With the continuous improvement of plastic processing and modification technology, the application field has expanded rapidly. Different applications have increased the requirements for plastic surface decoration, material protection, and improved adhesion. However, the structure and composition of various plastic materials are different, and the corresponding surface properties are also significantly different. Various surface treatment technologies and products adapted to different applications have emerged.
To meet the different needs of plastic surface treatment, a variety of processing technologies have been developed. Commonly used technologies include: solvent cleaning (degreasing), corona treatment, short wave ultraviolet radiation treatment, sandpaper treatment, sandblast treatment, plasma etching, chemical etching, heat treatment, and the like. For different materials, it is often necessary to choose different treatment methods.
Surface treatment method selection
Due to the low surface energy of most plastics, many processing methods, such as decoration, printing, painting, etc., cannot be applied directly, and surface treatment is required first. The adhesion of plastics to a variety of different materials is a key issue for surface treatment. In general, the plastic bonding properties are related to the material structure and components.
Structural influence
Polyolefin materials such as PP and PE have very low surface energy, usually only 30-34 dyne. To achieve good bonding, it is generally required that the surface energy be not less than 40 dyne. Adhesion tests show that PE can increase the bonding strength by 10 times after plasma treatment; after chromic acid treatment, the bonding performance can be increased by about 5 times. After the same treatment, the bonding strength of PP was increased by 200 times after ionization, and increased by 600 times after chromic acid treatment.
Why is the effect of chromic acid on PP so significant, but not on PE? This is because each carbon atom on the PP segment has a methyl group (-CH3). Methyl groups are easily oxidized by carboxyl groups after oxygen ionization or chromic acid treatment. Moreover, even if only a few methyl groups are oxidized, the adhesive properties and polarity of PP are significantly improved by the presence of carboxyl groups. PE does not have this group. It can be seen that the chemical structure of the polymer is an important factor that must be taken into account when performing the surface treatment.
Component influence
For various compounds or copolymers, the material components also influence the choice of surface treatment methods. For example, the fluoropolymers and their copolymers have lower surface energy than polyolefins, with a typical range of 18-26 dyne. For high-fluorine content resins such as PTFE, the adhesion performance is improved by 10 times after sodium naphthenate etching and only 3 times after oxygen or argon plasma treatment. The trend of PE is exactly the opposite.
However, the adhesion of the copolymer of fluororesin and PE after plasma treatment or sodium naphthenate treatment was increased by 10 times. It can be seen that the plasma treatment is more effective with PE, while the sodium naphthenate treatment is more important with the fluororesin. It can be seen that the copolymerization of different materials can improve the handling properties of the material. For the different components of the copolymer, also need to select the appropriate treatment method according to the characteristics of the material.
Selection tips
Different treatment methods have different effects on different polymer structures and components, so the choice of surface treatment method should also be based on the structure and components of the material.
For low surface energy plastics (<35 dyne), the choice is mainly based on experience. High surface energy plastics, because of their good adhesion, are suitable for almost every treatment method, and can be selected based on the convenience of use.
In general, the lower the surface energy of plastics, the more processing required. However, some polymers have low surface energy and can also be directly bonded with solvents such as ABS, PC, PS, AC and PVC. In fact, AC can be bonded because many acrylic adhesives themselves have a solvent effect. For those anti-solvent materials such as POM, PPO, PPS, and other benzene ring-containing polymers, surface oxidation or roughening is usually required. Materials that are more difficult to bond, such as polyamines and polyimines, usually require surface etching to bond.
For polar plastics, such as polyesters, epoxies, polyurethanes, polyamines, etc., the surface treatment methods also have different requirements. In general, the smaller the polarity, the less processing is needed. Among these materials, polyester and epoxy are the most polar and need to be bonded after the surface is roughened. Rigid polyurethanes are not very polar and can usually be bonded with a polyurethane adhesive but require epoxy for surface treatment. Polyamines are one of the least polar and can be bonded without treatment.
For the actual processing, it is usually necessary to consider the economics of processing so that it can better meet the actual processing needs. The various process parameters usually involved, such as processing time, temperature, exposure, and drying conditions, need to be carefully considered.
When selecting the treatment method, it is necessary to comprehensively consider the chemical characteristics of the corresponding material, the structure of the polymer chain segment, and the special requirements of the application field. High-reliability bonding usually requires more surface treatment.
Surface treatment application technology
As manufacturers increasingly demand higher quality products, cooperation technologies and materials for improving the working environment, improving work efficiency, and processing reliability have been continuously developed, and their market applications have been expanded.
Thermal molecular bonding processing technology
FTS Corporation is a professional company that manufactures plastic coating pretreatment equipment. The company has developed a thermal molecular bonding processing technology (AtmaP) that can effectively improve the bonding properties of materials, improve product quality, and has good environmental friendliness.
The implementation of AtmaP technology is achieved through the use of Cirqual burners. AtmaP processing is mainly to graft a layer of chemical coupling agent on the surface of olefin-based plastic parts to improve the bonding performance. The combustion flame provided by the Cirqual burner is the only driving force for the diffusion of the coupling agent on the surface of the plastic part. The burner is a lightweight aluminum structure that allows quick maintenance and operation, especially for automated handling.
This product is mainly suitable for surface treatment that requires spraying, bonding, decorating, laminating, printing or adhesive tape bonding. According to reports, other similar technologies used today cannot achieve the results that AtmaP can achieve.
Light-curing coatings for automotive plastic parts
Many auto parts have been made of engineering plastics or polymer-based composites. They not only need coatings to improve their surface properties, but they can sometimes achieve material performance improvements. Automotive lampshades and reflector materials Plastics instead of glass benefit from the treatment of photocurable coatings.
Polycarbonate has the advantages of easy processing and molding, light weight, strong flexibility, and no breakage, but its surface strength is not enough, it is not resistant to scratching and scratching, and it is poor in weather resistance and easily yellows. The use of photocurable coatings to improve the surface properties not only saves coating time but also has excellent optical abrasion resistance and can meet long-term weatherability requirements. Thanks to the advancement of new technologies, polycarbonate shades have now almost completely replaced glass shades.
Automotive mirrors are also made of plastic, but they must have high reflective properties. In order to achieve this goal, the plastic surface must be treated with three ultraviolet irradiation. First of all, the plastics are subjected to ultraviolet irradiation to increase the surface tension of the photochemical reaction to facilitate the leveling and adhesion of the photocurable coating. After the photocuring varnish is cured, the plastic surface becomes flat and easy to metallize; and then in the vacuum deposition tank. Metal deposition is completed. A layer of light-cured coating is also required after metallization of the plastic surface to protect the metal reflective layer.
Improve surface performance through modification
Due to its high brittleness (especially low-temperature brittleness), high crystallinity, and low molecular polarity, PP is poorly blended with other polymers (such as plastics and rubbers) and inorganic fillers, and it has limited adhesion. Field applications.
Through solid-phase graft modification, related products, such as chlorinated modified PP (MCPP) resins manufactured by Eastman, have been developed. The solid phase grafting method was used to modify isotactic PP to obtain MPP. MPP was chlorinated to obtain MCPP solid powdered resin. Modified PP (MPP) and MCPP as specialty PP special materials greatly expand the application of PP. The chlorinated modified resin has strong adhesion, improved adhesive properties, and is easy to blend or bond with other resins.
The film used for packaging usually requires surface treatment.
Surface treatment of plastic film
Plastic film is one of the largest quantities of plastic, accounting for about 35% of the total amount of plastic. Plastic film is difficult to print, difficult to bond, difficult composite, easy to produce droplets, easy to generate static electricity and other issues are more prominent. In China, corona technology is widely used for surface treatment of plastic films, but it is not applicable to many large-scale applications. Plasma surface treatment technology has not yet made a fundamental breakthrough and it is difficult to meet the surface modification needs of bulk industrial products. The development of new surface modification technologies is of great significance to expanding the market for plastic film applications.
Laboratory of Organic Materials Surface Engineering, School of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, China Since 1996, the continuous production of hydrophilic/hydrophobic asymmetric plastic films with surface light grafting as the main technical feature has been developed through intermittent small-scale tests, model tests, and pilot tests. New Technology. The plastic film product obtained by the surface treatment technology still has the original hydrophobicity of the film, and the polarity of the surface can be arbitrarily adjusted according to different needs until it is completely hydrophilic. This technology is suitable for almost all plastic films such as PE, PP, PVC, PET, nylon and so on. The characteristics of graft polymerization are that the modified layer is chemically bonded to the original base film and the properties are very stable.
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