JPH08311395A - Polyester resin for powder coating material for can and composition - Google Patents

Abstract

PURPOSE: To obtain a low cost polyester resin excellent in baking properties at a high temperature in a short time, adhesivity between a coating film and a material to be coated, retort resistance and processability of a coated material, capable of being made into a powder coating material suitable for coating a food can, a beverage can, etc. CONSTITUTION: This polyester resin for a powder coating material for a can comprises an acid component consisting essentially of an aromatic dicarboxylic acid and a diol component composed essentially of 2-butyl-2-ethyl-1,3-propanediol and another aliphatic diol in the molar ratio of 30/70 to 100/0 and has 0.1-0.25dl/g intrinsic viscosity and 1,000-3,000geq/10<6> g acid value. The polyester resin is mixed with an epoxy-based curing agent to give the objective polyester resin composition for a powder coating material for a can.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin and a resin composition which can be used as a powder coating suitable for coating food cans, beverage cans and the like.

[0002]

2. Description of the Related Art Conventionally, as a can for canning, a three-piece can in which a top and bottom can lid is fastened to a can body having a seam provided by soldering, bonding, welding, etc. on its side, drawing, drawing and ironing, impact molding For example, a two-piece can in which a can lid is fastened around a can body having no side seam is generally used. In addition, in any of these forms, a protective coating film is provided on the inner surface or the outer surface of the can in order to prevent corrosion of the metal substrate. This protective coating must be able to withstand hot water treatment such as retort sterilization at high temperatures, as well as with flange processing, neck-in processing, double winding, and other processing. From this point of view, as a paint for cans,
A solvent-type thermosetting resin having excellent adhesion (adhesion between a coating film and an object to be coated), corrosion resistance, and workability (workability of a coated object) is generally used. However, in recent years, environmental pollution due to organic solvents and the like has become a serious problem, and there is an increasing demand for low-pollution type paints that replace solvent-type paints.

Compared with conventional solvent-based paints, powder paints are pollution-free paints, can be used immediately after painting, do not require multi-layer overcoating, and are relatively inexpensive. The advantage of being able to collect and reuse the surplus at the time of painting has been recognized, and the demand has rapidly expanded in recent years for the protection of members such as home appliances, building materials, automobile parts, and decorative paints. ing. However, there has not been a powder coating material that satisfies all the properties required for a coating material for a can.

[0004]

DISCLOSURE OF THE INVENTION The present invention is excellent in bakeability at high temperature for a short time and has good adhesion between a coating film and an object to be coated,
It is an object of the present invention to provide a polyester resin and a polyester resin composition which have good retort resistance and processability of a coated product and can be used as a powder coating suitable for coating food cans, beverage cans and the like.

[0005]

The present invention solves the above-mentioned problems, and the gist thereof is as follows. 1. An acid component mainly composed of an aromatic dicarboxylic acid, mainly composed of 2-butyl-2-ethyl-1,3-propanediol and another aliphatic diol, and their molar ratio is 30/7 to 10 to 10.
A polyester resin comprising a diol component of 0/0, an intrinsic viscosity of 0.1 to 0.25 dl / g and an acid value of 1000 to 3000.
Polyester resin for can coating powder coatings, characterized by geq / 10 ⁶ g. 2. A polyester resin composition for a powder paint for can coating, wherein the above polyester resin is mixed with an epoxy curing agent.

The present invention will be described in detail below.

Aromatic dicarboxylic acids are used as the main acid component in the polyester resin of the present invention.

As the aromatic dicarboxylic acid component, terephthalic acid and isophthalic acid are preferable, and if necessary, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid and the like may be used in combination.

A small amount (about 10 mol% or less) of the aliphatic dicarboxylic acid component may be used together with these aromatic dicarboxylic acid components. Examples of such an aliphatic dicarboxylic acid component include succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid and the like.

Further, tricarboxylic or higher carboxylic acid components such as trimellitic acid, trimellitic acid anhydride, trimesic acid, pyromellitic acid and the like may be used in combination so long as the polyester resin is not gelled.

Further, p is used as the hydroxycarboxylic acid component.
-Hydroxybenzoic acid, tartaric acid, lactic acid, p-hydroxyethoxybenzoic acid, ε-caprolactone and the like may be used together as a copolymerization component.

On the other hand, the main diol component is 2-
It consists of butyl-2-ethyl-1,3-propanediol and other aliphatic diols, and their molar ratio is 30 / 70-10.
A diol component that is 0/0 is used. When the proportion of 2-butyl-2-ethyl-1,3-propanediol in the diol component is less than 30 mol%, a powder coating material which gives a coating film having sufficient retort resistance cannot be obtained.

The diol components which can be used in combination with 2-butyl-2-ethyl-1,3-propanediol include neopentyl glycol, ethylene glycol, 1,
2-propanediol, 1,3-propanediol, 1,3
-Butanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, 1,4-cyclohexanedimethanol and the like can be mentioned.

Further, a trifunctional or higher functional alcohol component such as glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol may be used together with the diol component in a small amount.

Polyester resin has an acid value of 1000 to 3000 ge
Must be q / 10 ⁶ g. When the acid value of the polyester resin is less than 1000 geq / 10 ⁶ g, sufficient coating strength cannot be obtained by baking at high temperature for a short time, and when it exceeds 3000 geq / 10 ⁶ g, the workability of the coated product deteriorates.

The polyester resin has an intrinsic viscosity of 0.
It should be 10 to 0.25 dl / g. When the intrinsic viscosity of the polyester resin is less than 0.10 dl / g, the blocking resistance of the powder tends to be poor, and
If it exceeds 0.25 dl / g, the adhesion to the object to be coated tends to decrease. Particularly preferred is an intrinsic viscosity of 0.12 to 0.
It is 20 dl / g.

Such polyester resin is, for example,
It can be prepared by the following method. That is, using the acid component and alcohol component as described above,
After the esterification reaction is carried out at a temperature of 260 ° C to obtain an esterification reaction product with a reaction rate of 90 to 95%, a polycondensation reaction catalyst such as antimony trioxide is added and the polycondensation reaction is carried out at 200 to 300 ° C under reduced pressure. , A polyester with a high degree of polymerization having an intrinsic viscosity of 0.45 or more, and adding a polycarboxylic acid component to this
A predetermined polyester resin can be prepared by performing a depolymerization reaction at 0 ° C, preferably 200 to 280 ° C.

In addition, if the above-mentioned components are added in excess of the acid component,
It can also be prepared by a method of carrying out an esterification reaction at 140 to 240 ° C., or by carrying out a similar esterification reaction in the presence of excess glycol component and then adding an acid component. At this time, a known esterification reaction catalyst may be used in the esterification reaction.

The polyester resin of the present invention is used by blending an epoxy curing agent in the case of powder coating. The epoxy-based curing agent is preferably an epi-bis type epoxy compound obtained by polycondensing bisphenol A and epichlorohydrin at various ratios from the viewpoint of mechanical strength and baking property. Specific examples of such an epoxy compound include YD-014 (epoxy equivalent of 90 to 10) manufactured by Tohto Kasei Co., Ltd.
00), AER-6003 (Epoxy equivalent 700
~ 820) and the like. The amount of epoxy-based curing agent blended
It is suitable that the amount is approximately equivalent to the amount of the carboxyl group of the polyester resin (0.8 to 1.2 times equivalent).

To prepare a resin composition for powder coating, a polyester resin is mixed with a curing agent and, if necessary, a curing catalyst, a leveling agent, a pigment such as titanium dioxide or carbon black, and other additives, and a kneader or Using a roll
Kneading may be performed at a temperature of 70 to 150 ° C.

[0021]

Since the polyester resin of the present invention has a high acid value, it has a large amount of functional groups that react with the curing agent, and when it is used as a powder coating, it can be baked at high temperature for a short time. In addition, 2-butyl-2-ethyl-1,3 as a part of the diol component
Since propanediol is used, the polyester resin is provided with high water resistance, and as a result, a coating film having good retort resistance is obtained.

[0022]

The present invention will be described below with reference to Examples and Comparative Examples. The characteristic values and the like were measured and evaluated by the following methods. (a) Intrinsic viscosity (unit: dl / g) Measurement was carried out at a temperature of 20 ° C. using a mixture of phenol and ethane tetrachloride in an equal weight as a solvent. (b) Acid value (unit: geq / 10 ⁶ g) 0.5 g of polyester resin is dissolved in 50 ml of dioxane,
It was determined by titration with a 1N potassium hydroxide methanol solution. (c) 60 degree specular gloss (unit:%) Obtained according to JIS K 54OO. (d) Cross grid Erichsen (unit: mm) Eleven crosscuts were inserted at a right angle at 1 mm intervals, the center part thereof was extruded by an Erichsen tester, and the extrusion length until peeling was measured. (e) Impact resistance (unit: cm) According to JIS K 54OO, it was measured using a sphere with a diameter of 1.27 cm and 1 kg. (f) Flex resistance The coated plate was bent 180 degrees with the coating film on the outside, and the presence or absence of cracks in the coating film was evaluated according to the following three grades. ◯: No crack in coating film, Δ: Very small crack in coating film, ×:
The coating film has cracks. (g) Salt spray resistance (Unit: mm) After spraying a 5% sodium chloride aqueous solution at 35 ° C for 500 hours on a cross-cut coated plate, the cross-cut part is peeled off with cellophane tape and the cut part is cut off. The peeling width on one side of was measured. (h) The initial weight (W ₀ ) of a coated plate having a gel fraction of 7 cm × 15 cm is measured. After extracting these coated plates in methyl ethyl ketone at 75 ° C. for 60 minutes, the coated plates are taken out and dried at 150 ° C. for 30 minutes, and the weight (W ₁ ) is measured. Next, the extraction residue on the plate is decomposed and removed with concentrated sulfuric acid, washed with water, and the weight (W ₂ ) of the dried plate is measured. The gel fraction is calculated by the following formula. Gel fraction (%) = [(W ₁ -W ₂ ) / (W ₀ -W ₂ )] × 100 The gel fraction was evaluated according to the following criteria. ◎: 85% or more, ○: 70 to 85%, △: 50 to 70%, ×: 50%
Less than. The gel fraction indicates the ratio of the crosslinked portion to the total coating film weight and serves as an index indicating the degree of curing by baking. (i) Retort whitening resistance A coated plate of 7 cm x 15 cm is immersed in an autoclave containing distilled water and retort treated at 125 ° C for 30 minutes. The retort whitening resistance was evaluated by the following four grades by visually judging the degree of whitening of the coating film after retort. ◎: No whitening, ○: Slight whitening, △: Whitening considerably,
X: Remarkably whitening.

Examples 1 to 8 and Comparative Examples 1 to 4 As raw material compounds, isophthalic acid (IPA), terephthalic acid (TPA), adipic acid (AD), 2-butyl-2.
-Ethyl-1,3-propanediol (BEPD), neopentyl glycol (NPG), ethylene glycol (EG), 1,6-hexanediol (HD) and diethylene glycol (DEG) in the amounts shown in Table 1 (parts by mole). )
The mixture was charged into an esterification reaction tank at, the temperature was gradually raised from 100 ° C, and the esterification reaction was carried out at 260 ° C for 4 hours. After transferring the obtained esterified product to the polycondensation reaction tank, antimony trioxide was used as a catalyst in an amount of 2 × 10 ⁻⁴ per mol of the acid component.
Molar amount was added, the pressure was reduced to 0.5 hPa or less, and polycondensation reaction was carried out at 280 ° C. for 3 hours to obtain a polyester having an intrinsic viscosity of 0.45. Next, IPA and trimellitic acid (TMA) as depolymerizing agents were added to 1 mol of this polyester in the amounts (mol parts) shown in Table 1, and the mixture was allowed to decompose at 250 ° C. for 2 hours at 250 ° C. under an inert atmosphere. Polymerization reaction was performed to obtain polyester resins Nos. 1 to 12 having the characteristic values shown in Table 1.

[0024]

[Table 1]

Polyester resins Nos. 1 to 12 and an epoxy-based curing agent; AER-6003 manufactured by Ciba-Geigy Co. were mixed in the proportions (parts by weight) shown in Table 2, and the total amount of the polyester resin and the curing agent was 100 parts by weight. Undecyl imidazole curing catalyst; Shikoku Kasei Co., Ltd., Cuazole C ₁₁ Z 0.3 part by weight, butyl polyacrylate leveling agent; Basuf's acronal 4F 1 part by weight, benzoin 0.5 part by weight, FM 10B type Henschel mixer. (Mitsui Miike Manufacturing)
After dry-blending with, melt-knead at 110 ° C using PR-46 type co-kneader (manufactured by Buss), cool and pulverize.
A powder coating was obtained by classification (105 μm or less) with a 0 mesh wire mesh. The obtained powder coating material was electrostatically coated on a zinc phosphate-treated steel sheet to a film thickness of 40 to 50 μm and baked at 250 ° C. for 30 seconds. The results of evaluation of coating film performance are shown in Table 2.

[0026]

[Table 2]

[0027]

According to the present invention, low cost, excellent baking property at high temperature and short time, good adhesion between the coating film and the object to be coated, good retort resistance and workability of the coated object, Food cans,
Provided are a polyester resin and a polyester resin composition which can be a powder coating suitable for coating beverage cans and the like.

Claims (2)

[Claims] 1. An acid component containing an aromatic dicarboxylic acid as a main component, 2-butyl-2-ethyl-1,3-propanediol and another aliphatic diol as a main component, and their molar ratios are
A polyester resin composed of a diol component of 30/70 to 100/0 with an intrinsic viscosity of 0.1 to 0.25 dl / g and an acid value of
Polyester resin for can coating powder coatings, which is 1000-3000 geq / 10 ⁶ g. 2. A polyester resin composition for a can coating powder coating, which comprises the polyester resin according to claim 1 mixed with an epoxy curing agent.