JP2003320556A - Surface modifying injection molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel injection molding method enabling modification of the surface of a molded article at the same time with injection molding and to efficiently and inexpensively manufacture the molded article of which the surface portion alone is so modified as to have necessary properties, without using a resin mixed with a modifier beforehand. <P>SOLUTION: The modifier is dissolved or dispersed in a pressure gas having solubility to a molten resin to be injected. The gas is poured into a mold cavity and then the molten resin is injected thereinto. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-modified injection molding method capable of modifying the surface of a molded article simultaneously with molding.

[0002]

2. Description of the Related Art Conventionally, for example, a molded product is colored by injection molding using a molten resin mixed with a coloring material in advance or by painting the molded product. In addition, imparting antistatic properties and electromagnetic wave shielding properties to molded products,
It is performed by injection molding using a molten resin in which an antistatic material or an electromagnetic wave shielding material is premixed, or by applying an antistatic material to the obtained molded product or by applying a metallic coating.

On the other hand, in molding using a thermoplastic resin, a gas body whose solubility in the resin is at least twice that of air and / or nitrogen at the solidification temperature of the resin is used, and a mold into which this gas body is injected is used. It is known to inject a molten resin into a cavity for molding (Japanese Patent Laid-Open No. 10-12878).
3 gazette). In addition, as a method for filling the mold cavity with a gas body, there is a method called a counter pressure method for improving the appearance of the surface of the molded body in foam molding.

[0004]

However, the above-mentioned conventional coloring, imparting antistatic property and electromagnetic wave shielding property, etc. are used when a modifying agent necessary for modifying these is mixed in advance with a molten resin. Since the modifier is mixed with the entire resin, not only will the consumption of the modifier increase, but depending on the type of modifier, the physical properties of the molded product will tend to deteriorate as the amount added increases. There is. Further, when the molded product is later coated, the consumption of the modifier is smaller than that when it is added to the entire resin used, but there is a problem that the number of manufacturing steps increases and the cost increases.

On the other hand, in a conventional injection molding method in which a gas body having a high solubility in a resin is injected into a mold cavity, the gas body is melted on the surface of the molten resin injected into the mold cavity to set the solidification temperature. To lower the mold surface transfer property.

To further explain, in general injection molding, in order to cool and solidify a resin material which is a polymer material whose thermal conductivity is significantly lower than that of a metal material, in a short time,
Usually, the mold temperature is kept sufficiently lower than the solidification temperature of the molding resin. However, since the mold temperature is set lower than the solidification temperature of the resin, the resin that comes into contact with the mold near the resin flow front end (flow front) is rapidly cooled and the viscosity increases, and Before the cavity is filled with resin, it solidifies while being pressed against the mold surface with a low pressure, so that it becomes difficult to transfer the mold surface state to the surface of the molded article to a high degree.

In order to solve these problems, in Japanese Patent Laid-Open No. 10-128783, the mold cavity is filled with carbon dioxide gas having excellent solubility in the resin, so that the resin in the resin filling step is It is intended to prevent solidification and increase in viscosity. In injection molding, the resin always flows in a laminar flow in the mold cavity, and when it contacts the cooled mold wall surface, a solidified layer is formed at its interface, and the resin filled later flows inside the solidified layer. In general, a flow behavior called a fountain flow that advances toward a resin flow front end (flow front) and reaches a mold wall surface is shown. When the mold cavity is filled with a specific gas that is easily dissolved in resin such as carbon dioxide and then the molten resin is filled in the mold cavity, the gas body in the mold cavity becomes the skin layer of the molded product due to the fountain flow. It is thought to dissolve. The gas body dissolved in the skin layer of this molded article acts as a plasticizer, lowering the solidification temperature only on the resin surface or lowering the melt viscosity of the resin, resulting in a marked improvement in the mold surface transferability of the molded article. Will be able to.

As described above, the conventional injection molding method of injecting a gas body having a high solubility in resin into the mold cavity is a method of pre-filling the mold body with the gas body. It is not intended to modify the surface of the obtained molded product.

In the counter pressure method, in order to prevent surface defects such as swirl marks on the surface of the molded product due to foaming gas in the injection molding of a foaming resin containing a foaming agent and water, an inert gas body is previously charged with gold. This is a method in which the material to be filled in the mold is filled with a pressure that prevents foaming when filling the resin. In this method, an inert gas that does not cause oxidative deterioration or modification of the resin surface, that is, nitrogen, air, or carbon dioxide is selected, and economical compressed air is used among them.

As described above, the conventional counter pressure method is also a method of preliminarily filling the mold cavity with a gas, but it is not intended to modify the surface of the obtained molded product.

The present invention provides a new injection molding method capable of modifying the surface of a molded product at the same time as injection molding, and only the surface portion is modified to a required property without using a resin mixed with a modifying material in advance. It is an object of the present invention to enable a quality molded product to be efficiently and inexpensively manufactured.

[0012]

According to the present invention, a pressurized gas having a solubility in a molten resin to be injected is used as a carrier of a reforming agent and a reforming accelerating material. In contrast, a pressurized gas having solubility is used, the pressurized gas in which the modifier is dissolved or dispersed is injected into the mold cavity, and then a molten resin is injected into the mold cavity. The present invention provides a surface-modified injection molding method, which is characterized in that a molded product surface-modified with a quality material is obtained.

In the above invention, the pressurized gas is injected as a supercritical fluid into the mold cavity, the pressurized gas is carbon dioxide, and the modifier dissolved or dispersed in the pressurized gas is colored. Material, antistatic material, electromagnetic wave shielding material or weather resistant material, modifying material dissolved or dispersed in pressurized gas is a resin material, modified material dissolved or dispersed in pressurized gas is an inorganic material Is included as a preferred embodiment.

The modification in the present invention includes not only changing the physical properties and chemical properties but also changing the color (coloring).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The resin used as an injection molding material in the present invention is a thermoplastic resin used in general injection molding. Specific examples include polystyrene, rubber-reinforced polystyrene, and styrene-acrylonitrile copolymer (SA
N resin), acrylonitrile-butyl acrylate rubber-styrene copolymer (AAS resin), acrylonitrile-ethylene propyl rubber-styrene copolymer (AE
S), acrylonitrile-polyethylene chloride-styrene copolymer (ACS), ABS resin (for example, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-butadiene-styrene-alphamethylstyrene copolymer, acrylonitrile-methylmethacrylate-).
Styrene resins such as butadiene-styrene copolymer), modified polyphenylene ether (m-PPE), acrylic resins such as polymethylmethacrylate (PMMA),
Olefin resin such as low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP), vinyl chloride resin such as polyvinyl chloride, polyvinylidene chloride, ethylene vinyl chloride vinyl acetate copolymer, ethylene vinyl chloride Vinyl chloride copolymer resin such as copolymer, polyethylene terephthalate (PET,
PET), polybutylene terephthalate (PBTP, P
Polyester resin such as BT), polycarbonate (PC), polycarbonate resin such as modified polycarbonate, polyamide resin such as polyamide 66, polyamide 6, polyamide 46, polyacetal (POM) such as polyoxymethylene copolymer and polyoxymethylene homopolymer ) Resins, other engineering resins, super engineering resins such as polyether sulfone (PES), polyether imide (PE)
I), thermoplastic polyimide (TPI), polyetherketone (PEK), polyetheretherketone (PEE)
K), polyphenylene sulfide (PSU), etc., as well as cellulose acetate (CA), cellulose acetate butyrate (CAB), ethyl cellulose (EC)
Examples thereof include liquid crystal polymers such as cellulose derivatives, liquid crystal polymers, and liquid crystal aromatic polyesters.
In addition, thermoplastic polyurethane elastomer (TPU),
Thermoplastic styrene butadiene elastomer (TSB
C), thermoplastic polyolefin elastomer (TP
O), thermoplastic polyester elastomer (TPE
E), thermoplastic vinyl chloride elastomer (TPVC),
A thermoplastic elastomer such as a thermoplastic polyamide elastomer (TPAE) can also be used.

The resin used as an injection molding material in the present invention may be one of the above-mentioned thermoplastic resins, a blend of two or more of the above-mentioned thermoplastic resins, a filler such as glass fiber and / or a filler. It may contain an additive material or the like.

As the gas used as the pressurized gas in the present invention, a gas having a solubility in the injected molten resin is used. The gas preferably has a high solubility in the molten resin to be injected, and specifically, a gas having a solubility in the resin to be used that is twice or more that of nitrogen at the solidification temperature of the resin is preferable. Specifically, it is a hydrocarbon such as carbon dioxide, methane, ethane, or propane, and a chlorofluorocarbon in which a part of hydrogen is replaced with fluorine, and an optimum one is selected depending on the resin used. Among them, carbon dioxide can be best used in terms of safety, price, handling, and environmental impact.

The solidification temperature of the above resin means a glass transition temperature for an amorphous resin and a crystallization start temperature for a crystalline resin. In the incompatible polymer alloy, it is the glass transition temperature or the crystallization start temperature of the resin forming the sea of the 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 to melt the resin, and then cooling at a rate of 20 ° C./min to generate heat due to crystallization of the resin. Refers to the temperature that is first observed.

In the present invention, the pressurized gas which is injected into the mold cavity prior to the injection of the molten resin is the one in which the modifying agent described later is dissolved or dispersed and is injected into the mold cavity. In addition to acting as a carrier for the molten resin, it dissolves on the surface of the molten resin injected into the mold cavity to facilitate the incorporation of the dissolved or dispersed modifier into the resin surface, thus promoting surface modification. Play a role.

The higher the pressure of the pressurized gas pressed into the mold cavity is, the more the surface of the resin filled in the mold is absorbed, and the more the modifier is dissolved or dispersed in the pressurized gas, the surface of the resin. Can be taken into account. Therefore, in order to highly modify the surface of the obtained molded body, it is preferable that the pressure of the pressurized gas is high. However, if the pressure is too high, it will be difficult to seal the mold cavity for filling the pressurized gas, and the force of the pressurized gas injected into the mold cavity to open the mold will be ignored. Since it becomes impossible to do so, 20 MPa or less is practical, preferably 15 MPa or less, more preferably 10 MPa or less. The lower the gas pressure, the more convenient and economical the facility is. Therefore, it is preferable to keep the gas pressure as low as possible within the range where the required surface modification can be obtained. If the pressure of the pressurized gas is too low, it will be difficult for the pressurized gas to dissolve on the resin surface, and the degree of modification of the surface of the molded product will easily decrease.Therefore, the lower limit of gas pressure is the solubility of the gas in the resin used. Depending on the solidification temperature of the resin used, the pressure is a pressure at which 0.1 wt% resin is dissolved at equilibrium, preferably a pressure at which 0.5 wt% is dissolved, and more preferably a pressure at which 2 wt% resin is dissolved. Is.

The modifier may be dissolved or dispersed in the pressurized gas. However, when the modifier is dissolved in the pressurized gas, the gas pressure and temperature at which the amount of dissolved material appears remarkably becomes large. preferable. That is, when the modifier exhibits a large solubility when the used gas is in the supercritical state, it is preferable that the pressurized gas has a pressure and temperature higher than the supercritical state. When carbon dioxide is used as the pressurized gas, it is preferable that the carbon dioxide is in a supercritical state at 31 ° C. and 73 atm (7.4 MPa) or higher.

When pressurizing the pressurizing gas into the mold cavity, the air existing in the mold cavity before pressurizing the pressurizing gas into the mold cavity is sucked with a vacuum pump or replaced with the pressurizing gas. Preferably. However, when the pressure of the pressurized gas is high, the air remaining in the mold cavity can be ignored.

When the pressurized gas in which the modifier is dissolved or dispersed is injected, the mold cavity is sealed and it is preferable to suppress the leakage of the injected pressurized gas. After injecting the molten resin into the mold cavity, release the pressurized gas remaining from the mold cavity,
It is preferable that the injected molten resin can be sufficiently pressed against the mold cavity surface. The release of the pressurized gas after the injection filling of the molten resin can be performed by opening the valve of the release path leading to the mold cavity and opening the mold cavity to the atmosphere. In addition to releasing the above pressurized gas, a resin holding pressure is applied to the molten resin in the mold cavity to give sufficient pressure to press the resin in the mold cavity against the mold cavity surface until the surface of the molded product is solidified. Is desirable.

The modifier incorporated into the surface layer of the resin is fixed on the surface layer due to the solidification of the surface layer, and the gas body dissolved in the resin gradually becomes air if the molded product is left in the air after molding of the resin. Dissipate in. As a result, the modifier remains on the surface of the molded article, and a surface-modified molded article can be obtained.

It is desirable to take measures to prevent the liquefaction of the gas body in the device for supplying and discharging the gas body in which the modifier is dissolved or dispersed in the mold cavity, the gas pipe and the mold. It is more preferable that the gas body is set to a gas pressure and a temperature at which it is preferably in a supercritical state. As a method for preventing the liquefaction of the gas body, it is effective to heat the gas. The heating of the gas body is preferably set to a predetermined temperature with a warmer or the like, and the temperature of the flow path of the gas body or the mold is also preferably set to the critical temperature of the gas body or higher.

In order to easily fill the mold cavity with the pressurized gas, it is preferable to use an airtight mold used in the counter pressure method. In this airtight mold, the parting surface and the space between the plates are sealed by O-rings, and the periphery of the movable pins such as the protruding pins that communicate with the mold cavity are also sealed by the O-rings to seal the mold cavity. Therefore, escape of the pressurized gas from the mold cavity can be prevented. Further, in order to prevent gas leakage from the gap around the protrusion pin, there is also a device provided with an ejector box which covers and seals the entire protrusion plate.

The gas body containing the modifier can be easily injected into the mold cavity from a location generally used for degassing the mold cavity. Specifically, slits provided on the parting surface on the outer periphery of the mold cavity, gaps between mold inserts and protruding pins, gaps between fixed pins provided on the mold cavity surface and the mold, and porous sintered body It can be easily injected through a nest, a movable poppet valve installed on the mold cavity surface, and the like.

Further, the gas body for accommodating the modifier in the mold cavity may be used alone, but a mixture may be used in order to increase the amount of the modifier dissolved and the dispersibility. As a specific example, when carbon dioxide is used as the gas body, a liquid vaporized substance and / or atomized particles that easily dissolve carbon dioxide can be included. The liquid here is
The amount of dissolved carbon dioxide is large, the boiling point is above the mold temperature,
It is a liquid that is soluble in a resin, and for example, water, ketones such as acetone and methyl ethyl ketone, alcohols such as ethyl alcohol, and various polar solvents can be used.

Examples of the modifier used in the present invention include coloring materials (dye, pigment) for coloring the surface of molded articles, antistatic materials, electric conductors having electromagnetic wave shielding properties, resin materials, inorganic materials, weather resistant materials. And so on. These modifiers can be used alone or as a mixture.

Examples of coloring materials include dyes and pigments. The dye is not particularly limited as long as it can be generally used, azo dye, anthraquinone dye, indigo and thio, indigo dye, solubilizing vat dye, sulfur dye, phthalocyanine dye, nitro and nitroso dye, acridine dye, Examples include azine dyes, azomethine dyes, polymethine dyes, di- and triallylmethane dyes. The pigment is not particularly limited, either an inorganic pigment or an organic pigment can be used. Typical examples of the inorganic pigments include titanium white (titanium oxide), yellow lead (chrome yellow), and red iron oxide.

Examples of the antistatic material include surfactants, carbon black and polymer alloy materials. As the surfactant, glycerin fatty acid ester,
Polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, N, N-bis (2-hydroxyethyl) alkylamine, N-2-hydroxyethyl-N-2-hydroxyalkylamine, polyoxyethylenealkylamine, polyoxy Nonionic surfactants such as ethylene alkyl amine fatty acid ester, alkyl diethanol amide, alkyl sulfonate,
Anionic surfactants such as alkylbenzene sulfonate and alkyl phosphate, cationic surfactants such as tetraalkylammonium salt and trialkylbenzeneammonium salt, and amphoteric surfactants such as alkylbetaine and alkylimidazolium betaine are used. Further, as the polymer type antistatic agent, polyether type polymer type such as polyethylene oxide, polyether ester amide, polyether amide imide, ethylene oxide / epiclohydrin copolymer, methoxy polyethylene glycol (meth) acrylate copolymer, etc. Antistatic agents, quaternary ammonium salt-based (meth) acrylate copolymers, quaternary ammonium salt-based polymer type antistatic agents such as quaternary ammonium salt group-containing maleimide copolymers, and polystyrene sulfonate. To be
A permanent antistatic resin obtained by kneading a conductive polymer with a plastic of any of these high molecular type antistatic agents can also be used as a modifier.

As the electromagnetic wave shielding material, a simple substance or a mixture of conductive materials such as silver, nickel, carbon and copper,
A conductive paint obtained by kneading a simple substance or a mixture of conductive materials with various resins can be used. The conductive material may be in the form of powder, fibers, flakes, fine particles, or the like, but it is preferable that it is easily dispersed or dissolved uniformly in high-pressure gas. To improve dispersibility and solubility,
If necessary, a part or surface of the conductive material can be modified. Alternatively, an organic metal complex that can be dissolved in supercritical carbon dioxide may be used to melt the resin on the resin surface, and then the organic matter may be released by heat treatment.

When a resin material is used as the modifier, the surface of the molded product is modified by using a material having functions such as surface hardness, weather resistance and slidability which are superior to those of the resin forming the molded product. The function of the surface can be improved.

As the weather resistant material, a general anti-aging agent or ultraviolet absorber can be used. As an anti-aging agent,
Aldol-α used for heat resistance and antioxidant
-Naphthylamine, phenyl-β-naphthylamine, phenyl-α-naphthylamine, octylated diphenylamine, 1,2-dihydro-2,2,4-trimethylquinoline, phenylcyclohexyl-P-phenylenediamine, 2,6-di- t-butyl-P-cresol,
2,5-di-t-amine hydroquinone, 2-2'-
Methylene-bis (4-methyl-6-t-butylpheno-
2-2'-methylene-bis (4-ethyl-6-t)
-Butylphenol), 4-4'-thiobis- (6-t
-Butyl-m-cresol), thiourea derivative, 2-mercaptobenzimidazole, alkylated aryl horse phyte and the like are used.

Although the modifier may be used alone, it may be used together with a compatibilizer or an entrainer for increasing the compatibility with the surface of the molded product, or may be used by mixing a plurality of modifiers. It is also possible to use a modifier obtained by coating the surface of another modifier with a particulate modifier such as silica or by adhering it to form a composite.

The molding method of the present invention will be described more specifically with reference to FIGS. 1 and 2.

FIG. 1 is a conceptual diagram showing an example of a pressurized gas supply device when carbon dioxide is used as a pressurized gas, FIGS. 2 to 5 show examples of the mold structure, and FIG. 2 shows the entire mold. FIG. 3 is a sectional view taken along line AA in FIG. 2, FIG. 4 is an enlarged view of portion I in FIG. 2, and FIG. 5 is an enlarged view of portion II in FIG.

In FIG. 1, 1 is a liquefied carbon dioxide cylinder, 2 is a booster, 3 is a heater, 4 is a main tank, 5
Is a modifier mixing device, and 6 is a mold.

The liquefied carbon dioxide cylinder 1 and the booster 2 are
It is connected via an electromagnetic on-off valve 7. When the electromagnetic opening / closing valve 7 is opened, the liquefied carbon dioxide is supplied from the liquefied carbon dioxide cylinder 1 as a liquid to the pressure increasing device 2 and is increased in pressure in the liquid state in the pressure increasing device 2.

A heater 3 is connected to the booster 2 via an electromagnetic opening / closing valve 8. When the electromagnetic opening / closing valve 8 is opened,
The liquefied carbon dioxide pressurized by the pressure booster 2 is sent to the heater 3 and gasified. The carbon dioxide after the heater 3 is maintained in a gasified state, and the temperature after the heater 3 is maintained at a temperature exceeding the critical temperature.

The carbon dioxide gasified by the heater 8 is stored in the main tank 4 (a sub tank can be provided if necessary) via the pressure reducing valve 9. The pressure in the main tank 4 can be controlled by the relief valve 10 and the pressure meter 11.

The main tank 4 is connected to a reforming material mixing device 5 via an electromagnetic opening / closing valve 12, and the reforming material mixing device 5 is connected to a mold 6 via an electromagnetic opening / closing valve 13. . The carbon dioxide gas stored in the main tank 4 is supplied to the mold 6 by opening or closing the electromagnetic opening / closing valves 12 and 13 so that the modifying material is dissolved or dispersed in the modifying material mixing device 5. ing.

Reference numeral 14 is an electromagnetic on-off valve for opening the interior of the reforming material mixing device 5 to the atmosphere, and 15 is a relief valve connected between the reforming material mixing device 5 and the electromagnetic on-off valve 13.

In the pressurized gas supply device shown in FIG. 1,
The modifier mixing device 5 provided between the main tank 4 and the mold 6 dissolves or disperses the modifier in the carbon dioxide gas. It can also be done at.

The mold 6 is, as shown in FIGS.
A gas supply / discharge gap 17 for supplying and discharging gas is provided on the outer periphery of the mold cavity 16 (the mold used in the embodiment has a depth of 0.05).
mm), and the gas supply / discharge gap 17 is connected to the gas flow channel groove 18 located on the outer peripheral side thereof. Further, in the gas flow channel groove 18, a gas flow channel hole 19 communicating with the outside of the mold 6 is provided.
Are connected to each other, and are connected to the pressurized gas supply device described in FIG. 1 through the gas passage holes 19.

An O-ring 20 for sealing the inside including the mold cavity 16 is provided outside the gas flow channel groove 18.
Is provided to prevent the pressurized gas from leaking from the parting surface of the mold 6. In addition, the clearance around the protrusion pin 21 has a U packing 2 inserted between the cavity block 22 and the backup plate 23.
Sealed by 4. As the U packing 24, "MPR" series manufactured by Nippon Bulker Industries, Ltd. can be used.

On the other hand, from the gap around the protrusion pin 21,
In order to prevent leakage through the gap between the cavity block 22 and the backup plate 23, the O-ring 2 is provided between the cavity block 22 and the backup plate 23.
5 is interposed. The gas passage hole 19 has a hole 28 that communicates with the outside of the mold 6 so that the pressurized gas entering the gap around the protrusion pin 21 and the gap between the cavity block 22 and the backup plate 23 can be discharged.
Inside the ring 25, it also communicates with the gap between the cavity block 22 and the backup plate 23.

The injection molding method according to the present invention will be sequentially described.

First, liquefied carbon dioxide is supplied from the liquefied carbon dioxide cylinder 1 of FIG. 1 to the pressure increasing device 2, and the pressure increasing device 2 increases the pressure to a predetermined pressure. Next, the pressurized liquefied carbon dioxide is gasified by the heater 3, adjusted to a predetermined pressure by the pressure reducing valve 9, and then stored in the main tank 4.

After preparing the pressurized carbon dioxide as described above, the electromagnetic on-off valve 1 located downstream of the main tank 4
2 is opened, pressurized carbon dioxide is pressed into the modifier mixing device 5, the modifier is dissolved or dispersed in the pressurized carbon dioxide, the electromagnetic opening / closing valve 13 is opened, and the modifier is dissolved or dispersed. Pressurized carbon dioxide is pressed into the mold cavity 16.

A large amount of the modifier may be filled in the modifier mixing device 5 in advance, but an appropriate amount can be supplied to the modifier mixing device 5 each time the pressurized carbon dioxide is supplied. This is preferable because the amount of the modifier to be dissolved or dispersed in the pressurized carbon dioxide can be easily controlled.

The pressurized carbon dioxide press-fitted into the mold cavity 16 is inside the mold cavity 16 because the mold cavity 16 is sealed by the O-rings 20 and 25 and the U packing 24 as described above. Is also filled with a predetermined pressure, and the modifying material dissolved or dispersed therein is also retained in the mold cavity 16.

In the above state, the mold cavity 16 is filled with the molten resin by injection. Along with this injection filling, pressurized carbon dioxide dissolves in the surface of the molten resin flowing in the mold cavity 16, and the modifier dissolved or dispersed therein is also taken in by the surface of the molten resin to form a surface layer. Reform.

After injection and filling of the molten resin, the electromagnetic on-off valve 13
Closed, and the electromagnetic shut-off valve (not shown) for taking out excess gas provided on the downstream side is opened to release excess carbon dioxide in the mold cavity 16 and each gap to the outside air. Or collect in a specified collection tank.
In addition, good mold reproducibility can be obtained by applying resin holding pressure in the mold cavity 16 together with taking out this excess carbon dioxide.

The molded article obtained as described above has the surface modified by dissolving or burying the modifier in the surface layer.

[0056]

EXAMPLES The present invention will be described in more detail with reference to the following examples.

The resin used for injection molding is rubber-reinforced polystyrene (A & M, polystyrene 8672). Carbon dioxide having a purity of 99% or more was used as the gas body of the pressurized gas. As a modifier, a red dye having a molecular weight of 408.51, a chemical formula of C ₂₆ H ₂₄ N ₄ O, and a melting point of 120 ° C. Oil Red O (manufactured by Aldrich, product number 1)
9,819-6) was used.

As the molding machine, S manufactured by Sumitomo Heavy Industries, Ltd.
G125M was used. The mold temperature was set to 60 ° C, and the tip of the injection cylinder was set to 220 ° C.

The molded product was a flat plate having a thickness of 2 mm, a length of 120 mm and a width of 60 mm.

In this example, a high pressure gas container was used as the modifier mixing device. The absorbent cotton in which the powder of Oil Red O was wrapped was inserted into this high-pressure gas container, and carbon dioxide was passed through to dissolve the oil red O in carbon dioxide.

Next, the injection molding process will be described.

First, the injection cylinder of the injection molding machine was moved forward, and the nozzle at the tip of the injection molding cylinder was pressed against the mold (nozzle touch) so that the inside of the mold cavity became airtight.

Next, after heating the pressurized carbon dioxide to 50 ° C., the pressure was reduced to 8.5 MPa, and the carbon dioxide accompanied by oil red O was passed through the modifier mixing device through the main tank. Pressed into the cavity. The carbon dioxide was pressed into the mold cavity so that the inside of the mold cavity reached 8.5 MPa.

After the carbon dioxide was pressed in, the mold cavity was filled with a molten resin whose resin temperature was set at 220 ° C., and the resin holding pressure was given, and at the same time, the carbon dioxide in the mold was released outside the mold to be cooled and solidified. After that, the molded product was taken out.

The surface of the obtained molded product was colored red.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of a pressurized gas supply device when carbon dioxide is used as a pressurized gas.

FIG. 2 is a sectional view of the entire mold.

3 is a cross-sectional view taken along the line AA in FIG.

FIG. 4 is an enlarged view of a portion I in FIG.

5 is an enlarged view of a portion II in FIG.

[Explanation of symbols]

1 Liquefied carbon dioxide cylinder 2 booster 3 heater 4 main tank 5 modifier mixing device 6 mold 7 solenoid valve 8 solenoid valve 9 Pressure reducing valve 10 relief valve 11 meters 12 solenoid valve 13 solenoid valve 14 solenoid valve 15 relief valve 16 mold cavity 17 Gas supply / discharge gap 18 gas flow channels 19 Gas channel hole 20 O-ring 21 protruding pin 22 Cavity block 23 Backup plate 24 U packing 25 O-ring

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Claims (6)

[Claims] 1. A pressurizing gas having a solubility to an injected molten resin is used, the pressurizing gas in which a modifier is dissolved or dispersed is injected into a mold cavity, and then inside the mold cavity. A surface-modified injection molding method, characterized in that a molded product whose surface is modified by a modifier is obtained by injecting a molten resin into the surface. 2. The surface modified injection molding method according to claim 1, wherein a pressurized gas is injected as a supercritical fluid into the mold cavity. 3. The surface-modified injection molding method according to claim 1, wherein the pressurized gas is carbon dioxide. 4. The modifying material dissolved or dispersed in a pressurized gas is a coloring material, an antistatic material, an electromagnetic wave shielding material or a weather resistant material, according to any one of claims 1 to 3. The surface-modified injection molding method described. 5. The surface modification injection molding method according to claim 1, wherein the modifying material dissolved or dispersed in the pressurized gas is a resin material. 6. The surface-modified injection molding method according to claim 1, wherein the modifying material dissolved or dispersed in the pressurized gas is an inorganic material.