JP3051816B2 - Powder coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating composition containing a small amount of a b-isocyanate-based curing agent and having excellent curability and coating film smoothness.

[0002]

2. Description of the Related Art In household appliances such as electric refrigerators and office machines such as steel desks, the use of solvent-based paints tends to be restricted from environmental and sanitary viewpoints. However, the water-based paint has drawbacks such as long drying time and poor coating workability.

On the other hand, powder coatings do not contain organic solvents which are harmful to the environment, and since they form a coating film by heat curing, they do not take much time to dry. Its use is thriving as an alternative. Among them, powder coatings using a polyester resin as a main resin and using an isocyanate-based curing agent are widely used because they can form a coating film having an excellent appearance.

[0004] Such a powder coating is usually of a two-component type in which a resin component and a curing agent component are separated because of the high reactivity of the isocyanate-based curing agent contained therein. In this case, it is necessary to mix the two components, which causes inconvenience in use. Preliminary mixing of the resin component and the curing agent component into a powder coating to eliminate the above-mentioned inconvenience is to use a isocyanate-based curing agent with blocked isocyanate groups for the first time when the curing agent exhibits reactivity when heated. It was made possible by doing so.

[0005] Japanese Patent Publication No. 49-2179 discloses such a technique, in which a polyisocyanate blocked with ε-caprolactam is converted to a hydroxyl group-containing softening point of 40-9.
About 10 to 50% by weight based on the polyester resin at 0 ° C.
A powdery coating composition preferably containing 15 to 30% by weight is disclosed. However, when a cured coating film is formed using this technique, the curability of the polyester resin is not always satisfactory, and since the content of polyisocyanate is large, the volatilization amount during heat curing is large. there were. Such volatile substances of polyisocyanate cause an unpleasant irritating odor to humans and have tearing properties, which may cause adverse effects such as deterioration of work environment such as harm to human health and decrease in work efficiency. There was a strong demand for reducing the amount of volatilization as much as possible.

[0006]

In the above-mentioned powder coating composition using a polyisocyanate in which isocyanate groups are blocked, the amount of isocyanate volatilized during heat curing is reduced to avoid the above-mentioned adverse effects. It is essential to reduce the amount of volatile isocyanate added. However, in the powder coatings described above, if the amount of isocyanate added is reduced, the amount of volatile matter during heating and curing is reduced, but the number of crosslinking reaction points is reduced and curability is deteriorated. Further, when a high molecular weight resin is used as the resin component in order to eliminate the above-mentioned drawbacks, the smoothness of the coating film is deteriorated even though the curability is secured. For this reason, the use of various surface conditioners including silicones has been attempted, but the contamination resistance is not sufficient, and there are practical problems such as deterioration of the smoothness of the coating film due to replacement of the coating material in a coating line or the like. Still existed.

[0007] The development of a technique for obtaining a powder coating excellent in practicability by reducing the amount of isocyanate added to reduce volatile substances during heat curing causes the above-mentioned undesired effects to coexist and is still effective. Appropriate measures had not been established.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a powder coating composition which has a small amount of volatile matter during heat curing and is excellent in curability and coating film smoothness. It is assumed that.

[0009]

The gist of the present invention is to provide a powder coating composition containing a polyester resin, a b-isocyanate-based curing agent and a silicone-based surface conditioner, wherein the polyester resin has a number average molecular weight of 5,000 to 5,000. 7000, a hydroxyl value of 18 to 24, a ratio of the hydroxyl value to the total of the hydroxyl value and the acid value of 85% or more, and the b-isocyanate-based curing agent in an amount of 8 to 13% by weight based on the polyester resin. %. Hereinafter, the present invention will be described in detail.

[0010] The first component of the present invention is a polyester resin. The polyester resin is produced by a condensation reaction between an acid or an acid anhydride and a polyol. The acid or acid anhydride is not particularly limited and includes, for example, phthalic acid, terephthalic acid, isophthalic acid, maleic acid, trimellitic acid, tetrahydrophthalic acid, benzol-1,2,4-
Carboxylic acids such as tricarboxylic acid, 3,6-dichlorophthalic acid, and tetrachlorophthalic acid; and acid anhydrides thereof.

The above-mentioned polyol is not particularly limited.
For example, diols such as neopentyl glycol, ethylene glycol, 1,2-propanediol, 1,3-butanediol, and 1,2-butanediol; polyols such as glycerin, hexanetriol, and trimethylolpropane; Can be. The polyester resin is prepared by a usual polyester synthesis method using the acid or acid anhydride and the polyol component as a resin having a desired molecular weight, a desired hydroxyl value and a ratio of a desired hydroxyl value to an acid value. can do.

The number average molecular weight of the polyester resin used in the present invention is from 5,000 to 7000. When the number average molecular weight of the polyester resin is less than 5,000, the crosslinked segments are small, so that the curability is poor, and when the number average molecular weight exceeds 7000, the fluidity of the resin at the time of melting is low and the smoothness is poor. Limited within the range. Preferably it is 5000-6000.

The polyester resin has a hydroxyl value of 18
２４24 mgKOH / g. When the hydroxyl value of the polyester resin is less than 18 mgKOH / g, the content of the hydroxyl group which is a reaction point with the isocyanate group is small, so that the curability is deteriorated. When the hydroxyl value exceeds 24 mgKOH / g, the content of the hydroxyl group becomes excessive and the smoothness is increased. Is deteriorated, so that it is limited within the above range. Preferably 20 to 24 mg KOH / g
It is.

The above polyester resin may contain an acid group. The content of the acid group is an index of the number of the acid group, and can be represented by an acid value indicating the number of mg of potassium hydroxide required to neutralize the free fatty acid contained in 1 g of the polyester resin. . In the polyester resin, the content of these groups is such that the ratio of the hydroxyl value to the total of the hydroxyl value and the acid value is 85% or more. When the ratio of the hydroxyl value to the total of the hydroxyl value and the acid value of the polyester resin is less than 85%, the content ratio of the hydroxyl group in the polyester resin is low, and the reaction between the isocyanate group and the hydroxyl group does not proceed promptly and the curability is poor. Since it becomes worse, it is limited within the above range. Preferably it is 87% or more.

The second component of the present invention is a b-isocyanate curing agent. In addition, in this specification, a b-isocyanate-based curing agent means an isocyanate-based curing agent in which an isocyanate group is blocked. The above b-
The isocyanate-based curing agent is not particularly restricted but includes, for example, polyisocyanates in which isocyanate groups are blocked by phenol, and polyisocyanates in which isocyanate groups are blocked by ε-caprolactam. Preferred is a polyisocyanate in which isocyanate groups are blocked with ε-caprolactam.
The polyisocyanate in which the isocyanate group is blocked with ε-caprolactam is not particularly limited, and examples thereof include tolylene diisocyanate blocked with bis-ε-caprolactam, hexamethylene diisocyanate blocked with bis-ε-caprolactam, and bis- diphenylmethyl-4,4'-diisocyanate blocked with ε-caprolactam, triphenylmethyl-4,4 blocked with tris-ε-caprolactam
Although 4 ', 4 "-triisocyanate and the like can be mentioned, commercially available ones such as BF-1530 manufactured by Hurz can be suitably used.

The content of the b-isocyanate-based curing agent is 8 to 13% by weight based on the polyester resin. When the content of the b-isocyanate-based curing agent is less than 8% by weight, the curability is poor because the content of the b-isocyanate-based curing agent is small, and when it exceeds 13% by weight, the content of the b-isocyanate-based curing agent is increased. And the amount of volatilization at the time of heating and curing increases, so that it is limited to the above range.

The third component of the present invention is a silicone-based surface conditioner. The silicone-based surface conditioner is usually
Those made of polysiloxane having a modifying group are used.

The polysiloxane having a modifying group is not particularly restricted but includes, for example, a polysiloxane having a chain structure and substituted by a modifying group. Among them, those having the same or different alkyl modifying groups as modifying groups, or those having an alkyl modifying group and a phenyl modifying group are excellent in the smoothness improving effect. Therefore, it can be suitably used in the present invention. Such products are commercially available, for example, TSF-4300 manufactured by Toshiba Silicone having a methyl-modified group and a phenyl-modified group, and YF-300 manufactured by Toshiba Silicone having a methyl-modified and a phenyl-modified group.
3919; CF-1056 manufactured by Toray Silicone Co., Ltd. having a methyl-modified group and a phenyl-modified group; KF-412 manufactured by Shin-Etsu Silicone Co., Ltd. having a methyl-modified group.

The molecular weight of the silicone-based surface conditioner is as follows:
It is preferably 1,000 or more. When the molecular weight of the silicone-based surface conditioner is less than 1,000, different kinds of powder coatings are mixed in the coating process in the case of changing the coatings, so that the coatings are liable to cause dents, cissing, etc., and are poor in contamination resistance, so they are smooth. Worse. The content of the silicone-based surface conditioner is usually 0.1 to 2%.

The powder coating composition of the present invention may further contain additives, if necessary. The additives are not particularly limited, and include, for example, other surface modifiers other than silicone-based, rheology control agents, pigments, anti-penetration agents, ultraviolet absorbers, antioxidants, and the like.

The surface conditioner is not particularly limited.
For example, an acrylic material can be used. The rheology control agent is not particularly limited,
For example, an epoxy-based material can be used. The pigment is not particularly limited and includes, for example, inorganic pigments such as carbon black, titanium dioxide, red iron oxide, and yellow iron oxide; phthalocyanine blue, phthalocyanine green,
Organic pigments such as quinacridone red pigments and the like can be mentioned. The anti-bake agent is not particularly limited, and examples thereof include benzoin.

The ultraviolet absorber is not particularly restricted but includes, for example, benzotriazoles, benzophenones and oxalic anilides. Tinuvin 900 (benzotriazole) manufactured by Ciba-Geigy. A commercially available product such as Sand Bar VSU (anilide oxalate) manufactured by Sando Co., Ltd. can be suitably used. The antioxidant is not particularly limited, and includes, for example, hindered amine-based and hindered phenol-based antioxidants. LS-770 manufactured by Sankyo Co., Ltd.
Commercially available products such as (hindered amine type) and Irganox 1010 (hindered phenol type) manufactured by Ciba-Geigy can be suitably used.

The powder coating composition of the present invention can be produced by a conventional method. For example, after preliminarily mixing raw materials such as a polyester resin, a curing agent, and a surface conditioner, the mixture is melt-kneaded, and further pulverized and classified. Alternatively, a method of mixing the raw materials in a solution state and then pulverizing the mixture by a spray drying method, or the like can be used. The average particle size of the powder coating composition of the present invention is usually preferably 50 μm or less. When the average particle size exceeds 50 μm, the smoothness of the coating film deteriorates.

The powder coating composition of the present invention can be applied by a coating method usually used for coating powder coatings such as an electrostatic spraying method and a fluid immersion method. After the above-mentioned coating, it is cured by heating to form a coating film. The heat curing is preferably performed at 120 to 230 ° C. for 10 to 30 minutes.

The powder coating composition of the present invention can be used on essentially any substrate, but in particular, a surface-treated iron plate, such as a zinc phosphate-treated iron plate, and an untreated surface iron plate And the like, and if desired, a surface coated with an undercoating material such as a rust preventive can be applied. The thickness of the coating varies depending on the application, but is usually 2
0 to 100 μm.

The powder coating composition of the present invention can be used for coating various products.
It can be suitably used for office supplies such as steel cabinets and steel shelves and various office machines; and household electric appliances such as electric refrigerators and electric washing machines.

[0027]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Preparation Example 1 Preparation of Polyester Resins A, B and C Terephthalic acid and isophthalic acid are used as acid components, and neopentyl glycol, ethylene glycol and trimethylolpropane are used as polyol components, which are usually used in polyester synthesis. By the method, polyester resins A, B and C having a predetermined molecular weight, a predetermined hydroxyl value, and a ratio of the hydroxyl value to the total of the predetermined hydroxyl value and the acid value were obtained. Polyester resin A (hereinafter referred to as “resin A”) has a molecular weight of 5,500 and a hydroxyl value of 17.0.
mgKOH / g, the ratio of the hydroxyl value to the total of the hydroxyl value and the acid value was 90%. Polyester resin B (hereinafter referred to as “resin B”) has a molecular weight of 5,400 and a hydroxyl value of 2
2.0 mgKOH / g, the ratio of the hydroxyl value to the total of the hydroxyl value and the acid value was 89%. Polyester resin C
(Hereinafter referred to as “resin C”) had a molecular weight of 5,400, a hydroxyl value of 22.3 mgKOH / g, and a ratio of the hydroxyl value to the total of the hydroxyl value and the acid value of 91%.

Example 1 90 parts by weight of resin B as a polyester resin, 10 parts by weight of BF-1530 (manufactured by Hurz) as a b-isocyanate-based curing agent, and TSF as a silicone-based surface conditioner
-4300 (manufactured by Toshiba Silicone Co., Ltd.) 0.4 parts by weight, dibutyltin dilaurate 0.4 parts by weight as a catalyst, titanium oxide CR-50 (manufactured by Ishihara Sangyo) 57 parts by weight as a pigment, epoxy resin NT-114 as an additive 4.3 parts by weight (manufactured by Toto Kasei) and acrylic resin PD-6600
After mixing 0.7 parts by weight (manufactured by Mitsui Toatsu Chemicals) and 0.7 parts by weight of benzoin as an anti-spitting agent, the mixture is melt-kneaded with a buscon kneader (manufactured by Buss Corporation), pulverized, and classified with a 150 mesh. Thus, a powder coating composition was obtained. The obtained powder coating composition is electrostatically coated on a 0.8 mm-thick zinc-iron phosphate plate using an electrostatic gun (manufactured by SAMES CORPORATION) to a thickness of 40 to 50 μm and then cured by heating to form a coating film. did. Heat curing is 180
C. for 15 minutes.

Evaluation method The smoothness of the obtained coating film was evaluated by visually observing the smoothness appearance. The evaluation criteria were as follows. The results are shown in Table 1. Good appearance: 良好 Bad appearance: × 2. The curable obtained coating film rubbed 10 times with a gauze impregnated with xylol was evaluated curable by the presence or absence of reduction in the gloss of the coating film. The evaluation criteria were as follows. The results are shown in Table 1. There is almost no gloss closing: ○ There is gloss closing: × 3. After electrostatic coating of the obtained powder coating composition, and before heat-curing, sprinkle with an acrylic powder coating P-100 (manufactured by Nippon Paint Co., Ltd.), and then heat-cur to coat. Was formed. At this time, the appearance of the coating film was visually observed and evaluated. The evaluation criteria were as follows. The results are shown in Table 1. There is no dent: ○ There is a dent: ×

Examples 2 to 4 and Comparative Examples 1 to 6 A powder coating composition was obtained in the same manner as in Example 1 except that the polyester resin and the silicone-based surface conditioner shown in Table 1 were used. After that, a coating film was formed and evaluated. The results are shown in Table 1.

Of the polyester resins used in the above Examples and Comparative Examples, those other than the resins A, B and C had a molecular weight, a hydroxyl value and a ratio of the hydroxyl value to the total of the hydroxyl value and the acid value of GV150 (Nippon Yupica). (Manufactured by K.K.), molecular weight 4600, hydroxyl value 34 mgK
OH / g, the ratio of the hydroxyl value to the total of the hydroxyl value and the acid value was 85%. For M8010 (manufactured by Dainippon Ink and Chemicals), the molecular weight was 6300 and the hydroxyl value was 24.5 m.
gKOH / g, the ratio of the hydroxyl value to the total of the hydroxyl value and the acid value was 89%, and GV130 (manufactured by Nippon Yupika Co., Ltd.)
About 5700 molecular weight, hydroxyl value 23.2 mgK
The ratio of the hydroxyl value to the total of OH / g, hydroxyl value and acid value was 84%.

The molecular weight and the type of the modifying group of the silicone-based surface conditioner used in the above Examples and Comparative Examples were TSF-484 (manufactured by Toshiba Silicone Co., Ltd.), the molecular weight was 810, and the modifying group was a methyl group and hydrogen. Yes,
About TSF-4300 (manufactured by Toshiba Silicone Co., Ltd.)
The molecular weight is 1600, the modifying group is a methyl group and a phenyl group. For CF-1056 (manufactured by Toray Silicone), the molecular weight is 2,000, the modifying group is a methyl group and a phenyl group, and the KF-412 (manufactured by Shin-Etsu Silicone) is used. Has a molecular weight of 5800, the modifying group is a methyl group, and KF-
6004 (Shin-Etsu Silicone Co., Ltd.) has a molecular weight of 4
400, the modifying groups were a methyl group and a polyether group.

[0034]

[Table 1]

[0035]

According to the present invention, a powder coating composition having a small amount of a b-isocyanate-based curing agent, a small amount of volatile matter during heat curing, and excellent curability and smoothness of a coating film. Can be provided. Further, since the powder coating composition of the present invention is excellent in contamination resistance, a high-quality coating film can be easily obtained even in a coating line or the like that requires replacement of the coating.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-45333 (JP, A) JP-A-51-24630 (JP, A) JP-A-2-218766 (JP, A) JP-A-2- 24365 (JP, A) JP-A-53-132034 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 5/03 C09D 175/06

Claims (3)

(57) [Claims] 1. A powder coating composition containing a polyester resin, a b-isocyanate-based curing agent and a silicone-based surface conditioner, wherein the polyester resin has a number average molecular weight of 5,000 to 7000 and a hydroxyl value of 18 to 24.
mgKOH / g, the ratio of the hydroxyl value to the total of the hydroxyl value and the acid value is 85% or more, and the b-isocyanate-based curing agent is used in an amount of 8 to
A powder coating composition comprising 13% by weight. 2. The silicone-based surface conditioner has the same or different alkyl-modified group, or has an alkyl-modified group and a phenyl-modified group, and has a molecular weight of 100.
The powder coating composition according to claim 1, which is 0 or more. 3. The powder coating composition according to claim 1, wherein the b-isocyanate-based curing agent is a polyisocyanate in which isocyanate groups are blocked with ε-caprolactam.