Wood-based panel is made by hot pressing wood shavings or scraps with a certain shape and size after applying adhesive. Also known as particle board. The qualitative descriptions of particleboard in different countries are not completely consistent. GB 4896 ~ 495-85, the national standard of particleboard in China, does not impose any restrictions on the adhesive of particleboard. Many countries stipulate that particleboard is limited to the use of organic synthetic resin glue. Others stipulate that the use of other types of adhesives is recognized as particleboard, but it does not include non-adhesive plates.
a brief history
the pressing of particleboard with scrap and adhesive began in the early 2th century. From 191 to 194, patents for particleboard appeared in the United States, Germany, France, Czechoslovakia, Switzerland and other countries. One of the most famous is the patent of making three-layer particleboard with flat shavings published by F. Pfohl of Switzerland in 1937. In 1941, the first particleboard factory appeared in Bremen, Germany, which used spruce sawdust and phenolic resin to press 3×2 m boards with a density of .9 ~ 1.1 g/cm3. But the product that is really similar to modern particleboard was invented by Fahrney, and in 1944, a particleboard factory called Novopan method was established in Switzerland. The density of the board is .6 g/cm3, and it has a three-layer structure. In the following years (to the early 195s), W.Klauditz, M.Himmelheber and others in the Federal Republic of Germany studied some important issues in particleboard manufacturing, such as raw material tree species, particle morphology, board density, board performance, etc., and gained knowledge and accumulated experience. In addition, some key equipment was successfully developed, so the modern particleboard industry began to appear. From 195 to 1955, the particleboard industry in the Federal Republic of Germany developed greatly, and other industrial countries, such as Belgium, France, Britain, Italy, Japan, the Netherlands, Austria, Czechoslovakia and the United States, competed to build factories. The particleboard manufacturing industry has become one of the emerging industries in the world. The output of particleboard in Europe only increased from 12, tons in 195 to 35, tons in 1955. From 1955 to 1958, not only the production of particleboard by extrusion method was rapidly popularized all over the world, but also in the flat pressing method, air flow paving, roll-throwing paving and other processes, as well as single-layer hot press and various material preparation equipment appeared one after another. The academic research and communication of particleboard and the coordination of all aspects were also carried out rapidly at this time. In 1957, FAO arranged a consultation meeting on particleboard and fiberboard in Geneva. In 1958, the European Branch of Particleboard Manufacturers Association (FESYP) was founded. From 1961 to 1963, many countries promulgated particleboard standards and studied and formulated quality control methods for particleboard. Because particleboard can use small wood, inferior wood and waste wood as raw materials, and has a good foundation in scientific research and development, modern mechanization, automation, enterprise management and other means have been applied in particleboard enterprises, and the output has risen rapidly. In 195, the world output of particleboard was only 2, cubic meters, and by 1977, the total output had grown to 32.5 million cubic meters. And the varieties are increasing day by day, mainly fine-surface particleboard, fiber particleboard, thin particleboard, oriented particleboard and waffle particleboard.
the production of particleboard in China began in the early 195s, when Shanghai Yangzi Wood Factory produced protein adhesive particleboard. On the basis of several years' experimental work, Beijing Timber Factory and Wood Industry Research Institute of Chinese Academy of Forestry established the earliest workshop for producing particleboard with synthetic resin adhesive in China in 1958. In the early 196s, Beijing Guanghua Wood Factory, Shanghai Wood-based Panel Factory, Chengdu Wood Comprehensive Processing Factory and Changsha Wood Factory successively introduced complete sets of production equipment for particleboard by extrusion and flat pressing from Switzerland and the Federal Republic of Germany. Due to the lack of rubber compound in China at that time, the particleboard industry developed slowly in the next ten years, and it didn't start to develop rapidly until the late 197s. By 1983, there were 127 particleboard enterprises in China with a design capacity of 1 million cubic meters.
raw materials
the fiber raw materials that can be used for particleboard production are increasingly extensive due to the development of science and technology, which is one of the important reasons for the rapid development of particleboard. The available raw materials are: ① small-diameter grade timber or inferior timber. Among the timber harvested in forest areas, the timber with larger diameter is mainly used in other industries, and the particleboard factory only uses the thinning timber, firewood, fast-growing timber, inferior timber, knotted and bent timber and fine branches. ② Wood processing residues. Board skin is an excellent raw material for particleboard, but it is generally used in pulp and paper industry. A large number of factory shavings planed and milled from wood are used, but simpler tree species are required. Wood chips can also be used together with other raw materials to produce particleboard. The leftover bits and pieces of joinery can also be used in particleboard production after being crushed by a suitable crusher. ③ Annual plant fiber raw materials. Flax chips and bagasse are excellent fiber raw materials for particleboard. The particleboard made of them has low density and good performance, especially for mechanical components with thermal insulation, which has its unique advantages and is reasonable in economy. Cotton stalk, wheat straw, rice husk and bamboo can also be used in the production of particleboard. According to the national conditions, China is developing annual plant fiber raw materials with large resources to meet the needs of particleboard industry.
Adhesive used
Adhesive is one of the main raw materials for particleboard production. Generally, the dosage is 6 ~ 12% of the amount of wood shavings, and it also needs 2 ~ 8% when using precious rubber seeds. Adhesive costs account for a considerable proportion of particleboard costs. The types of adhesives used in the world are: ① Urea-formaldehyde resin adhesive. Because of its rapid curing and low price, about 9% of particleboard in the world uses urea-formaldehyde resin adhesive, while China currently accounts for almost 1%. ② Melamine resin glue. The moisture resistance is worse than that of phenolic resin adhesive and better than that of urea-formaldehyde resin adhesive. Urea-formaldehyde resin modified by melamine resin is often used as adhesive for particleboard in high humidity air environment. ③ Phenolic resin adhesive. The particleboard made of it as adhesive still has quite high bonding strength in humid air or after being soaked in water, so it is mostly used for building stress components or outdoor materials. But its price is much higher than that of urea-formaldehyde resin adhesive. ④ isocyanate resin adhesive. It has strong water resistance and cementing power, and is suitable for the manufacture of fiber materials that are difficult to glue, such as grass particleboard. By using it, it can also save adding waterproof agent. Isocyanate resin adhesive can also bond wet fiber materials, which can save drying cost in particleboard manufacturing. Its disadvantage is that it is expensive, and it is easy to adhere to aluminum plate and steel plate, which brings difficulties to operation. Therefore, it is used as adhesive, and mold release agent or other resin adhesives should be used in hot pressing. In the world, the number of particleboard factories using isocyanate adhesive in the Federal Republic of Germany is the largest. ⑤ Natural adhesive. Tannin adhesive is the most important and promising one used in particleboard production. It is made by the reaction of tannin extracted from bark of some tree species with formaldehyde or formaldehyde. In use, a small amount of phenolic aldehyde or other rubber compound is often used to modify it. Sulfate pulp waste liquid (SSL) can also be made into adhesive for particleboard after refining.
specifications and properties
the specifications of particleboard can be cut into suitable sizes according to their different uses, and can also be endowed with various artificial properties according to the requirements of use. The existing national standard of particleboard in China is GB 4896 ~ 495-85. According to the regulations, its specifications and properties are: ① particleboard thickness. 6, 8, 1, (12), 13, 16, 19, 22, 25, 3, ... mm, etc. Other thickness sizes can be produced by agreement between the supplier and the buyer. ② Thickness deviation. Thickness deviation of matte particleboard with thickness less than 16mm is ≤ .8mm for first-class product and ≤ 1.mm for second-class product; Thickness ≥ 16mm, first-class product ≤ 1.mm, second-class product ≤ 1.2mm.. No matter how thick the flat-pressed sanding particleboard is, its deviation shall be ≤ .3mm.. The thickness deviation of extruded particleboard without sanding is less than or equal to .8 mm. ③ Size of particleboard format. 915mm in width and 915, 122, 1525, 183 and 2135mm in length; Width 1 mm, length 2 mm; The width is 122 mm and the length is 122, 1525, 183, 2135 and 244 mm. Other format sizes can be produced by agreement between the supplier and the buyer. The allowable deviation of width and length is ~+8mm. ④ Warpage. Flat-pressed particleboard: first-class product < 5/1, second-class product < 1/1. Physical and mechanical properties: moisture content is 5. ~ 11.%; The density is .5-.85g/cm3; The static bending strength is ≥18 MPa for the first-class product and ≥15 MPa for the second-class product; The plane tensile strength is ≥.4 MPa for the first-class product and ≥.3 MPa for the second-class product; The swelling rate of water absorption thickness (2℃, soaked in water for 2 hours) is ≤6.% for first-class products and ≤ 1.% for second-class products; The screw holding force is ≥ 1,1 N for the first-class product on the vertical board surface and ≥7 N for the first-class product on the parallel board surface; The elastic modulus is 2.×13 MPa for the first-class product; The release of free formaldehyde is less than 5 mg /1 g particleboard.