High-permeability humidity display film based on optical interference and its preparation process

Abstract

This invention discloses a high-permeability humidity display film based on optical interference and its fabrication process. It includes: a substrate layer, a humidity-responsive layer, an intermediate layer, and a hydrophobic layer; wherein, the substrate layer is made of a transparent material; a plurality of breathable micropores are formed on the substrate layer; the humidity-responsive layer is a 50-100 μm thick film layer made of a humidity-sensitive material, with micropores having a pore size of 0.5-2 μm; the intermediate layer is a nanofiber membrane, wherein the diameter of the nanofibers is controlled between 100-300 nm; the density of the intermediate layer varies gradient along its length to control the air permeability of the humidity-responsive layer corresponding to different densities of the intermediate layer; the hydrophobic layer is made of a transparent, breathable material, providing good protection for the humidity display film. This invention uses a hydrophilic microporous structure material and achieves rapid humidity conduction to the humidity-responsive layer through a multi-layer design, producing instantaneous color changes and making the humidity indication effect more sensitive.

Description

Technical Field

[0001] This invention relates to a high-permeability humidity display film based on optical interference and its preparation process. Background Technology

[0002] Humidity display films are widely used in packaging, smart labels, environmental monitoring, and other fields, intuitively reflecting changes in ambient humidity through visible color changes. Among existing technologies, hydrogel films, cellulose nanocrystal films, and layer-by-layer self-assembled (LBL) films have been reported.

[0003] However, cellulose nanocrystal films and hydrogel nanocavity films rely on the hygroscopic expansion of the material to display humidity, but their expansion rate is limited, resulting in a relatively slow humidity response that cannot quickly reflect humidity changes, and they lack gradient humidity display functionality. While humidity-responsive LBL films have a simple manufacturing process, their layered deposition structure increases the humidity conduction path, leading to a delayed humidity response. Hydrogel nanocavity films and cellulose nanocrystal films are prone to embrittlement after humidity expansion, resulting in decreased mechanical stability, and may crack or deform after cyclic humidity changes. Although the layered structure of humidity-responsive LBL films increases thickness, the interlayer bonding is weak, making them prone to delamination during prolonged use, reducing material durability. Furthermore, none of these three technologies incorporate breathable design in the selection of materials for the humidity-sensitive layer, making them susceptible to moisture accumulation in high-humidity environments, affecting humidity indication performance and limiting the application scenarios of the materials. Summary of the Invention

[0004] To overcome the above-mentioned defects, the present invention provides a high-permeability humidity display film based on optical interference and its preparation process.

[0005] To achieve the above objectives, the present invention provides a high-permeability humidity display film based on optical interference, comprising: a substrate layer, a humidity-responsive layer, an intermediate layer, and a hydrophobic layer;

[0006] The base layer is made of a transparent material; several breathable micropores are provided on the base layer; the pore size of the micropores is 1-10μm; and the porosity is 10-20%.

[0007] The humidity-responsive layer is a thin film layer with a thickness of 50-100μm made of humidity-sensitive material, on which micropores are provided, the pore size of which is 0.5-2μm; to ensure that air and water vapor can freely penetrate the humidity-responsive layer;

[0008] The intermediate layer is a nanofiber membrane, wherein the diameter of the nanofibers is controlled between 100-300 nm; the density of the intermediate layer varies in a gradient along its length to control the air permeability of the humidity-responsive layer corresponding to intermediate layers of different densities.

[0009] The hydrophobic layer is made of transparent and breathable material, and provides good protection for the humidity display film.

[0010] Further, the humidity-sensitive material is polyethylene glycol or polyvinyl alcohol.

[0011] To achieve the above purpose, the preparation process of the high-breathable humidity display film based on optical interference of the application at least includes the step of preparing the substrate layer, specifically:

[0012] Polyester or polycarbonate is used as the base film, and the thickness is 30-100 mu m;

[0013] The laser power is set to 5-15 W, and the scanning rate is 10-20 mu m / s, to prepare micropores with a pore size of 1-10 mu m and a porosity of 10-20%.

[0014] The perforated base film is subjected to oxygen plasma treatment, with a gas flow of 50-100 sccm, a power of 50-100 W, and a treatment time of 30-60 s, to improve the adhesion of the gradient humidity response layer.

[0015] Further, the process further includes the step of preparing the humidity response layer, specifically:

[0016] A water or ethanol solution of polyethylene glycol or polyvinyl alcohol is prepared, with a concentration of 5-10 wt%.

[0017] A spin coating method is used to form a film, with a spin coating speed controlled at 1000-1500 rpm and a time set to 30-60 s, to obtain a film with a thickness of 50-100 mu m;

[0018] During film formation, polystyrene microspheres are added as a template, with a particle size controlled at 0.5-2 mu m and a doping amount of 10-20 wt%.

[0019] After film coating, the microsphere template is volatilized to form a microporous structure through drying treatment at 40-60 DEG C for 1-2 h.

[0020] Further, the process further includes the step of preparing the intermediate layer, specifically:

[0021] A polyacrylonitrile electrospinning solution is prepared, with a concentration controlled at 8-12 wt% to ensure the fluidity and spinning formability of the solution;

[0022] A region with a slow humidity conduction rate is prepared to form a high-density fiber structure, with a voltage set in the range of 20-25 kV to increase the fiber deposition amount, and a spinning rate controlled at 1.0 mL / h to generate a dense fiber layer;

[0023] The area with faster humidity conduction is prepared to form a low-density fiber structure, the voltage is set to 15-20 kV, the spinning rate is adjusted to 0.5 mL / h, and a looser fiber layer is formed to enable the humidity to pass through faster.

[0024] After electrospinning, the formed PAN fiber membrane is subjected to low-temperature heat treatment at 60-80℃ for 1-2h.

[0025] Further, the step of preparing a hydrophobic layer is further included:

[0026] A PVDF solution with a concentration of 5-10wt% is prepared;

[0027] Phase separation is carried out in a cold water bath to form a PVDF porous membrane with a porosity of 10-30% and a pore size of 100-500nm;

[0028] Drying at room temperature for 30min.

[0029] The present application has the following advantages:

[0030] 1. Fast humidity response speed. The present application uses a hydrophilic microporous structure material, and realizes the rapid conduction of humidity through multi-layer design. The change of humidity will be quickly transmitted to the humidity response layer, producing immediate color change, and the humidity indication effect is more sensitive.

[0031] 2. High air permeability. The substrate layer and the hydrophilic layer (humidity response layer) of the present application are designed with microporous structure, which ensures the free penetration of water vapor through the film, while avoiding the accumulation of water vapor in the film. This high air permeability prolongs the stability of humidity display, and is particularly suitable for application scenarios that require rapid humidity display and high air permeability.

[0032] 3. Good mechanical stability. The multi-layer structure design makes each layer have specific functions, and the interlayer bonding force is enhanced through plasma treatment, improving the overall mechanical stability of the film. The film does not crack or deform during humidity change cycles, and has a longer service life.

[0033] 4. Reversible and durable humidity display effect. The present application realizes color change through the change of optical thickness of the humidity response layer, ensuring that the color effect of humidity display can be repeatedly displayed and restored, and has high stability under humidity change. DETAILED DESCRIPTION

[0034] In the description of the present application, it needs to be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0035] The terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0036] In the description of the present application, it needs to be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0037] The present application aims to design a high-breathable material with humidity display function according to the difference in humidity response of different materials. The material is composed of a porous structure substrate, a hydrophilic layer (humidity response layer), an intermediate nanofiber breathable layer and a hydrophobic layer. By alternating combination of hydrophilic and hydrophobic materials, the material shows different expansion or shrinkage behavior in a humidity environment, relying on optical interference and optical phase change to realize humidity indication effect.

[0038] Base layer

[0039] The substrate layer adopts transparent and microporous polyester (PET) or polycarbonate (PC) material, which has high light transmittance and excellent mechanical properties, and is suitable for supporting material of multi-layer humidity display film structure. The light transmittance of PET and PC is as high as 90% and 85% or more respectively, ensuring that the color change of the humidity display film is clear and visible; both materials have good thermal stability, the glass transition temperature of PET is about 80℃, while that of PC can reach 150℃, which gives it dimensional stability during processing and use. In addition, PET and PC have smooth surface and good flexibility, which is suitable for making humidity display film that needs to be bent or deformed, providing stable support for the subsequent layer structure.

[0040] To achieve the air permeability, the application carries out micro-hole processing on PET or PC material through laser drilling process to form a porous structure with air permeability function. Laser drilling process utilizes precisely controlled laser power and scanning rate to form uniform micro-holes, realizing effective balance between material air permeability and strength. A laser with power of 5-10 W is used to process micro-holes with diameter of 1-10 μm on PET or PC substrate at a scanning rate of 10-20 μm / s, and the porosity is controlled between 10-20%, ensuring the substrate layer to have required air permeability and structural integrity. Laser drilling has the advantage of flexible operation, which is suitable for substrate materials with different thickness and size, ensuring not only the air permeability but also the uniformity and stability of the overall performance of the film.

[0041] In addition, to enhance the adhesion of the hydrophilic layer and the substrate, the application carries out oxygen plasma treatment on the surface of the substrate layer after laser drilling. The gas flow of oxygen plasma is set to 50-100 sccm, the power is 50-100 W, and the processing time is 30-60 s, so as to introduce active functional groups on the surface of the substrate and improve the bonding force with the hydrophilic layer. The substrate layer processed by laser micro-hole processing and plasma treatment has good light transmission, air permeability and interlayer adhesion, providing a stable basic structure for the realization of humidity display film.

[0042] Humidity responsive layer

[0043] The humidity response layer, which is also the hydrophilic layer, utilizes the principle that if the optical path difference between layers in the film satisfies the constructive interference or destructive interference condition, the light of specific wavelength is enhanced or weakened, resulting in different colors of the film.

[0044] The optical path difference of light in the multilayer film is the key to color formation, and the formula of the optical path difference is: Δ = 2 × n × d × cos(θ), wherein Δ is the optical path difference, n is the refractive index of each layer of material, d is the thickness of each layer of material, and θ is the incident angle of light in the material. For the optical path difference Δ, the condition for constructive interference is: Δ = m × λ, and the condition for destructive interference is: Δ = (m + 1 / 2) × λ, wherein m is the interference order (integer), and λ is the wavelength of light (the visible light range is usually between 400-700nm). The hydrophilic layer (humidity response layer) of the present application can be selected from polyethylene glycol (PEG) or polyvinyl alcohol (PVA) materials with humidity sensitivity. Both of them can significantly swell and change the refractive index in a humidity changing environment, thereby changing the interference conditions of different wavelengths of light, and producing color display effect through optical phase change. The molecular weight of PEG material is controlled at 5000-10000g / mol, ensuring its proper solubility and hygroscopicity; the alcoholysis degree of PVA material is 87-89%, which can provide excellent humidity responsiveness and good mechanical strength. Both materials can exhibit good hygroscopic swelling performance in a high humidity environment, making the hydrophilic layer sensitive to humidity changes.

[0045] In order to make the hydrophilic layer have both air permeability and humidity response function, the present application prepares the hydrophilic layer by solution coating process combined with microporous structure. Solution coating process is simple and easy to operate, which can uniformly coat the hydrophilic polymer on the substrate in a short time. By controlling the rotation speed and time of spin coating, a uniform film thickness can be formed. The concentration of PEG or PVA in water or ethanol solution is controlled at 5-10wt%, so as to ensure that the solution can form a uniform film layer during film forming. The spin coating method is used for film forming, the spin coating speed is controlled at 1000-1500rpm, and the time is set at 30-60s, so as to obtain a film with a thickness of 50-100μm. During the film forming process, polystyrene (PS) microspheres are added as a template to realize the microporous structure, which can leave a size controllable microporous structure during the film drying process, realizing the required micropore size and uniform distribution drying. The microsphere template only guides the formation of micropores in a physical level, and does not affect the hygroscopic swelling properties and mechanical strength of the material. After the microspheres volatilize, no residues are generated, while the purity of the hydrophilic layer is maintained. The particle size of the microspheres is controlled at 0.5-2μm, and the doping amount is 10-20wt%, so as to ensure that the hydrophilic layer has appropriate air permeability while responding to humidity.

[0046] After coating and film forming, the microsphere template volatilizes to form a microporous structure through drying treatment at 40-60℃ for 1-2h, further enhancing the air permeability and humidity response effect of the film. The microporous structure ensures that air and water vapor can freely penetrate the hydrophilic layer, realizing rapid humidity conduction, while the uniform distribution of micropores ensures the stability of the material structure. The thickness and pore size of the dried hydrophilic layer are uniform, which has excellent humidity responsiveness and air permeability, and is the core component to realize the humidity display effect.

[0047] Intermediate layer (nanofiber air permeable layer)

[0048] The intermediate layer (nanofiber air-permeable layer) can use polyacrylonitrile (PAN) nanofiber membranes with different density gradients. The main function is to maintain the mechanical stability of the structure and enable the material to have a humidity gradient display function. Polyacrylonitrile has good mechanical properties and moisture resistance, and the nanofiber structure formed can ensure the free penetration of air and water vapor, while effectively buffering the humidity expansion of the hydrophilic layer. The fiber diameter of the PAN nanofiber is controlled in the range of 100-300 nm to provide appropriate porosity and air permeability, while maintaining the mechanical strength and overall integrity of the thin film structure. By adjusting the fiber density in different zones, a humidity conduction gradient is formed within the intermediate layer to meet the gradient response requirements of humidity display.

[0049] The PAN concentration of the electrospinning solution is controlled in the range of 8-12wt%, ensuring the fluidity and spinning formability of the solution. In order to form a high-density fiber structure in the area with a slower humidity conduction rate, the voltage is set in the range of 20-25kV, increasing the amount of fiber deposition, and the spinning rate is controlled at 1.0mL / h to generate a dense fiber layer; while in the area with faster humidity conduction, the voltage is set at 15-20kV, and the spinning rate is lowered to 0.5mL / h to form a looser fiber layer, allowing moisture to pass through more quickly.

[0050] After electrospinning, the formed PAN fiber membrane is subjected to low-temperature heat treatment at 60-80℃ for 1-2h to further improve the bonding force between fibers and the structural stability. After heat treatment, the fiber diameter and porosity of the intermediate layer are uniform, and the air permeability and mechanical properties are good, providing key support for the air permeability and durability of the humidity display film.

[0051] Hydrophobic layer (nanoporous protective layer)

[0052] The hydrophobic layer (nanoporous protective layer) can use polyvinylidene fluoride (PVDF) or polydimethylsiloxane (PDMS) materials, which aims to provide good protection for the humidity display film while ensuring the stability of the humidity indication function. PVDF and PDMS materials have good hydrophobicity and chemical stability, which can prevent water penetration in a humid environment, while providing the necessary air permeability through the surface nanoporous structure. The pore size of the porous hydrophobic layer is controlled in the range of 100-500nm to enable water vapor to pass through smoothly, while liquid water is difficult to penetrate, effectively protecting the humidity response layer and the internal structure.

[0053] The hydrophobic layer is prepared by phase separation method to ensure the uniformity of the nanoporous structure. The PVDF solution is prepared with dimethylformamide (DMF) as the solvent, and the concentration is controlled at 5-10 wt% to form an appropriate film thickness and porosity. The solution is phase separated in a cold water bath to form a PVDF porous film with a porosity of 10-30% to achieve the desired air permeability and hydrophobicity.

[0054] If PDMS material is used, the precursor solution is mixed at a ratio of 10:1 and uniformly coated on the intermediate layer to form a nanoporous film layer by natural volatilization. After film formation, the PDMS film is baked at 80-100°C for 30-60 min to achieve complete curing, and the PVDF film is naturally dried at room temperature. The cured hydrophobic layer has a uniform porous structure on the film surface, excellent hydrophobicity and air permeability, and protects the film structure from liquid water during humidity changes, ensuring the stability and durability of the humidity display.

[0055] The application will be further described below with reference to the examples:

[0056] Example 1

[0057] 1. Substrate layer preparation: transparent polyethylene terephthalate (PET) is used as the substrate, with a thickness of 50 μm. The substrate is processed by laser drilling, with a laser power of 8 W and a scanning speed of 15 μm / s to prepare a microporous structure with a pore size of 5 μm and a porosity of 15% to enhance air permeability. After oxygen plasma treatment, the gas flow is 80 sccm, the power is 80 W, and the treatment time is 45 s to improve the adhesion of the hydrophilic layer (humidity response layer).

[0058] 2. Preparation of the hydrophilic layer (humidity response layer): a PVA aqueous solution with a concentration of 7 wt% is prepared, and the alcoholysis degree of PVA is 88%. The PVA solution is coated on the microporous PET substrate, and the spin coating speed is 1200 rpm for 45 s to form a hydrophilic layer (humidity response layer) with a thickness of 80 μm.

[0059] Drying at 50°C for 1 h to form a microporous structure, using 1.5 μm polystyrene (PS) microspheres as a template, with a doping amount of 15 wt%, and volatilizing during drying to form a microporous structure, the final hydrophilic layer (humidity response layer) has a pore size of 1-1.5 μm.

[0060] 3. Middle layer preparation: A polyacrylonitrile (PAN) solution with a concentration of 10 wt% was used to deposit a nanofiber layer on the hydrophilic layer (humidity-responsive layer) using electrospinning. High-density area: slow humidity conduction rate, voltage set to 25 kV, spinning rate 1.0 mL / h, receiving distance 10 cm, spinning time 5 min, forming a dense fiber layer. Low-density area: fast humidity conduction rate, voltage set to 15 kV, spinning rate 0.5 mL / h, receiving distance 15 cm, spinning time 2 min, forming a sparse fiber layer. Heat treatment at 70°C for 1 h to increase the interlayer bonding force.

[0061] 4. Hydrophobic layer preparation: A PVDF solution with a concentration of 8 wt% was used to prepare a nanoporous membrane layer using the phase separation method, with a porosity of 20% and a pore size controlled at 300 nanometers. The hydrophobic layer thickness is 20 μm, dried at room temperature for 30 min to ensure waterproofness when humidity passes through.

[0062] 5. Test results: Under the condition of 30% to 90% relative humidity, the film color change response time is 3-5 s. When the humidity rises from 30% to 90%, the film color gradually changes from light blue to yellow, showing good humidity display effect. The film has no obvious cracking after 200 times of humidity cycle, indicating good mechanical durability. The refractive index of the 50 μm PET base layer and the 80 μm PVA hydrophilic layer is 1.65 and 1.49 respectively, the optical path difference Δ = 2 × (1.65 × 50 + 1.49 × 80) = 403.4 μm, the film color before coloration is light blue (λ ≈ 490), it can be concluded that the interference order = 403.4 / 0.49 ≈ 823, the thickness of the hydrophilic layer after absorbing moisture is 100 μm, the refractive index is 1.53, the optical path difference Δ = 2 × (1.65 × 50 + 1.53 × 100) = 471 μm, then the interference wavelength λ = 471 / 823 × 1000 = 572 nm, which is the wavelength of yellow light.

[0063] Example 2

[0064] 1. Base layer preparation: Polycarbonate (PC) material is used as the base, with a thickness of 60 μm and an optical transmittance of 85%. A microporous structure with a pore size of 7 μm and a porosity of 12% is made by laser drilling process (power 6 W, scanning speed 20 μm / s) to ensure air permeability. The base layer is treated by oxygen plasma, flow rate 70 sccm, power 90 W, treatment time 40 s, to enhance the adhesion of the humidity-responsive layer.

[0065] 2. Hydrophilic layer (humidity-responsive layer) preparation: 8wt% PEG solution with molecular weight of 8000g / mol was prepared. The PEG solution was coated on the PC substrate by spin-coating method at a speed of 1500 rpm for 30 s to form a hydrophilic layer (humidity-responsive layer) with a thickness of about 70 μm. The sample was dried at 40 °C for 90 min. The PS microspheres with a particle size of 2 μm were used as a template to form a microporous structure with a pore size of 1.8 μm and a doping amount of 10wt%, thereby improving the gas permeability.

[0066] 3. Intermediate layer preparation: A polyacrylonitrile (PAN) solution with a concentration of 9wt% was used to deposit a nanofiber membrane by electrospinning method. High-density area: slow humidity conduction rate, voltage setting of 25kV, spinning rate of 1.0mL / h, receiving distance of 10cm, spinning time of 5min, forming a dense fiber layer. Low-density area: fast humidity conduction rate, voltage setting of 15kV, spinning rate of 0.5mL / h, receiving distance of 15cm, spinning time of 2min, forming a sparse fiber layer.

[0067] Heat treatment at 70 °C for 1h to increase the interlayer bonding force.

[0068] 4. Hydrophobic layer preparation: PDMS precursor solution was used to uniformly coat the PAN layer at a ratio of 10:1. The nano-porous membrane with a pore size of 200-400nm and a porosity of 25% was formed by volatilization within 60min. Finally, the hydrophobic layer was cured by baking at 100 °C for 45min.

[0069] 5. Data test: When the humidity increases from 40% to 80%, the color of the film changes from yellow to red, and the humidity change response time is 2-4s. After 150 cycles of humidity test, the film shows no delamination or cracking, indicating high durability and stability. The refractive index of the 60 μm PC substrate layer and the 70 μm PEG hydrophilic layer was measured to be 1.58 and 1.47, respectively, and the optical path difference Δ = 2x(1.58x60+1.47x70) = 395.4 μm. The color of the film before coloration is yellow (λ≈580), and the interference order number = 395.4 / 0.58≈682. After the hydrophilic layer absorbs moisture, the thickness is 85 μm and the refractive index is 1.51, and the optical path difference Δ = 2x(1.65x50+1.51x100) = 467 μm. Therefore, the interference wavelength λ = 467 / 682x1000 = 685nm is the wavelength of red light;

[0070] Example 3

[0071] 1. Substrate layer preparation: A porous PET substrate with a thickness of 55 μm was used, the laser power was set to 7 W, the scanning rate was 12 μm / s, the aperture was 3 μm, and the porosity was 18%. Oxygen plasma treatment conditions: gas flow 100 sccm, power 75 W, time 50 s, to increase the adhesion of the hydrophilic layer (humidity-responsive layer).

[0072] 2. Hydrophilic layer (humidity-responsive layer) preparation: A 6 wt% PVA solution (alcoholysis degree 88%) was used, and 0.5 wt% polyacrylamide (PAM) was added to improve humidity responsiveness. The coating rotation speed was 1300 rpm, and the time was 60 s, forming a hydrophilic layer (humidity-responsive layer) with a thickness of 90 μm, PS microspheres with a particle size of 1.2 μm, and a doping amount of 15 wt%. After drying, a microporous structure of 1-1.5 μm was formed.

[0073] 3. Intermediate layer preparation: A PAN solution with a concentration of 11 wt% was used to deposit a nanofiber layer on the hydrophilic layer (humidity-responsive layer) using electrospinning. High-density area: slow humidity conduction rate, voltage set to 25 kV, spinning rate 1.0 mL / h, receiving distance 10 cm, spinning time 5 min, forming a dense fiber layer. Low-density area: fast humidity conduction rate, voltage set to 15 kV, spinning rate 0.5 mL / h, receiving distance 15 cm, spinning time 2 min, forming a sparse fiber layer. The fiber diameter was 180 nm, the porosity reached 40%, and the heat treatment temperature was 80°C for 2 h to ensure the interlayer bonding strength and stability.

[0074] 4. Hydrophobic layer preparation: PVDF nanoporous membrane was prepared using the phase separation method, with a solution concentration of 9 wt%, and a cold water phase separation method to form a hydrophobic layer with a porosity of 22% and a pore size of 300-500 nm. Dried at room temperature for 30 min to ensure humidity display stability.

[0075] 5. Data testing: The color of the film changed from orange to red in the relative humidity range from 20% to 90%, with significant and reversible changes. The humidity response time was 3 s, showing a fast humidity response speed. After 250 humidity cycles, the film structure showed no obvious damage, and the mechanical stability was excellent. The refractive index of the 55 μm PET substrate layer and the 90 μm PVA hydrophilic layer was 1.65 and 1.49, respectively, and the optical path difference Δ = 2 × (1.65 × 55 + 1.49 × 90) = 449.7 μm. The color of the film before coloration was orange (λ ≈ 600), and the interference order number = 449.7 / 0.6 ≈ 750. After the hydrophilic layer absorbed moisture, the thickness was 104 μm, and the refractive index was 1.53. The optical path difference Δ = 2 × (1.65 × 50 + 1.53 × 104) = 483.24 μm, and the interference wavelength λ = 483.24 / 750 × 1000 = 644 nm, which is the wavelength of red light.

[0076] The above detailed description has shown, described and illustrated the application by various specific embodiments. However, various changes and modifications can be made to the embodiments without departing from the spirit and scope of the application. Many other changes and modifications within the scope of the application disclosed herein will readily occur to those skilled in the art, and it is intended to protect all such variations and modifications as fall within the scope of the applicant's contribution to the art. Accordingly, the protection sought herein is to be given to all changes and modifications as fall within the purview of the claims.

[0077] In the description of the specification, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0078] The above described are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An optical interference-based high-transpiration humidity indicator film, characterized by, The application relates to a humidity display film, which comprises a substrate layer, a humidity response layer, an intermediate layer and a hydrophobic layer. The substrate layer is made of transparent material, and a plurality of air-permeable micropores are arranged on the substrate layer; the micropores have a pore diameter of 1-10 mu m and a porosity of 10-20%; the humidity response layer is made of humidity-sensitive material and has a thickness of 50-100 mu m; micropores are arranged on the humidity response layer; the micropores have a pore diameter of 0.5-2 mu m, so that air and water vapor can freely penetrate the humidity response layer; the intermediate layer is a nanofiber membrane, wherein the fiber diameter of the nanofiber is controlled to be 100-300 nm; the density of the intermediate layer changes in a gradient along the length direction, so as to control the air permeability of the humidity response layer corresponding to the intermediate layer with different densities; and the hydrophobic layer is made of transparent and air-permeable material and provides good protection for the humidity display film. The humidity-sensitive material is polyethylene glycol or polyvinyl alcohol. The process comprises at least the following steps of preparing the substrate layer, specifically: polyester or polycarbonate is used as the base film, and the thickness is 30 mu m-100 mu m; laser drilling process is used to process the base film, the laser power is set to be 5-15 W, the scanning speed is 10-20 mu m / s, the micropores with a pore diameter of 1-10 mu m and a porosity of 10-20% are prepared; 2. The optical interference based high-transpiration humidity indicator film of claim 1, wherein, the base film after drilling is subjected to oxygen plasma treatment, the gas flow is 50-100 sccm, the power is 50-100 W, and the treatment time is 30-60 s, so as to improve the adhesion of the gradient humidity response layer.

3. A process for the production of the high-transpiration humidity indicator film based on optical interference according to claim 2, characterized in that, The process further comprises the following steps of preparing the humidity response layer: polyethylene glycol or polyvinyl alcohol is prepared into an aqueous or ethanolic solution with a concentration of 5-10 wt%; the spin coating method is used to form a film, the spin coating speed is controlled to be 1000-1500 rpm, and the time is set to be 30-60 s, so as to obtain a film with a thickness of 50-100 mu m; polystyrene microspheres are added as templates during the film forming process, the particle diameter of the microspheres is controlled to be 0.5-2 mu m, and the doping amount is 10-20 wt%; after the film is coated, the microsphere templates are volatilized to form a microporous structure through drying treatment at 40-60 DEG C for 1-2 h. The process further comprises the following steps of preparing the intermediate layer: polyacrylonitrile electrospinning solution is prepared, the concentration is controlled to be 8-12 wt%, so as to ensure the fluidity and spinning formability of the solution; a high-density fiber structure is formed in a slow humidity conduction rate area, the voltage is set to be in the range of 20-25 kV, the fiber deposition amount is increased, the spinning speed is controlled to be 1.0 mL / h, so as to generate a dense fiber layer; a low-density fiber structure is formed in a fast humidity conduction rate area, the voltage is set to be 15-20 kV, the spinning speed is lowered to 0.5 mL / h, so as to form a relatively loose fiber layer, so that the humidity can pass through more quickly; after electrospinning, the PAN fiber membrane formed is subjected to low-temperature heat treatment at 60-80 DEG C for 1-2 h.

4. The process for preparing an optical interference-based high-transpiration humidity indicator film according to claim 3, wherein the step of forming the first and second layers is performed by a vacuum deposition method. The process further comprises the following steps of preparing the hydrophobic layer: a PVDF solution with a concentration of 5-10 wt% is prepared; the PVDF porous membrane is formed through phase separation in a cold water bath, the porosity is 10-30%, and the pore diameter is 100-500 nm; and the PVDF porous membrane is dried at room temperature for 30 min. ​ ​ ​ 5. The process for preparing an optical interference-based high-transpiration humidity indicator film according to claim 4, wherein the step of forming the first and second layers is performed by a vacuum deposition method. ​ ​ ​ ​ ​ 6. The process for preparing an optical interference-based high-transpiration humidity indicator film according to claim 5, wherein the step of forming the first and second layers is performed by a vacuum deposition method. ​ ​ ​ ​