JPH11256097A - Resin composition for can coating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition which is excellent in boiling water, retort and content resistances, processibility and sanitariness by blending a phenol resin with an epoxy modified polyester resin which is prepared by reacting a polyester resin and an epoxy resin. SOLUTION: A phenol resin (D) is blended with an epoxy modified polyester resin (C) which is prepared by reacting a polyester resin (A) containing desirably not more than 40% of preferably 1, 4-cyclohexanedicarboxylic acid as a dicarboxylic acid component and/or desirably 40-100% of 1, 2-propylene glycol and/or 1, 4-cyclohexanedimethanol as a glycol component with an epoxy resin (B) which is preferably a bisphenol A epoxy resin and/or a bisphenol F epoxy resin. The weight ratio of the resin A to resin B is preferably A/B=100/5-100/80. That of the resin C to resin D is preferably 100/1-100/50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is applied to food and beverage metal cans containing a saturated copolymerized polyester resin as an active ingredient, and is excellent in retort resistance, blocking resistance, processability and adhesion. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a can coating resin composition having excellent hygiene properties, and particularly to a can coating resin composition suitable for the inner surface of a can.

[0002]

2. Description of the Related Art A paint for the inner surface of a can is used for the purpose of not impairing the flavor and smell of the contents and for preventing the corrosion of the can material due to various foods.
First, it is required to be non-toxic, resistant to heat sterilization, excellent in adhesiveness and workability.

[0003] Polyvinyl chloride resins and epoxy-phenol resins are currently frequently used as coating agents for the inner surface of cans, but they have the following serious problems at present.

[0004] First, a polyvinyl chloride resin has excellent retort resistance, content resistance, and processability, but is a substance having serious hygiene problems such as carcinogenicity due to the vinyl chloride monomer remaining in the resin. It has been pointed out that. In addition, when incinerating discarded cans, toxic and corrosive chlorine gas, hydrogen chloride gas, and highly toxic dioxin are generated from polyvinyl chloride resin, which poses a problem that leads to corrosion of incinerators and environmental pollution. is there. Further, the coating process of the polyvinyl chloride resin is complicated, for example, the adhesiveness to metal as a can material is insufficient, and it is necessary to coat the resin after treatment with an epoxy resin.

Next, an epoxy-phenol resin has a high baking temperature, and tends to cause poor appearance such as foaming during baking. Further, they are mainly spray-painted because of their poor workability.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, a polyester resin can which is easy to paint and bake, has excellent workability and adhesion to metal, is toxic and does not generate corrosive gas when incinerated. Attempts have been made to apply it to paints for interior surfaces, but a polyester resin having excellent blister resistance and whitening resistance when heat-sterilizing contents showing salt or acidity has not been obtained. Furthermore, it is inferior in hygiene such as ethanol extractability.

[0007] For example, Japanese Patent Publication No. 60-42829,
Japanese Patent Application Publication No. 61-36548 discloses a can inner coating resin made of a saturated polyester resin alone, which is excellent in blister resistance and whitening resistance to heat treatment using only boiling water or steam, but still has insufficient performance and has poor coating performance. Deterioration of the surface state or reduction in gloss occurs, and blistering or whitening occurs in a heat treatment in a salt solution or an acidic atmosphere assuming the contents, resulting in poor appearance. Also, none of the resins obtained by blending these resins with an amino resin exhibit sufficient coating performance with respect to heat treatment.

Further, Japanese Patent Application Laid-Open No. 7-113059 proposes a combination of an epoxy-modified polyester resin and an amino resin, and Japanese Patent Application Laid-Open No. 8-325513 proposes a combination of a polyester resin, an epoxy resin and an amino resin. Although the mechanical properties of the coating film are relatively good, hygienic properties such as ethanol extractability are not sufficient.

[0009]

The inventor of the present invention has conducted intensive studies to solve the above-mentioned drawbacks of the polyester resin in terms of blister resistance and whitening resistance. The present inventors have succeeded in finding a can coating resin composition which is not only excellent, but also extremely excellent in hygiene, and reached the present invention.

That is, the present invention provides (1) an epoxy-modified polyester resin (C) obtained by reacting a polyester resin (A) with an epoxy resin (B) and a phenol resin (D).
A resin composition for can coatings, characterized by comprising
(2) A resin composition for can coating, wherein the epoxy resin (B) according to the above (1) is bisphenol A and / or bisphenol F epoxy resin, (3)
(1) The resin composition for can paint, wherein the dicarboxylic acid component in the polyester resin (A) according to (1) or (2) contains 1,4-cyclohexanedicarboxylic acid.
(4) The glycol component in the polyester (A) according to any one of (1), (2) and (3) is 1,2-
(5) The resin composition for a can coating, which comprises propylene glycol and / or 1,4-cyclohexanedimethanol, (5) any one of the above (1), (2), (3) or (4) (6) The metal plate for can formation, characterized in that a coating film containing the resin composition for can coating according to (1), (2), (3) or (4) is formed.
A metal can, wherein a coating film containing the resin composition for a can coating according to any one of the above is formed.

The polyester resin (A) used in the present invention
In the dicarboxylic acid component, the proportion of the aromatic dicarboxylic acid is preferably 60 to 100 mol%, more preferably 7 to 100 mol%.
0-100 mol%, and the proportion of terephthalic acid therein is preferably 40-100 mol%, more preferably 50-100 mol%. As aromatic dicarboxylic acids other than terephthalic acid, for example, isophthalic acid,
Orthophthalic acid, naphthalenedicarboxylic acid and the like can be mentioned, and isophthalic acid is preferred. If the proportion of the aromatic dicarboxylic acid is less than 60 mol%, or if the amount of terephthalic acid is less than 40 mol% of the total aromatic dicarboxylic acids, processability, blister resistance, and whitening properties are poor.

The polyester resin (A) used in the present invention
Other dicarboxylic acid components included in: succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecandionic acid, aliphatic dicarboxylic acids such as dimer acid, cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid Examples thereof include acids, alicyclic dicarboxylic acids such as cyclohexene dicarboxylic acid, and unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and terpene-maleic acid adduct. The other dicarboxylic acid component is preferably used at 0 to 40 mol%, more preferably 0 to 30 mol%. If the content of the other dicarboxylic acid component exceeds 40 mol%, the hot water resistance of the coating film is impaired, blistering and whitening are likely to occur, and flavor properties are reduced. As other dicarboxylic acids, sebacic acid and 1,4-cyclohexanedicarboxylic acid are hot water resistant,
From the viewpoint of processability, 1,4-cyclohexanedicarboxylic acid is more preferable.

The polyester resin (A) used in the present invention preferably contains 1,2-propylene glycol and / or 1,4-cyclohexanedimethanol among glycol components. Of the glycol components, 1,2-propylene glycol and / or 1,
The content of 4-cyclohexanedimethanol is 40 to 10
0 mol%, and more preferably 60 to 100 mol%.
Preferably it is mol%. If the proportion of 1,2-propylene glycol and / or 1,4-cyclohexanedimethanol is less than 40 mol%, the polyester resin becomes crystalline and becomes difficult to handle, and the hot water resistance of the coating film is impaired, causing blistering and whitening. Tends to occur.

Other glycol components used in the present invention include ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, Dimethylol heptane, dimethylol pentane,
2-ethyl-2-butylpropanediol, 3-methyl-1,5-pentanediol, 3-ethyl-1,5-pentanediol, 3-propyl-1,5-pentanediol, 3-methyl-1,6 -Hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8
-Octanediol, 4-propyl-1,8-octanediol, diethylene glycol, triethylene glycol, cyclohexane dimethylol, tricyclodecane glycols, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, bisphenols ethylene oxide or propylene oxide derivatives And water-added bisphenols. Preferred are ethylene glycol, diethylene glycol, 1,4-butanediol, and neopentyl glycol. Of these, ethylene glycol and diethylene glycol are particularly preferred from the viewpoint of hot water resistance and processability. .

[0015] The polyester resin (A) used in the present invention is used in an amount of 0 to 0 with respect to all acid components or all glycol components.
It is preferable to copolymerize a polyfunctional carboxylic acid and / or polyhydric alcohol having a functionality of 3 or more in an amount of 5 mol%, more preferably 0.5 to 3 mol%. Examples of the trivalent or higher polycarboxylic acid component include trimellitic acid, pyromellitic acid,
Benzophenone tetracarboxylic acid and the like are exemplified, and trifunctional or higher polyhydric alcohols include glycerin, trimethylolethane, trimethylolpropane, mannitol, sorbitol, pentaerythritol, α-methylglucoside and the like. Preferred are trimellitic acid and trimethylolpropane. By copolymerizing these three or more functional components, the crosslink density can be increased, and blistering and whitening can be suppressed. On the other hand, if the content of these trifunctional components exceeds 5 mol%, the polyester resin becomes hard and the processability deteriorates.

The polyester resin (A) used in the present invention preferably has a reduced viscosity of 0.3 dl /
g or more, more preferably 0.5 dl / g or more, and the glass transition temperature is 0 ° C. or more, more preferably 10 ° C. or more, and further preferably 45 ° C. or more. 0.3dl / reduced viscosity
If the amount is less than g, the coating film becomes brittle, resulting in poor workability and hot water resistance. When the glass transition temperature is less than 0 ° C., the hot water resistance is poor, and blistering and whitening are likely to occur.
In addition, flavor properties are also deteriorated.

Since the polyester resin (A) used in the present invention is epoxy-modified, it must be provided with an acid value (carboxyl group). Preferably 50~500eq / 10 ⁶ g as an acid number, more preferably from 80~200eq / 10 ⁶ g. 500eq
When the amount exceeds / 10 ⁶ g, blistering and whitening are liable to occur, and processability is also reduced. This acid value decreases after the epoxy modification because it reacts with a glycidyl group. The acid value of the epoxy-modified polyester resin (C) after epoxy modification is not limited, but is preferably 30 to 100 eq / 10 ⁶ g because the acid value has an effect of improving metal adhesion.
It is preferable to keep in the range of.

The acid value of the polyester resin (A) used in the present invention has an important meaning as described above. To adjust the acid value, a method of adding a polycarboxylic anhydride at the latter stage of the polycondensation is used. It is preferable to take

Examples of the polycarboxylic anhydride used for such acid addition include phthalic anhydride, tetrahydrophthalic anhydride, succinic anhydride, trimellitic anhydride,
Pyromellitic anhydride, hexahydrophthalic anhydride and the like can be mentioned. Preferred is trimellitic anhydride.

In the resin composition for can coating composition of the present invention, an epoxy resin is used to modify the polyester, and the epoxy equivalent of these epoxy resins is 170 to 5000 (g / e).
q) is preferred. More preferably, the epoxy equivalent is 800 to
2500. If the epoxy equivalent is less than 170, the adhesion is poor, and if it exceeds 5,000, the compatibility with the polyester resin (A) is reduced or the epoxy modification becomes difficult. Examples of the epoxy resin include bisphenol A epoxy resin, bisphenol F epoxy resin, phenol novolak type epoxy resin obtained by reacting phenol novolak resin with epichlorohydrin, epoxy-modified polybutadiene, various aliphatic epoxy resins, and alicyclic resins. Epoxy resins and the like can be mentioned. Of these, bisphenol A epoxy resin and bisphenol F epoxy resin are particularly preferably used alone or in combination, respectively, from the viewpoint of paint properties and hygiene.

The resin composition for can coating of the present invention has an epoxy-modified polyester resin obtained by previously reacting the polyester resin (A) with the epoxy resin (B) preferably in the ratio of the formula (1) by a known method. Use (C). If the epoxy resin (B) is less than 5% by weight with respect to the polyester resin (A), good curability cannot be obtained, and retort resistance and content resistance cannot be obtained. If it exceeds 50% by weight, the coating film becomes brittle and the workability decreases. In this case, since the glycidyl group of the epoxy resin is excessively mixed and modified in a stoichiometrically excess with respect to the acid value (concentration of carboxyl group) of the polyester resin, unreacted epoxy resin may remain. (A) / (B) = 100/5 to 100/80 (weight ratio) Formula 1

In the resin composition for can coating of the present invention, phenol resin (D) is preferably used as a cross-linking agent in a ratio represented by the formula (2). By using a phenol resin as a crosslinking agent in the epoxy-modified polyester resin of the present invention, compared with the amino resin of the prior art, surprisingly, sanitary properties such as ethanol extractability are remarkably improved, and further processing Excellent in properties and retort resistance. Epoxy-modified polyester resin (C) and phenolic resin (D)
The mixing ratio of (C) / (D) = 1 as shown in the second equation.
00/1 to 100/50, preferably (C) /
(D) = 100/5 to 20 (weight ratio). If the phenolic resin (D) is less than 1% by weight with respect to the resin composition (C), a sufficient cured coating film cannot be obtained, and good retort resistance and content resistance cannot be obtained. If the ratio is more than 50% by weight, the coating film becomes brittle, resulting in reduced workability and reduced hygiene. (C) / (D) = 100/1 to 100/50 (weight ratio) 2nd formula

The phenolic resin (D) used in the resin composition for can coating of the present invention is not particularly limited,
Examples thereof include resol-type resins obtained by reacting phenols with an aldehyde in the presence of an alkali catalyst, and novolak resins obtained by reacting phenols with an aldehyde in the presence of an acidic catalyst, which are preferable as a crosslinking agent. These phenolic resins include phenols such as phenol, cresol, bisphenol A and bisphenol F;
Mono- to trimethylol compounds such as alkylphenols such as t-butylphenol, condensates thereof, or alkyl ether compounds thereof, or various modified products thereof such as epoxy-modified, oil-modified, miramine-modified, amine-modified, and amide-modified products. Can be used.

Further, for the purpose of improving the curability, other curing agents such as a phenol resin and an amino resin may be used in combination within a range that does not lower the sanitary product. Examples of the amino resin include formaldehyde adducts such as urea, melamine, and benzoguanamine, and alkyl ether compounds of alcohols having 1 to 6 carbon atoms. Specifically, methoxymethylolated urea, methoxylated methylol-N, N-ethyleneurea, methoxymethylol dicyandiamide, methoxylated methylolmelamine,
Methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated methylol benzoguanamine, and the like, but preferably methoxylated methylol melamine, butoxylated methylol melamine, and methylolated benzoguanamine, each of which may be used alone or in combination. it can

The resin composition for can coating of the present invention contains known inorganic pigments such as titanium oxide and silica, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, phosphoric acid and its esterified products, and various amine-based curing catalysts. Known additives such as a surface smoothing agent, an antifoaming agent and a dispersant can be blended.

The resin composition for can coating of the present invention is formed into a coating in a state of being dissolved in a known organic solvent. As the organic solvent used for coating, for example, toluene, xylene, solvesso, ethyl acetate, butyl acetate, methyl ethyl ketone, cyclohexanone, isophorone, methyl cellosolve, butyl cellosolve, ethylene glycol monoacetate, etc. Selected.

The present invention will be specifically described below with reference to examples. In the examples, “part (s)” means “part (s) by weight”. Each measurement item followed the following method. (1) Measurement of Resin Composition The molar ratio of an acid component and an alcohol component was determined by nuclear magnetic resonance spectroscopy and analysis by gas chromatography after alcoholysis. (2) Measurement of reduced viscosity (dl / g) 0.1 g of polyester was dissolved in 25 cc of a mixed solvent of phenol / tetrachloroethane (weight ratio: 6/4) and measured at 30 ° C. using an Ubbelohde viscometer. (3) Measurement of glass transition temperature The glass transition temperature was measured at a heating rate of 20 ° C./min using a differential scanning calorimeter (DSC). The sample was placed in an aluminum pan and capped and sealed. (4) Measurement of acid value 0.2 g of polyester was dissolved in 20 ml of chloroform, and titrated with a 0.1N KOH ethanol solution.
0 per ⁶ g was determined equivalents (eq / 10 ⁶ g).

Evaluation Items (5) Preparation of Test Piece A paint composition was applied to a TFS plate (Tinfree Steel, 70 m
m × 150 mm × 0.3 mm) with a bar coater so that the film thickness becomes 10 to 15 μm.
After preliminary drying at 30 ° C. for 30 minutes, hardening and baking at 270 ° C. for 120 seconds was performed, and this was used as a test piece. (6) Boiling water resistance After treating the test piece for 2 hours in boiling distilled water, whitening of the coating film,
The state of blisters was visually determined. ：: good (excellent whitening, no blister) △: slight (within 5% of the entire area) whitening or blistering ×: remarkable (total area 5% or more) whitening or blistering (7) retort resistance After the test piece was treated under steam at 130 ° C. for 30 minutes, the coating film was whitened. The state of blistering was visually determined. ：: good excellent (no whitening at all, no blister) △: slight (within 5% of the entire area) whitening or blistering ×: remarkable (5% or more of total area) whitening or blistering (8) Content resistance After the test piece was treated in an aqueous solution containing 3 wt% of sodium chloride and 3 wt% of lactic acid at 130 ° C. for 30 minutes, the whitening of the coating film and the state of the blister were visually determined. Good: excellent (no whitening, no blister) Fair: slight (within 5% of the total area) whitening or blistering ×: significant (5% or more of total area) whitening or blistering (9) Processed part resistance Boiling water After two TFS substrates of the same thickness were sandwiched between two TFS substrates and bent in the direction of 180 °, the test pieces were treated in boiling distilled water for 2 hours, and the bent portion was observed with a loupe to check for cracks in the coating film. judge. ：: good (no cracks at all parts) Δ: slight cracks (5 or less cracks of about 1 mm in length or 1 or less cracks of about 3 mm over all parts) ×: cracks (all (6 or more cracks about 1 mm in length or 2 or more cracks about 3 mm or more in length) (10) Sanitary test A test piece with a coating area of 100 cm2 is immersed in 100 cc of a 20% ethanol aqueous solution, 60 at 120 ° C under pressure
Minute immersion treatment, weight loss before and after treatment (%)
Was measured. The extract after the immersion treatment was subjected to a wavelength of 200 using a U-3210 type spectrophotometer manufactured by Hitachi, Ltd.
An ultraviolet absorption spectrum of about 300 nm was measured, and the maximum value of the absorption value (%) was evaluated. The smaller the numerical value for both the weight loss and the absorption value, the better.

Synthesis Example: Synthesis of Polyester Resin (a) 485 parts of dimethyl terephthalic acid, 485 parts of dimethyl isophthalic acid, 200 parts of ethylene glycol, 510 parts of propylene glycol, 13 parts of trimethylolpropane, and 0.5 part of titanium butoxide were used. Charge 3L flask, 4
The temperature was gradually raised to 230 ° C. over a period of time to carry out transesterification. Then, the pressure-reduced initial polymerization was performed to 10 mmHg over 30 minutes, the temperature was raised to 250 ° C., and the late polymerization was performed at 250 ° C. and 1 mmHg or less for 60 minutes. Then, the mixture was cooled to 230 ° C. under a nitrogen stream, 9.2 parts of trimellitic anhydride was charged, stirred for 20 minutes, and then added to obtain a polyester resin (a). The polyester resin (a) was subjected to composition analysis by NMR or the like. As a result, the acid component was terephthalic acid 50 mol%, isophthalic acid 50 mol%, trimellitic acid 1 mol% (post addition), and the glycol component was propylene glycol 69 mol. %, Ethylene glycol 30 mol%, trimethylolpropane 1 mol%, reduced viscosity 0.62 dl / g, acid value 72 equivalent / 10
⁶ g, a pale yellow polyester resin having a glass transition temperature of 72 ° C. Table 1 shows the results.

Synthesis Example: Polyester resins (b) to (f)
In the same manner as in Synthesis Example (a), a polyester resin of the present invention having a resin composition shown in Table 1 was synthesized.

Synthesis Example: Synthesis of Epoxy-Modified Polyester Resin (g) 100 parts of the polyester resin (a) was replaced with cyclohexanone 4
Five parts and 45 parts of Solvesso-150 were heated and dissolved at 80 ° C., and then 20 parts of Epicoat # 1004 (Yukaka Epoxy Co., Ltd.), a bisphenol A epoxy resin, was dissolved. After complete dissolution, 1 part of N, N-dimethylbenzylamine was added, the temperature was raised to 100 to 110 ° C, and an addition reaction was performed. When the acid value of the reaction varnish reaches about 60% of the initial value, 30 parts of cyclohexanone, Solvesso-1
50 30 parts were added and cooled, and the resin for paint of the present invention (k)
I got Table 3 shows the results.

Synthesis Example: Synthesis of Epoxy-Modified Polyester Resins (h) to (l) In the same manner as the epoxy-modified polyester resin (g), the epoxy-modified polyester resin of the present invention whose resin composition is shown in Table 2 was used. Synthesized.

EXAMPLE 1 100 parts by weight of the epoxy-modified polyester resin (g) of the present invention and REGITOP PL-4523 which is a phenol resin
(Gunei Chemical Industry Co., Ltd.) 15 Solid parts As a catalyst, 0.15 part of dodecylbenzenesulfonic acid was mixed and evaluated by the method described above. This coating has good processability,
It has excellent retort resistance and content resistance, and has excellent hygiene. Table 3 shows the results.

Examples 2 to 6 Evaluations were made in the same manner as in Example 1. Table 3 shows the results.

Comparative Examples 1 to 4 Evaluations were made in the same manner as in Example 1. Comparative Example 1 uses an amino resin instead of a phenol resin. Comparative Example 2 is a combination of a polyester resin and a phenol resin that are not epoxy-modified. Comparative Examples 3 and 4 are combinations of a polyester resin, an epoxy resin, and an amino resin that are not epoxy-modified. Table 4 shows the results.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

[0038]

[Table 4]

As is clear from Table 5, the resin composition for can coating composition of the present invention has excellent coating film properties such as boiling water resistance, content resistance, and processed part boiling water resistance, and furthermore has excellent hygiene properties. It turns out that it is excellent.

[0040]

The paint applied to the inner surface of the food can must be non-toxic by nature and must be resistant to heat sterilization. The resin composition for can coating of the present invention has boiling water resistance,
It has excellent retort resistance, content resistance, workability, etc., and has excellent hygiene properties, and is particularly useful for the inner coating of food and beverage cans. Furthermore, since it is excellent in processability, it is possible to perform a pre-coating process in which a flat plate is applied before can-making and then processed in addition to a normal spray coat.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08G 59/24 C08G 59/24 59/62 59/62

Claims (6)

[Claims] 1. A resin composition for a can coating composition comprising a phenol resin (D) mixed with an epoxy-modified polyester resin (C) obtained by reacting a polyester resin (A) with an epoxy resin (B). Stuff. 2. A resin composition for can coating, wherein the epoxy resin (B) according to claim 1 is bisphenol A and / or bisphenol F epoxy resin. 3. A resin composition for can paint, wherein the dicarboxylic acid component in the polyester resin (A) according to claim 1 or 2, contains 1,4-cyclohexanedicarboxylic acid. 4. The polyester component (A) according to claim 1, wherein the glycol component contains 1,2-propylene glycol and / or 1,4-cyclohexanedimethanol. Resin composition for can coating. 5. A metal plate for forming a can, wherein a coating film containing the resin composition for a can coating according to claim 1, 2, 3, or 4 is formed. 6. A metal can, wherein a coating film containing the resin composition for a can coating according to claim 1, 2, 3, or 4 is formed.