High-temperature-resistant shielding film and preparation method thereof

Abstract

The invention belongs to the technical field of electromagnetic shielding materials, and particularly relates to a high-temperature-resistant shielding film and a preparation method thereof. The high-temperature-resistant shielding film is composed of a PI base film layer with the thickness of 12.5-100 [mu] m, a conductive metal coating with the thickness of 0.01-10 [mu] m and a PI protective film layer with the thickness of 3-10 [mu] m. The preparation method comprises the following steps: preparing a conductive metal coating on a PI base film layer by using conductive metal in a vacuum evaporation, electrostatic spraying or sputter coating manner, then coating a polyimide solution, and drying to form a film, so as to obtain the PI protective film layer. The PI film layer adopted by the invention has the advantages of high temperature resistance and high strength, and good protection of the conductive metal coating can be realized. The conductive metal coating is used as the shielding film layer, so that the shielding film layer has the advantages of good shielding effect, convenience in shielding performance adjustment, simple preparation process and low cost. And an organic silicon modified PI film layer is further adopted, so that the flexibility and the damp-heat-resistant stability of the film can be further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic shielding materials, and in particular relates to a high temperature resistant shielding film and a preparation method thereof. Background Art

[0002] With the rapid advancement of modern information technology, electronic and electrical equipment are developing towards density, miniaturization, high frequency and high speed. High-power and high-speed electronic equipment will radiate a large amount of electromagnetic waves, which will not only affect the performance of electronic products, but also cause certain harm to organisms. Therefore, electromagnetic shielding materials are used in the design of electronic products to resist interference and leakage.

[0003] Flexible electromagnetic shielding film is an important electromagnetic shielding material widely used in electronic products. It has good electromagnetic shielding effect and flexible and bendable characteristics, and is widely used in the electromagnetic shielding field of electronic products such as mobile phones, computers, and tablets. Flexible electromagnetic shielding film is a composite film material composed of conductive material and substrate. The conductive material is usually made of metal foil or conductive powder, and the substrate is made of flexible materials such as organic polymers. When a voltage is applied to the electromagnetic shielding film, the conductive material will form an effective shielding current and electromagnetic wave reflection, thereby achieving the effect of shielding electromagnetic interference.

[0004] Currently, the most widely used organic polymer substrates are polyurethane, polypropylene, epoxy resin, polyimide, etc. Among them, polyimide is attracting people's attention because of its good high temperature resistance, flame retardancy and high mechanical strength. For example, patent CN 113968987A discloses a method for preparing a polyimide-based high temperature resistant electromagnetic shielding film, in which a metal oxide dispersion is added to a polyamic acid resin solution, mixed evenly, and the obtained mixed resin solution is prepared by a thermal imidization method to obtain a polyimide-based high temperature resistant electromagnetic shielding film. However, the conductivity of metal oxides is relatively weak, and the shielding effect on high frequency interference is limited. Summary of the invention

[0005] In view of the shortcomings and deficiencies of the above prior art, the primary purpose of the present invention is to provide a high temperature resistant shielding film.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned high temperature resistant shielding film.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A high temperature resistant shielding film is composed of a PI base film layer with a thickness of 12.5-100 μm, a conductive metal plating layer with a thickness of 0.01-10 μm and a PI protective film layer with a thickness of 3-10 μm.

[0009] Furthermore, the conductive metal plating layer is a layer of aluminum, copper, nickel, silver, tin or an alloy of the above metals.

[0010] Furthermore, the PI base film layer and the PI protective film layer refer to the organosilicon-modified PI film layer prepared by the following method:

[0011] (1) subjecting a cyclosiloxane monomer, isocyanate propylmethyldimethoxysilane and a methylsilane end-capping agent to a polymerization reaction in the presence of a catalyst and anhydrous conditions to obtain an isocyanate polysiloxane;

[0012] (2) adding the dianhydride monomer, the diamine monomer, the dehydrating agent and the catalyst into an organic solvent and dissolving them uniformly, heating the solvent to 80 to 150° C. for prepolymerization, and then adding the isocyanate polysiloxane of step (1) for continued polymerization reaction at a temperature of 100° C. to obtain an organosilicon-modified polyimide solution;

[0013] (3) Drying the organosilicon-modified polyimide solution obtained in step (2) to form a film on a substrate to obtain an organosilicon-modified PI film layer.

[0014] Preferably, the cyclosiloxane monomer in step (1) is octamethylcyclotetrasiloxane (D4) or dimethylsiloxane mixed ring (DMC).

[0015] Preferably, the methylsilane capping agent in step (1) is hexamethyldisiloxane (MM), methoxytrimethylsilane or trimethylchlorosilane.

[0016] Preferably, the mass ratio of the cyclosiloxane monomer, isocyanatepropylmethyldimethoxysilane and methylsilane capping agent added in step (1) is 100:10-40:1-10.

[0017] Preferably, the catalyst in step (1) is sodium siliconate or potassium siliconate; the polymerization reaction temperature is 100 to 140° C., and the polymerization reaction time is 2 to 8 hours.

[0018] Preferably, the dianhydride monomer in step (2) is pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, 4,4'-phenylenedioxydiphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride or 3,3',4,4'-diphenylethertetracarboxylic dianhydride.

[0019] Preferably, the diamine monomer in step (2) is p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobiphenyl, hexamethylenediamine or polyetherdiamine.

[0020] Preferably, in step (2), the dehydrating agent is acetic anhydride, phthalic anhydride or maleic anhydride; and the catalyst is pyridine, triethylamine or 4-dimethylaminopyridine.

[0021] Preferably, the organic solvent in step (2) is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, toluene or tetrahydrofuran.

[0022] Preferably, in step (2), the molar ratio of the dianhydride monomer to the diamine monomer is 1.2 to 1.5:1, and the prepolymerization reaction time is 2 to 6 hours.

[0023] Preferably, the amount of the isocyanate polysiloxane added in step (2) is 20 to 60% of the total mass of the dianhydride monomer and the diamine monomer, and the time of the heat preservation polymerization reaction is 2 to 6 hours.

[0024] The principle of the present invention is: isocyanate groups are introduced into the side chains of polysiloxane by ring-opening copolymerization of isocyanate propylmethyldimethoxysilane and cyclosiloxane monomers, and the obtained isocyanate polysiloxane has the characteristics of high isocyanate content and high reactivity. The dianhydride monomer and the diamine monomer are prepolymerized under the condition of excessive anhydride, and the remaining anhydride can further react with the isocyanate polysiloxane to form a high-temperature resistant polyimide structure, thereby avoiding the formation of a polyurethane structure with low strength and heat resistance. At the same time, the high reactivity of the isocyanate group and the anhydride is used to introduce the polysiloxane with good high temperature resistance, water resistance and flexibility into the polymer structure, so as to improve the flexibility and moisture-heat resistance stability of the PI film layer.

[0025] The method for preparing the above-mentioned high temperature resistant shielding film comprises the following preparation steps:

[0026] The conductive metal is coated on the PI base film layer by vacuum evaporation, electrostatic spraying or sputtering, and then a polyimide solution is coated and dried to form a film to obtain a PI protective film layer.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The high temperature resistant shielding film of the present invention is composed of a PI base film layer, a conductive metal coating layer and a PI protective film layer, wherein the PI base film layer and the protective film layer have the advantages of high temperature resistance and high strength, and can achieve good protection of the conductive metal coating layer. The conductive metal coating layer is used as the shielding film layer, which has the advantages of good shielding effect, convenient shielding performance adjustment, simple preparation process and low cost.

[0029] (2) The present invention further improves the flexibility and moisture and heat resistance of polyimide by further modifying it with silicone. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0031] Example 1

[0032] A method for preparing a high temperature resistant shielding film comprises the following preparation steps:

[0033] (1) Octamethylcyclotetrasiloxane (D4) monomer, isocyanate propylmethyldimethoxysilane and hexamethyldisiloxane (MM) end-capping agent are added to a reaction kettle in a mass ratio of 100:20:5 and stirred to mix evenly. After nitrogen deoxygenation and water removal, the temperature is raised to 120° C., and then 0.02% of trimethylsilanol potassium catalyst is added to the reaction system and stirred for 4 hours. Unreacted raw materials are removed by vacuum extraction at 140-150° C. to obtain isocyanate polysiloxane.

[0034] (2) By mass, 140 parts of pyromellitic anhydride, 100 parts of 4,4'-diaminodiphenyl ether, 5 parts of dehydrating agent acetic anhydride and 0.3 parts of catalyst 4-dimethylaminopyridine were added to 1000 parts of N,N-dimethylformamide solvent and dissolved evenly, and the temperature was raised to 140° C. for prepolymerization reaction for 3 hours, and then 100 parts of isocyanate polysiloxane of step (1) were added and the polymerization reaction was continued at the temperature for 4 hours to obtain a silicone-modified polyimide solution.

[0035] (3) The organosilicon-modified polyimide solution obtained in step (2) is cast on a glass plate and dried to form a film, thereby obtaining an organosilicon-modified PI base film layer with a thickness of 50 μm.

[0036] (4) A metal aluminum coating with a thickness of 5 μm is formed on the organosilicon-modified PI base film layer of step (3) by vacuum evaporation, and then the organosilicon-modified polyimide solution of step (2) is coated on the metal aluminum coating, and the film is dried to obtain an organosilicon-modified PI protective film layer with a thickness of 5 μm.

[0037] The shielding film obtained in this embodiment has a shielding effectiveness of >100dB under 200KHz-50MHz electric field. The organosilicon modified PI film obtained in this embodiment has a 5% weight loss temperature of 568°C after high temperature performance test; the tensile strength test result is 157MPa, the elongation at break is 89%, and the moisture absorption rate of the moisture and heat stability test (immersed in 80°C hot water for 24h) is 0.5%.

[0038] Example 2

[0039] A method for preparing a high temperature resistant shielding film comprises the following preparation steps:

[0040] (1) Octamethylcyclotetrasiloxane (D4) monomer, isocyanate propylmethyldimethoxysilane and hexamethyldisiloxane (MM) end-capping agent are added to a reaction kettle in a mass ratio of 100:10:2 and stirred to mix evenly. After deoxygenation and dehydration with nitrogen, the temperature is raised to 120° C., and then 0.02% of potassium trimethylsilanol catalyst is added to the reaction system and stirred for 4 hours. Unreacted raw materials are removed by vacuum extraction at 140-150° C. to obtain isocyanate polysiloxane.

[0041] (2) Add 250 parts by mass of 4,4'-diphenylene oxide, 100 parts by mass of 4,4'-diaminodiphenyl ether, 10 parts by mass of phthalic anhydride as a dehydrating agent and 0.3 parts by mass of 4-dimethylaminopyridine as a catalyst to 1000 parts by mass of N,N-dimethylformamide solvent and dissolve them uniformly. Heat the mixture to 140°C for prepolymerization for 3 hours. Then, add 100 parts by mass of the isocyanate polysiloxane prepared in step (1) and continue the polymerization reaction for 4 hours to obtain a silicone-modified polyimide solution.

[0042] (3) The organosilicon-modified polyimide solution obtained in step (2) was cast on a glass plate and dried to form a film, thereby obtaining an organosilicon-modified PI base film layer with a thickness of 12.5 μm.

[0043] (4) A metal aluminum coating with a thickness of 0.05 μm is formed on the organosilicon-modified PI base film layer of step (3) by vacuum evaporation, and then the organosilicon-modified polyimide solution of step (2) is coated on the metal aluminum coating, and dried to form a film, thereby obtaining an organosilicon-modified PI protective film layer with a thickness of 3 μm.

[0044] The shielding film obtained in this embodiment has a shielding effectiveness of >80dB under 200KHz-50MHz electric field. The organosilicon modified PI film obtained in this embodiment has a 5% weight loss temperature of 545°C after high temperature performance test; the tensile strength test result is 132MPa, the elongation at break is 95%, and the moisture absorption rate of the moisture and heat stability test (immersed in 80°C hot water for 24h) is 0.6%.

[0045] Example 3

[0046] A method for preparing a high temperature resistant shielding film comprises the following preparation steps:

[0047] (1) Add dimethylsiloxane mixed ring (DMC) monomer, isocyanate propylmethyldimethoxysilane and methoxytrimethylsilane capping agent into a reaction kettle in a mass ratio of 100:40:10 and stir to mix evenly. After deoxygenation and dehydration with nitrogen, heat to 130° C., then add 0.02% of potassium trimethylsilanol catalyst to the reaction system and stir to react for 4 hours. Unreacted raw materials are removed by vacuum extraction at 140-150° C. to obtain isocyanate polysiloxane.

[0048] (2) By mass, 200 parts of 3,3',4,4'-diphenyl ether tetracarboxylic acid dianhydride, 100 parts of 4,4'-diaminodiphenyl ether, 6 parts of dehydrating agent maleic anhydride and 0.3 parts of catalyst 4-dimethylaminopyridine were added to 1000 parts of toluene solvent and dissolved evenly, and the temperature was raised to 110° C. for prepolymerization reaction for 5 hours, and then 100 parts of isocyanate polysiloxane of step (1) was added and the polymerization reaction was continued at the temperature for 5 hours to obtain a silicone modified polyimide solution.

[0049] (3) The organosilicon-modified polyimide solution obtained in step (2) is cast on a glass plate and dried to form a film, thereby obtaining an organosilicon-modified PI base film layer with a thickness of 100 μm.

[0050] (4) A metal aluminum coating with a thickness of 10 μm is formed on the organosilicon-modified PI base film layer of step (3) by vacuum evaporation, and then the organosilicon-modified polyimide solution of step (2) is coated on the metal aluminum coating, and dried to form a film, thereby obtaining an organosilicon-modified PI protective film layer with a thickness of 10 μm.

[0051] The shielding effectiveness of the shielding film obtained in this embodiment is >100dB under the electric field of 200KHz-50MHz. The temperature of 5% weight loss of the organosilicon-modified PI film layer obtained in this embodiment is 583℃ after high temperature performance test; the tensile strength test result is 170MPa, the elongation at break is 81%, and the moisture absorption rate of the moisture and heat stability test (immersed in 80℃ hot water for 24h) is 0.3%.

[0052] Example 4

[0053] A method for preparing a high temperature resistant shielding film, compared with Example 1, adopts a conventional PI film (made from pyromellitic anhydride and diaminodiphenyl ether) to replace the organosilicon modified PI film layer as the base film layer and the protective film layer.

[0054] The shielding film obtained in this embodiment has a shielding effectiveness of >100dB under 200KHz-50MHz electric field. The PI film layer used in this embodiment has a 5% weight loss temperature of 524℃ after high temperature performance test; the tensile strength test result is 165MPa, the elongation at break is 55%, and the moisture absorption rate of the heat and humidity stability test (immersed in 80℃ hot water for 24h) is 1.7%.

[0055] It can be seen from the results of Examples 1 to 4 above that the shielding film obtained by the present invention has good electromagnetic shielding performance and high temperature resistance. By further using a specific organic silicon modified PI film layer, the high temperature resistance, toughness and moisture and heat resistance stability can be further improved.

[0056] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A high temperature resistant shielding film, characterized in that: It consists of a PI base film layer with a thickness of 12.5-100 μm, a conductive metal plating layer with a thickness of 0.01-10 μm and a PI protective film layer with a thickness of 3-10 μm.

2. A high temperature resistant shielding film according to claim 1, characterized in that: The conductive metal plating layer is a layer of aluminum, copper, nickel, silver, tin or an alloy of the above metals.

3. A high temperature resistant shielding film according to claim 1, characterized in that: The PI base film layer and the PI protective film layer refer to the organosilicon-modified PI film layer prepared by the following method: (1) subjecting a cyclosiloxane monomer, isocyanate propylmethyldimethoxysilane and a methylsilane end-capping agent to a polymerization reaction in the presence of a catalyst and anhydrous conditions to obtain an isocyanate polysiloxane; (2) adding the dianhydride monomer, the diamine monomer, the dehydrating agent and the catalyst into an organic solvent and dissolving them uniformly, heating the solvent to 80 to 150° C. for prepolymerization, and then adding the isocyanate polysiloxane of step (1) for continued polymerization reaction at a temperature of 100° C. to obtain an organosilicon-modified polyimide solution; (3) Drying the organosilicon-modified polyimide solution obtained in step (2) to form a film on a substrate to obtain an organosilicon-modified PI film layer.

4. A high temperature resistant shielding film according to claim 3, characterized in that: In step (1), the cyclosiloxane monomer is octamethylcyclotetrasiloxane or a dimethylsiloxane mixed ring body; the methylsilane end-capping agent is hexamethyldisiloxane, methoxytrimethylsilane or trimethylchlorosilane.

5. The high temperature resistant shielding film according to claim 3, characterized in that: The mass ratio of the cyclosiloxane monomer, isocyanate propylmethyldimethoxysilane and methylsilane capping agent added in step (1) is 100:10-40:1-10.

6. A high temperature resistant shielding film according to claim 3, characterized in that: The catalyst in step (1) is sodium siliconate or potassium siliconate; the polymerization reaction temperature is 100-140° C., and the polymerization reaction time is 2-8 hours.

7. The high temperature resistant shielding film according to claim 3, characterized in that: The dianhydride monomer in step (2) is pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, 4,4'-phenylenedioxydiphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride or 3,3',4,4'-diphenylethertetracarboxylic dianhydride; the diamine monomer is p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminobiphenyl, hexamethylenediamine or polyetherdiamine.

8. The high temperature resistant shielding film according to claim 3, characterized in that: In step (2), the dehydrating agent is acetic anhydride, phthalic anhydride or maleic anhydride; the catalyst is pyridine, triethylamine or 4-dimethylaminopyridine; and the organic solvent is N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, toluene or tetrahydrofuran.

9. The high temperature resistant shielding film according to claim 3, characterized in that: The molar ratio of the dianhydride monomer and the diamine monomer added in step (2) is 1.2 to 1.5:1, and the time of the prepolymerization reaction is 2 to 6 hours; the amount of the isocyanate polysiloxane added is 20 to 60% of the total mass of the dianhydride monomer and the diamine monomer, and the time of the heat preservation polymerization reaction is 2 to 6 hours.

10. A method for preparing a high temperature resistant shielding film according to any one of claims 1 to 9, characterized in that: The method comprises the following preparation steps: The conductive metal is coated on the PI base film layer by vacuum evaporation, electrostatic spraying or sputtering, and then a polyimide solution is coated and dried to form a film to obtain a PI protective film layer.