JP2746455B2 - Aluminum material for cans with excellent corrosion resistance - Google Patents

Description

The present invention relates to an aluminum material for a can having excellent corrosion resistance,
More specifically, for example, the present invention relates to an aluminum material for a can excellent in corrosion resistance provided with an organic coating excellent in corrosion resistance by an electrodeposition coating method.

[Prior art] Conventionally, an organic solvent-based paint is used by a means such as roll coating for a coating film of an aluminum material for a can provided with an organic coating having excellent corrosion resistance. Therefore, there is a problem such as environmental pollution in the handling and baking thereof and production efficiency in response to an increasing demand for plate materials.

Therefore, an organic coating using a water-soluble resin mainly composed of a self-emulsifying epoxy resin instead of the organic solvent-based resin has been applied. However, since the water-soluble resin coating film contains a large amount of carboxyl groups and hydroxyl functional hydrophilic groups originally possessed by the water-soluble resin, the water resistance of the coating film, such as water content and water permeability, is an organic solvent-based resin. And it is difficult to achieve high corrosion resistance.

Therefore, in order for the aluminum material for a can coated with a water-soluble resin to have high corrosion resistance, it is necessary to increase the degree of curing of the matrix resin by increasing the curing temperature or prolonging the curing time, Have been made thicker and the coating film has been densified, but it is still not sufficient.

In addition, among aluminum materials for cans, in particular, as a precoat material for a can end, adhesion is required for processing into an end. And this pre-coat is a method of coating before the can forming such as coil in the rolling maker, not after the can forming, and this demand is increasing more and more from the can maker to the rolling maker. The adhesion of the paint is further required.

However, in general, the adhesion of a coating film made of a water-soluble resin is inferior to that of a coating film made of an organic solvent-based resin, and a base treatment such as a chromate treatment is performed to improve the adhesion. The treatment of waste liquid is a major problem.

[Problems to be Solved by the Invention] In view of the various problems of the conventional corrosion-resistant aluminum material for cans described above, the present inventors have conducted intensive studies and found that the surface of the aluminum material for cans was obtained. By strictly selecting the type of coating film to be coated, the aluminum material for cans that has excellent adhesion and excellent corrosion resistance of the coating film was developed.

[Means for Solving the Problems] The feature of the aluminum material for cans excellent in corrosion resistance according to the present invention is that the water-soluble epoxy resin of the matrix resin is
A coating film containing -25% by weight of a phenol resin and having a glass transition temperature of at least 90 ° C. is covered.

The aluminum material for a can having excellent corrosion resistance according to the present invention will be described in detail below.

First, the materials used in the aluminum material for cans having excellent corrosion resistance according to the present invention will be described.

As the water-soluble epoxy resin, it is preferable to use an epoxy resin grafted with a compound containing a carboxylic acid monomer, and is dispersed in water containing a basic solvent and a water-soluble organic solvent. It is preferable to use a water-dispersible anionic epoxy resin. In this case, as the basic solvent of the solvent, amines are preferable, and as the water-soluble organic solvent, alcohols, ethers, ketones, esters and the like can be mentioned.

As the phenol resin, I. 4-functional phenol compound II. 3-functional phenol compound III.2 Functional phenol compound and the like were synthesized with formaldehyde under an alkaline catalyst. Particularly, an initial condensate using a phenol compound having 4 or 3 functional groups is preferable. As the alkali catalyst in this case, a strong base catalyst such as sodium hydroxide and potassium hydroxide or a weak base catalyst such as sodium carbonate and aqueous ammonia can be used, and these catalysts can be used alone or in combination. .

 As a method of adjusting the glass transition temperature, curing conditions: adjustment of the curing temperature and the curing time.

Resin composition: For example, as a compound containing a carboxylic acid monomer to be grafted with an epoxy resin, a component originally having a high glass transition temperature such as styrene is used.

Molecular weight: For example, the molecular weight is reduced without changing the molecular structure, and the number of functional groups per molecular weight (the one that becomes a crosslinking point) is increased.

And the like.

Next, the content of the phenolic resin and the glass transition temperature with respect to the water-soluble epoxy resin of the matrix resin used for the aluminum material for cans having excellent corrosion resistance according to the present invention will be described.

In the case of a coating made of only a water-soluble epoxy resin that is a matrix resin, even if the glass transition temperature is adjusted to a range of 90 ° C. or higher, there is no improvement in the corrosion resistance of the aluminum material for cans provided with an organic coating. Phenolic resin content
If the content is less than 2% by weight, no improvement in corrosion resistance can be expected, but if the content of phenolic resin is 2% by weight or more, the corrosion resistance of the aluminum material for cans provided with an organic coating is remarkably improved.

By making the content of the phenolic resin more than 2 wt% based on the water-soluble epoxy resin as the matrix resin, the hydrophilic functionalities such as carboxyl groups inherent in the water-soluble epoxy resin as the matrix resin are originally possessed. In contrast to the hydrophilicity of the coating film caused by the presence of a large number of groups, it is possible to impart a hydrophobic property to the coating film that exceeds the hydrophilicity of the coating film. It is to improve. At the same time, the adhesion is improved. Therefore, it can be sufficiently used for cans, especially for can ends, and even if corrosion occurs, it is possible to suppress progress from pitting corrosion to undercoat corrosion.

Further, if the phenol resin is contained in an amount exceeding 25% by weight with respect to the water-soluble epoxy resin, separation of the water-soluble epoxy resin from the phenol resin and aggregation of the water-soluble epoxy resin are caused, so that the operation becomes impossible. Therefore, the content of the phenol resin relative to the water-soluble epoxy resin as the matrix resin is set to 2 to 25% by weight.

Further, the glass transition temperature needs to be 90 ° C. or higher. If the glass transition temperature is lower than 90 ° C., sufficient water resistance cannot be obtained even if the phenol resin content is in the range of 2 to 25 wt%.
Alternatively, adhesion cannot be obtained, and thus sufficient corrosion resistance cannot be obtained. The upper limit of the dislocation temperature is preferably set to 150 ° C. Above this temperature, the coating film tends to oxidize and deteriorate. Therefore, the glass transition temperature is set to 90 ° C. or higher.

The above-mentioned coating film is preferably coated by an electrodeposition coating method.

The coating film to be coated on the surface of the aluminum material for cans having excellent corrosion resistance according to the present invention by an electrodeposition coating method may include a colorant, a paint additive, a matting agent, a brightener, a rubber elastic agent, etc. By mixing an anionic composition having the following characteristics, any coating film can be produced.

Materials that can be used for the aluminum material for cans having excellent corrosion resistance according to the present invention are aluminum materials that are not subjected to pretreatment,
An aluminum material that has been subjected to a phosphate treatment, a chromate treatment, and an alumite treatment can be used.

[Example] An example of an aluminum material for a can having excellent corrosion resistance according to the present invention will be described.

Example 1) Method for preparing paint A dispersion of a water-soluble epoxy resin was subjected to distillation under reduced pressure to make the water-soluble solvent 2 wt% or less, and ion-exchanged water was added dropwise with stirring to dilute the solid content to 10 wt%.

Next, phenol resin (ammonia resol resin)
Was dissolved in 100 parts of butyl carbitol, and slowly added dropwise to the stirred dispersion of the water-soluble epoxy resin over 2 hours. The pH was adjusted to 8 with dimethylethanolamine. The material was used as a paint.

2) Sample preparation method The paint of the above 1) was coated on a 0.5 mm aluminum material subjected to ordinary alkali degreasing to a thickness of 5 μm by an electrodeposition coating method. In this case, the coating temperature is 30 ° C. and the curing conditions of the coating film are as shown in Table 1.

3) Corrosion test conditions The samples were immersed in an aqueous solution of 1% NaCl, pH 3, and 40 ° C. for 2 weeks to check for the occurrence of corrosion.

4) Method of Measuring Glass Transition Temperature In the same manner as in the above sample preparation method, a 25 μm aluminum foil was coated with 10 μm. This was immersed in dilute hydrochloric acid to dissolve the aluminum foil to obtain a thin film for measurement. For this measurement, viscoelasticity was measured by DMS (tensile mode, 2 Hz) manufactured by Seiko Instruments Inc.

Table 1 shows the amount of phenolic resin, curing conditions, glass transition temperature and corrosion resistance.

For example, after being immersed in boiling water for 1 hour, a pattern is cut into a 1 mm grid, and processed by Erichsen (typically 6 mm with a steel plate), and subjected to a tape peeling test. In the secondary adhesion test,
No peeling is observed.

As a result of conducting a test on Examples 1 to 10 of aluminum materials for cans excellent in corrosion resistance according to the present invention in Table 1 under these conditions,
No peeling was observed, and the adhesion of the coating film was good.

As is clear from Table 1, it can be seen that the aluminum material for cans having excellent corrosion resistance according to the present invention shows more excellent corrosion resistance than the comparative example.

[Effects of the Invention] As described above, the aluminum material for cans having excellent corrosion resistance according to the present invention is excellent in that the phenol resin content and the crow transition temperature of the coating material coated on aluminum are kept constant. An organic coating with corrosion resistance is obtained,
It is a very useful material as an aluminum material for cans.

Claims (1)

(57) [Claims] 1. A corrosion-resistant coating comprising a phenolic resin in an amount of 2 to 25% by weight based on a water-soluble epoxy resin of a matrix resin and having a glass transition temperature of at least 90 ° C. Aluminum material for cans with excellent properties.