Room temperature curable phosphate coating and method of making same

Abstract

This invention discloses a room-temperature curing phosphate coating and its preparation method. The room-temperature curing phosphate coating, by weight percentage, comprises: 80-90% aluminum chromium phosphate binder, 1.6-1.8% defoamer, 3.2-3.6% sodium bentonite, 3.2-3.6% nano-silica, 0.9-2.6% hydrotalcite, 0.4-9% molybdenum disulfide, and 0.3-2.0% metal powder. This invention provides a room-temperature curing phosphate coating. By adding calcined magnesium aluminum hydrotalcite, the high-temperature curing temperature of traditional phosphate coatings is reduced to room temperature. The addition of molybdenum disulfide effectively improves the adhesion of the room-temperature curing phosphate coating. The coating exhibits comparable adhesion, impact resistance, and hardness to existing high-temperature curing phosphate coatings. The addition of metal powder shortens the curing time and promotes coating curing. Simultaneously, through an electrochemical process, the metal powder is transformed into metal oxides, making the coating denser and better protecting the substrate material.

Description

Technical Field

[0001] This invention relates to the field of coatings, specifically to a room-temperature curing phosphate coating and its preparation method. Background Technology

[0002] Phosphate coatings are mainly used for heat-resistant protective coatings of metals and alloys, as well as for preparing anti-corrosion coatings by adding metal particles. As a type of inorganic coating, phosphate coatings are gradually replacing silicone coatings due to their advantages such as high-temperature stability, strong adhesion, abundant raw material resources, and environmental friendliness and low cost, becoming a new direction for coating development. However, the curing temperature of ordinary phosphate coatings is relatively high, making it difficult to promote their application. Therefore, there is a strong practical need to research and develop phosphate coatings that cure at room temperature. Summary of the Invention

[0003] This invention addresses the shortcomings of existing phosphate coatings, such as high curing temperatures, long curing times, and varying degrees of moisture re-entry at lower curing temperatures, leading to reduced coating adhesion and hardness. This invention provides a room-temperature curing phosphate coating, lowering the curing temperature of traditional phosphate coatings from 300–500°C to room temperature. The curing agent is composed of magnesium aluminum hydrotalcite, molybdenum disulfide, metal powder, sodium bentonite, nano-silica, and copper oxide. This novel curing agent not only lowers the curing temperature and increases the coating's hardness but also effectively improves the adhesion between the coating and the substrate, as well as its impact resistance. The phosphate coating synthesized by this invention is composed of inorganic materials, is heat-resistant, and can protect the substrate at both room and high temperatures, reaching up to 800°C, without producing environmentally damaging volatile organic compounds, making it suitable for widespread use.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] The first aspect of this invention provides a room-temperature curing phosphate coating, comprising, by weight percentage: 80-90% aluminum chromium phosphate binder, 1.6-1.8% defoamer, 3.2-3.6% sodium bentonite, 3.2-3.6% nano silica, 0.9-2.6% hydrotalcite, 0.4-9% molybdenum disulfide, and 0.3-2.0% metal powder.

[0006] Preferably, by weight percentage, the room-temperature curing phosphate coating comprises: 80-90% aluminum chromium phosphate binder, 1.6-1.8% defoamer, 3.2-3.6% sodium bentonite, 3.2-3.6% nano silica, 0.9-2.6% hydrotalcite, 7-9% molybdenum disulfide, and 0.3-2.0% metal powder; more preferably, the room-temperature curing phosphate coating comprises: 80-90% aluminum chromium phosphate binder, 1.6-1.8% defoamer, 3.2-3.6% sodium bentonite, 3.2-3.6% nano silica, 0.9-2.6% hydrotalcite, 7-9% molybdenum disulfide, and 1.0-2.0% metal powder.

[0007] Preferably, the metal powder includes one or more of Al powder, Zn powder, and Mg powder, which are combined to form a metal powder.

[0008] Preferably, the particle size of the metal powder is 180-2000 mesh; more preferably, the particle size of the Al powder is 800-2000 mesh, the particle size of the Zn powder is 200-500 mesh, and the particle size of the Mg powder is 180-500 mesh; in some preferred embodiments of the present invention, the metal powder is 800-2000 mesh spherical Al powder.

[0009] Preferably, the aluminum chromium phosphate binder is prepared by a method comprising the following steps:

[0010] Phosphoric acid and phosphorus pentoxide are mixed and heated under reflux at 130–150°C for 0.8–1.2 h. CrO3 is then added and stirring is continued for 0.4–0.6 h. After cooling to room temperature, water and aluminum hydroxide are added, and the mixture is then refluxed at 90–110°C for 0.8–1.2 h. The mixture is stirred until completely dissolved and cooled to obtain aluminum chromium phosphate binder, which is then packaged for later use.

[0011] More preferably, the mass ratio of phosphoric acid, phosphorus pentoxide, CrO3, and aluminum hydroxide is (11.5-12):(3.5-3.7):1:(4.5-5.0).

[0012] Preferably, the hydrotalcite is magnesium-aluminum hydrotalcite calcined at 300-800°C for 2.5-3.5 hours; in some preferred embodiments of the present invention, the hydrotalcite is magnesium-aluminum hydrotalcite calcined at 600°C.

[0013] In this invention, the molybdenum disulfide may be in the form of flake molybdenum disulfide, block molybdenum disulfide, or powder molybdenum disulfide; preferably, the molybdenum disulfide is powder molybdenum disulfide with a mesh size of 400 to 1000.

[0014] A second aspect of this invention provides a method for preparing the aforementioned room-temperature curing phosphate coating, comprising the following steps:

[0015] Weigh out aluminum chromium phosphate binder and defoamer, mix them together, then add sodium bentonite and nano silica, disperse them evenly, and finally add hydrotalcite, molybdenum disulfide and metal powder. After stirring, a room-temperature curing phosphate coating is obtained.

[0016] The third aspect of the present invention provides a method for preparing a room-temperature curing phosphate coating, comprising the following steps: coating the room-temperature curing phosphate coating onto a substrate and curing it at 20-35°C for 10-72 hours to obtain the coating.

[0017] The room-temperature curing phosphate coating of the present invention can be cured within 24 hours at 30°C.

[0018] Preferably, the substrate includes one of carbon steel, stainless steel, titanium, aluminum, aluminum alloy, and magnesium alloy; the coating method includes one of dip coating, brush coating, or spray coating.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] This invention provides a room-temperature curing phosphate coating. By adding calcined magnesium aluminum hydrotalcite, the high-temperature curing temperature of traditional phosphate coatings is reduced to room temperature. The addition of molybdenum disulfide effectively improves the adhesion of the room-temperature curing phosphate coating. Furthermore, the coating exhibits comparable adhesion, impact resistance, and hardness to existing high-temperature curing phosphate coatings. The addition of metal powder shortens the curing time and promotes coating curing. Simultaneously, through an electrochemical process, the metal powder transforms into metal oxides, resulting in a denser coating and better protection of the substrate material. The raw materials used in this coating are common chemical raw materials, which are abundant, environmentally friendly, and inexpensive. This invention has promising prospects for widespread application. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0023] The present invention first provides a room temperature curing phosphate coating, the components of which, by weight percentage, include: 80-90% aluminum chromium phosphate binder, 1.6-1.8% defoamer, 3.2-3.6% sodium bentonite, 3.2-3.6% nano silica, 0.9-2.6% hydrotalcite, 0.4-9% molybdenum disulfide, and 0.3-2.0% metal powder.

[0024] Traditional phosphate coatings rely primarily on high-temperature dehydration and cross-linking curing of the phosphate salts for film formation; therefore, the cross-linking strength of the phosphate affects the coating's adhesion. This invention incorporates calcined hydrotalcite into the composite curing agent, thereby lowering the cross-linking curing temperature of the coating. Furthermore, the addition of molybdenum disulfide to the composite curing agent allows it to react with the phosphate in conjunction with the calcined magnesium aluminum hydrotalcite curing agent, resulting in a higher coating adhesion. Simultaneously, the inclusion of metal powder in the composite curing agent reduces the curing reaction time.

[0025] This invention also provides a method for preparing room-temperature curing phosphate coatings, comprising the following steps:

[0026] Weigh out the aluminum chromium phosphate binder and defoamer according to the prescribed amounts and mix them. Then, slowly add the prescribed amounts of sodium bentonite and nano-silica to the aluminum chromium phosphate binder and disperse them evenly. Finally, add the prescribed amounts of the composite curing agent, which is a mixture of magnesium aluminum hydrotalcite, molybdenum disulfide, and metal powder, to the aluminum chromium phosphate binder and disperse it evenly. After stirring for 15 minutes, a room-temperature curing phosphate coating is obtained.

[0027] The preparation method of the aluminum chromium phosphate binder in this invention includes the following steps: 30 mL of phosphoric acid (analytical grade) is mixed with 17 g of phosphorus pentoxide, heated under reflux at 140 °C for 1 hour, then 4.73 g of CrO3 is added, and stirring is continued for 0.5 hours until completely dissolved. The mixture is then cooled to room temperature, 45 g of water and 23 g of aluminum hydroxide are added, and the mixture is refluxed at 100 °C for 1 hour, stirred until completely dissolved, cooled, and the aluminum chromium phosphate binder is obtained. This binder is then packaged for later use as the base material.

[0028] The present invention also provides a method for using the above-mentioned room temperature curing phosphate coating, comprising the following steps: coating the room temperature curing phosphate coating onto a substrate, treating it at room temperature, and preparing a room temperature curing phosphate coating.

[0029] The substrate is one of the following materials: carbon steel, stainless steel, titanium, aluminum, aluminum alloy, and magnesium alloy.

[0030] The coating methods include: dip coating, brush coating, or spray coating.

[0031] The present invention also provides a room-temperature curing phosphate coating prepared by the above method.

[0032] Examples 1-7

[0033] A method for preparing a room-temperature curing phosphate coating is prepared from aluminum chromium phosphate binder, defoamer, sodium bentonite, nano silica, magnesium aluminum hydrotalcite in different proportions, molybdenum disulfide, and aluminum powder. The weight percentage of each raw material is shown in Table 1.

[0034] Table 1

[0035]

[0036]

[0037] The magnesium-aluminum hydrotalcite in this example is calcined magnesium-aluminum hydrotalcite roasted in a muffle furnace at 600°C for 3 hours. The molybdenum disulfide has a particle size of 400-1000 mesh, the aluminum powder is spherical Al powder of 800-2000 mesh, and the defoamer used is SN-470 from Sanno Spectro.

[0038] Weigh and mix the aluminum chromium phosphate binder and defoamer according to the weight formula in Table 1. Then, slowly add the formulated amounts of sodium bentonite and nano-silica to the aluminum chromium phosphate binder and disperse evenly. Finally, add the formulated amounts of the composite curing agent, composed of magnesium aluminum hydrotalcite, molybdenum disulfide, and metal powder, to the aluminum chromium phosphate binder and disperse evenly. After stirring for 15 minutes, a room-temperature curing phosphate coating is obtained, which is uniformly dispersed and ready for coating preparation.

[0039] A room-temperature curing phosphate coating was applied to the test piece by brushing and then cured at room temperature to obtain a room-temperature curing phosphate coating.

[0040] Comparative Example 1

[0041] Comparative Example 1 uses unbaked magnesium aluminum hydrotalcite to prepare a room temperature phosphate coating based on the example. The formulation of the room temperature phosphate coating prepared by unbaked magnesium aluminum hydrotalcite is shown in Table 2, and the rest is the same as the example.

[0042] Table 2

[0043]

[0044] Comparative Example 1 uses a brush coating method to apply unbaked magnesium aluminum hydrotalcite curing agent to the test piece to prepare a room temperature phosphate coating. At room temperature, a phosphate coating is obtained.

[0045] The coatings prepared in the examples and comparative examples were subjected to performance tests, and the results are shown in Table 3 below.

[0046] Table 3

[0047]

[0048]

[0049] The curing test temperature was 30℃. As can be seen from the results of the examples and comparative examples, the addition of calcined hydrotalcite to the composite curing agent of this invention lowers the cross-linking curing temperature of the coating. The addition of molybdenum disulfide to the composite curing agent of this invention allows the molybdenum disulfide and calcined magnesium aluminum hydrotalcite curing agent to react with phosphate, thereby resulting in a coating with higher adhesion. Simultaneously, the addition of metal powder to the composite curing agent of this invention reduces the time required for the curing reaction.

[0050] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A room-temperature curing phosphate coating, characterized in that, By weight percentage, it comprises: 80-90% aluminum chromium phosphate binder, 1.6-1.8% defoamer, 3.2-3.6% sodium bentonite, 3.2-3.6% nano silica, 0.9-2.6% hydrotalcite, 7-9% molybdenum disulfide, and 0.3-2.0% metal powder; wherein the hydrotalcite is magnesium aluminum hydrotalcite calcined at 300-800℃ for 2.5-3.5h.

2. The room-temperature curing phosphate coating according to claim 1, characterized in that, The metal powder includes one or more of Al powder, Zn powder, and Mg powder, which are combined to form a metal powder.

3. The room-temperature curing phosphate coating according to claim 2, characterized in that, The particle size of the metal powder is 180~2000 mesh.

4. The room-temperature curing phosphate coating according to claim 1, characterized in that, The aluminum chromium phosphate binder is prepared by a method comprising the following steps: Phosphoric acid and phosphorus pentoxide are mixed and heated under reflux at 130-150℃ for 0.8-1.2h. Then CrO3 is added and stirring is continued for 0.4-0.6h. After cooling to room temperature, water and aluminum hydroxide are added, and then refluxed at 90-110℃ for 0.8-1.2h. Stirring is continued until completely dissolved. After cooling, aluminum chromium phosphate binder is obtained and packaged for later use.

5. The room-temperature curing phosphate coating according to claim 4, characterized in that, The mass ratio of phosphoric acid, phosphorus pentoxide, CrO3, and aluminum hydroxide is (11.5~12):(3.5~3.7):1:(4.5~5.0).

6. The room-temperature curing phosphate coating according to claim 1, characterized in that, The molybdenum disulfide is a powdered molybdenum disulfide with a mesh size of 400-1000.

7. A method for preparing a room-temperature curing phosphate coating according to any one of claims 1 to 6, characterized in that, Includes the following steps: Weigh out aluminum chromium phosphate binder and defoamer, mix them together, then add sodium bentonite and nano silica, disperse them evenly, and finally add hydrotalcite, molybdenum disulfide and metal powder. After stirring, a room-temperature curing phosphate coating is obtained.

8. A method for preparing a room-temperature curing phosphate coating, characterized in that, The process includes the following steps: applying the room-temperature curing phosphate coating according to any one of claims 1 to 6 onto a substrate and curing it at 20 to 35°C for 10 to 72 hours.

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