With the continuous improvement of plastic processing and modification technology, the application field has expanded rapidly. Different application fields have increasingly increasing requirements for plastic surface decoration, material protection, and improved bonding. 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.
Adapted to the different needs of plastic surface treatment, a variety of processing technologies have been developed. Commonly used technologies are: solvent cleaning (degreasing), corona treatment, short-wave ultraviolet radiation treatment, sandpaper treatment, sandblasting, plasma etching, chemical etching, heat treatment, and the like. Different treatments are often required for different materials.
Selection of surface treatment methods
Since most plastics have low surface energy, many treatment methods, such as decoration, printing, and spraying, are not directly applicable, and surface treatment is required first. The adhesion of plastics to a variety of different materials is a key issue that needs to be addressed in surface treatment. In general, plastic bonding properties are related to material structure and composition.
Structural influence
Polyolefin materials such as PP and PE have very low surface energy and usually only have 30-34 dyne. To achieve good bonding, the surface energy is generally required to be no less than 40 dynes. Bonding tests show that the bonding strength of PE can be increased 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 after ionization treatment is increased by 200 times, and after chromic acid treatment, it is increased by 600 times.
Why is the effect of chromic acid on PP being so significant, but not on PE? This is because each carbon atom in the PP segment has a methyl group (-CH3). The methyl group is easily oxidized by the carboxyl group after being subjected to oxygen ionization or chromic acid treatment. Moreover, even if only a small amount of methyl groups are oxidized, the bonding property and polarity of PP are remarkably improved by the presence of a carboxyl group. PE does not have this group. It can be seen that the chemical structure of the polymer is an important factor that must be considered when performing surface treatment.
Component influence
For various compounds or copolymers, the material composition also affects the choice of surface treatment method. For example, fluoropolymers and copolymers thereof have a lower surface energy than polyolefins, typically ranging from 18 to 26 dynes. 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 copolymer of fluororesin and PE has a 10-fold increase in adhesion after plasma treatment or sodium naphthenate treatment. It can be seen that plasma treatment is more active with PE, while sodium naphthenate treatment is more important with fluororesin. It can be seen that the copolymerization of different materials can improve the processing properties of the material. For copolymers of different compositions, it is also necessary to select the corresponding treatment method according to the characteristics of the materials.
Selection skills
Different treatment methods have different effects on different polymer structures and components, so the choice of surface treatment methods should also be based on the structure and composition of the materials.
For low surface energy plastics (<35 dyne), it 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 according to the convenience of use.
In general, the lower the surface energy of a plastic, the more processing is required. However, some polymers have lower 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 polymers containing benzene rings, surface oxidation or roughening is usually required. Materials that are more difficult to bond, such as polyamines and polyimides, typically require a surface etch to bond.
For plastics with polarity, such as polyester, epoxy, polyurethane, polyamine, etc., the surface treatment methods also have different requirements. In general, the smaller the polarity, the less processing is required. 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 are usually bonded with a polyurethane adhesive, but require epoxy for surface treatment. Polyamines are among the least polar and can be bonded without treatment.
For the actual process, it is usually necessary to consider the economics of the process to make it better to meet the actual processing needs. The various process parameters commonly involved, such as processing time, temperature, exposure, drying conditions, etc., need to be carefully considered.
When selecting a treatment method, it is necessary to comprehensively consider the chemical properties of the corresponding material, the structure of the polymer segment, and the special requirements of the application field. Highly reliable bonding usually requires more surface treatment.
Surface treatment application technology
As manufacturers demand higher and higher quality products, technologies and materials to improve the working environment, improve work efficiency and process reliability have been developed and expanded their market applications.
Thermal molecular bonding processing technology
FTS is a specialist in the manufacture of pre-treatment equipment for plastic coatings. The company has developed a thermal molecular bonding processing technology (AtmaP) that improves the bonding properties of materials, improves product quality, and is environmentally friendly.
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 construction that allows for quick maintenance and operation, especially for automated handling.
This product is mainly suitable for surface treatments that require spraying, bonding, decorating, laminating, printing or tape bonding materials. According to reports, other similar processes used today can not achieve the results that AtmaP can achieve.
Light curing coatings for automotive plastic parts
Many automotive components have been engineered plastic or polymer-based composites that not only require coatings to improve their surface properties, but sometimes improve material properties. Automotive lampshades and mirror materials use plastic instead of glass to benefit from the processing technology of photocurable coatings.
Polycarbonate has the advantages of easy processing, light weight, high flexibility and not easy to be broken, but its surface strength is not enough, it is not resistant to scoring and scratching, and its weather resistance is poor, and it is easy to turn yellow. The use of photocurable coatings to improve the surface properties not only saves coating time but also has good optical rub resistance and long-term weather resistance. It is precisely because of the advancement of new technologies that polycarbonate lampshades have almost completely replaced glass shades.
Automotive mirrors are also made of plastic, but require high levels of reflective performance. In order to achieve this, the plastic surface must be treated with three UV irradiations. First, the plastic is subjected to ultraviolet irradiation to cause photochemical reaction on the surface to increase the surface tension to facilitate the leveling and adhesion of the photocurable coating; after the cured photocuring varnish is cured, the surface of the plastic becomes flat and easy to be metallized; Complete metal deposition in the middle. After the metal surface is metallized, a layer of photocurable coating is needed to protect the metal reflective layer.
Improve surface properties through modification
Due to its high brittleness (especially low temperature brittleness), high crystallinity, low molecular polarity, blending and adhesion to other polymers (such as plastics, rubber) and inorganic fillers, PP is limited. Field applications.
By solid phase graft modification, related products such as chlorinated modified PP (MCPP) resins produced by Eastman have been developed. The isotactic PP was modified by solid phase grafting to obtain MPP, and the MPP was chlorinated to obtain MCPP solid powdery resin. Modified PP (MPP) and MCPP are special materials for special PP, which greatly expands the application range of PP. The chlorinated modified resin has strong adhesion, improved bonding properties, and is easily blended or bonded with other resins.
Films used for packaging typically require surface treatment.
Surface treatment of plastic film
Plastic film is one of the largest varieties of plastics, accounting for about 35% of the total plastics. Plastic film is difficult to print, difficult to bond, difficult to recombine, easy to produce droplets, easy to generate static and other issues are more prominent. In China, corona technology is used for surface treatment of plastic films, but it is not suitable for 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 for expanding the application market for plastic films.
Since 1996, the Laboratory of Organic Materials Surface Engineering of the School of Materials Science and Technology of Beijing University of Chemical Technology has developed a continuous production of hydrophilic/hydrophobic asymmetric plastic film with surface light grafting as the main technical feature through intermittent small test, mold test and pilot test. New Technology. The plastic film product obtained by the surface treatment technology still has the original hydrophobicity of the film, and the surface polarity 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, etc. The characteristics of graft polymerization make the modified layer and the primary base film chemically bonded, and the properties are very stable.
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