JP7585933B2 - Manufacturing method of foamed molded article - Google Patents

Description

The present invention relates to a method for producing a foamed molded article by injection foam molding of molten resin in a mold loaded with an insert film.

Thermoplastic resins, such as polycarbonate resins, are excellent in heat resistance, mechanical properties, and electrical properties, and are widely used, for example, in automobile materials, electrical and electronic equipment materials, housing materials, and materials for manufacturing parts in other industrial fields, etc. In particular, they are suitably used as parts for electrical and electronic equipment such as computers, notebook personal computers, various portable terminals, printers, copiers, and office automation and information equipment.
In recent years, these devices have been rapidly becoming smaller and lighter, and foam molding methods are being adopted to reduce the amount of resin used and make them lighter.

As the foam molding method, there are manufacturing methods using chemical foaming agents and physical foaming agents. However, the chemical foaming method is expensive because of the use of foaming agents, and has problems such as discoloration of the foam and odor generation due to decomposition residues of the foaming agent remaining in the foam, and contamination of the molding machine by the chemical foaming agents.
On the other hand, the gas foaming method using a physical foaming agent is a method in which a resin is melted in a molding machine, a low-boiling organic compound such as butane is fed and kneaded, and then released into a low-pressure region to foam and mold the resin. The low-boiling organic compound used in this method has an affinity for the resin, so it has excellent solubility and can produce a foam with a high expansion ratio. However, these foaming agents are expensive, and the low-boiling organic compound has dangers such as flammability.

To solve these problems, a method has been proposed in which inert gases such as nitrogen gas and carbon dioxide gas, which are clean and inexpensive among physical foaming agents, are used as the foaming agent. However, these inert gases have low affinity with resins as they are, and therefore poor solubility. The resulting foam has large, non-uniform air bubbles and a low cell density, resulting in problems with appearance and mechanical strength.

Patent Document 1 describes a technique for obtaining a foam having extremely fine cell diameters and large cell density by using a supercritical fluid as a foaming agent and impregnating the resin with the supercritical fluid. The foam molding method using a supercritical fluid as a foaming agent is a fine foam molding technique also called MuCell (registered trademark), in which a supercritical fluid is dissolved in a molten resin under high pressure, which is fed to a molding machine, and a molded product having fine foam cells is obtained by rapid decompression.
According to such supercritical foam molding, since a supercritical fluid has excellent solubility close to that of a liquid and excellent diffusivity close to that of a gas, it has high solubility in a resin and also has a high diffusion rate in the resin, so that it is possible to impregnate the foaming agent into the resin in a short period of time.

Incidentally, injection foam molding can produce streaky appearance defects called swirl marks. These are marks left by bubbles that form at the end of the molten resin flow and burst, stretching out on the surface of the molded product. In injection foam molding, countless bubbles are generated, causing streaks to form all over the surface of the molded product.

To address this issue, methods have been proposed to improve the appearance by providing a decorative layer on the surface using film insert molding or the like, as described in Patent Documents 2 and 3, in order to smooth the surface and improve the appearance. This method produces a foamed molded product with a surface layer formed by the inserted film.

However, in injection foam molding in which a surface layer is formed using an insert film, the presence of this surface layer makes it possible to obtain a foam molded article with a smooth surface. However, the presence of this surface layer makes the non-foamed layer thicker, and in thin molded products or products with a large weight reduction rate of the foamed layer, the proportion of the non-foamed layer becomes large in both weight and volume, resulting in a small weight reduction effect and low insulation effect.
In particular, when a thick film is inserted, the proportion of the film in the entire molded article increases, and the weight reduction effect and heat insulation effect are significantly impaired.
By reducing the thickness of the insert film, the proportion of the film in the entire molded product can be reduced, which can help reduce the weight and heat insulation effects. However, in that case, air bubbles can easily get caught between the film and the foam molded part, resulting in poor appearance, poor adhesion of the film, scratches and dents when handling the film, and the introduction of foreign matter.

Thus, while injection foam molding using an insert film can produce foamed molded articles with a smooth surface and good appearance, there is a problem in that the presence of the surface layer made of the insert film impairs the weight reduction and heat insulation effects.
On the other hand, if the insert film is not used, the inherent weight reduction and heat insulating effects of the foamed molded article can be obtained, but the foamed molded article will have a poor appearance due to the presence of streaky swirl marks on the surface.

Since the insert film is provided to form a surface layer of the resulting foam molded article, the surface layer of the insert film needs to be integrated with the foam molded part of the resulting foam molded article with good adhesion. For this reason, a resin film that is highly heat-sealable with the injected resin is currently selected as the insert film.
Furthermore, in conventional injection foam molding, there is no technical idea of removing the insert film from the foam molded article obtained after injection foam molding.

U.S. Pat. No. 5,158,986 Special Publication No. 2004-523375 JP 2004-98459 A

The present invention aims to solve the problems of the conventional technology described above, and to provide a method for producing a foamed molded article that uses an insert film during injection foam molding to obtain a foamed molded article with a smooth surface and excellent appearance, while eliminating the reduced weight reduction and reduced insulation effect that are caused by using an insert film.

As a result of extensive investigations to solve the above-mentioned problems, the inventors have discovered that by performing injection foam molding using an insert film that does not thermally seal with the resin to be injection foam molded, and by removing this insert film from the resulting foam molded product after injection foam molding, it is possible to obtain a foam molded product with a smooth surface and excellent appearance, while also obtaining the inherent weight reduction and heat insulation effects of foam molded products, and have arrived at the present invention.
That is, the present invention relates to the following.

[1] A method for producing a foamed molded article by injection foaming a molten resin in a mold containing an insert film,
As the insert film, a film that is not thermally fused to the thermoplastic resin composition is used,
A method for producing a foam molded article, comprising removing the insert film after injection foam molding to obtain a foam molded article.

[2] The method for producing a foamed molded article described in [1], characterized in that the insert film is made of a film selected from a resin having a melting point higher than the injection foam molding temperature of the molten resin, a resin having a glass transition temperature higher than the injection foam molding temperature of the molten resin, a biaxially stretched film of a thermoplastic resin having a melting point of 250°C or higher, or a film of a thermosetting resin.

[3] The method for producing a foamed molded article according to [1] or [2], characterized in that the molten resin is made of a polycarbonate resin, and the insert film is a biaxially stretched film made of a polyester resin.

[4] A method for producing a foam molded article according to any one of [1] to [3], characterized in that injection foam molding is performed using a volatile foaming agent, an inorganic foaming agent, or a decomposition type foaming agent.

[5] The method for producing a foamed molded article according to [4], characterized in that supercritical or subcritical injection foam molding is carried out using nitrogen, carbon dioxide or a mixture thereof in a supercritical or subcritical state as the inorganic foaming agent.

[6] The method for producing a foamed molded article according to any one of [1] to [5], characterized in that the side of the insert film that contacts the molten resin is release-treated.

According to the present invention, injection foam molding is performed using an insert film that is not thermally bonded to the resin to be injection foam molded. After injection foam molding, the insert film is removed from the resulting foam molded product, resulting in a foam molded product with a smooth surface and excellent appearance, while also providing the inherent weight reduction and heat insulation effects of the foam molded product.

FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a method for producing a foamed molded article of the present invention. 1A and 1B are schematic cross-sectional views showing an example of a foam molded article with a film obtained by injection foam molding according to the foam molded article manufacturing method of the present invention (FIG. 1A), and a foam molded article after the film has been removed (FIG. 1B).

The following describes in detail the embodiments of the present invention.

The method for producing a foamed molded article of the present invention is characterized in that, in the method for producing a foamed molded article, a molten resin is injection foam-molded in a mold loaded with an insert film, a film that does not thermally bond to the thermoplastic resin composition is used as the insert film, and the foamed molded article is obtained by removing the insert film after injection foam-molding.

Specifically, as shown in Figures 1(a) and (b), an insert film 2 is loaded onto the mold surface of one of the molds 1A and 1B (mold 1A in Figure 1(a)), and then the molds are clamped to inject and foam-mold molten resin 3 into the cavities of molds 1A and 1B. This results in a foam-molded body 4 having the insert film 2 on its surface, as shown in Figures 1(b) and 2(a). Then, as shown in Figure 2(b), the insert film 2 is removed from the foam-molded body 4 to obtain the foam-molded body 4 as a product.

As shown in Fig. 1(b) and Fig. 2(a) and (b), this foamed molded body 4 has a skin layer (a non-foamed layer formed in the vicinity of the mold during injection foam molding) 4a formed on both surfaces of a foamed layer 4b.
When the insert film 2 is integrally molded as the surface layer of the foam molded body 4, as shown in Figure 2(a), the sum ( _D1 + _D2 + _D3 ) of the thickness _D1 of the insert film 2 and the thicknesses _D2 and _D3 of the skin layer 4a becomes the non-foamed layer of the foam molded body 4, and the weight reduction and insulation effects are significantly impaired. However, when the insert film 2 is removed, the non-foamed layer remains only the thickness ( _D2 + _D3 ) of the surface skin layer 4a, and the problems of reduced weight reduction and insulation effects are solved.
Moreover, the surface 4A of the obtained foamed molded article 4 is smooth and has an excellent appearance due to the presence of the insert film 2.

[Injection foam molding]
In the present invention, the injection foaming method is not particularly limited, except that the insert film is used for injection foaming and then the insert film is removed. For example, the following method can be adopted.

A foaming agent is mixed or dissolved in molten resin in an injection molding machine, and the resin is foamed and filled into the mold when it is injected into the mold with an insert film inserted. This method includes (1) the short shot method, in which an amount of resin smaller than the cavity capacity is injected, air bubbles are generated by the reduced pressure during injection, and the air bubbles expand to fill the cavity; and (2) the core back method, in which a mold with a variable cavity capacity is used and an amount of resin equal to the cavity capacity is injected, and the cavity volume is expanded after filling to generate and expand air bubbles, resulting in a foamed molded product.

The blowing agent used may be any of volatile blowing agents, inorganic blowing agents, and decomposition type blowing agents. Volatile blowing agents include lower aliphatic hydrocarbon compounds such as n-butane, i-butane, n-pentane, i-pentane, and hexane; alicyclic hydrocarbon compounds such as cyclobutane and cyclopentane; aromatic hydrocarbon compounds such as benzene, toluene, and xylene; lower aliphatic monohydric alcohol compounds such as methanol and ethanol; lower aliphatic ketone compounds such as acetone and methyl ethyl ketone; and low-boiling halogenated hydrocarbon compounds such as chloromethyl, chloroethyl, and 1-chloro-1,1-difluoroethane. Inorganic blowing agents include nitrogen and carbon dioxide in a gaseous, supercritical, or subcritical state; and water.

Examples of decomposition type foaming agents include azo compounds such as barium azocarboxylate and azodicarbonamide, nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, hydrazine compounds such as hydrazocarbonamide, and bicarbonates such as sodium bicarbonate.

Of these, supercritical or subcritical nitrogen, carbon dioxide or a mixture thereof is preferred.
The foaming agents may be used alone or in combination of two or more kinds.
The amount of the foaming agent used can be appropriately determined depending on the type of foaming agent and the desired expansion ratio, but is preferably 0.1 to 20 parts by mass of the foaming agent per 100 parts by mass of the resin to be injection foamed.

As the injection foam molding method in the present invention, supercritical injection foam molding is preferred from the viewpoint of production efficiency in particular.
The gas used for the supercritical fluid is preferably nitrogen gas or carbon dioxide gas.
The supercritical injection foam molding can be performed using the short shot method, the core back method, etc. All of these methods have in common that a supercritical fluid is injected into a cylinder when measuring the resin and dissolving it, but the foaming process is different.
The generation of bubble nuclei is achieved by reducing the pressure in the mold to a pressure equal to or lower than the critical pressure of nitrogen or carbon dioxide, thereby causing the nitrogen or carbon dioxide to become supersaturated, and a large number of cell nuclei are generated in the supersaturated molten resin composition.

Specific examples of supercritical injection foam molding are as follows:

First, the resin pellets to be injection foamed are fed from the hopper of the injection molding machine into the molding machine, heated and melted in the conveying zone and compression zone of the molding machine screw, and then sent to the metering zone and compression zone of the molding machine screw. Then, nitrogen or carbon dioxide gas made into a supercritical fluid is injected from an inlet provided in the metering zone, and this supercritical fluid and molten resin are pressurized and made into a single phase, injected from the nozzle of the injection molding machine, and flowed through the sprue and runner while maintaining a single phase, and sent to the mold cavity in which the insert film has been previously loaded. After passing through the gate, bubble nuclei are generated, and the bubbles expand as they fill the mold, thereby performing supercritical injection foaming molding. Here, the generation of bubble nuclei is achieved when the pressure in the mold drops to a pressure below the critical pressure of nitrogen or carbon dioxide, causing the nitrogen or carbon dioxide to become supersaturated, and a large number of cell nuclei are generated in the molten resin composition in the supersaturated state.

Normal conditions can be used for injection foam molding. For example, the injection speed of the molten resin is usually 10 to 150 mm/sec, no pressure holding is required when clamping the mold, and the mold is completely filled by the pressure caused by foaming.

[Injection foam molding resin]
In the present invention, there is no particular limitation on the resin used in the injection foam molding, and the present invention can be applied to general thermoplastic resin compositions.
Examples of the resins include styrene-based resins such as polystyrene resin, AS resin, and ABS resin; olefin-based resins such as polyethylene resin and polypropylene resin; polyester-based resins such as polyethylene terephthalate resin and polybutylene terephthalate resin; polyacetal resin; polycarbonate resin; polyvinyl chloride; acrylic resin; polyarylate; polyphenylene ether, modified polyphenylene ether resin; polyetherimide; polyethersulfone; polyamide-based resin; polysulfone; polyetheretherketone; polyetherketone; olefin-based thermoplastic elastomer, etc. These resins may be used alone or in combination of two or more types depending on the application, etc., and these thermoplastic resins may be used by mixing various additives such as plasticizers, release agents, antistatic agents, flame retardants, and foaming agents, various fillers for improving physical properties, glass fibers, carbon fibers, etc., and further colorants, dyes, etc., as necessary.

As a resin for injection foam molding, a polycarbonate resin composition containing polycarbonate resin as the main component is particularly suitable.

The polycarbonate resin composition will be described below.
There are no particular limitations on the polycarbonate resin composition used in the present invention.
The polycarbonate resin composition is not limited to a composition in which other components are blended with a polycarbonate resin, but may be a polycarbonate resin alone. The polycarbonate resin composition preferably contains 30% by mass or more, particularly 50 to 100% by mass of a polycarbonate resin, since the effects of the present invention are effectively exhibited.

<Polycarbonate resin>
Examples of the polycarbonate resin contained in the polycarbonate resin composition include aromatic polycarbonate resins, aliphatic polycarbonate resins, and aromatic-aliphatic polycarbonate resins. An aromatic polycarbonate resin is preferable. Specifically, a thermoplastic aromatic polycarbonate polymer or copolymer obtained by reacting an aromatic dihydroxy compound with phosgene or a diester of carbonic acid is used.

Examples of aromatic dihydroxy compounds include 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), tetramethylbisphenol A, α,α'-bis(4-hydroxyphenyl)-p-diisopropylbenzene, hydroquinone, resorcinol, and 4,4'-dihydroxydiphenyl. In order to improve flame retardancy, a compound in which one or more tetraalkylphosphonium sulfonates are bonded to the aromatic dihydroxy compounds described above, a polymer containing phenolic OH groups at both ends and having a siloxane structure, or an oligomer thereof may also be used.

Preferred examples of polycarbonate resins include polycarbonate resins that use 2,2-bis(4-hydroxyphenyl)propane as a dihydroxy compound or 2,2-bis(4-hydroxyphenyl)propane in combination with other aromatic dihydroxy compounds.

The polycarbonate resin may be a homopolymer consisting of one type of repeating unit, or a copolymer having two or more types of repeating units. In this case, the copolymer may be of various copolymer forms, such as a random copolymer or a block copolymer.

There are no restrictions on the molecular weight of the polycarbonate resin, but the viscosity average molecular weight (Mv) calculated from the solution viscosity measured at 20°C using methylene chloride as a solvent is preferably 10,000 to 40,000, more preferably 14,000 to 32,000. If the viscosity average molecular weight is in this range, the resulting resin composition has good moldability in supercritical foam molding, and molded products with high mechanical strength are easily obtained. The most preferred molecular weight range for polycarbonate resin is 16,000 to 30,000.

In the present invention, the viscosity average molecular weight (Mv) of a polycarbonate resin is a value calculated from the intrinsic viscosity ([η]) obtained by measuring the viscosity of a methylene chloride solution of the polycarbonate resin at 20° C. using an Ubbelohde viscometer, and then calculating the intrinsic viscosity from the following Schnell viscosity formula:
[η]=1.23×10 ⁻⁴ Mv ^0.83

There are no particular limitations on the method for producing the polycarbonate resin, and polycarbonate resins produced by either the phosgene method (interfacial polymerization method) or the melting method (ester exchange method) can be used. Also preferred is polycarbonate resin produced by the melting method, which has been subjected to post-treatment to adjust the amount of OH groups at the terminals.

The polycarbonate resin may also contain a polycarbonate oligomer. The viscosity average molecular weight [Mv] of this polycarbonate oligomer is usually 1,500 or more, preferably 2,000 or more, and usually 9,500 or less, preferably 9,000 or less. Furthermore, the polycarbonate oligomer contained is preferably 30% by mass or less of the polycarbonate resin (including the polycarbonate oligomer).

In addition, polycarbonate resin can be made not only from virgin raw materials, but also from aromatic polycarbonate resins recycled from used products, so-called material recycled aromatic polycarbonate resins. Preferred examples of used products include optical recording media such as optical disks, light guide plates, automobile window glass, automobile headlamp lenses, transparent vehicle components such as windshields, containers such as water bottles, eyeglass lenses, soundproof walls, glass windows, corrugated sheets, and other building components. In addition, crushed products obtained from non-conforming products, sprues, or runners, or pellets obtained by melting these can also be used as recycled polycarbonate resins.

<Other ingredients>
The polycarbonate resin composition may contain, in addition to the polycarbonate resin, other thermoplastic resins other than the polycarbonate resin and additives.

Other thermoplastic resins include polyester resins, polyamide resins, polyolefin resins, polyphenylene ether resins, styrene resins, polysulfones, polyethersulfones, polyphenylene sulfides, polyacrylates, polyamideimides, polyetherimides, etc.

Examples of polyester resins include polybutylene terephthalate, polyethylene terephthalate, polybutylene naphthalate, and polyethylene naphthalate. Examples of polyolefin resins include polyethylene and polypropylene. Examples of polyphenylene ether resins include polyphenylene ether resins and mixed resins of polyphenylene ether and polystyrene and/or HIPS (high impact polystyrene). Examples of styrene resins include polystyrene, HIPS, AS resin, and ABS resin.

In addition, various additives, such as UV absorbers, antioxidants, stabilizers such as heat stabilizers, pigments, dyes, lubricants, flame retardants, drip prevention agents, release agents, and sliding improvers, can be added to the polycarbonate resin composition as needed to obtain the desired physical properties.

(Antioxidants)
The antioxidant includes a hindered phenol-based antioxidant.

When an antioxidant is contained in a polycarbonate resin composition, the amount of the antioxidant is usually 0.001 to 1 part by mass, and preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of polycarbonate resin in the polycarbonate resin composition. If the amount of the antioxidant is less than 0.001 part by mass, the antioxidant effect is insufficient, and if it exceeds 1 part by mass, the effect reaches a plateau and it is not economical.

(Heat stabilizer)
The heat stabilizer may be at least one selected from the group consisting of a phosphite compound in which at least one ester in the molecule is esterified with phenol and/or a phenol having at least one alkyl group having 1 to 25 carbon atoms, phosphorous acid, and tetrakis(2,4-di-tert-butylphenyl)-4,4'-biphenylene-di-phosphonite.

When a heat stabilizer is contained in a polycarbonate resin composition, the amount of the heat stabilizer is usually 0.001 to 1 part by mass, and preferably 0.01 to 0.5 parts by mass, per 100 parts by mass of polycarbonate resin in the polycarbonate resin composition. If the amount of the heat stabilizer is less than 0.001 part by mass, the effect as a heat stabilizer is insufficient, and if it exceeds 1 part by mass, hydrolysis resistance may deteriorate.

(Release Agent)
The release agent may be at least one compound selected from the group consisting of aliphatic carboxylic acids, esters of aliphatic carboxylic acids and alcohols, aliphatic hydrocarbon compounds having a number average molecular weight of 200 to 15,000, and polysiloxane-based silicone oils.

When a release agent is contained in the polycarbonate resin composition, the amount of the release agent is usually 0.001 to 2 parts by mass, and preferably 0.01 to 1 part by mass, per 100 parts by mass of the polycarbonate resin in the polycarbonate resin composition. If the amount of the release agent is less than 0.001 parts by mass, the release effect may not be sufficient, and if it exceeds 2 parts by mass, problems such as reduced hydrolysis resistance and mold contamination during injection foam molding may occur.

(Ultraviolet absorber)
Specific examples of the ultraviolet absorbing agent include inorganic ultraviolet absorbing agents such as cerium oxide and zinc oxide, as well as organic ultraviolet absorbing agents such as benzotriazole compounds, benzophenone compounds and triazine compounds.

When an ultraviolet absorber is added to a polycarbonate resin composition, the amount of the ultraviolet absorber is usually 0.01 to 3 parts by mass, and preferably 0.1 to 1 part by mass, per 100 parts by mass of polycarbonate resin in the polycarbonate resin composition. If the amount of the ultraviolet absorber is less than 0.01 parts by mass, the effect of improving weather resistance may be insufficient, and if it exceeds 3 parts by mass, problems such as mold deposits may occur.

(dyes and pigments)
The dyes and pigments include inorganic pigments, organic pigments, and organic dyes.

When a dye or pigment is contained in the polycarbonate resin composition, the amount of the dye or pigment is usually 20 parts by mass or less, preferably 15 parts by mass or less, and more preferably 12 parts by mass or less, per 100 parts by mass of the polycarbonate resin in the polycarbonate resin composition. If the amount of the dye or pigment exceeds 20 parts by mass, the impact resistance may be insufficient.

Among inorganic pigments, carbon black also functions as an inorganic conductive substance. When carbon black is used as an inorganic conductive substance, as mentioned above, the amount of carbon black blended can be set to be greater than the amount blended as a dye pigment.

(Flame retardant)
Examples of the flame retardant include halogen-based flame retardants such as halogenated bisphenol A polycarbonate, brominated bisphenol epoxy resin, brominated bisphenol phenoxy resin, and brominated polystyrene; phosphate-based flame retardants; organometallic salt-based flame retardants such as dipotassium diphenylsulfone-3,3'-disulfonate, potassium diphenylsulfone-3-sulfonate, and potassium perfluorobutanesulfonate; and polyorganosiloxane-based flame retardants. Phosphate-based flame retardants are particularly preferred.

When a flame retardant is added to a polycarbonate resin composition, the amount of the flame retardant is usually 1 to 30 parts by mass, preferably 3 to 25 parts by mass, and more preferably 5 to 20 parts by mass, per 100 parts by mass of polycarbonate resin in the polycarbonate resin composition. If the amount of the flame retardant is less than 1 part by mass, the flame retardancy may be insufficient, and if it exceeds 30 parts by mass, the heat resistance may decrease.

(Anti-drip agent)
Examples of the anti-dripping agent include fluorinated polyolefins such as polyfluoroethylene, and polytetrafluoroethylene, which has fibril-forming ability, is particularly preferred.

When an anti-dripping agent is added to the polycarbonate resin composition, the amount of the anti-dripping agent is usually 0.02 to 4 parts by mass, and preferably 0.03 to 3 parts by mass, per 100 parts by mass of the polycarbonate resin in the polycarbonate resin composition. If the amount of the anti-dripping agent exceeds 5 parts by mass, the appearance of the molded product obtained by molding the obtained CF/PC pellets may deteriorate.

<Method for producing polycarbonate resin composition>
There is no limitation on the method for producing the polycarbonate resin composition, and a wide variety of known methods for producing thermoplastic resin compositions can be used.
Specific examples include a method in which the polycarbonate resin and other components to be blended as necessary are premixed using various mixers such as a tumbler or a Henschel mixer, and then the mixture is melt-kneaded using a mixer such as a Banbury mixer, a roll, a Brabender, a single-screw kneading extruder, a twin- screw kneading extruder, or a kneader.

In addition, for example, the thermoplastic resin composition of the present invention can be produced by not mixing the components in advance, or by mixing only some of the components in advance, feeding the mixture to an extruder using a feeder, and melt-kneading the mixture.
In addition, for example, a portion of the components may be mixed in advance, fed to an extruder, and melt-kneaded to obtain a resin composition, which may be used as a masterbatch. The masterbatch may then be mixed again with the remaining components and melt-kneaded to produce a polycarbonate resin composition.
In addition, for example, when mixing a component that is difficult to disperse, the dispersibility can be improved by dissolving or dispersing the component in advance in a solvent such as water or an organic solvent, and kneading the component with the solution or dispersion.

[Insert film]
In the present invention, since the insert film is removed after injection foam molding, the insert film used is one that does not thermally fuse with the molten resin in the injection foam molding as described above during injection foam molding. The insert film that does not thermally fuse with the molten resin during injection foam molding is appropriately selected and used depending on the type of injection foam molding resin used, injection foam molding conditions, etc., and examples thereof include the following.
(1) Of course, films having a melting point or glass temperature higher than the molding temperature can be used, but in particular when the molding temperature is 320°C or lower, biaxially stretched films of thermoplastic resins having a melting point of 250°C or higher can also be used and are particularly preferable when the molding temperature is 320°C or lower, and films made of thermosetting resins can also be used when the molding temperature is over 320°C.
(2) If the insert film is not heat-sealed but is in an adhesive or adsorbed state and has adhesion that makes it difficult to peel off, the film surface may be further subjected to a release treatment.
(3) As a specific example, when the injection foaming resin is an aromatic polycarbonate, a biaxially oriented polyester film is preferable as the insert film, and when the resin has a high molding temperature or mold temperature, such as PPS or PEEK, a thermosetting polyimide film is preferable.

The insert film used in the present invention can be produced by molding the resin of its constituent material by a conventional method, such as T-die molding, and performing biaxial stretching as necessary. By making the cooling roll a mirror surface during T-die molding, a film with a more mirror-like and glossy surface can be obtained, and by transferring the surface of the insert film during insert molding and removing it, a smoother and glossier product can be obtained. In addition, by using a cooling roll with an uneven shape, a film with an uneven shape can be obtained, and by transferring the surface of the insert film during insert molding and removing it, a product with an uneven shape can be obtained.

If the thickness of the insert film is too thin, it may not have enough mechanical strength and may break during handling. In addition, air bubbles may get mixed in between the film and the foamed molded body, leaving traces of air bubbles when the insert film is removed after molding. If the insert film is too thin, the insulating properties of the film are low, so the contact temperature of the molten resin on the film surface is low, and the effect of surface smoothing by providing the insert film may not be fully obtained. Therefore, although it depends on the constituent resin of the insert film, it is preferable to use a thickness of 100 μm or more, especially 150 μm or more. On the other hand, if the thickness of the insert film is too thick, the film surface temperature is not easily transmitted to the surface, and it takes time for the temperature to rise, so the thickness of the insert film is preferably 1000 μm or less, especially 500 μm or less.

If the foamed molded product to be produced is not flat, such as a film or sheet, but has a three-dimensional shape with uneven or curved surfaces, an insert film that has been shaped by thermoforming, such as vacuum forming, to match the surface of the mold on which the insert film is to be placed may be used. Furthermore, if the surface of the insert film has an uneven pattern such as embossing or hairline, or a geometric pattern, it is possible to finish the surface with the same shape when the insert film is removed after molding.

[Foam molded product]
The foamed molded article produced by the foamed molded article producing method of the present invention (hereinafter, sometimes referred to as the "foamed molded article of the present invention") has an excellent appearance due to the use of an insert film, and also has excellent weight reduction and heat insulation effects.

There are no particular limitations on the expansion ratio, shape, dimensions, color, surface decoration, etc. of the foamed molded part of the foamed molded product of the present invention, and these may be set as desired depending on the application, but the foamed molded product of the present invention is effective for thin-walled foamed molded products, where the surface layer formed in conventional methods by using an insert film has a large effect on the weight reduction and heat insulation of the foamed molded product. Examples of such products include thin-walled foamed molded products with an overall thickness of 5 mm or less, for example, about 1.5 to 3 mm, particularly thin-walled foamed molded sheets and films.

There are no particular limitations on the uses of such foamed molded articles of the present invention, and they can be used in a variety of parts, including electrical and electronic equipment, office automation equipment, information terminal equipment, machine parts, home appliances, vehicle parts, building materials, various containers, and lighting equipment.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples, and can be modified as desired without departing from the gist of the present invention.

In the following, the following resins and insert films for injection foam molding were used.
Resin for injection foam molding: Bisphenol A polycarbonate resin (manufactured by Mitsubishi Engineering Plastics Corporation, product name: Iupilon (registered trademark) S-2000R)
Viscosity average molecular weight (Mv): 23,000
Tg = 145 ° C.
Insert film: 200 μm thick biaxially stretched PET film

[Example 1]
Polycarbonate resin pellets for injection foam molding were pre-dried at 120°C for 6 to 12 hours, and nitrogen was made into a supercritical state using a MuCell SCF device (model: T-100J) manufactured by Trexel Corporation. A predetermined amount of nitrogen was then injected into the cylinder of a J100ADS injection molding machine manufactured by Japan Steel Works, Ltd., mixed with the molten resin, and injected into a mold in which an insert film had been previously loaded. Supercritical foam molding was carried out by the short shot method, and a foam molded product having a thickness of 2 mm (thickness after the insert film was peeled off and removed), length of 80 mm, and width of 80 mm was obtained.
The molding conditions were as follows: nitrogen inflow amount 0.3 mass %, weighing 53 mm, injection time 1.3 seconds, and no pressure holding step.

The resulting foamed molded article was removed from the mold together with the insert film, and the insert film was then peeled off.

[Comparative Example 1]
After injection foam molding, the molded article from which the insert film was not removed after removal from the mold was used as the foam molded article of Comparative Example 1. The thickness was 2 mm including the insert film.

[Comparative Example 2]
Except for not using the insert film, injection foam molding was carried out in the same manner as in Example 1 to obtain a foam molded article. The wall thickness was 2 mm.

The foamed molded articles obtained in Example 1 and Comparative Examples 1 and 2 were evaluated as follows, and the results are shown in Table 1.

(1) Cross-sectional observation of foam molded article The foam molded article was cut in the thickness direction, and the cross section was observed with a Shimadzu X-ray CT scanner TDM1000H-II. The thicknesses of the film (in the case of Comparative Example 1), the skin layers on both surfaces, and the foam layer in the center were each measured, and the thickness ratio relative to the entire foam molded article was calculated.

(2) Measurement of surface roughness (Ra) The surface roughness (Ra) was measured according to JIS B 0601-2013 with an evaluation length of 1.25 mm, a cutoff wavelength of 0.25 mm, and a cutoff ratio of 100 using a Tokyo Seimitsu S3000 surface roughness meter.
The surface roughness (Ra) was measured on the surface from which the insert film was removed for the foam molded article of Example 1, on the insert film surface for the foam molded article of Comparative Example, and on the surface for the foam molded article of Comparative Example 2.

(3) Calculation of the weight reduction rate (%) of injected resin The difference between the weight (X) of a non-foamed molded body of the same shape obtained by ordinary injection molding and the weight (Y) of a foamed molded body is divided by the weight (X) of a non-foamed molded body of the same shape, and the result is the percentage {(X) - (Y)} / (X) x 100
The calculation was made as follows.

(4) Measurement of weight The weight of each foamed molded article was measured and converted into an area equivalent to 100 x 100 mm.

(5) Evaluation of Weight Reduction Effect and Heat Insulation Effect The weight reduction effect and heat insulation effect were evaluated according to the following criteria.
<Weight reduction effect>
○: The difference in the thickness ratio of the foam layer from the foamed molded product without the film inserted is less than ±5%. ×: The thickness ratio of the foam layer is reduced by 5% or more from the foamed molded product without the film inserted. <Thermal insulation effect>
◯: The ratio of the thickness of the non-foamed layer to the foamed molded product without a film inserted is less than ±5%. ×: The ratio of the thickness of the non-foamed layer is increased by 5% or more compared to the foamed molded product without a film inserted.

From Table 1, it is evident that according to the present invention, it is possible to obtain a foamed molded article which has a smooth surface and excellent appearance, as well as excellent weight reduction and heat insulation effects.
In contrast, when the insert film is left as the surface layer, the surface smoothness is excellent as in Comparative Example 1, but the proportion of non-foamed layers in the entire foamed molded article is large, and the weight reduction effect and heat insulation effect are significantly impaired.
On the other hand, in Comparative Example 2 in which no insert film was used, the surface roughness (Ra) was large and the appearance was poor.
Furthermore, comparing Example 1 with Comparative Example 2, it can be seen that in the method of the present invention in which the insert film is removed, the presence of the insert film during injection foam molding can actually make the thickness of the skin layer on the insert film side thinner, increasing the proportion of the foam layer thickness in the entire foam molded body, and improving the weight reduction effect and heat insulation effect.

Reference Signs List 1A, 1B Mold 2 Insert film 3 Molten resin 4 Foamed molded body 4a Skin layer 4b Foamed layer

Claims (4)

A method for producing a foamed molded article by injection foaming a molten resin in a mold in which an insert film is loaded,
As the insert film, a film that does not thermally fuse with the molten resin is used,
A method for producing a foam molded article, comprising removing the insert film after injection foam molding to obtain a foam molded article,
the molten resin is made of a polycarbonate resin,
The method for producing a foam molded article , wherein the insert film is a biaxially stretched film made of a polyester resin having a melting point higher than the injection foam molding temperature of the molten resin . 2. The method for producing a foamed molded article according to claim 1, characterized in that injection foam molding is carried out using a volatile foaming agent, an inorganic foaming agent, or a decomposition type foaming agent. 3. The method for producing a foamed molded article according to claim 2 , wherein supercritical or subcritical injection foaming molding is carried out using nitrogen, carbon dioxide or a mixture thereof in a supercritical or subcritical state as the inorganic foaming agent. 4. The method for producing a foamed molded article according to claim 1, wherein the insert film has a surface that comes into contact with the molten resin and is subjected to a release treatment.

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