JP4136904B2 - Injection foam molding method - Google Patents

Description

  The present invention relates to an injection foam molding method and a foam molded article obtained by the injection foam molding method.

  Conventionally, foamed molded articles made of a thermoplastic resin are molded using a chemical foaming agent or a physical foaming agent. In a foam molding method using a chemical foaming agent, a thermoplastic resin as a raw material is usually mixed with a low molecular weight organic foaming agent that decomposes at the molding temperature to generate gas, and the mixture is decomposed into an organic foaming agent. By heating above the temperature, the thermoplastic resin is melted and gas is generated by the decomposition of the foaming agent, thereby forming a foam molded product. On the other hand, in a molding method using a physical blowing agent, under pressure, a low-boiling organic compound such as butane, pentane, or dichlorodifluoromethane is supplied to a molten thermoplastic resin, and after kneading, the kneaded product is discharged to a low pressure region. Thus, a foam molded product is formed. Conventionally, as a general injection foam molding method, a method in which an amount of foamable melt molding material that is insufficient to fill the cavity is injected into the cavity and foamed is employed.

  However, in the molding method using these chemical foaming agents or physical foaming agents, it is difficult to achieve miniaturization of the foamed cells and high density and uniform dispersion of the foamed cells. For this reason, foam molded articles obtained by molding methods using these chemical foaming agents or physical foaming agents have problems such as relatively low mechanical strength.

  Accordingly, in order to achieve finer foam cells and higher density and uniform dispersion of the foam cells, Japanese Patent Application Laid-Open No. 10-230528 and Japanese Patent No. 2625576 disclose a foam molding method using a supercritical fluid as a foaming agent. Has been. In these foam molding methods, a supercritical inert gas as a supercritical fluid is sufficiently uniformly dissolved in a molten resin, and this is injected while applying pressure into a mold cavity, and then the pressure in the cavity is reduced. By foaming by rapidly decreasing, a foamed molded product is obtained.

  In the foam molding method using these supercritical fluids as foaming agents, the supercritical fluid can be used for its excellent solubility close to liquid and excellent diffusibility close to gas. It is possible to impregnate the molten resin in a short time. Therefore, the foamed cell diameter can be reduced, and the strength physical properties of the foamed molded product can be prevented from being lowered.

JP-A-10-230528 Japanese Patent No. 2625576

  By the way, in the foam molding method using the conventional supercritical fluid disclosed in these patent publications and patent publications, foam cells (bubbles) are also present on the surface of the foam molded article. It is difficult to obtain a molded product. In addition, it is possible to suppress the occurrence of local sink marks and warpage, but there is a problem that the strength of the entire foamed molded product is sacrificed.

  Accordingly, an object of the present invention is to provide a foamed molded article having no high-strength, having no foam cells (bubbles) on the surface, excellent appearance, suppressing the occurrence of local sink marks and warping. Another object of the present invention is to provide an injection foam molding method for molding such a foam molded article.

In order to achieve the above object, the injection foam molding method of the present invention comprises:
(A) resin plasticizing / melting means for plasticizing / melting the thermoplastic resin, and
(B) a cavity composed of a fixed mold part and a movable mold part, formed by clamping the fixed mold part and the movable mold part, a molten resin injection part opened in the cavity, and A mold assembly having a molten resin flow path connecting the molten resin injection portion and the resin plasticizing / melting means;
An injection foam molding method using an injection molding apparatus comprising:
(A) a step of plasticizing and melting the thermoplastic resin by a resin plasticizing and melting means, dissolving a gas in the molten thermoplastic resin, and measuring the molten thermoplastic resin;
(B) The measurement is performed in the cavity formed by clamping the fixed mold part and the movable mold part from the resin plasticizing / melting means via the molten resin flow path and the molten resin injection part. Injecting the molten thermoplastic resin made,
(C) The gas foamed in the molten thermoplastic resin injected into the cavity is suppressed by applying pressure to the molten thermoplastic resin in the cavity to suppress the foaming of the gas in the molten thermoplastic resin in the cavity. Re-dissolving in the molten thermoplastic resin in the cavity;
(D) a step of foaming a gas based on a pressure drop in the thermoplastic resin in the cavity caused by a volume reduction due to cooling and solidification of the thermoplastic resin in the cavity;
(E) a step of opening the fixed mold part and the movable mold part and taking out the foam molded product;
It is characterized by comprising.

  In the step (A), the gas is dissolved in the molten thermoplastic resin and the molten thermoplastic resin is measured. Specifically, after the gas is dissolved in the molten thermoplastic resin, the gas dissolved state is obtained. The molten thermoplastic resin may be weighed, or after the molten thermoplastic resin is weighed, the gas may be dissolved in the measured molten thermoplastic resin, or alternatively, the gas may be dissolved at a constant flow rate. May be measured while being dissolved in the molten thermoplastic resin.

  In the injection foam molding method of the present invention, when the gas is dissolved in the thermoplastic resin melted in the step (A), it is preferably in a supercritical state or a subcritical state. In general, when the state of the system depends on a certain parameter and the state changes discontinuously above and below the certain value, the condition represented by that value is called criticality. The condition where the parameter value is below the critical value is called subcritical, and the condition above the parameter value is called supercritical.

  In the injection foam molding method of the present invention including the above preferred embodiments, examples of the gas include carbon dioxide gas, nitrogen gas, or a mixed gas of carbon dioxide and nitrogen. The critical temperature (maximum temperature at which vaporization is possible) and critical pressure (pressure at that time) of carbon dioxide gas and nitrogen gas are as follows.

[Table 1]
Critical temperature Critical pressure Carbon dioxide gas 31.1 ° C 7.38 × 10 ⁶ Pa
Nitrogen gas 147 ° C 3.42 × 10 ⁶ Pa

In the injection foam molding method of the present invention including the various preferred embodiments described above, when measuring the molten thermoplastic resin in a gas-dissolved state in the step (A), the pressure of the molten thermoplastic resin is measured. In addition, it is desirable that it is high as long as it does not inhibit the dissolution of gas, and specifically, it is preferably 5 × 10 ⁶ Pa or more. If it is less than 5 × 10 ⁶ Pa, the molten thermoplastic resin that is in a gas-dissolved state in the resin plasticizing / melting means foams, and the metering operation may be hindered. In addition, the pressure (back pressure) to the molten thermoplastic resin can be applied by resin plasticizing / melting means.

  The measured value of the molten thermoplastic resin is an amount sufficient to fill the cavity in the unfoamed state. Then, at the end of the step (C), the amount of the molten thermoplastic resin remaining in the resin plasticizing / melting means (specifically, at the end of the injection / holding step, for example, in the injection cylinder) It is desirable that the amount of cushion remains). The measured value of the molten thermoplastic resin depends on the temperature and pressure at the time of plasticizing and melting the thermoplastic resin, but does not exceed the volume of the cavity. In addition, when the pressure of the molten thermoplastic resin when measuring the molten thermoplastic resin in the gas dissolved state is higher than the pressure of the molten thermoplastic resin during injection and the pressure during holding, the measured gas dissolved state Even when the volume of the thermoplastic resin in the chamber is smaller than the volume of the cavity, it may be possible to completely fill the cavity with the molten thermoplastic resin. ) To suppress the foaming of the gas in the molten thermoplastic resin in the cavity by applying pressure to the molten thermoplastic resin in the cavity, or the gas foamed in the molten thermoplastic resin injected into the cavity It is important to redissolve in the molten thermoplastic resin in the cavity.

  In the step (A), the resin plasticizing / melting means is composed of an in-line screw type injection molding machine, plasticizing and melting the thermoplastic resin, dissolving gas in the molten thermoplastic resin, and The molten thermoplastic resin may be weighed. Alternatively, it is composed of a plunger type injection molding machine, the resin plasticizing / melting means is composed of a heating cylinder and a reservoir, and the thermoplastic resin is plasticized / melted in advance in the heating cylinder. It may be transferred to a reservoir, gas is dissolved in the molten thermoplastic resin in the reservoir, and the molten thermoplastic resin may be measured. Note that the amount of gas dissolved cannot be uniquely determined because it depends on the type of thermoplastic resin, the type of gas, the pressure, and the temperature.

  In the injection foam molding method of the present invention including the various preferred embodiments described above, when the molten thermoplastic resin in a gas-dissolved state is injected into the cavity in the step (B), the molten thermoplastic resin is foamed in the cavity. May be. Even in such a state, in the injection foam molding method of the present invention, in the next step (C), by applying pressure to the molten thermoplastic resin in the cavity, Since the gas foamed in the plastic resin is redissolved in the molten thermoplastic resin, it is possible to reliably suppress the generation of foam cells (bubbles) on the surface of the foam molded product. That is, when the molten thermoplastic resin in the gas dissolved state is injected into the cavity and the molten thermoplastic resin does not foam in the cavity, the pressure is applied to the molten thermoplastic resin in the cavity in the step (C). The foaming of the gas in the molten thermoplastic resin in the cavity is suppressed. On the other hand, when the molten thermoplastic resin foams in the cavity when the molten thermoplastic resin in a gas-dissolved state is injected into the cavity, pressure is applied to the molten thermoplastic resin in the cavity in the step (C). The gas foamed in the molten thermoplastic resin injected into the cavity is redissolved in the molten thermoplastic resin in the cavity, and the foaming of the gas in the molten thermoplastic resin in the cavity is suppressed.

In addition, before injecting the molten thermoplastic resin measured in the step (B) into the cavity, the cavity may be filled with a pressurized fluid in advance. By adopting such a configuration, when molten thermoplastic resin that is in a gas-dissolved state is injected into the cavity, the occurrence of such a phenomenon that the molten thermoplastic resin is in a reduced pressure state and foaming occurs in the cavity is ensured. Can be avoided. Here, examples of the pressurized fluid filling the cavity include carbon dioxide gas, nitrogen gas, or a mixed gas of carbon dioxide and nitrogen. Further, the pressure of the pressurized fluid filled in the cavity may be less than the injection pressure of the molten thermoplastic resin into the cavity, and the foaming of the gas in the molten thermoplastic resin in the cavity is performed in the step (C). It is desirable that the pressure be lower than the lower limit of the pressure that can be suppressed, and more specifically, 1 × 10 ⁷ Pa or less. Since the cavity cannot be a completely sealed space, most of the pressurized fluid is discharged to the outside from the parting surface and the protruding portion when the molten thermoplastic resin in the gas dissolved state is injected into the cavity. A part of the pressurized fluid dissolves in the molten thermoplastic resin injected into the cavity.

In the injection foam molding method of the present invention including the above various preferred embodiments, in the step (C), a pressure can be applied to the molten thermoplastic resin in the cavity by a pressure holding operation. By adopting such a configuration, after injecting the molten thermoplastic resin in a gas-dissolved state into the cavity, at an undesired time, the molten thermoplastic resin is in a reduced pressure state and the molten thermoplastic resin is in the cavity. Occurrence of a phenomenon such as foaming can be suppressed. In the pressure holding operation, pressure is applied from the resin plasticizing / melting means to the thermoplastic resin in the cavity via the molten thermoplastic resin existing in the molten resin flow path and the molten resin injection portion. In the pressure holding operation, the pressure applied to the thermoplastic resin in the cavity depends on the mold temperature at the time of injection (temperature of the mold surface constituting the cavity when the molten thermoplastic resin is injected into the cavity), Although it varies depending on the type, temperature, type of gas used, etc. and cannot be determined uniquely, it is preferably 5 × 10 ⁶ Pa or more, more preferably 1.5 × 10 ⁷ Pa or more. In addition, the duration of holding pressure varies uniquely depending on the mold temperature during injection, the type and temperature of the thermoplastic resin, the type of gas used, the thickness of the molded product, and the desired weight reduction rate. However, it is preferably 0.2 seconds or longer, more preferably 1.0 seconds or longer, preferably 15 seconds or shorter, more preferably 10 seconds or shorter.

  Here, in the step (C), in the injection foam molding method of the present invention including the above-described various preferred forms adopting the form in which pressure is applied to the molten thermoplastic resin in the cavity by a pressure holding operation, In the step (D), the pressure applied to the molten thermoplastic resin in the cavity is set to be equal to or lower than the pressure at which the gas in the molten thermoplastic resin in the cavity can foam, and this is accompanied by cooling and solidification of the thermoplastic resin in the cavity. The gas may be foamed based on a pressure drop in the thermoplastic resin in the cavity due to volume reduction, but to stop the pressure on the molten thermoplastic resin in the cavity to ensure foaming of the gas, Gas is generated based on the pressure drop in the thermoplastic resin in the cavity due to the volume reduction caused by cooling and solidification of the thermoplastic resin in the cavity. So it is preferable to be.

In this case, in the step (D),
(1) Configuration that stops applying pressure to the molten thermoplastic resin in the cavity by stopping the pressure holding operation;
(2) A configuration in which the application of pressure to the molten thermoplastic resin in the cavity is stopped by solidifying the molten thermoplastic resin in the molten resin injection portion;
(3) A configuration that stops applying pressure to the molten thermoplastic resin in the cavity by mechanically closing the molten resin injection portion;
(4) A configuration that stops applying pressure to the molten thermoplastic resin in the cavity by mechanically closing the molten resin flow path;
(5) A configuration that stops applying pressure to the molten thermoplastic resin in the cavity by mechanically closing the resin plasticizing / melting means,
Adoption of any one of these or any combination of the configurations (1) to (5) ensures that foaming occurs reliably in the cavity because the molten thermoplastic resin in the cavity is in a reduced pressure state. From the viewpoint of, it is preferable.

  In the case of (2) above, as a specific method for solidifying the molten thermoplastic resin in the molten resin injection portion, for example, after the injection of the molten thermoplastic resin into the cavity is completed, it is disposed in the mold assembly. A method of lowering and solidifying the temperature of the molten thermoplastic resin existing in the molten resin injection part by disabling a part of the heating means (part of the heating means arranged in the vicinity of the molten resin injection part); can do. In the case of (3) above, the molten resin injection part can be a valve gate, for example, and a specific means for mechanically closing the molten resin injection part can be a shut-off pin. Furthermore, in the case of (4) above, as a means for mechanically closing the molten resin flow path, for example, a combination of a valve gate and a shut-off pin can be exemplified. In the case of (5) above, as a means for mechanically closing the resin plasticizing / melting means, for example, a shut-off valve can be exemplified.

  In the injection foam molding method of the present invention including the various preferred embodiments described above, in the step (C), the volume of the cavity is reduced to apply pressure to the molten thermoplastic resin in the cavity. You can also. By adopting such a configuration, after injecting the molten thermoplastic resin in a gas-dissolved state into the cavity, at an undesired time, the molten thermoplastic resin is in a reduced pressure state and the molten thermoplastic resin is in the cavity. Occurrence of a phenomenon such as foaming can be suppressed. In such a configuration, when the pressure of the molten thermoplastic resin injected into the cavity is high and the volume decrease due to cooling and solidification of the thermoplastic resin in the cavity is small, the step (D ), The volume of the cavity may be increased. When pressure is applied to the molten thermoplastic resin in the cavity by reducing the volume of the cavity, generally, pressure is applied to the molten thermoplastic resin in the portion of the cavity that is located far from the molten resin injection portion by reducing the volume of the cavity. Further, pressure is applied to the molten thermoplastic resin in the portion of the cavity located near the molten resin injection portion by volume reduction of the cavity and, for example, a pressure holding operation.

  In the step (D), it is preferable that the foamed molded product is cooled and solidified until local expansion due to foaming does not occur in the foamed molded product even if the foamed molded product is taken out from the mold assembly. The cooling time until this swelling does not occur depends on the mold temperature during injection and the mold temperature during cooling (the mold that forms the cavity when the thermoplastic resin injected into the cavity is cooled in the cavity. Surface temperature), the type and temperature of the thermoplastic resin, the type of gas used, the thickness of the molded product, the desired weight reduction rate, and cannot be determined uniquely, but preferably 5 seconds or more More preferably, it should be 20 seconds or longer.

In the injection foam molding method of the present invention including the above various preferred embodiments, at least a part of the mold surface constituting the cavity has a thermal conductivity of 13 (W · m ⁻¹ · K ⁻¹ ) or less. It is preferably composed of (15 Kcal · m ⁻¹ · hr ⁻¹ · deg ⁻¹ ) nesting. Furthermore, it is preferable that the insert is made of a ceramic material, and broadly, ceramics selected from the group consisting of zirconia-based materials, partially stabilized zirconia, alumina-based materials, K ₂ O—TiO ₂ , or soda. It is desirable to make from a glass selected from the group consisting of glass, quartz glass, heat resistant glass and crystallized glass. More specifically, as specific materials constituting the nesting, ZrO ₂ , ZrO ₂ —CaO, ZrO ₂ —Y ₂ O ₃ , ZrO ₂ —MgO, ZrO ₂ —SiO ₂ , ZrO ₂ —CeO ₂ , K ₂ O—TiO ₂ , Al ₂ O ₃ , Al ₂ O ₃ —TiC, Ti ₃ N ₂ , 3Al ₂ O ₃ -2SiO ₂ , MgO—SiO ₂ , 2MgO—SiO ₂ , MgO—Al ₂ O ₃ —SiO ₂ And ceramics selected from the group consisting of titania, or glass selected from the group consisting of quartz glass and crystallized glass, among which nesting from zirconia (ZrO ₂ ) including partially stabilized zirconia It is preferable that it is produced. The partial stabilizers in the partially stabilized zirconia include calcia (calcium oxide, CaO), yttria (yttrium oxide, Y ₂ O ₃ ), magnesia (magnesium oxide, MgO), silica (silicon oxide, SiO ₂ ), and ceria. It is preferably made of at least one material selected from the group consisting of (cerium oxide, CeO ₂ ). The proportion of the partial stabilizer contained in zirconia is 3 to 15 mol%, preferably 6 to 10 mol%, preferably 1 to 8 mol% for yttria when the partial stabilizer is calcia. Mol%, preferably 2 to 5 mol%, magnesia 4 to 15 mol%, preferably 8 to 10 mol%, ceria 3 to 18 mol%, preferably 6 It is desirable to be from mol% to 12 mol%.

In the injection foam molding method of the present invention including the various preferred embodiments described above, the thermoplastic resin can be an amorphous thermoplastic resin. In this case, in the step (B) and step (C), the temperature of the mold surface forming the cavity, and higher than the glass transition temperature T _g of the thermoplastic resin used in the step (D), cavity the temperature of the mold surface forming a is preferably less than the glass transition temperature T _g of the thermoplastic resin used. Alternatively, in the injection foam molding method of the present invention including the above various preferred embodiments, the thermoplastic resin can be a crystalline thermoplastic resin. In this case, in the step (B) and the step (C), the temperature of the mold surface constituting the cavity is set to be equal to or higher than the melting point T _m of the thermoplastic resin to be used, and the cavity is constituted in the step (D). The temperature of the mold surface to be used is preferably set to be equal to or lower than the crystallization start temperature _Tc of the thermoplastic resin to be used. In addition, it can also be set as the mixture comprised from the amorphous thermoplastic resin and the crystalline thermoplastic resin. Here, whether or not the thermoplastic resin is an amorphous thermoplastic resin is generally determined by whether or not a clear melting point (temperature showing a rapid endotherm) is confirmed by a differential scanning calorimetry (DSC) method. Is done. A resin that does not have a clear melting point is an amorphous thermoplastic resin. On the other hand, a resin having a clear melting point is a crystalline thermoplastic resin. In the amorphous thermoplastic resin, solidifying and softening of the thermoplastic resin is produced by longitudinal glass transition temperature T _g. On the other hand, in a crystalline thermoplastic resin, it melts at a melting point _Tm or higher, and crystals are generated and developed at a crystallization start temperature _Tc or lower, resulting in solidification of the thermoplastic resin.

Polycrystalline resins such as polyethylene resins and polypropylene resins as crystalline thermoplastic resins; Polyamide resins such as polyamide 6, polyamide 66 and polyamide MXD6; Polyoxymethylene (polyacetal, POM) resin; Polyethylene terephthalate (PET) resin, polybutylene integrators terephthalate (PBT) polyester resins such as a resin; can be exemplified polyphenylene sulfide resin. Amorphous thermoplastic resins include polystyrene resins, ABS resins, AES resins, AS resins such as styrene resins, methacrylic resins, polycarbonate resins (including linear polycarbonate resins and polycarbonate resins having branches in the main chain). , Modified polyphenylene ether (PPE) resin, polysulfone resin, polyethersulfone resin, polyarylate resin, polyetherimide resin, polyamideimide resin, and elastomer.

  Furthermore, a thermoplastic resin made of a polymer alloy material can be used. Here, the polymer alloy material is composed of a blend of at least two types of thermoplastic resins, or a block copolymer or graft copolymer in which at least two types of thermoplastic resins are chemically bonded. A polymer alloy material is widely used as a high-functional material that can have the unique performance of each of the individual thermoplastic resins. As a thermoplastic resin constituting a polymer alloy material in which at least two kinds of thermoplastic resins are blended, styrene resins such as polystyrene resin, ABS resin, AES resin, and AS resin; polyolefin resins such as polyethylene resin and polypropylene resin; methacrylic resin Polycarbonate resin; polyamide resin such as polyamide 6, polyamide 66, polyamide MXD6; modified PPE resin; polyester resin such as polybutylene terephthalate resin and polyethylene terephthalate resin; polyoxymethylene resin; polysulfone resin; polyimide resin; Polyarylate resin; Polyether sulfone resin; Polyether ketone resin; Polyether ether ketone resin; Polyester carbonate resin Can. As a polymer alloy material obtained by blending two types of thermoplastic resins, a polymer alloy material of a polycarbonate resin and an ABS resin can be exemplified. Such a combination of resins is expressed as polycarbonate resin / ABS resin. The same applies to the following. Furthermore, as a polymer alloy material blended with at least two types of thermoplastic resins, polycarbonate resin / PET resin, polycarbonate resin / PBT resin, polycarbonate resin / polyamide resin, polycarbonate resin / PBT resin / PET resin, modified PPE resin / HIPS Examples thereof include resin, modified PPE resin / polyamide resin, modified PPE resin / PBT resin / PET resin, modified PPE resin / polyamide MXD6 resin, polyoxymethylene resin / polyurethane resin, and PBT resin / PET resin.

  In addition, an additive, a filler, and a reinforcing agent can also be added to the various thermoplastic resins described above.

  Additives: Plasticizers; Stabilizers; Antioxidants: Ultraviolet absorbers; Ultraviolet stabilizers such as organic nickel compounds such as nickel bis (octylphenyl) sulfide, hindered amine compounds; Antistatic agents; Flame retardants; Vinadin, Priben Antifungal agents such as Thor and Thiabendazole; Lubricants such as liquid paraffin, polyethylene wax and fatty acid amide; Organic foaming agents such as ADCA; Transparent coloring agents; Various colorants such as organic pigments and inorganic pigments; Crosslinking agents; Acrylic graft polymers, Mention may be made of impact resistance enhancers such as MBS.

  Plasticizers such as diethyl phthalate, di-n-butyl phthalate, 2-ethylhexyl phthalate, diisononyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate; triethyl phosphate, tributyl phosphate, phosphoric acid Phosphate esters such as tricresyl and triphenyl phosphate; Fatty acid base esters such as butyl oleate, dibutyl adipate, adipic acid-n-hexyne, di-2-ethylhexyl adipate; alcohol esters such as diethylene glycol dibenzoate Oxyacid esters such as acetyltriethyl citrate and dibutyl maleate; trimellitic plasticizer; polyester plasticizer; epoxy plasticizer; chlorinated paraffinic plasticizer.

  As stabilizers, organotin stabilizers such as di-n-octyltin compounds, di-n-butyltin compounds, and dimethyltin compounds; lead compound systems such as tribasic lead sulfate, dibasic lead phosphite, and lead silicate Stabilizers; metal soap-based stabilizers such as cadmium soap, lead soap, zinc soap; trisnonyl phosphate; trisnonylphenyl phosphate;

  As antioxidants, phenolic antioxidants such as dibutylcresol and butylhydroxyanisole; bisphenolic antioxidants such as methylenebis (methylbutylphenol) and thiobis (methylbutylphenol); tris (methylhydroxybutylphenyl) butane, tocophenol, etc. And polyphosphoric antioxidants; organic sulfur compounds such as dimyristylthiodipropionate; and organic phosphorus compounds such as tris (mono / dinonylphenyl) phosphite.

  As UV absorbers, salicylic acid UV absorbers such as phenyl salicylate and butylphenyl salicylate; benzophenone UV absorbers such as dihydroxybenzophenone; benzotriazole UV absorbers such as (hydroxymethylphenyl) benzotriazole; ethylhexylcyanodiacrylate Examples include cyanoacrylate-based ultraviolet absorbers such as phenonyl.

  Antistatic agents such as poly (oxyethylene) alkylamines, poly (oxyethylene) alkylphenyl ethers, and other nonionic surfactant antistatic agents; alkylsulfonates, alkylbenzenesulfonates, alkylphosphates, etc. Examples include ionic surfactant-based antistatic agents; cationic surfactant-based antistatic agents such as quaternary ammonium chloride; amphoteric surfactants; and conductive resins.

  As flame retardants, halogen flame retardants such as tetrabromobisphenol A, polybromobiphenol, bis (hydroxydibromophenyl) propane, chlorinated paraffin; phosphorus flame retardants such as ammonium phosphate and tricresyl phosphate; antimony trioxide; red phosphorus ; Tin oxide etc. can be mentioned.

  As fillers and reinforcing agents, inorganic materials: stainless steel fibers, high-strength amorphous metal fibers, stainless steel foils, steel foils, copper foils and other metal materials; high-molecular polyethylene fibers, high-strength polyarate fibers, para-type all Examples include organic materials such as aromatic polyamide fibers, aramid fibers, PEEK fibers, PEI fibers, PPS fibers, fluororesin fibers, phenol resin fibers, vinylon fibers, polyacetal fibers, and powder materials.

  As inorganic fillers and reinforcing agents, glass materials such as glass fibers, long glass fibers, and quartz glass fibers; carbon materials such as PAN carbon fibers, pitch carbon fibers, and graphite whiskers; silicon carbide fibers, silicon carbide Silicon carbide materials such as continuous fibers, silicon carbide whiskers, silicon carbide whisker sheets; boron materials such as boron fibers; Si—Ti—C—O materials such as Si—Ti—C—O fibers; potassium titanate fibers, titanium Examples thereof include potassium titanate materials such as potassium acid whisker and potassium titanate conductive whisker; silicon nitride materials such as silicon nitride whisker and silicon nitride whisker sheet; and calcium sulfate materials such as calcium sulfate whisker.

  As powder filler and reinforcing agent, mica flake, mica powder, shirasu balloon, silica fine powder, talc powder, aluminum hydroxide powder, magnesium hydroxide powder, magnesium silicate powder, calcium sulfate fine powder, spherical hollow glass powder, metallization Powder, high purity synthetic silica fine powder, tungsten disulfide powder, tungsten carbide powder, zirconia fine powder, zirconia fine powder, partially stabilized zirconia powder, alumina-zirconia composite powder, composite metal powder, iron powder, aluminum powder, molybdenum metal Examples thereof include powder, tungsten powder, aluminum nitride powder, nylon fine particle powder, silicone resin fine powder, spinel powder, amorphous alloy powder, aluminum flake, and glass flake.

  The foam molded article of the present invention for achieving the above object is a foam molded article made of a thermoplastic resin molded by the injection foam molding method of the present invention including the various preferred embodiments described above. The following formula (1), preferably the following formula (1 ′), more preferably the following formula (1 ″) is satisfied.

0.001 × (1-ρ ₀ / ρ ₁ ) <V ₁ / V ₀ <1.2 × (1-ρ ₀ / ρ ₁ ) (1)
0.003 × (1-ρ ₀ / ρ ₁ ) <V ₁ / V ₀ <1.0 × (1-ρ ₀ / ρ ₁ ) (1 ′)
0.005 × (1−ρ ₀ / ρ ₁ ) <V ₁ / V ₀ <0.8 × (1−ρ ₀ / ρ ₁ ) (1 ″)

here,
V ₀ : Volume of the foam molded product V ₁ : Total volume of bubbles present in the foam molded product ρ ₀ : Density of molten thermoplastic resin (density of molten thermoplastic resin before gas dissolution)
ρ ₁ : Density of the thermoplastic resin used (not the density of the foam molded product)
It is.

The foamed molded article of the present invention has a thick part and a thin part, and the density ρ _{thick of the thick} part and the density ρ _{thin of the} thin part are the following formula (2), preferably the following formula (2 ′), It is more preferable that the following expression (2 ″) is satisfied.

ρ _thick <0.99 × ρ _thin (2)
ρ _thick <0.97 × ρ _thin (2 ')
ρ _thick <0.95 × ρ _thin (2 ”)

  The concept of the thick part and the thin part in the foam molded product is relative, and the thickness of the thick part is larger than the thickness of the thin part. In general, the molten thermoplastic resin located in the cavity portion where the thin-walled portion is to be molded starts cooling in step (C), and the thermoplastic resin located in the cavity portion does not foam or occurs. Even a few. On the other hand, the molten thermoplastic resin positioned in the cavity portion where the thick wall portion is to be molded starts cooling in the step (D), and foaming occurs in the thermoplastic resin positioned in the cavity portion. Therefore, in the foam molded product, the foamed state is different between the thin wall portion and the thick wall portion. For example, in a foam-molded product having a thin part having a thickness of 1 mm and a thick part having a thickness of 3 mm, the time length and pressure of the step (C) and the step (D) are adjusted to adjust the pressure to 1 mm. It is possible to cause foaming to occur in a thick part having a thickness of 3 mm without causing foaming in the thin part. For example, a foam molded product having a thin part having a thickness of 3 mm and a thick part having a thickness of 6 mm In the above, by adjusting the time length and pressure of the step (C) and the step (D), foaming is not caused in the thin portion having a thickness of 3 mm, but foaming is caused in the thick portion having a thickness of 6 mm. Is possible.

In the foamed molded article of the present invention, the thick part can be formed from a rib part or a boss part. That is, the foam molded product has an uneven thickness portion, and the uneven thickness portion can have a rib shape or a boss shape. The density ρ _base of the base portion of the rib part or the boss part and the density ρ ₁ of the thermoplastic resin used are the following formula (3), preferably the following formula (3 ′), more preferably the following formula (3 It is desirable to satisfy “)”.

ρ _base <0.99 × ρ ₁ (3)
ρ _base <0.97 × ρ ₁ (3 ')
ρ _base <0.95 × ρ ₁ (3 ”)

  Furthermore, in the foamed molded article of the present invention including the various preferred forms described above, no bubbles are present at a depth of at least 20 μm from the surface, preferably at a depth of at least 55 μm from the surface. Is desirable. That is, it is desirable that a foamed layer is not present on the surface of the foamed molded article of the present invention, and a foamed portion is present at a depth of 20 μm from the surface or deeper than that.

  The fixed mold part and the movable mold part can be made of a metal material such as carbon steel, stainless steel, an aluminum alloy, or a copper alloy. The structure of the molten resin injection part can be any known type of molten resin injection part (gate structure), for example, a direct gate structure, a side gate structure, a jump gate structure, a pinpoint gate structure, a tunnel gate. Examples include a structure, a ring gate structure, a fan gate structure, a disk gate structure, a flash gate structure, a tab gate structure, and a film gate structure. Examples of the structure of the molten resin flow path in the fixed mold part include a combination of a sprue and a cold runner, or a hot runner.

  In the injection foam molding method of the present invention, by applying pressure to the molten thermoplastic resin in the cavity in the step (C), the foaming of gas in the molten thermoplastic resin in the cavity is suppressed, or the cavity The gas foamed in the molten thermoplastic resin injected into the inside is re-dissolved in the molten thermoplastic resin in the cavity, and in step (D), the volume is reduced due to cooling and solidification of the thermoplastic resin in the cavity. Due to the pressure drop in the thermoplastic resin in the cavity, the gas dissolved in the thermoplastic resin is foamed to form a foamed portion. Usually, in the step (D), cooling and solidification of the molten thermoplastic resin in the cavity starts from the portion of the molten thermoplastic resin in the vicinity of the mold surface constituting the cavity. And before foaming starts in the molten thermoplastic resin portion, cooling and solidification of the molten thermoplastic resin portion is started, so the foam molded product obtained by the injection foam molding method of the present invention, or In the foamed molded product of the present invention, foamed cells (bubbles) are not formed on the surface, and a foamed molded product having an excellent appearance can be obtained. In addition, local sink marks and warpage can be suppressed. Further, in a foam molded product having a thin part and a thick part, the foamed state is different between the thin part and the thick part. Therefore, it is possible to reliably prevent the occurrence of a phenomenon that the strength of the thin portion is reduced. In addition, the pressure drop due to the cooling and solidification of the thermoplastic resin in the cavity is significant in the thick part, and as a result, foaming occurs more in the thick part than in the thin part. As a result, the thick part is reliably reduced in weight. can do.

  Hereinafter, the present invention will be described based on examples with reference to the drawings.

Example 1 relates to an injection foam molding method and a foam molded article of the present invention. A schematic cross-sectional view of the mold assembly 30 (in a state after the fixed mold part and the movable mold part are clamped) in Example 1 is shown in FIG. 1, and the thermoplastic resin is plasticized and melted. FIG. 2 shows a schematic view in which a part of the injection cylinder 10 which is a resin plasticizing / melting means for cutting out is cut out. FIG. 3 shows a schematic bottom view, front view, and right side view of the foam molded product. The foam molded product 50 has a rib part (thick part) 53 protruding from a plate-like part (thin part) 51. The size of the foamed molded product 50 is vertical x horizontal = 100 mm x 100 mm, the thickness (t ₁ ) of the plate-like part (thin part) 51 is 2.0 mm, and the thickness of the rib part (thick part) 53 ( t ₂ ) and height (h) were 5.0 mm. Reference numeral 52 indicates the design surface of the plate-like portion (thin portion) 51.

  The injection molding apparatus according to the first embodiment includes an injection cylinder 10 that is a resin plasticizing / melting unit for plasticizing / melting a thermoplastic resin, and a mold assembly 30. The screw 12 disposed in the injection cylinder 10 is not limited, but is an in-line screw type in which the thermoplastic resin is plasticized and melted and also has a plunger action. Specifically, the injection cylinder 10 includes a heating cylinder 11 and a screw 12. The screw 12 is rotated by a hydraulic motor 15 via a reduction gear 14. The heating cylinder 11 is provided with a gas introduction unit 20, and gas can be introduced into the heating cylinder 11 from a gas source (not shown) through a pipe (not shown) and the gas introduction unit 20. In FIG. 2, reference numeral 16 is a hopper, reference numeral 17 is an injection ram, reference numeral 18 is an injection hydraulic cylinder, reference numeral 19 is an injection device forward / backward cylinder, reference numerals 19A and 19B are hydraulic piping, reference numeral 19C is a pressure gauge.

As shown in FIG. 1, the mold assembly 30 includes a fixed mold part 31 and a movable mold part 32 made of steel, and the fixed mold part 31 and the movable mold part 32 are clamped. , A molten resin injection portion 34 opened to the cavity 35, and a molten resin flow path 33 that connects the molten resin injection portion 34 and the injection cylinder 10 that is a resin plasticizing / melting means. . Specifically, the molten resin injection part 34 has a side gate structure. Moreover, the molten resin flow path 33 is specifically composed of a combination of a sprue and a cold runner. The fixed mold part 31 is attached to a fixed mold part mounting plate (fixed platen) 36 provided in the injection molding apparatus. On the other hand, the movable mold part 32 is attached to a movable mold part mounting plate (movable platen) 37 provided in the injection molding apparatus. The movable mold part mounting plate (movable platen) 37 has a structure that can move in parallel on the tie bar 39 by the operation of the hydraulic piston 38B in the mold clamping hydraulic cylinder 38A, and is fixed by the operation of the hydraulic piston 38B. The mold part 31 and the movable mold part 32 are clamped (see FIG. 1) or opened. The shape of the cavity 35 was set to a shape capable of forming the foam molded product shown in FIG. The portion indicated by the arrow in FIG. 3 is a trace of the molten resin injection portion 34. Further, in the fixed mold part 31, at least a part of the mold surface constituting the cavity 35 [in Example 1, it is almost all, and the design surface 52 of the plate-like part (thin wall part) 51 of the foam molded product is provided. The mold surface to be formed] is a nesting 40 having a thermal conductivity of 13 (W · m ⁻¹ · K ⁻¹ ) or less, specifically a ceramic material, more specifically zirconia (thermal conductivity: A nesting 40 made of 4.2 W · m ⁻¹ · K ⁻¹ ) is disposed.

Hereinafter, although the foam molding method of Example 1 is demonstrated, Nippon Steel Corporation J85-EL-III-MuCel was used as an injection molding apparatus. Further, a polycarbonate resin (trade name: Iupilon H3000), which is an amorphous thermoplastic resin manufactured by Mitsubishi Engineering Plastics Co., Ltd., was used as the thermoplastic resin, and nitrogen gas was used as the gas. Furthermore, the molding conditions were as shown in Table 2 below. This polycarbonate resin has a glass transition temperature _Tg of 145 ° C.

[Step-100]
First, the thermoplastic resin was plasticized and melted by the resin plasticizing / melting means 10, gas was dissolved in the molten thermoplastic resin, and the molten thermoplastic resin was weighed. In Example 1, after melt | dissolving gas in molten thermoplastic resin, the molten thermoplastic resin in a gas-dissolved state was measured. Specifically, the thermoplastic resin introduced between the heating cylinder 11 and the screw 12 from the hopper 16 is heated, plasticized, and melted by the heating cylinder 11 and the screw 12, and further introduced from the gas introduction unit 20. After the dissolved gas is dissolved in the molten thermoplastic resin in the heating cylinder 11, the molten thermoplastic resin in a gas-dissolved state is measured, and the tip of the heating cylinder 11 (nozzle head portion 13) and the tip of the screw 12 are measured. In the gap 13A formed between the two. When the molten thermoplastic resin in a gas-dissolved state was weighed, the pressure of the molten thermoplastic resin (resin metering back pressure) was set to 5 × 10 ⁶ Pa or more. Further, when the gas is dissolved in the molten thermoplastic resin, the gas is in a supercritical state. Table 2 shows the resin temperature (temperature of the plasticized and melted resin), gas dissolution conditions, approximate gas dissolution amount, and resin measurement back pressure.

[Step-110]
Next, the cavity formed by clamping the fixed mold part 31 and the movable mold part 32 from the resin plasticizing / melting means 10 via the molten resin flow path 33 and the molten resin injection part 34. In 35, the measured molten thermoplastic resin was injected. Specifically, an injection ram 17 is attached to the rear end of the screw 12 constituting the injection cylinder 10 which is a resin plasticizing / melting means, and pressure is applied to the injection ram 17 by an injection hydraulic cylinder 18. It is done. By applying pressure to the injection ram 17 by the hydraulic cylinder 18 for injection, the screw 12 is pushed forward, and pressure is applied to the molten thermoplastic resin. As a result, the molten thermoplastic resin in the gas dissolved state stored in the gap 13A is Then, it is extruded from the nozzle head portion 13 at a high speed, and injected from the molten resin injection portion 34 to the cavity 35 via the molten resin flow path 33. The mold temperature and injection time during injection were as shown in Table 2. The injection amount of the molten thermoplastic resin in the gas-dissolved state was set to an amount sufficient to completely fill the cavity 35 with the unexpanded (in the gas-dissolved) molten thermoplastic resin. Furthermore, even when the injection is completed, the amount of molten thermoplastic resin remaining as a cushion amount in the gap 13A is set.

[Step-120]
Thereafter, pressure is applied to the molten thermoplastic resin in the cavity 35 to suppress foaming of the gas in the molten thermoplastic resin in the cavity 35, or foaming is performed in the molten thermoplastic resin injected into the cavity 35. The dissolved gas was redissolved in the molten thermoplastic resin in the cavity 35. Specifically, pressure was applied to the molten thermoplastic resin in the cavity 35 by a pressure holding operation. That is, by applying pressure to the injection ram 17 by the injection hydraulic cylinder 18, the screw 12 is pushed forward, and pressure is applied to the molten thermoplastic resin remaining in the gap 13 </ b> A. And the molten thermoplastic resin in the cavity 35 via the molten thermoplastic resin in the molten resin injection portion 34. The foaming suppression pressurization value (holding pressure) was 80 MPa, and the foaming suppression pressurization time (holding time) was 2.0 seconds. The mold temperature was set as the injection mold temperature.

[Step-130]
After 2.7 seconds from the start of injection, the application of pressure to the molten thermoplastic resin in the cavity 35 was stopped. Specifically, pressure is applied to the molten thermoplastic resin in the cavity 35 by stopping the pressure holding operation (that is, by stopping the pressure applied to the injection ram 17 by the injection hydraulic cylinder 18). Canceled. Then, the gas was foamed based on the pressure drop in the thermoplastic resin in the cavity 35 due to the volume reduction accompanying the cooling and solidification of the thermoplastic resin in the cavity 35. The mold temperature was the mold temperature during cooling shown in Table 2.

[Step-140]
After the thermoplastic resin in the cavity 35 is cooled and solidified from the start of injection to 62.7 seconds, that is, the cooling time is set to 60 seconds, and then the fixed mold portion 31 and the movable mold portion 32 are opened. The foamed molded product was taken out. During cooling, the mold temperature was maintained at the mold temperature during cooling shown in Table 2.

The obtained foamed molded article did not show sink marks and had an excellent appearance. Further, when the volume of the foam molded product is V ₀ , the total volume of bubbles existing in the foam molded product is V ₁ , the density of the molten thermoplastic resin is ρ ₀ , and the density of the thermoplastic resin used is ρ ₁ , The values of V ₀ , V ₁ , ρ ₀ , ρ ₁ are as shown in Table 3 below, and these values satisfied the formula (1). Further, a part of the plate part (thin part) 51 and a part of the rib part (thick part) 53 are cut out, and the density ρ _{thick of the} rib part (thick part) 53 and the plate part (thin part) 51 are obtained. The density ρ _thin was measured. The results are shown in Table 3, and these values satisfied the formula (2). Further, the density ρ _base of the base portion 54 of the rib portion 53 was measured. The results are shown in Table 3, and this value satisfied the expression (3). Moreover, when the obtained foamed molded article was cut and cross-sectional observation was performed and the foamed state was examined, it was at least 20 μm deep from the surface of the foamed molded article (specifically, the average of the surface of the foamed molded article was It was confirmed that no bubbles were present up to a depth of 55 μm.

[Table 3]
V ₁ / V _0: 0.003
ρ ₀ : 1.34 g / cm ³
ρ ₁ : 1.43 g / cm ³
ρ _thick : 1.36 g / cm ³
ρ _thin : 1.43 g / cm ³
ρ _base : 1.34 g / cm ³

[Comparative Example 1]
In Comparative Example 1, the gas is not dissolved in the molten thermoplastic resin in the same step as [Step-100] in Example 1, and the holding pressure in the same step as [Step-120] in Example 1 The same steps as [Step-100] to [Step-140] of Example 1 were performed except that the pressure holding time was changed. The molding conditions are shown in Table 2.

  Sink marks were produced in the rib portion of the obtained molded product (naturally, the inside was not foamed), and excellent surface quality could not be obtained.

[Comparative Example 2]
In Comparative Example 2, [Step-100] in Example 1 is the same as [Step-120] in Example 1, except that the foaming suppression pressurization time (holding time) is 0.1 second. The same step as in [Step-140] was performed. The molding conditions are shown in Table 2.

  Although no occurrence of sink marks was observed in the obtained foamed molded product, a fluffy appearance defect and swelling occurred, and an excellent appearance could not be obtained.

  The resin plasticizing / melting means for plasticizing / melting the thermoplastic resin in the injection molding apparatus used in Example 2 is composed of a heating cylinder 61 and a reservoir 70. Then, the thermoplastic resin is plasticized and melted in advance in the heating cylinder 61, the molten thermoplastic resin is transferred to the reservoir 70, the gas is dissolved in the molten thermoplastic resin in the reservoir 70, and the molten thermoplastic resin It was set as the structure which measures. A schematic diagram of the resin plasticizing / melting means in Example 2 is shown in FIG. Since the mold assembly can be the same as the mold assembly described in the first embodiment, detailed description thereof is omitted.

  In the second embodiment, a screw 62 is disposed in the heating cylinder 61. The screw 62 is rotated by a hydraulic motor 65 via a reduction gear 64. 4, reference numeral 66 is a hopper, reference numeral 67 is an extrusion ram, reference numeral 68 is a hydraulic cylinder for extrusion, reference numeral 69 is a cylinder for advancing and retreating an injection device, and reference numerals 69A and 69B are hydraulic pipes. Number 69C is a pressure gauge.

  In Example 2, in a step similar to [Step-100] of Example 1, first, the thermoplastic resin is plasticized and melted by the heating cylinder 61. Specifically, the thermoplastic resin put into the screw 62 from the hopper 66 is heated, plasticized, and melted by the heating cylinder 61 and the screw 62. Then, by applying pressure to the extrusion ram 67 by the extrusion hydraulic cylinder 68, the screw 62 is pushed forward and pressure is applied to the molten thermoplastic resin. As a result, the molten thermoplastic resin stored in the gap 63A is stored in the reservoir 70. It is transferred to. By controlling the volume of the reservoir 70 by the injection hydraulic cylinder 71, the molten thermoplastic resin can be measured in the reservoir 70. Further, the reservoir 70 is provided with a gas introduction part 72, and a gas can be introduced into the reservoir 70 from a gas source (not shown) through a pipe (not shown) and the gas introduction part 72. Furthermore, an injection hydraulic cylinder 71 (hydraulic piping, pressure gauge, and the like are not shown) is disposed at the rear end of the reservoir 70, and is stored in the reservoir 70 by the operation of the injection hydraulic cylinder 71. The molten thermoplastic resin in a gas-dissolved state can be extruded at a high speed and injected from the molten resin injection portion 34 to the cavity 35 via the molten resin flow path 33.

  In Example 2, a foamed molded article was molded based on substantially the same steps as [Step-100] to [Step-140] of Example 1. In Example 2, a foamed molded product was molded under the same molding conditions as in Example 1 shown in Table 2. Here, “resin temperature” in Table 2 means the temperature of the molten thermoplastic resin in the reservoir 70 in Example 2. The resin metering back pressure means a pressure applied to the molten thermoplastic resin in a gas-dissolved state stored in the reservoir 70 by the injection hydraulic cylinder 71. Further, by applying pressure to the molten thermoplastic resin in the reservoir 70 by the injection hydraulic cylinder 71, the pressure is applied to the inside of the cavity 35 via the molten thermoplastic resin in the molten resin flow path 33 and the molten resin injection portion 34. By being transmitted to the molten thermoplastic resin, pressure is applied to the molten thermoplastic resin in the cavity 35, gas foaming in the molten thermoplastic resin in the cavity 35 is suppressed, or the melt injected into the cavity 35. The gas foamed in the thermoplastic resin was redissolved in the molten thermoplastic resin in the cavity 35. Furthermore, by stopping the pressure holding operation (that is, by stopping the pressure applied to the molten thermoplastic resin in the reservoir 70 by the injection hydraulic cylinder 71), the pressure is applied to the molten thermoplastic resin in the cavity 35. Stopped adding. As in Example 1, the obtained foamed molded article was free from sink marks and had an excellent appearance.

  The third embodiment is a modification of the first or second embodiment. In Example 3, in the same process as [Step-130] of Example 1, the application of pressure to the molten thermoplastic resin in the cavity 35 is stopped by solidification of the molten thermoplastic resin in the molten resin injection part 34. To do.

  As a specific method for solidifying the molten thermoplastic resin in the molten resin injection part 34, after the injection of the molten thermoplastic resin into the cavity 35 is completed and 1 second has elapsed from the start of injection, the fixed mold part A part of the heating means (specifically a heater, but not shown in FIG. 1) disposed in 31 (a heater disposed in the vicinity of the molten resin injection portion) was inactivated. As a result, the temperature of the molten thermoplastic resin present in the molten resin injection portion 34 was set to 140 ° C. or lower and solidified.

  Except this point, the injection foam molding method in Example 3 can be the same as the injection foam molding method in Example 1 or Example 2, and the injection molding apparatus used in Example 3 is the same as in Example 1 or Example 2. Since it can be the same as that of the injection molding apparatus used in Example 2, these detailed description is abbreviate | omitted.

  The fourth embodiment is also a modification of the first or second embodiment. In Example 4, in the same process as [Process-130] of Example 1, the molten resin injection part 34 is mechanically closed to stop applying pressure to the molten thermoplastic resin in the cavity 35. To do. In the fourth embodiment, the molten resin flow path in the fixed mold part 31 is a hot runner 80, the molten resin injection part 34 is a valve gate 83, and specific means for mechanically closing the molten resin injection part 34 is shut off. The pin 84 was used. A schematic diagram of the molten resin flow path (hot runner 80), the valve gate 83, and the shut-off pin 84 is shown in FIG. In FIG. 5, reference numeral 81 is a runner manifold, reference numeral 82 is a heater, and reference numeral 85 is a hydraulic cylinder. The movement of the hydraulic cylinder 85 causes the shut-off pin 84 to open and close the valve gate 83 that is the molten resin injection portion 34. In Example 4, after the completion of the injection of the molten thermoplastic resin into the cavity 35 and after 2.7 seconds have elapsed from the start of the injection, the shut-off pin 84 is operated, whereby the molten resin injection part The valve gate 83 which is 34 was mechanically closed.

  Except for this point, the injection foam molding method in Example 4 can be the same as the injection foam molding method in Example 1 or Example 2, and the injection molding apparatus used in Example 4 is the same as in Example 1 or Example 2. Since it can be the same as that of the injection molding apparatus used in Example 2, these detailed description is abbreviate | omitted.

  The fifth embodiment is also a modification of the first or second embodiment. In Example 5, in the same process as [Step-130] of Example 1, the molten resin flow path 33 is mechanically closed to stop applying pressure to the molten thermoplastic resin in the cavity 35. To do. In the fifth embodiment, the molten resin flow path in the fixed mold part 31 is a hot runner 90, and the means for mechanically closing the molten resin flow path (hot runner 90) is a combination of the valve gate 93 and the shut-off pin 94. did. A schematic diagram of the molten resin flow path (hot runner 90), the valve gate 93 and the shut-off pin 94 is shown in FIG. In FIG. 6, reference numeral 91 is a runner manifold, reference numeral 92 is a heater, and reference numeral 95 is a hydraulic cylinder. The shutoff pin 94 opens and closes the valve gate 93 by the movement of the hydraulic cylinder 95. In Example 5, after the completion of the injection of the molten thermoplastic resin into the cavity 35 and after 2.7 seconds from the start of the injection, the valve gate 93 is closed by operating the shut-off pin 94. Therefore, the molten resin flow path (hot runner 90) was mechanically closed.

  Except this point, the injection foam molding method in Example 5 can be the same as the injection foam molding method in Example 1 or Example 2, and the injection molding apparatus used in Example 5 is the same as in Example 1 or Example 2. Since it can be the same as that of the injection molding apparatus used in Example 2, these detailed description is abbreviate | omitted. Further, the molten resin injection portion 34 in the injection molding apparatus used in the fifth embodiment may be a combination of the valve gate 83 and the shut-off pin 84 in the same manner as described in the fourth embodiment. It is preferable from the viewpoint that the molten thermoplastic resin in the molten resin flow path 33 is not solidified when the resin is cooled and solidified.

  The sixth embodiment is also a modification of the first or second embodiment. In Example 6, in the same process as [Step-130] of Example 1, pressure is applied to the molten thermoplastic resin in the cavity 35 by mechanically closing the resin plasticizing / melting means. Cancel. In Example 6, as schematically shown in FIG. 7, a means for mechanically closing the resin plasticizing / melting means was a shut-off valve 100 disposed in the nozzle head portion 13. The shut-off valve 100 is positioned at the forward end and the reverse end by the hydraulic cylinder 101. When the shut-off valve 100 is positioned at the forward end (see FIG. 7), the resin plasticizing / melting means is closed, and the shut-off valve 100 is closed. When 100 is positioned at the reverse end, the resin plasticizing / melting means is in an open state. In the sixth embodiment, after the injection of the molten thermoplastic resin into the cavity 35 is completed and 2.7 seconds have elapsed from the start of the injection, the shutoff valve 100 is operated by the operation of the hydraulic cylinder 101. The resin plasticizing / melting means was mechanically closed.

  Except this point, the injection foam molding method in Example 6 can be the same as the injection foam molding method in Example 1 or Example 2, and the injection molding apparatus used in Example 6 is also the same as in Example 1 or Example 2. Since it can be the same as that of the injection molding apparatus used in Example 2, these detailed description is abbreviate | omitted. As described in the second embodiment, when the resin plasticizing / melting means includes the heating cylinder 61 and the reservoir 70, a shut-off valve may be disposed at the tip of the reservoir 70.

The seventh embodiment is also a modification of the first or second embodiment. In Example 1 or Example 2, a polycarbonate resin, which is an amorphous thermoplastic resin, was used as the thermoplastic resin. On the other hand, in Example 7, polyacetal resin (Mitsubishi Engineering Plastics Co., Ltd., Iupital F20-03), which is a crystalline thermoplastic resin, was used as the thermoplastic resin. The crystalline thermoplastic resin has a melting point _Tm of 165 ° C.

  Except this point, the injection foam molding method in Example 7 can be the same as the injection foam molding method in Example 1 or Example 2, and the injection molding apparatus used in Example 7 is the same as in Example 1 or Example 2. Since it can be the same as that of the injection molding apparatus used in Example 2, these detailed description is abbreviate | omitted. The molding conditions in Example 7 are shown in Table 4. In addition, Example 3 to Example 6 can be applied to Example 7.

The eighth embodiment is also a modification of the first or second embodiment. In Example 1 or Example 2, the cavity 35 when the molten thermoplastic resin in a gas-dissolved state is injected into the cavity was set to an atmospheric atmosphere. On the other hand, in Example 8, the pressurized fluid was filled in the cavity 35 in advance before the measured molten thermoplastic resin was injected into the cavity 35. Here, the pressurized fluid filled in the cavity 35 was nitrogen gas having a pressure of 5 × 10 ⁶ Pa. Since the cavity 35 cannot be a completely sealed space, most of the pressurized fluid is discharged from the parting surface and the protruding portion to the outside when the molten thermoplastic resin in the gas dissolved state is injected into the cavity 35. A part of the pressurized fluid is dissolved in the molten thermoplastic resin injected into the cavity 35.

  Except for this point, the injection foam molding method in Example 8 can be the same as the injection foam molding method in Example 1 or Example 2, and the injection molding apparatus used in Example 8 is the same as in Example 1 or Example 2. Since it can be the same as that of the injection molding apparatus used in Example 2, these detailed description is abbreviate | omitted. The molding conditions in Example 8 can be the same as those shown in Table 2. In addition, Example 3 to Example 7 can be applied to Example 8.

  The ninth embodiment is also a modification of the first or second embodiment. In Example 9, in the same process as [Step-120] of Example 1, not only pressure was applied to the molten thermoplastic resin in the cavity 35 by a pressure-holding operation, but also the volume of the cavity 35 was reduced. Also, pressure is applied to the molten thermoplastic resin in the cavity 35. Specifically, in Example 9, after completion of the injection of the molten thermoplastic resin into the cavity 35 and 0.9 seconds have elapsed from the start of injection, the movable mold part 32 is fixed to the fixed mold. The volume of the cavity 35 was decreased by moving to the part 31 side. Specifically, when the volume of the cavity 35 before reduction is 1, the volume of the cavity 35 after reduction is 0.98.

  Except this point, the injection foam molding method in Example 9 can be the same as the injection foam molding method in Example 1 or Example 2, and the injection molding apparatus used in Example 9 is also a mold assembly. Since the fixed mold part 31 and the movable mold part 32 in the three-dimensional structure can be the same as the injection molding apparatus used in Example 1 or Example 2 except that they have a stamping structure, these details The detailed explanation is omitted.

As mentioned above, although this invention was demonstrated based on the preferable Example, this invention is not limited to these Examples. The structure and configuration of the mold assembly and the injection molding apparatus described in the examples, the thermoplastic resin used in the examples, molding conditions, and the like are examples and can be changed as appropriate. In the embodiment, one molded product is obtained, but a large number of molded products can be obtained. In the embodiment, the foam molded product having the rib portion is molded, but instead, the foam molded product having the boss portion can be molded. In this case, the density ρ _base of the base portion of the boss portion and the density ρ ₁ of the thermoplastic resin used are the above-described formula (3), preferably the following formula (3 ′), more preferably It is desirable that the following expression (3 ″) is satisfied.

1 is a schematic cross-sectional view of a mold assembly in Example 1. FIG. FIG. 2 is a schematic view in which a part of an injection cylinder, which is a resin plasticizing / melting means for plasticizing / melting the thermoplastic resin in Example 1, is cut away. FIG. 3 is a diagram illustrating a schematic bottom view, a front view, and a right side view of the foam-molded article in Example 1. FIG. 4 is a schematic diagram of a heating cylinder and a reservoir that are resin plasticizing / melting means for plasticizing / melting the thermoplastic resin in the second embodiment. FIG. 5 is a schematic partial cross-sectional view of the periphery of a molten resin injection part including a shut-off pin , which is a specific means for mechanically closing the molten resin injection part in the fourth embodiment. FIG. 6 is a schematic diagram of a molten resin flow path, a valve gate, and a shut-off pin in the fifth embodiment. FIG. 7 is a schematic diagram of a shut-off valve disposed in a nozzle head portion which is a means for mechanically closing the resin plasticizing / melting means in the sixth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Resin plasticizing / melting means (injection cylinder), 11 ... Heating cylinder, 12 ... Screw, 13 ... Nozzle head part, 13A ... Air gap, 14 ... Reduction gear, DESCRIPTION OF SYMBOLS 15 ... Hydraulic motor, 16 ... Hopper, 17 ... Injection ram, 18 ... Hydraulic cylinder for injection, 19 ... Cylinder for advance / retreat of injection device, 19A, 19B ... Hydraulic piping, 19C ... Pressure gauge, 20 ... Gas introduction part, 30 ... Mold assembly, 31 ... Fixed mold part, 32 ... Movable mold part, 33 ... Molten resin flow path, 34 ... Molten resin injection part, 35 ... Cavity, 36 ... Fixed mold part mounting plate (fixed platen), 37 ... Movable mold part mounting plate (movable platen), 38A ... Mold Hydraulic cylinder for fastening, 38B ... Hydraulic piston 38B, 39 ..Tie bar, 40 ... nest, 50 ... foamed molded product, 51 ... plate-like part (thin part), 52 ... design surface, 53 ... rib part (thick part), 54 ... Root part, 61 ... Heating cylinder, 62 ... Screw, 63A ... Gap, 64 ... Reduction gear, 65 ... Hydraulic motor, 66 ... Hopper, 67 ... Extrusion Ram, 68 ... hydraulic cylinder for extrusion, 69 ... cylinder for forward and backward injection, 69A, 69B ... hydraulic piping, 69C ... pressure gauge, 70 ... reservoir, 71 ... injection Hydraulic cylinder, 72 ... gas introduction part, 80,90 ... hot runner, 81,91 ... runner manifold, 82,92 ... heater heater, 83,93 ... valve gate, 84, 94 ... Shut-off pin, 85, 95 And hydraulic cylinder, 100 ... shut-off valve, 101 ... hydraulic cylinder

Claims (6)

(A) resin plasticizing / melting means for plasticizing / melting the thermoplastic resin, and
(B) a cavity composed of a fixed mold part and a movable mold part, formed by clamping the fixed mold part and the movable mold part, a molten resin injection part opened in the cavity, and A mold assembly having a molten resin flow path connecting the molten resin injection portion and the resin plasticizing / melting means;
An injection foam molding method using an injection molding apparatus comprising:
(A) a step of plasticizing and melting the thermoplastic resin by a resin plasticizing and melting means, dissolving a gas in the molten thermoplastic resin, and measuring the molten thermoplastic resin;
(B) The measurement is performed in the cavity formed by clamping the fixed mold part and the movable mold part from the resin plasticizing / melting means via the molten resin flow path and the molten resin injection part. Injecting the molten thermoplastic resin made,
(C) The gas foamed in the molten thermoplastic resin injected into the cavity is suppressed by applying pressure to the molten thermoplastic resin in the cavity to suppress the foaming of the gas in the molten thermoplastic resin in the cavity. Re-dissolving in the molten thermoplastic resin in the cavity;
(D) a step of foaming a gas based on a pressure drop in the thermoplastic resin in the cavity caused by a volume reduction due to cooling and solidification of the thermoplastic resin in the cavity;
(E) a step of opening the fixed mold part and the movable mold part and taking out the foam molded product;
It has
In the step (C), pressure is applied to the molten thermoplastic resin in the cavity by a pressure holding operation,
In the step (D), the application of pressure to the molten thermoplastic resin in the cavity is stopped by the solidification of the molten thermoplastic resin in the molten resin injection part, and the volume decreases due to the cooling and solidification of the thermoplastic resin in the cavity. An injection foam molding method characterized in that a gas is foamed based on a pressure drop in a thermoplastic resin in a cavity caused . (A) resin plasticizing / melting means for plasticizing / melting the thermoplastic resin, and
(B) a cavity composed of a fixed mold part and a movable mold part, formed by clamping the fixed mold part and the movable mold part, a molten resin injection part opened in the cavity, and A mold assembly having a molten resin flow path connecting the molten resin injection portion and the resin plasticizing / melting means;
An injection foam molding method using an injection molding apparatus comprising:
(A) a step of plasticizing and melting the thermoplastic resin by a resin plasticizing and melting means, dissolving a gas in the molten thermoplastic resin, and measuring the molten thermoplastic resin;
(B) The measurement is performed in the cavity formed by clamping the fixed mold part and the movable mold part from the resin plasticizing / melting means via the molten resin flow path and the molten resin injection part. Injecting the molten thermoplastic resin made,
(C) The gas foamed in the molten thermoplastic resin injected into the cavity is suppressed by applying pressure to the molten thermoplastic resin in the cavity to suppress the foaming of the gas in the molten thermoplastic resin in the cavity. Re-dissolving in the molten thermoplastic resin in the cavity;
(D) a step of foaming a gas based on a pressure drop in the thermoplastic resin in the cavity caused by a volume reduction due to cooling and solidification of the thermoplastic resin in the cavity;
(E) a step of opening the fixed mold part and the movable mold part and taking out the foam molded product;
It has
In the step (C), pressure is applied to the molten thermoplastic resin in the cavity by a pressure holding operation,
In the step (D), the resin plasticizing / melting means is mechanically closed to stop applying pressure to the molten thermoplastic resin in the cavity, and the volume accompanying cooling / solidification of the thermoplastic resin in the cavity. An injection foam molding method comprising foaming a gas based on a pressure drop in a thermoplastic resin in a cavity caused by a decrease. The injection foam molding method according to claim 1 or 2 , wherein when the gas is dissolved in the molten thermoplastic resin in the step (A), the gas is in a supercritical state or a subcritical state. The injection foam molding method according to any one of claims 1 to 3, wherein the gas is carbon dioxide gas, nitrogen gas, or a mixed gas of carbon dioxide and nitrogen. When metering a molten thermoplastic resin in the step (A), according to any one of claims 1 to 4, characterized in that the pressure of the molten thermoplastic resin with 5 × 10 ⁶ Pa or more Injection foam molding method. Before injecting the molten thermoplastic resin that has been weighed in the step (B) into the cavity, in advance, any one of claims 1 to 5, characterized in that be filled with pressurized fluid in the cavity 2. The injection foam molding method according to item 1.

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