JP2003105117A - Crosslinked polyolefinic resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crosslinked polyolefinic resin foam excellent in heat resistance and expansion, not suffering cuts in the sheet or pock marks in the surface in the vacuum forming process, and suitable for use as automobile interior materials. SOLUTION: For the formation of the crosslinked polyolefinic resin foam of 35-45% in gel fraction, a foaming resin composition containing a 10-62 wt.% of a linear polyethylene having a low density of 0.915-0.940 g/cm<3> , 30-82 wt.% of a propylene copolymer having a melting point of 125-155 deg.C, 8-15 wt.% of an isotactic homopropylene having a melting point of 155-165 deg.C, and a thermolytic foaming agent, is formed preferably into a sheet, irradiated with an ionizing beam, crosslinked, and then heated for foaming.

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 workability such as vacuum forming and suitable for automobile interior materials.

[0002]

2. Description of the Related Art Crosslinked polyolefin resin foams are generally excellent in flexibility and have been conventionally used in a wide range of materials such as heat insulating materials and cushioning materials. It is used as a heat insulating cushioning material for instrument panels and cooler covers. Then, in the use of the crosslinked polyolefin-based resin foam for automotive applications, generally, one surface of the crosslinked polyolefin-based resin foam is laminated and integrated with a skin material such as a soft polyvinyl chloride sheet, a thermoplastic elastomer sheet, and a leather sheet. A composite sheet is used, and the composite sheet is used after being formed into a desired shape by vacuum forming or the like.

However, when the above-mentioned composite sheet is vacuum-formed, a "sheet break" occurs in which a cross-linked polyolefin resin foam is broken or a cross-linked polyolefin resin foam is formed at a corner portion of a molded product which receives a strong force. There is a problem that air bubbles in the body are destroyed, so that so-called "avatar-like irregularities" occur on the surface of the skin material, and foams used as automobile interior materials are required to have heat resistance and molding processability. There is.

In order to solve this problem, for example, in Japanese Patent Laid-Open No. 10-45975, the total amount of polypropylene resin copolymerized with ethylene or butene and polyethylene copolymerized with α-olefin is compared. As a result, a crosslinked polyolefin resin foam obtained from a resin composition containing 1 to 7% by weight of a homopolypropylene resin has been proposed. However, the foam described in the above publication has a problem that avatar-like unevenness may occur on the surface of the skin material or the crosslinked polypropylene-based resin foam may be broken due to insufficient strength and insufficient elongation. .

[0005]

SUMMARY OF THE INVENTION In view of the problems of the above conventional crosslinked polypropylene resin foam, the present invention has excellent heat resistance and spreadability, and can be used for sheet breakage or skin material surface treatment during processing such as vacuum forming. An object of the present invention is to provide a crosslinked polyolefin-based resin foam that can be suitably used as an interior material for automobiles without generating avatar-like irregularities.

[0006]

In order to achieve the above object, the invention according to claim 1 has a density of 0.915 to 0.94.
Propylene copolymer 30 having a linear low-density polyethylene of 0 g / cm ³ of 10 to 62% by weight and a melting point of 125 to 155 ° C.
˜82 wt%, 8 to 15 wt% of isotactic homopolypropylene having a melting point of 155 to 165 ° C. and a pyrolytic foaming agent are obtained by cross-linking and foaming, and the gel fraction is Provided is a crosslinked polyolefin resin foam that is 35 to 45%.

The invention according to claim 2 is obtained by subjecting the foamable resin composition formed into a sheet shape to irradiation with ionizing radiation to crosslink and then heat-foaming. Provided is the crosslinked polyolefin resin foam described. Furthermore, the invention according to claim 3 has an area development rate of 345 to
390% and the tensile strength at 140 ° C is 0.0
The crosslinked polyolefin resin foam according to claim 1 having a pressure of 98 to 0.2 MPa is provided.

The resin component used in the present invention has a density of 0.
915 to 0.940 g / cm ³ of linear low-density polyethylene, propylene copolymer having a melting point of 125 to 155 ° C., and isotactic homopolypropylene having a melting point of 155 to 165 ° C. (hereinafter, in the present invention, A composition composed of resin components is referred to as a polyolefin resin composition).

The linear low-density polyethylene is a copolymer of more than 50% by weight of ethylene and an α-olefin such as 1-butene and has a density of 0.915 to 0.940 g.
/ Cm ³ and generally has a melt index (125
C., 10 minutes, hereinafter abbreviated as MI) 1 to 15 is used.

Examples of the propylene copolymer include copolymers of propylene exceeding 50% by weight (usually 90% by weight or more) and other α-olefin, and have a melting point of 1
A material having a temperature of 25 to 155 ° C. and an MI of 0.3 to 10 is generally used. The copolymer may be either a random copolymer or a block copolymer, and as an α-olefin other than propylene, for example, ethylene, 1-butene, 1-pentane, 4-methyl-1-pentene, 1-
Hexene, 1-heptene, 1-octene and the like can be mentioned. The MI is the same as the following isotactic homopolypropylene, measured according to JIS K 7210 at a temperature of 230 ° C. and a load of 21.2 N.

In general, the isotactic homoforipropylene is easily crystallized due to the regularity of the molecular structure and is superior in mechanical properties to atactic homoforipropylene. In the present invention, the melting point is 155 to 165. ℃
Is used. If the melting point of isotactic homopolypropylene is too low, the heat resistance of the obtained cross-linked polyolefin resin foam is lowered, and the melting point is 165.
If the temperature exceeds ° C, industrial production is difficult.

The method for producing the foam of the present invention will be described in detail later. After molding the expandable resin composition containing the above-mentioned polyolefin resin composition with a pyrolytic foaming agent into a sheet, for example. A method of irradiating with ionizing radiation and heating is preferable. In order to mold the foamable resin composition into a foamable sheet, extrusion molding is preferably used, although not limited thereto.

If the MI of the isotactic homopolypropylene becomes small, the melt viscosity at the time of extrusion molding into a sheet shape increases and primary foaming easily occurs, and a good foamable sheet cannot be obtained. Even when the sheet is crosslinked and foamed, a crosslinked polyolefin resin foam having uniform fine cells cannot be obtained, its moldability becomes poor, and when it becomes large, the resin does not follow when foaming, and its foamability decreases,
The flexibility of the obtained crosslinked polyolefin-based resin foam is lowered, and also a uniform and fine crosslinked polyolefin-based resin foam cannot be obtained, resulting in poor moldability.
Those of ˜30 are preferred.

If the amount of the linear low-density polyethylene blended in the polyolefin resin composition is too small,
The elongation and the like of the obtained crosslinked polyolefin-based resin foam are lowered, and sheet breakage easily occurs during vacuum forming,
If the amount is too large, the heat resistance of the obtained crosslinked polyolefin resin foam is lowered, and avatar-shaped irregularities are likely to occur during processing such as vacuum forming. Therefore, the content is required to be 10 to 62% by weight.

If the blending amount of the propylene copolymer in the polyolefin resin composition is too small, the heat resistance of the obtained crosslinked polyolefin resin foam is lowered,
Since avatar-like irregularities are likely to occur during processing such as vacuum forming, and when the amount is too large, the elongation and the like of the obtained crosslinked polyolefin-based resin foam decreases, and sheet breakage easily occurs during vacuum forming processing. It must be 82% by weight.

If the content of the isotactic homopolypropylene in the polyolefin resin composition is too small, the high temperature strength of the crosslinked polyolefin resin foam obtained will be low, and avatar-like irregularities will occur during vacuum forming. Since it tends to occur, and when the amount is too large, the elongation and the like of the obtained crosslinked polyolefin resin foam decreases and sheet breakage easily occurs during vacuum forming processing, so 8 to 15% by weight is preferable.

Crosslinked polyolefin resin foam of the present invention
When the apparent density of is small, the mechanical strength is
As it becomes harder, the flexibility and lightness decrease, so 0.02
5 to 0.05 g / cm³Is preferred, and more preferably
0.029-0.04g / cm ³Is.

The gel fraction of the crosslinked polyolefin-based resin foam is a criterion for judging the degree of crosslinking, and if it is too low, the high temperature strength of the obtained crosslinked polyolefin-based resin foam will be lowered, and the vacuum molding process will be performed. Avatar-shaped irregularities are likely to occur, and if it is too high, the elongation and the like of the obtained cross-linked polyolefin-based resin foam will decrease, and sheet breakage will easily occur during vacuum forming processing, so 35-45% is required. To do. The gel fraction was measured by weighing a cross-linked polyolefin resin foam (Ag) and adding it to xylene at 120 ° C. for 24 hours.
After soaking for a period of time, it is filtered through a wire mesh of 200 mesh, the insoluble matter on the wire mesh is vacuum dried, and the dry weight (B
g) was measured and calculated by the following formula. Gel fraction (wt%) = 100 x (B / A)

The crosslinked polyolefin resin foam has a surface temperature of 160.
Area expansion rate of ° C., the elongation of the crosslinked polyolefin-based resin foam obtained when the cross-linked polyolefin-based resin foam obtained is too small, the sheet breakage easily occurs during vacuum forming, and the cross-linked polyolefin-based resin foam obtained when it is too large High temperature strength decreases,
Since avatar-shaped irregularities are likely to occur during vacuum forming, 345 to 390% is preferable.

Surface area of about 160 ° C. with an infrared heater on both surfaces of the above-mentioned area expansion ratio and the crosslinked polyolefin resin foam.
The sample was heated at 1, and vacuum-molded with a female cup having a diameter of 50 mmφ using the depth as a variable, and the case where the surface layer cell was broken was determined as the molding limit.

One of the above crosslinked polyolefin resin foams
If the tensile strength at 40 ° C. is too small, the high-temperature strength of the obtained crosslinked polyolefin-based resin foam decreases, and avatar-shaped irregularities are likely to occur during vacuum forming, and if it is too large, the obtained crosslinked polyolefin-based resin foam is obtained. Since the elongation and the like of the sheet are reduced and a sheet breakage easily occurs during the vacuum forming process, it is preferably 0.098 to 0.2 MPa. In addition, the crosslinked polyolefin resin foam 140
The tensile strength at 0 ° C. was obtained by preparing two types of test pieces such that MD (resin extrusion direction) and TD (plane direction orthogonal to MD) of the crosslinked polyolefin resin foam are in the longitudinal direction of the test piece, The tensile strength of each piece was tested by the method A of JIS K 6767, except that the temperature was changed to 140 ° C., and the tensile strengths obtained from the two kinds of test pieces were averaged.

The method for producing the crosslinked polyolefin resin foam of the present invention is not particularly limited, and any conventionally known method may be adopted. It is needless to say that a foamable resin composition containing a heat-decomposable foaming agent in the polyolefin-based resin composition is used, but, for example, if necessary, an additive such as a crosslinking agent or a crosslinking aid may be further added. After adding and kneading, extruding into a sheet by an extruder, irradiating with ionizing radiation from at least one surface of the obtained foamable sheet to crosslink it, and then heating it to a temperature not lower than the decomposition temperature of the thermal decomposition type foaming agent. Then, a method of foaming can be mentioned.

The thermal decomposition type foaming agent is not particularly limited as long as it is one that has been used in conventional foam production.
For example, azodicarbonamide, dinitrosopentamethylenetetramine, hydrazidecarbonamide, azodicarboxylic acid barium salt, nitrosoguanidine, p, p-oxybisbenzenesulfonyl semicarbazide, benzenesulfonylhydrazide, N, N-dinitrosopentamethylenetetramine, toluenesulfonyl. Hydrazine, 4,4-
Examples thereof include oxybis (benzenesulfonylhydrazide) and azobisisobutyronitrile, which may be used alone or in combination of two or more kinds. The addition amount of the thermal decomposition type foaming agent is appropriately adjusted, but if it is too large, the foaming tends to be broken, and if it is too small, the foamability is lowered. Therefore, 1 to 100 parts by weight of the polyolefin resin composition is used. 30 parts by weight is preferable, and 5 to 20 parts by weight is more preferable.

The cross-linking agent (cross-linking aid) is not particularly limited, and examples thereof include divinylbenzene, trimethylolpropane trimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, and trimellit. Acid triallyl ester, triallyl isocyanurate, ethyl vinylbenzene, neopentyl glycol dimethacrylate, 1,2,4-benzenecarboxylic acid triallyl ester, 1,6-hexanediol dimethacrylate, etc., and these are used alone. You may use, or may use 2 or more types together. The amount of the cross-linking agent added is appropriately adjusted, but if the amount is too large, the cross-linking excessively progresses during the cross-linking of the foamable sheet to reduce the foamability, and if the amount is too small, the effect added cannot be obtained. 0.5 to 30 parts by weight is preferable relative to 100 parts by weight, and 0 to 15
More preferably parts by weight.

The ionizing radiation is not particularly limited as long as it has been conventionally used in the production of crosslinked foams, and examples thereof include α rays, β rays, γ rays and electron rays. The irradiation amount of the ionizing radiation is too small, the moldability of the crosslinked polyolefin resin foam obtained is reduced, if too much, it becomes difficult to obtain a crosslinked polyolefin resin foam having a good surface. 1-20 Mra
d is preferred.

Examples of additives other than the above-mentioned cross-linking agent (cross-linking aid) include phenol-based compounds such as 2,6-di-t-butyl-p-cresol and sulfur-based compounds such as dilauryl thidipropionate. , Phosphorus-based and amine-based antioxidants; metal benzotriazole and other metal-damage inhibitors; phosphorus-based, nitrogen-based, halogen-based, antimony-based or flame-retardant mixtures of these; fillers; antistatic agents; Examples include pigments and the like.

The above crosslinked polyolefin resin foam is
Usually, a skin material is laminated on one surface thereof and is formed into a desired shape. In particular, when it is used for an instrument panel pad, a door trim, a fender shield, etc. as an interior material for automobiles, it is preferably processed by a vacuum forming method.

For example, a composite sheet obtained by laminating a skin material on one surface of the crosslinked polyolefin resin foam is heated and softened, and then covered with a male mold and sucked through a hole formed in the mold to obtain a shape suitable for the mold. It is particularly preferable to perform molding (male molding), but it is also possible to employ female molding among the vacuum molding methods. Further, in some cases, compressed air pressure molding, which belongs to the widely used thermoforming method, may be adopted in addition to the vacuum molding method.

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, polyacrylate-based synthetic fiber sheets or non-woven fabrics; cellulose-based natural sheets or non-woven fabrics, etc. Is mentioned. It is preferable that the skin material be laminated and integrated with the crosslinked polyolefin resin foam by a heat laminate, an adhesive or the like before vacuum forming.

[0030]

EXAMPLE The following resin was used. LLDPE: linear low-density polyethylene (density = 0.
920 g / cm ³ , MI = 2.0 g / 10 minutes) Random PP: ethylene-propylene random copolymer (ethylene content 3.2% by weight, MI = 2.0 g / 1
0 minutes) ・ Homo PP: isotactic homopropylene (MI =
15g / 10 minutes)

(Examples 1 and 2) Using the above polyolefin resin, the compounding ratio was LLDPE / random P
A polyolefin resin composition with P / homo PP = 25/67/8 was obtained. To 100 parts by weight of this resin composition, 12 parts by weight of azodicarbonamide and 3.0 parts by weight of trimethylolpropane trimethacrylate and an effective amount of 2,6
-Di-t-butyl-p-cresol, dilaurylthiopropionate and methylbenzotriazole were added and mixed to obtain a foamable resin composition, which was supplied to a twin-screw extruder and melt-kneaded at a temperature of 190 ° C. Then, a foamable sheet having a thickness of 1 mm was extruded. Both sides of the obtained foamed sheet were irradiated with an electron beam with an accelerating voltage of 700 kV at 2.0 Mrad (Example 1) and 2.5 Mrad (Example 2) to crosslink the foamable sheet. Foams while continuously passing the flexible sheet through a foaming furnace maintained at about 250 ° C by hot air and an infrared heater, and has a thickness of about 2.0 mm.
To obtain a crosslinked polyolefin resin foam.

(Examples 3 and 4) Using the above polyolefin resin, the compounding ratio was LLDPE / random P
A polyolefin resin composition with P / homo PP = 25/65/10 was obtained. Using this resin composition, a foamable resin composition was obtained in the same manner as in Examples 1 and 2, and a foamable sheet having a thickness of 1 mm was extruded, and an electron beam with an accelerating voltage of 700 kV was irradiated with 2.0 Mrad (Example 3). And 2.5 Mrad (Example 4) were irradiated to crosslink the foamable sheet and heat-foamed to obtain a crosslinked polyolefin resin foam having a thickness of about 2.0 mm.

(Examples 5 and 6) Using the above polyolefin resin, the compounding ratio was LLDPE / random P.
A polyolefin resin composition with P / homo PP = 25/60/15 was obtained. Using this resin composition, in the same manner as in Examples 1 and 2, a foamable resin composition was obtained, a foamable sheet having a thickness of 1 mm was extruded, and an electron beam with an accelerating voltage of 700 kV was irradiated with 2.0 Mrad (Example 5). And 2.5 Mrad (Example 6) were irradiated to crosslink the foamable sheet and heat-foamed to obtain a crosslinked polyolefin resin foam having a thickness of about 2.0 mm.

(Comparative Examples 1 and 2) Using the above polyolefin resins, the compounding ratio was LLDPE / random P.
A polyolefin resin composition with P / homo PP = 25/70/7 was obtained. Using this resin composition, Examples 1 and 2
In the same manner as above, a foamable resin composition was obtained, a foamable sheet having a thickness of 1 mm was extruded, and an electron beam with an acceleration voltage of 700 kV was irradiated with 2.0 Mrad (Comparative Example 1) and 2.5 Mrad (Comparative Example 2). Crosslink the foamable sheet, heat foam,
A crosslinked polyolefin resin foam having a thickness of about 2.0 mm was obtained.

(Comparative Examples 3 and 4) Using the above polyolefin resins, the compounding ratio was LLDPE / random P.
A polyolefin resin composition with P / homo PP = 25/55/20 was obtained. Using this resin composition, a foamable resin composition was obtained in the same manner as in Examples 1 and 2, a foamable sheet having a thickness of 1 mm was extruded, and an electron beam with an accelerating voltage of 700 kV was irradiated with 2.0 Mrad (Comparative Example 3). And 2.5 Mrad (Comparative Example 4) were irradiated to crosslink the foamable sheet and heat-foamed to obtain a crosslinked polyolefin resin foam having a thickness of about 2.0 mm.

With respect to the crosslinked polyolefin resin foam obtained above, the area expansion ratio (vacuum moldability), high temperature strength,
The avatar phenomenon (surface irregularities) during molding and the presence or absence of foam breakage were measured or evaluated, and the results are shown in Table 1. The measuring method and the evaluating method of each physical property are as follows.

<Area development rate> When both surfaces of the cross-linked polyolefin resin foam are heated with infrared heaters at a surface temperature of about 160 ° C. and vacuum-formed with a depth of 50 mmφ female cup to make the surface cell broken. The area development rate was determined with the molding limit as. <High-temperature strength> After being left in a heat-retaining box set at a temperature of 140 ° C for 5 minutes, the strength was measured by a tensile tester (JIS.
(According to K-6767)

<Evaluation at the time of molding> A soft polyvinyl chloride resin sheet (thickness: 0.5 mm) was attached to one surface of the above crosslinked polyolefin resin foam with an adhesive to form a composite sheet. The composite sheet was heated to a surface temperature of about 160 ° C. with a double-sided infrared heater and vacuum-formed with a concave die having a diameter of 100 mm and a depth of 50 mm to obtain a molded product.

[Judgment of Surface Surface Unevenness (Surface Avatar Property)] The surface of the molded product is visually inspected, and there is no avatar-like unevenness on the surface ∘, and there is a little avatar-like unevenness on the surface. The ones are represented by Δ, and the ones having many avatar-shaped irregularities on the surface are represented by x. [Judgment of sheet breakage] At the corners of the molded product, those with no breakage of the crosslinked polyolefin resin foam are indicated by ○, those with slight breaks are indicated by △, and those with many breaks are indicated by ×. did.

[0040]

[Table 1]

As is clear from Table 1, the amount of homopolypropylene resin is 8 to 15%, the gel fraction is 35 to 45%, the area expansion rate is 345 to 390%, and the tensile strength at 140 ° C. is 0.098 to 0. It can be seen that the crosslinked polyolefin resin foam satisfying the requirement of 2 MPa has excellent vacuum moldability without surface unevenness (avatar-like unevenness) during vacuum molding and breakage of the crosslinked polyolefin resin foam.

[0042]

EFFECT OF THE INVENTION The crosslinked polyolefin resin foam of the present invention is configured as described above, and the specific linear low density polyethylene, propylene copolymer and isotactic homopolypropylene are contained in specific amounts. Since it is obtained by cross-linking and foaming the expandable resin composition containing the pyrolytic foaming agent in the blended polyolefin-based resin composition, the surface when processed by thermoforming such as vacuum forming In this case, so-called avatar-like irregularities do not occur, and the sheet is less likely to be broken, and it can be suitably used as an interior material for automobiles. When the crosslinked polyolefin resin foam of the present invention is obtained by heating the foamable resin composition molded into a sheet after irradiating with ionizing radiation, the productivity is good. Therefore, it can be provided relatively inexpensively. Further, the area expansion rate is 345 to 390%, and the tensile strength at 140 ° C. is 0.098 to 0.2.
When it is MPa, good workability due to the above-mentioned vacuum forming or the like can be further exhibited.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4F070 AA13 AA15 GA04 GC02 HA04                       HB01 HB05 HB07 HB08                 4F074 AA20 AA24 AB03 BA01 BA13                       BA31 CA29 CC04X CC04Y                       CC06X CC22X CC32X CC32Y                       CC48X CC49Y DA08 DA33                       DA35                 4J002 BB05X BB133 BB14W BB15W                       FD326 GN00

Claims (3)

[Claims] 1. A density of 0.915 to 0.940 g / cm ^3.
10 to 62% by weight of linear low-density polyethylene, melting point 1
Crosslinking a foamable resin composition containing 30 to 82% by weight of a propylene copolymer having a temperature of 25 to 155 ° C., 8 to 15% by weight of isotactic homopolypropylene having a melting point of 155 to 165 ° C., and a thermal decomposition type blowing agent. A crosslinked polyolefin resin foam obtained by foaming and having a gel fraction of 35 to 45%. 2. The crosslinked product according to claim 1, wherein the foamable resin composition formed into a sheet is obtained by irradiating with ionizing radiation to crosslink and then heat-foaming. Polyolefin resin foam. 3. The area expansion rate is 345 to 390%, and
Tensile strength at 140 ° C is 0.098-0.2MP
The crosslinked polyolefin resin foam according to claim 1 or 2, which is a.