Mechanism & Class: Both are high-efficiency Norrish Type II (hydrogen-abstracting) thioxanthone photoinitiators, ideal for long-wavelength UV-LED curing and overcoming oxygen inhibition when paired with amine synergists (e.g., amine acrylates or SINOCURE® EDB).
SINOCURE® CPTX (CAS 142770-42-1): Modified with 1-chloro and 4-propoxy groups. Features broad absorption peaks at 257 nm, 314 nm, and 389 nm. Offers superior monomer solubility and deep through-cure in 100% solids, heavy-pigmented inks, thick coatings, and electronics.
SINOCURE® CMTX (CAS 84434-05-9): Acid-functionalized with a carboxymethoxy group (—OCH₂COOH). Features a long-wavelength absorption peak at 395 nm. Specially designed for alkaline aqueous/waterborne UV systems and UV inkjet inks, offering high water solubility, low crystallization, low odor, and low migration.
In radiation curing formulations—especially with the widespread transition from conventional medium-pressure mercury lamps to energy-efficient UV-LED (365 nm, 385 nm, 395 nm, 405 nm) light sources—formulators face two persistent challenges:
Oxygen inhibition at the surface layer.
Poor light penetration (through-cure) in heavily pigmented inks (titanium dioxide white, carbon black, organic pigments) and thick film coatings.
Thioxanthone derivatives serve as premier Norrish Type II photoinitiators and photosensitizers. Among them, SINOCURE® CPTX and SINOCURE® CMTX represent two highly specialized pathways: one engineered for maximum organic compatibility and deep cure in solventless/100% solid systems, and the other designed for waterborne UV formulations and low-migration inkjet printing.
Chemical Name: 1-Chloro-4-propoxythioxanthone
CAS No.: 142770-42-1
Molecular Formula: C₁₆H₁₃ClO₂S | Molecular Weight: 304.79
Absorption Peaks (λmax): 257 nm, 314 nm, 389 nm
Optimized UV-LED & Mercury Matching: With major absorption bands extending into the near-UV and visible spectra (notably at 389 nm), CPTX overlaps perfectly with 385–395 nm UV-LED curing units as well as iron/gallium-doped lamps.
Superior Through-Cure in Pigmented Systems: Pigments like rutile TiO₂ strongly absorb light below 380 nm. CPTX captures photons above 385 nm where pigments become more transparent, ensuring complete bottom-layer curing in thick films (>50 μm) and dark/opaque inks.
High Monomer Solubility & Low Yellowing: Compared to traditional ITX (Isopropylthioxanthone) or DETX, the propoxy chain and chloro substitution of CPTX enhance solubility in acrylic monomers and oligomers while minimizing post-cure yellowing and crystallization.
UV Offset, Flexographic & Screen Printing Inks
Wood Coatings & Industrial Topcoats
Electronic Coatings & Solder Masks
Overprint Varnishes (OPVs) & Optical Adhesives
Chemical Name: 2-Carboxymethoxythioxanthone
CAS No.: 84434-05-9
Molecular Formula: C₁₅H₁₀O₄S | Molecular Weight: 286.3
Absorption Peak (λmax): 395 nm
Superior Aqueous / Alkaline Solubility: The introduction of the carboxylic acid group (—OCH₂COOH) enables CMTX to dissolve readily in aqueous alkaline media without phase separation or crystallization, eliminating a major bottleneck of conventional photoinitiators in waterborne UV formulations.
Exact 395 nm UV-LED Spectral Match: With an absorption maximum centered precisely at 395 nm, CMTX delivers exceptional surface and depth cure reactivity under common commercial UV-LED pinners and final curing arrays.
Low Migration & Low Odor: The carboxylic functionality facilitates anchoring into polymer networks or neutralization in waterborne acrylic emulsions, significantly lowering extractable residual volatiles and odor.
Waterborne UV Coatings & Emulsions
Alkaline Aqueous UV-Curable Systems
UV Inkjet Inks (where nozzle clogging from photoinitiator crystallization must be avoided)
Eco-Friendly Packaging Inks & Varnishes
| Technical Parameter | SINOCURE® CPTX | SINOCURE® CMTX |
|---|---|---|
| Chemical Name | 1-Chloro-4-propoxythioxanthone | 2-Carboxymethoxythioxanthone |
| CAS Number | 142770-42-1 | 84434-05-9 |
| Molecular Formula | C₁₆H₁₃ClO₂S | C₁₅H₁₀O₄S |
| Molecular Weight | 304.79 g/mol | 286.30 g/mol |
| Appearance | Yellow powder | Light yellow powder |
| Assay / Purity | ≥ 98.0% | ≥ 95.0% |
| Melting Point | 99 – 103 °C | 100 – 104 °C |
| Key Absorption (λmax) | 257 nm, 314 nm, 389 nm | 395 nm |
| Solubility Profile | High in acrylates & organic solvents | High in alkaline aqueous systems & water |
| Odor & Migration | Low volatility, low yellowing | Ultra-low migration, low odor |
| Optimal Light Source | Mercury lamp / 385–395 nm UV-LED | 395 nm UV-LED / Mercury lamp |
| Primary Systems | 100% solid UV coatings, thick films, screen/offset inks | Waterborne UV, UV inkjet, alkaline resins |
Because both CPTX and CMTX operate via a Norrish Type II hydrogen-abstraction mechanism, they require a co-initiator (hydrogen donor) to generate initiating free radicals efficiently.
Amine Synergist Pairing: Formulating with amine-modified polyether acrylates or amine co-initiators such as SINOCURE® EDB (Ethyl 4-dimethylaminobenzoate, CAS 10287-53-3) or DMB significantly accelerates radical generation.
Overcoming Oxygen Inhibition: The resulting α-aminoalkyl radicals rapidly consume dissolved oxygen (O₂), transforming peroxy radicals into active initiating species and ensuring a tack-free, hard surface finish.
Recommended Dosage:
CPTX / CMTX: 0.5% – 3.0% by weight.
Tertiary Amine Synergist: 1.0% – 5.0% by weight (adjusted based on pigment load and film thickness).
Choose SINOCURE® CPTX if:
You formulate 100% solid UV offset, flexo, or screen inks with heavy pigment loading (black, white, or dark colors).
You are curing thick film industrial coatings, electronics, or wood coatings requiring deep through-cure.
You need high solubility in conventional acrylic monomers without recrystallization during cold storage.
Choose SINOCURE® CMTX if:
You are developing waterborne UV-curable coatings, dispersions, or water-dilutable inks.
You formulate UV inkjet inks where low viscosity, zero nozzle crusting, and clean dissolution are critical.
Your target application demands low odor, low migration, and high responsiveness under 395 nm UV-LED arrays.
A: Yes. SINOCURE® CPTX possesses a strong absorption band peaking at 389 nm, which exhibits substantial spectral overlap with the emission curve of standard 385 nm and 395 nm UV-LED lamps, delivering fast curing speeds when paired with an amine synergist.
A: Traditional thioxanthones (like ITX or DETX) are hydrophobic and prone to precipitation in aqueous media. SINOCURE® CMTX incorporates a carboxylic acid moiety (—OCH₂COOH), allowing it to form water-soluble carboxylate salts in neutral-to-alkaline pH conditions, creating stable, crystal-free waterborne UV systems.
A: Both products are packaged in standard 20 kg / Carton containers. They should be stored in a dry, cool, well-ventilated warehouse away from direct sunlight, UV ambient light, and heat sources to prevent premature polymerization or degradation.
Sinocure Chemical Group provides high-purity, REACH-registered photoinitiators and specialty monomers for global coatings, inks, and adhesives manufacturers.
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