Label for time indication and preparation method and design method thereof

Abstract

The invention discloses a label for time indication as well as a preparation method and a design method of the label. The label comprises a label main body, an oxidation color-changing film arranged on the surface of one side of the label main body, and an oxygen permeation regulation and control layer wrapping the label main body and the oxidation color-changing film. According to the label for time indication, the nano-metal material has high specific surface area and high oxidation activity, and the oxidation rate of the nano-metal material is not restricted by the passivation layer. Meanwhile, after the nano metal particles are coated with the high-molecular polymer film, a stable oxygen permeation rate of the film is controlled, a stable oxygen environment is provided for the label, the oxidation discoloration process of the label can be accurately controlled, and the label is in approximately linear positive correlation with the air contact time. The preparation method is simple and convenient, and the indication period of the label is adjusted by adjusting the activity of the oxidation discoloration rate regulating agent and the oxygen permeability of the oxygen permeability regulating layer.

Description

Technical Field

[0001] The present invention relates to the technical field of indicating measurement labels, and in particular to a label for time indication and a preparation method and a design method thereof. Background Art

[0002] In the fields of food, medicine, and cosmetics used by people in daily life, it is necessary to monitor their usage time. Because the shelf life of traditional products depends on complete and effective packaging, and when the product is actually used, the effective packaging is destroyed and will be affected by factors such as air oxidation, microbial invasion, temperature and humidity interference, etc., and the validity period that ensures safety and can play the original function will be greatly discounted. There is an optimal use period for the product after opening. However, consumers of products such as food and medicine often forget the usage time after opening the package, especially the elderly and office workers. When the usage time exceeds its optimal use period, the product cannot play its original function and even harms personal safety and health. Therefore, it is very important to develop a smart label that can indicate the usage time of the product in real time and can display it in an intuitive way.

[0003] At present, researchers have developed volatile pigments, dyes or other organic solvents into timing inks / labels, and used the color changes caused directly or indirectly by their continuous volatilization to indicate the time process after the product is unsealed. Although the method is simple and easy to operate, the actual effect is restricted by the volatilization rate of the material affected by temperature and humidity, and it is difficult to ensure accuracy. For example, the Chinese patent with publication number CN104949972A discloses a color-changing composition for time indication and its use method. The method prepares a time-indicating color-changing coating by mixing volatile organic solvents, waxes, and titanium dioxide particles. Although the color of the coating gradually turns white with the volatilization of the organic solvent in the coating, it plays an indicating effect, but the volatilization rate of the organic solvent is easily affected by temperature and humidity, and the actual effect accuracy is not high. For example, the Chinese patent with publication number CN118620446A sets an activation layer and a color-changing layer, and the activated molecules in the activation layer slowly migrate to the color-changing layer to cause a color-changing reaction to achieve a color-changing effect. This method can reduce the influence of ambient air flow rate on the accuracy of color change, but it is difficult to operate, and it is uncertain when the label starts timing, which is easy to cause time errors. Therefore, how to design a smart label with stable time indication effect, simple operation and convenient use is a problem that technicians urgently need to solve. Summary of the invention

[0004] The technical problem to be solved by the present invention is to design a label indicating the use cycle of a product.

[0005] The first aspect of the present invention provides a label for time indication, comprising a label body, an oxidized color-changing film disposed on a surface of one side of the label body, and an oxygen permeability regulating layer covering the label body and the oxidized color-changing film; The label body is provided with a comparison color bar, on which the corresponding colors of the oxidation color-changing film at various stages of oxidation color-changing over time are distributed from left to right; The oxidochromic film has metal nanoparticles and an oxidochromic rate regulator evenly distributed therein; The oxygen permeability regulating layer is a high molecular polymer film with oxygen permeability.

[0006] Furthermore, the metal nanoparticles include any one of iron nanoparticles, copper nanoparticles and zinc nanoparticles.

[0007] Furthermore, the particle size of the metal nanoparticles is 50-200 nm.

[0008] Furthermore, the thickness of the oxidation discoloration film is 50-150 μm.

[0009] Furthermore, the oxidative discoloration rate regulator includes any one of MnO2 nanoparticles and SiO2 nanoparticles.

[0010] Furthermore, the material of the polymer transparent film includes any one of polydimethylsiloxane and polyvinylidene fluoride.

[0011] The second aspect of the present invention provides a preparation method, comprising the following steps: Step 1, preparing an oxidative discoloration film: uniformly dispersing metal nanoparticles and an oxidative discoloration rate regulator in a polylactic acid matrix containing a volatile solvent, wherein the mass ratio of the metal nanoparticles to the degradable polymer matrix is ​​3:7; then adding 1wt% of a magnesium stearate crystal form controller and 0.5wt% of a dispersant; continuing to stir to obtain a mixed solution; and spreading the mixed solution on a glass substrate under an inert gas environment by a solution casting method, wherein the volatile solvent gradually evaporates to form an oxidative discoloration film; Step 2, compounding the oxidative color-changing film obtained in step 1 onto one side surface of the label body to obtain a composite layer; Step 3, through a hot pressing packaging method, the high molecular polymer film completely covers the composite layer prepared in step 2 to prepare a label.

[0012] Furthermore, in step 1, the polylactic acid matrix consists of 10 wt % polylactic acid and 90 wt % ethanol.

[0013] Furthermore, the material of the label body includes any one of polyester film, polyethylene film, polypropylene film, coated paper, metal film and fiber nonwoven fabric.

[0014] Furthermore, in step 3, the high molecular polymer film includes any one of polydimethylsiloxane and polyvinylidene fluoride.

[0015] A third aspect of the present invention provides a method for designing a label for time indication, by adjusting the activity of an oxidative discoloration rate regulator and the oxygen permeability of an oxygen permeability regulating layer, thereby adjusting the indication period of the label.

[0016] The fourth aspect of the present invention provides a use of a time-indicating label. When the label uses an oxidation discoloration rate regulator MnO2 nanoparticles and a high molecular polymer film polydimethylsiloxane film, it is used for products with a short use cycle; when the label uses an oxidation discoloration rate regulator SiO2 nanoparticles and a high molecular polymer film polyvinylidene fluoride film, it is used for products with a long use cycle.

[0017] The present invention has the following beneficial effects: 1. The label for time indication of the present application uses nano-metal particles, oxidation discoloration rate regulator, degradable polymer matrix and high molecular polymer film with different oxygen permeability rates as raw materials. Unlike the traditional metal film, which generates a stable passivation layer due to oxidation discoloration, the nano-metal material has a high specific surface area and high oxidation activity, and its oxidation rate is not restricted by the passivation layer. At the same time, after the high molecular polymer film is coated with the nano-metal particles, the film is controlled to have a stable oxygen permeability rate, providing a stable oxygen environment for the label, so that the oxidation discoloration process of the label can be accurately controlled, and it is approximately linearly positively correlated with the air contact time, and has a stable and accurate product use time indication function. After consumers recognize the color of the label, they can know its current use time, and combined with the material of the product itself, they can get corresponding usage suggestions. It is simple and convenient for consumers to use and the information obtained is more intuitive.

[0018] 2. The label for time indication of the present application has an oxidative color-changing film inside for achieving oxidative color change, and an oxygen-permeable regulating layer outside for ensuring a stable oxygen environment. In order to highlight the time indication function of the oxidative color-changing film, it is combined with the label substrate, and the visual effect of the oxidative color-changing film is better.

[0019] 3. Compared with conventional ordinary metal films, the nano-metal particles used in the time indication label of the present application have a high specific surface area and high oxidation activity, which can ensure that the oxidation color change response speed is faster and more stable, and the oxidation color change process is linearly positively correlated with the air contact time, thereby improving the accuracy of the label time indication effect. The nano-metal particles are mixed with a degradable polymer matrix to prevent the metal particles from aggregating, making the color of the color change process more uniform.

[0020] 4. The high molecular polymer film of the label for time indication of the present application completely covers the oxidative color film and the label substrate, and serves as the oxygen permeability regulating layer of the label, thereby ensuring that the oxidative color film is at a stable low level of oxygen concentration, and also providing physical protection for it.

[0021] 5. The smart label with time indication function of the label for time indication of the present application adopts a multi-layer structure design. The high molecular polymer film not only protects and isolates the core material oxidative discoloration film, but also can extend or shorten the discoloration period of the label by selecting and designing the film oxygen permeability and oxidative discoloration rate regulator. It can be used for products with a short usage period of less than 15 days, such as fresh food, food, and medicine, and can also be used for products with a long usage period of less than 60 days, such as activated carbon, filter elements, and cosmetics. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The diagram is a schematic diagram of an exploded structure of a label for time indication according to the present invention.

[0023] Figure 2 It is a structural schematic diagram of a label body of a label for time indication of the present invention.

[0024] Figure 3 The present invention is a schematic structural diagram of a label for time indication applied to a commodity with a short use period.

[0025] Figure 4 for Figure 3 Schematic diagram of the structure of the oxidative color film after oxidation color change.

[0026] Figure 5 The present invention is a schematic structural diagram of a label for time indication applied to a commodity with a long use period.

[0027] Figure 6 It is a comparison chart of the oxidation discoloration rate test results of Example 1 of the present invention and Comparative Example 1 in air.

[0028] Figure 7 This is a comparison chart of the oxidation discoloration rate test results of the labels prepared in Example 1 and Example 2 of the present invention in the air.

[0029] In the figure, there is a label body 13 , a comparison color strip 131 , an oxidative color-changing film 12 , and an oxygen permeability regulating layer 11 . DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and with reference to data. It should be understood that the embodiments are only for illustrating the present invention and are not intended to limit the scope of the invention in any way.

[0031] like Figure 1In one embodiment shown, a label for time indication provided by the present invention includes a label body 13, an oxidized color-changing film 12 disposed on the front of the label body 13, and two layers of oxygen permeability regulating layers 11 covering the label body 13 and the oxidized color-changing film 12 from top to bottom; like Figure 2 As shown, in this embodiment, a comparison color strip 131 is provided on the back of the label body 13, and the corresponding colors of the oxidation color film at each stage of oxidation color change over time are distributed in sequence from left to right on the comparison color strip; the color of the oxidation color film 12 in the initial stage is as shown in FIG. Figure 3 As shown, the color of the oxidation color-changing film 12 in the final stage is as follows Figure 4 As shown, the user can know the oxidation discoloration time of the oxidation discoloration film by comparing the colors of the oxidation discoloration film 12 at various stages and the corresponding colors on the color bar 131.

[0032] The oxidation discoloration film is uniformly distributed with metal nanoparticles and an oxidation discoloration rate regulator, wherein the oxidation discoloration rate regulator can regulate the oxidation rate of the metal nanoparticles, that is, accelerate the oxidation discoloration rate of the metal nanoparticles, or slow down the oxidation discoloration rate of the metal nanoparticles. The oxygen permeability regulating layer is a transparent high molecular polymer film with oxygen permeability. The label is placed in an oxygen-free environment before use, for example, by an aluminum film oxygen-proof seal, or placed in a nitrogen-filled environment.

[0033] In one embodiment, the metal nanoparticles are iron nanoparticles.

[0034] In one embodiment, the metal nanoparticles are copper nanoparticles.

[0035] In one embodiment, the metal nanoparticles are zinc nanoparticles.

[0036] In one embodiment, the metal nanoparticles have a particle size of 50-200 nm.

[0037] In one embodiment, the thickness of the oxidative discoloration film is 50-150 μm.

[0038] In one embodiment, the oxidative discoloration rate regulator includes MnO2 nanoparticles that accelerate the oxidation rate of metal nanoparticles. In one embodiment, the oxidative discoloration rate modifier includes SiO2 nanoparticles that slow down the oxidation rate of metal nanoparticles.

[0039] In one embodiment, the material of the high molecular polymer film is polydimethylsiloxane.

[0040] In one embodiment, the material of the high molecular polymer film is polyvinylidene fluoride.

[0041] The present invention also provides a method for preparing a label, comprising the following steps: Step 1, preparing an oxidative discoloration film: uniformly dispersing metal nanoparticles and an oxidative discoloration rate regulator in a degradable polymer matrix containing a volatile solvent, wherein the mass ratio of the metal nanoparticles to the degradable polymer matrix is ​​3:7; then adding 1wt% of a magnesium stearate crystal form controller and 0.5wt% of a dispersant; continuing to stir to obtain a mixed solution; and spreading the mixed solution on a glass substrate under an inert gas environment by a solution casting method, wherein the volatile solvent gradually evaporates to form an oxidative discoloration film; Step 2, using hot pressing to laminate the oxidative color-changing film obtained in step 1 onto one side surface of the label body to obtain a composite layer; it can also be laminated by means of an adhesive, and the specific lamination method is not limited here.

[0042] Step 3, through a hot pressing packaging method, the high molecular polymer film completely covers the composite layer prepared in step 2 to prepare a label.

[0043] In one embodiment, the degradable polymer matrix in step 1 is polylactic acid.

[0044] In one embodiment, the degradable polymer matrix in step 1 is a polylactic acid matrix.

[0045] In one embodiment, the degradable polymer matrix in step 1 is polycaprolactone.

[0046] In one embodiment, the volatile solvent in step 1 is ethanol.

[0047] In one embodiment, the material of the label body includes polyester film.

[0048] In one embodiment, the material of the label body includes polyethylene film.

[0049] In one embodiment, the material of the label body includes polypropylene film.

[0050] In one embodiment, the material of the label body includes coated paper.

[0051] In one embodiment, the material of the tag body includes a metal film.

[0052] In one embodiment, the material of the label body includes fiber nonwoven fabric.

[0053] In one embodiment, the high molecular polymer film in step 3 includes polydimethylsiloxane.

[0054] In one embodiment, the high molecular polymer film in step 3 includes polyvinylidene fluoride.

[0055] Example 1 Step 1: Prepare an oxidative discoloration film with a thickness of 100 μm: Disperse copper powder with a particle size of 100 nm in a polylactic acid matrix at a mass ratio of 3:7, add 0.5 wt% of MnO2 nanoparticles, stir to mix evenly, add 1 wt% of magnesium stearate crystal form controller and 0.5 wt% of PVP dispersant, and continue stirring for 30 minutes to obtain a mixed solution. The mixed solution is spread on a glass substrate under an inert gas environment by solution casting, and the ethanol solvent gradually evaporates to form an oxidative discoloration film. The polylactic acid matrix is ​​composed of 10 wt% polylactic acid and 90 wt% ethanol. To ensure uniform film thickness, a coater can be used to evenly spread the mixed solution.

[0056] Step 2: Use the hot pressing method to heat the prepared oxidized color-changing film at 120℃ and 0.5MPa for 7s to combine it with the label substrate PET film; after the hot pressing is completed, cool it at room temperature to ensure stable adhesion. The back of the label substrate PET film is printed with color reference marks and QR codes in advance using segmented color strips. By comparing the reference marks, the current usage time of the product can be identified.

[0057] Step 3: Use a polydimethylsiloxane (PDMS) film with a high oxygen permeability coefficient as the oxygen permeability regulating layer, and use hot pressing packaging to completely cover the oxidative color-changing film and the label substrate. The packaging process temperature is 120°C, the pressure is 0.5MPa, and the hot pressing is 8s. After packaging, a smart label with a time indication function is obtained, which is suitable for fresh food, food, medicine and other products with a short usage cycle of less than 15 days.

[0058] Example 2 Step 1: Prepare an oxidative discoloration film with a thickness of 100 μm: Disperse copper powder with a particle size of 100 nm in a polylactic acid matrix at a mass ratio of 3:7, add 0.5wt% of SiO2 nanoparticles, stir to make it uniformly mixed, add 1wt% of magnesium stearate crystal form controller and 0.5wt% of PVP dispersant, continue stirring for 30 minutes to obtain a mixed solution. By solution casting, the mixed solution is spread on a glass substrate under an inert gas environment, and the ethanol solvent gradually evaporates to form an oxidative discoloration film. Wherein the polylactic acid matrix is ​​composed of 10wt% polylactic acid and 90wt% ethanol. To ensure uniform film thickness, a film applicator can be used to evenly spread the mixed solution.

[0059] Step 2: Use the hot pressing method to heat the prepared anodized color-changing film at 120°C and 0.5MPa for 7s to combine it with the label base polyethylene film; after the hot pressing is completed, cool it at room temperature to ensure stable adhesion. The back of the label base polyethylene film is printed with color reference marks and QR codes in advance using segmented color strips. The current usage time of the product can be identified by comparing the reference marks.

[0060] Step 3: Use a polyvinylidene fluoride film with a low oxygen permeability coefficient as the oxygen permeability regulating layer, and use hot pressing packaging to completely cover the oxidative color-changing film and the label substrate. The packaging process temperature is 120°C, the pressure is 0.5MPa, and the hot pressing is 8s. After packaging, a smart label with a time indication function is obtained, which is suitable for products with a long usage cycle of less than 60 days, such as activated carbon, filter elements, and cosmetics.

[0061] Comparative Example 1 On the basis of Example 1, the oxidative color-changing film is replaced by a copper metal film, as follows.

[0062] Step 1: Prepare a copper metal film with a thickness of 100 μm.

[0063] Step 2: Using the hot pressing method, heat the prepared metal film at 120°C and 0.5MPa for 7s to combine it with the label substrate PET film; after hot pressing, cool it at room temperature to ensure stable bonding.

[0064] Step 3: Use a polydimethylsiloxane (PDMS) film with a high oxygen permeability coefficient as the oxygen permeability regulating layer, and use hot pressing packaging to completely cover the oxidative color-changing film and the label substrate. The packaging process temperature is 120°C, the pressure is 0.5MPa, and the hot pressing is 8s. After packaging, a label with a time indication function is obtained.

[0065] Comparative test of oxidation discoloration rate of Example 1 and Comparative Example 1 The two groups of labels prepared in step 3 of Example 1 and step 2 of Comparative Example 1 were measured using a colorimeter LS171 under standard light source D65 for the initial color values ​​of the oxidation-discolored films of the two labels, and the chromaticity parameters such as L, a, and b were recorded. The measurement was repeated every day according to the above method, and the color difference value ΔE of the two labels during the oxidation process was calculated according to the color difference formula; The comparison results of oxidation discoloration process are as follows Figure 6 As shown, the color difference value ΔE of the ordinary copper metal film label prepared according to Comparative Example 1 is about 2.5 after being exposed to the air for 1 day, and the color difference value can only reach 29.24 after being exposed for 17 days. The whole oxidation discoloration process shows an obvious trend of first fast and then slow; the color difference value ΔE of the time indication label prepared by using nano metal particles in step 3 of Example 1 is about 4.28 after being exposed for 1 day, and the color difference value can reach 52.31 after being exposed for 17 days. The whole oxidation discoloration process basically shows a linear increase trend. This shows that the oxidation discoloration film prepared by mixing nano metal particles, catalysts and degradable polymers has a more stable oxidation discoloration process and a more accurate time indication function.

[0066] The present invention also provides a design method for a time-indicating label, which adjusts the activity of the oxidation discoloration rate regulator catalyst and the oxygen permeability of the oxygen permeability regulating layer, thereby adjusting the indication period of the label.

[0067] In one embodiment, when a shorter indication period is required, active oxidation discoloration rate regulator MnO2 nanoparticles and a high molecular polymer film polydimethylsiloxane (PDMS) film with a high oxygen permeability are selected, and the indication period of the label is short; when a longer indication period is required, inert oxidation discoloration rate regulator SiO2 nanoparticles and a high molecular polymer film polyvinylidene fluoride film with a low oxygen permeability are selected, and the indication period of the label is long.

[0068] Comparative test of oxidation discoloration rate of Example 1 and Example 2 The two groups of labels prepared in step 3 of Example 1 and step 3 of Example 2 are measured using a colorimeter under a standard light source for the initial color values ​​of the oxidation-discolored films of the two labels, and the chromaticity parameters such as L, a, and b are recorded. The measurement is repeated every day according to the above method, and the color difference value ΔE of the two labels during the oxidation process is calculated according to the color difference formula; The comparison results of oxidation discoloration process are as follows Figure 7 As shown, according to Example 1, the label made of active oxidation discoloration rate regulator MnO2 nanoparticles and high oxygen permeability polydimethylsiloxane (PDMS) film as the oxygen permeability regulating layer, the color difference value ΔE is about 4.31 after exposure to air for 1 day, and the color difference value can reach 50 after exposure for 15 days, and then basically remains stable as time increases; Example 2 selects inert oxidation discoloration rate regulator SiO2 nanoparticles and low oxygen permeability polyvinylidene fluoride film as the oxygen permeability regulating layer to make the label, the color difference value ΔE is about 0.85 after exposure to air for 1 day, and the color difference value can reach 52 after exposure for 60 days, and the whole oxidation discoloration process basically shows a linear increase trend. This shows that by using different oxidation discoloration rate regulator catalyst activity and oxygen permeability polymer film as the oxygen permeability regulating layer of the label, the length of the oxidation discoloration cycle of the label can be regulated, thereby developing a time indication label for use on commodities with different usage cycles.

[0069] The invention also discloses a use of a time indicating label. When labeling, active oxidative discoloration rate regulator MnO2 nanoparticles and high oxygen permeability polymer film polydimethylsiloxane (PDMS) film are used, which are used for products with short use cycles.

[0070] like Figure 3As shown in the application effect diagram of smart labels, smart labels use high molecular polymer films as oxygen permeability control layers to control the oxygen concentration entering the label, extend or shorten the label's color change cycle, and realize the time indication function for products with different usage cycles. For example, using highly oxygen permeable polymer films such as polydimethylsiloxane as oxygen permeability control layers to completely cover the oxidative color-changing film and label substrate, the label has a short color change cycle and can be applied to fresh food, food, medicine and other products with a short usage cycle of less than 15 days; When the label uses inert oxidation discoloration rate regulator SiO2 nanoparticles and low oxygen permeability high molecular polymer film polyvinylidene fluoride film, it is used for products with a long use cycle.

[0071] like Figure 5 , using low oxygen permeability polymer films such as polyvinylidene fluoride as the oxygen permeability regulating layer to completely cover the oxidative color-changing film and label substrate. The label has a long oxidative color-changing cycle and can be applied to products with a long usage cycle of less than 60 days, such as activated carbon, filter elements, and cosmetics.

[0072] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A label for time indication, characterized in that: It comprises a label body, an oxidative color-changing film arranged on one side of the label body, and an oxygen permeability regulating layer covering the label body and the oxidative color-changing film; The label body is provided with a comparison color strip, on which the corresponding colors of the oxidation-chromic film at various stages of oxidation-chromic change over time are distributed in sequence from left to right; The oxidative discoloration film is uniformly distributed with metal nanoparticles and an oxidative discoloration rate regulator; The oxygen permeability regulating layer is a high molecular polymer film with oxygen permeability.

2. The label for time indication as claimed in claim 1, characterized in that: The metal nanoparticles include any one of iron nanoparticles, copper nanoparticles and zinc nanoparticles.

3. The label for time indication as claimed in claim 1, characterized in that: The particle size of the metal nanoparticles is 50-200 nm.

4. The label for time indication as claimed in claim 1, characterized in that: The thickness of the oxidation color-changing film is 50-150 μm.

5. The label for time indication as claimed in claim 1, characterized in that: The oxidation discoloration rate regulator includes any one of MnO2 nanoparticles and SiO2 nanoparticles.

6. The label for time indication as claimed in claim 1, characterized in that: The material of the polymer transparent film includes any one of polydimethylsiloxane and polyvinylidene fluoride.

7. The method for preparing a label for time indication according to claim 1, characterized in that: The steps include: Step 1, uniformly dispersing metal nanoparticles and an oxidative discoloration rate regulator in a polylactic acid matrix containing a volatile solvent, wherein the mass ratio of the metal nanoparticles to the degradable polymer matrix is ​​3:7; then adding 1wt% of a magnesium stearate crystal form controller and 0.5wt% of a dispersant; continuing to stir to obtain a mixed solution; and spreading the mixed solution on a glass substrate under an inert gas environment by a solution casting method, wherein the volatile solvent gradually evaporates to form an oxidative discoloration film; Step 2, compounding the oxidative color-changing film obtained in step 1 onto one side surface of the label body to obtain a composite layer; Step 3, through a hot pressing packaging method, the high molecular polymer film completely covers the composite layer prepared in step 2 to prepare a label.

8. The method for preparing a label for time indication according to claim 7, characterized in that: In the step 1, the polylactic acid matrix consists of 10 wt % polylactic acid and 90 wt % ethanol.

9. The method for preparing a label for time indication according to claim 7, characterized in that: The material of the label body includes any one of polyester film, polyethylene film, polypropylene film, coated paper, metal film and fiber nonwoven fabric.

10. The method for designing a label for time indication according to claim 1, characterized in that: The indication period of the label is adjusted by adjusting the activity of the oxidation discoloration rate regulator and the oxygen permeability of the oxygen permeability regulating layer.

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