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I. Key points of the process
1. Surface treatment of the base film
Other additives, especially emulsifiers, will also have a significant impact on the performance of the adhesive for surface protective film. Domestic experts used semi-continuous pre-emulsified seed emulsion polymerization to synthesize emulsion-type sensitive adhesive for protective film, and studied the effect of the amount of emulsifier in the bottom phase seed emulsion and the amount of multifunctional aziridine crosslinker on the performance of emulsion-type sensitive adhesive. The results show that with the increase of the amount of emulsifier in the seed emulsion, the particle size of the latex particles decreases, and the viscosity, surface tension and contact angle of the emulsion increase; increasing the amount of crosslinker can significantly improve the aging resistance of the emulsion-type pressure-sensitive adhesive. Compared with temperature, humidity has a more significant effect on the aging resistance of emulsion-type pressure-sensitive adhesive. The polarity and smoothness of the surface of the protected material also have a significant effect on the aging resistance of the pressure-sensitive adhesive.
Domestic experts used the pre-emulsification method to prepare acrylic pressure-sensitive adhesive emulsion and explored the effects of different emulsifier systems on the physical properties of pressure-sensitive adhesives. Infrared spectrum test shows that reactive emulsifier participates in the reaction; transmission electron microscopy test shows that the particle size of the emulsion obtained by the reactive emulsifier system is small and evenly distributed. The experimental results show that when w(compound emulsifier)=3%, m(ANPE010):m(DNS-458):m(DNS-501)=1.5:1.1:0.4, the mass fraction of the solid content of the obtained emulsion is 48.03%, the monomer conversion rate reaches 97.66%, the emulsion viscosity is 38.8s, the average particle size is 238nm, the initial adhesion of the pressure-sensitive adhesive can absorb No. 8 steel ball, and the stickiness is greater than 24h; the 180¡ã peel strength reaches 0.304N/mm. After the protective film attached to the stainless steel surface is baked at 80¡æ for 24h, there is no residual glue and haze on the stainless steel surface. Domestic experts used ethyl acetate as solvent, azobisisobutyronitrile as initiator, and solution polymerization process to develop acrylic pressure-sensitive adhesive for surface protection film, and studied the effects of internal crosslinker TC, external crosslinker aziridine (SaC-100) and water-based polyisocyanate (Bayhydur3100) on the peel strength and heat resistance of adhesive. The results show that by introducing internal and external crosslinkers, the cohesion of the colloid can be significantly increased, and the effect of eliminating residual glue is obvious.
The external crosslinker SaC-100 is better than Bayhydur3100 in improving the heat resistance of the colloid and reducing the peel strength; the surface protection film prepared by using 0.80% of the monomer amount of the internal crosslinker TC and 1.0% of the glue liquid amount of the external crosslinker SaC-100 has better performance. In the heat resistance test of high-finish stainless steel plates, there is no residual glue and "shadow". When non-polar films such as polyethylene and polypropylene films are used as the base film of the surface protection film, due to the low surface tension of such films, it is not easy to be wetted by the pressure-sensitive adhesive solution (or emulsion). After the pressure-sensitive adhesive is applied, the bonding force (adhesive force) between the substrate and the pressure-sensitive adhesive is also low. Usually, the coated surface of the substrate must be surface treated to make its surface tension above 38N/m. The surface treatment of the base film can theoretically be carried out by chemical treatment, corona treatment, ozone exposure treatment, ultraviolet light irradiation treatment, flame treatment, plasma treatment and other methods. However, the corona treatment method that is convenient to implement, low in price and effective is generally used in industrial practice. When the base film is corona treated, polar groups can be given to the surface of the base film through oxidation reaction and the surface is roughened, which significantly increases the surface tension and improves the adhesive force. However, excessive corona treatment may damage the surface layer of the base film, weaken the surface strength and lead to a decrease in the adhesive force. Therefore, the surface tension after corona treatment is usually controlled within the range of 38~44N/m.
2. Applying primer
Applying primer means applying a layer of coating (primer layer) on the adhesive surface of the substrate before applying the adhesive to improve the adhesion between the pressure-sensitive adhesive layer of the surface protective film and the substrate. Commonly used primers include: chlorinated polypropylene, oxidized polyethylene, cellulose derivatives, epoxy resins, polyamide resins, water-soluble melamine resins, organic titanium compounds, etc. The role is similar to building a bridge between the substrate and the adhesive, through which the substrate and the adhesive are firmly connected.
3. Peel force stabilization treatment
Surface protective films that do not consider peel force stabilization, after being applied to the surface of the protected material, often show a trend of increasing peel force over time. When the film is left on for a long time, the surface protective film cannot be removed smoothly, so the surface protective film must be subjected to peel force stabilization treatment.
After the peeling force stabilization treatment, the peeling force of the surface protective film does not increase with the increase of the coating time during use (or the peeling force is controlled within a certain range), ensuring that the surface protective film can be easily peeled off from the surface of the protected object during use, and ensuring that after the surface protective film is peeled off from the surface of the protected object, the surface remains clean without residual pressure-sensitive adhesive. Examples of the peeling force stabilization treatment method are as follows.
(1) Stretching treatment of surface protective film
It is said that when manufacturing the surface protective film, after the substrate is coated with glue and dried, it is subjected to biaxial stretching treatment before winding, so that the prepared protective film has a shrinkage rate of 30% in the longitudinal and transverse directions when heated at 100¡ãC for 10 minutes. The internal stress existing during the heat shrinkage of the protective film can offset the increase in peeling force caused by factors such as temperature and time after the surface protective film is attached to the surface of the protected object, thereby improving the stability of the peeling force of the surface protective film.
(2) Adding surfactants
Adding surfactants can help improve the stability of the peeling force of the surface protective film. For example, adding an appropriate amount of surfactants of phosphate esters and their derivatives, amine surfactants, and organosilicon compounds [such as silicone (polysiloxane) oil, vinyl silane] to the glue. However, it should be noted that when the surface protective film is used at a higher temperature, the above additives tend to migrate from the glue to the surface and precipitate. At this time, it should be considered to use perfluoroalkyl surfactants, such as perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl trimethyl ammonium salts, perfluoroalkyl trimethyl ammonium ethyl lactone, etc. Its mechanism of action is to form a low-energy layer at the interface between the protected material and the protective film glue layer, which inhibits the increase of peeling force. Polyalkylene glycol fatty acid esters, such as polyethylene glycol stearate, polyethylene glycol oleate, etc., can also be added. Their function is to form a continuous or discontinuous non-sticky film between the glue and the protected material; thereby preventing the increase of peeling force, and the area of the film gradually increases with the increase of placement time until it reaches a constant value.
(3) Make the pressure-sensitive adhesive moderately cross-linked
Before coating or during the adhesive making process, add a cross-linking agent to the pressure-sensitive adhesive to improve the cohesive strength through moderate cross-linking between molecules and suppress the problem of peeling force increasing over time.
Nanjing Sumino Seiko Machinery Co., Ltd. has a professional cast film production line. The company's main cast film manufacturing production lines include: TPU hot melt adhesive film production line, CPP/CPE cast film production line, EVA solar encapsulation film production line, PE sanitary breathable film production line, PVDF cast film production line, PP three-dimensional film production line, medical blood purification film production line, multi-layer co-extrusion barrier film production line, LLDPE wrapping film production line, etc.
1. Surface treatment of the base film
Other additives, especially emulsifiers, will also have a significant impact on the performance of the adhesive for surface protective film. Domestic experts used semi-continuous pre-emulsified seed emulsion polymerization to synthesize emulsion-type sensitive adhesive for protective film, and studied the effect of the amount of emulsifier in the bottom phase seed emulsion and the amount of multifunctional aziridine crosslinker on the performance of emulsion-type sensitive adhesive. The results show that with the increase of the amount of emulsifier in the seed emulsion, the particle size of the latex particles decreases, and the viscosity, surface tension and contact angle of the emulsion increase; increasing the amount of crosslinker can significantly improve the aging resistance of the emulsion-type pressure-sensitive adhesive. Compared with temperature, humidity has a more significant effect on the aging resistance of emulsion-type pressure-sensitive adhesive. The polarity and smoothness of the surface of the protected material also have a significant effect on the aging resistance of the pressure-sensitive adhesive.
Domestic experts used the pre-emulsification method to prepare acrylic pressure-sensitive adhesive emulsion and explored the effects of different emulsifier systems on the physical properties of pressure-sensitive adhesives. Infrared spectrum test shows that reactive emulsifier participates in the reaction; transmission electron microscopy test shows that the particle size of the emulsion obtained by the reactive emulsifier system is small and evenly distributed. The experimental results show that when w(compound emulsifier)=3%, m(ANPE010):m(DNS-458):m(DNS-501)=1.5:1.1:0.4, the mass fraction of the solid content of the obtained emulsion is 48.03%, the monomer conversion rate reaches 97.66%, the emulsion viscosity is 38.8s, the average particle size is 238nm, the initial adhesion of the pressure-sensitive adhesive can absorb No. 8 steel ball, and the stickiness is greater than 24h; the 180¡ã peel strength reaches 0.304N/mm. After the protective film attached to the stainless steel surface is baked at 80¡æ for 24h, there is no residual glue and haze on the stainless steel surface. Domestic experts used ethyl acetate as solvent, azobisisobutyronitrile as initiator, and solution polymerization process to develop acrylic pressure-sensitive adhesive for surface protection film, and studied the effects of internal crosslinker TC, external crosslinker aziridine (SaC-100) and water-based polyisocyanate (Bayhydur3100) on the peel strength and heat resistance of adhesive. The results show that by introducing internal and external crosslinkers, the cohesion of the colloid can be significantly increased, and the effect of eliminating residual glue is obvious.
The external crosslinker SaC-100 is better than Bayhydur3100 in improving the heat resistance of the colloid and reducing the peel strength; the surface protection film prepared by using 0.80% of the monomer amount of the internal crosslinker TC and 1.0% of the glue liquid amount of the external crosslinker SaC-100 has better performance. In the heat resistance test of high-finish stainless steel plates, there is no residual glue and "shadow". When non-polar films such as polyethylene and polypropylene films are used as the base film of the surface protection film, due to the low surface tension of such films, it is not easy to be wetted by the pressure-sensitive adhesive solution (or emulsion). After the pressure-sensitive adhesive is applied, the bonding force (adhesive force) between the substrate and the pressure-sensitive adhesive is also low. Usually, the coated surface of the substrate must be surface treated to make its surface tension above 38N/m. The surface treatment of the base film can theoretically be carried out by chemical treatment, corona treatment, ozone exposure treatment, ultraviolet light irradiation treatment, flame treatment, plasma treatment and other methods. However, the corona treatment method that is convenient to implement, low in price and effective is generally used in industrial practice. When the base film is corona treated, polar groups can be given to the surface of the base film through oxidation reaction and the surface is roughened, which significantly increases the surface tension and improves the adhesive force. However, excessive corona treatment may damage the surface layer of the base film, weaken the surface strength and lead to a decrease in the adhesive force. Therefore, the surface tension after corona treatment is usually controlled within the range of 38~44N/m.
2. Applying primer
Applying primer means applying a layer of coating (primer layer) on the adhesive surface of the substrate before applying the adhesive to improve the adhesion between the pressure-sensitive adhesive layer of the surface protective film and the substrate. Commonly used primers include: chlorinated polypropylene, oxidized polyethylene, cellulose derivatives, epoxy resins, polyamide resins, water-soluble melamine resins, organic titanium compounds, etc. The role is similar to building a bridge between the substrate and the adhesive, through which the substrate and the adhesive are firmly connected.
3. Peel force stabilization treatment
Surface protective films that do not consider peel force stabilization, after being applied to the surface of the protected material, often show a trend of increasing peel force over time. When the film is left on for a long time, the surface protective film cannot be removed smoothly, so the surface protective film must be subjected to peel force stabilization treatment.
After the peeling force stabilization treatment, the peeling force of the surface protective film does not increase with the increase of the coating time during use (or the peeling force is controlled within a certain range), ensuring that the surface protective film can be easily peeled off from the surface of the protected object during use, and ensuring that after the surface protective film is peeled off from the surface of the protected object, the surface remains clean without residual pressure-sensitive adhesive. Examples of the peeling force stabilization treatment method are as follows.
(1) Stretching treatment of surface protective film
It is said that when manufacturing the surface protective film, after the substrate is coated with glue and dried, it is subjected to biaxial stretching treatment before winding, so that the prepared protective film has a shrinkage rate of 30% in the longitudinal and transverse directions when heated at 100¡ãC for 10 minutes. The internal stress existing during the heat shrinkage of the protective film can offset the increase in peeling force caused by factors such as temperature and time after the surface protective film is attached to the surface of the protected object, thereby improving the stability of the peeling force of the surface protective film.
(2) Adding surfactants
Adding surfactants can help improve the stability of the peeling force of the surface protective film. For example, adding an appropriate amount of surfactants of phosphate esters and their derivatives, amine surfactants, and organosilicon compounds [such as silicone (polysiloxane) oil, vinyl silane] to the glue. However, it should be noted that when the surface protective film is used at a higher temperature, the above additives tend to migrate from the glue to the surface and precipitate. At this time, it should be considered to use perfluoroalkyl surfactants, such as perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl trimethyl ammonium salts, perfluoroalkyl trimethyl ammonium ethyl lactone, etc. Its mechanism of action is to form a low-energy layer at the interface between the protected material and the protective film glue layer, which inhibits the increase of peeling force. Polyalkylene glycol fatty acid esters, such as polyethylene glycol stearate, polyethylene glycol oleate, etc., can also be added. Their function is to form a continuous or discontinuous non-sticky film between the glue and the protected material; thereby preventing the increase of peeling force, and the area of the film gradually increases with the increase of placement time until it reaches a constant value.
(3) Make the pressure-sensitive adhesive moderately cross-linked
Before coating or during the adhesive making process, add a cross-linking agent to the pressure-sensitive adhesive to improve the cohesive strength through moderate cross-linking between molecules and suppress the problem of peeling force increasing over time.
Nanjing Sumino Seiko Machinery Co., Ltd. has a professional cast film production line. The company's main cast film manufacturing production lines include: TPU hot melt adhesive film production line, CPP/CPE cast film production line, EVA solar encapsulation film production line, PE sanitary breathable film production line, PVDF cast film production line, PP three-dimensional film production line, medical blood purification film production line, multi-layer co-extrusion barrier film production line, LLDPE wrapping film production line, etc.