CA1187666A - Conductive fibers - Google Patents

Abstract

Abstract of the Disclosure Conductive fibers having excellent antistatic property, whiteness and stability are produced by forming a conductive layer consisting mainly of conductive metal oxide particles and a binder of polymer on surface of the fibers by after-processing.

Description

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The present invention relates to condwctive fibers, particularly fibers obtained by forming a conduc-tive layer on the surface of fibers with after-processing.
Conductive fibers wherein a conductive layer containing carbon black or metal particles has been formed on the surface of fibers (for example, film-like) by after-processing, have been well-known. These con-ductive fibers have been used for providing antis~atic property to fibrous articles by mixing these fibers with other fibers. These after-processed conductive fibers are excellent in the antistatic property because of presence of the conductive layer on the surface of fibers and the conductivity of the fibers can be improved by increasing the mixing ratio of the conductive particles, and furthermore it is possible to obtain the conductive fibers having excellent strength by selecting fibers having high mechanical property for a base fiber ~support) which is a component for retaining the strength.
In particular, the fibers using carbon black as the conductive particles are stable in the properties and easy in the production, so that the practicability is the highest and these fi'bers are 'broadly used.
However, the conductive fibers in which the conductive layer containing carbon 'black is present on the surface of fibers, are colored black and when such fibers are mi~ed in white or light color articles, the appearance of the products is deteriorated, so that such products almost cannot be practically used. Metal particles in most case do not show such a deep coloration as in carbon black b-ut in many cases the fibrous articles are .' ~

colorecl gray o-r black and oxidation proceeds during use and the color and the antistatic proper~y are deteriorated.
In general, metal partic]es are expensive and are poor in the practicability.
The inventors have made diligent s~udies in order to improve ~he prior drawbacks of conductive fibers and found that conductive fibers having excellent antistatic property, whiteness and stability can be obtained by using conductive metal oxide particles and accomplished the present invention.
The conductive fibers are obtained by forming the conductive layer consisting mainly of conductive metal oxide particles and a binding polymer on the s-urface of fibers by after-processing.
The invention will now be described in detail with reference to the accompanying drawings, wherein:
Figs. 1-4 are cross-sectional views of embodi-ments of conductive layer coa-ted fibers according to the present invention respectively; and Fig. 5 shows the relation of the mixing ratio of the conductive metal oxide particles to the binder polymer~ to the specific resistance.
The conductive metal oxide particles in the present invention are fine particles having conductivity based on conductive metal oxides and are concretely particles consisting mainly (not less than 50% by weight) of a conductive metal oxide and particles coated with a conductive metal oxide.
A major part of metal oxides are semi-condwctor and do not show the enough conductivity to satisfy the ~8~6 object of the present invention. ~owever, the conductivity is increased, for example, by adding a small amount (not more than 50%, particularly not more than 25%) of a proper secondary component (impurity) to the metal oxide, whereby ones having the sufficient conductivity to satisfy ~he object of the present invention can be obtained.
For example, a small amount of powdery oxide, hydroxide or inorganic acid salt of aluminum, gallium, indium, gelmanium, tin and the like is added to powdery zinc oxide and the resulting mixture is fired under a reducing atmosphere and the like to prepare conductive zinc oxide powder. Similarly, conductive ti.n oxide powder can be obtained by adding a small amount of antimony oxide to tin oxide powder and firing the resulting mixture. It is presumed that these added secondary components are diffused and permeated by heating to form a solid solution of a metal oxide (main component) and a foreign metal oxide (secondary component), by which the conductivity is developed. Furthermore, there is a case where metal oxide is partially reduced and the formed metal element has the function (improvement of conductivity) of the secondary component. Even in the other secondary component than the above described substances, if it can provide conductive particles which can increase the conductivity and do not considerably deteriorate whiteness and are stable to water, heat, light and chemical agents generally used for fibers, such a component can be used for the object of the present invention.
As the conductive metal oxides, the above 3Q described zinc oxide or tin oxide is e~cellent in the ~g7~

conductivity, whiteness and stability and is rnost preferable but even other metal oxides, if these oxides have the satisfactory conductivity, whiteness and stability, can be used for the object of the present S invention.
The conductivity of the conductive metal oxide particles is preferred to be not rnore than 104 n cm (order), particularly not more than 102 Q cm, most preferably not more than 101 Q-cm in the specific resistance in the powdery state. In fact, the particles having 102 Q cm-10~2 Q~cm are obtained and can be suitably applied to the object of the present invention. (The particles having the more excellent conductivity are more preferable.) The specific resistance (volume resistivity~
is measured by charging 5 gr of a sample into a cylinder of an insulator having a diameter of 1 cm and applying 200 kg of pressure to the cylinder from the ~Ipper portion by means of a piston and applying a direct current voltage (for example, 0.001-1,000 V, current of less than 1 ~).
The conductive metal oxide particles are preferred to be ones having high whiteness, that is having reflectivity in powder being not less than 40%, preferably not less than 50%, more particularly not less than 60%. T~le above describecl conductive zinc oxide can provide the reflectivity of not less than 60%, particularly not less than ~0%, and conductive tin oxide can provide the reflectivity of not less than 50%, particularly not less than 60%. Titanium oxide pa,rticles coated with conductive zinc oxide or conductive tin oxide film can provide reflectivity of 60-90%. While, the reflectivity 7!6~6 of carbon black particles is about 10% and the reflectivity of metallic iron fine particles ~average grain siæe 0 05 ~m) is about 20%.
The reflectivity of the particles can be measured by means of a reflection photometer by estimating the reflectivity of magnesium oxide powder to be 100%.
The con~uctive metal o~ide particles must be small in the grain size. It is not impossible to use the particles having an average grain size of 1-2 ~m but in general, the average grain size of less than 1 ~m, particularly less than 0.5 ~m, more pre~erably less than 0.3 ~m is used. As the grain size is smaller, a higher conductivit~ is shown in a lower mixing ratio, when a binder polymer is mixed.
In the present invention, the conductive layer is formed on the surface of ~ibers by after-processing.
The shape and arrangement of the conductive layer are opti.onal but may be selected by taking the conductivity and antistatic proper-ty, abrasion resistance and the like into consideration. Figs. 1-4 are embodiments of the cross section of the fibers of the present invention and in these drawings, a numeral 1 shows the conductive layer and a numeral 2 shows a support (base fiber). Fig. 1 is an embodiment wherein the conductive layer forms a coating film and surrounds completely the surface of the support and Fig. 2 is an embodiment wherein the conduct:ive layer covers a part of the surface of the support. The cross section of the support may be circular or non-circular.
Fig. 3 shows an embodiment wherein a non-circular cross-sectional support having recess po-rtions is used and the 7~

conductive layers are formed at the recess portions and this embodiment has the characteristic that the conductive layers can be prevented from deterioration and separation due to friction. Fig. 4 shows an embodiment wherein a plurality of fibers (supports) are bonded by a conductive layer. Other than the above described embodiments, there are a large number of embodiments in the bonding and arrangemen~ of the support and the conductive layer.
As the fibers applicable to the present inven-tion, every fibers can be used. Among them, polyamides, polyesters, polyolefins, polyvinyls and other synthetic fibers are generally high in the strength and preferable as the material for fibers of the present invention.
In general~ the fibers have been spun and then if necessary, subjected to drawing and heat treatment, after which the conductive layer is formed on the surface of fibers.
The conductive layer consists mainly of a con-ductive metal oxide and a polymer or a starting material for polymerizing the polymer, which is a binder and if necessary, contai.ns a stabilizer, an antioxidant, a dispersant for particles, a pigment and other additives.
rrhe formation of the conductive layer may be carried out by the following means. That is, the above described mixture of conductive layer-forming components is melted and the melt i5 coated or applied on the base fibers and then cooled and solidified (melting process). A soluti.on of the mixt-ure of the conductive layer-forming components in a proper solvent is coated or applied on the base fibers and then the solvent is removed to soliclify the conductive layer~forming components (solvent process).

Alternatively, the surface of the base fibers is softened by heating or a solvent and then the conductive particles are contacted and stuck (or applied with electrostatic force and the like) on -the surface of the base fibers, after which the softened sur~ace is cooled or the solvent is removed ~o solidify the conductive layer-forming components. In addition to these processes, any processes wherein the conductive layer consisting o~ the conductive particles and a binder can be formed on the surface of the fibers (possibly continuously in the longitudinal direction of the fiber), may be applied to the production of the fibers of the present invention.
The binders for forming the conductive layer are polymers, and polyamides, polyesters, polyethers, polyolefins, polyvinyl polymers, polyurethanes, polyureas, polycarbonates, any other thermoplastic polymers, epoxy series polymers, melamine series polymers, phenolformalin series poly~ers, unsaturated polyester series polymers and other thermosetting polymers, branched or cross-linked polymers may be used. From these polymers, suitable polymers may be easily selected depending upon the object in view of film-forming ability, adhesion to the base fibers, mixing ability to the conductive particles, abrasion resistance, heat resistance, chemical resistance and the like.
~he conductive layer must have the satisfactory conductivity. In general, the conductive layer must have a specific resistance of not more than about 106 n- cm, preferably not more than 104 Q-cm, most preferably not more than 102 Q-cm.

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Fig. 5 shows examples of the relation between the specific resistance and the mixing ratio of the conductive metal oxide particles ~o the polymer (binder).
The curve A is an embodiment of a mixture of conductive particles having usual grain size (0.05-0.5 ~m) and a crystalline polymer and shows the satisfactory conduc-tivity at the mixing ratio of more than about 65%.
In Fig. 5~ ~he solid line shows the zone where the mixture can be flowed by heating and the broken line shows the zone where the -flowing is difficultly attained by heating.
That i9, in the mixing ratio of more than the point P, a fluidity improving agen~, such as a solvent must be used. The curve B is an embodiment of a mixture of a polymer having a very low crystallinity and t~e conductive particles and shows that in order to obtain the satisfactory conductivity, the mixing ratio of the conductive particles must be larger than that of the case using the crystalline polymer (this is observed in many cases but is not always the absolute rule). The curve C is an embodiment of the mixture of the conductive particles having a very small grain size (0.005-0.05 ~m) (easily form a chain structure) and a crystalline polymer and shows the satisfactory conductivity at the mixing ratio of not less than 30%.
Thus, the conductivity of the mixture of the conductive particles and the binder polymer varies noticeably depending upon the size and kind of the conductive particles~ and the kind and crystallinity of the bi.nder polymer, so that it is necessary to make adjustmen-t so that the specific resistance is within the above described range by se].ecting the proper mixing ratio.

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The fibers according to the present invention have excellen~ conductivity and antistatic property and the fibers having a high whiteness (for example, a reflec-tivity of more than ~0%, particul.arly more than 60%) can be easily produced and the fibers can be used for wide scope of use and particularl~ may be satisfactorily used for light colored fibrous articles. The fibers of the present invention can provide the satisfactory antistatic property to fibrous articles by mixing a small amount (for example 0.1~10%) of natural or synthetic ibers in continuous filament or cut staple fiber form. In a higher mixing ratio (l0-100%), the articles having particularly excellent antistatic property can be obtained. The mixing with the other fibers may be carried out by blending, doubling, double twisting, mix spinning, mix knitting, mix weaving and any other well-known processes.
The following examples are given in illustration of the invention and are not intended as limitations thereof.
In the examples, all parts are by weight unless otherwise stated.
Example 1 A mixture of 100 parts of zinc oxide powder and

2 parts of aluminum oxide powder was fired at an elevated temperature in a nitrogen gas atmosphere containing carbon monoxide to obtain conductive zinc oxide fine particles Xl having an average grain size of 0.12 ~m, a reflectivity of 78% and a specific resistance of 33 Q-cm.
On the other hand, a mixtwre of 100 parts of tin oxide powder and 10 parts of antimony oxide was fired ~76~

at an elevated tempera~ure in a reducing atmoshere to obtain condutive tin oxide fine particles X2 having an average grain size of 0.10 ~m, a reflectivity of 70%
and a specific resistance of 12 Q-cm.
Furthermore, conductive fine particles X3 having an average grain size of 0.06 ~m, a reflectivity of 86% and a specific resist~nce of 12 Q cm were obtained by forming on surface of titanium oxide fine powder a fired film of about 15% by weight per titanium oxide of zinc oxide, mixing it with 2% by weight per zinc oxide of aluminum oxide fine powder (grain size: 0.01 ~m) and the-n firing them. Similarly, conductive fine particles X4 havi.ng an average grain size of 0.06 ~m, a reflectivity of 86% ancl a specific resistance of 10 Q cm were obtained by forming on surface of titanium oxide fine powder a fired film of about 12% by weight of tin oxide, mixing it with 8% by weight per tin oxide of an-timony oxide fine powder (grain size: 0.01 ~m) and then firing them.
To a resin composition of 100 parts of bisphenol-epichlorohydrin epoxy resin having an epoxy equivalent of 180-210 and 50 parts of polyamide resin having an amine value of 290-310 was added 4 parts of methaphenylene diamine and then methyl isobu-ty.l ketone was added thereto so as to adjust a solid content to 30%. To 100 parts of the resulting solution was added and mixed 75 parts of the aforementioned conductive fine particles Xl, X2, X3 or X~ to obtain a respective paste solution Pll P2, P3 or P4.
For comparison, 15 parts of conductive carbon black fine powder was mixed with 100 parts of the 30%

solution of epo~y resin-polyamide resin in rnethyl isobuty~
ketone to obtain a paste solution P5.
In each of the aforementioned paste solutions was i.mmersed a nylon monofilament o-f 15 deniers ~containing 1.7% of titanium oxide) at a yarn delivery rate of 1.5 m/min, which was then passed through a slit to adjust a thickness of a coating film, drie~ by passing through a hot-air dryer of ~0C and successivel~ passed through an air bath of 150C for 10 minutes to continuously form a condllctive coating film having an average thickness of 2.5 microns on the surface of the monofilament, whereby there were obtained conductive monofilaments Al-A5 of about 17 deniers having a sectional shape as shown in Fig. 1, respectively.
The electric resistance (Q/cm) and reflectivity (%) were measured wi,th respect to these conductive mono-filaments Al-A5 to obtain results as shown in the following Table l. As apparen-t from Table 1, the conductive mono-filaments A1-A4 according to the present invention had a good conductivity and were slightly greyish blue but substantially white, while the monofilament A5 of the comparative example was good in the conductivity but black.

~7~i~;6 Table 1 fil~ment C~ ~ r ~ r~ ~

Al X 68 1.0 x lOl Present . 1 lnvention A2 X2 67 8.0 x lO9 "
A3 X3 74 5.0 x 109 "
A4 X4 75 3.0 x lO9 ., A5carbon black 17 2.5 x 109 Comparative example . ....................... , __ Each of the conductive monofilaments A1-A5 was doubled with nylon-6 yarn (2,600 d/140 f) and thereafter subjected to a crimping treatment. Then, a tufted carpet (loop pile~ F1, F2, F3~ F4 or F5 was produced by using the conductive monofilament do~bled yarn (2617 d/141 f) in one course in every six courses and the nylon-6 crimped yarns (2600 d/140 f~ in other five courses. Similarly, a tufted carpet ~loop pile) F6 was produced as a reference example by using only nylon-6 crimped yarns (2600 d/140 f) containing no cond-uct~ve monofilament.
The resulting carpet (F1-F6) was subjected to a scouring, a dyeing (dyestuff: Nylon acid yellow C-3CS made by I.C.I., concentration of dyestuff: 0.7% owf, dyeing temperature: 100C) and a backing. Then, the appearance of the carpet (particularly color shading) was observed and also the charged voltage of human body when a rnan put on leather shoes walked (25C, 20%RH) on the carpet, was measurecl to obtain results as shown in the following Table 2.

The carpet F5 of the comparati~e example was conspicuously obse-rved in ~he color shading (warp lines) due to the black color of the conductive monofilament and was considerably poor in the commercial value, while all of the carpets Fl-F4 containing the conductive monofilament accorcling to the present invention hardly showed color shading and had an excellent antistatic property.
Moreover, the carpet F6 of the reference example had no antistatic property and when a human walked on the carpet and contacted with a metal, saisl human is applied to a violent electric shock due to spark discharge.

Table 2 Conductive Presence of Charged Carpet mono- co].or shading voltage of Remark ilament (warp llnes) (V) ~ .
F A substantially 1 700 Present 1 1 absence _ ,invention F2 A2 ~ -1,600 ,.
F3 A3 .. -2,000 "
F4 A4 ,. -1,600 ~, conspicuous Compara-tive F5 A5 presence -1,500 example F6 none absence -7,500 example Note) Charged voltage of human body is pre~ferred to be not higher than 3,000 V (absolute value), preferably not higher than 2,500 V.

Example 2 Fifteen parts of acrylonitrile-butacliene copolymer (nitrile content: 32%~ and 10 parts of modified l~B7666 phenol resin (trade ~ark: Durez 12687) were dissolved in 75 parts of methyl ethyl ketone, to which was added and mixed 80 parts of the same conductive fine particles Xl, X2, X3 or X4 as used in Example l, whereby a paste solution Q1~ Q2~ Q3 or Q4 was prepared. For comparison, a paste solution Q5 was prepared by mixing 15 parts of conductive carbon black with lO0 parts of the above-described solution.
In a bath of each of these paste solutions was immersed a polyethylene terephthalate ~hereinafter referred to as polyester) monofilament of 12 deniers at a yarn delivery rate of 3 m/min 3 which was then passed through a slit to adjust a thickness of a coating film, dried by passing through a hot-air dryer of 95C, and successively passed ~hrough an air bath of 190C for 25 seconds to contlnuously form a conductive coating film having an average thickness of 2.7 microns on the surface of the monofilament, whereby there were obtained conductive monofilaments Bl-B5 of about 14 deniers having a sectional shape as shown in Fig. 1, respectively.
The elec~ric resistance (Q/cm) and reflectivity (%) were measured with respect to these conductive mono-filaments Bl-B5 to obtain results as shown in the following Table 3. All of the conductive monofilaments (B1-B4) according to the present invention had an excellent con-ductivity and were slightly greyish blue but substantially white, while the conductive monofilament B5 of the comparative example was black.

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Table 3 . _ . ._ _ __ EilamenL particle e ivity resiscance le. "k Bl X 70 9.0 x 108 Present 1 invention B2X2 70 5.8 x 108 "
B3X3 76 1.2 x 108 "
B4X4 75 2.5 x lo8 ., B5carbon black 18 5.2 x 108 example Each of these conductive monofilaments Bl-B5 was doubled with polyester crimped yarn 12600 d/200 f~ at a tWistillg step. The resulting doubled yarn was scoured in form of cheese, dyed (dyestuff: Dianics yellow AC-E
made by Mits-ubishi Kayaku K.K., con.centration of dyestuff:
0.5% owf, dyeing assistant: Bisnol P-55 made by Ipposha, amount of dyeing assistant used: 2 g~Q, dyeing temperature:
130C), reduction cleared and dried. Then, a tufted carpet (loop pile~ Gl, G2, G3J G4 or G5 was produced by using the conductive monofilament doubled yarn (2614 d/201 f) in one course in every six courses and the polyester crimped yarns (2600 d/200 f) in other five courses.
After the resulting carpet was subjected to a backing, the appearance (particularly color shading) was observed and also the charged voltage of human body when a man put on leather shoes walked (25~C~ 20%RH) on the carpet, was measured to obtain results as shown in ~he following Table 4.
As apparent from Table 4 ~ in the carpet G5 of 7~

the comparative example, the color shading as (warp lines) was conspicuously observed due to the black color of the conductive monofilament and was considerably poor in the commercial value, while all of the c~rpets Gl-G4 containing the conductive monofilament according to the present invention hardly showed color shading (warp lines) and had an excellent antistatic property.

Table 4 .. _ , . __ ..

No Conductive color shading humangbody Remark . filament (warp lines) (V) G B substantially +1 600 Present 1 1 absence , invention lS G2 B2 ~ +1,500 I~
G3 B3 ,. ~1,300 ., G4 B4 ll +19200 ll G B conspicuous +1,500 Comparative presence example __ Note) The charged voltage of human body on a carpet consisting of 100% polyester containing no conductive monofilament was ~3,000 V.

Example 3 A mixtwre of 100 parts of tin oxide powder and 8 parts of antimony oxide was fired at an elevated temperature in a reducing atmosphere to obtain conductive ultrafine particles X5 having an average grain size of 0.012 ~m, a reflectivity of 66% and a specific resistance of 15 Q~cm.
Twenty parts of the conductive ultrafine particles 7~
X5 was thoroughly mixed with 100 parts of a 25% solution of acid dye-dyeable polyurethane (trade mark: Sunplene LQ
made by Sanyo Kasei K.K.) in dimethylformamide to prepare a transparent and viscous mixed solution Rl. Similarlyg a black paste mixed solution R2 was prepared as a compara-tive example by using conductive carbon black instead of the conductive ultrafine particle. In each of these mixed~solutions was immersed nylon-66 yarn of 20 dj3 f (containing 0.3/0 of ~itanium oxide~ at a yarn delivery rate of 1.5 m/min, which was then passed through a slit to adjust a thickness of a coating film. Thereafter, the resulting coating ilm was solidified by passing through a first bath of a 10% aqueous solution of dimethylformamide, a second bath of water of 25C and a third bath of hot water of 60C in this order and dried by passing through a hot-air dryer of 120aC to continuously form a conductive ~:
coating film having an average thickness of 3.5 microns on the surface of the yarn, whereby there were obtained conductive yarns Cl and C2 of about 22 d/3 f having a sectional shape as shown in Fig 4, respectively.
The electric resistance (Q/cm) and reflectivity (%) were measured with respect to these two conductive yarns C1 and C2 to obtain results as shown in the ollowing Table S.
The conductive yarn C2 of the comparative example was black, while the conductive yarn Cl according to the present invention was colorless and showed a good conductivity.

61~;6 Table 5 Yarn No. Conductive Reflectivity resistance Remark partlcle ( /o) (n/cm) __ ~ _ Cl X5 82.5 2.5 ~ 108 Present C2 carbon black lg 3.0 x 108 example Each of these conductive yarns Cl, C2 was doubled with nylon-66 yarn 2600 d/140 f) and subjected to a crimping treatment to obtain a crimped doubled yarn having the conductive yarn ~2622 d/143 f). Then, a tufted carpet (loop pile) Hl or H2 was produced by using the conductive yarn doubled yarn in one course in e~ery six lS courses and nylon-66 crimped yarn (2600 d/140 f) in other five courses. The resulting carpet (Hl, H2) was subjected to a scouring, a dyeing (dyestuff: Nylon acid yellow C-3&S made by I.C.I., concentration of dyestuff: 0.7% owf, dyeing temperature: 100C) and a backing. Thereafter, the appearance (particularly color shading) was observed and also the charged voltage of human body when a man put on leather shoes walked (25C, 20%RH) on the carpet was measured to obtain results as shown in the following Table 6.
The carpet H2 of the comparative example was conspicuously observed in the color shading (warp lines) due to the black colo-r of -the conductive yarn and was considerably poor in the commercial value, while the carpet Hl according to the present invention showed no color shading and had an excellent antistatic property.

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Table 6 Carpet Conduc- Presence of Charged voltage tive color shading of human body Remark No. yarn (warp lines) (V) H1 C1absence -1,300 invention H C2conspicuous -1,500 Co~parative 2 ~ __ presence _ example

Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. Conductive fibers in which a conductive layer consisting mainly of conductive metal oxide particles and a binder of polymer is formed on surface of fibers by after-processing.

2. Conductive fibers as claimed in claim 1, wherein a polymer to form the fibers is polyamide, polyester, polyolefin or vinyl polymer.

3. Conductive fibers as claimed in claim 1, wherein a reflectivity of the conductive metal oxide particles is not less than 40%.

4. Conductive fibers as claimed in claim 1, wherein the conductive metal oxide particles consist mainly of zinc oxide or tin oxide.

5. Conductive fibers as claimed in claim 1, wherein the conductive metal oxide particles are titanium oxide coated with zinc oxide or tin oxide film.

6. Conductive fibers as claimed in claim 1, wherein the binder is a thermoplastic or thermosetting polymer.