UV-curable adhesives are a type of product that cures quickly on demand and can form high-strength materials when exposed to UV light. Different UV adhesive products are designed based on different usage scenarios, different light source wavelengths, and curing speeds. The properties of cured UV adhesives include adhesion to the substrate, surface viscosity, curing depth, and mechanical properties (including hardness, tensile strength, tensile elongation, modulus, etc.). There are many factors that affect the performance of light-curing adhesives, such as material composition, photoinitiator selection, initiator concentration, temperature, peak wavelength and wavelength width of the light source, light intensity, exposure time, etc.
Depth of cure (DOC) is an important property to consider when evaluating the curing characteristics of adhesives and is an important guide for practical applications. Parameters that affect the depth of cure include the following:
1)Light intensity. (DOC increases with the intensity of the curing light source).
2)Light wavelength. UV light with a wavelength below 365nm can cure quickly on the surface, vitrifying the surface and blocking UV light, thereby preventing the material from curing internally. UV light to visible light (385nm and above) can cure the material more evenly and allow UV light to penetrate the surface and cure thicker areas of adhesive. The closer to the visible light region, the easier it is to cure deep.
3)Material opacity and color. Increasing opacity and color will reduce DOC.
4)Photoinitiator type. Select the photoinitiator based on the UV lamp.
5)Photoinitiator concentration. Different initiators are added in different amounts. Generally, as the initiator concentration increases, the depth of cure initially increases, but when the initiator concentration reaches the optimal level, it begins to decrease.
Our company's Uyracure-180 photoinitiator has a higher reactivity than Uyracure-160, and is suitable for mercury lamp curing or use with photosensitizers under LED light sources. It is colorless and transparent, odorless and non-migrating after reaction. Uyracure-2500L has very excellent photosensitivity. It has outstanding performance in acid production activity and long-wave absorption under different light source conditions. The cured coating does not turn yellow, does not release benzene, and has good compatibility.
In the 405nm band, the depth of cure decreases with increasing reactivity. However, as the activity of the initiator increases, the surface viscosity decreases.
Increasing the initiator concentration increases the cure rate, resulting in less oxygen inhibition and lower surface viscosity.
Increasing the initiator concentration decreases the depth of cure, which is due to the light blocking effect of the polymer gel formed on the resin surface. The depth of cure increases with the increase of curing light intensity and time.
Surface cure improves with increasing curing time.