JPH0350245A - Conductive polypropylene resin foam and its production - Google Patents

Abstract

PURPOSE:To obtain the title foam excellent in rigidity, elasticity, etc., and useful as a packaging material for electronic components, etc., by extrusion- foaming a resin composition constituted by mixing a resin based on a specified crystalline propylene/ethylene block copolymer and a specified high-density PE with a specified amount of carbon black. CONSTITUTION:A resin composition constituted by mixing 100 pts.wt. resin based on 90-50wt.% crystalline propylene/ethylene block copolymer of an ethylene content <=20wt.% and a melt index(MI) <=2g/10min and 10-50wt.% high- density PE of a density of 0.94-0.96g/cm<3> and an MI of 5-15g/10min with 5-20 pts.wt. carbon black is extrusion-foamed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a conductive polypropylene resin foam and a method for manufacturing the same. The present invention relates to a conductive polypropylene resin foam useful as a packaging material for precision machinery, etc., and a method for producing the same.

(Prior art) Polyolefin foam with an expansion ratio of about 1.5 to 5 times is a material with appropriate elasticity and cushioning properties, so it is widely used as a packaging material for various products and as a partition material for products. It is used.

However, since most of these polyolefin foams are electrical insulators, their surfaces are easily charged with static electricity.

When static electricity is charged, dust adheres to the surface of the foam, making it unsuitable as a packaging material for precision instruments and the like. Also, L.S.
If it is used to package electronic components such as ICs and circuit boards, as well as electronic devices incorporating them, the charged static electricity may cause these components and devices to lose their functions.

For this reason, attempts have been made to, for example, mix an appropriate amount of carbon black with polyethylene, foam the resulting composition with or without crosslinking, and make the resulting foam conductive to suppress static electricity charging. There is. Also,
Efforts are being made to create conductive foam by blending carbon black with polypropylene, which has excellent rigidity and heat resistance and is useful as a material for rain boxes and partitions.

(Problems to be Solved by the Invention) However, in the case of the former foam, the resulting foam is too soft and therefore lacks self-supporting properties, making it unsuitable for use as rain boxes or partition materials.

Furthermore, when carbon black is blended with the latter polypropylene, the foaming ratio generally decreases and the cushioning function becomes poor, making it unsuitable for use as a cushioning material.

In addition, in recent years, it has been said that in order to prevent static electricity and remove static electricity, it is optimal to have a surface resistivity of about lXl0' to lXl0''Ω. Little is known about what is being managed.

The present invention solves the above problems and has a foaming ratio of 1.
Approximately 5 to 5, it has appropriate elasticity and cushioning properties, and is also excellent in heat resistance and rigidity, and has a surface resistivity of lXl0' to lXl0.
The purpose of the present invention is to provide a conductive polypropylene resin foam that is within the Ω range and has small variations, and a method for producing the same.

(Means and effects for solving the problem) In order to achieve the above-mentioned object, in the present invention, the ethylene content is 20% by weight or less, the melt index is 2g/
90-50% by weight of crystalline propylene-ethylene block copolymer less than 10 minutes and density 0.94-0.96 g
/c! It is an extruded foam of a resin composition containing 5 to 20 parts by weight of carbon black to 100 parts by weight of a resin mainly consisting of 50% by weight of melt index 5-15. An extruded foam of a resin composition made of A method for producing a conductive propylene resin foam, which comprises mixing a batch mixture with a predetermined amount of a compounding material mainly composed of the crystalline propylene-ethylene block copolymer, and extruding and foaming the obtained resin composition. provided.

The foam of the present invention is manufactured by extruding and foaming the resin composition described below.

First, the resin composition contains a crystalline propylene-ethylene block copolymer, high-density polyethylene, and carbon black as essential components.

The crystalline propylene-ethylene copolymer serves as the skeleton of the foam of the present invention and contributes to the development of high rigidity and excellent heat resistance.

As this copolymer, one having an ethylene content of 20% by weight or less and an MI of 2 g/10 minutes or less is used.

Since such copolymers have a relatively low melting temperature during extrusion molding, which will be described later, they exhibit viscoelasticity suitable for foaming resin compositions over a wide temperature range, and as a result, form a good foam structure. This makes it possible to produce foams with excellent elasticity and cushioning properties.

Ethylene content exceeding 20% by weight, MI 2g/
If the copolymer is used for more than 10 minutes, it is extremely difficult to form a foam with a uniform and fine foam structure, and furthermore, the heat resistance of the resulting foam will be reduced.

Ethylene content from 1 to 15 by weight, MI from 0.1 to 1,5
g/10 min crystalline propylene-ethylene copolymer is preferred.

The next component, high-density polyethylene, works to solve the problem that the foaming ratio decreases when carbon black is blended with the above-mentioned copolymer and foamed, and it also prevents carbon plaque from dispersing into itself. The surface resistivity of the resulting foam can be adjusted as desired. In other words, high density polyethylene is
It is an essential component for increasing the dispersibility of carbon black and making it possible to adjust the surface resistivity of the foam while maintaining the rigidity and cushioning properties of the foam with the above-mentioned copolymer skeleton.
This makes it possible to suppress variations in surface resistance of the resulting foam to within a range of approximately two digits.

High-density polyethylene exhibiting such an effect has a density of 0.94 to 0.96 g/car, preferably 0.94 g/car.
-0.95 g/Cd, MI 5-15 g/10 min, preferably 7-12 g/10 min are used.

If the density is lower than 0.94 g/al, the properties as high-density polyethylene will begin to disappear, leading to a decrease in the rigidity of the resulting foam, and if the density is higher than 0.96 g/cd, the miscibility with the above copolymer will decrease. This is because it becomes difficult to produce a foam with a uniform structure.

In addition, in the case of high-density polyethylene such as less than M15g/10 minutes, the melt viscosity becomes too high and the miscibility with the copolymer and carbon black described below deteriorates.
If it is higher than g/10 minutes, it will reduce the viscoelasticity of the copolymer during mixing, thereby inhibiting its foaming properties and making it impossible to obtain a uniform and fine foamed structure.

The resin in the resin composition of the present invention is mainly composed of the crystalline propylene-ethylene block copolymer and the high-density polyethylene, and the blend of both is 90 to 50% by weight of the crystalline propylene-ethylene block copolymer. , high density polyethylene is set in the range of lO to 50% by weight.

If the blending ratio of the block copolymer is more than 901i (the high-density polyethylene is less than 10% by weight), the foamability will decrease and the surface properties of the resulting foam will deteriorate. In addition, the blending ratio of the block copolymer is 50% by weight.
Undropped (the high density polyethylene exceeds 50% by weight)
In some cases, the resulting foam lacks rigidity and heat resistance.

The preferred blending ratio is 80 to 60% by weight of crystalline propylene-ethylene block copolymer and 2% by weight of high-density polyethylene.
It ranges from 0 to 40% by weight.

The resin in the resin composition includes, in addition to the mixture of the propylene-ethylene block copolymer and high-density polyethylene, polypropylene homopolymer, propylene-ethylene random copolymer, etc. within 30% by weight of the total resin. These resins can be used together. In particular, it is preferable to blend a propylene-ethylene random copolymer for the purpose of improving the surface condition and extrusion stability.

The next component, high-density polyethylene, works to solve the problem that the foaming ratio decreases when carbon black is blended with the above-mentioned copolymer and foamed. The surface resistivity of the resulting foam can be adjusted as desired. In other words, high density polyethylene is
It is an essential component for increasing the dispersibility of carbon black and making it possible to adjust the surface resistivity of the foam while maintaining the rigidity and cushioning properties of the foam with the above-mentioned copolymer skeleton.
This makes it possible to suppress variations in surface resistance of the resulting foam to within a range of approximately two digits.

High-density polyethylene exhibiting such an effect has a density of 0.94 to 0.96 g/car, preferably 0.94 to 0.96 g/car.
94-0.95g/cdSMI8-l Ig/10 min,
Preferably, 9 to 10 g/10 minutes is used.

If the density is lower than 0.94 g/Cjr, the properties as high-density polyethylene will begin to disappear, leading to a decrease in the rigidity of the obtained foam, and if the density is higher than 0.96 g/a/, the miscibility with the above copolymer will decrease. This is because it becomes difficult to produce a foam with a uniform structure.

In addition, in the case of high-density polyethylene with an M of less than 18 g/10 minutes, the melt viscosity becomes too high and the miscibility with the copolymer and carbon black described below deteriorates.
If it is higher than g/10 minutes, it will reduce the viscoelasticity of the copolymer during mixing, thereby inhibiting its foaming properties and making it impossible to obtain a uniform and fine foamed structure.

Carbon black, which is the third essential component in the resin composition, is a component for imparting electrical conductivity to the foam. The carbon black used is preferably conductive furnace black or acetylene black, and specifically, Ketchen Black EC (trade name manufactured by Akzo Corporation), Palcan XC (trade name manufactured by Cabot Corporation), Asahi HC-500 (trade name manufactured by Cabot Corporation), etc.
(product name manufactured by Asahi Carbon Co., Ltd.).

The amount of carbon black in the resin composition is set at 5 to 20 parts by weight per 100 parts by weight of the resin.

If this amount is less than 5 parts by weight, the surface resistivity of the resulting foam will be higher than lXl0'Ω, and if it exceeds 20 parts by weight, the surface resistivity will be lXl0'Ω.
This is because the foaming properties are also lowered.

Although the resin composition is composed of the above-mentioned three components as essential, there is no problem in adding appropriate amounts of various fillers, flame retardants, antioxidants, etc., as necessary.

The foam of the present invention is produced by extruding and foaming the resin composition.

For the resin composition in that case, first, the above-described high-density polyethylene and carbon blank are mixed to prepare a masterbatch mixture. For mixing, a conventional mixing method using rolls, a Banbury mixer 1 pressure kneader, a Busco kneader, a twin-screw extruder, etc. may be adopted. At this time, mixing efficiency can be increased by simultaneously adding a small amount of additive fine powder such as talc and a lubricating oil such as silicone oil.

In this mixing process, carbon black is well dispersed in high-density polyethylene, and as a result, conductive fibers are formed in which carbon black is attached to the molecular chains of high-density polyethylene. It is believed that the carbon black is uniformly mixed into the crystalline propylene-ethylene copolymer in the subsequent stage, resulting in uniform dispersion of carbon black.

Next, the masterbatch mixture and the crystalline propylene-ethylene copolymer are mixed to form a resin composition, and this resin composition is further melt-mixed in an extruder equipped with a blowing agent injection port, and then extruded. A desired foam can be produced by foaming. At this time, the cylinder temperature of the extruder is preferably controlled at 160 to 190°C.

Further, as the foaming agent used for foaming, a gas that does not react with the resin composition, such as nitrogen, carbon dioxide, air, etc., may be used. Carbon dioxide gas is particularly suitable.

(Embodiments of the invention) Example 1.2 As shown in Table 1, density 0.942 g/cnf, M
High-density polyethylene with a property of 19 g/10 minutes and Ketschen Black EC8002 are mixed in a Banbury mixer at the indicated ratio to make a masterbatch mixture, and further, as indicated, an ethylene content of 11 weight is added to the masterbatch mixture. %, M [0.5 g/10 min of crystalline propylene-
Various resin compositions were prepared by blending and mixing ethylene copolymers in the indicated proportions.

These resin compositions were injected into a 65Io! 1 liter extruder, melted and mixed at a temperature of 180°C, and then pressurized carbon dioxide gas through the injection port and
The foam was extruded from a die into the atmosphere.

A foam was produced by molding into a sheet using a molding roll.

For the obtained foam, the density, flexural modulus,
Bending strength, tensile strength/elongation, and surface resistivity were measured.

Density: Measured according to JISK6767 Flexural modulus 9 Bending strength: Measured according to JISK7203.

Tensile strength/elongation + Measured according to JISK6767.

Surface resistivity: Measured according to JISK69i1.

The above results are collectively shown in Table 1.

Example 3 The high-density polyethylene and Ketschen Black used in Example 1 were mixed in a pantries mixer in the proportions shown in Table 1 to form a masterbatch mixture, and the same mixture used in Example 1 was further mixed. A foam was produced in the same manner as in Example 1 by blending the crystalline propylene-ethylene copolymer and the propylene-ethylene random copolymer in the proportions shown in Table 1. The properties of the obtained foam were measured in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Examples 1 to 5 Ketchen Black EC8002 and the polyolefin shown in Table 1 were mixed in the indicated proportions, and then the polypropylene used in Example 1 was mixed therein, and the resulting resin composition was used. A foam was produced in the same manner as in Example 1. The properties of the obtained foam were measured in the same manner as in Example 1, and the results are summarized in Table 1.

Comparative Example 6 A part of the crystalline propylene-ethylene copolymer used in Example 1 was mixed with Ketchen Black EC8002, and then the resulting compound and the remaining copolymer were mixed to obtain a resin composition. Example 1 using these resin compositions
A foam was produced in a similar manner. The properties of this foam are summarized in Table 1.

(The following is a blank space) (Effect of the invention) As is clear from the above explanation, the foam produced by the method of the present invention has the same rigidity as the foam made only of polypropylene (reference example), and also has a lower density. It has appropriate elasticity and cushioning properties, and its surface resistivity is lXl0' ~
lXl0''Ω, which is within the appropriate range, and the variation in the value is small.

Therefore, it is suitable for packaging materials and partitioning materials for precision machines and various electronic devices, and has great industrial value.

Claims (3)

[Claims] (1) A crystalline propylene-ethylene block copolymer having an ethylene content of 20% by weight or less, a melt index of 2g/10min or less, and a density of 0.94-0.
96g/cm^3, melt index 5-15g/1
5 to 5 parts by weight of carbon black to 100 parts by weight of a resin mainly composed of 10 to 50% by weight of high-density polyethylene
A conductive polypropylene resin foam, characterized in that it is an extruded foam of a resin composition containing 20 parts by weight. (2) The conductive propylene resin foam according to claim 1, which has a surface resistivity of 1 x 10^4 to 1 x 10^9 Ω. (3) When producing an extruded foam of the resin composition according to claim 1, a predetermined amount of the high-density polyethylene and the carbon black are mixed in advance to form a masterbatch mixture, and then the masterbatch mixture is A method for producing a conductive propylene resin foam, comprising mixing a predetermined amount of a compounding material mainly composed of the crystalline propylene-ethylene block copolymer, and extruding and foaming the obtained resin composition.