JPH0357967B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical Field The present invention relates to conductive fibers, particularly white conductive core-sheath type composite fibers having excellent bending durability. (b) Prior Art Thermoplastic polymers such as polyethylene, polyamide, and polyester are used in many applications as fibers, films, and other molded products, but they have the disadvantage of being easily charged due to poor antistatic properties. For example, clothing made of polyethylene terephthalate fibers tends to cling to the body when worn due to its electrostatic properties, easily gets dirty by attracting dust floating in the air, and even when walking on carpets made of such fibers. There are many problems such as being susceptible to discharge shock when touching the door handle. To address such problems, many proposals regarding conductive fibers have been made. The first method is to knead conductive carbon particles into fibers, or conductive carbon powder dispersed in thermoplastic polymer to form a core, and a fiber-forming polymer to form a sheath of composite fibers. There is a way to do it. However, such conductive fibers have the drawback that, because the conductive carbon is black, they are significantly colored and cannot be used in fields where aesthetics are required, and their uses are extremely limited. A second method is to provide a conductive material layer on the fiber surface. More specifically, it is a method of coating chemically plated metal-plated fibers, metal powder, or conductive powder such as carbon black on the fiber surface. Although these conductive fibers do have good initial conductivity, not only do the conductive agent layer on the surface peel off due to wear and washing, resulting in a significant decrease in conductivity, but they also have poor chemical resistance and are not dustproof. It becomes a source of dust in clothing, etc., and furthermore, coloring due to conductive substances is unavoidable. As a method for solving the above-mentioned drawbacks, a method of obtaining conductive fibers using a colorless or light-colored conductive metal compound has recently been proposed. (c) Problems to be solved However, conductive fibers manufactured based on these proposals lose their conductivity due to bending and abrasion several hundred times, and the expected antistatic effect cannot be achieved even after wearing for a short time. As a result, the above-mentioned clinging of clothes and adhesion of dust occur. (d) Means for Solving the Problem The inventors of the present invention have conducted extensive research in an effort to provide conductive fibers that do not have these drawbacks, and as a result, the core of conductive core-sheath type composite fibers contains a low-temperature fluid, highly crystalline polymer. Although conductive metal oxides are present in the combined matrix, conductivity cannot be observed if they are simply uniformly dispersed. The heat received during spinning, drawing, heat treatment, etc. causes a highly crystallized orientation phenomenon in the cold-flowing polymer, and as a result, the conductive metal oxide is thrown out of the cold-flowing polymer and phased out. As a result of the separation, the metal oxides aggregate and rearrange, forming a chain structure that develops a conductive function for the first time. However, when the fibers obtained in this manner are subjected to bending and abrasion, the electrical resistance value increases and the conductivity becomes poor. The present inventors conducted various analyzes on this phenomenon and found that it is caused by low interfacial adhesion between the highly crystallized low-temperature fluid polymer layer in the core and the polymer layer in the sheath. That is, it has been found that if the interfacial adhesion is poor, the core and sheath easily peel off during bending wear, and the chain structure of the metal oxide present in the core is destroyed. As a result of extensive research into technology to improve the interfacial adhesion between the core and sheath, we have found that flexural durability is improved by adding an organic acid to a mixed system of metal oxide and low-temperature fluid high-crystalline polymer. It was very successful. That is, by blending an organic acid in the core, when the low-temperature fluid polymer undergoes high crystal orientation, not only the conductive metal compound but also the organic acid is phase separated, and the core system is A bleed-out phenomenon occurs in which the released organic acid diffuses and permeates into the inner layer of the sheath. the result,
The interfacial adhesion between the core layer and the inner surface layer of the sheath has been dramatically improved, and the electrical resistance value of the conductive fiber after bending abrasion is 10 ⁹
The inventors have discovered that it is possible to obtain a fabric that is maintained at less than Ω/cm and is free from clinging and dust adhesion, and has thus arrived at the present invention. That is, the present invention provides a composite fiber comprising a sheath made of a fiber-forming polymer and a core made of a low-temperature fluid highly crystalline polymer in which conductive metal oxide fine powder is dispersed, The conductive fiber is made by diffusing and permeating an organic acid blended into the core so that the organic acid is present in the inner layer in contact with the core. The conductive fiber of the present invention is produced by blending an organic acid into a conductive composition consisting of a low-temperature fluid highly crystalline polymer and a finely powdered conductive metal oxide, and forming a core of the conductive composition. The fiber-forming polymer is melt-spun to form a composite fiber so that the fiber-forming polymer constitutes the sheath, and if necessary, it is produced by stretching and heat treatment. By blending an organic acid into the core component in this way, spinning and
As shown in Figure 1, organic acids are absorbed by the heat received during processes such as stretching and heat treatment, as well as during processes such as scouring and dyeing, which are carried out after fabrication. and come into existence. The presence of organic acids in the inner layer of the sheath can be easily identified in an electron micrograph of the fiber cross section magnified approximately 2000 times. The polymer constituting the sheath portion of the conductive fiber of the present invention may be a thermoplastic polymer having fiber-forming ability. For example, polyethylene terephthalate,
Examples include nylon-6, nylon-6,6, polypropylene, and the like. The low-temperature flowable highly crystalline polymer may be any thermoplastic polymer that has a flow temperature lower than the flow temperature of the fiber-forming polymer constituting the sheath and is highly crystalline, and specifically, polyethylene. ,polypropylene,
The main targets are polystyrene, polybutidiene, polyisoprene, Niton-6, nylon-6,6, polyethylene terephthalate, polypylene terephthalate, etc., but some of these may be replaced with copolymerized components, and low-temperature Depending on the purpose, materials other than those listed above may be used as long as they are fluid and highly crystalline.
It may be a mixture of more than one species. As the conductive metal oxide in the present invention, stannic oxide and zinc oxide are particularly preferred. The stannic oxide mentioned here also includes stannic oxide containing a small amount of antimony compound, and conductive metal composites obtained by coating the surface of titanium oxide particles with stannic oxide containing a small amount of antimony compound. It will be done. Zinc oxide also includes conductive zinc oxide in which small amounts of aluminum oxide, lithium oxide, indium oxide, etc. are dissolved. These are usually treated as fine powders. The organic acid to be blended in advance into the low-temperature-fluid highly crystalline polymer of the core is preferably an organic carboxylic acid or an organic sulfonic acid having 4 or more carbon atoms, particularly an organic acid having 24 carbon atoms.
Preferably. Organic residues that bind to carboxyl groups and sulfonic acid groups include alkyl groups,
Those having an alkylene group, aryl group, alkylaryl group, or aralkyl group are preferable, and as long as these groups are groups other than carboxyl or sulfonic acid groups, they may have any substituent. . Specific examples of such organic carboxylic acids include n-caproic acid, n-heptanoic acid, benzoic acid, n-caprylic acid, phenyl acid, toluic acid, n-nonanoic acid, and stearic acid. Specific examples of organic sulfonic acids include n-pentanesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, and the like. These organic carboxylic acids,
Organic sulfonic acids may be used alone or in appropriate combinations. In order to incorporate the above organic acid into a low-temperature fluid polymer, the thermal properties of the organic acids such as organic carboxylic acids and organic sulfonic acids should be taken into consideration.(1) Low-temperature fluid polymer, conductive metal oxide, and organic acid (2) A method in which a conductive metal oxide is previously treated with an organic acid and then melt-mixed with a low-temperature fluid polymer may be selected as appropriate. For example, it is undesirable to attempt to obtain a conductive composition by directly melt-mixing a low-boiling organic acid such as n-heptanoic acid with a conductive metal oxide into a relatively high-melting low-temperature fluid polymer. In such a case, it is preferable to treat the conductive metal oxide with n-heptanoic acid in advance and then melt-mix it with the low-temperature fluid polymer. On the other hand, even when n-heptanoic acid is used as an organic acid, if the low-temperature fluid polymer used has a relatively melting point, such as polyethylene, the conductive metal oxide and n-heptanoic acid can be directly added to polyethylene. There is no problem in melting and mixing. As a method of pre-treating a conductive metal oxide with an organic acid, the desired conductive metal oxide powder is inhaled and dispersed in a solution obtained by dissolving an organic acid in an organic solvent, stirred for several hours, and then treated with an organic acid. A very simple method is used in which the solvent and powder are separated by filtration. When pre-treating a conductive metal oxide with an organic acid, it is sufficient to simply add and disperse the conductive metal oxide in an organic solvent solution of an organic acid and stir it at room temperature for several hours as described above, but it is also possible to treat the conductive metal oxide in a shorter time. For this purpose, heating and stirring is effective. The organic solvent used here is not particularly limited as long as it dissolves the organic carboxylic acid and/or organic sulfonic acid compound that is the organic acid. Furthermore, when a large amount of organic acid is used in this treatment, the excess organic acid may be washed and removed after filtration. The amount of organic acid used is preferably kept to a necessary and sufficient minimum amount, and is generally preferably in the range of 0.1 to 3 parts by weight per 100 parts by weight of the conductive metal oxide powder. If the amount of the organic acid is less than 0.1 part by weight, the interfacial adhesion between the conductive layer core and sheath portion will not be sufficiently improved, and a sufficient effect of improving bending resistance will not be obtained. If the amount exceeds 3 parts by weight, it is not preferable because it becomes difficult to filter the dispersion into an organic solvent after treatment, or it becomes necessary to wash and remove excess organic acid after filtration.
Furthermore, when an organic acid and a conductive metal oxide are directly melt-mixed with a low-temperature fluid polymer, it is not preferable to add an excessive amount of the organic acid because this will impair the physical properties of the low-temperature fluid polymer. (f) Effects of the Invention The conductive fiber of the present invention has significantly improved bending abrasion resistance, and can be extremely effectively applied to any form such as yarn or fabric. Further, the white conductive fiber of the present invention showed no change in electrical resistance even after post-treatment such as washing, cleaning, and steaming. (g) Examples The present invention will be specifically explained below using examples. Measurement method (1) Flexural abrasion test method: 3 filaments of conductive fibers were sewn onto a 100% polyester plain weave at 0.5cm intervals, set in a universal abrasion tester, and subjected to a tensile load of 220g.
Bending and abrasion were repeated 0 to 1200 times without presser load (20°C x 50% RH). (2) Electrical resistance value (Rs) measurement method Ag doutite (conductive resin paint, manufactured by Fujikura Industries) was attached to the cross section of a conductive fiber whose ends were precisely cut to 2.0 cm in the cross-sectional direction on an insulating polyethylene terephthalate film. ,20℃×30%
Under RH, a DC voltage of 1 KV was applied and the electrical resistance value was measured (unit: Ω/cm). Example 1 1 kg of conductive powder with an average particle size of 0.2μ and a non-resistance of 10Ω・cm, which is made by coating the surface of titanium oxide fine particles with conductive tin oxide containing a small amount of antimony trioxide.
3 toluene was added to 20 g of stearic acid, and the mixture was heated under reflux for 5 hours with vigorous stirring. After the mixture was allowed to stand overnight, most of the toluene was removed by decantation, and the powder was filtered, thoroughly washed with toluene, and dried. 250 parts by weight of the powder thus obtained, liquid paraffin
20 parts by weight and melt index 75 (JIS K6760
-1971) was placed in a kneader, heated to 175°C, and mixed for 5 hours. The specific resistance of the obtained conductive composition was 1×10 ² Ω・
It was cm. By melt spinning, a core-sheath type composite fiber (core-sheath ratio = 1/6) having this conductive composition as a core and polyethylene terephthalate as a sheath was produced.
A conductive multifilament of 100 denier and 12 single filaments was obtained by stretching twice. Table 1 shows the results of investigating the relationship between the number of times of bending and abrasion of this conductive composite fiber and the electrical resistance value. Also,
Figure 1 shows a cross-sectional photograph magnified 2000 times using a scanning electron microscope. From the photograph, it can be seen that stearic acid, an organic acid, bleeds out from the inner layer of the sheath and forms a third layer. It is thought that this third layer improves the interfacial adhesion between the sheath and the core and improves the bending abrasion durability of the conductive material. Comparative Example A conductive composite fiber having a polyethylene terephthalate sheath was obtained in the same manner as in Example 1, except that zinc stearate was used instead of the stearic acid used in Example 1. This fiber was subjected to a bending test using the same method as in Example 1 to examine the relationship between the number of bends and the electrical resistance value, and the results shown in Table 1 were obtained. In the cross-sectional scanning electron micrograph, the third layer due to the bleed-out phenomenon as shown in Figure 1 is not observed, indicating that the interfacial adhesion between the core and sheath is poor and peeling occurs, resulting in a bend in the electrical resistance value. It has poor abrasion durability and is far below the practical level of conductivity.

[Table] Example 2 250 parts by weight of conductive metal powder made of stannic oxide containing a small amount of antimony trioxide and 50 parts by weight of polypropylene with a melt flow index of 1.0 (ASTM D1238-65T) were placed in a kneader and heated to 200°C. at 30
After melt-mixing for a minute, 2 parts by weight of dodecylbenzenesulfonic acid, 50 parts by weight of liquid paraffin, and 0.5 parts by weight of Irganox 1010 were added and kneaded for a further 4 hours. The specific resistance of the conductive composition thus obtained was 6.0×10 ²
It was Ω・cm. By melt-spinning, a core-sheath type composite fiber (core-sheath ratio = 1/5) with this conductive composition as a core and polyethylene terephthalate as a sheath was made, and it was drawn 4 times to produce a conductive fiber with a 100-denier single yarn count of 12. Obtained multifilament. This conductive composite fiber was subjected to dry heat treatment at 160° C. for 1 minute, and the relationship between the number of bending abrasion times and the electrical resistance value was investigated. The results are shown in Table 2.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a 2000x enlarged photograph of the cross section of the conductive fiber of the present invention taken with a scanning electron microscope.

Claims (1)

[Scope of Claims] 1 A composite fiber composed of a sheath made of a fiber-forming polymer and a core made of a low-temperature fluid highly crystalline polymer in which conductive metal oxide fine powder is dispersed. A conductive fiber characterized in that an organic acid blended in the core is diffused and permeated so that the organic acid is present in the inner layer of the sheath that contacts the core. 2. The conductive fiber according to claim 1, wherein the organic acid is at least one organic acid selected from organic carboxylic acids and organic sulfonic acids having 4 or more carbon atoms.