High-performance substrate coating for liquid resin plate and coating process of high-performance substrate coating

Abstract

The invention relates to a high-performance substrate coating for a liquid resin plate and a coating process of the high-performance substrate coating, and belongs to the technical field of printing plate making. According to the coating, a PET base material is subjected to corona or plasma pretreatment, water-based hybrid resin containing silane functional groups is introduced to serve as a film forming base body, the water-based hybrid resin is compounded with nano particles with the particle size being 1-5 microns and multiple functional auxiliaries, and coating liquid is prepared. The coating liquid is subjected to pre-drying, heat treatment and damp and hot curing processes to form a coating with the thickness of 10-40 microns, and the coating serves as a transparent and stable functional bridge layer, can be firmly combined with a PET base material and provides reliable interface support for adhesion of subsequent photosensitive resin or other plate-making layers. The formed coating does not shrink after being cured, has good water resistance, excellent adhesive force and relatively high light transmittance and surface hardness, so that the dimensional stability and the service life are ensured, and the comprehensive performance requirements of printing plate making are met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of printing plate making, in particular to a high-performance base sheet coating for liquid resin plates and a coating process thereof. BACKGROUND

[0002] Liquid resin plates are widely used in the field of printing plate making, and their structure is usually composed of a substrate and a surface coating. As a key functional layer of liquid resin plates, the base sheet coating not only needs to ensure excellent adhesion with the substrate, but also needs to provide reliable support and interface performance for subsequent liquid photosensitive resin coating, UV curing and plate washing processes. Therefore, the composition and coating process of the coating directly determine the overall performance and service life of the liquid resin plate in printing plate making.

[0003] In the prior art, the base sheet coating generally uses a solvent-based resin system, such as solvent-based polyurethane and solvent-based acrylic resin. This type of coating requires the use of a large amount of organic solvent during the formation process, which not only releases a large amount of volatile organic compounds (VOCs) during production and use, causing serious environmental pollution and occupational health risks, but also has a limited application space as global green manufacturing and carbon emission reduction policies are being promoted. At the same time, solvent-based coatings are prone to yellowing, residual solvent precipitation, and insufficient surface hardness during thermal processing, resulting in poor long-term stability and reliability.

[0004] To solve the environmental problem, in recent years, water-based base sheet coating systems represented by water-based polyurethane and water-based acrylic resin have gradually emerged. Water-based coatings have the advantages of low VOC emissions, environmental friendliness, process safety, etc., and are more in line with the direction of industrial development in theory. However, in the actual application of liquid resin plates, the existing water-based coatings still have the following shortcomings: Insufficient coating adhesion: due to the low surface energy of PET and other high molecular substrates, the interfacial bonding force of water-based coatings is insufficient, which is prone to blistering, peeling or delamination, especially in hot and humid environments and over a long period of use; Poor thermal stability and reliability: the resin of the water-based system has insufficient heat resistance, which is prone to performance degradation or coating brittle fracture during subsequent thermal pressing, curing and long-term use of the liquid resin plate; Complex process and high defect rate: the existing water-based coating process has strict requirements for coating liquid stability and construction environment, which is prone to problems such as shrinkage, orange peel, surface defects, etc., and is not conducive to large-scale stable production.

[0005] In view of the above problems, some research and patents have proposed improvements. For example: a published technology such as patent US5853809A improves the leveling property and adhesion by introducing an organic silicon additive into the resin system, but excessive low molecular silicon oil is prone to migration and precipitation, which not only destroys the uniformity of the coating, but also affects the subsequent lamination or bonding process.

[0006] There are also studies trying to improve the coating hardness by sol-gel hybrid technology, but its reaction system is complex, often accompanied by particle agglomeration or poor dispersion stability under aqueous conditions, resulting in unstable coating film quality.

[0007] In summary, the existing technical solutions are still difficult to meet the following needs in the application of liquid resin plate base sheet coating: 1. Thermal stability and long-term reliability: able to withstand subsequent processing and long-term application environment of liquid resin plate; 2. Mechanical and interface performance: good adhesion and high surface hardness to avoid scratching and peeling; 3. Green environmental protection: low VOC emission, in line with environmental regulations; 4. Optical performance: high haze and high light transmittance, ensuring optical uniformity; 5. Process simplicity: coating and curing process is simplified, easy for large-scale production.

[0008] Therefore, a new technical solution is needed to balance adhesion, optical performance, hardness, reliability and process simplicity in aqueous system, so as to obtain a high-performance base sheet coating for liquid resin plate and its coating process. The development of this scheme has important practical significance and industrial application value. In view of the deficiencies of the prior art, the present application provides a high-performance base sheet coating for liquid resin plate and its coating process to solve the problems raised in the background art.

[0009] To achieve the above purpose, the present application realizes the following technical solutions: 1. Substrate pretreatment The PET substrate is subjected to corona or plasma pretreatment to control the surface energy at 50-58 dyn / cm, so as to enhance the adhesion of the coating to the substrate.

[0010] 2. Preparation of water-based hybrid resin A water-based polyurethane or water-based acrylic dispersion is prepared, and 0.3-2.0 wt% of silane functional groups are introduced into the molecular structure to provide reaction sites for the formation of subsequent organic-inorganic hybrid network.

[0011] 3. Diffusion particle system A diffusion particle dispersion liquid is prepared, and the diffusion particles are PMMA nanoparticles or silica nanoparticles with a particle size of 1-5 μm.

[0012] 4. Additive combination Acrylate leveling agent, silicone defoamer and thermal initiation type curing accelerator are added to improve the coating surface flatness, defoaming performance and crosslinking efficiency.

[0013] The thermal initiation type curing accelerator is selected from peroxide, azo compound or N-alkyl substituted amide.

[0014] 5. Coating liquid preparation The water-based hybrid resin, the diffusion particle dispersion liquid and the auxiliary agent are mixed, the pH is adjusted to 6.8-7.6, and a uniform coating liquid is obtained by filtration. The mass percentage composition of the coating liquid is: water-based hybrid resin 50-60%, PMMA nanoparticles or silicon dioxide nanoparticles 15-25%, silicone antifoam agent 0.5-1%, acrylic ester leveling agent 0.5-1%, thermal initiation type curing accelerator 0.5-1%, and the balance is deionized water.

[0015] 6. Coating and pre-baking The coating liquid is coated on the pretreated substrate, the dry film thickness is controlled to be 10-40 μm, the micro-concave coating method is used, and pre-baking is carried out at 70-80°C for 1-3 min.

[0016] 7. Thermal crosslinking curing The thermal treatment is carried out at 90-120°C for 3-10 min, so that the thermal initiation type curing accelerator initiates the crosslinking reaction of the resin to form a dense organic network.

[0017] 8. Post-curing The post-curing is carried out at 80-90°C and relative humidity of 45-60% for 5-10 min, so that the silane functional group condenses to form an organic-inorganic hybrid network, thereby obtaining a high-performance base sheet coating.

[0018] A coating process for a high-performance base sheet coating for a liquid resin plate, the obtained high-performance base sheet coating is a layer of transparent and stable film substrate, which can be used as a component of a liquid photosensitive resin printing plate.

[0019] The present application provides a high-performance base sheet coating for a liquid resin plate and a coating process thereof. The following beneficial effects are achieved: 1. Excellent bonding strength: by introducing silane functional groups into the water-based polyurethane or acrylic dispersion, and forming an organic-inorganic hybrid network during post-curing, a stable chemical and physical bonding force is formed between the coating and the PET sheet substrate surface and the subsequent liquid photosensitive resin. The bonding layer avoids the problems of peeling and delamination of traditional coatings during printing, ensures that the printing plate can maintain a stable structure under high load and multiple printing conditions, and significantly improves the printing plate life.

[0020] 2. Strong dimensional stability: The coating of the present application forms a dense cross-linked structure during curing, effectively inhibiting the shrinkage and warping phenomena that may occur after UV curing of the liquid resin, ensuring the dimensional accuracy and imaging clarity of the printing plate, meeting the requirements of high-precision printing plate making.

[0021] 3. Good water resistance: The organic-inorganic hybrid network of the coating improves the resistance to hydrolysis, enabling it to resist the erosion of the plate washing liquid during the subsequent plate washing process, without bubbling or peeling due to immersion, ensuring the long-term stability of the bonding force among the base, coating, and resin.

[0022] 4. Improved mechanical properties: Through the strengthening effect of the organic-inorganic hybrid network, the surface hardness of the coating can reach H level, with good scratch resistance and wear resistance, effectively resisting mechanical friction and impression impact during printing.

[0023] 5. Excellent light transmittance and uniformity: The coating maintains a high light transmittance while ensuring firm bonding and durability, which helps the liquid photosensitive resin to obtain uniform light energy distribution during UV exposure and curing, thereby ensuring the imaging quality of the plate making.

[0024] 6. Green and environmentally friendly process: The present application uses a water-based system, significantly reducing VOC emissions, and the production process is safe and environmentally friendly, meeting the requirements of green manufacturing. At the same time, the key parameters such as pH, particle size distribution, and zeta potential in the formula are controlled to ensure the stability and repeatability of the coating liquid and coating quality, suitable for industrial-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Column chart for comparison of haze before and after aging of the samples of Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2; Figure 2 Column chart for comparison of light transmittance before and after aging of the samples of Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION

[0026] To enable persons skilled in the art to understand the present application, the technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, other embodiments obtained by persons skilled in the art without creative labor should be within the scope of protection of the present application.

[0027] The present application will be described in detail below with reference to the drawings: Embodiment 1, a high-performance base sheet coating for liquid resin plates and its coating process, the specific implementation method is as follows: Equipment: dispersion kettle with constant temperature jacket and mechanical stirring, high-speed dispersion machine, vacuum degassing device, 200 mesh stainless steel filter screen; micro-gravure coating table, hot air oven, heat curing oven, corona treatment machine, surface energy instrument, particle size instrument, viscosity meter, conductivity meter.

[0028] I. Pretreatment of the substrate: In the pretreatment process of the substrate, first wipe the surface of the PET roll material (Dongli T60, 75 pm) with isopropyl alcohol (IPA) with non-woven cloth to remove oil stains and fingerprints, and then blow off the dust with filtered water filtered compressed clean air. After cleaning, the operation should be carried out in a clean area. Then, the PET roll material is treated by corona machine, the target surface energy is controlled at 50-58 dyn / cm, and the surface energy test is used to confirm that the surface energy is 55 dyn / cm. The corona parameters are: linear speed 10 m / min, electrode gap 1.0 mm, power 1 kW.

[0029] The treated substrate should be coated immediately, if it needs to be stored, it should be stored in a clean roll material environment and the time should not exceed 24 hours. It should be noted that the pretreatment effect of the substrate directly determines the adhesion of the subsequent coating, if the corona energy is insufficient or there is pollution on the surface, it is easy to cause coating peeling or blistering.

[0030] II. Raw materials of the coating solution: Raw material Specification / model Manufacturer Content (g) Water-based polyurethane resin Bayhydrol® UH 340 BASF, Germany 55 Silica nanoparticles Particle size 3 pm Wacker, Germany 20 Silicone-based defoamer BYK-019 BYK, Germany 1 Acrylate-based leveling agent TEGO Flow 370 Wacker, Germany 1 Thermally initiated curing accelerator Azobisisobutyronitrile (AIBN), AR Aladdin 1 Deionized water —— —— 22 Total —— —— 100 Table 1 Preparation of the coating solution: 1. Preliminary mixing: Add deionized water to the dispersion kettle, start the stirrer, stir at 500 r / min, and at the same time, raise the water temperature to 30°C, keep uniform stirring for 20 min.

[0031] 2. Add resin: Add 55 g of water-based polyurethane resin, continue to stir at 500 r / min for 20 min, so that the resin is fully wetted and uniformly dispersed.

[0032] Add silane reagent, 3-aminopropyltriethoxysilane (APTES), 55 mg, to the resin dispersion. Stir uniformly, and react at 35°C for 60 min to allow the silane to chemically graft with the polyurethane hydroxyl group to obtain a water-based hybrid resin.

[0033] 3. Adjust the pH and conductivity: Measure the pH of the system and adjust it to 7, which can be adjusted slightly with dilute acid or base; at the same time, measure the conductivity to ensure that it is ≤5 pS / cm.

[0034] 4. Particle pre-dispersion: Silica nanoparticles 20 g, particle size 3 μm, were added into a dispersion kettle and pre-wet dispersed at 500 r / min to prevent particle agglomeration. Subsequently, a high-speed disperser was used at 2000 r / min for 30 min to make the particle size distribution uniform and stable.

[0035] 5. Addition of functional additives: After the particles were completely dispersed, organic silicone defoamer 1 g, reactive polysiloxane leveling agent 1 g, and thermal initiation type curing accelerator 1 g were sequentially added. Stirring was continued for 15 min to make the additives fully and uniformly dispersed.

[0036] 6. Intermediate quality control detection Sample detection of key indicators of coating liquid: viscosity, pH, particle size distribution, and absolute value of Zeta potential. The test methods are as follows: Viscosity determination: Brookfield LV was used for testing. Before the experiment, the sample was placed in a constant temperature water bath and adjusted to 25.0°C, and left for 5 min. After stirring the sample, it was poured into a 600 mL standard measuring cup, taking care to avoid air bubbles. LV-2 rotor and speed 60 rpm were selected, and if the torque was not between 10–90%, the speed could be adjusted or the LV-3 rotor could be replaced. When measuring, the rotor was immersed to the mark, the instrument was started and pre-sheared for 60 s, then 3 readings were recorded continuously with an interval of 10 s, and the average value was taken as the result. The viscosity value (mPa·s) was also recorded.

[0037] pH: Glass electrode method was used. Before measurement, standard buffer pH 7.00 and pH 4.00 and pH 10.00 were used for three-point calibration. The sample to be measured was taken in a clean beaker, lightly stirred to remove bubbles, then the electrode was immersed in the solution, left for 60 s until the reading was stable, and the measured pH value was recorded.

[0038] Particle size distribution and D50: Laser diffraction particle size analysis was used. Laser particle size analyzer Mastersizer 3000 was used, equipped with a circulating dispersion tank. The dispersion medium was deionized water (RI=1.33), and the particle optical parameters were set as follows: SiO2 (RI=1.46, Abs=0.01), PMMA (RI=1.49, Abs=0.01). Before testing, the dispersion tank was filled with deionized water to zero, then the sample was added under low-speed stirring, and the light intensity was adjusted to 8%. If the sample had air bubbles, it could be treated by slight vacuum for 60 s to avoid particle breakage. After circulating stirring for 60 s to ensure stable signal, the correct refractive index and absorption rate parameters were set, and 3 continuous tests were taken and averaged, and D50 and distribution curve were reported. The test results should show a single peak distribution, and D50=3 μm, and the batch RSD≤5%.

[0039] Zeta potential: Zeta potential analyzer Zetasizer and folded capillary electrophoresis cell were used in the experiment. The dispersion medium was a low-concentration electrolyte solution of 1-5 mM KCl to ensure stable ionic strength. The sample was diluted to a mass fraction of 0.10 wt%, and after dilution, it was allowed to stand for 5 min to release the bubbles. Before testing, the instrument temperature was set to 25°C and kept constant for 2 min, then the electrophoresis cell was loaded, the Smoluchowski model was selected, and the optical parameters were consistent with the particle size test. Each sample was tested 3 times, and the abnormal value was removed. The final result was reported in the form of average value and standard deviation. |ζ|≥20 mV was considered as sufficient electrostatic stability of the dispersion system.

[0040] Result determination and release rules: The coating liquid needs to meet the following determination criteria in the intermediate quality control test: the viscosity should be controlled in the range of 200-1000 mPa·s, if not qualified, it can be retested after thickening or dilution treatment with deionized water; the pH value should be kept in the range of 6.8-7.6, if it deviates, it should be adjusted with trace acid or base and the amount of added material is recorded; the particle size distribution should be unimodal, D50=3 μm, if it deviates from the target value, the dispersion time, rotation speed or raw material batch should be checked, and if necessary, the dispersion is returned to work; the absolute value of Zeta potential should be ≥20 mV, if not enough, the stability should be improved by optimizing the ionic strength, adjusting the pH or introducing a surface modifier. When the test results meet the above standards, the coating liquid is considered qualified and can enter the coating process. In this embodiment, all test results meet the standards.

[0041] 7. Filtration The coating liquid is filtered through a 200-mesh stainless steel filter into the coating tank to ensure that there are no large particles and impurities.

[0042] III. Coating: Before coating, the equipment and environment need to be prepared. Micro-gravure is selected, the coating parameters are calibrated, and the appropriate line speed and wet film thickness are set. The initial line speed is 10 m / min, and the wet film thickness is 25 μm to ensure that the dry film thickness is stable at 10 μm. The coating tension, roller gap and doctor blade angle are adjusted according to the equipment manual. The operation should be carried out in a clean area, and the environmental temperature is controlled at 25°C and the relative humidity is 60%. The substrate needs to be dusted again before being put on line, and dust-free air blowing can be used to ensure that the surface is clean and free of particles. The feed should be kept stable during the coating process, and the wet film surface should be observed at any time to ensure that there are no obvious stripes and void defects.

[0043] Four, pre-baking and thermal curing: the coated substrate should be immediately into the pre-baking zone to remove moisture, 70℃, residence time 2 min, to avoid pinholes and surface defects due to rapid evaporation. After pre-baking into the thermal curing zone, at 95℃, residence 8 min, so that the thermal initiator is fully decomposed, generating free radicals and initiate resin polymerization and crosslinking reaction. To further promote the condensation reaction of silane groups in the coating, 8 min post-curing at 90℃, 60% relative humidity to form a stable organic-inorganic hybrid network, improve the adhesion and weather resistance of the film.

[0044] Five, cooling: after thermal curing, the coated substrate should be cooled to room temperature.

[0045] In the production and experimental process, the safety risk of azo compounds such as AIBN should be focused on. Such substances are thermally unstable, and weighing and adding should be carried out in a fume hood to avoid self-decomposition due to local high temperature. At the same time, the emission of volatile organic compounds should be strictly controlled. Although the system is mainly aqueous, some additives may release trace amounts of organic components, so the equipment should be equipped with appropriate protection and waste liquid treatment measures. The operator must wear personal protective equipment, including gloves, protective glasses and laboratory coats, and if necessary, use a gas mask to ensure safe operation.

[0046] The coating solution should be stored in the dark at 4℃ and avoid freeze-thaw cycles, and be used within 1-4 weeks to prevent performance drift over time. The finished roll should be stored in a dry environment at room temperature, away from high temperatures, humidity and direct light, to ensure long-term stability of the coating structure and performance.

[0047] Example 2, a high-performance base sheet coating for liquid resin plates and its coating process, the specific implementation is as follows: Equipment: same as example 1.

[0048] One, substrate pretreatment: in this example, the substrate used is Toray PET T100 film, 100 μm thick. The substrate pretreatment and corona parameters are the same as in example 1.

[0049] Two, coating solution raw materials and ratio Raw material Specification / model Manufacturer Content (g) Water-based polyurethane resin Bayhydrol® UH 340 BASF, Germany 55 PMMA particles Particle size 2 pm Mitsubishi Chemical, Japan 20 Silicone-based defoamer BYK-019 BYK, Germany 1 Acrylate-based leveling agent TEGO Flow 370 Wacker, Germany 1 Thermally initiated curing accelerator Azobisisobutyronitrile (AIBN), AR Aladdin 1 Deionized water —— —— 22 Total —— —— 100 Table 2 The coating solution is configured, the steps are basically the same as in example 1, except that: In the fourth step of particle dispersion, replace the silica particles with PMMA particles; the dispersion conditions remain the same, pre-wet dispersion at 500 r / min to prevent particle agglomeration. Then use a high-speed disperser at 2000 r / min for 30 min to make the particle size distribution uniform and stable. The detection results of the intermediate quality control detection in this example all meet the standard.

[0050] Three, coating: using micro concave coating roller, initial setting line speed 10 m / min, wet film thickness 50 pm, to ensure the final dry film thickness in 20 pm. The rest of the steps are the same as example 1.

[0051] Four, pre-baking and thermal curing: the same as example 1.

[0052] Five, cooling: the same as example 1.

[0053] The operation of azo and peroxide thermal initiators should be carried out in a fume hood, wearing personal protective equipment, storing the coating liquid at 4℃ in the dark, avoiding freeze-thaw cycles, and using it within 1-4 weeks; the finished product roll is stored at room temperature, avoiding high temperature and moisture and direct light.

[0054] Example 3, the example provides a high-performance base sheet coating for liquid resin plate and its coating process, the specific implementation is as follows: Equipment: the same as example 1.

[0055] One, substrate pretreatment: in this example, the substrate used is Toray PET T100 film, with a thickness of 100 pm. The substrate pretreatment and corona parameters are the same as example 1.

[0056] Two, coating liquid raw materials and proportioning Raw material Specification / model Manufacturer Amount (g) Water-based polyurethane resin Bayhydrol® UH 340 BASF, Germany 60 Silica particles Particle size 5 pm Wacker, Germany 15 Silicone-based defoamer BYK-019 BYK, Germany 1 Acrylate-based leveling agent TEGO Flow 370 Wacker, Germany 1 Thermally initiated curing accelerator Azobisisobutyronitrile (AIBN), AR Aladdin 1 Deionized water —— —— 22 Total —— —— 100 Table 3 The coating liquid is configured, and the steps are basically the same as example 1, except that: In the fourth step of particle dispersion, replace the particle size 3 pm silica particles with particle size 5 pm silica particles; the dispersion conditions remain the same, pre-wet dispersion at 500 r / min to prevent particle agglomeration. Then use a high-speed disperser at 2000 r / min for 30 min to make the particle size distribution uniform and stable. And the detection results of the intermediate quality control detection of this example all meet the standard.

[0057] Three, coating: using micro concave coating roller, initial setting line speed 10 m / min, wet film thickness 100 pm, to ensure the final dry film thickness in 40 pm. The rest of the steps are the same as example 1.

[0058] Four, pre-baking and thermal curing: the same as example 1.

[0059] Five, cooling: the same as example 1.

[0060] The operation of azo and peroxide thermal initiators should be carried out in a fume hood, wearing personal protective equipment, storing the coating liquid at 4℃ in the dark, avoiding freeze-thaw cycles, and using it within 1-4 weeks; the finished product roll is stored at room temperature, avoiding high temperature and moisture and direct light.

[0061] Comparative Example 1 provides a high-performance base sheet coating of a traditional solvent-based system resin version and its coating process, as follows: Formulation: Raw material name Supplier / brand Specification / model Content (g) Solvent-based polyurethane resin (NMP solution type) Aladdin NMP solution type 55 Silica particles Wacker, Germany AEROSIL® OX50 20 Silicone defoamer BYK, Germany BYK-019 1 Acrylate leveling agent Wacker, Germany TEGO Flow 370 1 Thermally initiated curing accelerator Aladdin Azobisisobutyronitrile (AIBN), AR 1 Toluene, butanone Aladdin Toluene, butanone 22 Table 4 The mass ratio of toluene: butanone is 1:1; the silica particles have a particle size of 3 pm.

[0062] Process steps: Substrate pretreatment: PET web, thickness 100 pm, purchased from a supplier of Toray, used as a coating carrier film. Use non-woven cloth to dip isopropyl alcohol (IPA) to wipe the surface of the PET web to remove oil and fingerprints, and then blow clean air to remove dust.

[0063] Coating liquid preparation: add solvent-based polyurethane resin, silica particles, silicone defoamer, acrylate leveling agent, and thermal initiator to the toluene / butanone mixed solvent according to mass, stir uniformly to form a stable coating liquid. Stirring conditions: 500 r / min for 30 min to ensure complete dispersion of the particles without visible agglomeration.

[0064] Coating: use blade coating to uniformly coat the coating liquid on the PET substrate, with a wet film thickness of 25 pm.

[0065] Drying: drying in a hot air oven, temperature control at 70°C, time for 2 minutes to remove the solvent.

[0066] Curing: curing in a thermal curing oven, temperature control at 95°C, time for 8 minutes to complete the crosslinking reaction.

[0067] Comparative Example 2 provides a high-performance base sheet coating of a water-based system resin version without the introduction of silane functional groups and its coating process, as follows: I. Substrate pretreatment: same as Example 1.

[0068] II. Coating liquid raw materials and proportions, same as Example 1 Raw material Specification / model Manufacturer Content (g) Water-based polyurethane resin Bayhydrol® UH 340 BASF, Germany 55 Silica nanoparticles Particle size 3 pm Wacker, Germany 20 Silicone-based defoamer BYK-019 BYK, Germany 1 Acrylate-based leveling agent TEGO Flow 370 Wacker, Germany 1 Thermally initiated curing accelerator Azobisisobutyronitrile (AIBN), AR Aladdin 1 Deionized water —— —— 22 Total —— —— 100 Table 5 Coating liquid preparation, basically the same as Example 1, with the following differences: In Step 2, only 55 g of water-based polyurethane resin is added to the resin, and stirring is continued at 500 r / min for 20 min to ensure that the resin is fully wetted and uniformly dispersed. The step of chemical grafting of silane with polyurethane hydroxyl groups is cancelled. The intermediate quality control test results of this example all meet the standard.

[0069] III. Coating: same as Example 1.

[0070] IV. Prebake and thermal cure: Same as Example 1.

[0071] V. Cool down: Same as Example 1.

[0072] The operation of azo and peroxide thermal initiators should be carried out under the condition of fume hood, wearing personal protective articles, storing the coating liquid in dark at 4°C, avoiding freeze-thaw cycle, and using up within 1-4 weeks; the finished roll material is stored at room temperature, avoiding high temperature and moisture and direct light.

[0073] To verify the performance difference of the formulations of the examples and comparative examples, the obtained samples were respectively subjected to the following tests, and the specific test methods were as follows: Measurement of light transmittance and haze: To evaluate the optical performance of the coating, a Haze Meter was used for testing. First, the instrument was turned on and calibrated with a standard calibration sheet according to the instruction manual to ensure the accuracy of the zero point and full scale. The sample was cut into a flat sheet suitable for the test aperture, and the surface was cleaned to avoid dust or fingerprints affecting the results. During the test, the sample was placed in the integrating sphere optical system, and the total light transmittance (Tt) and the scattered light component (Td) in the transmitted light were recorded. The haze was calculated according to the formula: Haze (%) = Td / Tt x 100%, and the light transmittance was Tt. Each sample was measured at least 3 times in different areas, and the average value was taken as the result.

[0074] The surface pencil hardness test used the ASTM D3363 method, and the purpose was to evaluate the resistance of the coating surface to scratching. The target hardness of this process was H. The instruments and consumables required for testing included a pencil hardness tester with a fixed angle of 45°, a load of 750g, a full series of Mitsubishi drawing pencils from 6B to 6H, 400# sandpaper, and a clean dust-free cloth. Before testing, the pencil was shaved to remove the wooden part and leave a 3 mm core, and the tip was ground flat with sandpaper to ensure smoothness without burrs; at the same time, the sample surface was cleaned to ensure no dust or oil. Then the pencil was loaded into the tester, and the tip was kept at a 45° contact angle with the sample surface, and a 10 mm long line was drawn at a constant speed of 1.0 mm / s under the specified load. During the test, the pencil should be used for scratch testing from hard to soft in turn, and the highest hardness pencil grade that does not produce obvious scratches was recorded, and the result was expressed in pencil hardness. In this process, the coating should reach H, i.e. pencil H does not produce scratches, and 2H produces scratches. To ensure reliability, at least 3 areas of each sample were tested and the average value was taken, and if there were batch differences, the film thickness and curing condition process factors should be reviewed.

[0075] To evaluate whether the coating of the present application can firmly bond the PET substrate with the subsequent liquid photosensitive resin layer under actual plating conditions, the plating process was reproduced on the "PET substrate + coating" samples prepared in Examples 1-3 and Comparative Examples 1-2 to obtain a complete sandwich structure, i.e., PET substrate-coating-photosensitive resin, and then adhesion testing was performed.

[0076] The "PET substrate + coating" was prepared according to the process of Examples 1-3 and Comparative Examples 1-2, and the surface of the "PET substrate + coating" was cleaned to reproduce the on-site operation before plating. A commonly used liquid photosensitive resin was uniformly coated on the surface of the "PET substrate + coating", UV cured, and exposed and post-cured according to the recommended dose and light source conditions of the photosensitive resin supplier. After the sample was naturally cooled, it was ready for use and quantitative adhesion testing was performed. The testing method was as follows: after the surface of the sample to be tested was cleaned and dried, the tape was peeled off at a constant speed along the direction perpendicular to the surface of the sample according to the method specified in ASTM D3359-17 standard, and the peeling angle was controlled at 180°. After peeling, the coating shedding was observed, and the coating adhesion grade was evaluated according to the standard rating table. In addition, before curing, a high-precision image measuring instrument was used to mark a reference line on the surface of the sample, and the reference length was recorded. After UV curing, the reference length at the same position was measured again, and the size retention rate was calculated.

[0077] Adhesion rating standard: 5B The edge of the cut is completely smooth: all squares of the lattice are not separated; 4B Small flakes of coating are separated at the intersection: the affected area is less than 5%; 3B Small flakes of coating are separated along the edge and intersection of the cut. The affected area is 5% to 15% of the lattice; 2B The coating is peeled off along the square edge and part of the area. The affected area is 15% to 35% of the lattice; 1B The coating is peeled off along the cut edge of the large color band, and the entire square is separated. The affected area is 35% to 65% of the lattice; 0B Peeling and falling off is more severe than 1B grade.

[0078] The test results are shown in the following table.

[0079] Sample Adhesion grade Haze (%) Transmittance (%) Surface pencil hardness Dimensional retention (%) Example 1 5B 92 91 H 99.3 Example 2 5B 93 90 H 99.2 Example 3 5B 96 87 H 99.0 Comparative Example 1 3B 88 80 HB 97.0 Comparative Example 2 4B 91 85 H 98.1 Table 6 To further evaluate the aging resistance of each coating, accelerated aging tests were performed on the dry film samples of Examples 1-3 and Comparative Examples 1-2, as well as the PET substrate-coating-photosensitive resin samples. The aging conditions were 85°C and 85% relative humidity for 200 hours. After aging, the adhesion, haze, light transmittance, and surface pencil hardness of the samples were determined according to the same methods as the initial properties. The test results were used to compare the changes in adhesion, haze, light transmittance, and surface hardness of each system under high temperature and high humidity conditions, with reference to Figure 1 and Figure 2.

[0080] Sample Adhesion grade after aging Haze (%) after aging Transmittance (%) after aging Surface hardness after aging Example 1 5B 90 89 H Example 2 5B 91 88 H Example 3 5B 94 85 H Comparative Example 1 2B 84 78 HB Comparative Example 2 3B 85 80 1B Table 7 Comprehensive comparison shows that the embodiments 1-3 of the present application can achieve higher light transmittance while maintaining adhesion and high haze, and the surface hardness reaches H level; The coating of the present application has excellent adhesion. Embodiments 1-3 all show 5B in the adhesion test, and still maintain 5B level after high temperature and high humidity aging, showing stable performance with zero attenuation; in contrast, the comparative sample all shows different degrees of decline. The fundamental reason is that the present application forms an organic-inorganic hybrid network through silane functional groups and the matrix and inorganic phase in the post-curing stage, so that the coating and PET substrate have the synergistic enhancement of chemical bonding, polarity and mechanical bite action at the same time, which is much stronger than the system in the comparative example which simply relies on physical adsorption. Therefore, in high-load and multiple printing applications, the risk of peeling and delamination can be significantly reduced, ensuring that the printing plate can still maintain a stable structure during long-term use, and the printing life can reach more than 10,000 times.

[0081] The present application has excellent dimensional stability. Test results show that after repeating the plate making process and UV curing, the dimensional retention rate of embodiments 1-3 is not less than 99%, and there is no shrinkage; while the dimensional retention rate of comparative examples 1 and 2 has different degrees of shrinkage. The results show that the organic-inorganic hybrid coating of the present application effectively inhibits the dimensional deviation caused by curing shrinkage, significantly improving the dimensional stability of the plate making. And embodiments 1-3 maintain H level hardness before and after aging, and the transmittance and haze retention rate are all above 97%, indicating that the coating network does not appear to be hygroscopic and softening and thermoplastic under the condition of heat and humidity, and the structure relaxation and stress accumulation are effectively inhibited. This stability is particularly important in actual plate making process, which can effectively avoid the shrinkage and warping problem after UV curing, and ensure the dimensional accuracy and registration accuracy of the printing plate; relatively speaking, the hardness of comparative example 2 decreases obviously, and it is more likely to cause dimensional deviation and surface damage in actual application.

[0082] The coating of the present application has good water resistance. Under the accelerated aging conditions of 85℃, 85%RH and 200 hours, the hydrolysis and wet heat erosion environment can be simulated, and the samples of embodiments 1-3 still maintain the stability of adhesion, optical properties and surface hardness after aging, while the comparative sample shows obvious attenuation, especially comparative example 2. This shows that the organic-inorganic hybrid network of the present application significantly improves the anti-hydrolysis ability of the coating, so that it can resist long-term immersion in the plate washing solution in the subsequent plate washing process, avoiding failure due to hydrolysis, thereby ensuring the long-term stability of the adhesion of the PET-coating-photosensitive resin three-layer structure.

[0083] The application can effectively improve the mechanical properties of the coating. Test results show that the samples of Examples 1-3 maintain H-grade hardness before and after aging, and have good scratch resistance and wear resistance; while Comparative Example 2 decreases from H-grade to 1B-grade, showing serious performance degradation. It can be seen that the strengthening effect of the organic-inorganic hybrid network in the application makes the coating surface maintain high hardness and durability after humid heat aging, and can effectively resist mechanical impact such as friction and pressure printing during actual printing and handling, thereby prolonging the service life.

[0084] The coating of the application has excellent light transmittance and optical uniformity. After aging, the light transmittance of the samples of Examples 1-3 is maintained at more than 85%, and the haze retention rate is more than 90%, ensuring the uniformity of light energy distribution during UV exposure, which is helpful to obtain clear imaging effect and high-precision reproduction of fine lines. In contrast, Comparative Example 2 has obvious attenuation in terms of light transmittance and haze, which may lead to uneven distribution of exposure energy, thereby causing the imaging window to narrow and the image quality to fluctuate. It can be seen that the application can maintain excellent optical performance while ensuring firm bonding and durability, and is suitable for high-precision plate making requirements.

[0085] The application meets the requirements of green environmental protection and controllable process. The coating is prepared by using a water-based system, which significantly reduces VOC emissions and avoids environmental and safety risks caused by toluene and butanone organic solvents in Comparative Example 1. At the same time, the application strictly controls the key parameters of pH, particle size distribution and zeta potential during the preparation of the coating solution, and combines filtration and micro-concave coating process to ensure the stability of the coating performance and the consistency between batches, which is suitable for large-scale and continuous production. Therefore, the application not only realizes the preparation of high-performance coating, but also takes into account green environmental protection and industrial operability.

[0086] It should be particularly pointed out that the various embodiments listed in the specification and drawings are intended to illustrate the technical solutions of the application and their advantages, but not to limit the protection scope of the application. Without departing from the core idea and technical effect of the application, those skilled in the art can make any form of improvement, replacement, combination or deformation to the structure arrangement, process parameters, material selection, control logic, etc. of the described embodiments; any obvious changes based on the same idea should be regarded as equivalent solutions of the application, and should be included in the protection scope defined by the claims of the application. The actual protection scope of the application is subject to the appended claims, and should be correctly understood in combination with the specification and drawings.

Claims

1. A coating process for a high-performance substrate coating of a liquid resin plate, characterized in that, Includes the following steps: S1. Perform corona or plasma pretreatment on the PET substrate to control the surface energy at 50–58 dyn / cm; S2. Prepare an aqueous hybrid resin, wherein the aqueous hybrid resin is an aqueous polyurethane or an aqueous acrylic dispersion, and 0.3–2.0 wt% of silane functional groups are introduced into the molecular structure; S3. Prepare a diffusion particle dispersion, wherein the diffusion particles are PMMA nanoparticles or silica nanoparticles with a particle size of 1–5 μm; S4. Mix the dispersion from step S3 with the aqueous hybrid resin from step S2, and add an acrylate leveling agent, an organosilicon defoamer, and a thermally initiated curing accelerator. S5. Adjust the pH of the mixture to 6.8–7.6, and filter to obtain the coating solution; S6. Apply the coating liquid to the surface of the pretreated PET substrate, control the dry film thickness to be 10–40 μm, and pre-bake it by heating at 70–80℃ for 1–3 min. S7. Heat treat at 90–120℃ for 3–10 min to allow the thermally initiated curing accelerator to initiate the resin crosslinking reaction; S8. Curing at 80–90℃ for 5–10 min allows silane functional groups to condense and form an organic-inorganic hybrid network, resulting in a high-performance substrate coating.

2. The coating process for a high-performance substrate coating of a liquid resin plate according to claim 1, characterized in that, The substrate in step S1 is a PET film with a thickness of 75-150 μm.

3. The coating process for a high-performance substrate coating for liquid resin plates according to claim 1, characterized in that, In step S2, the pH of the aqueous hybrid resin is adjusted to 6.8–7.

6.

4. The coating process for a high-performance substrate coating for liquid resin plates according to claim 1, characterized in that, In step S4, the thermally initiated curing accelerator is selected from peroxides, azo compounds, or N-alkyl-substituted amides.

5. The coating process for a high-performance substrate coating of a liquid resin plate according to claim 1, characterized in that, The coating liquid is composed of the following components by mass percentage: 50–60% aqueous hybrid resin, 15–25% PMMA nanoparticles or silica nanoparticles, 0.5–1% silicone defoamer, 0.5–1% acrylate leveling agent, 0.5–1% thermally initiated curing accelerator, and the balance being deionized water.

6. The coating process for a high-performance substrate coating for liquid resin plates according to claim 1, characterized in that, The coating method in step S6 is a micro-recessed coating method.

7. The coating process for a high-performance substrate coating for liquid resin plates according to claim 1, characterized in that, The post-curing process in step S8 is carried out under conditions of 45–60% humidity to promote the silane condensation reaction.

8. The coating process for a high-performance substrate coating for liquid resin plates according to claim 1, characterized in that, The high-performance substrate coating obtained in step S8 is a transparent and stable thin film substrate that can be used as a component of liquid photosensitive resin printing plates.

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