A silicone washcoat and a method for its preparation

Abstract

The application discloses a silicone coating and a preparation method thereof, and comprises base glue 35-75 parts, viscosity regulator 2-20 parts, tackifier 0.5-10 parts, crosslinking agent 0.5-5 parts, coupling agent 0.1-1.5 parts, reinforcing agent 0.5-10 parts and catalyst 0.5-5 parts. The base glue is end-hydroxyl polysiloxane treated by end capping; and the tackifier is a reaction product of 3-isocyanate propyl trimethoxysilane, 3-hydroxypropionic acid and 3-ethyl-3-oxabicyclo-methanol. The end-hydroxyl polysiloxane treated by end capping is added to avoid viscosity peak phenomenon in the production and storage process of the coating, and the coating performance is more stable. The carboxyl and epoxy groups are introduced into the tackifier to improve the adhesion of the coating to a PCB and the bulk strength, so that the overall protection performance of the coating is improved, and the protection performance under harsh environment is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and in particular relates to an organosilicon conformal coating and a preparation method thereof. Background Art

[0002] The conformal coatings currently used on the market mainly include UV acrylates, polyurethanes and silicones. Each type of conformal coating has its own characteristics. UV acrylates have fast curing efficiency and poor resistance to low temperatures of -60°C. Polyurethanes are average, but their resistance to harsh salt spray and extremely low and high temperatures will be greatly reduced. Silicones are flexible and resistant to high and low temperatures, but their adhesion is weak, and they are difficult to meet the requirements for protection against high salt spray and high humidity in harsh environments.

[0003] Currently, the requirements for PCB protection in equipment such as automotive electronics, outdoor charging stations, photovoltaics, and offshore power generation are becoming increasingly stringent. They must withstand environmental challenges (high and low temperatures, salt spray, and moisture) and provide protection for decades. Silicone-based conformal coatings are particularly suitable for this demanding protection. However, many commercially available silicone products have poor adhesion. After several years of exposure to wind and sun, their protective performance deteriorates and they fail to meet medium- and long-term protection requirements. To address the need for PCB protection in harsh environments, ensure long-term protection effectiveness, and guarantee the stable operation of electronic products, and to address the shortcomings of these products, a silicone-based conformal coating with excellent protective performance has become increasingly necessary. Summary of the Invention

[0004] In order to overcome the problems in the prior art, the present invention provides an organosilicon conformal coating and a preparation method thereof. The obtained organosilicon conformal coating can be used in harsh environments and still has excellent adhesion.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] An organic silicon conformal coating comprises the following raw materials in parts by weight:

[0007] 35-75 parts of base rubber, 2-20 parts of viscosity modifier, 0.5-10 parts of tackifier, 0.5-5 parts of cross-linking agent, 0.1-1.5 parts of coupling agent, 0.5-10 parts of reinforcing agent, 0.5-5 parts of catalyst;

[0008] The base glue is end-capped hydroxyl-terminated polysiloxane; the tackifier is a reactant of 3-isocyanate propyltrimethoxysilane, 3-hydroxypropionic acid and 3-ethyl-3-oxetanol.

[0009] In this invention, the addition of end-capped hydroxyl-terminated polysiloxane to the silicone conformal coating can avoid viscosity peaks during the coating's production and storage processes. The introduction of carboxyl and epoxy groups into the tackifier can improve the coating's adhesion to PCBs and enhance its overall strength.

[0010] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the base glue is a substance obtained by capping terminal hydroxyl polysiloxane and methyl orthosilicate under the catalysis of alkali metal salt.

[0011] In the present invention, methyl orthosilicate is used for end-capping, which has high efficiency, strong activity and high strength of the cured product.

[0012] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the molar ratio of the terminal hydroxyl polysiloxane to methyl orthosilicate is 1:1.5-2.5.

[0013] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the alkali metal salt is selected from one or more of lithium carbonate, sodium carbonate, and potassium carbonate.

[0014] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the viscosity of the base glue at 25° C. is 100 to 1000 cps.

[0015] As an optional embodiment, in the silicone conformal coating provided by the present invention, the preparation method of the tackifier is as follows: under nitrogen protection, 3-isocyanatepropyltrimethoxysilane, 3-hydroxypropionic acid and 3-ethyl-3-oxetane methanol are mixed, nitrogen is filled and sealed and stirred, and the temperature is raised to 60°C to 80°C for reaction and then the material is discharged.

[0016] As an optional embodiment, in the silicone conformal coating provided by the present invention, the mass fraction ratio of 3-isocyanatepropyltrimethoxysilane, 3-hydroxypropionic acid and 3-ethyl-3-oxetanol is 10:1.5~4:1.5~4.

[0017] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the organosilicon conformal coating further comprises a fluorescent indicator, and the fluorescent indicator is 0.05 parts to 0.2 parts.

[0018] Adding fluorescent indicators to the coating is helpful for detecting coating uniformity.

[0019] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the fluorescent indicator is fluorescent OB-1.

[0020] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the viscosity modifier is methyl silicone oil, and the viscosity of the methyl silicone oil at 25° C. is 100 to 500 cps.

[0021] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the crosslinking agent is selected from one or more of methyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and phenyltrimethoxysilane.

[0022] As an optional embodiment, in the organosilicon conformal coating provided by the present invention, the reinforcing agent is selected from one or more of nano-calcium carbonate, silicon dioxide, and nano-silicon powder.

[0023] As an optional embodiment, in the silicone conformal coating provided by the present invention, the coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-aminopropyltrimethoxysilane.

[0024] As an optional embodiment, in the silicone conformal coating provided by the present invention, the catalyst is selected from one or more of di(ethyl acetoacetate) diisopropyl titanate, di(ethyl acetoacetate) di-n-butoxy titanate, di(ethyl acetoacetate) diisobutyl titanate and di(acetylacetonato) ethoxyisopropoxy titanate.

[0025] Based on the same technical concept, the present invention also provides a preparation method for the above-mentioned silicone conformal coating, comprising the following steps: under nitrogen protection throughout the process, adding the base glue, viscosity regulator, tackifier, cross-linking agent and coupling agent into the reactor, stirring evenly at 10°C to 30°C, then adding the reinforcing agent and fluorescent indicator and stirring evenly, and then adding the catalyst, stirring evenly and discharging, filtering to obtain the silicone conformal coating.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The addition of end-capped hydroxyl-terminated polysiloxane to the silicone coating provided by the present invention avoids viscosity peaks during the coating's production and storage processes, making the coating more stable. By introducing carboxyl and epoxy groups into the homemade tackifier, the coating's adhesion to PCBs and bulk strength are enhanced, improving the coating's overall protective performance, ensuring protection in harsh environments.

[0028] (2) In the preparation method of the organic silicon conformal coating provided by the present invention, the raw material reaction process is a dealcoholization reaction, the catalyst is tin-free and lead-free, and is environmentally friendly and non-corrosive to components. DETAILED DESCRIPTION

[0029] To facilitate understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0031] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0032] Example 1

[0033] Base glue treatment method: 1 mol of hydroxy-terminated polysiloxane with a viscosity of 1000 cps and 2 mol of methyl orthosilicate are capped under the catalysis of lithium carbonate and set aside.

[0034] Preparation of tackifier: Under nitrogen protection, mix 10 parts of 3-isocyanatepropyltrimethoxysilane, 2.9 parts of 3-hydroxypropionic acid and 2.2 parts of 3-ethyl-3-oxetanol, fill with nitrogen, seal and stir, heat to 60°C and react for 3 hours, then discharge the material to obtain the tackifier for use.

[0035] Preparation method of silicone conformal coating:

[0036] The temperature was controlled at 10°C to 30°C throughout the stirring process, and nitrogen was used for protection. A 1000 cps end-capped base rubber, a 100 cps viscosity methyl silicone oil, a homemade tackifier, vinyl trimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane were added to a reactor and stirred evenly under nitrogen. Nano-silica and fluorescent OB-1 were then added and stirred evenly under nitrogen. Finally, diisobutyl di(ethyl acetoacetate) titanate was added and stirred evenly under nitrogen. The mixture was discharged and filtered through a 60-mesh filter to obtain the product.

[0037] The components and their addition ratios are shown in Table 1 below:

[0038] Table 1: Components and addition ratios of Example 1

[0039]

[0040] Example 2

[0041] Base glue treatment method: 1 mol of hydroxy-terminated polysiloxane with a viscosity of 1000 cps and 2 mol of methyl orthosilicate are capped under the catalysis of lithium carbonate and set aside.

[0042] Preparation of tackifier: Under nitrogen protection, mix 10 parts of 3-isocyanatepropyltrimethoxysilane, 3.5 parts of 3-hydroxypropionic acid and 3.0 parts of 3-ethyl-3-oxetanol, fill with nitrogen, seal and stir, heat to 60°C and react for 3 hours, then discharge the material to obtain the tackifier for use.

[0043] Preparation method of silicone conformal coating:

[0044] The entire stirring process was temperature-controlled (10°C to 30°C) under nitrogen protection. 700 cps end-capped base rubber, 100 cps methyl silicone oil, a homemade tackifier, methyltrimethoxysilane, and γ-aminopropyltrimethoxysilane were added to a reactor and stirred evenly under nitrogen protection. Nanosilica and fluorescent OB-1 were then added and stirred evenly under nitrogen protection. Finally, diisobutyl di(ethyl acetoacetate) titanate was added and stirred evenly under nitrogen protection. The product was then discharged and filtered through a 60-mesh filter to obtain the product.

[0045] The components and their addition ratios are shown in Table 2 below:

[0046] Table 2: Components and addition ratios of Example 2

[0047]

[0048]

[0049] Example 3

[0050] Base glue treatment method: 1 mol of hydroxy-terminated polysiloxane with a viscosity of 1000 cps and 1.5 mol of methyl orthosilicate are capped under the catalysis of sodium carbonate and set aside.

[0051] Preparation of tackifier: Under nitrogen protection, mix 10 parts of 3-isocyanatepropyltrimethoxysilane, 2.9 parts of 3-hydroxypropionic acid and 2.2 parts of 3-ethyl-3-oxetanol, fill with nitrogen, seal and stir, heat to 80°C and react for 3 hours, then discharge the material to obtain the tackifier for use.

[0052] Preparation method of silicone conformal coating:

[0053] The entire stirring process was temperature-controlled (10°C to 30°C) under nitrogen protection. 500cps end-capped base rubber, 400cps methyl silicone oil, a homemade tackifier, methyltrimethoxysilane, and γ-aminopropyltrimethoxysilane were added to a reactor and stirred evenly under nitrogen protection. Nanosilica and fluorescent OB-1 were then added and stirred evenly under nitrogen protection. Finally, diisobutyl di(ethyl acetoacetate) titanate was added and stirred evenly under nitrogen protection. The product was then discharged and filtered through a 60-mesh filter to obtain the product.

[0054] The components and their addition ratios are shown in Table 3 below:

[0055] Table 3: Components and addition ratios of Example 3

[0056]

[0057] Example 4

[0058] Base glue treatment method: 1 mol of hydroxy-terminated polysiloxane with a viscosity of 1000 cps and 1.5 mol of methyl orthosilicate are capped under the catalysis of sodium carbonate and set aside.

[0059] Preparation of tackifier: Under nitrogen protection, mix 10 parts of 3-isocyanatepropyltrimethoxysilane, 2 parts of 3-hydroxypropionic acid and 1.8 parts of 3-ethyl-3-oxetanol, fill with nitrogen, seal and stir, heat to 80°C and react for 3 hours, then discharge the material to obtain the tackifier for use.

[0060] Preparation method of silicone conformal coating:

[0061] The entire stirring process was temperature-controlled (10°C to 30°C) under nitrogen protection. 500cps end-capped base rubber, 400cps methyl silicone oil, a homemade tackifier, methyltrimethoxysilane, and γ-aminopropyltrimethoxysilane were added to a reactor and stirred evenly under nitrogen protection. Nanosilica and fluorescent OB-1 were then added and stirred evenly under nitrogen protection. Finally, diisobutyl di(ethyl acetoacetate) titanate was added and stirred evenly under nitrogen protection. The product was then discharged and filtered through a 60-mesh filter to obtain the product.

[0062] The components and their addition ratios are shown in Table 4 below:

[0063] Table 4: Components and addition ratios of Example 4

[0064]

[0065] Comparative Example 1

[0066] The difference from Example 1 is that no tackifier is added to the coating, and the remaining steps and components are the same as in Example 1.

[0067] Comparative Example 2

[0068] The difference from Example 1 is that the base glue in the coating is not end-capped and is 1000 cps terminal hydroxyl siloxane. The remaining steps and components are the same as those in Example 1.

[0069] The coatings prepared in the examples and comparative examples were tested for performance, and the test standards were as follows:

[0070] Salt spray test: neutral salt spray 5% for 1000h, high and low temperature shock -60℃ to 120℃, 1000h, high temperature and high humidity test 85℃, 85% RH, 1000h.

[0071] The surface drying time was tested according to GB1728-1979, the method for determining the drying time of paint and putty films.

[0072] The coating adhesion was tested according to the pull-off adhesion test for paints and varnishes GB / T5210-2006.

[0073] According to GB-T 1771-2007, Determination of neutral salt spray resistance of paints and varnishes, the corrosion damage of the coating on the test panel surface after the salt spray resistance test is tested.

[0074] The corrosion damage of the coating on the test panel surface after the humidity and heat resistance test was tested according to GB-T 1740-2007.

[0075] According to GB / T 2423 "Basic Environmental Testing Procedures for Electrical and Electronic Products", the coating's corrosion damage to the test panel surface after the thermal shock test was tested. The results are shown in Table 5 below:

[0076] Table 5: Performance test of the products of the examples and comparative examples

[0077]

[0078]

[0079] As shown in the table above, the coating without a tackifier and an uncapped base exhibits poor adhesion and resistance to high temperature, high humidity, salt spray, and thermal shock. However, the coating with the addition of a tackifier exhibits good adhesion on several complex circuit boards. Compared to commercially available products and comparative examples, the coating exhibits superior corrosion resistance and protective properties in salt spray, thermal shock, and high temperature and humidity tests. All protective properties are superior to those of commercially available products.

[0080] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A silicone conformal coating, characterized in that: The invention comprises the following raw materials in parts by weight: 35-75 parts of base rubber, 2-20 parts of viscosity modifier, 0.5-10 parts of tackifier, 0.5-5 parts of cross-linking agent, 0.1-1.5 parts of coupling agent, 0.5-10 parts of reinforcing agent, 0.5-5 parts of catalyst; The base glue is a capped hydroxyl-terminated polysiloxane; the tackifier is a reactant of 3-isocyanate propyl trimethoxy silane, 3-hydroxypropionic acid, and 3-ethyl-3-oxetane methanol; the mass ratio of 3-isocyanate propyl trimethoxy silane, 3-hydroxypropionic acid, and 3-ethyl-3-oxetane methanol is 10:1.5-4:1.5-4; The preparation method of the tackifier is as follows: under nitrogen protection, 3-isocyanate propyltrimethoxysilane, 3-hydroxypropionic acid and 3-ethyl-3-oxetanol are mixed, nitrogen is filled and sealed, stirred, and the temperature is raised to 60° C. to 80° C. for reaction and then discharged to obtain the tackifier.

2. The silicone conformal coating according to claim 1, characterized in that: The base glue is a substance obtained by capping terminal hydroxyl polysiloxane and methyl orthosilicate under the catalysis of alkali metal salt.

3. The silicone conformal coating according to claim 2, characterized in that: The alkali metal salt is selected from one or more of lithium carbonate, sodium carbonate and potassium carbonate.

4. The silicone conformal coating according to claim 2, characterized in that: The molar ratio of the terminal hydroxyl polysiloxane to methyl orthosilicate is 1:1.5-2.

5.

5. The organic silicone conformal coating according to claim 1, characterized in that: The base glue has a viscosity of 100 to 1000 cps at 25°C.

6. The organic silicone conformal coating according to claim 1, characterized in that: The organosilicon conformal coating also includes a fluorescent indicator, and the fluorescent indicator is present in an amount of 0.05 to 0.2 parts.

7. The silicone conformal coating according to claim 1, characterized in that: The viscosity modifier is methyl silicone oil, and the viscosity of the methyl silicone oil at 25° C. is 100 to 500 cps; the crosslinking agent is selected from one or more of methyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, and phenyltrimethoxysilane; the reinforcing agent is selected from one or more of nano-calcium carbonate, silicon dioxide, and nano-silicon powder; the coupling agent is selected from one or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-aminopropyltrimethoxysilane; and the catalyst is selected from one or more of di(ethyl acetoacetate) diisopropyl titanate, di(ethyl acetoacetate) di-n-butoxy titanate, di(ethyl acetoacetate) diisobutyl titanate, and di(acetylacetonato)ethoxyisopropoxy titanate.

8. The method for preparing the organosilicon conformal coating according to any one of claims 1 to 7, wherein: The following steps are involved: Under nitrogen protection throughout the process, add the base rubber, viscosity regulator, tackifier, cross-linking agent and coupling agent into the reactor, stir evenly at 10℃~30℃, then add the reinforcing agent and fluorescent indicator and stir evenly, then add the catalyst, stir evenly and discharge the material, filter and obtain the silicone coating.

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