Dual-curing conformal coating as well as preparation method and application thereof

Abstract

The invention relates to the technical field of coatings, in particular to dual-curing conformal coating as well as a preparation method and application thereof. The dual-curing three-proofing paint is composed of siloxane containing oxazolidinyl groups, a UV oligomer containing isocyanate groups, a diluting monomer, a water removal agent, a photoinitiator, a wetting agent, a catalyst and the like. Wherein the siloxane containing the oxazolidinyl group has two functional groups of long carbon chain oxazolidine and siloxane, the long carbon chain oxazolidine can realize rapid moisture curing of oligomer and does not generate volatile harmful substances, and meanwhile, hydrolysis residues of the long carbon chain oxazolidine can plasticize the conformal coating and reduce adhesion loss caused by shrinkage. On the other hand, siloxane groups can form a stronger physical or chemical action with a base material, so that the adhesive force to the base material is improved. In conclusion, the three-proofing paint has excellent low surface tension and high wettability, can effectively wet the polluted surface of the PCB and form interaction, has the characteristics of excellent adhesive force, salt mist resistance, high flexibility and the like, and has very high market application value.

Description

A dual-curing conformal coating, its preparation method and application Technical Field

[0001] This invention relates to the field of coating technology, specifically to a dual-curing conformal coating, its preparation method, and its application. Background Technology

[0002] Conformal coating, also known as film coating, is a coating material with protective functions such as mildew resistance, moisture resistance, and salt spray resistance. It is widely used for the protection of printed circuit boards (PCBs). The most common conformal coatings on the market are solvent-based, which have advantages such as low price, short drying time, and excellent leveling and wetting. However, large amounts of solvent pose a significant fire hazard, and solvent use can also affect the health of operators. With increasingly stringent environmental requirements, many manufacturers have begun to promote the use of UV-moisture dual-curing conformal coatings. These utilize the synergistic effect of rapid UV curing and moisture curing to solve some curing problems in shaded areas. However, due to residual flux or oil on the circuit board, as well as the high shrinkage stress of the UV conformal coating itself, UV moisture-curing conformal coatings still suffer from poor wetting and adhesion. Furthermore, traditional UV conformal coatings have slow moisture curing speeds in the later stages, and higher isocyanate content can lead to bubbles and pinholes, which not only affect protective performance but also the adhesion between the coating and the substrate.

[0003] Chinese invention application CN117925153 discloses a high-adhesion UV moisture-curing conformal coating and its preparation method. It improves the film flexibility by introducing hydrogenated polybutadiene segments, thereby reducing shrinkage stress. Simultaneously, the modified dual-curing resin possesses rigid carbon-nitrogen heterocycles and abundant nitrogen and oxygen heteroatoms, giving the conformal coating good cohesiveness and thus improving adhesion. This patent primarily reduces internal stress by minimizing shrinkage, thus not affecting adhesion, but it does not address measures to improve the interaction force between the UV oligomer and the substrate.

[0004] Chinese invention application CN119463551A discloses a UV-cured moisture-curing conformal coating and its preparation method. This invention uses a specific oxazolidine latent curing agent, which can significantly shorten the curing time of the conformal coating in a dark environment, and effectively solves problems such as bubbles and pinholes caused by moisture during the curing process. While this solution addresses the slow curing speed and potential bubble and pinhole issues, it does not provide specific solutions to improve the adhesion of the conformal coating to difficult-to-adhere PCB substrates. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: in view of the shortcomings of the prior art, the present invention provides a double-curing conformal coating, its preparation method and application. The conformal coating has low surface tension and excellent wettability, and contains a special structural adhesion promoter that enhances the adhesion of the substrate. It can effectively wet the contaminated substrate and form strong intermolecular interaction forces or chemical bonds with the substrate, thereby providing high adhesion.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a dual-curing conformal coating is provided, comprising the following components in the following weight ratios: component A1: polyurethane acrylate oligomer containing isocyanate groups, 25-65 parts; component A2: diluent monomer, 20-60 parts; component A4: siloxane adhesion promoter containing oxazolidine, 0.5-10 parts; component A5: latent curing agent other than A4; the amount of component A5 is such that the total molar ratio of isocyanate groups in component A1 to the total molar ratio of isocyanate reactive groups in component A4 and component A5 is in the range of (2:1) to (1:2).

[0007] The moisture-curing conformal coating of the present invention incorporates an oxazolidine-containing siloxane adhesion promoter. Compared with conventional silane adhesion promoters containing double bonds, it is not bonded to the polymer during radiation curing. This retains greater freedom and forms a stronger physical or chemical interaction with the substrate, thereby improving the adhesion to the substrate.

[0008] Furthermore, the aforementioned dual-curing conformal coating is specifically composed of the following components by weight percentage: Component A1: Polyurethane acrylate oligomer containing isocyanate groups, 25-65%; Component A2: Diluent monomer, 20-60%; Component A3: Dehydrating agent, 0.5-4%; Component A4: Siloxane adhesion promoter containing oxazolidine, 0.5-10%; Component A5: Latent curing agent other than A4; its isocyanate reactive group equivalent is 122 g / mol, 2.5-5%; Component A6: Photoinitiator, 1-10%; Component A7: Wetting and leveling agent, 0.1-1%; Component A8: Acidic catalyst, 0.1-1%; Component A9: Isocyanate catalyst, 0.01-1%; Component A10: Antioxidant, 0.2-2%.

[0009] As described above, the oxazolidine adhesion promoter of the present invention can be rapidly hydrolyzed into an alkanolamine under the action of an organic acid catalyst and react with the NCO groups in the UV oligomer. This allows for rapid curing while avoiding the adhesion degradation caused by carbon dioxide generation. Simultaneously, the aldehyde produced by its hydrolysis is a high-carbon-number aldehyde, which can plasticize the conformal coating film, thereby reducing the high shrinkage rate caused by UV curing.

[0010] Furthermore, in the above-mentioned dual-curing conformal coating, component A4 is prepared from the following components: component I: oxazolidine containing hydroxyl groups; component II: silane containing isocyanate reactive groups; component III: difunctional or polyfunctional isocyanate.

[0011] As described above, oxazolidine and siloxane are bonded together through a chemical reaction to form a bifunctional adhesion promoter that combines rapid moisture curing with strong substrate bonding.

[0012] Furthermore, in the above-mentioned dual-curing conformal coating, the hydroxyl-containing oxazolidine in component I is formed by the condensation polymerization of diolamine compounds and alkyl or aralkyl aldehyde compounds using an acidic catalyst, and the structure of component I is as follows: Wherein R1 and R2 are ethylene or isopropyl. When both R1 and R2 are ethylene, the diolamine is diethanolamine. When both R1 and R2 are isopropyl, the diolamine is diisopropanolamine. R3 is an alkyl or aralkyl group with 8-30 carbon atoms. As can be seen from the above description, the oxazolidine structure formed by the condensation of long-chain aldehydes, after hydrolysis under acidic catalysis, generates high-carbon-number aldehydes, which can act as internal plasticizers and reduce curing shrinkage stress, thereby improving the flexibility and adhesion durability of the paint film.

[0013] Component II is one of 3-(N-cyclohexylamino)propyltrimethoxysilane, 3-(N-cyclohexylamino)propyltriethoxysilane, 3-(N-cyclohexylamino)propylmethyldimethoxysilane, N-(n-butyl)-γ-aminopropyltrimethoxysilane, N-(n-butyl)-γ-aminopropyltriethoxysilane, N-(n-butyl)-γ-aminopropylmethyldiethoxysilane, N-(phenyl)-γ-aminopropyltrimethoxysilane, N-(phenyl)-γ-aminopropyltriethoxysilane, and N-(phenyl)-γ-aminopropylmethyldiethoxysilane.

[0014] As described above, secondary aminosilanes have moderate reactivity and readily react with isocyanates to form stable bonds. At the same time, their siloxane groups can effectively form chemical bonds with hydroxyl and other groups on the surface of contaminated substrates, significantly improving adhesion.

[0015] Furthermore, in the above-mentioned dual-curing conformal coating, component A7 is a polyether-modified fluoropolymer with a perfluoroalkyl chain length of C4.

[0016] As described above, using short-chain perfluoroalkyl (C4) wetting and leveling agents can significantly reduce the surface tension of the system and improve the wetting and spreading ability on low surface energy contaminated substrates, while avoiding the environmental toxicity risks of long-chain perfluoroalkyl (≥C8) agents, and can achieve excellent leveling effect without the need for additional leveling agents.

[0017] Furthermore, in the above-mentioned dual-curing conformal coating, the isocyanate group content of component A1 is 2-18% by mass, and the polyurethane acrylate oligomer containing isocyanate group contains an olefinic unsaturated double bond with radiation curing activity. The olefinic unsaturated double bond can be selected from vinyl, propylene, allyl ether, acryloyl or methacryloyl.

[0018] As described above, by controlling the isocyanate content and double bond functionality of A1, the UV curing and wet curing in the shaded areas can be balanced, and the coating can be guaranteed to have sufficient crosslinking density and mechanical strength.

[0019] Furthermore, in the above-mentioned double-curing conformal coating, component A8 is selected from salicylic acid or benzoic acid.

[0020] As described above, using organic carboxylic acids as acidic catalysts can effectively catalyze the hydrolysis of oxazolyl groups, promote the rapid progress of moisture curing reactions, and avoid the use of strong acids that could lead to system instability or corrosion of the substrate.

[0021] Another technical solution provided by the present invention is: a method for preparing the above-mentioned dual-curing conformal coating, comprising the following steps: S1: under light-protected conditions, components A2, A6 and A10 are mixed and stirred under vacuum to form a homogeneous mixture; S2: component A3 is added, and after stirring until the water content of the system is less than 300 ppm, components A1, A4 and A5 are added, and stirring is continued; S3: component A7 is added, and after high-speed stirring and dispersion, components A8 and A9 are added, and the mixture is stirred under vacuum to remove bubbles.

[0022] Furthermore, in the above-mentioned method for preparing the dual-curing conformal coating, component A4 is prepared from the following components: component I: oxazolidine containing hydroxyl groups; component II: silane containing isocyanate reactive groups; component III: difunctional or polyfunctional isocyanate; the number of moles of component III is the same as that of component I. This design is so that each molecule of component A4 has an average of only one oxazolidine structure, and the ratio of the number of moles of isocyanate groups in component III to the total number of moles of isocyanate reactive groups in components I and II is 1:(1~1.05).

[0023] The preparation method of component A4 is as follows: (1) Add 1 mol of component III to the reaction vessel, set the stirring speed to 50-200 r / m, control the temperature to 20-40℃, and add 1 mol of component I to the reaction vessel within 30-90 minutes; (2) After the addition is completed, raise the temperature to 70-90℃ within 30-90 minutes and continue the reaction until the mass fraction of NCO reaches the theoretical value; (3) Cool down to 10-30℃, add an appropriate amount of component II to the reaction vessel within 30-90 minutes, and then raise the temperature to 50-70℃ and react until the mass fraction of NCO drops to 0%, to obtain component A4.

[0024] Another technical solution provided by the present invention is: to provide the application of the above-mentioned double-curing conformal coating in the protection of the surface of an uncleaned contaminated printed circuit board.

[0025] In summary, the beneficial effects of the present invention are as follows: 1. The UV moisture-curing conformal coating of the present invention uses a fluoropolymer with a special structure, which can effectively reduce the surface tension of the UV conformal coating, improve its wetting performance on difficult-to-adhere substrates, and achieve excellent leveling effect without adding other leveling agents, and does not contain PFOA, which complies with environmental regulations.

[0026] 2. The UV moisture-curing conformal coating of the present invention introduces an adhesion promoter containing oxazolidine. Compared with conventional silane coupling agents containing double bonds, it is not bonded to the polymer during radiation curing. This retains greater freedom and forms a stronger physical or chemical interaction with the substrate, thereby improving the adhesion to the substrate.

[0027] 3. The oxazolidine adhesion promoter of the present invention can be rapidly hydrolyzed into an alkanolamine under the action of an organic acid catalyst and react with the NCO groups in the UV oligomer, which can both accelerate curing and avoid the problem of decreased adhesion caused by carbon dioxide generation. At the same time, the aldehyde produced by its hydrolysis is a high carbon number aldehyde, which can plasticize the conformal coating film and thus reduce the high shrinkage rate caused by UV curing.

[0028] 4. The conformal coating obtained by this invention is particularly suitable for coating on the surface of PCB boards with residual flux, oil and other contaminants. It can achieve excellent adhesion of grade 0-1 and salt spray resistance of more than 500 hours without adding a cleaning process, significantly reducing production costs and improving protective reliability. Detailed Implementation

[0029] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments.

[0030] The technical solution of the present invention is a dual-curing conformal coating, which comprises the following composition: component A1: a polyurethane acrylate oligomer containing isocyanate groups; component A2: at least one diluent monomer; component A3: a dehydrating agent; component A4: a siloxane adhesion promoter containing oxazolidine; component A5: a latent curing agent other than A4; component A6: at least one photoinitiator; component A7: a wetting and leveling agent; component A8: an acidic catalyst; component A9: an isocyanate catalyst; component A10: an antioxidant.

[0031] When naming the monomers or compounds of this invention, the prefix "(meth)propene" should include "propene" and "methpropene", and the prefix "(n-, iso-, tertiary)alkyl ester" should include "n-alkyl ester", "iso-alkyl ester" and "tertiary alkyl ester".

[0032] The isocyanate group content in component A1 is 2-18% by mass, and the polyurethane acrylate oligomer containing isocyanate group contains an olefinic unsaturated double bond with radiation curing activity. The olefinic unsaturated double bond can be selected from vinyl, propylene, allyl ether, acryloyl or methacryloyl.

[0033] Preferably, the olefinic unsaturated double bond is acryloyl or methacryloyl, and its average double bond functionality is 1-6, preferably 1-4, and more preferably 1-2.

[0034] The average molecular weight Mn of the oligomer component A1 is 500-50000 Daltons, preferably 750-20000 Daltons, more preferably 1000-10000 Daltons, and the viscosity of the oligomer is 100-500000 mPa•s, preferably 500-50000 mPa•s, more preferably 1000-10000 mPa•s.

[0035] Component A1 can be prepared in-house or purchased from representative products on the market, such as Desmolux VPLS2396 (purchased from Bayer), EBECRYL 4150 (Zhanxin), EBECRYL 4250 (Zhanxin), CN1073 (Sartoma), CR93110 (Guangzhou Haohui New Materials), and CR93108 (Guangzhou Haohui New Materials).

[0036] The component A1 oligomer accounts for 25-65% of the total weight of the conformal coating, preferably 30-60%, and more preferably 35-55%.

[0037] The component A2 diluent monomer can be selected from (meth)acrylate monomers, which can be monofunctional, difunctional, trifunctional, tetrafunctional, pentafunctional, hexafunctional (meth)acrylate monomers and mixtures thereof. Representative examples of this class of monomers include, but are not limited to: monofunctional (meth)acrylate monomers, such as (meth)acrylic acid, hydroxyalkyl (meth)acrylates (e.g., 2-hydroxyethyl ester, hydroxypropyl ester, hydroxybutyl ester, etc.), (n-, iso-, tert-)butyl (meth)acrylate, (n-, hexyl (meth)acrylate), (n-, iso-)octyl (meth)acrylate, (n-, iso-)decyl (meth)acrylate, and lauryl (meth)acrylate; and difunctional (meth)acrylate monomers, such as alkyl glycol di(meth)acrylates (e.g., ethylene glycol, propylene glycol, butanediol, neopentyl glycol, hexanediol) and their ethoxylated and / or propoxylated derivatives, tricyclodecanediethanol diacrylate (DCPDA, Changxing Materials Industry), dicyclopentadiene acrylate (DCPA, Changxing Chemical), and isobornyl acrylate (IBOA, Zhanjiang Chemical). New, alicyclic monofunctional acrylate monomers with bridged ring structures (NBOA, IGM Corporation), tetrahydrofuran methacrylate (THFMA, Meiyuan), p-tert-butylcyclohexyl acrylate (TBCHA, Jurui Industrial); trifunctional (meth)acrylate monomers, such as tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and their ethoxylated and / or propoxylated derivatives; tetrafunctional (meth)acrylate monomers, such as pentaerythritol tetra(meth)acrylate, bis(trimethylolpropane tetra(meth)acrylate, and their ethoxylated and / or propoxylated derivatives; pentafunctional (meth)acrylate monomers, such as bispentaerythritol penta(meth)acrylate and its ethoxylated and / or propoxylated derivatives; hexafunctional (meth)acrylate monomers, such as bispentaerythritol hexa(meth)acrylate and its ethoxylated and / or propoxylated derivatives.

[0038] The diluent A2 comprises 20-60% of the total weight of the conformal coating, preferably 25-55%, and more preferably 30-50%. Particularly desirable diluents include at least one of isobornyl acrylate and tricyclodecanedimethyl diacrylate.

[0039] The component A3, the dehydrating agent or water-removing agent, is a substance that can preferentially react with water, thereby improving the stability of the system. Typically, it can be selected from siloxanes, such as vinyltrimethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, and methacryloxypropyltrimethoxysilane.

[0040] Component A3 can also be selected from monoisocyanate compounds, such as p-toluenesulfonyl isocyanate, purchased from Borchers Additive TI in Germany.

[0041] Component A3 can also be selected from low molecular weight active oxazolidine compounds, such as incozol 2, which is purchased from incozol.

[0042] The component A3, the water-removing agent, accounts for 0.5-4% of the total weight of the conformal coating, preferably 0.8-3%, and more preferably 1-2%.

[0043] Component A4, an oxazolidine-containing siloxane adhesion promoter, is obtained by reacting the following substances: Component I: at least one hydroxyl-containing oxazolidine; Component II: at least one isocyanate-containing silane; Component III: a difunctional or polyfunctional isocyanate; wherein the hydroxyl-containing oxazolidine in Component I is formed by the condensation polymerization of a diolamine compound and an alkyl or aralkyl aldehyde compound using an acidic catalyst. Its structure is as follows: Wherein R1 and R2 are ethylene or isopropyl. When both R1 and R2 are ethylene, the diolamine is diethanolamine. When both R1 and R2 are isopropyl, the diolamine is diisopropanolamine.

[0044] R3 is an alkyl or aralkyl group with 8-30 carbon atoms. It is a residual group formed by the condensation of an aldehyde group in an alkyl or aralkyl aldehyde with a hydroxyl group and a secondary amine group in a diolamine. The aldehyde compound has low toxicity, low volatility or non-volatility and low static surface tension. A representative aldehyde compound can be selected from one of lauraldehyde, cinnamaldehyde, hexadecaldehyde, stearaldehyde, phenylacetaldehyde, dodecylbenzaldehyde and hexadecylbenzaldehyde. Preferably, it is lauraldehyde or dodecylbenzaldehyde.

[0045] The acidic catalyst for the condensation of diolamines with alkyl or aralkyl aldehydes is salicylic acid or benzoic acid.

[0046] Component II: A silane containing an isocyanate reactive group, wherein the isocyanate reactive group may be selected from hydroxyl, mercapto, primary amine, secondary amine, epoxy, carboxyl, or urea, preferably the reactive group is a secondary amine. The silane containing the secondary amino group may be selected from one of 3-(N-cyclohexylamino)propyltrimethoxysilane, 3-(N-cyclohexylamino)propyltriethoxysilane, 3-(N-cyclohexylamino)propylmethyldimethoxysilane, N-(n-butyl)-γ-aminopropyltrimethoxysilane, N-(n-butyl)-γ-aminopropyltriethoxysilane, N-(n-butyl)-γ-aminopropylmethyldiethoxysilane, N-(phenyl)-γ-aminopropyltrimethoxysilane, N-(phenyl)-γ-aminopropyltriethoxysilane, and N-(phenyl)-γ-aminopropylmethyldiethoxysilane. Preferably, the secondary amino silane is N-(n-butyl)-γ-aminopropyltrimethoxysilane or N-(phenyl)-γ-aminopropyltrimethoxysilane.

[0047] The isocyanates in component III are either difunctional or polyfunctional. The difunctional isocyanates are selected from pentane 1,5-diisocyanate (PDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), toluene 2,4-diisocyanate (2,4-TDI), toluene 2,6-diisocyanate (2,6-TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), dicyclohexylmethane diisocyanate (HMDI), and tetramethylphenyl dimethyl diisocyanate (TMXDI). The polyfunctional isocyanates are selected from trimers or adducts of the above isocyanates, such as hexamethylene diisocyanate trimer (HT-100, Wanhua Chemical), diphenylmethane diisocyanate oligomer (PM200, Wanhua Chemical), and isophorone diisocyanate trimer (Desmodur). Z4470 (Covestro), preferably, the isocyanate component in this invention is isophorone diisocyanate.

[0048] The number of moles of component III is the same as that of component I. This design is to ensure that each component A4 molecule has an average of only one oxazolidine structure, and the ratio of the number of moles of isocyanate groups in component III to the total number of moles of isocyanate reactive groups in components I and II is 1:(1~1.05).

[0049] Furthermore, the preparation method of the oxazolidine-containing siloxane adhesion promoter of the above-mentioned component A4 is as follows: S1: Add 1 mol of component III to the reaction vessel, set the stirring speed to 50-200 r / m, control the temperature to 20-40℃, and drop 1 mol of component I into the reaction vessel within 30-90 minutes; S2: After the drop addition is completed, raise the temperature to 70-90℃ within 30-90 minutes, and continue the reaction until the NCO mass fraction reaches the theoretical value; S3: Cool down to 10-30℃, drop an appropriate amount of component II into the reaction vessel within 30-90 minutes, and then raise the temperature to 50-70℃ to react until the NCO mass fraction drops to 0%, to obtain component A4.

[0050] The adhesion promoter A4 component accounts for 0.5-10% of the total weight of the conformal coating, preferably 1-8%, and more preferably 2-6%.

[0051] Component A5 is a different latent curing agent from component A4. After hydrolysis, it can also react with the isocyanate groups in component A1 and cure rapidly. Typically, it can be selected from one of the latent curing agents such as aldehyde imine, ketimine, or oxazolidine, for example, products of INCOREZ such as Incozol 4, Incozol BH, and Incozol EH.

[0052] The molar ratio of the isocyanate groups provided in the oligomer of component A1 to the isocyanate reactive groups in components A4 and A5 is 2:1 to 1:2, preferably 1.5:1 to 1:1.5, and more preferably 1.3:1 to 1:1.3.

[0053] The photoinitiator A6 is a class of compounds that can generate free radicals under irradiation with a light source of a specific wavelength. Based on the mechanism, it can be selected from cleavage-type free radical photoinitiators and hydrogen-abstracting free radical photoinitiators, preferably cleavage-type free radical photoinitiators, such as 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173), 1-hydroxycyclohexylphenyl ketone (184), 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylpropanone (2959), and (2,4,6-trimethylphenylpropanone). One or more of the following: (2,4,6-trimethylbenzoyl)-diphenylphosphine oxide (TPO), (2,4,6-trimethylbenzoyl)-ethoxy-phenylphosphine oxide (TEPO), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), 2-methyl-1-(4-methylthiophenyl)-2-morpholino-1-propanone (907), 4-benzoyl-4'-methyl-diphenyl sulfide (BMS), and α,α-dimethoxy-α-phenylacetophenone (651).

[0054] The component A6 photoinitiator accounts for 1-10% of the total weight of the conformal coating, preferably 1.5-8%, and more preferably 2-6%.

[0055] The component A7 wetting and leveling agent is a type of polyether-modified fluoropolymer. This type of fluoropolymer uses short perfluoroalkyl groups (C4) instead of long carbon chain perfluoroalkyl groups (≥C8), such as FC-430 and FC-4430 from 3M Company in the United States.

[0056] The component A7 wetting and leveling agent accounts for 0.1-1% of the total weight of the conformal coating.

[0057] The A8 acid catalyst is an acidic catalyst that can catalyze the rapid hydrolysis of oxazolyl groups. It can be selected from organic carboxylic acid compounds with 2-20 carbon atoms, such as isooctanoic acid, neodecanoic acid, lauric acid, oleic acid, linoleic acid, benzoic acid, and salicylic acid.

[0058] Component A8 can also be selected from organic sulfonic acid compounds with 2-30 carbon atoms, such as p-toluenesulfonic acid, o-toluenesulfonic acid, p-tert-butylbenzenesulfonic acid, dodecylbenzenesulfonic acid, and hexadecylbenzenesulfonic acid.

[0059] Component A8 may also be selected from organic acid anhydrides with 4-30 carbon atoms, such as phthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride.

[0060] Component A8 is preferably one of benzoic acid or salicylic acid, and component A8 accounts for 0.1-1% of the total weight of the conformal coating.

[0061] The component A9 isocyanate catalyst is a catalyst that promotes the reaction of isocyanate with other groups (such as hydroxyl, secondary amine, water, etc.). It can be selected from organotin compounds such as dibutyltin dilaurate, tin isooctanoate, and dibutyltin diacetylacetone, or organobismuate compounds such as bismuth neodecanoate, bismuth isooctanoate, and bismuth laurate, with dibutyltin dilaurate being preferred.

[0062] The A9 isocyanate catalyst component accounts for 0.01-1% of the total weight of the conformal coating.

[0063] The antioxidant component A10 is tris(2,4-di-tert-butylphenyl) phosphite (168), which accounts for 0.2-2% of the total weight of the conformal coating.

[0064] The preparation method of the above-mentioned UV moisture-curing conformal coating is further provided as follows: S1: Under light-protected conditions, add components A2, A6 and A10 to a dry and clean reactor, set the vacuum degree of the reactor to (-0.75)-(-0.95) MPa, and stir at 100 r / m for more than 10 minutes until a homogeneous mixture is formed; S2: Under light-protected conditions, add component A3 to the reactor, stir for more than 15 minutes until the water content of the system is tested to be <300 ppm, then add components A1, A4 and A5, and stir at 100-300 r / m for 30-60 minutes; S3: Under light-protected conditions, add component A7 to the reactor, set the speed to 300-500 r / m, continue stirring for 10-30 minutes, add components A8 and A10, and stir at 50-150 r / m for 10-30 minutes. Open the vacuum valve and set the vacuum level to (-0.75) - (-0.95) MPa. Stir at a speed of 10-50 r / m for 30-60 minutes to remove bubbles.

[0065] The abbreviations and basic parameters of some raw materials and reagents in this invention are as follows: Dodecaldehyde: ≥95%, Aladdin reagent Octadecaldehyde: ≥98%, Maclean's reagent DEA: Diethanolamine, Aladdin reagent IPDI: Isophorone diisocyanate, Wanhua Chemical CG-A118: N-(phenyl)-γ-aminopropyltrimethoxysilane, Jiangsu Chenguang New Materials CG-1189: N-(n-butyl)-γ-aminopropyltrimethoxysilane, Jiangsu Chenguang New Materials CR93110: Polyurethane acrylate oligomer containing isocyanate groups, Guangzhou Haohui New Materials EM231: Trimethylolpropane triacrylate, Changxing Chemical EM70C: Isoborneol acrylate, Changxing Chemical EM2204: Tricyclodecanediethanol diacrylate, Changxing Chemical Additive TI: Dehydrating agent, Borchers KH570 (Germany): Methacryloxypropyltrimethoxysilane, Adhesion promoter, Jiangsu Chenguang New Materials Incozol 4: Isocyanate reactive group equivalent 122 g / mol, INCOREZ photoinitiator 1173: 2-hydroxy-2-methyl-1-phenyl-1-propanone photoinitiator 184: 1-hydroxycyclohexylphenyl ketone photoinitiator TPO: (2,4,6-trimethylbenzoyl)-diphenylphosphine oxide FC-4430: 3M fluorocarbon wetting agent, purchased from Guangzhou Haoyi New Materials Salicylic acid: purchased from Maclean's reagent T-12: dibutyltin dilaurate, Evonik Chemicals antioxidant 168: tris(2,4-di-tert-butylphenyl) phosphite, BASF oxazolidine 1 Preparation method: Add 105.14 g diethanolamine (1 mol) to a 1L four-necked flask, turn on the stirrer and set the speed to 150 r / m, heat to 50℃, and add dropwise 184.33 g dodecaldehyde (1 mol) preheated to a liquid state and 0.750 A mixture of g of salicylic acid was added dropwise, and the entire process was carried out under -0.9 MPa to remove water. After the addition was complete, the temperature was raised to 80℃ and the reaction was continued under reduced pressure for 4 h until no more water was released. The reaction was then stopped to obtain a pale yellow liquid, oxazolidine 1.

[0066] Preparation method of oxazolidine 2: 105.14 g of diethanolamine (1 mol) was added to a 1 L four-necked flask. The stirrer was turned on and set to a speed of 150 r / m. The temperature was raised to 50 °C. Over 30 minutes, a mixture of 268.48 g of octadecaldehyde (1 mol) preheated to a liquid state and 0.750 g of salicylic acid was added dropwise. The entire process was carried out under -0.9 MPa to remove water. After the addition was complete, the temperature was raised to 85 °C and the reaction was continued under reduced pressure for 4 h until no more water was released. The reaction was then stopped to obtain a pale yellow liquid, oxazolidine 2.

[0067] Preparation method of oxazolidine-containing siloxane adhesion promoter E1: S1: Add 222.32 g of IPDI to a dry and clean reaction vessel, set the stirring speed to 150 r / m, control the temperature at 40℃, and add 271.47 g of oxazolidine 1 dropwise to the reaction vessel within 60 minutes; S2: After the dropwise addition is completed, raise the temperature to 85℃ within 30 minutes and continue the reaction until the NCO mass fraction is 8.51%, then stop the reaction; S3: Cool down to 20℃, add 255.39 g of silane CG-A118 dropwise to the reaction vessel within 30 minutes, and raise the temperature to 50℃ after the dropwise addition is completed and react until the NCO mass fraction is 0%, thus obtaining adhesion promoter E1, whose isocyanate reactive groups (the sum of -NH and -OH) equivalent is approximately 375 g / mol.

[0068] Preparation method of oxazolidine-containing siloxane adhesion promoter E2: S1: Add 222.32 g of IPDI to a dry and clean reaction vessel, set the stirring speed to 150 r / m, control the temperature at 40℃, and add 271.47 g of oxazolidine 1 dropwise to the reaction vessel within 60 minutes; S2: After the dropwise addition is completed, raise the temperature to 85℃ within 30 minutes and continue the reaction until the NCO mass fraction is 8.51%, then stop the reaction; S3: Cool down to 20℃, add 235.40 g of silane CG-1189 dropwise to the reaction vessel within 30 minutes, and raise the temperature to 50℃ after the dropwise addition is completed and react until the NCO mass fraction is 0%, thus obtaining adhesion promoter E2, whose isocyanate reactive groups (the sum of -NH and -OH) equivalent is approximately 365 g / mol.

[0069] Preparation method of oxazolidine-containing siloxane adhesion promoter E3: S1: Add 222.32 g of IPDI to a dry and clean reaction vessel, set the stirring speed to 150 r / m, control the temperature at 50℃, and add 355.62 g of oxazolidine 2 dropwise to the reaction vessel within 60 minutes; S2: After the dropwise addition is completed, raise the temperature to 90℃ within 30 minutes and continue the reaction until the NCO mass fraction is 7.27%, then stop the reaction; S3: Cool down to 25℃, add 235.40 g of silane CG-1189 dropwise to the reaction vessel within 30 minutes, and raise the temperature to 50℃ after the dropwise addition is completed and react until the NCO mass fraction is 0%, thus obtaining adhesion promoter E3, whose isocyanate reactive groups (the sum of -NH and -OH) equivalent is approximately 407 g / mol.

[0070] Preparation method of oxazolidine-containing siloxane adhesion promoter E4: S1: Add 222.32 g of IPDI to a dry and clean reaction vessel, set the stirring speed to 150 r / m, control the temperature at 50℃, and add 355.62 g of oxazolidine 2 dropwise to the reaction vessel within 60 minutes; S2: After the dropwise addition is completed, raise the temperature to 90℃ within 30 minutes and continue the reaction until the NCO mass fraction is 7.27%, then stop the reaction; S3: Cool down to 25℃, add 255.39 g of silane CG-A118 dropwise to the reaction vessel within 30 minutes, and raise the temperature to 50℃ after the dropwise addition is completed and react until the NCO mass fraction is 0%, thus obtaining adhesion promoter E4, whose isocyanate reactive groups (the sum of -NH and -OH) equivalent is approximately 417 g / mol.

[0071] Example 1: A method for preparing a dual-curing conformal coating, comprising the following steps: S1: Under light-protected conditions, add components A2, A6, and A10 to a dry and clean reactor according to the amounts specified in the table. Set the vacuum degree of the reactor to -0.9 MPa and stir at 100 r / m for at least 10 minutes until a homogeneous mixture is formed; S2: Under light-protected conditions, add component A3 to the reactor and stir for at least 15 minutes until the water content of the test system is <300 ppm. Then add components A1, A4, and A5 and stir at 150 r / m for 30 minutes; S3: Under light-protected conditions, add component A7 to the reactor, set the stirring speed to 400 r / m, and continue stirring for 30 minutes. Add components A8 and A9 and stir at 50-150 r / m for 10-30 minutes. Open the vacuum valve, set the vacuum degree to -0.9 MPa, and stir at 20 r / m for 60 minutes to remove bubbles.

[0072] The preparation process of Examples 2-9 is the same as that of Example 1. The percentage of different components added to the total raw materials in each example is shown in Table 1 and Table 2.

[0073] The preparation processes of Comparative Examples 1-3 are the same as those of Example 1. The percentage of different components added to the total raw materials in each comparative example is shown in Table 2.

[0074] Table 1 Table 2 Performance Test (1) Hardness: The double-curing conformal coatings obtained in the above examples and comparative examples were poured into a PTFE mold under light-protected conditions. After being fully leveled, they were cured by a UV curing machine with a wavelength of 365 nm mercury lamp and a curing time of 300 mW / cm. 2(1) Radiation curing for 5 seconds, and the hardness 1 was tested with a Shore hardness tester. The sample was then placed at room temperature for another 3 days to continue curing and the hardness 2 was tested. Three specimens were tested for each example or comparative example, and the final test result was the average value. (2) Adhesion: The double-curing conformal coatings obtained in the above examples and comparative examples were applied to the PCB board (the PCB included both uncleaned and cleaned PCBs) using a 100μm wet film preparation device. After being fully leveled, the PCBs were cured by a UV curing machine with a wavelength of 365 nm mercury lamp and a wavelength of 300 mW / cm. 2 (3) Adhesion loss (%): The preparation method of the specimens of the above embodiments and comparative examples is the same as that of (1) above. Then, the weight loss of the paint film after being placed at 125℃ for 24 h is tested according to the standard ASTM E595 15 (2021). Three specimens are tested for each embodiment or comparative example. The final result is recorded as the adhesion grade. The test result on the cleaned plate is marked as adhesion 1, and the test result on the uncleaned plate is marked as adhesion 2. (4) Salt spray resistance: The double-cured conformal coatings obtained in the above embodiments and comparative examples are applied to a 50mm×50mm×1.5mm copper-clad board using a 100μm wet film preparer. After being fully leveled, the coatings are cured by a UV curing machine with a wavelength of 365 nm mercury lamp and a wavelength of 300mW / cm. 2 Radiation curing for 5 seconds, followed by curing at room temperature for 7 days, and then salt spray testing according to GB / T 2423.17 2008. The test is stopped when one of the following phenomena appears: bubbles, cracks, peeling or rust spots. The salt spray resistance time when the paint film defects appear is recorded.

[0075] The specific test results are shown in Table 3 below: Table 3 Summary of Performance Test Results As shown in Table 3, the dual-curing conformal coating achieves initial strength after UV curing, exhibiting low hardness (generally only Shore 60-75A) and high flexibility. After 3 days of moisture curing, the conformal coating shows significantly higher hardness and strength. Examples 1-9 of this invention provide dual-curing conformal coatings that, after UV curing and subsequent 3 days of room temperature moisture curing, all achieve a hardness of Shore 60D or higher, with thermal weight loss of <1.2% and salt spray resistance exceeding 500 h. Particularly on contaminated and uncleaned PCBs, the conformal coatings of this invention demonstrate significantly superior adhesion (0-1 level) compared to the comparative examples. Comparative Example 1 uses the commonly used UV adhesion promoter KH570, which exhibits higher final hardness, but shows very weak adhesion on uncleaned PCBs, and the lack of adhesion also leads to a decline in salt spray resistance. Comparative Example 2, without the adhesion promoter of this invention or other types of latent curing agents, experienced a significant decrease in wet curing speed, with a 3D hardness of only Shore 45D. Furthermore, some bubbles appeared in the conformal coating, severely impacting its adhesion and salt spray resistance. Comparative Example 3, lacking a fluorinated wetting agent, exhibited excellent adhesion (Grade 0) on clean PCBs, but showed poor wetting on contaminated PCBs, resulting in decreased adhesion and a slight decline in salt spray resistance.

[0076] In summary, the dual-curing conformal coating and its preparation method provided by this invention innovatively introduce an adhesion promoter (A4) with dual functions of oxazolidine and siloxane, and work synergistically with a short-chain fluorinated wetting and leveling agent (A7) and an acidic catalyst (A8). This systematically solves the core technical problem of poor wetting and insufficient adhesion of existing UV moisture-curing conformal coatings on contaminated or low-surface-energy PCB substrates. The dual-curing conformal coating provided by this invention features rapid performance build-up, high final hardness, low thermal weight loss, and good salt spray resistance. Especially for PCB boards with contaminated surfaces that have not been completely cleaned, this conformal coating exhibits excellent wetting and strong adhesion, making it highly valuable in the market.

[0077] Specifically: First, without prior substrate cleaning, excellent adhesion of grade 0-1 can be achieved on contaminated PCBs, significantly superior to solutions using traditional silane coupling agents (grades 3-5), fundamentally improving product reliability. Second, through the controlled hydrolysis of oxazolyl groups under acidic conditions, rapid moisture curing and the generation of internal plasticizers are achieved, effectively reducing curing shrinkage stress and preventing the formation of bubbles and pinholes, thereby synergistically ensuring the coating's excellent salt spray resistance and high hardness for over 500 hours. Finally, this invention provides a highly efficient, environmentally friendly, and simple protective solution, not only eliminating the expensive substrate cleaning process and reducing production costs, but also being free of harmful substances such as PFOA, complying with stringent environmental regulations, and possessing outstanding market competitiveness and broad prospects for industrial application.

[0078] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A dual-curing conformal coating, characterized in that, The product comprises the following components in the indicated weight ratios: Component A1: 25-65 parts of polyurethane acrylate oligomer containing isocyanate groups; Component A2: 20-60 parts of diluent monomer; Component A4: 0.5-10 parts of siloxane adhesion promoter containing oxazolidine; Component A5: latent curing agent other than A4; wherein the amount of component A5 is such that the total molar ratio of isocyanate groups in component A1 to the total molar ratio of isocyanate reactive groups in components A4 and A5 is in the range of (2:1) to (1:2).

2. The dual-curing conformal coating according to claim 1, characterized in that, Specifically, it consists of the following components by weight percentage. Composition: Component A1: Polyurethane acrylate oligomer containing isocyanate groups, 25-65%; Component A2: Diluent monomer, 20-60%; Component A3: Dehydrating agent, 0.5-4%; Component A4: Siloxane adhesion promoter containing oxazolidine, 0.5-10%; Component A5: Latent curing agent other than A4; its isocyanate reactive group equivalent is 122 g / mol, 2.5-5%; Component A6: Photoinitiator, 1-10%; Component A7: Wetting and leveling agent, 0.1-1%; Component A8: Acidic catalyst, 0.1-1%; Component A9: Isocyanate catalyst, 0.01-1%; Component A10: Antioxidant, 0.2-2%.

3. The dual-curing conformal coating according to claim 1, characterized in that, Component A4 is prepared from the following components: Component I: hydroxyl-containing oxazolidine; Component II: Silane containing isocyanate reactive groups; Component III: Difunctional or polyfunctional isocyanates.

4. The dual-curing conformal coating according to claim 3, characterized in that, The hydroxyl-containing oxazolidine in component I is formed by the condensation polymerization of diolamine compounds and alkyl or aralkyl aldehyde compounds using an acidic catalyst. The structure of component I is as follows: Wherein R1 and R2 are ethylene or isopropyl; when both R1 and R2 are ethylene, the diolamine is diethanolamine; when both R1 and R2 are isopropyl, the diolamine is diisopropanolamine; R3 is an alkyl or aralkyl group having 8-30 carbon atoms; and component II is one of 3-(N-cyclohexylamino)propyltrimethoxysilane, 3-(N-cyclohexylamino)propyltriethoxysilane, 3-(N-cyclohexylamino)propylmethyldimethoxysilane, N-(n-butyl)-γ-aminopropyltrimethoxysilane, N-(n-butyl)-γ-aminopropyltriethoxysilane, N-(n-butyl)-γ-aminopropylmethyldiethoxysilane, N-(phenyl)-γ-aminopropyltrimethoxysilane, N-(phenyl)-γ-aminopropyltriethoxysilane, and N-(phenyl)-γ-aminopropylmethyldiethoxysilane.

5. The dual-curing conformal coating according to claim 3, characterized in that, Component A7 is a polyether-modified fluoropolymer with a perfluoroalkyl chain length of C4.

6. The dual-curing conformal coating according to claim 1, characterized in that, The isocyanate group content in component A1 is 2-18% by mass, and the polyurethane acrylate oligomer containing isocyanate group contains an olefinic unsaturated double bond with radiation curing activity. The olefinic unsaturated double bond can be selected from vinyl, propylene, allyl ether, acryloyl or methacryloyl.

7. The dual-curing conformal coating according to claim 1, characterized in that, Component A8 is selected from salicylic acid or benzoic acid.

8. A method for preparing the dual-curing conformal coating according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Under light-protected conditions, mix components A2, A6 and A10 and stir under vacuum to form a homogeneous mixture; S2: Add component A3, stir until the water content of the system is below 300 ppm, then add components A1, A4 and A5, and continue stirring and mixing; S3: Add component A7, disperse by high-speed stirring, then add components A8 and A9, and stir and degas under vacuum conditions.

9. The method for preparing the dual-curing conformal coating according to claim 8, characterized in that, The component A4 is prepared from the following components: Component I: hydroxyl-containing oxazolidine; Component II: silane containing isocyanate reactive groups; Component III: difunctional or polyfunctional isocyanate; The preparation method of the component A4 is as follows: (1) Add 1 mol of component III to the reaction vessel, set the stirring speed to 50-200 r / m, control the temperature to 20-40℃, and add 1 mol of component I to the reaction vessel dropwise within 30-90 minutes; (2) After the dropwise addition is completed, raise the temperature to 70-90℃ within 30-90 minutes and continue the reaction until the NCO mass fraction reaches the theoretical value; (3) Cool down to 10-30℃, add the component II to the reaction vessel dropwise within 30-90 minutes, and then raise the temperature to 50-70℃ and react until the NCO mass fraction drops to 0%, to obtain component A4.

10. The application of the double-curing conformal coating according to any one of claims 1-7 in the protection of an uncleaned, contaminated printed circuit board surface.

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