Liquid phthalocyanine resin monomer capable of being pre-cured by ultraviolet light at room temperature as well as preparation method and application of liquid phthalocyanine resin monomer

Abstract

The invention discloses a liquid phthalocyanine resin monomer capable of being pre-cured by ultraviolet light at room temperature as well as a preparation method and application thereof, and belongs to the fields of high polymer materials and composite materials. The preparation method of the phthalocyanine resin monomer comprises the following steps: under the protection of inert gas, dissolving a phthalonitrile monomer containing a phenolic hydroxyl group, a catalyst and vinyl halogenated silane in a molar ratio of 1: (2.2-3.2): (1.2-1.4) in a solvent, and reacting at 80-90 DEG C for 12-24 hours to obtain the liquid phthalocyanine resin monomer capable of being pre-cured by ultraviolet light at room temperature. The phthalocyanine resin monomer prepared by the invention has the advantages of low melting point, low initial curing temperature and wide process window, and can realize room-temperature photocuring.

Description

Technical Field

[0001] This invention belongs to the fields of polymer materials and composite materials, specifically a low-melting-point liquid phthalocyanine resin monomer that can be pre-cured at room temperature under ultraviolet light, its preparation method, and its application. Background Technology

[0002] In the 1960s, Marvel first proposed a strategy to prepare high-temperature resistant polymer materials using bis(phthalonitrile). The reaction yielded polymers containing phthalocyanine structures, which significantly improved their heat resistance and received widespread attention and research in the field of high-temperature resin synthesis and preparation.

[0003] Phthalocyanine resin, also known as polyphthalonitrile resin, is a high-temperature resistant organic thermosetting resin obtained by crosslinking phthalonitrile monomers through a high-temperature polyaddition reaction under the action of an external catalyst. During the polyaddition process, no small molecules are generated, significantly reducing stress concentration induced by volatile matter compared to thermosetting resins prepared by polycondensation. The molecular structure of phthalocyanine resin cured products is mainly composed of rigid structures such as conjugated aromatic heterocycles, primarily including isoindoline rings, triazine rings, phthalocyanine rings, and dehydrophthalocyanine rings. The main body of the material belongs to aromatic porphyrin-like compounds (POR), which readily generate π-π stacking interactions. Phthalocyanine resin possesses numerous excellent thermomechanical properties, a high heat distortion temperature, and can be used for extended periods in high-temperature environments.

[0004] The development, design, and mass production of novel polymer materials are a significant indicator of the vigorous development of advanced manufacturing in China. Common phthalonitrile resin monomers are primarily phthalonitrile derivatives containing aromatic heterocyclic structures. Due to the high polarity of the cyano group, the monomers exhibit strong inter-monomer interactions. At room temperature, the monomers are in solid powder form with high melting points, low melt viscosity, and high initial curing temperatures. Once in the molten state, the monomers rapidly initiate cross-linking reactions and enter the gel stage. General-purpose phthalonitrile powder monomers only exhibit superior solubility in high-boiling-point aprotic polar solvents, making them unsuitable for many current polymer molding technologies. Therefore, lowering the monomer melting point, designing and synthesizing low-melting-point liquid phthalonitrile monomers, and achieving room-temperature pre-curing of phthalonitrile resins will significantly promote the development and application of phthalonitrile resins. Summary of the Invention

[0005] To address the technical problems of high melting point, high initial curing temperature, and short process window of phthalonitrile resin monomers in existing technologies, which make it difficult to achieve room temperature UV curing, the main objective of this invention is to provide a novel low-melting-point phthalonitrile monomer that can be pre-cured at room temperature using ultraviolet light, along with its preparation method and applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A liquid phthalocyanine resin monomer that can be pre-cured at room temperature under ultraviolet light, the basic structure of which is shown below:

[0008]

[0009] In this system, R and R' are independent organic substituents, Ar is an aromatic ring structure, and the oxygen atom attached to Ar can be located in the ortho, meta, or para position.

[0010] A method for preparing a room-temperature UV-curable liquid phthalocyanine resin monomer includes the following steps: under inert gas protection, a phenolic hydroxyl-containing phthalonitrile monomer, a catalyst, and a vinyl halosilane are dissolved in a solvent in a molar ratio of 1:2.2-3.2:1.2-1.4 and reacted at 80-90°C for 12-24 hours to obtain a room-temperature UV-curable liquid phthalocyanine resin monomer.

[0011] Furthermore, the phenolic hydroxyl-containing phthalonitrile monomer includes one or more of 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxylon, 4-(4-hydroxyphenoxy)benzene-1,2-dicarboxylon, 4-(4-aldehyde-3-hydroxyphenoxy)benzene-1,2-dicarboxylon, 4-(2'-hydroxyphenoxy)phthalonitrile, and 4-hydroxy-5-methoxybenzene-1,2-dicarboxylon.

[0012] Furthermore, the catalyst comprises one or more of sodium hydride, potassium hydride, lithium diisopropylamino, lithium bis(trimethylsilyl)amino, sodium hexamethyldisilanediazo, sodium carbonate, and potassium carbonate.

[0013] Furthermore, the halogen element in the vinyl halosilane cannot be directly bonded to the silicon atom. The vinyl halosilane includes one or more of vinyl(chloromethyl)dimethylsilane, vinyl(iodomethyl)dimethylsilane, divinyl(chloromethyl)methylsilane, vinyl(bromomethyl)dimethylsilane, chloromethyltrivinylsilane, iodomethyltrivinylsilane, 3-iodopropyldimethylvinylsilane, 3-iodopropyldiallylmethylsilane, and 3-iodopropyldivinylmethylsilane.

[0014] Furthermore, the solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, acetonitrile, dioxane, and xylene.

[0015] An application of the phthalocyanine resin monomer described above or the phthalocyanine resin monomer prepared by the preparation method described above includes the following steps: mixing the phthalocyanine resin monomer with a crosslinking agent, a thiol and a photoinitiator uniformly, and then curing it under ultraviolet light at room temperature to obtain a room temperature ultraviolet light pre-cured phthalocyanine resin, wherein the total molar number of vinyl groups in the phthalocyanine resin monomer and the total molar number of double bonds in the crosslinking agent is equal to the total molar number of thiol groups in the thiol.

[0016] Furthermore, the phthalocyanine resin monomer, crosslinking agent, thiol and photoinitiator are mixed evenly and then ultrasonically mixed for 15-30 minutes; the curing time is 2-5 minutes.

[0017] Furthermore, the crosslinking agent includes one or more of tetravinylsilane, tetramethyltetravinylcyclotetrasiloxane, octavinylPOSS, tetra(4-vinylphenyl)silane, triallyl isocyanurate, and 2,4,6-trivinylcycloboroxane; the thiol includes one or more of pentaerythritol tetramercaptoacetate, pentaerythritol tetra(3-mercaptopropionic acid), propane-1,2,3-trithiol, and trimethylpropane tris(2-mercaptoacetic acid).

[0018] Furthermore, the photoinitiator includes one or a combination of two of 2,2-dimethoxy-2-phenylacetophenone and 2-hydroxy-2-methylacetophenone.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The phthalonitrile resin monomers described in this invention can be applied in the field of polymer materials and can also serve as resin matrices for composite materials. By utilizing the Finkelstein reaction and Williamson etherification reaction, phthalonitrile monomers containing phenolic hydroxyl groups are reacted with halogenated hydrocarbons containing silicon linkages to prepare phthalonitrile monomers containing silicon linkages. The excellent flexibility of the silicon linkages results in a low melting point for the synthesized phthalonitrile monomers, which are liquid at room temperature and can be pre-cured under UV light at room temperature through a click chemistry reaction with thiols, thus partially compensating for the poor processability of current phthalonitrile resins. Simultaneously, the Finkelstein and Williamson etherification reactions have high reaction yields, allowing for the acquisition of high-purity products through extraction and other methods, effectively avoiding complex purification operations such as column chromatography. The phthalonitrile monomers prepared in this invention exhibit excellent compatibility with traditional powdered phthalonitrile monomers and can be used to improve the processability of general-purpose powdered phthalonitrile monomers. Attached Figure Description

[0021] Figure 1 Photograph of the low-melting-point phthalonitrile monomer SiViPN prepared in Example 1;

[0022] Figure 2A digital photograph of the room temperature UV precured product in Example 4;

[0023] Figure 3 This is a DSC data graph of the low-melting-point phthalonitrile monomer SiViPN from Example 1.

[0024] The monomer has a melting point of -26℃;

[0025] Figure 4 The differential scanning calorimetry curve of the low-melting-point phthalonitrile monomer SiViPN in Example 1 after adding a catalyst, with a gel temperature of 264°C.

[0026] Figure 5 The thermogravimetric curve of the low-melting-point phthalonitrile monomer SiViPN in Example 1 under nitrogen atmosphere is shown. d5% The temperature was 453.4℃, C y800℃ It was 71.49%;

[0027] Figure 6 The thermogravimetric curve of the low-melting-point phthalonitrile monomer SiViPN in Example 1 under air conditions is shown. d5% The temperature was 465.64℃, and the temperature was C. y800℃ It is 15.51%;

[0028] Figure 7 The rotational rheology curve of the low-melting-point phthalonitrile monomer SiViPN in Example 1 shows a gel point of approximately 272°C under the condition of an external catalyst. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] A method for synthesizing a liquid phthalocyanine resin monomer that can be pre-cured at room temperature under ultraviolet light includes the following steps:

[0032] Step 1: Under nitrogen protection, add 24g of resorcinol to a three-necked flask with a stirrer, add 80-100mL of DMF and stir thoroughly until completely dissolved, then heat to 40℃. Next, add 33g of anhydrous potassium carbonate in three portions to the above solution, with an interval of 15-20min, and continue stirring for 4h. Dissolve 8g of 4-nitrophthalonitrile in 30-50mL of DMF and add it dropwise to the three-necked flask through a constant pressure dropping funnel. Stir at 40-45℃ for 36-40h, then let stand for 2h. Centrifuge to collect the reaction solution, add it to a beaker, add dilute hydrochloric acid, stir rapidly, let stand, filter to collect the precipitate, wash with plenty of deionized water until neutral, and vacuum dry at 80℃ for 6h. Then add it to 20mL of ethanol, stir thoroughly, filter, collect the precipitate, and vacuum dry at 80℃ for 2-6h to obtain 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxynitrile.

[0033] Step 2: Under a nitrogen atmosphere, 10.17 g of vinyl(chloromethyl)dimethylsilane, 20 g of anhydrous potassium iodide, and 100 mL of acetone were added sequentially to a three-necked flask equipped with a stirrer. The mixture was heated to 55 °C and refluxed for 24 h. After vacuum filtration, 100 mL of n-hexane was added to the filtrate. After filtration again, the solvent was removed by rotary evaporation to obtain a pale yellow transparent liquid, which is vinyl(iodomethyl)dimethylsilane. The product was dried under vacuum at 60-70 °C for 2 h for later use.

[0034] Step 3: Take 12g of 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxynitrile obtained in Step 1 and add it to a flask containing 80-100mL of ultra-dry acetonitrile. Stir until completely dissolved. Then add 20-22g of anhydrous potassium carbonate and stir at 80℃ for 30min. Then add 14g of vinyl(iodomethyl)dimethylsilane from Step 2 to the flask and react at 80-90℃ for 12-24h. After cooling to room temperature, filter and collect the filtrate. Rotate at 75℃ until no solvent flows out, and then dry in a vacuum oven at 80℃ for 4-6h to obtain the product 4-(3-((dimethyl(vinyl)siloxy)methoxy)phenoxy)phthalonitrile monomer, denoted as SiViPN.

[0035] Figure 1 The image shows the prepared low-melting-point phthalonitrile monomer SiViPN. As can be seen from the image, SiViPN is a reddish-brown liquid at room temperature and has a certain degree of fluidity.

[0036] Figure 3 This is a DSC data graph of the low-melting-point phthalonitrile monomer SiViPN. Differential scanning calorimetry analysis of SiViPN monomer shows that its melting point is -26℃.

[0037] The phthalonitrile monomer SiViPN from Example 1 was added to 5 wt% of amino-autocatalytic phthalonitrile as a curing catalyst for SiViPN. The melting point of amino-autocatalytic phthalonitrile is approximately 135°C. No melting endothermic peak of the amino-autocatalytic phthalonitrile monomer was observed during the heating process, indicating that SiViPN has excellent compatibility with general-purpose powdered phthalonitrile monomers. Simultaneously, the curing exothermic peak appeared at 264°C. Figure 4 As shown, this indicates that the processing window for SiViPN monomers is relatively wide.

[0038] Under nitrogen atmosphere, the initial decomposition temperature T of SiViPN cured material is... d5% Reaching 453.4℃, C y800℃ It is 71.49%, such as Figure 5 As shown.

[0039] The initial decomposition temperature of SiViPN cured material in air reaches 465.6℃. y800℃ It is 15.51%, such as Figure 6 As shown.

[0040] The phthalonitrile monomer SiViPN from Example 1 was added to 5 wt% of an amino-autocatalytic phthalonitrile monomer as a curing catalyst. Rotational rheological analysis of SiViPN showed that the viscosity was low in the initial stage. When the temperature was raised to approximately 271.12℃, the storage modulus and loss modulus intersected, indicating the curing stage. Afterward, the viscosity of the system rapidly increased, indicating that SiViPN has excellent processability. Figure 7 As shown.

[0041] Example 2:

[0042] A method for synthesizing a liquid phthalocyanine resin monomer that can be pre-cured at room temperature under ultraviolet light includes the following steps:

[0043] Step 1: Under nitrogen protection, add 24g of resorcinol to a three-necked flask with a stirrer, add 80-100mL of DMF and stir thoroughly until completely dissolved, then heat to 40℃. Next, add 33g of anhydrous potassium carbonate in three portions to the above solution, with an interval of 15-20min, and continue stirring for 4h. Dissolve 8g of 4-nitrophthalonitrile in 30-50mL of DMF and add it dropwise to the three-necked flask through a constant pressure dropping funnel. Stir at 40-45℃ for 36-40h, then let stand for 2h. Centrifuge to collect the reaction solution, add it to a beaker, add dilute hydrochloric acid, stir rapidly, let stand, filter to collect the precipitate, wash with plenty of deionized water until neutral, and vacuum dry at 80℃ for 6h. Then add it to 20mL of ethanol, stir thoroughly, filter, collect the precipitate, and vacuum dry at 80℃ for 2-6h to obtain 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxynitrile.

[0044] Step 2: Under a nitrogen atmosphere, 12.30 g of 3-chloropropyldimethylvinylsilane, 20 g of anhydrous potassium iodide, and 100 mL of acetone were added sequentially to a three-necked flask equipped with a stirrer. The mixture was heated to 55 °C and refluxed for 24 h. After vacuum filtration, 100 mL of n-hexane was added to the filtrate, and the mixture was filtered again. The solvent was then removed by rotary evaporation to obtain a pale yellow transparent liquid, which is 3-iodopropyldimethylvinylsilane. The product was dried under vacuum at 60-70 °C for 2 h for later use.

[0045] Step 3: Take 12g of 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxynitrile obtained in Step 1 and add it to a flask containing 80-100mL of ultra-dry acetonitrile. Stir until completely dissolved. Then add 20-22g of anhydrous potassium carbonate and stir at 80℃ for 30min. Then add 16g of 3-iodopropyldimethylvinylsilane from Step 2 to the flask and react at 80-90℃ for 12-24h. After cooling to room temperature, filter and collect the filtrate. Rotate at 75℃ until no solvent flows out, and then dry in a vacuum oven at 80℃ for 4-6h to obtain the product 4-(3-(3-(ethyldimethylsiloxy)propoxy)phenoxy)phthalonitrile, denoted as PrSiViPN.

[0046] Example 3:

[0047] A method for synthesizing a liquid phthalocyanine resin monomer that can be pre-cured at room temperature under ultraviolet light includes the following steps:

[0048] Step 1: Under nitrogen protection, add 24g of resorcinol to a three-necked flask with a stirrer, add 80-100mL of DMF and stir thoroughly until completely dissolved, then heat to 40℃. Subsequently, add 33g of anhydrous potassium carbonate to the above solution in three portions, with an interval of 15-20min, and continue stirring for 4h. Dissolve 8g of 4-nitrophthalonitrile in 30-50mL of DMF and add it dropwise to the three-necked flask through a constant pressure dropping funnel. Stir at 40-45℃ for 36-40h, let stand for 2h, centrifuge to collect the reaction solution, add it to a beaker, add dilute hydrochloric acid, stir rapidly, let stand, filter to collect the precipitate, wash with a large amount of deionized water until neutral, and vacuum dry at 80℃ for 6h. Then add it to 20mL of ethanol, stir thoroughly, filter, collect the precipitate, and vacuum dry at 80℃ for 2-6h to obtain 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxynitrile.

[0049] Step 2: Under a nitrogen atmosphere, 15.30 g of 3-chloropropyldiallylmethylsilane, 20 g of anhydrous potassium iodide, and 100 mL of acetone were added sequentially to a three-necked flask equipped with a stirrer. The mixture was heated to 55 °C and refluxed for 24 h. After vacuum filtration, 100 mL of n-hexane was added to the filtrate, and the mixture was filtered again. The solvent was then removed by rotary evaporation to obtain a pale yellow transparent liquid, which is 3-iodopropyldiethylenepropylmethylsilane. The product was dried under vacuum at 60-70 °C for 2 h for later use.

[0050] Step 3

[0051] Take 12g of 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxynitrile obtained in step one and add it to a flask containing 80-100mL of ultra-dry acetonitrile. Stir until completely dissolved. Then add 20-22g of anhydrous potassium carbonate and stir at 80℃ for 30min. Then add 18g of 3-iodopropyldivinylmethylsilane obtained in step two to the flask and react at 80-90℃ for 12-24h. After cooling to room temperature, filter and collect the filtrate. Rotary evaporate at 75℃ until no solvent flows out, and then dry in a vacuum oven at 80℃ for 4-6h to obtain the product 4-(3-(3-(divinylmethylsiloxy)propoxy)phenoxy)phthalonitrile, denoted as 2ViPrSiPN.

[0052] Example 4:

[0053] A novel method for preparing phthalocyanine resin includes the following steps:

[0054] Take 1g of 4-(3-((dimethyl(vinyl)siloxy)methoxy)phenoxy)phthalonitrile monomer obtained in Example 1, and separately take 1g of triallyl isocyanurate and 1.62g of pentaerythritol tetramercaptoacetate. Mix them thoroughly by ultrasonication, then add 0.15g of 2-hydroxy-2-methylphenylacetone and ultrasonicate in the dark for 10-20 minutes. Transfer to a UV curing lamp and irradiate for 5-8 minutes to obtain UV-cured phthalic acid resin. Figure 2 As shown, the solution changes from a liquid state to a pale yellow transparent solid; then it is cured at high temperature in a high-temperature oven with a heating program of 200℃ / 2h, 210℃ / 2h, 220℃ / 2h, 240℃ / 2h, 260℃ / 2h, and 280℃ / 2h.

[0055] Example 5:

[0056] A novel method for preparing phthalocyanine resin includes the following steps:

[0057] Take 1g of 4-(3-((dimethyl(vinyl)siloxy)methoxy)phenoxy)phthalonitrile obtained in Example 1, and separately take 1g of tetramethyltetravinylcyclotetrasiloxane and 1.57g of pentaerythritol tetramercaptoacetate. Mix them thoroughly by ultrasonication, and then add 0.15g of 2-hydroxy-2-methylphenylacetone and ultrasonicate in the dark for 10-20 minutes. Transfer to a UV curing lamp and irradiate for 5-8 minutes to obtain UV-precured phthalic acid resin. Then, perform high-temperature post-curing in a high-temperature oven with a temperature increase program of 200℃ / 2h, 210℃ / 2h, 220℃ / 2h, 240℃ / 2h, 260℃ / 2h, and 280℃ / 2h.

[0058] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A liquid phthalocyanine resin monomer that can be pre-cured at room temperature under ultraviolet light, characterized in that: The basic structure of the phthalonitrile resin monomer is shown below: In this system, R and R' are independent organic substituents, Ar is an aromatic ring structure, and the oxygen atom attached to Ar can be located in the ortho, meta, or para position.

2. A method for preparing the room-temperature UV-curable liquid phthalocyanine resin monomer as described in claim 1, characterized in that, Includes the following steps: Under inert gas protection, phthalonitrile monomers containing phenolic hydroxyl groups, catalysts, and vinyl halosilanes are dissolved in a solvent in a molar ratio of 1:2.2-3.2:1.2-1.4 and reacted at 80-90°C for 12-24 hours to obtain liquid phthalocyanine resin monomers that can be pre-cured by UV light at room temperature.

3. The preparation method according to claim 2, characterized in that: The phthalonitrile monomer containing phenolic hydroxyl groups includes one or more of 4-(3-hydroxyphenoxy)benzene-1,2-dicarboxylon, 4-(4-hydroxyphenoxy)benzene-1,2-dicarboxylon, 4-(4-aldehyde-3-hydroxyphenoxy)benzene-1,2-dicarboxylon, 4-(2'-hydroxyphenoxy)phthalonitrile, and 4-hydroxy-5-methoxybenzene-1,2-dicarboxylon.

4. The preparation method according to claim 2, characterized in that: The catalyst includes one or more of sodium hydride, potassium hydride, lithium diisopropylamino, lithium bis(trimethylsilyl)amino, sodium hexamethyldisilanediazo, sodium carbonate, and potassium carbonate.

5. The preparation method according to claim 2, characterized in that: The halogens in the vinyl halogenated silanes cannot be directly bonded to silicon atoms. The vinyl halogenated silanes include one or more of the following: vinyl(chloromethyl)dimethylsilane, vinyl(iodomethyl)dimethylsilane, divinyl(chloromethyl)methylsilane, vinyl(bromomethyl)dimethylsilane, chloromethyltrivinylsilane, iodomethyltrivinylsilane, 3-iodopropyldimethylvinylsilane, 3-iodopropyldiallylmethylsilane, and 3-iodopropyldivinylmethylsilane.

6. The preparation method according to claim 2, characterized in that: The solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, acetonitrile, dioxane, and xylene.

7. The application of a phthalocyanine resin monomer according to claim 1 or a phthalocyanine resin monomer prepared by the preparation method according to any one of claims 2-6, characterized in that, Includes the following steps: Phthalocyanine resin monomers are mixed uniformly with crosslinking agents, thiols and photoinitiators, and then cured by ultraviolet light at room temperature to obtain room temperature ultraviolet light pre-cured phthalocyanine resins, wherein the total molar number of vinyl groups in the phthalocyanine resin monomers and the total molar number of thiol groups in the crosslinking agent are equal.

8. The application according to claim 7, characterized in that: The phthalocyanine resin monomer, crosslinking agent, thiol and photoinitiator are mixed evenly and then ultrasonically mixed for 15-30 minutes; the curing time is 2-5 minutes.

9. The application according to claim 7, characterized in that: The crosslinking agent includes one or more of tetravinylsilane, tetramethyltetravinylcyclotetrasiloxane, octavinylPOSS, tetra(4-vinylphenyl)silane, triallyl isocyanurate, and 2,4,6-trivinylcycloboroxane; the thiol includes one or more of pentaerythritol tetramercaptoacetate, pentaerythritol tetra(3-mercaptopropionic acid), propane-1,2,3-trithiol, and trimethylpropane tris(2-mercaptoacetic acid).

10. The application according to claim 7, characterized in that: The photoinitiator includes one or a combination of two of 2,2-dimethoxy-2-phenylacetophenone and 2-hydroxy-2-methylacetophenone.

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