JPH0747703B2 - Surface treated aluminum fin material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention imparts hydrophilicity to the surface of a metal so that water droplets are not formed, and durability and solvent resistance are imparted to the surface of the metal. The present invention relates to an aluminum fin material surface-treated with a resin composition for surface treatment, which is useful for preventing corrosion.

[Prior Art and its Problems] Recently, particularly with the rapid spread of room air conditioners, the demand for heat exchanger fin materials has increased significantly. As the heat exchanger fin material, aluminum, which is lightweight, and has excellent workability and thermal conductivity, is widely used (in this specification, aluminum includes aluminum and aluminum alloys).

Since the conventional heat exchanger fin material has been used without surface treatment, aluminum in the air is corroded by moisture in the air during use, or the layer of water condensed on the fin surface becomes ventilation resistance, and Because there was a drawback that lowered the exchange rate,
The demand of users for a pre-coated fin material in which the surface of the fin material is coated with corrosion resistance and hydrophilicity has been extremely increased.

The adoption of pre-coated fin material is extremely effective in saving energy and making room air conditioners compact.

There is also a method (post-coating method) of forming this coating layer after fin forming, but recently, due to the simplification of the process, the uniformity of the coating layer, etc., a film is formed on the aluminum thin plate before fin forming and it is There is a strong demand for a fin forming method (precoat method).

For use in this precoat method, the coating layer must not cause the wear of the forming tool in addition to the above-mentioned corrosion resistance and hydrophilicity.

Further, a lubricating oil is used at the time of molding, but the above-mentioned coating layer must not dissolve out when the oil is washed with an organic solvent such as trichloroethylene after molding.

In order to meet these requirements, there is known a technique for forming a coating layer in which an inorganic substance such as silica or alumina is mixed with an organic resin as a material having excellent hydrophilicity (JP-A-54-142650).
And 55-99976).

However, these have large tool wear and very poor corrosion resistance.

Further, as a treatment method using an organic surface treatment agent, by using a water-soluble acrylic resin for the first coating layer and a water-soluble cellulose resin for the second coating layer, chemical resistance (solvent resistance) and hydrophilicity are further improved. Is known (Japanese Patent Laid-Open No. 61-101798).

Compared with the inorganic surface treatment method, this method is more flexible when both the water-soluble acrylic resin for the first coating layer and the water-soluble cellulose resin for the second coating layer are organic and flexible when performing fin forming (pre-coating method). Therefore, the wear of the molding tool is small,
Further, the acrylic resin of the first coating layer has been widely put into practical use because it is superior in corrosion resistance as compared with the inorganic type, but further improvement is desired.

That is, when molding the aluminum fin material having the first coating layer and the second coating layer formed thereon, after washing the adhering oil and the like with trichloroethylene, a short time during which trichloroethylene still remains, If it comes into contact with water, the water droplets may be whitened and stains may remain, resulting in a problem that the appearance of the product is poor and the value is reduced.

[Means for Solving the Problems] As a result of intensive studies, the present inventors have found that such a problem is caused by combining a specific water-soluble acrylic resin as the first coating layer and a water-soluble amino resin that crosslinks with the specific water-soluble acrylic resin. It has excellent solvent resistance and corrosion resistance, and even if it comes into contact with water while trichloroethylene still remains, the water droplets do not whiten and leave stains, and the water content of the second coating layer is high. It was found that a coating film having excellent adhesiveness with a hydrophilic cellulose resin can be obtained. That is, the present invention is a resin composition for aluminum fin material surface treatment, which comprises a mixture of a water-soluble acrylic resin and a water-soluble amino resin, wherein acrylonitrile or methacrylonitrile is contained in an amount of 3 to 30 parts by weight and a hydrophilic monomer. Body 10
To 50 parts by weight and 87 to 20 parts by weight of a monomer having an unsaturated double bond copolymerizable therewith, 100 parts by weight of a water-soluble acrylic resin and 5 parts by weight of a water-soluble amino resin. The surface-treated aluminum fin material is obtained by coating a first coating layer made of a resin composition for surface treatment of aluminum fin material containing 40 parts by weight and a second coating layer made of a water-soluble cellulose resin.

Hereinafter, the present invention will be described in detail.

In the present invention, the water-soluble acrylic resin means 3 to 30 parts by weight of acrylonitrile or methacrylonitrile, 10 to 50 parts by weight of a hydrophilic monomer, and a monomer having an unsaturated double bond copolymerizable therewith. 87 to 20 parts by weight of the body is copolymerized in an aqueous system or in a mixed system with an organic solvent compatible with water, or copolymerized in an organic solvent compatible with water and then mixed with water. It was made water-based.

Acrylonitrile or methacrylonitrile, which may be used alone or in combination, is 3 to 30 parts by weight based on the solid content of the water-soluble acrylic resin. If the amount is less than 3 parts by weight, the solvent resistance is insufficient, and if it exceeds 30 parts by weight, the water resistance is reduced, and when baking-cured, the coating film becomes yellowish and the product value is visually deteriorated. To do.

Examples of the hydrophilic monomer include monomers having a carboxyl group such as acrylic acid, methacrylic acid and itaconic acid, monomers having an amide group such as acrylamide or methacrylamide and derivatives thereof, N-methylol acrylamide, N. Examples thereof include (meth) acrylamide derivatives having an N-methylol group such as methylol methacrylamide and derivatives thereof, and monomers having a hydroxyl group represented by the following general formula (1).

General formula (1) (In the formula, R is a methyl group or a hydrogen atom, m is 0 or 1 to 19
, N is 0 or an integer of 1 to 20, and m + n is 1 to 20. ) Among the compounds represented by the general formula (1), preferably used monomers are hydroxyethyl acrylate, hydroxyethyl methacrylate, Bremmer PE90, Bremmer PE200, manufactured by NOF CORPORATION, BAISOMER PPM5S, manufactured by BRITISH SHU PETRO CHEMICAL, Bisomer PPM6E etc. can be mentioned.

Examples of the monomer having an unsaturated double bond capable of copolymerizing with the acrylonitrile or methacrylonitrile and the hydrophilic monomer include methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate and i-butyl. Acrylic esters such as acrylate, t-butyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, dodecyl acrylate, steacrylic acrylate, methyl methacrylate, ethyl methacrylate,
Propyl methacrylate, n-butyl methacrylate,
Methacrylic acid esters such as i-butyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, 2 ethylhexyl methacrylate, lauryl methacrylate, dodecyl methacrylate and stearyl methacrylate, aromatic vinyl compounds such as styrene, α-methylstyrene and vinyltoluene, glycidyl acrylate. , Glycidyl methacrylate, vinyl acetate and the like.

In the present invention, the method for polymerizing the water-soluble acrylic resin is (1)
Polymerization is carried out by adding copolymerizable monomers in an aqueous medium all at once or gradually, and then solubilizing by adding an organic solvent and / or an alkaline substance compatible with water. Method of synthesizing water-soluble acrylic resin, (2) After carrying out solution polymerization in which a copolymerizable monomer is polymerized at once or gradually in an organic solvent compatible with water, alkali substance and / or A method of solubilizing water by adding water to synthesize a water-soluble acrylic resin, (3) while adding a copolymerizable monomer all at once or gradually in a uniform water mixed solvent containing an organic solvent After the polymerization, there is a method of solubilizing by adding water or an organic solvent and / or an alkaline substance compatible with the above mixed solvent to synthesize a water-soluble acrylic resin.

In the present invention, any of these methods can be adopted, but the emulsion polymerization of (1) is more preferable because of less risk of polymerization.

Examples of the water-soluble amino resin include methylated urea resin, methylated melamine resin, and methylated benzoguanamine resin, and these may be used alone or as a mixture with each other.

The mixing ratio of the water-soluble acrylic resin and the water-soluble amino resin is 5 to 40 parts by weight of the solid content of the water-soluble amino resin with respect to 100 parts by weight of the solid content of the water-soluble acrylic resin. If it is less than 5 parts by weight, the degree of crosslinking is low and trichlorethylene resistance (solvent resistance) is insufficient, and if it exceeds 40 parts by weight, the coating film after curing becomes too hard, resulting in poor adhesion and water resistance. ,
Physical properties such as solvent resistance are also deteriorated.

The water-soluble acrylic resin and the water-soluble amino resin may be mixed immediately before use, or may be used in a premixed state.

Further, the water-soluble cellulose resin of the second coating layer in the aluminum fin material of the present invention is a hydroxyl group (-OH) which is a hydrophilic group.
The water-soluble cellulose resin is a general term for cellulose and its derivatives such as ester and ether, and may be a mixture thereof.

Further, the water-soluble cellulose resin of the second coating layer preferably contains a water-soluble amino resin as an organic curing agent for causing a crosslinking reaction with the water-soluble cellulose resin.

Examples of the water-soluble amino resin include water-soluble melamine resins, benzoguanamine resins and urea resins, each alone or in a mixture thereof.

By including such an organic curing agent to cause a crosslinking reaction, the corrosion resistance can be improved without impairing the hydrophilicity of the surface.

Here, the melamine resin also includes a derivative of a methylated melamine resin. Further, it goes without saying that two or more kinds of organic curing agents may be mixed and used.

The aluminum fin material in the present invention means, for example, an aluminum fin heat exchange fin material.

The surface-treated aluminum fin material of the present invention is obtained by degreasing, for example, an aluminum fin heat exchange fin material, and then applying a first coating layer and a second coating layer on the surface thereof, for example, using a bar coater or the like. It can be formed by baking. It should be noted that the surface of the aluminum fin material before coating may be treated by graining or the like.

Thickness after baking of the first covering layer and the second coating layer in the present invention, the first coating layer is preferably 1 to 5 g / m ^2, more preferably 1 to 3 g / m ^2, and the second coating layer Is preferably 0.3 to 3 g / m ² , and more preferably 0.5 to 1 g / m ² .

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples.

Example 1 In a two-necked three-necked flask equipped with a stirrer, 0.5 g of sodium dodecylbenzenesulfonate was added to 300 g of water, and the mixture was heated to 65 ° C.
Warm to. Separately 50 g of acrylonitrile, 75 g of hydroxyethyl methacrylate, 25 g of methacrylic acid, 200 g of methyl methacrylate, 150 g of n-butyl acrylate and 200 g of water
And pre-emulsified with 1 g of sodium dodecylbenzene sulfonate. 2.5g of potassium persulfate was heated to 65 ℃ 2
In a three-necked flask and continuously add 10% by weight of the number of pre-emulsified emulsified monomers, polymerize for 30 minutes, then continuously drop the remaining emulsified monomer over 3 hours, and continue the polymerization for 2 hours, followed by acrylic emulsion. Got To this, 200 g of isopropyl alcohol was added, and further 500 g of the hydrophilic solvent was added, then 20 g of ammonia water and 300 g of dilution water were added,
A water-soluble water-soluble acrylic resin (A) was obtained. Cymel 350 (manufactured by Mitsui Cyanamid Co., Ltd.), which is a methylated melamine resin, is added to the aqueous solution (A) as a water-soluble amino resin, and the resin composition A-1 to aluminum fin material surface treatment of the present invention is added. Got 16. These are shown in Table 1. The breakdown of hydrophilic monomers and unsaturated monomers is shown in Table 1A.

Preparation of test piece After degreasing an industrial pure aluminum (JIS A1100) plate having a plate thickness of 0.12 mm, a resin composition for surface treatment of aluminum fin material was applied with a # 7 bar coater and baked at 250 ° C for 20 seconds. The amount of coating film after baking was 1.6 g / m ² . This was used as a first coating layer, and a second coating layer was formed on the second coating layer by using Soridite WH-10 (manufactured by Mitsui Toatsu Chemical Co., Ltd.) as a water-soluble cellulose resin and Cymel 350 (Mitsui Cyanamid Co., Ltd.) as a water-soluble amino resin. A test piece was prepared by applying a mixture of the product name and product name) with a # 7 bar coater and baking it. The coating amount after baking of the second coating layer was 0.7 g / m ² .

Evaluation Test The following test was performed on the obtained test piece.
The results are shown in Table 2.

(1) Adhesion test: A peeling test using cellophane tape was performed to check the adhesion between the first coating layer and the second coating layer, and those that did not peel completely were marked with a circle, those that peeled in places marked with a triangle, and the whole peeled. Those that do are marked with an X.

(2) Solvent resistance test: A rubbing test was performed with trichloroethylene, and the number of times of rubbing before the surface of aluminum was exposed was determined.

(3) Corrosion resistance test: The presence of white rust after 2000 hours was checked by a salt spray test. Those that occur from the entire surface are marked with x, those that occur in places are marked with Δ, and those that do not occur at all are ○
It was a mark.

(4) Whitening phenomenon: Immersed in trichlorethylene at room temperature for 10 minutes and then taken out,
Leave at room temperature for 10 minutes (trichloroethylene still remains), then drop water and let it dry naturally, then mark the water drop part with a whitening phenomenon and mark the drop part at all. It is marked with a circle. The evaluation results are shown in Table 2.

Among the comprehensive evaluations, the ⊚ mark was given to those for which satisfactory results were obtained for all the above evaluation tests. In addition, the mark “◯” is attached to the one which was slightly inferior to the solvent resistance but gave practically no problem and satisfied with other evaluation tests. △
The mark and the mark x were distinguished by the degree of difference with respect to the case where one or more items failed, but both were marked as not satisfying the present invention.

Example 2 500 g of isopropyl alcohol was placed in a two-necked three-necked flask equipped with a stirrer and heated to 65 ° C. After adding 5 g of azobisisobutyronitrile, 15 g of acrylonitrile,
Acrylic acid 25g, Hydroxyethyl methacrylate 75g,
A monomer mixture obtained by mixing 210 g of methyl methacrylate and 175 g of 2-ethylhexyl acrylate was added dropwise over 3 hours, and the polymerization was continued for 2 hours to obtain an acrylic resin solution. 20 g of dimethylethanolamine was added thereto, and 1000 g of water was gradually added dropwise to obtain a water-soluble acrylic resin (B).

Cymel 350, which is a methylated melamine resin, was added to the water-soluble (B) as a water-soluble amino resin to obtain resin compositions B-1 to 16 for surface treatment of the present invention. These are shown in Table 3, and the results of evaluation as in Example 1 are shown in Table 4. The breakdown of hydrophilic monomers and unsaturated monomers is shown in Table 3A.

As is clear from the results of the characteristic evaluation of Tables 2 and 4, the solvent resistance of A-12 and B-12 containing 0 parts of acrylonitrile is very poor. After soaking in trichlorethylene, if it comes into contact with water within a short time when trichlorethylene still remains, it will be whitened and leave a stain.

The resin compositions A-1 and B-1 contain 3 parts of acrylonitrile, and have considerably improved solvent resistance. After immersion in trichlorethylene, no whitening occurs even if it comes in contact with water within a short time while trichlorethylene still remains. If the content of acrylonitrile is 40 parts (A-13, B-13), the corrosion resistance will decrease.

Further, when the hydrophilic monomer is 5 parts (A-14, B-14), there are few hydrophilic groups that react with the curing agent such as amino resin, so that the solvent resistance and the adhesion are deteriorated. On the other hand, when the amount is too large, 60 parts by weight, the corrosion resistance is lowered due to residual water groups that did not contribute to curing like A-15 and B-15.

With A-16 and B-16 in which the water-soluble amino resin and the like are 0 parts, curing does not occur, so that the solvent resistance is particularly poor and the adhesion is also reduced.

If the amount of water-soluble amino resin is unnecessarily large, it is costly.

Within the composition range of the resin composition of the present invention, the adhesion, corrosion resistance and solvent resistance are good without impairing the hydrophilicity of the second coating layer.

[Effects of the Invention] As is clear from the above description, the resin composition for surface treatment of aluminum fin material of the present invention has a unique composition and a unique blending amount of a water-soluble acrylic resin and a unique blending amount of a water-soluble acrylic resin. Since it contains an amino resin, it has excellent solvent resistance and corrosion resistance, and does not leave stains due to whitening even when it comes into contact with water while trichloroethylene is still remaining. A coating film having excellent adhesion with a water-soluble cellulose resin can be obtained. Further, the surface-treated amino fin material in which the first coating layer made of this resin composition and the second coating layer made of the water-soluble cellulose resin are applied on the surface of the aluminum fin material also has a hydrophilic property of the coating layer. It is excellent in both adhesion, corrosion resistance and solvent resistance without causing stains due to the above-mentioned whitening phenomenon without damaging it.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location F28F 19/04 (72) Inventor Masatsugu Saito 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd. (72) Inventor Nobuyoshi Sasaki 4-3-18 Nihonbashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd. (72) Inventor Yoshitaka Hirosaki 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Sky Aluminum Co., Ltd. (56) Reference JP 61-101798 (JP, A) JP 49-102724 (JP, A) JP 59-179567 (JP, A) JP 61-238864 (JP , A)

Claims (2)

[Claims] 1. A resin composition for surface treatment of an aluminum fin material, comprising a mixture of a water-soluble acrylic resin and a water-soluble amino resin, comprising 3 to 30 parts by weight of acrylonitrile or methacrylonitrile, and a hydrophilic monomer. 10 to 50 parts by weight and a monomer 87 to 20 having an unsaturated double bond copolymerizable therewith
1 part by weight of a water-soluble acrylic resin comprising 100 parts by weight of a solid content, and 5-40 parts by weight of a water-soluble amino resin in a solid content and a first coating layer comprising a resin composition for surface treatment of an aluminum fin material. A surface-treated aluminum fin material obtained by applying a second coating layer made of a hydrophilic cellulose resin. 2. The surface-treated aluminum fin material according to claim 1, wherein the water-soluble cellulose resin of the second coating layer contains a water-soluble amino resin.