JPH10130416A - Polypropylene resin foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foam having low density, a high closed-cell rate, a large cross-sectional area, a large wall thickness and excellent heat resistance and chemical resistance by mixing a polypropylene resin with an aromatic vinyl polymer in a specified ratio and extrusion-foaming the resulting mixture. SOLUTION: This invention provides a foam having a density of 10-100kg/m<3> , a mean cell diameter of 0.02-5mm, a closed-cell rate of 50% or above and a minimum area of a cross section crossing to the machine direction of 1,000mm<2> or above, wherein the cell walls are characterized in that (A) they are composed of at least 80wt.% polypropylene resin and at most 20wt.% aromatic vinyl polymer (especially desirably, a styrene polymer) and that (B) the coagulates of the aromatic vinyl polymer are uniformly dispersed in a size of 1μm or below. The resin having properties (A) and (B) is obtained by for example grafting an aromatic vinyl monomer onto a polypropylene resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polypropylene resin foam having excellent heat resistance and chemical resistance.

[0002]

2. Description of the Related Art In general, foams made of a thermoplastic resin are lightweight and have good heat insulating properties and good buffering properties against external stress, so that they are widely used in heat insulating materials, cushioning materials, core materials, food containers and the like. It's being used. Above all, foams made of polypropylene resin are preferably used as cushioning materials because of their good chemical resistance, impact resistance and heat resistance.

However, since the polypropylene resin is a crystalline resin, the viscosity and tension at the time of melting are low,
When this resin is foamed, the strength of the cell wall cannot be sufficiently maintained during foaming. In order to improve the foamability of such a polypropylene resin, for example, a method of blending polyethylene with a polypropylene resin and foaming the same (for example, Japanese Patent Publication No. 44-2574), blending polystyrene with a polypropylene resin, (For example, Japanese Patent Publication No. 43-13375)
Is being done.

[0004] However, simply blending other resins while maintaining the characteristics of polypropylene-based resin,
A foam having a low density, a high closed cell rate and a large wall thickness cannot be obtained.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low-density, high-closed-cell-porosity, high-thickness polypropylene resin foam made of a polypropylene resin and having excellent heat resistance and chemical resistance. is there.

[0006]

According to the present invention, a polypropylene resin is extruded and foamed to obtain a resin of 10 to 100 kg / m.
Density of ³ , average cell diameter of 0.02-5 mm and 50%
In the foam having the above-mentioned closed cell ratio and having a minimum cross-sectional area of 1000 mm ² or more in a cross section orthogonal to the extrusion direction, the cell wall is (1) 80% by weight of a polypropylene resin.
The above and 20% by weight or less of the aromatic vinyl polymer,
(2) A foam, wherein the agglomerated portion of the aromatic vinyl polymer is substantially uniformly dispersed in a size of 1 micron or less.

Preferably, the foam is a plate-like foam having a minimum thickness of at least 10 mm in a cross section perpendicular to the extrusion direction.

It is preferable that the polypropylene resin is a propylene homopolymer or a propylene copolymer containing at least 70% by weight of a propylene component.

Further, it is preferable that the aromatic vinyl polymer is a styrene polymer.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A polypropylene resin foam to which the present invention is directed is obtained by extrusion foaming a polypropylene resin, and has a density of 10 to 100 kg / m ^{3 and} a density of 0.02 to 100 kg / m ^3.
It has an average cell diameter of 5 mm, a closed cell ratio of 50% or more, and a minimum cross-sectional area of a cross section orthogonal to the extrusion direction of 1000.
mm ² or more. Such foams
Polypropylene resin has not been manufactured so far,
At present, it is manufactured by adding a polystyrene resin with a polyethylene resin. However, in this foam, about 30% by weight of the cell wall is a polystyrene resin, and the aggregated portion is stretched by foaming, but has a size of several microns to several tens of microns. The body had poor chemical resistance and heat resistance.

However, according to the present invention, the bubble wall is
(1) Consisting of 80% by weight or more of a polypropylene-based resin and 20% by weight or less of an aromatic vinyl polymer, and (2) substantially uniformly dispersing the aggregated portion of the aromatic vinyl polymer in a size of 1 micron or less. As a result, these problems could be solved.

The polypropylene-based resin foam of the present invention comprises:
Since the agglomerated portion of the aromatic vinyl polymer component in the cell wall is finely dispersed, unlike the case where other resins are simply blended, the chemical resistance and heat resistance characteristic of the polypropylene resin foam are different. It is not spoiled.

The method of observing the size of the agglomerated portion of the aromatic vinyl polymer component in the cell wall is not particularly limited. For example, the foam cell is embedded in a resin, and the aromatic vinyl polymer is coated with ruthenium tetraoxide. After staining the region, an ultrathin section can be prepared and observed by using a transmission electron microscope. FIG. 1 described below shows an electron micrograph of the foam obtained in Example 1 of the present invention by this method.

In the present invention, the agglomerated portion of the aromatic vinyl polymer means a portion which is stained black by the transmission electron microscope observation. As the substance of this black part,
Examples thereof include an agglomerated portion of an aromatic vinyl polymer portion existing in the form of a graft copolymer or a block copolymer and an aggregate portion of an aromatic vinyl homopolymer. Further, the aromatic vinyl polymer site of the copolymer and the degree of polymerization of the aromatic vinyl polymer are not particularly limited.

The foam of the present invention preferably has a density of 10 to 100 kg / m ³ from the viewpoint of lightness, heat insulation, cushioning of external stress or compressive strength, and 15 to 100 kg / m ^3. More preferably, it is で 300 kg / m ³ .

The foam of the present invention preferably has an average cell diameter of 0.02 to 5 mm from the viewpoint that the appearance, buffering of external stress and compressive strength are suitable. More preferably, it is 3 mm.

Further, the foam of the present invention preferably has a closed cell ratio of 50% or more, and more preferably 70% or more, from the viewpoint that heat insulation, buffering of external stress and compressive strength are suitable. Is more preferable.

In addition, the foam in the present invention preferably has a cross-sectional area orthogonal to the extrusion direction of the foam of at least 1000 mm ^{2 in view of} being used as a cushioning material or a heat insulating material.

When the foam in the present invention is a plate-like foam, the minimum thickness of a cross section orthogonal to the extrusion direction of the foam is 10 mm from the viewpoint that buffering of external stress is preferable. It is preferable that it is above.

The resin constituting the cell wall of the present invention is a resin containing at least 80% by weight of a polypropylene resin.
The polypropylene resin means a propylene homopolymer or a propylene copolymer such as a random copolymer or a block copolymer of propylene and another monomer. In the case of a propylene-based copolymer, it preferably has a propylene component of 70% by weight or more, more preferably 90% by weight or more of a propylene component. Other monomers include ethylene, butene-
1 selected from the group consisting of α-olefins such as 1, cyclic olefins such as cyclopentene, diene monomers such as 5-ethylidene-2-norbornene, and vinyl monomers such as vinyl acetate. Or two or more monomers. Also, as this monomer, ethylene is easily copolymerized with propylene and is inexpensive.
α-Olefin or diene monomers are preferred.

The aromatic vinyl monomer constituting the agglomerated portion of the aromatic vinyl polymer component present in the cell wall is, for example, styrene; o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene. Methylstyrene such as methylstyrene, β-methylstyrene, dimethylstyrene and trimethylstyrene; α-chlorostyrene, β-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, dichlorostyrene, trichlorostyrene and the like Chlorostyrene; bromostyrene such as o-bromostyrene, m-bromostyrene, p-bromostyrene, dibromostyrene, tribromostyrene; o-fluorostyrene, m-fluorostyrene, p
-Fluorostyrene such as fluorostyrene, difluorostyrene and trifluorostyrene; nitrostyrene such as o-nitrostyrene, m-nitrostyrene, p-nitrostyrene, dinitrostyrene and trinitrostyrene; o-hydroxystyrene, m-hydroxystyrene , P-hydroxystyrene, dihydroxystyrene,
Vinylphenol such as trihydroxystyrene; o-
Divinylbenzene such as divinylbenzene, m-divinylbenzene and p-divinylbenzene; one or more kinds such as isopropenylstyrene such as o-diisopropenylbenzene, m-diisopropenylbenzene and p-diisopropenylbenzene Is raised. Of these, methylstyrene such as styrene, α-methylstyrene, and p-methylstyrene, divinylbenzene, or a mixture of divinylbenzene isomers are preferable because they are inexpensive.

As described above, the aromatic vinyl polymer is incorporated into the polypropylene resin in the form of a homopolymer, a random copolymer or a block copolymer, or in the form of a graft chain grafted on the polypropylene resin. Exists.

The polypropylene-based resin contains at least 80% by weight, and the agglomerated portion of the aromatic vinyl polymer component is 0.001%.
Various methods are also possible for producing a resin having a size of about 1.0 micron and being uniformly dispersed. For example, a polypropylene resin may be graft-modified with an aromatic vinyl monomer, and the grafted aromatic vinyl polymer portion may constitute an agglomerated portion having a size specified in the present invention, or a polypropylene resin may be used. It is also possible to mix an aromatic vinyl polymer with a compatibilizer such as a hydrogenated styrene-butadiene-styrene block copolymer to form an aggregate portion having a size specified in the present invention. In order to form a uniform aggregate portion having a size specified in the present invention, a method of graft-modifying a polypropylene resin with an aromatic vinyl monomer is preferable.

The method for producing the foam of the present invention is not limited. For example, a resin containing 80% by weight or more of a polypropylene-based resin and in which an agglomerated portion of an aromatic vinyl polymer component is uniformly dispersed in a size of 0.001 to 1.0 micron is melted in an extruder. A method in which a volatile foaming agent is press-fitted into the resin in a molten state, kneaded while maintaining the pressure at a high pressure, and then discharged from a die to extrude and foam.

[0025]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 100 parts by weight of propylene homopolymer, 10 parts by weight of styrene monomer, and 1.0 part by weight of α, α'-bis (t-butylperoxy-m-isopropyl) benzene as a radical polymerization initiator The mixture was melt-kneaded using a twin screw extruder (LABOTEX) manufactured by Japan Steel Works, Ltd., and melt-extruded to obtain a molded product of a rod-shaped modified polypropylene resin composition having a diameter of 4 mm. The molded product of the rod-shaped modified polypropylene resin composition was chopped to a thickness of 3 mm to obtain pellets of the modified polypropylene resin composition.

The twin-screw extruder was of the same-direction twin-screw type, had a cylinder bore diameter of 32 mmφ, and had a maximum effective screw length (L / D) of 25.5. The twin-screw extruder was heated at a set temperature of the cylinder section of 200 ° C. and at a set temperature of the feed section of 160 ° C., and the rotation speed of the screw was set to 100 rpm for each axis.

Using the pellets of the modified polypropylene resin composition, a plate-like foam was produced by the following method.

100 parts by weight of the modified polypropylene resin composition pellets, 0.05 parts by weight of the blended oil, and 0.1 parts by weight of sodium bicarbonate-citric acid as a foam nucleating agent were mixed for 15 minutes using a ribbon blender. . This mixture was tandem-type extruder (the first-stage extruder cylinder diameter was 65 mmφ, the second-stage extruder cylinder diameter was 90 mm
φ), and melted at 230 ° C. in the first-stage extruder. Then, as a blowing agent, butane gas (iso-rich butane gas; a mixture ratio of normal butane / isobutane is 1 by weight).
5/85) into 100 parts by weight of the modified polypropylene resin composition, 10 parts by weight were pressed and kneaded, and the mixture was cooled in a second-stage extruder so that the temperature of the resin composition became 150 ° C., A plate-shaped foam was obtained by extruding from a rectangular die having a slit of width 60 mm and thickness 1.0 mm and passing through a molding die directly connected to the rectangular die.

The size of the agglomerated portion of the aromatic vinyl polymer component of the obtained plate-like foam, the density of the plate-like foam, the average cell diameter, the closed cell ratio, the cross-sectional area of the cross section orthogonal to the extrusion direction, and The minimum thickness of the foam cross section was measured by the following method. Size of aggregated portion of aromatic vinyl polymer component of foam:
The foam cell portion is embedded in a resin and stained with ruthenium tetroxide to prepare an ultrathin section, which is then enlarged to 10000 parts by a transmission electron microscope and observed. Density: Calculated from the weight and the volume determined by the submersion method. Average cell diameter: A plate-like foam is placed on a flat surface, cut on a plane perpendicular to the extrusion direction using a cutter, and the cut surface is observed under a scanning electron microscope. Closed cell rate: ASTM D using multi-pycnometer
Measure according to -2856. Cross-sectional area: Calculated by copying the cross-sectional shape used in the measurement of the average cell diameter on paper whose weight per area has been measured in advance, cutting out the paper, and measuring the weight. Minimum thickness of cross section: Using the cross section used in the measurement of the average cell diameter, the thickness of the thinnest portion 5 mm or more inside from the end is measured with a vernier caliper.

FIG. 1 shows a transmission electron micrograph (10) of the aggregated portion of the aromatic vinyl polymer component of the obtained plate-like foam.
000 times). Here, the portion dyed black is the agglomerated portion, and it is understood that the size is 1 μm or less. As a result of evaluating the obtained plate-like foam,
The density is 34 kg / m ³ and the average bubble diameter is 0.9 mm
, The closed cell ratio is 70%, and the cross-sectional area is 1500
mm ² and the minimum thickness was 14 mm.

Example 2 A modified polypropylene resin was produced in the same manner as in Example 1 except that the amounts of the aromatic vinyl monomer and the radical polymerization initiator supplied to the twin-screw extruder were changed as shown in Table 1. A pellet of the composition was obtained.

Using the obtained pellets of the modified polypropylene resin composition, a plate-like foam was obtained in the same manner as in Example 1.

The size of the agglomerated portion of the aromatic vinyl polymer component in the plate-like foam, the density of the foam, the average cell diameter, the closed cell ratio, the cross-sectional area, and the minimum thickness were the same as those in Example 1. The method was evaluated. Table 2 shows the results.

Example 3 Pellets of a modified polypropylene resin composition were obtained in the same manner as in Example 1, except that the type of the polypropylene resin supplied to the twin-screw extruder was changed as shown in Table 1.

A plate-like foam was produced in the same manner as in Example 1 except that the obtained pellets of the modified polypropylene resin composition were used and the temperature of the resin composition in the second-stage extruder was changed to 130 ° C. I got a body.

The size of the agglomerated portion of the aromatic vinyl polymer component in the plate-like foam, the density of the foam, the average cell diameter, the closed cell ratio, the cross-sectional area, and the minimum thickness were the same as those in Example 1. The method was evaluated. Table 2 shows the results.

Comparative Example 1 A plate-like foam was produced in accordance with the method for producing a plate-like foam of Example 1 using a propylene homopolymer.

The density, average cell diameter, closed cell ratio, cross-sectional area, and minimum thickness of the plate-like foam were evaluated in the same manner as in Example 1. Table 2 shows the results.

Comparative Example 2 100 parts by weight of a propylene homopolymer and 100 parts by weight of a polystyrene resin were mixed with a twin screw extruder (L) manufactured by Japan Steel Works, Ltd.
ABOtex), melt-kneaded and extruded.
A pellet was produced in the same manner as described above.

Using the obtained pellets of the blended resin, a plate-like foam was produced in accordance with the method for producing a plate-like foam of Example 1.

The size of the agglomerated portion of the aromatic vinyl polymer component in the plate-like foam, the density of the foam, the average cell diameter, the closed cell ratio, the cross-sectional area, and the minimum thickness were the same as in Example 1. The method was evaluated. Table 2 shows the results.

[0043]

[Table 1]

[0044]

[Table 2]

In the foams of the examples, the agglomerated portion of the aromatic vinyl polymer component was finely dispersed in the cell walls, the density of the foams was low, the closed cell ratio was high, and the cross-sectional area was large.
While the minimum thickness is large, the foam in Comparative Example 1 is:
High foam density, low closed cell ratio, low cross-sectional area,
Although the foam in Comparative Example 2 has a small thickness, the foam has a relatively low density, a high cross-sectional area, and a large thickness,
It can be seen that the area of the aromatic vinyl polymer is large and the closed cell ratio is low.

[0046]

The foam of the present invention has a low density, a high closed cell ratio, a large cross-sectional area and a large thickness, and is excellent in heat resistance and chemical resistance, and is useful as a cushioning material and the like. Can be provided.

[Brief description of the drawings]

FIG. 1 is a transmission electron micrograph of a cross section of the foam of the present invention obtained in Example 1, showing a finely dispersed state of resin on a cell wall.

Claims (4)

[Claims] 1. A polypropylene-based resin obtained by extrusion foaming, having a density of 10 to 100 kg / m ³ , 0.02 to 5 m
m having an average cell diameter of 50% and a closed cell ratio of 50% or more,
The minimum cross-sectional area of the cross section perpendicular to the extrusion direction is 1000 mm
^In the foam of ² or more, the cell wall is composed of (1) at least 80% by weight of a polypropylene resin and an aromatic vinyl polymer 2
(2) A foam characterized in that the agglomerated portion of the aromatic vinyl polymer is substantially uniformly dispersed in a size of 1 micron or less. 2. The foam according to claim 1, wherein the foam has a minimum thickness of at least 10 mm in a cross section orthogonal to the extrusion direction. 3. The foam according to claim 1, wherein the polypropylene resin is a propylene homopolymer or a propylene copolymer containing at least 70% by weight of a propylene component. 4. The foam according to claim 1, wherein the aromatic vinyl polymer is a styrene polymer.