Photosensitive resin and closed-loop recycling and circulating 3D printing method thereof

Abstract

The photosensitive resin comprises a precursor containing an active functional group, a precursor containing sulfydryl and a light activation catalyst, and the active functional group is selected from an aldehyde group, a carbonyl group or a hindered unsaturated double bond. The invention further discloses a closed-loop recovery and cyclic 3D printing method of the photosensitive resin, which comprises the following steps: after the photosensitive resin is irradiated by a light source of the photocuring 3D printing equipment, obtaining a 3D printed product; the method comprises the following steps: dissolving a to-be-recovered 3D printing product, depolymerizing after dissolving to generate an oligomer or monomer with sulfydryl and active functional groups as end groups, and then adding a neutralizing reagent as a recovery system; and adding the photo-activated catalyst into the recovery system again to prepare new photosensitive resin for cyclic 3D printing. The photosensitive resin can realize closed-loop recovery and multiple-cycle photocuring 3D printing, and has the characteristics of mild recovery conditions and complete recycling of waste materials.

Description

Technical Field

[0001] The present invention relates to the field of photocurable 3D photosensitive resin, and in particular to a photosensitive resin and a closed-loop recycling and cyclic 3D printing method thereof. Background Art

[0002] 3D printing technology, as an additive manufacturing method, has gained increasing attention and application in the global manufacturing industry due to its unique flexibility, customization and multi-degree-of-freedom characteristics. Among them, photosensitive resin, as an important type of 3D printing raw material, is widely used in a variety of 3D printing technologies, such as stereolithography (SLA), digital light processing (DLP) and selective area light curing (LCD). This type of resin is usually composed of monomers containing photosensitive groups (such as acrylate groups, epoxy groups) and photoinitiators. When irradiated by a light source (usually ultraviolet light or visible light), the photoinitiator is activated, initiating free radical or cationic polymerization of the monomer to form a cross-linked network. In addition to 3D printing, this type of resin can also be used in lithography, coatings, adhesives and other fields. However, after polymerization, photosensitive resins usually form a network backbone composed of carbon-carbon single bonds or carbon-oxygen single bonds. This chemical structure is very stable, and the formed network is in a three-dimensional cross-linked state and does not have the ability to depolymerize, so it cannot be recovered to a precursor liquid state that can be polymerized again. As 3D printing technology becomes increasingly popular as a next-generation manufacturing tool, designing resin materials that can be recycled and printed in a closed loop has become the focus and difficulty of current sustainable development research.

[0003] By introducing dynamic covalent bonds into the traditional acrylic resin system, the 3D printing network can be depolymerized, and chemical recycling of materials can be achieved to a certain extent. In order to achieve circular printing, the existing practice is to redisperse the recycled material as a filler into a new photosensitive resin, or to recover part of the material through the depolymerization of dynamic ester bonds / hindered urea bonds, and re-graft the acrylate group to achieve re-printing (for example: paper Repeatedly recyclable 3D printing catalyst-freedynamic thermosetting photopolymers, Recyclable photoresins for light-mediatedadditive manufacturing towards loop 3D printing). When the above systems achieve circular printing, a large amount of new photosensitive monomers must be introduced. Therefore, there are problems such as low recycling rate (the proportion of recycled raw materials in new printing materials is less than 25%) and changes in the performance of the printing precursor (increased viscosity). Summary of the invention

[0004] The object of the present invention is to provide a photosensitive resin and a method for closed-loop recycling and cyclic 3D printing thereof, wherein the photosensitive resin can realize closed-loop recycling and multiple-cycle light-curing 3D printing.

[0005] The present invention provides the following technical solutions:

[0006] A photosensitive resin comprises a precursor containing active functional groups, a precursor containing thiol groups, and a photoactivated catalyst, wherein the active functional groups are selected from aldehyde groups, carbonyl groups, or hindered unsaturated double bonds; wherein the precursor containing active functional groups is a monomer or an oligomer, and the precursor containing thiol groups is a monomer or an oligomer.

[0007] The precursor in the photosensitive resin provided by the present invention comprises monomers and / or polymers having thiol and aldehyde groups, carbonyl groups or hindered unsaturated double bonds; by adjusting the structure and composition of the polymers, the mechanical properties of the material can be effectively regulated to meet the needs of different application scenarios.

[0008] The photosensitive resin provided by the present invention can generate a high-efficiency catalyst after being irradiated by the light source of a photocuring 3D printing device, thereby achieving rapid polymerization of the resin and obtaining a 3D printed product.

[0009] Preferably, the aldehyde-containing precursor includes, but is not limited to, one or more of vanillin, p-hydroxybenzaldehyde, p-anisaldehyde, p-tert-butylbenzaldehyde, p-cyanobenzaldehyde, m-hydroxybenzaldehyde, benzaldehyde, two-arm aldehyde or multi-arm aldehyde derived from vanillin, furfural, 5-methylfurfural, 2-thiophenecarboxaldehyde, 5-methyl-2-thiophenecarboxaldehyde and aldehyde-containing oligomers, and some of the structural formulas are as follows:

[0010]

[0011] Preferably, the carbonyl-containing precursor includes, but is not limited to, one or more of 2,5-octanedione, spiro[5.5]undecane-3,9-dione, 2,7-dimethyl-3,6-octanedione, 2,15-hexadecanedione, 4,5-octanedione, 3-ethyl-2,4-pentanedione, 1,3-diphenylpropanetrione, 1,3,5-tribromo-1,3,5-thiazinane-2,4,6-trione, 1,3-dibenzoylacetone, 2,3,5-hexanetrione, heptane-2,3,5-trione or keto-containing oligomers, and the partial structural formula is as follows:

[0012]

[0013] Preferably, the precursor containing hindered unsaturated double bonds includes but is not limited to one or more of diisopropylidene oxide, 5-methylhexa-1,4-diene-3-one, octenone, 2,6-dimethyl-2,5,7-octatriene-4-one, 2,6-dimethyl-2,5-octadiene-4-one, dimethylphenyl ketone or oligomers containing hindered unsaturated double bonds, and some of the structural formulas are as follows:

[0014]

[0015] Preferably, the thiol-containing precursor includes but is not limited to 2,2-(1,2-ethanediyldioxy)bisethanethiol, distilbene-4,4-dithiol, 1,11-undecanedithiol, dithiothreitol, 1,16-hexadecanedithiol, hexa(ethylene glycol)disulfide, 1,6-hexyldithiol, 2,3-pentanedithiol, 3,7-dithia-1,9-nonaneedithiol, bis(3-mercaptopropionic acid)ethylene glycol, 2-ethyl-2-(mercaptomethyl)-1,3-propanedithiol, tetrakis(3-mercaptoacetic acid)pentaerythritol ester, tetrakis(3-mercaptopropionic acid)pentaerythritol ester, tetrakis(3-mercaptobutyric acid)pentaerythritol ester or one or more of the oligomers with thiol as the end groups.

[0016] Preferably, the photoactivated catalyst is selected from photoacid or photobase generation, and the wavelength of its light excitation is 200nm to 800nm.

[0017] More preferably, the photoacid generator includes, but is not limited to, one or more of aromatic diazonium salts, diaryliodonium salts, triarylsulfonium salts, dialkylformylmethylsulfonium salts or ferrocenium salt chemicals.

[0018] More preferably, the photobase generator includes, but is not limited to, one or more of cobalt ammonia complexes, benzoyl photobase generators, benzoylamide photobase generators, quaternary ammonium salts containing aromatic ketone structures, or triaryl carbinols.

[0019] Preferably, the photosensitive resin includes a light absorber, which is eosin Y, methyl red, Sudan red, Sudan black B, phthalocyanine red, phthalocyanine blue or aureole.

[0020] The present invention also provides a method for closed-loop recycling and cyclic 3D printing of photosensitive resin, the method comprising:

[0021] (1) After the above-mentioned photosensitive resin is irradiated by a light source of a light-curing 3D printing device, a 3D printed product is obtained;

[0022] (2) dissolving the 3D printed product to be recycled, and depolymerizing it to generate oligomers and / or monomers with terminal groups of thiol groups and active functional groups, and then adding a neutralizing agent to serve as a recycling system;

[0023] (3) Re-adding the photoactivated catalyst into the recycling system to prepare new photosensitive resin for circular 3D printing.

[0024] Different from the traditional photocuring 3D printing which is based on chain polymerization mechanisms such as free radical or cationic polymerization, the present invention adopts light-activated catalyst-catalyzed step-by-step polymerization as the printing mechanism, with dynamic thioether bonds as the basic building blocks; under mild conditions, the dynamic thioether bonds can be depolymerized into monomers and / or oligomers containing active groups, and thus the present invention achieves minimal or no resin consumption in the cyclic printing process, thereby realizing the full resource utilization of waste; this is not only sustainable in terms of environmental protection, but also can significantly reduce the cost of 3D photosensitive resins through recycling.

[0025] Preferably, the photocuring 3D printing includes but is not limited to stereolithography (SLA), digital light processing (DLP), and selective area light curing (LCD).

[0026] In step (2), the neutralizing agent includes an acidic agent and an alkaline agent. The acidic agent includes but is not limited to hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrocyanic acid, boric acid, citric acid, aluminum chloride, ferric chloride, zinc chloride, hexafluoroantimonic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphonium salt or diaryliodonium salt. The alkaline agent includes but is not limited to sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidine, 1,5,7-triazabicyclo [4.4.0] dec-5-ene, 1,8-diazabicyclo [5.4.0] undec-7-ene or 7-methyl-1,5,7-triazabicyclo [4.4.0] dec-5-ene.

[0027] In step (2), the 3D printed product to be recycled is depolymerized under the action of a depolymerization catalyst; wherein the photoactivated catalyst remaining in the 3D printed product to be recycled is directly used as a depolymerization catalyst, or an acidic agent or an alkaline agent is additionally added and used as a depolymerization catalyst for depolymerization, wherein the acidic agent is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrocyanic acid, boric acid, citric acid, aluminum trichloride, ferric chloride, zinc chloride, hexafluoroantimonic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphonium salts or diaryliodonium salts. The alkaline agent is selected from one or more of sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidine, 1,5,7-triazabicyclo [4.4.0] dec-5-ene, 1,8-diazabicyclo [5.4.0] undec-7-ene or 7-methyl-1,5,7-triazabicyclo [4.4.0] dec-5-ene; the amount of the depolymerization catalyst is 0.01 to 50 wt% of the mass of the photosensitive resin.

[0028] In step (2), a solvent is added to the 3D printed product to be recycled to dissolve it; the solvent includes but is not limited to one or more of water, formamide, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoramide, alcohol, pyridine, furan, tetrahydrofuran, methyltetrahydrofuran, chloroform or toluene; the amount of the solvent used in the depolymerization process is 0.1 to 100 times the mass of the photosensitive resin.

[0029] More preferably, the solvent can be separated by vacuum distillation, absorption, condensation, adsorption, membrane separation and the like to achieve recycling of the solvent.

[0030] The depolymerization reaction temperature is 25 to 200°C; the reaction time is 1 min to 50 h;

[0031] It should be noted that the inherent moisture in the material or the additionally added moisture can react with the dynamic thioether bonds in the polymer to generate oligomers and monomers containing active functional groups. The depolymerization catalyst can effectively promote this reaction process.

[0032] The method is simple to operate, has a short reaction time, the solvent is easy to recover, and all the recovered products can be recycled, thus having good economic benefits and social value.

[0033] Further preferably, taking polythioacetal as an example, the thioacetal bond can be depolymerized under acid catalysis to generate aldehyde groups and thiol groups after the reaction (as shown in reaction formula I).

[0034]

[0035] Preferably, the oligomers and monomers recovered have active functional groups on their end groups including aldehyde, carbonyl or hindered unsaturated double bonds and thiol. The topological structure of the oligomers can be linear, branched or hyperbranched macromolecules.

[0036] More preferably, the recycled oligomers and monomers account for 90% to 100% of the new photosensitive resin.

[0037] The photosensitive resin provided by the present invention can be closed-loop recycled and cyclically printed multiple times by the above method. Preferably, the number of closed-loop recycled and cyclically printed is 1-10 times.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The photosensitive resin recovered by the present invention can be directly used for printing without adding additional monomers, thereby realizing multiple cycles of photocuring 3D printing. It has the advantages of mild recycling conditions, simple recycling path, and complete resource utilization of waste materials. It can solve the problem that the photosensitive resin obtained by the prior art cannot achieve complete closed-loop recycling and full cycle printing.

[0040] (2) Different from the existing free radical or cationic chain polymerization, the photosensitive resin provided by the present invention adopts photocatalytic step-by-step polymerization as its photocuring mechanism, which effectively solves the problem that traditional 3D printing materials are difficult to achieve closed-loop recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the recovery process in Example 1.

[0042] Figure 2 This is the product obtained by 3D printing in Example 1. DETAILED DESCRIPTION

[0043] The present invention will be further described in detail below in conjunction with examples. It should be pointed out that the examples described below are intended to facilitate the understanding of the present invention and do not serve as any limitation.

[0044] Example 1 (Hard Polydithioacetal Polymer)

[0045] raw material:

[0046] Vanillin, McLean Company; 2,2-(1,2-ethanediyldioxy)bis(ethanethiol), pentaerythritol tetrakis(3-mercaptopropionate), TCI Company; bis[(4-diphenylsulfonium)benzene] sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba Company; sodium bicarbonate, tetrahydrofuran, Sinopharm Company; deionized water, Wahaha Company.

[0047] 3D Printing:

[0048] Mix vanillin, 2,2-(1,2-ethylenedioxy)diethanethiol, and pentaerythritol tetrakis(3-mercaptopropionic acid) at a molar ratio of 1.4:0.6:0.4 and add 3wt% of PAG6976 to obtain a colorless and transparent resin. Pour the resin into the SLA 3D printing instrument with a laser intensity of 300mW / cm 2 The printing speed is 500mm / s, and the printing thickness of each layer is 200μm. After printing, it is placed in a 70-degree vacuum oven for heat treatment for 24 hours, and the yellow transparent 3D printed product (such as Figure 2 The mechanical properties were tested in a universal material testing machine, and the modulus of the material was 141 MPa and the elongation at break was 682%.

[0049] Recycling and Recycling Printing:

[0050] like Figure 1 As shown, the 3D printed product, water and tetrahydrofuran were added to the flask at a ratio of 1:0.02:4 (mass ratio), and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The residual photoacid generated therein is the depolymerization catalyst. The solution was then treated with an excess of the neutralizing agent sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration, and the tetrahydrofuran was removed by a rotary evaporator to finally obtain a liquid resin. Subsequently, 3wt% of PAG6976 and 10wt% of the solvent 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing processes are consistent with the above method. The obtained product was tested for mechanical properties in a universal material testing machine, and the modulus of the material was 143MPa and the elongation at break was 539%.

[0051] Example 2 (Crystalline Polydithioacetal Polymer)

[0052] raw material:

[0053] Vanillin, McLean Company; 2,2-(1,2-ethanediyldioxy)bis(ethanethiol), pentaerythritol tetrakis(3-mercaptopropionate) and dibutyltin dilaurate, TCI Company; bis[(4-diphenylsulfonium)benzene] sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba Company; sodium bicarbonate, toluene, methanol, 2-methyltetrahydrofuran, Sinopharm Company; deionized water, Wahaha Company; ε-caprolactone, ethylene glycol, triethylamine, 2-isocyanatoethyl acrylate, Aladdin Company.

[0054] Synthesis of mercapto-terminated polycaprolactone oligomers:

[0055] First, polycaprolactone was synthesized by mixing ε-caprolactone (50 g), ethylene glycol (0.48 g) and dibutyltin dilaurate (0.1 g, catalyst) and stirring at 120°C for 8 hours under a nitrogen atmosphere. The product was then dissolved in toluene (100 mL) and subsequently precipitated in methanol. This dissolution-precipitation process was repeated three times for purification. The final product was dried under vacuum at room temperature for 24 hours.

[0056] Further synthesis of polycaprolactone diacrylate: polycaprolactone (30 g), 2-isocyanatoethyl acrylate (1 g) and dibutyltin dilaurate (0.1 g, catalyst) were dissolved in toluene (15 mL), followed by stirring at 80° C. for 4 hours under a nitrogen atmosphere. The solution was precipitated in methanol, and the product was obtained after dissolution-precipitation purification. The final product was dried under vacuum at room temperature for 24 hours.

[0057] Finally, the thiol-terminated polycaprolactone oligomer was synthesized: polycaprolactone diacrylate (10 g), 2,2-(1,2-ethylenedioxy)bis(ethanethiol) (0.62 g), toluene (10 g) and triethylamine (0.2 g) were added to a round-bottom flask and mixed evenly at room temperature until completely dissolved. The mixture was heated at 80°C for 6 hours, and then the product was obtained by methanol precipitation and filtration.

[0058] 3D Printing:

[0059] Vanillin (0.24 g), PTMP (0.19 g), thiol-terminated polycaprolactone oligomer (5.4 g), acetonitrile (2.7 g) and 1 wt% PAG were uniformly mixed until completely dissolved. A colorless and transparent resin was obtained. The resin was poured into the SLA 3D printing instrument with a laser intensity of 300 mW / cm 2 , the printing speed is 500mm / s, and the printing thickness of each layer is 200μm. After printing, it is placed in a 70-degree vacuum oven for heat treatment for 24 hours to obtain a white crystalline 3D printed product. The mechanical properties were tested in a universal material testing machine, and the modulus of the material was 41.1MPa and the elongation at break was 1250%.

[0060] Recycling and Recycling Printing:

[0061] The 3D printed product, 2wt% of water and 2-methyltetrahydrofuran were added to a flask at a ratio of 1:0.02:4 (mass ratio), and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The solution was then treated with an excess of sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration, and the 2-methyltetrahydrofuran was removed by a rotary evaporator to finally obtain a liquid resin. Subsequently, 3wt% of PAG6976 was added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing processes were consistent with the above method. The obtained product was tested for mechanical properties in a universal material testing machine, and the modulus of the material was 39.7MPa and the elongation at break was 1207%.

[0062] Example 3 (Polydithioacetal polymer, DLP printing)

[0063] raw material:

[0064] Furanaldehyde, Aladdin; 2,2-(1,2-ethylenedioxy)bis(ethanethiol), pentaerythritol tetrakis(3-mercaptopropionate), TCI; H6-isopropylferrocenium hexafluorophosphate (PAG261), Alibaba; sodium bicarbonate, tetrahydrofuran, Sinopharm; deionized water, Wahaha. 3D printing:

[0065] Mix furanaldehyde, 2,2-(1,2-ethylenedioxy)bis(ethanethiol) and pentaerythritol tetrakis(3-mercaptopropionic acid) at a molar ratio of 1.4:0.6:0.4 and add 3wt% PAG261 to obtain a colorless and transparent resin. Pour the resin into the DLP 3D printing instrument with a light source intensity of 30mW / cm 2 , the printing speed is 50mm / s, and transparent 3D printed products can be obtained.

[0066] Recycling and Recycling Printing:

[0067] The 3D printed product, water and tetrahydrofuran were added to a flask at a ratio of 1:0.02:4 (mass ratio), and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The solution was then treated with an excess of sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration, and the tetrahydrofuran was removed by a rotary evaporator to finally obtain a liquid resin. Subsequently, 3wt% of PAG261 was added to the recovered resin to obtain a re-photocurable resin. The above printing process was repeated to obtain a 3D printed product.

[0068] Example 4 (Polydithioketal polymer, organic solvent-free recovery)

[0069] raw material:

[0070] 2,15-hexadecanedione, Aladdin; 2,2-(1,2-ethylenedioxy)bis(ethanethiol), pentaerythritol tetrakis(3-mercaptopropionate), TCI; bis[(4-diphenylsulfonium)benzene]sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba; sodium bicarbonate, Sinopharm; deionized water, Wahaha;

[0071] 3D Printing:

[0072] Mix 2,15-hexadecanedione, 2,2-(1,2-ethylenedioxy)bis(ethanethiol) and pentaerythritol tetrakis(3-mercaptopropionic acid) at a molar ratio of 0.7:0.6:0.4 and add 3wt% of PAG6976 to obtain a transparent resin. Pour the resin into the SLA 3D printing instrument with a laser intensity of 300mW / cm 2 , the printing speed is 500mm / s, and 3D printed products can be obtained.

[0073] Recycling and Recycling Printing:

[0074] The 3D printed product and water were added to a flask at a ratio of 1:0.05, and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The solution was then treated with an excess of sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration to finally obtain a liquid resin. Subsequently, 3wt% PAG6976 was added to the recycled resin to obtain a reprintable resin. The above printing process was repeated to obtain a 3D printed product.

[0075] Example 5 (Polydithioketal polymer, LCD printing)

[0076] raw material:

[0077] 2,5-Octanedione, Aladdin; 2,2-(1,2-ethanediyldioxy)bis(ethanethiol), pentaerythritol tetrakis(3-mercaptopropionate), TCI; H6-isopropylferrocenium hexafluorophosphate (PAG 261), Alibaba; sodium bicarbonate, tetrahydrofuran, Sinopharm; water, Wahaha; 3D printing:

[0078] Mix 2,5-octanedione, 2,2-(1,2-ethylenedioxy)bis(ethanethiol) and pentaerythritol tetrakis(3-mercaptopropionic acid) at a molar ratio of 0.7:0.6:0.4 and add 3wt% of PAG261 to obtain a transparent resin. Pour the resin into the LCD 3D printing instrument with a light source intensity of 30mW / cm 2 , the printing speed is 50mm / s, and transparent 3D printed products can be obtained.

[0079] Recycling and Recycling Printing:

[0080] The photocurable polymer, water and tetrahydrofuran were added to the flask at a ratio of 1:0.02:4 (mass ratio), and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The solution was then treated with an excess of sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration, and the tetrahydrofuran was removed by a rotary evaporator to finally obtain a liquid resin. Subsequently, 3wt% of PAG261 was added to the recovered resin to obtain a recurable resin. The above printing process was repeated to obtain a 3D printed product.

[0081] Example 6 (Polythiodiene polymer)

[0082] raw material:

[0083] Diisopropyl acetone, Sudan red, Aladdin Company; 2,2-(1,2-ethanediyldioxy)bis(ethanethiol), pentaerythritol tetrakis(3-mercaptopropionate), ketoprofen, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), TCI Company; toluene, acetic acid, Sinopharm Company.

[0084] Preparation of photobase generation:

[0085] 1,5,7-Triazabicyclo[4.4.0]dec-5-ene is complexed with ketoprofen to obtain photobase. The detailed steps are as follows: 0.200g of TBD, 0.384g of ketoprofen and 2.366g of toluene are weighed and added into a brown glass bottle wrapped in tin foil (light protection is a key step), and stirred at room temperature for 2 hours until the reaction is almost complete. The solution after the reaction is kept away from light.

[0086] 3D Printing:

[0087] Mix diisopropyl acetone, 2,2-(1,2-ethylenedioxy)diethanethiol, and pentaerythritol tetrakis(3-mercaptopropionic acid) at a molar ratio of 1.4:0.6:0.4 and add 3wt% of photobase and 0.1wt% of Sudan red to obtain a transparent red resin. Pour the resin into the SLA 3D printing instrument with a laser intensity of 300mW / cm 2 , the printing speed is 500mm / s, and 3D printed products can be obtained.

[0088] Recycling and Recycling Printing:

[0089] The 3D printed product was heated to 80°C for 120 minutes until the polymer turned into a liquid, and then acetic acid was added to neutralize it to neutrality. Further, 3wt% of photobase was added to the recycled resin to obtain a reprintable resin. The above printing process was repeated to obtain a 3D printed product.

[0090] Example 7 (Multiple Cycle Printing of Hard Polydithioacetal Polymer)

[0091] raw material:

[0092] Vanillin, MacLean Company; 2,2-(1,2-ethanediyldioxy)bis(ethanethiol), pentaerythritol tetrakis(3-mercaptoacetate), TCI Company; bis[(4-diphenylsulfonium)benzene] sulfide-bis-hexafluoroantimony phosphate (PAG6976), Alibaba Company; sodium bicarbonate, tetrahydrofuran, Sinopharm Company; deionized water, Wahaha Company.

[0093] 3D Printing:

[0094] Mix vanillin, 2,2-(1,2-ethylenedioxy)diethanethiol, and pentaerythritol tetrakis(3-mercaptoacetic acid) at a molar ratio of 1.4:0.6:0.4 and add 3wt% of PAG6976 to obtain a colorless and transparent resin. Pour the resin into the SLA 3D printing instrument with a laser intensity of 300mW / cm 2 The printing speed is 500mm / s, and the printing thickness of each layer is 200μm. After printing, it is placed in a 70-degree vacuum oven for heat treatment for 24 hours, and the yellow transparent 3D printed product (such as Figure 2 ). The mechanical properties were tested in a universal material testing machine, and the modulus of the material was 141MPa and the elongation at break was 682%.

[0095] The first loop prints:

[0096] The 3D printed product, water and tetrahydrofuran were added to the flask at a ratio of 1:0.02:4 (mass ratio), and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The solution was then treated with an excess of sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration, and the tetrahydrofuran was removed by a rotary evaporator to finally obtain a liquid resin. Subsequently, 3wt% of PAG6976 and 10wt% of 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing process was consistent with the above method. The obtained product was tested for mechanical properties in a universal material testing machine, and the modulus of the material was 143MPa and the elongation at break was 539%.

[0097] The second loop prints:

[0098] The 3D printed product, water and tetrahydrofuran were added to the flask at a ratio of 1:0.02:4 (mass ratio), and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The solution was then treated with an excess of sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration, and the tetrahydrofuran was removed by a rotary evaporator to finally obtain a liquid resin. Subsequently, 3wt% of PAG6976 and 10wt% of 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing processes were consistent with the above method. The obtained product was tested for mechanical properties in a universal material testing machine, and the modulus of the material was 143MPa and the elongation at break was 757%.

[0099] The third loop prints:

[0100] The 3D printed product, water and tetrahydrofuran were added to the flask at a ratio of 1:0.02:4 (mass ratio), and the mixture was heated to 80°C for 120 minutes until the polymer was completely dissolved to obtain a transparent orange solution. The solution was then treated with an excess of sodium bicarbonate and stirred at room temperature for 5 minutes to neutralize the residual acid in the system. The excess sodium bicarbonate was removed by filtration, and the tetrahydrofuran was removed by a rotary evaporator to finally obtain a liquid resin. Subsequently, 3wt% of PAG6976 and 10wt% of 2-butoxyethanol were added to the recovered resin to obtain a reprintable resin. The 3D printing and post-processing process was consistent with the above method. The obtained product was tested for mechanical properties in a universal material testing machine, and the modulus of the material was 153MPa and the elongation at break was 530%.

Claims

1. A photosensitive resin, characterized in that: The photosensitive resin comprises a precursor containing active functional groups, a precursor containing thiol groups and a photoactivated catalyst, wherein the active functional groups are selected from aldehyde groups, carbonyl groups or hindered unsaturated double bonds; wherein the precursor containing active functional groups is a monomer or an oligomer, and the precursor containing thiol groups is a monomer or an oligomer.

2. The photosensitive resin according to claim 1, characterized in that: When the precursor containing active functional groups is an aldehyde-containing precursor, the aldehyde-containing precursor is selected from one or more of vanillin, p-hydroxybenzaldehyde, p-anisaldehyde, p-tert-butylbenzaldehyde, p-cyanobenzaldehyde, m-hydroxybenzaldehyde, benzaldehyde, a two-arm aldehyde or a multi-arm aldehyde derived from vanillin, furfural, 5-methylfurfural, 2-thiophenecarboxaldehyde, 5-methyl-2-thiophenecarboxaldehyde or an aldehyde-containing oligomer; When the precursor containing an active functional group is a carbonyl-containing precursor, the carbonyl-containing precursor is selected from one or more of 2,5-octanedione, spiro[5.5]undecane-3,9-dione, 2,7-dimethyl-3,6-octanedione, 2,15-hexadecanedione, 4,5-octanedione, 3-ethyl-2,4-pentanedione, 1,3-diphenylpropanetrione, 1,3,5-tribromo-1,3,5-thiazinane-2,4,6-trione, 1,3-dibenzoyl acetone, 2,3,5-hexanetrione, heptane-2,3,5-trione or a keto-containing oligomer; When the precursor containing active functional groups is a precursor containing hindered unsaturated double bonds, the precursor containing hindered unsaturated double bonds is selected from one or more of diisopropylidene oxide, 5-methylhexa-1,4-diene-3-one, octenone, 2,6-dimethyl-2,5,7-octatriene-4-one, 2,6-dimethyl-2,5-octadiene-4-one, dimethylphenyl ketone or oligomers containing hindered unsaturated double bonds; The thiol-containing precursor is selected from one or more of 2,2-(1,2-ethanediyldioxy)bisethanethiol, distilbene-4,4-dithiol, 1,11-undecanedithiol, dithiothreitol, 1,16-hexadecanedithiol, hexa(ethylene glycol)disulfide, 1,6-hexyldithiol, 2,3-pentanedithiol, 3,7-dithia-1,9-nonaneedithiol, bis(3-mercaptopropionic acid)ethylene glycol, 2-ethyl-2-(mercaptomethyl)-1,3-propanedithiol, tetrakis(3-mercaptoacetic acid)pentaerythritol ester, tetrakis(3-mercaptopropionic acid)pentaerythritol ester, tetrakis(3-mercaptobutyric acid)pentaerythritol ester or oligomers with thiol as terminal groups.

3. The photosensitive resin according to claim 1, characterized in that: The photoactivated catalyst is selected from photoacid or photobase, the wavelength of light excitation of the photoactivated catalyst is 200nm to 800nm, the photoacid is selected from one or more of aromatic diazonium salts, diaryl iodonium salts, triaryl sulfonium salts, dialkyl formylmethyl sulfonium salts or ferrocenium salt chemicals, and the photobase is selected from one or more of cobalt ammonia complexes, benzoyl photobases, benzoylamide photobases, quaternary ammonium salts containing aromatic ketone structures or triaryl methanols.

4. The photosensitive resin according to claim 1, characterized in that: The photosensitive resin includes a light absorber.

5. A method for closed-loop recycling and cyclic 3D printing of photosensitive resin, characterized in that: The method comprises: (1) After the photosensitive resin according to any one of claims 1 to 4 is irradiated by a light source of a photocuring 3D printing device, a 3D printed product is obtained; (2) dissolving the 3D printed product to be recycled, and depolymerizing it to generate oligomers and / or monomers with terminal groups of thiol groups and active functional groups, and then adding a neutralizing agent to serve as a recycling system; (3) Re-adding the photoactivated catalyst into the recycling system to prepare new photosensitive resin for circular 3D printing.

6. The closed-loop recycling and cyclic 3D printing method of photosensitive resin according to claim 5, characterized in that: In step (2), the neutralizing agent is selected from an acidic agent or an alkaline agent, the acidic agent is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrocyanic acid, boric acid, citric acid, aluminum chloride, ferric chloride, zinc chloride, hexafluoroantimonic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphonium salts or diaryliodonium salts, and the alkaline agent is selected from one or more of sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.

7. The closed-loop recycling and cyclic 3D printing method of photosensitive resin according to claim 5, characterized in that: In step (2), the 3D printed product to be recycled is depolymerized under the action of a depolymerization catalyst; wherein the photoactivated catalyst remaining in the 3D printed product to be recycled is directly used as a depolymerization catalyst, or an acidic agent or an alkaline agent is additionally added and used as a depolymerization catalyst for depolymerization, wherein the acidic agent is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, carbonic acid, hydrocyanic acid, boric acid, citric acid, aluminum trichloride, ferric chloride, zinc chloride, hexafluoroantimonic acid, boron trifluoride, boron chloride, phosphorus pentachloride, antimony pentafluoride, triarylphosphonium salts or diaryliodonium salts. The alkaline agent is selected from one or more of sodium bicarbonate, sodium carbonate, potassium carbonate, sodium acetate, sodium hydroxide, potassium hydroxide, methylamine, ethylamine, dimethylamine, trimethylamine, triethylamine, aniline, pyridine, pyrrole, imidazole, morpholine, piperidine, guanidine, 1,5,7-triazabicyclo [4.4.0] dec-5-ene, 1,8-diazabicyclo [5.4.0] undec-7-ene or 7-methyl-1,5,7-triazabicyclo [4.4.0] dec-5-ene; the amount of the depolymerization catalyst is 0.01 to 50 wt% of the mass of the photosensitive resin.

8. The method for closed-loop recycling and circular 3D printing of photosensitive resin according to claim 5, characterized in that: In step (2), a solvent is added to the 3D printed product to be recycled to dissolve it; the solvent is selected from one or more of water, formamide, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoramide, alcohol, pyridine, furan, tetrahydrofuran, methyltetrahydrofuran, chloroform or toluene; the amount of the solvent is 0.1 to 100 times the mass of the photosensitive resin.

9. The closed-loop recycling and cyclic 3D printing method of photosensitive resin according to claim 5, characterized in that: In step (3), the recycled oligomers and / or monomers account for 90% to 100% of the new photosensitive resin.

10. The closed-loop recycling and cyclic 3D printing method of photosensitive resin according to claim 5, characterized in that: The number of closed-loop recycling and cyclic 3D printing is 1-10 times.

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