Quick answer: Buyers comparing Photoinitiator 184, Photoinitiator 1173, and Photoinitiator TPO-L usually get the clearest shortlist when they separate three decisions early: a routine clear or light-color UV benchmark, a liquid acrylic-varnish route with strong appearance control, and a liquid low-yellowing route that can reach deeper cure or white-system pressure more comfortably. 184 is usually the practical first benchmark when the job is a conventional low to medium film-build UV coating, ink, or adhesive. 1173 moves up when the formulator wants a liquid photoinitiator with good compatibility and a stronger fit for acrylic UV-curable varnishes that need only slight yellowing. TPO-L becomes the sharper first screen when the project still wants liquid handling but also needs a wider absorption window, lower yellowing, and better confidence in white or deeper-curing systems.
That is the commercially useful split. These three products are all relevant to lower-yellowing UV work, but they should not be treated as interchangeable.
Why this comparison matters
Longchang already has live pages for 184 vs 1173 vs 819, clear UV coatings, and narrower application pages such as release coatings and soft touch coatings. This page answers a different buyer question.
Here the buyer is not choosing between a routine hydroxyketone benchmark and a deep-cure solid like 819. Instead, the real question is whether the project should stay with a conventional solid benchmark, move to a liquid acrylic-friendly slight-yellowing route, or go to a liquid phosphinate route for broader cure depth and white or light-pigmented pressure.
That is a common decision in clear coatings, light-colored inks, overprint varnishes, and appearance-sensitive adhesive work where yellowing, handling, and cure depth all matter.
Quick comparison table: 184 vs 1173 vs TPO-L
| Product | Best first fit | Why buyers shortlist it | When it is not the first option |
|---|---|---|---|
| 184 | Routine low to medium-thickness clear coatings, lighter-color inks, and conventional UV systems | Longchang positions 184 around strong 365 nm relevance, fast curing in low to medium-thickness coatings, inks, and adhesives, with low-yellowing value in transparent, white, and lighter-color applications | When the project needs liquid handling, stronger acrylic-varnish workflow convenience, or deeper cure in white or more difficult films |
| 1173 | Liquid acrylic UV-curable varnishes on paper, metal, and plastic where slight yellowing and compatibility matter | Longchang directly describes 1173 as a multifunctional liquid photoinitiator with good compatibility, easy blending with other photoinitiators and prepolymers, and special relevance for UV coatings that require only slight yellowing even after longer sunlight exposure | When the project is more pressured by white-system cure depth or broader absorption needs than by acrylic-varnish handling and appearance control |
| TPO-L | Liquid low-yellowing route for white or light-pigmented systems, deeper cure, and broader UV-process flexibility | Longchang positions TPO-L as a liquid photoinitiator with low yellowing, low odor, a relatively wide absorption range, and direct suitability for curing white deep-layer systems while also covering coatings, inks, adhesives, and clear varnishes | When the job is a simple routine low-to-medium-build system that does not need broader cure depth or the TPO-L handling and white-system advantages |
When 184 is the better fit
184 deserves the first sample slot when the formulator needs a practical conventional benchmark rather than a more specialized liquid route.
- Routine cure fit is supported: Longchang ties 184 to low to medium-thickness coatings, inks, and glues.
- Transparent and lighter-color logic is already there: the current company page emphasizes low yellowing and specifically discusses transparent and lighter-color applications, including white systems.
- 365 nm benchmark value is commercially useful: Longchang describes strong UV absorption around 365 nm, which makes 184 a sensible first screen for many traditional UV lines.
- It remains broadly practical: coatings, offset inks, screen inks, flexo inks, inkjet inks, adhesives, and some electronics-related uses are all already connected to 184 on the current company page.
If the project is not especially thick, not especially hard to cure, and not especially dependent on liquid handling, 184 is often the cleanest starting benchmark in this trio.
When 1173 is the better fit
1173 moves ahead when the buyer wants a liquid route for acrylic UV varnishes and appearance-sensitive coatings, not just a basic free-radical benchmark.
- Liquid handling is a direct reason to shortlist it: Longchang explicitly positions 1173 as a multifunctional liquid photoinitiator.
- Acrylic UV-curable varnish fit is company-supported: the current page directly says it can be used for acrylic UV-curable varnishes on paper, metal, and plastic surfaces.
- Yellowing control is central to its positioning: Longchang says it is especially recommended for UV coatings that require only slight yellowing even when exposed to sunlight for a long time.
- Compatibility helps formulation work: the product page also states that 1173 has good compatibility and can be easily mixed with other photoinitiators and prepolymers.
That makes 1173 the sharper choice when the project is a liquid acrylic varnish or coating where handling, blending convenience, and color stability all matter early in the selection process.
When TPO-L is the better fit
TPO-L belongs in the shortlist when the formulator still wants a liquid route but the project is moving beyond what a routine benchmark or acrylic-varnish route can comfortably solve.
- Wider absorption is part of the supported value: Longchang states that TPO-L has a relatively wide absorption range.
- White deep-layer relevance is explicit: the current company page directly says TPO-L can be used for the curing of white deep-layer systems.
- Low-yellowing and low-odor positioning stay important: this is part of the product’s core company-supported fit for coatings, inks, adhesives, and sealants.
- Liquid form still helps formulation handling: TPO-L gives easier mixing than a solid route while still reaching into more demanding cure situations.
If the project needs lower yellowing, liquid handling, and more confidence in white or deeper-curing sections, TPO-L often becomes the stronger first review point.
How buyers should choose before sampling
1. Decide whether the system is routine or demanding
A routine clear coating and a white or light-pigmented harder-to-cure film should not use the same default shortlist. The more demanding the cure window becomes, the more likely TPO-L deserves earlier screening.
2. Separate appearance pressure from cure-depth pressure
If slight yellowing under service exposure is the biggest concern, 1173 usually deserves strong attention. If the bigger issue is deeper cure or white-system behavior, TPO-L often moves ahead.
3. Keep physical form visible
184 remains useful as a solid benchmark. But if the team wants easier dosing and blending from the beginning, 1173 and TPO-L should be considered early rather than only after a failed trial.
4. Match the first trial to the real substrate and film build
Clear varnish on paper, clear coating on plastic, white or light-colored ink, and appearance-sensitive adhesive work can all change the right first screen. One generic answer is usually too loose.
5. Keep the first lab round narrow
For many projects, a practical first screen is one conventional 365 nm benchmark, one liquid acrylic appearance-control route, and one liquid broader-window route. That usually creates a cleaner buying decision than testing too many initiators without a structure.
Recommended Longchang product and article paths
- Routine low-to-medium-build benchmark: Photoinitiator 184
- Liquid acrylic-varnish route: Photoinitiator 1173
- Liquid wider-window route for white or deeper-cure work: Photoinitiator TPO-L
- Related comparison page: 184 vs 1173 vs 819
- Related application page: Photoinitiator for Clear UV Coatings
- Broader family guide: How to Choose a Photoinitiator for UV Curing
- Related curing-window page: Photoinitiator for UV LED Curing
FAQ
What is the main difference between 184 and 1173?
In Longchang’s current product positioning, 184 is the conventional solid benchmark for low to medium-thickness UV systems, while 1173 is a liquid route with good compatibility that is especially recommended for acrylic UV coatings needing only slight yellowing.
When should I choose TPO-L before 1173?
Choose TPO-L earlier when the project still wants liquid handling but also needs broader absorption, lower yellowing, and better confidence in white or deeper-curing systems than a routine liquid acrylic-varnish route.
Is 184 still useful if I care about low yellowing?
Yes. Longchang already positions 184 for low-yellowing transparent, white, and lighter-color applications. It remains a useful benchmark, especially when the system is not especially difficult to cure.
Can this page replace formulation validation?
No. It is a shortlist tool, not a substitute for lab work. Final selection still depends on resin chemistry, film build, pigment burden, lamp output, line speed, and the practical targets of the finished formulation.
Need a faster shortlist?
If your project is stuck between a routine benchmark, a liquid acrylic route, and a wider-window liquid route, define the bottleneck first and then compare only the most relevant Longchang option. That usually produces a faster first sample plan than treating 184, 1173, and TPO-L as if they solve the same problem.