Patent Grant
6849302
The present invention relates to a resin-coated metal sheet with conductivity to be used to make parts of electronic machinery and tools, a production method thereof, and parts of electronic machinery and tools obtained by forming or working the metal sheet.
Recently, in electronic machinery and tools, such as a drive case for a CD-ROM, a related machinery and tools for a personal computer, and a measuring machinery and tools, further smaller size and light weight are tried to be achieved more than before, and as materials for machinery and tools parts, those compatible thereto are required. For the machinery and tools part material, a good anti-fingerprint property, a high formability and workability (hereinafter, formability and workability are collectively referred to as formability), and electric characteristics (a grounding property and a shield property) not affecting the performance of a precision electronic machinery and tools main body, are required.
Conventionally, as electronic machinery and tools part materials, the following are representative. However, none of them can satisfy all of the above-mentioned required qualities.
First, as a material of parts of electronic machinery and tools, a steel sheet (in particular, plated steel sheet) is most common. However, since the specific gravity of steel sheet is high, it is not suited for the trend toward mobile and lighter-weight electronic machinery and tools. Moreover, an aluminum bear material is widely used as well. Although the aluminum bear material has good conductivity, it has a disadvantage in that fingerprints are left on the surface easily at the time of handling (inferior in stain-proofing property). Therefore, an aluminum-coated material, obtained by applying a resin coat on an aluminum sheet, has been proposed. However, although the aluminum-coated material has a good anti-fingerprint property, it has a large electric resistance value in a coated resin layer, so that desired electric characteristics (a grounding property and a shield property) cannot be obtained when it is made into an electronic machinery and tools part.
Further, an aluminum material has a benefit that it has excellent elongation and expanding property in comparison to other metal materials. Therefore, it is suitable to be applied to forced forming. However, when the above-mentioned conventional metal materials, each having a resin coating on the surface, was applied to forced working, there was such a defect that the resin layer could not keep sufficiently the elongation and expanding property of the aluminum material of base material, to cause peeling or cracking of the resin layer, or the like.
Moreover, these aluminum-coated materials include a material having a coated film that is formed on the surface and that is composed of a mixture obtained by adding a metal soap, for improving the lubricant property and the formability, and a conductive powder (1% by weight or less), for improving the welding property, to a water-soluble lubricant high polymer wax as the main component, as disclosed in JP-A-5-320685 (“JP-A” means unexamined published Japanese patent application). However, in terms of the above-mentioned electric characteristics (a grounding property and a shield property) required for recent electronic machinery and tools parts, a target effect cannot be obtained.
Furthermore, Japanese Patent No. 2,133,521 discloses a part of electronic machinery and tools obtained by forming a resin-coated film, containing a lubricating agent, only on one side of an aluminum alloy sheet, and applying forming process to the sheet into a floppy disc drive case, with the coated surface on the outer side, so that electrical ground can be obtained through the surface without the coated film on the inner side. Since the side with the resin-coated film does not have conductivity at all, it cannot satisfy the above-mentioned electric characteristics, and there is a limitation in use.
JP-A-6-240469 discloses a resin layer, on a steel sheet provided with a layer subjected to chromate process, which resin layer comprises one or two or more resin selected from the group consisting of epoxy, alkyd, acrylic, urethane, phenol, melamine, polyvinyl butylal, and polyester resins, and is added a powdery lubricating agent, and a conductive auxiliary agent (particles of one or two or more selected from the group consisting of Cu, Ni, Ag, Al, Zn, Cr, Fe, Co, an alloy thereof, carbon black, and carbon graphite) having a 0.1 to 5 μm average particle size. However, as a result of our testing of the above steel sheet having a resin layer, scattering of conductivity of it was large, and it could not satisfy the grounding property and shield property required.
Moreover, as a conventional coating method, a roll coat has been the mainstream. In particular, a bottom-up method, shown in
As a result of elaborate study to overcome the problems of conventional resin-coated metal sheets, the present inventors have found that, in order to provide the above-mentioned high electric characteristics (a grounding property and a shield property) without affecting the performance of electronic machinery and tools, it is necessary that, as a material for a part of electronic machinery and tools, the resin layer has electrical resistance value equal to or less than a given value (preferably 10 Ω or less with a measurement method described later). We also have found that, to attain the above resistance value, formation of a resin layer, in which nickel having a specific size is contained with a certain amount, as a conductive auxiliary agent, on the surface of the metal sheet, is effective, and we also have found that optimum kind of the resin, the addition amount, the size and the shape of the nickel necessary in such a resin layer. Moreover, we have found a production method of forming the resin layer stably.
That is, according to the present invention, there are provided:
The nickel content in the present invention is 2 to 60 parts by weight, preferably 4 to 50 parts by weight of nickel, to 100 parts by weight of the resin in the resin layer. If the nickel content is less than 2 parts by weight, a target electric characteristic cannot be obtained. On the other hand, if it is more than 60 parts by weight, since the resin layer may easily be brittle, film cracking may be occurred when processing, so that contact of the metal material and the molding mold takes place so as to easily rupture the material. Nickel is advantageous for its ease to be dispersed in a coating material, inexpensiveness, and excellent conductivity. In the present invention, nickel is essential, and a metal, such as carbon, zinc, titanium, gold, silver, and copper, or an alloy or an oxide thereof can be added, as long as it is within the range not hindering the desired performance.
In the present invention, it is preferable that the surface occupation ratio of the nickel (the ratio of the projected area of nickel that occupies in a certain area, when a resin layer is projected from vertical direction) is 0.1% or more.
As to the size of the nickel particle for use in the present invention, those having a 0.1 to 100 μm average value (average diameter) in terms of maximum longer diameters of each particle are preferable. The maximum longer diameter denotes the particle size, in the case of the spherical, spike spherical, scale-like, or chain-like particle, and it is the distance of the two points with the longest linear distance. More specifically, the average diameter of a spherical or spike spherical nickel, and a chain-shape nickel is preferably 0.1 to 20 μm, and the average particle diameter of a scale-like nickel is preferably 0.1 to 100 μm. Here, in the case the nickel diameter is larger than the coated film thickness, the resin surface and the metal sheet are conducted via the nickel. In contrast, in the case the nickel diameter is smaller than the coated film thickness, according to the contact of a plurality of particles in the resin, the resin surface and the metal sheet can be conducted. However, with a less than 0.1 μm average longer diameter, since the conductivity irregularity (scattering) is large, it becomes unstable. That is, in the case the average value in terms of maximum longer diameters is less than 0.1 μm, since a large number of those having a maximum longer diameter smaller than 0.1 μm are contained, the ratio of the nickel to be buried in the resin layer becomes large so that the conductivity irregularity is large. With a more than 100 μm average longer diameter, since the nickel can easily fall off from the resin layer, it is accumulated on the mold so as to easily generate galling or rupture of the material.
The nickel shape to be used in the present invention is preferably spherical, spike spherical, scale-like, or chain-shape. Among these, it is more preferable to include one or two or more. Here, the spike spherical denotes a shape with a plurality of projections protruding from the surface of a sphere like spikes. The scale-like denotes a sheet-like shape. These nickels are added to the resin as a simple substance in a state independent of each other, or with the minute particles bonded with each other (i.e., bonded like a chain or a rosary form) in a narrow long chain shape like a filament. Moreover, spherical includes a shape close to a sphere, such as a ellipsoid body of rotation and a distorted sphere with a rugged part or a flat surface. The same is applied to the spike spherical shape. If conductivity is regarded as important, since a higher height of the nickel projection from the surface is more preferable, it is more preferable to add the spherical or spike spherical nickel as a simple substance, or nickel in a chain shape. The conductivity of the resin layer is preferably 10 Ω or less, and more preferably 8 Ω or less, as a value measured in the test method described in the following Example 1. Moreover, if the formability and the external appearance are regarded as important, a scale-like shape capable of obtaining a relatively flat surface is preferable. Furthermore, in order to achieve both the conductivity and the formability, it is effective to mix and add those with a scale-like shape and those of a chain-like shape. As to the mixing ratio, a ratio by weight of the scale-like and the chain-like shape of 99:1 to 1:1 is preferable, and 9:1 to 7:3 is more preferable.
The resin to be used in the present invention can be selected depending on the use of a resin-coated metal sheet, or the kind of a part for electronic machinery and tools to which the metal sheet is formed, or the like. In view of the formability, one or two or more resin selected from the group consisting of polyester-series, epoxy-series, phenol-series, and alkyd-series is preferable. Further, in view of the formability, those containing a polyester-series, or alkyd-series resin are most preferable. As the kind of the polyester-series resin, a phenol denatured polyester, an epoxy denatured polyester, or the like can be presented, and as the kind of the alkyd-series resin, a melamine alkyd resin, an amino alkyd resin, or the like can be presented, but it is not particularly limited. Those having a 2,000 to 30,000 number average molecular weight of the resin in the coating material are preferable in terms of the formability.
In the present invention, the resin layer can be provided either on both surfaces on the metal sheet, or only on one side. The thickness (film thickness) of the resin layer is 0.1 to 10 μm, more preferably 0.1 to 5 μm. With a less than 0.1 μm thickness, galling is generated at the time of forming due to rupture of the resin so as to deteriorate the formability. Moreover, with a more than 10 μm thickness, the conductivity is deteriorated as well as it is not preferable in terms of the production cost. The relationship between the coating film thickness and the nickel average diameter is not limited as long as it does not impair the performance of the resin-coated metal sheet according to the present invention, but the average diameter is preferably 50 times as much as the coating film thickness or less. The coating film thickness is the thickness of the resin layer, as shown in FIG. 3.
In the present invention, the material of the metal sheet for forming such a resin layer on the surface is not particularly limited, and a steel sheet, copper, aluminum, magnesium, an alloy thereof, or the like can be presented. Among these, a steel sheet can be employed if the purpose is not to form a lightweight product, however, an aluminum material is preferable if the purpose is to achieve mobile and weight saving, and superior formability. The shape can be coil-like, a cut sheet-like, or the like, and it is not particularly limited, but for the homogeneity of performance, the cost, and the productivity, it is preferable to coating on a coil-like material. The sheet thickness is not particularly limited, but it is determined spontaneously in view of the formability and the shape-keeping property, and furthermore, it can be determined according to its application. For example, in the case of an aluminum alloy, in general, those of a thickness in the range of 0.1 to 2.5 mm are used preferably.
In the present invention, in order to improve the formability, a lubricating agent may be added to the resin. As the addition amount, 30 parts by weight or less to 100 parts by weight of the resin is preferable. If the amount of a lubricating agent to be added is too much, the conductivity is deteriorated so that a desired electric characteristic cannot be obtained. As the kind of the lubricating agent to be used at that time, olefin-series waxes, such as polyethylene wax; fluorine-series waxes, such as PTFE (polytetrafluoroethylene); paraffin wax, micro crystalline wax, honey wax, lanolin, carnauba wax, or the like, can be presented.
Moreover, a settling-preventing agent, an anti-foaming agent, a leveling agent, or the like, can be added to the resin, as needed, as long as it does not impair the performance of the resin-coated metal sheet of the present invention.
In the present invention, in order to form a resin layer on a metal sheet, in general, a coating and drying step is executed. Moreover, as needed, a degreasing treatment or an undercoat treatment can be executed before the coating step. For example, in the case for forming a resin layer by applying a coating material of resin on an aluminum sheet, it is preferable to clean the surface by a degreasing treatment, or the like. It is further preferable to form an undercoat, in order to improve the adhesion property and the anti-corrosion property. As the undercoat, a chemical conversion coating is commonly used, but the kind of the chemical conversion coating is not particularly limited. For example, the rinse type or the no-rinse type undercoat of chromate-series, or non-chromate-series (e.g. zirconium-series, titanium-series, phosphate-series, and oxalate-series) can be presented. In view of the performance stability, the productivity, and the cost, it is preferable to select among the chromate-series, the zirconium-series, and the titanium-series. As to the method of forming a chemical conversion coating, the coating can be formed by an ordinary method, such as the rinse type and the no-rinse type, and it is not particularly limited.
As the method for applying a nickel-containing coating material onto a metal sheet, preferable is the top-feed method, shown in
In the present invention, after the application of a coating material by the above-mentioned method, drying is executed by an ordinary manner. The drying process is preferably conducted at 100 to 300° C., which is the maximum temperature that the metal sheet can reach (PMT).
A resin-coated metal sheet material according to the present invention can be used in every part of electronic machinery and tools, such as casings including a drive case for a CD-ROM, CD-R/RW, DVD-ROM, DVD-RW, FD, and MO, a related machinery and tools for a personal computer, and a measuring machinery and tools part that requires grounding and/or shielding property.
The resin-coated metal sheet of the present invention is excellent in conductivity as well as formability, so that it can be used preferably in a part of electronic machinery and tools. Moreover, according to the production method of a resin-coated metal material of the present invention, a resin-coated metal material for a part of electronic machinery and tools, with a high nickel content, a homogeneous distribution thereof in the entirety, and the excellent conductivity, can be produced.
Furthermore, the part of electronic machinery and tools of the present invention is light in weight, excellent in conductivity, good in grounding property and shield property, and it is capable of taking the grounding from the resin-coated surface side, and it has good anti-fingerprint property and handling property, and thus it is preferable for precision electronic machinery and tools, wherein high electric characteristics are required.
Hereinafter the present invention will be explained in further detail based on examples. The present invention is not limited to the following examples in the range not departing from the scope of the claims.
An aluminum coil (5052-0, sheet thickness 0.5 mm) was subjected to a degreasing treatment with a commercially available alkaline-series degreasing agent. After washing with water, a undercoat treatment was applied so as to form a chromate phosphate coating (chemical name: Alsurf 407/47 (trade name), manufactured by Nippon Paint Corp.). The undercoat amount at that time was 15 mg/m2 in terms of the metal chromium amount. Thereafter, on both surfaces of the resultant aluminum sheet, a coating material with a nickel added was coil-coated by a top-feed—direct-roller-coating method, as shown in
The specific features of resins employed are as follows:
The conductivity and the formability of the obtained resin-coated aluminum sheets were tested by the following method. The results are shown in Table 1.
(1) Conductivity
With respect to the obtained resin-coated aluminum sheets, according to the four-point probe method as shown in
(2) Formability
The obtained resin-coated aluminum sheets each were applied with a commercially-available volatile lubricating oil (viscosity: 1.2 cSt), and deep-drawn, with a 40-mmφ punch diameter and a 84-mmφ blank diameter, into a cylindrical shape. The forming height is the height when ruptured (a height of the drawn sample when the sample was ruptured; see
[Evaluation Standards]
In the same manner as in the Examples 1 to 8 according to the present invention, an aluminum coil was subjected to a chemical conversion treatment and coating, to form a resin layer. The thickness of the resin layer at that time was 2 μm. In this series of example, the kind of the resin was changed for examining the influence thereby. The kind of the resin, the shape, the average diameter, and the content of the nickel contained in the resin layer are shown in Table 2. The conductivity and the formability of the obtained resin-coated aluminum sheets were tested by the same method as in the Examples 1 to 8 according to the present invention. The results are shown in Table 2.
In the same manner as in the Examples 1 to 8 according to the present invention, an aluminum coil was subjected to a chemical conversion treatment and coating, to form a resin layer. In this series of examples, the coating film thickness was changed for examining the influence thereby. The kind of the resin, the coating film thickness, and the shape, the average diameter, and the content of the nickel contained in the resin layer are shown in Table 3. The conductivity and the formability of the obtained resin-coated aluminum sheets were tested by the same method as in the Examples 1 to 8 according to the present invention. The results are shown in Table 3.
In the same manner as in the Examples 1 to 8 according to the present invention, an aluminum coil was subjected to a chemical conversion treatment and coating, to form a resin layer. The kind of the resin, the thickness of the resin layer, and the shape, the average diameter, and the content of the nickel contained in the resin layer are shown in Table 4. The average diameter of a chain-shape nickel denotes an average value of a longest diameter, when particles (average diameter 1 to 5 μm) bonded with each other so as to be like a narrow long filament are considered as one particle. In this series of examples, the shape and the average diameter of the nickel were changed for examining the influence thereby. The conductivity and the formability of the obtained resin-coated aluminum sheets were tested by the same method as in the Examples 1 to 8 according to the present invention. The results are shown in Table 4.
In the same manner as in the Examples 1 to 8 according to the present invention, an aluminum coil was subjected to a chemical conversion treatment and coating, to form a resin layer. The thickness of the resin layer was 2 μm. The shape, the average diameter, the mixing ratio, the total content, of the nickel contained in the resin layer, and the kind of the resin are shown in Table 5. In this series of examples, the influence by the combination of the nickels were examined. The conductivity and the formability of the obtained resin-coated aluminum sheets were tested by the same method as in the Examples 1 to 8 according to the present invention. The results are shown in Table 5.
After providing a chemical conversion coating on an aluminum coil in the same manner as in the Examples 1 to 8 according to the present invention, a coat was applied thereon in the method shown in Table 6, to form a 2-μm-thickness resin layer for each side. The nickel amount to be added in the coating material, the shape, the average diameter, the mixing ratio, and the total content of the nickel contained in the resin layer, and the kind of the resin are shown in Table 6. Samples were collected after 30 min from the start of the coating step. In this series of examples, the coating transfer method was changed to each of the methods, as shown in
As is apparent from the results shown in Table 6, according to the top-feed coating, a resin layer containing nickel in high concentration was stably obtained. In contrast, according to the bottom-up coating, since nickel particle was settled in a short period of time, a resin layer having stable nickel content could not be obtained with coating for a long time.
In the same manner as in the Examples 1 to 8 according to the present invention, an aluminum coil was subjected to a chemical conversion treatment and coating, to form a resin layer. The thickness of the resin layer was 2 μm. The kind of the resin, the kind and the addition amount of the lubricating agent, the shape, the average diameter, and the content of the nickel contained in the resin layer are shown in Table 7. In this series of examples, a lubricating agent was added for examining the influence thereby. The conductivity and the formability of the obtained resin-coated aluminum sheets were tested by the same method as in the Examples 1 to 8 according to the present invention. The results are shown in Table 7.
After an aluminum coil was subjected to a degreasing treatment with a commercially available alkaline-series degreasing agent, followed by washing with water, a chemical conversion coating shown in Table 8 was provided thereon. Thereafter, the resultant coil was coil-coated in a top-feed/direct-roller method with the same coating material as the Example 6, followed by baking and drying, to form a 2-μm thickness resin layer for each side. The conductivity of the obtained resin-coated aluminum sheets were tested by the same method as in the Examples 1 to 8 according to the present invention. The results are shown in Table 9.
From the results shown above, the resin-coated aluminum sheet according to the present invention was excellent in conductivity and formability. Moreover, according to the production method of the present invention, such a resin-coated aluminum sheet with the excellent conductivity and formability could be obtained. Since Examples 9, 12, 13 and 14 according to the present invention contained a polyester-series, or alkyd-series resin, they had a better formability compared with the Examples 10, and 11 according to the present invention. Since Example 15 according to the present invention had a relatively thin coating thickness, it had a slightly poorer formability compared with Examples 16 to 19 according to the present invention. Since Examples 29 to 32 according to the present invention used a scale-like nickel, they had a better formability, compared with Examples 20 to 28, and 33 to 35 according to the present invention. Since Example 44 according to the present invention had a small ratio of the scale-like, it had a slightly poorer formability compared with Examples 39 to 43 according to the present invention. Since Example 49 according to the present invention had a small ratio of the scale-like, it had a slightly poorer formability compared with Examples 45 to 48 according to the present invention. Since a lubricating agent was added in Examples 54 to 61 according to the present invention, they had a better formability compared with Examples 1 to 53 according to the present invention.
In contrast, among Comparative Examples 1 to 14, since a nickel was not added in No. 1, it did not show conductivity. Since a nickel addition amount was too small in No. 2, it was poor in conductivity. Since a nickel addition amount was too large in No. 3, it had a poorer formability compared with Examples according to the present inventions. Since the kind of the resin was outside the scope of the claims in Nos. 4 to 6, they were poor in formability as compared to Examples according to the present invention. Since the coating thickness was too thin in No. 7, the formability was poor. Since the coating thickness was too thick in No. 8, the conductivity was poor. Since the nickel average diameter was too small in No. 9, it was poor in conductivity as compared to Examples according to the present invention. Since the nickel average diameter was too large in No. 10 it was poor in formability as compared to Examples according to the present invention. Since the coating material was supplied in the bottom-up method in Nos. 11 to 14, nickel settlement was observed in the coater pan, and satisfactory conductivity was not obtained due to the insufficient nickel content in the resin layer. In Reference Example 1, since the addition amount of the lubricant was too large, although the formability was good, the conductivity was poor.
Having described our invention as related to the present embodiments, it is our intention that the invention not be limited by any of the details of the description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1999304289 | Oct 1999 | JP | national |
This application is a divisional of U.S. application Ser. No. 09/699,092, filed Oct. 26, 2000 now Pat. No. 6,670,031, and is incorporated by reference in its entirety.
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| Number | Date | Country | |
|---|---|---|---|
| 20040071959 A1 | Apr 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09699092 | Oct 2000 | US |
| Child | 10668852 | US |
