JPH02272039A - Production of electrically conductive polyolefin foam - Google Patents

Abstract

PURPOSE:To obtain the subject foam, having a low surface resistance value and high expansion radio and useful as electromagnetic wave absorbers, etc., by adding a foaming agent to a polyolefinic resin in a stage for preparing a masterbatch, melting the resultant mixture in a powdery or granular substance mixer, adding and mixing electrically conductive carbon therewith and thermally expanding the prepared mixture. CONSTITUTION:The objective foam obtained by melting (A) a polyolefinic resin and (B) a foaming agent in a powdery or granular substance mixer, adding and mixing (C) electrically conductive carbon black therewith to prepare a masterbatch product, kneading the above-mentioned masterbatch product with (D) compounding components in, e.g. a horizontal multi-shaft type kneading with a fixed container, for 10-17min and thermally expanding the obtaining expandable composition.

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.

(Prior Art) In recent years, the uses of conductive foams have expanded widely, such as packaging, transportation, and storage materials for various devices using electronic components, and antistatic mats.

Urethane foam has been known as a conductive plastic foam (for example, Japanese Patent Publication No. 52-36902), but it has problems such as carbon shedding and discoloration, and because the base material is urethane. 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 eight patents (Japanese Patent Laid-Open No. 58
-198537, JP-A-58-198538). However, when producing a conductive polyolefin foam by adding a blowing agent, etc. together with conductive carbon to the base polyolefin resin, the conductive carbon often scatters on the surface of the foam. 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 masterbatch product by melting and kneading a polyolefin resin and conductive carbon in advance, especially a method that involves kneading conductive carbon into a molten polyolefin resin and molding it into a pellet shape. Various methods including the process of manufacturing masterbatch products have been developed (Japanese Patent Application Laid-Open Nos. 59-129237 and 1983-1989).
No. 81237, Japanese Patent Publication No. 61-31440, Special Publication No. 5
No. 9-25815).

(Problems to be Solved by the Invention) In the case of conventional conductive polyolefin foams in which a masterbatch product as described above is manufactured in advance and then foamed, the action of so-called high shearing force occurs in the process of making the masterbatch product. Possible kneading machines, such as mixing roll 5 extruders, especially two-wheeled 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.

In addition, the above-mentioned kneading machines generally cause a large amount of carbon to scatter during kneading, resulting in unstable quality.
In order to provide a conductive polyolefin foam with low surface resistance (and stable quality), fillers are added at the stage of making the masterbatch product, and the mixer does not apply substantially high shearing force. We have developed a method for producing conductive polyolefin foam, which is characterized by using a powder mixer.
No. 79).

Thereafter, in order to provide a conductive polyolefin foam with a high expansion ratio, the applicant preheated a masterbatch product to which fillers such as flame retardants were added, and then kneaded it with compounding ingredients in a kneader in a short time. We have developed a method for producing conductive polyolefin foams characterized by
No. 388).

However, even in these methods, when an inorganic filler is added to a polyolefin resin, the elongation of the resin becomes poor during foaming, making it impossible to obtain a conductive foam with a foaming ratio exceeding 15 times. Furthermore, if a flame retardant is added instead of an inorganic filler at the stage of making a masterbatch product, a conductive polyolefin foam with a foaming ratio of 20 times and a surface resistance value of 500 Ω or less can be obtained; It adheres to the inner wall of the machine and must be removed with a spatula each time, resulting in poor workability.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and to provide a method for producing a conductive polyolefin foam having a low surface resistance value (and a high expansion ratio).

(Means for Solving the Problems) According to the method of the present invention, in order to achieve the above object, basically, in the step of making a masterbatch product, a blowing agent is added and a mixer is substantially used. It is characterized by using a powder mixer that does not apply high shearing force.

That is, the first method according to the present invention is a step of melting a polyolefin resin and a blowing agent in a powder mixer, and adding and mixing conductive carbon thereto to create a masterbatch product. - A method characterized by comprising a step of kneading the product with a compounding agent in a kneader to obtain a foamable composition, and a step of heating and foaming the foamable composition.

Further, the second method according to the present invention is a step of melting a polyolefin resin and a blowing agent in a powder mixer, and adding and mixing conductive carbon thereto to create a masterbatch product.
This method is characterized by comprising a step of kneading the above-mentioned masterbatch product with a polyolefin resin and a compounding agent in a kneader to obtain a foamable composition, and a step of heating and foaming the above-mentioned foamable composition. This method allows the carbon concentration to be adjusted by diluting the polyolefin resin of the product.

In addition, in the above two methods, after preheating as a masterbatch product, a foamable composition can be obtained by kneading with a compounding agent or a polyolefin resin and a compounding agent in a short time.

(Function) - Electron movement in the polyolefin resin in which conductive carbon black is combined with M is movement in the π-electron chain in the pseudographite structure of carbon black, and in the polyolefin matrix, which is an insulator. It is assumed that this is done by the transfer of electrons between carbon black particles (Reference: Hisashi Yamada, Michibe Narita "Conductive carbon black (Ketchen Black EC) and conductivity of resin")
, Plastic Age, 34 [41, (1988))
.

However, if a high shear force is applied during kneading, the carbon chains will be broken and the electrical 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.

When the polyolefin resin is melted in the presence of a filler at the stage of producing a masterbatch product, carbon black can be uniformly dispersed. However, polyolefin resins to which fillers are added lack elongation during foaming, and cannot be molded into conductive foams with a high expansion ratio.

First of all, the present invention involves melting the polyolefin resin in the presence of a blowing agent instead of a filler in the step of producing a masterbatch product, and melt-mixing without applying substantially high shear force. By carrying out the process using a powder mixer, the contradictory requirements described in 1Iil can be satisfied at the same time.

That is, by melt-mixing the polyolefin resin together with a blowing agent, it is possible to prevent the foaming agent from adhering to the surface of the polyolefin resin pellet when it melts and forming a large lump. Therefore, when making a masterbatch product by adding and mixing conductive carbon, it is possible to sufficiently disperse the conductive carbon using a powder mixer without using a kneader that applies high shear force as in the past. can be done. As a result, the carbon chain is not broken,
Conductivity can be significantly improved.

Furthermore, since the foaming agent does not adhere to the inner wall of the mixer, there are no problems with workability. Furthermore, since the blowing agent is heated during foaming and decomposes into a gas, it does not have a negative effect on the elongation of the polyolefin resin. Obtainable. Furthermore, in the present invention, in the step of adding and kneading the polyolefin resin and/or compounding agent to the masterbatch product, the masterbatch product is preheated in advance and then mixed with the polyolefin resin and/or compounding agent in a kneading machine in a short time. By kneading, a conductive polyolefin foam having a low surface resistance value and a high expansion ratio can be obtained.

That is, by preheating the masterbatch product, the temperature of the masterbatch product can be raised to an upper limit, and the melting time of the masterbatch product in the two kneaders can be shortened. Therefore, the time during which high shearing force is applied is shortened, the degree of carbon chain breakage is reduced, and a foam having sufficient electrical conductivity can be obtained even when producing a foam with a high expansion ratio.

As described above, according to the method of the present invention, in the step of making a masterbatch product, polyolefin resin and filler are melt-mixed using a powder mixer, and polyolefin resin and At the stage of adding/kneading the compounding agents, the masterbatch product is preheated, then put into a kneading machine, and kneaded with the polyolefin FM@ and/or the compounding agents in a short time. It was possible to stably obtain a conductive Boolefin foam having a surface resistance value on the order of 101 Ω, which could not be obtained by conventional methods, and a high expansion ratio of 20 times (aspects of the invention): , 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, the polyolefin resin is mixed with a foaming agent in a powder mixer. Melt and mix inside.

A predetermined amount of conductive carbon is added to this, thoroughly mixed, and then discharged through a cooling mixer to obtain a granular masterbatch product. Alternatively, a pellet-shaped masterbatch product can be obtained by extruding the mixture into, for example, a sheet shape, and then performing a pelletizing process such as cutting the mixture with a pelletizer.

A mixer for obtaining a masterbatch product must have as little shearing force as possible, in other words, it must have no kneading effect. In general, mixing and kneading machines can be divided into kneading machines 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 device that does not affect the chain of conductive carbon, a so-called powder mixer, and the kneader used conventionally
, Banbury mixer, mixing rolls, etc. are unsuitable. Such powder mixers include container rotating type,
Various types such as fixed container types are known, and powder mixers such as ribbon mixers can be used, but
High-velocity jet mixers are preferred, and among these, Henschel mixers are particularly preferred.

In the production of a masterbatch product, 3 to 20 parts by weight of a blowing agent, preferably 6 to 17 parts by weight, and 5 to 30 parts by weight, preferably 10 to 20 parts by weight of conductive carbon, per 100 parts by weight of a polyolefin resin. Added.

As described above, the blowing agent has the effect of preventing molten polyolefin resins from sticking together and forming large lumps. If the amount of the blowing agent added is less than 3 parts by weight, the above effects cannot be fully exhibited, and the molten polyolefin resin becomes large lumps, making it difficult to disperse the conductive carbon using a powder mixer with almost no shearing force. Can not.

On the other hand, if the amount of the foaming agent added exceeds 20ff [9 parts, the polyolefin resin to which conductive carbon is added will have insufficient elongation during foaming, making it impossible to mold a foam.

In the first method of the present invention, a conductive polyolefin foam is obtained by heating and foaming the masterbatch product obtained as described above.5 A foam is obtained using such a masterbatch product. As the method, various conventionally known methods can be used. For example, a method in which the masterbatch product of the present invention is crosslinked with an electron beam or a chemical crosslinking agent, and heated and foamed; a batch method in which a crosslinking agent is added to the masterbatch product and foamed under high temperature and high pressure and/or under normal conditions; A method such as heating and melting the batch product in an extruder and extruding it into a low pressure zone and foaming it can be selected as appropriate. Among these methods, the batch method for producing a high foam with a foaming ratio of 10f8 or more is most suitable as a conductive foam for a radio wave absorber.

To describe in detail the batch method suitable for application of the present invention, a suitable crosslinking agent is added to the masterbatch product, and if necessary, a foaming aid, a filler, and a pigment are added to the masterbatch product in the process of making the masterbatch product. The remaining blowing agent that was not added was added and kneaded, and the resulting crosslinkable, foamable composition was heated in a mold under pressure to a temperature at which the blowing agent did not substantially decompose, thereby crosslinking the composition. Then, the obtained crosslinked foamable composition is foamed without rapidly foaming or expanding, and is heated and foamed under normal pressure, for example, in one stage or in two stages. Although a conductive foam having a high expansion ratio can be obtained by such a method, it is also possible to use 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 are not the same as those in the past (Japanese Patent Application Laid-open No. 58-198537, Japanese Patent Application Laid-Open No. 58-1
98538q public [e reference], MA may be set appropriately in the range of 130 to 200 °C depending on the method used, but for example, the heating conditions in the above preferred method include pressurization and heating at 130 °C depending on the type of blowing agent. What is necessary is just to set the heat foaming to the range of 145 to 200°C.

Polyolefin-based crosslinking agents are suitable for use in the batch method described above! 84, which has a decomposition temperature equal to or higher than the flow start temperature, and is decomposed by heating,
Organic peroxides, such as dicumyl peroxide, which are radical generators that generate free radicals and create crosslinks between or within the molecules; 1. 1-Ditertiary-butylperoxy-3,3,5-1-limethylchlorohexane, 2,5-dimethyl-2,5-ditertiary-butylperoxyhexane, 2,5-dimethyl-2,5-ditertiary- Butyl peroxyhexine, α, α-ditertiary butyl peroxydiisobrobylbenzene, tertiary butyl peroxyketone,
Tertiary-butyl peroxybenzoate, etc.
The blowing agent is a chemical blowing agent having a decomposition temperature higher than the melting temperature of the polyolefin resin, such as azo compounds such as azodicarbonamide and barium azodicarboxylate; nitroso compounds such as dinitrosopentamethylenetetramine and trichloride. Nitrosotrimethyltriamine po-oxybisbenzenesulfonyl hydrazide, etc.;
p. of sulfonyl semicarbazide compounds. Examples include p'-oxybisbenzenesulfonyl semicarbazide and toluenesulfonyl semicarbazide 1ζ. Further, 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 of the present invention is characterized by adding an appropriate amount of a diluent polyolefin resin to a masterbatch product obtained in the same manner as the first method,
The other ingredients and foaming method are exactly the same as in the first method.

The masterbatch product after dilution is preferably 00ffiff.
i%, particularly preferably 95% by weight,
Is the masterbatch product WA3? The amount of conductive carbon can be adjusted after heating, and a conductive foam of constant quality can be obtained.

In addition, since polyolefin resin for dilution is added,
Although the conductivity is slightly reduced, even if there is variation in the conductivity of the masterbatch 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 masterbatch product.However, other polyolefin resins that are highly compatible with the polyolefin resin used for the masterbatch product are used. A system resin can also be used for dilution.

In the present invention, the polyolefin resin includes olefin homopolymers or copolymers as well as copolymers with Ike's monomers, for example, commercially available olefin monomers.

Polyethylene produced by medium 5 low pressure method, poly-1,
2-butadiene, ethylene-propylene copolymer, ethylene-butene copolymer, ethylene. -Vinyl acetate copolymer, ethylene and methyl-5-ethyl, propyl, and butyl acrylates! - or a copolymer with methacrylate, a chlorinated product of these, a mixture of two or more of these, or a mixture of these and polypropylene having an atactic or isotactic structure.

In the first and second methods of the present invention, the masterbatch product obtained as described above is preheated, and then mixed with necessary ingredients such as a crosslinking agent, a foaming aid, and other additives in a kneader. It is also possible to obtain a foamable composition by kneading for a period of time.

As a means for preheating, an air oven, a heating box having a heat medium conduit for heating (heat medium Nisteam, hot water, etc.) or an electric heater on the outer wall can be used. The preheating temperature is preferably 70 to 115°C2, particularly preferably 90 to 110°C, and the heating time is preferably 1-1
0 hours, particularly preferably 2 to 7 hours.

As the kneading machine, a kneading machine capable of so-called high shearing force can be used, such as a mixing roll, an extruder, especially a twin-screw extruder, a Banbury mixer, a kneader, etc., but a pressure kneader, a Banbury mixer, etc. can be used. A fixed container/horizontal double-shaft type kneading machine such as - is preferable. The total kneading time by the kneader is preferably 10 to 17 minutes, particularly preferably 12 to 16 minutes.
It's a minute. When using a fixed container/horizontal multi-shaft type kneading machine, finishing kneading, sheeting, etc. are performed using mixing rolls, but these times are not included in the kneading time referred to here. If the kneading time is less than 10 minutes, sufficient dispersion will not be achieved, while if the kneading time exceeds 17 minutes, the carbon chains will be severed.
This is not preferable because the conductivity decreases.

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, carbon blacks such as furnace black and acetylene black are generally most preferred, particularly conductive furnace blacks having a specific surface area of 900 rr1'/g or more and a hollow shell structure.

A small amount of metal soap such as zinc stearate or waxes can be added to the composition of the present invention as a lubricant. In some cases, UV deterioration inhibitors,
It is also possible to add oxidation stabilizers and the like.

(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 Polyethylene resin (trade name "Tubatic L-300" manufactured by Mitsubishi Chemical Industries, Ltd.) f00ffl, azodicarbonamide (trade name "Vinihole AC30S" manufactured by Hydraulic Chemical Industries Ltd.)
(manufactured by M. Co., Ltd.) 12 stacked parts were placed in a Henschel mixer heated to 140°C, and melt-mixed. Next, add Furnace Black (product name: ``Ketchen Black ECJ'' manufactured by Ketchien Black International ■) 16ffi.
After adding a certain amount and mixing well, the molten mixture was passed through a cooling mixer and then discharged to obtain a granular masterbatch product.

Next, the obtained masterbatch product 5 was preheated in an air oven at 100°C for 4 hours, and then 0.1 part by weight of zinc white, α, α゛-bis( t-Butylperoxy) diisopropylbenzene (trade name: Bariki Dox-14/P4
0J Kayaku Nuichiri ■wA) 0.50mff 1 part, urea-based foaming aid 0.0Bffi part, triallyl isocyanurate (trade name "TAICJ made by Nippon Kasei ■)" O, 1Tff
Iffi part, 25 parts by weight of ethylene top 1 to labromophthalimide as flame retardants and 0.5 parts by weight of antimony dioxide were added, kneaded for 14 minutes in a pressure kneader heated to 110°C, and then transferred to a mixing roll. and make it into a sheet.
Gold in a press heated to 145℃ (770X365
The above-mentioned kneaded material was filled into a tube (X36ms) and heated under pressure for 45 minutes to obtain a crosslinked foamable sheet.

Next, this foam sheet was heated to 160°C and heated to a non-closed system (a heating medium conduit was provided on its outer wall, and the cavity size was 1900 x 900 x
90 mm), heated for 180 minutes, cooled, and then taken out to obtain a conductive foam.

The obtained foam has a thickness of 90 m + hoof, and an apparent density of 0.05
g/cm3, and when its surface resistance was measured, it was 3
The conductive foam had a resistance of 50Ω and a good appearance.

In addition, the electrical resistance value is manufactured by John, Fluke, Mf.
g, Co, Inc, wlJ's "8060ATRUE"
RMS MULTIMETER", terminal 2
The value was measured 30 seconds after the terminal was inserted into the foam between C and C.

Furthermore, as a result of the combustion test, the obtained conductive foam had self-extinguishing properties.

Example 2 A masterba Sochi product obtained in exactly the same manner as in Example 1 was treated with polyethylene resin (trade name "Tubatic L-300").
4 above) to reduce the amount used of the masterbatch product to 98%.
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 obtained conductive foam was 350Ω, and the appearance was also good.

In addition, as a result of a combustion test, it was found to have self-extinguishing properties.

Comparative Example 1 The same formulation and method as in Example 1 except that flame retardants ethylene, tetrabromophthalimide, and antimony trioxide were added instead of azodicarbonamide in the process of preparing the masterbatch product of Example 1. A masterbatch product was obtained using the following method.After that, when the Henschel mixer was opened and the inside was observed, U refueling agent was found to have adhered to the inside and could only be removed by rubbing it strongly with a spatula, which was a time-consuming and labor-intensive work. It was bad sex.

Comparative Example 2 A granular masterbatch product was produced using the same formulation and method as in Example 1, except that 6 parts by weight of heavy calcium carbonate was added instead of azodicarbonamide in the process of making the masterbatch product in Example 1. Obtained.

Next, 8,100 parts by weight of the obtained masterbatch was added with azodicarbonamide! Foaming was carried out using the same formulation and method as in Example 1, except that 2 ffl parts were added and the flame retardants ethylene bistetrabromophthalimide and antimony trioxide were not added.

However, polyethylene containing fillers did not have enough elongation during foaming, causing cracks on the surface of the foam, making it unusable as a product.

(Effects of the Invention) As described above, according to the two methods of the present invention (the first method and the second method), the two polyolefin resins are mixed with a foaming agent in a powder mixer at the stage of making a batch of five masters. Because it melts and mixes the polyolefin resin, there is no adverse effect on the physical properties of the polyolefin resin (like the addition of fillers), and it does not inhibit foaming. In addition, there is almost no trace of conductive carbon during mixing, and the breakage of conductive carbon chains is completely reduced, so the surface resistance of the final foam is homogeneous and stable, and the surface A conductive foam with a very low resistance value (on the order of 10"Ω) and a high expansion ratio exceeding 15 times can be obtained.Such a foam can be used for radio wave absorbers, and is of practical use. It has extremely high value.

In addition, according to the second method of the present invention, the masterbatch product is diluted with a polyolefin resin and then heated and foamed, so that the conductive carbon fireflies can be adjusted after the masterbatch product is manufactured. Even if there are variations in conductivity in batch products, the variations in conductivity in the final foam can be alleviated, and a conductive polyolefin foam of stable and uniform quality can be obtained.

Claims (6)

[Claims] (1) A step of melting a polyolefin resin and a blowing agent in a powder mixer and adding and mixing conductive carbon thereto to create a masterbatch product; kneading the masterbatch product with the compounding agent in a kneader; A method for producing a conductive polyolefin foam, comprising the steps of: obtaining a foamable composition; and heating and foaming the foamable composition. (2) Process of melting polyolefin resin and blowing agent in a powder mixer, adding and mixing conductive carbon to this to create a masterbatch product, mixing the above masterbatch product with polyolefin resin in a kneading machine 1. A method for producing a conductive polyolefin foam, comprising the steps of: obtaining a foamable composition by kneading it with a foaming agent; and heating and foaming the foamable composition. (3) The method according to claim 1 or 2, wherein the powder mixer is a high-speed fluid type. (4) Claim 1, wherein the kneading machine is a horizontal double-shaft type with a fixed container;
The method described in 2 or 3. (5) The method according to any one of claims 1 to 4, wherein the masterbatch product is preheated and then kneaded with a compounding agent or a polyolefin resin and a compounding agent in a kneader for a short time to obtain a foamable composition. (6) The method according to any one of claims 1 to 5, wherein the kneading time in the kneader is 10 to 17 minutes.