First, process points
1. Surface treatment of base film
Other additives, especially emulsifiers, also have a significant impact on the performance of the adhesive used in the surface protective film. Domestic experts used semi-continuous pre-emulsified seed emulsion polymerization method to synthesize emulsion type sensitive adhesive for protective film, and studied the effects of the amount of emulsifier and multi-functional aziridine crosslinking agent in the bottom phase seed emulsion on the properties of emulsion type sensitive adhesive. The research results showed that: With the increase of the amount of emulsifier in seed emulsion, the particle size of latex decreased, and the viscosity, surface tension and contact Angle of emulsion increased. The aging resistance of emulsion pressure-sensitive adhesive can be significantly improved by increasing the amount of crosslinking agent. Compared with temperature, the influence of humidity on the aging resistance of emulsion pressure-sensitive adhesive is more significant. The polarity and finish of the surface of the protected material also have significant influence on the aging resistance of the pressure-sensitive adhesive.
Domestic experts prepared acrylate pressure sensitive adhesive emulsion by preemulsification method, and discussed the influence of different emulsifier systems on the physical properties of pressure sensitive adhesive. The infrared spectrum test showed that reactive emulsifier was involved in the reaction. The results of TEM showed that the emulsion obtained from the reactive emulsifier system had small particle size and uniform distribution. 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 obtained emulsion was 48.03%, the monomer conversion was 97.66%, the emulsion viscosity was 38.8s, the average particle size was 238nm, and the initial adhesion of the pressure-sensitive adhesive was able to absorb No.8 steel ball, and the adhesion was greater than 24h. 180° peeling strength reached 0.304N/mm. The protective film attached to the stainless steel surface, after baking at 80° C for 24h, the stainless steel surface without residual glue and fog shadow. Using ethyl acetate as solvent and azodiisobutadionitrile as initiator, the acrylic pressure sensitive adhesive for surface protective film was prepared by solution polymerization process. The effects of internal crosslinking agent TC, foreign linking agent SaC-100 and waterborne polyisomer (Bayhydur3100) on the peel strength and heat resistance of adhesive were studied. The results showed that the cohesive force of colloid could be significantly increased and the residual glue could be eliminated by the introduction of internal agent.
SaC-100 was better than Bayhydur3100 in improving heat resistance and reducing peel strength. Using 0.80% monomer of internal crosslinking agent TC and 1.0% of adhesive liquid of diplomatic linking agent SaC-100, the surface protective film has good performance, and there is no residual glue and "shadow" in the heat resistance detection of high finish stainless steel plate. When using non-polar films such as polyethylene and polypropylene films as the base film of the surface protective film, due to the low surface tension of such films, it is not easy to wet the pressure sensitive adhesive solution (or emulsion), after coating the pressure sensitive adhesive, the adhesive force (adhesive base force) between the substrate and the pressure sensitive adhesive is also low, usually the surface treatment of the coating surface of the substrate must be made so that the surface tension is above 38N/m. In theory, chemical treatment, corona treatment, ozone exposure treatment, ultraviolet irradiation treatment, flame treatment, plasma treatment and other methods can be used to treat the surface of the base film, but the industrial practical application is generally easy to implement, low price, good effect of corona treatment. When the base film is subjected to corona treatment, the polar groups on the surface of the base film can be endowed by oxidation reaction and the surface roughness can significantly improve the surface tension and improve the adhesive base force. However, excessive corona treatment may damage the surface layer of the base film and weaken the surface strength, resulting in the decrease of the adhesive base force. Therefore, the surface tension after corona treatment is usually controlled within the range of 38~44N/m.
2. Apply primer
Substrate coating refers to the coating surface of the substrate before coating the adhesive, a layer of coating to improve the adhesion between the surface protective film pressure sensitive adhesive layer and the substrate (the substrate layer). Commonly used base adhesives are: chlorinated polypropylene, oxidized polyethylene, cellulose derivatives, epoxy resin, polyamide resin, water-soluble melamine resin, organic titanium compounds, etc. The function is similar to building a bridge between the substrate and the stock adhesive, and through this bridge, the substrate and the adhesive are firmly connected.
3. Stabilization of stripping force
Without considering the peeling force stabilization of the surface protective film, after coating on the surface of the protected material, often with the passage of time, the peeling force will continue to increase the trend, when the film time is long, the surface protective film can not be smoothly removed, so the surface protective film must be peeled force stabilization treatment.
After the stabilization of the peeling force, the peeling force of the surface protective film does not increase with the growth of the coating time during use (or the peeling force is controlled within a certain range) to ensure that the surface protective film is easy to peel off the surface of the protected object during use, and to ensure that the surface protective film is removed from the surface of the protected object. The surface is kept clean without residual pressure sensitive adhesive. Examples of stabilization of stripping force can be given as follows.
(1) Tensile treatment of surface protective film
It is said that in the manufacture of the surface protective film, after the substrate is coated and dried, the bidirectional stretching treatment is carried out before winding, so that the produced protective film has a 30% shrinkage rate in the vertical and horizontal direction when heated for 10min at 100 ° C, and the internal stress existing in the thermal contraction of the protective film can be offset after the surface protective film is attached to the surface of the protected object. The peeling force is increased by temperature, time and other factors, thereby improving the stability of the peeling force of the surface protective film.
(2) Add surfactant
The addition of surfactants helps to improve the stability of the peeling force of the surface protective film, such as surfactants, amine surfactants, organosilanes [such as silicone (polysiloxane) oil, vinyl silane], adding appropriate amounts of phosphate esters and their derivatives to the glue. However, it should be noted that when the surface protective film is used at a higher temperature, the above additives have a tendency to migrate from the rubber to the surface and precipitate out, so it should be considered to use perfluoroalkyl surfactants, such as perfluoroalkyl carboxylate, perfluoroalkyl phosphate, perfluoroalkyl trimethylammonium salt, perfluoroalkyl trimethylammonium ethyl lactone. The mechanism of action is that a low-energy layer is formed at the interface between the protected material and the protective film adhesive layer, which inhibits the growth of stripping force. Also can add polyalkyl glycol fatty acid ester, such as polyethylene glycol stearate, polyethylene glycol oleate, etc., their role is to form a layer of continuous or discontinuous non-viscous film between the glue and the protected material; This prevents the rise of the peeling force, and the area of the membrane gradually increases with the increase of the placement time until it reaches a constant value.
(3) Make the pressure sensitive adhesive moderately crosslinked
Before coating or in the process of gluing, crosslinking agent is added to the pressure sensitive adhesive to improve the cohesion strength through moderate cross-linking between molecules, and to restrain the peeling force increasing with time.
