High-air-permeability humidity display film and preparation process thereof

Abstract

The invention discloses a high-air-permeability humidity display film and a preparation process thereof. Comprising a substrate layer, a gradient humidity response layer and a hydrophobic layer which are sequentially arranged from bottom to top, wherein the substrate layer is made of a transparent material; a plurality of breathable micropores are formed in the substrate layer; the diameter of each micropore is 1 to 10 [mu] m; the porosity is 10 to 20 percent; the gradient humidity response layer is formed by stacking more than three developing ink layers up and down; in every two adjacent color developing ink layers, the length of the lower color developing ink layer is larger than that of the upper color developing ink layer; a separation layer is arranged between every two adjacent developing ink layers. Through the multiple humidity sensitive material layers with different lengths, the film develops colors layer by layer under the condition that the humidity is increased, and the gradient display effect of the humidity is achieved. A user can visually judge the humidity state and the increase trend of the urine amount through color changes, and humidity display is more readable.

Description

Technical Field

[0001] The invention relates to a high-air-permeability humidity display film and a preparation process thereof. Background Art

[0002] Humidity display films are widely used in packaging, smart labels, environmental monitoring and other fields, and can directly reflect changes in environmental humidity through visible color changes. In the prior art, hydrogel films, cellulose nanocrystal films and layer-by-layer self-assembled (LBL) films have been reported.

[0003] However, cellulose nanocrystal films and hydrogel nano-microcavity films rely on the hygroscopic expansion of materials to achieve humidity display, but their expansion speed is limited, resulting in a relatively delayed humidity response, unable to quickly reflect humidity changes, and no gradient humidity display function. Although the humidity-responsive LBL film has a simple process, the layer-by-layer deposition structure increases the humidity conduction path, resulting in a delayed humidity response. Hydrogel nano-microcavity films and cellulose nanocrystal films are prone to brittleness after humidity expansion, and their mechanical stability decreases. They may crack or deform after humidity changes cycle. Although the humidity-responsive LBL film has a layered structure that increases the thickness, the interlayer bonding force is weak, and interlayer separation is prone to occur during long-term use, reducing the durability of the material. In addition, these three technologies do not include breathable design in the selection of materials for the humidity-sensitive layer, which makes it easy for water vapor to accumulate in the material in a high humidity environment, affecting the humidity indication effect and limiting the material's usage scenarios. Summary of the invention

[0004] In order to overcome the above defects, the present invention provides a high air permeability humidity display film and a preparation process thereof.

[0005] To achieve the above object, the highly breathable humidity display film of the present invention comprises a base layer, a gradient humidity response layer and a hydrophobic layer arranged in sequence from bottom to top;

[0006] The base layer is made of transparent material; a plurality of air-permeable micropores are arranged on the base layer; the diameter of the micropores is 1-10 μm; and the porosity is 10-20%;

[0007] The gradient humidity response layer is formed by stacking three or more color ink layers; in two adjacent color ink layers, the length of the color ink layer located at the lower layer is greater than the length of the color ink layer located at the upper layer; and a separation layer is provided between the two adjacent color ink layers;

[0008] The hydrophobic layer is made of a transparent and breathable material, providing good protection for the humidity display film.

[0009] Furthermore, the separation layer is a hydrophilic high molecular polymer; the separation layer is provided with micropores, wherein, in two adjacent separation layers, the diameter of the micropores of the lower separation layer is larger than the diameter of the micropores of the upper separation layer.

[0010] Furthermore, the length of the separation layer is greater than the length of the adjacent upper color developing ink layer, and less than the length of the adjacent lower color developing ink layer.

[0011] Furthermore, the separation layer is a hydrophobic high molecular polymer; the length of the separation layer is slightly smaller than the length of the adjacent upper color developing ink layer.

[0012] Furthermore, the process at least includes the step of preparing a base layer, and the steps are specifically:

[0013] Use polyethylene terephthalate as the base film with a thickness of 30μm-100μm;

[0014] The base film is processed by laser drilling, the laser power is set to 5-15W, the scanning rate is 10-20μm / s, and a microporous structure with a pore size of 3-8μm and a porosity of 10-20% is prepared;

[0015] The punched base film is treated with oxygen plasma at a gas flow rate 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.

[0016] Furthermore, the method further includes the step of preparing a gradient humidity response layer, specifically:

[0017] 61) preparing a bottom humidity sensitive layer on the base film using humidity sensitive ink, wherein the bottom humidity sensitive layer has the strongest sensitivity;

[0018] Uniformly coating a hydrophilic polymer on the upper surface of the bottom humidity sensitive layer by spin coating to form a bottom separation layer;

[0019] Micropores are prepared on the bottom separation layer, and the pore size of the micropores is 201-300 nm;

[0020] The length of the bottom separation layer is shorter than the length of the bottom moisture sensitive layer;

[0021] 62) preparing an intermediate humidity sensitive layer on the bottom separation layer using humidity sensitive ink, wherein the length of the intermediate humidity sensitive layer is 1 / 2-4 / 5 of the length of the bottom humidity sensitive layer and is smaller than the length of the bottom separation layer; the sensitivity of the intermediate humidity sensitive layer is moderate;

[0022] Spin coating the hydrophilic polymer evenly on the upper surface of the bottom humidity sensitive layer to form an intermediate separation layer;

[0023] Micropores are prepared on the intermediate separation layer, and the pore diameter of the micropores is 100-200 nm;

[0024] The length of the intermediate separation layer is shorter than the length of the intermediate humidity sensitive layer;

[0025] 63) An upper humidity sensitive layer is prepared on the middle layer separation layer using humidity sensitive ink, the length of the upper humidity sensitive layer is 1 / 2-4 / 5 of the length of the middle layer humidity sensitive layer and is smaller than the length of the middle layer separation layer; the upper humidity sensitive layer has the lowest sensitivity.

[0026] Furthermore, the method further includes the step of preparing a gradient humidity response layer, specifically:

[0027] 71) preparing a bottom humidity sensitive layer on the base film using humidity sensitive ink, wherein the bottom humidity sensitive layer has the strongest sensitivity;

[0028] Uniformly coating a hydrophobic polymer on the upper surface of the bottom humidity sensitive layer by spin coating to form a bottom separation layer;

[0029] The length of the bottom separation layer is shorter than the length of the bottom moisture sensitive layer;

[0030] 72) preparing an intermediate humidity sensitive layer on the bottom separation layer using humidity sensitive ink, wherein the length of the intermediate humidity sensitive layer is 1 / 2-4 / 5 of the length of the bottom humidity sensitive layer and is greater than the length of the bottom separation layer; the sensitivity of the intermediate humidity sensitive layer is moderate;

[0031] Spin coating the hydrophobic polymer evenly on the upper surface of the bottom humidity sensitive layer to form an intermediate separation layer;

[0032] The length of the intermediate separation layer is shorter than the length of the intermediate humidity sensitive layer;

[0033] 73) An upper humidity sensitive layer is prepared on the middle layer separation layer using humidity sensitive ink, the length of the upper humidity sensitive layer is 1 / 2-4 / 5 of the length of the middle layer humidity sensitive layer, and is greater than the length of the middle layer separation layer; the upper humidity sensitive layer has the lowest sensitivity.

[0034] Furthermore, the method also includes the step of preparing a hydrophobic layer: using a PVDF solution with a concentration of 8wt%, using a phase separation method to prepare a nanoporous membrane layer with a porosity of 20% and a pore size controlled at 300nm; the hydrophobic layer has a thickness of 20μm and is dried at room temperature for 30min to ensure waterproofness when humidity passes through.

[0035] The present invention is composed of a porous structure substrate, a gradient humidity response layer and a hydrophobic layer. By designing a multi-layer humidity sensitive layer (humidity color development layer) and using a humidity response material with a length gradient, a gradient display effect of color development layer by layer as the humidity increases is achieved. The present invention can be applied to products such as diaper bottom films. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the structure of the present invention.

[0037] Figure 2 Schematic diagram of the structure of the gradient humidity response layer in Example 1 of the present invention.

[0038] Figure 3 Schematic diagram of the structure of the gradient humidity response layer in Example 2 of the present invention. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0040] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0041] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] The present invention aims to provide a highly breathable humidity color-developing film with a gradient humidity display function, such as Figure 1As shown, it is composed of a porous structure base layer, a gradient humidity response layer and a hydrophobic layer. By designing a multi-layer humidity sensitive layer (humidity color development layer) and using a humidity response material with a length gradient, a gradient display effect of color development layer by layer as the humidity increases is achieved. This can be applied to disposable sanitary products such as diaper bottom films.

[0044] In the present invention, the base layer is preferably made of transparent and microporous materials such as PET, PC, PE, PP, etc., which have high light transmittance and excellent mechanical properties and are suitable for supporting materials of multi-layer humidity display film structures. In order to achieve air permeability, the base layer material can be processed into micropores by laser drilling to form a porous structure with air permeability. The laser drilling process uses precisely controlled laser power and scanning rate to form uniform micropores and achieve an effective balance between the air permeability and strength of the material. For example, a laser with a power of 5-10W is used to process micropores with a diameter of 1-10μm on the base at a scanning rate of 10-20μm / s, and the porosity is controlled between 10-20%, ensuring that the base layer has the required air permeability and structural integrity. The advantage of laser drilling is that it is flexible in operation and is suitable for base materials of different thicknesses and sizes. It not only ensures air permeability, but also maintains the uniformity and stability of the overall performance of the film.

[0045] In addition, in order to enhance the adhesion between the gradient humidity response layer and the substrate, the present invention performs oxygen plasma treatment on the surface of the substrate layer after laser drilling. The gas flow rate of oxygen plasma is set to 50-100sccm, the power is 50-100W, and the treatment time is 30-60s to introduce active functional groups on the substrate surface to enhance its bonding with the gradient humidity response layer. The substrate layer after laser microporous processing and oxygen plasma treatment has good light transmittance, air permeability and interlayer adhesion, providing a stable basic structure for the realization of humidity display film.

[0046] In the present invention, the gradient humidity response layer material uses humidity sensitive ink for color development, and a separation layer is added between each layer of humidity sensitive ink for design, so as to realize the gradient humidity display function of layer-by-layer color development. The separation layer not only prevents the mutual penetration of each layer of humidity sensitive ink, but also ensures that the humidity is gradually conducted according to the layers, so as to achieve the effect of graded color development. The following is a specific technical scheme for preparing the gradient humidity response layer material:

[0047] First, a moisture-sensitive ink layer and a separation layer are sequentially coated on the substrate layer, wherein the number of moisture-sensitive ink layers can be selected as 3 to 5 layers as needed to construct a humidity-responsive structure that displays color layer by layer. The substrate layer is hydrophobically treated to support and isolate the humidity-responsive layer to prevent the substrate from absorbing moisture and ensure structural stability. The moisture-sensitive ink layer can be made of urine-developing glue or similar humidity-responsive materials, and a small amount of hygroscopic agent (such as glycerol, sorbitol, polyethylene glycol, polyvinyl pyrrolidone, etc.) is added to the moisture-sensitive ink to improve the moisture absorption capacity, and the humidity graded display is realized through the length gradient design. The length of each layer of moisture-sensitive ink is shortened in sequence, gradually decreasing from the bottom layer to the top layer. The bottom ink layer has the longest length and is used for the initial humidity response, and the top ink layer has the shortest length and is used for the final color development. The moisture absorption capacity and molecular weight of the moisture-sensitive ink are regulated at different levels. The molecular weight of the bottom ink layer is relatively low and the moisture absorption rate is fast to ensure that moisture is absorbed first and the color is quickly displayed; while the molecular weight of the upper ink layer increases layer by layer, and the moisture absorption rate decreases, so that moisture is conducted layer by layer in sequence.

[0048] In order to prevent the moisture-sensitive ink from penetrating each other between layers, a thin film separation layer is added between each layer of moisture-sensitive ink. The material of the separation layer can be a hydrophilic polymer or a hydrophobic polymer:

[0049] When a hydrophilic polymer is used to prepare the separator layer, the thickness of the separator layer is controlled within 5μm to ensure the isolation effect while not affecting the conduction of moisture. The separator layer is evenly coated on the surface of the lower ink layer by spin coating, and then dried at 40-60℃ to form a uniform film. This separator layer can prevent the diffusion of the moisture-sensitive ink and allow moisture to gradually penetrate into the upper ink layer. The conduction speed of moisture is further adjusted by the microporous structure on the separator layer. The microporous design of the separator layer adjusts the pore size and porosity layer by layer according to the conduction path of moisture to ensure that moisture can gradually penetrate into each color development layer in a predetermined order. For example, the micropore pore size of the bottom separator layer is designed to be 200-300nm, and moisture passes faster and preferentially reaches the moisture-sensitive ink at the bottom layer; while the micropore pore size of the middle and top separator layers is reduced layer by layer to 100-200nm, so that the moisture conduction rate is reduced layer by layer, ensuring that moisture is transferred to the upper layer only after the color development of the lower ink is completed.

[0050] When a hydrophobic polymer is used to prepare the separation layer, the thickness of the separation layer is controlled within 5 μm and is evenly coated on the surface of the lower ink layer by spin coating, and the coating length is slightly shorter than the upper humidity-sensitive ink layer. It is then dried at 40-60°C to form a uniform film of the separation layer.

[0051] The hydrophobic layer (nanoporous protective layer) of the present invention can be made of polyvinylidene fluoride (PVDF) or polydimethylsiloxane (PDMS) materials, the purpose of which is to provide good protection for the humidity display film and ensure the stability of the humidity indication function. PVDF and PDMS materials have good hydrophobicity and chemical stability, can prevent moisture penetration in the air under a humid environment, and provide necessary air permeability through the surface nanoporous structure. The pore size of the porous hydrophobic layer is controlled in the range of 100-500nm, so that water vapor can pass smoothly, while liquid water is difficult to penetrate, effectively protecting the humidity response layer and the internal structure.

[0052] The hydrophobic layer is prepared by phase separation to ensure the uniformity of the nanoporous structure. The PVDF solution uses dimethylformamide (DMF) as a solvent, and the concentration is controlled at 5-10wt% to form an appropriate membrane thickness and porosity. The solution is phase separated in a cold water bath to form a PVDF porous membrane with a porosity of 10-30%, achieving the required permeability and hydrophobicity. If PDMS material is used, its precursor solution is mixed in a 10:1 ratio and evenly coated on the intermediate layer to form a nanoporous membrane layer through natural volatilization.

[0053] After film formation, the PDMS membrane is baked at 80-100℃ for 30-60min to achieve complete curing, while the PVDF membrane is dried naturally at room temperature. The surface porous structure of the hydrophobic layer membrane after curing is uniform, with excellent hydrophobicity and air permeability, while protecting the film structure from the influence of liquid water during humidity changes, ensuring the stability and durability of humidity display.

[0054] Example

[0055] 1. Preparation of the substrate layer: Transparent polyethylene terephthalate (PET) was used as the substrate with a thickness of 50 μm. The substrate was processed by laser drilling, with the laser power set to 8W and the scanning rate to 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 rate was 80 sccm, the power was 80 W, and the treatment time was 45 s to improve the adhesion of the gradient humidity response layer.

[0056] 2. Preparation of gradient humidity response layer: Three layers of color-changing humidity sensitive layers are used, each layer has a different length, and the thickness decreases from bottom to top. The thickness of each color-changing ink layer is 10μm. Bottom layer: The color-changing ink layer is 5cm long and is designed to be the most sensitive layer. It starts to show color when the humidity increases slightly. Middle layer: The color-changing ink is 3cm long and shows color when the humidity reaches a medium level, producing a color superposition effect. Top layer: The color-changing ink is 1cm long and starts to show color when the humidity increases, making the humidity change more clearly visible. A microporous PVA separator is added between each layer to prevent penetration.

[0057] 3. Preparation of hydrophobic layer: A PVDF solution with a concentration of 8wt% was used to prepare a nanoporous membrane layer using a phase separation method, with a porosity of 20% and a pore size of 300nm. The hydrophobic layer was 20μm thick and dried at room temperature for 30min to ensure waterproofness when humidity passes through.

[0058] The present invention is described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. Many other changes and modifications that do not depart from the concept and scope of the present invention should be regarded as the protection scope of the present invention.

[0059] In the description of this specification, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0060] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A highly air-permeable humidity display film, characterized in that: It includes a base layer, a gradient humidity response layer and a hydrophobic layer arranged in sequence from bottom to top; The base layer is made of transparent material; a plurality of air-permeable micropores are arranged on the base layer; the diameter of the micropores is 1-10 μm; and the porosity is 10-20%; The gradient humidity response layer is formed by stacking three or more color ink layers; in two adjacent color ink layers, the length of the color ink layer located at the lower layer is greater than the length of the color ink layer located at the upper layer; and a separation layer is provided between the two adjacent color ink layers; The hydrophobic layer is made of a transparent and breathable material, providing good protection for the humidity display film.

2. The highly air-permeable humidity display film according to claim 1, characterized in that: The separation layer is a hydrophilic high molecular polymer; the separation layer is provided with micropores, wherein, in two adjacent separation layers, the diameter of the micropores in the lower separation layer is larger than the diameter of the micropores in the upper separation layer.

3. The highly air-permeable humidity display film according to claim 2, characterized in that: The length of the separation layer is greater than the length of the adjacent upper color developing ink layer, and less than the length of the adjacent lower color developing ink layer.

4. The highly air-permeable humidity display film according to claim 1, characterized in that: The separation layer is a hydrophobic high molecular polymer; the length of the separation layer is slightly smaller than the length of the adjacent upper color developing ink layer.

5. A process for preparing a highly breathable humidity display film, characterized in that: The process at least includes the steps of preparing a base layer, and the steps are specifically: Use polyethylene terephthalate as the base film with a thickness of 30μm-100μm; The base film is processed by laser drilling, the laser power is set to 5-15W, the scanning rate is 10-20μm / s, and a microporous structure with a pore size of 3-8μm and a porosity of 10-20% is prepared; The punched base film is treated with oxygen plasma at a gas flow rate 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.

6. The process for preparing the highly breathable humidity display film according to claim 5, characterized in that: The step of preparing a gradient humidity response layer is also included, specifically: 61) preparing a bottom humidity sensitive layer on the base film using humidity sensitive ink, wherein the bottom humidity sensitive layer has the strongest sensitivity; Uniformly coating a hydrophilic polymer on the upper surface of the bottom humidity sensitive layer by spin coating to form a bottom separation layer; Micropores are prepared on the bottom separation layer, and the pore size of the micropores is 201-300 nm; The length of the bottom separation layer is shorter than the length of the bottom moisture sensitive layer; 62) preparing an intermediate humidity sensitive layer on the bottom separation layer using humidity sensitive ink, wherein the length of the intermediate humidity sensitive layer is 1 / 2-4 / 5 of the length of the bottom humidity sensitive layer and is smaller than the length of the bottom separation layer; the sensitivity of the intermediate humidity sensitive layer is moderate; Spin coating the hydrophilic polymer evenly on the upper surface of the bottom humidity sensitive layer to form an intermediate separation layer; Micropores are prepared on the intermediate separation layer, and the pore diameter of the micropores is 100-200 nm; The length of the intermediate separation layer is shorter than the length of the intermediate humidity sensitive layer; 63) An upper humidity sensitive layer is prepared on the middle layer separation layer using humidity sensitive ink, the length of the upper humidity sensitive layer is 1 / 2-4 / 5 of the length of the middle layer humidity sensitive layer and is smaller than the length of the middle layer separation layer; the upper humidity sensitive layer has the lowest sensitivity.

7. The process for preparing the highly breathable humidity display film according to claim 5, characterized in that: The step of preparing a gradient humidity response layer is also included, specifically: 71) preparing a bottom humidity sensitive layer on the base film using humidity sensitive ink, wherein the bottom humidity sensitive layer has the strongest sensitivity; Uniformly coating a hydrophobic polymer on the upper surface of the bottom humidity sensitive layer by spin coating to form a bottom separation layer; The length of the bottom separation layer is shorter than the length of the bottom moisture sensitive layer; 72) preparing an intermediate humidity sensitive layer on the bottom separation layer using humidity sensitive ink, wherein the length of the intermediate humidity sensitive layer is 1 / 2-4 / 5 of the length of the bottom humidity sensitive layer and is greater than the length of the bottom separation layer; the sensitivity of the intermediate humidity sensitive layer is moderate; Spin coating the hydrophobic polymer evenly on the upper surface of the bottom humidity sensitive layer to form an intermediate separation layer; The length of the intermediate separation layer is shorter than the length of the intermediate humidity sensitive layer; 73) An upper humidity sensitive layer is prepared on the middle layer separation layer using humidity sensitive ink, the length of the upper humidity sensitive layer is 1 / 2-4 / 5 of the length of the middle layer humidity sensitive layer, and is greater than the length of the middle layer separation layer; the upper humidity sensitive layer has the lowest sensitivity.

8. The process for preparing the highly breathable humidity display film according to claim 6 or 7, characterized in that: The method also includes the steps of preparing a hydrophobic layer: using a PVDF solution with a concentration of 8wt%, using a phase separation method to prepare a nanoporous membrane layer with a porosity of 20% and a pore size controlled at 300nm; the hydrophobic layer has a thickness of 20μm and is dried at room temperature for 30min to ensure waterproofness when humidity passes through.

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