What Is Timber Cladding?
Glue wood to the surface of wood or other objects into one material. With the advent of new adhesives and the continuous improvement of the methods of using adhesives, the definition of adhesives has continued to evolve.
Wood adhesive
Right!
- Chinese name
- Wood adhesive
- Foreign name
- wood adhesive
- Use
- Glued wood
- Ingredients
- Paraformaldehyde
- Glue wood to the surface of wood or other objects into one material. With the advent of new adhesives and the continuous improvement of the methods of using adhesives, the definition of adhesives has continued to evolve.
- Wood adhesive
- wood adhesive
- Humans have a long history of using wood adhesives. In the 17th to 18th centuries, European and American countries have established adhesive factories. In the early 19th century, there were commercial caseins in Europe, and the commercial production of adhesives gradually developed. From the late 19th century to the early 20th century, synthetic resins entered the field of adhesives. In the 1930s, the wood industry began to use phenolic and urea-formaldehyde resin glues, which caused profound changes in the process and structure of the manufacture of wood products, and later promoted the development of wood-based panels, especially particleboard industry. Since the 1970s, the world's synthetic resin adhesive production has accounted for more than 80% of the total adhesives, of which the adhesives for the wood industry are particularly important. In the 1970s, Japanese woodworking adhesives accounted for 75% of the total adhesive production. In 1978, the urea and phenolic resins used in the wood industry in the United States accounted for 37% of the total thermosetting resin output.
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- Add paraformaldehyde to the urea aqueous solution (the first dose), heat to 60 ° C, adjust the pH to 7 with sodium hydroxide; reflux the mixture for 20 minutes, adjust the pH to 5 with formic acid, and reflux for 30 minutes. Then neutralize with 40% sodium hydroxide solution, add urea (second dosage), and adjust the pH value to 5.8 with formic acid solution; heat to reflux until the viscosity reaches 11.5 centipoise (20 ° C) to obtain the adhesive.
- When in use, first use a sander to shave the adhesive surface, or sand the surface with sandpaper, and then apply the agent on the surface of the adherend. After a while, the two adherends are bonded together and the weight is increased. Tighten. [1]
- polarity
- Wood-based polar substances have polar genes on their surface that are partially unsaturated. Adhesives with polar genes can cause opposite sex genes to attract each other and produce strong glue on the wood surface.
- Wettability
- , That is, the adhesion and diffusion effect on the surface of objects such as wood. The wettability of the glue is related to its surface tension and cohesion. The smaller the surface tension, the smaller the cohesion, and the greater its adhesion and diffusion effect. Otherwise the smaller it is. However, the wettability is too large, and it is easily absorbed by the wood, which causes the lack of glue and the excessive consumption of glue. Different glue materials should adopt the corresponding concentration and viscosity.
- PH (pH)
- Strong acid and alkali adhesives will reduce the mechanical properties of wood, especially strong acid.
- The molecular weight distribution
- Adjusting (or designing) the molecular weight range and molecular weight distribution required for different uses of the adhesive can improve the adhesive strength and accelerate curing.
Wood glue soybean glue
- It is made by crushing soybean meal into 100-300 mesh soybean flour. Its protein content is 40-50%. Bean protein is a globulin. Its protein molecule contains polar genes, which are combined into hydrogen bonds inside the molecule to make the molecule spiral. When making glue, a small amount of sodium hydroxide solution should be added to destroy its hydrogen bonds, so that the protein molecules are dispersed in water with free polar genes, and the glue layer will become sticky when the water in the glue layer evaporates. Adding water glass can control the viscosity of the glue and extend the usable time of the glue. Adding calcium hydroxide makes it react with the protein to become an irreversible substance, which can improve the water resistance of the gum. The styrene-butadiene or nitrile emulsion is mixed with soybean gum to obtain a water-resistant, sticky, and tough glue layer, and the pressing time can be shortened. Bean gum is mainly used for cold-pressed veneers with a moisture content of 15-20%. Odorless and tasteless, suitable for glued food packaging materials, such as tea boxes.
Wood glue blood glue
- The highest protein content in animal blood is pig and bovine blood, which can reach 17 to 18%. During slaughter, the blood is stirred to remove the remaining serum proteins and globulins from fibrin, which are spray-dried to be sold in powder form. It can also be adjusted directly with fresh blood. Due to different drying conditions, blood meal is divided into soluble grade (80 ~ 95% dissolved), partially dissolved grade (15 ~ 80%) and insoluble grade (less than 15%). The latter can only be used as fertilizer. Adding alkali during mixing can make a rubber compound with a solid content of 10-30%. Blood glue has better water resistance than soybean glue, but its color is darker. Can be used for cold pressing and hot pressing.
- Protein glue can be modified with cross-linking agent to improve its water resistance. Various protein materials can be used as fillers for synthetic resin glue to improve the toughness of the glue layer.
Wood adhesive amino resin adhesive
- Urea and the resin obtained by the reaction of melamine and formaldehyde are amino resins. Urea-formaldehyde resin is made by the condensation polymerization of urea and formaldehyde. Due to the advantages of low raw material cost, light color, short hot pressing time, and anti-mold, anti-bacteria, etc., it is used most in the production of plywood, particle board, blockboard, furniture, and sandwich doors. The main factors in the preparation of urea-formaldehyde resin are the molar ratio of urea to formaldehyde, the pH value and concentration of the reaction solution, the reaction temperature and time. By changing these factors to control the degree of resin polycondensation, resins with different properties can be prepared to meet different needs. The polymer obtained by the reaction must be subjected to vacuum dehydration to achieve a solid content of 60 to 70%. Resins made with high concentration of formaldehyde (40-50%) can achieve the required solid content without dehydration. It can also add a certain amount of urea in the production of concentrated formaldehyde solution, react under alkaline conditions and 50-55 ° C to make a prepolymer of resin, and then add urea as required to achieve the required urea and The molar ratio of formaldehyde is then heated and stirred to form a high concentration formaldehyde solution. The prepolymer is stable in storage, convenient for transportation, and can eliminate the dehydration process. Urea-formaldehyde resin glue is used for the pre-pressing process of plywood. A small amount of polyvinyl alcohol can be added during the reaction of the urea-formaldehyde resin to improve its initial adhesion performance. A larger amount of flour and other extenders can also be added to the general urea-formaldehyde resin. Urea-formaldehyde resin can accelerate curing under acidic conditions, so a certain amount of hardener such as ammonium chloride or ammonium sulfate should be added when using. Urea-formaldehyde resin contains a certain amount of unreacted free formaldehyde, and some are released during the pressurization process, causing environmental pollution, which can be prevented by adding a part of melamine and improving the polycondensation process conditions. Melamine formaldehyde resin or modified resin is widely used for impregnating decorative paper, preparing melamine decorative boards or directly pasting on wooden substrates, and its wear resistance, heat resistance, hardness and gloss are excellent.
Wood adhesive phenolic resin adhesive
- Resin formed by polycondensation of phenols (mainly phenol, resorcinol, cresol) and formaldehyde. In wood processing, thermosetting phenolic resins are mainly used. Due to different catalysts, the properties of the resins produced are also different. If ammonium hydroxide is used as a catalyst, an alcohol-soluble resin can be prepared, which is mainly used for impregnating sulfate paper as a glue film; if sodium hydroxide is used as a catalyst, it is made into a water-soluble resin; Resin molecular weights are also different. The reaction temperature and reaction time also have an effect on the properties of the resin. Phenolic resin glue has good resistance to boiling water and weather. Its products belong to a class of high water resistance outdoor products, which are used in aircraft, ship, and building components. It is mainly hot-pressed (temperature 125-150 ° C), and the pressing time is longer than that of urea-formaldehyde resin glue, but it can be shortened by adding resorcinol or hardwood extract or adding some blood powder and improving the preparation process. For example, polycondensation under basic conditions and then polycondensation under acidic conditions will result in a high molecular weight resin, which is insoluble in water and can be made into an emulsion by adding natural resin or polyvinyl alcohol. Phenolic resins are also widely used in kraft paper for impregnating the bottom layer of decorative boards. In order to make the impregnated paper have toughness, cresol or xylenol is usually co-condensed with phenol and formaldehyde. Resorcinol formaldehyde resin glue can be cured at neutral and room temperature. It has the best resistance to boiling water and weathering by cold pressing. The gluing process is simple. It is mostly used for thick wood or board such as bridges, sleepers and outdoor applications. Building blocks. After curing the amino resin and phenolic resin, the adhesive layer shrinks and becomes brittle. Adding extenders or fillers makes the adhesive layer have certain plasticity and can improve its aging resistance.
Wood adhesive hot melt adhesive
- Abbreviated as hot melt adhesive, it is a mixture of thermoplastic resins. They are all solid and have a certain fluidity at high temperature. After cooling the surface of the adherend, it will become solid and become sticky. Fast gluing, low energy consumption, and no solvent pollution. In plywood production, it is used for splicing of veneer, filling holes or edge sealing of some artificial boards. The main components of hot melt adhesive are polymer resin, tackifier, extender, plasticizer, filler and antioxidant. Woodworking hot melt adhesives are mainly ethylene-vinyl acetate copolymers, followed by polyamide or polyethylene. Hot melt adhesives have poor heat resistance and are not resistant to oil and organic solvents. Their performance and equipment used need to be improved.
Lignin tannin
- Lignin is a regenerative plant-based woodworking adhesive. In recent years, due to the increasing shortage of petroleum resources, it has been valued. A large amount of lignin in papermaking waste liquid can also be used as a gluing raw material. Now, replacing some phenolic resins with lignin has been successful. There are many types of tannin-containing plants, but they contain different components. The reaction of tannin with formaldehyde and formaldehyde can be used to make a medium temperature curing adhesive.
- In addition, the polyisocyanate used in recent years can reduce the amount of glue and shorten the pressing time when manufacturing particleboard. The product can be used outdoors. Its durability and weather resistance are slightly worse than those of phenolic resin glue. It is also used for modification or with Other rubber types are mixed to improve water resistance. Canadian trial-produced phenolic resin with high solid content (70-90%) is particularly suitable for gluing straw, rice husk, wheat straw and other materials, and the effect is better than ordinary phenolic resin. Secondary wood processing, joinery, and wood composite materials can be used with neoprene, acrylate and its copolymer emulsion, vinyl acetate homopolymer, and vinyl acetate and ethylene copolymer emulsion.
- In short, the correct selection of adhesives can not only achieve good adhesion, but also improve economic benefits.