JPH01141961A - Coating composition for preventing filamentous corrosion of aluminum material - Google Patents

Abstract

PURPOSE:To obtain a coating composition which inhibits the formation of filamentous corrosion and can increase the beauty of various aluminum materials, by mixing a polyester, acrylic or polyether resin, as a base, having a specified hydroxyl group equivalent with, optionally, a specified resin as a curing agent. CONSTITUTION:This coating composition comprises a polyester, acrylic or polyether resin, as a base, having a hydroxyl equivalent in the range of at least 2,200g/equivalent (in terms of solid component) and, optionally, at least one curing agent selected from among amino, isocyanate, epoxy and silanol resins.

Description

Detailed Description of the Invention [Field of Application] The present invention is directed to improving the resistance of aluminum materials to suppress filiform corrosion (Filifor+i Corrosion), which occurs on clear coated aluminum materials and often significantly impairs their appearance. The present invention relates to a rust-resistant coating composition.

[Conventional technology]

Aluminum materials generally have good corrosion resistance, so they can be used for cosmetic purposes by simply etching, polishing, or machining the surface. However, in order to minimize changes in appearance when used in a wide range of environments, they are usually painted or anodized.

Painting is simple and is commonly used for various products, whereas alumite coatings have excellent weather resistance and good abrasion resistance, so they are widely used for building materials.

When looking at the occurrence of filiform corrosion in pure aluminum materials that have been painted or alumite-treated, the following is known.

(1) (W,
Il, SIabaugh;0official Dige
st, 0DSP^-1962, P (2) It can be significantly suppressed by performing anodization or chromate treatment on the painted material as a base treatment.

(G, M, Hoch: Corrosion-NACE-
3/1974; P134) [Problems to be Solved by the Present Invention] As mentioned above, at least when the aluminum material is pure aluminum, there are substantially effective countermeasures against filiform corrosion even at present.

However, for example, there are materials such as die-casting alloys that contain as essential components elements such as silicon and iron that are undesirable from the viewpoint of thread rust resistance, or materials that contain impurities such as copper and zinc, which are known to have a similar effect. When clear coating is applied to materials that must be included in the form,
No method has been found to effectively suppress filamentous corrosion.

Under such circumstances, the current measures taken are to make the paint film thicker so that scratches are less likely to occur, since filamentous corrosion almost always starts from scratches or thin parts of the paint film. Alternatively, only passive methods have been adopted, such as eliminating parts of the object to be coated that are difficult to coat, such as sharp edges.

[Means for solving problems]

In the present invention, aluminum or aluminum alloy materials are degreased or treated with a chromate conversion coating, drained and dried at 130°C, preferably 80°C or lower, and then polyester or acrylic having a water ai equivalent of 2200 g/equivalent or more on a solid content basis. Alternatively, a thread rust-resistant coating composition for aluminum material containing polyether resin as a main component, or containing at least one of amino resin, isocyanate resin, epoxy resin, or silanol resin as a hardening agent, is used. It is characterized by painting.

As mentioned above, the thread rust resistance of a coating material is strongly influenced by the alloying elements or impurity elements of the material. That is, St, Fe
s The presence of elements such as Cu or Zn lowers thread rust resistance. In this regard, the present inventors have previously conducted a patent comparison @ (Japanese Patent Application No. 1983/237527) on a thread rust-resistant material discovered from the viewpoint of the composition of the aluminum association material.

Unlike conventional coating compositions, the thread rust-resistant coating composition of the present invention is hardly affected by such materials and can be applied to a wide range of aluminum alloy materials. That is, the composition has a hydroxyl equivalent of 2,200 g/equivalent or more on a solid content basis, preferably in a range of 5,000 to 14,000 g/equivalent, and a number average molecular weight of 5,000 to 30.
An aluminum material whose main component is polyester, acrylic or polyether resin in the range of 0.000, and which is crosslinked by containing at least one of amino resin, isocyanate resin, epoxy resin or silanol resin as a curing agent if necessary. This is a thread rust-resistant coating composition.

Incidentally, in order to increase the reactivity and crosslinking density of ordinary curable coating resins, the hydroxyl group I (in terms of solid content) is set at around 300-600 gr/eq, and from the viewpoint of ease of handling, especially viscosity. 3000 for number average molecular weight from
When comparing the two, the differences between the coating composition of the present invention and those commonly used are: ■ Longer molecular chain length; ■ Longer molecules. The number of crosslinking points connecting the two is small (several minutes to several tens of minutes). In other words, this means that the coating film of the thread rust-resistant coating composition of the present invention is more porous than ordinary coating compositions, and if we focus on the molecules that constitute the coating film, at least the glass transition point (hereinafter referred to as Tg This means that it can move quite freely at temperatures above (referred to as a point).

The question here is why filamentous corrosion is difficult to occur in the coating film made of the composition of the present invention, but at present no clear reasoning has been established regarding this. However,
For example, when isocyanate is added as a crosslinking agent to the composition, isocyanate groups (NGO) and hydroxyl groups (Ol
l) exceeds the equivalent value (in this case N
In addition to the reaction with OH, GO also reacts with moisture in the air, and this product is thought to fill the voids in the equivalently crosslinked state. The two points mentioned and the things that can be inferred from them are considered to be important requirements for a thread rust-resistant coating.

The allowable addition amount of incyanate from the viewpoint of thread rust resistance varies depending on the composition, but is generally 3:1 or less in terms of NGO10H ratio. However, this value is determined when the Tg point of the composition is 1.
When the temperature is as low as 0°C or lower, the coating exhibits good thread rust resistance even at a value of about 10;I.

On the other hand, an amino resin or an epoxy resin can be used as a crosslinking agent for the polyester or acrylic resin as the composition.
etc., the amount of crosslinking agent should be 1% to the total solid content.
It is preferable to keep it within 0% from the point of view of thread rust resistance.
As this value increases, thread rust resistance becomes relatively worse as in the case of isocyanate.

[Example 1] Castings of an aluminum alloy for die casting containing 9% silicon, less than 1% each of Mg, Mn and Fe, and about 0.1% copper as impurities were treated with a slightly alkaline cleaner; trade name FC315 ( It was degreased by immersing it in a 5% solution (manufactured by Nippon Parr Ising Co., Ltd.) at 65°C for 5 minutes. After washing with water, the casting material was immersed in a 0.1χ solution of a chromate-based chemical conversion treatment agent (trade name: Allozin 1000 (manufactured by Nippon Bainted Company) for 50 seconds at 35°C, and the surface of the casting material was immersed in a chromate treatment agent with a concentration of 5 mg/m'' in terms of Cr content. A film was formed.Then, the casting material was washed with water, washed with pure water, and finally dried with hot air at 80°C.

Subsequently, the hydroxyl equivalent is 2200gr/eq in terms of solid content.
A commercially available polyisocyanate resin (trade name: Takenate DI) is used as a base.
ION (manufactured by Takeda Pharmaceutical Company Ltd.) was added so that the NGO10H ratio was equivalent, and was applied to the surface of the alloy casting material so that the dry film thickness was 20 μm. The coating film was cured at 80° C. for 30 minutes. The thread rust resistance of the coating material obtained in this way was investigated (see [Note] for the corrosion test) and the results are shown in Table 1. It was as shown.

C Note] Test method for examining filamentous corrosion and method for judging results Test method: After making scratches on the surface of the painted material with a cutter knife, this area is rusted in a 0.5N l1cl bath, and from this area The degree of progression of filamentous corrosion at 40℃, 85χR1+
The study will be conducted for 10 days in the same atmosphere.

Judgment method: Judgment is made on a 10-point scale based on the degree of filamentous corrosion growth. 10 indicates that no filamentous growth is possible, and 1 indicates that filamentous growth cannot be suppressed at all (see Figure 1).

[Example 2] Polyester polyol (trade name: Byron G) was applied to an aluminum material having the same history as that used in Example 1.
K150 (manufactured by Toyobo ■) is used as a base, and the above-mentioned polyisocyanate resin (hereinafter referred to as Isocyanate II) is used as a base.
IION) was added in an equivalent ratio at 80°C.
A curing treatment was carried out for 30 minutes.

The thread rust resistance of this product was as shown in Table 1.

Incidentally, the hydroxyl equivalent of the polyester polyol of this example was 7000-14000 QO/eq in terms of solid content, the number average molecular weight was 1000-15000, and the Tg point was 26°C.

[Example 3] For the aluminum material having Mu similar to that used in Example 1, the hydroxyl equivalent (in terms of solid content) was 6700-101.
00QO/eq, number average molecular weight is 15000-2000
0 and a Tg point of 67°C (trade name: Vylon 200 [manufactured by Toyobo Co., Ltd.]) is used as a base, and the above incyanate 0110 is added to it at NC07.
3:1 at 80°C after application.
Curing was performed for 0 minutes. The thickness of the dry coating film here was 20 μm. The thread rust resistance of this was as shown in Table 1.

[Example 4] For an aluminum material having the same history as that used in Example 1, the hydroxyl equivalent (solid content equivalent) was 6700-101.
00O0/eq, number average molecular weight is 20000-250
00 and a 7g point of 6°C (trade name: Byron 300 [manufactured by Toyobo Co., Ltd.]) was used as a hese, and the above-mentioned isocyanate) 0110 was added to NGO1.
After coating, the mixture was added at an 0H ratio of 10:1 and then cured at 80° C. for 30 minutes. Here, the thickness of the dry coating film is 20μ
It was m. The thread rust resistance of this was as shown in Table 1.

[Example 5] For an aluminum material having the same history as that used in Example 1, the polyester polyol (Vylon 200) used in Example 3 was used as a base, and highly methylated melamine resin (trade name: Cymel 325) was added to this. After applying a paint containing 10% of the total solid content (manufactured by Mitsui Toatsu), baking was performed at 140°C for 30 minutes. The thickness of the dry coating film here was 20 μm. The thread rust resistance of the thus obtained coating was as shown in Table 1.

[Example 6] For an aluminum material having the same history as that used in Example 1, the hydroxyl equivalent (solid content equivalent) was 3300 g on average.
r/eq, the above isocyanate 011ON was added to the prototype acrylic polyol with a number average molecular weight of 19,000.
After applying GO10H at a ratio of 2:1,
It was cured at ℃ for 30 minutes. Here, the thickness of the dry coating film is 2
It was 0 μm. The thread rust resistance of this was as shown in Table 1.

[Comparative Example 1] For an aluminum material having the same history as that used in Example 1, the hydroxyl equivalent (in terms of solid content) was 825 gr/eq.
, a polyester polyol with a number average molecular weight of 3300-3500 (product name: Takelac u25 [Narita Pharmaceutical ■
]), and the above-mentioned isocyanate DIIO is added to this as a base.
An equivalent amount of N t -NC010R was added to give a dry coating thickness of 20 μm. The thread rust resistance of this product is as shown in Table 1, and is clearly inferior to those of Examples 1 to 6 described above.

(Comparative Example 2) For an aluminum material having the same history as that used in Example 1, the hydroxyl equivalent (in terms of solid content) was 620 gr/eq.
, is based on an acrylic polyol (trade name: Thermolac 5u-28 (Soken Kagaku)) with a number average molecular weight of 3300, and the isocyanate DIION is added to this by NGO.
The equivalent amount added at a ratio of 10R gives a dry coating thickness of 20μ.
It was applied so that the thickness was m. The thread rust resistance of this product was as shown in Table 1, and was extremely low.

'24 In the embodiment, the casting material for die casting has been described, but the present invention is not limited to this and can be applied to other aluminum alloy materials.

[Effects of the present invention]

According to the present invention, coating that suppresses the occurrence of filiform corrosion and improves the cosmetic appearance of a wide range of aluminum materials can be easily and quickly performed.
Furthermore, a stable surface condition can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing an evaluation of the growth degree of filamentous corrosion according to 10 levels (each number indicates a rating number). Patent Applicant Nippon Light Metal Co., Ltd. Procedural Amendment ■, Myogyu no Goin 1962 Patent Application No. 3000! 51 No. 3, Relationship with the person making the amendment case Patent Applicant

Claims (2)

[Claims] (1) A filamentous rust-resistant coating composition for aluminum material whose main component is polyester, acrylic, or polyether resin having a hydroxyl equivalent of 2,200 g/equivalent or more on a solid content basis. (2) The main component is polyester, acrylic or polyether resin with a hydroxyl equivalent of 2200 grams/equivalent or more based on solid content, and contains at least one of amino resin, isocyanate resin, epoxy resin or silanol resin as a curing agent. A thread rust-resistant coating composition for aluminum material.