Physical and chemical methods to inhibit oxygen blocking.

Oxygen impedance has always been a problem in UV curing
when UV curing is carried out in air, the presence of oxygen impedance often leads to the condition that the bottom layer of the coating is cured, but the surface is not cured and sticky.
oxygen impedance can eventually lead to a large number of oxidizing structures such as hydroxyl, carboxyl, peroxygen and so on on the surface of the coating, which may affect the long-term stability of the coating, and may even affect the hardness, gloss and scratch resistance of the cured paint film.
does oxygen blocking occur?
the base state of the general substance is a single-line state, the stable state of O2 is a three-line state, there are two spin direction of the same pair of

. Therefore, it competes with the polymerization reaction of free fundamentals and consumes free fundamentals.
Since the vast majority of photo-curing processes are carried out in the air environment, and the main applications are coatings and inks with large surface area/volume ratio of materials, so O2 on photo-curing material free-based polymerization reaction of the blocking effect can not be ignored.
the coating film thickness is thin, the oxygen concentration in the system is usually about 2 x 10-3 mol/L. Not only do dissolved oxygen molecules in the formulation system hinder polymerization, but in the light-triggering process, with the consumption of oxygen molecules in the curing system, oxygen in the air on the coating surface can also spread rapidly into the curing coating, continuing to hinder polymerization. The concentration of dissolved oxygen in the system is very low and easy to consume.
for closed systems, the process of consumption of dissolved oxygen by primary active free agents is basically equivalent to the polymerization induction period. Relatively speaking, the oxygen that continues to spread from the outside to the inside of the coating is the main reason that hinders polymerization. Oxygen blocking is also most likely to occur in the shallow surface of the coating or throughout the thinner coating, because in these areas, the diffusion of oxygen molecules in the environment is easier.
Ax oxygen affects free fundamentals in three ways
annihilation
the three-line state O2 in the base state can be used as an annihilation agent and photoactivated trigger (expressed in Phi) reaction to form a mate, thereby stimulating the three-line state of the light trigger annihilation. The process is expressed as follows:
Phi s (Phi) s (Phi) s, (Phi) s (O2) s (O2) s Phi s (O2)
In the above process, O2 is stimulated to a lively single state, and the light trigger is returned from the excitation state to the base state, thus hindering the production of active free fundamentals. Most lysate light triggers have a relatively short excitation three-line life, and the trigger has been decomposed before the excitation trigger and O2 act, so the chances of double molecular annihilation between O2 and light triggers are relatively low and can often be ignored.
O2, which eliminates
-based states, is essentially a double free agent, so there is a strong addition activity for the active free fundamentals produced during light-triggering, forming a relatively stable free-peroxide base. This process has a relatively fast rate and can compete with the active free-form-to-monosome addition reaction, which is most significant for the blocking effect of the polymerization process. It can be divided into the following 2
:
active free-═-CH2═ R-CH2-C. XY-monomers, polymers
active freelances and O2 additives
R.-O2-R-O-O- ( Peroxy free
R-CH2-C. XY-O2-R-CH2-CXY-O-O
oxygen
also oxidize freebies that have been polymerized with monobodies into peroxides, preventing polymerization of monobodies. The mechanism of action is as follows:
it is clear that in all three cases the polymerization rate decreases and the formation of peroxides affects the performance of the curing coating. It should be noted that the reaction rate constants of free-form R. and O2 are 104 to 105 times longer than their reaction rate constants with monolith molecules, so even if only trace amounts of oxygen are present in the coating, the peroxide free-based ROO generated when R.and O2 react cannot be ignored.
because ROO is very stable and does not have the ability to trigger polymerization reactions, the presence of O2 consumes the active free agent R. Therefore, O2 is the blocker of free-based polymerization of light curing system at room temperature.
Existing methods of inhibiting oxygen impedance
physical methods: inert gas protection, floating wax, coating, bright light exposure, step-by-step irradiation
Chemical method: add substances that provide active hydrogen - thiol, amine, ether acrylic (acrylic) Acid esters can be integrated with coatings to prevent surface cracking, can also reduce odor), the same conditions to provide hydrogen atomic capacity: thiol-like amines and ethers
with amines as an example, the reaction structure of the following diagram: amines have 6 lively hydrogen, can consume 6 oxygen.
in UV photo-curing, especially low-film thick coating, is important to improve coating performance, so Runo Chemical has developed related products in the chemical methods for inhibiting oxygen impedance.
/////////
A series of experimental results on these methods show that
, regardless of curing energy, can improve surface reactivity as long as it is modified by thiol,
ammonia or ether;
can work in synergy with polyether acrylics or highly reactive structures, and
can also provide surface reactivity by changing the formulation or thickness of coatings. Shorten the distance of low-energy exposure to the substrate to prevent surface curing from being destroyed.
the advantages and disadvantages of various methods
two UV resins
thiol products FSP7814 can effectively overcome oxygen resistance. At 365nm wavelengths, 120mJ/cm2 can be dried, while at 395nm wavelengths, 150mJ/cm2 can be dried, with high reaction activity and very fast curing speed. Good toughness and excellent toughness also enable it to meet bend testing requirements. Good water resistance, boiling water for an hour adhesion did not decrease. Good adhesion, conventional plastic substrates, thermoplastic primers, bamboo substrates have excellent adhesion.
two-phenolic polyether amine modified acrylic LuCure5186. Excellent antioxidant impedance, 500mJ/cm2 energy can be fully dried even in the harder-to-table dry 395nm band; The initial yellowing b in about 1.9, and placed within a few hours will be significantly further yellowing, the formulation of the overall yellow resistance effect is very small;
compiled from The References
.