Stress luminescent material, aqueous stress luminescent coating, and method for producing the same

Abstract

To provide a stress luminescent material that has water resistance, an aqueous stress luminescent coating including the material, and methods for producing the same.SOLUTION: A method for producing a stress luminescent material includes the steps of generating a mixed liquid by mixing stress luminescent particles and a non-aqueous surfactant-type dispersant in a non-aqueous solvent; preparing a dispersion solution containing the stress luminescent particles, the non-aqueous surfactant-type dispersant, and the non-aqueous solvent by stirring the mixed liquid; subjecting the dispersion solution to vacuum degassing; evaporating the vacuum-degassed dispersion solution to a semi-dried slurry state; and further evaporating and drying the slurry-like dispersion solution to yield a powdered stress luminescent material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a stress-luminescent material, a water-based stress-luminescent paint containing a stress-luminescent material as a pigment, and a method for producing the same. [Background technology]

[0002] A method is known in which stress-stimulated luminescent materials that emit light in response to external mechanical stimuli (friction, impact, compression, tension, twisting, etc.) are fixed to the surface of the object to visualize the strain state of the object. A practical method for fixing stress-stimulated luminescent materials to the surface of the object is to apply a paint made of powdered stress-stimulated luminescent materials dispersed as pigments in a resin matrix to the surface of the object to form a coating film.

[0003] The mechanoluminescent material is in powder form and is composed of ceramic particles (hereinafter also referred to as "mechanoluminescent particles") with particle sizes on the order of microns. The mechanoluminescent particles have low water resistance, and when they come into contact with water, their crystalline structure collapses and they lose their luminescence.

[0004] As a measure to improve the water resistance of stress-stimulated luminescent particles, for example, Japanese Patent Laid-Open Publication No. 2005-320425 (Patent Document 1) discloses that stress-stimulated luminescent particles are surface-treated with a compound containing an acidic group or an ester thereof to impart water resistance to the stress-stimulated luminescent particles. Patent Document 1 also discloses that the surface-treated stress-stimulated luminescent particles are used as pigments in water-based paints. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-320425 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the surfaces of stress-stimulated luminescent particles are generally not smooth and have multiple surface pores of nanometer order size. These surface pores include micropores with diameters of 2 nm or less, mesopores with diameters of 2 to 50 nm, macropores with diameters of 50 nm or more, and cracks. Therefore, to prevent water from coming into contact with stress-stimulated luminescent particles, these multiple surface pores must be completely covered. Patent Document 1 discloses a surface treatment method in which a surface treatment agent is dissolved in an organic solvent, stress-stimulated luminescent particles are added to the solution, and the solution is stirred. However, it does not mention any technology for completely covering the surface pores of stress-stimulated luminescent particles. Therefore, there is a concern that surface treatment may not provide water resistance to stress-stimulated luminescent particles.

[0007] The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide a water-resistant stress-luminescent material, an aqueous stress-luminescent paint containing the same, and methods for producing the same. [Means for solving the problem]

[0008] A method for producing a stress-stimulated luminescent material according to one embodiment of the present disclosure includes the steps of: mixing stress-stimulated luminescent particles and a non-aqueous surfactant-type dispersant with a non-aqueous solvent to produce a mixed solution; stirring the mixed solution to prepare a dispersion solution containing stress-stimulated luminescent particles, the non-aqueous surfactant-type dispersant, and the non-aqueous solvent; vacuum-degassing the dispersion solution; evaporating the vacuum-degassed dispersion solution to semi-dryness until it becomes a slurry; and evaporating the slurry dispersion solution to dryness to obtain a powder of stress-stimulated luminescent material.

[0009] A method for producing an aqueous stress-luminescent paint according to one embodiment of the present disclosure includes a step of kneading a stress-luminescent material produced using the above-described method for producing a stress-luminescent material with an aqueous vehicle to obtain a kneaded mixture, and a step of degassing the kneaded mixture to obtain an aqueous stress-luminescent paint.

[0010] A stress-stimulated luminescent material according to one embodiment of the present disclosure includes stress-stimulated luminescent particles having a plurality of surface pores, and a non-aqueous surfactant-type dispersant that covers the surfaces of the stress-stimulated luminescent particles. The non-aqueous surfactant-type dispersant covers the surface pores of the stress-stimulated luminescent particles by vacuum-degassing a dispersion solution containing the stress-stimulated luminescent particles, the non-aqueous surfactant-type dispersant, and a non-aqueous solvent.

[0011] An aqueous stress-stimulated luminescent paint according to one embodiment of the present disclosure comprises a water-based vehicle and the above-described stress-stimulated luminescent material dispersed in the water-based vehicle. [Effects of the Invention]

[0012] According to the present disclosure, it is possible to realize a water-resistant stress-luminescent material and a water-based stress-luminescent paint. [Brief explanation of the drawings]

[0013] [Figure 1] 1A to 1C are diagrams showing the manufacturing process of a stress-luminescent material. [Figure 2] FIG. 1 is a manufacturing process diagram of a water-based stress-luminescent paint. [Figure 3] 1 is a photograph of an aqueous stress-luminescent paint according to a comparative example and an aqueous stress-luminescent paint according to the present example. [Figure 4] This is a TIFF image capturing the luminescence of the coating. [Figure 5] 1 is a graph showing the change over time in the average luminescence intensity within the ROI during a tensile test. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0015] <Stimuli-luminescent materials> Stress-luminescent materials have the property of emitting light by releasing the energy stored in the material when subjected to external mechanical stimuli (friction, impact, compression, tension, twisting, etc.). Stress-luminescent materials are made by dissolving an element that acts as a luminescent center in the skeleton of an inorganic crystal (base material). A typical example is europium-doped strontium aluminate (SrAl2O4):Eu 2+ ) is available.

[0016] Stress-luminescent materials are powders composed of ceramic particles (hereinafter referred to as "stress-luminescent particles") with particle sizes on the order of microns. Because stress-luminescent particles do not have adhesive properties by themselves, they must be mixed with an adhesive matrix and then fixed to the substrate to be inspected in order to be used in non-destructive testing, such as for visualizing stress concentration areas and identifying deteriorated areas. One practical example of such a fixing method is to apply a paint containing stress-luminescent particles dispersed as pigments in a resin matrix (hereinafter referred to as "stress-luminescent paint") to the surface of a substrate to form a coating film.

[0017] However, mechanoluminescent particles have low water resistance, and when they come into contact with water, hydrolysis begins immediately, causing the crystalline structure to gradually collapse from the particle surface. This hydrolysis reduces the luminescent ability of the mechanoluminescent particles, and they eventually lose their luminescence ability. For this reason, mechanoluminescent paints have inevitably been limited to oil-based mechanoluminescent paints that use oils and fats as a vehicle (a liquid component that disperses pigments, also known as a vehicle).

[0018] On the other hand, from the viewpoint of protecting the global environment, there is a demand for water-based mechanoluminescent paints, which have a water-based vehicle. However, the SrAl2O4-based mechanoluminescent elements currently in practical use have a high reactivity with water, and ultimately react with the water-based vehicle to decompose into hydroxides, resulting in a loss of luminescence ability.

[0019] In this embodiment, from the viewpoint of realizing a water-based stress-luminescent paint, a water-resistant stress-luminescent material and a method for producing the same are proposed.

[0020] <Mechanical manufacturing method for mechanoluminescent material> A method for producing a stress-stimulated luminescent material according to this embodiment will be described below.

[0021] Fig. 1 is a diagram showing the steps of producing a mechanoluminescent material. As shown in Fig. 1, the method of producing a mechanoluminescent material includes a mixing step S10, a preparation step S20, a vacuum degassing step S30, an evaporation to semi-dryness step S40, an evaporation to dryness step S50, and a recovery step S60.

[0022] (Mixing process S10) First, a mixing step S10 is performed. In the mixing step S10, the stress-luminescent particles and the non-aqueous surfactant-type dispersant are mixed with a non-aqueous solvent to produce a mixed liquid. The non-aqueous solvent is, for example, an organic solvent. The stress-luminescent particles are, for example, SrAl2O4-based stress-luminescent particles. The non-aqueous surfactant-type dispersant is, for example, an ester-based surfactant-type dispersant. As will be described later, the non-aqueous surfactant-type dispersant adsorbs to the surface of the stress-luminescent particles, covering the surface of the stress-luminescent particles and thereby imparting water resistance to the stress-luminescent particles.

[0023] In the mixing step S10, a non-aqueous surfactant-type dispersant is first added to the non-aqueous solvent dispensed in a container. Then, the stress-luminescent particles are added. Because both the surfactant-type dispersant and the solvent are non-aqueous, the stress-luminescent particles can be prevented from coming into contact with water and being decomposed.

[0024] (Preparation step S20) Next, a preparation step S20 is carried out. In the preparation step S20, the mixture produced in the mixing step S10 is stirred to prepare a dispersion solution containing stress-luminescent particles, a non-aqueous surfactant-type dispersant, and a non-aqueous solvent.

[0025] (Vacuum degassing process S30) Next, a vacuum degassing step S30 is carried out. In the vacuum degassing step S30, the dispersion solution prepared in the preparation step S20 is subjected to vacuum degassing. Vacuum degassing is a process in which the dispersion solution is evacuated while being stirred, thereby expanding the air dissolved in the dispersion solution and removing bubbles from the surfaces in contact with the vacuum.

[0026] Generally, the surfaces of stress-stimulated luminescent particles are not smooth and have multiple surface pores of nanometer order size. These surface pores include micropores with diameters of 2 nm or less, mesopores with diameters of 2 to 50 nm, macropores with diameters of 50 nm or more, and cracks. The vacuum degassing step S30 is performed to ensure that the non-aqueous surfactant dispersant penetrates between the stress-stimulated luminescent particles and into the surface pores of the stress-stimulated luminescent particles, thereby forming a defect-free protective layer on the surface of the stress-stimulated luminescent particles. Vacuum degassing a liquid dispersion prepared by adding stress-stimulated luminescent particles to a non-aqueous solvent containing a non-aqueous surfactant dispersant makes it easier for the dispersion to penetrate into the fine surface pores of the stress-stimulated luminescent particles than vacuum degassing a dispersion containing solid components.

[0027] (Evaporation to semi-dryness step S40) Next, the evaporation to semi-dryness step S40 is carried out. In this step, the vacuum-degassed dispersion solution is evaporated to semi-dryness until it becomes a slurry. The reason for the evaporation to semi-dryness is to prevent damage to the stress-luminescent particles and the non-aqueous surfactant-type dispersant caused by oxidation heat by heating the dispersion solution to completely evaporate the non-aqueous solvent (evaporate to dryness).

[0028] Therefore, it is preferable to keep the dispersion solution at as low a temperature as possible during evaporation to semi-dryness, and it is preferable to subject the dispersion solution to a heat treatment in which the temperature is raised while maintaining the temperature below the boiling point of the non-aqueous solvent.

[0029] (Evaporation to dryness step S50) Next, the evaporation-to-dryness step S50 is carried out. In this step, the non-aqueous solvent is completely evaporated from the slurry dispersion solution, resulting in crystallized stress-luminescent particles. The surfaces of the resulting stress-luminescent particles are covered with a protective layer made of a non-aqueous surfactant-type dispersant. The non-aqueous surfactant-type dispersant that has penetrated into the surface pores of the stress-luminescent particles in the vacuum degassing step S30 eventually becomes a protective layer that covers the surface pores of the stress-luminescent particles through the evaporation-to-dryness step S50. This protective layer prevents the stress-luminescent element from coming into direct contact with water, thereby imparting water resistance to the stress-luminescent particles.

[0030] (Recovery process S60) Finally, the recovery step S60 is carried out. In the recovery step S60, the stress-stimulated luminescent particles obtained in the evaporation-to-dryness step S50 are recovered. This results in a water-resistant powdered stress-stimulated luminescent material.

[0031] <Method of manufacturing water-based mechanoluminescent paint> A method for producing a water-based stress-luminescent paint according to this embodiment will be described below. The water-based stress-luminescent paint is produced using a stress-luminescent material produced by the production method shown in Fig. 1 as a pigment.

[0032] 2 is a diagram showing the manufacturing process of the water-based stress-luminescent paint. As shown in FIG. 2, the manufacturing method of the water-based stress-luminescent paint includes a kneading step S70 and a degassing step S80.

[0033] (Kneading process S70) First, a kneading step S70 is carried out. In the kneading step S70, the mechanoluminescent material produced by the production method shown in Fig. 1 is kneaded as a pigment into an aqueous vehicle. The aqueous vehicle is a vehicle containing water as a solvent.

[0034] The solvent of the aqueous vehicle may contain solvent components other than water. Specific examples of such solvents include ethyl alcohol, 1-propanol, and 2-propanol. Considering the lifespan of the aqueous mechanoluminescent paint, it is preferable that the aqueous vehicle contains at least 1-propanol. The lifespan of the aqueous mechanoluminescent paint will be described later. The aqueous vehicle may further contain a resin and an additive.

[0035] The stress-stimulated luminescent material is composed of stress-stimulated luminescent particles whose surfaces are coated with a non-aqueous surfactant-type dispersant, and is water-resistant. Therefore, the aqueous vehicle is not absorbed by the stress-stimulated luminescent particles, and a paste-like kneaded product is obtained.

[0036] (Defoaming process S80) Next, a degassing step S80 is carried out. In the degassing step S80, the paste-like kneaded material is degassed, and finally, an aqueous stress-stimulated luminescent paint is prepared. The prepared aqueous stress-stimulated luminescent paint is macroscopically transparent and in a paste form, and can be used as a paint as it is.

[0037] The method for producing the mechanoluminescent material and the aqueous mechanoluminescent paint according to the present embodiment will be described in more detail below with reference to examples, although the methods for producing the mechanoluminescent material and the aqueous mechanoluminescent paint according to the present embodiment are not limited to these examples. [Example]

[0038] [Preparation of mechanoluminescent materials] (Mixing process S10) In the mixing step S10, ethanol (volume: 80 ml) was dispensed into a container as a non-aqueous solvent, a non-aqueous surfactant-type dispersant (mass: 132 mg) was added to it, and then stress-luminescent particles (mass: 2.50 g) were added to generate a mixed liquid.

[0039] The non-aqueous surfactant dispersant used was an ester surfactant dispersant (SN Dispersant 9228, manufactured by San Nopco Ltd.), and the stress-luminescent particles used were SrAl2O4 stress-luminescent elements (ML-032, manufactured by Sakai Chemical Industry Co., Ltd., D50=3.3 μm, D90=5.2 μm, emission wavelength λ=520-530 nm).

[0040] The manufacturer recommends adding SN Dispersant 9228 at a ratio of 0.5 to 2.0% relative to the pigment, so we added a slight excess of SN Dispersant 9228, about 5%, to the ethanol after removing the ethanol in the subsequent evaporation-to-dryness step S50.

[0041] (Preparation step S20) In the preparation step S20, the mixture obtained in the mixing step S10 was stirred at room temperature to prepare a dispersion solution in which the SrAl2O4-based stress-luminescent particles and the ester-based surfactant dispersant were pre-dispersed in ethanol. A magnetic stirrer was used for stirring. The rotation speed of the magnetic stirrer was set to 600 rpm, and the stirring time was set to 30 minutes.

[0042] (Vacuum degassing process S30) In the vacuum degassing step S30, the container containing the dispersion solution was placed in a vacuum chamber. A rotary pump was connected to the vacuum chamber via a liquid nitrogen trap to capture ethanol volatilizing from the dispersion solution. In this state, the vacuum chamber was gradually depressurized from atmospheric pressure (0 Pa) to -0.1 MPa over a period of approximately 5 minutes. After this depressurization, the vacuum state of the vacuum chamber was maintained for approximately 5 minutes until the foaming generated from the dispersion solution subsided. After the foaming of the dispersion solution subsided, the pressure inside the vacuum chamber was returned to atmospheric pressure. Approximately 10 to 20 ml of ethanol was evaporated and lost by this vacuum degassing.

[0043] (Evaporation to semi-dryness step S40) In the evaporation semi-drying step S40, the container containing the vacuum-degassed dispersion was again stirred using a magnetic stirrer until it became a slurry. During stirring, the temperature on the magnetic stirrer was set to 100°C, and the rotation speed of the magnetic stirrer was set to 600 to 300 rpm. The measured temperature of the dispersion in the container was approximately 50°C, which is lower than the boiling point of ethanol (approximately 78°C). The dispersion was stirred for approximately 1.5 hours until the volume of the dispersion was reduced to approximately 10 ml.

[0044] (Evaporation to dryness step S50) In the evaporation-to-dryness step S50, the container containing the slurry dispersion was placed in a thermostatic bath and heated to approximately 80°C. This state was maintained for 12 hours or more to completely volatilize and remove the ethanol from the dispersion. Thereafter, the thermostatic bath was cooled to room temperature and the container was removed.

[0045] (Recovery process S60) In the recovery step S60, the stress-stimulated luminescent particles adhering to the inner surface of the container removed from the thermostatic bath were scraped off with a spatula to recover the stress-stimulated luminescent particles.

[0046] The mechanoluminescent material produced by the above-mentioned manufacturing method includes SrAl2O4-based mechanoluminescent particles and an ester-based surfactant-type dispersant that covers the surfaces of the SrAl2O4-based mechanoluminescent particles. The ester-based surfactant-type dispersant covers a plurality of surface pores of the SrAl2O4-based mechanoluminescent particles by vacuum-degassing a dispersion solution containing the SrAl2O4-based mechanoluminescent particles, the ester-based surfactant-type dispersant, and ethanol.

[0047] [Preparation of water-based mechanoluminescent paint] (Kneading process S70) In the kneading step S70, an aqueous vehicle (mass: 5.5 g) was dispensed into a container, and SrAl2O4-based stress-luminescent particles (mass: 2 g) produced by the above-described method for producing a stress-luminescent material were added thereto as a pigment.

[0048] The water-based vehicle used was a water-based acrylic resin paint (Tamiya Color X-22 Clear, manufactured by Tamiya Co., Ltd.). This water-based acrylic resin paint is a transparent liquid containing water (content: 20-30%), 1-propanol (content: 10-20%), 2-propanol (content: 5-10%), propylene glycol monomethyl ether (content: 10-20%), and acrylic resin (content: 20-30%).

[0049] The mixture of water-based acrylic resin paint and SrAlO-based stress-emitting device was lightly mixed with a spatula and then kneaded using a kneader (Nanko Rentaro, manufactured by Thinky Corporation). The kneader was rotated at 2000 rpm and operated for 1.5 minutes.

[0050] (Defoaming process S80) In the degassing step S80, the kneader was further operated at a rotation speed of 2200 rpm for about 20 seconds to degas the kneaded material, thereby obtaining a paste-like, transparent, water-based mechanoluminescent coating material.

[0051] The water-based stress-luminescent paint produced by the above-mentioned manufacturing method includes a water-based vehicle and a stress-luminescent material dispersed in the water-based vehicle. The stress-luminescent material is composed of SrAl2O4-based stress-luminescent particles whose surfaces are covered with an ester-based surfactant-type dispersant.

[0052] [Evaluation of mechanoluminescent materials] In order to evaluate the water resistance of the stress-stimulated luminescent particles produced in this example, a water-based stress-stimulated luminescent paint containing the stress-stimulated luminescent material according to the comparative example as a pigment was also produced.

[0053] The comparative stress-luminescent material is composed of the same SrAl2O4-based stress-luminescent particles as the stress-luminescent material of this example. However, it differs from the stress-luminescent material of this example in that the process for covering the surfaces of the SrAl2O4-based stress-luminescent particles with an ester-based surfactant-type dispersant (processes S10 to S60 in FIG. 1) is not performed. The water-based stress-luminescent paint of this comparative example was produced by performing processes S70 and S80 in FIG. 2 on the stress-luminescent material of this comparative example under the same conditions as those for the stress-luminescent material of this example.

[0054] Figure 3 shows photographs of the aqueous stress-luminescent paint according to the comparative example and the aqueous stress-luminescent paint according to the present example. Figure 3(A) shows an image of the aqueous stress-luminescent paint according to the comparative example, and Figure 3(B) shows an image of the aqueous stress-luminescent paint according to the present example. Both aqueous stress-luminescent paints were contained in white plastic containers for ointments.

[0055] As shown in Figure 3(A), the water-based stress-luminescent paint of the comparative example did not become paste-like because the stress-luminescent particles absorbed the water-based vehicle (water-based acrylic resin paint), and instead became a mass of white powder.

[0056] In contrast, the aqueous stress-luminescent paint of this example was a transparent paste, as shown in Fig. 3(B), in which stress-luminescent particles were dispersed in an aqueous vehicle (aqueous acrylic resin paint). This indicates that the process of covering the surfaces of stress-luminescent particles with a non-aqueous surfactant-type dispersant (steps S10 to S60 in Fig. 1) is essential to improving the water resistance of stress-luminescent particles.

[0057] Furthermore, in this example, the stress-luminescent material was prepared without performing the vacuum degassing step S30, one of the steps for covering the surfaces of stress-luminescent particles with a non-aqueous surfactant-based dispersant (steps S10 to S60 in Figure 1). In this case, the prepared stress-luminescent particles did not have sufficient water resistance, and it was confirmed that the stress-luminescent particles absorbed the aqueous vehicle (aqueous acrylic resin paint) during the preparation of the aqueous stress-luminescent paint, resulting in a decrease in the luminescence ability of the stress-luminescent particles. This indicates that the non-aqueous surfactant-based dispersant penetrated into the surface pores of the stress-luminescent particles by vacuum degassing, forming a defect-free protective layer on the surface of the stress-luminescent particles, thereby improving the water resistance of the stress-luminescent particles.

[0058] [Evaluation of water-based mechanoluminescent paint] (Luminescence evaluation) An experiment was conducted to evaluate the luminescence performance of the water-based mechanoluminescent paint according to this example. In this experiment, the water-based mechanoluminescent paint according to this example was applied with a brush to one side of an A6061 test piece (JIS13B shape, 0.5 mm thick), and then the A6061 test piece was pre-dried indoors for 3 hours, and then further dried in a thermostatic chamber at 80°C for 3 hours, thereby creating a test specimen with a coating film (stress-luminescent film) formed on its surface.

[0059] Next, a tensile test was performed on this specimen. For the tensile test, a stress measurement system was installed under darkroom conditions and the specimen was placed in it. The stress measurement system includes a tensile testing machine (Shimadzu Corporation, Autograph AG-Xplus), a camera, an excitation light source, a control device, and a memory device. The tensile testing machine is configured to apply a load (tensile force) to the specimen by raising the crosshead under the control of the control device.

[0060] As part of the excitation process to accumulate energy in the coating on the specimen, blue light (wavelength λ = 470 nm) was irradiated from the excitation light source for 60 seconds, followed by 120 seconds in a dark place. A load was then applied to the specimen at a crosshead speed of 5 mm / min (maximum load: 3 kN). The light emitted by the coating during the load application was captured by an imaging device at a frame rate of 500 ms and saved as a TIFF (Tag Image File Format) image in a storage device. The saved TIFF image is shown in Figure 4.

[0061] Figure 4(A) is an image of the light emitted by the coating film before applying load, and Figure 4(B) is an image of the light emitted by the coating film when the maximum load is reached.

[0062] The image shown in Figure 4(A) confirms that the coating emits light by releasing the accumulated energy, although there are variations in the luminescence intensity due to unevenness in the coating. Furthermore, the image shown in Figure 4(B), taken while a load was being applied, confirms that the luminescence intensity of the coating increases due to luminescence caused by stress (stress luminescence) generated by the load.

[0063] Next, a region of interest (ROI) was set within the series of TIFF images captured during the tensile test, and values based on the luminescence intensity within the ROI were calculated for each frame of the TIFF image. The white frames in Figures 4(A) and 4(B) indicate the ROI. Values based on the luminescence intensity within the ROI can be calculated by statistically processing the luminescence intensity within the ROI. In this example, the average luminescence intensity within the ROI was calculated.

[0064] Figure 5 is a graph showing the time course of the average luminescence intensity within the ROI during the tensile test. The horizontal axis of the graph represents the frame number of the TIFF image, and the vertical axis represents the luminescence intensity. The graph was created by plotting the average luminescence intensity within the ROI calculated for each frame of the series of TIFF images.

[0065] As shown in Fig. 5, the luminescence intensity of the coating film increased with the passage of time from the start of load application, i.e., as the load increased. The luminescence intensity peaked when the set maximum load of 3 kN was reached, and then gradually decreased as the load decreased. This confirmed the luminescence characteristics. This demonstrates that the water-based mechanoluminescent paint of this example effectively functions as a fixing means for fixing the mechanoluminescent material to the substrate.

[0066] (Lifespan assessment) A lifespan evaluation was carried out on the water-based mechanoluminescent paint according to this example. In this lifespan evaluation, the water-based mechanoluminescent paint prepared according to this example was placed in several sealed containers, and stored in a refrigerator and indoors, respectively, and the progress was observed.

[0067] In both sealed containers, it was confirmed that the pigment precipitated over time after preparation, and the aqueous vehicle and pigment separated into two layers. However, it was confirmed that the pigment could be redispersed by stirring with a brush or vortex mixer, and the water-based mechanoluminescent paint returned to its original paste state. Furthermore, the luminescence performance of the water-based mechanoluminescent paint restored to a paste state was evaluated using the same method as the luminescence performance evaluation described above, and it was confirmed that it exhibited the same luminescence properties as the water-based mechanoluminescent paint immediately after preparation.

[0068] In this example, we further investigated the phenomenon of pigment precipitation. In this investigation, two types of water-based vehicles, A and B, with different components were prepared. Water-based vehicle A was a water-based acrylic resin paint containing 1-propanol (content: 10%). Water-based vehicle B was a water-based acrylic resin paint containing 2-propanol (content: 10%). Water-based mechanoluminescent paints were prepared by adding the same amount of SrAl2O4-based mechanoluminescent particles (mass: 2.2 g) to each of water-based vehicles A and B (mass: 5.5 g), and the progress of the preparation was observed.

[0069] Observation showed that the rate of precipitation was slower in aqueous vehicle A than in aqueous vehicle B. This suggests that the phenomenon of pigment precipitation depends on the components of the aqueous vehicle. It is also speculated that 1-propanol may be effective in delaying pigment precipitation.

[0070] In this embodiment and this example, a method for preparing an aqueous stress-luminescent paint by kneading a stress-luminescent material with an aqueous vehicle has been described. However, by storing the stress-luminescent material and the aqueous vehicle separately and mixing the stress-luminescent material with the aqueous vehicle at the site where the stress-luminescent material is fixed to the substrate to prepare the aqueous stress-luminescent paint, the above-mentioned precipitation of the pigment can be avoided.

[0071] Furthermore, the mechanoluminescent material according to the present embodiment can be expected to be used in applications other than water-based paints by mixing it with a solvent other than a water-based vehicle.

[0072] [Aspect] It will be understood by those skilled in the art that the above-described embodiments are examples of the following aspects.

[0073] (Item 1) A method for producing a stress-stimulated luminescent material according to one embodiment includes the steps of: mixing stress-stimulated luminescent particles and a non-aqueous surfactant-type dispersant with a non-aqueous solvent to produce a mixed solution; stirring the mixed solution to prepare a dispersion containing stress-stimulated luminescent particles, the non-aqueous surfactant-type dispersant, and the non-aqueous solvent; vacuum-degassing the dispersion; evaporating the vacuum-degassed dispersion until it becomes a slurry to semi-dryness; and evaporating the slurry dispersion to dryness to obtain a powder of stress-stimulated luminescent material.

[0074] According to the manufacturing method described in paragraph 1, a defect-free protective layer can be formed on the surface of the stress-stimulated luminescent element by infiltrating the non-aqueous surfactant-type dispersant into the surface pores of the stress-stimulated luminescent particles through vacuum degassing. This makes it possible to impart water resistance to the stress-stimulated luminescent particles. Furthermore, by evaporating the vacuum-degassed dispersion solution to semi-dryness, it is possible to prevent damage to the stress-stimulated luminescent particles and the protective layer due to oxidation heat.

[0075] (Item 2) In the manufacturing method described in Item 1, the stress-stimulated luminescent particles have a plurality of surface pores. The step of vacuum-degassing the dispersion solution includes a step of vacuum-degassing the dispersion solution to allow the dispersion solution to penetrate into the plurality of surface pores of the stress-stimulated luminescent particles.

[0076] This allows the multiple surface pores of the stress-stimulated luminescent particles to be completely covered with the non-aqueous surfactant-type dispersant, thereby imparting water resistance to the stress-stimulated luminescent particles.

[0077] (Item 3) In the manufacturing method described in item 1 or 2, the step of evaporating the dispersion solution to semi-dryness includes a step of stirring the dispersion solution while maintaining it at a temperature below the boiling point of the non-aqueous solvent, thereby converting the dispersion solution into a slurry.

[0078] This can prevent the stress-luminescent particles and the non-aqueous surfactant-type dispersant from being damaged by oxidation heat when the non-aqueous solvent is removed from the dispersion solution.

[0079] (Item 4) In the manufacturing method according to items 1 to 3, the stress-stimulated luminescent particles are europium-doped strontium aluminate (SrAl2O4), and the non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

[0080] According to this, SrAl2O4-based stress-luminescent particles having water resistance can be realized by covering the surface with an ester-based surfactant-type dispersant.

[0081] (Item 5) A method for producing an aqueous stress-luminescent paint according to one embodiment includes the steps of kneading a stress-luminescent material produced using the production method described in items 1 to 4 into an aqueous vehicle to obtain a kneaded mixture, and degassing the kneaded mixture to obtain the aqueous stress-luminescent paint.

[0082] According to the manufacturing method described in item 5, it is possible to realize a water-based stress-luminescent paint containing a water-resistant stress-luminescent material as a pigment.

[0083] (Item 6) In the manufacturing method according to item 5, the aqueous vehicle contains at least 1-propanol.

[0084] This can delay the precipitation of the pigment contained in the water-based stress-luminescent paint.

[0085] (Item 7) A stress-stimulated luminescent material according to one embodiment includes stress-stimulated luminescent particles having a plurality of surface pores, and a non-aqueous surfactant-type dispersant that covers the surfaces of the stress-stimulated luminescent particles. The non-aqueous surfactant-type dispersant covers the surface pores of the stress-stimulated luminescent particles by vacuum-degassing a dispersion solution containing the stress-stimulated luminescent particles, the non-aqueous surfactant-type dispersant, and a non-aqueous solvent.

[0086] The mechanoluminescent material described in item 7 is composed of mechanoluminescent particles whose surfaces are covered with a non-aqueous surfactant-type dispersant, and is water resistant.

[0087] (Item 8) In the mechanoluminescent material according to item 7, the mechanoluminescent particles are europium-doped strontium aluminate (SrAl2O4), and the non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

[0088] This makes it possible to realize SrAl2O4-based stress-luminescent particles whose surfaces are covered with an ester-based surfactant-type dispersant and which have water resistance.

[0089] (Item 9) An aqueous stress-stimulated luminescent paint according to one embodiment includes a water-based vehicle and the stress-stimulated luminescent material according to item 7 or 8 dispersed in the water-based vehicle.

[0090] The water-based stress-luminescent paint described in paragraph 9 is a water-based paint that uses a stress-luminescent material as a pigment, which has a low environmental impact and is gentle on the user's body.

[0091] (Item 10) In the aqueous stress-luminescent paint according to item 9, the aqueous vehicle contains at least 1-propanol.

[0092] This can delay the precipitation of the pigment contained in the water-based stress-luminescent paint.

[0093] (Item 11) The water-based stress-luminescent paint according to item 9 or 10 is in a paste form.

[0094] According to this, the water-based stress-luminescent paint can be applied to the substrate, and the stress-luminescent material can be fixed to the surface of the substrate as a coating film.

[0095] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0096] S10 mixing process, S20 preparation process, S30 vacuum degassing process, S40 evaporation to semi-dryness process, S50 evaporation to dryness process, S60 recovery process, S70 kneading process, S80 degassing process.

Claims

1. A method for producing a stress-stimulated luminescent material, comprising: a step of mixing stress-luminescent particles and a non-aqueous surfactant-type dispersant into a non-aqueous solvent to produce a mixed liquid; a step of stirring the mixture to prepare a dispersion containing the stress-luminescent particles, the non-aqueous surfactant-type dispersant, and the non-aqueous solvent; a step of vacuum degassing the dispersion solution; a step of evaporating the vacuum-degassed dispersion solution to semi-dryness until it becomes a slurry; and evaporating the slurry-like dispersion solution to dryness to obtain the stress-stimulated luminescent material in powder form.

2. the stress-luminescent particle has a plurality of surface pores; 2. The method for producing a stress-stimulated luminescent material according to claim 1, wherein the step of vacuum-degassing the dispersion solution includes the step of vacuum-degassing the dispersion solution to allow the dispersion solution to penetrate into the plurality of surface pores of the stress-stimulated luminescent particles.

3. 2. The method for producing a stress-stimulated luminescent material according to claim 1, wherein the step of evaporating the dispersion solution to semi-dryness includes a step of stirring the dispersion solution while maintaining the dispersion solution at a temperature lower than the boiling point of the non-aqueous solvent, thereby forming the dispersion solution into a slurry.

4. The stress-stimulated luminescent particles are europium-doped strontium aluminate (SrAl ２ O ４ ) and The method for producing a stress-stimulated luminescent material according to claim 1 , wherein the non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

5. A method for producing an aqueous mechanoluminescent paint, a step of kneading the mechanoluminescent material produced by the method according to any one of claims 1 to 4 into an aqueous vehicle to obtain a kneaded mixture; and a step of degassing the kneaded mixture to obtain the water-based stress-luminescent paint.

6. 6. The method for producing an aqueous stress-luminescent paint according to claim 5, wherein the aqueous vehicle contains at least 1-propanol.

7. a stress-luminescent particle having a plurality of surface holes; a non-aqueous surfactant-type dispersant that coats the surfaces of the stress-luminescent particles, The non-aqueous surfactant dispersant covers the surface pores of the stress-luminescent particles by vacuum-degassing a dispersion solution containing the stress-luminescent particles, the non-aqueous surfactant dispersant, and a non-aqueous solvent.

8. The stress-stimulated luminescent particles are europium-doped strontium aluminate (SrAl ２ O ４ ) and 8. The mechanoluminescent material according to claim 7, wherein the non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

9. an aqueous vehicle; 9. An aqueous mechanoluminescent paint comprising the mechanoluminescent material according to claim 7 or 8 dispersed in the aqueous vehicle.

10. 10. The water-based stress-luminescent paint according to claim 9, wherein the water-based vehicle contains at least 1-propanol.

11. The water-based stress-luminescent paint according to claim 9, wherein the water-based stress-luminescent paint is in a paste form.

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