Synthesis method and application of heat-adhesive polyimide and polyimide film

Abstract

The application relates to a synthesis method and application of a heat-adhesive polyimide and polyimide film, and steps are as follows: a plurality of portions of diamine monomers and a plurality of portions of dianhydride monomers are prepared into a polyimide acid solution, then a glue film is prepared, and a heat-adhesive polyimide film is obtained after complete imidization at high temperature. The application proposes a novel heat-adhesive polyimide film containing N and S atom coordination elements, which has a low thermal expansion coefficient, high heat adhesion, high heat resistance and high tensile strength, and can be applied to the production of glue-free double-sided flexible copper-clad plates (2L-FCCL) by a laminating method. Compared with existing commercial polyimide films, the heat-adhesive polyimide film in the application can be strongly attached to copper foil in a heat processing process without an additional epoxy resin or acrylic adhesive, and thus is suitable for the rapid production of 2L-FCCL by a hot pressing method, the peel strength of the heat-adhesive polyimide film reaches above 0.6 N / mm, and the highest peel strength reaches 1.2 N / mm, and the heat-adhesive polyimide film has a good application prospect in the field of glue-free flexible copper-clad plates.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of preparation of flexible copper-clad plates, in particular to a hot-bonding type polyimide and a synthesis method and application of a polyimide film. BACKGROUND

[0002] In the field of electronic devices, traditional rigid circuit boards are being replaced by flexible printed circuit boards (FPC) with light, thin and flexible characteristics, so that special polymer films meeting high insulation requirements and high temperature processing requirements become the first choice. Polyimide (PI) has excellent dielectric properties, thermal stability, chemical stability, mechanical properties and flame retardancy, and is praised by the electronic industry as "a problem solver". Polyimide film (PI film) can be used to produce high-quality flexible copper-clad plates (FCCL), and is a major focus of current thin film application research.

[0003] FCCL can be divided into three-layer flexible copper-clad plates (3L-FCCL) and two-layer flexible copper-clad plates (2L-FCCL) according to its structure. The main difference between the two is whether there is an adhesive between the polyimide film and the copper foil substrate. 3L-FCCL is a mature technology as a traditional FPC material. Its main structure is that an adhesive is used to bond the copper foil and the PI film. The adhesive is mostly epoxy resin or acrylate, which has the disadvantage that the adhesive strength, thermal stability and dielectric properties are affected by the properties of the adhesive itself. For example, in the high-frequency communication field, the loss of electrical signals has a "skin effect", and the adhesive on the surface of the copper foil increases the transmission loss. At the same time, due to the presence of the adhesive, the size deviation occurs during precision processing, and peeling and delamination occur at high temperatures, and the thickness is large, etc. Therefore, there is a strong demand for FCCL with better performance. 2L-FCCL directly uses copper foil and polyimide film to be combined, and cancels the intermediate adhesive layer, that is, a no-adhesive copper-clad plate, which overcomes the performance deficiencies of the above 3L-FCCL caused by the adhesive, and has a broad application prospect.

[0004] The PI film for 2L-FCCL has the difficulty that thermal adhesion and dimensional stability cannot be achieved. Some existing researches realize the bonding with the surface of the copper plate by increasing the flexibility of the PI molecular chain, but the dimensional stability at high temperature is sacrificed, which is not conducive to precision processing. The hot-bonding type polyimide film involved in the present application introduces N and S strong coordination atoms, uses Cu---N and Cu---S coordination bonds to enhance the bonding of the film and the copper plate, does not affect the thermal performance of the PI film, has low thermal expansion coefficient, high bonding force with the copper plate and high tensile strength, and can be applied to the lamination method to quickly prepare a no-adhesive double-sided flexible copper-clad plate. SUMMARY

[0005] The technical problem solved by the present application: In view of the technical problem that heat adhesion and dimensional stability cannot be achieved in the prior art, the present application provides a synthesis method and application of a heat-adhesion polyimide and a polyimide film. The film has a structure containing N and S atoms that can provide coordination sites and spatial positions in the structural unit. The introduction of such a strong coordination structure can form a coordination bond with a strong bond energy between the copper element on the surface of the copper-clad plate and the polyimide film during thermal processing, so that the polyimide film has super strong adhesion with the copper-clad plate. The heat-adhesion polyimide film prepared by the method has excellent mechanical properties, thermal properties, and excellent adhesion properties with copper foil, and can be used to prepare a glue-free 2L-FCCL, which is worth being widely promoted and applied.

[0006] Technical solution: A synthesis method of a polyimide film, comprising the following steps: preparing a polyimide acid solution (PAA) from a plurality of diamine monomers and a plurality of dianhydride monomers, then preparing a glue film, and obtaining a polyimide film after complete imidization at high temperature. The diamine monomer is thiourea or a diamine monomer containing at least one aromatic ring or aromatic heterocycle, and the aromatic ring or aromatic heterocycle or the structure connected thereto contains at least one of N atoms and S atoms. The dianhydride monomer is a dianhydride monomer containing at least one aromatic ring or aromatic heterocycle.

[0007] As a preferred, the diamine monomer is at least one of the following structures:

[0008]

[0009] Further, the diamine monomer is at least one of the following structures:

[0010]

[0011] As a preferred, the dianhydride monomer is

[0012] Further, the dianhydride monomer is

[0013] As a preferred, the diamine monomer and the dianhydride monomer are polycondensed in a solvent at a temperature of 5-10°C to prepare a polyimide acid solution, the total molar ratio of the dianhydride monomer to the diamine monomer is 0.95-1.05:1, the solid content in the polyimide acid solution is 10-30%, and the viscosity is 5000-30000 mPa·s. The polycondensation reaction formula is as follows:

[0014]

[0015] In the formula, n is an integer greater than or equal to 1, and Ar2 is a dianhydride monomer. In the formula, the value of n is selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Ar1 is a diamine monomer.

[0016] As preferred, the solvent is a strong polar solvent, specifically at least one of acetone, acetonitrile, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methylpyrrolidone and gamma-butyrolactone.

[0017] As preferred, the polyimide acid solution is further formed into a wet film with a thickness of 800-2000 um on a glass or steel plate by using a flow casting method, and then the wet film is dried in a vacuum oven at 60-80℃ to obtain a glue film, which is then peeled off, clamped by a clamp rod at four edges, and sent into a high-temperature oven for imidization.

[0018] As preferred, after the glue film is completely imidized at high temperature, the polyimide film is obtained by the following steps: the imidization temperature ladder in the high-temperature oven is 150℃ for 2h, 200℃ for 1h, 250℃ for 1h, 300℃ for 0.5h, and 350℃ for 0.5h, and then naturally cooled.

[0019] As preferred, the film after natural cooling is soaked in water, peeled off from the glass or steel plate, and dried at 80℃ for 2h.

[0020] A heat-adhesive polyimide based on the above synthesis method of polyimide film.

[0021] Application of the heat-adhesive polyimide based on the above in preparation of a two-layer flexible copper-clad plate.

[0022] As preferred, the copper foil and the polyimide film can be directly pressed into a two-layer flexible copper-clad plate by using a hot-pressing method under the conditions of 330-360℃, a pressure of 0.5Mpa, and a hot-pressing time of 30-60s.

[0023] The heat-adhesive polyimide has a high thermal stability due to the conjugated structure of aromatic rings, so that the polyimide film has a high glass transition temperature, and the polyimide film has a low thermal expansion coefficient due to the stacking effect between the conjugated structures of multiple aromatic rings. The introduction of the N and S atom-containing monomer by the diamine monomer enhances the electron-donating and accepting effect between the polyimide molecules, strengthens the stacking effect and the entanglement between the chains, and provides excellent thermal stability and mechanical properties; the coordination bond strength between the N and S atom-containing monomer and the copper atoms on the surface of the copper foil at high temperature is much greater than the coordination effect between the copper and the conjugated bond, so that the copper foil has a stronger bonding effect in the form of coordination bond.

[0024] Beneficial effects: (1) the application introduces benzothiazole, thiazole, thiourea and other N, S atom containing structure monomers into polyimide, and the heat-adhesive polyimide film containing N, S atom coordination elements prepared by the method has excellent thermal expansion coefficient and high heat adhesion, and solves the contradictory between heat adhesion and thermal expansion.

[0025] The heat-adhesive polyimide containing N, S atom coordination elements prepared by the application has excellent mechanical properties and glass transition temperature, can meet the application in the field of 2F-FCCL, and is worth being widely popularized and applied.

[0026] In conclusion, the heat-adhesive polyimide provided by the application contains N, S atom fragments, such as thiazole and thiophene, which can provide coordination sites and spatial positions, strong coordination structures, can form strong coordination bonds with exposed copper elements on the surface of copper-clad plates in the heat processing process, and then form strong adhesion, and the film body has excellent mechanical properties, thermal properties and copper plate heat bonding properties. Compared with the existing commercial polyimide film, the heat-adhesive polyimide film in the application can be strongly attached to the copper foil in the heat processing process without additional epoxy resin or acrylic adhesive, and therefore is suitable for the rapid preparation of 2L-FCCL by hot pressing, and the peel strength reaches more than 0.6 N / mm, and the highest reaches 1.2 N / mm, and has a good application prospect in the field of glue-free flexible copper-clad plates. DETAILED DESCRIPTION

[0027] The embodiments of the application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the application, and should not be regarded as limiting the scope of the application. The specific conditions are not indicated in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not indicated by the manufacturer, and are conventional products that can be purchased on the market. EXAMPLES

[0028] The synthesis method of the polyimide film in the embodiment is as follows:

[0029] Preparation of PAA solution: 100 mol of diamine monomer and 98 mol of dianhydride monomer are condensed in a solvent to prepare a polyimide acid solution (PAA), and the total mole ratio of the dianhydride monomer to the diamine monomer is 0.98:1, and the condensation reaction formula is as follows:

[0030] , the solvent is at least one of acetone, acetonitrile, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N-methyl pyrrolidone and gamma-butyrolactone, and the solid content is 10%.

[0031] Imidization film forming: the polyimide acid solution is again formed into a wet film with a thickness of 2000 um on a glass or steel plate by using a flow casting method, and then the wet film is dried in a vacuum oven at 80°C to obtain a glue film, which is then removed, the four edges are clamped with clamping rods, and then sent into a high-temperature oven for imidization. After the high-temperature complete imidization, the polyimide film is obtained by the following steps: the temperature ladder of imidization in the high-temperature oven is 150°C, 2h; 200°C, 1h; 250°C, 1h; 300°C, 0.5h; 350°C, 0.5h, and then naturally cooled, and the naturally cooled film is immersed in water, removed from the glass or steel plate, and dried at 80°C for 2h.

[0032] Based on Example 1, the preparation of PAA solution and imidization film forming process of diamine and dianhydride in Examples 2-10 and Comparative Examples 1 and 2 are consistent, except that different diamine monomers and dianhydride monomers are selected (see Table 1), and then the diamine monomers and dianhydride are prepared into polyimide films for testing at room temperature 25°C, and the thickness is 30um. The polyimide film is directly hot-pressed with a 25um thick copper foil, and the peel strength is tested, and the test results are shown in Table 2.

[0033] Table 1 Structure of diamine monomers and dianhydride monomers corresponding to Examples 1-10 and Comparative Examples 1 and 2

[0034]

[0035] Table 2 Test results of the properties of the products prepared in Examples 1-10 and Comparative Examples 1 and 2

[0036]

[0037] Note: The tensile strength testing instrument in Table 2 is a universal material testing machine, and the detection standard is GB / T 1040.1-2018, and when the tensile strength is > 140MPa, it is qualified;

[0038] The glass transition temperature testing instrument is a differential scanning calorimeter (DSC), and the detection standard is GB / T 19466.2-2004, and when the glass transition temperature is > 280°C, it is qualified;

[0039] The thermal expansion coefficient testing instrument is a dynamic mechanical analyzer (DMA), and the detection standard is GB / T 12027-2004, and when the thermal expansion coefficient is < 25ppm / K, it is qualified;

[0040] The peeling strength detector of the non-glue copper clad plate is a universal material testing machine, and the detection standard is GB / T 13555-2017. When the peeling strength is greater than or equal to 0.6 N / mm, it is qualified.

[0041] The tensile strength, glass transition temperature, thermal expansion coefficient and peeling strength after hot pressing of PI and copper clad plate of the PI films prepared in Examples 1-10 and Comparative Examples 1-2 were analyzed. It can be found that the PI with fluorine element introduced in Examples 3 and 10 weakens the adhesion to copper plate, tensile strength and heat resistance. In addition, most of the examples use diamines and dianhydrides containing N, S atom coordination elements in monomers, which can prepare PI films with high tensile strength, high glass transition temperature and low thermal expansion coefficient, and PI copper clad plates with high peeling strength can be obtained after hot pressing of PI film and copper clad plate. Especially in Example 5, the adhesion to copper plate is the strongest, the peeling strength is 1.2 N / mm, the tensile strength of the film is 220 MPa, which is the highest value in the examples, the glass transition temperature is 330℃, which fully meets the requirement of ≥260℃ for the welding requirement of copper clad plate circuit, and the thermal expansion coefficient is close to the copper foil, which is 15 ppm / K. Comparative Examples 1 and 2 do not add monomers containing N, S coordination elements, but only use common PI monomers, i.e. the main monomers involved in the film with the trade name Kapton. The peeling strength of the prepared film and copper plate is ≤0.3 N / mm, which cannot be used for the preparation of double-layer FCCL by lamination method.

[0042] Finally, it can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the principles of the present application, and the present application is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the principles and essence of the present application, and these modifications and improvements are also considered as the protection scope of the present application.

Claims

1. A method for synthesizing a polyimide film, characterized in that: The steps are as follows: a plurality of diamine monomers and a plurality of dianhydride monomers are prepared into a polyimide acid solution, which is then made into a film, and a hot-adhesive polyimide film is obtained after complete imidization at high temperature. , the dianhydride monomer is .

2. The method for synthesizing a polyimide film according to claim 1, wherein: A polyimide acid solution is prepared by polycondensing several parts of diamine monomers and several parts of dianhydride monomers in a solvent at a temperature of 5-10° C., wherein the total molar ratio of the dianhydride monomer to the diamine monomer is 0.95-1.05:

1.

3. The method for synthesizing a polyimide film according to claim 2, wherein: The solvent is a highly polar solvent, specifically at least one of acetone, acetonitrile, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and γ-butyrolactone.

4. The method for synthesizing a polyimide film according to claim 1, wherein: The polyimide acid solution is then cast on a glass or steel plate to form a wet film, which is then dried in a vacuum oven at 60-80°C to obtain an adhesive film.

5. The method for synthesizing a polyimide film according to claim 4, wherein: The steps of obtaining a polyimide film after the film is fully imidized at high temperature are as follows: the imidization temperature ladder in a high temperature oven is 150°C, 2h; 200°C, 1h; 250°C, 1h; 300°C, 0.5h; 350°C, 0.5h, and then naturally cooled.

6. A heat-adhesive polyimide synthesized based on the method for synthesizing a polyimide film according to claim 1.

7. Use of the heat-adhesive polyimide according to claim 6 in the preparation of a two-layer flexible copper-clad laminate.

8. The use according to claim 7, characterized in that Under the conditions of 330-360℃, pressure 0.5Mpa and hot pressing time 30-60s, copper foil and polyimide film can be directly pressed into two layers of flexible copper clad laminate by hot pressing.

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