JP2013132889A - Cushioning material for hot pressing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cushioning material easy to handle and excelling in durability of maintaining a thickness dimension and cushioning property even under repeated use without deterioration at a high temperature while applying uniform pressure and heat to the whole surface of material to be pressed in a hot pressing process of holding a plurality of sheets to be worked between hot plates and applying constant pressure and heat.SOLUTION: Fluororubber is foam-molded at a temperature higher than a hot pressing process temperature and then irradiated with radiation and cured.

Description

  The present invention relates to a cushioning material for a hot press process.

In the production of printed circuit boards, when a printed circuit board is molded in a hot press process, a material to be pressed is sandwiched between hot plates and a certain pressure and heat are applied. In such press molding, in order to apply uniform pressure and heat to the entire surface of the material to be pressed, a flat cushion material is interposed between the hot platen and the material to be pressed.

Recently, flexible printed circuit boards (hereinafter abbreviated as "FPC") are thin, light, flexible, and film-like printed boards that can be used for precise wiring. doing. A typical FPC attaches a circuit pattern of a metal foil such as copper on a resin film such as polyimide (copper-clad laminate, hereinafter abbreviated as CCL), and further separates a conductive portion and an insulating portion. It has a structure to which a resin coverlay film is attached. Further, depending on the FPC, a reinforcing base material is bonded to a portion where reinforcement is required. The cushion material is used in the manufacturing process and the circuit stacking process.

In the FPC manufacturing process, as described above, there are many hot pressing processes at high temperatures such as a reinforcing base material bonding process, a coverlay molding process or a lamination process. For mass production, the FPC material is sandwiched and stacked between release films, a cushioning material is installed between the hot platen, and high temperature and pressure are applied for a certain period of time. In this heating and pressurizing step, if the cushion material has uneven thickness, distortion due to heat, or uneven temperature due to poor heat transfer, a uniform temperature and pressure cannot be applied to the FPC material that will be the product later. As a result, defects such as defective plate thickness, cracks, and warp occur in the product. Therefore, a cushioning material is used in press molding in order to eliminate defective product thickness. As the cushion material, paper such as craft paper or linter paper, woven fabric, needle punched nonwoven fabric, rubber, woven fabric, laminated body of nonwoven fabric and rubber, or the like is used. This cushion material is referred to as a heat press cushion material.

The following is mentioned as a characteristic calculated | required by the cushion material for hot presses used for the hot press process at the time of FPC manufacture as mentioned above. 1
. A uniform pressure can be applied to the entire surface of the FPC material (cushioning). 2. No decomposition or gas generation at high temperatures in the manufacturing process (heat resistance). 3. To follow the complicated circuit pattern of FPC well (trackability). Furthermore, the demand for repeated use is increasing in order to increase production efficiency in order to cope with the increase in production volume and cost reduction. Withstand repeated use under high temperature and high pressure (durability). In particular, due to the nature of the cushion material, it is essential that the thickness change is as small as possible. When CCL and cushion seat are in contact, 5. Good peeling from CCL (releasability) is required. In particular, due to the nature of the cushion material, it is essential that the thickness change is as small as possible.

Kraft paper has been widely used from the viewpoint of performance and price for printed circuit board manufacture, particularly for FPC manufacture. However, it was insufficient for repeated use. Silicone rubber and fluororubber have been developed as heat-resistant cushioning materials for repeated use.

  However, although silicone rubber is excellent in cushioning properties and heat resistance, it has insufficient strength, and therefore has a drawback of causing cracks and cracks during hot pressing. Even if it is reinforced with fibers or the like to improve this point, separation between fibers and rubber occurs during pressing, which may cause a difference in cushion thickness for each part, and further cause poor adhesion of FPC. The separation between the fiber and the rubber also causes the cushion material itself to break when the press is repeated. For this reason, the silicone rubber cushion material is also discarded after several uses. Further, the silicone rubber has a problem that siloxane and the like contained in the rubber are generated and contaminates the FPC and the like. This contamination may cause, for example, poor conductivity due to deposition of siloxane, deterioration of printing characteristics on the FPC, and deterioration of adhesion between the FPC and other members such as a reinforcing plate. These tendencies are accelerated as the repeated use time of the cushioning material becomes longer. In the case of FPC, such contamination was a serious defect.

A cushion material using fluororubber has high heat resistance. However, the unevenness of the FPC material remained strongly in the fluororubber after heating and pressurization and could not withstand repeated use. In order to improve such a cushioning material, a fluoro rubber having a loss tangent of dynamic viscoelasticity of 0.04 or less in polyol vulcanization has been developed as a rubber excellent in resilience and durability (Japanese Patent No. 3461291). ). However, the rubber hardness may increase and the circuit pattern of the printed circuit board may not be easily followed. In addition, when the rubber is used alone, repeated use from compression set may accumulate thickness distortion and cause cracking. In order to improve the durability of repeated use at high temperature and high pressure, and to make the rubber layer have an air part and improve the cushioning property, the bulk of the woven fabric or non-woven fabric is impregnated with a fluororubber solution and dried inside the cushion material A rubber composite material in which a gap is provided has been developed (Japanese Patent No. 4746523). However, fluororubber is expensive, and the process of preparing and impregnating the rubber solution causes environmental pollution with organic solvents, which complicates the process and increases the manufacturing cost of FPC when used as a cushioning material for hot press. was there. In addition, there is a problem of flattening due to heat fusion.

It is widely known that a rubber layer generally has an air portion to improve cushioning properties. In many cases, rubber is foamed to give a good cushioning property to the gas layer (air part). It is often applied to cushion materials near room temperature. For example, urethane foam rubber is used favorably. In the FPC manufacturing process, a process temperature of 150 to 170 ° C. is employed, and recently, the process temperature is further increased, and heat resistance at 200 ° C. may be required. A cushioning material produced by a normal foaming method cannot be used because the rubbers are fused at such a high temperature. Therefore, a heat resistant rubber containing an independent foam that can withstand high temperatures is required. The primary vulcanization temperature of fluororubber is 160 to 180 ° C. for both polyol vulcanization and peroxide vulcanization, and when the maximum foaming temperature is lower than that, the foamed state disappears due to the pressure by hot pressing. In the case of polyol vulcanization, the vulcanization reaction proceeds even at a temperature lower than that, and the rubber vulcanized before foaming has no foaming effect by the foaming agent. In order to meet the FPC manufacturing temperature of 150 to 200 ° C., foaming using a foaming agent that starts expansion at 200 ° C. or higher will cause the foams that are independently foam to shrink if an attempt is made to vulcanize the rubber at a temperature higher than 200 ° C. Disappear.

  The inventor has a foaming agent having an expansion start temperature of 200 ° C. or more and kneaded with a fluoro rubber together with a polyfunctional vulcanizing agent to produce a foamed rubber, which is then irradiated with radiation, particularly with an electron beam. It was found that a fluororubber cushioning material that is excellent in heat resistance by being vulcanized and sufficiently withstand repeated use is useful as a cushioning material for a printed circuit board, particularly for FPC.

Patent No. 3461291 Patent No. 4440963

An object of the present invention is to provide a foam rubber for a hot press cushioning material excellent in heat resistance and repeated use, and a hot press cushioning material using the same, in view of the above-mentioned present situation in a printed circuit board, particularly in a hot press of an FPC manufacturing process. It is to provide at a lower cost.

The invention according to claim 1 includes 2 to 10% by weight of the fluororubber component and the vulcanizing agent having a polyfunctional group that are at least 80% by weight of the total, and further has an expansion start temperature of 200 ° C. or higher and 240 ° C. A fluororubber composition containing 2 to 12% by weight of a foaming agent for forming closed cells at a temperature of less than or equal to 0.degree. C. is foamed at a foaming start temperature or higher, and then irradiated with radiation to cause crosslinking.

  The invention according to claim 2 is characterized in that the fluororubber according to claim 1 is a rubber capable of peroxide vulcanization.

The invention of claim 3 is characterized in that the radiation of claim 1 is an electron beam and the dose is 50 to 200 kGy.

According to a fourth aspect of the present invention, there is provided a hot press cushioning material comprising the rubber for a hot press cushioning material according to the first, second or third aspect.

  The invention of claim 5 is laminated and integrated using one or more layers made of rubber and one or more layers selected from woven fabric, nonwoven fabric, paper, film, foil, sheet and plate. A heat press cushioning material according to claim 4.

In the invention of claim 6, the woven fabric, non-woven fabric, paper, film, foil, sheet and plate are single or composite materials selected from synthetic resin, natural rubber, synthetic rubber, metal, glass and ceramics. A hot press cushioning material according to claim 5.

Invention of Claim 7 is a manufacturing method of the printed circuit board which heats and press-molds in the state which laminated | stacked printed circuit board material and the cushion material between the heat | fever boards, Comprising: The hot press of Claim 1, 2 or 3 It is characterized by comprising rubber for cushion material.

The invention of claim 8 is the method of manufacturing a printed circuit board according to claim 7, wherein the printed circuit board is a flexible printed circuit board.

According to the first aspect of the present invention, the gas part (air layer) of closed cells gives high cushioning properties, and the closed cells can endure repeated use without causing thermal fusion even under high pressure. Further, the amount of expensive fluororubber per thickness can be reduced, and a cushion rubber for hot press excellent in cushioning properties and durability against repeated use can be produced at low cost. If the amount of the polyfunctional vulcanizing agent is less than 2%, a sufficient crosslinking density cannot be obtained, and if it exceeds 10%, the rubber becomes brittle. When the expansion start temperature is less than 200 ° C., the foaming agent contracts by heating in the FPC manufacturing process. Further, if it exceeds 240 ° C., it exceeds the heat resistance temperature of fluororubber, which is not practical. The amount of foaming agent is required to be 2% or more, and if it exceeds 12%, cushioning properties and restoration properties as rubber become difficult.

According to invention of Claim 2, sufficient intensity | strength can be obtained by bridge | crosslinking by using a rubber raw material of a peroxide vulcanization system for fluororubber.

According to the third aspect of the present invention, a sufficiently high strength rubber material can be obtained without damaging the foamed closed cells by irradiating with an electron beam in the presence of a vulcanizing agent and crosslinking. However, if the electron dose is less than 50 kGy, sufficient crosslinking cannot be obtained, and if it is more than 200 kGy, it becomes brittle even if pressurized, and is preferably 50 kGy or more and 200 kGy or less.

According to invention of Claim 4, the cushion material for hot press provided with the said foaming vulcanized rubber can be manufactured. This improves handling during production and reduces dirt and breakage.

  According to invention of Claim 5, according to a manufacturing process, the layer which consists of the said rubber | gum 1 layer or more, and 1 or more types chosen from woven fabric, a nonwoven fabric, paper, a film, foil, a sheet | seat, and a board are included. By using one or more layers and integrating them, a heat press cushioning material having good heat resistance and durability for repeated use can be obtained.

  According to the invention described in claim 6, among materials of woven fabric, non-woven fabric, paper, film, foil, sheet, and plate of a material suitable for the manufacturing process, among synthetic resin, natural rubber, synthetic rubber, metal, glass and ceramics A single material or a composite material selected from the above can be laminated with the rubber.

According to a seventh aspect of the present invention, in the method for manufacturing a printed circuit board, in which the printed circuit board material and the cushioning material are stacked between the hot plates, the printed circuit board is heated and pressure-molded. The heat press cushion material provided with the rubber for the heat press cushion material can be stably and repeatedly used at low cost.

  According to invention of Claim 8, the rubber for cushion materials of the hot press of Claim 1, 2, or 3 was provided in the hot press process of the flexible printed circuit board in which the printed circuit board of Claim 7 is a flexible printed circuit board. The cushioning material for hot press can be used stably and repeatedly at low cost.

In the present invention, a commercially available rubber can be used as the fluororubber. For example, as a polyol vulcanization system, DuPont Viton A500, Daikin Daiel G501, 3M Florel FC2145 and the like can be mentioned. Examples of peroxide vulcanization systems include DuPont Viton GBL200S, Daikin Daiel G902, Asahi Glass Afras 150E, and the like. As the polyfunctional vulcanizing agent, for example, commercially available triallyl isocyanurate (TAIC) is generally used. A commercially available foaming agent having an expansion start temperature of 200 ° C. or higher can be used. An example is Matsumoto Yushi Microsphere 2800D. Various devices exist for electron beam irradiation, and the strength (eV) and dose (Gy) can be selected according to the depth of penetration into the rubber layer and the vulcanization strength.

Examples of the present invention will be described below. In the examples of the present invention, the limited rubber, vulcanizing agent, and foaming agent were used and the electron beam irradiation apparatus was used. However, it is obvious that the embodiment of the present invention is not limited to the contents described. Examples 1, 2, 3, 4 and Comparative Example 1 will be specifically described below.

(Electron beam irradiation)
The foamed rubber and foamed rubber composite of the example were irradiated with electron beams from above and below the cushion material surface by an electron beam irradiation apparatus EPS-800 manufactured by NHV Corporation.

DuPont Viton GBL200S, 100 parts, Nippon Kasei's triallyl sinurate (hereinafter referred to as TAIC), 4 parts, Matsumoto Yushi microsphere 2800D (hereinafter referred to as 2800D), 5 parts are kneaded and 120 ° C. A sheet of 150 mm square and 1 mm thickness was prepared at 10 MPa. Asahi Glass Aflex 12NA was spread as a release film on a 150 mm square and 4 mm deep mold, and the sheet was installed. Heating and pressing were performed at 235 ° C. and 30 MPa for 30 minutes. After cooling, it was taken out and irradiated with 50 kGy of electron beams from above and below. The thickness after irradiation was 4.11 mm. The repeated hot press evaluation results are shown in Table 1.

DuPont Viton GBL200S, 100 parts, TAIC, 4 parts, 2800D, 5 parts were kneaded to prepare a sheet of 150 mm square and 1 mm thickness at 120 ° C. and 10 MPa. Asahi Glass's Aflex 12NA is laid as a release film on a 150 mm square, 4 mm deep mold, and the rubber sheet is sandwiched between bamboo cloth 9050-01 as shown in FIG. 1 and heated at 235 ° C. and 30 MPa for 30 minutes. Pressed. After cooling, it was taken out and irradiated with 50 kGy of electron beams from above and below. The thickness after irradiation was 4.31 mm. The repeated hot press evaluation results are shown in Table 1.

Asahi Glass Aphras 150E, 100 parts, TAIC, 4 parts, 2800D, 5 parts and 1 part of sodium stearylate were kneaded to prepare a sheet of 150 mm square and 1 mm thickness at 120 ° C. and 10 MPa. Asahi Glass's Aflex 12NA was laid as a release film on a 150 mm square and 4 mm deep mold, and the rubber sheet was sandwiched with bamboo cloth 9050-01 as shown in FIG. 1 and placed in the mold. Heating and pressing were performed at 230 ° C. and 30 MPa for 30 minutes. After cooling, it was taken out and irradiated with 756 kGy of electron beams from above and below. The thickness after irradiation was 3.03 mm. The repeated hot press evaluation results are shown in Table 1.

DuPont Viton GBL200S, 100 parts, TAIC, 4 parts, 2800D, 5 parts were kneaded to prepare two sheets of 150 mm square and 1 mm thickness at 120 ° C. and 10 MPa. Asahi Glass's Aflex 12NA is laid as a release film on a 150 mm square and 8 mm deep mold, and the rubber sheet is sandwiched with bamboo cloth 9050-01 as shown in FIG. 2, and Nittobo glass cloth plain weave 1080 on the interlining. Was installed and heated and pressurized at 230 ° C. and 30 MPa for 30 minutes. After cooling, it was taken out and irradiated with electron beams of 100 kGy each up and down. The thickness after irradiation was 8.44 mm. The repeated hot press evaluation results are shown in Table 1.

(Comparative Example 1)
Ten craft papers of 500 g of commercially available Oji Paper white cardboard were stacked. The thickness was 6.03 mm. The results of repeated hot press evaluation are shown in Table 2.

(Cushion material repeated use evaluation test)
Samples prepared according to the examples were pretreated and pressurized at 180 ° C. and 2.5 MPa × 10 minutes. The sample after pre-treatment pressurization was set to 0 as a test sample, and subsequent repeated use tests were started. The test sample was pressurized at 180 ° C. and 2.5 MPa × 10 minutes, the thickness of the sample that had passed 5 minutes after opening was measured at 5 points, and the average value was taken as the thickness after pressurization.

(Resistance test of cushion material)
A stainless steel plate was placed up and down on the surface of the large press, and the sample was compressed at 5 MPa and room temperature for 10 minutes, and the thickness was measured with pressure applied. The thickness at the time of pressurization / thickness before pressurization × 100% was defined as the compression ratio. Thereafter, the pressure was released and the thickness was measured as the thickness after the pressure was released after 30 minutes. The thickness after pressurization release / thickness before pressurization × 100% was taken as the restoration rate. The results are shown in Tables 1 and 2.

The rubber for hot press cushioning material and the hot press cushioning material according to the present invention follow a complicated shape well due to high cushioning properties, and can be used in a manufacturing process requiring high temperature and high pressure due to excellent recoverability and heat resistance. It is used effectively when a longer life of the cushion material is required.

Represents a cushioning material with foam rubber sandwiched between cotton. A cushioning material in which a glass woven cloth is inserted into the interlining and the upper and lower sides are sandwiched between cotton cloths.

Claims (8)

Closed-cells containing at least 80% by weight of the fluororubber component and a vulcanizing agent having a polyfunctional group in an amount of 2 to 10% by weight with respect to the fluororubber component, and having an expansion start temperature of 200 ° C. or higher and 240 ° C. or lower. A rubber for a cushioning material for hot press, characterized by foaming a fluororubber composition containing 2 to 12% by weight of a foaming agent for forming at a foaming start temperature or higher and then irradiating with radiation to cause crosslinking. . A rubber for hot press cushioning material, wherein the fluororubber according to claim 1 is a peroxide vulcanizable rubber. The rubber for hot press cushioning material, wherein the radiation according to claim 1 is an electron beam and the dose is 50 to 200 kGy. A hot press cushioning material comprising the rubber for a hot press cushioning material according to claim 1, 2 or 3. 5. The layer according to claim 4, wherein one or more layers made of rubber are laminated and integrated using one or more layers selected from woven fabric, nonwoven fabric, paper, film, foil, sheet and plate. Cushion material for heat press. The woven fabric, non-woven fabric, paper, film, foil, sheet and board are single materials or composite materials selected from synthetic resin, natural rubber, synthetic rubber, metal, glass and ceramics. Cushion material for heat press. A method for manufacturing a printed circuit board, in which a printed circuit board material and a cushioning material are heated and pressure-molded in a state where the cushioning material is laminated between the heating plates, comprising the rubber for a cushioning material for a hot press according to claim 1. A method for producing a printed circuit board, comprising: The printed circuit board manufacturing method according to claim 7, wherein the printed circuit board is a flexible printed circuit board.