Semi-polyester is a market term for a type of two-component paint called acid curing or drying polyesters with an acid catalyst.
Semi-polyester was used in the world since the late 50s, and today it is only used in hot and dry regions such as the Middle East, Central Asia and North Africa. The most common use of semi-polyester is in the furniture industry, and sometimes it is also used in smaller polymer industries. will be
Semi-polyester consists of a physical mixture of short-oil alkyd resins with urea-formaldehyde resin with appropriate ratios calculated based on desired experimental properties.
In fact, based on customer needs, by changing the ratio of two components in semi-polyester, a harder or more flexible product can be produced.
The plasticizer component is semi-polyester alkyd resin and the hardener component is urea formaldehyde resin.
In the production of semi-polyesters, only short-oil alkyd resins based on soybean fatty acid and sometimes coconut fatty acid are used in smaller quantities, alkyd resins with hydroxyl type 1 OH- in the presence of an acid catalyst, initially with the methylol CH2OH- group attached to Urea amine enters the reaction and with the release of water from the reaction, it strengthens the ether bond, and in this way, the semi-polyester film is formed.
Semi-polyester catalysts are always super acid macromolecules based on sulfur and phosphorus, and due to their electronegative properties, they can easily enter an H+ proton into the environment, therefore, the amount of catalyst acid should be controlled when using semi-polyester. Because the higher the acid, the faster the reaction speed in semi-polyester, and this factor will lead to the brittleness of the semi-polyester color film in the future. Mainly, the consumption ratio of acid in semi-polyester is at least 3% to a maximum of 10%.
They determine the weight of half polyester.
One of the conditions for film formation by semi-polyester is to create an environment temperature from 18 to 30 degrees Celsius with a humidity percentage below 30%. Because one of the gases coming out of semi-polyester is water vapor, which leaves the surface of the film along with the evaporation of thinner and alcohols, and the humidity of the environment prevents water from evaporating from the reaction, that is why the reaction is not complete and semi-polyester is never hard. It is not possible, in such environments, warm and moisture-proof rooms must be used. Sometimes it has been observed that a semi-polyester rink that has already hardened completely when it enters an environment with a relative humidity above 50% does not dry and becomes scratched. it manifests itself, this is because that semi-polyester did not have a complete reaction, which mainly has three reasons; One is due to the use of too little catalyst acid, the second is due to the use of an inappropriate thinner that contains large amounts of methanol alcohol with cleaning solvent that remain in the depth of the film, and the third reason is the lack of selection of appropriate raw materials and the incorrect composition ratio in the initial formula.
In choosing short oil alkyd resin for semi-polyester, you should always pay attention to the iodine number of the fatty acid used, the lower it is, the better, mostly the iodine number of soybean fatty acid is approved at 140, on the other hand, urea formaldehyde resin should not contain formalin. should be free and these aspects should be taken into account in the design of semi-polyesters.
One of the advantages of semi-polyester is its easy use by the operator and suitable solubility with instant thinners that create a favorable drying speed, on the other hand, instant paints have excellent adhesion on the film, so it is a popular and effortless coating for the furniture industry.
But its disadvantages include problems of yellowing on white and light colors, and on the other hand, semi-polyesters based on alkyd resins have low dry film solids due to their false viscosity; But this problem was solved forever in Iran by the experts of Rangin Kimia Company in 2014, in fact, this company was able to make super shiny, full solid and hard clear by using the model of hardening by acid catalyst and using special resins. design that follows the semi-polyester mechanism that does not have their yellowing problems and has an acceptable drying time and hardness, on the other hand, the thickness of the final dry film is equal to polyurethane clears.
The design of Clear Super Glossy Bicolor by Rangin Kimia actually created a revolution in the furniture paint industry, so that it is a serious competitor against polyurethane in terms of cost-effectiveness and was born at a time when semi-alkyd polyester is practically going out of use. It should be mentioned that according to the manufacturers of this product in Rangin Kimia, this type of colorless clear is only used as a top coat (final layer) and is never used for gold plating, and alkyd-based semi-polyesters are always used for gold plating. Recommends.
In any case, even today, with proper scientific and industrial innovation and research, semi-polyesters with various applications can be designed.
It is noteworthy that Rangin Kimia company has always been a leader in this matter, and its white semi-polyester does not have yellowness, and its shiny semi-polyester is the best option for under and over gold leaf. It has been proven that they dry and harden well even in wet weather if the appropriate thinner is used and the amount of standard acid is used.
