutylene terephthalate resin and (D) polyhydroxyl group-containing compound is accelerated. When the reaction between (A) polybutylene terephthalate resin and (D) polyhydroxyl group-containing compound is slow and it takes a long time to reach the desired fluidity, the desired fluidity can be quickly achieved by using an ester exchange reaction catalyst.

The transesterification catalyst is not particularly limited, and for example, a metal compound can be used as the transesterification catalyst. Among them, titanium compounds, tin compounds, and antimony compounds are preferably used.

Specific examples of titanium compounds include inorganic titanium compounds such as titanium oxide, titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, and titanium phenolates such as tetraphenyl titanate. Specific examples of tin compounds include dibutyltin oxide, hexaethylditin oxide, didodecyltin oxide, triethyltin hydroxide, tributyltin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, methylstannoic acid, ethylstannoic acid, and butylstannoic acid. Examples of antimony compounds include antimony trioxide. Among these, the use of tetrabutyl titanate, tributyltin acetate, and antimony trioxide is particularly preferred.

In addition, if the transesterification reaction proceeds too far, the physical properties of the molded article produced by molding the resin composition may deteriorate. By adding an transesterification reaction terminator after the transesterification reaction, it is possible to adjust the fluidity to the desired level without causing problems such as deterioration of physical properties.

As the transesterification reaction terminator, a phosphorus compound can be preferably used. The type and amount of the phosphorus compound are not particularly limited, and can be appropriately adjusted depending on conditions such as the type of compound contained in the composition of the present invention.

Examples of phosphorus compounds that can be used include, but are not limited to, phosphines, phosphinites, phosphonites, phosphites, phosphinamides, phosphonasdiamides, phosphorus triamides, phosphoramidites, phosphorodiamidites, phosphine oxides, phosphinates, phosphonates, phosphates, phosphinic amides, phosphonodiamidates, phosphoramides, phosphoramidates, phosphorodiamidates, phosphine imides, and phosphine sulfides. Phosphorus compounds also include those that form salts with metals.

<Hydrolysis resistance>
The molded article made of the flame-retardant polybutylene terephthalate resin composition of the present invention is characterized in that it has a tensile strength retention of 90% or more in a thermal cycle test in accordance with USCAR-2 (5.6.2 Temperature/Humidity Cycling) Class 5, and has a melt viscosity of 0.2 kPa s or less as measured at 260°C according to ISO 11443.

USCAR-2 is a test condition defined by North American automobile standards, and Class 5 is a test condition in which the following environmental test conditions are repeated 40 times: -40°C (0.5 hour) → 80 to 90°C, 80 to 100% RH (4 hours) → 175°C (1.5 hours).
This indicates that the flame-retardant polybutylene terephthalate resin composition of the present invention is at a level that allows it to be used sufficiently even in a Class 5 temperature environment.

The tensile strength retention rate can be calculated by measuring the tensile strength before and after the test in accordance with ISO 527-1 and 2.

<Method for producing flame-retardant polybutylene terephthalate resin composition>
The method for preparing the flame-retardant polybutylene terephthalate resin composition of the present invention is not particularly limited, and generally known equipment and methods for preparing resin compositions can be used. For example, the necessary components are mixed and kneaded using a single-screw or twin-screw extruder or other melt kneading equipment, and prepared into pellets for molding.

A plurality of extruders or other melt kneading devices may be used. All components may be fed simultaneously from a hopper, or some components may be fed from a side feed port. Here, it is preferable to set the extruder cylinder temperature so that the resin temperature in the extruder is 240 to 350°C. More preferably, it is 270 to 330°C.

If the temperature is lower than 240°C, the reaction between (A) polybutylene terephthalate resin and (B) carbodiimide compound and/or (D) polyhydric group-containing compound may be insufficient, resulting in insufficient hydrolysis resistance of the flame-retardant polybutylene terephthalate resin composition, or insufficient kneading due to high viscosity of the molten material, which may result in failure to obtain a flame-retardant polybutylene terephthalate resin composition with uniform properties. On the other hand, if the temperature exceeds 350°C, decomposition of (A) polybutylene terephthalate resin may occur easily, resulting in insufficient mechanical properties and hydrolysis resistance of the flame-retardant polybutylene terephthalate resin composition.

When producing the flame-retardant polybutylene terephthalate resin composition of the present invention, (A) the polybutylene terephthalate resin and (D) the polyhydric hydroxyl group-containing compound may be melt-kneaded first, and then (B) the carbodiimide compound and (C) the halogen-based flame retardant and/or the transesterification reaction terminator may be added. In this case, (B) the carbodiimide compound is added in a state where the melt viscosity of (A) the polybutylene terephthalate resin is reduced, so that uniform melt-kneading can be performed efficiently.

The method of adding the (B) carbodiimide compound etc. later may be to add it from a side feed port, or to melt-knead (A) polybutylene terephthalate resin and (D) polyhydroxyl group-containing compound to form pellets, and then re-melt-knead this with (B) the carbodiimide compound and (C) the halogen-based flame retardant and transesterification reaction stopper to produce the product.

On the other hand, if polybutylene terephthalate resin (A) and carbodiimide compound (B) are melt-kneaded first and then polyhydroxyl-containing compound (D) is added, the viscosity of polybutylene terephthalate resin (A) increases due to the reaction between polybutylene terephthalate resin (A) and carbodiimide compound (B), preventing sufficient melt-kneading with polyhydroxyl-containing compound (D). Furthermore, heat generation due to shear increases, which may lead to thermal decomposition of polybutylene terephthalate resin (A).

Similarly, when adding a reinforcing filler, if the (A) polybutylene terephthalate resin and (D) polyhydroxyl group-containing compound are first melt-kneaded and then the reinforcing filler is added, the viscosity of the (A) polybutylene terephthalate resin is already reduced, which reduces breakage of the reinforcing filler due to shear and does not impair mechanical properties. Therefore, when using a reinforcing filler, it is particularly preferable to first melt-knead the (A) polybutylene terephthalate resin and (D) polyhydroxyl group-containing compound.

Furthermore, when the (B) carbodiimide compound and the reinforcing filler are mixed, adding the reinforcing filler first is preferable because the reaction between the (A) polybutylene terephthalate resin and the surface treatment agent of the reinforcing filler is not inhibited, and the interfacial adhesion between the (A) polybutylene terephthalate resin and the reinforcing filler is stronger, making it easier to improve mechanical properties.

The carbodiimide compound (B) can also be compounded as a masterbatch with a resin as the matrix, and using a masterbatch is often easier in terms of practical handling. A masterbatch made of polybutylene terephthalate resin is preferably used, but a masterbatch prepared with another resin may also be used. In the case of a masterbatch made of polybutylene terephthalate resin, the amount of the masterbatch may be adjusted so that it falls within the specified range.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. Evaluations were carried out in an atmosphere of 23° C. and 55% RH unless otherwise specified.
The compounds listed in Tables 1 and 2 are as follows.

<Materials>
(A) Polybutylene terephthalate resin (PBT)
A-1: Polybutylene terephthalate resin (intrinsic viscosity = 1.14 dL/g, terminal carboxyl group amount = 4 meq/kg, manufactured by Polyplastics Co., Ltd.)
A-2: Polybutylene terephthalate resin (intrinsic viscosity = 1.14 dL/g, terminal carboxyl group amount = 9 meq/kg, manufactured by Polyplastics Co., Ltd.)
A-3: Polybutylene terephthalate resin (intrinsic viscosity = 0.95 dL/g, terminal carboxyl group amount = 9 meq/kg, manufactured by Polyplastics Co., Ltd.)
A-4: Polybutylene terephthalate resin (intrinsic viscosity = 1.13 dL/g, terminal carboxyl group amount = 12 meq/kg, manufactured by Polyplastics Co., Ltd.)
A-5: Polybutylene terephthalate resin (intrinsic viscosity = 0.84 dL/g, terminal carboxyl group amount = 15 meq/kg, manufactured by Polyplastics Co., Ltd.)

(B) Carbodiimide compound B-1: Stavaxol P100 carbodiimide equivalent 3625 meq/kg (aromatic carbodiimide compound manufactured by LANXESS KK)

(C) Halogen-based flame retardants C-1: Brominated acrylate polymer (polypentabromobenzyl acrylate polymerized using ethylene glycol monomethyl ether as a solvent (containing 8 ppm of halogenated aromatic compounds other than flame retardants and 20 ppm of methoxyethanol as a protic compound))
C-2: Brominated epoxy compound (brominated epoxy compound having an epoxy equivalent of 36,800 g/eq, an organic solvent amount of 5 ppm, and a weight average molecular weight of about 18,000)
C-3: Brominated polycarbonate (Teijin Limited, Fireguard 7500)
C-4: Brominated polystyrene (Pyrocheck 68PB, manufactured by Foro)
C-5: Brominated phthalimide (Albemarle Japan, ethylene bistetrabromophthalimide, SAYTEX BT-93W)

(D) Polyhydric hydroxyl group-containing compound D-1: Glyceryl hydroxystearate (hydroxyl value 480, manufactured by Riken Vitamin Co., Ltd., Rikemal HC100)
The hydroxyl value of the polyhydroxyl-containing compound (D) was measured in accordance with the Hydroxyl Value (Pyridine-Acetic Anhydride Method) of Japan Oil Chemists' Society 2.3.6.2-1996.

(others)
Flame retardant assistant: antimony trioxide (PATOX-M, manufactured by Nihon Seiko Co., Ltd.)
Anti-drip agent: Polytetrafluoroethylene (Fluon CD-076, manufactured by Asahi Glass Co., Ltd.)
Antioxidant: phenolic antioxidant (BASF, Irganox 1010)
Lubricant: diglycerol tetrabehenate (Riken Vitamin Co., Ltd., Rikemal B74)
Alkaline compound: Potassium acetate (Wako Pure Chemical Industries, Ltd.)

<Examples 1 to 10 and Comparative Examples 1 to 7>
(A) polybutylene terephthalate resin, (B) carbodiimide compound, (C) halogen-based flame retardant, (D) polyhydric hydroxyl group-containing compound, and other components were weighed out and dry-blended according to the composition shown in Tables 1 and 2, and melt-kneaded in a twin-screw extruder (TEX-30 manufactured by The Japan Steel Works, Ltd.) at a cylinder temperature of 300°C, a screw rotation speed of 130 rpm, and an extrusion rate of 12 kg/h. The discharged strand-like molten resin was cooled and cut with a pelletizer to obtain a pellet-shaped sample of the resin composition. The pellets were then used to carry out the following various evaluations.

[Equivalent ratio of carbodiimide functional group amount to terminal carboxyl group amount]
The amount of terminal carboxyl groups was determined by dissolving a ground sample of the obtained pellets in benzyl alcohol at 215° C. for 10 minutes, and then titrating with a 0.01 N aqueous sodium hydroxide solution. The measurement results for the amount of terminal carboxyl groups and the equivalent ratio of the amount of carbodiimide functional groups to be mixed are shown in Tables 1 and 2.
Equivalent ratio of carbodiimide functional group amount to terminal carboxyl group amount=
Amount of carbodiimide functional groups/amount of terminal carboxyl groups

[Value obtained by subtracting the amount of terminal carboxyl groups from the amount of carbodiimide functional groups]
The amount of terminal carboxyl groups in the polybutylene terephthalate resin minus the amount of carbodiimide functional groups in the carbodiimide compound was calculated by subtracting the amount of terminal carboxyl groups in 1 kg of polybutylene terephthalate resin from the amount of carbodiimide functional groups mixed per 1 kg of polybutylene terephthalate resin, and was calculated using the following formula. The values are shown in Tables 1 and 2.
Amount of carbodiimide functional groups minus terminal carboxyl groups =
Amount of carbodiimide functional groups mixed per 1 kg of polybutylene terephthalate resin - Amount of terminal carboxyl groups contained in 1 kg of polybutylene terephthalate resin (meq/PBT kg)

[Flame retardancy]
The pellets obtained were dried at 140° C. for 3 hours, and then injection molded at a cylinder temperature of 250° C. and a mold temperature of 70° C. to prepare rectangular test pieces of 125 mm×13 mm×1/32 inch thickness in accordance with UL94, and the flammability was evaluated. The results are shown in Tables 1 and 2.

[Fluidity (melt viscosity)]
The pellets thus obtained were dried at 140°C for 3 hours, and then measured in accordance with ISO11443 using a Capillograph 1B (manufactured by Toyo Seiki Seisakusho) 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 unit is kPa s. The results are shown in Tables 1 and 2.

[Hydrolysis resistance (tensile strength retention)]
The pellets obtained were dried at 140°C for 3 hours, and then injection molded into ISO3167 tensile test pieces at a resin temperature of 260°C, a mold temperature of 80°C, an injection time of 15 seconds, and a cooling time of 15 seconds. The test pieces were subjected to 40 cycles of environmental test conditions of -40°C (0.5 hours) → 85°C, 85% RH (4 hours) → 175°C (1.5 hours) in accordance with USCAR-2 (5.6.2 Temperature/Humidity Cycling) Class 5, and the tensile strength was measured before and after the thermal cycle test in accordance with ISO527-1, 2. The tensile strength retention was calculated based on the following formula, and this was used as an index of hydrolysis resistance. The results are shown in Tables 1 and 2.
Tensile strength retention rate (unit: %) = (tensile strength after treatment/tensile strength before treatment) x 100

The results of the Examples and Comparative Examples confirm that the present invention can provide a flame-retardant polybutylene terephthalate resin composition with excellent hydrolysis resistance and fluidity.

Claims (6)

The connector is made of a flame-retardant polybutylene terephthalate resin composition containing at least (A) a polybutylene terephthalate resin having a terminal carboxyl group amount of 1 to 9 meq/kg or less, (B) an aromatic carbodiimide compound, and (C) a halogen- based flame retardant, wherein the aromatic carbodiimide compound has a carbodiimide functional group amount of 5 to 40 equivalents per equivalent of the terminal carboxyl group amount, and the value obtained by subtracting the terminal carboxyl group amount of the polybutylene terephthalate resin from the carbodiimide functional group amount of the aromatic carbodiimide compound is 30 meq/PBT kg or more. 2. The connector according to claim 1, which has a tensile strength retention of 90% or more in a thermal cycle test conforming to USCAR-2 (5.6.2 Temperature/Humidity Cycling) Class 5. 3. The connector according to claim 1, wherein the flame-retardant polybutylene terephthalate resin composition has a melt viscosity of 0.2 kPa·s or less as measured at 260° C. in accordance with ISO 11443. 4. The connector according to claim 1, wherein the flame-retardant polybutylene terephthalate resin composition contains (D) a polyhydric hydroxyl group-containing compound. A relay comprising a flame-retardant polybutylene terephthalate resin composition containing at least (A) a polybutylene terephthalate resin having a terminal carboxyl group amount of 1 to 9 meq/kg or less, (B) an aromatic carbodiimide compound, and (C) a halogen-based flame retardant, wherein the amount of carbodiimide functional groups of the aromatic carbodiimide compound is 5 to 40 equivalents per equivalent of the amount of the terminal carboxyl groups, and the value obtained by subtracting the amount of the terminal carboxyl groups of the polybutylene terephthalate resin from the amount of the carbodiimide functional groups of the aromatic carbodiimide compound is 30 meq/PBT kg or more. A switch made of a flame-retardant polybutylene terephthalate resin composition containing at least (A) a polybutylene terephthalate resin having a terminal carboxyl group amount of 1 to 9 meq/kg or less, (B) an aromatic carbodiimide compound, and (C) a halogen-based flame retardant, wherein the aromatic carbodiimide compound has a carbodiimide functional group amount of 5 to 40 equivalents per equivalent of the terminal carboxyl group amount, and the value obtained by subtracting the terminal carboxyl group amount of the polybutylene terephthalate resin from the carbodiimide functional group amount of the aromatic carbodiimide compound is 30 meq/PBT kg or more.