JP2000290585A - Can coating material, coated can and coated can cap - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide polyester/acrylic can coating materials which are bisphenol A-free heat-curable coating materials and remarkably reduced in the amount of the coating components eluted, and coated cans and coated can caps which use such can coating materials. SOLUTION: Heat-curable can coating materials contain (A) a thermoplastic polyester resin having an acid value of not higher than 30 and a hydroxyl number of not higher than 40 and (B) a heat-curable acrylic resin at a weight ratio of component (A) to component (B) of 90:10 to 40:60. The thermoplastic polyester resin (A) preferably has a number average molecular weight of not smaller than 7,000, and the heat-curable acrylic resin (B) preferably has a number average molecular weight of not smaller than 2,000.

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 painted can and a painted can lid, and more particularly to a thermoplastic polyester resin and a self-curing acrylic resin in which the elution of low molecular weight components is significantly reduced. The present invention relates to a thermosetting can coating composition, and a painted can and a can lid using the thermosetting can coating composition.

[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.

[0003] As a paint for cans containing no bisphenol A, a polyester paint which has excellent adhesion to metals and does not generate toxic corrosive gas when incinerated is used.
Since the polyester resin alone has insufficient blister resistance and whitening resistance during heat sterilization, an alkyd-amino paint containing an amino resin or the like has been conventionally used. However, such alkyd-amino paints have a problem that fumes are generated at the time of baking due to the presence of relatively low molecular weight amino resins and low molecular weight substances in polyester resins in the paint components.

[0004]

Japanese Patent Application Laid-Open No. 10-60069 discloses a paint which prevents the generation of such fumes by synthesizing an amino resin in the presence of a polyester resin and an acrylic resin. A thermosetting coating composition comprising a so-called polyester-acryl-amino composite resin in which a resin, an acrylic resin and an amino resin are partially bonded is described. However, in the thermosetting coating composition, a low molecular weight curing agent such as melamine is blended, and such a low molecular weight curing agent has a three-dimensional structure in a coating film formed by thermosetting. Cannot be expected to be completely taken in, and unreacted ones inevitably remain. For this reason, when used as an inner coating, the elution of this low molecular weight component becomes a problem. Accordingly, an object of the present invention is to provide a bisphenol A-free thermosetting paint, in which the amount of the paint component eluted is remarkably reduced, a polyester-acrylic can paint, a paint can using such a can paint, and a paint. It is to provide a can lid.

[0005]

That is, according to the present invention, a thermoplastic polyester resin (A) having an acid value of 30 or less and a hydroxyl value of 40 or less, and a thermosetting acrylic resin (B).
(A) and (B) in a weight ratio of A: B = 90: 10 to 40:60. The thermoplastic polyester resin (A) is 7000
It has the above number average molecular weight, the carboxylic acid component is composed of 80 to 100 mol% of terephthalic acid and 20 to 0 mol% of carboxylic acids other than terephthalic acid, and the alcohol component is composed of 60 to 100 mol% of propylene glycol and other than propylene glycol. It is preferred that the polyester is composed of 40 to 0 mol% of the alcohol component. The thermosetting acrylic resin (B) has a number average molecular weight of 2,000 or more, has a crosslinkable functional group of 60 mmol / 100 g or more, (meth) acrylic acid ester of 30 to 70% by weight, and styrene of 10 to 70% by weight. An acrylic resin derived from 60% by weight, 10 to 40% by weight of (meth) acrylamide or a functional derivative thereof, and 0 to 5% by weight of (meth) acrylic acid is preferred.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Acrylic resin is cured by forming a network structure by heating, and in a polyester-acrylic paint, a linear polyester resin or a curing agent resin is incorporated in the network structure. Form a film. However, if a low molecular weight component is present in the polyester resin or a low molecular weight curing agent resin is blended, it is difficult to completely incorporate these low molecular weight components into this network structure, and the unreacted curing agent component Etc. inevitably remain. For this reason, these low molecular weight components were eluted, and there was a problem in using such a polyester-acrylic paint as a paint for the inner surface of a can.

In the present invention, a highly polymerized thermoplastic polyester resin having an acid value of 30 or less and a hydroxyl value of 40 or less is used as the thermoplastic polyester resin. In addition, the elution of low molecular weight components can be effectively reduced. In addition, since a self-curing acrylic resin that causes a curing reaction by heating itself is used as the acrylic resin, it is not necessary to contain a low-molecular-weight curing agent component, which has conventionally been a problem of elution, and the curing agent component is There is no elution.

The thermoplastic polyester resin and the thermosetting acrylic resin hardly react when mixed in a solvent and then heat-cured. The polyester resins pass through the network structure of the acrylic resin and mutually react. Since a penetrating three-dimensional network structure is formed, a coating film excellent in processability, coating film adhesion, retort resistance, and curability can be obtained.
That is, the coating film formed by the coating material of the present invention does not cause peeling of the coating film even when the coated plate is subjected to processing such as bending, and also when subjected to retort sterilization, whitening and blisters, soaking. No boiling or peeling of the coating film occurs, and the film has excellent coating film characteristics with a boiling methyl ethyl ketone extraction rate of 40 wt% or less, which will be described in the examples below.

In the thermosetting paint of the present invention, the thermoplastic polyester resin (A) and the acrylic resin (B) are mixed with 9
0:10 to 40:60, especially 80:20 to 50: 5
It is important that it is contained at a weight ratio of 0, and it is preferable that the main component be a thermoplastic polyester resin. That is, when the thermoplastic polyester resin is contained more than the above range, a mutual penetrating network structure by the network structure of the acrylic resin is not formed, and the above characteristics cannot be maintained. Further, when the amount of the thermoplastic polyester resin is less than the above range and the amount of the thermosetting acrylic resin is more than the above range, the curing of the coating film proceeds excessively and, among the above-mentioned properties, the decrease in workability particularly becomes remarkable.

(Thermoplastic polyester resin) In the present invention, the thermoplastic polyester resin (A) has an acid value of 30.
Hereinafter, it is particularly preferably 10 or less, and the hydroxyl value is also preferably 40 or less, particularly preferably 15 or less. That is, as described above, the thermoplastic polyester resin used in the present invention is highly polymerized so that low molecular weight components are not present, and therefore, the amount of eluted substances is extremely reduced.

The thermoplastic polyester resin (A) comprises:
The carboxylic acid component is composed of 80 to 100 mol% of terephthalic acid and 20 to 0 mol% of carboxylic acid other than terephthalic acid, and the alcohol component is propylene glycol 60.
It is preferable that the polyester is made of from 100 to 100 mol% and from 40 to 0 mol% of alcohol components other than propylene glycol. When the terephthalic acid component is less than the above range, the flexibility and the whitening resistance, particularly the whitening resistance to water vapor, decrease. If the propylene glycol component is less than the above range, the solvent solubility and the whitening resistance will decrease.

The carboxylic acids other than terephthalic acid include:
Isophthalic acid, orthophthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, dicarboxylic acids such as dimer acid, and polyvalent carboxylic acids such as trimellitic acid include, but more than aliphatic carboxylic acids Aromatic carboxylic acids are preferred because the amount of eluted substances is small. As alcohols other than propylene glycol, ethylene glycol, 1,3-propanediol,
1,4-butanediol, 2,3-butanediol,
1,3-butanediol, 1,5-pentanediol,
1,6-hexanediol, neopentyl glycol,
In addition to glycols such as diethylene glycol, dipropylene glycol, glycerin, 1,4-cyclohexanediol and p-xylylene glycol, polyols such as trimethylolpropane and pentaerythritol can be mentioned.

The thermoplastic polyester resin (A) used in the present invention is produced by an ordinary method for producing a high molecular weight polyester by a transesterification method or a direct esterification method.
It is highly polymerized so that the number average molecular weight is 7000 or more, especially 10,000 or more. However, when used as a paint for the inner surface of a can, it is necessary to avoid using heavy metals or compounds which pose a problem in hygiene as a catalyst or an additive.
Suitable polycondensation catalysts include oxides and acetates of metals such as titanium, antimony, magnesium, and germanium, tetraisopropyl titanate, and tetra-n-butyl titanate. 0.01 to 0.5 mol%.

The thermoplastic polyester resin (A) used in the present invention is a polyester having a glass transition temperature of 60 ° C. or higher, particularly 70 ° C. or higher, as measured by a differential scanning calorimeter. It is preferable from the viewpoint of properties and the like. If the glass transition temperature is lower than 60 ° C., blisters and whitening tend to occur in the heat sterilization temple, and the coating film has a strong tendency to adsorb playbar components in food.

(Thermosetting Acrylic Resin) The thermosetting acrylic resin (B) used in the present invention is a self-curing acrylic resin configured to cause a curing reaction by itself without requiring the presence of a curing agent. The thermosetting acrylic resin (B) is an acrylic resin mainly composed of a (meth) acrylic ester, an aromatic vinyl monomer, and an ethylenically unsaturated monomer having a crosslinkable functional group. It is preferably a resin. This thermosetting acrylic resin is also preferably highly polymerized so as to have a number average molecular weight (Mn) of 2000 or more, especially 3500 or more.

The (meth) acrylates include:
Methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl (meth) acrylate, (meth) acryl Examples thereof include isoamyl acid, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and n-octyl (meth) acrylate. Among them, preferred esters are ethyl acrylate and methyl methacrylate. However, the (meth) acrylic acid described above or below indicates acrylic acid or methacrylic acid.

The aromatic vinyl monomer improves the compatibility between the thermoplastic polyester resin (A) and the thermosetting acrylic resin (B). Examples thereof include styrene,
α-methylstyrene and the like can be mentioned, and styrene can be particularly preferably used. Examples of the ethylenically unsaturated monomer include (meth) acrylamides such as methylolacrylamide and butoxymethylacrylamide, and functional derivatives such as N-methylol compounds thereof, and (meth) acrylic acid. These components contain a crosslinkable functional group such as a hydroxyl group, a methylol group, or an amino group in an amount of 60 mmol or more, particularly 90 mmol or more per 100 g of the thermosetting acrylic resin. Is preferred, because the molecular weight associated with curing can be increased.

The most preferred thermosetting acrylic resin (B) is (meth) acrylic ester 30 to 70
% Of styrene, 10 to 60% by weight of styrene, 10 to 40% by weight of (meth) acrylamide or a functional derivative thereof, and 0 to 5% by weight of (meth) acrylic acid. The thermosetting acrylic resin is synthesized by performing a polymerization reaction of the above components at 50 to 130 ° C. for 1 to 4 hours in the presence of a radical polymerization initiator or the like. Benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile and the like can be used as the radical polymerization initiator. The radical initiator is used in an amount of about 0.5 to 7 parts by weight based on 100 parts by weight of the monomer component.

(Thermosetting Can Coating) The thermosetting can coating of the present invention comprises a thermoplastic polyester resin (A) and a thermosetting acrylic resin (B) having the above composition, and (A): (B) = 90: 10 to 40:60, preferably 80:20 to 50:50
The thermoplastic polyester resin (A) and the thermosetting acrylic resin (B) separately prepared are mixed in a solvent at a temperature of 50 to 150 ° C. for about 1 to 5 hours. A coating composition can be prepared by dissolving in a solvent. Alternatively, the coating composition can also be prepared by subjecting a separately prepared thermoplastic polyester resin (A) solution to a polymerization reaction of the above-mentioned thermosetting acrylic resin (B). The solvent is appropriately selected from conventionally known solvents used in solvent-type paints, for example, toluene, xylene, solvesso, ethyl acetate, butyl acetate, methyl ethyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoacetate and the like. Among them, cyclohexanenone and Solvesso can be preferably used. The above-mentioned coating composition is preferably dissolved in a solvent at a concentration of 15 to 40% by weight as a solid content, though it varies depending on the coating means used.

The paint for a thermosetting can of the present invention can be compounded with various compounding agents conventionally used in this kind of paint based on a formulation known per se.
Fillers, matting agents, lubricants, leveling agents and the like can be added. The paint for a thermosetting can of the present invention is baked at a temperature of 160 to 260 ° C. for 1 to 20 minutes,
The thermoplastic polyester resin and the thermosetting acrylic resin hardly react and form a network structure in which the thermosetting acrylic resin involves the polyester resin and are cured.

(Coating Can and Coating Lid) The can to which the above-mentioned thermosetting can coating material of the present invention is applied is formed by drawing / deep drawing or drawing / ironing of a metal material or a resin-coated metal material. A conventionally known can body such as a seamless can or a three-piece can by bonding or welding can be employed. 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 above-mentioned thermosetting paint of the present invention is applied to both the outer surface and the inner surface or only the inner surface of the coating can body and the coating can lid of the present invention. The thermosetting can coating composition of the present invention is highly safe because it is composed only of food-hygienic substances, and the amount of resin components eluted is significantly reduced. Is preferred. 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 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 200 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 film thickness of 1 to 20 μm, especially 3 to 20 μm
It is preferably in the range of 15 μm.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. “%” And “parts” used in this example are based on weight unless otherwise indicated.

(1) Measurement of acid value 0.2 g of polyester resin was dissolved in 20 ml of a mixed solvent (benzyl alcohol 10 ml + chloroform 10 ml), and 0.1 M phenol red / ethanol solution was used as an indicator. Mg of KOH per gram of resin required for neutralization by titration with alcohol solution
The number was determined.

(2) Measurement of hydroxyl value 1.0 g of a polyester resin was dissolved in 5 ml of nitrobenzene, and 0.5 ml of bromoacetyl bromide was added for bromoacetylation. After precipitating the polymer with acetone and collecting by filtration, the polymer was thoroughly washed with acetone and the sample was dried.
A fixed amount of the bromoacetylated sample was hydrolyzed with 30 ml of a 2M KOH ethanol-water (1:10 volume ratio) solution, and the solution was acidified by adding 20 ml of a 4M HNO ₃ aqueous solution. Known amount of 0.04 M AgNO ₃ solution (5-15 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 the color was obtained. The hydroxyl value was determined as the number of mg of KOH required to neutralize bromoacetic acid necessary for bromoacetylating a hydroxyl group contained in 1.0 g of the resin.

(3) Measurement of molecular weight The molecular weight of polyester resin and acrylic resin is GP
Method C (gel permeation chromatography)
A calibration curve was prepared from the polystyrene standard sample, and the number average molecular weight (Mn) in terms of styrene was determined.

(4) Measurement of Polyester Resin Composition Analysis by NMR method (nuclear magnetic resonance spectrum) and GC method (gas chromatograph) after alcoholysis,
The molar ratio of the acid component and the alcohol component was determined.

(5) Measurement of acrylic resin composition IR method (infrared absorption spectrum) and G of thermal decomposition product
The resin composition was analyzed by the C method and the MS method (mass spectrum). Further, the amount of the crosslinkable functional group was measured for the resin 1 by NMR.
It was determined as the number of m-mol per 00 g.

(6) Preparation of Coated Plate The paint composition was applied on a tin plate (thickness: 0.22 mm, # 25 tin plating) so that the coating amount was 60 to 65 mg / dm ² , It was baked under the condition of minutes.

(7) Evaluation of Curability (MEK Extraction Rate) of Coating Film A coated plate (W1) of known weight was prepared, and 1 ml of MEK (methyl ethyl ketone) was extracted per 2 cm ^{2 of} the coating film at a boiling point for 1 hour. Do. The extracted coated plate is dried at 130 ° C. for 1 hour, and the weight (W2) of the extracted coated plate is determined. Further, the coating film is peeled by a decomposition method using concentrated sulfuric acid or an electrolytic peeling method, and the weight (W3) of the plate is determined. The MEK extraction rate of the coated plate was obtained from the following equation. MEK extraction rate (%) = (W1-W2) / (W1-W3) Evaluation ：: Less than 20% ：: 20-40% ×: 4
0% or more A coating film having a curability of 40% or more has poor scratch resistance and corrosion resistance, causing blocking due to a stack of painted plates, and particularly, in a sheet coat, a coating film is softened in a wicket oven and melted. Is generated.

[0034] (8) with distilled water evaluation coating 1 cm ² per 1ml of dissolution, 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 5 ppm △: 5 to 10 ppm
×: 10 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 judged. Evaluation ：: Good △: Slight whitening, blistering, and scorching ×: Remarkable whitening, blistering, and scorching

(10) Evaluation of Adhesion The coated plate was retorted at 125 ° C. for 30 minutes, and cut into 2 × 10 × 10 × 10 grids on the coating film.
A cellophane peel test was performed to measure the peel%. ：: less than 10% △: 10 to 40% ×: 40% or more

(11) Evaluation of workability The painted plate was bent with the painted surface outside, two plates having the same thickness as the painted plate were sandwiched, and a 2 kg weight was dropped from a height of 50 cm.
A degree of bending was performed. 5 at 6V for 2cm width of processed part
The current was applied for 5 seconds, and the current value after the application for 5 seconds was obtained. Evaluation ：: Less than 5 mA Δ: 5 to 40 mA ×: 4
0mA or more

(Example 1) 400 parts of dimethyl terephthalate, 370 parts of propylene glycol, 1.
50 parts of 4-butanediol and 0.29 parts of tetra-n-butyl titanate were added, and the temperature was gradually raised.
The reaction was continued for 4 hours until the temperature reached 20 ° C. Then 250 ° C
The temperature of the reaction system was gradually reduced to 0.2 mmH
The reaction was carried out for 4 hours under reduced pressure of not more than g to obtain a thermoplastic polyester resin. The obtained thermoplastic polyester resin had an acid value of 2 mgKOH and a hydroxyl value of 5 mgKOH. As a result of GPC measurement, the number average molecular weight (Mn)
Was 16,000. The resin composition by NMR was such that the carboxylic acid component was 100 mol% of terephthalic acid, and the alcohol component was 80 mol% of propylene glycol and 20 mol% of 1.4 butanediol.

330 parts of butoxymethylacrylamide,
420 parts of ethyl acrylate, methyl methacrylate 3
00 parts, styrene 450 parts, benzoyl peroxide 75 parts,
550 parts of Solvesso 150 are mixed, and 750 parts of cyclohexanone and 200 parts of Solvesso 150 are mixed in a solvent.
At 110 ° C. under a nitrogen stream, the mixture was added dropwise over 1 hour to carry out a polymerization reaction. After completion of the dropwise addition, the temperature was maintained at 110 ° C. for another 2 hours to polymerize the thermosetting acrylic resin. Mn of the obtained thermosetting acrylic resin was 3,800, and the crosslinkable reactive group was present in the resin in an amount of 140 m-mol / 100 g.

A part of the above thermosetting acrylic resin solution is taken, and the above thermoplastic polyester resin and a mixed solvent of cyclohexanone-sorbesso 150 (mixing ratio = 1: 1 by weight, hereinafter referred to as mixed solvent). And add 1
The mixture was dissolved and mixed for 3 hours while stirring at 10 ° C. The mixing ratio between the thermoplastic polyester resin and the thermosetting acrylic resin was 80/20 in weight ratio, and the coating solid content was adjusted to 25%.

From the evaluation of the baked coating film, the results were as follows: curability: 32%, dissolution: 1.1 ppm, retort resistance: slightly whitened, adhesion: 0% peeling, workability: 0.9 mA. The evaluation results are shown in Table 1 together with other examples and comparative examples.

(Examples 2 to 4) Using the thermoplastic polyester resin and the thermosetting acrylic resin prepared in Example 1, the mixing ratio of the thermoplastic polyester resin and the thermosetting acrylic resin was the same as in Example 1. 70/30 each,
A 60/40, 50/50 solid content 25% paint was prepared. Table 1 summarizes the evaluation results of the baked coating films.

(Comparative Examples 1 to 3) Using the thermoplastic polyester resin and the thermosetting acrylic resin prepared in Example 1, the mixing ratio of the thermoplastic polyester resin and the thermosetting acrylic resin was the same as in Example 1. 100/0 each,
A 95/5, 30/70 solid content 25% paint was prepared.
Table 2 summarizes the evaluation results of the baked coating films.

In Comparative Example 2 in which the mixing ratio of the thermoplastic polyester resin and the thermosetting acrylic resin was 95/5, the curing was insufficient, the curability was 88%, the dissolution was 0.9 ppm,
As a result, retort resistance: remarkable flakes, adhesion: 0% peeling, and workability: 0.3 mA were obtained. In Comparative Example 3 in which the mixing ratio of the thermoplastic polyester resin and the thermosetting acrylic resin was 30/70, the composition was too cured, and the curability was 6%, the dissolution was 5.2 ppm, and the retort resistance was significant whitening. , Adhesion: 20% peeling, workability: 56 mA
The result was obtained. In addition, microscopic observation of the coating film after the retort showed that resin components which were not completely compatible with each other were precipitated in the inside of the coating film. It is assumed that the precipitate is an excessive thermosetting acrylic resin component.

Comparative Example 4 600 parts of methacrylic acid, 900 parts of methyl methacrylate, 75 parts of benzoyl peroxide,
A mixed solution of 550 parts of Solvesso 150 was prepared, and dropped into a solvent of 750 parts of cyclohexanone and 200 parts of Solvesso 150 at 110 ° C. for 1 hour under a nitrogen stream to carry out a polymerization reaction. After completion of the dropwise addition, the temperature was kept at 110 ° C. for another 2 hours to polymerize the acrylic resin.

The Mn of the obtained acrylic resin was 4000, and the carboxyl group was present in the resin in an amount of 465 m-mol / 100 g. A portion of the acrylic resin solution was taken, the thermoplastic polyester resin used in Example 1 and a mixed solvent were added, and the mixture was dissolved and mixed at 110 ° C. for 3 hours while stirring. The mixing ratio between the thermoplastic polyester resin and the acrylic resin was 60/40 by weight, and the solid content of the paint was adjusted to 25%. From the evaluation of the baked coating film, the results were as follows: curability: 99%, dissolution: 5.1 ppm, retort resistance: remarkable whitening and scumming, adhesion: 0% peeling, workability: 91 mA. The evaluation results are shown in Table 2 together with other comparative examples.

In this comparative example in which the acrylic resin did not have a crosslinkable functional group, the coating film did not show curability, and the retort resistance was extremely poor. In addition, the compatibility between the thermoplastic polyester resin and the acrylic resin was poor, and the processability was extremely poor.

(Comparative Example 5) 480 parts of dimethyl terephthalic acid, 480 parts of dimethyl isophthalic acid, 1.4
200 parts of butanediol, 150 of ethylene glycol
Parts, 360 parts of propylene glycol, 15 parts of trimethylolpropane, and 0.5 part of titanium butoxide were added, and the temperature was gradually raised to 220 ° C. over 4 hours to start the esterification reaction. Then, a low-pressure initial polymerization for 0.5 hour was carried out, the temperature was raised to 250 ° C, and further 250 ° C,
The reaction was performed at 0.2 mmHg or less for 1 hour. Then 2
Cool to 00 ° C, add 4 parts of trimellitic anhydride, add 22 parts
The mixture was reacted at 0 ° C. for 1 hour to obtain a polyester resin.

The acid value of the obtained polyester resin is 40 m
gKOH, and the hydroxyl value was 45 mgKOH.
As a result of GPC measurement, the number average molecular weight (Mn) was 50
00. A thermosetting acrylic resin solution was prepared in the same manner as in Example 1. From the obtained polyester resin and mixed solvent, the mixing ratio of the polyester resin and the thermosetting acrylic resin was 70/30, and the solid content was 25%. A paint was prepared. From the evaluation of the baked coating film, curability: 8%, dissolution: 1
6 ppm, retort resistance: slight whitening, adhesion: 15
%, Workability: 53 mA was obtained. The evaluation results are shown in Table 2 together with other examples and comparative examples.

When the polyester resin was a polyester resin having a high acid value and a high hydroxyl value, the result that the dissolution property and processability were remarkably inferior was obtained in combination with the thermosetting acrylic resin.

Comparative Example 6 330 parts of butoxymethylacrylamide, 420 parts of ethyl acrylate, 300 parts of methyl methacrylate, 450 parts of styrene, 150 parts of benzoyl peroxide, and 550 parts of Solvesso 150 were mixed.
750 parts of cyclohexanone and Solvesso 150 200
In a portion of the solvent, the mixture was added dropwise at 110 ° C. over 1 hour under a nitrogen stream to carry out a polymerization reaction. After completion of the dropwise addition, the temperature was kept at 110 ° C. for another 2 hours to polymerize the thermosetting acrylic resin.

The Mn of the obtained thermosetting acrylic resin is 1
200, and the crosslinkable reactive group was 140 m-mol / 10
It was present in the resin in an amount of 0 g. A part of the above thermosetting acrylic resin was taken and, in the same manner as in Example 1, combined with the thermoplastic polyester resin of Example 1 to obtain a solid content of 25%
A paint was prepared. The mixing ratio between the thermoplastic polyester and the thermosetting acrylic resin was 60/40 by weight. According to the evaluation of the baked coating film, curability: 34%, dissolution: 17 pp
m, retort resistance: slightly whitened, adhesion: 0% peeling, workability 57 mA were obtained. The evaluation results are shown in Table 2 together with other comparative examples. When the thermosetting acrylic resin was an acrylic resin having a small number average molecular weight, a result was obtained in which the dissolution property and processability were extremely poor.

(Examples 5 to 8) Various thermoplastic polyester resins and thermosetting acrylic resins were synthesized in the same manner as in Example 1. Furthermore, various paints were prepared by combining a thermoplastic polyester resin and a thermosetting acrylic resin in the same manner as in Example 1. Table 3 shows the details of the obtained paints and the evaluation results of the baked coating films.

(Example 9) The thermoplastic polyester resin and the mixed solvent used in Example 8 were placed in a reaction vessel and dissolved by heating to prepare a thermoplastic polyester resin solution. Butoxymethylacrylamide 270 parts, ethyl acrylate 150 parts, methyl methacrylate 330 parts, styrene 750 parts, benzoyl peroxide 60 parts, Solvesso 15
0550 parts were mixed and dissolved to prepare a thermosetting acrylic monomer solution, which was dropped into the thermoplastic polyester resin solution at 100 ° C. for 1 hour under a nitrogen stream to carry out a polymerization reaction. After the completion of the dropping, 100 ° C. for another 2 hours
And the thermosetting acrylic resin was polymerized.

The solid content of the obtained coating composed of the thermoplastic polyester resin and the thermosetting acrylic resin was 25%, and the mixing ratio between the thermoplastic polyester resin and the thermosetting acrylic resin was 70/30. The details of the paint and the evaluation results of the baked coating film are shown in Table 3.

[0056]

[Table 1]

[0057]

[Table 2]

[0058]

[Table 3]

[0059]

According to the present invention, in the thermosetting can coating composition,
The weight ratio of the thermoplastic polyester resin (A) having an acid value of 30 or less and a hydroxyl value of 40 or less and the self-curing thermosetting acrylic resin (B) in a ratio of A: B = 90: 10 to 40:60. Thus, the elution of low molecular weight components, which had conventionally been a problem of elution, can be effectively reduced. Further, since the thermosetting acrylic resin (B) forms a three-dimensional network structure and cures, it has a network structure penetrating through with the thermoplastic polyester resin (A). It is possible to obtain a coating film having excellent properties, corrosion resistance, retort resistance, and curability. Further, as the thermoplastic polyester resin (A), the carboxylic acid component is composed of 80 to 100 mol% of terephthalic acid and 20 to 0 mol% of carboxylic acid other than terephthalic acid, and the alcohol component is composed of 60 to 100 mol% of propylene glycol. Alcohol components other than propylene glycol 4
By using a polyester comprising 0 to 0 mol%, a thermosetting paint which is particularly preferable as an inner coating can be obtained. Furthermore, in the thermosetting paint of the present invention, bisphenol A is not contained, the elution of low molecular weight components is significantly reduced, and the adhesion of the coating film is maintained even when subjected to retort sterilization. Since the coating film is hardly peeled off, the can body and the can lid using this thermosetting coating material as the inner coating material have an advantage that the content is excellent in flavor and flavor characteristics.

Claims (11)

[Claims] 1. A thermoplastic polyester resin (A) having an acid value of 30 or less and a hydroxyl value of 40 or less, and a thermosetting acrylic resin (B), wherein A: B = 90: 10 to 40:60 by weight. A thermosetting paint for cans, characterized in that it is contained in a proportion. 2. A thermoplastic polyester resin (A) comprising 70
The coating composition for cans according to claim 1, wherein the coating composition has a number average molecular weight of 00 or more. 3. The thermoplastic polyester resin (A) is 10
The paint for cans according to claim 1, wherein the paint has a following acid value and a hydroxyl value of 15 or less. 4. The thermoplastic polyester resin (A) wherein the carboxylic acid component is composed of 80 to 100 mol% of terephthalic acid and 20 to 0 mol% of carboxylic acid other than terephthalic acid, and the alcohol component is composed of 60 to 100 mol of propylene glycol. The coating composition for a can according to any one of claims 1 to 3, wherein the coating composition is a polyester composed of 40% to 0% by mole of an alcohol component other than propylene glycol. 5. The thermosetting acrylic resin (B) is 2,000
The paint for cans according to any one of claims 1 to 4, wherein the paint has a number average molecular weight as described above. 6. The thermosetting acrylic resin (B) contains 60 mmol.
The paint for cans according to any one of claims 1 to 5, wherein the paint has a crosslinkable functional group of at least / 100g. 7. The thermosetting acrylic resin (B) is (meth)
Acrylic ester 30 to 70% by weight, styrene 10
7 to 60% by weight, an acrylic resin derived from (meth) acrylamide or 10 to 40% by weight of a functional derivative thereof, and 0 to 5% by weight of (meth) acrylic acid. The paint for cans according to 1. 8. A coated can which is obtained by applying and baking the paint for a can according to any one of claims 1 to 7 on a metal. 9. The coated can according to claim 8, wherein the coating has a boiling MEK extraction rate of 40% by weight or less. 10. A coated can lid obtained by applying and baking the paint for a can according to any one of claims 1 to 7 on a metal. 11. The coating can lid according to claim 10, wherein the coating has a boiling MEK extraction rate of 40% by weight or less.