JP2003212942A - Resin material for blow injection molding and blow molded article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blow injection molded article of a polyacetal resin excellent in appearance on the surface of the molded article and stability of its dimensions. <P>SOLUTION: The blow injection molded article comprises a polyacetal resin material wherein a melt flow rate is 5-45 g/10 min and an initiation temperature of crystallization is 140-155°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyacetal resin-based hollow injection molding resin material and a polyacetal resin molding having a hollow portion formed by molding this resin material by a hollow injection molding method. More specifically, the present invention provides a polyacetal resin molded product having a hollow portion having excellent appearance and dimensional stability on the surface of the molded product.

[0002]

2. Description of the Related Art As a method of improving the appearance of a resin molded product (improving the mold transferability), a resin pressure-holding method in which a resin pressure-holding method is applied when injection of a molten resin is completed, or a gas is injected instead of the resin pressure-holding pressure A method (hollow injection molding method) is known. However, in the case of obtaining a molded product having a large wall thickness, the above-mentioned molding method cannot satisfy both the appearance and the dimensional stability.

The hollow injection molding method is a molding method which is performed by combining an injection molding machine and a gas injection device, and a pressurized gas is injected into a mold during or after the injection of molten resin to form a hollow portion. By the molding method in which the molded product is cooled while appropriately maintaining the gas pressure in the hollow portion, the molded product obtained is a hollow molded product. In the resin pressure-holding method, after the gate is sealed, the resin is solidified at the gate portion and the supply of the molten resin is stopped, so that the resin pressure-holding cannot be applied. When the two molding methods are compared, the hollow injection molding method has an advantage that the mold transfer property can be improved because the pressure holding state can be maintained by the pressurized gas even after the gate sealing. Therefore, in the hollow injection molding method, it is easy to obtain a molded article having a good surface appearance because the pressure-holding state can be ensured and the resin content that shrinks with cooling is reduced (the hollow portion expands). However, no matter which polyacetal resin is used, the appearance of the surface of the molded product is not improved, and the dimensional stability cannot be satisfied.

[0004]

Polyacetal resin is an engineering plastic excellent in slidability, heat resistance, chemical resistance, and creep resistance, and is widely used in mechanical parts such as automobile parts and electric / electronic parts. Widely used throughout. Due to the recent advancement of technology, demands for appearance and dimensional stability of polyacetal resin molded products are further increasing. Responding to this is a technical issue. However, since the polyacetal resin is a crystalline resin, it greatly shrinks when it is solidified from the molten state. Therefore, the appearance and dimensional stability of the surface of the molded product cannot be sufficiently satisfied only by the molding method such as the hollow injection molding method.

[0005]

[Means for Solving the Problems] That is, the present invention comprises a polyacetal resin as a main component and has a melt flow rate of 5%.
~ 45g / 10 minutes and the crystallization start temperature is 140 ~ 15
A polyacetal resin-based hollow injection molding resin material having a temperature of 5 ° C. and a polyacetal resin molded product having a hollow portion molded by a hollow injection molding method.

The polyacetal resin as the main component in the present specification means a formaldehyde monomer, or its trimer (trioxane) or tetramer (tetraoxane).
A polyoxymethylene homopolymer obtained by terminal-stabilizing an oxymethylene homopolymer substantially composed of oxymethylene units produced from a cyclic oligomer such as a raw material, and the above raw material and a hindered phenol-based antioxidant. Ethylene oxide, propylene oxide, epichlorohydrin, 1 added at 10 to 500 ppm
-Oxymethylene containing 0.1 to 20% by weight of an oxyalkylene unit having 2 to 8 carbon atoms, which is produced from 3-dioxolane, 1,4-butanediol, cyclic formal such as glycol formal or diglycol formal Examples thereof include a polyoxymethylene copolymer obtained by subjecting an oxyalkylene copolymer to a terminal stabilization treatment.

Further, a mixed composition of a polyacetal resin containing 50% by weight or more of a polyacetal resin and another resin, and a polyacetal resin composition containing a commonly used additive, filler, colorant, etc., or a branched structure 50% by weight or more of an oxymethylene-oxyalkylene copolymer and a polyoxymethylene (POM) block having a molecular chain of less than 50% by weight of a polymer block different from POM containing 50% by weight or more of the repeating unit of oxymethylene. Oxymethylene-based block copolymers such as block polymers are also included.

An oxymethylene-based block copolymer is a linear polymer composed of repeating oxymethylene units, one end of which is represented by the general formula (1) or (2).

[0009]

[Chemical 1]

(R ₁ is selected from hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group and may be the same or different. Also, R ₁ bonded to different carbon atoms may be the same. R ₂ may be the same or different, and R ₂ is selected from an alkyl group, a substituted alkyl machine, an aryl machine, and a substituted aryl machine, m = 2 to 6, and n = 1.
~ 1000) capped with a compound selected from the group consisting of an alkylene oxide addition residue to an alcohol and an alkylene oxide addition residue to a carboxylic acid,
Number average molecular weight excluding terminal groups is 10,000 to 500,000
Is an oxymethylene polymer.

The other resin which can be used as a mixture with the polyacetal resin is not particularly limited as long as it is compatible with the polyacetal resin. For example, olefin compounds such as polyethylene and polypropylene, polystyrene, ABS resin, Polyvinyl chloride, polyamide, polycarbonate, modified polyphenylene ether, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyimide, polyetherimide, polyarylate, polysulfone, polyethersulfone, polyetheresterketone, liquid crystal polymer, polytetrafluoroethylene , A thermoplastic elastomer, a polymer composed of an isocyanate compound and polyalkylene oxide, and the like.

When a mixture composition of a polyacetal resin and another resin is used, the content of the polyacetal resin is 5
It is necessary to be 0% by weight or more, and if the content of the polyacetal resin is too small, the characteristics of the polyacetal resin are impaired, which is not preferable. The olefin compound may be an olefin compound composed of at least one olefin unit represented by the general formula (3).

[0013]

[Chemical 2]

(R ₃ and R ₄ are selected from hydrogen, an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group and an ether group, and they may be the same or different. K =
10-500)

The olefin compound also includes a polyethylene modified by grafting an aromatic vinyl monomer alone or an active hydrogen-containing vinyl monomer. The aromatic vinyl monomer is a vinyl monomer having a benzene ring, and includes alkyl group-substituted styrene such as styrene, methylstyrene, and ethylstyrene.

The active hydrogen-containing vinyl monomer is 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2-hydroxybutyl methacrylate, p-hydroxyphenyl methacrylate, p-hydroxybenzyl methacrylate. , Hydroxyl group-containing esters of α, β-unsaturated carboxylic acids such as glycerin monomethacrylate, polyethylene glycol methacrylate, polypropylene glycol methacrylate, acrylic acid, methacrylic acid, acrylamide, allylamine, and allyl alcohol.

The polyethylene constituting the graft modified product is a polyethylene comprising 90% by weight or more of ethylene units and 10% by weight or less of vinyl monomer units such as butene-1 and propylene. Preferred molecular weight is 2,000-
In the range of 1,000,000 and a specific gravity of 0.91
Those having a melting point of ˜0.98 and a melting point of 100 to 140 ° C. are preferable. Specific examples thereof include polyethylene wax, low-density polyethylene, linear low-density polyethylene, high-density polyethylene, and ultra-high-molecular-weight polyethylene. Low-density polyethylene that is a homopolymer of ethylene having a number average molecular weight of 20,000. Is preferred.

The content of the aromatic vinyl monomer in the graft modified product of the present invention is 20 to the total amount of the graft product.
40% by weight is preferable. More preferably, 2
It is 5 to 35% by weight. The amount of the active hydrogen-containing vinyl monomer based on the total amount of the graft product is preferably 0.1 to 3% by weight. Among the graft modified products in the present invention, preferred is a graft polymer of a styrene-α, β-unsaturated carboxylic acid hydroxyl group-containing ester copolymer onto polyethylene. The amount of the above-mentioned aromatic vinyl monomer alone or polyethylene modified by grafting with an active hydrogen-containing vinyl monomer is 0.5 to 25 parts by weight based on 100 parts by weight of the polyacetal resin.

The polymer obtained by polymerizing an isocyanate compound with a polyalkylene oxide and optionally a low molecular weight diol compound is tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, At least one selected from cyclohexylene diisocyanate, diisocyanate methylhexane, hexamethylene diisocyanate, triphenylmethane triisocyanate, tris (isocyanatophenyl) thiophosphate, and hexamethylene didiisocyanate cyclic trimer. Among these, tolylene diisocyanate , Xylylene diisocyanate, naphthylene diisocyanate, Phenyl methane di Socia sulfonate are preferred, tolylene diisocyanate, diphenylmethane Socia sulfonates are more preferred.

Examples of the polyalkylene oxide include polyethylene glycol having a degree of polymerization of 4 to 1000, a copolymer of ethylene oxide and propylene oxide, a copolymer of ethylene oxide and 1,4-butanediol, and ethylene oxide. Copolymer with tetramethylene glycol, polypropylene glycol, poly-
At least one selected from 1,4-butanediol and polytetramethylene glycol. (The copolymer may be a block copolymer or a random copolymer.) The preferred degree of polymerization is in the range of 10 to 500. The ratio of the polyethylene oxide component to the component other than polyethylene oxide in the polyalkylene oxide component is 40% by weight or more, preferably 60% by weight or more, and more preferably 80% by weight or more.

The low molecular weight diol compound used as required is ethylene glycol, propylene glycol, 1,
4-butanediol, 1,6-hexanediol, polyalkylene oxide having a degree of polymerization of less than 4 (polyethylene glycol, ethylene oxide propylene oxide copolymer, polypropylene glycol, poly 1,4-butanediol, polytetramethylene glycol, etc.) Although they can be used, ethylene glycol, propylene glycol, 1,4-butanediol and 1,6-hexanediol are preferable.

Polymers obtained by polymerizing this isocyanate compound, polyalkylene oxide and optionally a low molecular weight diol compound are disclosed in JP-A-6-144889, JP-A-7-316421 and JP-A-8-
It can be manufactured by the method described in Japanese Patent No. 92476. Specifically, it can be obtained by reacting an isocyanate compound with a polyalkylene oxide and optionally a low molecular weight diol compound using an extruder, a kneader, a Banbury mixer or the like. Reaction temperature is 30 ~
230 ° C., preferably 40-200 ° C., reaction time 1
Minutes to 30 hours, preferably 3 minutes to 5 hours. This reaction may use a solvent, in this case, a solvent such as acetone, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, dioxane, methyl ethyl ketone and toluene, or an organic metal compound such as dibutyltin laurate or dioctyltin laurate, triethylamine or diamine. It is also possible to use urethanization catalysts such as amines such as zabicycloundecene.

The molecular weight of the polymer obtained by polymerizing an isocyanate compound, a polyalkylene oxide and optionally a low molecular weight diol compound is in the range of 10,000 to 500,000 in terms of polystyrene measured by gel permeation chromatography using chloroform as a solvent. The range of 30,000 to 300,000 is more preferable. The above polyacetal resin composition, in the range that does not affect the melt flow rate and the crystallization start time, usual additives, for example, antioxidants, flame retardants, release agents, antistatic agents, colorants, lubricants , Lubricants, plasticizers, heat stabilizers, weathering agents, rust inhibitors, nucleating agents such as boron nitride and talc, glass fibers and beads, potassium whisker titanate,
Compounds that have been conventionally added to polyacetal resins, such as well-stoning agents, reinforcing agents such as calcium carbonate, and pigments can be added.

Specifically, octadecyl-3- (3,5
-Di-t-butyl-4-hydroxyphenyl) propionate, 1,6-hexanediol-bis [3- (3,3
5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate] or triethylene glycol-bis [3- (3-t-butyl-5-methyl-4-hydroxyphenyl) propionate] or the like, a compound containing formaldehyde-reactive nitrogen or a polymer thereof, an alkali metal Or alkaline earth metal hydroxide,
Examples of the heat stabilizer include an inorganic acid salt, a carboxylate, an alkoxide, dicyandiamide, an amino-substituted triazine, and a cocondensation product of amino-substituted triazine and formaldehyde.

Examples of amino-substituted triazines include:
Guanamine (2,4-diamino-sym-triazine), melamine (2,4,6-triamino-sym-triazine), N-butylmelamine, N-phenylmelamine, N, N-diphenylmelamine, N, N-diallyl Melamine, N, N ', N "-triphenylmelamine, N-methylolmelamine, N, N'-dimethylolmelamine, N, N', N" -trimethylolmelamine, benzoguanamine (2,4-diamino- 6-phenyl-sym-triazine).

Also, 2,4-diamino-6-methyl-s
ym-triazine, 2,4-diamino-6-butyl-s
ym-triazine, 2,4-diamino-6-benzyloxy-sym-triazine, 2,4-diamino-6-butoxy-sym-triazine, 2,4-diamino-6-
Cyclohexyl-sym-triazine, 2,4-diamino-6-chloro-sym-triazine, 2,4-diamino-6-mercapto-sym-triazine, 2,4-dioxy-6-amino-sym-triazine (amelite) , 2-oxy-4,6-diamino-sym-triazine (amerine), N, N ′, N′-tetracyanoethylbenzoguanamine and the like.

Examples of the cocondensation product of amino-substituted triazine and formaldehyde include melamine-formaldehyde polycondensation product. Of these, dicyandiamide, melamine and melamine-formaldehyde polycondensates are preferred. Further, as the polymer having a formaldehyde-reactive nitrogen group, a polymer obtained by polymerizing polyamide resin, acrylamide and its derivative or acrylamide and its derivative and other vinyl monomer in the presence of metal alcoholate, acrylamide and its derivative. Alternatively, it may be a polymer obtained by polymerizing acrylamide or a derivative thereof and another vinyl monomer in the presence of radical polymerization, or a polymer containing a nitrogen group such as amine, amide, urea and urethane.

As the polyamide resin, nylon 4-6,
Nylon 6, Nylon 6-6, Nylon 6-10, Nylon 6-12, Nylon 12, etc. and their copolymers,
For example, nylon 6 / 6-6, nylon 6 / 6-6 / 6
-10, nylon 6 / 6-12 and the like. Examples of the polymer obtained by polymerizing acrylamide and its derivative or acrylamide and its derivative and other vinyl monomer in the presence of a metal alcoholate include a poly-β-alanine copolymer. These polymers can be produced by the methods described in JP-B-6-12259, JP-B-5-87096, JP-B-5-47568 and JP-A-3-234729. (3) Acrylamide and its derivative or a polymer obtained by polymerizing acrylamide and its derivative and other vinyl monomer in the presence of radical polymerization can be produced by the method described in JP-A-3-28260. .

The alkali metal or alkaline earth metal hydroxide, inorganic acid salt, carboxylate or alkoxide is, for example, a hydroxide of sodium, potassium, magnesium, calcium or barium, a carbonate of the above metal, Examples include phosphates, silicates, borates, and carboxylates. The carboxylic acid of the carboxylic acid salt is 10 to
These include saturated or unsaturated aliphatic carboxylic acids having 36 carbon atoms, which carboxylic acids may be substituted with hydroxyl groups.

As the saturated aliphatic carboxylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid,
Examples include cerotic acid, montanic acid, melissic acid, and ceroplastic acid. Further, examples of the unsaturated aliphatic carboxylic acid include undecylenic acid, oleic acid, elaidic acid, cetoleic acid, erucic acid, brassic acid, sorbic acid, linoleic acid, linolenic acid, arachidonic acid, propiolic acid and stearolic acid. . Further, examples of the alkoxide include methoxide and ethoxide of the above metals.

The weather resistance (light) stabilizer is preferably a benzotriazole type substance, an oxalic acid anilide type substance and a hindered amine type substance. Examples of the benzotriazole-based substance include 2- (2′-hydroxy-5′-methyl-phenyl) benzotriazole, 2- [2′-hydroxy-3,5-di-t-butyl-phenyl] benzotriazole, 2 -[2'-hydroxy-3,5-di-isoamyl-phenyl] benzotriazole, 2- [2'-
Hydroxy-3,5-bis- (α, α-dimethylbenzyl) phenyl] -2H-benzotriazole, 2-
(2'-hydroxy-4'-octoxyphenyl) benzotriazole etc. are mentioned.

Examples of the oxalic acid anilide type substance include 2-ethoxy-2'-ethyl oxalic acid bisanilide and 2-ethoxy-5-t-butyl-2'-.
Examples thereof include ethyl oxalic acid bisanilide and 2-ethoxy-3′-dodecyl oxalic acid bisanilide. These substances may be used alone or in combination of two or more.

As the hindered amine-based substance, 4-
Acetoxy-2,2,6,6-tetramethylpiperidine, 4-stearoyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-2,2
6,6-Tetramethylpiperidine, 4- (phenylacetoxy) -2,2,6,6-tetramethylpiperidine-
4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-methoxy-2,2,6,6-tetramethylpiperidine, 4-stearyloxy-2,2,6
6-tetramethylpiperidine, 4-cyclohexyloxy-2,2,6,6-tetramethylpiperidine, 4-benzyloxy-2,2,6,6-tetramethylpiperidine, 4-phenoxy-2,2,6,6 6-tetramethylpiperidine, 4- (ethylcarbamoyloxy) -2,
2,6,6-tetramethylpiperidine, 4- (cyclohexylcarbamoyloxy) -2,2,6,6-tetramethylpiperidine, 4- (phenylcarbamoyloxy) -2,2,6,6-tetramethylpiperidine Can be mentioned.

Further, bis (2,2,6,6-tetramethyl-4-piperidine) -carbonate, bis (2,2,2)
6,6-Tetramethyl-4-piperidyl) -oxalate, bis (2,2,6,6-tetramethyl-4-piperidyl) -malonate, bis (2,2,6,6-tetramethyl-4-piperidyl) ) -Sebacate, screw (2,
2,6,6-Tetramethyl-4-piperidyl) -adipate, bis (2,2,6,6-tetramethyl-4-piperidyl) -terephthalate, 1,2-bis (2,2,2)
6,6-Tetramethyl-4-piperidyloxy) -ethane, α, α′-bis (2,2,6,6-tetramethyl-
4-piperidyloxy) -p-xylene.

Furthermore, bis (2,2,6,6-te
Tramethyl-4-piperidyl) tolylene-2,4-dicarbamate, bis (2,2,6,6-tetramethyl-4)
-Piperidyl) -hexamethylene-1,6-dicarbamate, tris (2,2,6,6-tetramethyl-4-piperidyl) -benzene-1,3,5-tricarboxylate, tris (2,2,2) 6,6-tetramethyl-4-piperidyl) -benzene-1,3,4-tricarboxylate and the like. The above hindered amine-based substances may be used alone or in combination of two or more.

Examples of the lubricant include long chain alcohols, low molecular weight alcohols, fatty acids, esters of alcohols and fatty acids, esters of alcohols and dicarboxylic acids, polyalkylene glycols, and silicon compounds. As the ester composed of dicarboxylic acid and aliphatic alcohol, dicarboxylic acid is oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanoic acid, brassylic acid, maleic acid. , Fumaric acid, glutaconic acid, etc., and the aliphatic alcohol is methyl alcohol, ethyl alcohol, propyl alcohol, n-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, n-amyl alcohol, 2-pentanol, n-.
Peptyl alcohol, n-octyl alcohol, n-nonyl alcohol, decyl alcohol, undecyl alcohol, lauryl alcohol, tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, oleyl alcohol, nonadecyl alcohol,
It is an ester composed of saturated / unsaturated alcohols such as eicosyl alcohol, ceryl alcohol, behenyl alcohol, melysyl alcohol, hexyldecyl alcohol, octyldodecyl alcohol, decylmyristyl alcohol, decylstearyl alcohol, and uniline alcohol.

These esters may be monoesters or diesters, and may each contain a small amount of unreacted aliphatic alcohol or dicarboxylic acid during the ester reaction. The ester composed of the dicarboxylic acid and the aliphatic alcohol is a polyacetal resin 10
It is 0.1 to 20 parts by weight with respect to 0 parts by weight. As the silicon compound, low density polyethylene, linear low density polyethylene, high density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, ethylene ethyl acrylate copolymer, polymethylpentene, polypropylene and Polyolefin represented by the following formula (4) is added to a polyolefin resin such as tetrafluoroethylene-ethylene copolymer (these may optionally contain a small amount of a vinyl monomer such as vinyl acetate). Those obtained by graft-polymerizing a silicone compound represented by siloxane are also included.

[0038]

[Chemical 3]

(In the formula, the methyl group is hydrogen, an alkyl group, a phenyl group, an ether group, an ester group or a reactive substituent such as a hydroxy group, an amino group, an epoxy group, a carboxyl group, a carbinol group, a methacryl group or a mercapto group. Group, phenol group, vinyl group, aryl group, polyether group,
It may be substituted with a substituent having a fluorine-containing alkyl group or the like, and it is necessary to have a substituent having a vinyl group or an aryl group, preferably a vinyl group for grafting. In the formula, n represents the average degree of polymerization, and n is in the range of 1,000 to 10,000 from the viewpoint of sliding performance. Further, it is preferable that the content of the cyclic low molecular weight monomer or oligomer is minimized. )

Wollastonite that can be added as a reinforcing material is a finely pulverized natural wollastonite or synthetic wollastonite which is usually present in nature. A bar-shaped product is obtained. These wollastonite may be needle-like or particle-like or may be used in combination thereof, and the particle size thereof is preferably 30 μm or less in terms of volume average particle size from the viewpoint of surface appearance and slidability.

Wollastonite is surface-treated,
Untreated surface-treated ones can be used, but in some cases it is preferable to use surface-treated ones in terms of smoothness and mechanical properties of the molding surface. As the surface treatment agent, conventionally known ones can be used. For example, various coupling agents such as silane-based, titanate-based, aluminum-based, zirconium-based can be used. Specifically N
Examples include-(2-aminoethyl) -3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, isopropyltrisstearoyl titanate, diisopropoxyammonium ethyl acetate and n-butylzirconate.

The pigment includes inorganic pigments and organic pigments. Inorganic pigments are those commonly used for coloring resins, for example, zinc sulfide, zinc oxide, titanium oxide, barium sulfate, titanium yellow, iron oxide, ultramarine blue, cobalt blue, fuel pigment, carbonic acid. It refers to salts, phosphates, acetates, carbon black, acetylene black, lamp black, etc., and organic pigments are condensed azo, isoindoline, disazo, monoazo, anthraquinone,
Heterocyclic pigments, pennon pigments, quinacridone pigments, thioindico pigments, berylylene pigments, dioxazine pigments, phthalocyanine pigments and the like.

The polyacetal resin-based hollow injection molding resin material containing the polyacetal resin as a main component has a melt flow rate of 5 to 45 g / 10 minutes and crystallized from the viewpoints of both appearance and dimensional stability of the molded product. Start temperature is 1
40-155 degreeC. The polyacetal resin molded product having a hollow portion according to the present invention is a polyacetal resin molded product having a hollow portion molded by a hollow injection molding method using the above-described polyacetal resin-based hollow injection molding resin material.

The hollow injection molding method referred to here is to form a hollow portion in the molten resin in the mold cavity by injecting a pressurized gas into the mold during or after the injection of the molten resin. A molding method in which cooling of a molded product is performed while appropriately maintaining the pressure of the pressurized gas in the hollow portion. Explaining the hollow injection molding method further, the injection amount of the molten resin in the hollow injection molding method is a sufficient amount to fill the mold cavity even if it is a full shot in which a sufficient amount is injected to fill the mold cavity. You can use any of the short shots.

The pressurized gas may be any gas as long as it is inert to the polyacetal resin, and examples thereof include inert gases such as nitrogen, helium, neon and argon. Further, in order to prevent decomposition and burn of the polyacetal resin during molding, it is preferable to use a gas containing few impurities. Pressurized gas is injected by the method of introducing the pressurized gas stored in the accumulator into the mold, or by continuously supplying it into the mold with a pump, and installing it in the gas nozzle built into the injection nozzle or the mold. Any method of leading from the gas passage may be used.

When the gas is injected from the gas nozzle built in the injection nozzle, if the gas passage is opened to the spool or runner, the pressurized gas will be injected into the mold cavity through the gate. It is also possible to directly open the mold cavity and pressurize the pressurized gas into the mold cavity. Usually, the molded product is taken out of the mold after the pressurized gas in the hollow part is discharged and the inside of the hollow part is opened to the atmospheric pressure after cooling is completed. Therefore, the hollow part of the molded product according to the present invention is usually at atmospheric pressure, but a molded product in which a pressurized gas is sealed in the hollow part may be used.

The polyacetal resin molded product having a hollow portion of the present invention is a molded product having a hollow portion formed by a hollow injection molding method and has a hollow ratio of 15 to 60%.
The hollow portion of the polyacetal resin molded product having a hollow portion of the present invention is a hollow portion formed by a pressurized gas in hollow injection molding, and is different from a hollow portion formed by so-called voids or foaming. Is. The melt flow rate and the crystallization start temperature defined in the present invention are numerical values measured by the following method. The melt flow rate can be usually measured by a method for evaluating the fluidity of a polyacetal resin, specifically, ISO 1133 ('97) condition D.

On the other hand, the crystallization initiation temperature is the differential calorimeter (D) which is usually used when measuring the melting point of the polyacetal resin.
SC) device. Specifically, an exothermic peak is observed when 5 mg of polyacetal resin material is heated from room temperature to 200 ° C. using DSC-7 manufactured by Perkin Elmer and then cooled. It can be measured by determining the crystallization start temperature at that time.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The hollow injection molding method, the method for measuring the melt flow rate and the crystallization start temperature, and the method for evaluating the dimensional stability of a polyacetal resin molded product having a hollow portion are shown below. The appearance was visually observed and ranked according to ○, ×, and △.

(1) Hollow injection molding method: Nitrogen gas was used as a pressurized gas, and an injection nozzle having a built-in shutoff valve was used for the purpose of preventing backflow of nitrogen gas. Other than that, it was molded under the following molding conditions. Cylinder temperature: 200 ° C Mold temperature: 70 ° C Nitrogen gas pressure: 10 MPa Nitrogen gas pressure injection start time: 0.5 seconds after molten resin injection Nitrogen gas pressure injection time: 10 seconds Gas pressure holding time 25 seconds (2) Melt flow rate: ISO1133 ('97)
It measured according to the condition D.

(3) Crystallization initiation temperature: 5 mg of sample was heated from 30 ° C. to 200 ° C. at a rate of 320 ° C./min,
Hold for 2 minutes. Thereafter, the temperature was lowered to 100 ° C. at a rate of 2.5 ° C./min, and the temperature at which the peak rises when an exothermic peak was observed with crystallization was taken as the crystallization start temperature.
. (4) Hollow ratio: Calculated by the following formula from the apparent volume V of the obtained molded product, the density ρ of the polyacetal resin used, and the mass M of the obtained molded product. Hollow ratio (%) = [(V × ρ-M) / (V × ρ)] × 100 (5) Dimensional stability: difference between the center axis length L (mm) of the molded product and the mold dimension and molding The roundness of the cylindrical part was evaluated.
The roundness was measured using the following device. Roundness RA Roundness RA made by Mitutoyo
-400

(6) Appearance: visually determined ○: No hesitation mark (good) Δ: Longitudinal direction of the surface of the molded product Hesitation mark occurs at a length of about 1/5 x: Longitudinal direction of the surface of the molded product Hesitation marks are generated with a length of 1/5 or more

The abbreviations used in the table are as follows. -Polyacetal resin a-1: Tenac 3010 (manufactured by Asahi Kasei Corporation) melt flow rate 2.8 g / 10 minutes a-2: Tenac 4010 (manufactured by Asahi Kasei Corporation) melt flow rate 10 g / 10 minutes a-3: Tenac 5010 (manufactured by Asahi Kasei Corporation) Melt flow rate 22 g / 10 minutes a-4: Tenac 7010 (manufactured by Asahi Kasei Corporation) Melt flow rate 34 g / 10 minutes a-5: Tenac-C 7520 (manufactured by Asahi Kasei Corporation) Melt flow rate 30 g / 10 min a-6: Tenac-C 9520 (manufactured by Asahi Kasei Corp.) Melt flow rate 70 g / 10 min

Polyacetal block copolymer b-1: The melt flow rate in which the terminal group of the polyacetal homopolymer is a stearyl alcohol group added with propylene oxide (40 mol) and an acetyl group is 1
5 g / 10 min polyacetal block copolymer / olefin compound c-1: liquid ethylene-propylene copolymer (ethylene / propylene = 50/50 molar ratio, degree of polymerization (n) = 55) c-2: ethylene-butene copolymer Combined (melt flow rate 70g / 10min, Mw = 2500)

Polyethylene d-1: Graft polymer of low-density polyethylene having Mn = 30,000 and styrene (28% by weight) -2-ethylhexyl methacrylate (2% by weight) / ester compound e-1: cetyl millimeter State e-2: Dilauryl adipate

Polymer f-1 obtained by polymerizing an isocyanate compound, a polyalkylene oxide and optionally a low molecular weight diol compound: 90 parts by weight of polyethylene glycol having an average molecular weight of 6000 and polyoxyethyleneoxypropylene glycol having an average molecular weight of 8500 ( 120 parts by weight of polypropylene glycol having an average molecular weight of 1700 and ethylene oxide added thereto and 7 parts by weight of 4-4'-diphenylene methane diisocyanate were reacted at 160 ° C for 2.5 hours using a kneader having a volume of 5 liters. It was The polystyrene conversion molecular weight of the obtained resin measured by gel permeation chromatography (chloroform solvent) was 58,000.

Silicon compound g-1: Silicon-g-EMMA (silicon = 60 wt%) Inorganic filler h-1: Wollastonite (volume average particle diameter 3 μm,
Granules with aspect ratio of 3) Others i-1: Synthetic higher alcohol (molecular weight = 425)

[0058]

Examples 1 to 6 and Comparative Examples 1 to 3 As shown in Tables 1 and 2, polyacetal resin materials having different melt flow rates and crystallization start temperatures are melted in a cylinder of an injection molding machine, and mold cavitation is performed. It was injected at (1 point at the gate). The cylinder temperature and the mold temperature at this time were 190 ° C. and 80 ° C., and the hollow ratio was changed while changing the measured value of the molten resin, and molding was performed. Nitrogen gas was used as the pressurized gas, a shut-off valve was provided to prevent the gas from flowing back into the injection cylinder, and the gas was injected from the gas nozzle incorporated in the injection nozzle.

The pressurization of pressurized gas is 150 kg of nitrogen gas.
The pressure was increased to / cm ² and stored in an accumulator, and 1 second after the molten resin was injected, it was sent to the mold from the gas nozzle and transferred to the mold. Gas injection time and pressure holding time 5 seconds, 6
It was set to 0 seconds. The mold opening was performed 5 seconds after discharging the pressurized gas in the hollow portion and after the pressure holding time was completed. The appearance and dimensional stability of the obtained molded product were measured. The drawing shown in FIG. 1 is a cross section of the obtained molded product, and the central part of the molded product shows a hollow portion. The results are shown in Tables 1 and 2.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

EFFECTS OF THE INVENTION A molded product obtained by hollow injection molding using the polyacetal resin-based hollow injection molding resin material of the present invention has excellent surface appearance and dimensional stability (roundness), and is a resin cap component. The present invention provides a material and a molded product effective for a molded product used for the purpose of sealing a liquid such as a solution, a liquid such as a solvent and a gas.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a molded product obtained in Examples 1 to 6 in a state of being axially cut.

FIG. 2 is a cross-sectional view of the molded product obtained in each of Examples 1 to 6, taken in a direction perpendicular to the axial direction.

[Explanation of symbols]

1: Hollow part

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 59:00 C08L 59:00

Claims (2)

[Claims] 1. A polyacetal resin-based hollow injection molding resin material comprising a polyacetal resin as a main component, a melt flow rate of 5 to 45 g / 10 minutes, and a crystallization initiation temperature of 140 to 155 ° C. 2. A polyacetal resin molded article comprising the polyacetal resin material according to claim 1 and having a hollow portion formed by a hollow injection molding method.