Due to the development of bottom and top coating materials, continuous improvement, continuous and large-scale vacuum coating equipment, vacuum coating has entered the industrialized production stage, and has penetrated into various scientific fields at the same time . One of the professional surface treatment technologies, it is widely used on metal, wood, paper, plastic and other substrates , and gradually demonstrates the unique role of vacuum plating in the application. Among them, the selection and application of paint are important factors related to the quality of decorative vacuum coating.
What are the coatings used for vacuum plating? How to improve the coating technology in these coating applications in actual production? The following focus on this discussion. In the decorative vacuum coating, depending on the perfect paint coating technology, strong wear resistance, combined
Coating with good strength and high brightness.
1. The function and requirements of the coating
Decorative vacuum plating coatings are generally divided into two types: primer coating and top coating. In order to meet the different technical requirements , a base coat and a top coat can be applied, or a color coat, a protective coat, etc. can be applied on the top coat. The main functions of these coatings are:
Improve the bonding force of the film layer. Using the same coating method, applying a primer on the plastic substrate and then vacuum coating can improve the bonding force of the film layer. Reduce the roughness of the surface of the plated parts and improve the brightness. Generally, there are microscopic unevennesses on the surface of the plated parts, not necessarily the leveling of the thickness of the coating, it can fill the defects on the surface of the plated parts, so that the surface of the plated parts can reach the flatness of the mirror surface. Can protect the metal film layer. The vacuum coating layer is generally only !&&67, and the wear resistance and discoloration resistance of the film layer are poor. After the top coat is applied, the coating layer does not directly contact with the outside world, which can protect the coating layer.
Requirements for undercoating in vacuum plating:
①It has good contact performance and high bonding force between the plated parts and the coating layer, the difference in thermal expansion coefficient is small, it does not react and the leveling performance is good.
②It has good vacuum performance. After the undercoating is cured, the outgassing amount is small, the thermal stress is small, and the heat resistance is good.
③The film-forming performance is good, and the coating has good properties such as density, coverage, solvent resistance and light resistance.
④ Good compatibility with top coat. Since the coating layer is extremely thin and has pores, it is required that the solvents and diluents of the primer and top coat have good compatibility.
⑤ Good application performance. Good leveling performance, proper viscosity and short curing time.
Requirements for vacuum plating on the top coat:
① There must be good contact performance with the coating layer;
② There must be a certain compatibility with the primer;
③Excellent film-forming performance and application performance; with appropriate mechanical strength;
④ moisture-proof, solvent-resistant, corrosion-resistant performance is good. Strong anti-aging performance.
Due to the special needs of the product, a superhard coating or color coating can be further applied on the top coat.
2. Commonly used coatings
Commonly used coatings for vacuum plating include UV-curable coatings, acrylic ester coatings, alkyd resin coatings, epoxy resin coatings , and polyurethane coatings.
(1) UV curing coating:
UV-curable coatings are coatings that are chemically cured under the irradiation of ultraviolet light with a wavelength of !$% & '$%() .
feature is:
The coating does not need to be directly heated, as long as it is not curable by ultraviolet light, it can save energy. The curing speed is fast, measured in minutes and seconds, and is suitable for automatic assembly lines; the coating has excellent performance, strong coating adhesion, high coverage, and surface roughness. Low, good vacuum performance, low solvent content, good for environmental protection, etc. This UV-curable coating mainly includes photosensitizer (photopolymerization initiator), photosensitive resin (prepolymer) and reactive diluent, as well as adding necessary stabilizers, leveling agents and pigments.
The photosensitive resin contains double bonds and can be cured to form a film by self-radical polymerization. Selecting a suitable photosensitizer can shorten the curing reaction time and improve the performance and stability of the film. Commonly used photosensitizers are benzoin ethers, and the combination of thioxanthone compounds and N, N-dimethylethanolamine developed in recent years can obtain extremely high hardness films.
Photosensitive resin contains double bonds that can undergo photopolymerization. It is the main film-forming material in coatings, and it determines the performance of the film layer . Commonly used photosensitive resins include vinyl type and acryl type.
Reactive diluents are monomers or oligomers containing unsaturated double bonds, which can not only reduce the viscosity of coatings, but also participate in photocuring reactions, and can form films together with photosensitive resins. Commonly used reactive diluents also include vinyl and There are two types .
Usually adding a leveling agent can improve the surface tension of the coating and promote the rapid leveling of the film layer. Commonly used leveling agents include cellulose and sorbitol surfactants.
(2) Acrylic paint:
Acrylate paints are generally made from copolymer resins of methacrylates and acrylates. The characteristics of acrylic paint: excellent color and luster, good gloss and color retention, moisture resistance, mildew resistance, solvent resistance, acid and alkali resistance, heat resistance, and can be used below 180 °C.
(3) Alkyd resin coating:
Alkyd resin is a resin formed by the esterification of polyols, polyacids and fatty acids. Coatings with alkyd resin as the main film-forming substance are called alkyd resin coatings.
The characteristics of alkyd resin coatings: excellent gloss, good gloss and color retention, flexible and firm , but poor anti-salt spray, anti-mildew and moisture-proof performance.
(4) Epoxy resin coating:
Epoxy resin coating is a film former coating based on epoxy resin.
The characteristics of epoxy resin coatings: stable chemical properties, particularly strong alkali resistance, excellent adhesion of the coating film layer, good thermal stability , electrical insulation and color retention, but poor weather resistance, easy loss of light, and chalking.
(5) Polyurethane coating:
This coating contains a considerable amount of urethane linkages.
The characteristics of polyurethane coatings: particularly strong wear resistance, excellent adhesion, can obtain extremely hard coating and extremely flexible elastic coating, chemically stable, can be dried at high temperature, and can also be cured at low temperature, the coating has excellent protection
Function, beautiful decoration and so on.
3. Application method
Commonly used coating methods include dip coating, spray coating and brush coating, all of which can be applied manually or automatically
