JP2010214625A - Conductive foamed sheet and conductive foamed resin container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive foamed sheet suitable for applications in which the sheet comes in contact with members including a semiconductor element easily affected by corruption and electric damage and to provide a conductive foamed resin container suitable for holding such members. <P>SOLUTION: The conductive foamed sheet is formed in the shape of a sheet having a lamination structure which is formed by a foamed layer formed in a foamed state by a resin composition and non-foamed layers which are formed in a non-foamed state by a resin composition containing carbon black to be arranged on both sides of the foamed layer through the foamed layer. The conductive foamed sheet is formed to have a volume resistivity to be 1×10<SP>10</SP>Ωcm or more and 1×10<SP>13</SP>Ωcm or less by incorporating an antistatic agent in the resin composition forming the foamed layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a conductive foam sheet and a conductive foam resin container, and more specifically, is formed into a sheet shape having a laminated structure, and the laminated structure is formed into a foamed state by a resin composition. And a non-foamed layer formed in a non-foamed state by a resin composition containing carbon black, and the non-foamed layer is formed on both sides of the foamed layer via the foamed layer. The present invention also relates to a conductive foamed resin container having excellent cushioning properties, which is formed by sheet molding of such a conductive foam sheet.

Conventionally, a foamed sheet obtained by foaming a resin composition into a sheet has been widely used in applications where lightness and buffering properties are required.
In particular, it is widely used as a material for producing a foamed resin container having a container shape formed of a resin foam by sheet molding.
In particular, a foam sheet in which a three-layer structure of non-foamed layer / foamed layer / non-foamed layer is formed by providing non-foamed layers on both the front and back surfaces of the molded article formed by the foamed sheet. It is widely used because it can improve the surface smoothness.

  Such a foamed resin container is also used as a transport container for transporting a semiconductor element such as a semiconductor package such as an IC or an LSI or a semiconductor bare chip. It is required to impart antistatic properties to the foamed resin container so as to prevent electrical damage caused by the above.

By the way, as a method for imparting antistatic properties to not only a foam sheet but also a general resin sheet, the surface resistivity is lowered by incorporating an antistatic agent into the resin composition which is a sheet forming material. The method is known.
This antistatic agent usually contains a highly polar polymer or compound, which has a high migration property in the resin sheet and tends to cause a phenomenon called “bleed out” that exudes to the sheet surface. Is used to reduce the surface resistivity.
Therefore, if an antistatic agent is included in the material for forming the non-foamed layer so as to prevent the foamed resin container from being charged, there is a risk that it may be unsuitable for housing a member that does not like deposits such as a semiconductor element. is there.

  In addition, as another method for preventing static charge, it is carried out by adding carbon black to the resin composition used for forming the non-foamed layer to impart conductivity and reducing the surface resistivity. In Patent Document 1 described below, a conductive resin foam containing carbon black having a specific DBP oil absorption amount in a predetermined ratio is useful as a packaging material for electronic parts and the like. The production of a conductive foam sheet extruded into a shape is described.

However, the conductive foamed resin container provided with conductivity by using such a conductive foam sheet is likely to generate dust due to rubbing between the container and the container or rubbing between the containers. There is a possibility that the contamination of the material becomes a problem.
Therefore, it is important to reduce the surface resistivity while suppressing the amount of carbon black used, but such a method has not been established.
Therefore, it has been difficult to obtain a conductive foam sheet with excellent buffering properties suitable for applications that require desired electrical characteristics and reduced contamination to the surroundings, such as containers for housing semiconductor elements. It has become.

JP 2004-083804 A

  The present invention provides, for example, a conductive foam sheet suitable for use in contact with a member such as a semiconductor element that is susceptible to contamination or electrical damage, and a conductive foam resin container suitable for housing such a member. Offering is an issue.

From the standpoint of preventing static electricity and contaminating the surroundings, it may be possible to adopt a metal tray as a transport container. However, the metal tray is not only inferior to the conductive foam resin container but also has a buffering property. When a transfer container with excellent conductivity is adopted, when static electricity accumulated in another resin container is discharged to the transfer container, the current is transmitted as it is to the internal semiconductor element. Will end up.
In such a point, it is important to select a container forming material from the viewpoints of both antistatic properties and volume resistivity.
In order to solve the above problems, the present inventor preferably has a conductive foam sheet having a volume resistivity of 1 × 10 ¹⁰ Ω · cm to 1 × 10 ¹³ Ω · cm. Moreover, in order to impart such a volume resistivity to the conductive foam sheet, it has been found that it is important to reduce the resistance value of the foam layer.

  Then, the surface resistivity of the foam film surface of the foam layer is reduced by using the antistatic agent that has been conventionally used for reducing the surface resistivity on the sheet surface side for the purpose of preventing the static charge. It was found that the resistance value of the conductive foam sheet can be easily reduced, and the present invention has been completed.

That is, the present invention relating to a conductive foam sheet for solving the above problems is formed in a sheet shape having a laminated structure, and the laminated structure is formed in a foamed state by a resin composition; The conductive foam sheet is formed of a non-foamed layer formed in a non-foamed state by a resin composition containing carbon black, and the non-foamed layer is formed on both sides of the foamed layer. Then, by adding an antistatic agent to the resin composition forming the foamed layer, the volume resistivity becomes any value of 1 × 10 ¹⁰ Ω · cm to 1 × 10 ¹³ Ω · cm. It is characterized by being formed.

In addition, the present invention relating to the conductive foamed resin container is formed into a sheet having a laminated structure, and the laminated structure is a resin containing a foamed layer formed in a foamed state by a resin composition, and carbon black. And a non-foamed layer formed in a non-foamed state by the composition, and the conductive foamed sheet in which the non-foamed layer is formed on both sides of the foamed layer is formed by sheet molding. A conductive foamed resin container, wherein the conductive foamed sheet contains an antistatic agent in the resin composition forming the foamed layer, so that it is 1 × 10 ¹⁰ Ω · cm or more and 1 × 10 ¹³ Ω · cm. It is characterized by being formed so as to have one of the following volume resistivity.

In the conductive foam sheet of the present invention, the resistance value of the foam layer is reduced by the antistatic agent, so that the use of carbon black that can be a cause of generation of dust and the like can be suppressed.
Moreover, in the conductive foam sheet in which the non-foam layer is formed on both sides of the foam layer, since the antistatic agent is used as described above, the antistatic agent from the foam layer to the surface of the conductive foam sheet is used. The non-foamed layer can function as a barrier layer against the transition of the film, and the antistatic agent used in the foam layer forming material can be prevented from bleeding out on the sheet surface.
That is, according to the present invention, it is possible to make the conductive foam sheet suitable for use in contact with a member that is easily damaged or electrically damaged, and the conductive foam having excellent buffering property suitable for housing the member. A resin container may be provided.

Sectional drawing which shows the structure of the conductive foam sheet which concerns on this embodiment. Schematic which shows the apparatus structure used for the manufacturing method of an electroconductive foam sheet. Sectional drawing which shows the structure of a confluence | merging metal mold | die.

An embodiment according to the present invention will be described with reference to FIG. 1 which is a cross-sectional view of a conductive foam sheet.
As shown in FIG. 1, the conductive foam sheet 1 according to the present embodiment is composed of three layers of surface layers 11 and 12 constituting the respective surfaces of the upper surface side and the lower surface side and an intermediate layer 20 formed therebetween. It has a laminated structure.

The surface layers 11 and 12 are both formed in a non-foamed state.
In the conductive foam sheet 1 of the present embodiment, the upper surface layer 11 in FIG. 1 (hereinafter also referred to as “first non-foamed layer 11”) and the lower surface layer 12 (hereinafter referred to as “second surface layer 12”). Is not necessarily required to have the same configuration, and the thicknesses thereof may be different.
The intermediate layer 20 is formed in a foamed state.
That is, the conductive foam sheet 1 of this embodiment is formed in a state having non-foamed layers on both sides of the intermediate layer 20 (hereinafter also referred to as “foam layer 20”).
In the present embodiment, the thickness of the intermediate layer 20 and the expansion ratio thereof are not particularly limited and can be appropriately selected.

The “non-foamed state” of the surface layer (non-foamed layer) does not have to be a completely non-foamed state, and may be in a substantially non-foamed state.
For example, if the volume is about 5% or less, it can be said that even if it contains bubbles, it is in a substantially non-foamed state. In the present invention, the term “non-foamed” It is used with the intention of including things.

In the case where the conductive foam sheet 1 according to the present embodiment is used for forming a conductive foam resin container for housing a semiconductor element or the like, the first non-foam layer 11 and the second non-foam layer The thickness of 12 can increase the strength of the conductive foamed resin container, and more reliably prevent the antistatic agent of the foam layer 20 described later from moving to the surface of the conductive foam sheet 1. sell.
That is, it is possible to form a conductive foamed resin container having excellent anti-contamination effect and strength for the contents.
On the other hand, when the thickness of the first non-foamed layer 11 and the second non-foamed layer 12 is excessively increased, it is difficult to impart appropriate cushioning (cushioning) and light weight to the conductive foamed resin container. Become.
From such a viewpoint, it is preferable that the thickness of each non-foamed layer is 50 μm or more and 150 μm or less.

On the other hand, the thickness of the foamed layer 20 and the expansion ratio thereof are the lightness and strength required for the conductive foamed resin container when the conductive foamed sheet 1 is used for forming the conductive foamed resin container. From these viewpoints, it can be selected as appropriate.
While the foaming ratio of the foamed layer 20 is higher and the thicker the thickness is, the better the cushioning property is imparted to the conductive foamed resin container. On the other hand, if the foaming layer 20 is excessively thickened by increasing the foaming ratio, It may be difficult to give sufficient strength to the conductive foamed resin container, and it becomes difficult to sufficiently reduce the electrical resistance value of the foamed layer 20, so that the conductive foam sheet 1 is 1 × 10 ¹⁰ Ω · cm. There is a risk that it may be difficult to achieve any volume resistivity of 1 × 10 ¹³ Ω · cm or less.

From this viewpoint, the thickness of the foam layer 20 is preferably 1.5 mm or more and 5.0 mm or less, and the apparent density is within the range of 0.18 g / cm ³ or more and 0.6 g / cm ³ or less. It is preferable that the expansion ratio be one of the following.

Further, the first non-foamed layer 11 and the second non-foamed layer 12 may have the same or different thickness as described above, and the resin composition used for the formation thereof may be the same. It can be different.
Furthermore, the resin composition used for the foam layer 20 may have the same component as or different from the first non-foam layer 11 and the second non-foam layer 12.

  Examples of the resin composition used for forming the first non-foamed layer 11 and the second non-foamed layer 12 include a resin composition used for forming a general conductive foamed sheet.

For example, a resin composition containing, as a base polymer, a polyolefin resin such as a polyethylene resin or a polypropylene resin, or a thermoplastic resin such as a polystyrene resin can be suitably used.
Among these, a polyolefin resin is preferably used as a base polymer, and a polyolefin resin composition in which a polyolefin resin is used as a base polymer for forming the first non-foamed layer 11 and the second non-foamed layer 12. A thing can be used suitably.

  Examples of the polyethylene (PE) resin include high density polyethylene resin, medium density polyethylene resin, linear low density polyethylene resin, (high pressure method) low density polyethylene resin, and ultra low density polyethylene resin.

Examples of the polypropylene (PP) resin include a homopolypropylene resin composed only of a propylene component, and a random copolymer and a block copolymer containing an olefin component such as ethylene in addition to the propylene component.
In particular, a high melt tension polypropylene (HMS-PP) resin is suitable as the base polymer.
This high melt tension polypropylene (HMS-PP) resin is, for example, from Borealis, trade names “WB130HMS”, “WB135HMS” and “WB140HMS”, from Basell, trade names “Pro-fax F814”, Nippon Polypro Co., Ltd. To “FB3312”, “FB5100”, “FB7200”, and “FB9100”.
When a copolymer is used as the polypropylene resin, an olefin other than propylene is contained in the copolymer in an amount of 0.5% by weight to 30% by weight, particularly preferably 1% by weight to 10% by weight. It is desirable to use what is contained in any proportion.
Examples of the olefin component in this case include ethylene or an α-olefin having 4 to 10 carbon atoms.

  In addition to these, the polyolefin resin composition of the present embodiment includes ethylene-ethyl acrylate copolymer resin, ethylene-vinyl acetate copolymer resin, polybutene resin, poly-4-methylpentene-1 resin, and the like. The polyolefin resin may be contained as a part of the base resin.

In the case of using the polystyrene resin, one or more polymers selected from styrene monomers, and a styrene monomer and a vinyl monomer copolymerizable with the styrene monomer. A copolymer is mentioned.
Examples of the styrene monomer include styrene, α-methyl styrene, vinyl toluene, chlorostyrene, ethyl styrene, i-propyl styrene, t-butyl styrene, and dimethyl styrene.
Examples of the vinyl monomer include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate, (meth) acrylonitrile, and dimethyl. Examples include maleate, dimethyl fumarate, diethyl fumarate, and ethyl fumarate.

  Further, in the resin composition used for forming the non-foamed layer in the present embodiment, a polymer component other than these polyolefin resin and polystyrene resin can be used as a base polymer, and other together with the polyolefin resin and polystyrene resin. It is also possible to use a mixture of these polymer components.

The resin composition used for forming the first non-foamed layer 11 and the second non-foamed layer 12 is imparted with conductivity by adding carbon black to such a polymer component.
As this carbon black, general carbon black called acetylene black, ketjen black, thermal black, furnace black, etc. can be adopted.
This carbon black can reduce the resistance of the non-foamed layer (improve electrical conductivity) by high filling, but can also cause generation of dust.
Therefore, in the resin composition used for forming the non-foamed layer, the carbon black is in a proportion of 10 to 30 parts by weight with respect to 100 parts by weight of all polymer components including the base polymer. It is preferably contained.

Among them, a primary particle diameter of 30nm or more 40nm or less, acetylene black DBP oil absorption amount is less than 130 cm ^3/100 g or more 180cm ^3/100 g is preferable.

Such carbon black is a sheet obtained by forming the resin composition into a non-foamed sheet in the resin composition used for forming the first non-foamed layer 11 and the second non-foamed layer 12. The surface resistivity is preferably 1 × 10 ⁴ Ω or more and 1 × 10 ⁸ Ω or less.

  Furthermore, the resin composition used for forming the non-foamed layer can contain an additive used as a general resin sheet forming material in addition to the above-described components. Various stabilizers such as anti-aging agents, processing aids such as lubricants, slip agents, pigments, fillers and the like can be further contained.

  In addition, when such an additive is contained in the resin composition used for the first non-foamed layer 11 or the second non-foamed layer 12, an additive having a high migration property such as an antistatic agent used in the foamed layer 20 is used. It is preferable not to contain an agent.

  The resin composition used for forming the foamed layer 20 is obtained by further adding a component for foaming and an antistatic agent to the polymer component used for forming the non-foamed layer as described above. Can be used.

When the foamed layer 20 is coextruded together with the first non-foamed layer 11 and the second non-foamed layer 12 to produce the conductive foamed sheet 1, the affinity of the interface between the non-foamed layer and the foamed layer is improved. It is preferable to make these base polymers common to some extent in that a conductive foam sheet having a large force (peel strength) required for peeling between the non-foamed layer and the foamed layer can be easily formed.
For example, in any formation of the non-foamed layer and the foamed layer, a conductive foamed sheet having excellent strength can be obtained by using the polyolefin resin composition.

In the present embodiment, as the antistatic agent, a low molecular type or a high molecular type can be adopted without any particular limitation. Usually, the antistatic agent is a polypropylene resin or a polyethylene resin. It is expensive compared to base polymers such as resins, especially polymer antistatic agents are expensive, and lower surface resistivity unless they are contained in relatively large amounts compared to low molecular antistatic agents. Is difficult.
Therefore, the antistatic agent used in the conductive foam sheet of this embodiment is a low molecular weight antistatic agent in that it is relatively inexpensive and easily available, and the resistance value of the foamed layer 20 can be reduced with a small amount of use. It can be said that is more preferable than the polymer type antistatic agent.
Examples of the low molecular weight antistatic agent include nonionic low molecular weight antistatic agents, anionic low molecular weight antistatic agents, cationic low molecular weight antistatic agents, and amphoteric low molecular weight antistatic agents.

Examples of the nonionic low molecular weight antistatic agent include alcohol antistatic agents such as polyethylene glycol, ether antistatic agents such as polyoxyethylene alkyl ether and polyoxyalkylene alkyl ether, sorbitan fatty acid esters, Ester antistatic agents such as polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester and glycerin fatty acid ester, amine antistatic agents such as aliphatic alkylamine and aliphatic alkylesteramine, and glycerin such as polyoxyethylene glyceride Amide type antistatic agents such as an antistatic agent and an alkylalkanolamide.
Examples of the anionic low molecular weight antistatic agent include alkyl sulfonates. Examples of the cationic low molecular weight antistatic agent include tetraalkylammonium salts. Amphoteric low molecular weight antistatic agents. Examples thereof include alkylbetaines.

  Examples of the polymer antistatic agent include ionomers such as polyethylene oxide, polypropylene oxide, polyethylene glycol, polyester amide, and polyether ester amide, quaternary ammonium salts thereof, and polyether-polyolefin block copolymers (polyethylene And a copolymer of an olefin block and a hydrophilic block such as a block copolymer of an ether block and a polyolefin block).

Among these, when a polypropylene resin is employed as the base polymer, it is particularly preferable to use a combination of an aliphatic alcohol and an aliphatic amine as a low molecular weight antistatic agent.
In addition, although the low molecular type antistatic agent can suppress bleeding out to the surface of the conductive foamed sheet 1 by the first non-foamed layer 11 and the second non-foamed layer 12, it has a high migration property and is excessively contained. And the first non-foamed layer 11 and the second non-foamed layer 12 may pass through the surface of the conductive foam sheet 1.
In addition, even if the content is more than necessary, not only the material cost of the conductive foam sheet 1 is increased, but it may be difficult to expect further improvement in the conductivity of the foam layer 20.

  In such a case, when a low molecular weight antistatic agent used in combination with an aliphatic alcohol and an aliphatic amine is added to a polyolefin resin composition in which a polypropylene resin is employed as a base polymer. In general, the low-molecular-type charging is performed so that the ratio is in the range of 0.4 to 5.0 parts by weight with respect to 100 parts by weight of the polymer component contained in the resin composition. It is preferable that an inhibitor is contained.

  Further, if necessary, for the purpose of further adjusting the electric resistance value of the foam layer, the carbon black exemplified in the material for forming the non-foam layer can be contained in the material for forming the foam layer together with the antistatic agent. is there.

  Examples of the foaming component include a gas component that is in a gaseous state at least at the melting point of the base polymer, a nucleating agent that serves as a nucleus when bubbles are formed by the gas component, and thermal decomposition at least at the melting point of the base polymer. And a pyrolytic foaming agent that generates gas by generating gas.

Examples of the gas component include aliphatic hydrocarbons such as propane, butane, and pentane; 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1-difluoroethane (HCFC-142b), 2 -Freon such as chloro-1,1,1,2-tetrafluoroethane (HCFC-124), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1-difluoroethane (HFC-152a) System gas components: nitrogen, carbon dioxide, argon, water and the like.
These gas components may be used alone or in combination.

Examples of the nucleating agent include talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, and sulfuric acid. Examples thereof include inorganic compound particles such as potassium, barium sulfate and glass beads, and organic compound particles such as polytetrafluoroethylene.
This nucleating agent can be contained in the foam layer forming material by, for example, a masterbatch method previously contained in a polyolefin-based resin, and the nucleating agent is any one of 5 wt% to 50 wt%. The nucleating agent can be used more effectively by using a master batch dispersed in a polyolefin resin.

Furthermore, examples of the thermal decomposition type foaming agent include azodicarbonamide, sodium hydrogen carbonate, a mixture of sodium hydrogen carbonate and citric acid, and the like.
About this heat decomposable foaming agent, it can be used more effectively by dispersing it in a polyolefin resin so as to have a content of 10 wt% or more and 50 wt% or less. it can.

Normally, when a voltage is applied in the thickness direction by sandwiching a molded product formed by foaming a resin composition between electrodes, the current passes through a bubble film slightly present between the bubbles, and carbon black is added to the resin composition. Except for the case where the electrical resistance value is sufficiently reduced by adding a conductive component such as, observe a current value sufficient to obtain the volume resistivity in the measurement using a general super insulation resistance meter. This is difficult and exceeds the measurement limit.
However, if the resin composition for forming the foam layer contains carbon black in an amount sufficient to lower its electrical resistance, the fluidity of the resin composition is lowered and the growth of bubbles is suppressed, or open cells It is difficult to obtain a desired foamed state.
Further, as a result of reducing the elongation during molding, there is a possibility that a large amount of dust containing carbon black is generated from the cut surface of the molded body.

In the present embodiment, as described above, the antistatic agent effectively acts to reduce the surface resistivity on the surface of the bubble film.
Therefore, the value of the volume resistivity is reduced by forming the electric path along the surface of the bubble film inside the foamed molded body.
That is, in this embodiment, it is possible to reduce the resistance value of the foamed layer while preventing the formation of a foamed state and preventing mass blending of carbon black, which is feared to generate dust.

Such a conductive foam sheet can be produced using an apparatus as shown in FIGS.
2 is a schematic configuration diagram according to the manufacturing apparatus of the conductive foam sheet 1, and FIG. 3 is a cross-sectional view showing an internal state of the confluence mold (symbol XH) also shown in FIG. is there.

As shown in FIG. 2, the conductive foam sheet manufacturing apparatus in this embodiment includes two series of a first extruder 70 that is a tandem extruder and a second extruder 80 that is a single extruder. Extruder is equipped.
Further, a merge mold XH into which the resin composition melt-kneaded in these extruders is merged, and a circular die CD for discharging the resin composition merged in the merge mold XH into a cylindrical shape are provided. Yes.

  Further, the manufacturing apparatus includes a cooling device CL for air-cooling the conductive foam sheet discharged in a cylindrical shape from the circular die CD, and a cylindrical shape having a predetermined size by expanding the diameter of the cylindrical conductive foam sheet. And a slitting device for slitting the conductive foam sheet after passing through the mandrel MD into two sheets (not shown: FIG. 2 shows only the state of being divided vertically) A winding roller 92 for winding the slit conductive foam sheet 1 after passing the plurality of rollers 91 is provided.

The first extruder 70 is for forming the foamed layer 20, and the upstream extruder (hereinafter also referred to as “upstream extruder 70 a”) has a resin for forming the foamed layer 20. A hopper 71 for introducing a composition (hereinafter also referred to as “foamable resin composition”) and a gas introduction part 72 for supplying gas components such as hydrocarbons into the cylinder are provided.
Further, on the downstream side of the upstream side extruder 70a, an extruder (hereinafter referred to as "downstream side") that melts and kneads the foamable resin composition containing the base resin and the gaseous component and discharges it to the joining mold XH. Extruder 70b ").

  The second extruder 80 is for forming the first non-foamed layer 11 and the second non-foamed layer 12, and a resin composition for forming the non-foamed layer (hereinafter referred to as “non-foaming property”). The resin composition ”(also referred to as“ resin composition ”) is introduced from the hopper 81, and the non-foamable resin composition is melted and kneaded inside the cylinder and discharged to the joining mold XH.

As shown in the schematic cross-sectional view of FIG. 3, the confluence mold XH includes a first resin flow path W1 that passes through the center from the right side to the left side of the front view of FIG. 3, and the first resin flow path. A second resin flow path W2 for allowing the resin to flow into the first resin flow path W1 in the middle of W1, and the upstream side of the second resin flow path W2 (right side in front view in FIG. 3) A third resin flow path W3 for allowing the resin to flow into the first resin flow path W1 is formed.
The second resin flow path W2 is formed so that the resin composition can flow into the resin flow path W1 from an annular slit S1 opened in a wall surface forming the resin flow path W1. The resin flow path W3 is connected to a tube P having an open end at the center of the first resin flow path W1, so that the resin composition can flow into the center of the first resin flow path W1. Is formed.

The first resin flow path W1 has an upstream side connected to the first extruder 70 and a downstream side connected to the circular die CD, and the second resin flow path W2 and the third resin flow path W3. Is connected to the second extruder 80 via the distribution pipe D so that the non-foamable resin composition can flow from the second extruder 80.
That is, the merge mold XH of the present embodiment is a circle having a triple structure of non-foamable resin composition / foamable resin composition / non-foamable resin composition on the downstream side of the first resin flow path W1. It is provided so that a columnar flow can be supplied toward the circular die CD.

  The circular die CD is a triple resin (non-foamed resin composition in the center / foamable resin composition on the outside / and non-foamed resin composition on the outside) that flows from the converging mold XH. It is formed so that the flow of the composition is expanded into a cylindrical shape, and is expanded to be coextruded from the discharge hole.

In order to produce a conductive foam sheet using such an apparatus, first, a resin material used for forming the foam layer 20 is introduced from the hopper 71 of the first extruder 70, and a non-foamable resin is supplied to the second extruder 80. There is a method in which materials are charged and melt-kneading at a temperature equal to or higher than the melting temperature of the resin is carried out in each extruder and then co-extruded from the circular die CD.
In addition, when adding an additive etc. to a foamable resin composition or a non-foamable resin composition, these should also be thrown in from a hopper and melt-kneaded with each extruder.

Among these extruders, in the first extruder 70, it is necessary to melt and knead the components for foaming. Therefore, the gas component is press-fitted from the gas introduction part 72 provided in the upstream extruder 70a. Mixing with the molten resin is performed.
In order to co-extrude from the circular die CD, the foamable resin composition melt-kneaded by the upstream extruder 70a in the first extruder 70 is adjusted to a temperature suitable for extrusion foaming by the downstream extruder 70b. In the second extruder 80, on the other hand, the non-foamable resin composition is adjusted to a temperature suitable for forming the first and second non-foamed layers 11 and 12, and the merge mold XH It is important to form a laminated structure of molten resin in the merge mold XH.

Then, the respective resin compositions merged in the merge mold XH are co-extruded into a cylindrical shape from the annular discharge hole of the circular die CD, and foamed in the foamable resin composition to form the foam layer 20. A non-foamed layer is formed in the non-foamable resin composition.
At this time, in the formation of the foam layer 20, innumerable bubbles are formed inside by the gas component, and a thin bubble film is formed between the bubbles and the resin composition.

Since the resin composition used for forming the foamed layer contains an antistatic agent, when the foamable resin composition in a molten state is cooled and solidified while forming bubbles by foaming, the antistatic agent is used. Migrates to the surface of the bubble film and effectively acts to lower the surface resistance.
That is, since the antistatic agent is bleed out on the surface of the bubble film, the surface resistivity of the bubble film can be greatly reduced while suppressing the use of carbon black in the foam layer forming material.
In particular, when a polyolefin resin composition is used for forming the foam layer, the polyolefin resin is generally low in polarity and low in compatibility with an antistatic agent (especially a low molecular type antistatic agent). For this reason, a larger amount of the contained antistatic agent can be deposited on the surface of the bubble film and effectively utilized for lowering the resistance value.

In addition, since the conductive foam sheet according to the present embodiment reduces the volume resistivity of the foam layer portion that has a large influence on the volume resistivity, the first non-foam layer and the second non-foam layer are reduced. The content of carbon black can be reduced on the side, and the volume resistivity of the conductive foam sheet is 1 × 10 ¹⁰ Ω · cm or more and 1 × 10 ¹³ Ω · cm or less while suppressing the use of carbon black. Value.
Therefore, the surface of the conductive sheet formed by the non-foamed layer can be made smoother.
By improving the surface smoothness of the non-foamed layer, it is possible to improve the aesthetics of this conductive foam sheet and molded products formed by this conductive foam sheet, and surface friction is suppressed. Therefore, generation of dust due to rubbing with other members can be suppressed.

As described above, the conductive foam sheet of the present embodiment is suitable for forming a conductive foam resin container for housing a semiconductor element or the like while suppressing the amount of carbon black that may cause dust or the like. Volume resistivity (1 × 10 ¹⁰ Ω · cm or more and 1 × 10 ¹³ Ω · cm or less).
That is, it can be said that the conductive foam sheet of this embodiment is a conductive foam sheet suitable for use in a state where it is in contact with a member such as a semiconductor element which is easily damaged or electrically damaged.

In addition, the value of the surface resistivity of the obtained sheet | seat can be calculated | required based on the method of JISK6911: 1995 "Thermosetting plastics-general test method".
Specifically, using a test apparatus (manufactured by Advantest Corporation, digital ultra-high resistance / microammeter R8340 and resiliency chamber R12702A), a voltage of 500 V is applied by pressing an electrode to the sample with a load of about 30 N. Then, the resistance value after 1 minute can be measured and calculated by the following formula (1).
As the size of the sample used at this time, a flat square shape having a side of 10 cm (thickness is 10 mm or less) can be used.

ρs = π (D + d) / (D−d) × Rs (1)

However,
ρs: Surface resistivity (MΩ)
D: Inner diameter of surface annular electrode (cm)
d: outer diameter of inner circle of surface electrode (cm)
Rs: Surface resistance (MΩ)

Further, the volume resistivity value of the obtained sheet can be determined in accordance with the method described in JIS K 6911: 1995 “Thermosetting Plastics—General Test Method”.
Specifically, using a test apparatus (manufactured by Advantest Corporation, digital ultra-high resistance / microammeter R8340 and resiliency chamber R12702A), a voltage of 500 V is applied by pressing an electrode to the sample with a load of about 30 N. Then, the resistance value after 1 minute can be measured and calculated by the following formula (2).
As the size of the sample used at this time, a flat square shape having a side of 10 cm (thickness is 10 mm or less) can be used.

ρv = πd ² / (4t) × Rv (2)

However,
ρv: Volume resistivity (MΩ · cm)
d: outer diameter of inner circle of surface electrode (cm)
t: sample thickness (cm)
Rv: Surface resistance (MΩ · cm)

In addition, the conductive foam sheet having such a volume resistivity can be easily formed into a desired container shape by adopting a general sheet forming method such as vacuum forming or vacuum / pressure forming. .
For example, as a conductive foamed resin container, when a foam tray or the like is produced by sheet molding using the conductive foam sheet as a raw material, the entire tray is formed of a conductive foam sheet. The electrical properties of the foamed sheet will be reflected in the foamed tray, and the volume resistivity of the bottom plate part and the side wall part of the foamed tray is usually 1 × 10 ¹⁰ Ω · cm or more and 1 × 10 ¹³ Ω · cm or less. It becomes.

When this foam tray is used as a container / container for semiconductor elements, it is prevented that static electricity is accumulated in the foam tray because the foam tray is formed in a state having an appropriate electrical resistance, Even if the foam tray is discharged from another container or the like in which static electricity is accumulated, the semiconductor element accommodated therein can be prevented from being greatly damaged.
In addition, generation of dust due to carbon black and the like, and bleeding out of the antistatic agent to the tray surface are suppressed, so that the semiconductor element can be accommodated in a clean state.

  In addition, when the entire container is not formed of the conductive foam sheet and constitutes only a part of the container for housing the semiconductor element, for example, it is conductive as a part of a member such as a partition plate for partitioning the semiconductor elements. Even in the case of using a porous foam sheet for a container, the same effect is obtained in that the effect of preventing contamination and electrical damage due to deposits or the like is exhibited in applications where it contacts a semiconductor element.

In the above embodiment, a conductive foam sheet having a three-layer structure in which a non-foamed layer is arranged on both sides of the foamed layer so as to be in contact with the foamed layer is exemplified. When a plurality of foamed layers are formed between two non-foamed layers by providing different foamed layers between the foamed layer formed of the resin composition and the non-foamed layer, In the case where a plurality of non-foamed layers are formed on both the upper and lower sides, a case where various laminated structures are formed is also within the intended scope of the present invention.
Although not described in detail here, conventionally known technical matters regarding the conductive foam sheet and the conductive foam resin container can be employed in the present invention as long as the effects of the present invention are not significantly impaired.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

Example 1
For the production of the conductive foam sheet, the same type of equipment as that shown in FIG. 2 was used.
That is, the non-foamable resin composition is supplied from the second extruder 80 through the branch pipe D at two locations upstream and downstream of the resin flow path W1 into which the foamable resin composition flows from the first extruder 70. The first and second extruders were connected to the merging die XH so as to flow in, and the circular die CD was connected to the downstream side of the merging die XH to perform co-extrusion.

First, the first extruder is composed of a single-screw extruder (upstream extruder) having a diameter of 90 mm and a single-screw extruder (downstream extruder) having a diameter of 115 mm connected to the single-screw extruder. A tandem extruder was prepared.
As a polypropylene resin for the foam layer, the product name “WB135HMS” (melt tension 31 g, melt index 2.4 g / 10 min) manufactured by Borealis has a ratio of 0.2 parts by weight to 100 parts by weight of the resin. Baking soda-citric acid foaming agent (manufactured by Dainichi Seika Co., Ltd., trade name “Fine Cell Master PO410k”) and 1.5 parts by weight of antistatic agent (mixture of aliphatic alcohol and aliphatic amine, manufactured by Kao Corporation) Product name “TS-2B”) was added, and this mixture was supplied to the first stage hopper of a single screw extruder having an upstream diameter of 90 mm, heated and melted at 200 ° C., and then melted. Butane (isobutane / normal butane = 35/65 wt%), which is a gas component, is press-fitted and kneaded so that the ratio with respect to 100 parts by weight of the resin is 4 parts by weight. .
The foamable resin composition is supplied to the downstream extruder 70b through the connecting pipe, the temperature of the foamable resin composition is lowered to 170 ° C., and the joint connected to the tip of the extruder at a discharge amount of 100 kg / hour. Supplied to mold XH.

  On the other hand, a single screw extruder having a diameter of 60 mm is prepared as the second extruder 80, and 90% by weight of carbon black master pellets manufactured by Dainichi Seika Kogyo Co., Ltd. as a conductive resin layer for forming a non-foamed layer to be a surface layer, A mixture obtained by mixing 10 wt% of a trade name “WB135HMS” (melt tension 31 g, melt index 2.4 g / 10 min) manufactured by Borealis as a polypropylene resin is supplied to the second extruder, and 200 After heat melting at 0 ° C., the temperature was maintained at 190 ° C. with a single tube provided at the tip of the extruder.

Next, after this molten non-foamable resin composition is bisected by a distribution pipe having a branch flow path, the total amount is 20 kg / hour from the tube P and the slit S1 of the confluence mold XH. After discharging and laminating and joining the inner layer side and outer layer side of the foamable resin composition, resin discharge becomes 120 kg / hour from a circular die (caliber 110 mm, slit gap 0.95 mm) connected to the tip of the converging mold A conductive foam sheet in which a non-foamed layer was laminated on both the inner and outer sides through a foamed layer was formed by co-extrusion in a cylindrical shape.
This conductive foam sheet is further expanded on a cooled mandrel having a diameter of 200 mm, and its outer surface is cooled by blowing air from an air ring, and cut by a cutter at one point on the mandrel. It was flat.

The obtained plate-like conductive foam sheet had a surface specific resistance value of 5.0 × 10 ⁴ Ω and a volume resistivity of 3.0 × 10 ¹¹ Ω · cm.

(Comparative Example 1)
A conductive foam sheet was produced in the same manner as in Example 1 except that the foam layer forming material did not contain an antistatic agent (trade name “TS-2B”, manufactured by Kao Corporation).
The surface resistivity of the conductive foam sheet of Comparative Example 1 was 2.0 × 10 ⁴ Ω, and the volume resistivity was 3.0 × 10 ¹⁵ Ω · cm.

  Due to the difference in electrical characteristics between the conductive foam sheet of Example 1 and the conductive foam sheet of Comparative Example 1, an antistatic agent is included in the foam layer forming material while having the same surface resistivity. It can be seen that a conductive foam sheet having a volume resistivity suitable for a material for forming a container such as a semiconductor element can be formed.

  1: conductive foam sheet, 11, 12: non-foamed layer, 20: foamed layer

Claims (5)

A foamed layer formed in a sheet shape having a laminated structure, and the laminated structure is formed in a foamed state by a resin composition, and a non-foamed layer formed in a non-foamed state by a resin composition containing carbon black An electrically conductive foam sheet in which the non-foamed layer is formed on both sides of the foamed layer through the foamed layer,
By adding an antistatic agent to the resin composition forming the foamed layer, the volume resistivity is set to any value of 1 × 10 ¹⁰ Ω · cm to 1 × 10 ¹³ Ω · cm. A conductive foam sheet characterized by comprising:   2. The resin composition used for forming the foamed layer and the non-foamed layer is a polyolefin-based resin composition having a polyethylene-based resin or a polypropylene-based resin as a base polymer, respectively. Conductive foam sheet.   The conductive foam sheet according to claim 1 or 2, wherein the foam layer and the non-foam layer are formed by co-extrusion.   The conductive foam sheet according to any one of claims 1 to 3, wherein the conductive foam sheet is used for forming a container for housing a semiconductor element and used to form a portion in contact with the semiconductor element. A foamed layer formed in a sheet shape having a laminated structure, and the laminated structure is formed in a foamed state by a resin composition, and a non-foamed layer formed in a non-foamed state by a resin composition containing carbon black A conductive foamed resin container formed by sheet-molding a conductive foam sheet in which the non-foamed layer is formed on both sides of the foamed layer via the foamed layer,
When the conductive foam sheet contains an antistatic agent in the resin composition forming the foam layer, the volume resistivity is 1 × 10 ¹⁰ Ω · cm to 1 × 10 ¹³ Ω · cm. It is formed so that it may become. The conductive foamed resin container characterized by the above-mentioned.

Images