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In recent years, the fire situation in China's cities and towns is severe, and the economic losses and casualties caused by fires are on the rise, which is related to the use of a large amount of wood and other combustible materials in interior decoration. At present, the wood materials used in important parts of interior decoration such as construction, vehicles and ships are required to reach a certain level of flame retardancy. Therefore, it is necessary to further develop and develop flame retardant MDF.
Flame-retardant MDF can be grade A or B1 by adding a suitable chemical flame retardant.
2 flame retardant treatment
There are three main types of flame retardant treatment.
2. 1 immersion treatment
The board product is placed in a refractory liquid, soaked under normal pressure or vacuum pressure, and then dried. The biggest advantage of this method is that there is no loss of the agent. The disadvantages are (I) the need to increase the subsequent process of immersion of the agent; (2) the amount of impregnation of the agent is limited and unstable, and it is difficult to achieve a higher degree of flame resistance; (3) the moisture of the agent during the impregnation process destroys the bond between some of the fibers in the plate, Reduce the strength of the board; (4) The dielectric will cause the paraffin to fall off during the impregnation process, resulting in improved water absorption, and the hot-cold tank method or autoclave can be used for the immersion treatment.
For the pressure impregnation method, the impregnation should be carried out in an environment with a concentration of 50% solution, a temperature of 650 C, and a time of 10 min, and the amount of the agent in the plate can be up to 15% (based on dry matter).
2.2 board surface treatment
The method can be applied to the surface of the board by a brush, a spray coater or a roll coater. After the surface is coated, it can be slowly dried in the air or intensively dried by hot air, and the coating amount is 500-600 g / m 2 . Its advantages do not require special impregnation equipment, and the operation method is more flexible. The disadvantages are (1) low productivity of the board; (2) difficulty in venting the formed flammable volatiles; (3) affecting the quality of the decorative surface and limiting the application; (4) generating internal stress during heating, The film is cracked; (5) The fiber decomposition product in the plate is concentrated in the plate to form pressure, which can destroy the integrity of the film.
2.3 fiber treatment
The application of the flame retardant can be carried out simultaneously with the adhesive without increasing the production process and equipment. However, this method has high temperature drying of the fiber, high temperature decomposition of the fireproof inorganic salt during hot pressing and lowering of the fiber pH, causing partial curing of the adhesive or fiber component. Severe degradation, so that the strength and water resistance of MDF products are greatly reduced.
3 flame retardant
The flame retardant is composed of a flame retardant main agent, a flame retardant synergist and a base material.
3. 1 flame retardant agent
About 20%-30% of the total amount of flame retardant, commonly used the following four.
3.1.1 Phosphorus-nitrogen flame retardant (PN series): This kind of flame retardant mainly contains three elements of phosphorus, nitrogen and oxygen. Among them, the effect of hydrogen phosphate, dihydrogen phosphate and polyphosphoric acid is the best. .
3. 1.2 Boron-based flame retardant: It is an intumescent retardant. It generates water vapor when it is heated. It expands to form a covering to prevent heat and air, thus achieving the purpose of flame retardant. Its advantage is that it has both antiseptic and insecticidal properties. Function and low toxicity. It has little effect on the strength of raw materials.
3.1.3 Halogen flame retardants: mainly include inorganic chlorides, bromides and organochlorines, brominated hydrocarbons, etc. The halogen flame retardant is explained at high temperature to explain that HX and the fiber component in the flame generate free radicals, so that the concentration is lowered, thereby slowing or terminating the chain reaction of combustion to achieve the flame retarding purpose.
3. 1.4 air-based resin flame retardant: dicyandiamide, melamine and other reacted with formaldehyde, urea and phosphoric acid, used for impregnation or application of fiber to the manufacture of flame retardant MDF, its flame retardant mechanism is in 150- The foaming starts at 180 ° C, acts as a fire barrier, and releases nitrogen at a high temperature to dilute the surrounding oxygen.
3. 2 flame retardant synergist
The role of the flame retardant is to enhance and enhance the flame retardant effect of the main agent, reducing the amount of the main agent, generally accounting for 5%-10% of the formula, such as halogen series, pentaerythritol, aluminum hydroxide, urea, sodium silicate, dioxide Silicon and sulfuric acid money, etc.
3. 3 base material
Mostly water, the dosage is about 50%-70% of the formula weight
China's flame retardant MDF often uses hydrated alumina, phosphorus and nitrogen compounds and silica hydrate as flame retardant fire retardant to improve the fire performance of MDF. When selecting the flame retardant, it should be noted that it has good compatibility with the aldehyde rubber. The active period of the rubber is not greatly affected after mixing; the mechanical properties of the board are small; the compatibility with the paraffin emulsion is good; the adhesive must be used. a certain degree of water resistance
The board has a water absorption thickness expansion performance that meets the requirements; the cost is low.
4 Development and production progress
China's development and production of flame-retardant MDF has developed in the 1990s. At present, it has been invested in mass production manufacturers: the special adhesive for flame-retardant MDF developed by the Institute of Wood Research of the Chinese Academy of Forestry and sealed in Guangdong. Industrial Group Co., Ltd. put into production; Hubei Ningde MDF Co., Ltd. successfully researched flame retardant MDF and Shanghai artificial board factory successfully developed flame retardant medium (high) density fiberboard
Invested in mass production; Fuzhou artificial board factory uses phosphorus, halogen, nitrogen and other compounds as the main flame retardant, such as APP, KM, chlorinated paraffin, starch, melamine, etc., and some inorganic substances as synergistic flame retardants, The flame retardant performance of the flame retardant to the flame retardant grade of the GB8625-88 standard can be obtained by adding the flame retardant to the flame retardant veneer produced by the urea-formaldehyde glue. In addition, the new fireproof product Co., Ltd. of Ji'an County, Jiangxi Province has developed QX-2199 flame retardant, which is colorless, non-toxic, non-corrosive and non-polluting. The pH value is 6.2. The flame retardant dose required for the treatment of MDF is 5%. -7%, and diluted with KM flame retardant to make a flame retardant adhesive, brushed in MDF
board. The thickness of the 12mm MDF flame retardant adhesive is 176.9g/m2, and the decorative material is hot pressed. The flame retardant performance of the product reaches the flame retardant (B1) grade of GB8625-88. Nanjing Forestry University selects APP (polyphosphoric acid money), MDFP consists of melamine, dicyandiamide, formaldehyde and phosphoric acid) and UFPDN (composed of urea, formaldehyde, phosphoric acid, dicyandiamide, ammonia) as flame retardant, the amount of flame retardant 7%. The flame retardant performance can reach the JISD 1322-77 flame retardant level standard.
Although the development and production of flame-retardant MDF in China has achieved certain results in recent years. However, there are still problems such as low variety, low yield and high cost, and the problems of flame retardant resistance to delamination, gluing property and hygroscopicity of the sheet, and aging resistance have not been completely solved, and further research is needed on flame retardant workers engaged in wood-based panels. And explore.
Development and development of flame retardant MDF
1 Introduction