JP7718878B2 - Precoated fin material and its manufacturing method - Google Patents

Description

The present invention relates to precoated fin materials and their manufacturing methods.

Fin-and-tube heat exchangers, which have numerous fins and tubes that intersect with these fins, are commonly used as heat exchangers in air conditioners, refrigerators, and other appliances. The fins are made by pressing pre-coated fin material, which has a substrate made of aluminum (including pure aluminum and aluminum alloys; the same applies below) and a resin coating formed on the substrate.

The resin coating of precoated fin material is designed to impart various properties to the fins, such as corrosion resistance to suppress corrosion caused by condensation water and hydrophilicity to prevent clogging of the fins due to condensation water. For example, Patent Document 1 describes an aluminum fin material for heat exchangers, characterized in that a corrosion-resistant coating made of one or more components selected from acrylic resin, epoxy resin, and urethane resin is formed on an aluminum substrate, a hydrophilic coating made of acrylic resin is formed on top of the corrosion-resistant coating, and a water-soluble lubricant layer made of polyethylene glycol is formed on top of the hydrophilic coating.

JP 2013-130320 A

However, in the precoated fin material of Patent Document 1, multiple types of resin coatings with different functions are applied to the substrate in order to impart the required properties to the fin. This tends to complicate the manufacturing process of the precoated fin material, which can easily lead to increased processing costs.

The present invention was made in light of this background, and aims to provide a precoated fin material that can be manufactured using a simple process and has excellent corrosion resistance and hydrophilicity, as well as a method for manufacturing the same.

One aspect of the present invention is a precoated fin material having an aluminum substrate and a resin coating provided on at least one surface of the substrate,
The mass per unit area of the resin film is 0.2 g/m ² or more and 2.5 g/m ² or less,
The average value of the natural potential from the time when the precoated fin material is immersed in a 5 mass% NaCl aqueous solution of pH 3 until one hour has elapsed is +0.040 V or more and +0.2 V or less relative to the average value of the natural potential from the time when the base material is immersed in a 5 mass% NaCl aqueous solution of pH 3 until one hour has elapsed, and
The precoated fin material has a characteristic that the contact angle of water after immersion in running water for 10 minutes is 20° or more and 40° or less,
the resin film contains a hydrophilic polymer (A) and a crosslinking agent (B) capable of crosslinking the hydrophilic polymer (A);
the content of the hydrophilic polymer (A) is 60 parts by mass or more and 97 parts by mass or less, relative to 100 parts by mass of the total of the hydrophilic polymer (A) and the crosslinking agent (B);
The hydrophilic polymer (A) includes
Structural units derived from a hydrophilic monomer (a1) having one polymerizable double bond and a polyoxyalkylene chain per molecule: 2% by mass or more and 50% by mass or less;
Structural units derived from a (meth)acrylamide-based monomer (a2) represented by the following general formula (1): 1% by mass or more and 70% by mass or less;
Structural units derived from a carboxyl group-containing polymerizable unsaturated monomer (a3) containing a carboxyl group: 1% by mass or more and 50% by mass or less;
The precoated fin material contains 0% by mass or more and 50% by mass or less of structural units derived from the hydrophilic monomer (a1), the (meth)acrylamide-based monomer (a2), and a polymerizable unsaturated monomer (a4) other than the carboxyl group-containing polymerizable unsaturated monomer (a3).

In the general formula (1), m and n each independently represent 0 or 1, ^R1 represents a hydrogen atom or a methyl group, ^R2 and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and ^R4 and ^R5 each independently represent a methylene group or an ethylene group.

Another aspect of the present invention is a method for producing a precoated fin material of the above aspect,
applying a coating material containing the hydrophilic polymer (A) and the crosslinking agent (B) onto at least one surface of the substrate;
The method for producing a precoated fin material includes heating the base material to which the paint has been applied for 4 seconds to 20 seconds in a heating furnace at a temperature of 240°C to 300°C to bake the paint, thereby forming the resin film on the base material.

The precoated fin material is provided with a resin coating containing the specific hydrophilic polymer (A) and crosslinking agent (B). Furthermore, the precoated fin material has the characteristics that the difference in average natural potential with the substrate and the contact angle, when measured under the specific conditions, are both within the specific ranges. By having this configuration, the precoated fin material can achieve a balanced improvement in both corrosion resistance and hydrophilicity.

Furthermore, the precoated fin material combines excellent corrosion resistance and hydrophilicity with a single resin coating. Therefore, the precoated fin material can be manufactured using a simple process, making it easy to reduce manufacturing costs.

In the precoated fin material manufacturing method, a paint containing the specific hydrophilic polymer (A) and crosslinking agent (B) is applied to a substrate, and then the paint is baked under the specific conditions, thereby forming the resin film on the substrate. In this way, the manufacturing method makes it easy to obtain a precoated fin material with excellent corrosion resistance and hydrophilicity through the simple process of applying the paint and baking the paint once each.

As described above, the above-described aspect provides a precoated fin material and its manufacturing method that can be manufactured using a simple process and has excellent corrosion resistance and hydrophilicity.

FIG. 1 is a cross-sectional view of a precoated fin material in an embodiment. FIG. 2 is an explanatory diagram of a device for measuring spontaneous potential in the examples.

(Pre-coated fin material)
The precoated fin material has a substrate and a resin coating formed on one or both sides of the substrate. The configuration of each part of the precoated fin material will be described below.

A. Substrate In the precoated fin material, the aluminum constituting the substrate may be pure aluminum or an aluminum alloy. For example, the substrate may be made of pure aluminum having a chemical composition represented by an alloy number such as A1200 or A1050.

B. Undercoat An undercoat made of an inorganic material may be provided on the surface of the substrate, and the resin coating may be laminated on the undercoat. By providing the undercoat between the substrate and the resin coating, it is possible to further improve the adhesion of the resin coating and further improve the corrosion resistance of the substrate.

The base coating may be, for example, a chemical conversion coating formed by chemical conversion treatment. The chemical conversion coating may be formed by a reactive chemical conversion treatment or a paint-type chemical conversion treatment. More specifically, the base coating may be a chromium-containing coating formed by a chromate treatment using chromate phosphate or the like, or a chromium-free coating formed by a non-chromate treatment using a chromium-free compound such as titanium phosphate, zirconium phosphate, molybdenum phosphate, zinc phosphate, or zirconium oxide.

C. Resin Film A resin film is provided on at least one surface of the precoated fin material. The resin film may be laminated directly on the substrate or on an undercoat film. The resin film may also be exposed on the outermost surface of the precoated fin material. The resin film has excellent corrosion resistance and hydrophilicity, as well as excellent lubrication during press molding. Therefore, providing the resin film on the outermost surface can also improve the press moldability of the precoated fin material.

The resin film contains a hydrophilic polymer (A) and a crosslinking agent (B) capable of crosslinking the hydrophilic polymer (A).

C-1. Hydrophilic polymer (A)
The hydrophilic polymer (A) is a copolymer containing a structural unit derived from a hydrophilic monomer (a1), a structural unit derived from a (meth)acrylamide-based monomer (a2), and a structural unit derived from a carboxyl group-containing polymerizable unsaturated monomer (a3). In addition to the structural units derived from the monomers (a1) to (a3), the hydrophilic polymer (A) may further contain a structural unit derived from a polymerizable unsaturated monomer (a4) other than the monomers (a1) to (a3).

Hydrophilic Monomer (a1)
The hydrophilic monomer (a1) has one polymerizable double bond and a polyoxyalkylene chain per molecule. The hydrophilic polymer (A) may contain structural units derived from one type of hydrophilic monomer (a1), or may contain structural units derived from two or more types of hydrophilic monomers (a1). The content of the structural units derived from the hydrophilic monomer (a1) in the hydrophilic polymer (A) is 2% by mass or more and 50% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4). The content of the structural units derived from the hydrophilic monomer (a1) is preferably 5% by mass or more and 45% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4).

The hydrophilic monomer (a1) may have, for example, a chemical structure represented by the following general formula (2):

In the general formula (2), R ⁶ to R ⁸ each independently represent a hydrogen atom or a methyl group, R ⁹ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and p represents an integer of 2 to 200. In the general formula (2), p is preferably 9 to 120, and more preferably 20 to 100.

Examples of hydrophilic monomers (a1) having such a structure include "FA-1000MW" and "FA-2000MW" manufactured by Hitachi Chemical Co., Ltd., and "BLEMMER PME-100," "BLEMMER PME-400," "BLEMMER PME-1000," "BLEMMER PME-4000," and "BLEMMER PLE-200" manufactured by NOF Corporation. "BLEMMER" is a registered trademark of NOF Corporation.

The structural units derived from the hydrophilic monomer (a1) maintain the hydrophilicity of the precoated fin material for a long period of time and allow water droplets adhering to the surface of the precoated fin material to easily slide off.

(Meth)acrylamide-based monomer (a2)
The (meth)acrylamide monomer (a2) has a chemical structure represented by the following general formula (1). The aforementioned "(meth)acrylamide" includes acrylamide and methacrylamide. The hydrophilic polymer (A) may contain structural units derived from one type of (meth)acrylamide monomer (a2), or may contain structural units derived from two or more types of (meth)acrylamide monomers (a2). The content of the structural units derived from the (meth)acrylamide monomer (a2) in the hydrophilic polymer (A) is 1% by mass or more and 70% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4). The content of the structural units derived from the (meth)acrylamide monomer (a2) is preferably 5% by mass or more and 60% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4).

In the general formula (1), m and n each independently represent 0 or 1, ^R1 represents a hydrogen atom or a methyl group, ^R2 and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and ^R4 and ^R5 each independently represent a methylene group or an ethylene group.

Examples of (meth)acrylamide monomers (a2) include N-methylol(meth)acrylamide; N-alkoxymethyl(meth)acrylamides such as N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, N-propoxymethyl(meth)acrylamide, N-isopropoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, and N-isobutoxymethyl(meth)acrylamide; (meth)acrylamide, N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, and N-n-butyl(meth)acrylamide.

Carboxyl group-containing polymerizable unsaturated monomer (a3)
The carboxyl group-containing polymerizable unsaturated monomer (a3) has at least one carboxyl group and one polymerizable unsaturated group per molecule. The hydrophilic polymer (A) may contain structural units derived from one type of carboxyl group-containing polymerizable unsaturated monomer (a3), or may contain structural units derived from two or more types of carboxyl group-containing polymerizable unsaturated monomers (a3). The content of the structural units derived from the carboxyl group-containing polymerizable unsaturated monomer (a3) in the hydrophilic polymer (A) is 1% by mass or more and 50% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4). The content of the structural units derived from the carboxyl group-containing polymerizable unsaturated monomer (a3) is preferably 5% by mass or more and 35% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4).

Examples of the carboxyl group-containing polymerizable unsaturated monomer (a3) include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid. The structural units derived from the carboxyl group-containing polymerizable unsaturated monomer (a3) can improve the water resistance of the precoated fin material.

Other polymerizable unsaturated monomers (a4)
In addition to the structural units derived from the aforementioned monomers (a1) to (a3), the hydrophilic polymer (A) may optionally contain a structural unit derived from a polymerizable unsaturated monomer (a4) other than these monomers (a1) to (a3). The hydrophilic polymer (A) may contain a structural unit derived from one type of polymerizable unsaturated monomer (a4), or may contain structural units derived from two or more types of polymerizable unsaturated monomers (a4). The content of the structural unit derived from the polymerizable unsaturated monomer (a4) in the hydrophilic polymer (A) is 0% by mass or more and 50% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4). The content of the structural unit derived from the polymerizable unsaturated monomer (a4) is preferably 5% by mass or more and 45% by mass or less, based on 100% by mass of the total structural units derived from the monomers (a1) to (a4).

As the polymerizable unsaturated monomer (a4), for example, a hydroxyl group-containing polymerizable unsaturated monomer containing a hydroxyl group and a polymerizable unsaturated group in one molecule can be used. Examples of hydroxyl group-containing polymerizable unsaturated monomers include (meth)acrylic acid hydroxyalkyl esters having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

Furthermore, examples of the polymerizable unsaturated monomer (a4) include methylene bis(meth)acrylamide, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butanediol diacrylate, glycerin dimethacrylate, glycerin trimethacrylate, trimethylolpropane dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol dimethacrylate, and pentaerythritol dimethacrylate. polymerizable unsaturated monomers having two or more polymerizable unsaturated bonds in one molecule, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, and cyclohexyl (meth)acrylate; (meth)acrylic acid alkyl esters and (meth)acrylic acid cycloalkyl esters having 1 to 24 carbon atoms, such as acrylate; polymerizable unsaturated nitriles such as acrylonitrile and methacrylonitrile; aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and α-chlorostyrene; (meth)acrylic acid nitrogen-containing alkyl esters having 2 to 8 carbon atoms, such as N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate; α-olefins such as ethylene and propylene; diene compounds such as butadiene and isoprene. vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as ethyl vinyl ether and n-propyl vinyl ether; unsaturated compounds having a hydrolyzable silyl group such as gamma-methacryloyloxypropyltrimethoxysilane, gamma-acryloyloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, 2-styrylethyltrimethoxysilane, and vinyltris(methoxyethoxy)silane; and unsaturated compounds having an epoxy group such as glycidyl (meth)acrylate and allyl glycidyl ether. Note that the aforementioned "(meth)acrylic acid" includes acrylic acid and methacrylic acid.

Method for Producing Hydrophilic Polymer To produce the hydrophilic polymer (A), a monomer mixture containing a hydrophilic monomer (a1), a (meth)acrylamide-based monomer (a2), and a carboxyl group-containing polymerizable unsaturated monomer (a3) may be copolymerized in a suitable solvent. The monomer mixture may optionally contain a polymerizable unsaturated monomer (a4). Examples of the solvent that can be used include water and water-miscible organic solvents.

The content of each of the monomers (a1) to (a4) in the monomer mixture may be appropriately set depending on the desired content of each structural unit in the hydrophilic polymer (A). That is, the content of each of the monomers (a1) to (a4) in the monomer mixture may be appropriately set within the following ranges, relative to 100% by mass of the total of the monomers (a1) to (a4): hydrophilic monomer (a1): 2% by mass to 50% by mass; (meth)acrylamide-based monomer (a2): 1% by mass to 70% by mass; carboxyl group-containing polymerizable unsaturated monomer (a3): 1% by mass to 50% by mass; and polymerizable unsaturated monomer (a4): 0% by mass to 50% by mass.

Copolymerization of the monomer mixture is usually carried out in the presence of a radical polymerization initiator. The amount of radical polymerization initiator used can be appropriately set within the range of, for example, 0.2 to 5 parts by mass per 100 parts by mass of the total of monomers (a1) to (a4).

The temperature when copolymerizing the monomer mixture may be set appropriately depending on the type of radical polymerization initiator used, etc. The temperature when copolymerizing the monomer mixture may be, for example, in the range of about 50°C to about 160°C. The reaction time when copolymerizing the monomer mixture may be, for example, about 0.5 to 10 hours.

- Form of hydrophilic polymer (A) The hydrophilic polymer (A) may be particulate or not. When the hydrophilic polymer (A) is particulate, the hydrophilic polymer (A) preferably has a particle size distribution in which the cumulative 50% particle diameter on a volume basis is 5 nm or more and 1 μm or less. In this case, in the process of forming a resin film, the stability of the hydrophilic polymer (A) in the coating material can be further improved and aggregation of the hydrophilic polymer (A) can be more effectively suppressed. From the viewpoint of further enhancing such effects, it is more preferable that the hydrophilic polymer (A) has a particle size distribution in which the cumulative 50% particle diameter on a volume basis is 10 nm or more and 500 nm or less.

The particle size distribution of the hydrophilic polymer (A) can be measured using a particle size measuring device (e.g., Beckman Coulter Coulter Model N4MD).

Molecular Weight of Hydrophilic Polymer (A) When the hydrophilic polymer (A) is not in a particulate form, the weight average molecular weight of the hydrophilic polymer (A) is preferably 10,000 or more, more preferably 20,000 or more and 250,000 or less, and even more preferably 50,000 or more and 250,000 or less.

The weight-average molecular weight of the hydrophilic polymer (A) is the value obtained by converting the weight-average molecular weight measured using a gel permeation chromatograph (GPC) to the molecular weight of standard polystyrene. A GPC measurement device such as the "HLC8120GPC" manufactured by Tosoh Corporation can be used. This measurement device is equipped with four columns manufactured by Tosoh Corporation: "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000HXL." A chromatogram can be obtained by using tetrahydrofuran at a temperature of 40°C as the mobile phase, setting the mobile phase flow rate to 1 mL/min, and measuring the refractive index difference of the eluate using an RI detector.

- Content of Hydrophilic Polymer (A) The content of the hydrophilic polymer (A) is 60 parts by mass or more and 97 parts by mass or less, based on 100 parts by mass of the total of the hydrophilic polymer (A) and the crosslinking agent (B). By setting the content of the hydrophilic polymer (A) in the resin film within the specific range, the hydrophilicity and corrosion resistance of the precoated fin material can be improved in a balanced manner. If the content of the hydrophilic polymer (A) is less than the specific range, the proportion of the hydrophilic polymer (A) in the resin film will be reduced, which may result in a decrease in hydrophilicity. On the other hand, if the content of the hydrophilic polymer (A) is more than the specific range, the crosslinking of the hydrophilic polymer (A) in the resin film will be insufficient, which may result in a decrease in corrosion resistance.

From the perspective of achieving a more balanced improvement in the hydrophilicity and corrosion resistance of the precoated fin material, the content of the hydrophilic polymer (A) is preferably 76 to 97 parts by mass, and more preferably 78 to 95 parts by mass, per 100 parts by mass of the total of the hydrophilic polymer (A) and the crosslinking agent (B).

C-2. Crosslinking agent (B)
The hydrophilic polymer (A) in the resin film is crosslinked by a crosslinking agent (B). The crosslinking agent (B) can be a compound capable of crosslinking the hydrophilic polymer (A). More specifically, examples of the crosslinking agent (B) include amino resins, phenolic resins, polyisocyanate compounds, blocked polyisocyanate compounds, oxazoline group-containing resins, polyepoxy compounds, and carbodiimide compounds. These crosslinking agents (B) may be used alone, or two or more crosslinking agents (B) may be used in combination.

The crosslinking agent (B) is preferably one or more resins selected from the group consisting of amino resins and phenolic resins. In this case, the water resistance of the resin film is further improved, and the elution of components from the resin film upon contact with water can be suppressed for a longer period of time.

Examples of amino resins include melamine resins, urea resins, and benzoguanamine resins. The melamine resin may be, for example, an etherified melamine resin in which the methylol groups of a methylolated melamine resin are etherified with a monohydric alcohol having 1 to 8 carbon atoms. The etherified melamine resin may be a fully etherified melamine resin in which all of the methylol groups of the methylolated melamine resin are etherified. Alternatively, the etherified melamine resin may be a partially etherified melamine resin in which some of the methylol groups are etherified, with methylol groups and imino groups remaining.

The melamine resin may be a fully alkylated methyl/butyl mixed etherified melamine resin. Examples of fully alkylated methyl/butyl mixed etherified melamine resins include "Cymel 232," "Cymel 232S," "Cymel 235," "Cymel 236," "Cymel 238," "Cymel 266," "Cymel 267," and "Cymel 285," manufactured by Daicel-Allnex Corporation.

The melamine resin may be a methylol group-type methyl/butyl mixed etherified melamine resin. Examples of methylol group-type methyl/butyl mixed etherified melamine resins include "Cymel 272" manufactured by Daicel Allnex Corporation.

The melamine resin may be an imino-type methyl/butyl mixed etherified melamine resin. Examples of imino-type methyl/butyl mixed etherified melamine resins include "Cymel 202," "Cymel 207," "Cymel 212," "Cymel 253," and "Cymel 254," manufactured by Daicel-Allnex Corporation.

The melamine resin may be a fully alkylated methylated melamine resin. Examples of fully alkylated methylated melamine resins include Cymel 300, Cymel 301, Cymel 303, and Cymel 350 manufactured by Daicel-Allnex Corporation.

The melamine resin may be an imino group-type methylated melamine resin. Examples of imino group-type methylated melamine resins include "Cymel 325," "Cymel 327," "Cymel 701," "Cymel 703," "Cymel 712," "Cymel 254," "Cymel 253," "Cymel 212," and "Cymel 1128," manufactured by Daicel-Allnex Corporation.

The melamine resin may be a butyl etherified melamine resin. Examples of butyl etherified melamine resins include "U-Ban 20SE60" manufactured by Mitsui Cytec Co., Ltd.

The urea resin may be, for example, a methylated urea resin or a butylated urea resin. Examples of methylated urea resins include "Cymel U-65" manufactured by Daicel Allnex Corporation, and "Nicalac MX-270," "Nicalac MX-280," and "Nicalac MX-290" manufactured by Sanwa Chemical Co., Ltd. Examples of butylated urea resins include "Nicalac MX-279" manufactured by Sanwa Chemical Co., Ltd., "U-Ban 10S60" and "U-Ban 10R" manufactured by Mitsui Cytec Co., Ltd., and "Beckamine P-138," "Beckamine P-196-M," and "Beckamine G-1850" manufactured by DIC Corporation.

The benzoguanamine resin may be, for example, a methylated benzoguanamine resin or a butylated benzoguanamine resin. Examples of methylated benzoguanamine resins include "Nicalac BL-60" manufactured by Sanwa Chemical Co., Ltd. Examples of butylated benzoguanamine resins include "Super Beckamine TD-126" and "Super Beckamine 15-594" manufactured by DIC Corporation.

These amino resins may be used alone, or two or more types may be used in combination. "Cymel" is a registered trademark of Allnex Netherlands AB, "Uban" is a registered trademark of Mitsui Chemicals, Inc., "Nicalac" is a registered trademark of Nippon Carbide Industries Co., Ltd., and "Beckamin" is a registered trademark of DIC Corporation.

The phenolic resin may be, for example, a novolac-type phenolic resin obtained by condensing a phenolic compound and an aldehyde in the presence of an acidic catalyst, or a resol-type phenolic resin obtained by condensing a phenolic compound and an aldehyde in the presence of a basic catalyst. Methylol groups may also be introduced into the phenolic resin. Furthermore, some or all of the methylol groups introduced into the phenolic resin may be alkyl-etherified with an alcohol having six or fewer carbon atoms.

Examples of phenolic resins include "SUMITERESINPR-HF-3," "SUMITERESINPR-HF-6," "SUMITERESINPR-53194," "SUMITERESINPR-53195," "SUMITERESINPR-54869," "SUMITERESINPR-16382," "SUMITERESINPR-51939," "SUMITERESINPR-53153," and "SUMITERESINPR-16382," manufactured by Sumitomo Bakelite Co., Ltd. INPR-53364, SUMILITERESINPR-53365, SUMILITERESINPR-50702, and DIC Corporation's PHENOLITETD-2131, PHENOLITETD-2106, PHENOLITETD-2093, PHENOLITETD-2091, PHENOLITETD-2090, PHENOLITEVH-4150, PHENOLITEVH-4170, PHENOLITEVH-4240, and PHENOLITEKH -1160", "PHENOLITEKH-1163", "PHENOLITEKH-1165", "PHENOLITETD- 2093-60M”, “PHENOLITETD-2090-60M”, “PHENOLITELF-4711”, “PHENOLITE LITELF-6161”, “PHENOLITELF-4871”, “PHENOLITELA-7052”, “PHENOL ITELA-7054”, “PHENOLITELA-7751”, “PHENOLITELA-1356”, “PHENOLI TELA-3018-50P," and Showa Polymer Co., Ltd.'s "Shounol BKM-262," "Shounol BRG-555," "Shounol BRG-556," "Shounol BRG-558," "Shounol CKM-923," "Shounol CKM-983," "Shounol BKM-2620," "Shounol BRL-2854," "Shounol BRG-5590M," "Shounol CKS-3898," "Shounol CKS-3877A," and "Shounol CKM-937."

These phenolic resins may be used alone, or two or more types of phenolic resins may be used in combination. "SUMITERESIN" is a registered trademark of Sumitomo Bakelite Co., Ltd., "PHENOLITE" is a registered trademark of DIC Corporation, and "SHONUL" is a registered trademark of AICA Kogyo Co., Ltd.

A polyisocyanate compound is a compound that has two or more isocyanate groups in one molecule. Examples of polyisocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, and naphthalene diisocyanate; aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; alicyclic diisocyanates such as methylenebis(cyclohexyl isocyanate), isophorone diisocyanate, methylcyclohexane diisocyanate, cyclohexane diisocyanate, and cyclopentane diisocyanate; biuret-type adducts and isocyanuric ring-type adducts of these polyisocyanates; and free isocyanate group-containing prepolymers obtained by reacting these polyisocyanates with low- or high-molecular-weight polyol compounds (e.g., acrylic polyol, polyester polyol, polyether polyol, etc.) in an excess of isocyanate groups.

These polyisocyanate compounds may be used alone, or two or more polyisocyanate compounds may be used in combination.

A blocked polyisocyanate compound is a compound in which the free isocyanate groups of a polyisocyanate compound are blocked with a blocking agent such as a phenol compound, oxime compound, active methylene compound, lactam compound, alcohol compound, mercaptan compound, acid amide compound, imide compound, amine compound, imidazole compound, urea compound, carbamic acid compound, or imine compound. A blocked polyisocyanate compound may be used alone, or two or more types of blocked polyisocyanate compounds may be used in combination.

C-3. Other Components The resin film may be composed of a hydrophilic polymer (A) and a crosslinking agent (B). The resin film may also contain paint additives, provided that the effects described above are not impaired. Examples of additives include pigments, rust inhibitors, aqueous organic resins, surfactants, rheology control agents, surface conditioners, ionic liquids, antifoaming agents, and film-forming aids.

The resin film may also contain one or more compounds (C) selected from the group consisting of tannic acid, gallic acid, ascorbic acid, and salts thereof. These compounds (C) have the effect of further improving the corrosion resistance of the precoated fin material. The content of compound (C) is preferably 1 to 10 parts by mass, and more preferably 1 to 5 parts by mass, per 100 parts by mass of the total of the hydrophilic polymer (A) and crosslinking agent (B). In this case, the stability of the paint during the resin film formation process can be further improved, and the corrosion resistance and water resistance of the precoated fin material can be further improved.

C-4. Mass per unit area of resin film The mass per unit area of the resin film in the precoated fin material is 0.2 g/ ^m2 or more and 2.5 g/ ^m2 or less. By containing the specific hydrophilic polymer (A) and crosslinking agent (B), the resin film can improve the corrosion resistance and hydrophilicity of the precoated fin material even at a very thin thickness such as a mass per unit area of 0.2 g/ ^m2 .

If the mass per unit area of the resin film is less than 0.2 g/ ^m2 , the thickness of the resin film will be too thin, which may result in a deterioration in the corrosion resistance of the precoated fin material. On the other hand, if the mass per unit area of the resin film exceeds 2.5 g/ ^m2 , the amount of paint used in the manufacturing process of the precoated fin material will increase, which may result in an increase in manufacturing costs.

The mass per unit area of the resin film in the precoated fin material is preferably 0.2 g/ ^m2 or more and 1.0 g/ ^m2 or less, and more preferably 0.2 g/ ^m2 or more and 0.9 g/ ^m2 or less. In this case, the amount of paint used in the manufacturing process of the precoated fin material can be further reduced while ensuring the corrosion resistance and hydrophilicity of the precoated fin material. This can be expected to have the effect of further reducing the manufacturing cost of the precoated fin material.

D. Characteristics of Precoated Fin Material The precoated fin material has a characteristic that the average natural potential from the time the precoated fin material is immersed in a 5 mass % NaCl aqueous solution of pH 3 until one hour has elapsed is +0.040 V or more and +0.2 V or less relative to the average natural potential from the time the base material is immersed in a 5 mass % NaCl aqueous solution of pH 3 until one hour has elapsed. Furthermore, the precoated fin material has a characteristic that the water contact angle after the precoated fin material is immersed in running water for 10 minutes is 20° or more and 40° or less.

Precoated fin materials in which the potential difference between the precoated fin material and the substrate and the water contact angle are each within the specified ranges can achieve both high corrosion resistance and high hydrophilicity. If the average natural potential of the precoated fin material is less than +0.040 V relative to the average natural potential of the substrate, the corrosion resistance of the precoated fin material may be insufficient. Furthermore, if the water contact angle of the precoated fin material after immersion in running water exceeds 40°, the hydrophilicity of the precoated fin material may be insufficient.

(Method for manufacturing precoated fin material)
When producing the precoated fin material,
applying a coating material containing the hydrophilic polymer (A) and the crosslinking agent (B) onto at least one surface of the substrate;
The base material coated with the paint may be heated in a heating furnace at a temperature of 240° C. to 300° C. for 4 to 20 seconds to bake the paint, thereby forming the resin film on the base material.

The substrate can be, for example, an aluminum plate. The thickness of the substrate may be, for example, within the range of 0.05 to 0.30 mm. Furthermore, the substrate may be subjected to a surface treatment such as a chemical conversion treatment before the paint is applied. By performing a chemical conversion treatment on the surface of the substrate in advance, a base film is formed on the substrate, which can improve the adhesion of the resin film.

The coating material contains a hydrophilic polymer (A) and a crosslinking agent (B). In addition to these, the coating material may also contain the additives and solvents mentioned above. There are no particular limitations on the method for applying the coating material to the substrate, and various methods such as using a bar coater or roll coater can be used.

After the paint is applied to the substrate, the substrate is heated for 4 to 20 seconds in a heating furnace at a temperature of 240°C to 300°C to bake the paint. This allows the resin film to be formed. If the temperature in the heating furnace is lower than the specified range, or if the baking time is shorter than the specified range, the paint may not be heated sufficiently, resulting in insufficient crosslinking of the hydrophilic polymer (A). This may result in a deterioration in the corrosion resistance of the pre-coated fin material. Furthermore, if the temperature in the heating furnace is higher than the specified range, the paint may be overheated, resulting in deterioration of the resin film.

When baking the paint, it is preferable to use a fan with a wind speed of 1 m/s to 5 m/s to create convection in the atmosphere inside the heating furnace. This allows the paint on the substrate to be heated more uniformly, more reliably forming a resin film with excellent corrosion resistance and hydrophilicity.

In the paint baking process, it is preferable to heat the substrate so that the maximum temperature (Peak Metal Temperature, PMT) of the substrate in its dry state is within the range of 170°C or higher and 220°C or lower. In this case, the hydrophilic polymer (A) can be more reliably crosslinked, more reliably obtaining a precoated fin material with excellent corrosion resistance and hydrophilicity.

Examples of the precoated fin material and its manufacturing method will be described with reference to Figures 1 and 2. Note that the specific aspects of the precoated fin material and its manufacturing method according to the present invention are not limited to those of the examples, and the configuration can be modified as appropriate within the scope of the spirit of the present invention.

As shown in Figure 1, the precoated fin material 1 of this example has a substrate 2 made of aluminum and a resin coating 3 formed on both sides of the substrate 2. A base coating 21 is interposed between the substrate 2 and the resin coating 3. The resin coating 3 contains a hydrophilic polymer (A) and a crosslinking agent (B).

A. Base material 2
In this example, the substrate 2 is an aluminum plate made of A1050 aluminum and having a thickness of 0.1 mm. The surface of the substrate 2 is covered with an undercoat 21. Specifically, the undercoat 21 in this example is a chromate film formed by a chromate treatment using chromate phosphate. The deposition amount of the chromate film is 20 mg/ ^m2 in terms of the mass of Cr atoms per side of the substrate.

B. Resin film 3
The resin film 3 in this example is composed of 80 parts by mass of the hydrophilic polymer (A) and 20 parts by mass of the crosslinking agent (B). Specifically, as shown in Table 1, either the hydrophilic polymer (A1) or the hydrophilic polymer (A2) is used as the hydrophilic polymer (A).

The hydrophilic polymer (A1) is a copolymer of a monomer mixture consisting of 30% by weight of hydrophilic monomer (a1), 42% by weight of (meth)acrylamide-based monomer (a2), 20% by weight of carboxyl group-containing polymerizable unsaturated monomer (a3), and 8% by weight of polymerizable unsaturated monomer (a4). Specifically, the hydrophilic monomer (a1) in the hydrophilic polymer (A1) is "Blemmer PME-1000" manufactured by NOF Corporation. The (meth)acrylamide-based monomer (a2) is composed of 20 parts by weight of acrylamide, 5 parts by weight of N-methylolacrylamide, and 27 parts by weight of N-methoxymethylacrylamide. The carboxyl group-containing polymerizable unsaturated monomer (a3) is acrylic acid. The polymerizable unsaturated monomer (a4) is composed of 6 parts by weight of 2-hydroxyethyl acrylate and 2 parts by weight of methylenebisacrylamide.

The hydrophilic polymer (A2) is a copolymer of a monomer mixture consisting of 20% by mass of hydrophilic monomer (a1), 52% by mass of (meth)acrylamide-based monomer (a2), 20% by mass of carboxyl group-containing polymerizable unsaturated monomer (a3), and 8% by mass of polymerizable unsaturated monomer (a4). The hydrophilic monomer (a1), carboxyl group-containing polymerizable unsaturated monomer (a3), and polymerizable unsaturated monomer (a4) in the hydrophilic polymer (A2) are the same as those in the hydrophilic polymer (A1). The (meth)acrylamide-based monomer (a2) in the hydrophilic polymer (A2) is composed of 20 parts by mass of acrylamide, 5 parts by mass of N-methylolacrylamide, and 27 parts by mass of N-methoxymethylacrylamide.

Hydrophilic polymer (A1) and hydrophilic polymer (A2) are both particulate and have a particle size distribution in which the 50% cumulative diameter in the volume-based particle size distribution is 50 nm. Furthermore, the weight-average molecular weights of hydrophilic polymer (A1) and hydrophilic polymer (A2) are both 200,000 in terms of polystyrene.

The crosslinking agent (B) is an imino group-type methylated melamine resin (Daicel Allnex Corporation's "Cymel 701").

In this example, nine types of precoated fin materials (test materials S1 to S9) were prepared with different resin coating 3 masses per unit area and different paint baking conditions, as shown in Table 1, and various properties were evaluated using these materials. The test materials S1 to S9 shown in Table 1 were prepared using the following method.

C. Production Method First, the hydrophilic polymer (A1) or the hydrophilic polymer (A2) and the crosslinking agent (B) are mixed in the mass ratio shown in Table 1. Pure water is added to this mixture so that the solid content, i.e., the total amount of the hydrophilic polymer (A1), the hydrophilic polymer (A2), and the crosslinking agent (B) becomes 7 mass %, to prepare a coating material.

The paint is applied to the base coating 21 of the substrate 2, which has been prepared in advance, using a bar coater, and then the paint is pre-dried. The substrate 2 is then placed in a heating furnace maintained at the temperature shown in Table 1, and heated for the time shown in Table 1 to bake the paint. The atmosphere inside the heating furnace is forced by convection using a fan. The maximum temperature (PMT) when the substrate is in a dry state, calculated from the temperature inside the furnace and the air speed of the fan, is as shown in Table 1.

After the paint baking is complete, the precoated fin material 1 is removed from the heating furnace and cooled to room temperature. This process allows the test materials S1 to S9 shown in Table 1 to be obtained.

Test materials R1 to R3 shown in Table 1 are test materials for comparison with test materials S1 to S9. Test materials R1 and R2 can be prepared using the same method as test materials S6 to S9, except that the paint baking conditions are changed as shown in Table 1. Test material R3 has the same structure as test materials S6 to S9, except that it has a resin film consisting only of hydrophilic polymer (A2). Test material R3 can be prepared using the same method as test materials S6 to S9, except that the paint is prepared without adding crosslinking agent (B) and the paint baking conditions are changed as shown in Table 1.

D. Evaluation - Measurement of Potential Difference Between Precoated Fin Material and Substrate A measuring device 4 shown in Figure 2 is used to measure the natural potential of the precoated fin material and the substrate. The measuring device 4 has a first container 41 for holding a solution in which the test piece 5 is immersed, a second container 42 for holding a solution in which the reference electrode 6 is immersed, a salt bridge 43 for electrically connecting the solution in the first container 41 and the solution in the second container 42, a potentiostat 44 for measuring the potential of the test piece 5 relative to the reference electrode 6, and a recording device 45 for recording the measured potential.

When measuring the natural potential, first, a rectangular test piece 5 measuring 40 mm in length and 10 mm in width is taken from the test material or substrate. One longitudinal end of this test piece 5 is provided with a connection part 51 for connecting to the potentiostat 44, and the other end is provided with a square potential measurement part 52 with sides of 5 mm. Then, as shown in Figure 2, insulating paint 53 is applied to the areas other than the connection part 51 and the potential measurement part 52.

Separately, a 5% NaCl aqueous solution with a pH adjusted to 3 using acetic acid is prepared in a first container 41, and a saturated NaCl aqueous solution is prepared in a second container 42. The solutions in the first container 41 and the second container 42 are then electrically connected via a salt bridge 43.

Next, the connection portion 51 of the test strip 5 and the reference electrode 6 are each connected to the potentiostat 44. Note that, for example, an Ag/AgCl electrode can be used as the reference electrode 6.

In this state, the potential measuring portion 52 of the test strip 5 is immersed in the 5% NaCl aqueous solution in the first container 41, and the reference electrode 6 is immersed in the saturated NaCl aqueous solution in the second container 42, thereby measuring the natural potential of the test strip 5 relative to the reference electrode 6. In this example, the natural potential of the test strip 5 is measured every three minutes and recorded in the recording device 45.

The natural potential of the test piece gradually decreases as time passes from the start of measurement, and tends to reach a roughly constant value after 10 hours. In this example, the average natural potential value from the start of measurement to 1 hour later is used as the natural potential value of the test material. The natural potential values of each test material are shown in Table 2.

The same measurement as above is also performed using the substrate 2 before the resin film 3 is formed. The average value of the natural potential from the start of the measurement until one hour has elapsed is taken as the natural potential value of the substrate 2. The natural potential of the substrate 2 is -0.720 V vs. Ag/AgCl. The "Potential Difference" column in Table 2 shows the natural potential of the test material minus the natural potential of the substrate 2.

In addition, to measure the natural potential of the substrate 2, a substrate 2 prepared by polishing the surface of the precoated fin material 1 and removing the resin coating 3 and base coating 21 can also be used.

Water contact angle: After taking a test piece from each test material, it was immersed in running water at a temperature of 25°C and a flow rate of 5 L/min for 10 minutes. 2 μL of pure water was dropped onto the surface of the test piece removed from the running water, and the water contact angle was measured 30 seconds after the drop. Table 2 shows the water contact angle of each test material.

Mass per unit area of resin film 3 A square test piece with sides of 100 mm was taken from each test material. The mass W1 (unit: g) of this test piece was measured, and then the test piece was heated in an electric furnace at 500°C for 15 minutes. The mass W2 (unit: g) of the test piece removed from the electric furnace was measured, and then the mass loss W1-W2 (unit: g) from before heating was calculated. The mass per unit area of the resin film 3 can be calculated by dividing this mass loss W1-W2 by the total area S (unit: cm ² ) of the resin film 3 formed on the test piece. Table 1 shows the mass per unit area of the resin film 3 for each test material.

Corrosion Resistance A rectangular test piece measuring 100 mm in length and 50 mm in width is taken from the test material so that the rolling direction of the substrate 2 is parallel to the longitudinal direction. Using this test piece, a salt spray test is carried out according to a method in accordance with JIS Z2371:2000. The test time is 1000 hours. The corrosion area ratio of the test material after the test is calculated, and a rating number is determined according to the rating number method of JIS Z2371:2000. A higher rating number indicates better corrosion resistance. Table 2 shows the rating numbers for each test material.

Appearance The surface of the test material is visually observed, and the properties of the resin film 3 are evaluated.

As shown in Table 1, test materials S1 to S9 have a resin film made of a hydrophilic polymer (A) and a crosslinking agent (B) formed on a substrate. Furthermore, as shown in Tables 1 and 2, the mass per unit area of the resin film for these test materials, the potential difference with the substrate, and the water contact angle after immersion in running water are all within the specified ranges. Therefore, these test materials have excellent corrosion resistance and hydrophilicity, as shown in Table 2.

On the other hand, as shown in Table 1, the resin film on test material R1 was formed by heating at a lower furnace temperature than test materials S1 to S9. Therefore, as shown in Table 2, the potential difference between test material R1 and the substrate is smaller than the specified range. As a result, the corrosion resistance of test material R1 is inferior to that of test materials S1 to S9.

As shown in Table 1, the resin film on test material R2 was formed by heating at a higher furnace temperature than test materials S1 to S9. As a result, as shown in Table 2, the resin film on test material R2 deteriorated and discolored during heating.

As shown in Table 1, the resin coating of test material R3 does not contain crosslinking agent (B). Therefore, as shown in Table 2, the potential difference between test material R3 and the substrate is smaller than the specified range. As a result, the corrosion resistance of test material R3 is inferior to that of test materials S1 to S9.

1 Precoated fin material 2 Substrate 3 Resin coating

Claims (7)

A precoated fin material having an aluminum substrate and a resin coating provided on at least one surface of the substrate,
The mass per unit area of the resin film is 0.2 g/m ² or more and 2.5 g/m ² or less,
The average value of the natural potential from the time when the precoated fin material is immersed in a 5 mass% NaCl aqueous solution of pH 3 until one hour has elapsed is +0.040 V or more and +0.2 V or less relative to the average value of the natural potential from the time when the base material is immersed in a 5 mass% NaCl aqueous solution of pH 3 until one hour has elapsed, and
The precoated fin material has a characteristic that the contact angle of water after immersion in running water for 10 minutes is 20° or more and 40° or less,
the resin film contains a hydrophilic polymer (A) and a crosslinking agent (B) capable of crosslinking the hydrophilic polymer (A);
the content of the hydrophilic polymer (A) is 60 parts by mass or more and 97 parts by mass or less, relative to 100 parts by mass of the total of the hydrophilic polymer (A) and the crosslinking agent (B);
The hydrophilic polymer (A) includes
Structural units derived from a hydrophilic monomer (a1) having one polymerizable double bond and a polyoxyalkylene chain per molecule: 2% by mass or more and 50% by mass or less;
Structural units derived from a (meth)acrylamide-based monomer (a2) represented by the following general formula (1): 1% by mass or more and 70% by mass or less;
Structural units derived from a carboxyl group-containing polymerizable unsaturated monomer (a3) containing a carboxyl group: 1% by mass or more and 50% by mass or less;
and structural units derived from the hydrophilic monomer (a1), the (meth)acrylamide-based monomer (a2), and a polymerizable unsaturated monomer (a4) other than the carboxyl group-containing polymerizable unsaturated monomer (a3): 0% by mass or more and 50% by mass or less.
(In the general formula (1), m and n each independently represent 0 or 1, ^R1 represents a hydrogen atom or a methyl group, ^R2 and ^R3 each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and ^R4 and ^R5 each independently represent a methylene group or an ethylene group.) The precoated fin material according to claim 1, wherein the hydrophilic polymer (A) is a fine particle having a particle size distribution in which the cumulative 50% particle diameter on a volume basis is 5 nm or more and 1 μm or less. The precoated fin material according to claim 1 or 2, wherein the weight-average molecular weight of the hydrophilic polymer (A) is 10,000 or more. The precoated fin material according to any one of claims 1 to 3, wherein the crosslinking agent (B) is one or more resins selected from the group consisting of amino resins and phenolic resins. The precoated fin material according to any one of claims 1 to 4, wherein the hydrophilic polymer (A) contains structural units derived from the hydrophilic monomer (a1): 5% by mass to 45% by mass, structural units derived from the (meth)acrylamide-based monomer (a2): 5% by mass to 60% by mass, structural units derived from the carboxyl group-containing polymerizable unsaturated monomer (a3): 5% by mass to 35% by mass, and structural units derived from the polymerizable unsaturated monomer (a4): 5% by mass to 45% by mass. A method for producing a precoated fin material according to any one of claims 1 to 5,
applying a coating material containing the hydrophilic polymer (A) and the crosslinking agent (B) onto at least one surface of the substrate;
The base material to which the paint has been applied is heated in a heating furnace at a temperature of 240°C or higher and 300°C or lower for 4 seconds or longer and 20 seconds or shorter to perform paint baking, thereby forming the resin coating on the base material. The method for manufacturing precoated fin material described in claim 6, wherein the atmosphere in the heating furnace is circulated using a fan with a wind speed of 1 m/s or more and 5 m/s or less during the paint baking.