High-reflectivity photosensitive white oil and preparation method thereof

Abstract

The invention discloses high-reflectivity photosensitive white oil and a preparation method thereof, the photosensitive white oil comprises the following components: modified alkali-soluble resin, a photopolymerizable compound, a photoinitiator, titanium dioxide, a solvent and an auxiliary agent, and the core of the photosensitive white oil is that the modified alkali-soluble resin is acrylic resin into which phosphorus-containing groups and / or sulfur-containing groups are introduced; the intrinsic refractive index of the resin is improved through molecular design, so that the use amount of titanium dioxide is remarkably reduced while high reflectivity is ensured, and the leveling property, printing adaptability and curing depth of the ink are effectively improved. The obtained product is good in adhesive force, good in heat resistance, small in lateral erosion, excellent in comprehensive performance and suitable for the field of manufacturing of PCBs with high requirements for reflectivity.

Description

Technical Field

[0001] This invention belongs to the technical field of materials for printed circuit board manufacturing, specifically relating to a high-reflectivity photosensitive white oil and its preparation method. Background Technology

[0002] Photosensitive white oil (or photosensitive solder resist white oil) is a key material in PCB manufacturing, widely used in fields requiring high reflectivity, such as LED bracket boards and backlight panels (BLU). Its high reflectivity is crucial for improving the light extraction efficiency of LEDs and the brightness uniformity of backlight modules.

[0003] Currently, the mainstream technical approach in the industry to improve the reflectivity of photosensitive white oil is to increase the amount of high-refractive-index inorganic pigments (mainly titanium dioxide). The refractive index of titanium dioxide (rutile type is about 2.7) is much higher than that of organic resins (about 1.5~1.6), and it achieves high reflectivity through its scattering effect in the resin system.

[0004] However, this technical approach has obvious drawbacks: 1. Deterioration of rheological and printability: Excessive titanium dioxide content will cause the ink viscosity to rise sharply and the thixotropy to deteriorate, affecting the printing leveling and uniformity on the PCB board surface, and easily causing problems such as printing streaks and screen clogging.

[0005] 2. Decreased curing performance: A large number of titanium dioxide particles will severely scatter and reflect ultraviolet light, hindering the photoinitiator from absorbing effective light energy, resulting in insufficient ink curing depth, sticky surface, or incomplete curing.

[0006] 3. Deterioration of mechanical properties: Excessive inorganic fillers can disrupt the continuity of the organic resin system, leading to a decrease in the adhesion, flexibility, and chemical resistance of the cured film, making it prone to cracking and peeling during subsequent processing (such as bending and thermal shock).

[0007] Therefore, there is an urgent need for a new method that can effectively improve the reflectivity of photosensitive white oil without significantly increasing the amount of titanium dioxide used. Summary of the Invention

[0008] To address the above problems, the present invention aims to provide a high-reflectivity photosensitive white oil and its preparation method.

[0009] The specific technical solution is as follows: A high-reflectivity photosensitive white oil comprises the following components by weight: 20-50 parts of modified alkali-soluble resin 10-30 parts of photopolymerizable compound 1-5 parts of photoinitiator 15-35 parts titanium dioxide 15-30 parts of solvent Additives: 0.5-3 parts; The modified alkali-soluble resin is an acrylic resin incorporating phosphorus-containing groups and / or sulfur-containing groups.

[0010] Furthermore, the phosphorus-containing group is selected from one or more of phosphate ester group, phosphonate group, and phosphonium oxide group, and the sulfur-containing group is selected from one or more of sulfate ester group, sulfone group, and thioether bond.

[0011] Furthermore, the modified alkali-soluble resin is copolymerized from a mixture of phosphorus-containing acrylate monomers and / or sulfur-containing acrylate monomers, wherein the total weight of the phosphorus-containing acrylate monomers and / or sulfur-containing acrylate monomers accounts for 5-50% of the total weight of the monomer mixture.

[0012] Furthermore, the phosphorus-containing acrylate monomer is methacryloyloxyethyl phosphate, and the sulfur-containing acrylate monomer is ethyl methacrylate-2-sulfonate.

[0013] Furthermore, the photopolymerizable compound is a compound having at least one olefinic unsaturated group, such as dipentaerythritol penta / hexaacrylate (DPHA), trimethylolpropane triacrylate (TMPTA), ethoxylated trimethylolpropane triacrylate, etc.

[0014] Furthermore, the titanium dioxide is rutile titanium dioxide, with a particle size controlled between 0.1 and 0.5 μm. Furthermore, the solvent is propylene glycol methyl ether acetate (PMA), diethylene glycol butyl ether acetate, or carbitol.

[0015] Furthermore, the additives are leveling defoamers and dispersants.

[0016] A method for preparing a high-reflectivity photosensitive white oil includes the following steps: 1) Premix a portion of the modified alkali-soluble resin, titanium dioxide, a portion of the solvent, and a dispersant; 2) Disperse and grind the mixture from step 1) until the fineness is ≤15μm to obtain a slurry; 3) The slurry from step 2) is thoroughly mixed with the remaining modified alkali-soluble resin, photopolymerizable compound, photoinitiator, remaining solvent and leveling defoamer under stirring conditions, and then filtered to obtain high reflectivity photosensitive white oil.

[0017] The beneficial effects of this invention are as follows: 1) This invention introduces phosphorus and sulfur groups, which improves the refractive index of the resin at the resin molecule design level, and directly improves the reflectivity of the photosensitive white oil. 2) Under the premise of achieving the same level of reflectivity, the amount of titanium dioxide can be reduced by 20% to 40%, resulting in suitable ink viscosity, good leveling properties, good printability, and less screen clogging. 3) Due to the reduced amount of titanium dioxide used, the penetration depth of ultraviolet light increases, resulting in more thorough curing; 4) The cured ink of this invention maintains good adhesion and heat resistance, and has passed various reliability tests related to PCB. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited thereto.

[0019] Example 1 Synthesis of phosphorus-containing acrylic resin: In a four-necked flask equipped with a stirrer, condenser, thermometer, and dropping funnel, 50 parts of propylene glycol methyl ether acetate (PMA) were added, and the temperature was raised to 110°C. Over 3 hours, a mixed solution consisting of 20 parts of methyl methacrylate (MMA), 15 parts of styrene (St), 10 parts of methacrylic acid (MAA), 10 parts of methacryloyloxyethyl phosphate (PAM-100), 2 parts of hydroxyethyl acrylate (HEA), and 3 parts of azobisisobutyronitrile (AIBN) was added dropwise at a uniform rate. After the addition was complete, the reaction was maintained at this temperature for 2 hours. Then, 1 part of AIBN was added, and the reaction was continued for another 2 hours. The temperature was then lowered to below 50°C, and the product was discharged to obtain a phosphorus-modified alkali-soluble resin A with a solid content of approximately 50%.

[0020] Preparation of photosensitive white ink: 15 parts of phosphorus-modified alkali-soluble resin A, 25 parts of titanium dioxide, 10 parts of PMA and 1 part of dispersant were added to a mixing tank and pre-dispersed. The mixture was then ground to a fineness of ≤10μm using a sand mill to obtain a slurry. The slurry was transferred to a paint mixing tank and the remaining 20 parts of phosphorus-modified alkali-soluble resin A, 15 parts of DPHA, 3 parts of photoinitiator, 10 parts of PMA and 0.5 parts of leveling defoamer were added. The mixture was stirred at low speed for 1 hour until completely homogeneous. The mixture was then filtered through an 800-mesh screen to obtain the photosensitive white ink.

[0021] Example 2 Synthesis of sulfur-containing acrylic resin: In a four-necked flask equipped with a stirrer, condenser, thermometer, and dropping funnel, 50 parts of propylene glycol methyl ether acetate (PMA) were added, and the temperature was raised to 110°C. Over 3 hours, a mixed solution consisting of 20 parts of methyl methacrylate (MMA), 15 parts of styrene (St), 10 parts of methacrylic acid (MAA), 10 parts of ethyl methacrylate-2-sulfonate (sulfur-containing monomer), 2 parts of hydroxyethyl acrylate (HEA), and 3 parts of azobisisobutyronitrile (AIBN) was added dropwise at a uniform rate. After the addition was complete, the reaction was maintained at this temperature for 2 hours. One part of AIBN was added, and the reaction continued for another 2 hours. The temperature was lowered to below 50°C, and the product was discharged to obtain sulfur-modified alkali-soluble resin B with a solid content of approximately 50%.

[0022] 2) Preparation of photosensitive white ink: 15 parts of sulfur-modified alkali-soluble resin B, 25 parts of titanium dioxide, 10 parts of PMA and 1 part of dispersant are added to a mixing tank. After pre-dispersion, the mixture is ground to a fineness of ≤10μm using a sand mill to obtain a slurry. The slurry is then transferred to a paint mixing tank, and the remaining 20 parts of sulfur-modified alkali-soluble resin B, 15 parts of DPHA, 3 parts of photoinitiator, 10 parts of PMA and 0.5 parts of leveling defoamer are added. The mixture is stirred at low speed for 1 hour until completely homogeneous. After filtration through an 800-mesh screen, the photosensitive white ink is obtained.

[0023] Example 3 Following the procedures in Examples 1 and 2, phosphorus-modified alkali-soluble resin A and sulfur-modified alkali-soluble resin B were prepared respectively. 7.5 parts of phosphorus-modified alkali-soluble resin A, 7.5 parts of sulfur-modified alkali-soluble resin B, 25 parts of titanium dioxide, 10 parts of PMA, and 1 part of dispersant were added to a mixing tank. After pre-dispersion, the mixture was ground to a fineness ≤10 μm using a sand mill to obtain a slurry. This slurry was transferred to a paint mixing tank, and the remaining 10 parts of phosphorus-modified alkali-soluble resin A, 10 parts of sulfur-modified alkali-soluble resin B, 15 parts of DPHA, 3 parts of photoinitiator, 10 parts of PMA, and 0.5 parts of leveling defoamer were added. The mixture was stirred at low speed for 1 hour until completely homogeneous. The resulting photosensitive white ink was obtained by filtering through an 800-mesh screen.

[0024] Comparative Example 1 Using ordinary unmodified acrylic resin (copolymerized from MMA, St, MAA, and HEA), 15 parts of ordinary unmodified acrylic resin, 25 parts of titanium dioxide, 10 parts of PMA, and 1 part of dispersant were added to a mixing tank. After pre-dispersion, the mixture was ground to a fineness of ≤10μm using a sand mill to obtain a slurry. The slurry was then transferred to a paint mixing tank, and the remaining 20 parts of ordinary unmodified acrylic resin, 15 parts of DPHA, 3 parts of photoinitiator, 10 parts of PMA, and 0.5 parts of leveling defoamer were added. The mixture was stirred at low speed for 1 hour until completely homogeneous. After filtration through an 800-mesh screen, a photosensitive white ink was obtained.

[0025] Comparative Example 2 Referring to Comparative Example 1, the amount of titanium dioxide added was increased to 30 parts, while other operating conditions remained unchanged, resulting in a photosensitive white ink.

[0026] Performance testing The photosensitive white oils prepared in Examples 1-3 and Comparative Examples 1-2 were screen-printed onto a standard LED test substrate, pre-baked at 75°C for 30 minutes, exposed to UV (500mj / cm²), developed with a 1% sodium carbonate aqueous solution, and cured at 150°C for 60 minutes to form a cured photosensitive ink layer.

[0027] Test Standards Adhesion: After cross-cutting with a cross-cutting tool using IPC-SM-840 3.5.2.1 / IPC-TM-650 2.4.28.1, a peel test was performed using adhesive tape. Solder-resistant: Rosin-based flux; Floating solder method: 288℃ / 10 seconds x 3 times; Pencil hardness: IPC-SM-840C 3.5.1 / IPC-TM-650 2.4.2 7.2; Scratches should not damage the coating or expose the copper foil surface. It is qualified; Sensitivity: Exposure energy 500mj / cm², 21-stop exposure scale; Reflectivity: GB / T 23981-2009, wavelength 450nm; Lateral erosion: 3D depth-of-field microscopic observation; Acid resistance: 100 vol% H2SO4; after soaking at room temperature for 30 minutes, a peel test is performed using adhesive tape. Alkali resistance: 10wt% NaOH; after soaking at room temperature for 30 minutes, a peel test is performed using adhesive tape.

[0028] Table 1 Summary of test results for the examples and comparative examples Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Pre-baking Non-sticky Slightly sticky Non-sticky Non-sticky Non-sticky Adhesion 100 / 100 100 / 100 100 / 100 100 / 100 98 / 100 Solder-resistant Pass Pass Pass Pass Pass Pencil hardness 6H 5H 6H 6H 5H Sensitivity 10 9 10 10 9 reflectivity 93.1 91.8 93.5 89.2 92.2 Lateral erosion good good excellent good Difference Acid resistance Pass Pass Pass Pass Pass Alkali resistance Pass Pass Pass Pass Pass The test results show that, under the same titanium dioxide dosage, the photosensitive white oils prepared in Examples 1-3 of this invention have significantly better reflectivity than Comparative Example 1. Comparative Example 2 increased reflectivity by adding titanium dioxide, but its lateral etching performance was poor, adhesion decreased, and sensitivity decreased. This fully demonstrates the effectiveness and superiority of this invention in improving reflectivity through resin modification.

Claims

1. A high-reflectivity photosensitive white oil, characterized in that, It includes the following components in parts by weight: 20-50 parts of modified alkali-soluble resin 10-30 parts of photopolymerizable compound 1-5 parts of photoinitiator 15-35 parts titanium dioxide 15-30 parts of solvent Additives: 0.5-3 parts; The modified alkali-soluble resin is an acrylic resin incorporating phosphorus-containing groups and / or sulfur-containing groups.

2. The high-reflectivity photosensitive white oil as described in claim 1, characterized in that, The phosphorus-containing group is selected from one or more of phosphate ester group, phosphonate group, and phosphonium oxide group, and the sulfur-containing group is selected from one or more of sulfate ester group, sulfone group, and thioether bond.

3. The high-reflectivity photosensitive white oil as described in claim 1, characterized in that, The modified alkali-soluble resin is copolymerized from a mixture of phosphorus-containing acrylate monomers and / or sulfur-containing acrylate monomers, with the total weight of the phosphorus-containing acrylate monomers and / or sulfur-containing acrylate monomers accounting for 5-50% of the total weight of the monomer mixture.

4. The high-reflectivity photosensitive white oil as described in claim 3, characterized in that, The phosphorus-containing acrylate monomer is methacryloyloxyethyl phosphate, and the sulfur-containing acrylate monomer is ethyl 2-methacrylate.

5. The high-reflectivity photosensitive white oil as described in claim 1, characterized in that, Photopolymerizable compounds are compounds having at least one olefinic unsaturated group.

6. The high-reflectivity photosensitive white oil as described in claim 1, characterized in that, The solvent is propylene glycol methyl ether acetate, diethylene glycol butyl ether acetate, or carbitol.

7. The high-reflectivity photosensitive white oil as described in claim 1, characterized in that, The additives are leveling defoamers and dispersants.

8. A method for preparing a high-reflectivity photosensitive white oil as described in claim 7, characterized in that, Includes the following steps: 1) Premix a portion of the modified alkali-soluble resin, titanium dioxide, a portion of the solvent, and a dispersant; 2) Disperse and grind the mixture from step 1) until the fineness is ≤15μm to obtain a slurry; 3) The slurry from step 2) is thoroughly mixed with the remaining modified alkali-soluble resin, photopolymerizable compound, photoinitiator, remaining solvent and leveling defoamer under stirring conditions, and filtered to obtain high reflectivity photosensitive white oil.