JP2001019877A - Can coating, coated metal plate, can body and can cap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a can coating, particularly a coating for a can inner face having an excellent combination of adhesive properties to a metal plate, workability, curability, suppressed elution and the resistance to retorting sterilization process. SOLUTION: A can coating comprises (A) a thermoplastic polyester resin having a glass transition temperature of at least 65 deg.C, an acid value of not more than 15, a hydroxy number of not more than 20 and a number average molecular weight of at least 11,000, and (B) a heat curable resin comprising a heat curable benzoguanamine resin as a principal component, wherein a weight ratio of the (A) component/the (B) component is 90/10-55/45. The thermoplastic polyester resin (A) desirably comprises a polyester derived from a dibasic acid component comprising terephthalic acid as a main component and a glycol component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paint for a can, a coated metal plate for a can, and a can body and a can lid formed from the coated metal plate, and more particularly to a thermoplastic polyester and a thermosetting resin. The present invention relates to a paint for cans, comprising a water-soluble resin and capable of forming a coating film having a novel interpenetrating network structure (IPN). The present invention also relates to a coated metal sheet for can making having a coating film formed from the coating material, and a can body and a can lid formed from the coated metal sheet.

[0002]

2. Description of the Related Art Paints for cans are used for the purpose of preventing corrosion of can materials, and are required to have workability and adhesion of coating films to metals. In particular, the paint used for the inner surface of the can is required to not impair the flavor and flavor of the contents, be non-toxic, and not to elute the paint components, in addition to the workability and the like. Conventionally, as a paint for cans, epoxy-phenol-based paint, epoxy-amino-based paint,
Epoxy-based paints such as epoxy-acrylic-based paints are widely used. However, since many epoxy-based paints are produced from bisphenol A, which has recently become a topical environmental hormone, paints used on the inner surface of cans are particularly preferred. A paint containing no bisphenol A is desired.

As a paint for cans containing no bisphenol A, a polyester paint having excellent adhesion to metals and not generating toxic corrosive gas upon incineration is used. For example, Japanese Patent Publication No. 60-42829 discloses that 80 to 100 mol% of terephthalic acid and 20 to 0 mol% of dicarboxylic acid other than terephthalic acid are used as a dicarboxylic acid component, and propylene glycol 60 to 100% is used as a glycol component.
A coating agent for the inner surface of a metal can, which is a polyester having a reduced viscosity of 0.4 or more, comprising 100 mol% and 40 to 0 mol% of glycols other than propylene glycol, is described.

[0004]

Although the above thermoplastic polyester coating has excellent workability and adhesion to a metal plate, it still has a problem in heat resistance, so that it is difficult to apply when passing through a coating and printing line. The film tends to soften and become scratched. Further, there is a problem that the blister resistance and whitening resistance under retort sterilization conditions (125 ° C. × 30 minutes) are still insufficient.

Accordingly, an object of the present invention is to provide a paint for cans, particularly a paint for the inner surface of a can, which is excellent in combination with adhesion to a metal plate, workability, curability, suppressed dissolution properties and retort sterilization resistance. To be. Another object of the present invention is to provide a coated metal sheet for cans with a coating comprising a combination of a specific thermoplastic polyester and a thermosetting resin and forming a novel interpenetrating network, and the coated metal sheet. It is an object to provide a can body and a can lid formed from a plate.

[0006]

According to the present invention, (A)
With a thermoplastic polyester resin having a glass transition point of 65 ° C. or more, particularly 70 ° C. or more, an acid value of 15 or less, particularly 10 or less, a hydroxyl value of 20 or less, particularly 15 or less, and a number average molecular weight of 11,000 or more, particularly 15,000 or more. , (B)
A paint for cans comprising: a thermosetting resin mainly composed of a thermosetting benzoguanamine resin in a weight ratio of A: B = 90: 10 to 55:45. In the paint for cans of the present invention, any thermoplastic polyester that satisfies the above conditions can be used.However, a polyester derived from a dibasic acid component mainly composed of terephthalic acid and a glycol component may be used. preferable. In the paint for cans of the present invention, the M
The EK (methyl ethyl ketone) extraction rate (MEK boiling point, 1 hour) is preferably 40% or less. According to the present invention, there is also provided a coated metal plate for can making, which is obtained by applying the above-mentioned coating material for a can on a metal plate and curing the same, and a can body and a can lid formed from the coated metal plate. You. In this coated metal plate, the thermoplastic polyester (A) and the thermosetting resin (B) in the coating film have an interpenetrating network structure (I).
PN).

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Action] The paint for cans of the present invention has the following features: (1) (A) a glass transition point of 65 ° C. or higher;
A thermoplastic polyester resin having an acid value of 15 or less, a hydroxyl value of 20 or less, and a number average molecular weight of 11,000 or more, and (B) a thermosetting resin mainly composed of a thermosetting benzoguanamine resin; (2) that the thermoplastic polyester resin (A) and the thermosetting resin (B) are substantially non-reactive, and (3) heat The combination of the features that the thermoplastic polyester resin (A) and the thermosetting resin (B) can form an interpenetrating network structure in the coating film.

The above-mentioned specific thermoplastic polyester resin (A) serves as a base resin for a coating film, and this specific base resin imparts excellent heat resistance, retort resistance and workability to the coating film and has a low level. The acid value and the hydroxyl value substantially prevent the reaction with the thermosetting resin (B) mainly composed of the thermosetting benzoguanamine resin even under the curing conditions, whereby the curability and the retort resistance of the coating film are obtained. And improve workability.

As described above, in the paint of the present invention, the thermoplastic polyester resin (A) and the thermosetting resin (B) mainly composed of the thermosetting benzoguanamine resin are substantially non-reactive, and Curing of the resin in the paint proceeds by a self-curing reaction of the thermosetting resin (B), and enables formation of an interpenetrating network (IPN) in the coating film.

[0010] The interpenetrating network (IPN) is defined as a structure in which two or more three-dimensional polymer networks are entangled with each other without being connected by a covalent bond. A network accompanying the curing of the thermosetting resin (B) is formed in a form incorporating the resin (A), and a thermoplastic polyester resin penetrates in a form entangled with the network, and this structure has excellent adhesion. This is considered to be the reason for improving the curability and retort resistance while maintaining the properties and workability.

[Thermoplastic polyester resin] The thermoplastic polyester resin (A) used in the present invention has a glass transition point (Tg) of 65 ° C or higher, an acid value of 15 or lower, a hydroxyl value of 20 or lower and a number average of 11,000 or higher. It must have a molecular weight (Mn). That is, the Tg of the thermoplastic polyester resin serving as the base resin of the paint has a significant effect on the heat resistance and retort sterilization resistance of the coating film. In the present invention, the above-mentioned glass transition point of 65 ° C. or higher, particularly 70 ° C. or higher. By using a material having (Tg), it is possible to prevent the occurrence of scratches on the coating film during baking during painting and printing,
In addition, it becomes possible to improve hot water resistance during retort sterilization and prevent whitening and the like. In a thermoplastic polyester resin having a Tg lower than the above range, even in combination with a thermosetting resin (see Comparative Example 2 described later),
It should be understood that heat resistance and retort resistance as in the paint of the present invention cannot be obtained and workability is low.

Next, the thermoplastic polyester resin used in the present invention has an acid value of 15 or less, especially 10 or less, and 20 or less.
In particular, having a hydroxyl value of 15 or less is also important from the viewpoint of a combination of processability, curability, suppressed dissolution, and retort sterilization resistance. That is, as already pointed out, in the paint of the present invention, the thermoplastic polyester and the thermosetting resin are substantially non-reactive, and form an interpenetrating network structure in the coating film. The carboxyl group and hydroxyl group involved in the reaction with the resin must be kept low so as to satisfy the above-mentioned acid value and hydroxyl value. In general, when a thermoplastic resin is used in combination with a thermosetting resin component, it is better to cause a reaction between the two,
It is common sense that hot water resistance also improves,
In the combination paint of the present invention, such an interaction rather leads to a decrease in curability and hot water resistance, and further to a decrease in workability. Polyesters having an acid value or a hydroxyl value exceeding the above ranges, when combined with a thermosetting resin (see Comparative Examples 3 and 4 described later), have higher curability, hot water resistance, and processing than the paint of the present invention. And the unexpected effect of the present invention becomes apparent.

[0013] The thermoplastic polyester resin used in the present invention further has a workability of 110 from the viewpoint of processability required for paint for cans.
It should have a number average molecular weight of at least 00, especially at least 15,000. Even if other conditions are the same, the number average molecular weight is 11
In a paint using a polyester having a molecular weight of less than 000 (see Comparative Example 5 described later), a tendency that the processability is remarkably reduced is recognized as compared with a paint using a polyester having a number average molecular weight of 11,000 or more.

The thermoplastic polyester resin used for the base resin may be any thermoplastic polyester resin derived from a dibasic acid component and a glycol component as long as the above requirements are satisfied. Generally, in order to realize that Tg is 65 ° C. or more, as a dicarboxylic acid component,
It is preferable to use a dicarboxylic acid component mainly composed of terephthalic acid, generally from 80 to 100 mol%, particularly from 90 to 100 mol%, and from 20 to 0 mol%, particularly from 10 to 0 mol%, of dicarboxylic acids other than terephthalic acid. Is preferred. As dicarboxylic acids other than terephthalic acid,
Examples include isophthalic acid, orthophthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, and dimer acid.

On the other hand, glycol components include propylene glycol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol and 1,6-hexane. Examples include diol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanediol, and p-xylylene glycol.

The thermoplastic polyester resin used in the present invention is preferably a thermoplastic polyester derived from a glycol component mainly composed of propylene glycol from the viewpoint of solubility in a solvent, and the glycol component in the polyester is propylene glycol. 60 to 100 mol%, preferably 70 to 99 mol%, and 40 to 0 mol% of glycols other than propylene glycol, preferably 3
It is best comprised from 0 to 1 mol%.

The polyester used in the present invention can be obtained from a dicarboxylic acid and a glycol. However, a polycarboxylic acid or polyol having three or more functional groups can be copolymerized within a range not exceeding the above-mentioned limit. Examples of trifunctional or higher polycarboxylic acids include trimellitic acid or anhydride thereof, pyromellitic acid or anhydride thereof, and examples of trifunctional or higher polyols include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. it can. These polycarboxylic acids and polyhydric alcohols are preferably used in an amount of 2 mol% or less, particularly 1 mol% or less.

The polyester used in the present invention is produced by a usual method for producing a high molecular weight polyester by a transesterification method or a direct esterification method. However, in consideration of food applications, use of heavy metals or compounds that pose a problem in hygiene as catalysts and additives should be avoided.

[Thermosetting resin] In the present invention, a thermosetting resin (B) mainly composed of a thermosetting benzoguanamine resin is used in combination with the thermoplastic polyester resin (A). That is, in the present invention, among the various thermosetting resins, the use of a thermosetting benzoguanamine resin as a main component is particularly effective for exhibiting the above-mentioned properties as a paint for cans.

For example, when a melamine resin also belonging to the amino resin is used, there is a slight difficulty in the dissolution property,
Similarly, when a phenolic resin belonging to the methylolated resin is used, although a little difficulty is recognized in retort resistance, a benzoguanamine resin is also selected from among the thermosetting resins, and this is selected from the thermoplastic polyester described above. By combining, curability, elution resistance, retort resistance,
It becomes possible to provide a paint for cans, particularly a paint for the inner surface of a can, which is excellent in all combinations of adhesion and workability.

The benzoguanamine resin used in the present invention is benzoguanamine, that is, the following formula (1)

Embedded image And a resin obtained by condensing formaldehyde with formaldehyde. Particularly, an etherified amino resin etherified with methanol, ethanol, n-butanol, iso-butanol or the like is preferably used. These amino resins are commercially available in the form of a solution dissolved in a solvent such as methanol, butanol, xylol, and the like, and this solution is added to use in forming a paint.

As the benzoguanamine resin, resin 10
Per 0 gram, the basic nitrogen atom concentration is 7 to 11 gram atoms, especially 8 to 10 gram atoms, and the concentration of methylol groups and etherified methylol groups is 0.5 to 1.2 mol, especially 0.7 to 1. Those in the range of 0 moles,
This is advantageous in terms of the above characteristics.

In the present invention, the term "mainly composed of a benzoguanamine resin" means that the thermosetting resin may be composed of only the benzoguanamine resin, or that the benzoguanamine resin may contain a small amount of another thermosetting resin. I do. The thermosetting resin that can be blended with the benzoguanamine resin is, of course, not limited thereto, but includes, for example, a phenol-formaldehyde resin, a furan-formaldehyde resin, a xylene-formaldehyde resin,
Ketone-formaldehyde resin, urea-formaldehyde resin, alkyd resin, unsaturated polyester resin, bismaleimide resin, triallyl cyanurate resin, thermosetting acrylic resin, silicone resin, urethane resin and the like can be mentioned. These resins may be used alone or in combination of two or more. When a thermosetting resin other than the benzoguanamine resin is blended, 3% of the entire thermosetting resin (B) is used.
It should be present in an amount up to 0% by weight.

[Paint] In the present invention, the thermoplastic polyester resin (A) and the thermosetting resin (B) are used in the form of A: B = 90: 10 to 55:45, particularly 85:15 to 65: An important feature is that it is contained at a weight ratio of 35.

That is, when the content of the thermosetting resin (B) mainly composed of the thermosetting benzoguanamine resin falls below the above range, as shown in Comparative Example 6 described later, when the content is within the above range, Curability, retort resistance and workability are inferior to those of Thermosetting resin (B)
When the content exceeds the above range, as shown in Comparative Example 7 described later, in addition to the curability and processability, the elution resistance and the adhesion are also higher than when the content is within the above range. Will begin to fall.

The coating composition of the present invention comprising the above resin components can be generally produced by mixing solutions of the respective resins and, if necessary, diluting the mixture to a predetermined concentration with a solvent. Of course, when the resin component is obtained as a solid resin, the solid resin can be dissolved in an appropriate solvent and used for mixing.

Examples of the organic solvent for the coating solution include aromatic hydrocarbon solvents such as toluene, xylene, and mixed aromatic hydrocarbons (eg, Solvesso manufactured by Shell Co.); and acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Ketone solvents; ether solvents such as tetrahydrofuran and dioxane; alcohol solvents such as ethanol, propanol and butanol; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; one or two of ester solvents such as ethyl acetate and butyl acetate; More than one species can be used.

The solid content concentration in the coating solution may be a concentration at which the solid content can be applied to the material for can making, and is generally from 10 to 40.
%, Especially in the range of 20 to 35% by weight.

The coating composition of the present invention preferably contains a curing catalyst. As the curing catalyst, an inorganic acid such as phosphoric acid and an organic acid such as toluenesulfonic acid and dodecylbenzenesulfonic acid can be used. These curing catalysts can be blended in an amount of 0.01 to 1 part by weight, particularly 0.1 to 0.7 part by weight, per 100 parts by weight of the resin component in the paint.

The paint for cans of the present invention can be blended with various compounding agents conventionally used in this type of paint based on a formulation known per se. For example, various pigments, fillers,
Matting agents, lubricants, leveling agents and the like can be added.

[Coating Metal Sheet for Can Making] The coating for can of the present invention is applied to the surface of a metal material for can making and baked to form a cured coating film having an interpenetrating network structure (IPN). It can be formed on the surface of a metal material. In the interpenetrating network structure (IPN) of the present invention, a network accompanying the mutual curing of the thermosetting resin (B) is formed in a form incorporating the thermoplastic polyester resin (A), and the network is entangled with this network. Thermoplastic polyester resin penetrates, and this structure improves curability and retort resistance while maintaining excellent adhesion and workability.

In the present invention, the interpenetrating network structure is ME
It is very specific in the dependence of the K extraction rate on paint baking time. As shown in FIG. 1, in the case of an epoxy / phenol-based paint, which is the most typical thermosetting paint for can-making, a negative correlation is shown that the MEK extraction rate decreases as the baking time increases. This is recognized as a matter of course because the longer the baking time, the more the reticulation proceeds. On the other hand, in the paint of the present invention, the MEK extraction rate shows a minimum value in a very short baking time, and the positive correlation that the MEK extraction rate increases with time in a baking time beyond this minimum value. It is shown.

As already pointed out, in the present invention, a network accompanying the mutual curing of the thermosetting resins (B) is formed in a form incorporating the thermoplastic polyester resin (A), and in this state, the entire coating film is formed. Although the MEK extraction rate is suppressed to a fairly low level, if the degree of heating during curing of the paint becomes excessive, phase separation occurs due to melting of the thermosetting resin network and the thermoplastic polyester. However, it is recognized that this increases the MEK extraction rate.

Of course, as shown in FIG. 1, in the paint of the present invention, the time required for curing may be extremely short, and the energy for curing may be extremely small. Has a tremendous advantage that the steps for the above can be significantly simplified and shortened.

The thermosetting can coating composition of the present invention also differs depending on the type of resin and cannot be specified unconditionally. However, in general, baking at a temperature of 170 to 230 ° C. for 1 to 15 minutes allows mutual calcination. A coating film having a penetrating network structure can be formed.

[Coated Can and Painted Lid] As the can-made material to which the above-described can-coated material of the present invention is applied, there can be mentioned a conventional metal material for producing three-piece cans. Examples include seamless cans formed by drawing and deep drawing or drawing and ironing of a metal material. Also, as the can lid, using a material similar to the can body to which the can lid is to be applied, a conventionally known score such as an easy open end provided with a score for forming an opening for discharging contents and a tab for opening is provided. Shapes can be employed.

It is preferable that the paint of the present invention described above is applied to both the outer surface and the inner surface or only the inner surface of the paint can body and the paint can lid of the present invention. The paint for cans of the present invention is high in safety because it is composed of only substances that are preferable for food hygiene, and the amount of resin components eluted is significantly reduced, so that it is particularly preferable to use it as an inner paint. It is. In the painted can and painted can lid of the present invention, such a thermosetting can paint may be applied to the entire surface of the metal material, or a welded portion of the can or can lid made of a resin-coated metal material. Of course, it is also possible to use as a correction paint on a part of the can body and the can lid, such as a score part.

As the metal plate constituting the can and the can lid, various surface-treated steel plates and light metal plates such as aluminum are used. As a surface-treated steel sheet, a cold-rolled steel sheet is annealed and then subjected to secondary cold rolling, and is subjected to one or more surface treatments such as zinc plating, tin plating, nickel plating, electrolytic chromic acid treatment, and chromic acid treatment. Can be used. Further, an aluminum-coated steel sheet subjected to aluminum plating, aluminum rolling, or the like is used. As the light metal plate, an aluminum alloy plate is used in addition to a so-called pure aluminum plate.

The original plate thickness of the metal plate varies depending on the type of the metal, the use or the size of the container, but is generally 0.10.
It is preferable that the surface-treated steel sheet has a thickness of 0.10 to 0.30 mm, and the light metal plate has a thickness of 0.15 to 0.40 mm. Is good. As the thermoplastic resin coated on the metal plate, a conventionally known crystalline thermoplastic resin used for metal coating can be used, but the adhesiveness with the thermosetting can paint of the present invention can be used. From the viewpoint, those made of a thermoplastic polyester resin are preferred. For example, a film made of polyethylene terephthalate, polybutylene terephthalate, or an ethylene terephthalate / isophthalate copolymer can be suitably used. The thickness of the thermoplastic resin is
Generally, it is desirable to be in the range of 3 to 50 μm, particularly 5 to 40 μm. In the case of heat fusion using a film, it may be unstretched or stretched.

The application of the thermosetting paint to the material for cans is performed using a metal.
Roll coater, bar coater when applying to the entire surface of the plate
-, A known coater such as a knife coater
be able to. When applying partially, these
Of course, it is also possible to apply using a spray etc.
is there. The application amount is 10 to 220 mg / dm², Special
30 to 150mg / dm ²Coating amount
It is preferable to apply a coating film under the above-mentioned baking conditions.
Heat cured to a thickness of 1 to 20 μm, especially 3 to
It is preferably in the range of 15 μm.

[0041]

The present invention will be specifically described below with reference to examples. “%” And “parts” used in this example are based on weight unless otherwise indicated.

(1) Measurement of glass transition point (Tg) Temperature rise rate was determined by analysis using DSC (differential scanning calorimeter).
The measurement was performed at 0 ° C./min. (2) Measurement of acid value 0.2 g of polyester resin was added to 10 m of benzyl alcohol.
l + chloroform dissolved in a mixed solvent of 10 ml, 0.1
% Phenol red / ethanol solution as indicator
Titration was performed with a 0.1 M KOH benzyl alcohol solution, and the number of mg of KOH per 1 g of the resin required for neutralization was determined. (3) Measurement of hydroxyl value 1.0 g of polyester resin was dissolved in 5 ml of nitrobenzene, and bromoacetylation was performed by adding 0.5 ml of bromoacetyl bromide. After precipitating the polymer with acetone and collecting by filtration, the polymer was thoroughly washed with acetone and the sample was dried.
A certain amount of the bromoacetylated sample was hydrolyzed with 30 ml of a 2M KOH solution in ethanol-water (volume ratio 1:10), and acidified by adding 20 ml of a 4M aqueous HNO ₃ solution. Known amount of 0.04 M AgNO ₃ solution (5 to 15 m
l) and 2 ml of a saturated solution of iron ammonium alum were added, and titration was performed with a 0.05 M NH ₄ SCN solution until color was obtained. The hydroxyl value was determined as the number of mg of KOH required to neutralize bromoacetic acid necessary for bromoacetylating the hydroxyl group contained in 1.0 g of the resin.

(4) Measurement of molecular weight The molecular weight of the polyester resin was determined by the GPC method (gel permeation chromatography). A calibration curve was prepared from a polystyrene standard sample, and the number average molecular weight (Mn) in terms of styrene was determined. (5) Measurement of polyester resin composition The resin composition was analyzed by an NMR method (nuclear magnetic resonance spectrum) and an IR method (infrared absorption spectrum). (6) Preparation of Coated Plate The paint composition was coated on a tin plate (thickness: 0.22 mm, # 25 tin plating) so that the coating amount was 60 to 65 mg / dm ² , and the baking was not particularly described. 205 ° C
Baking was performed for -10 minutes.

(7) Evaluation of Curability (MEK Extraction Rate) of Coating Film A coated plate (W ₁ ) of known weight was prepared, and 1 ml of MEK (methyl ethyl ketone) was used per 2 cm ^{2 of} the coating film at a boiling point of 1 hour. Perform the extraction. Painted plate after extraction at 130 ° C for 1
After drying under the condition of time, the weight (W ₂ ) of the coated plate after extraction is determined. Further, the coating film is peeled by a decomposition method using concentrated sulfuric acid or an electrolytic peeling method, and the weight (W ₃ ) of the plate is determined. MEK of painted board
The extraction rate is obtained by the following equation. MEK extraction rate (%) = (W ₁ −W ₂ ) / (W ₁ −W ₃ ) × 1
00 evaluation ○: less than 20%, Δ: 20 to 40%, ×: 40%
Larger MEK extraction rate exceeds 40%, coating film has poor scratch resistance and corrosion resistance, blocking occurs due to stacking of coated plates, and especially in sheet coating, coating film softens in a wicket oven and melts. Occurs. (8) Evaluation of dissolution property Using 125 ml of distilled water per 1 cm ^{2 of the} coating film at 125 ° C.
An eluate was prepared by performing retort extraction for 30 minutes. The potassium permanganate consumption (ppm) of the eluate was measured by the method specified in the Ministry of Health and Welfare Notification No. 20. Evaluation ：: less than 10 ppm, Δ: 10 to 20 ppm,
×: 20 ppm or more

(9) Evaluation of retort resistance The coated plate was subjected to a retort treatment at 125 ° C. for 30 minutes, and the state of whitening, blisters, and flakes of the coating film was visually observed. Evaluation ：: good, Δ: slight whitening, blistering, and flakes ×: significant whitening, blisters, and flakes (10) Evaluation of adhesion The coated plate was subjected to retort treatment at 125 ° C. for 30 minutes, followed by coating. The film was cut in a 2 mm square in a 10 × 10 grid pattern, a cellophane tape peeling test was performed, and the peeling rate (%) was measured. Evaluation ：: less than 10%, Δ: 10 to 40%, ×: 40%
(11) Evaluation of workability The painted plate is bent with the painted surface outside, two plates of the same thickness as the painted plate are sandwiched, and then a 2 kg weight is dropped from a height of 50 cm and bent at 180 degrees. Processing was performed. Electric current was applied to the processed portion at a width of 2 cm at 6 V for 5 seconds, and a current value after 5 seconds was measured. Evaluation ：: less than 5 mA, Δ: 5 to 40 mA, ×: 40 m
A or more

(12) Confirmation Test of Interpenetrating Network Structure In the paint for cans of the present invention, the thermoplastic polyester resin and the thermosetting resin are substantially non-reactive, and the coating film is formed by the thermosetting resin. The network forms an interpenetrating network structure in which a thermoplastic polyester resin penetrates. The presence or absence of the formation of the interpenetrating network structure can be determined from the dependence of the MEK extraction rate upon baking time at 205 ° C. baking. A coating film having an interpenetrating network structure has an MEK extraction rate that tends to increase as the baking time increases, and exhibits properties not seen in conventional epoxy-phenol-based paints for cans. This is because the degree of interpenetration between the thermoplastic polyester resin and the thermosetting resin decreases due to the thermal motion of the thermoplastic polyester resin molecules. It was determined by IR and NMR measurements that the increase in MEK extraction rate during baking was not due to thermal decomposition of the resin. Evaluation ：: MEK extraction rate ≦ 40% and interpenetrating network structure ×: MEK extraction rate> 40% and / or non-interpenetrating network structure

Example 1 400 parts of dimethyl terephthalate, 370 parts of propylene glycol, 21 parts of ethylene glycol, and 1,4-butanediol 13 were placed in a reaction vessel.
And 0.18 part of magnesium acetate, and 0.29 part of tetra-n-butyl titanate were gradually added, and the reaction was continued for 4 hours until the reaction temperature reached 220 ° C. Next, 0.14 parts of triphenyl phosphite was added to raise the reaction temperature to 250 ° C., and the pressure of the reaction system was gradually reduced.
The mixture was reacted for 4 hours under reduced pressure of 5 mmHg or less to obtain a polyester resin. The glass transition point (Tg) of the obtained thermoplastic polyester resin is 81 ° C., and the acid value is 2 mg KO.
H / g, and the hydroxyl value was 4 mgKOH / g.
As a result of GPC measurement, the number average molecular weight was 16,000. The resin composition determined by the NMR method is such that the dicarboxylic acid component is 100 mol% of terephthalic acid, and the glycol component is 85 mol% of propylene glycol, 10 mol% of ethylene glycol, or 5 mol% of 1,4-butanediol. Met.

The thermoplastic polyester resin and Mycoat 1 which is a benzoguanamine resin manufactured by Mitsui Cytec Co., Ltd.
And a mixed solvent of cyclohexanone-solvesso 150 (mixing ratio =
1: 1, hereinafter referred to as a mixed solvent).
The paint solids content was adjusted to 25%. Note that 0.5 parts of dodecylbenzenesulfonic acid was added as an acid catalyst. According to the evaluation of the baked coating film, curability: 19%, dissolution: 2.5 pp
m, retort resistance: good, adhesion: 0% peeling, workability:
A result of 38 mA was obtained. The evaluation results are shown together with other examples in Table 1. In the confirmation test of the interpenetrating network structure, MEK extraction ratio ≦ 40%, no thermal decomposition of the resin, and it was confirmed that an interpenetrating network structure was formed.

Examples 2 to 4 Various polyester resins were produced in the same manner as in the thermoplastic polyester resin prepared in Example 1. The composition of each polyester resin is shown in Table 1. In the table, each component is shown in mol%. With respect to these polyester resins, Mycoat 105, which is a benzoguanamine resin, was mixed at a weight ratio of 80/20, and a mixed solvent was added to reduce the solid content of the paint to 25%.
Was prepared. In the same manner as in Example 1, a coating material containing 0.5 part of dodecylbenzenesulfonic acid as an acid catalyst was prepared. According to the evaluation of the baked film, Example 2; curability: 10%, dissolution: 2.0 ppm, retort resistance: good, adhesion: 0% peeling, workability: 33 m
A, Example 3: curability: 12%, dissolution: 2.5 ppm, retort resistance: good, adhesion: 0% peeling, workability: 37 m
A, Example 4; curability: 15%, dissolution: 4.1 ppm, retort resistance: good, adhesion: 0% peeling, workability: 36 m
A, the result was obtained. Table 1 shows the test results of the coating films obtained using each polyester.

Example 5 The thermoplastic polyester resin prepared in Example 1 and Mycoat 1128, a benzoguanamine resin manufactured by Mitsui Cytec Co., Ltd. in a weight ratio of 80 /
The mixture was adjusted to 20 and a mixed solvent was added to adjust the solid content of the paint to 25%. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. The paint was baked under baking conditions of 205 ° C. for 3 minutes, and the baked coating film was evaluated. Curability: 13%, dissolution: 6.3 p
pm, retort resistance: good, adhesion: 0% peeling, workability: 0.1 mA. The paint shown in this embodiment can be used for applications requiring curing by baking for a short time, such as a paint for correcting the inner surface of a can.

Comparative Example 1 A mixed solvent was added to the thermoplastic polyester resin prepared in Example 1, and
It was adjusted to 5%. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. When a coating film test was performed on this in the same manner as in Example 1, curability: 100%, dissolution: 0.1 ppm, and retort resistance:
Significant whitening, blistering, scouring, adhesion: 0%
Peeling and workability: A result of 0.3 mA was obtained. The evaluation results are shown in Table 2 together with other comparative examples.
In this comparative example having no thermosetting resin mainly composed of a thermosetting benzoguanamine resin, the coating film did not show curability, resulting in remarkably inferior retort resistance, and could not be applied as a can inner coating. Was.

Comparative Example 2 A polyester resin was prepared in the same manner as in Example 1. The glass transition temperature (Tg) of the obtained polyester resin is 60 ° C., and the acid value is 2 mgKOH /
g, and the hydroxyl value was 6 mgKOH / g. As a result of GPC measurement, the number average molecular weight (Mn) was 15,000.
Met. In the same manner as in Example 1, a polyester resin and Mycoat 105 were prepared at a weight ratio of 80/20 and a coating solid content of 25% using Mycoat 105, a benzoguanamine resin manufactured by Mitsui Cytec, and a mixed solvent.
Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. By evaluation of the baked coating film,
Curability: 32%, dissolution: 3.5 ppm, retort resistance: remarkable whitening, blistering, swelling, adhesion:
A result of 0% peeling and workability: 42 mA was obtained. The evaluation results are shown in Table 2 together with other comparative examples. When the Tg of the polyester resin is as low as 60 ° C., it is difficult to obtain sufficient retort resistance and workability even when combined with a thermosetting resin mainly composed of a thermosetting benzoguanamine resin. Was. Further, when applied as a paint for the inner surface of a can, the result that the adsorption of the flavor component was enormous was obtained.

Comparative Example 3 A polyester resin was prepared in the same manner as in Example 1. The glass transition temperature (Tg) of the obtained polyester resin is 70 ° C., and the acid value is 18 mg KOH.
/ G, and the hydroxyl value was 23 mgKOH / g.
As a result of GPC measurement, the number average molecular weight (Mn) was 700.
It was 0. In the same manner as in Example 1, a polyester resin and Mycoat 105 were prepared at a weight ratio of 80/20 and a coating solid content of 25% using Mycoat 105, a benzoguanamine resin manufactured by Mitsui Cytec, and a mixed solvent. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. When the baked coating film was evaluated, curability: 27%, dissolution: 8.9 ppm,
The results were as follows: retort resistance: slight whitening, blistering, flakes, adhesion: 0% peeling, workability: 73 mA. The evaluation results are shown in Table 2 together with other comparative examples. As shown here, when the acid value and hydroxyl value of the polyester resin were high and the molecular weight was low, the result that the processability was remarkably inferior was obtained.

Comparative Example 4 A polyester resin was prepared in the same manner as in Example 1. The obtained polyester resin has a glass transition temperature (Tg) of 52 ° C. and an acid value of 40 mg KOH.
/ G, and the hydroxyl value was 45 mgKOH / g.
As a result of GPC measurement, the number average molecular weight (Mn) was 330
It was 0. In the same manner as in Example 1, a polyester resin and Mycoat 105 were prepared at a weight ratio of 80/20 and a coating solid content of 25% using Mycoat 105, a benzoguanamine resin manufactured by Mitsui Cytec, and a mixed solvent. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. When the baked film was evaluated, the curability was 22%, the dissolution was 12 ppm, and the retort resistance was slight whitening, blistering, and scumming.
The results were as follows: adhesion: 35% peeling, workability: 90 mA. The evaluation results are shown in Table 2 together with other comparative examples. As shown here, the acid value of the polyester resin,
When the hydroxyl value was remarkably high and the molecular weight was low, the result was that the processability was remarkably deteriorated and that no interpenetrating network structure was formed.

Comparative Example 5 A polyester resin was prepared in the same manner as in Example 1. The glass transition temperature (Tg) of the obtained polyester resin is 71 ° C., and the acid value is 2 mgKOH /
g, and the hydroxyl value was 10 mgKOH / g. As a result of GPC measurement, the number average molecular weight (Mn) was 1000.
It was 0. In the same manner as in Example 1, a polyester resin and Mycoat 105 were prepared at a weight ratio of 80/20 and a coating solid content of 25% using Mycoat 105, a benzoguanamine resin manufactured by Mitsui Cytec, and a mixed solvent. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. When the baked coating film was evaluated, curability: 30%, dissolution: 7.3 ppm,
The results were as follows: retort resistance: slight whitening, blistering, flakes, adhesion: 0% peeling, workability: 48 mA. The evaluation results are shown in Table 2 together with other comparative examples. As shown here, when the number average molecular weight (Mn) of the polyester resin was as low as 10,000, the result that the processability was inferior was obtained.

(Comparative Examples 6 and 7) The thermoplastic polyester resin prepared in Example 1 was mixed with Mycoat 105, a benzoguanamine resin manufactured by Mitsui Cytec Co., Ltd., and the mixing ratio was 95/5 and 50/50. Two types of paints were made. 25% of paint solid content by adding mixed solvent
Was prepared. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. When the baked coating film was evaluated, the curability of Comparative Example 6 was 91:
%, Dissolution: 4.0 ppm, retort resistance: remarkable whitening, blistering, swelling, adhesion: 0% peeling, workability: 13 mA. In Comparative Example 7, the results were as follows: curability: 25%, dissolution: 22 ppm, retort resistance: good, adhesion: 40% peeling, and workability: 85 mA. The evaluation results are shown in Table 2 together with other comparative examples.
Are shown together. As shown here, when the mixing ratio of the polyester resin and the thermosetting benzoguanamine resin is as low as 5%, it is difficult to obtain sufficient curability and retort resistance. Was as high as 50%, it was difficult to obtain sufficient dissolution, adhesion and processability.

Comparative Example 8 The thermoplastic polyester resin prepared in Example 1 and Epicoat 1001, an epoxy resin manufactured by Yuka Shell Epoxy Co., were used in a weight ratio of 80/2.
The mixture was adjusted to 0, and a mixed solvent was added to adjust the solid content of the paint to 25%. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. When the baked coating film was evaluated, curability: 98%, dissolution:
26 ppm, retort resistance: remarkable whitening, blister,
The results were as follows: occurrence of scouring, adhesion: 0% peeling, workability: 73 mA. The evaluation results are shown in Table 2 together with other comparative examples. As shown here, when an epoxy resin that does not exhibit self-thermosetting is combined with a thermoplastic polyester resin, the results were that the curability, dissolution, retort resistance, and processability were significantly poor.

Comparative Example 9 The thermoplastic polyester resin prepared in Example 1 and Cymel 350, a melamine resin manufactured by Mitsui Cytec, were mixed at a weight ratio of 80/20, and a mixed solvent was added. The solid content of the paint was adjusted to 25%. Further, as in Example 1, 0.5 part of dodecylbenzenesulfonic acid was added as an acid catalyst. When the baked coating film was evaluated, curability: 1.0%, dissolution: 25 p
pm, retort resistance: good, adhesion: 0% peeling, workability: 0.3 mA. The evaluation results are shown in Table 2 together with other comparative examples. As shown here, when the melamine resin was used as the thermosetting resin in combination with the thermoplastic polyester resin, the result that the dissolution property was remarkably poor was obtained.

(Comparative Example 10) The thermoplastic polyester resin prepared in Example 1 and a phenolic resin, Hitachi Chemical Co., Ltd., Hitachi 4010, were mixed in a weight ratio of 80/20, and a mixed solvent was added. 25% paint solids
Was prepared. When the baked coating film was evaluated, the curability was:
86%, dissolution: 3.3 ppm, retort resistance: remarkable whitening, blistering, flakes, adhesion: 100% peeling, workability: 3.6 mA. The evaluation results are shown in Table 2 together with other comparative examples. As shown here, when the phenolic resin was combined with the thermoplastic polyester resin as the thermosetting resin, the results were remarkably inferior in curability, retort resistance and adhesion.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

The paint for cans of the present invention has the following features: (1) (A) a glass transition point of 65 ° C. or higher, an acid value of 15 or less, a hydroxyl value of 20 or less, and a number average molecular weight of 11,000 or more. And (B) a thermosetting resin mainly composed of a thermosetting benzoguanamine resin having a weight ratio of A: B = 90: 10 to 55:45. The thermoplastic polyester resin (A) and the thermosetting resin (B) mainly composed of a thermosetting benzoguanamine resin are substantially non-reactive, and (3) the thermosetting resin (A) and the thermosetting resin And a thermosetting resin (B) mainly composed of a water-soluble benzoguanamine resin, which can form an interpenetrating network structure in the coating film. Curable, curable Out resistance and retort sterilization of the combination excellent paint cans, in particular providing the can inner coating.

The specific thermoplastic polyester resin (A) serves as a base resin for the coating film. This specific base resin imparts excellent heat resistance, retort resistance and workability to the coating film and has a low level. The acid value and the hydroxyl value substantially prevent the reaction with the thermosetting resin (B) even under curing conditions, thereby improving the curability, retort resistance and workability of the coating film. Thus, in the paint of the present invention, the thermoplastic polyester resin (A) and the thermosetting resin (B) mainly composed of benzoguanamine are substantially non-reactive, and therefore, the curing of the resin in this paint is thermosetting. It proceeds by the reaction between the curable resins (B) and enables the formation of an interpenetrating network (IPN) in the coating film. In the paint of the present invention, a network accompanying the mutual curing of the thermosetting resins (B) is formed in a form incorporating the thermoplastic polyester resin (A), and the thermoplastic polyester resin penetrates in a form entangled with this network. This structure improves curability and retort resistance while maintaining excellent adhesion and workability.

[Brief description of the drawings]

FIG. 1 is a graph showing the correlation between paint baking time and MEK extraction rate for paint.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) B65D 43/02 B65D 43/02 Z F term (Reference) 3E061 AA15 AB04 AC02 AC09 AD01 BA01 BA02 BB02 3E084 AA02 AA12 AA22 AB01 BA01 CA01 CB01 CB04 GB17 LA02 4J038 DA172 DD001 DD071 GA03 GA06 MA13 MA14 PA19 PB04 PC02

Claims (9)

[Claims] (A) a glass transition point of 65 ° C. or more,
A thermoplastic polyester resin having the following acid value, a hydroxyl value of 20 or less, and a number average molecular weight of 11,000 or more,
(B) A paint for cans comprising: a thermosetting resin mainly composed of a thermosetting benzoguanamine resin in a weight ratio of A: B = 90: 10 to 55:45. 2. The coating composition for cans according to claim 1, wherein the thermoplastic polyester resin (A) is a polyester derived from a dibasic acid component mainly composed of terephthalic acid and a glycol component. 3. The paint for cans according to claim 1, wherein the thermoplastic polyester resin (A) and the thermosetting resin (B) are substantially non-reactive. 4. The method according to claim 1, wherein the thermoplastic polyester resin (A) and the thermosetting resin (B) can form an interpenetrating network structure in the coating film. Paint for cans. 5. The paint for cans according to claim 1, wherein the MEK extraction rate (MEK boiling point, 1 hour) in a cured state is 40% or less. 6. A coated metal plate for can making, which is obtained by applying the coating material for a can according to claim 1 to a metal plate and curing the metal plate. 7. The coating metal for cans according to claim 6, wherein the thermoplastic polyester resin (A) and the thermosetting resin (B) in the coating film form an interpenetrating network structure. Board. 8. A can comprising the coated metal plate according to claim 6. Description: 9. A can lid comprising the painted metal plate according to claim 6. Description: