A thermoset polyurethane neutron conversion screen and method of making the same

Abstract

The application discloses a kind of thermosetting polyurethane neutron conversion screen and preparation method thereof, adopt zinc sulfide fluorescent powder first in oligomer dihydric alcohol fully dispersed, then by in-situ polymerization method, prepare a kind of isocyanate group end-capped fluorescent powder polyurethane prepolymer, finally with the solidification crosslinking of low molecular polyhydric alcohol, high resolution, high brightness thermosetting polyurethane neutron conversion screen is prepared by pouring, with high sensitivity, high resolution and the like advantages.The in-situ polymerization process of fluorescent polyurethane prepolymer in the preparation of neutron conversion screen of the application is that the feeding ratio of diisocyanate and dihydric alcohol is (2.1-3.1):1, and the content of zinc sulfide fluorescent powder in the neutron conversion screen is 50-75%.

Description

TECHNICAL FIELD

[0001] The application relates to the field of neutron detector nondestructive testing photography, in particular to a thermosetting polyurethane neutron conversion screen and a preparation method thereof. BACKGROUND

[0002] The composition of a neutron radiography system mainly has three components: a neutron source, a collimator, and an image detector system (including a neutron fluorescent conversion screen). The key component for detecting the spatial distribution of the neutrons penetrating the sample is a position-sensitive neutron detector, which is referred to as a neutron-fluorescent conversion screen in the neutron radiography technology. The neutron-fluorescent conversion screen is actually a functional composite material in the form of a plate with a certain thickness, which functions to convert the neutrons penetrating the sample to be measured into backscattered protons by means of the interaction between the protons of a large number of hydrogen atoms in the neutron conversion material and the neutrons, and the backscattered protons make the fluorescent material emit light, thereby generating a material image on the photographic film which can be detected.

[0003] The neutron conversion screen is a key component of neutron radiography, and its performance directly affects the final imaging quality. At present, in the field of neutron radiography, the neutron conversion screens mainly used are mixed pressing screens composed of polyethylene, polypropylene, epoxy resin and fluorescent materials (mainly zinc sulfide (Ag) or Gd2S2O), organic scintillators containing aromatic benzene ring structures, and array waveguide fiber type neutron-fluorescent conversion screens. Among them, the scintillator screen and the array waveguide fiber screen have high detection efficiency (high brightness), but low resolution (more than 2 mm), and the mixed pressing screen has high resolution (less than 0.5 mm), but low detection efficiency (low brightness). The above three kinds of neutron conversion screens cannot provide satisfactory photographic effects. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a high-brightness thermosetting polyurethane neutron conversion screen and a preparation method thereof. The surface defects of the fluorescent powder are modified, and the uniform distribution of the fluorescent powder is realized. Thus, a high-resolution and high-brightness thermosetting polyurethane neutron conversion screen is obtained.

[0005] The present application provides a preparation method of an in-situ polymerized fluorescent polyurethane prepolymer, characterized by comprising the following steps:

[0006] a) raw material pretreatment:

[0007] A certain amount of polyether diol or polyester diol is weighed in a 250ml three-necked flask, and vacuum drying is performed at 110 DEG C for 1-2h using a water ring vacuum pump; a certain amount of silver-doped zinc sulfide fluorescent powder ZnS:Ag is weighed and placed in a vacuum oven at 80-100 DEG C for drying for 1-2h;

[0008] b) preparation of oligomer diol pre-dispersion:

[0009] A certain amount of the finished silver-doped zinc sulfide fluorescent powder ZnS:Ag and polyether glycol or polyester glycol, coupling agent, catalyst, antioxidant are dissolved in a solvent, and then dispersed in a high-speed disperser for 15-45 minutes to obtain a pre-dispersion of oligomeric diol, wherein the components are composed as follows in percentage by weight:

[0010]

[0011] c) Preparation of fluorescent polyurethane prepolymer:

[0012] A certain amount of fluorescent polyurethane prepolymer is taken at room temperature and put into a reactor equipped with a reflux condenser and a stirrer, then the pre-dispersion of diisocyanate: oligomeric diol is put into the diisocyanate at a molar ratio of 2.1-3.1:1.0, stirred at room temperature-40℃ for 1 hour, then slowly heated to 60-80℃ and stirred for 2-5 hours, and the reaction process is protected by nitrogen; the reaction is ended, and the tetrahydrofuran in the reaction mixture is removed by vacuum distillation with a water ring vacuum pump to obtain an in-situ polymerized fluorescent polyurethane prepolymer.

[0013] Further, the diisocyanate includes toluene diisocyanate (HDI), diphenyl methane diisocyanate (MDI), hydrogenated diphenyl methane diisocyanate (HMDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hexamethylene diisocyanate trimer (PHDI), lysine diisocyanate (LDI) or a combination thereof.

[0014] Further, the diisocyanate is in excess of 5-55% to ensure low degree of polymerization of the prepolymer and surface modification of the zinc sulfide fluorescent powder.

[0015] Further, the polyether glycol or polyester glycol includes ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, phthalic acid, adipic acid, halogenated phthalic acid, polyethylene glycol, polypropylene glycol, polytetrahydrofuran glycol or polyester diol prepared by esterification of phthalic anhydride or a combination thereof.

[0016] Further, the silver-doped zinc sulfide fluorescent powder ZnS:Ag includes silver-doped ZnS:Ag / Mn, ZnS:Ag / Cu, ZnS:Ag / Si or a combination thereof.

[0017] The present application provides a preparation method of a thermosetting polyurethane neutron conversion screen using the aforementioned fluorescent polyurethane prepolymer, characterized by comprising the following steps:

[0018] a) Preparation of curing agent:

[0019] The low-molecular polyol, the solvent, and the oligomer dihydric alcohol are mixed in a ratio of 1:1-2 by weight, and the alcohol hydroxyl equivalent weight of the oligomer dihydric alcohol is not more than that of the low-molecular polyol, to obtain the curing agent by stirring and mixing uniformly at room temperature.

[0020] b) mixing, pouring, and curing of the curing system:

[0021] b1) the fluorescent polyurethane prepolymer is put into a mixer equipped with a stirrer and a vacuum device, the curing agent is added at room temperature, and fast stirring is performed; after 3 minutes of stirring, vacuum is applied while stirring; the total mixing and stirring time is controlled to be 10-15 minutes;

[0022] b2) the stirring mixture is poured into a square plate cavity mold with a thickness of 1-6 mm, the mold is placed in a closed container that can be vacuumed, vacuum is applied for 30-60 minutes, and curing is performed at room temperature (25-40℃) for 20-72 hours;

[0023] b3) then the mold is heated to 60℃, curing is performed for 2 hours, natural cooling to room temperature is performed for 6 hours, the mold is heated to 80℃ again, curing is performed for 1 hour, and the mold is cooled and demolded; the edges are trimmed, and the defects are cleaned, to obtain the thermosetting polyurethane neutron conversion screen.

[0024] Further, the low-molecular polyol includes glycerol, triethanolamine, or a combination thereof.

[0025] Further, the curing agent contains a polyol with multiple functional groups and a dihydric alcohol with a long chain molecule, which has the effects of adjusting the reaction speed and reducing the viscosity of the curing system, and facilitates rapid degassing.

[0026] The application provides a thermosetting polyurethane neutron conversion screen, which is prepared according to the preparation method of the thermosetting polyurethane neutron conversion screen.

[0027] Further, the thermosetting polyurethane neutron conversion screen has a thickness of 0.5-0.8 mm. The greater the thickness, the higher the brightness, and the resolution decreases. Conversely, the greater the thickness, the lower the brightness, and the resolution increases. In the case of a certain composition of the fluorescent polyurethane functional material, the optimal balance between the resolution and the sensitivity can be adjusted by adjusting the thickness of the conversion screen.

[0028] In the reaction mixture composed of the above-mentioned various materials, the diisocyanate and the oligomeric diol are raw monomers for synthesizing the polyurethane, the synthesized polyurethane is the base material of the conversion screen, and also plays the role of an adhesive, and is also a material for generating recoil protons through nuclear reactions of neutrons; the role of the zinc sulfide fluorescent powder is to convert the energy of the deposited charged ions into visible light for the purpose of developing and photographing; the role of the coupling agent is to make the fluorescent powder more uniformly dispersed in the oligomeric diol; the role of the added solvent is to reduce the viscosity of the mixture with a high powder content; the role of the antioxidant is to prevent the organic polymer from being oxidized and discolored; the role of the catalyst is to promote the condensation reaction between the diisocyanate and the diol; the in-situ polymerization process used in the preparation of the polyurethane prepolymer has two advantages: firstly, the lower viscosity before the prepolymer is formed facilitates the uniform dispersion of the zinc sulfide fluorescent powder; and secondly, the surface defects of the zinc sulfide powder are modified during the polymerization process, thereby enhancing the light-emitting efficiency. The above-mentioned percentage ranges of the components, and the process conditions of the prepolymer preparation and curing process are determined through a large number of experiments. The above-mentioned matching percentages and the thickness range of the conversion screen enable the neutron conversion screen of the present application to have a good balance of high brightness, high resolution and formability.

[0029] Advantages of the present application:

[0030] The present application provides a neutron fluorescent conversion screen with the advantages of low cost, high brightness, high resolution, etc. It can overcome the poor imaging quality of the existing neutron conversion screen under the condition of low collimation ratio and high gamma background, and solve the problem that the existing neutron photographic conversion screen cannot simultaneously consider high sensitivity and high resolution. The neutron conversion screen of the present application has important significance for improving the quality of neutron imaging. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 Schematic diagram of the fluorescent spectra of ZnS:Ag, PU and ZSPU in Example 1 of the present application;

[0032] Figure 2 Schematic diagram of surface detection of the neutron conversion screen in Example 1 of the present application and four kinds of neutron conversion screens of the prior art;

[0033] Figure 3 Light-emitting brightness detection effect diagram of the neutron conversion screen in Example 1 of the present application and four kinds of neutron conversion screens of the prior art. DETAILED DESCRIPTION

[0034] The present application provides a preparation method of a fluorescent polyurethane prepolymer prepared by in-situ polymerization, characterized by comprising the following steps:

[0035] a) raw material pretreatment:

[0036] The weighed amount of polyether or polyester diol is placed in a 250 ml three-necked flask and vacuum dried at 110°C for 1-2 hours using a water ring vacuum pump to remove water. The weighed amount of silver-doped zinc sulfide fluorescent powder ZnS:Ag is placed in a vacuum oven at 80-100°C and dried for 1-2 hours.

[0037] b) Preparation of oligomeric diol pre-dispersion:

[0038] The weighed amount of silver-doped zinc sulfide fluorescent powder ZnS:Ag and polyether or polyester diol, coupling agent, catalyst, and antioxidant are dissolved in a solvent and dispersed thoroughly in a high-speed disperser for 15-45 minutes to obtain an oligomeric diol pre-dispersion. The components are present in the following weight percentages:

[0039]

[0040] c) Preparation of fluorescent polyurethane prepolymer:

[0041] The weighed amount of fluorescent polyurethane prepolymer is placed in a reactor equipped with a reflux condenser and a stirrer at room temperature. The pre-dispersion of diisocyanate: oligomeric diol is then added to the diisocyanate at a molar ratio of 2.1-3.1:1.0. The mixture is stirred at room temperature to -40°C for 1 hour, and then slowly heated to 60-80°C for 2-5 hours under nitrogen protection. The reaction is terminated, and the tetrahydrofuran in the reaction mixture is removed by vacuum distillation using a water ring vacuum pump to obtain an in-situ polymerized fluorescent polyurethane prepolymer.

[0042] Further, the diisocyanate includes toluene diisocyanate (HDI), diphenyl methane diisocyanate (MDI), hydrogenated diphenyl methane diisocyanate (HMDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hexamethylene diisocyanate trimer (PHDI), lysine diisocyanate (LDI), or a combination thereof.

[0043] Further, the diisocyanate is present in an excess of 5-55% to ensure low oligomerization of the prepolymer and surface modification of the zinc sulfide fluorescent powder.

[0044] Further, the polyether or polyester diol includes ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, phthalic acid, adipic acid, halogenated phthalic acid, polyethylene glycol, polypropylene glycol, polytetrahydrofuran diol, or polyester diol prepared by esterification of phthalic anhydride, or a combination thereof.

[0045] Further, the silver-doped zinc sulfide fluorescent powder ZnS:Ag includes silver-doped ZnS:Ag / Mn, ZnS:Ag / Cu, ZnS:Ag / Si, or a combination thereof.

[0046] The application provides a preparation method of the thermosetting polyurethane neutron conversion screen using the fluorescent polyurethane prepolymer, and is characterized by comprising the following steps.

[0047] a) curing agent preparation:

[0048] The low-molecular polyol, the solvent, and the oligomer dihydric alcohol are proportioned according to the weight ratio of the low-molecular polyol to the solvent being 1: (1-2), and the alcohol hydroxyl equivalent number of the oligomer dihydric alcohol is not more than the alcohol hydroxyl equivalent number of the low-molecular polyol, and the mixture is uniformly stirred at room temperature to obtain the curing agent;

[0049] b) mixing, pouring and curing of the curing system:

[0050] b1) the fluorescent polyurethane prepolymer is put into a mixer provided with a stirrer and a vacuumizing device, the curing agent is added at room temperature, and fast stirring is performed; after 3 minutes of stirring, vacuumizing is performed while stirring, and the total mixing and stirring time is controlled to be 10-15 minutes;

[0051] b2) the stirring mixture is poured into a square plate cavity mold with a thickness of 1-6 mm, the mold is placed into a closed container capable of being vacuumized, vacuumizing is performed for 30-60 minutes, and curing is performed at room temperature (25-40℃) for 20-72 hours;

[0052] b3) then the mold is heated to 60℃, curing is performed for 2 hours, natural cooling is performed to room temperature for 6 hours, heating is performed to 80℃ again, curing is performed for 1 hour, cooling and demolding are performed, the burrs are repaired, and the defects are cleaned, to obtain the thermosetting polyurethane neutron conversion screen.

[0053] Further, the low-molecular polyol includes glycerol, triethanolamine or a combination thereof.

[0054] Further, the curing agent comprises a polyfunctional polyol and a long-chain dihydric alcohol, which has the functions of adjusting the reaction speed and reducing the viscosity of the curing system, and facilitates rapid degassing.

[0055] The application provides a thermosetting polyurethane neutron conversion screen, which is obtained according to the preparation method of the thermosetting polyurethane neutron conversion screen.

[0056] Further, the thermosetting polyurethane neutron conversion screen has a thickness of 0.5-0.8 mm. The greater the thickness, the higher the brightness, and the resolution decreases. Conversely, the same is also true. In the case of a certain composition of the fluorescent polyurethane functional material, the optimal balance between the resolution and the sensitivity can be adjusted by adjusting the thickness of the conversion screen.

[0057] Example 1

[0058] Quantitatively weigh 12g (0.006mol) of PPG2000 (after vacuum dehydration at 110℃ for 1 hour), 0.22g of dodecyltrimethoxysilane, 15.78g of ZnS:Ag, 0.6g of tetrahydrofuran, 0.015g of antioxidant 1010, and the catalyst dibutyltin dilaurate (DBTDL) into a beaker. Stir thoroughly for 1 hour using a high-speed disperser, then transfer to a 100ml three-necked flask. Add 2.83g (0.01275mol) of IPDI to the flask and stir at room temperature for half an hour. Then, react at 60℃ for 2 hours. Afterward, remove the THF solvent under vacuum to obtain a composite prepolymer of zinc sulfide / polyurethane in situ polymerization. Cool to 40℃, add 0.5967g of triethanolamine (TEOA) dissolved in 1.5ml of THF solvent and 0.12g of PPG2000 solution, and continue stirring for 5 minutes. After stirring, the mixture was sonicated for 10 minutes to remove most of the air bubbles. Then, a vacuum pump was used to further remove tetrahydrofuran solvent and air bubbles from the product. The product was then poured into a polytetrafluoroethylene (PTFE) disc and left at room temperature for 24 hours. It was then placed in a vacuum oven and cured at 60°C for 6 hours. Finally, after resting for 6 hours, it was cured in an oven at 80°C for 1 hour. Cooling and demolding yielded a thermosetting polyurethane conversion screen with a zinc sulfide content of 50% and a thickness of 2 mm. Figure 1 A schematic diagram of the fluorescence spectra of ZnS:Ag, PU, ​​and ZSPU in Example 1 of this invention.

[0059] Example 2

[0060] Quantitatively weigh 12g (0.006mol) of PPG2000 (after vacuum dehydration at 110℃ for 1 hour), 0.22g of dodecyltrimethoxysilane, 3.67g of ZnS:Ag2, 1.0g of tetrahydrofuran, 0.015g of antioxidant 300, and the catalyst dibutyltin dilaurate (DBTDL) into a beaker. Stir thoroughly for 1 hour using a high-speed disperser, then transfer to a 100ml three-necked flask. Next, weigh 2.83g (0.01275mol) of IPDI and add it to the flask. Stir at room temperature for half an hour, then react at 60℃ for 2 hours. Afterward, remove the solvent THF under vacuum to obtain a composite prepolymer of zinc sulfide / polyurethane in situ polymerization. Cool to 40℃, add 0.5967g of triethanolamine (TEOA) and 0.12g of PPG2000 solution dissolved in 1.5ml of THF solvent, and continue stirring for 5 minutes. After stirring, the mixture was sonicated for 10 minutes to remove most of the air bubbles. Then, a vacuum pump was used to further remove tetrahydrofuran solvent and air bubbles from the product. The product was then poured into a polytetrafluoroethylene (PTFE) disc and left at room temperature for 24 hours. It was then placed in a vacuum oven and cured at 60°C for 6 hours. Finally, after resting for 12 hours, it was cured in an oven at 80°C for 0.5 hours. Cooling and demolding yielded a thermosetting polyurethane conversion screen with a zinc sulfide content of 60% and a thickness of 2 mm.

[0061] Example 3

[0062] Example 3

[0063] Example 4

[0064] Example 4

[0065] Example 5-8, operating method same as example 1, thickness changed to 0.5mm, 1.0mm, 1.5mm, 3mm.

[0066] Example 9-12, operating method same as example 2, thickness changed to 0.5mm, 1.0mm, 1.5mm, 3mm.

[0067] Example 13-16, operating method same as example 3, thickness changed to 0.5mm, 1.0mm, 1.5mm, 3mm.

[0068] Example 17-20, operating method same as example 4, thickness changed to 0.5mm, 1.0mm, 1.5mm, 3mm.

[0069] The relative brightness of the neutron conversion screen prepared by the method of the above 20 examples is shown in Table 1. The brightness of the conversion screen of example 1 is compared with the brightness of the existing mixed pressure type neutron conversion screen, Figure 2 The surface detection schematic diagram of the neutron conversion screen of example 1 of the application and four kinds of neutron conversion screens of the prior art, Figure 3 The light-emitting brightness detection effect diagram of the neutron conversion screen of example 1 of the application and four kinds of neutron conversion screens of the prior art, wherein F0, EVA, EP, PP and ZSPU respectively represent imported commercial neutron conversion screen, domestic EVA conversion screen, domestic EP (epoxy) conversion screen, domestic PP conversion screen and example 1 thermosetting polyurethane conversion screen. At the same time, the resolution of the thermosetting polyurethane conversion screen is equivalent to that of the existing neutron conversion screen with the same thickness. It can be seen that the thermosetting polyurethane conversion screen prepared by the in-situ polymerization method can maintain a high resolution while greatly increasing the brightness and improving the detection sensitivity. This has important significance for improving the imaging quality in the field of neutron photography.

[0070] Table 1 brightness analysis results of ZSPU with different contents and thicknesses

[0071]

[0072] The thickness of the neutron conversion screen of the application is 0.1-8.0mm, and the most preferred thickness is 1.5-3.0mm. The main function of the neutron conversion screen is to convert the spatial distribution of the undetectable neutron into the spatial distribution of the detectable visible light. The fluorescence generated by the luminescent material zinc sulfide in the conversion screen is weakened in inverse proportion to the square of the distance on the one hand, and is attenuated by the absorption of the screen material itself on the other hand. Therefore, the thickness of the neutron conversion screen should be balanced between sensitivity (detection efficiency) and resolution. After a large amount of theoretical calculation and experiment, it is determined that the thickness of the neutron conversion screen is 1.5-3.5mm.

[0073] The present application is described in detail above with reference to specific embodiments and exemplary examples. The foregoing description is exemplary and explanatory only, and is not intended to be exhaustive or to limit the application to the precise embodiments disclosed; the description is not intended to limit the application to the embodiments described above, which are presented as examples. The description is not intended to limit the application to the precise embodiments described above. Many modifications, equivalents, and variations are possible in light of this disclosure, which is intended to be broadly applicable to the various embodiments disclosed and to all equivalent structures and processes. The scope of the application is not limited to the specific embodiments described above, but rather only by the claims below.

Claims

1. A process for the preparation of in-situ polymerized fluorescent polyurethane prepolymer characterized in that, Comprising the following steps: a) raw material pretreatment: Take a certain amount of polyether diol or polyester diol in a 250 ml three-necked flask, vacuum drying at 110°C for 1-2 hours with a water ring vacuum pump; take a certain amount of silver-doped zinc sulfide fluorescent powder ZnS:Ag and place it in a vacuum oven at 80-100°C for drying for 1-2 hours; b) preparation of oligomer diol pre-dispersion: Take a certain amount of treated silver-doped zinc sulfide fluorescent powder ZnS:Ag and polyether diol or polyester diol, coupling agent, catalyst, and antioxidant, and dissolve them in a solvent, and then disperse them in a high-speed disperser for 15-45 minutes to obtain an oligomer diol pre-dispersion, wherein the components are composed as follows in terms of weight percentage: Polyether diol or polyester diol 17-30% Silver-doped zinc sulfide fluorescent powder ZnS:Ag 50-70% Coupling agent 0.05-1.5% Antioxidant 0.1-0.2% Solvent 5-15% Catalyst 0.05-0.3% The sum of the weight percentages of the above components is 100%; c) preparation of fluorescent polyurethane prepolymer: Take a certain amount of oligomer diol pre-dispersion at room temperature and put it into a reactor equipped with a reflux condenser and a stirrer, then add diisocyanate: oligomer diol pre-dispersion at a molar ratio of 2.1-3.1:1.0, stir the diisocyanate at room temperature-40°C for 1 hour, then slowly warm it up to 60-80°C and stir for 2-5 hours, and use nitrogen protection during the reaction; end the reaction, and use a water ring vacuum pump to reduce pressure and distill tetrahydrofuran from the reaction mixture to obtain in-situ polymerized fluorescent polyurethane prepolymer.

2. A process for the preparation of in-situ polymerized fluorescent polyurethane prepolymer according to claim 1, characterized in that, The diisocyanate includes toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, lysine diisocyanate, or a combination thereof.

3. A process for the preparation of in-situ polymerized fluorescent polyurethane prepolymer according to claim 1, characterized in that, The diisocyanate is in an excess of 5-55%.

4. A process for the preparation of in-situ polymerized fluorescent polyurethane prepolymer according to claim 1, characterized in that, The polyether diol includes polyethylene glycol, polypropylene glycol, polytetrahydrofuran diol, or a combination thereof, and the polyester diol includes ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, phthalic acid, adipic acid, halogenated phthalic acid, or phthalic anhydride prepared by esterification, or a combination thereof.

5. A process for the preparation of in-situ polymerized fluorescent polyurethane prepolymer according to claim 1, characterized in that, The silver-doped zinc sulfide fluorescent powder ZnS:Ag includes silver-doped ZnS:Ag / Mn, ZnS:Ag / Cu, ZnS:Ag / Si, or a combination thereof.

6. A process for the production of a thermoset polyurethane neutron conversion screen prepared from a fluorescent polyurethane prepolymer produced by the process according to any one of claims 1 to 5, characterised in that, Comprising the following steps: a) curing agent preparation: Mix low molecular polyol, solvent, and oligomer diol at a weight ratio of 1: (1-2) of low molecular polyol to solvent, and the alcohol hydroxyl equivalent number of oligomer diol does not exceed that of low molecular polyol, stir and mix uniformly at room temperature to obtain a curing agent; b) mixing, pouring, and curing of the curing system: b1) Put the fluorescent polyurethane prepolymer into a mixer equipped with a stirrer and a vacuum device, add the curing agent at room temperature, stir quickly, and start stirring for 3 minutes, then stir while vacuuming, and the total mixing and stirring time is controlled at 10-15 minutes; b2) pouring the stirred mixture into a square cavity mold with a thickness of 1-6 mm, placing the mold into a vacuumable closed container, vacuuming for 30-60 min, and curing at room temperature for 20-72 hours; b3) subsequently heating the mold to 60°C, curing for 2 hours, naturally cooling to room temperature for 6 hours, heating again to 80°C, curing for 1 hour, cooling and demolding, trimming the edges, and cleaning the defects to obtain the thermosetting polyurethane neutron converter.

7. Process for the production of a thermosetting polyurethane neutron converter screen according to claim 6, characterized in that The low molecular polyol includes glycerol, triethanolamine, or a combination thereof.

8. A thermoset polyurethane neutron conversion screen characterized by, The thermosetting polyurethane neutron converter is prepared according to the method of any one of claims 6-7.

9. The thermoset polyurethane neutron conversion screen according to claim 8, characterized in that, The thermosetting polyurethane neutron converter has a thickness of 0.5-0.8 mm.

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