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Common problems with solid Wood Furniture--Yellow change
Aug 10, 2018

Whether it is standard products such as wooden furniture or customized products such as wooden cabinet wooden door, the industry has long been difficult to solve all kinds of after-sale quality problems. Due to the characteristics of solid wood products, many products in the factory inspection and no problem, but in the consumer's home after a period of time there are quality problems. At this time, the return and repair of goods not only cause a lot of extra manpower and material costs, but also seriously affect the brand reputation. Among these problems, the more concentrated and representative are yellowing, cracking and deformation. These are all questions. It has a lot to do with wood.


All white paint actually turns yellow because white pigment titanium dioxide turns yellow after ultraviolet radiation. So whether it is white appliances, white plastic windows, white cars will slowly turn yellow. Thus white wooden furniture will certainly produce yellowing, of course, slower, usually difficult to detect. Such a situation if the sales phase in advance to the consumer, will not constitute a quality problem.


The local yellowing of the product is completely different, obviously not natural aging. The frequency of this situation is so high that almost every factory cannot completely avoid it. This is the local yellowing we are going to discuss.


According to the above situation and experience analysis, the local yellowing has the following characteristics:


A. Mainly white paint;


B. mainly open lacquer;


C. wood is mainly red oak;


It has nothing to do with geography. It is a problem in factories in both the North and the South;


Generally, problems occur within 3 to 12 months. If there is no yellowing problem within 12 months, there will be no further problems.


In order to analyze the reason, we sand the door board of the factory and find that the local yellowing part of the wood has already changed blue, that is, the wood has changed in color. Mild blue change is light gray to gray blue, heavy blue change is blue to black. What about blue change?


Blue change is when wood is infected with color-changing bacteria and turns gray blue. Cyanobacteria are very sensitive to temperature and humidity, and are very active in high humidity environment of 23 ℃ -35 ℃, that is, in humid and hot summer, if logs are not cut and dried in time after cutting, it is easy to be infected by cyanobacterium. After drying the wood in a dry kiln, there will be no more blue changes.


It should be noted that blue change is only a change in color strength hardness and other physical properties so the mechanical processing and coating properties of wood are not affected at all. So why cause the paint to turn yellow? The reason is that the blue part contains a lot of tannic acid, the activity of tannic acid is very strong, it will gradually release from the wood, penetrate through the primer and react with the titanium dioxide in the top paint. The result is that the paint turns yellow.


The characteristics of yellow change are analyzed here:


a. Why white paint?


Other colors of paint can also change color, but very slight, most people do not notice. The yellowing of white lacquer is very obvious, and yellow and white form obvious contrast.


b. Why open paint?


The opening paint is thinner and less closed, so the open paint is more likely to be yellow. The bottom paint also turns yellow, but because tannic acid penetrates the primer is more difficult and takes longer, so it is less likely.


c. Why red oak?


All wood contains tannic acid, but oak (including white and red oak) has a very high tannic acid content, so must use oak barrels to make red wine, tannic acid can provide a sour taste for red wine. The tannic acid content of other tree species is too low to achieve the effect of oak.


Red oak is also one of the species that is prone to blue change, so it is not surprising that the content of tannic acid in the blue part is much higher than that of other species, so it is not surprising that it often causes yellowing of white lacquer.


d. Is yellowing related to the production process?


Since yellowing is caused by wood blues and has nothing to do with the production process, it has nothing to do with the location of the processing plant.


e. Yellow time?


The infiltration of tannic acid takes time, so it will not yellowing immediately after coating, after the factory. As to why yellowing occurs rarely after 12 months, it is speculated that the activity of tannic acid is relatively strong, it will be released centrally in the initial stage, and then the release amount will gradually decrease. If the high release amount does not cause yellowing after the initial period, it will be basically safe in the future.


f. Supplement:


Red oak white development effect is a very popular style in recent years, for many wood-custom factories, this product often accounts for more than half of the total orders, such a large base, the problem is a big probability event.


Since the root of local yellowing is wood blue, how should production enterprises avoid it?


In the procurement phase, try to avoid buying blue red rubber sheet. Generally speaking, plates produced in summer are bluer than in winter, and in the south, because they are hotter, they are bluer than those produced in the north. In the purchase of plates, notice whether there are signs of blue on the side of the plate, if possible, planing the panel for inspection.


However, the more common case is that the blue plate has been stored, but there are ways to save it. The most important step is to do color sorting in the cutting process, white paint to avoid the use of blue materials, will be picked out of the blue material used alone. It has been proved that the quality problem is rarely caused by the use of blue modified material in dark coating. It is not that tannic acid no longer causes paint discoloration, but that dark paint discoloration is far less obvious than white paint, and naturally does not cause customer complaints when it is difficult to discern with the naked eye.


Many small factories in the customization industry are still in the workshop mode of placing orders individually. And because of management problems, blanking workers often do not pay attention to the color of the finished product, only to cut the size of the material to complete the work. This is the problem of yellow change is difficult to root out the institutional reasons. In order to improve the quality control systematically, we must adopt the mode of uniform cutting in advance, first process the sheet into semi-finished products, and then take it from the semi-finished products when there are specific orders. Only in this way can the quality inspection and sorting be carried out in the semi-finished product stage.


In addition, we should also remind that although the blue change itself does not affect the physical properties of the wood, if the blue change continues to develop, it will degenerate into decay. In this case, not only will the material become black, but the hardness, density, and coating properties of the material will all change. Rotten materials cannot be used. Therefore, we must pay attention to the difference between blue change and decay.


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