JPH0348273B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides a corrosion-resistant hydrophilic film treatment agent (hereinafter referred to as a treatment agent) capable of forming a film imparting hydrophilicity and corrosion resistance to the surface of aluminum and aluminum alloy products (hereinafter referred to as aluminum materials). (referred to as agents). [Prior art and problems] Aluminum materials are widely used for various purposes, but in recent years, forming a hydrophilic film on the surface of aluminum materials has been used to prevent condensation on heat exchanger fins, building materials, etc. , anti-fog reflector,
Alternatively, it is used as a means to increase water retention and increase the amount of water evaporated from the surface of the aluminum material. However, if a hydrophilic film is directly formed on the surface of an aluminum material, the aluminum material may be corroded or the film may easily peel off, so there are many methods and treatment agents for forming a corrosion-resistant hydrophilic film that can prevent these problems. proposals have been made. As one of these, the present inventors previously proposed a hydrophilic metal surface treatment agent based on a chromium compound-acrylic acid polymer-fluoride-silica type (Japanese Patent Application Laid-open No. 39169/1983). As a result of continuing studies on this type of treatment agent, the present inventors have found that a unique phenomenon occurs when treatment is performed with a treatment agent that uses chromium nitrate as the chromium compound. In other words, it has been acknowledged that hexavalent chromium ions (CrO ^2- ₄ ) may be leached from the film when the concentration of chromium nitrate is high or when the blending ratio of silica or acrylic acid polymer is low. . The cause of this is not certain, but it is believed that part of the trivalent chromium changes to hexavalent chromium during the baking process of the coating, and this is present in the coating and leaches out when it comes into contact with water. Presumed. However, when such elution of hexavalent chromium ions is observed, there is a problem in that the corrosion resistance and long-term hydrophilicity of the film are reduced at the same time, and a solution to these problems is desired. [Means and effects for solving the problem] As a result of repeated research to obtain a treatment agent that can prevent the elution of hexavalent chromium ions from the formed film when chromium nitrate is used, the present inventor has discovered a number of treatments. By blending alcohols and sugars in a state that has a reducing effect and allowing them to remain and coexist in the formed film, it is possible to prevent the elution of hexavalent chromium ions during use, and by blending phosphoric acid, long-term hydrophilicity can be achieved. Can prevent sexual decline,
The present invention was made based on the discovery that a treatment agent capable of forming a corrosion-resistant hydrophilic film having a three-layer structure in one step can be obtained. That is, in the present invention, chromium nitrate is 2 to 20 g in terms of CrO ₃ / and if desired, hexavalent chromium ions are added in an amount of 2 to 20 g in terms of CrO ₃
g/or less, the solid content of acrylic acid polymer is 2~
20g/, fluoride as F ^- 0.1-5g/,
Corrosion-resistant hydrophilic coating treatment for aluminum materials consisting of 0.1 to 50 g of phosphoric acid as PO ^3-4 , 0.2 to 0.8 of silica/total solids ratio, 0.2 to 20 _g of polyhydric alcohol or/and sugar, and balance water. It is a drug. The processing agent of the present invention has the above composition,
The sources of each component that is dissolved or suspended in water and that constitutes the treatment agent are as follows. Chromium nitrate as a chromium compound forms a chromate film layer, and when it is desired to further improve the corrosion resistance of the chromate film layer, chromium nitrate such as hexavalent chromium compounds such as chromic acid (CrO ₃ ) and ammonium chromate can be used. An acid salt or a dichromate such as ammonium dichromate may be added as desired. As the acrylic acid polymer, water-soluble acrylic acid polymer (hereinafter referred to as resin) is used.
For example, acrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-methacrylate.
- Water-soluble compounds obtained by polymerization or copolymerization of compounds such as butyl, isobutyl methacrylate, maleic acid, and itaconic acid are used.
In addition, during the relatively low-temperature, short-time heat treatment process,
It is necessary to cause a chelation reaction with chromium ions coexisting in the treatment agent and become insoluble in water, and the average molecular weight is preferably 10,000 to 300,000. As such resin,
For example, Primal A-1, A-3, A-5
(trade name, Rohm & Haas) is commercially available. As the fluoride, for example, soluble salts of hydrofluoric acid such as hydrofluoric acid, silicon fluoride, boron fluoride, titanium fluoride, zirconium fluoride, and zinc fluoride are used. It is also preferable to use fluoric acid as the fluoride, but although the mechanism of its addition effect cannot be confirmed, it acts on aluminum materials in cooperation with chromium compounds and has a slight dissolving effect on silica. It is believed that the silica particles are finely dispersed in the resin to form a dense, robust, hydrophilic, and corrosion-resistant film. Silica is used in the form of silica powder or silica sol. As the silica, for example, fumed silica or hydrous amorphous silicic acid produced by a wet method can be used. Commercially available products include, for example, Kabosil (trade name, Kabot Co., Ltd.). and Carplex (trade name, Shionogi & Co., Ltd.). The size of these particles is preferably small in terms of uniform hydrophilicity, moldability, and corrosion resistance of the film, and the average particle size is 1 μm or less, especially the size of the primary particles.
It is preferable that at least 50% or more is 1 μm or less. As the phosphoric acid, for example, orthophosphoric acid, pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid, phosphorous acid, etc. are used. In addition, when the amount used is as small as 5 g/or less, alkaline salts of the various phosphoric acids mentioned above, such as sodium phosphate, sodium pyrophosphate, sodium polyphosphate, and sodium hexametaphosphate, may also be used. Polyhydric alcohols, sugars (hereinafter referred to as reducing agents)
Any substance can be used as long as it is water-soluble, remains in the film without decomposing or volatilizing during baking after application of the treatment agent, and can be used as an organic reducing agent. For example, ethylene glycol, glycerin,
Erythrite, arabite, mannite, glucose, fructose, etc. are preferable, and they are used alone or in combination of two or more, and polyhydric alcohols are particularly preferable. It is added and mixed with.
Therefore, in the case of a treatment agent containing hexavalent chromium, it is desirable to adjust the treatment agent to such a state that hexavalent chromium and the reducing agent coexist immediately before use. Note that water has a soluble solids content of 300 to 400.
Tap water, ion-exchanged water, distilled water, etc. below mg/mg are used. Therefore, the blending ratio of these various components is that chromium nitrate needs to be in the range of 2 to 20 g/, preferably 3 to 12 g/in terms of CrO ₃ , and if it is less than 2 g/, the hydrophilic A film with sufficient corrosion resistance and corrosion resistance cannot be obtained, and the crosslinking reaction of the resin is not carried out to a satisfactory degree. If the amount exceeds 20g/20g, the aluminum material surface will be colored, chromium will be locally concentrated, and the film will deteriorate. Non-uniformity tends to occur, and furthermore, a film larger than necessary is formed, which is economically disadvantageous. In addition, in order to improve the corrosion resistance of the film, a hexavalent chromium compound can be contained in an amount of 2 g or less in terms of CrO ₃ as desired. More preferably, the amount is less than 1 g/g, as this reduces problems in the treatment of aging baths and waste liquids. The blending ratio of resin is 2 to 20g/solid content.
, preferably in the range of 3 to 14 g/2
If the amount is less than 20 g/g, the amount of film formed will be insufficient.
If the amount exceeds g/g, the stability of the processing agent tends to decrease. Therefore, as mentioned above, the insolubilization of the resin is due to the formation of a poorly soluble organic chromate compound through a crosslinking reaction with the coexisting chromium compound, and the amount of chromium required for crosslinking is Cr() or Cr(Cr).
It is said that it is sufficient to add 0.2% or more of () to the resin in terms of CrO ₃ , and the amount of the resin can be changed substantially arbitrarily as long as the chromium compound content of the treatment agent of the present invention is present. Note that it is of course possible to improve the corrosion resistance of the film by adding a small amount of thermosetting water-soluble resin. The blending ratio of fluoride is 0.1 to 5 as ^F- .
g/, preferably in the range of 0.3 to 3.5 g/. If F ^- is less than 0.1g/, good corrosion resistance of the film, which is mainly composed of reaction products between aluminum material and chromium compound, cannot be obtained, and if it is more than 5g/, the aluminum material may elute or react with silica during treatment. This makes it difficult to control the treatment solution and to obtain a film with desired characteristics. The blending ratio of phosphoric acid is 0.1 _{to 50 as PO 3-4} ^.
g/, preferably in the range of 0.3 to 8 g/. If PO ^3-4 is 0.1 g _/ or less, hydrophilicity is limited, and even if it is effective under mild conditions of use, problems arise in long-term hydrophilicity under severe conditions of use.
In addition, if it is 8g/or more, there is no problem with hydrophilicity, but
Corrosion resistance deteriorates slightly, and this tendency becomes particularly pronounced when the amount exceeds 50 g/min. The blending ratio of silica changes depending on the solid content in the processing agent, and the ratio of silica to total solid content, more specifically, the ratio of silica to [acrylic acid polymer (solid content)]
+ Chromium compound (CrO ₃ equivalent) + Silica + Reducing agent]
The weight ratio (hereinafter referred to as silica ratio) is 0.2~
0.8, preferably in the range of 0.3 to 0.6. If the silica ratio is less than 0.2, a durable hydrophilic film cannot be obtained, and if it is more than 0.8, the film surface becomes powdery, which is not preferable. Note that the silica component is preferably blended in a state coated with a resin, so that the silica particles can be uniformly dispersed and the reaction with hydrofluoric acid can be appropriately controlled. In addition, when forming a film, it preferentially gathers in the surface layer portion and imparts hydrophilicity to the film. By coexisting in the film, the reducing agent reduces the hexavalent chromium that is about to be eluted to trivalent chromium and prevents it from eluting as hexavalent chromium ions. It also has the effect of improving hydrophilicity and preventing a decrease in hydrophilicity, and the blending ratio necessary to express these effects is 0.2 to 20 g/, preferably 0.3 to 10
Blend within the range of g/g. Below 0.2g/,
The blending effect is insufficient, and if the amount exceeds 20 g, the stability of the processing agent will deteriorate and the adhesion of the upper layer film will also decrease, which is not preferable. The method for preparing this treatment agent includes, for example, an aqueous solution A in which silica powder is uniformly dispersed in a resin solution and a reducing agent added thereto, and B in which chromium nitrate, fluoride, and phosphoric acid are mixed and dissolved in water. A method in which both liquids are prepared separately and used by mixing both liquids immediately before use, a method in which all components are mixed and prepared as one liquid, and a method in which a hexavalent chromium compound is blended. Appropriate methods can be used, such as adding a hexavalent chromium compound solution to a solution prepared with other components as a single solution immediately before use, or mixing all components in a predetermined ratio immediately before use. It is something. However, when a hexavalent chromium compound is blended, it is preferable to keep the hexavalent chromium compound and the reducing agent separated until just before use, and then mix the two just before use as in the method. Therefore, the treatment agent of the present invention can be applied to roll coating or spraying methods in the same way as conventional treatment agents, for example, in the case of simple shaped materials such as continuous plates and extruded materials. In the case of a product with a complicated shape, the coating can be applied to the surface of the aluminum material by an appropriate method depending on the shape of the aluminum material, such as brushing, dipping, or spraying. In other words, the treatment agent is applied to the coated surface at a liquid temperature of 20 to 40℃, and the amount applied is as solid content after drying at 70℃ for 10 minutes.
It is coated at a concentration of 0.1 to 5 g/m ² , preferably 0.5 to 3 g/m 2 , and then heated at 100 to 250°C by a conventional method.
Heat treatment is performed for 10 seconds to 30 minutes, and a treatment that also serves as normal baking and promotion of the reaction between hexavalent chromium ions and the reducing agent is performed. Here, if the heating temperature and heating time are below the respective lower limits, baking and the reduction and insolubilization reaction of hexavalent chromium will be insufficient and the adhesion of the film will be low;
If the temperature is higher than 0.degree. C., there is a risk that the component resins will decompose and deteriorate in quality. In this way, the resin is insolubilized, and a film rich in hydrophilicity and corrosion and rust prevention properties can be formed on the surface of the aluminum material. Note that if the processing agent of the present invention is applied also for cooling after heat treatment such as thermal refining of aluminum materials, residual heat can be utilized and energy costs can be reduced. Furthermore, before the film is insolubilized, the treatment agent can be repeatedly applied many times to increase the film thickness. Alternatively, a solution of a chromium compound and fluoride and a solution of resin, silica, phosphoric acid and a reducing agent are prepared within the above composition range, and these solutions are simultaneously sprayed onto the surface of an aluminum material using a spray method or the like. They may be mixed. The film thickness can be set to an appropriate film thickness within the above range depending on the degree of need, but for example,
Even if it is about 0.1 μm (after drying), it can sufficiently provide the high degree of hydrophilicity and corrosion resistance required for the fin material of a heat exchanger. Therefore, if corrosion resistance is particularly required, the liquid should be made with a high content of chromium compounds, including hexavalent chromium ions within the above composition range, and if particularly hydrophilicity is required, phosphoric acid may be added. By using a liquid containing a large amount of silica, the film characteristics can be adjusted even if the film thickness is the same. The film obtained by baking the treatment agent in this way forms a very thin layer (first layer) of aluminum fluoride, aluminum silica, etc. at the boundary between the film and the aluminum material, and then contains a chromium compound and silica. A relatively thick inorganic layer (second layer) is formed, and a resin layer containing silica, phosphoric acid, and a reducing agent is formed as the outermost layer (third layer), forming three layers as a whole. . Unlike conventional hydrophilic paints, where the corrosion resistance of the film is affected by the type and thickness of the paint film, and the type or amount of additives to the resin, in the present invention, the corrosion resistance is almost exclusively determined by the inorganic film. Therefore, there are not many restrictions on the thickness of the resin layer or the amount of silica added, at least from the perspective of corrosion resistance. Therefore, there is a high degree of freedom in hydrophilic treatment.
As a result, it is possible to provide a film with higher hydrophilicity than conventional hydrophilic paints. This is due to the fact that by adding fluoride, the fluoride is formed as a boundary layer with the aluminum material as mentioned above, or the particle surface of silica is activated by the fluoride and the bonding property with the resin increases. Furthermore, by adding phosphoric acid, phosphoric acid is distributed mainly from the outermost layer to the second layer,
Particularly in the outermost layer, the properties of the outermost film are improved by acting on the -COOH groups of the resin, and the properties of the entire film are thought to be significantly improved, maintaining hydrophilicity for a long period of time, and it also shows good performance in wet tests. No defects are observed, and due to the presence of the reducing agent in the film, when hexavalent chromium ions try to elute, the hexavalent chromium is reduced and the hexavalent chromium ions do not elute. The formation of a hydrophilic film with excellent corrosion resistance was observed. Thus, the treatment agent of the present invention can be applied to heat exchanger fins,
It can form a corrosion-resistant hydrophilic film by applying it to the surface of various aluminum materials such as building materials that require prevention of dew condensation and reflective mirrors that require prevention of fogging. [Effect of the invention] The present invention provides chromium nitrate, acrylic acid polymer,
It is a non-rinse type corrosion-resistant hydrophilic film treatment agent that contains fluorides, phosphoric acid, silica, polyhydric alcohols, and/or saccharides, and contains predetermined amounts of each of these in water. Chromium nitrate, which is chromium, changes to hexavalent chromium and exists in the film, and even if it tries to elute out of the film, polyhydric alcohols and sugars exist in the outermost layer and reduce it to trivalent chromium. By doing so, excellent effects such as preventing the elution of hexavalent chromium ions from the film and improving long-term hydrophilicity are observed. [Example] Next, an example of the present invention will be described. Examples 1 to 8 (1) Preparation of corrosion-resistant hydrophilic film treatment agent As a chromium compound, chromium nitrate [Cr
(NO ₃ ) ₃・9H ₂ O] and chromium trioxide, a hexavalent chromium compound, and orthophosphoric acid (100%
H ₃ PO ₄ ) and a 25% by weight aqueous solution of polyacrylic acid as a resin (product name Primal A-
1. Molecular weight less than 50,000, manufactured by Rohm & Haas)
Silica powder (trade name: CABOSIL M-5, manufactured by Kabot Co., Ltd.) with an average primary particle diameter of 0.01 μm is uniformly dispersed in the solution, and an aqueous solution (solution B) in which a reagent grade reducing agent is mixed is shown in the separate table. It was prepared in advance with the following blending ratio. (2) Film formation Aluminum material (AA3102, 0.15mm thick x 100mm
x 100 mm) in a conventional manner, and then a treatment agent prepared by mixing liquids A and B prepared as in (1) above was applied to the surface by roll coating. Apply at a rate of 40ml/m ² and heat to 130°C using a hot air heating oven.
The film was heated and baked for 10 minutes to make it insoluble. (3) Evaluation test (a) Hydrophilicity test method (a) Initial hydrophilicity (before testing): Water wetness when the sample is immersed in deionized water at room temperature for 1 minute, then taken out and left at room temperature for about 30 seconds. Hydrophilicity was investigated using the water immersion method, which determines hydrophilicity based on area ratio. (b) Long-term hydrophilicity (72 hours): Cold/heat cycle method (−10℃×1hr→−10℃～70℃×1hr→70℃
x 1 hr → 70°C to -10°C x 1 hr (repeated), the sample was allowed to stand for 72 hours, and then taken out and examined by determining the water wet area ratio using the water immersion method. (b) Corrosion resistance test method The corrosion area rate was measured and investigated after 240 hours and 500 hours according to the salt spray test JIS Z2371 (1955). (c) Elution test of hexavalent chromium ions The presence or absence of elution of hexavalent chromium ions was investigated when the sample was immersed in deionized water at 35°C for one week. (4) Evaluation The results of the above tests are shown in the attached table.
All of them fully satisfy various characteristics,
No elution of hexavalent chromium ions was observed. Comparative Examples 1 to 3 A film treatment agent was prepared in the same manner as in the example with the compounding ratio shown in the attached table, a film was formed on the surface of the aluminum material in the same manner as in the example, and various tests were conducted in the same manner as in the example. I did this. These results are shown in the attached table. In Comparative Example 1, the concentration of chromium nitrate was low, and since it did not contain phosphoric acid or a reducing agent, both corrosion resistance and long-term hydrophilicity were poor, and hexavalent chromium ions were eluted. Comparative Example 2 and Comparative Example 3 had good corrosion resistance and hydrophilicity, but
Since no reducing agent was added, it was observed that hexavalent chromium ions were eluted, and the effect of adding the reducing agent and phosphoric acid was clear.

【table】

【table】

Claims (1)

[Claims] 1 Chromium nitrate is 2 to _20g in terms of CrO3/Additionally, if desired, hexavalent chromium ion is 2 to _20g in terms of CrO3.
g/or less, the solid content of acrylic acid polymer is 2~
20g/, fluoride as F ^- 0.1-5g/,
An aluminum material comprising 0.1 to 50 g of phosphoric acid as PO ₄ ^2- , 0.2 to 0.8 of silica/total solids ratio, 0.2 to 20 g of polyhydric alcohol or/and saccharide, and the balance water. Corrosion-resistant hydrophilic coating treatment agent.