JPH0243781B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel epoxy-phenolic coating composition with excellent extraction properties and adhesion properties. Three-piece cans with seams on the sides and two-piece cans without seams are generally used as metal cans for canning, and the base metals include tin plated steel sheets (tinplate sheets) and chromium-treated steel sheets (tain-free steel sheets). , aluminum plate etc.
Various metal plates are used. In any metal can, a protective coating is generally provided on the inner surface of the can to prevent metal elution and corrosion. Such paints for the inside of cans include epoxy-phenol paints, epoxy-urea paints,
Epoxy-acrylic paints, straight vinyl paints, vinyl organosol paints, etc. are widely used, but epoxy-phenol paints are the most effective in terms of adhesion to the underlying metal, corrosion resistance, processability, etc. Commonly used. On the other hand, recently, there has been a noticeable trend that the types of contents that can be filled into metal cans are rapidly expanding and that the sterilization temperature after filling is becoming higher. In such a situation,
While maintaining or improving the adhesion and corrosion resistance characteristics of current epoxy-phenolic interior paints,
There is a growing need to reduce the amount of substances extracted (transferred) from can interior coatings into the contents and to increase flavor retention. Conventionally known epoxy-phenol interior paints are made by mixing a bisphenol A type epoxy resin and a resol type phenolic resin obtained by reacting one or more phenols with an aldehyde in the presence of a basic catalyst. Or it is produced by precondensation. According to the results of the study by the inventors,
It has been found that when the resol type phenolic resin used in the epoxy-phenol internal coating is synthesized by the above method, about 10% by weight of unreacted phenols usually remain in the phenolic resin. Methods for reducing the residual amount of unreacted phenols include increasing the degree of condensation and increasing the average molecular weight of the phenol resin, and increasing the amount of aldehyde added. - The properties of a phenolic inner surface paint, such as adhesion and processability, are reduced, and this is not a desirable direction for a can inner surface paint. In addition, regarding the method of extracting and removing unreacted phenols with an appropriate solvent, since the solubility of unreacted phenols and methylolated phenols is extremely similar, it is necessary to remove only unreacted phenols. It is extremely difficult to simultaneously extract a part of low molecular weight condensates containing methylolated phenols.
This results in removal, resulting in unsatisfactory results similar to those achieved with higher average molecular weights. As a result of repeated research on reducing unreacted phenols in epoxy-phenol paints and improving the extraction characteristics of paint films, the present inventors have discovered that phenolic resins are produced by condensing compositions containing methylolated phenols as the main components. proposed the use of phenolic resin as a component of phenolic resin (Japanese Patent Application No. 11622/1983). As a result of further research, the present inventors discovered that when a specific condensation product is used, a paint for the inside of a can can be obtained that has particularly excellent adhesion to the underlying metal and hardenability as a paint. This led to the present invention. That is, the present invention uses 40 to 95 parts by weight of a bisphenol A type epoxy resin and 5 to 60 parts by weight of a phenol resin.
In a coating composition containing a product obtained by mixing or precondensing parts by weight, the phenolic resin is obtained by addition-condensation reaction of formaldehyde to an alkylphenol represented by the following general formula,
A coating composition characterized in that it is a phenolic resin whose main component is a methylolated product of a dimer or tetramer phenol, and which contains at least 40% by weight of a methylolated product of a trimer phenol based on the phenolic resin component. . (In the formula, R ₁ is an alkyl group having 1 to 12 carbon atoms.) The bisphenol A type epoxy resin used in the present invention is produced by condensation and polyaddition reaction of epihalohydrin and bisphenol A. Generally, an epoxy resin having an average molecular weight of 800 to 5,500 is used, but it is also possible to use a high condensation resin, so-called phenoxy resin, which has an average molecular weight of about 30,000 and is substantially free of epoxy groups. An important feature of the present invention is that the main component of the phenolic resin component is of the following formula: (In the formula, R ₁ is an alkyl group having 1 to 12 carbon atoms, R ₂ and R ₃ are a hydrogen atom or a methylol group, and at least one of R ₂ and R ₃ is not a hydrogen atom. n is 1 represents an integer from 3 to 3). By using such a phenolic resin, it is possible to reduce the content of unreacted phenols in the coating film to an extremely low level compared to known epoxy-phenolic paints, thereby improving the extraction properties. It brings the quality to an excellent level. Furthermore, the paint for the inside of a can according to the present invention has extremely high adhesion and curing properties compared to known epoxy-phenol paints, which is a feature of the present invention along with excellent extraction properties. The phenolic resin represented by the above formula is obtained by addition condensation of formaldehyde to alkyl phenol in the presence of an alkali catalyst, but it can be obtained from room temperature to
It is possible to use a method in which an alkylphenol dialcohol is produced in high yield at a relatively low temperature of about 60° C. and then proceed with condensation, or other known synthetic means can be used. As the alkylphenol, p-cresol, o-cresol, p-ethylphenol, p-tert-butylphenol, p-octylphenol, p-nonylphenol, etc. can be used. In addition, a methylolated product of trimer phenol (in the above formula, n
When the amount of the compound (3) in the phenol resin component is 40% by weight or more, it exhibits especially excellent adhesive properties with the underlying metal. The reaction conditions for producing such a phenolic resin can be freely selected within a range that satisfies the above requirements. It is also possible to prepare two or more types of alkylphenols with different types or with different n numbers, and use them by mixing them. The phenolic resin obtained by this method is combined with the above-mentioned epoxy resin to create an epoxy phenol paint for the inside of cans.
It is also possible to perform so-called precondensation, which is a reaction at a temperature of about 150°C for about 10 minutes to 3 hours. The appropriate ratio of epoxy resin to phenol resin is about 40 to 90% by weight of epoxy resin and 10 to 60% by weight of phenol resin.If the content of epoxy resin is higher than this, sufficient curing properties can be obtained. First, the water resistance and corrosion resistance are lowered, and if the amount of phenolic resin is higher than this, the coating film becomes hard and the workability and adhesion to the base metal decrease. Furthermore, if necessary, a known phenolic resin can be used in combination with the phenolic resin obtained by the method described above. As the phenolic resin used in combination, there are resol type phenolic resins and novolak type phenolic resins which have been used in conventional epoxy-phenolic paints. These phenolic resins can be used in an amount that does not impair the properties of the phenolic resin, that is, in an amount that does not exceed about 50% by weight. In addition, the inner surface paint for cans of the present invention also contains a curing catalyst used in conventional epoxy-phenol paints,
For example, acidic catalysts such as phosphoric acid and phosphoric esters can be used. Furthermore, epoxy resins and phenolic 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 coating for cans obtained according to the present invention is applied by a known method such as roll coating, spray coating, dip coating, or brush coating, and is cured by baking at 180° C. to 300° C. for about 10 seconds to 30 minutes. There is no particular limit to the coating thickness as long as there are no pinholes, but a thickness of about 1μ to 50μ is appropriate depending on the application. A coating film obtained by baking the inner surface coating for cans according to the present invention forms a coating film particularly excellent in extraction resistance. When a coating film is extracted with an organic solvent such as methyl ethyl ketone or chloroform, the amount of components soluble in the solvent is at a level of 10% to 20% in a normal epoxy-phenol coating film, but the coating film according to the present invention In the film, it was about 1/2 or less, indicating that the amount of low molecular weight substances in the film was extremely small. This indicates that when a can is filled with contents and stored for a long time, the change in the coating film over time is small, and the shelf life of the can is extended. From the perspective of food hygiene, for example, the amount of potassium permanganate consumed as stipulated by the Food Sanitation Law is reduced to about 1/2 or less compared to ordinary epoxy-phenol coatings, as well as the amount extracted by solvents. be able to. Furthermore, the flavor retention of the contents is also extremely good. Furthermore, the inner surface paint for cans according to the present invention has extremely excellent adhesiveness to base metals used as materials for metal cans, such as tinplate, stain-free steel, and aluminum. Considering the current situation where various problems with metal cans are ultimately linked to peeling of the paint film, adhesion is the most important performance for can paints. As described above, the present invention is particularly useful as a paint for cans;
It can be used for all applications of epoxy-phenol paints that have been used for inner can surfaces, primers for adhesive cans, etc., and can also be applied to can exterior surfaces. Furthermore, by utilizing the extremely high adhesiveness to metal materials, which is one of the characteristics of the present invention, it is useful as a paint for furniture, electrical appliances, automobiles, toys, steel pipes, tanks, etc. The present invention will be specifically explained below. In the example, "part",
"%" indicates parts by weight or weight %. Example 1 [Preparation of phenolic resin solution] 136 parts of p-tert-butylphenol, 162 parts of a 37% formaldehyde aqueous solution, and 160 parts of a 25% aqueous sodium hydroxide solution were placed in a flask, reacted at 50°C for 3 hours, and then treated with hydrochloric acid. Neutralize and separate water. After water separation, 250 parts p-tert-butylphenol, 10%
Add 3.7 parts of hydrochloric acid and 250 parts of water, stir for about 30 minutes, and when the heat generation has finished, add 160 parts of 25% sodium hydroxide.
part, add 120 parts of 37% formaldehyde aqueous solution to 50 parts.
After reacting for 3 hours at ℃ and neutralizing with hydrochloric acid to separate the aqueous layer, washing with water and water separation were repeated 3 times, and the mixture was dissolved in a mixed solvent of n-butanol/xylene/=1/1.
% phenolic resin solution was obtained. The obtained resin
As a result of GPC analysis, 91% of p-tert-butylphenol was methylolated as a trimer, and the rest contained small amounts of methylolated monomer, methylolated dimer, and methylolated tetramer. It was contained. [Adjustment of paint] 80 parts of Epicoat 1007 (epoxy resin manufactured by Yuka Ciel Epoxy Co., Ltd.) was mixed with Solbetsuso 100 (manufactured by Etsuso Chemical Co., Ltd.).
The mixture was dissolved in 60 parts of ethylene glycol monoethyl ether, 50 parts of ethylene glycol monoethyl ether, and 50 parts of cyclohexanone, and 60 parts of the phenolic resin solution obtained in the previous section was added to obtain a paint with a solid content of 33%. [Paint Test] The obtained paint was applied to a tin plate using a #50 tin coating using a roll coater so that the dry coating film was 5μ, and then baked at 200°C for 10 minutes to form a painted plate. 1% of the obtained painted board (coating area 400cm ² )
Immerse in a 500ml beaker containing 400ml of sodium chloride aqueous solution, cover with aluminum foil, and heat to 118°C.
When a painted board was retorted for 90 minutes and stored at 50°C for 3 months, a cellophane tape test was performed, and no peeling was observed. (100/100) In addition, a painted plate was created using an aluminum plate instead of a tin plate, and a test piece with a coating area of 400 cm ² was immersed in 400 ml of water in a 500 ml beaker, and the lid was covered with aluminum foil. After that, an extraction process was performed at 118℃ for 90 minutes, and the amount of potassium permanganate consumed was measured for the extract according to the test method described in the Food Sanitation Law, and the amount of potassium permanganate consumed was 1.8 ppm. . Example 2 [Preparation of phenolic resin solution] 136 parts of p-tert-butylphenol, 162 parts of 37% formaldehyde aqueous solution, and 160 parts of 25% sodium hydroxide aqueous solution were charged into a flask, reacted at 50°C for 2 hours, and then heated to 100°C. Increase the temperature to 100℃ and further increase the temperature to 1
After reacting for hours and neutralizing with hydrochloric acid, n-butanol/
Extraction was performed with a mixed solvent of xylene = 1/1 to obtain a 33% phenolic resin solution. As a result of GPC analysis,
At 50°C for 2 hours, more than 90% of the reaction product was p.
The final product is a dimethylol compound of p-tert butylphenol, and 9% of the final product is a methylol compound of p-tert butylphenol, 36% is a methylolated dimer, 41% is a methylolated trimer, and 9% is a quaternary methylol compound. Of the methylolated products, 5% were methylolated products of pentamer or more. [Preparation of paint] Example 1 except that the phenolic resin solution in the previous section was used instead of the phenolic resin solution in Example 1.
A paint with a solid content of 33% was obtained using the same procedure as above. [Paint Test] Coated #50 tin plates and aluminum plates were prepared in the same manner as in Example 1, and the same tests were conducted. A tin coated plate was immersed in a 1% aqueous sodium chloride solution, retorted at 118°C for 90 minutes, and then stored at 50°C for 3 months. No peeling was observed in the cellophane tape test. In addition, the amount of potassium permanganate consumed was 2.3 ppm. Comparative Example 1 [Preparation of phenolic resin solution] 136 parts of p-tert-butyl phenol, 162 parts of 37% formaldehyde aqueous solution, and 80 parts of 25% sodium hydroxide aqueous solution were placed in a flask, reacted at 100°C for 2.5 hours, and then diluted with hydrochloric acid. After mixing, extract with a mixed solvent of n-butanol/xylene = 1/1 to obtain 33%
A phenolic resin solution was prepared. As a result of GPC analysis, 8% of unreacted p-tert-butylphenol,
Methylolated product of p-tert-butylphenol 16
%, 21% of methylolated dimers to tetramers, and 55% of methylolated pentamers or more. [Preparation of paint] Example 1 except that the phenolic resin solution in the previous section was used instead of the phenolic resin solution in Example 1.
A paint with a solid content of 33% was obtained using the same procedure as above. [Paint test] As a result of testing in the same manner as in Examples 1 and 2,
After retort treatment at 118°C for 90 minutes and storage at 50°C for 3 months, 75% peeling was observed in a cellophane tape test. Also, potassium permanganate consumption is
It was 16.4ppm. Examples 3 and 4 and Comparative Examples 2 and 3 [Synthesis of monomethylol and dimethylol products of p-cresol] 108 parts of p-cresol, 162 parts of a 37% formaldehyde aqueous solution, and 160 parts of a 25% aqueous sodium hydroxide solution were charged into a flask. After reacting at 50° C. for 2 hours, the precipitate was neutralized with hydrochloric acid, filtered, washed with water four times, and then dried to obtain a dimethylol compound with a purity of 97%. [Synthesis of methylol compound of p-cresol trimer] In a flask, 216 parts of p-cresol, 168 parts of p-cresol dimethylol compound, and 3.7 parts of 10% hydrochloric acid were charged and stirred for about 30 minutes. 350
of water was added to the flask, and 162 parts of a 37% formaldehyde aqueous solution and 160 parts of a 25% sodium hydroxide aqueous solution were added to the flask, and after reacting at 50°C for 2 hours, it was neutralized with hydrochloric acid, and the precipitate was filtered. , water washing, and filtration were repeated four times, followed by drying to obtain a trimeric methylol compound with a purity of 90%. [Synthesis of resol solution of p-cresol] 108 parts of p-cresol, 162 parts of a 37% formaldehyde aqueous solution, and 40 parts of a 25% aqueous sodium hydroxide solution were placed in a flask, and after reacting at 100°C for 3 hours, n- Dissolve the resin in 130 parts of butanol and 130 parts of xylene, let it stand, and separate the aqueous layer. Solid content: 33%
A phenolic resin solution was obtained. As a result of GPC analysis, 6% of unreacted p-cresol, 13% of methylolated p-cresol, 24% of methylolated dimers to tetramers, and 57% methylolated pentamers or higher.
It was %.

[Table] Based on the formulation shown in Table 1, epoxy resin and phenolic resin were dissolved to prepare paints each having a solid content of 33%. [Test] Using the obtained paint, a chromium-treated steel plate with a thickness of 0.23 mm was coated with a roll coat so that the dry coating film was 5μ, and baked in two ways: 210℃ for 10 minutes and 260℃ for 30 seconds. I went there. Using painted plates, we measured the amount of potassium permanganate consumed and observed the state of the coating film after retort treatment at 118°C for 90 minutes. In addition, an adhesive test piece was prepared by sandwiching a nylon 12 film with a thickness of 60μ between painted plates and pressing it at 200℃ for 30 seconds.
T-peel strength was measured for the adhesive pieces stored at 50°C for 3 months. The results are shown in Table 2. As is clear from Table 2, Examples 3 and 4 had better curing properties in high-temperature, short-time baking than Comparative Examples, and exhibited excellent performance as primers for adhesive cans.

【table】

Claims (1)

[Claims] 1. Bisphenol A type epoxy resin 40 to 95
In a coating composition containing a product obtained by mixing or premixing 5 to 60 parts by weight of a phenolic resin and 5 to 60 parts by weight of a phenolic resin, the phenolic resin is obtained by addition-condensation reaction of formaldehyde to an alkylphenol represented by the following general formula. A coating material characterized by being a phenolic resin containing a methylolated product of a dimer or tetramer phenol as a main component, and at least 40% by weight of a methylolated product of a trimer phenol based on the phenolic resin component. Composition. (In the formula, R ₁ is an alkyl group having 1 to 12 carbon atoms.)