Method for detecting heat shrinkage of a film

Abstract

The application discloses a kind of detection methods of film heat shrinkage, film is sequentially divided into three regions along film width direction;Three square marks are selected in each region, and each mark is labeled;Reference line is demarcated on the surface of each mark, and the initial size of the mark is determined;For individual sample, cutting is carried out at the position of first distance from the outside of reference line, and individual sample is separated, and all marks are sequentially cut into samples;All samples are placed in standard temperature and humidity environment for a first time;Sample is heated and heat treated at constant temperature, and maintained for a second time;Sample is cooled to first temperature at first rate gradient, then to second temperature, and placed for a third time;Mark is placed on substrate with organic solvent, and the re-measured size of the mark is determined;Based on initial size and re-measured size, the heat shrinkage of film is determined. It can effectively reduce measurement deviation, improve the accuracy and repeatability of detection data.

Description

Technical Field

[0001] This application relates to the field of thin film performance testing technology, and in particular to a method for testing the thermal shrinkage rate of thin films. Background Technology

[0002] Functional thin films, with their lightweight, flexibility, stable mechanical properties, and ease of processing, are widely used in electronic devices, optical components, and precision products. With the development of precision manufacturing technology, the requirements for the dimensional stability of thin films are increasing. However, thin films are prone to shrinkage and deformation when heated. Traditional testing methods lack standardized operating procedures, resulting in large measurement errors and poor data repeatability, making it difficult to accurately detect thermal shrinkage rates. Summary of the Invention

[0003] This application aims to provide a method for detecting the thermal shrinkage rate of a film, so as to improve the detection accuracy of the thermal shrinkage rate of a film.

[0004] This application proposes a method for detecting the thermal shrinkage rate of a thin film, characterized by the following steps: dividing the thin film into three regions along its width direction; selecting three square standard samples within each region and labeling each standard sample; drawing a baseline on the surface of each standard sample to determine its initial size; cutting a single standard sample at a first distance from the baseline to separate it into individual specimens, and sequentially cutting all standard samples into specimens; placing all specimens in a standard temperature and humidity environment and allowing them to stand for a first time; subjecting the specimens to constant temperature heating and maintaining the temperature for a second time; cooling the specimens to a first temperature at a first rate gradient, then cooling them to a second temperature, and allowing them to stand for a third time to set; placing the standard samples on a substrate containing an organic solvent and determining the remeasured size of the standard samples; and determining the thermal shrinkage rate of the thin film based on the initial size and the remeasured size.

[0005] In some embodiments, determining the initial size of the standard sample includes: aligning the standard sample with the length direction of the film and the width direction of the film; and determining the original length and original width of the standard sample. This alignment unifies the measurement benchmark, reduces measurement errors introduced by directional deviations, ensures consistency of detection conditions for different standard samples, and improves the comparability of detection results.

[0006] In some embodiments, the remeasured dimensions include the remeasured length and remeasured width of the standard sample placed on the substrate; determining the thermal shrinkage rate of the film based on the initial dimensions and the remeasured dimensions includes: determining the thermal shrinkage rate of the film in the length direction based on the initial length and the remeasured length; and determining the thermal shrinkage rate of the film in the width direction based on the initial width and the remeasured width. By calculating the thermal shrinkage rates in the length and width directions respectively, the differences in shrinkage characteristics of the film in different directions can be accommodated, resulting in accurate detection results in two dimensions, which better reflects the overall dimensional thermal stability of the film.

[0007] In some embodiments, selecting three square standard samples within each region and labeling each standard sample includes: selecting placement points within the region, with the distance between the standard sample and the edge of the film not less than 25 mm, and the distance between the edges of adjacent standard samples not less than 40 mm; drawing the outline of the square standard sample at each point, and sequentially assigning a unique number to all standard samples. By controlling the placement spacing of the standard samples, the mutual influence of internal stress at different locations of the film is reduced, while avoiding deformation errors caused by processing and molding in the edge areas, ensuring that the selected standard samples can uniformly reflect the overall shrinkage characteristics of the film, and improving the representativeness of the test samples.

[0008] In some embodiments, the step of cutting a single standard sample at a first distance from the outside of the baseline to separate it into a single specimen, and then sequentially cutting all the standard samples into specimens, includes: using the baseline corresponding to the standard sample as the inner boundary, extending outwards along the outer perimeter of the baseline by a first distance to form a cutting edge line, the first distance being 18mm to 23mm; cutting along the cutting edge line to obtain a specimen that wraps around the standard sample and has an outer clamping allowance. By setting a reserved allowance at the first distance, sufficient operating space can be provided for subsequent specimen clamping, reducing additional tensile deformation of the core detection area of ​​the standard sample during the clamping process, preventing clamping stress from interfering with the final shrinkage rate detection result, while ensuring sufficient tolerance for the cutting operation and improving the convenience of the sampling operation.

[0009] In some embodiments, placing all samples under standard temperature and humidity conditions for a first time includes: uniformly placing all cut samples in an environment with a temperature of 23±2℃ and a relative humidity of 50±5%RH for 1.8h to 2.2h. By placing them under standard temperature and humidity conditions, the stress generated inside the film during the cutting process can be reduced, reducing the interference of cutting stress on subsequent deformation and heat shrinkage rate detection. At the same time, it allows the temperature and humidity of the samples to balance with the environment, improving the consistency of deformation during subsequent heat treatment.

[0010] In some embodiments, the isothermal heating heat treatment of the sample and its maintenance for a second time includes: clamping the outer margin area of ​​the sample for transfer and placement, with the clamping position avoiding the baseline area of ​​the standard sample; laying isolation paper on the upper and lower sides of the sample, and then moving the settled sample into the heating device for isothermal treatment; the heating temperature is set to 140°C to 160°C and maintained for 25 min to 32 min. By clamping the outer margin area, direct contact with the core detection area can be reduced, reducing the introduction of additional deformation; laying isolation paper on the upper and lower sides can reduce direct adhesion or contamination between the sample and the heating device, facilitating the stability of the sample surface during heat treatment; the isothermal holding setting allows the film to fully complete thermal shrinkage deformation, which is beneficial for a full and uniform shrinkage process and reduces large errors in the detection results caused by incomplete shrinkage.

[0011] In some embodiments, the step of cooling the sample to a first temperature at a first rate gradient, then cooling it to a second temperature, and then allowing it to stand for a third time includes: cooling the sample to 60°C at a rate gradient of 5°C / min to 10°C / min, allowing it to cool naturally to 23±2°C, and then allowing it to stand for a third time for 55 to 65 minutes. By controlling the cooling rate through gradient cooling, the additional thermal stress deformation of the film caused by rapid cooling is reduced. Natural cooling to room temperature followed by standing allows the shrinkage morphology of the film to stabilize, ensuring that the remeasured dimensions accurately reflect the actual shrinkage state after heat treatment, and improving the stability of the test results.

[0012] In some embodiments, the substrate is a glass substrate, and the organic solvent is selected from either anhydrous ethanol or isopropanol. Supporting the standard sample on a glass substrate facilitates its flat unfolding, reduces interference from substrate deformation in dimensional measurements, and allows the addition of organic solvent to utilize liquid surface tension to automatically smooth out any wrinkles in the sample. Furthermore, the solvent does not react with the film to corrode the sample, ensuring the sample remains flat during measurement and improving the accuracy of dimensional measurements.

[0013] In some embodiments, determining the initial size and the remeasured size of the standard sample are both performed using an industrial microscope; the dimensional reading accuracy of the industrial microscope is not less than 0.001 mm, and the magnification is 5x to 50x. Using a high-precision industrial microscope for dimensional readings improves the measurement accuracy of the initial and remeasured sizes, reduces reading errors from conventional ruler measurements, and accurately captures even minute shrinkage, effectively meeting high-precision testing requirements.

[0014] The advantages of the film heat shrinkage rate detection method in this application, which differs from existing technologies, are: In the embodiments of this application, a standardized testing process is implemented, which sequentially involves dividing the film into zones, laying out and labeling standard samples, defining baselines to collect initial dimensions, preparing samples through standardized cutting, pre-treatment under standard temperature and humidity, constant temperature heating, gradient cooling for shaping, and organic solvent-assisted leveling and dimension re-measurement. Finally, the thermal shrinkage rate is calculated by combining the initial and final dimensions. This process optimizes the traditional film thermal shrinkage testing methods, addressing issues such as inconsistent operating standards, large measurement errors, and poor data repeatability. The entire process is clear and standardized, forming a complete closed loop from sampling, sample preparation, environmental treatment, heating and cooling to dimension re-measurement and data calculation. It controls test conditions throughout the process, effectively reducing interference from human operation and the test environment, lowering measurement deviations, and improving the accuracy and repeatability of test data. This allows for precise detection of film thermal shrinkage rate and objective evaluation of film dimensional thermal stability, better meeting the testing needs of functional films in fields such as electronic devices, optical components, and precision products.

[0015] Additional aspects and advantages of the embodiments of this application will be described or shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0016] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0017] Figure 1 This is a schematic flowchart of the detection method of some embodiments of this application; Figure 2 This is a schematic diagram of the structure of the divided regions in some embodiments of this application; Figure 3 This is a schematic diagram of the structure of a standard sample for some embodiments of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments. In this application, the term "embodiment" means that a particular feature, structure, or characteristic commonly described with respect to that embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. In the explanation of the embodiments of this application, technical terms such as "first" and "second" are used to distinguish different objects and should not be construed as indicating or implying relative importance, nor do they mean that the specified technical features have a specific meaning in terms of quantity, specific order, or primary and secondary relationship. In the explanation of the embodiments of this application, "multiple" refers to two or more, unless otherwise explicitly and specifically defined.

[0019] In the description of the embodiments of this application, the term "and / or" is used to describe the relationship between related objects, which can reflect three types of relationships. For example, A and / or B can present the following three situations: only A exists, A and B exist simultaneously, and only B exists. In addition, the character " / " in this document usually means that the related objects before and after are in an "or" relationship; " / " can also represent a proportional relationship; when " / " appears in a table, it can also indicate that the corresponding substance and parameter do not exist, and its specific meaning needs to be determined according to the actual scenario.

[0020] The technical features described in the different embodiments of this application below can be combined with each other as long as they do not conflict with each other.

[0021] Functional films, with their outstanding advantages such as thinness, flexibility, stable mechanical properties, and ease of processing, have been widely used in many fields, including electronic devices, optical components, precision products, and flexible packaging. With the rapid development of the precision manufacturing industry, more stringent requirements have been placed on the dimensional stability of film products. Furthermore, films are prone to shrinkage and deformation under heating conditions, making thermal shrinkage rate a core performance indicator for evaluating film quality. Currently, the industry generally refers to conventional standards such as ASTM D1204-25 for testing. However, existing traditional testing methods still have many technical shortcomings: the conventional standard environmental conditioning takes a long time and the testing efficiency is low; the samples are mostly taken from large-size single points, which is difficult to cover the stress and material distribution differences of the entire width of the film, resulting in insufficient representativeness; the heating temperature is not properly selected, with low temperature resulting in small shrinkage and low data differentiation, while high temperature easily causes film melting and wrinkling, and deformation and failure of the reference mark; at the same time, there is a lack of standardized isolation protection and gradient cooling processes, and the samples are easily affected by the airflow disturbance in the oven, and natural cooling can easily generate secondary internal stress and additional deformation; in addition, there is no unified longitudinal and transverse measurement numbering rule, and the manual use of film rulers has large estimation errors, high data dispersion, and poor repeatability, making it difficult to achieve high-precision and standardized testing of film thermal shrinkage rate, and failing to meet the needs of high-end precision fields for accurate evaluation of film dimensional stability.

[0022] To mitigate the aforementioned problems, this application proposes a method for detecting the thermal shrinkage rate of thin films. Please refer to [the relevant documentation]. Figure 1 The detection method includes the following steps: S10: Divide the film into three regions sequentially along its width direction. The test samples used in this application can be industrially produced roll-to-roll films, with an overall film thickness controlled between 5 μm and 200 μm. Because the outermost layer of the roll-to-roll film is in long-term contact with the outside air during winding, storage, and transportation, it easily absorbs dust and moisture; simultaneously, the outer layer bears greater winding tension, and its internal stress distribution differs significantly from that of the inner film of the roll core. Direct sampling would cause distortion of the test data. Therefore, before formal sampling, 2 to 4 turns of the outer film can be discarded, preferably 3 turns, and a film with uniform material and stable stress state inside the roll core should be selected as the test substrate.

[0023] Lay the screened film flat on a clean, level work surface, ensuring that the film is not stretched, wrinkled, or shifted throughout the process, maintaining its natural, relaxed state. Please refer to... Figure 2 The length direction (longitudinal direction) is defined by the direction in which the film extends, and the width direction is defined by the transverse direction perpendicular to the length. Along the width direction of the film, the entire film is evenly divided into three independent detection areas: the left area, the middle area, and the right area. The three areas are arranged sequentially along the width direction, and the area of ​​each area is basically the same.

[0024] Setting up three detection areas (left, center, and right) along the width of the same film facilitates the coverage of differences in the lateral material distribution and stress distribution of the film. By conducting tests with multiple sets of parallel samples, the stability of the test data can be verified through comparison of multiple sets of test data, and the random deviation caused by single-point sampling can be reduced, so as to comprehensively characterize the thermal shrinkage performance of the entire film.

[0025] S20: Select three square standard samples within each area and label each standard sample. After completing the membrane zoning operation, the standard sample points are laid out and their outlines are drawn in three independent testing areas: left, middle, and right. Unique numbering is then performed. When laying out the standard samples, the spacing between them can be strictly limited. For example, the distance between all standard samples and the outer edge of the membrane should not be less than 25mm, and within the same testing area, the distance between the edges of two adjacent standard samples should not be less than 40mm.

[0026] The edge area of ​​the film is prone to processing defects such as uneven thickness, local overstretching, and stress concentration during the forming, cutting, and winding process, which makes it difficult to objectively reflect the performance of the film itself. Setting a safety edge distance of 25mm can effectively reduce the edge effect. The spacing of no less than 40mm between adjacent standard samples can reduce the contact and compression between samples during cutting, heating, and cooling, reduce secondary deformation, and at the same time provide sufficient operating space to facilitate subsequent manual cutting and clamping operations.

[0027] In the embodiments of this application, three uniformly sized square standard samples are arranged in each detection area, for example, please refer to Figure 2 and Figure 3 The preferred standard specimens are square, with a size of 10mm × 10mm, and a total of 9 specimens are laid out on the entire film. This application uses a 10mm × 10mm stainless steel plate to press square reference lines onto the film surface. The width of the reference lines is controlled between 0.8mm and 1.5mm, and the lines are clear, continuous, without breaks or smudging. After the specimens are drawn, each of the 9 specimens is assigned a unique, consecutive numerical label. These labels are uniformly marked in the blank area outside the specimen, and are prohibited from being marked inside the 10mm × 10mm core test area to reduce the risk of handwriting obscuring the reference lines or corroding the film, which could affect subsequent dimensional measurements. By setting unique labels, confusion between different specimens can be effectively avoided, facilitating the corresponding recording of subsequent test data and reducing data errors caused by misaligned test records.

[0028] The 10mm×10mm small-sized standard sample is not only convenient to sample and requires less consumables, but it can also be adapted to the observation field of industrial microscopes, making it easy for the lens to capture the reference line completely; the 9-point full-area sampling mode can easily cover the structural and stress differences in the width direction of the film, which is conducive to truly reflecting the thermal shrinkage characteristics of the whole roll of film.

[0029] S30: Draw a baseline on the surface of each standard sample to determine the initial dimensions of the standard sample. A closed baseline is drawn inside each square standard sample. The baseline is parallel to the outer contour of the standard sample. This baseline serves as an effective boundary for subsequent cutting, sample preparation, dimensional measurement, and heat shrinkage calculation, and is used to distinguish the outer clamping allowance from the central core detection area.

[0030] Please refer to Figure 2 and Figure 3 After the baseline is drawn, all standard samples are calibrated in a unified direction, ensuring that the length direction of the standard samples matches the length direction of the film to be tested, and the width direction of the standard samples matches the width direction of the film to be tested. Simultaneously, this application establishes a fixed dimension measurement numbering rule, defining the two longitudinal edges of the standard samples as edge length 1 and edge length 3, and the two transverse edges as edge length 2 and edge length 4. This fixed longitudinal and transverse measurement dimension helps avoid the problem of directional confusion during multiple measurements. During the stretching and forming process, the polymer chains of the film exhibit orientation, and the longitudinal and transverse thermal shrinkage properties differ. By unifying the placement orientation and measurement edge numbering, the original dimensional data in both directions can be obtained separately.

[0031] In this step, all initial dimensions were acquired using an industrial microscope. An IM-3 industrial microscope was selected, with a reading accuracy of no less than 0.001 mm and magnification adjusted to 5x to 50x. The original lengths of each standard sample before heating were read for longitudinal side length 1 and side length 3, and transverse side lengths 2 and side length 4. To reduce random errors from a single measurement, the same sideline was measured three times, and the arithmetic mean was taken as the final initial dimension. A data log was established to record and save all data. Microscope photographic measurement enables high-precision readings at the micrometer level, reducing human visual error.

[0032] S40: For a single standard sample, cut it at a position one distance outside the baseline to separate it into a single specimen. Repeat this process for all standard samples. Using the baseline inside the standard sample as the inner boundary, a cutting edge is formed by extending a certain distance outward along the outer perimeter of the baseline. In this application, the first outward extension distance is set to 18mm to 23mm, preferably 20mm. The operator uses a dedicated film cutting tool to cut smoothly and at a uniform speed along the defined cutting edge, ensuring a clean, burr-free, tear-free, and compression-free cut. After cutting, an independent sample is obtained, encasing the central standard sample and having an outer clamping allowance. Following the same operating procedures, the cutting of all nine standard samples is completed sequentially.

[0033] In the embodiments of this application, the clamping allowance is limited to the range of 18mm to 23mm, providing a dedicated operating area for sample transfer, clamping, and placement. All subsequent operations only apply to the outer allowance area, avoiding the core test sample throughout the process, reducing compression and tensile deformation of the sample during manual clamping and handling; at the same time, it standardizes the shape and specifications of all samples, ensuring that the test conditions of the 9 groups of samples are consistent in pretreatment, heating, and cooling processes, reducing systematic errors.

[0034] S50: Place all samples in a standard temperature and humidity environment and allow them to stand for the first time. After the cutting process is completed, the nine prepared samples are neatly placed inside a constant temperature and humidity equipment. During the placement process, gaps are left between the samples, and stacking, pressing, and squeezing are prohibited. This application sets a standardized pretreatment environment: ambient temperature 23±2℃, relative humidity 50±5%RH, and the samples are left to stand in this environment for 1.8h to 2.2h, preferably 2h.

[0035] This pretreatment method is simple and time-efficient, significantly reducing testing time compared to the industry-standard 4-hour settling period. It is suitable for rapid quality inspection in laboratories and high-frequency sampling inspection on production lines. The settling stage effectively releases the instantaneous residual stress generated during the cutting process, balances the initial stress on the sample surface and inside, keeps the initial state of all samples uniform, reduces data dispersion caused by differences in initial stress, and improves test repeatability.

[0036] S60: Perform isothermal heating heat treatment on the sample and maintain it for a second time. After the pretreatment process is completed, the staff can use paperclips to hold the remaining area around the sample to complete the transfer and placement of the sample. The holding position must strictly avoid the test area inside the baseline of the standard sample. It is forbidden to directly hold the 10mm×10mm core standard sample to prevent the external force of the clamping from causing plastic deformation of the sample and generating additional stress that interferes with the test results.

[0037] To block the high-speed circulating airflow inside the oven and reduce the direct impact of airflow on the sample, which could cause sample displacement, warping, and morphological disturbance, this application places a clean A4-sized release paper at the bottom of the sample and covers it with a release paper of the same size on top, achieving all-round airflow protection. The sample is then moved into the heating equipment for constant-temperature heat treatment, with the heating temperature set to 140°C to 160°C and the holding time to 25 to 32 minutes; in this preferred embodiment, the heating temperature is set to 150°C and the holding time to 30 minutes.

[0038] 150℃ is the optimal testing temperature window for this application, which can reduce the problems of insufficient film shrinkage, low data differentiation, and performance evaluation distortion under conventional low-temperature conditions of 100℃. It also reduces defects caused by excessive melting of the film, overall wrinkling and warping, and distortion and failure of the reference mark due to high temperatures above 160℃, ensuring that the sample only undergoes pure thermal shrinkage deformation and that the measurement reference is stable. For special films with poor temperature resistance such as PE and PC, the heating temperature can be appropriately lowered within the range of 140℃ to 160℃ to adapt to the testing needs of films of different materials.

[0039] S70: Cool the sample to the first temperature according to the first rate gradient, then cool it to the second temperature, and let it stand for a third time to set. After the constant temperature heating process is completed, the gradient temperature control program is started, for example, the sample is cooled at a constant rate of 5℃ / min to 10℃ / min until the internal temperature of the cavity drops to 60℃. After the gradient cooling is completed, the temperature control program is turned off, the oven cavity is kept sealed, and the sample is allowed to dissipate heat naturally with the equipment and cool to room temperature of 23±2℃. Finally, the sample is left to stand for 55min to 65min at room temperature, preferably 60min (1h). During the entire cooling process, the sample is kept horizontal and is not stretched or squeezed.

[0040] If a high-temperature sample is directly and rapidly cooled, the huge temperature difference will cause additional internal stress in the film, triggering secondary non-targeted shrinkage deformation, making it difficult to reflect the true thermal shrinkage performance of the film. This application adopts a three-stage cooling process of gradient cooling, natural cooling, and isothermal setting. The gradual cooling rate can effectively reduce the additional deformation caused by sudden temperature changes; the standardized 1-hour setting time can ensure that the thermal stress generated by the film heating is completely released and the shrinkage shape is completely fixed, preventing dimensional rebound during subsequent handling and measurement. This solves the industry pain points of arbitrary cooling time and large data dispersion in traditional testing.

[0041] S80: Place the standard sample on a substrate containing organic solvent and determine the remeasurement dimensions of the standard sample. After the sample has cooled and solidified, the clamping allowance around the sample is removed, and the 10mm × 10mm standard sample at the center is taken out separately. This application uses a glass substrate with a smooth surface, free from unevenness, deformation, and scratches as the carrier substrate; the organic solvent used can be either anhydrous ethanol or isopropanol, both of which are chemically mild and will not corrode or dissolve the polymer film material.

[0042] An appropriate amount of organic solvent is evenly dripped onto the surface of a glass substrate. The standard sample is then placed flat in the coated area. Utilizing the wetting, spreading, and penetrating properties of the organic solvent, air between the standard sample and the substrate is expelled, allowing the standard sample, which may have warped or wrinkled after heating, to quickly flatten and adhere to the substrate surface. After the organic solvent has completely evaporated naturally, the dimensions of the standard sample are remeasured using an industrial microscope. The equipment parameters remain consistent with the initial measurement, with magnification maintained between 5x and 50x and an accuracy of no less than 0.001mm. The dimensions of the longitudinal side length 1 and side length 3, and the transverse side length 2 and side length 4 of the standard sample under the remeasurement state are read respectively. The average of three measurements is taken, and the remeasured length and width of each set of standard samples are recorded. This wetting and leveling process completely eliminates interference from sample deformation, ensuring that all standard sample measurement references are uniformly flat.

[0043] S90: Determine the thermal shrinkage rate of the film based on the initial and remeasured dimensions. By combining the initial dimensions of the standard sample before heating with the remeasured dimensions after heating, the thermal shrinkage rate of the film in different directions is calculated. The basic calculation formula for the thermal shrinkage rate in this application is as follows: Thermal shrinkage rate = [(length of side before heating)] [Length of side after heating ÷ Length of side before heating] × 100% This application can also employ a hierarchical and step-by-step calculation logic to sequentially complete the statistical analysis of four layers of data: single side length, single standard sample, single region, and the entire film. Longitudinal shrinkage rate of a single standard sample: Calculate the arithmetic mean of the thermal shrinkage rates of the longitudinal side length 1 and side length 3 of the standard sample; Transverse shrinkage rate of a single standard sample: Calculate the arithmetic mean of the thermal shrinkage rates of the standard sample with a transverse side length of 2 and a side length of 4; Regional average shrinkage rate: Calculate the longitudinal and transverse average shrinkage rates for the three standard samples on the left, three in the middle, and three on the right, respectively; The final shrinkage rate of the entire film: the average of the longitudinal shrinkage rates of all 9 standard samples is taken as the overall longitudinal thermal shrinkage rate of the film, and the average of the transverse shrinkage rates of all 9 standard samples is taken as the overall transverse thermal shrinkage rate of the film.

[0044] During the film forming process, polymer chains exhibit anisotropic orientation, and there are significant differences in longitudinal and transverse shrinkage properties. Independent calculations for each direction can comprehensively evaluate the dimensional stability of the film. The multi-level data statistical mode can effectively eliminate random abnormal data, making the test results more objective and accurate.

[0045] In the embodiments of this application, a standardized testing process is implemented, which sequentially involves dividing the film into zones, laying out and labeling standard samples, defining baselines to collect initial dimensions, preparing samples through standardized cutting, pre-treatment under standard temperature and humidity, constant temperature heating, gradient cooling for shaping, and organic solvent-assisted leveling and dimension re-measurement. Finally, the thermal shrinkage rate is calculated by combining the initial and final dimensions. This process optimizes the traditional film thermal shrinkage testing methods, addressing issues such as inconsistent operating standards, large measurement errors, and poor data repeatability. The entire process is clear and standardized, forming a complete closed loop from sampling, sample preparation, environmental treatment, heating and cooling to dimension re-measurement and data calculation. It controls test conditions throughout the process, effectively reducing interference from human operation and the test environment, lowering measurement deviations, and improving the accuracy and repeatability of test data. This allows for precise detection of film thermal shrinkage rate and objective evaluation of film dimensional thermal stability, better meeting the testing needs of functional films in fields such as electronic devices, optical components, and precision products.

[0046] Example (75μm transparent PET film, size 10mm×10mm, conditions 150 degrees for 30 minutes, microscopic measurement method)

[0047] Comparative example (75μm transparent PET film, size 100mm×100mm, conditions 150 degrees for 30 minutes, standard caliper measurement method)

[0048] As can be seen from the above embodiments and comparative examples, the traditional method of measuring with large-size samples using conventional calipers has low testing accuracy and is difficult to effectively detect minute lateral shrinkage deformation of the film, while the longitudinal test results are also relatively coarse. In contrast, this application uses small-size standard samples with industrial microscopes for precise measurement, which can accurately capture minute dimensional changes in the longitudinal and lateral dimensions of the film. It has high test resolution, small data dispersion, and good repeatability, and can truly and objectively characterize the thermal shrinkage performance of the film at different locations across its width. This effectively solves the problems of insufficient accuracy, unclear dimensional differentiation, and poor data reliability of existing testing methods.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for detecting the thermal shrinkage rate of a thin film, characterized in that, Includes the following steps: The film is divided into three regions along its width direction; Three square standard samples are selected and marked within each area, and each standard sample is labeled. A baseline is drawn on the surface of each standard sample to determine the initial dimensions of the standard sample; For a single standard sample, it is cut at a position a first distance from the outside of the baseline to separate it into a single specimen, and all standard samples are cut into specimens in sequence. All samples were placed in a standard temperature and humidity environment and left to stand for an immediate period of time. The sample was subjected to constant-temperature heating heat treatment and maintained for a second time; The sample is cooled to a first temperature at a first rate gradient, then cooled to a second temperature, and left to stand for a third time to set. The standard sample was placed on a substrate containing organic solvent, and the remeasurement dimensions of the standard sample were determined. The thermal shrinkage rate of the film is determined based on the initial size and the remeasured size.

2. The detection method according to claim 1, characterized in that, Determining the initial size of the standard sample includes: The standard sample is oriented so that the length direction of the standard sample matches the length direction of the film, and the width direction of the standard sample matches the width direction of the film. Determine the original length and original width of the standard sample.

3. The detection method according to claim 2, characterized in that, The remeasured dimensions include the remeasured length and remeasured width of the standard sample placed on the substrate; Determining the thermal shrinkage rate of the film based on the initial size and the remeasured size includes: Based on the initial length and the remeasured length, the thermal shrinkage rate of the film in the length direction is determined; Based on the initial width and the remeasured width, the thermal shrinkage rate of the film in the width direction is determined.

4. The detection method according to claim 1, characterized in that, The step of selecting and defining three square markers within each region, and labeling each marker, includes: Select deployment points within the area, with the distance between the standard sample and the edge of the film not less than 25mm, and the distance between the edges of adjacent standard samples not less than 40mm; Draw a square outline at each point and assign a unique number to each of the squares in sequence.

5. The detection method according to claim 1, characterized in that, The step of cutting a single standard sample at a position a first distance outside the baseline to separate it into a single specimen, and then sequentially cutting all the standard samples into specimens, includes: Using the baseline corresponding to the standard sample as the inner boundary, extend outward a first distance along the outer perimeter of the baseline to form a cutting edge line, the first distance being 18mm to 23mm; Cut along the cutting edge to obtain a sample that wraps around the standard sample and has an outer clamping allowance.

6. The detection method according to claim 1, characterized in that, The step of placing all samples under standard temperature and humidity conditions for a period of time includes: All cut samples were placed in an environment with a temperature of 23±2℃ and a relative humidity of 50±5%RH and left to stand for 1.8h to 2.2h.

7. The detection method according to claim 1, characterized in that, The process of subjecting the sample to constant-temperature heating heat treatment and maintaining it for a second time includes: The sample is transferred and placed using the outer margin area of ​​the clamping device, while the clamping position avoids the baseline area of ​​the standard sample. Place isolation paper on the upper and lower sides of the sample, and then move the sample after it has been left to stand into the heating equipment for constant temperature treatment; the heating temperature is set to 140℃ to 160℃ and kept at that temperature for 25 min to 32 min.

8. The detection method according to claim 1, characterized in that, The step of cooling the sample to a first temperature at a first rate gradient, then cooling it to a second temperature, and allowing it to stand for a third period of time to set includes: The temperature was gradually reduced to 60℃ at a rate of 5℃ / min to 10℃ / min, then allowed to cool naturally to 23±2℃, and finally allowed to stand for 55min to 65min to set.

9. The detection method according to claim 1, characterized in that, The substrate is a glass substrate, and the organic solvent is selected from either anhydrous ethanol or isopropanol.

10. The detection method according to claim 1, characterized in that, The determination of the initial size of the standard sample and the determination of the remeasured size of the standard sample are both completed using an industrial microscope; the dimensional reading accuracy of the industrial microscope is not less than 0.001 mm, and the magnification is 5 to 50 times.

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