GB2269261A

GB2269261A - Notice board system.

Info

Publication number: GB2269261A
Application number: GB9315544A
Authority: GB
Inventors: Keiji Kasahara
Original assignee: Abisare Co Ltd
Current assignee: Abisare Co Ltd
Priority date: 1992-07-29
Filing date: 1993-07-28
Publication date: 1994-02-02
Anticipated expiration: 2013-07-28
Also published as: DE4323812C2; GB2269261B; JPH0695596A; DE4323812A1; FR2694436A1; FR2694436B1; GB9315544D0

Abstract

An electrostatic notice board system in which characters can be written on the surface, while attractive forces sufficient to hold objects thereon are maintained, comprises a hard coating material layer (5) formed at the surface of the attraction layer (2) consisting of a layered dielectric substance. The back of the attraction layer (2) is provided with positive and negative electrodes (3) in the form of comb-teeth, so that objects such, as paper sheets are attracted and held by coulomb force on the surface of the hard coating material layer (5). The hard coating material layer (5) is, for example, formed by applying acrylic urethane coating material to the surface of the attraction layer (2) and hardening the material with ultraviolet irradiation. The hard coating material layer (5) has a volume resistivity of 10<10> ??? cm or more and thickness of 50 g or less. The system may also include an adhesive, insulating layer (4) disposed on the face of electrodes (3) and remote from attracting layer (2). <IMAGE>

Description

2269261

DESCRIPTION NOTICE BOARD SYSTEM Background of the Invention (1) Technical Field

The present invention relates to an electrostatic notice board system for attracting objects by coulomb force so as to be held thereon, and more particularly, an electrostatic notice board system arranged such that characters can be written on its posting-up surface on which sheet-like notices are to be attracted and held for the purpose of advertisement, providing information or the like.

(2) Prior Art

One known electrostatic notice board system for attracting objects, such as sheets, by coulomb force so as to be held thereon comprises an attraction layer consisting of a layered dielectric substance and a pair of electrodes electrically separated from each other and formed in a laminate structure on the back face of the attraction layer. In this conventional electrostatic notice board system, the electrodes are connected to a d.c. power source, thereby utilizing coulomb force to attract and hold an object on the surface of the attraction layer.

Summary of the Invention If such an electrostatic notice board system is -2not only provided with the primary function, that is, attracting and holding of e.g., sheet-like objects on its posting-up surface, but also to enable characters to be written, in a s-IMilar manner to the case of a whiteboard, on the posting-up surface with a writing implement such as a marker, the system becomes very useful and will be extensively used in various occasions It is conceivable that, for providing an electrostatic notice board system with both posting-up function and whiteboard-like function, another layer on which characters can be written may be disposed on the surface of the attraction layer. The provision of another surface layer simply disposed on the attraction layer, however, has proved to have the problem that the interior of the surface layer becomes electrically conductive when the electrodes aze connected to a power source so that an electrostatic field for causing.polarization charge necessary for attraction and holding of an object cannot be satisfactorily generated or the llelectretll phenomenon occurs on the surface layer, resulting in a loss of attractive force.

In order to overcome the above problem, an object of the invention is to provide an electrostatic notice board system wherein characters can be written on its posting-up surface whilst coulomb force sufficient for -3attracting and holding an object can be maintained on the same surface.

An electrostatic notice board system, according to the invention, comprises:

(a) an attraction layer (2) consisting of a layered dielectric substance; (b) a hard coating material layer having a volume resistivity of 10109 cm or more and a specified surface hardness, the coating layer being formed at one face side of the attraction layer; and (c) at least one pair of electrodes formed on the other face of the attraction layer such that the electrodes are electrically separated from each other in a laminate structure for generating an electric field in order to cause polarization charge at the attraction layer, whereby an object placed on the face of the attraction layer with the coating layer interposed therebetween can be attracted and held by coulomb force.

The hard coating material layer may be formed by applying acrylic urethane resin or polyester resin to one face of the attraction layer and hardening the resin by means of ultraviolet irradiation. Alternatively, it may be formed by applying methacrylic resin to one face of the attraction layer -4and hardening the resin, utilizing heat of reaction. Another alternative is such that acrylic resin or urethane resin is applied to one face of the attraction layer and hardened. It is also possible to apply fluorine-containing enamel resin to one face of the attraction layer by baking. In these cases, the thickness of the hard coating material layer is most preferably SOM or less, and the hard coating material layer may be composed of one layer or more. The preferable surface hardness of the hard coating material layer is 3E or more.

The attraction layer is preferably made of a plastic material including one or more conductive materials, such as gold, silver, tin, zinc oxide, conductive oxides, conductive ionic resins or carbon black, the conductive material(s) being made into minute pieces and dispersed in the plastic material. In this case, the volume resistivity of the attraction layer is preferably set in the range of 1011 to 1014 52 cm Preferably, an insulating layer is formed at the face of the pair of electrodes remote from the face adjacent to the attraction layer. In this case, the insulating layer is made of an insulating adhesive and has a volume resistivity of 1014 9 cm or more.

According to such an electrostatic notice board system as described above, there is a hard coating material layer having a volume resistivity of 1010 92 cm and a specified surface hardness disposed on one face of an attraction layer so that an electrostatic field generated by applying d.c. voltage across a pair of electrodes microscopically causes polarization charge throughout the attraction layer and hard coating material layer. With this arrangement, not only can an attractive force sufficient for holding objects be ensured, but also characters can be written on the surface of the hard coating material layer.

In this case, the thickness of the hard coating material layer is set to SOM or less and the hard coating material layer is formed by applying acrylic urethane resin to one face of the attraction layer by painting, coating, screen printing or a similar method and hardening the resin by ultraviolet irradiation, whereby a coated"film having a desired resistivity, high hardness and excellent abrasion resittance can be achieved. Brief Description of the Drawings

The present invention will be further described by way of example. with reference to the accompanying drawings which illustrate one embodiment of an electrostatic notice board system according to the -6invention and in which:- Fig. 1 is an exploded perspective view; Fig. 2 is a fragmentary plan view; Fig. 3 is a partly diagrammatic sectional view; and Fig. 4 is a perspective view of the electrostatic notice board system in use. Description of the Preferred Embodiment

Referring now to the drawings, an electrostatic notice board system 1 comprises an attraction layer 2. a pair of comb-teeth-like electrodes 3 consisting of positive and negative electrodes formed in a laminate structure on the rear face of the attraction layer 2, and an insulating adhesive layer 4 disposed on the face of the comb-teeth like electrodes 3, remote from the attraction layer 2. Disposed on the front face of the attraction layer 2 is a hard coating material layer 5 consisting of a single layer, and an object 6, such as a paper sheet, is held and attracted by coulomb force at the front face of the attraction layer 2, with the hard coating material layer 5 therebetween.

The attraction layer 2 is made of a plai3tic material containing minute pieces of material(s) dispersed therein. The above plastic material can be polyester, polyvinyl, chloride, acrylic, -7polycarbonate, polyacetal, phenol or epoxy. The dispersed material(s) is (are) metal pieces of gold. silver or tin; conductive materials, such as zinc oxide, conductive oxides; or conductive ionic resins. The attraction layer 2 has a thickness of 0.5 to 0.1 min and a volume resistivity of 1011 to 1014 0 cm.

The comb-teeth like electrodes 3 are formed such that oppositely directed teeth portions are alternately arranged in an interdigitated manner as shown in Figs. 1 and 2 and each terminal is connected to a d.c. power source 7 through a selector switch 8. When the selector switch 8 is operated, the polarity of the pair of comb-teeth like electrodes 3 is switched The selector switch 8 is operated when the object 6 is held by attraction for a long time and this operation prevents the occurrence of the Ilelectret,' phenomenon which causes a decrease in the attractive force of the attraction layer 2 etc. The adhesive layer 4 is formed of a high-insulating material of which volume resistivity is 10142 cm or more.

The hard coating material layer 5 is formed by applying acrylic urethane resin to the front face of the attraction layer 2 by painting, coating, screen printing o r a similar method, and hardening the resin by ultraviolet ray irradiation. The electrostatic -8notice board system 1 having the above-described structure is fitted into a rectangular supporting frame 9, as shown in Fig. 4, with the adhesive layer 4 facing to the inside, and mounted together with the supporting frame 9 on a stand or easel 10 when it is used. The electrostatic notice board system 1 may be fixed to or hung on a wall with the help of a mounting bracket or the like, instead of mounting it on the stand 10. In Fig. 4, a power unit 11 includes a power supply switch (not shown) and the selector switch 8.

In this embodiment, the volume resistivity of the hard coating material layer 5 disposed on the front face of the attraction layer 2 is 10102 cm or more irrespective of the volume resistivity of the attraction layer 2, and more preferably falls within the range of 1010 to 1013 Q cm. The thickness of the hard coating material layer 5 is SOM or less (10g/m2 or less). With the volume resistivity and thickness of the hard coating material layer 5 as specified above, an electrostatic field generated by the application of voltage macroscopically causes sufficient polarization charge throughout the attraction layer 2 and the hard coating material layer 5 for sufficient attractive force to act on the object 6. If the volume resistivity of the hard coating material layer 5 is less than 1010 Q cm, the interior -9of the hard coating material layer becomes conductive at the time of supplying power, with the result that no polarization charge can be built up. On the other hand. if the volume resistivity exceeds 1013 2 cm. the great "electret" phenomenon occurs at the hard coating material layer 5 so that a satisfactory attractive force for the object 6 cannot be obtained. In such a case, the decrease of attractive force can be prevented by manipulating the selector switch 8 in order to make the electrostatic notice board system 1 operable satisfactorily.

According to the electrostatic notice board system 1 of the embodiment, since the surface of zhe attraction layer 2 is white or pale grey, it is possible to write characters etc. on the surface with a marker or the like used for a whiteboard and the characters etc. written on the surface can be seen clearly.

The use of W-hardenable acrylic urethane resin as the hard coating material makes it possible to use writing units having a hard writing tip. Since the system has a hardness of 3E or more at the surface, the surface is resistant to and freefrom abrasion even when hard-type writing units are used so that high abrasion resistance and high durability can be achieved. In contrast with the above resin, when an -10epoxy coating material is hardened, the resistivity becomes too high. Soft type polyvinyl chloride exhibits appropriate resistivity but has a problem in the surface hardness whilst hard type polyvinyl chloride has an excessively high resistivity. It has been ascertained that the surface of the hard coating material layer 5 according to the embodiment has quality equivalent to that of the whiteboard (porcelain enamelled whiteboard) stipulated by JIS Japanese Industrial Standard S 6052 in terms of appearance. colour, the ability of holding marker ink, the removability of marker ink, and the roughness of the surface etc.

A Table 1

Itard Coating Material Embodiment Comparative Comparative Comparative Example 1 Example 2 Example 3 Attraction A B A B A 13 A 13 Sheet 1.01.1 1? Clu(zIlle 6 6 1 5 0 0 5 5 oxide) 1013 9? em(zlne 3 5 2 5 0 5 5 oxide) 1014 Q cm(zllic 3 4 1 5 0 4 4 oxide) 1 A: straight D: SW1 tell: no resIdue Table 1 shows, as an examplep the result of a test for checking the relationship between the volume resistivity of the hard coating material layer and attractive force. This test was conducted at a temperature of 230 C and a humidity of 67% in such a way that: a high-quality paper sheet of 90g in weight (A-4 size) was first placed on the surface of the hard coating material layer 5 as the object 6, and then a d.c. voltage of 20OV was applied to the power source 7. 10 seconds after the voltage application, the attractive force (kg) was measured by pulling the object 6 with a spring balance. In Table 1, the hard coating material used in the embodiment is an acrylic urethane hard coating material having a volume resistivity of 4.7 X 10119 cm and thickness of SOM. The hard coating material used in the comparative example 1 is a polyester hard coating material having a volume resistivity of 2.3 X 10152 cm and thickness of SOP. In the comparative example 2, a metal hard coating material, such as aluminium, copper or stainless steel, whose thickness and volume resistivity were 20 p and 10-4 2 cm respectively, was applied by vapour deposition or sputtering. In the comparative example 3. no hard coating material was used. In Table 1, "straight.' indicates a case where -1 'the polarity of voltage applied to the electrodes was not changed whilst "switch" indicates a case where the polarity of the applied voltage was changed every specified hour. "No residue" means that, when voltage application was stopped, electrostatic charge generated in a hard coating material layer has disappeared.

According to the test result, when the volume resistivity of a hard coating material was set to the order of 10112 cm. like. in the case of the embodiment, no big difference was found between the attractive force of the "straight" condition and that of the "switch" condition. on the other hand. when the volume resistivity was set to the order of 1015 2 cm like the comparative example 1, it was found that the attractive force of the "straight" condition was smaller than that of the "switch" condition. This indicates there occurred the "electret" phenomenon in the hard coating material layer 5. Although the invention has been particularly described with the hard coating material layer 5 of 50 p or less in thickness in the foregoing embodiment, the thickness of the hard coating material layer 5 is not necessarily limited to this and could be appropriately set in accordance with the thickness of the attraction layer 2.

Although the attraction layer 2 of the above embodiment is formed such that minute metal pieces or minute pieces of conductive material(s), such as zinc oxide, are dispersed in a plastic material, such as polyvinyl chloride. it is also possible to form the attraction layer 2 such that carbon black is dispersed in a resin. In the case of carbon black, the electrostatic notice board system assumes a black colour as a whole and therefore specified writing units with ink of white or pastel hues should be used for writing on it.

Further. the hard coating material layer need not be formed by hardening acrylic urethane resin applied to the surface of the attraction layer by means of ultraviolet irradiation. The hard coating material layer could be obtained by other methods, such as, for example, (1) hardening polyester resin with ultraviolet irradiation; (ii) coating the attraction layer with methacrylic resin of several microns in thickness and hardening the resin utilizing heat reaction; (iii) hardening acrylic resin or urethane resin by heat or at ordinary temperature; (iv) applying fluorine-containing enamel resin by baking. Any one of the above methods should be selected taking the following factors into consideration: (i) drying temperature that does not affect the plastic base -15material of the attraction layer; (ii) adhesive properties with respect to the plastic base material; (iii) cracking resistance coping with the flexibility of the plastic material; and (iv) chemical resistance and contamination resistance to the ink of a marker, achieved after a coating material has been applied.

The invention being thus described, the same may be varied in many ways.

Claims

-16 CLAIMS

1. An electrostatic notice board system comprising:

(a) an attraction layer (2) consisting of a layered dielectric substance; (b) a coating layer (5) formed at one face of the_ attraction layer (2) so as to coat this face; and (c) at least two of electrodes (3) formed on the other face of the attraction layer (2) such that the electrodes are electrically separated from each other in a laminate structure for generating an electrostatic field to cause a polarization charge at the attraction layer (2); whereby an object (6) placed on the face of the attraction layer (2) with the coating layer (5) interposed therebetween can be attracted and held by coulomb force, characterised in that the coating layer (5) is a hard coating material layer having a volume resistivity of 1010 2 cm or more and a specified surface hardness.

2. The electrostatic notice board system as claimed in claim 1, wherein the volume resistivity of the attraction layer (2) is within the rang of 1011 to 1014 92 cm.

3. The electrostatic notice board system as claimed in claim 1 or 2, wherein the attraction layer is made of a plastic material.

4. The electrostatic notice board system as claimed in claim 3, wherein the plastic material contains minute pieces of conductive material dispersed therein.

5. The electrostatic notice board system as claimed in claim 4, wherein the conductive material is one or more materials selected from gold, silver, tin, zinc oxide, conductive oxides and conductive ionic resins.

6. The electrostatic notice board system as claimed in claim 4, wherein the conductive material is carbon black.

7. The electrostatic notice board system as claimed in any preceding claim, wherein the hard coating material layer (5) is composed of one layer or more.

8. The electrostatic notice board system as claimed in claim 7, wherein the hard coating material layer (5) has a surface hardness of 3H or more.

g. The electrostatic notice board system as claimed in claim 7 or 8, wherein the hard coating material layer (5) is formed by applying acrylic urethane resin to the surface of the attraction layer -18(2) and hardening the resin by means of ultraviolet irradiation.

10. The electrostatic notice board system as claimed in claim 7 or 8, wherein the hard coating material layer (5) is formed by applying polyester resin to the surface of the attraction layer (2) and hardening the resin by means of ultraviolet irradiation.

11. The electrostatic notice board system as claimed in any of claims 1 to 8, wherein the hard coating material layer (5) is formed by applying methacrylic resin to the surface of the attraction layer (2) and hardening the resin, utilizing heat of reaction.

12. The electrostatic notice board system as claimed in claim 7 or 8, wherein the hard coating material layer (5) is formed by applying acrylic resin to the surface of the attraction layer (2) and hardening the resin.

13. The electrostatic notice board system as claimed in claim 7 or 8, wherein the hard coating material layer (5) is formed by applying urethane resin to the surface of the attraction layer (2) and hardening the resin.

14. The electrostatic notice board system as claimed in claim 7 or 8, wherein the hard coating -19material layer (5) is formed by applying fluorinecontaining enam 1 resin to the surface of the attraction layer (2) by baking.

15. The electrostatic notice board system as claimed in any preceding claim, wherein the hard coating material layer (5) has a thickness of 50 p or less.

16. The electrostatic notice board system as claimed in any preceding claim, wherein an insulating layer (4) is disposed at the face of the electrodes (3) remote from the attraction layer (2).

17. The electrostatic notice board system as claimed in claims 16, wherein the insulating layer (4) is formed of an insulating adhesive.

18. The electrostatic notice board system as claimed in claim 16 or 17, wherein the insulating layer (4) has a volume resistivity of 1014 ú2 em or more.

19. An electrostatic notice board system, constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.