JP2022163991A - Manufacturing method of injection-foamed molding - Google Patents

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 The present invention relates to a method for producing an injection foam molded article made of a thermoplastic resin.

Injection foam moldings made of thermoplastic resins have a low specific gravity and are excellent in moldability and recyclability. , are used in various fields. As for automobile parts, the use ratio of propylene-based resin composition containing propylene-based polymer is increasing due to the improvement of vehicle safety, comfort and comfort, and the increase in IT equipment. is growing. In particular, foamed molded articles made of propylene-based resin compositions are suitable for automobile parts because of their light weight and excellent molded appearance.

As one method of manufacturing an injection foam molded article made of a thermoplastic resin such as a propylene polymer, a mold with a variable cavity volume is used. There is known a molding method (core-back method) in which the cavity volume is increased after filling to actively promote the generation and expansion of air bubbles.

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 air bubbles, and then the foamed molded body is compressed before the foamed body solidifies. (Patent Literature 1, Patent Literature 2, Patent Literature 3, etc.), these foams basically have a three-layer structure with a solid skin layer on the surface and a foam layer on the inside.

JP-A-8-318542 JP 2009-196284 A JP 2009-208299 A

Parts made of thermoplastic resin generally have various patterns such as subtle unevenness and leather-like patterns, and these patterns are called shibo. Such grains can be formed only by injection molding and do not require painting, so there is an advantage that costs can be reduced while maintaining the quality of interior parts of automobiles and home appliances. However, even if the texture is attached, the thermoplastic resin molded product without the skin is hard to the touch, lacks a cushioning feeling, and lacks a sense of luxury compared to the parts with the actual skin (skin lamination). there was a problem.

The object of the present invention is to provide the rigidity characteristic of injection foaming by using a molding method called injection foaming, while at the same time achieving the cushioning properties of a foamed molded product that feels soft when pressed with a finger. To provide a method for producing a foam molded article having properties that cannot be obtained with a molded article.

The inventors of the present invention have achieved a molding that has both bending rigidity when a bending force is applied to the molded body and cushioning properties when pressed with a finger by only injection foam molding of a thermoplastic resin composition instead of skin lamination. In the injection foam molding, the cavity volume is expanded by the core back, and after the foam cell walls are solidified, the cavity volume of the mold is narrowed, and a compression process is added. The present inventors have found that forming a new compressive deformation layer inside the foam layer of (1) yields a molded article imparted with a cushion feeling, and completed the present invention.

That is, the present invention relates to the [crystallization temperature (Tc) of the thermoplastic resin (D) which is the main component constituting the thermoplastic resin composition (the glass transition temperature when the thermoplastic resin (D) is amorphous ( Tg) −50° C.)] to [(Tc or Tg) −90° C.] to the cavity thickness (V0) of the mold, and a molten thermoplastic resin composition containing a foaming agent (H) is added. 1 second to 12 seconds after injection filling, 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 (V1)], After cooling for 5 seconds or more, the expanded thickness of the cavity is compressed (reduced) to a thickness of 4 to 90% of the expanded thickness (V1-V0) [cavity thickness when compressed: V2), 0 In the method of manufacturing an injection foam molded article by removing the foam from the mold after holding the pressure for 1 second or more, the thickness (V3) of the obtained foam is such that (V1) > (V3) > (V2 ), it relates to a method for producing an injection foam molded article.

According to the present invention, only by injection foam molding of a thermoplastic resin composition instead of skin lamination, the molded body has both bending rigidity when a bending force is applied and cushioning properties when pressed with a finger. A molded body is obtained.

FIG. 1 is a cross-sectional image of an injection foam molded article according to the present invention and a schematic diagram of the cross-sectional image. FIG. 2 is a schematic diagram showing the operation of the mold (the thickness of the thermoplastic resin composition in the mold) in the method for producing an injection foam molded article of the present invention.

<Manufacturing method of injection foam molding>
[ Crystallization temperature (Tc) (glass transition temperature (Tg) -50°C when the thermoplastic resin (D) is amorphous)] to [(Tc or Tg) -90°C] A molten thermoplastic resin composition containing a blowing agent (H) is injected and filled into a cavity having a thickness (V0) of 1 second to 12 seconds, and the thickness (V0) of the mold cavity is reduced to 210 to 600% after 1 second to 12 seconds. After expanding and foaming the thermoplastic resin composition [at this time, the cavity thickness (V1)] and cooling for 5 seconds or more, the thickness of the cavity is increased to 4 to the expanded thickness (V1-V0). A method of compressing (reducing) to 90% thickness [cavity thickness at compression: V2), holding the pressure for 0.1 second or more, and then taking out the foam from the mold to produce an injection foam molded product. 3, the thickness (V3) of the resulting foam satisfies (V1)>(V3)>(V2).

Hereinafter, the method for manufacturing an injection foam molded article will be described in detail by dividing each step.
FIG. 2 shows the operation of the mold (the thickness of the thermoplastic resin composition in the mold) in the method for producing an injection foam molded article. From the left side of the figure, the thickness of the thermoplastic resin composition containing the foaming agent (H) obtained in the injection process [resin filling amount in the figure] is the same as the mold cavity thickness (V0). be. The foaming step then expands the thickness of the mold cavity (V1), resulting in a foam of thickness (V1). Next, the cooling process is obtained, and in the compression process, the thickness of the cavity of the mold becomes V2, and the thickness of the foam becomes (V2). After the compression step is completed, the thickness of the foamed molded article taken out from the mold is restored to be a foamed molded article having a thickness (V3).

《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.

The mold temperature is the [crystallization temperature (Tc) of the thermoplastic resin (D), which is the main component of the thermoplastic resin composition (if the thermoplastic resin (D) is amorphous, the glass transition temperature (Tg ) −50° C.)] to [(Tc or Tg) −90° C.], and a thermoplastic resin composition containing a foaming agent (H) in the cavity formed between the fixed side and the movable side of the mold. to inject.

A thermoplastic resin composition containing a molten foaming agent (H) is injected and filled into a cavity in a mold from a cylinder of an injection molding apparatus through a nozzle, runner, gate, and the like. The cavity used for molding may be plate-shaped, but is not limited to this, as long as it has a desired shape based on the shape of the intended injection foam molded product, and the surface may be textured. is also a desirable form of the present molding method.

The initial thickness of the cavity when the mold is clamped is usually 0.7 to 5 mm, preferably 1 to 3 mm.
The injection speed at this time is not particularly limited, but the injection time for filling the thermoplastic resin composition containing the foaming agent (H) into the cavity is usually 0.3 to 10 seconds, preferably 0.4 to 5 seconds. , more preferably 0.5 to 3 seconds. In general injection foaming, holding pressure is often not applied after injection filling. is expected to be generated.

《Foaming process》
The foaming step is a step of expanding the cavity volume (called core back) by moving the movable mold in the mold opening direction, thereby foaming the foaming agent-containing thermoplastic resin composition injected and filled in the injection step.

The filled thermoplastic resin composition is held in that state for 1 to 12 seconds, whereby the temperature of the surface layer is lowered. After that, the cavity thickness (V0) is expanded to 210 to 600%, and the foaming agent dissolved inside forms foam cells inside the thermoplastic resin composition, thereby performing foaming (at this time, the cavity thickness (V1 )). At this time, the time for performing core-back (the time from the start to the end of core-back) is usually 0.1 to 3 seconds, preferably 0.1 to 1.5 seconds, more preferably 0.1 to 1.0 seconds. is.

Regarding the expansion of the cavity by the core back, if the cavity volume is less than 210%, the foamed cell walls are thick and a good deformation area of the cell walls in the foamed layer cannot be created during compression. In this case, the wall surface of the cell wall breaks due to the core back, causing a crack in the center or the cell wall to become fibrous, so that the rigidity cannot be maintained when an external force such as bending is applied.

《Cooling process》
The cooling step is a step of solidifying the foam cell walls by cooling the foam molded body in the cavity.

By cooling the foamed molded body in the cavity for 5 seconds or longer, the cell walls solidify, and this is the time for cooling to a state where the cell walls do not adhere in the subsequent compression step.
Although it depends on the thickness of the obtained molded body, it is considered that in the main molding, the resin temperature inside the molded body cools down to the crystallization temperature or less when 5 seconds or more have passed after core-backing.

《Compression process》
The compression step is a step of moving the movable mold in the mold clamping direction and compressing the foamed molding in the cavity.

With the cell walls solidified after foaming, the movable mold is moved in the closing direction to compress (reduce) 4 to 90% of the thickness (V1-V0) obtained by expanding the volume of the molded body (thickness at compression S: 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, preferably 0.5 to 10 seconds.

This compression process can be performed after the molded body is removed from the molding machine, but by performing it before the cooling time of the molded body in the molding machine is completed, compression using the molding machine is possible and the compression accuracy is good. Also, it is efficient because there is no need to perform an extra process after taking out.

The foamed molded article obtained by the method for producing an injection foamed molded article of the present invention (hereinafter sometimes referred to as "molded article") has a solid skin from the surface side in a cross section in the plate thickness direction of the injection foamed molded article. Composed of five layers: layer (A1) / foam layer (B1) / foam layer (C) / foam layer (B2) / solid skin layer (A2) (back surface),
Solid skin layers (A1) and (A2) are layers in which no cellular foam structure is observed, and foam layer (B1) and foam layer (B2) are layers satisfying the following (bi) to (b-iii). , The foam layer (C) does not satisfy at least one of the following (bi) to (b-iii), and has a curved cell wall in the front and back direction of the cross section;
(bi): having a foamed cell structure in which the inside of the cells is filled with gas and 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): Cells having an average diameter of 1 or more and 6 or less with respect to the average diameter in the planar direction of the cross section in the plate thickness direction.

(Simple prediction and adjustment of injection molding conditions)
The production method of the present invention has the steps of injection/filling, core-backing, and compression, and also requires the setting of a large number of conditions, such as the timing of transition between steps. The temperature range in which foaming is possible and the temperature range during compression change depending on factors such as the viscosity of the resin and the amount of foaming agent added. Predicting subsequent temperature changes using CAE or the like makes it possible to quickly set conditions even when setting changes such as changes in plate thickness of the compact are made.

<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 capable of producing an injection foam molded article. , propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene. LLDPE), high density polyethylene (so-called HDPE), polypropylene (propylene homopolymer), propylene random copolymer, propylene block copolymer, poly 1-butene, poly 4-methyl-1-pentene, ethylene/propylene random copolymer Polymers, 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 , polym-xylene adipamide, etc.), polyvinyl chloride, polyimide, ethylene/vinyl acetate copolymer, ethylene/vinyl alcohol copolymer, ethylene/(meth)acrylic acid copolymer, ethylene-acrylic acid ester- Examples include carbon oxide 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-based polymers such as propylene block copolymers, polyethylene terephthalate, polyamides, etc. is more preferred. These thermoplastic resins (D) may be used alone or in combination of two or more thermoplastic resins (D).

<<Propylene Polymer (E)>>
The propylene-based polymer (E) according to the present invention refers to a polymer in which the content of structural units derived from propylene is 50 mol% or more, and the content of structural units derived from propylene in the propylene-based polymer is The amount is preferably 90 mol % or more.

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

The structure of the propylene-based polymer (E) according to the present invention is not particularly limited. For example, the structural unit portion derived from propylene may have an isotactic structure, a syndiotactic structure, or an atactic structure. A structure is preferred. In the case of the copolymer, any of a random type [also called random PP], a block type [block PP: also called bPP], and a graft type may be used.

As the comonomer, any other monomer copolymerizable with propylene may be used, and an α-olefin having 2 or 4 to 10 carbon atoms is preferable. Specific examples include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene and 1-decene. , ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene and 1-octene are preferred. 1 type may be used for a comonomer and 2 or more types may be used for it.

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 polymers (E), a propylene homopolymer segment obtained by polymerizing propylene alone and a propylene/ethylene block copolymer containing a propylene/ethylene copolymer segment obtained by copolymerizing propylene and ethylene. It is preferable because the physical properties such as rigidity and impact resistance of the injection foamed molded product from which the polymer (E1) is obtained are well balanced.

The propylene-based polymer (E) according to the present invention may be synthesized by a conventionally known method, or a commercially available product may be used. Examples of commercially available products include polypropylene manufactured by SunAllomer Co., Ltd., Prime Polypro manufactured by Prime Polymer Co., Ltd., Novatec manufactured by Nippon Polypropylene Co., Ltd., and SCG PP manufactured by SCG Plastics.

The MFR of the propylene-based polymer (E) according to the present invention (according to the measuring method of ASTM D 1238, 230° C., 2160 g load) is preferably 20 to 200 g/10 min, more preferably 30 to 150 g/10. minutes.

When the MFR of the propylene-based polymer (E) according to the present invention is within the above range, the injection moldability is excellent.
The crystallization temperature (Tc) of the propylene-based polymer (E) according to the present invention varies depending on factors such as comonomer content, molecular weight and isotacticity. ~130°C, about 80-110°C for random copolymers. When a filler, a nucleating agent, or the like is added to the propylene-based polymer, the crystallization temperature shown above becomes higher by 5 to 15°C. In order to use an accurate crystallization temperature, it is desirable to measure the crystallization temperature and use that value to determine the mold temperature.
Here, the crystallization temperature is the temperature at which the sample is once melted using a differential scanning calorimeter (DSC) and then cooled at a rate of 10 (° C./min), and the sample crystallizes during the cooling process. is a value measured as

<Ethylene/α-olefin copolymer (F)>
The thermoplastic resin composition according to the present invention may contain an ethylene/α-olefin copolymer (F).

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, 1-dodecene and the like. Among these, from the viewpoint of imparting flexibility, α-olefins having 3 to 12 carbon atoms are preferred, propylene, 1-butene and 1-octene-1 are more preferred, and 1-octene is even more preferred.

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 an α- Units derived from olefin are in the range of 1 to 30 mol%, preferably 3 to 20 mol% [However, the total amount of units derived from ethylene and units derived from α-olefins having 3 to 20 carbon atoms is 100 mol %. 〕It is in.

The ethylene/α-olefin copolymer (F) according to the present invention may optionally be copolymerized with a monomer having an unsaturated bond. Examples of monomers having unsaturated bonds 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. preferable. Among these, ethylidenenorbornene (ENB) and dicyclopentadiene (DCP) are more preferable from the viewpoint of flexibility.

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

The ethylene/α-olefin copolymer (F) according to the present invention usually has a density in the range of 0.8 to 0.9 g/cm ³ .
The ethylene/α-olefin copolymer (F) according to the present invention can be produced using known polymerization catalysts such as Ziegler-Natta catalysts, vanadium catalysts and metallocene catalysts. The polymerization method is not particularly limited, and liquid phase polymerization methods such as solution polymerization, suspension polymerization and bulk polymerization, gas phase polymerization, and other known polymerization methods can be used. Moreover, these copolymers are not limited as long as the effects of the present invention are exhibited, and they are available as commercial products. Commercially available products include Engage 8842 (ethylene/1-octene copolymer) manufactured by Dow Chemical Company, Engage 8407 (ethylene/1-octene copolymer) manufactured by Dow Chemical Company, and Vistalon (manufactured by ExxonMobil). registered trademark), Esprene (registered trademark) manufactured by Sumitomo Chemical Co., Ltd., Mitsui EPT (registered trademark) manufactured by Mitsui Chemicals, Inc., Toughmer P (registered trademark), Toughmer A (registered trademark), etc. .

<Filler (G)>
The thermoplastic resin composition according to the present invention may contain fillers (G) such as inorganic fillers and organic fillers. These fillers (G) may be used singly or in combination of two or more.

<Inorganic filler>
Various known inorganic fillers can be used as the inorganic filler according to the present invention. Specifically, oxides such as aluminum oxide, titanium oxide, zinc oxide, calcium oxide, silica, sulfates such as barium sulfate, carbonates such as calcium carbonate, magnesium carbonate, barium carbonate, talc, clay, mica, etc. Examples include, but are not limited to, silicates and the like.

<Organic filler>
Various known organic fillers can be used as the organic filler according to the present invention. Specific examples include polymethoxysilane-based compounds, polystyrene, styrene-acryl, styrene-methacrylic and methacrylic-based compounds, polyurethane-based compounds, polyester-based compounds, fluoride-based compounds, and phenol-based compounds. Not limited.

<Foaming agent (H)>
The type of foaming agent (H) contained in the thermoplastic resin composition according to the present invention is not particularly limited. It may be a solvent type foaming agent, a decomposition type foaming agent, a gaseous foaming agent such as nitrogen, carbon dioxide, argon, or air, or a thermal expansion type microcapsule foaming agent.

The gaseous foaming agent can be used by injecting nitrogen or carbon dioxide directly into the cylinder and kneading and dissolving it with molten resin using a screw, or by injecting it into the cylinder in a supercritical state and kneading and melting it. may

A solvent-type foaming agent is a substance that is injected from the hopper or cylinder of an injection molding machine, absorbed or dissolved in the molten raw material resin, and then vaporized in the injection mold to function as a foaming agent. Specific examples include low boiling point aliphatic hydrocarbons such as propane, butane, neopentane, heptane, isohexane, hexane, isoheptane and heptane, and low boiling point fluorine-containing hydrocarbons represented by freon gas. Thermal expansion type microcapsules are obtained by confining this solvent-type foaming agent in microcapsules such as acrylonitrile, methacrylonitrile, and vinylidene chloride, and the capsules are expanded and foamed by vaporization inside the capsules.

The decomposable foaming agent is preliminarily blended with the raw material resin composition and then supplied to the injection molding machine, where the foaming agent decomposes under the cylinder temperature conditions of the injection molding machine to generate gases such as carbon dioxide gas and nitrogen gas. is a compound. It may be an inorganic foaming agent or an organic foaming agent, and may include an organic acid such as citric acid that promotes gas generation, an organic acid metal salt such as sodium citrate, and the like. You may add together as a foaming auxiliary agent.

Degradable foaming agents include inorganic foaming agents and organic foaming agents. Specific examples of inorganic blowing agents include sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate and ammonium nitrite. Specific examples of organic foaming agents include N-nitroso compounds such as N,N'-dinitrosoterephthalamide and N,N'-dinitrosopentamethylenetetramine: azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile , azodiaminobenzene, barium azodicarboxylate, and other azo compounds; hydrazide compounds; azide compounds such as calcium azide, 4,4'-diphenyldisulfonyl azide and p-toluenesulfonyl azide;

The foaming agent (H) according to the present invention may be used alone or in combination of two or more. The addition amount of the foaming agent (actual component in the case of the masterbatch type) according to the present invention is selected in consideration of the required physical properties of the foamed molded product, the amount of gas generated from the foaming agent, the expansion ratio, etc. It is usually 1 to 8 parts by mass with respect to 100 parts by mass of the plastic resin composition.

<<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).

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

The foaming agent (H) foams the thermoplastic resin composition in the mold after injection molding, but the foaming gas is discharged from the inside of the molten resin during molding or replaced with outside air over time from the molded product after molding. pass through.

The present invention will be further illustrated by the following examples. However, the present invention is not limited to these.
The following polymers and the like were used as the thermoplastic resin (D) contained in the thermoplastic resin compositions used in Examples and Comparative Examples.

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

(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 Examples and Comparative Examples, the physical properties of thermoplastic resin compositions, polymers, and injection foam molded articles were measured by the following methods.

[Melt flow rate (MFR)]
It was measured at 190° C. or 230° C. under a load of 2.16 kg according to ASTM D-1238 without containing a blowing agent.

[Contents of n-decane insoluble portion (a1) and n-decane soluble portion (a2) in propylene/ethylene block copolymer (E1)]
About 3 g of the propylene/ethylene block copolymer (measured to the unit of 10-4 g. This mass was expressed as b (g) in the following formula), n-decane, were placed in a glass measuring container. 500 mL and a small amount of a heat stabilizer soluble in n-decane were added, and the temperature was raised to 150° C. in 2 hours while stirring with a stirrer under a nitrogen atmosphere to convert the propylene/ethylene block copolymer into n-decane. Dissolved. Then, after holding at 150° C. for 2 hours, it was gradually cooled to 23° C. over 8 hours. The resulting liquid containing the precipitate of the propylene/ethylene block copolymer was filtered under reduced pressure through a 25G-4 standard glass filter manufactured by Iwata Glass Co., Ltd. 100 mL of the filtrate was sampled and dried under reduced pressure to obtain a part of the component (a2). This mass was measured to the nearest 10-4 g (this mass was designated as a(g) in the formula below). Next, the contents of the components (a1) and (a2) in the propylene/ethylene block copolymer (E1) were determined by the following formula.
Content of component (a2) [% by mass] = 100 x 5a/b
Content of component (a1) [% by mass] = 100 - content of component (a2)

[Intrinsic viscosity ([η]: dl/g)]
Measured at 135° C. using decalin solvent.
[density]
It was measured according to ISO 1183 (JIS K7112).

[Measurement of thickness of solid skin layer]
The thickness of the solid skin layer of the injection foam molded product was measured by the following method.
First, the cross section of the injection foam molded product was cut with a sharp knife so as not to break the cells, and the cross section was photographed using a digital microscope VHX-6000 (manufactured by Keyence Corporation). The cross-sectional image is taken at a magnification of 100 times or more, and the border between the solid skin layer and the foam layer is taken from the cross-sectional image using the measurement function of the digital microscope. A perpendicular line was drawn to the surface of the solid layer, and the distance from the surface of the solid layer was measured in μm to obtain the thickness of the solid skin layer. In addition, if the surface layer has grains (excluding parts that clearly protrude from the surface such as ribs) and the thickness varies depending on the location, the midpoint between the peak and valley of the grains will be the end of the solid layer. , similarly measured.
The thickness of the obtained solid skin layers (solid skin layers on the front and back surfaces without foam cells sandwiching the foam layer) was measured in units of μm, and the average was defined as the solid skin layer thickness (μm).

[Measurement of Foam Cell Diameter of Foam Cell Layers (B1) and (B2)]
The cell diameter in the plate thickness direction and the cell diameter in the plane direction (perpendicular to the plate thickness) of the foam cells distributed in the foam cell layers (B1) and (B2) in contact with the solid skin layer of the injection foamed molding are as follows. It was measured by the method of

Using the measurement function of the digital microscope from the cross-sectional image used to measure the thickness of the solid skin layer, determine 10 or more foam cells so that they are arranged almost evenly in the direction of the plate thickness. The cell diameter in the thickness direction and the cell diameter in the plane direction were measured, and the average diameter of each was defined as the foam cell diameter (μm).

[Measurement of meandering angle of foam layer (C)]
The meandering angle for examining 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 foam molding was measured by the following method.

Using the measurement function of the digital microscope from the cross-sectional image used to measure the thickness of the solid skin layer, draw a line perpendicular to the surface of the molded product, and determine the horizontal inclination of the meandering portion from the upper and lower 1/2 regions of the foam layer (C). Each point was picked up to measure the inclination from the vertical line, and the measured inclinations were averaged to obtain the meandering angle. If the meandering angle is small, deformation of the cell walls of the foam layer (C) is difficult to occur, so the meandering angle was evaluated based on a standard of 25° or more.

[Thickness of injection foam molding (board thickness)]
The thickness (board thickness) of the injection foam molded product is 0 when the digital caliper CD-S15C (manufactured by Mitutoyo Co., Ltd.) is used and the outer jaw of the caliper is tightened without the molded product. After confirming in advance, slowly tighten the molded product so that it is sandwiched between the outside jaws of the vernier caliper so that it is perpendicular to the ground or in the front direction, and the molded product is not tilted. gone. At this time, a thumb roller was used, and the measurement was performed in units of mm while taking care to hold the compact with a uniform force as much as possible so as not to apply an excessive force to the compact.

[Rigidity (flexural elastic gradient)]
An injection foam molded product was cut into a size of 50 mm x 150 mm, and an autograph (AG-1kNX plus, manufactured by Shimadzu Corporation) was used as a testing machine to apply a load at a bending speed of 50 mm/min to the center position with a support interval of 100 mm. In the "load-deflection curve" obtained when the amount of deflection is between 0 and 10 mm when an additional bending test (three-point bending) is performed, the slope of the line drawn by the method described in JIS K7221-2 (= load /deflection) was taken as the flexural elastic slope (N/cm), which was used for stiffness comparison.

The bending elastic gradient used for rigidity comparison was evaluated as having a feeling of rigidity when the bending elastic gradient was 27 N/cm or more obtained by the measurement under the same conditions as described above for a compact with a bending elastic modulus of 1000 MPa and a plate thickness of 2.3 mm. .

[Push softness (push elasticity gradient)]
Using an Autograph (manufactured by Shimadzu Corporation, AG-100kNX) as a testing machine, a load was applied by pressing a circular indenter with a diameter of 4 mm and a flat tip onto the plane of the injection foam molding at a speed of 1 mm/min. In the "force-deformation curve" obtained when the amount of reduction in the molded body thickness is between 0 and 10% when the test is conducted, the slope of the line drawn by the method described in JIS K7220 (= force / deformation amount ) was taken as the push elasticity gradient (N/mm), which was used as an index of push softness.
The push elasticity gradient used for comparison of push softness is the push elasticity gradient obtained by measuring under the same conditions as described above for a molded product with a plate thickness of 1.8 mm using Milastomer 7030BS (manufactured by Mitsui Chemicals, Inc.). 90% or less (push elasticity gradient of 120 N/mm or less) was evaluated as having push softness.

[Cushioning]
The following evaluations were carried out based on whether or not the molded product felt soft when pressed with a finger.
There is a cushion feeling when you press the surface with your finger: ○
There is no cushion feeling when the surface is pressed with a finger: ×

<Example 1>
76 parts by mass of the above PP-1 and 24 parts by mass of the above F-1 (100 parts by mass in total) are mixed, and the thermoplastic resin composition obtained by usually processing into pellets using an extruder A CO2 _- based foaming agent masterbatch (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name: EE515) was used as a composition: 5 parts by mass of an inorganic foaming agent per 100 parts by mass, and an _N2 -based foaming agent masterbatch (Eiwa Kasei Kogyo Co., Ltd. ), trade name EE206) in an amount of 2.5 parts by weight per 100 parts by weight of the composition, and 3 parts by weight of a black masterbatch as a coloring agent are added, mixed, and put into the hopper of an injection molding machine and melted. kneading was performed. Since the foaming agent used is a masterbatch obtained by kneading the foaming agent into low-density polyethylene, the actual foaming agent component is equivalent to 3% by mass. Table 1 shows the composition of the thermoplastic resin composition used in Example 1. An injection molding machine (manufactured by Japan Steel Works, Ltd., device name: J350ADS) performed core-back injection foam molding under the following conditions to obtain a plate-like injection foam-molded product whose surface was covered with a skin layer.

Cavity size: length 400mm, width 200mm, filling resin thickness 1.8mm
Gate: 1-point direct gate in the center of the cavity Injection temperature: 205°C
Mold surface temperature: 50°C
Mold cavity clearance during injection (L0): 1.8mm
Ejection rate: 309cc/s
Molding machine core-back time setting: 0.1s (time from core-back start to end)
Time from completion of injection to start of core back: 5.8s
Core back amount: 5mm
Compression start time: 40s after completion of core back
Amount of compression from the core-back state: 1mm

The obtained molded body had a plate thickness of 6.3 mm. The physical properties of the obtained molded article were measured by the methods described above. The molded product obtained has a five-layer structure, and the state of the foamed cells of the foamed cell layers (B1) and (B2), the meandering state of the foamed layer (C), the bending elastic gradient, the pushing elastic gradient, and the cushioning property are good. Met.
Table 1 shows the results.

<Example 2>
A compact was obtained in the same manner as in Example 1, except that the amount of compression from the core-back state was 2 mm. The obtained molded body had a plate thickness of 6.2 mm. The physical properties of the obtained molded article were measured by the methods described above. The molded product obtained has a five-layer structure, and the state of the foamed cells of the foamed cell layers (B1) and (B2), the meandering state of the foamed layer (C), the bending elastic gradient, the pushing elastic gradient, and the cushioning property are good. Met.
Table 1 shows the results.

<Example 3>
A compact was obtained in the same manner as in Example 1, except that the amount of compression from the core-back state was 3 mm. The obtained molded body had a plate thickness of 5.9 mm. The physical properties of the obtained molded article were measured by the methods described above. The molded product obtained has a five-layer structure, and the state of the foamed cells of the foamed cell layers (B1) and (B2), the meandering state of the foamed layer (C), the bending elastic gradient, the pushing elastic gradient, and the cushioning property are good. Met.
Table 1 shows the results.

<Example 4>
The filled resin thickness was set to 1.5 mm, and the cavity clearance during injection was also set to 1.5 mm. Further, molding was performed in the same manner as in Example 2 except that the core-back start time from the completion of injection was set to 3.8 seconds, the core-back amount was set to 3 mm, and the compression start time was set to 30 seconds. The obtained molded body had a plate thickness of 4.1 mm. The physical properties of the obtained molded article were measured by the methods described above. The molded product obtained has a five-layer structure, and the state of the foamed cells of the foamed cell layers (B1) and (B2), the meandering state of the foamed layer (C), the bending elastic gradient, the pushing elastic gradient, and the cushioning property are good. Met.
Table 1 shows the results.

<Example 5>
Molding was carried out under the same conditions as in Example 4, except that the foaming agent was 6 parts by mass per 100 parts by mass of the inorganic foaming agent masterbatch (manufactured by Eiwa Kasei Kogyo Co., Ltd., trade name EE515). The obtained molded body had a plate thickness of 4.1 mm. The physical properties of the obtained molded article were measured by the methods described above. Although the cells in the foamed state were slightly larger, the resulting molded article had a five-layer structure, and the state of the foamed cells of the foamed cell layers (B1) and (B2), the meandering state of the foamed layer (C), The flexural elasticity gradient, push elasticity gradient, and cushioning property were good.
Table 1 shows the results.

<Example 6>
A molded article was obtained in the same manner as in Example 1, except that the PP-2 (talc-containing propylene resin composition) was used instead of the propylene resin composition used in Example 1. The resulting molded body had a plate thickness of 5.9 mm. The physical properties of the obtained molded article were measured by the methods described above. The molded product obtained has a five-layer structure, and the state of the foamed cells of the foamed cell layers (B1) and (B2), the meandering state of the foamed layer (C), the bending elastic gradient, the pushing elastic gradient, and the cushioning property are good. Met.
Table 1 shows the results.

<Example 7>
A molded body was obtained in the same manner as in Example 1, except that the propylene resin composition used in Example 1 was replaced with PP-3 (talc-containing propylene resin composition). The obtained molded body had a plate thickness of 6.1 mm. The physical properties of the obtained molded article were measured by the methods described above. The molded product obtained has a five-layer structure, and the state of the foamed cells of the foamed cell layers (B1) and (B2), the meandering state of the foamed layer (C), the bending elastic gradient, the pushing elastic gradient, and the cushioning property are good. Met.
Table 1 shows the results.

<Comparative Example 1>
Molding was carried out under the same conditions as in Example 1, except that after injection, the molded body was taken out without performing core backing or compression. The molded article obtained was not foamed and was a solid molded article having a plate thickness of 1.8 mm. The physical properties of the obtained molded article were measured by the methods described above. The molded article was in a solid state, had a low bending elastic gradient, a high pushing elastic gradient, and lacked a cushioning feel.
Table 1 shows the results.

<Comparative Example 2>
Molding was performed under the same conditions as in Example 1, except that the amount of core-back: 1 mm and the amount of compression from the core-back state: 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The resulting molded product had a three-layer structure without the foam layer (C), had a plate thickness of 2.8 mm, had a good foaming state, and satisfied the bending elastic gradient, but had a high pushing elastic gradient. It lacked cushioning.
Table 1 shows the results.

<Comparative Example 3>
Molding was performed under the same conditions as in Example 1, except that the amount of core-back: 3 mm and the amount of compression from the core-back state: 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The resulting molded product had a three-layer structure without the foam layer (C), had a plate thickness of 4.6 mm, had a good foaming state, and satisfied the bending elastic gradient, but had a high pushing elastic gradient. It lacked cushioning.
Table 1 shows the results.

<Comparative Example 4>
Molding was performed under the same conditions as in Example 1, except that the amount of core-back: 5 mm and the amount of compression from the core-back state: 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The resulting molded product had a three-layer structure without the foam layer (C), had a plate thickness of 6.5 mm, had a good foaming state, and satisfied the bending elastic gradient, but had a high pushing elastic gradient. It lacked cushioning.
Table 1 shows the results.

<Comparative Example 5>
Molding was carried out under the same conditions as in Example 4, except that after injection, the molded body was taken out without performing core-backing or compression. The physical properties of the obtained molded article were measured by the methods described above. The molded product obtained was not foamed, was solid with a plate thickness of 1.5 mm, had an insufficient bending elastic gradient, a high pushing elastic gradient, and an insufficient cushioning feeling.
Table 1 shows the results.

<Comparative Example 6>
Molding was performed under the same conditions as in Example 4, except that the amount of core-back: 3 mm and the amount of compression from the core-back state: 0 mm. The physical properties of the obtained molded article were measured by the methods described above. The resulting molded article had a three-layer structure without the foam layer (C), had a plate thickness of 4.4 mm, had a good foaming state, and satisfied the flexural elasticity gradient, but had a high pressing elasticity gradient and a cushion. I lacked feeling.
Table 1 shows the results.

Since the injection foam molded article of the present invention has both weight reduction and texture, it can be suitably used for various applications such as automobile interior parts, electric appliances, and building materials. In particular, it has an excellent balance of lightness, rigidity, and appearance, and is also excellent in heat insulation, so it can be particularly suitably used for interior parts of automobiles.

A1, A2: solid skin layers B1, B2: foam cell layer C: foam layer without foam cells

Claims (8)

[Crystallization temperature (Tc) of the thermoplastic resin (D), which is the main component constituting the thermoplastic resin composition (glass transition temperature (Tg) -50 ° C. when the thermoplastic resin (D) is amorphous) 1 After 12 seconds to 12 seconds, the thickness (V0) of the mold cavity was expanded to 210 to 600% to foam the thermoplastic resin composition [at this time, the cavity thickness (V1)], and cooled for 5 seconds or more. After that, the expanded thickness of the cavity is compressed (reduced) to a thickness of 4 to 90% of the expanded thickness (V1-V0) [cavity thickness during compression: V2), pressure for 0.1 seconds or more In the method of manufacturing an injection foam molded article by removing the foam from the mold after holding, the thickness (V3) of the obtained foam is (V1)>(V3)>(V2) A method for producing an injection foam molding characterized by: 2. The method for producing an injection foam molded article according to claim 1, wherein said thermoplastic resin (D) is a propylene polymer (E). 3. The method for producing an injection foam molded article according to claim 1, wherein the thermoplastic resin composition contains an ethylene/α-olefin copolymer (F). The method for producing an injection foam molded article according to any one of claims 1 to 3, wherein the thermoplastic resin composition contains a filler (G). Any one of claims 1 to 4, wherein the content of the foaming agent (H) contained in the thermoplastic resin composition is 1 to 8 parts by mass with respect to 100 parts by mass of the thermoplastic resin composition. 2. A method for producing an injection foam molded article according to claim 1. The method for producing an injection foam molded article 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. . The injection foam molded article has a cross section of solid skin layer (A1)/foam layer (B1)/foam layer (C)/foam layer (B2)/solid skin layer (A2) from the surface side. and the back surface solid skin layer (A2) (back surface) consists of 5 layers,
Solid skin layers (A1) and (A2) are layers in which no cellular foam structure is observed, and foam layer (B1) and foam layer (B2) are layers satisfying the following (bi) to (b-iii). Claims 1 to 6, wherein the foam layer (C) does not satisfy at least one of the following (bi) to (b-iii) and has cell walls curved in the front and back direction of the cross section. A method for producing an injection foam molded article according to any one of items;
(bi): having a foamed cell structure in which the inside of the cells is filled with gas and 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): Consists of cells having a diameter of 1 or more and 6 or less with respect to the average diameter in the plane direction of the cells in the cross-sectional direction. The method for producing an injection foam molded article according to any one of claims 1 to 7, wherein at least part of the inner surface of the mold is textured.

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