JPH08325402A - Crosslinked polyolefin resin foam - Google Patents

Abstract

PURPOSE: To obtain a crosslinked polyolefin resin foam excellent in heat resistance and flexibility and amenable to fabrication into a complicated shape by specifying the energies of fusion of a crosslinked resin foam comprising a polypropylene resin and a polyethylene resin. CONSTITUTION: This crosslinked polyolefin resin foam is the one which comprises a polypropylene resin and a polyethylene resin and in which the energy of fusion at 120 deg.C or above ΔH120 included in the value obtained by dividing the calorific value determined from the fusion peak area as measured by differential scanning calorimetry by the weight of the sample, namely, the energy of fusion per unit weight of the sample ΔH is 30-60mJ/mg, and the energy of fusion at 140 deg.C or above ΔH140 is 20-40mJ/mg. By laminating this foam with a skin material, a laminated composite material having excellent fabricability can be obtained. Examples of such skin materials which can be desirably used include vinyl chloride resin sheets, vinyl chloride/ABS resin mixed sheets, urethane resin sheets, cloths and leathers.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a crosslinked polyolefin resin foam.

[0002]

2. Description of the Related Art Foams of polyolefin resins are generally excellent in flexibility and heat insulation and have been conventionally used as interior materials for vehicles such as ceilings, doors and instrument panels. These interior materials are mainly polyolefin resin foams, laminated with a vinyl chloride resin sheet, a thermoplastic elastomer sheet, a cloth-like material, a skin material such as leather, and then vacuum-molding or compression-molding the laminated body. It is obtained by molding by secondary processing.

However, when the above-mentioned secondary processing is compression molding, high heat resistance is required, and the foam and the skin material are separated from each other in a portion to which a strong force is applied, or bubbles are broken inside the foam. Further, there is a problem that the surface of the skin material is peeled off and a blistering phenomenon occurs.

In order to prevent such peeling of the foam and the skin material, studies have been conducted to improve the adhesion between the foam and the skin material. For example, Japanese Unexamined Patent Publication (Kokai) No. 2-255740 discloses a method in which a polyolefin resin foam is surface-treated with a nitrate or a nitrite to enhance the adhesiveness with a skin material. Further, Japanese Patent Publication No. 4-17784 discloses a method of improving adhesiveness by providing an adhesive layer in advance on the surface of a foam and heating and adhering it to a skin material.

However, in any of the above methods, the blistering phenomenon caused by the peeling of the skin material due to the poor adhesion between the foam and the skin material can be reduced, but an effective solution to the bubble destruction inside the foam body. There was a problem that it did not become.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is a crosslinked polyolefin having excellent heat resistance and flexibility and capable of being subjected to secondary processing in a complicated shape. To provide a resin foam.

[0007]

The crosslinked polyolefin resin foam of the present invention has a value obtained by dividing the calorific value obtained from the melting peak area measured by differential scanning calorimetry by the sample weight, that is, the melting per unit weight. Melting energy above 120 ° C in energy ΔH and 140 ° C
It is characterized in that the above-mentioned melting energy shows a specific value.

The polyolefin resin used in the present invention comprises a polypropylene resin and a polyethylene resin. As the polypropylene resin, a homopolymer of propylene or α-other than propylene and propylene
A copolymer having an olefin as a constitutional unit is exemplified. Examples of the α-olefin other than propylene include, for example,
Ethylene, 1-butene, 1-pentene, 1-hexene,
4-methyl-1-pentene, 1-octene, 1-heptene and the like can be mentioned.

When the melt index (hereinafter referred to as MI) of the polypropylene resin is small, the moldability of the obtained resin foam is deteriorated, and when it is large, the heat resistance of the resin foam is deteriorated. ~ 12 (g /
10 minutes) is preferable, and more preferably 0.3 to 10 (g
/ 10 minutes). The MI is JIS K721.
Based on 0, it is a value measured at 230 ° C. and 2.15 kgf.

Examples of the above-mentioned polyethylene resins include ethylene homopolymers and copolymers having ethylene and α-olefin as constitutional units. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like.

When the MI of the polyethylene resin is small, the appearance of the resin foam is impaired, and when it is large, the material strength is lowered, so that the MI is preferably 0.1 to 40 (g / 10 minutes).

In the above polyolefin resin, when the proportion of the polypropylene resin is small, the heat resistance of the resin foam obtained is low, and when it is large, the moldability is low and the flexibility of the resin foam is lost. It is preferably 50 to 90% by weight, more preferably 50 to 85% by weight.

The above polyolefin resin may be a thermoplastic resin other than the above polyethylene resin and polypropylene resin, such as low density polyethylene, if necessary.
Linear low density polyethylene, medium density polyethylene, high density polyethylene, ethylene-propylene rubber, polyvinyl acetate, polybutene and the like may be added.

As a method of foaming the above polyolefin resin, for example, a predetermined amount of polyolefin resin,
The thermoplastic resin other than the polyethylene-based resin and the polypropylene-based resin, a crosslinking aid, a pyrolytic foaming agent, etc. are supplied to an extruder, melt-kneaded to obtain a resin sheet by extrusion molding, and then the resin sheet is formed. A method of irradiating with ionizing radiation to crosslink, and the resulting crosslinked sheet being heated and foamed in a foaming furnace; a method of supplying the above-mentioned predetermined amounts of various components to an extruder and foaming with a heating roll simultaneously with extrusion; A conventionally known method such as a method of supplying various components of (1) to a mold and heating to perform foaming in a batch system is used.

The cross-linking aid is a monofunctional or polyfunctional monomer and is not particularly limited as long as it causes a cross-linking reaction with ionizing radiation or peroxide, and examples thereof include a vinyl group, an allyl group or ( Examples thereof include compounds containing at least one (meth) acryloyloxy group in one molecule.

Examples of the cross-linking aid include divinylbenzene, trimethylolpropane trimethacrylate, 1,6-hexanediol dimethacrylate, 1,
9-nonanediol dimethacrylate, 1-nonane monomethacrylate, 1,10-decanediol dimethacrylate, trimellitic acid triallyl ester, triallyl isocyanurate, ethyl vinylbenzene, 1,2,
4-benzenetricarboxylic acid triallyl and the like,
These may be used alone or in combination of two or more.

If the blending amount of the above-mentioned cross-linking aid is small, it is difficult to obtain a uniform foam due to insufficient cross-linking, and if it is too large, the cross-linking density becomes too high, which causes a problem in moldability. 0.5 to 1
The amount is preferably 0 part by weight, more preferably 0.8 to 6 parts by weight.

Examples of the thermal decomposition type foaming agent include azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide and 4,4-oxybis (benzenesulfonylhydrazide), which are used alone. Or two or more kinds may be used in combination.

When the amount of the above-mentioned pyrolyzable organic foaming agent added decreases, the foamability of the foam decreases, and when it increases, the strength of the foam decreases, so 1 to 50 parts by weight per 100 parts by weight of the polyolefin resin is added. Parts by weight are preferred.

The ionizing radiation is, for example, α
Rays, β rays, γ rays, electron rays and the like can be mentioned.

The cross-linked polyolefin resin foam obtained by the above-mentioned method may optionally contain a phenol-based, amine-based, sulfur-based, etc. antioxidant, within a range not impairing the properties of the foam; Inhibitors: phosphorus-based, nitrogen-based, halogen-based,
In addition to antimony-based and mixed flame retardants,
Fillers, antistatic agents, pigments and the like may be added.

In the above crosslinked polyolefin resin foam, the melting energy ΔH _{120 at} 120 ° C. or higher in the melting energy ΔH per unit weight is 30 to 60.
Limited to mJ / mg, preferably 35-55 mJ / m
g. Also, the melting energy per unit weight ΔH
The melting energy ΔH ₁₄₀ of 140 ° C or higher in the inside is
Limited to 20-40 mJ / mg, preferably 20-3
It is 5 mJ / mg.

The above melting energies ΔH ₁₂₀ and ΔH
_{When 140} becomes smaller, the heat resistance of the foam becomes insufficient, and the foam collapses during secondary processing, resulting in irregularities on the surface of the skin material and peeling of the foam. Therefore, the flexibility of the foam is insufficient.

Melting energy ΔH per unit weight
Is obtained by using a differential scanning calorimeter in accordance with JIS K7122 to obtain a DSC melting curve, and then the values at the melting start temperature and the melting end temperature and a line connecting these values (hereinafter referred to as “baseline”) and DSC. The melting energy ΔH per unit weight was calculated from the area surrounded by the melting curve.

Also, the melting energy ΔH above 120 ° C.
The measurement of ₁₂₀ was performed as follows. First, after obtaining the DSC melting curve shown in FIG. 1 by the above measurement, the values at the melting start temperature and the melting end temperature, the baseline and the D
The melting energy ΔH per unit weight was calculated from the area A surrounded by the SC melting curve. The area A can be calculated using an analysis job program.
Next, in the DSC melting curve obtained by the above measurement, the area B of the portion at 120 ° C. or higher shown in FIG. 2 was measured, and ΔH ₁₂₀ was calculated from the area ratio. 140 ° C
For the above measurement of melting energy ΔH ₁₄₀ , see 12
The same method was used according to the melting energy ΔH ₁₂₀ of 0 ° C. or higher.

In the above crosslinked polyolefin resin foam
And the apparent density decreases, the strength of the foam decreases.
By doing so, bubble destruction occurs when pressure is applied,
When the strain recovery becomes worse and becomes larger, the flexibility of the foam
Is 0.02 to 0.2 (g / cm³) Is good
More preferably, 0.03 to 0.1 (g / c)
m ³).

The above crosslinked polyolefin resin foam is
It may be used by being laminated with a skin material. As the above-mentioned skin material, conventionally known materials can be used, for example, vinyl chloride resin sheet, vinyl chloride resin-ABS resin mixed sheet, olefin resin sheet, urethane resin sheet,
Cloth, leather, etc. are preferably used, and a flame retardant may be added to these skin materials.

Examples of the method for laminating the crosslinked polyolefin resin foam and the skin material include an adhesive method and a heat laminating method. Examples of the adhesive used in the bonding method include polyester-based and polyurethane-based adhesives; and water-based emulsion adhesives composed of polar acrylic resin, urethane resin-aligiline, urethane resin-epoxy resin and the like.

[0029]

Embodiments of the present invention will be described below. (Examples 1 to 6, Comparative Examples 1 and 2) [Production of cross-linked polyolefin resin foam] A predetermined amount of polypropylene resin (shown by PP in the table) and polyethylene resin (shown by PE in the table) shown in Table 1. 100 parts by weight of a polyolefin-based resin consisting of 100 parts by weight), a predetermined amount of a crosslinking aid shown in Table 1, 7.5 parts by weight of azodicarbonamide as a thermal decomposition type foaming agent, and 2,6-diene as an antioxidant. -T
-Butyl-p-cresol (0.3 parts by weight), dilaurylthiodipropionate (0.3 parts by weight) and methylbenzotriazole (0.5 parts by weight as a metal damage inhibitor) were added to a resin composition prepared by a twin-screw extruder (Ikegai). Tekkosha "Type: P
CM87 ″), and melt-kneaded at a temperature of 190 ° C. and extrusion-molded to obtain a resin sheet having a thickness of 1.3 mm. An electron beam of 10Mr was applied to the obtained resin sheet at an acceleration voltage of 600kV.
The ad was irradiated to crosslink. Then, this crosslinked sheet was put in an oven and allowed to freely foam at a temperature of 250 ° C. for 5 minutes to obtain a crosslinked polyolefin resin foam. In Examples 5 and 6, the amount of azodicarbonamide used was 9 parts by weight.

[0030]

[Table 1]

The following are used in Table 1. [Polypropylene resin] -a: Ethylene-propylene random copolymer (ethylene content: 3.2% by weight, MI: 2 g / 10 minutes) -c: Ethylene-propylene block copolymer [Polyethylene resin] -b : Linear low-density polyethylene (density: 0.920 g
/ Cm ³ , MI: 2 g / 10 minutes) d: Linear low-density polyethylene (density: 0.920 g
/ Cm ³ , MI: 4g / 10 minutes)

[Cross-linking aid] 1,9-nonanediol dimethacrylate (indicated by "I" in the table) -trimethylolpropane trimethacrylate (indicated by "II" in the table) -divinylbenzene ("III" in the table)・ Displayed with 1,6-hexanediol dimethacrylate (displayed as “IV” in the table) · Triallyl 1,2,4-benzenetricarboxylate (displayed as “V” in the table)

The crosslinked polyolefin resin foams obtained in the above Examples and Comparative Examples were evaluated as follows.
The results are shown in Table 2.

(1) Measurement of Melting Energy Using a differential scanning calorimeter “SSC5200” manufactured by Sekiko Denshi Co., a DSC melting curve was obtained at a temperature rising rate of 10 ° C./min.
Then, the obtained DSC melting curve is analyzed using an analysis job program, and the melting energy per unit weight is calculated from the values at the melting start temperature and the melting end temperature and the area surrounded by the baseline and the DSC melting curve. ΔH was calculated. Furthermore, from this melting energy ΔH, 12
The melting energies ΔH ₁₂₀ and ΔH ₁₄₀ above 0 ° C. and above 140 ° C. were calculated, respectively.

(2) Measurement of degree of cross-linking 0.1 g of a foam sample was weighed to collapse air bubbles, and the temperature was set to 1
After being placed in 50 ml of a xylene solvent at 20 ° C. and kept for 24 hours, the dry weight (g) of the residue passed through a 200-mesh wire net was measured, and the degree of crosslinking was calculated by the following formula. Crosslinking degree (% by weight) = (dry weight of residue / 0.1) × 1
00

(3) Measurement of Density The density was measured using a gravimeter “ED120T” manufactured by Mirage.

[Manufacture of Laminated Composite] The surface of the foam obtained above is subjected to corona discharge treatment, and a two-component curing type polyester adhesive (polyester: "Hybon" manufactured by Hitachi Chemical Polymer Co., Ltd., isocyanate: Sumitomo Bayer Co., Ltd.) Made "Desm
odurR ") and a thickness of 0.65 m with the foam.
A vinyl chloride resin of m and an ABS (acrylonitrile-butadiene-styrene) copolymer mixed resin sheet were bonded as a skin material to obtain a laminated composite.

The above-mentioned laminated composite was evaluated as follows, and the results are shown in Table 2. (4) Vacuum formability A female die with a deep drawing ratio (H / D) of 0.7 (diameter 10 cm,
The depth of 7 cm) was used for vacuum forming so that the skin material was on the outside, and the vacuum formability was evaluated according to the following criteria. ◯: Molding was performed satisfactorily with no breaks or cracks. X: Breakage, cracking, etc. occurred.

(5) Hot stamping property (4) In the molded product of the laminated body vacuum-formed, the aggregate resin (MI = 30, talc 15% by weight) heated to 200 ° C.
Filled with the added block polypropylene resin),
90 with a male die under a pressure of 100 kg / cm ^2.
By holding for 2 seconds, hot stamping molding (die clearance 3.5 mm) was performed, and hot stamping property was evaluated according to the following criteria. ◯: There was no intrusion or breakage of the aggregate resin in the foam, and no abnormalities such as blistering or unevenness were observed in the skin material. Poor: Aggregate resin was invaded or broken in the foam, and blisters or irregularities were generated on the skin material.

[0040]

[Table 2]

[0041]

The structure of the crosslinked polyolefin resin foam of the present invention is as described above, has excellent heat resistance and flexibility, and can be subjected to secondary processing in a complicated shape. As a result, it can be used as a laminated composite having excellent secondary workability.

[Brief description of drawings]

FIG. 1 is a graph showing values at a melting start temperature and a melting end temperature of a DSC melting curve, and an area of a portion surrounded by a baseline and a DSC melting curve.

FIG. 2 is a graph showing the area of 120 ° C. or higher of the values of the melting start temperature and the melting end temperature of the DSC melting curve and the area surrounded by the baseline and the DSC melting curve.

[Explanation of symbols]

A Area of the part surrounded by the baseline and DSC melting curve B Area of 120 ° C or more of A

Claims (1)

[Claims] 1. A cross-linked polyolefin resin foam comprising a polypropylene resin and a polyethylene resin, wherein a calorific value obtained from a melting peak area measured by differential scanning calorimetry is divided by a sample weight, that is, per unit weight. Occupying the melting energy ΔH of 120 ℃
Melting energy ΔH _{120 above} is 30-60 mJ / m
g and melting energy ΔH above 140 ° C
₁₄₀ is 20-40 mJ / mg, The crosslinked polyolefin resin foam characterized by the above-mentioned.