JPH01256574A - Resin composition for surface-treating aluminum fin material and surface-treated aluminum fin material - Google Patents

Abstract

PURPOSE:To obtain the title composition which can give a first coating layer which is prevented from being stained by whitening of water drops and is improved in corrosion and solvent resistances, by mixing a specified water-soluble acrylic resin with a water-soluble amino resin. CONSTITUTION:A water-soluble acrylic resin (A) is obtained by copolymerizing 3-30pts.w.t. (meth)acrylonitrile (a) with 10-50pts.wt. hydrophilic monomer (b) (e.g., hydroxyethyl methacrylate) and 87-20pts.wt. compound of the formula (wherein R is methyl or H, m is 0-19, n is 0-20, and m+n=1-20), which is a monomer having an unsaturated double bond and being copolymerizable therewith in a solvent comprising water and, optionally, a water-miscible organic solvent. 100pts.wt. (in terms of the solid matter) component A is mixed with 5-40pts.wt. (in terms of the solid matter) water-soluble amino resin to obtain the title composition. A first coating layer comprising said composition is formed on the surface of an aluminum fin material, and a second coating layer comprising a water-soluble cellulose resin is formed on it by coating.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides hydrophilicity to the surface of metal to prevent the formation of water droplets, as well as imparting durability and solvent resistance. The present invention relates to a surface treatment resin composition useful for preventing corrosion and a surface treated aluminum fin material.

[Prior art and its problems] Recently, the demand for heat exchanger fin materials has increased significantly, especially with the rapid spread of room air conditioners. Aluminum (in this specification, aluminum includes aluminum and aluminum alloys) is widely used as a heat exchanger fin material because it is lightweight and has excellent workability and thermal conductivity.

Conventional heat exchanger fin materials have been used without surface treatment, so the aluminum may corrode due to moisture in the air during use, or a layer of water condensed on the fin surface may act as ventilation resistance, causing heat loss. Because it had the disadvantage of lowering the exchange rate,
User demand for pre-coated fin materials whose surfaces are coated with corrosion-resistant and hydrophilic properties is rapidly increasing.

The use of pre-coated fin materials is extremely effective in saving energy and making room air conditioners more compact.

There is a method (post-coat method) in which this coating layer is formed after the fins are formed, but recently, in order to simplify the process and ensure uniformity of the coating layer, a coating layer is formed on the aluminum thin plate before the fins are formed. There is a strong demand for a method of forming fins (pre-coating method).

In order to be used in this precoating method, the coating layer must not only have the above-mentioned corrosion resistance and hydrophilic properties, but also must not cause wear of the forming tool.

Furthermore, lubricating oil is used during molding, but the coating layer must not dissolve when it is washed with an organic solvent such as trichlorethylene after molding.

In order to meet these demands, a technique is known in which a coating layer is formed by mixing an organic resin with an inorganic substance such as silica or alumina, which has particularly excellent hydrophilic properties (Japanese Patent Application Laid-Open No. 54-14
No. 2850 and No. 55-99978).

However, these tools cause large wear on the tool and have very poor corrosion resistance.

In addition, as a treatment method using an organic surface treatment agent, water-soluble acrylic resin is used for the first coating layer and water-soluble cellulose resin is used for the second coating layer, which improves chemical resistance (solvent resistance) and hydrophilicity. A method for improving this is known (Japanese Unexamined Patent Publication No. 101798/1981).

Compared to inorganic surface treatment methods, when molding fins (pre-coating method), this method requires that both the water-soluble acrylic resin in the first coating layer and the water-soluble cellulose resin in the second coating layer be organic and flexible. Because of this, there is less wear on the forming tool,
In addition, the acrylic resin of the first coating layer has excellent corrosion resistance compared to inorganic systems, so it has been widely put into practical use, but further improvements are desired.

That is, when molding the aluminum fin material on which the first coating layer and the second coating layer are formed, after cleaning the attached oil etc. with trichlorethylene, during a short period of time when trichlorethylene still remains, If the product comes into contact with water, the water droplets may turn white and leave stains, resulting in a problem that the product's appearance deteriorates and its value decreases.

[Means to Solve the Problem] As a result of extensive studies, the present inventors have found that this problem can be solved by combining a specific water-soluble acrylic resin as the first coating layer and a water-soluble amino resin crosslinked with this. It has excellent solvent resistance and corrosion resistance, and even if it comes into contact with water while trichlorethylene still remains, the water droplets will not turn white and leave stains, and the second coating layer is water-soluble. It has been found that a coating film with excellent adhesion to cellulose resin can be obtained.

That is, the present invention uses 3 to 30 parts by weight of acrylonitrile or methacrylonitrile, 10 to 50 parts by weight of a hydrophilic monomer, and 87 to 20 parts by weight of a monomer having an unsaturated double bond copolymerizable with these. The solid content of water-soluble acrylic resin is 100 parts by weight, and the water-soluble amino resin is 5 parts by solid content.
A resin composition for surface treatment of an aluminum fin material containing ~40 pieces, and a first coating layer made of the resin composition and a second coating layer made of a water-soluble cellulose resin are coated on the surface of the aluminum fin material. It is a surface-treated aluminum fin material.

The present invention will be explained in detail below.

In the present invention, water-soluble acrylic resin refers to 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 that can be copolymerized with these. by copolymerizing 87 to 20 parts by weight in an aqueous system or in a mixed system with an organic solvent that is compatible with water, or by copolymerizing in an organic solvent that is compatible with water and then mixing with water. It is water-based.

Acrylonitrile or methacrylonitrile may be used alone or in combination, and is used in an amount of 3 to 30 parts by weight based on the solid content of the water-soluble acrylic resin. If it is less than 3 parts by weight, solvent resistance will be insufficient, and if it exceeds 30 parts by weight, water resistance will decrease, and when baking hardening is performed, a yellowish tinge will appear in the coating film, reducing the product value in terms of appearance. 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 its derivatives, N-methylol acrylamide, N Examples include acrylamide derivatives having an N-methylol group such as -methylolmethacrylamide and derivatives thereof, and monomers having a water group such as hydroxyethyl acrylate or hydroxyethyl methacrylate.

In addition, as a monomer having an unsaturated double bond copolymerizable with the hydrophilic monomer etc., the following general formula (I) CH2=C, -R (wherein, R is a methyl group or Hydrogen atom, m is O or 1-1
An integer of 8, n is O or an integer of 1 to 20, and man is 1 to 20.
It is 20. ) are listed.

- Among the compounds represented by formula (I), monomers preferably used include Blenmar PE90 manufactured by NOF Corporation;
Blenmar PE200, British Petrochemical's Bitesmar PPM5S, Pi/? -PPM8
Examples include E.

In the present invention, the method for polymerizing water-soluble acrylic resin is (1)
After performing emulsion polymerization in which copolymerizable monomers are polymerized in an aqueous medium while being added all at once or gradually, solubilization is achieved by adding an organic solvent and/or an alkaline substance that is compatible with water. (2) Solution polymerization in which copolymerizable monomers are polymerized in an organic solvent that is compatible with water, either all at once or gradually added, followed by an alkali substance and/or a water-soluble acrylic resin. or a method of synthesizing a water-soluble acrylic resin by making it water-solubilized by adding water; (3) adding a copolymerizable monomer all at once or gradually in a homogeneous water mixed solvent containing an organic solvent; There is a method in which a water-soluble acrylic resin is synthesized by performing polymerization, and then adding an organic solvent and/or an alkaline substance compatible with water or the above-mentioned mixed solvent to solubilize the resin.

Although any of these methods can be employed in the present invention, emulsion polymerization (1) is more preferred because it is less dangerous during polymerization.

Examples of water-soluble amino resins include methylated urea resins, methylated melamine resins, and methylated benzoguanamine resins, each of which may be used alone or as a mixture of 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 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 will be low and trichlorethylene resistance (solvent resistance) will be insufficient, and if it exceeds 40 parts by weight, the cured coating will become too hard, resulting in poor adhesion and poor water resistance. , physical properties such as solvent resistance also deteriorate.

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

In addition, the water-soluble cellulose resin of the second coating layer in the aluminum fin material of the present invention has a hydroxyl group (-OH
) and has good hydrophilicity, but the water-soluble cellulose resin here is a general term for cellulose and its derivatives such as esters and ethers, and may also be a mixture thereof.

Moreover, it is preferable that the water-soluble cellulose resin of this second coating layer 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 singly or a mixture thereof.

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

Here, the melamine resin also includes derivatives of methylated melamine resin. Moreover, it goes without saying that two or more types of organic curing agents may be used in combination.

The aluminum fin material in the present invention refers to, for example, a heat exchange fin material made of aluminum fins.

The surface-treated aluminum fin material of the present invention is obtained by, for example, degreasing a heat exchange fin material made of aluminum fins, and then coating the surface thereof with a first coating layer and a second coating layer using, for example, a bar coater. , can be formed by baking. Note that this does not mean that the surface of the aluminum fin material may be treated by graining or the like before coating.

In the present invention, the thickness of the first coating layer and the second coating layer after baking is preferably 1 to 5 g/rn', more preferably 1 to 3 g/rn', and the thickness of the second coating layer is preferably 1 to 5 g/rn'. The thickness of the coating layer is preferably 0.3 to 3 g/rn'', more preferably 0.5 to 1 g/rn'.

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

Example 1 2 with a stirrer! ;Water 300 in L Mitsuro flask
0.5g of sodium dodecylbenzenesulfonate per g
and heat to 65℃. Acrylonitrile 50 separately
g, 75 g of hydroxyethyl methacrylate, 25 g of methacrylic acid, 200 g of methyl methacrylate, 150 g of butyl acrylate) were pre-emulsified with 200 g of water and 1 g of sodium dodecylbenzenesulfonate, and 2.5 g of potassium persulfate was heated to 65°C. Then, 10% by weight of the pre-emulsified emulsifying monomer liquid was added, and after polymerizing for 30 minutes, the remaining emulsifying monomer was continuously added dropwise over 3 hours, and polymerization was continued for another 2 hours. An acrylic emulsion was obtained. Add 200g of isopropyl alcohol to this and further add 50g of hydrophilic solvent.
After adding 0g, add 20g of ammonia water and 300g of dilution water.
g was added to obtain a water-soluble acrylic resin (A). Seitul 350 (manufactured by Mitsui Cyanamid Co., Ltd., trade name), which is a methylated melamine resin, is added as a water-soluble amino resin to the aqueous solution (A) to prepare resin compositions A-1 to A-1 for surface treatment of aluminum fin materials of the present invention. I got 16. These are shown in Table 1.

Creating a test piece Industrial pure aluminum (JIS A) with a plate thickness of 0.12 mm
IIQQ) After degreasing the plate material, a resin composition for surface treatment of aluminum fin material was applied using a #7 bar coater and baked at 250°C for 20 seconds. The coating amount after baking is 1.6g/m
"Met.

This was used as the first coating layer, and on top of this, the second coating layer was made of a water-soluble cellulose resin Solidite W)l-10 (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name) and a water-soluble amino resin Cyitl 350 (Mitsui Toatsu Chemical Co., Ltd., trade name). A test piece was prepared by applying a mixture of Cyanamid Co., Ltd. (trade name) using a #7 bar coater and baking it. The coating amount after baking of the second coating layer is 0
．． It was 7g/m'.

evaluation test The following tests were conducted on the obtained test piece.

The results are shown in Table 2.

(1) Adhesion test: Perform a peel test using cellophane tape to check the adhesion between the first coating layer and the second coating layer. If the entire surface does not peel off, mark O. If peeling occurs in some places, mark Δ. Those that do are marked with an X.

(2) Solvent resistance test A rubbing test was performed using nitric chlorethylene, and the number of times of rubbing was determined until the aluminum surface was exposed.

(3) Corrosion resistance test: The presence or absence of white rust was checked after 2000 hours using a turt spray test. Mark X for those that are generated from the entire surface.
Δ marks were given for those that occurred in some places, and 0 marks were given for those that did not occur at all.

(4) Whitening phenomenon After immersing in nitric chlorethylene for 10 minutes at room temperature, take it out, leave it for 10 minutes at room temperature (trichlorethylene still remains), then add water dropwise and dry naturally. A case where there was a whitening phenomenon was marked with an X mark, and a case where no dripping area could be observed was marked with an O mark.

These evaluation results are shown in Table 2.

In the overall evaluation, a ■ mark was given to those for which satisfactory results were obtained for all of the above evaluation tests. Further, the O mark was given to those which had slightly inferior solvent resistance but had no practical problems and had satisfactory results in other evaluation tests. Δ
Marks and X marks were given to cases in which one or more items failed according to the degree of failure, but both marks were given to cases that did not satisfy the present invention.

Example 2 500 g of isopropyl alcohol is placed in a 21-size three-piece flask equipped with a stirrer and heated to 65°C. After adding 5 g of azobisisobutyronitrile, 40 g of methacrylate trile, 20 g of acrylic acid, 40 g of hydroxyethyl methacrylate, 200 g of methyl methacrylate
, 200 g of 2-ethylhexyl acrylate was added dropwise over 3 hours, and polymerization was continued for an additional 2 hours to obtain an acrylic resin solution. 20 g of dimethylethanolamino was added to this, and 1000 g of water was gradually added dropwise to obtain a water-soluble acrylic resin (B).

Seitul 350, which is a methylated melamine resin, was added as a water-soluble amino resin to the aqueous solution (B) to obtain surface treatment resin compositions B-1 to B-18 of the present invention. These are shown in Table 3, and the results of evaluation in the same manner as in Example 1 are shown in Table 4.

As is clear from the property evaluation results in Table 2.4, A to 12.0 containing 0 parts of acrylonitrile. B-12 has very poor solvent resistance, and if it comes into contact with water within a short period of time when trichlorethylene still remains after immersion in trichlorethylene, it will turn white and leave stains.

Resin compositions A-1 and B-1 have considerably improved solvent resistance with 3 parts of acrylonitrile. Corrosion resistance decreases when 40 parts of acrylonitrile (A-13, B-13) does not whiten even if it comes into contact with water within a short period of time when trichlorethylene still remains after dipping in trichlorethylene.

Moreover, when the hydrophilic monomer content is 5 parts (A-14, B-14), there are few hydrophilic groups that react with the amino resin etc. that are the curing agent, and thus the solvent resistance and adhesiveness deteriorate. On the other hand, if the amount is too high (60 parts by weight), the corrosion resistance will decrease due to the remaining parent wood groups that did not contribute to hardening, as in A-15 and B-15.

A-18, B-1ft with 0 parts of water-soluble amino resin etc.
Since curing does not occur, the solvent resistance is particularly poor and the adhesion is also reduced.

Note that if the amount of water-soluble amino resin is more than necessary, it is disadvantageous in terms of cost.

Within the composition range of the resin composition of the present invention, the second coating layer does not impair the hydrophilicity and has good adhesion, corrosion resistance, and solvent resistance.

[Effects of the Invention] As is clear from the above description, the resin composition for surface treatment of aluminum fin materials of the present invention has a specific composition and a specific amount of a water-soluble acrylic resin and a specific amount of a water-soluble acrylic resin. Because it contains amino resin, it has excellent solvent resistance and corrosion resistance, and even if it comes into contact with water while trichlorethylene still remains, it will not whiten and leave stains, and the second coating layer A coating film with excellent adhesion to water-soluble cellulose resin can be obtained. In addition, the surface-treated aluminum fin material, in which the first coating layer made of this resin composition and the second coating layer made of water-soluble cellulose resin are coated on the surface of the aluminum fin material, has a hydrophilic property of the coating layer. It has good adhesion, corrosion resistance, and solvent resistance without causing stains due to the whitening phenomenon described above.

Patent applicant: Mitsui Toatsu Chemical Co., Ltd. (1 other person)

Claims (1)

[Claims] 1. Acrylonitrile or methacrylonitrile from 3 to
30 parts by weight, 10 to 50 parts by weight of a hydrophilic monomer, and 87 to 87 parts of a monomer having an unsaturated double bond that can be copolymerized with these.
Water-soluble acrylic resin consisting of 20 parts by weight with a solid content of 10
A resin composition for surface treatment of aluminum fin materials, which contains 0 parts by weight and 5 to 40 water-soluble amino resins in solid content. 2. A surface-treated aluminum fin material comprising a first coating layer made of the resin composition according to claim 1 and a second coating layer made of a water-soluble cellulose resin applied to the surface of the aluminum fin material.