JP2009101535A - Low dust-generating sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low dust-generating sheet which can properly used in a clean room and is excellent in antistatic performance. <P>SOLUTION: In the low-dust generating sheet, a substrate formed of heat-fusible fibers is impregnated with an impregnation liquid containing a water-soluble polymer as a main component, conductive paint is applied on at least one side of the impregnated substrate, and the treated substrate is heat-treated. The surface specific resistance of the coating surface under the conditions of 23°C and 50% relative humidity is preferably 1.0×10<SP>4</SP>Ω/sq. to 1.0×10<SP>9</SP>Ω/sq. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sheet having antistatic properties and low dust generation properties, which is suitable as a material used for storage, packaging, and the like of electronic components in a clean room.

  In product manufacturing lines such as the electronics industry, medical / pharmaceutical industry, and precision machinery industry, dust causes serious adverse effects such as product defects, quality, and yield reduction. Work is being done. In the clean room, it is necessary to select the material so that the dust is prevented from being brought into the interior as much as possible and the carried material is not generated by various internal operations. For example, low dust generation paper, which is one of the materials suitable for use in a clean room, is used as a process paper or wrapping paper used for recording purposes such as slips and in the production process of products. In particular, in the electronics industry that handles semiconductors, it is used as a slip sheet for use in superposition with a thin metal plate used for a lead frame for mounting electronic components such as VLSI and a shadow mask for CRT. The metal thin plate is easily scratched on the surface and is easily oxidized. By sandwiching the slip sheet, abnormal current, abnormal heat generation, disconnection, and the like due to the scratch can be prevented. Further, in the manufacture and transportation of electronic components, a paper with low conductivity is often used for the purpose of avoiding electrical troubles such as dielectric breakdown due to electrostatic charging and preventing dust adhesion.

Such conductive low dust generation paper is often a synthetic paper made of a combination of synthetic fibers and conductive materials. For example, Patent Document 1 discloses a conductive paper obtained by coating synthetic fibers or the like with silver or copper. An invention characterized by containing a conductive fiber has been proposed. Patent Document 2 discloses a sheet obtained by heat-treating a sheet obtained by mixing paper making of heat-fusible fibers and organic conductive fibers at a temperature equal to or higher than the melting point of the heat-fusible fibers. The invention has been proposed.

  However, the low dust generation paper of the type in which the heat-fusible fiber and the conductive fiber are mixed and then heat-sealed has a drawback that it is more likely to generate dust than the resin film. For example, when carbon fiber is used as the conductive fiber, the carbon fiber has low flexibility, and there is a problem that when bent, the fiber is cut and easily becomes dust. Further, when metal fibers are used, the electrical conductivity is too high, and if a product touches the exposed portion of the fibers, an electrical trouble is likely to occur, so improvement has been demanded. On the other hand, the use of conductive organic fibers is superior to other conductive fibers in terms of the above-described flexibility, conductivity, and the like. However, due to the large amount of dust generated by processing and rubbing with the product, and the difficulty of unfused fibers falling off, these currently do not meet the requirements for dust generation. . In addition, since the conductive organic fiber itself is expensive, there is a problem in cost.

  As a low dust generation sheet that does not use conductive fibers, Patent Document 3 proposes a low dust generation conductive fiber sheet in which a sheet base material is coated with a conductive polymer. This enhances the adhesion between the base material and the conductive polymer by the binder resin, but this alone cannot sufficiently suppress dust generation.

Japanese Patent Laid-Open No. 2-159898 JP-A-8-74193 JP 2007-169823 A

  Accordingly, an object of the present invention is to provide a low dust generation sheet having reduced dust generation and moderate conductivity.

  As a result of intensive studies to solve the above problems, the present inventors applied a conductive paint to the surface of a base material made of heat-fusible fibers to impart conductivity, and then heat-treated this. It has been found that the above object can be achieved by melting and adhering the base material and the coating layer to suppress dust generation from the base material or the coating layer, and the present invention has been completed.

  That is, the invention described in claim 1 is a low dust-generating sheet characterized in that a conductive paint is applied to at least one surface of a base material made of heat-fusible fibers and this is treated with heat.

  The invention described in claim 2 is that a water-soluble polymer layer is provided on at least one surface of a base material made of heat-fusible fibers, a conductive paint is applied thereon, and this is treated with heat. It is a low dust generation sheet characterized.

  According to a third aspect of the present invention, a base material composed of heat-fusible fibers is impregnated with an impregnating liquid mainly composed of a water-soluble polymer, and a conductive paint is applied to at least one surface thereof, which is heated. It is a low dust generation sheet | seat characterized by processing by.

  The invention according to claim 4 is the low dust-generating sheet according to claims 1 to 3, wherein the heat-fusible fiber of the base material is a polyolefin fiber.

In the invention of claim 5, the surface specific resistance value under the conditions of 23 ° C. and 50% relative humidity is 1.0 × 10 ⁴ Ω / □ or more, and 1.0 × 10 ⁹ Ω / □. The low dust-generating sheet according to claim 1, which is □ or less.

The low dust generation sheet of the present invention employs a means for imparting conductivity to a substrate by applying a conductive agent. As a result, it is possible to avoid dusting troubles caused by dropping of unfused fibers, which are seen in a sheet of a type in which conductive fibers are made. Further, by covering the substrate surface with resin, the surface strength of the sheet is increased, and there is an effect of suppressing fiber dusting generated by rubbing or the like. In addition, when the conductive agent is present inside the sheet, the strength of the sheet is reduced. However, in the present invention, conductivity can be imparted only to the surface of the sheet by coating, so that a decrease in strength inside the sheet can be prevented. Furthermore, a cost-effective structure can be achieved by concentrating relatively expensive conductive materials only on surfaces that require electrical conductivity.

The low dust-generating sheet of the present invention employs a means for bringing the base material and the coating layer into close contact with each other by heat-welding the base material after applying the conductive agent. It can be said that it is effective for the following reason as a method of bringing a paint into close contact with a porous substrate having a hydrophobic surface characteristic such as a nonwoven fabric. In general, polyolefin fibers such as polyethylene and polypropylene which are widely used as heat-fusible fibers are nonpolar molecules, and have extremely low adhesion to any water-based or solvent-based resin. For this reason, only by coating the surface of the base material, the fiber and the paint do not adhere, and the coating layer easily peels off due to rubbing or the like. However, when heat treatment is performed after coating as in the present invention, the heat-fusible fiber melts and adheres while taking in the binder resin at the interface between the base material and the coating layer in the sheet, thereby exhibiting strong adhesiveness. It becomes possible.

Moreover, the adhesiveness of a base material and a coating layer can further be improved by providing a water-soluble polymer layer in the said base material. By impregnating or coating the base material with a water-soluble polymer in advance, a hydrophilic group such as a hydroxyl group or a carboxyl group is provided on the surface layer and inside of the base material. As a result, the component of the conductive coating applied to the upper layer of the water-soluble polymer layer becomes easier to adhere than when directly applied to the nonpolar heat-fusible fiber.

In the present invention, the base material composed of heat-fusible fibers is a material in which fibers are melted by heating at a temperature equal to or higher than the melting point of the fibers, and a continuous sheet shape is constructed by fusing each other. . The base material can be produced by dispersing the heat-fusible fiber in water and subjecting it to a known wet papermaking process.

As the material of heat-fusible fiber, polyolefin fiber such as polyethylene and polypropylene, microfibrillated fiber of these, hot water-soluble fiber such as polyvinyl alcohol fiber, polyethylene, polypropylene, polyester, etc. combined with low melting point Although fiber etc. are preferable, it is not limited to these. As the structure, a composite spun fiber having a core / sheath structure of polyethylene / polyester or a side-by-side structure composed of two or more kinds of polyesters having different melting points is preferable. Particularly preferred are polyolefin fibers, which have a melting point of about 125 ° C. and can be easily heat-sealed. For base materials composed of synthetic fibers with a high melting point exceeding 150 ° C, the heat roll body is kept at a high temperature when heat-sealing in the heat treatment step after coating the conductive paint, so it exists on the surface of the base material. This is not preferable because the layer of the conductive paint to be peeled is likely to be transferred to the heating roll side. Moreover, the mixing of heat-fusible short fibers having a low melting point is effective as an auxiliary component for binding the base material. The short fibers are melted before the main heat-fusible fibers in the sheet-forming process by wet papermaking. Thereby, since it is possible to compensate for the insufficient mechanical strength of the base material at the stage where the main component fibers are completely heat-sealed, it is possible to avoid production machine troubles such as running out of paper.

The base material can be mixed with fibrous materials such as wood pulp, non-heat-synthetic synthetic pulp, and synthetic fiber within a range not impairing the performance of the present invention. For example, the mixing of wood pulp has an effect of improving the adhesion with a solution to be coated or impregnated, and further, an appropriate strain remains even after heating, so that an effect of improving workability can be imparted. Wood pulp includes softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood bleached sulfite pulp (NBSP), thermomechanical A known pulp such as pulp can be used singly or as a mixture, and the blending ratio is not particularly limited.

Examples of the component of the coating material applied to provide a water-soluble polymer layer on the substrate in the present invention include fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, unsaponified polyvinyl alcohol, and various modified polyvinyl alcohols. Polyvinyl alcohol such as alcohol, starch such as polyacrylamide, oxidized starch and modified starch, cellulose derivatives such as carboxymethylcellulose, synthetic and natural polymer compounds such as casein and polyvinylpyrrolidone, or a mixture of two or more kinds, and the coating concentration is 0 It can be prepared to be 5% to 50%, and can be prepared by blending an auxiliary agent such as a surfactant as necessary. In particular, a water-soluble polymer having good film properties at the time of drying represented by polyvinyl alcohol is preferable because adhesion between the film and the conductive layer is improved.

As a method for providing the water-soluble polymer layer on the substrate, a known coating method such as a bar coater, an air knife coater, a blade coater, a rod coater, a gravure coater, a size press coater, or a gate roll coater may be employed. The coating amount after drying is preferably not particularly limited but is in the range of ^{0.1g / m 2 ~20g / m 2} . If the coating amount is less than 0.1 g / m ^2, the effect of improving the adhesion between the base material and the conductive layer cannot be obtained, and if the coating amount exceeds 20 g / m ² , there are inconveniences in machine production such as defective drying. It is not appropriate because it is likely to occur.

Even when the substrate is impregnated with a water-soluble polymer, the same water-soluble polymer as the above-mentioned paint component can be used. In order to increase the permeability of the water-soluble polymer, a surfactant is used. Adjustments such as adding more may be necessary. When water-soluble polymer is impregnated into the base material, fiber binding by the polymer film is formed even inside the base material compared to the coating method, so dust generation from the cut surface of the sheet is suppressed. can do. The impregnation rate in the case of impregnating the paint is not particularly limited, but it is preferable to impregnate so that the impregnation rate is 1% to 30% for the same reason as in the coating.

The conductive paint used in the present invention can be prepared by mainly comprising a binder that can be dissolved or dispersed in water and conductive particles, and if necessary, an auxiliary agent such as a surfactant. Use of an organic solvent-based conductive agent and binder is not preferable. The reason is that since the permeability to the base material made of heat-fusible fibers is high, it causes adverse effects such as paint penetration, dissolution of the base material surface, and expansion and contraction of the base material.

Examples of binders that can be dissolved or dispersed in water used in the conductive paint include styrene / butadiene latex, modified styrene / butadiene latex, acrylonitrile / butadiene latex, methyl methacrylate / butadiene latex, modified methyl methacrylate / butadiene latex, chloroprene latex, Aqueous latex such as butyl latex, polybutene latex, polyurethane latex, thiocol latex, polyethylene emulsion, polystyrene emulsion, vinyl acetate emulsion, acrylic emulsion, ethylene vinyl acetate emulsion, vinylidene chloride emulsion, aqueous emulsion such as vinyl chloride emulsion and polyvinyl alcohol, Carboxymethylcellulose, starch, casein Can be used those synthetic or mixed alone or two or more types of natural polymeric substance, but is not limited thereto.

Examples of the conductive particles used in the conductive paint include carbon black conductive pigments such as carbon black and conductive carbon, metal oxides doped with conductive polymers, or conductive organic substances. It can be used by mixing. In particular, a conductive organic material is particularly preferable. For example, an aqueous dispersion of polypyrrole can exhibit a target conductivity by using a very small amount.

As a means for applying the conductive paint to the substrate, known coating methods such as a blade coater, an air knife coater, a roll coater, a gravure coater, a curtain coater, and a bar coater can be used.

As a particularly preferable composition as the conductive coating, a composition in which 10 to 50 parts by mass of conductive particles are added to 100 parts by mass of the binder can be preferably used as having both functions of low dust generation and conductivity. . If the conductive particles exceed 50 parts by mass, the coating layer strength tends to be insufficient and powder falling (a phenomenon in which the conductive particles fall off) tends to occur. On the other hand, if the conductive particles are less than 10 parts by mass, the target is obtained. It is difficult to obtain conductivity.

As a means for the heat treatment performed after the conductive paint is applied to the base material, for example, there is a method using a hot press machine or a thermal calendar. The thermal calendar is preferably used because it can be continuously processed. When using a heat calendar, the material and surface properties of the heat roll and backup roll, processing speed, nip pressure, etc. not only greatly affect the mechanical strength, transparency, dust generation, and conductivity of the heated sheet, Since it is also related to the operational stability of the machine, it is necessary to select appropriately according to the basis weight, thickness, composition, etc. of the sheet to be pressure-bonded. In addition, since the surface resistivity of the sheet tends to increase as the melting of the substrate progresses, it is possible to set conditions for suppressing melting as much as possible in consideration of the balance with dust generation properties. preferable.

The temperature of the roll subjected to heat treatment is preferably in the range of 100 ° C. to 150 ° C., although it depends on the melting point of the heat-fusible fiber. If the temperature is lower than this, melting of the fibers does not proceed, and the heated sheet is not sufficiently low in dust generation due to the fuzzing and dropping off of the unfused fibers. On the other hand, when heated at 150 ° C. or higher, the fibers and the resin constituting the sheet are too melted to become viscous and adhere to the roll, so that heat treatment becomes difficult. Also, depending on the type of conductive particles, the set temperature may exceed the decomposition point of the particles, and as a result, it is necessary to note that the desired conductivity cannot be obtained.

The conductivity of the sheet after heat treatment is preferably in the range of a surface resistivity of 1.0 × 10 ⁴ Ω / □ or more and 1.0 × 10 ⁹ Ω / □ or less. When the surface specific resistance value is higher than 1.0 × 10 ⁹ Ω / □, the antistatic performance is insufficient. On the other hand, high electrical conductivity of less than 1.0 × 10 ⁴ Ω / □ is not preferable because there is a possibility that, for example, an electronic component in contact with the sheet may be destroyed by local energization.

When the low dust generation sheet of the present invention is used for each application in a clean room in a semiconductor-related field, dust is not generated when the low dust generation sheet is rubbed, and it is used by being punched into an arbitrary shape. Sometimes it is required that no dust be generated. As a method for evaluating the performance, a rubbing test, a stagnation test, and a tear sag test measured in accordance with SEMI (SEMICONDUCTOR EQUIIPMENT MATERIALS INTERNALIONAL) standard G67-0996 are preferable, and the dust generation amount is 500 pieces / ft or less, respectively. If it is.

Hereinafter, the present invention will be specifically described with reference to examples. However, each example is illustrative and does not limit the scope of the present invention.

Example 1
[Manufacture of base materials]
Synthetic fiber made of polyethylene (trade name: SWP E-620, manufactured by Mitsui Chemicals Co., Ltd.) 80 parts by mass, core-sheath composite binder fiber (trade name: NBF (H)) whose core component is polypropylene and whose sheath component is polyethylene , Manufactured by Daiwabo Co., Ltd.) was subjected to wet papermaking according to a conventional method to obtain a sheet-like substrate having a basis weight of 65 g / m ² .

[Coating of conductive paint]
20 parts by mass of a colloidal polypyrrole aqueous solution (trade name: PPY-12, manufactured by Maruhishi Oil Chemical Co., Ltd.) and ethylene-vinyl acetate emulsion (trade name: Sumikaflex 410HQ, manufactured by Sumitomo Chemical Co., Ltd.) as a binder, 80 masses A nonionic surfactant (trade name: Surfynol 504, manufactured by Shin-Etsu Chemical Co., Ltd.) 0.5 part by mass is added to 100 parts by mass of the coating base composed of parts to obtain a conductive paint. . This was coated on one side of the sheet-like substrate with a bar coater so that the coating amount after drying was 3 g / m ² and dried for 1 minute with a dryer at 105 ° C. to form a conductive layer.

[Heat treatment]
The sheet on which the conductive layer was formed was heat-treated using a thermal calendar while running at a temperature of 130 ° C., a nip pressure of 40 kg / cm ² , and a speed of 5 m / min to obtain a low dust generation sheet.

(Example 2)
After the base material obtained by the base material manufacturing method described in Example 1 was subjected to the impregnation treatment described below, the single-sided coating and heat treatment of the conductive paint were performed in the same manner as in Example 1, A dust-generating sheet was obtained.

[Impregnation treatment]
The base material is impregnated with a fully saponified polyvinyl alcohol (trade name: Kuraray Poval PVA105, manufactured by Kuraray Co., Ltd.) as a water-soluble polymer so that the impregnation amount after drying is 1.0 g / m ^2. Processed.

Example 3
On one side of the substrate obtained by the method for producing a substrate described in Example 1, a completely saponified polyvinyl alcohol (trade name: Kuraray Poval PVA105) as a water-soluble polymer was dried by a bar coater with a coating amount of 2 g. / M ² was applied and dried at 105 ° C. for 1 minute to provide a water-soluble polymer layer. This was subjected to the same conductive coating and heat treatment as in Example 1 to obtain a low dust generation sheet.

Example 4
A low dust-generating sheet was obtained in the same manner as in Example 1 except that the conductive coating in Example 1 was applied to both sides of the substrate (each coated amount after drying was 3 g / m ² ). It was.

(Comparative Example 1)
As base materials, 70 parts by mass of NBKP, 30 parts by mass of LBKP, 0.2 parts by mass of wet paper strength enhancer based on polyamide / epichlorohydrin resin (trade name: WS4012, manufactured by Seiko PMC Co., Ltd.), polyacrylamide (trade name: polymer) Set 500L, manufactured by Arakawa Chemical Industries, Ltd.) 0.2 parts by mass and 3 parts by mass of a sulfuric acid band were mixed, and paper having a basis weight of 65 g / m ² was produced by wet papermaking. This was subjected to one-side coating and heat treatment of the conductive paint in the same manner as in Example 1 to obtain a sheet.

(Comparative Example 2)
A sheet was obtained in the same manner as in Example 1 except that the heat treatment was not performed.

(Comparative Example 3)
In Example 1, a sheet was obtained in the same manner as in Example 1 except that the heat treatment performed after forming the conductive layer was performed in advance before forming the conductive layer, and no heat treatment was performed after forming the conductive layer.

The conductivity and dust generation of the low dust generation sheets obtained in the above examples and the sheets obtained in the comparative examples were evaluated. Moreover, the paint peelability at the time of heat fusion and the surface strength after heat fusion were also evaluated. The method of each evaluation is described below.

[Surface specific resistance]
As the evaluation of conductivity, the surface resistivity was measured. For this measurement, Hiresta MCP-HT450 (manufactured by Mitsubishi Chemical Corporation) was used as a measuring instrument. The measurement method was as follows: a 10 cm × 10 cm sheet was prepared as a test piece under the conditions of 23 ° C. and relative humidity of 50%, and this was applied to a measurement electrode box MCP-JB03 (manufactured by Mitsubishi Chemical Corporation) to provide a voltage of 10V. The value after 30 seconds was defined as the surface specific resistance value.

[Paint peelability during heat treatment]
Regarding the paint peelability during heat treatment, the surface of the hot roll was visually observed after heat treatment of the sheet, and the presence or absence of adhesion of the conductive paint was evaluated as follows.
A: Conductive layer adhesion to the heat roll is not observed at all O: Conductive layer adhesion to the heat roll is slightly observed ×: Conductive layer adhesion to the heat roll is often observed

[Surface strength after heat fusion]
Adhesive cellophane tape (trade name: cello tape No. 405 (18 mm), manufactured by Nichiban Co., Ltd.) is pasted on the sheet surface under conditions of 23 ° C. and 50% relative humidity so that the length becomes 10 cm (“cello tape” Is a registered trademark), a 2 kg weight is placed on the tape, and when the tape is peeled off after rubbing 5 times in one direction, whether or not the conductive layer is peeled off from the substrate is visually evaluated. Was passed.
○: The conductive layer does not peel off.
X: The conductive layer peels off.

  Dust generation was evaluated by a rubbing test, a stagnation test, and a tearing sag test measured according to SEMI Standard G67-0996. All were evaluated under conditions of 23 ° C. and 50% relative humidity.

[Rubbing test]
After two A5 size test pieces were rubbed together by hand for 3 minutes and 20 seconds at a speed of 3 times per 10 seconds in the measuring instrument (trade name: glove box, manufactured by Japan Airtech Co., Ltd.) Then, the air in the glove box was sucked and the number of generated dusts of 0.1 μm or more was measured with a particle counter (model: KC-22A, manufactured by Lion Co., Ltd.).

[Itching test]
A test piece of A5 size is rubbed by hand in a measuring instrument (trade name: glove box, manufactured by Japan Airtech Co., Ltd.) at a rate of once / 15 seconds for 3 minutes and 20 seconds, and the same as above. The number of dusts of 0.1 μm or more was measured.

[Tear sag test]
In a measuring instrument (trade name: glove box, manufactured by Japan Airtech Co., Ltd.), one A5 size test piece is torn into 4 pieces (4 cm intervals) by hand to make 5 pieces. Overlapping, and then squeezing by hand for 3 minutes at a rate of once / 15 seconds as in the stagnation test, the number of dusts of 0.1 μm or more was measured in the same manner as described above.

Each evaluation result is shown in Table 1. As can be seen from Table 1, the low dust generation sheets obtained in Examples 1 to 4 had a small amount of dust generation, and further, there was no paint peeling during heat treatment, and the surface strength after heat fusion was high. And the surface specific resistance value of the sheet was 1.0 × 10 ⁴ Ω / □ or more and 1.0 × 10 ⁹ or less. That is, it was shown that the low dust generation sheets of Examples 1 to 4 have both good dust generation and conductivity. And the following became clear from the comparison with an Example and each comparative example.
From the comparison between Example 1 and Comparative Example 1, the use of heat-fusible fibers as the base material has an excellent effect in reducing the dust generation of the sheet after heat treatment.
From the comparison between Example 1 and Comparative Example 2, the heat treatment after coating the conductive layer has an excellent effect in reducing the dust generation of the sheet.
From the comparison between Example 1 and Comparative Example 3, the base fiber fusion by heat treatment is more effective in reducing the adhesion of the conductive layer and reducing the dust generation of the sheet when applied after the conductive layer is applied. .

Claims (5)

A low dust-generating sheet, wherein a conductive paint is applied to at least one surface of a base material made of heat-fusible fibers, and this is treated with heat. A low dust-generating sheet, wherein a water-soluble polymer layer is provided on at least one surface of a base material made of heat-fusible fibers, a conductive paint is applied thereon, and this is treated with heat. A base material made of heat-fusible fibers is impregnated with an impregnating liquid mainly composed of a water-soluble polymer, and at least one surface thereof is coated with a conductive paint, which is treated with heat. Dusty sheet. The low dust generation sheet according to claim 1, wherein the heat-fusible fiber of the base material is a polyolefin fiber. The surface specific resistance value under the conditions of 23 ° C. and 50% relative humidity is 1.0 × 10 ⁴ Ω / □ or more and 1.0 × 10 ⁹ Ω / □ or less. The low dust generation sheet described.