JP2006240243A - Precoated aluminium alloy plate excellent in heat release nature - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precoated aluminium alloy plate having an outstanding heat release nature and applicable also to a case for an electronic device of high generation of heat. <P>SOLUTION: The precoated aluminum alloy plate comprises a precoat layer 2 which is formed on both surfaces or one surface of a substrate 10. The precoat layer 2 comprises a titanium oxide, carbon, silica, a zirconium oxide, and one or more sorts of rust preventive pigments, wherein the integral emissivity of the infrared rays of a wave length of 2.5-25 μm is at least 70%. In addition, the precoat layer uses a synthetic-resin based lacquer and preferably comprises, based on a base resin of 100 pts.wt., 50-200 pts.wt. titanium oxide having 0.1-100 μm average particle diameter, 1-25 pts.wt. fine carbon powder; 50-200 pts.wt. silica, 50-200 pt.wt. alumina, 50-200 pts.wt. zirconium oxide and 2-25 pts.wt. of one or more sorts of rust preventive pigments. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes, for example, a housing for an electronic device such as a personal computer, a CD-ROM drive, a PDP (plasma display panel) back panel, a housing for an inverter such as a hybrid vehicle or an electric vehicle, and an ECU (electronic control unit). In particular, the present invention relates to a precoated aluminum alloy plate excellent in heat dissipation.

  Conventionally, a pre-coated aluminum plate, which is obtained by coating the surface of an aluminum alloy plate with a synthetic resin coating, has excellent characteristics that it has excellent corrosion resistance, is lightweight, and does not need to be painted after molding. ing. For this reason, pre-coated aluminum alloy plates are widely used as materials for housings of home appliances and OA equipment. Recently, household appliances and OA equipment are becoming lighter, smaller, and more sophisticated, and accompanying this, the amount of heat generation is increasing, while improving the forced cooling capacity from the viewpoint of power saving and space saving. It has become difficult to improve heat dissipation from the housing surface.

  In addition, from the viewpoint of preventing malfunction of peripheral electronic devices due to electromagnetic waves emitted from electronic devices, the electronic device casing is required to have electromagnetic shielding properties, and the coating film has an electrical resistance of about several ohms or less. High conductivity is required. On the other hand, formability and scratch resistance are required from the viewpoint of cost reduction and yield improvement.

  As described above, future electronic devices will be increased in strength for size reduction, weight reduction, and thickness reduction. Therefore, as the casing, it is more desirable to use an aluminum alloy material that is lightweight and has a higher strength than a resin. In addition, among aluminum alloy materials, functional pre-coated aluminum alloy plates that are lower in cost than post-coated materials that are subjected to surface treatment and coating after press working can be said to be more promising materials in the future. Conventional pre-coated aluminum alloy plates are disclosed in, for example, Patent Document 1 and the like, but are not necessarily sufficient in terms of heat dissipation.

JP 2002-226783 A

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a pre-coated aluminum alloy plate having excellent heat dissipation that can be applied to a housing of a highly heat-generating electronic device.

The present invention comprises a precoat layer on both sides or one side of a substrate made of an aluminum alloy plate,
The precoat layer is made of a synthetic resin-based coating film having a single-layer structure or a multi-layer structure, and contains one or more of titanium oxide, carbon, silica, and zirconium oxide, and an infrared ray (wavelength: 2.5 μm to 25 μm). ) Integrated emissivity is 70% or more, and is a precoated aluminum alloy plate excellent in heat dissipation (Claim 1).

  In the precoated aluminum alloy plate of the present invention, the precoat layer contains one or more of titanium oxide, carbon, silica, and zirconium oxide as the specific component, as a heat dissipating pigment, and thereby, The integral emissivity of infrared rays is adjusted to be 70% or more. Therefore, heat dissipation can be improved as compared with the prior art, and it becomes more suitable as a housing material for electronic equipment, for example.

  Moreover, the precoat aluminum alloy plate of this invention has provided the precoat layer previously as mentioned above, and has given this the function of heat dissipation. Therefore, it can be molded while the precoat layer is provided, and heat radiation can be imparted even to portions that are difficult to apply after molding. In addition, the cost can be significantly reduced as compared with the case of post coating in which coating is performed after molding.

  Thus, according to this invention, the precoat aluminum alloy plate provided with the outstanding heat dissipation applicable also to the housing | casing of a highly heat-emitting electronic device can be provided.

As described above, the precoat layer in the present invention is composed of a single layer or a plurality of layers of a synthetic resin-based coating film. That is, it may be composed of only one layer of a synthetic resin-based coating film, or may be formed by laminating two or more synthetic resin-based coating films. And when a precoat layer is comprised with the coating film of two or more layers, said specific component may be contained in all the coating film layers, and may be contained only in any one layer.
Moreover, about content of the component contained in the precoat layer mentioned later, it is in the whole precoat layer, even if it is contained only in one layer, it means the ratio in the whole precoat layer, and it may be contained in a plurality of layers. The ratio in the whole precoat layer is meant.

  Further, as described above, the precoat layer is adjusted so that the integrated emissivity of infrared rays is 70% or more. This infrared integrated emissivity can be measured by comparing the amount of infrared radiation of a sample and an ideal black body by FT-IR. Moreover, when the integrated emissivity of the infrared rays is less than 70%, it is difficult to ensure heat dissipation.

  In addition, the precoat layer uses a synthetic resin-based paint containing a base resin whose main component is a synthetic resin having a number average molecular weight of 5000 to 40000, and an average particle size of 0 with respect to 100 parts by weight of the base resin. 0.1 to 100 μm of titanium oxide 50 to 200 parts by weight, fine powder of carbon 1 to 25 parts by weight, silica 50 to 200 parts by weight, alumina 50 to 200 parts by weight, zirconium oxide 50 to 200 parts by weight It is preferable to contain 1 type (s) or 2 or more types (Claim 2).

That is, as the precoat layer, a base resin containing a synthetic resin having a number average molecular weight of 5000 to 40000 as a main component is preferably used. When the number average molecular weight of this synthetic resin is less than 5000, there is a problem that the coating film becomes hard and the moldability is deteriorated. On the other hand, when it exceeds 40000, the coating film is too soft and has scratch resistance. There is a problem of lowering.
In addition, it is preferable to apply polyester as said synthetic resin with a number average molecular weight of 5000-40000.

  Further, when titanium oxide is contained in the precoat layer, the average particle size is preferably in the range of 0.1 to 100 μm. When the average particle diameter of titanium oxide is less than 0.1 μm, there is a problem that the infrared integrated emissivity decreases. On the other hand, when the average particle diameter exceeds 100 μm, the number of drops of titanium oxide from the coating film increases. There's a problem.

  Moreover, when the titanium oxide is contained in the precoat layer, the content is preferably 50 to 200 parts by weight with respect to 100 parts by weight of the base resin. When the content of titanium oxide is less than 50 parts by weight, there is a problem that the infrared integrated emissivity is lowered. On the other hand, when the content exceeds 200 parts by weight, the number of drops of titanium oxide from the coating film increases. There is a problem.

  The fine powder carbon is preferably carbon having a particle size of 1 nm to 500 nm. Moreover, it is preferable that content in the case of making the said precoat layer contain carbon is 1-25 weight part. When the carbon content is less than 1 part by weight, there is a problem that the infrared integrated emissivity is lowered. On the other hand, when the carbon content is more than 25 parts by weight, there is a problem that the number of falling off of the carbon film increases. is there.

  Moreover, it is preferable that content in the case of making the said precoat layer contain a silica is 50-200 weight part. When the silica content is less than 50 parts by weight, there is a problem that the infrared integrated emissivity is lowered. On the other hand, when the silica content is more than 200 parts by weight, the number of silica drops from the coating film is increased. There is.

  Further, the content when alumina is contained in the precoat layer is preferably 50 to 200 parts by weight. When the content of alumina is less than 50 parts by weight, there is a problem that the infrared integrated emissivity is lowered. On the other hand, when it exceeds 200 parts by weight, the number of falling off of the alumina from the coating film is increased. There is.

  Moreover, it is preferable that content when making the said precoat layer contain a zirconium oxide is 50-200 weight part. When the content of zirconium oxide is less than 50 parts by weight, there is a problem that the infrared integrated reflectance is lowered. On the other hand, when the content exceeds 200 parts by weight, the number of zirconium oxides falling from the coating film increases. There is a problem.

  Moreover, it is preferable that the film thickness of the said precoat layer is 0.5-100 micrometers. When the film thickness is less than 0.5 μm, there is a problem that the infrared integrated emissivity is lowered, while when it exceeds 100 μm, there is a problem that the cost is increased.

  Further, the precoat layer contains at least one of Ni spherical filler having an average particle diameter of 0.3 to 100 μm, or scaly Ni filler having a thickness of 0.2 to 5 μm and a long diameter of 2 to 50 μm. The total content of these both is preferably 1 to 1000 parts by weight with respect to 100 parts by weight of the base resin. Thereby, in addition to the heat dissipation improvement effect mentioned above, the conductivity improvement effect can also be acquired.

When the average particle size of the Ni spherical filler is less than 0.3 μm, there is a problem that the conductivity is lowered. On the other hand, when the average particle size is more than 100 μm, there is a problem that the amount of the Ni spherical filler dropped from the coating film is increased. .
Further, when the thickness of the flake shaped Ni filler is less than 0.2 μm, there is a problem that the conductivity is lowered, and when it exceeds 5 μm, there is a problem that the cost is increased. Further, when the major axis of the flaky Ni filler is less than 2 μm, there is a problem that the conductivity is lowered. On the other hand, when it exceeds 50 μm, the number of flaky Ni fillers dropped from the coating film is increased. There is.

  And the total content (including the case of containing only one) of these Ni fillers (Ni spherical filler and scaly Ni filler) is 1-1000 parts by weight with respect to 100 parts by weight of the base resin. Is preferred. When the content is less than 1 part by weight, the conductivity is insufficient, while when it exceeds 1000 parts by weight, there is a problem that the number of Ni fillers falling from the coating film increases.

  The precoat layer contains 1 to 90 parts by weight of resin beads having an average particle diameter D of 3 to 100 μm with respect to 100 parts by weight of the base resin, and the film thickness T of the part where the resin beads do not exist is 1 It is preferable that the average particle diameter D / the film thickness T is in the range of 1 to 3 (claim 4). In this case, in addition to the effect of improving heat dissipation, an effect of improving scratch resistance can be obtained.

When the average particle diameter D of the resin beads is less than 3 μm, there is a problem that the scratch resistance is lowered. On the other hand, when the average particle diameter exceeds 100 μm, there is a problem that dropping of the resin beads from the coating film increases.
Further, when the resin bead content is less than 1 part by weight with respect to 100 parts by weight of the base resin, there is a problem that the scratch resistance is lowered. There is a problem that the number of omissions increases.

Further, when the thickness T of the portion where the resin beads do not exist is less than 1 μm, there is a problem that the number of dropping of the resin beads increases or the scratch resistance decreases, whereas when it exceeds 30 μm, the scratch resistance is increased. There is a problem that decreases.
Further, when the average particle diameter D / film thickness T (hereinafter simply referred to as D / T) of the resin beads is less than 1, there is a problem that the scratch resistance is lowered, whereas, when D / T exceeds 3. However, there is a problem that the number of dropping of resin beads from the coating film increases.

The precoat layer preferably contains 0.05 to 3 parts by weight of one or two inner waxes of lanolin, carnauba, and polyethylene with respect to 100 parts by weight of the base resin. 5). Thereby, while being able to acquire the flaw resistance improvement effect, workability can also be improved.
When the content of the inner wax is less than 0.05 parts by weight with respect to 100 parts by weight of the base resin, there is a problem that the scratch resistance is lowered. On the other hand, when the content exceeds 3 parts by weight, blocking occurs. There is a problem.

Moreover, it is preferable that the said precoat layer contains a 2-25 weight part antirust pigment with respect to 100 weight part of said base resins. Thereby, the corrosion resistance of the substrate can be further improved. When the content of the anticorrosive pigment is less than 2 parts by weight, there is a problem that the corrosion resistance is lowered. On the other hand, when the content is more than 25 parts by weight, there is a problem that the number of falling off from the coating film increases.
Examples of the rust preventive pigment include Na ₂ Cr ₄ , polysilicate, polymer phosphate, NaClO ₃ , Zn (NO ₃ ) _{2 and the} like.

  The precoat layer is preferably formed in an upper layer of a coating type or reactive type chromate or non-chromate layer formed on the surface of the substrate. In this case, adhesion between the aluminum alloy plate and the precoat layer can be improved, and workability, durability, and the like can be improved.

In this example, a plurality of types of samples (pre-coated aluminum alloy plates) were produced as examples and comparative examples of the present invention, and their characteristics were evaluated.
In preparing each sample, first, a 5052-H34 aluminum alloy plate having a thickness of 0.5 mm was prepared as a substrate, the surface was degreased with an alkaline degreasing agent, and then phosphoric acid chromate in a phosphoric acid chromate bath. Processing was carried out. The amount of chromate film is 20 ± 5 mg / m ² as the Cr content in the film.

  Next, a predetermined amount of a polyester resin coating is applied to one surface of the aluminum alloy plate after the above-mentioned base treatment using a bar coater, and an oven at 240 ° C. is used so that the temperature of the aluminum surface becomes 230 ° C. A precoat layer was formed by baking and curing for 60 seconds. The components contained in the precoat layer in each sample are shown in Tables 1 and 2.

  Moreover, the typical structure of the produced sample (precoat aluminum alloy plate 1) is shown in FIG. As shown in the figure, each sample includes a substrate 10 made of an aluminum alloy plate and a precoat layer 2 formed on one surface of the substrate 10. The precoat layer 2 is made of a synthetic resin-based coating film in which the base resin 20 contains one or more heat-radiating pigments 3 such as titanium oxide. The precoat layer 2 is formed via a chemical conversion film layer 8 formed on the surface of the substrate 10. The precoat layer 2 may contain Ni filler or resin beads (not shown).

  In this example, for each sample, in addition to heat dissipation, evaluation of conductivity and scratch resistance was performed according to the application, and each level was set to pass.

<Infrared integrated emissivity>
Infrared integrated emissivity is measured by measuring the infrared reflectance of each wavelength in the range of 2.5-25 μm using PERKIN ELMER FT-IR Spectrometer 1725X, and subtracting the reflected light from the incident light of each wavelength. The absorptivity of each wavelength was defined as reflectance. The reflectance at each wavelength was integrated in the wavelength range of 2.5 to 25 μm to obtain infrared integrated emissivity. The evaluation criteria are as follows, and level 3 or higher was regarded as acceptable.
-Evaluation criteria-
Level 1: Less than 60%, Level 2: 60% or more and less than 70%, Level 3: 70% or more and less than 80%, Level 4: 80% or more and less than 90%, Level 5: 90% or more

<Conductivity>: Used for the evaluation of the conductive coating plate Part of the precoat layer of each sample is scraped off with a scraper, and one terminal of the tester is directly connected to the base of the aluminum alloy plate. A copper electrode having a spherical tip and a self-weight of 100 g was connected, and the electrode was supported by an auxiliary tool so as to contact the precoat layer perpendicularly. The electrical resistance value at that time was read and used for evaluation. The evaluation criteria are as follows, and level 3 or higher was regarded as acceptable.
-Evaluation criteria-Level 1: 1000Ω or more, Level 2: 300Ω or more and less than 1000Ω, Level 3: 30Ω or more and less than 300Ω, Level 4: 10Ω or more and less than 30Ω, Level 5: Less than 10Ω

<Scratch resistance>: Used for evaluation of scratch-resistant coated plate In the Bowden test, the width of a sliding trace when a steel ball having a load of 500 g and a 1/4 inch was slid 100 times was used for evaluation. The evaluation criteria are as follows, and level 2 or higher was regarded as acceptable.
-Evaluation criteria-Level 1: 1.0 mm or more, Level 2: 0.5 mm or more and less than 1.0 mm, Level 3: 0.3 mm or more and less than 0.5 mm, Level 4: 0.1 mm or more and less than 0.3 mm, Level 5 : Less than 0.1 mm The evaluation results are shown in Table 3.

From the results in Table 3, the following was confirmed.
It can be seen that Samples 1 and 2 have a higher infrared emissivity than Sample 3 with a low titanium oxide content, and satisfy Level 3 or higher.
It can be seen that Samples 4 and 5 have higher infrared emissivity than Sample 6 having a small titanium oxide particle size, and satisfy Level 3 or higher.
It can be seen that Samples 7 and 8 have a higher infrared emissivity than Sample 9 with a low carbon content, and satisfy Level 3 or higher.

Samples 10 and 11 have a high infrared emissivity as compared with sample 12 having a low silica content, and satisfy the level 3 or higher.
Samples 13, 14, and 15 have an infrared emissivity satisfying level 3 or higher, but sample 15 with a large amount of anticorrosive pigment is not desirable as a coating film for pre-coating because it has a large number of drops from the coating film.
It can be seen that Samples 16 and 17 have higher conductivity than Sample 18 in which the particle size of the spherical Ni filler is small and satisfy Level 3 or higher.

It can be seen that Samples 19 and 20 have higher conductivity than Sample 21 with a low Ni filler content and satisfy Level 3 or higher.
It can be seen that Samples 22 and 23 have higher conductivity compared to Sample 24 where the major axis of the scaly Ni filler is small and satisfy Level 3 or higher.

It can be seen that Samples 25 and 26 have higher conductivity than Sample 27 with a small content of flaky Ni filler and satisfy Level 3 or higher.
It can be seen that Samples 28 and 29 have higher scratch resistance than the sample 30 with a small resin bead diameter, and satisfy Level 3 or higher.

It can be seen that Samples 31 and 32 have high scratch resistance compared to Sample 33 with a small resin bead content and satisfy Level 3 or higher.
It can be seen that Samples 34 and 35 have high scratch resistance compared to Sample 36 with a low inner wax content, and satisfy Level 3 or higher.
It can be seen that Samples 37 and 38 have a higher infrared emissivity than Sample 39 having a thin coating film thickness and satisfy Level 3 or higher.

Explanatory drawing which shows the structure of the precoat aluminum alloy plate excellent in heat dissipation in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Precoat aluminum alloy board excellent in heat dissipation 10 Board | substrate 2 Precoat layer 20 Base resin 3 Radiation pigment

Claims (7)

A precoat layer is formed on both sides or one side of a substrate made of an aluminum alloy plate,
The precoat layer is made of a synthetic resin-based coating film having a single-layer structure or a multi-layer structure, and contains one or more of titanium oxide, carbon, silica, and zirconium oxide, and an infrared ray (wavelength: 2.5 μm to 25 μm). A pre-coated aluminum alloy plate excellent in heat dissipation, characterized in that the integral emissivity of) is 70% or more.   In Claim 1, the said precoat layer is using the synthetic resin type coating material containing the base resin which has as a main component the synthetic resin whose number average molecular weight is 5000-40000, and is average with respect to 100 weight part of said base resins. 50 to 200 parts by weight of titanium oxide having a particle size of 0.1 to 100 μm, 1 to 25 parts by weight of fine carbon, 50 to 200 parts by weight of silica, 50 to 200 parts by weight of alumina, and 50 to 200 of zirconium oxide A precoated aluminum alloy plate having excellent heat dissipation by containing one or more parts by weight.   3. The precoat layer according to claim 2, wherein the precoat layer contains at least one of a Ni spherical filler having an average particle diameter of 0.3 to 100 μm or a scaly Ni filler having a thickness of 0.2 to 5 μm and a long diameter of 2 to 50 μm. And the total content of these both is 1-1000 weight part with respect to 100 weight part of said base resins, The precoat aluminum alloy plate excellent in the heat dissipation characterized by the above-mentioned.   4. The precoat layer according to claim 2, wherein the precoat layer contains 1 to 90 parts by weight of resin beads having an average particle diameter D of 3 to 100 μm with respect to 100 parts by weight of the base resin. A precoated aluminum alloy plate excellent in heat dissipation, wherein the film thickness T is 1 to 30 μm and the average particle diameter D / film thickness T is in the range of 1 to 3.   5. The precoat layer according to claim 2, wherein the precoat layer comprises 0.05 to 3 parts by weight of lanolin, carnauba, or polyethylene, one or two types of inner wax with respect to 100 parts by weight of the base resin. A precoated aluminum alloy plate excellent in heat dissipation, characterized by containing.   In any 1 item | term of the Claims 2-5, the said precoat layer is 2 to 25 weight part with respect to 100 weight part of said base resins, and is excellent in the heat dissipation characterized by the above-mentioned. Pre-coated aluminum alloy plate.   7. The heat release property according to claim 1, wherein the precoat layer is formed on a coating type or reactive type chromate or non-chromate layer formed on the surface of the substrate. Excellent pre-coated aluminum alloy plate.

Images