JP7386719B2 - Thermosetting powder coating, a coating formed using the coating, and a coated object equipped with the coating - Google Patents

Description

The present invention relates to a thermosetting powder coating (composition), a coating film (cured product) formed using this coating, and an object to be coated (coated article) provided with this coating film on an object to be coated. ) and related to.

Epoxy resin powder coating, which is a type of thermosetting powder coating, is an insulating powder coating based on epoxy resin, and its coating film has excellent mechanical properties, chemical resistance, corrosion resistance, and electrical properties. There is. In particular, since the coating film formed has excellent electrical properties and corrosion resistance, it is used as an insulating material to coat objects to be painted in the field of metal processing such as bus bars and steel pipes.
As epoxy resin powder coatings, those containing a bisphenol A type epoxy resin, a phenolic curing agent, dicyandiamide, an imidazole curing accelerator, and/or an imidazoline curing accelerator are known (Patent Document 1).

Japanese Patent Application Publication No. 10-323616

In the metal processing field, the object to be painted is obtained by applying paint to the object to be painted (for example, processed steel materials, etc.) and forming a coating film on the surface of the object. , it may be used by bending it to any angle. When a coating film is formed using the epoxy resin powder coating of Patent Document 1, it is formed in a relatively short time (8 to 16 minutes at 140°C, 2 to 4 minutes at 160°C, and 1 to 2 minutes at 180°C). (Paragraph 0044) However, the coating film formed on the surface of the object to be painted is easily deformed by the stress generated by the bending process, causing cracks and peeling of the coating film. .

When used in such metal processing fields, the coating film formed on the surface of the object to be painted must be able to be bent without cracking or peeling (i.e., the coating film has sufficient flexibility and the coating film does not need to be painted). It is important that the adhesive has excellent adhesion to the surface of the object.
Further, the epoxy resin powder coating of Patent Document 1 may be used (painted) in a high temperature environment (for example, about 80 to 90 degrees Celsius), and in this case, the temperature is even higher than that environment (for example, about 150 to 190 degrees Celsius). of heat is required for curing (film formation) after painting.

However, when forming a coating film by high temperature curing using the epoxy resin powder coating of Patent Document 1, it is difficult to achieve desired properties (for example, sufficient flexibility is imparted to the resulting coating film, and It takes a long time (for example, about 2 hours) to reach a cured state that provides excellent adhesion to the surface of the object, which poses an issue in terms of productivity of the cured product (coating film). had.

Since the polymerization reaction of epoxy is a chemical reaction, it is widely known that the higher the temperature, the faster the epoxy cures and the shorter its pot life. Therefore, for example, if a powder coating designed for curing conditions of 150°C for 2 hours is heated to 180°C, it will not take the originally designed time (2 hours) to reach the desired curing state. (For example, about a few minutes).
However, when used in a high-temperature environment, curing time of several minutes is still a problem in terms of productivity. On the other hand, if productivity is prioritized and the curing temperature is further increased (for example, around 200°C) and the curing time is further shortened to around 20 seconds, the coating film may be insufficiently cured and the intended properties may not be obtained. This may cause problems such as the curing reaction not proceeding properly.

The present invention relates to a thermosetting powder coating that is suitable for use (painting) in high-temperature environments and has fast curing properties that allow it to reach a cured state that provides the intended properties in an extremely short time; To provide a coating film made of a cured product of the present invention and having sufficient flexibility and adhesion to an object to be coated (processed steel, etc.), and an object to be coated with the coating film on the object to be coated. That is the issue.

The present inventors include (A), (C), and (D) shown below (however, (B) is not included), (A) includes (A2), and (D) includes The above problem is solved by adjusting the blending range of (A2) in a composition containing (A1) and (A2) and the equivalent ratio range of (C) to (A) while including (D1). They discovered that it can be done and completed the present invention.

That is, according to the present invention, a thermosetting powder coating having the following configuration is provided.
According to the present invention, there is also provided a coating film obtained by thermally curing a thermosetting powder coating having the configuration shown below, and an object to be coated in which the coating film is formed on at least a part of the object to be coated. Ru.

Below,
(A) mixed epoxy resin (base resin) that is solid at room temperature;
(A1) Bifunctional epoxy resin with an epoxy equivalent of 1450 to 2010 g/eq,
(A2) a polyfunctional epoxy resin having three or more epoxy groups in the molecule and having an epoxy equivalent of 450 to 550;
(B) rubber-modified epoxy resin,
(C) dicyandiamide (curing agent),
(D) a compound that activates dicyandiamide (curing catalyst or curing accelerator),
(D1) imidazole compound,
(D2) amine-epoxy adduct compound,
shall be.

At this time, the thermosetting powder coating according to the present invention is
A paint for forming a cured product that coats the surface of a metal object to be painted,
It is composed of a finely ground composition,
The composition contains (A), (C), and (D) and does not contain (B),
(A) includes (A1) and (A2), and the mass ratio of (A2) to (A1):1 in all (A) is 0.5 or more and less than 1;
(D) includes (D1) and (D2),
It is characterized in that the equivalent ratio of (C) to (A) is 1.0 or more and 1.2 or less.

In the present invention, the mass ratio of (D2) to (D1):1 in all (D) is preferably 5 or more and 7 or less.
In the present invention, the content of (D) relative to 100 parts by mass of (A) is preferably 1.2 parts by mass or more and 1.6 parts by mass or less.

Since the coating film of the present invention is obtained by thermosetting the thermosetting powder coating of the present invention,
A test piece with the coating film formed on the surface with a thickness of 150 to 250 μm was prepared using a method compliant with JIS K 5600-5-1:1999 Type 1 (cylindrical mandrel method) so that the coating film was on the outside. Flexibility that does not cause cracking or peeling of the coating on the wrapped part when wrapped around a cylindrical mandrel with a diameter of 3 mm;
Adhesion of the coating film having a shear adhesive strength of 20 MPa or more in a tensile test using a test piece formed between two iron plates with a thickness of 10 to 80 μm;
It can be equipped with the following.

The object to be coated of the present invention is one in which the coating film of the present invention is formed on at least a part of the object to be coated.

The thermosetting powder coating of the present invention contains (A), (C), and (D) (but does not contain (B)), contains (A2) in (A), and (D) The blending range of (A2) in the composition constituting the finely pulverized product, which includes (D1) and (A1) and (A2), and the equivalent ratio range of (C) to (A). It has been adjusted. Therefore, while being suitable for use (painting) in high-temperature environments, it can be cured in a very short time (for example, several tens of seconds) to obtain the intended properties (sufficient flexibility and adhesion to the object to be painted). Powder coatings with attainable fast curing properties (eg gel time at 200° C. of less than 17 seconds) can be provided. Furthermore, a coating film made of the cured product of this specific coating material and having sufficient flexibility and adhesion to objects to be coated (processed steel materials, etc.) can be provided. Furthermore, it is possible to provide an object to be coated with this specific coating film on the object to be coated.

The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiments, and will be described based on the common knowledge of those skilled in the art without departing from the spirit of the present invention. However, the scope of the present invention includes modifications, improvements, etc. made to the following embodiments as appropriate.

The powder coating of the present invention is a coating for forming a cured product that coats the surface of a metal object to be coated, and is composed of a finely pulverized composition. The composition includes at least (A) a mixed epoxy resin that is solid at room temperature, (C) dicyandiamide, and (D) a compound that activates dicyandiamide. (A) contains (A1) a bifunctional epoxy resin and (A2) a polyfunctional epoxy resin. (D) contains (D1) an imidazole compound and (D2) an amine-epoxy adduct compound. Since it is "at least", it may contain components other than (A), (C) and (D), but from the viewpoint of suppressing the decrease in heat resistance after coating film formation (cured coating film), the present invention The powder coating does not contain (B) rubber-modified epoxy resin.
That is, the powder coating of the present invention is composed of a finely pulverized composition containing (A), (C), and (D) but not containing (B).

The details of the powder coating of the present invention will be explained below.

<(A)>
It is essential that (A) used in the powder coating of the present invention is formed by combining a plurality of epoxy resins that are solid at room temperature, and in particular, as (A), at least (A1) a bifunctional epoxy resin, (A2) Multifunctional epoxy resin is used in combination.

<(A1)>
(A1) used as a part of (A) is a compound that is solid at room temperature (25° C.) and contains two epoxy groups in one molecule. (A1) includes, for example, bisphenol type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin; biphenyl type epoxy resins, phenoxy type epoxy resins, and the like. (A1) may be used in combination of two or more types. Among these, it is preferable to use bisphenol-type epoxy resins from the viewpoint of good balance of properties such as resin strength, heat resistance, chemical resistance, and adhesiveness.

The epoxy equivalent (functional group concentration) of (A1) is 1450 g/eq or more and 2010 g/eq or less. This adjusts the crosslinking density and contributes to improving flexibility and adhesion. Specifically, by setting the epoxy equivalent to 1450 g/eq or more, flexibility can be increased, and by setting the epoxy equivalent to 2010 g/eq or less, heat resistance can be maintained. (A1) may be used in combination of two or more so that the epoxy equivalent is in the range of 1450 g/eq or more and 2010 g/eq or less.
The physical properties of (A1) are not particularly limited, but in consideration of paintability, it is preferable that the softening point is 118 to 130°C. When using two or more types of (A1) in combination, it is preferable to combine them so that the softening point falls within the above range. By setting the softening point of (A1) within the above range, uniformity of the coating film can be ensured, and a smooth coating film with few irregularities can be obtained.

<(A2)>
(A2), which is used as a part of (A), is solid at room temperature and has more than two epoxy groups in one molecule on average, that is, it has epoxy groups at locations other than the ends in the longitudinal direction of the molecule. It is a compound. (A2) includes a trifunctional epoxy resin with an average number of functional groups of three, a tetrafunctional epoxy resin with four functional groups, and other polyfunctional epoxy resins.

Trifunctional epoxy resins include, for example, novolak epoxy resins, 1,1,1-(triglycidyloxyphenyl)methane, and the like.

Examples of the tetrafunctional epoxy resin include N,N,N',N'-tetraglycidylaminodiphenylmethane, tetraglycidyl-4,4-(4-aminophenyl)-p-diisopylbenzene, 1,1,2 , 2-(tetraglycidyloxyphenyl)ethane, 1,3,5-tris(2,3-epoxypropyl)1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1 , 1,2,2-tetrabis(hydroxyphenyl)ethane tetraglycidyl ether, triphenylglycidyl ethermethane, tetraglycidyl metaxylene diamine, tetraglycidyl-1,3-bisaminomethylcyclohexane, and the like.

Other polyfunctional epoxy resins include, for example, glycerol polyglycidyl ether, trimethylpropanol glycidyl ether, pentaerystol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, and sorbitol polyglycidyl ether. Contains glycidyl ether.
Other polyfunctional epoxy resins include
Product names "jER-152", "jER-154", "jER-157S70", "jER-1031S", "jER-1032H60", "jER-604", "jER-630" (all products manufactured by Mitsubishi Chemical Corporation) ),
Product names "EPICLON5500", "EPICLON5800", "EPICLON5300-70", "EPICLON5500-60" (manufactured by DIC),
Product name "YH-434", "YH-434L" (manufactured by Toto Kasei Co., Ltd.),
Product name: "Denacol EX-313", "Denacol EX-314", "Denacol EX-321", "Denacol EX-411", "Denacol EX-421", "Denacol EX-512", "Denacol EX-521" , "Denacol EX-611", "Denacol EX-612", "Denacol EX-614", "Denacol EX-614B", "Denacol EX-622" (manufactured by Nagase ChemteX),
Commercially available products such as can also be used.

(A2) may be used in combination of two or more types. Among them, it is preferable to use other multifunctional epoxy resins from the viewpoint that resin strength and flexibility can be expressed even with a short curing time, and in particular, use of product names "EPICLON 5500" and "EPICLON 5800" manufactured by DIC Corporation. is more preferable.

The epoxy equivalent of (A2) is 450 g/eq or more and 550 g/eq or less. This shortens gelation time and contributes to improved flexibility and rapid curing performance. Specifically, by setting the epoxy equivalent to 450 g/eq or more, the flexibility can be increased, and by setting the epoxy equivalent to 550 g/eq or less, the crosslinking density can be increased and the reaction rate can be accelerated. (A2) may be used in combination of two or more types so that the epoxy equivalent falls within the above range.
The physical properties of (A2) are not particularly limited, but in consideration of paintability, it is preferable that the softening point is 82 to 88°C. When using two or more types of (A2) in combination, it is preferable to combine them so that the softening point falls within the above range. By setting the softening point of (A2) within the above range, uniformity of the coating film can be ensured, and a smooth coating film with few irregularities can be obtained.

For (A1) and (A2), the softening point can be measured by the ring and ball method of JIS K 7234.

In the present invention, the mass ratio of (A1) and (A2) in all (A) is (A1):1 to (A2): 0.5 or more and less than 1.0. In other words, (A1):(A2)=(66.7 or less and more than 50):(33.3 or more and less than 50). Preferably, (A1): 1 and (A2): 0.53 or more and 0.82 or less. That is, (A1):(A2)=(65 or less and 55 or more):(35 or more and 45 or less). By using (A1) and (A2) in combination within this mass ratio range, it is possible to impart flexibility (flexibility) while maintaining the strength of the cured product (coating film) of the powder coating. Be expected. If the proportion of (A1) is too high, the melting point of the coating material will become high and the appearance of the coating film will deteriorate, and the crosslinking density will increase, making it difficult to obtain the necessary resin strength and heat resistance. If the ratio of (A2) to (A1):1 is too small (that is, if the ratio of (A1) is too high), the crosslinking density of the cured product (coating film) will be too low (the mesh will be large), and as a result, The strength of the coating film tends to weaken. If the ratio of (A2) to (A1):1 is too high, the crosslinking density of the coating film will be too high (the mesh size will be small), and as a result, the coating film will lack flexibility (do not stretch), become hard, and become brittle. Cheap.

In the present invention, a cresol novolac-modified epoxy resin may be blended into (A), but in order not to reduce the flexibility and considering the complexity of blending adjustment, (A) may be blended with a cresol novolak modified epoxy resin. , it is preferable not to mix cresol novolac modified epoxy resin. Commercial products of cresol novolak modified epoxy resin include the product names "NPCN-702", "NPCN-704" (manufactured by Taiwan Nanya Plastics Co., Ltd.), the product names "EPICLON-670", "EPICLON-680", and " EPICLON-695'' (manufactured by DIC).

Furthermore, as described below, neither (A1) nor (A2) includes rubber-modified materials (things that fall into the category of (B)).

<(B)>
In the powder coating of the present invention, the rubber-modified epoxy resin (B) is not used. The rubber component (B) does not contribute to the crosslinking reaction of (A) and does not have an adhesion function. This is because the adhesive strength (adhesion) of the coating film on the surface of the object becomes weaker.
In the present invention, a rubber-modified epoxy resin refers to one obtained by reacting (modifying) an epoxy group in an epoxy resin with a rubber component.
Examples of epoxy resins include, but are not limited to, bisphenol-type epoxy resins, naphthalene-type epoxy resins, biphenyl-type epoxy resins, glycidylamine-type epoxy resins, cyclic epoxy resins, dicyclopentadiene-type epoxy resins, and phenol novolak-type epoxy resins. , all-socresol novolak type epoxy resins, and the like.

The rubber component refers to a rubber having a functional group that reacts with the epoxy group in the epoxy resin, and includes, but is not particularly limited to, butadiene rubber, acrylic rubber, silicone rubber, butyl rubber, olefin rubber, styrene rubber, NBR ( butadiene/acrylonitrile rubber), SBR, IR, EPR, etc. Examples of the functional group of the rubber component include amino-modified, hydroxy-modified, or carboxyl-modified functional groups.
A product obtained by reacting these rubber components and an epoxy resin at an appropriate blending ratio by a known polymerization method is (B), which is excluded from blending in the present invention. By excluding the blending of (B), it is possible to suppress a decrease in heat resistance after coating film formation (cured coating film), and it is possible to contribute to maintaining the required heat resistance.

<(C)>
Generally available dicyandiamide (DICY) to be blended as (C) in the powder coating of the present invention can be used. (C) acts as a curing agent for (A), and in particular improves the adhesion (adhesion) of the cured product to the surface of the object to be painted, and causes gelation even when the powder coating is stored for a long time. There are effects such as improving so-called storage stability.

For (C), it is preferable to use solid particles having an average particle size in the range of 3 to 18 μm. If the average particle size of (C) is too small, the storage stability of the powder coating tends to decrease. If the average particle size of (C) is too large, the curing speed of the powder coating tends to be slow, resulting in insufficient curing, which tends to have an adverse effect on imparting flexibility to the cured product.

The amount of (C) to be blended may be determined so that the equivalent ratio of (C) to (A) is preferably 1.0 or more and 1.2 or less (more preferably 1.05 or more and 1.15 or less). desirable. By blending in this equivalent ratio range (that is, equivalent or more of (C) to (A)), it is possible to achieve a cured state that provides the desired properties (sufficient flexibility and adhesion to the object to be painted). This gives the powder coating a fast curing property that can be achieved in a short period of time. If the equivalent ratio of (C) to (A) is too small (that is, less than the equivalent), the crosslinking density will decrease and the strength of the cured product (coating film) will likely be insufficient. On the other hand, if the equivalent ratio of (C) to (A) is too large, the coating film lacks flexibility and tends to be difficult to spread, hard, and brittle. Specifically, for example, 2.6 parts by mass or more and 3.1 parts by mass or less of (C) may be blended with 100 parts by mass of (A).

<(D)>
It is essential that (D) used in the powder coating of the present invention is formed by combining a plurality of compounds that can activate (C), and in particular, as (D), at least (D1) an imidazole compound, (D2) An amine-epoxy adduct compound is used in combination.
In the present invention, (D) acts as a curing catalyst (curing accelerator) for (A). In the present invention, the reason why (D1) is not used alone as (D) but in combination with (D2) is as follows. As a catalyst, (D1) has higher reactivity than (D2) (contributes to the reaction at a lower temperature), so when (D1) alone constitutes (D), the storage stability of the powder coating deteriorates. Furthermore, due to the rapid progress of the reaction, the coating film becomes hard and less flexible (easily becomes brittle). Therefore, compared to (D1) alone, it was decided to use (D2) in combination, which is activated at a higher temperature to contribute to the reaction and causes the reaction to proceed slowly. In addition, in the present invention, in particular, by using a combination of (D1) and (D2) at a predetermined mass ratio, sufficient flexibility is imparted to the cured product, and rapid curing properties are realized to improve efficiency. Expresses the effect of causing

<(D1)>
(D1) used as a part of (D) includes imidazole and imidazole derivatives. Imidazole derivatives are compounds in which a substituent or the like is introduced into imidazole, such as 2-methylimidazole, 2-undecylimidazole, 2-heptadecyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl Imidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-un These include decyl imidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-aminomethyl-2-methylimidazole, and the like. (D1) may be used in combination of two or more types. Among them, it is preferable to use 2-methylimidazole from the viewpoint of rapid curing.

<(D2)>
(D2) used as a part of (D) is formed by adding an epoxy compound to an amine compound. When (D2) is used alone, it becomes activated and exhibits an effect at a higher temperature (around 80°C) than (D1), so when used in combination with (D1), the effect that occurs when (D1) is used alone It contributes to rapid curing while suppressing the disadvantages (reduction in the flexibility of the coating film, mentioned above). In addition to this effect, when (D2) is used in combination with (D1), it is also expected that the storage stability of the powder coating will be improved.

Examples of epoxy compounds include polyglycidyl ethers obtained by reacting epichlorohydrin with polyhydric phenols such as bisphenol A, bisphenol F, catechol, and resorcinol, or polyhydric alcohols such as glycerin and polyethylene glycol, and p-hydroxybenzoin. glycidyl ether ester obtained by reacting a hydroxycarboxylic acid such as β-hydroxynaphthoic acid with epichlorohydrin; a polyglycidyl ester obtained by reacting a polycarboxylic acid such as phthalic acid or terephthalic acid with epichlorohydrin; Glycidylamine compounds obtained by reacting 4,4'-diaminodiphenylmethane, m-aminophenol, etc. with epichlorohydrin, epoxidized phenol novolak resins, epoxidized cresol novolac resins, polyfunctional epoxy compounds such as epoxidized polyolefins, and butyl Examples include monofunctional Epoquine compounds such as glycidyl ether, phenylglycidyl ether, and glycidyl methacrylate.

Examples of amine compounds include aliphatic amines such as diethylenetriamine, triethylenetetramine, n-propylamine, 2-hydroxyethylaminopropylamine, cyclohexylamine, 4,4-diaminodicyclohexylmethane, 4,4'-diamino Aromatic amine compounds such as diphenylmethane and 2-methylaniline, nitrogen-containing heterocyclic compounds such as 2-ethyl-4-methylimidazole, 2-ethyl-4-methylimidazoline, 2,4-dimethylimidazoline, piperidine and piperazine, dimethyl Amine compounds such as aminopropylamine, diethylaminopropylamine, di-n-propylaminopropylamine, dibutylaminopropylamine, dimethylaminoethylamine, diethylaminoethylamine, N-methylpiperazine, 2-methylimidazole, 2-ethylimidazole, - Primary or secondary amines having a tertiary amino group in the molecule, such as imidazole compounds such as ethyl-4-methylimidazole and 2-phenylimidazole, 2-dimethylaminoethanol, 1-methyl -2-dimethylaminoethanol, 1-phenoxymethyl-2-dimethylaminoethanol, 2-diethylaminoethanol, 1-butoxymethyl-2-dimethylaminoethanol, 1-(2-hydroxy-3-phenoxypropyl)-2-methyl Imidazole, 1-(2-hydroxy-3-phenoxypropyl)-2-ethyl-4-methylimidazole, 1-(2-hydroxy-3-butoxypropyl)-2-methylimidazole, 1-(2-hydroxy-3 -butoxypropyl)-2-ethyl-4-methylimidazole, 1-(2-hydroxy-3-phenoxypropyl)-2-phenylimidazoline, 1-(2-hydroxy-3-butoxypropyl)-2-methylimidazoline, 2-(dimethylaminomethyl)phenol, 2,4,6-tris(dimethylaminomethyl)phenol, N-β-hydroxyethylmorpholine, 2-dimethylaminoethanethiol, 2-mercaptopyridine, 2-benzimidazole, 2- Mercaptobenzimidazole, 2-mercaptobenzothiazole, 4-mercaptopyridine, N,N-dimethylaminobenzoic acid, N,N-dimethylglycine, nicotinic acid, isonicotinic acid, picolinic acid, N,N-dimethylglycine hydrazide, N , N-dimethylpropionic acid hydrazide, nicotinic acid hydrazide, isonicotinic acid hydrazide, etc., alcohols, phenols, thiols, carboxylic acids, and hydrazides having a tertiary amino group in the molecule.

(D2) includes, for example, an addition reaction product of 2-methylimidazole and bisphenol A type epoxy resin, and an addition reaction product of 2-ethyl-4-methylimidazole and bisphenol A type epoxy resin. Two or more amine-epoxy adduct compounds may be used in combination.

Some of (D2) are, for example, "Amicure PN-23", "Amicure MY-24", "Amicure AH-203" (manufactured by Ajinomoto Co., Ltd.), "Epicure P-101", "P- 103'', ``P-104'', ``P-108'' (all manufactured by Hexion), ``Hardner X-3361S'', ``Hardner X-3670S'' (all manufactured by Asahi Denka Kogyo), etc. has been done. Among them, an addition reaction product of 2-ethyl-4-methylimidazole and bisphenol A type epoxy resin (Amicure PN-23) is used from the viewpoint of imparting higher flexibility at low temperatures to the cured coating film (cured product). It is preferable to use

In the present invention, (D1) and (D2) have a mass ratio of (D1):1 to (D2): 5 or more and 7 or less (especially 5.5 or more and 6. 5 or less) is preferable. By using a specific combination of (D1) and (D2) within this mass ratio range, the curing speed can be adjusted, which is expected to improve flexibility. If the proportion of (D1) is too high, the curing speed becomes too fast, and when formed into a coating film, the crosslinking density becomes high and the coating film tends to become brittle. Moreover, if the ratio of (D1) is too small, the curing speed will be insufficient, resulting in insufficient curing when formed into a coating film.

In the present invention, the blending amount of (D) is, for example, 1.2 parts by mass or more and 1.6 parts by mass or less, preferably 1.3 parts by mass or more and 1.5 parts by mass, based on 100 parts by mass of (A). below. If the amount of (D) is too small, rapid curing will not be achieved, the crosslinking density will be low, and the strength of the coating will be insufficient, making the coating easy to crack. If the amount is too large, the crosslinking density will be high, the coating will be hard, and the flexibility will decrease, making the coating easy to crack.

<Auxiliary ingredients>
In the powder coating of the present invention, auxiliary components other than the above-mentioned components ((A), (C), and (D)) may be appropriately blended as necessary within a range that does not impair the effects of the invention. . Auxiliary components include epoxy resins other than (A), curing agents other than (C), curing accelerators other than (D), flame retardants, colorants, fillers, leveling agents, sagging agents, coupling agents, Examples include antifoaming agents, mold release agents, fluidity modifiers, and the like.
Examples of flame retardants include phosphorus compounds, halogen compounds, antimony compounds, and metal hydroxides.

Examples of the coloring agent include titanium oxide, carbon black, phthalocyanine blue, and copper.
As fillers, oxides such as silica, alumina, zirconia, titania, magnesia, ceria, yttria, zinc oxide, iron oxide, barium titanium oxide, alumina-silica composite oxide; silicon nitride, titanium nitride, boron nitride, Nitrides such as aluminum nitride; poorly soluble ionic crystals such as calcium fluoride, barium fluoride, barium sulfate; covalent crystals such as silicon and diamond; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate , talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, boehmite, apatite, mullite, spinel, olivine, etc. Alternatively, compounds containing these can be mentioned.

<Production method of powder coating>
Although the method for producing the powder coating of the present invention is not particularly limited, it can be produced, for example, by the following method. First, the ingredients are dry mixed using a mixer or the like, and then melt-kneaded using an extruder. The mixing temperature and mixing time are not particularly limited, and are set depending on the type of raw materials, composition ratio, etc. Usually, the mixing temperature is preferably 80 to 150°C. Thereafter, the resulting mixture is cooled and solidified, and the solidified kneaded mixture (melt kneaded product) is pulverized and classified to obtain a powder coating.

<Powder paint>
The powder coating of the present invention contains at least (A), (C), and (D). Depending on the mixing conditions, polymerization may partially proceed to contain a polymer containing structural units derived from (A).

(i) Volume average particle size The particle size of the powder coating of the present invention is not particularly limited, but it is preferable that the volume average particle size as measured by laser diffraction/scattering method (JIS Z8825) is in the range of 30 to 60 μm. The volume average particle size can be measured using a laser diffraction particle size distribution measuring device (manufactured by SYMPATEC, HELOS and PRODOS analysis software: WINDOX5). By using a powder coating material having a volume average particle diameter within the above range, better film forming properties can be obtained.

(ii) Fast curing property The powder coating of the present invention has fast curing properties such that gelation time at 200°C is less than 17 seconds according to JIS C 2104. If the gelation time is less than 17 seconds, fast curing properties are satisfied and excellent coating film properties are likely to be obtained. The gelation time of the powder coating is more preferably 10 seconds or more and 15 seconds or less. If the gelation time is too long, the fast curing property will not be satisfied and the strength of the coating will be poor. If the gelation time after the test under the above-mentioned predetermined conditions exceeds 17 seconds, the required rapid curing property will not be achieved.

<How to apply powder paint>
The coating method of the powder coating of the present invention is not particularly limited, and any known coating method can be applied. Specifically, electrostatic coating, triboelectric coating, non-charged coating, fluidized dipping, etc. may be mentioned. Among these methods, the fluidized dipping method is preferred in order to obtain a coating film of sufficient thickness. According to the method described above, a coating film can be obtained by applying a powder coating onto the surface of an object to be coated and then curing the powder coating. If necessary, the adhesion of the coating film can also be improved by subjecting the object to be coated to a surface treatment in advance.
The thickness of the coating film obtained from the powder coating of the present invention is not particularly limited, but is preferably 100 to 300 μm.

<Object to be painted>
Although the type and shape of the object to be coated (member) to which the powder coating of the present invention is applied is not particularly limited, the powder coating of the present invention can form a cured coating film by curing after being applied. After that, it is suitably used for processed steel materials that can be subjected to advanced bending (for example, hairpin bending) at any angle, and the effects of the present invention are effectively exhibited. The processed steel material to be painted is not limited to the field of metal processing such as bus bars and steel pipes, but can also be used for reinforcing bars contained in concrete and other fields of civil engineering and construction.
That is, the powder coating of the present invention has good conformability to processed steel materials that can be subjected to advanced bending after coating film formation, so it can be applied to, for example, rod-shaped objects, linear objects, cylindrical objects, and corrugated objects. It is also suitably used for plate-shaped objects.

<Cured film of powder coating (paint film)>
(i) Flexibility The coating film obtained by applying and curing the powder coating of the present invention is obtained by testing a test piece with the coating film formed on the surface with a thickness of 150 to 250 μm according to JIS K 5600-5- 1:1999 Type 1 (cylindrical mandrel method), when the coating is wound around a cylindrical mandrel with a diameter of 3 mm with the coating on the outside, cracks and peeling may not occur in the coating at the wrapped portion. Adjust to provide flexibility. If the coating film cracks or peels after the test under the above-mentioned predetermined conditions, it does not have the required flexibility.

The coating film obtained by applying and curing the powder coating of the present invention is further adjusted to have flexibility such that the elongation rate measured by a method based on JIS K 7161-2 is 5% or more. It's good to do that. If the elongation rate of the coating film after the test under the predetermined conditions is less than 5%, it may not have the required flexibility.

(ii) Adhesion The coating film obtained by applying and curing the powder coating of the present invention has an adhesion property with a tensile shear adhesive strength of 20 MPa or more in a tensile test measured in accordance with JIS K 6850. Adjust so that it is prepared. If the tensile shear adhesive strength of the coating film after the test under the predetermined conditions is less than 20 MPa, it will not have the required adhesion.

<Object to be painted>
The object to be coated of the present invention only needs to have the coating film of the present invention formed on at least a part of the object to be coated, and may be formed on the entire object.

The present invention will be specifically described below based on experimental examples (including examples and comparative examples), but the present invention is not limited to these examples. In the following description, "part" indicates "part by mass" and "%" indicates "% by mass."

[Components of powder coating]
The following was prepared as A1 (bifunctional epoxy resin).
・A12: Bisphenol A type (solid) epoxy resin with an epoxy equivalent of 780 to 810 g/eq (GESR904S, Epoxy Base Electronic Material Corporation Limited (CN))
・A13: Bisphenol A type (solid) epoxy resin with an epoxy equivalent of 1450 to 1600 g/eq (GESR907S, Epoxy Base Electronic Material Corporation Limited (CN))
・A14: Cresol novolac modified epoxy resin with epoxy equivalent of 200 to 220 g/eq (NPCN-704, Nanya Plastics Co., Ltd. (Taiwan))

The epoxy equivalent of A and B as a whole is the blending amount of each component when the total is 100 parts by mass (for example, in the case of Experimental Example 3, A13 is 60 parts by mass, A22 is 40 parts by mass, and B1 is 0 parts by mass). ) divided by the median value of the epoxy equivalent of each component (for example, the median value of A13 has a lower limit of 1450 g/eq and an upper limit of 1600 g/eq, so (1450 + 1600)/2 = 1525) (in the case of A13, 0 .03934, A22, 0.08368, B1 is 0), the denominator is the value (0.12302), and the total mass of A and B (100) is the numerator. In the case of Example 3, it is approximately 812).

The following was prepared as A2 (polyfunctional epoxy resin).
・A21: Polyfunctional component-containing (solid) epoxy resin with an epoxy equivalent of 750 to 850 g/eq (EPICLON5800, DIC)
・A22: Polyfunctional component-containing (solid) epoxy resin with an epoxy equivalent of 450 to 500 g/eq (EPICLON5500, DIC)

The following was prepared as B (rubber modified epoxy resin).
・B1: Butadiene/acrylonitrile rubber modified epoxy resin with epoxy equivalent of 950 to 1200 g/eq (EPOX-MK SR-35K, Printec, softening point 95°C)

The following was prepared as C (dicyandiamide).
・C1: jER Cure DICY20
(Solid dispersion type amine curing agent, Mitsubishi Chemical Company)

The following was prepared as D1 (imidazole compound).
・D11: 2-methylimidazole (Curezol 2MZ-H, Shikoku Kasei Co., Ltd.)

The following was prepared as D2.
・D21: Amine-epoxy adduct compound (addition reaction product of 2-ethyl-4-methylimidazole and bisphenol A type epoxy resin, Amicure PN-23, Hexion)
・D22: Urea compound (aromatic dimethylurea, U-CAT3512T, San-Apro Co., Ltd.)
・D23: Amine-urea adduct compound (Fujicure FXE-1000, T&K TOKA)

The following were prepared as E (auxiliary component).
・E1: Filler (titanium oxide)
(Tiepeke R-830, Ishihara Sangyo Co., Ltd.)
・E2: Filler (carbon black)
(Mitsubishi Carbon Black, Mitsubishi Chemical Corporation)
・E3: Leveling agent (acrylic acid ester copolymer, Nippon Carbide Co., Ltd.)

1. Preparation of powder coating [Experimental Examples 1 to 15]
After dry blending all the materials for each experimental example at the blending ratio (mass) shown in Table 1, a kneaded product was obtained by kneading with an extruder at 90° C. to 130° C. for about 30 to 100 seconds. The obtained kneaded material was cooled and solidified, and then finely pulverized to obtain a powder coating.

2. Evaluation The fast curing properties of the powder coatings obtained in each experimental example were evaluated by the method shown below. In addition, various properties (flexibility, adhesion) of the cured powder coatings (thermocured coating films) obtained in each experimental example were evaluated by the methods shown below. The results are shown in Table 1.

(2-1) Fast curing property The fast curing property of the powder coating was evaluated based on the following criteria by measuring gelation time.
Approximately 0.05 to 0.1 g of the powder coating obtained in each experimental example was placed in a circular concave part of a hot plate kept at 200°C, and stirred with a stirring rod. The time (seconds) it took to reach this point was measured. Measured according to JIS C 2104. The evaluation criteria are as follows.

◎: Gelation time is 15 seconds or less ○: Gelation time is less than 17 seconds ×: Gelation time is 17 seconds or more

(2-2) Flexibility The flexibility of the thermoset coating film was determined by evaluating and measuring the bending resistance and elongation.

(a) Flexibility A rectangular SPCC-SB plate (length 100 mm, width 50 mm, thickness 1 mm) preheated to 240°C was prepared, and one side of the plate was coated with the powder coating obtained in each experimental example. The coating was applied by a fluidized dipping method so that the thickness after curing was 150 to 250 μm. The coating time was 0.5 to 2 seconds. It was cured for 30 seconds at 240°C in a constant temperature blast furnace. Immediately after curing, the sample was immersed in water for 20 to 30 seconds to cool it, and a test piece was obtained. The obtained test piece was subjected to a bending resistance test according to JIS K 5600-5-1:1999 Type 1 using a cylindrical mandrel bending tester (manufactured by TQC). After clamping and fixing the test piece with the main body clamp in a tester equipped with a cylindrical mandrel with a diameter of 3 mm, bring the roller close to the non-coated surface of the test piece and turn the handle rapidly for 1 to 2 seconds. Instead, it was rotated 180 degrees evenly. Thereafter, cracks in the coating film and peeling of the coating film from the SPCC-SB board were visually confirmed. The evaluation criteria are as follows.

◎: No cracking or peeling of the paint film at all 〇: Some cracking or peeling of the paint film, but no problem ×: Cracking or peeling of the paint film, yes ××: Cracking or peeling of the paint film, There are many

(b) Elongation rate (%)
A type 1A test piece with a coating film having a thickness of 200 to 400 μm was prepared by a method based on JIS K 7161-2. The coating film was obtained by applying the powder coating obtained in each experimental example to a test substrate so that the thickness after curing would be 200 to 400 μm, and leaving it at 240° C. for 30 seconds. Using a universal tensile tester (manufactured by Instron Japan), the prepared test piece was pulled at a speed of 5 mm per minute along its main axis at room temperature until the test piece broke. The elongation of the test piece (and thus the coating film) was measured, and the elongation rate was calculated. The elongation rate of the test piece was calculated from the amount of displacement between the grips from the start of the test. The evaluation criteria are as follows.

〇: Calculated value of paint film elongation rate is 5% or more ×: Calculated value of paint film elongation rate is less than 5%

(2-3) Adhesion The adhesion of the thermoset coating film was evaluated based on the following criteria by measuring tensile shear adhesive strength according to a method based on JIS K 6850.
Two rectangular SPCC-SD plates (length 100 mm, width 25 mm, thickness 1.6 mm) heated to 240°C were prepared, and each was heated to a position approximately 12.5 mm from the end of one side in the longitudinal direction. The powder coatings obtained in each experimental example were applied to a thickness of 10 to 80 μm after curing. After that, stack the two boards so that the painted parts are facing each other, and rub the boards against each other to spread the molten paint to spread the paint (the size of the painted surface is 25 mm long x 12 mm wide). 5mm).
Next, the overlapping portion was held between double clips and left at 240° C. for 30 seconds, and then at room temperature. The two plates were joined together by the paint on the overlapping portion, and a test piece was obtained. Both ends of the obtained test piece were stretched at room temperature using a universal tensile tester (manufactured by Instron Japan) to measure the tensile shear adhesive strength. The evaluation criteria are as follows.

○: Shear adhesive strength is 20 MPa or more ×: Shear adhesive strength is less than 20 MPa

3. Discussion As shown in Table 1, when the types of components included in the paint are the same (Experimental Examples 1 to 7), the mass ratio of A2 component to A1 component:1 in all A components is less than 0.5 ( Experimental Example 1) and 1 or more (Experimental Example 7), it was not possible to satisfy all of the rapid curing properties of the paint and the flexibility and adhesion of the coating film. On the other hand, when the mass ratio of A2 component to A1 component:1 is 0.5 or more and less than 1 (Experimental Examples 2 to 6), it is possible to satisfy all of fast curing properties, flexibility, and adhesion. did it.

Unless the A2 component was included in the A component (Experimental Examples 8, 12 to 15), at least one of fast curing property, flexibility, and adhesion could not be satisfied. The same results were obtained when the A1 component was not included in the A component (Experimental Examples 9 to 11).

When component B was included in the paint (Experimental Examples 8 to 15), the adhesion of the paint film deteriorated. When the D2 component was not included in the D component (Experimental Examples 12 and 13), the flexibility (especially the bending resistance) of the coating film deteriorated.

In addition, when the mass ratio of D2 component to D1 component:1 in all D components is less than 5 (Experimental Example 4), exceeds 7 (Experimental Example 5), or is 5 or more and 7 or less (Experimental Example Compared to 3), the flexibility (flexibility) tended to deteriorate slightly, but there was no problem in terms of performance.

However, if component B is included in the paint and the mass ratio of component D2 to component D1 is too large (Experimental Examples 14 and 15), the flexibility ( It was also confirmed that the deterioration of bending resistance was likely to progress.

Claims (5)

A thermosetting powder coating for forming a cured product that coats the surface of a metal object to be painted,
It is composed of a finely ground composition,
The composition contains (A), (C) and (D) shown below, and does not contain (B),
(A) contains (A1) and (A2) shown below, and is contained in the total (A) at a mass ratio of (A2) to (A1):1 of 0.5 or more and less than 1. has been
(D) includes (D1) and (D2) shown below,
(C) is a powder coating that is blended with (A) in an equivalent ratio of 1.0 to 1.2.
(A) Mixed epoxy resin that is solid at room temperature (A1) Bifunctional epoxy resin with an epoxy equivalent of 1450 to 2010 (A2) Polyfunctional epoxy resin with 3 or more epoxy groups in the molecule and an epoxy equivalent of 450 to 550 Epoxy resin (B) Rubber-modified epoxy resin (C) Dicyandiamide (D) Compound that activates (C) (D1): Imidazole compound (D2): Amine-epoxy adduct compound The powder coating according to claim 1, wherein (D2) is contained in the total (D) at a mass ratio of 5 to 7 to (D1):1. The powder coating according to claim 1 or 2, wherein (D) is contained in a range of 1.2 parts by mass or more and 1.6 parts by mass or less with respect to 100 parts by mass of (A). A coating film obtained by thermosetting the thermosetting powder coating according to any one of claims 1 to 3, comprising:
A test piece with the coating film formed on the surface with a thickness of 100 to 300 μm was prepared using a method based on JIS K 5600-5-1:1999 Type 1 (cylindrical mandrel method) so that the coating film was on the outside. It has flexibility that will not cause cracking or peeling of the coating film at the wrapped portion when it is wound around a cylindrical mandrel with a diameter of 3 mm, and the coating film is placed between two iron plates with a thickness of 10 to 80 μm. A coating film with adhesiveness and a shear adhesive strength of 20 MPa or more in a tensile test using a test piece formed. An object to be painted, the coating film according to claim 4 being formed on at least a part of the object.