Furniture paint, also known as wood paint, generally refers to the special paint on the surface of wood furniture. In the panel furniture industry, coating quality and furniture quality are inextricably linked. The environmental protection of coating determines the environmental protection of furniture. Have a certain understanding of paint, is a must for every furniture practitioners. Therefore, this paper combs out 10 common sense of furniture coating, and answers questions for practitioners.
How to classify many furniture paints on the market?
Answer: basically, there are six kinds of paint for furniture:
Pu (polyurethane paint) is widely used in advanced furniture, which has two kinds of water and oil properties. Its advantages are high hardness and its disadvantages are yellowing.
NC, PU, PE, etc. are all named after the film-forming substance, while UV (light curing paint) is named after the curing method of the paint and solidified into the film under UV irradiation. Its advantages are fast drying and environmental protection, and its disadvantages are high cost and difficult operation of irregular objects.
Water based paint is the future development trend of environmental protection paint. Its advantages and disadvantages have been explained in many previous articles, which will not be covered in this paper.
2、 Paint = paint? What's the difference between the two?
First of all, paint ≠ paint, there is a difference in the definition between the two. Most of the early paints were made of vegetable oil, so they were named as paints. Later, synthetic resin completely refers to vegetable oil, and it is not appropriate to name it paint, so it was renamed paint.
In short, the term paint can cover liquid paint and solid powder paint, basically can refer to all kinds of products in the industry; but paint is only a liquid paint, which belongs to a kind of paint.
3、 What's the difference between primer and finish?
Primer is the material directly applied to the surface of furniture, that is, the first layer of paint system. The primer is generally firmly attached to the surface, which is used to reduce the cost and fill the paint surface.
Topcoat is the final coating of coating. Oxidation resistance, yellowing resistance, hand feel and luster are all reflected in the quality of topcoat. Generally, the thickness of the paint film can be increased by increasing the number of layers of the top coat.
So why is primer applied first in painting process?
Because the primer is designed for filling. The filling and polishing properties are good, and the cost is low. If the primer is not applied and the top coat is applied directly, the cost will be high and the filling effect will be poor.
In addition, the standard for priming is to thoroughly fill the wooden holes. That is to say, the smooth film effect can be obtained by grinding.
4、 Why do some paints need to be used with adjuvants?
Generally speaking, in addition to the main paint, some paints also need to cooperate with curing agent, accelerator, diluent, etc. Taking PU paint as an example, PU paint emphasizes the common use of main paint, curing agent and diluent. Different Pu paints have different dilution systems and different solid content. If the use of non matching diluent or curing agent, it will affect the cross-linking reaction of paint, resulting in insufficient hardness, non drying, film-forming cracking and other problems.
In addition, AC acid curing paint is two liquid type (main paint + curing agent); PE unsaturated polyester paint is three liquid type (main paint, accelerator, curing agent).
Only the main paint can be applied: NC nitro paint (single liquid self drying type); UV curing paint (single liquid curing type).
5、 Is there any requirement for environment in painting?
The answer is clearly yes. Good lacquer art level is not only related to the quality of lacquer, but also closely related to the working environment. Specifically, the environment needs to meet the following conditions:
1. Temperature: the best temperature shall be 15 ℃ - 25 ℃.
2. Humidity: the appropriate environmental humidity is 30% - 70%.
3. Ventilation is required.
4. Environmental cleanliness shall be ensured.
5. Good lighting.
6、 There is sagging phenomenon after painting, how to solve it?
Sagging is a common problem in coating construction. Generally speaking, there are the following reasons:
1. Too much diluent
2. The temperature of the construction site is low, and the coating drying is slow
3. The paint brush is too large, the hair is too long or too soft
4. When brushing uneven objects, thick surfaces are easy to hang
5. The brushed surface is not clean, and it cannot be attached after the brush.
After finding the root cause according to the above summary, we can make reasonable measures according to the specific situation, which can effectively avoid the phenomenon of sagging.
7、 What is the cause of paint cracking?
There are many reasons for paint cracking.
Generally speaking, the hardness of the top coating is too high, the flexibility is poor, the coating is too thick, the surface coating is not dried thoroughly, there are too many driers, the surface layer is too dry, the coating is not matched, the hardness difference of the bottom layer is too large, the coating is out of date, the pigment and resin are layered, the mixing is uneven and easy to crack, and the environment is bad, etc. all of these may cause the paint to crack.
8、 Will the moisture content of wood affect the coating quality?
Will affect. The moisture content of general wood should be controlled at 8-12%. If the moisture content exceeds the controlled moisture content, the wood of furniture will be wet. When finishing, the coating will dry slowly, which will reduce the adhesion of the paint film and make the volatile paint white. It will make the curing and drying paint, such as PU paint produce bubbles, pinholes and other paint film defects.
When the climate is dry, the moisture in the wood evaporates and shrinks, which is easy to produce cracks and damage the surface of the paint film. Therefore, the wood for furniture must be dried and the moisture content should be controlled within the specified range.
9、 Why does nitrocellulose paint film whiten? How to prevent it?
The phenomenon that the paint film presents turbid or milky white after film forming is called paint film whitening, also called whitening, whitening, etc. The analysis of the origin of the whitening of nitrocellulose paint film during spraying is as follows:
1. The solvent release ability of nitrolacquer is better, and the solvent in NC lacquer is easier to volatilize to atmosphere;
2. The formulation of NC paint contains more volatile solvents;
The above two points are the preconditions of whiteness.
3. The solvent volatilizes rapidly, absorbs the internal energy of the wet film of NC paint film just sprayed, makes the surface temperature of wet film drop 2-30c instantly, and provides a "cold bed" for "condensation";
4. The high temperature and high humidity environment makes the high content of water vapor around the wet film condense rapidly into micro water droplets on the "cold bed";
The above two points are the process of whitening. After the process is generated, it will cause the result of whitening.
5. The phenomenon of turbidity or milky white is caused by the bad miscibility of water droplets and wet film, which is called "whitening".
The measures to prevent the whitening of NC paint film are as follows:
1. Check the effect of oil-water separator when spraying, and remove the moisture in compressed air in time;
2. Adopt proper methods to keep the indoor painting environment in line with the requirements;
3. In the environment of high temperature and high humidity, white water can be added in case of flashing during construction.
10、 Why can bubble, pinhole and other defects appear?
In the process of coating, there are often such problems: first, there are many big and small bubbles on the surface of the coating, and then the bubbles break or break when the paint film is abraded, forming a dense pinhole like hole.
The causes of such blistering and pinholes are as follows:
1. There is gas in the coating, which breaks through the coating and bulges to form bubbles, then cracks or abrades to form pinholes;
2. The pressure of spraying air is too high and too much air is mixed in the coating;
3. Oil, dust and sweat on the coating surface;
4. The temperature difference between the coating and the coated surface is too large;
5. Improper use of diluent, excessive addition of curing agent or wrong curing agent;
6. The paint itself brings bubbles, and the bubbles generated during mixing are not eliminated, etc.
In a word, there are many reasons for blistering and pinhole. According to the above reasons, the coating process conditions can be checked, the appropriate viscosity of the coating can be adjusted, appropriate amount of diluent and curing agent can be used, and control