JPH0569871B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an organic solvent-based can paint with improved coating film adhesion, and more specifically, a three-component paint containing an epoxy resin, a phenolic resin or an amino resin, and an acrylic resin. Concerning a can paint consisting of. (Prior art) Conventionally, in the can manufacturing industry, metal materials for can manufacturing and the can itself have been painted with various paints in order to prevent metal from leaching into the contents and to prevent metal corrosion. It is being done. This coating film undergoes severe mechanical processing such as flanging, seaming, necking, beading, and drawing during the can manufacturing process, and is also subjected to harsh hot water treatments such as retort sterilization during the can manufacturing process. However, it is required to have strong adhesion to the metal during these processing, sterilization, and subsequent aging. Furthermore, coatings for can manufacturing may be required to have properties other than the above-mentioned properties. For example, in the field of can making, so-called tain-free steel TFS, such as chrome-plated steel sheets and chromic acid-treated steel sheets with a chromium oxide film on the surface, are being used instead of tin-plated steel sheets as metal materials for cans.
is widely used. Since this metal material for cans is difficult to solder, the side seam of the can body is formed by joining the opposing edges of the metal material for cans with an organic adhesive such as polyamide. It is carried out exclusively. According to the known adhesive can making method, first, a primer serving as an adhesion promoter and an undercoat is applied to both surfaces of the metal material for the can, and then, after baking,
By melting the polyamide adhesive located between the opposing edges of the metal material for the can, and then cooling and solidifying the molten polyamide adhesive under pressure, the two edges of the metal material for the can are melted. to join. The can body thus formed is sealed with a can lid,
Next, a top coat is applied to the inner surface of the can by spraying or the like to produce a can product. Conventionally, organic solvent-based paints consisting of epoxy resin and phenolic resin or amino resin (curing agent resin) have been widely used as paints with particularly excellent adhesion to metal materials for cans. It is also known to be useful as a primer. (Problems to be Solved by the Invention) Among can paints, adhesive can paints require the most adhesion and workability. This is because, in the case of adhesive cans, the bond between the polyamide adhesive and the primer layer is strong, and therefore, failure of the joint (broken shell) or leakage at the joint is due to the close contact between the primer layer and the metal material. This is because it occurs due to destruction or decreased adhesion. Moreover, in the case of adhesive cans, the side seam part has a structure in which the metal material is double layered with an adhesive layer in between, and in this part, the inner side is axially bent during flanging and seaming. The bonded portion is subjected to complex shear stress as it is stretched and compressed on the outside in the axial direction, and also stretched in the circumferential direction. In the above-mentioned epoxy resin-curing agent resin paints, attempts have been made to improve the film processability by increasing the molecular weight of the epoxy resin used or lowering the usage ratio of the curing agent resin, but in the case of the former. In the case of the latter, the adhesion of the paint film decreases and the paint film tends to lift due to heat sterilization.In the latter case, it becomes easier for moisture or corrosive components to permeate from the contents to the metal, resulting in a decrease in the corrosion resistance of the painted can. In addition, the uncured epoxy resin content may be eluted into the contents, which may have a negative effect on hygienic properties and flavor retention properties. Therefore, an object of the present invention is to solve the above-mentioned drawbacks of conventional epoxy resin-hardener resin can paints, and to provide a can paint that has excellent adhesion to metal while maintaining excellent workability and corrosion resistance. is to provide. Another object of the present invention is to provide an organic solvent type paint for cans which is particularly useful as the aforementioned primer for adhesive cans and has particularly excellent adhesion. (Means for Solving the Problems) The present inventors have discovered that when an acrylic resin having an acid value within a certain range is blended into an epoxy resin-curing agent resin-based organic solvent can paint in a certain amount ratio. , while maintaining the excellent processability and corrosion resistance of the paint,
It has been found that the adhesion to metal can be greatly improved. That is, according to the present invention, a bisphenol type epoxy resin and a curing agent resin selected from the group consisting of a phenolic aldehyde resin and an amino resin are combined into 95:
An organic solvent type can with improved adhesion characterized by containing an acrylic resin with an acid value of 35 to 350 in a weight ratio of 5 to 40:60 and 3 to 30% by weight based on the total amount of both. Paint provided. (Function) The can paint of the present invention contains a bisphenol type epoxy resin and a phenol resin or an amino resin in a ratio of 95:
It is contained in a weight ratio of 5 to 40:60, especially 90:10 to 50:50, and a paint with a weight ratio within this range is a paint for cans with excellent corrosion resistance, processing resistance, and retort resistance, especially This is a well-known primer coating for adhesive cans. In other words, if the amount of the epoxy resin component is larger than the above range, the corrosion resistance of the coating film tends to decrease, and the extraction resistance and flavor retention properties of the coating film tend to decrease, and conversely, the amount of phenolic resin and amino resin tends to decrease. When the curing agent resin component of is more than the above range,
The workability of the coating film decreases. In the present invention, an acrylic resin having an acid value of 35 to 350, particularly 60 to 320, is used based on the total amount of epoxy resin and curing resin.
By incorporating it in an amount of 5% to 25% by weight, the adhesion of the coating film to metal can be significantly improved. The fact that adhesion to metals is significantly improved by blending an acrylic resin with an acid value within the above range into an epoxy-phenol or epoxy-amino paint is not a phenomenon discovered. Although the theoretical explanation has not yet been clarified, it is believed that the carboxyl groups of acrylic resins, which correspond to the acid value, contribute to improving the adhesion to metals, and that epoxy-phenol Both epoxy-based and epoxy-amino based coating resins are composed of hard polymer segments, but acrylic resins are composed of soft polymer segments, and the coexistence of these soft segments tends to remain when the coating film cures. This is thought to be due to the fact that it acts to relieve the stress caused by this. It is also important that the acid value of the acrylic resin used is within the above range; if the acid value is lower than the above range, the adhesion strength will not be improved much; on the other hand, if it is higher than the above range, the retort Hot water-resistant adhesion and time-resistant adhesion decrease during sterilization and afterward. It is also important to use the acrylic resin in the above amount ratio; if the amount is less than the above range, the desired degree of adhesion may not be obtained.
Moreover, when the amount exceeds the above range, the corrosion resistance of the coating film tends to decrease. The acrylic resin used in the present invention has a molecular weight of 10,000 to 200,000, especially from the viewpoint of processability and extraction resistance of the coating film.
It is desirable to have a number average molecular weight of 20,000 to 150,000. (Preferred embodiment of the invention) As the epoxy resin in the paint of the present invention,
Bisphenol type epoxy resins obtained by polycondensation of bisphenols such as bisphenol A and epihalohydrin are preferred, and their epoxy equivalents are generally in the range of 400 to 20,000, particularly in the range of 1,000 to 5,000, and the number average molecular weight is in the range of 1,000 to 1,000. 20000, especially
Preferably, it is in the range of 2,000 to 13,000. As the phenol-aldehyde resin used as a curing agent resin for the epoxy resin component, so-called resol type resins obtained by polycondensing various phenols and formaldehyde in the presence of an alkali catalyst are advantageously used. As the phenols, monocyclic monovalent phenols and polycyclic divalent phenols can be used, or a combination thereof can also be used.
In the case of phenols, a methylol group can be introduced into the ortho or rose position of the phenolic hydroxyl group, and its functionality is determined by whether or not these positions are substituted. An example is as follows. o-cresol, p-cresol, p-tert-
Butylphenol, p-ethylphenol, 2,
Lower alkyl-substituted bifunctional phenols such as 3-xylenol and 2,5-xylenol; Other bifunctional phenols such as p-tert-amylphenol, p-nonylphenol, p-phenylphenol, and p-cyclohexylphenol Class: Phenol (carbolic acid), m-cresol,
m-ethylphenol, 3,5-xylenol,
Trifunctional phenols such as m-methoxyphenol; monofunctional phenols such as 2,4-xylenol and 2,6-xylenol; 2,2'-bis(4-hydroxyphenyl)propane (bisphenol A) , 2,2'-bis(4-hydroxyphenyl)butane (bisphenol B), 1,1'-bis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)methane (bisphenol F) , 4-hydroxyphenyl ether, p-(4-hydroquine)phenol, and polycyclic polyhydric phenols. The phenolic resin used is generally 200 to 2000,
In particular, it is desirable to have a number average molecular weight of 250 to 1000. For the amino resin, an amine component such as urea, thiourea, guanidine, dicyandiamide, melamine, acetoguanamine, benzoguanamine, etc. is reacted with formaldehyde, and if necessary, at least a portion of the methylol groups in the resulting resin are converted to a higher alcohol such as butanol. A resin obtained by reacting with is used. The amino resin used is 200 to
It is preferred to have a number average molecular weight of 3000, especially 300 to 2000. As the acrylic resin, any acrylic resin can be used as long as the acid value is within the above range. This acrylic resin is made of an ethylenically unsaturated carboxylic acid or its anhydride that provides a carboxyl group with the above-mentioned acid value in the resin, an acrylic ester or a methacrylic ester, and optionally other ethylene that can be copolymerized with these. Consists of a copolymer with a system unsaturated monomer. Examples of the ethylenically unsaturated carboxylic acid or its anhydride include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, and itaconic anhydride. Examples of esters of acrylic acid and methacrylic acid include methyl (meth)acrylate and (meth)acrylate.
Ethyl acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-(meth)acrylate hexyl, (meth)acrylic acid 2-
Examples include ethylhexyl and n-octyl (meth)acrylate. However, the above (meth)acrylic acid refers to acrylic acid or methacrylic acid. Other comonomers copolymerized with these monomers include styrene, vinyltoluene, acrylonitrile, methacrylonitrile, and the like. Examples of suitable combinations of acrylic copolymers include (1) methyl methacrylate/2-ethylhexyl acrylate/acrylic acid, (2) styrene/methyl methacrylate/ethyl acrylate/methacrylic acid, and (3) styrene/acrylic. (4) Methyl methacrylate/ethyl acrylate/acrylic acid, etc. These acrylic resins can be easily obtained by polymerizing these monomers in an organic solvent in the presence of azobisisobutyronitriles or peroxides. In the present invention, there is no particular restriction on the order of adding and mixing the epoxy resin, phenolic resin, or amino resin, and acrylic resin, but generally, the epoxy resin and the phenolic resin or amino resin are mixed together with ketones, esters, alcohols, or acrylic resins. Mix in a dissolved state in a hydrocarbon solvent or a mixed solvent thereof, and if necessary, heat for 1 hour at a temperature of 80 to 130°C.
After preliminary condensation for about 10 hours, an acrylic resin is mixed therein in the form of a solution to obtain the can paint of the present invention. If necessary, a curing catalyst such as phosphoric acid or sulfuric acid, a lubricant such as wax, and a fluidity improver such as Modaflow (acrylic resin manufactured by Monsanto) may be added to this paint. The blending ratio of each resin component in the paint is as described above, but it is generally desirable that the solid content concentration be within the range of 10 to 70% by weight. The can paint of the present invention is particularly useful as an undercoat paint for adhesive cans. In this case, the paint is applied to the entire surface of a can material made of stain-free steel, and the resulting paint film is cured. The thickness of the coating film is 0.5 to 20 μm in terms of solid content, especially 1 to 20 μm.
It is best to be in the range of 10 μm, while the hardening of the coating film is
Curing is preferably carried out so that the gel fraction when extracted with chloroform at 60° C. for 60 minutes is 70% or more, particularly 80 to 98%. The curing reaction in the coating material of the present invention is mainly carried out through a condensation reaction between the methylol group or etherified methylol group in the curing agent resin and the hydroxyl group in the epoxy resin. It is recognized that reactions with the hydroxyl groups and carboxyl groups in the acrylic resin also contribute to the crosslinking reaction. The paint of the present invention is of course useful not only as an undercoat paint for adhesive cans as described above, but also as an inner surface paint for welded cans, deep drawn cans, drawn and ironed cans, and the like. (Effects of the Invention) According to the present invention, by blending an acrylic resin with a specific acid value into an organic solvent-based can coating consisting of an epoxy resin and a phenol resin-based or amino resin-based curing agent, It was possible to significantly improve the adhesion while maintaining the corrosion resistance and process resistance of the paint. Example 1 A solution of 800 parts by weight of bisphenol A type epoxy resin (epoxy resin 1) having a number average molecular weight of about 3750 and an epoxy equivalent of about 3000 was dissolved in 1600 parts of butyl cellosolve was prepared, and bisphenol A, para-cresol, and formaldehyde were dissolved. 200 parts by weight of resol-type phenolic resin derived using an ammonia catalyst (phenol resin 1; bisphenol A/para-cresol = 80/20, number average molecular weight 650) was added to a mixed solvent of xylene, methyl isobutyl ketone, and cyclohexanone (xylene/ Methyl isobutyl ketone/cyclohexanone = 1/1/1) 400
A solution was prepared and mixed with the epoxy resin solution described above. On the other hand, 20 parts of ethyl acrylate, 20 parts of methyl methacrylate, 40 parts of methacrylic acid, 20 parts of styrene
50 parts of ethyl cellosolve and 25 parts of the above mixture were prepared in a flask equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, and an inert gas inlet. After raising the temperature to 90°C with stirring under a nitrogen stream, the remaining amount of the above monomer mixture was added dropwise over 3 hours into a flask maintained at the same temperature for copolymerization, and further, tert-butyl After adding 0.1 part of hydroperoxide and continuing stirring at the same temperature for 3 hours, 50 parts of ethyl cellosolve was added and cooled to complete the reaction. The number average molecular weight of the obtained acrylic resin (acrylic resin 1) was approximately 120,000, the acid value was 124, and the solid content of the resin solution was 50%. 3000 parts by weight of the mixed solution of the above epoxy resin solution and phenolic resin solution was pre-condensed at 110°C for 4 hours to obtain an organic solvent type paint, and the solution of the above acrylic resin based on 400 parts by weight of the paint is shown in Table 1. 7 types of acrylic resin-containing organic solvent-based paints (Paints 1 to 7) were prepared by adding the following amounts and stirring to mix them uniformly. These paints were applied to an electrolytic chromic acid treated steel sheet (hereinafter referred to as TFS) using a roll coater.
It was cured by baking at ℃ for 10 minutes. These painted boards were cut into 5mm width pieces and glued with nylon adhesive.
Bonding was achieved by pressing for 2 minutes with a hot press heated to 200°C. Peel strength was measured using T-peel, and Table 1 shows the initial peel strength immediately after adhesion and the peel strength over time after being immersed in hot water at 90°C for one week.
It was shown to. In addition, these adhesive test pieces were heated at 125℃30
After being subjected to retort treatment for several minutes, the presence or absence of whitening of the coating film and adhesive strength were evaluated, and the results are shown in Table 1. Also, coat one side of TFS with a roll coater,
After baking and drying at 210℃ for 10 minutes, paint and bake the other side in the same way to prepare a double-sided coated board. Using this coated board and nylon adhesive, glue the 202 diamond can body (both ends was processed into 200 diamonds). The adhesive width was 5 mm. After the bottom lid was double-sealed, the coffee beverage was filled and the canopy was double-sealed, resulting in a canned coffee beverage. The canned coffee beverage was sterilized in a retort at 125°C for 30 minutes, cooled and air-dried, and then stored in a warehouse. After 6 months of storage, the can was opened and the presence or absence of abnormalities such as whitening of the paint film and internal corrosion, as well as adhesive strength, were evaluated. The results are shown in Table 1. Comparative Example 1 The same evaluation as in Example 1 was conducted using the organic solvent-based paint of Example 1 (Comparative Paint 1) without adding the acrylic resin solution. The results are also shown in Table 1. Example 2 Eight types of acrylic resin solutions were prepared in the following manner. First, a mixed monomer of ethyl acrylate, methyl methacrylate, and styrene (ethyl acrylate/methyl methacrylate/styrene =
1/1/2) was prepared, mixed with methacrylic acid in the proportions shown in Table 2, and further added with 1 part of benzoyl peroxide to prepare a mixture. Using this mixture, all procedures were the same as in Example 1 except for using benzoyl peroxide instead of tert-butyl hydroperoxide and adjusting the heating and stirring time after the completion of dropping the monomer mixture. Solutions of eight types of acrylic resins were prepared.
The acid value of the obtained acrylic resin is shown in Table 2. 10 parts by weight of these acrylic resin solutions and 150 parts by weight of the organic solvent-based paint of Example 1 were mixed and stirred until homogeneous to obtain acrylic resin-containing organic solvent-based paints (paints 8 to 15). These paints were evaluated by the method shown in Example 1, and the results are also listed in Table 2. Example 3 A bisphenol A type epoxy resin with a number average molecular weight of 1950 and an epoxy equivalent of 1100, and a phenol resin derived from para-cresol and formaldehyde using an alkali metal salt as a catalyst (number average molecular weight 300)
An organic solvent-based paint was prepared in the same manner as in Example 1, and 25 parts of the solution of acrylic resin 1 of Example 1 was mixed with 300 parts by weight of the paint, and the mixture was stirred until uniform. A resin-containing organic solvent type paint (Paint 16) was obtained. The initial peel strength, peel strength over time, and retort whitening of these paints were evaluated using the method shown in Example 1. As a result, the initial peel strength was 6.7 kg/5 mm, the peel strength over time was 5.8 kg/5 mm, and the retort whitening was 6.7 kg/5 mm. Nakatsuta. Comparative Example 2 The same evaluation as in Example 3 was conducted using the organic solvent-based paint (Comparative Paint 2) of Example 3 without adding an acrylic resin solution. As a result, the initial peel strength was 5.5Kg/5mm, and the peel strength over time.
The weight was 4.1Kg/5mm, and there was no retort whitening. Example 4 85 parts of bisphenol A type epoxy resin having a number average molecular weight of 12,700 and an epoxy equivalent of 5,300 were dissolved in 80 parts of ethyl cellosolve, and 15 parts of urea formaldehyde resin was dissolved in a mixed solvent of butanol and butyl cellosolve (butanol/butyl cellosolve = 1). /
1) is mixed with a solution dissolved in 15 parts to form an organic solvent-based paint.Furthermore, 20 parts of the solution of acrylic resin 1 from Example 1 is added, and the mixture is stirred and mixed until homogeneous to form an organic solvent containing acrylic resin. A mold paint (paint 17) was obtained. The initial peel strength and peel strength over time of this paint were evaluated according to the method shown in Example 1 except that a polyester adhesive was used. As a result, the initial peel strength was 4.3 kg/5 mm, and the peel strength over time was 3.6 kg/5 mm. It was 5mm. Comparative Example 3 The same evaluation as in Example 4 was conducted using the organic solvent-based paint of Example 4 (Comparative Paint 3) without adding the acrylic resin solution. As a result, the initial peel strength was 2.5Kg/5mm, and the peel strength over time.
It was 1.7Kg/5mm. Example 5 A bisphenol A type epoxy resin with a number average molecular weight of 21,000 and an epoxy equivalent of 19,000 and a phenol resin (number average molecular weight) derived from para-cresol and formaldehyde using an alkali metal salt as a catalyst
300) in the ratio shown in Table 3, butanol/butyl cellosolve/xylene/Solbetsuso 100 = 1/
Dissolved in a 1/1/1 mixed solvent to achieve a solid concentration of 30%.
Six types of organic solvent-based paints were used. By adding 35 parts of the solution of acrylic resin 1 of Example 1 to 100 parts by weight of these organic solvent-based paints and stirring and mixing, an acrylic resin-containing organic solvent-based paint (paint 1) was prepared.
8-23) were obtained. The initial peel strength, peel strength over time, and retort whitening of these paints were evaluated by the methods shown in Example 1, and the results are also shown in Table 3. Comparative Example 4 Six types of organic solvent-based paints of Example 5 (Comparative Examples 4 to
The same evaluation as in Example 5 was conducted using Example 9) without adding the acrylic resin solution. The results are also shown in Table 3. Example 6 Seven acrylic resins having different molecular weights were synthesized in the same manner as in Example 1 except that the reaction time was adjusted. The number average molecular weights of these acrylic resins are shown in Table 4. Dissolve 850 parts of bisphenol A type epoxy resin with a number average molecular weight of 9,600 and epoxy equivalent of 4,200 in 800 parts of butyl cellosolve, and dissolve 150 parts of melamine resin in 150 parts of a mixed solvent of butanol and butyl cellosolve (butanol/butyl cellosolve = 1/1). 50 parts of each of the above acrylic resin solutions were added per 200 parts by weight of the organic solvent-based paint to obtain seven types of acrylic resin-containing organic solvent-based paints. Paint (Paint 24-3
0) was obtained. The initial peel strength and peel strength over time of these paints were evaluated according to the method shown in Example 1, except that a polyester adhesive was used, and the results are also shown in Table 4. Comparative Example 3 The same evaluation as in Example 6 was conducted using the organic solvent-based paint of Example 6 (Comparative Paint 10) without adding an acrylic resin solution. The results are also shown in Table 4.

【table】

【table】

【table】

【table】

【table】

【table】

【table】

Claims (1)

[Claims] 1. Contains a bisphenol type epoxy resin and a curing agent resin selected from the group consisting of phenolic aldehyde resins and amino resins in a weight ratio of 95:5 to 40:60, and based on the total amount of both. An organic solvent type can paint with improved adhesion, characterized by containing 3 to 30% by weight of an acrylic resin with an acid value of 35 to 350. 2. The can paint according to claim 1, wherein the acrylic resin has a number average molecular weight of 10,000 to 200,000.