Patent Description:
Polybutylene terephthalate resins (PBT resins) have various excellent electrical properties and are therefore widely used as engineering plastics in many applications such as electrical/electronic components. In these applications, flame retardance is demanded of the materials used in order to prevent ignition by tracking and the like. Polybutylene terephthalate resins themselves do not have sufficient flame retardance and are therefore used as flame-retardant resin compositions in which a flame retardant has been added.

Patent Document <NUM> introduces polypentabromobenzyl acrylate (PBBPA) as a halogenated benzyl acrylate-based flame retardant, which is one kind of flame retardant added to polybutylene terephthalate resins.

Meanwhile, in order to enhance the fluidity of polybutylene terephthalate resins, Patent Document <NUM> introduces adding a chain polyester oligomer. However, the objective thereof is to cause the chain polyester oligomer to react with a glycidyl group-containing elastomer.

Moreover, in order to improve melt fluidity while maintaining properties such as excellent mechanical strength that polybutylene terephthalate-based resins possess, Patent Document <NUM> introduces adding a cyclic polyester oligomer.

Furthermore, Patent Document <NUM> describes adding an oligomer to a polybutylene terephthalate-based resin. However, there is no mention of whether the added oligomer is a chain or cyclic oligomer and only polymers are used in the examples.

Furthermore, Patent Document <NUM> relates to polymers as well as copolymers, a method of preparing such polymers and copolymers, and the use of such polymers and copolymers in normally flammable plastic compositions.

Furthermore, Patent Document <NUM> relates to methyltetrahalobenzylacrylates and methacrylates, polymers produced therefrom and the use of such polymers as flameproofing agents for polymeric materials.

The present invention addresses the problem of enhancing the fluidity of a polybutylene terephthalate resin composition that uses a halogenated benzyl acrylate-based flame retardant as a flame retardant while maintaining properties such as excellent mechanical strength that the polybutylene terephthalate-based resin possesses.

This object is solved by the subject matter of the independent claim. Further aspects are disclosed in the subclaims. In the process of research addressing the problem of enhancing the fluidity of polybutylene terephthalate resin compositions that use a halogenated benzyl acrylate-based flame retardant as a flame retardant, the present inventors found that the problem can be solved by adding a protic compound, completing the present invention.

According to the present invention, fluidity can be enhanced by adding a protic compound to a polybutylene terephthalate resin composition that uses a halogenated benzyl acrylate-based flame retardant as a flame retardant.

[<FIG>] A figure illustrating an example of a molded article used when measuring the melt fluidity of the present invention.

An embodiment of the present invention shall be explained in detail below. The present invention is not limited by the following embodiment and can be carried out with the addition of appropriate modifications so long as the effects of the present invention are not hindered.

Below, the details of the components of the flame-retardant polybutylene terephthalate resin composition of the present embodiment shall be explained with examples.

Polybutylene terephthalate resins (PBT resins) are obtained by condensation polymerizing a dicarboxylic acid component comprising at least terephthalic acid or an ester-forming derivative thereof (a C<NUM>-<NUM> alkylester, an acid halide, etc.) and a glycol component comprising an alkylene glycol with a carbon number of at least <NUM> (<NUM>,<NUM>-butanediol) or an ester-forming derivative thereof (an acetylate, etc.). In the present embodiment, the polybutylene terephthalate resin is not limited to homopolybutylene terephthalate resins and may be a copolymer containing <NUM> mol% or more of butylene terephthalate units.

The amount of terminal carboxyl groups of the polybutylene terephthalate resin is not particularly limited so long as the objective of the present invention is not hindered but is preferably <NUM> meq/kg or less and more preferably <NUM> meq/kg or less.

The intrinsic viscosity of the polybutylene terephthalate resin is not particularly limited so long as the objective of the present invention is not hindered, but is preferably <NUM> dL/g or more and <NUM> dL/g or less and more preferably <NUM> dL/g or more and <NUM> dL/g or less. When a polybutylene terephthalate resin with an intrinsic viscosity in such a range is used, the obtained polybutylene terephthalate resin composition has particularly excellent moldability. Further, the intrinsic viscosity can be adjusted by blending polybutylene terephthalate resins having different intrinsic viscosities. For example, by blending a polybutylene terephthalate resin having an intrinsic viscosity of <NUM> dL/g with a polybutylene terephthalate resin having an intrinsic viscosity of <NUM> dL/g, a polybutylene terephthalate resin having an intrinsic viscosity of <NUM> dL/g can be prepared. The intrinsic viscosity of the polybutylene terephthalate resin can be measured under conditions of, for example, a temperature of <NUM> in o-chlorophenol.

In preparing the polybutylene terephthalate resin, when using an aromatic dicarboxylic acid other than terephthalic acid or an ester-forming derivative thereof as a comonomer component, for example, a C<NUM>-<NUM> aromatic dicarboxylic acid such as isophthalic acid, phthalic acid, <NUM>,<NUM>-naphthalenedicarboxylic acid, or <NUM>,<NUM>'-dicarboxydiphenylether; a C<NUM>-<NUM> alkanedicarboxylic acid such as succinic acid, adipic acid, azelaic acid, or sebacic acid; a C<NUM>-<NUM> cycloalkanedicarboxylic acid such as cyclohexanedicarboxylic acid; or an ester-forming derivative of these dicarboxylic acid components (a C<NUM>-<NUM> alkylester derivative, an acid halide, etc.) can be used. These dicarboxylic acid components may be used alone or in a combination of two or more.

Among these dicarboxylic acid components, a C<NUM>-<NUM> aromatic dicarboxylic acid such as isophthalic acid and a C<NUM>-<NUM> alkanedicarboxylic acid such as adipic acid, azelaic acid, or sebacic acid are more preferred.

In preparing the polybutylene terephthalate resin, when using a glycol component other than <NUM>,<NUM>-butanediol as a comonomer component, for example, a C<NUM>-<NUM> alkylene glycol such as ethylene glycol, propylene glycol, trimethylene glycol, <NUM>,<NUM>-butylene glycol, hexamethylene glycol, neopentyl glycol, or <NUM>,<NUM>-octanediol; a polyoxyalkylene glycol such as diethylene glycol, triethylene glycol, or dipropylene glycol; an alicyclic diol such as cyclohexanedimethanol or hydrogenated bisphenol A; an aromatic diol such as bisphenol A or <NUM>,<NUM>'-dihydroxybiphenyl; a C<NUM>-<NUM> alkylene oxide adduct of bisphenol A such as an ethylene oxide <NUM>-mol adduct of bisphenol A or a propylene oxide <NUM>-mol adduct of bisphenol A; or an ester-forming derivative of these glycols (an acetylate, etc.) can be used. These glycol components may be used alone or in a combination of two or more.

Among these glycol components, a C<NUM>-<NUM> alkylene glycol such as ethylene glycol or trimethylene glycol, a polyoxyalkylene glycol such as diethylene glycol, an alicyclic diol such as cyclohexanedimethanol, etc. is more preferred.

As comonomer components that can be used beyond the dicarboxylic acid component and the glycol component, there are, for example, aromatic hydroxycarboxylic acids such as <NUM>-hydroxybenzoic acid, <NUM>-hydroxybenzoic acid, <NUM>-hydroxy-<NUM>-naphthoic acid, and <NUM>-carboxy-<NUM>'-hydroxybiphenyl; aliphatic hydroxycarboxylic acids such as glycolic acid and hydroxycaproic acid; C<NUM>-<NUM> lactones such as propiolactones, butyrolactones, valerolactones, and caprolactones (ε-caprolactone, etc.); and ester-forming derivatives of these comonomer components (C<NUM>-<NUM> alkylester derivatives, acid halides, acetylates, etc.).

The content of the polybutylene terephthalate resin is preferably <NUM>-<NUM>% by mass of the total mass of the resin composition, more preferably <NUM>-<NUM>% by mass, and still more preferably <NUM>-<NUM>% by mass.

As examples of the halogenated benzyl acrylate-based flame retardant used in the present invention, there are brominated acrylic polymers represented by general formula (I) below. <CHM>
<CHM>.

At least one X in the formula is bromine. The number of X is from <NUM> to <NUM> in one constituent unit, but in view of the flame retarding effects, <NUM>-<NUM> is preferred. The average degree of polymerization m is <NUM>-<NUM>,<NUM> and preferably in the range of <NUM>-<NUM>,<NUM>. Thermal stability worsens in flame retardants in which the average degree of polymerization is low and the moldability of the polybutylene terephthalate resin worsens if a flame retardant in which the average degree of polymerization exceeds <NUM>,<NUM> is added thereto. Further, one of the above brominated acrylic polymers or a mixture of two or more may be used.

The halogenated benzyl acrylate-based flame retardant used in the present invention can contain, other than the brominated acrylic polymers above, which are flame retardants themselves, halogenated aromatic compounds derived from the solvent when polymerizing or from degradation products of the brominated acrylic polymer as impurities, but the content of halogenated aromatic compounds other than the flame retardant, which are such impurities, is preferably <NUM> ppm or less, more preferably <NUM> ppm or less, still more preferably <NUM> ppm or less, and especially preferably <NUM> ppm or less. The content of halogenated aromatic compounds other than the flame retardant can be determined from, for example, the amount of gas derived from halogenated aromatic compounds when measuring, with a gas chromatograph, the gas generated when a sample in which the halogenated benzyl acrylate-based flame retardant has been crushed is heat-treated in headspace.

The brominated acrylic polymer represented by general formula (I) is obtained by polymerizing, alone, a benzyl acrylate containing bromine, but benzyl methacrylates, etc. with similar structures may be copolymerized. As bromine-containing benzyl acrylates, there are pentabromobenzyl acrylate, tetrabromobenzyl acrylate, tribromobenzyl acrylate, and mixtures thereof. Among these, pentabromobenzyl acrylate is preferred. Moreover, as benzyl methacrylates that are copolymerizable components, there are methacrylates corresponding to the abovementioned acrylates. Furthermore, copolymerization with vinyl-based monomers is possible and examples include acrylic acid esters such as acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, and benzyl acrylate, methacrylic acid esters such as methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and benzyl methacrylate, styrene, acrylonitrile, unsaturated carboxylic acids such as fumaric acid and maleic acid or anhydrides thereof, vinyl acetate, vinyl chloride, etc. Moreover, crosslinkable vinyl-based monomers, xylylene diacrylate, xylylene dimethacrylate, tetrabromoxylylene diacrylate, tetrabromoxylylene dimethacrylate, butadiene, isoprene, divinylbenzene, etc. can also be used. These are used in a molar amount equivalent to or less than and preferably <NUM> times the molar amount or less than that of the benzylacrylate or benzyl methacrylate.

Showing an example of the manufacturing method for the brominated acrylic polymer, there is the method of reacting brominated acrylic monomers at a predetermined degree of polymerization by liquid polymerization or bulk polymerization. In the case of liquid polymerization, it is preferable that a halogenated aromatic compound such as halogenated benzene or chlorobenzene not be used as the solvent. Further, an aprotic solvent such as ethylene glycol monomethyl ether, methyl ether ketone, ethylene glycol dimethyl ether, or dioxane is preferred as the solvent in the case of liquid polymerization. However, as will be discussed later, because a substance comprising a protic compound is set as the resin composition in the present invention, a substance comprising a protic compound can be used as the polymerization solvent.

The abovementioned brominated acrylic polymer is preferably washed in water and/or an aqueous solution containing alkali (earth) metal ions in order to remove reaction byproducts such as residual sodium polyacrylate. The aqueous solution containing alkali (earth) metal ions is easily obtained by putting an alkali (earth) metal salt in water, but a hydroxide which is an alkali (earth) metal that does not comprise chloride ions, phosphate ions, etc. (for example, calcium hydroxide) is optimum. When using, for example, calcium hydroxide as the alkali (earth) metal salt, generally about <NUM> of calcium hydroxide is soluble in <NUM> of water at <NUM> and the concentration of the aqueous solution is not particularly specified as far as the solubility allows. Further, the technique for washing with water and/or the aqueous solution containing alkali (earth) metal ions is not particularly limited and may be a technique such as that for immersing the brominated acrylic polymer in water and/or the aqueous solution containing alkali (earth) metal ions for an appropriate period of time. In the brominated acrylic polymer after the washing process with water and/or the aqueous solution containing alkali (earth) metal ions is complete, the dry solid content in the warm water extraction generally becomes <NUM> ppm or less and when using such a brominated acrylic polymer, the emergence of foreign matter on the surfaces of molded articles thereof is largely eliminated.

The content of halogenated aromatic compounds other than the flame retardant, which are the aforementioned impurities, in the flame-retardant polybutylene terephthalate resin composition of the present invention is preferably less than <NUM> ppm, more preferably <NUM> ppm or less, and yet more preferably <NUM> ppm or less. Due to the content of halogenated aromatic compounds other than the flame retardant in the flame-retardant polybutylene terephthalate resin composition being in the above range, corrosion of metal terminals in insert-molded articles using the polybutylene terephthalate resin composition can be suppressed. The content of such halogenated aromatic compounds other than the flame retardant can be determined from, for example, the amount of gas derived from halogenated aromatic compounds when measuring, with a gas chromatograph, the gas generated when a sample in which the polybutylene terephthalate resin composition has been crushed is heat-treated in headspace.

In making the resin flame-retardant, use together with an antimony-based flame retardant promoter is preferred. As representative flame retardant promoters, there are antimony trioxide, antimony tetroxide, antimony pentoxide, sodium pyroantimonate, etc. Furthermore, with the objective of preventing the spread of fire due to the resin dripping when burnt, use together with a drip prevention agent such as polytetrafluoroethylene is preferred.

The range of addition of the brominated acrylic polymer and the antimony-based flame retardant promoter to the resin is preferably <NUM>-<NUM> parts by mass of the polymer and <NUM>-<NUM> parts by mass of the antimony-based flame retardant promoter with respect to <NUM> parts by mass of the polybutylene terephthalate resin. If the added amounts of the brominated acrylic polymer and the antimony-based flame retardant promoter are too small, sufficient flame retardance cannot be imparted and, if the amounts added are too large, physical properties as molded articles worsen.

In the present invention, protic compound means a compound that donates protons (hydrogen ions).

As the protic compound in the present invention, compounds derived from a polymerization solvent of the halogenated benzyl acrylate-based flame retardant are raised as one example and the protic compound is an alkoxy alcohol, which is preferably a C<NUM>-C<NUM> dialkoxy C<NUM>-C<NUM> alcohol and, as the C<NUM>-C<NUM> dialkoxy C<NUM>-C<NUM> alcohol, <NUM>,<NUM>-diethoxypropanol is most preferred.

Alternatively, as the protic compound in the present invention, a compound derived from a raw material of the halogenated benzyl acrylate-based flame retardant is raised as one example, and the protic compound is an aromatic carboxylic acid and preferably benzoic acid. As the protic compound in the present invention, a compound derived from a polymerization solvent is more preferred than that derived from a raw material of the halogenated benzyl acrylate-based flame retardant.

The amount of the protic compound contained in the halogenated benzyl acrylate-based flame retardant in the present invention is <NUM>-<NUM>,<NUM> ppm, but is preferably <NUM>-<NUM> ppm and more preferably <NUM>-<NUM> ppm. If the amount of the protic compound contained in the halogenated benzyl acrylate-based flame retardant is less than <NUM> ppm, the effect of improving fluidity of the flame-retardant polybutylene terephthalate resin composition is not readily obtained. Further, if the amount of the protic compound contained in the halogenated benzyl acrylate-based flame retardant is greater than <NUM>,<NUM> ppm, the amount of gas generated when compounding increases and strand breakage readily occurs when pelleting.

In the flame-retardant polybutylene terephthalate resin composition of the present invention, the protic compound contained by the halogenated benzyl acrylate-based flame retardant generates a linear compound which is a reactant with a linear low-molecular weight body (oligomer) of the polybutylene terephthalate resin and this is presumed to provide effects similar to those of a plasticizer and improve the fluidity of the terephthalate resin composition. Therefore, the polybutylene terephthalate resin contains a linear low-molecular weight body. The amount of the linear low-molecular weight body contained in the polybutylene terephthalate resin is <NUM>-<NUM>,<NUM> ppm, preferably <NUM>-<NUM> ppm, and more preferably <NUM>-<NUM> ppm. If the amount of the linear low-molecular weight body is less than <NUM> ppm, the effect of improved fluidity of the flame-retardant polybutylene terephthalate resin composition is not readily obtained and if the amount exceeds <NUM>,<NUM> ppm, mold deposits readily occur, so this is not preferred.

A filler can be used in the composition of the present invention, as necessary. Such a filler is preferably blended in order to obtain excellent properties in performance such as mechanical strength, thermal resistance, dimensional stability, and electrical properties and is particularly effective with the objective of increasing rigidity. In accordance with the objective, a fibrous, granular, or tabular filler is used.

As fibrous fillers, there are glass fibers, asbestos fibers, carbon fibers, silica fibers, silica/alumina fibers, zirconia fibers, boron nitride fibers, silicon nitride fibers, boron fibers, potassium titanate fibers, and further, fibrous materials of metals such as stainless steel, aluminum, titanium, copper, and brass, etc. High-melting point organic fibrous substances such as polyamides, fluorine resins, and acrylic resins can also be used.

As granular fillers, there are carbon black, quartz powder, glass beads, glass powder, silicates such as calcium silicate, aluminum silicate, kaolin, talc, clay, diatomaceous earth, and wollastonite, metal oxides such as iron oxide, titanium oxide, and alumina, metal carbonates such as calcium carbonate and magnesium carbonate, metal sulfates such as calcium sulfate and barium sulfate, and, additionally, silicon carbide, silicon nitride, boron nitride, various metal powders, etc..

Further, as tabular inorganic fillers, there are mica, glass flakes, various metal foils, etc..

The type of the filler is not particularly limited and one or more types of filler can be added. In particular, using potassium titanate fibers, mica, talc, or wollastonite is preferred.

The amount of the filler added is not particularly specified, but is preferably <NUM> parts by mass or less with respect to <NUM> parts by mass of the polybutylene terephthalate resin. When the filler is added in excess, inferior moldability and decreases in toughness are observed.

Furthermore, in order to impart desired properties other than flame retardance, publicly known substances generally added to thermoplastic resins and the like can be added in combination to the composition of the present invention in accordance with the objective thereof. Any of, for example, an antioxidant, an ultraviolet absorbing agent, a stabilizer such as a photostabilizer, an anti-static agent, a lubricant, a mold release agent, a colorant such as a dye or pigment, a plasticizing agent, etc. can be blended. In order to improve thermal resistance, in particular, the addition of an antioxidant is effective.

The form of the flame-retardant polybutylene terephthalate resin composition of the present invention may be a granular mixture and may be a molten mixture (melt-kneaded article) such as pellets. The manufacturing method for the polybutylene terephthalate resin composition of one embodiment of the present invention is not particularly limited and the composition can be manufactured with equipment and methods known in this technical field. For example, the composition can be prepared as pellets for molding by mixing the necessary components and kneading using a single-screw or twin-screw extruder or other melt-kneading device. Multiple extruders or other melt-kneading devices may be used. Further, all the components may be simultaneously charged from a hopper or some components may be charged from a side feed port.

Moreover, the flame-retardant polybutylene terephthalate resin composition of the present invention is preferably manufactured by vacuum drying (vacuum drawing). Generally used evaporators, ovens, etc. can be used in vacuum drying.

The present invention will be explained specifically with the following examples, but the present invention is not limited by these examples so long as the gist thereof is not exceeded. Examples <NUM>, <NUM>, <NUM>, and <NUM> are reference examples.

After using halogenated benzyl acrylate-based flame retardants containing protic compounds of the types and in the amounts indicated in Table <NUM> and polybutylene terephthalate resins containing linear low-molecular weight bodies in the amounts shown in Table <NUM> to weigh and blend the components in the blending amounts indicated in Table <NUM>, melt-kneading with a TEX-<NUM> twin-screw extruder manufactured by The Japan Steel Works, LTD. under the conditions of a cylinder temperature of <NUM>, a screw rotation speed of <NUM> rpm, and an extrusion amount of <NUM>/hr, and extruding in strands from a die, flame-retardant polybutylene terephthalate resin compositions were obtained in pellet form by cooling and shearing. When doing so, the occurrence of strand breakage was confirmed and the compositions in which strand breakage largely did not occur were evaluated as ○ and those in which it often occurred were evaluated as ×. The results are shown in Table <NUM>.

Using the pellets of the obtained examples and comparative examples, melt fluidity, flame retardance, and mold deposits were evaluated. The results are shown in Table <NUM>.

The box-like molded article (the thickness of the four sidewalls and the bottom is <NUM>) shown in <FIG> was injection molded at a resin temperature of <NUM>, a mold temperature of <NUM>, an injection speed of <NUM>/s, and a holding pressure of <NUM> MPa and the compositions that completely filled the article were evaluated as ○ and those that could not fill the article to the top due to insufficient fluidity were evaluated as ×.

In conformance with UL94, flame retardance was evaluated using <NUM> × <NUM> × <NUM> strip-shaped test pieces.

The strip-shaped test pieces used in the evaluation of flame retardance were shot molded <NUM>,<NUM> times in a row and evaluation was performed by visual inspection of the mold cavity surface. Cases in which mold deposits were not observed were evaluated as ○ and those in which deposits were observed were evaluated as ×.

Claim 1:
A flame-retardant polybutylene terephthalate resin composition containing a polybutylene terephthalate resin and
a halogenated benzyl acrylate-based flame retardant in which the content of a protic compound is <NUM>-<NUM>,<NUM> ppm as measured by headspace gas chromatography (<NUM>, <NUM> hour heating), wherein the protic compound is an alkoxy alcohol or an aromatic carboxylic acid, and the aromatic carboxylic acid is derived from a raw material of the halogenated benzyl acrylate-based flame retardant, and wherein the polybutylene terephthalate resin comprises <NUM>-<NUM>,<NUM> ppm of a linear low-molecular weight-body, determined as indicated in the description, and wherein the linear low-molecular weight-body is an oligomer of the polybutylene terephthalate.