Analysis of factors influencing the quality of melamine impregnated paper Laminated wood based panels
Guide: To produce high-quality products, we must select excellent impregnated paper and substrate, and adopt reasonable processing technology; In addition, operators and inspectors should cooperate with each other to control the quality of products, find out the causes of problems and solve them in time, so as to ensure the quality of products.
In order to expand the use range and improve the use value of wood-based panels, their surfaces need to be decorated. The use of melamine impregnated paper to finish MDF and chipboard has the advantages of less materials, low energy consumption, less processes, low cost and beautiful appearance. It not only improves the strength, stiffness and dimensional stability of the board, but also makes its surface wear resistant, heat resistant, water resistant and chemical pollution resistant.
The quality problems that often occur in the production process are analyzed as follows.
1、 Production process quality control 1. The production process of melamine impregnated paper facing MDF (particleboard) is as follows: base material preparation → dust removal on the board surface → preforming → hot pressing → trimming → inspection → warehousing. 2. During the production of substrate quality control, the quality of MDF substrate and impregnated paper shall be checked frequently, and the production can only be started after all technical indicators are qualified. (1) Paper quality and impregnation process To ensure the quality of impregnated paper, high-quality decorative base paper must be used. No matter what kind of paper is used, it can only be used after passing the inspection, and the unqualified paper can not enter the production line. During the impregnation process, the operation shall be carried out in strict accordance with the process requirements. Sampling inspection shall be carried out every 39min to ensure that the glue content is 130% – 150%, the volatile content is 6% – 7%, and the degree of pre solidification is ≤ 65%; The impregnated and dried adhesive film paper shall be immediately packaged with plastic film and sealed with adhesive tape. It shall be stored in the warehouse with air conditioner and temperature of 20 ℃ – 25 ℃ and humidity of 55% – 65%. The paper that cannot be used at one time shall be immediately sealed and sent to the warehouse for storage to prevent its moisture absorption from causing the adhesive film paper to stick up and cannot be used, resulting in unnecessary economic losses. In addition, avoid damage during the movement of impregnated paper; If the slab surface is found not clean in the process of assembling, clean it in time; Carefully check the base material when feeding. (2) The substrate of Laminated wood based panels ed wood-based panels requires that the commonly used MDF and chipboard should be purchased according to the different requirements of customers, but the chipboard products must meet the requirements of GB/T489792 first-class products. ① The board surface shall be flat and clean, free of water and oil stains, and the effective size shall be free of defects such as edge slipping and head gnawing; ② The thickness deviation of the plate shall not exceed 0.2mm, and the sanding shall be uniform. No sand leakage is allowed; ③ The moisture content of plates shall be controlled within 6% – 10%. As most particleboards are purchased, changes in the environment may cause changes in the moisture content of the board. If the water content is too high, blasting, layering and other phenomena may occur in the Laminated wood based panels process; If the moisture content is low, or the volatile content of impregnated paper is low, cardboard delamination may occur during hot pressing. Therefore, it is necessary to observe at any time during the production process and remove unqualified base materials in time. (3) After centering, the base material for assembling will enter the assembling process. During the assembling operation, ensure that the impregnated paper is completely covered on the surface of the base material, and ensure that the center line of the slab coincides with the center line of the press, so as to ensure that the position of the slab after entering the press is accurate, and avoid the pollution of the formwork due to the slab displacement. 3. Quality control of hot pressing process The three elements of hot pressing process (hot pressing temperature, hot pressing pressure and hot pressing time) are interdependent and mutually restrictive, and need to be analyzed and adjusted uniformly when adjusting the process. The three factors have different effects on the Laminated wood based panels s. The hot pressing temperature mainly catalyzes the chemical reaction of the impregnated resin, that is, accelerating the curing. According to the actual requirements and experience of production, it is appropriate to pressurize the hot pressing plate at a temperature of 170 ℃~200 ℃, a unit pressure of 2.0-3.0MPa and a hot pressing time of 25-50s. The temperature and time can be adjusted appropriately according to the color and quality of the paper. The dark color paper should adopt a low temperature and long time process, with the general temperature of 170 ℃ – 180 ℃ and pressure holding for more than 40s; Light colored paper should adopt high pressure and short time process. At the same time, the appearance quality of the decorative panel shall be checked at any time to prevent paper scraps, insects, fingerprints, etc. from polluting the panel surface. The proper hot pressing pressure can ensure a good combination between the substrate and the impregnated paper. Under the proper temperature and pressure, the resin in the impregnated paper can be melted and solidified to form a closed and dense surface, so that the micro pores on the substrate surface can be filled. Generally, lower pressure should be used as far as possible without affecting the product quality, which is beneficial to the service life of equipment and hydraulic oil and the internal structure of the base material; However, too low pressure will affect the adhesive strength and resin flow ability of the substrate and impregnated paper. Therefore, in actual production, the unit pressure of hot pressing plate should be appropriately adjusted according to the new and old degree of different base materials and cushion pads. 4. Product quality control The product quality control shall be carried out according to the superior product indicators in the standard CGBT15,102-94 Impregnated Film Paper Decorated Wood based Panel.
2、 Common quality defects of melamine impregnated paper faced MDF (patterned board) and their causes 1. Poor physical properties ① Low hot pressing temperature or short hot pressing time, incomplete tree curing, and easy adhesion of dust on the board surface during use, not easy to clean, resulting in dirty surface. ② The hot pressing temperature is too high, the surface temperature of the formwork is uneven or the degree of the base material is uneven, which is easy to form cracks on the board surface (commonly known as cracking). ③ Paper resin content is too low, resulting in low surface separation strength of the substrate. ④ Excessive unit pressure, uneven plate density, asymmetric structure and high hot pressing temperature cause panel warping. ⑤ The moisture content of the board is too high, the base material is broad, and the board density is too low. When pressing and pasting, the core layer will generate large steam pressure, which will make it bubble or delaminate. 2. Uneven gloss of the board surface ① The dipping amount of the impregnated paper is uneven, the water content of the board is too high, and bubbles appear locally on the board surface when pressing, resulting in uneven light selection of the board surface. ② The formwork surface is polluted, the surface is dirty or the cushion pad is damaged, and the temperature of the base plate is uneven, resulting in poor demoulding. ③ The water content of the board is too high, the hot pressing temperature is too low or the hot pressing time is too short, which leads to the water penetration of the board surface and uneven luster of the board surface. ④ Low hot pressing pressure or long storage time of impregnated paper. The resin has a high degree of pre solidification, and the resin fluidity is poor during hot pressing, resulting in poor board surface brightness. ⑤ Dirt or hand print on the surface of the board when assembling, paper, etc. 3. Board surface dry flowers (also known as dye white flowers or white spots) ① There is a local pre curing layer on the surface of the substrate, resulting in low board density at this place, resulting in large resin absorption, resulting in poor resin fluidity on the board. ② The base material is locally depressed Insufficient pressure at the concave during hot pressing affects resin flow. ③ The hot pressing temperature is too high, the hot pressing pressure is too low or the formwork surface is painted with dirt. ④ The cushion is partially damaged or has been used for a long time, resulting in excessive local temperature of the pressing plate and uneven heating of the plate surface. ⑤ The storage period of impregnated paper is too long, the degree of pre solidification is too high, the fluidity of tree land is poor, or the resin impregnation amount is too large, resulting in steam bubbles on the board surface and dry flowers when pressing. 4. The water content of the base material is too high, and excessive blisters are produced when pressing. ② The volatile content in the impregnated paper is too large or the impregnated paper is affected with moisture. ③ The hot pressing temperature is low or the hot pressing time is short. 5. Die bonding electrode plate (i.e. bad demoulding) ① The amount of resin impregnated is too large or the surface of the template is dirty. ② The hot pressing temperature is low, the time is short, and the resin is not completely cured. ③ The flushing pad is partially damaged, resulting in uneven formwork surface and low local temperature. ④ The high moisture content of the board affects the resin curing and leads to poor demoulding. To sum up, in order to produce high-quality products, we must select excellent impregnated paper and substrate, and adopt reasonable processing technology; In addition, operators and inspectors should cooperate with each other to control the quality of products, find out the causes of problems and solve them in time, so as to ensure the quality of products.
