When the veneer is applied to the surface of the substrate, different adhesives are used depending on the adhesive method selected. The dry method uses hot melt adhesive, and the hot melt adhesive is applied on the substrate. After it is cooled and solidified, it is heated by an iron to activate it, and the thin wood is attached. The commonly used hot melt adhesives are bone glue and polyvinyl acetate. Ester resin glue. The wet method selects the thermosetting resin, and the thermosetting resin is applied on the substrate, and the thin wood glue is directly attached without drying. The commonly used thermosetting resin glue is a mixed glue of urea-formaldehyde glue and polyvinyl acetate emulsion. Urea-formaldehyde glue is convenient to use, low in cost and good in water resistance, but has strong permeability and is easy to cause penetration. The initial tackiness is small, and the thin wood is easy to be displaced after being stuck on the substrate. Although the method of adding the filler can increase the initial tackiness, the operation of the thin wood paste is difficult, so the urea-formaldehyde glue is mixed with other adhesives. Polymethylene acid emulsion is a thermoplastic adhesive, which has poor permeability, does not cause penetration, and has a soft film. It is helpful for preventing cracking of thin wood, but the water resistance is poor. Therefore, urea-formaldehyde resin glue and polyvinyl acetate emulsion are generally mixed in a certain proportion. Use, learn from each other. And adding an appropriate amount of filler to the mixed rubber to increase the initial tack of the adhesive.
The more the amount of urea-formaldehyde glue added in the polyvinyl acetate emulsion, the better the water resistance of the adhesive and the stronger the bonding strength. On the contrary, with the increase of the proportion of polyvinyl acetate emulsion, the adhesive penetration and aging of the adhesive are improved.
1 .
The moisture content of the thin wood wet paste is more than 60%. If the water-soluble urea-formaldehyde resin glue with good permeability is used alone, the adhesive easily oozes out the thin wood and penetrates into the substrate, causing the rubber and the lack of glue, and the thicker the thin wood conduit The more serious the glue. In order to prevent the penetration of the glue, some polyvinyl acetate emulsion must be mixed in the porpod resin, and some flour is added as a filler. Generally, when the ratio of the polyvinyl acetate emulsion glue to the flour is larger than that of the porphyrin resin, the penetration of the rubber can be prevented. The size of the scale can be adjusted according to the size of the thin wood conduit.
2. Thin wood
When veneer veneer is used, it is often necessary to spell out a certain pattern and pattern. After the veneer is placed on the surface of the substrate to form a pattern, the veneer cannot be displaced during the handling process before entering the hot press, so the adhesive is required to have a certain initial viscosity. The virgin resin and the polyvinyl acetate emulsion have poor initial adhesion properties, but if a small amount of flour is added to the mixed rubber, the initial viscosity of the adhesive can be improved because the gluten contained in the flour can be combined with the formaldehyde in the dolphaldehyde resin. Or hydroxymethyl reaction to form a very viscous substance, so that the initial viscosity of the mixed rubber is greatly improved. When the thin wood is hard or uneven, the ratio of urea-formaldehyde resin and flour should be increased to increase the initial tack of the adhesive. balance.
3. Surface crack
Cracking behind the wet wood wet patch is also one of the most prone defects in the wet-bonding process. This is because the wet thin water is in a wet state, and after the hot pressing, the thin wood shrinks, and the substrate is pinched, so that the thin wood horizontal stripes are subjected to a large tensile pressure, and the harder the material, such as ash, eucalyptus Etc., the greater the stress, the thin wood is easy to crack, but if the adhesive has good water resistance to overcome the above stress, the thin wood is not easy to crack, so for the easy cracking of the thin wood, the mixing of the urea should be increased. Than to improve its water resistance.
4 deformation
Although the thickness of the thin wood is small, the veneer is easily deformed due to the uneven moisture content caused by the moisture absorption on both sides of the veneer. However, if the rubber layer between the thin wood and the substrate has a certain elasticity and plasticity, the stress caused by the difference in properties between the two materials can be partially or completely compensated, thereby reducing the deformation of the plate, which requires adding polyacetic acid to the mixed rubber. The configuration of the ethylene emulsion.
After combining the above various factors, the ratio of the commonly used mixed rubber of the aldehyde resin glue and the polyvinyl acetate emulsion is: polyvinyl acetate emulsion: urea-formaldehyde resin glue = 10:2~3, and adding 10~3O filler .
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