JPH0665524A - Material for aluminum fin for heat exchanger - Google Patents

Abstract

PURPOSE:To obtain a composition for the priming of an Al fin whose composi tion has good Al plate adhesion even after the baking of a hydrophilic coating film by incorporating a hardener comprising a melamine, urea, or phenolic resin and a softener comprising a non-crosslinkable acrylic or epoxy resin into a specific base resin. CONSTITUTION:This material is a composition comprising: 100 pts.wt. base resin comprising a crosslinkable acrylic, epoxy, urethane, polyester, or polyamide resin having a mol.wt. of 5,000-50,000 or a copolymer or mixture of these; 10-30 pts.wt. hardener comprising a melamine, urea, or phenolic resin; and 1-50 pts.wt. softener comprising a non-crosslinkable acrylic resin and/or a non-crosslinkable epoxy resin each having an average mol.wt. of 400-2,000.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to aluminum or aluminum alloys (hereinafter referred to as aluminum or aluminum alloys) used for heat exchangers for condensers, evaporators, etc. of commercial and household air conditioners, or heat exchangers for automobile radiators, etc. Regarding the heat exchanger fin material, it has good adhesion to the aluminum plate material even after baking the hydrophilic resin coating film and adhesion to the hydrophilic coating film, and also follows the processing of the aluminum plate material well. The present invention relates to a composition for surface treatment which has excellent corrosion resistance, a material for aluminum fins coated with the composition, and a precoated aluminum fin material coated with a hydrophilic resin paint by baking.

[0002]

2. Description of the Related Art As a fin material for a heat exchanger, aluminum, which is lightweight, has excellent workability and thermal conductivity, has been widely used.

In recent years, in order to make room air conditioners more compact and to save energy, various measures have been taken to further improve the heat transfer efficiency, such as raising the louvers and shortening the distance between the fins.

Therefore, when water is condensed on the fins, the water droplets form a bridge between the fins, which increases ventilation resistance, and the water droplets resonate with the ventilation to generate noise. It is known that the fin material is corroded by water, and aluminum hydroxide powder (white powder) as a corrosion product is scattered.

As a measure for preventing corrosion, a corrosion resistant film is provided on the fin surface, for example, a chromate treatment agent which is a known surface treatment agent for aluminum, a non-chromate treatment agent using a titanium or zirconium compound, an organic coating agent such as an acrylic resin. Are used. However, since these are water-repellent, the condensed water adheres to the fins in a hemispherical shape or promotes the existence of a bridge between the fins, which further hinders the air flow and increases the ventilation resistance. This caused the heat exchange efficiency to decrease.

Therefore, in recent years, after performing a water-repellent treatment,
Further, a treatment for forming a film having hydrophilicity is performed. For example, 1: Chromate treatment-water glass treatment (JP-A-50-38645), 2: Boehmite treatment-water glass treatment (JP-A-62-50477), 3: Hydrophobic organic resin-Hydrophilic organic resin (JP-A-SHO) 62-105629) and the like.

On the other hand, the aluminum fin material pre-coated with a treating agent such as an anticorrosive treating agent or a hydrophilic treating agent is subjected to secondary forming such as pressing, drawing and ironing when it is incorporated in a heat exchanger. It will be processed.

In this secondary molding process, there is an increasing number of cases in which a volatile lubricating oil that does not require a degreasing step with an organic solvent is used to prevent environmental pollution and to prevent destruction of the ozone layer.

However, since this volatile lubricating oil has an extremely low viscosity and is volatile, the lubricating oil is volatilized due to heat generated during molding and natural volatilization, which causes the lubricating oil to volatilize during secondary molding. There has been a problem that the anticorrosive hydrophilic coating film that has been painted is easily scratched, and problems such as peeling of the coating film, buckling, and color jump are likely to occur.

In order to improve the secondary molding processability, a method of adding wax or the like to the hydrophilic coating to form a film with lubricity, or a hydrophilic substance on the hydrophilic coating provided on the surface There is also a proposal to apply a to improve lubricity.

However, although the secondary molding processability is certainly improved by these methods, since a hydrophobic substance is further present in the hydrophilic coating film or on the hydrophilic coating film, aluminum for heat exchangers is used. Not only the surface hydrophilicity required for fin materials is greatly reduced, but also the adhesion between each film (coating film), the adhesion between the aluminum material and the anticorrosive coating, and also the corrosion resistance can be avoided. There will be a problem that there is no.

A proposal in which an inorganic substance such as silica is used as a lubricant instead of the wax-type lubricant (JP-A-61-60)
766), even though they have a certain degree of hydrophilicity and can avoid the above-mentioned problems, when they are used as cross fins of a heat exchanger, they have a slight odor (cement odor) peculiar to silica and cause an uncomfortable feeling. However, there is another problem that the wear of an expensive molding die is greatly promoted, which is a particularly serious problem.

[0013]

DISCLOSURE OF THE INVENTION According to the present invention, aluminum fins used in heat exchangers such as condensers, radiators, and evaporators have excellent anticorrosion properties, and have excellent adhesion to aluminum and adhesion to hydrophilic resin coatings. Good and good for secondary processing using volatile lubricating oil, as well as imparting lubricity of this lubricating oil, and for surface treatment without scratches, peeling, buckling, color jumping etc. on the coating film due to processing The purpose of the present invention is to develop a composition, an aluminum fin material coated with the undercoating composition, and a precoated aluminum fin material coated with a hydrophilic resin paint by baking.

[0014]

The present invention has a molecular weight of 500.
Melamine resin, urea resin or phenol per 100 parts by weight of a base resin made of an acrylic resin, an epoxy resin, a urethane resin, a polyester resin, a polyamide resin, a copolymer thereof, or a mixture thereof having a crosslinking property of 0 to 50,000. Resin hardener 10-30
1 part by weight and a softening agent of 1 to 50 parts by weight of a non-crosslinking acrylic resin and / or a non-crosslinking epoxy resin having an average molecular weight of 400 or more and 2000 or less are blended, and an aluminum fin undercoating composition for a heat exchanger, aluminum or Aluminum fin material for heat exchanger, which is obtained by applying a hydrophilic resin coating on the surface of the aluminum fin material for heat exchanger and the aluminum fin material for heat exchanger, which is obtained by coating the aluminum alloy plate material with the above composition for undercoating. Through development, the above objectives have been almost achieved.

The base resin for the base treatment composition of the present invention has a molecular weight of 5,000 to 50,000 and is a cross-linkable polymer or copolymer of acrylic acid, methacrylic acid or their derivatives such as esters. An aqueous or organic solvent-based solution or emulsion of an acrylic resin such as a combination, an epoxy resin such as an epoxy resin or an epoxy ester resin, a urethane resin, a polyester resin, a polyamide resin, or a copolymer thereof can be used.

These base resins contain various additives such as various pigments, neutralizing agents (organic acids), solvents (hydrophilic and hydrophobic), dispersants, defoamers and leveling agents depending on the purpose. It may be one.

When the molecular weight is lower than 5000, water resistance,
Abrasion resistance and moldability are deteriorated, and corrosion resistance is greatly deteriorated, so that it cannot be used for surface treatment.

On the other hand, if the molecular weight exceeds 50,000, flexibility increases due to an increase in the molecular weight, resulting in a decrease in moldability and a decrease in corrosion resistance, which is not preferable.

As the curing agent, melamine resin, urea resin, phenol resin or the like is used. This curing agent is added in an amount of 10 to 30 parts by weight based on 100 parts by weight of the base resin. If this amount is less than 10 parts by weight, the hardness of the undercoating film will be insufficient, and if it is more than 30 parts by weight, the film will become too hard and lack flexibility, so it must be avoided. Is.

The curing agent serves to improve the chemical resistance, water resistance and weather resistance of the film.

A film obtained from a composition comprising two components of a base resin and a curing agent is satisfactory in performance such as water resistance and abrasion resistance, but is slightly lacking in flexibility, so that a volatile lubricating oil can be used. Molding is difficult.

In the present invention, in addition to the above-mentioned two components, a softening agent composed of a non-crosslinking acrylic resin and / or a non-crosslinking epoxy resin having an average molecular weight of 400 to 2000 is added in an amount of 1 to 50 parts by weight based on 100 parts by weight of the base resin. It is a composition for base treatment which is partly mixed.

This softening agent, which is present in the composition, does not adversely affect the corrosion resistance, the solvent resistance and the film adhesion of the film, and imparts flexibility to the composition film, as well as water resistance and abrasion resistance. It has the effect of maintaining it as it is.

If the average molecular weight is less than 400, it easily moves to the interface in the film, which causes film peeling.

On the other hand, if the average molecular weight exceeds 2000, the crosslinking of the base resin may be hindered, and the water resistance of the composition film,
Abrasion resistance decreases.

If the blending amount of this softening agent is less than 1 part by weight with respect to 100 parts by weight of the base resin, the effect of the softening agent will not be exhibited. Further, if the amount is more than 50 parts by weight, the composition will be hardened.

As the material of the aluminum plate material to which the present invention is applied, all aluminum fin materials used in heat exchangers can be used. For example, JIS 1100,10
A pure aluminum plate such as 50 or an aluminum alloy plate containing various alloying elements may be used depending on the purpose, and the shape thereof may be either a sheet or a coil.

In producing the material for precoat fins for heat exchangers of the present invention, the above aluminum thin plate is degreased, washed with water and dried to clean the surface, and then coated with an organic resin having corrosion resistance and cured by baking. Form a film.

Next, the above-mentioned composition for surface treatment is applied to a thickness of 0.2.
To about 5 μm, preferably 0.5 to about 2 μm. If it is less than 0.2 μm, the corrosion resistance is significantly deteriorated and it cannot be used. On the other hand, even if the coating is thicker than about 5 μm, the corrosion resistance is saturated and does not improve, and conversely, problems such as a decrease in heat transfer of the heat exchanger and deterioration of formability occur.

This base treatment composition is coated and dried,
It is preferable to bake before coating the hydrophilic film. The baking conditions vary depending on the type of resin, the composition, the amount of coating, etc., but cannot be generally stated, but generally 150-
The temperature is 320 ° C. and the range is 5 to 120 seconds.

If the temperature is lower than 150 ° C. (time is in the range of 5 to 120 seconds) and less than 5 seconds (range of 150 to 320 ° C.), insufficient curing occurs, and this insufficient curing cannot be improved by adjusting the composition of the coating material.

The aluminum fin material thus obtained is then coated with a hydrophilic resin coating material and baked to obtain a pre-coated aluminum fin material.

The hydrophilic resin paint may be any known paint, for example, as the base resin thereof, cellulose derivative, acrylic acid (polyacrylic acid) or its derivative, methacrylic acid or its derivative, polyamide or its derivative, polyvinyl alcohol or It may be a water-soluble resin such as a derivative thereof, a copolymer or a mixture thereof, or a hydrophilic resin emulsion thereof.

The coating composition obtained by adding a usual compound to these base resins is applied with a coating film thickness of 0.1 to 10 μm, preferably 0.2 to 3 μm, and then baked.

The conditions such as the baking temperature and the baking time may be appropriately selected according to the hydrophilic resin used. Generally, a thermoplastic resin of several tens of degrees C. to 100's of several tens of degrees C. and 10's of seconds to 1
For a few minutes, thermosetting resin 100 to several tens of degrees Celsius to 300 degrees Celsius,
Bake for a few seconds to a few minutes.

[0036]

[Function] When forming a pre-coated aluminum fin material, if the coated film is soft and has low wear resistance,
The film is scraped off from the aluminum surface by the mold during molding, resulting in a decrease in corrosion resistance. Further, when the flexibility of the coating is poor, the coating cannot follow the deformation of aluminum and cracks (cutting of the coating) occur, which also leads to deterioration of corrosion resistance.

Therefore, in the case of molding with a volatile lubricating oil, it is important to give the film a certain degree of wear resistance and flexibility.

Generally, the abrasion resistance of the coating is determined by the hardness of the coating, and in the undercoating composition of the present invention, it is governed by the crosslink density of the resin. The crosslink density depends on the baking temperature and the baking time, but it changes depending on the amount of the curing agent (crosslinking agent) added.

Therefore, when the amount of the curing agent is small, the number of crosslinks is small,
The film has low wear resistance. Further, in such a film, the molecular weight of the film resin remains small, so that the solvent resistance is also poor.
When the amount of the curing agent is too large, the number of crosslinks increases and the abrasion resistance and the solvent resistance increase, but the flexibility is lost, resulting in defective molding (film crack).

It is difficult to control the amount of the curing agent so as to satisfy these contradictory properties, because the change of the properties of the film with respect to the amount of the curing agent is large.

In the present invention, by using this together with an appropriate amount of a curing agent and an appropriate amount of a non-crosslinking softening agent, the base resin is crosslinked-polymerized to improve abrasion resistance and solvent resistance.
A non-crosslinking softening agent is dispersed between polymerized base resins to suppress unnecessary cross-linking, and since it also has flexibility, it is possible to impart flexibility to the film relatively easily. I'm estimating.

As a result, the film of the composition for base treatment not only provides a film having corrosion resistance and wear resistance to the aluminum fin material and the precoated aluminum fin material, but also has low lubricity such as volatile lubricating oil. I think that it is possible to form a coating film that is free from peeling, buckling, and color jumping even in the molding process using lubricating oil.

[0043]

EXAMPLES The characteristics of the coating films obtained in the examples were evaluated as follows. a) Moldability evaluation Volatile lubricating oil Product name: Daphne Punch Oil AF-2
A Idemitsu Kosan is used and it is formed by the actual fin press. ○ Good △ Poor Scratch on inner surface of color, film peeling × No buckling, color jump

B) Evaluation of Corrosion Resistance A salt spray test was conducted with a test time of 1000 hours. ○ Good Total corrosion area 0.25% or less △ Slightly bad 〃 0.25 to 2.5% × Bad 〃 2.5% or more

C) Evaluation of hydrophilicity Evaluation by water contact angle ○ Good 20 degrees or less △ Slightly bad 20 to 30 degrees × Poor 30 degrees or more

(Example 1) Thickness of 0.115 mm, width of 25
A 0 mm JIS3003 equivalent rolled aluminum alloy coil was degreased, washed with water and dried. Water-soluble polyacrylic acid having a molecular weight of 20,000 was used as a base resin, and 20 parts by weight of a melamine resin as a curing agent was added to 100 parts by weight of the base resin, and an average molecular weight of 40 as a softening agent.
0 to 2000 non-crosslinking epoxy resin, 30 parts by weight of the composition for base treatment is applied by a roll coating method,
It was baked at 250 ° C. for 20 seconds to form a 1.0 μm film. The results are shown in Table 1.

Comparative Example 1 An aluminum plate coil treated in the same manner as in Example 1 was used as a base resin of a water-soluble acrylic resin having a molecular weight of 20000, and 20 parts by weight of a melamine resin as a curing agent was added to 100 parts by weight of this. And a non-crosslinking epoxy resin having an average molecular weight of less than 400 and more than 2000 as a softening agent are added in an amount of 30 parts by weight, and the composition is applied by a roll coating method.
It was baked at 0 ° C. for 20 seconds to obtain a 1.0 μm film. The resulting film was evaluated for moldability and corrosion resistance (SST: 1000h) when a volatile lubricating oil was used. The results are shown in Table 1.

[0048]

[Table 1]

(Example 2) Thickness of 0.115 mm, width of 25
A 0 mm JIS 3003 equivalent rolled aluminum alloy plate coil was washed with water and dried after degreasing. Water-soluble polyacrylic acid having a molecular weight of 20,000 was used as a base resin, and 20 parts by weight of a melamine resin as a curing agent was added to 100 parts by weight of the base resin.
Of the non-crosslinking epoxy resin of 1.0 to 50 parts by weight is applied to the aluminum plate coil by a roll coating method and baked at 250 ° C. for 20 seconds,
A 1.0 μm film was formed.

(Comparative Example 2) The molecular weight was 20 as in Example 2.
000 water-soluble polyacrylic acid as a base resin, 20 parts by weight of a melamine resin as a curing agent is added to 100 parts by weight of the base resin, and a non-crosslinking epoxy resin having a molecular weight of 1000 is less than 1.0 and 50 parts by weight. To give a base treatment composition. This was coated on the aluminum plate coil by a roll coating method and baked at 250 ° C. for 20 seconds to obtain a 1.0 μm film.

[0051]

[Table 2]

(Example 3) A water-soluble polyacrylic acid having a molecular weight of 5,000 to 50,000 was used as a base resin in an aluminum plate coil treated in the same manner as in Example 1, and 20 parts by weight of a melamine resin as a curing agent was added to 100 parts by weight of this. Parts, 30 parts by weight of a non-crosslinking epoxy resin having a molecular weight of 1000 as a softening agent was applied by a roll coating method and baked at 250 ° C. for 20 seconds to form a 1.0 μm film.

(Comparative Example 3) A water-soluble polyacrylic acid having a molecular weight of less than 5,000 and a water-soluble polyacrylic acid having a molecular weight of more than 50,000 were used as base resins. 20 parts by weight of a melamine resin and 100 parts by weight of this non-crosslinking epoxy resin were used. The same operation as in Example 3 was performed except that the undercoating composition containing 30 parts by weight of the resin was applied by the roll coating method.

[0054]

[Table 3]

Example 4 Water-soluble polyacrylic acid having a molecular weight of 20,000 was used as a base resin, and 20 parts by weight of a melamine resin and 30 parts by weight of a non-crosslinking epoxy resin having a molecular weight of 1000 were added to 100 parts by weight of the base resin. To obtain a composition for base treatment. This was applied to the aluminum plate coil of Example 1 by a roll coating method and baked at 250 ° C. for 20 seconds to obtain a film of 0.2 to 5.0 μm. The results are shown in Table 4.

Comparative Example 4 The same aluminum plate coil and undercoating composition as in Example 4 were used, except that the coating thickness was less than 0.2 μm or more than 5 μm, and baking was performed under the same conditions. The results are shown in Table 4.

[0057]

[Table 4]

Example 5 A water-soluble polyacrylic acid base resin having a molecular weight of 20,000 was added to the pretreated aluminum plate coil of Example 1, 20 parts by weight of a lamin resin was added to 100 parts by weight of this resin, and a non-crosslinking agent having a molecular weight of 1,000 was used. 30 parts by weight of a hydrophilic epoxy resin was added to prepare a composition for base treatment, which was coated by a roll coating method and baked at 250 ° C. for 20 seconds to obtain a film of 0.5 to 1.5 μm.

A water-soluble cellulose resin was applied thereon by a roll coating method and baked at 230 ° C. for 20 seconds,
Films of 0.4 μm and 0.8 μm were obtained. The results are shown in Table 5.

[0060]

[Table 5]

[0061]

INDUSTRIAL APPLICABILITY The present invention, when applied to a pre-coated aluminum fin material used for a heat exchanger, has good adhesion to an aluminum or aluminum alloy plate material and excellent anticorrosion properties. Was developed. A coating film obtained by applying and baking this surface treatment agent has excellent adhesion to an aluminum plate material and adhesion to a hydrophilic resin coating film even after baking a hydrophilic resin on the coating film. The coating film of the precoated aluminum fin material, which is obtained by baking both coating films of the hydrophilic resin, can well follow the deformation of the plate material even if a volatile lubricating oil with insufficient lubricity is used in the processing, so the coating film peels, Problems such as cracking and buckling can be greatly improved, and deterioration of corrosion resistance due to damage to the coating film can be prevented.In addition, even in heat exchangers with short fin-to-fin distances, increased ventilation resistance due to water droplet bridges and It was possible to prevent the generation of noise due to resonance and the scattering of white powder due to the corrosion of aluminum plate materials.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C09D 161/28 PHK 8215-4J 163/00 PKC 8830-4J 167/02 PLB 8933-4J 177/00 PLS 9286-4J

Claims (5)

[Claims] 1. Melamine with respect to 100 parts by weight of a base resin made of an acrylic resin, an epoxy resin, a urethane resin, a polyester resin, a polyamide resin having a molecular weight of 5,000 to 50,000 and having a crosslinkability, a polyamide resin, a copolymer thereof, or a mixture thereof. Curing agent consisting of resin, urea resin or phenol resin 10 to 30 parts by weight and average molecular weight of 4
Softener 1 to 50 composed of a non-crosslinking acrylic resin and / or a non-crosslinking epoxy resin of 00 or more and 2000 or less
An aluminum fin undercoating composition for a heat exchanger, characterized by containing parts by weight. 2. An aluminum fin material for a heat exchanger, characterized in that a plate material of aluminum or an aluminum alloy is coated with the composition for surface treatment of claim 1. 3. The aluminum fin material for a heat exchanger according to claim 2, wherein the thickness of the base treatment composition is about 0.2 to about 5.0 μm. 4. An aluminum fin material for a heat exchanger, wherein the surface of the aluminum fin material for a heat exchanger according to claim 2 or 3 is coated with a hydrophilic resin paint and baked. 5. A cellulose derivative, (meth) acrylic acid (poly (meth) acrylic acid) or a derivative thereof, a polyamide derivative, polyvinyl alcohol or a derivative thereof,
5. An aluminum fin material for a heat exchanger according to claim 4, wherein a hydrophilic resin paint containing a water-soluble resin or a hydrophilic resin emulsion made of a copolymer or a mixture of these is baked and applied to a thickness of about 0.1 to about 10 .mu.m. .