JPH08104765A - Cross-linked polyolefin resin foam with excellent moldability - Google Patents

Abstract

PURPOSE: To obtain a foam which causes neither blistering nor pockmarks in forming, such as vacuum forming, and is excellent in skin strength and formability by producing a crosslinked polyolefin resin foam in a prescribed sheet form so as to satisfy specified relations among the gel fractions under various conditions. CONSTITUTION: A crosslinked polyolefin resin foam in sheet form is produced from a polyolefin resin containing 50-100wt.% PP resin and 0-50wt.% PE resin, which foam satisfies the following relations of the formulas A<40%, B/A >=0.85, C >=35%, D >=30%, C<D, (|A-C|) <=10% and (|A-|) <=10%, wherein A and B respectively are the gel fractions when the foam is extracted with xylene at 120 deg.C for 24hr and 72hr, and C and D respectively are the gel fractions of the 0.5mm thick skin layers on one side and the other side of the foam in sheet form.

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 having excellent moldability, and more specifically, in forming by lamination with a skin material or vacuum forming,
The present invention relates to a crosslinked polyolefin resin foam that does not cause blistering or avatar phenomenon. The crosslinked polyolefin resin foam of the present invention has excellent skin strength, heat resistance, and moldability, and in particular, one surface is laminated with a skin material such as a soft vinyl chloride resin sheet, and the other surface is heat-treated for aggregate. It is suitable for applications such as automobile interior moldings in which a plastic resin layer is integrally molded.

[0002]

2. Description of the Related Art Crosslinked polyolefin resin foams are used in a wide variety of fields as heat insulating materials, cushioning materials and the like. Particularly, in the field of automobiles, it is used as a vehicle interior material such as a ceiling material, a door, an instrument panel, a console box, a rear wheel house cover, a luggage house cover, and a luggage compartment cover. These heat insulating materials and the like are generally laminated with a skin material such as a soft vinyl chloride resin sheet on one side of a sheet-shaped cross-linked polyolefin resin foam, and then molded into a predetermined shape by vacuum molding or compression molding, It has been commercialized.

In recent years, crosslinked polyolefin resin foams have been required to have excellent toughness, heat resistance, moldability and the like in order to mold and process them into complicated and deep shapes. Therefore, various improvements have been proposed in the past. For example,
A radiation-crosslinked polypropylene resin foam having a ratio of the gel fraction of the central layer to the gel fraction of the foam surface layer of 1.5 or less has been proposed (JP-A-63-175041).
issue). However, it has been very difficult to obtain a crosslinked polyolefin resin foam which is capable of deep drawing and has excellent moldability in which so-called blistering phenomenon and avatar phenomenon do not occur.

That is, in recent years, as the shape of molded articles such as doors and instrument panels has become deeper, the skin material and the foamed material, especially in the armrest and the wood grain portion where the expansion rate (extension rate) of the foamed material is large, during the molding process. Air accumulates between the and the so-called blistering phenomenon is likely to occur. Further, in the matched die method in which a male mold and a female mold are combined and vacuum-molded, as a result that the foam is squeezed by a strong shearing force in the clearance between the molds, the same blistering phenomenon is likely to occur.

As measures against such blistering phenomenon, in addition to increasing the peel strength of the skin material at a high temperature of 100 ° C. or higher, it is possible to increase the high temperature elongation and decrease the high temperature elastic modulus. If the cross-linking degree of the foam is lowered, the high temperature elongation can be increased and the high temperature elastic modulus can be lowered, but the heat resistance of the foam surface is reduced and the foam surface becomes uneven at high temperature, a so-called avatar phenomenon occurs. Occurs.

As a method of lowering the elastic modulus at high temperature, it is considered that the crosslinked structure is not a crosslinked bridged structure but a bundled bridged structure, and the characteristic is that the gel fraction by solvent extraction remarkably decreases with the extraction time. It is possible to use one. However, such a foam requires a high degree of crosslinking with a gel fraction of 40% or more to suppress the avatar phenomenon, and as a result, the high temperature elongation is reduced. Also,
To obtain a foam with a high degree of crosslinking by general-purpose electron beam irradiation,
More irradiation dose is required, but this causes resin deterioration, that is, deterioration of physical properties.

Further, the avatar phenomenon is likely to occur even when the foamed body is attached to the skin material. Therefore, when the skin material is attached to the foam, not only heat resistance but also resistance to ironing by pinch rolls or the like is required. However, hitherto, a cross-linked polyolefin resin foam excellent in moldability that sufficiently suppresses the blistering phenomenon and the avatar phenomenon has not been proposed.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a crosslinked polyolefin resin foam which is free from blistering phenomenon and avatar phenomenon and has excellent moldability. The present inventors have conducted extensive studies to overcome the problems of the prior art, and as a result, in a crosslinked polyolefin-based resin foam containing a polypropylene-based resin as a main component, the degree of crosslinking of the entire foam (gel fraction) and solvent extraction. The relationship between time and the rate of change of gel fraction, the gel fraction of the skin layer on the surface where the skin material is attached, the gel fraction of the opposite surface, the relationship between the degree of crosslinking and the gel fraction of each skin layer, etc. It has been found that the above object can be achieved by setting the content within a specific selected range. The present invention has been completed based on these findings.

[0009]

According to the present invention, a sheet-like crosslinked polyolefin resin formed from a polyolefin resin containing 50 to 100% by weight of a polypropylene resin and 0 to 50% by weight of a polyethylene resin. In the foam, (a) the foam was added in xylene at 120 ° C.
The gel fraction A when extracted for 4 hours is less than 40%, and the gel fraction A and the gel fraction B when extracted in xylene at 120 ° C. for 72 hours are B / A ≧ 0. And (b) the gel fraction C of the skin layer having a thickness of 0.5 mm from one surface of the foam sheet (b) is 35% or more,
The gel fraction D of the skin layer from the other surface to a thickness of 0.5 mm is 30% or more, and has a relationship of C> D, and (c) the gel fraction A and the gel fraction C. Difference with (| A-C
|, And the difference between the gel fraction A and the gel fraction D (| A-D
All of |) are within 10%, and thus a crosslinked polyophine resin foam having excellent moldability is provided. (However, the gel fractions A, C and D are 100m for the sample.
After immersing g in xylene at 120 ° C. for 24 hours, the insoluble matter was filtered off and vacuum dried for 8 hours, and the weight was measured, and the value obtained by dividing the measured value by the weight of the original sample was multiplied by 100. Is. The gel fraction B is 100 mg of the sample is 12
After being soaked in xylene at 0 ° C. for 72 hours, insoluble matter was filtered off and vacuum dried for 8 hours, and the weight was measured. . )

The present invention will be described in detail below. A feature of the present invention is that, in a sheet-like cross-linked polyolefin resin foam containing a polypropylene resin as a main component, the gel fractions A to D and the relationship between them are controlled within a specific selected range. It is in. (1) Providing high elongation and heat resistance at high temperature By using a polypropylene resin as a main component, it is possible to impart heat resistance, toughness, and elongation at high temperature to a foam. By adding a polyethylene resin, resistance to compression can be improved, and foamability, moldability, appearance and the like can be improved. The expansion ratio is preferably in the range of 10 to 35 cc / g from the viewpoint of secondary workability.

(2) Providing high elongation and low elastic modulus at high temperature The gel fraction A when the foam is extracted in xylene at 120 ° C. for 24 hours represents the degree of crosslinking of the entire foam. By setting the gel fraction A to less than 40%, the foamed body is easily deformed, high elongation and low elastic modulus are obtained at high temperature, and blister phenomenon is less likely to occur. When the gel fraction A is 40% or more,
The elongation decreases, and the blistering phenomenon easily occurs. Gel fraction A
The ratio (B / A) of the gel fraction B with respect to is required to be 0.85 or more. If this ratio is less than 0.85, the avatar phenomenon is likely to occur even if the gel fraction A is less than 40%.

(3) Suppression of Avatar Phenomenon and Maintenance of Peel Strength and Elongation at High Temperature The surface of the crosslinked polyolefin resin foam is usually smooth, but when heated to a high temperature of 150 ° C. or higher, or by a roll. When compressed or buckled, wrinkle-like irregularities are generated on the surface. This is called the avatar phenomenon.
The unevenness is about 0.5 mm or more, and can be easily identified visually and by touch. The reason why the avatar phenomenon occurs is not clear, but it is presumed that it occurs because the cell membrane of the foam surface layer is weak. That is, it is considered that the cross-linking state of the polyolefin resin forming the foam has a great relation to the avatar phenomenon.

In the present invention, the gel fraction C of the skin layer having a thickness of 0.5 mm from one surface of the sheet foam (foam sheet) is 35% or more, and the thickness of the other surface is 0.5 mm.
Gel fraction D of the skin layer up to 30% or more, and C> D
The cross-linked state of the foam is controlled so that To measure the gel fractions C and D, a slicer or a cutter is used to slice a skin layer having a thickness of 0.5 mm from the surface to prepare a sample.

When a skin material such as a soft vinyl chloride resin sheet is attached to the foam and pressure-bonded, the surface of the gel fraction C is attached. In the lamination of the skin material, usually, an adhesive is applied to the adhered surface of the foam, the skin material is pasted on the adhesive, and pressure is applied by a roll or the like. In the present invention, the gel fraction C of the surface to which the skin material is attached is set to be higher than the gel fraction D of the other surface because the avatar phenomenon occurs due to compression or buckling received in the attaching process. This is to prevent

By controlling the gel fraction (crosslinking degree) of the laminated surface of the skin material to 35% or more, the occurrence of the avatar phenomenon at the time of laminating the skin material is suppressed, and the gel fraction of the other surface is 30% or more. By setting the above, it is possible to suppress the avatar phenomenon due to heating during the molding process. More specifically, by setting the degree of cross-linking of the laminated surface of the skin material to 35% or more, even if the molecular chains are broken by stress under high temperature during lamination of the skin material, an excessive decrease in molecular weight occurs. Since it is difficult, the avatar phenomenon can be suppressed. The degree of crosslinking on the other side is 3
When the content is 0% or more, even if the molecular chain is broken by being exposed to a high temperature during molding, an excessive decrease in the molecular weight is unlikely to occur, so that the avatar phenomenon is suppressed. The reason why the gel fraction C is made larger than the gel fraction D is that the skin material bonding surface is subjected to higher temperature heating and higher stress.

In the present invention, the difference between the gel fraction A and the gel fraction C (| A-C |), and the gel fraction A and the gel fraction D.
It is necessary to control the difference (| A−D |) between and within 10%. If these differences exceed 10%,
There are places where the gel fraction (crosslinking degree) is unnecessarily high, which causes a decrease in elongation. By keeping the difference in gel fraction within 10%, the variation in the degree of crosslinking in the thickness direction of the foamed sheet is suppressed to a small extent, and the occurrence of a portion having a higher degree of crosslinking than necessary is prevented. For example, if the gel fraction C becomes too large and | AC−> 10, the degree of cross-linking on the surface to which the skin material is attached becomes too high as compared with other portions, which reduces the elongation of the entire foam. Occurs. If the elongation decreases, the molding processability such as compression moldability decreases.

As the method for producing the polyolefin resin foam of the present invention, first, a pyrolytic foaming agent, a crosslinking accelerator, an antioxidant, a pigment and other additives are mixed with the polyolefin resin, An unfoamed sheet is manufactured by melt molding at a temperature lower than the decomposition temperature of the pyrolytic foaming agent. Next, the unfoamed sheet is cross-linked with ionizing radiation or a chemical cross-linking agent.

In the present invention, as a method for providing a difference in the degree of crosslinking between the skin layers on both sides of the foam sheet and the skin layer and the entire foam, the thickness of the unfoamed sheet can be increased by irradiating with ionizing radiation from only one side. The method of forming a specific distribution of the degree of cross-linking in the depth direction, the method of irradiating at the same dose from both sides, and then the method of additionally irradiating low energy only to the surface to be bonded to the skin material, and the difference in irradiation dose on both sides Examples of the method include a method of providing the agent and a method of providing a concentration distribution of the chemical crosslinking agent.

The polypropylene resin used in the present invention is a homopolymer of propylene, a copolymer containing propylene as a main component, or a mixture of two or more thereof.
Examples of the copolymer include a propylene-ethylene copolymer containing 85% by weight or more of a propylene unit and a propylene-α-olefin copolymer. More specifically,
Propylene-ethylene random copolymer, propylene-
Examples thereof include ethylene block copolymers and propylene-ethylene-butene terpolymers. Examples of the α-olefin include 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene and the like.

Melt index of polypropylene resin used in the present invention (abbreviated as MI: ASTM D-12)
38) is usually 0.3 to 10 (g / 10 minutes), preferably 0.4 to 2.0, which is M of polypropylene resin.
When I is in this range, heat resistance and high temperature high elongation can be suitably imparted to the foam. The polyethylene resin used in the present invention is a homopolymer of ethylene, a copolymer containing ethylene as a main component, or a mixture of two or more thereof. Examples of the copolymer include ethylene-α-containing 80% by weight or more of ethylene units.
An olefin copolymer can be mentioned. Examples of the α-olefin include 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-pentene and the like. Specifically, low density polyethylene (LDP
E), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene (LL)
DPE), ultra low density polyethylene (VLDPE) and the like.

M of the polyethylene resin used in the present invention
I is usually 2 to 20 (g / 10 minutes). In particular, L-LDPE is preferable in order to impart high elongation. 50/5 for polypropylene resin and polyethylene resin
It is used in a ratio of 0 to 100/0 (weight ratio). When the content is within the range of these compounding ratios, it is possible to obtain a crosslinked foam having good physical properties at high temperature such as heat resistance, moldability, and appearance.

In the present invention, a crosslinking accelerator can be added to the polyolefin resin. As a crosslinking accelerator,
Examples thereof include polyfunctional monomers such as divinylbenzene, diallylbenzene, divinylnaphthalene, polyethylene dimethacrylate, trimethylolpropane trimethacrylate and triallyl isocyanurate. These are used alone or as a mixture, and preferably 1 to 30 relative to 100 parts by weight of the polyolefin resin.
It is used in an amount of about 2 to 15 parts by weight, more preferably 2 to 15 parts by weight. When cross-linking, ionizing radiation and chemical cross-linking may be used together.

The thermal decomposition type foaming agent used for producing the polyolefin resin foam is not particularly limited as long as it has a decomposition temperature higher than the melting temperature of the resin component used in the present invention. The thermal decomposition type foaming agent is a compound that generates a decomposition gas when heated, and includes, for example, azodicarbonamide, hydrazodicarbonamide, azodicarboxylic acid amide, azodicarboxylic acid barium salt, dinitrosoventaethylenetetramine, nitrosoguanidine, p. , P′-oxybisbenzenesulfonyl semicarbazide, trihydrazine symmetric triazine, bisbenzenesulfonyl hydrazide, barium azodicarboxylate, azobisisobutyronitrile, toluenesulfonyl hydrazide and the like. Among these, azodicarbonamide is preferable, and it is also preferable to use it in combination with a foaming agent having a decomposition point equal to or higher than that of azodicarbonamide. The blending amount of the thermal decomposition type foaming agent is usually 1 to 50 parts by weight with respect to 100 parts by weight of the resin component, and the blending amount can be appropriately selected according to the desired foaming ratio.

In the present invention, the polyolefin resin may be optionally mixed with, for example, an antioxidant, a heat stabilizer, a pigment, a colorant, an antistatic agent, a flame retardant, a plasticizer, a filler and the like. Polyolefin resin, cross-linking accelerator, thermal decomposition type foaming agent, other additives, using a kneading device such as a single-screw extruder, twin-screw extruder, Banbury mixer, kneader mixer, rolls, the thermal decomposition-type foaming agent It is melt-kneaded at a temperature lower than the decomposition temperature of, and usually formed into a sheet by an extruder. You may press-mold. The resulting expandable sheet (unfoamed sheet) is irradiated with ionizing radiation to crosslink.
Ionizing radiation includes electron rays, α rays, β rays, γ rays, and X rays.
Lines can be used. Next, the crosslinked foamable sheet is put in a heating oven or the like to heat it to a temperature equal to or higher than the decomposition temperature of the thermal decomposition type foaming agent to foam it. Crosslinking with a chemical crosslinking agent may be performed.

As the skin material used for forming the foam, a cloth formed of synthetic fibers such as polyester, polyamide and acrylic resin and natural fibers such as cellulose;
Examples thereof include a sheet formed of vinyl chloride resin, thermoplastic elastomer and the like. As a method for laminating the skin material, an adhesive, a heat laminating method, an extrusion laminating method, or the like can be arbitrarily used.

[0026]

EXAMPLES The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1] Polypropylene resin (MI
= 1.0; propylene with an ethylene content of 3.6% by weight
60 parts by weight of ethylene random copolymer) and 40 parts by weight of polyethylene resin (MI = 8.0; linear low density polyethylene having a density of 0.920 g / cm ³ ) were mixed to prepare a polyolefin resin. 100 parts by weight of this polyolefin resin, 10 parts by weight of azodicarbonamide as a thermal decomposition type foaming agent, 1.5 parts by weight of trimethylolpropane trimethacrylate as a crosslinking aid and 1.5 parts by weight of 1,9-nonadiol dimethacrylate. , And 0.3 parts by weight of 2,6-di-t-butyl-4-methylphenol as an antioxidant were mixed to prepare a resin blend.

This resin composition was prepared by using an extruder.
Molded into a sheet at a temperature below the decomposition temperature of the thermal decomposition type foaming agent,
A foamable sheet having a thickness of 1.5 mm was obtained. 0.5M including electron beam (800KV) from both sides to this foaming sheet
The resin was cross-linked by irradiating with rad and subsequently with 1 Mrad of a low voltage electron beam (300 KV) from one side. Next, the crosslinked foamable sheet was heated in a hot air type foaming furnace at 280 ° C. to be foamed to obtain a crosslinked resin foamed sheet. This cross-linked resin foam sheet had a thickness of 3 mm, a magnification of 25 cc / g, and had a gel fraction A of 33% after being extracted in xylene at 120 ° C. for 24 hours and after being extracted in xylene at 120 ° C. for 72 hours. Has a gel fraction B of 31% and B / A = 0.9
It was 4.

A gel fraction C after extraction of a slice of a 0.5 mm-thick skin from the surface of the additionally irradiated surface of this crosslinked resin foam sheet for 24 hours in xylene at 120 ° C. is 35%, 0.5mm thickness from the surface of the other surface
2 slices of the epidermis in 120 ° C xylene
The gel fraction D after extraction for 4 hours was 31%. The presence or absence of irregularities (avatar phenomenon) was visually confirmed on the surface of this crosslinked resin foam sheet, and those having no irregularities were regarded as acceptable products. As a result, there was no unevenness on the surface of the sheet, and the sheet was acceptable. In order to evaluate the vacuum formability of this crosslinked resin foam sheet, a urethane adhesive is applied and dried on one surface (the surface having gel fraction C), and then heated to give a soft vinyl chloride resin sheet (thickness 0.4 mm). ) Was adhered and pressure-bonded to obtain a foam sheet with a skin material. At this time, the presence or absence of irregularities (avatar phenomenon) on the surface of the skin material was confirmed, and those without irregularities were regarded as acceptable products. As a result, there was no unevenness on the surface of the sheet, and the sheet was acceptable.

This foamed sheet with skin material (10 samples)
Using, to heat the sheet surface to 180 ℃,
A compression molding test was conducted by using a shearing mold for testing as shown in FIG. 1 and setting the clearance of the mold to 1.0 mm. The case where no blistering occurred was regarded as an acceptable product, and the compression moldability, that is, the ease of blistering was evaluated by the number. As a result, all the molded products (10 pieces) passed. The above results are summarized in Table 1.

[Example 2] As a crosslinking aid, 0.9 parts by weight of trimethylolpropane trimethacrylate, 1,9
-The crosslinked resin foam sheet shown in Table 1 was prepared in the same manner as in Example 1 except that 2.0 parts by weight of nonadiol dimethacrylate and 0.3 parts by weight of divinylbenzene were used. Similarly, the vacuum moldability, compression moldability and the like were evaluated. The results are summarized in Table 1.

[Comparative Examples 1 to 5] The crosslinked resin foam sheet shown in Table 1 was prepared by changing the type and mixing ratio of the crosslinking aid, the irradiation dose, the heating and foaming conditions, and the like as in Example 1. ,
The vacuum moldability and compression moldability were evaluated. The results are summarized in Table 1.

[0033]

[Table 1]

[0034]

EFFECTS OF THE INVENTION According to the present invention, a crosslinked polyolefin resin foam capable of obtaining a high-quality molded product without causing problems such as blistering phenomenon and avatar phenomenon at the time of laminating a skin material or forming processing such as vacuum forming. Can be provided. The crosslinked polyolefin resin foam of the present invention is particularly suitable as an interior material for vehicles such as automobiles.

[Brief description of drawings]

FIG. 1 Shear mold for compression molding test

[Explanation of symbols]

 10: Shearing mold 11: Upper mold 12: Lower mold 20: Cross-linked resin foam sheet with skin material 21: Skin material 22: Cross-linked resin foam sheet 30: Clamp

Claims (1)

[Claims] 1. A sheet-like crosslinked polyolefin resin foam formed from a polyolefin resin containing 50 to 100% by weight of a polypropylene resin and 0 to 50% by weight of a polyethylene resin. 12
The gel fraction A when extracted in xylene at 0 ° C. for 24 hours is less than 40%, and the gel fraction A and the gel fraction B when extracted in xylene at 120 ° C. for 72 hours are , B
/A≧0.85, and (b) the gel fraction C of the skin layer from one surface of the sheet-like foam to a thickness of 0.5 mm is 35% or more, and the thickness is from the other surface. The gel fraction D of the skin layer up to 0.5 mm is 30% or more, and C>
And (c) the difference between the gel fraction A and the gel fraction C (| A−C |), and the gel fraction A and the gel fraction D.
And the difference (| A-D |) are all within 10%, and a crosslinked polyophine resin foam excellent in moldability. (However, gel fractions A, C and D are
After immersing 0 mg in xylene at 120 ° C. for 24 hours,
The insoluble matter was filtered off and vacuum dried for 8 hours, and the weight was measured, and this measured value was divided by the weight of the original sample to obtain 100.
It is the value multiplied by. The gel fraction B is 1 for 100 mg of sample.
After being soaked in xylene at 20 ° C. for 72 hours, the insoluble matter was filtered off and vacuum dried for 8 hours, and the weight was measured. . )