A method for intuitively visualizing the stretching amount of flexible adhesive tape

Abstract

This invention relates to the fields of functional materials and intelligent sensing technology, and discloses a method for intuitively visualizing the stretching amount of a flexible adhesive. The method includes: providing a flexible adhesive with an elastic substrate capable of elastic deformation along the stretching direction; setting multiple patterned marking regions corresponding to different preset stretching thresholds on the surface of the elastic substrate; forming microgroove structures with differentiated structural parameters at corresponding positions on the elastic substrate to generate a differentiated stress concentration effect; forming color-developing layers containing mechanochromic materials with different bulk crosslinking densities in each patterned marking region, with each color-developing layer collectively constituting a patterned color-developing functional layer; through the synergistic effect of the differentiated stress concentration effect of the microgroove structure and the difference in bulk crosslinking density of the color-developing layers, each patterned marking region changes from a hidden state to a visible state when the corresponding stretching threshold is reached, thereby characterizing the stretching amount of the flexible adhesive through pattern visualization. This invention provides clear thresholds and high readability, and is suitable for scenarios such as motion protection, flexible electronics, intelligent packaging, and structural condition early warning.

Description

Technical Field

[0001] This invention belongs to the field of functional materials and intelligent sensing technology, specifically relating to an intuitive visualization method for the stretching amount of flexible adhesive tape, and more particularly to a visualization method that, through the collaborative design of the local microstructure of the flexible adhesive tape and the patterned color-displaying functional layer, allows different patterned markings to appear sequentially under different stretching thresholds. Background Technology

[0002] Flexible adhesive tapes have wide applications in sports protection, rehabilitation therapy, flexible electronics, smart packaging, and stress warning systems. These products typically require appropriate stretching during use to ensure stable performance of their support, adhesion, monitoring, or warning functions. Current usage methods largely rely on operator experience, tactile estimation, or external testing equipment, which not only presents a high operational barrier but also lacks immediate, intuitive, and low-cost stretching feedback mechanisms.

[0003] Some existing technologies attempt to indicate stress states through color-changing coatings, shape changes, or additional sensing units, but significant limitations remain. For example, Chinese patent application CN201920072517.X uses a homogenized stretchable color-changing coating without multi-threshold indication; Chinese patent application CN201610183157.1 indicates elasticity through shape changes, lacks visual color display, and cannot determine multi-level stretching; Chinese patent application CN202122630801.4 only reflects stretching through the application of a color-changing film, without differentiated threshold design. In academic research, the temperature- and tension-sensitive dual-sensor color-changing patch developed by Smith JD et al. (2023) still relies on continuous color gradients to indicate tension, resulting in large subjective judgment errors; the multi-material inkjet printing mechanical color-changing pattern preparation technology developed by Mauron M et al. (2024) has not achieved differentiated control of the micromechanical environment of the color-changing unit. The specific shortcomings of existing technologies are as follows: schemes relying on continuous color gradation lack clear visual boundaries, resulting in significant subjective errors when users judge the stretching threshold; color-changing responses lack differentiated control over the micromechanical environment of the color-changing units, and color-changing coatings are mostly homogeneous designs with low information capacity, making it impossible to construct a multi-threshold stretching indication system; in addition, current color-changing schemes convey information almost entirely through color changes, which significantly reduces the recognizability of color changes in dimly lit environments with strong visual interference, and is extremely unfriendly to users with color vision impairments such as red-green color blindness. Summary of the Invention

[0004] The purpose of this invention is to provide a method for intuitively visualizing the stretching amount of flexible adhesive tape. By synergistically controlling the substrate micro-groove structure parameters and the cross-linking density of the color development layer in different pattern marking areas on the flexible adhesive tape, each pattern marking area is sequentially colored and displayed under different preset stretching thresholds, thereby enabling intuitive reading of the stretching amount of the flexible adhesive tape without the need for external equipment.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: This invention first identifies two or more preset stretch thresholds based on the intended use scenarios, allowable stretching range, and warning requirements of the flexible adhesive tape. Each preset stretch threshold is then mapped to a different pattern marking area on the flexible adhesive tape. Each pattern marking, such as the number "10," constitutes an independent pattern marking area with uniform microgroove structural parameters and cross-linking density of the color development layer. The pattern marking area can be numbers, letters, symbols, warning text, or other identifiable patterns. Preferably, it maintains low contrast or is hidden from the substrate in the unstretched state to avoid interfering with normal use. When the flexible adhesive tape is stretched to the corresponding threshold, the color development layer of the corresponding pattern marking area changes from a hidden state to a visible state, thereby enabling intuitive hierarchical reading of the stretching amount through the display order or display result.

[0006] As a further technical solution, in terms of structural design: This invention forms microgroove structures on an elastic substrate at positions corresponding to each pattern marking area, and assigns differentiated parameters to the microgroove structures in different areas. These differentiated parameters include, but are not limited to, one or more of the following: groove depth, groove width, groove spacing, groove length, cross-sectional shape, extension direction, and distribution density. These parameters can be adjusted according to a target stress concentration factor, which is negatively correlated with a preset tensile threshold; that is, the lower the threshold, the higher the required stress concentration factor. By designing these parameters in zones, different degrees of local stress concentration effects can be established in different areas during the stretching process of the flexible adhesive, causing the overall external stretching to preferentially transform into a local strain response within the pattern marking area. Typically, areas corresponding to lower preset tensile thresholds can employ deeper microgrooves, higher groove density, or geometries more conducive to stress concentration; areas corresponding to higher preset tensile thresholds employ relatively shallower, sparser, or less stress-concentrated microgroove structures, thus establishing the basis for the sequential triggering of different pattern areas.

[0007] As a further technical solution, in terms of material design: This invention provides a color-developing layer containing a mechanochromic material in each pattern marking area, and differentiates the bulk crosslinking density of the color-developing layers in different pattern marking areas. The bulk crosslinking density can be achieved by adjusting one or more of the polymer binder, crosslinking agent, diluent, filler, and curing conditions. Preferably, a color-developing layer with a lower bulk crosslinking density is provided for pattern marking areas with a lower preset tensile threshold to improve their color development sensitivity under localized strain; a color-developing layer with a higher bulk crosslinking density is provided for pattern marking areas with a higher preset tensile threshold to increase their color development trigger threshold. By differentiating the bulk crosslinking density of the color-developing layer in different areas, the color development threshold range between different pattern marking areas can be further widened.

[0008] As a further technical solution, in terms of quantitative design: Those skilled in the art can establish a model of the correspondence between the stress concentration factor, the cross-linking density of the color development layer and the target color development trigger threshold corresponding to the structural parameters of the micro-groove through finite element simulation or standardized pre-experimentation, thereby accurately guiding the parameter design of the pattern marking area corresponding to different preset stretching thresholds.

[0009] As a further technical solution, regarding process implementation: Microgroove structures can be first formed on an elastic substrate using methods such as laser etching, molding, photolithography, or screen printing etching. Then, color-developing layers are formed in corresponding areas using methods such as zone printing, spraying, scraping, or transfer printing. After drying and curing, a patterned color-developing functional layer is obtained. After preparation, threshold calibration of each pattern marking area can be performed using a standard stretching device. Under constant temperature and humidity conditions combined with pre-stretching cycles, the correspondence between microgroove structure parameters, cross-linking density of the color-developing layer, and pattern development threshold can be established to ensure that the flexible adhesive has good repeatability and readability in actual use.

[0010] As a further technical solution, based on the aforementioned structural design, material design, and process calibration, this invention does not rely solely on a single material color change to characterize the stretching amount. Instead, it transforms the continuously changing stretching process into a process of sequentially displaying patterns under multiple discrete thresholds through the synergistic regulation of the "local stress concentration effect of substrate micro-grooves" and the "difference in cross-linking density of the color-developing layer." Thus, a graded visual display of the stretching amount of flexible sheets can be achieved without introducing complex electronic components and external reading devices.

[0011] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention transforms the traditional continuous color gradient prompt into a discrete pattern display prompt triggered sequentially according to a threshold. Users do not need to rely on subjective judgment of color depth; they can directly identify the stretching range of the flexible patch based on whether the pattern appears and the order in which it appears, thereby improving the clarity and consistency of the reading results.

[0012] 2. By designing the microgroove structure parameters and the crosslinking density of the color development layer in a zoned and coordinated manner, this invention can construct two or more different stretching thresholds on the same flexible patch, which has a higher information carrying capacity and a stronger hierarchical indication capability than the traditional single color change indication method.

[0013] 3. Since this invention uses pattern display as the main form of information output, it can directly identify the stretching level using numbers, letters or symbols, or combine it with warning text to provide risk warnings. Therefore, compared with the solution that simply relies on color difference recognition, it is more friendly to people with color vision disorders, and still has a good recognition effect in low light, complex background or fast observation scenarios.

[0014] 4. This invention is mainly based on mature processes such as microstructure processing of elastic substrates, adjustment of conventional coating formulations, and partitioned printing and curing. The process path is clear, easy to be compatible with existing flexible film production processes, and has good manufacturability and prospects for large-scale application.

[0015] 5. This invention, through threshold calibration and parameter matching, can customize the trigger range according to different application scenarios, and is therefore suitable for medical stretch monitoring, rehabilitation assistance prompts, sports protection, and other flexible patch scenarios that require visual force warning. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the flexible patch using three stretching thresholds in Example 1.

[0017] Figure 2 This is a schematic diagram of the overall structure of the flexible patch using five stretching thresholds in Example 2.

[0018] Figure 3 A schematic diagram of the cross-section of the microgroove structure corresponding to the low-threshold pattern marking area (the microgroove structure of number 10 corresponds to the low-threshold deep groove design as follows). Figure 3 (As shown).

[0019] Figure 4 A schematic diagram of the cross-section of the microgroove structure corresponding to the high-threshold pattern marking area (the microgroove structure of number 30 corresponds to the low-threshold deep groove design as shown). Figure 4 (As shown).

[0020] Figure 5This is a schematic diagram of the process flow of the method of the present invention (the comprehensive crosslinking density control process flow diagram is shown below). Figure 5 (As shown).

[0021] Explanation of reference numerals in the attached figures: 1—Elastic substrate; 2—Patterned color development functional layer, where 10 / 20 / 30 in Example 1 are pattern marks corresponding to the stretching threshold, and 10 / 15 / 20 / 25 / 30 in Example 2 are pattern marks corresponding to the stretching threshold; 3—A portion of the micro-groove structure framework; 4—The portion of the color development layer filled in the micro-groove. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or modifications made by those skilled in the art based on the present invention without departing from the concept of the present invention should all fall within the scope of protection of the present invention.

[0023] In this invention, the term "hidden state" refers to the state where the color-developing layer of the pattern marking area has low contrast or the same color as the elastic substrate under visible light, making it difficult for users to directly identify the corresponding pattern under normal observation conditions. The term "manifest state" refers to the state where the pattern marking area changes color due to force after being stretched, forming a recognizable contrast with the elastic substrate, thus allowing for intuitive identification of the corresponding pattern. The term "bulk crosslinking density" refers to the relative density of the polymer network structure after the color-developing layer has cured. Different bulk crosslinking densities can be achieved by adjusting the composition of the color-developing layer formulation or curing conditions, such as by changing the type or content of the adhesive, the amount of crosslinking agent, the proportion of diluent, the proportion of filler, or the curing conditions, to make the color-developing layer form different degrees of polymer network structure density. The degree of network structure density can be characterized by the swelling ratio, storage modulus, gel content, or other parameters that can reflect the characteristics of the polymer network structure.

[0024] Example 1 This embodiment provides a method for intuitively visualizing the stretching amount of flexible tape using a three-level threshold pattern display. A unidirectional stretch polyurethane elastic fabric with a flesh-colored base is selected. First, the base is cleaned, then subjected to a three-level pre-stretching and shaping treatment: Level 1 pre-stretching to 10% elongation, held at room temperature for 10 minutes, and then reset; Level 2 pre-stretching to 20% elongation, held at 40°C for 8 minutes, and then reset; Level 3 pre-stretching to 30% elongation, held at 40°C for 10 minutes, and then reset, to reduce elastic hysteresis and stabilize subsequent threshold response.

[0025] Microgrooves were formed by laser etching in the areas where the numerical patterns "10", "20", and "30" were to be formed. The spacing between the three sets of pattern areas was 4 cm. The groove depths corresponding to "10", "20", and "30" were 0.40 mm, 0.25 mm, and 0.10 mm, respectively, with a uniform groove width of 0.20 mm. The deeper grooves exhibited a more pronounced stress concentration effect and were used to match lower color development thresholds; the shallower grooves were used to match higher color development thresholds.

[0026] Three types of mechanochromic inks were prepared. The low-threshold region ink, by weight, consisted of 9 parts PU resin, 2 parts spiropyran mechanochromic powder, and 1 part reactive diluent; the medium-threshold region ink consisted of 10 parts PU resin, 1.5 parts spiropyran mechanochromic powder, 0.5 parts reactive diluent, 0.3 parts nano-silica, and 0.05 parts crosslinking agent; the high-threshold region ink consisted of 11 parts PU resin, 1 part spiropyran mechanochromic powder, 0.5 parts nano-silica, and 0.10 parts crosslinking agent. Each ink was mechanically stirred for 30 minutes and then allowed to stand for 40 minutes to degas.

[0027] Three types of ink were printed in sections using an 80-100 mesh screen, forming a color-developing layer in each patterned marking area, thus constituting a patterned color-developing functional layer. The dry film thickness was controlled at 80-120 μm. After printing, the film was dried in hot air at 60℃ for 30 min, and then cured at 80℃ for 60 min, forming a transparent polyurethane elastic protective layer on the surface of the color-developing functional layer. Subsequently, a stretch-reset cycle test was performed on the flexible film at 25℃ and 50%RH at a speed of 5 mm / min. Without stretching, all three number areas were the same color as the substrate and remained hidden. When the stretch rate reached 10%, the number "10" appeared; when the stretch rate reached 20%, the number "20" appeared; and when the stretch rate reached 30%, the number "30" appeared. After 10 stretch-reset cycles, the color development threshold drift of each area did not exceed ±3%.

[0028] Table 1. Formulation ratio of force-induced color-changing ink for each threshold region in Example 1 (parts by mass) Example 2 This embodiment provides a method for intuitively visualizing the stretching amount of flexible adhesive using a five-level threshold pattern display. A warp and weft-shaped polyurethane elastic fabric is selected as the elastic substrate, and the processing method is the same as in Embodiment 1. Five pattern marking areas corresponding to the numbers "10", "15", "20", "25", and "30" are formed on the substrate, with a spacing of 3 cm between adjacent areas. The depths of the micro-grooves in each area are 400 μm, 320 μm, 240 μm, 160 μm, and 100 μm, respectively.

[0029] Five composite slurries were prepared, using waterborne polyurethane adhesive as the film-forming component, conjugated polymer as the color-changing material, carbon nanotubes as the optical enhancer, and silica microspheres as the crosslinking control filler. By progressively increasing the silica microsphere content and decreasing the deionized water content, different bulk crosslinking densities were achieved in different patterned marking areas. Each slurry was then screen-printed onto its corresponding patterned marking area using 80-100 mesh screen printing, forming a patterned color-developing functional layer with a thickness controlled at 95-105 μm. Subsequently, a gradient temperature curing process was performed, holding the layer at 40℃, 60℃, and 80℃ for 60 min each, resulting in a transparent polyurethane elastic protective layer approximately 10 μm thick on the surface.

[0030] Tensile-reset cyclic tests were conducted at 5 mm / min in an environment of 25℃ and 50%RH. The results showed that the numbers "10", "15", "20", "25", and "30" appeared sequentially with increasing tensile strength, and the color boundaries were clear. After 10 cycles, they still maintained good reversible response performance.

[0031] Table 2. Relationship between tensile strength threshold and micro-groove depth in Example 2 Table 3. Reference proportions (wt%) of the force-induced color-changing composite slurry for each threshold region in Example 2. Note: In this system, silica microspheres are cross-linking control fillers. By increasing their content, polymer chain segment movement can be physically hindered, chain segment mobility can be reduced, and the bulk cross-linking density of the color development layer can be increased, thereby achieving differentiated control of the color development trigger threshold in different threshold regions.

[0032] Comparison and explanation To illustrate the synergistic effect of differences in microgroove structure and crosslinking density of the developing layer, samples with consistent developing layer formulations but only varying microgroove depths, and samples with consistent microgroove structures but only varying developing layer formulations, were compared with embodiments of the present invention under a unified testing environment of 25°C and 50% RH. The comparison results show that when adjusting the microgroove depth alone while maintaining a consistent developing layer formulation, the trigger threshold separation between adjacent pattern marking areas is only 3%-5%; when adjusting the developing layer formulation alone while maintaining a consistent microgroove structure, the trigger threshold separation between adjacent areas is 4%-6%; while when using both differentiated microgroove structures and differentiated crosslinking densities, the trigger threshold separation between adjacent areas can reach 8%-10%, resulting in more stable threshold differentiation and improved color boundary clarity by more than 50%.

[0033] The above comparison shows that the present invention does not simply rely on a single color-changing material or a single microstructure design, but achieves the sequential display of multiple thresholds through the combined use of two types of technical means, thereby improving the grading accuracy of the visualization of flexible film stretching.

Claims

1. A method for intuitively visualizing the stretching amount of a flexible adhesive, characterized in that, Includes the following steps: S1. Provide a flexible adhesive, the flexible adhesive comprising an elastic substrate that can be elastically deformed along the stretching direction, and a plurality of pattern marking areas are provided on the surface of the elastic substrate, each pattern marking area corresponding to a preset stretching threshold, and the micro-groove structure parameters and crosslinking density of the color development layer body corresponding to each pattern marking area are determined according to the preset stretching threshold. S2. Microgroove structures are formed on the elastic substrate at positions corresponding to each pattern marking area. The microgroove structures corresponding to different pattern marking areas have different structural parameters so that each area produces a different degree of stress concentration effect when stretched. S3. A color-developing layer containing mechanochromic material is formed in each pattern marking area. The color-developing layers in different pattern marking areas have different bulk cross-linking densities. The color-developing layers together constitute a patterned color-developing functional layer. S4. When the flexible patch is stretched, under the combined effect of stress concentration in the microgroove structure and the difference in crosslinking density of the color development layer, each pattern mark area changes from a hidden state to a visible state when the corresponding preset stretching threshold is reached, so as to characterize the stretching amount of the flexible patch by the display order or display result of the pattern marks.

2. The method according to claim 1, characterized in that, The pattern marking area is set in at least two groups, each corresponding to at least two different preset stretching thresholds; when the stretching amount reaches each preset stretching threshold in sequence, each pattern marking area is displayed in sequence according to the corresponding preset stretching threshold from low to high, thereby forming a stepped stretching visual feedback.

3. The method according to claim 1, characterized in that, The structural parameters of the micro-groove structure include at least one of groove depth, groove width, cross-sectional shape, distribution density, and geometric orientation; different pattern marking areas form differentiated stress concentration effects by using different structural parameters.

4. The method according to claim 3, characterized in that, Preferably, in the pattern marking area corresponding to a lower preset stretching threshold, the groove depth of the micro-groove structure is greater than the groove depth in the pattern marking area corresponding to a higher preset stretching threshold.

5. The method according to claim 1, characterized in that, Preferably, in the pattern marking area corresponding to a lower preset stretching threshold, the bulk crosslinking density of the color developing layer is lower than the bulk crosslinking density in the pattern marking area corresponding to a higher preset stretching threshold.

6. The method according to claim 5, characterized in that, The bulk crosslinking density is adjusted by changing the ratio of one or more components among the polymeric adhesive, diluent, filler, and crosslinking agent in the color development layer.

7. The method according to claim 4 or 6, characterized in that, The mechanochromic material is one or more of the following: spiropyran-based mechanochromic materials, azobenzene-based mechanochromic materials, diarylethylene-based mechanochromic materials, conjugated polymers, or conjugated polymer / carbon nanotube composite systems.

8. The method according to claim 1, characterized in that, The pattern mark is one or more combinations of numbers, letters, symbols or warning text, and the pattern mark corresponds one-to-one with a preset stretching threshold.

9. The method according to claim 3, characterized in that, The microgroove structure is formed by laser etching, molding, screen printing etching, or photolithography.

10. The method according to claim 1, characterized in that, The color-developing layer is formed on the surface of the elastic substrate by means of partition printing, spraying, scraping or transfer, and color-developing materials with different bulk crosslinking densities are respectively set in different pattern marking areas.

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