Thermoplastic polyurethane composite fast neutron conversion screen and method of making same

Abstract

The application discloses a thermoplastic polyurethane composite fast neutron conversion screen and a preparation method thereof. The surface-treated zinc sulfide fluorescent powder is first fully dispersed in an oligomer diol, and then an isocyanate group terminated fluorescent powder polyurethane prepolymer is prepared through an in-situ polymerization method. Finally, with the aid of chain extension of a low molecular diol, a thermoplastic polyurethane in-situ composite functional composite material is obtained. The thermoplastic composite material is hot-pressed into a high-resolution and high-brightness thermoplastic polyurethane fast neutron conversion screen with different thicknesses and different width sizes, and has the advantages of high sensitivity and high resolution, and can overcome the defects of poor imaging quality of the existing fast neutron conversion screen under a high gamma background.

Description

Technical Field

[0001] This application relates to the field of nondestructive testing and imaging of neutron detectors, and in particular to a thermoplastic polyurethane composite fast neutron conversion screen and its preparation method. Background Technology

[0002] A neutron radiography system mainly consists of three components: a neutron source, a collimator, and an image detector system (including a neutron-fluorescence conversion screen). The key component for detecting the spatial distribution of neutrons transmitted through the sample is the position-sensitive neutron detector, known in neutron radiography as the neutron-fluorescence conversion screen. The neutron-fluorescence conversion screen is actually a plate-shaped functional composite material of a certain thickness. Its function is to convert neutron rays transmitted through the sample into recoil protons by the interaction of protons and neutrons in a large number of hydrogen atoms in the neutron conversion material within the screen. These recoil protons cause the fluorescent material to emit light, thus producing a detectable image of the material on the photographic film.

[0003] The fast neutron conversion screen is a key component in fast neutron radiography, and its performance directly affects the final image quality. Currently, in the field of fast neutron radiography, the fast neutron conversion screens used are mainly composite screens made of polyethylene, polypropylene, epoxy resin, etc., combined with fluorescent materials (mostly zinc sulfide (Ag) or Gd₂S₂O), containing aromatic... benzene ring Organic scintillators and arrayed wave-shifting fiber optic fast neutron-fluorescence conversion screens are among the options. Scintillator screens and arrayed wave-shifting fiber optic screens offer high detection efficiency (high brightness) but low resolution (above 2 mm), while mixed-voltage screens offer relatively high resolution (below 0.5 mm) but low detection efficiency (low brightness). None of these three types of fast neutron conversion screens can provide satisfactory photographic results. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a thermoplastic polyurethane composite fast neutron conversion screen and its preparation method. This invention prepares a thermoplastic polyurethane fluorescent conversion screen containing phosphor through in-situ polymerization. The surface of the phosphor is modified using an appropriate method to achieve uniform distribution of the phosphor. This results in a high-resolution, high-brightness thermoplastic polyurethane fast neutron conversion screen. The high-brightness, high-resolution thermoplastic polyurethane fast neutron conversion screen of this invention is characterized by the following: the preparation of the fluorescent conversion screen includes a process of preparing a transparent polyurethane prepolymer from diisocyanate and oligomeric diols (polyether diols or polyester diols), an in-situ chain extension reaction process between the transparent polyurethane prepolymer and zinc sulfide phosphor, and a hot-pressing process of the thermoplastic fluorescent polyurethane composite material.

[0005] This invention provides a method for preparing a transparent polyurethane prepolymer, characterized by comprising the following steps:

[0006] Step 1: Raw material pretreatment

[0007] The amount of polyether diol or polyester diol is weighed in a 250ml three-necked flask, and vacuum drying at 110℃ for 1-2h using a water ring vacuum pump; the amount of silver-doped zinc sulfide fluorescent powder ZnS:Ag is weighed, and surface modification is performed using hydrogen peroxide or ammonia solution to improve the luminescent properties of the zinc sulfide fluorescent powder and the bonding and dispersion properties with polyurethane, and then dried in a vacuum oven at 80-100℃ for 1-2h;

[0008] Step 2: Preparation of transparent polyurethane prepolymer

[0009] The amount of oligomeric diol is taken into a reactor equipped with a reflux condenser and a stirrer, and the diisocyanate is added at a molar ratio of diisocyanate to oligomeric diol of 2.1-3.1:1.0, and a small amount of catalyst is added, and stirred at room temperature (25-40℃) for 1h, and slowly heated to 60-80℃ and stirred for 2-5h, and nitrogen protection is adopted during the reaction, and the double-functional transparent polyurethane prepolymer is obtained after the reaction is completed.

[0010] 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.

[0011] Further, the oligomeric 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.

[0012] 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.

[0013] The present application provides a transparent polyurethane prepolymer, which is prepared by the above-mentioned preparation method.

[0014] The present application provides a preparation method of a thermoplastic polyurethane composite fast neutron conversion screen using the above-mentioned transparent polyurethane prepolymer, which comprises the following steps:

[0015] Step 1: Preparation of a pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder

[0016] A certain amount of zinc sulfide fluorescent powder ZnS:Ag and transparent polyurethane prepolymer, dispersant, antioxidant, solvent are dispersed in a high-speed disperser for 30-60 minutes to obtain a pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder, wherein the zinc sulfide fluorescent powder ZnS:Ag and transparent polyurethane prepolymer, dispersant, antioxidant, solvent are composed as follows in percentage by weight:

[0017]

[0018] Step 2: Chain extension of fluorescent polyurethane prepolymer

[0019] According to the formula of the fluorescent polyurethane prepolymer pre-dispersion system, the molar content of diisocyanate groups is calculated, and the corresponding low molecular chain extender is added to the pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder prepared in step 1 at room temperature;

[0020] A certain amount of the pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder after reaction is subjected to vacuum distillation to remove the solvent in the reaction mixture, then stirred at room temperature for 30 minutes, and then slowly heated to 70-90°C for 2-5 hours of stirring reaction, and then discharged, and then cut into particles to obtain in-situ polymerized thermoplastic polyurethane fluorescent composite particles.

[0021] Step 3: Hot pressing of thermoplastic polyurethane fast neutron fluorescent conversion screen

[0022] The thermoplastic polyurethane fluorescent composite particles obtained in step 2 are dried, preheated, placed in a certain plate mold on a flat vulcanizing machine for hot pressing, then cold pressed, cooled, demolded, trimmed, and cleaned to obtain a thermoplastic polyurethane composite fast neutron conversion screen with a desired thickness.

[0023] Further, the hot pressing process is first plasticized at 160°C for 20 min, then hot pressed at 160°C for 5 min at a pressure of 10.0 Mpa, and finally cold pressed at room temperature for 20 min.

[0024] The present application provides a thermoplastic polyurethane composite fast neutron conversion screen, characterized in that it is obtained according to the preparation method of the thermoplastic polyurethane composite fast neutron conversion screen.

[0025] Further, the thermosetting polyurethane neutron conversion screen has a thickness of 0.1-8.00 mm, and the greater the thickness, the higher the brightness, and the resolution decreases. Conversely, the same is true. Under the condition that the composition of the fluorescent polyurethane functional material is constant, the optimal balance between resolution and sensitivity can be adjusted by adjusting the thickness of the conversion screen.

[0026] In the reaction mixture composed of the above-mentioned various materials, the diisocyanate and the oligomer diol are raw monomers for synthesizing 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 producing recoil protons through nuclear reactions of fast neutrons; the role of the zinc sulfide fluorescent powder is to convert the energy deposited by fast neutrons into visible light for the purpose of developing and photographing; the purpose of surface modification of the zinc sulfide fluorescent powder is to improve the luminescent performance of the fluorescent powder and the combination and dispersion performance with the polyurethane prepolymer; the main role of the solvent added is to reduce the viscosity of the mixture with a high powder content, and 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 chain extension process of the polyurethane prepolymer is a process of in-situ chain extension after mixing with the zinc sulfide fluorescent powder, which is beneficial to the uniform dispersion of the zinc sulfide fluorescent powder at a lower viscosity before the formation of the thermoplastic polyurethane polymer. The above-mentioned percentage ranges of the components, the preparation process of the thermoplastic polyurethane prepolymer, and the in-situ chain extension process after mixing with the zinc sulfide fluorescent powder are determined through a large number of experiments. The above-mentioned matching percentages and the thickness range of the conversion screen make the fast neutron conversion screen of the present application have a good balance of high brightness, high resolution, and moldability.

[0027] Advantages of the present application:

[0028] The present application provides a fast neutron fluorescent conversion screen with the advantages of low cost, high brightness, high resolution, etc. At the same time, it is convenient to shape and can be repeatedly processed and used. It can overcome the shortcomings of the existing fast neutron conversion screen in that the imaging quality is poor under the condition of low collimation ratio and high gamma background, and solve the problem that the existing fast neutron photographic conversion screen cannot simultaneously consider high sensitivity and high resolution. The fast neutron conversion screen of the present application has important significance for improving the imaging quality of fast neutrons. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The fluorescence intensity histogram of the composite film containing zinc sulfide fluorescent powder before and after H2O2 treatment in Example 1 of the present application;

[0030] Figure 2 The fluorescence spectrum detection graph of the thermoplastic polyurethane composite film with different contents of zinc sulfide fluorescent powder in Example 1 of the present application. DETAILED DESCRIPTION

[0031] The present application provides a preparation method of a transparent polyurethane prepolymer, characterized by comprising the following steps:

[0032] Step 1: raw material pretreatment

[0033] A certain amount of polyether diol or polyester diol is weighed in a 250ml three-necked flask, and vacuum drying at 110℃ using a water ring vacuum pump for 1-2h; a certain amount of silver-doped zinc sulfide fluorescent powder ZnS:Ag is weighed, and surface modification is performed using hydrogen peroxide or ammonia solution to improve the luminescent properties of the zinc sulfide fluorescent powder and the bonding and dispersion properties with polyurethane, and then dried in a vacuum oven at 80-100℃ for 1-2h;

[0034] Step 2: Preparation of transparent polyurethane prepolymer

[0035] A certain amount of oligomeric diol is taken into a reactor equipped with a reflux condenser and a stirrer, diisocyanate is added at a molar ratio of diisocyanate to oligomeric diol of 2.1-3.1:1.0, and a small amount of catalyst is added, and stirred at room temperature (25-40℃) for 1h, and slowly heated to 60-80℃ and stirred for 2-5h, and nitrogen protection is adopted during the reaction, and a bifunctional transparent polyurethane prepolymer is obtained after the reaction is completed.

[0036] 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.

[0037] Further, the oligomeric 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.

[0038] 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.

[0039] The present application provides a transparent polyurethane prepolymer, which is prepared by the above-mentioned preparation method.

[0040] The present application provides a preparation method of a thermoplastic polyurethane composite fast neutron conversion screen using the above-mentioned transparent polyurethane prepolymer, which comprises the following steps:

[0041] Step 1: Preparation of a pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder

[0042] A certain amount of zinc sulfide fluorescent powder ZnS:Ag and transparent polyurethane prepolymer, dispersant, antioxidant, solvent are dispersed in a high-speed disperser for 30-60 minutes to obtain a pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder, wherein the zinc sulfide fluorescent powder ZnS:Ag and transparent polyurethane prepolymer, dispersant, antioxidant, solvent are composed as follows in percentage by weight:

[0043]

[0044] Step 2: Chain extension of fluorescent polyurethane prepolymer

[0045] According to the formula of the fluorescent polyurethane prepolymer pre-dispersion system, the molar content of diisocyanate groups is calculated, and the corresponding low molecular chain extender is added to the transparent polyurethane prepolymer and fluorescent powder pre-dispersion system prepared in step 1 at room temperature;

[0046] A certain amount of the transparent polyurethane prepolymer and fluorescent powder pre-dispersion system after reaction is subjected to vacuum distillation to remove the solvent in the reaction mixture, followed by stirring at room temperature for 30 minutes, and then slowly heating to 70-90°C for 2-5 hours of stirring reaction, and then discharging, and cutting to obtain in-situ polymerized thermoplastic polyurethane fluorescent composite particles.

[0047] Step 3: Hot pressing of thermoplastic polyurethane fast neutron fluorescent conversion screen

[0048] The thermoplastic polyurethane fluorescent composite particles obtained in step 2 are dried, preheated, and placed in a certain plate mold on a flat vulcanizing machine for hot pressing, and then cooled, cooled, demolded, trimmed, and cleaned to obtain a thermoplastic polyurethane composite fast neutron conversion screen with a desired thickness.

[0049] Further, the hot pressing process is first plasticized at 160°C for 20 min, then hot pressed at 160°C for 5 min at a pressure of 10.0 Mpa, and finally cold pressed at room temperature for 20 min.

[0050] The present application provides a thermoplastic polyurethane composite fast neutron conversion screen, characterized in that it is obtained according to the preparation method of the thermoplastic polyurethane composite fast neutron conversion screen.

[0051] Further, the thermosetting polyurethane neutron conversion screen has a thickness of 0.1-8.00 mm, and the greater the thickness, the higher the brightness, and the resolution decreases. Conversely, the same is true. Under the condition that the composition of the fluorescent polyurethane functional material is constant, the optimal balance between resolution and sensitivity can be adjusted by adjusting the thickness of the conversion screen.

[0052] The fast neutron conversion screen of the present application has a thickness of 0.1-8.0 mm, and the most preferred thickness is 1.0-3.0 mm. The main function of the fast neutron conversion screen is to convert the spatial distribution of the undetectable fast neutrons into the spatial distribution of the detectable visible light. The fluorescent light generated by the luminescent material zinc sulfide in the conversion screen is weakened in inverse proportion to the square of the distance, and is also attenuated by the absorption of the screen material itself. Therefore, the thickness of the fast neutron conversion screen should be selected to balance the sensitivity (detection efficiency) and the resolution. After a large number of theoretical calculations and experiments, it is determined that the thickness of the fast neutron conversion screen is 1.0-3.5 mm.

[0053] Example 1

[0054] First, the surface-modified zinc sulfide fluorescent powder is prepared. 20 g of ZnS:Ag fluorescent powder is mixed with 100 ml of hydrogen peroxide in a conical flask, and then placed on a magnetic stirrer at 50°C for 4 hours. After filtration, the filter residue is dried in a vacuum oven at 60°C for 4 hours to obtain the surface-modified fluorescent powder. A quantitative amount of polypropylene glycol PPG2000 (12 g, 0.006 mol) which has been vacuumed at 110°C for 1 hour to remove water, 0.015 g of antioxidant 1010, and 2.83 g of isophorone diisocyanate (IPDI) (0.01275 mol) are added to a three-necked flask. The mixture is stirred at room temperature for half an hour, and then reacted at 60°C for 2 hours to obtain a transparent polyurethane prepolymer. The temperature is reduced to below 40°C, 1.5 ml of tetrahydrofuran is added, and then transferred to a dispersion cup. 15 g of the surface-modified fluorescent powder and 0.1 g of Span-80 are added, and then dispersed by a high-speed disperser for 1 hour. The mixture is then transferred to a 100 ml three-necked flask. Then, 0.805 g of dipropylene glycol is added, and the mixture is stirred at 40°C for 30 min. The temperature is then increased to 60°C, and the mixture is reacted for 3 hours. The reaction is continued at 80°C for 1 hour to complete the reaction. After the reaction is completed, the product is poured into a polytetrafluoroethylene square tray, and then placed in a fume hood at room temperature for 24 hours to allow the solvent to evaporate. Then, the product is placed in a vacuum oven at 60°C for 6 hours to dry. The dried film is cut into particles by a scissors to obtain the thermoplastic polyurethane fluorescent composite particles. Finally, the particles are placed in a 2 mm thick plate mold, and then placed on a flat vulcanizing machine to be hot-pressed. The hot-pressing process is as follows: preheating at 160°C for 20 min, hot-pressing at 160°C for 8 min, and pressure of 10.0 MPa. Then, the mixture is cold-pressed at room temperature for 20 min. After cooling and demolding, a thermoplastic polyurethane conversion screen with a zinc sulfide content of 50% and a thickness of 2 mm is obtained. Figure 1 The bar graph of the fluorescent intensity of the composite film containing the zinc sulfide fluorescent powder (16.6%) before and after H2O2 treatment. The thermoplastic polyurethane composite is prepared by in-situ chain extension polymerization, and the zinc sulfide fluorescent powder is treated by 7.5% hydrogen peroxide at 50°C for 4 hours. Figure 2The thermoplastic polyurethane composite film of the embodiment 1 of the present application is shown in the fluorescence spectrum of the different content of zinc sulfide fluorescent powder, wherein the content of zinc sulfide fluorescent powder is the weight percentage of the composite.

[0055] Embodiment 2

[0056] First, the surface modified zinc sulfide fluorescent powder is prepared, 20g of ZnS:Ag fluorescent powder is mixed with 100ml of 5% potassium permanganate aqueous solution in a conical flask, and then placed on a magnetic stirrer at 50°C for 4 hours, filtered, washed with water for 4-5 times, and the filter residue is dried in a vacuum oven at 60°C for 4 hours to obtain the surface modified fluorescent powder; 12g (0.006mol) of polypropylene glycol PPG2000 which is vacuumed at 110°C for 1 hour to remove water, 0.015g of antioxidant 1010, catalyst dibutyltin dilaurate (DBTDL), 3.34g (0.01275mol) of 4,4-dicyclohexylmethane diisocyanate (HMDI) are weighed and added into a three-necked flask, stirred at room temperature for half an hour, and then reacted at 60°C for 2 hours to obtain a transparent polyurethane prepolymer. The temperature is reduced to below 40°C, 1.5ml of tetrahydrofuran is added, and then transferred into a dispersion cup, 15.6g of surface modified fluorescent powder and 0.1g of Span-80 are added, and dispersed by a high-speed disperser for 1h, and then transferred into a 100ml three-necked flask. Then 0.805g of dipropylene glycol is added, and stirred at 40°C for 30min, and then heated to 60°C for 3 hours, and then continued to stir at 80°C for 1 hour to complete the reaction. After the reaction is completed, the product is poured into a polytetrafluoroethylene square plate, and placed in a fume hood at room temperature to volatilize the solvent for 24 hours, and then placed in a vacuum oven at 60°C for 6h, and then the dried film is taken out, cut into particles with scissors, and then a thermoplastic polyurethane fluorescent composite particle is obtained. Finally, the particle is placed in a 2mm thick plate mold, and placed on a flat vulcanizing machine to heat and press into a shape. The heat pressing process is 160°C preheating for 20min, heat pressing at 160°C for 8min, and the pressure is 10.0MPa; and then cooled and pressed at room temperature for 20min. The vulcanized zinc content is 50%, and the thickness of the thermoplastic polyurethane conversion screen is 2mm.

[0057] Embodiment 3

[0058] Firstly, the surface-modified zinc sulfide fluorescent powder was prepared. 20 g of ZnS:Ag fluorescent powder was mixed with 100 ml of hydrogen peroxide in a conical flask, and then placed on a magnetic stirrer at 50°C for 4 hours. After filtration, the filter residue was dried in a vacuum oven at 60°C for 4 hours to obtain the surface-modified fluorescent powder. A quantitative amount of polytetrahydrofuran PTMG2000 (0.006 mol) which was vacuumed to remove water at 110°C for 1 hour, 0.015 g of antioxidant 1010, catalyst dibutyltin dilaurate (DBTDL), and 4,4-dicyclohexylmethane diisocyanate (HMDI) 3.34 g (0.01275 mol) were added to a three-necked flask, stirred at room temperature for half an hour, and then reacted at 60°C for 2 hours to obtain a transparent polyurethane prepolymer. The temperature was reduced to below 40°C, 1.5 ml of tetrahydrofuran was added and stirred, poured into a dispersion cup, 10.6 g of surface-modified fluorescent powder and 0.1 g of Span-40 were added, and dispersed by a high-speed dispersion machine for 1 hour. Then, it was transferred into a 100 ml three-necked flask. Then, 0.805 g of dipropylene glycol was added, and stirred at 40°C for 30 min, and then heated to 60°C for 3 hours, and continued to stir at 80°C for 1 hour to complete the reaction. After completion, the product was poured into a polytetrafluoroethylene square plate, and placed in a fume hood at room temperature to allow the solvent to evaporate for 24 hours, and then placed in a vacuum oven at 60°C for 6 hours. The dried film was cut into particles with a scissors, and a thermoplastic polyurethane fluorescent composite particle was obtained. Finally, the particles were placed in a 2 mm thick plate mold, and placed on a flat vulcanizing machine to heat press. The heat pressing process was preheating at 160°C for 20 min, hot pressing at 160°C for 8 min, and the pressure was 10.0 MPa. Then, it was cooled and demolded at room temperature for 20 min. A thermoplastic polyurethane conversion screen with a zinc sulfide content of 40% and a thickness of 2 mm was obtained.

[0059] Example 4

[0060] Firstly, the surface-modified zinc sulfide fluorescent powder was prepared. 20 g of ZnS:Ag fluorescent powder and 100 ml of hydrogen peroxide were mixed in a conical flask, and then placed on a magnetic stirrer at 50°C for 4 hours. After filtration, the residue was washed with water for 4-5 times, and then dried in a vacuum oven at 60°C for 4 hours to obtain the surface-modified fluorescent powder. 12 g (0.006 mol) of polypropylene glycol PPG2000, which was vacuum-dried at 110°C for 1 hour, 0.015 g of antioxidant 1010, catalyst dibutyltin dilaurate (DBTDL), and 3.34 g (0.01275 mol) of 4,4-dicyclohexylmethane diisocyanate (HMDI) were weighed into a three-necked flask, and stirred at room temperature for half an hour. Then, the reaction was carried out at 60°C for 2 hours to obtain a transparent polyurethane prepolymer. The temperature was reduced to below 40°C, 1.5 ml of tetrahydrofuran was added, and then transferred into a dispersion cup. 10.6 g of the surface-modified fluorescent powder and 0.1 g of Span-80 were added, and dispersed by a high-speed disperser for 1 hour. Then, the product was transferred into a 100 ml three-necked flask. 0.805 g of dipropylene glycol was added, and stirred at 40°C for 30 min. Then, the temperature was increased to 60°C, and the reaction was carried out for 3 hours. The reaction was continued at 80°C for 1 hour. After the reaction was completed, the product was poured into a polytetrafluoroethylene square plate, and placed in a fume hood at room temperature for 24 hours to volatilize the solvent. Then, the product was placed in a vacuum oven at 60°C for 6 hours to dry. The dried film was cut into particles by a scissors to obtain the thermoplastic polyurethane fluorescent composite particles. Finally, the particles were placed in a 2 mm thick plate mold, and hot-pressed on a flat vulcanizing machine. The hot-pressing process was as follows: preheating at 160°C for 20 min, hot-pressing at 160°C for 8 min, and pressure of 10.0 MPa. Then, the product was cooled and demolded at room temperature for 20 min to obtain a thermoplastic polyurethane conversion screen with a zinc sulfide content of 40% and a thickness of 2 mm.

[0061] Examples 5-8 were prepared by the same method as in Example 2, except that the thickness was changed to 0.5 mm, 1.0 mm, 1.5 mm, and 3 mm.

[0062] Examples 9-12 were prepared by the same method as in Example 4, except that the thickness was changed to 0.5 mm, 1.0 mm, 1.5 mm, and 3 mm.

[0063] From the brightness of the fluorescent screen in the fast neutron photographic test, the brightness influencing factors of the above 12 examples were mainly the content of zinc sulfide fluorescent powder and the thickness of the screen. Therefore, in terms of brightness, Examples 1 and 2, and Examples 3 and 4 were equivalent, respectively. The thermoplastic polyurethane composite material prepared by the method of Examples 2 and 4 was named ZSTPU-50% and ZSTPU-40%, respectively. The relative brightness of the fast neutron conversion screen prepared by the method of Examples 2, 4, and 5-12 was shown in Table 1. The brightness of the commercially available polypropylene mixed pressure fluorescent screen was taken as 1 as a reference value.

[0064] Table 1 Analysis results of relative brightness of ZSPU with different contents and thicknesses

[0065]

[0066] At the same time, the resolution of the thermoplastic polyurethane conversion screen is equivalent to that of the existing polypropylene mixed pressure type fast neutron conversion screen with the same thickness. It can be seen that the thermoplastic 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 is of great significance to improve the imaging quality in the field of fast neutron photography.

[0067] The present application is described in detail above in conjunction with specific embodiments and exemplary embodiments. The above description is exemplary and is not exhaustive, and is not limited to the disclosed embodiments; the above description cannot be understood as limiting the present application. Those skilled in the art understand that various equivalent substitutions, modifications or improvements can be made to the technical solutions and embodiments of the present application without departing from the spirit and scope of the present application, and these fall within the scope of the present application; the scope of protection of the present application is subject to the appended claims.

Claims

1. A method for the production of a fast neutron conversion screen of a thermoplastic polyurethane composite material of a transparent polyurethane prepolymer, characterized in that, Comprising the following steps: Step 1: raw material pretreatment The amount of polyether diol or polyester diol is weighed in a 250 ml three-necked flask, and vacuum drying is performed at 110°C for 1-2 hours using a water ring vacuum pump; the amount of silver-doped zinc sulfide fluorescent powder ZnS:Ag is weighed, and surface modification is performed using hydrogen peroxide or ammonia solution, and then the sample is dried in a vacuum oven at 80-100°C for 1-2 hours; Step 2: preparation of transparent polyurethane prepolymer The amount of oligomeric diol is taken and placed in a reactor equipped with a reflux condenser and a stirrer, and the amount of diisocyanate is added according to a molar ratio of diisocyanate to oligomeric diol of 2.1-3.1:1.0, and a small amount of catalyst is added, and stirring is performed at room temperature for 1 hour, and the temperature is slowly increased to 60-80°C, and stirring is performed for 2-5 hours, and nitrogen protection is adopted during the reaction, and the double-functional transparent polyurethane prepolymer is obtained after the reaction is completed; Step 3: preparation of a pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder The amount of zinc sulfide fluorescent powder ZnS:Ag and transparent polyurethane prepolymer, dispersant, antioxidant, and solvent are dispersed in a high-speed dispersion machine for 30-60 minutes to obtain a pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder, wherein the zinc sulfide fluorescent powder ZnS:Ag and transparent polyurethane prepolymer, dispersant, antioxidant, and solvent are composed of the following weight percentages: Transparent polyurethane prepolymer 25-50% Zinc sulfide fluorescent powder ZnS:Ag 40-70% Dispersant 0.05-1.5% Antioxidant 0.1-0.2% Solvent 5-15% The sum of the weight percentages of the above components is 100%; Step 4: chain extension of the fluorescent polyurethane prepolymer According to the formula of the fluorescent polyurethane prepolymer pre-dispersion, the molar content of diisocyanate groups is calculated, and the corresponding low-molecular-weight chain extender is added to the pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder prepared in step 3 at room temperature; The amount of the pre-dispersion system of transparent polyurethane prepolymer and fluorescent powder after the reaction is weighed, and the solvent in the reaction mixture is removed by vacuum distillation using a vacuum pump, and then stirring is performed at room temperature for 30 minutes, and then the temperature is slowly increased to 70-90°C, and stirring is performed for 2-5 hours, and the in-situ polymerized thermoplastic polyurethane fluorescent composite particles are obtained after discharging and pelletizing; Step 5: hot-pressing of the thermoplastic polyurethane fast neutron fluorescent conversion screen The thermoplastic polyurethane fluorescent composite particles obtained in step 4 are dried and preheated, and then placed in a certain thickness of a plate mold on a flat vulcanizing machine for hot-pressing, and then cold-pressed, cooled, demolded, trimmed, and cleaned to obtain a thermoplastic polyurethane composite fast neutron conversion screen with the desired thickness.

2. A process for the production of a thermoplastic polyurethane composite fast neutron conversion screen according to claim 1, characterized in that The hot-pressing process is first plasticized at 160°C for 20 minutes, then hot-pressed at 160°C for 5 minutes at a pressure of 10.0 Mpa, and finally cold-pressed at room temperature for 20 minutes.

3. A thermoplastic polyurethane composite fast neutron conversion screen characterized by, The thermoplastic polyurethane composite fast neutron conversion screen is prepared by the method of claim 2.

4. A thermoplastic polyurethane composite fast neutron conversion screen according to claim 3, characterised in that, The thickness of the thermoplastic polyurethane composite fast neutron conversion screen is 0.1-8.00 mm.

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