JP2007297520A - Polyester resin for overcoat clear coating, and overcoat clear coating resin composition using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester resin for an overcoat clear coating and an overcoat clear coating resin composition excellent in processability and wet-ink properties and having sufficient coating film strength and blocking resistance. <P>SOLUTION: The polyester resin for an overcoat clear coating comprises an alicyclic dicarboxylic acid and isophthalic acid as polybasic components and a glycol and ethylene glycol having a specific side chain alkyl group and other at-least-bivalent alcohols as polyol components. The overcoat clear coating resin composition comprises the polyester resin for an overcoat clear coating and a curing agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a polyester resin for overcoat clear paint used for painting various metal objects such as cans, home appliances, and metal appliances, and an overcoat clear paint resin composition using the same.

Metal processed products used in art cans for packaging such as chocolate, biscuits and seaweed, and oil cans are painted for the purpose of preventing rust and aesthetics. Usually, these coatings are performed by first applying an undercoat (white coating) or the like to a metal plate, then printing characters / designs, and then applying a transparent overcoat clear paint. . In the past, baking and curing were performed for each of the coating processes, but today, to improve productivity, the overcoat clear paint of the next process is applied with the printing ink uncured after application of the printing ink. Then, many film forming methods for subsequent baking are performed.

However, when an overcoat clear paint is applied on an uncured ink layer, the ink flows together with the overcoat clear paint, and in particular, at the edges of the printed part, the ink flows like a “whisker”. 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, the metal plate used in the can is processed into a metal workpiece suitable for each application after ink and overcoat clear paint are applied and cured, so that it is excellent in workability and the painted plate is stacked before processing One of the important factors is the anti-blocking property that does not leave any impression on the coated plate.

In general, these overcoat clear paints are mainly composed of acrylic or epoxy ester resins having relatively good wet ink suitability. The film has problems such as cracks and peels, making it difficult to use as an overcoat clear paint for cans.

Therefore, in recent years, polyester resins having excellent processability have been used. However, polyester resins generally have insufficient wet ink suitability. Moreover, aromatic carboxylic acid and hydrogenated dimer acid as carboxylic acid components, and 2,2-diethyl-1,3-propanediol and 2-n-butyl-2-ethyl-1,3-diol as diol components of polyester resins Polyester resins having improved wet ink suitability by using propanediol have been developed (see Patent Document 1), but further improvement in properties is desired.

JP-A-10-265558

An object of the present invention is to provide an overcoat clear paint resin composition having sufficient coating strength and blocking resistance while being excellent in processability and wet ink suitability.

一般式（２）

As a result of intensive studies to solve the above problems, the present inventor used alicyclic dicarboxylic acid and isophthalic acid as the polybasic component, and a glycol containing a specific side chain alkyl group as the polyol component. And an ethylene glycol, and more preferably, an overcoat clear paint resin composition obtained by using an ester-based resin in which other divalent or higher alcohols are used in combination and having these in a predetermined ratio As a result, the present invention has been completed.
That is, the present invention provides a polybasic acid component of 5 to 30 mol% of an alicyclic dicarboxylic acid represented by the general formula (1), 10 to 20 mol% of isophthalic acid, and 50 to 85 mol% of another dicarboxylic acid component. And a general formula (2) as a polyol component (wherein R1, R2, and R3 represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and at least the total number of carbon atoms of R1, R2, and R3 is 3 or more. 1) One or more side chain alkyl group-containing glycols represented by the formula: 30 to 70 mol%, ethylene glycol of 10 to 40 mol%, and other dihydric or higher alcohols of 0 to 60 mol% Polyester resin for coat clear paint. The present invention relates to an overcoat clear paint resin composition comprising the polyester resin for overcoat clear paint and a curing agent.
General formula (1)

General formula (2)

The coating resin composition of the present invention is excellent in wet ink suitability as well as processability which is a characteristic of polyester. Furthermore, the ink curing time can be omitted, and the productivity can be greatly improved.

In the present invention, as the polybasic acid component of the polyester resin, at least one alicyclic dicarboxylic acid (including anhydride) represented by the general formula (1) is contained in an amount of about 5 to 30 mol% and isophthalic acid 10 to 20 About mol% is used. The alicyclic dicarboxylic acid is not particularly limited, and specific examples include hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, cyclohexane-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid and the like. .
When the amount of the alicyclic dicarboxylic acid represented by the general formula (1) and its anhydride is less than 5 mol%, it becomes difficult to obtain good wet ink suitability, and when it exceeds 30 mol%, the hardness of the coating film is poor. Tend to be.

The other polybasic acid component is used in an amount of about 60 to 85 mol%, preferably about 30 to 60 mol%. Specific examples of other polybasic acid components include terephthalic acid, orthophthalic acid, 2,6-naltalenedicarboxylic acid, trimellitic acid, pyromellitic acid and the like, or their reactive derivatives such as acid anhydrides or dimethyl terephthalate. Aromatic polybasic acid components such as Moreover, you may use together 30 mol% of aliphatic dibasic acid components, such as adipic acid, azelaic acid, sebacic acid, fumaric acid, itaconic acid, glutaric acid, and maleic acid, to the following limits.

As the polyol component of the polyester resin of the present invention, at least one glycol represented by the general formula (2) is about 30 to 70 mol%, ethylene glycol is about 10 to 40 mol%, and other divalent or higher alcohols. From 0 to 60 mol%. When the content of the glycol represented by the general formula (2) is less than 30 mol%, wet ink suitability is deteriorated, and when it exceeds 70 mol%, the coating film hardness tends to be deteriorated. Further, when the ethylene glycol content is less than 10 mol%, it is difficult to make the polyester sufficiently high in molecular weight, and the processability is insufficient. However, when it exceeds 40 mol%, the wet ink suitability tends to be deteriorated. is there.
Specific examples of the glycol represented by the general formula (2) include 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2,2, Examples include 4-trimethyl-1,3-pentanediol and 2-ethyl-1,3-hexanediol.

  In addition, other dihydric or higher alcohols can be used in combination as the polyol component of the polyester resin of the present invention. The other dihydric or higher alcohols refer to dihydric or higher alcohols that do not correspond to at least one of the glycols represented by the general formula (2) and ethylene glycol, such as 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, neopentyl glycol, 1,4-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, Examples include known diol components such as dipropylene glycol and cyclohexanedimethanol, and known tri- or higher valent polyol components such as trimethylolpropane, trimethylolethane, glycerin, and pentaerythritol. The amount of other dihydric or higher alcohol used is preferably within a range not exceeding 60 mol%.

In order to impart reactivity with the curing agent, all or part of the other divalent or higher alcohols are preferably trivalent or higher alcohols. The amount of trihydric or higher alcohol used is preferably in the range of 1 to 10 mol% in the polyol component. When the amount of the trivalent alcohol used is less than 1 mol%, the reactivity with the curing agent is insufficient, and when it exceeds 10 mol%, the workability is reduced.

Although the number average molecular weight of the polyester resin for overcoat clear paints of this invention is not specifically limited, It is preferable to set it as about 6000-25000. The lower limit of the number average molecular weight is that considering that the coating film becomes brittle, and the upper limit is that considering that the gloss of the coating film and wet ink suitability are reduced, more preferably 8000 to 15000. It is good to do.

The hydroxyl value is about 2 to 200 KOHmg / g, preferably 2 to 100 KOHmg / g. When the hydroxyl value is higher than 200 KOH / g, the crosslinking with the curing agent proceeds too much, and the processability of the resulting overcoat clear coating resin tends to be inferior. The acid value is about 0.1 to 50 KOHmg / g, preferably about 0.1 to 30 KOHmg / g. If the acid value is higher than 50 KOHmg / g, there may be a problem in terms of water resistance. In order to balance workability and blocking resistance, the glass transition point (Tg) is preferably 10 to 50 ° C.

  The method for producing the polyester resin for overcoat clear paint of the present invention is not particularly limited, and may be a normal esterification reaction, that is, a polycondensation reaction, and the reaction may be performed at 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. You may perform processes, such as an addition reaction by acid anhydrides, such as an acid.

After completion of the reaction, the obtained polyester resin is dissolved in a solvent to obtain a resin solution. As a solvent to be used, any solvent capable of diluting the polyester resin can be used without any limitation. For example, aromatic hydrocarbon solvents such as toluene, xylene, Solvesso # 100 (made by ExxonMobil Chemical), Solvesso # 150 (made by ExxonMobil Chemical), and aliphatic hydrocarbons such as hexane, heptane, octane and decane Solvent: ester solvents such as methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate, ethyl formate, butyl propionate, methoxypropyl acetate; methanol, ethanol, propanol, butanol, 2-ethylhexanol, ethylene glycol, methoxy Alcohol solvents such as propanol; Ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; Ether solvents such as dioxane, diethyl ether, and tetrahydrofuran; Cellosolve acetate , Ethyl cellosolve, include various solvents cellosolve solvent butyl cellosolve. The resin solid content concentration of the resin solution is not particularly limited, but is usually about 20 to 70% by weight, preferably 30 to 60% by weight. If it exceeds 70% by weight, it is difficult to handle due to high viscosity, and if it is less than 20% by weight, the viscosity may be too low when blended with a curing agent.

The overcoat clear paint resin composition of the present invention comprises the polyester resin solution and a curing agent. Examples of the curing agent include amino resins, epoxy compounds, and isocyanate compounds.
Examples of amino resins include condensation reaction products of urea, melamine, benzoguanamine and the like with aldehydes, or resins in which a part or all of them are alkoxylated, and commercially available products include Cymel 303 and Cymel 350 (Nippon Cytec Industries). (Manufactured by Co., Ltd.), Delamin T-100S (manufactured by Fuji Kasei Co., Ltd.), Uban 120 (manufactured by Nippon Cytec Industries, Inc.), and the like.

Epoxy compounds include bisphenol A diglycidyl ether and oligomers thereof, orthophthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyalkylene glycol And diglycidyl ethers.

Isocyanate compounds include aromatic and aliphatic diisocyanates and tri- or higher polyisocyanates, which may be either low molecular compounds or high molecular compounds. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate and the like can be mentioned.

The compounding ratio of the polyester resin and the curing agent is usually about 95/5 to 50/50, preferably 90/10 to 60/40, as a solid weight ratio of the polyester resin and the curing agent. When the blending ratio of the polyester resin and the curing agent is out of the above range, the workability tends to be lowered or the coating film hardness tends to be lowered.

The overcoat clear paint resin composition of the present invention may contain various known additives. Known additives include, for example, curing catalysts, leveling agents, ultraviolet absorbers, viscosity modifiers and the like. The coating resin composition may be diluted with the same solvent as used for the reaction, and the concentration is usually about 20 to 70% by weight, preferably 30 to 60% by weight. When it exceeds 70% by weight, coating becomes difficult due to high viscosity, and when it is less than 20% by weight, the film thickness when applied tends to be too thin.

The resin composition for paints of the present invention thus obtained is applied to a metal plate for cans after being applied with an ink without being heated, and further applied to improve the workability and wet ink suitability. A coating film excellent in both performances can be formed. The coating method may be a normal method such as a roll coater, and the resin used in the ink is not particularly limited, but oil-modified alkyd is preferable, and dry oil-modified alkyd, semi-dry oil-modified alkyd, Any of dry oil-modified alkyds and the like may be used. In addition, in order to improve the adhesion of the ink, the metal plate for cans is preferably coated with an ink through an undercoat layer, for example, an undercoat (white coating) or size coat by a known method. Is preferably used. The coating resin composition of the present invention is excellent in wet ink suitability as described above, but can of course be applied to dried ink and UV cured ink.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples. In each example, parts and% are based on weight unless otherwise specified.

Example 1
In a flask equipped with a thermometer, a nitrogen inlet tube, a reflux dehydrator, and a stirrer, 182.6 parts of dimethyl terephthalic acid (40 mol% in all polybasic acid components), 37.9 parts of ethylene glycol (in all polyol components) 20 mol%), neopentyl glycol 85.9 parts (27 mol% in all polyol components), 2-n-butyl-2-ethyl-1,3-propanediol 245.3 parts (50 in all polyol components) Mol%), 8.2 parts of trimethylolpropane (3 mol% in all polyol components) and 0.1 part of titanium tetrabutoxide were added, and when the raw materials were melted and could be stirred, stirring was started at 170 ° C. To 210 ° C. over 3 hours. Methanol produced at this time was distilled out of the system. Next, 78.1 parts of isophthalic acid (20 mol% in all polybasic acid components), 90.6 parts of hexahydrophthalic anhydride (25 mol% in all polybasic acid components) and 71.3 parts of sebacic acid ( 15 mol% in all polybasic acid components) was added, the temperature was gradually raised from 170 ° C. to 240 ° C. over 3 hours, and the temperature was kept at 240 ° C. for 3 hours. The water produced at this time was distilled out of the system. Next, the temperature was raised to 250 ° C., and a polycondensation reaction was performed at 670 Pa under reduced pressure for 1 hour and 30 minutes. Thereafter, the mixture was cooled to 180 ° C. and 291.2 parts of Solvesso # 150 and 124.8 parts of ethylene glycol monobutyl ether were added and dissolved uniformly. The non-volatile content was 60%, the acid value was 0.6 KOHmg / g, the hydroxyl value was 25 KOHmg / g, glass A polyester resin solution (A) having a transition point of 20 ° C. and a number average molecular weight of 11,000 was obtained.

The constant of the obtained polyester resin solution was measured by the following method.
(Acid value)
A sample 1.0 g precisely weighed and dissolved in 20 ml of tetrahydrofuran was determined by titration with 0.1N potassium hydroxide (ethanol solution) using phenolphthalein as an indicator.

(Hydroxyl value)
2.0 g of the sample was precisely weighed and the hydroxyl value was determined according to JIS K 0070 2.5.

(Glass transition point)
Using a differential scanning calorimeter (EXTRA6000 DSC, manufactured by Seiko Instruments Inc.), the measurement was performed at a heating rate of 10 ° C./min.

(Molecular weight)
By gel permeation chromatography (manufactured by Tosoh Corporation, HLC8120, column used: TSKgel SuperHM-L × 3, developing solvent: tetrahydrofuran), the weight average molecular weight was converted to polystyrene at a flow rate of 0.60 ml / min and a measurement temperature of 40 ° C. It was measured.

Examples 2-4
In Example 1, the polyester resin solution (B) was prepared in the same manner as in Example 1 except that the types of polybasic acid component and polyol component, which are constituents of the polyester resin, or the amounts used thereof were changed as shown in Table 1. , (C) and (D) were obtained. Table 1 shows the respective constants.

Comparative Examples 1-4
In Example 1, the polyester is the same as in Example 1 except that the type of polybasic acid component, which is a constituent component of the polyester resin, or the amount of use thereof, and the type of diol component or the amount of use thereof are changed as shown in Table 1. Resin solutions (E), (F), (G), and (H) were obtained. Table 1 shows the respective constants.

  The polyester resin solutions and amino resins (manufactured by Nippon Cytec Industries Co., Ltd.) and Delamine T-100S obtained in the above Examples and Comparative Examples were blended in order at 70/15/15 (solid content weight ratio), and Solvesso # 150 / Butyl cellosolve is diluted with a 70/30 (weight ratio) mixed solvent, and the curing catalyst (paratoluenesulfonic acid, 0.4% of clear paint) is mixed uniformly, and the coating viscosity is an IHS cup 40 seconds overcoat A clear paint composition was prepared.

The following tests were performed on the obtained overcoat clear coating composition.

Apply a polyester-based white coating agent to a 0.5 mm thick tin plate (dry film thickness 10 μm), dry at 170 ° C. for 10 minutes, and print ink with a dry oil alkyd resin as the main component of the vehicle on this. Then, the above overcoat clear paint was applied (film thickness 8 μm) in an uncured state (not baked). This was followed by baking at 160 ° C. for 10 minutes. About the obtained test piece, the wet ink suitability test, workability, and blocking resistance were investigated. The evaluation results are shown in Table 1.

Wet ink suitability test: The degree of ink bleeding phenomenon and embossing phenomenon was visually determined according to the following criteria.
A: Excellent, B: Good, B: Somewhat bad, B: Bad.

Workability: The degree of peeling of the coating film of the four-piece can punched out was visually judged according to the following criteria.
○: Excellent, Δ: Good, ×: Poor.

Blocking resistance: Two test pieces were stacked, a load of 0.5 MPa was applied, and after 12 hours at 40 ° C., the presence or absence of indentation was determined.
○: no indentation, Δ: slight indentation, x: indentation.

Pencil hardness: According to JIS K 5600-5-4, “Uni” (registered trademark) manufactured by Mitsubishi Pencil Co., Ltd. was used to examine the hardness that does not cause scratches.

Claims (4)

As the polybasic acid component, an alicyclic dicarboxylic acid represented by the general formula (1) (wherein R represents hydrogen or a methyl group) 5 to 30 mol%, isophthalic acid 10 to 20 mol%, and other dicarboxylic acids The acid component is contained in an amount of 50 to 85 mol%, and the polyol component is represented by the general formula (2) (wherein R1, R2, and R3 each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and at least R1, R2, and R3). The total number of carbon atoms is 3 or more.) One or more side chain alkyl group-containing glycols represented by 30 to 70 mol%, ethylene glycol 10 to 40 mol%, and other divalent or higher alcohols 0 to 60 Polyester resin for overcoat clear paint containing mol%.
General formula (1)

General formula (2)

  2. The polyester resin for overcoat clear paint according to claim 1, wherein all or part of the other divalent or higher alcohol component is a trivalent or higher alcohol.   An overcoat clear paint resin composition comprising the paint polyester resin according to claim 1 or 2 and a curing agent. The overcoat clear paint resin composition according to claim 3, wherein the curing agent is an amino resin.