阅读说明：本技术 一种无色透明聚酰亚胺薄膜 (Colorless transparent polyimide film ) 是由 王文静 王海生 于 2019-10-23 设计创作，主要内容包括：本发明属于功能性薄膜技术领域,具体涉及一种无色透明聚酰亚胺薄膜,包括物质A和物质B；所述物质A为硝酸盐无机填料；所述物质B为由二胺与二酸酐经过缩聚反应得到酸酐基封端的聚酰胺酸树脂；将所述物质A和物质B共混后进行双向拉伸、亚胺化处理,即得到聚酰亚胺薄膜；所述硝酸盐无机填料占聚酰亚胺薄膜总重量的0.1wt％-7.2wt％。本发明的有益效果是：通过添加溶剂可溶性硝酸盐无机填料,确保无色透明聚酰亚胺合成过程中的无机填料在不降低薄膜的机械性能、热学性能(收缩率、热膨胀系数等)和绝缘性能(电气强度、介电常数等)之外,实现无色透明聚酰亚胺薄膜较高的折射率及较低的双折射参数,更能满足市场的需求,扩大产品应用领域。(The invention belongs to the technical field of functional films, and particularly relates to a colorless transparent polyimide film which comprises a substance A and a substance B; the substance A is nitrate inorganic filler; the substance B is polyamide acid resin with anhydride group end capping obtained by the polycondensation reaction of diamine and dianhydride; blending the substance A and the substance B, and then carrying out biaxial tension and imidization treatment to obtain a polyimide film; the nitrate inorganic filler accounts for 0.1-7.2 wt% of the total weight of the polyimide film. The invention has the beneficial effects that: by adding the solvent soluble nitrate inorganic filler, the inorganic filler in the synthesis process of the colorless transparent polyimide is ensured to realize higher refractive index and lower birefringence parameters of the colorless transparent polyimide film without reducing the mechanical property, the thermal property (shrinkage, thermal expansion coefficient and the like) and the insulating property (electrical strength, dielectric constant and the like) of the film, thereby better meeting the market demand and expanding the product application field.)

1. A colorless transparent polyimide film is characterized by comprising a substance A and a substance B;

the substance A is a nitrate inorganic filler, and the nitrate inorganic filler is any one of zinc nitrate, magnesium nitrate and calcium nitrate;

the substance B is polyamide acid resin with anhydride group end capping obtained by the polycondensation reaction of diamine and dianhydride;

blending the substance A and the substance B, and then carrying out biaxial tension and imidization treatment to obtain a polyimide film;

the nitrate salt inorganic filler was treated as follows before blending: heating the nitrate inorganic filler at 98-136 ℃ for 0.5-10h for pretreatment to perform partial dehydration;

the nitrate inorganic filler accounts for 0.1-7.2 wt% of the total weight of the polyimide film.

2. The colorless and transparent polyimide film according to claim 1, wherein the substance B is prepared by mixing diamine and dianhydride in a molar ratio of 1: (1.0-1.1) uniformly dispersing in the polar aprotic solvent, and stirring and reacting for 2-24h at the speed of 100-1500r/min to obtain the anhydride group-terminated polyamic acid resin;

the blending condition is that the stirring reaction is carried out for 3-16h at the temperature of 15-35 ℃ and the speed of 200-;

the imidization treatment method comprises the steps of forming a product after blending into a polyamic acid resin solution film with the thickness of 20-800 mu m, drying and curing at the temperature of 100-250 ℃ for 0.1-6h, removing 20-90 wt% of solvent in the polyamic acid resin solution film to obtain the polyamic acid film with self-supporting property, and then sequentially carrying out the steps of stretching at the temperature of 60-138 ℃ for 0.1-5.5h by 0.8-2.8 times, imidization at the temperature of 150-550 ℃ for 0.1-8.8h, and shaping at the temperature of 180-360 ℃ for 0.1-7.5h to obtain the colorless transparent polyimide film with the thickness of 2.5-120 mu m.

3. The colorless transparent polyimide film as claimed in claim 2, further comprising a step of adding a catalyst and a dehydrating agent to the polyamic acid resin solution before blending, and stirring at 100-1500r/min for 3-24 h;

the catalyst is a tertiary amine compound, including triethylamine, pyridine, isoquinoline and picoline;

the dehydrating agent is aliphatic acid anhydride comprising acetic anhydride, propionic anhydride and butyric anhydride; or a mixture of an aliphatic anhydride and an aromatic monocarboxylic anhydride.

4. The colorless transparent polyimide film according to claim 2, wherein the diamine is selected from the group consisting of 3,4' -diaminodiphenyl ether (3,4' -ODA), 4' -diaminodiphenyl ether (4,4' -ODA), 2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (2,2' -TFDB), 3' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (3,3' -TFDB), 4' -diaminobiphenyl, m-phenylenediamine (m-PDA), p-phenylenediamine (p-PDA), 2' -bistrifluoromethyl-4, 4' -diaminodiphenyl ether (TFODA), 3' -diamino-5, 5 ' -bistrifluoromethylbiphenyl (s-TFDB), 2, 2-bis (trifluoromethyl) -4,4 '-diaminophenylsulfone (SFTA), 4' -bis (2-trifluoromethyl-4-aminophenoxy) diphenylsulfone, 2- (4-aminophenyl) -5-aminobenzimidazole (APBIA), 4 '-bis (3-aminophenoxy) diphenylsulfone (M-BAPS), bis (3-aminophenyl) sulfone (3-DDS), bis (4-aminophenyl) sulfone (4-DDS), 4' -bis (4-aminophenoxy) biphenyl (BAPB), 1, 3-bis (3-aminophenoxy) benzene (TPE-M), 1, 3-bis (4-aminophenoxy) benzene (TPE-R), 1, 4-bis (4-aminophenoxy) benzene (TPE-Q), 2,2' -bis [4- (4-aminophenoxy phenyl) ] propane (BAPP), 2-bis [4- (4-aminophenoxy) phenyl ] Hexafluoropropane (HFBAPP), 9-bis (3-fluoro-4-aminophenyl) fluorene (FFDA), 9-bis (3-methyl-4-aminophenyl) fluorene (BMAPF), 9-bis (4-aminophenyl) Fluorene (FDA), 1, 3-cyclohexanediamine, 1, 3-cyclobutanediamine or a combination of any of them;

the dianhydride is selected from 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 3,4 '-hexafluoroisopropylphthalic anhydride (a-6FDA), 4- (2, 5-dioxotetrahydrofuran-3-yl) -1,2, 3, 4-tetrahydronaphthalene-1, 2-dicarboxylic anhydride (TDA), 4' - (4,4 '-isopropyldiphenoxy) bis (phthalic anhydride) (HBDA), 2,3,3',4 '-biphenyltetracarboxylic dianhydride (a-BPDA), 4' -triphendiether tetracarboxylic dianhydride (HQDPA), thiobisbenzenetetracarboxylic dianhydride (3,4,3',4' -TDPA, 2,3,2',3' -TDPA, 2,3,3',4' -TDPA), 2,3,3',4' -diphenylether tetracarboxylic dianhydride (a-ODPA), 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane dianhydride (BPADA), 3,3',4,4' -diphenylsulfone tetracarboxylic dianhydride, 2,3',4' -diphenylsulfone tetracarboxylic dianhydride, pyromellitic acid (PMDA), 3,3',4,4' -biphenyltetracarboxylic dianhydride (BPDA), 2',3,3' -biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4' -benzophenonetetracarboxylic dianhydride (a-BTDA), benzophenonetetracarboxylic dianhydride (BTDA), 4,4' -oxydiphthalic anhydride (ODPA), 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3, 4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4, 5-cyclohexanetetracarboxylic dianhydride (HPMDA), or a combination of any two or more thereof.

5. The colorless and transparent polyimide film according to claim 2, wherein the amounts of the diamine, the dianhydride and the polar aprotic solvent are controlled such that the ratio of the solid content M in the polyamic acid resin solution formed in the present step is 8 to 60 wt%.

6. The colorless transparent polyimide film according to claim 1, wherein the nitrate inorganic filler is present in an amount of 0.2 wt% to 5.8 wt% based on the total weight of the polyimide film.

7. The colorless transparent polyimide film according to claim 1, wherein the nitrate inorganic filler is present in an amount of 0.3 wt% to 3.2 wt% based on the total weight of the polyimide film.

8. The colorless transparent polyimide film according to claim 1, wherein the partially dehydrated nitrate inorganic filler is blended with the acid anhydride group-terminated polyamic acid resin by the following method,

a. adding the partially dehydrated nitrate inorganic filler directly in solid form to the anhydride group-terminated polyamic acid resin, or,

b. Adding the partially dehydrated nitrate inorganic filler into the polar aprotic solvent, and uniformly mixing and stirring to obtain nitrate slurry, wherein the mass ratio of the nitrate inorganic filler to the polar aprotic solvent is (0.1-1.5): the resulting nitrate slurry was added to the anhydride group-terminated polyamic acid resin 10.

9. The colorless and transparent polyimide film according to claim 2 or 7, wherein the polar aprotic solvent is selected from any one or a combination of any more of low molecular weight carboxylic acid amides, specifically N, N '-Dimethylacetamide (DMAC), N' -Dimethylformamide (DMF), N-methylpyrrolidone (NMP), Dimethylsulfoxide (DMSO), tetramethylsulfoxide, N '-dimethyl-N, N' -propyleneurea (DMPU), cyclopentanone, cyclohexanone, dichloromethane, monochlorobenzene, dichlorobenzene, chloroform, tetrahydrofuran, 3-methyl-N, N-dimethylpropionamide, N-dialkylcarboxylic acid amides, m-cresol, γ -butyrolactone.

10. The colorless transparent polyimide film as claimed in claim 8, wherein the specific mixing and stirring method of the nitrate inorganic filler and the polar aprotic solvent comprises sequentially performing low-speed shear stirring at 50-200r/min for 0.5-6.5h, high-speed shear stirring at 600-1360r/min for 0.5-8h, emulsification treatment at 800-1400r/min for 0.5-10h, high-pressure homogenization treatment at 10-60MPa for 0.2-3h, and ultrasonic dispersion treatment at 28khz for 1-5h to obtain the nitrate slurry.

11. The colorless transparent polyimide film according to claim 1, wherein the viscosity of the polyamic acid resin is controlled to 10000-1000000 cps.

12. The colorless and transparent polyimide film according to claim 1, wherein the pH of the nitrate inorganic filler is controlled to 4.8 to 7.6 at the time of blending.

13. The colorless and transparent polyimide film according to claim 1, wherein the pH of the nitrate inorganic filler is controlled to 5.0 to 6.8 at the time of blending.

Technical Field

The invention belongs to the technical field of functional films, and particularly relates to a colorless transparent polyimide film.

Background

The development of the photoelectric device in the future gradually shows the trend of light weight, large size, ultra-thin and flexibility, the glass serving as the traditional transparent substrate material cannot meet the development requirement of the flexible packaging technology in the future, and the high-transparency polymer material becomes the first choice of the flexible photoelectric packaging substrate material in the future due to the advantages of transparency, flexibility, light weight, high impact resistance and the like. The polyimide film has excellent heat-resistant stability, and can meet the requirements of high-temperature processes such as electrode film deposition, annealing treatment and the like in the processing process of photoelectric devices, so that the development of high-transparency polyimide materials becomes a key point of research. The traditional polyimide film is brown or yellow due to high aromatic ring density, has low transmittance in the range of visible light (wavelength of 400nm-700nm), and has high birefringence, so that the application of the traditional polyimide film in the advanced photoelectric field, such as optical waveguide materials, photoelectric packaging materials, photovoltaic materials, nonlinear optical materials, light refraction edge materials, photoelectric materials, orientation film materials in the liquid crystal display field and the like, is severely limited.

The existing colorless transparent polyimide film preparation technology mainly avoids or reduces conjugated units, reduces the charge transfer effect in molecules or between molecules and improves the light transmittance and transparency of the polyimide film by introducing monomers such as fluorine-containing groups, bulky substituents, alicyclic structures, main chain bending structures, asymmetric structures, conjugated double bond structures and the like. At present, researchers at home and abroad develop a new formula by adopting the structural monomers and mutually combining the structural monomers, and prepare the colorless transparent polyimide film with high light transmittance, high modulus, relatively high glass transition temperature (Tg), relatively low CTE (coefficient of thermal expansion) and low thermal shrinkage rate by methods such as block polymerization and chemical polymerization, but the improvement of the comprehensive performance of the film is limited, for example, the defects of high haze, low refractive index, high birefringence, low surface hardness and the like exist. Even if polymerization is carried out after a refining pretreatment of the polymerization monomers and the solvent, the improvement of the overall properties is greatly limited. In addition, in the prior art, some high-molar-refractive-index groups are introduced through molecular structure design, namely, the rigid chain segment is added to endow the polyimide with high refractive index, high heat-resistant stability, high mechanical property and dielectric property. Furthermore, the thermal stability and mechanical properties of the polyimide are somewhat reduced by excessive retention of the flexible links. How to expand the application field of polyimide films (especially in the fields of solar cells, liquid crystal displays, optoelectronic integrated circuits and the like) and further improve the optical properties of colorless transparent polyimide films (such as haze reduction, refractive index improvement, birefringence reduction, intrinsic surface hardness enhancement and the like) is a problem to be solved urgently by researchers at present.

Disclosure of Invention

In order to solve the problems, the invention provides a colorless transparent polyimide film, which is prepared by adding inorganic filler nitrate into a polyamic acid resin solution and adopting molding processes such as extrusion casting, biaxial stretching, high-temperature imidization, shaping and the like, wherein the refractive index of the transparent polyimide film is optimized by introducing solvent soluble nitrate, and the transparent polyimide film has optical properties such as low haze, low birefringence and the like. The colorless polyimide film product prepared by the method maintains the original high transparency, mechanical property and heat resistance of the film, effectively improves the optical characteristics of the film with birefringence less than 0.01, haze less than or equal to 0.2% and refractive index greater than 1.76, and greatly expands the application of the colorless transparent polyimide film in various aspects in the optical field.

The invention provides the following technical scheme:

a colorless transparent polyimide film is characterized by comprising a substance A and a substance B;

the substance A is a nitrate inorganic filler, and the nitrate inorganic filler is any one of zinc nitrate, magnesium nitrate and calcium nitrate;

the substance B is polyamide acid resin with anhydride group end capping obtained by the polycondensation reaction of diamine and dianhydride;

blending the substance A and the substance B, and then carrying out biaxial tension and imidization treatment to obtain a polyimide film;

the nitrate salt inorganic filler was treated as follows before blending: heating the nitrate inorganic filler at 98-136 ℃ for 0.5-10h for pretreatment to perform partial dehydration;

the nitrate inorganic filler accounts for 0.1-7.2 wt% of the total weight of the polyimide film.

Preferably, the substance B is prepared by specifically preparing diamine and dianhydride in a molar ratio of 1: (1.0-1.1) uniformly dispersing in the polar aprotic solvent, and stirring and reacting for 2-24h at the speed of 100-1500r/min to obtain the anhydride group-terminated polyamic acid resin;

the blending condition is that the stirring reaction is carried out for 3-16h at the temperature of 15-35 ℃ and the speed of 200-;

the imidization treatment method comprises the steps of forming a product after blending into a polyamic acid resin solution film with the thickness of 20-800 mu m, drying and curing at the temperature of 100-250 ℃ for 0.1-6h, removing 20-90 wt% of solvent in the polyamic acid resin solution film to obtain the polyamic acid film with self-supporting property, and then sequentially carrying out the steps of stretching at the temperature of 60-138 ℃ for 0.1-5.5h by 0.8-2.8 times, imidization at the temperature of 150-550 ℃ for 0.1-8.8h, and shaping at the temperature of 180-360 ℃ for 0.1-7.5h to obtain the colorless transparent polyimide film with the thickness of 2.5-120 mu m.

Preferably, the method also comprises the steps of adding a catalyst and a dehydrating agent into the polyamic acid resin solution and stirring for 3-24h at 100-1500r/min before blending;

the catalyst is a tertiary amine compound, including triethylamine, pyridine, isoquinoline and picoline;

the dehydrating agent is aliphatic acid anhydride comprising acetic anhydride, propionic anhydride and butyric anhydride; or a mixture of an aliphatic anhydride and an aromatic monocarboxylic anhydride.

Preferably, the diamine is selected from the group consisting of 3,4' -diaminodiphenyl ether (3,4' -ODA), 4' -diaminodiphenyl ether (4,4' -ODA), 2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (2,2' -TFDB), 3' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (3,3' -TFDB), 4' -diaminobiphenyl, m-phenylenediamine (m-PDA), p-phenylenediamine (p-PDA), 2' -bis-trifluoromethyl-4, 4' -diaminodiphenyl ether (TFODA), 3' -diamino-5, 5 ' -bis-trifluoromethyl-biphenyl (s-TFDB), 2-bis (trifluoromethyl) -4,4 '-diaminophenylsulfone (SFTA), 4' -bis (2-trifluoromethyl-4-aminophenoxy) diphenylsulfone, 2- (4-aminophenyl) -5-aminobenzimidazole (APBIA), 4 '-bis (3-aminophenoxy) diphenylsulfone (M-BAPS), bis (3-aminophenyl) sulfone (3-DDS), bis (4-aminophenyl) sulfone (4-DDS), 4' -bis (4-aminophenoxy) biphenyl (BAPB), 1, 3-bis (3-aminophenoxy) benzene (TPE-M), 1, 3-bis (4-aminophenoxy) benzene (TPE-R), 1, 4-bis (4-aminophenoxy) benzene (TPE-Q), 2,2' -bis [4- (4-aminophenoxy phenyl) ] propane (BAPP), 2-bis [4- (4-aminophenoxy) phenyl ] Hexafluoropropane (HFBAPP), 9-bis (3-fluoro-4-aminophenyl) fluorene (FFDA), 9-bis (3-methyl-4-aminophenyl) fluorene (BMAPF), 9-bis (4-aminophenyl) Fluorene (FDA), 1, 3-cyclohexanediamine, 1, 3-cyclobutanediamine or a combination of any of them;

the dianhydride is selected from 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 3,4 '-hexafluoroisopropylphthalic anhydride (a-6FDA), 4- (2, 5-dioxotetrahydrofuran-3-yl) -1,2, 3, 4-tetrahydronaphthalene-1, 2-dicarboxylic anhydride (TDA), 4' - (4,4 '-isopropyldiphenoxy) bis (phthalic anhydride) (HBDA), 2,3,3',4 '-biphenyltetracarboxylic dianhydride (a-BPDA), 4' -triphendiether tetracarboxylic dianhydride (HQDPA), thiobisbenzenetetracarboxylic dianhydride (3,4,3',4' -TDPA, 2,3,2',3' -TDPA, 2,3,3',4' -TDPA), 2,3,3',4' -diphenylether tetracarboxylic dianhydride (a-ODPA), 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane dianhydride (BPADA), 3,3',4,4' -diphenylsulfone tetracarboxylic dianhydride, 2,3',4' -diphenylsulfone tetracarboxylic dianhydride, pyromellitic acid (PMDA), 3,3',4,4' -biphenyltetracarboxylic dianhydride (BPDA), 2',3,3' -biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4' -benzophenonetetracarboxylic dianhydride (a-BTDA), benzophenonetetracarboxylic dianhydride (BTDA), 4,4' -oxydiphthalic anhydride (ODPA), 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3, 4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4, 5-cyclohexanetetracarboxylic dianhydride (HPMDA), or a combination of any two or more thereof.

Preferably, the amounts of the diamine, the dianhydride and the polar aprotic solvent are controlled such that the ratio of the solid content M in the polyamic acid resin solution formed in this step is 8 wt% to 60 wt%.

Preferably, the nitrate inorganic filler accounts for 0.2 wt% to 5.8 wt% of the total weight of the polyimide film.

Preferably, the nitrate inorganic filler accounts for 0.3 wt% to 3.2 wt% of the total weight of the polyimide film.

Preferably, the partially dehydrated nitrate salt inorganic filler is blended with the anhydride group-terminated polyamic acid resin by a method comprising,

a. adding the partially dehydrated nitrate inorganic filler directly in solid form to the anhydride group-terminated polyamic acid resin, or,

b. Adding the partially dehydrated nitrate inorganic filler into the polar aprotic solvent, and uniformly mixing and stirring to obtain nitrate slurry, wherein the mass ratio of the nitrate inorganic filler to the polar aprotic solvent is (0.1-1.5): the resulting nitrate slurry was added to the anhydride group-terminated polyamic acid resin 10.

Preferably, the polar aprotic solvent is selected from any one or a combination of any more of low molecular weight carboxyamides, in particular N, N '-Dimethylacetamide (DMAC), N' -Dimethylformamide (DMF), N-methylpyrrolidone (NMP), Dimethylsulfoxide (DMSO), tetramethylsulfoxide, N '-dimethyl-N, N' -propyleneurea (DMPU), cyclopentanone, cyclohexanone, dichloromethane, monochlorobenzene, dichlorobenzene, chloroform, tetrahydrofuran, 3-methyl-N, N-dimethylpropionamide, N-dialkylcarboxyamide, m-cresol, γ -butyrolactone.

Preferably, the specific method for mixing and stirring the nitrate inorganic filler and the polar aprotic solvent comprises the steps of sequentially carrying out low-speed shearing stirring at a speed of 50-200r/min for 0.5-6.5h, high-speed shearing stirring pretreatment at a speed of 600-1360r/min for 0.5-8h, emulsification treatment at a speed of 800-1400r/min for 0.5-10h, high-pressure homogenization treatment at a pressure of 10-60MPa for 0.2-3h and ultrasonic dispersion treatment at 28khz for 1-5h, so as to prepare the nitrate slurry.

Preferably, the viscosity of the polyamic acid resin at the time of blending is controlled to 10000-1000000 cps.

Preferably, the pH of the nitrate inorganic filler is controlled to 4.8-7.6 during blending.

Preferably, the pH of the nitrate inorganic filler is controlled to 5.0 to 6.8 during blending.

The application is characterized in that the selective solvent isAn agent-soluble nitrate is introduced into the polyimide matrix as an inorganic filler, the above-mentioned solvent-soluble nitrate being a partially dehydrated nitrate inorganic filler, and specifically defining a partially dehydrated nitrate (trihydrate Zn (NO) by high-temperature pretreatment)₃)₂·3H₂O, dihydrate Zn (NO)₃)₂·2H₂O) mixtures, the above solvents being referred to as polar aprotic solvents as defined in the present invention, since the applicant found in numerous experiments, research tests, systematic analyses:

when the nitrate inorganic filler is not subjected to a partial dehydration pretreatment at a high temperature, its initial state at room temperature is hexahydrate (zinc nitrate Zn (NO)₃)₂·6H₂O, magnesium nitrate Mg (NO)₃)₂·6H₂O) and tetrahydrate (calcium nitrate Ca (NO)₃)₂·4H₂O), poor compatibility (or solubility) with polyamic acid or polyimide, especially polar solvent, causing insignificant effect in modifying polyimide film, and reducing and deteriorating the performance of polyimide film by dehydration reaction in the subsequent forming process; if the high-temperature pretreatment is carried out for complete dehydration, the compatibility with polyamic acid or polyimide, particularly a polar solvent, is poor, and the high-temperature pretreatment is a substance with higher oxidizability, so that the potential safety hazard exists. Zinc nitrate hexahydrate (Zn (NO) as shown in FIG. 1₃)₂6H2O) Compound X-ray diffraction Pattern, FIG. 2 Zinc nitrate trihydrate (Zn (NO)₃)₂·3H₂O), zinc nitrate dihydrate (Zn (NO)₃)₂·2H₂O) mixture, the high temperature pretreatment can transform the crystal state of the hexahydrate into a sheet crystal state of a trihydrate, dihydrate mixture more soluble in polar solvents, as shown in fig. 1 and 2, zinc nitrate hexahydrate (NO) is shown in fig. 1 and 2₃)₂·6H₂O) compound was pretreated by high-temperature partial dehydration, and its strong characteristic peak at 2 θ -15.869 °,2 θ -17.221 °,2 θ -20.959 ° and the like completely disappeared, and zinc nitrate trihydrate (Zn (NO) (20.959 ° was formed after the treatment₃)₂·3H₂O), zinc nitrate dihydrate (Zn (NO)₃)₂·2H₂O) are mixedThe method is characterized in that relatively obvious strong characteristic peaks appear at positions such as 2 theta 18.46 degrees, 2 theta 28.51 degrees and 2 theta 30.63 degrees in an X-ray diffraction pattern of a substance, zinc nitrate is flaky crystals after dehydration, the zinc nitrate is very easy to dissolve in a polar solvent due to the crystal form conversion of the substance, and a solvent soluble nitrate inorganic substance reduces aggregation in the film forming process of a polyamic acid or polyimide resin solution so as to precipitate in a colorless transparent polyimide film and show nano distribution; meanwhile, on the basis, when the water removed by the nitrate inorganic filler is in the forms of pentahydrate, tetrahydrate, monohydrate and the like, through a large number of tests, research tests and system analysis, the binding effect of the interface between the nitrate inorganic filler of the partially-dehydrated non-trihydrate and dihydrate mixture and the polyimide molecule cannot be completely and effectively embodied, the capability of inhibiting the polyimide molecule interface defect generated is lacked, namely the capability of improving the optical property of the colorless transparent film is limited, and the characteristics of improving the refractive index of the transparent film, reducing the birefringence and the like cannot be realized. In addition, in the technical scheme of the application, the polyamic acid or polyimide resin solution with the end capped by the anhydride group is prepared by adopting a control method of non-diamine monomer excess, and simultaneously, the nitrate inorganic filler is added after the polymerization reaction of the polyamic acid or polyimide resin solution with the end capped by the anhydride group is completely carried out, so that the purpose of inhibiting the redox reaction of the polyamic acid or polyimide resin solution with the end capped by the amino group and the nitrate inorganic filler is mainly realized, and the discoloration of the polyamic acid or polyimide resin solution further influences the optical properties such as light transmittance and the like of the colorless transparent polyimide film.

Preparation of nitrate of trihydrate and dihydrate mixture (high-temperature pretreatment):

partial dehydration high-temperature pretreatment of mixture of zinc nitrate trihydrate and zinc nitrate dihydrate, and weighing inorganic filler zinc nitrate hexahydrate Zn (NO) with formula amount₃)₂·6H₂Removing partial water molecules of the O mixture for 3 hours in a vacuum high-temperature oven at the temperature of between 102 and 108 ℃ to prepare zinc nitrate trihydrate Zn (NO)₃)₂·3H₂O, Zinc nitrate dihydrate Zn (NO)₃)₂·2H₂A mixture of O; zinc nitrate hexahydrate of zinc(NO₃)₂·6H₂O compound and zinc nitrate trihydrate Zn (NO)₃)₂·3H₂O, Zinc nitrate dihydrate Zn (NO)₃)₂·2H₂The X-ray diffraction patterns of the O mixture are respectively shown in figure 1 and figure 2.

The invention has the beneficial effects that:

1. the nitrate inorganic filler is added into the colorless transparent polyimide film, so that the obtained polyimide film has excellent mechanical properties, thermal properties (shrinkage rate, thermal expansion coefficient and the like), insulating properties (electrical strength, dielectric constant and the like), and simultaneously, the controllable refractive index and the lower birefringence parameters of the colorless transparent polyimide film are further realized, the market requirements can be further met, and the product application field is enlarged.

2. According to the invention, nitrate inorganic fillers with low refractive index (zinc nitrate, magnesium nitrate and calcium nitrate) are used as optical property modifiers of the polyimide film, the high-temperature partial dehydration pretreatment is carried out on the nitrate inorganic fillers (zinc nitrate, magnesium nitrate and calcium nitrate), so that the optical properties of the colorless transparent polyimide film, such as refractive index, birefringence, light transmittance, haze and the like, can be improved, the nitrate inorganic fillers can be more effectively uniformly dispersed in a polyamide acid resin matrix through the high-temperature partial dehydration pretreatment, and the optical properties are very good and isotropic; further, limiting the amount of the nitrate inorganic filler to 0.1 to 7.2 wt% based on the weight of the polyimide is considered to be unsatisfactory in the refractive performance parameters of the transparent film when the amount is less than 0.1 wt%; when the amount is more than 7.2 wt%, the mechanical properties, optical properties, etc. of the obtained film are deteriorated, and non-uniform dispersion (sedimentation and incomplete dissolution) is liable to occur in the polyamic acid resin, and the prepared film has poor uniformity of properties, and the production cost of the film is increased. The reason why the nitrate inorganic filler is added to the polyamic acid resin solution and the heating pretreatment is performed first is to partially dehydrate the nitrate inorganic filler to form a mixture of trihydrate and/or dihydrate, and to partially dehydrate a commercially available hexahydrate nitrate mixture at a high temperature to form a nitrate of trihydrate and/or dihydrateSuch that it is converted from a relatively insoluble state to a very soluble state in a polar solvent, e.g. zinc nitrate is subjected to a high temperature dehydration pretreatment at a temperature of 102-108 ℃ to form a trihydrate Zn (NO) containing a portion of molecular water₃)₂·3H₂O, dihydrate Zn (NO)₃)₂·2H₂O, and the like. The nitrate hexahydrate mixture has the unsafe characteristics of flammability and the like with partial polar solvent, the dissolving capacity in most polar solvent is smaller, the oxidation and interface combination characteristics of the nitrate inorganic filler in polar solvent-containing polyamic acid resin can be effectively adjusted by partial dehydration pretreatment, the nitrate inorganic filler soluble in solvent is formed after partial dehydration treatment, the dispersing process is very simple, the dispersing uniformity of the nitrate inorganic filler is high, the introduction of the nitrate inorganic filler can promote the dehydration and cyclization of polyamic acid molecules and inhibit the oxidation to a certain extent, and the nitrate inorganic filler and the carboxyl hydroxyl in the dehydrated molecules and the polyamic acid molecules form a transitional unstable complex intermediate to eliminate the oxidation of the nitrate inorganic filler, and a synergistic effect is generated with the polyimide molecules at the interface position in the further high-temperature treatment process to effectively improve the refractive index of the colorless transparent polyimide film, reduce birefringence, etc.

3. The existing colorless transparent polyimide film is mainly prepared by selecting different structural polymerization monomers or introducing inorganic nano-fillers for blending, heterogeneous interface defects exist among molecules of the prepared colorless polyimide film, so that the light transmittance, the haze, particularly the refractive index, the birefringence and other optical characteristics of the existing polyimide film are relatively poor. Meanwhile, because polyimide has a molecular chain with high rigidity (an amido bond exists), the molecular chain is easy to orient along the plane direction of the film, so that the refractive index nTE in the plane direction of the film is obviously larger than the refractive index nTM in the vertical direction, and the birefringence delta n of the film is larger. The sheet crystal of the mixture of the trihydrate and the dihydrate prepared by high-temperature pretreatment is introduced into a polyimide matrix, and due to the synergistic effect of polyimide molecules and the sheet crystal, the refractive index nTM in the vertical direction of the film is enhanced to a certain extent, the molecular chain orientation tends to be isotropic while the stacking density of the molecular chain is not weakened, and further, the birefringence optical property of the polyimide film can be reduced while the refractive index of the polyimide film is remarkably improved.

4. According to the invention, through the synergistic effect of the introduced partially dehydrated solvent-soluble nitrate inorganic filler and the biaxial stretching and high-temperature imidization forming process, part of metal oxides (such as zinc oxide, magnesium oxide and calcium oxide) are formed on the surface of zinc nitrate dispersed in a film in the high-temperature treatment process, so that the added inorganic filler is subjected to surface migration and creeping in a polyimide matrix and is subjected to uniform self-assembly behavior to generate an irregularly formed modified surface, and the influence of partial haze of the nitrate caused by a self crystal structure is reduced; meanwhile, a complex thermochemical reaction is caused in the polyimide substrate molecules, potential problems of micro-phase and macro-phase separation and the like are eliminated under the condition of synergistic effect of various factors, and optical properties such as refractive index, birefringence and the like of the colorless transparent polyimide film are further effectively improved.

5. The pH of the nitrate inorganic filler of the invention is 4.8 to 7.6, preferably 5.0 to 6.8. The required range of the pH value range of the nitrate inorganic filler is related to the compatibility of the filler and polyamic acid or polyimide, particularly polar solvent, simultaneously can weaken the thermochemical reaction effect caused in the polyimide matrix molecule, possibly has negative effects on eliminating the potential problems of micro-phase and macro-phase separation and the like, and if the pH value range is beyond the required range, the effect is not obvious when the nitrate inorganic filler is applied to the modification of the polyimide film, and the optical property of the colorless transparent polyimide film cannot be improved.

6. The polyimide film prepared by the prior art has the light transmittance of more than 88.0 percent (wavelength of 550nm), the birefringence of less than 0.2, the haze of less than or equal to 1.0 percent, the refractive index of less than 1.65, the tensile strength of more than or equal to 180MPa, the elongation of more than 20 percent and the elastic modulusMore than 2.5GPa, Coefficient of Thermal Expansion (CTE) less than or equal to 30 x 10^-6/℃，Tg＞300℃；

The thickness of the colorless transparent polyimide film prepared by the invention is 2.5-150 mu m, the light transmittance is more than 90.0 percent (wavelength is 550nm), the birefringence is less than 0.01, the haze is less than or equal to 0.2 percent, the refractive index is more than 1.76, the tensile strength is more than or equal to 200MPa, the elongation is more than 30 percent, the elastic modulus is more than 4.0GPa, and the Coefficient of Thermal Expansion (CTE) is less than or equal to 20 x 10^-6/℃，Tg＞330℃。

Drawings

FIG. 1 Zinc nitrate hexahydrate of inorganic Filler nitrate (Zn (NO)₃)₂·6H₂O) an X-ray diffraction pattern of the compound;

FIG. 2 inorganic Filler nitrate Zinc nitrate trihydrate (Zn (NO) pre-treated with high temperature partial dehydration₃)2·3H₂O), zinc nitrate dihydrate Zn (NO)₃)₂·2H₂X-ray diffraction pattern of the O-mixture.

Detailed Description

The present invention will be described in detail with reference to the following examples.