JPH06184491A - Coating compound for precoated metal plate and precoated metal plate - Google Patents

Abstract

PURPOSE:To obtain a fluororesin-based coating compound useful for a precoated metal plate not damaging excellent processability immediate after production in change with time after the production and to produce a precoated metal plate by coating a metal plate with the coating compound. CONSTITUTION:A fluororesin-based coating compound comprises (A) a polyvinylidene fluoride and (B) an acrylic resin as main components. (p) A thermoplastic resin is blended with (s) a thermosetting resin in the weight ratio of 15:85 to 90:10 to give (B) the acrylic resin, which is mixed with (A) the polyvinylidene fluoride in the ratio of the component A:B=50:50 to 90:10 to give the objective coating compound for a precoated metal plate. A precoated metal plate is obtained by coating a metal plate with this coating compound and has a top coating compound composed of the above-mentioned coating compound at least on one side of the metal plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paint for a precoated metal plate and a precoated metal plate produced by using this paint. This technique described below is, for example, a material for consumer products and an interior of a vehicle. This is a proposal for materials that are advantageously used as interior and exterior materials for buildings.

[0002]

2. Description of the Related Art A precoated metal sheet is a coated metal sheet obtained by coating a material metal sheet before processing with a paint in advance. Generally, it is a hot dip galvanized steel sheet, an alloy plated steel sheet of zinc and aluminum, or aluminum. A paint is applied on a metal plate such as a plated steel plate or a stainless steel plate.

Such a pre-coated metal plate does not require painting after processing, and parts requiring long-term weather resistance such as metal roofs and outer walls of buildings and constructions, interiors of electric equipment and vehicles, interiors of elevators. Widely used as interior wall material. In fact, when this pre-coated metal sheet is used for roofs, outer walls of buildings and structures, it is common to perform forming processing such as press bending and bending of up to 90 degrees, Moreover, long-term quality assurance is required for the coating film on the metal plate.

Therefore, in such a precoated metal sheet for which a long-term guarantee of coating film is required, it is usual to use a fluororesin-based coating material as the topcoat (finishing) coating material. Furthermore, in recent years, the demands of the market have increased, and there is a marked trend toward higher performance in the field of this precoated metal sheet.
A long-term guarantee that the warranty period of the coating film is 20 years or more has come to be required. As a coating film that meets such requirements, the color change in the accelerated weathering test 1500 hours is 7 or less in NBS color difference (ΔE), and AST in the salt spray test 2000 hours
It is required to show performance of M 8F or higher. In such quality requirements, the part of the precoated metal sheet that is particularly problematic is the part that is subjected to forming processing such as 90-degree or 180-degree press bending and bending.

On the other hand, conventionally, as a coating material satisfying the above-mentioned required properties for a coating film, a fluororesin type coating material containing 50% by weight or more of polyvinylidene fluoride as a resin component in the coating material is mainly used.

However, the polyvinylidene fluoride resin is
Since it is a crystalline polymer and has poor processability, when manufacturing a precoated metal sheet by molding, a coating consisting of polyvinylidene fluoride-based paint cannot overcome the elongation and cracks of the material, and cracks and peeling can not be overcome. There is a problem in that coating film defects such as the above tend to occur. Therefore, the polyvinylidene fluoride resin is rarely used alone as a resin component in the precoat metal plate coating composition,
Various improvements have been proposed.

For example, first, by blending a polyvinylidene fluoride resin with a non-crystalline thermoplastic acrylic resin that is compatible with this resin, the melting point of polyvinylidene fluoride is lowered and crystallization is suppressed, Techniques for improving the workability of precoated metal sheets have been proposed (Japanese Patent Publication No. 45-96).
62, Japanese Patent Publication No. 3-11266 and Japanese Patent Application Laid-Open No. 2-174977). Secondly, a technique has been proposed in which the crystallinity of polyvinylidene fluoride is lowered by rapidly cooling to near room temperature after baking the fluororesin-based paint and improving the workability of the precoated metal sheet (special feature). Kai 61-1148
(See Japanese Patent Publication No. 46).

[0008]

According to the above-mentioned prior art, a precoated metal sheet coated with a fluororesin-based coating has a low degree of crystallinity of the coating film immediately after production, and is press bent at 90 degrees or 180 degrees. It can withstand molding such as bending and bending. However, the problem that the crystallization of polyvinylidene fluoride progresses with the lapse of time after production and the workability of the precoated metal sheet deteriorates still remains. That is, in the pre-coated metal sheet according to the conventional technique, the forming process of the pre-coated metal sheet needs to be performed immediately after the production of the pre-coated metal sheet, and further, the pre-coated metal sheet has to be produced in accordance with the forming process. . Furthermore, when the manufacturing time of the pre-coated metal plate does not match the molding processing time, there is a manufacturing and production defect that the metal plate is baked again and subjected to a quenching process.

An object of the present invention is to overcome the above-mentioned various problems of the prior art, and in particular, pre-coated metal which does not impair the excellent workability immediately after the production in the aging after the production. It is an object to provide a suitable fluororesin-based paint for a plate and a precoated metal plate obtained by coating the paint on a metal plate.

[0010]

Means for Solving the Problems As a result of intensive studies to realize the above-mentioned objects, the inventors have made the acrylic resin component in the fluororesin coating a blend of thermoplasticity and thermosetting property. As a result, they have found that it is possible to effectively suppress an increase in the crystallinity of the coating film with the lapse of time after production, and the present invention has been made.

That is, the coating material for a precoated metal plate of the present invention is a coating material containing as a main component a resin composition comprising a mixture of polyvinylidene fluoride (A) and an acrylic resin (B). B) is a blend of the thermoplastic acrylic resin (p) and the thermosetting acrylic resin (s), and the proportion of the blend is (p) by weight:
(S) = 15: 85 to 90:10. Further, in this coating composition, the resin composition comprising a mixture of polyvinylidene fluoride (A) and an acrylic resin (B) has a mixing ratio of (A) :( B) = 50: 50 by weight. It is characterized by being in the range of 90:10. The precoated metal sheet of the present invention is characterized by having an overcoat coating film obtained by applying the above coating material on at least one surface of the steel sheet.

[0012]

By using the coating material for a precoated metal sheet according to the present invention, a precoated metal sheet capable of maintaining excellent workability for a long period of time can be easily and reliably produced. The coating material for such a precoated metal plate and the precoated metal sheet obtained using this coating material will be described in detail below.

1 to 4 show X-rays of a coating film on a precoated metal plate obtained by applying an overcoating material on the uppermost surface of a metal plate and baking it as shown in Examples and Comparative Examples described later. It is a diffraction diagram, and shows the crystallized state of a coating film. In these figures, X _c represents the diffraction area of the polyvinylidene fluoride, which is the resin component in the coating film, due to the crystalline portion, and X _a is the polyvinylidene fluoride, which is the resin component in the coating film, and the amorphous acrylic resin. The diffraction area by a part is shown. 1 and 2 are diagrams relating to Comparative Example 1 described later, and FIGS. 3 and 4 are diagrams relating to Example 2.

As is clear from the results shown in the X-ray diffraction diagrams of FIGS. 1 and 2, the conventional fluororesin paint in which the acrylic resin is composed of only the thermoplastic resin has a low crystallinity immediately after production, On the other hand, it becomes very high in 3 months after manufacturing. This is a result consistent with the deterioration of the workability of the precoated metal sheet. In this respect, as is apparent from FIGS. 3 and 4, a coating film obtained from the fluororesin-based coating material of the present invention, that is, the fluororesin-based coating material in which the acrylic resin in the coating material is a mixture of thermoplasticity and thermosetting property. The crystallinity of
It is as low as just after the production even after 9 months from the production.
Therefore, it is understood that the workability does not decrease and the excellent workability can be maintained for a long period of time after the manufacturing.

The X-ray diffraction intensity test method is, for example, a device in which the target material is copper, the filter is nickel, the divergent slit is 1 degree, and the receiving slit for receiving the diffracted X-ray is 0.3 mm. At a tube voltage of 40 kV and a tube current of 80 mA
It is possible to use a method of measuring the diffraction intensity with a scintillation counter under the measurement conditions of a time constant of 1 second and a goniometer scanning speed of 1 degree / minute.

As described above, according to the coating material for a pre-coated metal plate of the present invention, two publicly known thermosetting and thermoplastic acrylic resins are simply mixed with polyvinylidene fluoride to achieve an extremely simple means. It becomes possible to reliably prevent the deterioration of workability due to a change with time after the production of the precoated metal plate, which could not be achieved by the conventional fluororesin-based paint mixed with only the thermoplastic acrylic resin.

The polyvinylidene fluoride used in the coating material for a precoated metal plate of the present invention preferably has a weight average molecular weight of 400,000 or more and a melting point of 150 to 180 ° C. For example, Kainer 500 (manufactured by Japan Penwalt, weight average molecular weight 650,000, melting point 160 to 165 ° C.) and the like can be mentioned.

In the precoat metal plate coating composition of the present invention, the quality of the acrylic resin to be mixed must be one that does not impair the excellent properties of the conventional coating composition and its coating film. Specifically, it has compatibility with polyvinylidene fluoride, suppresses crystallization of polyvinylidene fluoride, can improve the workability of the coating film formed by baking, the workability of the coating film formed by baking is It is required that it does not deteriorate with time after manufacturing.

That is, when an acrylic resin compatible with polyvinylidene fluoride is mixed and a coating material containing these as a main component is applied on a metal plate and baked to form a coating film, the polymer in the coating film is formed. This is because it is necessary to maintain the microscopic morphology of the above for a long time.

However, in the conventional fluororesin-based paint, polyvinylidene fluoride and acrylic resin, which are the main components, are thermoplastic ones, and therefore, the high paint content in the coating film formed after coating and baking the paint. The morphology of the molecules at the molecular level changes over time, and as a result, the pre-coated metal sheet produced using the conventional fluororesin-based coating,
The workability gradually deteriorates with the passage of time after manufacturing.

In this respect, since the thermosetting acrylic resin is mixed in the fluororesin type paint in the coating material for a precoated metal sheet of the present invention, the workability of the coating film immediately after the production of the precoated metal sheet is maintained for a long time. It will be. Here, the thermosetting acrylic resin is a crosslinkable polymer,
As such, it has a property of poor workability. Therefore, it is not preferable to replace the entire acrylic resin component in the fluororesin paint with this thermosetting acrylic resin. Therefore, in the present invention, a part of the acrylic resin component in the conventional fluororesin coating material is replaced with the thermosetting acrylic resin to form a mixture of the thermoplastic acrylic resin and the thermosetting acrylic resin. That is, the mixing ratio of the thermoplastic acrylic resin and the thermosetting acrylic resin is preferably 15:85 to 90:10 by weight,
More preferably, the range is 40:60 to 85:15.

As the above-mentioned thermoplastic acrylic resin, 70% by weight or more of its polymerized units are alkyl (meth) acrylate monomers having 3 to 12 carbon atoms, such as methyl (meth) acrylate or ethyl (meth) acrylate, It is composed of one or more monomers selected from propyl (meth) acrylate, butyl (meth) acrylate, amyl (meth) acrylate, octyl (meth) acrylate, etc., and has a weight average molecular weight of 40,000. Those of up to 300,000 are preferred. More desirably, 50% by weight or more of the polymerized units constituting the thermoplastic acrylic resin is methyl methacrylate.

On the other hand, of the polymerized units of the thermoplastic acrylic resin
The monomer that constitutes 30% by weight or less may be any monomer that can be copolymerized with the acrylic monomer. Examples of such a monomer include styrene, vinyltoluene, (meth) acrylonitrile, and vinyl chloride.

Examples of the thermosetting acrylic resin include an acrylic resin having a crosslinkable reactive group such as a hydroxyl group, a carboxy group, a glycidyl group, an active halogen of bromine or iodine, and an isocyanate group, an alkylated melamine or a polyol, It is composed of a curing agent such as polyamine, polyamide, polyoxirane, etc. and has an average molecular weight of 1,000-
It may be 20,000.

In contrast to the conventional fluororesin-based coating composition containing polyvinylidene fluoride and a single thermoplastic acrylic resin as main components, in the present invention, instead of this thermoplastic acrylic resin,
The above-mentioned acrylic resin (B), which is a mixture of the thermoplastic resin (p) and the thermosetting resin (s) in a weight ratio of 15:85 to 90:10, is added to The vinylidene chloride (A) is mixed in a ratio of (A) :( B) = 50: 50 to 90:10. The reason for this is that if the ratio (A) / (B) is 0 to 1, problems with long-term weather resistance occur, while if the ratio (A) / (B) is 9 or more, the degree of crystallinity of the baked coating film becomes high and This is because the property deteriorates. That is, the main component resin of the coating material for a precoated metal plate of the present invention is a resin having a low cross-linking structure and has neither the property of being too hard nor the property of being too soft.

In addition to the above essential components, the precoat metal plate coating material of the present invention may contain inorganic aggregates, organic aggregates, color pigments, extender pigments, solvents and additives as required. .

Examples of the inorganic aggregate include glass beads, glass fibers, alumina fibers, alumina particles, silica, and pyrogenic silica. Examples of the organic aggregate include polyacrylonitrile beads, benzoguanamine beads, and nylon beads.
Examples of the coloring pigment include titanium oxide, carbon black, iron oxide, lead chromate, metal powder (Al, Cu),
Examples include calcined pigments (cobalt blue, green) and pearl pigments. Examples of the extender pigment include calcium carbonate, clay, talc, antimony trioxide, barium sulfate and kaolin. Examples of the solvent include toluene, xylene, ethyl acetate, butyl acetate, cellosolve-based solvent, methyl isobutyl ketone, methyl ethyl ketone, diisobutyl ketone, isophorone,
Examples thereof include cyclohexanone.

Next, a method for producing a precoated metal sheet using the above-described coating material for a precoated metal sheet will be described. First, in general, metal plates are degreased before painting, and in some cases chemical polishing such as pickling or electrolytic pickling, and then chemical conversion coating such as chromate treatment or phosphoric acid treatment. Is applied. Here, as the metal plate, for example, a hot dip galvanized steel plate, a zinc-aluminum alloy plated steel plate, an aluminum plated steel plate, a cold rolled steel plate, a stainless steel plate, an aluminum plate, or the like is used.

The next step is a step of applying the precoat metal plate paint on the metal plate on which the chemical conversion film has been formed. In this step, the paint for the precoated metal plate can be directly coated on the chemical conversion film, but in order to improve the performance such as the corrosion resistance of the precoated metal plate and the adhesion of the coating film, it is usually applied to the coated metal plate. It is desirable that the undercoating material used, for example, an epoxy resin-based, polyester-based, polyurethane-based undercoating material containing a metal pigment is applied, baked, and then applied.

The viscosity of the coating material for this pre-coated metal plate at the time of coating may be the same as that of an ordinary coating material used for the pre-coated metal sheet. For example, in the case of roll coating,
Ford cup # 4 (25 ° C) preferably 40-180 seconds.

The method of applying the paint for precoat metal plate is not particularly limited, and the methods used in the conventional coating of solvent-based paint, such as brush coating, tampo coating, roll coating, spray coating. And the like can be used. Among them, the roll coating method is the most suitable method for coating the precoated metal sheet as in the present invention.

The next step is a treatment for baking and curing the coating film applied on the metal plate. This bake cure is 260
Heat the metal plate at a temperature near ℃ for 15 to 180 seconds.
It is carried out by reaching 100 ° C or higher, preferably 160 ° C or higher. The reason for this is that the curing of the resin component is insufficient when the baking time is less than 15 seconds, while the curing of the resin component becomes excessive when the baking time exceeds 180 seconds,
This is because the original performance of the paint cannot be exhibited in either case.

The heating method in this bake-hardening is not particularly limited, and any method is selected from, for example, an external heating method such as a convection heating method and a radiant heating method, or an internal heating method such as high frequency. be able to.

The cooling method after heating and baking is described in JP-A-61-
The quenching method described in Japanese Patent No. 114846 may be used, but it may also be performed under slightly milder conditions, for example, a shower method using tap water or a dip method.

The thickness of the coating film thus formed on the metal plate is 5 to 80 μm, preferably 10 after baking and curing.
The range is up to 50 μm. If it is desired to increase the final coating film thickness, this coating-baking and curing treatment may be repeated once or more.

[0036]

【Example】

According to the formulation ratio of the adjustment Table 1 (Examples and Comparative Examples) top coat was prepared various top coating by the following method. That is, polyvinylidene fluoride,
Put the pigment and solvent in separate containers and stir them to mix them uniformly in the mixture consisting of the thermoplastic acrylic resin, the thermosetting acrylic resin (A, B) and other components, and apply various top coats. Prepared.

[0037]

[Table 1]

The various components in the top coating in Table 1 are
Specifically, it is as follows. * 1: PVDF polyvinylidene fluoride (Kainer 500, manufactured by Nihon Penwalt, weight average molecular weight: 650,000, melting point: 160-165 ° C) * 2: PVDF polyvinylidene fluoride (NEOFLON VP-850, manufactured by Daikin Industries, weight average molecular weight:
(600,000, melting point: 160-165 ° C) * 3: Thermoplastic acrylic resin, acrylic resin for paint, weight average molecular weight: 55,000, glass transition point: 85 ° C * 4: Thermosetting acrylic resin A, B A ··· Hydroxyl value: 34mgKOH / g, weight average molecular weight: 7,000
, Hardener: Methylated melamine B..Hydroxyl value: 22mgKOH / g, Weight average molecular weight: 11,00
0, Curing agent: Butylated melamine * 5: Pigment Pigment composition: Titanium oxide: 3 wt%, Firing brown: 49 wt
%, Baked black: 43 wt%, antimony trioxide: 5 wt% * 6: Pearl pigment Fostaflon TF-9205, manufactured by Hoechst Japan * 7: Glass fiber Micro Glass Surface TRAND REV-9, manufactured by Nippon Sheet Glass * 8: Solvent solvent composition ..Isophorone: 98 wt%, methyl isobutyl ketone: 2 wt%

Preparation of Test Piece First, the coated surface of the metal plate was degreased and then phosphoric acid treated to form a coating film on the metal plate to form a coating film. Next, an epoxy resin-based paint (trade name: pre-color primer F-1, manufactured by NOF CORPORATION) was used as an undercoat paint on the metal plate on which the chemical conversion film was formed, using a bar coater to give a dry paint film thickness of 5 μm. And was dried and cured at an ultimate plate temperature of 210 ° C. Next, the topcoat paints shown in Table 1 were applied to the metal plate coated with the basecoat paint using a bar coater so that the thickness of the dry coating film would be 30 μm, and dried and cured at the ultimate plate temperature of 250 ° C. Then, the coated metal plate was immersed in a water tank filled with tap water and cooled to prepare a test piece. The test piece thus produced was evaluated by the test method and evaluation method described below.

Test Method and Evaluation Method (1) Workability After each test, the workability of each test piece was tested in a room at 25 ° C. The same metal plate as the test piece to be processed is sandwiched inside the test piece (1T and 2T to 6T in Table 2 are
Insert one or two to six metal plates), test piece
The test piece was bent 180 degrees, and the tip of the bent test piece was observed with a 10-fold loupe and evaluated. As a result of observation, Table 2 shows the processing levels at which no cracks were formed in the coating film. The pass level of this workability is 0T to 2T. (2) Adhesion test Each test piece immediately after the production is kept in the normal state and in boiling water 2
In the state after immersion for a period of time, perform the workability test of (1) above (performed from 1T to 3T), press-fit the cellophane tape to the tip of the bent test piece and forcibly peel it off. It was evaluated according to the standard. ◎: No abnormalities ○: Very slightly peeled coating film ●: Slightly peeled coating film △: Very peeled coating film ×: Significantly peeled coating film (3) Weather resistance test JIS B 7752 " UV carbon arc lamp type weather resistance tester "
Using the UV carbon arc lamp accelerated weathering tester (manufactured by Suga Test Instruments Co., Ltd.) specified in Section 1, the test pieces were subjected to an irradiation test for 5000 hours. After the test was completed, the 60-degree specular gloss of the test piece was measured using a gloss meter (manufactured by Suga Test Instruments Co., Ltd.), and the gloss retention with respect to the initial gloss was determined to evaluate the weather resistance.

Evaluation Results The evaluation results of the test pieces are shown in Tables 2, 3 and 4. As is clear from the results shown in these tables, the precoated metal sheet of the present invention is slightly inferior in its long-term weather resistance as compared with the conventional fluororesin-coated metal sheet,
It was confirmed that the coating film has excellent adhesion and that it can maintain excellent workability for a long period of time after being manufactured.

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

As described above, in the coating material for a precoated metal plate of the present invention, since the acrylic resin in the coating material is composed of a mixture of a thermoplastic resin and a thermosetting resin, The crystallinity is low and does not change in the long term. Therefore, according to the coating material for a precoated metal plate of the present invention, it is possible to easily and reliably provide a stable quality precoated metal plate that can maintain excellent workability for a long period of time after being manufactured. As a result, long-term durability can be guaranteed without being affected by the processing time of the precoated metal plate. As a result, it becomes possible to collectively carry out small-quantity, multi-product manufacturing, and it is possible to significantly improve the productivity of the precoated metal sheet.

[Brief description of drawings]

FIG. 1 is a view showing an X-ray diffraction measurement result immediately after production of a coating film obtained by using a conventional coating material for a precoated metal plate.

FIG. 2 is a diagram showing an X-ray diffraction measurement result of a coating film obtained using a conventional coating material for a pre-coated metal plate, 3 months after the production.

FIG. 3 is a view showing an X-ray diffraction measurement result immediately after the production of a coating film obtained by using the coating material for a precoated metal plate of the present invention.

FIG. 4 is a diagram showing the results of X-ray diffraction measurement 9 months after the production of a coating film obtained by using the coating material for a precoated metal plate of the present invention.

Claims (3)

[Claims] 1. A paint containing as a main component a resin composition comprising a mixture of polyvinylidene fluoride (A) and acrylic resin (B), wherein the acrylic resin (B) is a thermoplastic acrylic resin (p). And a thermosetting acrylic resin (s), and the proportion of the mixture is (p) :( s) = 15: 85 to 90:10 in weight ratio. Paint. 2. The resin composition comprising a mixture of polyvinylidene fluoride (A) and an acrylic resin (B) has a mixing ratio of (A) :( B) = 50: 50 to 90: by weight. Ten
The coating composition for a precoated metal plate according to claim 1, wherein 3. A precoated metal plate obtained by applying the paint according to claim 1, wherein the metal plate has a top coating film of the paint on at least one surface of the metal plate.