" " wisno wood furniture finishing: Polyurethane clear coating for furniture finishing

Thursday, October 22, 2009

Polyurethane clear coating for furniture finishing

Polyurethane coating is the coating made from the urethane polymerization reaction. The urethane is the result from the reaction between the poly isocyanate with resins that contains the hydroxyl group such as: alkyd, castor oil, urea, acrylic, cellulose, polyester, etc. The common resin to make PU coating are: the polyester and saturated polyester. Isocyanate is a toxic substance and usually is used as prepolymer with pylol to minimize his gas emissions to the air. According to the resin used, there are many types polyurethane coating. But the polyurethane coating that is most widely used in the furniture finishing is the 2 components polyurethane. It is the polyurethane coating that is made from the hydroxyl group resin and the isocyanate. In the application both chemical is packed separately. The resin is mentioned as the coating, while the isocynate is the hardener. In the application, both material need to be mixed in the proper composition to make the Polyurethane coating.
The application and handling of the polyurethane 2 components must be done carefully; the thinner used should not react with the isocyanate. Materials such as: water, alcohol, and glycol should be kept out of polyurethane. The isocyanae should not be exposed at the open air; the water in the air could react with the isocyanate and make the make it dry and harden. 

The polyurethane coating for wood furniture is used, when the furniture need strong film and maximum protection. The coating resulted is high build and strong, resist to the scratch, chemical, solvent and chemical. 

The advantages of polyurethane coating

  • The resulting film layer is very strong.
The film produced by polyurethane coating has high strength, resistance to heat, solvents and scratches. The polyurethane clear coating is believed to have greater hardness and strength than the acid curing. The coating is used for products that require strength and maximum protection. It is the common coating for the: caf├ęs, bars, hotels, furniture. It also can be used for the dining table, kitchen cabinet and some wood flooring. 
The PU coating is also the proper material to make the high gloss and high build film finish. With its high built and strong film layer, it will give you the perfect high gloss finish.
  • The resulting coating film has a soft appearance.
This clear coating will give the soft appearance of the film layer is very unique and liked by many peoples. The look of this finish will be difficult to duplicate with other types of paint. For people who is familiar with the the polyurethane appearance of course will have more receptive to the finishing product with this coating. The Polyurethane coating is most used for Italian furniture. With its high built film and its soft and special looked it bring the luxury to the Italian style furniture. 
  • Polyurethane coating is considered less toxic than the acid curing.
Some people think that the polyurethane is more healthier and environmental friendly than the acid curing coating. This is actually not exactly right, because both isocyanate and formaldehyde are substances that are toxic and will interfere the human health. In fact gas emissions depends on the quality of the coating itself. 
  • Polyurethane has high solid content.
The polyurethane clear coating has a solid content higher than the acid curing or nitrocellulose at the same viscosity. Therefore this paint will be easier to produce finishing with thick film. The film is thermosetting, then he has ability to fill and close the pores and grain with many layer application.

The disadvantages of Polyurethane coating

  • The price is relatively expensive.
The PU usually is more expensive compared with the acid curing or nitrocellulose paint. The coating is also has shorter life time then the NC or AC. The isocyanate is easy to react with the water in the air; it should be kept in the closed cane and put in the dry air room for his longer life. The proper handling and storage system is needed, and it will increase the price of the chemical.
  • The application is difficult.
The polyurethane is very sensitive to the environmental conditions, the material consists of 2 components with short pot life. The PU coating will hard after 1 hour after being mixed with  its hardener. The perfect mixing ratio is needed to get the good result.
The polyurethane is very sensitive to the humidity environment. In the humid and cold air it easy to get problem with the blushing. He as long time to reach the touch drying. It means that the coating is sensitive to the dust. A little dust that does not cause problems in the nitrocellulose coating, will be big problem for the polyurethane coating.
The finishing room and the drying room for the PU coating has to be clean and dry; free from dust and humid air. 

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