JPH09143423A - Coating composition for metal plate, resin-coated metal plate produced by using the composition and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating composition for a resin-coated metal plate having excellent coating workability, a resin-coated metal plate having excellent press- formability and adhesivity and produced by using the coating composition and a method for producing the resin-coated metal plate. SOLUTION: This coating composition contains a copolymerized polyester resin (having a number-average molecular weight of >=8,000), a crosslinking agent (an alkyl- etherified aminoformaladehyde resin and/or an isocyanate compound) and a polyolefin wax (having an average primary particle diameter of 0.3-2.0μm and a melting point of 40-150 deg.C) at a weight ratio (copolymerized polyester)/(crosslinking agent) of 70/30 to 90/10. The amount of the polyolefin wax is 0.1-5 pts.wt. based on 100 pts.wt. of the sum of the copolymerized polyester resin and the crosslinking agent in terms of solid component. The present invention also relates to a resin-coated metal plate having an uppermost resin coating layer formed by using the coating composition and a method for producing the resin-coated metal plate by baking the applied coating composition under a condition to keep the viscosity of the applied composition to <=50cp for 5-60sec.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a coating composition for a resin-coated metal plate which is excellent in coating workability, a resin-coated metal plate which is excellent in moldability and adhesiveness using the coating composition, and its production. Regarding the method.

[0002]

2. Description of the Related Art For example, in the case of manufacturing an outer box part of a household electric appliance, conventionally, after cold-rolled steel plate or plated steel plate is cut, it is processed and formed into a predetermined shape, and they are joined by welding and assembled. Later, it was painted. However, in recent years, a method of using a resin-coated metal plate such as a precoated steel plate on which a flat plate is preliminarily coated, cutting this into a predetermined shape, processing it, and then assembling it is becoming the mainstream. According to this method, it is not necessary to paint after assembling, so that it is possible to reduce various processes and facilities in a manufacturer of home electric appliances.

However, when a resin-coated metal sheet such as a pre-coated steel sheet is subjected to severe forming such as drawing or roll forming, the steel sheet may crack if the surface of the resin layer does not have proper lubricity. The press die may cause so-called "scratching" or the like on the surface of the die, or "roughness" or the like on the surface of the coating film.

In order to ensure good formability of resin-coated metal sheets such as pre-coated steel sheets, it is known that the addition of polyolefin wax to the resin coating layer coated on the uppermost layer is effective. . This is because the wax particles are present on the surface of the resin coating layer to avoid direct contact between the resin coating metal plate and the press die.

In order to ensure good moldability, it is necessary to control the amount of wax present on the surface of the uppermost resin layer, but all the wax added to the resin layer is present on the surface of the resin layer. However, the amount of wax added is determined based on the results of the evaluation of the formability of the resin-coated metal sheet obtained by actually adding the wax.

However, since the addition of wax to the resin layer coated on the uppermost layer may lead to deterioration of the adhesive performance of the resin layer surface and deterioration of the strength of the resin layer, moldability and these performances are not always compatible. There are cases. In addition, when manufacturing resin-coated metal plates, if a large amount of wax is present in the paint, the paint will foam, pick-up defects in the roll coater, or unpainted parts (so-called "solo") will occur. May impair sexuality.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and provides a coating composition for a resin-coated metal plate which is excellent in coating workability, and a roll forming property and a press using the coating composition. It is an object of the present invention to provide a resin-coated metal plate having excellent moldability and excellent surface adhesion performance, and a method for producing the same.

[0008]

The present inventors have found that a coating composition for a resin-coated metal sheet having excellent coating workability, a resin-coated metal sheet having excellent moldability and adhesiveness, and a method for producing the same. As a result of repeated studies on the above, the following unexpected findings were obtained.

(A) Between the total volume of the polyolefin wax particles protruding from the surface of the uppermost resin coating layer (coating film) and the dynamic friction coefficient and moldability of this resin coating layer surface which is an index of moldability. There is a clear correlation. That is, when the total volume of the wax particles protruding from the surface of the uppermost resin coating layer is large, the dynamic friction coefficient of the surface decreases and the moldability becomes good. Further, if the total volume of the wax particles is small, the dynamic friction coefficient becomes large and the moldability deteriorates.

(B) When forming the uppermost resin coating layer,
After applying a coating composition in which a wax satisfying a predetermined condition is added to a specific polyester resin, the temperature of the metal plate is raised at a temperature of 40 ° C. or higher and 140 ° C. or lower, and the viscosity of the coating film is 50 cp (centipoise). The time kept below 5
By performing the baking treatment so as to fall within the range of not less than 2 seconds and not more than 60 seconds, the ratio of (amount of wax protruding to the surface of the uppermost resin coating layer) / (amount of wax added to the uppermost resin coating layer) The amount of wax added to the resin coating layer can be suppressed to be low. As a result, it is possible to secure good moldability of the resin-coated metal plate without causing a decrease in adhesive performance on the surface of the resin-coated layer and a decrease in strength of the resin-coated layer.

(C) Since the amount of wax added to the paint can be suppressed to a lower level than before, foaming of the paint, defective pick-up, etc. can be suppressed, and safe coating workability can be obtained.

The present invention was made on the basis of the above findings, and the gist thereof is the following coating composition (1), resin coated metal plate using (2), and method for producing (3). It is in.

(1) Copolyester resin having a number average molecular weight of 8000 or more, one or both of an alkyl etherified aminoformaldehyde resin and an isocyanate compound as a cross-linking agent, and an average primary particle diameter of 0.
3 μm or more and 2.0 μm or less, melting point 40 ° C. or more 150
Copolymerization including a polyolefin wax at a temperature of ℃ or less, in a solid content weight ratio, (weight of copolymerized polyester resin) / (weight of cross-linking agent) is 70/30 or more and 90/10 or less, and solid content weight. A coating composition for a resin-coated metal sheet excellent in coating workability, characterized in that the amount of the polyolefin wax is 0.1 part by weight or more and 5 parts by weight or less based on 100 parts by weight of the total amount of the polyester resin and the crosslinking agent. Stuff.

(2) A polyolefin wax having a coating film having a dry film thickness of 5 μm or more and 30 μm or less formed by the coating composition described in (1) above as an uppermost layer and protruding from the surface of the coating film. A resin-coated metal sheet excellent in moldability and adhesiveness, characterized in that the total volume of particles is 3.0 × 10 ^-10 m ³ or more and 3.0 × 10 ^-8 m ³ or less per 1 m ^{2 of} the coating film. .

(3) After applying the coating composition as described in (1) above to the surface of the base metal plate subjected to the base treatment, the temperature rising rate of the metal plate is 1.25 ° C./sec or more 7. 5 ° C / sec or less, and the metal plate temperature is 40 ° C or more and 140 ° C or more during the temperature rise
When it is within the following range, a baking treatment is performed so that the viscosity of the coating composition after application is kept at 50 cp or less for 5 seconds or more and 60 seconds or less. An excellent method for producing a resin-coated metal plate.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The invention (1) is a coating composition for forming the uppermost resin coating layer (top coating resin coating layer).

The resin constituting the polyester resin overcoat resin coating layer has a number average molecular weight of 8
000 or more copolymerized polyester resins. This resin has excellent processability and is inexpensive. Number average molecular weight is 8
If it is less than 000, the workability decreases. The upper limit is not particularly limited, but if it exceeds 25,000, the viscosity of the coating composition increases and the coating properties decrease, so the number average molecular weight is 25,000.
It is preferred that:

Used with a copolyester resin,
Crosslinking agents that react with this resin during the baking process are alkyl etherified aminoformaldehyde resins (melamine resins) and isocyanate compounds. Either one or both of these may be used. However, the isocyanate compound is expensive and inferior in adhesive performance to the surface of the resin coating layer, and therefore is not actually used in many cases.

Among the alkyl etherified amino formaldehyde resins, the alkyl etherified methylol melamine resin is preferable from the viewpoint of processability. Among them, more preferred are methoxylated methylol melamine, methoxylated butoxylated mixed methylol melamine, and further relatively small amount of alkyl etherification methylol melamine, or imino melamine, which are used alone or in combination. Can be used.

When a predetermined amount of these alkyl etherified amino formaldehyde resins are blended with a copolyester resin and baked and cured, the alkyl etherified amino formaldehyde resin or the copolyester resin is different due to the difference in surface free energy and the compatibility. Is concentrated on the surface. At this time, the resin having a small surface free energy has a strong tendency to be concentrated on the surface, and the wettability with the adhesive is determined by the type of the resin concentrated on the surface.

Further, since the alkyl etherified amino formaldehyde resin has a self-condensation property, if the resin is concentrated on the surface, the crosslinking density near the surface becomes high. This dense crosslinked structure hinders the migration of the adhesive into the resin coating layer to some extent, so that the swelling and softening of the resin coating layer is suppressed and the adhesive strength is improved.

The compounding ratio (solid content weight ratio) of the above-mentioned copolymerized polyester resin and alkyl etherified amino formaldehyde resin, that is, (weight of copolymerized polyester resin) / (weight of alkyl etherified amino formaldehyde resin) is 70. When it is less than / 30, the surface concentration of the alkyl etherified aminoformaldehyde resin is too large, so that the wettability between the adhesive and the resin layer is lowered, and the interface peeling easily occurs. On the other hand, when (weight of copolyester resin) / (weight of alkyl etherified amino formaldehyde resin) exceeds 90/10, the amount of surface concentrated alkyl etherified amino formaldehyde resin is small and wettability is secured. However, since the cross-linking density in the vicinity of the surface is insufficient, the adhesive strength is reduced, and the workability, the secondary adhesion, and the corrosion resistance are reduced. This applies not only to the alkyl etherified aminoformaldehyde resin but also to the above-mentioned isocyanate compound. Therefore,
In the coating composition of the present invention, (weight of copolymerized polyester resin) / (weight of crosslinking agent) is 70/3 in terms of solid content weight ratio.
It was limited to 0 or more and 90/10 or less.

When molding a polyolefin wax resin-coated metal sheet, if the overcoat resin coating layer has a high friction coefficient, the die of the roll former or press and the resin coating layer come into direct contact with each other, resulting in peeling of the coating film and Since breakage occurs, it is necessary that the above-mentioned coating composition for forming the overcoat resin coating layer contains a polyolefin wax for reducing the friction coefficient of the surface of the coating layer.

The polyolefin wax added to the coating composition has an average primary particle size of 0.3 μm or more.2.
It is less than 0 μm. The average primary particle size is
The average particle size of the polyolefin wax in the coating composition, which can be easily measured with a laser microscope, an optical microscope or the like. If the average primary particle diameter exceeds 2.0 μm, the dispersibility of the polyolefin wax in the coating composition deteriorates, and problems such as poor pick-up occur in roll coater coatability. Further, in the case of a polyolefin wax having an average primary particle diameter of less than 0.3 μm, the wax particle diameter on the surface of the coating film after baking is small, the surface concentration of the wax is small, and the lubricity is not improved. Therefore, the lower limit of the average primary particle diameter is set to 0.3 μm.

The melting point of the above polyolefin wax is
When the temperature is lower than 40 ° C., the lubricity at room temperature is good, but the wettability with an adhesive is lowered and the adhesiveness is lowered. On the other hand, when the melting point exceeds 150 ° C, the lubricity at around room temperature is significantly reduced. Therefore, the melting point of the polyolefin wax is limited to 40 ° C or higher and 150 ° C or lower.

The amount of the polyolefin wax added also has a great influence on the formability and adhesiveness of the resin-coated metal sheet and the coating workability of the paint. When the amount of the polyolefin wax added exceeds 5 parts by weight with respect to 100 parts by weight of the total amount of the copolyester resin and the cross-linking agent, the wax holding power of the resin coating layer decreases, and wax residue is left behind during press molding. It adheres to the mold and the wettability of the resin coating layer surface to the adhesive decreases. In addition, the coating workability is deteriorated, such as the foaming of the coating material and the pick-up failure in the roll coater. On the other hand, if the amount of the wax added is less than 0.1 parts by weight based on 100 parts by weight of the total amount of the copolyester resin and the cross-linking agent, the absolute amount of the wax concentrated on the surface is insufficient, and it becomes difficult to secure moldability. Become. Therefore, the addition amount of the polyolefin wax is limited to 0.1 part by weight or more and 5 parts by weight or less based on 100 parts by weight of the total amount of the copolyester resin and the cross-linking agent in terms of solid content.

The above-mentioned coating composition of the present invention has good coating workability, and the resin-coated metal sheet using this coating composition as the top coating has excellent moldability, and also has good wettability and adhesive strength upon adhesion. It has a good balance with and has excellent adhesiveness. It should be noted that no special method is required for producing this coating composition. The copolymerizing polyester resin satisfying the predetermined conditions may be mixed with the crosslinking agent and the polyolefin wax as described above, and diluted with an appropriate solvent such as cyclohexanone, acetone or isophorone.

The invention of (2) is a resin-coated metal plate using the coating composition of (1) as an overcoating material.

The type of the metal plate used as a base metal plate base material is not particularly limited. In addition to cold-rolled steel sheets, surface-treated steel sheets such as zinc-based steel sheets and zinc-aluminum-based steel sheets, stainless steel sheets,
Furthermore, an aluminum plate, a copper plate or the like can be used. When using plated steel sheet, to use a plating basis weight is per side 10g / m ² ~120g / m ² is desirable.

Base Treatment There is no particular limitation as long as it is a method used for a base treatment of a usual resin-coated metal plate. For example, coating type chromate treatment, electrolytic chromate treatment, reactive chromate treatment, zinc phosphate treatment, etc. may be performed. The adhesion amount at this time is
In the case of the coating type chromate treatment, the amount of adhesion per one surface is converted to chromium (Cr), that is, the amount of adhesion is represented by the amount of Cr contained therein and is 20 mg / m ^{2 to} 100 mg /
is preferably m ^2, and it is desirable in the zinc phosphate treatment adhesion amount per one side is ^{0.2g / m 2 ~1.5g / m 2} .

Undercoating resin coating layer The resin coating layer formed on the undercoating layer is generally a two-layer coating, but may be a one-layer coating or a three-layer coating. The undercoat resin coating layer means the first resin coating layer from the base material side in the case of two-layer coating, and the first and second resin coating layers in the case of three-layer coating.

The undercoat resin coating layer is not always essential, but it is desirable to provide it particularly when end face corrosion resistance, hiding property and adhesion are required. The resin system used for this coating layer is not particularly limited, but a polyester resin system, a polyurethane resin system, an epoxy resin system, and a combination system of these resins are preferable in order to secure processability and adhesion.

Further, it is desirable that the undercoat resin coating layer contains a rust preventive pigment in order to improve the corrosion resistance of the end face. As the anticorrosive pigment, chromate-based pigments such as strontium chromate, zinc chromate, calcium chromate and barium chromate, phosphate-based pigments such as zinc phosphate and calcium phosphate, molybdenum such as calcium molybdate and aluminum molybdate. Examples thereof include acid salt-based pigments, but it is desirable to use a chromate-based rust preventive pigment in combination with another rust preventive pigment from the viewpoint of rust preventive power.

The amount of these rust preventive pigments added is preferably 4% by weight to 60% by weight based on the dry weight of the resin coating layer.
If less than 4% by weight, sufficient corrosion resistance cannot be obtained, and 60% by weight
If it exceeds, the workability is remarkably reduced. More preferably 1
It is 0% to 50% by weight.

Topcoat resin coating layer This is a topcoat resin coating layer using the coating composition described in (1) above. When the dry film thickness is 5 μm or more and 30 μm or less,
Moreover, the total volume of the polyolefin wax particles protruding from the surface of the resin coating layer (coating film) is 3.0 × 10 ^-10 m ³ or more and 3.0 × 10 ^-8 m ³ or less per 1 m ^{2 of} the coating film. It is necessary. The total volume of the polyolefin wax particles protruding from the surface of the coating film is measured by surface analysis using a commonly used SEM (scanning electron microscope) or FE-SEM (field emission scanning electron microscope), and roughness measurement. It is possible to

When the dry film thickness is less than 5 μm, sufficient corrosion resistance and hiding property cannot be obtained, while when it exceeds 30 μm, workability and moldability are impaired.

The total volume of the polyolefin wax particles protruding from the surface of the coating film is 3.0 per 1 m ^{2 of} the coating film.
If it is less than × 10 ^-10 m ³ , the dynamic friction coefficient of the coating film surface is large and the formability is deteriorated. If it exceeds 3.0 × 10 ^-8 m ³ , the wettability with the adhesive is deteriorated and the interfacial peeling occurs. Is likely to occur.

The resin coating layer may contain various pigments and additives such as titanium oxide, silica, defoaming agents, etc., which are usually added.

The above resin-coated metal sheet of the present invention is excellent in roll forming property and press formability, and is also excellent in surface adhesiveness and the like, and is particularly subjected to a high degree of forming process such as drawing process. It is suitable as an air conditioner outdoor unit, a ventilation fan, or a material for automobiles.

The invention (3) is the method for manufacturing a resin-coated metal plate according to the above (2) (the method of the present invention). That is,
Using the above-mentioned base metal plate, subjecting it to a base treatment according to a conventional method and, if necessary, applying an ordinary undercoat to form an undercoat coating film, and then applying the coating composition of (1) above. This resin-coated metal plate can be manufactured by applying a top coat.

Coating Method The top coating method is not particularly limited as long as it is a method used in the production of ordinary resin-coated metal plates. A roll coating method, a curtain flow coating method, a spray method or the like may be used.

Drying / baking On the other hand, it is necessary to dry / bak after coating under the predetermined conditions described below.

Taking the case of using a continuous dry baking line as an example, the temperature range required for curing the polyester resin and the cross-linking agent (alkyletherified aminoformaldehyde resin or isocyanate compound) is 17
Since the temperature of the metal plate before drying and baking is 25 ° C, the heating rate is 1.25 ° C.
/ Sec to 7.5 ° C / sec. Therefore, in the method of the present invention, when the coating film is dried and baked, the heating rate of the oven is limited to within the range of 1.25 ° C / sec to 7.5 ° C / sec, and the other conditions are as follows. Stipulated in.

By the way, it is known that the viscosity change occurring in the process of drying and baking the coating material containing the polyester resin and the alkyl etherified aminoformaldehyde resin takes the process shown in FIG. In addition, pattern 1 of FIG.
2 and 3 are Comparative Examples I or IV, Example II or V of the present invention, and Example III or VI of the present invention, which will be described later.
Corresponding to As shown in FIG. 1, the viscosity of the coating film first decreases as the temperature rises from room temperature. Next, the viscosity of the coating film increases as the solvent contained in the coating film evaporates. After that, when the curing temperature of the crosslinking agent is exceeded, the crosslinking reaction in the coating film rapidly progresses, the viscosity of the coating film increases to 10 ⁵ cp or more, and the coating film cures.

In the method of the present invention, in this drying / baking process,
As mentioned above, the temperature of the metal plate during the temperature rise is 40 ° C. or higher 1
Within the range of 40 ° C. or lower, the temperature in the oven is controlled so that the time for which the viscosity of the coating film is kept at 50 cp or lower falls within the range of 5 seconds or more and 60 seconds or less. This makes it possible to form a surface with an increased amount of wax protruding on the surface of the uppermost resin coating layer (coating film). That is, the ratio of (amount of wax protruding to the surface of the uppermost resin coating layer) / (amount of wax added to the uppermost resin coating layer) is increased to keep the amount of wax added to the resin coating layer low. be able to. As a result, it is possible to secure good moldability of the resin-coated metal plate without causing a decrease in adhesive performance on the surface of the resin-coated layer and a decrease in strength of the resin-coated layer.

The temperature of the metal plate during the temperature rise is 40 ° C. or higher and 140
Within the range of ℃ or less, if the metal plate temperature is less than 40 ℃, the convection in the coating film necessary for the surface concentration of the wax does not occur, while if it exceeds 140 ℃, it is a cheap solvent usually used. This is because there are very few substances that are difficult to evaporate, and the resin is hardened by the evaporation of the solvent to increase the viscosity.

Further, the reason why the viscosity of the coating film is kept at a low viscosity of 50 cp or less for 5 seconds or longer is that the duration of convection generated in the coating film is short when the coating time is less than 5 seconds, so that the coating surface This is because the wax is difficult to thicken, and the lubricity required for high-level molding cannot be imparted to the coating film surface.
On the other hand, although the upper limit of the holding time at the low viscosity is not particularly limited, it is set to 60 seconds or less in consideration of the rate of temperature rise, the curing start temperature of the crosslinking agent, and the drying ability of the oven.

The viscosity of the coating film can be easily measured by using a commercially available general conical flat plate rotational viscometer.

According to the above-mentioned method of the present invention, a resin-coated metal sheet which is excellent in roll forming property, press formability, and surface adhesion performance can be easily prepared by controlling the temperature in the oven during the drying / baking process. It can be manufactured.

[0051]

【Example】

(Example 1) Hot-dip galvanized steel sheet having a thickness of 0.6 mm and plated on both sides (amount of coating: 60 g / m ^{2 on} one side,
Fe content in the plating layer: 0.2% by weight, Al content:
0.3 wt%, Pb content: 50 ppm) as the base material,
Zinc phosphate treatment on its surface (both sides) (0.8g / m on one side)
² ) is applied and an undercoat resin coating layer is provided thereon, and then a topcoat resin coating layer is provided (this layer is the uppermost layer),
A resin-coated metal plate was used.

To form the undercoat resin coating layer, PB-10P (trade name) manufactured by Dainippon Ink and Chemicals, Inc. was used as a paint, and this was applied with a bar coater to a dry film thickness of 7 μm. The maximum steel plate temperature (hereinafter PM
B) to 210 ° C.

In forming the overcoat resin coating layer, first, 100 parts by weight of a copolyester resin having a number average molecular weight of 5,000 to 30,000 is used as a cross-linking agent butoxylated methylolated mixed melamine resin (Dainippon Ink and Chemicals, Inc.).
Manufactured by the present invention), and then the polyolefin waxes having different melting points and average primary particle diameters shown in Table 1 were added.
Up to 10 parts by weight was added at various ratios and diluted with cyclohexanone to prepare a coating material having a nonvolatile content of 40%. This paint was applied using a bar coater to a dry film thickness of 13 μm, and the PMT was 2 at a wind speed of 2 m / s and a baking time of 60 seconds.
It was baked and cured at 32 ° C. At this time, the temperature rising rate was 3.5 ° C / sec, and the viscosity of the coating composition was 50c.
The holding time of p or less was 6.3 seconds, and the temperature range of the steel sheet at this time was 70 to 90 ° C.

The resin-coated metal plate obtained as described above was subjected to the following tests to evaluate moldability and adhesiveness. Further, the coating workability of the above-mentioned top coating material was evaluated by the following method.

[Moldability] Evaluation was carried out by a cylindrical drawing test.
The test is a punch diameter of 40 mmφ, a blank diameter of 96 mmφ,
The drawing was performed under the conditions of a drawing ratio of 2.4 and a drawing speed of 60 mm / min, and the outer wall portion of the test piece (resin-coated metal plate) after passing through the drawing was visually observed. The evaluation criteria are the following three levels,
When the result was ◯ or Δ, the result was good.

◯: No abnormal appearance of the wall part Δ: Scratching occurs ×: Base material fracture occurred [Adhesiveness] T The peel strength was evaluated. An epoxy adhesive (one-component thermosetting type manufactured by Sunstar Giken) was used to prepare the test piece, and this was applied using a spacer so that the adhesive thickness would be 150 μm. After the plates were bonded, they were baked and cured at 165 ° C. for 25 minutes. The case where the T peel strength was 14.0 kgf / 25 mm or more was considered good.

[Coating workability] Put the paint in the paint pan,
The lifting property (pickup property) of the paint was investigated. ○ When the liquid film is completely lifted, the liquid film is partially cut off, but when the liquid film is completely transferred to the applicator roll, Δ, the transferred liquid film is cut and the unpainted part (so-called solo ) Occurs, it is marked as ×, and if ○,
It was good.

The test results are shown in Table 2. As is clear from this result, in the present invention examples (Nos. 12 to 17), the moldability and adhesiveness of the resin-coated metal plate and the coating workability of the paint were all good.

Comparative Examples 1 to 5 together with Examples 12 to 17 of the present invention show the influence of the properties and type of the polyolefin wax on the moldability and adhesiveness, and the coating workability of the paint. The symbols in the columns such as wax properties correspond to those in Table 1.

In Comparative Example 1, the wax had a low melting point so that sufficient adhesiveness was not ensured, and in Comparative Example 2, the polyolefin wax had a large average primary particle diameter, which caused a problem in coating workability. In Comparative Example 3, since the melting point was too high, the lubricity of the coating film surface was poor, and the moldability was poor. In Comparative Examples 4 and 5, the average primary particle size was smaller than 0.3 μm, so that the surface concentration of the wax was small, the lubricity was poor, and the moldability was poor.

Comparative Examples 6 to 11, together with Examples 12 to 17 of the present invention, show the influence of the amount of the polyolefin wax added on moldability, adhesiveness, and coating workability of paint. The parts by weight in the column of wax amount in the table are parts by weight based on 100 parts by weight of the copolyester resin and the crosslinking agent. When the amount of the polyolefin wax added is less than 0.1 parts by weight, the lubricity is small, resulting in poor moldability. On the other hand, when the amount of the polyolefin wax added exceeds 5 parts by weight, the adhesiveness is poor and the coating workability is also poor. Cause trouble. That is, when the amount of wax contained in the resin coating layer is 0.1 parts by weight or more and 5 parts by weight or less, good lubricity is exhibited and moldability is secured.

When the amount of the polyolefin wax added is 0.1 parts by weight or more and 5 parts by weight or less, the top coating resin coating layer is dried and baked under the conditions defined by the method of the present invention to form the resin coating layer. It can be seen that the total volume of the polyolefin wax particles protruding from the surface can be controlled within the range of 3.0 × 10 ⁻¹⁰ m ³ or more and 3.0 × 10 ⁻⁸ m ³ or less.

(Example 2) The base material used in Example 1 was treated with zinc phosphate to form an undercoating resin coating layer and an overcoating resin coating layer (this layer is the uppermost layer), and resin coating was performed. It was a metal plate. The conditions of the zinc phosphate treatment and the formation of the undercoat resin coating layer are the same as in the case of Example 1.

Regarding the overcoat resin coating layer, first, 100 parts by weight of a copolyester resin having a number average molecular weight of 20,000 is used as a cross-linking agent butoxylated methylolated mixed melamine resin (curing start temperature 160 ° C., Dainippon Ink and Chemicals, Inc.). 16 parts by weight, and then polyethylene wax having a melting point of 82 ° C. and an average primary particle diameter of 1.1 μm as shown in B of Table 1 was added to 0 parts by weight based on 100 parts by weight of the copolymerized polyester and the crosslinking agent. 1 part by weight or 0.5 part by weight, and diluted with a mixed solvent of cyclohexanone and acetone to prepare a coating material. This coating material was applied using a roll coater to a dry film thickness of 13 μm, and baked and cured so that the PMT was 225 ° C. at a wind speed of 2 m / s and a baking time of 50 seconds.

An example of the drying / baking time-viscosity curve of the topcoat paint at this time is shown in FIG. In FIG. 1, patterns 1, 2, and 3 are Comparative Examples I or IV, Inventive Examples II or V, and Inventive Examples III or VI, respectively, shown in Table 3 below.
Corresponding to As shown in this figure, in Pattern 1 (Comparative Example I or IV), the viscosity of the coating film was kept at 50 cp or less for less than 5 seconds, while in Pattern 2,
And 3 (invention examples II or V and III or respectively)
VI) is over 5 seconds.

The resin-coated metal plate obtained as described above was tested in the same manner as in Example 1 to evaluate the formability and adhesiveness. Further, the coating workability of the top coating material was evaluated.

The test results are shown in Table 3. As is clear from these results, in Invention Examples II, III, V and VI, both the moldability and adhesiveness of the resin-coated metal sheet and the coating workability of the paint were good. On the other hand, in Comparative Examples I and IV, although there was no problem in coating workability of the paint, the moldability was poor in both cases because the amount of wax concentrated on the surface was small. In particular, it can be seen that Comparative Example IV does not have sufficient lubricity necessary for drawing, although the coating contains a wax amount 5 times that of Inventive Examples II and III. .

[0068]

[Table 1]

[0069]

[Table 2]

[0070]

[Table 3]

[0071]

EFFECT OF THE INVENTION The coating composition of the present invention has good coating workability, and a resin-coated metal sheet using this coating composition as a top coating has excellent moldability and adhesiveness. In particular, it is suitable as a material for an air conditioner outdoor unit, a ventilation fan, or an automobile that is subjected to a high degree of forming such as drawing. This resin-coated metal plate can be easily manufactured by the method of the present invention.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a relationship between a drying / baking time and a viscosity of a topcoat paint.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B32B 15/08 B32B 15/08 G C09D 175/06 PHX C09D 175/06 PHX

Claims (3)

[Claims] 1. A copolymerized polyester resin having a number average molecular weight of 8000 or more, one or both of an alkyl etherified aminoformaldehyde resin and an isocyanate compound as a crosslinking agent, and an average primary particle diameter of 0.3 μm.
A polyolefin wax having a melting point of 40 ° C. or more and 150 ° C. or less and a solid content weight ratio of
(Weight of copolyester resin) / (weight of crosslinking agent)
Is 70/30 or more and 90/10 or less, and the total amount of the copolymerized polyester resin and the cross-linking agent is 100 by weight of the solid content.
The amount of the polyolefin wax is 0.1 with respect to parts by weight.
A coating composition for a resin-coated metal plate having excellent coating workability, characterized in that the content is at least 5 parts by weight. 2. A polyolefin wax particle having a coating film having a dry film thickness of 5 μm or more and 30 μm or less formed by the coating composition according to claim 1 in the uppermost layer and protruding from the surface of the coating film. Total volume is 3.0 x per 1 m ^{2 of} coating film
A resin-coated metal sheet having excellent formability and adhesiveness, characterized in that it is 10 ⁻¹⁰ m ³ or more and 3.0 × 10 ⁻⁸ m ³ or less. 3. The temperature rising rate of the metal plate after applying the coating composition according to claim 1 to the surface of a base metal plate subjected to a base treatment is 1.25 ° C./sec or more and 7.5 ° C. / Sec or less, and
When the temperature of the metal plate is in the range of 40 ° C. or higher and 140 ° C. or lower during heating, the baking treatment is performed so that the viscosity of the coating composition after coating is kept at 50 cp or lower for 5 seconds or longer and 60 seconds or shorter. A method for producing a resin-coated metal sheet having excellent formability and adhesiveness, which comprises: