Mask-free dual-curing three-proof adhesive and preparation method thereof

Abstract

The present invention discloses a shield-free dual-curing conformal coating and a preparation method thereof. The shield-free dual-curing conformal coating comprises 40-65 parts of a main resin; 20-40 parts of an acrylate monomer; 1-5 parts of a photoinitiator; 1-5 parts of an auxiliary agent; and 1-5 parts of a rheological modifier. The main resin comprises a polyurethane acrylate prepolymer A and a polyurethane acrylate prepolymer B, and the acrylate monomer comprises a phosphate-modified acrylate monomer and two or more monofunctional acrylate monomers. The shield-free UV conformal coating provided by the present invention can achieve precise coating of the conformal coating, especially precise thick coating, without shielding, thereby improving production efficiency, reducing costs, and achieving high-precision production and processing.

Description

Technical Field

[0001] The present invention relates to the field of processing of conformal coatings, and in particular to a mask-free dual-curing conformal coating and a preparation method thereof. Background Art

[0002] Printed circuit board assemblies (PCBAs), core components of electronic devices, are often exposed to harsh environments such as high humidity, salt spray, temperature shock, and mechanical vibration. These conditions can easily lead to component corrosion, solder joint cracking, and reduced insulation performance. Coating with conformal coating (moisture-proof, salt spray-proof, and mildew-proof) is a key process for improving PCBA reliability and significantly extending the lifespan of electronic products.

[0003] Since there are areas on the PCBA that cannot be coated, such as connectors, sockets, heat sinks, high-power components, and sensors, in order to prevent these areas from being coated with glue, the existing solution is to mask the non-coated areas before spraying the conformal coating. Common masking methods include:

[0004] 1. Masking with tape, for example: the invention patent with publication number CN118791980A discloses a weather-resistant and environmentally friendly masking tape. Although this masking tape improves the coordinated balance between peelability and adhesion performance, as well as the safety and environmental performance when used in high-temperature operations compared to existing masking tape products, there may still be problems of local adhesive residue when the tape is torn off; at the same time, attaching the tape before spraying and peeling the tape after spraying both need to be done manually, which will extend the processing time of the entire process and require a lot of time to cover the device with masking tape, reducing process efficiency and increasing production costs; in addition, the sealing performance of the tape, especially at the edge of the tape, is insufficient, which may lead to masking failure.

[0005] 2. Masking with peelable adhesive, for example: the invention patent with authorization announcement number CN116496750B discloses a masking adhesive for triple-proof coating suitable for connectors, and its preparation method and application method. This method has better sealing performance than tape masking, and can use machines instead of manual glue coating or peeling of the adhesive layer, which relatively improves production efficiency. However, the coating, curing and peeling of the masking adhesive still prolongs the processing time, and there is still a risk of glue residue.

[0006] 3. Use prefabricated masking tools such as masking hoods and masking films. For example, the invention patent with authorization announcement number CN114650664B discloses a method and device for masking conformal coating of a printed circuit board. The printed circuit board can be set on the supporting surface, and the positioning structure is used to position the printed circuit board. The conformal coating can be applied to the conformal coating area through the coating port, and the limiting raised layer is used to cover the masking area. This method can improve the efficiency of conformal coating masking for specific product models, but it requires separate molds for different types of products, which is costly and inflexible. After changing the PCBA product, the masking hood must be replaced or the mold must be redesigned.

[0007] The core idea of ​​the above process is to mask key components or areas in advance, and then remove the masking parts after the conventional spraying operation is completed, so as to achieve selective spraying of PCBA. These methods inevitably increase the work and consumables of masking and removing the masking.

[0008] By improving the precise positioning performance of the three-proof adhesive, it is possible to ensure that the three-proof adhesive is accurately applied without masking adhesive, thereby achieving the effect of improving production efficiency. However, existing three-proof adhesive products are usually difficult to achieve the above effects. In particular, for some specific PCBA usage environments, in order to adapt to extreme environments such as high humidity, salt spray, high temperature and mechanical vibration, thick three-proof adhesive is required to achieve a protective effect. The thickness of the three-proof adhesive of some products even needs to reach 0.5mm-3mm. The three-proof adhesive with lower viscosity cannot achieve a larger thickness. At the same time, the fluidity of the colloid is good, and it is very easy to extend to areas that do not require glue coating, so precise glue coating cannot be achieved. The three-proof adhesive with higher viscosity is difficult to apply evenly, resulting in poor appearance or even protection failure. In addition, the existing dual-curing three-proof adhesive requires a lot of time to complete moisture curing. At the same time, the hydrophobic properties of the product after curing, especially the steam resistance, are poor, making the coating unsuitable for high temperature and high humidity environments.

[0009] Therefore, there is an urgent need to propose a shield-free UV conformal adhesive, which aims to achieve precise coating of the conformal adhesive under shielding conditions, especially precise thick coating, so as to improve production efficiency, reduce costs and achieve high-precision production and processing. Summary of the Invention

[0010] Therefore, in order to solve the above problems and achieve precise coating of conformal coating without shielding, the present invention provides.

[0011] The present invention is achieved through the following technical solutions:

[0012] The mask-free dual-curing conformal adhesive comprises the following raw material components in parts by weight:

[0013] Main resin 40-65 parts;

[0014] 20-40 parts of acrylate monomer;

[0015] 1-5 parts of photoinitiator;

[0016] 1-5 parts of additives;

[0017] 1-5 parts of rheological additive;

[0018] The main resin includes polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B, the viscosity of polyurethane acrylate prepolymer A is 9500 cps-25000 cps, the viscosity of polyurethane acrylate prepolymer B is 5000 cps-10000 cps, the mass ratio of polyurethane acrylate prepolymer A to polyurethane acrylate prepolymer B is (1-3):1, and the NCO content of polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B is both 0%-1%; the acrylate monomer includes a phosphate-modified acrylate monomer and two or more monofunctional acrylate monomers.

[0019] Preferably, the mass ratio of the monofunctional acrylate monomer to the phosphate-modified acrylate monomer is (20-50):1.

[0020] Preferably, the monofunctional acrylate monomer includes an acrylate monomer with a Tg>50°C and an acrylate monomer with a Tg<25°C, and the mass ratio of the acrylate monomer with a Tg>50°C to the acrylate monomer with a Tg<25°C is (4-12):1.

[0021] Preferably, the acrylate monomer with Tg>50°C includes but is not limited to one or more of 4-tert-butylcyclohexyl acrylate, isobornyl acrylate, acryloylmorpholine, N,N-dimethylacrylamide, cyclohexyl methacrylate, isobornyl methacrylate, methyl methacrylate, and phenyl methacrylate; and / or the acrylate monomer with Tg<25°C includes but is not limited to one or more of 2-phenoxyethyl acrylate, cyclotrimethylolpropane formal acrylate, tetrahydrofurfuryl acrylate, lauric acid acrylate, ethoxyethoxyethyl acrylate, and tetrahydrofurfuryl ethoxy acrylate; and / or the phosphate-modified acrylate monomer includes but is not limited to one or more of 2-hydroxyethyl methacrylate phosphate, di(methacryloyloxyethyl) hydrogen phosphate, bis(2-acryloyloxyethyl) phosphate, and ethylene oxide-modified diacrylate phosphate.

[0022] Preferably, the photoinitiator includes but is not limited to two or more of methyl benzoylformate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoylphenylphosphonate, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and methyl o-benzoylbenzoate.

[0023] Preferably, the auxiliary agent includes one or more of a fluorescent agent, a silane coupling agent, and a wetting agent, and the rheological auxiliary agent is hydrophobic fumed silica.

[0024] The preparation method of the mask-free dual-curing conformal adhesive comprises the following steps:

[0025] Step S1: Preparation of raw materials: Prepare the raw materials of the mask-free dual-curing conformal adhesive as described above;

[0026] Step S2: Pretreatment of raw materials: preheating polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B in an oven at 60° C.-90° C. for 30 minutes to reduce the viscosity of the prepolymers;

[0027] Step S3: Mixing and dispersing of raw materials:

[0028] Step S31: Under yellow light, polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B in a mass ratio of (1-3) : 1 are added to a stirred tank, and acrylate monomer, photoinitiator, and auxiliary agent are added in sequence. The above materials are stirred at a speed of 50 RPM-500 RPM for 1 hour-2 hours to ensure that the materials are evenly mixed;

[0029] Step S32: Under the stirring state of step S31, the rheological additive is slowly added to the stirring tank, and the high-speed disperser of the stirring tank is turned on to disperse the raw materials after the rheological additive, wherein: a high-speed disperser with a rotation speed ≥1000RPM is used, the processing time is 1 hour to 2 hours, and the edge linear speed of the high-speed disperser is ≥15m / s; or a three-roll grinder with a roller spacing of 5μm-40μm is used for processing, the grinding speed is <150RPM, and the grinding is carried out at least twice; after the dispersion is completed, a three-proof adhesive with a viscosity of 2000cps-6000cps and a thixotropic index of 2-6 is obtained.

[0030] Preferably, it also includes:

[0031] Step S4: Degassing and packaging of the conformal adhesive: The packaging container containing the conformal adhesive prepared in step S3 is directly placed in a homogenizer, degassed for ≥5 minutes at a vacuum degree ≤-0.080 MPa and a rotation speed ≥600 RPM, and then packaged; alternatively, the conformal adhesive prepared in step S3 is first placed in a turnover barrel, the turnover barrel is placed in a homogenizer, and degassing for ≥5 minutes at a vacuum degree ≤-0.080 MPa and a rotation speed ≥600 RPM, then the conformal adhesive is poured into the packaging container, and then a second vacuum treatment is performed in a vacuum barrel for 10-20 minutes before packaging, where the vacuum degree of the vacuum barrel is ≤-0.095 MPa.

[0032] The beneficial effects of the technical solution of the present invention are mainly reflected in:

[0033] 1. The mask-free dual-cure conformal coating of the present invention achieves optimal viscosity (2000-6000 cps) and thixotropic properties (thixotropic index 2-6) by precisely controlling the synergistic ratio of two polyurethane acrylate prepolymers of different viscosities, as well as acrylic monomers and rheological modifiers. These properties enable the conformal coating to reduce viscosity under shear force during dispensing, facilitating rapid dispensing and ensuring uniform dispensing. After dispensing, the conformal coating regains its high viscosity at rest, instantly forming a stable structure and preventing the conformal coating from flowing or spreading along the dispensing boundary. This ensures that the conformal coating maintains its precise coating shape before curing. Furthermore, by precisely controlling the conformal coating's thixotropic index, excessive sagging caused by an excessively high thixotropic index can be avoided for uneven areas of printed circuit boards, thereby preventing poor conformal coating coverage and ensuring precise control of the coating area.

[0034] 2. The mask-free dual-cure conformal coating is a dual-resin system formed by compounding high-viscosity polyurethane acrylate prepolymer A with low-viscosity polyurethane acrylate prepolymer B. Polyurethane acrylate prepolymer A is used to provide structural support, while polyurethane acrylate prepolymer B is used to optimize rheological properties. This dual-resin system avoids the impact of viscosity fluctuations of a single resin on the overall viscosity of the product. At the same time, the synergistic effect of acrylic monomers, rheological additives, and other additives (such as silane coupling agents) not only enhances thixotropic properties but also improves storage stability, avoiding delamination or sedimentation after long-term storage. This creates a conformal coating system with system stability and batch consistency, ensuring product reliability and enabling the conformal coating to meet the requirements of precision dispensing.

[0035] 3. The mask-free dual-curing conformal adhesive uses a polyurethane acrylate resin system with a low NCO content, combined with a surface / deep composite system of a photoinitiator combination, to achieve rapid curing under UV radiation. The hardness after curing is ≥D65. Subsequent production processes can be carried out after UV curing. The residual NCO groups of the resin provide moisture-assisted curing for local shadow areas, ensuring that areas with insufficient UV light can still achieve complete cross-linking. A dual curing system of rapid UV curing and moisture curing can be realized, thereby improving production efficiency. At the same time, the volume shrinkage rate of the coating after curing is <1%, avoiding cracking, warping and other coating effects caused by shrinkage.

[0036] 4. Through the use of phosphate-modified acrylate and the optimized ratio of acrylate monomer with Tg>50℃ and acrylate monomer with Tg<25℃, the cured conformal coating has a mechanical hardness of Shore hardness ≥D65 while maintaining good flexibility. Its elongation at break is ≥150%, tensile strength is ≥4MPa, and adhesion to PCBA substrate can reach 5B, combining excellent mechanical properties and adhesion.

[0037] 5. The mask-free dual-cure conformal adhesive uses polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B with low NCO content, which makes the cured conformal adhesive coating have good hydrophobicity. At the same time, combined with the suitable viscosity and thixotropic properties of the conformal adhesive, the conformal adhesive coating thickness can reach 0.5 mm-3 mm. Therefore, compared with the thin coating design (≤100μm) of conventional conformal adhesive, the mask-free dual-cure conformal adhesive has excellent resistance to moisture and heat, chemical resistance, high and low temperature impact resistance, and steam shock resistance, ensuring long-term and reliable protection.

[0038] 6. In the preparation method of the mask-free dual-cure conformal adhesive, the polyurethane acrylate prepolymer A and the polyurethane acrylate prepolymer B are preheated to reduce the viscosity of the prepolymers, thereby facilitating subsequent uniform dispersion. At the same time, to avoid bubbles in the conformal adhesive, the conformal adhesive is deaerated and vacuum-packed during packaging, thereby avoiding the generation of bubbles during subsequent storage and transportation, ensuring the stability of continuous dispensing and the density of the coating, improving the protective effect of the coating, and providing guarantees for precision dispensing, thereby achieving high-thickness, high-precision dispensing and avoiding contamination of non-coated areas. DETAILED DESCRIPTION

[0039] In order to make the purpose, advantages and features of the present invention more clearly and in detail, the following preferred embodiments will be used to explain. This embodiment is only a typical example of the application of the technical solution of the present invention. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection claimed by the present invention.

[0040] It is also stated that the term "multiple" in this solution means two or more, unless otherwise clearly and specifically defined.

[0041] The present invention discloses a mask-free dual-curing conformal adhesive, comprising the following raw material components in parts by weight:

[0042] Main resin 40-65 parts;

[0043] 20-40 parts of acrylate monomer;

[0044] 1-5 parts of photoinitiator;

[0045] 1-5 parts of additives;

[0046] 1-5 parts of rheological additive;

[0047] The main resin includes polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B, the viscosity of polyurethane acrylate prepolymer A is 9500 cps-25000 cps, and the viscosity of polyurethane acrylate prepolymer B is 5000 cps-10000cps. Specifically, the viscosity range of the above-mentioned resin A and resin B refers to the viscosity value range of resin A and resin B at 60°C. The mass ratio of the polyurethane acrylate prepolymer A to the polyurethane acrylate prepolymer B is (1-3):1. High-viscosity polyurethane acrylate prepolymer A and low-viscosity polyurethane acrylate prepolymer B are used, wherein the polyurethane acrylate prepolymer A is used to provide structural support, and the polyurethane acrylate prepolymer B is used to optimize the rheological properties. The dual-resin system avoids the influence of the viscosity fluctuation of a single resin on the overall viscosity of the product, and facilitates the precise adjustment of the overall viscosity of the mask-free dual-cure three-proof adhesive. The acrylate monomer includes a phosphate-modified acrylate monomer and two or more monofunctional acrylate monomers, wherein the monofunctional acrylate monomer provides flexibility and ensures the cohesive strength of the coating / adhesive layer. The phosphate-modified acrylate monomer can enhance the crosslinking density of the three-proof adhesive and optimize the mechanical properties. The phosphate group can also strengthen the interfacial bonding.

[0048] Among them, the NCO content of the polyurethane acrylate prepolymer A and the polyurethane acrylate prepolymer B are both 0%-1%. Due to the use of a polyurethane acrylate resin system with a low NCO content, combined with the application of a photoinitiator, rapid light curing can be achieved without consuming a lot of time waiting for moisture curing; at the same time, a small amount of isocyanate can perform moisture curing treatment on local shadows that cannot be reached by UV light during light curing, thereby improving the overall curing performance of the coating; in addition, the resin system with a low NCO content can facilitate improving the hydrophobicity of the coating after curing to adapt to extreme environments of high temperature and high humidity.

[0049] In some embodiments, the polyurethane acrylate prepolymer A is a polyurethane acrylate resin with a branched structure, which is formed by reacting a multifunctional polyol with a functionality ≥3 with a diisocyanate at 70°C-90°C, wherein the molar ratio of the multifunctional polyol to the diisocyanate is 1:(2.2-3.0), then lowering the temperature to 50°C-60°C, adding a hydrophobic branched segment diol for reaction, wherein the molar ratio of the hydrophobic branched segment diol to the multifunctional polyol is (0.8-1.2):1, and finally slowly adding a hydroxyl acrylate monomer for reaction, wherein the molar ratio of the hydroxyl acrylate monomer to the multifunctional polyol is (0.5-1.5):1. The residual NCO group content of the terminal of the polyurethane acrylate prepolymer A is ≤1% but not 0; in a preferred embodiment, the hydrophobic branched segment diol includes a C12-C18 long-chain aliphatic diol; the polyurethane acrylate prepolymer A further improves the hydrophobic properties of the product by adopting a hydrophobic branched structure.

[0050] In some other embodiments, the polyurethane acrylate prepolymer A may also directly use existing products that meet the viscosity and NCO content requirements of the polyurethane acrylate prepolymer A, such as: LuCure8674 produced by Guangzhou Runao Chemical Materials Co., Ltd., DM88A produced by Double Bond Chemical Co., Ltd., or A2888-1 of Guangzhou Handong New Materials Technology Co., Ltd. In addition, other products in the prior art that meet the viscosity and NCO content requirements of the polyurethane acrylate prepolymer A may also be used as substitutes for the above-mentioned products. Therefore, these specific product brands should not be used as a limitation on the scope of protection of the present invention.

[0051] In some embodiments, the polyurethane acrylate prepolymer B is an unbranched polyurethane acrylate resin, which is formed by reacting a linear soft segment polyol with a diisocyanate at 70°C-90°C, wherein the molar ratio of the linear soft segment polyol to the diisocyanate is 1:(2.05-2.25), and then introducing a hydroxyl acrylate for reaction, wherein the molar ratio of the hydroxyl acrylate to the linear soft segment polyol is (1.00-1.15):1. The residual NCO group content at the end of the polyurethane acrylate prepolymer B is ≤1% but not 0; the polyurethane acrylate prepolymer B adopts a linear structure, its molecular chains are linearly arranged, there is no cross-linking or only weak physical cross-linking, it has good flexibility and ductility, and has good mechanical properties.

[0052] In some embodiments, the polyurethane acrylate prepolymer B can also directly use existing products that meet the viscosity and NCO content requirements of the polyurethane acrylate prepolymer B, such as FSP8394 produced by Guangzhou Runao Chemical Materials Co., Ltd. or DM5212 produced by Double Bond Chemical Co., Ltd. Other products in the prior art that meet the viscosity and NCO content requirements of the polyurethane acrylate prepolymer B can also be used as substitutes for the above products. Therefore, these specific product brands should not be used as a limitation on the scope of protection of the present invention.

[0053] In some embodiments, the mass ratio of the monofunctional acrylate monomer to the phosphate-modified acrylate monomer is (20-50):1, and the hydrophobicity of the conformal adhesive is ensured by limiting the added content of the phosphate-modified acrylate monomer.

[0054] In some embodiments, the monofunctional acrylate monomer includes an acrylate monomer with a Tg>50°C and an acrylate monomer with a Tg<25°C, wherein the higher Tg monomer provides rigidity, improves scratch resistance, strength and high hydrophobicity, and the low Tg monomer imparts flexibility, impact resistance, and ductility, reduces brittle fracture by dispersing stress, is suitable for environments with dynamic loads or large temperature differences, and avoids the problem of a single material being too brittle or too soft. The mass ratio of the acrylate monomer with a Tg>50°C to the acrylate monomer with a Tg<25°C is preferably (4-12):1.

[0055] In some embodiments, the acrylate monomer with Tg>50°C includes but is not limited to one or more of 4-tert-butylcyclohexyl acrylate (TBCHA), isobornyl acrylate (IBOA), acryloylmorpholine (ACMO), N,N-dimethylacrylamide (DMAA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBOMA), methyl methacrylate (MMA), and phenyl methacrylate (PhMA); and / or the acrylate monomer with Tg<25°C includes but is not limited to one or more of 2-phenoxyethyl acrylate (PHEA), cyclotrimethylolpropane formal acrylate (CTFA), tetrahydrofurfuryl acrylate (THFA), lauric acid acrylate (LA), ethoxyethoxyethyl acrylate (EOEOEA), and tetrahydrofurfuryl ethoxy acrylate (THFEOA).

[0056] In some embodiments, the phosphate-modified acrylate monomer includes, but is not limited to, one or more of 2-hydroxyethyl methacrylate phosphate, di(methacryloyloxyethyl) hydrogen phosphate, bis(2-acryloyloxyethyl) phosphate, and ethylene oxide-modified phosphoric acid diacrylate.

[0057] In some embodiments, the photoinitiator includes but is not limited to two or more of methyl benzoylformate (MBF), 2-hydroxy-2-methyl-1-phenyl-1-propanone (UV1173), 2,4,6-trimethylbenzoylphenylphosphonate (TPO), ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), methyl o-benzoylbenzoate (OMBB), etc.

[0058] In some embodiments, the auxiliary agent includes one or more of a fluorescent agent, a silane coupling agent, and a wetting agent, and the rheological auxiliary agent is fumed silica, preferably hydrophobic fumed silica.

[0059] According to the above raw material ratio, the following Examples 1 to 6 are provided, and Comparative Examples 1 to 8 are added for comparison with the Examples. The raw material ratios of Examples 1 to 6 and Comparative Examples 1 to 8 are as follows: Example 1

[0060] It includes the following raw material components by weight:

[0061] Polyurethane acrylate prepolymer A: 35 parts;

[0062] Polyurethane acrylate prepolymer B: 20 ​​parts;

[0063] Acrylate monomer with Tg>50℃: 30 parts;

[0064] Acrylate monomer with Tg < 25°C: 5 parts;

[0065] Phosphate modified acrylate monomer: 1 part;

[0066] Photoinitiator: 4 parts;

[0067] Additives: 2 parts;

[0068] Rheological additive: 3 parts;

[0069] In this embodiment, polyurethane acrylate prepolymer A is LuCure8674 produced by Guangzhou Runao Chemical Materials Co., Ltd., polyurethane acrylate prepolymer B is FSP8394 produced by Guangzhou Runao Chemical Materials Co., Ltd., and acrylate monomers with Tg>50°C are acryloylmorpholine (ACMO, Tg=145°C) and isobornyl acrylate (IBOA, Tg=88°C), and the ratio of the two is m(ACMO): m (IBOA)=2∶1;

[0070] The acrylate monomer with a Tg of <25°C used in this embodiment is tetrahydrofurfuryl acrylate (THFA, Tg = -20°C);

[0071] The phosphate-modified acrylate monomer used in this embodiment is 2-hydroxyethyl methacrylate phosphate;

[0072] The photoinitiators used in this example are 2-hydroxy-2-methyl-1-phenyl-1-propanone (UV1173) and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), with a ratio of m (UV1173) m (BAPO)=1∶1;

[0073] The auxiliary agent combination used in this embodiment is a combination of a fluorescent agent, a silane coupling agent and a wetting agent, wherein the fluorescent agent is 0.1 parts by mass, the silane coupling agent is 1 part by mass, and the wetting agent is 0.9 parts by mass. Example 2

[0074] It includes the following raw material components by weight:

[0075] Polyurethane acrylate prepolymer A: 30 parts;

[0076] Polyurethane acrylate prepolymer B: 30 parts;

[0077] Acrylate monomer with Tg>50℃: 25 parts;

[0078] Acrylate monomer with Tg < 25°C: 5 parts;

[0079] Phosphate modified acrylate monomer: 1 part;

[0080] Photoinitiator: 4 parts;

[0081] Additives: 2 parts;

[0082] Rheological additive: 3 parts;

[0083] The acrylate monomer with a Tg>50°C used in this embodiment is methyl isobornyl acrylate (IBOMA, Tg=155°C); other raw materials are the same as those in Example 1. Example 3

[0084] It includes the following raw material components by weight:

[0085] Polyurethane acrylate prepolymer A: 45 parts;

[0086] Polyurethane acrylate prepolymer B: 20 ​​parts;

[0087] Acrylate monomer with Tg>50℃: 21 parts;

[0088] Acrylate monomer with Tg < 25°C: 2 parts;

[0089] Phosphate modified acrylate monomer: 0.5 parts;

[0090] Photoinitiator: 4.5 parts;

[0091] Additives: 2 parts;

[0092] Rheological additive: 5 parts;

[0093] In this embodiment, the polyurethane acrylate prepolymer A is DM88A produced by Double Bond Chemical Co., Ltd., and the acrylate monomer with a Tg of <25°C used in this embodiment is ethoxyethoxyethyl acrylate (EOEOEA, Tg = -56°C); the photoinitiator is a combination of methyl benzoylformate (MBF), 2-hydroxy-2-methyl-1-phenyl-1-propanone (UV1173) and 2,4,6-trimethylbenzoylphenylphosphonate (TPO), with a ratio of m (MBF): m (UV1173) m (TPO)=1:1:1; other raw materials used in this embodiment are the same as those in Example 1. Example 4

[0094] It includes the following raw material components by weight:

[0095] Polyurethane acrylate prepolymer A: 30 parts;

[0096] Polyurethane acrylate prepolymer B: 17 parts;

[0097] Acrylate monomer with Tg>50°C: 33 parts;

[0098] Acrylate monomer with Tg < 25°C: 5 parts;

[0099] Phosphate modified acrylate monomer: 2 parts;

[0100] Photoinitiator: 5 parts;

[0101] Additives: 4.5 parts;

[0102] Rheological additive: 1.5 parts;

[0103] Except for the above ratio, the raw materials used in this embodiment are the same as those in Example 3. Example 5

[0104] It includes the following raw material components by weight:

[0105] Polyurethane acrylate prepolymer A: 20 parts;

[0106] Polyurethane acrylate prepolymer B: 20 ​​parts;

[0107] Acrylate monomer with Tg>50℃: 16 parts;

[0108] Acrylate monomer with Tg < 25°C: 3 parts;

[0109] Phosphate modified acrylate monomer: 1 part;

[0110] Photoinitiator: 1 part;

[0111] Additives: 1 part;

[0112] Rheological additive: 1 part;

[0113] Except for the above ratio, the raw materials used in this embodiment are the same as those in Example 1. Example 6

[0114] It includes the following raw material components by weight:

[0115] Polyurethane acrylate prepolymer A: 45 parts;

[0116] Polyurethane acrylate prepolymer B: 20 ​​parts;

[0117] Acrylate monomer with Tg>50°C: 34 parts;

[0118] Acrylate monomer with Tg < 25°C: 5 parts;

[0119] Phosphate modified acrylate monomer: 1 part;

[0120] Photoinitiator: 5 parts;

[0121] Additives: 5 parts;

[0122] Rheological additive: 5 parts;

[0123] Except for the above ratio, the raw materials used in this embodiment are the same as those in Example 3.

[0124] Comparative Example 1:

[0125] It includes the following raw material components by weight:

[0126] Polyurethane acrylate prepolymer A: 55 parts;

[0127] Acrylate monomer with Tg>50℃: 30 parts;

[0128] Acrylate monomer with Tg < 25°C: 5 parts;

[0129] Phosphate modified acrylate monomer: 1 part;

[0130] Photoinitiator: 4 parts;

[0131] Additives: 2 parts;

[0132] Rheological additive: 3 parts;

[0133] In this comparative example, except that polyurethane acrylate B is not added, the other raw materials are the same as those in Example 1.

[0134] Comparative Example 2:

[0135] It includes the following raw material components by weight:

[0136] Polyurethane acrylate prepolymer A: 35 parts;

[0137] Polyurethane acrylate prepolymer B: 20 ​​parts;

[0138] Acrylate monomer with Tg < 25°C: 35 parts;

[0139] Phosphate modified acrylate monomer: 1 part;

[0140] Photoinitiator: 4 parts;

[0141] Additives: 2 parts;

[0142] Rheological additive: 3 parts;

[0143] In this comparative example, except that the acrylic acid ester monomer with Tg>50° C. is not added, the other raw materials are the same as those in Example 1.

[0144] Comparative Example 3:

[0145] It includes the following raw material components by weight:

[0146] Polyurethane acrylate prepolymer A: 35 parts;

[0147] Polyurethane acrylate prepolymer B: 20 ​​parts;

[0148] Acrylate monomer with Tg>50℃: 31 parts;

[0149] Acrylate monomer with Tg < 25°C: 5 parts;

[0150] Photoinitiator: 4 parts;

[0151] Additives: 2 parts;

[0152] Rheological additive: 3 parts;

[0153] In this comparative example, except that the phosphate-modified acrylate monomer is not added, the other raw materials are the same as those in Example 1.

[0154] Comparative Example 4:

[0155] It includes the following raw material components by weight:

[0156] Polyurethane acrylate prepolymer A: 30 parts;

[0157] Polyurethane acrylate prepolymer B: 27 parts;

[0158] Acrylate monomer with Tg>50℃: 25 parts;

[0159] Acrylate monomer with Tg < 25°C: 5 parts;

[0160] Phosphate modified acrylate monomer: 1 part;

[0161] Photoinitiator: 4 parts;

[0162] Additives: 2 parts;

[0163] Rheological additive: 6 parts;

[0164] In this comparative example, except for the above ratio, the other raw materials used in this comparative example are the same as those in Example 1.

[0165] Comparative Example 5:

[0166] It includes the following raw material components by weight:

[0167] Polyurethane acrylate prepolymer A: 36 parts;

[0168] Polyurethane acrylate prepolymer B: 27 parts;

[0169] Acrylate monomer with Tg>50℃: 25 parts;

[0170] Acrylate monomer with Tg < 25°C: 4.5 parts;

[0171] Phosphate modified acrylate monomer: 1 part;

[0172] Photoinitiator: 4 parts;

[0173] Additives: 2 parts;

[0174] Rheological additive: 0.5 parts;

[0175] In this comparative example, except for the above ratio, the other raw materials used in this comparative example are the same as those in Example 1.

[0176] Comparative Example 6:

[0177] In this comparative example, the polyurethane acrylate prepolymers used were a combination of polyurethane acrylate prepolymer C and polyurethane acrylate prepolymer D, wherein the polyurethane acrylate prepolymer C used Desmodur® VPLS 2371 produced by Covestro; the polyurethane acrylate prepolymer D used DM5212 produced by Double Bond Chemical Co., Ltd. The remaining raw materials used in this comparative example were the same as those in Example 1.

[0178] Comparative Example 7:

[0179] It includes the following raw material components by weight:

[0180] Polyurethane acrylate prepolymer B: 55 parts;

[0181] Acrylate monomer with Tg>50℃: 30 parts;

[0182] Acrylate monomer with Tg < 25°C: 5 parts;

[0183] Phosphate modified acrylate monomer: 1 part;

[0184] Photoinitiator: 4 parts;

[0185] Additives: 2 parts;

[0186] Rheological additive: 3 parts;

[0187] In this comparative example, except that polyurethane acrylate A is not added, the other raw materials are the same as those in Example 1.

[0188] Comparative Example 8:

[0189] It includes the following raw material components by weight:

[0190] Polyurethane acrylate prepolymer A: 20 parts;

[0191] Polyurethane acrylate prepolymer B: 35 parts;

[0192] Acrylate monomer with Tg>50℃: 30 parts;

[0193] Acrylate monomer with Tg < 25°C: 5 parts;

[0194] Phosphate modified acrylate monomer: 1 part;

[0195] Photoinitiator: 4 parts;

[0196] Additives: 2 parts;

[0197] Rheological additive: 3 parts;

[0198] In this comparative example, except for the replacement of the mass ratio of polyurethane acrylate A to polyurethane acrylate prepolymer B, the other raw materials are the same as those in Example 1.

[0199] The present invention also discloses a method for preparing a mask-free dual-curing conformal adhesive, comprising the following steps:

[0200] Step S1: Preparation of raw materials: Prepare the raw materials of the mask-free dual-curing conformal adhesive as described above;

[0201] Step S2: Pretreatment of raw materials: preheating polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B in an oven at 60° C.-90° C. for 30 minutes to reduce the viscosity of the prepolymers;

[0202] Step S3: Mixing and dispersing of raw materials:

[0203] Step S31: Under yellow light, polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B at a mass ratio of (1-3) : 1 are added to a stirred tank, and acrylate monomer, photoinitiator, and auxiliary agent are added in sequence. The above materials are stirred at a speed of 50-500 RPM for 1-2 hours to ensure that the materials are evenly mixed;

[0204] Step S32: Under the stirring state of step S31, the rheological additive is slowly added to the stirring tank, and the high-speed disperser of the stirring tank is turned on to disperse the raw materials after the rheological additive, wherein: a high-speed disperser with a rotation speed ≥1000RPM is used, the processing time is 1 hour to 2 hours, and the edge linear speed of the high-speed disperser is ≥15m / s; or a three-roll grinder with a roller spacing of 5μm-40μm is used for processing, the grinding speed is <150RPM, and the grinding is carried out at least twice; after the dispersion is completed, a three-proof adhesive with a viscosity of 2000cps-6000cps and a thixotropic index of 2-6 is obtained.

[0205] The preparation method also includes step S4: degassing and packaging the three-proof adhesive: directly placing the packaging container containing the three-proof adhesive prepared in step S3 into a homogenizer, degassing for ≥5 minutes at a vacuum degree of ≤-0.080 MPa and a rotation speed of ≥600 RPM, and then packaging; or first placing the three-proof adhesive prepared in step S3 into a turnover barrel, placing the turnover barrel into the homogenizer, degassing for ≥5 minutes at a vacuum degree of ≤-0.080 MPa and a rotation speed of ≥600 RPM, then pouring the three-proof adhesive into the packaging container, and then using a vacuum barrel for a second vacuum treatment for 10 minutes to 20 minutes before packaging, wherein the vacuum degree of the vacuum barrel is ≤-0.095 MPa.

[0206] Based on the raw material ratios of the above embodiments and comparative examples, and the above preparation method, the following preparation steps are used to prepare the three-proof adhesive product:

[0207] Under yellow light, all raw materials except the rheological additive were added to the stirring kettle and stirred at a speed of 100±10RPM for 1 hour to ensure that the materials were evenly mixed; under stirring, the rheological additive was added to the stirring kettle, and the high-speed dispersion disk of the stirring kettle was turned on at a speed of 1200±50RPM for 1 hour. The linear speed of the dispersion disk edge was ≥15m / s. After the dispersion was completed, the three-proof adhesive was prepared. Subsequently, the three-proof adhesive prepared in each embodiment and comparative example was deaerated, and the three-proof adhesive after dispersion was poured into an opaque bag. The mixture was placed in a container and then placed in a homogenizer for degassing at a vacuum degree of ≤-0.080 MPa and a speed of ≥600 RPM for 5 minutes to obtain a three-proof adhesive product. The packaging container used in Example 3 was a non-circular container and could not be directly degassed using a homogenizer. Therefore, a turnover barrel was first used to degas the mixture in a homogenizer at a vacuum degree of ≤-0.080 MPa and a speed of ≥600 RPM for 5 minutes, and then poured into a packaging container. A vacuum barrel with a vacuum degree of -0.095 MPa was used for a second vacuum treatment for 10 minutes to obtain a three-proof adhesive product.

[0208] At the same time, a comparative example 9 is also provided, in which the degassing treatment method is different from the above method. The raw materials, proportions, and dispersion steps of the raw materials in comparative example 9 are the same as those in Example 1. However, when preparing the three-proof adhesive, the three-proof adhesive is only vacuum-treated in a vacuum barrel with a vacuum degree of -0.095 MPa for 20 minutes before being poured into the packaging container.

[0209] Subsequently, the three-proof adhesive products prepared by each embodiment and comparative example were dispensed on three different PCB test boards using a precision dispensing machine with a nozzle diameter of 0.1mm. The dispensing thickness was 1mm. After the dispensing was completed, a radiation energy of 2000mJ / cm 2 UV lamp for curing.

[0210] After curing on different PCB test boards, the three-proof adhesive products prepared in each embodiment and comparative example were subjected to the following performance tests:

[0211] 1. Rheological properties test:

[0212] (1) Viscosity test: Use a Brookfield DV2T rotational viscometer (14# rotor) to measure viscosity at a constant temperature of 25±1°C and a rotation speed of 20RPM;

[0213] (2) Thixotropic index: Use a Brookfield DV2T rotational viscometer (spindle 14) at a temperature of 25 ± 1 °C to measure the viscosity at a rotation speed of 2 RPM (η1) and the viscosity at a rotation speed of 20 RPM (η2). The viscosity value is the viscosity value when Ti = η1 / η2.

[0214] The rheological properties test results of Examples 1-6 and Comparative Examples 1-9 are shown in Table 1:

[0215] Table 1: Rheological properties test results of three-proof adhesive:

[0216]

[0217] 2. Mechanical properties test:

[0218] (1) Adhesion test: Refer to ASTM D3359 and GB / T 9286-2021 standards and use the cross-cut method for test evaluation;

[0219] (2) Hardness test: Refer to GB / T 2411-2008 and use Shore D hardness tester to measure the hardness of the cured coating;

[0220] (3) Elongation at break: Tested in accordance with GB / T 1040.1-2018;

[0221] (4) Tensile strength: Tested in accordance with GB / T 1040.1-2018 standard;

[0222] The mechanical property test results of Examples 1-6 and Comparative Examples 1-9 are shown in Table 2:

[0223] Table 2: Test results of mechanical properties of three-proof adhesive:

[0224]

[0225] 3. Process suitability test

[0226] (1) Flat dispensing performance: The test was conducted on a bare PCB board without components. A precision dispensing machine was used to apply 1mm thick non-shielding three-proof adhesive lines (3cm) and square patterns (3cm×3cm). The differences in dispensing conditions were observed with the naked eye and a microscope. The test contents included line width uniformity, square pattern uniformity, area comparison before and after 10 minutes of dispensing, and bubble conditions.

[0227] (2) PCBA dispensing performance: The test was conducted on a PCBA panel containing devices. A 1mm thick three-proof adhesive coating was applied on the PCBA board using a precision dispensing machine. The dispensing time was recorded. The dispensing status of the coating after UV curing was observed with the naked eye and a microscope, as well as the consistency of each micro-board. The test content included observing with the naked eye and a microscope whether there were bubbles in the coating, whether the three-proof adhesive overflowed, and whether there was excessive sagging. The PCBA panel consisted of 20 small / micro PCBA boards, and the size of the entire board was 13cm×35cm.

[0228] The process applicability test results of Examples 1-6 and Comparative Examples 1-9 are shown in Table 3:

[0229] Table 3: Test results of the applicability of the three-proof adhesive process:

[0230]

[0231] in:

[0232] D represents the average width of the dispensing line, in mm;

[0233] ΔD represents the difference in width between the widest and narrowest points of the dispensing line, in mm;

[0234] δD represents the line width deviation, δD=ΔD / D;

[0235] A0 represents the area of ​​the dispensing area, in cm 2 ;

[0236] A 10 Indicates the area after 10 minutes of dispensing, in cm 2 ;

[0237] ΔA represents the area difference, in cm 2 ;

[0238] δA represents the area deviation before and after dispensing for 10 minutes, δA=ΔA / A0;

[0239] T represents the PCBA panel dispensing time, in seconds.

[0240] In the above test, due to the problem of insufficient addition of rheological additive in Comparative Example 5, the viscosity and thixotropy were both low, so the dispensing thickness could not reach 1 mm. In the above test results, the dispensing thickness used in Comparative Example 5 was 0.3 mm.

[0241] 4. Environmental reliability test

[0242] (1) Power-on water immersion test: Apply 1mm of conformal coating to the circuit board with the debug indicator light. After UV curing, connect the circuit board to a 10V small power supply. When the debug indicator light is on, immerse the circuit board in water at 25±1℃ and observe for 72 hours to see if the coating changes color and if the debug light turns off.

[0243] (2) Steam shock test: Apply 1mm of conformal coating to the circuit board with the debug indicator light. After UV curing, connect the circuit board to a 10V small power supply. When the power is on, the debug indicator light will be on. Use saturated water vapor to spray the circuit board for 8 hours to observe whether the coating changes color and whether the debug light goes out.

[0244] (3) Hot and cold shock test: The coating is cured on a certain type of PCBA panel with a coating thickness of 1mm. The PCBA board is placed in a high and low temperature alternating test chamber with a temperature of -60-125℃, one cycle every 30 minutes, and 100 cycles are performed. After the test, the coating appearance is observed to see if there are cracks, delamination, separation, etc.

[0245] (4) Constant temperature and humidity weathering test: The coating was cured on an IPC B25A comb-type electrode plate with a coating thickness of 1 mm and placed in a constant temperature and humidity chamber at 85°C / 85%RH for 1000 hours. After the test, the coating was observed for white spots, bubbles, pinholes, cracks, wrinkles, peeling, separation, discoloration, etc.

[0246] (5) Salt spray resistance test: The coating is cured on a certain type of PCBA panel with a coating thickness of 1mm. The PCBA board is placed in a salt spray test chamber. After the test, the coating appearance is observed to see if there are any adverse phenomena such as blistering, rust, creep, whitening, blackening, and falling off.

[0247] The environmental reliability test results of Examples 1-6 and Comparative Examples 1-9 are shown in Table 4:

[0248] Table 4: Environmental reliability of shield-free conformal coating:

[0249]

[0250] In the above test results, failure* refers to the debug light going out or the coating exhibiting abnormalities during the experiment. Also, in the above test, the dispensing thickness used in Comparative Example 5 was 0.3mm. The coating thickness in Comparative Example 5 was 0.3mm.

[0251] By analyzing the test results in Tables 1 to 4, it can be seen that Examples 1-6 use appropriate raw materials and proportions to control the viscosity within a range of 2000 cps to 6000 cps and the thixotropic index within a suitable range of 2 to 6. This allows Examples 1-4 to achieve a balance between toughness and strength, and exhibits good performance in mechanical properties, dispensing process applicability, and environmental reliability.

[0252] Compared with Examples 1-6, each comparative example has deficiencies in different aspects:

[0253] Comparative Example 1 uses only high-viscosity, branched-structured polyurethane acrylate resin A as the main resin. This choice results in a relatively higher viscosity and a relatively low thixotropic index for Comparative Example 1. In terms of mechanical properties, due to the lack of the regulating effect of the linear polyurethane acrylate resin B with a soft segment, Comparative Example 1 exhibits high hardness and strength but relatively poor toughness. Although it excels in process performance, in terms of environmental reliability, especially in thermal shock tests, cracking occurs at the pins of the PCBA device, indicating that Comparative Example 1 lacks toughness and cannot adapt to extreme environments.

[0254] The acrylate monomer of Comparative Example 2 only uses THFA with a Tg of <25°C, and the formula lacks a high-Tg monomer. Although Comparative Example 2 has similar effects to Examples 1-4 in terms of rheological properties and dispensing processability, the overall strength of the material is relatively low due to the use of only low-Tg monomers. In the absence of the synergistic effect of high-Tg monomers with high hydrophobicity and rigid structure, the coating has relatively weak waterproof performance and performs poorly under harsh environmental conditions such as steam shock and double 85 shock.

[0255] Comparative Example 3 did not add phosphate-modified acrylate monomer to the formulation system. This monomer plays a key role in promoting adhesion between the coating and the substrate and improving the adhesion of the coating. Due to the absence of this key component, the adhesion of Comparative Example 3 showed a small amount of detachment at the intersection position in the cross-cut test.

[0256] The amount of rheological additive added in Comparative Example 4 is too large, resulting in high overall viscosity and thixotropic index. Although the addition of a high amount of rheological additive gives Comparative Example 4 higher mechanical strength, it also brings the disadvantages of excessive strength and decreased toughness. In addition, due to the high viscosity and thixotropy, the dispensing speed slows down and the dispensing line width becomes narrower, resulting in a significant decrease in the dispensing efficiency of Comparative Example 4 for the same area of ​​coating. Moreover, due to the high thixotropy, obvious shrinkage occurs after dispensing is completed. In PCBA spraying applications, shrinkage may cause insufficient coverage and increase the risk of product failure. In the dispensing test of the PCBA panel, excessive glue was found, and bubbles and even gaps appeared at the bottom of the high device, affecting the protective effect of Comparative Example 4 in the environmental reliability test.

[0257] Comparative Example 5 has the problem of insufficient addition of rheological additives, resulting in low viscosity and thixotropy. During the test, Comparative Example 5 had excessively wide line widths and poor glue area maintenance during the actual dispensing process, posing a risk of glue overflow in PCBA applications. In the PCBA panel dispensing test, Comparative Example 5 overflowed into the V-CUT, severely impacting production. At the same time, due to its low thixotropic index, Comparative Example 5 could not be dispensed to a thickness of 1 mm like other materials, with a maximum thickness of only 0.3 mm. This also led to a decrease in the protective performance of the material in Comparative Example 5, which was mainly manifested in poor performance in water resistance-related tests.

[0258] Comparative Example 6 employed a polyurethane acrylate prepolymer with the same configuration but a higher NCO content. While similar in dispensing and processability to Examples 1-6, the high NCO content of the primary resin prevented rapid UV curing, requiring an additional 5-7 days to reach the final cured hardness, impacting production efficiency. Furthermore, the cured hardness was relatively low, resulting in lower coating strength. Furthermore, the use of a high-NCO resin resulted in poor performance in water resistance tests.

[0259] Comparative Example 7 uses only low-viscosity linear polyurethane acrylate prepolymer B as the main resin. This choice makes the coating relatively soft, with high toughness and poor strength under the same ratio conditions. However, at the same time, the coating prepared in this comparative example performs poorly in water resistance related tests.

[0260] Although Comparative Example 8 also uses two types of polyurethane acrylate prepolymers A and polyurethane acrylate prepolymers B, it uses linear polyurethane acrylate as the main resin. Therefore, under the same ratio of other materials, the hardness of the cured coating is relatively low, the tensile strength decreases, and the coating strength is also low. In terms of hydrophobicity, it is not as good as the sample with polyurethane acrylate prepolymer A as the main resin.

[0261] In the preparation process of Comparative Example 9, only vacuum barrel degassing was used, and no homogenizer was used for degassing. This difference in process resulted in poor performance of the finished product during the dispensing process, with a large number of bubbles inside after dispensing. The appearance of a large number of bubbles weakened the protective effect of the coating. In the steam shock, hot and cold shock, double 85 shock and salt spray resistance tests, the appearance of a large number of bubbles weakened the protective effect, affecting the reliability and stability of the material.

[0262] There are many implementation methods of the present invention, and all technical solutions formed by equivalent transformation or equivalent transformation fall within the protection scope of the present invention.

Claims

1. Mask-free dual-curing conformal adhesive, characterized by: It includes the following raw material components by weight: Main resin 40-65 parts; 20-40 parts of acrylate monomer; 1-5 parts of photoinitiator; 1-5 parts of additives; 1-5 parts of rheological additive; The main resin includes a polyurethane acrylate prepolymer A and a polyurethane acrylate prepolymer B, and the mass ratio of the polyurethane acrylate prepolymer A to the polyurethane acrylate prepolymer B is (1-3):1; the acrylate monomer includes a phosphate-modified acrylate monomer and two or more monofunctional acrylate monomers; the mass ratio of the monofunctional acrylate monomer to the phosphate-modified acrylate monomer is (20-50):1; the monofunctional acrylate monomer includes an acrylate monomer with a Tg>50°C and an acrylate monomer with a Tg<25°C, and the mass ratio of the acrylate monomer with a Tg>50°C to the acrylate monomer with a Tg<25°C is (4-12):1; the polyurethane acrylate prepolymer A uses LuCure8674 produced by Guangzhou Runao Chemical Materials Co., Ltd. or DM88A produced by Double Bond Chemical Co., Ltd., and the polyurethane acrylate prepolymer B uses FSP8394 produced by Guangzhou Runao Chemical Materials Co., Ltd.

2. The mask-free dual-curing conformal adhesive according to claim 1, characterized in that: The acrylate monomer with Tg>50°C includes one or more of 4-tert-butylcyclohexyl acrylate, isobornyl acrylate, acryloylmorpholine, N,N-dimethylacrylamide, cyclohexyl methacrylate, isobornyl methacrylate, methyl methacrylate, and phenyl methacrylate; and / or the acrylate monomer with Tg<25°C includes one or more of 2-phenoxyethyl acrylate, cyclotrimethylolpropane formal acrylate, tetrahydrofurfuryl acrylate, lauric acid acrylate, ethoxyethoxyethyl acrylate, and tetrahydrofurfuryl ethoxy acrylate; and / or the phosphate-modified acrylate monomer includes one or more of 2-hydroxyethyl methacrylate phosphate, di(methacryloyloxyethyl) hydrogen phosphate, bis(2-acryloyloxyethyl) phosphate, and ethylene oxide-modified diacrylate phosphate.

3. The mask-free dual-curing conformal adhesive according to claim 2, characterized in that: The photoinitiator includes two or more of methyl benzoylformate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoylphenylphosphonate, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and methyl o-benzoylbenzoate.

4. The mask-free dual-curing conformal adhesive according to claim 1, characterized in that: The auxiliary agent includes one or more of a fluorescent agent, a silane coupling agent, and a wetting agent, and the rheological auxiliary agent is hydrophobic fumed silica.

5. A method for preparing a mask-free dual-curing conformal adhesive, characterized by: The steps include: Step S1: Preparation of raw materials: Prepare the raw materials of the mask-free dual-curing conformal adhesive as described in any one of claims 1 to 4; Step S2: Pretreatment of raw materials: preheating polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B in an oven at 60° C.-90° C. for 30 minutes to reduce the viscosity of the prepolymers; Step S3: Mixing and dispersing of raw materials: Step S31: Under yellow light, polyurethane acrylate prepolymer A and polyurethane acrylate prepolymer B in a mass ratio of (1-3) : 1 are added to a stirred tank, and acrylate monomer, photoinitiator, and auxiliary agent are added in sequence. The above materials are stirred at a speed of 50 RPM-500 RPM for 1 hour-2 hours to ensure that the materials are evenly mixed; Step S32: Under the stirring state of step S31, the rheological modifier is slowly added to the stirring tank, and the high-speed dispersing disk of the stirring tank is turned on to disperse the raw materials after the rheological modifier, wherein: a high-speed dispersing disk with a rotation speed of ≥1000 RPM is used, the processing time is 1 hour to 2 hours, and the edge linear speed of the high-speed dispersing disk is ≥15 m / s; or a three-roll mill with a roller spacing of 5μm-40μm is used for processing, the grinding speed is <150 RPM, and the grinding is carried out at least twice; after the dispersion is completed, a three-proof adhesive with a viscosity of 2000 cps-6000 cps and a thixotropic index of 2-6 is obtained.

6. The method for preparing the mask-free dual-curing conformal adhesive according to claim 5, characterized in that: Also includes: Step S4: Degassing and packaging of the conformal adhesive: The packaging container containing the conformal adhesive prepared in step S3 is directly placed in a homogenizer, degassed for ≥5 minutes at a vacuum degree ≤-0.080 MPa and a rotation speed ≥600 RPM, and then packaged; alternatively, the conformal adhesive prepared in step S3 is first placed in a turnover barrel, the turnover barrel is placed in a homogenizer, and degassing for ≥5 minutes at a vacuum degree ≤-0.080 MPa and a rotation speed ≥600 RPM, then the conformal adhesive is poured into the packaging container, and then a second vacuum treatment is performed in a vacuum barrel for 10-20 minutes before packaging, where the vacuum degree of the vacuum barrel is ≤-0.095 MPa.

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