JP2004195993A - Antistatic transparent resin plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antistatic transparent resin plate which can demonstrate an outstanding antistatic property with little variation in surface resistivity despite improvement in transparency and see-through property by a pressing. <P>SOLUTION: A pressed, clear antistatic transparent resin plate P having a transparent antistatic layer 2 on a surface of its thermoplastic clear resin substrate 1, wherein the antistatic layer contains 2 to 8 wt. % of a very thin, winding, entangled long carbon fiber and has a thickness of 0.05 to 0.50μm. The resin plate P has a total light transmission of 75% or more, a haze of 5% or lower, a surface resistivity of less than 10<SP>10</SP>Ω, and a variation between the average value X and the standard deviation σ in the surface resistivity at X-3σ and X+3σ of two digits at maximum. The winding long fiber has a diameter of 3.5 to 100 μm and an aspect ratio of 5 or more. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an antistatic transparent resin plate having both good transparency and antistatic properties.

  2. Description of the Related Art Conventionally, a transparent antistatic resin plate that allows static electricity to escape and prevent dust from adhering has been used for applications that can see through like a partition in a clean room or a viewing window of a test device and dislike dust.

  A typical example of such an antistatic resin plate is one in which a thin antistatic layer containing a large amount of a metal oxide powder such as tin oxide is formed on the surface of a transparent resin substrate. The anti-static property is developed by mutual contact.

Recently, a transparent panel has been proposed in which a transparent antistatic layer containing 0.01 to 1% by weight of hollow carbon microfiber and 1 to 40% by weight of metal oxide powder is formed on at least one surface. (JP-A-9-115334).
JP-A-9-115334

  When the surface smoothness of the antistatic layer is increased by a relatively simple press, which is one of various means, the transparent antistatic resin plate or panel described above reduces light scattering and haze. , Transparency and transparency can be improved.

  However, when the pressing is performed, the antistatic layer containing a large amount of the metal oxide powder flows, and particularly, the flow at the end of the antistatic layer is large, the interval between the powder particles is widened, and the metal oxide is spread. The dispersion state of the powder is likely to be non-uniform, so that there has been a problem that the dispersion of the surface resistivity at the central portion and the end portion of the antistatic layer or at each of the end portions increases.

  The present invention has been made in view of the above-described problems, and has as its object the case where the transparency and the see-through property are improved by pressing, and the antistatic property with less variation in the surface resistivity. The object of the present invention is to provide an antistatic transparent resin plate capable of exhibiting the following.

In order to achieve the above object, the invention according to claim 1 has a thickness of 0.05 to 0.about.8 which contains 2 to 8% by weight of ultrafine long carbon fibers which are twisted and entangled on the surface of a transparent substrate made of thermoplastic resin. A pressed antistatic transparent resin plate having a transparent antistatic layer of 50 μm thermoplastic resin, having a total light transmittance of 75% or more, a haze of 5% or less, and a surface resistivity of 10 ¹⁰ Ω. And a difference between X-3σ and X + 3σ between the average value X of the surface resistivity and the standard deviation σ is a maximum of two digits.

  The invention according to claim 2 is the antistatic transparent resin plate according to claim 1, wherein the long carbon fibers are winding fibers having a wire diameter of 3.5 to 100 nm and an aspect ratio of 5 or more, It is characterized by being entangled and dispersed in the antistatic layer.

  In the antistatic transparent resin plate according to the first aspect, the antistatic layer is a very thin layer having a thickness of 0.05 to 0.50 μm, and the content of ultrafine long carbon fibers is as small as 2 to 8% by weight. The total light transmittance is as high as 75% or more, and the haze is as small as 5% or less because the surface smoothness is increased by pressing and light scattering is reduced. Therefore, this antistatic transparent resin plate has good transparency and transparency even though the antistatic layer contains ultrafine long carbon fibers.

The ultra-fine long carbon fibers contained in the antistatic layer are not only dispersed and maintained at a small interval capable of contacting or conducting with each other while winding and entangled, but also the interval between the long carbon fibers in the vertical direction by pressing. (The thickness direction of the antistatic layer), the frequency of contact between the fibers and the minute gaps that can be conducted are increased, so that even if the content of long carbon fibers is as small as 2 to 8% by weight, the antistatic layer Has a low surface resistivity of less than 10 ¹⁰ Ω, and exhibits sufficient antistatic performance.

  Moreover, even if the antistatic layer containing long carbon fibers flows during pressing, the particles spread as widely as the conventional antistatic layer containing metal oxide powder, and the particles are electrically connected to each other. Since there is no tendency to be able to maintain a possible minute interval, and the long carbon fibers are entangled, the dispersion state of the long carbon fibers is less likely to be non-uniform than that of the metal oxide. Therefore, even when the antistatic transparent resin plate is improved in transparency and transparency by pressing, the variation in surface resistivity is within a range of up to two digits, and the variation in surface resistivity is small. In addition, there is no large variation in the surface resistivity not only at the center and the end of the antistatic layer but also at each end.

  In addition, since it is an antistatic layer containing ultra-fine long carbon fibers that are twisted and entangled, it is unlikely that the flow during pressing will increase the surface resistivity and adversely affect the antistatic performance. In this case, a wide selection range of the heating temperature is possible, and therefore, the degree of freedom in selecting the temperature adjustment in the process of forming the antistatic transparent resin plate is increased. Good results can be obtained.

  In the present invention, the ultrafine long carbon fiber is a meandering fiber having a wire diameter of 3.5 to 100 nm and an aspect ratio of 5 or more as described in claim 2, and is entangled to form an aggregate or Aggregates are preferably used. The aggregate or aggregate may be finely divided using an apparatus, and dispersed in the antistatic layer as ultrafine long carbon fibers having the same wire diameter and aspect ratio as in the form of winding and entanglement. The carbon fiber having a wire diameter larger than the above and an aspect ratio smaller than the above is insufficient in the winding and entanglement, so that the surface resistivity may increase and the antistatic property may decrease, and the antistatic layer may be darkened. This may lead to a decrease in transparency. The upper limit of the aspect ratio of the long carbon fiber is not particularly limited, but those having a length of 3000 or less are preferably used.

  FIG. 1 is a sectional view showing one embodiment of the antistatic transparent resin plate of the present invention.

  This antistatic transparent resin plate P is formed by pressing a transparent antistatic layer 2 on the surface of a transparent substrate 1 made of a thermoplastic resin.

  The substrate 1 is made of a transparent thermoplastic resin, for example, an olefin resin such as polyethylene or polypropylene, a vinyl resin such as polyvinyl chloride, polymethyl methacrylate, or polystyrene, polycarbonate, polyethylene terephthalate, polydimethylcyclohexane terephthalate, or an aromatic polyester. A substrate made of an ester-based resin, an ABS resin, a copolymer resin of each of these resins, or the like is preferably used. A substrate having a total light transmittance of 85% or more and a haze of 5% or less is preferably used. The substrate 1 is appropriately blended with a plasticizer, a stabilizer, an ultraviolet absorber, and the like, so that moldability, thermal stability, weather resistance, and the like are improved.

  There is no particular limitation on the formation process and thickness of the substrate 1. That is, it is only necessary to form the substrate 1 of the antistatic transparent resin plate. The forming process is not limited in terms of means or procedure, and the thickness may be set to a thickness that can provide practical strength according to the application. Usually, a substrate having a thickness of about 1 to 10 mm is used.

  The antistatic layer 2 formed on the surface of the substrate 1 is a transparent layer of a thermoplastic resin containing ultra-fine long carbon fibers (not shown) that are twisted and entangled. Alternatively, since the particles are dispersed with a minute interval capable of conducting, they have a function of discharging static electricity and preventing adhesion of dust. The antistatic layer 2 may be formed on one side of the substrate 1 as shown in FIG. 1 or may be formed on both sides.

  As the thermoplastic resin of the antistatic layer 2, a thermoplastic resin of the same kind as the above-described thermoplastic resin of the substrate 1 or a different kind of compatible thermoplastic resin is used. Since the antistatic layer 2 is formed on the surface of the substrate 1, it is desirable to select and use a thermoplastic resin having excellent weather resistance, surface hardness, abrasion resistance and the like.

  The long carbon fibers to be contained in the antistatic layer 2 are ultrafine winding long fibers having a large aspect ratio and a small wire diameter, and are dispersed in the antistatic layer 2 while being entangled with each other. The fiber may be either a porous fiber or a graphite fiber, or a carbon fiber in which amorphous carbon and graphite coexist in a raw fiber.

  A particularly preferred long carbon fiber is a graphite fiber in structure, and is a very thin graphite fiber having a circular cross section in which a graphite layer is laminated and formed coaxially with the fiber axis, and has a wire diameter of 3.5. 100 nm and an aspect ratio of 5 or more. The upper limit of the aspect ratio is not particularly limited, but those having 3000 or less are preferably used. The production method of such a graphite fiber is disclosed in Japanese Patent Publication No. 3-64606, and an iron group metal or an oxide thereof in a mixed gas stream of aromatic or non-aromatic hydrocarbon and hydrogen. This is an ultrafine fiber formed by depositing a coaxial graphite layer on the fiber axis by the contact reaction. This fiber has a structure in which the C axis of the graphite layered crystal is orthogonal to the fiber axis, and preferably has a small amount of amorphous carbon.

  Carbon fibers having a wire diameter larger than 100 nm and an aspect ratio (ratio of length to wire diameter) of less than 5 have insufficient winding and entanglement, and the frequency of contact between the fibers is reduced, so that the surface resistance of the antistatic layer 2 is reduced. The value may increase to cause a decrease in the antistatic property, and the antistatic layer 2 may be darkened to cause a decrease in transparency. On the other hand, when the wire diameter is smaller than 3.5 nm, the long carbon fiber is easily cut, and the antistatic property may be reduced.

The content of long carbon fibers in the antistatic layer 2 needs to be 2 to 8% by weight, and the thickness of the antistatic layer 2 needs to be 0.05 to 0.50 μm. When the content of the long carbon fiber is less than 2% by weight and the thickness of the antistatic layer is less than 0.05 μm, the surface resistivity exceeds 10 ¹⁰ Ω and the antistatic property is reduced, On the other hand, when the content of long carbon fibers is more than 8% by weight and the thickness of the antistatic layer is more than 0.50 μm, there is a possibility that transparency may be reduced. The more preferable content of the long carbon fiber is in the range of 2 to 5% by weight, and the more preferable thickness of the antistatic layer 2 is in the range of 0.1 to 0.5 μm.

  As a means for forming the antistatic layer 2, for example, a coating solution is prepared by uniformly dispersing the long carbon fibers in a solution in which the above-mentioned thermoplastic resin is dissolved in a volatile solvent. Coating means for applying the composition to the surface and curing the composition is preferably employed. In that case, in order to form the antistatic layer 2 having excellent antistatic properties, it is necessary to prepare a coating liquid in which long carbon fibers are dispersed very finely and uniformly, so that a high-speed impeller, sand mill, attritor, It is important to mix and disperse sufficiently with a mixing device such as a three roll.

  The coating liquid can be applied to the surface of the substrate 1 by knife edge coating, roll coating, spray coating, etc. Among them, gravure printing by roll coating is one of the following means for coating a thermoplastic resin film. It is preferably adopted in the case. When the coating liquid is applied by such a gravure printing method, there is an advantage that the coating thickness can be easily adjusted to be constant.

  Further, instead of the above-mentioned coating means, a coating of an antistatic layer containing the long carbon fiber is formed on the surface of a thermoplastic resin film of the same kind as the substrate 1 or a compatible thermoplastic resin film. A method of preparing an electroconductive film and thermocompression-bonding the antistatic film to the surface of the substrate 1 by a hot press or a roll press may be adopted.

  In addition, it does not exclude that the above-mentioned antistatic layer 2 contains a powder of a transparent conductive metal oxide in addition to the long carbon fiber. For example, the powder contains about 30 to 50% by weight of the powder. You may. When the conductive metal oxide powder is contained as described above, there is an advantage that the surface resistivity of the antistatic layer 2 is reduced and the antistatic property is improved. Further, additives such as a dispersant such as a surfactant and a coupling agent, an ultraviolet absorber, a surface modifier, and a stabilizer are appropriately added to the antistatic layer 2 to enhance the dispersibility of long carbon fibers. Alternatively, the weather resistance and other physical properties of the antistatic layer 2 may be improved.

This antistatic transparent resin plate P is obtained by forming an antistatic layer 2 on the surface of the substrate 1 and further pressing the same. By this press, it is possible to further improve transparency, transparency and antistatic properties. It is intended. That is, when pressed under heating using a glossy plate, the surface smoothness is increased and the scattering of light is reduced, so that the transparency and transparency are improved, and the antistatic layer has a thickness of 0.05 to 0.50 μm. The transparency and transparency having a total light transmittance of 75% or more and a haze of 5% or less combined with being a thin layer and having a content of ultrafine long carbon fibers as small as 2 to 8% by weight. A good resin plate P can be obtained. Since the ultrafine long carbon fibers contained in the antistatic layer 2 are compressed in the vertical direction (the thickness direction of the antistatic layer) by pressing, the contact frequency of the fibers and the minute intervals that can be conducted are increased. Even if the content of long carbon fibers is as small as 2 to 8% by weight, the surface resistivity of the antistatic layer 2 is low at less than 10 ¹⁰ Ω, and sufficient antistatic performance is exhibited.

When the press is performed in this manner, in the conventional resin plate on which the antistatic layer containing the metal oxide powder is formed, the particles of the powder spread at the ends where the flow of the antistatic layer is particularly large during the pressing, and the particles are mutually separated. And the probability of maintaining a fine gap capable of conducting between the particles becomes low, and the dispersion state of the powder is likely to be non-uniform, so that the surface resistivity is increased, and furthermore, the central part and the end part of the antistatic layer, or Although the variation of the surface resistivity at each end portion is large, if the antistatic layer 2 including the long carbon fibers twisted and entangled like the antistatic transparent resin plate P is formed, Since the long and entangled long carbon fibers follow the flow at the time of pressing while stretching, even if the fluidity at the end of the antistatic layer 2 is large, contact between the conductive long carbon fibers can be achieved. Alternatively, a minute interval is maintained. Therefore, even if the antistatic transparent resin plate P is improved in transparency and transparency by pressing, the variation in the surface resistivity is reduced, so that not only the center and the end of the antistatic layer but also the end of the antistatic layer are provided. There is no large variation in the surface resistivity in each part, and the surface resistivity of the antistatic layer 2 is as low as less than 10 ¹⁰ Ω as described above, and sufficient antistatic performance can be obtained.

The temperature and pressure conditions of the press are not particularly limited and may be appropriately set in consideration of the softening temperature and the like of the thermoplastic resin of the antistatic layer. Generally, the temperature condition and the temperature condition of about 140 to 190 ° C. It is preferable to press under a pressure condition of about 30 to 120 kg / cm ² .

  In the case where the above-described antistatic film is prepared and thermocompression-bonded to the surface of the substrate 1 by a heat press or a roll press, the press is already performed at the thermocompression bonding stage, and the transparency, the transparency, the antistatic The above-mentioned press is unnecessary because the properties and the like are improved. In addition, when the surface of the substrate 1 is in a heated state, heating may not always be required at the time of pressing.

  The antistatic transparent resin plate P has a transparent antistatic layer 2 provided on one surface of a transparent substrate 1 made of a thermoplastic resin, and a sheet colored in a desired color on the opposite surface of the substrate 1 or When the plate members are joined, a laminated plate can be formed from the antistatic layer 2 side so that a color having the same depth as the actually colored color of the sheet or the plate member can be seen through.

  Next, more specific examples and comparative examples of the present invention will be described.

[Examples 1 to 6]
A powder of a vinyl chloride resin as a thermoplastic resin is added to and dissolved in cyclohexanone as a solvent, and in this solution, graphite fibers [product name “Graphite Fibrils” manufactured by Hypillion Catalysis International Co., Ltd. GF in Table 1), an average wire diameter of 10 nm, an average length of 10 μm, and an aspect ratio of 1000] were added at various concentrations and uniformly mixed and dispersed to form a coating liquid.

As the substrate, a vinyl chloride resin substrate having a thickness of 3 mm, a total light transmittance of 86%, and a haze of 1.5% was used. The antistatic transparent chloride of Examples 1 to 6 in which an antistatic layer having the content and thickness of long carbon fibers shown in Table 1 below was formed on the surface by pressing at 160 ° C. and a pressure of 30 kg / cm ^2. A vinyl resin plate was produced.

For the antistatic transparent vinyl chloride resin plates of Examples 1 to 6, the total light transmittance, haze, and surface resistivity (surface resistivity at the edge portion of the resin plate) were measured, and the results were as shown in Table 1 below. The result was obtained. The total light transmittance and haze were measured in accordance with ASTM D1003, and the surface resistivity was measured according to ASTM.
It is measured according to D257.

[Comparative Examples 1 to 6]
For comparison, an antistatic layer having a thickness shown in Table 1 containing tin oxide (SnO ₂ ) powder in a vinyl chloride resin at a ratio shown in Table 1 was formed to a thickness of 3 mm, a total light transmittance of 86%, and a haze of 1 The antistatic transparent vinyl chloride resin plates of Comparative Examples 1 to 6 were produced by forming on the surface of a 0.5% vinyl chloride resin substrate and further pressing. When the total light transmittance, haze, and surface resistivity (surface resistivity at the end of the resin plate) were measured, the results shown in Table 1 below were obtained.

As shown in Table 1, Examples 1 to 6 in which the antistatic layer having a thickness of 0.05 to 0.50 μm containing graphite fibers in the range of 2.0 to 8.0% by weight was formed on the surface. The antistatic transparent vinyl chloride resin plate has an average value of the surface resistivity at the end portion in the range of 1 × 10 ^{5 to} 6 × 10 ⁸ Ω, indicating that the antistatic transparent vinyl chloride resin plate has good antistatic properties. This is because the graphite fibers meander and entangle in the antistatic layer, and furthermore, the frequency of contact between the fibers and the minute space where conduction is possible are increased by pressing. Moreover, the antistatic transparent vinyl chloride resin plates of Examples 1 to 6 have the surface resistivity of X-3σ and X + 3σ (X is equivalent to the average of the obtained data of the surface resistivity, and σ is the standard deviation thereof). It can be seen that the variation in (corresponding to) is within a range of two digits numerically at the maximum, and the variation is small. This is because the graphitic fibers twisted and entangled follow the flow of the antistatic layer at the time of pressing while elongating, so that the contact comb between the conductive graphite fibers can be obtained with a small interval. This is because the dispersion state of the graphite fibers is less likely to be non-uniform.

On the other hand, in the antistatic transparent vinyl chloride resin plates of Comparative Examples 1 to 6 in which the antistatic layer containing the tin oxide powder was formed, the tin oxide content was as large as 40 to 70% by weight, and Although the layer was formed as thick as 0.4 to 2.4 μm, the average value of the surface resistivity at the end of the resin plate was as high as 4 × 10 ⁸ to 2 × 10 ¹⁰ Ω. It can be seen that the antistatic property is inferior to the antistatic transparent vinyl chloride resin plate of No. 6. This is because, since the conductive material is tin oxide powder, the frequency of conductive contact is low even if the conductive material is contained in a considerably large amount. Moreover, the antistatic transparent vinyl chloride resin plates of Comparative Examples 1 to 6 show that the variation in the surface resistivity between X-3σ and X + 3σ reaches a maximum of four digits numerically, and the variation is large. This is because the antistatic layer flows at the time of pressing, the particles of the tin oxide powder spread, and the probability of maintaining a small interval that allows conduction between the particles becomes low, and the dispersion state of the tin oxide becomes uneven. Because it is easy to become.

  The pressed antistatic transparent polyvinyl chloride resin plates of Examples 1 to 6 were slightly lower in total light transmittance than the pressed antistatic transparent polyvinyl chloride resin plates of Comparative Examples 1 to 6. However, haze, which is considered to be important in transparency and transparency, shows values superior to those of Comparative Examples 1 to 6. In addition, all of the numerical values of 75% or more of total light transmittance and 5% or less of haze, which can be regarded as good transparency and transparency, are satisfied. Therefore, Comparative Examples 1 to 6 show overall transparency and transparency. It can be seen that this is an excellent product not inferior to.

It is a sectional view of an antistatic transparent resin board concerning one embodiment of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Substrate 2 Antistatic layer P Antistatic transparent resin plate

Claims (2)

A press having a thermoplastic resin transparent antistatic layer having a thickness of 0.05 to 0.50 μm containing 2 to 8% by weight of ultrafine long carbon fibers winding and entangled on the surface of a transparent substrate of a thermoplastic resin; A transparent resin plate having a total light transmittance of 75% or more, a haze of 5% or less, a surface resistivity of less than 10 ¹⁰ Ω, and an average value X of the surface resistivity and a standard deviation σ. An antistatic transparent resin plate wherein the variation in X-3σ and X + 3σ is up to two digits.   2. The fiber according to claim 1, wherein the long carbon fibers are winding fibers having a wire diameter of 3.5 to 100 nm and an aspect ratio of 5 or less, and are entangled and dispersed in the antistatic layer. Conductive transparent resin plate.