JPH03143973A - Can coating composition - Google Patents

Abstract

PURPOSE:To improve adhesion to a base metal, processability, extractability and corrosion resistance by incorporating a product obtd. by mixing or precondensing a bisphenol A type epoxy resin and a phenol resin contg. a specified compd. CONSTITUTION:A phenol resin contg 30-90wt.% compd. of the formula (wherein R is H or a 1-12C alkyl; X is H or methyl; a and b are each 1 or 2 and a+b is 3 or 4) is obtd. by reacting 1mol of bisphenol and 5-10mol of formaldehyde in the presence of 1.5-4mol of alkali catalyst at 30-70 deg.C for 30min to 4hr. Then, a product is obtd. by mixing 50-95wt.% bisphenol A epoxy resin with an average mol.wt. of 800-5,500 and 50-5wt.% phenol resin and if necessary, precondensing the mixture at 50-150 deg.C for 10min to 3hr. Then, the product, a curing catalyst, a leveling agent, a slip agent and an eyehole preventive are compounded to obtain a can coating compsn.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention provides a hardened material that has excellent adhesion to a base metal, processability, and extractability, and is excellent in corrosion resistance of the base metal. This article relates to a new epoxy/phenol paint for cans that can be quickly applied.

(Prior art) In recent years, DI cans, which do not have side seams, have become the mainstream metal cans for canning because of their aesthetic appearance and production cost. This technology is being expanded from carbonated drinks to beverages such as coffee and oolong tea that require retort sterilization.

Metal cans based on steel or aluminum are coated with thermosetting or thermoplastic resin paint on the inside and outside of the can to protect the metal and give it a beautiful appearance.DI can interior paint Traditionally, epoxy/amino, epoxy/phenol, modified vinyl, vinyl organosol, straight vinyl, etc. have been used by spray painting. Among these paints, epoxy phenol resin has the advantage of superior corrosion resistance of the base metal compared to other paints. however,
For DI cans that require short-time baking (usually in the range of about 30 seconds to 2 minutes in an atmosphere of 170 to 210°C), a sufficiently cured coating cannot be obtained, and the coating on the contents cannot be obtained by retort sterilization. Flavor due to elution of low molecular weight substances in ingredients (
A decrease in flavor was observed. For this reason, it has become necessary to develop an inner surface coating material that accelerates the curing of the coating film and has a reduced amount of elution.

On the other hand, as paints for the exterior of DI cans, paints that are generally made by blending alkyd, polyester, acrylic, or eponester resins with epoxy resins, amino resins, etc. have been used. However, the baking conditions for this DI can exterior paint are shorter than the exterior coating for a 3-piece can with seams on the sides (3-piece cans are baked in a 180°C atmosphere for about 122 minutes). In contrast to baking, DI cans have a low degree of film hardening (about 60 to 90 seconds under 200°C atmosphere), and are susceptible to deterioration of the film due to retort sterilization (softening of the film, blistering, whitening, etc.), Corrosion of the base metal is likely to occur due to this. Therefore, at present, as long as the above resin system is used, it is only practical when using aluminum DI cans, which are less corrosive and have excellent adhesion to paint films; In this case, it is not practical for applications requiring retort sterilization treatment. By the way, as a good means to compensate for such drawbacks, Japanese Patent Publication No. 63-45689 discloses a compound obtained by etherifying a solid resol whose main component is bis(3,5-dihydroxymethyl-4-hydroxyphenyl)alkane. A paint containing epoxy resin is described. This etherification improves the compatibility with the epoxy resin and the solvent solubility of the solid resol before etherification, but on the other hand, the bake hardening rate is lower than that of the solid resol before etherification. For this reason, as a DI can inner surface paint that requires short baking time, it still provides insufficient coating performance.

JP-A-57-182361 discloses a fast-curing paint comprising a phenol resin containing a phenol trinuclear component and an epoxy resin. However, since this phenol dinuclear substance has only two hydroxymethyl groups in one molecule, its contribution to the reticulation of the paint film is small, and the paint film whitens during retort sterilization treatment, resulting in poor corrosion resistance. There was a drawback.

(Problems to be Solved by the Invention) As a result of intensive research to improve the various drawbacks of the conventional methods described above, the present inventors have found that not only the conventional long-time printing (approximately 5 to 30 minutes) but also the short printing time. The present inventors have discovered a can coating composition that exhibits excellent adhesion to the base metal, processability, extractability, and corrosivity of the base metal even during time baking (30 seconds to 5 minutes).

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a paint for cans containing a product obtained by mixing or precondensing 50 to 95% by weight of a bisphenol A type epoxy resin and 5 to 50% by weight of a phenol resin. The phenol resin is a compound (hereinafter abbreviated as compound (+)) represented by the following general 2N) in all the phenol components.
2 alkyl group, X is a hydrogen atom or methyl group, a, b
are both 1 or 2, and a + b = 3 or a + b =
It is 4. ) The bisphenol A type epoxy resin used in the present invention is produced by condensing shrimp helohydrin and bisphenol A to a high molecular weight in the presence of an alkali catalyst, or by condensing epihalohydrin and bisphenol A to a low molecular weight epoxy resin in the presence of an alkali catalyst. It is produced by subjecting a low molecular weight epoxy resin to a polyaddition reaction with bisphenol A. Generally, the average molecular weight is between 800 and 5.
500 epoxy resin is used, but it is also possible to use a so-called phenoxy resin, a high condensation resin having an average molecular weight of about 30,000 and substantially free of epoxy groups.

In the present invention, the phenolic resin is obtained by synthesizing, purifying and isolating compound (I) using various synthesis methods, and then mixing or precondensing the compound with other phenolic resins to form the phenolic resin component in the paint. By synthesizing with the following synthesis method, compound (I) can be synthesized from 30% to 90%.
Phenol resin initial condensate (II
) can be used alone, or mixed or precondensed with other phenolic resins and used as the phenolic resin component in paints.

The phenolic resin initial condensate (II) is a mixture of bisphenol A or bisphenols such as bisphenol F and formaldehyde, and 5 to 10 moles of formaldehyde and 1.5 to 4 moles of an alkali catalyst per mole of bisphenol A. using relatively mild reaction conditions, i.e., at a reaction temperature of 30 to 70°C.
from 0 minutes to 4 hours, more preferably at 45-55°C for 2 hours.
It can be obtained by reacting for ~3 hours.

When the compound (I) is used after being purified and isolated, the compound (I) is purified and isolated in the following manner:
- It can be obtained using trifunctional mononuclear phenol such as xylenol and m-methoxyphenol as a raw material.

Furthermore, the phenolic resin initial condensate (II) can be obtained by using the above trifunctional mononuclear phenol as a raw material phenol, or by using the above trifunctional mononuclear phenol and p-cresol, 0-cresol, ptert-butylphenol, p-ethylphenol, 2,3-xylenol, m
- It can also be obtained in combination with a difunctional phenol such as methoxyphenol. It is also possible to use it in combination with bisphenol A or bisphenol F. A phenol resin initial condensate (II
) may be adjusted under the same reaction conditions as those for bisphenols.

The alkali catalyst used in the synthesis of the phenol resin initial condensate (If) is preferably a strong base such as sodium hydroxide or potassium hydroxide, but sodium carbonate or the like can also be used alone or in combination. Formaldehyde is
It can also be used as formalin and rose formaldehyde.

The important point in this synthesis is to suppress the condensation reaction and allow only the addition reaction of formaldehyde to the phenols to occur.To this end, the reaction temperature is as low as possible, an alkaline catalyst is used in excess of the number of moles of the phenols, and formaldehyde is also added to the phenols. Use more than the equivalent number of the class.

For example, when 1 mole of bisphenol A is used as the phenol, it is customary to use about 2 moles of the alkali catalyst and about 8 moles of formaldehyde.

The end point of the reaction is determined by GPC measurement, but in cases where the hue changes from pale yellow to dark red depending on the degree of condensation, such as in the reaction of carbolic acid, it can also be determined by controlling the hue.

Furthermore, if the reaction conditions can be controlled sufficiently, it can also be determined by the reaction time.

In order to separate the phenol resin initial condensate (II) from the reaction product, the reaction mixture can be acidified with hydrochloric acid, sulfuric acid, etc., and the precipitate can be filtered and washed with water. In the case of reaction products with high solubility in organic solvents, such as bisphenols, the organic solvent and acid can be added simultaneously and extracted into the solvent. The extracted reaction product can be purified by washing with acid, alkali, water, etc., if necessary.

The amount of compound (■) produced in the phenol resin initial condensate (II) can be confirmed by GPC measurement. Furthermore, the methylol concentration can be confirmed from nuclear magnetic resonance spectroscopy.

The resin composition ratio in the paint is 50 to 95% by weight of bisphenol A epoxy resin, more preferably 70 to 90% by weight and 5 to 50% by weight of phenol resin, more preferably 10 to 30% by weight. As the content of the phenolic resin increases, the degree of curing of the coating film increases and the retort resistance improves, but processability, adhesion, and water extractability deteriorate. Moreover, when the content of phenolic resin decreases, retort resistance deteriorates.

Further, the content of compound (I) in the phenol resin is 30 to 90% by weight, more preferably 50 to 80% by weight. As the content of compound (I) increases, the curing speed of the coating film increases, and in particular, retort resistance and water extractability improve. Generally, when the retort resistance and water extractability of phenolic resin improve, the processability and adhesion deteriorate.
It is difficult to satisfy all of these properties, but by taking advantage of the curing speed of compound N
), retort resistance and water extractability can be imparted with a relatively small amount, so compound (I) is contained in the phenol resin component in an amount of 70 to 90% by weight, and a large amount of bisphenol A type epoxy resin is added. That is, by blending up to 95% by weight of the total resin components, the above-mentioned coating film performance can be balanced.

Compound (I) itself has poor compatibility with epoxy resins, but by increasing the ratio of compound (I) with phenol resins other than compound () to more than 10% by weight in the phenol resin, it can be easily treated. Can be made compatible with epoxy resin. Changes in this ratio and changes in compatibility with the epoxy resin also vary depending on the molecular weight of the epoxy resin used, the type of solvent, etc. If this ratio is less than 10% by weight, if the epoxy resin contains a large amount of epoxy resin with a molecular weight of 5000 or more, or if it contains aromatic solvents or alcohol solvents in an amount of about 30% by weight or more of the total solvent, It becomes cloudy after being made into a paint, and also causes fine irregularities on the surface of the paint film after painting. This coating film suffers from non-uniform curing during baking and coating defects (pinholes, orange beer, craters), etc., making it impossible to obtain sufficient coating performance. The content of compound (I), which is not affected by the molecular weight of the epoxy and the type of solvent, is preferably 80% by weight or less in the phenol resin component. Furthermore, if the content of compound (I) is less than 30% by weight in the phenolic resin component, the effects of the present invention due to compound N) cannot be achieved.

Phenol resins other than compound (I) include resol type phenol resins or novolac type phenol resins obtained by condensing any phenol component with formaldehyde in the presence of a basic catalyst or an acidic catalyst. The phenolic components constituting these phenolic resins include o-cresol, p-cresol, and p-t.
ert-butylphenol, p-ethylphenol, 2
．． 3-xylenol, 2,5-xylenol, p-te
rt-aminophenol, p-nonylphenol, p-
Bifunctional phenols such as phenylphenol and p-cyclohexylphenol, carbolic acid, m-cresol, m-
Trifunctional phenols such as ethylphenol, 35-xylenol, m-methoxyphenol, l-functional phenols such as 2,4-xylenol, 2,6-xylenol, bisphenol A, bisphenol B, bisphenol F, etc. The hydric phenols may be used alone or in combination of two or more.

The epoxy resin and phenol resin obtained by this method are combined to create an epoxy/phenol type paint for cans, and at that time, they may be simply mixed, or they may be heated at 50°C to 1000°C after mixing. Precondensation may be carried out at a temperature of about 10 minutes to about 3 hours.

Furthermore, in the preparation of this epoxy-phenol type coating material, an inorganic or organic acid can be used as a curing catalyst during mixing or precondensation. Also,
Epoxy resins and phenol resins to which so-called aluminum chelates such as aluminum butyrate and aluminum isopropylate are added can also be used. It is also possible to use commonly used paint additives such as leveling agents, slip agents, anti-eyehole agents, and surfactants, or to color with pigments such as titanium dioxide, zinc oxide, and aluminum.

The inner surface paint for cans and the outer surface paint for cans obtained by the present invention are applicable not only to the above-mentioned DI cans, but also to other two-piece cans (DR cans, oval cans, pudding cans, etc.) or three-piece cans. It can also be widely used for cans (solder cans, welded cans, adhesive cans).

These paints for the inner and outer surfaces of cans are applied by known means such as roll coating, spray coating, dip coating, etc., and are cured by baking at 180° C. to 330° C. for about 15 seconds to 30 minutes. The coating thickness is not particularly limited, but is 1μ.
Approximately 50 to 50 copies is appropriate.

(Example) [Preparation of epoxy solution 1] 30 parts by weight of AER669 (bisphenol A type epoxy resin manufactured by Asahi Kasei Corporation) was dissolved in 50 parts by weight of propylene glycol mono-n-propyl ether and 20 parts by weight of cyclohexanone.

[Epoxy] 30 parts by weight of phenoxy PKHH (phenoxy resin manufactured by Union Carbide), 50 parts by weight of propylene glycol monomethyl ether acetate, 20 parts by weight of cyclohexanone
Parts by weight were dissolved.

[Preparation of phenolic resin initial condensate 1] Bisphenol A 228 g (1 mol), 37% formalin 649 g
(8 mol), 302 g (2,6 mol) of 35% sodium hydroxide
After reacting at 50°C for 2 hours, 250g of ethyl acetate and 250g of n-butyl alcohol were added, followed by 401g (2.2mol) of 20% hydrochloric acid, and the mixture was heated at 60°C.
After stirring at C for 10 minutes, the mixture was allowed to stand still and separated into two layers within a few minutes. The upper layer was an organic compound layer and the yield was 430 g. Wash and neutralize the organic layer using water and aqueous ammonia,
330g light purple transparent phenolic resin first! iJI condensate 1 was obtained. Solid content was 30%. When this solution was analyzed by high performance liquid chromatography and nuclear magnetic resonance absorption spectroscopy, it was confirmed that it contained 75% of 2.2bis(3,5-dihydroxymethyl-4-hydroxyphenyl)propane. The remaining 25% was a mixture of polymethylolated bisphenol A dimers and trimers condensed at the methylol group.

[Preparation of 2,2-bis(3,5-dihydroxymethyl-4-hydroxyphenyl)propane] 2,2-bis(3
After separating 5-dihydroxymethyl-4-hydroxyphenyl)propane by liquid chromatography, the solvent was removed under reduced pressure at 40°C to obtain a light brown solid. High performance liquid chromatography and nuclear magnetic resonance spectroscopy of this solid revealed that 2.2bis(35-dihydroxymethyl-4
-Hydroxyphenyl)propane was confirmed to contain 99%.

[Preparation of phenolic resin initial condensate 2] Carbolic acid 188
g (2 mol), 37% formalin 974 g (I2 mol), 35% sodium hydroxide 302 g (2.64 mol)
Mix and heat at 50°C for 1 hour.

The reaction was allowed to proceed for 30 minutes. The subsequent operations were carried out in the same manner as the preparation and analysis of phenolic resin initial condensate I, and initial condensate 2 containing 82% of the compound having the following structural formula was obtained.

[Adjustment of phenolic resin l]

1 mol of bisphenol A was dissolved in 2.4 mol of 37% formaldehyde aqueous solution, 0.2 mol of 25% aqueous ammonia was added, and the mixture was reacted at 95° C. for 1 hour. The resulting condensation product was extracted into a mixed solvent consisting of 30 parts of methyl isobutyl ketone (MIBK), 30 parts of cyclohexanone, and 40 parts of xylene, and after washing with water, it was left to stand day and night to separate the aqueous layer, and the solid content was 30%. A resol solution was obtained.

[Preparation of phenolic resin 2] 50 parts of p-cresol, 50 parts of carbolic acid, 102 parts of a 37% formaldehyde aqueous solution, 1 25% ammonia aqueous solution
5 parts of methyl isobutyl ketone and 1/2 of xylene were reacted for 3 hours under reflux at 98°C.
After extraction with the mixed solvent of No. 1, water was removed by azeotropic dehydration to obtain a 35% solution of resol type phenolic resin.

[Preparation of Phenol Resin 3] 2 parts of phosphoric acid was added to 50 parts of p-cresol, 50 parts of carbolic acid, and 102 parts of a 37% aqueous solution of formaldehyde, and the mixture was reacted under reflux at 98°C for 4 hours. 3 with 80℃ hot water
After washing twice, the water is separated by standing, and the pressure is reduced to 200°C.
After drying for 2 hours, the mixture was dissolved in a 1/1 ratio solvent of butyl cellosolve and xylene to obtain a 35% solution of novolak type phenolic resin.

Below, each paint of Examples 1 to 9 and Comparative Examples 1 to 9 was adjusted,
The paint was baked and the performance of the paint film was evaluated.

[Paint adjustment]

Each paint was mixed or precondensed to have the resin composition shown in Table 1, resulting in a paint with a solid content of 30%. 22-bis(3,
5-dihydroxymethyl-4-hydroxyphenyl)propane was added to a mixed solution of a phenol resin solution and n-butanol to form a phenol resin solution with a solid content of 30%, and then mixed with an epoxy resin solution. 2-
When dissolving 2-bis(3,5-dihydroxymethyl-4-hydroxyphenyl)propane, approximately 1O
Stirring for about a minute was required. Further, each paint was diluted to a solid content of 30% using a mixed solvent of N-butanol:cyclohexanone:xylene-40=30:30.

[Painting method]

The resulting paint was baked on a #25 tin plate using a roll coater under the conditions shown in Table 2 so that the dry coating film had a thickness of 5 μm to obtain each coated plate.

However, an aluminum plate was used for the potassium permanganate consumption test.

〔Test method〕

1) A painted plate with a consumption of 300 cm of potassium permanganate was immersed in 300 cc of distilled water and sterilized in a retort at 125°C for 30 minutes. Potassium permanganate consumption was measured according to the test method.

2) Adhesive Use a knife to make 11 vertical and horizontal cuts, each about 1.5 mm wide, on the surface of the adhesive coating.

It represents the number of unpeeled goblin parts when a cellophane adhesive tape with a width of 24IIIrs is applied and strongly peeled off.

3) Processability Using a special fold-type DuPont impact tester, place a sample folded in half at the bottom and drop a 1 kg iron weight with a flat contact surface from a height of 50 cm. The length of cracks in the paint film was measured.

4> Corrosion Resistance A test piece with an x mark made on the coating surface using a knife was treated in 1% saline at 125°C for 30 minutes, and the degree of corrosion near the x mark was determined.

The resin compositions and coating film performance evaluations of Examples and Comparative Examples are described below.

Comparative Example 10 Epoxy Solution 1 100 parts by weight was added with Super Beckamine P-138 (manufactured by Nippon Reichhold Co., Ltd.), which is a urea resin.
10.6 parts by weight of 60% by weight resin component were mixed and
Using this method, an epoxy-urea paint with a solid content of 30% was obtained.

Comparative Example 11 After dissolving 50 parts by weight of Byron GK-130 (manufactured by Toyobo Co., Ltd.) using 25 parts by weight of cyclohexanone and 25 parts by weight of xylene, Super Beckamine 15-594 (manufactured by Nippon Reichhold Co., Ltd.), which is a benzoguanamine resin, was dissolved. Solid content 50% by dissolving 100 parts by weight of resin component (55% by weight) and propylene glycol mono-n-propyl ether
A polyester/amino paint was obtained by mixing 20 parts by weight of the AER661 solution.

In Comparative Examples 1 and 2, 2,2-bis(3,5-dihydroxymethyl-4-hydroxyphenyl)propane was not completely dissolved and coating was impossible.

〔Effect of the invention〕

The following effects were confirmed by the present invention.

When baked at 200°C for 30 seconds, which corresponds to the baking conditions for DI can paints, the paint of the present invention has significantly lower potassium permanganate consumption and adhesion than conventional epoxy/phenol paints. Excellent. Also, compared to other conventional resin-based paints, it has particularly excellent corrosion resistance. In other words,
As paint for the inside of cans, it has superior potassium permanganate consumption, adhesion, processability, and corrosion resistance compared to conventional epoxy/phenol paints and epoxy/urea paints, and as paint for the outside of cans, conventional polyester・Very superior corrosion resistance compared to amino-based paints. Therefore, as a paint for the exterior of cans, it can be used as a base coat (coating directly on the substrate) for steel DI cans, which are inferior to aluminum DI cans in terms of corrosion resistance, and require retort sterilization. I was able to:

Claims (1)

[Scope of Claims] 1. A paint for cans containing a product obtained by mixing or precondensing 50 to 95% by weight of a bisphenol A type epoxy resin and 5 to 50% by weight of a phenolic resin, in which the phenolic resin has the general formula A paint composition for cans, characterized in that the compound represented by (I) is contained in an amount of 30 to 90% by weight based on the total phenolic resin component. General formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, in the formula, R is a hydrogen atom or has 1 or 1 carbon atoms.)
2 alkyl group, X is a hydrogen atom or methyl group, a, b
are both 1 or 2 and a+b=3 or a+b=4
It is. )