Manufacturing method for injection-molded foam

Abstract

To provide a manufacturing method of a foamed molding having rigidity as well as cushioning property.SOLUTION: A manufacturing method of an injection-foamed body molding includes the steps of: injecting and filling a molten thermoplastic resin composition containing a foaming agent (H) in a cavity having a mold thickness (V0), set in a temperature range of [a crystallization temperature (Tc) (when a thermoplastic resin (D) is amorphous, a glass-transition temperature (Tg)-50°C)] to [(Tc or Tg)-90°C] of the thermoplastic resin (D) which is the main component constituting the thermoplastic resin composition; after 1 second to 12 seconds, enlarging the thickness (V0) of the mold cavity to 210-600%, making the thermoplastic resin composition foam [thickness: (V1)]; cooling for 5 seconds or over, followed by compressing the enlarged thickness of the cavity to a thickness [thickness: (V2)] which is 4-90% of the enlarged thickness (V1-V0); retaining its pressure for 0.1 second or over; and taking a foamed body from the mold. A thickness (V3) of the obtained foamed body satisfies (V1)>(V3)>(V2).SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing an injection-molded foam made of a thermoplastic resin. [Background technology]

[0002] Injection foam molded articles made of thermoplastic resins have a low specific gravity and excellent moldability and recyclability, and are therefore used in a variety of fields, including daily necessities, kitchen utensils, packaging films, home appliances, machine parts, electrical parts, and automobile parts. In the case of automobile parts, the use of propylene-based resin compositions containing propylene-based polymers has been increasing due to a trend toward increased on-board weight accompanying improvements in automobile safety, livability, and comfort, as well as an increase in IT equipment. In particular, foam molded articles made of propylene-based resin compositions are lightweight and have excellent molded appearance, and are therefore suitable for use in automobile parts.

[0003] One known method for producing injection-molded foamed articles made from thermoplastic resins such as propylene-based polymers is the core-back method, which uses a mold with a variable cavity volume. The cavity volume is kept small when filling the mold with molten thermoplastic resin containing a foaming agent, and then the cavity volume is expanded after filling to actively promote the generation and expansion of bubbles.

[0004] In addition, in the core-back method, a molding method has been proposed in which the cavity volume is expanded after filling to actively promote the generation and expansion of bubbles, and then the foamed molded body is compressed before the foam solidifies (Patent Documents 1, 2, 3, etc.).These foams basically have a three-layer structure with a solid skin layer on the surface and a foam layer inside. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-318542 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-196284 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-208299 Summary of the Invention [Problem to be solved by the invention]

[0006] Parts made from thermoplastic resins generally have various patterns, such as subtle irregularities or those that resemble leather, and these patterns are called grain. Such grain can be formed using injection molding alone and does not require painting, so it has the advantage of reducing costs while maintaining the texture of the interior parts of automobiles and home appliances. However, even with graining, thermoplastic resin molded parts without a skin feel hard and lack a cushiony feel when actually touched, and there is a problem in that they lack the luxurious feel of parts with an actual skin attached (skin-laminated parts).

[0007] The object of the present invention is to provide a method for producing a foam molded article using a molding method called injection foam molding, which has the rigidity characteristic of injection foaming, while also having a cushioning property that feels soft when pressed with a finger, a property not available with conventional injection foam molded articles. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to obtain a molded article that, using only injection foam molding of a thermoplastic resin composition without the use of a skin layer, has bending rigidity when a bending force is applied to the molded article, while also providing cushioning when pressed with a finger. They have found that in injection foam molding, the cavity volume is expanded by using a core back to perform foaming, and after the foam cell walls have solidified, the cavity volume of the mold is narrowed, and a compression step is added to form a new compressed and deformed layer inside the foam layer of the foam molded article, thereby providing a molded article with a cushioning feel, and have completed the present invention.

[0009] That is, the present invention provides a method for producing a thermoplastic resin composition by injecting a molten thermoplastic resin composition containing a foaming agent (H) into a cavity thickness (V0) of a mold set at a temperature range of [crystallization temperature (Tc) (when the thermoplastic resin (D) is amorphous, glass transition temperature (Tg) - 50°C)] to [(Tc or Tg) - 90°C] of the thermoplastic resin (D), which is a main component of the thermoplastic resin composition, and then expanding the mold cavity thickness (V0) by 210 to 600% after 1 to 12 seconds to produce a thermoplastic resin composition. (The cavity thickness at this time is designated as (V1)), and after cooling for 5 seconds or more, the expanded thickness of the cavity is compressed (reduced) to 4 to 90% of the expanded thickness (V1-V0) (cavity thickness at compression: V2), and the pressure is maintained for 0.1 seconds or more. After that, the foam is removed from the mold, and the thickness (V3) of the resulting foam satisfies the relationship (V1)>(V3)>(V2). [Effects of the Invention]

[0010] According to the present invention, a molded article can be obtained by injection foam molding of a thermoplastic resin composition without laminating a skin, which has bending rigidity when a bending force is applied to the molded article and also has cushioning properties when pressed with a finger. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows a cross-sectional image of an injection foam molded article according to the present invention and a schematic diagram of the cross-sectional image. [Figure 2] FIG. 2 is a schematic diagram showing the operation of a mold (thickness of a thermoplastic resin composition in a mold) in the method for producing an injection-molded foam of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Method for producing injection foam molded products> The method for producing an injection-molded foam of the present invention (hereinafter sometimes abbreviated as "the production method of the present invention") involves injecting a molten thermoplastic resin composition containing a blowing agent (H) into a cavity of a thickness (V0) of a mold set at a temperature in the range of [crystallization temperature (Tc) (if the thermoplastic resin (D) is amorphous, glass transition temperature (Tg) - 50°C)] to [(Tc or Tg) - 90°C] of the thermoplastic resin (D), which is the main component constituting the thermoplastic resin composition, and filling the cavity with a thickness (V0). This method for producing an injection-molded foam involves expanding (V0) by 210 to 600% to foam a thermoplastic resin composition (the cavity thickness at this time is designated as (V1)), cooling for 5 seconds or more, and then compressing (reducing) the cavity thickness to 4 to 90% of the expanded thickness (V1-V0) (cavity thickness upon compression: V2), maintaining the pressure for 0.1 seconds or more, and then removing the foam from the mold, whereby the thickness (V3) of the resulting foam satisfies the relationship (V1)>(V3)>(V2).

[0013] Each step of the method for producing an injection-molded foam will be described in detail below. Figure 2 shows the operation of the mold (thickness of the thermoplastic resin composition inside the mold) in the manufacturing method for injection-molded foams. Starting from the left side of the figure, the thickness of the thermoplastic resin composition containing blowing agent (H) obtained in the injection process (resin filling amount in the figure) is shown, which is the same as the mold cavity thickness (V0). Next, in the foaming process, the thickness of the mold cavity is expanded (V1), resulting in a foam of thickness (V1). Next, in the cooling process, the mold cavity thickness becomes V2 in the compression process, and the foam thickness also becomes (V2). After the compression process is completed, the foam removed from the mold returns to its original thickness, becoming a foam of thickness (V3).

[0014] 《Injection process》 The injection step is a step of injecting the plasticized and kneaded thermoplastic resin composition containing the foaming agent (H) in the melt-kneading step into a mold.

[0015] The mold temperature is set to between [crystallization temperature (Tc) (glass transition temperature (Tg) - 50°C if thermoplastic resin (D) is amorphous)] and [(Tc or Tg) - 90°C] of the thermoplastic resin (D), which is the main component constituting the thermoplastic resin composition, and a thermoplastic resin composition containing a blowing agent (H) is injected into a cavity formed between the fixed side and the movable side of the mold.

[0016] The thermoplastic resin composition containing the molten blowing agent (H) is injected from the cylinder of the injection molding machine through a nozzle, runner, gate, etc. into the cavity in the mold and filled in. The cavity used for molding may be plate-shaped, but is not limited to this, and may have any desired shape based on the shape of the intended injection-molded foam, and it is also a desirable embodiment of this molding method to provide a textured surface.

[0017] The initial thickness of the cavity when the mold is clamped is usually 0.7 to 5 mm, and preferably 1 to 3 mm. The injection speed at this time is not particularly limited, but the injection time for filling the cavity with the thermoplastic resin composition containing the blowing agent (H) is usually 0.3 to 10 seconds, preferably 0.4 to 5 seconds, and more preferably 0.5 to 3 seconds. Note that in general injection foaming, no dwell pressure is applied after injection filling, and the thermoplastic resin composition containing the blowing agent (H) in the cavity is cooled, and the resin pressure is reduced, which is expected to produce foam nuclei inside.

[0018] <<Foaming process>> The foaming step is a step in which the movable mold is moved in the mold opening direction (called a core back) to expand the cavity volume, thereby foaming the foaming-agent-containing thermoplastic resin composition injected and filled in the injection step.

[0019] The filled thermoplastic resin composition is held in this state for 1 to 12 seconds, causing the temperature to drop from the surface. The cavity thickness (V0) is then expanded by 210 to 600%, and the foaming agent dissolved inside creates foam cells within the thermoplastic resin composition, resulting in foaming (cavity thickness (V1) at this time). The core-back time (the time from the start to the end of core-back) is typically 0.1 to 3 seconds, preferably 0.1 to 1.5 seconds, and more preferably 0.1 to 1.0 second.

[0020] Regarding the expansion of the cavity by the core back, if the cavity volume is less than 210%, the foam cell walls are too thick and it is not possible to create a good deformation area for the cell walls within the foam layer during compression. Conversely, if it exceeds 600%, the cell wall surface is broken by the core back, causing cracks in the center or the cell walls becoming fibrous, making it impossible to maintain rigidity when external forces such as bending are applied.

[0021] 《Cooling process》 The cooling step is a step in which the foamed cell walls are solidified by cooling the foamed molded article in the cavity.

[0022] The foamed molded body in the cavity is cooled for at least 5 seconds, which is the time required for cooling to harden the cell walls and prevent them from adhering together in the subsequent compression process. Although it depends on the thickness of the resulting molded body, in this molding, the resin temperature inside the molded body is thought to have cooled to below the crystallization temperature after 5 seconds or more have passed since core-back.

[0023] <Compression process> The compression step is a step in which the movable mold is moved in the mold clamping direction to compress the foamed molded body in the cavity.

[0024] After the cell walls have solidified after foaming, the movable mold is moved in the closing direction, and the volume of the molded body is compressed (reduced) by 4 to 90% of the expanded thickness (V1-V0) (thickness when compressed: V2). The compression time (the time from the start of compression to the end of compression) is not particularly limited, but it is desirable to perform compression for 0.1 to 30 seconds, and more desirably 0.5 to 10 seconds.

[0025] This compression process can be carried out after the molded body is removed from the molding machine, but if it is carried out inside the molding machine before the end of the cooling time for the molded body, compression using the molding machine is possible, the compression accuracy is good, and there is no need to perform an extra process after removal, which is efficient.

[0026] The foam molded article (hereinafter, sometimes referred to as "molded article") obtained by the method for producing an injection-molded foam of the present invention comprises, in a thickness direction cross section of the injection-molded foam, five layers, from the surface side, of a solid skin layer (A1) / a foam layer (B1) / a foam layer (C) / a foam layer (B2) / a solid skin layer (A2) (back side), The solid skin layers (A1) and (A2) are layers in which no cellular foam structure is observed, the foam layers (B1) and (B2) are layers that satisfy the following (bi) to (b-iii), and the foam layer (C) does not satisfy at least one of the following (bi) to (b-iii), and the molded article has curved cell walls in the front-to-back direction of the cross section: (bi): The cells are filled with gas and have a foam cell structure surrounded by cell walls. (b-ii): The average diameter of the cells in the planar direction is 50 μm or more and 200 μm or less, (b-iii): The cell consists of cells whose average diameter in the thickness direction is 1 to 6 times the average diameter in the planar direction.

[0027] (Simple prediction and adjustment of injection molding conditions) The manufacturing method of the present invention involves the processes of injection / filling, core-backing, and compression, and requires the setting of numerous conditions, such as the timing of transitions between each process. The temperature ranges at which foaming is possible and the temperature ranges during compression vary depending on factors such as the viscosity of the resin and the amount of foaming agent added, but by preparing the data in advance and easily predicting the temperature change after the thermoplastic resin composition is filled into the cavity using CAE or other methods, it becomes possible to quickly set conditions even when changes are made to the plate thickness of the molded body or other settings.

[0028] <Thermoplastic resin (D)> The thermoplastic resin (D) constituting the thermoplastic resin composition used in the production method of the present invention is not particularly limited as long as it is a thermoplastic resin that can be used to produce an injection foamed molded article. Specific examples include high-pressure low-density polyethylene, which is a homopolymer or copolymer of α-olefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene, linear low-density polyethylene (so-called LLDPE), high-density polyethylene (so-called HDPE), polypropylene (propylene homopolymer), propylene random copolymer, propylene block copolymer, poly-1-butene, poly-4-methyl-1-pentene, and ethylene-propylene random copolymer. Examples of suitable thermoplastic resins include polyolefins such as ethylene-1-butene random copolymers and propylene-1-butene random copolymers, polyesters (polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyamides (nylon-6, nylon-66, polymetaxylene adipamide, etc.), polyvinyl chloride, polyimides, ethylene-vinyl acetate copolymers, ethylene-vinyl alcohol copolymers, ethylene-(meth)acrylic acid copolymers, ethylene-acrylate-carbon monoxide copolymers, polyacrylonitrile, polycarbonate, polystyrene, ionomers, and mixtures thereof. Among these, high-pressure low-density polyethylene, linear low-density polyethylene (so-called LLDPE), high-density polyethylene, polypropylene and propylene random copolymers, propylene block copolymers, and other propylene polymers, polyethylene terephthalate, and polyamides are more preferred. These thermoplastic resins (D) may be used alone or in combination of two or more.

[0029] <Propylene polymer (E)> The propylene polymer (E) according to the present invention refers to a polymer having a content of structural units derived from propylene of 50 mol% or more, and the content of structural units derived from propylene in the propylene polymer is preferably 90 mol% or more.

[0030] The propylene polymer (E) according to the present invention may be one type or two or more types. The propylene polymer (E) according to the present invention may be a propylene homopolymer or a copolymer of propylene and a comonomer other than propylene.

[0031] The structure of the propylene polymer (E) according to the present invention is not particularly limited, and for example, the propylene-derived structural unit portion may be an isotactic structure, a syndiotactic structure, or an atactic structure, but is preferably an isotactic structure. Furthermore, in the case of the copolymer, it may be any of a random type (also called random PP), a block type (also called block PP: bPP), and a graft type.

[0032] The comonomer may be any other monomer copolymerizable with propylene, and is preferably an α-olefin having 2 or 4 to 10 carbon atoms. Specific examples include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. Of these, ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene are preferred. One or more types of comonomers may be used.

[0033] The content of the structural unit derived from the comonomer in the copolymer is preferably 10 mol % or less from the viewpoint of flexibility and the like. Among these propylene-based polymers (E), a propylene-ethylene-based block copolymer (E1) containing a propylene homopolymer segment obtained by polymerizing propylene alone and a propylene-ethylene copolymer segment obtained by copolymerizing propylene and ethylene is preferred because the resulting injection-molded foam has a good balance of physical properties such as rigidity and impact resistance.

[0034] The propylene polymer (E) according to the present invention may be synthesized by a conventionally known method, or may be a commercially available product, such as polypropylene from SunAllomer Co., Ltd., Prime Polypro from Prime Polymer Co., Ltd., Novatec from Nippon Polypropylene Co., Ltd., or SCG PP from SCG Plastics.

[0035] The MFR (measured in accordance with ASTM D 1238, 230°C, 2160g load) of the propylene polymer (E) according to the present invention is preferably 20 to 200g / 10min, more preferably 30 to 150g / 10min.

[0036] When the MFR of the propylene polymer (E) according to the present invention is within the above range, it has excellent injection moldability. The crystallization temperature (Tc) of the propylene polymer (E) according to the present invention varies depending on factors such as the comonomer content, molecular weight, and isotacticity, but is approximately 100 to 130°C for homopolymers and block copolymers, and approximately 80 to 110°C for random copolymers. When a filler, a nucleating agent, or the like is blended with the propylene polymer, the crystallization temperature shown above becomes 5 to 15°C higher. To accurately determine the crystallization temperature, it is desirable to measure the crystallization temperature and use the measured value to determine the mold temperature. Here, the crystallization temperature is a value measured using a differential scanning calorimeter (DSC) by melting a sample and then cooling it at a rate of 10°C / min, and the temperature at which the sample crystallizes during the cooling process.

[0037] Ethylene-α-olefin copolymer (F) The thermoplastic resin composition according to the present invention may contain an ethylene-α-olefin copolymer (F).

[0038] The ethylene-α-olefin copolymer (F) according to the present invention can be obtained by copolymerizing at least ethylene and an α-olefin having 3 to 20 carbon atoms. Examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene. Among these, from the viewpoint of imparting flexibility, α-olefins having 3 to 12 carbon atoms are preferred, with propylene, 1-butene, and 1-octene-1 being more preferred, and 1-octene being even more preferred.

[0039] The ethylene-α-olefin copolymer (F) according to the present invention usually contains 70 to 99 mol %, preferably 80 to 97 mol %, of units derived from ethylene, and 1 to 30 mol %, preferably 3 to 20 mol %, of units derived from an α-olefin having 3 to 20 carbon atoms (wherein the total amount of units derived from ethylene and units derived from an α-olefin having 3 to 20 carbon atoms is 100 mol %).

[0040] If necessary, a monomer having an unsaturated bond can be copolymerized into the ethylene-α-olefin copolymer (F) according to the present invention. Examples of preferred monomers having an unsaturated bond include conjugated diolefins such as butadiene and isoprene, non-conjugated diolefins such as 1,4-hexadiene, cyclic diene compounds such as dicyclopentadiene and norbornene derivatives, and acetylenes. Among these, ethylidene norbornene (ENB) and dicyclopentadiene (DCP) are more preferred from the viewpoint of flexibility.

[0041] The ethylene-α-olefin copolymer (F) according to the present invention usually has an MFR (ASTM D1238 load 2160 g, temperature 190° C.) in the range of 3 to 70 g / 10 min, preferably 10 to 50 g / 10 min.

[0042] The ethylene-α-olefin copolymer (F) according to the present invention usually has a density of 0.8 to 0.9 g / cm 3 is in the range. The ethylene-α-olefin copolymer (F) according to the present invention can be produced using a known polymerization catalyst, such as a Ziegler-Natta catalyst, a vanadium catalyst, or a metallocene catalyst. The polymerization method is not particularly limited, and can be a liquid-phase polymerization method such as solution polymerization, suspension polymerization, or bulk polymerization, a gas-phase polymerization, or any other known polymerization method. These copolymers are also commercially available, and are not limited as long as they achieve the effects of the present invention. Examples of commercially available copolymers include ENGAGE 8842 (ethylene-1-octene copolymer) and ENGAGE 8407 (ethylene-1-octene copolymer) manufactured by Dow Chemical Company, Vistalon® manufactured by ExxonMobil Corporation, Esprene® manufactured by Sumitomo Chemical Company, and Mitsui EPT®, Tafmer P®, and Tafmer A® manufactured by Mitsui Chemicals, Inc.

[0043] <Filler (G)> The thermoplastic resin composition according to the present invention may contain a filler (G) such as an inorganic filler, an organic filler, etc. These fillers (G) may be used alone or in combination of two or more.

[0044] <Inorganic fillers> The inorganic filler used in the present invention may be any of various known inorganic fillers, including, but not limited to, oxides such as aluminum oxide, titanium oxide, zinc oxide, calcium oxide, and silica, sulfates such as barium sulfate, carbonates such as calcium carbonate, magnesium carbonate, and barium carbonate, and silicates such as talc, clay, and mica.

[0045] <Organic filler> The organic filler used in the present invention may be any of various known organic fillers, including, but not limited to, polymethoxysilane compounds, polystyrene, styrene-acrylic, styrene-methacrylic and methacrylic compounds, polyurethane compounds, polyester compounds, fluoride compounds, and phenolic compounds.

[0046] <Blowing Agent (H)> The type of blowing agent (H) contained in the thermoplastic resin composition according to the present invention is not particularly limited, and may be a solvent-type blowing agent, a decomposition-type blowing agent, a gaseous blowing agent such as nitrogen, carbon dioxide, argon, or air, or a thermally expandable microcapsule blowing agent.

[0047] The gaseous blowing agent may be nitrogen or carbon dioxide, which is injected directly into a cylinder and kneaded and dissolved with the molten resin by a screw, or may be injected in a supercritical state into a cylinder and kneaded and melted.

[0048] Solvent-based blowing agents are substances injected into the hopper or cylinder of an injection molding machine, absorbed or dissolved in the molten raw resin, and then vaporize in the injection mold to function as a blowing agent. Specific examples include low-boiling aliphatic hydrocarbons such as propane, butane, neopentane, heptane, isohexane, hexane, isoheptane, and heptane, as well as low-boiling fluorine-containing hydrocarbons such as chlorofluorocarbons. Thermally expandable microcapsules contain solvent-based blowing agents in microcapsules of acrylonitrile, methacrylonitrile, vinylidene chloride, or the like, and vaporize them inside the capsules to expand and foam.

[0049] The decomposition-type foaming agent is a compound that is blended in advance with the raw resin composition and then fed to the injection molding machine, and decomposes under the cylinder temperature conditions of the injection molding machine to generate gases such as carbon dioxide gas, nitrogen gas, etc. The foaming agent may be an inorganic or organic foaming agent, and an organic acid such as citric acid or an organic acid metal salt such as sodium citrate, which promotes gas generation, may also be added in combination as a foaming assistant.

[0050] Decomposition-type blowing agents include inorganic and organic blowing agents. Specific examples of inorganic blowing agents include sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate, and ammonium nitrite. Specific examples of organic blowing agents include N-nitroso compounds such as N,N'-dinitrosoterephthalamide and N,N'-dinitrosopentamethylenetetramine; azo compounds such as azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene, and barium azodicarboxylate; sulfonylhydrazide compounds such as benzenesulfonylhydrazide, toluenesulfonylhydrazide, p,p'-oxybis(benzenesulfenylhydrazide), and diphenylsulfon-3,3'-disulfonylhydrazide; and azide compounds such as calcium azide, 4,4'-diphenyldisulfonylazide, and p-toluenesulfonylazide.

[0051] The blowing agent (H) according to the present invention may be used alone or in combination of two or more. The amount of the blowing agent (H) according to the present invention (actual component in the case of a masterbatch) added is selected in consideration of the required physical properties of the foamed molded article, the amount of gas generated from the blowing agent, the expansion ratio, etc., and is usually 1 to 8 parts by mass per 100 parts by mass of the thermoplastic resin composition.

[0052] 《Thermoplastic resin composition》 The thermoplastic resin composition according to the present invention is injection molded using a mixture of the thermoplastic resin (D) and the foaming agent (H).

[0053] The blowing agent (H) according to the present invention may be blended in advance with the thermoplastic resin (D), or may be mixed during injection molding or injected into the middle of the cylinder. Alternatively, a masterbatch may be prepared by blending the blowing agent, foaming aid, etc. with the thermoplastic resin (D) in advance, and this masterbatch may be mixed with the thermoplastic resin (D) during injection molding.

[0054] The foaming agent (H) foams the thermoplastic resin composition in the mold after injection molding, but the foaming gas is discharged from inside the molten resin during molding, or is replaced with outside air and escapes from the molded article over time after molding. [Example]

[0055] The present invention will be further described below with reference to examples, although the present invention is not limited to these examples. The following polymers and the like were used as the thermoplastic resin (D) contained in the thermoplastic resin compositions used in the Examples and Comparative Examples.

[0056] (1) Propylene polymer (E) (1-1) Propylene-ethylene block copolymer (E1-1) The propylene-based polymer (E) used was a propylene-ethylene-based block copolymer (n-decane soluble fraction = 11 mass%, ethylene content = 41 mol%, intrinsic viscosity [η] = 8 dl / g, MFR (230 °C, 2.16 kg) = 85 g / 10 min) (E1-1) [referred to as (PP-1) in Table 1]. (1-2) Propylene-ethylene block copolymer (E1-2) As the propylene polymer (E), Prime Polypropylene (trade name: NA600) (MFR (230°C, 2.16 kg) = 63 g / 10 min, density = 970 kg / m 3 The propylene-ethylene block copolymer (E1-2) (referred to as (PP-2) in Table 1) was used. PP-2 contains 11% by mass of talc as a filler (G). (1-3) Propylene-ethylene block copolymer (E1-3) As the propylene polymer (E), Prime Polypropylene (trade name: X5061) (MFR (230°C, 2.16 kg) = 32 g / 10 min, density = 1030 kg / m 3 The propylene-ethylene block copolymer (E1-2) (referred to as (PP-3) in Table 1) was used. PP-3 contains 20% by mass of talc as a filler (G).

[0057] (2) Ethylene-α-olefin copolymer (F) As the ethylene-α-olefin copolymer (F), an ethylene-1-octene copolymer (manufactured by The Dow Chemical Company, trade name EG8407, MFR (190°C, 2.16 kg) = 30 g / 10 min, density = 0.87 kg / m 3 ) [F-1] was used. In the examples and comparative examples, the physical properties of the thermoplastic resin composition, polymer, injection foam molded article, etc. were measured by the following methods.

[0058] Melt Flow Rate (MFR) The measurement was carried out without the use of a foaming agent at 190°C or 230°C under a load of 2.16 kg according to ASTM D-1238.

[0059] [Contents of n-decane insoluble (a1) and n-decane soluble (a2) fractions in propylene-ethylene block copolymer (E1)] Approximately 3 g of propylene-ethylene block copolymer (measured to the nearest 10-4 g; this mass is represented as b(g) in the following formula) was placed in a glass measuring vessel, along with 500 mL of n-decane and a small amount of a heat stabilizer soluble in n-decane. The vessel was heated to 150°C over 2 hours while stirring under a nitrogen atmosphere, allowing the propylene-ethylene block copolymer to dissolve in the n-decane. The vessel was then held at 150°C for 2 hours and then slowly cooled to 23°C over 8 hours. The resulting solution, containing the precipitate of the propylene-ethylene block copolymer, was filtered under reduced pressure using a 25G-4 glass filter manufactured by Iwata Glass Co., Ltd. 100 mL of the filtrate was collected and dried under reduced pressure to obtain a portion of the above-mentioned component (a2). The mass was measured to the nearest 10-4 g (this mass is represented as a(g) in the following formula). Next, the contents of components (a1) and (a2) in the propylene-ethylene block copolymer (E1) were calculated using the following formula. Content of component (a2) [mass%]=100×5a / b Content of component (a1) [mass%] = 100 - Content of component (a2)

[0060] [Intrinsic viscosity ([η]:dl / g)] Measurements were carried out at 135°C using decalin solvent. [density] Measurements were made in accordance with ISO 1183 (JIS K7112).

[0061] [Solid Skin Thickness Measurement] The thickness of the solid skin layer of the injection-molded foam was measured by the following method. First, the cross section of the injection-molded foam was cut with a sharp blade without destroying the cells, and the cross section was photographed using a VHX-6000 digital microscope (Keyence Corporation). The cross section image was magnified 100 times or more, and the measurement function of the digital microscope was used to identify two points on the left and right sides of the boundary between the solid skin layer and the foam layer. A perpendicular line was drawn to the line connecting these points, and the distance from the surface of the solid layer was measured in μm units to determine the thickness of the solid skin layer. Note that if the surface layer contained texture (excluding areas that clearly protrude from the surface, such as ribs) and the thickness varied depending on the location, the midpoint between the peak and valley of the texture was used as the edge of the solid layer, and similar measurements were performed. The thickness of the resulting solid skin layer (the solid skin layers on the front and back surfaces sandwiching the foam layer and having no foam cells) was measured in μm, and the average was taken as the solid skin layer thickness (μm).

[0062] [Measurement of foam cell diameter in foam cell layers (B1) and (B2)] The cell diameters in the thickness direction and the planar direction (direction perpendicular to the thickness direction) of the foam cells distributed in the foam cell layers (B1) and (B2) in contact with the solid skin layer of the injection foam molded article were measured using the following method.

[0063] Using the measurement function of a digital microscope, 10 or more foam cells were determined from the cross-sectional image used to measure the thickness of the solid skin layer so that they were approximately evenly distributed in the thickness direction. The cell diameters of the foam cells in the thickness direction and in the planar direction were measured, and the average diameters of each were taken as the foam cell diameter (μm).

[0064] [Measurement of the meandering angle of the foam layer (C)] The meandering angle, which is used to measure the degree of curvature of the cell walls of the foam layer (C) sandwiched between the foam cell layers (B1) and (B2) of the injection-molded foam, was measured by the following method.

[0065] Using the measurement function of a digital microscope, a perpendicular line was drawn to the surface of the molded article from the cross-sectional image used to measure the thickness of the solid skin layer, and one point was picked up from the top and bottom half of the foam layer (C) to measure the inclination from the perpendicular line on each side of the meandering part, and the measured inclinations were averaged to determine the meandering angle. If the meandering angle is small, deformation of the cell walls of the foam layer (C) is unlikely to occur, so a meandering angle of 25° or more was used as the standard for evaluation.

[0066] [Thickness of injection foam molding (plate thickness)] The thickness (plate thickness) of the injection foam molded product was measured using a digital caliper CD-S15C (Mitutoyo Corporation). After tightening the outer jaw of the caliper without the molded product and confirming that the reading was 0, the molded product was then clamped slightly toward the back of the outer jaw of the caliper, with the molded product facing vertically to the ground or toward the viewer, and slowly tightened to ensure that the molded product was not tilted. At this time, a thumb roller was used to clamp the molded product with as uniform a force as possible so as not to apply excessive force, and measurements were taken in millimeters.

[0067] Stiffness (flexural elasticity gradient) The injection foam molded article was cut into a size of 50 mm x 150 mm, and a bending test (three-point bending) was performed using an Autograph (AG-1kNX plus, manufactured by Shimadzu Corporation) as a testing machine, applying a load at the center position with a support interval of 100 mm at a bending speed of 50 mm / min. When the deflection amount was between 0 and 10 mm, the slope of the line (= load / deflection) drawn using the method described in JIS K7221-2 on the "load-deflection curve" was taken as the bending elastic gradient (N / cm), and this was used for rigidity comparison.

[0068] The bending elasticity gradient used for rigidity comparison was a bending elasticity gradient of 27 N / cm or more obtained by measuring a molded body with a bending elasticity modulus of 1000 MPa and a plate thickness of 2.3 mm under the same conditions as above, and was evaluated as having a sense of rigidity.

[0069] [Pressure softness (pressure elasticity gradient)] An Autograph (AG-100kNX, manufactured by Shimadzu Corporation) was used as the testing machine. A 4 mm diameter, flat-tipped circular indenter was pressed against the flat surface of the injection foam molded article at a speed of 1 mm / min to apply a load. When the reduction in thickness of the molded article was between 0 and 10%, the slope of the line (= force / deformation) drawn using the method described in JIS K7220 was taken as the compression elasticity gradient (N / mm), which was used as an index of compression softness. The compressive elasticity gradient used to compare compressive softness was a product manufactured by Mitsui Chemicals, Inc., under the trade name of Mirastomer 7030BS, with a thickness of 1.8 mm. A compressive elasticity gradient of 90% or less (a compressive elasticity gradient of 120 N / mm or less) of the compressive elasticity gradient obtained by measurement under the same conditions as above was evaluated as having compressive softness.

[0070] [Cushioning] The molded product was evaluated as follows based on whether it felt soft when pressed with a finger. When you press the surface with your finger, there is a cushioning feeling: No cushioning when pressing the surface with your finger: ×

[0071] Example 1 76 parts by weight of the above PP-1 and 24 parts by weight of the above F-1 (total 100 parts by weight) were mixed and processed into conventional pellets using an extruder to obtain a thermoplastic resin composition. A CO2-based blowing agent masterbatch (manufactured by Eiwa Chemical Industry Co., Ltd., product name EE515) was added to the mixture, resulting in 5 parts by weight of inorganic blowing agent per 100 parts by weight of the composition, and an N2-based blowing agent masterbatch (manufactured by Eiwa Chemical Industry Co., Ltd., product name EE206) was added in an amount of 2.5 parts by weight per 100 parts by weight of the composition. Also, 3 parts by weight of black masterbatch was added as a colorant. The mixture was then loaded into the hopper of an injection molding machine and melt-kneaded. The blowing agent used was a masterbatch prepared by kneading the blowing agent into low-density polyethylene, so the actual blowing agent content was equivalent to 3% by weight. The composition of the thermoplastic resin composition used in Example 1 is shown in Table 1. An injection molding machine (manufactured by The Japan Steel Works, Ltd., machine name J350ADS) performed core-back injection foam molding under the following conditions, and a plate-shaped injection foam molded article whose surface was covered with a skin layer was obtained.

[0072] Cavity size: 400mm length, 200mm width, filled resin thickness 1.8mm Gate: Direct gate at one point in the center of the cavity Injection temperature: 205℃ Mold surface temperature: 50℃ Injection mold cavity clearance (L0): 1.8 mm Injection rate: 309cc / s Molding machine core-back time setting: 0.1 seconds (time from start to finish of core-back) Time from completion of injection to start of core back: 5.8 seconds Core back amount: 5mm Compression start time: 40 seconds after core back completion Compression amount from core back state: 1mm

[0073] The obtained molded article had a plate thickness of 6.3 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a five-layer structure, and the foam cell state of the foam cell layers (B1) and (B2), the meandering state of the foam layer (C), the bending elasticity gradient, the compressive elasticity gradient, and the cushioning properties were good. The results are shown in Table 1.

[0074] <Example 2> A molded article was obtained in the same manner as in Example 1, except that the compression amount from the core-back state was 2 mm. The obtained molded article had a plate thickness of 6.2 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a five-layer structure, and the foam cell state of the foam cell layers (B1) and (B2), the meandering state of the foam layer (C), the bending elasticity gradient, the compressive elasticity gradient, and the cushioning properties were good. The results are shown in Table 1.

[0075] Example 3 A molded article was obtained in the same manner as in Example 1, except that the compression amount from the core-back state was 3 mm. The obtained molded article had a plate thickness of 5.9 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a five-layer structure, and the foam cell state of the foam cell layers (B1) and (B2), the meandering state of the foam layer (C), the bending elasticity gradient, the compressive elasticity gradient, and the cushioning properties were good. The results are shown in Table 1.

[0076] Example 4 The filled resin thickness was 1.5 mm, and the cavity clearance during injection was also 1.5 mm. Molding was performed in the same manner as in Example 2, except that the time from the completion of injection to the start of core backing was 3.8 s, the core back amount was 3 mm, and the compression start time was 30 s. The obtained molded product had a plate thickness of 4.1 mm. The physical properties of the obtained molded product were measured using the methods described above. The obtained molded product had a five-layer structure, and the foam cell state of the foam cell layers (B1) and (B2), the meandering state of the foam layer (C), the bending elasticity gradient, the pushing elasticity gradient, and the cushioning properties were good. The results are shown in Table 1.

[0077] <Example 5> Molding was carried out under the same conditions as in Example 4, except that the foaming agent was an inorganic foaming agent masterbatch (manufactured by Eiwa Chemical Industry Co., Ltd., product name EE515) at 6 parts by mass per 100 parts by mass of the composition. The obtained molded article had a plate thickness of 4.1 mm. The physical properties of the obtained molded article were measured by the method described above. Although the cells were somewhat larger in the foamed state, the obtained molded article had a five-layer structure, and the foam cell state of the foam cell layers (B1) and (B2), the meandering state of the foam layer (C), the flexural elasticity gradient, the compressive elasticity gradient, and the cushioning properties were good. The results are shown in Table 1.

[0078] Example 6 A molded article was obtained in the same manner as in Example 1, except that the propylene-based resin composition used in Example 1 was replaced with PP-2 (talc-containing propylene-based resin composition). The obtained molded article had a plate thickness of 5.9 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a five-layer structure, and was good in the foam cell state of the foam cell layers (B1) and (B2), the meandering state of the foam layer (C), the flexural elasticity gradient, the compressive elasticity gradient, and the cushioning properties. The results are shown in Table 1.

[0079] Example 7 A molded article was obtained in the same manner as in Example 1, except that the propylene-based resin composition used in Example 1 was replaced with the above-mentioned PP-3 (talc-containing propylene-based resin composition). The obtained molded article had a plate thickness of 6.1 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a five-layer structure, and the foam cell state of the foam cell layers (B1) and (B2), the meandering state of the foam layer (C), the flexural elasticity gradient, the compressive elasticity gradient, and the cushioning properties were good. The results are shown in Table 1.

[0080] <Comparative Example 1> Molding was carried out under the same conditions as in Example 1, except that the molded body was removed after injection without core backing or compression. The obtained molded body was not foamed and was a solid molded body with a plate thickness of 1.8 mm. The physical properties of the obtained molded body were measured using the methods described above. The molded body was in a solid state, had a low bending elasticity gradient, a high compression elasticity gradient, and lacked cushioning. The results are shown in Table 1.

[0081] <Comparative Example 2> Molding was carried out under the same conditions as in Example 1, except that the core-back amount was 1 mm and the compression amount from the core-back state was 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a three-layer structure without the foam layer (C), a plate thickness of 2.8 mm, a good foaming state, and a satisfactory bending elasticity gradient, but a high compression elasticity gradient and insufficient cushioning. The results are shown in Table 1.

[0082] <Comparative Example 3> Molding was carried out under the same conditions as in Example 1, except that the core-back amount was 3 mm and the compression amount from the core-back state was 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a three-layer structure without the foam layer (C), a plate thickness of 4.6 mm, a good foaming state, and a satisfactory bending elasticity gradient, but a high compression elasticity gradient and insufficient cushioning. The results are shown in Table 1.

[0083] <Comparative Example 4> Molding was carried out under the same conditions as in Example 1, except that the core-back amount was 5 mm and the compression amount from the core-back state was 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a three-layer structure without the foam layer (C), a plate thickness of 6.5 mm, a good foaming state, and a satisfactory bending elasticity gradient, but a high compression elasticity gradient and insufficient cushioning. The results are shown in Table 1.

[0084] <Comparative Example 5> Molding was carried out under the same conditions as in Example 4, except that the molded body was removed after injection without core-backing or compression. The physical properties of the obtained molded body were measured using the methods described above. The obtained molded body was not foamed and was solid with a plate thickness of 1.5 mm. It had an insufficient bending elasticity gradient, a high compression elasticity gradient, and an insufficient cushioning feel. The results are shown in Table 1.

[0085] <Comparative Example 6> Molding was carried out under the same conditions as in Example 4, except that the core-back amount was 3 mm and the compression amount from the core-back state was 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The obtained molded article had a three-layer structure without a foam layer (C), a plate thickness of 4.4 mm, a good foaming state, and a satisfactory bending elasticity gradient, but a high compression elasticity gradient and insufficient cushioning. The results are shown in Table 1.

[0086] [Table 1] [Industrial Applicability]

[0087] The injection foam molded article of the present invention has both light weight and good texture, and therefore can be suitably used for various applications such as automobile interior parts, electrical appliances, building materials, etc. In particular, since it has an excellent balance of light weight, rigidity, and appearance, and also has excellent heat insulation properties, it can be particularly suitably used for automobile interior parts. [Explanation of symbols]

[0088] A1, A2: Solid skin layer B1, B2: foam cell layers C: Foam layer without foam cells

Claims

1. a molten thermoplastic resin composition containing a blowing agent (H) is injected and filled into a cavity of a thickness (V0) of a mold set at a temperature in the range of [crystallization temperature (Tc) (or glass transition temperature (Tg) - 50°C when thermoplastic resin (D) is amorphous)] to [(Tc or Tg) - 90°C] of thermoplastic resin (D), which is a main component of the thermoplastic resin composition; after 1 to 12 seconds, the thickness (V0) of the mold cavity is expanded to 210 to 600% to foam the thermoplastic resin composition (the cavity thickness at this time is defined as (V1)); after cooling for 30 seconds or more, the expanded thickness of the cavity is compressed (reduced) to 4 to 90% of the expanded thickness (V1 - V0) (cavity thickness at compression: V2); the pressure is maintained for 0.1 seconds or more, and the foam is then removed from the mold, to produce an injection-molded foam, wherein the thickness (V3) of the resulting foam satisfies the relationship (V1) > (V3) > (V2); The cross section of the injection foam molded article is composed of five layers, from the surface side, of a solid skin layer (A1) / a foam layer (B1) / a foam layer (C) / a foam layer (B2) / a solid skin layer (A2) (back surface), The solid skin layers (A1) and (A2) are layers in which no cellular foam structure is observed, the foam layers (B1) and (B2) are layers that satisfy the following (bi) to (b-iii), and the foam layer (C) does not satisfy at least one of the following (bi) to (b-iii) and has curved cell walls in the front-to-back direction of the cross section: A method for producing an injection foamed molded article, (bi): The cell has a foamed cell structure in which the inside of the cell is filled with gas and is surrounded by a cell wall. (b-ii): The average diameter of the cells in the planar direction is 50 μm or more and 200 μm or less, (b-iii): The cell consists of cells whose diameter in the cross-sectional direction is 1 to 6 times the average diameter in the planar direction.

2. 2. The method for producing an injection-molded foam according to claim 1, wherein the thermoplastic resin (D) is a propylene-based polymer (E).

3. 3. The method for producing an injection-molded foam according to claim 1, wherein the thermoplastic resin composition contains an ethylene / α-olefin copolymer (F).

4. The method for producing an injection-molded foam according to any one of claims 1 to 3, wherein the thermoplastic resin composition contains a filler (G).

5. 5. The method for producing an injection-molded foam according to claim 1, wherein the content of the blowing agent (H) in the thermoplastic resin composition is 1 to 8 parts by mass per 100 parts by mass of the thermoplastic resin composition.

6. The method for producing an injection-molded foam according to any one of claims 1 to 5, wherein the blowing agent (H) is a carbon dioxide-based blowing agent, a nitrogen-based blowing agent, or both.

7. The method for producing an injection-molded foam according to any one of claims 1 to 6, wherein at least a part of the inner surface of the mold is textured.

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