JP2019089891A - Foam molding and method for producing the same - Google Patents

Abstract

To provide a foam molding which has good appearance, is lightweight, and is excellent in rigidity and impact resistance, and a method for producing the same.SOLUTION: There are provided a foam molding that has a foam resin portion whose surface is covered with a skin layer, where average thickness (s=(s+s)/2) obtained by dividing thickness (s) of the skin layer on one surface and thickness (s) of the skin layer on the opposite surface by 2 is 250-600 μm, and total thickness (2s+f) obtained by adding total thickness (2 s=s+s) of the skin layers of the one surface and the opposite surface and thickness (f) of the foam resin portion is 1.5-4.0 mm, and a ratio (2s/(2s+f)×100) of total thickness (2s) of the skin layers to total thickness (2s+f) is 20-70%; and a method for producing the same.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a foam molding useful for various applications such as automobile interior and exterior parts, and relates to a foam molding having a good appearance, light weight, and excellent in rigidity and impact resistance, and a method for producing the same.

  In recent years, injection foams have begun to be adopted as interior and exterior parts for automobiles in order to reduce the weight of automobiles. However, injection foams tend to have reduced impact resistance as they foam. Improving the impact resistance of injection foams is an important issue, especially in applications such as automotive parts.

  In Patent Document 1, a primary injection step of injection-filling a specific propylene-based foamed resin composition into a cavity having a volume smaller than the total volume of the final product with a movable mold fixed, and thereafter From the secondary injection process of filling the remaining foamable resin composition into the enlarged cavity while retracting the movable mold, and the foaming process of further retracting the movable mold to foam-mold the foamable resin composition A method of producing a resin foam for automobile parts is disclosed. And the resin foam for motor vehicle parts obtained by this method is described as having a good appearance and being lightweight as a whole and excellent in rigidity and impact resistance.

  Patent Document 2 discloses a specific polypropylene resin composition. And, this resin composition is suitable for producing a foamed molded article having high rigidity and penetration impact strength by injection molding, and described as being suitable as a raw material for injection molding of automobile parts, electric products, building materials, etc. It is done.

  Patent Document 3 discloses a specific injection foaming resin composition. And this resin composition for injection foaming expresses melt viscosity and melt tension suitable for injection foaming, and it is explained that a good impact-resistant injection foam molded article is obtained by using this resin composition. .

  However, there is still room for improvement in impact resistance of injection foam molded articles using conventional propylene-based resin compositions.

Japanese Patent Application Laid-Open No. 2002-011748 JP 2003-253084 JP, 2013-001826, A

  An object of the present invention is to provide a foamed molded article which has a good appearance, is lightweight, and is excellent in rigidity and impact resistance, and a method for producing the same.

  As a result of intensive studies to solve the above problems, the inventors of the present invention adjusted the thickness ratio of the solid layer portion (hereinafter referred to as "skin layer") on the surface of the molded body to obtain impact resistance of the foam molded body. It has been found that it can be improved, and the present invention has been completed. That is, the present invention is specified by the following matters.

[1] In a foam molded article having a foamed resin portion whose surface is covered with a skin layer,
The average thickness (s = (s ₁ + s ₂ ) / 2) of the thickness (s ₁ ) of the skin layer on one side and the thickness (s ₂ ) of the skin layer on the opposite side is 250 to 600 μm,
The total thickness (2s + f) of the total thickness (2s = s ₁ + s ₂ ) of the skin layer on one side and the opposite side and the thickness (f) of the foamed resin portion is 1.5 to 4.0 mm,
A ratio of the total thickness (2s) of the skin layer to the total thickness (2s + f) (2s / (2s + f) × 100) is 20 to 70%.

[2] The foamed molded article according to [1], wherein the initial thickness (f ′) of the foamed molded article before foaming is 0.7 to 2.0 mm.

[3] The foam-molded article according to [1] or [2], which comprises a polypropylene resin composition.

[4] The polypropylene resin composition is
Propylene / ethylene block copolymer (A) 65 to 85 parts by mass,
15 to 30 parts by mass of ethylene / α-olefin copolymer (B) having a density of 0.86 to 0.92 g / cm ³ and a melt flow rate (190 ° C., 2.16 kg load) of 1 to 50 g / 10 min ,
0 to 5 parts by mass of the inorganic filler (C) [The total of component (A), component (B) and component (C) is 100 parts by mass. ]
The foam-molded body as described in [3] containing.

[5] Propylene-ethylene block copolymer (A) is
N-decane insoluble part (Dinsol) 70-95 mass% in 23 ° C whose melt flow rate (230 ° C, 2.16 kg load) is 50-200 g / 10 min, and
5-30 mass% of n-decane-soluble parts (Dsol) at 23 ° C. having an intrinsic viscosity [η] of 5-10 dl / g
The foam-molded body as described in [4] containing.

[6] The molded foam according to any one of claims 1 to 5, which is an injection molded foam.

[7] A method for producing a foam molded article according to any one of [1] to [6], wherein core back injection foam molding is performed.

[8] The method for producing a foam molded article according to [7], wherein core back injection foam molding is performed under the conditions of an initial thickness (f ') of 0.7 to 2.0 mm and a delay time of 0 to 4 seconds.

  The foam molded article of the present invention has a good appearance, is lightweight, and is excellent in rigidity and impact resistance. Such foam molded articles are suitable for various uses such as automotive interior and exterior parts, for example.

It is a graph which shows the relationship between the ratio of the total thickness of the skin layer of the foaming molding in an Example and a comparative example, and tensile strain at break.

The foam molded article of the present invention has a foamed resin portion whose surface is covered with a skin layer. The average thickness (s = (s ₁ + s ₂ ) / 2) of the thickness (s ₁ ) of the skin layer on one side and the thickness (s ₂ ) of the skin layer on the opposite side is 250 to 600 μm, preferably 280 It is -600 micrometers, More preferably, it is 300-600 micrometers. The total thickness (2s + f) of the total thickness (2s = s ₁ + s ₂ ) of the skin layer on one side and the opposite side and the thickness (f) of the foamed resin portion is 1.5 to 4.0 mm. It is 0 to 4.0 mm, more preferably 2.4 to 4.0 mm. The ratio of the total thickness (2s) of the skin layer to the total thickness (2s + f) (hereinafter also referred to as "skin layer ratio") (2s / (2s + f) x 100) is 20 to 70%, preferably 22 to 60% And more preferably 25 to 55%. With such a layer configuration, a foam molded article having excellent impact resistance can be obtained.

  Further, the initial thickness (f ') before foaming of the foamed resin portion is preferably 0.7 to 2.0 mm, more preferably 1.0 to 1.8 mm, and the foaming ratio is preferably 1.3 to 3 It is 0. 0 times, more preferably 1.5 to 2.8 times.

  When the foamed molded article of the present invention is a plate-shaped molded article, the average thickness (s) of the skin layer is the average thickness of both skin layers on one side and the opposite side of the plate, and the total thickness (2s + f) is the entire plate The skin layer ratio (2s / (2s + f) × 100) is the ratio of the total thickness of the skin layer to the thickness of the whole plate. However, the shape of the foam molded article of the present invention is not limited to a plate. For example, the shape may be a curved shape, or a shape having a convex portion or a concave portion in part. In the case of a shape having a partially different thickness, at least a part (preferably, the main part) of the foam molding may satisfy the relationship among the thickness, total thickness, and skin layer ratio of the skin layer of the present invention.

  The foam molded article of the present invention preferably comprises a polypropylene resin composition. Furthermore, the polypropylene-based resin composition contains the following propylene / ethylene-based block copolymer (A), ethylene / α-olefin copolymer (B) and, optionally, an inorganic filler (C) Is preferred.

<Propylene-Ethylene-Based Block Copolymer (A)>
The propylene / ethylene-based block copolymer (A) may be a block copolymer containing a propylene unit and an ethylene unit. In particular, 70 to 95% by mass (more preferably 75 to 93% by mass) of n-decane insoluble portion (Dinsol) at 23 ° C and 5 to 30% by mass (more preferably) of n-decane soluble portion (Dsol) at 23 ° C Propylene-ethylene block copolymers containing 7 to 25% by mass) are preferred. The separation of the soluble part and the insoluble part by the n-decane solvent is described in the column of Examples described later.

  The n-decane insoluble portion is mainly composed of a propylene homopolymer, and preferably contains, as a comonomer, a structural unit derived from another α-olefin monomer of preferably 10 mol% or less, more preferably 5 mol% or less. It may be done. Specific examples of such α-olefins include ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene is mentioned.

  The n-decane insoluble portion preferably has a melt flow rate (MFR) value measured at 230 ° C. under a load of 2.16 kg according to ASTM D-1238, preferably 50 to 250 g / 10 min, more preferably 100 to 220 g It is 10 minutes. The insoluble portion having such properties imparts excellent fluidity to the propylene / ethylene block copolymer (A).

The n-decane insoluble portion preferably has an isotactic pentad fraction (mm mm fraction) of 97% or more as measured by ¹³ C-NMR. Here, the isotactic pentad fraction (mm mm fraction) is a value that serves as an index of stereoregularity of a propylene polymer, and the larger the value, the higher the stereoregularity, and such insoluble The propylene / ethylene block copolymer (A) containing part exhibits high crystallinity.

The isotactic pentad fraction (mmmm fraction) indicates the proportion of isotactic chains in pentad units in the propylene polymer molecular chain, and specifically, five consecutive propylene monomer units The absorption peak of the ¹³ C-NMR spectrum of the propylene monomer unit at the center of the meso-linked chain is a value determined as a ratio to the total absorption peak of the methyl carbon region.

  On the other hand, the n-decane soluble portion is mainly composed of a propylene / ethylene random copolymer, and in addition, a high molecular weight propylene homopolymer, a part of a low molecular weight propylene homopolymer, or another α-olefin A part of the copolymer as a comonomer, and further, a by-product generated at the time of producing the block copolymer may be contained.

  The n-decane soluble portion preferably has an ethylene content of 20 to 50 mol%, more preferably 23 to 45 mol%, and a propylene content of preferably 50 to 80 mol%, more preferably 55 to 77 mol. %. The intrinsic viscosity [η] measured in a decaline solvent at 135 ° C. of the n-decane soluble portion is preferably 5 to 10 dl / g, more preferably 7 to 10 dl / g. The soluble portion having such properties gives the propylene / ethylene block copolymer (A) an excellent foamability.

  A propylene / ethylene block copolymer (A) containing an n-decane insoluble portion and a soluble portion has a melt flow rate (MFR) measured under a load of 2.16 kg at 230 ° C. in accordance with ASTM D-1238. The value is preferably 40 to 200 g / 10 minutes, more preferably 50 to 150 g / 10 minutes. When the MFR value is in this range, the resin composition is provided with good moldability and high mechanical strength.

  As a method for producing a propylene / ethylene block copolymer (A), for example, the following two steps ([Step i] and [Step ii]) can be carried out in the presence of a known Ziegler-Natta catalyst or a metallocene catalyst: There is a method to carry out continuously.

  [Step i] is a step of propylene homopolymerization or, if necessary, copolymerization of ethylene and propylene at a polymerization temperature of 0 to 100 ° C. and a polymerization pressure of normal pressure to 5 MPa gauge pressure. In [Step i], the polymer produced in [Step i] is adjusted to be the main component of the n-decane insoluble portion by using propylene homopolymerization or by setting the feed amount of ethylene to propylene small. can do.

  [Step ii] is a step of copolymerizing propylene and ethylene at a polymerization temperature of 0 to 100 ° C. and a polymerization pressure of normal pressure to 5 MPa gauge pressure. In [Step ii], the polymer produced in [Step ii] becomes a main component of the n-decane soluble portion by increasing the feed amount of ethylene to propylene compared with [Step i]. It can be adjusted.

  The ethylene content in the soluble portion can be controlled by controlling the feed amount of ethylene to propylene in the polymerization system in [Step ii]. After completion of the polymerization, the propylene / ethylene-based block copolymer (A) can be obtained as a powder by performing post-treatment steps such as known catalyst deactivation treatment step, catalyst residue removal step, drying step and the like as necessary.

<Ethylene-α-olefin copolymer (B)>
The ethylene / α-olefin copolymer (B) is a copolymer of ethylene and an α-olefin. The carbon atom number of the α-olefin is preferably 3 to 10. Specific examples of the α-olefin include propylene, 1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene and 1-decene. Among these, 1-butene and 1-octene are preferable.

  The melt flow rate (MFR) of the ethylene / α-olefin copolymer (B) measured under the conditions of 190 ° C. and a load of 2.16 kg according to ASTM D-1238 is preferably 1 to 50 g / 10 min. And more preferably 4 to 40 g / 10 min.

The density of the ethylene / α-olefin copolymer (B) is preferably 0.86 to 0.92 g / cm ³ , more preferably 0.86 to 0.89 g / cm ³ .

<Inorganic filler (C)>
As an inorganic filler (C) used as needed, the inorganic substance utilized as plastics compounding materials, such as a talc, clay, calcium carbonate, mica, silicates, carbonates, and glass fiber, can be used. Among them, talc is preferred. The average particle size of the inorganic filler (C) is preferably 1 to 10 μm, more preferably 2 to 7 μm.

<Polypropylene-based resin composition>
The polypropylene-based resin composition preferably contains the above-described propylene / ethylene-based block copolymer (A), ethylene / α-olefin copolymer (B) and, if necessary, an inorganic filler (C). . When the total of component (A), component (B) and component (C) is 100 parts by mass, the content of the propylene / ethylene-based block copolymer (A) is preferably 65 to 85 parts by mass, and more preferably Is 67 to 83 parts by mass. The content of the ethylene / α-olefin copolymer (B) is preferably 15 to 30 parts by mass, more preferably 17 to 28 parts by mass. The content of the inorganic filler (C) is preferably 0 to 5 parts by mass, more preferably 0 to 3 parts by mass.

  The polypropylene resin composition may contain various polymers and additives other than polypropylene, as long as the object of the present invention is not impaired. Specific examples of the polymer include low density polyethylene, linear low density polyethylene, high density polyethylene, ethylene / unsaturated carboxylic acid ester copolymer, and carboxylic acid modified polyolefin. Specific examples of the additives include antioxidants, heat stabilizers, weather stabilizers, light stabilizers, ultraviolet absorbers, antistatic agents, antioxidants, fatty acid metal salts, softeners, dispersants, nucleating agents, lubricants. Flame retardants, pigments, dyes, organic fillers.

  Injection molding is carried out by uniformly mixing predetermined amounts of each component and other additives using a Henschel mixer, V-blender, ribbon blender, tumbler blender or the like, and then processing into pellets usually using an extruder. It can be used as a resin composition suitable for

<Foam molded body>
The foam molded article of the present invention can be obtained by adding a foaming agent to a resin composition as a raw material and performing foam molding.

  The type of blowing agent is not particularly limited. It may be a solvent-type foaming agent or a decomposition-type foaming agent, and may be a gaseous foaming agent such as nitrogen, carbon dioxide, argon or air, or a microcapsule-type foaming agent of a thermal expansion type.

  The solvent type foaming agent is a substance which is injected from the hopper or cylinder portion of the injection molding machine, absorbed or dissolved in the molten raw resin, and then evaporated in the injection molding die to function as a foaming agent. Specific examples thereof include low boiling aliphatic hydrocarbons such as propane, butane, neopentane, heptane, isohexane, hexane, isoheptane, and heptane, and low boiling fluorine-containing hydrocarbons represented by chlorofluorocarbons. The thermal expansion type microcapsules are obtained by encapsulating the solvent-type foaming agent in microcapsules of acrylonitrile, methacrylonitrile, vinylidene chloride and the like, and the capsules are expanded and vaporized by being vaporized inside the capsules.

  The decomposition-type foaming agent is compounded in advance to the raw resin composition and then supplied to the injection molding machine, and the foaming agent is decomposed under the cylinder temperature conditions of the injection molding machine to generate gases such as carbon dioxide gas and nitrogen gas. It is a compound. It may be an inorganic foaming agent or an organic foaming agent, and an organic acid such as citric acid which promotes gas generation, an organic acid metal salt such as sodium citrate, etc. You may add together as a foaming adjuvant.

  The degradable foaming agents include inorganic foaming agents and organic foaming agents. Specific examples of the inorganic blowing agent include sodium bicarbonate, sodium carbonate, ammonium bicarbonate, ammonium carbonate and ammonium nitrite. Specific examples of the organic foaming agent include N-nitroso compounds such as N, N'-dinitrosoterephthalamide, N, N'-dinitrosopentamethylenetetramine, etc .: azodicarbonamide, azobisisobutyronitrile, azocyclohexyl nitrile And azo compounds such as azodiaminobenzene and barium azodicarboxylate; sulfonyls such as benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, p, p'-oxybis (benzenesulfenyl hydrazide) and diphenyl sulfone-3,3'-disulfonyl hydrazide Hydrazide compounds; and azide compounds such as calcium azide, 4,4'-diphenyldisulfonyl azide, p-toluenesulfonyl azide and the like can be mentioned.

  The foaming agent may be previously blended in the resin composition, may be blended in injection molding, or may be injected from the middle of the cylinder. The gaseous blowing agent may be used in the supercritical state. In addition, a foaming agent, a foaming aid, and the like may be blended in advance with the polymer to form a master batch, and then it may be blended in the resin composition when it is injection-molded.

  The addition amount (of the actual component) of the foaming agent is selected in consideration of the required physical properties of the foamed molded product, the amount of gas generated from the foaming agent, the foaming ratio, etc. 0.1 to 6 parts by mass.

  The foam molded article of the present invention is preferably, for example, an injection foam molded article obtained by injection foam molding of the above-described resin composition using an injection molding machine.

  The injection foam molding can also be performed, for example, by injection filling the resin composition from the injection molding machine to the cavity of the mold and compensating for shrinkage due to cooling by foaming (fine foam molding or anti-sinking foam molding), It can also be carried out by a method (volume expansion foaming method or core back foaming method) in which the volume of the cavity is increased after injection filling to foam the resin composition. The molding die used for this injection foam molding is comprised of a fixed mold and a movable mold, and it is preferable that these be in a clamped state at the time of injection filling of the resin composition. Further, as a method of expanding the volume of the cavity, it is general to retract the movable mold (core back) to expand the cavity, but it can also be increased by moving a part of the mold. In particular, after injection and filling, it is preferable to move the movable mold at an appropriate time to increase the cavity volume.

  The initial position of the movable mold is a position when the fixed mold and the movable mold are closest to each other and in the mold clamping state in which the mold clamping force is applied. A cavity close to the shape of the product is formed at a location where the volume of the melt of the resin composition used in one molding is approximately equal to the volume filled in the unfoamed state.

  The injection speed of the resin composition into the cavity of the mold varies depending on the size of the molding machine and the size and thickness of the molded product, but preferably the injection speed corresponding thereto so that the injection time is 0.5 to 10 seconds. Apply. After completion of injection, a delay time of preferably 0 to 4 seconds is provided to grow the skin layer, and then the movable mold is retracted (core back) to expand the cavity volume. The thickness of the skin layer can be controlled by conditions such as injection speed and delay time. The skin layer can be thickened by increasing the delay time or decreasing the injection speed.

  The thickness of the skin layer can also be controlled by the mold temperature of the fixed and movable molds upon injection. The skin temperature can be increased by lowering the mold temperature. The mold temperature is preferably in the range of 20 to 70 ° C., as long as condensation does not occur.

  The moving speed of the core (or movable type) during core back depends on the thickness of the molded product, the type of resin, the type of foaming agent, the mold temperature, and the resin temperature, but for example, about 1.0 to 100 mm / sec. preferable. The core back can also be performed in several stages or can be performed while changing the moving speed of the movable mold, whereby a foam molded article in which the cell structure and the shape of the end portion are controlled can be obtained. Note that this movable mold moving speed can not usually be set directly in toggle type injection molding machines because it is generally not constant (it is often set by the ball screw speed that drives the toggle), and measurement of the toggle characteristic curve and moving speed Can be obtained as an average moving speed or the like.

  The temperature of the resin composition to be injected varies depending on the thickness of the molded product, the type of resin, the type and the addition amount of the foaming agent, etc., but the temperature usually used for molding the resin composition is sufficient and the product thickness is thin When obtaining a product having a high expansion ratio, the temperature may be set higher than the normal mold temperature. Specifically, the temperature of the resin composition to be injected is preferably 170 to 250 ° C.

Further, the injection rate of the injection molding machine in filling the resin composition into the mold is preferably 90 to 2000 cm ³ / sec. Moreover, the injection pressure of the injection molding machine at this time is preferably 50 to 200 MPa.

  In the present invention, the resin composition is filled in the cavity at one time, and after the skin layer thickness is grown, the resin in the portion in contact with the mold solidifies faster than the resin in the inside by foaming. A foam molded article having a foamed resin portion covered with a skin layer is obtained. This foamed molded product is highly rigid but light in weight, and the appearance and appearance are good due to the smoothness and rigidity of the skin layer even if some distribution of cell shape, cell density and foaming ratio occurs inside the foamed molded product. Excellent in impact resistance.

  After the end of foaming, it is possible to cool as it is and take out the foamed molded product, or by slightly clamping the mold while controlling the contact state of the foamed molded product and the mold to accelerate the cooling while shortening the molding cycle. It is also possible to obtain a good foamed molded article having a dent or cell shape.

  In the method for producing a foam molded article of the present invention, for example, a foam molded article having a thickness of about 1.5 to 4.0 mm can be suitably obtained. When this foam has independent cells, the average cell diameter is about 0.05 to 1.0 mm, but depending on the shape of the molded body and the application, even if the cell diameter is several mm, A part in communication may partially exist. In particular, when the expansion ratio is high, the plurality of cells associate and communicate together, and the inside of the foam molding becomes hollow, but since the resin columns are formed in this cavity, the foam molding has a high degree of It is lightweight and has strong rigidity.

  The invention is further illustrated by the following examples. However, the present invention is not limited to these.

<Measurement method>
In Examples and Comparative Examples, each physical property was measured by the following methods.

[Flowability (melt flow rate: MFR)]
It measured on the conditions of 190 degreeC or 230 degreeC, and 2.16 kg of loads based on ASTMD-1238 method in the state which does not contain a foaming agent.

[Contents of n-Decane-Insoluble Portion (a1) and n-Decane-Soluble Portion (a2) in Propylene / Ethylene-Based Block Copolymer]
About 3 g of a propylene-ethylene block copolymer (measured to a unit of 10 ^-4 g, this mass is expressed as b (g) in the following formula), n-in a measuring container made of glass. Add 500 mL of decane and a small amount of heat-resistant stabilizer soluble in n-decane, raise the temperature to 150 ° C for 2 hours while stirring with a stirrer under nitrogen atmosphere, and n-decane the propylene-ethylene block copolymer It was dissolved in Then, after holding at 150 ° C. for 2 hours, it was gradually cooled to 23 ° C. over 8 hours. The liquid containing the precipitate of the obtained propylene ethylene block copolymer was filtered under reduced pressure with a glass filter of 25 G-4 standard manufactured by Shibata Glass Co., Ltd. 100 mL of the filtrate was collected and dried under reduced pressure to obtain a part of the component (a2). This mass was measured to a unit of 10 ^-4 g (this mass was expressed as a (g) in the following formula). Next, the contents of the components (a1) and (a2) in the propylene / ethylene-based block copolymer were determined by the following formula.
Content of component (a2) [mass%] = 100 × 5a / b
Content of Component (a1) [mass%] = 100−Content of Component (a2)

[Intrinsic viscosity ([η]: dl / g)]
It was measured at 135 ° C. using decalin solvent.

[density]
It measured according to ISO 1183 (JIS K7112).

[Measurement of thickness (s) of skin layer]
The thickness (s) of the skin layer was measured by the following method. First, the cross section of the injection molded foam was cut with a sharp blade so as not to damage the cells, and the cross section photograph was taken. The thickness of the solid skin layer (the first skin layer and the second skin layer) of the surface layer portion with respect to the entire plate thickness was measured in mm from the cross-sectional photograph, and the average was taken as the skin layer thickness (s) .

<Raw resin composition for injection molding>
Each component used in the Example and the comparative example is as follows.

[Propylene / Ethylene-based block copolymer (A)]
“B-PP1”: Propylene / ethylene block copolymer (n-decane soluble portion = 11 mass%, ethylene content = 41 mol%, intrinsic viscosity [η] = 8 dl / g, MFR (230 ° C., 2. 16 kg) = 85 g / 10 min)
"B-PP2": Propylene / ethylene block copolymer (n-decane soluble portion = 10% by mass, ethylene content = 40 mol%, intrinsic viscosity [η] = 4 dl / g, MFR (230 ° C, 2. 16 kg) = 95 g / 10 min)

[Ethylene-α-olefin copolymer (B)]
"EOR": ethylene 1-octene copolymer (The Dow Chemical Company, trade name EG 8407, MFR (190 ° C, 2.16 kg) = 30 g / 10 min, density = 0.87 kg / m ³ )
"EBR 1": ethylene / 1-butene copolymer (manufactured by Mitsui Chemicals, Inc., trade name A- 35070 S, MFR (190 ° C, 2.16 kg) = 35 g / 10 min, density = 0.87 kg / m ³ )
"EBR2": ethylene / 1-butene copolymer (Mitsui Chemical Co., Ltd., trade name A-6050, MFR (190 ° C, 2.16 kg) = 6 g / 10 min, density = 0.86 kg / m ³ )

[Inorganic filler (C)]
"TALC": Talc (manufactured by Asada Powder Co., Ltd., trade name JM 209, average particle size 4.0 μm)

Example 1
4 parts by mass as a masterbatch per 100 parts by mass of a resin based on a foaming agent masterbatch (manufactured by Eiwa Chemical Industry Co., Ltd., trade name: EE65C) containing an inorganic chemical foaming agent relative to a polypropylene resin composition (inorganic chemical foaming) The amount of the actual component of the agent was about 1.6 parts by mass). The composition of the obtained polypropylene resin composition is shown in Table 1. Then, using a injection molding machine (manufactured by Ube Industries, Ltd., device name MD 350 S-III), core back injection foam molding is performed under the following conditions, and a plate-like foam molded body having a surface covered with a skin layer is obtained. Obtained.
Cavity size: Vertical 400 mm, Horizontal 200 mm, Thickness 1.4 mm
Gate: Cavity center 1 point direct gate Injection temperature: 210 ° C
Mold surface temperature: 45 ° C
Mold clearance after completion of foaming process: 2.8 mm
Moving speed setting of molding machine: 200 mm / s (The setting value is the speed of the ball screw, actual moving speed is about 20 mm / s)
Mold cavity clearance (L0) at injection: 1.4 mm
Expansion ratio: 2.0 times Delay time: 1.5 seconds Injection speed: 140 mm / s
Initial thickness (f ') before foaming: 1.4 mm

  The thickness (2s + f) of the obtained plate-like foam molded article was 2.8 mm, the thickness (s) of the skin layer was 346 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 25%.

Example 2
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the delay time was changed to 1.9 seconds. The thickness (2s + f) of this plate-like foam molded article was 2.8 mm, the thickness (s) of the skin layer was 404 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 29%.

Example 3
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the initial thickness (f ') was changed to 1.0 mm and the delay time to 0.5 seconds. The thickness (2s + f) of this plate-like foam-molded article was 2.0 mm, the thickness (s) of the skin layer was 281 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 28%.

Example 4
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the expansion ratio was changed to 1.9 times, the delay time to 1.9 seconds, and the injection speed to 160 mm / s. The thickness (2s + f) of this plate-like foam molded article was 2.7 mm, the thickness (s) of the skin layer was 402 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 30%.

Example 5
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the expansion ratio was changed to 1.9 times and the delay time to 1.9 seconds. The thickness (2s + f) of this plate-like foam molded article was 2.7 mm, the thickness (s) of the skin layer was 389 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 29%.

Example 6
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the expansion ratio was changed to 1.9 times, the delay time to 1.7 seconds, and the injection speed to 100 mm / s. The thickness (2s + f) of this plate-like foam-molded article was 2.7 mm, the thickness (s) of the skin layer was 396 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 29%.

Example 7
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the expansion ratio was changed to 1.9 times and the injection speed was changed to 60 mm / s. The thickness (2s + f) of this plate-like foam-molded article was 2.7 mm, the thickness (s) of the skin layer was 393 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 29%.

Example 8
The procedure of Example 1 was repeated except that the component mixture ratio of the resin composition was changed to the ratio described in Table 1 (talc composition), the foaming ratio was changed to 2.1 times, and the delay time was changed to 2.0 seconds. Thus, a plate-like foam was obtained. The thickness (2s + f) of this plate-like foam-molded article was 3.0 mm, the thickness (s) of the skin layer was 419 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 28%.

Comparative Example 1
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the delay time was changed to 0 seconds. The thickness (2 s + f) of this plate-like foam molded article was 2.8 mm, the thickness (s) of the skin layer was 233 μm, and the ratio of the skin layer (2 s / (2 s + f) × 100) was 17%.

Comparative Example 2
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the initial thickness (f ') was changed to 1.6 mm and the delay time was changed to 0.5 seconds. The thickness (2s + f) of this plate-like foam molded article was 3.2 mm, the thickness (s) of the skin layer was 272 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 17%.

Comparative Example 3
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the expansion ratio was changed to 2.2 and the delay time to 0.5 seconds. The thickness (2s + f) of this plate-like foam-molded article was 3.1 mm, the thickness (s) of the skin layer was 255 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 16%.

Comparative Example 4
A plate-like foam molded article was obtained in the same manner as in Example 8 except that the expansion ratio was changed to 2.3 times and the delay time was changed to 0 seconds. The thickness (2s + f) of this plate-like foam molded article was 3.2 mm, the thickness (s) of the skin layer was 246 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 15%.

Comparative Example 5
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the component mixture ratio of the resin composition was changed to the ratio described in Table 1 and the delay time was changed to 0 seconds. The thickness (2s + f) of this plate-like foam-molded article was 2.8 mm, the thickness (s) of the skin layer was 242 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 17%.

Comparative Example 6
A plate-like foam molded article was obtained in the same manner as in Example 1 except that the delay time was changed to 0.5 seconds. The thickness (2s + f) of this plate-like foam-molded product was 2.8 mm, the thickness (s) of the skin layer was 264 μm, and the ratio of the skin layer (2s / (2s + f) × 100) was 19%.

<Evaluation of impact resistance>
Charpy impact test, Izod impact test, falling ball test and puncture impact test are generally used as methods for evaluating the impact resistance of molded articles, but basically, materials with high elongation generally have high impact properties. As it is known, the breaking elongation of the tensile test was used as the evaluation index this time. That is, the nominal strain at break according to JIS K7162 of the foam molded articles obtained in the above Examples and Comparative Examples was measured under the following conditions. The results are shown in Tables 1 and 2. Moreover, the graph which shows the relationship between the ratio of the total thickness of the skin layer in Examples 1 to 7 and Comparative Examples 1 to 3 and Example 8 and Comparative Example 4 in which the resin compositions are the same and the tensile strain at break. The graph is shown in FIG.
Test specimen: JIS K7139 type A2, dumbbell (punched)
Total length of dumbbell 170 mm, width 10 mm of parallel part × length 60 mm × thickness of molded body Tensile speed: 50 mm / min Distance between chucks: 115 mm

  As shown in Tables 1 and 2, the foam molded articles of Examples 1 to 8 in which the ratio (2 s / (2 s + f) × 100) of the total thickness (2 s) of the skin layer is 20% have high tensile rupture nominal strain. The foam molded article was excellent in impact resistance. On the other hand, the foam molded articles of Comparative Examples 1 to 6 in which the ratio is less than 20% had a low tensile break nominal strain. In particular, it can be understood from the graph of FIG. 1 that when the ratio is 20% or more, the nominal strain at break is sharply increased.

  The foam molded article of the present invention has a good appearance, is light in weight, and is excellent in rigidity and impact resistance, and therefore, can be suitably used, for example, in parts for automobile interior and exterior.

Claims (8)

In a foam molded article having a foamed resin portion whose surface is covered with a skin layer,
The average thickness (s = (s ₁ + s ₂ ) / 2) of the thickness (s ₁ ) of the skin layer on one side and the thickness (s ₂ ) of the skin layer on the opposite side is 250 to 600 μm,
The total thickness (2s + f) of the total thickness (2s = s ₁ + s ₂ ) of the skin layer on one side and the opposite side and the thickness (f) of the foamed resin portion is 1.5 to 4.0 mm,
A ratio of the total thickness (2s) of the skin layer to the total thickness (2s + f) (2s / (2s + f) × 100) is 20 to 70%.   The foamed molded article according to claim 1, wherein an initial thickness (f ') before foaming of the foamed molded article is 0.7 to 2.0 mm.   The foamed molded article according to claim 1 or 2, which comprises a polypropylene resin composition. The polypropylene resin composition is
Propylene / ethylene block copolymer (A) 65 to 85 parts by mass,
15 to 30 parts by mass of ethylene / α-olefin copolymer (B) having a density of 0.86 to 0.92 g / cm ³ and a melt flow rate (190 ° C., 2.16 kg load) of 1 to 50 g / 10 min ,
0 to 5 parts by mass of the inorganic filler (C) [The total of component (A), component (B) and component (C) is 100 parts by mass. ]
The foamed molded article according to claim 3, comprising Propylene-ethylene block copolymer (A) is
N-decane insoluble part (Dinsol) 70-95 mass% in 23 ° C whose melt flow rate (230 ° C, 2.16 kg load) is 50-200 g / 10 min, and
5-30 mass% of n-decane-soluble parts (Dsol) at 23 ° C. having an intrinsic viscosity [η] of 5-10 dl / g
The foamed molded article according to claim 4, comprising   The molded foam according to any one of claims 1 to 5, which is an injection molded foam.   A method for producing a foam molded article according to any one of claims 1 to 6, wherein core back injection foam molding is performed.   The method for producing a foam molded article according to claim 7, wherein core back injection foam molding is performed under the conditions of an initial thickness (f ') of 0.7 to 2.0 mm and a delay time of 0 to 4 seconds.

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