JP2005097389A - Olefinic resin composition for foam-molding and foamed article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an olefinic resin composition which is used for foam-molding and gives foamed articles having high expansion ratios. <P>SOLUTION: [1] This olefinic resin composition for foam-molding is characterized by having at least one crystallization exothermic peak in a DSC crystallization exothermic curve obtained by measuring with a differential scanning calorimeter (DSC), while cooling from 200°C to 40°C at a rate of 10°C/min, satisfying the expression: Tc1-Tc2≥12°C (Tc1 is 2% crystallization temperature; Tc2 is 98 % crystallization temperature), and has melt tension of ≥0.5 g. [2] The foamed article is characterized by melting the resin composition to obtain the melted resin composition, mixing the melted resin composition with a foaming agent to obtain the mixture, and then foaming and molding the mixture. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an olefin resin composition for foam molding.

  Conventionally, foams made of olefin resin have been widely used for automobile parts, home appliance parts, etc. for the purpose of weight reduction, high rigidity and shock absorption. From the viewpoint of weight reduction, foaming with a high expansion ratio is used. Body development is desired.

In order to improve the foamability and obtain a foam having a high expansion ratio, it is known that the melt tension of the molten resin should be increased.
For example, a foam obtained by using a modified polypropylene resin composition (melt tension: 3 to 20 g) having a high melt tension obtained by melt-kneading a polypropylene resin and peroxydicarbonate is known (patent) Since the crystallization temperature range (Tc1-Tc2 described later) of the resin composition is 10 ° C., the foam has a foaming ratio of about 2, and a resin that gives a foam with a high foaming ratio. Development of a composition has been desired.

JP 2002-53714 A

  An object of the present invention is to provide an olefin resin composition for foam molding which gives a foam having a high expansion ratio.

  As a result of intensive studies to find an olefin-based resin composition for foam molding that can solve the above-described problems, the present inventors have found that a resin composition containing an olefin-based resin having a crystallization temperature range of 12 or more. The product has been found to give a foam with a high expansion ratio, and the present invention has been completed.

That is, the present invention relates to the following [1] to [6].
[1] In a DSC crystallization exothermic curve obtained when measured by a differential scanning calorimeter (DSC) with a temperature lowered from 200 ° C. to 40 ° C. at 10 ° C./min, it has at least one crystallization exothermic peak, Tc1 is a temperature at which 2% crystallization is performed, Tc2 is a temperature at which 98% crystallization is performed, and Tc1−Tc2 ≧ 12 ° C. is satisfied, and an olefin resin having a melt tension of 0.5 g or more is contained. An olefin resin composition for foam molding.
[2] The resin composition according to [1], wherein the olefin resin is a polypropylene resin.
[3] A molten resin composition is obtained by melting the resin composition according to [1] or [2], a foaming agent is mixed with the molten resin composition to obtain a mixture, and the mixture is obtained by foam molding. A foam characterized in that
[4] The foam according to [3], wherein the foaming agent is carbon dioxide in a supercritical state and / or nitrogen in a supercritical state.
[5] The foam according to [3] or [4], wherein the molten resin composition and the foaming agent are mixed in an injection machine cylinder.
[6] The foam according to [3] to [5], which has a skin layer and has an expansion ratio of 1.5 times or more.

  According to the present invention, it is possible to provide an olefin-based resin composition for foam molding that gives a foam having a high expansion ratio.

  The olefin-based resin of the present invention has at least one exothermic peak in a DSC crystallization exothermic curve obtained when measured by a differential scanning calorimeter (DSC) at a rate of 10 ° C./min from 200 ° C. to 40 ° C. When Tc1 is the temperature for crystallization of 2% and Tc2 is the temperature for crystallization of 98%, it is necessary that Tc1-Tc2 ≧ 12 ° C., and preferably Tc1-Tc2 ≧ 13 ° C.

  When Tc1-Tc2 of the olefin resin is less than 12 ° C., the temperature range width showing crystallization behavior suitable for foaming becomes narrow, and a foam with a high expansion ratio cannot be obtained.

FIG. 1 is a diagram showing a crystallization exothermic curve. For the measurement of the crystallization exothermic curve, a differential scanning calorimeter (DSC) (DSC7 type manufactured by Perkin Elmer) is used.
The crystallization exothermic curve is obtained by melting about 200 mg of a 0.2 mm-thick hot-pressed sheet at 200 ° C. for 5 minutes in a nitrogen atmosphere and then lowering the temperature to 40 ° C. at a rate of 10 ° C./min. can get.
FIG. 2 is a diagram showing the relationship between integrated crystallization heat generation by DSC and temperature. In the crystallization heat generation curve of FIG. 1, the temperature at which crystallization starts from a completely melted state and heat generation starts and the crystallization is completely complete. FIG. 5 is a diagram showing a ratio of an integrated crystallization heat generation amount from the temperature lowering side with respect to a total crystallization heat generation amount between the temperatures when the base line is drawn with a tangent to a temperature that is completed and in an unmelted state.

The olefin resin used in the present invention is required to have a melt tension of 0.5 g or more, preferably 0.7 g or more, and 0.8 g or more in order to produce a foam having a high expansion ratio. It is more preferable that If the melt tension is less than 0.5 g, the foamed resin cannot hold the foaming agent, and the bubbles are torn or the cell membrane is torn off, making it impossible to produce a good foam.
The upper limit of the melt tension is not particularly limited, but is preferably 30 g or less in terms of molding. If it exceeds 30 g, the moldability tends to decrease.

Examples of the olefin resin used in the present invention include ethylene, propylene, butene-1, pentene-1, hexene-1, 3-methylbutene-1, 4-methylpentene-1, etc. An olefin homopolymer, a copolymer obtained by copolymerizing at least two types of monomers selected from the α-olefin, the α-olefin, and other unsaturated compounds copolymerizable with the α-olefin Examples thereof include a copolymer with a monomer and a mixture of two or more of these.
Examples of other unsaturated monomers include unsaturated carboxylic acids such as acrylic acid and methacrylic acid; unsaturated compounds such as methyl (meth) acrylate, 2-ethylhexyl acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate. Alkyl ester derivatives of carboxylic acids; unsaturated dicarboxylic acids or acid anhydrides such as fumaric acid, maleic acid, maleic anhydride, itaconic acid; acrylamide, N- (hydroxymethyl) acrylamide, glycidyl (meth) acrylate, acrylonitrile, methacrylonitrile And unsaturated carboxylic acid or unsaturated dicarboxylic acid derivatives such as mono- or diethyl ester of maleic acid, N-phenylmaleimide, N, N′-metaphenylene bismaleimide, and the like.
Among olefin resins, polypropylene resins are preferably used.

Examples of the polypropylene resin include a propylene homopolymer, a copolymer of propylene and at least one selected from the group consisting of ethylene and an α-olefin having 4 to 12 carbon atoms. The homopolymer or copolymer may be used alone or in combination of two or more. Examples of the α-olefin having 4 to 12 carbon atoms include 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene.
A copolymer of propylene and at least one selected from the group consisting of ethylene and an α-olefin having 4 to 12 carbon atoms is a repeating unit derived from propylene (hereinafter sometimes referred to as “propylene unit”). A copolymer containing at least 50% by weight with respect to 100% by weight of the copolymer is preferable.
By selecting the amount of repeating units derived from ethylene or an α-olefin having 4 to 12 carbon atoms in the copolymer, the flexibility and impact resistance of the copolymer can be controlled.
Moreover, when this copolymer has 2 or more types of repeating units other than a propylene unit, it is preferable that the total amount of repeating units other than the propylene unit is 35 weight% or less.
Specific examples of the polypropylene resin include (i) a propylene homopolymer, (ii) a random copolymer of propylene and ethylene, (iii) a random copolymer of propylene and an α-olefin, and (iv) propylene. And a random copolymer of ethylene and α-olefin, and (v) a block copolymer of propylene and ethylene. Here, as an alpha olefin, a C4-C12 alpha olefin is mentioned.
The melt flow rate (MFR) measured based on JIS K6758 of the polypropylene resin is preferably 1 to 100 g / 10 min, more preferably 5 to 100 g / 10 min, and 8 to 100 g from the viewpoint of moldability. More preferably, it is / 10 minutes.

The method for producing the olefin resin used in the present invention is not particularly limited.
Examples of a method for producing a polypropylene resin, which is a typical example of an olefin resin, include a method in which the polymerization operation is performed in two or more stages. The production method comprises polymerizing a monomer having propylene as a main component in the first step to produce a crystalline polypropylene polymer (I) having an intrinsic viscosity of 5 dl / g or more as an ultrahigh molecular weight component; This is a method for continuously producing a crystalline polypropylene polymer (II) having an intrinsic viscosity of less than 3 dl / g by polymerizing a monomer mainly composed of propylene. From the viewpoint of melt viscosity, the polypropylene resin into which the ultrahigh molecular weight component obtained by such a method is introduced has a content of the polymer (I) of 0.05% by weight or more and less than 35% by weight, and the intrinsic viscosity of the entire resin. It is preferable that it is less than 3 dl / g and Mw / Mn is less than 10.

In addition, as a method for producing a polypropylene resin, for example, a method of introducing long chain branching by crosslinking with a low level of radiation described in JP-A-62-1121704, a polypropylene resin and a radical polymerizable monomer Examples thereof include a method of reacting a radical initiator and a method of mixing a polypropylene resin and a radical initiator under temperature conditions such that the main chain of the resin does not break preferentially.
The polypropylene resin preferably has a branched structure mainly having a long chain branch at the end thereof.

In the present invention, the olefin resin typified by the polypropylene resin may be used alone or mixed with an olefin resin not having a specific crystallization temperature range and a specific melt tension. It may be used.
When the resin is mixed, examples of the mixing method include dry blending and kneading with a single screw or twin screw extruder.

As long as the purpose of the present invention is not impaired, other resins and / or elastomers may be appropriately added to the olefin resin used in the present invention depending on applications.
Specifically, low-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, an α-olefin copolymer having 4 to 12 carbon atoms, an α-olefin copolymer, Hydrogen of propylene-α-olefin copolymer having 4 to 12 carbon atoms, ethylene-propylene-α-olefin copolymer having 4 to 12 carbon atoms of α-olefin, and styrene-butadiene diblock copolymer Additive, hydrogenated styrene-butadiene-styrene triblock copolymer, hydrogenated styrene-isoprene diblock copolymer, hydrogenated styrene-isoprene-styrene triblock copolymer, ethylene-ethyl acrylate Examples thereof include a copolymer, an ethylene-vinyl acetate copolymer, and polybutene. These resins and / or elastomers may be used alone or as a mixture of two or more.

  Resins and / or elastomers other than these olefinic resins may be added for the purpose of controlling the crystallization temperature range and the melt tension.

  The olefin-based resin composition of the present invention includes talc, mica, clay, calcium carbonate, aluminum hydroxide, magnesium hydroxide, wollastonite, barium sulfate, glass fiber, and carbon fiber as long as the object of the present invention is not impaired. Further, inorganic fillers such as silica, calcium silicate, potassium titanate, and wollastonite may be contained. The above inorganic fillers may be used alone or in combination of two or more.

Moreover, the olefin resin composition of the present invention may further contain various additives as long as the object of the invention is not impaired.
Specific additives include phenolic, organic phosphite, phosnite, etc. organic phosphorus, thioether and other antioxidants; hindered amines and other thermal stabilizers; benzophenone, benzotriazole, benzoate, etc. UV absorbers; nonionic, cationic, anionic and other antistatic agents; bisamides, waxes, organometallic salt-based dispersants; alkaline earth metal salt carboxylates, etc .; amides -Based, wax-based, organometallic salt-based, ester-based lubricants; oxide-based, hydrotalcite-based decomposing agents; hydrazine-based, amine-based metal deactivators; bromine-containing organic-based, phosphoric acid-based, three Flame retardants such as antimony oxide, magnesium hydroxide, red phosphorus; organic pigments; inorganic pigments; organic fillers; inorganic and organic antibacterial agents such as metal ions, organic phosphorus Systems, like crystal nucleating agent such as sorbitol based compounds.

The olefin resin composition of the present invention can be foamed by melting, mixing with a foaming agent and foam molding.
The foaming agent used by this invention is not specifically limited, Well-known things, such as a chemical foaming agent and a physical foaming agent, can be used.

The chemical foaming agent is not particularly limited as long as it does not decompose below the melting temperature of the olefinic resin and decomposes or reacts above the melting temperature of the olefinic resin. Or two or more of them may be used in combination.
Examples of the inorganic compound include hydrogen carbonates such as sodium hydrogen carbonate, ammonium carbonate, and the like.
Examples of the organic compound include polycarboxylic acid, azo compound, sulfone hydrazide compound, nitroso compound, p-toluenesulfonyl semicarbazide, isocyanate compound and the like.
Examples of the polycarboxylic acid include citric acid, citric acid, oxalic acid, fumaric acid, and phthalic acid.
Examples of the azo compound include azodicarbonamide (ADCA).
Examples of the sulfone hydrazide compound include p-methylurethanebenzenesulfonyl hydrazide, 2,4-toluenedisulfonyl hydrazide, 4,4′-oxybisbenzenesulfonyl hydrazide, and the like.
Examples of the nitroso compound include dinitrosopentamethylenetetramine (DPT).

  Examples of the physical foaming agent include inert gases such as nitrogen and carbon dioxide, and volatile organic compounds other than chlorofluorocarbons such as butane and pentane. Two or more physical foaming agents may be used in combination, or a chemical foaming agent and a physical foaming agent may be used in combination.

  The foaming agent used in the present invention is preferably an inert gas. The inert gas is preferably an inorganic substance which is gaseous at normal temperature and pressure and does not show reactivity with the target resin and does not cause deterioration of the resin. Examples of the inert gas include carbon dioxide, nitrogen, argon, neon, helium, oxygen, and the like. These may be used alone or in combination of two or more. Among these, carbon dioxide, nitrogen, and a mixture thereof are preferably used because they are inexpensive and highly safe, and supercritical carbon dioxide, supercritical nitrogen, and a mixture thereof are more preferably used.

  The foam molding method is not particularly limited as long as the olefin resin is used. Specifically, for example, known methods such as injection foam molding, press foam molding, extrusion foam molding, stampable foam molding, and heat foam molding can be employed.

  Among the foam molding methods, injection foam molding is the same as injection foam molding, in which a molten resin in which an inert gas is dissolved as a foaming agent is filled into a mold cavity of an injection molding apparatus, and the same melting is performed in the mold. In the process of foaming the resin and then cooling and solidifying the foamed resin to obtain a foamed molded product, a process of injecting the molten resin and forming a skin layer is included. It is preferable because a foam can be formed.

The foaming method by injection foam molding is not particularly limited. For example, immediately after the filling of the resin containing the foaming agent into the mold cavity, all of the cavity volume is filled with the resin, and the resin of the resin accompanying cooling is reduced. A method of expanding the foam volume by expanding the foaming agent gas (full pack method), injecting a resin containing a foaming agent with a volume smaller than the volume of the mold cavity, and expanding the foaming agent gas to mold cavity Fill the resin with foam (short shot method), inject the resin containing the foaming agent into the mold cavity, then recede the cavity wall surface of the mold to enlarge the cavity volume, A method of expanding and foaming the resin in the mold (core back method), attaching a hydraulic device to the mold, injecting a resin containing a foaming agent into the mold cavity, and filling the resin with a hydraulic device The cavity walls of the mold and a method of foaming the partially retracted so the resin in the mold to inflate the gas blowing agent.
In the present invention, a foam having a skin layer can be easily obtained, and the foaming agent is mixed and dissolved in the mold cavity of the injection molding apparatus from the viewpoint that the foaming ratio of the entire foam can be easily controlled. The core back method is preferred in which the molten resin is filled, and after filling the molten resin, the mold cavity volume is expanded to foam the molten resin, and then the foamed resin is cooled and solidified to obtain a foam.
In addition, immediately after the injection of the resin containing the foaming agent into the mold cavity, the entire cavity volume is filled with the resin, and the shrinkage volume of the resin accompanying the cooling is reduced by expanding the foaming agent gas and foaming. After forming the layer, expand the mold cavity volume to increase the expansion ratio, or inject a resin containing a foaming agent into the mold cavity, and then the cavity wall surface of the mold from the target foam. In order to reduce the volume of the mold, the mold wall is retracted by a small amount to expand the cavity volume, the foaming agent gas is expanded to expand the resin in the mold, and the mold cavity volume is further expanded. Thus, a method of increasing the expansion ratio is also preferably used.

  There is no particular limitation on the reduction / expansion of the mold cavity volume during filling of the resin containing the foaming agent in the mold cavity. For example, the mold cavity volume is kept constant from the start of filling of the molten resin to the completion of filling. Alternatively, the mold cavity volume at the start of filling the molten resin and at the completion of filling may be different.

  The injection foam molding method may be performed in combination with any method such as gas assist molding, melt core molding, insert molding, and two-color molding.

  Any known method may be used for mixing the olefin resin and the foaming agent in the present invention, but nitrogen and / or carbon dioxide is injected into the cylinder of the injection molding apparatus in a supercritical state as the foaming agent. Thus, a method of mixing, dispersing, and dissolving the molten resin and nitrogen and / or carbon dioxide is preferable from the viewpoint of reducing the molding cycle, and the foam has a uniform foamed state as a whole.

  When nitrogen and / or carbon dioxide in a supercritical state is used as a foaming agent, the gas has a high solubility rate in the resin, and the physical foaming agent can be uniformly diffused in the resin in a short time. Due to the effect of increasing the number of cells, a foam having a good foam cell structure can be obtained. Furthermore, since supercritical nitrogen and / or carbon dioxide as a foaming agent has high solubility in the resin, a large amount of foaming agent can be contained in the resin, and a foam with a high foaming ratio can be obtained. Preferably used.

The foam thus obtained is not particularly limited as long as the olefin resin is used, and the shape thereof is not particularly limited, and may be any known shape.
The foam preferably has a skin layer in order to be lightweight and excellent in rigidity and to have high added value such as shock absorption. When it does not have a skin layer, it tends to be difficult to achieve both weight reduction and high rigidity.

  The foam is more preferably composed of three layers of a skin layer, a low foam layer, and a high foam layer from the viewpoint of achieving both weight reduction and high rigidity.

  The foaming ratio of the foam is determined as a value obtained by measuring the specific gravity of the foam with a specific gravity meter of the foam and dividing the specific gravity of the unfoamed material by the specific gravity of the foam, and is preferably 1.5 times or more. For weight reduction, it is more preferably 2.0 times or more.

  The foam does not have to have the skin layer as described above, and the foaming ratio is not required to be 1.5 times or more, and the main part as the molded body is composed of the parts as described above. Just do it. Further, depending on the purpose of use of the foam, such a foamed part or non-foamed part may be integrally attached with another part made of the same material or a different material such as metal or wood. Furthermore, the sheet | seat and film which consist of an olefin resin, or the woven fabric and the skin material of an unemployed cloth ridge may be bonded by the desired position of the foam surface.

The olefin resin composition for foam molding of the present invention has the melt tension necessary for a wide molding temperature range and a high foaming ratio, is excellent in molding processability, is lightweight and rigid, and has high impact absorption and the like. It is possible to provide a foam with added value.
The foam can be suitably used for applications such as automobile parts, home appliance parts, other industrial parts, and daily necessities, taking advantage of its characteristics.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, it cannot be overemphasized that this invention is not what is limited by an Example.

[Evaluation methods]
Melt flow rate (MFR) (Unit: g / 10 min)
The analytical values in the examples were determined by the following method.
In accordance with JIS K7210, a resin mainly composed of a repeating unit derived from propylene was measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kgf.
Melt tension (unit: g)
Using a melt tension measuring machine manufactured by Toyo Seiki Co., Ltd., orifice: L / D = 5 (D = 2 mm), extrusion speed: 10 mm / min, take-up speed: 3 m / min, measurement temperature: 230 ° C. . However, when the string-like strand was cut at a take-off speed of less than 3 m / min, the tension immediately before cutting was measured and this was used as the melt tension.
Foaming ratio The foaming ratio of the foam was measured by measuring the specific gravity with a hydrometer (Mirage Trading Co., Ltd., electronic hydrometer EW-200SG), and the specific gravity of the unfoamed material was divided by the specific gravity of the foam.
Maximum foaming ratio Using the method described later, the maximum foaming ratio of an olefin resin foamable foam was shown.
3 times expansion ratio Using the method described later, the foaming state of the foam having a expansion ratio of 3 times was observed with an optical microscope.
◎ Bubbles are uniform and no bubble breaks or tears.
○ Bubbles are partially uneven, but no bubbles are broken or broken.
Δ: The state of the bubbles is not uniform, and some of the bubbles are broken or broken.
× Bubbles are severely torn and torn, or blisters occur, and evaluation is impossible.
As evaluated.

Example 1
80/20 ratio of linear homopolypropylene Z101S (MFR 20 g / 10 min, manufactured by Sumitomo Mitsui Polyolefin) and homopolypropylene PF814 (BAFR MFR 2.2 g / 10 min) having a long chain branch as the olefin resin. The melt tension, crystallization characteristics, and MFR of the polypropylene-based resin obtained by mixing were measured. The results are shown in Table 1. Using the above polypropylene resin, as an injection molding machine, ES2550 / 400HL-MuCell manufactured by Engel Co., Ltd. (clamping force: 400 tons), the mold part dimensions shown in FIG. 3 are 290 mm × 370 mm, height 45 mm, Foam molding was carried out using a box-shaped shape having a thickness of 2 mmt (gate structure: valve gate, central part of the molded body). Nitrogen in a supercritical state was used as a foaming agent, and the pressure was supplied to 20 MPa in a cylinder of a molding machine (foaming agent injection amount 1.2%). The mixture of the olefin resin and the foaming agent is injected at a molding temperature of 200 ° C. and a mold temperature of 60 ° C. so as to be fully filled in the mold, and then the mold resin is broken until the foamed resin breaks or no longer foams. The maximum expansion ratio was evaluated by a method of retracting the cavity wall surface to enlarge the cavity volume and cooling and solidifying the foamed resin. Further, the cavity wall surface of the mold was retracted by 3.9 mm to enlarge the cavity volume, and the foamed resin was cooled and solidified to obtain a foam having a foaming ratio of 3 times, and the foamed state was evaluated. The results are shown in Table 1.

Example 2
As an olefin resin, linear homopolypropylene Z101S (MFR 20 g / 10 min manufactured by Sumitomo Mitsui Polyolefin) and homopolypropylene PF814 having long chain branching (MFR 2.2 g / 10 min manufactured by BASELL) at a ratio of 90/10 The maximum foaming ratio was evaluated in the same manner as in Example 1 except that the polypropylene-based resin obtained by mixing was used to obtain a resin foam having a foaming ratio of 3 times, and the foamed state was evaluated. . The results are shown in Table 1.

Comparative Example 1
The maximum foaming ratio was evaluated in the same manner as in Example 1 except that linear homopolypropylene Y101 (MFR 13 g / 10 min, manufactured by Sumitomo Mitsui Polyolefin Co., Ltd.) was used as the olefin resin. It was impossible to mold a resin foam having a foaming ratio of 3 times. The results are shown in Table 1.

Comparative Example 2
Evaluation of the maximum expansion ratio was carried out in the same manner as in Example 1 except that linear propylene-ethylene random copolymer Z144 (MFR 20 g / 10 min, manufactured by Sumitomo Mitsui Polyolefin Co., Ltd.) was used as the olefin resin. A resin foam having an expansion ratio of 3 times was obtained, and the foamed state was evaluated. The results are shown in Table 1.

Comparative Example 3
As an olefin resin, linear homopolypropylene Z101S (Mitsui Sumitomo Polyolefin MFR 20 g / 10 min) and linear homopolypropylene D101 (Mitsui Sumitomo Polyolefin MFR 1 g / 10 min) are mixed at a ratio of 80/20. The maximum foaming ratio was evaluated in the same manner as in Example 1 except that the obtained polypropylene resin was used, and a foamed resin foam having a foaming ratio of 3 was obtained to evaluate the foamed state. The results are shown in Table 1.

It is a figure which shows the crystallization exothermic curve by DSC. It is a figure which shows the relationship between the integrated crystallization calorific value by DSC, and temperature. It is an external view of the molded object used at the time of preparation of a thermoplastic resin foam molded object.

Claims (6)

  In the DSC crystallization exotherm curve obtained when the temperature is measured at 10 ° C./min from 200 ° C. to 40 ° C. with a differential scanning calorimeter (DSC), it has at least one crystallization exothermic peak and 2% crystal Foam molding characterized by containing an olefin-based resin satisfying Tc1-Tc2 ≧ 12 ° C. and having a melt tension of 0.5 g or more, where Tc1 is the temperature to crystallize and Tc2 is the temperature to crystallize 98% Olefin-based resin composition.   The resin composition according to claim 1, wherein the olefin resin is a polypropylene resin.   It is obtained by melting the resin composition according to claim 1 or 2 to obtain a molten resin composition, mixing the molten resin composition with a foaming agent to obtain a mixture, and foaming and molding the mixture. Foam.   The foam according to claim 3, wherein the foaming agent is carbon dioxide in a supercritical state and / or nitrogen in a supercritical state.   The foam of Claim 3 or 4 which mixes a molten resin composition and a foaming agent within an injection machine cylinder. The foam according to claim 3, which has a skin layer and has an expansion ratio of 1.5 times or more.

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