Glass screen printing, as a precise and efficient glass surface decoration and functional processing technology, is widely used in various fields such as building curtain walls, appliance panels, electronic glass, and automotive glass. During the screen printing process, the protective film, acting as a "temporary protective barrier" on the glass surface, directly affects the screen printing accuracy, pattern adhesion, and the surface quality of the finished glass. Its performance adaptability further determines the stability and production efficiency of the screen printing process. The core requirements for protective films in glass screen printing revolve around key dimensions such as adhesion stability, surface cleanliness, temperature and solvent resistance, and residue-free peeling. PE (polyethylene) and CPP (cast polypropylene), two commonly used self-adhesive films, have differentiated applications in different screen printing scenarios due to their unique material properties, precisely matching the diverse needs of glass screen printing.

The unique characteristic of glass screen printing lies in its process, which involves multiple steps including ink coating, squeegee pressure application, and drying and curing. Furthermore, glass surfaces typically require high precision and cleanliness, necessitating highly specific and stringent requirements for the protective film. Each requirement directly impacts the yield rate, production efficiency, and smoothness of subsequent processing, making it a core prerequisite for ensuring the quality of glass screen printing. Considering the characteristics of the entire glass screen printing process, the core requirements for the protective film revolve around four main dimensions: adhesion stability, surface cleanliness, temperature and solvent resistance, and residue-free peeling. Auxiliary requirements such as flexibility, puncture resistance, and processability are also taken into account. Specific details are as follows:

First, adhesion stability is a fundamental requirement for glass screen printing protective films and a primary prerequisite for ensuring screen printing accuracy. During glass screen printing, a squeegee slides across the film surface with pressure, evenly coating the ink onto the glass. If the protective film does not adhere firmly to the glass surface, problems such as film displacement, peeling, and air bubbles can easily occur, leading to blurred, misaligned, and rough edges in the screen-printed pattern, or even serious defects such as missed prints and ghosting, directly resulting in product scrap. Therefore, the protective film must possess suitable adhesion, adhering tightly to the glass surface without air bubbles, gaps, or misalignment, while also adapting flexibly to the flatness of the glass surface—whether it's flat flat glass or slightly curved glass, its inherent characteristics should allow for seamless coverage, preventing film breakage due to squeegee pressure caused by poor adhesion. Simultaneously, adhesion stability requires the protective film to maintain its adherence throughout the entire screen printing process (including handling, transfer, and drying), without peeling or loosening, providing continuous and stable protection for the glass surface.

Secondly, surface cleanliness and smoothness are core performance requirements for glass screen-printed protective films, directly affecting the integrity and clarity of the printed pattern. Glass screen printing demands extremely high pattern precision, especially in applications such as electronic glass and high-end appliance panels, where even minor imperfections can lead to product defects. Therefore, the protective film surface must possess extremely high cleanliness, free of impurities, dust, crystal points, and adhesive dots. This prevents these impurities from being covered by ink during the screen printing process, resulting in defects such as pinholes, spots, and scratches. Simultaneously, the film surface must maintain extremely high smoothness, free of orange peel texture, scratches, and unevenness. This reduces friction with the screen printing squeegee, minimizing squeegee wear and preventing pattern smudging and ink bleeding caused by friction. It also ensures uniform ink coating, improving the edge clarity and gloss of the pattern. Furthermore, the surface tension of the protective film must be compatible with the characteristics of the screen printing ink. Too low a surface tension will cause ink diffusion, while too high a surface tension will result in poor ink adhesion. A good isolation effect is necessary to protect the ink pattern from contamination.

Furthermore, temperature and solvent resistance are key requirements for the adaptability of glass screen printing protective films to various processes, directly determining their suitability for different screen printing scenarios. During screen printing, various inks, thinners, cleaning agents, and other chemical reagents are used. The protective film must possess excellent solvent resistance, not reacting with these chemicals and exhibiting no swelling, discoloration, breakage, or adhesion. This prevents solvent corrosion and contamination of the glass surface due to film damage, and also prevents ink penetration to the film-glass contact surface, affecting the adhesion of the screen-printed pattern. More importantly, most glass screen printing processes require a drying process to improve ink adhesion and durability. This necessitates that the protective film withstand certain drying temperatures, maintaining its shape stability at high temperatures without shrinking, softening, peeling, or yellowing. This ensures continuous protection of the glass surface and screen-printed pattern during the drying process, preventing film deformation caused by high temperatures from affecting screen printing accuracy. The drying temperature varies depending on the screen printing application. For standard household glass screen printing, the drying temperature is approximately 40-60℃, while for high-end applications such as automotive and electronic glass, the drying temperature can reach 70-80℃. Therefore, the temperature resistance of the protective film needs to be adapted to the specific process requirements.

Finally, leaving no residue after peeling is a crucial final requirement for glass screen printing protective films, directly affecting the surface quality of the finished glass and subsequent processing steps. After screen printing, the protective film must be easily and completely peeled off, leaving no residue, marks, or adhesive marks, without damaging the glass surface's gloss, and without affecting subsequent ink curing, coating, tempering, and other deep processing steps. If residue remains after peeling, it will adhere to the glass surface, making it difficult to clean. This not only affects the glass's appearance but also prevents subsequent deep processing steps from proceeding normally, increasing rework costs. If the glass surface is damaged during peeling, it will directly lead to product defects. Therefore, the adhesive strength of the protective film needs to be controlled within a reasonable range to ensure both firm adhesion and smooth peeling. Simultaneously, the adhesive layer must possess good stability, preventing issues such as delamination or residue due to temperature changes or the passage of time.

In addition to the four core requirements mentioned above, the glass screen printing protective film also needs to possess suitable auxiliary properties to adapt to the actual operational needs of the screen printing process. First, flexibility is crucial. The protective film must possess a certain degree of flexibility to facilitate cutting and application, adapting to glass of different sizes and shapes. It must also withstand minor impacts and friction during screen printing, preventing film breakage and damage to the glass surface. Second, puncture resistance is essential. Screen printing may involve contact with sharp objects such as squeegees and knives; the protective film must have puncture resistance to prevent damage and loss of protective function. Third, processability is vital. The protective film must be easy to cut and slit, precisely tailored to the glass dimensions, with clean edges free of burrs and breakage, improving production efficiency. Fourth, environmental friendliness is paramount, especially for special applications like food-grade and medical glass. The protective film must be odorless, free of volatile organic compounds and toxic substances, meeting relevant environmental standards to avoid contaminating the glass.

PE self-adhesive film, one of the most widely used protective film types in glass screen printing, uses polyethylene as its base material and is produced through a three-layer co-extrusion process. Its advantages, including softness, easy application, moderate cost, and residue-free peeling, make it suitable for most conventional glass screen printing scenarios. PE self-adhesive film has a loosely arranged molecular chain, low crystallinity, and a soft, highly flexible texture. It can adhere tightly to glass surfaces of varying flatness, making it particularly suitable for screen printing protection of curved and irregularly shaped glass. It is less prone to air bubbles during application, and even with minor imperfections on the glass surface, its flexibility allows for seamless coverage, effectively preventing film damage caused by squeegee pressure during screen printing. In terms of surface properties, PE self-adhesive film undergoes special treatment, resulting in a high degree of cleanliness and freedom from impurities, meeting the smoothness requirements of conventional screen printing. Its moderate surface tension prevents reaction with screen printing inks, effectively protecting the ink pattern from contamination.

Regarding temperature and solvent resistance, PE self-adhesive film has a moderate temperature range, typically withstanding temperatures from -10℃ to 60℃. It is suitable for most conventional screen printing processes that do not require high-temperature drying, such as screen printing on architectural glass and ordinary household appliance glass. Its solvent resistance meets the requirements of conventional inks and thinners, without issues such as swelling or discoloration. Furthermore, the adhesive strength of PE self-adhesive film can be flexibly adjusted, with products available ranging from ultra-low to medium-high adhesion. Ultra-low adhesion PE self-adhesive film is suitable for screen printing on surface-sensitive glass such as optical glass and high-precision electronic glass, leaving no residue upon peeling and maximizing the protection of the glass surface's smoothness. Medium-high adhesion PE self-adhesive film is suitable for screen printing on ordinary flat glass and tempered glass, providing a strong bond and effectively resisting squeegee pressure and minor friction during the screen printing process. Simultaneously, PE self-adhesive film has a low processing threshold, can be flexibly cut to fit glass dimensions, and has relatively low cost, making it suitable for large-scale, routine glass screen printing production. It is one of the most cost-effective choices and is widely used for screen printing protection in architectural curtain wall glass, ordinary appliance panel glass, and civilian glass. It is worth noting that PE self-adhesive film has relatively weak puncture resistance and stiffness; it is easily damaged by impact with sharp objects during screen printing, therefore it is not suitable for scenarios requiring extremely high protective strength.

CPP self-adhesive film uses cast polypropylene as its base material and is manufactured through a casting process. It is a non-oriented, non-stretch film with a tightly packed molecular chain. Compared to PE self-adhesive film, it possesses higher stiffness, temperature resistance, and puncture resistance. These advantages make it ideal for mid-to-high-end, high-requirement glass screen printing applications, especially those requiring secondary processing. CPP self-adhesive film has excellent stiffness, making it resistant to wrinkles and deformation after application, maintaining a smooth surface. This makes it particularly suitable for high-precision screen printing processes, such as screen printing on electronic glass and high-end appliance panels, effectively preventing misalignment and blurring of the printed pattern due to film wrinkles, thus improving printing accuracy. After corona treatment, its surface cleanliness and smoothness surpass those of PE self-adhesive film, with no crystal points or scratches, meeting the stringent requirements of high-end screen printing for film surface quality. Simultaneously, its high surface tension provides excellent isolation from ink, further ensuring the clarity and integrity of the printed pattern.

In terms of temperature and solvent resistance, CPP self-adhesive film has a particularly outstanding advantage. Its temperature resistance range is -10℃ to 80℃, and its softening point is approximately 140℃. This allows it to withstand high-temperature drying processes after screen printing, such as screen printing on high-end household appliance glass and automotive glass. During high-temperature drying, CPP self-adhesive film will not shrink, soften, or peel off, nor will it yellow or discolor, providing stable protection for the glass surface and the screen-printed pattern. Simultaneously, CPP self-adhesive film has stronger solvent resistance, resisting corrosion from various high-strength solvents. It is suitable for screen printing processes using special inks, such as abrasion-resistant inks and high-temperature-resistant inks, without reacting with the inks or experiencing swelling or breakage. Furthermore, CPP self-adhesive film has significantly better puncture and tear resistance than PE self-adhesive film, effectively resisting impacts from sharp objects and squeegee friction during screen printing, preventing film breakage that could damage the glass surface. It is suitable for scenarios requiring high protective strength, such as screen printing protection for automotive glass, electronic glass, and high-end art glass.

CPP self-adhesive film also possesses excellent moisture-proof and oxygen-barrier properties, effectively isolating moisture and impurities in the air during screen printing, protecting the cleanliness of the glass surface. Furthermore, it is odorless, tasteless, and hygienic, making it suitable for screen printing protection in specialized fields such as food-grade and medical glass. However, CPP self-adhesive film has relatively poor flexibility, making it difficult to apply to curved or irregularly shaped glass, prone to problems such as peeling and loose adhesion. Its cost is also higher than PE self-adhesive film, making it unsuitable for routine, large-scale glass screen printing production. It is mainly used in mid-to-high-end, high-requirement screen printing scenarios, such as screen printing protection for electronic glass covers, automotive windshields, and high-end home appliance panels.

In summary, the requirements for protective films in glass screen printing processes are comprehensive and multi-layered. Four core requirements—adhesion stability, surface cleanliness, temperature and solvent resistance, and no residue after peeling—form the foundation for the adaptability of protective films to screen printing processes. Auxiliary requirements such as flexibility, puncture resistance, and processability further enhance the practical adaptability of protective films. These requirements are interconnected and mutually influential, and none can be omitted. If the adhesion is not firm, even the highest surface cleanliness cannot guarantee screen printing accuracy; insufficient temperature and solvent resistance will directly lead to film damage and glass contamination; any residue after peeling will severely affect the quality of the finished product and subsequent processing. It is these stringent requirements that determine the differentiated application scenarios of PE and CPP self-adhesive films: PE self-adhesive films, with their advantages of being soft, easy to apply, and moderately priced, are suitable for most conventional screen printing scenarios that do not require high-temperature drying and have low requirements for protective strength, meeting basic protection needs; CPP self-adhesive films, with their advantages of high stiffness, high temperature resistance, and high solvent resistance, focus on mid-to-high-end, high-requirement screen printing scenarios, precisely matching the process requirements of high precision, high-temperature drying, or special inks, perfectly meeting the stringent standards of glass screen printing for protective films. In actual production, it is necessary to combine the specific screen printing process, glass type, and finished product quality requirements to select a suitable protective film to maximize the stability and efficiency of the screen printing process and improve the pass rate of finished glass products.