Photoinitiator 819 is an acyl phosphine oxide photoinitiator, chemically named: phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide. The name comes from irgacure 819, or Omnirad 819, also known for photoinitiator XBPO, or photoinitiator BAPO. Its CAS Number is 162881-26-7.

Mechanism:

Photoinitiator 819 is a free radical photoinitiator and belongs to Norish type one style. Upon absorbing certain wavelength UV light, Irgacure 819 molecule becomes activated, which leads to homolytic cleavage of the excited α-carbon bond and produces two radical fragments. The free radicals then initiate the polymerization. See below figure shows the process:

Application:

As a new type of photoinitiator, acylphosphine oxides, such as photoinitiator 819, have been widely used in coatings, inks, adhesives and other industries for their excellent properties. They have greater absorption in the ultraviolet and visible regions, and can initiate curing more effectively than other photoinitiators for coatings containing pigments. Acyl phosphine oxide photoinitiators hardly yellows after curing and long-term light radiation, so they can be used in occasions where yellowing requirements are stricter, such as white, light ink and paint. In addition, acylphosphine oxides have bleaching effect on light, which can penetrate the coating and help the thick film to be cured thoroughly.

In an experiment, there introduced three phthalochlin oxide photoinitiators, they are photoinitiator 819, photoinitiator 1800 and photoinitiator 1700. Their structures and photodecomposition mechanism were discussed by means of ultraviolet-visible spectrophotometry. These three kinds of highly effective photoinitiators can be used to synthesize polyacrylic acid-acrylic superabsorbent resin by ultraviolet (UV) photopolymerization. The effects of exposure time and content of photoinitiator on the water absorption properties of the resin were compared comprehensively. The results showed that photoinitiator 819 had the highest activity, and only within one minute, the system was completely polymerized and the monomer content was only 2.55%. In the early stage of the reaction, due to the high activity of photoinitiator 819, the main product was linear polymer with small molecular weight, and the crosslinking rate was very low. Only when exposed to 20 minutes, the water-absorbent polymer with 83% crosslinking rate could be obtained.

In addition, photoinitiator 819 can also be used in colored UV curable plastic coatings. Because of its excellent performance and efficient production, UV coatings have been widely used in plastic shells of various electronic and household appliances products. However, the deep curing of UV coatings after color addition is not good, resulting in poor film adhesion, and the dispersion and arrangement of UV resins to pigments is poor, seriously affecting the appearance of the film, so the traditional construction process is to first coat solvent-based colored primer for coloring, after baking and then coated with UV varnish to improve the physical properties of the film surface.

The preparation method of a colored UV curable plastic coating is carried out under room temperature and light shielding conditions, which comprises the following steps:

Step 1: Take Photoinitiator 184, photoinitiator TPO and photoinitiator 819 in proportion, and dissolve them in environmentally friendly solvents to obtain photoinitiator solution for use.

Step 2: Put Hexagonal aliphatic polyurethane acrylic resin, tetragonal aliphatic polyurethane acrylic resin and Digonal aliphatic polyurethane acrylic resin into the mixing tank and stir for 8-15 minutes.

Step 3: Add adhesion promoter, wetting leveling agent and anti-sedimentation additive into the aliphatic polyurethane acrylic resin which prepared in step 2, in the meantime, continuing stirring for 8-15 minutes.

Step 4: Add the photoinitiator solution obtained in step 1 into the compound made in step 3, keep stirring while adding for 8-15 minutes.

Step 5: Add a pigment slurry to the material obtained in step 4, keep stirring while adding, then filtering. In the last, the colored UV curable plastic coating of in this experiment is obtained.