JP3179907B2 - Paint for pre-coated metal sheet and pre-coated metal sheet - Google Patents

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 pre-coated metal sheet and a pre-coated metal sheet manufactured by using the paint. It is a proposal for materials that are advantageously used as materials, building interior and exterior materials, and the like.

[0002]

2. Description of the Related Art A pre-coated metal sheet is a coated metal sheet obtained by applying a paint on a raw metal sheet before processing. Generally, a hot-dip galvanized steel sheet, an alloy-plated steel sheet of zinc and aluminum, aluminum Paint is applied on a metal plate such as a plated steel plate or a stainless steel plate.

[0003] Such a pre-coated metal sheet does not require painting after processing, and is required for long-term weather resistance, such as a metal roof or an outer wall of a building or a building, or an interior of an electric device, a vehicle, or an elevator. Widely used as indoor wall materials. In fact, when this pre-coated metal sheet is used for roofs, outer walls of buildings and structures, etc., it is normal that forming processing such as press bending and bending as much as 180 degrees is performed at 90 degrees, In addition, long-term quality assurance is required for the coating film on the metal plate.

[0004] Therefore, in the case of a pre-coated metal sheet for which such a long-term coating guarantee is required, it is common to use a fluororesin-based paint as the overcoat (finish) paint. Furthermore, in recent years, the demands on the market have become increasingly severe, and the field of pre-coated metal sheets also has a remarkable tendency toward higher performance.
A long-term warranty of 20 years or more for coating films has been required. As a coating film corresponding to such a request, a change in color at 1500 hours in the accelerated weathering test was 7 or less in NBS color difference (ΔE) and AST in 2000 hours in the salt spray test.
It is required to exhibit a performance of M8F or more. In such a quality requirement, a part of the precoated metal plate that is particularly problematic is a part to be subjected to forming processing such as press bending or bending of 90 or 180 degrees.

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

However, polyvinylidene fluoride resin is
Because it is a crystalline polymer and has poor workability, when manufacturing precoated metal sheets by molding, the coating film made of polyvinylidene fluoride paint cannot overcome the elongation and cracking of the material, and cracks and peels However, there is a problem that a coating film defect such as the above is likely to occur. Therefore, polyvinylidene fluoride resin is rarely used alone as a resin component in a paint component for a pre-coated metal plate,
Various improvements have been proposed.

For example, first, by blending a non-crystalline thermoplastic acrylic resin compatible with the polyvinylidene fluoride resin, the melting point of the polyvinylidene fluoride is lowered to suppress crystallization, A technique for improving the workability of a precoated metal sheet has been proposed (Japanese Patent Publication No. 45-96)
62, JP-B-3-11266 and JP-A-2-174977). Secondly, there has been proposed a technique of rapidly cooling to near room temperature after baking of a fluororesin-based paint, thereby reducing the crystallinity of polyvinylidene fluoride and improving the workability of a pre-coated metal plate. 61-1148 Kaisho
No. 46).

[0008]

According to the above prior art, a precoated metal sheet coated with a fluororesin paint has a low degree of crystallinity immediately after production and has a 90 ° or 180 ° press bending. It can withstand forming processes such as bending and bending. However, after the production, there still remains a problem that crystallization of polyvinylidene fluoride progresses with a lapse of time, and the workability of the precoated metal plate deteriorates. That is, in the precoated metal sheet according to the prior art, there is a problem that the forming process needs to be performed immediately after the production of the precoated metal sheet, and the precoated metal sheet must be manufactured at the time of the forming process. . Further, when the production time of the precoated metal sheet does not match the molding processing time, there are drawbacks in production and production such as baking this metal sheet again and performing a quenching treatment.

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

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and have found that the acrylic resin component in a fluororesin-based paint is a mixture of thermoplastic and thermosetting. As a result, the present inventors have found that it is possible to effectively suppress the increase in the degree of crystallinity of the coating film with the lapse of time after production, and reached the present invention.

That is, the paint for a precoated metal sheet of the present invention comprises polyvinylidene fluoride (A) and acrylic resin (B).
In paint containing as a main component a resin composition comprising a mixture of, said acrylic resin (B) is a thermoplastic acrylic resin (p) and uncured thermosetting acrylic resin
a blend of (s), the proportion of the blend is at a weight ratio (p) :( s) = 15 : 85~90: I 10 range der of the
And it is characterized in Rukoto that having a polyvinylidene fluoride compatibility. In this paint, the resin composition comprising a mixture of polyvinylidene fluoride (A) and acrylic resin (B) has a weight ratio of the mixture.
(A): (B) = 50: 50 to 90:10. And the pre-coated metal plate of the present invention has a top coat formed by applying the above-mentioned paint to at least one surface of a steel plate.

[0012]

When the paint for a precoated metal sheet according to the present invention is used, a precoated metal sheet capable of maintaining excellent workability for a long time can be easily and reliably produced. Hereinafter, the prepainted metal sheet paint and the precoated metal sheet obtained by using the paint will be described in detail.

FIG. 1 to FIG. 4 show X-rays of a coating film on a pre-coated metal plate obtained by applying a top coat on the top 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 crystallization state of a coating film. In these figures, X _c represents a diffraction area due crystalline portion of polyvinylidene fluoride which is a resin component in the coating film, X _a is amorphous polyvinylidene fluoride and an acrylic resin as a resin component in the coating film 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-based paint in which the acrylic resin is composed of only a thermoplastic resin has a low crystallinity immediately after production, On the other hand, it becomes very high three months after production. This is a result consistent with the deterioration in workability of the precoated metal sheet. In this regard, as apparent from FIGS. 3 and 4, the coating film obtained from the fluororesin paint of the present invention, that is, the fluororesin paint in which the acrylic resin in the paint is a blend of thermoplasticity and thermosetting properties. The crystallinity of
Even after 9 months of production, it is as low as immediately after production.
Therefore, it is understood that excellent processability can be maintained over a long period of time after production without deterioration in processability.

The X-ray diffraction intensity test method is, for example, an apparatus in which the target material is copper, the filter is nickel, the divergent slit is once, and the receiving slit for receiving the diffracted X-ray is 0.3 mm. , Using a concentrated X-ray beam with a tube voltage of 40 kV and a tube current of 80 mA,
Under a measurement condition in which the time constant is 1 second and the scanning speed of the goniometer is 1 degree / minute, a method of measuring the diffraction intensity with a scintillation counter can be used.

As described above, according to the prepainted metal sheet paint of the present invention, two kinds of conventionally known thermosetting and thermoplastic acrylic resins are simply mixed with polyvinylidene fluoride by an extremely simple means. This makes it possible to reliably prevent deterioration in workability due to a change over time after manufacturing a precoated metal sheet, which cannot be achieved by a conventional fluororesin-based paint in which only a thermoplastic acrylic resin is mixed.

The polyvinylidene fluoride used in the prepainted metal sheet paint 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, Kynar 500 (manufactured by Nippon Penwald, weight average molecular weight: 650,000, melting point: 160 to 165 ° C) and the like can be mentioned.

In the prepainted metal sheet paint of the present invention, the quality of the acrylic resin to be mixed must be such that the excellent properties of the conventional paint and its coating film are not impaired. Specifically, compatibility with polyvinylidene fluoride, suppression of crystallization of polyvinylidene fluoride, improvement in processability of a film formed by baking, and processability of a film formed by baking are improved. It is required that it does not deteriorate over time after production.

That is, when an acrylic resin compatible with polyvinylidene fluoride is mixed and a paint containing these as a main component is applied to 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 micro morphology over a long period of time.

However, in the conventional fluororesin-based paint, since the main components, polyvinylidene fluoride and acrylic resin, are thermoplastic, high paint in a coating film formed after applying and baking this paint is preferred. The form of the molecule at the molecular level changes with time, and as a result, the pre-coated metal plate manufactured using the conventional fluororesin-based paint,
The workability gradually deteriorates with the passage of time after production.

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

As the thermoplastic acrylic resin, 70% by weight or more of the polymerized units thereof 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, and has a weight average molecular weight of 40,000. ~ 300,000 are preferred. More desirably, those in which 50% by weight or more of the polymerized units constituting the thermoplastic acrylic resin are methyl methacrylate are preferred.

On the other hand, the polymerization unit of the thermoplastic acrylic resin
The monomer constituting 30% by weight or less may be any as long as it can be copolymerized with the acrylic monomer. Examples of such a monomer include styrene, vinyltoluene, (meth) acrylonitrile, and vinyl chloride.

The above-mentioned thermosetting acrylic resin includes, for example, an acrylic resin having a crosslinking reactive group such as a hydroxyl group, a carboxy group, a glycidyl group, an active halogen of bromine or iodine, an isocyanate group, an alkylated melamine or a polyol. Consists of curing agents such as polyamines, polyamides, and polyoxiranes, and has an average molecular weight of 1,000 to
It can be 20,000.

In contrast to the conventional fluororesin-based paint containing polyvinylidene fluoride and a single thermoplastic acrylic resin as main components, in the present invention, instead of the thermoplastic acrylic resin,
The acrylic resin (B) as described above, which is a mixture of two types, a thermoplastic type (p) and a thermosetting type (s), in a weight ratio of 15:85 to 90:10, is used as a polyfluoropolymer. The mixture is mixed at a ratio of (A) :( B) = 50: 50 to 90:10 with respect to vinylidene fluoride (A). The reason is that when the ratio (A) / (B) is 0 to 1, there is a problem in long-term weather resistance, while when the ratio (A) / (B) is 9 or more, the degree of crystallinity of the baked coating film increases and the processing becomes difficult. This is because the property deteriorates. That is, the main component resin of the paint for a precoated metal sheet of the present invention is a resin having a low cross-linking structure, and has a property of being neither too hard nor too soft.

The prepainted metal sheet paint of the present invention can contain, if necessary, inorganic aggregates, organic aggregates, coloring pigments, extender pigments, solvents and additives, in addition to the above essential components. .

Examples of the inorganic aggregate include glass beads, glass fibers, alumina fibers, alumina particles, silica, and calcined 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),
Calcined pigments (cobalt blue, green), pearl pigments and the like. Examples of the extender include calcium carbonate, clay, talc, antimony trioxide, barium sulfate, and kaolin. Examples of the solvent include toluene, xylene, ethyl acetate, butyl acetate, cellosolve solvents, methyl isobutyl ketone, methyl ethyl ketone, diisobutyl ketone, isophorone,
And cyclohexanone.

Next, a method of manufacturing a precoated metal sheet using the above-described paint for a precoated metal sheet will be described. First, generally, a metal plate is subjected to a degreasing treatment before painting, and, in some cases, a chemical polishing such as pickling or electrolytic pickling, followed by a chemical conversion treatment such as a chromate treatment or a 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 a pre-coated metal sheet paint on the metal sheet on which the chemical conversion film has been formed. In this step, the paint for the pre-coated metal sheet can be applied directly on the chemical conversion film.However, in order to improve the performance such as the corrosion resistance of the pre-coated metal sheet and the adhesion of the coating film, the coating is usually performed on the coated metal sheet. It is preferable to apply a base coat used, for example, an epoxy resin-based, polyester-based, or polyurethane-based base coat containing a metal pigment, and then apply the base coat.

The viscosity of the prepainted metal plate paint at the time of application may be the same as that of the usual paint used for the precoated metal plate. For example, in the case of roll coating,
It is preferably 40-180 seconds at Ford Cup # 4 (25 ° C).

The method of applying the paint for the precoated metal sheet is not particularly limited, but may be any of the methods used for coating conventional solvent-based paints, for example, brushing, tampo coating, roll coating, spray coating. Such a method can be used. Among them, the roll coating method is the most suitable method for coating a precoated metal sheet as in the present invention.

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

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

The cooling method after heating and baking is described in
The cooling may be performed by the quenching method described in Japanese Patent Publication No. 114846, but may be performed under milder conditions. For example, the cooling may be performed by a shower method or a dip method using tap water.

The thickness of the coating film formed on the metal plate in this manner is 5 to 80 μm after baking and curing, preferably 10 to 80 μm.
5050 μm. In order to increase the thickness of the final coating, this coating-baking hardening treatment may be repeated one or more times.

[0036]

【Example】

(Examples and Comparative Examples) Adjustment of Top Coating In accordance with the mixing ratio in Table 1, various top coatings were prepared by the following methods. That is, polyvinylidene fluoride,
The pigment and the solvent are placed in separate containers, respectively, and stirred, and uniformly mixed in a mixture of a thermoplastic acrylic resin, a thermosetting acrylic resin (A, B) and other components, and various top coatings are formed. Prepared.

[0037]

[Table 1]

Various components in the top coat in Table 1 are as follows:
The details are as follows. * 1: PVDF polyvinylidene fluoride (Kyner 500, manufactured by Nippon Penwald, weight average molecular weight: 650,000, melting point: 160 to 165 ° C.) * 2: PVDF polyvinylidene fluoride (NEOFLON VP-850, manufactured by Daikin Industries, weight average molecular weight:
* 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
, Curing agent: methylated melamine B... Hydroxyl value: 22 mgKOH / g, weight average molecular weight: 11,00
0, curing agent: butylated melamine * 5: pigment pigment composition: titanium oxide: 3 wt%, baked brown: 49 wt
%, Calcined black: 43 wt%, antimony trioxide: 5 wt% * 6: Pearl pigment Fostaflon TF-9205, manufactured by Hoechst Japan * 7: Glass fiber Microglass Surface Strand REV-9, manufactured by Nippon Sheet Glass * 8: Solvent Solvent composition ..Isophorone: 98% by weight, methyl isobutyl ketone: 2% by weight

Preparation of Test Piece First, the coated surface of the metal plate was degreased, and then subjected to phosphoric acid treatment to form a chemical conversion film on the metal plate on which a coating film was formed. Next, on the metal plate on which the chemical conversion film was formed, an epoxy resin-based paint (trade name: Precolor Primer F-1, made by Nippon Oil & Fat Co., Ltd.) was used as an undercoat paint using a bar coater to have a dry coating thickness of 5 μm. And dried and cured at an ultimate plate temperature of 210 ° C. Next, on the metal plate coated with the undercoat paint, various topcoat paints shown in Table 1 were applied using a bar coater so that the thickness of the dried coating film became 30 μm, and the coating was dried and cured at an 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 pieces thus prepared were evaluated by the following test methods and evaluation methods.

Test Method and Evaluation Method (1) Workability The workability of each test piece was tested in a room at 25 ° C. over time of each test. The same metal plate as the specimen to be processed is sandwiched inside the specimen (1T, 2T to 6T in Table 2 are:
One, two to six metal plates)
The test piece was bent 180 degrees, and the tip of the bent test piece was observed and evaluated with a 10-fold loupe. As a result of the observation, Table 2 shows processing levels at which cracks did not occur in the coating film. The acceptable level of the workability is 0T to 2T. (2) Adhesion test Immediately after the preparation, each test specimen was
After the immersion for a period of time, the workability test of the above (1) was performed (implemented from 1T to 3T), and a cellophane tape was pressure-bonded to the tip of the bent test piece and forcibly peeled off. The evaluation was based on criteria. ◎: No abnormality at all ○: Very slightly peeled coating ●: Slightly peeled coating △: Substantially peeled coating ×: Extremely peeled coating (3) Weather resistance test JIS B 7752 UV Carbon Arc Light Type Weathering Tester "
Using an ultraviolet carbon arc lamp accelerated weathering tester (manufactured by Suga Test Instruments Co., Ltd.), the test piece was 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), and the gloss retention relative to the initial gloss was determined to evaluate weatherability.

Evaluation Results The evaluation results of the test pieces are shown in Tables 2, 3 and 4. As is evident from the results shown in these tables, the precoated metal sheet of the present invention is not inferior in its long-term weather resistance, as compared with a conventional fluororesin coated metal sheet,
It was confirmed that the adhesiveness of the coating film was excellent and that excellent processability could be maintained over a long period of time after production.

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

As described above, in the paint for a precoated metal sheet according to the present invention, the acrylic resin in the paint is composed of a blend of a thermoplastic resin and a thermosetting resin. The crystallinity is low without change over time. Therefore, according to the paint for a precoated metal sheet of the present invention, it is possible to easily and reliably provide a precoated metal sheet of stable quality that can maintain excellent workability for a long time after production. Thereby, long-term durability can be guaranteed without being affected by the processing time of the precoated metal sheet. As a result, it becomes possible to collectively manufacture a small number of products of various types, and it is possible to greatly improve the productivity of the precoated metal sheet.

[Brief description of the drawings]

FIG. 1 is a diagram showing the results of X-ray diffraction measurement immediately after the production of a coating film obtained by using a conventional precoated metal plate paint.

FIG. 2 is a view showing the results of X-ray diffraction measurement three months after the production of a coating film obtained by using a conventional coating material for a precoated metal sheet.

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

FIG. 4 is a view showing the results of X-ray diffraction measurement 9 months after the production of a coating film obtained using the precoated metal sheet paint of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C09D 127/06 C09D 133/04-133/16 B05D ⁷ /14-7/18 B32B 15/08 102

Claims (3)

(57) [Claims] 1. A paint containing polyvinylidene fluoride (A) and as a main component a resin composition comprising a mixture of acrylic resin (B), said acrylic resin (B) is a thermoplastic acrylic resin (p) Not a blend of curing of thermosetting acrylic resin (s), the proportion of the blend is at a weight ratio (p) :( s) = 15 : 85~90: I 10 range der of the
Precoated metal plate for coating, characterized in Rukoto that having a polyvinylidene fluoride compatibility. 2. The resin composition comprising a mixture of polyvinylidene fluoride (A) and an acrylic resin (B), wherein the mixing ratio is (A) :( B) = 50: 50-90: Ten
The paint for a pre-coated metal sheet according to claim 1, wherein 3. A pre-coated metal plate coated with the paint according to claim 1, wherein the metal plate has an overcoat film of the paint on at least one surface of the metal plate.