JP2003002999A - Polyolefin resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin resin foam having high flexibility, good heat resistance, excellent secondary processability, excellent adhesion to a skin material and a beautiful appearance. SOLUTION: This polyolefin resin foam is obtained by cross-linking and foaming a polyolefin resin composition comprising 100 pts.wt. specific resin matrix, and the foam has <=90 mJ/mg melting heat capacity measured by a differential scanning calorimeter(DSC), and <=5% rate of dimensional change after leaving the foam in an oven at 120 deg.C for 60 min. The resin matrix comprises 30-90 wt.% polypropylene resin containing propylene and an α-olefin except propylene as constituent units regulated so that the contents of the α-olefin is 1-15 wt.%, and having 2-8 ratio of weight average molecular weight/ number average molecular weight, and 0.1-10 g/10 min melt index(MI), and 10-70 wt.% polyethylene resin having 0.86-0.92 kg/m<3> density, and 2-50 g/10 min melt index(MI).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyolefin resin foam, and more specifically, to flexibility, heat resistance,
The present invention relates to a crosslinked polyolefin-based resin foam having excellent mechanical strength and capable of secondary processing in a complicated shape.

[0002]

2. Description of the Related Art Polyolefin resin foams are generally excellent in flexibility, lightweight and heat insulating property, and have been conventionally used as interior materials for vehicles such as ceilings, doors and instrument panels. These interior materials are usually molded into a predetermined shape by subjecting a sheet-shaped polyolefin resin foam to secondary processing by vacuum molding, compression molding, or the like. Further, the polyolefin resin foam is usually used as a laminate in which a polyvinyl chloride resin sheet, a thermoplastic elastomer sheet, a natural or artificial cloth-like material, or a skin material such as leather is laminated.

In recent years, in vacuum molding of foams and compression molding such as stamping molding, a processing temperature is set to a high temperature of 120 to 200 ° C. to improve productivity, and deep drawing is performed to form a complicated shape. Is being asked,
Therefore, the polyolefin resin foam is required to have good moldability at high temperature.

In addition, the interior of automobiles is required to have a good feel and feel, and in pursuit of safety, the flexibility of interior materials is strongly demanded.

Originally, polyethylene resin foams are not suitable for molding at high temperature because they are excellent in flexibility but insufficient in heat resistance. On the other hand, the polypropylene resin foam has heat resistance as compared with the polyethylene resin, but is not flexible. Therefore, efforts have been made to impart heat resistance and flexibility by cross-linking / foaming a polypropylene-based resin and a polyethylene-based resin to improve moldability at high temperature.

However, as a problem in integrally molding such a laminated body with a high-pressure high-temperature resin such as compression molding, the foam is extremely compressed in a portion to which a strong pressure is applied. Since a part of the foam melts into the base resin due to contact with the melted base resin, the flexibility originally possessed by the foam may be impaired, resulting in a very hard product. There were many.

[0007]

In view of such background of the prior art, the present invention has both high flexibility and good heat resistance, and is excellent not only in secondary molding workability but also in adhesiveness to a skin material. The present invention aims to provide a polyolefin resin foam having a beautiful appearance.

[0008]

The present invention employs the following means in order to solve the above problems. That is, the polyolefin resin foam of the present invention has propylene and an α-olefin other than propylene as a constitutional unit, the above-mentioned α-olefin content is 1 to 15% by weight, and the weight average molecular weight / number average molecular weight is 2 ~ 8, melt index (MI) 0.1g ~ 10g
-10 minutes polypropylene resin 30 to 90% by weight
And a polyolefin resin composition comprising 100 parts by weight of a resin matrix comprising 10 to 70% by weight of a polyethylene resin having a density of 0.86 to 0.92 kg / m ³ and a melt index (MI) of 2 to 50 g / 10 minutes. The melting heat capacity of the foam measured by a differential scanning calorimeter (DSC) is 90.
mJ / mg or less, and the dimensional change rate after standing for 60 minutes in an oven at 120 ° C. is 5% or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has the above-mentioned problems, that is, high flexibility and good heat resistance, excellent secondary molding processability, and excellent adhesiveness with a skin material as described above. We have carefully studied beautiful polyolefin resin foams, and have a specific melt index as a resin component, a specific amount of α-olefin other than propylene, a polypropylene resin that has been copolymerized, and a specific density and melt index. By using this polyethylene resin to crosslink and foam this resin component using a polyfunctional monomer and an organic thermal decomposition type foaming agent, it was clarified that these problems can be solved all at once.

The resin composition containing the resin component, the polyfunctional monomer, and the organic thermal decomposition type foaming agent can be efficiently and continuously crosslinked uniformly by irradiating with ionizing radiation. . Further, when this is heat-foamed, it is possible to obtain a polyolefin resin foam which is excellent in heat resistance, flexibility, secondary processability, and adhesiveness with a skin material and has a beautiful appearance.

The polypropylene resin used in the present invention is a homopolymer of propylene or a copolymer of propylene and an α-olefin other than propylene. Examples of the α-olefin as a copolymerization component include ethylene,
1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like can be mentioned. The content of the propylene component in the copolymer is 85% by weight or more, preferably 90% by weight or more.

The polypropylene resin used in the present invention must have a MI of 0.1 to 10 g / 10 minutes. If the MI is too small, the moldability of the resulting foam will decrease, and conversely if it is too large, the heat resistance of the resulting foam will decrease. MI is preferably 0.3 to 10 (g / 10
Min), more preferably 0.5 to 8 (g / 10 min). The mixing ratio of polypropylene resin in the resin component is 3
It is necessary to be 0 to 90% by weight. If the blending ratio of the polypropylene-based resin is too small, the heat resistance of the obtained foam is lowered, and if the blending ratio is too large, the flexibility of the obtained foam is lowered.

Polyethylene resin used in the present invention
Ethylene homopolymer or ethylene and α-o
It is a copolymer with a reffin. As α-olefin
Is, for example, propylene, 1-butene, 1-pentene,
1-hexene, 4-methyl-1-pentene, 1-hepte
And 1-octene. The ports used in the present invention
The polyethylene resin has an MI of 2 to 50 g / 10 minutes
And the density is 0.86 to 0.92 kg / m.³Range of
And preferably 0.88 to 0.91 kg / m ³Demon
The ultra-low density linear polyethylene that surrounds the foam is flexible
It is preferable to increase

In the present invention, a polyfunctional monomer is used as a crosslinking aid. Examples of polyfunctional monomers include divinylbenzene, trimethylolpropane trimethacrylate, 1,9-nonanediol dimethacrylate, and 1,1.
It is possible to use 0-decanediol dimethacrylate, trimellitic acid triallyl ester, triallyl isocyanurate, ethyl vinyl benzene and the like.

These polyfunctional monomers may be used alone or in combination of two or more kinds. About 0.5 to 10 parts by weight of these polyfunctional monomers are added to 100 parts by weight of the resin matrix.

The organic thermal decomposition type foaming agent used in the present invention includes, specifically, azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, azobisisobutyronitrile and azodicarbonate. Barium acid or the like is used. These may be used alone or in combination,
It is used in a ratio of 1 to 50 parts by weight with respect to 100 parts by weight of the resin matrix. The amount of addition of these organic thermal decomposition type foaming agents, when the amount is too small, the foamability of the resin composition decreases,
If the amount is too large, the strength and heat resistance of the resulting foam will decrease. Therefore, the addition amount of the thermal decomposition type foaming agent is preferably 4 to 25 parts by weight.

In the present invention, other thermoplastic resins such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high-molecular-weight polyethylene can be used within the range not impairing the object of the present invention. , Polypropylene, ethylene-propylene rubber, polyvinyl acetate, polybutene and the like can be added as minor components. In addition, phenol-based, phosphorus-based, amine-based,
Sulfur-based antioxidants, metal damage inhibitors, flame retardants, fillers, antistatic agents, heat stabilizers, pigments and the like may be added.

In the present invention, the polyolefin resin foam composition obtained by blending the above components is molded into a predetermined shape, and then crosslinked and foamed to produce a polyolefin resin foam. Specifically, for example, the following manufacturing method may be mentioned. A predetermined amount of the polyolefin resin composition is uniformly melted at a temperature lower than the decomposition temperature of the thermal decomposition type foaming agent using a kneading device such as a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader mixer, and a mixing roll. It is kneaded and molded into a sheet. Next, the obtained sheet is irradiated with a predetermined dose of ionizing radiation to crosslink the olefin resin, and the crosslinked sheet is heated to a temperature equal to or higher than the decomposition temperature of the thermal decomposition type foaming agent to foam. Instead of crosslinking by irradiation with ionizing radiation, crosslinking by peroxide or silane crosslinking may be performed.

As ionizing radiation, α rays, β rays, γ
Ray, electron beam and the like. The irradiation dose of ionizing radiation varies depending on the type of polyfunctional monomer, the addition amount, the desired degree of crosslinking, etc., but is preferably 1 to 500 k.
Gy, more preferably 5 to 300 kGy. If the irradiation dose is too low, the heat resistance of the resulting foam will be insufficient, and if it is too high, the moldability of the resulting foam will deteriorate.

The foam of the present invention is characterized by having both flexibility and heat resistance. The melting heat capacity is mentioned as one of the indexes showing the flexibility of the foam in the present invention. It is a well-known fact that a polymer having a higher crystallinity has a larger heat capacity for fusion, but a polymer having a higher crystallinity has a higher rigidity. The foam in the present invention preferably has a heat capacity of fusion of 90 mJ / mg or less in order to maintain flexibility, and when it exceeds 90 mJ / mg, the flexibility of the foam is impaired as described above, and As a result, the flexibility of the molded product decreases, which is not preferable.

In general, when the raw material composition is the same, the flexibility of the foam increases as the expansion ratio increases, and the foam of the present invention has a horizontal axis of density and a vertical axis of In the two-dimensional graph with 25% compression hardness, (2
5% compression hardness) = 3.17 × (density) -60, which is characterized by being located in a region below the straight line. Positioning above the region indicated by this straight line is not preferable because the flexibility of the molded product, which is the problem to be solved by the present invention, is impaired.

The dimensional change rate at the time of heating is mentioned as one of the indexes showing the heat resistance of the foam in the present invention, and specifically, it is shown by the dimensional change rate after being left in an oven at 120 ° C. for 60 minutes. This dimensional change rate is preferably 5% or less. If the dimensional change rate exceeds 5%, the shrinkage of the foam increases due to heating during molding, which is not preferable.

Further, the gel fraction of the foam of the present invention is preferably 30 to 70% in order to maintain heat resistance and moldability at high temperature. When the gel fraction is 30% or less, the heat resistance of the foam is lowered, and the moldability at high temperature is remarkably lowered, which is not preferable, and when the gel fraction exceeds 70%, the elongation of the foam is lowered. However, this is not preferable because the moldability is reduced.

The expansion ratio of the foamed product of the present invention is preferably 5 to 50 times. When the expansion ratio is less than 5 times, the flexibility of the molded article decreases, and when the expansion ratio exceeds 50 times, the heat resistance becomes high. It is not preferable because it is deteriorated and the moldability at high temperature is remarkably deteriorated.

The gel fraction referred to in the present invention is a value calculated by the following method. Approximately 50 mg of modified polyolefin-based resin foam is accurately weighed, and xylene 25 at 120 ° C is used.
After immersing in ml for 24 hours, it is filtered through a 200-mesh stainless steel wire net, and the wire net-like insoluble matter is vacuum dried. Then, the weight of this insoluble matter was precisely weighed, and the gel fraction was calculated in percentage according to the following formula.

Gel fraction (%) = {weight of insoluble matter (m
g) / weight of polyolefin resin foam weighed (m
g)} × 100 The differential scanning calorimetric analysis in the present invention was performed by the following method. Approximately 10 mg of the polyolefin resin foam, which had been pressed at room temperature in advance, was placed in a platinum pan, and a differential scanning calorimeter (DSC: Seiko Denshi Kogyo RDC220) was used.
-Robot DSC). The measurement conditions were such that the sample was once melted, cooled to −50 ° C. at a rate of 10 ° C./minute, and then heated at a rate of 5 ° C./minute for measurement.

The heating dimensional change in the present invention was performed by the following method. The polyolefin resin foam is accurately cut into 15 cm square pieces and left in an oven set at 120 ° C. for 60 minutes. After 60 minutes, remove from the oven and cool at room temperature for about 30-60 minutes. The dimensions of the sample were measured, and the dimensional change rate was calculated as a percentage based on the following formula.

Heating dimensional change rate (%) = [{sample length before putting in oven-sample length after taking out from oven} / sample length before putting in oven] × 100
The 25% compression hardness in the present invention was measured by the following method. The foamed body was cut into 5 cm square pieces, and four pieces were stacked and measured with a compression tester (Model AF-200 manufactured by Kobunshi Keiki Co., Ltd.). The measuring method conforms to JIS K6767.

[0029]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited thereto.
In addition, "part" below means "part by weight".

Example 1 Propylene was randomly copolymerized with 3.6% by weight of ethylene to give MI of 2.5 g / 10 minutes and a density of 0.905 kg / m.
96 kg of polypropylene resin powder of 3 and MI of 5 g
/ 10 minutes, 64 kg of polyethylene resin powder having a density of 0.910 kg / m ³ , 0.95 kg of "Irganox 1010" as a stabilizer, 7.4 kg of azodicarbonamide as a foaming agent, and 8.0 kg of divinylbenzene. Then, add polypropylene resin, polyethylene resin, foaming agent and stabilizer to the Henschel mixer, and
Mix at low speed of 00 rpm for about 3 minutes, then 800
It is rotated at a high speed of 1000 rpm and mixed for 3 minutes to obtain a foaming resin composition.

This foaming resin composition was introduced into an extruder equipped with a vent which was heated to a temperature at which the foaming agent did not decompose, specifically 160 to 190 ° C., and extruded from a T die to form a crosslinked foam having a thickness of 1.5 mm. Molded into a sheet. This sheet was irradiated with an electron beam of 320 kGy to be crosslinked, then continuously introduced into a vertical hot air foaming device, heated and foamed, and wound as a continuous sheet-shaped crosslinked foam.

The foam thus obtained has a thickness of 3.
It was 0 mm, the gel fraction was 55%, and the expansion ratio was 15 times.

The characteristics of the polyolefin resin foam thus obtained are shown in Table 2.

Comparative Examples 1 and 2 Polyethylene resin and polypropylene resin shown in Table 1 were used to carry out the same operations as in Example 1 to obtain polyolefin resin foams having the characteristics as shown in Table 2. Obtained.

[0035]

[Table 1]

[0036]

[Table 2]

As is apparent from Table 2, the heat resistance of fusion of Example 1 is smaller than that of Comparative Examples 1 and 2, but the heat resistance equivalent to that of Comparative Examples 1 and 2, that is, It is a dimensional change rate upon heating, and it can be seen that the 25% compression hardness value is smaller than those of Comparative Examples 1 and 2, that is, the flexibility is excellent.

[0038]

EFFECTS OF THE INVENTION According to the present invention, a polyolefin resin foam having a beautiful appearance, which is excellent in secondary molding processability and adhesiveness with a skin material in addition to having high flexibility and good heat resistance, is stable. Can be provided.

Continued front page    F-term (reference) 4F074 AA17 AA24 AA98 AB01 AB05                       BA13 BB01 BB25 CA29 CC04Y                       CC06X DA02 DA04 DA22                 4J002 BB03X BB05X BB12W BB14W                       BB15W BB15X EA056 EH076                       EH146 EQ017 EQ027 ES007                       ET007 EV287 FD156 FD327                       GN00

Claims (3)

[Claims] 1. A propylene and an α-olefin other than propylene as a constitutional unit, wherein the α-olefin content is 1 to
15% by weight, the weight average molecular weight / number average molecular weight is 2 to 8, and the melt index (MI) is 0.1 g.
Polypropylene resin 30 to 9 which is 10 g / 10 minutes
A polyolefin composed of 100 parts by weight of a resin matrix composed of 0% by weight and 10 to 70% by weight of a polyethylene resin having a density of 0.86 to 0.92 kg / m ³ and a melt index (MI) of 2 to 50 g / 10 minutes. The resin composition is crosslinked / foamed, and the melting heat capacity of the foam measured by a differential scanning calorimeter (DSC) is 90 mJ / mg or less, and in an oven at 120 ° C.,
A polyolefin resin foam having a dimensional change rate of 5% or less after being left for 60 minutes. 2. In the foam according to claim 1, in a two-dimensional graph in which the horizontal axis represents the density and the vertical axis represents the 25% compression hardness, (25% compression hardness) = 3.17 × (density ) -6
A polyolefin resin foam characterized by being located in a region below a straight line represented by 0. 3. A gel fraction of 30 to 70% and an expansion ratio of 5
The polyolefin resin foam according to claim 1, wherein the polyolefin resin foam has a ratio of up to 50 times.