JPH0220536A - Production of conductive polyolefin foam - Google Patents

Abstract

PURPOSE:To obtain a conductive polyolefin foam having a low surface resistivity and a stbilized quality by melting a polyolefin resin and an inorganic filler in a powder mixer and adding conductive carbon to the mixture and expanding the obtained masterbatch by heating. CONSTITUTION:2-20pts.wt., desirably, 3-10pts.wt. inorganic filler (e.g., heavy calcium carbonate) is melt mixed with 100pts.wt. polyolefin resin in, desirably, a high-speed flow type mixer, particularly desirably a Henschel mixer, 5-30pts. wt., desirably, 10-20pts.wt. conductive carbon is added to the molten mixture, mixed sufficiently, and discharged through a cooling mixer to give a master batch. To this masterbatch are added suitable amounts of a blowing agent, a cross-linking agent, optionally, a blowing aid, a filler, a pigment, etc., and the obtained mixture is expanded by heating to obtain a conductive polyolefin foam useful as, e.g., a wave absorber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a conductive polyolefin foam. The present invention relates to a method for producing conductive polyolefin foam useful as an absorbent material.

[Conventional technology]

In recent years, the applications of conductive foams have expanded to include packaging, transportation, and storage materials for various types of equipment that use electronic components, as well as antistatic mats.

Urethane foam has been known as a conductive plastic foam (for example, Japanese Patent Publication No. 52-38902), but it has problems such as carbon falling off and discoloration, and the base material is urethane. Therefore, there are problems such as very poor weather resistance.

For this reason, various methods for manufacturing conductive foams based on polyolefins with excellent weather resistance, chemical resistance, water resistance, etc. have been developed, and the present applicant has already applied for a patent (Japanese Patent Laid-Open No. 58
-198537, JP-A-58-198538). However, when manufacturing a conductive polyolefin foam by adding a blowing agent, etc. together with conductive carbon to the polyolefin resin that serves as the base material, there is a lot of scattering of the conductive carbon when the carbon is kneaded, and the surface of the foam is There was a problem that the resistance value was not stable. In addition, when a blowing agent is kneaded with conductive carbon, shear heat generation of the conductive carbon increases, making it easier for the blowing agent to decompose, resulting in the generation of bubbles in the sheet before foaming and deterioration of extrudability. Problems have also been pointed out.

For this reason, a method that includes a process of manufacturing a master patch product by melting and kneading polyolefin resin and conductive carbon in advance, and in particular kneading conductive carbon with molten polyolefin resin and molding it into pellets. Various methods have been developed, including a process of manufacturing a master patch product using
-81237, Japanese Patent Publication No. 81-31440, Special Publication No. 5
No. 9-25815).

[Problem to be solved by the invention]

In the case of conventional conductive polyolefin foams in which a master patch product as described above is manufactured in advance and then foamed, a kneading machine capable of applying a so-called high shearing force, such as a mixing roll, is used in the process of making the master patch product. Extruders, especially twin-screw extruders, Banbury mixers, kneaders
etc. are used.

However, in the conventional method using such a kneading machine,
At best, only a foam having a surface resistance value of 10 3 Ω or more can be obtained. The reason for this is thought to be that the chain structure necessary for conductive carbon is lost to some extent due to the shearing force of the kneader as described above, resulting in a decrease in conductivity.

Further, in the above-mentioned kneading machines, there is generally a problem in that carbon scatters to a large extent when the wires are mixed, resulting in unstable quality.

Therefore, an object of the present invention is to provide a method for producing a conductive polyolefin foam having a low surface resistance value and stable quality by eliminating the drawbacks of the conventional methods as described above.

[Means to solve the problem]

According to the method of the present invention, in order to achieve the above object, basically, an inorganic filler is added at the stage of making a master patch product, and a mixer is used so that substantially high shearing force is not applied. It is characterized by the use of a powder mixer.

That is, the first method according to the present invention includes a step of melting a polyolefin resin and an inorganic filler in a powder mixer and adding and mixing conductive carbon thereto to create a master patch product; This method is characterized by comprising a step of heating and foaming the patch product.

The second method of the present invention includes a step of melting a polyolefin resin and an inorganic filler in a powder mixer, and adding and mixing conductive carbon thereto to create a master patch product, and the above-mentioned master patch product. This method is characterized by the step of adding a polyolefin resin to a master patch product and foaming it by heating, and the carbon concentration can be adjusted by diluting the polyolefin resin of the master patch product.

[Action of the invention]

In general, electron movement in a polyolefin resin composited with conductive carbon black occurs through π-electron chains in the pseudographite structure of carbon black, and between carbon black particles in the polyolefin matrix, which is an insulator. It is assumed that this is done by the movement of electrons.
PJ (Reference: Hisashi Niyamada, Sobe Narita "Conductive Carbon Black Ketchen Black EC and Conductivity of Resin", Plastic Age, 34 [4] (19
88)”).

However, if a high shear force is applied during crosstalk, the carbon chains will be broken and the conductivity will deteriorate. vice versa,
If a mixer does not apply shearing force, the molten polyolefin resins will stick together and form large lumps, making it impossible to uniformly disperse carbon black.

The present invention provides that, in the step of making a master patch product, the polyolefin resin is melted in the presence of an inorganic filler, and the melt mixing is performed using a powder mixer that does not apply substantially high shearing force. Accordingly, the above-mentioned contradictory requirements can be simultaneously satisfied.

That is, by melt-mixing the polyolefin resin together with the inorganic filler, it is possible to prevent the inorganic filler from adhering to the surface of the polyolefin resin pellet when it melts and forming a large lump. Therefore, when making a master patch product by adding and mixing conductive carbon, a powder mixer can be used to sufficiently disperse the conductive carbon without using a kneader that applies high shearing force as in the past. can be done. As a result, the electrical conductivity can be greatly improved without breaking the carbon chains.

As described above, according to the method of the present invention, in the stage of making a master patch product, a polyolefin resin is melt-mixed with an inorganic filler and a powder mixer is used, which is an extremely simple method. Surprisingly, a surface resistance value of the order of 102 Ω, which could not be obtained by conventional methods, was obtained, and the conductivity was greatly improved.

[Aspects of the invention]

Hereinafter, each step of the method for producing a conductive polyolefin foam according to the present invention will be specifically explained.

First, in both the first method and the second method,
Polyolefin resin and inorganic filler are melt-mixed in a powder mixer.

A predetermined amount of conductive carbon is added to this, thoroughly mixed, and then discharged through a cooling mixer to obtain a granular master patch product. Alternatively, a master patch product in the form of pellets can be obtained by a pelletizing process such as extruding the mixture into a sheet shape and then cutting the sheet with a pelletizer.

A mixer for obtaining a master patch product must apply as little shearing force as possible, in other words, it must have no kneading effect.

Cross-mixing mixers can be divided into mixers and powder mixers depending on whether or not they have a kneading effect and their size, but in the method of the present invention, there is almost no kneading effect, or even if there is, it is substantially dispersed. It is necessary to use a so-called powder mixer, which does not affect the chains of conductive carbon, and the conventionally used kneaders, Banbury mixer mixing rolls, etc. are unsuitable. Various types of powder mixers are known, such as a rotating container type and a fixed container type. For example, a powder mixer such as a ribbon mixer can be used, but a high-speed fluid mixer are preferred, and among these, Henschel mixer is particularly preferred.

In the production of master patch products, 2 to 20 parts by weight, preferably 3 to 10 parts by weight of inorganic filler and 5 to 3 parts by weight of conductive carbon are added to 100 parts by weight of polyolefin resin.
0 parts by weight, preferably 10 to 20 parts by weight.

As described above, the inorganic filler has the effect of preventing molten polyolefin resins from sticking together and forming large lumps. If the amount of inorganic filler added is less than 2 parts by weight, the above effects cannot be fully exhibited, and the molten polyolefin resin will form large lumps, making it difficult to disperse the conductive carbon in a powder mixer with almost no shearing force. I can't. On the other hand, if the amount of the inorganic filler added exceeds 20 parts by weight, this is not preferable because it will adversely affect the subsequent foaming process.

In addition, the amount of conductive carbon added to the master patch product is 3.
If it exceeds 0 parts by weight, the elongation of the resin decreases and it becomes impossible to obtain a good foam, which is undesirable.
If the amount is less than 3 parts by weight, sufficient conductive function cannot be obtained, which is not preferable.

In the first method of the present invention, a conductive polyolefin foam is obtained by heating and foaming the master patch product obtained as described above, and a foam is obtained using such a master patch product. As the method, various conventionally known methods can be applied. For example, a method in which the master patch product of the present invention is crosslinked with an electron beam or a chemical crosslinking agent, a foaming agent is added thereto, and foaming is carried out by heating; / Or a batch method of foaming under normal pressure, heating and melting the master patch product,
A method of mixing and melting a volatile or decomposable blowing agent under high temperature and high pressure and extruding the foam into a low pressure zone can be selected as appropriate. Among these methods, when a batch method is applied to produce a highly foamed material with a foaming ratio of 10 times or more, it is most suitable as a conductive foamed material for a radio wave absorber.

To describe in detail the batch method suitable for application of the present invention, appropriate amounts of a blowing agent and a crosslinking agent, as well as a blowing aid, a filler, and a pigment as needed, are added and kneaded to a master patch product, and the resulting crosslinking property is , the composition is crosslinked by heating the foamable composition in a mold under pressure to a temperature at which the foaming agent does not substantially decompose, and then the resulting crosslinked foamable composition is rapidly foamed or expanded. For example, foaming is carried out in one step or in two steps under normal pressure under normal pressure. Although a conductive foam having a high expansion ratio can be obtained by such a method, it is also possible to employ a conventional one-stage normal pressure or pressure foaming method, a two-stage pressure foaming method, and the like. The heating conditions for such a batch method may be the same as conventional ones (Japanese Unexamined Patent Publication No. 5
Publication No. 8-198537, JP 58-1911538
For example, the heating conditions in the above preferred method include pressure and heating at 130 to 160°C depending on the type of blowing agent. range, and heat foaming to 1
What is necessary is just to set it in the range of 45-200 degreeC.

The crosslinking agent suitably used in the above-mentioned batch method is one that has a decomposition temperature higher than the flow initiation temperature of the polyolefin resin, and is decomposed by heating, generating free radicals and causing damage between the molecules or molecules. organic peroxides that are radical generators that cause crosslinking in 2,5-ditertiary-butylperoxyhexane, 2,5-dimethyl-2
,5-ditertiary-butylperoxyhexine, α,
Examples include α-ditertiarybutylperoxydiisobutyrbenzene, tertiary-butylperoxyketone, and tertiary-butylperoxybenzoate.The blowing agent is a chemical blowing agent with a decomposition temperature higher than the melting temperature of polyolefin resin. For example, azo compounds such as azodicarbonamide and barium azodicarboxylate; nitroso compounds such as dinitrosopentamethylenetetramine and trinitrosotrimethyltriamine;
p of hydrazide compounds.

p'-oxybisbenzenesulfonyl hydrazide, etc.;
Examples include sulfonyl semicarbazide compounds such as p,p'-oxybisbenzenesulfonyl semicarbazide and toluenesulfonyl semicarbazide. Also,
A foaming aid can be added depending on the type of foaming agent. Examples of foaming aids include compounds containing urea as a main component, metal oxides such as zinc oxide and lead oxide, compounds containing salicylic acid and stearic acid as main components, ie, higher fatty acids or metal compounds of higher fatty acids.

The second method for unexploded IV knives is characterized by adding an appropriate amount of diluent polyolefin resin to the master patch product obtained in the same manner as the first method, and other methods. The ingredients and foaming method are exactly the same as in the first method. Preferably 90% by weight of the master patch product after dilution
, particularly preferably 95% by weight, it is possible to adjust the amount of conductive carbon after producing the master patch article and to obtain a conductive foam of constant quality.

In addition, since polyolefin resin is added for dilution,
Although the conductivity is slightly reduced, even if there is variation in the conductivity of the master patch product, the variation in the conductivity of the final foam can be alleviated.

The polyolefin resin for dilution used in this second method is generally the same as the polyolefin resin used for the master patch product. However, other polyolefin resins that are highly compatible with the polyolefin resin used in the master patch product can also be used for dilution.

The polyolefin resin used in the present invention includes olefin alone or copolymers as well as copolymers with other monomers, such as polyethylene, polyethylene, and 1,2-butadiene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, copolymer of ethylene with methyl, ethyl, propyl, or butyl acrylate or methacrylate These include polymers, chlorinated products of these, mixtures of two or more of these, and mixtures of these with polypropylene having an atactic or isotactic structure.

The conductive carbon used in the present invention may be any carbonaceous substance that can impart high conductivity by filling rubber, plastic, etc., such as natural graphite, artificial graphite, carbon black, carbon fiber, etc. However, in general, carbon black such as furnace black and acetylene black, particularly conductive furnace black having a specific surface area of 900 rf/g or more and a hollow shell structure, is most preferred.

In addition, as the inorganic filler used in the present invention, light or heavy calcium carbonate, gypsum, clay talc, diatomaceous earth, etc. are suitably used, but among these, surface-treated heavy calcium carbonate is used. It has no adverse effect on foaming and is optimal.

A small amount of a metal soap such as zinc stearate or a wax may be added to the composition of the present invention as a lubricant. Further, depending on the case, it is also possible to add an ultraviolet deterioration inhibitor, an oxidation stabilizer, and the like.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but it goes without saying that the present invention is not limited to the following Examples.

Example 1 100 parts by weight of polyethylene resin (trade name "Tsubachikushi-300" manufactured by Mitsubishi Chemical Industries, Ltd.) and 6 parts by weight of heavy calcium carbonate were charged into a Henschel mixer heated to 140°C and melt-mixed. Next, Furnace Black (product name "Ketchen Black ECJ Ketchen Black") was added to this.
After adding 16 parts by weight of Black International Co., Ltd. and mixing well, the molten mixture was passed through a cooling mixer and discharged to obtain a granular master patch product.

Next, azodicarbonamide (trade name "Vinihole AC3") was added to 100flfffi of the obtained master patch product.
0SJ Eiwa Kasei Kogyo Co., Ltd.)9. .

parts by weight, 0.15 parts by weight of zinc white, α, α'-bis(t-
butylperoxy) diisopropylbenzene (trade name:
Add 0.7 parts by weight of Parriki Doxu 14/P40 (manufactured by Kayaku Nouri Co., Ltd.) and 0.2 parts by weight of triallyl isocyanurate (trade name: rTA I Cl, manufactured by Nippon Kasei Co., Ltd.), and mix with a mixing roll. The mixture was kneaded, filled into a mold (1000 x 500 x 35 mm) in a press heated to 140°C, and heated under pressure for 60 minutes to obtain a crosslinked foamable sheet.

Next, this foam sheet was placed in a non-closed mold heated to 160°C (a heating medium conduit was provided on the outer wall of the mold, and the cavity size was 2000 x 1000 x 90 mm).
It was heated for 150 minutes, cooled, and then taken out to obtain a conductive foam.

The obtained foam has a thickness of 90 m and an apparent density of 0.06.
6g/cm3, and the measured surface resistance value was 3.0XIO2Ω, indicating that the conductive foam had good appearance.

In addition, the electrical resistance value is manufactured by John, Fluke, Mf.
8060A TRUE R manufactured by G. Co., Inc.
Use MS MULTIMETER' and connect terminal 2cI
The value 30 seconds after piercing the terminal into the foam between II
It is a fixed value.

Example 2 A master patch product obtained in exactly the same manner as in Example 1 was treated with polyethylene resin (trade name [Tubatic L-300
J above) to make the usage amount of the master patch product 95%.
I made it. To 100 parts by weight of the composition thus obtained, the same ingredients as in Example 1 were added in the same proportions, and foam molding was carried out in exactly the same manner. As a result, the surface resistance value of the conductive foam obtained was 5.0XIO2Ω, and the appearance was also good.

Comparative Example 1 100 parts by weight of polyethylene resin (trade name "Yukalon YF30J" manufactured by Mitsubishi Yuka Co., Ltd.) and 1 part by weight of heavy calcium carbonate were charged into a Henschel mixer heated to 140'C and melt-mixed. The resin formed into large clumps, to which 16 parts by weight of furnace black could not be dispersed, as the amount of filler was too small.

Comparative Example 2 In the process of making a master patch product, a pressure kneader was used.
A conductive foam was obtained under exactly the same compounding conditions as in Example 1 except that . The surface resistance value of the obtained conductive foam is a
-1 was determined to be 105Ω, and could not be used for absorbing radio waves.

〔Effect of the invention〕

As described above, according to the methods of the present invention (first method and second method), polyolefin resin and inorganic filler are melt-mixed in a powder mixer, and conductive carbon is added to this. Because the master hatch product is made by adding and mixing, the conductive carbon has excellent dispersibility in the polyolefin resin melt, and the conductive carbon does not scatter when the polyolefin resin and conductive carbon are mixed. , the surface resistance value of the final foam is stabilized, and a conductive foam of almost constant quality is obtained. Furthermore, since a powder mixer without a kneading effect is used, the chains of conductive carbon are not broken, so a conductive foam having an extremely low surface resistance value (on the order of 102Ω) can be obtained. Such a foam can be used as a radio wave absorber and has extremely high practical value.

Furthermore, according to the second method of the present invention, the master patch product is diluted with polyolefin resin and then heated and foamed, so the amount of conductive carbon can be adjusted after manufacturing the master patch product, and Even if there are variations in conductivity in the master patch product, variations in conductivity in the final foam can be alleviated, resulting in a conductive polyolefin foam of stable and uniform quality.

Claims (4)

[Claims] (1) A process of melting a polyolefin resin and an inorganic filler in a powder mixer, adding and mixing conductive carbon to this to create a master patch product, and a process of heating and foaming the master patch product. A method for producing a conductive polyolefin foam, characterized in that: (2) Melting polyolefin resin and inorganic filler in a powder mixer, adding and mixing conductive carbon to this to create a master patch product, and adding polyolefin resin to the master patch product. 1. A method for producing a conductive polyolefin foam, comprising the steps of heating and foaming. (3) Claim 1 or 2, wherein the powder/granular material mixer is of a high-speed fluid type.
Method described. (4) Claim 1 or 2, in which the inorganic filler is used in a ratio of 2 to 20 parts by weight per 100 parts by weight of the polyolefin resin.
Method described.