The wood grain on large-format fiberboard and particleboard can be manipulated by direct printing process. The base material wood-based panel→polishing→putty coating→drying (infrared or ultraviolet light)→polishing-coating primer→drying→printing wood grain→finishing→drying→finished product.
In order to prevent the board from warping, putty is also applied to the back of the substrate.
①Substrate polishing: Use a wide-band sander to adjust the thickness, and the thickness deviation is required to be less than 0.2 mm, and the surface should be smooth, so as to ensure the printing effect.
②. Apply putty: use putty to fill up the holes and unevenness on the surface to form a flat printing surface and reduce the consumption of primer. Nitro putty, amino alkyd putty or photosensitive putty can be used. The putty contains 60%~70% extender pigment, the resin is used as a binder, and the corresponding solvent is used to adjust the construction viscosity. The coating amount of fiberboard is the least, and the coating amount of particleboard and plywood is generally 120~150 g/m2.
The putty should be applied by a radial coating machine combined with a forward roller and a reverse roller, so as to ensure good filling and leveling properties and obtain a putty layer with uniform thickness.
③ Drying: The putty is often forced to dry. When the photosensitive putty is cured with ultraviolet rays, the time is only more than ten seconds. Other putties can be dried with infrared rays.
④Grinding: Use 180~-240 abrasive belts to smooth the putty. If the second putty cracks and collapses due to drying and shrinkage, you need to repeat the steps ② and ③. This ensures a flat and smooth base surface.
⑤ Primer: The primer is used to cover the base material, color it into the base color of the simulated wood, fix the putty, form a closed layer, and reduce the consumption of the top coat. Commonly used primers include nitro paint, amino alkyd paint, polyurethane paint, etc. In addition to resin paint, coloring pigments and body pigments are added to the primer.
⑥Drying: Most of them use forced drying. Conditions such as drying temperature and time should be determined according to the type and nature of the coating and the drying equipment. . Most of them are 60℃~90℃, 1~'2 minutes. Leave in room temperature air for a few minutes before force drying to prevent foaming.
⑦Wood grain printing: Immediately after the primer dries, use a gravure offset printing machine for wood grain printing. In order to obtain a layered and textured wood grain, you can use 2-3 gravure offset printing machines to connect and overprint. Due to the heat of the substrate book, the printed ink can be dried quickly, so there is no need to set up a drying device. The ink can be water-based, which is easy to clean, and photosensitive ink can also be used to make the wood grain thicker and have some three-dimensional effect, but it needs to be cured with light curing equipment. _The formula of water-based ink is shown in the table below:
Figure 29 is a schematic diagram of a gravure offset printing wood grain printing machine. It consists of gravure press, ink roller, rubber press, arrival knife and feeding press. When making plates, the rollers are plated, finely ground, and coated with photosensitive liquid. Take pictures of the changed wood grain at a ratio of 1:1 and make a plate, then turn it over to the carrying cylinder, and then corrode it with ferric chloride solution to corrode the wood grain on the newspaper cylinder to form pits, and then send it on One layer of pins for increased print durability. When printing, the ink roller applies ink to the grooves of the gravure roller, and the scraper scrapes off the excess ink outside the grooves. During the rotation of the gravure roller, the ink in the gravure is transferred to the rubber roller, and then the rubber roller transfers the wood grain ink to the surface of the printed substrate. Due to the elasticity of the rubber roller, everything can be transferred to a more rigid flat plate more satisfactorily without missing prints.
⑧Lacquer topcoat: The topcoat can be nitro varnish, amino alkyd varnish, photosensitive varnish, etc. Finishing with roller coater or shower paint machine;
⑨Drying: The drying method and drying procedure vary with the type of coating and the thickness of the coating. For example, nitro paint should be dried in hot air stage. The first stage is the solvent volatilization stage at room temperature, and the wind speed is 0.5 m/s. In the second stage, dry with hot air at 40°C~60°C at a wind speed of 0.5~5 m/s. The third stage is forced air drying. The temperature is 70°C~100°C, the air volume is large, and the wind speed is 0.5~5 m/s. The fourth stage is room temperature jet cooling. Photosensitive paints, on the other hand, only need a few seconds to minutes under ultraviolet light.
