JP2006193835A - Conductive conjugated fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive conjugated fiber having excellent durability in repetitive use, substantially enhancing the fiber density at the tip of the conductive fiber at a brush end when used in an image-forming apparatus such as an electrophotographic copier or printer and slightly causing unevennesses. <P>SOLUTION: The conductive conjugated fiber comprises a core component composed of a thermoplastic polymer containing conductive fine particles and covered with a non-conductive sheath component composed of a thermoplastic polymer. In the cross-sectional shape of the conjugated fiber, the ratio of the maximum length (major axis) in the cross section/minimum length (minor axis) in the cross section is within the range of >(1/1) to ≤(5/1) and the core component has a cross-sectional shape having 2-8 sharp projections. The minimum thickness Vi of the non-conductive component formed with the outer peripheral part of the sheath component and the outer peripheral part of the core component is 0.5-20 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention has excellent durability against repeated use, and when used in an image forming apparatus such as an electrophotographic copying machine or printer, the fiber density of the conductive fiber tip at the brush end is substantially reduced. The present invention relates to a conductive composite fiber that can be increased in number and has few spots.

  Thermoplastic resins such as polyethylene, polyamide, and polyester are used in many applications as fiber products, but they have the drawback of being easily charged due to their poor antistatic properties, and thus many studies on conductive fibers have been made. It was.

  As one of the methods, there is a method of coating the surface of the fiber with a conductive substance. The conductive fiber thus obtained has good initial conductive performance, but wear resistance when worn, and further resistance to resistance. Since the washing and chemical resistance are insufficient, there is a problem that it becomes a source of dust generation when used in dust-proof clothing.

  Also, a method in which a conductive material powder is dispersed in a thermoplastic resin to form a core component, and a fiber-forming thermoplastic resin is coated as a sheath component to form a core-sheath composite fiber, followed by electric discharge machining at a high voltage. (For example, JP-A-63-219624). In the composite fiber, when the core component is not covered with the sheath component, the conductive material falls off during use, causing trouble such as a decrease in function.

  On the other hand, even if the core component is covered with the sheath component, the following problems, that is, the electrical conductivity between the core portions at both ends of the fiber is good, but the sheath component is electrically an insulator. There was a problem that the electrical resistance value of the fiber surface was extremely high and the conductivity was poor.

Further, in the image forming apparatus, for example, a conductive brush including the conductive fiber is used as a current-carrying medium to the charging drum or the discharging drum, and in this case, the tip of the brush may make more uniform contact. Although extremely important, no method has yet been found to achieve this. Also, when these conductive fibers are used for cleaning brushes provided to remove residual toner on the photoconductor, the residual toner remains because the brush contact with the photoconductor is not uniform. There was a problem of getting worse.
JP-A-63-219624

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, have excellent durability against repeated use, and use a brush when used in an image forming apparatus such as an electrophotographic copying machine or printer. An object of the present invention is to provide a conductive composite fiber that can substantially increase the fiber density at the tip of the conductive fiber at the end and has few spots.

  As a result of diligent investigations to achieve the above object, the present inventors have found that a core-sheath type in which a powder of a conductive material is dispersed in a thermoplastic resin as a core component and a fiber-forming thermoplastic resin is coated as a sheath component When the cross-sectional shape of the composite fiber is made non-circular and the efficiency of electric discharge machining is increased, it has been found that a desired conductive composite fiber can be obtained, and the present invention has been achieved.

  Thus, according to the present invention, the core component made of a thermoplastic polymer containing conductive fine particles is a conductive conjugate fiber coated with a non-conductive sheath component made of a thermoplastic polymer, and the conjugate fiber The ratio of the longest length in the cross section (major axis) / the minimum length in the cross section (short axis) is in the range of more than 1/1 and less than 5/1, and the core component is sharp with 2-8 Discharge characterized by having a cross-sectional shape having various protrusions and a minimum thickness Vi of a non-conductive component formed by a sheath component outer peripheral portion and a core component outer peripheral portion being 0.5 to 20 μm A processed conductive conjugate fiber is provided.

  According to the present invention, it has excellent durability against repeated use, and when used in a brush, it is possible to substantially increase the fiber density at its end, and a conductive composite fiber with few spots is obtained. Therefore, it can be suitably used for an image forming apparatus such as an electrophotographic copying machine or a printer.

  The core component of the conductive fiber of the present invention contains a conductive substance, and as the conductive substance, known substances such as conductive carbon black and conductive metal compounds can be used. Examples of conductive carbon black include oil furnace type “Ketjen Black EC” (manufactured by Japan EC), “Conductex 975”, “Conductex SC” (Colombian) and acetylene type “DENKA”. In addition to known conductive carbon black such as “Black” (manufactured by Denka), thermal black, channel black, ketjen black and the like can be used.

  On the other hand, as the conductive metal compound, metal particles, metal oxide or metal compound particles, or particles having these films can be used. Examples of the metal particles include silver, nickel, copper, iron, aluminum, and alloys thereof. Particles having a metal oxide or metal oxide film include tin oxide obtained by mixing and firing antimony oxide as a second component, zinc oxide containing aluminum oxide as a second component, and conductivity such as tin oxide and zinc oxide. Inorganic particles such as titanium oxide, magnesium oxide, silicon oxide, and aluminum oxide having an oxide film can be used. As the metal oxide, copper iodide, copper sulfide, zinc sulfide, cadmium sulfide, or the like can be used. Among these, stannic oxide and zinc oxide excellent in whiteness are preferably exemplified. The stannic oxide here includes stannic oxide containing a small amount of an antimony compound, and conductive metal composites in which the surface of titanium oxide particles is coated with stannic oxide. Zinc oxide also includes zinc oxide containing a small amount of aluminum oxide, lithium oxide, indium oxide, and the like. These conductive materials are usually used as fine powder dispersed in a matrix polymer.

  The blending ratio of these conductive substances varies depending on the kind of particles, the particle diameter, the conductivity, and the properties and crystallinity of the matrix polymer, but is usually preferably 40 to 80 wt%. If the blending amount is too small, the conductivity tends to decrease, and if it is too large, uniform dispersion in the polymer becomes difficult, and the yarn forming property tends to decrease.

  The thermoplastic polymer constituting the core component can be arbitrarily selected, and examples thereof include polymers such as polyamide, polyester, polyolefin, and polyether. Nylon 6, polyethylene terephthalate, polybutylene terephthalate, polyethylene or a copolymer thereof is preferable.

  As the thermoplastic polymer used as the sheath component, polyester, polyolefin, or a copolymer thereof is preferable, and polyethylene terephthalate is particularly preferable. In addition, organic antistatics such as polyalkylene glycols, block polyether esters and block polyether amides containing surfactants such as organic sulfonic acids or their metal salts, organic phosphoric acids or their metal salts in the core-sheath component polymer. The sex component may be dispersed in an amount of 5% or less.

  In the conjugate fiber of the present invention, the cross-sectional shape has a ratio of the longest length in the cross section (long axis) / the minimum length in the cross section (short axis) of 1/1 as illustrated in FIG. It is an atypical cross section in the range of more than 5/1.

  That is, the composite fiber of the present invention has an atypical cross section to bring the conductive portion closer to the surface layer, improve the cross-sectional conductivity and surface conductivity of the fiber, and has excellent durability for repeated use. When used in a brush, the fiber density at the end can be substantially increased.

  In addition, the shape of the core component of the conductive fiber of the present invention in the fiber cross section is not particularly limited, but 2 to 8 sharp points from the viewpoint of efficiency and stability during electric discharge machining between high-voltage electrodes. The cross-sectional shape must have a protrusion. Here, the sharp protrusion means a cross-sectional shape having a convex shape or a protrusion-shaped convex portion as exemplified in FIGS.

  Furthermore, in the present invention, the minimum thickness Vi of the nonconductive component formed by the core component outer peripheral portion and the sheath component outer peripheral portion formed by the sharp protrusions needs to be 0.5 to 20 μm.

  When the minimum thickness Vi of the non-conductive component is smaller than 0.5 μm, the core and the sheath are peeled off, or a portion where the sheath component does not cover the core component is generated and the conductive material is dropped, and the conductive performance This causes problems such as lowering or causing contamination. On the other hand, when the minimum thickness Vi of the non-conductive component is larger than 20 μm, the applied voltage at the time of the discharge process described later must be extremely increased, so that the sheath component is easily damaged and the discharge process is performed. Problems such as thread breakage tend to occur.

  In the composite fiber cross section, the area occupied by the core component (A) is preferably 5 to 30%. When the area is smaller than 5%, the antistatic property may be inferior. On the other hand, when the area exceeds 30%, the mechanical properties, dust resistance, and durability of the fiber may be deteriorated.

  In the present invention, the composite fiber in which the sheath component is composed of the fiber-forming polymer has a high surface electric resistance value and poor conductivity even if the core component containing the conductive material has conductivity. Therefore, it still has the property of being easily charged.

For this reason, the conductive fiber of the present invention needs to be subjected to a discharge treatment as described later. Thus, the electrical resistance value of the fiber surface is 10 ¹¹ Ω / cm or less,
And what has the outstanding electroconductive performance that ratio of the internal electrical resistance value (measured in ohm / cm) between fiber cross sections and surface electrical resistance value (ohm / cm) is 10 < ³ > or less is obtained.

Usually, the surface resistance value of a fiber made of a fiber-forming polymer is very high, for example, on the order of 10 ¹³ Ω / cm, and even if the internal resistance value between cross sections is as low as 10 ⁷ Ω / cm order, the ratio of the internal electric resistance between the resistance value and the cross section is in this case ¹⁰⁶ degrees and larger, the effect of the most conductive not expressed on the surface of the fiber.

On the other hand, even if the conductive fiber of the present invention is composed of a fiber-forming polymer, the electrical resistance value on the surface is as low as 10 ¹¹ Ω / cm or less as described above, and the conductive performance is the length of the fiber. It is stable in direction.

  Examples of the discharge treatment method include an energization method in which a core-sheath composite fiber having the above-described configuration is brought into contact with a high-voltage electrode to apply a high voltage, a corona discharge having a different discharge shape, a fireworks discharge, a glow discharge, an arc discharge, and the like. It can be processed by a voltage discharge treatment method. As the applied voltage, a high voltage exceeding 1 kV and a voltage up to 100 kV can be used, and a voltage within a range of 2 to 50 kV is preferably exemplified. The polarity of the electrode may be positive, negative (direct current), or alternating current. The distance between the electrodes can be in the range of 0 to 10 cm, and can be arbitrarily determined depending on the discharge mode, processing speed, and target conductivity. Further, it is optimally exemplified that the core component containing conductive carbon black is one electrode and the other electrode is provided separately, a high voltage is applied to both electrodes, and discharge treatment is performed under the high voltage electrode. Furthermore, as in the present invention, the shape of the core needs to have a sharp and sharp projecting portion that can be easily subjected to discharge treatment. But even if it is the method of applying a high voltage to two poles provided separately and performing a discharge treatment, the effect of the present invention is not spoiled.

Further, such electric discharge treatment can be performed in the state of yarn, or in the state of a fabric such as a woven or knitted fabric or a nonwoven fabric. Further, in the case of yarn, it may be applied to drawn yarn or undrawn yarn. By such discharge treatment, not only the surface electrical resistance value can be reduced to the order of 10 ¹¹ Ω / cm or less, but also the ratio of the surface electrical resistance value to the cross-sectional electrical resistance value can be set to 10 ³ or less. The ratio can be 10 ² or less, particularly 10 or less when used under severe conditions.

  Hereinafter, an example is given and the composition and effect of the present invention are explained in detail. In addition, the physical property in an Example is measured with the following method.

(B) Cross section internal electrical resistance value Ag doutite (a conductive resin paint containing silver particles, Fujikura Kogyo Co., Ltd.) on both cross sections of the fiber having both ends cut in the cross section direction so that the length in the fiber axis direction is 2.0 cm. Sample is applied on an electrically insulating polyethylene terephthalate film under a condition of temperature and humidity of 20 ° C. × 30% RH, and a DC voltage of 1 kV is applied between the two cross sections. The electric resistance value Ω / cm is calculated according to Ohm's law.

(B) Surface electrical resistance value Using a sample in which the Ag doutite is adhered to the surface (fiber side surface) near both ends of the fiber cut to a length of about 2.0 cm in the fiber axis direction, the sample is electrically insulated. On a conductive polyethylene terephthalate film, a DC voltage of 1 kV was applied between the Ag doughites under the conditions of temperature and humidity of 20 ° C. × 30% RH to obtain a current value flowing between the Ag doughites, and between the Ag doutites The distance is measured, and the electrical resistance value Ω / cm is calculated according to Ohm's law.

(C) Washing durability test Using 84 dtex / 36 filament polyethylene terephthalate drawn yarn as the warp and 110 dtex / 48 filament polyethylene terephthalate false twisted yarn as the weft, conductive composite with 5/2 intervals on 3/2 reverse twill structure A woven fabric with fibers was obtained.
Next, the fabric was washed at 60 ° C. for 36 minutes, then rinsed for 30 minutes, and dried using a tumbler at 60 ° C. for 30 minutes.

[Example 1]
A conductive resin composition comprising 30 parts by weight of conductive carbon black and 70 parts by weight of polyethylene terephthalate is used as a core component, and polyethylene terephthalate copolymerized with 7% by weight of polyethylene glycol having a number average molecular weight of 1000 is used as a sheath component. A core-sheath type composite fiber having a cross-sectional shape with a major axis / minor axis ratio of 2.2 shown in (a) of 1 was spun by melt spinning, and then stretched 3.1 times to 28 dtex / 5. A filament multifilament yarn was obtained.
Next, the fiber was brought into contact with a high voltage electrode, a high voltage of 50 kV was applied, and a high voltage discharge treatment was performed at a yarn speed of 300 m / min.

The surface electrical resistance value of the obtained conductive conjugate fiber was as good as 8.3 × 10 ⁶ Ω / cm, and the internal electrical resistance value between the cross sections was 7.2 × 10 ⁶ Ω / cm. Further, when the conductive conjugate fiber was subjected to a washing durability test for 150 times, the conductive conjugate fiber was not cracked, the surface electrical resistance value was 8.9 × 10 ⁶ Ω / cm, and the internal electric power between the cross sections The resistance value was 7.6 × 10 ⁶ Ω / cm and was sufficiently satisfactory with no deterioration.

[Comparative Example 1]
In Example 1, it implemented like Example 1 except having set ratio of the major axis / minor axis to 1.
The obtained electrically conductive conjugate fiber had good surface electrical resistance value of 7.6 × 10 ⁶ Ω / cm and inter-section internal electrical resistance value of 6.8 × 10 ⁶ Ω / cm. When the fiber was subjected to a washing durability test for 150 times, cracks in the conductive composite fiber occurred in some portions, and there was a portion where the internal electrical resistance value between cross sections decreased to the order of 10 ⁷ Ω / cm.

  According to the present invention, it has excellent durability against repeated use, and when used in a brush, it is possible to substantially increase the fiber density at its end, and a conductive composite fiber with few spots is obtained. Therefore, it can be suitably used for an image forming apparatus such as an electrophotographic copying machine or a printer.

Sectional drawing for demonstrating the example of the fiber cross-sectional shape of the electroconductive composite fiber of this invention.

Explanation of symbols

  Vi Minimum thickness of non-conductive component

Claims (3)

  A core component made of a thermoplastic polymer containing conductive fine particles is a conductive composite fiber covered with a non-conductive sheath component made of a thermoplastic polymer, and the cross-sectional shape of the composite fiber is The ratio of the longest length (major axis) / minimum length (minor axis) in the cross section is in the range of more than 1/1 and less than 5/1, and a cross-sectional shape having sharp protrusions with a core component of 2-8. And having a minimum thickness Vi of 0.5 to 20 μm of the non-conductive component formed by the outer periphery of the sheath component and the outer periphery of the core component. fiber.   The conductive conjugate fiber according to claim 1, wherein the specific resistivity on the fiber surface is 1 to 104 times the specific resistivity on the fiber cross section.   A conductive brush for an electrophotographic image forming apparatus, comprising the conductive conjugate fiber according to claim 1.

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