Veneer decoration is a very important process in the production of panel furniture. It is used to decorate the furniture surface with veneer materials, to cover the defects of the material surface, improve the surface wear resistance, heat resistance, water resistance and corrosion resistance of the substrate, and at the same time improve And improve the strength and dimensional stability of the material. However, due to the different production methods of various enterprises, some quality problems often occur in the process of veneer decoration and use, and this paper proposes corresponding solutions.
1 veneer decoration quality requirements
Thin wood and other material veneers are not allowed to have degumming and bubbling. It is not allowed to have obvious transparent rubber. The veneer should be tight, flat and the texture should be similar. There should be no depressions, pitting, cracks, scratches, chipping and Cutting edge. In the national standards, the requirements for the veneer of furniture are put forward: enterprises should organize production strictly according to the requirements of national standards, and usually the internal standards of enterprises are stricter than national standards.
2 veneer processing technology
Before the veneer material is applied, the plain plate is subjected to thick sanding or surface sanding to make the thickness and surface roughness meet the veneer quality requirements; single-sided or double-sided coating is applied on the surface of the sanded plain plate; Then, the decorative material is laid on the surface of the glue, and the pressure is solidified on the cold press or the hot press to make the facing material and the substrate tightly adhered together; finally, the surface of the surface is trimmed and finished. The veneer work.
Thin wood veneers are commonly used in dry paste processes. The dry sticking process means that the adhesive is first applied to the substrate, and after it is cured, the thin wood is then laid up in a design pattern. A wet sticking process can also be used. The wet-sticking process refers to a process in which the thin wood is directly adhered to the substrate without drying (water content is 30 or more), and the surface of the substrate is coated with glue, and the thin-walled wood blank is cut and sewn thereon. The glue is pressed on the cold press or hot press, and the quality of the thin wood glue is checked after the glue is pressed and processed accordingly. Finally, the edge of the plate is trimmed and sanded.
3 Analysis of main problems and causes in veneer production
3.1 Whether it is veneer veneer or decorative paper veneer will have some quality problems in the process, the main reasons are as follows.
3.1.0 Substrate: The smoothness of the surface of the substrate, the bonding strength of the inner surface, and the uniformity of the thickness all affect the quality of the veneer.3.1.1 Surface quality of the substrate: The wood-based panel substrate used for panel furniture shall have the appearance quality and physical and chemical properties in accordance with the latest national standards. The surface of the substrate often has small areas of rubber spots, paraffin spots, oil stains and other impurities, which affect the penetration of the adhesive, so that the material can not be well glued, and there are problems such as degumming and bubbling.
3.1.2 Deviation of substrate thickness: The national standard of artificial board specifies that the thickness deviation is within ±0.2mm. The author conducted a thickness test on a brand of E1 grade sheet, and found that nearly 10 sheets of the thickness deviation exceeded the national standard. This creates a variety of quality problems for thinner facing materials.
3.2 Finishing material: If the impregnated paper is too dry, it will cause white spots; if the thickness of the impregnated paper is uneven, it will cause discoloration. The thickness of the thin wood is too thin, the structural structure causes the conduit to be too large, and the moisture content is too high, which will result in the surface of the adhesive. The thin wood has a high moisture content, which will cause black glue seam, seam or overlap at the thin joint of the wood. Sometimes it will warp the entire board. If the thickness of the veneer is too thin, the surface of the veneer will pass through.
3.2.1 Moisture content of decorative materials: Moisture content is one of the important factors affecting the quality of veneer. It affects the viscosity of the adhesive used in veneering, affects the wettability of the adhesive, and affects the apparent physical properties of the decorative material. Thin wood is a kind of wood thin veneer material with precious tree species. It usually has a water content of 8~15. If the moisture content of the thin wood is low, its heat transfer is slow and easy to break. However, the moisture content of the thin wood should not be too high, and the moisture content of the thin wood is large, and the drying shrinkage causes warpage deformation of the board surface. The moisture content of the decorative paper also affects the quality of the veneer. Usually, the processed paper is stored in an environment with a temperature of 25 ° C and a humidity of 55 to 65. If the decorative paper is too dry, there will be a white shift, and wrinkles will appear when the moisture is too high.
3.2.2 Decorative material thickness: Thin wood usually has a thickness ranging from 0.3mm to 1.5mm. When the surface of the substrate is flat, the thickness of the thin wood can be smaller; when the surface is uneven, the thickness is larger. Generally, the thickness of the thin wood used in the furniture company ranges from 0.4mm to 0.6mm, which can meet the requirements of the veneer process and meet the decorative requirements of the solid wood. The thickness of the thin wood is too thin. If the pipe is large, it will cause the rubber to penetrate the bottom. Color and other phenomena. The decorative paper used should also have a certain thickness, otherwise it will appear through the bottom. If the thickness is uneven, discoloration will occur.
3.3.0 veneer process
The veneering process includes the process method in the veneer, standardized operation, processing conditions, etc., which is the key link to ensure the quality of the veneer.
3.3.1 Process method
Thick sanding of plain plates is an important process to ensure uniform thickness of the plates and improve the quality of the plates. Failure to operate or reduce this process will cause veneer defects that cannot be remedied in later processes. The gluing process is to uniformly apply a certain amount of glue to the surface of the substrate. Too much glue will make the rubber layer hard and brittle; if the amount of glue is too small or the glue is uneven, local glue will be produced, resulting in bubbling; when the blank is used, the surface of the back surface of the adhesive should be symmetrical, otherwise it will cause the base. The surface of the material is unevenly stressed, causing the sheet to warp.
3.3.2 Processing conditions
Good processing conditions, such as a clean environment, suitable humidity and temperature and pressure, are required during the veneering process. Before the glue is applied, the surface of the board should be cleaned. After the glue is applied, the dust particles should be prevented from falling on the board surface. Otherwise, the surface of the board will have granular protrusions.
3.3.3 Standardized operation
In veneer processing, it must be operated in strict accordance with the process standards. Especially in the process of coating the substrate, the adhesive is first prepared in a certain proportion, stirred evenly, and then added to the glue applicator by a special container. In the actual operation, the worker will directly add the main agent of the adhesive to the rubber roller, and then add a modified material such as lignin powder to stir on the glue coating machine. This will occur, on the one hand, the adhesive is not evenly stirred, and large particles appear; on the other hand, the glue applicator is damaged; after the glue is applied, there are defects such as partial lack of glue and granules.
4 Measures and methods to solve the quality of veneer
4.1 Treatment of glue or crack
When the surface of the decorative surface is transparent or cracked, the thickness of the thin wood is increased or a layer of paper is sandwiched between the thin wood and the substrate, and the moisture content of the thin wood is not too high. In addition, the hot pressing temperature and pressure are appropriately reduced. After the hot pressing, the plates are stacked facing the surface to reduce evaporation of water. Adjust the viscosity of the adhesive and the amount of glue applied, and appropriately increase the ratio of solid content of the adhesive.
4.2 Treatment of surface grease or stains and undertones
When the surface of the decorative surface is contaminated with oil, grease or wax, it can be dissolved and dissolved by an organic solvent. The commonly used solvents are alcohol, ether, benzene and acetone. It is also possible to use a weakly alkaline 1 sodium hydroxide or sodium hydrogencarbonate. Scrub and wipe off with water. Most of the stains on the surface are contaminated with tannins, pigments and iron ions in the wood, which can be erased with hydrogen peroxide or 5 oxalic acid. When the surface of the board is transparent, apply a thinner piece of wood or a piece of paper of the same color as the thin wood to the substrate, and then affix the thin wood. In addition, the substrate is colored, and then the wood method is applied to color the substrate, and the substrate is directly colored by a coating method, or a small amount of a coloring agent is added to the adhesive, and the coloring is performed while the glue is applied.
4.3 Bubbling and degumming in a small area
The degumming or bubbling should be deflated and then glued. Use a sharp cutter to cut the bubbling wood in the direction of the wood grain to deflate, and use a thick syringe to inject the super glue into the bubbling, and then flatten it with an iron. For slightly larger bubbling, use a sharp blade to cut the thin wood at the bubbling direction and scrape the residual glue. Select the nearest thin wood to trim the desired size, and re-stick with the super glue, but note that The edge of the thin wood is also cut into a bevel to ensure that the repaired veneer is in contact with the original veneer slope, leaving no seam marks and a smooth surface.
4.4 Treatment of large area bubbling and degumming
When a large area of ​​bubbling, degumming occurs, and the number of workpieces is large, only the means of repair can not solve the problem fundamentally. It is necessary to query the reasons, analyze and discuss, and find corresponding measures.
First, the facing material is peeled off from the surface of the substrate, and the bonding material of the bubbling material, the adhesion of the substrate and the adhesive are observed. If there is almost no adhesive left on the surface of the substrate, it means that the substrate does not match the adhesive used. It can be exchanged or modified. It can also be changed to a good quality wood-based panel or sanded on the surface of the substrate to make it better. The surface quality, which in turn improves the surface bond strength. If the torn veneer material is coated with a lot of substrate debris, the internal bonding strength of the substrate does not meet the strength requirements of the veneer facing material. The simplest solution is to use a substrate that meets the E1 or E0 grade. However, since the construction period is tight and the existing raw materials cannot be wasted, it is impossible to replace the adhesive or the substrate. The following is a method for solving the problem by using the existing materials.
The process of treating the surface of the substrate: a good effect on solving the adhesion of the veneer.
The surface of the substrate is sanded and cleaned, and the low-solid content and low-viscosity (8~10s) closed primer is sprayed. The substrate processing process is because the drying speed is fast, it is not suitable for thick coating, generally it is sprayed once, each time. The amount of finishing is 60~90g/m2, and it should be completely dried after coating. After sanding, the amount of finishing material can be applied. The closed primer has good viscosity and permeability, and can penetrate into the deep surface of the substrate to form a film, which acts as a sealing function to prevent moisture absorption and dehydration of the substrate, and at the same time functions as a binder and a substrate to enhance the surface of the substrate. Inner bonding strength. However, it is necessary to take into account the matching of the closed primer used with the adhesive and topcoat used. The “Depot†primer is very effective. In summary, spraying a closed primer is a good measure to address insufficient bond strength or loose surface in the surface of the substrate.
4.5 The surface of the sticker appears uneven
In severe cases, the thin wood can be shaved and the surface of the part can be trimmed. The main reason is that the thickness deviation of the substrate is large, and the thickness deviation is reduced by the original sanding, and the curve is stable, which can basically meet the requirements of the veneer process. In addition, the surface of the plain wood-based panel has a high wax content, which will hinder the infiltration of the glue and reduce the bonding strength.
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