A two-component waterborne polyurethane coating for three-proof paint machine coating and preparation method thereof

Abstract

The invention discloses a two-component waterborne polyurethane coating for three-proof paint machine coating, comprising a component A and a component B, wherein, by weight, the component A comprises the following raw materials in parts by weight: waterborne hydroxy acrylic dispersion: 25.0-35.0 parts; anionic polyacrylate dispersion: 15.0-25.0 parts; organosilicon-modified styrene acrylic emulsion: 20.0-30.0 parts; silica sol: 3.5-6.5 parts; cosolvent: 3.6-7.8 parts; functional additive: 0.7-2.9 parts; water: 6.0-15.0 parts; by weight, the component B comprises the following raw materials in parts by weight: aliphatic polyisocyanate: 70.0-90.0 parts; propylene glycol diacetate: 15-25 parts. The two-component water-based polyurethane three-proof paint product used for three-proof paint machine coating has the advantages of waterproof, moisture-proof, mildew-proof, salt spray resistance, high hardness, high gloss, high transparency, resistance to cold and hot shocks, scratch resistance, strong adhesion, long activation period, no blistering when thickly coated, health and environmental protection, etc., and can be used to protect electronic circuit boards and their components.

Description

Technical Field

[0001] The invention belongs to the technical field of water-based coatings, and particularly relates to a two-component water-based polyurethane coating for three-proof paint machine coating and a preparation method thereof. Background Art

[0002] As an important electronic component in electronic instruments, PCB (printed circuit board) should have good waterproof, moisture-proof, corrosion-resistant, electrical insulation and other properties. Under this background, three-proof paint came into being. The "three-proof" of three-proof paint refers specifically to three special protective properties, however, the connotation of "three-proof" has different interpretations. The current more popular saying is that "three-proof" refers to the three major properties of waterproof, moisture-proof and dust-proof, but there are also three major protective properties of moisture-proof, mildew-proof and salt spray-proof. Regardless of which connotation of the "three-proof" performance, the three-proof paint must have waterproof, moisture-proof, mildew-proof, salt spray-proof, aging-resistant, cold and hot shock-resistant, radiation-resistant, ozone corrosion-resistant, vibration-resistant, good flexibility, strong adhesion and other properties in daily applications.

[0003] According to the different types of solvents, conformal coatings can be divided into solvent-based conformal coatings and water-based conformal coatings. The conformal coatings currently widely used in the market are still traditional solvent-based conformal coatings. Solvent-based conformal coatings use organic solvents such as toluene, xylene and halogenated hydrocarbons as diluents, which are harmful to human health, pollute the environment, and are flammable and explosive. There are great safety hazards during production, transportation and storage. Water-based conformal coatings are increasingly popular among companies and the public in the field of circuit board corrosion protection because they use water as a diluent, are non-flammable and non-explosive, are healthy and environmentally friendly, and are easy to operate.

[0004] The existing water-based conformal paints mainly include water-based acrylic paint, water-based epoxy paint, water-based polyurethane paint, water-based silicone paint and other types. Water-based acrylic paint has poor wear resistance and chemical resistance, and is prone to hot stickiness and cold brittleness; water-based epoxy paint has large stress and is prone to cracking and deformation; water-based silicone paint has good weather resistance, but slightly poor moisture resistance. Water-based polyurethane paint has extremely high flexibility and chemical resistance, and retains the excellent properties of traditional solvent-based polyurethane such as high and low temperature resistance and moisture resistance. Its flexibility is better than acrylic and epoxy, and its moisture resistance is better than silicone. However, water-based one-component polyurethane conformal paint has weak performance in adhesion and salt spray resistance, and its mechanical properties such as hardness and scratch resistance need to be improved.

[0005] Two-component waterborne polyurethane paint has the performance advantages of waterborne single-component polyurethane three-conformal paint in terms of flexibility, chemical resistance, high and low temperature resistance, moisture and heat resistance, electrical insulation, etc., and perfectly makes up for the performance deficiencies of waterborne single-component polyurethane three-conformal paint in terms of adhesion, salt spray resistance, hardness, scratch resistance, etc., which is the direction that many coating workers and researchers in the electronics industry are actively exploring. However, when the existing two-component waterborne polyurethane paint is used to coat PCBs, there are two common construction problems: First, the activation period (i.e., the applicable period) of the two-component waterborne polyurethane paint is short. The activation period of the commonly used two-component waterborne polyurethane paint on the market is 2h-4h, while the activation period of the three-conformal paint required by the three-conformal paint special coating equipment (also known as "three-conformal paint machine") is ≥8h. Second, there is the problem of blistering when thickly coated. The two-component water-based polyurethane paint commonly used on the market has a maximum paint film thickness of 20μm in one-time coating without blistering; while the paint film thickness required by the special coating equipment for triple-conformal paint (also known as "three-conformal paint machine") is ≥40μm in one-time coating without blistering. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a two-component waterborne polyurethane coating for three-proof paint machine coating and a preparation method thereof. The two-component waterborne polyurethane three-proof paint product for three-proof paint machine coating has the advantages of waterproof, moisture-proof, mildew-proof, salt spray resistance, high hardness, high gloss, high transparency, resistance to cold and hot shock, scratch resistance, strong adhesion, long activation period (also called applicable period), no blistering when thickly coated, health and environmental protection, etc., and can be widely used in the protection of electronic circuit boards and their components.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions:

[0008] A two-component waterborne polyurethane coating for three-proof paint machine coating comprises a component A and a component B, wherein, in parts by weight, the component A comprises the following raw materials in parts by weight: waterborne hydroxy acrylic dispersion: 25.0-35.0 parts; anionic polyacrylate dispersion: 15.0-25.0 parts; organosilicon-modified styrene acrylic emulsion: 20.0-30.0 parts; silica sol: 3.5-6.5 parts; cosolvent: 3.6-7.8 parts; functional additive: 0.7-2.9 parts; water: 6.0-15.0 parts; in parts by weight, the component B comprises the following raw materials in parts by weight: aliphatic polyisocyanate: 70.0-90.0 parts; propylene glycol diacetate: 15-25 parts.

[0009] Preferably, the equivalent molar ratio of the -NCO functional group in the A component to the -OH functional group in the B component is 1.1-1.3.

[0010] Preferably, the solid content of the aqueous hydroxylated acrylic dispersion is 40 wt% to 50 wt%, and the hydroxyl content based on the solid content is 3.5 wt% to 4.0 wt%.

[0011] Preferably, the solid content of the anionic polyacrylate dispersion is 45 wt%-55 wt%, and the hydroxyl content based on the solid content is 3.5 wt%-4.0 wt%.

[0012] Preferably, the concentration of SiO2 in the silica sol is 30wt%-35wt%, the pH value is 9-11, and the average particle size is 10-15nm.

[0013] Preferably, the cosolvent is composed of propylene glycol butyl ether and dipropylene glycol methyl ether in a weight ratio of (3.0-6.0): (0.6-1.8). The mixed cosolvent mixed in the above weight ratio has strong solubility and compatibility, and can significantly improve the spreadability and wetting effect of the two-component waterborne polyurethane coating on the PCB substrate, improve the leveling of the paint film, and enhance the gloss and transparency of the paint film.

[0014] Preferably, the functional additive includes at least one of a neutralizer, a dispersant, a wetting agent, a defoamer, a leveling agent, a mildew preventer and a bactericide.

[0015] Preferably, the functional additives are neutralizers, dispersants, wetting agents, defoamers, leveling agents, mildew inhibitors and bactericides in a weight ratio of (0.1-0.5): (0.1-0.3): (0.1-0.3)(0.1-0.3): (0.1-0.5): (0.1-0.5): (0.1-0.5).

[0016] Preferably, the component A further comprises a fluorescent indicator, and the weight proportion of the fluorescent indicator is 1.5-2.5 parts.

[0017] Preferably, the aliphatic polyisocyanate is composed of a hydrophilic aliphatic polyisocyanate and a lipophilic aliphatic polyisocyanate in a weight ratio of (30-40): (40-50).

[0018] Another object of the present invention is to provide a method for preparing the above-mentioned two-component waterborne polyurethane coating for three-proof paint machine coating:

[0019] A method for preparing the two-component waterborne polyurethane coating for coating with a conformal coating machine as described above comprises the following steps: (1) preparing component A: mixing the respective formulas of component A and dispersing them to obtain component A;

[0020] (2) Preparation of component B: After mixing the various formulas of component B, filtering, component B is obtained;

[0021] (3) Component A and component B are uniformly mixed according to an NCO / OH equivalent ratio of n(-NCO):n(-OH)=1.1-1.3, and the mixture is allowed to stand.

[0022] Preferably, the component A obtained after dispersion in step (1) has an Iwata No. 2 cup viscosity of 30-40s / 23±0.5°C.

[0023] The application of the two-component waterborne polyurethane coating as described above in the coating of the conformal coating machine.

[0024] The beneficial effects of the present invention are:

[0025] (1) The two-component waterborne polyurethane coating for three-proof paint machine coating of the present invention has strong paint film adhesion, high paint film hardness, good scratch resistance, and the properties such as breakdown voltage, dielectric constant and volume resistivity all meet the index requirements.

[0026] (2) The two-component waterborne polyurethane coating for conformal coating machine coating of the present invention has an extremely long activation period, which far exceeds the activation period index (2h) of conventional two-component waterborne polyurethane coatings, and can be used for more than 10h, meeting the activation period index (8h) required for conformal coating machine coating, and is suitable for promotion and use on conformal coating machines.

[0027] (3) The paint film of the two-component waterborne polyurethane coating for three-proof paint machine coating of the present invention has excellent resistance to cold and heat shock, salt spray, high temperature and high humidity, acid and alkali, and corrosive gas. There is no corrosion, bubbles, shedding, or white spots on the paint film surface during the inspection process. The product has good resistance to artificial aging. The paint film does not bubble, peel, or crack after 1000 hours; powdering ≤1 level; discoloration ≤2 level. The anti-mildew performance of the product meets the requirements of GB / T 1741-2007 indicators, and the inspection results are qualified.

[0028] (4) The content of volatile organic compounds (VOC) of the two-component waterborne polyurethane coating for coating with a conformal coating machine of the present invention is effectively controlled within 100 g / L, and is a truly healthy and environmentally friendly waterborne coating product. The two-component waterborne polyurethane coating for coating with a conformal coating machine of the present invention belongs to a two-component waterborne polyurethane paint, which has the performance advantages of a waterborne single-component polyurethane conformal coating in terms of flexibility, chemical resistance, high and low temperature resistance, moisture resistance, electrical insulation, etc., and makes up for the performance deficiencies of a waterborne single-component polyurethane conformal coating in terms of adhesion, salt spray resistance, hardness, scratch resistance, etc., and successfully solves the common problems of a short activation period and easy blistering of a one-time thick coating of a two-component waterborne polyurethane coating for coating with a conformal coating machine. It is an environmentally friendly waterborne conformal coating that can be automatically coated by a conformal coating machine and is widely used for the protection of PCB boards or LED display motherboards. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments.

[0030] Embodiment 1-5:

[0031] A method for preparing a two-component waterborne polyurethane coating for three-proof paint machine coating comprises the following steps:

[0032] (1) Preparation of component A (main paint): Add water-based hydroxy acrylic dispersion, anionic polyacrylate dispersion, propylene glycol butyl ether, dipropylene glycol methyl ether, neutralizer, dispersant, silicone-modified styrene acrylic emulsion, wetting agent, defoamer, leveling agent, fluorescent indicator, mildew inhibitor, bactericide, silica sol and water to the dispersion tank according to weight proportion, and disperse at medium speed for 30-40 minutes at a speed of 800-1200r / min. Take samples to test the viscosity of the finished product until the Iwata No. 2 cup viscosity of the finished product is 30-40s / 23±0.5℃, and then component A is obtained;

[0033] (2) Preparation of component B (curing agent): Add hydrophilic aliphatic isocyanate, lipophilic aliphatic isocyanate and propylene glycol diacetate in a dispersion tank according to weight proportions, disperse at medium speed for 10-20 minutes at a speed of 800-1200 r / min, filter and package to obtain component B;

[0034] (3) Preparation of a two-component waterborne polyurethane coating for conformal coating machine coating: Component A (main paint) and component B (curing agent) were uniformly mixed at an NCO / OH equivalent ratio of n(-NCO):n(-OH)=1.1-1.3, and allowed to stand for 15 minutes.

[0035] The raw materials used in Examples 1-5 are all commercially available, wherein the raw materials in component A are:

[0036] Water-based hydroxyl acrylic dispersion: AQUAPAC-8240 resin provided by Jiangsu Fuqisen New Materials Co., Ltd. AQUAPAC-8240 is a water-based hydroxyl acrylic dispersion that can be flexibly matched with water-based curing agents and oil-based curing agents. The solid content is (45±1)%, and the hydroxyl content (based on solids) is 3.9%. The water-based hydroxyl acrylic dispersion resin has the advantages of high hydroxyl content, high gloss, high fullness, and excellent water resistance.

[0037] Anionic polyacrylate dispersion: provided by Covestro Polymers (China) Co., Ltd. A2646, A2646 is a water-based hydroxyl acrylic dispersion with excellent flexibility and outstanding impact resistance. The solid content is (48-51)%, and the hydroxyl content (based on solid content) is 3.8%. This anionic polyacrylate dispersion has excellent mechanical properties and chemical resistance, high gloss, high hardness, scratch resistance, impact resistance and other advantages. This resin is mixed with the base resin AQUAPAC-8240 in component A of the present invention to significantly improve the flexibility of the paint film and further enhance the chemical resistance of the product.

[0038] Silicone-modified styrene-acrylic emulsion: HMP-3202 resin provided by Guangdong Haishun New Material Technology Co., Ltd. HMP-3202 is a silicon-modified styrene-acrylic emulsion. Due to its unique silicon modification, it has excellent weather resistance and water resistance. The resin has a short-circuit glass transition temperature Tg, high coating gloss, good transparency, and excellent salt spray resistance. The silicone-modified styrene-acrylic emulsion is compatible with the base resin AQUAPAC-8240 in component A of the present invention. A2646 and other resins have good compatibility. It is particularly worth mentioning that the addition of the silicon-modified styrene acrylic emulsion can greatly prolong the activation period (≥10h) of the two-component waterborne polyurethane coating of the present invention, and effectively solve the problem of easy blistering of the two-component waterborne polyurethane three-proof paint after one-time thick coating. The thickness of the paint film without blistering after one-time coating is ≥40μm.

[0039] Neutralizer: dimethylethanolamine.

[0040] Dispersant: BYK-190 dispersant.

[0041] Wetting agent: SN-1070 oil-resistant wetting agent provided by Guangzhou Sino Environmental Protection Materials Co., Ltd. SN-1070 is a non-silicone polymer oil-resistant agent. It is particularly effective for oil-pit shrinkage caused by defoaming agents, release agents, and oil stains on the surface of substrates. It can strongly reduce the surface tension of the system, thereby providing strong substrate wetting and anti-pollution capabilities, and providing reliable wetting and leveling effects in most polluted environments without affecting recoating properties.

[0042] Defoaming agent: BYK-024 defoaming agent provided by Dongyang Chemical (Hong Kong) Co., Ltd.

[0043] Leveling agent: TEGO Glide 450 leveling agent.

[0044] Fluorescent indicator: A water-based fluorescent indicator made by Zhongshan Blue Ocean Water-based Paint Co., Ltd. The preparation scheme of the water-based fluorescent indicator is as follows: the solid fluorescent brightener CBS-X provided by BASF New Materials Co., Ltd. is used as the solute, which is dispersed in water at a high speed to form a uniform and stable fluorescent indicator liquid with a concentration of 2%.

[0045] Antifungal agent: FUNGIPO-351 antifungal agent provided by Lian Gu Fine Chemical Co., Ltd.

[0046] Fungicide: ACTICIDE EW-PASTE, a water-based fungicide provided by THOR UK.

[0047] Silica sol: S-1430B provided by Guangdong Huihe Silicon Products Co., Ltd. The concentration of S-1430B silica sol (SiO2%) is 30.12%, the pH value is 10.05, and the average particle size is 13.2nm. The use of this silica sol in component A can significantly improve the high temperature resistance and anti-aging properties of the paint film.

[0048] The raw materials in component B are:

[0049] Hydrophilic aliphatic polyisocyanate: Bayhydur XP2655 provided by Covestro Polymers (China) Co., Ltd. Bayhydur XP 2655 is Covestro's third-generation sulfonate-modified HDI trimer. It is a hydrophilic aliphatic polyisocyanate based on hexamethylene diisocyanate (HDI) with a balance between moderate hydrophilicity and high functionality. The water-based two-component polyurethane coating prepared using Bayhydur XP 2655 has the characteristics of fast drying and fast hardening. The paint film has high final hardness and excellent chemical resistance. Manual stirring can be achieved without the need for co-solvents, which is more convenient to operate and more evenly dispersed, and can significantly improve the compatibility of the polyisocyanate curing agent with the hydroxyl component.

[0050] Lipophilic aliphatic isocyanate: Desmodur N3900 provided by Covestro Polymers (China) Co., Ltd. Desmodur N 3900 is a low-viscosity aliphatic polyisocyanate resin containing hexamethylene diisocyanate (HDI). It is an excellent lipophilic polyisocyanate that can significantly improve the chemical resistance and weather resistance of the paint film.

[0051] The amounts of component A and component B of the two-component waterborne polyurethane coating for machine coating of the three-proof coating of Examples 1-5 are shown in Table 1;

[0052] The viscosity of component A in the two-component waterborne polyurethane coating for machine coating of conformal coating of Examples 1-5 and the molar ratio of NCO / OH when component A and component B are mixed are shown in Table 2.

[0053] Table 1: Amount of component A and component B in the two-component waterborne polyurethane coating for machine coating of three-proof paint in Examples 1-5 (parts by weight)

[0054]

[0055] Table 2: Viscosity of component A in the two-component waterborne polyurethane coating for machine coating of three-proof paint in Examples 1-5 and the molar ratio of NCO / OH when component A and component B are mixed

[0056]

[0057] Test example:

[0058] The two-component waterborne polyurethane coating for machine coating of the conformal coating prepared in Examples 1-5 of the present invention and the commercially available one-component waterborne acrylic conformal coating were subjected to coating construction and performance testing.

[0059] Construction substrate and surface treatment. The coating substrate is a packaged mainboard such as a PCB board or LED display screen. Both the front and back of the board need to be coated. Before coating, stains on the board surface need to be removed and it must be dust-free, clean and dry.

[0060] Coating process: Use a special three-proof paint machine for coating construction, the number of coating layers is 1-2; the dry film thickness of the paint film is controlled at 30-40μm / pass; the total thickness of the dry film of the paint film is controlled at 40-60μm.

[0061] The temperature and drying time of the paint film curing environment. For coating with a conformal coating machine, the temperature of the drying oven is set to 80°C, and the time for the wet paint film to pass through the drying oven is set to 5 minutes; after the paint film comes out of the drying oven, it is left to dry at room temperature for 2 hours before the next coat of coating can be applied, or the coated workpiece can be directly packaged.

[0062] The test results are shown in Table 3.

[0063] Table 3: Performance test results

[0064]

[0065]

[0066] From the test results in Table 3, it can be seen that the activation period of the two-component waterborne polyurethane coating for three-conformal coating machine coating of the present invention is more than 10 hours, which is far longer than the activation period index (2 hours) of the conventional two-component waterborne polyurethane coating, and meets the activation period index (8 hours) required for three-conformal coating machine coating, and is suitable for promotion and use on three-conformal coating machines;

[0067] After the two-component waterborne polyurethane coating for machine coating of the present invention is made into a paint film of 40-60 μm, it will not bubble, peel or crack after 1000 hours; the powdering is ≤1 level; the discoloration is ≤2 level. The anti-mildew performance of the product meets the requirements of GB / T 1741-2007 index, and the inspection result is qualified;

[0068] The content of volatile organic compounds (VOC) of the two-component waterborne polyurethane coating for three-proof paint machine coating of the present invention is effectively controlled within 100g / L, and it is a truly healthy and environmentally friendly waterborne coating product;

[0069] The two-component waterborne polyurethane coating for three-proof paint machine coating of the present invention has an adhesion of ≤1 level, a hardness of up to H level, strong paint film adhesion, high paint film hardness, good scratch resistance, and properties such as breakdown voltage resistance, dielectric constant and volume resistivity, all of which meet index requirements.

[0070] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A two-component waterborne polyurethane coating for three-proof paint machine coating, characterized in that: The invention comprises component A and component B, wherein the component A comprises the following raw materials in parts by weight: Water-based hydroxy acrylic dispersion: 25.0-35.0 parts; Anionic polyacrylate dispersion: 15.0-25.0 parts; Silicone modified styrene acrylic emulsion: 20.0-30.0 parts; Silica sol: 3.5-6.5 parts; Solvent: 3.6-7.8 parts; Functional additives: 0.7-2.9 parts; Water: 6.0-15.0 parts; The water-based hydroxy acrylic dispersion is AQUAPAC-8240 resin; the anionic polyacrylate dispersion is Bayhydrol® A2646; the silicone-modified styrene acrylic emulsion is HMP-3202 resin; the silica sol is S-1430B; the cosolvent is composed of propylene glycol butyl ether and dipropylene glycol methyl ether in a weight ratio of (3.0-6.0): (0.6-1.8); the functional additives are neutralizer, dispersant, wetting agent, defoamer, leveling agent, mildew inhibitor and bactericide in a weight ratio of (0.1-0.5): (0.1-0.3): (0.1-0.3): (0.1-0.3) :(0.1-0.5):(0.1-0.5):(0.1-0.5), the neutralizer is dimethylethanolamine, the dispersant is BYK-190 dispersant, the wetting agent is SN-1070 oil-resistant wetting agent, the defoamer is BYK-024 defoamer, the leveling agent is TEGOGlide450 leveling agent, the mildewproof agent is FUNGIPOL-351 mildewproof agent, and the fungicide is ACTICIDEEW-PASTE; In terms of weight parts, the component B includes the following raw materials in weight parts: Aliphatic polyisocyanate: 70.0-90.0 parts; Propylene glycol diacetate: 15-25 parts.

2. A two-component waterborne polyurethane coating for machine coating of conformal coating according to claim 1, characterized in that: The equivalent molar ratio of the -NCO functional group in the A component to the -OH functional group in the B component is 1.1-1.

3.

3. The two-component waterborne polyurethane coating for three-proof coating machine coating according to claim 1, characterized in that: The aqueous hydroxylated acrylic dispersion has a solid content of 40 wt % to 50 wt %, and a hydroxyl content based on the solid content of 3.5 wt % to 4.0 wt %.

4. The two-component waterborne polyurethane coating for three-proof coating machine coating according to claim 1, characterized in that: The anionic polyacrylate dispersion has a solid content of 45 wt % to 55 wt %, and a hydroxyl content based on the solid content of 3.5 wt % to 4.0 wt %.

5. The two-component waterborne polyurethane coating for machine coating of conformal coating according to claim 1, characterized in that: The aliphatic polyisocyanate is composed of a hydrophilic aliphatic polyisocyanate and a lipophilic aliphatic polyisocyanate in a weight ratio of (30-40): (40-50).

6. A method for preparing a two-component waterborne polyurethane coating for machine coating of conformal coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) Preparation of component A: Mix the various formulas of component A and disperse them to obtain component A; (2) Preparation of component B: Mix the various formulas of component B and filter to obtain component B; (3) Mix component A and component B evenly according to the NCO / OH equivalent ratio of n(-NCO):n(-OH)=1.1-1.3, and let it stand.

7. Use of the two-component waterborne polyurethane coating according to any one of claims 1 to 6 in coating with a conformal coating machine.

Images