A chemically modified enhanced screen printing stencil

Abstract

This application discloses a chemically modified and enhanced screen printing stencil, belonging to the field of screen printing technology. The key technical point is that the stencil comprises a screen frame, a screen tensioned and fixed to a screen fixing surface on the screen frame, and a polyimide film laminated to the screen. A chemically modified layer is disposed between the screen and the polyimide film. This chemically modified layer is formed by coating the screen surface with a silane coupling agent and then drying it. The silane coupling agent includes diaminosilane and epoxysilane. This application provides a chemically modified layer formed by curing a silane coupling agent on the screen surface, which enables a strong chemical bond between the screen and the PI film, thereby significantly improving the interfacial adhesion between the screen and the PI film and providing good durability.

Description

Technical Field

[0001] This application relates to the field of screen printing technology, and in particular to a chemically modified enhanced screen printing stencil. Background Technology

[0002] Screen printing stencils, as a core tool in the precision printing industry, play a crucial role in graphic printing in numerous fields such as electronic components, circuit boards, and solar cells. With continuous technological advancements, the demands for printing precision and efficiency across various sectors are constantly increasing, requiring continuous optimization of screen printing stencil performance to meet these needs. Their widespread application has not only driven the development of the precision printing industry but also made significant contributions to improving product quality and production efficiency in related industries.

[0003] In existing technologies, common printing screen structures employ a composite method of screen mesh and polyimide (PI) film. Specifically, the PI film is first laminated onto the screen mesh, and then laser perforation is used to create the desired printing pattern, forming a complete printing screen. This composite structure offers advantages such as high pattern precision and short production cycle. To improve the adhesion between the PI film and the screen mesh, traditional processes also employ electro-plasma treatment to treat the screen mesh surface, increasing surface roughness and activity, thereby enhancing adhesion to the PI film.

[0004] However, existing technologies have many drawbacks. On the one hand, screens are typically made of woven metal wires with a smooth surface. The PI film is bonded to the screen surface via heat sealing, resulting in limited adhesion between the two and a tendency for film peeling during use. On the other hand, the surface modification effect after plasma treatment is short-lived, requiring the treated screen to complete the PI film bonding within a short timeframe, which places strict demands on production rhythm and is detrimental to process scheduling. Furthermore, plasma treatment equipment requires significant investment and has high operating and maintenance costs, increasing screen manufacturing costs. In addition, due to the limited bonding strength between the PI film and the screen, repeated scraping and pressure from the squeegee during printing can easily cause the film to peel or shift, affecting printing accuracy and reducing screen lifespan. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a chemically modified enhanced screen printing stencil.

[0006] This application provides a chemically modified enhanced screen printing stencil, which adopts the following technical solution:

[0007] A chemically modified and enhanced screen printing stencil includes a screen frame, a screen tensioned and fixed to a screen fixing surface of the screen frame, and a polyimide film laminated on the screen. A chemically modified layer is disposed between the screen and the polyimide film. The chemically modified layer is formed by coating the screen surface with a silane coupling agent and then drying it. The silane coupling agent includes diaminosilane and epoxysilane.

[0008] By adopting the above technical solution, this application provides a chemically modified layer on the surface of the screen mesh. This chemically modified layer is formed by coating the screen mesh surface with a silane coupling agent and then drying it. The functional groups in the silane coupling agent molecules chemically bond with the metal atoms on the screen mesh surface, forming a complex functional group structure on the screen mesh surface. This functional group structure can form a strong chemical bond with the subsequently laminated PI film, thereby significantly improving the adhesion between the screen mesh and the PI film and overcoming the defects of existing methods.

[0009] In a preferred embodiment, the weight ratio of the diaminosilane to the epoxysilane is (90-95):(5-10).

[0010] By adopting the above technical solution, this application uses a mixture of diaminosilane and epoxysilane in a certain ratio range, which can give full play to the synergistic effect of the two and form a dense, firm chemical bridge layer rich in active functional groups on the surface of the metal mesh, thereby significantly improving the subsequent bonding ability with the PI film.

[0011] Specifically, the diaminosilane possesses bifunctional amino groups, providing two highly reactive primary amino groups (-NH2). One amino group preferentially forms hydrogen bonds with hydroxyl groups (-OH) on the metal surface and eventually tends towards coordination bonding, while the other amino group is fully oriented towards the interface, providing dual opportunities for chemical reactions with the imide ring or carboxyl end group of the PI film, significantly increasing the bonding density and probability. Furthermore, it can provide long, flexible chain segments, with the ethyl and propyl chains in its molecular structure providing appropriate flexibility, which helps alleviate the internal stress caused by the difference in thermal expansion coefficients between the PI film and the metal, thus improving the interfacial toughness. Simultaneously, utilizing the methoxy hydrolysis properties, the three methoxy groups (-OCH3) hydrolyze to generate silanol (-SiOH), which has moderate activity and controllable hydrolysis and condensation shrinkage rates, contributing to the formation of a uniform film layer.

[0012] Epoxy silanes can undergo synergistic reactions with amino groups. Under heating and curing conditions, their epoxy groups can undergo ring-opening addition reactions with the amino groups of diamino silanes to form a strong covalent cross-linked network, which greatly enhances the cohesive strength and hydrolytic stability of the silane film itself, upgrading it from a layer of "molecular glue" to a robust "bridge structure". Furthermore, it can provide diverse reaction sites. The epoxy groups can react with the carboxyl groups of the PI film precursor, providing the PI film with additional chemical bonding channels besides the amino reaction pathway, enhancing the reliability and complexity of the interfacial bonding. At the same time, it can also adjust the hydrophobicity and compactness of the formed silane film.

[0013] In addition, this application optimizes the ratio of diaminosilane and epoxysilane to ensure that diaminosilane provides sufficient reactive amino groups and introduces enough epoxy groups to form effective crosslinks in the membrane and at the interface. If the proportion of epoxysilane is too large, the spread and film formation of diaminosilane will be affected due to incomplete reaction of epoxy groups or steric hindrance.

[0014] In a preferred embodiment, the polyimide film is prepared by the following method:

[0015] a. Bis(r-aminopropyl)polydimethylsiloxane BAPPDS and 4,4'-diaminodiphenyl ether ODA are co-dispersed in an organic solvent and stirred at room temperature until completely dissolved. Then, pyromellitic dianhydride PDMA is added to react and a polyamic acid solution is obtained.

[0016] b. Degas the polyamic acid solution, cast it into a film, cure it, cool it to room temperature, and demold it to obtain a polyimide film.

[0017] By adopting the above technical solution, this application uses BAPPDS as a macromolecular diamine monomer to participate in the polymerization reaction together with PMDA and ODA, forming a sequence structure of polyimide hard segment-polysiloxane soft segment-polyimide hard segment. Since polysiloxane (non-polar, flexible) and polyimide (polar, rigid) are thermodynamically incompatible, during the film formation and curing process, polysiloxane segments spontaneously aggregate and migrate. This results in the formation of a nanoscale "microphase separation" structure within the film body, while on the film surface, polysiloxane segments are strongly enriched, forming a surface layer mainly composed of polydimethylsiloxane, thereby reducing the surface energy of the film and improving the interfacial bonding ability between the PI film and the screen.

[0018] Furthermore, when the silane coupling agent is applied to the silicon-containing polyimide film of this application, due to the chemical affinity and reaction potential between the polysiloxane modified layer and the silane coupling agent, the two can fully exert their synergistic effect to construct an ideal interface layer with tight chemical bonding, sufficient physical interpenetration, and smooth mechanical transition, thereby providing excellent adhesion strength and long-term durability, and significantly increasing the bonding ability between the PI film and the screen.

[0019] In a preferred embodiment, the preparation process of the polyimide film further includes step c: precisely activating the side of the polyimide film to be bonded for 30-90 seconds using an alkaline solution with a concentration of 0.1-0.2 mol / L.

[0020] By adopting the above technical solution, this application uses a weak alkaline solution to precisely activate the surface of the PI film on the side that needs to be bonded. This can slightly increase the ring-opening degree of the imide ring in the PI body, exposing more carboxyl groups, while not damaging the polysiloxane layer. In this way, the silane coupling agent can react with the amino groups of the polysiloxane and the carboxyl groups of the PI film body to form a "double anchoring" fixation, which further improves the interfacial bonding force between the PI film and the screen.

[0021] In a preferred embodiment, the molar ratio of BAPPDS to ODA is (1-2):(4-7).

[0022] In a preferred embodiment, the number-average molecular weight of the BAPPDS is 900-2000 g / mol.

[0023] By adopting the above technical solution, this application optimizes the number-average molecular weight of BAPPDS. If the molecular weight is too low, the surface enrichment effect will be weak; if the molecular weight is too high, severe phase separation will occur, thereby affecting the transparency and mechanical uniformity of the film.

[0024] In a preferred embodiment, when BAPPDS and ODA are blended, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane HFBAPP is also added. The system is then cooled to 0-5°C, and PDMA is added and the reaction is maintained at this temperature for 0.8-1.2 h. The reaction is then continued at room temperature for 12-24 h.

[0025] In a preferred embodiment, the molar ratio of ODA to HFBAPP is (4-7):(2-4).

[0026] By adopting the above technical solution, this application further introduces fluorinated diamine during PI film polymerization. Its fluorinated groups, like the polysiloxane segments, have a strong tendency to migrate to the surface. When used in combination, they can form a "fluorine-silicon synergistic enrichment layer" on the film surface, thereby further reducing the surface energy of the film and improving the interfacial bonding between the PI film and the screen.

[0027] In a preferred embodiment, the curing is a staged curing process, specifically curing at 70-80°C for 1.5-3.0 hours, then at 140-160°C for 1-2 hours, then at 190-210°C for 1.0-1.5 hours, then at 240-260°C for 0.5-1.5 hours, and finally at 280-320°C for 0.5-1.0 hours.

[0028] By adopting the above technical solution, this application first performs gentle drying at a temperature of 70-80℃ to gently remove most of the solvent, forming a stable gel film and avoiding surface defects caused by rapid solvent evaporation, thus providing a structural basis for subsequent steps. Then, surface migration and initial alignment are initiated and dominated at a temperature of 140-160℃. This temperature is higher than the glass transition temperature of the polysiloxane segments, giving them sufficient mobility to migrate to the air interface, while the imidization reaction begins. The imidization reaction is then essentially completed at a temperature of 190-210℃, solidifying the main structure of the film and "locking" the initially formed surface rich layer. At this temperature, the imidization reaction proceeds rapidly, increasing the rigidity of the polymer chains and limiting further large-scale movement of the segments. Finally, the imidization reaction is ensured to be complete at a temperature of 240-260℃, eliminating residual ammonium acid structures, improving the film's heat resistance and chemical stability, and further orienting and densifying the molecular chains. Finally, the polymer chains are fully relaxed at a temperature of 280-320℃ to eliminate internal stress, making the microphase separation structure more complete and stable, and further improving the modulus and heat resistance.

[0029] In summary, this application has the following beneficial effects:

[0030] 1. This application provides a chemically modified layer formed by curing a silane coupling agent on the surface of the screen, which enables a strong chemical bond between the screen and the PI film, thereby significantly improving the interfacial bonding force between the screen and the PI film.

[0031] 2. In this application, BAPPDS is used as a macromolecular diamine monomer to participate in the polymerization reaction together with PMDA and ODA, which can reduce the surface energy of the film and have a synergistic effect with the silane coupling agent to jointly improve the interfacial bonding ability between the film and the screen.

[0032] 3. In this application, a fluorinated diamine is further introduced during the polymerization of the PI film. The fluorinated groups therein can migrate to the surface together with the polysiloxane segments and play a synergistic role with the silane coupling agent, thereby jointly improving the interfacial bonding force between the PI film and the screen. Detailed Implementation

[0033] The present application will be further described in detail below with reference to the embodiments. All reagents, unless otherwise specified, are commercially available conventional reagent products.

[0034] The diaminosilane used in this application is a commonly used diaminosilane in the art. In the specific embodiments of this application, N-(diaminoethyl)-3-aminopropyltrimethoxysilane is used as an example for illustration.

[0035] The epoxy silane used in this application is a commonly used epoxy silane in the art. In the specific embodiments of this application, 3-glycidyl etheroxypropyltrimethoxysilane is used as an example for illustration.

[0036] <Preparation Example 1.1>

[0037] Silane coupling agents are prepared by the following method:

[0038] The pH of a mixture of deionized water and ethanol (volume ratio of deionized water to ethanol of 10:90) was adjusted to 4.5 using acetic acid. Then, a mixture of N-(diaminoethyl)-3-aminopropyltrimethoxysilane and 3-glycidyl etheroxypropyltrimethoxysilane (weight ratio of 90:10) was slowly added to the acidified aqueous pure solution and stirred continuously for more than 30 minutes. The mixture was then placed in a sealed environment and allowed to stand at room temperature for 8 hours to mature.

[0039] <Preparation Example 1.2>

[0040] Silane coupling agents are prepared by the following method:

[0041] The pH of a mixture of deionized water and ethanol (volume ratio of deionized water to ethanol 5:95) was adjusted to 5.5 using acetic acid. Then, a mixture of N-(diaminoethyl)-3-aminopropyltrimethoxysilane and 3-glycidyl etheroxypropyltrimethoxysilane (weight ratio 95:5) was slowly added to the acidified aqueous pure solution and stirred continuously for more than 30 minutes. The mixture was then placed in a sealed environment and allowed to stand at room temperature for 24 hours to mature.

[0042] <Preparation Example 1.3>

[0043] Silane coupling agents are prepared by the following method:

[0044] The pH of a mixture of deionized water and ethanol (volume ratio of deionized water to ethanol 5:95) was adjusted to 5.5 using acetic acid. Then, a mixture of N-(diaminoethyl)-3-aminopropyltrimethoxysilane and 3-glycidyl etheroxypropyltrimethoxysilane (weight ratio 98:2) was slowly added to the acidified aqueous pure solution and stirred continuously for more than 30 minutes. The mixture was then placed in a sealed environment and allowed to stand at room temperature for 24 hours to mature.

[0045] <Preparation Example 1.4>

[0046] Silane coupling agents are prepared by the following method:

[0047] The pH of a mixture of deionized water and ethanol (volume ratio of deionized water to ethanol 5:95) was adjusted to 5.5 using acetic acid. Then, a mixture of N-(diaminoethyl)-3-aminopropyltrimethoxysilane and 3-glycidyl etheroxypropyltrimethoxysilane (weight ratio 80:20) was slowly added to the acidified aqueous pure solution and stirred continuously for more than 30 minutes. The mixture was then placed in a sealed environment and allowed to stand at room temperature for 24 hours to mature.

[0048] <Comparative Preparation Example 1.1>

[0049] The difference from Preparation Example 1.2 is that 3-glycidyl etheroxypropyltrimethoxysilane is not added, and N-(diaminoethyl)-3-aminopropyltrimethoxysilane is used entirely, while the rest is the same as Preparation Example 1.2.

[0050] <Preparation Example 2.1>

[0051] The polyimide film was prepared by the following method:

[0052] a. Disperse 4,4'-diaminodiphenyl ether (ODA) in an organic solvent (tetrahydrofuran (THF) and dimethylacetamide (MMAc) in a volume ratio of 1:1) and stir at room temperature until completely dissolved. Then add pyromellitic dianhydride (PDMA) and maintain the reaction for 12 hours to obtain a polyamic acid solution. The molar ratio of ODA to PDMA is 1:1.

[0053] b. Degas the polyamic acid solution and uniformly coat it onto a clean glass plate to cast a film. First, cure it at 70°C for 3 hours, then at 140°C for 2 hours, then at 190°C for 1.5 hours, then at 240°C for 1.5 hours, and finally at 280°C for 1 hour. Allow it to cool naturally to room temperature, then demold to obtain a polyimide film.

[0054] <Preparation Example 2.2>

[0055] The polyimide film was prepared by the following method:

[0056] a. Disperse 4,4'-diaminodiphenyl ether (ODA) in an organic solvent (tetrahydrofuran (THF) and dimethylacetamide (MMAc) in a volume ratio of 1:1) and stir at room temperature until completely dissolved. Then add pyromellitic dianhydride (PDMA) and maintain the reaction for 24 hours to obtain a polyamic acid solution. The molar ratio of ODA to PDMA is 1:1.

[0057] b. Degas the polyamic acid solution, coat it evenly on a clean glass plate, and cast it into a film. First, cure it at 80°C for 1.5 hours, then at 160°C for 1 hour, then at 210°C for 1 hour, then at 260°C for 0.5 hours, and finally at 320°C for 0.5 hours. Allow it to cool naturally to room temperature, then demold to obtain a polyimide film.

[0058] <Preparation Example 2.3>

[0059] The polyimide film was prepared by the following method:

[0060] a. Bis(r-aminopropyl)polydimethylsiloxane BAPPDS and 4,4'-diaminodiphenyl ether ODA were co-dispersed in an organic solvent (tetrahydrofuran THF and dimethylacetamide MMAC in a volume ratio of 1:1) and stirred at room temperature until completely dissolved. Then, pyromellitic dianhydride PDMA was added, and the reaction was maintained for 20 h to obtain a polyamic acid solution. The molar ratio of BAPPDS, ODA and PDMA was 1:7:8. The number average molecular weight of BAPPDS was 900 g / mol.

[0061] b. Degas the polyamic acid solution and uniformly coat it onto a clean glass plate to cast a film. First, cure it at 75°C for 2 hours, then at 150°C for 1.5 hours, then at 200°C for 1 hour, then at 250°C for 1 hour, and finally at 300°C for 0.5 hours. Allow it to cool naturally to room temperature, then demold to obtain a polyimide film.

[0062] <Preparation Example 2.4>

[0063] The polyimide film was prepared by the following method:

[0064] a. Bis(r-aminopropyl)polydimethylsiloxane BAPPDS and 4,4'-diaminodiphenyl ether ODA were co-dispersed in an organic solvent (tetrahydrofuran THF and dimethylacetamide MMAC in a volume ratio of 1:1) and stirred at room temperature until completely dissolved. Then, pyromellitic dianhydride PDMA was added, and the reaction was maintained for 20 h to obtain a polyamic acid solution. The molar ratio of BAPPDS, ODA and PDMA was 2:4:6. The number average molecular weight of BAPPDS was 2000 g / mol.

[0065] b. Degas the polyamic acid solution and uniformly coat it onto a clean glass plate to cast a film. First, cure it at 75°C for 2 hours, then at 150°C for 1.5 hours, then at 200°C for 1 hour, then at 250°C for 1 hour, and finally at 300°C for 0.5 hours. Allow it to cool naturally to room temperature, then demold to obtain a polyimide film.

[0066] <Preparation Example 2.5>

[0067] The polyimide film was prepared by the following method:

[0068] a. Bis(r-aminopropyl)polydimethylsiloxane BAPPDS and 4,4'-diaminodiphenyl ether ODA were co-dispersed in an organic solvent (tetrahydrofuran THF and dimethylacetamide MMAC in a volume ratio of 1:1) and stirred at room temperature until completely dissolved. Then, pyromellitic dianhydride PDMA was added, and the reaction was maintained for 20 h to obtain a polyamic acid solution. The molar ratio of BAPPDS, ODA and PDMA was 2:4:6. The number average molecular weight of BAPPDS was 2000 g / mol.

[0069] b. Degas the polyamic acid solution, coat it evenly on a clean glass plate to cast a film, first cure it at 75°C for 2 hours, then at 150°C for 1.5 hours, then at 200°C for 1 hour, then at 250°C for 1 hour, and finally at 300°C for 0.5 hours. Allow it to cool naturally to room temperature, demold it, and obtain a polyimide film.

[0070] c. Apply a 0.1 mol / L NaOH solution to the polyimide film surface where bonding is required, activate precisely for 90 seconds, and then rinse thoroughly with plenty of deionized water to terminate the reaction.

[0071] <Preparation Example 2.6>

[0072] The polyimide film was prepared by the following method:

[0073] a. Bis(r-aminopropyl)polydimethylsiloxane BAPPDS and 4,4'-diaminodiphenyl ether ODA were co-dispersed in an organic solvent (tetrahydrofuran THF and dimethylacetamide MMAC in a volume ratio of 1:1) and stirred at room temperature until completely dissolved. Then, pyromellitic dianhydride PDMA was added, and the reaction was maintained for 20 h to obtain a polyamic acid solution. The molar ratio of BAPPDS, ODA and PDMA was 2:4:6. The number average molecular weight of BAPPDS was 2000 g / mol.

[0074] b. Degas the polyamic acid solution, coat it evenly on a clean glass plate to cast a film, first cure it at 75°C for 2 hours, then at 150°C for 1.5 hours, then at 200°C for 1 hour, then at 250°C for 1 hour, and finally at 300°C for 0.5 hours. Allow it to cool naturally to room temperature, demold it, and obtain a polyimide film.

[0075] c. Apply a 0.2 mol / L KOH solution to the polyimide film surface where bonding is required, activate precisely for 30 seconds, and then rinse thoroughly with plenty of deionized water to terminate the reaction.

[0076] <Preparation Example 2.7>

[0077] The polyimide film was prepared by the following method:

[0078] a. Bis(r-aminopropyl)polydimethylsiloxane BAPPDS, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane HFBAPP, and 4,4'-diaminodiphenyl ether ODA were co-dispersed in an organic solvent (tetrahydrofuran THF and dimethylacetamide MMCAc in a volume ratio of 1:1) and stirred at room temperature until completely dissolved. The system was then cooled to 0°C, and pyromellitic dianhydride PDMA was added and the reaction was maintained at this temperature for 1.2 h. The reaction was then continued at room temperature for 20 h to obtain a polyamic acid solution. The molar ratio of BAPPDS, ODA, HFBAPP, and PDMA was 2:4:4:10. The number average molecular weight of BAPPDS was 2000 g / mol.

[0079] b. Degas the polyamic acid solution, coat it evenly on a clean glass plate to cast a film, first cure it at 75°C for 2 hours, then at 150°C for 1.5 hours, then at 200°C for 1 hour, then at 250°C for 1 hour, and finally at 300°C for 0.5 hours. Allow it to cool naturally to room temperature, demold it, and obtain a polyimide film.

[0080] c. Apply a 0.2 mol / L KOH solution to the polyimide film surface where bonding is required, activate precisely for 30 seconds, and then rinse thoroughly with plenty of deionized water to terminate the reaction.

[0081] <Preparation Example 2.8>

[0082] The polyimide film was prepared by the following method:

[0083] a. Bis(r-aminopropyl)polydimethylsiloxane BAPPDS, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane HFBAPP, and 4,4'-diaminodiphenyl ether ODA were co-dispersed in an organic solvent (tetrahydrofuran THF and dimethylacetamide MMCAc in a volume ratio of 1:1) and stirred at room temperature until completely dissolved. The system was then cooled to 5°C, and pyromellitic dianhydride PDMA was added and the reaction was maintained at this temperature for 0.8 h. The reaction was then continued at room temperature for 20 h to obtain a polyamic acid solution. The molar ratio of BAPPDS, ODA, HFBAPP, and PDMA was 1:7:2:10. The number average molecular weight of BAPPDS was 2000 g / mol.

[0084] b. Degas the polyamic acid solution, coat it evenly on a clean glass plate to cast a film, first cure it at 75°C for 2 hours, then at 150°C for 1.5 hours, then at 200°C for 1 hour, then at 250°C for 1 hour, and finally at 300°C for 0.5 hours. Allow it to cool naturally to room temperature, demold it, and obtain a polyimide film.

[0085] c. Apply a 0.2 mol / L KOH solution to the polyimide film surface where bonding is required, activate precisely for 30 seconds, and then rinse thoroughly with plenty of deionized water to terminate the reaction.

[0086] <Example 1>

[0087] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0088] S1. Immerse the wire mesh in a 5wt% NaOH solution at 60℃ and ultrasonically clean it for 15 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute hydrochloric acid solution. Treat it at room temperature for 2 minutes, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0089] S2. The silane coupling agent prepared in Preparation Example 1.1 was uniformly applied to the screen surface by spin coating at a speed of 2000 r / min, with a wet film thickness of 1 μm. It was dried in a circulating air oven at 80°C for 10 min, and then heated to 120°C and cured for another 30 min.

[0090] S3. The polyimide film prepared in Preparation Example 2.1 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 60 minutes at a pressure of 0.5 MPa and a temperature of 180°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0091] <Example 2>

[0092] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0093] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0094] S2. The silane coupling agent prepared in Preparation Example 1.2 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0095] S3. The polyimide film prepared in Preparation Example 2.2 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0096] <Example 3>

[0097] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0098] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0099] S2. The silane coupling agent prepared in Preparation Example 1.3 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0100] S3. The polyimide film prepared in Preparation Example 2.2 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0101] <Example 4>

[0102] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0103] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0104] S2. The silane coupling agent prepared in Preparation Example 1.4 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min. The wet film thickness was 3 μm. The screen was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0105] S3. The polyimide film prepared in Preparation Example 2.2 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0106] <Example 5>

[0107] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0108] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0109] S2. The silane coupling agent prepared in Preparation Example 1.2 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0110] S3. The polyimide film prepared in Preparation Example 2.3 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0111] <Example 6>

[0112] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0113] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0114] S2. The silane coupling agent prepared in Preparation Example 1.2 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0115] S3. The polyimide film prepared in Preparation Example 2.4 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0116] <Example 7>

[0117] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0118] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0119] S2. The silane coupling agent prepared in Preparation Example 1.2 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0120] S3. The polyimide film prepared in Preparation Example 2.5 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0121] <Example 8>

[0122] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0123] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0124] S2. The silane coupling agent prepared in Preparation Example 1.2 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0125] S3. The polyimide film prepared in Preparation Example 2.6 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0126] <Example 9>

[0127] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0128] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0129] S2. The silane coupling agent prepared in Preparation Example 1.2 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0130] S3. The polyimide film prepared in Preparation Example 2.7 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0131] <Example 10>

[0132] A method for preparing a chemically modified enhanced screen printing stencil includes the following steps:

[0133] S1. Immerse the wire mesh in a 5wt% KOH solution at 70℃ and ultrasonically clean it for 10 minutes. After taking it out, rinse it with water and then immerse it in a 10wt% dilute sulfuric acid solution. Treat it at room temperature for 1 minute, then rinse it with a large amount of deionized water until neutral. Finally, dry it thoroughly in an oven at 110℃ for 30 minutes.

[0134] S2. The silane coupling agent prepared in Preparation Example 1.2 was uniformly applied to the screen surface by spin coating at a speed of 4000 r / min, with a wet film thickness of 3 μm. It was dried in a circulating air oven at 100°C for 5 min, and then heated to 150°C and cured for another 20 min.

[0135] S3. The polyimide film prepared in Preparation Example 2.8 is precisely placed on the screen coated with the silane layer and put into a hot press. It is hot-pressed for 30 minutes at a pressure of 1.5 MPa and a temperature of 220°C. Then, it is held under pressure and cooled to below room temperature before being removed and trimmed to obtain a chemically modified reinforced screen printing stencil.

[0136] <Comparative Example 1>

[0137] The difference from Example 1.2 is that step S2 is removed, that is, the chemical modification layer is not placed between the screen and the polyimide film; otherwise, it is the same as Example 1.2.

[0138] <Comparative Example 2>

[0139] The difference from Example 1.2 is that the silane coupling agent prepared in step S2 of Example 1.2 is replaced with the silane coupling agent prepared in Comparative Example 1.1, and the rest is the same as in Example 1.1.

[0140] <Comparative Example 3>

[0141] The difference from Example 1.2 is that step S2 is removed, and the polyimide film prepared in Example 2.2 in step S3 is replaced with the polyimide film prepared in Example 2.5. The rest is the same as Example 2.2.

[0142] <Comparative Example 4>

[0143] The difference from Example 1.2 is that step S2 is removed, and the polyimide film prepared in Example 2.2 in step S3 is replaced with the polyimide film prepared in Example 2.7. The rest is the same as Example 2.2.

[0144] Performance Testing

[0145] 1. The printing screens prepared in the above examples and comparative examples were subjected to peel strength test according to the method in ASTM D903 (180° peel). One end of the PI film was peeled off from the screen substrate and stretched at a constant speed of 300 mm / min. The required force was measured. The results are shown in Table 1.

[0146] 2. The printing screens prepared in the above examples and comparative examples were immersed in printing solvent (ethanol is used as an example) for 48 hours. The adhesion was tested according to the cross-cut adhesion test in ASTM D3359. The adhesion grades were 0B-5B, with 5B being the best, indicating that the edges are completely smooth and there is no peeling. 0B is the worst. The results are shown in Table 1.

[0147] Table 1 Performance Test Results

[0148] project Average peel force (N / mm) Adhesion rating Example 1 4.23 5B Example 2 4.29 5B Example 3 4.11 5B Example 4 4.09 5B Example 5 4.56 5B Example 6 4.58 5B Example 7 4.69 5B Example 8 4.70 5B Example 9 5.11 5B Example 10 5.14 5B Comparative Example 1 0.83 0B Comparative Example 2 2.35 2B Comparative Example 3 4.21 3B Comparative Example 4 4.32 4B

[0149] As shown in Table 1, the average peel strength between the screen and the PI film in the printing screens prepared in Examples 1.1-1.2 of this application is 4.23-4.29 N / mm, and the adhesion in the cross-cut adhesion test after immersion in chemical reagents for 48 hours can still reach 5B. In contrast, the average peel strength between the screen and the PI film in the printing screen prepared in Comparative Example 1 is 0.83 N / mm, and the adhesion in the cross-cut adhesion test after immersion in chemical reagents for 48 hours is 0B (complete peeling). This indicates that the chemical modification layer set between the screen and the PI film in this application can significantly improve the bonding strength between the PI film and the screen, thereby improving the durability of the screen and extending its service life.

[0150] The difference between Examples 3-4 and Examples 1.2 is that the ratio of diaminosilane and epoxysilane in the silane coupling agent is different. As can be seen from Table 1, the average peel strength between the screen and the PI film in the printing stencils prepared in Examples 3-4 is lower than that in Examples 1.2. This indicates that the optimization of the ratio between diaminosilane and epoxysilane in this application can further improve the bonding strength between the PI film and the screen.

[0151] The difference between Examples 5-6 and Examples 1.2 is that bis(r-aminopropyl)polydimethylsiloxane BAPPDS was introduced during the polymerization of the PI film. As can be seen from Table 1, the average peel strength between the screen and the PI film in the printing stencils prepared in Examples 5-6 is higher than that in Examples 1.2. This indicates that the introduction of polysiloxane can further reduce the surface energy of the PI film, thereby improving the bonding strength between the PI film and the screen.

[0152] The difference between Examples 7-8 and Examples 1.2 is that a weak alkali was used to treat the surface of the PI film. As can be seen from Table 1, the average peel strength between the screen and the PI film in the printing stencils prepared in Examples 7-8 is higher than that in Examples 1.2. This indicates that treating the surface of the PI film with a weak alkali can further improve the bonding strength between the PI film and the screen.

[0153] The difference between Examples 9-10 and Examples 7-8 is that fluorinated diamine was further introduced during the polymerization process of the PI film. As can be seen from Table 1, the average peel strength between the screen and the PI film in the printing stencil prepared in Examples 9-10 is higher than that in Examples 7-8. This indicates that the introduction of fluorinated diamine can work synergistically with the polysiloxane segments, thereby further improving the bonding strength between the PI film and the screen.

[0154] The difference between Comparative Example 2 and Example 1.2 is that no epoxy silane was added to the silane coupling agent. As can be seen from Table 1, the average peel strength of the screen and PI film in the printing stencil prepared in Comparative Example 2 is lower than that in Example 1.2, and the adhesion of the screen by cross-cut adhesion test after soaking in chemical reagents for 48 hours is 2B. The experimental results show that the addition of epoxy silane can play a synergistic role with diamino silane, thereby improving the bonding strength and durability of the PI film and the screen.

[0155] Comparative Examples 3-4 were screens without silane coupling agent treatment, using only modified PI film. As shown in Table 1, the average peel strength between the screen and PI film in the printing stencils prepared in Comparative Examples 3-4 was lower than that in Examples 5-9, and the adhesion of the screen using the cross-cut adhesion test after immersion in chemical reagents for 48 hours was 3B-4B. The experimental results show that the modified PI film and silane coupling agent work together to fully exert their synergistic effect, thereby giving the PI film and screen a high bonding strength and durability.

[0156] The embodiments described herein are merely preferred embodiments and are not intended to limit the scope of protection of this invention. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this invention.

Claims

1. A chemically modified reinforced screen printing screen comprising a screen frame, a screen fixed to a screen fixing surface of the screen frame in tension, and a polyimide film complexed to the screen, characterized in that, A chemical modification layer is arranged between the screen and the polyimide film, which is formed by coating a silane coupling agent on the surface of the screen and drying treatment, and the silane coupling agent comprises aminosilane and epoxy silane.

2. A chemically modified enhanced screen printing screen according to claim 1, wherein, The weight ratio of the aminosilane and the epoxy silane is (90-95):(5-10).

3. A chemically modified enhanced screen printing screen according to claim 1, wherein, The polyimide film is prepared by the following method: a. Blending and dispersing bis(r-aminopropyl)polydimethylsiloxane BAPPDS and 4,4'-diamino diphenyl ether ODA in an organic solvent, and stirring at room temperature until completely dissolved, then adding pyromellitic dianhydride PDMA for reaction to obtain a polyamic acid solution; b. Defoaming the polyamic acid solution, casting a film, curing, cooling to room temperature, demolding to obtain a polyimide film.

4. A chemically modified enhanced screen printing screen according to claim 3, wherein, The preparation process of the polyimide film further comprises step c: precisely activating one side of the polyimide film that needs to be bonded with an alkali solution with a concentration of 0.1-0.2 mol / L for 30-90 s.

5. A chemically modified enhanced screen printing screen according to claim 3, wherein, The molar ratio of the BAPPDS and the ODA is (1-2):(4-7).

6. A chemically modified enhanced screen printing screen according to claim 3, wherein, The number average molecular weight of the BAPPDS is 900-2000 g / mol.

7. A chemically modified enhanced screen printing screen according to claim 4, wherein, The BAPPDS and the ODA are blended by further adding 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane HFBAPP, then cooling the system to 0-5℃, then adding PDMA for 0.8-1.2 h of heat preservation reaction, and then continuing to react at room temperature for 12-24 h.

8. A chemically modified enhanced screen printing screen according to claim 7, wherein, The molar ratio of the ODA and the HFBAPP is (4-7):(2-4).

9. A chemically modified enhanced screen printing form according to claim 3, wherein, The curing is staged curing, specifically, first curing at a temperature of 70-80℃ for 1.5-3.0 h, then curing at a temperature of 140-160℃ for 1-2 h, then curing at a temperature of 190-210℃ for 1.0-1.5 h, then curing at a temperature of 240-260℃ for 0.5-1.5 h, and finally curing at a temperature of 280-320℃ for 0.5-1.0 h.