JPH0236942A - Manufacture of antistatic synthetic resin sheet - Google Patents

Abstract

PURPOSE:To keep surface resistance stably by preventing falling off owing to a scratch of conductive impalpable powder by smoothing a surface part by a method wherein an antistatic dry paint film is treated with a hotpress. CONSTITUTION:Coating is prepared by a synthetic resin content (principally, polyvinyl chloride, polyester) as a binder, conductive impalpable powder, solvent (ketone, aromatic kinds etc.), and a minute amount of dispersing agent (anionic surface active agent). For a paint film, irrespective of either on one side or both sides of the sheet, a coating technique is limited to gravure printing and a thickness of the paint film is 1 to 10mum. In order to hot-press a dry paint film a sheet 1of which both sides, for instance, dry paint films 11, 12 are applied, is carried out between belts B and is discharged by receiving pressure and temperature. A heating range is a little lower than the softening point of synthetic resin in the dry paint film, for instance, 160 to 180 deg.C for polyvinyl chloride. An applied pressure range shall be in a range in which the impalpable powder is forced to fit inside the paint film by smoothing a surface part of the paint film by rolling, for instance, 4 to 60kg/cm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an antistatic synthetic resin film or sheet used as an auxiliary substrate for the production of electronic parts (wafers), a housing or packaging member for various types of light electrical equipment, household electrical equipment, audio equipment, etc. Alternatively, the present invention relates to an improvement in the manufacturing method of plates (these are distinguished simply by the thickness of the base material and others are distinguished by the laminate structure, but hereinafter referred to simply as sheets).

Firstly, synthetic sheets used for this type of application must have appropriate antistatic properties (conductivity) to prevent the adhesion of dust in the air due to electrostatic charging. There are two types: a mixed wire type and a surface coating type.

The former is a sheet in which conductive powder is kneaded into the inside of the sheet, but this requires a relatively large amount of conductive powder to prevent static electricity, and coloration due to this is unavoidable, making it suitable for applications that require transparency. Not only will it not be possible to provide it, but it will also increase costs. The latter involves applying and drying a paint containing conductive powder on the surface of the sheet, but the conductive powder remaining on the surface of the paint film easily peels off due to friction, increasing surface resistance and reducing antistatic ability. When the conductive powder that falls off adheres to the wafer, it induces a fatal defect that seriously affects the original electronic properties of the wafer. 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 will be emitted randomly and the surface will become semi-transparent due to sudden color development and skin defects. It just has to happen. In order to improve this problem, if the coating film is made thin (1 to 10 μ'), the smoothness of the coating film surface will be poor, and the above-mentioned fine powder will fall off frequently, and the surface resistance will increase even when simply wiped with cloth or other materials. This puts us in the dilemma of making it easier for them to increase.

The present invention has been made for the purpose of two improvements.In obtaining an antistatic synthetic resin sheet of the type that forms a coating film using conductive paint, it is possible to obtain The purpose of the present invention is to provide a method for producing a cylindrical material that has a highly smooth surface and does not cause conductive fine powder to fall off even when rubbed, thereby stably maintaining the electrical resistance value of the surface. The purpose of this is to dry the thin coating film,
This is achieved by hot pressing in the thickness direction.

Through this press, the conductive fine particles that are protrudingly present on the surface of the paint film are press-fitted into the softened synthetic resin of the paint film, and the surface is smoothed, even when friction is applied to the surface. Fine powder is prevented from being flaked off by friction. At the same time, since the coating method is gravure printing, the hot press described above imparts ductility to each coating film particle to fill the micro gaps between the microparticles, and the coating film after pressing is substantially coated. It also helps reduce surface resistance by providing a gapless solid quality to the surface. In addition, when conductive Sn○2 fine powder in the range of O01μ 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 realized. It is suitable as an electrically conductive lid. It is noteworthy that a thin coating film can contribute to a reduction in production cost I. both from the viewpoint of interest cost I. and drying cycle.

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Figure 2 is an enlarged schematic sectional view of the surface area of the coating film taken before hot pressing, Figure 3 is a view similar to Figure 2 after hot pressing, and Figure 4 is the same as in Figure 4. FIGS. 5(a) to 5(c), which are enlarged vertical cross-sectional views of main parts showing another example of the invention, are explanatory diagrams of a hot press.

The present invention involves the process of preparing a conductive synthetic resin paint containing conductive SnO2 fine powder, and applying the resulting paint to a desired thickness on the surface (regardless of one or both sides) of a synthetic resin base material by gravure printing. The method includes a step of coating and drying a thin layer, and a step of 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 component (mainly polyvinyl chloride, polyester) as a binder, conductive fine powder as described in "2," a solvent (ketone aromatic system, etc.),
Prepared with a small amount of dispersant (anionic surfactant). One of the characteristics of this paint is that when it is applied in a thin layer of about 1 to 10 microns, the fine powder must remain on the surface without settling to the bottom of the film due to its specific gravity. requires an appropriate blending relationship between the synthetic resin, fine powder, and solvent. -For example, the amount of conductive SnO2 fine powder is 15% (by weight...
The same applies hereafter), correspondingly, polyvinyl chloride is 3~]7
In the case of polyester, the proportion is 5 to 15%.

Even if the amount of fine powder exceeds this amount, the antistatic performance will not change and the varnish will only become a hair lump, and if the synthetic resin exceeds this amount, the antistatic performance will be affected.

The dispersant may be used in a trace amount of 0.2 to 0.6%. The conductive fine powder is the above-mentioned SnO2 fine powder, and in this case, it becomes a transparent coating film by hot pressing. The reason for this is that conductive SnO2 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 SnO2 is available with part of the Sn replaced by sb.

(b) Application and drying of paint: The base material to which the paint in (a) is applied is a synthetic resin sheet of desired thickness (depending on the thickness, it should be named film, sheet IN, or plate). are used, specifically polyvinyl chloride, polycarbonate, polyester, acrylic,
Examples include ABS resin and A, S resin. In an advanced embodiment of the present invention, after the above-mentioned paint is applied and dried on a film-like sheet, this sheet, another base sheet with good adhesiveness, and the film-like sheet having the above-mentioned dried coating are laminated. 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 may be applied to one or both sides of the sheet 1, 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 interest costs and heat costs. Drying can be done either naturally or by heating.

(c) Hot pressing of paint film: To press the dried paint film in (b), any of a direct pressure press, an en-1less roll bell, and a pair of upper and lower pinch rolls can be adopted. Figure 5(a) shows the direct pressure type press plate P.
□ For p2, a stainless steel mirror plate with a chrome finish, a brass mirror plate with the same gender, etc. are used. The endless roll belt in (b) is an endless belt B.

The belt B is driven in the direction of the arrow by the roll R, and the sheet 1-1 with the dry coating film IL, 12 on both sides is driven by the belt B,
It is carried in between I3, subjected to pressure and temperature, and then carried out. (
C)'-lower pair of vintilol groups R1-R□, Rp
, ``R2, R'3 It penetrates between R3 and receives heat and pressure.The heat source is omitted in Figure 5 for convenience.The heating range of the hot press is the softening of the synthetic resin in the dry coating film. Just before the point, for example, 1-60 for polyvinyl chloride
180'C. As already mentioned in the developed embodiment, when one base material having a dry coating film and another base material are heat-sealed by hot pressing, the above heating range is within the range of heat-sealing during the basic period. Possible temperature ranges must also be considered. The pressure range is such that the surface area of the coating film that has been softened by heating is rolled and smoothed and fine powder is injected into the coating film, for example, 4 to 60 kg/c111.

Next, a product embodying the present invention will be explained with reference to the drawings.

Figure 1 shows a case in which a coating film 11.12 is formed on both sides of a base material 1 and then dried and then pressed. It may be used as it is as an antistatic member, or it may be heat-sealed with another base material to supplement the necessary strength. FIG. 4 shows a pair of upper and lower base materials each having a dry coating film on one side only], ], ], 111], 1 is sandwiched from both sides of another synthetic resin base material 10, and the like is hot-pressed. This is an example in which a thick sheet having antistatic coatings on both sides was obtained by fusion bonding and integrally applying the antistatic coating. The changes in the properties of the surface area of the dried paint film due to the Hola l-press will be explained with reference to Figures 2 and 3. Figure 2 shows the dried paint film 111, and the surface area has conductive fine powder 110... A large number of fine powders 1]0 are present, and among these, the outermost fine powder 1]0 protrudes and has an uneven surface, but when hot-pressed as shown in Fig. 3, the surface is rolled in a softened state and the fine powder 110... As a result of being press-fitted into the inside of the coating film, the surface becomes smooth and the protrusion of the fine powder 110 on the outermost surface disappears. Even if the surface (substantially aligned with the surface) is rubbed with a cloth or other material, it will still be a fine powder] 1
0 is prevented from falling off, and the electrical resistance of the surface can be maintained stably over a long period of time, as is clear from the test results described later.

The dried coating film 11 made of conductive SnO2 fine powder of 0.1μ or less is semitransparent 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 this is hot pressed and the third
When the surface properties shown in the figure are obtained, a sheet with high transparency can be obtained, which has wide applicability in fields where transparency is particularly required, something that could not be achieved with conventional technology. .

The electrical resistance of the surface portion of the coating film of the present invention is significantly lowered by pressing. This is because in gravure printing, the transfer paint has micro-gaps between countless coating particles, so when it is hot-pressed, it fills in these micro-gaps and creates a virtually gapless solid. It is thought that this is to form quality.

Examples will be described below.

(Example) (a) Preparation of conductive paint 2 Conductive SnO2 fine powder with a particle size of 0.1μ or less 15% (weight, same below), polyester resin 8%, dispersant 0.6%, solvent 76.4 A paint was prepared from %.

(b) Application and drying of paint: Paint (a) was applied to a thickness of 10 μm on a 0.3 m thick transparent polyvinyl chloride sheet by gravure printing, and then dried at about 60° C. for several minutes.

(c) Hot press of paint film: The dry paint film of (b) is heated from room temperature to 160"C with a direct pressure press machine and pressed to 150 kg.
After pressing for several minutes under the conditions of /cr&, the cooling layer was released to room temperature while the pressure was being applied.

(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 conducted a friction test on the coating films of the example and comparative example. The results are shown in Table 1. Note that this friction test was conducted in the following manner. That is, a nylon cloth to which a load of 500 g was applied was made to perform simple harmonic reciprocation on the surface of each coating film, and the electrical resistance of each surface was actually measured.

(Table 1) From (Table 1), it is clear that the samples according to the examples of the present invention can stably maintain the original resistance value without any change in surface resistance due to friction, compared to the comparative examples. It is also seen that the electrical resistance value is reduced by -]l-103 to 102 due to hot pressing.

As already understood from the above description, according to the present invention, hot pressing is applied to the dry antistatic coating 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 because the coating film is formed as a thin layer containing solution-type synthetic resin, the material is It has the effect of eliminating the problems of known techniques, such as promising cost reductions in terms of cost and drying cycle.

Furthermore, the reduction in surface resistance due to 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 the drawing]

Fig. 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 Fig. 2 is an enlarged schematic diagram of the properties of the coating surface area of the sheet shown in Fig. 1 before hot pressing. The cross-sectional view, Figure 3, is similar to Figure 2 after hot pressing, and Figure 4.
The figure is an enlarged vertical sectional view of the main part showing another example of the present invention, and FIG.
a) to (c) are explanatory diagrams of a 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□, P7・
...Press plate, B...Roll conveyor, R,
R,, R2゜R3...Roll. one or more one

Claims (1)

[Claims] 1. Apply a thin layer of conductive paint in which conductive SnO_2 fine powder is dispersed in the synthetic resin of the coating film by gravure printing onto a synthetic resin base sheet such as polyvinyl chloride or ABS, and dry. The fine powder is left on the surface of the coating film, and then the dried coating film is hot-pressed in the thickness direction to press the fine powder on the surface area into the inside of the coating film, and the coating film on the surface area is softened and rolled to smooth it. A method for manufacturing an antistatic synthetic resin sheet, which is characterized by the ability to