Pressure test color development film and preparation method thereof

Abstract

The invention relates to the technical field of pressure-sensitive membranes, and particularly discloses a pressure test color development membrane and a preparation method thereof. The pressure test color development film comprises a base material, a capsule layer and a color development layer, wherein the capsule layer and the color development layer are formed on the base material; the capsule layer is connected with the color developing layer; the capsule layer comprises a first microcapsule containing an electron donating leuco dye precursor and a second microcapsule containing an electron accepting compound. When the color development film is pressed in a pressure test, the microcapsules are broken to different degrees and release the color former and the color developing agent respectively, and after the color former and the color developing agent are in contact reaction, the structure is changed and is absorbed by the color development layer to show color. The color former and the color developing agent respectively form the capsule layer in the form of microcapsules, so that the adaptability of the pressure test color development film to the storage environment is improved, the color development concentration of the pressure test color development film cannot be reduced along with the prolonging of the storage time especially in the high-temperature and high-humidity environment, the repeatability of the test result is better, and the color development performance is stable.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure-sensitive membranes, and in particular to a pressure-testing chromogenic membrane and a preparation method thereof. Background Art

[0002] Pressure testing is commonly performed using pressure testers in various production processes with stringent pressure requirements, such as printed circuit board lamination, roller pressure verification and adjustment, LCD glass panel bonding, and engine cylinder assembly. However, this pressure testing method is complex to operate, exhibits hysteresis in measurement results, and suffers from poor accuracy and sensitivity. It is only suitable for pressure testing of small areas and is not suitable for online pressure monitoring or pressure testing of areas with unique shapes. To facilitate these pressure testing applications, the use of pressure measurement chromogenic films is becoming increasingly widespread.

[0003] Pressure testing chromogenic films are electronic functional materials that accurately measure pressure distribution, magnitude, and balance through color density. They typically consist of a chromogenic portion and a color-developing portion. The chromogenic portion contains microcapsules containing electron-donating colorless dye precursors, while the color-developing portion contains electron-accepting compounds. Under pressure, the microcapsules in the chromogenic portion rupture, releasing the electron-donating colorless dye precursors. These electron-donating colorless dye precursors, upon contact with the electron-accepting compounds, color the color-developing portion. The measured pressure and its impact point can be determined based on the coloring area and chromaticity of the color-developing portion.

[0004] Chromogenic films for pressure measurement have high requirements for their storage environment. For example, they typically need to be used in high-temperature or high-humidity conditions. As storage time increases, the color concentration of existing chromogenic films decreases, affecting the accuracy of measurement results. Therefore, there is an urgent need for a chromogenic film for pressure measurement that is unaffected by the storage environment and has stable color development properties. Summary of the Invention

[0005] In response to the above problems, the present invention provides a pressure test chromogenic film and a preparation method thereof. By respectively forming an electron-donating colorless dye precursor and an electron-accepting compound into a capsule layer in the form of microcapsules, not only the environmental adaptability of the pressure test chromogenic film is improved, but also the stability and repeatability of the test results are better.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is: In a first aspect, the present invention provides a pressure test chromogenic film, comprising a substrate, a capsule layer and a color development layer formed on the substrate; the capsule layer is in contact with the color development layer; The capsule layer includes first microcapsules containing an electron-donating leuco dye precursor and second microcapsules containing an electron-accepting compound.

[0007] Compared with the prior art, the pressure test chromogenic film provided by the present invention uses microcapsules to form a capsule layer of an electron-donating colorless dye precursor and an electron-accepting compound. When the pressure test chromogenic film is subjected to pressure, the microcapsules in the capsule layer rupture to varying degrees depending on the magnitude of the pressure, releasing the corresponding electron-donating colorless dye precursor and electron-accepting compound. After the two come into contact and react, their structures change and are absorbed by the color-developing layer, thereby coloring the color-developing layer and showing color. The present invention uses microcapsules to simultaneously encapsulate the electron-donating colorless dye precursor and the electron-accepting compound, thereby improving the adaptability of the pressure test chromogenic film to the storage environment. In particular, in a high temperature and high humidity environment, the pressure test chromogenic film does not reduce the color concentration as the storage time increases, and the test results have good repeatability and stable color performance.

[0008] It should be noted that the pressure test chromogenic film of the present invention can contain only one substrate, that is, a single-sheet type, or it can contain two substrates, that is, a double-sheet type, as long as the capsule layer is located on the upper surface of the color-developing layer during use. In this way, the released electron-donating colorless dye precursor and electron-accepting compound can be absorbed by the color-developing layer by the action of gravity, thereby coloring the color-developing layer.

[0009] For example, for a single-piece pressure-tested chromogenic membrane, the substrate may be in contact with the capsule layer and also with the color-developing layer.

[0010] For example, for a double-sheet pressure test chromogenic film, the substrate includes a first substrate and a second substrate; the first substrate is connected to the capsule layer to form a first sheet; the second substrate is connected to the color development layer to form a second sheet.

[0011] Preferably, the pressure test range of the pressure test chromogenic film is 0.006MPa~300MPa.

[0012] Preferably, the particle size of the first microcapsule is D50=2μm~50μm, more preferably D50=8μm~30μm.

[0013] Preferably, the particle size of the second microcapsule is D50=2μm~50μm, more preferably D50=8μm~30μm.

[0014] Preferably, the number average wall thickness of the first microcapsules is ≥200 nm, more preferably 200 nm to 350 nm.

[0015] Preferably, the number average wall thickness of the second microcapsules is ≥200 nm, more preferably 200 nm to 350 nm.

[0016] More preferably, the ratio of the number average wall thickness of the first microcapsules to D50 is 0.01-0.1, more preferably 0.01-0.05.

[0017] More preferably, the ratio of the number average wall thickness of the second microcapsules to D50 is 0.01-0.1, more preferably 0.01-0.05.

[0018] The first microcapsules and the second microcapsules of the present invention adopt a specific range of particle size and wall thickness, so that under different pressures, the number of microcapsules ruptured is different, the amount of released color former and color developer is different, and the degree of color development reaction is different, thereby achieving the purpose of different color depths under different pressures to the greatest extent, and further improving the repeatability and stability of the test results.

[0019] Preferably, the core material of the first microcapsule comprises the following components in percentage by weight: 3% to 20% of electron-donating colorless dye precursor, 30% to 87% of solvent, and 0% to 50% of cosolvent.

[0020] More preferably, the core material of the first microcapsule comprises the following components in percentage by weight: 10% to 18% of an electron-donating colorless dye precursor, 40% to 75% of a solvent, and 10% to 40% of a cosolvent.

[0021] Preferably, the core material of the second microcapsule comprises the following components in percentage by weight: 3% to 20% of an electron-accepting compound, 30% to 87% of a solvent, and 0% to 50% of a cosolvent.

[0022] More preferably, the core material of the second microcapsule comprises the following components in percentage by weight: 10% to 18% of an electron-accepting compound, 40% to 75% of a solvent, and 10% to 40% of a cosolvent.

[0023] By limiting the component contents of the core materials of the first microcapsules and the second microcapsules, the present invention can ensure that the electron-donating leuco dye precursor of the first microcapsule and the electron-accepting compound of the second microcapsule are within a specific content range. Through extensive testing, the present invention has found that if the mass content of the electron-donating leuco dye precursor is less than 3%, the color development concentration is insufficient; if the mass content of the electron-donating leuco dye precursor is greater than 20%, the electron-donating leuco dye precursor will crystallize and precipitate in a low-temperature environment, resulting in a reduction in the effective color development components and affecting the accuracy of the pressure test results; if the mass content of the electron-accepting compound is less than 3%, the color development concentration is insufficient; and if the mass content of the electron-accepting compound is greater than 20%, the electron-accepting compound will crystallize and precipitate in a low-temperature environment, resulting in a reduction in the effective color development components and affecting the accuracy of the pressure test results.

[0024] Preferably, the electron-donating colorless dye precursor includes at least one of a fluoran compound, an indolyl peptide ketone compound, a rhodamine lactam compound, a spiropyran compound or a phenothiazine compound.

[0025] Further preferably, the electron-donating colorless dye precursor includes at least one of crystal violet lactone (CVL), methylene blue (BLMB) or phthalocyanine lactone (CK-16).

[0026] Preferably, the electron-accepting compound includes at least one of 4,4'-sulfonylbis[2-(2-propenyl)]phenol, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 2,4-diphenylsulfonylphenol, 4-hydroxy-4'-benzyloxydiphenyl sulfone or 4-[[4-(2-allyloxy)phenyl]sulfonyl]phenol.

[0027] More preferably, the solvent includes at least one of an alkylnaphthalene solvent, an aliphatic hydrocarbon solvent, a natural animal or plant oil solvent, or a mineral oil.

[0028] More preferably, the alkylnaphthalene solvent includes at least one of a diaryl alkane solvent, a diaryl olefin solvent or diisopropylnaphthalene.

[0029] Exemplary diarylalkane solvents include 1-phenyl-1-dimethylphenylethane.

[0030] More preferably, the natural animal and plant oil solvent includes at least one of corn oil, castor oil or rapeseed oil.

[0031] Further preferably, the co-solvent is a low boiling point solvent, including at least one of a ketone co-solvent or an ester co-solvent.

[0032] Illustratively, the ketone co-solvent includes at least one of acetone or methyl ethyl ketone.

[0033] Illustratively, the ester co-solvent includes at least one of methyl acetate or ethyl acetate.

[0034] The preferred cosolvent of the present invention can better dissolve the electron-donating colorless dye precursor or the electron-accepting compound in the solvent.

[0035] Preferably, the first microcapsules are prepared by interfacial polymerization.

[0036] Preferably, the second microcapsules are prepared by interfacial polymerization.

[0037] Preferably, the capsule wall material of the first microcapsule and the second microcapsule includes at least one of free polyurea, polyurethane urea, gelatin, melamine formaldehyde resin or polyurethane.

[0038] The capsule wall material of the present invention is insoluble in water and oil, and can effectively protect the electron-donating colorless dye precursor and the electron-accepting compound contained therein from the influence of the external environment, thereby improving the test stability of the pressure test chromogenic membrane.

[0039] More preferably, the capsule wall material is prepared from two or more reactive monomers through interfacial polymerization.

[0040] More preferably, the reactive monomers include a first reactive monomer and a second reactive monomer; The first reactive monomer comprises at least one of an aliphatic polyol, an aromatic polyol, a polyamine, or an alkylene oxide adduct of an aliphatic polyamine; The second reactive monomer includes at least one of dicyclohexylmethane diisocyanate (HDI), hexamethylene diisocyanate (HMDI), dimethyldiphenylmethane diisocyanate, a trimethylolpropane adduct of hexylene diisocyanate, or a trimethylolpropane adduct of xylylenediisocyanate.

[0041] Illustratively, the polyamine includes at least one of trimethylhexamethylenediamine, triethylenetetramine, or hexamethylenediamine.

[0042] Exemplary alkylene oxide adducts of aliphatic polyamines include butylene oxide adducts of ethylenediamine.

[0043] In the present invention, the second reactive monomer is a polyisocyanate oligomer. Preferably, the first reactive monomer contains two or more -NH or -NH₂ groups, which react with the second reactive monomer to form a stable urea group that can withstand high test temperatures. The first and second reactive monomers are dissolved in different reaction media / solvents. When one reaction medium / solvent is dispersed into the other, the two reactive monomers undergo polymerization at the (water-oil) interface, encapsulating the core material (i.e., the color former or developer) to form microcapsules.

[0044] Preferably, the capsule layer comprises the following components in parts by mass: 16 to 48 parts of first microcapsules, 16 to 48 parts of second microcapsules, 2 to 40 parts of first adhesive, and 0.5 to 20 parts of first auxiliary agent.

[0045] Further preferably, the capsule layer comprises the following components in parts by mass: 20 to 40 parts of first microcapsules, 20 to 40 parts of second microcapsules, 10 to 30 parts of first adhesive, and 5 to 15 parts of first auxiliary agent.

[0046] More preferably, the mass ratio of the first microcapsules to the second microcapsules is (0.6-1.5):1, more preferably (0.8-1.2):1.

[0047] Further preferably, the first adhesive comprises at least one of a starch aqueous solution, a carboxymethyl cellulose (CMC) aqueous solution or a polyvinyl alcohol (PVA) aqueous solution.

[0048] More preferably, the mass concentration of the first adhesive is 5% to 15%.

[0049] More preferably, the first auxiliary agent includes at least one of an emulsifier or a UV absorber.

[0050] More preferably, the first auxiliary agent includes at least one of a gelatin aqueous solution, a starch aqueous solution, a carboxymethyl cellulose (CMC) aqueous solution, a polyvinyl alcohol (PVA) aqueous solution, a sodium lauryl sulfate aqueous solution or a silicon dioxide aqueous solution.

[0051] More preferably, the mass concentration of the first auxiliary agent is 2% to 10%.

[0052] In the present invention, the first adhesive is a water-soluble polymer material, which can bond the first microcapsule and the second microcapsule together and adhere them to the substrate or the color development layer, making them difficult to fall off; the first auxiliary agent can improve the surface quality of the capsule layer.

[0053] Preferably, the thickness of the capsule layer is 7 μm to 40 μm, more preferably 15 μm to 40 μm.

[0054] Preferably, the color development layer comprises the following raw material components in percentage by weight: 40% to 80% of an inorganic porous filler, 2% to 40% of a second binder, and 0.5% to 20% of a second auxiliary agent.

[0055] Further preferably, the color development layer comprises the following raw material components in percentage by weight: 55% to 75% of an inorganic porous filler, 10% to 30% of a second binder, and 5% to 15% of a second auxiliary agent.

[0056] Further preferably, the inorganic porous filler includes at least one of gypsum powder, calcium sulfate, clay, kaolin, light calcium carbonate, titanium dioxide or silica powder.

[0057] The preferred inorganic porous material is white or light-colored, and has a lamellar structure, which is conducive to the penetration and absorption of the system after the reaction of the color former and the developer, and presents different degrees of color depth according to the different release amounts of the microcapsules, which is conducive to accurate comparison with the standard color card and precise correspondence of pressure values.

[0058] More preferably, the average particle size of the inorganic porous filler is 2 μm to 10 μm.

[0059] Further preferably, the second adhesive includes at least one of a styrene-butadiene rubber (SBR) aqueous solution, an acrylic latex aqueous solution, an arabic gum aqueous solution, a gelatin aqueous solution, a carboxymethyl cellulose (CMC) aqueous solution, or a polyvinyl alcohol (PVA) aqueous solution.

[0060] More preferably, the mass concentration of the second adhesive is 5% to 15%.

[0061] In the present invention, the second adhesive is a water-soluble adhesive, which can bond the inorganic porous fillers together and adhere them to the substrate or the capsule layer, and is not easy to fall off.

[0062] More preferably, the second auxiliary agent includes at least one of a surfactant, a defoaming agent, a UV absorber or a pH regulator.

[0063] Preferably, the color development layer has a thickness of 5 μm to 20 μm, more preferably 10 μm to 20 μm.

[0064] Preferably, the substrate comprises a plastic film or a paper-based material.

[0065] Illustratively, the plastic film includes at least one of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP) or polyvinyl chloride (PVC).

[0066] Illustratively, the paper-based material includes at least one of premium paper, coated paper, art paper, or synthetic paper.

[0067] For example, the synthetic paper is made of synthetic fibers, and the synthetic fibers include at least one of polyethylene, polyamide, and polyethylene terephthalate.

[0068] Preferably, the thickness of the substrate is 10 μm to 150 μm, more preferably 50 μm to 125 μm.

[0069] More preferably, the thickness of the first substrate is 10 μm to 150 μm, more preferably 50 μm to 125 μm.

[0070] More preferably, the thickness of the second substrate is 10 μm to 150 μm, more preferably 50 μm to 125 μm.

[0071] By controlling the thickness of the substrate, the capsule layer and the color development layer, the present invention can further improve the accuracy of the test results within the pressure bearing strength range and effectively reduce chemical costs.

[0072] In a second aspect, the present invention provides a method for preparing the pressure test chromogenic film, comprising the following steps: Dissolving the components of the capsule layer in water, coating the resulting first mixed liquid on a substrate, and drying to form a capsule layer; The components of the color development layer are dissolved in water, and the obtained second mixed liquid is coated on the capsule layer. After drying, the color development layer is formed to obtain a pressure test color film.

[0073] It should be noted that the pressure test chromogenic film prepared by this preparation method is a single piece. When in use, the substrate is on the upper side and the color development layer is on the lower side.

[0074] In a third aspect, the present invention provides a method for preparing the pressure test chromogenic film, comprising the following steps: Dissolving the components of the color-developing layer in water, coating the resulting second mixed liquid on a substrate, and drying to form a color-developing layer; The components of the capsule layer are dissolved in water, and the obtained first mixed liquid is coated on the color-developing layer. After drying, the capsule layer is formed to obtain a pressure test color-developing film.

[0075] It should be noted that the pressure test chromogenic film prepared by this preparation method is a single piece. When in use, the capsule layer is on the upper side and the substrate is on the lower side.

[0076] In a fourth aspect, the present invention provides a method for preparing the pressure test chromogenic film, comprising the following steps: Dissolving the components of the capsule layer in water, coating the resulting first mixed liquid on a first substrate, and drying to form a capsule layer to obtain a first sheet; The components of the color development layer are dissolved in water, and the obtained second mixed liquid is coated on the second substrate. After drying, the color development layer is formed to obtain a second sheet, that is, a pressure test color film.

[0077] It should be noted that the pressure test chromogenic film prepared by this preparation method is a double-sheet type. When in use, the first sheet is on the top and the second sheet is on the bottom, and the capsule layer is connected to the color development layer.

[0078] Preferably, the preparation method of the first mixed liquid comprises the following steps: S1, adding the first reaction monomer into water to obtain a mixed liquid a; S2, adding an electron-donating colorless dye precursor, a second reaction monomer, and a cosolvent into a solvent to obtain a mixed liquid b; S3, adding the electron-accepting compound, the second reaction monomer and the cosolvent into the solvent to obtain a mixed liquid c; S4, adding the mixed liquid b to the mixed liquid a, emulsifying and dispersing, and then performing a polymerization reaction at 40° C. to 90° C. to obtain a first reaction liquid containing first microcapsules; S5, adding the mixed liquid c to the mixed liquid a, emulsifying and dispersing, and then performing a polymerization reaction at 40° C. to 90° C. to obtain a second reaction liquid containing second microcapsules; S6, mixing the first reaction liquid, the second reaction liquid, a first adhesive, a first auxiliary agent and water to obtain a first mixed liquid.

[0079] It should be noted that the present invention does not limit the order between S1 to S3, nor does it limit the order between S4 to S5.

[0080] Further preferably, in S1, the mass ratio of the first reaction monomer to water is 1:(50-200), more preferably 1:(70-160).

[0081] More preferably, in S4 and S5, the emulsification and dispersion temperature is room temperature, and the reaction time is 10 s to 20 min (more preferably 5 min to 15 min).

[0082] More preferably, in S4 and S5, the polymerization reaction temperature is 60° C. to 80° C., and the reaction time is 1 h to 10 h (more preferably 1.5 h to 5 h).

[0083] Further preferably, in S4, the solid content of the first reaction liquid is 15% to 25%.

[0084] Further preferably, in S5, the solid content of the second reaction liquid is 15% to 25%.

[0085] Further preferably, in S6, the mass ratio of the sum of the masses of the first reaction liquid and the second reaction liquid to the water is (5~50):100.

[0086] Preferably, the mass ratio of the components of the color development layer and water in the second mixed liquid is (5~50):100.

[0087] For example, coating can be performed using a dedicated coater such as an air knife coater, a rod coater, a rod coater, a curtain coater, a gravure coater, an extrusion coater, a die coater, a bead coater, and a knife coater.

[0088] When using a pressure-measurement chromogenic membrane, the capsule layer is connected to the color-developing layer and positioned above it, forming a laminate. By applying pressure from the substrate side of the laminate (or, if two substrates are present, from at least one side), the first and second microcapsules rupture within the pressurized area. The electron-donating leuco dye precursor contained in the first microcapsule and the electron-accepting compound contained in the second microcapsule leak out of the microcapsules along with the solvent. The two react and are absorbed by the color-developing layer, dyeing the inorganic porous filler in the color-developing layer and producing color within the pressurized area. Therefore, the pressure P can be determined based on the degree of color development, thereby achieving the purpose of using a pressure-measurement chromogenic membrane to measure pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Figure 1 Schematic diagram of the structure of the pressure test chromogenic film in Examples 1 to 3 of the present invention; Figure 1In the figure, 100 represents the first sheet, 110 represents the first substrate, 120 represents the capsule layer, 121 represents the first microcapsule, and 122 represents the second microcapsule; 200 represents the second sheet, 210 represents the second substrate, and 220 represents the color development layer; Figure 2 is a cross-sectional SEM image of the microcapsule in Example 1 of the present invention; Figure 3 is a cross-sectional SEM image of the first sheet 100 in Example 1 of the present invention; Figure 4 This is a schematic structural diagram of a pressure test chromogenic film in Example 4 of the present invention; Figure 5 This is a schematic structural diagram of a pressure test chromogenic film in Example 5 of the present invention; Figures 4 and 5 10 represents a substrate; 20 represents a capsule layer; 21 represents a first microcapsule; 22 represents a second microcapsule; and 30 represents a color development layer. DETAILED DESCRIPTION

[0090] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0091] In the present invention, materials not otherwise specified are all commercially available products.

[0092] In the embodiments and comparative examples of the present invention, the particle size D50 of the first microcapsule and the second microcapsule is measured as follows: the first reaction liquid and the second reaction liquid are respectively taken, and the particle size distribution is tested using a BT-9300ST laser particle size distribution analyzer to obtain the particle size D50 values of the first microcapsule and the second microcapsule.

[0093] In the examples and comparative examples of the present invention, the number average wall thickness of the first microcapsules and the second microcapsules was measured by measuring the wall thickness of 10 microcapsules using a scanning electron microscope (SEM) and taking the average value.

[0094] Example 1 This embodiment provides a double-sheet pressure test chromogenic film (see Figure 1), comprising a substrate, a capsule layer 120, and a color-developing layer 220 formed on the substrate; the capsule layer 120 is located on the upper surface of the color-developing layer 220; the substrate comprises a first substrate 110 and a second substrate 210; the first substrate 110 and the capsule layer 120 are in contact with each other to form a first sheet 100; the second substrate 210 and the color-developing layer 220 are in contact with each other to form a second sheet 200. The capsule layer 120 includes first microcapsules 121 containing an electron-donating leuco dye precursor (CK-16) and second microcapsules 122 containing an electron-accepting compound (4-hydroxy-4'-benzyloxydiphenyl sulfone).

[0095] The particle size of the first microcapsule 121 is D50=8.3 μm, the number average wall thickness is 213 nm, and the ratio of the number average wall thickness to D50 is 0.026. The particle size of the second microcapsule 122 is D50=8.4 μm, the number average wall thickness is 216 nm, and the ratio of the number average wall thickness to D50 is 0.026.

[0096] The thickness of the capsule layer 120 is 9 μm, the thickness of the color development layer 220 is 7 μm, the thickness of the first substrate 110 (PET) is 75 μm, and the thickness of the second substrate 210 (PET) is 75 μm.

[0097] The capsule layer 120 includes the following components by mass: 20 parts of first microcapsules 121 , 20 parts of second microcapsules 122 , 5 parts of a first binder (10 wt % PVA aqueous solution), and 8 parts of a first auxiliary agent (5 parts of a 2 wt % silica aqueous solution, 2 parts of a 2 wt % sodium lauryl sulfate).

[0098] The core material of the first microcapsule 121 includes the following components in percentage by weight: 17% of electron-donating colorless dye precursor, 50% of solvent (isoparaffin), and 33% of cosolvent (ethyl acetate).

[0099] The core material of the second microcapsule 122 includes the following components in percentage by weight: 17% of the electron-accepting compound, 50% of the solvent (isoparaffin), and 33% of the cosolvent (ethyl acetate).

[0100] The color development layer 220 includes the following raw material components in percentage by weight: 68% of an inorganic porous filler (light calcium carbonate with an average particle size of 5 μm), 20.5% of a second binder (a 10 wt % CMC aqueous solution), and 11.5% of a second auxiliary agent (8% of 10 wt % sodium lauryl sulfate and 3.5% of a 2 wt % sodium hydroxide aqueous solution).

[0101] The method for preparing the pressure test chromogenic film comprises the following steps: S1, adding the first reaction monomer (trimethylhexanediamine) into water, with the mass ratio of the first reaction monomer to water being 1:100, to obtain a mixed liquid a.

[0102] S2, adding an electron-donating colorless dye precursor, a second reaction monomer (dimethyldiphenylmethane diisocyanate) and a cosolvent into a solvent to obtain a mixed liquid b.

[0103] S3, adding the electron-accepting compound, the second reaction monomer (dimethyldiphenylmethane diisocyanate) and the co-solvent into the solvent to obtain a mixed liquid c.

[0104] S4, adding the mixed liquid b to the mixed liquid a, emulsifying and dispersing at room temperature for 10 minutes, then performing a polymerization reaction at 70°C, keeping the temperature for 2 hours, and cooling to room temperature to obtain a first reaction liquid containing the first microcapsules 121 with a solid content of 20% (the solid content can be adjusted by adding water).

[0105] S5, adding the mixed liquid c to the mixed liquid a, emulsifying and dispersing at room temperature for 10 minutes, then polymerizing at 70°C, keeping the temperature for 2 hours, and cooling to room temperature to obtain a second reaction liquid containing the second microcapsules 122 with a solid content of 20%.

[0106] S6, mixing the first reaction liquid, the second reaction liquid, the first binder, the first auxiliary agent and water (the mass ratio of the sum of the mass of the first reaction liquid and the second reaction liquid to the mass of water is 30:100) to obtain a first mixed liquid.

[0107] S7, coating the first mixed liquid on the first substrate 110, and forming the capsule layer 120 after drying (see Figure 2 ), and the first sheet 100 is obtained (see Figure 3 ).

[0108] S8, dissolving the components of the color-developing layer 220 in water (the mass ratio of the components of the color-developing layer 220 to water is 40:100), and applying the resulting second mixed liquid on the second substrate 210. After drying, the color-developing layer 220 is formed, and the second sheet 200 is obtained, that is, the pressure test color film is obtained.

[0109] Example 2 This embodiment provides a double-sheet pressure test chromogenic film (see Figure 1 ), comprising a substrate, a capsule layer 120, and a color-developing layer 220 formed on the substrate; the capsule layer 120 is located on the upper surface of the color-developing layer 220; the substrate comprises a first substrate 110 and a second substrate 210; the first substrate 110 and the capsule layer 120 are in contact with each other to form a first sheet 100; the second substrate 210 and the color-developing layer 220 are in contact with each other to form a second sheet 200. The capsule layer 120 includes first microcapsules 121 containing an electron-donating leuco dye precursor (CVL) and second microcapsules 122 containing an electron-accepting compound (4-[[4-(2-allyloxy)phenyl]sulfonyl]phenol).

[0110] The particle size of the first microcapsule 121 is D50 = 10.7 μm, the number average wall thickness is 236 nm, and the ratio of the number average wall thickness to D50 is 0.022. The particle size of the second microcapsule 122 is D50 = 10.5 μm, the number average wall thickness is 238 nm, and the ratio of the number average wall thickness to D50 is 0.023.

[0111] The thickness of the capsule layer 120 is 15 μm, the thickness of the color development layer 220 is 10 μm, the thickness of the first substrate 110 (PE) is 50 μm, and the thickness of the second substrate 210 (PE) is 50 μm.

[0112] The capsule layer 120 includes the following components in parts by mass: 16 parts of first microcapsules 121 , 24 parts of second microcapsules 122 , 40 parts of a first binder (5 wt % starch aqueous solution), and 0.5 parts of a first auxiliary agent (15 wt % starch aqueous solution).

[0113] The core material of the first microcapsule 121 includes the following components in percentage by weight: 15% of an electron-donating colorless dye precursor and 85% of a solvent (1-phenyl-1-dimethylphenylethane).

[0114] The core material of the second microcapsule 122 includes the following components in percentage by weight: 15% of the electron-accepting compound and 85% of the solvent (1-phenyl-1-dimethylphenylethane).

[0115] The color development layer 220 includes the following raw material components in percentage by weight: 80% inorganic porous filler (gypsum powder and calcium sulfate of equal weight with an average particle size of 2 μm), 15% second binder (5 wt % SBR aqueous solution), and 5% second auxiliary agent (10 wt % sodium lauryl sulfate).

[0116] The method for preparing the pressure test chromogenic film comprises the following steps: S1, adding the first reaction monomer (triethylenetetramine) into water, with the mass ratio of the first reaction monomer to water being 1:80, to obtain a mixed liquid a.

[0117] S2, adding an electron-donating colorless dye precursor and a second reaction monomer (HDI) into a solvent to obtain a mixed liquid b.

[0118] S3, adding the electron-accepting compound and the second reaction monomer (HDI) into the solvent to obtain a mixed liquid c.

[0119] S4, adding mixed liquid b to mixed liquid a, emulsifying and dispersing at room temperature for 15 minutes, then polymerizing at 80°C, keeping the temperature for 2 hours, and cooling to room temperature to obtain a first reaction liquid containing the first microcapsules 121 with a solid content of 22%.

[0120] S5, adding the mixed liquid c to the mixed liquid a, emulsifying and dispersing at room temperature for 15 minutes, then polymerizing at 80°C, keeping the temperature for 2 hours, and cooling to room temperature to obtain a second reaction liquid containing the second microcapsules 122 with a solid content of 22%.

[0121] S6, mixing the first reaction liquid, the second reaction liquid, the first binder, the first auxiliary agent and water (the mass ratio of the sum of the mass of the first reaction liquid and the second reaction liquid to the mass of water is 40:100) to obtain a first mixed liquid.

[0122] S7 , coating the first mixed liquid on the first substrate 110 , and forming a capsule layer 120 after drying to obtain the first sheet 100 .

[0123] S8, dissolving the components of the color-developing layer 220 in water (the mass ratio of the components of the color-developing layer 220 to water is 30:100), and applying the resulting second mixed liquid on the second substrate 210. After drying, the color-developing layer 220 is formed, and the second sheet 200 is obtained, that is, the pressure test color film is obtained.

[0124] Example 3 This embodiment provides a double-sheet pressure test chromogenic film (see Figure 1 ), comprising a substrate, a capsule layer 120, and a color-developing layer 220 formed on the substrate; the capsule layer 120 is located on the upper surface of the color-developing layer 220; the substrate comprises a first substrate 110 and a second substrate 210; the first substrate 110 and the capsule layer 120 are in contact with each other to form a first sheet 100; the second substrate 210 and the color-developing layer 220 are in contact with each other to form a second sheet 200. The capsule layer 120 includes first microcapsules 121 containing an electron-donating leuco dye precursor (BLMB) and second microcapsules 122 containing an electron-accepting compound (4,4'-sulfonylbis[2-(2-propenyl)]phenol).

[0125] The particle size of the first microcapsule 121 is D50=18.5 μm, the number average wall thickness is 345 nm, and the ratio of the number average wall thickness to D50 is 0.019. The particle size of the second microcapsule 122 is D50=18.7 μm, the number average wall thickness is 350 nm, and the ratio of the number average wall thickness to D50 is 0.019.

[0126] The thickness of the capsule layer 120 is 30 μm, the thickness of the color development layer 220 is 18 μm, the thickness of the first substrate 110 (PP) is 125 μm, and the thickness of the second substrate 210 (PP) is 125 μm.

[0127] The capsule layer 120 includes the following components in parts by mass: 48 parts of first microcapsules 121 , 32 parts of second microcapsules 122 , 3 parts of a first binder (a 15 wt % CMC aqueous solution), and 20 parts of a first auxiliary agent (a 5 wt % PVA aqueous solution).

[0128] The core material of the first microcapsule 121 includes the following components in percentage by weight: 20% electron-donating colorless dye precursor, 40% solvent (corn oil and mineral oil of equal weight), and 40% cosolvent (methyl ethyl ketone).

[0129] The core material of the second microcapsule 122 includes the following components in percentage by weight: 20% electron-accepting compound, 40% solvent (corn oil and mineral oil of equal weight), and 40% co-solvent (methyl ethyl ketone).

[0130] The color development layer 220 includes the following raw material components in percentage by weight: 45% of an inorganic porous filler (white clay with an average particle size of 10 μm), 35% of a second binder (a 15 wt % aqueous solution of an acrylic latex), and 20% of a second auxiliary agent (8% of 10 wt % of sodium lauryl sulfate, 7% of a 10 wt % aqueous solution of silica, and 5% of a 2 wt % aqueous solution of sodium hydroxide).

[0131] The method for preparing the pressure test chromogenic film comprises the following steps: S1, adding the first reaction monomer (hexamethylenediamine) into water, with the mass ratio of the first reaction monomer to water being 1:120, to obtain a mixed liquid a.

[0132] S2, adding the electron-donating colorless dye precursor, the second reaction monomer (HMDI) and the co-solvent into the solvent to obtain a mixed liquid b.

[0133] S3, adding the electron-accepting compound, the second reaction monomer (HMDI) and the co-solvent into the solvent to obtain a mixed liquid c.

[0134] S4, adding mixed liquid b to mixed liquid a, emulsifying and dispersing at room temperature for 5 minutes, then polymerizing at 60°C, keeping the temperature for 3 hours, and cooling to room temperature to obtain a first reaction liquid containing the first microcapsules 121 with a solid content of 18%.

[0135] S5, adding the mixed liquid c to the mixed liquid a, emulsifying and dispersing at room temperature for 5 minutes, then polymerizing at 60°C, keeping the temperature for 3 hours, and cooling to room temperature to obtain a second reaction liquid containing the second microcapsules 122 with a solid content of 18%.

[0136] S6, mixing the first reaction liquid, the second reaction liquid, the first binder, the first auxiliary agent and water (the mass ratio of the sum of the mass of the first reaction liquid and the second reaction liquid to the mass of water is 15:100) to obtain a first mixed liquid.

[0137] S7 , coating the first mixed liquid on the first substrate 110 , and forming a capsule layer 120 after drying to obtain the first sheet 100 .

[0138] S8, dissolving the components of the color-developing layer 220 in water (the mass ratio of the components of the color-developing layer 220 to water is 15:100), and applying the resulting second mixed liquid on the second substrate 210. After drying, the color-developing layer 220 is formed, and the second sheet 200 is obtained, that is, the pressure test color film is obtained.

[0139] Example 4 This embodiment provides a single-piece pressure test chromogenic film (see Figure 4 ), from bottom to top, are substrate 10, color-developing layer 30 formed on substrate 10, and capsule layer 20. Capsule layer 20 includes first microcapsules 21 containing an electron-donating leuco dye precursor (CK-16) and second microcapsules 22 containing an electron-accepting compound (4-hydroxy-4'-isopropoxydiphenyl sulfone).

[0140] The particle size of the first microcapsule 21 is D50 = 17.2 μm, the number average wall thickness is 251 nm, and the ratio of the number average wall thickness to D50 is 0.015. The particle size of the second microcapsule 22 is D50 = 17.0 μm, the number average wall thickness is 249 nm, and the ratio of the number average wall thickness to D50 is 0.015.

[0141] The thickness of the capsule layer 20 is 40 μm, the thickness of the color development layer 30 is 20 μm, and the thickness of the substrate 10 (PVC) is 145 μm.

[0142] The capsule layer 20 includes the following components by mass: 20 parts of first microcapsules 21, 16 parts of second microcapsules 22, 20 parts of a first binder (a 10 wt % PVA aqueous solution), and 8 parts of a first auxiliary agent (4 parts of a 10 wt % CMC aqueous solution and 4 parts of a 10 wt % silica aqueous solution).

[0143] The core material of the first microcapsule 21 includes the following components in percentage by mass: 15% of electron-donating colorless dye precursor, 65% of solvent (castor oil), and 20% of cosolvent (acetone).

[0144] The core material of the second microcapsule 22 includes the following components in percentage by weight: 15% of the electron-accepting compound, 65% of the solvent (castor oil), and 20% of the cosolvent (acetone).

[0145] The color development layer 30 includes the following raw material components in percentage by weight: 55% of an inorganic porous filler (silica powder with an average particle size of 8 μm), 30% of a second binder (a 10 wt % aqueous solution of gum arabic), and 15% of a second auxiliary agent (10% of a 10 wt % sodium lauryl sulfate solution and 5% of a 2 wt % aqueous solution of sodium hydroxide).

[0146] The method for preparing the pressure test chromogenic film comprises the following steps: S1, adding the first reaction monomer (hexamethylenediamine) into water, with the mass ratio of the first reaction monomer to water being 1:100, to obtain a mixed liquid a.

[0147] S2, adding an electron-donating colorless dye precursor, a second reaction monomer (trimethylolpropane adduct of hexamethylene diisocyanate) and a cosolvent into a solvent to obtain a mixed liquid b.

[0148] S3, adding the electron-accepting compound, the second reaction monomer (trimethylolpropane adduct of hexamethylene diisocyanate) and the co-solvent into the solvent to obtain a mixed liquid c.

[0149] S4, adding the mixed liquid b to the mixed liquid a, emulsifying and dispersing at room temperature for 20 minutes, then polymerizing at 90°C, keeping the temperature for 1.5 hours, and cooling to room temperature to obtain a first reaction liquid containing the first microcapsules 21 with a solid content of 20%.

[0150] S5, adding the mixed liquid c to the mixed liquid a, emulsifying and dispersing at room temperature for 20 minutes, then polymerizing at 90°C, keeping the temperature for 1.5 hours, and cooling to room temperature to obtain a second reaction liquid containing the second microcapsules 22 with a solid content of 20%.

[0151] S6, mixing the first reaction liquid, the second reaction liquid, the first binder, the first auxiliary agent and water (the mass ratio of the sum of the mass of the first reaction liquid and the second reaction liquid to the mass of water is 45:100) to obtain a first mixed liquid.

[0152] S7, dissolving the components of the color development layer 30 in water (the mass ratio of the components of the color development layer 30 to water is 50:100), coating the obtained second mixed liquid on the substrate 10, and forming the color development layer 30 after drying.

[0153] S8, coating the first mixed liquid on the color development layer 30, and forming the capsule layer 20 after drying to obtain a pressure test color development film.

[0154] Example 5 This embodiment provides a single-piece pressure test chromogenic film (see Figure 5 ), from top to bottom are a substrate 10, a capsule layer 20 formed on the substrate 10, and a color development layer 30. The capsule layer 20 includes first microcapsules 21 containing an electron-donating colorless dye precursor (CVL) and second microcapsules 22 containing an electron-accepting compound (4,4'-dihydroxydiphenyl sulfone).

[0155] The particle size of the first microcapsule 21 is D50=12.9 μm, the number average wall thickness is 293 nm, and the ratio of the number average wall thickness to D50 is 0.023. The particle size of the second microcapsule 22 is D50=12.6 μm, the number average wall thickness is 290 nm, and the ratio of the number average wall thickness to D50 is 0.023.

[0156] The thickness of the capsule layer 20 was 25 μm, the thickness of the color development layer 30 was 12 μm, and the thickness of the substrate 10 (coated paper) was 100 μm.

[0157] The capsule layer 20 includes the following components by mass: 40 parts of first microcapsules 21, 48 parts of second microcapsules 22, 30 parts of a first binder (10 wt % CMC aqueous solution), and 15 parts of a first auxiliary agent (10 parts of a 10 wt % PVA aqueous solution, 5 parts of a 2 wt % sodium lauryl sulfate).

[0158] The core material of the first microcapsule 21 includes the following components in percentage by mass: 5% of electron-donating colorless dye precursor, 65% of solvent (1-phenyl-1-dimethylphenylethane), and 30% of cosolvent (ethyl acetate).

[0159] The core material of the second microcapsule 22 includes the following components in percentage by weight: 5% of an electron-accepting compound, 65% of a solvent (1-phenyl-1-dimethylphenylethane), and 30% of a cosolvent (ethyl acetate).

[0160] The color development layer 30 includes the following raw material components in percentage by weight: 70% of an inorganic porous filler (kaolin and titanium dioxide of equal weight with an average particle size of 6 μm), 17% of a second binder (a 10 wt % aqueous solution of gelatin), and 13% of a second auxiliary agent (10% of a 10 wt % aqueous solution of sodium lauryl sulfate and 3% of a 2 wt % aqueous solution of sodium hydroxide).

[0161] The method for preparing the pressure test chromogenic film comprises the following steps: S1, adding the first reaction monomer (butylene oxide adduct of ethylenediamine) into water, with the mass ratio of the first reaction monomer to water being 1:100, to obtain a mixed liquid a.

[0162] S2, adding an electron-donating colorless dye precursor, a second reaction monomer (trimethylolpropane adduct of xylylenediisocyanate) and a cosolvent into a solvent to obtain a mixed liquid b.

[0163] S3, adding the electron-accepting compound, the second reaction monomer (trimethylolpropane adduct of xylylenediisocyanate) and the co-solvent into the solvent to obtain a mixed liquid c.

[0164] S4, adding the mixed liquid b to the mixed liquid a, emulsifying and dispersing at room temperature for 1 minute, then polymerizing at 40°C, keeping the temperature for 6 hours, and cooling to room temperature to obtain a first reaction liquid containing the first microcapsules 21 with a solid content of 20%.

[0165] S5, adding the mixed liquid c to the mixed liquid a, emulsifying and dispersing at room temperature for 1 minute, then polymerizing at 40°C, keeping the temperature for 6 hours, and cooling to room temperature to obtain a second reaction liquid containing the second microcapsules 22 with a solid content of 20%.

[0166] S6, mixing the first reaction liquid, the second reaction liquid, the first adhesive, the first auxiliary agent and water (the mass ratio of the sum of the mass of the first reaction liquid and the second reaction liquid to the mass of water is 25:100) to obtain a first mixed liquid.

[0167] S7, coating the first mixed liquid on the substrate 10 and drying it to form a capsule layer 20; S8, dissolving the components of the color-developing layer 30 in water (the mass ratio of the components of the color-developing layer 30 to water is 35:100), applying the resulting second mixed liquid on the capsule layer 20, and drying to form the color-developing layer 30, thereby obtaining a pressure test color-developing film.

[0168] Comparative Example 1 This comparative example provides a two-sheet pressure test chromogenic membrane, similar to Example 1, except that the capsule layer does not contain a second microcapsule, and the electron-accepting compound is contained in the color-developing layer. Specifically, it comprises a substrate, a capsule layer, and a color-developing layer formed on the substrate; the capsule layer is in contact with the color-developing layer and positioned above it; the substrate comprises a first substrate and a second substrate; the first substrate and the capsule layer are in contact with each other, forming a first sheet; the second substrate and the color-developing layer are in contact with each other, forming a second sheet. The capsule layer includes first microcapsules containing an electron-donating leuco dye precursor (CK-16).

[0169] The particle size and number average wall thickness of the first microcapsules are the same as those in Example 1 and will not be described in detail.

[0170] The thicknesses of the capsule layer, the color development layer, the first substrate, and the second substrate are the same as those in Example 1 and will not be described in detail.

[0171] The capsule layer includes the following components in parts by weight: 40 parts of first microcapsules, 5 parts of a first binder (10 wt % PVA aqueous solution), and 8 parts of a first auxiliary agent (5 parts of a 10 wt % silica aqueous solution, 2 parts of a 10 wt % sodium lauryl sulfate).

[0172] The core material components of the first microcapsule are the same as those in Example 1 and will not be described in detail.

[0173] The color development layer includes the following raw material components in percentage by weight: inorganic porous filler (light calcium carbonate with an average particle size of 5 μm) 48%, electron-accepting compound (4-hydroxy-4'-benzyloxydiphenyl sulfone) 20%, second binder (10 wt% CMC aqueous solution) 20.5% and second auxiliary agent (10 wt% sodium lauryl sulfate 8%, 2 wt% sodium hydroxide aqueous solution 3.5%) 11.5%.

[0174] The method for preparing the pressure test chromogenic film comprises the following steps: S1~S2 are the same as S1~S2 in Example 1 and will not be described in detail.

[0175] S3 is the same as S4 in Example 1 and will not be described in detail.

[0176] S4, mixing the first reaction liquid, the first adhesive, the first auxiliary agent and water to obtain a first mixed liquid.

[0177] S5-S6 are the same as S7-S8 in Example 1 and will not be described in detail.

[0178] Comparative Example 2 This comparative example provides a monolithic pressure-test chromogenic membrane, similar to Example 4, except that the capsule layer does not contain a second microcapsule, and the electron-accepting compound is contained in the color-developing layer. Specifically, it comprises a substrate, a capsule layer, and a color-developing layer formed on the substrate; the capsule layer is in contact with the color-developing layer and located above it; and the substrate is in contact with the color-developing layer. The capsule layer includes first microcapsules containing an electron-donating leuco dye precursor (CK-16).

[0179] The particle size and number average wall thickness of the first microcapsules are the same as those in Example 4 and will not be described in detail.

[0180] The thicknesses of the capsule layer, color development layer and substrate are the same as those in Example 4 and will not be described in detail.

[0181] The capsule layer includes the following components by mass: 36 parts of first microcapsules, 20 parts of a first binder (a 10 wt % PVA aqueous solution), and 8 parts of an emulsifier (4 parts of a 10 wt % CMC aqueous solution and 4 parts of a 10 wt % silica aqueous solution).

[0182] The core material components of the first microcapsule are the same as those in Example 4 and will not be described in detail.

[0183] The color-developing layer includes the following raw material components in percentage by weight: 40% of an inorganic porous filler (silicon powder with an average particle size of 8 μm), 20% of an electron-accepting compound (4-hydroxy-4'-isopropoxydiphenyl sulfone), 25% of a second binder (a 10 wt % aqueous solution of gum arabic), and 15% of a second auxiliary agent (10% of a 10 wt % sodium lauryl sulfate solution and 5% of a 2 wt % aqueous solution of sodium hydroxide).

[0184] The method for preparing the pressure test chromogenic film comprises the following steps: S1~S2 are the same as S1~S2 in Example 4 and will not be described in detail.

[0185] S3 is the same as S4 in Example 4 and will not be described in detail.

[0186] S4, mixing the first reaction liquid, the first adhesive, the first auxiliary agent and water to obtain a first mixed liquid.

[0187] S5-S6 are the same as S7-S8 in Example 4 and will not be described in detail.

[0188] Verification test The pressure test chromogenic films of Examples 1 to 5 and Comparative Examples 1 to 2 were placed under environmental conditions of 20°C 50% RH, 50°C 90% RH, and 0°C 10% RH for 3 months. The pressure test stability of the pressure test chromogenic films was tested on day 0 (the day of preparation) and after 1 month, 2 months, and 3 months under the above conditions. The test results are shown in Table 1. The test method is as follows: first, cut the pressure test color-developing film into a size of 3cm×20cm. For the double-sheet type, the capsule layer of the first sheet and the color-developing layer of the second sheet need to be connected (the capsule layer is on top and the color-developing layer is on the bottom). Place the pressure test color-developing film between two smooth surfaces and apply pressure with different pressure gradients to make it color. Subsequently, use an X-rite colorimeter to measure the concentration value OD of the colored part on the color-developing layer. The initial color density (0 day) is recorded as OD0, and the color density after 1 month, 2 months and 3 months is marked as OD1, OD2 and OD3, respectively. OD1 / OD0, OD2 / OD0, and OD3 / OD0 are the preservation rates of the color-developing concentration under different storage times.

[0189] Table 1 Test results of the preservation rate (%) of the chromogenic film under pressure test

[0190] For pressure-test chromogenic films, if the preservation rate is above 95%, the product stability is good; if the preservation rate is between 80% and 95%, the product stability is acceptable and does not affect use; if the preservation rate is below 80%, the product is essentially ineffective. As shown in Table 1, under three different storage environments, compared with the comparative example of the prior art that only encapsulates the electron-donating leuco dye precursor with microcapsules and mixes the electron-accepting compound into the color-developing layer, the pressure-test chromogenic film provided by the present invention has a more stable preservation rate, meeting the storage stability requirements under different conditions.

[0191] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A pressure test chromogenic film, characterized in that: It comprises a substrate, a capsule layer and a color development layer formed on the substrate; the capsule layer is in contact with the color development layer; The capsule layer includes first microcapsules containing an electron-donating leuco dye precursor and second microcapsules containing an electron-accepting compound.

2. The pressure test chromogenic film according to claim 1, wherein: The particle size of the first microcapsule is D50=2μm~50μm, and the particle size of the second microcapsule is D50=2μm~50μm; and / or The number average wall thickness of the first microcapsules is ≥200 nm, and the number average wall thickness of the second microcapsules is ≥200 nm.

3. The pressure test chromogenic film according to claim 2, wherein: The ratio of the number average wall thickness of the first microcapsules to D50 is 0.01-0.1, and the ratio of the number average wall thickness of the second microcapsules to D50 is 0.01-0.

1.

4. The pressure test chromogenic film according to claim 1, wherein: The core material of the first microcapsule comprises the following components in percentage by weight: 3% to 20% of an electron-donating colorless dye precursor, 30% to 87% of a solvent, and 0% to 50% of a cosolvent; and / or The core material of the second microcapsule includes the following components in percentage by weight: 3% to 20% of an electron-accepting compound, 30% to 87% of a solvent, and 0% to 50% of a cosolvent.

5. The pressure test chromogenic film according to claim 4, wherein: The electron-donating colorless dye precursor comprises at least one of a fluoran compound, an indolyl peptide ketone compound, a rhodamine lactam compound, a spiropyran compound or a phenothiazine compound; and / or The solvent comprises at least one of an alkylnaphthalene solvent, an aliphatic hydrocarbon solvent, a natural animal or plant oil solvent or a mineral oil; and / or The co-solvent is a low boiling point solvent, including at least one of a ketone co-solvent and an ester co-solvent.

6. The pressure test chromogenic film according to claim 5, characterized in that: The electron-donating colorless dye precursor comprises at least one of crystal violet lactone, leuco methylene blue or phthalolactone; and / or The electron-accepting compound includes at least one of 4,4'-sulfonylbis[2-(2-propenyl)]phenol, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxy-4'-isopropoxydiphenyl sulfone, 2,4-diphenylsulfonylphenol, 4-hydroxy-4'-benzyloxydiphenyl sulfone or 4-[[4-(2-allyloxy)phenyl]sulfonyl]phenol.

7. The pressure test chromogenic film according to claim 1, wherein: The capsule layer comprises the following components in parts by weight: 16 to 48 parts of first microcapsules, 16 to 48 parts of second microcapsules, 2 to 40 parts of first adhesive, and 0.5 to 20 parts of first auxiliary agent; and / or The color development layer includes the following raw material components in percentage by weight: 40% to 80% of an inorganic porous filler, 2% to 40% of a second adhesive, and 0.5% to 20% of a second auxiliary agent.

8. The pressure test chromogenic film according to claim 7, wherein: The mass ratio of the first microcapsule to the second microcapsule is (0.6-1.5):1; and / or The first adhesive comprises at least one of a starch aqueous solution, a carboxymethyl cellulose aqueous solution or a polyvinyl alcohol aqueous solution; and / or The second adhesive includes at least one of a styrene-butadiene rubber aqueous solution, an acrylic latex aqueous solution, an arabic gum aqueous solution, a gelatin aqueous solution, a carboxymethyl cellulose aqueous solution, or a polyvinyl alcohol aqueous solution.

9. The pressure test chromogenic film according to claim 1, wherein: The substrate comprises a plastic film or a paper-based material; and / or The thickness of the capsule layer is 7 μm to 40 μm, the thickness of the color development layer is 5 μm to 20 μm, and the thickness of the substrate is 10 μm to 150 μm.

10. The method for preparing a pressure test chromogenic film according to any one of claims 1 to 9, characterized in that: The following steps are involved: Dissolve the components of the capsule layer in water, apply the resulting first mixed liquid on a substrate, and dry it to form a capsule layer; Dissolve the components of the color development layer in water, apply the resulting second mixed liquid on the capsule layer, and dry it to form a color development layer to obtain a pressure test chromogenic film; or Dissolve the components of the color development layer in water, apply the resulting second mixed liquid on the substrate, and dry it to form a color development layer; Dissolve the components of the capsule layer in water, apply the resulting first mixed liquid on the color development layer, and dry it to form a capsule layer to obtain a pressure test chromogenic film; or When the substrate includes a first substrate and a second substrate, the components of the capsule layer are dissolved in water, and the resulting first mixed liquid is coated on the first substrate. After drying, the capsule layer is formed to obtain a first sheet; the components of the color-developing layer are dissolved in water, and the resulting second mixed liquid is coated on the second substrate. After drying, the color-developing layer is formed to obtain a second sheet, that is, a pressure test chromogenic film.

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