A polyimide resin containing a photosensitive group and an ultraviolet light-cured coating based thereon

Abstract

The application discloses a polyimide resin containing a photosensitive group and an ultraviolet light curing coating based on the same, and belongs to the technical field of ultraviolet light curing coatings. The application adopts a ternary copolymerization hydroxyl-containing polyimide as a matrix, and adopts a blue light normal-temperature induced diazo monomer carbene insertion reaction to complete photosensitive grafting; the process does not need a catalyst, a polymerization inhibitor and high-temperature heating, has mild reaction conditions, few side reactions and low energy consumption. The application compounding an active diluent and a multifunctional acrylate crosslinking agent, optimizing a coating ratio system, and the obtained coating can be rapidly cured into a film by ultraviolet light, the coating has excellent heat resistance of polyimide, and simultaneously has excellent substrate adhesion, flexibility and heat resistance, the process is green and simple, and is suitable for high-end protection, electronic insulation and ultraviolet light curing coating scenes.

Description

Technical Field

[0001] This invention relates to the field of ultraviolet curable coating technology, and more particularly to a polyimide resin containing photosensitive groups and an ultraviolet curable coating based thereon. Background Technology

[0002] Polyimide (PI) is a class of high-performance polymer materials with excellent heat resistance, chemical corrosion resistance, dimensional stability, and mechanical properties. However, traditional polyimide materials often suffer from problems such as high processing temperatures, limited solubility, and harsh curing conditions, which increase production costs and limit their further application in the field of low-temperature rapid curing coatings.

[0003] UV curing technology boasts advantages such as rapid curing speed, low energy consumption, environmental friendliness, and suitability for continuous processing, making it a crucial development direction in the field of functional coatings. However, conventional UV-curable coatings are mostly based on acrylate resins, whose heat resistance, chemical resistance, and dimensional stability often fail to meet the requirements for high-performance protective coatings. Photosensitive polyimides, while retaining the excellent comprehensive properties of polyimides, also possess photosensitive characteristics, enabling rapid molding through UV curing technology. Therefore, incorporating photosensitive polyimide structures into UV-curable coating systems is an important approach to improving the overall performance of UV-curable coatings.

[0004] One common strategy for preparing photosensitive polyimides is to graft photosensitive units containing unsaturated double bonds (such as acrylates and methacrylates) onto the polyimide backbone or side chains. A typical chemical route for introducing photosensitive double bonds is to utilize the ring-opening reaction between the hydroxyl groups of the polyimide side chains and the epoxy groups of glycidyl methacrylate (GMA). This type of method usually requires a catalyst to promote the epoxy ring-opening reaction. Furthermore, to prevent the methacrylate double bonds from undergoing thermal polymerization or self-polymerization during grafting, polymerization inhibitors are needed to control side reactions. In the aforementioned traditional grafting process, the reaction generally requires heating at a certain temperature for several hours, resulting in a long reaction time, high energy consumption, and relatively complex process steps. Moreover, while the addition of catalysts and polymerization inhibitors helps the grafting reaction and stabilize the unsaturated double bonds, it may also introduce new problems. On the one hand, the residues of catalysts and polymerization inhibitors may affect the efficiency of subsequent photocuring reactions, the appearance and performance of the coating; on the other hand, prolonged heating reactions may lead to partial consumption of unsaturated double bonds, degradation of resin molecular chains or increase in system viscosity, thereby affecting the structural controllability of photosensitive polyimide resins and the processing performance of subsequent coatings.

[0005] Therefore, developing a novel photosensitive polyimide grafting method that requires no catalysts or polymerization inhibitors and operates under mild and rapid reaction conditions remains a pressing technical challenge in this field. Summary of the Invention

[0006] To address the shortcomings of existing photosensitive polyimide preparation processes, such as the need for catalysts and polymerization inhibitors, high-temperature and long-term heating, complex processes, and susceptibility to side reactions, this invention provides a polyimide resin containing photosensitive groups and a UV-curable coating based thereon. By employing a photosensitive active monomer containing an aryl diazonium ester group, the grafting functionalization of polyimide is achieved through a mild photochemical reaction, aiming to simplify the preparation process, improve product purity, and reduce energy consumption and the risk of side reactions.

[0007] To achieve its objectives, the present invention employs the following technical solution: This invention first provides a polyimide resin containing photosensitive groups, characterized in that the polyimide resin containing photosensitive groups is prepared by grafting a hydroxyl-containing polyimide with a photosensitive active monomer containing a diazo group; the molecular structure of the photosensitive active monomer containing a diazo group is shown in formula (1), formula (2) or formula (3): (1); (2); (3).

[0008] The grafting reaction mechanism is as follows: the aryl diazonium ester structure in the photosensitive active monomer containing the diazonium group undergoes photolysis under blue light irradiation, releasing nitrogen gas and generating an aryl ester carbene active intermediate; the aryl ester carbene active intermediate undergoes an OH insertion reaction with the phenolic hydroxyl group in the hydroxyl-containing polyimide to form an ether bond (COC), thereby realizing the grafting of the photosensitive active monomer onto the polyimide molecular chain.

[0009] Preferably, the grafting reaction method is as follows: dissolving a hydroxyl-containing polyimide in a solvent, adding a photosensitive active monomer containing a diazo group, mixing thoroughly, and then carrying out a grafting reaction under blue light irradiation to obtain the polyimide resin containing the photosensitive group. More preferably, the power of the blue light source is 30-40 W, the irradiation time is 18-24 h, the reaction temperature is room temperature, and the solvent is N-methylpyrrolidone.

[0010] The hydroxyl-containing polyimide is prepared by polycondensation and imidization reaction of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2'-bis(trifluoromethyl-4,4'-diaminobiphenyl) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and the structure of the hydroxyl-containing polyimide is shown in formula (4): (4).

[0011] Preferably, the photosensitive active monomer containing a diazonium group is a photosensitive active monomer containing a diazonium group with a molecular structure as shown in formula (1) (i.e., 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester). The photosensitive polyimide resin is prepared by reacting a hydroxyl-containing polyimide with a structure as shown in formula (4) with a 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester with a structure as shown in formula (1). The photosensitive polyimide resin has a structure as shown in formula (5). (5).

[0012] Preferably, the photosensitive active monomer containing the diazo group is prepared using a classic synthetic process for aromatic diazo compounds. For example, a photosensitive active monomer containing a diazonium group (i.e., 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester) with the structural formula shown in formula (1) is prepared as follows: 1 equivalent of 4-hydroxybutylacrylate and 1.1 equivalent of 4-nitrophenylacetic acid are taken in molar equivalents, and acetonitrile is used as solvent, 0.33 equivalents of 4-dimethylaminopyridine is used as catalyst, and 1.1 equivalents of 1-ethyl(3-dimethylaminopropyl)carbodiimide hydrochloride is used as condensing agent. After mixing in an ice-water bath at 0-5°C, the mixture is condensed at room temperature for 8-12 h. After concentration under reduced pressure, the mixture is purified by silica gel column chromatography to obtain the intermediate p-nitrobenzyl acetate. Then, 1 equivalent of the above intermediate and 1.1 equivalents of p-toluenesulfonyl azide are dissolved in acetonitrile, and the temperature is controlled at 0-5°C in an ice-water bath. 1 equivalent of triethylamine is added dropwise, and the mixture is stirred at low temperature for 5-10 min, then the temperature is raised to room temperature and reacted for 8-12 h. h, after concentration under reduced pressure and purification by silica gel column chromatography, 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester was obtained.

[0013] The present invention further provides a UV-curable coating comprising the polyimide resin containing photosensitive groups as described above. By weight, the raw materials of the UV-curable coating are: 25-30 parts of the polyimide resin containing photosensitive groups, 50-65 parts of the reactive diluent, 10-25 parts of the crosslinking agent, 1-2 parts of the silane coupling agent, and 2-3 parts of the photoinitiator.

[0014] Preferably, the reactive diluent comprises at least one of 1-vinyl-2-pyrrolidone, hydroxyethyl acrylate, butyl acrylate, isobornyl acrylate, and N,N-dimethylacrylamide; the crosslinking agent comprises at least one of ethylene glycol diacrylate, tripropylene glycol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol diacrylate, and 1,6-hexanediol diacrylate; the silane coupling agent comprises at least one of KH-560 (γ-glycidoxypropyltrimethoxysilane), KH-580 (γ-mercaptopropyltrimethoxysilane), KH-550 (γ-aminopropyltriethoxysilane), and KH-570 (γ-methacryloyloxypropyltrimethoxysilane); and the photoinitiator comprises Irgacure 819 (phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide), Irgacure 184 (1-hydroxycyclohexylphenyl ketone), and Darocur. At least one of 1173 (2-hydroxy-2-methyl-1-phenyl-1-propanone) and Darocur TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide).

[0015] The method for preparing the UV-curable coating of the present invention is as follows: placing the polyimide resin containing photosensitive groups, reactive diluent, crosslinking agent, silane coupling agent and photoinitiator in a light-proof container and stirring magnetically until they are mixed evenly, thereby obtaining the UV-curable coating.

[0016] The present invention also provides an ultraviolet curable coating, which is obtained by ultraviolet curing the above-mentioned ultraviolet curable coating.

[0017] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. This invention is the first to use a blue light-induced grafting method of diazo compounds, which has the following significant advantages compared with the traditional high-temperature catalytic grafting process: ① No catalyst needs to be added, avoiding the impact of catalyst residue on coating performance; ② No polymerization inhibitor needs to be added, simplifying the post-processing process; ③ No long-term high-temperature heating is required, and grafting can be completed at room temperature by blue light irradiation, resulting in low energy consumption and high efficiency; ④ The grafting process is gentle, which can effectively avoid the degradation of the PI main chain and the side reaction of double bond self-polymerization.

[0018] 2. This invention systematically optimizes the formulation of photocurable coatings, investigates the effect of the amount of crosslinking agent 1,6-hexanediol diacrylate added on the coating performance, and screens out the optimal formulation combination. The coating with this formulation has the best comprehensive performance, providing experimental basis for the formulation design of photocurable coatings.

[0019] 3. This invention uses a copolymer of fluorinated diamine (2,2'-bis(trifluoromethyl-4,4'-diaminobiphenyl) and hydroxyl-containing diamine (2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane) to impart good solubility and low dielectric constant to the polyimide backbone, while the hydroxyl groups provide reaction sites for subsequent grafting of photosensitive groups.

[0020] 4. The photosensitive polyimide coating prepared by the present invention can be rapidly cured by ultraviolet light, and the cured coating has excellent adhesion, heat resistance, mechanical properties and low dielectric constant. Attached Figure Description

[0021] Figure 1 The image shows the FT-IR spectrum of the hydroxyl-containing polyimide prepared in Example 1 of this invention.

[0022] Figure 2 The results of cross-cut tests on the four groups of coatings prepared in Example 2 of this invention are shown.

[0023] Figure 3 The TGA images are of the four coatings prepared in Example 2 of this invention.

[0024] Figure 4 The dielectric constant diagrams are for the four coatings prepared in Example 2 of this invention.

[0025] Figure 5 The dielectric loss factor diagrams are for the four groups of coatings prepared in Example 2 of the present invention.

[0026] Figure 6 The photosensitive active monomer containing a diazo group prepared in Example 3 of this invention 1 H NMR spectrum.

[0027] Figure 7 The image shows the FT-IR image of the blue light-induced diazo-grafted photosensitive polyimide prepared in Example 3 of this invention.

[0028] Figure 8 The blue light-induced diazo-grafted photosensitive polyimide prepared in Example 3 of this invention 1 H NMR spectrum.

[0029] Figure 9 The results are cross-cut test results of the coatings obtained in Examples 2 (PSPI-3), 3 and the comparative examples of the present invention.

[0030] Figure 10 The TGA images are of the coatings obtained in Embodiment 2 (PSPI-3), Embodiment 3, and the comparative example of the present invention.

[0031] Figure 11 The dielectric constant diagrams are for the coatings obtained in Example 2 (PSPI-3), Example 3, and the comparative example.

[0032] Figure 12 The dielectric loss factor diagrams are for the coatings obtained in Example 2 (PSPI-3), Example 3, and the comparative example. Detailed Implementation

[0033] The present invention will be further described below with reference to the embodiments. All raw materials used in the embodiments were purchased through commercial channels, and the test methods are conventional methods unless otherwise specified.

[0034] The performance testing methods for the UV-cured coatings obtained in the following examples are as follows: Adhesion: Tested according to national standard GB / T 9286-1998; Flexibility: Tested according to the national standard GB / T1731-2020 "Determination of Flexibility of Paint Film and Putty Film"; Thermogravimetric analysis: Tests were performed using a STA449F3 thermogravimetric analyzer from Netzsch GmbH, Germany. Dielectric analysis: The dielectric analysis was performed using a Concept 40 broadband dielectric impedance spectrometer from Novocontrol GmbH, Germany, in accordance with GB / T 1409-2006 standard.

[0035] Example 1 This embodiment provides a method for preparing a hydroxyl-containing polyimide matrix, the specific steps of which are as follows: N-methylpyrrolidone was added to a 250 mL three-necked flask. Under a nitrogen atmosphere, 4.395 g (12 mmol) of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 3.843 g (12 mmol) of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl were added separately. The mixture was magnetically stirred for 2 h to ensure homogeneity of the two monomers. Then, under an ice-water bath, 7.888 g (24 mmol) of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride was added in portions, and stirring was continued for 24 h to obtain a clear, yellow solution.

[0036] The reaction system temperature was increased using a gradient polymerization process: 100℃+1 h, 120℃+1 h, 160℃+1 h, 205℃+8 h, to obtain a hydroxyl-containing polyimide solution. After the solution cooled to room temperature, it was slowly poured into ethanol to precipitate the precipitate. The solution was allowed to stand, the supernatant was discarded, and the mixture was washed 2-3 times alternately with deionized water and anhydrous ethanol. Finally, it was dried in a vacuum oven at 50℃ for 24 h to obtain the hydroxyl-containing polyimide resin.

[0037] The infrared image of the hydroxyl-containing polyimide resin obtained in this embodiment is as follows: Figure 1 As shown, at 1785 cm -1 1725 cm -11370 cm -1 725 cm -1 The appearance of new, sharp, and strong characteristic peaks indicates that the carbonyl (C=O) in the imide ring undergoes asymmetric stretching, symmetric stretching, CN stretching vibration, and carbonyl bending vibration in the imide ring, respectively. This suggests that the polyamic acid underwent a ring-closure dehydration reaction, and PI was successfully synthesized.

[0038] Example 2 This embodiment provides a UV-curable coating for GMA-grafted photosensitive polyimide, and the specific preparation steps are as follows: Step 1: Preparation of GMA-grafted photosensitive polyimide After cooling the hydroxyl-containing polyimide solution prepared in Example 1 to room temperature, 0.085 g of triphenylphosphine catalyst, 2.56 g of glycidyl methacrylate and 0.085 g of hydroquinone inhibitor were added. The mixture was reacted at 100°C for 5 h. After cooling to room temperature, the solution was slowly poured into ethanol to precipitate the polyimide. After standing, the supernatant was discarded. The polyimide was washed 2-3 times alternately with deionized water and anhydrous ethanol. After drying in a vacuum oven at 50°C for 24 h, GMA-grafted photosensitive polyimide was obtained, and its structural formula is shown in formula (6). (6).

[0039] Step 2: Preparation of UV-curable coatings based on GMA-grafted photosensitive polyimide By weight, 25 parts of the GMA-grafted photosensitive polyimide resin prepared in Example 2, a certain amount of reactive diluent N,N-dimethylacrylamide, a certain amount of 1,6-hexanediol diacrylate, 10 parts of polyethylene glycol diacrylate, 1.5 parts of KH-570, and 2.5 parts of Irgacure 819 were placed in a light-proof container and magnetically stirred until uniformly mixed to obtain a UV-curable coating.

[0040] Step 3: Prepare UV-curable coating After the tinplate is polished, the above coating is applied to the tinplate surface by scraping to form a film. After drying in an oven at 80°C for 3 hours, it is irradiated with a 365 nm wavelength ultraviolet lamp for 10 minutes to cure into a 100 μm thick coating.

[0041] The reactive diluent N,N-dimethylacrylamide was used in amounts of 61 parts, 56 parts, 51 parts, and 46 parts, respectively, with a total amount of N,N-dimethylacrylamide and 1,6-hexanediol diacrylate of 61 parts. The resulting coatings were named PSPI-1, PSPI-2, PSPI-3, and PSPI-4, respectively. The performance test results of the resulting coatings are shown in Table 1 and [Table data would be inserted here]. Figures 2-5 .

[0042] Table 1 From Table 1 and Figure 2 It can be seen that as the amount of reactive diluent N,N-dimethylacrylamide changes, the coating adhesion and flexibility exhibit regular changes.

[0043] Regarding adhesion, when the reactive diluent dosage was 61 parts, the coating adhesion was grade 1; when reduced to 56 parts, the adhesion improved to grade 0; when further reduced to 51 parts, it still maintained the optimal adhesion grade of 0; however, when further reduced to 46 parts (i.e., the reactive diluent dosage was too low, and the relative proportion of crosslinking agent increased), the adhesion dropped to grade 1. The reason for this is that when the reactive diluent dosage was too low, the viscosity of the coating system increased, reducing its wettability to the substrate. Simultaneously, the excessively high crosslinking density led to increased internal stress in the coating, weakening the interfacial bonding between the coating and the substrate. When the reactive diluent dosage was 56 and 51 parts, the system had a moderate crosslinking density and good fluidity, which could fully wet the substrate surface, resulting in a good interfacial bond between the coating and the substrate after curing.

[0044] In terms of flexibility, all four formulations achieved an optimal flexibility of 0 mm. This indicates that the requirements for highly flexible coatings can be met within the formulation range, thanks to the excellent molecular chain flexibility of the polyimide backbone and the moderate crosslinking density of the system.

[0045] Depend on Figure 3 It can be seen that as the amount of reactive diluent N,N-dimethylacrylamide changes, and the amount of crosslinking agent 1,6-hexanediol diacrylate increases from 0 to 15 parts, the 5% weight loss temperature (Td5) of the coating increases from 251℃ to 280℃, and the 10% weight loss temperature (Td5) decreases. 10 The temperature was increased from 350℃ to 375℃, and the carbon residue Rw at 800℃ increased from 36.9% to 37.9%. This indicates that increasing the amount of crosslinking agent can effectively improve the crosslinking density of the coating, thereby significantly improving its thermal stability.

[0046] Depend on Figure 4 It was found that as the amount of reactive diluent N,N-dimethylacrylamide decreased from 61 parts to 46 parts (i.e., the amount of crosslinking agent 1,6-hexanediol diacrylate increased from 0 to 15 parts), the dielectric constant of the coating showed a decreasing trend. Increasing the amount of crosslinking agent increased the crosslinking density of the coating, restricted the movement of polymer chain segments, and reduced the polarization response, thereby lowering the dielectric constant. This result indicates that the dielectric properties of the coating can be effectively optimized by controlling the amount of crosslinking agent.

[0047] Figure 5The results show that the coatings obtained from each formulation have low dielectric loss factors. The dielectric loss did not increase significantly with changes in the crosslinking agent content, indicating that the cured crosslinked network structure is uniform and stable, which is beneficial for reducing polarization loss and improving the material's performance in high-frequency electric fields.

[0048] comprehensive Figures 2-5 As shown in Table 1, the test results indicate that different ratios of reactive diluent and crosslinking agent have a significant impact on the overall performance of the UV-cured coating. With the increase of 1,6-hexanediol diacrylate content, the thermal stability of the coating gradually improves, with the 5% weight loss temperature (Td5) and 10% weight loss temperature (Td...) decreasing. 10 Both the adhesion and residual char rate showed an upward trend; meanwhile, all formulations maintained good flexibility and low dielectric constant and dielectric loss. Regarding adhesion, both PSPI-2 and PSPI-3 achieved grade 0, but PSPI-3, while maintaining excellent adhesion and flexibility, exhibited higher thermal stability and more balanced dielectric properties. Therefore, considering factors such as adhesion, flexibility, thermal stability, and dielectric properties, PSPI-3 was selected as the optimal formulation for the subsequent preparation and performance evaluation of blue light-induced diazo-grafted photosensitive polyimide UV-curable coatings, to ensure the accuracy and consistency of the coating performance comparison under different grafting processes.

[0049] Example 3 This embodiment provides a UV-curable coating based on blue light-induced diazo-grafted photosensitive polyimide. The specific preparation steps are as follows: Step 1: Preparation of a photosensitive active monomer containing a diazonium group: 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester First, 4-hydroxybutyl acrylate (20 mmol, 1.0 equivalent), 4-nitrophenylacetic acid (22 mmol, 1.1 equivalent), and 4-dimethylaminopyridine (6.6 mmol, 0.33 equivalent) were added to a 250 mL round-bottom flask. Acetonitrile (100 mL) was then added as a solvent, and the resulting solution was cooled to 0 °C with stirring in an ice-water bath. Next, 1-ethyl(3-dimethylaminopropyl)carbodiimide hydrochloride (22 mmol, 1.1 equivalent) was added in a single batch, and the mixture was stirred at 0 °C for 10 min before the cooling bath was removed. The reaction proceeded at room temperature for 12 h. After the starting materials were completely consumed, the mixture was concentrated under reduced pressure to remove volatiles. Purification was performed by silica gel rapid column chromatography to finally obtain the intermediate p-nitrobenzyl acetate, a pale yellow oil (3.56 g, 58%). Subsequently, p-nitrobenzyl acetate (15 mmol, 1 equivalent) and p-toluenesulfonyl azide (16.5 mmol, 1.1 equivalent) were added sequentially to a 250 mL round-bottom flask, followed by 100 mL of acetonitrile as the reaction solvent. The mixture was cooled to 0–5 °C and placed in an ice-water bath and maintained at this temperature. Then, triethylamine (15 mmol, 1 equivalent) was added dropwise through a constant-pressure feeding funnel under magnetic stirring. After complete addition, the reaction was maintained at 0 °C for 10 min. The ice-water bath was then removed, and the mixture was gradually heated to room temperature (20–25 °C) and stirred for 10 h. The crude mixture was concentrated under reduced pressure to remove volatiles, and the residue was then purified by silica gel flash column chromatography to give 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester, a yellow solid (3.4 g, 69% yield).

[0050] Figure 6 It is 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester 1 The 1H NMR spectrum shows characteristic signal peaks for acrylate double bond protons, aromatic ring protons, and aliphatic chain methylene protons. The positions of these peaks are consistent with the structure of the target product, indicating that a photosensitive active monomer containing a diazo group has been successfully synthesized.

[0051] Step 2: Preparation of blue light-induced diazo-grafted photosensitive polyimide After cooling the polyimide solution prepared in Example 1 to room temperature, 1.5 equivalents of the diazo-group-containing photosensitive monomer prepared in Step 2 were slowly added under magnetic stirring. After stirring evenly, the solution was irradiated with a 40 W blue light source at room temperature for 24 hours. After the reaction was completed, the solution was slowly poured into ethanol to precipitate, allowed to stand, the supernatant was discarded, and then washed 2-3 times with anhydrous ethanol before drying in a vacuum oven at 50°C for 24 hours to obtain diazo-grafted photosensitive polyimide.

[0052] Figure 7 This indicates that the grafted product retains the characteristic absorption peaks of the polyimide structure, and also exhibits peaks at 1630 and 870 cm⁻¹. -1 New characteristic peaks appeared at each grafting point, namely the stretching vibration peak of the acrylate double bond (C=C) and the out-of-plane bending vibration peak of the p-nitrobenzene ring (CH), confirming that the diazo-photosensitive active monomer was successfully introduced into the polyimide molecular chain. The characteristic peaks of the imide ring did not change significantly, indicating that the polyimide backbone structure remained intact during the grafting process.

[0053] Figure 8The results showed that, in addition to retaining the original aromatic hydrogen signal, the grafted polyimide also exhibited a new characteristic peak at δ 5.7-6.5 ppm, which is attributed to the double bond of the photosensitive monomer acrylate. This proved that the photosensitive group had been successfully grafted onto the polyimide molecular chain, thereby endowing the material with UV curing capability.

[0054] Step 3: Preparation of UV-curable coatings based on blue light-induced diazo-grafted photosensitive polyimide By weight, 25 parts of the GMA-grafted photosensitive polyimide resin prepared in Example 2, 51 parts of the reactive diluent N,N-dimethylacrylamide, 10 parts of 1,6-hexanediol diacrylate, 10 parts of polyethylene glycol diacrylate, 1.5 parts of KH-570, and 2.5 parts of Irgacure 819 were placed in a light-proof container and magnetically stirred until uniformly mixed to obtain a UV-curable coating.

[0055] Step 4: Prepare UV-curable coating After the tinplate is polished, the above-mentioned coating is applied to the tinplate surface by scraping to form a film. After drying in an oven at 80°C for 3 hours, it is irradiated with a 365 nm wavelength ultraviolet lamp for 10 minutes to cure into a 100 μm thick coating. Testing showed that the adhesion and flexibility of the coating obtained in this embodiment were both grade 0.

[0056] Comparative Example This comparative example prepared a UV-curable coating based on pure polyimide without grafted photosensitive reactive monomers, as follows: By weight, 25 parts of the hydroxyl-containing polyimide resin prepared in Example 1, 51 parts of the reactive diluent N,N-dimethylacrylamide, 10 parts of 1,6-hexanediol diacrylate, 10 parts of polyethylene glycol diacrylate, 1.5 parts of KH-570, and 2.5 parts of Irgacure 819 were placed in a light-proof container and magnetically stirred until uniformly mixed to obtain a UV-curable coating.

[0057] After the tinplate was polished, the above-mentioned coating was applied to the tinplate surface by scraping to form a film. After drying in an oven at 80°C for 3 hours, it was irradiated with a 365 nm wavelength ultraviolet lamp for 10 minutes to cure into a 100 μm thick coating. Tests showed that the coating obtained in this comparative example had an adhesion grade of 3 and a flexibility grade of 5.

[0058] The performance of the PSPI-3 coating obtained in Example 2 and the coatings obtained in Example 3 and the comparative examples were compared, and the results are as follows: Figures 9-12 As shown.

[0059] Figure 10The results show that both GMA-grafted photosensitive polyimide and blue light-induced diazo-grafted photosensitive polyimide coatings exhibit high thermal decomposition temperatures and low char residues, demonstrating excellent thermal stability. In particular, the blue light-induced diazo-grafting system maintains high thermal stability while avoiding potential side reactions associated with traditional high-temperature grafting processes.

[0060] Figure 11 The results show that both photosensitive polyimide coatings maintain a low dielectric constant. The fluorinated polyimide backbone structure effectively reduces the material's polarization ability, resulting in coatings with excellent electrical insulation properties, which can meet the application requirements of microelectronic packaging and insulation protection.

[0061] Figure 12 The results show that both photosensitive polyimide coatings have low dielectric loss factors, indicating low internal polarization loss and stable electrical properties. The blue light-induced diazo grafting system maintains comparable dielectric properties to the traditional GMA grafting system, demonstrating that the blue light-induced diazo grafting process simplifies the preparation process and avoids catalyst / inhibitor residues without sacrificing the coating's dielectric properties. In fact, it may exhibit more stable dielectric response characteristics due to improved product purity.

[0062] comprehensive Figures 9-12 The comparative test results show that the polyimide system without photosensitive groups cannot form an effective UV-curable network structure, resulting in a significant decrease in coating adhesion and flexibility. However, after grafting photosensitive groups, the polyimide can rapidly crosslink and cure under UV irradiation, forming a stable and dense three-dimensional network structure, thereby significantly improving the coating's adhesion, mechanical properties, and thermal stability. In particular, the blue light-induced diazo grafting process proposed in this invention can achieve comprehensive performance comparable to or even better than the traditional GMA grafting system without the need for catalysts, polymerization inhibitors, or high-temperature heating, verifying the feasibility and advancement of the technical solution of this invention.

[0063] Table 2 Comparison of two photosensitive polyimide preparation processes The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A polyimide resin containing photosensitive groups, characterized in that, The polyimide resin containing photosensitive groups is prepared by grafting hydroxyl-containing polyimide with a photosensitive active monomer containing diazo groups. The grafting reaction is as follows: the aryl diazonium ester structure in the photosensitive active monomer containing the diazonium group generates an aryl ester carbene active intermediate under blue light irradiation. The aryl ester carbene active intermediate undergoes an OH insertion reaction with the phenolic hydroxyl group in the hydroxyl-containing polyimide to form an ether bond COC connection, thereby grafting the photosensitive active monomer onto the polyimide backbone.

2. The polyimide resin containing photosensitive groups according to claim 1, characterized in that, The molecular structure of the photosensitive active monomer containing the diazonium group is shown in formula (1), formula (2) or formula (3): （1）； （2）； （3）。 3. The polyimide resin containing photosensitive groups according to claim 2, characterized in that, The hydroxyl-containing polyimide is prepared by polycondensation and imidization reaction of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.

4. The polyimide resin containing photosensitive groups according to claim 3, characterized in that, The photosensitive active monomer containing the diazonium group is 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester with the molecular structure shown in formula (1). Its preparation method is as follows: Take 1 equivalent of 4-hydroxybutyl acrylate and 1.1 equivalent of 4-nitrophenylacetic acid in molar equivalents, using acetonitrile as solvent, 0.33 equivalents of 4-dimethylaminopyridine as catalyst, and 1.1 equivalents of 1-ethyl(3-dimethylaminopropyl)carbodiimide hydrochloride as condensing agent. After mixing in an ice-water bath at 0-5°C, the mixture undergoes a condensation reaction at room temperature for 8-12 h. After concentration under reduced pressure, the mixture is purified by silica gel column chromatography to obtain the intermediate p-nitrobenzyl acetate. Then, take 1 equivalent of the intermediate p-nitrobenzyl acetate and 1.1 equivalents of p-toluenesulfonyl azide, dissolve them in acetonitrile, and control the temperature in an ice-water bath at 0-5°C. Add 1 equivalent of triethylamine dropwise, stir at low temperature for 5-10 min, and then raise the temperature to room temperature for 8-12 h. h, after concentration under reduced pressure and purification by silica gel column chromatography, 4-(acryloyloxy)butyl-2-(4-nitrophenyl)-2-diazoacetic acid ester was obtained.

5. The polyimide resin containing photosensitive groups according to claim 1 or 4, characterized in that, The grafting reaction method is as follows: dissolve hydroxyl-containing polyimide in a solvent, add a photosensitive active monomer containing a diazo group, mix evenly, and then carry out a grafting reaction under blue light irradiation to obtain the polyimide resin containing the photosensitive group.

6. The preparation method according to claim 5, characterized in that, The power of the blue light source is 30-40W, the irradiation time is 18-24 h, and the reaction temperature is room temperature; the solvent is N-methylpyrrolidone.

7. A UV-curable coating, characterized in that, Includes the polyimide resin containing photosensitive groups as described in any one of claims 1 to 6.

8. The UV-curable coating according to claim 7, characterized in that, By weight, the raw materials of the UV-curable coating are as follows: 25-30 parts of polyimide resin containing photosensitive groups, 50-65 parts of reactive diluent, 10-25 parts of crosslinking agent, 1-2 parts of silane coupling agent, and 2-3 parts of photoinitiator.

9. A method for preparing the UV-curable coating as described in claim 8, characterized in that: The polyimide resin containing photosensitive groups, reactive diluent, crosslinking agent, silane coupling agent, and photoinitiator are placed in a light-proof container and magnetically stirred until uniformly mixed to obtain the UV-curable coating.

10. A UV-curable coating, characterized in that, It is obtained by UV curing the UV-curable coating as described in claim 7 or 8.

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