Guide: Veneer furniture is one of the modern furniture. It is made of thin pieces of wood pasted on the furniture panel, making the furniture have the natural appearance of solid wood furniture.
The veneering process makes the wood-based panel furniture have a beautiful and natural appearance, can cover the wood surface defects, and protect the furniture to a certain extent to reduce cracking. There are many decorative patterns and rich textures, which greatly enhance the diversity of panel furniture in appearance. Compared with solid wood furniture, panel furniture has a lower price, specifications and dimensions that can be mass produced, and can also bring consumers the appearance and experience of solid wood, which makes panel furniture popular. Nowadays, many man-made boards are green composite boards, which greatly reduces the development of forest resources. The recycling rate of panel furniture is also generally high.
However, due to the different production methods of various enterprises, some quality problems often occur in the process of veneer decoration processing and use. This paper proposes corresponding solutions.
- The veneer and other materials shall be free of degumming and bubbling, and clear glue penetration. The splicing of veneer shall be tight and flat, with similar texture, and shall be free of dents, pits, cracks, scratches, chippings and cutting edges. In the national standards, the requirements for furniture veneer are put forward: enterprises should organize production in strict accordance with the national standards. Generally, the internal standards of enterprises are stricter than the national standards.
- Main problems and cause analysis in veneer production
Whether it is veneer veneer or decorative paper veneer, there will be some quality problems in the process of processing. The main reasons are as follows.
(1) Surface quality of base material
The appearance quality and physical and chemical properties of the wood-based panel substrate used for panel furniture must comply with the latest national standards. The surface of the substrate often has small areas of glue spots, paraffin spots, oil stains and other impurities, which affect the penetration of the adhesive, so that the materials can not be bonded well, and problems such as degumming and bubbling occur.
(2) Thickness deviation of base material
The national standard of artificial board stipulates that its thickness deviation is within ± 0.2 ㎜. The author tested the thickness of E1 grade plates of a brand, and found that the thickness deviation of nearly 10 plates exceeded the national standard. This will result in various quality problems for thinner facing materials.
(3) Finishing materials
If the impregnated paper is too dry, it will cause white spots; The uneven thickness of impregnated paper will cause discoloration. Too thin veneer, too large conduit due to material structure and too high moisture content will produce glue penetration on the surface of the adhesive; The moisture content of veneer is high, which will cause black glue joint, parting joint or overlapping at the seam of veneer; Sometimes, the whole board surface will be warped and deformed. The thickness of veneer is too thin, which will make the board surface transparent.
(4) Moisture content of decorative materials
Water content is one of the important factors affecting the quality of veneers. It affects the viscosity of adhesives used in veneers, affects the wettability of adhesives, and affects the apparent physical properties of decorative materials. Thin wood is a kind of thin wood veneer material with the characteristics of precious tree species. Generally, its moisture content should be 8~15. If the moisture content of thin wood is low, its heat transfer is slow and it is easy to break. However, the moisture content of the veneer can not be too high. The moisture content of the veneer is large, and the drying shrinkage will produce warping deformation of the board surface. The moisture content of the decorative paper also affects the veneer quality. Generally, the processed paper is stored in an environment with a temperature of 25 ℃ and a humidity of 55~65. If the decorative paper is too dry, the day shift will occur and wrinkles will appear.
(5) Decorative material thickness
Generally, the thickness of thin wood ranges from 0.3mm to 1.5mm. When the surface of base material is flat, the thickness of thin wood can be smaller; In case of unevenness, the thickness is large. Generally, the thickness of veneer used in furniture companies ranges from 0.4 ㎜ to 0.6 ㎜, which can not only meet the requirements of veneer technology, but also meet the requirements of solid wood decoration. If the thickness of veneer is too thin, such as large conduits, it will cause glue penetration and color penetration. The decorative paper used should also have a certain thickness, otherwise there will also be transparency, and if the thickness is uneven, there will also be discoloration.
(6) Process method
The thickness setting sanding of plain plates is an important process to ensure the uniform thickness of plates and improve the surface quality. Poor operation or reduction of this process will cause veneer defects, which cannot be remedied in later processes. The gluing process is to evenly coat a certain amount of glue on the surface of the substrate. Too much glue will make the glue layer hard and brittle; Too little glue or uneven glue will cause local glue shortage, leading to blistering; During blank preparation, the adhesive facing materials on the back of the surface shall be symmetrical, otherwise, uneven stress on the surface of the base material will be caused, which will lead to plate warping.
(7) Processing conditions
Good processing conditions, such as clean environment, suitable humidity, temperature and pressure, shall be guaranteed during the veneer process. Before gluing, ensure that the board is clean. After gluing, prevent dust particles from falling on the board, otherwise, the board will have granular protrusions.
(8) Standardized operation
The veneer processing shall be carried out in strict accordance with the process standards. Especially for the process of gluing the base material, the adhesive shall be prepared in a certain proportion, stirred evenly, and then added into the gluing machine with a special container. In actual operation, workers will directly add the main agent of the adhesive to the cots, and then add modified materials such as lignin powder, which will be stirred on the gluing machine. This will result in, on the one hand, uneven mixing of adhesive and large particles; On the other hand, it will damage the gluing machine; Defects such as local glue deficiency and granular protrusion appear after gluing.
3 Measures and methods to solve veneer quality
(1) Treatment of sealant penetration or cracks of decoration
If there is glue penetration or cracks on the surface of the veneer, increase the thickness of the veneer or clip a layer of paper between the veneer and the substrate for buffering, and the moisture content of the veneer should not be too high. In addition, reduce the hot pressing temperature and pressure appropriately. After hot pressing, stack the plates face to face to reduce water evaporation. Adjust the viscosity and coating amount of adhesive, and appropriately increase the solid content ratio of adhesive.
(2) Treatment of grease or stain and transparent color on the surface of the veneer
When the decorative surface is polluted by oil, grease and wax, it can be dissolved and wiped with organic solvent. The common solvents are alcohol, ether, benzene and acetone. It can also be wiped with weak alkaline sodium hydroxide or sodium bicarbonate, and then wiped with clean water. The stain on the surface of the veneer is mostly caused by the pollution of tannin, pigment and iron ions in the wood, which can be erased with hydrogen peroxide or 5 oxalic acid. When the bottom color of the board is revealed, use a slightly thick veneer or paper with the same color as the veneer to paste it on the substrate first, and then use the veneer for decoration. In addition, the base material shall be colored first, and then the thin wood method shall be applied to color the base material. The base material shall be directly colored by coating, or a small amount of colorant shall be added to the adhesive for coloring while gluing.
(3) Bubble and degumming in small area
The degumming or bubbling area shall be deflated before gluing. Use a sharp knife to cut the thin wood at the bubble along the direction of the wood grain to deflate, use a thick syringe to inject super glue into the bubble, and then use an iron to flatten it. For slightly larger bubbles, use a sharp blade to cut the thin wood at the bubble along the direction of the wood grain, scrape off the residual glue, select similar thin wood to trim to the required size, and use super glue to re paste. However, it should be noted that the edge of the thin wood is also cut into a slope to ensure that the repaired thin wood contacts the original veneer slope, leaving no seam marks, and the surface is smooth and flat.
(4) Treatment of large area bubbling and degumming
When there is a large area of bubbling and degumming, and there are a large number of workpieces, repair alone cannot fundamentally solve the problem. It is necessary to query the causes, analyze and discuss again, and find corresponding measures. Firstly, peel the veneer material off the surface of the substrate, and observe the bonding of the veneer material, substrate and adhesive at the bubbling position. If there is almost no adhesive left on the surface of the base material, it means that the base material does not match the adhesive used. The adhesive can be replaced or modified, or the wood-based panel with good quality can be used, or the surface of the base material can be sanded to obtain better surface quality, thus improving the surface bonding strength. If there are many base material chips on the torn facing material, it indicates that the internal bonding strength of the base material does not meet the strength requirements of the adhesive facing material. The simplest solution is to select the base material that meets the E1 or E0 level. However, due to the tight construction period and the existing raw materials can not be wasted, it is impossible to replace adhesives or base materials. The following is a process solution using existing materials. The process of treating the surface of the base material: it has achieved good results in solving the adhesion of the veneer. Sand and clean the surface of the base material, and spray the sealing primer with low solid content and low viscosity (about 8-10s). The process of base material treatment is that, due to its fast drying speed, it is not suitable for thick coating. Generally, it is sprayed once, and the amount of each coating is 60-90g/㎡. After the coating, it is completely dry, and the finishing material can be applied after proper sanding. The sealing primer has good viscosity and permeability, can penetrate into the depth of the substrate to form a film, plays a sealing role, prevents the substrate from moisture absorption and dissipation, and also plays a role in sticking to the substrate debris, enhancing the internal bonding strength of the substrate surface. However, the compatibility of the sealing primer with the adhesive and finish paint shall be considered. The sealing effect of “Didebao” primer is very good. In a word, spraying sealing primer is a good measure to solve the problem of insufficient internal bonding strength or loose surface of the substrate surface.
(5) The adhesive surface is uneven
In serious cases, the thin wood can be planed off to trim the surface of components. The main reason is that the thickness deviation of the base material is large. The thickness deviation is reduced by setting the original sanding, and the change curve is stable, which can basically meet the requirements of the veneer process. In addition, the surface of plain wood-based panels contains higher wax components, which will hinder the infiltration of glue and reduce the bonding strength.
The defects of veneer furniture, such as cracking, stain, degumming and bubbling, often occur in the course of use. This paper puts forward corresponding solutions to these defects. Improving the veneer quality of panel furniture can greatly improve the dimensional stability of materials, and can also bring consumers a better aesthetic appearance, which is the key to improving the quality of panel furniture.
