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Applications of Visible-Light Initiators

Release time:

2014-06-04 09:18

Applications of Visible-Light Initiators
Applications of Visible-Light Initiators

Visible-light initiator

1. Visible light refers to electromagnetic waves in the range of 400–700 nm—light that is visible to the human eye and constitutes the primary component of sunlight.

2. Matter absorbs light

• All colored substances are the result of absorbing visible light.

• Black: Absorption across the entire visible light spectrum

• White: Reflects the entire visible light spectrum

• Absorbs and reflects part of the visible light spectrum.

• Changes in a substance after absorbing light of different wavelengths

• Jablongsky energy dissipation diagram

3. Absorption of the photoinitiator

• Light with high energy absorption causes electronic transitions in molecules, raising their energy to a higher energy level and then transitioning them to a relatively stable triplet state, which subsequently triggers the polymerization reaction. Generally speaking, when a substance’s molecular absorption spectrum exhibits a strong absorption peak in the ultraviolet-visible range, it can undergo electronic transitions upon absorbing UV-Vis light, reaching an excited state. However, substances that can serve as photoinitiators typically possess a relatively stable excited transition state—the triplet state—and also must be capable of decomposing into free radicals or readily abstracting hydrogen atoms.

4. Visible-light initiator

• Compounds that absorb visible light in the 400–700 nm range can generate sufficiently stable excited-state transition states.

• Currently, the two main systems with broad and strong absorption in the visible light region are diarylferrocenium compounds and arylferrocene salts.

5. Advantages and Disadvantages of Visible Light Curing

• Stable light source, low cost; more environmentally friendly, safe, and hygienic—no UV radiation, no ozone generation.

• Red-light operation, photosensitivity too high.

6. Bis(2,6-difluoro-3-pyrrolyl)dimethyltitanium (GR-FMT, 784)

Advantages and Applications of GR-FMT

1) High photosensitivity and high sensitivity from ultraviolet to visible light.

2) It can effectively cure thick films and is capable of curing coatings with thicknesses exceeding 70 μm.

3) Suitable for dark-colored light-curing coatings

4) Safe, environmentally friendly, and hygienic

•GR-FMT has a maximum absorption wavelength of up to 560 nm and exhibits both high photosensitivity and strong photoinitiating activity. In acrylate systems, polymerization can be initiated with as little as 0.8 mJ/cm² of 488-nm light exposure.

• Previously, it was mainly used for argon-ion laser scanning curing, holographic laser imaging, polyimide light-curing, PCB inks, solder masks, and photopolymer printing plates. Recently, it has been applied to light-curable dental materials related to food and hygiene products, light-curable nail polishes, and light-curable adhesives.

Usage Notes:

a. Dissolution and storage must be performed under red light;

b. Moist and hot air affects its stability;

c. The addition amount ranges from 0.1% to 0.8% in the formulation.

7. η6-Isopropylferrocene(II) hexafluorophosphate (i-261)

Advantages and Applications of i-261

Advantages:

1) The spectrum exhibits broad absorption from the ultraviolet to visible region; cationic photoinitiators are rare.

2) It can serve as a free-radical initiator, but is primarily used for photopolymerization of cationic systems such as epoxies and vinyl ethers.

3) It exhibits superior stability compared to iodonium salts, lower costs than iodonium salts, and a sensitivity comparable to that of diphenyliodonium salts.

Application:

• Epoxy cationic UV-curing system, vinyl ether cationic UV-curing system, radical/cationic

Self-mixing curing system.

• Operating precautions:

• Red-light operation; add 1-3%. The system’s color will tend to be deeper and darker.

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