Melamine faced panel is also called prelaminated panel with a different color or texture. Melamine impregnated paper is paved onto wood based panels like MDF, particle board, plywood, block board, and then laminated with high temperature and high pressure.Currently low pressure low pressure lamination is popular. The melamine paper surface not only can improve the panel strength, stiffness and dimensional stability, but also can make its surface has the advantages of wear resistance, high temperature resistance, anti pollution, environmental protection, health and performance.
Prelaminated panels process: Panels Preparation →Panels Clean→Melamine Impregnated Paper→ Lamination→ Reclean → Inspection→Store. Before lamination, we must choose the high quality wood based panels and melamine impregnated paper,only qualified raw materials could be selected for production.
Impregnated paper requires the resin content is 130-150%, volatile content 6-7%, the pre curing degree ≦ 65%. Melamine impregnated paper should be in good condition, and packed with film to prevent the absorption of moisture. It is better to laminate before 3 months after production,and stored in the warehouse with relative moisture of 60 + 5%, the temperature 20-25℃. The most popular panels are fiber board, particle board and plywood. Quality panels requirements: 1) double side sanding, the surface is smooth and bright, uniform thickness, thickness tolerance 0.2mm. 2) board edges are intact, not eating, no oil or water pollution. 3) moisture content of the board is controlled in the range of 6-10%.
During the lamination process, we must strictly follow the technical specification, control pressing temperature 140-190℃, unit pressure 2.0-3.0MPa, pressing time 25-50s. Pressing temperature, pressure and pressing time are mutually dependent and mutually restricted, which can be adjusted according to the actual press affection. Hot temperature is mainly to accelerate the chemical reaction of melamine resin, the most workable temperature is 140-190℃. Higher temperature can help release after press, and can shorten the press time,improve production efficiency.But too high temperature will make resin curing before uniform flow, which cause pore on the board surface. Suitable pressure can guarantee the good adhesion between boards and impregnated paper, the workable pressure is generally 2.0-3.0MPa, which is favorable to the resin melt and solidify, forming the closed and compact surface. Under the premise of good quality, the low pressure should be used to prolong the service life of the equipment, and it is beneficial to the inner structure of boars. But too low pressure will affect the adhesive strength and resin flow capacity. According to the different kinds of panels, the unit pressure need to be adjusted by buffer mat. The pressing time depends on the curing speed of resin in the impregnated paper and the pressing temperature, and 25-50s is the best. Time is too long will cause resin curing excessive and lose elastic, resulting in crack or inside intention and in the following process will bring crack, warping. Time is too short, resin curing is not sufficient, make the boards sticky and affect the product durability.
Analysis of common quality defects and causes of prelaminated panels:
1) White spot, the main reason is the bad flow of in impregnated paper or less resin content. Reasons may be: no sanding on board surface or sanding not uniform, where the density is lower, resulting in large amount of resin absorption at this area, and bring the bad flow of resin which cause white spot.Deep depression in some areas, and pressure is not enough at these areas during lamiantion, and bring bad flow of resin,then cause white spot.Too high temperature,with too low pressure, and polluted steel plate may affect the resin flow,then cause white spot.Mat damages, leading to different temperature on different position of steel plate and cause white spot.Overtime storage of melamine impregnated paper, high pre-curing degree,or too low the PH value on boards,will affect the resin flow and cause white spot. Too high resin content on melamine impregnated paper may bring bubbles during lamination and cause white spot.
2) Wet spot, refers to the wave traces on prelaminated boards surface, and there are obvious defects.The main reasons are: High volatile content on impregnated paper or impregnated paper becomes damp will cause wet spot during lamination.Low pre-curing, low pressing temperature or shot pressing time, easy to occur wet spot.High moisture content on boards leads to wet spot during lamination.
3) Sticky with steel plate refers to the melamine board stick with steel plate during lamination. Slightly sticky will influence the surface quality, seriously sticky will affect production.Main reasons are: high resin content or polluted steel plate, leading to bad release. High volatile content of impregnated paper, low pressing temperature and short pressing time, resulting in resin was not fully cured to bad release. Damages on mat resulting in not uniform temperature on steel plate brings bad release. High moisture content or high PH value on boards brings bad release.
4)Bubbles, main reasons: too high pressing temperature, too long pressing time brings demix or bubbles. Too high moisture or too thin of boards may bring demix or bubbles during lamination.Too low density resulting in demix or bubbles.
5) Bow warping refers to surface uneven surface or cutting bending because of bad uniformity of inside intention strength. Main reasons are: Big difference in pressing temperature between upper and lower steel plate cause different curing speed and lead to bow warping. Different melamine impregnated paper on both surfaces may cause bend after lamination.If the hot prelaminated boards are loaded onto un-flat pallets,it may cause bend.
In short, we must choose the excellent impregnated paper and wood-based panel as raw materials, and optimize the production process as per different production equipment, under the collaboration of the operation and inspection persons, that can ensure the stability of product quality.