JP2001172363A - Modified epoxy resin and can coating composition containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a modified epoxy resin which, while enabling the excellent properties of conventional can coating materials to be retained, has a reduced content of low-mol.-wt. components, especially phenols, causative of the deterioration of flavor and to obtain a can coating composition containing the same. SOLUTION: This modified epoxy resin is prepared by reacting an epoxy resin having a number average mol.wt. of 2,000-8,000 with an alkyl-substituted monophenol the sum of carbon atoms of substituents of which is 0-4 and an alkyl-substituted aromatic monocarboxylic acid the sum of carbon atoms of substituents of which is 0-4. The modified resin satisfies the requirements that the monophenol and the aromatic carboxylic acid block 40-80% and 5-40% of epoxy groups, respectively; that 60-95% of epoxy group are blocked; and that the contents of unreacted monophenol and unreacted aromatic monocarboxylic acid are each 300 ppm or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a modified epoxy resin, a method for producing the same, and a composition for a can coating composition using the modified epoxy resin.

[0002]

2. Description of the Related Art A high-molecular epoxy resin is a material suitable for a paint for cans using a phenol formaldehyde resin or a melamine formaldehyde resin as a curing agent. In particular, it has excellent water resistance, processability, chemical resistance, and adhesiveness, and is therefore regarded as a material that is extremely suitable for a paint for the inner surface of a can. A so-called food can filled with food is usually subjected to a heat sterilization treatment after filling. It is known that when this treatment is performed, a very small amount of a low-molecular component is eluted from the coating film, although the amount is extremely small. This eluted component is not preferable in terms of taste and hygiene. Among them, phenols have a great influence on flavor properties.

[0003] Japanese Patent Application Laid-Open No. 8-319339 discloses a method for improving flavor and workability, but does not disclose elution of phenols. According to the prior art, it has been extremely difficult to reduce low-molecular components, especially phenols, which are in doubt about flavor and hygiene.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to remove low molecular weight components, in particular, phenols, which cause deterioration of flavor while maintaining excellent physical properties of conventional can coatings, and which are in doubt about hygiene. We are trying to reduce it. Furthermore, the present invention provides a paint for cans which has an extremely small amount of elution from the coating film and has excellent hygiene properties and flavor properties.

[0005]

Means for Solving the Problems The composition for can coating of the present invention, which has excellent performance as a can coating excellent in hygiene and flavor, having very little elution from the coating film, is prepared by the following method. Is achieved by using a modified epoxy resin synthesized by the method as a raw material for paint for cans.

That is, the present invention is as follows. (1) (a) An epoxy resin having a number average molecular weight of 2,000 to 8,000, an alkyl-substituted monophenol having a total carbon number of 0 to 4 and an alkyl-substituted aromatic compound having a total carbon number of 0 to 4 A modified epoxy resin obtained by reacting an aromatic monocarboxylic acid, wherein (b) 40 to 80% of epoxy groups are sealed by the monophenol and 5 to 5% of epoxy groups are reacted by the aromatic monocarboxylic acid. 40% sealed and (c)
The total sealing ratio of the epoxy group is 60% or more and 95% or less,
Further, (d) the unreacted amount of the monophenol and the unreacted amount of the aromatic monocarboxylic acid are each 3
A modified epoxy resin having a content of not more than 00 ppm. (2) The modified epoxy resin according to the above (1), wherein the total sealing ratio of epoxy groups is 85% or more and 95% or less. (3) First, an epoxy resin having a number average molecular weight of 2,000 to 8,000 is reacted with an alkyl-substituted monophenol having a total of 0 to 4 carbon atoms of a substituent, and then the total number of carbon atoms of the substituent is further reduced to 0. A method for producing a modified epoxy resin, comprising reacting an alkyl-substituted aromatic monocarboxylic acid of (1) to (4) with each other. (4) 5 to 50 parts by weight of at least one resin selected from phenol formaldehyde resin and melamine formaldehyde resin and 100 parts by weight of the modified epoxy resin according to the above item 1 or 2, and a curing accelerator. A composition for paint for cans, comprising 1 part by weight or less and a solvent.

Hereinafter, the present invention will be described in detail. As the epoxy resin used as a raw material of the present invention, any epoxy resin having two or more glycidyl groups in the molecule can be used. Examples include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, etc. Among them, bisphenol type epoxy resin, especially bisphenol A type epoxy resin is particularly preferable. If necessary, two or more epoxy resins may be used.

The number average molecular weight of the starting resin is preferably from 2,000 to 8,000. If the number average molecular weight of the raw material resin is less than 2,000, the final coating film becomes brittle, and if it exceeds 8,000, the viscosity becomes high, and none of them is suitable for the purpose of the present invention as a paint.

The substituent used in the present invention has 0 to 4 carbon atoms.
Alkyl-substituted monophenols (hereinafter sometimes simply referred to as monophenols) include o-cresol and m-
Cresol, p-cresol, o-ethylphenol,
m-ethylphenol, p-ethylphenol, o-propylphenol, m-propylphenol, p-propylphenol, o-isopropylphenol, m-isopropylphenol, p-isopropylphenol,
o-normal butylphenol, m-normal butylphenol, p-normal butylphenol, o-isobutylphenol, m-isobutylphenol, p-isobutylphenol, o-tert-butylphenol,
There are m-tert-butylphenol, p-tert-butylphenol and the like, and phenol having 0 carbon atoms in the substituent can also be used, and these can be used alone or in combination of two or more. Among them, p-tert-butylphenol is suitable.

The substituent used in the present invention has 0 to 4 carbon atoms.
Examples of the alkyl-substituted aromatic monocarboxylic acid (hereinafter sometimes simply referred to as aromatic monocarboxylic acid) include o-methylbenzoic acid, m-methylbenzoic acid, p-methylbenzoic acid, o-ethylbenzoic acid, m-ethylbenzoic acid, p-ethylbenzoic acid, o-propylbenzoic acid, m-propylbenzoic acid, p-propylbenzoic acid, o-isopropylbenzoic acid, m-isopropylbenzoic acid, p-isopropylbenzoic acid, o- N-butyl benzoic acid, m-n-butyl benzoic acid, p-n-butyl benzoic acid, o-isobutyl benzoic acid, m-isobutyl benzoic acid, p-isobutyl benzoic acid, o-tert-butyl benzoic acid, m-tert-butyl There are benzoic acid, p-tert-butyl benzoic acid, etc., and benzoic acid having 0 carbon atoms in the substituent can also be used. It can be used in combination or German or two. Above all, benzoic acid is suitable.

The sealing ratio of the epoxy group by the above-mentioned monophenol is required to be 40% to 80%. The sealing ratio of the epoxy group by the aromatic monocarboxylic acid is 5%.
~ 40% is required. When the sealing ratio of the epoxy group by the monophenol is less than 40% or the sealing ratio of the epoxy group by the aromatic monocarboxylic acid is less than 5%, the total sealing ratio of the target modified epoxy resin is 60% to It is difficult to make it 95%. When the sealing ratio of the epoxy group by the monophenol exceeds 80% or when the sealing ratio of the epoxy group by the aromatic monocarboxylic acid exceeds 40%, the monophenol and the aromatic monocarboxylic acid are used in combination. By doing so, the purpose of the present invention of reducing the unreacted monophenol and the aromatic monocarboxylic acid is lost.

The total epoxy resin encapsulation rate of the starting epoxy resin must be 60% to 95%. When the total sealing ratio is 85% to 95%, the amounts of unreacted monophenol and aromatic monocarboxylic acid can be further reduced, which is advantageous. If the total encapsulation rate exceeds 95%, a large amount of the unreacted aromatic monocarboxylic acid remains, and if the total encapsulation rate is less than 60%, a large amount of residual epoxy groups remains, and both have poor elution properties. Become. The encapsulation rate is adjusted by adjusting the amount of the alkyl-substituted monophenol having a total of 0 to 4 carbon atoms of the substituent and the alkyl-substituted aromatic monocarboxylic acid having a total of 0 to 4 carbon atoms of the substituent to be reacted. can do.

The reaction is carried out at a temperature between 100 ° C. and 250 ° C.
It is preferable to proceed by stirring at a temperature of preferably 150 ° C. to 200 ° C. for 1 hour to 100 hours in the presence of a catalyst. If the reaction temperature is lower than 100 ° C., the viscosity of the resin becomes extremely high, and if the reaction temperature exceeds 250 ° C., an undesirable side reaction occurs and gelation is likely to occur.

It is preferable to use a catalyst for the reaction. For example, sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium methoxide, potassium methoxide, sodium carbonate, potassium carbonate, lithium carbonate,
Alkaline metal hydroxides such as calcium carbonate, tertiary amines such as imidazole, 2-methylimidazole and tributylamine; onium salts such as tetrabutylammonium bromide and tetraphenylphosphonium iodide;
There are phosphines such as triphenylphosphine, and metal salts of lithium naphthenate, cobalt naphthenate, tin octoate, and the like, and two or more kinds can be used in combination. The amount of the catalyst is preferably used in the range of 5 ppm to 1000 ppm. If it is less than 5 ppm, there is substantially no effect of adding the catalyst, and if it exceeds 1000 ppm, the reaction becomes extremely fast,
Not practically suitable.

In the reaction, a solvent such as toluene, xylene, methyl isobutyl ketone or methyl ethyl ketone may be used. Particularly when a high molecular weight epoxy resin is reacted, the use of a solvent is advantageous because the viscosity in the reaction system is reduced. Two or more solvents may be used in combination.

In order to reduce the unreacted monophenol and the unreacted aromatic monocarboxylic acid in the obtained modified epoxy resin to 300 ppm or less, respectively, first, the above-mentioned monophenol is first reacted to increase the epoxy equivalent. After confirming that the reaction does not occur, the object is achieved by reacting the aromatic monocarboxylic acid. When the order of the reaction is reversed and the aromatic monocarboxylic acid is reacted first and then the monophenol is reacted, a large amount of the unreacted monophenol remains in the resin.

The modified epoxy resin is prepared by adding a resin such as a phenol formaldehyde resin or a melamine formaldehyde resin in an amount of 5 to 50 parts by weight based on 100 parts by weight of the modified epoxy resin, and if necessary, a curing accelerator such as phosphoric acid or paratoluene sulfate. Acids such as sulfonic acid, imidazoles such as imidazole, 2-methylimidazole, 2-ethyl-4-methyl-imidazole, and the like were mixed in an amount of 1 part by weight or less with respect to 100 parts by weight of the modified epoxy resin, and a solvent was excellent. Can paint can be produced.

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, each measuring method adopted in the examples is as follows.

(1) Measurement of Monophenols and Aromatic Monocarboxylic Acids Remaining in Modified Epoxy Resin Residual monophenols and aromatic monocarboxylic acids contained in the modified epoxy resin were measured by gel permeation chromatography (GPC method). ) Was measured under the following conditions. The sample was prepared by dissolving a modified epoxy resin in THF so as to obtain 0.4 g / 10 cc. The residual amount was determined from a separately prepared calibration curve. Analyzer: Waters 840 system Column: Showa Denko SHODEX 805L x 4 Detector: Waters Mode1 440 UV 280nm Flow rate: 1ml / mim. Mobile phase: tetrahydrofuran Injection amount: 15 μl (2) Measurement of epoxy equivalent The epoxy equivalent was measured by the method shown in JIS K7236.

(3) Measurement of potassium permanganate consumption Among the eluted components from the coating film, potassium permanganate consumption is determined by the following method with reference to the method shown in the Food Sanitation Law. It was measured. Extraction conditions: Distilled water and a coating film sample were placed in an autoclave at a rate of 1 cm ² / ml and extracted at 125 ° C. for 30 minutes. Measurement: The method described in the Food Sanitation Law
Titration was performed with a 0.01 N aqueous potassium permanganate solution. (4) Measurement of the elution amount of p-tert-butylphenol The elution amount of p-tert-butylphenol was measured by the liquid chromatography under the following conditions. The extract for potassium permanganate consumption measurement was concentrated 1000-fold to obtain a sample. The residual amount was determined from a separately prepared calibration curve. Analyzer: Waters 840 system Column: Waters NOVA PACK C18 Detector: Waters M-490 UV280nm Flow rate: 1.5 ml / min. Mobile phase: Solution A = distilled water / methanol (80/20% by weight) Solution B = acetonitrile Injection amount: 15 μl Gradient Time (min) 0 5 30 40 60 Solution A (%) 80 50 200 00 Solution B (% ) 20 50 80 100 100

[0021]

Example 1 Bisphenol A type epoxy resin 1 having a number average molecular weight of 4000 and an epoxy equivalent of 2000 g / eq
000 g was charged into a reaction vessel having an internal volume of 2 L, and heated to 180 ° C. At the time of uniform dissolution, 52.5 g of p-tert-butyl phenol was added with stirring. It was confirmed that 2 g of an n-butanol solution of potassium hydroxide (10% potassium hydroxide concentration) was added dropwise and mixed uniformly. 10
The reaction was carried out for 180 hours at 180 ° C. with stirring. When the epoxy equivalent of the reaction product was measured, it was 7030 g / eq, and it was confirmed that 70% of the epoxy groups of the raw material resin had reacted. Further, 12.0 g of benzoic acid was added and reacted at 180 ° C. for further 10 hours. The epoxy equivalent of the reaction product was 21,000 g / eq, which was 90% of the raw material resin.
It was confirmed that the epoxy group had reacted. When the amounts of unreacted p-tert-butylphenol and benzoic acid were measured by the GPC method, they were 120 ppm and 90 pp, respectively.
m. Using this modified epoxy resin, a paint for cans was prepared with the following composition, and the film thickness was 60 to 70 mg / 10
It was applied to an aluminum foil having a thickness of 0.1 mm so as to be 0 cm ² and dried at 200 ° C. for 10 minutes to obtain a coating film sample. When the eluted amount from the coating film was measured, the consumption amount of potassium permanganate was 2.0 ppm, and the eluted amount of p-tert-butylphenol was 10 ppb.

Amount (parts by weight) Modified epoxy resin 24.0 Xylene 28.35 Ethylene glycol monoisopropyl ether 12.16 Isobutanol 12.16 Cyclohexanone 12.16 Hitachilanol 3013 (*) 15.0 * Trade name of Hitachi Chemical Co., Ltd .: (Phenol formaldehyde resin, solid form 40%)

[0023]

Example 2 1000 g of the bisphenol A type epoxy resin used in Example 1 was charged into a 2 L reaction vessel,
Heated to 180 ° C. At the time of uniform dissolution, 45.0 g of p-tert-butyl phenol was added with stirring. It was confirmed that 2 g of an n-butanol solution of potassium hydroxide (10% potassium hydroxide concentration) was added dropwise and mixed uniformly. The reaction was carried out with stirring at 180 ° C. for 15 hours.
When the epoxy equivalent of the reaction product was measured, it was 5300 g / eq.
It was confirmed that 60% of the epoxy groups of the starting resin had reacted. Further, 6.1 g of benzoic acid was added, and the mixture was further reacted at 180 ° C. for 10 hours. When the epoxy equivalent of the reaction product was measured, it was 7050 g / eq, and it was confirmed that 70% of the epoxy groups of the raw material resin had reacted.
The amounts of unreacted p-tert-butylphenol and benzoic acid measured by GPC were 90 ppm and 7 ppm, respectively.
It was 0 ppm. Using this modified epoxy resin, a paint for cans was prepared in the same composition as in Example 1, and applied to an aluminum foil having a thickness of 0.1 mm so as to have a film thickness of 60 to 70 mg / 100 cm ² . After drying for 10 minutes, a coating film sample was obtained. When the eluted amount from the coating film was measured, the consumption amount of potassium permanganate was 6.0 ppm, and the eluted amount of p-tert-butylphenol was 8 ppb.

[0024]

Example 3 1000 g of the bisphenol A type ethoxy resin used in Example 1 was charged into a 2 L internal volume reaction vessel.
Heated to 180 ° C. At the time of uniform dissolution, 42.7 g of p-ethylphenol was added while stirring. It was confirmed that 2 g of an n-butanol solution of potassium hydroxide (10% potassium hydroxide concentration) was added dropwise and mixed uniformly. 10
The reaction was carried out for 180 hours at 180 ° C. with stirring. When the epoxy equivalent of the reaction product was measured, it was 6950 g / eq, and it was confirmed that 70% of the epoxy groups of the raw material resin had reacted. Furthermore, p-tert-butyl benzoic acid 17.8
g of the mixture was further reacted at 180 ° C. for 10 hours. When the epoxy equivalent of the reaction product was measured, it was 21,200 g / eq, and it was confirmed that 90% of the epoxy groups of the raw material resin had reacted. The amounts of unreacted p-ethylphenol and p-tert-butylbenzoic acid measured by GPC were 70 ppm and 130 ppm, respectively. Using this modified epoxy resin, a paint for cans was prepared in the same composition as in Example 1, and the film thickness was 60 to 70 mg / 100 cm.
As become ² was applied to the aluminum foil with a thickness of 0.1mm 200
It dried at 10 degreeC for 10 minutes, and obtained the coating film sample. When the eluted amount from the coating film was measured, the potassium permanganate consumption was 3.0 ppm and the eluted amount of p-ethylphenol was 9 ppb.

[0025]

Comparative Example 1 1000 g of the bisphenol A type epoxy resin used in Example 1 was charged into a 2 L reaction vessel.
Heated to 180 ° C. When uniformly dissolved, benzoic acid 1
2.0 g was charged with stirring. Potassium hydroxide n
-2 g of butanol solution (10% potassium hydroxide concentration)
It was confirmed that the mixture was dropped and mixed uniformly. 10 hours, 180
The reaction was carried out with stirring at ℃. When the epoxy equivalent of the reaction product was measured, it was 2520 g / eq.
% Of epoxy groups were found to have reacted. Further, 52.5 g of p-tert-butyl phenol was added, and the mixture was further reacted at 180 ° C. for 15 hours. When the epoxy equivalent of the reaction product was measured, it was 21,000 g / eq, and it was confirmed that 90% of the epoxy groups of the raw material resin had reacted. When the amounts of unreacted p-tert-butylphenol and benzoic acid were measured by the GPC method,
It was 0 ppm and 50 ppm. Using this modified epoxy resin, a paint for cans was prepared in the same composition as in Example 1,
The film was applied to an aluminum foil having a thickness of 0.1 mm so as to have a film thickness of 60 to 70 mg / 100 cm ² and dried at 200 ° C. for 10 minutes to obtain a coating film sample. When the amount of eluted from the coating film was measured, potassium permanganate consumption was 15.0 ppm.
And the amount of p-tert-butylphenol eluted is 1
It was 50 ppb.

[0026]

Comparative Example 2 1000 g of the bisphenol A type epoxy resin used in Example 1 was charged into a reaction vessel having an internal volume of 2 L.
Heated to 180 ° C. When homogeneously dissolved, 52.5 g of p-tert-butyl phenol and 12.0 g of benzoic acid were added.
g was added simultaneously with stirring. Potassium hydroxide n
-2 g of butanol solution (10% potassium hydroxide concentration)
It was confirmed that the mixture was dropped and mixed uniformly. 12 hours, 180
The reaction was carried out with stirring at ℃. When the epoxy equivalent of the reaction product was measured, it was 20500 g / eq, and 9
It was confirmed that 0% of the epoxy groups had reacted. GP
When the amounts of unreacted p-tert-butylphenol and benzoic acid were measured by the method C, they were 650 ppm and 2 respectively.
It was 30 ppm. Using this modified epoxy resin, a paint for cans was prepared in the same composition as in Example 1 and the film thickness was 60
0.1mm thickness to become 70mg / 100cm ²
And dried at 200 ° C. for 10 minutes to obtain a coating film sample. When the amount of eluted from the coating film was determined, the potassium permanganate consumption was 11.0 ppm, and p
-The elution amount of tert-butyl phenol was 70 ppb.

[0027]

Comparative Example 3 1000 g of the bisphenol A type epoxy resin used in Example 1 was charged into a reaction vessel having an internal volume of 2 L.
Heated to 180 ° C. At the time of uniform dissolution, 75.0 g of p-tert-butyl phenol was added with stirring. It was confirmed that 2 g of an n-butanol solution of potassium hydroxide (10% potassium hydroxide concentration) was added dropwise and mixed uniformly. The reaction was carried out with stirring at 180 ° C. for 15 hours.
When the epoxy equivalent of the reaction product was measured, it was 20,000 g / e.
q, and it was confirmed that 90% of the epoxy groups of the raw material resin had reacted. When the amount of unreacted p-tert-butylphenol was measured by the GPC method, 15,000 pp
m. Using this modified epoxy resin, a paint for cans was prepared in the same composition as in Example 1, and the film thickness was 60 to 70.
mg / 100 cm ² was applied to an aluminum foil having a thickness of 0.1 mm and dried at 200 ° C. for 10 minutes to obtain a coating film sample. When the eluted amount from the coating film was measured, the consumption amount of potassium permanganate was 20 ppm, and the eluted amount of p-tert-butylphenol was 230 ppb.

[0028]

Comparative Example 4 1000 g of the bisphenol A type epoxy resin used in Example 1 was charged into a 2 L internal volume reaction vessel.
Heated to 180 ° C. At the time of uniform dissolution, 37.5 g of p-tert-butyl phenol was added with stirring. It was confirmed that 2 g of an n-butanol solution of potassium hydroxide (10% potassium hydroxide concentration) was added dropwise and mixed uniformly. The reaction was carried out with stirring at 180 ° C. for 15 hours.
When the epoxy equivalent of the reaction product was measured, it was 4200 g / eq.
It was confirmed that 50% of the epoxy groups of the raw material resin had reacted. The amount of unreacted p-tert-butylphenol measured by GPC was 50 ppm. Using this modified epoxy resin, a paint for cans was prepared in the same composition as in Example 1 and the film thickness was 60 to 70 mg / 1.
It was applied to an aluminum foil having a thickness of 0.1 mm so as to be 00 cm ² and dried at 200 ° C. for 10 minutes to obtain a coating film sample. When the eluted amount from the coating film was measured, the consumption amount of potassium permanganate was 12.0 ppm, and the eluted amount of p-tert-butylphenol was 6 ppb. Table 1 shows the results.

[0029]

[Table 1]

[0030]

According to the modified epoxy resin of the present invention, the amount of residual monophenols and residual aromatic monocarboxylic acid in the resin is extremely small, and the coating of a coating material produced using the modified epoxy resin of the present invention is applied. It can be seen that the amount eluted from the film is very small, and it is excellent in hygiene and flavor, and is extremely preferable for use as a paint for cans.

Claims (4)

[Claims] (1) a number average molecular weight of 2,000 to 80
A modified resin obtained by reacting an epoxy resin of No. 00 with an alkyl-substituted monophenol having a total of 0 to 4 carbon atoms of a substituent and an alkyl-substituted aromatic monocarboxylic acid having a total of 0 to 4 carbon atoms of a substituent. (B) 40 to 80% of the epoxy groups are sealed by the monophenol and 5 to 40% of the epoxy groups are sealed by the aromatic monocarboxylic acid; c) The total sealing ratio of the epoxy group is 60% or more and 95% or less, and (d) the unreacted amount of the monophenol and the unreacted amount of the aromatic monocarboxylic acid are each 300 pp.
m or less. 2. The total sealing ratio of epoxy groups is 85% or more and 95% or more.
The modified epoxy resin according to claim 1, wherein: 3. An epoxy resin having a number average molecular weight of 2,000 to 8,000 is first reacted with an alkyl-substituted monophenol having a total of 0 to 4 carbon atoms of a substituent, and then further reacted with a total of carbon atoms of a substituent. Wherein the alkyl-substituted aromatic monocarboxylic acid having a value of 0 to 4 is reacted. 4. A resin composition according to claim 1 or 2, wherein 5 to 50 parts by weight of one or more resins selected from phenol formaldehyde resin and melamine formaldehyde resin, and a curing accelerator are added to 100 parts by weight of the modified epoxy resin according to claim 1 or 2. A composition for paint for cans, comprising 1 part by weight or less and a solvent.