Polyimide film with high peel strength and preparation method thereof

Abstract

The invention discloses a polyimide film with high peel strength and a preparation method thereof, and belongs to the technical field of polyimide films. The method comprises the following steps: dissolving p-phenylenediamine in an aprotic polar solvent, and adding excessive 3, 3 ', 4, 4'-biphenyl tetracarboxylic dianhydride at one time to synthesize a 3, 3 ', 4, 4'-biphenyl tetracarboxylic dianhydride-terminated polyamide acid resin solution 1; dissolving m-phenylenediamine in the polyamide acid resin solution 1, and adding 3, 3 ', 4, 4'-biphenyltetracarboxylic dianhydride which is not excessive in batches to synthesize a polyamide acid resin solution 2 terminated by m-phenylenediamine; casting the polyamide acid resin solution 2 onto an annular steel belt, drying and stripping to obtain a gel film, introducing the gel film into a multi-section temperature gradient oven, and carrying out longitudinal stretching, transverse stretching and thermal imidization reaction on the gel film to obtain a polyimide film; wherein active amido in the end-capping structure can be subjected to nucleophilic ring-opening reaction with an epoxy group of the epoxy adhesive, a C-N covalent bond network is formed at an interface, and the interface bonding force with the epoxy adhesive is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyimide films, and in particular relates to a polyimide film with high peeling strength and a preparation method thereof. Background Art

[0002] Flexible copper clad laminate is a key material composed of copper foil, adhesive and polyimide (PI) film. Its preparation process is to coat epoxy adhesive on both sides of PI film and then heat press it with copper foil. According to the product standard, qualified flexible copper clad laminate must meet the technical requirement of 90° peel strength ≥1.0kgf / cm.

[0003] However, in order to meet the stringent requirements of PI film in terms of mechanical properties, thermal expansion coefficient (need to be similar to copper foil) and thermal shrinkage, the existing preparation method usually uses rigid dianhydride monomer 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and rigid diamine monomer p-phenylenediamine (PPD) as synthetic raw materials. Although this raw material selection ensures the various properties of the film, it also leads to insufficient surface activity of the prepared polyimide film, which exhibits poor interfacial bonding when combined with epoxy adhesives, ultimately causing the problem of insufficient peel strength.

[0004] In order to improve the interfacial bonding strength between polyimide (PI) film and epoxy adhesive, the industry generally uses oxygen plasma treatment or high-power corona treatment as film post-treatment process. These two surface modification technologies can significantly improve the interfacial peeling strength by increasing the surface roughness of the film and introducing polar groups. However, this type of high-energy surface treatment process has two significant technical limitations: first, high-energy particle bombardment will inevitably cause damage to the microstructure of the film surface, affecting the intrinsic properties of the material; second, the treatment effect has obvious time dependence, and the surface activity will gradually decay with the extension of storage time, which will eventually lead to problems such as interface failure in the actual use of the product. Summary of the invention

[0005] In view of the deficiencies in the prior art, the object of the present invention is to provide a polyimide film with high peel strength and a preparation method thereof, thereby solving the problems in the prior art.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a polyimide film comprises the following steps:

[0008] dissolving p-phenylenediamine in a non-protonic polar solvent, and adding an excess of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride at one time to synthesize a polyamic acid resin solution 1 terminated with 3,3',4,4'-biphenyltetracarboxylic acid dianhydride;

[0009] Dissolving m-phenylenediamine in a polyamic acid resin solution 1, and adding a moderate amount of 3,3',4,4'-biphenyltetracarboxylic dianhydride in batches to synthesize a polyamic acid resin solution 2 terminated with m-phenylenediamine;

[0010] The polyamic acid resin solution 2 is cast onto an endless steel belt, and a gel film is obtained by drying and peeling. The gel film is introduced into an oven with a multi-stage temperature gradient, and the gel film is subjected to longitudinal stretching, transverse stretching, and thermal imidization reaction to obtain a polyimide film.

[0011] Furthermore, when the polyamic acid resin solution 1 is synthesized, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to p-phenylenediamine is 1.05:1.

[0012] Furthermore, when the polyamic acid resin solution 2 is synthesized, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to m-phenylenediamine is (0.9-0.94):1.

[0013] Furthermore, the aprotic polar solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

[0014] Furthermore, the temperature gradient in the oven is: 160°C, 240°C, 320°C, 400°C, 400°C, 320°C, 240°C, and 160°C.

[0015] Furthermore, the heating time corresponding to each gradient temperature in the oven is 30s.

[0016] Furthermore, the ratio of longitudinal stretching × the ratio of transverse stretching is 1.2-1.4.

[0017] A polyimide film is prepared using the above-mentioned method for preparing a polyimide film.

[0018] The above-mentioned polyimide film is used in the preparation of flexible copper-clad laminates.

[0019] A flexible copper-clad laminate is composited from copper foil, adhesive and the above-mentioned polyimide film.

[0020] Beneficial effects of the present invention:

[0021] 1. The present invention synthesizes a polyamic acid resin solution end-capped with m-phenylenediamine through molecular structure design. After casting, gradient drying and biaxial stretching processes, a polyimide film with a specific end group structure is obtained through programmed temperature-controlled thermal imidization. The active amine group in the end-capping structure can undergo a nucleophilic ring-opening reaction with the epoxy group of the epoxy adhesive to form a CN covalent bond network at the interface, which significantly improves the interfacial bonding force between the PI film and the epoxy adhesive, and the 90° peel strength test reaches more than 1.0 kgf / cm.

[0022] 2. Different from the surface etching defects caused by traditional oxygen plasma or high-power corona treatment, the present invention achieves an essential improvement in the interface bonding force through the intermolecular chemical bonding mechanism, avoids the damage to the microstructure of the film surface caused by high-energy particle bombardment, and will not decay with prolonged storage time.

[0023] 3. The preparation method of the present invention realizes interface self-reaction functionalization through molecular design, omits the surface treatment process and related equipment investment, shortens the process cycle, reduces the overall cost, and has significant economic benefits and market competitive advantages. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] In the examples and comparative examples, the names of the raw materials used and their corresponding abbreviations are as follows:

[0026] Diamines: p-phenylenediamine (PPD), m-phenylenediamine (MPD);

[0027] Dianhydride: 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA);

[0028] Aprotic polar solvents: N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc);

[0029] In addition, the sources of the raw materials used in the embodiments and comparative examples are as follows:

[0030] p-Phenylenediamine (PPD): CAS No.: 106-50-3, purchased from Tianjin Zotye Materials Technology Co., Ltd.;

[0031] Metaphenylenediamine (MPD): CAS No.: 108-45-2, purchased from Tianjin Zotye Materials Technology Co., Ltd.;

[0032] 3,3',4,4'-Biphenyltetracarboxylic dianhydride (s-BPDA): CAS No.: 2420-87-3, purchased from Tianjin Zotye Materials Technology Co., Ltd.;

[0033] N-Methylpyrrolidone (NMP): CAS No.: 872-50-4, Anyang Jiutian Fine Chemical Co., Ltd.;

[0034] N,N-Dimethylformamide (DMF): CAS No.: 68-12-2, Anyang Jiutian Fine Chemical Co., Ltd.;

[0035] N,N-Dimethylacetamide (DMAc): CAS No.: 127-19-5, Anyang Jiutian Fine Chemicals Co., Ltd.

[0036] Example 1

[0037] A method for preparing a polyimide film with high peel strength comprises the following steps:

[0038] S1, add 200 kg of DMAc solvent and 6.48 kg of PPD monomer into a polymerization reactor, replace with nitrogen, stir, and add 18.522 kg of s-BPDA monomer at once after complete dissolution, the reaction time is 2 h, the reaction temperature is 25 ° C, and a polyamic acid resin solution 1 (PAA-1) is prepared;

[0039] S2, adding 6.48 kg of MPD monomer to PAA-1, nitrogen replacement, stirring, and dissolving completely, adding 15.876 kg of s-BPDA monomer in batches, the reaction time is 2 hours, and vacuum degassing is performed for 24 hours to prepare polyamic acid resin solution 2 (PAA-2);

[0040] S3. PAA-2 is cast onto an endless steel belt, and a self-supporting gel film is obtained after drying and peeling. The gel film is introduced into an oven with a multi-stage temperature gradient, and the multi-stage temperature gradients are 160°C, 240°C, 320°C, 400°C, 400°C, 320°C, 240°C, and 160°C, respectively. The heating time of each stage is 30 seconds. The gel film is heated and stretched in the multi-stage stretching oven, and the total stretching ratio (longitudinal stretching ratio × transverse stretching ratio) is controlled to be 1.2, so as to obtain a polyimide film with high peeling strength.

[0041] Example 2

[0042] A method for preparing a polyimide film with high peel strength, the steps of which are as follows:

[0043] S1, add 200 kg of DMAc solvent and 6.48 kg of PPD monomer into a polymerization reactor, replace with nitrogen, stir, and add 18.522 kg of s-BPDA monomer at once after complete dissolution, the reaction time is 2 h, the reaction temperature is 25 ° C, and a polyamic acid resin solution 1 (PAA-1) is prepared;

[0044] S2, adding 6.48 kg of MPD monomer to PAA-1, nitrogen replacement, stirring, and dissolving completely, adding 16.229 kg of s-BPDA monomer in batches, the reaction time is 2 hours, and vacuum degassing is performed for 24 hours to prepare polyamic acid resin solution 2 (PAA-2);

[0045] S3. PAA-2 is cast onto an endless steel belt, and a self-supporting gel film is obtained after drying and peeling. The gel film is introduced into an oven with a multi-stage temperature gradient, and the multi-stage temperature gradients are 160°C, 240°C, 320°C, 400°C, 400°C, 320°C, 240°C, and 160°C, respectively. The heating time of each stage is 30s. The gel film is stretched while being heated in the multi-stage stretching oven, and the total stretching ratio (longitudinal stretching ratio × transverse stretching ratio) is controlled to be 1.3, so as to obtain a polyimide film with high peeling strength.

[0046] Example 3

[0047] A method for preparing a polyimide film with high peel strength, the steps of which are as follows:

[0048] S1, add 200 kg of DMAc solvent and 6.48 kg of PPD monomer into a polymerization reactor, replace with nitrogen, stir, and add 18.522 kg of s-BPDA monomer at once after complete dissolution, the reaction time is 2 h, the reaction temperature is 25 ° C, and a polyamic acid resin solution 1 (PAA-1) is prepared;

[0049] S2, adding 6.48 kg of MPD monomer to PAA-1, nitrogen replacement, stirring, and dissolving completely, adding 16.582 kg of s-BPDA monomer in batches, the reaction time is 2 hours, and vacuum degassing is performed for 24 hours to prepare polyamic acid resin solution 2 (PAA-2);

[0050] S3. PAA-2 is cast onto an endless steel belt, and a self-supporting gel film is obtained after drying and peeling. The gel film is introduced into an oven with a multi-stage temperature gradient, and the multi-stage temperature gradients are 160°C, 240°C, 320°C, 400°C, 400°C, 320°C, 240°C, and 160°C, respectively. The heating time of each stage is 30s. The gel film is heated and stretched in the multi-stage stretching oven, and the total stretching ratio (longitudinal stretching ratio × transverse stretching ratio) is controlled to be 1.4, so as to obtain a polyimide film with high peeling strength.

[0051] Comparative Example

[0052] A method for preparing a polyimide film comprises the following steps:

[0053] Add 200 kg of DMAc solvent, 6.48 kg of PPD monomer, and 6.48 kg of MPD monomer into a polymerization reactor. After nitrogen replacement, stirring, and complete dissolution, add 18.522 kg of s-BPDA monomer at once, and then add 16.229 kg of s-BPDA monomer in batches. The reaction time is 2 h, the reaction temperature is 25 ° C, and vacuum degassing is performed for 24 h to prepare a polyamic acid resin solution;

[0054] The polyamic acid resin solution is cast onto an endless steel belt, and a self-supporting gel film is obtained after drying and peeling. The gel film is introduced into an oven with a multi-stage temperature gradient, and the multi-stage temperature gradients are 160°C, 240°C, 320°C, 400°C, 400°C, 320°C, 240°C, and 160°C, respectively. The heating time of each stage is 30s. The gel film is stretched while being heated in a multi-stage stretching oven, and the total stretching ratio (longitudinal stretching ratio × transverse stretching ratio) is controlled to be 1.3 to obtain a polyimide film.

[0055] Experimental verification

[0056] The surfaces of the polyimide films prepared in Examples 1-3 of the present invention and the comparative example were first coated with epoxy adhesive and then laminated with copper foil, and then placed in a laminating device for laminating (laminating conditions were 120 kg / 100 s). The laminated samples were treated at 180° C. / 3 h, and a 90° peel strength test was performed according to ASTM D3330. The test results are shown in Table 1 below:

[0057] Table 1 Performance data of polyimide films prepared in Examples 1-3 and Comparative Examples

[0058]

[0059] As can be seen from Table 1, the present application synthesized a polyamic acid resin solution end-capped with m-phenylenediamine through molecular structure design. After casting, gradient drying and biaxial stretching processes, a polyimide film with a specific end group structure was obtained through programmed temperature-controlled thermal imidization. The active amine group in the end-capping structure can undergo a nucleophilic ring-opening reaction with the epoxy group of the epoxy adhesive to form a CN covalent bond network at the interface, which significantly improves the interfacial bonding strength between the polyimide film and the epoxy adhesive, and the 90° peel strength test reaches more than 1.0 kgf / cm.

[0060] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0061] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for preparing a polyimide film, characterized in that: The following steps are involved: dissolving p-phenylenediamine in a non-protonic polar solvent, and adding an excess of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride at one time to synthesize a polyamic acid resin solution 1 terminated with 3,3',4,4'-biphenyltetracarboxylic acid dianhydride; Dissolving m-phenylenediamine in a polyamic acid resin solution 1, and adding a moderate amount of 3,3',4,4'-biphenyltetracarboxylic dianhydride in batches to synthesize a polyamic acid resin solution 2 terminated with m-phenylenediamine; The polyamic acid resin solution 2 is cast onto an endless steel belt, and a gel film is obtained by drying and peeling. The gel film is introduced into an oven with a multi-stage temperature gradient, and the gel film is subjected to longitudinal stretching, transverse stretching, and thermal imidization reaction to obtain a polyimide film.

2. The method for preparing a polyimide film according to claim 1, characterized in that: When the polyamic acid resin solution 1 is synthesized, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to p-phenylenediamine is 1.05:

1.

3. The method for preparing a polyimide film according to claim 1, characterized in that: When the polyamic acid resin solution 2 is synthesized, the molar ratio of 3,3',4,4'-biphenyltetracarboxylic dianhydride to m-phenylenediamine is (0.9-0.94):

1.

4. The method for preparing a polyimide film according to claim 1, characterized in that: The aprotic polar solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

5. The method for preparing a polyimide film according to claim 1, characterized in that: The temperature gradient in the oven is: 160°C, 240°C, 320°C, 400°C, 400°C, 320°C, 240°C, and 160°C.

6. The method for preparing a polyimide film according to claim 5, characterized in that: The heating time corresponding to each gradient temperature in the oven is 30s.

7. The method for preparing a polyimide film according to claim 1, characterized in that: The ratio of longitudinal stretching × the ratio of transverse stretching is 1.2-1.

4.

8. A polyimide film, characterized in that: The polyimide film is prepared using the method for preparing the polyimide film according to any one of claims 1 to 7.

9. Use of the polyimide film according to claim 8 in the preparation of flexible copper clad laminates.

10. A flexible copper clad laminate, characterized in that: It is composited by copper foil, adhesive and the polyimide film as claimed in claim 8.

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