One-component thioxanthone photoinitiators for uv-led curing systems, their preparation and use

Abstract

This invention provides a single-component thioxanthone photoinitiator suitable for UV-LED curing systems and its preparation method. The photoinitiator provided by this invention absorbs wavelengths in the 300-400 nm range, making it well-matched to UV-LED light sources. This photoinitiator introduces hydrogen-donating groups onto the thioxanthone matrix, enabling it to efficiently initiate the polymerization of acrylate monomers without the addition of hydrogen donors, avoiding the odor and toxicity problems associated with the use of hydrogen donors. When used alone, this photoinitiator exhibits a higher double bond conversion rate than commercially available ITX photoinitiators. When combined with iodized salts, even with small dosages, the double bond conversion rate can reach over 90%.

Description

Technical Field

[0001] This invention relates to the field of photoinitiators, and in particular to a single-component thioxanthone photoinitiator suitable for UV-LED curing, its preparation method, and its application. Background Technology

[0002] Photocuring refers to the curing process of reactive diluents, oligomers, and photoinitiators under light induction, and is generally used in film formation. Under light irradiation, the photoinitiator transforms into active species such as free radicals, thereby initiating the cross-linking polymerization of reactive monomers and prepolymers. Compared to thermosetting technology, photocuring technology has the "5E" characteristics of high efficiency, energy saving, environmental protection, economy, and wide applicability. Currently, photocuring technology has been widely used in functional coatings, inks, adhesives, medical devices, photoresists, and 3D printing.

[0003] Photoinitiators are an important component of photocuring systems, and are classified into free radical photoinitiators and cationic photoinitiators. Free radical photoinitiators are compounds that can generate free radicals under light irradiation and initiate free radical polymerization; they are the most widely used type of photoinitiator. Free radical photoinitiators are further divided into two types: cleavage type (Type I) and hydrogen abstraction type (Type II). Thioxanthones are among the most common hydrogen abstraction type photoinitiators. Thioxanthone compounds have advantages such as simple synthetic routes, low cost, and high initiation efficiency. Furthermore, thioxanthone derivatives have low triplet energy and high quantum yield, exhibiting good absorption in the 360-420 nm wavelength range. The absorption spectrum can be easily tuned to match the emission spectrum of the light source, demonstrating significant development and application potential. These compounds do not undergo cleavage in the excited state; instead, they extract a hydrogen from the hydrogen donor, generating an inactive carbonyl free radical and a highly reactive donor free radical, thereby initiating the polymerization reaction. Tertiary amines are the most commonly used hydrogen donors, but these compounds tend to emit an unpleasant odor and exhibit problems such as toxic yellowing after exposure to light.

[0004] Common light sources for photopolymerization technology include xenon lamps, mercury lamps, pulsed light sources, and laser light sources. Traditional photopolymerization technology mainly uses medium- or high-pressure mercury lamps, but mercury lamps have a wide emission spectrum and a short lifespan of only 1500-2000 hours. Furthermore, mercury lamps have disadvantages such as high energy consumption, significant heat generation, and the emission of toxic mercury. Currently, LED light sources, as a new type of light source, have advantages such as high energy conversion efficiency, high energy utilization, long lifespan, and the absence of substances harmful to the environment and human health. In addition, LED light sources can provide a narrow spectrum to meet the needs of specific applications.

[0005] Therefore, it is particularly important to develop photoinitiators with high initiation activity that are suitable for LED light sources and can be used as single components. Summary of the Invention

[0006] In view of the properties of thioxanthone and the current development trend of LED photoinitiators, the purpose of this invention is to provide a low-cost, high-activity UV-LED photoinitiator, its preparation method and application.

[0007] The photoinitiator of this invention modifies the molecular structure of the xanthonone structure by introducing a group that can provide hydrogen atoms during photoinitiated polymerization. This allows it to initiate the photocuring process independently without the need for a co-initiator, avoiding problems such as toxicity, odor, and yellowing associated with small molecules of co-initiators like tertiary amines. The introduced group R is connected to the xanthonone structure via an electron-withdrawing ester group, causing the entire molecular structure to directionally donate electrons from the xanthonone structure towards group R. This enables the photoinitiator to initiate monomer polymerization efficiently even at low concentrations.

[0008] The technical solution of the present invention is as follows: a single-component thioxanthone photoinitiator suitable for UV-LED curing systems, wherein the photoinitiator has the following general structural formula:

[0009]

[0010] Where X is S, O, N, Se, or Te;

[0011] R is a phenyl group containing at least one substituent or a C1-C10 straight-chain alkyl group substituted with at least one substituent; each substituent is independently methoxy, methylthio, methylenedioxy, ethylenedioxy, propylenedioxy, or dimethylamino.

[0012] Some specific photoinitiators have X as S or O;

[0013] R is a phenyl group containing at least one substituent or a C1-C5 straight-chain alkyl group substituted with at least one substituent; each substituent is independently methoxy, methylthio, methylenedioxy, ethylenedioxy, propylenedioxy, or dimethylamino.

[0014] Some specific photoinitiators, where X is S;

[0015] R is a phenyl group containing at least one substituent or a C1-C3 straight-chain alkyl group substituted with at least one substituent; each substituent is independently methoxy, methylthio, methylenedioxy, ethylenedioxy, propylenedioxy, or dimethylamino.

[0016] Some specific photoinitiators, where R is a phenyl group containing at least one substituent;

[0017] Each of the substituents is independently methoxy, methylthio, methylenedioxy, ethylenedioxy, propylenedioxy, or dimethylamino.

[0018] Some specific photoinitiators, where R is a phenyl group containing at least one substituent;

[0019] The substituents are individually methoxy, methylthio, methylenedioxy, and ethylenedioxy.

[0020] For some specific photoinitiators, R is selected from the following structures:

[0021]

[0022] The preparation method of the single-component thioxanthone photoinitiator suitable for UV-LED curing systems, and the reaction formula and reaction steps are as follows:

[0023]

[0024] 2,4-Thiodibenzoic acid is obtained by reacting m-thiosalicylic acid and p-iodobenzoic acid under anhydrous potassium carbonate and copper powder conditions; 2,4-Thiodibenzoic acid undergoes a dehydration reaction to obtain 2-carboxythioxanthonone; 2-carboxythioxanthonone and R-OH are esterified to obtain the photoinitiator.

[0025] Specifically, the preparation method of the single-component thioxanthone photoinitiator suitable for UV-LED curing systems is as follows:

[0026] a: Preparation of 2-carboxythixanthone

[0027] Thiosyl salicylic acid, p-iodobenzoic acid, anhydrous potassium carbonate, and copper powder were added to a two-necked flask. DMF was used as the reaction solvent. The mixture was stirred and dissolved, heated to 155°C, and reacted for 50 hours under nitrogen protection. After cooling, the mixture was filtered. The filtrate was acidified with dilute hydrochloric acid to pH < 1, filtered again, and the filter cake was washed with a large amount of water and dried under vacuum to obtain 2,4-thiodibenzoic acid.

[0028] 2,4'-thiodibenzoic acid and 7 ml of concentrated sulfuric acid were added to a single-necked flask and stirred at 25°C for 40 h. Then the mixture was poured into cold water and heated at 100°C for 1 h. After cooling and filtration, the filter cake was washed with water and dried to obtain 2-carboxythixanthrone.

[0029] b: Preparation of the single-component thioxanthone photoinitiator suitable for UV-LED curing systems

[0030] The R-OH group, 2-carboxythixanthrone, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine were dissolved in a dry dichloromethane solution and stirred at room temperature in the dark for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. The crude product was recrystallized from anhydrous ethanol to obtain the final product. The molar ratio of 2-carboxythixanthrone to R-OH was 1:1-1.1.

[0031] A specific structure of a one-component thioxanthone photoinitiator suitable for UV-LED curing systems:

[0032]

[0033] A specific structure of a one-component thioxanthone photoinitiator suitable for UV-LED curing systems:

[0034]

[0035] A specific structure of a one-component thioxanthone photoinitiator suitable for UV-LED curing systems:

[0036]

[0037] A specific structure of a one-component thioxanthone photoinitiator suitable for UV-LED curing systems:

[0038]

[0039] Beneficial technical effects of the present invention:

[0040] 1. The photoinitiator provided by this invention has absorption in wavelengths in the range of 300-400nm, which can be matched with UV-LED light sources.

[0041] 2. The photoinitiator obtained by this invention does not require an external solvent and can be directly dissolved in the monomer. It also does not require a co-initiator to quickly and effectively initiate the free radical polymerization of the monomer, thus avoiding environmental pollution caused by solvent evaporation. At the same time, it can also avoid the problems of odor and toxicity caused by the use of small molecule hydrogen donors.

[0042] 3. When used alone, the photoinitiator provided by this invention exhibits a higher double bond conversion rate in monomers than that induced by commercially available photoinitiators of the same type (ITX). When combined with iodized salts, even with a small dosage, the double bond conversion rate of monomers can reach over 90%.

[0043] 4. The introduced group R is connected to the xanthonone structure through an electron-withdrawing ester group, so that the entire molecular structure is directionally pushed towards the group R, enabling the photoinitiator to initiate monomer polymerization with high efficiency at low concentrations. Attached Figure Description

[0044] Figure 1 The diagram shows the structure of the four photoinitiators of this invention.

[0045] Figure 2 The UV-Vis absorption spectra of the photoinitiators prepared in Examples 1-4 are shown.

[0046] Figure 3 This is the UV-Vis absorption spectrum of the photoinitiator photodegradation process in Example 1.

[0047] Figure 4 The double bond conversion rate curves of the monomer TPGDA during photocuring initiated by the photoinitiators prepared in Examples 1-4 are shown.

[0048] Figure 5 This is a graph showing the double bond conversion rate during the photocuring process of TPGDA, a monomer synergistically initiated by photoinitiator, Iod, and NPG in Example 2. Detailed Implementation

[0049] The present invention will be further described below with reference to specific implementation methods. All raw materials used in the examples are commercially available. Unless otherwise specified, the reagents, methods, and equipment used in this invention are all conventional reagents, methods, and equipment within the technical field. Specifically, the monomer TPGDA used is tripropylene glycol diacrylate, and the monomer HDDA is 1,6-hexanediol diacrylate; w / w represents weight percentage.

[0050] Example 1

[0051] Preparation of TX-A1

[0052]

[0053] a: Preparation of 2-Carboxythixanthone

[0054] Thiosyl salicylic acid (1.23 g, 8 mmol), p-iodobenzoic acid (1.80 g, 7.27 mmol), anhydrous potassium carbonate (3.02 g, 21.82 mmol), copper powder (92.43 mg, 1.45 mmol), and DMF (30 mL) were added to a two-necked flask. The mixture was stirred to dissolve, heated to 155 °C, and reacted under nitrogen protection for 50 h. The solution turned caramel color. After cooling, the mixture was filtered, and the filtrate was light yellow. The filtrate was acidified with dilute hydrochloric acid to pH < 1, resulting in the formation of a white jelly-like precipitate. The precipitate was filtered, washed with a large amount of water, and dried under vacuum to obtain 2,4-thiodibenzoic acid (1.230 g, yield 61.81%). 1H NMR (400MHz, DMSO) δ13.21 (s, 2H), 8.02–7.96 (m, 2H), 7.92 (dd, J = 7.7, 1.5Hz, 1H), 7.60–7.52 (m,2H),7.43(dd,J=8.0,1.5Hz,1H),7.32(dd,J=7.6,1.0Hz,1H),6.96(dd,J=8.1,0.8Hz,1H).

[0055] 0.960 g of 2,4'-thiodibenzoic acid and 7 ml of concentrated sulfuric acid were added to a single-necked flask and stirred at 25 °C for 40 h. The mixture was then poured into cold water and heated at 100 °C for 1 h. After cooling and filtration, the filter cake was washed with water and dried to obtain 2-carboxythixanthrone (0.387 g, yield 43.15%). ¹H NMR (400 MHz, DMSO) δ 13.43 (s, 1H), 8.99 (s, 1H), 8.49 (d, J = 8.0 Hz, 1H), 8.22 (d, J = 8.3 Hz, 1H), 7.98 (d, J = 8.5 Hz, 1H), 7.90 (d, J = 7.8 Hz, 1H), 7.82 (t, J = 7.6 Hz, 1H), 7.64 (t, J = 7.6 Hz, 1H).

[0056] b: p-hydroxyanisole (136.55 mg, 1.1 mmol), 2-carboxythione (256.28 mg, 1 mmol), dicyclohexylcarbodiimide (DCC, 0.78 g, 10 mmol), and 4-dimethylaminopyridine (0.12 g, 1 mmol) were dissolved in 20 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete consumption of p-hydroxyanisole, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized with anhydrous ethanol to obtain product TX-A1) (0.89 g, yield: 24.56%). 1H NMR(600MHz, CDCl3) δ9.36(d,J=1.5Hz,1H),8.59(d,J=7.4Hz,1H),8.29(dd,J=8.4,1.8Hz,1H),7.66–7.59(m ,2H),7.55(d,J=7.7Hz,1H),7.48(t,J=7.5Hz,1H),7.11(d,J=9.0Hz,2H),6.89(d,J=9.0Hz,2H),3.77(s,3H).

[0057] Example 2

[0058] Preparation of TX-A2

[0059]

[0060] a: The preparation of 2-carboxythione is the same as in Example 1a.

[0061] b: 3,4-Methylenedioxyphenol (59.29 mg), 2-carboxythione (100 mg), dicyclohexylcarbodiimide (805.12 mg), and 4-dimethylaminopyridine (47.67 mg) were dissolved in 8 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete consumption of piperine, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized with anhydrous ethanol to obtain product TX-A2) (65 mg, yield: 44.52%). 1H NMR (600MHz, CDCl3) δ9.34(d,J=1.6Hz,1H),8.58(d,J=8.1Hz,1H),8.28(dd,J=8.4,1.8Hz,1H),7.64(d,J=8.4Hz,1H),7.62–7.59(m,1H ),7.55(d,J=8.0Hz,1H),7.48(t,J=7.6Hz,1H),6.78(d,J=8.3Hz,1H),6.70(d,J=2.2Hz,1H),6.63(dd,J=8.3,2.3Hz,1H),5.96(s,2H).

[0062] Example 3

[0063] Preparation of TX-A3

[0064]

[0065] a: The preparation of 2-carboxythione is the same as in Example 1a.

[0066] b: p-Methiophenol (60.18 mg), 2-carboxythione (100 mg), dicyclohexylcarbodiimide (805.12 mg), and 4-dimethylaminopyridine (47.67 mg) were dissolved in 8 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete consumption of p-methiophenol, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized with anhydrous ethanol to obtain product TX-A3) (69 mg, yield: 46.72%). 1H NMR (400MHz, CDCl3) δ9.45(d,J=1.7Hz,1H),8.68(d,J=8.0Hz,1H),8.38(dd,J=8.5,1.8Hz,1H),7.73(dd,J=15.1,7 .7Hz,2H),7.65(d,J=7.6Hz,1H),7.58(t,J=7.5Hz,1H),7.37(d,J=8.6Hz,2H),7.22(d,J=8.6Hz,2H),2.54(s,3H).

[0067] Example 4

[0068] Preparation of TX-A4

[0069]

[0070] a: The preparation of 2-carboxythione is the same as in Example 1a.

[0071] b: 3,4-Dimethoxyphenol (661.72 mg), 2-carboxythione (1 g), dicyclohexylcarbodiimide (8.05 g), and 4-dimethylaminopyridine (476.72 mg) were dissolved in 30 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete consumption of 3,4-dimethoxyphenol, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized with anhydrous ethanol to obtain product TX-A4) (520 mg, yield: 33.99%). 1H NMR (400MHz, CDCl3) δ9.45(d,J=1.7Hz,1H),8.67(d,J=8.0Hz,1H),8.38(dd,J=8.4,1.9Hz,1H),7.76–7.67(m,2H),7 .64(d,J=7.5Hz,1H),7.58(dd,J=11.0,4.0Hz,1H),6.94(d,J=8.9Hz,1H),6.88–6.82(m,2H),3.93(d,J=5.0Hz,6H).

[0072] Example 5

[0073] Preparation of TX-B1

[0074]

[0075] a: The preparation of 2-carboxythione is the same as in Example 1a.

[0076] b: p-Methoxybenzyl alcohol (59.30 mg), 2-carboxythixanthone (100 mg), dicyclohexylcarbodiimide (805.12 mg), and 4-dimethylaminopyridine (47.67 mg) were dissolved in 8 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete reaction, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized with anhydrous ethanol to obtain product TX-B1) (51 mg, yield: 34.72%). 1H NMR (600MHz, CDCl3) δ9.26(d,J=1.9Hz,1H),8.62(dd,J=8.1,1.2Hz,1H),8.24(dd,J=8.4,1.9Hz,1H),7.67–7.62(m ,2H),7.59(d,J=7.5Hz,1H),7.54–7.49(m,1H),7.44–7.40(m,2H),6.93(d,J=8.7Hz,2H),5.36(s,2H),3.83(s,3H).

[0077] Example 6

[0078] Preparation of TX-B2

[0079]

[0080] a: The preparation of 2-carboxythione is the same as in Example 1a.

[0081] b: 3,4,5-Trimethoxybenzyl alcohol (85.08 mg), 2-carboxythixanthone (100 mg), dicyclohexylcarbodiimide (805.12 mg), and 4-dimethylaminopyridine (47.67 mg) were dissolved in 8 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete reaction, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized with anhydrous ethanol to obtain product TX-B2) (47 mg, yield: 27.60%). 1 H NMR (600MHz, CDCl3) δ9.29(d,J=1.9Hz,1H),8.62(dd,J=8.1,1.2Hz,1H),8.26(dd,J=8.4,1.9Hz,1H),7.68– 7.63(m,2H),7.60(d,J=7.8Hz,1H),7.55–7.51(m,1H),6.72(s,2H),5.34(s,2H),3.91(s,6H),3.87(s,3H).

[0082] Example 7

[0083] Preparation of XT-C1

[0084]

[0085] p-Methoxyphenol (56.85 mg), 2-carboxyxanthone (100 mg), dicyclohexylcarbodiimide (858.95 mg), and 4-dimethylaminopyridine (47.67 mg) were dissolved in 8 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete reaction, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized from anhydrous ethanol to obtain product O-Cl) (50 mg yield: 34.68%). 1 H NMR (600MHz, CDCl3) δ9.14(s,1H),8.44(d,J=8.7Hz,1H),8.31(d,J=7.8Hz,1H),7.72(t,J=7.7Hz,1H),7.55(d,J=8 .7Hz,1H),7.49(d,J=8.4Hz,1H),7.38(t,J=7.5Hz,1H),7.11(d,J=8.5Hz,2H),6.89(d,J=8.5Hz,2H),3.77(s,3H).

[0086] Example 8

[0087] Preparation of XT-C2

[0088]

[0089] p-Methoxybenzyl alcohol (63.27 mg), 2-carboxyxanthone (100 mg), dicyclohexylcarbodiimide (805.12 mg), and 4-dimethylaminopyridine (47.67 mg) were dissolved in 8 mL of dry dichloromethane solution and stirred at room temperature for 24 hours. The reaction was monitored by thin-layer chromatography. After complete reaction, the product was washed with water, dried, and the solvent was evaporated to obtain the crude product. (After complete reaction, the product was washed with water (3 × 50 mL), dried overnight with anhydrous sodium sulfate, evaporated under reduced pressure to obtain the crude product, and recrystallized from anhydrous ethanol to obtain product O-C2) (20 mg, yield: 13.33%). 1 H NMR (600MHz, CDCl3) δ9.04 (s, 1H), 8.39 (d, J = 8.7Hz, 1H), 8.35 (d, J = 7.8Hz, 1H), 7.76 (t, J = 7.8Hz, 1H),7.53(t,J=9.1Hz,2H),7.43(d,J=7.3Hz,3H),6.93(d,J=7.6Hz,2H),5.35(s,2H),3.83(s,3H).

[0090] Test Example 1

[0091] Four photoinitiator molecules, TX-A1, TX-A2, TX-A3, and TX-A4, were prepared into a 40 μM anhydrous acetonitrile solution and injected into a cuvette with a 1 cm optical path length. The UV-Vis absorption spectrum of the solution was measured using a UV-Vis spectrophotometer (Cary60UV-Vis). The test results are as follows. Figure 2 As shown, the photoinitiator molecules TX-A1, TX-A2, TX-A3, and TX-A4 obtained in this invention all have strong absorption in the 300-400nm range, and can be used in UV-LED light sources and UV-LED curing systems.

[0092] Test Example 2

[0093] The photoinitiator molecule TX-A1 described in Example 1 was prepared as a 40 mM anhydrous acetonitrile solvent and injected into a cuvette with an optical path length of 1 cm. It was irradiated for a certain period using a 365 nm LED light source. The UV-Vis absorption spectra after irradiation for 0 s, 10 s, 100 s, 200 s, and 300 s were measured to observe the degradation of the photoinitiator molecule with increasing irradiation time. The test results are as follows: Figure 3 As shown, the photoinitiator molecules exhibit rapid degradation under light irradiation, indicating that these initiator molecules can rapidly initiate polymerization in the UV-LED curing system.

[0094] Test Example 3

[0095] Single-component polymerization experiment

[0096] The photoinitiators TX-A1, TX-A2, TX-A3, and TX-A4 obtained in this invention were respectively formulated with TPGDA to prepare a mixed solution containing 0.1% w / w of photoinitiator. A small amount was evenly coated on a potassium bromide salt sheet and irradiated under a 385nm LED light source. The changes in monomer double bonds were tested and recorded in real time using a real-time infrared spectrometer. Figure 4 The test result refers to the double bond conversion rate when the photoinitiator molecules TX-A1, TX-A2, TX-A3, and TX-A4 of the present invention initiate the polymerization of monomer TPGDA.

[0097] The photoinitiator molecules TX-A1, TX-A2, TX-A3, and TX-A4 obtained in this invention were respectively formulated with TPGDA to prepare mixed solutions containing 0.1% w / w, 0.25%, and 0.5% photoinitiator. A small amount was uniformly coated onto a potassium bromide salt sheet and irradiated under a 385nm LED light source. The changes in the monomer double bonds were measured and recorded in real time using a real-time infrared spectrometer (Nicolet 5700FT-IR spectroscope). The double bond conversion rate of the monomer after 3 minutes of irradiation was calculated using Formula 1. The experimental results are shown in Table 1 below.

[0098] Conversion% = (1-S) t / S0)×100% Formula 1

[0099] Among them, S t S0 and S0 represent the peak areas of the characteristic peaks of the resin system at time t (when the light exposure time is t) and the unexposed resin system, respectively.

[0100] Table 1. Experimental data on monomer polymerization initiated by a single-component photoinitiator.

[0101] PI(w / w) monomer Time / min Conversion rate / % TX-A1 (0.1%) TPGDA 3 87 TX-A1 (0.25%) TPGDA 3 95 TX-A1 (0.5%) TPGDA 3 96 TX-A2 (0.1%) TPGDA 3 90 TX-A2 (0.25%) TPGDA 3 93 TX-A2 (0.5%) TPGDA 3 94 TX-A3 (0.1%) TPGDA 3 76 TX-A3 (0.25%) TPGDA 3 92 TX-A3 (0.5%) TPGDA 3 90 TX-A4 (0.1%) TPGDA 3 85 TX-A4 (0.25%) TPGDA 3 91 TX-A4 (0.5%) TPGDA 3 91

[0102] As shown in Table 1, all four photoinitiators can effectively initiate the polymerization of TPGDA monomer. Among them, TX-A2 exhibits the highest double bond conversion rate when initiating TPGDA monomer polymerization. In the curing system, the double bond conversion rate is not significantly different when the photoinitiator concentration is 0.1% w / w or 0.5% w / w, indicating that the photoinitiator described in this invention can initiate efficient monomer polymerization even with a small dosage.

[0103] The photoinitiator TX-A2 obtained in this invention and the commercial photoinitiator ITX were respectively formulated into HDDA mixtures with a photoinitiator content of 0.1% w / w. A small amount was evenly coated on a potassium bromide salt sheet and irradiated under a 385nm LED light source.

[0104] Table 2 Comparison data of monomer polymerization initiated by TX-A2 and ITX

[0105] monomer Time (min) Conversion rate (%) TX-A2 HDDA 3 87 ITX HDDA 3 56

[0106] As can be seen from Table 2, compared with ITX, the photoinitiator obtained by this invention has a faster polymerization rate, a higher monomer double bond conversion rate, and a better polymerization effect.

[0107] Test Example 4

[0108] Two- or three-component photoinitiated polymerization experiments

[0109] The photoinitiator TX-A2 (0.1% w / w) obtained in this invention was mixed with NPG (0.5% w / w), Iod (0.5% w / w), and monomer TPGDA to prepare TX-A2 / NPG / TPGD mixed solutions (containing 0.1% w / w TX-A2 and 0.5% w / w NPG), TX-A2 / Iod / TPGD mixed solutions (containing 0.1% w / w TX-A2 and 0.5% w / w Iod), and TX-A2 / NPG / Iod / TPGD mixed solutions (containing 0.1% w / w TX-A2, 0.5% w / w NPG, and 0.5% w / w Iod). A small amount of the mixed solution was evenly coated onto a potassium bromide salt sheet and irradiated with a 385nm LED light source. The results were analyzed using a real-time infrared spectrometer (model: Nicolet 5700FT-IR). The spectroscope was used to test and record changes in single-cell double bonds in real time. The test results are as follows: Figure 5 As shown in the figure, it can be clearly seen that in the TX-A2 / NPG / Iod three-component system, the double bond has the highest conversion rate and the fastest conversion speed; in the two-component system, the synergistic effect of TX-A2 and Iod is more obvious than that of the TX-A2 / NPG system, and the double bond conversion rate is higher.

[0110] The double bond conversion rate of the monomer after 3 minutes of illumination was calculated using Formula 1. The experimental results are shown in Table 3 below.

[0111] Table 3 Comparative data of monomer polymerization experiments initiated by TX-A2 in combination with NPG and Iod

[0112] monomer Time (min) Conversion rate (%) TX-A2 / NPG TPGDA 3 92 TX-A2 / Iod TPGDA 3 94 TX-A2 / NPG / Iod TPGDA 3 97

[0113] As can be seen from Table 3, in the presence of Iod, the synergistic effect of TX-A2 and Iod improves both the conversion rate and conversion speed to a certain extent. TX-A2 can achieve a high conversion rate with a small dosage.

Claims

1. The use of monocomponent thioxanthone photoinitiators suitable for UV-LED curing systems, characterized in that, Applications of the aforementioned photoinitiator in the field of photocuring; The photoinitiator has the following structural formula: 、 、 。 2. Use according to claim 1, characterized in that, The preparation method, reaction formula, and reaction steps of the initiator are as follows: ； wherein R is , , ; 2,4'-Thiodibenzoic acid is obtained by reacting m-thiosalicylic acid and p-iodobenzoic acid under anhydrous potassium carbonate and copper powder conditions; 2,4'-Thiodibenzoic acid undergoes a dehydration reaction to obtain 2-carboxythioxanthonone; 2-carboxythioxanthonone and R-OH are esterified to obtain the photoinitiator.

3. Use according to claim 2, characterized in that, The molar ratio of 2-carboxythionone to R-OH is 1:1-1.1.

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