A preparation method of thermosetting polyurethane elastomer for 3D printing

Abstract

The present invention relates to a method for preparing a thermosetting polyurethane elastomer for 3D printing, belonging to the field of rapid prototyping and manufacturing technology. This method utilizes a blocked isocyanate process to quantitatively control the reaction rate of a highly reactive polyurethane system, thereby obtaining a single-component thermosetting polyurethane elastomer stock solution. A polyurethane prepolymer is prepared using diisocyanate and oligomer polyol as raw materials. A blocked prepolymer is then prepared using an active hydrogen-containing blocking agent and a blocked prepolymer. A metered diamine chain extender and catalyst are then added to obtain a single-component thermosetting polyurethane elastomer stock solution. This method quantitatively controls the reaction rate of the highly reactive polyurethane system. The polyurethane elastomer stock solution is stable and low-toxic upon storage at room temperature. The raw material viscosity is adjusted by heating to meet the viscosity requirements for 3D printing, thereby achieving the green production of high-performance polyurethane elastomers.

Description

Technical Field

[0001] The invention belongs to the technical field of rapid prototyping and manufacturing, and relates to a method for preparing a thermosetting polyurethane elastomer for 3D printing. Background Art

[0002] Liquid deposition modeling (LDM) involves pumping a viscous liquid through a print head under computer control, depositing it layer by layer based on a three-dimensional model of the product. UV light polymerization or a hardener is then used to induce solidification. LDM eliminates the need for expensive molds, simplifies the production process, enables rapid prototyping, and significantly improves production efficiency. It also precisely controls the microstructure of the printed material, enabling the creation of highly optimized yet geometrically complex structures, significantly increasing design flexibility. It is widely used in prototyping, large-scale customization, and on-demand printing, making it one of the most popular 3D printing technologies.

[0003] Thermoset polyurethane elastomers (PUs) have gained widespread application due to their excellent mechanical properties. However, the inability of conventional PU preparation processes to overcome the limitations of high reactivity has hindered the development of high-performance PU elastomer formulations. The blocked isocyanate process utilizes active hydrogen compounds to block the NCO groups of the isocyanate. Upon heating, the blocks are deblocked and free NCO groups are regenerated, enabling quantitative control of the reaction rate and providing a new approach to overcoming the limitations of high reactivity. Furthermore, quantitative control of high reactivity also opens up the possibility of using PUs in 3D printing.

[0004] Research on the application of curable polyurethane elastomers in 3D printing has largely focused on photocuring or dual-curing with light and heat. Patent CN 112812259 A discloses a photocurable resin adhesive and its synthesis method. Patents CN 110938175A, CN 110128773 B, and CN 109320666 B, among others, investigate the preparation and printing of dual-curing polyurethanes for 3D printing. While the resulting materials exhibit excellent performance, photocuring requires low viscosity of the raw materials, necessitating the addition of a high level of diluent to the formulation. This leads to volatilization of the diluent during curing, a significant environmental hazard. Thermosetting polyurethane elastomers, on the other hand, can address this issue by adjusting the raw material viscosity through heating to meet extrusion requirements. Therefore, utilizing blocked isocyanate technology to prepare thermosetting polyurethane elastomers for liquid deposition 3D printing is of great significance for promoting the green and sustainable development of polyurethane elastomers. Summary of the Invention

[0005] The technical challenge addressed by this invention is to overcome the shortcomings of existing technologies by inventing a method for preparing a thermosetting polyurethane elastomer suitable for 3D printing. This polyurethane elastomer utilizes a blocked isocyanate process to overcome the shortcomings of traditional polyurethane elastomer preparation processes, enabling quantitative control of the reaction rate of highly reactive polyurethane systems. The resulting single-component thermosetting polyurethane elastomer can be heated to adjust the raw material viscosity to meet the viscosity requirements of 3D printing, thus overcoming the environmental risks associated with the addition of large amounts of diluents to photocurable formulations.

[0006] The technical solution adopted by the present invention is a method for preparing a thermosetting polyurethane elastomer for 3D printing. The method is characterized in that the reaction rate of the polyurethane elastomer of the highly reactive polyurethane system is quantitatively controlled by the blocked isocyanate process to obtain a single-component thermosetting polyurethane elastomer. The specific steps of the preparation method are as follows:

[0007] Step 1: preparing a thermosetting polyurethane elastomer prepolymer;

[0008] Preparation of polyurethane prepolymer: using diisocyanate and diol as raw materials to prepare polyurethane prepolymer, the chemical reaction formula (1) is:

[0009]

[0010] Weigh vacuum-dried diol into a three-necked flask, heat to 60°C, and then add a measured amount of diisocyanate, wherein the molar ratio of diisocyanate NCO group to diol OH group is 1.05-5:1. After free reaction for 20-30 minutes, react at 75-85°C in a nitrogen atmosphere for 1.5-3 hours to prepare a polyurethane prepolymer.

[0011] Step 2: preparing a blocked thermosetting polyurethane elastomer prepolymer;

[0012] To prepare the end-capped prepolymer, an end-capping agent containing active hydrogen and an NCO-end-capped polyurethane prepolymer are used to prepare the end-capped prepolymer. The chemical reaction formula (2) is:

[0013]

[0014] After cooling the prepolymer prepared in step 1 to 50-60°C, add the end-capping agent in batches, react naturally for 30 minutes, and then heat to 70-100°C for end-capping reaction for 2-3 hours; the molar ratio of active hydrogen of the end-capping agent to NCO groups in the prepolymer is 1.05-1.5:1.

[0015] Step 3: preparing a single-component thermosetting polyurethane elastomer stock solution;

[0016] Add a measured amount of a diamine chain extender and a catalyst to the end-capped prepolymer prepared in step 2, and mix and stir evenly under a vacuum pressure of -0.10 MPa to -0.06 MPa and a temperature of 75-95°C to prepare a single-component thermosetting polyurethane elastomer stock solution. The diamine chain extender is one of diaminodiphenylmethane and p-phenylenediamine, or a mixture thereof, and the chain extension coefficient of the diamine chain extender relative to the prepolymer prepared in step 1 is 0.8-1.1. The catalyst is dibutyltin dilaurate (DBTL), and its amount is 0.5%-3.0% by mass of the end-capped prepolymer.

[0017] The method for preparing a thermosetting polyurethane elastomer for 3D printing is characterized in that in step 1 of the method, the diisocyanate is a mixture of one or more of p-phenylene diisocyanate (PPDI), 1,5-naphthalene diisocyanate (NDI) and diphenylmethane diisocyanate (MDI); the diol is a mixture of one or both of polycaprolactone diol (PCL) with a molecular weight Mn of 1000-3000 and polytetramethylene ether glycol (PTMG);

[0018] The method for preparing a thermosetting polyurethane elastomer for 3D printing is characterized in that the end-capping agent in step 2 of the method is an alcohol-type, aliphatic secondary amine-type, or alcoholamine-type end-capping agent with a relatively high deblocking temperature; the end-capping rate is ≥99% to be qualified, and the end-capping rate is calculated according to the following formula;

[0019]

[0020] The beneficial effects of the present invention are as follows: the 3D printable thermosetting polyurethane elastomer provided by the present invention is prepared using a blocked isocyanate process, breaking the limitation of high reactivity of the traditional polyurethane preparation process and providing a new idea for the development of high-performance polyurethane elastomers; the one-component polyurethane elastomer stock solution prepared by the present invention has the advantages of stable storage at room temperature and low toxicity; the material can be used for liquid deposition 3D printing molding, and the viscosity of the raw materials is adjusted by preheating to meet extrusion requirements, overcoming the environmental risks of high-content diluents added to reduce the viscosity of the raw materials in the light curing or light-heat dual curing process, which volatilizes during molding, thereby realizing the green preparation of high-performance polyurethane elastomers. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure is a flow chart of the preparation method of the thermosetting polyurethane elastomer in the present invention. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention is described in detail below with reference to the accompanying drawings and technical solutions.

[0023] The flow chart of the preparation method of a thermosetting polyurethane elastomer for 3D printing of the present invention is as follows: Figure 1As shown, the specific implementation steps of the embodiment are as follows:

[0024] Step 1: preparing a thermosetting polyurethane elastomer prepolymer;

[0025] A polyurethane prepolymer was prepared by using diisocyanate and diol as raw materials. The process was carried out according to chemical reaction formula (1). Vacuum-dried polycaprolactone diol (PCL) with a diol molecular weight of Mn1000 was weighed and added to a three-necked flask. The mixture was heated to 60°C. Then, a measured amount of diisocyanate p-phenylene diisocyanate (PPDI) was added. The molar ratio of the diisocyanate NCO group to the diol OH group was 1.05:1. After free reaction for 20 minutes, the mixture was reacted at 75°C in a nitrogen atmosphere for 1.5 hours to obtain a polyurethane prepolymer.

[0026] Step 2: preparing a blocked thermosetting polyurethane elastomer prepolymer;

[0027] Prepare a blocked prepolymer by using a blocking agent containing active hydrogen and an NCO-blocked polyurethane prepolymer. The process is carried out according to chemical reaction formula (2). After cooling the prepolymer prepared in step 1 to 60° C., add trichloroethanol, an alcohol-type blocking agent, in batches. After a natural reaction for 30 minutes, heat the mixture to 70° C. and block the reaction for 3 hours. The molar ratio of active hydrogen in the blocking agent to NCO groups in the prepolymer is 1.05:1.

[0028] Step 3: preparing a single-component thermosetting polyurethane elastomer stock solution;

[0029] Add the measured amount of diamine chain extender diaminodiphenylmethane and catalyst dibutyltin dilaurate (DBTL) to the capped prepolymer prepared in step 2, and mix and stir evenly at a vacuum pressure of -0.10 MPa and a temperature of 95°C to prepare a single-component thermosetting polyurethane elastomer stock solution. The chain extension coefficient of the diamine chain extender relative to the prepolymer prepared in step 1 is 0.8; the amount of catalyst dibutyltin dilaurate (DBTL) is 0.5% by mass of the capped prepolymer.

[0030] The method for preparing a thermosetting polyurethane elastomer for 3D printing is characterized in that the end-capping agent in step 2 of the method is an alcohol-type, aliphatic secondary amine-type, or alcoholamine-type end-capping agent with a relatively high deblocking temperature; the end-capping rate is ≥99% to be qualified, and the end-capping rate is calculated according to the following formula;

[0031]

[0032] Among them, the NCO mass fraction in the blocked prepolymer is 3.55%, and the NCO mass fraction in the prepolymer is 3.52%, then the blocking rate = 99.2, which is qualified.

Claims

1. A method for preparing a thermosetting polyurethane elastomer for 3D printing, characterized in that: This preparation method utilizes a blocked isocyanate process and a single-component blocked polyurethane elastomer solution to quantitatively control the reaction rate of a highly reactive polyurethane system. The resulting single-component thermosetting polyurethane elastomer is heated to adjust the raw material viscosity to meet the viscosity requirements of 3D printing, reducing the environmental risks associated with the large amount of diluent added to the photocuring formula. The specific steps of the method are as follows: Step 1: preparing a thermosetting polyurethane elastomer prepolymer; Preparation of polyurethane prepolymer: using diisocyanate and diol as raw materials to prepare polyurethane prepolymer, the chemical reaction formula (1) is: Weigh vacuum-dried diol into a three-necked flask, heat to 60°C, and then add a measured amount of diisocyanate, wherein the molar ratio of diisocyanate NCO groups to diol OH groups is 1.05-5:

1. After free reaction for 20-30 minutes, react at 75-85°C under a nitrogen atmosphere for 1.5-3 hours to prepare a polyurethane prepolymer; Step 2: preparing a blocked thermosetting polyurethane elastomer prepolymer; The end-capping prepolymer is prepared by using an active hydrogen-containing end-capping agent and an NCO-terminated polyurethane prepolymer. The chemical reaction formula (2) is: After cooling the prepolymer prepared in step 1 to 50-60°C, add the end-capping agent in batches, react naturally for 30 minutes, and then heat to 70-100°C for end-capping reaction for 2-3 hours; the molar ratio of active hydrogen of the end-capping agent to NCO groups in the prepolymer is 1.05-1.5:1; Step 3: preparing a single-component thermosetting polyurethane elastomer stock solution; Add a measured amount of a diamine chain extender and a catalyst to the end-capped prepolymer prepared in step 2, mix and stir evenly under a vacuum pressure of -0.10 MPa to -0.06 MPa and a temperature of 75-95° C. to prepare a single-component thermosetting polyurethane elastomer stock solution; wherein the diamine chain extender is one of diaminodiphenylmethane and p-phenylenediamine or a mixture of the two, and the chain extension coefficient of the diamine chain extender relative to the prepolymer prepared in step 1 is 0.8-1.1; and the catalyst is dibutyltin dilaurate, and its amount is 0.5%-3.0% by mass of the end-capped prepolymer.

2. The method for preparing a thermosetting polyurethane elastomer for 3D printing according to claim 1, wherein: In step 1 of the method, the diisocyanate is a mixture of one or more of p-phenylene diisocyanate, 1,5-naphthalene diisocyanate and diphenylmethane diisocyanate; and the diol is a mixture of one or two of polycaprolactone diol and polytetramethylene ether glycol with a molecular weight Mn of 1000-3000.

3. The method for preparing a thermosetting polyurethane elastomer for 3D printing according to claim 1 or 2, wherein: In step 2 of this method, the end-capping agent is an alcohol-type, aliphatic secondary amine-type, or alcoholamine-type end-capping agent having a relatively high deblocking temperature; the end-capping rate is ≥99% to be qualified, and the end-capping rate is calculated according to the following formula:

Images