JPS6221829B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to coating compositions for metals, and in particular to coating compositions for metal cans. Traditionally, epoxy/phenol resin paints have excellent adhesion to metals, corrosion resistance, water resistance, chemical resistance, solvent resistance, processability, etc. (hereinafter, these performances are abbreviated as practical performance), so they are used for tinplate coatings. It is widely used as a coating agent for metals such as , chiin-free steel, and aluminum. In addition, it is harmless in terms of safety and hygiene, and does not impair the flavor of the contents, so it is particularly suitable as a pre-coating agent for metals used in food packaging materials, especially as a paint for metal cans, and has secured a major position as a high-grade baking paint. are doing. Currently, the above-mentioned epoxy/phenol resin paints are produced by selecting the phenols, aldehydes, and catalysts to be used according to the required coating performance, forming a phenol/aldehyde addition condensate, and then using this as a curing agent. It is used by blending it with epoxy resin in an appropriate ratio. In order for the above-mentioned epoxy/phenol resin paint to become a protective coating film for metals with the above-mentioned practical performance, the phenol resin must be combined with the functional group that the epoxy resin in the epoxy/phenol resin paint has, that is, the hydroxyl group or epoxide group. It is necessary to form a three-dimensional network structure from the functional groups that the epoxide group has, i.e., methylol groups or phenolic hydroxyl groups, and for this reason, heating is required. In particular, the reaction of epoxide groups requires a higher temperature, 180 to 230°C.
It is common to bake for 10 to 15 minutes. However, in recent years there has been a growing trend toward resource conservation and productivity improvement, and it has become necessary to shorten the baking time and save thermal energy. Therefore, we developed an epoxy resin that forms a protective coating on metals with the above-mentioned practical performance using less heat energy and especially in a shorter time.
There has been a demand for phenolic resin paints, that is, epoxy phenolic resin paints that have a faster curing reaction. As a method for accelerating the curing reaction of epoxy/phenolic resin paints, the following methods are generally used in the production of epoxy/phenolic resin paints: (1) selection of phenols, (2) amount of aldehydes used, type and amount of catalyst used. (3) Types of functional groups possessed by the phenolic resin; (4)
Selection of the blending ratio of epoxy resin and phenolic resin, (5) application of curing agents other than phenolic resin, and
The use of this curing agent in combination with a phenolic resin curing agent is being considered, but for methods (1), (2), and (4), the curing speed is only slightly affected by the molecular weight effect. It is difficult to significantly accelerate the curing reaction between the functional groups in the phenolic resin and the functional groups in the epoxy resin. Regarding method (3), attempts have been made to modify the functional groups with epoxy, amide, carboxyl, etc., but the practical performance and curing speed are insufficient. Curing agents other than phenolic resins in (5) include polyamines and polyamides, inorganic acids or organic acids such as phosphoric acid and hydrochloric acid,
There are amino resins, etc., which are effective in accelerating the curing reaction, but each has problems with storage stability.
Those that use these types of paints are two-component type paints, which impairs work efficiency. Furthermore, it has drawbacks such as poor adhesion and processability, making it impractical. Therefore, an effective means has been found that can accelerate the curing reaction of epoxy/phenolic resin paints, save energy and time in the baking process, and provide sufficient practical performance required as a coating composition for metals. It has not been. Therefore, the present inventors attempted to maintain the practical performance required for a metal coating composition and accelerate the curing speed by using an aluminum alcoholate or an aluminum complex compound. It has been known to use aluminum alcoholates or aluminum complex compounds as curing agents for epoxy resins and phenolic resins. It is also known that aluminum alcoholates or aluminum complex compounds are used as hardening agents for epoxy resins and phenolic resins and are effective in shortening baking time and improving chemical resistance, water resistance, solvent resistance, corrosion resistance, etc. However, like other conventionally known curing agents, processability is significantly deteriorated, and even if this is used, a practical coating composition for metals cannot be obtained. That is, it is considered that processability cannot be improved only by using a curing agent to accelerate the curing reaction and increase the crosslink density. This deterioration in workability may result in destruction of the continuous coating film when the metal to be coated with the metal coating composition is further subjected to post-forming. , this also reduces the adhesion to the metal, making it impossible to protect the metal from corrosion. Particularly when the metal is used for metal cans used as food packaging materials, there is a risk of serious defects. However, the present inventors conducted further research and found that by reacting a bisphenol type epoxy resin with an aluminum alcoholate or an aluminum complex compound in advance, the paint can be used in a shorter time or at a lower temperature than conventional epoxy/phenol resin paints. Can be baked, and the protective coating formed by baking has the properties required as a protective coating for metals, such as water resistance, solvent resistance, chemical resistance, and corrosion resistance, and can also withstand post-forming. We have developed a coating composition for metals that has both processability. That is, in the present invention, the average molecular weight is from 1000 to
5800, 100 parts by weight of a bisphenol type epoxy resin with an epoxy equivalent of 450 to 4000 and general formula Al
(OR) _o (L) _3-o (where R is an alkyl group, L is a ketoenol type tautomeric compound, and n is an integer of 0 to 3) or an aluminum complex compound 0.2 to 15 This is a coating composition for metals having excellent rapid curing properties, which is characterized by containing a product soluble in an organic solvent obtained by heating parts by weight. It is not clear what kind of reaction mechanism the metal coating composition of the present invention follows during baking, but due to the high reactivity of aluminum alcoholate or aluminum complex compound, the reaction between epoxy resins, phenolic resins, and between epoxy and phenolic resins is unknown. It is thought that cross-linking occurs through the metal, accelerating curing, and that the increase in molecular weight due to the prior reaction between the epoxy resin and aluminum alcoholate or aluminum complex compound compensates for the deterioration in processability that accompanies accelerated curing. . Each component used in the metal coating composition of the present invention will be described in detail below. Average molecular weight is 1000-5800, epoxy equivalent is 450
~4000, bisphenol type epoxy resin has two highly reactive epoxide groups in one molecule obtained mainly from the reaction of 2,2'-bis(4-hydroxyphenyl)propane and epichlorohydrin. It is a colorless or yellow solid resin at room temperature, and commercially available products include Epicote 1001, 1002, 1004, 1007, 1009 manufactured by Ciel Chemical Co., DER661, 662, 664, 667 manufactured by Dow Chemical Company, 669
etc. It is desirable to use the above-mentioned bisphenol type A as a precoat agent for metals for food packaging materials, but for other metal coatings, other epoxy resins with different starting materials may also be used with average molecular weights and epoxy equivalents within the above range. It can be used within. Further, these epoxy resins may be used alone or in combination of two or more. If the average molecular weight is less than 1000 or the epoxy equivalent is less than 450, the flexibility of the cured coating will be insufficient, causing problems in post-molding, and if the average molecular weight is more than 5800,
Or, if the epoxy equivalent is greater than 4000,
This is undesirable because it impairs adhesion and water resistance. The aluminum alcoholate or aluminum complex compound that is heated and reacted with the epoxy resin is represented by the general formula Al(OR) _o (L) _3-o . Examples of the aluminum alcoholate where n=3 above include aluminum triisopropoxide, aluminum tri-n-butoxide, aluminum triisobutoxide, and the like. Also, n=0,
In the aluminum complex compounds 1 and 2, (L) is bis-(β-
diketone), acetoacetic acid ester, malonic acid ester, etc., and can be easily obtained by mixing the above-mentioned ketoenol type tautomeric compound with aluminum alcoholate. In the present invention, either an aluminum alcoholate or an aluminum complex compound can be used. However, since aluminum alcoholates are easily hydrolyzed, care must be taken when handling them, and the storage stability of the resulting composition may be impaired, so some or all of the alkoxy groups are replaced with ketoenol-type tautomeric compounds. Among these, aluminum tributoxide and diisopropoxyaluminum acetoacetate exhibit excellent effects favorable for achieving the object of the present invention. To produce the coating composition for metals of the present invention, first, 0.2 to 15 parts by weight of the above aluminum alcoholate or aluminum complex compound is blended with 100 parts by weight of the above epoxy resin, and the mixture is heated at 60 to 150°C.
to react for 0.5 to 5 hours. Here, the epoxy resin is bonded via metal and polymerized. In addition, not all of the aluminum alcoholate or aluminum complex compound is consumed in crosslinking the epoxy resin, and some of it remains as a crosslinking agent and is thought to contribute to accelerating the curing of the phenolic resin and epoxy resin that are added later. It is also believed that the polymerization of this epoxy resin suppresses molecular movement, accelerates the drying rate, and prevents deterioration in processability due to promotion of crosslinking. If the amount of aluminum alcoholate or aluminum complex compound is less than 0.2 parts by weight per 100 parts by weight of the epoxy resin, the curing accelerating effect will be extremely weak and impractical, and if it is more than 15 parts by weight, the deterioration of processability due to curing acceleration will be significant, resulting in high Since there is a risk that the effect obtained by molecularization may be lost, the amount of compounding should be 100 parts by weight of epoxy resin.
The amount of aluminum alcoholate or aluminum complex compound is 0.2 to 15 parts by weight, preferably 2 to 10 parts by weight per 100 parts by weight of epoxy resin. In the present invention, in order to achieve an appropriate increase in the molecular weight of the epoxy resin, the epoxy resin is reacted with an aluminum alcoholate or an aluminum complex compound in an organic solvent. At this time, it is necessary to set reaction conditions so that the epoxy resin does not react more than necessary and produce insolubilized substances. The reaction conditions are 60-150°C for 0.5-5 hours, preferably 100-120°C for 2-4 hours. The phenol-formaldehyde resin that can be used in the present invention is obtained by a known method of addition-condensing formaldehyde to phenols under a catalyst, and also includes resins modified with phenolic hydroxyl groups or alcoholic hydroxyl groups. In addition, as phenols, phenol, O-cresol, m-
Cresol, P-cresol, P-tert-butylphenol, P-nonylphenol, P-octylphenol, P-phenylphenol, methylphenol, ethylphenol, propylphenol, isopropylphenol, butylphenol, P-tert-amylphenol , 4・4'-sec
-butylidene diphenol, P-cyclohexylphenol, 4,4'-isopropylidene diphenol, xylenol, phenyl O-cresol,
Catalysts include organic amines such as ammonia, ethylamine, butylamine, diethanolamine, sodium hydroxide, magnesium hydroxide, calcium hydroxide,
Basic compounds such as barium hydroxide, acidic compounds such as hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, oxalic acid, etc., and formaldehyde in 37% aqueous solution or
A 40% butanol solution or the like is used. Conventionally, epoxy/phenolic resin paints have been made by selecting the epoxy resin, selecting the blending ratio of epoxy resin and phenolic resin, and
It is made by selecting the phenol monomers used during phenol resin synthesis, the type and amount of catalyst used, the amount of aldehyde used, the reaction time, etc.
In particular, the phenolic resin used as a curing agent has a significant impact on the performance of the final baked coating, so there were major restrictions on the synthesis conditions of the phenolic resin, as well as the type and properties of the phenolic resin. . However, in the present invention, by adding phenol formaldehyde resin to the product obtained by heat-reacting epoxy resin and aluminum alcoholate or aluminum complex compound in advance to form an epoxy/phenol resin paint, water resistance, which can be seen as a problem of crosslinking density, can be improved. Since the properties such as hardness, solvent resistance, and chemical resistance are fully satisfied by the curing accelerating effect of aluminum alcoholate or aluminum complex compound, the above-mentioned restrictions regarding the phenol formaldehyde resin to be used are significantly reduced, and the phenol formaldehyde resin that can be used is The range of has become wider. The coating composition for metals of the present invention is effective even without the use of phenol formaldehyde resin;
It is preferable to use a phenol formaldehyde resin in a range not exceeding parts by weight. At this time, when corrosion resistance is particularly important, it is desirable to use a large amount of phenol formaldehyde resin within this range, and when processability is particularly important, it is desirable to use a small amount, but phenol formaldehyde resin that provides sufficient corrosion resistance and processability is desirable. In order to expect the effect of the resin, it is recommended to use 10 to 50 parts by weight. The phenol formaldehyde resin is not involved in the crosslinking of the epoxy resin, but the crosslinking of itself or with the epoxy resin is promoted by the aluminum alcoholate or the aluminum complex compound, which is a factor in achieving the object of the present invention. In the production of the coating composition for metals of the present invention, an organic solvent is used in consideration of work efficiency, ease of reaction, and suitability for coating on the underlying metal. Such organic solvents include ketone, ether, ester, and alcohol organic solvents, and are usually used as a mixed solvent to dissolve in advance the epoxy resin to be heated and reacted with the aluminum alcoholate or aluminum complex compound. .
It is also used as a diluent for phenol formaldehyde resin. In the metal coating composition of the present invention, if necessary, a resin such as phenoxy resin, epoxy ester resin, acrylic resin, etc. may be added within 40% by weight (solid content) of the metal coating composition. It can also be used to adjust the properties of the coating. The coating composition for metals of the present invention is applied onto the object to be coated by a general method such as brush painting, spray painting, or roll coating, and is baked at a high temperature of 200°C to 350°C for several seconds to several minutes. It becomes a coating film by drying. It also forms excellent coatings when baked using conventional baking methods at 180°C to 230°C for 10 to 15 minutes. The amount of coating film is suitably about 1 μ to 20 μ, but there is no particular limitation. As the object to be coated, common metal materials such as steel materials such as mild steel and hard steel, galvanized steel sheets, tin-plated steel sheets, chromium-treated steel sheets (tein-free steel), aluminum sheets, and copper sheets can be used. The coating composition for metals according to the invention is useful as a protective coating for the metal materials mentioned above, either by using the product obtained from the epoxy resin as an organic solvent-based coating or by combining it with other resins. Coatings in combination with phenolic resins are particularly useful for metal can applications. The uses of metal cans include:
So-called 3-piece cans with side seams (solder cans,
It is useful as a protective paint for the top, bottom and body of cans (adhesive cans, welded cans) or as a repair paint for side seams, and is also useful for so-called two-piece cans (DI
It is also useful for the bottom and top of cans (cans, DR cans, square cans, PC cans, etc.). It is particularly effective when used to repair aluminum lids for beverage cans, inner surfaces (body, bottom) of DI cans, and side seams that require baking in a short time. It is also useful as an adhesive primer for the bodies and top and bottom lids of food cans and beverage cans, and for adhesive cans. Also, paints that use products obtained from epoxy resins as they are are useful as sizing agents for the exterior of cans. Thus, the metal coating composition of the present invention provides excellent adhesion, with less energy consumption or baking time.
Water resistance, solvent resistance, corrosion resistance, resistance to post-forming,
It provides a baked coating film with safety and hygiene properties. Examples and comparative examples are shown below. Example "Central part" refers to parts by weight. Example 1 Preparation of epoxy resin solution (A) After dissolving 100 parts of Epicoat 1007 (manufactured by Ciel Chemical Co., Ltd.) in a mixed solvent of 100 parts of cellosolve acetate and 100 parts of xylene, 5 parts of aluminum tributoxide prepared in advance and acetate were added to this. A mixed solution of 5 parts of ethyl acetate was added, and the mixture was reacted at 110°C for 3 hours. Preparation of phenol formaldehyde resin (B) 228 parts of bisphenol A, formaldehyde
After reacting 225 parts of 40% n-butanol solution and 17 parts of 25% ammonia water at 100°C for 5 hours, diluted with 100 parts each of xylene, n-butanol, and cyclohexanone, and further dehydrated to obtain a phenol resin. Ta. The above epoxy resin solution (A) and phenol formaldehyde resin (B) were mixed at a solid content ratio of 85:15, and the resulting composition was rolled onto a 0.35 mm thick aluminum plate so that the coating thickness was 5 μm. Coat painted and 280
Baking was performed at 185°C for 60 seconds or 10 minutes at 185°C. Comparative Example 1 Preparation of epoxy resin solution (C) 100 parts of Epicote 1007 was added to cellosolve acetate.
It was dissolved in a mixed solvent of 100 parts of xylene and 100 parts of xylene. A composition obtained by mixing epoxy resin solution (C) and phenol formaldehyde resin (B) at a solid content ratio of 85:15 is roll coated onto a 0.35 mm thick aluminum plate so that the coating thickness is 5 μm. Then, it was baked at 280°C for 60 seconds or at 205°C for 10 minutes. The performance test results of the coating films obtained in Example 1 and Comparative Example 1 are shown in the table.

Table 1 Thus, the composition according to Example 1 provides a protective coating with excellent coating performance in a much shorter time and at lower temperatures compared to currently practiced baking conditions. Example 2 Preparation of epoxy resin solution (D) The following procedure was the same, using Epicote 1009 instead of Epicote 1007 in the epoxy resin solution (A). Preparation of phenol formaldehyde resin (E) 108 parts of P-cresol, 40 parts of formaldehyde
% n-butanol solution 75 parts, magnesium hydroxide
After reacting 0.56 parts at 100°C for 1.5 hours, neutralize with phosphoric acid, add 30 parts each of xylene, n-butanol, cyclohexanone and 90 parts of water, and leave for 5 hours.
The aqueous layer containing the generated salt was separated and removed, and further azeotropically dehydrated to produce the product. The epoxy resin solution (D) and the phenol formaldehyde resin (E) were mixed in the same manner as in Example 1, and the same test was conducted. Comparative Example 2 Preparation of epoxy resin solution (F) 100 parts of Epicote 1009 was added to cellosolve acetate.
It was dissolved in a mixed solvent of 100 parts of xylene and 100 parts of xylene. The epoxy resin solution (F) and the phenol formaldehyde resin (E) were mixed in the same manner as in Comparative Example 2, and the same test was conducted. The performance of the coating films obtained in Example 2 and Comparative Example 2 is shown in the table.

[Table] It was found that the composition according to Example 2 sufficiently progressed the curing reaction in half the typical baking time and provided a practical protective coating. In addition, no changes in appearance such as increased viscosity or opacity were observed in this product during a two-month storage test at 50°C. Example 3 Preparation of epoxy resin solution (G) The same operation was carried out using ethyl diisopropoxyacetoacetate instead of aluminum tributoxy in the epoxy resin solution (A). The epoxy resin solution (G) and the phenol formaldehyde resin (B) were mixed in the same manner as in Example 1, and the same test was conducted. Example 4 Epoxy resin solution (A) and phenol formaldehyde resin (B) were mixed at a solid content ratio of 75:25, and the same test as in Example 1 was conducted. Example 5 Preparation of phenol-formaldehyde resin (H) 55 parts of phenol, 43 parts of O-cresol, 105 parts of formalin, and 28 parts of 25% aqueous ammonia were mixed at 100°C.
After reacting for an hour, 80 parts each of xylene n-butanol and cyclohexanone and 200 parts of water were added, and the mixture was left to stand for 3 hours, the separated aqueous layer was removed, and further azeotropic dehydration was performed. The epoxy phenol resin solution (A) and the phenol formaldehyde resin (H) were mixed in the same manner as in Example 1, and the same test was conducted. Example 6 Preparation of epoxy resin solution (I) 5 parts of aluminum tributoxide and 5 parts of ethyl acetoacetate were added to the epoxy resin solution (A).
It was changed to 10 copies each. Epoxy resin solution of Example 1
A similar test was conducted using epoxy resin solution (I) instead of (A). Example 7 Preparation of epoxy resin solution (J) The reaction at 110°C for 3 hours during the production of epoxy resin solution (A) was changed to 1.5 hours at 110°C. Preparation of phenol formaldehyde resin (K) After reacting 228 parts of bisphenol A, 150 parts of formalin, and 3.7 parts of hydrochloric acid at 100°C for 3 hours, neutralization with phosphoric acid, xylene, n-butanol, and cyclohexanone were added to 150 parts each. The mixture was left to stand for 5 hours, and the aqueous layer containing the formed salt was separated and further azeotropically dehydrated. The epoxy resin solution (J) and the phenol formaldehyde resin (K) were mixed in the same manner as in Example 1, and the same test was conducted. Example 8 A test similar to Example 1 was conducted using only the epoxy resin solution (A). The performance test results of the baked coating films obtained in Examples 3 to 8 at 280°C for 60 seconds are shown in the table.

[Table] Example 9 In the epoxy resin solution (D), the amounts of aluminum tributoxide and ethyl acetoacetate used were each 7 parts, and the following operations were carried out in the same manner. Comparative Example 3 A paint was prepared by blending 10 parts of Melan 11D (urea resin manufactured by Hitachi Chemical Co., Ltd.) in place of the aluminum compound in the epoxy resin solution (D). The paints obtained in Example 9 and Comparative Example 3 were baked at 280°C for 60 seconds or at 205°C for 10 minutes.
The results of a similar test are shown in the table.

[Table] As described above, the coating composition for metal cans of the present invention is cured by baking in a shorter time than the usual baking conditions for current epoxy paints, and the resulting coating composition is The film has excellent coating properties as a protective coating for metals. The coating film performance test method is shown below. MEK resistance: Rub a gauze moistened with methyl ethyl ketone (MEK) with a load of 1 kg, and measure the number of times of friction until the coating surface is eroded.
The resistance to hardening was evaluated and used as a measure of the degree of hardening. Retort resistance: Visually observe the whitening state of the paint film after retorting at 125℃ for 40 minutes. Corrosion salt water resistance: After immersing the coated plate in a 3% sodium chloride aqueous solution, the above-mentioned retort treatment was performed, and the whitening state of the coating film was visually observed. Bendability: After bending the painted plate 180 degrees, a 2 kg load was dropped on the bent portion from a height of 50 cm, and the cracking of the paint film was observed using a magnifying glass. Adhesion...Cross cuts are made in the paint film, cellophane tape is pressed onto the cross cuts, then immediately peeled off and the state of peeling of the paint film is observed. ◎ Very good behavior △ Slight change 〇 Good behavior × Significant change

Claims (1)

[Claims] 1 Average molecular weight is 1000-5800, epoxy equivalent is
Bisphenol type epoxy resin which is 450~4000
100 parts by weight and the general formula Al(OR) _o (L) _3-o (where R
represents an alkyl group, L represents a ketoenol type tautomeric compound, and n represents an integer of 0 to 3. ) A coating composition for metals with excellent fast curing properties, which is obtained by dissolving a product obtained by heating and reacting 0.2 to 15 parts by weight of an aluminum alcoholate or an aluminum complex compound in an organic solvent. thing.