JP2002003631A - Crosslinked polyolefin resin foam, its manufacturing method and vehicular interior material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crosslinked polyolefin resin foam and its manufacturing method and a vehicular interior material using the crosslinked polyolefin resin foam having good heat-resistant, flexible and cushioning properties, hardly causing sheet break or resin leakage during forming, and free from pockmarked irregularity on the surface of a skin material after the forming. SOLUTION: The crosslinked polyolefin resin foam is characterized in comprising components consisting of 20-60 wt.% of polyethylene resin and 40-80 wt.% of polyolefin resin except polyethylene resin, wherein a melting energy of 140 deg.C or higher included in the melting energy per unit weight (heat quantity value per weight obtained from a melting peak area in differential scanning calorimetry) is 28-50 mJ/mg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosslinked polyolefin resin foam which is excellent in heat resistance and moldability and is preferably used for automobile interior materials and the like, a method for producing the same, and the use of the crosslinked polyolefin resin foam. Automobile interior materials.

[0002]

2. Description of the Related Art Conventionally, crosslinked polyolefin resin foams have been used in a wide range of fields as heat insulating materials, cushioning materials and the like. Particularly, in the field of automobiles, it is suitably used as a heat insulating cushion material for interior materials such as ceilings, doors, instrument panels, and cooler covers. In the automotive interior material application, a skin material such as a soft polyvinyl chloride resin sheet, a thermoplastic elastomer sheet, cloth, and synthetic leather is laminated on the crosslinked polyolefin resin foam to form a composite sheet. Forming is performed by molding, stamping, or the like to obtain a molded product having a desired shape. Here, the stamping molding is a molding method in which a molten thermoplastic resin for a core material is supplied to the crosslinked polyolefin-based resin foam surface of the composite sheet, followed by press molding.

However, when the above-mentioned composite sheet is formed, the cross-linked polyolefin-based resin foam may be broken at a corner portion of the formed product subjected to a strong force, or the foam of the cross-linked polyolefin-based resin foam may be broken. However, there is a problem that avatar-like irregularities are generated on the surface of the skin material due to breakage. In stamping molding, the molten thermoplastic resin for the core material breaks through the crosslinked polyolefin resin foam and penetrates into the foam. There is a problem that resin leakage occurs. Further, there is also a problem that the thickness of the crosslinked polyolefin-based resin foam does not recover after the molding process, and the flexibility and the cushioning property are reduced.
For this reason, foams used for automotive interior materials are required to have heat resistance, moldability, formability after molding, and the like.

[0004] In order to solve the above problems, for example, Japanese Patent Application Laid-Open No. 10-45975 discloses homopolypropylene 1 in which polypropylene in which ethylene or butene is copolymerized and polyethylene in which α-olefin is copolymerized.
A crosslinked polyethylene resin foam to which about 7% by weight has been added has been proposed.

[0005] However, the foam described in the above publication has problems in that elongation is insufficient, so that avatar-like irregularities occur on the surface of the skin material, and resin leakage occurs in stamping molding. There is also a problem that the cushioning property of the molded product is not sufficient.

[0006]

DISCLOSURE OF THE INVENTION The present invention is excellent in heat resistance, flexibility and cushioning property, hardly causes sheet breakage and resin leakage during molding, and has avatar-like irregularities on the surface of the skin material after molding. An object of the present invention is to provide a crosslinked polyolefin-based resin foam which does not occur and can be suitably used as an interior material for an automobile, a method for producing the same, and an interior material for an automobile using the crosslinked polyolefin-based resin foam.

[0007]

The crosslinked polyolefin resin foam of the present invention has a resin component of polyethylene resin 2
0 to 60% by weight and 40 to 80% by weight of a polyolefin resin other than the polyethylene resin, and is included in the melting energy per unit weight (caloric value / weight obtained from the melting peak area of the differential scanning calorimetry). 140
It is characterized by having a melting energy of 28 ° C. or more at 28 to 50 mJ / mg.

The resin component used in the present invention comprises a polyethylene resin and a polyolefin resin other than the polyethylene resin.

As the polyethylene resin, for example, linear low-density polyethylene, low-density polyethylene,
Examples include medium-density polyethylene, high-density polyethylene, and copolymers with α-olefins other than ethylene containing 50% by weight or more of ethylene, and these may be used alone or in combination of two or more. The copolymer may be either a random copolymer or a block copolymer, and as the α-olefin other than ethylene, for example, propylene, 1-
Butene, 1-pentene, 4-methyl-1-pentene, 1
-Hexene, 1-heptene, 1-octene and the like. The blending amount of the polyethylene resin in the resin component is as follows:
When the amount is reduced, the flexibility and elongation of the obtained cross-linked polyolefin-based resin foam are reduced, and the sheet is liable to be cut or leaked during molding. Is reduced,
It is necessary to be 20 to 60% by weight because the sheet is likely to be broken or resin leakage occurs during molding.

The above-mentioned polyolefin resin is other than the above-mentioned polyethylene resin, and examples thereof include a polypropylene resin and a polybutene resin. Among them, a polypropylene resin is preferable. Examples of the polypropylene resin include homopolypropylene, copolymers with α-olefins other than propylene containing 50% by weight or more of propylene, and these may be used alone or in combination of two or more. Is also good. The copolymer may be any of a random copolymer or a block copolymer, and as the α-olefin other than propylene, for example, ethylene,
Examples thereof include 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene.

When the amount of the polyolefin resin other than the above-mentioned polyethylene resin in the resin component is reduced, the heat resistance of the obtained crosslinked polyolefin resin foam decreases, and sheet breakage, resin leakage, etc. during molding processing. When the amount increases, the flexibility and elongation of the obtained crosslinked polyolefin-based resin foam decrease, and sheet breakage, resin leakage and the like easily occur at the time of molding, so that the content is 40 to 80% by weight. It is necessary.

Further, among the above-mentioned polypropylene resins, it is preferable to use homopolypropylene, and it is more preferable to use isotactic homopolypropylene. Melt index of isotactic homopolypropylene (hereinafter, referred to as “MI”), when reduced, the melt viscosity increases, primary foaming tends to occur at the time of extrusion, good foamable sheet is not obtained, Even when the foamable sheet is cross-linked and foamed, a cross-linked polyolefin resin foam having uniform and fine cells cannot be obtained, and its molding processability is deteriorated. And the flexibility of the obtained crosslinked polyolefin-based resin foam decreases, and a uniform fine crosslinked polyolefin-based resin foam cannot be obtained, and its molding processability deteriorates. Are preferred. Note that the above MI is based on JIS K7210,
It is measured at a temperature of 230 ° C. and a load of 21.2 N.

When the amount of the isotactic homopolypropylene in the resin component is small, the high-temperature strength of the obtained crosslinked polyolefin resin foam is reduced, and sheet breakage and resin leakage are likely to occur during molding. When the content increases, the resulting crosslinked polyolefin-based resin foam deteriorates in elongation at room temperature, so that the content is preferably 7 to 40% by weight.

The crosslinked polyolefin resin foam of the present invention has a melting energy per unit weight of 140.
The melting energy at or above C is 28 to 50 mJ / mg. When the melting energy decreases, the high-temperature melting crystal component decreases, heat resistance and mechanical strength decrease, and moldability deteriorates. When the melting energy increases, the elongation at room temperature decreases. It must be in the mg range.

Hereinafter, the melting energy per unit weight of the melting will be described with reference to FIG. The term “melting energy per unit weight” refers to the calorific value (mJ) obtained from the melting peak area of the differential scanning calorimetry, and the sample weight (mg).
Divided by The melting peak area of the differential scanning calorimetry is a portion surrounded by a melting peak curve measured according to JIS K 7211 and a straight line connecting the melting start temperature portion and the melting end temperature portion of the melting peak curve. (The area of the hatched portion in FIG. 1A).

As a specific method for measuring the melting peak per unit weight, a melting peak curve of the differential scanning calorimetry is measured using a differential scanning calorimeter (trade name “SSC5200” manufactured by Seiko Denshi). A method of calculating a melting peak area from the melting peak curve and obtaining a calorific value from the melting peak area. The melting energy of 140 ° C. or more contained in the melting energy per unit weight refers to the percentage of the melting peak area of the portion of 140 ° C. or more (the hatched portion in FIG. 1B) with respect to the melting peak area of the differential scanning calorimetry. Is calculated by multiplying the calorific value obtained from the melting peak area of the above differential scanning calorimetry by the above calculated percentage.

As a specific method of calculating the melting energy of 140 ° C. or more contained in the melting energy per unit weight, for example, a melting peak curve of differential scanning calorimetry is copied on paper, A portion surrounded by a straight line connecting the melting start temperature portion and the melting end temperature portion of the melting peak curve is cut out, and while the weight (mg) of the cut paper is measured, 140 of the cut paper is measured. A method of measuring the weight (mg) of the paper at a temperature of 140 ° C. or higher, and dividing the weight of the paper at a temperature of 140 ° C. or higher by the weight of the entire cut paper.

The apparent density of the above-mentioned crosslinked polyolefin-based resin foam is 0.02 to 0.02 because the mechanical strength decreases as the density decreases, and the flexibility and weight decrease as the density increases.
0.2 g / cm ³ is preferred, more preferably 0.03
０．１0.1 g / cm ³ .

The above-mentioned crosslinked polyolefin resin foam preferably has an elongation percentage and a 100% elongation strength in the following ranges.

The crosslinked polyolefin resin foam is
When the elongation at 20 ° C. is small, the crosslinked polyolefin-based resin foam does not follow during molding and the sheet is likely to be cut, and when it is large, the heat resistance is reduced.
200% to 400%, and 160 ° C.
When the elongation percentage at is small, resin leakage easily occurs at the corners during molding, especially during stamping molding,
As the heat resistance increases, the heat resistance decreases.
%.

The elongation at 20 ° C. is determined by the MD (resin extrusion direction) and TD (M
2 so that the plane direction perpendicular to D) is the length of the sample piece.
A seed sample was prepared, and the temperature of the sample was set to 20 ° C.
The elongation was measured in accordance with the method A of JIS K6767 except that the elongation was changed, and the average value of the elongation obtained for the two kinds of sample pieces was used. The same applies to the elongation at 160 ° C. described above, except that a sample piece was prepared in the same manner as above and the temperature was changed to 160 ° C. in accordance with JIS K6.
This is a value obtained by measuring elongation in accordance with Method A of 767 and averaging the elongation obtained for two types of sample pieces.

The above crosslinked polyolefin resin foam 1
When the 00% elongation strength decreases, the cells of the crosslinked polyolefin-based resin foam are destroyed during the molding process, and the surface of the obtained molded article tends to have irregularities. When the 00% elongation strength increases, the crosslinked polyolefin-based resin foam is molded. Thereafter, since the obtained molded product warps with time, it is preferably 0.25 to 0.40 MPa at 120 ° C. and 0.10 to 0.20 MPa at 160 ° C.

The 100% elongation at 120 ° C. is determined by the MD (resin extrusion direction) of the crosslinked polyolefin resin foam.
And two types of sample pieces are prepared such that TD (the plane direction perpendicular to the MD) is the length of the sample piece.
JIS K 6767 except that the temperature was changed to 120 ° C
A tensile strength test was carried out in accordance with the method A, and the tensile strength when the elongation of the sample became 100% was measured.
It is a value obtained by averaging the tensile strengths obtained for various types of sample pieces. The same applies to the above-mentioned 100% elongation at 160 ° C., except that a sample piece was prepared in the same manner as above and the temperature was changed to 160 ° C. in accordance with JIS K67.
A tensile strength test was conducted in accordance with Method A of No. 67.
It is a value obtained by measuring the tensile strength when the elongation of the sample reaches 100% and averaging the tensile strengths obtained for the two types of sample.

The method for producing the crosslinked polyolefin resin foam is not particularly limited, and any conventionally known method may be employed. For example, in addition to the thermal decomposition type foaming agent, an additive such as a crosslinking assistant is added to the resin component, if necessary, and the mixture is kneaded and extruded into a foamable sheet by an extruder, and at least one surface of the obtained foamable sheet. And then cross-linking by irradiating with ionizing radiation, and then heating the foam to a temperature equal to or higher than the decomposition temperature of the thermal decomposition type foaming agent.

The thermal decomposition type foaming agent is not particularly limited as long as it has been conventionally used for producing foams. Examples thereof include azodicarbonamide, dinitrosopentamethylenetetramine, hydradodicarbonamide, and azodicarbonate. Barium acid salt, nitrosoguanidine, p,
p, -oxybisbenzenesulfonyl semicarbazide,
Benzenesulfonyl hydrazide, N, N, -dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, 4,4-oxybis (benzenesulfonyl hydrazide), azobisisobutyronitrile, and the like. More than one species may be used in combination.

The amount of the thermal decomposition type foaming agent to be added is appropriately adjusted. When the amount is large, the foam tends to be broken, and when the amount is small, the foaming property is reduced. Parts by weight, more preferably 5 to 20 parts by weight.

The crosslinking aid is not particularly restricted but includes, for example, divinylbenzene, trimethylolpropane trimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, triallylic acid triallyl ester, Triallyl isocyanurate, ethylvinylbenzene, neopentyl glycol dimethacrylate, 1,2,4-benzenetricarboxylic acid triallyl ester, 1,6-hexanediol dimethacrylate, and the like. More than one species may be used in combination.

The addition amount of the crosslinking aid is appropriately adjusted. If the amount is too large, crosslinking proceeds excessively at the time of crosslinking of the foamable sheet, and the foaming property is reduced. If the amount is small, the added effect cannot be obtained. For 100 parts by weight of the resin component,
It is preferably from 0.5 to 30 parts by weight, more preferably from 2.0 to 15 parts by weight.

The ionizing radiation is not particularly limited as long as it has been conventionally used for producing a crosslinked foam, and examples thereof include α rays, β rays, γ rays, and electron beams.

The ionizing radiation is preferably irradiated with ionizing radiation having different accelerating voltage. Specifically, low energy ionizing radiation having an acceleration voltage of 200 to 400 kV and high energy ionizing radiation having an acceleration voltage higher than that of the low energy ionizing radiation are preferably irradiated simultaneously or separately. Irradiating with low-energy ionizing radiation after irradiating with ionizing radiation is preferred because of good crosslinking efficiency.

Regardless of whether the amount of irradiation of the low energy ionizing radiation is small or large, the molding processability of the obtained crosslinked polyolefin resin foam is deteriorated, so
0 Mrad is preferred.

When the irradiation amount of the high-energy ionizing radiation is reduced, the molding processability of the obtained crosslinked polyolefin resin foam decreases, and when the irradiation amount increases, a crosslinked polyolefin resin foam having a good surface is obtained. Therefore, 0.5 to 10 Mrad is preferable.

When the total irradiation amount of the above-mentioned ionizing radiation decreases, the moldability of the obtained crosslinked polyolefin resin foam decreases, and when it increases, the crosslinked polyolefin resin foam having a good surface is obtained. Therefore, 1 to 20 Mrad is preferable.

The amount of the cross-linking aid and the amount of ionizing radiation are adjusted so that the gel fraction of the cross-linked polyolefin resin foam is preferably 20 to 75% by weight, more preferably 30 to 65% by weight. It is preferable to adjust each of them so that

The gel fraction is determined by weighing a cross-linked polyolefin resin foam (Ag), immersing the same in xylene at 120 ° C. for 24 hours, filtering through a 200-mesh wire gauze, and removing the insoluble matter on the wire gauze. Is vacuum-dried, the dry weight (Bg) of the insoluble portion is measured, and calculated by the following formula. Gel fraction (% by weight) = 100 × (B / A)

Examples of the additives other than the crosslinking aid include phenolic compounds such as 2,6-di-t-butyl-p-cresol, sulfuric compounds such as dilaurylthiodipropionate, and phosphorus-based compounds. Antioxidants such as amines; metal harm inhibitors such as methylbenzotriazole;
Nitride-based, halogen-based, antimony-based or a mixture of these, a flame retardant; a filler; an antistatic agent; a pigment, and the like.

The above crosslinked polyolefin resin foam is
A skin material is laminated on one surface thereof and formed into a desired shape. In particular, for use as interior materials for automobiles, it is preferable that a skin material is laminated on one surface of the crosslinked polyolefin-based resin foam, a molten thermoplastic resin for a core material is supplied on the other surface, and then press molding is performed. (Such a molding method is generally called “stamping molding”).

As a form of the stamping molding, for example, a composite sheet in which a skin material is laminated on one surface of the crosslinked polyolefin resin foam is disposed between a convex mold and a concave mold, and the mold is closed. After injection and supply of the molten thermoplastic resin for the core material to the crosslinked polyolefin-based resin foam side of the composite sheet, the convex mold and the concave mold are clamped and press-molded. After supplying the molten thermoplastic resin for the core material and mounting the composite sheet so that the crosslinked polyolefin resin foam side of the composite sheet is the molten thermoplastic resin side, the convex mold and the concave mold are molded. The method of tightening and press forming, disposing the composite sheet between the convex mold and the concave mold, and before closing the mold, the molten thermoplastic for the core material is placed on the crosslinked polyolefin resin foam side of the composite sheet. Place resin, then clamp And a method of press-molding and the like and.

The skin material is not particularly limited. For example, resin sheets such as polyolefin-based resin sheets, soft polyvinyl chloride-based resin sheets, and thermoplastic elastomer sheets; polyester-based, polyamide-based, and polyacrylate-based synthetic resin sheets; Fiber sheet or nonwoven fabric; natural fiber sheet or nonwoven fabric of cellulosic or the like;

The above-mentioned skin material is preferably laminated and integrated with the above-mentioned crosslinked polyolefin-based resin foam by a heat laminating, an adhesive or the like before supplying the below-mentioned molten thermoplastic resin. After supplying the resin, the laminate may be integrated by the heat at the time of press molding.

Examples of the thermoplastic resin used for the above-mentioned molten thermoplastic resin include a polypropylene resin and a polyethylene resin. When the low-energy ionizing radiation is irradiated from only one surface during the cross-linking in the process of producing the cross-linked polyolefin resin foam, it is preferable to supply the molten thermoplastic resin to the irradiated surface. By performing the molding process as described above, the set of the crosslinked polyolefin-based resin foam due to heat, pressure, shear force, and the like during the molding process can be minimized,
The cushioning property and flexibility are secured.

[0042]

EXAMPLES In Examples 1 to 3 and Comparative Examples 1 to 5, the following polyolefin resins were used. LLDPE; linear low density polyethylene (density = 0.9
20 g / cm ³ , MI = 2.0 g / 10 min) Homo PP; isotactic homopropylene (MI = 1
5 g / 10 min) random PP; ethylene-propylene random copolymer (ethylene content 3.2% by weight, MI = 2.0 g / 10)
Minutes)

(Examples 1 to 3, Comparative Examples 1 to 5) 100 parts by weight of resin components, 10 parts by weight of azodicarbonamide, 3.0 parts by weight of trimethylolpropane trimethacrylate and the effective amount shown in Table 1 were used. Quantity of 2,6-di-
t-Butyl-p-cresol, dilaurylthiopropionate and methylbenzotriazole were supplied to a twin screw extruder, melt-kneaded at a temperature of 190 ° C., and extruded into a foamable sheet having a thickness of about 1 mm.

From both sides of the obtained foamable sheet, an electron beam having an acceleration voltage of 700 kV was irradiated with 3 Mrad, and then an electron beam having an acceleration voltage of 300 kV was irradiated with 3 Mrad to crosslink the foamable sheet. The crosslinked foamable sheet was foamed while continuously passing through a foaming furnace maintained at about 250 ° C. by hot air and an infrared heater to obtain a crosslinked polyolefin resin foam.

140 ° C. contained in the melting energy per unit weight of the obtained crosslinked polyolefin resin foam
Above melting energy, apparent density, 20 ° C and 160
The elongation at 100 ° C., 100% elongation at 120 ° C. and 160 ° C., and the thickness were as shown in Table 1. The crosslinked polyolefin resin foam obtained in Comparative Example 4 was 1
At 60 ° C, the elongation percentage did not reach 100%, so that the 100% elongation strength at 160 ° C could not be measured.

On one side of the crosslinked polyolefin resin foam, a soft polyvinyl chloride resin sheet (0.7 m thick)
m) was bonded with an adhesive to form a composite sheet. The composite sheet is provided between a concave mold having a concave portion having a diameter of 100 mm × a depth of 50 mm and a convex mold having a convex portion corresponding to the concave portion, and a crosslinked polyolefin-based resin foam surface is provided on the concave mold side. It was arranged so that it might become. Thereafter, a molten polypropylene resin for a core material at about 200 ° C. is supplied into the concave portion of the concave mold, and the concave mold and the convex mold are clamped, and stamping is performed to form a molded product. Obtained.

The following evaluation was performed on the molded product, and the results are shown in Table 1. (1) Thickness retention: The thickness (remaining thickness) of the crosslinked polyolefin-based resin foam of the molded product was measured. (2) Surface condition (surface avatar property): The surface of the molded product was visually observed, and the surface having no avatar-like irregularities on the surface was evaluated as ○, and the surface with slightly avatar-like irregularities on the surface was evaluated as Δ,
Those having a large number of avatar-like irregularities on the surface were represented by x. (3) Leakage of resin: at the corner of the molded product, ○ indicates that the polypropylene resin for the core material has not penetrated into the crosslinked polyolefin resin foam at all. △ indicates that a large number of invading parts occurred, and x indicates that a large number of invading parts occurred. The molded product obtained from the crosslinked polyolefin resin foam of Comparative Example 4 could not be evaluated for resin leakage because the sheet was cut during stamping molding. (4) Sheet break: A corner of the molded product that has no break in the crosslinked polyolefin-based resin foam,
△ indicates that there was a slight break, and X indicates that a large number of breaks occurred. (5) Warpage of molded product: Observation of the flat part (the top of the convex part of the convex mold) of the molded product. .

[0048]

[Table 1]

[0049]

The crosslinked polyolefin-based resin foam of the present invention has excellent heat resistance, flexibility and cushioning property, and does not generate avatar-like irregularities on the surface when subjected to secondary molding. It is hard to cause cutting and resin leakage and can be suitably used as an interior material for automobiles. Furthermore, even after molding, the molded product does not warp, and is excellent in shape stability.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a melting peak curve of a crosslinked polyolefin resin foam.

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Claims (5)

[Claims] 1. A resin component comprising polyethylene resin 20 to 6
140 ° C. consisting of 0% by weight and 40 to 80% by weight of a polyolefin resin other than the polyethylene resin and contained in the melting energy per unit weight (caloric value / weight obtained from the melting peak area of the differential scanning calorimetry). A crosslinked polyolefin-based resin foam characterized in that the above melting energy is 28 to 50 mJ / mg. 2. The crosslinked polyolefin resin foam according to claim 1, wherein 7 to 40% by weight of the resin component is an isotactic homopolypropylene having a melt index of 1 to 30 g / 10 minutes. 3. An elongation percentage of 200 to 400% at 20 ° C.
And at 130 ° C. at 160 ° C.
00% elongation strength is 0.25 to 0.40MP at 120 ° C
The crosslinked polyolefin-based resin foam according to claim 1 or 2, wherein a is 0.10 to 0.20 MPa at 160 ° C. 4. Polyethylene resin 20 to 60% by weight and polyolefin resin 40 other than polyethylene resin
100 parts by weight of a resin component consisting of 80 to 80% by weight and 1 to 50 parts by weight of a pyrolytic foaming agent are extruded into a foamable sheet, and at least one surface of the foamable sheet is subjected to low energy ionization at an acceleration voltage of 200 to 400 kV. Irradiating with high-energy ionizing radiation having a higher accelerating voltage than the low-energy ionizing radiation and the low-energy ionizing radiation at the same time or separately to crosslink, and then heating the foam to a temperature equal to or higher than the decomposition temperature of the pyrolytic foaming agent. The method for producing a crosslinked polyolefin-based resin foam according to any one of claims 1 to 3, characterized in that: 5. A cross-linked polyolefin-based resin foam according to any one of claims 1 to 4, wherein a skin material is laminated on one surface and a molten thermoplastic resin is supplied to the other surface, followed by press molding. Automotive interior materials.