Formable antistatic resin molded article

Details Formable antistatic resin molded article Formable antistatic resin molded article

1998-08-10

2001-04-10

Cole, Elizabeth M. (Department: 1771)

Stock material or miscellaneous articles

Structurally defined web or sheet

Physical dimension specified

C428S904000, C428S926000, C428S922000, C428S297400, C428S299100, C428S300700

Reexamination Certificate

active

06214451

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an antistatic resin molded article which is provided with antistatic properties on the surface thereof without substantially increasing in surface resistance even in forming.
BACKGROUND OF THE INVENTION
Antistatic synthetic resin articles are used in their applications which dislike adhesion and deposition of dusts and other fine particles and hence provided with antistatic properties on the article surfaces in order to scatter electrostatic charge on the surfaces.
In order to impart antistatic properties to the synthetic resin molded articles, conventionally, conductive microparticles or fibers of stannic oxide, carbon, etc. are formulated and uniformly dispersed in the resin. The antistatic properties are produced by mutual contacts among the microparticles and/or fibers, thereby reducing the electric resistance of the molded articles.
Also, the applying of the antistatic property to only the surface of the molded article has been performed by including the conductive particles or fibers in only a surface layer of molded articles. For example, the molded articles have been produced by applying, to the surface of a resin substrate, a coating layer or film formed which includes the conductive particles or fibers and some synthetic resin, these molded articles being utilized as antistatic resin plates or the like.
In the conventional antistatic resin plates, a thermoplastic resin substrate is molded and the above antistatic film is then laminated on the substrate, and thereby the plates are obtained on which the surface exhibits high antistatic properties with the surface electric resistivity of 10
11
&OHgr;/□ or less.
However, as the resin plate formed in this manner is further heated and deformed in a manner that the surface area is extended, for example, by bending or vacuum forming, the surface resistance after the secondary forming is increased, posing the problem of a reduction in antistatic properties. The surface electric resistivity is generally increased by the extending deformation of antistatic resin plate. It is considered that this is caused by reduced frequencies of mutual contact among the microparticles or fibers or increased intervals between the particles due to extension of the resin in which the conductive particles or fibers are dispersed.
When the deformation in the forming step is so large as to produce plastic deformation, it is observed that the surface resistivity is increased since the conductive fibrous materials are oriented in the deforming direction to decrease the frequency of the mutual contact of the fibers and also the frequency of intervals of the fibers needed for the conductivity. This tendency will be clearly significant if the conductive materials are stiff and short fibers.
The molded article, which increases in surface resistivity with the antistatic properties decreased when the antistatic resin plate is formed such as a secondary processing after molded, must have limitations to its uses. In this case, the antistatic properties can be imparted by applying an antistatic paint to desired positions on the surface of the molded article after forming the molded article from the normal thermoplastic resin plate, whereas this requires any steps of applying the antistatic paint in which in the molded particles with complicated shapes, the formation of uniform coating layers having excellent surface qualities is difficult, no uniform antistatic properties being imparted.
In view of the above problems, the present invention has an object of providing an antistatic resin molded article having thermal-formability, which is not accompanied by a substantial increase in surface resistivity even by forming after imparting antistatic properties therein.
SUMMARY OF THE INVENTION
The antistatic resin molded article of the present invention comprises a thermoplastic resin substrate and an antistatic resin layer applied to any one of the surfaces of the resin substrate, wherein the antistatic resin layer is formed of a coating in which conductive elongated fibers are dispersed in a manner that they are flexuous in keeping contact with each another and/or such intervals between them as in conduction with each another. Even if this molded article is subjected to deformation due to reduction in area, tension or bending by subsequently thermoforming the article, the flexuous elongated fibers are intended only to be straightened but can never maintain neither mutual contact with each another nor conductible intervals between them, therefor ensuring the antistatic properties in the resin layer formed. Thus, the antistatic resin molded article can be obtained which possess both formability and antistatic properties, without losing the antistatic capability even in the secondary processing such as heat forming.
As such an conductive elongated fiber, a carbon fiber, metal fiber, and conductive organic fiber may be used, and preferably the thinnest and longest fibers are desirable since such fibers are easily entangled in contact with each another and also are readily flexuous. The most desirable fiber is a extremely fine carbon long-fiber.
The extremely fine carbon long-fibers has a property of being naturally entangled with each another to gather into a woolen-pill form and a great number of fibers are allowed to projected out of said pill-shaped aggregate, and by dispersing a great number of aggregates of such a structure uniformly in a thermoplastic resin, the fiber aggregates in the resin layer are brought into contact with each another and/or are allowed to hold such intervals between them in conduction, imparting the antistatic properties to the resin layer.
Conventional carbon fibers are large in fiber diameter having stiffness, which are hard to be not entangled with each another, whereas the long-fibers, especially, the extremely fine carbon long-fibers used in the present invention are extremely fine, specifically, with a large ratio of the length to the fiber diameter so that the carbon fibers can be dispersed in a manner that these are entangled with each another. Extremely fine carbon fibers which are entangled pill form are also easily dispersed with the pilled form and the pilled aggregates are easily entangled with each another. In order to form pilled aggregate of the carbon fibers, preferably the carbon fibers are so extremely fine as to be 3.5 to 500 nm in fiber diameter and 100 to 3,000 in aspect ratio (a ratio of the length relative to the fiber diameter). Such pilled carbon fiber aggregates make a condition of projecting many carbon fibers and under the condition that the pilled aggregates are close to each another, the carbon fibers projecting and extending radially from the pilled aggregates are in contact with each another in the resin layer or maintain conductible intervals among them to form the electric conductive condition.
In the present invention, a coating layer of an resin solution to which an conductive long-fiber is added is applied on the surface of a substrate to allow even a small amount of the conductive long-fiber to maintain the widespread dispersion condition in the resin layer. Even if the resin article on which the coating layer has been applied is deformed in heating as a secondary processing, the entangled conductive long-fibers in the resin layer are hardly disentangled whereby its conductive condition can be held and a reduction on the antistatic properties is hence made small. In the coating layer to which an extremely fine long-fiber is added, far from being reduced in antistatic properties by forming, appropriate compressing the coating layer by appropriately forming ensures that the probability of contacting and approaching electrocoductively the mutual pilled aggregates or many mutual carbon fibers projecting from the aggregates rather increase, result in exhibiting increased antistatic properties.


REFERENCES:
patent: 4540624 (1985-09-01), Cannady, Jr.
patent: 4579902 (1986-04-01), O'Brien
patent: 5571859 (1996-11-01), Yukishige et al.
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