Abstract:
A bisoxime ester photoinitiator as represented by general formula (I). By introducing a bisoxime ester group and a cycloalkylalkyl group into the chemical structure, this photoinitiator not only has excellent performance in aspects of storage stability, photosensitivity, developability, pattern integrity, and the like, but also exhibits obviously improved photosensitivity and thermal stability compared to similar photoinitiators.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International Application No. PCT/CN2015/074360, filed on Mar. 17, 2015, which claims priority to Chinese Application No. 201410100523.3, filed on Mar. 18, 2014. The contents of both applications are hereby incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     This invention pertains to the technical field of photoinitiators, and particularly to a bisoxime ester photoinitiator and a preparation method and a use thereof. 
     BACKGROUND ART 
     The use of compounds having an oxime ester structure as photoinitiators has been well known in the art, and for example, patent documents having Publication Nos. CN1241562A, CN101508744A, CN101565472A, CN103293855A, etc., have disclosed different carbazole oxime ester photoinitiators and ketoxime ester photoinitiators. These disclosed photoinitiators can satisfy normal application requirements in the current field of photocuring such as display panels, color filters, etc., to different extents. 
     However, since the development of electronic technologies changes rapidly, the existing products started to exhibit deficiencies in some application fields, and the requirements for photoinitiators are higher due to replacement and upgrade of products. At present, for example, most of photoresists used for space control materials do not have good heat resistance, collapse is prone to occur in the process of baking or packaging to result in the shrinkage of space materials, whereas intended increase of the height of the space control material in the process of coating, development by exposure, or the like will result in increased cost, and small molecules melted out upon collapse due to heating will cause contamination of liquid crystal. Furthermore, for example, in the production of premium color filters, the photoinitiator has to meet basic requirements of having high solubility and good thermal stability on the one hand, and its high color quality performance requires a highly colored resist on the other hand. However, as the content of pigments increases, the curing of color resist becomes more difficult, and there are also relatively high requirements for the clarity and the integrity of images after curing. This requires an initiator having a higher photosensitivity to solve the problems described above. 
     In the field of photocuring, a photoinitiator, which has a high photosensitivity and a high stability and is easy to be prepared, is still the first choice in the development of this field, and the research and development of a photoinitiator having higher performances is always a key task in this field. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a bisoxime ester photoinitiator having excellent application performances. By introducing a bisoxime ester group into the chemical structure, this photoinitiator not only has excellent performance in aspects of storage stability, photosensitivity, developability, pattern integrity, and the like, but also exhibits obviously improved photosensitivity and thermal stability compared to similar photoinitiators. 
     In order to achieve the technical effect described above, a technical solution used in this invention is as follows: 
     a bisoxime ester photoinitiator, having a structure represented by general formula (I): 
     
       
                 
         
             
             
         
      
     
     wherein, 
     R 1  is 
                                
wherein * represents a binding position, and X is blank (i.e., two benzene rings on the left and on the right are connected with each other only by Y), a single bond, or a C 1 -C 5  alkylene group; and Y is O, S, or a R 5 N— group, wherein R 5  is hydrogen, a C 1 -C 20  linear or branched alkyl group, a C 3 -C 20  cycloalkyl group, a C 4 -C 20  cycloalkylalkyl group, or a C 4 -C 20  alkylcycloalkyl group;
 
     R 2  and R 3  each independently represents a C 1 -C 20  linear or branched alkyl group, a C 3 -C 20  cycloalkyl group, a C 4 -C 20  cycloalkylalkyl group, a C 4 -C 20  alkylcycloalkyl group, and optionally, hydrogen in the above groups may be substituted with a group selected from the group consisting of halogen, a nitro group, a hydroxy group, a carboxyl group, a sulfonic acid group, an amino group, a cyano group, and an alkoxy group; provided that at least one of R 2  and R 3  is a cycloalkylalkyl group which is unsubstituted or substituted with one or more group selected from the group consisting of halogen, a nitro group, a hydroxy group, a carboxyl group, a sulfonic acid group, an amino group, a cyano group, and an alkoxy group, and the structure of said cycloalkylalkyl group is 
                                
wherein n is an integer of 1-5 and m is an integer of 1-6;
 
     R 4  represents a C 1 -C 20  linear or branched alkyl group, a C 3 -C 20  cycloalkyl group, a C 4 -C 20  cycloalkylalkyl group, a C 4 -C 20  alkylcycloalkyl group, a C 3 -C 20  heteroaryl group, and a C 6 -C 20  aryl group, and optionally, hydrogen in the above groups may be substituted with a group selected from the group consisting of halogen, a phenyl group, a nitro group, a hydroxy group, a carboxyl group, a sulfonic acid group, an amino group, a cyano group, and an alkoxy group. 
     As a preferable option of this invention, in the bisoxime ester photoinitiator represented by the general formula (I) described above: 
     in R 1 , X is blank, a single bond, a methylene group, an ethylene group, or a propylene group; and Y is O, S, or a R 5 N— group, wherein R 5  is hydrogen or a C 1 -C 10  linear or branched alkyl group; 
     R 2  and R 3  each independently represent a C 1 -C 5  linear or branched alkyl group or a C 4 -C 15  cycloalkylalkyl group, and optionally, hydrogen in the above groups may be substituted with a group selected from the group consisting of halogen, a nitro group, a cyano group, and an alkoxy group; provided that at least one of R 2  and R 3  is a cycloalkylalkyl group which is unsubstituted or substituted with one or more group selected from the group consisting of halogen, a nitro group, a cyano group, and an alkoxy group, and the structure of said cycloalkylalkyl group is 
                                
wherein n is an integer of 1-5 and m is an integer of 1-3;
 
     R 4  represents a C 1 -C 5  linear or branched alkyl group, a C 3 -C 8  cycloalkyl group, a C 4 -C 8  cycloalkylalkyl group, a C 4 -C 8  alkylcycloalkyl group, a C 3 -C 5  heteroaryl group, and a C 6 -C 10  aryl group, and optionally, hydrogen in the above groups may be substituted with a group selected from the group consisting of halogen, a nitro group, and an alkoxy group. 
     Further preferably, R 1  is selected from the group consisting of the following structures: 
     
       
                 
         
             
             
         
      
     
     This invention also relates to a preparation method of the bisoxime ester photoinitiator represented by the general formula (I) described above, comprising the steps of: 
     (1) synthesis of an intermediate 1, wherein: 
                                
as a starting material and an acid halide compound containing a R 2  group and a R 3  group are used to synthesize the intermediate 1 through a Friedel-Crafts reaction under the action of aluminum trichloride or zinc chloride, and the reaction formula is as follows:
 
     
       
                 
         
             
             
         
      
     
     wherein Z represents halogen, such as F, Cl, Br, or I; 
     (2) synthesis of an intermediate 2, wherein: an oximation reaction is performed between the intermediate 1 and a nitrite ester (such as ethyl nitrite, isopentyl nitrite, isooctyl nitrite, etc.) or a nitrite salt (such as sodium nitrite, potassium nitrite, etc.) under the action of hydrogen chloride, sodium alkoxide, or potassium alkoxide to generate an intermediate 2, and the reaction formula is as follows: 
     
       
                 
         
             
             
         
      
     
     (3) synthesis of the bisoxime ester photoinitiator, wherein: an esterification reaction is performed between the intermediate 2 and an acid halide compound or an acid anhydride containing a R 4  group to synthesize a bisoxime ester photoinitiator product, and the reaction formula is as follows: 
     
       
                 
         
             
             
         
      
     
     wherein Z represents halogen, such as F, Cl, Br, or I. 
     All of the raw materials used in the preparation method described above are compounds which are known in the prior art, commercially available, or prepared by known synthetic methods. This preparation method is simple, does not produce polluted wastes in the preparation process thereof, has high product purity, and is suitable for industrial batch production. 
     This invention also relates to use of the bisoxime ester photoinitiator represented by the general formula (I) described above in a photocurable composition (i.e., a photosensitive composition). Without limitation, this photoinitiator may be used in aspects such as color photoresists (RGB), black photoresists (BM), photo-spacers, dry films, semiconductor photoresists, inks, etc. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereafter, this invention will be further illustrated in conjunction with specific Examples, but it is not to be understood that the scope of this invention is limited thereto. 
     PREPARATION EXAMPLE 
     Example 1 
     Preparation of bis-{[4-(3-cyclopentyl-1,2-dione-2-oxime-O-propionate)propyl]phenylene}-sulfide 
     
       
                 
         
             
             
         
      
     
     Step (1): preparation of bis-{[4-(3-cyclopentyl-1-one)propyl]phenylene}-sulfide 
     
       
                 
         
             
             
         
      
     
     18.6 g of diphenyl sulfide, 29.4 g of AlCl 3  (finely ground), and 100 mL of dichloromethane were charged into a 500 mL four-neck flask, stirred, and cooled in an ice bath. When the temperature decreased to 0° C., a mixed liquid of 33.7 g of cyclopentylpropionyl chloride and 50 g of dichloromethane were begun to be dropped for about 1.5 h with the temperature being controlled at 10° C. or less, stirring was continued for 2 h, and then the reaction was stopped. The reaction liquid was poured into a diluted hydrochloric acid formulated with 400 g of ice and 65 mL of concentrated hydrochloric acid, the liquid in the lower layer was separated using a separation funnel, and the upper layer was extracted with 50 mL of dichloromethane. The extract and the liquid were combined with each other, washed with a NaHCO 3  solution formulated with 10 g of NaHCO 3  and 200 g of water, and were further washed with 200 mL of water for 3 times until pH value become neutral. Water was removed by drying with 30 g of anhydrous MgSO 4 , and dichloromethane was evaporated by rotation. After evaporation, the crude product in a rotary evaporation flask presented the form of light yellow liquid and was poured into 200 mL of petroleum ether evaporated under normal pressure to obtain a white powdery solid upon stirring and suction filtration, and a product of 39.1 g was obtained after drying in an oven at 50° C. for 5 h, with a yield of 90% and a purity of 96.2%. 
     The structure of the product in step (1) was determined by hydrogen nuclear magnetic resonance spectroscopy, and the specific characteristic result is as follows: 
       1 H-NMR(CDCl 3 , 500 MHz): 1.4274-1.5412 (22H, m), 2.5214-2.6276 (4H, t), 7.2738-7.3818 (4H, d), 7.7908-7.9824 (4H, d). 
     Step (2): preparation of bis-{[4-(3-cyclopentyl-1,2-dione-2-oxime)propyl]phenylene}-sulfide 
     
       
                 
         
             
             
         
      
     
     21.7 g of the product of step (1), 100 mL of tetrahydrofuran, 13.2 g of concentrated hydrochloric acid, and 11.8 g of isopentyl nitrite were added into a 250 mL four-neck flask, stirred at normal temperature for 5 h, and then the reaction was stopped. Materials were poured into a 2000 mL large beaker and stirred after 1000 mL of water was added, and 200 g of dichloromethane was used for extraction. The extract was dried by adding 50 g of anhydrous MgSO 4 , followed by suction filtration. The solvent was removed by rotary evaporation of the filtrate under reduced pressure, and an oily viscous matter was obtained in a rotary bottle. The viscous matter was poured into 150 mL of petroleum ether and was precipitated with stirring, followed by suction filtration, a white powdery solid was obtained, and after drying at 60° C. for 5 h, a product of 20.9 g was obtained with a yield of 85% and a relative purity of 95.2%. 
     The structure of the product in step (2) was determined by hydrogen nuclear magnetic resonance spectroscopy, and the specific characteristic result is as follows: 
       1 H-NMR(CDCl 3 , 500 MHz): 1.4037-1.5431 (18H, m), 2.0321-2.1735 (2H, s), 2.5001-2.7221 (4H, d), 7.3034-7.3241 (4H, d), 7.8002-7.9922 (4H, m). 
     Step (3): preparation of bis-{[4-(3-cyclopentyl-1,2-dione-2-oxime-O-propionate) propyl]phenylene}-sulfide 
     19.7 g of the product of step (2), 100 g of dichloromethane, and 4.1 g of triethylamine were added into a 250 mL four-neck flask and were stirred at room temperature for 5 min, and then 7.8 g of propionyl chloride was dropped within about 30 min. Stirring was continued for 2 h, and then 5% NaHCO 3  aqueous solution was added to adjust pH value to become neutral. An organic layer was separated with a separation funnel, followed by washing twice with 200 mL of water and drying with 50 g of anhydrous MgSO 4 , and the solvent was evaporated by rotation to obtain a viscous liquid. Recrystallization with methanol obtained a white solid powder, which was filtered to obtain a product of 23.1 g with a purity of 99%. 
     The structure of the final product was determined by hydrogen nuclear magnetic resonance spectroscopy, and the specific characteristic result is as follows: 
       1 H-NMR(CDCl 3 , 500 MHz): 0.9351-1.1213 (6H, t), 1.3351-1.4913 (18H, m), 2.1737-2.2923 (4H, m), 2.6981-2.8821 (4H, m), 7.3201-8.1241 (8H, d). 
     Example 2 
     Preparation of [2-(3-cyclopropyl-1,2-dione-2-oxime-O-propionate)propyl]-[7-(4-cyclopentyl-1,2-dione-2-oxime-O-propionate)butyl]-thioxanthene 
     
       
                 
         
             
             
         
      
     
     Step (1): preparation of [2-(3-cyclopropyl-1-one)propyl]-[7-(4-cyclopentyl-1-one)butyl]-thioxanthene 
     
       
                 
         
             
             
         
      
     
     19.8 g of thioxanthene, 14.7 g of AlCl 3  (finely ground), and 100 mL of dichloromethane were charged into a 500 mL four-neck flask, stirred, and cooled in an ice bath. When the temperature decreased to 0° C., a mixed liquid of 13.5 g of cyclopropylpropionyl chloride and 25 g of dichloromethane were begun to be dropped for about 1.5 h with the temperature being controlled at 10° C. or less, and stirring was continued for 2 h. 14.7 g of AlCl 3  (finely ground) was then added into the four-neck flask, a mixed liquid of 17.8 g of cyclopentylbutanoyl chloride and 25 g of dichloromethane was dropped for about 1.5 h with the temperature being controlled at 10° C. or less, the temperature was raised to 15° C., stirring was continued for 2 h, and then the reaction was stopped. The reaction liquid was poured into diluted hydrochloric acid formulated with 400 g of ice and 65 mL of concentrated hydrochloric acid, the liquid in the lower layer was separated using a separation funnel, and the upper layer was extracted with 50 mL of dichloromethane. The extract and the liquid were combined with each other, washed with NaHCO 3  solution formulated with 10 g of NaHCO 3  and 200 g of water, and were further washed with 200 mL of water for 3 times until pH value become neutral. Water was removed by drying with 30 g of anhydrous MgSO 4 , and dichloromethane was evaporated by rotation. After evaporation, the crude product in a rotary evaporation flask presented the form of light yellow liquid and was poured into 200 mL of petroleum ether evaporated under normal pressure to obtain a white powdery solid upon stirring and suction filtration, and a product of 38.1 g was obtained after drying in an oven at 50° C. for 5 h, with a yield of 88% and a purity of 96.2%. 
     The structure of the product in step (1) was determined by hydrogen nuclear magnetic resonance spectroscopy, and the specific characteristic result is as follows: 
       1 H-NMR(CDCl 3 , 500 MHz): 0.19366-0.2114 (5H, m), 1.2744-1.5831 (15H, m), 2.5762-2.6144 (4H, t), 3.7659-3.8407 (2H, s), 7.1908-7.2824 (2H, d), 7.4457-7.5763 (4H, m). 
     Step (2): preparation of [2-(3-cyclopropyl-1,2-dione-2-oxime)propyl]-[7-(4-cyclopentyl-1,2-dione-2-oxime)butyl]-thioxanthene 
     
       
                 
         
             
             
         
      
     
     21.6 g of the product of step (1), 100 mL of tetrahydrofuran, 13.2 g of concentrated hydrochloric acid, and 11.8 g of isopentyl nitrite were added into a 250 mL four-neck flask, stirred at normal temperature for 5 h, and then the reaction was stopped. Materials were poured into a 2000 mL large beaker and stirred after 1000 mL of water was added, and 200 g of dichloromethane was used for extraction. The extract was dried by adding 50 g of anhydrous MgSO 4 , followed by suction filtration. The filtrate was removed by rotary evaporation under reduced pressure, and an oily viscous matter was obtained in a rotary bottle. The viscous matter was poured into 150 mL of petroleum ether and was precipitated with stirring, followed by suction filtration, a white powdery solid was obtained, and after drying at 60° C. for 5 h, a product of 21.1 g was obtained with a yield of 86% and a relative purity of 95.2%. 
     The structure of the product in step (2) was determined by hydrogen nuclear magnetic resonance spectroscopy, and the specific characteristic result is as follows: 
     1H-NMR(CDCl 3 , 500 MHz): 0.2037-0.2431 (5H, m), 1.4355-1.5032 (11H, m), 2.0117-2.1349 (2H, s), 2.5132-2.7065 (4H, m), 3.8002 (2H, s), 7.3034-7.5241 (6H, d). 
     Step (3): preparation of [2-(3-cyclopropyl-1,2-dione-2-oxime-O-propionate) propyl]-[7-(4-cyclopentyl-1,2-dione-2-oxime-O-propionate) butyl]-thioxanthene 
     19.6 g of the product of step (2), 100 g of dichloromethane, and 4.1 g of triethylamine were added into a 250 ml four-neck flask and were stirred at room temperature for 5 min, and then 7.6 g of propionyl chloride was dropped within about 30 min. Stirring was continued for 2 h, and then 5% NaHCO 3  aqueous solution was added to adjust pH value to become neutral. An organic layer was separated with a separation funnel, followed by washing twice with 200 mL of water and drying with 50 g of anhydrous MgSO 4 , and the solvent was evaporated by rotation to obtain a viscous liquid. Recrystallization with methanol obtained a white solid powder, which was filtered to obtain a product of 22.1 g with a purity of 99%. 
     The structure of the final product was determined by hydrogen nuclear magnetic resonance spectroscopy, and the specific characteristic result is as follows: 
       1 H-NMR(CDCl 3 , 500 MHz): 0.1981-0.2209 (5H, m), 1.1038-1.2004 (6H, m), 1.498-1.5703 (11H, m), 2.2765-2.3951 (4H, m), 2.5964-2.7123 (4H, m), 3.8678 (2H, s), 7.2854-7.3409 (2H, d), 7.3988-7.5028 (4H, m). 
     Examples 3-13 
     Referring to the method illustrated in Example 1 or 2, compounds shown in Examples 3-13 were prepared from 
                                
and corresponding acylating agents.
 
     The structures of compounds of interest and  1 H-NMR data thereof were listed in Table 1. 
                             TABLE 1               Examples   Compounds (3-13)     1 H NMR δ[ppm]                   Example 3                                 0.1771-0.2134(5H, m) 2.2191-2.2721(6H, s) 2.3176-2.4481(2H, d) 3.0211-3.3113(2H, s) 7.2853-7.9062(8H, d)                Example 4                                 0.1801-0.2068(5H, m) 1.1067-1.2024(6H, s) 1.4431-1.5199(11H, m) 2.3308-2.4542(4H, m) 2.7150-2.8604(4H, t) 7.2743-8.0032(8H, m)                Example 5                                 0.1799-0.2134(5H, m) 1.0056-1.1387(9H, m) 1.4500-1.6583(10H, m) 2.2165-2.3566(4H, s) 2.7381-2.8436(4H, t) 3.8655(2H, s) 7.2433-7.5741(6H, m)                Example 6                                 0.1801-0.2104(5H, m) 0.9560-1.0801(6H, t) 1.4991-1.6630(13H, m) 2.2001-2.3708(4H, m) 2.6754-2.8318(4H, m) 7.3093-8.1061(6H, m)               Example 7                                 1.0016-1.1023(9H, t) 1.4128-1.5319(11H, m) 2.2100-2.3106(4H, m) 2.6128-2.8012(4H, m) 7.2098-7.9531(8H, m)                Example 8                                 1.3921-1.5129(11H, m) 2.0309-2.2237(6H, s) 2.5998-2.6879(2H, t) 3.2231-3.2456(3H, s) 3.4002-3.5023(2H, s) 3.8001-3.9123(2H, s) 6.9618-7.7239(6H, m)                Example 9                                 1.0239-1.1123(3H, t) 1.3906-1.5248(11H, m) 2.6540-2.8761(H, m) 5.3501-5.3501(H, s) 7.6681-8.2871(6H, m)                Example 10                                 0.9981-1.1031(3H, t) 1.3909-1.5216(11H, m) 2.1659-2.8192(16H, m) 3.5602-3.9768(2H, t) 7.3982-8.0007(6H, m)               Example 11                                 0.9567-1.0389(9H, t) 1.2908-1.5345(18H, m) 1.8665-2.0954(2H, m) 2.1981-2.3041(4H, s) 2.6260-2.7893(8H, m) 3.6782-3.9348(4H, m) 7.5562-8.1008(6H, m)               Example 12                                 0.9217-1.1129(6H, t) 1.3781-1.7961(15H, m) 2.6981-2.8045(4H, m) 3.8109-3.9861(2H, m) 7.4723-8.4018(16H, m)                Example 13                                 0.9549-1.0036(3H, t) 1.4029-1.5632(17H, m) 2.6102-2.8982(4H, m) 3.9651-4.1071(1H, m) 7.3031-8.4089(16H, m)                    
Performance Evaluation
 
     By formulating exemplary photocurable compositions, respective application performances of the photoinitiators represented by the general formula (I) of this invention, were evaluated, including aspects of storage stability, photosensitivity, developability, pattern integrity, thermal stability, etc. 
     1. Formulation of Photocurable Compositions 
     (1) Uncolored Photocurable Composition A 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Acrylate copolymer 
                 100 
               
               
                   
                 (Benzyl methacrylate/methacrylic 
               
               
                   
                 acid/hydroxyethyl methacrylate (molar ratio of 
               
               
                   
                 70/10/20) copolymer (Mw: 10,000)) 
               
               
                   
                 Trimethylolpropane triacrylate (TMPTA) 
                 100 
               
               
                   
                 Photoinitiator 
                 2 
               
               
                   
                 Butanone (solvent) 
                 25 
               
               
                   
                   
               
             
          
         
       
     
     (2) Colored Photocurable Composition B 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Acrylate copolymer 
                 100 
               
               
                   
                 (Benzyl methacrylate/methacrylic acid/methyl 
               
               
                   
                 methacrylate (molar ratio of 
               
               
                   
                 50/15/30) copolymer (Mw: 15,000)) 
               
               
                   
                 Dipentaerythritol hexaacrylate 
                 100 
               
               
                   
                 Photoinitiator 
                 2 
               
               
                   
                 Butanone (solvent) 
                 25 
               
               
                   
                 Dye blue 15 
                 5 
               
               
                   
                   
               
             
          
         
       
     
     In the compositions A and B described above, the photoinitiator was a bisoxime ester compound represented by the general formula (I) disclosed by this invention or a photoinitiator known in the prior art as a comparison, and the respective components were represented in parts by mass. 
     2. Development by Exposure 
     The photocurable compositions A and B described above were stirred, respectively, under protection from light. Materials were taken on a PET template and film coating was performed with a wire bar, the solvent was removed by drying at 90° C. for 5 min, and a coating film with a film thickness of about 2 μm was formed. The substrate on which the coating film was formed was cooled to room temperature, a mask plate was attached thereon, and a long wavelength irradiation was achieved with a high pressure mercury lamp 1PCS light source through a FWHM color filter. Exposure was performed on the coating film through a seam of the mask plate under an ultraviolet having a wavelength of 370-420 nm. Subsequently, development was performed by soaking in a 2.5% sodium carbonate solution at 25° C. for 20 s, followed by washing with ultra-pure water and air drying. The pattern was fixed by hard baking at 220° C. for 30 min, and the obtained pattern was evaluated. 
     3. Performance Evaluation of Photocurable Compositions 
     (1) Storage Stability 
     After naturally storing a liquid-state photocurable composition at room temperature for 1 month, the degree of precipitation of substances was visually evaluated according to the following criteria: 
     A: No precipitation was observed; 
     B: Precipitation was slightly observed; 
     C: Significant precipitation was observed. 
     (2) Photosensitivity 
     Upon exposure, the minimum exposure amount of the irradiated region having a residual film rate of 90% or more after development in the step of exposure was evaluated as the demand of exposure. A smaller exposure demand represents a higher sensitivity. 
     (3) Developability and Pattern Integrity 
     The pattern on the substrate was observed using a scanning electron microscope (SEM) to evaluate the developability and the pattern integrity. 
     The developability was evaluated according to the following criteria: 
     ∘: No residue was observed in unexposed portions; 
     ⊚: A small amount of residue was observed in unexposed portions, but the residue is acceptable; 
     •: Significant residue was observed in unexposed portions. 
     The pattern integrity was evaluated according to the following criteria: 
     ⋄: No pattern defects were observed; 
     □: A few defects were observed in some portions of the pattern; 
     ♦: A number of defects were significantly observed in the pattern. 
     (4) Thermal Stability 
     The change of the film thickness before and after hard baking was measured using a thickness measurer to evaluate the thermal stability of the material. 
     Evaluation results were as shown in Table 2 and Table 3: 
     
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Photocurable composition A 
               
             
          
           
               
                   
                   
                   
                 Demand 
                   
                   
                 Thickness 
                 Thickness 
                   
               
               
                   
                   
                   
                 of 
                   
                   
                 before 
                 after 
                 Change 
               
               
                   
                   
                 Storage 
                 exposure 
                   
                 Pattern 
                 hard 
                 hard 
                 of film 
               
               
                   
                 Photoinitiator 
                 stability 
                 mJ/cm 2   
                 Developability 
                 integrity 
                 baking 
                 baking 
                 thickness 
               
               
                   
                   
               
             
          
           
               
                 Example 
                 Compound 1 
                 A 
                 55 
                 ◯ 
                 ⋄ 
                 2.1 
                 2.0 
                 4.8%  
               
               
                   
                 Compound 3 
                 A 
                 53 
                 ◯ 
                 ⋄ 
                 2.0 
                 1.9 
                  5% 
               
               
                   
                 Compound 5 
                 A 
                 51 
                 ◯ 
                 ⋄ 
                 2.0 
                 1.9 
                  5% 
               
               
                   
                 Compound 
                 A 
                 48 
                 ◯ 
                 ⋄ 
                 1.9 
                 1.8 
                 5.2%  
               
               
                   
                 10 
               
               
                   
                 Compound 
                 A 
                 40 
                 ◯ 
                 ⋄ 
                 2.1 
                 2.0 
                 4.8%  
               
               
                   
                 12 
               
               
                   
                 Compound 
                 A 
                 32 
                 ◯ 
                 ⋄ 
                 2.0 
                 1.9 
                  5% 
               
               
                   
                 13 
               
               
                 Comparative 
                 PBG-304 
                 A 
                 70 
                 ⊚ 
                 □ 
                 2.0 
                 1.7 
                 15% 
               
               
                 Example 
                 OXE-01 
                 B 
                 105 
                 ⊚ 
                 ♦ 
                 2.0 
                 1.6 
                 20% 
               
               
                   
                 OXE-02 
                 B 
                 85 
                 ⊚ 
                 ♦ 
                 2.0 
                 1.6 
                 20% 
               
               
                   
                 Irgacure907 
                 C 
                 160 
                 ● 
                 ♦ 
                 2.1 
                 1.4 
                 33% 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Photocurable composition B 
               
             
          
           
               
                   
                   
                   
                 Demand 
                   
                   
                 Thickness 
                 Thickness 
                   
               
               
                   
                   
                   
                 of 
                   
                   
                 before 
                 after 
                 Change 
               
               
                   
                   
                 Storage 
                 exposure 
                   
                 Pattern 
                 hard 
                 hard 
                 of film 
               
               
                   
                 Photoinitiator 
                 stability 
                 mJ/cm 2   
                 Developability 
                 integrity 
                 baking 
                 baking 
                 thickness 
               
               
                   
               
             
          
           
               
                 Example 
                 Compound 1 
                 A 
                 60 
                 ◯ 
                 ⋄ 
                 2.0 
                 1.9 
                  5% 
               
               
                   
                 Compound 3 
                 A 
                 58 
                 ◯ 
                 ⋄ 
                 2.0 
                 1.9 
                  5% 
               
               
                   
                 Compound 5 
                 A 
                 56 
                 ◯ 
                 ⋄ 
                 2.1 
                 2.0 
                 4.8%  
               
               
                   
                 Compound 
                 A 
                 53 
                 ◯ 
                 ⋄ 
                 2.0 
                 1.9 
                  5% 
               
               
                   
                 10 
               
               
                   
                 Compound 
                 A 
                 46 
                 ◯ 
                 ⋄ 
                 2.1 
                 2.0 
                 4.8%  
               
               
                   
                 12 
               
               
                   
                 Compound 
                 A 
                 40 
                 ◯ 
                 ⋄ 
                 2.0 
                 1.9 
                  5% 
               
               
                   
                 13 
               
               
                 Comparative 
                 PBG-304 
                 A 
                 88 
                 ⊚ 
                 □ 
                 2.1 
                 1.9 
                 9.5%  
               
               
                 Example 
                 OXE-01 
                 B 
                 117 
                 ⊚ 
                 ♦ 
                 1.9 
                 1.6 
                 21% 
               
               
                   
                 OXE-02 
                 B 
                 98 
                 ⊚ 
                 ♦ 
                 2.0 
                 1.8 
                 10% 
               
               
                   
                 Irgacure907 
                 C 
                 176 
                 ● 
                 ♦ 
                 2.1 
                 1.6 
                 24% 
               
               
                   
               
             
          
         
       
     
     In Table 2 and Table 3, PBG-304 represents a photoinitiator, 1-(6-o-methylbenzoyl-9-ethylcarbazol-3-yl)-(3-cyclopentylacetone)-1-oxime-acetate, disclosed in CN101508744A; OXE-01 represents 1-(4-phenylthio-phenyl)-octan-1,2-dione-2-oxime-O-benzoate; OXE-02 represents 1-(6-o-methylbenzoyl-9-ethylcarbazol-3-yl)-(3-ethanone)-1-oxime-acetate; and Irgacure907 represents 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-propane-1-one. 
     It can be seen from the results of Table 2 and Table 3 that the photocurable composition comprising the bisoxime ester photoinitiator represented by the general formula (I) of this invention has good storage stability, exhibits extremely good photosensitivity, developability, and pattern integrity in both colorless systems and pigment systems, and has a thermal stability obviously superior to those of existing photoinitiators. By comparison, there are significant shortages for PBG-304, OXE-01, OXE-02, and Irgacure 907 in aspects of storage stability, photosensitivity, developability, pattern integrity, and thermal stability. 
     In summary, the bisoxime ester photoinitiator represented by the general formula (I) disclosed by this invention has excellent application performances, and can greatly improve the performances of photocured products when used in photocurable compositions.