A protective coating agent for flexible circuit boards

Abstract

The present invention discloses a protective coating agent for flexible circuit boards, which is composed of a modified fluoropolymer and a dissolving component. The modified fluoropolymer is composed of a fluoroester monomer, a first unsaturated comonomer, a second unsaturated comonomer and a fluorine-modified monomer. The protective coating agent for flexible circuit boards of the present invention has excellent hydrophobicity and oleophobicity, corrosion resistance, recoatability and good heat dissipation effect.

Description

Technical Field

[0001] The present invention relates to the technical field of high-end electronic component protection, and in particular to a protective coating agent for a flexible circuit board. Background Art

[0002] Flexible printed circuit boards, also known as FPCs, are printed circuits made from a flexible insulating substrate. As the fastest-growing subsector within the PCB industry, FPCs are poised for positive development. Compared to rigid circuit boards, flexible circuit boards, made from polyimide or polyester film substrates, can bend, wind, and fold freely, withstand millions of dynamic bends without damaging the conductors, and can be freely arranged to meet spatial layout requirements and moved and extended in three dimensions, achieving integrated component assembly and conductor connection.

[0003] Due to the thinness and flexibility of FPCs, Apple has been using them extensively since the iPhone 4 to replace rigid boards in various applications, including antennas, cameras, display modules, and touchscreen modules. Following Apple's lead, Samsung and domestic smartphone manufacturers have also begun increasing their use of FPCs. Innovations in smartphones are driving rapid growth in FPC usage, fueled by new technologies such as wireless charging, OLED and full-screen displays, and high-end automotive electronics such as dashboard displays, audio systems, and monitors, as well as the increasingly popular wearable electronics. Just as OLEDs replaced LEDs, FPCs will also replace some high-end PCBs on a large scale.

[0004] Flexible printed circuits (FPCs) are often subject to environmental damage during use, including exposure to corrosion, moisture, perspiration, high temperature and humidity, irregular vibration, bending and stretching, and other factors. Unprotected electronic components can easily corrode and short-circuit, paralyzing electrical systems and causing significant losses. These complex operating environments place increasingly stringent demands on FPCs.

[0005] Currently, surface protective coatings, known as "conformal coatings," are commonly used to extend the lifespan of PCBs. Conformal coatings, applied to circuit boards, provide multiple layers of protection against moisture, dirt, salt spray, and insulation, ultimately increasing their stability, safety, and service life. Traditional conformal coatings, such as polyurethane, silicone, and epoxy resin, are relatively inexpensive, but their coating thicknesses typically exceed 20 to 50 microns or even higher, increasing overall costs and failing to align with the modern trend toward lightweight and miniaturized electronic components. Furthermore, heat dissipation from these coatings has become a major pain point for integrated circuits, leading to their gradual decline in use.

[0006] For example, patent CN104073101A is a fluorine-free conformal coating that combines the advantages of silicone resins and acrylic resins. The system has good compatibility, and the addition of ocimene aids film formation. It is a water-based coating that fully adheres to flexible circuit boards and resists cracking during vibration and bending. However, the coating is too thick, which significantly impairs heat dissipation at the flexible surface and solder joints. Furthermore, the organic solvent-based eutectic system is difficult to remove, is environmentally unfriendly, and is difficult to remove and repair.

[0007] For example, patent CN 115873503 A discloses a silicone conformal coating for flexible circuit boards, its preparation method, and its application. Tertiary amine pyridine rings are grafted onto a methyl vinyl MQ silicone resin and chemically integrated into the silicone backbone via hydrosilylation, ensuring a stronger bond between the tertiary amine pyridine rings and the polyimide film of the flexible circuit board. This silicone conformal coating is colorless, transparent, solvent-free, and has low viscosity. It also exhibits low hardness and excellent toughness, ensuring it withstands the high-frequency and high-intensity bending conditions of flexible circuit boards without cracking or delamination, providing long-lasting and effective protection. The disadvantages are: (1) it cannot be re-coated and repaired; (2) the silicone oil, hydrogenated silicone oil and siloxane therein have low activity due to the influence of the silicon-based main chain, and the monomer conversion is not complete, resulting in small molecular monomers and metal catalyst residues, which have a great impact on corrosion resistance and dielectric properties; (3) due to the presence of silane alkoxy groups that react with air and moisture, the technical difficulty in production and storage is increased, and self-crosslinking during synthesis and unstable storage are prone to problems; (4) the high viscosity leads to a large coating thickness, which is not conducive to heat dissipation, especially not conducive to the use of high-frequency heat dissipation in connectors of precision equipment.

[0008] Fluororesin protective coatings have garnered significant attention in recent years due to their excellent electrical isolation, hydrophobicity, and excellent corrosion resistance. However, these common fluororesin protective coatings are primarily designed for rigid PCBs. Their high film hardness makes them susceptible to internal stress, which can cause peeling or cracking when subjected to external forces, making them unsuitable for use on FPCs.

[0009] For example, patent CN116239924A discloses an electronic-grade protective agent containing a fluoropolymer and a volatile solvent. The raw materials for the fluoropolymer include fluoromonomers and unsaturated non-fluoromonomers, with the fluoromonomers comprising perfluoropolyether monomers and fluoroalkyl monomers. This agent exhibits excellent hydrophobicity and oleophobicity, as well as corrosion resistance, effectively preventing damage to the protected products during production and use in harsh environments, water vapor contamination, and chemical corrosion. Furthermore, the electronic protective agent can be repaired and re-coated. However, the fluoroalkyl monomers in this coating agent are rigid, and the comonomers also exhibit rigidity. While this coating is effective on rigid PCBs, its durability is limited when used in flexible printed circuit boards (FPCs).

[0010] Based on the analysis of existing technologies, most of the existing "three-proof" coating agents are only suitable for rigid PCB boards, and generally have defects such as high rigidity, high coating thickness that makes heat dissipation difficult, high cross-linking density that makes it difficult to repair and recoat, and lack of visual leak detection. These defects make it difficult to apply them to the long-term use protection of increasingly sophisticated, miniaturized, and high-end flexible circuit boards (FPCs). Summary of the Invention

[0011] The purpose of the present invention is to overcome the practical problems of the existing "three-proof" coating agents in the FPC, such as poor continuous protection, easy falling off and cracking, difficulty in heat dissipation, inability to visually detect leaks and poor recoating properties, and to provide a flexible circuit board protective coating agent.

[0012] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a flexible circuit board protective coating agent, composed of a modified fluoropolymer and a dissolved component, wherein the modified fluoropolymer is composed of a fluoroester monomer, a first unsaturated comonomer, a second unsaturated comonomer and a fluorine-modified monomer.

[0013] As a preferred embodiment of the present invention, the weight percentage of the modified fluoropolymer is 0.5-20%.

[0014] As a preferred embodiment of the present invention, the weight average molecular weight of the modified fluoropolymer is 10,000-500,000.

[0015] As a preferred embodiment of the present invention, based on the total weight of the modified fluoropolymer, the total content of the first unsaturated comonomer and the second unsaturated comonomer is 4.5-35%, and the content of the fluorine-modified monomer is 0.5-5%.

[0016] As a preferred embodiment of the present invention, the structural formula of the fluoroester monomer is:

[0017]

[0018] Wherein, PFPE represents a perfluoropolyether group, R1 is one of H, CH3, CH2CH3, and Cl, and R1 is more preferably H or Cl.

[0019] As a preferred embodiment of the present invention, the perfluoropolyether group is one of Z-type, Y-type, K-type and D-type, and its weight average molecular weight is 500-3000.

[0020] As a preferred embodiment of the present invention, the first unsaturated comonomer is an unsaturated monomer containing a polyether group, the second unsaturated comonomer is one or both of N-(methoxymethyl)methacrylamide and acrylamide, and the weight ratio of the first unsaturated comonomer to the second unsaturated comonomer is 0.8-2:1.

[0021] As a preferred embodiment of the present invention, the first unsaturated comonomer is one or more of polyethylene glycol methyl ether (meth)acrylate, isopentenyl polyethylene glycol ether, hydroxybutyl vinyl polyethylene glycol ether, and ethoxy vinyl polyethylene glycol ether with a weight average molecular weight of 600-1500.

[0022] As a preferred embodiment of the present invention, the structural formula of the fluorine-modified monomer is:

[0023]

[0024] Wherein Rf is one of 2-fluorophenol, 3-fluorophenol, 4-fluorophenol, 4-trifluoromethylphenol, and pentafluorophenol groups.

[0025] As a preferred embodiment of the present invention, the dissolving component is selected from one or more of HFE-7200, HFE-7100, HFE-347, HFE-458, HFE-374, HFE-449 and HFE-356mec.

[0026] The flexible circuit board protective coating agent of the present invention is composed of a modified fluoropolymer and a dissolved component, wherein the modified fluoropolymer is composed of a fluoroester monomer, a first unsaturated comonomer, a second unsaturated comonomer and a fluorine-modified monomer. The present invention does not limit the specific preparation method of the modified fluoropolymer, which can be a conventional solution polymerization and emulsion polymerization in the art. In a specific embodiment of the present invention, taking solution polymerization as an example, the preparation method of the fluoropolymer includes the following steps: adding the fluoroester monomer and the first unsaturated comonomer, the second unsaturated comonomer and the fluorine-modified monomer in proportion to a jacketed kettle with an agitator, a reflux condenser and a thermometer, then adding a solvent and an initiator, and then replacing with nitrogen to a moisture content of ≤20ppm, sealing and heating to the reaction temperature (60-90°C) and maintaining it for a specified reaction time (3-12h) to obtain a fluoropolymer solution with a certain solid content. The solvent is one or more of HFE-7200, HFE-7100, HFE-347, HFE-458, HFE-374, HFE-449, and HFE-356mec. It is understood that the specific amounts of the solvent and initiator, the specific reaction temperature, and the reaction time can be determined based on the amounts and specific selections of the fluoroester monomer, the first unsaturated comonomer, the second unsaturated comonomer, and the fluorine-modified monomer, as long as the reaction is complete. The weight percentage of the modified fluoropolymer is preferably 0.5-20%. The weight-average molecular weight of the modified fluoropolymer is preferably 10,000-500,000. If the molecular weight of the modified fluoropolymer is too small, the film-forming properties will be poor, and it will not be able to form a continuous film layer, which will have an adverse effect on the protective performance. If the molecular weight is too large, on the one hand, the solubility will be poor, the dispersion system will be uneven, or even precipitation will occur. On the other hand, the viscosity of the dispersion will be too high, which will affect the leveling properties during the film-forming process and easily cause coating defects.

[0027] The fluoroester monomer described in this invention features long-chain perfluoropolyether groups, resulting in low surface tension. During film formation, the fluorinated segments protrude toward the air due to self-stratification. As the solvent evaporates, they become relatively fixed and curl and shrink, forming a nano-convex upper film layer, resulting in exceptionally strong hydrophobic and oleophobic properties. The other end of the fluoroester monomer is an acrylate with an unsaturated group, providing a polymerizable base while also providing relatively good film-forming properties.

[0028] The first unsaturated comonomer described in the present invention is an unsaturated monomer containing a polyether group, that is, a flexible chain unsaturated monomer containing a long chain structure. After polymerization, on the one hand, it can form a large number of hydrogen bonds, and on the other hand, the flexible long chain has a certain plasticity. After film formation, it is accumulated in the lower layer with the second unsaturated comonomer due to the self-stratification effect, thereby improving the adhesion to the flexible circuit board substrate. The entanglement of the long chain can also enable the flexible circuit board to have a certain buffering effect when subjected to external forces such as vibration and bending, without stress cracking or even falling off. The first unsaturated comonomer is one or more of polyethylene glycol methyl ether (meth)acrylate, isopentenyl polyethylene glycol ether, hydroxybutyl vinyl polyethylene glycol ether, and ethoxyvinyl polyethylene glycol ether with a weight average molecular weight of 600-1500. The second unsaturated comonomer is one or both of N-(methoxymethyl) methacrylamide and acrylamide, wherein the amide group provides a hydrogen bonding site, so that after the flexible circuit board protective coating of the present invention is formed, multiple hydrogen bonds are formed between the molecules due to the presence of amide bonds, etc., which can be used as physical crosslinking points to obtain good mechanical properties and bonding strength. At the same time, it also imparts excellent self-repairing properties. It can dissociate when subjected to physical effects such as bending, vibration, and stretching. After the external force disappears, the dislocation or even the reformation of hydrogen bonds between micro-sections and the entanglement of molecular chains enable the polymer to achieve rapid and efficient self-repair. The interaction between the long molecular chains of the resin is strengthened, thereby increasing the strength of the coating and extending the service life. The weight ratio of the first unsaturated comonomer to the second unsaturated comonomer is preferably 0.8-2:1.

[0029] The fluorine-modified monomer of the present invention is a reactive monomer derived from perylene imide, and its preparation process can be simply expressed as follows (Rf is 4-trifluoromethylphenol as an example):

[0030]

[0031] The fluorine-modified monomer is a flaky structured substance having a heterocyclic structure and a perylene imide derivative structure, which can participate in the polymerization process of the modified fluoropolymer and exist in the polymer. The Rf thereof is one of 2-fluorophenol, 3-fluorophenol, 4-fluorophenol, 4-trifluoromethylphenol, and pentafluorophenol groups. After partial fluorination modification, the system compatibility of the polymer is improved, which is conducive to the formation of an overall uniform film layer during the film formation process. The flaky structure of the fluorine-modified monomer can extend the erosion path of pollutants, water vapor, chemicals, etc., thereby improving corrosion resistance. In addition, the attraction between the Rf contained in the structure and the fluoroester monomer and the large angle between the benzene ring plane and the perylene ring plane destroys the planarity of the perylene imide molecule. In addition, the large steric hindrance of the rigid fluorinated benzene ring reduces the crystallinity, causing the Rf to tend to stand upright. The interaction between the amide bond and the polar bond of the lower layer of the coating forms hydrogen bonds to relatively fix the flaky monomer to the middle layer, and also makes the coating more integrated without obvious delamination within the film, thereby strengthening the protective performance of the coating. In addition, the perylene ring in the fluorine-modified monomer of the present invention has a strong fluorescence effect, which gives the coating a special property of good detection of coating leaks. Compared with the form of externally added fluorescent components, internally added fluorescence detection is more representative and more practical.

[0032] Furthermore, existing protective agents are difficult to remove after forming a protective layer on the product. Consequently, if part of the protective layer is damaged, it is almost impossible to repair it, resulting in high costs. The protective coating formed by the flexible circuit board protective coating agent provided by the present invention has a non-chemically cross-linked structure, allowing for repair and recoating, reducing costs. Furthermore, the solvent component in the coating system is an environmentally friendly fluorocarbon solvent. It does not contain ozone-depleting atoms such as chlorine, bromine, or iodine, and has no damaging effect on the ozone layer. Its ODP value is zero, making it safe and non-toxic, and more in line with the development trend of modern green industry.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The flexible circuit board protective coating of the present invention exhibits excellent hydrophobic and oleophobic properties. The fluoroester monomers contain long-chain perfluoropolyether groups with low surface tension. During film formation, the fluorinated segments protrude toward the air due to self-stratification. As the solvent evaporates, the segments become relatively fixed and curl and shrink, forming a nano-convex upper film layer. This provides exceptional hydrophobic and oleophobic properties, protecting the safe operation of components.

[0035] 2. The flexible circuit board protective coating agent of the present invention has excellent corrosion resistance. The fluorine-modified monomer is a flaky structured substance having a heterocyclic structure and a perylene imide derivative structure. It can participate in the polymerization process of the modified fluoropolymer and exist in the polymer. After partial fluorination modification, the system compatibility of the polymer is improved, which is conducive to the formation of an overall uniform film layer during the film formation process. The flaky structure of the fluorine-modified monomer can extend the erosion path of pollutants, water vapor, chemicals, etc., thereby improving corrosion resistance. In addition, due to the attraction between the Rf contained in the structure and the fluoroester monomer and the large angle between the benzene ring plane and the perylene ring plane, the planarity of the perylene imide molecule is destroyed. In addition, the large steric hindrance of the rigid fluorinated benzene ring reduces the crystallinity, causing the Rf to tend to stand upright. The interaction between the amide bond and the polar bond of the lower layer of the coating forms a hydrogen bond to relatively fix the flaky monomer in the middle layer, making the coating more integrated without obvious stratification within the film, strengthening the protective performance of the coating, and having a good heat dissipation effect.

[0036] 3. The protective coating formed by the flexible circuit board protective coating agent of the present invention has a non-chemically cross-linked structure and is recoatable, which can be repaired and re-coated, reducing the cost of replacing components due to damage to the protective layer; at the same time, the solvent component in the coating system is an environmentally friendly fluorocarbon solvent, which is environmentally friendly, has an ODP value of zero, is safe and non-toxic, and is more in line with the development trend of modern green industry.

[0037] 4. The flexible circuit board protective coating agent of the present invention has a long service life. After film formation, multiple hydrogen bonds are formed between molecules due to the presence of amide bonds, etc., which can be used as physical cross-linking points to obtain good mechanical properties and bonding strength. At the same time, it also has excellent self-repairing properties. It can dissociate under physical effects such as bending, vibration, and stretching. After the external force disappears, the dislocation or even the reformation of hydrogen bonds between micro-sections and the entanglement of molecular chains enable the polymer to achieve rapid and efficient self-repair. The interaction between the long molecular chains of the resin is strengthened, thereby increasing the strength of the coating and extending the service life.

[0038] 5. The self-stratification effect during the film-forming process of the protective coating for flexible circuit boards of the present invention causes the fluorine-containing portion to face upward and curl and entwine to form nano-scale micro-protrusions, thereby improving the waterproof and oil-proof properties; the intermediate layer is flaky, which enhances the corrosion resistance and has a fluorescent effect. The internal addition form makes the protective coating system extremely compatible, and visual detection of coating leaks can be achieved; the highly polar chain segment portion faces downward, and has good adhesion to the flexible board; the polymer coating has a synergistic effect, and the hydrogen bonds between the amide bonds and carbon-oxygen bonds of the flaky monomers enhance the binding density of the coating, resulting in better performance.

[0039] 6. The flexible circuit board protective coating of the present invention exhibits excellent permeability, allowing it to quickly spread to form a protective film layer in areas prone to coating leaks, such as contact points and solder joints in narrow or complex structures. The modified fluoropolymer in the flexible circuit board protective coating of the present invention exhibits excellent compatibility and thixotropic flow properties. Furthermore, the use of an environmentally friendly fluorocarbon solvent forms an excellent dissolution system. The coating solution, with its sufficiently low surface tension, rapidly levels and penetrates, preventing coating leaks and providing enhanced protective performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the film-forming structure of the protective coating agent for flexible circuit boards of the present invention;

[0041] Figure 2 This is a flexible connection circuit between the motherboard and the inner screen of a domestic smartphone brand, used for performance testing;

[0042] Figure 3 This is an ICP-B-24 type circuit board used for performance testing.

[0043] In the figure: flexible board substrate 1, lower layer fluorine-free segment 2, Mi sheet structure group 3, fluorine-containing segment part 4, hydrogen bonding site 5, Rf upright structure 6. DETAILED DESCRIPTION

[0044] The technical solutions of the present invention are further clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0045] The raw materials used in the examples and comparative examples are all commercially available, some of which are described as follows:

[0046] (1) The structural formula of the fluoroester monomer Mf in the examples and comparative examples is:

[0047]

[0048] Here, PFPE represents a perfluoropolyether group.

[0049] The composition of the fluoroester monomer Mf is shown in Table 1.

[0050] Table 1 Composition of fluoroester monomer Mf

[0051] Mf PFPE Type Molecular weight Mw <![CDATA[R1]]> P-1 Z 2500 H P-2 Y 500 <![CDATA[CH3]]> P-3 K 1500 <![CDATA[CH3]]> P-4 Y 1000 <![CDATA[CH2CH3]]>

[0052] (2) The structural formula of the fluorine-modified monomer Mi in the examples and comparative examples is:

[0053]

[0054] (3) The compositions of the comonomer Mco in the examples and comparative examples are shown in Table 2.

[0055] Table 2 Composition of comonomer Mco

[0056]

[0057]

[0058] Examples 1-7

[0059] The compositions of the protective coating agent for flexible circuit boards and the modified fluoropolymer in the embodiment are shown in Table 3. The contents and proportions in Table 3 are all based on weight.

[0060] Table 3 Composition of protective coating agents and modified fluoropolymers of Examples 1-7

[0061]

[0062]

[0063] Comparative Examples 1-4

[0064] The compositions of the protective coating agent for flexible circuit boards and the modified fluoropolymer in the comparative example are shown in Table 4. The contents and proportions in Table 4 are all based on weight.

[0065] Table 4 Comparative Examples 1-4 Protective coating agent and modified fluoropolymer composition

[0066]

[0067] Performance Testing

[0068] 1. Preparation of physical and chemical properties test samples and samples:

[0069] (1) Connect the flexible connection line between the motherboard and the inner screen of a domestic smart phone ( Figure 2 ) as a test piece for bending and vibration resistance, the flexible connecting circuit sheet was cleaned with acetone, then cleaned and dried with HFE-7100, and then the flexible connecting circuit sheet was immersed in the flexible circuit board protective coating agent of the embodiment and the comparative example, and dried at room temperature to prepare a test sample for use;

[0070] (2) Install the ICP-B-24 circuit board ( Figure 3 ) was cleaned with acetone, then cleaned and dried with HFE-7100, and then the circuit board was immersed in the flexible circuit board protective coating agent of the embodiment and the comparative example, and dried at room temperature to prepare a sample for use.

[0071] 2. Test methods

[0072] (1) Appearance of protective coating: Observe the transparency of the protective coating by visual inspection or by shining a normal flashlight.

[0073] (2) Surface test of protective coating: Observe the coating surface under a 10-100x magnifying glass to see if there is any cracking or peeling.

[0074] (3) Fluorescence characteristics: Use an ultraviolet flashlight (central wavelength ≈ 365nm) to illuminate the surface of the protective coating and observe whether it has fluorescent color. If there is obvious color, mark "Y"; if there is no color or the color is not obvious, mark "N".

[0075] (4) Hydrophobicity: The static contact angle of a 2 μL water droplet was measured using a Shanghai Zhongchen JC2000D1 dynamic contact angle measuring instrument.

[0076] (5) Oleophobicity: The static contact angle of n-hexadecane with a droplet volume of 2 μL was measured using a Shanghai Zhongchen JC2000D1 dynamic contact angle measuring instrument.

[0077] (6) Saltwater corrosion resistance: The durability of the offshore environment was simulated according to the neutral salt water spray test GB / T 2423.17-2008 standard; the appearance of the samples and panels was evaluated according to the following standards: "none" if the sample or panel showed almost no change; "+" if the corrosion points or surfaces of the sample reached 1-10% of the entire sample area; "++" if the corrosion points or surfaces reached 10% or more of the entire sample area;

[0078] (7) Bending Test: Using an RW-8619S FPC bending tester, secure the FPC device and the sample coated with the protective coating agent for flexible circuit boards according to the examples and comparative examples to the tester. Bend the device at a constant speed of 50 times / min with a weight of 100 g. Bend at 0° / 90° / 180° / 0° as one degree. After 50 and 100 bends, respectively, the coating surface condition was observed under a microscope.

[0079] (8) Self-healing test: The samples that have undergone 100 bending tests are tested for surface morphology, hydrophobicity, oleophobicity, and salt spray resistance.

[0080] (9) Water vapor oscillation test: Fix the two ends of the coating sample with clamps 3-5 cm above the water surface of the SHZ-A water bath oscillator, and oscillate at a constant temperature of 60°C and 100 times / min for 800 hours to accelerate the simulation of the dynamic protection effect under high temperature transportation and temperature and humidity conditions.

[0081] (10) Connect the sample after the above test to the internal screen of the mobile phone according to the procedure, and then power on for testing. If the screen is on, mark "√"; if the screen is off, mark "×".

[0082] 3. Test results

[0083] (1) The prepared sample was subjected to the above performance test. The test results of the sample are shown in Table 4.

[0084] Table 4 Test results of coating samples

[0085] Serial number Appearance Fluorescence color rendering Hydrophobicity / oleophobicity (water / oil)° Salt spray resistance 144h Example 1 Colorless and transparent Y 117 / 69 none Example 2 Colorless and transparent Y 118 / 69 none Example 3 Colorless and transparent Y 116 / 71 none Example 4 Colorless and transparent Y 119 / 68 none Example 5 Colorless and transparent Y 116 / 67 none Example 6 Colorless and transparent Y 120 / 69 none Example 7 Colorless and transparent Y 117 / 67 none Comparative Example 1 Colorless and transparent Y 119 / 68 + Comparative Example 2 Colorless and transparent Y 118 / 68 + Comparative Example 3 Colorless and transparent N 118 / 67 ++ Comparative Example 4 Nearly colorless and transparent Y 118 / 67 +

[0086] (2) The prepared samples were subjected to bending resistance and water vapor shock resistance tests, and the results are shown in Table 5.

[0087] Table 5 Running performance of coating samples

[0088]

[0089]

[0090] Note: “-” means not tested.

[0091] As can be seen from the above table, the flexible circuit board protective coating agents of the embodiments all have good performance, while the comonomer in Comparative Example 1 does not add acrylamide monomers, the hydrogen bond sites are few, and the self-repair performance is significantly affected, thereby affecting the durability of use. The comonomer in Comparative Example 2 does not add long-chain polyether group monomers, the adhesion and flexibility of the coating deteriorate, and cracking and even falling off quickly occur in the bending test. In Comparative Example 3, no fluorine-modified monomer Mi is added, and the prepared protective coating has no fluorescent properties and poor corrosion resistance. Mi in Comparative Example 4 is not bonded to fluorinated phenol, the compatibility of the coating is affected to a certain extent, and the corrosion resistance also deteriorates to a certain extent. Therefore, the components and proportions of the present invention have good synergistic properties, and can only show the best performance characteristics when all components are present at the same time.

Claims

1. A protective coating agent for flexible circuit boards, comprising a modified fluoropolymer and a dissolving component, characterized in that: The modified fluoropolymer is composed of a fluoroester monomer, a first unsaturated comonomer, a second unsaturated comonomer and a fluorine-modified monomer. The structural formula of the fluoroester monomer is: Wherein, PFPE is a perfluoropolyether group, R1 is one of H, CH3, CH2CH3, and Cl, the first unsaturated comonomer is an unsaturated monomer containing a polyether group, the second unsaturated comonomer is one or both of N-(methoxymethyl)methacrylamide and acrylamide, and the structural formula of the fluorine-modified monomer is: Wherein Rf is one of 2-fluorophenol, 3-fluorophenol, 4-fluorophenol, 4-trifluoromethylphenol, and pentafluorophenol groups.

2. The protective coating agent for flexible circuit boards according to claim 1, characterized in that: The weight percentage of the modified fluoropolymer is 0.5-20%.

3. The protective coating agent for flexible circuit boards according to claim 1, characterized in that: The weight average molecular weight of the modified fluoropolymer is 10,000-500,000.

4. The protective coating agent for flexible circuit boards according to claim 1, characterized in that: Based on the total weight of the modified fluoropolymer, the total content of the first unsaturated comonomer and the second unsaturated comonomer is 4.5-35%, and the content of the fluorine-modified monomer is 0.5-5%.

5. The protective coating agent for flexible circuit boards according to claim 1, characterized in that: The perfluoropolyether group is one of Z-type, Y-type, K-type and D-type, and has a weight-average molecular weight of 500-3000.

6. The protective coating agent for flexible circuit boards according to claim 1, characterized in that: The weight ratio of the first unsaturated comonomer to the second unsaturated comonomer is 0.8-2:

1.

7. The protective coating agent for flexible circuit boards according to claim 1, characterized in that: The first unsaturated comonomer is one or more of polyethylene glycol methyl ether (meth)acrylate, isopentenyl polyethylene glycol ether, hydroxybutyl vinyl polyethylene glycol ether, and ethoxy vinyl polyethylene glycol ether with a weight average molecular weight of 600-1500.

8. The protective coating agent for flexible circuit boards according to claim 1, characterized in that: The dissolving component is selected from one or more of HFE-7200, HFE-7100, HFE-347, HFE-458, HFE-374, HFE-449 and HFE-356mec.

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