JP2003175525A - Method for gas pressed injection molding and molded product thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an acceptable injection molded product of polytrimethylene terephthalate which is a crystalline resin, low in melt flow viscosity, high in rate of contraction by molding and prone to surface sinking. <P>SOLUTION: A method for a gas pressed injection molding which is characterized in that; filling in a cavity of a die by injecting a molten thermoplastic resin composition comprising polytrimethylene terephthalate as the main component, pressing a compressed gas into the cavity between a back side of the molded product and a corresponding cavity surface of the die in a gas press-in area and, push a surface of the molded product against the cavity surface of the die; in the injection molding of the molded product which has a protruded heavy-walled part in its back side. <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 an injection molding method, and more particularly, to gas pressurization involving pressurization of a pressurized gas between a resin injected into a mold cavity and a mold cavity surface. The present invention relates to an injection molding method and a molded article molded by the method.

[0002]

2. Description of the Related Art Generally, in injection molding, when molding a molded product having a thick portion protruding to the back surface (non-designed surface) side, the thick portion on the back surface side is accommodated by shrinkage of the resin due to cooling. It is widely known that a depression called a sink mark is formed on the surface (design surface) side of a molded product. The polytrimethylene terephthalate used in the present invention is a crystalline resin, has a low viscosity during melt flow, has a large molding shrinkage ratio, and is susceptible to sink marks. Conventionally, the most common measure to prevent sink marks is to increase the injection pressure, extend the injection time, and cool the resin in the mold cavity to some extent while applying the supply pressure of the molten resin (resin pressure method). Has been.

However, the sinking prevention by the resin pressurizing method described above is complicated because the molding conditions are different depending on the thickness of the molded product and the like, and the sinking cannot be sufficiently prevented unless a high resin pressure is applied. However, it causes burr on the parting surface, and there is a problem that the work burden of removing the burr increases. Further, when excessive resin pressure is applied, there is a problem in dimensional accuracy that warpage occurs in the molded product (for example, refer to Patent Document 1). Further, in the resin pressurization method, pressure can be easily transmitted to the thick wall portion near the gate, but sufficient pressure is not applied to the thick wall portion distant from the gate portion, and depending on the position of the thick wall portion, the pressure may not be completely applied. It happens that the sink cannot be eliminated. Therefore, after injecting general molten resin into the mold cavity, one side of the molded product is pushed up by the valve body to form a void between the one side of the molded product and the core molding this one side. Then, a gas pressure injection molding method has been proposed in which a pressurized gas is pressed into this void and the other surface of the molded product is brought into pressure contact with the corresponding die cavity surface (see, for example, Patent Document 1). ). In addition, there is an example showing a similar gas pressure injection molding method (for example, refer to Patent Document 2).

[0004]

[Patent Document 1] Japanese Patent Laid-Open No. 50-75247

[Patent Document 2] Japanese Unexamined Patent Publication No. 10-156861

[0005]

In recent years, the demand for large-sized molded articles such as housings for office automation equipment and household electric appliances, as well as automobile parts has increased, and thinning of the molded articles has been attempted to reduce the cost of the products. Demand is growing. In the case of a thin, large-sized molded product, it is usual to provide a reinforcing portion generally called a rib or a boss on the back surface in order to maintain the strength. The thicker the ribs and bosses are, the higher the reinforcing effect is, and the flow assisting effect that allows the resin to be easily filled in the mold is also obtained. When injection molding is performed using a thermoplastic resin composition containing polytrimethylene terephthalate as the main component, which has a large molding shrinkage ratio, if thick ribs or bosses are provided, the surface of the molded product corresponding to the ribs or bosses will be damaged. , Appearance problems are likely to occur. Thin and large molded products, which are in high demand in recent years, are equipped with thick ribs and bosses to maintain the required strength. Preventing sink marks when such thick ribs and bosses are provided. Technology is required. An object of the present invention is to prevent sink marks in an injection-molded article having a thick portion of a thermoplastic resin composition containing polytrimethylene terephthalate as a main component, which has a large molding shrinkage ratio and is susceptible to sink marks.

[0006]

Means and Actions for Solving the Problems That is, the present invention is as follows. In injection molding of a molded product having a thick part protruding to the back side, while removing the gas in the mold cavity from the atmosphere opening path that opens in a part of the mold cavity surface, the melted polytri A thermoplastic resin composition containing methylene terephthalate as a main component is injection-filled, and then a pressurized gas is injected between the back surface of the molded article and the corresponding mold cavity surface in the gas injection area to form a gas injection area. 1. The gas pressure injection molding method, characterized in that the surface of the molded product corresponding to is pressed against the mold cavity surface corresponding thereto. 2. The gas pressure injection molding method according to 1 above, in which an excessive amount of molten resin is injected into the mold cavity as compared with the volume of the mold cavity. The amount of the molten resin injected into the mold cavity is 101 to 110% by weight when the weight of the molten resin corresponding to the volume of the mold cavity is 100% by weight. Pressure injection molding method,

4. 4. The gas pressure injection molding method according to any one of 1 to 3 above, wherein a resin holding pressure is applied after the injection of the molten resin. 5. The gas pressure injection molding method as described in 4 above, wherein a resin holding pressure is applied even when pressurizing gas is injected. Pressurized gas is pressed between the back surface of the molded product and the corresponding mold cavity surface in the gas injection region, and the surface of the molded product corresponding to the gas injection region is pressed against the corresponding mold cavity surface. 6. The method for gas pressure injection molding according to any one of 1 to 5 above, wherein a hollow gas is formed by injecting a pressurized gas into the molten resin filled in the mold cavity. A molded product molded by the method according to any one of 1 to 6 above.

The present invention will now be described in detail. The thermoplastic resin composition containing polytrimethylene terephthalate as a main component of the present invention means polytrimethylene terephthalate
It is a thermoplastic resin containing 0% by weight or more, preferably 20% by weight or more, and more preferably 30% by weight or more. As the substance constituting the thermoplastic resin, in addition to polytrimethylene terephthalate, polycarbonate, polyphenylene ether, ABS resin,
Various thermoplastic resins generally used for injection molding, such as polybutylene terephthalate, polyethylene terephthalate, polystyrene, rubber-reinforced polystyrene, and polyamide.
Various thermoplastic elastomers composed of ethylene-α-olefin copolymers, various fiber reinforcements such as glass fiber and carbon fiber, talc, mica, kaolin, calcium carbonate,
Inorganic powder filler such as wollastonite, combined use of fibrous reinforcement and powder reinforcement, halogen-based flame retardant such as brominated polystyrene, non-halogen flame retardant such as ammonium polyphosphate, melamine polyphosphate, etc. And the like.

If necessary, known additives generally used in the past, such as antioxidants, heat stabilizers, ultraviolet absorbers, release agents, lubricants, pigments, dyes, etc. may be added. Good. Examples of polymers to be blended with polytrimethylene terephthalate as a component of the polymer alloy include polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, ABS.
Resins are preferable, and polycarbonate is particularly preferable.

Although the present invention is used for general extrusion molding, a thermoplastic resin having poor fluidity for injection molding, a thermoplastic resin having a too large molecular weight for injection molding, and the like can be preferably used. In general, the higher the molecular weight, the better the chemical resistance and impact resistance of the molded product, but the fluidity at the time of molding deteriorates and injection molding becomes difficult. High molecular weight polymers are commonly used in extrusion because they do not require as high a fluidity as injection molding, and high molecular weight polymers used in these extrusions and not in injection molding in the present invention. Can be used well. As the reinforcing material, glass fiber, carbon fiber, and inorganic powder filler are preferable. Next, each of the particularly preferred components constituting the present invention,
Polytrimethylene terephthalate and polycarbonate will be described in detail.

<Polytrimethylene terephthalate> Polytrimethylene terephthalate (hereinafter referred to as P in the present invention)
It may be abbreviated as TT. ) Is a polyester polymer using mainly terephthalic acid as an acid component and trimethylene glycol as a glycol component. Examples of acid components other than terephthalic acid include aromatic dicarboxylic acids other than terephthalic acid, such as phthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylmethane. Dicarboxylic acids, diphenyl ketone dicarboxylic acids, diphenyl sulfone dicarboxylic acids, etc .; Aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, etc .; Alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; ε-oxycaproic acid, hydroxybenzoic acid, Examples thereof include oxydicarboxylic acids such as hydroxyethoxybenzoic acid. The terephthalic acid content is preferably 80 mol% or more of the acid component.

As trimethylene glycol, 1,3
-Propanediol, 1,2-propanediol, 1,
It is selected from 1-propanediol, 2,2-propanediol or a mixture thereof, but from the viewpoint of stability, 1,3-propanediol is particularly preferable, and 80 mol% or more of the glycol component is preferable. Examples of other glycol components include ethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, neopentyl glycol, cyclohexanedimethanol, xylylene glycol, diethylene glycol, polyoxyalkylene glycol and hydroquinone. .

The above-mentioned polyesters include branched components such as tricarballylic acid, trimesic acid, trimellitic acid, and other trifunctional or tetrafunctional ester-forming acids or glycerin, trimethylolpropane, pentaerythritol, and the like. The trifunctional or tetrafunctional ester-forming alcohol may be copolymerized, in which case the amount of the branching component is 1.0 mol% of the total dicarboxylic acid component.
It is preferably 0.5 mol% or less, more preferably 0.3 mol% or less. Further, PTT may be a combination of two or more of these copolymerization components.

The method for producing PTT used in the present invention is as follows:
Although not particularly limited, for example, JP-A-51-1
40992, JP-A-5-262862, JP-A-8-311177, and the like, and terephthalic acid or its ester-forming derivative (for example, lower alkyl ester such as dimethyl ester, monomethyl ester) Trimethylene glycol or an ester-forming derivative thereof is heated and reacted in the presence of a catalyst at a suitable temperature / time, and the resulting glycol ester of terephthalic acid is subjected to a desired polymerization at a suitable temperature / time in the presence of a catalyst. A method in which the polycondensation reaction is performed up to a certain degree is included. The PTT of the present invention has a number average molecular weight of 5,000.
It is preferably 100 to 100,000, and Mw / Mn showing a molecular weight distribution is preferably 1.2 to 4.5. Furthermore, a molecule having a molecular weight of 100,000 or more is 1
˜20% is preferable.

The number average molecular weight and the molecular weight distribution can be measured by, for example, an osmotic pressure method, a terminal quantitative method, or a GPC method (gel permeation chromatography). Specifically, Tosoh Corp. HLC-8120 is used as a measuring device, and Showa Denko HFI is used as a column.
P804-803 (two 30 cm columns), hexafluoroisopropanol (hereinafter referred to as HFIP) as a carrier, and PMMA manufactured by Polymer Laboratory as a standard sample, at a temperature of 40 ° C. and a flow rate of 0.5 ml / min. You can Further, the polytrimethylene terephthalate of the present invention may be a mixture of polytrimethylene terephthalate and another polyester resin such as polyethylene terephthalate or polybutylene terephthalate as long as the characteristics thereof are not impaired.

<Polycarbonate> The polycarbonate resin used in the present invention has a main chain composed of a repeating unit represented by the following formula (1). -(O-Ar-O-CO)-(1) (In the formula, Ar is a divalent aromatic residue, for example, phenylene, naphthylene, biphenylene, pyridylene, or
Examples thereof include groups represented by the following formula (2). ) -Ar ¹ -Y-Ar ^2- (2) (In the formula, Ar ¹ and Ar ² are each an arylene group, and for example, represent a group such as phenylene, naphthylene, biphenylene, and pyridylene. Y is an alkylene group or It is a substituted alkylene group.) Further, a divalent aromatic residue represented by the following formula (3) may be contained as a copolymer component. -Ar ¹ -Z-Ar ^2- (3) (In the formula, Ar ¹ and Ar ² are the same as those in the formula (2). Z is a mere bond, or -O-, -CO-, -S-, -SO.
_{2 -, - CO 2 -,} - CON (R 1) - (R 1 are each independently a hydrogen atom, a lower alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, 6 carbon atoms ~ 3
It is an aryl group having 0 or an aralkyl group having 7 to 31 carbon atoms, which may be optionally substituted with a halogen atom or an alkoxy group having 1 to 10 carbon atoms. ) Is a divalent group. ) Examples of these divalent aromatic residues include those represented by the following formula.

[0017]

[Chemical 1]

(In the formula, R ⁷ and R ⁸ are each independently hydrogen, halogen, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms, or It is an aryl group having 6 to 30 carbon atoms.
m and n are integers of 1 to 4, and when m is 2 to 4, each R
⁷ may be the same or different, and n
When R is 2 to 4, each R ⁸ may be the same or different. Among these, a group represented by the following formula (4) is a preferred example.

[0019]

[Chemical 2]

In particular, the group represented by the above formula (4) is an Ar group.
A polycarbonate containing 85 mol% or more of the repeating units (based on all the monomer units in the polycarbonate) is particularly preferable. The polycarbonate that can be used in the present invention may contain a trivalent or higher aromatic residue as a copolymerization component. The molecular structure of the polymer terminal is not particularly limited, but one or more terminal groups selected from a phenolic hydroxyl group, an aryl carbonate group and an alkyl carbonate group can be bonded. Among these, phenolic hydroxyl group, phenyl carbonate group,
Pt-butylphenyl carbonate group, p-cumylphenyl carbonate and the like are preferable as the terminal structure.

In the present application, the ratio of the terminal of the phenolic hydroxyl group to the other terminal is not particularly limited, but from the viewpoint of obtaining better color tone and mechanical properties, the ratio of the terminal of the phenolic hydroxyl group is 20 of the total number of terminal groups. % Or more, and preferably 80% or less from the viewpoint of thermal stability during melting. The phenolic hydroxyl group terminal amount is generally measured using NMR (NM
R method) or a method using titanium (titanium method)
Alternatively, it can be determined by a method of measuring using UV or IR (UV method or IR method).

The weight average molecular weight (Mw) of the polycarbonate resin used in the present invention is generally 5,000 to 20.
It is preferably in the range of 10,000, more preferably 10,000 to 60,000, still more preferably 15,000 to 40,000, and particularly preferably 18,000 to 30,000. The weight average molecular weight (Mw) is measured by gel permeation chromatography (GPC), and the measurement conditions are as follows. That is, using tetrahydrofuran as a solvent and polystyrene gel, the conversion molecular weight calibration curve according to the following equation is used to determine from the constitutional curve of standard monodisperse polystyrene. ^{_{M PC = 0.3591M PS 1.0388 (M}} PC, M PS , respectively polycarbonate, weight average molecular weight of polystyrene)

The polycarbonate resin used in the present invention may be one produced by a known method. Specifically, for example, a known method of reacting an aromatic dihydroxy compound and a carbonate precursor, for example, reacting an aromatic dihydroxy compound and a carbonate precursor (for example, phosgene) in the presence of an aqueous sodium hydroxide solution and a methylene chloride solvent. The crystallized carbonate prepolymer obtained by the interfacial polymerization method (eg, phosgene method), the transesterification method (melting method) in which an aromatic dihydroxy compound is reacted with a carbonic acid diester (eg, diphenyl carbonate), or the phosgene method or the melting method is solidified. Phase polymerization method [JP-A-1-158033 (corresponding to US Pat. No. 4,948,871), JP-A-1-27)
1426, JP-A-3-68627 (corresponding to US Pat. No. 5,204,377)] and the like are used.

The preferred polycarbonate resin is
A polycarbonate resin containing substantially no chlorine atom, which is produced from a dihydric phenol (aromatic dihydroxy compound) and a carbonic acid diester by a transesterification method can be used. In the present invention, it is also possible to use two or more different polycarbonate resins having different structures and molecular weights in combination. The composition of the polycarbonate resin is preferably 90% by weight or less based on the total amount of the alloy. It is more preferably 70% by weight or less, and most preferably 50% by weight.
It is less than or equal to wt.

<Glass Fiber> The glass fiber in the present invention is not particularly limited as long as it is one usually used in polyester resins. The number average length of glass fibers in the composition (hereinafter referred to as L), the number average fiber diameter (hereinafter referred to as D), and the ratio of L to D (hereinafter referred to as L / D) are not particularly limited, but L Is preferably 100 μm or more and L / D is 20 or more. The glass fiber content is preferably 70% by weight or less of the total amount of the polytrimethylene terephthalate resin composition from the viewpoint of the surface appearance of the molded product. or,
As the glass fiber of the previous term, those subjected to surface treatment are particularly preferably used. The surface treatment is performed using a known coupling agent or film forming agent. Examples of coupling agents that are preferably used include silane coupling agents and titanium coupling agents.

As the silane coupling agent, triethoxysilane, vinyltris (β-methoxy-ethoxy) silane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (1,1) -Epoxycyclohexyl) ethyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyl Trimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyl-tris (2-methoxy-ethoxy) silane, N-methyl-γ-aminopropyltrimethoxysilane, N-vinyl Benzyl-γ-a Minopropyltriethoxysilane, triaminopropyltrimethoxysilane,
3-ureidopropyltrimethoxysilane, 3-4,5
Examples thereof include dihydroimidazolepropyltriethoxysilane, hexamethyldisilazane, N, O- (bistrimethylsilyl) amide, N, N-bis (trimethylsilyl) urea and the like.

Among these, γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (1,1-epoxycyclohexyl) ) Aminosilanes such as ethyltrimethoxysilane and epoxysilanes are preferably used. Titanium-based coupling agents include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, tetraisopropyl bis (dioctyl phosphate) titanate, tetraoctyl bis (ditridecyl phosphite) titanate, Tetra (1,1-diallyloxymethyl-1-butyl) bis (ditridecyl) phosphite titanate, bis (dioctylpyrophosphate) oxyacetate titanate, bis (dioctylpyrophosphate) ethylene titanate, isopropyl trioctanoyl titanate,
Isopropyl dimethacryl isostearoyl titanate, isopropyl isostearoyl diacrylic titanate, isopropyl tri (dioctyl phosphate) titanate, isopropyl tricumyl phenyl titanate,
Isopropyltri (N-amidoethyl, aminoethyl)
Examples thereof include titanate, dicumylphenyloxyacetate titanate, diisostearoyl ethylene titanate and the like.

As the film forming agent, urethane type polymer, acrylic acid type polymer, maleic anhydride and ethylene, styrene, α-methylstyrene, butadiene, isoprene, chloroprene, 2,3-dichlorobutadiene,
Examples thereof include copolymers with unsaturated monomers such as 1,3-pentadiene and cyclooctadiene, and polymers such as epoxy-based polymers, polyester-based polymers, vinyl acetate-based polymers and polyether-based polymers. Among these, epoxy-based polymers, urethane-based polymers, acrylic acid-based polymers, butadiene maleic anhydride copolymers, ethylene-maleic anhydride copolymers, styrene-maleic anhydride copolymers, and mixtures thereof are preferably used.

The object to be molded according to the present invention is a molded product having a thick portion protruding toward the back surface, which is likely to cause sink marks on the surface. The thick portion includes, for example, locally protruding thick portions such as ribs and bosses, as well as regions where the thickness varies in a certain wide range. In the present invention, the recess on the back surface side of the molded product which is adjacent to the thick portion or includes the thick portion is referred to as a gas injection region. The recess serving as the gas press-fitting region is provided auxiliary to form, for example, a thick portion such as a reinforcing rib, a side wall of the molded product, a curved portion of the molded product, and a recess serving as the gas press-fitting region. It is a region surrounded by auxiliary ribs and the like. The mold used in the present invention is one in which the atmosphere opening path is opened in a part of the mold cavity in a region other than the above-mentioned gas injection region. The atmosphere open path connects the mold cavity to the atmosphere, and when the mold cavity is filled with the molten resin, air and the like (air and / or gas generated from the molten resin composition in the mold cavity). Etc.) is discharged to the outside of the mold.

The air release path may use the gap left on the parting surface of the mold as it is,
In order to smoothly discharge the gas in the cavity, it is preferable to provide it as a groove formed on the parting surface of the mold, and it is particularly effective to open it near the flow end of the molten resin. can get. Also, the atmosphere opening path should be opened at a position where the side opposite to the opening side is the gas injection region when the molten resin is filled in the mold cavity, specifically, the cavity surface on the surface side of the molded product. Is desirable. In the present invention, by using a mold with good gas release as described above, preferably by injecting and filling a molten resin having an excessively low melt viscosity with respect to the volume of the mold cavity, the purpose of forming a parting surface, etc. It is possible to obtain a gas sealability of the pressurized gas that can obtain a sufficient sink-preventing effect without taking a structure for sealing.

That is, according to the present invention, when the molten resin is injected and filled, the molten resin can be filled into the die cavity while smoothly discharging the air in the die cavity out of the die. It is possible to prevent air or the like from being trapped between the mold cavity surfaces. In addition, the air inside the mold cavity can be discharged smoothly,
By injecting and filling an excessive amount of molten resin having a low melt viscosity with respect to the mold cavity volume, the molten resin can be filled into every corner of the mold cavity, and the resin in the mold cavity and the mold cavity surface Adhesion is improved. Therefore, the gas injection region can be a closed region in which the pressurized gas injected between the resin in the region and the mold cavity surface is unlikely to leak, and the gas at the time of injecting the pressurized gas into the gas injection region described below can be used. It is possible to prevent leakage. That is, according to the present invention, a gas leak necessary for sink mark prevention is prevented by using an unsealed mold and by injecting and filling a molten resin having an excessively low melt viscosity as compared with the mold cavity volume. You can

In the present invention, the excess amount of molten resin relative to the mold cavity volume means the amount of molten resin in which the volume of the molten resin becomes larger than the mold cavity volume,
Preferably, the weight of molten resin corresponding to the mold cavity volume is 1
An amount of 101 to 110% by weight when set to 00% by weight,
The amount is more preferably 103 to 107% by weight. If the amount of molten resin to be injected and filled is too small, it will be difficult to set the gas injection region as a closed region. Conversely, if the amount of molten resin to be injected and filled is too large, burrs on the parting surface and warpage will reduce the dimensional accuracy. It tends to occur.

The pressurization of the pressurized gas is such that the molten resin does not enter at the time of injection, but a pin that forms a slit-shaped gap that allows the pressurized gas to pass therethrough, a sintered body, and a valve body having a poppet mechanism. Etc. are available. The method using a fixing pin that forms a slit-shaped gap is most suitable. Further, as the fixing pin, it is also possible to use a portion around the ejector pin that does not move when the pressurized gas is pressed. In the method according to the present invention, after the molten resin is filled in the mold cavity by injecting the molten resin, the resin holding pressure is continuously performed within the range where burrs are not generated on the parting surface. The leakage prevention effect can be enhanced.

In conventional gas-assisted injection in which a pressurized gas is injected into a molten resin, resin holding pressure is rarely used in combination in order to smoothly inject the pressurized gas. However, when resin holding pressure is used in combination with the method of the present invention, it is possible to prevent unnecessary backflow of the resin to the runner and the nozzle portion at the time of pressurizing the pressurized gas, thereby preventing unnecessary shrinkage near the resin gate portion. It has been found that this makes it possible to more effectively prevent the pressurized gas from leaking out of the mold. It was also found that the amount of narrowing down of the root of the thick portion (hereinafter referred to as "squeeze") by pressurization of pressurized gas can be controlled by the resin holding pressure.

Further, when the resin holding pressure is used together with the gas pressurization, the entire molded product can be pressed uniformly against the mold, so that unnecessary residual stress is unlikely to remain in the molded product, which causes a problem in ordinary injection molding. It was found that the occurrence of warp and the like can be prevented. The resin holding pressure is effective whether a normal cold runner die or a hot runner die is used. In the case of a hot runner, if a hot runner having a valve element having an opening / closing function, which is generally called a valve gate, is used, it is possible to prevent gas from entering the hot runner portion, and at the same time, prevent backflow of resin. It is effective.

In the present invention, the pressurized gas is press-fitted between the back surface of the molded product in the gas press-fitting region and the corresponding mold cavity surface, and the surface of the molded product corresponding to the gas press-fitting region corresponds to this. Pressurized gas that is press-fitted into the gas press-fitting region or provided separately inside the molten resin filled in the mold cavity tee (particularly inside the resin that constitutes the thick wall portion) while being pressed against the mold cavity surface. It is also possible to form a hollow portion by injecting a pressurized gas from the pressurized gas inlet.

When the hollow portion is formed as described above,
It is possible to synergistically obtain the advantages of the gas pressure injection molding method and the advantages of the gas assist injection. Specifically, since the pressurized gas is injected into the molded product, especially in the thick part, while the surface of the molded product is pressed against the cavity surface corresponding thereto by the pressurized gas, the thick part and the thin part The difference in the pressing force to the cavity surface of the mold between and the second transfer is less likely to occur due to the introduction of the pressurized gas into the resin.

Therefore, it is possible to eliminate the uneven gloss and luster that occur between the surface corresponding to the thick portion and the other surface, which is a problem in the conventional gas-assisted injection. In addition, the pressurized gas injected into the thick portion is less likely to squeeze out into the thin portion, and it is possible to prevent a defective appearance due to the squeeze out of the pressurized gas. In particular, when a molded product of crystalline resin was molded by ordinary gas-assisted injection in which a pressurized gas was injected into the molten resin, the gas easily spilled out from the thick part to the thin part, but there was a problem in appearance. According to the method involving the formation of the hollow portion, the appearance can be significantly improved.

Furthermore, since sink marks can be prevented by both the pressurized gas press-fitted between the back surface of the molded product and the corresponding mold cavity surface and the pressurized gas injected into the molded product, sink marks are prevented. Will be certain. The mold temperature in the present invention can be the normal mold temperature of the thermoplastic resin composition containing polytrimethylene terephthalate as a main component used in the present invention, but a molded article having a higher appearance and no sink marks. For molding, it is preferable to set the temperature higher than the mold temperature used in ordinary injection molding.

Further description will be given below with reference to the drawings. FIG. 1 is a sectional view showing an example of a mold 1 used in the present invention. As shown in the figure, the mold 1 is composed of a fixed mold 2 and a movable mold 3, and a mold cavity 4 filled with molten resin at the time of molding is formed between them. FIG. 2 shows a molded product 20 produced by the mold 1.
(A) is a perspective view and (b) is a plan view. Molded product 20
Is a box-shaped one having two side wall parts 14a to 14d in the periphery and two thick parts (reinforcing ribs) 13 provided across the base part 24 on the bottom surface, and the inside is the back surface (non-). The design surface) and the outside are the surface (design surface). In addition, the side wall portions 14a to 14
The enclosed recess (the entire inside of the molded product 20) is the gas press-fitting region 25, and the thick portion 13 is included in the gas press-fitting region 25. Reference numeral 26 indicates a gas injection port formed by a gas injection pin 8 described later.

A groove is formed on the fixed mold 2 side of the parting surface to form an atmosphere open path. The atmosphere open path 5 is a molded product 2 formed in the mold cavity 4.
The mold cavity surface 4a corresponding to the surface of No. 0 is open, and the mold cavity surface 4a side is open to the atmosphere. At least the opening to the mold cavity 4 or the vicinity thereof is not exposed to the resin when the molten resin is injected into the mold cavity 4, and the atmosphere opening path 5 is provided inside the mold cavity 4. Air mold 1
It has a thickness that can be discharged to the outside. This thickness depends on the type of resin and molding conditions, but is generally 1 /
It is preferably 200 mm or more and 1/10 mm or less, more preferably 1/100 mm or more and 1/10 mm or less, and further preferably 3/100 mm or more and 7/100 m.
m or less.

On the other hand, on the mold cavity surface 4b side corresponding to the back surface of the molded product 20, the ejector pin 6 connected to the atmosphere.
The circumference is sealed by an O-ring 7a, and there is no opening of the atmosphere opening path 5, and communication with the atmosphere is blocked. A gas injection pin 8 is provided on the mold cavity surface 4b side. The gas injection pin 8 is embedded in the mold 3 on the moving side with its tip facing the mold cavity surface 4b into the mold cavity 4, and a pressurized gas source (illustrated in the figure) is provided via a valve 9a. The pressurized gas sent from the gas introduction path 10a connected to the mold cavity 4 is supplied to the mold cavity 4 through the gap left between the movable mold 3 and the mold. In the figure, 7b is an O for preventing pressurized gas from escaping from the joint of the mold constituent members.
It's a ring.

The parting surface of the mold 1 shown in the figure is
It is located along the outer surface of the base portion 24 of the box-shaped molded product 20, and the atmosphere opening path 5 is the mold cavity surface 4a corresponding to the surface of the molded product 20 and is the base portion 24 of the molded product 20. It has an opening at a position corresponding to. The opening position of the atmosphere opening path 5 is not limited to such a position, but may be the position shown in FIGS. 3 and 4 according to the position of the parting surface. In FIG. 3, the parting surfaces are located at the tips of the side wall portions 14a to 14d of the molded product 20, and the atmosphere opening path 5 is the mold cavity surface 4a corresponding to the surface of the molded product 20. Side wall 14 of product 20
It is opened at a position corresponding to the tip of a to 14d. A gas injection pin 8 for pressurizing the pressurized gas is provided on the mold cavity surface 4b side corresponding to the back surface of the molded product 20.

In FIG. 4, the side wall portion 14 of the molded product 20 is shown.
The parting surface is located in the middle of a to 14d,
The atmosphere opening path 5 is the mold cavity surface 4a corresponding to the surface of the molded product 20, and the side wall portions 14a to 14a of the molded product 20.
It is opened at a position corresponding to the middle portion of 14d. Also,
The gas injection pin 8 for pressurizing the pressurized gas is the molded product 2
It is provided on the side of the mold cavity surface 4b corresponding to the back surface of 0. Further, the molding method of the present invention will be described with reference to FIGS.

First, with the mold 1 closed, an excessive amount of molten resin is injected into the mold cavity 4 as compared with the volume of the mold cavity 4. At this time, air in the mold cavity 4 etc. Is discharged from the atmosphere opening path 5 together with the filling of the molten resin, so that the bubbles are prevented from remaining between the resin and the mold cavity surfaces 4a and 4b. Further, in order to ensure this discharge, it is preferable to open the atmosphere opening path 5 in the vicinity of the flow end, which is a position away from the gate 11.

Immediately after the injection and filling of the molten resin, the valve 9a is opened to supply the pressurized gas from the pressurized gas source (not shown) to the gas introduction passage 10a provided in the mold 1. The pressurized gas may be, for example, air, carbon dioxide gas, etc., but an inert gas such as nitrogen is preferable. The type of gas used is preferably selected depending on the pressure of the pressurized gas, the molding material, the molding conditions and the like. The pressure of the pressurized gas varies depending on the type of resin used, the shape of the molded product, the size of the molded product, etc., but is usually 10 to 250 kgf / cm ² , and preferably 40 to 200 kgf / cm ² .

The pressurized gas supplied to the gas introduction passage 10a passes through the gap between the gas injection pin 8 and the moving side mold 3,
It is pressed into the mold cavity 4 from the mold cavity surface 4b side. This pressurizing gas is applied to the back surface of the molded product 20 in the gas injection area 25 and the corresponding mold cavity surface 4
It is press-fitted between the surface of the molded product 20 and the mold cavity surface 4a corresponding thereto. The pressing with the pressurized gas suppresses the occurrence of sink marks on the surface of the molded product 20 on the side of the mold cavity surface 4a, improves the transferability on the side of the mold cavity surface 4a, and causes sink marks, uneven gloss, etc. The problem of poor appearance due to is also reduced. Further, the releasability when the molded product 20 is taken out from the mold 1 is also improved.

As shown in FIG. 5, the gap between the gas injection pin 8 and the moving mold 3 is a hole 1 provided in the moving mold 3.
It is preferable to form the gas injection pin 8 not only in a circular shape but also in a shape in which a part of the circular shape is scraped off, as well as 2 in a circular shape, because the desired width s can be easily formed.
In particular, the width s of the gap around the tip of the gas injection pin 8 is preferably set to a size that allows the pressurized gas to smoothly pass therethrough and prevents molten resin from entering during injection filling. The width s of this gap depends on the shape of the mold cavity 4, the position where it is provided, the material used, the molding conditions, etc., but is preferably 1 /
200 mm or more and 1/5 mm or less, more preferably 1/1
00 mm or more and 1/10 mm or less, more preferably 1 /
It is about 20 mm. Further, in the region closer to the root than the tip of the gas injection pin 8, the amount of cutting for forming a gap may be increased so that the pressurized gas can smoothly pass, and in some cases, it may be cut into a groove shape. preferable.

In order for the pressure of the pressurized gas introduced into the mold cavity 4 to effectively press the surface of the molded article 20 against the mold cavity surface 4a, it is pressed into the mold cavity 4. It is necessary to prevent the pressurized gas from leaking out of the mold 1. FIG. 6 is a schematic view of a state in the vicinity of the thick portion 13 and the side wall portion 14b when a pressurized gas is pressed into the cavity 4 after the mold 1 of FIG. 1 is excessively filled with the molten resin. The pressurized gas injected through the gap around the gas injection pin 8 reaches the base of the rib 13 while pressing the molded product 20 against the cavity surface 4a. At this time, the surface side corresponding to the position of the rib 13 where sink marks are likely to be formed in the normal molding is pressed by the pressurizing pressurized gas to prevent the sink marks.

On the other hand, the pressurized gas also travels to the side wall portion 14b side and presses the side wall portion 14b in the direction shown by the arrow, and as a result, the side wall portion 14b of the molded product 20 is moved to the mold cavity surface 4
It is pressed against a. Generally, the higher the pressure of the pressurized gas is, the more likely it is for leakage to occur, but as shown in FIG. 6, the higher the pressure of the pressurized gas is, the side wall portion 14b is closer to the mold cavity surface 4.
Since the gas is strongly pressed against a, and the gas injection region 25 is used as a closed region, the pressurized gas is prevented from flowing around to the mold cavity surface 4a side where the atmosphere opening path 5 (see FIG. 1) is opened.

The prevention of leakage of the pressurized gas can be achieved only by sufficiently filling the mold cavity 4 with an excessive amount of molten resin. That is, if the resin is not sufficiently filled in the mold cavity 4 when the pressurized gas tries to flow around to the mold cavity surface 4a side, the pressurized gas pushes away the resin and the mold cavity surface 4a side. And the gas passage is attached to the side wall 14
Gas sealing by b becomes difficult (side wall parts 14a, 14
The same applies to c and 14d. ). Although leakage of the pressurized gas to the outside of the mold 1 is likely to occur when the parting surface is in the form of FIG. 3, the method according to the present invention, that is, degassing in which the molten resin is likely to be filled in every corner of the mold 1. By filling an excessive amount of resin using the excellent mold 1, the leakage of the pressurized gas to the outside of the mold 1 can be sufficiently prevented.

Further, at the time of pressurization of the pressurized gas, the resin flows back to the runner and the nozzle portion, and unnecessary contraction occurs near the resin gate portion, and the high pressure gas may leak depending on the shape of the mold cavity 4. There is also. To prevent this,
Combined with resin holding pressure that is used in normal injection molding,
It is preferable to supplement a part of the resin for the shrinkage of the molded product. The resin holding pressure mentioned here is a pressure that is used in general injection molding, and is a pressure that does not cause burrs in the molded product 20. By using this resin holding pressure together,
The thickness of the thick portion 13 such as the ribs and bosses can be made larger than in the case where the resin holding pressure is not used together, the strength of the molded product 20 is easily improved, and the degree of freedom in product design is further expanded. be able to.

The pressurization of the pressurized gas does not necessarily have to be performed from the moving side mold 3 as shown in FIG. Which side of the fixed-side mold 2 and the moving-side mold 3 is used to introduce the gas is generally due to the shape of the mold 1, and the molded product 2
When the surface of 0 is on the fixed side mold 2 side, the pressurized gas is
It is easier to introduce from the movable side mold 3 side as shown in, and conversely, when the surface is on the movable side mold 3 side, it is easier to introduce the pressurized gas from the fixed side mold 2 side. is there.

After the pressurizing gas has been injected as described above, the pressurizing gas is discharged out of the mold 1 if necessary, and then the molded product 2 is formed.
Remove 0 from mold 1. In the present invention, as shown in FIG. 7, when the width of the thick wall portion 13 is w and the thickness around the thick wall portion 13 is t, w ≧ (3/5) t It is effective for the molded product 20 having 13. That is, in the molded product 20 having such a thick wall portion 13, it is difficult to prevent sink marks by ordinary injection molding, but according to the present invention, this can be reliably eliminated.

FIG. 8 shows the mold 1 of FIG. 1 and the molded product 20 of FIG.
At the time of molding, after the molten resin is filled, the pressurized gas is pressed between the back surface of the molded product 20 in the gas injection area 25 and the cavity surface 4b corresponding thereto, and the pressurized gas is applied to the thick portion 13
FIG. 6 is a schematic view of a state in the vicinity of the thick wall portion 13 and the side wall portion 14b when the resin is made to penetrate into the resin. Gas injection pin 8
The pressurized gas pressed in from the surrounding gap reaches the base of the thick portion 13 while pressing the molded product 20 against the mold cavity surface 4a. At this time, the surface of the molded product 20 corresponding to the position of the thick portion 13 where sink marks are likely to occur in normal molding is prevented from sinking by pressing with the pressurizing pressurized gas.
Further, the pressurized gas penetrates into the thick portion 13 and forms the hollow portion 17 therein, which also prevents sink marks. The prevention of sink marks by the hollow portion 17 is the same as that of the conventional gas-assisted injection, but the pressurized gas also exists around the thick portion 13, and at the same time, the surface of the molded product 20 corresponding to the position near the thick portion 21. Since it is pressed against the mold cavity surface 4a, the molded product 2 corresponding to the position of the thick portion 13 as in the conventional gas-assisted injection.
The occurrence of gloss and uneven gloss on the surface of No. 0 is prevented.

FIG. 9 is a schematic view of the hollow portions 17 and 19 formed by the pressurized gas injected into the thick portion 13, (a) is an example of the hollow portion 17 according to the present invention, and (b) is conventional. It shows an example of the hollow portion 19 by the gas-assisted injection of. Even in the conventional gas-assisted injection, depending on the pressure of the pressurized gas and the design of the thick portion 13,
Although it is possible to prevent the gas from protruding as shown in the hollow portion 19 in (b), a crystalline resin which is a thermoplastic resin composition containing polytrimethylene terephthalate as a main component of the present invention is particularly used. It is not easy to prevent the gas from squeezing out when a high pressure gas is used. However, according to the present invention, it is possible to easily prevent the gas from protruding.

FIG. 10 shows that after the mold 1 is filled with the molten resin,
Resin in the gas injection region 25 (see FIG. 2) and the cavity surface 4
It is a schematic diagram of the state near thick part 13 and side wall part 14 when pressurizing gas (backside gas) is pressed in between b, and then pressurizing gas (internal gas) is separately pressed inside molten resin. The back surface gas press-fitted through the gap around the gas press-fit pin 8 reaches the base of the thick wall portion 13 while pressing the molded product 20 against the mold cavity surface 4a. At this time, the surface side corresponding to the position of the thick portion 13 where sink marks are likely to be generated in the normal molding is pressed by the back gas press-fitted to prevent sink marks.
Further, the internal gas injected into the molten resin is injected into the thick portion 13 which is the thick portion, and the hollow portion 17 is formed therein, whereby the sink mark is completely prevented. The prevention of sink marks by the hollow portion 17 is the same as that of the conventional gas-assisted injection, but the back surface gas introduced from another route reaches between the mold cavity surface 4b and the molten resin, and the thick portion 13 is also surrounded. Since it exists, and at the same time, the opposite surface side corresponding to the position of the vicinity of the thick portion 21 is also pressed against the mold cavity surface 4a, the surface corresponding to the position of the thick portion 13 as in the conventional gas-assisted injection. The occurrence of gloss and uneven gloss on the side is prevented. The situation of the hollow portion 17 and the hollow portion 19 formed by conventional gas injection when the method is used is shown in FIG.
Similar to the above description, the gas is prevented from squeezing out into a thin portion such as the hollow portion 19.

[0058]

BEST MODE FOR CARRYING OUT THE INVENTION The effects of the present invention will be described more specifically with reference to the following examples. Using the following resins,
Use a mold according to. (Polytrimethylene terephthalate) Intrinsic viscosity [η] is 1.02, and number average molecular weight is 9800, Mw
/Mn=2.5 Polytrimethylene terephthalate in which the proportion of molecular weight of 100,000 or more is 5.8% The intrinsic viscosity [η] is a value obtained by the following defining equation. [Η] = lim1 / C × (η _r −1) [C → 0] In the formula, η _r is a polyester resin having a purity of 98% or more.
-The value obtained by dividing the viscosity of a diluted solution dissolved in chlorophenol at 35 ° C by the viscosity of the solvent at the same temperature, which is defined as the relative viscosity.
C is the weight (g) of the solute in 100 ml of the diluted solution.

(Polycarbonate) Iupilon S-20
00 (manufactured by Mitsubishi Engineering Plastics Co., Ltd.) (Glass fiber) A chopped strand having a fiber diameter of 10 μm and a length of 3 mm, which is surface-treated with a mixture of an aminosilane coupling agent and an epoxy sizing agent.

[0060]

Example 1 A molded product having a curved housing shape and a main part thickness of 2.5 mm as shown in FIG. 11 is molded. Injection of the pressurized gas and its gas seal are the same as those described in FIG. 1, and the gas injection position G is between the ribs a to g. The position of one parting surface is H in the figure.
1 and the position of the other parting surface is the one shown in FIG. 4 at the position I in the figure. The thickness of each rib shown by a, b, c, d, e, f, g is 2.5 mm, 2.5 mm, 1.
5mm, 3.75mm, 2.5mm, 1.25mm,
It is 2.5 mm. Polytrimethylene terephthalate is used as a resin, and it is plasticized by heating at an injection cylinder temperature of 240 ° C, and an excessive amount (103% by weight) of the molding material is injected at an injection pressure of 100 kg / cm ² (gauge pressure) compared to the mold cavity volume. Resin holding pressure 20 kg / cm ² (gauge pressure)
Immediately after switching to, the molded product is molded by pressurizing a pressurized gas of 100 kg / cm ² . The weight of the molded product is 100% by weight when the molded product is molded in an amount that exactly fills the cavity by normal molding. The obtained injection-molded product has a good appearance, a sink mark of 18 μm and a small warp. When injection molding is performed under the same conditions without pressurizing a pressurized gas, the sink mark is large and the sink mark reaches 200 μm.

[0061]

Example 2 A 50/50 (weight ratio) polymer alloy of polytrimethylene terephthalate and polycarbonate was used as a resin for injection molding, and injection molding was carried out in the same manner as in Example 1. A result similar to that of the first embodiment is obtained.

[0062]

Example 3 As a resin to be injection-molded, a resin in which polytrimethylene terephthalate is mixed with 30% by weight of glass fiber is used and injection-molded in the same manner as in Example 1. A result similar to that of the first embodiment is obtained.

[0063]

As described above, according to the present invention, it is possible to obtain an injection-molded article which is free of sink marks and burrs and has an excellent appearance, with a mold having a small facility load.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a mold used in the present invention.

FIG. 2 shows a molded product obtained with the mold of FIG.

FIG. 3 is a schematic cross-sectional view showing another example of the formation position of the atmosphere release path.

FIG. 4 is a schematic cross-sectional view showing another example of the formation position of the atmosphere release path.

FIG. 5 is an enlarged cross-sectional view around a gas injection pin.

FIG. 6 is an explanatory view of a gas sealing action and a sink preventing action in the present invention.

FIG. 7 is an explanatory diagram of a thick portion suitable for applying the present invention.

FIG. 8 is an explanatory diagram of the vicinity of the thick portion when the pressurized gas is also introduced into the thick portion in the present invention.

FIG. 9 is an explanatory diagram of a hollow portion formed.

FIG. 10 is an explanatory diagram of the vicinity of a thick portion when a pressurized gas is introduced into the thick portion from another route in the present invention.

FIG. 11 is a schematic view of molded products molded in Example 1, Example 2 and Example 3.

[Explanation of symbols]

1: Mold 2: Fixed side mold 3: Mold on the moving side 4: Mold cavity 4a, 4b: Mold cavity surface 5: Atmosphere release route 6: Ejector pin 7a to 7e: O-ring 8: Gas injection pin 9a-9b: valve 10a-10b: Gas introduction path 11: Gate 12: hole 13: Thick part 14a-14d: Side wall 15: protruding plate 16: Sprue 17: hollow part 18: Lanna 19: Hollow part 20: Molded product 21: Near thick part 22a, 22b: rising ribs 23: Auxiliary rib 24: Base part 25: Gas injection area 26: Gas inlet

Claims (7)

[Claims] 1. In injection molding of a molded product having a thick portion protruding to the back surface side, while degassing the gas in the mold cavity from an atmosphere opening path opening to a part of the mold cavity surface, A molten thermoplastic resin composition containing polytrimethylene terephthalate as a main component is injection-filled, and then a pressurized gas is press-fitted between the back surface of the molded article and the corresponding mold cavity surface in the gas press-fitting area. Then, the surface of the molded product corresponding to the gas injection region is pressed against the surface of the mold cavity corresponding to the gas injection region. 2. The gas pressure injection molding method according to claim 1, wherein an excessive amount of molten resin is injected into the mold cavity as compared with the volume of the mold cavity. 3. The injection amount of the molten resin into the mold cavity is 101 to 110% by weight when the weight of the molten resin corresponding to the volume of the mold cavity is 100% by weight. The gas pressure injection molding method according to claim 2. 4. The gas pressure injection molding method according to claim 1, wherein resin holding pressure is applied after the molten resin is injected. 5. The gas pressure injection molding method according to claim 4, wherein the resin holding pressure is applied even when pressurizing the pressurized gas. 6. A pressurizing gas is press-fitted between the back surface of the molded product in the gas press-fitting region and the corresponding mold cavity surface, and the surface of the molded product corresponding to the gas press-fitting region is held in the mold cavity corresponding thereto. The gas pressurization according to claim 1, wherein a hollow portion is formed by injecting a pressurized gas into the molten resin filled in the mold cavity while being pressed against the surface. Injection molding method. 7. A molded product molded by the method according to claim 1.