JP2009202117A - Powder coating, its manufacturing method and electronic device housing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel combination of a plurality of powder coatings capable of obtaining a coating film wherein a plurality of coating film layers are formed in parallel to the coating surface on the cross-section vertical to a coating surface. <P>SOLUTION: The combination of a plurality of the powder coatings is ejected to a surface to be coated from a jet nozzle to obtain the coating surface and the coating surface is subsequently heat-treated. In this case, a plurality of the coating film layers parallel to the coating surface are formed so as to be recognized on the cross section vertical to the coating surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a powder coating technique.

  Conventionally, coating methods using oil-based paints, water-based paints, powder paints, and the like have been used for surface coating of electronic device products such as mobile phones and notebook personal computers. Of these, organic solvent-type paints and water-based emulsion-type paints both contain VOC (Volatile Organic Compounds), but powder paints do not use solvents, and thus VOCs are not generated at all. There is no environmental impact.

  In the case of powder paints, colored paints are measured at a certain ratio in advance so that the target colors are red and blue primary color paints with respect to the base paint such as gray. After mixing and toning, the toned paint was sent to a coating machine for coating.

  However, in this case, the automatic metering and mixing device that transports and weighs the base paint and color paint from the storage tank at a constant ratio and further mixes them has high equipment costs, a large control system device, and a wide installation location. It was necessary to secure. In addition, it is necessary to increase the tank capacity, and it is necessary to dispose of a large amount of paint that is no longer necessary at the time of color change. In addition, since it is necessary to have a paint inventory for each color to be painted, it is necessary to manufacture extra paint, which is a problem in a small amount of many kinds of painting. Furthermore, since the chargeability and electrical resistance differ for each colorant, it is necessary to precisely control the chargeability and electrical resistance in order to attach the paint electrostatically to the painted surface. It is difficult to paint.

  As a conventional technique, an invention of mixing a plurality of powders having different hues has been disclosed (for example, see Patent Document 1). In this method, if a primary color paint is manufactured in advance, it is possible to paint a new color with a short delivery time. However, there is a problem that the paint must be stocked for each color.

In addition, although the above demonstrated the surface coating of the electronic device product, the various invention aspect demonstrated in this specification is not limited to the surface coating of an electronic device product, and is applied to powder coating generally Needless to say.
Japanese Patent Application Laid-Open No. 11-100534 (Claims)

  An object of this invention is to obtain the coating film which formed the some coating-film layer parallel to this coating surface in the cross section perpendicular | vertical to a coating surface. Still other objects and advantages of the present invention will become apparent from the following description.

  According to one aspect of the present invention, when a painted surface is obtained by spraying from a spray nozzle onto a surface to be painted, and then the painted surface is heat-treated, a plurality of cross sections perpendicular to the painted surface are parallel to the painted surface. A powder coating combination is provided in which a coating layer is seen.

  According to another aspect of the present invention, there is provided a combination of powder coating materials in which the surface tension of each powder coating material in a molten state at 200 ° C. is different by 2 dyne / cm or more.

  According to still another aspect of the present invention, when a painted surface is obtained by spraying from a spray nozzle onto a surface to be painted, and then the painted surface is heat-treated, a cross section perpendicular to the painted surface is parallel to the painted surface. Provided is a powder coating method in which a plurality of coating layers can be seen. This method can be performed independently of using the powder paint combination or in connection with using the powder paint combination.

  Specifically, each powder coating in a combination of a plurality of powder coatings is separately sprayed from a plurality of spray nozzles onto the surface to be coated with overlapping spray timings to obtain a painted surface, Heat the painted surface. In the heat treatment, by adjusting at least one of the heating temperature and the heating time, a plurality of coating layers parallel to the painted surface can be seen in a cross section perpendicular to the painted surface after the heat treatment. It is made. Instead of the above-described operation before the heat treatment, there is also a method of obtaining a painted surface by spraying a combination of a plurality of powder coating materials together from one spray nozzle onto a surface to be coated.

  By these aspects, a coating film having various color effects, touch effects, and the like can be obtained. Such a combination has not been known so far.

  According to one embodiment of the present invention, it is possible to obtain a coating film in which a plurality of coating film layers parallel to the painted surface are formed on a cross section perpendicular to the painted surface. In addition, in connection with obtaining such a coating film, a uniform color coating surface can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, tables, formulas, examples and the like. In addition, these figures, tables, formulas, examples, etc., and explanations exemplify the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention.

  Hereinafter, coating in which powder coating material is sprayed from a spray nozzle onto a surface to be coated and the obtained coating surface is heat-treated (also referred to as baking) is also referred to as “powder coating”.

  When a combination of powder coatings is sprayed from the spray nozzle onto the surface to be painted to obtain a painted surface, and then the painted surface is heat-treated, a plurality of powder coatings in a cross section perpendicular to the painted surface are parallel to the painted surface. It has been found that a coating layer may be seen. In the present specification, “a plurality of coating film layers in a cross section perpendicular to the coating surface and parallel to the coating surface” is also referred to as a “specific multiple coating film layer”.

  Specifically, when a powder coating combination having two colors (a chromatic color and an achromatic white color) is used and supplied to a plurality of spray nozzles, and powder coating is performed, color unevenness occurs. It has been found that there are cases where uniform colors can be obtained. About this difference, when the coating cross section (cross section perpendicular | vertical to a coating surface) after heat processing was observed, it was discovered that the cross section may be divided into two layers parallel to the coating surface. Furthermore, when the cross section is divided into two layers parallel to the painted surface, the color unevenness is less when viewed from a direction perpendicular to the painted surface than when the cross section is not divided into two layers parallel to the painted surface. It has also been found that uniform colors can be obtained with little or no.

  This state is schematically shown in FIGS. 1 and 2 showing a cross section perpendicular to the surface to be coated. These figures show a cross section enlarged by a magnifying glass. FIG. 1 shows a case where it is not divided into two layers, and FIG. 2 shows a case where it is divided into two layers.

  As a result of observation with a magnifying glass, there was no difference between the two at the stage (a). However, in FIG. 1B, in the case of FIG. 1, two color regions are mixed in one coating film layer, whereas in the case of FIG. 2, two coating films corresponding to the respective colors are mixed. It was found that a layer was formed.

  In the case of FIG. 1, even if it cannot be recognized by the naked eye that two color areas are mixed in one coating layer, it is considered that the color is recognized as uneven color. On the other hand, in the case of FIG. 2, since the coating layers of the respective colors have no color unevenness, it seems that a uniform color was obtained when viewed from the direction perpendicular to the painted surface. It is.

  Such a relationship is possible even if the number of powder coatings is three or more. That is, as a result of the above, specifically, it can be considered that a combination of powder coating materials satisfying the following conditions gives a coating film having a uniform color.

  (1) Use a combination of a plurality of independent powder coatings.

  (2) The powder coating in this combination is separately sprayed from a plurality of spray nozzles onto the surface to be coated with overlapping spray timings to obtain a painted surface.

  (3) Next, when the painted surface is heat-treated, a specific multiple coating layer is seen.

  Here, the respective powder coatings in the combination of the plurality of powder coatings are not mixed with each other, but are individually supplied to the plurality of spray nozzles separately. However, one or more of the plurality of powder coating materials may be a mixture of a plurality of powder coating materials.

  The general purpose when using multiple powder coatings is to obtain a hue, lightness or saturation that is different from the single use. Therefore, it is general that these plurality of powder coating materials have different hue, lightness, or saturation. However, if there is a purpose such as imparting other characteristics such as a touch, these may be the same. If this is viewed as the composition of the powder paint, the composition of the powder paint is generally different from each other, but it can also be said that it may be the same.

  In the above, the reason why the spraying is repeated is to form a coating layer as shown in FIG. 2A in which the powder coating is mixed. The injection amount ratio may not be 1: 1.

  If the powder coating combination itself has no interaction between the powder coatings, the same effect can be obtained by mixing after exiting the injection nozzle or mixing before entering the injection nozzle. Conceivable. Therefore, specifically, it can be considered that even a combination of powder paints satisfying the following conditions gives a uniform color coating film.

  (A) Use a combination of powder coatings.

  (B) The powder coating combination is sprayed together from one spray nozzle onto the surface to be coated to obtain a painted surface.

  (C) Next, when the painted surface is heat-treated, a specific multiple coating layer is seen.

  The combination of the plurality of powder coatings in this case is mixed before being sprayed from the spray nozzle. Such mixing can be realized by mixing a plurality of powder coating materials in advance or by supplying each powder coating material separately to the suction side of the injection nozzle.

  By using the powder coating material of these forms, a novel coating film in which a specific plural coating film layer is seen can be realized. Various practical effects can be expected from this specific plural coating layer. Examples thereof include the following.

  -A coating film with a transparent light-resistant top coat on the surface layer and a colored layer below it.

  A coating film having a top coat with specific characteristics (for example, specific texture, feel, air purification ability, odor removal ability) on the surface layer and a colored layer underneath.

  -A coating film that aims at certain color effects (neutral colors, iridescent colors, morpho butterfly-like colors, etc.) by matching the colors of the surface layer and its lower layer.

  -Coating film with no or uneven color or a uniform color.

  The cross section perpendicular to the painted surface can be observed under a magnifier such as a microscope by cutting the object to be coated, which has been cooled after the heat treatment, perpendicularly to the painted surface. Although there is no restriction | limiting in particular in the thickness of a coating film, When it is too thin, it may become difficult to recognize that it is a several layer. On the other hand, if it is too thick, the layer formation itself may be difficult. For this reason, it is preferable that it exists in the range of 5-50 micrometers in the whole coating-film layer.

  “It is possible to see a specific plurality of coating layers” is sufficient to recognize that there are a plurality of layers as a result of observation under a magnifier such as the naked eye or a microscope. The lines indicating the layers may be distorted, cut off in the middle, or partially overlapped with the lines indicating the other layers. There are cases where the layers are blurred, or the layers themselves can be recognized as thin layers.

  Note that the number of the specific plural coating layers does not necessarily match the number of powder coatings used.

  In the above, “seen” also assumes that there may be a portion where the specific plural coating film layers are not seen. Moreover, even if it may not be seen depending on the coating conditions such as the heat treatment time, it means that the above condition is satisfied as long as it is “seen”.

  The specific multiple coating layer is observed whether the painted surface is horizontal or vertical. Therefore, it is considered that the influence of gravity does not work or hardly works as a cause of obtaining a plurality of coating films. As a result of the investigation, it was found that the surface tension at the time of melting of the powder coating was involved. Specifically, a plurality of coating layers are often seen when a combination of a plurality of powder coatings, each having a surface tension in a molten state at 200 ° C. of 2 dyne / cm or more different from each other. It is considered that when the powder coating is softened during the heat treatment, it is separated from each other due to the difference in surface tension, and a plurality of coating layers are formed. A coating film of a paint having a lower surface tension is formed on the surface of the coating film, and a coating film of a paint having a higher surface tension is formed near the surface to be coated. In this case, any coating method may be used, but it is advantageous to apply the above method.

  When the powder coating is usually heat-treated at a temperature range of 100 to 250 ° C., the powder is melted and leveled to form a coating film. The surface tension at this time can vary depending on the temperature. In the above description, the surface tension in the molten state at various temperatures is typically grasped by the surface tension of the powder coating in the molten state at 200 ° C.

  There is no particular limitation on the method for measuring the surface tension, and a known method can be employed. Examples include the Wilhelmi method. When the powder coating contains a thermosetting resin, the measurement may be performed in a state where the thermosetting agent is removed. Such a method may be used as long as it is possible to quickly measure and interpolate the measurement time at zero (0) to obtain the surface tension immediately before the start of thermosetting.

  Specifically, for example, a surface tension measuring device (Degiomatic ESB-V, manufactured by Kyowa Kagaku Co., Ltd.) based on the Wilhelmi method can be used for the surface tension measurement. For example, 10 g of powder coating material is put in a stainless steel petri dish and heated for 10 minutes in a thermostat at 200 ° C. to melt. And surface tension can be measured with the surface tension meter set to 200 degreeC.

  The surface tension of the powder coating is affected by its composition. In particular, the influence of the type of resin used and the influence are great when a surfactant is used. Therefore, in order to obtain a powder coating material having a specific surface tension, it is useful to study the types and / or amounts of resins and surfactants described later. As described above, the powder coating materials having different surface tensions in the melted state at 200 ° C. by 2 dyne / cm or more include surfactants, and the ratios to the resin in the powder coating materials are different from each other. It is preferable. Further, the surfactant is preferably a silicone surfactant. The same applies to the combination of powder paints in which this specific multiple coating layer can be seen when a painted surface is obtained by spraying from the spray nozzle onto the surface to be painted and then the painted surface is heat-treated. Can be considered.

  In addition, the conditions “different from each other by 2 dyne / cm or more” and “conditions containing surfactants and the ratios of resin in the powder coating are different from each other” are satisfied for all the powder coatings used. It is preferable to do this, but there are cases where this is not necessary.

  Depending on the embodiment, whether or not surface tension is involved in the formation of the “specific multiple coating layer” is not an essential requirement. Furthermore, for example, when it is required that a specific plural coating film layer is actually seen by spraying, when the resin contained in the paint is a thermosetting resin, the surface tension itself at the time of melting is specifically measured. Can be difficult. However, as described above, when it is required that a specific plural coating film layer is actually observed by spraying, a plurality of powders whose surface tensions in a molten state at 200 ° C. are different from each other by 2 dyne / cm or more. It is preferred to use a combination of paints. The requirements for the surfactant in that case are the same as described above.

  There are no particular restrictions on the type of powder coating that can be used. Specifically, it is preferable to have at least one color among magenta, yellow, cyan, white, gray and black because various colors can be realized. There is no particular limitation on the combination of colors in the powder coating. If you choose a combination of a first paint with an achromatic color selected from white, gray, or black and a second paint with a chromatic color selected from yellow, magenta, or cyan, you can choose a wide range of colors. In many cases, it is preferable.

  The powder coating used, that is, the “plurality of powder coatings” described above often includes a plurality of powder coatings having different hue, brightness, or saturation. However, a plurality of powder paints having the same hue, lightness, and saturation may be included. For example, since the components and particle sizes thereof are different, a case where a plurality of powder paints having different easiness of attachment to a painted surface is included even if they are the same color. In addition, when the powder coating used is a mixture of a plurality of separate powder coatings in advance, one powder is used depending on whether a single nozzle is used or a plurality of nozzles are used. It may be considered as a paint, and may be considered as a combination of a plurality of different powder paints.

  Here, the “powder coating material” means a set of solid particles containing a resin, a colorant, a charge control agent, an electric resistance control agent, a surfactant and the like. There are no particular limitations on the resin, colorant, charge control agent, electrical resistance control agent, and the like used, and it can be appropriately selected from known ones.

  The resin used may be referred to as a binder in the sense that it holds the colorant. As the resin used, for example, it is usually used for powder coatings such as epoxy resin, acrylic resin, phenol resin, xylene resin, urea resin, melanin resin, polyester resin, polyethylene resin, silicone resin, polyurethane resin, polyamide resin and the like. Can be used. One powder coating material may contain a plurality of resins. In that case, there may be a case where a plurality of resins coexist in one particle of powder coating particles, or a case where only one resin exists in one particle of powder coating particles.

  The polyester resin is mainly an esterified product of a polybasic acid (or methyl ester) such as dicarboxylic acid and a polyhydric alcohol such as diol.

    Examples of the diol include alkylene glycols having 2 to 36 carbon atoms (ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, octanediol, decanediol, Dodecanediol, tetradecanediol, neopentyl glycol, 2,2-diethyl-1,3-propanediol, etc .; alkylene ether glycols having 4 to 36 carbon atoms (diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol) Polytetramethylene ether glycol, etc.); alicyclic diols having 4 to 36 carbon atoms (1,4-cyclohexanedimethanol, hydrogenated bisphenol A, etc.); Or an alkylene oxide of an alicyclic diol (hereinafter abbreviated as AO) [EO, propylene oxide (hereinafter abbreviated as PO), butylene oxide (hereinafter abbreviated as BO), etc.] an adduct (addition mole number 1 to 120); AO (EO, PO, BO, etc.) addition product (addition mole number 2-30) of bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.); polylactone diol (poly ε-caprolactone diol, etc.); and polybutadiene diol, etc. Is mentioned.

  As the diol, in addition to the diol having no functional group other than the hydroxyl group, a diol having another functional group may be used.

  Examples of the diol having another functional group include a diol having a carboxyl group.

Examples of the diol having a carboxyl group include dialkylol alkanoic acids [ _C6-24 , such as 2,2-dimethylolpropionic acid (DMPA), 2,2-dimethylolbutanoic acid, 2,2-dimethylolheptane. Acid, 2,2-dimethylol octanoic acid, etc.].

  Polyols having 3 to 8 or more valences are useful for introducing a crosslinked structure. Examples of the polyol having 3 to 8 or more valences include 3 to 8 or more polyhydric aliphatic alcohols having 3 to 36 carbon atoms (alkane polyols and intramolecular or intermolecular dehydrates thereof such as glycerin, trimethylolethane, etc. , Trimethylolpropane, pentaerythritol, sorbitol, sorbitan, and polyglycerol; saccharides and derivatives thereof such as sucrose and methylglucoside); AO adducts of polyhydric aliphatic alcohols (addition mole number 2 to 120); trisphenol Adducts (such as trisphenol PA) (addition moles 2 to 30); AO adducts (novolaks such as phenol novolac and cresol novolac) (addition moles 2 to 30); acrylic polyol [hydroxyethyl (meta Acrylate and other vinyl Copolymers of Nomar etc.]; and the like.

  Examples of the dicarboxylic acid include alkane dicarboxylic acids having 4 to 36 carbon atoms (succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, octadecanedicarboxylic acid, decylsuccinic acid, etc.) and alkenyl succinic acids (dodecenyl succinic acid, pentadecethic acid). Nyl succinic acid, octadecenyl succinic acid, etc.); C6-C40 alicyclic dicarboxylic acid [dimer acid (dimerized linoleic acid), etc.], C4-C36 alkene dicarboxylic acid (maleic acid, fumar Acid, citraconic acid, etc.); aromatic dicarboxylic acids having 8 to 36 carbon atoms (phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, etc.).

  Examples of the tricarboxylic acid having 3 to 6 or more polyvalent acids include aromatic polycarboxylic acids having 9 to 20 carbon atoms (such as trimellitic acid and pyromellitic acid).

  Examples of the acrylic resin include (meth) acrylic acid and derivatives thereof, and if necessary, (co) polymerized monomers other than these containing ethylenically unsaturated bonds (C = C). Any of plastic type may be sufficient.

  Examples of (meth) acrylic acid derivatives include (meth) acrylic acid esters, (meth) acrylamides, and (meth) acrylonitriles.

  Specific examples of (meth) acrylic acid esters include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, 2- Ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, lauryl (meth) acrylate [dodecyl (meth) acrylate], glycidyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, amyl (meth) acrylate, vinyl (meth) acrylate , Β-methallyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, ethyl-α-hydroxymethyl (meth) acrylate, ethylene glycol diacrylate, Examples include seryl tri (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 2-hydroxybutyl (meth) acrylate.

  Specific examples of (meth) acrylamides include (meth) acrylamide and N-methylolacrylamide.

  Specific examples of (meth) acrylonitriles include (meth) acrylonitrile, ethyl cyano (meth) acrylate, and the like.

  Such an “acrylic resin” may be copolymerized with “other monomers” other than those described above. Specific examples of such “other monomers” include, for example, styrene, vinyl acetate, vinyltoluene. Ethylenically unsaturated bond (C = C) -containing monomers such as maleic acid, itaconic acid, (meth) acrylic acid, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and glycidyl (meth) acrylate Can be mentioned.

  As the epoxy resin, any one having two or more epoxy groups in the molecule can be used. For example, bisphenol A type, bisphenol F type, bisphenol S type, phenol novolac type, cresol novolac type, Biphenyl type, trishydroxyphenyl methane type, tetraphenylol ethane type, naphthalene type, heterocyclic, alicyclic, various modified epoxy resins, or halogenated epoxy resins in which halogens are introduced are used.

  Examples of the bisphenol type epoxy resin include Epicoat 828, Epicoat 1001, Epicoat 1004, Epicoat 1007, and Epicoat 1009 (all trade names, manufactured by Shell Chemical Co., Ltd.). A chain-extended one can also be used.

  In addition, these resins including the above-mentioned other resins are preferably melted at 200 ° C. so that they can be appropriately modified and the degree of polymerization can be adjusted. Adjustment of the degree of polymerization includes adjusting the molecular weight in the so-called oligomer region.

  When the main component of the resin in these powder coating materials is a thermosetting resin, it is preferable to use a curing agent for promoting the crosslinking reaction.

  As such a curing agent, for example, known curing agents used for powder coatings such as amines, amides, dicyandiamides, carboxylic acids, acid anhydrides, isocyanates, polysulfides, acid dihydrazides, imidazoles, etc., alone or It can be used by mixing.

  Examples of the colorant include inorganic or organic pigments such as titanium dioxide, ben pattern, yellow iron oxide, carbon black, phthalocyanine blue, and quinacridone red pigment. Charge control agents include nigrosine electron donating dyes, other metal salts of naphthenic acid or higher fatty acids, alkoxylated amines, quaternary ammonium salts, alkylamides, chelates, pigments, fluorination activators, electron-accepting organics Examples include complexes and sulfonylamines of copper phthalocyanine. Examples of the electrical resistance control agent include granular titanium oxide, acicular titanium oxide, iron powder, ferrite powder, and magnetite powder.

  When considering the influence of these components as the physical properties of the powder coating material, the resistance, charge amount, and particle size of the powder coating material are important. Regarding the particle size, it is known that the small particle size powder coating particles have higher chargeability than the large particle size powder coating particles. The charge control agent in the powder coating has a function of increasing the chargeability, and the electrical resistance control agent has a function of decreasing the chargeability. Therefore, it is also possible to control the addition amount of these powder coatings. It is possible to control the charge amount.

  There is no restriction | limiting in particular about the kind of surfactant which can be used in the above, It can select suitably from well-known surfactant. A nonionic surfactant having a hydrophilic group and a hydrophobic group is preferred because it hardly affects the chargeability of the powder coating material and has good dispersion stability in the resin. However, this does not exclude other types of surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants.

  As such nonionic surfactants, for example, silicone surfactants such as polydimethylsiloxane-polyether and polydimethylsiloxane-polyester represented by the following general formula can be used. Moreover, a fluorine-type surfactant, an alkyl ether derivative, and an alkyl ester derivative can also be used. These may be used in combination. Among these, a silicone-based surfactant is preferable because of its great effect.

  The surfactant may be added at the stage of polymerizing the resin from the monomer or at the stage of melting and kneading the constituent materials of the powder coating material. However, when the surfactant is added in the polymerization stage of the resin, it is limited to materials that do not inhibit the polymerization of the resin or induce side reactions.

The number average molecular weight of the silicone polymer in the silicone surfactant is preferably 5 × 10 ^{2 to} 5 × 10 ⁴ . When the number average molecular weight exceeds this range, the dispersibility in the resin tends to be reduced. If it is less than 5 × 10 ² , the degree of decrease in surface tension may be insufficient.

  There is no restriction | limiting in particular in the addition amount of surfactant, It can select suitably based on the kind of surfactant, and the surface tension of resin to be used. In the case of a polyester resin, 0.01 to 2% by weight is generally preferable with respect to the total weight of the powder coating material. In the above, there is no particular limitation on the degree to which the ratio of the surfactant to the resin in the powder coating is different, but in general, the difference is considered to be in the range of 0.02 to 2% by weight. If it is less than 0.02% by weight, it is difficult to obtain the effect, and even if it exceeds 2% by weight, a special effect is often not expected. Note that the above “different from each other” includes a case where one is 0 (zero, that is, a case where no surface activity is included).

  The surfactant in the above may include a substance not called a surfactant. That is, any surfactant can be considered as long as it can change the surface tension of the powder coating in a molten state at 200 ° C. regardless of its name. In addition, when a specific multiple coating layer appears by adding a certain substance, or when the appearance and disappearance of a specific multiple coating layer is observed by changing the amount of a certain substance added, May be considered an activator. Changing the surface tension can be realized by increasing or decreasing the surface tension, but the addition of the surfactant acts in the direction of decreasing the surface tension. Increasing the surface tension can be achieved by reducing the amount of the surfactant added.

  There is no restriction | limiting in particular in the injection nozzle in the above, What kind of thing may be used if it can be used for powder coating. A nozzle called a so-called corona charging type coating gun can be suitably used. The plurality of spray nozzles may be realized using a plurality of paint guns, or may be realized using a paint gun having a plurality of nozzles. When one spray nozzle is used and there is only one powder coating material supply port, a plurality of powder coating materials are mixed in advance and then supplied to the spray nozzle. If a plurality of powder coating supply ports are provided, it is also possible to supply them separately.

  FIG. 3 shows that two different color powder coatings 1, 2 indicated by a black circle 1 and a hollow circle 2 are sprayed simultaneously from two separate spray nozzles 3, 4 onto the surface to be coated. It shows a state where spraying is performed with overlapping times and painting is performed. The coating surface 7 is grounded, and the powder coatings 1 and 2 charged by the applied voltage are sprayed from the tip of the spray nozzles 3 and 4 toward the coating surface 7 by the accompanying gas (for example, air). It adheres to the surface 7. The guide 8 is for changing the spraying direction of the powder paint. In FIG. 3, HV1 and HV2 mean the applied load voltage (high voltage). The applied voltages may be the same or different from each other.

  In such a configuration, when the load voltage is changed, the adhesion ratio of the powder coatings 1 and 2 adhering to the painted surface 7 may change. Therefore, it is possible to achieve a painted surface having a desired color by adjusting the load voltage. In this case, the load voltage of both the load voltage application devices 5 and 6 may be changed, or one of them may be fixed and only the other may be changed. Furthermore, you may add changing the gas amount to accompany and the supply amount itself of the powder coating materials 1 and 2 itself. Although there is no restriction | limiting in particular about the change range of a load voltage, It can be said that the range of 30-100 kV is practically preferable.

  Any method of applying the load voltage may be used. Since what is called a corona charging type paint gun has such a function, it can be used. A corona charging type paint gun usually employs a load voltage of 30 to 100 kV. The load voltage may be changed for the powder paint passing through all the nozzles or for the powder paint passing through some of the nozzles.

  In this case, the amount of powder coating applied to the surface to be coated is affected by the design of the nozzle (for example, the diameter of the narrowest part), the amount of powder coating supplied, the flow velocity of the entrained air flow, the applied voltage value, etc. Receive. The amount of powder coating applied to the surface to be coated and the amount of powder coating supplied are not necessarily the same for a plurality of powder coatings, but may be different from each other.

  The spray nozzle is usually placed perpendicular to the surface to be coated, but this need not be the case. The surface to be coated may be placed vertically, horizontally, or at some other angle.

 There is no restriction | limiting in particular about the heat processing apparatus of a coating surface, A well-known heat processing apparatus can be used. The same applies to the heating method, heating temperature, heating time, cooling method, cooling time, and the like.

  Whether or not a specific multiple coating layer appears may depend on the type of powder coating used, the coating conditions and / or the heat treatment conditions, so it is confirmed by trial that the specific multiple coating layer appears. You may need to

  Regardless of the powder coating material, the powder coating method itself has not been known so far for a technique for obtaining a specific plural coating layer when coating is performed simultaneously.

  Specifically, this novel powder coating method can be realized by adopting a powder coating method including the following operations so that a specific plural coating film layer can be seen. In this case, it is often preferable to appropriately adjust the heat treatment conditions. The contents of the heat treatment conditions can be appropriately determined according to the actual situation, but it is practical and preferable to adjust at least one of the heating temperature and the heating time. The adjustment of the heating temperature and the heating time includes simple selection of the heating temperature and the heating time.

  ・ Use a combination of individual powder coatings.

  -The powder coating in this combination is separately sprayed from a plurality of spray nozzles onto the surface to be coated by overlapping the spraying timing to obtain a painted surface.

  -Next, heat the painted surface.

  Moreover, when using one injection nozzle, the powder coating method including the following operation is employable instead.

  ・ Use a combination of multiple powder paints.

  ・ To obtain a painted surface by spraying this powder coating combination together from one spray nozzle onto the surface to be coated.

  -Next, heat the painted surface.

  Needless to say, it is preferable to use the powder coating combinations described so far as the powder coating combinations.

  In this way, it is possible to realize a coating film in which a plurality of coating film layers parallel to the coating surface are seen in a cross section perpendicular to the coating surface. Such a coating film can be applied to various uses that are not particularly limited. There is no particular limitation on the object to be coated on which such a coating film is formed. In addition to any product, a paint test piece made of metal, ceramic, or the like may be included.

  There is no restriction | limiting in particular as a coating object which applies said coating method and powder coating system, It can apply to what is well-known. However, it can be said that an electronic device housing that has a wide variety of objects and requires rapid painting is a particularly preferable application. In this case, an electronic device housing having various kinds of colors can be manufactured at low cost.

  Such electronic device cases include electronic device cases such as notebook computers, personal digital assistance (PDA), mobile phones, car navigation systems, and the like. FIG. 4 is a front view of a notebook PC casing showing an example of the electronic apparatus casing of the present invention. The powder coating material of the present invention is applied to the surface of the housing of FIG.

  Next, examples and comparative examples of the present invention will be described in detail.

  In addition, the surface tension measuring apparatus (Degeomatic ESB-V, Kyowa Kagaku Co., Ltd.) by the Wilhelmi method was used for the measurement of the surface tension in a 200 degreeC molten state.

[Example 1] (Preparation of polyester resin)
Polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane 5.0 mol, ethylene glycol 5.0 mol, terephthalic acid 8.0 mol, 1,2,4-benzenetricarboxylic anhydride Product (trimellitic anhydride) 1.0 mol and 5.9 g of dibutyltin oxide were placed in a glass four-necked flask, and a thermometer, a stainless steel stirring bar, a flow-down condenser and a nitrogen inlet tube were attached. The reaction was completed by reacting in a nitrogen stream in a heater at 190 ° C. for 3 hours, 220 ° C. for 3 hours, 240 ° C. for 3 hours, and further at the same temperature for 1 hour under reduced pressure of 60 mmHg.

  The obtained resin was a pale yellow solid, the softening point by a flow tester was 120 ° C., and the glass transition temperature by DSC was 68 ° C.

[Example 2] (Control of surface tension)
Table 1 shows the results of measuring the surface tension of various resins in a molten state at 200 ° C. In Table 1, “polyester resin” means the polyester resin prepared in Example 1, “epoxy resin” is bisphenol A type epoxy resin, “Epicoat 1055” (epoxy equivalent 850) manufactured by Japan Epoxy Resin Co., Ltd. “Acrylic resin” means polymethacrylate, and “styrene acrylic resin” means a copolymer of polymethacrylate and styrene. These are all thermoplastic resins.

  The polyester resin powder (surface tension 21 dyne / cm, average particle size 10 μm) prepared in Example 1 was used as the first powder coating, and acrylic resin (polymethacrylate) powder (surface) was used as the second powder coating. A coating test was performed using a tension of 10 dyne / cm and an average particle size of 10 μm. In addition, about the 1st powder coating material, when the resin was 100 weight part as a colorant, 50 weight part of white colorants were mixed. For the second powder coating, 20 parts by weight of a magenta colorant was mixed as the colorant when the resin was 100 parts by weight. The supply amount of the first powder paint and the supply amount of the second powder paint were the same.

  As the coating machine, a powder coating machine (product name: OptiFlex, manufactured by Landsburg Industry Co., Ltd.) having two spray nozzles was used. After coating, it was heat-treated in an oven heated to 150 ° C. for 15 minutes, cooled to room temperature, and then observed for a cross-section of the coating film with a microscope having a magnification of 500 times. The total film thickness (total of the two films) of the coating film was 30 μm.

  As a result, the paint was separated into layers, and two layers parallel to the painted surface were formed. Specifically, it was found that a second paint film having a low surface tension was formed on the surface of the paint film, and the first paint was formed in a portion close to the surface to be coated. The thickness of the two layers was equivalent.

[Example 3] (Control of surface tension)
The result of having measured the surface tension in the molten state of 200 degreeC of the composition obtained by using the same polyester resin as Example 2, and adding the silicone type surfactant as a surface tension reducing agent to the polyester resin of a molten state Is shown in Table 2. As the silicone-based surfactant, FZ-2162 manufactured by Toray Dow Corning was used.

[Example 4] (Control of surface tension)
A melt having 0.001% by weight of the silicone surfactant in Table 2 was solidified and pulverized to obtain a powder coating material A having an average particle size of 10 μm.

  Similarly, a 2.00 wt% melt of the silicone surfactant in Table 2 was solidified and pulverized to obtain a powder coating B having an average particle size of 10 μm. However, in this case, when the total amount of the resin and the surfactant was 100 parts by weight, 20 parts by weight of a magenta colorant was mixed instead of the white colorant.

  These powder coatings were powder-coated in the same manner as in Example 2 to obtain a coating film having a total film thickness of 30 μm. As a result, the paint is separated into layers, and a paint film of paint B having a lower surface tension is formed on the surface of the paint film. It was found that it was formed. The thickness of the two layers was equivalent.

[Example 5] (Evaluation of uneven color)
The powder paint of Table 3 was used. No ingredients other than those listed in Table 3 were used.

  The resin, colorant and surfactant described in Table 3 were melted and mixed, cooled and solidified, and then pulverized to obtain each powder coating having an average particle size of 10 μm. The surface tension is a value in a molten state of 200 ° C. of each powder coating material.

  These powder coating materials were combined and sprayed simultaneously from different nozzles in the same manner as in Example 2 to adhere to the flat magnesium alloy surface. Thereafter, baking was carried out at 150 ° C. for 15 minutes to form a coating film. Table 4 shows the result of observing the color unevenness with the naked eye when the painted surface is corrected from the direction orthogonal to the painted surface.

  Three people in charge of evaluation were appointed for evaluation of color unevenness. Evaluation was made with 1 point for no color unevenness, 0 point for uneven color, 3 for a total of 3 points, and x for 2 points or less.

  As a result, it was proved that all the ◯ marks were obtained when the surface tension was 2 dyne / cm or more. For some of these, the cross section of the coating film was observed. As a result, the coating material of the first coating group and the coating material of the second coating group were phase-separated, and a specific multiple coating layer was formed.

  In addition, the invention shown to the following additional remarks can be derived from the content disclosed above.

(Appendix 1)
A combination of powder coatings,
When the powder coating combination is sprayed from the spray nozzle onto the surface to be painted to obtain a painted surface, and then the painted surface is heated, a cross section perpendicular to the painted surface is parallel to the painted surface. The coating layer of
Combination of powder paint.

(Appendix 2)
A combination of powder coatings,
The surface tension in the molten state at 200 ° C. of each powder coating of the combination differs from each other by 2 dyne / cm or more.
Combination of powder paint.

(Appendix 3)
A combination of powder coatings,
The surface tension of each powder coating of the combination in the molten state at 200 ° C. is different from each other by 2 dyne / cm or more,
When the powder coating combination is sprayed from the spray nozzle onto the surface to be painted to obtain a painted surface, and then the painted surface is heated, a cross section perpendicular to the painted surface is parallel to the painted surface. The coating layer of
Combination of powder paint.

(Appendix 4)
The combination of powder coating materials according to any one of appendices 1 to 3, wherein the ratio of the surfactant contained in each powder coating material in the combination to the resin contained in the powder coating material is different from each other.

(Appendix 5)
The combination of the powder coating materials of Claim 4 whose said surfactant is a silicone type surfactant.

(Appendix 6)
Use multiple spray nozzles,
When the powder coating of each combination is separately sprayed from the plurality of spray nozzles onto the surface to be coated while overlapping the spraying timing to obtain the painted surface, and then the painted surface is heat-treated The combination of powder coating materials according to any one of appendices 1 to 5, wherein a plurality of coating layers parallel to the painted surface are seen in a cross section perpendicular to the painted surface.

(Appendix 7)
Using one injection nozzle,
When the powder coating combination is sprayed onto the surface to be coated from the one spray nozzle together to obtain a painted surface, and then the painted surface is heat-treated, in a cross section perpendicular to the painted surface, The combination of powder coating materials according to any one of appendices 1 to 5, wherein a plurality of coating film layers parallel to the painted surface can be seen.

(Appendix 8)
Using a combination of powder coatings;
Each of the powder paints in the combination is separately sprayed from a plurality of spray nozzles on the surface to be coated, with the spray timing overlapping, to obtain a painted surface;
Then heat treating the painted surface,
In the heat treatment, by adjusting at least one of the heating temperature and the heating time, a plurality of coating layers parallel to the painted surface can be seen in a cross section perpendicular to the painted surface after the heat treatment. Like
How to apply powder paint.

(Appendix 9)
Using a combination of powder coatings;
The powder coating combination is sprayed together from one spray nozzle onto the surface to be coated to obtain a painted surface;
Then heat treating the painted surface,
In the heat treatment, by adjusting at least one of the heating temperature and the heating time, a plurality of coating layers parallel to the painted surface can be seen in a cross section perpendicular to the painted surface after the heat treatment. Like
How to apply powder paint.

(Appendix 10)
The powder coating method according to appendix 8 or 9, wherein the powder coating combination according to appendices 1 to 7 is used as the powder coating combination.

(Appendix 11)
The coating film by which the some coating film layer parallel to the said coating surface is seen in the cross section perpendicular | vertical to the coating surface coated using the coating method in any one of appendix 8-10.

(Appendix 12)
An electronic device casing coated by using the coating method according to any one of appendices 8 to 10.

In powder coating, it is a typical sectional view for explaining the case where it does not separate into two layers. In powder coating, it is typical sectional drawing for demonstrating the case where it divides into two layers (a kind of specific multiple coating film layer). It is a schematic diagram for demonstrating powder coating. In the figure, two different color powder coatings are sprayed simultaneously from two separate spray nozzles. It is a figure which illustrates the housing | casing by which the powder coating material was coated on the surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Powder coating material 2 Powder coating material 3 Injection nozzle 4 Injection nozzle 5 Load voltage application device 6 Load voltage application device 7 Paint surface 8 Guide

Claims (7)

A combination of powder coatings,
When the powder coating combination is sprayed from the spray nozzle onto the surface to be painted to obtain a painted surface, and then the painted surface is heated, a cross section perpendicular to the painted surface is parallel to the painted surface. The coating layer of
Combination of powder paint. A combination of powder coatings,
The surface tension in the molten state at 200 ° C. of each powder coating of the combination differs from each other by 2 dyne / cm or more,
Combination of powder paint.   The combination of powder paints according to claim 1 or 2, wherein the ratio of the surfactant contained in each powder paint in the combination to the resin contained in the powder paint is different from each other. Use multiple spray nozzles,
Each of the powder coatings in the combination is separately sprayed from the plurality of spray nozzles to the surface to be coated with overlapping spraying timing to obtain the painted surface.
The combination of the powder coating material in any one of Claims 1-3. Using a combination of powder coatings;
Each of the powder paints in the combination is separately sprayed from a plurality of spray nozzles on the surface to be coated, with the spray timing overlapping, to obtain a painted surface;
Then heat treating the painted surface,
In the heat treatment, by adjusting at least one of the heating temperature and the heating time, a plurality of coating layers parallel to the painted surface can be seen in a cross section perpendicular to the painted surface after the heat treatment. Like
How to apply powder paint.   The powder coating method according to claim 5, wherein the powder coating combination according to claim 1 is used as the powder coating combination.   An electronic device casing coated by using the coating method according to claim 5.

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