Colored polyimide film with high insulation and high shielding property

Abstract

The application discloses a colored polyimide film with high insulation and high shielding property, which comprises a carrier film and a polyimide varnish layer in sequence; the thickness of the carrier film ranges from 12.5 to 250 microns; the surface roughness Rz of the carrier film is 0.001-10 microns; the total thickness of the polyimide varnish layer is 1-150 microns, the polyimide varnish layer is a single layer or multiple layers generated by one-time curing or multiple-time curing; the polyimide varnish layer is composed of the following components: polyimide resin, 45-98% by weight; cross-linking agent, 0.5-40% by weight; dye, 0-50% by weight; curing agent and catalyst, 0-20% by weight. The application introduces dye into the coating type polyimide formula structure, so that the mechanical strength of the whole film is not damaged, the bending resistance and the overall blackness are improved, and the high mechanical strength, insulation, surface hardness, operability, heat resistance, dimensional stability, surface energy, blackness and matte appearance are considered.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board technology, and in particular relates to a colored polyimide film with high insulation and high shielding properties. Background Technology

[0002] Polyimide (PI) is a class of polymers containing repeating imide units, possessing advantages such as wide operating temperature range, chemical resistance, and high strength. As a special engineering material, polyimide is now widely used in aerospace, microelectronics, nanotechnology, liquid crystals, separation membranes, lasers, and other fields.

[0003] In industrial design, due to the trend towards thinner and lighter electronic products, polyimide film manufacturers, in order to reduce film thickness, often design thicknesses of 2–7.5 μm. However, this results in poor mechanical strength, making film fabrication difficult and processing challenging during use. Especially when a colored appearance is desired (usually black), insufficient blackness leads to poor masking properties and susceptibility to defects, causing the film to fail to meet industry standards and resulting in low yield rates. Furthermore, in applications such as high-current scenarios and high signal transmission volumes, the insulation performance of the film material is subject to even stricter requirements within the total thickness limit. Biaxial stretching methods for producing polyimide films often encounter difficulties below 7.5 μm, with the bottleneck being more severe in black polyimide films. While uniaxial stretching methods exist to lower the manufacturing process threshold, the material's properties differ significantly between the stretching and other directions.

[0004] To address the bottlenecks in applying thin and colored polyimide films to high-density assembly, high-voltage, and high-shield applications, polyimide films produced by the stretching method can be replaced with polyimide varnish-type insulating layers coupled with a carrier or release film. In existing solutions, polyimide varnish-type insulating layers can be achieved through multilayer design and by altering the resin ratio or doping with powders. Furthermore, improvements in powder content and particle size design can yield insulating layers with various advantages, including colorability, high flame retardancy, high ionic purity, high hardness, high thermal conductivity, and high mechanical properties. Compared to films produced by the casting process, varnish-type insulating layers exhibit better dimensional stability due to the absence of residual stretching stress during the process. Moreover, in thin-film applications, varnish-type insulating layers are directly formed on the carrier film, making them easier to process in downstream processes. Colored cover films made using this type of film possess excellent ion migration, superior adhesion, low rebound, high flexibility, low-temperature processing capability, high heat dissipation, high hardness, excellent heat resistance, excellent dimensional stability, and excellent electrical properties.

[0005] Based on the above, this application addresses the demand from customers for aesthetically pleasing, secure, and scratch-resistant polyimide films, such as black ones. It also considers the increasing trend towards thinner and lighter electronic products and novel product designs. Key customers, in their FPC production, are designing ultra-thin products to reduce the required thickness of flexible circuit board materials. To reduce film thickness, polyimide manufacturers, when designing thicknesses from 2 to 7.5 μm, not only struggle to achieve the currently required matte surface (Gloss < 25 GU), but also fail to meet industry standards for general technical indicators such as mechanical strength, processability, insulation, and shielding properties, resulting in low yields.

[0006] Furthermore, in applications such as high-current scenarios with high thickness variations and high insulation requirements, where the total thickness is limited, there are even more stringent performance and reliability requirements for both thin-film and shielding materials. This necessitates finding an ultra-thin material capable of high thickness variation filling, long-term resistance to high temperature and humidity conditions, and high voltage resistance. To address these requirements, this invention, based on existing coated polyimide (polyimide varnish-type insulating layer), introduces dyes into the coated polyimide formulation structure. This preserves the overall mechanical strength of the film while increasing its bending resistance and overall blackness. Moreover, this formulation design helps improve surface appearance and insulation, enabling its use as an insulating protective layer in shielding films, cover films, and other applications. Summary of the Invention

[0007] The main technical problem solved by this invention is to provide a colored polyimide film with high insulation and high shielding properties, which takes into account high mechanical strength, insulation, surface hardness, operability, heat resistance, dimensional stability, surface energy, blackness and matte appearance. It is especially suitable for use as a protective layer in high-segmentation and high-voltage scenarios where shielding is required.

[0008] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: a colored polyimide film with high insulation and high shielding properties, comprising a carrier film and a polyimide varnish layer in sequence; The thickness of the carrier membrane ranges from 12.5 to 250 μm; The carrier film is used on the outside of the insulating layer. The surface roughness Rz of the carrier film is 0.001-10um, preferably 0.1-5.0um. This morphological control allows the colored carrier film and the insulating layer to be quickly pressed together, resulting in a better product appearance with de-rotation properties for the customer. The total thickness of the polyimide varnish layer is 1-150 μm, and for ultra-thin applications, the thickness is preferably 1-20 μm. The polyimide varnish layer is a single or multiple layers that are cured in one or multiple times. By applying and curing multiple layers of varnish-type resin insulating layer, the micropores in the coating process can be solved, the micropore problem on the surface can be solved, and the mechanical properties can be improved. The polyimide varnish layer can be multiple layers, which can solve the defects in the coating appearance, reduce the risk of adverse mechanical properties, and improve the operability and appearance of production and processing. The polyimide varnish layer is composed of the following components: (1) Polyimide resin, 45-98% by weight; (2) Crosslinking agent, 0.5% to 40% by weight; (3) Dyes, 0-50% by weight; (4) Curing agent and catalyst, weight percentage 0-20%.

[0009] Furthermore, the carrier membrane material includes at least one of polypropylene, biaxially oriented polypropylene, polyethylene terephthalate, polyimide, polyphenylene sulfide, polyethylene naphthalate, polyurethane, and polyamide. The carrier membrane also includes inorganic powder with a particle size of 10-20000nm to achieve a non-natural color. The inorganic powder includes at least one of calcium sulfate, carbon black, silicon dioxide, titanium dioxide, zinc sulfide, zirconium oxide, calcium carbonate, silicon carbide, boron nitride, aluminum oxide, talc, aluminum nitride, glass powder, quartz powder, and clay.

[0010] Inorganic powder is added to increase the overall opacity of the cover film and to match the surface roughness variation to reduce the gloss after peeling. In other layers, such as the polyimide varnish layer, no powder is added and only dye is used to improve the overall mechanical properties and appearance. At the same time, the powder-free design also helps to improve the yield when making the film. The surface roughness Rz of the carrier layer is 0.001-10um.

[0011] Furthermore, the polyimide resin material includes at least one of bismaleimide resin, styrene-ethylene-butene-styrene block copolymer, polyimide resin, and polyamide-imide, preferably at least one of polyimide resin and polyamide-imide; The crosslinking agent is an epoxy resin, which includes at least one of glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, epoxidized olefin compound, alicyclic epoxy resin, polyphenol type glycidyl ether epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic glycidyl ether epoxy resin, heterocyclic epoxy resin and mixed epoxy resin. The polyimide varnish layer contains dyes to form a non-natural colored insulating layer, the dyes including at least one of azo dyes, anthraquinone dyes, thio / benzothiazole dyes, metal complex dyes, and indigoid / sulfonamide dyes. The curing agent is selected from at least one of 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, diaminodiphenyl sulfone, diaminodiphenyl ether, p-phenylenediamine, 2,3,5,6-tetrafluoro-1,4-phenylenediamine, 2-sulfonyl-1,4-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminodiphenyl ether, and 2,2'-bis(trifluoromethyl)diaminobiphenyl. The catalyst is selected from at least one of the following: trimethylamine, triethylenediamine and other aliphatic tertiary amines, N-hydroxyphthalimide, peracetic acid, m-chloroperbenzoic acid, hydroperoxide, tert-butyl hydroperoxide, azobisisobutyronitrile, acetophenones, cyclic amine-N-oxy compounds, nitric acid, nitrite, nitrite, nitrogen dioxide, and benzaldehyde.

[0012] This invention also provides a method for preparing a colored polyimide film with high insulation and high shielding properties, comprising the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film.

[0013] A shielding film comprises, in sequence, a carrier film, a polyimide varnish layer, a colored coating layer, a metal layer, a conductive adhesive layer, and a release layer.

[0014] Furthermore, the metal layer is a metal foil layer or a metal plating layer; When the metal layer is a metal foil layer, the thickness of the metal foil layer is 0.5 to 18 μm, and the metal foil layer is selected from copper foil, silver foil, aluminum foil, or an alloy foil of at least one of the above components; When the metal layer is a metal plating layer, the thickness of the metal plating layer is 0.01 to 5 μm, and the metal plating layer is selected from at least one of copper, silver, nickel, chromium, iron, cobalt and aluminum, and the process is selected from one of water plating, sputtering, vacuum sputtering, evaporation and electroplating. The conductive adhesive layer is selected from at least one of epoxy resin, acrylic resin, phenolic resin, polyurethane, polyimide, and polyamide-imide; The conductive adhesive layer contains conductive particles, which are at least one of copper, silver, nickel, tin, gold, palladium, aluminum, chromium, titanium, zinc, and carbon, or at least one of nickel-gold, gold-silver, copper-nickel, copper-silver, nickel-silver, and copper-nickel-gold, with the conductive particles accounting for 25% to 85% of the total weight of the conductive adhesive layer. The release layer is made of at least one of polypropylene, biaxially oriented polypropylene, and polyethylene terephthalate, or release paper.

[0015] This invention also provides a method for preparing a shielding film, comprising one of the following two methods: Method 1 includes the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film; Step 4: Coat the aforementioned thin film with a colored coating layer and cure it at 50–180°C. Then, form a metal coating layer through vapor deposition, electroplating, sputtering, or electroless plating processes. Step 5: Form a conductive adhesive layer onto the metal plating layer by coating or transfer method; Step 6: Remove the release layer and attach it to the conductive adhesive layer to obtain an ultra-thin shielding film.

[0016] Method 2 includes the following steps: S1. A polyimide varnish layer is coated on a carrier film and dried in an oven to form a polyimide varnish layer; S2. Other polyimide varnish layers can be applied on the dried polyimide varnish layer. S3. After all the polyimide varnish layers have been applied, cure at a low temperature of 50-180°C to form a film. S4. A colored coating layer is coated on the aforementioned film and a metal foil layer is pressed onto the colored coating layer, and then cured at 50-180°C to form a composite material. S5. A conductive adhesive layer is formed on the metal foil of the above-mentioned composite material by coating or transfer method, and a release layer is taken out and attached to the conductive adhesive layer to obtain an ultra-thin shielding film.

[0017] A cover film, comprising, in sequence, a carrier film, a polyimide varnish layer, an adhesive layer, and a release layer.

[0018] Furthermore, the adhesive layer is selected from at least one of epoxy resin, acrylic resin, phenolic resin, polyurethane, polyimide, and polyamide-imide; The release layer is made of at least one of polypropylene, biaxially oriented polypropylene, and polyethylene terephthalate, or release paper.

[0019] The present invention also provides a method for preparing a covering film, comprising the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film; Step 4: Apply adhesive to the film using a coating or transfer method; Step 5: Take out the release layer, attach the release layer to the adhesive, and roll it up to obtain the cover film.

[0020] The beneficial effects of the present invention include at least the following: This invention provides a protective film with a carrier film, which can also be used as an insulating resin film in ultra-thin EMI shielding films, and as an insulating layer in applications such as circuit protection covering films. The film provided by this invention consists of a carrier film and a polyimide varnish layer, and has high flame retardancy, low gloss, high blackness, high shielding, high dimensional stability, high mechanical strength, high surface hardness, and high surface energy. It is particularly suitable for use in ultra-dense assembled circuits, scenarios with high shielding requirements, and high step difference applications. This invention changes the surface roughness and surface energy of the carrier film by adding powder or surface treatment, so that the matching insulating layer ensures its matting degree and surface energy. In addition, the polyimide varnish of this invention effectively improves the shortcomings of appearance defect frequency, insufficient shielding, and poor process yield in the design of the film layer by selecting and adding different resins and dyes. The present invention utilizes a thin film produced by a carrier film. The matching of the surface energy and roughness design of the carrier film and the insulating layer gives it a matte surface and protects it from contamination during the process before the carrier film is peeled off. The high surface energy of the insulating layer is easy to use for lamination and bonding processes. Since the carrier film provides protection, it is usually not necessary to use additional surface treatment processes such as corona treatment to further enhance the surface energy. This invention utilizes a multi-layer coating composition of coated polyimide, which easily balances various properties and can match the downstream processing requirements, resulting in sufficient blackness, excellent scratch and abrasion resistance, and superior mechanical properties. The carrier film coating varnish design of the present invention is less expensive than films produced by casting process of the same size, and can produce ultra-thin (2-7.5μm) films. Furthermore, it eliminates the need for additional film preparation in downstream processes to avoid tearing and other process problems, making it easier to operate and process. Compared with films produced by casting process, the varnish-type insulating layer of the present invention has better dimensional stability due to the absence of residual stress from stretching during the process. From a microstructural analysis perspective, the carrier film has a high surface roughness, which in turn leads to a high surface roughness of the insulating layer it contacts. This results in a stronger adhesion strength on a macroscopic scale and is beneficial for reducing the overall thickness of the finished product after lamination. Attached Figure Description

[0021] Figure 1 This is a specific stacked structure of a thin film with a carrier film provided by the present invention. The thin film includes a carrier film and a polyimide varnish layer, wherein the varnish layer can be designed to have two or more resin layers. Figure 2 The specific stacked structure of the ultrathin shielding film provided by the present invention includes a carrier film, a polyimide varnish layer, a colored coating layer, a metal layer, a conductive adhesive layer, and a release layer.

[0022] Figure 3 The specific stacked structure of the cover film provided by the present invention includes a carrier film, a polyimide varnish layer, an adhesive layer, and a release layer; The parts in the attached diagram are labeled as follows: 100. Thin film; 101. Carrier film; 102. Polyimide varnish layer; 200. Shielding film; 201. Colored coating layer; 202. Metal layer; 203. Conductive adhesive layer; 204. Release layer; 300. Cover film; 301. Adhesive layer. Detailed Implementation

[0023] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0024] Example: A colored polyimide film 100 with high insulation and high shielding properties, such as Figure 1 As shown, it includes a carrier film 101 and a polyimide varnish layer 102 in sequence; The thickness of the carrier membrane ranges from 12.5 to 250 μm; The carrier film is used on the outside of the insulating layer. The surface roughness Rz of the carrier film is 0.001-10um, preferably 0.1-5.0um. This morphological control allows the colored carrier film and the insulating layer to be quickly pressed together, resulting in a better product appearance with de-rotation properties for the customer. The total thickness of the polyimide varnish layer is 1-150 μm, and for ultra-thin applications, the thickness is preferably 1-20 μm. The polyimide varnish layer is a single or multiple layers that are cured in one or multiple times. By applying and curing multiple layers of varnish-type resin insulating layer, the micropores in the coating process can be solved, the micropore problem on the surface can be solved, and the mechanical properties can be improved. The polyimide varnish layer can be multiple layers, which can solve the defects in the coating appearance, reduce the risk of adverse mechanical properties, and improve the operability and appearance of production and processing. The polyimide varnish layer is composed of the following components: (1) Polyimide resin, 45-98% by weight; (2) Crosslinking agent, 0.5% to 40% by weight; (3) Dyes, 0-50% by weight; (4) Curing agent and catalyst, weight percentage 0-20%.

[0025] The carrier membrane material includes at least one of polypropylene, biaxially oriented polypropylene, polyethylene terephthalate, polyimide, polyphenylene sulfide, polyethylene naphthalate, polyurethane, and polyamide. The carrier membrane also includes inorganic powder with a particle size of 10-20000nm to achieve a non-natural color. The inorganic powder includes at least one of calcium sulfate, carbon black, silicon dioxide, titanium dioxide, zinc sulfide, zirconium oxide, calcium carbonate, silicon carbide, boron nitride, aluminum oxide, talc, aluminum nitride, glass powder, quartz powder, and clay.

[0026] Inorganic powder is added to increase the overall opacity of the cover film and to match the surface roughness variation to reduce the gloss after peeling. In other layers, such as the polyimide varnish layer, no powder is added and only dye is used to improve the overall mechanical properties and appearance. At the same time, the powder-free design also helps to improve the yield when making the film. The surface roughness Rz of the carrier layer is 0.001-10um.

[0027] The polyimide resin material includes at least one of bismaleimide resin, styrene-ethylene-butene-styrene block copolymer, polyimide resin and polyamide-imide, preferably at least one of polyimide resin and polyamide-imide; The crosslinking agent is an epoxy resin, which includes at least one of glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, epoxidized olefin compound, alicyclic epoxy resin, polyphenol type glycidyl ether epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic glycidyl ether epoxy resin, heterocyclic epoxy resin and mixed epoxy resin. The polyimide varnish layer contains dyes to form a non-natural colored insulating layer, the dyes including at least one of azo dyes, anthraquinone dyes, thio / benzothiazole dyes, metal complex dyes, and indigoid / sulfonamide dyes. The curing agent is selected from at least one of 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, diaminodiphenyl sulfone, diaminodiphenyl ether, p-phenylenediamine, 2,3,5,6-tetrafluoro-1,4-phenylenediamine, 2-sulfonyl-1,4-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminodiphenyl ether, and 2,2'-bis(trifluoromethyl)diaminobiphenyl. The catalyst is selected from at least one of the following: trimethylamine, triethylenediamine and other aliphatic tertiary amines, N-hydroxyphthalimide, peracetic acid, m-chloroperbenzoic acid, hydroperoxide, tert-butyl hydroperoxide, azobisisobutyronitrile, acetophenones, cyclic amine-N-oxy compounds, nitric acid, nitrite, nitrite, nitrogen dioxide, and benzaldehyde.

[0028] This invention also provides a method for preparing a colored polyimide film with high insulation and high shielding properties, comprising the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film.

[0029] A shielding film 200, such as Figure 2 As shown, it sequentially includes a carrier film 101, a polyimide varnish layer 102, a colored coating layer 201, a metal layer 202, a conductive adhesive layer 203, and a release layer 204.

[0030] The metal layer is a metal foil layer or a metal plating layer; When the metal layer is a metal foil layer, the thickness of the metal foil layer is 0.5 to 18 μm, and the metal foil layer is selected from copper foil, silver foil, aluminum foil, or an alloy foil of at least one of the above components; When the metal layer is a metal plating layer, the thickness of the metal plating layer is 0.01 to 5 μm, and the metal plating layer is selected from at least one of copper, silver, nickel, chromium, iron, cobalt and aluminum, and the process is selected from one of water plating, sputtering, vacuum sputtering, evaporation and electroplating. The conductive adhesive layer is selected from at least one of epoxy resin, acrylic resin, phenolic resin, polyurethane, polyimide, and polyamide-imide; The conductive adhesive layer contains conductive particles, which are at least one of copper, silver, nickel, tin, gold, palladium, aluminum, chromium, titanium, zinc, and carbon, or at least one of nickel-gold, gold-silver, copper-nickel, copper-silver, nickel-silver, and copper-nickel-gold, with the conductive particles accounting for 25% to 85% of the total weight of the conductive adhesive layer. The release layer is made of at least one of polypropylene, biaxially oriented polypropylene, and polyethylene terephthalate, or release paper.

[0031] This invention also provides a method for preparing a shielding film, comprising one of the following two methods: Method 1 includes the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film; Step 4: Coat the aforementioned thin film with a colored coating layer and cure it at 50–180°C. Then, form a metal coating layer through vapor deposition, electroplating, sputtering, or electroless plating processes. Step 5: Form a conductive adhesive layer onto the metal plating layer by coating or transfer method; Step 6: Remove the release layer and attach it to the conductive adhesive layer to obtain an ultra-thin shielding film.

[0032] Method 2 includes the following steps: S1. A polyimide varnish layer is coated on a carrier film and dried in an oven to form a polyimide varnish layer; S2. Other polyimide varnish layers can be applied on the dried polyimide varnish layer. S3. After all the polyimide varnish layers have been applied, cure at a low temperature of 50-180°C to form a film. S4. A colored coating layer is coated on the aforementioned film and a metal foil layer is pressed onto the colored coating layer, and then cured at 50-180°C to form a composite material. S5. A conductive adhesive layer is formed on the metal foil of the above-mentioned composite material by coating or transfer method, and a release layer is taken out and attached to the conductive adhesive layer to obtain an ultra-thin shielding film.

[0033] A covering film, such as Figure 3 As shown, it includes, in sequence, a carrier film 101, a polyimide varnish layer 102, an adhesive layer 301, and a release layer 204.

[0034] The adhesive layer is selected from at least one of epoxy resin, acrylic resin, phenolic resin, polyurethane, polyimide, and polyamide-imide; The release layer is made of at least one of polypropylene, biaxially oriented polypropylene, and polyethylene terephthalate, or release paper.

[0035] The present invention also provides a method for preparing a covering film, comprising the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film; Step 4: Apply adhesive to the film using a coating or transfer method; Step 5: Take out the release layer, attach the release layer to the adhesive, and roll it up to obtain the cover film.

[0036] This invention offers excellent flexibility, low rebound force, high heat dissipation, high flame retardancy, high surface hardness, high mechanical properties, high adhesion, high blackness, matte finish, and ease of processing. The protective film can be used in circuit board applications such as shielding films, protective films, and insulating layers on copper foil substrates. Its high blackness is particularly advantageous for designs requiring shielding.

[0037] Table 1: Polyimide Clear Coating Ratio

[0038] The crosslinking agent is dicyclopentadiene phenol epoxy resin (DCPD phenol epoxy resin), the black dye is an azo dye, and the curing agent is 2-methylimidazole.

[0039] The polyimide resin was synthesized as follows: 32.02 g of 2,2'-di(trifluoromethyl)diaminobiphenyl (TFMB), 21.99 g of hexafluorodianhydride (6FDA), and 12.41 g of bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride (B1317) were added to 349 g of N-methylpyrrolidone (NMP) at 80°C. The temperature was raised to 150°C, and 0.80 g of N-ethylpiperidine was added. The temperature was then raised to 190°C and reacted for 4 hours to obtain the polyimide resin.

[0040] Table 2: Examples A1 to A6 are films made from the structural examples of this patent with different specifications (carrier removed). Comparative Examples B1 and B2 are polyimide films of similar specifications to those using uniaxially stretched films on the market. Comparative Examples B3 and B4 are polyimide films of similar specifications to those using biaxially stretched films on the market. Comparative Examples B5 and B6 are films made without coating with colored paint under the polyimide varnishes of proportions 2 and 3 in Table 1 (carrier removed).

[0041] (The polyamide-imide varnish layers of Examples A1-A6 and Comparative Examples B5 and B6 are polyimide resin layers with imide bonds in their resin skeleton. The formulations are shown in Table 1. Examples A1 and A3 use formulation 2, Examples A2 and A5 use formulation 1, A4 uses formulation 3, and A6 uses formulation 4. The colored coating layers of Examples A1-A6 consist of 50% nitrile rubber, 6% carbon black, 14% flame retardant (aluminum hydroxide and silica, 1:1), 27% DCPD phenolic epoxy resin, and 3% curing agent (2-methylimidazole). Comparative Examples B1 and B2 are HB-N polyimide films from Shenzhen Ruihuatai, and Comparative Examples B3 and B4 are Kapton black polyimide films from DuPont.) Table 2:

[0042] As shown in Table 2, all examples exhibited good elongation and dimensional stability, and their overall performance met industry requirements. Among examples A1 to A6, the mechanical strength (tensile strength, elongation, and modulus of elasticity) and blackness (according to ASTM D3265 standard) of the polymer films could be improved by adjusting the formulation ratios in Table 1. Comparing B1 and B2, which are polyimide films produced by the casting method without biaxial stretching, although their mechanical strength is acceptable, their finished product has the worst dimensional stability.

[0043] Table 3: Examples A1, A3, A6 and Comparative Examples B3 and polyurethane ink obtained from Table 2 were used as insulating layers for shielding films in Examples E1 to E3 and Comparative Examples F1 and F2 in Table 3. All of them were paired with a metal plating layer of the same thickness (0.2μm electroplated copper) and a conductive adhesive of the same composition (60% silver-coated copper metal powder, 10% 4,4'-diaminodiphenyl sulfone as curing agent, and the remaining part was made by mixing bisphenol A epoxy resin BE501A80 (purchased from Changchun Chemical) and acrylic resin JT-A1767 (purchased from Qiaoyi Technology) in a 1:1 weight ratio). This was used to make Examples E1 to E3 and Comparative Examples F1 and F2.

[0044]

[0045] The data in Table 3 shows that the shielding film obtained in the embodiment has good shielding performance, bonding strength and insulation performance, which can meet the client's step requirements, SMT simulation test and SMT conduction resistance value, and can effectively meet the client's special requirements.

[0046] 1. Peel strength test: The test was conducted according to the standard IPC-TM-650 2.4.9 D.

[0047] 2. Solderability test: The test shall be conducted in accordance with the specification IPC-TM-650 2.4.13 F.

[0048] 3. Thermal stress test: The test shall be conducted in accordance with the standard IPC-TM-650 2.6.8.1 (9 / 91).

[0049] 4. Surface Hardness Test: Hardness testing was conducted using a pencil according to ASTM D3363 standard. (The test surface is the polyimide varnish layer.) 5. Electromagnetic shielding performance test: The test was conducted in accordance with the standard GB / T 30142-2013 "Measurement Method for Shielding Effectiveness of Planar Electromagnetic Shielding Materials".

[0050] 6. Gloss value test: Prepare a sample with a size greater than 3*8cm, measure it in the longitudinal direction (MD direction) of the sample with a gloss meter, and read the value at 60° as the measured value.

[0051] 7. Insulation Resistance Test: Cut an A4-sized piece of the unplated shielding film semi-finished product. Coat the bright side of a 1oz thick electrolytic copper foil with epoxy resin adhesive. Press the cut semi-finished product against the foil and cure at 160℃ for 1 hour to obtain the test sample. Use the ohm setting of a digital multimeter to test the resistance between the conductors. Take 8 test lines (6cm long and 0.8cm wide) and measure 6 sets along the MD direction (1-8). Take the average value.

[0052] 8. Resistance value test: Using a handheld digital four-point probe, measure two sets of data along the MD direction and three sets along the TD direction (lateral direction) of the 30 mm * 514 mm (MD * TD) sample, for a total of six sets of data to obtain the average result.

[0053] 9. Client SMT simulation test: After heating to 120°C at 2°C / sec, preheat for 2 minutes, then heat to 245°C at 3°C / sec and maintain for 0.5 minutes. Cool to room temperature at 4°C / sec, then remove and check for any cracks in the appearance.

[0054] 10. Tensile strength, modulus of elasticity, and elongation tests: Tested in accordance with standard IPC-TM-650 2.4.19C (5 / 98).

[0055] 11. Breakdown voltage: Performed using a withstand voltage analyzer in accordance with ASTM D149.

[0056] 12. Dimensional stability: Use a two-dimensional coordinate measuring machine and perform the test according to IPC-TM-650 2.2.4C standard.

[0057] 13. Step difference test: Take a cover film with a 2.0mm aperture and cut it into the conductivity test strip. After quick pressing, cure it at 160°C for 1 hour. Press the reinforcing plates with different step heights (100 / 150 / 200 / 250 / 300μm) onto the conductivity test strip using a quick press machine. Then vacuum quick press the test strip shielding film and use a multimeter to measure its resistance. If it is less than 0.2Ω, it is considered to pass.

[0058] 14. Blackness test: in accordance with ASTM D3265 standard.

[0059] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A colored polyimide film with high insulation and high shielding properties, characterized in that: It consists of, in sequence, a carrier film and a polyimide varnish layer; The thickness of the carrier membrane ranges from 12.5 to 250 μm; The surface roughness Rz of the carrier film is 0.001-10 μm; The total thickness of the polyimide varnish layer is 1-150 μm, and the polyimide varnish layer is a single or multiple layers formed by one curing or multiple curing. The polyimide varnish layer is composed of the following components: (1) Polyimide resin, 45-98% by weight; (2) Crosslinking agent, 0.5% to 40% by weight; (3) Dyes, 0-50% by weight; (4) Curing agent and catalyst, weight percentage 0-20%.

2. The colored polyimide film with high insulation and high shielding properties according to claim 1, characterized in that: The carrier membrane material includes at least one of polypropylene, biaxially oriented polypropylene, polyethylene terephthalate, polyimide, polyphenylene sulfide, polyethylene naphthalate, polyurethane, and polyamide. The carrier membrane also includes inorganic powder with a particle size of 10-20000 nm, and the inorganic powder includes at least one of calcium sulfate, carbon black, silicon dioxide, titanium dioxide, zinc sulfide, zirconium oxide, calcium carbonate, silicon carbide, boron nitride, aluminum oxide, talc, aluminum nitride, glass powder, quartz powder, and clay.

3. The colored polyimide film with high insulation and high shielding properties according to claim 1, characterized in that: The polyimide resin material includes at least one of bismaleimide resin, styrene-ethylene-butene-styrene block copolymer, polyimide resin and polyamide-imide; The crosslinking agent is an epoxy resin, which includes at least one of glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, epoxidized olefin compound, alicyclic epoxy resin, polyphenol type glycidyl ether epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic glycidyl ether epoxy resin, heterocyclic epoxy resin and mixed epoxy resin. The polyimide varnish layer comprises a colored insulating layer with a non-natural color formed by dyes, wherein the dyes include at least one of azo dyes, anthraquinone dyes, thiophene / benzothiazoles, copper complex dyes, and indole / sulfonamide dyes. The curing agent is selected from at least one of 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, diaminodiphenyl sulfone, diaminodiphenyl ether, p-phenylenediamine, 2,3,5,6-tetrafluoro-1,4-phenylenediamine, 2-sulfonyl-1,4-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-diaminodiphenyl ether, and 2,2'-bis(trifluoromethyl)diaminobiphenyl. The catalyst is selected from at least one of the following: trimethylamine, triethylenediamine and other aliphatic tertiary amines, N-hydroxyphthalimide, peracetic acid, m-chloroperbenzoic acid, hydroperoxide, tert-butyl hydroperoxide, azobisisobutyronitrile, acetophenones, cyclic amine-N-oxy compounds, nitric acid, nitrite, nitrite, nitrogen dioxide, and benzaldehyde.

4. A shielding film, characterized in that: The invention comprises a colored polyimide film with high insulation and high shielding as described in any one of claims 1-3, comprising, in sequence, a carrier film, a polyimide varnish layer, a colored coating layer, a metal layer, a conductive adhesive layer, and a release layer.

5. A shielding film according to claim 4, characterized in that: The metal layer is a metal foil layer or a metal plating layer; When the metal layer is a metal foil layer, the thickness of the metal foil layer is 0.5 to 18 μm, and the metal foil layer is selected from copper foil, silver foil, aluminum foil, or an alloy foil of at least one of the above components; When the metal layer is a metal plating layer, the thickness of the metal plating layer is 0.01 to 5 μm, and the metal plating layer is selected from at least one of copper, silver, nickel, chromium, iron, cobalt and aluminum, and the process is selected from one of water plating, sputtering, vacuum sputtering, evaporation and electroplating. The conductive adhesive layer is selected from at least one of epoxy resin, acrylic resin, phenolic resin, polyurethane, polyimide, and polyamide-imide; The conductive adhesive layer contains conductive particles, which are at least one of copper, silver, nickel, tin, gold, palladium, aluminum, chromium, titanium, zinc, and carbon, or at least one of nickel-gold, gold-silver, copper-nickel, copper-silver, nickel-silver, and copper-nickel-gold, with the conductive particles accounting for 25% to 85% of the total weight of the conductive adhesive layer. The release layer is made of at least one of polypropylene, biaxially oriented polypropylene, and polyethylene terephthalate, or release paper.

6. A covering film, characterized in that: The invention comprises a colored polyimide film with high insulation and high shielding as described in any one of claims 1-3, comprising, in sequence, a carrier film, a polyimide varnish layer, an adhesive layer, and a release layer.

7. A covering film according to claim 6, characterized in that: The adhesive layer is selected from at least one of epoxy resin, acrylic resin, phenolic resin, polyurethane, polyimide, and polyamide-imide; The release layer is made of at least one of polypropylene, biaxially oriented polypropylene, and polyethylene terephthalate, or release paper.

8. A method for preparing a colored polyimide film with high insulation and high shielding properties as described in any one of claims 1-3, characterized in that: Includes the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film.

9. A method for preparing a shielding film as described in any one of claims 4-5, characterized in that: Includes one of the following two methods: Method 1 includes the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film; Step 4: Coat the aforementioned thin film with a colored coating layer and cure it at 50–180°C. Then, form a metal coating layer through vapor deposition, electroplating, sputtering, or electroless plating processes. Step 5: Form a conductive adhesive layer onto the metal plating layer by coating or transfer method; Step 6: Remove the release layer and attach it to the conductive adhesive layer to obtain an ultra-thin shielding film; Method 2 includes the following steps: S1. A polyimide varnish layer is coated on a carrier film and dried in an oven to form a polyimide varnish layer; S2. Other polyimide varnish layers can be applied on the dried polyimide varnish layer. S3. After all the polyimide varnish layers have been applied, cure at a low temperature of 50-180°C to form a film. S4. A colored coating layer is coated on the aforementioned film and a metal foil layer is pressed onto the colored coating layer, and then cured at 50-180°C to form a composite material. S5. A conductive adhesive layer is formed on the metal foil of the above-mentioned composite material by coating or transfer method, and a release layer is taken out and attached to the conductive adhesive layer to obtain an ultra-thin shielding film.

10. A method for preparing a covering film as described in any one of claims 6-7, characterized in that: Includes the following steps: Step 1: Coat a polyimide varnish layer onto the carrier film and dry it in an oven to form the polyimide varnish layer; Step 2: On the dried polyimide varnish layer, other polyimide varnish layers can be applied. Step 3: After all the polyimide varnish layers have been applied, cure at a low temperature of 50–180°C to form a film; Step 4: Apply adhesive to the film using a coating or transfer method; Step 5: Take out the release layer, attach the release layer to the adhesive, and roll it up to obtain the cover film.

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