JP2005133149A - Surface treated metallic material having excellent conductivity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface treated metallic material having excellent conductivity which can be subjected to resistance welding, and is utilizable as an electrostatic prevention material, an electromagnetic wave shielding material or the like. <P>SOLUTION: The surface treated metallic material excellent in conductivity is provided with a coating layer containing, as a main component, at least one kind selected from among an organic resin, an inorganic compound or the composite body thereof in at least a part of the surface of the metallic material, wherein microcarbon fibers having an average aspect ratio of ≥3 is incorporated into the coating layer. When carbon nanotubes are used as the microcarbon fibers, in particular, and the content thereof is controlled to 0.01 to 25% in a mass ratio to the whole of the coating layer, highly excellent effect can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface-treated metal material that requires a particularly high electrical conductivity among surface-treated metal materials used for home appliances, automobiles, building materials, and the like. Specifically, the present invention relates to a surface-treated metal material having excellent electrical conductivity that can be resistance-welded and can be used as an antistatic material, an electromagnetic shielding material, or the like.

  In general, metal materials are lightweight, high in strength, and excellent in workability, and thus are used in various applications. Among these, metal materials whose surfaces are coated are widely used in the fields of automobiles, home appliances, building materials and the like because of their beautiful appearance and excellent corrosion resistance.

  An organic resin is generally used as a coating film of a metal material, and polyester resin, acrylic resin, polyurethane resin, and the like are well known. On the other hand, there is a great need for inorganic coatings with higher heat resistance and excellent chemical stability, and coatings such as silica-based coatings have been put into practical use.

However, in any of the above organic resin coating films or inorganic coatings including silica, most materials are insulators having a resistance value of 10 ¹² Ω · cm or more. When a film is formed, the electrical conductivity inherent to the metal material is often impaired.

  As a result, for example, inconveniences often occur in metal materials that require high electrical conductivity such as resistance welding and prevention of static electricity.

  To solve this problem, a method of adding carbon black, graphite, metal powder or the like to an organic resin as a means for improving the electrical conductivity of the coating film and consequently improving the electrical conductivity of the entire steel sheet is disclosed (Patent Document 1). And Patent Document 2), and a method of adding carbon black having a large specific surface area is disclosed (see Patent Document 3).

  Moreover, the method of adding a metal or alloy powder as electroconductive particle is disclosed (refer patent document 4, patent document 5, patent document 6, and patent document 7).

  In these technologies, when spherical or flat carbon powder such as carbon black or graphite is used as the conductive particles, an addition amount of 10% or more is usually required in order to ensure good conductivity. I was trying. As a result, the amount added is increased, and the properties inherent to the resin are often lost in addition to the conductivity.

  Regardless of whether or not it is desired, the coating film is often colored blackish, and it has been difficult to ensure conductivity while maintaining a light color or transparency.

  On the other hand, when a metal or alloy-based conductive powder is added, although the effect of improving the electrical conductivity of the coating film is recognized even with a small amount of addition, the metal or alloy-based powder has a large specific gravity, There was a drawback that a significant mass increase occurred.

  Moreover, in the coating film which has an inorganic type compound as a main component, the trial which improves electrical conductivity has not been made so far.

JP-A-63-83172 Japanese Patent Laid-Open No. 10-43677 Japanese Unexamined Patent Publication No. 7-90601 JP 2001-170558 A JP 2001-172778 A JP 2001-279468 A JP 2001-279469 A

  The present invention solves the above-mentioned problems and has a surface having a coating layer with improved electrical conductivity with a small amount of additive without significant increase in mass as in the case of adding metal or alloy-based powder. An object of the present invention is to provide a surface-treated metal material having excellent electrical conductivity that can be obtained as a treated steel plate, that is, resistance welding can be used as an antistatic material, an electromagnetic shielding material, or the like.

  As a result of intensive studies to solve the above problems, the present inventors have found that the problem can be solved by adding a fine carbon fiber having an average aspect ratio of 3 or more as a conductive material. It came to complete. Specifically, it is as follows.

  (1) A surface-treated metal material having a coating layer mainly comprising at least one of an organic resin, an inorganic compound, or a composite thereof on at least a part of the surface of the metal material, And a surface-treated metal material excellent in electrical conductivity, characterized by containing fine carbon fibers having an average aspect ratio of 3 or more.

  (2) The surface-treated metal material having excellent electrical conductivity according to (1), wherein the content of the minute carbon fiber is 0.01 to 25% by mass with respect to the entire coating layer.

  (3) The surface-treated metal material having excellent electrical conductivity according to (1) or (2), wherein the fine carbon fiber has a fiber diameter of 10 μm or less.

  (4) The surface-treated metal material having excellent electrical conductivity according to any one of (1) to (3), wherein the minute carbon fiber is a carbon nanotube.

  (5) The metal material is one type selected from a plated steel material, a stainless steel material, a titanium material, a titanium alloy material, an aluminum material, and an aluminum alloy material. The surface-treated metal material having excellent electrical conductivity as described.

  According to the present invention, a surface-treated metal plate having conductivity as a whole material can be easily obtained because the coating layer on the surface has conductivity. Since a small amount of conductive additive is added to the coating layer on the surface having conductivity, conductivity can be imparted without impairing the properties of the coating film serving as a matrix and without a significant increase in mass. it can.

  The surface-treated metal material of the present invention will be described below.

  The coating layer formed on the surface-treated metal material of the present invention contains fine carbon fibers having an average aspect ratio of 3 or more. The fine carbon fiber mentioned here is a general term for carbon compounds having a fiber shape whose diameter does not exceed 10 μm, and any carbon fiber can be suitably used as long as it is fibrous.

  Those often used as fibrous carbon include carbon fibers, whiskers, and carbon nanotubes. Among these, the whisker refers to a single crystal material containing almost no dislocations, and carbon whiskers, fullerene whiskers, and the like are known as whiskers of carbon compounds.

  Carbon nanotubes are particularly preferable as the fine carbon fibers contained in the coating layer of the present invention. A carbon nanotube is a tube (tube) material having a diameter of 0.4 to 50 nm composed only of carbon atoms, and generally has a structure in which one atomic layer of a hexagonal mesh surface of graphite is rolled into a tube shape. The thing which has.

  In addition, the carbon nanotubes refer to those made of crystalline carbon in a narrow sense. Here, however, carbon nanotubes including those having amorphous carbon in an amorphous state are called carbon nanotubes.

  There are various types of carbon nanotubes such as single-walled, double-walled, and multi-walled nanotubes, and any of these can be used without any problem.

  Moreover, as a manufacturing method, a CVD method, an arc jet method, or the like is known, but the nanotube used in the present invention can be suitably used by any manufacturing method. When a catalyst or the like is used in the process of synthesis, the catalyst may remain as an impurity in the nanotube, but these nanotubes are also suitable because they do not significantly affect the electrical conductivity of the nanotube. Can be used.

  The reason why the average aspect ratio of the fine carbon fibers used in the present invention is limited to 3 or more is that excellent electrical conductivity can be obtained with a small amount of addition, preferably, the average aspect ratio is 5 or more, more preferably It is preferable to contain fine carbon fibers having an average aspect ratio of 10 or more.

  By using these fine carbon fibers, it is possible to impart remarkable conductivity to the coating layer with a small addition amount. This is considered to be due to the fact that a path through which electricity passes with an additive amount smaller than that of a conductive additive having an isotropic shape is secured by contacting the fibers extending in the longitudinal direction.

  On the other hand, if the average aspect ratio of the fine carbon fibers contained in the coating layer is too large, the fibers tend to agglomerate with each other, making it difficult to form a large number of flocs and uniformly disperse them in the coating layer. become. From these points, the preferable average aspect ratio is 10,000 or less, more preferably 5000 or less, and still more preferably 3000 or less.

  Here, the aspect ratio refers to a value obtained by dividing the length of the fiber by the diameter of the fiber. That is, the fine carbon fiber having an aspect ratio of 3 or more refers to a fine carbon fiber having a fiber length of 3 times or more of the diameter.

  In the present invention, the properties of the fine carbon fibers are defined by the average aspect ratio. The average aspect ratio is a numerical value obtained by dividing the number average of the fiber lengths of the fine carbon fibers by the number average of the fiber diameters. In this case, when micro carbon fibers having various aspect ratios are included, first, the average fiber length of the micro carbon fibers contained is obtained, and this is divided by the average fiber diameter of the carbon fibers. The ratio can be determined.

  Further, there are cases where a plurality of aspect ratios can be defined for a single fiber, such as when the minute carbon fiber is branched, bent, or has a complicated shape. In this case, the average aspect ratio can be calculated using the fiber length and fiber diameter that give the largest aspect ratio.

  In principle, the aspect ratio of the fine carbon fibers in the coating layer used in the present invention can be substituted by the average aspect ratio of the fine carbon fibers used as the additive raw material.

  In addition, when the average aspect ratio of the fine carbon fibers at the raw material stage is not required, the fine carbon fibers obtained by dissolving the coating layer with a solvent or the like or decomposing the chemical with a chemical were observed with a microscope. It can be obtained from an image or by analyzing the image with an image analyzer.

  As a simpler method, a cross-section with a coating layer can be observed with a microscope, and can be obtained by calculation from the observed shape of the cut surface of the fine carbon fiber. When calculating the average aspect ratio by these methods, it is desirable to perform the measurement on as many microcarbon fibers as possible. However, there is a limit to the observable microcarbon fibers, and the measurement results of at least 100 microcarbon fibers. And can be represented as a property of the fine carbon fiber.

  The fine carbon fiber used in the present invention is contained in a coating layer (matrix) containing as a main component at least one of an organic resin, an inorganic compound, or a composite thereof. Of these, the material of the organic resin, the inorganic compound, or the composite thereof serving as a matrix is not particularly limited.

  As the organic resin, generally known resin compositions such as polyester resins, urethane resins, epoxy resins, melamine resin paints, acrylic resin paints, fluorine resins and the like are preferably used.

  In general, known drying and curing methods can be used as a paint. For example, melamine curing, isocyanate curing, radical polymerization type and the like are preferably used. Moreover, the coating film obtained by simply drying without hardening can also be used suitably.

  Further, representative examples of inorganic compounds include silica-based, alumina-based, and titania-based materials that can form a film at a relatively low temperature. Usually, in these compounds, metal elements and oxygen atoms form a three-dimensional network, or fine particles are often bonded by sintering or the like. Of course, other metal elements or fine-particle additives may be included therein as required.

  Furthermore, a mixed component system in which an inorganic component is combined with the resin-based paint described above can also be suitably used. In addition, these matrices may contain generally known pigments or components for the purpose of coloring, rust prevention and the like, if necessary.

  The content of the fine carbon fiber of the present invention is 0.01% or more and 25% or less, preferably 0.1% or more and 20% or less, more preferably, in a ratio to the mass of the entire coating layer. It is 0.1% or more and 10% or less.

  If the content of the minute carbon fiber is too small beyond these ranges, the desired conductivity is often not obtained, and conversely, if the content is too much beyond these ranges, the matrix Various inherent properties may be impaired, and good adhesion to the substrate may not be obtained.

  Considering these points, it is preferable that the addition amount be as small as possible, and it is desirable to set the content to the minimum as long as the necessary conductivity is obtained.

  The thickness of the coating layer is not particularly limited and may be appropriately determined depending on the purpose. However, in order to ensure conductivity, the thickness is preferably 15 μm or less, and preferably 10 μm or less. There is no particular lower limit on the thickness, and it is preferable to determine the thickness by balance with other characteristics.

  The coating layer of the present invention is usually formed directly on the surface of the metal material. However, for example, a treatment layer for ensuring adhesion can be provided between the metal material and the coating layer. Alternatively, an intermediate layer having a specific function can be provided.

  Moreover, even if a film having other functions is formed on the surface of the coating layer used in the present invention, there is no problem. However, when it is intended to obtain conductivity as a whole material, it should be noted that the intermediate layer or the surface layer must also be a conductive film.

  The surface-treated metal material at least partially coated with the coating layer of the present invention has conductivity, and the coated portion is protected from corrosive gas, heat, friction, oxygen, water, water vapor, various chemicals, etc. Insensitive to external environment.

  The metal material here is not particularly limited, but a plated steel material, a stainless steel material, a titanium material, a titanium alloy material, an aluminum material, and an aluminum alloy material are preferable.

  As plated steel materials, galvanized steel materials, zinc-iron alloy plated steel materials, zinc-nickel alloy plated steel materials, zinc-chromium alloy plated steel materials, zinc-aluminum alloy plated steel materials, aluminum-plated steel materials, zinc-aluminum-magnesium alloy plated steel materials, Examples thereof include zinc-aluminum-magnesium-silicon alloy plated steel, aluminum-silicon alloy plated steel, galvanized stainless steel, and aluminum plated stainless steel.

  Examples of stainless steel materials include ferritic stainless steel materials, martensitic stainless steel materials, and austenitic stainless steel materials.

  Examples of titanium materials and titanium alloy materials include α-β titanium, β-titanium, etc. in addition to high-purity α-titanium. There are component systems such as Ti-6Al-4V for α + β titanium and Ti-15V-3Cr-3Sn-3Al, Ti-22V-4Al for β titanium, and any of these can be suitably used.

  Aluminum alloy materials include JIS 1000 series (pure Al series), JIS 2000 series (Al-Cu series), JIS 3000 series (Al-Mn series), JIS 4000 series (Al-Si series), JIS 5000 series (Al -Mg system), JIS6000 system (Al-Mg-Si system), JIS7000 system (Ai-Zn system), and the like.

  The shape of the metal material used in the present invention is not limited to a flat plate shape, but may be a pipe shape, a rod shape, or a special shape such as an H shape or a sheet pile. The thickness of these metal materials is not particularly limited, and can be applied to materials having a wide range of thickness from thin to thick. Further, the surface of the metal material may be subjected to a treatment such as bright annealing, buffing, or blasting.

  The coating layer used in the present invention can be generally formed using a known technique. Fine carbon fibers are mixed in a coating layer base material (matrix) mainly composed of at least one of an organic resin, an inorganic compound, or a composite thereof. For mixing, a known technique such as a roll mill or a paint shaker, or a method of mixing finely divided fine fibers with a paint by combining with a finely pulverizing technique of particles such as a ball mill or a vibration mill can be suitably used.

  It is needless to say that the fine carbon fibers of the present invention are uniformly dispersed in the coating film serving as a matrix, but the uniform dispersion is not necessarily required. The fine carbon fiber used in the present invention is preferably smaller than the thickness of the coating film even if the aggregate is large. When the size of the fine carbon fiber is larger than the thickness of the coating film, unevenness due to aggregates is generated on the coating film surface, which is not appropriate.

  Examples of the coating method include immersion, brush coating, spray coating, roll coater coating, curtain flow coater coating, roller curtain coater coating, bar coater coating, electrodeposition coating, electrostatic coating, and the like. It is also possible to heat the coated film layer for the purpose of curing.

  As a heating method, a generally known method such as a hot air heating furnace, a far-infrared furnace, an induction heating furnace, a direct-fired furnace, or the like can be used. Moreover, the method of drying at normal temperature and the hardening method by an ultraviolet-ray and an electron beam can also be used as needed. In the curing method by heating, the temperature can be set according to the components of the matrix, the amount of carbon fiber added, and the like.

  The above-described coating layer may be formed in the state of a metal material before processing, or may be performed after processing into a predetermined shape. It can be appropriately determined according to the purpose of use, the method of use, the site of use, etc.

  The present invention is specifically illustrated by the following examples.

(Example 1)
As a matrix component, a melamine curable polyester resin and ILJIN multi-walled carbon nanotubes (abbreviated as CNT) (diameter: 10 to 25 nm, length: 1 to 50 μm; average aspect ratio of 180) are selected as Table 1 and Table 1 The paint was prepared by mixing at the ratio shown in the above.

  In mixing the CNTs in the resin, first, using a ball mill containing balls made of steel balls, the aggregates were pulverized for about several hours to 24 hours, and then mixed with a paint shaker using glass beads. The addition amount of CNT is a mass ratio with respect to the whole solid content of a matrix.

  The prepared paint was applied and baked on a 0.8 mm thick hot dip galvanized steel sheet that had been chromated to obtain a galvanized steel sheet having a coating layer. The coating was baked at 230 ° C. for 1 minute, and the thickness of the formed coating layer was about 5 μm. Further, when the cross section was observed with a scanning electron microscope, CNT formed aggregates, but the size of the aggregates was about 4 μm at the maximum.

  About the obtained surface-treated galvanized steel sheet, pencil hardness was measured as a representative value of coating film properties, and DC resistance was measured as an evaluation of conductivity. The pencil hardness was measured by a hand-drawing method specified in JIS K 5400, and the direct current resistance was measured by a direct current four-end needle method.

  The test results are shown in Table 1. It can be seen that when 0.01% of CNT is contained, the resistance value of the coating film rapidly decreases and gradually decreases until the addition amount reaches 1%. A coating having a higher content has a low resistance value. From the above results, it can be seen that good conductivity is obtained in the coating film to which CNTs within the range of the present invention are added.

  On the other hand, the pencil hardness is almost constant regardless of the amount of CNT added and shows good characteristics, but it can be seen that the hardness decreases when the amount of CNT added is 25% or more.

  In summary, it can be seen that both high pencil hardness and good electrical conductivity are obtained within the scope of the present invention.

(Example 2)
As a matrix component, a siloxane bond forms a three-dimensional network, and an organic-inorganic hybrid material having a methyl group in the side chain and network. As a fine carbon fiber, (1) Tokai Carbon carbon whisker (diameter 0.3) ˜0.6 μm, length 5-15 μm; average aspect ratio 16), (2) Nanofiber A synthesized by vapor phase method (diameter 200 nm, length 0.5-5 μm; average aspect ratio 3.5, 6) And nanofiber B synthesized with different synthesis conditions (diameter 150 nm, length 10-20 μm; average aspect ratio 75), (3) ILJIN multi-walled carbon nanotubes (diameter 10-25 nm, length 1-50 μm; (Average aspect ratio 180), (4) single-walled carbon nanotubes manufactured by Shenzhen Nanotechport (diameter 2 nm, length 1 10 μm; average aspect ratio 1200) was added to prepare a paint.

  Moreover, the coating material which added the carbon black (40 nm diameter, average aspect ratio 1.0) instead of the coating material which does not contain an additive, and said carbon fiber was produced as a comparison material. The coating material was produced by the method according to Example 1. The addition amount of the fine carbon fibers was 1% in terms of mass ratio with respect to the entire solid content of the matrix.

  The prepared paint was applied and baked on a 0.6 mm thick stainless steel plate (SUS430, No. 4 finish) subjected to chromate treatment to obtain a surface-treated stainless steel plate. The coating film was baked at 250 ° C. for 1 minute, and the thickness of the formed coating layer was about 1.5 μm. Also in this example, aggregation of fine carbon fibers was observed, but the maximum size of the aggregation was about 1 μm.

  For the coating layer on the surface of the obtained surface-treated stainless steel plate, pencil hardness and DC resistance were measured in the same manner as in Example 1. The results are shown in Table 2. A steel sheet on which a coating film containing an additive having an average aspect ratio of 1 (carbon black) is formed has a high direct current resistance value and cannot be said to be imparted with electrical conductivity. On the other hand, it can be seen that the resistance value is remarkably reduced in the steel plate using fine carbon fibers having an average aspect ratio of 3 or more.

  In summary, in the steel sheet using the fine carbon fiber having the average aspect ratio of the present invention as an additive, even when the addition amount is small, the resistance value is remarkably reduced, and conductivity is imparted to the coating film. I understand that.

  According to the present invention, as described above, since the surface coating layer has conductivity, a surface-treated metal plate having conductivity as a whole material can be easily obtained. Furthermore, since a small amount of conductive additive is added to the coating layer on the surface having conductivity, conductivity is imparted without impairing the properties of the coating film that becomes the matrix and without a significant increase in mass. be able to.

  As a result, according to the present invention, a surface-treated metal material that can be resistance-welded and can be used as an antistatic material and an electromagnetic wave shielding material can be easily obtained on an industrial scale.

Claims (5)

  A surface-treated metal material having a coating layer mainly composed of at least one of an organic resin, an inorganic compound, or a composite thereof, on at least a part of the surface of the metal material, A surface-treated metal material excellent in electrical conductivity, characterized by containing fine carbon fibers having an aspect ratio of 3 or more.   2. The surface-treated metal material excellent in electrical conductivity according to claim 1, wherein the content of the minute carbon fibers is 0.01 to 25% by mass with respect to the entire coating layer.   The surface-treated metal material excellent in electric conductivity according to claim 1 or 2, wherein the fine carbon fiber has a fiber diameter of 10 µm or less.   The surface-treated metal material excellent in electrical conductivity according to any one of claims 1 to 3, wherein the minute carbon fibers are carbon nanotubes.   5. The electric conduction according to claim 1, wherein the metal material is one selected from a plated steel material, a stainless steel material, a titanium material, a titanium alloy material, an aluminum material, and an aluminum alloy material. Surface treated metal material with excellent properties.