Stress luminescent material, aqueous stress luminescent paint, and methods for producing stress luminescent material and aqueous stress luminescent paint

Abstract

The invention relates to a stress luminescent material, a water-based stress luminescent coating and a preparation method thereof. This method for producing a stress-emitting material comprises: a step in which stress-emitting particles and a non-aqueous surfactant-type dispersant are mixed in a non-aqueous solvent to produce a mixed solution; a step for preparing a dispersed solution containing the stress-emitting particles, the non-aqueous surfactant-type dispersant, and the non-aqueous solvent by stirring the mixed solution; a step in which the dispersed solution is subjected to vacuum defoaming; evaporating the dispersed solution subjected to vacuum defoaming to be semi-dry and solid until the dispersed solution is in a slurry state; and a step in which the slurry-like dispersion solution is evaporated and dried to obtain a powder-like stress-light-emitting material.

Description

Technical Field

[0001] The present application relates to a stress luminescent material, a water-based stress luminescent coating using the stress luminescent material as a pigment, and methods for manufacturing the same. Background Art

[0002] Methods are known for visualizing the strain state of an object by attaching a stress luminescent material that emits light in response to external mechanical stimulation (friction, impact, compression, tension, twisting, etc.) to the surface of the object. A practical method for attaching a stress luminescent material to the surface of an object is to apply a coating film formed by dispersing a powdered stress luminescent material as a pigment in a resin matrix to the surface of the object.

[0003] The stress luminescent material is in powder form and consists of ceramic particles with a particle size of micrometers (hereinafter referred to as "stress luminescent particles"). Stress luminescent particles have low water resistance and their crystal structure collapses upon contact with water, resulting in the loss of luminescence.

[0004] As a means of improving the water resistance of stress luminescent particles, Japanese Patent Application Laid-Open No. 2005-320425 (JP-A-2005-320425) discloses surface treatment of stress luminescent particles with a compound containing an acidic group or an ester thereof, thereby imparting water resistance to the particles. Patent Document 1 discloses using the surface-treated stress luminescent particles as pigments for water-based coatings. Summary of the Invention

[0005] However, in general, the surface of stress luminescent particles is not smooth and has multiple surface pores of nanometer size. Multiple surface pores include pores with a diameter of less than 2nm (micropores), pores with a diameter of 2 to 50nm (mesopores), pores with a diameter of 50nm or more (macropores), and crack gaps. Therefore, in order to prevent water from contacting the stress luminescent particles, these multiple surface pores need to be covered to prevent them from leaking out. Patent Document 1 shows the following method for surface treatment: dissolving a surface treatment agent in an organic solvent, adding stress luminescent particles to the solution and stirring, but does not mention the technology for covering the surface pores of stress luminescent particles to prevent them from leaking out. Therefore, there is a concern that even if surface treatment is performed, it may not be possible to impart water resistance to stress luminescent particles.

[0006] The present application is made to solve this problem, and an object of the present application is to provide a water-resistant stress luminescent material, a water-based stress luminescent paint containing the same, and methods for producing the same.

[0007] A method for producing a stress luminescent material according to one embodiment of the present application includes the following steps: mixing stress luminescent particles and a non-aqueous surfactant-type dispersant in a non-aqueous solvent to produce a mixed solution; stirring the mixed solution to prepare a dispersion solution containing the stress 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-like dispersion solution to dryness to obtain a powdered stress luminescent material.

[0008] A method for producing a water-based stress luminescent coating according to one embodiment of the present application includes the following steps: kneading a stress luminescent material produced using the above-mentioned method for producing a stress luminescent material in an aqueous vehicle to obtain a kneaded product; and degassing the kneaded product to obtain a water-based stress luminescent coating.

[0009] One embodiment of the present application provides a stress luminescent material comprising: stress luminescent particles having a plurality of surface pores; and a non-aqueous surfactant-type dispersant that covers the surface of the stress luminescent particles. The non-aqueous surfactant-type dispersant covers the plurality of surface pores of the stress luminescent particles by vacuum degassing a dispersion solution containing the stress luminescent particles, the non-aqueous surfactant-type dispersant, and a non-aqueous solvent.

[0010] A water-based stress luminescent paint according to one embodiment of the present application includes: an aqueous vehicle; and the stress luminescent material dispersed in the aqueous vehicle.

[0011] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a diagram of the manufacturing process of stress-luminescent materials.

[0013] Figure 2 This is a diagram of the manufacturing process of water-based stress-luminescent paint.

[0014] Figure 3 These are images obtained by photographing the water-based stress luminescent paint described in the comparative example and the water-based stress luminescent paint described in this embodiment.

[0015] Figure 4 This is a TIFF image obtained by photographing the light emission of the coating film.

[0016] Figure 5 This is a graph showing the temporal change in average luminescence intensity within the ROI during the tensile test. DETAILED DESCRIPTION

[0017] Hereinafter, embodiments of the present application will be described in detail with reference to the accompanying drawings. It should be noted that the same or corresponding parts in the drawings are denoted by the same reference numerals, and their description will not be repeated.

[0018] <Stress luminescent materials>

[0019] Stress luminescent materials have the property of releasing energy stored in the material and emitting light in response to external mechanical stimulation (friction, impact, compression, tension, twisting, etc.). Stress luminescent materials are materials in which an element that becomes a luminescent center is dissolved in the skeleton of an inorganic crystal (parent material). Representative materials include strontium aluminate (SrAl2O4) doped with europium: Eu 2+ ).

[0020] Stress luminescent materials are powdered ceramic particles with a particle size on the micron scale (hereinafter referred to as "stress luminescent particles"). Stress luminescent particles themselves lack adhesive properties. Therefore, to be used for non-destructive inspections such as visualizing stress concentration areas and identifying deteriorated areas, they must be mixed with an adhesive matrix and then fixed to the substrate being inspected. As an example of such a fixing method, a coating (hereinafter referred to as "stress luminescent coating") using stress luminescent particles as pigments dispersed in a resin matrix is now practically applied to the surface of the substrate to form a coating film.

[0021] Stress-luminescent particles, however, have low water resistance and immediately begin to hydrolyze upon contact with water, gradually disintegrating their crystal structure from the particle surface. This hydrolysis reduces the luminescence of the stress-luminescent particles, ultimately leading to their complete luminescence loss. Consequently, stress-luminescent coatings are limited to oil-based stress-luminescent coatings that use oil as a vehicle (a liquid component containing dispersed pigments, also known as a vehicle).

[0022] Meanwhile, from the perspective of global environmental protection, there is a growing demand for water-based stress-luminescent coatings with water-based vehicles. However, currently commercially available SrAl2O4-based stress-luminescent elements are highly reactive with water, reacting with the water-based vehicle and ultimately decomposing into hydroxides, resulting in a loss of luminescence.

[0023] In this embodiment, from the viewpoint of realizing a water-based stress luminescent coating, a stress luminescent material having water resistance and a method for producing the same are proposed.

[0024] <Method for producing stress luminescent material>

[0025] Hereinafter, a method for producing a stress luminescent material according to this embodiment will be described.

[0026] Figure 1Figure 2 is a diagram of the manufacturing process of stress luminescent materials. Figure 1 As shown, the method for manufacturing the stress luminescent material includes a mixing step S10 , a preparation step S20 , a vacuum degassing step S30 , an evaporation semi-solidification step S40 , an evaporation dryness step S50 , and a recovery step S60 .

[0027] (Mixing Step S10)

[0028] First, a mixing step S10 is performed. In this mixing step S10, stress luminescent particles and a non-aqueous surfactant-type dispersant are mixed in a non-aqueous solvent to form a mixed solution. 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 described later, the non-aqueous surfactant-type dispersant adsorbs onto the surface of the stress luminescent particles, coating them and thereby imparting water resistance to the stress luminescent particles.

[0029] In the mixing step S10, a non-aqueous surfactant-type dispersant is first added to the non-aqueous solvent dispensed into the container. Subsequently, the stress luminescent particles are added. Since both the surfactant-type dispersant and the solvent are non-aqueous, they prevent the stress luminescent particles from decomposing upon contact with water.

[0030] (Preparation Step S20)

[0031] Next, a preparation step S20 is performed. In the preparation step S20, the mixed solution generated 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.

[0032] (Vacuum Degassing Step S30)

[0033] Next, a vacuum degassing step S30 is performed. In this step, the dispersion solution prepared in the preparation step S20 is subjected to vacuum degassing. Vacuum degassing involves vacuum evacuating the dispersion solution while stirring it, causing the air dissolved in the dispersion solution to expand and remove bubbles from the surface exposed to the vacuum.

[0034] Generally speaking, the surface of stress luminescent particles is not smooth and has multiple surface pores of nanometer size. Multiple surface pores include pores with a diameter of less than 2nm (micropores), pores with a diameter of 2 to 50nm (mesopores), pores with a diameter of 50nm or more (macropores), and crack gaps. The vacuum degassing step S30 is implemented to ensure that the non-aqueous surfactant-type dispersant reliably penetrates into the spaces between the stress luminescent particles and the surface pores of the stress luminescent particles, and to form a defect-free protective layer on the surface of the stress luminescent particles. It should be noted that vacuum degassing of a liquid dispersion solution prepared by adding stress luminescent particles to a non-aqueous solvent in which a non-aqueous surfactant-type dispersant is dissolved can make the dispersion solution more easily penetrate into the fine surface pores of the stress luminescent particles than when vacuum degassing a dispersion solution containing solid components.

[0035] (Evaporation semi-solidification step S40)

[0036] Next, the evaporation step S40 is performed. In this step, the vacuum-degassing dispersion solution is evaporated to a semi-solid state until it becomes a slurry. This evaporation step is performed to completely evaporate the non-aqueous solvent (evaporation to a semi-solid state) by heating the dispersion solution, thereby preventing damage to the stress luminescent particles and the non-aqueous surfactant-type dispersant due to oxidative heat.

[0037] Therefore, during evaporation to semi-solidity, the dispersion solution is preferably kept at a low temperature as much as possible, and preferably subjected to a heat treatment in which the dispersion solution is heated while being kept at a temperature lower than the boiling point of the non-aqueous solvent.

[0038] (Evaporation and drying step S50)

[0039] Next, an evaporation and drying step S50 is performed. In this step, the non-aqueous solvent is completely evaporated from the slurry-like dispersion solution, yielding crystallized stress luminescent particles. The surfaces of the resulting stress luminescent particles are covered with a protective layer comprising a non-aqueous surfactant-type dispersant. The non-aqueous surfactant-type dispersant, which had penetrated the surface pores of the stress luminescent particles during the vacuum degassing step S30, undergoes the evaporation and drying step S50, ultimately forming a protective layer covering the surface pores of the stress luminescent particles. This protective layer prevents the stress luminescent elements from coming into direct contact with water, thereby imparting water resistance to the stress luminescent particles.

[0040] (Recovery Step S60)

[0041] Finally, a recovery step S60 is performed. In the recovery step S60, the stress luminescent particles obtained by the evaporation and drying step S50 are recovered. In this way, a water-resistant powdered stress luminescent material can be obtained.

[0042] <Method for producing water-based stress-luminescent paint>

[0043] The following describes a method for producing a water-based stress luminescent coating according to this embodiment. Figure 1 The stress luminescent material produced by the production method shown is produced as a pigment.

[0044] Figure 2 The following is a diagram of the manufacturing process of water-based stress luminous paint. Figure 2 As shown, the method for producing the water-based stress luminescent paint includes a kneading step S70 and a degassing step S80.

[0045] (Mixing Step S70)

[0046] First, the kneading step S70 is performed. In the kneading step S70, Figure 1 The stress luminescent material produced by the production method shown in the figure is used as a pigment and kneaded into an aqueous vehicle. The aqueous vehicle refers to a vehicle containing water as a solvent.

[0047] The solvent in the aqueous vehicle may contain solvent components other than water. Specific examples of such solvents include ethanol, 1-propanol, and 2-propanol. Considering the lifespan of the aqueous stress-luminescent coating, the aqueous vehicle preferably contains at least 1-propanol. The lifespan of aqueous stress-luminescent coatings will be discussed below. The aqueous vehicle may also contain resins and additives.

[0048] The stress luminescent material is composed of stress luminescent particles coated with a non-aqueous surfactant-type dispersant, making it water-resistant. Therefore, the aqueous vehicle is not absorbed by the stress luminescent particles, resulting in a paste-like kneaded product.

[0049] (Degassing Step S80)

[0050] Next, a degassing step S80 is performed. In the degassing step S80, the kneaded material in the paste form is degassed, and finally a water-based stress-luminescent paint is prepared. The prepared water-based stress-luminescent paint is macroscopically transparent and in the form of a paste, and can be used directly as a paint.

[0051] The following examples further illustrate the method for producing the stress luminescent material and water-based stress luminescent coating according to this embodiment. However, the method for producing the stress luminescent material and water-based stress luminescent coating according to this embodiment is not limited to these examples.

[0052] Example

[0053] [Preparation of stress-luminescent materials]

[0054] (Mixing Step S10)

[0055] In the mixing step S10, ethanol (volume: 80 ml) as a non-aqueous solvent is dispensed into a container, a non-aqueous surfactant-type dispersant (mass: 132 mg) is added thereto, and then stress luminescent particles (mass: 2.50 g) are added to generate a mixed solution.

[0056] An ester surfactant-type dispersant (SNDISPERSANT 9228, manufactured by Sannopco) was used as the non-aqueous surfactant-type dispersant. SrAl2O4-based 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) were used as the stress luminescent particles.

[0057] The manufacturer recommends adding 0.5-2.0% of SN DISPERSANT 9228 to the pigment. Therefore, after removing the ethanol in the subsequent evaporation and drying step S50, a slightly excessive amount of about 5% of SN DISPERSANT 9228 is added to the ethanol.

[0058] (Preparation Step S20)

[0059] In preparation step S20, the mixed solution obtained in mixing step S10 was stirred at room temperature to prepare a dispersion solution in which SrAl2O4-based stress-luminescent particles and an ester-based surfactant-type dispersant were temporarily 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.

[0060] (Vacuum Degassing Step S30)

[0061] In the vacuum degassing process S30, the container containing the dispersed solution is placed in a vacuum chamber. The vacuum chamber is connected to a rotary pump by means of a liquid nitrogen trap for capturing ethanol volatilized from the dispersed solution. In this state, it takes about 5 minutes to slowly reduce the pressure of the vacuum chamber from normal pressure (0 Pa) to -0.1 MPa. After the decompression, the vacuum state of the vacuum chamber is maintained for about 5 minutes until the bubbles generated in the dispersed solution converge. After the bubbles of the dispersed solution converge, the vacuum chamber is restored to normal pressure. Through this vacuum degassing, about 10 to 20 ml of ethanol evaporates and disappears.

[0062] (Evaporation semi-solidification step S40)

[0063] In the evaporation semi-drying step S40, the container of the dispersion solution that has been subjected to vacuum degassing is stirred again using a magnetic stirrer until it becomes a slurry. During stirring, the set temperature on the magnetic stirrer is set to 100°C, and the rotation speed of the magnetic stirrer is set to 600-300rpm. It should be noted that the measured temperature of the dispersion solution in the container is about 50°C, which is lower than the boiling point of ethanol (about 78°C). The dispersion solution is stirred for about 1.5 hours until the capacity of the dispersion solution reaches about 10ml.

[0064] (Evaporation and drying step S50)

[0065] In the evaporation-to-drying step S50, the container containing the slurry-like dispersion solution is placed in a thermostatic bath and heated to approximately 80°C. This temperature is maintained for at least 12 hours to completely evaporate and remove the ethanol from the dispersion solution. The thermostatic bath is then cooled to room temperature, and the container is removed.

[0066] (Recovery Step S60)

[0067] In the recovery step S60 , the stress luminescent particles adhering to the inner surface of the container taken out of the thermostatic bath are scraped off with a spatula, thereby recovering the stress luminescent particles.

[0068] The stress luminescence material produced by the above-described manufacturing method includes SrAl2O4-based stress luminescence particles and an ester-based surfactant-type dispersant that covers the surface of the SrAl2O4-based stress luminescence particles. By vacuum degassing a dispersion solution containing the SrAl2O4-based stress luminescence particles, the ester-based surfactant-type dispersant, and ethanol, the ester-based surfactant-type dispersant covers the numerous surface pores of the SrAl2O4-based stress luminescence particles.

[0069] [Preparation of water-based stress-luminescent paint]

[0070] (Mixing Step S70)

[0071] In the kneading step S70, an aqueous vehicle (mass: 5.5 g) is dispensed into a container, and SrAl2O4-based stress luminescent particles (mass: 2 g) produced by the above-mentioned stress luminescent material production method are added thereto as a pigment.

[0072] The water-based vehicle used was a water-based acrylic resin paint (TAMIYA COLOR X-22CLEAR, manufactured by TAMIYA). 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%).

[0073] The mixture of the aqueous acrylic resin coating and the SrAl2O4-based stress-luminescent element was gently mixed with a spatula and then kneaded using a kneader (manufactured by THINKY Co., Ltd., Nanko Rentarou) at a rotation speed of 2000 rpm and a running time of 1.5 minutes.

[0074] (Degassing Step S80)

[0075] In the degassing step S80, the kneading machine is further operated at a rotation speed of 2200 rpm for about 20 seconds to degas the kneaded product, thereby obtaining a paste-like transparent water-based stress-luminescent paint.

[0076] The water-based stress luminescent paint prepared by the above-mentioned manufacturing method comprises an aqueous vehicle and a stress luminescent material dispersed in the aqueous vehicle. The stress luminescent material is composed of SrAl2O4-based stress luminescent particles whose surfaces are coated with an ester-based surfactant-type dispersant.

[0077] [Evaluation of stress luminescent materials]

[0078] In order to evaluate the water resistance of the stress luminescent particles produced in this example, a water-based stress luminescent coating was further produced using the stress luminescent material described in the comparative example as a pigment.

[0079] The stress luminescent material of the comparative example is composed of the same SrAl2O4 stress luminescent particles as in the present embodiment. However, the step of coating the surface of the SrAl2O4 stress luminescent particles with an ester surfactant type dispersant is not performed ( Figure 1 The stress luminescent material of this comparative example is different from the stress luminescent material of this embodiment in that the steps S10 to S60 are repeated. Figure 2 The steps S70 and S80 are performed to produce the water-based stress luminescent paint described in the comparative example.

[0080] Figure 3 These are images obtained by photographing the water-based stress luminescent paint described in the comparative example and the water-based stress luminescent paint described in this embodiment. Figure 3 (A) shows an image of the water-based stress luminescent coating described in the comparative example. Figure 3 (B) shows an image of the water-based stress luminescent paint described in this example. Each water-based stress luminescent paint was stored in a white plastic container for ointment.

[0081] like Figure 3As shown in (A), the water-based stress luminescent paint of the comparative example does not appear as a paste, but appears as a white powder mass because the stress luminescent particles absorb the water-based vehicle (water-based acrylic resin paint).

[0082] In contrast, the water-based stress luminescent coating described in this embodiment is as follows Figure 3 As shown in (B), the stress luminescent particles are dispersed in a water-based vehicle (water-based acrylic resin paint) to form a transparent paste. This indicates that the step of coating the surface of the stress luminescent particles with a non-aqueous surfactant-type dispersant ( Figure 1 The steps S10 to S60) are indispensable.

[0083] In this embodiment, the step of covering the surface of the stress luminescent particles with a non-aqueous surfactant-type dispersant is not further performed ( Figure 1 The stress luminescent material was produced by performing the vacuum degassing step S30 in the steps S10 to S60. In this case, the produced stress luminescent particles lacked sufficient water resistance. During the production of a water-based stress luminescent coating, the stress luminescent particles absorbed the aqueous vehicle (water-based acrylic resin coating), resulting in a decrease in the luminescence ability of the stress luminescent particles. This suggests that vacuum degassing allows the non-aqueous surfactant-type dispersant to penetrate the surface pores of the stress luminescent particles, forming a defect-free protective layer on the surface of the stress luminescent element, thereby improving the water resistance of the stress luminescent particles.

[0084] [Evaluation of water-based stress-luminescent paint]

[0085] (Luminescence ability evaluation)

[0086] An experiment was conducted to evaluate the luminescence ability of the water-based stress-luminescent coating described in this example. In this experiment, the water-based stress-luminescent coating described in this example was applied to one side of an A6061 test piece (JIS 13B shape, 0.5 mm thickness) using a pen. The A6061 test piece was then pre-dried indoors for 3 hours and then dried in a thermostatic oven at 80°C for 3 hours to produce a test piece with a coating film (stress-luminescent film) formed on the surface.

[0087] Next, a tensile test was performed on the specimen. During the tensile test, a stress measurement system was set up in a darkroom, and the specimen was placed. The stress measurement system consisted of a tensile testing machine (Autograph AG-Xplus, manufactured by Shimadzu Corporation), an imaging device, an excitation light source, a control device, and a storage device. The tensile testing machine was configured to apply a load (tensile force) to the specimen by raising a slide under control of the control device.

[0088] As an excitation process for accumulating energy in the coating film on the specimen, blue light (wavelength λ = 470nm) is irradiated from an excitation light source for 60 seconds, and then kept in a dark place for 120 seconds. Thereafter, a load is applied to the specimen at a slider speed of 5mm / min (maximum load set: 3kN). During the load application process, the light emitted by the coating film is photographed at a frame rate of 500ms using a camera, and saved in a storage device as a TIFF (Tag Image File Format) image. The saved TIFF image is shown in Figure 4 .

[0089] Figure 4 (A) is an image obtained by photographing light emitted from the coating film before a load is applied. Figure 4 (B) is an image obtained by photographing the light emitted by the coating film when the maximum load is reached.

[0090] according to Figure 4 The image shown in (A) shows that although there are different luminescence depths due to uneven coating, the coating releases the stored energy and emits light. Figure 4 The image (B) shows that the coating film has an increased luminescence intensity due to luminescence caused by stress generated by the load (stress luminescence).

[0091] Next, a region of interest (ROI) is set in a series of TIFF images captured during the tensile test, and a value based on the luminescence intensity within the ROI is calculated for each frame of the TIFF image. Figure 4 (A) Figure 4 The white box in (B) represents the ROI. The value based on the luminous intensity within the ROI can be calculated by performing statistical processing on the luminous intensity within the ROI. In this embodiment, the average luminous intensity within the ROI is calculated.

[0092] Figure 5 This graph shows the temporal changes in average luminescence intensity within the ROI during a tensile test. The horizontal axis represents the TIFF image frame number, and the vertical axis represents luminescence intensity. The graph was created by plotting the average luminescence intensity within the ROI, calculated for each frame of a series of TIFF images.

[0093] like Figure 5As shown, the luminescence intensity of the coating film increases with the passage of time from the start of load application, that is, as the load increases. Furthermore, the following luminescence characteristics were confirmed: the luminescence intensity peaked at the set maximum load of 3 kN and then gradually decreased as the load decreased. This demonstrates that the water-based stress-luminescent coating described in this example effectively functions as a means of securing the stress-luminescent material to the substrate.

[0094] (Lifespan evaluation)

[0095] The lifespan of the water-based stress-luminescent paint described in this example was evaluated. In this lifespan evaluation, the water-based stress-luminescent paint prepared in this example was placed in multiple sealed containers, stored in a refrigerator and indoors, and their lifespan was observed.

[0096] In all sealed containers, it was confirmed that the pigment settled over time after production, with the aqueous vehicle and pigment separating into two layers. Stirring with a pen, a vortex, or other methods confirmed that the pigment redispersed, returning the water-based stress-luminescent paint to its original paste state. Furthermore, the luminescence properties of the water-based stress-luminescent paint, once restored to a paste state, were evaluated using the same method as described above, and the results showed luminescence properties comparable to those of the water-based stress-luminescent paint immediately after production.

[0097] In this example, the phenomenon of pigment precipitation was further verified. Two aqueous vehicles, A and B, with different compositions were prepared. Vehicle A was a water-based acrylic resin coating containing 1-propanol (content: 10%). Vehicle B was a water-based acrylic resin coating containing 2-propanol (content: 10%). Equal amounts of SrAl2O4-based stress-luminescent particles (mass: 2.2g) were added to each of Vehicles A and B (mass: 5.5g) to produce the water-based stress-luminescent coatings, and their behavior was observed.

[0098] Observations confirmed that the precipitation rate of aqueous vehicle A was slower than that of aqueous vehicle B. This suggests that pigment precipitation depends on the composition of the aqueous vehicle. Furthermore, it is speculated that 1-propanol may be effective in delaying pigment precipitation.

[0099] It should be noted that, in this embodiment and this example, a method for preparing a water-based stress luminescent coating by mixing a stress luminescent material with an aqueous color carrier is described. However, by storing the stress luminescent material and the aqueous color carrier separately and mixing the stress luminescent material with the aqueous color carrier to prepare the water-based stress luminescent coating at the site where the stress luminescent material is fixed to the substrate, the above-mentioned precipitation of the pigment can be avoided.

[0100] Furthermore, the stress luminescent material according to this embodiment can be mixed with a solvent other than an aqueous vehicle, and thus can be used in applications other than aqueous coatings.

[0101] [Way]

[0102] It should be understood by those skilled in the art that the above-mentioned embodiments are specific examples of the following aspects.

[0103] (Item 1) A method for producing a stress luminescent material according to one embodiment includes the following steps: a step of mixing stress luminescent particles and a non-aqueous surfactant-type dispersant in a non-aqueous solvent to produce a mixed liquid; a step of stirring the mixed liquid to prepare a dispersion solution 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 a step of evaporating the slurry-like dispersion solution to dryness to obtain a powdered stress luminescent material.

[0104] According to the manufacturing method described in item 1, vacuum degassing allows the non-aqueous surfactant-based dispersant to penetrate the surface pores of the stress luminescent particles, thereby forming a defect-free protective layer on the surface of the stress luminescent element. This imparts water resistance to the stress luminescent particles. Furthermore, by evaporating the vacuum-degassed dispersion solution to a semi-solid state, damage to the stress luminescent particles and protective layer due to oxidation heat can be suppressed.

[0105] (Item 2) In the manufacturing method described in Item 1, the stress luminescent particles have a plurality of surface pores. 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 luminescent particles.

[0106] According to this, the plurality of surface pores of the stress luminescent particles can be covered with the non-aqueous surfactant-type dispersant without leaking out, thereby imparting water resistance to the stress luminescent particles.

[0107] (Item 3) In the manufacturing method described in Item 1 or Item 2, the step of evaporating the dispersed solution to semi-dryness includes the step of stirring the dispersed solution while maintaining it at a temperature lower than the boiling point of the non-aqueous solvent, thereby making the dispersed solution into a slurry.

[0108] According to this, when the non-aqueous solvent is removed from the dispersion solution, it is possible to suppress damage to the stress luminescent particles and the non-aqueous surfactant-type dispersant due to oxidation heat.

[0109] (Item 4) In the production method described in Items 1 to 3, the stress luminescent particles are strontium aluminate (SrAl2O4) doped with europium, and the non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

[0110] According to this, by coating the surface with an ester-based surfactant-type dispersant, water-resistant SrAl 2 O 4 -based stress luminescent particles can be realized.

[0111] (Item 5) A method for producing a water-based stress luminescent coating according to one embodiment includes the following steps: mixing a stress luminescent material produced using the production method described in Items 1 to 4 in an aqueous vehicle to obtain a kneaded product; and degassing the kneaded product to obtain a water-based stress luminescent coating.

[0112] According to the manufacturing method described in item 5, a water-based stress luminescent paint using a water-resistant stress luminescent material as a pigment can be realized.

[0113] (Item 6) In the production method described in Item 5, the aqueous vehicle contains at least 1-propanol.

[0114] This can delay the precipitation of the pigment contained in the water-based stress luminescent paint.

[0115] (Item 7) One embodiment of a stress luminescent material includes stress luminescent particles having a plurality of surface pores and a non-aqueous surfactant-type dispersant that covers the surface of the stress luminescent particles. A dispersion solution containing the stress luminescent particles, the non-aqueous surfactant-type dispersant, and a non-aqueous solvent is vacuum degassed, thereby coating the plurality of surface pores of the stress luminescent particles with the non-aqueous surfactant-type dispersant.

[0116] The stress luminescent material described in item 7 is composed of stress luminescent particles whose surfaces are covered with a non-aqueous surfactant-type dispersant and has water resistance.

[0117] (Item 8) In the stress luminescent material according to Item 7, the stress luminescent particles are strontium aluminate (SrAl2O4) doped with europium. The non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

[0118] Thus, it is possible to realize SrAl2O4-based stress luminescent particles whose surfaces are covered with an ester-based surfactant-type dispersant and which have water resistance.

[0119] (Item 9) One embodiment of the water-based stress luminescent paint comprises an aqueous vehicle and the stress luminescent material according to Item 7 or Item 8 dispersed in the aqueous vehicle.

[0120] The water-based stress luminescent paint described in Item 9 is a water-based paint that has low environmental impact, is user-friendly, and uses a stress luminescent material as a pigment.

[0121] (Item 10) In the water-based stress luminescent paint described in Item 9, the water-based vehicle contains at least 1-propanol.

[0122] This can delay the precipitation of the pigment contained in the water-based stress luminescent paint.

[0123] (Item 11) The water-based stress luminescent paint described in Item 9 or Item 10 is in the form of a paste.

[0124] According to this, the water-based stress luminescent coating can be applied to the substrate, and thus the stress luminescent material can be fixed to the surface of the substrate in the form of a coating film.

[0125] While the embodiments of the present invention have been described, the embodiments disclosed herein are illustrative in all respects and should not be construed as limiting. The scope of the present invention is indicated by the claims, which are intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A method for manufacturing a stress luminescent material, comprising the following steps: a step of mixing stress luminescent particles and a non-aqueous surfactant-type dispersant into a non-aqueous solvent to produce a mixed solution; A step of stirring the mixed solution to prepare a dispersion solution containing the stress luminescent particles, the non-aqueous surfactant-type dispersant, and the non-aqueous solvent; The process of vacuum degassing the dispersed solution; The process of evaporating the dispersed solution subjected to the vacuum degassing to semi-dryness until it becomes a slurry; and The step of evaporating the slurry-like dispersion solution to dryness to obtain the powdered stress luminescent material.

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

3. The method for producing a stress 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 method for producing a stress luminescent material according to claim 1, wherein: The stress luminescent particles are strontium aluminate (SrAl2O4) doped with europium. The non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

5. A method for producing a water-based stress-luminescent coating, comprising the following steps: A step of kneading the stress luminescent material produced by the production method according to any one of claims 1 to 4 in an aqueous vehicle to obtain a kneaded product; and and degassing the kneaded product to obtain the water-based stress luminescent paint.

6. The method for producing a water-based stress-luminescent coating according to claim 5, wherein: The aqueous vehicle contains at least 1-propanol.

7. A stress luminescent material comprising: A stress luminescent particle having a plurality of surface pores; and a non-aqueous surfactant-type dispersant covering the surface of the stress luminescent particles, The non-aqueous surfactant-type dispersant covers the plurality of surface pores of the stress luminescent particles by vacuum degassing a dispersion solution containing the stress luminescent particles, the non-aqueous surfactant-type dispersant, and a non-aqueous solvent.

8. The stress luminescent material according to claim 7, wherein: The stress luminescent particles are strontium aluminate (SrAl2O4) doped with europium. The non-aqueous surfactant-type dispersant is an ester-based surfactant-type dispersant.

9. A water-based stress-luminescent coating comprising: an aqueous vehicle; and The stress luminescent material according to claim 7 or 8 is dispersed in the aqueous vehicle.

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

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

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