JPH0649845B2 - Overcoat clear coating composition for can and coating film forming method using the composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel can overcoat clear coating composition and a coating film forming method using the composition.

2. Description of the Related Art Metallic products used for cosmetic packaging cans such as chocolate, biscuits, seaweed, and petroleum cans are coated for the purpose of rust prevention and aesthetics. Usually, these coatings are performed by first applying an undercoat (white coating) or the like on a metal plate, then printing characters and patterns, and then applying a transparent overcoat clear paint. .

In the past, baking and curing were performed in each step of the above-mentioned coating, but today, to improve productivity, after printing ink is applied, the printing ink remains uncured and the overcoat clear paint in the next step is applied. The method of forming a coating film by baking after that is becoming popular. When the overcoat clear paint is applied on the uncured ink layer, the ink flows with the overcoat clear paint, especially at the edges of the printed part, the ink flows like a "whisker", the so-called "bleed phenomenon". In addition, there arises a problem of wet ink suitability called "embossing phenomenon" in which a step is formed at the edge of the printing portion.

In addition, since the metal plate used for cans is coated with ink and overcoat paint, and after being cured, it is processed into a metal processed product suitable for each application, it is also an important factor that the workability of can paints is excellent. Is one.

Generally, these overcoat clear paints were mainly composed of an acrylic or epoxy ester resin, which has relatively good suitability for wet ink, but these resins have poor processability. The film has problems such as cracks and peeling, making it difficult to use as an overcoat clear paint for cans. Therefore, in recent years, a polyester resin having excellent processability has come to be used, but suitability for wet ink is insufficient, and what is practically used as an overcoat clear paint for cans is still unknown. Absent.

Therefore, an object of the present invention is to provide an overcoat paint for a can, which uses a polyester resin having both excellent processability and wet ink suitability.

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the inventors have found that a polyester resin having a specific composition and having a specific molecular weight or more can solve the above-mentioned problems. The invention was completed.

That is, the present invention includes: (In the formula, R represents hydrogen or a methyl group) and at least one kind of an alicyclic dibasic acid and its anhydride is 0 to 8
Polybasic acid component containing 0 mol%, general formula (In the formula, R ¹ , R ² , and R ³ represent hydrogen or an alkyl group having 1 to 4 carbon atoms, and the total carbon number of R ¹ , R ² , and R ³ is 3 or more). 0 to 80 mol% of at least one of diols and cyclohexanedimethanol
The alicyclic dibasic acid of the general formula (I) and its anhydride, and the total weight of the diols of the general formula (II) and at least one of the cyclohexanedimethanol. 20 to 80% by weight based on the resin solid content of the obtained polyester resin,
An overcoat clear coating composition for a can, which comprises a polyester resin having a number average molecular weight of 3,000 to 30,000, and (b) an amino resin, and a can plate directly or on an undercoat layer. Remains uncured after applying the ink via, then applying the above coating composition,
The present invention relates to a method for forming a coating film, which is characterized by heat-curing thereafter.

In the present invention, at least one of the alicyclic dibasic acid of the general formula (I) and its anhydride is used as the polybasic acid component. Specific examples thereof include hexahydrophthalic anhydride, methylhexahydrophthalic anhydride and cyclohexane-1,4-dicarboxylic acid. The amount of the polybasic acid component used is 0 to 80 mol%, preferably 20 to 60 mol%. Further, the alicyclic dibasic acid of the general formula (I) can be used in combination with other polybasic acids, and as the other polybasic acids, adipic acid, azelaic acid, sebacic acid, fumaric acid, itacone Acids, aliphatic dibasic acids such as glutaric acid and maleic acid, terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, trimellitic acid, aromatic polybasic acids such as pyromellitic acid or these acids Various known compounds such as anhydrides or reactive derivatives such as dimethyl terephthalate can be used.

As the polyol component, at least one of cyclohexanedimethanol and diols represented by the general formula (II) is used.
Use seeds. As cyclohexanedimethanol,
1,4-cyclohexanedimethanol and the like are preferable. In the diols represented by the general formula (II), R ¹ ,
R ² and R ³ are hydrogen or an alkyl group having 1 to 4 carbon atoms, and the total carbon number of R ¹ , R ² , and R ³ is 3 or more.
That is, when the total carbon number of R ¹ , R ² and R ³ is less than 3, sufficient wet ink suitability cannot be obtained. Specific examples of the diols represented by the general formula (II) include 2,
2-diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, 2,
2,4-trimethyl-1,3-pentanediol, 2-
Examples include ethyl-1,3-hexanediol and the like. The amount used is 0 to 80 mol%, preferably 20 to 70 mol% in the polyol component. As the polyol component which can be used in combination with the diol of the general formula (II) or cyclohexanedimethanol, various known ones can be used, and specifically, ethylene glycol, neopentyl glycol, propylene glycol, 1,4- Examples include butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol and dipropylene glycol. Although it is optional to use a polyol having a valence of 3 or more, it is preferably 30 mol% or less in the polyol component. If it is used in excess of 30 mol%, the workability tends to be lowered. Examples of trihydric or higher polyols include trimethylolpropane, trimethylolethane, glycerin, and pentaerythritol.

As described above, in the present invention, the object of the present invention can be achieved by using only one of the specific dibasic acid component or the specific polyol component, or by using both in combination,
The total weight of both is 20 to 80% by weight, preferably 30 to 70% by weight, based on the resin solid content of the obtained polyester resin. If the total weight is less than 20% by weight of the resin weight, the effect of improving wet ink suitability is small, and 80% by weight
If it exceeds the above range, it is economically disadvantageous and the hardness of the coating film tends to decrease.

A polyester resin having such a composition having a number average molecular weight in a wide range of 3,000 to 30,000, that is, an oil-free polyester resin having a relatively low molecular weight to a high molecular weight polyester resin can be used, but further considering processability and the like. For example, it is preferable to use a high molecular polyester resin of 5000 to 30000. If it is less than 3,000, it is difficult to use as an overcoat clear paint for cans because the workability is poor. On the other hand, if it exceeds 30,000, the coating material has a high viscosity and the coating workability is deteriorated.

The hydroxyl value is 2 to 200 KOHmg / g, preferably 2
It is good to be ~ 100 KOHmg / g. Hydroxyl value is 200K
If it is higher than OHmg / g, the processability tends to be poor because crosslinking with the amino resin proceeds too much. The acid value is 0.
1 to 50 KOHmg / g, preferably 0.1 to 30 KOHmg / g
Is. When the number value is higher than 30 KOHmg / g, the water resistance decreases.

The polyester resin of the present invention may be produced by a usual esterification reaction, that is, a polycondensation reaction, and the reaction may be carried out under normal pressure or reduced pressure. The molecular weight may be adjusted by appropriately adjusting the reduced pressure state, and further, after the polycondensation reaction, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, maleic anhydride, succinic anhydride. A step such as an addition reaction of an acid with an acid anhydride may be performed.

After completion of the reaction, the obtained polyester resin is dissolved in a solvent to prepare a resin solution. As the solution, any solvent that can dilute the polyester resin can be used without any limitation. For example, aromatic hydrocarbons such as toluene, xylene, Solvesso # 100, Solvesso # 150; aliphatic hydrocarbons such as hexane, heptane, octane, decane; methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate , Ester formates such as ethyl formate and butyl propionate; alcohol series such as methanol, ethanol, propanol, butanol, 2-ethylhexanol, ethylene glycol; ketone series such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone;
Examples include ether solvents such as dioxane, diethyl ether, and tetrahydrofuran; and various cellosolve solvents such as cellosolve acetate, ethyl cellosolve, and butyl cellosolve. The resin solid content concentration of the resin solution is usually 20 to 70.
%, Preferably 30 to 60% by weight. If it exceeds 70% by weight, the viscosity is high and handling becomes difficult.
If it is less than 0% by weight, the viscosity becomes too low when blended with an amino resin.

The overcoat clear coating composition of the present invention comprises the above polyester resin solution and an amino resin. Examples of the amino resin include condensation products of urea, melamine, benzoguanamine and the like with aldehydes, and resins partially or wholly alkoxylated. Commercially available products are Cymel 303 and Cymel 350.
(Mitsui Cyanamide Co., Ltd.), Delamin T-100S
(Fuji Kasei Co., Ltd.), U-VAN 120 (manufactured by Santo Toatsu Chemical Co., Ltd.) and the like.

The blending ratio of the polyester resin and the amino resin is 95/5 to 50/50, preferably 90/10 to 60 in terms of solid content weight ratio.
/ 40. When the compounding ratio of the polyester resin and the amino resin is out of the above range, the workability and the hardness tend to decrease, which is not preferable.

Further, the coating composition may contain various additives, and examples thereof include a curing catalyst, a leveling agent, an ultraviolet absorber and a viscosity modifier. The coating composition may be diluted with the same solvent as described above, and the concentration is usually 20 to 70% by weight, preferably 30 to 60% by weight. If it exceeds 70% by weight, the viscosity is high and coating becomes difficult.
If the amount is less than wt%, the film thickness when applied tends to be too thin.

Thus obtained, the overcoat clear coating composition of the present invention is obtained by applying an ink to a metal plate for a can and then uncuring it without heat treatment, further applying it, and then heat-curing it. It is possible to form a coating film having both excellent processability and wet ink suitability.
At this time, the coating method may be a usual method such as a roll coater, and it is preferable to use an oil-modified alkyd resin as the resin used in the ink, a dry oil-modified alkyd resin, a semi-dry oil-modified alkyd resin, Any non-drying oil-modified alkyd resin or the like may be used. The conditions for heat curing are not particularly limited, but usually about 120 to 200 ° C. and about 1 to 30 minutes are preferable.

Further, the metal plate for a can is preferably coated with the ink through an undercoat layer in order to improve the adhesion of the ink.
It is preferable to use an undercoat (white coating) or size-coated material by a known method.

EFFECT OF THE INVENTION The overcoat clear coating composition of the present invention is excellent in wet ink suitability as well as processability which is a characteristic of the polyester resin, and can be suitably used for coating a beautiful can, and further The curing time can be omitted, and the productivity can be greatly improved.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Production Examples, Comparative Production Examples, Examples, and Comparative Examples. In each example, part and%
Indicates a weight basis in principle.

Production Example 1 123.6 parts of dimethyl terephthalic acid, 77.0 parts of ethylene glycol, 12.3 parts of trimethylol propane, diethyl propane diol 182.4 were placed in a flask equipped with a thermometer, a nitrogen introducing tube, a reflux dehydrator and a stirrer. Department,
0.2 part of zinc acetate was added. When the raw materials are melted and can be agitated, agitation is started and the temperature is changed from 170 ° C to 220
The temperature was gradually raised to 3 ° C over 3 hours, and the temperature was kept at 220 ° C for 2 hours. At this time, the produced methanol was distilled out of the system. Cooled to 170 ° C, isophthalic acid 70.5
Parts, 77.5 parts of adipic acid, and 81.7 parts of hexahydrophthalic anhydride, and heated to 230 ° C. over 3 hours,
Hold for another 3 hours. At this time, the produced water was distilled out of the system. Next, the reflux dehydrator was replaced with a vacuum depressurizer, 0.1 part of antimony trioxide was further added, the temperature was raised to 260 ° C., and a vacuum condensation reaction was carried out at 5 mmHg for 4 hours. 150 ° C
Then, 250 parts of Solvesso # 100 and 250 parts of butyl cellosolve are added and uniformly dissolved to obtain a nonvolatile content of 50.0.
%, Resin acid value 1.1 KOHmg / g, resin hydroxyl value 19.
1 KOHmg / g, viscosity (Gardner) YZ, number average molecular weight 15,000, total weight of dibasic acid component specific to the present invention and polyol component specific to the present invention in polyester resin solids (hereinafter, simply "specific dibasic A polyester resin solution a of 52.8% (referred to as "total weight of acid component and polyol component") was obtained. The total amount of reaction by-products distilled out of the system was 125.0 parts.

Production Examples 2 to 6 and Comparative Production Examples 1 and 2 Resin solutions b to h were obtained in the same manner as in Production Example 1 based on the prepared compositions shown in Table 1. These resin characteristic values are
Shown in the table.

Production Example 7 185.0 parts of isophthalic acid, 65.1 parts of adipic acid, and 102.
8 parts, neopentyl glycol 67.3 parts, trimethylol propane 58.1 parts, diethyl propane diol 1
When 70.4 parts were charged and the raw material was melted and could be stirred, the stirring was started and the temperature was increased from 170 ° C to 220 ° C.
The temperature was gradually raised over a period of time and kept at 220 ° C. for 3 hours. The water generated at this time was distilled out of the system. Next, 30 parts of xylene was added dropwise and the reaction was continued by an xylene reflux method until the acid value became 6. Cool to 150 ° C and Solvesso # 10
185 parts of butyl cellosolve and 185 parts of butyl cellosolve were added and dissolved uniformly.
g, a hydroxyl value of the resin of 75 KOHmg / g, a viscosity (Gardner) Z, a number average molecular weight of 3800, and a total weight of the specific dibasic acid component and the oriol component of 47.1% were obtained as a resin solution i.

The total amount of reaction by-products distilled out of the system was 48.7 parts.

Production Examples 8 and 9 and Comparative Production Examples 3 and 4 Resin solutions j to m were obtained in the same manner as in Production Example 7 based on the prepared compositions shown in Table 2.

Examples 1 to 9 and Comparative Examples 1 to 4 The polyester resin solutions obtained in Production Examples 1 to 9 and Comparative Production Examples 1 to 4 were mixed with an amino resin at a ratio of 70/30 (solid content ratio), and butyrocellosolve was added. And a Solvesso # 100 mixed solvent were diluted, and the curing catalyst was uniformly mixed to prepare a clear paint. Examples of these formulations are shown in Table 3.

The following tests were performed on the obtained clear paint.

Apply a polyester-based white coating agent to a tin plate with a thickness of 0.5 mm (dry film thickness 10 μm), and apply 170
After drying at 10 ° C for 10 minutes, an ink containing a drying oil alkyd resin as a main component of the vehicle was printed (2 µm), and the above clear paint was applied in an uncured state (not baked) (8 µm). ). After that, baking was performed at 160 ° C. for 10 minutes. With respect to the obtained test piece, the wet ink suitability test, the workability and the hardness were examined, and the results are shown in Table 3.

The various test methods are as follows.

Wet ink suitability test The degree of bleeding phenomenon and embossing phenomenon of the ink was visually judged according to the following criteria.

∘: Excellent ○: Good ×: Poor Workability A four-sided can punched product was boiled, and the degree of peeling of the coating film was visually determined according to the following criteria.

◎ ... Excellent ○ ... Good × ... Poor Hardness According to JIS K 5400, the hardness without scratches was examined using a Mitsubishi pencil “Uni”.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C09D 161/28 PHH 8215-4J // C08G 63/199 NNA 7107-4J NNE 7107-4J

Claims (4)

[Claims] 1. A general formula (In the formula, R represents hydrogen or a methyl group) and at least one kind of an alicyclic dibasic acid and its anhydride is 0 to 8
Polybasic acid component containing 0 mol%, general formula (In the formula, R ¹ , R ² , and R ³ represent hydrogen or an alkyl group having 1 to 4 carbon atoms, and the total carbon number of R ¹ , R ² , and R ³ is 3 or more). 0 to 80 mol% of at least one of diols and cyclohexanedimethanol
The alicyclic dibasic acid of the general formula (I) and its anhydride, and the total weight of the diols of the general formula (II) and at least one of the cyclohexanedimethanol. 20 to 80% by weight based on the resin solid content of the obtained polyester resin,
An overcoat clear coating composition for a can, comprising a polyester resin having a number average molecular weight of 3,000 to 30,000, and (b) an amino resin. 2. The can overcoat clear coating composition according to claim 5, wherein the solid content weight ratio of component (a) / component (b) is 95/5 to 50/50. 3. The coating composition according to claim 1 is applied uncured directly after applying the ink to the metal plate for a can or through the undercoat layer, and then the composition is heat-cured. And a method for forming a coating film. 4. The coating film forming method according to claim 1, wherein the ink is at least one selected from oil-modified alkyd resins.