0 ITEM
Methods for surface treatment of plastics
With the continuous improvement of plastic processing and modification technology, the application field is expanding rapidly.
Different application fields of plastic surface decoration, material protection, improvement of bonding and other properties are increasingly required, but the structure and composition of various plastic materials are different, the corresponding surface properties also have obvious differences.
Various surface treatment technologies and products adapted to different applications emerge as The Times require.
To meet the different needs of plastic surface treatment, a variety of treatment technologies have been developed.
Commonly used technologies are: solvent cleaning (degreasing), corona treatment, short wave ultraviolet radiation treatment, sandpaper treatment, sandblasting treatment, plasma etching, chemical etching, heating treatment, etc.
Different treatment methods are often needed for different materials.
Selection of surface treatment methods
Due to the low surface energy of most plastics, many treatment methods, such as decoration, printing, spraying, etc., are not directly applicable, but need to be first surface treatment.
Adhesiveness of plastics to various materials is a key problem to be solved in surface treatment.
Generally speaking, the bonding properties of plastics are related to the material structure and composition.
Structure influence
The surface energy of polyolefin materials, such as PP and PE, is very low, usually only 30-34 dunes.
For good bonding, it is generally required that the surface energy be no less than 40 dynes.
The bonding test shows that the bonding strength of PE can be increased by 10 times after plasma treatment.
After chromic acid treatment, the bonding property can be increased about 5 times.
After the same treatment, the bonding strength of PP increased by 200 times after ionization and 600 times after chromic acid treatment.
Why is the effect of chromic acid so significant for PP but not for PE?
This is because each carbon in the PP segment has a methyl group.
The methyl group is easily oxidized by the carboxyl group after being treated with oxygen ionization or chromic acid.
Moreover, even if only a small number of methyl groups are oxidized, the bonding properties and polarity of PP will be significantly improved by the presence of carboxyl groups.
PE doesn't 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 carrying out surface treatment.
Components affect
For various mixtures or copolymers, the material composition also affects the choice of surface treatment methods.
For example, fluoropolymers and their copolymers have a lower surface energy than polyolefin, typically ranging from 18 to 26 dynes.
For resins with high fluorine content, such as PTFE, the bonding property is improved by 10 times after etching with sodium naphthenate, but only 3 times after treating with oxygen or argon plasma.
The trend in PE is the opposite.
However, the adhesion properties of the copolymer of fluorine resin and PE increased by 10 times after plasma treatment or sodium naphthenate treatment.
It can be seen that plasma treatment mainly interacts with PE, while sodium naphthenate treatment mainly interacts with fluorine resin.
It can be seen that the processing properties of materials can be improved through the copolymerization of different materials.
For the copolymer of different components, the corresponding treatment methods should be selected according to the characteristics of the materials.
Choose 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 components of the materials.
For low surface energy plastics (lt;
35 dyne), mainly chosen by experience.
And high surface energy plastics, because of its good adhesion, so almost every treatment method is applicable, can be selected according to the convenience of use.
In general, the lower the surface energy of a plastic, the more treatment it requires.
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 act as solvents themselves.
For solvent resistant materials such as POM, PPO, PPS, and other polymers containing benzene rings, surface oxidation treatment or hairing is usually required.
For more difficult bonding materials such as polyamines and polyimines, surface etching is usually required to bond.
For plastics with polarity, such as polyester, epoxy, polyurethane, polyamine, etc., the method of surface treatment also has different requirements.
In general, the smaller the polarity, the less processing is required.
Polyesters and epoxides are the most polarized of these materials and need to be bonded after surface brushing.
Rigid polyurethane polarity is not high, usually with polyurethane adhesive can be bonded, but need to use epoxy surface treatment.
Polyamine is one of the least polarity, can be bonded without treatment.
For the actual processing process, usually need to consider the processing economy, make it better 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.
In choosing the treatment method, the chemical properties of the corresponding material, the structure of the polymer segment and the special requirements of the application field should be considered comprehensively.
Bonding with high reliability usually requires more surface treatment.
Hot molecular bonding processing technology
FTS Company is a professional manufacturer of pre-treatment equipment for plastic spraying.
The company has developed a Thermal Molecule Adhesion Processing (ATMAP) technology that can effectively improve the bonding properties of materials, improve product quality, and be environmentally friendly.
The ATMAP technology is realized by using Cirqual burner.
ATMAP processing is mainly on the surface of olefin - based plastic parts grafting a layer of chemical coupling agent 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 parts.
The burners are lightweight aluminum construction, which allows quick maintenance and operation and is especially suitable for automatic handling.
The product is mainly used for surface treatment of materials that need to be sprayed, bonded, decorated, laminated, printed or bonded with adhesive tape.
According to the report, other similar processes in use today cannot achieve the same results as ATMAP.
Light curing coatings are applied to automotive plastic parts
Many automotive parts are already made of engineered plastics or polymer-based composites that require coatings not only to improve their surface properties, but sometimes to achieve material performance improvements.
The replacement of glass with plastic for car lampshades and mirrors has benefited from the treatment of photocurable coatings.
Polycarbonate has the advantages of easy processing and forming, light weight and flexible strong and not easy to break, but its surface strength is not enough, not resistant to scratching and scratching and poor weather resistance, easy to turn yellow.
Using light curing coating to improve its surface properties, not only can greatly save the coating time, but also the coating has good optical abrasion resistance, and can meet the long-term weather resistance requirements.
As a result of the advancement of new technology, now polycarbonate lampshade has replaced glass lampshade almost completely.
Car mirror is also made of plastic, but the requirements must have a very high reflective performance.
To achieve this, the surface of the plastic has to be exposed to ultraviolet radiation three times.
First of all, the surface of the plastic through UV irradiation to produce a photochemical reaction to increase the surface tension, in order to facilitate the leveling and adhesion of the light curing coating;
After coating light curing varnish curing, the plastic surface becomes flat and easy to metallization;
The metal is then deposited in a vacuum deposition chamber.
In the plastic surface after metallization also need to be coated with a layer of light curing coating, in order to protect the metal reflective layer.
Surface properties were improved by modification
PP due to the brittleness (especially low temperature brittleness), high crystallinity, small molecular polarity, and other polymer (such as plastic, rubber) and inorganic fillers blend and adhesion is poor, limited its application in some fields.
Solid phase graft modification has led to the development of products such as chlorinated modified PP (MCPP) resin produced by Eastman.
MPP was modified by solid phase grafting method, and the solid powder resin MCPP was obtained by chlorination of MPP.
Modified PP (MPP) and MCPP are special materials for PP, which greatly expand the application range of PP.
The chlorinated modified resin has strong adhesion, improved bonding performance, and is easy to blend or bond with other resins.
Surface treatment of plastic film
Plastic film is one of the largest types of plastic, accounting for about 35% of the total amount of plastic.
Plastic film is difficult to print, difficult to bond, difficult to compound, easy to produce fog drops, easy to generate static electricity and other problems are more prominent.
In China, corona technology is used for plastic film surface treatment, but it is not suitable for many large applications.
Plasma surface treatment technology has not made a fundamental breakthrough so far, it is difficult to meet the needs of surface modification of bulk industrial products.
It is of great significance to develop new surface modification technology for expanding the application market of plastic film.
