CN115975381A

CN115975381A - High-reflectivity single-layer white polyimide cover film for LED display screen

Info

Publication number: CN115975381A
Application number: CN202310056854.0A
Authority: CN
Inventors: 胡修远; 陈征; 黎迈俊
Original assignee: Huangpu Institute of Materials
Current assignee: Huangpu Institute of Materials
Priority date: 2023-01-16
Filing date: 2023-01-16
Publication date: 2023-04-18
Anticipated expiration: 2043-01-16
Also published as: CN115975381B

Abstract

The invention relates to the technical field of polyimide materials, in particular to a high-reflectivity single-layer white polyimide cover film for an LED display screen and a preparation method thereof. The single-layer white polyimide coverlay comprises: polyimide, a white colorant, a surfactant, epoxy resin, an epoxy resin curing agent and a solvent; the polyimide has the following structural general formula:

wherein each X is independently substituted or unsubstituted aromatic containingA diether group of structure; a is a substituted or unsubstituted cycloalkyl-containing group; b is a substituted or unsubstituted aromatic group-containing group; the substituted substituent is alkyl with 1-5 carbon atoms, and the number of the substituted substituent is 0-5; wherein n: m = 5-7:3-5. The cover film has the advantages of low thickness, high reflectivity, high whiteness, high glass transition temperature (Tg), high heat resistance, high mechanical property and high peel strength.

Description

High-reflectivity single-layer white polyimide cover film for LED display screen

Technical Field

The invention relates to the technical field of polyimide materials, in particular to a high-reflectivity single-layer white polyimide cover film for an LED display screen and a preparation method thereof.

Background

The flexible printed circuit board (FPC for short) is an indispensable material in electronic products, and is mainly used in products such as mobile phones, pads, digital cameras and the like, the FPC flexible printed circuit is a flexible printed circuit which is made of polyimide or polyester film as a base material and has high reliability and excellent flexibility, a white cover film is used for a backlight FPC, and when an LED lamp on the FPC is lightened, the product can increase the backlight brightness and improve the uniformity. In recent years, with the development of display screens, new demands for a flexible printed circuit board (FPC) having higher wiring density, lighter weight, and thinner thickness have been made. Meanwhile, new requirements of being lighter, thinner and more resistant to high temperature and incapable of reducing reflectivity are provided for the white covering film.

Known white cover films include two types in particular: the first is to coat a layer of epoxy resin or polyurethane white ink on the other side of the resin, and coat epoxy resin or acrylic resin on the other side of the resin as a cross-linking layer to be attached to the FPC, although the multilayer white cover film can meet the white requirement, the cover film is generally thick, the preparation process is complex, the process cost is high, the white ink layer has poor heat resistance and is easy to degrade or yellow, and the white ink layer is easy to fall off due to the difference of the heat resistance of each layer; the second method is to add a large amount of inorganic particles to a resin and then coat the resin to form a film. The resin material is polyimide, and although the film can avoid the phenomenon of falling caused by the difference of heat resistance among the ink layer, the resin layer and the crosslinking layer, the related product does not explain and test the reflectivity of the film, so that the development requirements of lighter and thinner LED screens are not met while the brightness is increased. At present, most of the synthetic raw materials of the polyimide product are fluorine-containing diamine monomers or alicyclic dianhydride monomers, the preparation cost is high, and the polyimide product cannot be applied on a large scale.

In view of the above problems of the white cover film of the LED display panel, it is necessary to provide a single-layer white polyimide cover film which is low in cost and can ensure reflectivity and stability.

Disclosure of Invention

Based on this, the invention provides a high-reflectivity single-layer white polyimide cover film for an LED display screen, which comprises: polyimide, white colorant, surfactant, epoxy resin curing agent and solvent;

the polyimide has the following structural general formula:

wherein each X is independently a substituted or unsubstituted diether group containing an aromatic structure; a is a substituted or unsubstituted cycloalkyl-containing group; b is a substituted or unsubstituted aromatic group-containing group; the substituted substituent is alkyl with 1-5 carbon atoms, and the number of the substituted substituent is 0-5; wherein n: m = 5-7:3-5.

In one embodiment, X in the polyimide is selected from any one of the following structures: 4,4' -bisphenol A diether, biphenyl diether, 4,4' - (2,2 ' -dimethyl) diphenoxy, 4,4' - (3,3 ' -ditert) diphenoxy, 4,4' - (2,3-dicarboxyphenoxy) diphenoxy ether, or 4,4' - (3,4-dicarboxyphenoxy) diphenoxy ether.

In one embodiment, a in the polyimide is selected from:

one or more of (a).

In one embodiment, B in the polyimide is selected from:

one or more of (a).

In one embodiment, the method of preparing the polyimide comprises:

a) Under inert atmosphere, alicyclic diamine H ₂ N-A-NH ₂ With aromatic diamines H ₂ N-B-NH ₂ Dissolving in a solvent, adding an acetic acid solution for reaction to obtain a suspension;

b) Mixing the suspension with tetracarboxylic dianhydride of the following structure to react to obtain a polyamic acid solution;

c) And adding isoquinoline and toluene into the polyamic acid solution, heating for reaction to obtain a polyimide solution, and performing post-treatment to obtain the polyimide.

In one embodiment, the molar ratio of the tetracarboxylic dianhydride to the diamine is 0.08 to 1.01; the diamine is the sum of the mole numbers of alicyclic diamine and aromatic diamine;

the solvent in the step a) is one or more of N, N-dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, cyclopentanone, cyclohexanone, gamma-butyrolactone and dimethyl sulfoxide;

the conditions for obtaining the polyamic acid solution by the mixing reaction in the step b) are as follows: reacting for 18-24 h at-5-5 ℃;

the heating reaction in the polyimide solution obtained by the heating reaction in the step c) is a gradient heating reaction, and comprises the following steps: stirring and reacting for 0.5-0.6h at 95-105 ℃, then stirring and reacting for 0.9-1.2h at 115-125 ℃, and then stirring and reacting for 3-5h at 145-155 ℃;

the post-treatment in the step c) comprises the following steps: adding the polyimide solution into absolute ethyl alcohol for precipitation, filtering to obtain precipitate, washing with absolute ethyl alcohol for multiple times, and drying at 55-65 ℃ for 20-28h.

In one embodiment, the mass ratios of the white colorant, surfactant, solvent, epoxy resin and the polyimide are 55 to 75, 0.1 to 1, 100, 35 to 15, 10 to 20;

the molar ratio of the epoxy curing agent to the epoxy resin is 1-2:1.

In one embodiment, the weight average molecular weight of the polyimide is 28000 to 35000g/mol; and/or

The colorant is one or more of titanium dioxide, aluminum oxide, silicon dioxide, zirconium oxide, barium sulfate, zinc oxide and lead carbonate; the average grain diameter of the colorant is 0.1-10 μm;

the surfactant is one or more of polyether modified polydimethylsiloxane solution, polyester modified polydimethylsiloxane solution, aralkyl modified alkyl siloxane or polyether modified siloxane solution;

the solvent is one or more of cyclohexanone, N-dimethylacetamide, N-methyl-2-pyrrolidone, gamma-butyrolactone, butanone, butyl acetate, toluene and xylene;

the epoxy resin is one or more of TDE-85, AG-80 and KR-470;

the epoxy resin curing agent is one or more of 2,2' -bis [4- (4-aminophenoxy phenyl) ] propane, o-phenylenediamine, 4,4' -diaminodiphenyl ether, 1,3-bis (4 ' -aminophenoxy) benzene, and 1,4-bis (4-aminophenoxy) benzene.

The embodiment of the invention also provides a preparation method of the single-layer white polyimide cover film, which comprises the following steps:

adding the polyimide into a solvent for dissolving, adding a coloring agent and a surfactant for stirring and dispersing, then adding epoxy resin and an epoxy resin curing agent, stirring, and then performing bubble removal treatment to obtain white ink;

and coating, drying, semi-curing and demolding the white ink to obtain the covering film.

In one embodiment, the step of coating, drying, semi-curing and demolding the white ink comprises the following steps:

coating the white ink on a release surface of a release film, and pre-baking for 1-5 min at the temperature of 120-150 ℃; semi-curing for 0.5-2h at 150-160 ℃; and (5) cooling and demolding.

Has the beneficial effects that:

the white polyimide cover film is prepared by matching polyimide containing two different blocks with auxiliary materials such as a coloring agent and the like, the thickness of the cover film is lower than 25 mu m, the reflectivity is higher than 85%, the L value is higher than 90%, the glass transition temperature (Tg) is higher than 120 ℃, the peel strength is higher than 1.1N/m, the tensile modulus is higher than 2.37GPa, the tensile strength is higher than 80MPa, the elongation at break is higher than 3.0%, and the white polyimide cover film has the advantages of low thickness, high reflectivity, high whiteness, high glass transition temperature (Tg), high heat resistance, high mechanical property and high peel strength.

The cover film is prepared by white ink, and then the white ink is prepared by coating, drying, curing and demolding, so that the cover film has the advantages of simple process and simple operation compared with a double-layer white cover film, and the thickness of the white cover film can be further reduced. The flexible printed circuit board cover film can be widely applied to flexible printed circuit board cover films with high linear density, light weight and thin thickness, and further can be applied to light, thin, light and high-brightness LED display screens.

Drawings

FIG. 1 is an infrared spectrum of a polyimide provided in example 1 of the present invention;

FIG. 2 is an infrared spectrum of a polyimide provided in example 2 of the present invention;

FIG. 3 is an infrared spectrum of a polyimide provided in example 3 of the present invention;

FIG. 4 is an infrared spectrum of a polyimide provided in example 4 of the present invention.

Detailed Description

The technical solution of the present invention will be described in further detail with reference to the following embodiments and accompanying drawings. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Term(s)

Unless otherwise stated or contradicted, terms or phrases used herein have the following meanings:

the term "alkyl" refers to a saturated hydrocarbon containing a primary (normal) carbon atom, or a secondary carbon atom, or a tertiary carbon atom, or a quaternary carbon atom, or a combination thereof. Phrases containing the term, e.g., "C ₁ ～C ₉ Alkyl "means an alkyl group containing from 1 to 9 carbon atoms, which at each occurrence may be independently of each other C ₁ Alkyl radical, C ₂ Alkyl radical, C ₃ Alkyl radical, C ₄ Alkyl radical, C ₅ Alkyl radical, C ₆ Alkyl radical, C ₇ Alkyl radical, C ₈ Alkyl or C ₉ An alkyl group. Suitable examples include, but are not limited to: methyl (Me, -CH) ₃ ) Ethyl (Et, -CH) ₂ CH ₃ ) 1-propyl (n-Pr, n-propyl, -CH) ₂ CH ₂ CH ₃ ) 2-propyl (i-Pr, i-propyl, -CH (CH)) ₃ ) ₂ ) 1-butyl (n-Bu, n-butyl, -CH) ₂ CH ₂ CH ₂ CH ₃ ) 2-methyl-1-propyl (i-Bu, i-butyl, -CH) ₂ CH(CH ₃ ) ₂ ) 2-butyl (s-Bu, s-butyl, -CH (CH) ₃ )CH ₂ CH ₃ ) 2-methyl-2-propyl (t-Bu, t-butyl, -C (CH) ₃ ) ₃ ) 1-pentyl (n-pentyl, -CH) ₂ CH ₂ CH ₂ CH ₂ CH ₃ ) 2-pentyl (-CH (CH) ₃ )CH ₂ CH ₂ CH ₃ ) 3-pentyl (-CH (CH) ₂ CH ₃ ) ₂ ) 2-methyl-2-butyl (-C (CH) ₃ ) ₂ CH ₂ CH ₃ ) 3-methyl-2-butyl (-CH (CH) ₃ )CH(CH ₃ ) ₂ ) 3-methyl-1-butyl (-CH) ₂ CH ₂ CH(CH ₃ ) ₂ ) 2-methyl-1-butyl (-CH) ₂ CH(CH ₃ )CH ₂ CH ₃ ) 1-hexyl (-CH) ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₃ ) 2-hexyl (-CH (CH) ₃ )CH ₂ CH ₂ CH ₂ CH ₃ ) 3-hexyl (-CH (CH) ₂ CH ₃ )(CH ₂ CH ₂ CH ₃ ) 2-methyl-2-pentyl (-C (CH)) ₃ ) ₂ CH ₂ CH ₂ CH ₃ ) 3-methyl-2-pentyl (-CH (CH) ₃ )CH(CH ₃ )CH ₂ CH ₃ ) 4-methyl-2-pentyl (-CH (CH) ₃ )CH ₂ CH(CH ₃ ) ₂ ) 3-methyl-3-pentyl (-C (CH) ₃ )(CH ₂ CH ₃ ) ₂ ) 2-methyl-3-pentyl (-CH (CH) ₂ CH ₃ )CH(CH ₃ ) ₂ ) 2,3-dimethyl-2-butyl (-C (CH) ₃ ) ₂ CH(CH ₃ ) ₂ ) 3,3-dimethyl-2-butyl (-CH (CH) ₃ )C(CH ₃ ) ₃ And octyl (- (CH) ₂ ) ₇ CH ₃ )。

The term "cycloalkyl" refers to a non-aromatic hydrocarbon containing ring carbon atoms and may be a monocycloalkyl, or spirocycloalkyl, or bridged cycloalkyl. Phrases containing the term, e.g., "C ₃ ～C ₉ Cycloalkyl "means a cycloalkyl group containing from 3 to 9 carbon atoms, which at each occurrence may be independently of each other C ₃ Cycloalkyl radical, C ₄ Cycloalkyl, C ₅ Cycloalkyl radical, C ₆ Cycloalkyl, C ₇ Cycloalkyl radical, C ₈ Cycloalkyl or C ₉ A cycloalkyl group. Suitable examples include, but are not limited to: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl.

The term "aryl" refers to an aromatic hydrocarbon group derived by the removal of one or more hydrogen atoms from an aromatic ring compound, and may be a monocyclic aryl groupOr a fused ring aryl group, or a polycyclic aryl group, at least one of which is an aromatic ring system for a polycyclic ring species. For example, "C ₅ ～C ₂₀ Aryl "means an aryl group containing from 5 to 20 carbon atoms, which may be, independently for each occurrence, C ₅ Aryl radical, C ₆ Aryl radical, C ₁₀ Aryl radical, C ₁₄ Aryl radical, C ₁₈ Aryl or C ₂₀ And (4) an aryl group. Suitable examples include, but are not limited to: benzene, biphenyl, naphthalene, anthracene, phenanthrene, perylene, triphenylene, and derivatives thereof. It will be appreciated that multiple aryl groups may also be interrupted by short non-aromatic units (e.g. by short non-aromatic units)<10% of atoms other than H, such as C, N or O atoms), such as acenaphthene, fluorene, or 9,9-diarylfluorene, triarylamine, diarylether systems, in particular, should also be included in the definition of aryl.

In the present invention, "+" attached to a single bond represents a connection site or a fusion site. When no attachment site is indicated in the group, it is meant that an optional attachment site in the group is the attachment site. The single bond to which a substituent is attached extending through the corresponding ring, meaning that the substituent may be attached at an optional position on the ring, e.g.

Wherein R is attached to any substitutable site of cyclohexane.

The invention provides a high-reflectivity single-layer white polyimide cover film for an LED display screen.

Wherein the single layer white polyimide coverlay comprises: polyimide, a white colorant, a surfactant, epoxy resin, an epoxy resin curing agent and a solvent.

The polyimide has the following structural general formula:

wherein each X is independently a substituted or unsubstituted diether group containing an aromatic structure; a is a substituted or unsubstituted cycloalkyl-containing group; b is a substituted or unsubstituted aromatic group-containing group; the substituted substituent is alkyl with 1-5 carbon atoms, and the number of the substituted substituent is 0-5;

wherein n: m = 1-9:1-5. From the viewpoint of exhibiting an excellent transparent polyimide effect and obtaining a white coating film having a high reflectance and a high whiteness, n: m is preferably 5 to 7:3 to 5. The polyimide is transparent, has good mechanical properties of tensile strength, tensile modulus and elongation at break, and has wide raw material sources and low cost.

In specific examples, the X is selected from any one of the following structures: 4,4' -bisphenol A diether, biphenyl diether, 4,4' - (2,2 ' -dimethyl) diphenoxy, 4,4' - (3,3 ' -ditert) diphenoxy, 4,4' - (2,3-dicarboxyphenoxy) diphenoxy ether, or 4,4' - (3,4-dicarboxyphenoxy) diphenoxy ether. Of these, 4,4' -bisphenol a diether is preferably used.

In specific examples, the a is selected from:

among them, preferred is

In specific examples, the B is selected from:

wherein preference is given to using->

The preparation method of the polyimide comprises the following steps:

a) Under inert atmosphere, alicyclic diamine H ₂ N-A-NH ₂ With aromatic diamines H ₂ N-B-NH ₂ Dissolving in solvent, adding acetic acidReacting the solution to obtain a suspension;

c) And adding isoquinoline and toluene into the polyamic acid solution, heating for reaction to obtain a polyimide solution, and performing post-treatment to obtain the polyimide. In the reaction process, the water is separated out of the system in time by a water separator.

In a specific example, the solvent in step a) is one or more of N, N-dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, cyclopentanone, cyclohexanone, gamma-butyrolactone, and dimethyl sulfoxide. N, N-dimethylacetamide is preferred. The conditions for obtaining the polyamic acid solution by the mixing reaction in the step b) are as follows: reacting for 18-24 h at-5-5 ℃. The heating reaction in the polyimide solution obtained by the heating reaction in the step c) is a gradient heating reaction, and comprises the following steps: firstly, stirring and reacting for 0.5-0.6h at the temperature of 95-105 ℃; then stirring and reacting for 0.9-1.2h at the temperature of 115-125 ℃; then stirring and reacting for 3-5h at 145-155 ℃. The post-treatment in the step c) comprises the following steps: adding the polyimide solution into anhydrous alcohol for precipitation, filtering to obtain precipitate, washing with anhydrous alcohol for multiple times, and drying at 55-65 deg.C for 20-28h. The anhydrous alcohol can be selected from anhydrous ethanol and anhydrous propanol, and preferably anhydrous ethanol.

In a specific example, the molar ratio of the tetracarboxylic dianhydride to the diamine is 0.05 to 1.05; the diamine is the sum of the mole numbers of alicyclic diamine and aromatic diamine; the molar ratio is preferably 0.08 to 1.01.

In a specific example, the weight average molecular weight of the polyimide is 20000 to 50000g/mol, and preferably 28000 to 35000g/mol. The weight ratios of the white colorant, the surfactant, the solvent, the epoxy resin and the transparent polyimide are respectively 55-75, 0.1-1; the molar ratio of the epoxy curing agent to the epoxy resin is 1-2:1.

In a specific example, the colorant is one or more of titanium dioxide, aluminum oxide, silicon dioxide, zirconium oxide, barium sulfate, zinc oxide, and lead carbonate, and preferably the white colorant is titanium dioxide. The white colorant has an average particle diameter of 0.1 to 10 μm. The white colorant preferably has an average particle diameter of 0.1 to 5.0. Mu.m. The surfactant is one or more of polyether modified polydimethylsiloxane solution, polyester modified polydimethylsiloxane solution, aralkyl modified alkyl siloxane or polyether modified siloxane solution, and preferably the surfactant is the polyether modified siloxane solution. The solvent is one or more of cyclohexanone, N-dimethylacetamide, N-methyl-2-pyrrolidone, gamma-butyrolactone, butanone, butyl acetate, toluene and xylene. Preferably, the solvent is cyclohexanone. In one embodiment, the epoxy resin is one or more of TDE-85, AG-80, KR-470. The preferred epoxy resin is TDE-85. The epoxy resin curing agent is one or more of 2,2 '-bis [4- (4-aminophenoxyphenyl) ] propane, o-phenylenediamine, 4,4' -diaminodiphenyl ether, 1,3-bis (4 '-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, and the epoxy resin curing agent is 2,2' -bis [4- (4-aminophenoxy phenyl) ] propane.

The invention also provides a preparation method of the high-reflectivity single-layer white polyimide cover film for the LED display screen, which comprises the following steps:

adding polyimide into a solvent for dissolving, adding a white coloring agent and a surfactant, stirring and dispersing, adding epoxy resin and an epoxy resin curing agent, stirring, and performing bubble removal treatment to obtain white ink; wherein the bubble removing treatment process comprises the following steps: and (3) placing the stirred mixed solution in a vacuum oven to remove bubbles for 1-2 h under the normal-temperature vacuum condition.

In a specific example, the coating, drying, semi-curing and demolding treatment of the white ink includes:

The invention also provides a preparation method of the flexible circuit board containing the cover film, which comprises the following steps: covering the LED display screen on the FPC by using the non-release surface of the high-reflectivity covering film, and performing laminating, rapid pressing, baking and curing; an FPC containing a coverlay film was obtained. The laminating, pressing and baking curing process comprises the following steps: the temperature in the attaching process is 50-100 ℃, and the pressure is 5-20 kg/cm ² (ii) a The temperature of the pressing process is 100-200 ℃, and the pressure is 60-200 kg/cm ² Preheating time is 0-30 s, and pressing time is 50-6000 s; the temperature of the baking and curing process is 180-220 ℃, and the curing time is 1-2 h.

The present invention will be further described with reference to the following specific examples; all the raw materials can be purchased from the market.

Example 1

Preparing polyimide: in an ice-water bath, 40 parts (parts by mass) of 1,3-cyclohexyldimethylamine (1,3-BAC) and 24 parts of 4,4' -diaminodiphenyl ether (ODA) were uniformly dispersed in 540 parts of N, N-dimethylacetamide (DMAc) as a solvent to form a uniform transparent diamine monomer solution. 37 parts of 85% acetic acid solution was added dropwise to the solution, and the mixture was stirred until the transparent diamine solution became a uniformly dispersed white suspension. To the above solution was added 210 parts of 4,4' -bisphenol a diether dianhydride (BPADA), followed by addition of 540 parts of DMAc, and stirring was continued for 24 hours while maintaining an ice-water bath state to obtain a polyamic acid (PAA) solution. Then, 3% to 5% (by mass of PAA) of isoquinoline and 740 parts of toluene were added to the PAA solution to obtain PAA solution 2. And (3) heating the mixed solution 2 according to the temperature gradient of 100 ℃ (30 min) -120 ℃ (1 h) -150 ℃ (3-5 h), and timely dividing water by a water divider to obtain a transparent polyimide resin (PI-1) solution. After the reaction, the PI solution was added to absolute ethanol to obtain a white precipitate. The precipitate was collected by filtration, washed 3 times with ethanol, and dried in a vacuum dryer at 60 ℃ for 24 hours to obtain a white transparent polyimide powder.

Preparing white ink: 25g of the transparent polyimide powder (PI-1) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent 2,2' -bis [4- (4-aminophenoxyphenyl) ] propane (BAPP) are added, stirred and dispersed for 1h at 850rpm at room temperature, and then placed in a vacuum oven for 2h to remove bubbles at normal temperature.

Preparing a white covering film: the white ink with complete defoaming is coated on the release surface of the release film by a blade coating method, and then prebaking is carried out, wherein the prebaking time is 5min, and the prebaking temperature is 145 ℃. After the pre-baking is finished, high-temperature semi-curing is immediately carried out, wherein the semi-curing time is 0.5h and the semi-curing temperature is 160 ℃. And after the semi-solidification is finished, taking out the covering film, cooling, and placing the covering film in a constant-temperature constant-humidity drying place for later use after the temperature is reduced to normal temperature.

Preparation of FPC containing white coverlay: covering the non-release surface of the cover film on the FPC subjected to the pre-treatment (namely, cutting, drilling, copper plating and etching the conductive layer), wherein the attaching temperature is 85 ℃, and the pressure is 20kg/cm & lt 2 > then pressing by using a quick press, wherein the pressing temperature is 180 ℃, the pressure is 120kg/cm < 2 >, the preheating time is 10s, and the pressing time is 120s; and baking and curing after the pressing is finished, wherein the curing temperature is 180 ℃, and the curing time is 1h.

Example 2

Preparing polyimide: the polyimide (PI-2) of example 2 was obtained by the same polyimide preparation method as example 1, with the main difference that: in example 2, the diamine monomers employed include: 24 parts of 2,2-bis [4- (4-aminophenoxy) phenyl ] propane (BAPP) and 40 parts of 1,3-BAC. In example 2, the charge ratio and the solid content of the PAA solution are shown in table 1.

Preparation of white ink: 25g of the transparent polyimide powder (PI-2) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Example 3

Preparing polyimide: the transparent polyimide (PI-3) of example 3 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in example 3, the diamine monomers employed include: 24 parts of BAPP and 40 parts of Isophoronediamine (IPDA). In example 3, the charge ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-3) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Preparing a white covering film: the white ink with complete defoaming is coated on the release surface of the release film by a blade coating method, and then prebaking is carried out, wherein the prebaking time is 5min, and the prebaking temperature is 145 ℃. After the pre-baking is finished, high-temperature semi-curing is immediately carried out, wherein the semi-curing time is 0.5h, and the semi-curing temperature is 160 ℃. And after the semi-solidification is finished, taking out the covering film, cooling the covering film, and placing the covering film in a constant-temperature constant-humidity drying place for storage after the temperature is reduced to normal temperature.

Preparation of FPC containing white coverlay: covering the non-release surface of the cover film on the FPC subjected to pretreatment (namely, cutting, drilling, copper plating and etching the conductive layer), and attaching at the temperature of 85 ℃ and under the pressure of 20kg/cm & lt 2 > then pressing by using a quick press, wherein the pressing temperature is 180 ℃, the pressure is 120kg/cm & lt 2 & gt, the preheating time is 10s, and the pressing time is 120s; and baking and curing after the pressing is finished, wherein the curing temperature is 180 ℃, and the curing time is 1h.

Example 4

Preparing polyimide: the transparent polyimide (PI-4) of example 4 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in example 4, the diamine monomers employed include: 24 parts of ODA and 40 parts of IPDA. In example 4, the charge ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-4) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the solution after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Example 5

Preparing polyimide: the transparent polyimide (PI-5) of example 5 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in example 5, the diamine monomers employed include: 32 parts of ODA and 34 parts of 1,3-BAC. In example 5, the charge ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-5) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Preparation of FPC containing white coverlay: covering the non-release surface of the cover film on the FPC subjected to the pre-treatment (namely, cutting, drilling, copper plating and etching the conductive layer), wherein the attaching temperature is 85 ℃, and the pressure is 20kg/cm & lt 2 > then pressing by using a quick press, wherein the pressing temperature is 180 ℃, the pressure is 120kg/cm & lt 2 & gt, the preheating time is 10s, and the pressing time is 120s; and baking and curing after the pressing is finished, wherein the curing temperature is 180 ℃, and the curing time is 1h.

Example 6

Preparing polyimide: the transparent polyimide (PI-6) of example 6 was obtained by the same polyimide preparation method as example 1, with the main difference that: in example 6, the diamine monomers employed include: 32 parts of BAPP and 34 parts of 1,3-BAC. In example 6, the charge ratio and the solid content of the PAA solution are shown in table 1.

Preparation of white ink: 25g of the transparent polyimide powder (PI-6) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Coating, drying, semi-curing and demolding the white covering film: the white ink with complete defoaming is coated on the release surface of the release film by a blade coating method, and then prebaking is carried out, wherein the prebaking time is 5min, and the prebaking temperature is 145 ℃. After the pre-baking is finished, high-temperature semi-curing is immediately carried out, wherein the semi-curing time is 0.5h and the semi-curing temperature is 160 ℃. And after the semi-solidification is finished, taking out the covering film, cooling, and placing the covering film in a constant-temperature constant-humidity drying place for later use after the temperature is reduced to normal temperature.

Example 7

Preparing polyimide: the transparent polyimide (PI-7) of example 7 was obtained by the same polyimide preparation method as example 1, with the main difference that: in example 5, the diamine monomers employed include: 40 parts of ODA and 28 parts of 1,3-BAC. In example 7, the charge ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-7) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the solution after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Preparing a white covering film: the white ink with complete defoaming is coated on the release surface of the release film by a blade coating method, and then prebaking is carried out, wherein the prebaking time is 5min, and the prebaking temperature is 145 ℃. After the pre-baking is finished, high-temperature semi-curing is immediately carried out, wherein the semi-curing time is 0.5h and the semi-curing temperature is 160 ℃. And after the semi-solidification is finished, taking out the covering film, cooling the covering film, and placing the covering film in a constant-temperature constant-humidity drying place for storage after the temperature is reduced to normal temperature.

Comparative example 1

Preparing polyimide: the transparent polyimide (PI-a) of comparative example 1 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in comparative example 1, the diamine monomers used included: 64 parts of BAPP, without any addition of diamine monomer containing an alicyclic component. In example 1, however, the diamine monomers used include: 1,3-BAC and ODA. In comparative example 1, the feed ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-A) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1 hour at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles for 2 hours at normal temperature.

Comparative example 2

Preparing polyimide: the transparent polyimide (PI-B) of comparative example 2 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in comparative example 2, the diamine monomers used included: 40 parts of 1,3-BAC and 24 parts of IPDA, without adding any aromatic-containing diamine monomer. In example 1, however, the diamine monomers used include: 1,3-BAC and ODA. In comparative example 2, the feed ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-B) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the resulting solution after completion of the dissolution, and the resulting mixture was stirred at 850rpm at room temperature for 24 hours to disperse the mixture. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Comparative example 3

Preparing polyimide: the transparent polyimide (PI-C) of comparative example 3 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in comparative example 3, the diamine monomers used included: 24 parts of ODA and 64 parts of aliphatic diamine monomer D230 (the structural general formula is as follows: CH) ₃ CH(NH ₂ )CH ₂ [OCH ₂ CH(CH ₃ )]nNH ₂ ). In example 1, however, the diamine monomers used include: 1,3-BAC and ODA. In comparative example 3, the feed ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-C) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1 hour at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles for 2 hours at normal temperature.

Comparative example 4

Preparing polyimide: the transparent polyimide (PI-D) of comparative example 4 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in comparative example 2, the diamine monomers used included: 51 parts of 1,3-BAC and 8 parts of IPDA, without adding any aromatic-containing diamine monomer. In example 1, however, the diamine monomers used include: 1,3-BAC and ODA. In comparative example 4, the feed ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-D) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1h at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles at the normal temperature for 2h.

Comparative example 5

Preparing polyimide: the transparent polyimide (PI-E) of comparative example 5 was obtained by the same polyimide preparation method as example 1, with the difference mainly that: in comparative example 2, the diamine monomers used included: 17 parts of 1,3-BAC and 56 parts of IPDA, without adding any aromatic-containing diamine monomer. In example 1, however, the diamine monomers used include: 1,3-BAC and ODA. In comparative example 5, the feed ratio and the solid content of the PAA solution are shown in table 1.

Preparing white ink: 25g of the transparent polyimide powder (PI-E) was dissolved in 100g of cyclohexanone, 18.75g of titanium dioxide and 0.3% polyether-modified siloxane solution were added to the system after completion of the dissolution, and the mixture was stirred at 850rpm at room temperature for 24 hours. Then 1.25g of epoxy resin TDE-85 and 0.94g of epoxy curing agent BAPP are added, stirred and dispersed for 1 hour at the high speed of 850rpm at room temperature, and then placed in a vacuum oven for removing bubbles for 2 hours at normal temperature.

Preparing a white covering film: coating white ink with complete bubble removal on a release surface of a release film by a blade coating method, and then pre-baking for 5min at the pre-baking temperature of 145 ℃. After the pre-baking is finished, high-temperature semi-curing is immediately carried out, wherein the semi-curing time is 0.5h and the semi-curing temperature is 160 ℃. And after the semi-solidification is finished, taking out the covering film, cooling, and placing the covering film in a constant-temperature constant-humidity drying place for later use after the temperature is reduced to normal temperature.

TABLE 1 formulation of raw materials and thickness of coating film for examples and comparative examples

Examples of the experiments

The white cover films obtained in examples 1 to 7 and comparative examples 1 to 5 were subjected to long-path transmittance, color composition L value, color composition b value, tensile strength, tensile modulus, elongation at break, and peel strength tests. The specific test method is as follows:

determination of Long-Path transmittance, color composition L and b

First, the white cover films of examples 1 to 7 and comparative examples 1 to 5 were each prepared as a film material having a length and width of 5cm × 5 cm. Next, the reflectance at a wavelength of 550nm, the color composition L and b (expressed in Lab color space) were measured using a desktop spectrocolorimeter (manufactured by Sanchen technologies, inc., shenzhen, model: YS 6060). In the standard set in the industry, a b value between 0 and 3.5 indicates that the polyimide film has a low yellowness. In the standard set in the industry, a high reflectivity of polyimide film is indicated when the reflectivity is between 85 and 100. In the standards set in the industry, a value of L between 90 and 100 indicates a high degree of whiteness of the polyimide film.

Measurement of tensile Strength, tensile modulus, and elongation at Break

First, the white cover films of examples 1 to 7 and comparative examples 1 to 5 were each prepared as a long film material having a length (dot pitch) of 10.0cm × 1.0 cm. Next, the tensile strength (MPa), tensile modulus (GPa) and elongation at break (%) of the films were measured using a universal tester (AG-1S, manufactured by Shimadzu scientific instruments, inc. (SHIMADZU)).

Tensile strength represents the maximum strength that the film can withstand during stretching. Specifically, the maximum engineering stress when the films are stretched to a stretch length at which no break occurs under the condition that the tensile strength is initially set to zero, wherein a larger value indicates better mechanical properties. The elongation at break indicates the degree of deformation when the film is stretch broken. Specifically, the elongation is the amount of deformation obtained when the film materials are stretched to break under the condition that the tensile strength is initially set to zero, wherein a larger value indicates better mechanical properties. The tensile modulus is an index of how easily the film is elastically deformed. The larger the value, the larger the stress required for elastic deformation, i.e., the greater the rigidity of the material; the smaller the value, the better the flexibility or softness.

Measurement of peeling Strength

First, the white inks according to examples 1 to 7 and comparative examples 1 to 5 were applied to the surface of a 17.0cm X17.0 cm PI film (50 μm thickness), followed by baking the above materials at 150 ℃ for 5min to remove the solvent, followed by covering the surface of the above materials with a 17.0cm X17.0 cm copper foil (12.5 μm thickness), placing the above materials in an FPC flash press (model: SZB-80T-01A, manufactured by Shenzhen Bion electronics Co., ltd.), and press-fitting under the conditions of 180 ℃ to 120kg/cm2 to 120 s. The laminated sample was then cut into a strip of film material having dimensions of 10.0cm by 1.0 cm. The peel strength (N/m) of the films was measured using an FPC peel strength tester (model: WBE9010B, manufactured by Guangdong Weibang instruments & science, ltd.). In the standards set in the industry, a peel strength value between 1.1 and 1.3 indicates that the white cover film has a high peel strength.

The test results are shown in table 2.

TABLE 2 characterization results and Effect data of examples and comparative examples

As can be seen from Table 2, the transparent polyimides of examples 1 to 7 were prepared by imidizing using alicyclic diamine monomers (including but not limited to 1,3-BAC, IPDA), aromatic diamine monomers (including but not limited to ODA, BAPP) and tetracarboxylic dianhydride monomers thereof (including but not limited to BPADA). Compared with the raw materials containing alicyclic dianhydride, fluorine-containing diamine and the like, the raw materials used in the embodiment are low in price and easy to obtain. Meanwhile, the obtained transparent polyimide has good mechanical properties such as tensile strength, tensile modulus, elongation at break and the like.

By adding a sufficient amount of white colorant, solvent and surfactant to the transparent polyimide, the obtained white cover film has good performance in terms of reflectance, color composition L, color composition b, and the like at 550 nm. Compared with the existing white polyimide cover film, the emphasis is that the L value represents high whiteness of the product, and on the basis that the L value is larger than 90%, the embodiment emphasizes that the reflectivity of the white cover film at 550nm is larger than 85%, and the white cover film has high whiteness and high reflectivity and is more suitable for being used as a white cover film in an LED screen. And the white covering film is smooth as a whole, the white colorant is uniformly dispersed, and shrinkage cavities and agglomeration phenomena are avoided. As is apparent from example 1 and comparative examples 1, 2 and 3, when the composition of the diamine monomer of the present application is changed, wherein comparative example 1 adds only an aromatic diamine, comparative example 2 adds only an alicyclic diamine, and comparative example 3 replaces the alicyclic diamine with an aliphatic diamine having no alicyclic structure, the reflectance and the like of comparative example 1 and comparative example 3 are significantly reduced, and the mechanical properties of comparative example 3 are deteriorated; according to example 1 and comparative examples 4 and 5, in which the ratio of the alicyclic diamine and the aromatic diamine in comparative examples 4 and 5 is out of the range of the present invention, the reflectance and the like are significantly reduced.

By adding the epoxy resin and the epoxy curing agent into the system, the product has the characteristic of crosslinking, the peel strength can be kept above 1.1N/m, the process that a crosslinking layer needs to be coated between a white ink layer and a circuit board when the product is used is reduced, the operation process is simplified, and the thickness of the product is further reduced. The flexible printed circuit board cover film can be widely applied to flexible printed circuit board cover films with high linear density, light weight and thin thickness, and further can be applied to light, thin, light and high-brightness LED display screens.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that various changes and modifications can be made by those skilled in the art without departing from the spirit of the invention, and these changes and modifications are all within the scope of the invention. Therefore, the protection scope of the present patent should be subject to the appended claims.

Claims

1. The utility model provides a LED display screen is with white polyimide cover film of high reflectivity individual layer which characterized in that, white polyimide cover film of individual layer includes: polyimide, a white colorant, a surfactant, epoxy resin, an epoxy resin curing agent and a solvent;

the polyimide has the following structural general formula:

2. The cover film of claim 1, wherein X in the polyimide is selected from any one of the following structures: 4,4' -bisphenol A diether, biphenyl diether, 4,4' - (2,2 ' -dimethyl) diphenoxy, 4,4' - (3,3 ' -ditert) diphenoxy, 4,4' - (2,3-dicarboxyphenoxy) diphenoxy ether, or 4,4' - (3,4-dicarboxyphenoxy) diphenoxy ether.

3. The single-layer white polyimide coverlay with high reflectivity for LED display screen according to claim 1, wherein A in the polyimide is selected from the group consisting of:

one or more of (a).

4. The high-reflectivity single-layer white polyimide cover film for the LED display screen according to claim 1, wherein B in the polyimide is selected from the group consisting of:

/>

one or more of (a).

5. The high-reflectivity single-layer white polyimide cover film for the LED display screen according to claim 1, wherein the preparation method of the polyimide comprises the following steps:

6. The high-reflectivity single-layer white polyimide cover film for the LED display screen according to claim 5, wherein the molar ratio of the tetracarboxylic dianhydride to the diamine is 0.08-1.01; the diamine is the sum of the mole numbers of alicyclic diamine and aromatic diamine;

the conditions for obtaining the polyamic acid solution by mixing reaction in the step b) are as follows: reacting for 18-24 h at-5-5 ℃;

7. The high-reflectivity single-layer white polyimide coverlay for the LED display screen according to any one of claims 1-6, wherein the mass ratio of the white colorant, the surfactant, the solvent, the epoxy resin and the polyimide is 55-75, 0.1-1, 100;

the molar ratio of the epoxy curing agent to the epoxy resin is 1-2:1.

8. The high reflectance single-layer white polyimide coverlay for LED display screens of any one of claims 1-6, wherein the weight average molecular weight of the polyimide is 28000-35000g/mol;

the epoxy resin is one or more of TDE-85, AG-80 and KR-470;

the epoxy resin curing agent is one or more of 2,2' -bis [4- (4-aminophenoxy phenyl) ] propane, o-phenylenediamine, 4,4' -diaminodiphenyl ether, 1,3-bis (4 ' -aminophenoxy) benzene and 1,4-bis (4-aminophenoxy) benzene.

9. The method for preparing the high-reflectivity single-layer white polyimide cover film for the LED display screen according to any one of claims 1 to 8, wherein the method comprises the following steps:

adding the polyimide into a solvent for dissolving, adding a coloring agent and a surfactant, stirring for dispersing, adding epoxy resin and an epoxy resin curing agent, stirring, and then performing bubble removal treatment to obtain white ink;

10. The method for preparing the high-reflectivity single-layer white polyimide cover film for the LED display screen according to claim 9, wherein the steps of coating, drying, semi-curing and demolding the white ink comprise: