JP2002292674A - Injection molding method for molding having good appearance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of molding and to reduce a temperature load applied to a mold 1 by sufficiently fluidizing a molding material ranging from a skin layer to a core layer without heating the surface of the mold at a high temperature, when the generation of a weld line is controlled by fluidizing the molten molding material packed in a mold cavity 22. SOLUTION: After the molten molding material in which at least 0.2 wt.% of carbon dioxide is dissolved is packed in the mold cavity 22, at least part of the molten molding material is discharged from the cavity 22 and charged into the cavity 22 to be fluidized in the cavity 22.

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 capable of obtaining a molded article having a high appearance without deterioration in appearance due to a weld line.

[0002]

2. Description of the Related Art For example, in the injection molding of a molded article having an opening such as a hole or a window, molten molding material wrapping around from both sides of a location to be an opening merges on the opposite side to form a weld. It is known to produce weld lines on the surface. It is also known that in injection molding using a mold of a multi-point gate, a weld line is also generated by the joining of the molten molding material supplied from each gate to the mold cavity. The weld line causes a deterioration in the appearance of the obtained molded product, and sometimes the presence of the weld forming the weld line greatly impairs the mechanical properties of the obtained molded product.

[0003] The above weld line is made of glass fiber,
This tends to be remarkable when a molding material to which reinforcing fillers such as mica and metal, particularly metal flakes such as aluminum flakes are used is used.

Conventionally, as a method for preventing the occurrence of the weld line, a molten molding material filled in a mold cavity is repeatedly reciprocated by operating two cylinder / piston mechanisms connected to the mold cavity. There is known a method of solidifying after shearing in a mold cavity (Japanese Patent Publication No. 4-3893).

Further, when the molten molding material is supplied into the mold cavity, the mold surface is heated to a temperature higher than the heating deformation temperature of the molding material, preferably to a melting molding temperature by high frequency induction heating or the like. There is also known a method in which a molten molding material supplied into a mold cavity having a heated mold surface is sheared as described above and then solidified (Japanese Patent Application Laid-Open No. 9-1611).

[0006]

Problems to be Solved by the Invention
In the case of the method disclosed in Japanese Patent No. 3893, the inner layer (core layer) of the molten molding material supplied into the mold cavity is easily maintained in a molten state. Since the layer (skin layer) starts to solidify immediately upon contact with the mold surface, it is difficult for the layer to reciprocate. For this reason, even though the weld in the core layer can be eliminated and the mechanical properties of the obtained molded article can be prevented from deteriorating, rapid solidification of the skin layer impairs the transferability of the mold surface and causes surface roughness. There is a problem that easily occurs.

On the other hand, in the case of the method disclosed in Japanese Patent Application Laid-Open No. 9-1611, the mold surface is heated to a temperature higher than the heating deformation temperature of the molding material, preferably to the melting molding temperature.
While delaying the solidification of the skin layer, it is possible to reciprocate sufficiently from the skin layer to the core layer and to shear it.This eliminates the weld from the skin layer to the core layer without causing surface roughness, and reduces the weld line. Can be prevented from occurring.

However, the surface of the mold must be heated to a considerably high temperature in advance, so that a time for this heating is required for each molding cycle, and the cooling time is prolonged, so that the molding efficiency is reduced. There's a problem. In addition, since the temperature difference between heating and cooling repeatedly applied to the mold increases, there is also a problem that the durability of the mold decreases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is intended to suppress the occurrence of a weld line by flowing a molten molding material filled in a mold cavity. Without heating, make it flow from the skin layer to the core layer sufficiently,
Accordingly, it is an object to improve the molding efficiency and reduce the temperature load applied to the mold.

[0010]

A first aspect of the present invention to achieve the above object is to fill a mold cavity with a molten molding material in which carbon dioxide is dissolved in an amount of 0.2% by weight or more.
An injection molding method for a high-appearance molded product, characterized in that at least a part of a molten molding material is caused to flow in a mold cavity.

The first aspect of the present invention includes, as a preferred embodiment, filling a mold cavity into which a melt molding material is applied with a counter gas pressure.

Further, a second aspect of the present invention is to provide a molten molding material,
After filling a gas body having a solubility in the molten molding material at least three times that of nitrogen at the time of molding into a mold cavity filled with a pressure of 0.1 MPa or more, at least a part of the molten molding material is
This is an injection molding method for a high-appearance molded product characterized by flowing in a mold cavity.

A second aspect of the present invention includes that the gaseous substance is carbon dioxide as a preferred embodiment.

Further, the first and second aspects of the present invention are characterized in that the flow of the molten molding material is such that the molten molding material in the mold cavity is pushed out of the mold cavity and the molten molding material pushed out of the mold cavity is pushed out of the mold cavity. The preferred embodiments of the present invention include pushing back the material into the mold cavity, using a heat insulating mold whose mold surface is covered with a heat insulating layer, and that the molten molding material contains a filler. It is a thing.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The present invention relates to an injection molding method in which at least a part of a molten molding material filling and filling a mold cavity is cooled and solidified through a step of flowing in a mold cavity. It can be roughly classified into a form and a second form. The present invention can be used for both cases where a single gate mold is used and where a multipoint gate mold is used. In the present specification, the mold cavity refers to a space in a mold for forming a molded product to be a product, such as a runner, a sprue, and a space for taking in and out a molten molding material in a mold cavity described later. Is not included.

First, a first embodiment of the present invention is a method of using a molten molding material in which carbon dioxide is dissolved in advance to improve fluidity and lower its solidification temperature. The carbon dioxide dissolved in the melt molding material acts as a plasticizer, improving the fluidity and lowering the solidification temperature. Therefore, even if the mold surface temperature is not heated to a conventional high temperature, the skin layer of the molten molding material filled in the mold cavity and in contact with the mold surface can also maintain good fluidity, It is possible to easily flow from the skin layer to the core layer. And, by this flow, the weld from the skin layer to the core layer can be eliminated,
It is possible to prevent the occurrence of weld lines on the surface of the molded product and the deterioration of mechanical properties.

In the first embodiment of the present invention, the temperature of the mold surface is set in advance by carbon dioxide so that the molten mold material filled in the mold cavity can flow from the skin layer to the core layer without fail. It is preferable to keep the temperature equal to or higher than the solidification temperature lowered by melting. Here, the solidification temperature refers to a glass transition point of a molding material using an amorphous resin and a crystallization start temperature of the resin in a molding material using a crystalline resin. In the case of the incompatible polymer alloy, it is the glass transition temperature or the crystallization start temperature of the resin constituting the sea having a sea-island structure.
Here, the crystallization start temperature of the crystalline resin is determined by heating the resin to a temperature at the time of molding using a differential calorimeter and melting the resin.
Cool at a rate of 0 ° C./min to a temperature at which heat generation due to crystallization of the resin is first observed.

In the first embodiment of the present invention, carbon dioxide is used as a substance which acts as a plasticizer to improve the fluidity of the molding material and lower the solidification temperature. Alternatively, a liquid such as a fluorocarbon, water, or alcohol in which a saturated hydrocarbon having 1 to 5 carbon atoms and / or a part of the hydrogen is replaced with fluorine can be used in combination.

It is necessary that the amount of carbon dioxide to be dissolved in the molten molding material in advance is 0.2% by weight or more, and preferably 0.3% by weight or more in order to remarkably improve the fluidity. The upper limit of the amount of dissolved carbon dioxide in the melt-molded material is not particularly limited, but a high gas pressure is required to dissolve a large amount of carbon dioxide. The practical amount of dissolved carbon dioxide is 10% by weight or less, more preferably 5% by weight or less, depending on the type of thermoplastic resin used, since the effect of improving the fluidity of the material and lowering the solidification temperature is reduced. It is.

Since it is difficult to directly measure the amount of carbon dioxide dissolved in the molten molding material, the present invention uses a counter gas having a pressure sufficient to suppress foaming of the molten molding material in which carbon dioxide is dissolved. With the pressure applied to the mold cavity, the weight of the molded product immediately after injection molding using a molten molding material containing carbon dioxide, and the obtained molded product, the glass transition temperature for amorphous resin In the case of crystalline resin, the difference between the weight of the molded article and the weight of the molded article after leaving carbon dioxide contained in the molded article for 24 hours or more in a hot air dryer whose melting point is lower than about 30 ° C. Is the amount of carbon dioxide in the molten molding material injected into the mold cavity.

As a method of dissolving carbon dioxide in the molten molding material in advance, the following two methods are preferable.

One is a method in which a granular or powdery resin used as a molding material is placed in a carbon dioxide atmosphere in advance, and carbon dioxide is absorbed and supplied to an injection molding machine. In this case, the amount of absorption is determined by the pressure of carbon dioxide, the ambient temperature, and the time for absorption. In this method, a part of carbon dioxide is volatilized by heating during plasticization of the molding material, so that the amount of carbon dioxide in the molten molding material is smaller than the amount previously absorbed. For this reason, it is desirable that the supply path of the molding material such as the hopper of the injection molding machine is also in a carbon dioxide atmosphere.

Another method is to plasticize the molding material in the injection cylinder of the injection molding machine or to dissolve carbon dioxide in the plasticized molding material. Or a method of injecting carbon dioxide into a molten molding material in an injection cylinder. When injecting carbon dioxide into the molten molding material in the injection cylinder, the depth of the screw groove near the injection part is increased, as in the vent part of a vent type screw cylinder, to transfer the molten molding material in that part. It is preferable to reduce the pressure of the molten molding material in a starvation state because carbon dioxide can be easily injected. As an injection molding machine, either an in-line screw system or a screw pre-plastic system can be used.

In the first embodiment of the present invention, in order to prevent the molten molding material in which carbon dioxide has been dissolved from foaming during the filling of the mold cavity, foaming marks are formed on the surface of the molded product. It is preferable to fill the mold cavity with the molten molding material while applying a counter gas pressure capable of suppressing the formation of foaming marks due to the foaming into the mold cavity. In this case, in order to easily obtain a necessary counter gas pressure, it is preferable to use a mold in which the periphery of the mold cavity is sealed with an O-ring or the like.

The counter gas pressure does not hinder the filling of the molten molding material into the mold cavity, minimizes the amount of gas used in one process, seals the mold cavity, and supplies gas. In order to simplify the structure of the apparatus, it is preferable that the temperature is as low as possible within a range where foaming marks on the surface of the molded product can be prevented. Counter gas pressure is 1
If it exceeds 5 MPa, problems tend to occur such that the force for opening the mold cannot be ignored, and the sealing of the mold cavity becomes difficult.

As the gas used to apply the counter gas pressure, a single substance or a mixture of various gases such as air and nitrogen can be used, but the solubility in the molten molding material at the time of molding (temperature and temperature during molding) can be used. A gas having a solubility in a molten material under pressure of 3 times or more than that of nitrogen is preferable. When such a gas body is used, since the solubility in the molten molding material is high, it is possible to not only improve the fluidity and lower the solidification temperature by dissolving in the molten molding material, but also to reduce the molding material and the mold surface. It is easy to prevent a gas body from being trapped in between and to form a depression on the surface of the molded article.

Examples of the gaseous material having a solubility in the molten molding material at least three times that of nitrogen in the above molding include carbon dioxide, hydrocarbons such as methane, ethane, and propane, and fluorocarbons in which some of them are replaced with fluorine. Among them, carbon dioxide, which has a high solubility in the molten molding material, and has a large effect of improving the fluidity of the molten molding material and lowering the solidification temperature, is most preferable.

In the first embodiment of the present invention, carbon dioxide in the molding material is gradually released into the atmosphere by leaving the molding in the atmosphere after the molding material has solidified. Therefore,
A molded article similar to that obtained by ordinary injection can be obtained without foaming and without the occurrence of weld lines.

Next, a second embodiment of the present invention will be described.

A second aspect of the present invention is a method of filling a molten molding material into a mold cavity previously filled with a gas having a solubility in the molten molding material of at least three times that of nitrogen during molding. When the mold cavity is filled with such a gas and then filled with the molten molding material, the gas is absorbed at the flow front of the molten molding material or enters the interface between the mold surface and the molten molding material. Dissolves in the skin layer of the molten molding material. The gas dissolved in the skin layer of the melt molding material acts as a plasticizer, improving the fluidity of the skin layer and lowering the solidification temperature. Therefore, even if the mold surface temperature is not heated to a conventional high temperature, the skin layer of the molten molding material filled in the mold cavity and in contact with the mold surface can also maintain good fluidity, The fluid can easily flow from the layer to the core layer. And
By this flow, the weld from the skin layer to the core layer can be eliminated, and the occurrence of weld lines on the surface of the molded product and the deterioration of mechanical properties can be prevented.

That is, in general injection molding, since the solidification of the molten molding material proceeds from the skin layer from which heat is first taken from the mold cavity surface, the propulsive force is applied to the molten molding material once filled in the mold cavity. It is difficult to make the skin layer flow even if it is applied and made to flow again. However, if the skin layer absorbs the gaseous substance and improves the fluidity of the skin layer and lowers the solidification temperature,
By applying a propulsive force to the molten molding material filled in the mold cavity, the molten molding material filled in the mold cavity can easily flow from the skin layer to the core layer.

In the second embodiment of the present invention, the temperature of the mold surface is controlled so that the molten molding material filled in the mold cavity flows from the skin layer to the core layer without fail. It is preferable that the temperature is set to a temperature equal to or higher than the solidification temperature of the skin layer, which is lowered by dissolving the gas body previously filled in the skin layer.

In the second embodiment of the present invention, the melt-forming material is rapidly dissolved in the melt-forming material, the fluidity of the skin layer is improved, and the solidification temperature is lowered. A gas whose solubility is three times or more that of nitrogen is used. As such a gas body, as described as the gas body used for the counter gas pressure in the first embodiment of the present invention, in addition to carbon dioxide, hydrocarbons such as methane, ethane, and propane and a part thereof are converted to fluorine. Can be used, but carbon dioxide, which has a high solubility in the molten molding material, and has a large effect of improving the fluidity of the molten molding material and lowering the solidification temperature, is most preferable.

In the second embodiment of the present invention, the gas body previously filled in the mold cavity is for dissolving in the skin layer of the molten molding material as described above. Although it is not intended to suppress foaming like the counter gas pressure, the higher the pressure of carbon dioxide filled in the mold cavity, the greater the decrease in the solidification temperature of the skin layer. Usually, preferably 1 to 8 MPa,
More preferably, the mold cavity is filled with carbon dioxide in the range of 3 to 6 MPa.

In the second embodiment of the present invention, it is preferable to use a mold in which the periphery of the mold cavity is sealed with an O-ring or the like. When the inside of the mold cavity of the seal mold is replaced with the low-pressure gas body and the molten molding material is injected and filled, the injected molten molding material causes the gas body in the mold cavity whose periphery is sealed. Are compressed and the pressure increases. When the gas pressure increases,
The amount of gas dissolved in the skin layer of the melt molding material increases,
The skin layer of the melt-molded material is plasticized by the dissolved gas body, the fluidity is improved, and the solidification temperature is lowered.

Also in the second embodiment of the present invention, the gas dissolved in the skin layer of the molten molding material is gradually released into the atmosphere by leaving the molded article in the atmosphere after the molten molding material has solidified. . Therefore, a molded article similar to that obtained by ordinary injection can be obtained without foaming, without the occurrence of weld lines.

In both the first embodiment and the second embodiment of the present invention,
Although a normal injection speed is sufficiently effective, it is preferable to use high-speed injection molding, which is effective for producing a thin molded product such as a material having a high viscosity, because the effect is further improved. What is high-speed injection molding?
Injection speed is 100 mm / sec or more, preferably 300 mm / sec.
mm / sec.

In both the first embodiment and the second embodiment of the present invention,
It is preferable to use a heat insulating mold in which the mold surface is covered with a heat insulating layer. With the use of this heat-insulating mold, the presence of the heat-insulating layer delays the cooling of the skin layer of the melt-molded material injected and filled in the mold cavity. Coupled with the lowering of the solidification temperature, it becomes easier to flow from the skin layer to the core layer.
Accordingly, the range of the mold temperature allowed during the injection filling of the molten molding material is widened, and the adjustment of the mold temperature becomes easy.

It is preferable to use a heat-resistant polymer as the heat-insulating layer of the heat-insulating mold. A heat-resistant polymer that is used well is a polymer having a higher softening temperature than the resin in the molding material used, and preferably has a glass transition temperature of 1
It is preferably a heat-resistant polymer having a glass transition temperature of 40 ° C. or higher, more preferably 160 ° C. or higher, most preferably 190 ° C. or higher, and / or a melting point of 200 ° C. or higher, more preferably 250 ° C. or higher. The thermal conductivity of the heat-resistant polymer is generally about 0.1 to 0.3 W / m · K,
It is significantly smaller than about 10 to 100 W / m · K of metal. Further, in order to obtain the durability of the heat insulating layer, the elongation at break of the heat-resistant polymer is preferably at least 4%, preferably at least 5%, more preferably at least 10%. The elongation at break is measured according to ASTM D638, and the tensile speed at the time of measurement is 5 mm / min.

Specific examples of the heat-resistant polymer which can be favorably used as the heat-insulating layer of the heat-insulating mold include a heat-resistant polymer having an aromatic ring in the main chain. For example, various non-crystalline heat-resistant polymers soluble in organic solvents, various polyimides and the like can be used favorably. Examples of the non-crystalline heat-resistant polymer include polysulfone and polyether sulfone.
These amorphous heat-resistant polymers can be preferably used as a heat-insulating layer of a heat-insulating mold by lowering the thermal expansion coefficient by blending carbon fibers and various inorganic fillers. There are various types of polyimides, and linear high molecular weight polyimides and partially crosslinked polyimides can be used favorably. The straight-chain high-molecular-weight polyimide has a large breaking elongation, is tough, and has excellent durability, so that it can be used particularly favorably. The straight-chain high-molecular-weight polyimide includes polyamideimide and polyetherimide.

Further, as a heat insulating layer of the heat insulating mold, an epoxy resin cured product having a small thermal expansion coefficient, that is, an epoxy resin cured product obtained by combining a curing agent having a small thermal expansion coefficient and an epoxy resin, or a proper amount of various fillers is blended. A cured epoxy resin product or the like can also be used (hereinafter, the cured epoxy resin product is abbreviated as an epoxy resin). Epoxy resins generally have a large coefficient of thermal expansion, and the difference in coefficient of thermal expansion from a metal mold is large. However, an appropriate amount of powder, particles such as glass, silica, talc, clay, zirconium silicate, lithium silicate, calcium carbonate, alumina, and mica having a small coefficient of thermal expansion, glass fiber, whisker, and carbon fiber are blended into the epoxy resin. In addition, a filler-filled epoxy resin having a small difference in thermal expansion coefficient from that of a metal mold can be favorably used as a heat insulating layer.

The heat insulating layer made of the above heat-resistant polymer preferably has a thickness of 0.0 to 0.3 mm from the viewpoint of processability and heat insulating properties. Further, for the purpose of improving the surface hardness of the surface on which the heat insulating layer is provided, or imparting the releasability of the molded product, a top coat layer of a heat resistant hard material may be provided on the surface of the heat insulating layer made of a heat resistant polymer.

In the present invention, the injection pressure or the injection secondary pressure generally called resin holding pressure can be used to reflow the molten molding material once filled and stopped in the mold cavity. . When using this injection pressure or injection secondary pressure to flow, the molten molding material can be easily re-flowed by providing a space that can fill the mold cavity and allow the filled molten molding material to flow out. Can be done.

For example, using a mold having a disposal cavity connected to the mold cavity via the opening / closing means, filling the inside of the mold cavity with the opening / closing means closed, and injecting and filling the molten molding material. Opening and closing means with the injection pressure and injection secondary pressure applied, and while feeding new molten molding material into the mold cavity from the injection cylinder of the injection molding machine, dispose of the molten molding material in the mold cavity to the cavity. It can be made to flow by extruding. As the opening / closing means, an opening / closing valve that is opened / closed by pneumatic pressure, hydraulic pressure, magnetic force, a motor, or the like can be used.

As described above, the flow of the molten molding material filled in the mold cavity is caused by pushing the new molten molding material into the mold cavity while the molten molding material already filled in the mold cavity is being pressed. Can be performed only by extruding at least a part of the molten molding material out of the mold cavity.However, the molten molding material in the mold cavity is extruded from the mold cavity, and the extruded molten molding material is injected into the mold cavity. Is preferably performed by pushing back. By doing so, a shearing force can be applied to the molten molding material in the mold cavity by the extrusion and the pushback, and the disappearance of the weld can be performed more reliably.

The extruding and pushing back of the molten molding material in the mold cavity is performed by at least two places where the molten molding material can be pushed into the mold cavity and the molten molding material extruded from the mold cavity can be received. This can be performed by using a mold connected to the local mold cavity. For example, two cylinders in a mold cavity
The piston mechanism is connected, and one of the two cylinder-piston mechanisms is retracted, and the other piston is advanced, injecting and filling the mold cavity with the molten molding material. Is filled with the molten molding material, and then one piston that has been retracted is advanced, and the other piston that has been advanced is retracted, so that the molten molding material in one cylinder is pushed into the mold cavity and At least a part of the molten molding material in the mold cavity is extruded into the other cylinder, and the molten molding material in the mold cavity flows. Next, while retracting the one piston,
When the other piston is advanced, the molten molding material extruded into the other cylinder is pushed again into the mold cavity, and at least a part of the molten molding material in the mold cavity is pushed out into the one cylinder. .

The extrusion of the molten molding material in the mold cavity to the outside of the mold cavity and the extrusion of the extruded molten molding material back into the mold cavity facilitate the formation of a molded product having no surface roughness. In addition, it is preferable to perform the process while the mold cavity is always filled with the molding material. In addition, the extrusion and pushback of the molten molding material,
What is necessary is just to repeat the minimum number of times that a weld disappears.

In the present invention, at least one molding material is used.
It contains various kinds of thermoplastic resins, and is not particularly limited as long as it is generally used for injection molding. For example, rubber-reinforced styrene resins such as polystyrene, high impact polystyrene, and medium impact polystyrene, styrene-acrylonitrile copolymer (SAN resin), acrylonitrile-butyl acrylate rubber-styrene copolymer (AAS resin), acrylonitrile-ethylene propyl Rubber-styrene copolymer (AES), acrylonitrile-chlorinated polyethylene-styrene copolymer (ACS), ABS resin (for example, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-butadiene-styrene-alpha-methylstyrene copolymer, Styrene resins such as acrylonitrile-methyl methacrylate-butadiene-styrene copolymer), modified polyphenylene ether (m-PPE), polymethyl methacrylate Over door (PMM
A) and other acrylic resins, low density polyethylene (LD
Olefin resins such as PE), high-density polyethylene (HDPE) and polypropylene (PP); vinyl chloride resins such as polyvinyl chloride and polyvinylidene chloride; ethylene-vinyl chloride-vinyl acetate copolymer; ethylene-vinyl chloride copolymer Polyvinyl chloride resins such as polymers, polyester resins such as polyethylene terephthalate (PETP, PET) and polybutylene terephthalate (PBTP, PBT), polycarbonate resins such as polycarbonate (PC) and modified polycarbonate, polyamide 6
6, polyamide resins such as polyamide 6, polyamide 46, polyacetal (POM) such as polyoxymethylene copolymer and polyoxymethylene homopolymer, other engineering resins, and super engineering resins such as polyether sulfone (PES) and polyether Imide (PEI), thermoplastic polyimide (T
PI), polyetherketone (PEK), polyetheretherketone (PEEK), polyphenylenesulfide (PSU), cellulose acetate (CA), cellulose derivatives such as cellulose acetate butyrate (CAB), ethylcellulose (EC), liquid crystal polymer,
Liquid crystal polymer such as liquid crystal aromatic polyester,
Furthermore, thermoplastic polyurethane elastomer (TPU),
Thermoplastic styrene butadiene elastomer (SBC),
Examples include thermoplastic elastomers such as thermoplastic polyolefin elastomer (TPO), thermoplastic polyester elastomer (TPEE), thermoplastic vinyl chloride elastomer (TPVC), and thermoplastic polyamide elastomer (TPAE). In the present invention, the above-mentioned thermoplastic resin may be synthesized in the molding process of the present invention. Also, a blend of one or more thermoplastic resins can be used.

The molding material of the present invention can be obtained by adding additives and fillers such as generally used plasticizers, coloring agents, ultraviolet absorbers and antistatic agents to the above-mentioned thermoplastic resin. .

The filler which can be added to the thermoplastic resin also includes an inorganic substance. For example, in addition to glass fiber, glass beads, calcium carbonate, mica, and asbestos, powders of metals such as iron, copper, zinc, and aluminum, hollow bodies, flakes, and metal oxides and metal hydroxides of these metals It may be a thing. The present invention is particularly effective for injection molding using a molding material generally called a metallic material, to which a metal filler such as aluminum flake, which is liable to cause poor appearance due to a weld line, is added.

The present invention also relates to a sandwich molding method in which a molten molding material to be a skin layer is injected in a small amount that is insufficient to fill a mold cavity, and then a molten molding material to be a core layer is injected to fill a mold cavity. Is also effective. The improvement of the molded article according to the present invention is carried out for both the skin layer and the core layer, and is particularly effective in the above-mentioned sandwich molding, even when the skin layer is stretched thin like a coating film.

The present invention relates to molded articles requiring high external appearance quality, especially home appliance parts housings, panels, limoncon housings having a metallic appearance, automobile exterior parts such as resin foil caps and bumpers, and the like. , Automobile interior parts such as instrument panels and clusters, and communications such as mobile phones,
It is suitable for molding IT-related parts housings.

The present invention will be further described with reference to the drawings.

First, an example of the present invention will be described with reference to FIGS.

FIG. 1 is an overall view showing an example of an injection molding apparatus used in the present invention, and FIGS. 2 to 3 are enlarged sectional views of the tip of the injection cylinder 3, the manifold 4 and the mold 1 in FIG. 1 shows the operating state of each part when molding is performed based on the present invention.

In FIG. 1, 1 is a mold, 2 is a carbon dioxide supply device, 3 is an injection cylinder, and 4 is a manifold.

The carbon dioxide supply device 2 is connected to the mold 1 and the injection cylinder 3. The carbon dioxide supplied to the mold 1 gives a counter gas pressure to the mold cavity,
The carbon dioxide supplied to the injection cylinder 3 is dissolved in a molding material that is plasticized and melted in the injection cylinder 3.

The injection cylinder 3 plasticizes and melts the molding material supplied from the rear end hopper 5 and dissolves the carbon dioxide supplied from the carbon dioxide supply device 2 into the molten molding material. A manifold 4 having a cylinder / piston mechanism is connected to the tip of the injection cylinder 3, and the injection cylinder 3 is connected to the mold 1 via the manifold 4.

As shown in FIG. 2, the injection cylinder 3 has a screw 6. The screw 6 is provided coaxially in the injection cylinder 3 so that it can rotate around its axis and move in the axial direction within the cylindrical injection cylinder 3.

The injection nozzle 7 provided at the tip of the injection cylinder 3 is connected to the bush 8 of the manifold 4. The bush 8 is connected to a bifurcated passage 9 in the manifold 4, and each end of the branched passage 9 is connected to a cylinder 10, 11. Cylinder 10,
Numeral 11 includes pistons 12 and 13 which are respectively slid in the axial direction. In addition, cylinders 10 and 11
Are connected to separate manifold nozzles 16 and 17 via channels 14 and 15, respectively.

The manifold nozzles 16 and 17 are connected to two sprues 18 and 19 provided on the mold 1, respectively. Each sprue 18, 19 is 2
Runners 20, 21 and each runner 20,
21 is connected to a mold cavity 22.

The mold 1 is generally set at a temperature of 20 ° C. to 80 ° C. by using a normal refrigerant temperature controller.

The granular molding material is supplied into the injection cylinder 3 from the hopper 5 shown in FIG. 1, and is heated by a cylindrical barrel heater (not shown). The molding material is
As the screw 6 rotates, it is heated while being advanced in the injection cylinder 3, plasticized, and sufficiently homogenized. At this time, carbon dioxide is injected from the carbon dioxide supply device 2 into the intermediate portion (generally, a vent portion) of the injection cylinder 2 and dissolved in the molten molding material.

When the viscosity of the melt-molded material obtained by melting carbon dioxide has reached an appropriate level, the mold 1 previously heated to a desired temperature is heated.
Inject to. The injected molten molding material passes through the passage 9, the cylinder 10 and the channel 14 in the manifold 4.
Through the sprue 18 and the runner 20 of the mold 1 and into the mold cavity 22, and further the runner 21 and the sprue 1
9. It reaches the cylinder 11 through the passage 15 and fills the whole. The arrows in FIG. 2 indicate the flow of the molten molding material during injection filling.

Next, as shown in FIG. 3, the pistons 12, 13 are reciprocated in the same cycle, preferably with a phase difference of 180 degrees. The reciprocating motion of the pistons 12 and 13 gives a periodic driving force to the molten molding material filled in the mold cavity 22 and causes the molten molding material to flow.

Specifically, after injection molding of the molten molding material, as shown in FIG. 3, while maintaining the pressure from the injection cylinder 3, the piston 12 is advanced and the piston 1 is moved forward.
3 is retracted, the molten molding material is pushed out of the cylinder 10 by the advance of the piston 12, and the channel 1
4. While being pushed into the mold cavity 22 through the sprue 18 and the runner 20, the mold cavity 22
The molten molding material filled in the inside is extruded toward the runner 21. Subsequently, when the piston 12 is retracted and the piston 13 is advanced, the molten molding material is pushed into the mold cavity 22 from the runner 21 side, and the molten molding material in the mold cavity 22 is moved to the runner 20 side. Will be extruded. Therefore, the molten molding material reciprocates in the mold cavity 22, and the shearing force can be continuously applied by this reciprocating reciprocation.

During the flow of the molten molding material due to the reciprocating movement, it is preferable to control the cooling rate of the molten resin material by, for example, a microprocessor control (not shown). The contraction of the molding material in the mold cavity 22 due to cooling is compensated for by the molten molding material supplied from the injection cylinder 3 and the manifold 4.

It is preferable that the application of the shearing force is performed while maintaining the mold 1 in a state of being filled with the molten molding material.
Further, the flow of the molten molding material for applying the shearing force can be started immediately before the mold cavity 22 is completely filled with the molten molding material. In this way, the time required for the flow of the molten molding material after the completion of the injection filling of the molten molding material into the mold cavity 22 can be reduced.

After the reciprocating operation of the molten molding material in the mold cavity 22 is completed, the molded product in the mold cavity 22 is substantially solidified, but when the gate portion is not yet solidified, In order to compensate for the pressure from the injection cylinder 3, the pistons 12, 1
It is preferable that the pressure of the molten molding material in the mold cavity 22 is maintained by urging the mold cavities 3 in the same direction in the forward direction.

Next, the molded product is released from the mold 1 and, as shown in FIG. 4, the screw 6 of the injection cylinder 3 moves upstream to prepare for the next molding cycle, Weigh the molding material.

In a continuous injection molding cycle, the molten molding material is injected into the cylinder 10 in order to prevent the supplied molten molding material from being trapped on the way and to be deteriorated.
It is preferable to alternate between the side and the cylinder 11 side. Also,
The manifold 4 preferably has a heater (not shown) so that the fluidity of the molten molding material can be maintained.

FIG. 5 shows an example of a mold used in the injection molding method of the present invention. Two manifolds 51 and 52 forming a cylinder / piston mechanism are embedded in a mold 53. Each of the manifolds 51 and 52 has a piston 54 and 55, respectively, and is connected to a mold cavity 58 through gates 56 and 57. In addition, each manifold 5
1, 52, so that the fluidity of the molten molding material can be maintained,
Heaters 59 and 60 are provided.

In the present embodiment, after the injection molding of the molten molding material from the injection cylinder 61 into the mold cavity 58, the pistons 54, 55 are advanced and retracted by a hydraulic pressure with a phase difference of 180 degrees, so that the inside of the mold cavity 58 is reduced. The molten molding material can be reciprocated. Each manifold 51,
It is preferable that the capacity 52 is set to a capacity that allows the molten molding material in the mold cavity 58 to reciprocate effectively. Incidentally, 62 is a sprue.

FIG. 6 shows a modified example of the mold shown in FIG. 5, in which the manifolds 51 and 52 are protruded to the side of the mold 53, and the manifolds 51 and 52 are provided for flow support.
52 is the same as the mold 53 of FIG. 5 except that heaters 63 and 64 are also provided at the gates 56 and 57. FIG.
The same reference numerals indicate the same members.

FIG. 7 shows another example of a mold used in the injection molding method of the present invention, in which a single manifold 71 is provided on one side of a mold 72. The manifold 71 forms a cylinder-piston mechanism, has a piston 73, and has a mold cavity 75 through a gate 74.
Is in communication with The manifold 71 has heaters 76 and 77 so that the fluidity of the molten molding material can be maintained.
9 are provided.

In this example, after the molten molding material is injected into the mold cavity 75 from the injection cylinder 80, the piston 73 and the screw 81 of the injection cylinder 80 are
By causing the molten molding material in the mold cavity 75 to reciprocate by moving forward and backward with a phase difference of 0 degrees. It is preferable that the manifold 71 has a capacity capable of effectively causing the molten molding material in the mold cavity 75 to reciprocate and flow.

FIG. 8 shows a modification of the mold 72 shown in FIG. 7, in which the manifold 71 is embedded in the mold 72 and the piston 73 of the manifold 71 is moved forward by a spring 82 in the forward direction. It is the same as the mold 72 of FIG. 7 except that it is pressed. The same reference numerals as those in FIG. 7 indicate the same members.

In the case of the present embodiment, the piston 73 is automatically advanced and retracted by the spring 82 simply by moving the screw 81 of the injection cylinder 80 forward and backward, and the molten molding material in the mold cavity 75 can flow.

When the molds shown in FIGS. 5 to 8 are used, an injection cylinder having a general injection nozzle can be used, and the trouble of preparing and replacing a special injection nozzle can be omitted. In addition, since it is easy to freely select the installation position of the manifold, and the manifold can be provided at a position close to the mold cavity, the molten molding material in the mold cavity can flow quickly and with low pressure. .

[0081]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 In this example, molding was performed using the injection molding apparatus with a carbon dioxide supply device described with reference to FIGS.

As a molding material, an ABS resin containing 1.5% by weight of aluminum flakes prepared by compounding aluminum flakes having an average particle diameter of 30 μm and transparent ABS was used. The die was made of steel, and the molded product was a rectangular flat plate having a thickness of 2 mm, a length of 50 mm, and a width of 150 mm, and a shape having a hole in the flat plate portion.

The temperature of the injection cylinder of the injection molding machine was set so that the temperature of the molten molding material was 240 ° C. Carbon dioxide was supplied to a mold and an injection cylinder as shown in FIG. Carbon dioxide is 10MPa in the injection cylinder
Under an atmosphere of carbon dioxide in the injection cylinder, and was dissolved in the kneaded molten molding material. Carbon dioxide was supplied into the mold at 5 MPa. At this time, a sealing material was provided around the mold cavity so that carbon dioxide did not leak from inside the mold cavity, and the injection port of the molten molding material was closed by nozzle touch.

Next, the molten molding material was charged into the mold at an injection speed of 200 mm / sec through a manifold. Immediately move the two pistons shown in FIG.
Reciprocating motion was performed at the same cycle with a phase difference of 80 degrees as shown in FIG. The reciprocation was performed for 3 seconds in one cycle. Next, at a set pressure of 40% of the maximum output of the hydraulic pump, the molded product was cooled while applying static holding pressure for 20 seconds with both pistons, and then released.

The obtained molded product was excellent in appearance without a weld line despite having a hole.

Comparative Example 1 Molding was performed under the same conditions as in Example 1 except that the same injection molding machine, mold and molding material as in Example 1 were used, and that no carbon dioxide was supplied. As a result, weld lines were generated in the vicinity of the hole of the molded product, and only those having poor appearance could be molded.

Example 2 As a molding material, an aluminum flake having an average particle diameter of 10 μm and a transparent ABS were prepared.
The same molded article was molded by the same injection molding apparatus as in Example 1 using the ABS resin containing aluminum flakes by weight.

In molding, carbon dioxide is not supplied to the injection cylinder, only the mold cavity is filled. After filling the mold cavity with carbon dioxide of 3 MPa, the molten molding material is molded. Other than filling inside,
The molding was performed in the same manner as in Example 1.

The obtained molded product was excellent in appearance without a weld line, despite being a molded product having holes.

Example 3 In this example, molding was performed by providing the mold shown in FIG. 6 in the injection molding apparatus shown in FIG. 1 (the injection nozzle was a normal one). The mold was a heat-insulating mold in which the mold surface was covered with a polyimide heat-insulating layer. The thickness of the polyimide layer is about 0.1 mm
Then, the polyimide layer was covered with 0.01 mm of epoxy-silicone.

As the molding material, AB containing 1% by weight of aluminum flake was prepared by compounding aluminum flake having an average particle diameter of 10 μm and transparent ABS.
S resin was used. The molded product was the same as in Example 1.

The injection cylinder temperature of the injection molding machine was set so that the temperature of the molten molding material was 240 ° C. Carbon dioxide was fed only into the injection cylinder (not into the mold cavity). Carbon dioxide is injected into the injection cylinder
The pressure was supplied at 0 MPa, and the inside of the injection cylinder was placed in a carbon dioxide atmosphere to dissolve the kneaded molten molding material.

Next, the molten molding material was charged into a mold at an injection speed of 200 mm / sec. Immediately, the two pistons shown in FIG. 6 were reciprocated in the same cycle with a phase difference of 180 degrees. The reciprocating motion was performed in one cycle for 3 seconds. Then, at a set pressure of 40% of the maximum output of the hydraulic pump, the molded product was cooled while applying static holding pressure with both pistons for 20 seconds, and then released.

The obtained molded article was a molded article having no weld line and excellent in appearance, despite being a molded article having holes.

As a result, according to the present invention, it was possible to eliminate the appearance defect due to the weld line when using the molding material containing metal flakes which could not be improved so far, and it was possible to obtain a high appearance molded product. .

[0097]

The present invention is as described above. According to the first embodiment, the flowability of a molten molding material is improved by the action of dissolved carbon dioxide as a plasticizer, and Since the temperature is lowered, a molded article having a high appearance without a weld line can be obtained even if the surface temperature of the mold is lower than in the past. Further, according to the second embodiment, by dissolving a gaseous substance such as carbon dioxide filled in the mold cavity, the fluidity of the skin layer of the molten molding material in the mold cavity is increased, and the solidification temperature is increased. Can be lowered,
Even if the mold surface temperature is lower than in the past, a high appearance molded product without a weld line can be obtained. Therefore, the molding efficiency can be increased, the temperature load on the mold can be reduced, and the life of the mold can be extended.

[Brief description of the drawings]

FIG. 1 is an overall view showing an example of an injection molding apparatus used in the present invention.

FIG. 2 is an enlarged cross-sectional view of a tip portion, a manifold, and a mold portion of the injection cylinder in FIG. 1, showing a state at the time of injection of a molten molding material.

FIG. 3 is an enlarged cross-sectional view of a tip portion, a manifold, and a mold portion of the injection cylinder in FIG. 1, illustrating a state in which a molten molding material flows in a mold cavity.

FIG. 4 is an enlarged cross-sectional view of a tip portion, a manifold, and a mold portion of the injection cylinder in FIG. 1, showing a state in preparation for a next molding cycle.

FIG. 5 is a diagram showing an example of a mold used in the present invention.

FIG. 6 is a view showing a modification of the mold of FIG. 5;

FIG. 7 is a view showing another example of a mold used in the present invention.

FIG. 8 is a view showing a modification of the mold of FIG. 7;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 carbon dioxide supply device 3 injection cylinder 4 manifold 5 hopper 6 screw 7 injection nozzle 8 bush 9 passage 9 10, 11 cylinder 12, 13 piston 14, 15 channel 16, 17 manifold nozzle 18, 19 sprue 20, 21 runner 22 Mold cavity 51, 52 Manifold 53 Mold 54, 55 Piston 56, 57 Gate 58 Mold cavity 62 Sprue 59, 60, 63, 64 Heater 61 Injection cylinder 71 Manifold 72 Mold 73 Piston 74 Gate 75 Mold cavity 76 , 77, 79 Heater 78 Sprue 80 Injection cylinder 81 Screw 82 Spring

Continued on the front page F term (reference) 4F202 AA13 AB11 AB16 AJ03 AJ09 AJ13 CA11 CB01 CK01 CK11 4F206 AA13 AB11 AB16 AF16 AJ03 AJ09 AJ13 AM36 JA07 JF02 JN27 JQ81

Claims (7)

[Claims] 2. A method according to claim 1, wherein after filling a molten molding material in which carbon dioxide is dissolved in an amount of 0.2% by weight or more into a mold cavity, at least a part of the molten molding material is caused to flow in the mold cavity. Molding method for high appearance molded products. 2. The injection molding method for a high-appearance molded product according to claim 1, wherein the molten molding material is filled in a mold cavity to which a counter gas pressure is applied. 3. After filling the molten molding material into a mold cavity filled with a gas having a solubility in the molten molding material three times or more of nitrogen at the time of molding at a pressure of 0.1 MPa or more, at least a part thereof. Injection molding method for a high appearance molded product, wherein the molten molding material is flowed in a mold cavity. 4. The injection molding method for a high-profile molded article according to claim 3, wherein the gas having a solubility in the molten molding material at the time of molding that is three times or more that of nitrogen is carbon dioxide. 5. The flow of the molten molding material includes extruding the molten molding material in the mold cavity out of the mold cavity;
5. The injection molding method for a high-appearance molded product according to claim 1, wherein the injection molding is performed by pushing back the molten molding material extruded out of the mold cavity into the mold cavity. 6. The injection molding method for a high-appearance molded product according to claim 1, wherein a heat-insulating mold whose surface is covered with a heat-insulating layer is used. 7. The injection molding method for a high-appearance molded product according to claim 1, wherein the molten molding material contains a filler.