JPH0435508B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coating composition for the inner surface of a can that has excellent processing resistance and extraction resistance. Conventionally, cans for cans have been coated with a protective paint on their inner surfaces to prevent metal from leaching and corrosion of the can. usually,
An epoxy-phenol paint for the inside of a can is used as such a paint for the inside of a can. That is, a mixture of an epoxy resin as a main component and a resol type phenol resin as a crosslinking agent component, or a partial condensate generally referred to as precondensation, is widely used and serves as a protective coating. On the other hand, in recent years, cans of various shapes have been developed, and the types of contents of cans have rapidly increased, and demands for paints for the inside of cans have become more sophisticated. Therefore, there is a demand for the development of paints that have higher processability and excellent corrosion resistance. In addition, the contents of the can include beverages such as carbonated drinks, fruit juice drinks, and coffee drinks.
There are many types of food such as meat, vegetables, and retort food. Among these contents, those other than carbonated drinks are
After packing the contents, a high temperature sterilization process is required. At that time, the substance is extracted (transferred) from the paint for the inner surface of the can to the contents, and the extracted substances impair the taste and aroma of the contents, and are also problematic in terms of food hygiene. Therefore, reducing the amount of extracted substances becomes a very important issue from the viewpoint of food hygiene and flavor retention. In order to reduce the amount of extraction, thermosetting resins can promote cross-linking reactions and reduce low molecular weight substances, but this results in a hard and brittle coating, resulting in poor processability and adhesion. . Therefore, they could not be used in applications where those physical properties were particularly required. Therefore, in order to solve the above problem, the present inventors conducted extensive research and found that by using phenoxy resin in combination with epoxy resin, which is the main component of the coating film of epoxy-phenol paint for the inside of cans, the coating film can be improved. molecular weight. That is, the amount of low molecular weight substances in the coating film is reduced. As a result, the extraction resistance and adhesion are excellent, the toughness of the coating film is increased, and the processability is improved. Furthermore, by using the phenoxy resin in combination, it has become possible to reduce the amount of the phenol resin as a crosslinking agent, which is the main molecular weight substance, to an extent that is hardly practical in the prior art.
It has been found that the coating film thus obtained has excellent extraction resistance, and that the reduction in crosslinking density increases the elongation rate of the coating film and improves processability. That is, the present invention provides bisphenol A type epoxy resin (A), phenoxy resin (B) and phenol resin (C) in a weight ratio of (A):(B) of 60:40 to 95:5, and (A+B). :(C) consists of 90:10 or 98:2,
Furthermore, the present invention relates to a coating composition for the inner surface of a can, in which 0.1 to 3 parts by weight of an acidic catalyst (D) is added, if necessary, to 100 parts by weight of the resins (A), (B) and (C). The bisphenol A type epoxy resin (A) used in the present invention can be produced by condensing epichlorohydrin and bisphenol A to a high molecular weight in the presence of an alkali catalyst, or by condensing epichlorohydrin and bisphenol A to a low molecular weight compound in the presence of an alkali catalyst. It is produced by condensation with an epoxy resin and polyaddition reaction between this low molecular weight epoxy resin and bisphenol A. The phenoxy resin (B) used in the present invention has the same resin skeleton as (A), has an extremely high molecular weight of 20,000 or more, and does not contain any epoxy groups. In the present invention, the phenol resin (C) is a resin obtained by condensing an arbitrary phenol component and formaldehyde in the presence of a basic catalyst. Also,
The phenol components constituting the phenolic resin include O-cresol, p-cresol, p-tert-
Butylphenol, p-ethylphenol, 2,
3-xylenol, 2,5-xylenol, p-
Bifunctional phenols such as tert-aminophenol, p-nonylphenol, p-phenylphenol, p-cyclohexylphenol, carbolic acid, m-cresol, m-ethylphenol,
Trifunctional phenols such as 3,5-xylenol and m-methoxyphenol, monofunctional phenols such as 2,4-xylenol and 2,6-xylenol, bisphenol A, bisphenol B, bisphenol F, etc. Tetrafunctional phenols and the like may be used alone or in combination of two or more. As the basic catalyst for the phenol resin (C), any of the basic catalysts conventionally used in the production of resol type resins may be used, such as ammonia, amines, alkali metal hydroxides, and alkaline earth metal hydroxides. oxides of metals, alkali metal oxides, and alkaline earth metal oxides can be used. Furthermore, the paint for the inside of cans according to the present invention can be heated to 50°C or 50°C like conventional epoxy-phenol paints.
Heat the reaction at 200℃ for 10 minutes to 10 hours. A partial condensate produced by performing an operation called precondensation can be contained. Such precondensation is normally carried out for the purpose of reducing coating defects such as repellency or reducing changes over time as a coating material, but in the present invention, bisphenol type epoxy resin (A),
This is important in terms of adjusting the compatibility between the phenoxy resin (B) and the phenol resin (C) or adjusting the heterogeneous structure in the coating film, and it It can be done in the presence of An important feature of the present invention is that it contains a bisphenol A type epoxy resin (A), a phenoxy resin (B), and a phenol resin (C) in a specific weight ratio,
The coating film obtained using the paint for the inside of a can of the present invention has excellent extraction resistance, high processability, and adhesion. The weight ratio of bisphenol A type epoxy resin (A) and phenoxy resin (B) is preferably in the range of 60:40 to 95:5, and when the weight ratio of component (B) exceeds 40, The viscosity is high and workability is poor, and if the weight ratio of component (B) is less than 5, the effect of adding the high molecular weight substance is lost. Furthermore, the weight ratio of the phenol resin (C) to the mixture of the bisphenol A type epoxy resin (A) and the phenoxy resin (B) is preferably in the range of 90:10 to 98:2; If the weight ratio of the components exceeds 10, conventional epoxy
Same as phenol-based paint, it contains many low molecular weight substances. Thus, the coating film has poor extraction resistance, high crosslinking density, and poor processability. If the weight ratio of component (C) is less than 2, the crosslinking density will decrease despite the addition of a high molecular weight substance.
Retort resistance under high temperature sterilization conditions is insufficient. In the can inner coating composition according to the present invention,
As with conventional epoxy-phenol paints, phosphoric acid or phosphoric acid esters (D) can be added to the resin as needed.
From 3 parts by weight for the total of (A) + (B) + (C) 100 parts by weight
It can be used in a range of 0.1 parts by weight. phosphoric acid,
In addition to acting as a curing catalyst, phosphoric acid esters are also effective as surface treatment agents for underlying metals.
Effective in improving corrosion resistance. Furthermore, when forming a coating, an amino resin or a novolac resin can be appropriately blended within a range that does not impede the effects of the present invention, and the amount of the above resin blended is preferably less than 10 parts by weight per 100 parts by weight of the coating composition of the present invention. If this amount exceeds 10 parts by weight, the resistance to extraction by low molecular weight substances decreases. Examples of the amino resin include those obtained by etherifying a part of a condensate of formaldehyde with one or more of urea, melamine, benzoguanamine, etc. with alcohol. Furthermore, various additives such as a repelling agent and an antifoaming agent can be used in the present invention. Above, we have explained about the paint for the inside of cans.
It can also be applied as is to paints for the inside of cans. According to the present invention, it is possible to significantly improve processability, so instead of using various types of paint for the inside of cans depending on the shape and contents of the can, it is now possible to use only one type of paint for the inside of cans. I can do it.
Therefore, can manufacturing can be significantly streamlined. Furthermore, since it is possible to significantly reduce the amount extracted from the can inner surface paint to the contents, it is also possible to significantly improve food hygiene characteristics and flavor retention characteristics when stored as a can for a long period of time. For example, in the case of a three-piece can, the paint for the inner surface of a can of the present invention can be applied to a black plate, a tin plated steel plate, a stain-free steel plate, an aluminum plate,
It can be applied to the surface of the composite metal material in advance, then baked, and then joined to form a can body by means such as soldering, welding, or adhesive bonding. Alternatively, two-piece cans and three-piece cans can also be coated and baked after can manufacturing. Further, the paint for the inside of a can according to the present invention can be used as a single coat or a double coat. The can interior paint of the present invention can be applied to can materials, can bodies, can lids, and cans by any means such as roller coating, spray coating, flow coating, etc., and the coating thickness is from 1 to 20 microns. range is preferred.
Appropriate conditions for baking the paint are a temperature of 150 to 250°C for 30 seconds to 20 minutes. The present invention will be specifically explained below with reference to Examples. In the examples, "part" and "%" indicate parts by weight and weight %. [Production of epoxy resin solution (A)] Epicote 1009 manufactured by Yuka Ciel Epoxy Co., Ltd. was dissolved in a mixed solvent of butyl cellosolve and xylene 1/1 to obtain a 35% epoxy resin solution (A). [Production of epoxy resin solution (B)] Epicote 1007 manufactured by Yuka Ciel Epoxy Co., Ltd. was dissolved in a 1/1 mixed solvent of butyl cellosolve and xylene to obtain a 35% epoxy resin solution (B). [Production of phenoxy resin solution (C)] Phenoxy PKHH manufactured by Union Carbide Chem.
was dissolved in a mixed solvent of butyl cellosolve and xylene (1/1) to obtain a 20% resin solution (C). [Manufacture of phenolic resin solution (D)] 100 parts of carbolic acid and 100 parts of 37% formaldehyde aqueous solution
and add 10 parts of 28% ammonia water to 80 parts.
Heat for 60 min at °C. Water was removed under reduced pressure at 60° C. (requiring about 40 minutes), and then 100 parts of butanol was added to dissolve the resin. The methylol groups of this resol-type phenolic butanol solution were converted to butyl ether while refluxing butanol at 110 to 120°C for 2 hours, and the butyl-etherified resol type had a resin content of 50% and a viscosity of about 60 seconds (Food Cup No. 4, 26.7°C). Approximately 200 parts of phenolic resin solution was obtained. [Production of phenolic resin solution (E)] Add 100 parts of 37% formaldehyde aqueous solution to 50 parts of carbolic acid and 50 parts of orthocresol, add 1 part of caustic soda to this, react at 80°C for 90 minutes, and then dehydrate at 60°C under reduced pressure. (It takes about 40 minutes). Next, add 100 parts of butanol to dissolve the resin.
Add 1 g of 85% phosphoric acid to this. Then 110-120
Heated at ℃ for 2 hours, and after heating, filtered the solution to separate the generated sodium phosphate, leaving 50% of the heated residue.
%, viscosity approximately 40 seconds (Food Cup No. 4, 26.7℃)
Approximately 200 parts of a resol type phenolic resin solution was obtained. [Manufacture of phenol resin solution (F)] 100 parts of bisphenol A, 140 parts of a 37% formaldehyde aqueous solution, and 2 parts of caustic soda were added, reacted at 60°C for 3 hours, and then dehydrated at 50°C for 1 hour under reduced pressure. Next, 100 parts of butanol and 3 parts of phosphoric acid were added, and a reaction was carried out at 110 to 120°C for 2 hours. After the reaction was completed, the solution was filtered to remove the produced sodium phosphate, yielding about 200 parts of a phenolic resin solution with a heating residue of 50% and a viscosity of N (Gardner foam viscometer, 25°C). [Manufacture of paint] Each component shown in Table 1 was mixed, 0.5 PHR of phosphoric acid was added to the total amount of resin, and precondensation was performed at 100°C for 3 hours to obtain the results of Examples 1 to 4 and Comparative Examples 1 to 3. Manufactured 76 types of paint. The obtained paint was coated on an aluminum plate and a stain-free steel (thickness
0.23 mm) and a tin plate (thickness 0.23 mm, tin content #50) using a roll coater and baking at 210°C for 10 minutes to obtain a coated plate. Table 2 shows the results of the coating film performance test for the obtained coated board.

【table】

[Table] The test method for coating film performance in Table 2 above is as follows. Test method for potassium camangate consumption 400cm ²
An aluminum coated plate with a coating area of Potassium permanganate consumption was measured in accordance with the test method described. Processability test method Punch out a #301 can lid from a stain-free steel coated plate with the coated side facing inside. This was made acidic with hydrochloric acid.
Immerse it in a 20% copper sulfate solution for 5 minutes and check whether copper sulfate precipitates on the surface of the paint film. Processability is 0
Evaluate with -10. A rating of 0 is given when copper is deposited on the entire surface of the shoulder and expansion ring part of the can lid, and a score of 10 is given when no copper is deposited at all. Adhesion test method: Reach the material with a razor blade on a tin plate 5
Make 3 straight cuts with a length of about 30mm at mm intervals, then make 3 similar cuts at right angles to these.
Sekisui Chemical's cellophane adhesive tape is applied over the cut, and then the tape is rapidly pulled off. Examine the surface of the removed tape and check to see if any paint film has adhered to the tape and peeled off. Evaluate the state of peeling of the paint film on a scale of 0-10. A rating of 0 is given when the paint film completely adheres to the tape and peels off, and a score of 10 is given when no peeling occurs at all. Steam resistance test method Place a tin coated plate in a pressure cooker with water so that about 1/2 of the coated plate is submerged in water, cover with a lid, and heat.
Treat for 80 minutes at a steam pressure of 1 Kg/cm ² . After steam treatment for 80 minutes, the coated plate was removed and the steam resistance of the coating film was evaluated by checking for whitening of the coating film (0-10). Rating is 0 if the paint film is completely whitened, and 10 if there is no whitening at all.

Claims (1)

[Claims] 1 Bisphenol A type epoxy resin (A), phenoxy resin (B) and phenol resin (C) in weight ratio
(A):(B) is 60:40 to 95:5, and (A+B):
(C) consists of 90:10 to 98:2, and the resin
A coating composition for the inner surface of a can, comprising 0.1 to 3 parts by weight of an acidic catalyst (D) added as needed to 100 parts by weight of the total amount of (A), (B) and (C).