US 3746573 A
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United States Patent US. Cl. 117-139.5 C 3 Claims ABSTRACT OF THE DISCLOSURE A method of producing carpet of low static charge, wherein a binder containing therein a quantity of carbon fiber is applied to the base cloth for the carpet as well as to the flocked fibers.
This invention relates to manufacture of carpet having very low static charging, and, more particularly, to an improved method of antistatic processing of the carpet.
Known type of carpet is mostly manufactured from woven cloth of hemp or cotton yarn as the base, into which other fibrous material such as wool, polyester, nylon, etc. are enmeshed so as to be flocked thereinto. Also, in most cases, a rubbery material is coated on or impregnated in the base cloth as a binder with a view to securing adhesion between the base cloth and the flocking.
Since these fibrous materials are insulative, static electricity tends to generate. Therefore, the carpet is not only charged with static electricity, but it tends to cause static charging of an opposite potential against an object which contacts therewith such as living bodies, etc. This static charging often imparts to such living body a shock at the time of electric discharge, or, where there is inflammable gas or liquid, explosion or fire is inevitably caused. In recent days, synthetic fibers are used widely in various purposes such as for carpet, clothing, rfurnitures and fittings, and so forth with the consequent increase in the abovementioned phenomenon, which tends to become unavoidably remarkable in the dry season.
Heretofore, it has been attempted to prevent static charging by mixing a small quantity of metallic fibers such as stainless steel with fibers for weaving the base cloth or for flocking so as to make the product electroconductive. This attempt resulted in the antistatic effect to a certain degree. However, not only was it difficult to manufacture uniformly interwoven base cloth, but also, when a mixing quantity of the metallic fiber is increased with a View to attaining sufficient effect, outer appearance of the product is impaired. Also, fine stainless steel fiber is extremely expensive, which is another cause for preventing the material from practical use.
It is therefore an object of the present invention to provide a method for manufacturing carpet or like articles free from static charge, the method of which is simply attained by mixing quantity of electroconductive carbon fibers with a binding material to be applied onto the carpet.
The above object and other objects of the present invention will become more apparent from the following description along with a few preferred examples thereof.
As the characteristic point of the present invention is to mix carbon fibers with rubbery or plastic material as a binder, outer appearance of the flocked fibers is not impaired, because the carbon fiber does not appear on the flocked surface. Hence, it is possible to manufacture carpet in exactly same manner as in the ordinary carpet production.
It is really surprising that static charging in the overall carpet is prevented by simply mixing carbon fibers with insulative rubber or plastic material as a binder. This antistatic phenomenon due to carbon fiber is assumed to be that static electricity generated at a portion of the flocked surface is spread widely thereover on account of the carbon fibers existing in the binder, and is discharged therethrough into air or ground.
Carbon fibers to be used in the present invention designate generally carbonaceous or graphitic fiber of electroconductive property. Diameter of a carbon monofilament usually ranges from about 3 microns to about 30 microns, and its length ranges in average between 0.5 mm. and 10 mm. Over 10 mm. of the fiber length, it becomes difficult to uniformly disperse the carbon fiber in the binder by kneading, and to cause the carbon-fiber-containing binder to be uniformly coated on or impregnated in the base cloth. Less than 0.5 mm. of the fiber length, electroconductive effect in the product becomes low.
Adding quantity of carbon fiber to the binder should preferably be from 0.1 to 10.0% by weight with respect to parts by weight of the solid content of the binding material. Quantity of less than 0.1% by weight of the carbon fiber would not produce the electroconductivity in the binder to a suflicient degree. Excessive quantity over 10.0% by weight results in diificulty in coating or impregnating operation. The adding quantity is in any way determined in relation to the fiber length.
As the carbon fiber has its specific gravity of about 1.5 to 1.9, and is smaller than that of stainless steel fiber by a few fractions, its volume becomes several times as large as that of stainless steel fiber for the same weight, hence the desired effect of electroconductivity can be easily exhibited.
It has so far between known to add carbon black to impart electroconductivity to rubbery material. However, as the carbon black is in very fine powder, the intended object cannot be achieved with addition of a small quantity thereof. Usually, 10 to. 35% by weight of carbon black is added to the binder material. From this comparison, it can be understood that the use of carbon fiber brings an advantageous result to the product.
Material for the binder may be those available in the market such as natural rubber, butadiene-styrene rubber (SBR), butadiene-acrylonitrile rubber (NBR), polyvinyl chloride (PVC), polyethylene, polyurethane, and so on.
Mixing of the carbon fiber with these binding materials is carried out by an ordinary method such as roll-kneading, solvent dispersion, etc. Any known method may likewise be adopted in accordance with actual situation. Same can be said of coating or impregnating the base of cloth with the binder.
According to the method of the present invention, it is possible that the antistatic effect may be suificiently exhibited by adding a predetermined quantity of electroconductive carbon fiber to the binding material alone, so that any complicated process such as mixing or interweaving the carbon fiber with the flocking fiber or the base cloth is no longer necessary. Further, the carbon fiber, once mixed with the binding material, is no longer required to be subjected to bending action due to external force, against which the carbon fiber is most fragile, hence the resultant article of manufacture is durable enough against external force and has wide varieties of use.
In order to enable skilled persons in the art to readily reduce the present invention into practice, the following actual examples are presented. It should however be noted that these examples are illustrative only and do not intend to narrow the scope of protection as recited in the appended claims.
3 EXAMPLE 1 Carpet was manufactured from a woven base cloth of hemp yarn and nylon pile having the fiber length of 6 mm. when flocked. The back surface of the base cloth was coated with liquid butadiene-styrene rubber. The rubber material used was a product of Yokohama Rubber (30., Japan, and identified as No. Y-460."
Carbon fibers of an average length of about 3 mm. and a diameter of about 7 microns was mixed with the liquid rubber component at the mixing ratios of 0.5% by Weight and 2.0% by weight, respectively, with respect to the solid rubber content. The quantity of the rubber component applied to the base cloth was 150 g./m. and 3,600 g./m. for the respective test pieces of diiferent carbon fiber contents.
From the carpets thus manufactured, test pieces of 3 cm. x 4 cm. were cut out. The specimens were subjected to test for measuring the charged value of static electricity by means of a rotary static tester (produced by Koa Shokai Co., Japan). The test results are shown in Table 1 below, from which remarkable antistatic effect is recognized with the binder containing the carbon fiber.
friction in the same manner as in Example 1 above. The results are shown in the following Table 3.
EXAMPLE 4 Carbon fiber of about 12 microns in diameter and about 3 mm. in average length was added to liquid SBR No. Y-460 (product of Yokohama Rubber (30., Japan) at a ratio of 0.3% by Weight with respect to the solid rubber content to prepare a binder. This binder was applied onto carpet made of base hemp cloth and woolen pile having fiber length of 6 mm. in a quantity of 500 g./m. and then the carpet was dried.
From the thus produced carpet, a test piece of cm. x 30 cm. was cut out, and dried at a temperature range of from 100 to 110 C. for 2 hours. After drying, the test TABLE 1 Quantity of binlde Static voltage (v.) after friction forapp 1e Binder (g./m. 10 sec. 20 sec. 30 sec. 60 sec. 120 sec.
1 SBR 150 1, 450 1, 700 1, 800 1, 900 2, 000 R 3, 600 1, 450 1, 600 1, 700 1, 750 1, 750 150 700 850 950 1, 100 1, 300 -dO 3, 600 400 500 600 680 750 SBR plus 2.0 wt. percent carbon fiber. 150 200 500 600 800 1,050 .do 3, 600 200 500 550 600 800 N orE.Rotary Static Tester used in this example is an apparatus for measuring static electricity charged by friction between the test pieces and friction cloth. The test piece is fitted on the outer surface of a cylinder 01 this apparatus, and, while the cylinder is in rotation, the test piece is in contact-motion with the tnctmn cloth placed in opposite side of the cylinder. The measurement was conducted in a chamber of 26 C. and 65% of relative humidity.
EXAMPLE 2 300 g./m. of SBR binder was coated on carpet produced from woven base cloth of cotton yarn and woolen pile of 6 mm. fiber length.
For comparisons sake, following three kinds of the binder were prepared: (1) SBR alone; (2) SBR 5 Wt. percent of stainless steel fiber of about 7 microns in diameter and about 5 mm. in average length; and (3) SBR 5 wt. percent of carbon fiber of about 7 microns in diameter and 5 mm. in average length.
In the same manner as in Example 1, static electricity was measured, the results of which are shown in the folpiece was placed on a board of 5 mm. thick made of polyvinyl chloride, on which there stood a human being of 170 cm. tall, 60 kg. of weight, who wore cotton undershirt and fatigue cloth thereover, put a rubber-sole footwear on, and held in hand an iron plate of 30 cm. x 30 cm. x 5 mm. After making several steppings on this test piece, static charge was measured for each of the iron plate in hand and the carpet. The results are shown in Table 4 below.
For the sake of comparison, same measurement was carried out on both ordinary carpet and a carpet made of the base cloth, in which stainless steel monofilament of 8 microns in diameter was interwoven with the hemp yarn lowing Table 2. at a rate of 0.3% by weight with respect to the hemp TABLE 2 Static voltage (v.) after friction for- Specimen number Binder 20 sec. 30 sec. sec. 120 sec 1 SBR (Y-460) 500 740 1, 180 1, 430 2. SBR (Y-460) plus 5 wt. percent stainless steel fiber 370 550 700 700 3 SBR (Y-460) plus 5 wt. percent carbon fiber 70 80 170 400 EXAMPLE 3 To viscous liquid of natural rubber dissolved into carbon tetrachloride, carbon fiber of about 7 microns in diameter and about 0.1 mm. in average length was added so as to be a content of 0.1% by weight with respect to solid rubber content.
The binder was impregnated in carpets made of a base hemp cloth and nylon piles having fiber length of 3 mm. and 6 mm., respectively, so that the final quantity of the binder as applied to the respective carpets may be 500 g./m. and then the carpet was dried. Another carpet for comparison purpose was also manufactured in the same manner, except that no carbon fiber was added to the binder. Test pieces were taken from each of these caryarn, and woolen pile, in which the same metallic filament is enmeshed in the same amount as the base cloth. It was found that the static charging in the carpet according to the present invention was very small.
Living body (iron plate) -1, 500
What we claim: 1. A method for preventing static charge in a pile carpet pets and tested for the static voltage after 60 seconds which comprises binding the base cloth for the carpet and pile with a binder selected from the group consisting of natural rubber, butadiene-styrene rubber, butadieneacrylonitrile rubber, polyvinyl chloride, polyethylene and polyurethane, containing therein a uniform dispersion of 0.1-10% by weight of carbon fibers having a single fiber length of 05-10 mm. and a diameter of 3-30 microns, based on the weight of the solid content of the binder, and drying the treated carpet.
2. The method as claimed in claim 1, in which the dispersion of binder and fiber is applied to the base cloth by coating.
3. The method as claimed in claim 4, in which the dispersion of binder and fiber is applied to the base cloth by impregnating.
References Cited UNITED STATES PATENTS 2,302,003 11/1942 Cadwell et al 161-66 3,166,465 1/1965 Rahmes 161-66 3,235,323 2/1966 Peters 8116.2 3,486,920 12/1969 Sington 161-66 X WILLIAM D. MARTIN, Primary Examiner 10 T. G. DAVIS, Assistant Examiner U.S. C1. X.R.
11713'8.8 F, 138.8 N, 161 UD, 161 UP, 161 KP, 162, 226