JP2006022251A - Barrier coat composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a barrier coat composition suitable for an under coat of a heat-curable water-based alkali silicate coating material. <P>SOLUTION: The barrier coat composition contains an aqueous solution of lithium silicate, an inorganic compound filler and a water repellant as essential components. Preferably, the lithium silicate is represented by the general formula: Li<SB>2</SB>O-nSiO<SB>2</SB>(wherein, n is the weight molar ratio of SiO<SB>2</SB>/Li<SB>2</SB>O of 3-7), the inorganic compound filler is mica having ≤40 μm weight average flake diameter, and the water repellent is a water-soluble alkali-alkyl siliconate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a barrier coat composition that serves as a primer for a thermosetting aqueous alkaline silicate paint.

  For heat-curable aqueous alkali (sodium, potassium) silicate paints (hereinafter referred to as “alkali silicate paints” as appropriate), they are made of base corrosion metal materials such as aluminum alloys, galvanized steel sheets, zinc alloys and magne alloys. When the material is directly painted / heat-cured, the paint reacts with the metal material to generate hydrogen gas, which causes a fatal defect that the coating film swells. As a means to solve this problem, there is a method of preventing direct contact between the alkali silicate paint and the base corrosion metal material. For example, in the case of an aluminum alloy, the surface of the alloy is anodized prior to coating. A so-called alumite film is formed (see, for example, Patent Documents 1 and 2). According to this, since direct contact between the coating material and the substrate can be controlled, it is possible to effectively prevent the coating film from swelling.

JP-A-11-019587 JP 2003-055594 A

  The problem is that the equipment for anodizing is extremely large and expensive, so it is a heavy burden in terms of cost to introduce the equipment in a painting factory, and an increase in painting cost is inevitable. When alumite processing is outsourced, the cost is higher than when processing at the own factory, and the management burden is greatly increased. In addition, other metals other than aluminum alloys, such as galvanized steel sheets, zinc alloys, and magne alloys, can even find a way to control the contact between metal materials and alkali silicate paints, just like anodizing in aluminum alloys. Therefore, it has been impossible to apply an alkaline paint to these metal materials.

  Alkali silicate paints are water-based, environmentally friendly, and are considered to be resource-friendly, and have made significant progress despite having excellent properties such as high weather resistance, stain resistance, and mold prevention. What can not be seen is that there is a limit to the types of base materials that can be applied as described above, and that there is a process that cannot be processed in a general coating factory, and that processing costs will rebound to coating costs. .

  An object of the present invention is to solve the above-mentioned problems, and provides a barrier coat composition suitable as a primer for a heat-curable aqueous alkaline silicate paint on a substrate (particularly a base corrosion metal material). There is.

  The conditions required for the barrier coat composition according to the present invention are (1) that it does not react with the base corrosion metal material during heating. (2) Good adhesion to the base corrosion metal material. (3) Adhesion between the barrier coat film and the thermosetting aqueous alkali silicate coating film is good. (4) The finished thermosetting aqueous alkaline silicate coating film maintains its original performance. And so on. As a result of intensive studies, the present inventors have found that a lithium silicate aqueous solution containing an inorganic compound filler and a water repellent satisfies the above conditions well, and has completed the present invention.

  That is, the present invention is a barrier coat composition that serves as a primer for a thermosetting aqueous alkaline silicate paint, characterized by comprising an aqueous lithium silicate solution, an inorganic compound filler, and a water repellent as essential components. (Claim 1). Specific examples of the heat-curable aqueous alkali silicate paint include water-based inorganic paints disclosed in, for example, JP-A-10-330646. The barrier coat composition according to the present invention is preferably used as a primer for forming a thermosetting aqueous alkali silicate coating film on a base material made of a base corrosion metal. The base corrosion metal material mentioned here means, for example, an aluminum alloy, a galvanized steel sheet, a zinc alloy, a magne alloy, or the like.

Specifically, lithium silicate is a lithium silicate aqueous solution represented by the general formula Li ₂ O · nSiO ₂ (where n is SiO ₂ / Li ₂ O weight molar ratio n = 3 to 7), and is filled with an inorganic compound. The agent is mica having a weight average flake diameter of 40 μm or less, and the water repellent is a water-soluble alkali alkylsiliconate (Claim 2). A SiO ₂ / Li ₂ O weight molar ratio n of less than 3 (less than 3.2 in the test example) cannot be used because the liquid is unstable and crystals precipitate. There arises a problem with the adhesion. Specifically, when the SiO ₂ / Li ₂ O weight molar ratio n exceeded 7, swelling occurred in the boiling water test, and peeling of the film occurred in the moisture resistance test.

  By adding an inorganic compound filler, the coating workability of the barrier coat composition can be improved. Above all, such an inorganic compound filler is required to have an effect of smoothly scattering water in the composition at the time of coating / heat-curing of the barrier coat composition, and mica is optimal in the present invention. is there.

  That is, according to the knowledge of the present inventors, if moisture remains in the film after coating / heat-curing of the barrier coat composition, the stage for heat-curing the heat-curable aqueous alkali silicate paint Then, this moisture becomes water vapor, breaks through the alkali silicate coating film and goes out of the film, and at this time, fine pores are formed in the alkali silicate coating film, resulting in a rough surface. In that respect, the above problem can be solved well if mica is included so that the water in the barrier coat composition can be smoothly scattered outside the film.

  The type of such mica is not particularly limited, but the weight average flake diameter is preferably in the range of 40 μm or less. When the thickness exceeds 40 μm, the coating workability is difficult, and the surface of the barrier coat film becomes rough.

  The addition amount of the inorganic compound filler is preferably in the range of 25 to 150 parts by weight with respect to 100 parts by weight of the lithium silicate solid content. If it is less than 25 parts by weight, not only the coating workability of the barrier coat composition is deteriorated, but also the effect of smoothly scattering the moisture in the composition out of the film becomes unstable. If it exceeds 150 parts by weight, the composition becomes powder-rich, and the barrier coat film becomes an excessively porous film. For this reason, when a heat-curable aqueous alkali silicate paint is applied on the film, a blister is formed when the paint enters the hole and replaces the air in the hole, or a blister is generated during the heat-curing of the paint. Or If it exceeds 150 parts by weight, the adhesion to the substrate will be adversely affected, and blistering or peeling will be exhibited in a boiling water test or a moisture resistance test.

  In other words, the effect of being able to smoothly disperse the moisture in the barrier coat film to the outside of the film is that the barrier coat film becomes a fine porous film by adding an inorganic compound filler, and the moisture is passed through the pores. Means that it can be scattered. However, when an alkali silicate coating film is formed on the barrier coat film and then the coated base material is immersed in water, water is introduced from the end face of the coated base material without the alkali silicate coating film through the above holes. May penetrate into the coating. In order to prevent this, in the present invention, water repellent is an essential component to prevent moisture from penetrating into the barrier coat film.

  The water repellent used in the present invention is required to have a dispersibility or solubility in water and be able to withstand a heating step. As a result of studying various compounds, water-soluble alkali alkyl siliconate is optimal.

  The addition amount of the water repellent is preferably in the range of 3 to 20 parts by weight as an active ingredient solid based on 100 parts by weight of lithium silicate solids. If the amount is less than 3 parts by weight, the penetration of water from the end face of the coated substrate cannot be prevented. If the amount exceeds 20 parts by weight, the penetration of water can be prevented, but the water repellency of the surface of the barrier coat film becomes strong. Thus, it is impossible to obtain a good finish by repelling the heat-curable aqueous alkali silicate coating applied to the surface. Including a large amount of expensive water repellent is also uneconomical. As mentioned above, the preferable addition amount of a water repellent is the range of 3-20 weight part with an active ingredient solid with respect to 100 weight part of lithium silicate solid content.

  The barrier coat composition may contain an inorganic colorant in order to achieve color stability of the alkali silicate paint applied thereon. That is, in order to prevent the color of the heat-curable aqueous alkali silicate paint from being impaired due to the presence of the barrier coat composition, an inorganic colorant is mixed in the barrier coat composition so that the barrier coat film is heat-curable. It is preferable to approximate the color of the aqueous alkali silicate paint.

  The addition amount of the inorganic colorant is preferably in the range of 5 to 40 parts by weight with respect to 100 parts by weight of the lithium silicate solid content. If it is less than 5 parts by weight, the coloring power is weak, and if it exceeds 40 parts by weight, it is not only uneconomical, but also the barrier coat composition becomes excessive in powder and inhibits adhesion to the substrate. In short, an amount sufficient to approximate the color of the heat-curable aqueous alkali silicate paint may be mixed with the barrier coat composition.

  In addition, it goes without saying that water can be added to the barrier coat composition in order to improve the paintability.

  The barrier coat composition according to the present invention was applied to a steel plate made of a base-corrosion metal that had been well defatted and had good wettability, and the temperature was raised from room temperature to a curing temperature of 140 ° C. or more over about 10 minutes. After that, after keeping at the curing temperature for 10 minutes or more to disperse moisture to the outside of the film, the coated steel sheet is cooled to room temperature to form a barrier coat film. Next, a heat-curable aqueous alkali silicate paint is applied and heat-cured on the barrier coat film based on the specifications to form an alkali silicate film.

  The thickness of the barrier coat film is preferably in the range of 5 to 50 μm. If the thickness is less than 5 μm, it is not enough to provide a barrier to the base material (base-corrosion metallic steel plate), and if it exceeds 50 μm, it is difficult for water to easily escape from the coating during heating, causing phenomena such as blistering and nail skipping. Cannot be obtained. Furthermore, when stability (easiness of coating) and economy are taken into consideration, the range of 10 to 40 μm is preferable.

  The barrier coat composition is particularly suitable for use in applying a heat-curable aqueous alkali silicate paint to a base-corrosive metal material. Needless to say, it can also be used as a primer.

  The following experiments 1 to 8 clarify the characteristics of the barrier coat composition according to the present invention and the critical significance of various numerical values.

(Experiment 1: Barrier property of the base coat metal material of the barrier coat composition (lithium silicate))
Mica (clarite mica 400W, manufactured by Kuraray Co., Ltd.) as an inorganic compound filler with respect to 100 parts by weight of the solid content of an aqueous solution of lithium silicate having a molar ratio of 3.4 (lithium silicate 35, manufactured by Nippon Chemical Industry Co., Ltd.) ) And 100 parts by weight of water and 450 parts by weight of water in the total composition are put in a plastic container, and 2 mmφ titanium beads are added as a dispersion medium and mixed for 1 hour in a paint shaker. Dispersed to obtain a barrier coat composition according to the present invention (but no water repellent).

  Next, a commercially available aluminum alloy plate (A1100, 100 × 100 × 2 mm, (sand paper removed by polishing the oxide film on the surface of the aluminum alloy plate, degreased with a commercially available alkaline degreasing agent, and washed with water)) , Commercially available hot-dip galvanized steel sheets (100 × 100 × 2 mm (thickened and washed with sandpaper)) and commercially available magnesium alloy plates (AZ61, 100 × 100 × 2 mm (thickened and washed)) The previous barrier coat composition was spray-coated so that the thickness of the cured film was about 20 μm. These were heated in an electric furnace from room temperature to 200 ° C. over about 10 minutes, further held at 200 ° C. for 10 minutes, then removed from the electric furnace and cooled to room temperature.

  100 g each of a commercially available potassium silicate aqueous solution having a molar ratio of 3 (A potassium silicate, manufactured by Nippon Chemical Industry Co., Ltd.) and an aqueous sodium silicate solution having a molar ratio of 3 (J sodium silicate No. 3, manufactured by Nippon Chemical Industry Co., Ltd.) On the other hand, white titanium oxide (TITANIX JR-600E, manufactured by Teika Co., Ltd.) 10 g, mica as an inorganic compound filler (clarite mica 300W, manufactured by Kuraray Co., Ltd.) 10 g, water 20 g for obtaining coating suitability, 2 mmφ titanium beads were added as a dispersion medium and mixed and dispersed in a paint shaker for 1 hour in the same manner as above to obtain two types of heat-curable aqueous alkali silicate paints of potassium and sodium.

  Both paints were spray-coated on the coated plate of the barrier coat composition prepared previously so that the thickness of the cured film was approximately 20 μm. For comparison, the same coating was applied to a board not coated with the barrier coat composition, and all test plates were heated in an electric furnace from room temperature to 200 ° C. over 10 minutes, and further held at 200 ° C. for 20 minutes. The film was removed from the electric furnace, and the presence or absence of swelling of the coating film was visually observed. The results are shown in Table 1.

  Table 1 shows that lithium silicate does not react with the base corrosion metal even in a solution having a high alkalinity, in other words, a low molar ratio. Further, as is apparent from the presence or absence of a barrier coat, those without a barrier coat react violently with the base corrosion metal during heating of the thermosetting alkali silicate paint, generating hydrogen gas, Peeling was observed. On the other hand, there was no swelling when the barrier coat was present. Therefore, it was confirmed that lithium silicate, which is an active ingredient of the present invention, was extremely effective as a primer for the heat-curable aqueous alkaline silicate paint.

(Experiment 2: Role of water repellent in barrier coat composition)
A lithium silicate (lithium silicate 35: same as above) aqueous solution with a molar ratio of 3.4 and an aqueous solution of lithium silicate (trade name: lithium silicate 75, manufactured by Nippon Chemical Industry Co., Ltd.) with a molar ratio of 7.8 in a ratio of 7: 3. 80 parts by weight of mica as an inorganic compound filler (clarite mica 300W, manufactured by Kuraray Co., Ltd.), white titanium oxide (R-550, manufactured by Ishihara Sangyo Co., Ltd.) with respect to 100 parts by weight of the solid content of the mixed aqueous solution. ) 20 parts by weight, alkali / alkylsiliconate (dry seal C, manufactured by Toray Dow Corning Silicone Co., Ltd.) as a water repellent, 0 to 20 weights in solid content (active ingredient) as shown in Table 2 8 types of barrier coat compositions were prepared by mixing and dispersing each of them.

  Next, each of the above eight barrier coat compositions was coated and cured under the same conditions as in Experiment 1 on an aluminum alloy plate (A1100, 100 × 100 × 2 mm) treated in the same manner as in Experiment 1, and cooled to room temperature. Thus, eight coated steel plates were obtained. As the heat-curable aqueous alkali silicate paint, an aqueous pure inorganic paint disclosed in Japanese Patent Application No. 9-157339 was used. Specifically, 250 g of soluble potassium silicate (A potassium silicate (same as above)), 260 g of aqueous silica sol (Snowtex 20, manufactured by Nissan Chemical Industries, Ltd.), an anionic organic compound (TSW-870, GE Toshiba Silicone ( Co., Ltd.) 3 g was mixed and heated and stirred at 90-100 ° C. for 30 minutes, and water was added to make the total amount 630 g to obtain a molar ratio 5.4, 24% aqueous solution. 15 g of pigment (white rutile type titanium oxide) R-550 (same as above), 20 g of inorganic filler (clarite mica 400W, manufactured by Kuraray Co., Ltd.), and 10 g of water were added to form a paint in the same manner as in Experiment 1. Next, this paint was applied to each of the eight coated steel sheets prepared previously so that the cured film thickness was approximately 25 μm, and eight test bodies were obtained.

  When each test specimen was immersed in water for 10 hours and immersed in boiling water for 2 hours, the presence or absence of penetration of water into the coating film was visually observed. The results are shown in Table 2. In the table, “◯” indicates that no penetration into the coating film was observed, “Δ” indicates that slight penetration was observed, and “×” indicates that significant penetration was observed.

  From Table 2, it can be seen that the addition of the water repellent plays a role in preventing water from penetrating into the coating film. The amount added is preferably 3 parts by weight or more in terms of water repellent solid content (active ingredient) relative to 100 parts by weight in terms of lithium silicate solid content, and 3-10 parts by weight is the most preferable range in consideration of economy. is there.

(Experiment 3: Lithium silicate molar ratio and barrier properties against base corrosion metal materials)
A mixture of a lithium silicate aqueous solution (same as above) having a molar ratio of 3.4 and a lithium silicate aqueous solution (same as above) having a molar ratio of 7.8, or 7 kinds having a molar ratio as shown in Table 3 were used alone. An aqueous solution was obtained. 80 parts by weight of Clarite Mica 300W (same as above) as an inorganic compound filler, 20 parts by weight of white titanium oxide and R-550 (same as above), and 100 parts by weight of a solid content of each aqueous solution, Alkali / alkyl siliconate and dry seal (same as above) were mixed in an amount of 6 parts by weight in solid content (active ingredient) to prepare barrier coat compositions having respective molar ratios as in Experiment 1.

  Next, each barrier coat composition was applied to an aluminum alloy plate (A1100, 100 × 100 × 2 mm) treated in the same manner as in Experiment 1 in the same manner as in Experiment 1, to obtain seven coated steel plates. Furthermore, the paint used in Experiment 2 as a thermosetting aqueous alkali silicate paint was applied onto the barrier coat film of these coated steel sheets to obtain seven specimens.

  Each test specimen was subjected to the same underwater immersion test and boiling water immersion test as in Experiment 2 for evaluation. In addition, the presence or absence of swelling of the coating film in boiling water was visually observed. The results are shown in Table 3. The evaluation relating to the permeation of water and boiling water is the same as in Experiment 2. Regarding the presence or absence of swelling of the coating film in boiling water, ◯ indicates no swelling, Δ indicates that slight swelling is observed, and × indicates that significant swelling and peeling are observed.

  It can be seen from Table 3 that the effective lithium silicate molar ratio is in the range of approximately 3-7. When the molar ratio was less than 3, the liquid was unstable and could not be used.

(Experiment 4: Relationship between Addition of Inorganic Filler (Mica) in Barrier Coat Composition and Barrier Property)
Solid content of an aqueous solution obtained by mixing a lithium silicate aqueous solution with a molar ratio of 4.5 (lithium silicate 45, manufactured by Nippon Chemical Industry Co., Ltd.) and a lithium silicate aqueous solution with the molar ratio of 7.8 (same as above) at a ratio of 7: 3. 7 types of barrier coat compositions prepared by mixing Clarite mica 300W (same as above) as an inorganic compound filler in a range of 0 to 160 parts by weight in the range of 0 to 160 parts by weight with respect to parts by weight. It was created. The other components in each barrier coat composition were 20 parts by weight of white titanium oxide (R-550 (same as above)) with respect to 100 parts by weight of lithium silicate, and an alkali alkylsiliconate (dry seal C ( Same as above)) The solid content (active ingredient) was fixed at 7 parts by weight. Next, each of the above barrier coat compositions was cured on a commercially available galvanized steel sheet (100 × 100 × 0.5 mm, degreased with a commercially available alkaline degreasing agent and washed with water) under the same conditions as in Experiment 1, Until cooled. Furthermore, on each of these barrier coat films, the paint used in Experiment 2 was treated under the same conditions as a heat-curable aqueous alkali silicate paint to prepare a test specimen.

  Each test specimen was subjected to the same test as the boiling water test of Experiment 3, and the presence or absence of swelling of the coating film was visually observed. The evaluation of the presence or absence of coating film swelling in the boiling water test was: ○: no swelling, Δ: slight swelling was observed, ×: significant swelling was observed.

  From Table 4, it can be seen that an appropriate range of the inorganic compound filler (mica) in the barrier coat composition is 25 to 150 parts by weight. If it is less than 25 parts by weight, the moisture in the barrier coat composition is difficult to escape and bubbles are present in the gasified state and appear as a film swelling in the boiling water test. Excessive body, poor adhesion to the substrate, causing blistering and peeling.

(Experiment 5: Relationship between Weight Average Flake Diameter (μ) of Inorganic Compound Filler (Mica), Paintability and Film Surface Condition)
70 weights of 5 kinds of inorganic compound fillers (mica) having different flake diameters as shown in Table 5 with respect to 100 parts by weight of solid content of lithium silicate aqueous solution having a molar ratio of 4.5 and lithium silicate 45 (same as above). 5 types of barrier coat compositions were prepared by mixing them partially. The other components in each barrier coat composition were 20 parts by weight of white titanium oxide (R-550 (same as above)) with respect to 100 parts by weight of lithium silicate, and an alkali alkylsiliconate (dry seal C ( Same as above)) The solid content (active ingredient) was 7 parts by weight. Next, spray coating properties when the above barrier coating compositions were cured under the same conditions as in Experiment 1 on the aluminum plate (A1100, 300 × 300 × 2 mm) treated in the same manner as in Experiment 1, and the barrier coat film. The surface smoothness (finish) was visually observed. The results are shown in Table 5.

  As shown in Table 5, when the flake diameter (μm) of the inorganic compound filler (mica) exceeded 40 μm, it was found that both the paintability and the finished film surface state were poor. This means that the heat-curable aqueous alkali silicate paint film placed on the barrier coat film also has a poor finish with poor smoothness. As inappropriate.

(Experiment 6: Barrier coat film thickness and barrier properties)
A cured film thickness on an aluminum alloy plate (A1100, 100 × 100 × 2 mm) treated in the same manner as in Experiment 1 with the same composition as in Experiment 4, with 90 parts by weight of inorganic compound filler, Clarite mica 300W (same as above). Then, the cured film thickness as shown in Table 6 was changed from 3 to 53 μm, spray-coated, and coated and cured under the same conditions as in Experiment 1. Further, a test specimen was prepared by applying and forming the thermosetting aqueous alkali silicate paint used in Experiment 2 on these barrier coat films.

  In each specimen, the state of the coating film when the heat-cured aqueous alkali silicate coating was cured was observed, and the same test as the boiling water test in Experiment 3 was performed, and the presence or absence of swelling of the coating film was visually observed. . The evaluation of the presence or absence of coating film swelling in the boiling water test indicates that ◯: no swelling, Δ: slight swelling was observed, ×: significant swelling and peeling were observed.

  From Table 6, it can be seen that the thickness of the barrier coat film is preferably in the range of 5 to 50 μm. Furthermore, in view of coating stability and economy, a range of 10 to 40 μm is preferable. In mounting, it is difficult to uniformly apply to a substrate at 10 μm or less, and a coating portion of 5 μm or less is likely to be formed. Moreover, if it exceeds 40 micrometers, it cannot be said that it is economical.

(Experiment 7: Minimum curing temperature condition of the barrier coat composition)
Using the barrier coat composition of Experiment 6, coating was performed so as to have two types of film thicknesses of 10 to 30 μm and 31 to 40 μm in cured film thickness. These were heated at the temperature shown in Table 7 to obtain a coated plate. On top of that, a thermosetting aqueous alkali silicate paint was prepared in the same manner as in Experiment 6 under the same conditions. In this experiment, heating was performed at a temperature shown in Table 7 for 10 minutes.

  From Table 7, it can be seen that the minimum curing temperature of the barrier coat composition is 140 ° C. At a temperature of 140 ° C. or lower, moisture remains in the barrier coat film, and when the heat-curable aqueous alkaline silicate paint applied on the film is cured, the moisture gasifies and forms bulges. Such a tendency appears particularly when the film thickness is increased.

(Experiment 8: Performance of barrier coat composition)
The base corrosion metal as shown in Table 8 was spray-coated with the same barrier coat composition as in Experiment 6 so that the cured film thickness was about 20 μm, and cured under the same conditions as in Experiment 1 to obtain each specimen. .

  Next, each specimen was subjected to the test. That is, in the boiling water test, it was immersed in boiling water for 10 hours. In the alkali resistance test, a 5% aqueous sodium hydroxide solution was dropped on the surface of each test specimen and allowed to stand for 30 minutes. In the acid resistance test, a 5% sulfuric acid aqueous solution was dropped on each test surface and left for 30 minutes. Table 8 shows the state after a predetermined time of each test.

  From Table 8, it can be seen that any of the steel sheets having the barrier coat film has no change in the specimen and is excellent in boiling water resistance and chemical resistance. On the other hand, the sample without the barrier coat film shows a change in the specimen, indicating that it is inferior in boiling water resistance and chemical resistance. In addition, as is clear from comparison with aluminum / alumite, it can be seen that this barrier coat film exhibits sufficient performance to protect the substrate.

  A barrier coat composition was prepared by the same adjustment method as in Experimental Example 6, and this was spray-coated on an aluminum alloy plate treated in the same manner as in Experiment 1 so that the cured film thickness was about 20 μm. The coated plate was heated from room temperature to 180 ° C. for about 10 minutes in an electric furnace, held at 180 ° C. for 10 minutes, and then taken out of the furnace and cooled to room temperature to form a barrier coat film. A coated steel sheet was obtained.

  On this coated steel plate, the heat-curable aqueous alkali silicate paint used in Experiment 2 was spray-coated to a cured film thickness of about 20 μm, and the coated steel plate was heated in an electric furnace from room temperature to 220 ° C. for about 10 minutes. Then, the temperature was kept at 220 ° C. for 20 minutes, and then taken out of the furnace and cooled to room temperature. The specimen obtained as described above was subjected to a performance test as shown in Table 9.

  As is apparent from Table 9, the barrier coat composition according to the present invention not only exhibits a complete barrier coat property with respect to the aqueous alkali silicate paint to be heat-cured thereon, but also an aqueous alkali silicate paint. It was confirmed that the original performance of the coating film was not impaired.

  A lithium silicate aqueous solution having a molar ratio of 4.5 (lithium silicate 45 (same as above)) and a lithium silicate aqueous solution having a molar ratio of 7.8 (lithium silicate 75 (same as above)) were mixed at a ratio of 5: 5. As an inorganic compound filler, 85 parts by weight of mica (clarite mica 400W (same as above)), 20 parts by weight of white titanium oxide (R-550 (same as above)) with respect to 100 parts by weight of the solid content of the lithium silicate aqueous solution, As a water repellent, an alkyl / alkyl siliconate (Dry Seal C) was mixed with 5.5 parts by weight of a solid content, and a barrier coat composition was prepared by the same preparation method as in Experimental Example 1.

  Next, each commercially available base corrosion metal material shown in Table 10 was washed with a commercially available alkaline degreasing agent and washed with water, and then the above barrier coat composition was spray coated so as to have a cured film thickness of 20 μm. The coated steel sheet was heated in an electric furnace from room temperature to 180 ° C. over about 10 minutes, held at 180 ° C. for 10 minutes, and then taken out of the furnace and cooled to room temperature.

  On this coated steel plate, the heat-curable aqueous alkali silicate paint used in Experiment 2 was spray-coated to a cured film thickness of about 20 μm, and the coated plate was heated in an electric furnace from room temperature to 220 ° C. for about 10 minutes. Then, the temperature was kept at 220 ° C. for 20 minutes, and then taken out of the furnace and cooled to room temperature. The specimen obtained as described above was subjected to the same performance test as in Table 9 above. The results are shown in Table 10.

  As is clear from Table 10, as in Example 1, the barrier coat composition of the present invention not only exhibits a complete barrier coat property with respect to the aqueous alkali silicate paint to be heat-cured thereon, It was confirmed that the original performance of the aqueous alkali silicate coating film was not impaired.

  A lithium silicate aqueous solution having a molar ratio of 4.5 (lithium silicate 45 (same as above)) and a lithium silicate aqueous solution having a molar ratio of 7.8 (lithium silicate 75 (same as above)) were mixed at a ratio of 6: 4. 20 parts by weight of mica (clarite mica 600W (same as above)), 20 parts by weight of white titanium oxide (R-550 (same as above)) as an inorganic compound filler with respect to 100 parts by weight of the solid content of the lithium silicate aqueous solution, As a water repellent, an alkyl / alkyl siliconate (Dry Seal C) was mixed with 5.5 parts by weight of a solid content, and a barrier coat composition was prepared by the same preparation method as in Experimental Example 1.

  Next, after washing a commercially available magnesium alloy plate (AZ80, 70 × 150 × 2 mm) with a commercially available alkaline degreasing agent and washing with water, the above barrier coat composition is sprayed to a cured film thickness of about 10 μm. Painted. Each coated steel sheet was heated from room temperature to 180 ° C. in an electric furnace over about 10 minutes, held at 180 ° C. for 10 minutes, and then taken out of the furnace and cooled to room temperature.

  In the heat-curable aqueous alkali silicate paint used in Experiment 2, the heat-cured obtained by changing white titanium oxide to a pearl pigment (trade name: Iliondin 300, Gold Pearl, manufactured by Merck Japan Ltd.) The mold-type aqueous alkali silicate paint was spray-coated on the above-mentioned coated steel plate so that the cured film thickness was about 20 μm. This coated plate was heated from room temperature to 200 ° C. in an electric furnace over about 10 minutes, held at 200 ° C. for 20 minutes, and then taken out of the furnace and cooled to room temperature. The specimen obtained as described above was subjected to the same performance test as in Table 9 above. The results are shown in Table 11.

  The obtained alkali silicate coating film had a wonderful gold color as intended. From this, it was confirmed that an alkali silicate coating film can be formed on the barrier coating film without impairing the color by including an appropriate amount of an appropriate inorganic coloring agent in the barrier coating composition according to the present invention. Further, as apparent from Table 11, the barrier coat composition of the present invention exhibits a complete barrier coat property with respect to the heat-curable aqueous alkali silicate coating applied and formed thereon, The performance was impeccable.

  As explained in detail above, the barrier coat composition according to the present invention is not required to react with the base corrosive metal material during heating ((1) heating. 2) Good adhesion to the base corrosion metal material (3) Good adhesion between the barrier coat film and the thermosetting aqueous alkaline silicate coating (4) Finished thermosetting aqueous alkaline silicate coating The film maintains its original performance.) In other words, by using the barrier coat composition according to the present invention as an undercoat agent, a heat-curable aqueous alkali silicate coating film that is smooth and excellent in aesthetics is formed on a base material made of a base corrosion metal, such as swelling or peeling. And can be formed stably.

  This barrier coating composition can be applied by known spray coating without requiring a large-scale equipment such as alumite treatment, and therefore, the coating cost of the thermosetting aqueous alkaline silicate coating can be reduced. Can contribute to Further, the barrier coat composition can be applied to a base material made of a base corrosive metal that cannot be anodized, such as a galvanized steel sheet or a magnesium alloy. It can greatly contribute to the expansion of the range of application of salt paint.

Claims (4)

A barrier coat composition that serves as a primer for a heat-curable aqueous alkaline silicate paint,
A barrier coat composition comprising an aqueous lithium silicate solution, an inorganic compound filler, and a water repellent as essential components. The lithium silicate is a lithium silicate aqueous solution represented by a general formula Li ₂ O · nSiO ₂ (wherein n is SiO ₂ / Li ₂ O weight molar ratio n = 3 to 7),
The inorganic compound filler is mica having a weight average flake diameter of 40 μm or less,
The barrier coat composition according to claim 1, wherein the water repellent is a water-soluble alkali / alkyl siliconate.   The barrier coat composition according to claim 1 or 2, comprising 25 to 150 parts by weight of the inorganic compound filler and 3 to 20 parts by weight of the water repellent solid content with respect to 100 parts by weight of the lithium silicate solid content.   The barrier coat composition according to claim 1, 2 or 3, comprising 5 to 40 parts by weight of an inorganic colorant with respect to 100 parts by weight of lithium silicate solids.