JP2598021B2 - Steel sheet surface treatment method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method of a powder coated steel sheet for exterior use of household electric appliances such as a refrigerator, a washing machine, and a large heating appliance. is there.

[Problems to be solved by conventional technology and invention]

The powder coating method has advantages such as easy control of coating operation conditions and reduction of correction coating operation because of good paint wraparound during coating. This coating method is advantageous in terms of processing as compared with other coating methods, and is also excellent in the corrosion resistance of the coating film. For this reason, it has been considered to use a powder-coated steel sheet as an exterior decorative board for the household electric appliance. However, exterior decorative panels such as household electric appliances are painted parts that require high designability, whereas painted surfaces by the powder coating method are rougher than painted surfaces formed by other painting methods. Therefore, a technology for compensating this and improving the design is required.

As a means of improving the design, it is conceivable to apply a pattern or coloring to the powder-coated steel sheet by screen printing or transfer, but in this case, the effect of blurring the rough surface can be expected, but the smoothness of the painted surface is obtained It is not possible. In order to obtain the smoothness of the painted surface, a method of removing irregularities on the painted surface by polishing or the like can be considered. However, in this case, an extremely long processing time is required, and mass production is difficult.

In addition, in order to smooth the surface of a yuzu skin-like coating such as a powder-coated steel plate, a UV-curable resin is applied on the coating by the powder coating method, and a laminate film is adhered on top of it. The thickness of the UV-curable resin is adjusted through the laminate film, and the UV-curable resin is irradiated with ultraviolet rays to cure the UV-curable resin, and then the laminate film is peeled off. (See JP-A-62-53776).

According to this proposal, the surface of a powder-coated steel sheet can be smoothed, but there is no consideration for surface treatment of the pressed steel sheet. It is not sufficient as a surface treatment method.

The present invention solves the above-mentioned problems of the prior art, and performs a desired pattern or coloring on any desired range of a powder coated surface and a mirror finish even for a pressed steel plate. It is an object of the present invention to provide a method for surface treatment of a steel sheet which can be performed.

[Means for solving the problem]

The present invention provides a transparent resin layer made of a touch-dried ultraviolet curable resin on the peelable surface of a peelable film having a UV-permeable property and a peelable surface being a mirror surface, in order to achieve the above object. Forming a transfer sheet provided with a colored picture layer made of a composition containing a UV-curable resin, pressing a steel sheet and applying powder coating to the steel sheet, powder coating the steel sheet A step of applying a fluid ultraviolet curable resin to the surface by screen printing, and a step of pressing the colored picture layer or the transparent resin layer of the transfer sheet and the ultraviolet curable resin applied surface of the steel sheet so as to face each other, And a step of irradiating the steel sheet with ultraviolet rays from the peelable film side, and a step of peeling the peelable film.

[Action]

As described above, the present invention applies a flowable ultraviolet curable resin to a powder coated surface of a steel sheet by a screen printing method, and transfers the powder to a transfer layer of a transfer sheet via the flowable ultraviolet curable resin. Since the coated surface of the body-coated steel sheet is pressed and hardened and the UV-curable resin is transferred onto the steel sheet, even if the steel sheet is pressed, the desired amount of UV-curable Resin can be applied, and thereby, a smooth transfer layer is transferred to the surface of the steel sheet with the flowable ultraviolet curable resin filling the irregularities of the powder coating surface in any desired range, and the transfer is performed. By the hardening of the layer, it is possible to obtain a flat and excellent steel plate.

The powder coating of the powder-coated steel sheet is mainly formed of a polyester-based powder coating, and its molecular skeleton is similar to the ultraviolet curable resin and the SP value is similar, and The transfer layer adheres strongly to the powder-coated steel sheet because it is cured in a state where the fluid ultraviolet curable resin is hardly embedded in the powder-coated layer.

In addition, since the colored pattern layer penetrates into the ultraviolet curable resin layer, it has excellent physical strength, and further, the ultraviolet curable resin layer, the colored pattern layer, and the transparent resin layer are copolymerized at the interface of each layer. And has strong chemical contact, so that delamination or the like does not occur.

〔Example〕

In the present invention, first, a desired transfer layer is provided on a release film to form a transfer sheet. As the releasable film, a film which is transparent to ultraviolet rays and whose releasable surface is a highly glossy mirror surface is used. Further, the releasable film only needs to have a releasable surface on at least one side, and a film obtained by applying a releasable paint on the surface of an appropriate plastic film can be used. Examples of the plastic film include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyethylene terephthalate, polybutylene terephthalate, polyamide, acrylic (for example, polymethyl methacrylate), rubber hydrochloride, ethylene / vinyl acetate copolymer or ionomer. Plastic film is used.

As the releasable paint, a paint prepared by adding a silicone resin or a wax to an appropriate vehicle that adheres to the above-mentioned plastic film is used.

Instead of applying the above-mentioned releasable paint to a plastic film, a plastic film having a releasable surface formed by extrusion coating with a releasable resin such as polyethylene or polypropylene can also be used. Furthermore, the above-mentioned plastic film alone may be used as a peelable film in view of the adhesiveness with the vehicle in the pattern.

Examples of the transfer layer formed on the peelable film include a transparent resin layer made of a UV-curable resin that has been touch-dried, and a colored picture layer made of a composition containing the same UV-curable resin. When it is desired to form only the mirror-finished protective layer on the powder-coated steel sheet as the transfer object, only the transparent resin layer made of the touch-dried ultraviolet curable resin is formed on the peelable film. When it is desired to form a patterned mirror-finished protective layer on a powder-coated steel sheet, two layers, a transparent resin layer made of an ultraviolet-curable resin and a colored picture layer made of a composition containing the ultraviolet-curable resin, are sequentially formed. Form. In any case, the transparent resin layer can be colored to give a colored mirror finish. If there is no problem in use even without the transparent resin layer, only the colored pattern layer may be formed on the peelable film.

In the present invention, the ultraviolet curable resin used for forming the transparent resin layer means a coating type resin which can be easily cured in several seconds to several minutes by irradiation with ultraviolet rays to form a tough coating film.

The UV-curable resin contains a resin component, an organic solvent, and a photopolymerization initiator as essential components, and may further include a reactive diluent, a non-reactive resin, a wax, a plasticizer, and the like. .

The resin component is a polymer or oligomer having at least one loaded polymerizable double bond in the molecule,
It may be solid or liquid at room temperature. The liquid resin component can also serve as a reactive diluent. Such polymers or oligomers include unsaturated polyester resins, acryloyl group-reactive resins, allyl group-reactive resins,
There are sol-type resins, etc., but workability of forming a coating film, light resistance,
From the viewpoints of weather resistance and abrasion resistance, an acryloyl group reactive resin is preferable. Specific examples of the acryloyl group-reactive resin include, for example, acrylate of a simple polyol, side-chain acryloyl-type acrylic resin prepolymer, telomerized polyester acrylate, telomerized polyamide acrylate, acrylate of urethane resin, and acrylate of silicone resin.

Examples of the organic solvent include, for example, methyl ethyl ketone, methyl isobutyl ketone, cyclohexane, ethyl acetate, butyl acetate, amide amide, dimethylformamide, 1,4-dioxane, n-hexane, benzene, toluene, xylene, methyl cellosolve, butyl cellosolve, and the like. Is mentioned. These organic solvents are used alone or in combination of two or more.

The reactive diluent is an addition-polymerizable compound that is liquid at room temperature, and has an action of crosslinking the resin component, or of polymerizing or crosslinking by itself to help form a tough coating film. Things. Although many such reactive diluents are known, acrylic diluents are particularly effective. Specific examples of the acrylic diluent include, for example, polyethylene glycol diacrylate, 2-ethylhexyl acrylate, tetrahydrofurfuryl acrylate,
Hydroxypropyl acrylate, diethylene glycol ethyl ether acrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, neopentyl hydropivalate diacrylate, trimethylolpropane triacrylate, 1,6
-Hexanediol diacrylate, dipentaerythritol hexaacrylate, neopentyl adipate diacrylate, tetramethylol methane tetraacrylate, (bisphenol A) bisdiethylene glycol ether diacrylate, and the like.

The photopolymerization initiator is a compound that easily generates free radicals upon irradiation with ultraviolet light, and includes, for example, benzoylalkyl ethers, α-acyloxime esters, acetophenones, henzophenones, benzine ketals, and ketone-amines. Such compounds are preferably used.

The ratio of the organic solvent to the resin component is preferably 20 to 400 parts by weight of the organic solvent to 100 parts by weight of the resin component. If the proportion of the organic solvent is less than 20 parts by weight, the coatability is undesirably reduced. On the other hand, when the amount is 400 parts by weight or more, not only the touch drying property is reduced and productivity is deteriorated, but also the coating properties such as light resistance, weather resistance and abrasion resistance are reduced, which is not preferable.

The photopolymerization initiator is usually used in an amount of about 1 to 8 parts by weight based on 100 parts by weight of the resin component or the total amount of the resin component and the reactive diluent.

In the present invention, the intended purpose is achieved by using an ultraviolet-curable resin having the above-mentioned composition, and further, when the following non-reactive resin is blended into the ultraviolet-curable resin, touch drying is achieved. It has been found that the properties are improved. Such non-reactive resins include, for example, cyclohexanone ketone resin, polyvinyl butyral resin, cellulose derivative, polyamide resin, cyclized rubber, phenolic resin, polyester resin, vinyl acetate resin, acrylic resin, silicone resin And the like. Further, wax having the same function as the non-reactive resin can be used.

The non-reactive resin is used in an amount of usually 20 parts by weight or less based on 100 parts by weight of the resin component or the total amount of the resin component and the reactive diluent. If the amount of the non-reactive resin exceeds 20 parts by weight, poor curing occurs, and the physical properties of the transparent resin layer are undesirably reduced.

Next, the ultraviolet-curable ink used for forming the colored picture layer is obtained by mixing a pigment with the ultraviolet-curable resin used for forming the transparent resin layer described above to form an ink. As the pigment, for example, azo pigments, anthraquinone pigments, indanthrene pigments, quinacridone pigments, copper phthalocyanine pigments, perylene pigments, perinone pigments, indigo pigments, titanium dioxide pigments, graphite,
Cobalt blue, ultramarine, navy blue, iron oxide, zinc white, barium sulfate, clay talc, mica, titanium dioxide, pearl pigment, carbon black and the like.

In the present invention, a photocurable coloring composition disclosed in Japanese Patent Publication No. 58-8401 can also be used as the colored picture layer forming ultraviolet curable ink.

The transparent resin layer made of an ultraviolet curable resin is formed on a peelable film by a coating means such as a roll coat or a gravure coat after adjusting the above resin to an appropriate viscosity.

The colored pattern layer is formed by a printing means such as a gravure printing method or a silk screen printing method using the ink composition containing the above-mentioned ultraviolet curable resin. As the ink composition, it is preferable to use an ink composition that does not easily shield ultraviolet rays from the viewpoint of sufficiently curing the transparent resin layer interposed between the transfer sheet and the powder-coated steel sheet. In addition to pigments having a small diameter, pearl pigments are also preferable examples.

The powder-coated steel sheet used in the present invention is a steel sheet obtained by applying a powder coating to a steel sheet by an electrostatic coating method or the like and then heating and hardening the steel at a predetermined temperature and time.

The powder coating used was prepared by melting a thermosetting synthetic resin, kneading this with a pigment for coloring and / or a coating and an additive such as a surfactant, then solidifying by cooling, pulverizing and pulverizing. Examples of the paint and the thermosetting synthetic resin include a polyester resin, an acrylic resin, and an epoxy resin. The powder coated steel sheet used in the present invention may be a flat plate-shaped steel sheet, or may be cut, formed, or attached with other parts so as to have a desired shape.

The colored pattern layer or the transparent resin layer of the prepared transfer sheet is opposed to the painted surface of the powder coated steel sheet, and the two are pressed together with a fluid ultraviolet curable resin interposed therebetween.

The ultraviolet curable resin having fluidity to be interposed between the transfer sheet and the powder coated steel sheet is an ultraviolet curable resin similar to the ultraviolet curable resin used to form the above-described transparent resin layer, It contains a resin component, an organic solvent, and a photopolymerization initiator as essential components, and further contains a reactive diluent, a non-reactive resin, a wax, a plasticizer, and the like. It can be easily cured in seconds or minutes by irradiating a line of sight to form a tough resin layer.It exhibits a liquid state so that it can be easily applied at room temperature. The transfer sheet is applied to the powder-coated steel sheet and applied to the powder-coated steel sheet by applying it in a bi-method.

Pressing of both is performed by means such as a roll, a flat belt, and a press, and in the pressed state, ultraviolet rays are irradiated from the side of the peelable film, and the transparent resin layer and / or the colored picture layer, the transfer sheet, and the powder coating are applied. The ultraviolet curable resin interposed between the steel sheet and the steel sheet is cured, and then the peelable film is peeled.

By the way, depending on the product, there is a case where it is desired to form a colored picture layer and / or a transparent resin layer only in a desired area of the powder coated steel sheet. In such a case, a desired transfer layer is partially formed when the transfer sheet is manufactured. Alternatively, at the time of ultraviolet irradiation, only a desired portion can be cured by limiting an irradiated portion using an ultraviolet shielding mask. In this case, it is not necessary to partially form a transfer layer. As for the method of providing the mask,
A method of forming an ultraviolet shielding portion on a transfer unnecessary portion using a composition containing a substance having an ultraviolet shielding property such as carbon black on the back surface of the transfer sheet, that is, on the side without the transparent resin layer or the colored pattern layer, another There is a method of forming an ultraviolet shielding portion on a film or glass and interposing it between the ultraviolet light source and the transfer sheet, and a method of providing an ultraviolet shielding portion around a quartz cylinder or the like covered with the ultraviolet light source.

The powder-coated steel sheet treated as described above is filled with irregularities on the powder-coated surface by a flowable ultraviolet curable resin, and a mirror-like surface protection layer having excellent hardness is formed on the surface. However, if necessary, it can be further pressed with a mirror roll to further promote the mirror surface state.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 (A) is a process explanatory view showing one example of a surface treatment method for a powder coated steel sheet according to the present invention. As shown in this figure, in this embodiment, a steel plate 1 is used as a substrate, which is pressed into a desired shape 2 and then subjected to powder coating.

In the present invention, a transfer film F shown in a schematic sectional view in FIG. 3 is used. That is, in FIG.
Is a peelable film made of a long polyethylene terephthalate having a thickness of 150μ. An ultraviolet curable resin consisting of 28 parts by weight of a urethane acrylate resin, 2 parts by weight of benzophenone, 35 parts by weight of ethyl acetate, and 35 parts by weight of toluene is provided on one surface thereof. Coated with gravure roll coater, 60
The transparent resin layer 5 is formed by drying with hot air at -80 ° C for 1 minute.

Next, using a UV curable ink having the following composition on the transparent resin layer 5 and printing it with a gravure plate,
Is formed.

Polyurethane acrylate resin 30 parts by weight Copper phthalocyanine pigment 0.5 parts by weight Pearl pigment 20.0 parts by weight Benzophenone 2.0 parts by weight Ethyl acetate 27.5 parts by weight Toluene 20.0 parts by weight Using the transfer film F constructed as described above, its transparent resin layer 5 and coloring The pattern layer 6 is transferred onto the coating layer 3 of the powder coated steel sheet via a fluid ultraviolet curable resin. For example, as shown in FIG. 2 (A), a screen printing machine 8, a transfer device 9, and an ultraviolet irradiation device 10 are disposed along a roller conveyor 7, and the transfer device 9 has a delivery roller for delivering a transfer film F. 9a, a transfer roller 9b, and a peel roller 9c for peeling off and transferring the transferred film F '
And a powder coated steel plate 1 ′ on the roller conveyor 7.
Are supplied at regular intervals. First, a fluid ultraviolet curable resin 11 is applied on the coating layer 3 of the powder-coated steel sheet by the screen printing machine 8, and then the transfer film F is coated with the ultraviolet curable resin 11. Then, the transparent resin layer 5, the colored pattern layer 6 and the ultraviolet curable resin 11 are cured by irradiating ultraviolet rays from an ultraviolet lamp 10a on the powder coated steel sheet by a transfer roller 9b, and the transferred film F 'is peeled off by the peeling roller 9c to transfer the transparent resin layer 5 and the colored picture layer 6 onto the powder-coated steel sheet.

In the above embodiment, the transparent resin layer 5 and the colored pattern layer 6 were transferred to the powder-coated steel sheet. However, the present invention is not limited to such an example, and a colored pattern is required. If not, only the transparent resin layer may be transferred, or the transparent resin layer may be omitted and only the colored picture layer may be transferred.

〔The invention's effect〕

As described above, the present invention relates to the peelable surface of the peelable film, which has a UV-transmitting property and the peelable surface is a mirror surface,
A step of forming a transfer sheet provided with a transparent resin layer made of a UV-curable resin dried to the touch and / or a colored picture layer made of a composition containing the UV-curable resin; A step of applying powder coating, a step of applying a fluid ultraviolet curable resin to the powder coated surface of the steel sheet by a screen printing method, and a step of applying a colored pattern layer or a transparent resin layer of the transfer sheet and an ultraviolet ray of the steel sheet. A step of crimping with the curable resin applied surface facing,
A step of irradiating the steel sheet with ultraviolet rays from the peelable film side and a step of peeling the peelable film, so that even in the case of a pressed steel sheet, a desired amount of the steel sheet in any desired range An ultraviolet curable resin can be applied, whereby a smooth transfer layer is transferred to the surface of the steel sheet in a state where the fluid ultraviolet curable resin fills the irregularities of the powder coating surface in any desired range, By curing the transfer layer, it is possible to obtain an exterior plate such as a household electric appliance which is smooth and excellent in design.

[Brief description of the drawings]

FIG. 1 (A) is a process explanatory view showing an example of a surface treatment method for a powder coated steel sheet according to the present invention, and FIG. 2 (A) is an apparatus for carrying out the process shown in FIG. 1 (A). FIG. 3 is a schematic cross-sectional view showing an example of a powder-coated steel sheet and a transfer film before transfer, and FIG. 4 is a schematic cross-sectional view showing a state after transfer. 1 ... steel plate, 3 ... powder coating layer, F ... transfer film,
4 ... Releasable film, 5 ... Transparent resin layer, 6 ... Colored picture layer, 11 ... Ultraviolet curable resin with fluidity during transfer.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Kimio Fukatsu 800, Tomita, Ohira-machi, Shimotsuga-gun, Tochigi Prefecture Inside Tochigi Plant, Hitachi, Ltd. No. Dai Nippon Printing Co., Ltd. (72) Inventor Yasushi Ishii 1-1-1, Ichigaya Kagacho, Shinjuku-ku, Tokyo Dainippon Printing Co., Ltd. No. 6 Inside Dainichi Seika Kogyo Co., Ltd. (72) The inventor ▲ Takaichiro Miya 1-7-6 Nibashi Bakurocho, Chuo-ku, Tokyo Dainichi Seika Kogyo Co., Ltd. (56) References JP-A-62-53776 (JP, A) JP-A-61-161178 (JP, A)

Claims (1)

(57) [Claims] 1. A peelable film having a UV-transmitting property and a mirror-finish peelable surface, wherein the peelable surface contains a transparent resin layer made of a UV-curable resin dried by touch and / or an ultraviolet-curable resin. Forming a transfer sheet provided with a colored pattern layer composed of a composition to be pressed, pressing a steel plate and applying powder coating to the steel plate, and flowing the powder-coated surface of the steel plate by a screen printing method. A step of applying an ultraviolet curable resin having a property, a step of pressing a colored pattern layer or a transparent resin layer of the transfer sheet and an ultraviolet curable resin applied surface of the steel sheet so as to face each other, and from the peelable film side. A method for treating a surface of a steel sheet, comprising: irradiating the steel sheet with ultraviolet light; and peeling the peelable film.