JPS6197371A - Paint composition for inner surface of can - Google Patents

Abstract

PURPOSE:To provide an epoxy phenol paint for use in coating the inner surface of a can, which has excellent processability, curability, and adhesion to steel sheet, by using a specified resin as a phenolic resin component. CONSTITUTION:One mol of a trifunctional or polyfunctional phenol (e.g. bisphenol A) is reacted with 1-1.5mol of formaldehyde at 40-80 deg.C for 2-6hr. A bifunctional phenol (e.g. t-butylphenol) is reacted with the resulting phenolic resin (weight-average MW: 500-800, methylol group concn. per phenyl nucleus: 0.35-0.55mol) at 80-100 deg.C for 20min to 1hr to obtain a resol type phenolic resin. 15-60pts.wt. said phenolic resin, 85-40pts.wt. bisphenol A type epoxy resin (average MW: 800 or above) and an org. solvent are blended together to obtain a paint compsn. for the inner surface of a can.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to an epoxy-phenolic paint,
More specifically, the present invention relates to a coating composition containing a resol type phenolic resin that has a high methylol group concentration and is likely to form a network during curing.

(Prior art) It is well known that the performance of epoxy-phenol paints is greatly influenced by the properties of the resol type phenolic resin, and in reality, the type and composition ratio of the phenol component used, the type and amount of the catalyst, and the amount of formaldehyde used. Amount, epoxy/
Various epoxy-phenol paints are used, with the balance of performance changing depending on the phenol ratio, etc., depending on the application.

Furthermore, regarding resol type phenolic resins used in epoxy-phenolic paints, except in special cases, 2
A method for producing a resol-type phenolic resin by mixing one or more functional phenols and one or more trifunctional or higher functional phenols (Japanese Unexamined Patent Publication No. 51-52439+Ia),
A method is known in which difunctional and trifunctional phenols are used individually to produce a resol type phenolic resin and then mixed (Japanese Patent Laid-Open No. 53-64238).

In any of these cases, the performance of the coating material is improved by imparting flexibility to the resin using bifunctional phenols and adjusting the crosslinking density using trifunctional or higher functional phenols. However, in the former method, it is difficult to proceed with a uniform condensation reaction due to the difference in the reaction rate of phenols, and undesired low-molecular-weight resol-type phenolic resins or conversely high-molecular-weight ones are likely to be produced. Epoxy-phenol paints have the drawback of poor processability and adhesive properties. On the other hand, the latter method uses linear 2
Mixing a functional phenol condensate and a trifunctional or higher functional phenol condensate with a network structure reacts like a block polymer during baking hardening, but it is time-consuming and practical because the resol type phenolic resin is synthesized separately and then mixed. This is disadvantageous.

(Problems to be Solved by the Invention) The present inventor has discovered that i
In resol-type phenolic resins, which play an important role in manufacturing, we maintain processability and curing properties while maintaining content resistance, corrosion resistance, and adhesion to polyamide adhesives.

In particular, the adhesion to steel plates has been improved.

[Structure of the invention]

(Means for solving problems) Namely, the present invention is a resol type phenolic resin.

In a can inner coating composition comprising a bisphenol A type epoxy resin and an organic solvent, the resol type phenol resin has a weight average molecular weight of 500 obtained by reacting a trifunctional or higher functional phenol with formaldehyde in the presence of an alkali catalyst. The can inner surface coating composition is characterized in that it is a phenolic resin (B) obtained by reacting a phenolic resin (A) having 800 to 800 methylol groups with a difunctional phenol.

In the present invention, the trifunctional or more functional phenol is 1
Commonly used phenols include carbolic acid, metacresol, resorcinol, m-methoxyphenol, and bisphenol A. These trifunctional or higher functional phenols can be used alone or in combination of two or more in the first stage reaction.

Examples of the bifunctional phenol used in the second stage reaction include commonly used phenols such as vala-cresol, orthocresol, para-tertiary 7-butylphenol, para-methoxyphenol, and para-nonylphenol; Alternatively, two or more types can be used in combination.

Examples of alkaline catalysts include sodium hydroxide.

Alkaline catalysts such as calcium hydroxide, magnesium hydroxide, basic metal salts, ammonia, hexamethylenetetramine, trimethylamine, triethylamine, pyridine, etc. can be used. Further, as formaldehyde, an aqueous solution, one dissolved in an organic solvent, and one dissolved in an aqueous organic solvent system can be used.

The phenol resin (A) in the present invention is prepared by using 1.0 to 1.5 moles of formaldehyde per mole of trifunctional or higher functional phenol as an essential component, and at a temperature of 40 to 80%.
The reaction was carried out at °C for 2 to 6 hours, and the weight average molecular weight range was 500 to 800. Next, 3 used in the first stage reaction
Difunctional phenols were added so that the ratio of functional or higher functional phenols/bifunctional phenols was 80/20 to 40/60 in terms of molarization, and the mixture was reacted at 80 to 100°C for 20 minutes to 1 hour to form a phenol resin (B ) can be obtained. During this second stage reaction, additional formaldehyde and an alkali catalyst are usually not required to be added, but may be added in some cases.

The reason why the paint according to the present invention has the above-mentioned features will be explained in more detail regarding the resol type phenolic resin (hereinafter referred to as phenol resin), which is the most important part of the present invention.

Conventional phenol resins made from mixed phenols are obtained by adding and mixing phenols with different condensation reaction rates at the same time and reacting - their molecular weight, methylol group concentration,
It is difficult to control factors related to the reaction, such as crosslinking density, in a well-balanced manner, and this has a large effect on the properties of epoxy-phenol paints containing the phenolic resin as a component.

On the other hand, the first feature of the phenolic resin obtained by the present invention is that trifunctional or higher functional phenols are reacted with formaldehyde in the presence of an alkali catalyst in the first stage reaction, followed by a second stage reaction. It was obtained through a two-step reaction in which difunctional phenol was added as a phenol. In other words, in the present invention, the first stage reaction is carried out at 40 to 80°C.
3 in the presence of an alkali catalyst by carrying out the reaction at a relatively low temperature of
The molecular weight, methylol group concentration, and phenolic resin obtained by the condensation reaction of functional phenol and formaldehyde.
It is possible to adjust the crosslinking density, etc., and it is thought that these factors give favorable results to the properties of the phenol resin obtained in the second stage reaction as an epoxy phenol paint for the inside of two cans.

The phenol resin (A) obtained by the first stage condensation reaction using trifunctional or higher functional phenols of the present invention has a weight average molecular weight (M w ) when measured by high performance liquid chromatography excluding the solvent. It is in the range of 500-800. Within this range, when the MW is 650 to 750, the adhesion of the epoxy-phenol paint improves, and it can be used particularly preferably. Also.

When the Mw of the phenol resin (A) is greater than 800, the crosslinking reaction of trifunctional or higher functional phenols proceeds too much, resulting in poor processability. Conversely, if the Mw of phenolic resin (A) is 5
If it is less than 00, the condensation reaction of trifunctional or higher phenol formaldehyde is actually carried out at a low temperature, such as 40°C or lower, and the reaction progresses (if the first stage reaction is lower than 80°C in a short time). This is the case when the phenol-formaldehyde condensation reaction cannot be carried out uniformly by raising the temperature to the reaction temperature of Curability decreases and processability becomes poor.

The second feature of the phenolic resin of the present invention is that it is obtained by always using trifunctional or higher functional phenols in the first reaction and using difunctional phenols in the second reaction. It is. For example, contrary to the method of the present invention, epoxy-phenol paints containing phenolic resins obtained by first reacting difunctional phenols with formaldehyde and then adding and reacting trifunctional or higher functional phenols are mostly used on steel sheets. It does not show adhesion to.

This result is thought to be due to the slow reaction rate of the difunctional phenol used initially, which is difficult to increase the molecular weight, and the low concentration of methylol groups.

The methylol group concentration of the phenol resin (A) obtained in the present invention is 0°35 to 0.
．． 55 mol, and within this range, an epoxy-phenol paint with particularly excellent adhesion to steel plates can be obtained.

The production and characteristics of phenolic resins have been explained above, but these contents can be more effectively combined with the important characteristics of paints by forming the epoxy-phenol paint of the present invention.

The bisphenol A type epoxy resin in the present invention is obtained by the reaction of epichlorohydrin and 2,2-bis(4-hydroxyphenyl)propane, and those with an average molecular weight calculated from the epoxy equivalent of 800 or more can be used, but those with an average molecular weight of 2000 to 4000 can be used. Those having an average molecular weight are preferred.

Organic solvents used in the present invention include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone, benzene, toluene, xylene,
Aromatics such as other alkylbenzenes.

Cellosolves such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, methyl cellosolve acetate, butyl cellosolve acetate, ethyl acetate.

Esters such as phtyl acetate, isopropyl alcohol,
Alcohols such as butyl alcohol and diacetone alcohol, or a mixed solvent thereof can be used.

In the can inner coating composition according to the present invention, bisphenol A type epoxy resin can be used in a range of 85 to 40 parts by weight based on 15 to 60 parts by weight of phenol resin.

In addition, additives such as coloring agents such as pigments, fillers, rust preventives, various surfactants, etc. can be used in the coating composition for can inner surfaces according to the present invention, if necessary.

The can inner surface coating composition according to the present invention is applied to a steel plate by roller coating, spray coating, or the like in an amount of about 20 to 70 mg/100 cnl as a dry coating. The baking conditions are approximately 180°C to 220°C, 5
It will be baked in 15 minutes.

As a steel plate to which the paint according to the present invention is applied and baked.

In addition to tin plated with tin, which has traditionally been used for general cans such as food cans.

Chrome plated steel plates, nickel plated bales, aluminized steel plates, aluminum plates, cold tiff 1814 plates, etc., which have been used in recent years as materials to replace tinplate, can be used.

The present invention will be specifically explained below using examples.

(Example) Synthesis of epoxy-phenol paint (1) 1 mol of bisphenol A was dissolved in 2.5 mol of 37% formaldehyde aqueous solution and 0.2 mol of 25% aqueous ammonia was added to the mixture at 65°C.
The mixture was reacted for 3 hours to obtain a first stage phenol resin.

Subsequently, p-Ler-butylphenol (p-TBP)
Add 1 mol and react at 95°C for 30 minutes.

The resulting condensation product was converted into methyl isobutyl ketone 3011
f [parts by weight, extracted with a mixed solvent consisting of 30 parts by weight of cyclohexanone and 40 parts by weight of xylene, washed with water, left to stand for 1 day and night to separate the aqueous layer, and a phenol resin solution with a solid content of 30% f
Made by lil.

In addition, Epicoat 1009 was added to a mixed solvent with the same composition as above.
(bisphenol A type epoxy resin manufactured by Shell) was dissolved to obtain an epoxy resin solution with a solid content of 40%.

A phenol resin solution and the above epoxy resin solution were mixed at a solid content ratio of 40/60 to prepare an epoxy-phenol paint (1).

Production of epoxy-phenol paint (2) p-T used in the second stage reaction in epoxy-phenol paint (1)
Phenol resin was synthesized using the same procedure as for epoxy-phenol paint (1), except that p-cresol was used instead of BP, and then epoxy-phenol paint (2) was synthesized.
It was created.

Production of epoxy-phenol paint (3) In the epoxy-phenol paint (1), carbolic acid was used in place of bisphenol A used in the first reaction, and p was used in the second reaction.
-Instead of TBP. - Phenol resin was synthesized by the same procedure as for epoxy-phenol paint (1) except that cresol was used.

Then, an epoxy-phenol paint (3) was prepared.

Production of epoxy-phenol paint (4) The epoxy-phenol paint (1) used a phenol resin synthesized by changing the first stage reaction temperature to 55°C. Epoxy by the same operation as
Phenol-based paint (4) 8 was created.

Production of epoxy-phenol paint (5) Epoxy-phenol paint (1) except that a phenol resin synthesized by changing the first stage reaction temperature to 75°C was used. Epoxy by the same operation as
A phenolic paint (5) was created.

Production of epoxy-phenol paint (6) In the epoxy-phenol paint (1), an 8/2 mixture of bisphenol A and 0-cresol was used in place of the bisphenol A used in the first reaction. - A phenol resin was synthesized by the same procedure as for the phenol paint (1), and then an epoxy-phenol paint (6) was created.

Production of epoxy-phenol paint (7) P-TBP was used instead of bisphenol A used in the first stage reaction in the epoxy-phenol paint (1).

Epoxy-phenol paint (1) except that bisphenol 8 was used instead of p-TBP used in the second reaction.
Synthesize phenolic resin using the same procedure.

Then, an epoxy-phenol paint (7) was prepared.

Production of epoxy-phenol paint (8) The phenol resin in the first stage synthesized in the epoxy-phenol paint (1) is used as an epoxy thief without leaking into the second stage reaction.
-, a nol-based paint (8) was created.

Preparation of epoxy-phenol paint (9) As the phenol used in the epoxy-phenol paint (8), 1 mole of mixed phenol of bisphenol A/p-TBP (1/1) was used.

A phenol resin was synthesized by the same procedure as for the epoxy-phenol paint (8), except that the reaction was carried out at 90°C for 50 minutes, and then an epoxy-phenol paint (9) was prepared.

Manufacture of epoxy-phenolic paint (10)Epoxy-
The phenol resin was synthesized by the same procedure as in the epoxy-phenol paint (1), except that the reaction conditions for the first stage phenol resin in the phenol paint (1) were 85°C and X hours, and then the epoxy Phenolic paint (
10) was created.

The solvent was removed from the first stage phenolic resin used in each paint to prepare a sample, and the weight average molecular weight (Mw>) was measured by high performance liquid chromatography and is shown in Table 1.

In addition, pyridine/acetic anhydride (
Add 10 cc of an acetylation reagent consisting of a volume ratio of 1/1) and heat at 80°C for 3 hours. Add 100 cc of condensate, then extract with ethyl ether, and add 6-NHCI aqueous solution 7.
After repeating ethyl ether extraction after adding 0 cc and ethyl ether extraction after adding 70 cc of O, iN sodium bicarbonate, the ethyl ether was removed at room temperature under reduced pressure to obtain an acetylated phenol resin, which was dissolved in chloroform and analyzed by H-NMR.
Quantitate the peak around 5 ppm measured by , calculate the number of moles of methylol group added to one phenyl nucleus,
It is shown in Table 1.

Next, the epoxy-phenol paints (1) to (10) were applied to a tin plate (0.23 mm thick, #50150ET) with a roller, and then baked at 200°C for 10 minutes.

A coated plate with a coating weight of 50 mg/dm was obtained.

A No. 2 can is formed from the above-mentioned painted board, and a commercially available can of boiled salmon is made.
The No. 2 can was reheated and subjected to retort treatment at 117° C. for 4 hours, and then opened to observe sulfide blackening on the inner surface (sulfurization blackening resistance test).

Next, a cap with a diameter of 30 mm and a height of 30 mm was punched out from the painted plate using a press, and peeling of the paint film was observed (
Punching workability test).

The sulfide blackening test evaluates the degree of sulfide blackening using a 5-point scale (〇-no change to 5-full blackening), and the punching workability test evaluates the degree of paint film peeling after punching the cap using a 5-point scale. Table 1 shows the evaluation results (〇 - no peeling to 5 - significant peeling).

Next, epoxy-phenol paints (1) to (10)
The phenol resin solution and epoxy resin solution used in the formulation were mixed at a solid content ratio of 25/75 to prepare epoxy-phenol paints (1') to (10'). This paint was applied with a roller to a 0.22 mm thick chromium-treated steel plate, and then baked and dried at 210°C for 10 minutes.

The coating amount was 50 mg/dm. Between this coated plate is a 1,2-aminolauric acid polymer (relative viscosity 2.3).
) After sandwiching the film and pressing it with a hot press at 200°C for 10 seconds and cooling it, the adhesive sample was cut into 5 mm pieces during adhesion, and a T-peel test was conducted on this with a Schopper type tensile strength tester at an ambient temperature of 25°C. . Also, hold this adhesive sample at 90°
After immersion in hot water of C for 10 days (hot water aging treatment), cooling and drying, a T-peel test was conducted at 25°C.

Next, it is the epoxy-phenol resin coating film of the painted board.
50 times the amount of methyl ethyl ketone (MEK) was added and heated under reflux at 80''C for 30 minutes, and the MEK extraction rate of the resin coating was measured as the ratio (%) of the remaining coating film extracted/total weight of the coating film.

Table 2 shows the results of T-peel strength and MEK extraction amount after untreated and hot water treatment over time.

As is clear from the results in Tables 1 and 2.

The epoxy-phenol paint of the present invention has excellent properties such as sulfurization resistance, hardening processability, adhesion to polyamide adhesives, and MEK extractability.
Paint N with different types of phenols used in two-stage synthesis
11 (7), paint m (7), paint No. (8) that uses a phenolic resin that is not a two-step synthesis.

Paint floor (8'), paint + lh (9), paint N[L
(9) and paint No. where the reaction temperature in the first stage is high and the molecular weight of the phenolic resin is not within the range of the present invention.
(10) and paint bottle (10) both have a poor balance of various properties (they can only obtain products that are inferior in practical terms).

〔Effect of the invention〕

The coating composition for the inner surface of a can of the present invention has excellent curability and good corrosion resistance against contents such as foods.

In addition, even after being applied to a steel plate and subjected to post-treatment processing, the coating film remains
Shows excellent adhesion between steel plates. Furthermore, the adhesive strength of polyamide adhesives, especially after heat treatment, does not decrease, making it useful as an adhesive primer for metal cans.

Claims (1)

[Scope of Claims] 1. In a can inner coating composition comprising a resol type phenol resin, a bisphenol A type epoxy resin, and an organic solvent, the resol type phenol resin converts trifunctional or higher functional phenols and formaldehyde into an alkali catalyzed mixture. The weight average molecular weight obtained by reacting in the presence of
The above coating composition for the inside of a can, characterized in that it is a phenolic resin (B) obtained by reacting a phenolic resin (A) having 800 methylol groups with a difunctional phenol. 2. The coating composition for the inner surface of a can according to claim 1, wherein the phenol resin (A) has a methylol group concentration of 0.35 to 0.55 mol per phenyl nucleus. 3. The coating composition for the inner surface of a can according to claim 1 or 2, wherein the trifunctional or higher functional phenol is bisphenol A.