JP2005126489A - Method for producing cross-linked polyolefin-based resin foam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a cross-linked polyolefin-based resin foam having excellent heat resistance and flexibility. <P>SOLUTION: This method for producing the cross-linked polyolefin-based resin foam, comprising twice irradiating with ionizing radiations a foamable resin molded article comprising a cross-linking auxiliary, a thermally decomposable foaming agent, and a polyolefin-based resin containing ≥30 wt.% of a polypropylene-based resin polymerized in the presence of a metallocene catalyst and having a number-average mol. wt. (Mn)/weight-average mol. wt. (Mw) ratio of ≤3.2 to cross-link the foamable resin molded article, and then thermally foaming the foamable resin molded article, is characterized in that the ratio of the gel fraction (A) of the molded article after the first irradiation of the ionizing radiations to the gel fraction (B) of the molded article after the second irradiation of the ionizing radiations exceeds 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for producing a crosslinked polyolefin resin foam having excellent heat resistance and flexibility.

Conventionally, the crosslinked polyolefin resin foam has been widely used as various heat insulating materials and sundries because of its flexibility and heat resistance, and recently, it is also used as an interior material for vehicles.

And in using the crosslinked polyolefin resin foam as a vehicle interior material,
Although molding is performed using a general-purpose molding method such as vacuum molding or stamping molding, in recent years, the interior of a vehicle has become complicated.

Therefore, when a crosslinked polyolefin resin foam is molded into a desired shape using a general-purpose molding method, the crosslinked polyolefin resin foam is greatly stretched or compressed, and as a result, the crosslinked polyolefin resin foam is broken or damaged. There was a problem that occurred.

Therefore, in order to improve the mechanical properties of the crosslinked polyolefin resin foam and prevent the crosslinked polyolefin resin foam from being broken or wrinkled, Patent Document 1 discloses a crystallinity of 60.
Polypropylene resin copolymerized with ethylene or butene within a range of ˜80%, polyethylene resin copolymerized with α-olefin having 4 or more carbon atoms, and homopolypropylene resin with crystal purity of 95% or more. 1 to resin and polyethylene resin
A crosslinked polyolefin resin foam obtained by foaming a polyolefin resin composition characterized by comprising 7% by weight has been proposed.

However, as the amount of the polypropylene resin having a high crystallinity increases, the above-mentioned crosslinked polyolefin resin foam has a marked decrease in the elongation and flexibility of the foam, particularly at room temperature. Therefore, there is a problem that the amount of the polypropylene resin added is limited, and sufficient mechanical properties cannot be imparted to the crosslinked polyolefin resin foam.

Japanese Patent Laid-Open No. 10-45975 (Claims)

The present invention provides a method for producing a crosslinked polyolefin resin foam having excellent heat resistance and flexibility.

The method for producing a crosslinked polyolefin resin foam of the present invention is polymerized using a metallocene catalyst, and the ratio (Mw / Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) is 3.2.
Foaming resin molding by irradiating ionizing radiation in two portions to a foaming resin molding comprising a polyolefin resin containing 30% by weight or more of the following polypropylene resin, a crosslinking aid and a pyrolytic foaming agent. A method for producing a crosslinked polyolefin resin foam in which the foamed resin molded body is heated and foamed after the body is crosslinked, and the gel content of the foamable resin molded body after the first irradiation with ionizing radiation. The ratio between the ratio (A wt%) and the gel fraction (B wt%) of the foamable resin molded article after irradiation with the second ionizing radiation satisfies the following formula 1.
B / A> 1

The polyolefin resin constituting the crosslinked polyolefin resin foam is polymerized using a metallocene catalyst and the ratio of the number average molecular weight (Mn) to the weight average molecular weight (Mw) (Mw).
/ Mn) contains 30% by weight or more of a polypropylene resin having 3.2 or less.

The metallocene catalyst generally refers to a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds, and a bis (cyclopentadienyl) metal complex can be given as a representative example.

Specific examples of the metallocene catalyst used in the present invention include tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, platinum, and one or more cyclopentadienyl rings or analogs thereof. The compound which exists as a ligand (ligand) is mentioned.

Specific examples of the ligand include, for example, a cyclopentadienyl ring; a cyclopentadienyl ring substituted with a hydrocarbon group, a substituted hydrocarbon group, or a hydrocarbon-substituted metalloid group; a cyclopentadienyl oligomer ring; An indenyl ring; an indenyl ring substituted by a hydrocarbon group, a substituted hydrocarbon group, or a hydrocarbon-substituted metalloid group.

Examples of the hydrocarbon group substituted on the cyclopentadienyl ring or indenyl ring include, for example, a methyl group, an ethyl group, a propyl group, a butyl group, an amyl group, an isoamyl group, a hexyl group, an isobutyl group, a heptyl group, and an octyl group. , Nonyl group, decyl group, cetyl group, 2-ethylhexyl group, phenyl group and the like.

Further, transition metals include monovalent anion ligands such as chlorine and bromine, divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, in addition to the above π-electron unsaturated compounds. Aryl amide, phosphide, aryl phosphide and the like may be coordinated.

Examples of such metallocene catalysts include cyclopentadienyl titanium tris (dimethylamide) and methylcyclopentadienyl titanium tris (dimethylamide).
Bis (cyclopentadienyl) titanium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamidozirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamidohafnium dichloride, dimethylsilyltetramethylcyclopentadi Enyl-pn-butylphenylamidozirconium chloride, methylphenylsilyltetramethylcyclopentadienyl-tert-
Butyramide hafnium dichloride, indenyl titanium tris (dimethylamide),
Indenyl titanium tris (diethylamide), indenyl titanium tris (di-n
-Propylamide), indenyl titanium bis (di-n-butylamide) (di-n-propylamide) and the like.

The metallocene catalyst changes the type of metal and the structure of the ligand,
In combination with a cocatalyst, the catalyst acts as a catalyst during olefin polymerization.

Examples of the cocatalyst include methylaluminoxane (MAO) and boron compounds. The amount of the cocatalyst added is 10 to 10,000 with respect to the metallocene catalyst.
00 molar times are preferable and 50-5000 molar times are more preferable.

Examples of the olefin polymerization method using the metallocene catalyst include a solution polymerization method using an inert medium, a bulk polymerization method substantially free of an inert medium, and a gas phase polymerization method. Is preferably −100 to 300 ° C., and the polymerization pressure is from normal pressure to 1 × 1
0 ⁷ Pa is preferred.

The metallocene catalyst has the characteristic that the properties of the active sites are uniform, and each active site has the same activity. Therefore, the polymer polymerized using the metallocene catalyst has its molecular weight and molecular weight distribution. , The uniformity of composition and composition distribution is improved.

Therefore, the polypropylene resin obtained by polymerization using the metallocene catalyst has a narrow molecular weight distribution, and in the case of a copolymer, the copolymer component is introduced into the molecular weight component at an approximately equal ratio. Such a crosslinked polyolefin resin foam made of a polyolefin resin containing a polypropylene resin has a uniform cross-linking distribution and good tensile properties while preventing a decrease in elongation. In addition, as a polypropylene-type resin obtained by superposing | polymerizing using a metallocene catalyst as a polymerization catalyst, it is marketed with the brand name "WFX6" from Nippon Polychem, for example.

When the ratio (Mw / Mn) between the number average molecular weight (Mn) and the weight average molecular weight (Mw) in the polypropylene resin polymerized using the metallocene catalyst is large, the foamed resin molded product is irradiated with an electron beam. Since the normal temperature elongation after being reduced, it is limited to 3.2 or less, preferably 2.8 or less, more preferably 1.5 to 2.8, and particularly preferably 2.0 to 2.8.

In addition, when the melt index of the polypropylene resin polymerized using the metallocene catalyst and the ratio (Mw / Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) is 3.2 or less is high, Since the foamed resin molded article may not be sufficiently crosslinked, it is preferably 15 g / 10 min or less, and more preferably 10 g / 10 min or less. In addition, the melt index of a polypropylene-type resin means what was measured based on JISK7210.

Furthermore, when the density of the polypropylene resin polymerized using the metallocene catalyst and the ratio (Mw / Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) is 3.2 or less is high, While the normal temperature elongation of the polyolefin resin foam may decrease, if low,
Since the heat resistance of the cross-linked polyolefin resin foam may decrease, 0.87 to 0.9
2 g / cm ³ is preferred.

Here, in general, among polyolefin resins, polyethylene resins are suitable for crosslinking by ionizing radiation, and when ionizing radiation is irradiated multiple times, the gel fraction increases with irradiation of ionizing radiation. On the other hand, the polypropylene resin does not crosslink even when irradiated with ionizing radiation in the absence of a crosslinking aid, and is irradiated with ionizing radiation multiple times when a crosslinking aid is added. Although it is sometimes cross-linked by the first irradiation with ionizing radiation, it is considered that all or most of the crosslinking aid is consumed by the first irradiation with ionizing radiation. There is a tendency that it is not cross-linked by irradiation of radiation, or conversely, the gel fraction decreases.

Furthermore, when the crosslinked polyolefin resin foam is molded by a general-purpose molding method such as stamping molding, a polypropylene resin is added to the polyolefin resin constituting the crosslinked polyolefin resin foam from the viewpoint of heat resistance and strength. While it is necessary to contain more than a certain amount, the molten resin is in direct contact with the crosslinked polyolefin resin foam, so that it is necessary to improve the heat resistance of the surface portion of the crosslinked polyolefin resin foam.

On the other hand, it is polymerized using a metallocene catalyst as described above and has a number average molecular weight (
Unlike a conventional polypropylene resin, a polypropylene resin having a ratio (Mw / Mn) of Mn) to a weight average molecular weight (Mw) of 3.2 or less is less deteriorated by irradiation with ionizing radiation. In the case of irradiation with ionizing radiation divided into two, even when the second ionizing radiation is irradiated after most of the crosslinking aid is consumed by the first ionizing radiation irradiation, The gel fraction can be improved while suppressing the breakage of the resin molecular chain.

Therefore, in the present invention, 30% by weight or more of a polypropylene resin polymerized using a metallocene catalyst and having a ratio (Mw / Mn) of number average molecular weight (Mn) to weight average molecular weight (Mw) of 3.2 or less. By using the polyolefin-based resin to be contained, the foamable resin molded body in which this polyolefin-based resin is added with a crosslinking aid and a thermal decomposable foaming agent is irradiated with ionizing radiation twice to be crosslinked. A polyolefin resin foam having excellent heat resistance and flexibility can be produced.

Here, content in a polyolefin resin of a polypropylene resin polymerized using a metallocene catalyst and having a ratio (Mw / Mn) of a number average molecular weight (Mn) to a weight average molecular weight (Mw) of 3.2 or less If the amount is too small, the heat resistance and flexibility of the resulting crosslinked polypropylene resin foam are reduced, so the amount is limited to 30% by weight or more, and preferably 40% by weight or more.

The polyolefin resin used in the present invention is polymerized using the metallocene catalyst described above, and the ratio (Mw / Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) is 3.
In addition to the polypropylene resin that is 2 or less, other polypropylene resins and polyethylene resins may be contained.

Other polypropylene resins are not particularly limited as long as they are conventionally used in the production of foams, such as homopolypropylene, ethylene-propylene random copolymers, ethylene-propylene block copolymers, and the like. Is mentioned.

The polyethylene resin is not particularly limited as long as it has been conventionally used for the production of foams. For example, high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene. Linear low density polyethylene is preferable. In addition, a polyethylene-type resin may be used independently or may be used together.

And, if the content of the polypropylene resin in the polyolefin resin is small, the heat resistance of the resulting crosslinked polypropylene resin foam may be lowered, so that it is preferably 40% by weight or more, more preferably 45% by weight or more. Preferably, 50% by weight is particularly preferable, but if it is too much, the flexibility of the crosslinked polyolefin resin foam may be lowered, so 90% by weight or less is preferable, and 80% by weight or less is more preferable. The polypropylene resin referred to here is a polypropylene resin polymerized using a metallocene catalyst and having a ratio (Mw / Mn) of number average molecular weight (Mn) to weight average molecular weight (Mw) of 3.2 or less. And all other polypropylene resins including other polypropylene resins.

Furthermore, if the melt index of the polyolefin resin is small, it may be difficult to produce a foamed resin molded product, whereas if it is large, the heat resistance of the crosslinked polyolefin resin foam may be reduced. 0.5 to 70 g / 10 min is preferable, 1.5 to 50
g / 10 min is more preferable, and 2 to 40 g / 10 min is particularly preferable. In addition, the melt index of polyolefin resin means what was measured based on JISK7210.

The crosslinking aid is not particularly limited as long as it is conventionally used in the production of foams. For example, divinylbenzene, trimethylolpropane trimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, trimellitic acid triallyl ester, triallyl isocyanurate, ethyl vinylbenzene, neopentyl glycol dimethacrylate, 1,2,4-benzenetricarboxylic acid triallyl ester, 1,6-hexanediol Examples include dimethacrylate, lauryl methacrylate, stearyl methacrylate, diallyl phthalate, diallyl terephthalate, diallyl isophthalate, and the like. These may be used alone or in combination.

If the addition amount of the crosslinking aid is small, it may not be possible to impart the desired gel fraction to the foamable resin molded article, but at most, the effect of adding the crosslinking aid should not change. Therefore, 2 to 30 parts by weight is preferable with respect to 100 parts by weight of the polyolefin resin, and 2.2
-20 parts by weight is more preferable, and 2.5-10 parts by weight is particularly preferable.

The pyrolytic foaming agent is not particularly limited as long as it has been conventionally used in the production of foams. For example, azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl Examples thereof include hydrazide and 4,4-oxybis (benzenesulfonylhydrazide), and these may be used alone or in combination.

When the amount of the pyrolytic foaming agent added is large, the foamable resin molded body may break during foaming. On the other hand, when the amount is small, the foamable resin molded body may not foam. 1 to 50 parts by weight is preferable with respect to parts by weight, and 4 to 25 parts by weight is more preferable.

Next, the method for producing a foamable resin molded article comprising the polyolefin-based resin, the crosslinking aid and the thermal decomposition-type foaming agent is not particularly limited. For example, the polymer is polymerized using a metallocene catalyst and has a number average molecular weight (Mn ) And a weight average molecular weight (Mw) ratio (Mw / Mn) of a polyolefin resin containing 30% by weight or more of a polypropylene resin having a ratio of 3.2 or less, a crosslinking aid and a thermally decomposable foaming agent. The resin composition is supplied to a general-purpose kneading apparatus such as an extruder, a Banbury mixer, and a roll, and melted and kneaded to obtain a foamed resin molded body having a desired shape, preferably a foamable resin sheet.

In addition, since the bubble diameter may vary when the thickness of the foamable resin sheet is large, it is preferably 3 mm or less, more preferably 2.5 mm or less, and particularly preferably 2 mm or less. Since there may be variations in diameter, 0.5 mm or more is preferable,
0.7 mm or more is more preferable.

The foamable resin composition includes a cell-forming agent such as calcium carbonate, talc, clay, and magnesium oxide; 2,6-di-t-butyl, as long as the physical properties of the crosslinked polyolefin resin foam are not impaired. -Antioxidants such as phenol-based antioxidants such as p-cresol, phosphorus-based antioxidants, amine-based antioxidants, sulfur-based antioxidants such as dilauryl thiopropionate; metal hazards such as methylbenzotriazole Inhibitors; flame retardants such as halogen flame retardants such as hexabromodiphenyl ether and decabromodiphenyl ether, phosphorus flame retardants such as ammonium polyphosphate and trimethyl phosphate; fillers; antistatic agents; stabilizers; additives such as pigments May be added.

Then, the foamable resin molded body is irradiated with ionizing radiation twice, that is, the foamable resin molded body is irradiated separately or simultaneously with ionizing radiation having different acceleration voltages. Is crosslinked. Examples of ionizing radiation include α-rays, β-rays, γ-rays, and electron beams, with electron beams being preferred.

The procedure for irradiating the foaming resin molding with ionizing radiation includes the gel fraction (A wt%) of the foaming resin molding after the first irradiation with ionizing radiation and the second ionizing radiation irradiation. It is necessary to irradiate with ionizing radiation so that the gel fraction (B weight%) of the foamable resin molded body afterwards satisfies the following formula 1, and the ionizing radiation may be irradiated so as to satisfy the following formula 2. Preferably, it is more preferable to irradiate ionizing radiation so as to satisfy the following formula 3.
B / A> 1 Formula 1
B / A> 1.01 Formula 2
B / A> 1.05 Formula 3

In addition, the gel fraction of a foaming resin molding says what was measured in the following way. That is, W ₀ g of the foamed resin molded body was weighed, immersed in xylene at 120 ° C. for 24 hours, the insoluble matter was filtered through a 200 mesh wire mesh, and the residue on the wire mesh was vacuum dried to dry residue. Weight (W ₁ g
) And was calculated by the following formula.
Gel fraction (% by weight) = (W ₁ / W ₀ ) × 100

And even if the gel fraction of the foamable resin molding after the first irradiation with ionizing radiation is low or high, the heat resistance or flexibility of the resulting crosslinked polyolefin resin foam may be lowered. Therefore, it is preferably 20 to 70% by weight, more preferably 25 to 65% by weight,
˜63% by weight is particularly preferred.

As a specific procedure for crosslinking the foamable resin molded product, an acceleration voltage lower than the acceleration voltage of this ionizing radiation (high-voltage ionizing radiation) after the ionizing radiation is irradiated to the foamable resin molded product for the first time. It is preferable to crosslink the foamed resin molding by irradiating with ionizing radiation (low voltage ionizing radiation). In addition, when a foaming resin molding is a sheet form, it is preferable to irradiate ionizing radiation from both surfaces.

As described above, first, the foamable resin molded body is irradiated with high voltage ionizing radiation to crosslink the entire foamable resin molded body, and then the foamable resin molded body is irradiated with low voltage ionizing radiation. By further crosslinking only the part, it is possible to obtain a crosslinked polyolefin resin foam having excellent flexibility and heat resistance, particularly excellent heat resistance of the surface part, and this crosslinked polyolefin resin foam is particularly suitable for stamping. It is excellent for molding.

The stamping molding means that a cross-linked polyolefin resin foam is provided by disposing a cross-linked polyolefin resin foam in a cavity formed between a male and female mold and supplying a molten thermoplastic resin into the cavity. And a thermoplastic resin are molded into a desired shape while being laminated and integrated.

Here, if the acceleration voltage of the high-voltage ionizing radiation is small, the transmission of the high-voltage ionizing radiation in the thickness direction of the foamable resin molded product becomes insufficient, and the degree of crosslinking inside the foamable resin molded product is insufficient. On the other hand, if it is large, the high voltage ionizing radiation may pass through the surface portion of the foamable resin molded article, and the crosslinking of the surface portion of the foamable resin molded article may be insufficient. ~ 1
200 kV is preferable, and 700 to 1000 kV is more preferable.

And the irradiation dose of high voltage ionizing radiation improves the residual rate of the crosslinking aid in the foamable resin molding after irradiating the foamable resin molding with high voltage ionizing radiation. In order to efficiently perform crosslinking of the foamable resin molded body by irradiation with radiation, 10 Mrad
The following is preferable, 5 Mrad or less is more preferable, and 3 Mrad or less is particularly preferable. However, if it is too low, the foamable resin molded article may not be sufficiently crosslinked.
Mrad or higher is preferable, and 0.3 Mrad or higher is more preferable.

On the other hand, if the acceleration voltage of the low-voltage ionizing radiation is small, the transmission performance of the low-voltage ionizing radiation is lowered, and the surface portion of the foamable resin molded article may be insufficiently cross-linked. ,
The transmission performance of low-voltage ionizing radiation is so high that it may be cross-linked not only to the surface portion but also to the inside of the foamed resin molded article. Therefore, 100 to 300 kV is preferable, and 150 to 300 kV.
Is more preferable.

And, if the irradiation dose of the low-voltage ionizing radiation is small, the foamed resin molded article may not be sufficiently crosslinked, so 1 Mrad or more is preferable, 1.5 Mrad or more is more preferable, and 2 Mrad or more is particularly preferable. However, if the amount is too large, the surface property of the resulting crosslinked polyolefin resin foam deteriorates.
d or less is more preferable, and 12 Mrad or less is particularly preferable.

Further, the elongation at break (C%) at 170 ° C. of the foam obtained by heating and foaming the foamable resin molded article after the first ionizing radiation was irradiated, and the second ionizing radiation. Elongation at break (D%) at 170 ° C. of a foam obtained by heating and foaming a foamable resin molded article after irradiation
The ratio (D / C) is preferably satisfied with the following formula 4 because a defect such as tearing may occur when the resulting crosslinked polyolefin resin foam is molded. Is more preferable, the following formula 6 is particularly preferably satisfied, and the following formula 7 is most preferably satisfied.
D / C> 0.70 Formula 4
D / C> 0.75 ... Formula 5
D / C> 0.80 ... Formula 6
D / C> 0.85 ... Formula 7

Here, the elongation at break at 170 ° C. of the foam obtained by heating and foaming the foamable resin molded product is JIS K676 for the foam obtained by heating and foaming the foamable resin molded product.
7, the elongation at break (a) was measured, and the measured elongation at break (a%)) was corrected based on the following formula.

Elongation at break (%) = Measured elongation at break (a) × (1 / (18 × b)) ^−1/3
However, b is the density of the foam (g / cm ³ ).

And, when the elongation at break (C%) at 170 ° C. of the foam obtained by heating and foaming the foamable resin molded article after the first ionizing radiation is irradiated is low, the crosslinked polyolefin type On the other hand, the stamping moldability of the resin foam may be lowered. On the other hand, if the resin foam is high, the surface of the cross-linked polyolefin resin foam may be roughened, so 100 to 500% is preferable.

The method for producing a crosslinked polyolefin resin foam of the present invention is polymerized using a metallocene catalyst, and the ratio (Mw / Mn) of the number average molecular weight (Mn) to the weight average molecular weight (Mw) is 3.2.
Foaming resin molding by irradiating ionizing radiation in two portions to a foaming resin molding comprising a polyolefin resin containing 30% by weight or more of the following polypropylene resin, a crosslinking aid and a pyrolytic foaming agent. A method for producing a crosslinked polyolefin resin foam in which the foamed resin molded body is heated and foamed after the body is crosslinked, and the gel content of the foamable resin molded body after the first irradiation with ionizing radiation. Since the ratio of the rate (A wt%) and the gel fraction (B wt%) of the foamable resin molded article after the second ionizing radiation irradiation satisfies the above-mentioned formula 1, The crosslinked polyolefin resin foam having the property and flexibility can be easily produced, and this crosslinked polyolefin resin foam can be accurately formed into a complicated shape without being broken or wrinkled by stamping molding. It can be.

In the method for producing a crosslinked polyolefin resin foam, the elongation at break at 170 ° C. of the foam obtained by heating and foaming the foamable resin molded article after the first irradiation with ionizing radiation ( C%) and the ratio (D / C) of the elongation at break (D%) at 170 ° C. of the foam obtained by heating and foaming the foamable resin molded article after the second ionizing radiation irradiation ) Satisfies the above formula 4, it is possible to easily produce a crosslinked polyolefin resin foam further excellent in heat resistance and flexibility.

(Example 1)
Polypropylene resin polymerized using a metallocene catalyst (trade name “WFX6” manufactured by Nippon Polychem, Mw / Mn: 2.8, density: 0.90 g / cm ³ ) 60 parts by weight, linear low density polyethylene ( Product name “ZF231” manufactured by Tosoh Corporation, melt index: 2.0 g
/ 10 minutes, density: 0.917 g / cm ³ ) 40 parts by weight, 3 parts by weight of divinylbenzene as a crosslinking aid, 13 parts by weight of azodicarbonamide as a pyrolytic foaming agent, 2 parts as an antioxidant
, 6-Di-t-butyl-p-cresol 0.3 part by weight and dilauryl thiopropionate 0.3 part by weight, and methylbenzotriazole 0.5 part by weight as a metal damage inhibitor And melt-kneaded at 185 ° C. to prepare a foamable resin sheet having a thickness of 1 mm.

An electron beam was irradiated on both surfaces of the obtained expandable resin sheet for 1.5 Mrad at an acceleration voltage of 800 kV, and the expandable resin sheet was crosslinked to obtain a first expandable resin sheet. Thereafter, both surfaces of the first foamable resin sheet were further irradiated with an electron beam at an acceleration voltage of 150 kV for 10 Mrad to crosslink the first foamable resin sheet to obtain a second foamable resin sheet. And the second foamable resin sheet is 25
It was heated and foamed at 0 ° C. to obtain a crosslinked polyolefin resin sheet having a density of 0.051 g / cm ³ .

Further, the first foamable resin sheet was heated to 250 ° C. and foamed to a density of 0.064 g / cm.
The first foamed sheet ³ and the second foamable resin sheet were heated to 250 ° C. and foamed to a density of 0.06.
A second foamed sheet of 8 g / cm ³ was obtained.

(Example 2)
The both sides of the foamable resin sheet were irradiated with an electron beam at an acceleration voltage of 800 kV for 4 Mrad, the foamable resin sheet was cross-linked to obtain a first foamable resin sheet, and an electron beam was further applied to both sides of the first foamable resin sheet. Was irradiated with 5 rad at an acceleration voltage of 250 kV, and the first foamable resin sheet was crosslinked to obtain the second foamable resin sheet. A two foam sheet was obtained.

(Comparative Example 1)
An electron beam was irradiated to both surfaces of the foamable resin sheet for 12 Mrad at an acceleration voltage of 800 kV, and the foamable resin sheet was crosslinked to obtain a first foamable resin sheet. Further, an electron beam was further applied to both surfaces of the first foamable resin sheet. Was irradiated with 0.5 Mrad at an acceleration voltage of 100 kV, and the first foamable resin sheet was crosslinked to obtain a second foamable resin sheet. And the 2nd foam sheet was obtained.

(Comparative Example 2)
As a polypropylene resin, a polypropylene resin (trade name “RB4” manufactured by Tokuyama Corporation)
10 ”, Mw / Mn: 4.1, melt index: 0.5 g / 10 min) in the same manner as in Example 1 except that the crosslinked polyolefin resin sheet, the first foamed sheet, and the second foamed sheet were used. Obtained.

The stamping moldability of the obtained crosslinked polyolefin resin sheet was measured in the following manner, the gel fraction of the first foamable resin sheet and the second foamable resin sheet, and the first foamed sheet and the second foamed sheet Table 1 shows the elongation at break at 170 ° C.

(Stamping formability)
A flat square test piece having a side of 150 mm was cut out from the crosslinked polyolefin resin sheet. Next, the test piece is placed between a pair of upper and lower press dies in the mold open state, and a polypropylene resin at 200 ° C. (melt index at 230 ° C .: 20 g / 1 on the lower mold).
(0 min) After supplying 20 g, the upper and lower molds were immediately closed at a pressure of 4.9 MPa for 5 seconds, and then the upper and lower molds were closed at a pressure of 0.98 MPa for 50 seconds.

Thereafter, water was passed through the upper and lower molds to cool the test piece, and then the upper and lower molds were opened to obtain a sheet-like molded product in which the polypropylene resin was laminated and integrated on the surface of the test piece.

The surface of the obtained molded product was visually observed, and stamping moldability was evaluated according to the following criteria.
○ ... No tearing or wrinkle was confirmed on the cross-linked polyolefin resin foam sheet (test piece)
It was.
×: Torn or wrinkle was confirmed on the crosslinked polyolefin resin foam sheet (test piece).

Claims (2)

A polyolefin-based resin containing 30% by weight or more of a polypropylene-based resin polymerized using a metallocene catalyst and having a ratio (Mw / Mn) of number average molecular weight (Mn) to weight average molecular weight (Mw) of 3.2 or less, After the foamable resin molded body composed of a crosslinking aid and a thermally decomposable foaming agent is irradiated twice with ionizing radiation to crosslink the foamable resin molded body, the foamable resin molded body is heated to foam. A method for producing a crosslinked polyolefin-based resin foam, the gel fraction (A wt%) of the foamable resin molded article after the first ionizing radiation irradiation and the second ionizing radiation irradiation. A method for producing a crosslinked polyolefin resin foam, characterized in that the ratio (B / A) to the gel fraction (B wt%) of the subsequent foamable resin molded article satisfies the following formula.
B / A> 1 Elongation at break (C%) at 170 ° C. of the foam obtained by heating and foaming the foamable resin molded article after the first ionizing radiation irradiation and the second ionizing radiation irradiation The ratio (D / C) to the elongation at break (D%) at 170 ° C. of the foam obtained by heating and foaming the foamed resin molded product after being satisfied the following formula: The manufacturing method of the crosslinked polyolefin resin foam of Claim 1.
D / C> 0.7