JP2004244720A - Antirust and anticorrosive coated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antirust and anticorrosive coated steel sheet whose workability is improved without damaging excellent characteristics of a polymer cement mortar. <P>SOLUTION: The antirust and anticorrosive coated steel sheet is obtained by coating at least one surface of a plated steel sheet or a plated steel sheet subjected to chemical conversion treatment with a film formed by applying a mixed solution of a polymer containing an acrylic resin emulsion and cement thereon and drying the solution. The water content of the mixed film after drying is not more than 0.1 by water/cement mass ratio. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a rust-proof and anti-corrosion coated steel sheet. More specifically, the present invention relates to a coated steel sheet which has a polymer cement film composed of an acrylic resin emulsion and cement on a steel sheet or a plated steel sheet and is excellent in rust prevention, corrosion resistance and scratch resistance.

  Conventionally, there are many methods for preventing corrosion of steel sheets and steel materials, and plating, painting, thermal spraying, lining and the like are widely used. As a method using cement, a mortar in which cement and sand are mixed is often used. Further, as a method for improving various properties such as impact resistance, adhesiveness, and abrasion resistance of mortar, polymer cement mortar in which a mortar is mixed with a polymer has already been widely used.

  This mortar or polymer cement mortar is generally excellent in weather resistance as compared with the above-mentioned coating and lining, because the main component is an inorganic substance. In addition, corrosion protection by mortar or polymer cement mortar protects steel by the effect of a barrier of the film, so that sacrificial corrosion protection is lost by disappearance of the film, such as plating or metal spraying, which is the same inorganic coating. Not even. Further, it is possible to carry out the spraying at a lower cost and more easily than the spraying of an inorganic substance such as ceramics which prevents corrosion of a steel material by the same effect as a barrier [for example, Japanese Patent Publication No. 57-50739 (Patent Document 1), JP-A-60-105709 (Patent Document 2) and JP-B-57-37176 (Patent Document 3).

JP-B-57-50739 JP-A-60-105709 JP-B-57-37176

  As described above, mortar has excellent characteristics as an anticorrosion film. However, anticorrosion methods using ordinary mortars or polymer cement mortars are generally used by painting on-site structures, etc., locally, except for steel pipe linings. Not used much. Moreover, it is hardly used in the case of a use to be processed like a steel sheet, and is actually applied to the steel sheet when evaluating the flexibility of the film. This is because hydrated cement mortars cannot be practically subjected to plastic working, and plastic working is practically difficult even in the case of polymer cement mortar.

  In the polymer cement, when the ratio of the polymer is high, some workability can be obtained, but it goes without saying that the characteristics of cement, which is an inorganic substance, are lost. By improving the workability of the mortar, in particular, if it can be applied to a so-called pre-coated steel sheet which is formed in advance on a steel sheet and then used as it is, it is expected that its application range will be expanded. Then, in order to solve the above-mentioned subject, an object of the present invention is to provide an anticorrosion-corrosion-coated steel sheet with improved workability without impairing the excellent properties of polymer cement mortar.

The inventor studied repeatedly to impart workability to the mortar-coated steel sheet, and as a result of satisfying specific conditions, endured simple processing and hydrated and hardened during actual use. The present inventors have found that a surface-treated steel sheet having a film exhibiting the properties as a cement thus obtained can be obtained, and have completed the present invention.
That is, the first aspect of the present invention is to prevent a coating obtained by coating a mixed solution of a polymer containing an acrylic resin emulsion and a cement and then drying the coating on at least one surface of a plated steel plate or a plated steel plate subjected to a chemical conversion treatment. A rust / corrosion-coated steel sheet, wherein the water content of the mixed coating is 0.1 or less in terms of water / cement mass ratio.

Second, at least one surface of a plated steel sheet or a chemically treated plated steel sheet is coated with a mixed solution of a polymer containing an acrylic resin emulsion, a crosslinking agent and cement, and then dried to form a rust-proof and corrosion-resistant coating. It is a coated steel sheet, wherein the water content of the mixed film after drying is 0.1 or less in terms of a water / cement mass ratio, which is a rust-proof and corrosion-resistant coated steel sheet.
Thirdly, the rust-proofing and anti-corrosion-coated steel sheet according to the first or second aspect, wherein the polymer / cement mass ratio of the mixed film is 0.05 to 0.6.

Fourth, the rust-proof and corrosion-resistant coated steel sheet according to any one of the first to third aspects, wherein the glass transition temperature of the acrylic resin emulsion is 50 ° C or lower.
Fifthly, the rust-proofing and anti-corrosion-coated steel sheet according to any one of the first to fourth aspects, having a primer film below the mixed film.
A sixth aspect is the rust-proofing and anti-corrosion coated steel sheet according to the fifth aspect, further comprising an organic coating layer between the primer coating and the mixed coating.

  According to the present invention, since a steel sheet having a polymer cement film can be processed and used, it is possible to provide a precoated steel sheet having a coating as an inorganic material having excellent weather resistance and corrosion resistance.

Hereinafter, the present invention will be described in detail.
Even a polymer cement which cannot be subjected to plastic working at all can sufficiently withstand simple working by forming a film under the above conditions. The greatest feature of the present invention is that the processability is ensured by controlling the water / cement ratio (W / C) in the polymer cement film at the time of resin curing to 0.1 or less to suppress hydration of the cement. That was done.

  The polymer used in the present invention is a polymer containing an acrylic resin emulsion. As the polyacrylate ester that is the main component of the resin emulsion, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, or the like, or a copolymer or a mixture thereof can be used. As the surfactant forming the emulsion, a cationic surfactant, an anionic surfactant, a nonionic surfactant, a zwitterionic surfactant, or a mixture thereof can be used. In addition, a stabilizer such as methyl cellulose, a coloring pigment, and the like can be added to the emulsion, if necessary. It has been confirmed that if the glass transition temperature (Tg) of the polymer is 50 ° C. or lower, the setting of the cement during use proceeds sufficiently.

  In addition, it is almost common sense to add a crosslinking agent in a general paint. However, in the case of polymer cement, a baking step cannot usually be performed, and therefore, resins developed for polymer cement do not usually contain a crosslinking agent. However, in the case of the present invention, the processability, particularly the paint adhesion after the process, is improved by adding the crosslinking agent. Here, the cross-linking agent means a general cross-linking agent for a polymer compound, or an additive such as a silane coupling agent that bonds an inorganic substance and an organic substance. Therefore, it is desirable to add an appropriate crosslinking agent in consideration of the baking conditions, the pot life of the paint, and the like. Further, by adding the crosslinking agent, the hardness of the coating film in a state where the cement is not hydrated is increased, and the scratch resistance is also improved. It is also effective in controlling the outflow of the fine particle cement to be described later, and leads to maintenance of the denseness of the film.

  As the cement used in the present invention, it is not desirable to use a cement having large particles from the standpoint of emphasizing the workability of the film. Preventing the mixing of particles having an extremely large particle size is more important than controlling the average particle size. To this end, it is desirable to reduce the particle size distribution and remove large particles. This is because, when there is a cement particle larger than the film thickness, it tends to be a starting point of a crack during processing. This is particularly important when forming a thin polymer cement film.

  If the particle size is extremely small, cement particles may aggregate and the apparent particle size may increase, so an anti-agglomeration agent is usually added. The impact on air quality needs to be thoroughly investigated. Attention must be paid to the fact that the particles are likely to be washed away by rain before being exposed and cured outdoors. For this reason, the preferred particle size of the cement particles used is such that the minimum particle size is at least 2 μm and the maximum particle size is at most the film thickness.

  As the type of cement, it is desirable to use blast furnace cement in which granulated slag is mixed with ordinary Portland cement. This is because the blast furnace cement has a small amount of free calcium hydroxide, and thus has a small amount of efflorescence. Calcium carbonate generated by efflorescence dissolves in rain and flows out, so that in the long term the film loses its denseness and reduces its durability. As a general theory, it is advantageous from the viewpoint of appearance that there is less white flower. Further, an intended color tone can be obtained by adding a smaller amount of a coloring pigment. For the same reason, depending on the required color tone, a white cement having a low iron oxide content may be used.

  Since blast furnace cement has a problem such as low initial hardness, there is a problem in adding the blast furnace cement exceeding a ratio (5 to 70%) defined by JIS. For this reason, it is not desirable that the addition ratio of the granulated slag exceeds 80%. As for the particle size range of the granulated slag, the minimum particle size is 2 μm or more and the maximum particle size is the film thickness or less as described above.

  The polymer / cement ratio can be set in the range of 0.05 to 0.6. When this ratio is small, the film becomes hard and has excellent weather resistance, but has poor adhesion and low impact resistance. On the other hand, if it is larger than 0.6, the opposite occurs, and if the temperature and the humidity are high, surface tackiness may occur. Therefore, it is necessary to set an appropriate value according to the application. By setting the polymer / cement ratio to 0.1 to 0.3, a film having a better balance of processability, weather resistance and hardness can be obtained.

  Many kinds of materials such as aggregates, pigments, and fibers are mixed in ordinary cement as needed. In the present invention, many of these admixtures can be used after confirming compatibility with the resin. For example, in the production, in order to extend the pot life of the polymer cement, it is effective to add a cement coagulation retarder. As setting retarders for cement, oxycarboxylic acids and sugar alcohols are used for organic substances, and fluorides and phosphates are used for inorganic substances. It was effective.

  The cement paste usually loses its fluidity in about 2 to 3 hours. However, by adding an appropriate amount of the setting retarder, the pot life can be extended to 30 days or more. Even in such a polymer cement coated steel sheet, the added setting retarder is washed away due to the exposure of the coating to rain during actual use, and thus does not significantly hinder the curing of the coating.

  As other admixtures, in the study of the inventors, the addition of an antifoaming agent was effective in preventing pinholes, especially when a thin film was formed. As the defoaming agent, besides commercially available defoaming agents such as polyoxyalkylene derivatives generally used for cement, alcohols such as ethanol, propanol and butanol can also be used as defoaming agents. It should be noted that depending on the type of the polymer, when these admixtures are used in a large amount, the polymer cement paste becomes unstable and may aggregate in some cases. However, it is very difficult to use aggregate from the viewpoint of workability.

  Examples of pigments that are not usually added to cement include the addition of rust preventive pigments. It is particularly effective when the polymer cement film alone requires high corrosion resistance, or when the film is particularly thin and a barrier effect cannot be expected. As the rust preventive pigment, in addition to chromates such as strontium chromate, phosphate rust preventive pigments such as calcium silicate, ferrosilicon, aluminum phosphate and zinc phosphate, and molybdenum such as aluminum molybdate and barium molybdate. Pigments usually used in paints, such as acid-based rust-preventive pigments and other tannates, can be used alone or in combination of two or more. However, since the polymer cement is a film having high hydrophilicity, a pigment having high solubility in water, for example, simple chromium trioxide, is unsuitable because it easily elutes during rainfall.

  Since the steel sheet is intended for long-term use, a pure metal or alloy plated steel sheet is subjected to a chemical conversion treatment for a coating base, for example, a coating chromate treatment, a phosphate treatment, a non-chromium-based chemical conversion treatment, for example, silane. A coupling or tannic acid-based chemical conversion treatment is used. However, polymer cement is strongly alkaline and may react depending on the type of chemical conversion treatment. For example, a chemical conversion treatment in which a chromium trioxide aqueous solution is simply applied to a plated steel sheet is unsuitable because it may dissolve during coating. In addition, when long-term weather resistance is required, when strong adhesion is required due to severe processing, or when it is required to make the polymer cement film thinner, similar to ordinary pre-coated steel sheet It is desirable to apply a polymer cement after performing a primer coating including various pigments and the like.

  Although there is no particular limitation on the primer coating, since the polymer cement applied thereon is strongly alkaline, it is necessary to have resistance thereto, and it is necessary to sufficiently confirm compatibility. The thicker the primer, the higher the corrosion resistance, but the lower the workability. When the film thickness is small, sufficient corrosion resistance cannot be obtained. Therefore, the preferable thickness of the primer is in the range of 1 to 10 μm.

  Furthermore, a polymer cement coating can be used mainly for the purpose of utilizing the characteristics of the film such as lack of luster and darkening when wetted with water. In this case, workability can be prioritized by making the film thickness extremely thin. However, in this case, since a barrier effect of the film cannot be expected, a polymer cement may be further applied on the film structure of a general pre-coated steel sheet in which an organic film layer is top-coated on a primer. In such a usage, a direct anticorrosion effect cannot be expected on the polymer cement film, but an effect of preventing top coat coating from ultraviolet rays can be expected as a film having a large amount of inorganic matter. In this case, as the thickness of the organic film layer is larger as in the case of the primer film, the corrosion resistance is higher, but the workability is lower. In addition, when it is thin, the corrosion resistance decreases. For this reason, the thickness is desirably about the same as the thickness of the top coat layer in a normal pre-coated steel sheet, and is preferably 5 to 50 μm.

  The kneading of the polymer cement composition of the present invention may be performed by various mixers or the like in the same manner as ordinary polymer cement. As a method for coating a steel sheet, a usual roll coater or curtain flow coater can be used. The thicker the film, the better the corrosion resistance and weather resistance, but the lower the workability, and there is a possibility that a foaming phenomenon called "side" may occur during baking of the paint. For this reason, the film thickness at the time of curing the resin is preferably in the range of 10 to 120 μm.

  The painted bolimer cement is baked under predetermined conditions determined by the resin, water / cement ratio and equipment conditions, and a film is formed. At this time, it is important to control the water content in the polymer cement film. If the water / cement ratio is larger than 0.1, the hydration of the cement progresses and the cement becomes hard, and the workability as a precoated steel sheet is reduced. I can't secure it. Desirable moisture content is less than 0.1 in water / cement ratio, more preferably less than 0.05. The lower limit of the water content is not particularly limited. However, in order to reduce the water content, the baking conditions become strict, which may affect the productivity. Furthermore, since the time required for the cement to sufficiently hydrate and harden during use increases, reducing the water content does not necessarily give good results in aspects other than processability, so it is decided according to the application. It is desirable to do.

  The obtained coated steel sheet is used naked after being subjected to a predetermined process and in a place where it is directly exposed to rain outdoors. Although the film is affected by rainfall, temperature, etc., hydration proceeds to such an extent that hardness as cement can be obtained in about 6 months to 1 year. From the follow-up observations of long-term exposure tests and examples of ordinary polymer cement, it can be expected to function as a long-term anticorrosion film. In addition, since the film is soft at the beginning of construction, it may be damaged during use depending on the use and environment. In order to prevent this, hydration of the cement may be promoted by spraying water for several days after construction.

Hereinafter, the present invention will be described in detail with reference to examples.
(Example 1)
1 part by mass of an emulsion (Tg: 25 ° C.) containing 5% by mass of ordinary Portland cement and containing a polymethyl acrylate resin and a nonionic surfactant as main components and having a water content having a water content shown in Table 1 as a solid content The polymer cement paste obtained by partially mixing and thoroughly stirring was coated on a galvanized steel sheet subjected to a coating type chromate treatment (total chromium amount: 50 mg / m ² ) by a curtain flow coater to a film thickness of 70% when dried. The coated surface was heated to 100 to 120 ° C. for 1 to 3 minutes by electric heating. This steel sheet was subjected to a workability test and a corrosion resistance test.

  In the workability test, after bending the mandrel to a diameter of 4 mmφ with a bending tester, the steel plate was further bent with a press, and the bent portion was observed with a stereoscopic microscope to evaluate the critical conditions under which no cracks occurred. In the corrosion resistance test, a steel plate cut into a size of 150 mm x 60 mm was subjected to a 7 mm Erichsen process, then sealed at the end face, and subjected to a salt spray test for 30 days to observe the condition of the Erichsen processed portion. Table 1 shows the results. As can be seen from Table 1, by setting the water / cement ratio at the time of film formation to 0.1 or less, a polymer cement film having excellent workability can be obtained, and as a result, high corrosion resistance at the processed portion can be obtained. .

(Example 2)
An emulsion having a copolymer of butyl acrylate and methyl acrylate, a nonionic surfactant, and a zwitterionic surfactant as the main components with respect to 5 parts by mass of the fine particle cement, and having a water content having a water content shown in Table 2 (Tg: 46 ° C.), 2 parts by mass as a solid content thereof were mixed, and the resulting mixture was thoroughly stirred. The polymer cement paste obtained was mixed with an acrylic resin-based primer-coated zinc-coated steel sheet using a curtain flow coater at 120 to 120 ° C. It was coated to a thickness of 140 μm, and the coated surface was heated by electric heating to 100 to 120 ° C. for 1.5 to 3 minutes. The taper abrasion index of this steel sheet was examined using an ASTM D1044-56 taper-type abrasion tester under the following conditions three days after coating and after one year of an outdoor exposure test. Table 2 shows the obtained results.
Temperature 20 ℃
Humidity 50%
Wear wheel CS-17
Load 1kg
As can be seen in Table 2, the polymer cement film that was soft immediately after the film formation had a hydration reaction of the cement that gradually progressed during outdoor exposure, and after one year, had a hardness equivalent to that of a normal polymer cement film. Is obtained.

(Example 3)
Fine particle cement having an average particle size of 4 μm (cut particles of 10 μm or more), or 5 parts by mass of ordinary Portland cement having an average particle size of 20 μm, based on 5 parts by mass of a polymethyl acrylate resin and a zwitterionic surfactant as main components, An emulsion (Tg: 46 ° C.) having a water content having a water content shown in Table 3 was mixed by 1 part by mass as a solid content, and a polymer cement paste obtained by sufficiently stirring was subjected to a coating type chromate treatment (total chromium amount). : 50-mg / m ² ) coated on a zinc-aluminum alloy plated steel sheet with a curtain flow coater at an average film thickness of 30 to 35 μm when dried, and the coated surface is heated to 100 to 120 ° C. for 1 to 2 minutes by electric heating. did. This steel sheet was subjected to a workability test and a corrosion resistance test. In the workability test, after bending the mandrel to a diameter of 4 mmφ with a bending test machine, the steel plate was further bent with a press machine with a steel plate interposed therebetween, and the bent portion was observed with a stereoscopic microscope to evaluate the marginal conditions under which cracks did not occur. When fine particle cement was used, a setting retarder containing oxycarboxylate as a main component was added in order to prevent aggregation of the cement particles. Table 3 shows the results of the workability test.

  As can be seen from Table 3, by setting the water / cement ratio at the time of film formation to 0.1 or less, a polymer cement film having excellent workability can be obtained. In the case of forming a thin film having a thickness of 30 μm, not only controlling the water / cement ratio within the range of the present invention but also using cement having a small particle size is important for maintaining workability. You can see that.

(Example 4)
For 5 parts by mass of Portland cement having an average particle size of 10 μm or blast furnace cement containing 70% by mass of granulated slag with an equivalent average particle size, 1 part by mass of the emulsion used in Example 3 was used as a solid content. The polymer cement paste obtained by mixing and stirring sufficiently was applied on a galvanized steel sheet subjected to a coating type chromate treatment (total chromium amount: 30 mg / m ² ) by a roll coater to have an average film thickness of 20 to 20 when dried. The coated surface was heated to 100 to 120 ° C. for 1 to 2 minutes by a hot air drier. This steel plate was subjected to an outdoor exposure test. Table 4 shows the results of the appearance observation. As can be seen from Table 4, the use of blast furnace cement suppresses the formation of efflorescence, and even if it is formed, it is quickly washed away by rain, so that a steel sheet having a color tone expected at the time of production can be obtained.

(Example 5)
For 8 parts by mass of blast furnace cement containing 60% by mass of slag and having an average particle size of 4 μm, 2 parts by mass of the emulsion used in Example 2 as a solid content and an epoxy resin equivalent to a bisphenol type epoxy resin emulsion as a crosslinking agent The polymer cement paste obtained by mixing 0 to 0.4 parts by mass of a hardener for the solid content and thoroughly stirring the mixture is dried on a galvanized steel sheet that has been subjected to a tannic acid-based non-chromium conversion treatment by a roll coater. Was applied to a thickness of 100 to 110 μm, and the coated surface was heated to 100 to 120 ° C. for 5 minutes by electric heating. A workability test was performed on this steel sheet.
In the workability test, after bending the mandrel to a diameter of 4 mmφ with a bending tester, the steel plate was further sandwiched, 3T bending was performed with a press machine, and the bent portion was tape-peeled to evaluate the peeling state of the paint. Further, the hardness of the film in an unhydrated state after coating was evaluated by a pencil hardness test.
Table 5 shows the results. As shown in Table 5, it can be seen that the addition of the crosslinking agent to the emulsion improves both the paint adhesion of the processed portion and the film hardness when the cement is not hydrated.

(Example 6)
For 8 parts by mass of blast furnace cement containing 60% by mass of slag and having an average particle size of 4 μm, 2 parts by mass of the emulsion used in Example 2 as a solid content and an epoxy resin equivalent to a bisphenol type epoxy resin emulsion as a crosslinking agent The polymer cement paste obtained by mixing the hardening agent for solids at 0, 0.1 parts by mass and sufficiently stirring is coated on a coated steel plate with a roll coater so that the film thickness when dried becomes 10 to 12 μm. After coating, the coated surface was heated to 100 to 120 ° C. for 3 minutes by electric heating. The coated steel sheet used here was a coating-type chromate treatment (total chromium amount: 20 mg / m ² ), an acrylic resin primer coating (5 μm), and a polyester resin top coat coating (15 μm) on a galvanized steel sheet. is there.
This steel sheet was subjected to the same workability test as in Example 5 and a corrosion resistance test by salt spray. However, the bending test was 1T bending. As a comparative example, the above coated steel sheet without polymer cement coating was used. Table 6 shows the results.

  As can be seen from Table 6, the tape peeling results after processing were good despite the processing being more severe than the 3T bending shown in Table 5. This is because the effect of making the film thinner with priority given to workability has appeared. Further, as a result of the corrosion resistance evaluation by the salt spray test, no clear difference was observed in the time until the occurrence of white rust, and the contribution of the polymer cement film to corrosion prevention was not confirmed. From these results, when the polymer / cement ratio is as low as 0.2 and the film does not contain a rust-preventive pigment in a thin film having a thickness of 10 μm, the direct anticorrosion effect of the polymer cement film is small. You can see that there is.

Claims (6)

At least one side of a plated steel sheet or a plated steel sheet that has been subjected to a chemical conversion treatment, a rust-proof and corrosion-resistant coated steel sheet coated with a coating obtained by coating and then drying a mixed liquid mixture of a polymer and cement containing an acrylic resin emulsion, A rust-proof and anti-corrosion coated steel sheet, wherein the water content of the mixed coating is 0.1 or less in terms of water / cement mass ratio. A rust-proof and anti-corrosion coated steel sheet obtained by coating at least one surface of a plated steel sheet or a plated steel sheet subjected to a chemical conversion treatment with a coating obtained by coating a mixture of a polymer containing an acrylic resin emulsion, a crosslinking agent, and cement and then drying. Wherein the moisture content of the mixed film after drying is 0.1 or less in terms of water / cement mass ratio. The rust-proof and anti-corrosion coated steel sheet according to claim 1 or 2, wherein the polymer / cement mass ratio of the mixed film is 0.05 to 0.6. The rust-proof and anti-corrosion coated steel sheet according to any one of claims 1 to 3, wherein the acrylic resin emulsion has a glass transition temperature of 50C or lower. The rust-proof and anti-corrosion coated steel sheet according to any one of claims 1 to 4, further comprising a primer film below the mixed film. The rust-proof and corrosion-resistant coated steel sheet according to claim 5, further comprising an organic coating layer between the primer coat and the mixed coating.