Preparation method of PTC heating film

Abstract

The invention discloses a preparation method of a PTC heating film. The preparation method comprises the following steps: S1, selecting a PI original film as a base material; s2, carrying out preshrinking treatment on the PI original film by adopting high-temperature dry and hot air so as to eliminate the shrinkage stress of the PI original film; s3, printing conductive silver paste on the pre-shrunk PI original film, and moving the PI original film printed with the conductive silver paste to a baking area in a roll-to-roll mode to be dried to form a silver paste layer; s4, carbon paste is printed on the basis of the silver paste layer, and the PI original film printed with the carbon paste is moved to a baking area in a roll-to-roll mode to be dried to form a carbon paste layer; s5, laminating the PI original film treated in the step S4 to form a semi-finished product; and S6, carrying out post-treatment on the semi-finished product. Compared with the prior art, preshrinking treatment is carried out before the sizing agent is printed, the size stability of the PI original film is improved, and the printing quality is also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of PTC heating films, and in particular relates to a method for preparing a PTC heating film. Background Art

[0002] In the new energy field, power batteries such as lithium batteries have strict requirements on the ambient temperature of use. In low temperature environments, the charging and discharging performance of lithium batteries is reduced, which will affect the normal starting of the vehicle. Therefore, lithium batteries are usually equipped with heating devices.

[0003] The traditional heating device is heated by a metal heating wire, which needs to be matched with a temperature control sensor. This places extremely high demands on the reliability of the sensor. If a failure occurs, it will directly cause the battery to burn. The PTC heating film can be started at a high power in a low temperature environment, with a high heating rate and a fast heating rate. After reaching thermal equilibrium, the resistance becomes larger and the power becomes smaller. It can self-control the temperature to prevent overheating problems and has high safety. Based on this advantage, the PTC heating film is widely used to heat power batteries.

[0004] Application No. CN202310739087.3 discloses a method for preparing a PTC heating film, and the steps are as follows: S1, use a printer to print conductive silver paste on a PI film, measure the thickness of the conductive silver paste, and bake; S2, print carbon paste, measure the thickness of the carbon paste, and bake; S3, cover the film, cut; S4, punch and weld the wire; S5, attach the ear material at the soldering point; S6, hot press the ear material to obtain a PTC heating film. In the process of manufacturing PTC heating film based on this printing process, the applicant found that: directly printing and baking on the PI film to form silver paste and carbon paste, during the drying process, the PI film undergoes stress contraction under the action of high temperature, and the circuit layer printed on the PI film is prone to offset or breakage; second, during the production process of the PI film, processing aids or solvents will remain on its surface. If silver paste and carbon paste are printed directly on the PI film, this will not only reduce the bonding strength of the silver paste and carbon paste, but also easily cause the problem of peeling off the PI film. In addition, the residual solvent may form conductive residual substances between the conductive layers, posing a short circuit risk. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a PTC heating film.

[0006] To achieve the above objectives, the present invention discloses a method for preparing a PTC heating film, comprising the following steps:

[0007] S1, select PI original film as substrate;

[0008] S2, using high-temperature dry hot air to pre-shrink the PI original film to eliminate the shrinkage stress of the PI original film;

[0009] S3. Print conductive silver paste on the pre-shrunk PI original film, and move the PI original film printed with conductive silver paste to the baking area by a roll-to-roll method to dry and form a silver paste layer;

[0010] S4. Print carbon paste on the basis of the silver paste layer, and move the PI original film printed with carbon paste to the baking area by a roll-to-roll method to dry and form a carbon paste layer;

[0011] S5. Laminate the PI original film processed in step S4 to form a semi-finished product;

[0012] S6. Perform post-treatment on the semi-finished product.

[0013] Preferably, the conditions for the pre-shrinking treatment are: temperature 130°C to 180°C, time 0.5 - 2 hours.

[0014] Preferably, the conditions for the pre-shrinking treatment are: temperature 150°C, time 1 hour.

[0015] Preferably, the pre-treatment includes the following steps:

[0016] Step S21. Heat up to 100°C at a rate of 5 - 10°C / min and keep warm for 10 minutes;

[0017] Step S22. Heat up to 150°C at a rate of 3 - 5°C / min and keep warm for 1 hour;

[0018] Step S23. Cool down to room temperature at a rate of 2 - 4°C / min.

[0019] Preferably, before the pre-shrinking treatment, the PI original film is pre-dried, and the drying conditions are: temperature 80°C, humidity ≤ 20%, time 30 - 60 minutes.

[0020] Preferably, before performing step S3, the PI original film is cooled to room temperature, and the humidity of the cooling environment ≤ 30%.

[0021] Preferably, after performing step S5 and before performing step S6, the semi-finished product is refrigerated, and the refrigeration treatment conditions are: temperature 0 - 5°C, time 8 - 24 hours.

[0022] Preferably, before the refrigeration treatment, the semi-finished product is pre-cooled, and the pre-cooling conditions are: temperature 10 - 15°C, time 0.5 - 1 hour.

[0023] Preferably, after the refrigeration treatment, it is heated up to room temperature at a gradient, and the heating rate is 1 - 3°C / min.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] Perform pre - shrinking treatment before printing the conductive layer (silver paste layer + carbon paste layer) to eliminate the shrinkage stress of the original PI film, which has the following beneficial effects:

[0026] (1) First, perform pre - shrinking treatment on the original PI film to eliminate its shrinkage stress, improve the dimensional stability of the original PI film. During the subsequent drying process of the silver paste and carbon paste, the size of the original PI film remains basically stable, improving the printing accuracy of the silver paste and carbon paste and the product quality. It greatly avoids problems such as the printed circuit shifting or breaking due to the shrinkage of the original PI film after drying. For example, when the carbon paste enters the drying process after printing, the shrinkage of the original PI film changes the distribution and thickness of the carbon paste, resulting in a large fluctuation in the final resistivity of the PTC heating film, affecting the heating accuracy and effect.

[0027] In the prior art, when processing the PTC heating film, the movement of the PI film is realized by a roll - to - roll device, which also adapts to the processing requirements of continuous production. By performing pre - shrinking treatment on the PI to improve its dimensional stability and reduce the shrinkage rate, the tension fluctuation during the roll - to - roll pulling process is reduced, avoiding uneven stretching or breakage of the film material. In addition, the stable substrate size ensures accurate positioning of the printing fiducial mark and improves the overprint accuracy (such as the interlayer alignment of the silver paste and carbon paste).

[0028] (2) The high - temperature environment of the pre - shrinking treatment can accelerate the volatilization of the residual substances on the original PI film, avoid the generation of bubbles or delamination due to the volatilization of the residues during the subsequent baking process, enhance the bonding strength at the interface between the conductive layer and the original PI film, thereby improving the conductive stability, long - term reliability of the heating film, and the printing quality of the conductive layer. At the same time, it also avoids the short - circuit risk caused by the residue of conductive substances.

[0029] (3) Performing pre - shrinking treatment before printing the conductive layer can avoid problems such as oxidation or deformation of the conductive material caused by "printing first and then pre - shrinking treatment". BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the process flow chart of the preparation method of the PTC heating film in the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] To make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0032] A preparation method of a PTC heating film includes the following steps:

[0033] S1. Select the original PI film as the substrate;

[0034] S2. Perform pre-shrinking treatment on the PI original film with high-temperature dry hot air to eliminate the shrinkage stress of the PI original film;

[0035] In this step, by performing pre-shrinking treatment on the PI original film, the shrinkage stress of the PI original film is eliminated, and the dimensional stability of the PI original film is improved. During the subsequent drying processes of the silver paste and carbon paste, the size of the PI original film remains basically stable, improving the printing accuracy of the silver paste and carbon paste and the product quality, and greatly avoiding problems such as the printed circuit shifting or breaking due to the shrinkage of the PI original film after drying. For example, when the carbon paste enters the drying process after printing, the shrinkage of the PI original film changes the distribution and thickness of the carbon paste, resulting in a large fluctuation in the final resistivity of the PTC heating film, affecting the heating accuracy and effect.

[0036] In the prior art, when processing the PTC heating film, the movement of the PI film is achieved through a roll-to-roll device, which also adapts to the processing requirements of continuous production. By performing pre-shrinking treatment on the PI, its dimensional stability is improved, the shrinkage rate is reduced, the tension fluctuation during the roll-to-roll pulling process is reduced, and uneven stretching or breaking of the film material is avoided. In addition, the stable substrate size ensures accurate positioning of the printing fiducial mark and improves the overprint accuracy (such as the interlayer alignment of the silver paste and carbon paste).

[0037] The high-temperature environment of the pre-shrinking treatment can accelerate the volatilization of the residual substances on the PI original film, avoid the generation of bubbles or delamination due to the volatilization of the residues during the subsequent baking process, enhance the bonding strength at the interface between the conductive layer and the PI original film, thereby improving the conductive stability, long-term reliability of the heating film, and the printing quality of the conductive layer, and also avoiding the short-circuit risk caused by the residual conductive substances.

[0038] S3. Print conductive silver paste on the PI original film after pre-shrinking treatment, and move the PI original film printed with conductive silver paste to the baking area for drying to form a silver paste layer. The drying conditions are: temperature 130°C, time 20 min;

[0039] S4. Print carbon paste on the basis of the silver paste layer, and move the PI original film printed with carbon paste to the baking area for drying to form a carbon paste layer. The drying conditions are: temperature 135°C, time 20 min;

[0040] S5. Perform film lamination on the PI original film processed in step S4 to form a semi-finished product;

[0041] S6. Perform post-treatment on the semi-finished product.

[0042] Among them, pre-shrinking treatment is performed before printing the conductive layer, which can avoid problems such as oxidation or deformation of the conductive material caused by "printing first and then pre-shrinking treatment".

[0043] It should be noted that there is a technical means of "pre-shrinkage treatment" in the prior art, which is used in the field of fabrics. In principle, the two are essentially different. Specifically, fabric pre-shrinkage treatment relies on a humid and hot environment (water + heat) to achieve fiber expansion and stress release, which is a physical structural change of the fiber, while PI film is treated with high-temperature dry heat to enhance the thermal motion of the molecular chain, and the internal stress is released through the rearrangement of the molecular chain. This is to optimize the molecular chain structure through a pure thermodynamic process (dry heat treatment). In addition, the wet heat pre-shrinkage treatment in the fabric field cannot be directly used in the manufacture of PTC heating films for the following reasons: (1) Water vapor in a wet heat environment may cause the PI film to absorb water, reducing its insulation performance or mechanical strength; (2) Steam penetration during wet heat treatment causes different areas of the PI film to absorb different amounts of moisture, triggering anisotropic shrinkage, resulting in uneven shrinkage of the PI film, affecting the dimensional accuracy and processing quality of the finished product; (3) Wet heat treatment requires higher corrosion resistance of the equipment, which increases equipment requirements, maintenance costs, and energy consumption costs; (4) The synergy with subsequent process steps is poor because: the PI film requires an additional drying step after absorbing moisture, otherwise the residual moisture may cause bubbles or stratification during subsequent high-temperature baking.

[0044] In this embodiment, step S2 is preferred, and the conditions for the pre-shrinkage treatment are: temperature 130°C ~ 180°C, time 0.5-2 hours, by heating the PI film for a long time, so that it can fully stress shrink, ensuring its dimensional stability in subsequent processing.

[0045] More preferably, the pre-shrinkage treatment conditions are: temperature 150° C., time 1 hour, and shrinkage rate less than 0.5%.

[0046] In this embodiment, preferably, the preprocessing includes the following steps:

[0047] Step S21, heating to 100°C at 5-10°C / min and keeping warm for 10 minutes, which softens the molecular chains of the PI film and provides a basis for subsequent stress release; the insulation stage can repair micro cracks or wrinkles on the surface of the substrate and improve the flatness of the printed surface.

[0048] Step S22, raising the temperature to 150°C at 3-5°C / min and keeping the temperature for 1 hour, which promotes the full extension and rearrangement of the molecular chains and improves the long-term thermal stability of the substrate.

[0049] Step S23, cooling to room temperature at 2-4°C / min, slowly cooling to gradually fix the molecular chains and reduce local crystallization defects caused by rapid cooling; gradient cooling avoids excessive temperature difference between the substrate and the equipment contact surface to ensure uniformity of thermal shrinkage in the thickness direction.

[0050] By controlling the gradient heating and cooling, we can avoid stress concentration or micro cracks on the substrate caused by sudden temperature changes, thus ensuring the quality of the original PI film.

[0051] In this embodiment, before the pre-shrinking treatment, the PI original film is pre-dried. The drying conditions are: temperature 80°C, humidity ≤ 20%, and time 30 - 60 minutes. By performing the pre-drying treatment, the initial hygroscopicity of the substrate is eliminated, and the size shrinkage caused by water evaporation during the pre-shrinking treatment is reduced; the adsorbed water and low-boiling impurities (such as environmental pollutants) are also removed, avoiding hydrolysis reactions (such as the breaking of the imide ring of the PI film) at high pre-shrinking temperatures and protecting the integrity of the chemical structure of the material.

[0052] In this embodiment, before performing step S3, the pre-shrunk PI original film is cooled to room temperature, and the humidity of the cooling environment ≤ 30%. This can control the environmental humidity and avoid secondary deformation caused by substrate moisture absorption.

[0053] In order to further improve the slurry adhesion effect, after the cooling is completed, polar groups are formed on the film surface by discharging at a high frequency and high voltage of 15 - 30 kHz and 10 - 30 kV, increasing the surface energy, making the slurry easier to adhere, and further improving the adhesion effect between the slurry and the PI original film.

[0054] In this embodiment, after performing step S5 and before performing step S6, the semi-finished product is refrigerated. The refrigeration conditions are: temperature -10°C, and time 12 hours. By performing the refrigeration treatment, not only can the cooling of the semi-finished product be accelerated, but also the molecular chains of the pre-shrunk PI original film can be made more stable, reducing the size shrinkage in subsequent processing.

[0055] Among them, preferably, the refrigeration conditions are: temperature -10°C, and time 12 hours.

[0056] Among them, before the refrigeration treatment, the semi-finished product is pre-cooled. The pre-cooling conditions are temperature: 0 - 10°C, and time 0.5 - 1 hour. This can avoid the concentration of internal stress in the material caused by a sudden drop in temperature.

[0057] Among them, after the refrigeration treatment, the temperature is increased to room temperature at a gradient, and the heating rate is 1 - 3°C / min. This can prevent the formation of condensed water and ensure the surface dryness of the film material.

[0058] In this embodiment, the post-treatment in step S6 includes steps such as cutting, punching and welding wires, pasting ear materials at the solder joints, and hot-pressing ear materials. These are existing conventional steps and will not be elaborated here.

[0059] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a PTC heating film, characterized in that, It includes the following steps: S1. Select a PI original film as the substrate; S2. Perform pre-shrinking treatment on the PI original film with high-temperature dry hot air to eliminate the shrinkage stress of the PI original film; S3. Print conductive silver paste on the pre-shrunk PI original film, and move the PI original film printed with conductive silver paste to the baking area by a roll-to-roll method to dry and form a silver paste layer; S4. Print carbon paste on the basis of the silver paste layer, and move the PI original film printed with carbon paste to the baking area by a roll-to-roll method to dry and form a carbon paste layer; S5. Laminate the PI original film processed in step S4 to form a semi-finished product; S6. Perform post-treatment on the semi-finished product.

2. The preparation method of the PTC heating film according to claim 1, wherein: The conditions of the pre-shrinking treatment are: temperature 130°C to 180°C, time 0.5 - 2 hours.

3. The preparation method of the PTC heating film according to claim 2, wherein: The conditions of the pre-shrinking treatment are: temperature 150°C, time 1 hour.

4. The preparation method of the PTC heating film according to claim 1, characterized in that: The pretreatment includes the following steps: Step S21. Heat up to 100°C at a rate of 5 - 10°C / min and keep warm for 10 minutes; Step S22. Heat up to 150°C at a rate of 3 - 5°C / min and keep warm for 1 hour; Step S23. Cool down to room temperature at a rate of 2 - 4°C / min.

5. The preparation method of the PTC heating film according to claim 1, wherein: Before performing the pre-shrinking treatment, perform pre-drying treatment on the PI original film, and the drying conditions are: temperature 80°C, humidity ≤20%, time 30 - 60 minutes.

6. The preparation method of the PTC heating film according to claim 1, wherein: Before performing step S3, cool the PI original film to room temperature, and the humidity of the cooling environment ≤30%.

7. The preparation method of the PTC heating film according to claim 1, wherein: After performing step S5 and before performing step S6, perform refrigeration treatment on the semi-finished product, and the refrigeration treatment conditions are: temperature 0 - 5°C, time 8 - 24 hours.

8. The preparation method of the PTC heating film according to claim 7, characterized in that: Before the refrigeration treatment, perform pre-cooling on the semi-finished product, and the conditions of the pre-cooling are: temperature 10 - 15°C, time 0.5 - 1 hour.

9. The preparation method of the PTC heating film according to claim 1, wherein: After the refrigeration treatment, perform gradient heating to room temperature, and the heating rate is 1 - 3°C / min.

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