JP6939142B2 - Paint for metal plate and manufacturing method of painted metal plate using it - Google Patents

Description

The present invention relates to a paint for a metal plate and a method for manufacturing a coated metal plate using the paint.

Painted metal plates are often used for outdoor buildings and civil engineering structures. In such a painted metal plate, there is a problem of contamination due to adhesion of carbon-based pollutants (hereinafter, also referred to as "hydrophobic carbon") contained in automobile exhaust gas, soot from factories, and the like. Among the stains, the stains that adhere along the rain streaks (hereinafter, also referred to as "rain streak stains") are easily noticeable. In the conventional painted metal plate, it is inevitable that such rain streak stains become conspicuous in a relatively short time, and there has been a demand for a painted metal plate in which rain streak stains are unlikely to occur.

In recent years, it has been proposed to prevent rain streak stains by making the contact angle of the coating film with water 60 ° or less, that is, hydrophilic. On the surface of the hydrophilic coating film having a low contact angle with water, it is considered that the hydrophobic carbon is easily lifted by rainwater, and the raised hydrophobic carbon is washed away. As one of the methods for making the surface of a coated metal plate hydrophilic, a method of including tetraalkoxysilane or a condensate thereof (hereinafter, these are also referred to as "organosilicates") in a paint has been proposed (Patent Document 1).

International Publication No. 1994/6870

The paint described in Patent Document 1 contains various resins and organosilicates. When such a paint is applied to the surface of a metal plate, the organosilicate moves to the surface side of the film. Then, when the film is cured, the organosilicate reacts with moisture and the like in the air, and silanol groups and siloxane bonds are formed on the surface of the coating film. It is believed that this makes the surface of the coating film hydrophilic and suppresses rain streak stains.

However, organosilicates are very reactive and easily react with the moisture in the paint. Therefore, the paint containing the organosilicate has low storage stability, and it is difficult for the organosilicate to move to the surface of the paint after a lapse of time after the addition of the organosilicate, and it is difficult to sufficiently hydrophilize the surface of the coating film.

Therefore, the present inventors have studied to replace the organosilicate contained in the conventional paint with a silicone resin. Silicone resins are milder in reactivity than organosilicates and are less likely to react with moisture in the paint. Moreover, due to its three-dimensional structure, it tends to thicken on the surface after application of the paint. Therefore, by applying a paint containing such a silicone resin and performing a frame treatment on the cured film, the surface can be easily hydrophilized (the organic group of the silicone resin is replaced with an OH group or a siloxane bond). .. That is, according to the paint containing the silicone resin, it is easy to obtain a coating film having very high hydrophilicity and less likely to cause rain streak stains.

However, there is a problem that the storage stability of a paint containing a polyester resin and a melamine resin-based curing agent as well as a silicone resin tends to be low. The reasons for this are as follows. In order to cure the silicone resin, it is common to add an acid catalyst to the paint. Here, it is known that a melamine resin-based curing agent tends to react and becomes unstable when mixed with an acidic compound. Therefore, conventionally, the use of an alkaline acid catalyst in which sulfonic acid is blocked with an amine has been studied as an acid catalyst for curing a silicone resin. However, silicone resins tend to become unstable when mixed with an alkaline acid catalyst, and such paints tend to thicken over time.

The present invention has been made in view of such a situation. That is, an object of the present invention is to provide a paint for a metal plate capable of forming a coating film having extremely high storage stability and less likely to cause rain streak stains on the surface of a metal plate, and a method for producing a coated metal plate using the paint. And.

The first aspect of the present invention relates to the following paints for metal plates.
[1] A paint for a metal plate containing a polyester resin, a melamine resin-based curing agent, a silicone resin, and a block sulfonic acid catalyst having a pH of 6 to 8.

（一般式（１）において、Ｒ^１は、一価もしくは多価の炭素数１〜１８のアルキル基、炭素数１〜１８のアルキル基が１つまたは２つ結合したフェニル基、またはナフチル基を表し、Ｒ^２およびＲ^３は、それぞれ独立に水素原子、炭素数１〜１２のアルキル基を表し（ただし、Ｒ^２およびＲ^３は互いに結合して環を形成していてもよい）、Ｘ^１は、単結合、−ＣＨ_２−Ｏ−Ｒ^６−、または−ＣＨ_２−Ｏ−Ｃ（＝Ｏ）−Ｒ^７−を表し（Ｒ^６およびＲ^７は、単結合、または炭素数１〜２０の二価の有機基を表す）、Ｘ^２は、単結合、または−Ｃ（＝Ｏ）ＮＨ−を表し、Ｒ^４は、水素原子、一価もしくは多価の炭素数１〜１８のアルキル基、置換基を有していてもよいビスフェノールＡ残基、または置換基を有していてもよいビスフェノールＦ残基を表し、Ｒ^５は、水素原子、一価もしくは多価の炭素数１〜１８のアルキル基、炭素数１〜１８のシクロアルキル基、炭素数１〜１８のアルキレン基、炭素数１〜１８のアリール基、または炭素数１９〜１００の有機基を表し、ｎは１〜１０の整数を表し、ｘ、ｙ、およびｚはそれぞれ独立に、１以上の整数を表す） [2] The paint for a metal plate according to [1], wherein the block sulfonic acid catalyst has a structure represented by the following general formula (1).

(In the general formula (1), R ¹ is a monovalent or polyvalent alkyl group having 1 to 18 carbon atoms, a phenyl group in which one or two alkyl groups having 1 to 18 carbon atoms are bonded, or a naphthyl group. ^{R 2} and R ³ each independently represent a hydrogen atom and an alkyl group having 1 to 12 carbon atoms (however, R ² and R ³ may be bonded to each other to form a ring), and X ¹ represents a single ^{_{bond, -CH 2 -O-R 6 -}} , or _{-CH 2 -O-C (= O} ) -R 7 - a represents ^{(R 6} and ^{R 7} are a single bond or a carbon number from 1 to 20 (Representing a divalent organic group), X ² represents a single bond, or -C (= O) NH-, and R ⁴ is a hydrogen atom, a monovalent or polyvalent alkyl group having 1 to 18 carbon atoms. good bisphenol a residue which may have a substituent or have a substituent represents also good bisphenol F residue, R ⁵ is a hydrogen atom, a monovalent or polyvalent carbon atoms 1 to 18, , A cycloalkyl group having 1 to 18 carbon atoms, an alkylene group having 1 to 18 carbon atoms, an aryl group having 1 to 18 carbon atoms, or an organic group having 19 to 100 carbon atoms, in which n is 1 to 10. Represents an integer, x, y, and z each independently represent an integer of 1 or more)

（一般式（２）において、Ｒ^１１は、炭素数１〜１８のアルキル基、置換基を有していてもよいビスフェノールＡ残基、または置換基を有していてもよいビスフェノールＦ残基を表し、Ｒ^１２は、炭素数１〜１２のアルキル基を表す）
［５］前記シリコーンレジンが、Ｓｉ原子の総モル数に対して、５〜５０モル％のシラノール基を含む、［１］〜［４］のいずれかに記載の金属板用塗料。 ^{[3] The paint for a metal plate according to [2], wherein R 1} in the general formula (1) is a p-tolyl group or a 4-dodecylphenyl group.
[4] The coating material for a metal plate according to [1] or [2], wherein the block sulfonic acid catalyst contains a compound represented by the following general formula (2).

(In the general formula (2), R ¹¹ is an alkyl group having 1 to 18 carbon atoms, a bisphenol A residue which may have a substituent, or a bisphenol F residue which may have a substituent. R ¹² represents an alkyl group having 1 to 12 carbon atoms)
[5] The coating material for a metal plate according to any one of [1] to [4], wherein the silicone resin contains 5 to 50 mol% of silanol groups with respect to the total number of moles of Si atoms.

The second aspect of the present invention relates to the following method for manufacturing a coated metal plate.
[6] A step of applying the paint for a metal plate according to any one of [1] to [5] to the surface of the metal plate and curing it to form a coating film, and a step of performing a frame treatment on the coating film. And, including, a method of manufacturing a painted metal plate.

The paint for metal plates of the present invention has extremely high storage stability. Furthermore, according to the metal plate paint, it is possible to produce a coated metal plate having high scratch resistance, which is less likely to cause rain streak stains on the surface.

1. 1. Paint for Metal Plate The present invention relates to a paint for a metal plate to be applied to the surface of a metal plate in order to protect the metal plate and prevent rain streaks from becoming dirty. The paint for a metal plate is used, for example, by applying it on a metal plate and then frame-treating the surface of the coating film.

As described above, the paint for metal plates containing silicone resin has higher storage stability than the paint containing organosilicate. Further, when the paint for a metal plate is applied, the silicone resin moves to the film surface, so that a coating film having high scratch resistance and less likely to cause rain streak stains can be obtained. However, when the paint for metal plates contains polyester resin, melamine resin-based curing agent, and acid catalyst in addition to silicone resin, the storage stability of the paint tends to decrease, and thickening and gelation occur over time. It was easy to occur.

To solve such a problem, the coating material for a metal plate of the present invention includes a block sulfonic acid catalyst having a pH of 6 to 8 as an acid catalyst together with a polyester resin, a melamine resin-based curing agent, and a silicone resin. The block sulfonic acid catalyst has a structure in which the sulfonic acid catalyst is protected by a high molecular weight compound or the like (hereinafter, also referred to as "block group"). Since the pH of such a block sulfonic acid catalyst is 6 to 8, it is difficult to react with a silicone resin or a melamine resin-based curing agent when the paint for a metal plate is stored, and the storage stability is very good. On the other hand, since the block group of the block sulfonic acid catalyst is easily desorbed from the sulfonic acid by heating or the like, the sulfonic acid catalyst easily functions sufficiently when the silicone resin (paint for a metal plate) is cured. Therefore, according to the paint for a metal plate of the present invention, a coating film having high scratch resistance and less likely to cause rain streak stains can be obtained.
Hereinafter, each component of the paint for a metal plate of the present invention will be described in detail.

(1) Block sulfonic acid catalyst The block sulfonic acid catalyst is a catalyst having a pH of 6 to 8 and in which sulfonic acid is blocked by an arbitrary blocking group, and the blocking group is removed by heating or the like to cure the silicone resin. It is not particularly limited as long as it acts as a catalyst. The paint for a metal plate may contain only one type of block sulfonic acid catalyst, or may contain two or more types of block sulfonic acid catalyst. Further, the pH of the block sulfonic acid catalyst can be specified by extracting only the block sulfonic acid catalyst from the paint for a metal plate by a conventional method and measuring it with a pH measuring device or the like. The pH of the block sulfonic acid catalyst is usually adjusted by the structure of the block group. The pH of the block sulfonic acid catalyst is more preferably 6.5 to 7.5 from the viewpoint of further improving the storage stability of the paint for metal plates.

Examples of the block sulfonic acid catalyst include a compound having a structure represented by the following general formula (1).

上記一般式（１）において、Ｒ^１は一価もしくは多価の炭素数１〜１８の直鎖状または分岐鎖状のアルキル基、炭素数１〜１８の直鎖状または分岐鎖状のアルキル基が１つまたは２つ結合したフェニル基、またはナフチル基を表す。Ｒ^１は上記の中でも、炭素数１〜１８のアルキル基が１つ結合したフェニル基であることが好ましく、ブロック基が脱離した後のスルホン酸の安定性の観点から、ｐ−トリル基または４−ドデシルフェニル基であることがより好ましい。

In the above general formula (1), R ¹ is a monovalent or polyvalent linear or branched alkyl group having 1 to 18 carbon atoms, and a linear or branched alkyl group having 1 to 18 carbon atoms. Represents a phenyl group or a naphthyl group in which one or two are bonded. Among the above, R ¹ is preferably a phenyl group to which one alkyl group having 1 to 18 carbon atoms is bonded, and from the viewpoint of stability of the sulfonic acid after the blocking group is eliminated, a p-tolyl group or a p-tolyl group or It is more preferably a 4-dodecylphenyl group.

Further, in the above general formula (1), R ² and R ³ independently represent a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, respectively. When R ² or R ³ is an alkyl group, they may have either a linear or branched chain structure. In addition, R ² and R ³ may be bonded to each other to form an alicyclic structure. Among the above, R ² and R ³ are particularly preferably hydrogen atoms.

Further, in the above general formula (1), ^{X 1} is a single ^{_{bond, -CH 2 -O-R 6 -}} , or _{-CH 2 -O-C (= O} ) -R 7 - a represents ^{(R 6} and R ⁷ represents a single bond or a divalent organic group having 1 to 20 carbon atoms), and X ² represents a single bond or −C (= O) NH−. When ^{R 6} or R ⁷ contained in ^{X 1} is a divalent organic group, the number of carbon atoms is more preferably 5 to 15. The structure of the organic group contained in X ¹ is not particularly limited, and for example, an alkyl group, an aryl group, or the like can be directly bonded or can be a group bonded via a linking group.

Further, R ⁴ contains a hydrogen atom, a linear or branched alkyl group having 1 to 18 monovalent or polyvalent carbon atoms, a bisphenol A residue which may have a substituent, or a substituent. Represents a bisphenol F residue that may be present. On the other hand, R ⁵ is a hydrogen atom, a monovalent or polyvalent linear or branched alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 1 to 18 carbon atoms, an aryl group having 1 to 18 carbon atoms , Or an organic group having 19 to 100 carbon atoms. When R ⁵ is an organic group, its structure is not particularly limited, and for example, it can be a group in which an alkyl group, an aryl group, or the like is directly bonded or bonded via a linking group. Among the above, R ⁴ is preferably a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, and R ⁵ is preferably a hydrogen atom among the above.

Further, n represents an integer of 1 to 10. On the other hand, x, y, and z represent one or more integers appropriately selected according to the valences of ^{R 1} , R ⁴ , and R ^5. It is preferable that n, x, y, and z are all 1.

一般式（２）において、Ｒ^１１は、炭素数１〜１８の直鎖状または分岐鎖状のアルキル基、置換基を有していてもよいビスフェノールＡ残基、または置換基を有していてもよいビスフェノールＦ残基を表し、炭素数が１〜１２のアルキル基であることが特に好ましい。一方、Ｒ^１２は、炭素数１〜１２のアルキル基を表し、メチル基またはドデシル基であることが特に好ましい。 Here, the block sulfonic acid catalyst represented by the general formula (1) is particularly preferably a compound represented by the following general formula (2).

In the general formula (2), R ¹¹ has a linear or branched alkyl group having 1 to 18 carbon atoms, a bisphenol A residue which may have a substituent, or a substituent. It represents a good bisphenol F residue, and is particularly preferably an alkyl group having 1 to 12 carbon atoms. On the other hand, R ¹² represents an alkyl group having 1 to 12 carbon atoms, and is particularly preferably a methyl group or a dodecyl group.

In the above-mentioned block sulfonic acid catalyst, the block group is released by heating or the like. For example, in the compound represented by the above general formula (2), the blocking group is removed from the p-alkylphenyl sulfonic acid, and the p-alkylphenyl sulfonic acid functions as an acid catalyst for curing the silicone resin.

Here, the block sulfonic acid catalyst may function not only as a curing catalyst for the silicone resin but also as a catalyst in the reaction between the polyester resin and the melamine resin-based curing agent described later. Polyester resins and melamine resin-based curing agents are highly reactive, and the reaction usually proceeds without a catalyst. However, when the polyester resin has a high molecular weight, it may be difficult to sufficiently react with the polyester resin and the melamine resin-based curing agent. In such a case, if the paint for a metal plate contains a block sulfonic acid catalyst, the reaction between the polyester resin and the melamine resin-based curing agent tends to proceed, and a coating film having good curability can be easily obtained.

The amount of the block sulfonic acid catalyst contained in the paint for a metal plate is appropriately selected depending on the molecular weight of the block groups and the number of sulfonyl groups contained in one molecule. For example, in a block sulfonic acid catalyst containing only one sulfonyl group in one molecule, the amount of the sulfonic acid catalyst after desorption of the block group is 1.8 to 0. It is preferably contained so as to be 05 parts by mass, and more preferably 1.0 to 0.2 parts by mass. When the amount of the block sulfonic acid catalyst with respect to the solid content of the paint for a metal plate is within this range, the silicone resin is easily cured efficiently, and a coating film having a high hardness is easily obtained.

Here, the method for preparing the block sulfonic acid catalyst is not particularly limited, and the block sulfonic acid catalyst can be prepared by a known method. For example, it can be prepared by reacting a sulfonic acid such as p-toluenesulfonic acid or dodecylbenzenesulfonic acid with an epoxy compound having one or more epoxy groups in the molecule according to a conventional method.

(2) Silicone resin In the present specification, the "silicone resin" is a compound obtained by partially hydrolyzing and condensing alkoxysilane, which mainly has a three-dimensional crosslinked structure, but does not reach gelation. Use a polymer that is soluble in organic solvents. The three-dimensional crosslinked structure contained in the silicone resin is not particularly limited, and may be, for example, a basket shape, a ladder shape, or a random shape. In the present specification, the silicone resin does not include tetraalkoxysilane and a condensate (organosilicate) obtained by hydrolyzing and condensing only tetraalkoxysilane.

Since the silicone resin contains a three-dimensional crosslinked structure, when the metal plate paint is applied to the metal plate, it migrates to the surface side of the film and is uniformly arranged along the surface of the film. Then, when such a silicone resin is cured by the above-mentioned block sulfonic acid catalyst and then subjected to a frame treatment, organic groups (for example, methyl group, phenyl group, etc.) contained in the silicone resin are evenly removed and coated. Silanol groups and siloxane bonds are introduced on the film surface. As a result, the hydrophilicity of the surface of the coating film (painted metal plate) becomes uniformly high, and the rain streak stain resistance becomes very good. Further, when the cured product of the silicone resin is uniformly arranged on the surface of the coating film, the scratch resistance of the coating film is also improved.

As described above, the silicone resin is a compound obtained by partially hydrolyzing and condensing alkoxysilane, and its molecular chain is usually represented by the following general formula, T-1 unit to T-3 derived from trialkoxysilane. Includes any one or more of the units (collectively referred to as "T units").

上記一般式において、Ｒ^１は置換基を有していてもよい炭化水素基を表す。また、Ｘ^１は水素原子、または炭化水素基を表す。シリコーンレジンには、上記Ｒ^１やＸ^１の種類が異なる複数種類のＴ単位が含まれていてもよい。

In the above general formula, R ¹ represents a hydrocarbon group which may have a substituent. Further, X ¹ represents a hydrogen atom or a hydrocarbon group. The silicone resin may contain a plurality of types of T units having different types of ^{R 1} and X ^1.

R ¹ is preferably a hydrocarbon group having 1 to 12 carbon atoms, and specific examples thereof include an alkyl group such as a methyl group, an ethyl group, a propyl group, a hexyl group and an octyl group; a phenyl group, a tolyl group and a xylyl group. An aryl group such as a group and a naphthyl group; a cycloalkyl group such as a cyclohexyl group, a cyclobutyl group and a cyclopentyl group; and the like are included. Of these, a methyl group and a phenyl group are particularly preferable.

On the other hand, X ¹ is preferably a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and examples of the hydrocarbon group include alkyl groups such as methyl group, ethyl group, propyl group and hexyl group; phenyl group. , Aryl groups such as trill group and xsilyl group; cycloalkyl groups such as cyclohexyl group, cyclobutyl group and cyclopentyl group; and the like. Of these, a methyl group and an ethyl group are particularly preferable.

In addition, the molecular chain of the silicone resin includes either one of the D-1 unit and the D-2 unit derived from dialkoxysilane (collectively referred to as "D unit") or one of them, which is represented by the following general formula. Both may be included.

上記一般式において、Ｒ^２およびＲ^３はそれぞれ独立に、置換基を有していてもよい炭化水素基を表す。また、Ｘ^２は、水素原子、または炭化水素基を表す。なお、シリコーンレジンには、上記Ｒ^２やＲ^３、Ｘ^２の種類が異なる複数種類のＤ単位が含まれていてもよい。

In the above general formula, R ² and R ³ each independently represent a hydrocarbon group which may have a substituent. Further, X ² represents a hydrogen atom or a hydrocarbon group. The silicone resin may contain a plurality of types of D units having different types of ^{R 2} , R ³ , and X ^2.

Each of R ² and R ³ is preferably a hydrocarbon group having 1 to 12 carbon atoms, and specific examples thereof include a group similar to ^{R 1 of the T unit described above.} On the other hand, X ² is preferably a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and specific examples thereof include the same group as ^{X 1 of the T unit described above.}

Further, the molecular chain of the silicone resin includes any one of Q-1 units to Q-4 units (collectively referred to as "Q units") derived from tetraalkoxysilane represented by the following general formula. Alternatively, two or more may be included.

上記一般式において、Ｘ^３は水素原子、または炭化水素基を表す。なお、シリコーンレジンには、上記Ｘ^３の種類が異なる複数種類のＱ単位が含まれていてもよい。

In the above general formula, X ³ represents a hydrogen atom or a hydrocarbon group. Incidentally, the silicone resin may be the type of the X ³ is contains different types of Q units.

X ³ is preferably a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and specific examples thereof include a group similar to ^{X 1 of the T unit described above.}

The silicone resin has a structure in which the above T units, D units, and / or Q units are three-dimensionally bonded. The amount (number of moles) of silanol groups in the silicone resin contained in the paint for metal plates of the present invention is 5 to 50 mol% and 15 to 40 mol% with respect to the total number of moles of Si atoms. Is more preferable. When the amount of silanol groups exceeds 50 mol% with respect to the total number of moles of Si atoms, the reactivity of the silicone resin becomes high, and even if the above-mentioned block sulfonic acid catalyst is used, the storage stability of the paint for metal plates is stable. May be low. On the other hand, if the amount of silanol groups is less than 5 mol% with respect to the total number of moles of Si atoms, it becomes difficult for the silicone resin to hydrogen bond with other components (for example, epoxy resin) in the paint for metal plates. Silicone resin may evaporate when the paint for metal plates is cured. Further, if the amount of silanol groups is less than 5 mol%, the silicone resin is difficult to sufficiently crosslink when the paint for a metal plate is cured, and the scratch resistance of the coating film may not be sufficiently improved.

On the other hand, when the amount of silanol groups in the silicone resin is within the above range, not only the storage stability of the paint for metal plates is improved, but also the silicone resin is less likely to evaporate when the film made of the paint for metal plates is cured. , It becomes difficult to contaminate the heating device, etc. Furthermore, the scratch resistance of the coating film made of the paint for metal plates is also improved.

The number of moles of Si contained in the silicone resin and the amount of silanol groups contained in the silicone resin can be specified by analysis ^{by 29} Si-NMR and analysis by ^{1 H-NMR.} The amount of silanol groups in the silicone resin can be adjusted by the charging ratio of T units, D units, and Q units and the degree of condensation reaction. For example, when a silicone resin is prepared using trialkoxysilane, the amount of T-3 units increases and the amount of silanol groups decreases by lengthening the condensation reaction time.

Further, the silicone resin preferably contains 50 to 100 mol% of Si atoms derived from trialkoxysilane, that is, Si atoms constituting the T unit, based on the total number of moles of Si atoms contained in the silicone resin, and is preferably 60 to 100. It is more preferable to contain mol%. When the T unit amount is less than 50 mol% (particularly, the D unit amount is more than 50 mol%), the silicone resin tends to form a micellar structure, and the silicone resin tends to be concentrated in a sea-island shape on the coating film surface. .. As a result, it becomes difficult to uniformly increase the hydrophilicity and hardness of the coating film surface, and the scratch resistance and rain streak stain resistance of the coating film tend to be uneven. It is possible to confirm that the silicone resin is concentrated in a sea-island shape on the surface of the coating film by analyzing the surface of the coating film after the frame treatment with an AFM (atomic force microscope). For example, the etching depth by frame processing differs between the sea part and the island part of the coating film surface. Therefore, it is possible to confirm the distribution of silicone resin on the sea islands by the unevenness of the coating film surface.

On the other hand, when the T unit amount is 50 mol% or more, it becomes difficult for the silicone resin to form a micelle structure, and the silicone resin tends to be uniformly concentrated on the surface of the coating film. As a result, the rain streak stain resistance of the coated metal plate obtained by applying the paint for the metal plate is improved, and the scratch resistance of the coating film is improved. The amount of Si atoms constituting the T unit can be specified by analysis by ^{29 Si-NMR.}

When the silicone resin contains an alkyl group and an aryl group, the number of moles of the aryl group directly bonded to the Si atom of the silicone resin, that is, the ratio of the aryl group / alkyl group to the number of moles of the alkyl group directly bonded to the Si atom. Is preferably 20 to 80%, more preferably 30 to 70%. The higher the molar ratio of aryl groups, the easier it is for the silicone resin to dissolve in other components in the metal plate paint. In addition, the storage stability of the paint is likely to increase. However, if the proportion of aryl groups is excessive, the reaction rate at the time of forming the coating film is significantly reduced, and it may be difficult to obtain a sufficient crosslink density. The ratio of the alkyl group to the aryl group ^{can be specified by 1} H-NMR analysis.

Here, the weight average molecular weight of the silicone resin is preferably 700 to 50,000, and more preferably 1,000 to 10,000. When the weight average molecular weight of the silicone resin is less than 700, the silicone resin tends to evaporate easily when the paint (film) for a metal plate is cured, which tends to contaminate the heating device or reduce the hardness of the coating film. On the other hand, when the weight average molecular weight exceeds 50,000, the viscosity of the paint for metal plates tends to increase, and the storage stability tends to decrease. The weight average molecular weight of the silicone resin is a polystyrene-equivalent amount measured by gel permeation chromatography (GPC).

The paint for a metal plate preferably contains 1 to 10 parts by mass of a silicone resin, and more preferably 2 to 6 parts by mass, based on 100 parts by mass of the solid content. By including the silicone resin in the metal plate paint in the above range, the hydrophilicity of the obtained coating film surface can be sufficiently increased, and rain streak stains are less likely to occur. In addition, the hardness of the coating film surface also increases.

The above-mentioned silicone resin can be prepared by hydrolyzing and polymerizing trialkoxysilane or the like. Specifically, an alkoxysilane such as trialkoxysilane and a partial condensate thereof are dispersed in a solvent such as water or alcohol. Then, the pH of the dispersion is adjusted to preferably 1 to 7, more preferably 2 to 6, and the alkoxysilane or the like is hydrolyzed. Then, the hydrolyzate is dehydrated and condensed to obtain a silicone resin. The molecular weight and the like of the obtained silicone resin can be adjusted by the dehydration condensation time and the like. The condensation of the hydrolyzate can be carried out continuously with the above-mentioned hydrolysis, and the condensation reaction can be promoted by distilling off the alcohol or water produced by the hydrolysis.

The alkoxysilane used for preparing the silicone resin is appropriately selected according to the desired structure of the silicone resin. Examples of trialkoxysilane compounds include methyltrimethoxysilane, methyltriethoxysilane, methyltriisopropoxysilane, methyltributoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, and propyltrimethoxysilane. , Ppropyltriethoxysilane, propyltriisopropoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, methyltrisilanol, phenyltricilanol, etc. Is included.

Examples of dialkoxysilanes include methylhydrogendimethoxysilane, methylhydrogendiethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, methylethyldimethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, methylpropyldimethoxysilane, and methyl. Propyldiethoxysilane, diisopropyldimethoxysilane, phenylmethyldimethoxysilane, diphenyldimethoxysilane and the like are included.

Further, examples of tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetramethoxysilane and the like.

When preparing the silicone resin, the above-mentioned partial condensate of trialkoxysilane, dialkoxysilane, or tetramethoxysilane may be used as a raw material.

(3) Polyester resin The polyester resin functions as a binder in a coating film obtained from a paint for a metal plate. The polyester resin can be, for example, a known resin obtained by polycondensing a polyvalent carboxylic acid and a polyhydric alcohol. Examples of polyvalent carboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid and their anhydrides; succinic acid, adipic acid. , Azelaic acid, sebacic acid, dodecandicarboxylic acid, aliphatic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and anhydrides thereof; lactones such as γ-butyrolactone and ε-caprolactone; trimellitic acid, trimedic acid, pyro Merit Acids and other trivalent or higher valent carboxylic acids; etc. are included. The polyester resin may contain only one type of the structure derived from the polyvalent carboxylic acid, or may contain two or more types.

Examples of polyhydric alcohols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2- Pentandiol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 1,4-hexanediol, 2,5-hexanediol, 1,5-hexanediol, 3-methyl-1 , 5-Pentane Glycol, Diethylene Glycol, Triethylene Glycol, 1,2-Dodecanediol, 1,2-Octadecanediol, Neopentyl Glycol, 1,4-Cyclohexanediol, 1,4-Cyclohexanedimethanol, Bisphenol A alkylene Oxide Addition Glycols such as bisphenol S alkylene oxide adduct; trihydric or higher polyhydric alcohols such as trimethylpropane, glycerin, and pentaerythritol are included. The polyester resin may contain only one type of the structure derived from the polyhydric alcohol, or may contain two or more types.

The number average molecular weight (in terms of polystyrene) measured by GPC of the polyester resin is preferably 2,000 to 35,000. If the number average molecular weight is smaller than 2,000, the processability of the coated metal plate may be lowered, and the coating film may be easily cracked. On the other hand, when the above-mentioned block sulfonic acid catalyst is used, the reactivity between the polyester resin and the melamine resin-based curing agent can be enhanced even if the polyester resin has a relatively high molecular weight. However, when the number average molecular weight is larger than 35,000, even if the above-mentioned block sulfonic acid catalyst is used, the crosslink density of the obtained coating film tends to be low, and the weather resistance of the coating film may be lowered. From the balance between workability and weather resistance, the number average molecular weight is particularly preferably 3,000 to 20,000.

The paint for a metal plate preferably contains 30 to 70 parts by mass of polyester resin, and more preferably 40 to 60 parts by mass, based on 100 parts by mass of the solid content. When the polyester resin is included in the paint for the metal plate in the above range, the film strength of the obtained coating film surface is increased, and the metal plate can be protected.

(4) Melamine Resin-based Curing Agent The melamine resin-based curing agent is not particularly limited as long as it functions as a curing agent for curing the polyester resin. By cross-linking the polyester resin with a melamine resin-based curing agent, the properties and physical properties of the coating film (for example, the surface hardness and durability of the coating film) can be adjusted.

The melamine resin-based curing agent is not particularly limited as long as it has a structure derived from melamine and has a structure capable of cross-linking a polyester resin, and examples thereof include methylation of methylol melamine methyl ether and the like. Melamine-based resin; n-butylated melamine-based resin such as methylol melamine butyl ether; mixed etherified melamine resin of methyl and n-butyl and the like are included.

The amount of the melamine resin-based curing agent contained in the coating film for a metal plate is appropriately selected according to the type of the melamine resin-based curing agent. The paint for a metal plate preferably contains 5 to 50 parts by mass of a melamine resin-based curing agent with respect to 100 parts by mass of the polyester resin, and more preferably 7 to 45 parts by mass. When the amount of the melamine resin-based curing agent is in the above range, the curability of the polyester resin becomes good, and the curability of the coating film obtained from the paint for metal plates becomes good.

(5) Other Components The paint for a metal plate may contain inorganic particles or organic particles. When these are contained in the paint for a metal plate, the surface roughness and the like of the obtained coating film can be easily adjusted. Here, the average particle size of the inorganic particles or organic particles is preferably 4 to 80 μm, more preferably 10 to 60 μm. The average particle size of inorganic particles and organic particles is a value measured by the Coulter counter method. The shape of the inorganic particles and the organic particles is not particularly limited, but it is preferably substantially spherical from the viewpoint that the surface state of the obtained coating film can be easily adjusted.

Examples of inorganic particles include silica, barium sulphate, talc, calcium carbonate, mica, glass beads and glass flakes. Examples of organic particles include resin beads made of acrylic resin or polyacrylonitrile resin. These resin beads may be manufactured by a known method or may be commercially available products. Examples of commercially available acrylic resin beads include "Tuftic AR650S (average particle size 18 μm)", "Tuftic AR650M (average particle size 30 μm)", "Tuftic AR650MX (average particle size 40 μm)", and "Toughtic" manufactured by Toyobo Co., Ltd. "AR650MZ (average particle size 60 μm)" and "Tuftic AR650ML (average particle size 80 μm)" are included. Examples of commercially available polyacrylonitrile resin beads include "Tuftic A-20 (average particle size 24 μm)", "Tuftic YK-30 (average particle size 33 μm)" and "Tuftic YK-50 (average particle size 33 μm)" manufactured by Toyobo Co., Ltd. "Average particle size 50 μm)" and "Tuftic YK-80 (average particle size 80 μm)" and the like are included.

The amount of inorganic particles and / or organic particles contained in the paint for a metal plate is appropriately selected according to the desired surface condition of the coating film and the like. Usually, the total amount of the inorganic particles and / or the organic particles with respect to 100 parts by mass of the solid content of the paint for a metal plate can be 1 to 40 parts by mass.

Furthermore, the paint for a metal plate may contain a coloring pigment, if necessary. The average particle size of the coloring pigment can be, for example, 0.2 to 2.0 μm. Examples of such colored pigments include titanium oxide, iron oxide, yellow iron oxide, phthalocyanine blue, carbon black, cobalt blue and the like. When the paint for metal plates contains a coloring pigment, the amount thereof is preferably 20 to 60 parts by mass and 30 to 55 parts by mass with respect to 100 parts by mass of the solid content of the paint for metal plates. Is more preferable.

Further, the paint for a metal plate may contain wax, if necessary. Examples of waxes include polyolefin waxes (polyethylene, polypropylene, etc.), fluorine-based waxes (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, etc.), paraffin-based waxes, stearic acid-based waxes, etc. Includes, but is not limited to. The amount of wax is appropriately selected depending on the type of wax and the like, but can be about 2 to 15% by mass with respect to 100 parts by mass of the solid content of the paint for metal plates.

Further, the paint for a metal plate may contain an organic solvent, if necessary. The organic solvent is not particularly limited as long as it can sufficiently dissolve or disperse the above-mentioned silicone resin, block sulfonic acid catalyst, polyester resin, melamine resin-based curing agent, inorganic particles, organic particles and the like. Examples of organic solvents include toluene, xylene, Solvesso® 100 (trade name, manufactured by Exxon Mobile), Solvesso® 150 (trade name, manufactured by Exxon Mobile), Solvesso® 200 (registered trademark). Hydrocarbon solvents such as (trade name, Exxon Mobile Co., Ltd.); ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester solvents such as ethyl acetate, butyl acetate, and ethylene glycol monoethyl ether acetate; methanol, Alcohol-based solvents such as isopropyl alcohol and n-butyl alcohol; ether alcohol-based solvents such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether; and the like are included. The paint may contain only one kind of these, or may contain two or more kinds of these. Among these, xylene, Solvesso (registered trademark) 100, Solvesso (registered trademark) 150, cyclohexanone, and n-butyl alcohol are preferable from the viewpoint of compatibility with the resin.

(6) Paint preparation method The paint preparation method is not particularly limited. Similar to known paints, it can be prepared by mixing, stirring or dispersing each of the above materials. The silicone resin may be mixed with other components in advance. Alternatively, a material other than the silicone resin may be mixed in advance, and the silicone resin may be mixed later.

2. Method for Producing Painted Metal Plate A method for producing a painted metal plate using the above-mentioned paint for a metal plate will be described below. The method for manufacturing the coated metal plate includes a step of applying the above-mentioned paint for a metal plate to the surface of the metal plate and curing it to form a coating film, and a step of performing a frame treatment on the coating film. Can be.

Here, as the metal plate to which the paint for the metal plate is applied, a metal plate generally used as a building plate can be used. Examples of such metal plates include plated steel plates such as molten Zn-55% Al alloy plated steel plates; steel plates such as ordinary steel plates and stainless steel plates; aluminum plates; copper plates and the like. A chemical conversion treatment film, an undercoat film, or the like may be formed on the surface of the metal plate as long as the effects of the present invention are not impaired. Further, the metal plate may be subjected to uneven processing such as embossing or draw forming as long as the effect of the present invention is not impaired.

The thickness of the metal plate is not particularly limited, and is appropriately selected depending on the application and the like. For example, when a coated metal plate is used as a metal siding material, the thickness of the metal plate can be 0.15 to 0.5 mm.

The method of applying the above-mentioned paint for a metal plate to the surface of the metal plate is not particularly limited, and a known method can be appropriately selected. Examples of the method of applying the paint for a metal plate include a roll coating method, a curtain flow method, a spin coating method, an air spray method, an airless spray method and a dipping pulling method. Among these, the roll coating method is preferable from the viewpoint that it is efficient and it is easy to obtain a coating film having a desired thickness.

Further, the curing method of the paint for a metal plate can be, for example, baking by heating. The temperature during the baking process is such that the block group of the above-mentioned block sulfonic acid catalyst is desorbed while the decomposition of the resin or the like in the paint is prevented, or the polyester resin and the melamine resin-based curing agent are sufficiently reacted. From the viewpoint, it is preferably 120 to 300 ° C, more preferably 150 to 280 ° C, and even more preferably 180 to 260 ° C. The baking treatment time is not particularly limited, and from the same viewpoint as described above, it is preferably 3 to 90 seconds, more preferably 10 to 70 seconds, and further preferably 20 to 60 seconds.

Further, when the metal plate paint is baked, the wind may be blown so that the plate surface wind speed is 0.9 m / s or more in order to cure the metal plate paint in a short time. In the above-mentioned paint for metal plates, the silicone resin and other components are hydrogen-bonded. Therefore, even if the paint for the metal plate is cured while blowing wind, the silicone resin is less likely to evaporate and the heating device is less likely to be contaminated.

Here, the thickness of the coating film formed on the metal plate is appropriately selected depending on the application of the coated metal plate and the like, but is usually in the range of 3 to 30 μm. The thickness is a value obtained by the gravimetric method from the specific gravity of the baked coating film and the weight difference of the coated metal plate before and after removing the coating film by sandblasting or the like. If the coating is too thin, the durability and hiding properties of the coating may be inadequate. On the other hand, if the coating film is too thick, the manufacturing cost increases and armpits may easily occur during baking.

On the other hand, the method for frame-treating the coating film (paint after curing) is not particularly limited, and can be the same as the normal frame-treating method. When the coating film (cured film) obtained from the above-mentioned coating material for metal plates is frame-treated, the hydrocarbon groups (for example, methyl group, phenyl group, etc.) of the silicone resin on the coating film surface are decomposed, and silanol groups and siloxane bonds are formed. Occurs. As a result, the hydrophilicity of the coating film surface is increased, and rain streak stain resistance is exhibited.

The frame processing can be a method of placing a metal plate on which a coating film is formed on a conveyor such as a belt conveyor and radiating a flame to the coating film with a frame processing burner while moving the metal plate in a certain direction. ..

The frame processing amount is preferably 30~1000kJ / ^{m 2,} and more preferably 100~600kJ / ^{m 2.} The "frame processing amount" in the present specification is the amount of heat per unit area of the coated metal plate calculated based on the supply amount of combustion gas such as LP gas. The frame processing amount can be adjusted by the distance between the burner head of the frame processing burner and the coating film surface, the transport speed of the coating film, and the like. If the frame processing amount is ^{less than 30 kJ / m 2} , the processing may be uneven, and it is difficult to uniformly hydrophilize the coating film surface. On the other hand, if the frame processing amount ^{exceeds 1000 kJ / m 2} , the coating film may be oxidized and yellowed.

Further, before the frame treatment, a preheat treatment for heating the coating film surface to 40 ° C. or higher may be performed. When a coating film formed on the surface of a metal plate having a high thermal conductivity (for example, a metal plate having a thermal conductivity of 10 W / mK or more) is irradiated with a flame, the water vapor generated by the combustion of combustible gas is cooled and water is used. And temporarily accumulates on the surface of the coating film. Then, the water absorbs the energy during the frame treatment and becomes water vapor, which may hinder the frame treatment. On the other hand, by preheating the coating film surface (metal plate), it is possible to suppress the generation of water during flame irradiation.

The means for preheating the coating film is not particularly limited, and a heating device generally called a drying furnace can be used. For example, a batch-type drying oven (also referred to as a "safe oven") can be used, and specific examples thereof include a low-temperature incubator manufactured by Isuzu Seisakusho Co., Ltd. (model Mini Catalina MRLV-11) and Tojo Co., Ltd. An automatic discharge type dryer manufactured by Atsugaku Co., Ltd. (model ATO-101), a simple explosion-proof desiccator manufactured by Tojo Thermal Science Co., Ltd. (model TNAT-1000), and the like are included.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

1. 1. Preparation of paint for metal plate A paint for metal plate was prepared by the following method.

1-1. Materials The following polyester resins, block sulfonic acid catalysts, silicone resins, and organosilicates were used in each of the examples and comparative examples.

[Polyester resin]
-Polyester resin A: Byron KS-1520V, manufactured by Toyobo Co., Ltd., number average molecular weight 6400, glass transition temperature 3 ° C., hydroxyl value 42 mgKOH / g
-Polyester resin B: Byron KS-1460V, manufactured by Toyobo Co., Ltd., number average molecular weight 15000, glass transition temperature 7 ° C., hydroxyl value 11 mgKOH / g
-Polyester resin C: Byron KS-1860V, manufactured by Toyobo Co., Ltd., number average molecular weight 32000, glass transition temperature -8 ° C, hydroxyl value 17 mgKOH / g

[Melamine resin-based curing agent]
-Methoxy group 90 mol% methylated melamine resin-based curing agent: Cymel (registered trademark) 303, manufactured by Mitsui Cytec Co., Ltd.

（Ｒ^１１は、平均炭素数１０．４の分岐アルキル鎖を表す）
・ブロックスルホン酸触媒Ｂ（ｐＨ９．０）：パラトルエンスルホン酸にトリエチルアミンを添加して調製した。トリエチルアミンの添加量は、ブロックスルホン酸触媒ＢのｐＨが９．０となるように調整した。 [Block sulfonic acid catalyst]
-Block sulfonic acid catalyst A (pH 7.0): A paratoluenesulfonic acid ester having a structure represented by the following chemical formula.

(R ¹¹ represents a branched alkyl chain having an average carbon number of 10.4)
-Block sulfonic acid catalyst B (pH 9.0): Prepared by adding triethylamine to paratoluenesulfonic acid. The amount of triethylamine added was adjusted so that the pH of the block sulfonic acid catalyst B was 9.0.

[Silicone resin]
The silicone resin was prepared as follows.
-Preparation of Methyl Silicone Resin A 408 g (3.0 mol) of methyltrimethoxysilane was placed in a 2 L flask, 800 g of water was added at 10 ° C. or lower, and the mixture was mixed well. Then, under ice-cooling, 216 g (12.0 mol) of a 0.05 N aqueous hydrochloric acid solution was added dropwise at 5 ° C. over 40 minutes. After completion of the dropping, the mixture was stirred at 10 ° C. for 6 hours to complete hydrolysis and dehydration condensation. As a result, a preparation solution containing a methyl silicone resin A was obtained. Then, methanol produced by hydrolysis was distilled off from the prepared solution at 70 ° C. and 60 mmHg under reduced pressure for 1 hour. The prepared solution after distilling off methanol was cloudy and was separated into two layers by allowing it to stand overnight. The lower layer is a silicone resin that is insoluble in water and settled. 469 g of methyl isobutyl ketone (MIBK) was added to the prepared solution, and the mixture was stirred at room temperature for 1 hour. As a result, the precipitated silicone resin was completely dissolved in MIBK. Then, the prepared liquid was allowed to stand, and the aqueous layer and the MIBK layer were separated. Then, the lower aqueous layer was removed with a flask with a cock to obtain a colorless and transparent silicone resin solution having a solid content of 50% by mass. Table 1 shows the weight average molecular weight, molecular weight distribution, T unit (structure derived from trifunctional silicone resin) / D unit (structure derived from bifunctional silicone resin), and silanol group amount with respect to Si atomic weight of silicone resin A. The weight average molecular weight and the molecular weight distribution were specified by GPC analysis. In addition, T / D units and silanol group amounts were ^{identified by 29} Si-NMR and ¹ H-NMR analysis.

-Synthesis of Methyl Silicone Resin B 286 g (2.1 mol) of methyltrimethoxysilane and 108 g (0.9 mol) of dimethyldimethoxysilane were placed in a 2 L flask, 800 g of water was added at 10 ° C. or lower, and the mixture was mixed well. .. Then, under ice-cooling, 198 g (11.0 mol) of a 0.05 N aqueous hydrochloric acid solution was added dropwise at 5 to 25 ° C. over 20 minutes. After completion of the dropping, the mixture was stirred at 15 ° C. for 6 hours for hydrolysis and dehydration condensation. After completion of the dropping, the same operation as the synthesis of the methyl silicone resin A was carried out to obtain a silicone resin solution containing the methyl silicone resin B having a solid content of about 50% by mass. Table 1 shows the weight average molecular weight, molecular weight distribution, T unit / D unit, and silanol group weight with respect to the Si atomic weight of the silicone resin B.

-Synthesis of Methyl / Phenyl Silicone Resin C 272 g (2.0 mol) of methyltrimethoxysilane and 119 g (1.0 mol) of phenyltrimethoxysilane were placed in a 2 L flask, and 800 g of water was added at 10 ° C. or lower. Mix well. Then, under ice-cooling, 198 g (11.0 mol) of a 0.05 N aqueous hydrochloric acid solution was added dropwise at 5 to 25 ° C. over 30 minutes. After completion of the dropping, the mixture was stirred at 10 ° C. for 6 hours to complete hydrolysis and dehydration condensation. After completion of the dropping, the same operation as the synthesis of the methyl silicone resin A was carried out to obtain a preparation liquid containing the methyl / phenyl silicone resin C having a solid content of about 50% by mass. Table 2 shows the weight average molecular weight, molecular weight distribution, T unit / D unit, content ratio of methyl group to phenyl group (methyl / phenyl), and silanol group amount with respect to Si atomic weight of silicone resin C.

-Synthesis of Methyl / Phenyl Silicone Resin D 109 g (0.8 mol) of methyltrimethoxysilane, 198 g (1.0 mol) of phenyltrimethoxysilane, and 144 g (1.2 mol) of dimethyldimethoxysilane were placed in a 2 L flask. The mixture was charged, 800 g of water was added at 10 ° C. or lower, and the mixture was mixed well. Then, under ice-cooling, 216 g (12.0 mol) of a 0.05 N hydrochloric acid aqueous solution was added dropwise at 5 to 25 ° C. over 40 minutes, and the mixture was stirred at 10 ° C. for 6 hours to complete hydrolysis and dehydration condensation. After completion of the dropping, the same operation as the synthesis of the methyl silicone resin A was carried out to obtain a silicone resin solution containing the methyl / phenyl silicone resin D having a solid content of about 50% by mass. Table 2 shows the weight average molecular weight, molecular weight distribution, T unit / D unit, content ratio of methyl group to phenyl group (methyl / phenyl), and silanol group amount with respect to Si atomic weight of silicone resin D.

[Organosilicate]
The following organs were used as the organosilicates.
-Methyl silicate E (condensate of tetramethoxysilane): Methyl silicate 53A, manufactured by Corcote, weight average molecular weight (Mw) 840, number average molecular weight (Mn) 610, Mw / Mn = 1.4
-Ethyl silicate F (condensate of tetraethoxysilane): Ethyl silicate 48, manufactured by Corcote, weight average molecular weight (Mw) 1300, number average molecular weight (Mn) 850, Mw / Mn = 1.5

1-2. Preparation The polyester resin shown in Tables 3 and 4 and the melamine resin-based curing agent were mixed to obtain a composition containing the polyester resin and the melamine resin-based curing agent. The blending ratio of the polyester resin A and the methylated melamine resin-based curing agent was 100:40, the blending ratio of the polyester resin B and the methylated melamine resin-based curing agent was 100:30, and the blending ratio of the polyester resin C and the methylated melamine resin was 100:30. The blending ratio with the melamine resin-based curing agent was 100:20.

Titanium oxide ((pigment), JR-603, TAYCA Corporation) having an average particle size of 0.28 μm is 45% by mass and an average particle size of 5.5 μm is hydrophobic in the above composition, respectively, with respect to the solid content of the coating material. Silica A (Silysia 456, Fuji Silysia Chemical Ltd.) was added in an amount of 4% by mass, and hydrophobic silica B (Silysia 476, Fuji Silysia Chemical Ltd.) having an average particle size of 12 μm was added in an amount of 3% by mass. Further, when the amount of the sulfonic acid after the block group is removed from the block sulfonic acid catalysts shown in Tables 3 and 4 is 0.5 mass with respect to the solid content of the paint for the metal plate when the polyester resin A is used. In the case of polyester resin B, it is 0.8% by mass with respect to the solid content of the paint for metal plates, and in the case of polyester resin C, it is the solid content of paint for metal plates. It was added so as to be 1.0% by mass. In the paints for metal plates of Examples and Comparative Examples, the block sulfonic acid catalyst also acts as a cross-linking catalyst between the polyester resin (particularly the polyester resin C) and the melamine resin-based curing agent.

Further, as shown in Tables 3 and 4, methyl silicone resin, methyl / phenyl silicone resin, methyl silicate, or ethyl silicate was added so as to be 5% by mass based on the solid content of the coating material, respectively. Further, for the paint for metal plates to which methyl silicate or ethyl silicate was added, triethyl orthoformate was added so as to be 5% by mass with respect to the solid content of the paint for metal plates.

2. Evaluation Using the above-mentioned paint for metal plate, a painted metal plate was prepared as follows and evaluated. The results are shown in Tables 3 and 4.

2-1. Preparation of metal plate A molten Zn-55% Al alloy plated steel plate having a plate thickness of 0.27 mm, A4 size (210 mm × 297 mm), and a plating adhesion amount of 90 g / m ² per side was prepared as a metal plate, and the surface was alkali degreased. Then, a coating type chromate treatment liquid (NRC300NS manufactured by Nippon Paint Co., Ltd.) was applied to the surface so that the ^{amount of Cr adhered was 50 mg / m 2.} Further, an epoxy resin-based primer paint (700P manufactured by Nippon Fine Coatings Co., Ltd.) was applied with a roll coater so that the cured film thickness was 5 μm. Subsequently, a plated steel sheet (hereinafter, also simply referred to as “plated steel sheet”) on which a primer coating film was formed was obtained by baking so that the maximum temperature of the metal plate reached 215 ° C.

2-2. Coating and Curing of Paint The paint for a metal plate prepared as described above was stored in a constant temperature room at 40 ° C. for 15 days, and then coated on the above-mentioned plated steel sheet with a roll coater so that the cured film thickness was 18 μm. Then, the plate was baked at a maximum plate temperature of 225 ° C. and a plate surface wind speed of 0.9 m / s for 45 seconds.

2-3. Frame treatment The coating films coated with the metal plate paints of Examples 1 to 12 and Comparative Examples 1 to 12 were frame-treated by the following methods. No frame processing was performed on Comparative Examples 13 to 24.
As the frame processing burner, F-3000 manufactured by Flynn Burner (USA) was used. Further, as the combustible gas, a mixed gas (LP gas: clean dry air (volume ratio) = 1: 25) in which LP gas (combustion gas) and clean dry air were mixed with a gas mixer was used. The flow rate of each gas was adjusted so that LP gas (combustion gas) was 1.67 L / min and clean dry air was 41.7 L / min with respect to ^{1 cm 2 of the burner flame opening.} The length of the flame port of the burner head in the transport direction of the coating film was set to 4 mm. On the other hand, the length of the burner head in the direction perpendicular to the transport direction of the flame port was 450 mm. Further, the distance between the flame port of the burner head and the surface of the coating film was set to 20 mm according to the desired frame processing amount. Further, the frame processing amount was adjusted to ^{265 kJ / m 2} by setting the transport speed of the coating film to 24 m / min.

2-4. Mirror surface gloss The 60 ° mirror surface gloss specified by JIS K5600-4-7 (ISO 2813: 1994) was measured with a gloss meter VG-2000 manufactured by Nippon Denshoku Co., Ltd. for the coated metal plates produced in Examples and Comparative Examples. bottom. As a result, the 60 ° mirror surface gloss was 30 to 40 in all the coated metal plates.

2-5. Evaluation of storage stability of paint for metal plates Each paint for metal plates is stored in a constant temperature room at 40 ° C, and the viscosity of the paint after 15 days, 1 month, 3 months, and 6 months is measured with a B-type viscometer. bottom. Then, the viscosities before and after storage were compared and evaluated according to the following criteria.
⊚: Paint viscosity increase rate is less than 30% before and after storage in a constant temperature room ○: Paint viscosity increase rate is 30% or more and less than 100% before and after storage in a constant temperature room △: Paint viscosity increase rate is 100% or more before and after storage in a constant temperature room × : Gelation occurred. △, ○, and ◎ were regarded as acceptable.

2-6. Pencil hardness evaluation A pencil hardness test was conducted to evaluate the scratch resistance of the coating film surface of the above-mentioned coated metal plate in accordance with JIS K5600-5-4 (ISO / DIS 15184). The scratch resistance of the coating film surface was evaluated according to the following criteria.
◯: H or more Δ: B to HB
X: 2B or less In addition, Δ or more was evaluated as passing.

2-7. Measurement of water contact angle The water contact angle of the coating film surface of the above-mentioned coated metal plate was measured. The measurement was carried out using a contact angle meter DM901 manufactured by Kyowa Interface Science Co., Ltd. by forming water droplets of 0.01 cc of purified water in a constant temperature and humidity chamber having a temperature of 23 ± 2 ° C. and a relative humidity of 50 ± 5%.

2-8. Evaluation of rain-resistant streak stain resistance The rain-resistant streak stain resistance was evaluated as follows.
First, the above-mentioned painted metal plates were attached to the vertical exposure tables. Further, a corrugated plate was attached to the upper part of the painted metal plate so as to have an angle of 20 ° with respect to the ground. At this time, a corrugated plate was installed so that rainwater would flow in a streak on the surface of the painted metal plate. In this state, an outdoor exposure test was conducted for 6 months, and the state of dirt adhesion was observed. The rain-resistant streak stain resistance was evaluated as follows based on the difference in brightness (ΔL) of the coated metal plate before and after exposure.
⊚: ΔL was less than 1 (rain stains were not visible at all)
〇: ΔL was less than 1 (rain stains are almost invisible)
X: ΔL was 1 or more and less than 2 (rain stains are inconspicuous but visible)
XX: ΔL was 2 or more (dirt is conspicuous)
In addition, ○ and ◎ were accepted.

As shown in Tables 3 and 4, the viscosity of the paint for metal plates containing organosilicates increases after 15 days regardless of which block sulfonic acid catalyst (curing catalyst) is used. After one month, most of them gelled (Comparative Examples 13 to 24).

On the other hand, even in the coating material for metal plates containing silicone resin, when the block sulfonic acid catalyst B (pH 9.0) is used as the curing catalyst, it is easy to gel when the molecular weight of the polyester resin is high, and a low molecular weight polyester resin is used. Even if it was present, gelation occurred one month later (Comparative Examples 1 to 12). On the other hand, when the block sulfonic acid catalyst A (pH 7.0) was used as the curing catalyst for the silicone resin, the paint for any metal plate was stable within 3 months (Example). 1-12). In particular, as the molecular weight of the polyester resin increases, the amount of the block sulfonic acid catalyst is increased. Therefore, when the molecular weight of the polyester resin is large (particularly the polyester resin C), the storage stability of the paint tends to be significantly reduced. Was there. However, by using the block sulfonic acid catalyst A, the storage stability was remarkably improved even when such a high molecular weight polyester resin was used (Examples 9 to 12).

The paint for metal plates of the present invention has very good storage stability. Further, according to the paint for the metal plate, it is possible to obtain a coated metal plate which is less likely to cause rain streak stains and has high scratch resistance. Further, the paint for a metal plate is less likely to contaminate an apparatus for producing a coated metal plate. Therefore, the paint for metal plates is very useful as a paint for manufacturing exterior building materials and the like of various buildings.

Claims (6)

With polyester resin
Melamine resin-based curing agent and
Silicone resin containing a structure derived from trialkoxysilane,
With a block sulfonic acid catalyst having a pH of 6-8,
Only including,
The block sulfonic acid catalyst has a structure represented by the following general formula (1).
Paint for metal plates.

(In the general formula (1)
R ¹ represents a monovalent or polyvalent alkyl group having 1 to 18 carbon atoms, a phenyl group in which one or two alkyl groups having 1 to 18 carbon atoms are bonded, or a naphthyl group.
R ² and R ³ independently represent a hydrogen atom and an alkyl group having 1 to 12 carbon atoms (however, R ² and R ³ may be bonded to each other to form a ring).
X ¹ is a single _{^{bond, -CH 2 -O-R 6 -}} , or _{-CH 2 -O-C (= O} ) -R 7 - a represents ^{(R 6} and ^{R 7} are a single bond or a carbon number 1 Represents ~ 20 divalent organic groups),
X ² represents a single bond or -C (= O) NH-
R ⁴ is a hydrogen atom, a monovalent or polyvalent alkyl group having 1 to 18 carbon atoms, a bisphenol A residue which may have a substituent, or a bisphenol F residue which may have a substituent. Represents
R ⁵ is a hydrogen atom, a monovalent or polyvalent alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 1 to 18 carbon atoms, an alkylene group having 1 to 18 carbon atoms, an aryl group having 1 to 18 carbon atoms, and the like. Alternatively, it represents an organic group having 19 to 100 carbon atoms.
n represents an integer from 1 to 10 and represents
x, y, and z each independently represent an integer of 1 or more) ^{R 1} in the general formula (1) is a p-tolyl group or a 4-dodecylphenyl group.
The paint for a metal plate according to claim 1. The block sulfonic acid catalyst contains a compound represented by the following general formula (2).
The paint for a metal plate according to claim 1.

(In the general formula (2), R ¹¹ is an alkyl group having 1 to 18 carbon atoms, a bisphenol A residue which may have a substituent, or a bisphenol F residue which may have a substituent. R ¹² represents an alkyl group having 1 to 12 carbon atoms) The silicone resin contains 5 to 50 mol% silanol groups with respect to the total number of moles of Si atoms.
The paint for a metal plate according to any one of claims 1 to 3. The silicone resin contains 50 to 100 mol% of Si atoms derived from trialkoxysilane.
The paint for a metal plate according to any one of claims 1 to 4. A step of applying the paint for a metal plate according to any one of claims 1 to 5 to the surface of the metal plate and curing the coating film to form a coating film.
The process of frame processing the coating film and
including,
Manufacturing method of painted metal plate.