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Type I Photoinitiators

Type I photoinitiators, also known as cleavage photoinitiators, are a fundamental class of compounds used in UV and visible light curing systems. Upon exposure to light of appropriate wavelength, these photoinitiators undergo homolytic bond cleavage, directly generating free radicals that initiate polymerization. Because radical formation occurs without the need for co-initiators, Type I photoinitiators are highly efficient and widely applied in industrial photocuring technologies.

Photochemical Mechanism

The defining characteristic of Type I photoinitiators is their unimolecular photolysis mechanism. When irradiated, the photoinitiator absorbs photon energy and transitions to an excited state, which rapidly cleaves into two radical species. These radicals are highly reactive and readily attack the double bonds of acrylate or methacrylate monomers, triggering chain-growth polymerization. This direct radical generation leads to fast curing rates and high initiation efficiency, even under relatively low light intensities.

Representative Examples

Type I photoinitiators encompass several important chemical families, including but not limited to α-hydroxy ketones, benzil ketones, α-amino ketones, and phosphine oxides. Each structure offers distinct absorption characteristics and reactivity profiles. For example, α-hydroxy ketones are valued for their balanced reactivity and low yellowing; benzil ketones and α-amino ketones provide high initiation efficiency and fast curing, while phosphine oxides exhibit strong absorption at longer wavelengths, making them suitable for thicker coatings and pigmented systems.

Performance Advantages

One of the major advantages of Type I photoinitiators is their rapid curing capability. Since radical formation is immediate and efficient, they enable short exposure times and high production throughput. In addition, these photoinitiators typically provide excellent surface curing and consistent mechanical properties. Their broad compatibility with acrylate-based formulations makes them a preferred choice in many UV-curable inks, coatings, and adhesives.

Our Products

Type I	Catalog Number	CAS	Description	Reactivity	Surface Cure	Depth Cure	Yellowing	Odor	LED Cure
α-Hydroxy ketone	ALCM-PI-0001	7473-98-5	Transparent yellow liquid, cost effective photoinitiator with low molecular weight.	••	•••	•	Low	Medium	No
	ALCM-PI-0002	947-19-3	White crystalline powder, effective for improving surface cure.	••	•••	•	Low	Medium	No
	ALCM-PI-0003	106797-53-9	White crystalline powder, odorless for food contact and medical applications.	•	•••	•	Low	Low	No
Benzil Ketones	ALCM-PI-0004	24650-42-8	White crystalline powder. Effective for both surface and depth cure.	••	•••	••	Medium	Medium	No
Phosphine Oxides	ALCM-PI-0005	75980-60-8	Yellow crystalline powder. Responds to LED wavelengths, great depth curing. Use with α-Hydroxy ketone to improve surface cure.	••••	••	••••	Photo-bleaching	Low	Yes
	ALCM-PI-0006	162881-26-7	Pale yellow powder, highly reactive. Responds to LED wavelengths, great depth curing. Use with α-Hydroxy ketone to improve surface cure.	••••	•••	••••	High	Low	Yes
	ALCM-PI-0007	84434-11-7	Light yellow viscous clear liquid. Responds to LED wavelengths, great depth curing. Use with α-Hydroxy ketone to improve surface cure.	••	•	••••	Photo-bleaching	Medium	Yes
α-Amino Ketones	ALCM-PI-0008	119313-12-1	Yellowish green crystal, highly reactive.	••••	•••	••	High	Low	With thioxanthones only
	ALCM-PI-0009	119344-86-4	Pale yellow solid, highly reactive.	••••	•••	••	High	Low	With thioxanthones only
	ALCM-PI-0010	71868-10-5	White powder, highly reactive.	••••	••••	••	Medium	High	With thioxanthones only
Benzil Formate Esters	ALCM-PI-0011	15206-55-0	Clear liquid photoinitiator with low yellowing. Good balance of surface and depth cure,	•	••••	•	Low	Low	No

If you are interested in our products or would like more detailed technical information, please feel free to contact us. Our team will be pleased to discuss your specific application requirements and provide tailored solutions.

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