JPH0412308B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating composition containing a modified epoxy resin as a resin component, which is mainly used for coating metal plates. Conventional paints for metal plates, such as those applied to the inside and outside surfaces of cans for cans and soft drink cans, are made by adding 1% or less of a curing accelerator such as phosphoric acid to epoxy resin paint at 180°C for about 20 minutes. Burning was taking place. However, although short-time baking is desired to improve productivity, baking at high temperatures is not preferred from the standpoint of energy conservation. In addition, increasing the amount of the curing accelerator has been considered as an alternative, but this would reduce the stability of the varnish and increase the amount of free components in the cured coating, which is undesirable from a sanitary standpoint. On the other hand, when making cans, usually after applying epoxy resin paint to metal plates such as tin plates and aluminum plates,
Bending, drawing, and punching are performed using a press or the like, but conventional epoxy resin paint films have the disadvantage that they are easily damaged during this process. The present invention provides a coating composition that is free from such drawbacks and has a high curing rate. That is, the composition of the present invention has an epoxy equivalent of about 400
~4000 epoxy resin 100 parts by weight; (However, n is an integer of 1 to 4, R is H or a methyl group.) A product obtained by reacting 2 to 20 parts by weight of a lactone represented by and a coating composition obtained by blending an amino resin. The main component of the present invention is a reaction product of an epoxy resin and a lactone, and preferred epoxy resins include polyglycidyl ethers having an epoxy equivalent of about 400 to 4,000 and obtained by reacting polyhydric phenols with epihalohydrin. It will be done. Examples of polyhydric phenols include resorcinol,
Mononuclear polyphenols such as hydroquinone, bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)methane,
-hydroxyphenyl)sulfone, 1,1,2,
2-tetrakis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (known as bisphenol A), 2,2-bis(3,5-dibromo-4 Polynuclear polyhydric phenols such as -hydroxyphenyl)propane can be mentioned. Among such epoxy resins, diglycidyl ether of bisphenol A is particularly preferred. If the epoxy equivalent of the epoxy resin of the present invention is too small, such as less than 400, the chemical resistance of the coating film will be insufficient.
If it exceeds 4000 and is too large, the workability during painting will decrease and the coating film performance will also be adversely affected. Examples of lactones other than ε-caprolactone include β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, β-butyrolactone, γ-valerolactone, δ-caprolactone, and ε-enantholactone. γ-butyrolactone, δ-valerolactone, γ-valerolactone, and δ-caprolactone are preferred, and δ-valerolactone and γ-valerolactone are particularly preferred. For the reaction of epoxy resin with lactone, about 2 to 20 parts by weight, preferably 5 to 10 parts by weight of lactone is used for 100 parts by weight of epoxy resin. If the amount of lactone is too small, the desired rapid curing property cannot be obtained. Further, the flexibility of the coating film is insufficient, and the coating film is easily damaged during processing such as drawing, punching, and bending during can manufacturing. On the other hand, if the amount of lactone is too large, the benefits of using the epoxy resin will be lost and the rigidity, adhesion, and chemical resistance of the coating will decrease, which is not preferable. The reaction usually suffices if the lactone is added while stirring while the epoxy resin is melted, and then stirring is continued at about 160 to 180°C for about 3 to 6 hours. The main reaction seems to be the ring-opening addition of lactone to the hydroxyl group of the epoxy resin to form a graft-like product. In the reaction, it is preferable to use a catalyst such as tetrabutoxytitanate or sodium phenate in a proportion of about 10 to 100 PPM based on the epoxy resin. The curing agent used in the reaction product obtained above is preferably a resol type phenolic resin or an amino resin, and both may be used in combination. A preferred example of the resol type phenolic resin is an ammonia resol type phenolic resin. Here, the ammonia resol type phenolic resin is obtained by adding phenols and formaldehyde to an ammonia aqueous solution and reacting them. Resole-type phenolic resins in which the methylol groups bonded to the phenol bone core are etherified with aliphatic alcohols such as isopropanol and butanol have good stability and compatibility, and are preferably used, and of course, they are suitable for resol-type phenolic resins as referred to in the present invention. Included. As resol-type phenolic resins, Phenodyl (product of Hoechst), Hytanol (product of Hitachi Chemical), etc. are commercially available and can be used. The amino resin of the present invention includes a very general amino resin obtained by reacting urea or melamine with formaldehyde and converting it into methylol, and those obtained by etherifying the methylol group with an aliphatic alcohol such as isopropanol or butanol. do. As amino resins, Rezamin (product of Hoechst), Euban (product of Mitsui Toatsu), Melan (product of Hitachi Chemical), etc. are commercially available and can be used. The amount of curing agent used is usually about 10 to 50 parts by weight per 100 parts by weight of the reaction product of the epoxy resin and lactone. If the amount of curing agent used is too large or too small, the coating film will become brittle and will lack processability. The composition of the present invention may optionally contain curing accelerators such as phosphoric acid, P-toluenesulfonic acid,
0.01 to 1.0 of maleic acid etc. to the reaction product
It may be added in an amount of about % by weight. The coating composition of the present invention is prepared, for example, as follows. The epoxy resin reacted with lactone is dissolved in a polar solvent such as ketones or cellosolves, while the curing agent is dissolved in an alcohol solvent such as n-butanol or a mixed solvent of an alcohol solvent and an aromatic hydrocarbon solvent such as xylene. do. Thereafter, the modified epoxy resin solution and the curing agent solution are mixed. Furthermore, it is diluted with cellosolves, aromatic hydrocarbons, ketones, or a mixed solvent thereof to a viscosity suitable for coating, and then used. It is also possible to add a curing accelerator if necessary. Painting is generally done continuously using a roll coater on metal plates such as tin or aluminum plates, but air spraying, brush painting, flow painting, etc. are also possible. The coating is usually applied to a dry film thickness of 6 to 8 microns, and then baked. Baking conditions of 180 to 210° are sufficient; for example, with conventional epoxy resin paint, 210°
When using the composition of the present invention, the same hardening as when baking at 210°C for 5 minutes can be obtained by baking at 210°C for 3 minutes and 30 seconds. Further, when using the composition of the present invention, curing equivalent to that achieved when using 0.5% by weight of phosphoric acid as a curing accelerator in conventional epoxy resin paints can be achieved using 0.3% by weight. When manufacturing cans, for example, from a metal plate obtained by painting and baking the coating composition of the present invention, bending, drawing, and punching processes are performed using a press, etc., but conventionally, these processes often occur during this process. Defects such as cracking and peeling of the paint film are significantly improved. As detailed above, the paint using the composition of the present invention is extremely excellent as a primer paint for the inner and outer surfaces of metal plates, such as food cans, soft drink cans, and other metal cans. A supplementary explanation will be given below using examples. Note that % and parts in Comparative Examples are based on weight unless otherwise specified. Example 1 (1) Reaction of epoxy resin and lactone A reactor equipped with a stirrer, a thermometer, a dropping bottle, and a reflux condenser was prepared with an epoxy equivalent of 1940 and a Gardner-Holtz viscosity of Y-Z (40% butyl carbitol solution). epoxy resin (Mitsui Petrochemical, epoxy
Add 90 parts of EPOMIKR-307) and melt at 160℃. From a dropper bottle, dissolve δ of tetrabutoxytitanate equivalent to 10 PPM of epoxy resin.
- add 10 parts of caprolactone with stirring;
The reaction was allowed to proceed for 5 hours. The resulting reaction product had an epoxy equivalent of 2700 and a Gardner-Holtz viscosity of Y ⁺ . (2) Preparation of paint 70 parts of the reaction product obtained above and 30 parts (solid content) of resol type phenolic resin (Hoechst PR-217) were mixed in a weight ratio of xylene/cellosolve acetate/diacetone alcohol 1/2/ 1 was dissolved in a mixed solvent to prepare a paint with a solid content concentration of 50%. Note that the solid content here refers to what remains as non-volatile content after heating at 160° C. for 1 hour. (3) Measurement of gelation time A depression (diameter 20mm, depth 2mm) on the hot plate of a gel time tester (manufactured by Nisshin Kagakusha) controlled at 180℃
0.5 g of the paint prepared above was poured into the solution and stirred with a glass rod having a diameter of 6 mm. The gelation time until the reaction progressed and the gel no longer exhibited a liquid state was measured, and this was used as a guideline for the curing speed. The results are shown in Table 1. (4) Impact flexibility test of paint film A mixed solvent containing xylene/cellosolve acetate mixed at a weight ratio of 1/1 was added to the paint prepared above, further diluted to a solid content concentration of 30%, and this was applied to a tin plate ( 150 x 50 x 0.24 mm (JIS-G-3303) using a bar coater to give a dry film thickness of 6 to 8 μm. Bake hardening was performed at temperatures of 180°C, 200°C, and 210°C for 30 to 5 minutes. The coated and baked tin plate is bent at 180 degrees around a 2 mm diameter rod, a 1 mm thick spacer is inserted between the bends, and the plate is placed on the flat base of a DuPont impactor. Furthermore, 50mm above this
Place a flat plate with a thickness of φ and 10 mm. A bullet is connected to the center of the flat plate to evenly transmit the impact to the flat plate, and a hammer weighing 1 kg is dropped from a height of 50 cm onto this bullet, impacting the bent tin plate. The degree of damage to the coating film on the curved surface was evaluated under these impact conditions and used as a measure of flexibility. ◎ indicates no damage to the paint film, 〇 indicates damage to several bent surfaces, △ indicates damage to 10 bent surfaces.
If less than % is damaged, × is 10% to 50% of the bending surface
is damaged. The results are shown in Table 1. Comparative example 1 Epoxy equivalent: 1940, Gardner-Holtz viscosity: Y-
Z epoxy resin (manufactured by Mitsui Petrochemical Epoxy Co., Ltd.,
xylene/
Dissolved in a mixed solvent of cellosolve acetate/diacetone alcohol at a weight ratio of 1/2/1, and the solid content concentration
50% paint. The gelation time of this paint and the impact flexibility of the paint film were measured in the same manner as in Example 1, and the results are shown in Table 1. Example 2 The same procedure as in Example 1 was carried out except that γ-valerolactone was used instead of δ-caprolactone used in Example 1 and the reaction was carried out at 170°C, and the epoxy equivalent was 2450,
A resin having a Gardner-Holtz viscosity Z was obtained. In the same manner as in Example 1, the paint was prepared and the gel time and impact flexibility were measured, and the results are shown in Table 1. 【table】

Claims (1)

[Claims] 1. Epoxy resin 100 having an epoxy equivalent of about 400 to 4000
parts by weight, lactone represented by the formula (where n is an integer of 1 to 4, and R represents H or a methyl group)
Excludes caprolactone. ) 2 to 20 parts by weight of lactone to the hydroxyl group of the epoxy resin,
A coating composition obtained by blending a resol type phenolic resin and/or an amino resin as a curing agent with a product obtained by a graft reaction. 2. The coating composition according to claim 1, which is used for coating metal plates. 3 Claim 1 or 2 in which the epoxy resin is polyglycidyl ether of bisphenol A
The coating composition described in .