JP2002361690A - Injection mold and injection molding method using the same - Google Patents

Abstract

(57) [Summary] (Problem corrected) [Problem] To obtain an injection molded product of a mixture of a thermoplastic resin and carbon dioxide pressurized to an atmospheric pressure or more, more mold transferability, dimensional accuracy, and dimensional stability. To provide an injection mold having a high injection molding quality. An injection mold capable of injection molding a mixture of a thermoplastic resin and carbon dioxide pressurized to an atmospheric pressure or higher, comprising a mold cavity and a gap communicating with the outside of the mold cavity. Has at least one gas flow path 3 capable of filling a mold cavity with a pressurized gas supplied from outside the mold, and has a structure closed from the outside of the mold. An injection mold, wherein the pressurized gas can be discharged from a flow end portion of the resin filled in the mold cavity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection mold capable of injection molding a thermoplastic resin and an injection molding method using the same.

[0002]

2. Description of the Related Art It has been known that a thermoplastic resin absorbs carbon dioxide to act as a plasticizer for the thermoplastic resin and lower the glass transition temperature. A
ppl. Polym. Sci. , Vol. 30,263
3 (1985). However, until now, it has not been widely applied to molding of thermoplastic resins.

[0003] Japanese Patent Application Laid-Open No. Hei 5-318541 discloses that a resin such as carbon dioxide or nitrogen is contained in a thermoplastic resin, and the resin is filled into the cavity while removing the gas in the cavity. Of obtaining a thermoplastic resin molded article after improving the fluidity of the resin. However, this method, when using carbon dioxide gas,
Since the amount of gas contained in the thermoplastic resin is as small as about 0.18% by weight at maximum, and it is difficult to obtain a sufficient effect of improving the fluidity, an injection molded product having high dimensional accuracy and dimensional stability is obtained. That can be difficult.

In addition, the injection molding method disclosed in the above-mentioned publication discloses a mold cavity in which a thermoplastic resin containing a compound which becomes a gas at atmospheric pressure and 40 ° C. is opened to the atmosphere or depressurized. It is a method of injecting to. When a thermoplastic resin containing the above compound is injected into a mold cavity under an atmospheric pressure or reduced pressure environment, a gas body foams, so that a foaming pattern is generated on the surface of the obtained molded article. Since this foam pattern has a fine uneven shape, it has a dull appearance and easily becomes a starting point of destruction.

[0005] WO 98/52734 discloses that
In injection molding of thermoplastic resin,
Shows a method of filling molten resin whose viscosity has been reduced by dissolving more than 1% by weight into a mold cavity that has been kept pressurized with a gas such as carbon dioxide at a pressure higher than the pressure at which foaming does not occur at the flow front of the molten resin. The mold surface reproducibility, glossiness, and weld lines are less noticeable.
It is described that the method is effective for reproducibility of a sharp edge on a mold surface, reproducibility of fine irregularities on a mold surface, and the like.

However, when the same technique is used, gas accumulation is likely to occur in a weld portion. For this reason, the thermoplastic resin filled in the weld portion does not easily adhere to the mold cavity wall surface, and burns may occur. As a result, the dimensional accuracy of the portion and its peripheral portion tends to decrease. For this reason, it is necessary to provide a mold structure capable of discharging the gas, which has been maintained in a pressurized state in the mold cavity, to the outside of the mold so as not to hinder the flow after the start of filling with the thermoplastic resin.

On the other hand, conventionally, injection molded articles made of a thermoplastic resin have been widely used as mechanical parts and interior / exterior parts in various fields such as electric and electronic equipment, automobiles, general machines, and precision machines. Recently, the range of use has been expanding because of its excellent productivity, light weight, rust resistance and easy recycling. further,
The demand for dimensional accuracy and appearance characteristics for injection-molded products made of thermoplastic resin is increasing due to the high technology, high functionality, miniaturization, and complicated product design in each field. Is an important issue.

In order to improve the precision of injection molded articles made of thermoplastic resin, deformation after molding is suppressed and shrinkage is uniform by increasing the number of gates, making the wall thickness as thin as possible, and making it uniform. Product design and die design are generally performed. In addition, various efforts have been made in setting conditions during injection molding. Injection molding methods that reduce the distortion of the injection molded product and improve dimensional accuracy include increasing the temperature setting during injection molding and reducing the melt viscosity of the thermoplastic resin when filling the mold cavity. Conceivable.

However, when the resin temperature is increased, there is a certain range and there is a limit. For example, when the resin temperature is too high, the decomposition of the resin is promoted, so that there is a concern about the occurrence of problems such as deterioration of the resin. In addition, appearance defects called silver (or "silver streaks") are generated on the surface of the injection molded product, and the mold is easily stained by a decomposition gas generated from the thermoplastic resin. These are not preferable because they cause deterioration of workability such as deterioration of working environment and occurrence of disassembling and cleaning work of a mold.

In addition, when the temperature of the resin is set high, the amount of change in the volume of the resin itself during cooling and solidification becomes large, which tends to cause sink marks, voids, and the like. However, there is a concern that productivity may decrease. On the other hand, by increasing the mold temperature, a decrease in resin temperature and an increase in viscosity in the mold cavity can be suppressed. However, when the mold temperature is increased,
Since the cooling time of the resin filled in the mold becomes longer, the molding cycle time inevitably becomes longer, and the size of the molded product at the time of taking out becomes smaller.

In addition, in the case of injection molding in which the temperature of the mold is raised, if the cooling time is not sufficient and the cooling of the resin is insufficient, the temperature of the injection molded product at the time of removal is high.
For this reason, after the injection molded product is taken out of the mold, there is a possibility that volume shrinkage or deformation due to its own weight may occur before the temperature of the injection molded product itself gradually decreases to the ambient temperature. This causes the dimensional accuracy to deteriorate, which is not preferable.

[0012]

DISCLOSURE OF THE INVENTION The present invention relates to a method for obtaining an injection molded product of a mixture of a thermoplastic resin and carbon dioxide pressurized to a pressure higher than the atmospheric pressure. It is an object of the present invention to provide an injection molding die for obtaining an injection molded product having a high level and an injection molding method using the same. Specifically, without limiting the composition of the thermoplastic resin to be used and the product design, an injection molding mold for obtaining an injection molded product of a mixture of the thermoplastic resin and carbon dioxide pressurized to above atmospheric pressure. , And improved injection molding methods using it, mold transferability, dimensional accuracy and dimensional stability required for injection molded products made of a mixture of thermoplastic resin and carbon dioxide pressurized above atmospheric pressure It is an object to improve the performance.

[0013]

SUMMARY OF THE INVENTION The present inventors have found that when obtaining an injection-molded article made of a mixture of a thermoplastic resin and carbon dioxide pressurized to above atmospheric pressure, the mold transferability, dimensional accuracy, and the like are improved.
In order to provide an injection molding die for obtaining an injection molded product having high dimensional stability and an injection molding method using the same, an investigation was made. Specifically, without limiting the composition of the thermoplastic resin to be used and the product design, an injection molding mold for obtaining an injection molded product of a mixture of the thermoplastic resin and carbon dioxide pressurized to above atmospheric pressure. Mold transferability, dimensional accuracy, and dimensional stability required for injection molded products made of a mixture of a thermoplastic resin and carbon dioxide pressurized above atmospheric pressure by improving the injection molding method using the same. Was found to be improved, and the present invention was accomplished.

That is, the present invention provides: An injection mold capable of injection-molding a mixture of a thermoplastic resin and carbon dioxide pressurized to an atmospheric pressure or higher, wherein a gap communicating with the outside of the mold cavity and the mold cavity is formed by the mold. It has a closed structure from the outside, and has at least one gas flow path capable of filling the mold cavity with a pressurized gas supplied from outside the mold, and fills the inside of the mold cavity. Injection molding die, characterized in that it is possible to discharge the pressurized gas from the flow terminal portion of the resin

2. The above-mentioned item 1 is characterized in that the pressurized gas previously filled in the mold cavity can be discharged from a portion where the resin filled in the mold cavity forms a weld in the flow process thereof. 2. The injection mold according to the above. After filling the mold cavity with a gas pressurized to above atmospheric pressure, fill the mixture of thermoplastic resin and carbon dioxide pressurized to above atmospheric pressure, and then into the mold cavity before opening the mold. The injection molding method using the injection mold according to the above 1 or 2, wherein the enclosed pressurized gas is released;

4. After filling the mold cavity with a mixture of thermoplastic resin and carbon dioxide pressurized above atmospheric pressure,
4. The injection molding method using the injection molding die as described in 3 above, wherein the mixture is kept under pressure for a certain time; Injection molding method using an injection mold according to the above 3 or 4, wherein the thermoplastic resin is a polyacetal resin containing at least a polyacetal component as a main component,

6. 6. The injection molding method using the injection mold according to the above item 3 or 4, wherein the thermoplastic resin is a polyamide resin containing at least a polyamide component as a main component. Wherein the gas is carbon dioxide
7. An injection molding method using the injection mold according to any one of 6. An injection molding method using the injection mold according to any one of the above 3 to 6, wherein the gas is nitrogen.
About.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. In the present invention, the thermoplastic resin refers to a resin composition containing a thermoplastic resin as a main component, which has a characteristic of softening when heated and showing plasticity, and solidifying when cooled. Further, the thermoplastic resin can be used without distinction between a crystalline resin and an amorphous resin.

The above-mentioned resin composition specifically refers to polyacetal or polyoxymethylene (hereinafter referred to as “POM”).
) Resin, polyamide (hereinafter abbreviated as “PA”) resin, polyethylene terephthalate (hereinafter abbreviated as “PET”) resin, polybutylene terephthalate (hereinafter “PB”)
T ”), high-density polyethylene (hereinafter“ HDP ”)
E ”), low-density polyethylene (hereinafter“ LDP ”)
E "), linear low-density polyethylene (hereinafter abbreviated as" LLDPE ") resin, polyetheretherketone (hereinafter abbreviated as" PEEK ") resin, polypropylene (hereinafter abbreviated as" PP "), polystyrene (hereinafter abbreviated as" PP ") "PS"
) Resin, polyphenylene ether (hereinafter referred to as “PP”).
E "), a modified PPE obtained by blending a resin or a PPE resin with another resin or by graft polymerization.
Resin, acrylonitrile / butadiene / styrene copolymer (hereinafter abbreviated as “ABS resin”), acrylonitrile / styrene copolymer (hereinafter abbreviated as “AS resin”),
Examples thereof include a polycarbonate (hereinafter abbreviated as “PC”) resin and a methacryl (hereinafter abbreviated as “PMMA”) resin.

As the thermoplastic resin used in the present invention, a POM resin containing a POM component and a PA resin containing a PA component are preferable because a molded article having excellent mechanical strength and high heat resistance is easily obtained. It can be said that. Here POM
Is a POM homopolymer represented by the following chemical formula 1,
The POM / random copolymer shown in Chemical Formula 2 is preferably used, or a mixture thereof. Further, the terminal group of the POM molecule may be a POM / block copolymer in which components other than the POM and a molecular structure are chemically bonded, such as a lubricating polymer and silicon.

[0021]

Embedded image Here, n is an arbitrary natural number.

[0022]

Embedded image

Here, X is a monomer component, n ₁ , n ₂ , n
₃ and n ₄ are each an arbitrary natural number. The preferred range of the number average molecular weight of the POM suitably used in the present invention is 10,000 to 150,000, more preferably 15,000 to 100,000, and most preferably 20,000 to 100,000. In the range of 80,000. In addition, the above PO which is preferably used in the present invention
The preferred range of the melt index value of M is 0.1 to 75 (gr / 10 min), more preferably 1.0 to 70 (gr / 10 min), and most preferably 1.0 to 50 (gr / 10 min). (Gr / 10min)
It is in the range of. In addition, any PA can be used as long as it has an acid amide bond shown in Chemical Formula 3 below.

[0024]

Embedded image

Generally, PA resins are obtained by ring-opening polymerization of lactams, polycondensation of diamine and dicarboxylic acid, polycondensation of aminocarboxylic acid, and the like, but are not limited thereto. P which can be suitably used in the present invention
As the A-based resin, PA6, PA6-6, PA4-6,
PA11, PA12, PA6-10, PA6-12, P
A6 / 6-6, PA6 / 6-12, PA6 / MXD (m
-Xylylenediamine), PA6-T (terephthalic acid), PA6-I (isophthalic acid), PA6 / 6-T,
PA6 / 6-I, PA6-6 / 6-T, PA6-6 / 6
-I, PA6 / 6-T / 6-I, PA6-6 / 6-T /
6-I, PA6 / 12 / 6-T, PA6-6 / 12/6
-T, PA6 / 12 / 6-I, PA6-6 / 12 / 6-
I and the like.

PAs obtained by copolymerizing a plurality of PAs with an extruder or the like can also be used. Preferred PA resins are PA6, PA6-6, and mixtures thereof. The preferred range of the number average molecular weight of the POM suitably used in the present invention is from 5,000 to 100,000, and more preferably from 10,000 to 30,000. Further, the composition of these thermoplastic resins may be composed of thermoplastic resin components having the same molecular structure and different in molecular weight and molecular weight distribution.

Further, the thermoplastic resin in the present invention comprises 2
It may be a polymer alloy which is a composite resin material in which two or more kinds of resin components are physically and chemically mixed. Resins having different properties that can be used in combination with the thermoplastic resin as the main component are resin components having the same molecular structure as the thermoplastic resin as the main component, and have different molecular weights and molecular weight distributions. It may be a resin component or another resin component having a different molecular structure.

The resin component having different properties which can be used by mixing with the thermoplastic resin as the main component is not particularly limited as long as it is compatible with the thermoplastic resin as the main component. , PP, PA, PET, PBT, P
EEK, polyethylene, PS, ABS resin, polyvinyl chloride, PC, modified PPE, polyphenylene sulfide (hereinafter abbreviated as "PPS"), polyimide, polyamideimide, polyetherimide, polyarylate, polysulfone, polyethersulfone, liquid crystal polymer (Hereinafter abbreviated as “LCP”), polytetrafluoroethylene, thermoplastic elastomer, polytetrafluoroethylene, polyvinyl alcohol, and the like.

Examples of the polymer alloy include “PA / PPE polymer alloy” using a PA resin and a PPE resin, and “PP / PP” using a PP resin and a PPE resin.
"E-based polymer alloy", "PC / ABS-based polymer alloy" using PC-based resin and ABS-based resin, "PA / ABS-based polymer alloy" using PA-based resin and ABS-based resin, PC-based resin and PET-based resin "PC / PET
-Based polymer alloys "," LCP / PPE-based polymer alloys "using LCP-based resins and PPE-based resins, and" PPS / PPE-based polymer alloys "based on PPS-based resins and PPE-based resins.

An inorganic or organic filler can be added to the thermoplastic resin used in the present invention for the purpose of imparting specific gravity, strength, and ensuring dimensional accuracy. Examples of the specific gravity imparting agent include inorganic salts, oxides, and metal powders such as barium sulfate, red iron oxide, and tungsten powder. Further, as a strength imparting agent, glass fiber, carbon fiber, metal fiber, aramid fiber,
Potassium titanate, asbestos, silicon carbide, ceramic, silicon nitride, barium sulfate, calcium sulfate, kaolin, clay, pyrophyllite, bentonite, sericite, zeolite, mica, mica, nepheline cinite, talc, atalpargite, water Last night,
Slag fiber, ferrite, silicon, calcium, calcium carbonate, magnesium carbonate, dolomite, zinc oxide,
Gypsum, glass beads, glass powder, glass balloon, quartz, quartz glass, alumina and the like can be considered.

The shape of the inorganic or organic filler is not limited, and a fibrous, plate-like, spherical or the like can be arbitrarily selected. In addition, two or more of the above-mentioned inorganic or organic fillers can be used in combination. Further, if necessary, it can be used after being pre-treated with a silane-based or titanium-based coupling agent. The amount of the inorganic or organic filler added to the thermoplastic resin of the present invention is not limited, but the specific gravity of the thermoplastic resin is adjusted, rigidity is improved, and dimensional accuracy is secured. In order to sufficiently obtain the effect of adding an additive, such as suppressing deformation such as warpage, the amount is preferably 5% by weight or more, more preferably 10% by weight or more. When the amount is less than 5% by weight, the effect of adding the above-mentioned filler is small.

Here, the amount of the inorganic or organic filler to be added refers to the amount of the filler to be added when only one kind is added, and the total amount of the fillers to be added when two or more kinds are added. Point. Further, the amount of the inorganic or organic filler added indicates a ratio when the total amount of the resin component, the inorganic or organic filler, and other additives is 100% by weight.
In the thermoplastic resin of the present invention, commonly used additives such as antioxidants, flame retardants, mold release agents, lubricants, heat stabilizers, weather resistance stabilizers, rust inhibitors, fillers, coloring agents One or more antibacterial agents, antifungal agents and the like can be added as necessary.

As other additives, carbon fiber,
By selecting one or more of metal fibers and graphite, the electrical resistance of the thermoplastic resin can be reduced. This is preferable because it is possible to prevent small powder such as dust from attaching to the gear made of the thermoplastic resin due to static electricity. In the present invention, the carbon dioxide mixed with the thermoplastic resin is pressurized to an atmospheric pressure or higher. This is because it is difficult to uniformly mix the carbon dioxide with the thermoplastic resin when the carbon dioxide is below the atmospheric pressure. Uniform carbon dioxide in thermoplastic resin, and
In order to mix in a short time, it is necessary that carbon dioxide is pressurized to above atmospheric pressure.

In the present invention, the method of mixing the thermoplastic resin with carbon dioxide pressurized to above atmospheric pressure is not limited, but it is easy to uniformly mix the carbon dioxide with the molten thermoplastic resin. It is preferable that the mixture be easy to mix in a short time, the adjustment of the mixing amount is easy, the setup before molding is not complicated, and the mixture is easily filled into the mold cavity. It is further preferable that parts and peripheral devices constituting the injection molding machine such as a molding machine hopper and the like do not need to have a pressure-resistant structure.

In consideration of these points, a method of mixing carbon dioxide with the thermoplastic resin in a molten state is preferable. In addition, in the heating cylinder of the injection molding machine, the nozzle of the molding machine,
It is preferable that carbon dioxide be mixed with the thermoplastic resin in a molten state by providing a facility for supplying carbon dioxide at any position between the nozzle of the molding machine and the mold. Here, in the heating cylinder of the injection molding machine, as a method of mixing the thermoplastic resin and the carbon dioxide in a molten state, the middle portion and the tip of the screw of the molding machine,
A method of supplying carbon dioxide from a heating cylinder to a thermoplastic resin in a molten state can be considered.

When carbon dioxide is supplied from the screw of the molding machine or the intermediate part of the heating cylinder, the depth of the screw groove near the carbon dioxide supply part is increased as in the vent part of a vent type screw. It is preferable that the resin pressure in the heating cylinder be lowered and the resin transfer be starved. Further, in order to uniformly mix the carbon dioxide with the thermoplastic resin after supplying the carbon dioxide, it is conceivable to provide a mixing mechanism such as a dalmage or a kneading pin on the screw, and to provide a static mixer in the resin flow path.

The viscosity of the thermoplastic resin in a molten state is reduced by mixing the same with carbon dioxide pressurized to an atmospheric pressure or higher. This is presumed to be because carbon dioxide is efficiently dispersed as a plasticizer in the thermoplastic resin. On the other hand, a decrease in the viscosity of the thermoplastic resin in a molten state means an improvement in fluidity. As a result, the filling pressure when filling the mold cavity is reduced. For this reason, the pressure of the thermoplastic resin filled in the mold cavity is easily transmitted to the flow end portion, and the mold transferability is improved. In addition, it is not necessary to raise the resin temperature and mold temperature more than necessary to improve the mold transferability, dimensional accuracy, and dimensional stability of injection molded products made of thermoplastic resin, and to limit product design. In addition, it is possible to obtain an injection-molded article made of a thermoplastic resin having a higher molecular weight.

The injection molding method using the injection mold according to the present invention is characterized by filling a mold cavity with a mixture of a thermoplastic resin and carbon dioxide pressurized to above atmospheric pressure. When the pressure of the carbon dioxide mixed in the thermoplastic resin is equal to or higher than a certain value, when the mixture is filled in the mold cavity, the pressure of the carbon dioxide mixed in the thermoplastic resin is released, thereby foaming. It is possible. When this foaming phenomenon occurs, there is a possibility that a foamed pattern is generated on the surface of the obtained injection molded product.

In order to suppress the foaming phenomenon in the mold cavity, it is necessary that the injection mold according to the present invention has a structure in which a gap communicating with the outside of the mold cavity is sealed from the outside of the mold. is there. By having a structure in which the mold cavity is sealed from the outside of the mold, a foaming phenomenon due to carbon dioxide mixed with the thermoplastic resin is prevented from occurring at the leading end of the thermoplastic resin filled in the mold cavity. Then, the pressurized gas can be sealed in the mold cavity. As a result, generation of a foaming pattern on the surface of the obtained molded article is suppressed.

At this time, the pressure of the pressurized gas sealed in the mold cavity may be a pressure necessary to suppress the occurrence of a foaming pattern on the surface of the molded product, and may be higher than necessary. do not have to. The gas pressure is preferably as low as possible in order to minimize the amount of gas used during the molding cycle and simplify the structure of the mold cavity and the structure of the gas supply device. If the gas pressure exceeds 15 MPa, the mold may be opened by the gas pressure sealed in the mold cavity, and a problem that the pressurized gas flows out of the mold from the mold cavity may easily occur. Therefore, it can be said that the pressure of the gas for pressurizing the mold cavity is preferably not lower than atmospheric pressure and not higher than 15 MPa.

At this time, as the pressurized gas sealed in the mold cavity, a single substance or a mixture of various gases inert to the thermoplastic resin can be used. Carbon dioxide, a hydrocarbon having a high solubility in a thermoplastic resin, and a gas in which hydrogen is partially replaced by fluorine are preferable. The purity of the pressurized gas used may be a purity that satisfies that the thermoplastic resin in a molten state is not deteriorated, or a higher purity. It is possible to carry out even if the purity is not higher than necessary. In addition, in consideration of the fact that a gas having a high purity can be obtained relatively inexpensively, although the solubility in the thermoplastic resin is low, it is possible to use nitrogen gas.

In the present invention, the gap communicating with the outside of the mold specifically means a mold plate, an ejector pin, various small pieces (also referred to as “insertion pieces” and “nesting”), a sprue bush, and the like. This is a gap existing between parts required to construct a mold. A clearance required during assembly and operation is provided between these components. It is also conceivable that a gap exists on the parting surface or the like in a state where the mold is closed.

The mold for injection molding according to the present invention is characterized in that the gap communicating with the outside of the mold cavity is sealed from the outside of the mold, and the method is not limited. Is preferably sealed with a sealing material that does not thermally degrade under the temperature environment in injection molding. Specifically, the O-ring, U-packing, or the like made of a flexible material such as rubber can be considered as the sealing material. For example, a U-packing is used for a sliding portion such as a boundary portion between a template and an ejector pin, and an O-ring is used for other portions.

These O-rings, U-packings and the like are preferably made of silicon rubber, nitrile rubber, fluorine rubber, super rubber, or the like, from the viewpoint of heat resistance and weather resistance. The mold for injection molding according to the present invention is characterized in that the gap communicating with the outside of the mold cavity and the mold cavity is a structure sealed from the outside of the mold,
In order to fill the inside of the mold cavity with a pressurized gas, it is necessary to supply the pressurized gas from outside the mold and exhaust the gas outside the mold.

The gas supply path for supplying the pressurized gas from outside the mold only needs to be capable of supplying the pressurized gas to the mold cavity. The position and the like are not limited. However, when the volume of the supply path is large, the amount of pressurized gas consumed during the molding process increases. Considering economics, it is preferable that gas consumption is low,
The gas supply path preferably has a cross section as small as possible and a flow distance as short as possible within a range that does not hinder the gas supply.

On the other hand, the gas discharge path for exhausting the outside of the mold can exhaust the pressurized gas sealed in the mold cavity from the flow end of the thermoplastic resin filled in the mold cavity. is necessary. This is because the flow of the mixture of the thermoplastic resin and the carbon dioxide in the mold cavity is not hindered, and the gas in the mold cavity can be efficiently discharged. Specifically, a method of discharging gas from a mold cavity through a gap provided in a parting surface, a small piece constituting a mold cavity, a mold plate, or a mold frame constituting a mold plate, Since the gap communicates with the outside of the mold through the gap provided at the boundary between the individual pieces, the pressurized gas sealed in the mold cavity can be discharged to the outside of the mold.

The gas discharge path needs to have a shape and a size that do not hinder the flow of the gas body, while it is necessary that the filled thermoplastic resin does not flow into the mold cavity. Specifically, the size of the gap is 0.20 mm
Or less, more preferably 0.15
mm or less, and most preferably 0.10 m
m or less. Further, it is effective in terms of gas exhaust efficiency to provide a gas discharge path for exhausting gas out of the mold at a flow end portion of the thermoplastic resin filled in the mold cavity. In the case where a mixture of the thermoplastic resin and carbon dioxide filled in the fluidization process forms a weld portion, the gas sealed in the mold cavity can be exhausted from the portion forming the weld, It is further preferable to provide a gas discharge path.

In addition to being able to exhaust the pressurized gas without obstructing the flow of the mixture of the thermoplastic resin and carbon dioxide,
This is because a gas component generated from the thermoplastic resin when filling the mold cavity is easily discharged at the same time as the exhaust of the pressurized gas supplied into the mold cavity. Since the weld portion and the flow end portion are portions where the gas component generated from the thermoplastic resin is present in the mold cavity in a compressed state, the flow of the thermoplastic resin may be hindered depending on the situation. For this reason, it causes a molding failure such as generation of an unfilled portion and reduction of mold transferability.

Further, the gas supply path and the gas exhaust path can be implemented by sharing the same gas flow path. On the other hand, in the injection molding method of the present invention, after filling the inside of the mold cavity with a pressurized gas supplied from outside the mold, the mold cavity is pressurized with the thermoplastic resin and the atmospheric pressure or higher. The mixture of carbon dioxide is charged into the mold cavity, but at any time from the start of filling of the mixture to opening of the mold to remove a molded product obtained from the inside of the mold, the mold cavity is It is necessary to exhaust the pressurized gas enclosed inside.

This is because, when the mold is opened while the pressurized gas is sealed in the mold cavity, the pressure of the pressurized gas is released in a short time, so that the obtained molded product is obtained. And the mold itself may be damaged. The step of exhausting the pressurized gas sealed in the mold cavity must be performed during one step of the injection molding until the mold is opened to take out a molded product obtained from the inside of the mold. Is preferably performed until the start of the cooling step, more preferably until 2 seconds have elapsed since the completion of the filling, and most preferably until the completion of the filling.

Further, in the ordinary injection molding method, after the resin is filled in the mold cavity, a step of further holding the resin in the cavity under pressure is provided. This process is called the “pressure-holding process”,
The degree of the pressure is referred to as "holding pressure". In the gear injection molding method according to the present invention, after filling a mixture of a thermoplastic resin and carbon dioxide into a mold cavity, a filling pressure of 3% is applied.
It is preferred to hold the mixture in the mold cavity under pressure with a pressure corresponding to 0-150%.

In the present invention, the holding pressure is 30% of the filling pressure.
If it is less than 1, the thickness of the non-foamed layer formed on the surface layer of the molded article becomes thin, and the proportion of the foamed portion in an arbitrary cross section becomes large. On the other hand, when the holding pressure exceeds 150% of the filling pressure, burrs may be generated, and a foamed portion may not be easily formed inside the molded product, and sink and warpage may easily occur after molding.

In order for an injection molded article made of a mixture of a thermoplastic resin and carbon dioxide to have a moderately foamed portion inside the molded article while forming a non-foamed layer having an appropriate thickness on the surface layer, the injection molding must be performed. A preferable range of the holding pressure in the molding step is a range of 30 to 150%, more preferably a range of 30 to 90%, and most preferably a range of 30 to 85% with respect to the filling pressure. It is in the range of. Here, the filling pressure refers to a resin pressure generated when the molten resin is charged into the mold cavity. Specifically, the screw position in the in-line screw type injection molding machine, and the plunger position in the pre-plasticity type injection molding machine, are the maximum values of the resin pressure generated when moving from the measuring position to the VP (holding pressure) switching position. Point to.

The holding time is not limited, but if the holding time is extremely short, pressurized carbon dioxide mixed with the thermoplastic resin before filling into the mold cavity is used. Expanding is not preferable because a swelling phenomenon may occur in the molded product. Specifically, the dwell time is preferably 3 seconds or more, more preferably 5 seconds or more, and most preferably 7 seconds or more.

In the present invention, the injection molding method is a usual molding and processing method for a thermoplastic resin. In addition to the most common injection molding method, a hollow injection molding method, a gas assist molding method, a blow molding method and the like. Methods, injection and compression molding methods, and the like. Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples. The resin used for injection molding is a POM resin (Asahi Kasei Kogyo Co., Ltd.)
"Tenak 4010", an ABS resin ("Styrac-ABS 220", manufactured by the company), each in a pellet shape before injection molding. As a molding machine, “SG125-HP” injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. was used. The temperature of the heating cylinder of the injection molding machine is 195 when a POM-based resin (hereinafter abbreviated as “POM”) is injection-molded.
° C, and when the ABS resin (hereinafter referred to as “ABS”) is injection-molded, the temperature is set to 220 ° C, and the mold temperature is set to 8 ° C.
It was set to 0 ° C.

[0056]

Embodiments 1 to 4 A disk-shaped injection-molded article having the cross section shown in FIG. 1 and having the shape shown in FIG. 2 can be injection-molded. Was prepared, and further connected to a gas supply device provided outside the mold by a gas supply path. The gas supply path is further connected to a gas passage having a thickness of 0.05 mm provided at a position corresponding to the outer peripheral portion of the disk-shaped injection molded product, that is, at a position serving as a flow end portion in the mold cavity. The communication allows the pressurized gas supplied from outside the mold to be supplied and sealed into the mold cavity.

Carbon dioxide adjusted to an arbitrary pressure in the range of 2.2 to 12.8 MPa is supplied from a gas supply path provided at the center of the heating cylinder of the injection molding machine to the molten POM in the heating cylinder. After mixing, 2.2 to 5.
The disc-shaped injection molded product shown in FIG. 2 was obtained by filling the mold cavity filled with carbon dioxide pressurized to 2 MPa. The roundness of the obtained injection-molded product was measured using a “roundness cylindrical shape measuring instrument (“ Round Test RA-400 ”manufactured by Mitutoyo Corporation)”, and the surface roughness was measured using a “surface roughness shape measuring instrument ((KK) ) "Surfcom 570A" manufactured by Tokyo Seimitsu Co., Ltd.)
Was measured using the method described above. In each example, the average value measured for five obtained injection-molded products was used as a measurement result and is shown in Table 1.

[0058]

Comparative Example 1 A disk-shaped injection-molded product having the cross section shown in FIG. 3 and having the shape shown in FIG. 2 can be injection-molded.
A mold having a sealing structure with a sealing material was prepared, and further connected to a gas supply device provided outside the mold by a gas supply path. This gas supply path is further provided at a position corresponding to the outer peripheral portion of the disk-shaped injection molded product, that is, at a position provided at the center portion of the mold cavity in the mold cavity.
The pressurized gas supplied from outside the mold can be supplied and sealed into the mold cavity by being connected to the gas flow path having a thickness of mm. Carbon dioxide adjusted to 8.6 MPa is supplied from a gas supply path provided at the center of the heating cylinder of the injection molding machine to the POM in a molten state in the heating cylinder, mixed, and then pressurized to 5.2 MPa in advance. The disc-shaped injection-molded article shown in FIG. 2 was obtained by filling the filled mold cavity with the filled carbon dioxide. As in Examples 1 to 4, the roundness and surface roughness of the obtained injection molded product were measured. The average value measured for the five obtained injection-molded articles was used as a measurement result and is shown in Table 1.

[0059]

Comparative Example 2 FIG. 4 is a cross-sectional view shown in FIG.
A disk-shaped injection molded product with the shape shown in (1) can be injection-molded, a mold that does not have a sealing structure with a sealing material is prepared, and it is connected to a gas supply device provided outside the mold by a gas supply path did. The gas supply path is further connected to a gas passage having a thickness of 0.05 mm provided at a position corresponding to the outer peripheral portion of the disk-shaped injection molded product, that is, at a position serving as a flow end portion in the mold cavity. The communication allows the pressurized gas supplied from outside the mold to be supplied and sealed into the mold cavity.

Carbon dioxide adjusted to 8.6 MPa is supplied from a gas supply path provided at the center of the heating cylinder of the injection molding machine to the molten POM in the heating cylinder and mixed.
The disc-shaped injection molded product shown in FIG. 2 was obtained by filling the mold cavity filled with carbon dioxide pre-pressurized to 5.2 MPa. Because the mold does not have a closed structure, pressurized carbon dioxide cannot be satisfactorily enclosed,
The pressure of carbon dioxide in the mold cavity during resin filling dropped to 0.8 MPa. The roundness and surface roughness of the obtained injection molded product were measured. The average value measured for the five obtained injection-molded articles was used as a measurement result and is shown in Table 1.

[0061]

Comparative Example 3 A disk-shaped injection-molded article having the cross section shown in FIG. 5 and having the shape shown in FIG. 2 can be injection-molded.
A mold having the same structure as a mold used for ordinary injection molding, which does not have a sealed structure using a sealing material, a gas flow path, and the like, was prepared. After supplying carbon dioxide adjusted to 8.2 MPa from a gas supply path provided at the center of the heating cylinder of the injection molding machine to the POM in a molten state in the heating cylinder and mixing,
By filling the mold cavity, a disk-shaped injection molded product shown in FIG. 2 was obtained. The roundness and surface roughness of the obtained injection molded product were measured. In each embodiment,
The average value measured for the five obtained injection-molded articles was used as a measurement result and is shown in Table 1.

[0062]

[Table 1]

[0063]

Embodiments 5 to 7 A disk-shaped injection-molded article having the cross section shown in FIG. 1 and having the shape shown in FIG. It was prepared and connected to a gas supply device provided outside the mold by a gas supply path. The gas supply path is further connected to a gas passage having a thickness of 0.05 mm provided at a position corresponding to the outer peripheral portion of the disk-shaped injection molded product, that is, at a position serving as a flow end portion in the mold cavity. The communication allows the pressurized gas supplied from outside the mold to be supplied and sealed into the mold cavity.

Carbon dioxide adjusted to an arbitrary pressure in the range of 2.2 to 12.8 MPa is supplied from a gas supply path provided at the center of the heating cylinder of the injection molding machine to ABS in a molten state in the heating cylinder. After mixing, 2.2 to 5.
The disc-shaped injection molded product shown in FIG. 2 was obtained by filling the mold cavity filled with carbon dioxide pressurized to 2 MPa. The appearance of the obtained injection molded article was observed. Specifically, the presence or absence of unfilled portions and the occurrence of burns were visually checked. In addition, roundness and surface roughness of the obtained injection molded product were measured. In each example, the average value measured for five obtained injection molded articles was taken as a measurement result, and is shown in Table 2.

[0065]

Comparative Example 4 A disk-shaped injection-molded article having the cross section shown in FIG. 5 and having the shape shown in FIG. 2 can be injection-molded.
A mold having the same structure as a mold used for ordinary injection molding, which does not have a sealed structure using a sealing material, a gas flow path, and the like, was prepared. After supplying carbon dioxide adjusted to 8.2 MPa from a gas supply path provided at the center of the heating cylinder of the injection molding machine to ABS in a molten state in the heating cylinder, and mixing,
By filling the mold cavity, a disk-shaped injection molded product shown in FIG. 2 was obtained. In the same manner as in Examples 5 to 7, the appearance of the obtained injection molded product was observed, and the roundness and surface roughness were measured. Table 2 shows the average values measured for the five obtained injection molded articles as measurement results.

[0066]

Comparative Example 5 A disk-shaped injection molded product having the cross section shown in FIG. 6 and having the shape shown in FIG. 2 can be injection molded.
A mold having a sealing structure with a sealing material was prepared, and further connected to a gas supply device provided outside the mold by a gas supply path. The gas supply path is connected to small pieces constituting the mold cavity, but no gas flow path to the mold cavity is provided. Carbon dioxide adjusted to 8.6 MPa is supplied from a gas supply path provided at the center of the heating cylinder of the injection molding machine to ABS in a molten state in the heating cylinder, mixed, and then pressurized to 5.2 MPa in advance. The disc-shaped injection-molded article shown in FIG. 2 was obtained by filling the filled mold cavity with the filled carbon dioxide. In the same manner as in Examples 5 to 7, the appearance of the obtained injection molded product was observed, and the roundness and surface roughness were measured. Table 2 shows the average values measured for the five obtained injection molded articles as measurement results.

[0067]

[Table 2]

[0068]

The mold for injection molding of the present invention is more suitable for obtaining an injection molded product of a mixture of a thermoplastic resin and carbon dioxide pressurized to an atmospheric pressure or higher than the mold transferability, dimensional accuracy and dimensions. It is possible to obtain an injection molded product having high stability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an injection mold used in carrying out an example.

FIG. 2 shows a perspective view of a disk-shaped injection molded product.

FIG. 3 shows a cross-sectional view of an injection molding die used when implementing Comparative Example 1.

FIG. 4 shows a cross-sectional view of an injection molding die used in carrying out Comparative Example 2.

FIG. 5 is a cross-sectional view of a molding and injection mold used in carrying out Comparative Examples 3 and 4.

FIG. 6 shows a cross-sectional view of an injection molding die used when performing Comparative Example 5.

[Explanation of symbols]

 Reference Signs List 1 cavity 2 gas supply path 3 gas flow path 4 gas exhaust path 5 sealing material 6 disk-shaped injection molded product 7 roundness measurement position

Claims (8)

[Claims] An injection mold capable of injection-molding a mixture of a thermoplastic resin and carbon dioxide pressurized to a pressure higher than the atmospheric pressure, wherein the mold communicates with a mold cavity and outside the mold cavity. The gap has a structure closed from the outside of the mold, and has at least one gas flow path capable of filling the mold cavity with a pressurized gas supplied from outside the mold, and An injection mold, wherein the pressurized gas can be discharged from a flow end portion of the resin filled in the mold cavity. 2. The method according to claim 1, wherein the pressurized gas previously filled in the mold cavity can be discharged from a portion where the resin filled in the mold cavity forms a weld in the flow process. The injection mold according to claim 1, wherein: 3. A mold cavity is filled with a gas pressurized at a pressure higher than the atmospheric pressure, and then a mixture of a thermoplastic resin and carbon dioxide pressurized at a pressure higher than the atmospheric pressure is filled. 3. An injection molding method using an injection mold according to claim 1, wherein the pressurized gas sealed in the mold cavity is released. 4. The method according to claim 3, wherein a mixture of the thermoplastic resin and carbon dioxide pressurized to a pressure higher than the atmospheric pressure is filled in the mold cavity, and then the mixture is kept under pressure for a certain period of time. Injection molding method using the injection molding die of the present invention. 5. The injection molding method according to claim 3, wherein the thermoplastic resin is a polyacetal resin containing at least a polyacetal component as a main component. 6. The injection molding method using an injection mold according to claim 3, wherein the thermoplastic resin is a polyamide resin containing at least a polyamide component as a main component. 7. An injection molding method using an injection mold according to claim 3, wherein the gas is carbon dioxide. 8. An injection molding method using an injection mold according to claim 3, wherein the gas is nitrogen.