JP2001348452A - Polyolefin resin foam and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide a polyolefin resin foam excellent in softness and cushioning property without remarkable shrinkage or deformation after foaming. SOLUTION: The polyolefin resin foam is 230
It is composed of a polyolefin resin having a melt tension at 1 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component. In this polyolefin resin foam, the repulsion load at the time of 50% compression is about 9 N / cm ² or less, and the relative density is about 0.01 to 0.14. The polyolefin-based resin foam can be produced by foam-forming a resin composition containing a polyolefin-based resin having a melt tension at 230 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component. In this case, a high-pressure gas such as carbon dioxide or nitrogen can be used as a foaming agent. As the high-pressure gas, carbon dioxide in a supercritical state may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin foam and a method for producing the same, and more particularly, to a polyolefin resin foam excellent in softness, cushioning properties, heat insulation and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Foams used as internal insulators, cushioning materials, sound insulating materials, heat insulating materials, food packaging materials, clothing materials, building materials, etc. of electronic equipment, etc., have sealing properties when incorporated as parts. From the viewpoint of ensuring the properties, characteristics such as flexibility, cushioning property and heat insulation property are required. Polyolefin-based resin foams such as polyethylene and polypropylene are known as such foams, but these foams have a problem in that they are weak in strength and insufficient in softness and cushioning. As an attempt to improve these, attempts have been made to increase the foaming ratio or to blend the rubber component or the like with the polyolefin resin to soften the material itself. However, in ordinary polyethylene and polypropylene, the tension at high temperature, that is, the melt tension, is weak, and even if an attempt is made to obtain a high expansion ratio, the cell wall is broken at the time of foaming and gas escape occurs, or coalescence of cells occurs. It was difficult to obtain a soft foam having a high expansion ratio as desired.

Heretofore, chemical methods and physical methods have been known as methods for producing polymer foams. A common physical method is to disperse a low-boiling liquid (blowing agent) such as chlorofluorocarbons or hydrocarbons in the polymer and then heat to volatilize the blowing agent to form bubbles. In the chemical method, a foam is obtained by forming cells using gas generated by thermal decomposition of a compound (foaming agent) added to the polymer base.

In recent years, as a method for obtaining a foam having a small cell diameter and a high cell density, a gas such as nitrogen or carbon dioxide is dissolved in a polymer at a high pressure, and then the pressure is released to reduce the glass transition of the polymer. A method has been proposed in which bubbles are formed by heating to a temperature or near the softening point. In this foaming method, a nucleus is formed from a thermodynamically unstable state, and the nucleus expands and grows to form cells, thereby obtaining a microporous foam. According to this method, there is an advantage that an unprecedented microporous foam can be obtained. Various attempts have been made to apply this foaming method to thermoplastic elastomers such as thermoplastic polyurethane. However, in these methods, when the pressure is released to, for example, the atmospheric pressure, the nucleus expands and grows to form bubbles, and once a foam having a high magnification is formed,
Gases such as nitrogen and carbon dioxide remaining in the bubbles gradually permeate through the polymer wall, thereby shrinking the polymer after foaming, gradually deforming the cell shape, and reducing the cell size, There was a problem that the expansion ratio could not be obtained.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a polyolefin resin foam which does not significantly shrink or deform after foaming and is excellent in softness and cushioning property, and a method for producing the same.

[0006]

Means for Solving the Problems As a result of research conducted to solve the above problems, the present inventor has found that a resin composition containing a polyolefin resin having a melt tension at 230 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component is obtained. The present inventors have found that foaming does not cause significant shrinkage or deformation after foaming and that a foam having excellent cushioning properties can be obtained, and the present invention has been completed.

That is, the present invention provides a polyolefin resin foam comprising a polyolefin resin having a melt tension at 230 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component. The present invention also provides a method for producing a polyolefin-based resin foam by foam-molding a resin composition containing a polyolefin-based resin having a melt tension at 230 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polyolefin resin foam of the present invention is composed of a polyolefin resin having a melt tension at 230 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component. 230 ° C of the polyolefin resin
Is preferably 1.2 cN or more (for example, about 1.2 to 30 cN), more preferably 1.5 cN.
This is the above (for example, about 1.5 to 30 cN). The shape of the foam is not particularly limited, and may be any of a sheet shape, a prism shape, and the like.

Such a polyolefin resin foam is excellent in shape fixability, does not significantly shrink even after foaming while maintaining the expansion ratio at the time of foaming, and maintains high cushioning properties. For example, the polyolefin resin foam
The rebound load (50% compressive strength) when compressed 0% is 9N
/ Cm ² or less (for example, about 0.1 to 9 N / cm ² ), and particularly preferred foam is about 8.5 N / cm ² or less (for example, about 0.3 to 8.5 N / cm ² ). Further, the relative density of the polyolefin resin foam is 0.0
It is about 1 to 0.14, and in a particularly preferred foam, it is 0.1 to 0.14.
It is about 015 to 0.10.

The polyolefin resin foam having such excellent properties is obtained by foam molding a resin composition containing, for example, a polyolefin resin having a melt tension at 230 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component. Can be manufactured. Hereinafter, this manufacturing method will be described.

(1) Foam Molding Resin Material As the polyolefin resin used as the material of the foam of the present invention, any polyolefin resin having a melt tension at 230 ° C. of more than 1 cN can be used. There is no particular limitation. The melt tension is preferably 1.2 cN or more (for example, about 1.2 to 30 cN), more preferably 1.5 cN or more (for example, 1.5 to 30 cN).
N).

The polyolefin resin has a melt tension outside the above range in addition to a polyolefin resin having a melt tension within the above range, but the melt tension of the resin itself is out of the above range. The polyolefin-based resin composition adjusted to the above range is also included. As such a melt tension adjusting agent, for example, a fiber-based additive,
Among them, a polytetrafluoroethylene-based additive containing polytetrafluoroethylene as a main component is exemplified.

Examples of the polyolefin resin having the melting property include a resin having a wide molecular weight distribution and having a shoulder on the high molecular weight side, a finely crosslinked resin, and a long chain branched resin. Such types of polyolefin resins include, for example, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, copolymers of ethylene and propylene, ethylene or propylene and other α-olefins. Any of ethylene, vinyl acetate, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, vinyl alcohol and the like, and a mixture thereof. Examples of the “other α-olefin” include butene-1, pentene-
1, hexene-1, 4-methylpentene-1 and the like can be exemplified. Further, the copolymer may be any of a random copolymer and a block copolymer.

The rubber or the thermoplastic elastomer component used as the material of the foam of the present invention is not particularly limited as long as it can be foamed. For example, natural rubber, polyisobutylene, polyisoprene, chloroprene rubber, butyl rubber, nitrile Natural or synthetic rubbers such as butyl rubber; ethylene-propylene copolymer, ethylene-propylene-
Olefinic elastomers such as diene copolymers, ethylene-vinyl acetate copolymers, polybutenes, chlorinated polyethylenes; styrene-butadiene-styrene copolymers, styrene-isoprene-styrene copolymers, and hydrogenated products thereof Various thermoplastic elastomers such as styrene-based elastomer; polyester-based elastomer; polyamide-based elastomer; and polyurethane-based elastomer. These rubbers or thermoplastic elastomer components can be used alone or in combination of two or more.

The amount of the rubber or the thermoplastic elastomer component is based on 100 parts by weight of the polyolefin resin.
10 parts by weight or more (for example, about 10 to 1000 parts by weight),
Especially 30 parts by weight or more (for example, about 30 to 500 parts by weight)
It is preferred that When the amount of the rubber or the thermoplastic elastomer component is less than 10 parts by weight, the cushioning property of the foam tends to be reduced.

(2) Foaming agent The foaming agent used in the foam is not particularly limited as long as it is usually used for foam molding of a polyolefin-based resin. From the viewpoint, it is preferable to use a high-pressure gas. In this specification, the term "high-pressure gas" is used to include a fluid in a supercritical state.

The high-pressure gas is not particularly limited as long as it impregnates the above-mentioned polyolefin resin, rubber or thermoplastic elastomer under high pressure, and examples thereof include carbon dioxide, nitrogen and air. These high-pressure gases may be used as a mixture. Among them, the use of carbon dioxide is preferred because the polyolefin resin, rubber or thermoplastic elastomer used as a material of the foam has a large amount of impregnation and a high impregnation rate. Further, from the viewpoint of increasing the rate of impregnation into the resin, it is preferable that the high-pressure gas (for example, carbon dioxide) is in a supercritical state. The critical temperature of carbon dioxide is 31 ° C., and the critical pressure is 7.4 MPa.
It is. When a gas in a supercritical state (supercritical fluid) is used, the solubility in the resin increases and high-concentration mixing is possible. In addition, when the pressure is rapidly reduced, the concentration of the bubbles increases due to the high concentration. Even if the density of the bubbles formed by growing the nucleus is the same, the porosity is higher than in the other states, so that fine bubbles can be obtained.

When producing the polyolefin resin foam, an additive may be added to a mixture of the polyolefin resin and rubber or a thermoplastic elastomer, if necessary. The type of the additive is not particularly limited, and various additives commonly used for foam molding can be used. Examples of the additive include a bubble nucleating agent, a crystal nucleating agent, a plasticizer, a lubricant, a coloring agent, an ultraviolet absorber, an antioxidant, a filler, a reinforcing agent, a flame retardant, and an antistatic agent. The amount of additives
The amount can be appropriately selected within a range that does not impair the formation of bubbles and the like, and the addition amount used for molding a normal thermoplastic resin can be employed.

(3) Foam Molding Method The method for producing the polyolefin resin foam of the present invention is a method capable of foam molding using the resin composition containing the polyolefin resin and a rubber or a thermoplastic elastomer component. The method is not particularly limited, and may be performed by any method such as a batch method and a continuous method.

An example of producing a polyolefin resin foam by a batch method using a high-pressure gas as a foaming agent will be described below. First, a polymer mixture of the polyolefin-based resin and a rubber or a thermoplastic elastomer component is extruded by using an extruder such as a single screw extruder or a twin screw extruder to prepare a resin sheet for foam molding. Alternatively, the polyolefin resin and the rubber or the thermoplastic elastomer component are uniformly kneaded using a kneader provided with blades such as a roller, a cam, a kneader, and a Banbury type, and a hot plate press or the like. By press molding to a predetermined thickness using
A resin sheet for foam molding is formed. The unfoamed sheet thus obtained is placed in a high-pressure vessel, and a high-pressure gas composed of carbon dioxide, nitrogen, air, or the like is injected, and the unfoamed sheet is impregnated with the high-pressure gas. When the high-pressure gas is sufficiently impregnated, the pressure is released (usually to the atmospheric pressure), and bubble nuclei are generated in the base resin. The bubble nuclei may be grown at room temperature as it is, or may be grown by heating in some cases. After the cells are grown in this manner, the foam is rapidly cooled with cold water or the like, and the shape is fixed, whereby a polyolefin-based resin foam can be obtained. In addition, the molded object to be foamed is not limited to a sheet-like material, and various shapes can be used depending on the application. Further, the molded article to be foamed can be produced by other molding methods such as injection molding, in addition to extrusion molding and press molding.

An example of producing a polyolefin resin foam by a continuous method using a high-pressure gas as a foaming agent will be described below. While kneading the polyolefin-based resin and the rubber or thermoplastic elastomer component using an extruder such as a single-screw extruder or a twin-screw extruder, a high-pressure gas is injected, and the high-pressure gas is sufficiently impregnated in the resin. After that, the pressure is released by extruding (usually to atmospheric pressure) and, optionally, heating to grow the bubbles. After growing the bubbles,
By rapidly cooling with cold water or the like and fixing the shape, a polyolefin-based resin foam can be obtained. In addition, foam molding can also be performed using an injection molding machine other than an extruder.

The pressure at which the gas is impregnated into the molded article or the resin kneaded material to be subjected to foaming can be appropriately selected in consideration of the type of gas, the operability, and the like. About 100 MPa (preferably 7.4
１００100 MPa). The temperature in the gas impregnation step varies depending on the type of gas used, the glass transition temperature of the polymer, and the like, and can be selected in a wide range. However, considering operability and the like, it is preferably about 10 to 300 ° C.

The polyolefin-based resin foam comprising the polyolefin-based resin thus obtained and a rubber or a thermoplastic elastomer is excellent in shape fixability and has the above-mentioned excellent characteristics. The repulsion load and relative density of the polyolefin resin foam at the time of 50% compression are determined by appropriately selecting and combining the type and the melt tension of the polyolefin resin used as a raw material and the type and hardness of the rubber or the thermoplastic elastomer component. Can be adjusted. The polyolefin resin foam of the present invention, for example,
It can be used as an internal insulator for electronic equipment, a cushioning material, a sound insulating material, a heat insulating material, a food packaging material, a clothing material, a building material and the like.

[0024]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The melt tension, relative density, and 50% compressive strength (repulsive load when compressed by 50%) were measured and calculated by the following methods.

(Melt tension) Apparatus: Melt tension type II, manufactured by Toyo Seiki Co., Ltd. Heating temperature: 230 ° C Orifice diameter: 2 mmΦ Extrusion speed: 20 mm / min Take-off speed: 3.14 m / min

(Relative density) Relative density = ｛Density after foaming (density of foam) (g / cm)
³ ) {Density before foaming (density of sheet etc. before foaming) (g / cm ³ )}

(50% compressive strength) A plurality of test pieces cut out into a circular shape having a diameter of 30 mm are stacked, and a thickness of about 25 mm is obtained.
The stress when compressed to 50% at a compression speed of 10 mm / min is converted to 50 per unit area (cm ² ).
% Compressive strength.

Example 1 Polypropylene 5 having a melt tension at 230 ° C. of 4 cN
0 parts by weight and 50 parts by weight of an ethylene propylene-based elastomer having a JIS-A hardness of 69 were mixed with a kneader equipped with roller-type blades [Laboplast Mill, manufactured by Toyo Seiki Co., Ltd.]
After kneading at a temperature of 80 ° C., the mixture was formed into a sheet having a thickness of 0.5 mm and a diameter of 80 mm using a hot plate press also heated to 180 ° C. Put this sheet in a pressure vessel,
It was impregnated with carbon dioxide by holding in an atmosphere at a pressure of 15 MPa for 10 minutes. After 10 minutes, the pressure was rapidly reduced to obtain a foam made of an olefin-based polymer. The relative density of the foam is 0.028,
The 50% compressive strength was 1.79 N / cm ² .

Example 2 Polypropylene 5 having a melt tension at 230 ° C. of 6 cN
0 parts by weight and 50 parts by weight of an ethylene propylene-based elastomer having a JIS-A hardness of 69 were mixed with a kneader equipped with roller-type blades [Laboplast Mill, manufactured by Toyo Seiki Co., Ltd.]
After kneading at a temperature of 80 ° C., the mixture was formed into a sheet having a thickness of 0.5 mm and a diameter of 80 mm using a hot plate press also heated to 180 ° C. Put this sheet in a pressure vessel,
It was impregnated with carbon dioxide by holding in an atmosphere at a pressure of 15 MPa for 10 minutes. After 10 minutes, the pressure was rapidly reduced to obtain a foam made of an olefin-based polymer. The relative density of the foam is 0.026,
The 50% compressive strength was 1.54 N / cm ² .

Example 3 50 parts by weight of polypropylene having a melt tension at 230 ° C. of 12 cN and 50 parts by weight of an ethylene propylene-based elastomer having a JIS-A hardness of 65 were mixed with a kneader equipped with roller-type blades [Laboplast] Mill, manufactured by Toyo Seiki Co., Ltd.] at a temperature of 180 ° C., and then formed into a sheet having a thickness of 0.5 mm and a diameter of 80 mm using a hot plate press also heated to 180 ° C. Place this sheet in a pressure vessel,
Carbon dioxide was impregnated in an atmosphere of 0 ° C. under a pressure of 15 MPa for 10 minutes. After 10 minutes, the pressure was rapidly reduced to obtain a foam made of an olefin-based polymer. The relative density of the foam was 0.039 and the 50% compressive strength was 6.75 N / cm ² .

EXAMPLE 4 50 parts by weight of polypropylene having a melt tension at 230 ° C. of 12 cN and 50 parts by weight of an ethylene propylene-based elastomer having a JIS-A hardness of 56 were mixed with a kneader equipped with roller-type blades [Laboplasto] Mill, manufactured by Toyo Seiki Co., Ltd.] at a temperature of 180 ° C., and then formed into a sheet having a thickness of 0.5 mm and a diameter of 80 mm using a hot plate press also heated to 180 ° C. Place this sheet in a pressure vessel,
Carbon dioxide was impregnated in an atmosphere of 0 ° C. under a pressure of 15 MPa for 10 minutes. After 10 minutes, the pressure was rapidly reduced to obtain a foam made of an olefin-based polymer. The relative density of the foam was 0.053 and the 50% compressive strength was 7.51 N / cm ² .

Example 5 Polypropylene 5 having a melt tension at 230 ° C. of 2 cN
0 parts by weight and 50 parts by weight of an ethylene propylene-based elastomer having a JIS-A hardness of 69 were mixed with a kneader equipped with roller-type blades [Laboplast Mill, manufactured by Toyo Seiki Co., Ltd.]
After kneading at a temperature of 80 ° C., the mixture was formed into a sheet having a thickness of 0.5 mm and a diameter of 80 mm using a hot plate press also heated to 180 ° C. Put this sheet in a pressure vessel,
It was impregnated with carbon dioxide by holding in an atmosphere at a pressure of 15 MPa for 10 minutes. After 10 minutes, the pressure was rapidly reduced to obtain a foam made of an olefin-based polymer. The relative density of the foam is 0.032,
The 50% compressive strength was 0.71 N / cm ² .

Example 6 Polypropylene 5 having a melt tension at 230 ° C. of 2 cN
0 parts by weight and 50 parts by weight of an ethylene propylene-based elastomer having a JIS-A hardness of 56 were mixed with a kneader equipped with roller-type blades [Laboplast Mill, manufactured by Toyo Seiki Co., Ltd.]
After kneading at a temperature of 80 ° C., the mixture was formed into a sheet having a thickness of 0.5 mm and a diameter of 80 mm using a hot plate press also heated to 180 ° C. Put this sheet in a pressure vessel,
It was impregnated with carbon dioxide by holding in an atmosphere at a pressure of 15 MPa for 10 minutes. After 10 minutes, the pressure was rapidly reduced to obtain a foam made of an olefin-based polymer. The relative density of the foam is 0.022,
The 50% compressive strength was 1.01 N / cm ² .

Comparative Example 1 Polypropylene 5 having a melt tension at 230 ° C. of 1 cN
0 parts by weight and 50 parts by weight of an ethylene propylene-based elastomer having a JIS-A hardness of 65 were mixed with a kneader equipped with roller-type blades [Laboplast Mill, manufactured by Toyo Seiki Co., Ltd.]
After kneading at a temperature of 80 ° C., the mixture was formed into a sheet having a thickness of 0.5 mm and a diameter of 80 mm using a hot plate press also heated to 180 ° C. Put this sheet in a pressure vessel,
It was impregnated with carbon dioxide by holding in an atmosphere at a pressure of 15 MPa for 10 minutes. After 10 minutes, the pressure was rapidly reduced to obtain a foam made of an olefin-based polymer. The relative density of the foam is 0.148,
The 50% compressive strength was 9.83 N / cm ² .

The polyolefin resin foam obtained in each of the above examples is excellent in shape fixability, and has a high cushion without remarkably shrinking at the high expansion ratio obtained by releasing the pressure of the high-pressure gas in the foaming step. Had the nature. On the other hand, the polyolefin resin foam obtained in the comparative example was inferior in softness and cushioning property without promoting the foaming effect.

[0036]

According to the present invention, the polyolefin resin foam of the present invention does not cause significant shrinkage or deformation after foaming, and is excellent in softness and cushioning property. Further, according to the production method of the present invention, the above-mentioned excellent foam can be easily and efficiently produced.

Continued on the front page (72) Inventor Mitsuhiro Kaneda 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 4F074 AA05 AA16 AA24 AA25 BA32 BA33 CA29 CC04X CC10X DA02 DA08 DA32 DA33 DA38 DA47 DA50 DA57 4J002 AC01X AC06X AC09X BB03W BB05W BB06W BB06X BB07W BB08W BB12W BB15W BB15X BB17X BB18X BB22W BB24X BP01X CF00X CK02X CL00X GC00 GG02 GL00 GQ00 GQ01 GQ01

Claims (7)

[Claims] 1. A polyolefin resin foam comprising a polyolefin resin having a melt tension at 230 ° C. of more than 1 cN and a rubber or a thermoplastic elastomer component. 2. The repulsive load at the time of 50% compression is 9 N / cm.
The polyolefin-based resin foam according to claim 1, which is ² or less. 3. The polyolefin resin foam according to claim 1, wherein the relative density is in the range of 0.01 to 0.14. 4. A method for producing a polyolefin-based resin foam, which comprises foam-forming a resin composition containing a polyolefin-based resin having a melt tension at 230 ° C. exceeding 1 cN and a rubber or a thermoplastic elastomer component. 5. A high pressure gas is used as a foaming agent.
A method for producing the polyolefin resin foam according to the above. 6. The method for producing a polyolefin resin foam according to claim 5, wherein the high-pressure gas is carbon dioxide or nitrogen. 7. The method for producing a polyolefin resin foam according to claim 5, wherein carbon dioxide in a supercritical state is used as the high-pressure gas.