TPO will be banned, what photoinitiator options for LED UV curing?

The European light-curable coating and ink industry reported in the first half of this year that the photoinitiator TPO is likely to be reclassified by the European Union ECHA as a reproductive toxicity 1B substance in the CMR, and ECHA issued 2020-2022 on October 23, 2019. In the Community Rolling Action Draft (CoRAP) of 2015, TPO was announced as possible to be reclassified. If this change in classification becomes a reality, it means that TPO will be banned or restricted in many applications. This news has caused a considerable degree of panic in the industry, because the photoinitiator TPO is a photoinitiator widely used in photocuring formulations. And because of its longer absorption wavelength, it is the most popular photoinitiator in LED UV curing. At the same time, there are rumors that this is a “conspiracy” of artificial barriers led by a large industry company in order to promote its alternative photoinitiator products.

The photoinitiator is an important part of the photocuring formula. Although the proportion in the formula is usually not high, it is indispensable. Compared with the oligomer in the formulation, the molecular weight of the photoinitiator is relatively small; unlike the monomer, another important component in the formulation, the photoinitiator is usually not cured and cross-linked into the system. Moreover, due to the incomplete photolysis of the photocuring reaction and the cracking of the photoinitiator to produce small molecules, the photoinitiator has become an important source of harm to human health and food safety in the photocuring formula.　　In the world's chemical safety supervision, the European Chemicals Agency (ECHA) under the European Union should be the most stringent agency. This agency is the central management agency responsible for the registration of all chemicals used in the EU. It is responsible for operating and managing the central database, reviewing whether the registration documents are complete and meeting requirements, and coordinating the evaluation process. The specific implementation of REACH is also carried out by ECHA. Based on the GHS system (English full name: Globally harmonised system of classification and labelling of chemicals, Chinese full name: Globally harmonised system of classification and labelling of chemicals) widely adopted by countries around the world, one class of substances is called CMR substances (English full name: substances) classified as carcinogenic, mutagenic, or toxic for reproduction, full Chinese name: carcinogenic, mutagenic, or toxic for reproduction).

According to the European Union's CLP regulations (English full name: Classification, Labelling and Packaging Regulation, Chinese full name: Classification, Labelling and Packaging Regulation), the classification of CMR substances is the classification of carcinogenic, mutagenic and reproductive toxicity. It can be seen from ECHA's website that the nature of TPO's attention now is "Suspected to be Toxic to Reproduction", which is classified as reproductive toxicity in CLP2. There is another category of CLP that is toxic to reproduction. And 1 is divided into 1A and 1B. 1A means "Known human reproductive toxicant", which is based on a large amount of human evidence. And 1B means "Presumed human reproductive toxicant", which is based on evidence from a large number of animal experiments. For category 2, which is suspected of reproductive toxicity, it is based on the evidence obtained from existing humans or experimental animals, which may be supplemented by other data to prove that it has an adverse effect on sexual function and fertility, or development, but the evidence is insufficient If people convincingly include the substance in category 1, the substance is classified as reproductive toxicity category 2. This shows that TPO is now listed as Reproductive Toxicity 2, which has been classified based on actual data. So with the addition of more experimental data, it is not surprising that TPO is classified as a reproductive toxicity 1B category.

It has been listed as a photoinitiator of CMR reproductive toxicity 1B by the European Union ECHA, including morpholino butyl phenone (CAS: 119313-12-1) (alias 369), 4-(dimethylamino)benzoic acid 2-ethyl Ethylhexyl ester (CAS: 21245-02-3) (abbreviated as EHA), 4-(dimethylamino) ethyl benzoate (CAS: 10287-53-3) (abbreviated as EDB), 4-phenylbenzyl Ketone (CAS: 2128-93-0) (PBZ for short) and 2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-acetone (CAS: 71868-10-5) (alias 907).

All photoinitiators listed in CMR 1B are greatly restricted in their use and will be banned in many products, especially those that are related to food and are in close contact with the human body.

Regarding the time when TPO may be banned, Pan Li, general manager of Shanghai Caineng Chemical Technology Co., Ltd., said that the ban is likely to be announced in the first half of 2020. The announcement is expected to have a 6-month buffer period (special applications for individual companies will continue to be extended for 12 months), so it is expected that after 2021, the market size of the photoinitiator TPO will shrink rapidly. The European market will be the first to be hit by then, and then it will expand to the US and Asian markets. Compared with the previous 369 and 907, TPO has a wider range of uses and a larger amount, which will have a much greater impact on the terminal light-curing coating and ink market. Therefore, domestic coating and ink manufacturers need to respond early. With regard to the problem of dealing with this negative impact, Mr. Pan said that they have made adequate preparations for this problem, and the main way to deal with it is to replace the original TPO with TPO-L and 819.　　From the information provided by ECHA, 819 and TPO-L have no reproductive health risks. For 819, there are concerns about skin sensitivity, while for TPO-L, there are no considerations that need to be paid attention to, and neither has the risk of being disabled.

In terms of chemical structure, TPO-L replaces the original phenyl group in the TPO molecule with an ethoxy group, which greatly reduces the chemical toxicity of the molecule, and at the same time it changes from a solid to a liquid, which is more convenient to use. However, the initiation efficiency of TPO-L is slightly lower than that of TPO. Unlike TPO, which has only one benzoyl group, 819 has two benzoyl groups and has a longer absorption wavelength. However, the color of the 819 photoinitiator itself will be a little yellower, and the color of the cured product will be slightly darker. 819 was first invented by the Swiss Ciba company, and its trade name was IRGACURE 819. Later, due to the merger and reorganization of multinational companies, the product now belongs to IGM (IGM) and its trade name is changed to OMNIRAD 819. It is reported that it is still in the patent protection period.

Pan Li, the general manager of Shanghai Color Energy Chemical Technology Co., Ltd., introduced that they also launched a compound liquid photoinitiator product 2100, which is more environmentally friendly and also meets the requirements of EU regulations. At the same time, it matches the absorption spectrum of TPO very well (as follows Figure), it can almost completely replace TPO.

As human beings pay more and more attention to environmental protection and health, photoinitiators are constantly updated. Moreover, with the continuous promotion and development of UV LEDs, the demand for low-toxic, long-wavelength photoinitiators has been very strong. Therefore, many companies are developing new photoinitiators to meet this growing new demand for photoinitiators. The upcoming TPO ban will inject new impetus into this research and development work. Judging from the European Radiation Curing Conference held in 2019 and the reports at the Asian Radiation Curing Conference, benzoyl phosphine oxide derivatives based on TPO and 819 are an important direction of recent photoinitiator research.

For the current popular UV LED light curing applications, in addition to the long-wavelength photoinitiator, a very important factor, the formula uses FSP7814, which has higher reactivity, and LuCure5366, which has better anti-oxidant polymerization resistance. Body is also very important. In addition, the use of some ultra-low viscosity monofunctional monomers (such as LuCure4305) and resins (such as Unicryl R7162) that can still maintain sufficient activity, etc., can solve some UV LED curing that requires fast curing speed and low construction viscosity Application requirements.

Europe is the birthplace of modern industry. After so many years of development, it has now become the most conservative and traditional region in the world today, and its attention to regulations, health and safety will continue to be strengthened. The influence of this trend on other emerging countries is also gradually showing. Now many countries in the world have launched their own version of REACH is a good example. The sound and long-term development of any industry requires not only the strengthening of government supervision, but also the joint efforts of all relevant stakeholders. This includes the coordination, promotion and promotion of the industry by industry associations, and the development of better products by related companies can enable the industry to achieve sustainable, long-term and stable development.　　 I hope that the upcoming crisis of banning and restricting TPO will also become the driving force and promoter of a more healthy development of the light curing industry. For photoinitiator production and use companies, supporting suppliers and downstream companies, this is indeed a challenge that must be faced, and relevant parties need to make corresponding preparations in advance.