Recently, the generation of static electricity has been avoided in various environments to prevent damage to sensitive electronic components. For example, when a worker charged with static electricity comes into contact with electronic parts in a factory in which electronic parts are handled, there is a possibility that the electronic parts may be damaged by discharge of the static electricity from the worker through the electronic parts.

Accordingly, prior to the worker handling electronic parts, it is necessary to discharge static electricity from the worker so as to enhance the yield and reliability of the electronic parts. Discharge of static electricity from workers is accomplished in many cases by placing films made of conductive material on the floor. However, the floor is often made of concrete. Since a hard concrete floor does not have a cushion property, a worker standing on the hard floor becomes fatigued more rapidly than a working standing on a softer floor material.

An example of an antistatic mat in which importance is attached to the cushion property of the mat is found in Japanese Unexamined Patent Publication No. 9-276205.

This mat is made by accumulating loops of mono-filament at random. Accordingly, the cushion property of the mat is excellent. However, it is impossible for the mat to exhibit a sufficiently high antistatic function because the mono-filaments are long. Further, the mono-filament loops are exposed on the surface of the mat on which a worker walks, making it difficult for the worker to walk on the mat. Furthermore, mono-filament loops originally oriented in the thickness direction of the mat when the mat is new tend to fall or lie down inside the mat when the mat is used over a long period of time. As a result, the cushion property of the mat deteriorates over time. Furthermore, this mat is disadvantageous in that dust tends to accumulate inside the mat.

Summary of the Invention The present invention provides an antistatic mat having excellent antistatic capabilities and which maintains its cushion property over a long period of time.

In one embodiment of an antistatic mat according to the invention, an antistatic mat comprises a lattice composing member made of elastic conductive material arranged in a lattice-shape so that a large number of lattice holes of substantially the same profile are formed. The lattice composing member is in the range of 15% to 90% of the area of an arbitrarily selected 20 mm square region of the antistatic mat.

In another embodiment according to the invention, the lattice composing member is in the range of 40% to 60% of the area of the arbitrarily selected 20 mm square region of the antistatic mat.

In another embodiment according to the invention, an upper end portion of the lattice composing member is formed to be slender.

In another embodiment according to the invention, a lower end portion of the lattice composing member is formed to be flat.

In another embodiment according to the invention, the lattice composing member is composed of straight line members extruded from a slot of an extrusion mold at a first speed and a wave-shaped member extruded from a slot of an extrusion mold between adjacent straight line members at a second speed higher than the first speed, such that the wave-form member is bent and formed into a wave-shape between the adjacent straight line members.

In another embodiment according to the invention, the lattice composing member is formed into a honeycomb-shape.

In another embodiment according to the invention, the conductive material has a durometer hardness in the range of 40 to 70, as measured by the plastics durometer harness testing method stipulated in JIS 7215.

In another embodiment according to the invention, the leakage resistance of the conductive material is in the range of 10 kQ to 100 MQ.

Brief Description of the Drawings Fig. 1 is a top view of a first embodiment of an antistatic mat according to the invention.

Figs. 2 (A) and 2 (B) are alternate sectional views of the antistatic mat of Fig. 1 taken along line II-II in Fig. 1.

Fig. 3 is a sectional view of the antistatic mat of Fig. 1 taken along line III-III in Fig. 1.

Fig. 4 illustrates the face of an extrusion mold for manufacturing the antistatic mat of Fig. 1.

Fig. 5 is a top view of a second embodiment of an antistatic mat according to the invention.

Fig. 6 is a top view showing a half element used in one method of manufacturing the antistatic mat of Fig 5.

Fig. 7 is a top view showing a hexagonal section element used in another method of manufacturing the antistatic mat of Fig. 5.

Fig. 8 is a top view showing another method of manufacturing the antistatic mat of Fig. 5.

Fig. 9 (A) illustrates an exemplary use of an antistatic mat according to the invention, wherein the antistatic mat is laid on a conductive floor material Fig. 9 (B) illustrates another exemplary use of an antistatic mat according to the invention, wherein the antistatic mat is laid on a non-conductive floor material via a conductive sheet Fig. 9 (C) illustrates another exemplary use of an antistatic mat according to the invention, wherein conductive fibers are woven into the antistatic mat and connected to ground.

Detailed Description Referring to the accompanying drawings, embodiments of anti-static mats according to the present invention will be explained below.

Fig. 1 is a top view of a first embodiment of an antistatic mat 1 according to the present invention. The antistatic mat 1 comprises a lattice composing member 10. Lattice composing member 10 includes straight line members 11 and wave-form members 12. In the illustrated structure, wave-form member 12 is interposed between two straight line members 11 which are arranged adjacent to each other, and the straight line members 11 and the wave-form member 12 are connected to each other.

In antistatic mat 1 of Fig. 1, an upper protruding portion of one wave-form member 12 in the drawing is defined as a top, and a lower protruding portion of one wave-form member 12 in the drawing is defined as a bottom. Then, a bell-shaped lattice hole 13a is formed between the two tops, which are adjacent to each other, and the straight line member 11 comes into contact with these two tops. As shown in Fig. 1, the bell-shaped lattice hole 13a is extended upward. Further, a bell-shaped lattice hole 13b is formed between the two bottoms, which are adjacent to each other, and the straight line member 11 comes into contact with these two bottoms. As shown in Fig. 1, the bell-shaped lattice hole 13b is extended downward. The bell-shaped lattice holes 13a and 13b are collectively referred to as lattice holes 13.

In one embodiment, the size of the antistatic mat 1 is approximately 90 cm x 60 cm. In an arbitrarily selected square region of 20 mm x 20 mm of the antistatic mat 1, t there is formed at least one lattice hole 13. Preferably, there are formed not less than two lattice holes 13, and the lattice composing member 10 is in the range of 15% to 90% of the area of the arbitrarily selected square region. Preferably, the lattice composing member 10 is in the range of 40 to 60% of the area of the arbitrarily selected square region. In the case where the lattice composing member 10 is not more than 15% of the area of the arbitrarily selected square region, the antistatic mat 1 is excessively deformed in the vertical direction, and it is impossible to maintain the profile of the lattice composing member 10. In the case where the lattice composing member 10 is not less than 90% of the area of the arbitrarily selected square region, the quantity of generated static electricity is increased.

The reason for arbitrarily selecting a square region of 20 mm x 20 mm is explained as follows. A worker steps on the antistatic mat 1 with his feet (shoes). For example, the size of the antistatic mat is approximately 90 cm x 90 cm. Accordingly, if the area of the lattice composing member 10 is specified with respect to the entire area of the antistatic mat, the possibility exists that a lattice hole is formed that is large enough that the worker's feet (shoes) entirely enter the lattice hole and do not contact the conductive lattice composing member.

Figs. 2 (A) and 2 (B) are alternate sectional views of the wave-form member 12 taken along line II-II in Fig. 1. As shown in Fig. 2 (A), the upper end portion of the

wave-form member 12 is arcuate and has radius r. Alternatively, as shown in Fig. 2 (B), the upper end portion of the wave-form member 12 is trapezoidal. In both Figs. 2 (A) and 2 (B), the upper end portion of the wave-form member 12 is formed to be long and slender.

On the contrary, the lower end portion of the wave-form member 12 is flat. When the upper end portion of the wave-form member 12 is formed long and slender as described above, the generation of static electricity is more suppressed. When the lower end portion of the wave-form member 12 is formed flat, the generated static electricity is more easily discharged.

In both Figs. 2 (A) and 2 (B), the wall thickness tl of wave-form member 12 is in the range of 0.8 to 2.0 mm. It is preferable that the wall thickness tl is in the range of 1.0 to 1.4 mm. It is more preferable that the wall thickness tl is 1.2 mm. In the case where the wall thickness tl is determined as described above, the height hl is in the range of 2 to 20 mm. It is preferable that the height hl is in the range of 5 to 10 mm. It is more preferable that the height is 7 mm.

In the case shown in Fig. 2 (A), the radius r of the arc of the upper end portion is in the range of 0. 5tl to 4tl. In the case shown in Fig. 2 (B), the height h'of the trapezoid is in the range of 0. 25tl to 0. 5tl.

When the length Wf (shown in Fig. 1) is defined as a distance in which five wave- form members 12 come into contact with the straight line member 11, Wf is in the range of 10 mm to 60 mm. It is preferable that Wf is 38 mm.

Fig. 3 is a sectional view of the straight line member 11 taken along line III-III in Fig. 1. The thickness t2 is in the range of 0.5 to 1.5 mm. It is preferable that the thickness t2 is 0.8 mm. The height h2 is a value obtained when the height of the upper end portion of the wave-form member 12 (r in Fig. 2 (A) and h'in Fig 2 (B) ) is subtracted from the height hl of the wave-form member 12. That is, h2 is substantially equal to hl-r in the embodiment of Fig. 2 (S), or alternately h2 is substantially equal to hl-h'in the embodiment of Fig. 2 (B). Accordingly, in the first embodiment, the wave-form members 12 are taller than the straight line members 11, and thus the wave-form members 12 come into contact with the feet (shoes) of a worker.

In the first embodiment, the material of the lattice composing member 10 is made in such a manner that a conductive plasticizer is kneaded into vinyl chloride. The conductive plasticizer to be kneaded into vinyl chloride is a surface active agent. When

the surface active agent is kneaded into vinyl chloride, the surface of the resin is made to be conductive and also the generation of an electrical charge caused by surface friction is prevented.

On the basis of ionicity, the surface active agent is classified into four types, including anionic surface active agents, cationic surface active agents, amphoteric surface active agents and nonionic surface active agents.

Examples of surface active agents suitably used together with vinyl chloride include alkyl sulfonate (anionic surface active agent), amide-type cations (cationic surface active agent), alkyl betaine (amphoteric surface active agent), fatty acid monoglyceride (nonionic surface active agent) and sorbitan fatty acid ester.

The conductive plasticizer in the range of 80 to 180 parts by weight is added to vinyl chloride of 100 parts by weight. Further, a small quantity of stabilizer is added.

Metallic soap (a metallic salt of a higher fatty acid) is used as a stabilizer. Concerning the metal, for example, two components of Ba (barium) /Zn (zinc) are used. In this case, Zn soap traps HCl and substitutes aryl chloride, and Ba soap traps HCl and regenerates Zn soap by ligand exchange with ZnC12. Regeneration of Zn soap by ZnCl2 and Ba soap exhibits an excellent stabilization effect.

The hardness of the material produced as described above is adjusted to be in a range from 40 to 70 of durometer hardness, measured as described in"Method of Testing Durometer Hardness of Plastic"stipulated in JIS K7215. It is preferable that the hardness of the material produced as described above is adjusted to be 55 of durometer hardness. In the case where durometer hardness is not higher than 40, the antistatic mat is excessively deformed in the vertical direction. In the case where durometer hardness is not lower than 70, elasticity of the antistatic mat is deteriorated and the cushion property of the antistatic mat is insufficient for worker comfort.

The conductive plasticizer is kneaded so that the leakage resistance can not be higher than the following values, at various stages of processing: Sheet-shaped Material Before Processing Lower limit = 10 ka Upper limit = 100 MQ Preferable upper limit = 500 kQ

Material Formed into Profile of Fig. 1 (Arranged on Conductive Plate of Stainless Steel) Lower limit = 100 kg2 Upper limit = 10 MQ Preferable upper limit = 10 MQ Material Formed into Profile of Fig. 1 (Arranged on Another Non-Conductive Floor Material) Lower limit = 100 kQ Upper limit = 200 MQ Preferable Upper limit = 25 MQ All of the leakage resistance values are determined using the testing method of ESD STM7. 1.

When the leakage resistance is not more than the lower limit value, there is a possibility of electrification. When the leakage resistance is not lower than the upper limit value, static electricity is not discharged.

The antistatic mat 1 of the embodiment of Fig. 1 is manufactured in such a manner that the material produced as described above is heated, melted and extruded from an outlet of an extrusion mold 50 as shown in Fig. 4. This method of extrusion molding is disclosed in Japanese Examined Patent Publication No. 6-55403. Therefore, the method of extrusion molding will be only briefly explained herein.

The first slot 51 of extrusion mold 50 is used for molding the straight line member 11, and the second slot 52 of extrusion mold 50 is used for molding the wave-form member 12. The width of the first slot 51 is narrow with respect to the width of second slot 52. Accordingly, the speed of material extruded from the first slot 51 is low with respect to the speed of material extruded from second slot 52. As a result of the material extrusion speed differential, the material is linearly extruded from first slot 51, while the profile of material extruded from second slot 52 is curved and formed into a wave-form.

This wave-form material from second slot 52 is connected with the straight line material from first slot 51 to form the embodiment of Fig. 1.

Performance of the antistatic mat 1 of Fig. 1 molded as described above is described below. In the case of the antistatic mat of the embodiment of Fig. 1, the durometer hardness of which was adjusted to be 55, it was possible to provide an excellent cushion property, and the electric potential of a human body, which was measured by the Testing Method of STM 97.2 of the Unites States ESD Association, was not higher than 1 V.

A second embodiment of an antistatic mat according to the present invention is described with reference to Fig. 5. As shown in Fig. 5, the antistatic mat 1 of the second embodiment has a hexagonal honeycomb lattice. In this case, the wall thickness t3 of the lattice composing member 20 is the same as the wall thickness tl of the wave-form portion of the first embodiment illustrated in Figs. 1-2 (b). That is, the wall thickness t3 of the lattice composing member 20 is in the range of 0.8 to 2.0 mm. It is preferable that the wall thickness t3 of the lattice composing member 20 is in the range of 1.0 to 1.4 mm. It is more preferable that the wall thickness t3 of the lattice composing member 20 is 1.2 mm. When the wall thickness t3 is set as described above, the height h3 is in the range of 2 to 20 mm. It is preferable that the height h3 is in the range of 5 to 10 mm. It is more preferable that the height h3 is 7 mm.

The method of manufacturing the antistatic mat of Fig. 5 is different from that of the embodiment of Fig. 1 as follows. As shown in Fig. 6, the half element 21 is molded.

The molded half elements 21 are successively arranged being opposed to each other so that hexagonal holes are formed and then joined to each other by means such as heating or adhesion.

Alternatively, the manufacturing method shown in Fig. 7 may be adopted. First, the hexagonal member 22 is made by means of extrusion. Then, a large number of extruded hexagonal members 22 are bundled and joined to each other by means of such as heating or adhesion. Next, the joined hexagonal members 22 are cut into a predetermined height to form an antistatic mat.

Alternatively, the manufacturing method shown in Fig. 8 may be adopted. As shown in Fig. 8, rifts 24 are formed in substantially parallel alignment on the sheet-shaped conductive material 23. Then, the sheet 23 is pulled in the direction perpendicular to the rifts 24 so that the rifts 24 open up and hexagons are formed.

As explained above, in the embodiment of Fig. 1, the lattice is formed so that the

lattice holes composed of the straight line members 11 and wave-form members 12 are formed into a wave-form. In the embodiment of Fig. 5, the lattice is formed so that the lattice holes can be formed into a honeycomb-shape. However, it should be noted that the profile of the lattice or the profile of the lattice hole is not limited to the above specific embodiments, and it is possible to form the lattice or the lattice holes into an arbitrary profile. For example, it is possible to form the lattice hole into a square.

Next, referring to Figs. 9 (A) -9 (C), examples of the use of the antistatic mat of the present invention manufactured as described above are explained.

In the exemplary use shown in Fig. 9 (A), the antistatic mat 1 is laid on the conductive floor 100 made of, for example, tiles, painted floor members or long metallic sheets. In this example, the antistatic mat 1 of the present invention need only be laid at a desired position.

In the exemplary use shown in Fig. 9 (B), the antistatic mat 1 is laid on the usual non-conductive floor 100'. First, a conductive sheet 110 is put on the non-conductive floor 100', and then the antistatic mat 1 of the present invention is laid on the conductive sheet 110. Next, the conductive sheet 110 is connected to the ground potential. The conductive sheet 110 may be made of, for example, conductive resin or a metallic sheet such as a stainless steel sheet. Alternatively, the conductive sheet 110 may be made in such a manner that metallic foil is partially bonded.

In the exemplary use shown in Fig. 9 (C), conductive fibers 120 are woven into the antistatic mat 1 and connected to the ground potential.

The invention described herein provides an antistatic mat having a lattice composing member made of elastic conductive material arranged in a lattice-shape so that a large number of lattice holes of substantially the same profile are formed. The antistatic mat of the invention can compatibly provide both an excellent cushion property and an antistatic function.

Description of the Reference Numerals 1'"Antistatic mat 10...Lattice composing member 11'"Straight line member 12...Wave-form member 13'"Lattice holes 20...Lattice composing member 21...Half element 22'''Hexagonal member 23...Conductive material on sheet 24...Slot 50....Extrusion mold 51... First slot 52 Second slot 100...Conductive floor 100'...Non-conductive floor 110....Conductive sheet 120....Conductive fibers