Photoinitiator ITX CAS 5495-84-1
Introduction
UV photoinitiator serves as the key raw ingredient for light-curing substances such as UV coatings, UV inks, UV adhesives, and more. These substances are an effective weapon in the war against air pollution and a feasible replacement for conventional solvent-based coatings, inks, and adhesives.
Wood coating, plastic product coating, decorative building material coating, paper printing, packaging printing, automotive parts, electrical / electronic coating, printed circuit board manufacturing, fibre optic manufacturing, 3D printing, electronic glue, and numerous other applications benefit greatly from the use of light-curing materials.
The three most important properties of a photoinitiator are: (a) a high quantum yield of synthesis-initiating species, (b) a high molar extinction coefficient at the exposure wavelength, and (c) a strong radical reactivity toward the monomer.
UV-Curing Process
During the process known as ultraviolet curing, a liquid goes through an immediate polymerization reaction that turns it into a solid. The utilisation of ultraviolet radiation with a particular wavelength and intensity is required for this operation. Prepolymers (oligomers), monomers, pigments, and photoinitiators—all extremely photoactive substances—are combined to create UV curing ink. The printing industry is interested in two potential polymerization methods due to their commercial appeal. By far, the most typical procedure is the first one, also known as free radical polymerization. The second kind of polymerization is called cationic polymerization, and it has a fundamentally different photoinitiator chemistry. The photoinitiator initially uses UV energy and generates free radicals. With the characteristic acrylic unsaturated groups present in prepolymers and monomers, these free radicals can then start rapid addition polymerization.
What is ITX?
As 2-Isopropylthioxanthone, also known as ITX, is a popular and efficient Type II photoinitiator it is suggested for use in formulations. This is because ITX is capable of absorbing the light energy visible to the human eye. Because ITX has the ability to absorb light energy in the visible range, this is the result. Radiation has the potential to cause ITX to transition from its ground state to a singlet state with a higher energy. After that, it is possible to pass through intersystem barriers and transform into a triplet state, denoted by the number 3, which is more stable but has less energy. This state is represented by the number 3(marked by ISC). In order to hasten the drying process while working outside in the fresh air, it is necessary to have direct sunlight.
The two highest absorption peaks of ITX can be found in the CH2Cl2 UV-vis spectra 258 nm (ε = 1.3 × 105 M−1 cm−1) and 386 nm (ε = 6.1 × 104 M−1 cm−1) , with a tailing to approximately 420 nm. This allows it to be useful at low temperatures and be easily activated by sunlight.
Alternate names of ITX
- Photoinitiator-ITX
- Photocure-Itx
- 2-Isopropylthioxanthen-9-one
- 9H-Thioxanthen-9-one
- 2-(1-methylethyl)-
- 2-Isopropyl-9H-thioxanthen-9-one;
- Isopropylthioxanthone
- 2-(propan-2-yl)-9H-thioxanthen-9-one.
Physical Properties of ITX
- ITX is yellow in color.
- It is a dry powder in final form.
- ITX is volatile in nature.
- The Molecular Formula of ITX is C16H14
- The Molecular Weight of ITX is35 g/mol
- The melting point of ITX is 398.9°C while the boiling point is 72-76°C.
Structure of Photo initiator ITX
Applications of ITX
Applications for photoinitiator ITX include offset printing, flexography, screen printing, and electronic coatings. ITX, a photoinitiator, has many potential applications, including in wood coatings, lithographic inks, silk screen inks, flexo inks, composites, electronics, and overprint varnishes.
As an Analytical Standard
Liquid chromatography-tandem mass spectrometry (LC-MS/MS) research is used to determine the presence of the analyte in commercially prepared foods employing analytical standards based on 2-isopropylthioxanthone. When evaluating milk, fruit drinks, and packaged beverages using high performance liquid chromatography (HPLC) coupled to mass spectrometry (MS/MS) and micellar electrokinetic chromatography (MEKP), it can be utilised as a reference standard (MEKC).
In Direct Laser Writing (DWL)
Recent years have seen a rise in the number of people interested in using direct laser writing (DLW) photopolymerization for nanolithographic printing. This is due to the fact that printing technology has become more efficient, but at the same time, the sizes of printed features have decreased all the way down to the nanoscale. Because of its powerful photoinitiating effectiveness and ability to be stopped by a second wavelength of light, isopropyl thioxanthone, often known as ITX, has been one of the photoinitiators that has been used in DLW polymerization techniques one of the most frequently. Therefore, it is possible to apply it in DLW polymerization processes in the capacity of a photoinitiator. However, in order to deploy enhanced high-throughput nanomanufacturing processes, academic and industrial circles will require improved photoinitiating materials that are based on this successful approach. Since that time, computational designs for thioxanthone-based photoinitiators that have the ability to tune their optical properties as well as their charge transfer properties have been developed and synthesised. On the thioxanthone substrate from the beginning, in particular, branches were connected that had precisely calibrated electron donor and electron acceptor qualities. The ITX core has at long last been completed. After meticulous examination of both their molecular and optical properties, it was determined that these initiators had a photopolymerization initiation rate that was higher than ITX. This was obvious due to the fact that it was plain to see that these trailblazers had come a long way. A unique photoinitiator chemical was developed in order to achieve higher two-photon polymerization DLW in a manner that enabled the display of superresolution capabilities. This was accomplished by creating a novel photoinitiator.
Isopropylthioxanthone case in 2005
Italy notified the RASFF (with reference number 2005.631) on September 8, 2005, of the migration of isopropylthioxanthone at a concentration of 250 g/l from the packing of Spanish breast milk intended for infants. Italian officials originally seized 2 million litres of milk on November 9, 2005, after determining that it was “unfit for human consumption.” Two weeks later, on November 22, a court decision led to the recall of several milk varieties, taking 30 million litres of milk off the Italian market. Subsequent recalls in France, Spain, and Portugal had a similar effect. 7 Due of the significant impact on public opinion, the European Food Safety Authority (EFSA) released its first press release on November 24, 2005. 8 Based on toxicity data and the outcomes of analytical tests carried out on a variety of milk products and fruit juices packaged in cartons printed with UV inks containing ITX and EHDAB as photoinitiators, the Scientific Panel on Food Additives, Flavourings, Processing Aids, and Materials in Contact with Food (AFC) of the European Food Safety Authority (EFSA) published their opinion on ITX and EHDAB on December 7. According to the European Food Safety Authority (EFSA) and the German Institute for Risk Assessment (Bundesinstitut für Risikobewertung10), these cartons were printed with UV inks that included ITX, although current in vivo genotoxicity tests have not revealed ITX’s genotoxicity. The resulting 50 micrograms per kilogramme ITX specific migration limit (SML) was established. ITX is presently associated with benzophenone as the photoinitiator undertaking the most research, both analytically and migratorily, as a result of the circumstances surrounding ITX in 2005.
ITX and Food Packaging Inks
Because it has not been determined whether or not ITX is genotoxic, it is currently permissible to use it in food packaging. On the other hand, newborn milk is a special condition that can call for a reassessment of the structure of the package.
In UV-curing inks, the utilisation of ITX, which is an essential photoinitiator, has been a standard practise for a very long time. It is especially important in the production of dark-colored inks due to the significant role it plays in giving the essential through-cure and adhesion properties.
ITX is not utilised in the manufacturing of food contact plastic; consequently, it is not included in the Synoptic Document, nor has it been examined by the Food Additives, Flavourings, Processing Aids, and Materials in Contact with Food (AFC) Panel of the European Food Safety Authority (EFSA) or the former Scientific Committee on Food. These omissions are due to the fact that ITX is not used in the production of food contact plastic (SCF). This is due to the fact that ITX is not utilised in the manufacturing of polymers that come into contact with food. Experts are unable to come to an agreement on either a specified migration limit or a tolerated daily intake (TDI) (SML).
Due to the lack of a standardised body of information on what constitutes an acceptable degree of migration, the AFC, SCF, and EFSA professionals who have investigated the problem of component approvals for materials that come into direct contact with food advised that ITX be established. Because experts were unable to reach a consensus on the suitable amount of migration, this objective was successfully realised. ITX was subjected to a variety of in-vitro and in-vivo mutagenicity tests in accordance with the most recent testing protocols developed by the Organization for Economic Co-operation and Development (OECD) and guidelines developed by the Good Laboratory Practice (GLP) organisation (Good Laboratory Practice).
The results of this study provide conclusive evidence against the concept that ITX is a genotoxic substance. Because ITX does not have a genotoxic effect, the EFSA’s standards for food contact materials permit concentrations as high as 0.05 mg/kg food, which is also referred to as 50 ppb. This is the case even after taking into account any potential reduction variables that might be pertinent to the food at hand. In spite of the fact that migration may reach a higher number than this estimate, it is predicted that additional development of the compliance evaluation will take place in the near future. Because there is a dearth of information regarding ITX’s chronic toxicity, it is difficult to determine a NOAEL (No Observed Adverse Effect Level) and a safer migration threshold for the substance. Depending on the way in which rules and EFSA assessment criteria are updated in the future, it may be necessary to modify the exposure in order to demonstrate that the application can be used safely in the future.
It is anticipated that approximately five percent of the primary market for food packaging will be comprised of goods that have UV printing on the exteriors of their containers. Because the current EU model makes the assumption that every kilogramme of food consumed every day comes in impacted packaging, it significantly overestimates the amount of people who are exposed. As a direct consequence of this, the converter is now able to print food packaging that is in accordance with the requirements as a result of the incorporation of ITX into UV curing inks and varnishes. If more feasible requirements for printed packaging verifications become available in the future, the company that provides the filler and the package could want to take other factors into consideration. It is essential that this be kept in mind at all times. All food containers that have been printed with any printing ink technology or printing technique need to be tested for migration, risk, exposure, and compliance with the criteria that have already been defined.
When analysing migration, it is common practise to ignore the distinctive qualities of milk, as was mentioned earlier. It is anticipated that the European Commission and the European Food Safety Authority (EFSA) would look into this topic and provide up-to-date recommendations for milk substitutes after conducting an investigation. In the meantime, we strongly recommend that all parties involved in the packaging of milk and milk products make note of our results and take the appropriate steps to ensure that they are in conformity with applicable laws.
Conclusion
- ITX does not have genotoxic properties.
- The usage of ITX-containing UV curing inks and varnishes in food packaging is not being phased out.
- Existing models used to achieve compliance with Article 3 of Framework Regulation (EC) No. 1935/2004 overestimate the adult consumer’s exposure to ITX.
- Migration with corrected values less than 0.05 mg/kg food (50 ppb) is permitted, albeit this is not specifically mentioned.
- If the figure exceeds this threshold, the compliance evaluation criteria will need to be revised in the future.
- Manufacturers of milk products, particularly infant formula, should be aware that existing relevant assessment procedures for these commodities (i.e., utilising distilled water as the food simulant) severely undervalue the unique nature of these items.
- The design of the final container for baby milk must be carefully considered.
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