JPH0440185B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an antistatic synthetic resin film, sheet, or plate (these are simply base materials) used as an auxiliary base material for manufacturing electronic parts (wafers), and as a housing or packaging member for various types of light electrical equipment, household electrical equipment, audio equipment, etc. There are cases where the difference is made by the thickness of the material, and there is also a distinction based on the laminate structure, but in the following, it is simply referred to as a sheet). It is the first synthetic sheet that can be used for this kind of purpose.
Appropriate antistatic properties (conductivity) are required to prevent the adhesion of dust in the air due to electrostatic charging, and there are two types of antistatic properties (conductivity) that have been used so far: a kneading type and a surface coating type. There is. The former is a sheet in which conductive powder is kneaded into the interior of the sheet, but this requires a relatively large amount of conductive powder to prevent static electricity, which inevitably causes coloration and requires transparency. Not only can it not be used for any other purpose, but it also increases costs. The latter involves applying a paint containing conductive powder to the sheet surface and drying it.
The conductive powder remaining on the coating surface easily peels off due to friction, increasing the surface resistance and deteriorating the antistatic ability, and if the fallen conductive powder adheres to the wafer, it will seriously affect the original electronic properties of the wafer. induces a fatal flaw that gives In addition, color development and skin defects due to conductive powder are unavoidable, and even if ultra-differential powder is used, after the coating film dries, light is emitted randomly on the sheet surface due to color development and skin defects, resulting in only a semi-transparent surface.
In order to improve this, if the coating film is made thin (1 to 10μ), the surface smoothness of the coating film is poor, the above-mentioned fine particles tend to fall off, and the surface resistance tends to increase even when simply wiped with cloth or other materials. This leads to a dilemma. The present invention has been made for the above-mentioned improvement, and in obtaining an antistatic synthetic resin sheet of a coating film-forming type using a conductive paint, the coating film itself is a thin film (1 to 1).
10μ), the surface is highly smooth, conductive fine powder does not fall off even under friction, and the electrical resistance value of the surface can thereby be stably maintained. It is. This objective is achieved by hot-pressing the thin coating film in the thickness direction after drying. By this hot press, the conductive fine powder that is protrudingly present on the surface of the paint film is pressed into the synthetic resin of the paint film in a softened state, and the surface is smoothed. is prevented from coming off due to friction. At the same time, since the coating method is gravure printing, the above-mentioned hot press imparts ductility to each coating film particle to fill in the micro gaps between the microscopic coating film particles, and the coating film after pressing is essentially coated with a gear press. It also helps to provide solidity and reduce surface resistance. In addition, when a conductive SnO ₂ fine powder of 0.1 μm or less is used as the conductive fine powder, hot pressing is useful for imparting clear transparency within the above thickness range. In the case of this example, therefore, stability of surface resistance not found in conventional products is guaranteed, and transparency, which could not be achieved in the past, is achieved. This makes it suitable as an antistatic lid. It is noteworthy that a thin coating film can contribute to reducing production costs both in terms of material costs and drying cycles. Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Fig. 1 is an enlarged longitudinal cross-sectional view of essential parts showing an example of an antistatic synthetic resin sheet obtained by the present invention. , FIG. 2 is an enlarged schematic cross-sectional view of the surface area of the coating film shown in FIG. 1 taken before hot pressing, FIG. 3 is a view similar to FIG. 2 after hot pressing, and FIG. FIGS. 5a to 5c are enlarged longitudinal sectional views of main parts showing an example, and are explanatory diagrams of a hot press. The present invention involves the process of preparing a conductive synthetic resin paint containing conductive SnO ₂ fine powder, and applying the resulting paint to the surface of a synthetic resin base material of a desired thickness (regardless of whether it is on one side or both sides) by gravure printing. ) and drying it in a thin layer, and hot pressing the obtained dry coating film in the thickness direction. The following will be explained in further detail. (a) Paint preparation process: The paint consists of a synthetic resin as a binder (mainly polyvinyl chloride, polyester), the above-mentioned conductive fine powder, a solvent (ketone aromatic, etc.), and a small amount of a dispersant (anionic). (surfactant). The characteristic of this paint is that when it is applied in a thin layer of about 1 to 10 microns, the fine powder does not settle to the bottom of the paint film due to its specific gravity, but remains on the surface. requires an appropriate blending relationship between the synthetic resin, fine powder, and solvent. For example, the amount of conductive SnO ₂ fine powder is up to 15% (by weight, the same applies hereafter), the corresponding proportion is 3 to 10% for polyvinyl chloride, and 5 to 15% for polyester. . If the amount of fine powder exceeds this amount, the antistatic performance will not change and the cost will only increase, and if the amount of synthetic resin exceeds this amount, the antistatic performance will be impaired. The dispersant may be used in a trace amount of 0.2 to 0.6%. The conductive fine powder is the above-mentioned SnO ₂ fine powder, and in this case, it becomes a transparent coating film by hot pressing. The reason for this is that conductive SnO ₂ is available on the market in the order of 0.1 μm or less, which is much finer than other conductive fine powders. As an example, this conductive SnO ₂ is available with some of the Sn replaced by a small amount of Sb. (b) Application and drying of paint: The base material to which the paint in (a) is applied is a synthetic resin sheet of the desired thickness (depending on the thickness, it may be called a film, sheet, or plate). ) is used, but
Specifically, polyvinyl chloride, polycarbonate, polyester, acrylic, ABS resin and
Examples include AS resin. In an advanced embodiment of the present invention, after the coating material is coated and dried on a film-like sheet, this sheet, another adhesive base sheet, and the film-like sheet having the dried coating film are laminated together. The two are thermally fused together by hot pressing, and the hot pressing effect is also exerted on the dried coating film. The coating film can be applied to either one side or both sides of the sheet, and the coating method is limited to gravure printing. The thickness of the coating film is a thin layer of 1 to 10 μm, and although thicker thicknesses are not excluded, as mentioned above, this thin layer range is desired from the viewpoint of material cost and heat cost. Drying can be done either naturally or by heating. (c) Hot pressing of the paint film: To hot press the dried paint film in (b), any of a direct pressure press, an endless roll belt, or a pair of upper and lower pinch rolls can be adopted. Figure 5a shows the direct pressure type, and the press plates P ₁ and P ₂ are mirror-finished stainless steel plates with a chrome finish, mirror-finished brass plates with the same finish, etc. In the endless roll belt shown in (b), the endless belts B and B are driven in the direction of the arrow by the rolls R..., and the sheet 1 with the dry coating films 11 and 12 on both sides is carried between the belts B and B, and the sheet 1 is brought under pressure. and temperature, and then transported out. It is heated and pressurized by passing between the pair of upper and lower pinch roll groups R ₁ -R ₁ , R ₂ -R ₂ , and R ₃ -R ₃ shown in (c). Note that in FIG. 5, the heat source is omitted for convenience. The heating range of the hot press is just before the softening point of the synthetic resin in the dry coating, for example 160 to 180 for polyvinyl chloride.
℃. As already mentioned in the developed embodiment, when one base material having a dry coating film and another base material are heat-sealed together by hot pressing, the above heating range covers the heat-sealing between the base materials. It is also necessary to consider this as a possible temperature range. The pressure range is such that the surface area of the coating film that has been softened by heating is rolled and smoothed, and the fine powder is press-fitted into the coating film, for example, from 4 to 60 kg/cm ² . Next, a product embodying the present invention will be explained with reference to the drawings. Figure 1 shows a case where coating films 11 and 12 are formed on both sides of a base material 1, dried, and then hot-pressed. It may be used as an antistatic member, or it may be heat-sealed with another base material to supplement the necessary strength. Figure 4 shows a dry coating film 111 on one side only.
A pair of upper and lower base materials 1, 1, each having 111, is sandwiched from both sides of another synthetic resin base material 10, and the two are fused together using a hot press to form a thick material having antistatic coatings 11, 11 on both sides. This is an example of obtaining a sheet. The change in the properties of the surface area of the dried paint film due to hot pressing will be explained with reference to Figures 2 and 3. Figure 2 shows the dried paint film 111.
A large number of conductive fine powders 110 are present on the surface, and the outermost fine powders 110 protrude and form an uneven surface, but when hot pressed as shown in Fig. 3, the surface becomes soft. As a result, the fine powder 110... is pressed into the inside of the coating film, resulting in a smooth surface, and the fine powder 110...
(However, the fine powder 1 on the outermost part
(The outermost surface of 10... is substantially aligned with the smoothed surface) Even if the surface is rubbed with a cloth or other material, fine powder 11
0... is prevented from falling off, and the electrical resistance of the surface can be stably maintained over a long period of time, as is clear from the test results described later. The dried coating film 11 made of conductive SnO ₂ fine powder of 0.1μ or less is almost translucent at a thickness of 1 to 10μ, but this is because the surface does not have minute irregularities as shown in Figure 2. This is because there is diffuse reflection, and when this is hot-pressed to give the surface texture shown in Figure 3, a sheet with high transparency can be obtained, which could not be achieved with conventional technology, and especially Widely applicable to fields where transparency is required. The electrical resistance of the surface portion of the coating film of the present invention is noticeably reduced by hot pressing. This is because in gravure printing, from a microscopic perspective, the transfer paint has micro-gaps between countless paint film particles, so when it is hot-pressed, it fills in these micro-gaps and essentially forms the solid material of the gear press. It is thought that this is to do so.
Examples will be described below. (Example) (a) Preparation of conductive paint: Conductive paint with a particle size of 0.1μ or less
A paint was prepared from 15% SnO ₂ fine powder (weight: same below), 8% polyester resin, 0.6% dispersant, and 76.4% solvent. (b) Paint application and drying: Paint (a) was applied to a thickness of approximately 10 μm by gravure printing on a 0.3 mm thick transparent polyvinyl chloride sheet, and then dried at approximately 60° C. for several minutes. (c) Hot pressing of paint film: The dried paint film of (b) is heated from room temperature to 160℃ using a direct pressure press machine, and heated to 50Kg/cm ²
After pressing for several minutes under these conditions, it was cooled to room temperature and released under pressure. (Test results) We compared the changes in surface resistance between the test piece of the example and a comparative example piece without hot pressing under the same conditions, and also conducted a friction test on the coating films of the example and comparative example. The results are shown in Table 1. This friction test was conducted in the following manner. That is, a nylon cloth to which a load of 500 g was applied was moved back and forth in simple harmonic motion on the surface of each coating film, and the electrical resistance of each surface was actually measured.

[Table] From Table 1, it is clear that, compared to the comparative example, the samples according to the examples of the present invention do not change the surface resistance due to friction and can stably maintain the original resistance value. In addition, the electrical resistance value is 10 ³ due to hot pressing.
It can be seen that the value has decreased by ~ ¹⁰² . As already understood from the above description, according to the present invention, hot pressing is applied to a dry antistatic coating film to smooth the surface area and prevent conductive fine powder from falling off due to abrasion. Because the surface resistance can be maintained stably, the structure is the same, but it contributes to increased suitability for antistatic properties, and the coating film is formed as a thin layer containing solution-type synthetic resin, reducing material costs. This method has the effect of eliminating the problems of known techniques, such as promising cost reductions in terms of drying cycles. Furthermore, the reduction of surface resistance by gravure printing and the formation of a transparent sheet as an effect of the embodiment should be evaluated as excellent characteristics of the present invention along with the above-mentioned effects of the present invention.

[Brief explanation of drawings]

Figure 1 is an enlarged vertical cross-sectional view of the main part showing an example of an antistatic synthetic resin sheet obtained by the present invention, and Figure 2 is an enlarged view of the properties of the coating surface area of the sheet in Figure 1 taken before hot pressing. A schematic sectional view, FIG. 3 is a view similar to FIG. 2 after the same hot press, FIG. 4 is an enlarged longitudinal sectional view of the main part showing another example of the present invention, and FIGS. 5 a to 5 c are clear views of the hot press. . Explanation of symbols, 1, 10...Synthetic resin base material, 11,
12... Hot pressed coating film, 111... Dry coating film before hot pressing, 110... Conductive fine powder, P ₁ ,
_P2 ...Press plate, B...Roll conveyor, R, _R1 ,
R ₂ , R ₃ ... roll.

Claims (1)

[Claims] 1 A thin layer of conductive paint in which conductive SnO ₂ fine powder is dispersed in a synthetic resin is applied onto a synthetic resin base sheet such as polyvinyl chloride or ABS using gravure printing, and then dried. The fine powder is left on the surface of the paint film, and then this dried paint film is hot pressed in the thickness direction to force the fine powder on the surface into the inside of the paint film, and the paint film on the surface is softened and rolled to smooth it. A method for manufacturing an antistatic synthetic resin sheet characterized by