JP2020094117A - Resin composition for injection molding, injection molded article, and manufacturing method of injection molded article - Google Patents

Abstract

To provide a resin composition for injection molding providing an injection molded article excellent in moldability, high in mechanical strength and impact strength, having massive feeling, excellent in dimensional stability, and excellent in appearance, and the injection molded article and a manufacturing method therefor.SOLUTION: There is provided a resin composition for injection molding containing a vinyl chloride resin having an average polymerization degree of 400 to 1000, barium sulphate, a modifier, a lubricant and a stabilizer, with a ratio of the barium sulphate of 10 to 300 pts.mass based on 100 pts.mass of the vinyl chloride resin. There is provided an injection molded article using the resin composition for injection molding. There is provided a manufacturing method of the injection molded article by injection molding the resin composition for injection molding at 160 to 220°C.SELECTED DRAWING: None

Description

The present invention relates to a resin composition for injection molding, an injection molded article, and a method for producing an injection molded article.

Injection molded products are widely used in various fields such as building materials, housing, and civil engineering. By using a hard resin as the resin composition used for producing the injection-molded product, an injection-molded product having excellent durability and weather resistance can be obtained.
Examples of the injection molded product include an injection molded product manufactured using a resin composition containing a PBT resin. Further, an injection-molded article manufactured using a resin composition in which PBT resin is mixed with barium sulfate has also been proposed.

JP, 2006-233306, A

By adding barium sulfate to the injection-molded product, the mechanical strength is increased and the solid feeling is increased. However, since the resin composition using the PBT resin as in Patent Document 1 has a high shrinkage ratio at the time of injection molding, the dimensional stability of the obtained injection molded product tends to be poor, and sink marks and flow marks are generated. And the appearance tends to deteriorate.
In injection molding, it is also important that the moldability is excellent and defects such as burns can be suppressed.

The present invention is excellent in moldability, also has high mechanical strength and impact strength, has a solid feeling, has excellent dimensional stability, and an injection-molded resin composition capable of obtaining an injection-molded article having an excellent appearance, and An object of the present invention is to provide an injection molded product using a resin composition for injection molding and a method for producing the same.

The present invention has the following configurations.
[1] A vinyl chloride resin having an average degree of polymerization of 400 to 1000, barium sulfate, a modifier, a lubricant and a stabilizer,
A resin composition for injection molding, wherein the ratio of barium sulfate to 100 parts by mass of the vinyl chloride resin is 10 to 300 parts by mass.
[2] The resin composition for injection molding according to [1], wherein the ratio of the plasticizer to 100 parts by mass of the vinyl chloride resin is less than 5 parts by mass.
[3] An injection molded product comprising the resin composition for injection molding according to [1] or [2].
[4] A method for producing an injection-molded article, comprising injection-molding the resin composition for injection molding according to [1] or [2] at 160 to 220°C.
[5] The method for producing an injection-molded product according to [4], wherein injection molding is performed using an injection molding machine equipped with a full flight screw having a compression ratio of 1.5 to 2.5.
[6] The method for producing an injection-molded product according to [4] or [5], in which the injection-molded product after molding is rapidly cooled.

According to the present invention, a resin composition for injection molding, which is excellent in moldability, has high mechanical strength and impact strength, has a solid feeling, has excellent dimensional stability, and can obtain an injection-molded article excellent in appearance, and It is possible to provide an injection molded product using the resin composition for injection molding and a method for producing the same.

[Resin composition for injection molding]
The resin composition for injection molding of the present invention contains a vinyl chloride resin having an average degree of polymerization of 400 to 1000 (hereinafter referred to as "PVC resin"), barium sulfate, a modifier, a lubricant and a stabilizer. ..

The PVC resin is a polymer in which the proportion of repeating units derived from vinyl chloride is 50% by mass or more based on all repeating units. The PVC resin may be a homopolymer of vinyl chloride or a copolymer of vinyl chloride and a vinyl monomer copolymerizable with vinyl chloride. When the PVC resin is a copolymer, it may be a random copolymer, a block copolymer, or a graft copolymer.
The PVC-based resin contained in the resin composition for injection molding of the present invention may be one type or two or more types.

The proportion of vinyl chloride-derived repeating units in the PVC resin is 50% by mass or more, preferably 75% by mass or more, more preferably 80% by mass or more, still more preferably 85% by mass or more, based on all repeating units. 100% by mass is particularly preferable.

The average degree of polymerization of the PVC resin is 300 to 1000, preferably 400 to 900, and more preferably 500 to 800. When the average degree of polymerization of the PVC resin is not less than the lower limit value of the above range, an injection-molded article having high mechanical strength can be obtained. When the average degree of polymerization of the PVC resin is equal to or lower than the upper limit value of the above range, fluidity is excellent, moldability is excellent, flow marks and weld lines can be suppressed, and an injection-molded article excellent in appearance can be obtained.

The vinyl monomer copolymerizable with vinyl chloride is not particularly limited, and examples thereof include fatty acid vinyl ester, methacrylic acid ester, methacrylic acid ester, vinyl cyanide, vinyl ether, α-olefin, unsaturated carboxylic acid or the like. Examples thereof include acid anhydrides, vinylidene chloride, vinyl bromide and various urethanes.

Examples of the fatty acid vinyl ester include vinyl acetate, vinyl propionate, vinyl laurate and the like. Examples of the acrylate ester include methyl acrylate, ethyl acrylate, butyl acrylate and the like. Examples of the methacrylic acid ester include methyl methacrylate and ethyl methacrylate. Examples of vinyl cyanide include acrylonitrile and methacrylonitrile. Examples of vinyl ethers include vinyl methyl ether, vinyl butyl ether, vinyl octyl ether and the like. Examples of the α-olefin include ethylene, propylene, butylene and the like. Examples of unsaturated carboxylic acids or acid anhydrides thereof include acrylic acid, methacrylic acid, maleic anhydride and the like.
The vinyl-based monomer copolymerizable with vinyl chloride may be used alone or in combination of two or more kinds.

Examples of the polymer which can be graft-polymerized with vinyl chloride include ethylene/vinyl acetate copolymer, ethylene/vinyl acetate/carbon monoxide copolymer, ethylene/ethyl acrylate copolymer, ethylene/ethyl acrylate/monomer. Carbon oxide copolymer, ethylene/methyl methacrylate copolymer, ethylene/propylene copolymer, acrylonitrile/butadiene copolymer, polyurethane, chlorinated polyethylene, chlorinated polypropylene, methyl methacrylate/butadiene/styrene copolymer, Examples thereof include acrylonitrile/butadiene/α-methylstyrene copolymer, polybutyl acrylate, butyl rubber, polystyrene, styrene/butadiene copolymer, and acrylic rubber.

Barium sulfate is not particularly limited, and commercially available ones can be used. The barium sulfate may be surface-treated with silica, alumina or the like. However, barium sulfate that is not surface-treated is preferable because it has excellent dispersibility in PVC resin.
The barium sulfate contained in the resin composition for injection molding of the present invention may be one type or two or more types.

0.1-10 micrometers is preferable and, as for the average primary particle diameter of barium sulfate, 0.5-5 micrometers is more preferable. When the average primary particle size of barium sulfate is not less than the lower limit value of the above range, barium sulfate is less likely to aggregate, blocking during compounding and adhesion to metal do not occur, and moldability is excellent. When the average primary particle diameter of barium sulfate is not more than the upper limit value of the above range, it is easy to obtain an injection molded product having good physical properties and particularly excellent impact resistance and appearance.
The average primary particle size of barium sulfate is measured by an electron microscope or a laser diffraction/scattering particle size analyzer.

The pH of barium sulfate is preferably 5.0 to 9.0, more preferably 6.5 to 8.5. When the pH of barium sulfate is within the above range, the thermal stability of the resin composition for injection molding is excellent, and the dispersibility of barium sulfate in the PVC resin is excellent.
The pH value of barium sulfate is measured by the boiling method according to JIS K5101.

The proportion of barium sulfate in the resin composition for injection molding of the present invention is 10 to 300 parts by mass, preferably 30 to 200 parts by mass, and more preferably 50 to 150 parts by mass with respect to 100 parts by mass of the PVC resin. preferable. When the proportion of barium sulfate is at least the lower limit value of the above range, the mechanical strength will be excellent and a weighty feeling will be obtained. When the proportion of barium sulfate is at most the upper limit value of the above range, the moldability will be excellent and the surface hardness will be improved.

Examples of the modifier include impact modifiers, gelation accelerators, heat resistance modifiers, flame retardants, elasticity imparting agents, antistatic agents, surfactants, conductivity imparting agents, and the like. The modifier contained in the resin composition for injection molding of the present invention may be one type or two or more types.

As the impact modifier, ethylene/vinyl acetate copolymer, ethylene/ethyl acrylate copolymer, chlorinated polyethylene, methyl methacrylate/butadiene/styrene copolymer, acrylonitrile/butadiene/styrene copolymer, acrylic rubber, etc. Is mentioned. Examples of the gelling accelerator include polymethylmethacrylate and the like.
Examples of the heat resistance modifier include a methyl methacrylate/acrylic acid ester copolymer (hereinafter referred to as “MMA-based copolymer”), a copolymer using maleimide, and the like.
Examples of the flame retardant include antimony trioxide, aluminum hydroxide, sodium antimonate, phosphoric acid ester and phosphoric acid compound, chlorinated paraffin, chlorinated olefin, hexabromobenzene and the like.
Examples of the elasticity imparting agent include partially crosslinked NBR, acrylic rubber, polyurethane and the like.

As the modifier, an MMA copolymer is particularly preferable.
Examples of the acrylate ester used for the MMA copolymer include, for example, methyl acrylate, ethyl acrylate, acrylate-n-butyl, isobutyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate, methacrylic acid-n-. Butyl, isobutyl methacrylate, 2-ethylhexyl methacrylate and the like can be mentioned. The acrylic ester used for the MMA-based copolymer may be one type or two or more types.

The weight average molecular weight of the MMA copolymer is preferably 3,000,000 or more. When the weight average molecular weight of the MMA copolymer is at least the lower limit value of the above range, the dispersibility and melt strength of the MMA copolymer will be improved.

The proportion of the modifier in the resin composition for injection molding of the present invention is preferably 1 to 100 parts by mass, more preferably 5 to 70 parts by mass, based on 100 parts by mass of the PVC resin.
The proportion of the MMA copolymer in the resin composition for injection molding of the present invention is preferably 1 to 30 parts by mass and more preferably 3 to 15 parts by mass with respect to 100 parts by mass of the PVC resin. When the proportion of the MMA copolymer is at least the lower limit value of the above range, the mechanical strength and melt strength of the injection molded product will be improved. When the proportion of the MMA copolymer is at most the upper limit value of the above range, the fluidity of the resin composition for injection molding will be improved and the moldability will be excellent.

The lubricant is not particularly limited, and a commercially available lubricant can be used. Specific examples of the lubricant include, for example, aliphatic hydrocarbon lubricants, higher aliphatic alcohol lubricants, aliphatic amide lubricants, fatty acid ester lubricants, and metallic soaps.

Examples of the aliphatic hydrocarbon lubricant include low molecular weight wax, polyethylene wax, paraffin wax, liquid paraffin and the like. Examples of the higher aliphatic alcohol lubricant include stearyl alcohol and the like. Examples of the aliphatic amide-based lubricant include stearic acid amide, palmitic acid amide, and methylene bistearamide. Examples of the fatty acid ester lubricant include glyceryl monostearate, ethyl diaminostearate, and butyl stearate.

As the lubricant, a lubricant having high external lubricity is preferable, and polyethylene wax and paraffin wax are more preferable. The lubricant contained in the resin composition for injection molding of the present invention may be one type or two or more types.

The proportion of the lubricant in the resin composition for injection molding of the present invention is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the PVC resin. When the proportion of the lubricant is at least the lower limit value of the above range, the mold releasability of the injection-molded product is improved, and the injection-molded product having an excellent appearance is easily obtained. When the proportion of the lubricant is not more than the upper limit value of the above range, the moldability is excellent.

The stabilizer is not particularly limited, and examples thereof include lead stabilizers, tin stabilizers, organometallic salt stabilizers, metal soap stabilizers, antimony stabilizers, phosphate stabilizers, epoxidized oil stabilizers. Agents, dibutylhydroxytoluene (BHT), ultraviolet absorbers and the like. The stabilizer contained in the resin composition for injection molding of the present invention may be one type or two or more types.

Examples of the lead-based stabilizer include tribasic lead sulfate, dibasic lead phosphite, basic lead sulfite, dibasic lead phthalate, lead white, and lead laurate or stearate.
Examples of the tin stabilizer include butyltin malate, octyltin maleate, di-n-alkyltin mercaptide, di-n-alkyltin dilaurate, dibutyltin dimalate, dibutyltin lauryl mercaptide, dioctyltin S,S'-bis-. (Isooctyl mercaptoacetate), dibutyltin bis-isooctyl thioglycolate, di-(n-octyl)tin malate polymer, dibutyltin mercaptopropionate and the like.
Examples of the organic metal salt-based stabilizer and the metal soap-based stabilizer include calcium, cadmium, barium or zinc laurate or stearate.
Examples of the antimony stabilizer include antimony mercaptocarboxylic acid salts or ester salts.
Examples of the epoxidized oil stabilizer include epoxidized soybean oil and epoxidized linseed oil.
Examples of the ultraviolet absorber include hindered phenols such as bisphenol dimerized with sulfur and methylene groups, salicylic acid esters, benzophenone, and benzotriazole.

The proportion of the stabilizer in the resin composition for injection molding of the present invention is preferably 1 to 15 parts by mass and more preferably 2 to 10 parts by mass with respect to 100 parts by mass of the PVC resin. When the proportion of the stabilizer is at least the lower limit value of the above range, the thermal stability is improved and burns and foreign matter do not occur. When the proportion of the stabilizer is not more than the upper limit value of the above range, the workability is excellent.

The resin composition for injection molding of the present invention may contain components other than PVC resin, barium sulfate, a modifier, a lubricant and a stabilizer as long as the effects of the present invention are not impaired. Examples of other components include a filler, a coloring agent, a foaming agent and the like.

The filler is not particularly limited, and examples thereof include oxide-based fillers, hydroxide-based fillers, sulfate-based fillers and sulfite-based fillers, carbon-based fillers, inorganic fiber-based fillers, metal powders. Examples include system-based fillers and heat resistant resins. As the filler, one kind may be used alone, or two or more kinds may be used in combination.

Examples of carbonate fillers include magnesium carbonate and dawsonite. Examples of the oxide-based filler include silica, diatomaceous earth, titanium oxide and the like. Aluminum hydroxide, magnesium hydroxide, etc. are mentioned as a hydroxide type filler. Examples of the sulfate type filler and the sulfite type filler include calcium sulfate and the like. Examples of the silicate-based filler include talc, clay, mica, calcium silicate and the like. Examples of the carbon-based filler include carbon black and graphite. Examples of the inorganic fiber filler include hollow or solid glass beads, glass short fibers, metal fibers, carbon short fibers, carbon fibers and the like. Examples of the metal powder filler include iron powder and copper powder. Examples of the heat resistant resin include polyimide and silicone.

The colorant is not particularly limited, and examples thereof include an inorganic pigment, an organic pigment, and a dye. As the colorant, one kind may be used alone, or two or more kinds may be used in combination.
Examples of inorganic pigments include metal powders (aluminum powder, bronze powder, etc.), carbon salts (carbon black, etc.), oxides (titanium oxide, zinc oxide, red iron oxide, etc.), sulfates (precipitable barium sulfate, etc.). , Carbonates (calcium carbonate, basic magnesium carbonate, etc.), silicates (clay, ultramarine blue, etc.), chromates (yellow lead, etc.), aluminates (cobalt blue, etc.), ferrocyanine compounds (dark blue, etc.) Etc.

Examples of organic pigments include azo pigments (toluidine red, permanent carmine FB, disazo yellow AAA, lake red C, etc.), polycyclic pigments (phthalocyanine blue, indanthrone blue, quinacridone red, etc.), dyed lakes. (Victoria pure blue BO lake, alkali blue toner, etc.), azine pigments, fluorescent pigments and the like.
Examples of the dye include basic dyes, acid dyes, oil-soluble dyes, disperse dyes and the like.

The foaming agent is not particularly limited, and examples thereof include azodicarbonamide (ADCA), azoisobutyronitrile (AIBN), oxybisbenzenesulfonyl hydrazide (OBSH), and paratoluenesulfonyl hydrazide (TSH).

The resin composition for injection molding of the present invention may contain a plasticizer as long as the effect of the present invention is not impaired, but it does not contain a plasticizer from the standpoint of hardly causing burns and having excellent moldability. preferable. Even if the resin composition for injection molding of the present invention contains a plasticizer, the proportion of the plasticizer in the resin composition for injection molding of the present invention is less than 5 parts by mass with respect to 100 parts by mass of the vinyl chloride resin. Is preferred and less than 1 part by mass is more preferred.

Examples of the plasticizer include phthalic acid esters (dimethyl phthalate, diethyl phthalate, dibutyl phthalate, di-n-octyl phthalate, diisodecyl phthalate, diisononyl phthalate, butylbenzyl phthalate, or a carbon number of 11 to 11). Phthalates of higher alcohols of about 13), aliphatic dibasic acid esters (dibutyl adipate, di-n-hexyl adipate, dibutyl sebacate, etc.), phosphoric acid esters (tributyl phosphate, triphosphate) 2-n-ethylhexyl, tricresyl phosphate, triphenyl phosphate, etc.), trimellitic acid esters (trimellitic acid-tri-2-ethylhexyl, trimellitic acid tributyl, etc.), glycol esters (pentaerythritol ester, diethylene glycol) Benzoate etc.), epoxidized esters (epoxidized soybean oil, epoxidized linseed oil etc.), citric acid esters (acetyl tributyl citrate, acetyl trioctyl citrate, tri-n-butyl citrate etc.), tetra-n -Octylpyromellitate, polypropylene adipate, other polyester plasticizers and the like.

The viscosity of the resin composition for injection molding of the present invention at 190° C. and 6.08×10 ³ s ⁻¹ is 1.3×10 ^{2 to} 2.5×10 ² Pa·s, and 1.5×10 2. ^{2 to} 2.2×10 ² Pa·s is preferable. When the viscosity of the resin composition is at least the lower limit value of the above range, burrs, warpage and deformation can be suppressed. When the viscosity of the resin composition for injection molding is not more than the upper limit value of the above range, the flowability of the resin composition is excellent, so that the occurrence of flow marks and weld lines is suppressed, and an injection molded article having an excellent appearance is obtained. Be done.
The viscosity of the resin composition for injection molding can be adjusted, for example, by adjusting the average degree of polymerization of the PVC resin and the content of the lubricant.
The viscosity of the resin composition for injection molding is measured with a capillary rheometer.

The method for producing the resin composition for injection molding of the present invention is not particularly limited, and for example, after mixing with a mixer such as a super mixer, a Henschel mixer, or a ribbon blender, kneading with a Banbury mixer, a mixing roll, an extruder, or the like. It can be manufactured.

[Injection molded product]
The injection-molded article of the present invention is a molded article obtained by injection-molding the above-mentioned resin composition for injection molding of the present invention. The aspect of the injection molded article of the present invention is not particularly limited, except that the resin composition for injection molding of the present invention is used.

The flexural modulus of the injection-molded product is preferably 3000 to 5000 MPa, more preferably 3500 to 4500 MPa. When the bending elastic modulus of the injection-molded product is at least the lower limit value of the above range, the injection-molded product will have high strength, and the injection-molded product will be thin. If the bending elastic modulus of the injection-molded product is at most the upper limit value of the above range, the workability will be excellent. The flexural modulus of the injection-molded product can be adjusted by, for example, the average degree of polymerization of PVC, the content of the modifier or the filler.
The bending elastic modulus of the injection-molded product is measured according to JIS K7171 or ASTM D790.

The pencil hardness of the surface of the injection molded product is preferably HB to 2H, more preferably F to H. When the pencil hardness of the surface of the injection-molded product is at least the lower limit value of the above range, scratches generated on the surface are less noticeable. When the pencil hardness of the surface of the injection-molded product is not more than the upper limit value of the above range, the injection-molded product is flexible and does not crack when bent. The pencil hardness of the surface of the injection-molded article can be adjusted by, for example, the content of the modifier.
The pencil hardness of the surface of the injection-molded product is measured according to JIS K5600.

The Rockwell hardness of the surface of the injection-molded article is preferably 80 to 140, more preferably 100 to 130. When the Rockwell hardness of the surface of the injection-molded product is at least the lower limit value of the above range, the strength of the injection-molded product is excellent. When the Rockwell hardness of the surface of the injection-molded product is at most the upper limit value of the above range, the mold releasability from the mold is excellent. The Rockwell hardness of the surface of the injection-molded article can be adjusted by the content of the plasticizer, for example.
The Rockwell hardness of the surface of the injection-molded product is measured according to JIS K7202.

The injection molded product has a density of preferably 1.5 to 2.0, more preferably 1.6 to 1.9. When the density of the injection molded product is at least the lower limit value of the above range, the strength of the injection molded product is excellent. When the density of the injection-molded product is at most the upper limit value of the above range, the workability of the injection-molded product will be excellent. The density of the injection-molded product can be adjusted by, for example, the content of the filler or the plasticizer.
The density of the injection-molded product is measured according to JIS K7112 or JIS K7222.

The shape of the injection-molded article of the present invention is not particularly limited and can be set appropriately according to the application.
The application of the injection-molded product of the present invention is not particularly limited, and examples thereof include a ceramic product substitute, a metal product substitute, and a wood product substitute. By controlling the pencil hardness, Rockwell hardness, and density of the injection-molded product within the ranges described above, an injection-molded product having physical properties like ceramics can be obtained.

[Method of manufacturing injection molded products]
The method for producing an injection-molded article of the present invention is a method of heating the resin composition for injection-molding of the present invention to 160 to 220°C to perform injection molding.
The method for producing an injection-molded article of the present invention uses the resin composition for injection-molding of the present invention and controls the temperature (injection temperature) of the resin composition for injection-molding injected into a mold to 160 to 220°C. Well-known methods can be adopted. For example, the resin composition for injection molding of the present invention is melt-kneaded in an injection unit of an injection molding machine, injected into a mold at 160 to 220° C., cooled to a predetermined temperature, and then the injection molded product is released from the mold.

As an injection molding machine to be used, it is easy to suppress the occurrence of defects such as resin burns and sink marks due to the generation of gas, and it is easy to obtain an injection-molded article having an excellent appearance. An injection molding machine with a 2.5 full flight screw is preferred. The compression ratio is 2 or more for a standard screw, and is preferably less than 2 for a low compression screw in order to prevent burning of highly viscous resin and generation of gas. Further, the full-flight screw is more preferably one without a check valve, since the resin is less likely to stay and burn is less likely to occur.
The mold of the injection molding machine may be appropriately designed according to the shape of the intended injection molded product.

The injection temperature of the resin composition for injection molding is 160 to 220°C, preferably 170 to 200°C, and more preferably 170 to 190°C. When the injection temperature is at least the lower limit value of the above range, the workability of the injection molded product will be excellent. When the injection temperature is equal to or lower than the upper limit value of the above range, it is possible to suppress burning of the injection molded product and generation of gas.

In the present invention, it is preferable to quench the injection-molded article after molding. A resin composition containing a PVC resin tends to have a high viscosity, but by adopting a heat cycle method in which the surface side is heated to a high temperature to enhance the fluidity and then rapidly cooled after molding, the surface gloss of an injection molded product is improved. Can be improved.

The temperature of the cavity surface of the mold at the time of solidifying the resin composition for injection molding is 20 to 140°C, preferably 30 to 70°C, more preferably 30 to 50°C. When the temperature of the cavity surface is at least the lower limit value of the above range, the fluidity of the resin composition for injection molding is improved and the moldability is excellent. When the temperature of the cavity surface is equal to or lower than the upper limit value of the above range, the injection molded product is excellent in sink mark and deformation.

The method of quenching the injection-molded article is not particularly limited, and examples thereof include a method of bringing the injection-molded article removed from the mold into contact with water to quench it. The mode of bringing the injection-molded product into contact with water is not particularly limited, and examples thereof include a method of immersing the injection-molded product in water.
The temperature of the water contacted with the injection-molded article is preferably 10 to 50°C, more preferably 20 to 40°C.

As described above, in the present invention, the PVC-based resin having an average degree of polymerization of 400 to 1000, barium sulfate, a modifier, a lubricant and a stabilizer are contained, and the compounding amount of barium sulfate is controlled within a specific range. A resin composition for injection molding is used. PVC-based resins have a lower shrinkage rate during molding than PBT resins. In addition, since the deformation and shrinkage of the PVC-based resin is reduced by adding barium sulfate, an injection-molded article having excellent dimensional stability can be obtained. In addition, deformation and shrinkage at the time of molding are reduced, and since a moldability and releasability are excellent due to the addition of a lubricant, it is possible to prevent defects such as sink marks, flow marks, and burns from occurring. An excellent injection-molded product can be obtained. Further, since the PVC resin used is a hard resin, the obtained injection-molded product has excellent durability and weather resistance.

In addition, the injection-molded article of the present invention has high mechanical strength and impact strength, and also has a solid feeling, because barium sulfate is blended. Therefore, for example, it is useful as a substitute for pottery or the like, which has a profound feeling but is prone to breakage such as cracking.

In addition, in injection molding, sink marks are apt to occur when an injection molded product having a portion having a difference in wall thickness is generally produced, and the appearance tends to be deteriorated. However, by using the resin composition for injection molding of the present invention, even when producing an injection-molded product having a portion having a difference in wall thickness, it is possible to sufficiently suppress the occurrence of sink marks and to obtain an injection-molded product having an excellent appearance. Obtainable.
Therefore, the present invention is useful for manufacturing an injection-molded product in which the ratio of the thickness of the thickest part to the thickness of the thinnest part is 1 to 30 times, and the ratio is 2 to 5 times. It is especially useful in the manufacture of goods.

Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following description.
[material]
The raw materials used in this example are shown below.
(PVC resin)
A-1: Product name "TK-700" (vinyl chloride homopolymer, average degree of polymerization: 700, manufactured by Shin-Etsu Chemical Co., Ltd.).
A-2: Product name "TK-500" (a homopolymer of vinyl chloride, average degree of polymerization: 500, manufactured by Shin-Etsu Chemical Co., Ltd.).

(PBT resin)
X-1: Product name "Trecon 1101H" (polybutylene terephthalate, manufactured by Toray Industries, Inc.).

(Barium sulfate)
B-1: Product name “B-54” (barium sulfate, average primary particle size: 1.2 μm, pH: 7.5, manufactured by Sakai Chemical Industry Co., Ltd.).

(Modifier)
C-1: MMA-based copolymer (product name "Metablene P-530A", manufactured by Mitsubishi Chemical Corporation, weight average molecular weight: 3.1 million).

(Lubricant)
D-1: VPN-963 (product name "ester wax", manufactured by Cognis Japan KK).

(Stabilizer)
E-1: Tin-based stabilizer (product name "ADEKA STAB 465E", manufactured by ADEKA Corporation).

[viscosity]
The viscosity of the resin composition at 190° C. and 6.08×10 ³ s ⁻¹ was measured by Capillograph 1D manufactured by Toyo Seiki Seisakusho.

[Example 1]
50 parts by mass of PVC resin A-1, 50 parts by mass of PVC resin A-2, 80 parts by mass of barium sulfate B-1, 8 parts by mass of modifier C-1, 2 parts by mass of lubricant D-1. Parts and 5 parts by mass of the stabilizer E-1 were mixed to obtain a resin composition for injection molding. The viscosity of the obtained injection-molding resin composition at 190° C. and 6.08×10 ³ s ⁻¹ was 1.8×10 ² Pa·s.
Using a injection molding machine equipped with a screw with a standard compression ratio of 2.5, injection molding was performed with the injection temperature at 190°C and the cavity surface temperature of the mold during solidification at 40°C. Obtained.

[Example 2]
An injection molding resin composition was prepared in the same manner as in Example 1 except that the composition was changed as shown in Table 1.
Using an injection molding machine equipped with a full-flight screw (low compression screw) with a compression ratio of 1.8, except that the injection-molded product at 100° C. was demolded after molding and immersed in water at 30° C. to be rapidly cooled. An injection molded product was obtained in the same manner as in Example 1.

[Examples 3 and 4]
An injection molding resin composition was prepared in the same manner as in Example 1 except that the composition was changed as shown in Table 1.
An injection molded product was obtained in the same manner as in Example 1 except that an injection molding machine equipped with a full flight screw (low compression screw) having a compression ratio of 1.5 was used.

[Comparative Examples 1 and 2]
An injection-molding resin composition was prepared in the same manner as in Example 1 except that the composition was changed as shown in Table 1, and an injection-molded article was obtained in the same manner as in Example 2.

[Comparative Example 3]
An injection-molding resin composition was prepared in the same manner as in Example 1 except that the composition was changed as shown in Table 1 to obtain an injection-molded article.

[Comparative Example 4]
The composition was changed as shown in Table 1, and the obtained resin composition for injection molding had a viscosity at 230° C. of 6.08×10 ³ s ⁻¹ of 0.6×10 ² Pa·s, except that A resin composition for injection molding was prepared in the same manner as in Example 1 to obtain an injection molded product.

[Evaluation method]
The evaluation method of each example is as follows.
(Moldability)
Regarding the moldability in injection molding of each example, the moldability (fluidity) at the time of injection molding was evaluated according to the following criteria.
Good: Can be molded without any problem.
Δ: Molding is somewhat difficult (demolding defect, burn defect, product deformation defect).
X: Molding is difficult (demolding defect, burn defect, product deformation defect).

(Appearance of molded product)
The appearance of the injection-molded product of each example was evaluated by visually observing the surface and by the following criteria.
◯: There is no problem in appearance.
Δ: Flow marks, weld lines, and burrs can be confirmed faintly.
X: Flow marks, weld lines, burrs, and poor dispersion of barium sulfate can be confirmed.

(Flexural modulus)
The flexural modulus of the injection-molded article of each example was measured using a tensile/compression/bending tester according to JIS K 7171 at a test speed of 10 mm/min.

(Pencil hardness)
The pencil hardness of the surface of the injection-molded article of each example was measured by using a pencil scratch hardness tester in accordance with JIS K 5600-5-4 under conditions of a load of 750 g at the tip, an angle of 45° at the tip, and a speed of 1 mm/s. It was measured at.

(Rockwell hardness)
The Rockwell hardness of the surface of the injection-molded article of each example was measured by using a Rockwell hardness tester in accordance with JIS K 7202 under R scale conditions.

(density)
The density of the injection-molded product of each example was measured under the condition of method A according to JIS K7112 using an automatic densimeter.

(Molding shrinkage)
The molding shrinkage of the injection-molded product of each example was such that n=10 test pieces molded by a test piece mold of 150 mm×150 mm×3.2 mm were taken, and after 24 hours at 23° C., the test pieces were lengthwise and widthwise. The dimension was measured with a caliper to calculate the shrinkage rate.

Table 1 shows the production conditions and evaluation results of each example.

As shown in Table 1, in Examples 1 to 4 using the resin composition for injection molding of the present invention, the moldability was excellent, and the obtained injection molded products had high mechanical strength and a solid feeling. It had excellent dimensional stability and excellent appearance.
On the other hand, the injection-molded articles obtained in Comparative Examples 1 to 3 which did not contain barium sulfate had a low flexural modulus, an insufficient mechanical strength, a low density, a poor profound feeling, and the same PVC system. The molding shrinkage was high and the dimensional stability was inferior as compared with the examples using the resin. Furthermore, the injection-molded articles obtained in Comparative Examples 1 and 3 had low surface hardness. Further, in Comparative Example 4 in which the PBT resin was used instead of the PVC resin, the deformation after molding was large, the surface hardness was low, the surface was easily scratched, the molding shrinkage rate was high, and the dimensional stability was poor.

Claims (6)

Including vinyl chloride resin having an average degree of polymerization of 400 to 1000, barium sulfate, a modifier, a lubricant and a stabilizer,
A resin composition for injection molding, wherein the ratio of barium sulfate to 100 parts by mass of the vinyl chloride resin is 10 to 300 parts by mass. The resin composition for injection molding according to claim 1, wherein the ratio of the plasticizer to 100 parts by mass of the vinyl chloride resin is less than 5 parts by mass. An injection-molded article comprising the resin composition for injection molding according to claim 1 or 2. A method for producing an injection-molded article, comprising injection-molding the resin composition for injection molding according to claim 1 or 2 at 160 to 220°C. The method for producing an injection-molded article according to claim 4, wherein injection molding is performed using an injection molding machine equipped with a full flight screw having a compression ratio of 1.5 to 2.5. The method for producing an injection-molded article according to claim 4, wherein the injection-molded article after molding is rapidly cooled.