JPS599572B2 - Manufacturing method of polyolefin foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a foam whose heat resistance is greatly improved compared to conventional polyolefin foams.

More specifically, in a method for producing a highly foamed polyolefin foam in which a pressurized melt polyolefin resin mixed with a volatile blowing agent is extruded into a low temperature and low pressure section to form a foam, the polyolefin resin (a) has a melt index MI of 0.5.
60-98% by weight of propylene-ethylene block copolymer with an ethylene content of 5-15% that is ~2.0 (mouth)
A polyolefin foam characterized in that it is a mixture of 1 to 20% by weight of polybutene or butene copolymer having a melt index of 2 to 10 and 1 to 20% by weight of low density polyethylene having a melt index of 2 to 10. Relating to the manufacturing method. The aim is to highly foam a highly crystalline polyolefin resin with excellent heat resistance, which was conventionally considered difficult to foam mold, using a non-crosslinking extrusion foaming method, and to create a material that is rich in flexibility, elasticity, and surface beauty. The purpose is to produce polyolefin foam. Conventionally, the non-crosslinking extrusion foaming method, in which an organic solvent blowing agent is forced into the extruder midway through the extruder, melt-mixed in the extruder, and then extruded to a low-temperature, low-pressure region to achieve high foaming, has a relatively wide temperature range suitable for foam molding. Because it is relatively easy to mold, it is used to manufacture foams mainly composed of low-crystalline low-density polyethylene and amorphous polystyrene, and is used for applications such as insulation, joint materials, and cushioning materials. However, due to the nature of the raw material resin,
It has a low heat resistance, with a practical maximum temperature of 100° C. or lower, and cannot be used for higher temperature applications. Foams used for higher-temperature applications include foams made using the crosslinking foaming method, in which a pyrolytic blowing agent, crystalline polyolefin, and peroxide are kneaded in advance, formed into a sheet, and then foamed in a heating furnace. , these processes involve several steps and are therefore more expensive.

In addition, high-temperature foams include isocyanurated polyurethane foam, phenol foam, etc., but all of these are hard systems and are unsuitable for heat insulating materials for places with curved surfaces or irregularly curved piping systems. Furthermore, a method is known in which a highly crystalline polyolefin is extruded from an extruder together with an organic solvent blowing agent or a thermally decomposable blowing agent to obtain a foam having a specific gravity of about 0.1 to 0.8.

This foam is in the field called structural foam, and is intended for use as a hard structural member, which is different from the purpose of the present invention, which is to obtain a flexible, highly foamed material. Structural foam has a foaming ratio of about 1.5 to 10 times, and the highly foamed material targeted by the present invention, which has a thick foam membrane, has a foaming ratio of 20 to 40 times. Bubble membranes are extremely thin compared to structural foams. In the production of highly foamed foam, the key to the technology is how thinly and uniformly the foam membrane can be stretched.If the foam membrane is not stretched sufficiently or uniformly, the foam membrane will break and high foaming cannot be achieved. Furthermore, if the size of the bubbles contained in the foam is not uniform, the surface of the foam becomes uneven and lacks commercial value. For the reasons mentioned above, highly expanded foam is technically more difficult than structured foam. Compared to low-crystalline or amorphous resins with low softening points such as low-density polyethylene and polystyrene, crystalline resins with high softening points such as high-density polyethylene and polypropylene have a tendency to change the viscosity of the melt near the foaming temperature. is extremely large, and due to the heat of crystallization, the viscoelastic changes in the resin extruded into the low temperature and low pressure region are extremely large, so the temperature range suitable for foaming is extremely narrow, so the surface is beautiful even at high magnification. It has been very difficult to obtain a foam with a homogeneous cell structure.

In view of the above problems, the present invention was developed with the aim of producing a polyolefin foam with excellent heat resistance, flexibility, elasticity, and surface beauty.As a result, the present invention was developed using propylene which is a crystalline polyolefin resin and has an extremely high melting point. - A foam with good flexibility and elasticity can be obtained for resins with a certain range of ethylene content and melt index MI of the ethylene block copolymer, and that polybutene or butene copolymers and low-density polyethylene, respectively. MI of
It has been found that by blending a small amount of a resin with a larger diameter than the above-mentioned block copolymer, a foam with greatly improved surface beauty and elasticity can be obtained.

That is, the gist of the present invention is to provide a method for producing a highly foamed polyolefin foam in which a pressurized melted polyolefin resin mixed with a volatile blowing agent is extruded into a low-temperature and low-pressure section to form a foam, in which the polyolefin resin has (a) a melt index MI of 0;
．． 60 to 98 parts by weight of a propylene-ethylene block copolymer having an ethylene content of 5 to 15% and (
b) A mixture consisting of 1 to 20% by weight of polybutene or butene copolymer having a melt index of 2 to 10 and (c) 1 to 20% by weight of low density polyethylene having a melt index of 2 to 10. The feature lies in the manufacturing method of polyolefin foam.

The propylene-ethylene block copolymer used as the main component of the present invention is produced by polymerizing only propylene in the first stage of polymerization in the presence of stereoregularity, and adding ethylene or both ethylene and propylene in the second stage. It is obtained by copolymerization.

When the fracture surface of the resin is observed under an electron microscope, the structure shows that islands of polyethylene dotted in a sea of polypropylene have a particle size of 1.
It has a spherically dispersed structure with a size of 0 to 50μ. Because it has such an island-in-the-sea structure, propylene-ethylene block copolymers have higher elasticity (impact resistance) than polypropylene homopolymers, and have a melting point close to that of polypropylene, which corresponds to the ocean. The propylene-ethylene random copolymer, which does not have the above structure, has a much lower resistance than the block copolymer. By the way, the melting peak with more than half of the total heat of fusion based on differential scanning calorimeter DSC analysis is the polypropylene homopolymer at 160°C at a heating rate of 5°C/min.
Propylene with 10% ethylene content - ethylene block copolymer 158°C, propylene with 6% ethylene content
Ethylene random copolymer temperature is 130°C.

For the reasons mentioned above, propylene-ethylene block copolymer is the most suitable material for obtaining a foam that is flexible, elastic, and has excellent heat resistance. That is, polypropylene homopolymer foam is hard and has no elasticity, and propylene-random copolymer has poor heat resistance. In order to stably produce a foam with a high expansion ratio by melt-mixing a propylene-ethylene block copolymer with a volatile blowing agent in an extruder and extruding it from the extruder into a low-temperature, low-pressure region, it is necessary to Only resins with specific properties are compatible.

That is, the content of block-bound ethylene is 5 to 15%.
, Melt Index MI (2300C 10 minutes ASTM
D1238-62T) is a propylene-ethylene block copolymer with a molecular weight of 0.5 to 2.0. The reason for this is that propylene-ethylene block copolymers within this range change their viscosity with respect to temperature near the melting point much more slowly than propylene-ethylene block copolymers outside this range. This is thought to be because the viscoelastic changes of the resin extruded from the high temperature, high pressure extruder to the low temperature, low pressure region become more gradual, thus expanding the temperature range suitable for foaming, resulting in excellent extrusion foamability. Among propylene-ethylene block copolymers, foams made with copolymers with an ethylene content of less than 5% have no elasticity and do not return to their original shape when crushed, and those with an ethylene content of more than 15% are a dispersion of ethylene and propylene. It became difficult to mix uniformly with the foaming agent, resulting in foam collapse and failure to foam while maintaining its shape.

Furthermore, even with foams made from propylene-ethylene block copolymers with an ethylene content in the range of 5 to 15%, melt index MI (230-C 10 minute AST)
Resins with MDl238-62T) smaller than 0.5 had severe irregularities on the surface, and resins with MDl238-62T) larger than 2.0 did not form a foam due to gas leakage, probably because the viscosity during foaming was too low.

Foams made mainly of low-density polyethylene, which have been produced for a long time using the non-crosslinking extrusion foaming method, have a heat resistance of 100° C. or less, but are widely known for their elasticity and beautiful surfaces.

The foam made from the propylene-ethylene block copolymer had insufficient surface beauty and elasticity compared to the foam made from low density polyethylene. Therefore, as a result of trying various modifications for the purpose of improving surface beauty and elasticity within a range that does not impair heat resistance, we found that polybutene or butene copolymer is larger than the propylene-ethylene block copolymer of which MI is the main component. found that by adding a small amount of low-density polyethylene, not only the surface beauty became equivalent to that of a foam made from low-density polyethylene, but also the elasticity was greatly improved. That is, Melt Index MI (2300C105+ASTMDl238
Polybutene or butene copolymer with 162T) of 2 to 10 and melt index MI (1900C10 minutes ASTM
D1238-62T) is achieved by mixing 1 to 20% of each of 2 to 10 low density polyethylenes. The reason why surface beauty and elasticity are improved by adding polybutene or butene copolymer and low-density polyethylene, respectively, is not clear, but it is probably that polybutene or butene copolymer is more effective than propylene-ethylene block copolymer and low-density polyethylene. This is thought to be due to the fact that the propylene-ethylene block copolymer, which has poor compatibility, and low-density polyethylene are compatible with each other via the polybutene or butene copolymer due to their good compatibility with polyethylene.

By improving compatibility, the tension and elongation of the resin during melting are greatly improved, and the destruction of bubbles that occur during foaming is reduced.
It seems that the elasticity of the foam is improved. In fact, even when low-density polyethylene was blended with propylene-ethylene block copolymer, the bubbles were destroyed during foaming, causing gas to escape, and no foaming was possible, probably due to poor compatibility. In addition, resins whose foam elasticity can be further improved by blending include styrene-butene block copolymer, polybutene,
Ethylene-butene copolymers and propylene-butene copolymers may be used, but their surface properties were insufficient. When low-density polyethylene is further blended into the above-mentioned blended resin, foamability is improved (expansion rate is improved), elasticity is further improved, and surface beauty is greatly improved. Propylene-ethylene block copolymer which is the main component in the present invention (
The polybutene or butene copolymer to be blended with an ethylene content of 5 to 15% (MI = 0.5 to 2.0) is added to the above block copolymer in an amount of 1 to 20%, and the MI is 2 to 2.0.
Resins with a range of 10 are suitable.

If the addition amount and MI are within the above ranges, compatibility with the third component, low density polyethylene, is good. The third component, low density polyethylene, is added in an amount of 1 to 20% to the propylene-ethylene block copolymer, polybutene or butene copolymer mixture, and has an MI of 2 to 1.
Resins with a range of 0 are suitable.

If the amount added is less than 1%, there will be no effect on improving elasticity or surface properties, and if it is more than 20%, compatibility will deteriorate and foaming will not be possible. Moreover, if MI is less than 2, it will not be effective in improving surface properties, and if it is larger than 10, it will not be effective in improving elasticity. The heat resistance of the foam produced by adding a small amount of polybutene or butene copolymer and low density polyethylene to the propylene-ethylene block copolymer in the present invention is 15.
0°C, and was no different from foams made only from polypropylene homopolymer or propylene-ethylene block copolymer. Any known non-crosslinking extrusion foaming method can be used to produce a non-crosslinking extrusion foam by mixing a small amount of polybutene or butene copolymer and low density polyethylene with the propylene-ethylene block copolymer used in the present invention. method may also be used. The extruder screw usually uses a two-stage type with L/D of 20 or more, and the blowing agent is pressurized into the pressurized molten resin in the cylinder from the cylinder in the latter half of the first stage or the first half of the second stage, and the cooling zone at the screw tip area is used. The resin containing the foaming agent is extruded into the atmosphere or into a reduced pressure section and foamed. If two extruders are connected and used, the screw may be a general full-flight type. In this case, the blowing agent is press-injected into the middle of the cylinder of the first extruder or into the joint of the extruder, and the second extruder is used only for cooling. There is also a method that uses a multi-screw extruder to improve quantitative performance and mixing properties. The resin is usually introduced into the extruder hopper in the form of a dry blend or masterbatch together with a fine powder called a nucleating agent.

The nucleating agent is 5 in order to form a foaming starting point from a mixed sol of a foaming agent and resin, and is usually a mixture of talc, inorganic fine powder such as calcium carbonate, and a mixture of baking soda and sodium citrate. However, in the present invention, any material may be used. The polybutene or butene copolymer resin used in the present invention includes polybutene-1, propylene ethylene-butene copolymer, propylene-butene copolymer, ethylene-butene copolymer,
There are butene-styrene copolymers, but these resins can be mixed or used by mixing with other resins for modification purposes.4
It's okay to do that.

In addition, the resin, which is a mixture of propylene-ethylene block copolymer with a small amount of polybutene or butene copolymer and low density polyethylene, contains heat stabilizers, antioxidants, ultraviolet absorbers, heavy metal deactivators, lubricants, colorants, and electrostatic charges. It is also possible to add inhibitors and the like depending on the purpose.

In carrying out the present invention, the blowing agent is generally a halogen-based, fluorocarbon-based, or alkane-based low-boiling organic solvent, such as methyl chloride, methylene chloride, trichloromonofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane. , dichlorotetrafluoroethane, propane, butane,
Examples include pentane.

The present invention will be explained in more detail below using Examples and Comparative Examples.

Examples 1 to 4 and Comparative Examples 1 to 6 Melt index MI (230°C 10 minutes ASTM D
123ε-62T) is 1.0, a propylene-ethylene block copolymer resin with an ethylene content of 10% (calculated from infrared absorption spectrum A720/A974) and a melt index MI (2300C 10 minutes ASTM D1238).
-62T) is 8, butene content (infrared absorption spectrum A
770/A974) 15% propylene-butene random copolymer and melt index MI (1
90°C105+ASTMD1238-62T) is 3.
Talc O. Three parts were dry blended and charged into the tandem extruder hopper described below.

The device consists of a first extruder (diameter 50nφL/D=24) with a foaming agent injection hole in the center of the screw calculation section, and a second extruder (diameter 6) equipped with a cooling oil jacket in the barrel.
5mTLφL/D=27) connected in series. The first extruder screw was a full-flight type, and the temperature conditions were 150°C in the supply section, 200°C in the compression section, and 200°C in the metering section, and the screw rotation speed was adjusted so that the extrusion rate was 15 kg/hour. Dichlorotetrafluoroethane as a blowing agent was injected through the injection hole using a high-pressure pump at a rate of 33 parts by weight (4.95 kg/hour) per 100 parts by weight of the resin. This mixture was fed to a second extruder through a connecting pipe. The screw in the second extruder was a pineapple type with notches in the flights to increase mixing efficiency, and the cooling temperature of the oil jacket was 130°C. This mixture was extruded into the atmosphere through a pipe die having an inner diameter of 511φ and an outer diameter of 8.311φ. Table 1 shows the properties of the foam obtained.

Table 1 shows that foams manufactured with resin compositions containing propylene-ethylene-ethylene block copolymer, propylene-butene random copolymer, and low-density polyethylene belonging to the present invention in the mixing ratio of the present invention have a high expansion ratio ( It can be seen that a foam with a specific gravity of 0.02 to 0.04) and excellent elasticity and surface beauty was obtained.

Examples 5 to 8 and Comparative Examples 7 to 8 Using the same extrusion and foaming equipment as in Examples 1 to 4, propylene-ethylene block copolymer resin with an ethylene content of 10% MI = 1 and 90% by weight and MI in Table 2 were prepared. To 100 parts by weight of a resin prepared by mixing 5% by weight of a propylene-ethylene-butene random terpolymer having a 5% by weight e of a propylene-ethylene-butene random terpolymer and a 5% by weight low-density polyethylene having an MI of Table 2, talc O. 3 parts by weight were dry blended and charged into the hopper of an extruder, and extrusion foaming was performed under the same temperature conditions as in Examples 1 to 4.

Table 2 shows the properties of the foam obtained. In Table 2, among the resin compositions in which a propylene-ethylene block copolymer, a propylene-ethylene-butene random terpolymer, and a low-density polyethylene were mixed at 5% by weight, each MI was within the range of the present invention. It can be seen that the foam manufactured from the resin having M■ has good elasticity and surface beauty.

Examples 9 to 12 and Comparative Examples 9 to 11 Using the same extrusion foaming equipment as in Examples 1 to 4, 85% by weight of a propylene-ethylene block copolymer with an MI of 1.0 and an ethylene content of 10% was used as shown in Table 3. 10% by weight of various resins and 5% by weight of low density polyethylene with MI=5
To 100 parts by weight of the mixed resin, talc O. 2 parts by weight were dry blended and put into the hopper of an extruder, and extrusion foaming was performed under the same temperature conditions as in Examples 1-4.

Table 3 shows the properties of the foam obtained. As shown in Table 3, foams produced by mixing propylene-ethylene block copolymer, low-density polyethylene, and polybutene or butene copolymer resin having an MI within the range of the present invention have excellent elasticity and surface beauty. Foams with improved surface properties can be obtained on both sides, whereas foams produced by mixing butene-free resins or, for example, polybutene but with MI resins outside the scope of the present invention, can provide foams with good both elasticity and surface properties. I couldn't get it.

Claims (1)

[Claims] 1. A method for producing a highly foamed polyolefin foam in which a pressurized melt polyolefin resin mixed with a volatile blowing agent is extruded into a low temperature and low pressure region to form a foam, in which the polyolefin resin (a) has a melt index MI of 0.5 to 2.0. (b) 60 to 98% by weight of a propylene-ethylene block copolymer having an ethylene content of 5 to 15%; (b) 1 to 20% by weight of a polybutene or butene copolymer having a melt index of 2 to 10; ) melt index is 2
A method for producing a polyolefin foam, characterized in that it is a mixture consisting of 1 to 20% by weight of low density polyethylene of ~10.