A method of making and using a 3D printed crystal violet lactone temperature monitoring label

Abstract

The application discloses a preparation method and use method of a 3D-printed crystal violet lactone temperature monitoring label, and belongs to the technical field of material synthesis and indication products. The application provides a preparation method of a 3D-printed crystal violet lactone temperature monitoring label, utilizes specific temperature phase state changes of an acid solvent and acid color developing principles of crystal violet lactone, and realizes monitoring of different temperature thresholds; the application combines 3D printing technology, and designs a label for temperature monitoring; the temperature monitoring label has the advantages of simple preparation process, controllable preparation cost, and customized production according to actual monitoring requirements, and is suitable for temperature monitoring requirements in multiple scenes. The temperature monitoring label can provide real-time visual signal responses for temperature changes of a transportation and storage environment through color changes of an inner circle.

Description

Technical Field

[0001] This invention relates to a method for preparing and using a 3D-printed crystal violet lactone temperature monitoring tag, belonging to the technical field of material synthesis and indicator products. Background Technology

[0002] Temperature monitoring is a core and crucial link in ensuring food safety and quality. Its essence lies in the precise control and full traceability of temperature throughout the entire food storage, transportation, and sales chain. Most fresh foods, dairy products, vegetables, and other categories are extremely sensitive to temperature fluctuations. Even short-term deviations from the suitable preservation temperature range can easily lead to problems such as the proliferation of microorganisms, oxidation and loss of nutrients, and rapid deterioration of inherent flavor. This not only significantly reduces the edible value and commercial attributes of the food but may also induce foodborne safety risks, posing a potential threat to consumer health.

[0003] Traditional temperature monitoring methods rely heavily on electronic sensors and temperature recorders. While they can record temperature data continuously, they generally suffer from significant drawbacks such as high hardware costs, cumbersome installation and operation, inability to provide intuitive feedback on whether the temperature exceeds the standard, and difficulty in monitoring and tracing individual food items independently. They are particularly unsuitable for scenarios such as bulk food, short-distance delivery, and small-batch circulation, making it difficult to meet the food industry's practical application needs for temperature monitoring that is "low-cost, visual, wide-coverage, and traceable."

[0004] Crystal violet lactone, a classic leuco dye, owes its core color-changing properties to a molecular structural transformation induced by an acidic environment. A generalized Lewis acid (a proton or metal cation of a weak acid) abstracts electrons from crystal violet lactone, inducing ring-opening and thus expanding its conjugated system to produce color. The literature "Irreversible temperature indicator-based cellulose membranes conjugated with leuco-dye pigment" discloses the preparation of a thermochromic bilayer membrane using cellulose acetate, crystal violet lactone, and salicylic acid, exhibiting irreversible color changes. However, this method only works at fixed temperature points (15 °C or 35 °C), failing to provide a simple method for multi-threshold, serialized temperature monitoring, or sub-zero temperature monitoring, making it unsuitable for end-to-end temperature monitoring from refrigeration to ultra-low temperature freezing. Furthermore, this structure has significant shortcomings in practical applications. The acid must diffuse through the upper membrane to contact and trigger the color-developing layer; this process is inefficient and highly dependent on the tightness of the membrane adhesion, resulting in delayed color response, uneven color change, and weak intensity.

[0005] With the continuous innovation of intelligent manufacturing technology, 3D printing technology has gained widespread application and rapid development in the field of functional device fabrication due to its significant advantages such as flexible customization, high molding accuracy, low material cost, and simple production process. However, there are currently few applications of 3D printing technology in temperature detection labels.

[0006] Therefore, developing a 3D-printed crystal violet lactone temperature monitoring tag that can adjust the temperature detection range according to actual application scenarios has extremely high practical and economic value. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a method for fabricating a 3D-printed crystal violet lactone temperature monitoring tag. Utilizing the phase change of an acidic solvent at a specific temperature and the acidic color development principle of crystal violet lactone, a specific temperature threshold can be monitored. Combined with 3D printing technology, a tag for temperature monitoring is designed. The temperature monitoring tag provided by this invention features a simple fabrication process, controllable manufacturing costs, and can be customized to meet specific monitoring needs, adapting to various temperature monitoring scenarios. The temperature monitoring tag of this invention provides a real-time visual signal response to changes in the temperature of the transportation and storage environment through changes in the color of its inner circle.

[0008] The first objective of this invention is to provide a method for using a 3D-printed crystal violet lactone temperature monitoring label, which monitors the runaway status of product storage temperature by measuring the proportion of discolored area in the inner circle of the 3D-printed crystal violet lactone temperature monitoring label.

[0009] If the discoloration area of ​​the inner circle is less than 15%, it indicates that the product storage temperature is not out of control and the product storage is stable.

[0010] If the discoloration area of ​​the inner circle is 15% to 20%, it indicates that the product storage temperature fluctuates, and it is necessary to confirm whether the product quality has deteriorated.

[0011] If the discoloration area of ​​the inner circle is greater than 20%, it indicates that the product storage temperature is out of control and the product quality has deteriorated irreversibly.

[0012] The preparation method of the 3D printed crystal violet lactone temperature monitoring tag includes the following steps:

[0013] (1) Cellulose acetate is dissolved in acetone and heated and stirred to obtain a cellulose acetate-acetone solution; after cooling the cellulose acetate-acetone solution, crystal violet lactone is added, and after stirring, glycerol is added and stirred to obtain a mixed solution; the mixed solution is poured into the inner circular area of ​​the label mold to form a film;

[0014] (2) The acidic solution was frozen and sealed in the outer ring area of ​​the label mold to obtain a 3D printed crystal violet lactone temperature monitoring label;

[0015] The label mold is an integrated mold made by 3D printing technology. Its structure includes an inner circular area, an inclined surface and an outer ring area. The inner circular area and the outer ring area are connected by the inclined surface. The radius of the inner circular area is 6~8 mm, the ring width of the outer ring area is 5~7 mm, the slope ratio of the inclined surface at the connection is 1:0.8~1.2, and the slope angle is 40°~50°.

[0016] The acidic solution is methacrylic acid, an acidic binary mixed solvent consisting of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid, or an acidic aqueous solution of ethylene glycol adjusted by dilute hydrochloric acid.

[0017] The product storage temperature is monitored to be between -68℃ and 15℃.

[0018] In one implementation, the out-of-control status of ambient temperature is monitored by the proportion of the inner circle discoloration area in a 3D-printed crystal violet lactone temperature monitoring label.

[0019] Slight discoloration of the inner circle (area <15%): This indicates that the temperature fluctuation was slight and short-lived, and the product under these storage conditions is within the acceptable range.

[0020] Localized color development (area 15%~20%): This indicates that the product has experienced a certain period of temperature runaway and has reached the critical window for quality and safety under these storage conditions, requiring attention.

[0021] Significant color development / complete color change (area > 20%): This indicates that the product is under clear high temperature exposure risk. The product has experienced severe or prolonged temperature runaway under these storage conditions, and its quality has deteriorated irreversibly. Continued use is not recommended.

[0022] The preparation method of the 3D printed crystal violet lactone temperature monitoring tag includes the following steps:

[0023] (1) Cellulose acetate is dissolved in acetone and heated and stirred to obtain a cellulose acetate-acetone solution; after cooling the cellulose acetate-acetone solution, crystal violet lactone is added, and after stirring, glycerol is added and stirred to obtain a mixed solution; the mixed solution is poured into the inner circular area of ​​the label mold to form a film;

[0024] (2) The acidic solution was frozen and sealed in the outer ring area of ​​the label mold to obtain a 3D printed crystal violet lactone temperature monitoring label;

[0025] The label mold is an integrated mold made by 3D printing technology. Its structure includes an inner circular area and an outer ring area. The radius of the inner circular area is 6~8 mm, the ring width of the outer ring area is 5~7 mm, the slope ratio of the connecting surface is 1:0.5~1.8, and the slope angle is 30°~60°.

[0026] In one embodiment, the slope angle is 40° to 50°, and the slope ratio is 1:0.8 to 1.2.

[0027] In one implementation, the slope ratio is 1:0.58 when the slope angle is 30°; 1:1 when the slope angle is 45°; and 1:1.73 when the slope angle is 60°.

[0028] In one embodiment, the temperature monitoring range is changed by altering the acidic solution; the acidic solution includes methacrylic acid, an acidic binary mixed solvent consisting of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid, and an acidic aqueous solution of ethylene glycol adjusted by dilute hydrochloric acid.

[0029] Among them, when the 3D-printed crystal violet lactone temperature monitoring tag is used to monitor 15℃, the acidic solution is methacrylic acid;

[0030] When the 3D-printed crystal violet lactone temperature monitoring tag is used to monitor 4°C, the acidic solution is a binary mixed solvent composed of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid.

[0031] When 3D-printed crystal violet lactone temperature monitoring tags are used to monitor temperatures from -0 to -68 ℃, the acidic solution is an aqueous solution of ethylene glycol adjusted with dilute hydrochloric acid.

[0032] In one embodiment, the volume fraction of tetradecane in the binary mixed solvent is 48% to 52%;

[0033] The volume fraction of ethylene glycol in the ethylene glycol aqueous solution adjusted with dilute hydrochloric acid is 0-100%.

[0034] In one embodiment, the ratio of cellulose acetate, acetone, crystal violet lactone and glycerol in step (1) is 1~3 g: 20~50 mL: 0.25~1 g: 500~1000 mL.

[0035] In one embodiment, the heating and stirring in step (1) is at 65~75°C and 400~800 rpm for 10~30 min.

[0036] In one embodiment, the amount of mixed solution used in step (1) is 0.5~2 mL.

[0037] In one embodiment, the amount of acidic solution packaged in step (2) is 0.5~1.5 mL.

[0038] The second objective of this invention is to provide a method for preparing a 3D-printed crystal violet lactone temperature monitoring tag, comprising the following steps:

[0039] (1) Cellulose acetate is dissolved in acetone and heated and stirred to obtain a cellulose acetate-acetone solution; after cooling the cellulose acetate-acetone solution, crystal violet lactone is added, and after stirring, glycerol is added and stirred to obtain a mixed solution; the mixed solution is poured into the inner circular area of ​​the label mold to form a film;

[0040] (2) The acidic solution was frozen and sealed in the outer ring area of ​​the label mold to obtain a 3D printed crystal violet lactone temperature monitoring label;

[0041] The label mold is an integrated mold made by 3D printing technology. Its structure includes an inner circular area, a slope and an outer ring area. The inner circular area and the outer ring area are connected by the slope. The radius of the inner circular area is 6~8 mm, the ring width of the outer ring area is 5~7 mm, the slope ratio of the slope at the connection is 1:0.5~1.8, and the slope angle is 30°~60°.

[0042] The acidic solution is a mixture of methacrylic acid, a binary acidic solvent consisting of tetradecane and octanoic acid adjusted with dilute hydrochloric acid, or an acidic aqueous solution of ethylene glycol adjusted with dilute hydrochloric acid.

[0043] In one implementation, the slope ratio is 1:0.58 when the slope angle is 30°; 1:1 when the slope angle is 45°; and 1:1.73 when the slope angle is 60°.

[0044] In one embodiment, the temperature monitoring range is changed by altering the acidic solution; the acidic solution includes methacrylic acid, an acidic binary mixed solvent consisting of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid, and an acidic aqueous solution of ethylene glycol adjusted by dilute hydrochloric acid.

[0045] Among them, when the 3D-printed crystal violet lactone temperature monitoring tag is used to monitor 15℃, the acidic solution is methacrylic acid;

[0046] When the 3D-printed crystal violet lactone temperature monitoring tag is used to monitor 4°C, the acidic solution is a binary mixed solvent composed of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid.

[0047] When 3D-printed crystal violet lactone temperature monitoring tags are used to monitor temperatures from -0 to -68 ℃, the acidic solution is an aqueous solution of ethylene glycol adjusted with dilute hydrochloric acid.

[0048] In one embodiment, the volume fraction of tetradecane in the binary mixed solvent is 48% to 52%;

[0049] The volume fraction of ethylene glycol in the ethylene glycol aqueous solution adjusted with dilute hydrochloric acid is 0-100%.

[0050] In one embodiment, the ratio of cellulose acetate, acetone, crystal violet lactone and glycerol in step (1) is 1~3 g: 20~50 mL: 0.25~1 g: 500~1000 mL.

[0051] In one embodiment, the heating and stirring in step (1) is at 65~75°C and 400~800 rpm for 10~30 min.

[0052] In one embodiment, the amount of mixed solution used in step (1) is 0.5~2 mL.

[0053] In one embodiment, the amount of acidic solution packaged in step (2) is 0.5~1.5 mL.

[0054] A third objective of this invention is to provide a 3D-printed crystal violet lactone temperature monitoring tag prepared by the above-described method.

[0055] A fourth objective of this invention is to provide the above-mentioned 3D-printed crystal violet lactone temperature monitoring tag for temperature monitoring applications during the transportation and storage of food, pharmaceuticals, or biological products.

[0056] Beneficial effects of the present invention

[0057] (1) This invention combines the specific temperature phase transition characteristics of acidic solvents with the acid-induced color development principle of crystal violet lactone to realize the monitoring of different temperature thresholds and provide intuitive and clear visual temperature warning signals.

[0058] (2) In this invention, the color change of the inner circle of the label is an irreversible process, which can effectively prevent the tampering of temperature monitoring data that may occur during food storage and transportation, and provide a more reliable basis for temperature monitoring.

[0059] (3) This invention relies on 3D printing technology to prepare label molds in an integrated manner. The process is simple and the cost is controllable. The shape, size and structure of the label can be flexibly adjusted according to actual monitoring needs, and it supports customized production for multiple scenarios and multiple temperature thresholds.

[0060] (4) This invention is applicable to temperature monitoring during food transportation and storage. It can be applied to food packaging through label design to reflect changes in ambient temperature in real time, play an early warning role in food quality, and ensure product quality and safety. Attached Figure Description

[0061] Figure 1 The images show a schematic diagram of the mold's half-section dimensions, the structure of the 3D-printed temperature monitoring label mold, and actual photos.

[0062] Figure 2 Images showing the color change of the crystal violet lactone film before and after being affected by an acidic reagent.

[0063] Figure 3 The images are scanning electron microscope (SEM) images of the color change of the crystal violet lactone membrane before and after being affected by an acidic reagent.

[0064] Figure 4 Infrared images showing the color change of the crystal violet lactone film before and after being affected by an acidic reagent.

[0065] Figure 5 DSC curve of methacrylic acid, an acidic solvent on the outer ring of a temperature monitoring tag at 15 ℃.

[0066] Figure 6 A schematic diagram of the construction of a temperature monitoring tag and an actual photo of a 15°C temperature monitoring tag placed at 4°C.

[0067] Figure 7 The color change of a 15°C temperature monitoring tag during a runaway temperature rise.

[0068] Figure 8 Images taken at different temperature points for a 15 ℃ temperature monitoring tag.

[0069] Figure 9 The results of temperature runaway monitoring for a 15 ℃ temperature monitoring tag.

[0070] Figure 10 DSC curve of the acidic solution on the outer ring of the temperature monitoring tag at 4 ℃.

[0071] Figure 11 Freezing point curves and phase diagrams of the acidic ethanol aqueous solution on the outer ring of the temperature monitoring tag from 0 to -68 ℃. Detailed Implementation

[0072] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0073] The integrated mold in this invention features a specific slope at the connection between the inner circle and the outer ring, creating an active, directional fluid channel. When the temperature reaches the threshold and the acid in the outer ring melts, this slope effectively guides the acid to flow rapidly and centrally towards the inner ring color-developing film, ensuring sufficient, uniform, and reproducible contact between the acid and the color-developing components, further enhancing the color development effect.

[0074] Compared to traditional molding and coating processes, 3D printing technology can precisely control the shape, thickness, and internal functional layer distribution of temperature monitoring tags according to the needs of actual application scenarios. This achieves uniform dispersion and precise arrangement of functional materials without the need for complex molds, effectively shortening the product development and mass production cycle. Furthermore, its flexible molding capabilities can adapt to the shape and usage requirements of different food packaging, successfully solving the technical pain points of traditional temperature tags, such as limited form, poor fit to packaging, and limited adaptability. Most importantly, combined with a flexibly replaceable acidic solution system, 3D printing technology provides an innovative and efficient way to conveniently produce a series of monitoring tags covering different temperature thresholds.

[0075] By combining the crystal violet color-changing principle with the precise design of 3D printed labels, temperature monitoring labels can be prepared. This ensures that the labels develop color quickly and stably when the critical temperature is reached, and the color traces are permanently retained. This provides an intuitive and accurate basis for judging whether the temperature exceeds the standard during the entire food transportation chain.

[0076] Raw materials used in the examples:

[0077] Cellulose acetate and crystal violet lactone were both purchased from Aladdin Reagent Network.

[0078] Test method:

[0079] Color change test

[0080] Acidic environment was created by adding methacrylic acid to the crystal violet lactone membrane, and the color development of the crystal violet lactone membrane under acidic conditions was photographed.

[0081] Temperature monitoring tags were placed in ambient temperature chambers, and the changes in the tags were recorded at different temperature points.

[0082] The prepared temperature monitoring tags were used to monitor the temperature in an ambient temperature chamber, and images of tag changes were recorded.

[0083] DSC curve testing:

[0084] DSC tests were performed on the externally acidic reagent methacrylic acid. The test conditions were: heating range of 0 ℃ to 30 ℃, test amount of 10 mg, heating rate and cooling rate of 10 ℃ / min, to investigate the thermodynamic phase transition characteristics of the prepared material.

[0085] Scanning electron microscopy tests:

[0086] The morphological changes of the crystal violet lactone membrane in both plane and cross-section before and after the color change were captured using a scanning electron microscope.

[0087] Infrared testing:

[0088] Infrared spectroscopy was used to characterize the crystal violet lactone membrane before and after the color change, and the changes in functional groups were investigated.

[0089] Example 1

[0090] 1. A 3D-printed crystal violet lactone temperature monitoring tag, the preparation method of which includes the following steps:

[0091] (1) Label mold design and printing:

[0092] A circular label mold was designed using Blender software. The mold consists of an inner circle and an outer ring. The radius of the inner circle is 6 mm, and the width of the outer ring is 5 mm. The slope ratio of the joint is 1:1, and the slope angle is 45° (see details). Figure 1 The mold features a guide ramp at the connection between the inner circle and the outer ring. This ramp guides the acidic solution from the outer ring to flow directionally towards the inner circle region when the solution melts, ensuring full contact with the temperature-sensitive film and thus optimizing the reliability and consistency of the colorimetric reaction. The mold is designed and 3D printed using polylactic acid material.

[0093] (2) Preparation of crystal violet lactone membrane:

[0094] 2.5 g of cellulose acetate was slowly added to 40 mL of acetone and stirred at 70 °C and 600 rpm for 10 min until the cellulose acetate was completely dissolved (forming a clear, slightly viscous solution), thus obtaining a cellulose acetate-acetone solution.

[0095] After cooling the cellulose acetate-acetone solution, add 0.25 g of crystal violet lactone, stir at 600 rpm for 30 min, add 500 μL of glycerol dropwise, and stir at 600 rpm for 24 h to obtain a mixed solution;

[0096] 1 mL of the mixed solution is poured evenly into the inner circular area of ​​the label mold, and gently shaken to level it and form a uniform thin layer; the mold is placed in a fume hood at room temperature, and after the acetone evaporates naturally for about 30 minutes, a crystal violet lactone film (white film) is formed.

[0097] (3) External ring solvent loading

[0098] Based on the temperature threshold (15 °C), methacrylic acid was selected as the outer ring acid solvent and frozen at -20 °C. It was then encapsulated in the outer ring area of ​​the label mold with a volume of 1 mL, resulting in a 3D-printed crystal violet lactone temperature monitoring label suitable for 15 °C.

[0099] 2. Performance testing of 3D-printed crystal violet lactone temperature monitoring tags

[0100] (1) Circular label mold

[0101] The structure and actual photos of the round label mold are as follows. Figure 1 As shown.

[0102] (2) Crystal violet lactone membrane

[0103] The crystal violet lactone membrane prepared in step 1 was used to construct an acidic environment by adding methacrylic acid. Colorimetric imaging, scanning electron microscopy, and infrared spectroscopy were then performed. The results are as follows:

[0104] Images showing the color change of the crystal violet lactone membrane before and after exposure to acidic reagents, as shown below. Figure 2 As shown, the results indicate that the crystal violet lactone film changed from white to blue-violet after the addition of methacrylic acid.

[0105] Scanning electron microscopy images of the crystal violet lactone membrane before and after exposure to acidic reagents are shown below. Figure 3 As shown, the results indicate that the surface morphology of the crystal violet lactone film changes significantly with the influence of environmental pH.

[0106] Infrared images of the crystal violet lactone membrane before and after exposure to acidic reagents, as shown below. Figure 4 As shown, the results indicate that the functional groups of the crystal violet lactone membrane undergo significant changes due to the influence of environmental pH, with the lactone undergoing ring-opening transformation into a carboxyl group.

[0107] (3) Methacrylic acid

[0108] The DSC curve of methacrylic acid is as follows Figure 5 As shown, the results indicate that the melting process of the material occurs between 10 and 20 °C, and a melting point of 15 °C can meet the requirements of subsequent experiments.

[0109] (4) Temperature monitoring tag

[0110] The prepared 3D-printed crystal violet lactone temperature monitoring tag, fabricated at 15℃, exhibits the following behavior: during a runaway temperature rise (prolonged exposure to temperatures exceeding 15℃), the outer ring solvent melts and diffuses into the inner circle, placing the crystal violet lactone film in an acidic environment and causing an irreversible color change from white to blue. A schematic diagram and actual photograph of the temperature monitoring tag construction are shown below. Figure 6 As shown.

[0111] A 3D-printed crystal violet lactone temperature monitoring tag, initially set at 15℃, was placed at 4℃ and 25℃, then recooled to 4℃. The changes were as follows: Figure 7 As shown in the figure. The results indicate that during the heating process, the prepared temperature monitoring tag changes from white to blue, and even after recooling, the prepared temperature monitoring tag remains blue, which can effectively prevent data tampering during the temperature monitoring process.

[0112] A 3D-printed crystal violet lactone temperature monitoring tag at 15℃ was placed in an ambient temperature test chamber heated from 14℃ to 26℃ at a rate of 2℃ / min. The color change of the tag during the heating process was recorded. The results are as follows: Figure 8 As shown in the figure. The results indicate that as the outer ring solvent melts, the inner circle of the label gradually changes from white to blue.

[0113] A 3D-printed crystal violet lactone temperature monitoring tag, initially set at 15℃, was placed under conditions of temperature runaway for testing. The results are as follows: Figure 9 As shown, as the temperature runaway process continues, the outer solvent gradually melts, and the inner circle of the label gradually changes from white to blue.

[0114] Based on the quantitative relationship between the discoloration area and the cumulative degree of temperature exposure, the following visual early warning classification for product quality and safety can be established:

[0115] Slight coloration (area <15%): This indicates that the product has experienced slight and brief temperature fluctuations, which are within an acceptable range.

[0116] Localized color development (area 15%~20%): This indicates that the product has experienced a certain period of temperature runaway and has reached the critical window for quality and safety, requiring attention.

[0117] Significant color development / complete color change (area > 20%): This indicates that the product is under clear high temperature exposure risk, has experienced severe or prolonged temperature runaway, and its quality may have undergone irreversible deterioration. Continued use is not recommended. Figure 9 A large area of ​​blue appeared in the middle after 3 hours.

[0118] Comparative Example 1

[0119] Based on Example 1, other 3D printing materials, acrylonitrile-butadiene-styrene and ethylene glycol-modified polyethylene terephthalate, were used to replace polylactic acid, while keeping the other steps the same, and the color development effect was tested.

[0120] The results showed that polylactic acid (PLA) exhibited excellent interlayer bonding and dimensional stability during the printing process, and the surface finish of its molded parts was significantly better than that of other comparative materials. The low warpage of this material effectively ensured the forming accuracy of large-sized components, while producing almost no irritating odor during printing, demonstrating its good environmental friendliness. Furthermore, PLA also possesses a certain degree of acid resistance, meeting the corrosion resistance requirements of subsequent experiments.

[0121] Labels printed using acrylonitrile-butadiene-styrene or ethylene glycol-modified polyethylene terephthalate as raw materials showed varying degrees of corrosion on the mold surface after the addition of an externally acidic solvent, making it impossible to continue the experiment.

[0122] In contrast, polylactic acid (PLA) was chosen because of its excellent chemical resistance to the acidic solution, ensuring the mold maintains structural integrity and dimensional stability throughout the experiment. PLA, a commonly used 3D printing material, also offers advantages such as high printing precision, good mechanical properties of the molded parts, low thermal deformation, and low-temperature resistance. It is particularly suitable for fabricating functional molds with intricate structures and requiring dimensional stability, and can also meet the needs of cryogenic monitoring. PLA itself is available in a variety of colors and transparency options (such as high transparency, white, or other colors), which helps to further enhance the visual contrast and warning effect of the labels.

[0123] Comparative Example 2

[0124] Based on Example 1, the stirring temperature in step (2) was changed to 50 ℃, 60 ℃ and 80 ℃ respectively, while the remaining steps remained the same as in Example 1, and the film effect was tested.

[0125] The results showed that when the heating and stirring temperature was 70℃, cellulose acetate had good solubility and was dispersed relatively evenly, forming a clear, slightly viscous solution.

[0126] In solutions prepared at 50℃ and 60℃, cellulose acetate did not dissolve completely, resulting in a white flocculent precipitate.

[0127] When the heating and stirring temperature is 80 ℃, acetone evaporates excessively, which affects the actual ratio of cellulose acetate-acetone solution, resulting in poor film formation and easy cracking on the film surface.

[0128] Comparative Example 3

[0129] Based on Example 1, other acids (acrylic acid) were used to replace methacrylic acid, while the remaining steps remained the same, and the color development effect was tested.

[0130] The results showed that acrylic acid could not effectively trigger the expected temperature monitoring function;

[0131] Because acrylic acid and methacrylic acid have significantly different physical properties, acrylic acid's melting point (approximately 13°C), while close, is slightly lower than the target threshold of 15°C, and it is also highly volatile. In practical applications, acrylic acid may partially evaporate or undergo a phase change before reaching the precise monitoring threshold, making accurate monitoring of the temperature threshold impossible.

[0132] Comparative Example 4

[0133] Temperature tags were prepared according to the method described in the literature "Irreversible temperature indicator based cellulose membranes conjugated with leuco-dye pigment".

[0134] Comparing the temperature labels of Example 1 and Comparative Example 4, the results show that the method described in Comparative Example 4, which is based on a literature method, produces a physically overlapping bilayer film structure, where the acid layer (containing solid acid and solvent) and the color-developing layer (CVL film) are only in surface contact. This structure has significant shortcomings in practical applications: its color development process relies on the passive diffusion of the acid through the upper film, which is inefficient and significantly affected by fluctuations in the tightness of the film adhesion, directly leading to response delays, uneven color development, and even failure. Furthermore, this mechanism is sluggish in its temperature response; after reaching the set temperature, a long diffusion process is required to trigger a color change, affecting the sensitivity to temperature response. Because the acid diffusion path is not fixed and is affected by environmental interference, the reliability of this structure's response to specific temperature thresholds is low, making it difficult to achieve the precise, rapid, and reproducible monitoring effect based on an integrated mold as described in Example 1.

[0135] The label in Example 1 features a specially designed sloped surface at the connection between the inner circle and the outer ring in its integrated mold, creating an active, directional fluid channel. When the temperature reaches the threshold and the acid in the outer ring melts, this slope effectively guides the acid to flow rapidly and centrally towards the inner ring color-developing film, ensuring sufficient, uniform, and reproducible contact between the acid and the color-developing components. This design physically overcomes the reliance on random diffusion in Comparative Example 4 and is a key structural innovation for achieving rapid start-up, high sensitivity, and reliable color development.

[0136] Comparative Example 5

[0137] A reversible temperature-sensitive material composed of crystal violet lactone and bisphenol A was prepared according to the patent (CN119060585B), and it was printed into a temperature label by means of a QR code ellipse.

[0138] Comparing the temperature labels of Example 1 and Comparative Example 5, the results show that there are fundamental differences in their monitoring mechanisms. The QR code label prepared in Comparative Example 5 relies on the reversible thermochromic properties of the crystal violet lactone-bisphenol A system; its irreversible mechanism is that the QR code pattern becomes blurred due to temperature rise, resulting in unrecognizable text. This is an indirect, functionally irreversible method based on graphic readability. This method is greatly affected by the viewing angle, lighting, pattern printing quality, and color contrast. In contrast, the label of Example 1 is based on the irreversible ring-opening chemical reaction of crystal violet lactone under acid, resulting in an intrinsic, objectively existing permanent color change, which is intuitive and reliable for interpretation.

[0139] Comparative Example 6

[0140] Based on Example 1, the slope of the inclined surface at the connection between the inner circle and the outer ring in the 3D printed mold was changed to 30° and 60°.

[0141] The results show that when the slope is 30°, the slope is too gentle and the driving force for liquid diffusion is insufficient, which directly leads to a lag in the color development response. The response time is delayed by 10 minutes compared with the actual temperature change.

[0142] When the slope is 60°, the slope is too steep, causing the acid to accumulate too quickly. The color development starts rapidly but the diffusion is uneven, and the color development area grows too fast in the early stage.

[0143] Example 2

[0144] Based on Example 1, a crystal violet lactone temperature monitoring tag suitable for 3D printing at 4°C was prepared, the difference being that the outer ring solvent was changed to an acidic binary mixed solvent composed of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid.

[0145] 1. External ring solvent loading

[0146] Based on the temperature threshold (4 ℃), tetradecane and n-octanoic acid were selected in different volume ratios to form an outer ring solvent, with tetradecane volume fractions of 48%, 50%, and 52%. The pH of the mixture was adjusted to less than 5 using 0.01 mol / L dilute hydrochloric acid, and confirmed using pH test paper. The prepared acidic solvent was frozen at -20℃ and then sealed in the outer ring area of ​​the label mold with a sealing volume of 1 ml, resulting in a crystal violet lactone temperature monitoring label suitable for 3D printing at 4 ℃.

[0147] 2. Performance Testing

[0148] DSC curves of acidic binary mixed solvents composed of tetradecane and n-octanoic acid in different volume ratios are shown below. Figure 10 As shown, the results indicate that the melting process of the material occurs between 0 and 10 °C. When the volume fraction of tetradecane is 50%, the melting point of the mixed solvent is closest to 4 °C. Using this acidic solution to prepare the temperature label can meet the requirements of subsequent experiments.

[0149] Example 3

[0150] Based on Example 1, a 3D-printed crystal violet lactone temperature monitoring tag suitable for various sub-zero temperatures (0~-68 °C) was prepared, the difference being that the outer ring solvent was changed to an ethylene glycol aqueous solution adjusted by dilute hydrochloric acid.

[0151] 1. External ring solvent loading

[0152] Based on different sub-zero temperature thresholds, ethylene glycol aqueous solutions were prepared, and the pH of the mixtures was adjusted to less than 5 using 0.01 mol / L dilute hydrochloric acid, confirmed using pH test paper. The prepared acidic solvent was frozen at -80 °C and sealed in the outer ring area of ​​the label mold with a sealing volume of 1 ml, resulting in 3D-printed crystal violet lactone temperature monitoring tags suitable for various sub-zero temperature points (0~-68 °C).

[0153] 2. Performance Testing

[0154] The freezing points of ethylene glycol-water mixtures with different volume fractions were determined using an ethylene glycol freezing point apparatus. The results are as follows: Figure 11 As shown in the figure. Experiments show that the freezing point of the solution decreases systematically with increasing ethylene glycol volume fraction, and its effective control range covers 0℃ to -68℃, allowing for precise selection of the appropriate solution ratio for the target temperature threshold.

[0155] For example, for a temperature threshold of -30℃, a 47.8% volume fraction of ethylene glycol aqueous solution can be used for subsequent experiments. Figure 11 The phase diagram analysis results provide further theoretical basis for determining the correspondence between freezing point and solution composition.

[0156] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for using a 3D-printed crystal violet lactone temperature monitoring tag, characterized in that, By using the proportion of discolored area in the inner circle of a 3D-printed crystal violet lactone temperature monitoring label, the uncontrolled state of product storage temperature can be monitored. If the discoloration area of ​​the inner circle is less than 15%, it indicates that the product storage temperature is not out of control and the product storage is stable. If the discoloration area of ​​the inner circle is 15% to 20%, it indicates that the product storage temperature fluctuates, and it is necessary to confirm whether the product quality has deteriorated. If the discoloration area of ​​the inner circle is greater than 20%, it indicates that the product storage temperature is out of control and the product quality has deteriorated irreversibly. The preparation method of the 3D printed crystal violet lactone temperature monitoring tag includes the following steps: (1) Cellulose acetate is dissolved in acetone and heated and stirred to obtain a cellulose acetate-acetone solution; after cooling the cellulose acetate-acetone solution, crystal violet lactone is added, and after stirring, glycerol is added and stirred to obtain a mixed solution; the mixed solution is poured into the inner circular area of ​​the label mold to form a film; (2) The acidic solution was frozen and sealed in the outer ring area of ​​the label mold to obtain a 3D printed crystal violet lactone temperature monitoring label; The label mold is an integrated mold made by 3D printing technology. Its structure includes an inner circular area, an inclined surface and an outer ring area. The inner circular area and the outer ring area are connected by the inclined surface. The radius of the inner circular area is 6~8 mm, the ring width of the outer ring area is 5~7 mm, the slope ratio of the inclined surface at the connection is 1:0.8~1.2, and the slope angle is 40°~50°. The acidic solution is methacrylic acid, an acidic binary mixed solvent consisting of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid, or an acidic aqueous solution of ethylene glycol adjusted by dilute hydrochloric acid. The product storage temperature is monitored to be between -68℃ and 15℃.

2. The method of use according to claim 1, characterized in that, By changing the acidic solution, the monitoring range of product storage temperature can be altered; Among them, when the storage temperature of the product detected by the 3D printed crystal violet lactone temperature monitoring label is 15℃, the acidic solution is methacrylic acid; When the storage temperature of the product detected by the 3D printed crystal violet lactone temperature monitoring label is 4℃, the acidic solution is a binary mixed solvent composed of tetradecane and n-octanoic acid adjusted by dilute hydrochloric acid. When the 3D-printed crystal violet lactone temperature monitoring label detects the product storage temperature of 0~-68 ℃, the acidic solution is an ethylene glycol aqueous solution adjusted by dilute hydrochloric acid.

3. The method of use according to claim 2, characterized in that, The volume fraction of tetradecane in the binary mixed solvent is 48%~52%; The volume fraction of ethylene glycol in an aqueous solution is 0-100%.

4. The method of use according to claim 1, characterized in that, In step (1), the ratio of cellulose acetate, acetone, crystal violet lactone and glycerol is 1~3 g: 20~50 mL: 0.25~1 g: 500~1000 mL.

5. The method of use according to claim 1, characterized in that, In step (1), the heating and stirring are carried out at 65~75℃ and 400~800 rpm for 10~30 min.

6. The method of use according to claim 1, characterized in that, The amount of mixed solution used in step (1) is 0.5~2 mL.

7. The method of use according to claim 1, characterized in that, In step (2), the amount of acidic solution packaged is 0.5~1.5 mL.

8. A method for preparing a 3D-printed crystal violet lactone temperature monitoring tag, characterized in that, Including the following steps: (1) Cellulose acetate is dissolved in acetone and heated and stirred to obtain a cellulose acetate-acetone solution; after cooling the cellulose acetate-acetone solution, crystal violet lactone is added, and after stirring, glycerol is added and stirred to obtain a mixed solution; the mixed solution is poured into the inner circular area of ​​the label mold to form a film; (2) The acidic solution was frozen and sealed in the outer ring area of ​​the label mold to obtain a 3D printed crystal violet lactone temperature monitoring label; The label mold is an integrated mold made by 3D printing technology. Its structure includes an inner circular area, an inclined surface and an outer ring area. The inner circular area and the outer ring area are connected by the inclined surface. The radius of the inner circular area is 6~8 mm, the ring width of the outer ring area is 5~7 mm, the slope ratio of the inclined surface at the connection is 1:0.8~1.2, and the slope angle is 40°~50°. The acidic solution is a mixture of methacrylic acid, a binary acidic solvent consisting of tetradecane and octanoic acid adjusted with dilute hydrochloric acid, or an acidic aqueous solution of ethylene glycol adjusted with dilute hydrochloric acid.

9. The 3D-printed crystal violet lactone temperature monitoring tag prepared by the preparation method of claim 8.

10. The application of the 3D-printed crystal violet lactone temperature monitoring tag of claim 9 in monitoring the transport and storage temperature of food, pharmaceuticals or biological products.

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