▎ 摘　　要

NOVELTY - Preparing medium density plate comprises (1) placing formaldehyde and methylphenol with a molar ratio of (1.1-1.2):1 into the reactor, adding 7-10% potassium hydroxide to the total mass of the reactants and uniformly mixing, heating to 65-75℃ and reacting for 30-40 minutes, adding 3-aminopropyltriethoxysilane, continuously reacting, and continuously stirring to obtain adhesive, (2) uniformly mixing pine fiber powder and bamboo fiber powder according to the mass ratio of (1-2):(8-9), hot-pressing to form medium density board, and double-sided polishing, (3) adding 5-10 pts. wt. hydroxy-modified nano-graphene sheets to 50-70 pts. wt. phenolic resin and 3-5 pts. wt. tributyl phosphate, and (4) coating ultraviolet (UV) varnish on the double surface of the medium density plate, drying, curing, and forming the polyurethane acrylate resin layer that thickness is 0.2-0.3 mm on the surface, and (5) polishing the surface of the polyurethane acrylate resin layer. USE - The plate is useful as backing board for printed circuit board (PCB) drilling (claimed) and field of printed circuit boards (PCBs). ADVANTAGE - The method provides medium density plate with good hardness, which can reduce PCB drilling burrs, avoids drilling cuttings remaining in the drilling, reduces the abrasion of the drill needle, and improves PCB drilling quality. The middle density plate prepared by the method is used as the base plate when drilling the PCB, which reduces the displacement deviation of the hole, hole wall roughness, burr, drilling temperature, burrs, improves the hole position precision, and ensures the quality of the drilling. The method has high thermal conductivity and low thermal expansion coefficient, improves the whole hardness, ensures the performance of the subsequent drilling, realizes good heat conduction and reduces the drilling temperature. DETAILED DESCRIPTION - Preparing medium density plate comprises (1) placing formaldehyde and methylphenol with a molar ratio of (1.1-1.2):1 into the reactor, adding 7-10% potassium hydroxide to the total mass of the reactants and uniformly mixing, heating to 65-75℃ and reacting for 30-40 minutes, adding 3-aminopropyltriethoxysilane with a total mass of reactants of 0.2-0.3% when the temperature is raised to 90-100℃, continuously reacting for 60-90 minutes, lowering the temperature to 25-35℃ for vacuum dehydration after the reaction, adding boron nitride powder with a total weight of 1-2% of the reactants, and continuously stirring to obtain adhesive, (2) uniformly mixing pine fiber powder and bamboo fiber powder according to the mass ratio of (1-2):(8-9), uniformly mixing the adhesive and curing agent prepared above according to the mass ratio (75-85):(15-25), uniformly mixing, immediately using the sizing device to sizing the mixed fiber powder, paving the mixed fiber powder, hot-pressing to form medium density board, and double-sided polishing, (3) adding 5-10 pts. wt. hydroxy-modified nano-graphene sheets to 50-70 pts. wt. phenolic resin and 3-5 pts. wt. tributyl phosphate, fully stirring, soaking the medium density plate in the above mixture for 20-30 minutes, allowing to stand and drying to form phenolic resin layer with thickness of 0.2-0.3 mm on the surface after taking it out, and (4) coating ultraviolet (UV) varnish on the double surface of the medium density plate in the step (3), drying, curing, forming the polyurethane acrylate resin layer that thickness is 0.2-0.3 mm on the surface, where the composition of the UV varnish is 50-70 pts. wt. polyurethane acrylate resin, 10-20 pts. wt. 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 5-10 pts. wt. hydroxyethyl methacrylate, 5-10 pts. wt. hydroxy-modified nano graphene sheets and 150-200 pts. wt. isopropanol, and (5) polishing the surface of the polyurethane acrylate resin layer. An INDEPENDENT CLAIM is also included for medium density plate for PBC prepared by the above-mentioned preparation method.