TW201311764A - Low chroma polyimide film and manufacturing method thereof - Google Patents

Abstract

A low chroma polyimide film comprises a polyimide base polymer formed by reacting a diamine component with a dianhydride component. The diamine component includes 2, 2'-bis(trifluoromethyl)benzidine, and the dianhydride component includes 3, 3', 4, 4'-biphenyltetracarboxylic dianhydride and 2, 2-bis[4-(3, 4-dicarboxyphenoxy) phenyl]propane dianhydride. The low chroma polyimide film of this invention has 85% and above of transmission rate, a coefficient of thermal expansion (CTE) less than about 65 ppm/ DEG C in a temperature range between about 100 DEG C and about 200 DEG C, an elongation rate between about 10% and about 60%. The low chroma polyimide film has absorption of 400 nm wavelength in the spectrum. In some embodiments, a method of manufacturing the low chroma polyimide film is also described.

Description

Low chroma polyimine film and preparation method thereof

The present invention relates to a polyimide film and a method for producing the same, and more particularly to a low chroma polyimine film and a method for producing the same, that is, a transparent polyimide film and a method for producing the same.

In the application of soft electronic products, such as liquid crystal display (LCD), touch panel, flexible rpinted circuit (FPC), e-book, etc., the industry is committed to developing light Thin, flexible, and highly transparent design, therefore, high-transparency plastic materials must be used, and these materials must withstand high temperatures of about 250 ° C or higher in the process, and meet other special design needs. . Since PI films are mostly excellent in heat resistance, they are suitable materials for soft electronic products.

Polyimide (PI) film has the characteristics of light weight, good elasticity, excellent mechanical properties, and good resistance to heat and chemical. It is often used in electrical products with insulation or high temperature resistance. However, with the development of the electronics industry, there are more and more requirements for the quality and characteristics of PI films, such as low color PI, thermal conductivity PI, low dielectric PI, and the like. Therefore, the conventional PI film has gradually become unsatisfactory.

However, the conventional PI film is affected by a charge transfer complex effect, so that the PI film is yellow or reddish brown. In order to improve the transparency of the PI film, a considerable number of studies have been proposed for the composition and production of various transparent PI films, such as, for example, U.S. Patent No. 7,078,477, U.S. Patent Publication No. 2008/0113120, U.S. Patent Publication No. 2008/0286498, etc. In the previous case, a one-step method was used to produce a transparent PI film, that is, a diamine monomer, a dianhydride monomer, and a solvent were subjected to a condensation polymerization reaction and a ring closure reaction in the same reactor. A solution containing polyimine is obtained, followed by removing the solvent in the polyimine solution to obtain a solid polyimide film. However, the polyimide film formed by the one-step method has poor chemical resistance, poor mechanical properties, and is liable to yellowing or deterioration at high temperatures, and cannot meet the process requirements of the aforementioned soft electronic product application. In addition, the one-step process control is difficult to control and the raw material cost is high, and it cannot be practically applied to the mass production scale.

Therefore, there is still a need for a transparent polyimide film having improved properties and a process for producing the transparent polyimide film.

The present invention provides a low chroma polyimine film obtained by reacting a diamine component with a dianhydride component. In particular, in one embodiment, the low chroma polyimine film may comprise a polyamidimide polymer consisting of the structures represented by the following formulas (I) and (II):

Wherein the ratio of m: n represents the molar ratio of the molecular structure of the formulae (I) and (II) in the polyamidimide-based polymer, and the ratio of m: n is 0.15-0.95: 0.85-0.05.

The present invention also provides a low chroma polyimine film composed of a polyamidimide-based polymer characterized by a total transparence of 85% or more and a coefficient of thermal expansion between 100 and 200 ° C ( The CTE) is 65 ppm/°C or less, the elongation rate is between 10% and 60%, and ultraviolet rays can be absorbed.

In other embodiments, the present invention also provides a method for preparing a low chroma polyimine film, comprising: performing a condensation polymerization reaction with a monomer including a diamine and a dianhydride to obtain a polyamic acid. a solution; adding a dehydrating agent and a catalyst to the solution containing polyamic acid to obtain a precursor solution; coating the precursor solution on a substrate to form a layer; and baking the coated layer to form a low Chroma polyimine film.

The invention prepares a low chroma polyimine film (PI film) in a two-step process, and can adjust the structure/ratio of the polyamidimide polymer according to the material conditions required for different kinds of electronic products. In the present invention, the PI film is "low chroma", that is, a PI film having a b* value of less than 10 in the L*a*b* color space.

The PI membrane of the present invention is obtained by reacting a diamine component with a dianhydride component. In one embodiment, the low chroma polyimine film may comprise a polyamidimide polymer consisting of the structures represented by the following formulas (I) and (II):

Wherein the ratio of m: n represents the molar ratio of the molecular structure of the formulae (I) and (II) in the polyamidimide-based polymer, and the ratio of m: n is 0.15-0.95: 0.85-0.05.

In an embodiment, the ratio of m:n may be between about 0.15-0.95: 0.85-0.05. Specifically, the polyamidomino group may include from about 95 mole% (mol%) to about 15 mol. % of the structure of formula (I) (i.e., m), and from about 5 mol% to about 85 mol% of the structure of formula (II) (i.e., n).

As described above, the low chroma PI film of the present invention can be structurally and proportionally adjusted according to the characteristics required for various end products, for example but not limited, for example, when the low chroma PI film is used for preparing a display. The optical properties of the material are important considerations and must be of high transparency. The ratio of m:n can be adjusted to 0.75-0.25: 0.25-0.75, ie, the polyamidomino group can comprise from about 75 mol% to about 25 mol%. The structure of formula (I) is from about 25 mol% to about 75 mol% of the structure of formula (II). Moreover, for example, when the low chroma PI film is applied to prepare a flexible circuit board, the mechanical properties of the material are required to be high, and the ratio of m: n can be adjusted to 0.9-0.6: 0.1-0.4, that is, the poly-Asian The amine group may comprise from about 90 mol% to about 60 mol% of the structure of formula (I), and from about 10 mol% to about 40 mol% of the structure of formula (II).

In other embodiments, the polyamidomino group can include, for example, from about 85 mol% to about 15 mol% of m and from about 20 mol% to about 80 mol% of n, such as from about 80 mol% to about 20 mol%. m is from about 40 mol% to about 60 mol% n, such as about 50 mol% m and about 50 mol% n.

In one embodiment, suitable dianhydride components include 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 2,2- Bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and the like. The dianhydride components are as follows:

In one embodiment, suitable diamine components may include 2,2'-bis(trifluoromethyl)benzidine (TFMB), etc., and TFMB is as follows:

The low chroma polyimine film is synthesized by a condensation polymerization reaction comprising a diamine monomer and a dianhydride monomer. The molar ratio of the dianhydride monomer to the diamine monomer is about 1:1, for example, about 0.90: 1.10 or about 0.98: 1.02.

Referring to Fig. 1, in step 102 , a monomer including a diamine component and a dianhydride component is first reacted in a solvent during a condensation polymerization reaction to obtain a polyglycine solution. The diamine component can include TFMB, and the dianhydride component can include BPDA and BPADA. The solvent can be an aprotic polar solvent. Considering economic benefits and ease of handling, the solvent can have a relatively low boiling point (e.g., below about 225 ° C), and the solvent can be removed from the polyimide film at relatively low temperatures. Examples of suitable solvents may include, but are not limited to, dimethylacetamide (DMAC), diethyl acetamide, N, N' -dimethylformamide (DMF), N, N' -di Ethylformamide, N -methylpyrrolidone (NMP), dimethyl hydrazine (DMSO), tetramethyl hydrazine, N,N' -dimethyl- N,N' -propenyl urea (DMPU) , tetramethylurea (TMU), N -methyl indoleamine, hexamethylphosphonium triamine, m-cresol, phenol, p-chlorophenol, 2-chloro-4-hydroxytoluene, diethylene glycol Dimlyme, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dioxane, dioxolane, cyclohexanone, cyclopentanone, and butyrolactone , or a combination of the above. In one embodiment, the solvent is DMAC.

Referring to step 104 of Figure 1, a dehydrating agent and a catalyst can then be added to the polyamic acid solution, and a homogeneous precursor solution can be obtained after stirring. The dehydrating agent may be selected from aliphatic acid anhydrides (such as acetic anhydride and propionic anhydride) and aromatic acid anhydrides (such as phthalic anhydride and phthalic anhydride), and may be used singly or in combination. In one embodiment, the dehydrating agent is acetic anhydride and is used in an amount of from about 2 to 3 moles per equivalent of polyamic acid.

The catalyst may be selected from heterocyclic tertiary amines (e.g., picoline, pyridine, lutidine, quinoline, isoquinoline, cinnoline, quinoline, phthalazine, quinazoline). , imidazole, N -methyl fluorenone, N -ethyl quinone, N -methylpiperidine, N -ethylpiperidine, etc.), aliphatic tertiary amines (eg triethylamine (TEA) ), tripropylamine, tributylamine, triethanolamine, N,N -dimethylethanolamine, triethylenediamine, and diisopropylethylamine (DIPEA), and aromatic tertiary amines ( For example, xylylene) can be used singly or in combination. In one embodiment, the catalyst is mepyridine, such as alpha-methylpyridine, beta-methylpyridine, or gamma-methylpyridine. Polyamine: Dehydrating Agent: The molar ratio of the catalyst can be about 1:2:1, i.e., about 2 moles of dehydrating agent and about 1 mole of catalyst per mole of polyamic acid.

Referring to step 106 of Figure 1, the precursor solution is applied as a layer on a glass plate or stainless steel plate.

Referring to step 108 of Figure 1, the coated layer is baked to form a low chroma polyimine film which can then be peeled from the substrate. A suitable baking temperature is between about 90 ° C and about 350 ° C.

In step 104 , other additives may also be added to the polyamic acid solution to impart desired properties to the polyimide film. For example, suitable additives may include, but are not limited to, processing aids, antioxidants, light stabilizers, extinction coefficient modifiers, flame retardants, antistatic agents, thermal stabilizers, ultraviolet absorbers, reinforcing agents, and the like, They can be used alone or in combination.

The resulting low chroma polyimine film may have a thickness of from about 5 micrometers (μm) to about 150 μm, such as between about 5 μm and about 75 μm, such as between about 10 μm and about 50 μm. between.

The low chroma polyimine described herein has the advantage of having a full transparency (i.e., light transmission, TT) of greater than about 85%, such as greater than 90%, such as greater than 92%, or greater than 94%.

The low-color polyimine film is prepared by the above two-step method, and a higher molecular weight polyimine is obtained by chemical conversion, and the obtained film has better physicochemical properties, and the film is prepared. The high temperature resistance to yellowing is also superior to the PI film prepared by the one-step method. In addition, the two-step process conditions are easier to control (as opposed to one-step) and increase production rates while reducing costs.

In summary, the low chroma polyimine film of the present invention has the following advantages:

(1) Excellent optical transparency: suitable for FPC, which increases luminous flux, makes assembly easier to align, and helps simplify component design;

(2) Anti-ultraviolet light: The low-color polyimine film of the invention has an absorption function in the 400 nm spectral region, and can absorb a certain amount of ultraviolet rays, and can achieve the effect of protecting the components in the application of the electronic product;

(3) Excellent ductility: the elongation of the low chroma polyimine film of the present invention is between about 10% and about 60%, especially between about 15% and about 50%, It is not easy to be broken in the same kind of materials, so it can provide better processing operability, and is suitable for FPC field requiring high flexibility, especially coverlay;

(4) Improved mechanical properties and heat resistance: The low chroma polyimine film has a glass transition temperature (Tg) of about 200-300 ° C and can withstand high temperature processes for subsequent applications. Further, the coefficient of thermal expansion (CTE) thereof is 65 ppm/° C. or less between about 100 and 200 °C. It can be observed that the CTE of the low chroma polyimide film is related to improving the heat resistance of the film, especially when the CTE is lower than 50 ppm/° C. (for example, 30 ppm/° C.), more specifically less than 30 ppm/° C.

(5) Low dielectric constant (indicated by Dk), suitable for high frequency substrates;

(6) High temperature resistance to yellowing, not easy to deteriorate or yellow.

In addition to the above properties, the low chroma polyimine film of the present invention has an L* value of greater than about 90, an a* value between -5 and +5, and a b* value between -10 and 10 . Specifically, both the a* value and the b* value are closer to zero. L*, a*, b* are indicators of the conventional "L*a*b*Lab color space", where the L* value represents the color brightness and the a* value defines the color between red and green. The color dimension, the b* value defines the color boundary between yellow and blue. Among the polyimines described herein, even when the low chroma polyimine film is subjected to a thermal environment (e.g., baking), its color characteristics maintain relative stability. The stability of the color characteristic is expressed by the difference value Δb* of the b* value, and Δb* is less than about 5 in the range between the typical baking temperatures of 250 ° C and 320 ° C. In particular, the difference value Δb* of the b* value is about 0.1 to 1.5.

Example

Example 1

(a) Polymerization

Nitrogen gas was fed into a 500 ml (ml) three-necked flask as a polymerization vessel at ambient temperature. All reactions were carried out under a nitrogen atmosphere. About 160 g (g) of dimethylacetamide (DMAC) as a solvent was added to the flask. About 19.789 g (0.064 mole) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was dissolved in DMAC. After the TFMB was completely dissolved in DMAC, about 16.891 g (0.057 moles) of biphenyltetracarboxylic dianhydride (BPDA) and about 3.32 g (0.006 moles) of 2,2-bis[4-(dicarboxyphenoxy) were added. Phenyl]propane dianhydride dianhydride (BPADA) was added to the solution and stirring was continued for about 4 hours, and the above monomers were reacted to form a polyaminic acid (PAA) solution. (b) Formation of transparent polyimide film

The PAA composition was mixed with an acetic anhydride dehydrating agent and a picoline catalyst to obtain a precursor solution. PAA: Acetic anhydride: The molar ratio of methotrex is about 1:2:1. Next, the precursor solution was applied as a layer on a glass plate with a doctor blade. The coated layer has a thickness of about 1 mil (ie, 25 μm) and is baked at a stage temperature in a circulating oven at a temperature of about 100 ° C for 30 minutes followed by about 200 ° C. Bake for 30 minutes, then bake at about 300 ° C for 30 minutes. Thereby, a transparent polyimide film was formed and peeled off from the glass substrate.

Example 2

A polyimide film was prepared as described in Example 1, except that about 19.1 g (0.061 mole) of TFMB, about 14.492 g (0.049 moles) of BPDA, and about 6.408 g (0.012 moles) of BPADA were used.

Example 3

A polyimide film was prepared as described in Example 1, except that about 18.774 g (0.060 mole) of TFMB, about 13.354 g (0.045 moles) of BPDA, and about 7.873 g (0.015 moles) of BPADA were used.

Example 4

A polyimide film was prepared as described in Example 1, except that about 17.294 g (0.056 mole) of TFMB, about 8.201 g (0.028 moles) of BPDA, and about 14.505 g (0.028 moles) of BPADA were used.

Example 5

A polyimide film was prepared as described in Example 1, except that about 17.857 g (0.058 mole) of TFMB, about 10.161 g (0.035 moles) of BPDA, and about 11.982 g (0.023 moles) of BPADA were used.

Example 6

A polyimide film was prepared as described in Example 1, except that about 16.031 g (0.050 mole) of TFMB, about 3.801 g (0.013 moles) of BPDA, and about 20.168 g (0.038 moles) of BPADA were used.

Example 7

A polyimide film was prepared as described in Example 1, except that about 15.8 g (0.050 mole) of TFMB, about 2.997 g (0.010 moles) of BPDA, and about 21.203 g (0.040 moles) of BPADA were used.

Comparative example 1

A polyimide film was prepared as described in Example 1, except that about 20.53 g (0.066 mole) of TFMB was used as the diamine component, and about 19.47 g (0.066 moles) of BPDA was used as the dianhydride component.

Comparative example 2

A polyimide film was prepared as described in Example 1, except that about 14.94 g (0.048 mole) of TFMB was used as the diamine component, and about 25.06 g (0.048 moles) of BPADA was used as the dianhydride component.

Comparative example 3

In addition to the conventional polyamidene component, about 19.14 g (0.096 moles) of 4,4'-oxydiphenylamine (4,4'-ODA) is used as the diamine component, and about 20.86 g (0.096 moles) of coke. Polymyimide film was prepared as described in Example 1 except that the phthalic acid dianhydride (PMDA) was used as the dianhydride component.

The polyimine films prepared according to the above examples and comparative examples were respectively tested to test the mechanical properties and color properties of the polyimide film.

Test example 1

Mechanical properties and thermal properties

The detection includes Young's modulus (expressed in Kgf/mm ² ), elongation, CTE (expressed in %), and glass transition temperature (Tg). The mechanical elongation is measured by a universal tensile machine in accordance with the ASTM 882 standard test method. CTE is measured by a thermomechanical analyzer TMA 2940 (sold by TA Instruments, Inc.), applying a standard load bearing force under thermal stress ranging from about 100 ° C to about 200 ° C (change rate of about 10 ° C / min) (eg About 0.05 N), the stretch of the film was measured. The Tg test was tested in accordance with the method of ASTM D-696-91 using a thermomechanical analyzer TMA 2940.

The results are shown in Tables 1 and 2.

Table 1, mechanical properties

Table 2, thermal properties

As shown in Tables 1 and 2, Comparative Example 3 is a component of a conventional PI film, and although the elongation and the glass transition temperature are extremely high, the film strength and heat resistance are poor (CTE is related to film heat resistance). In Comparative Example 1, only BPDA was used as the dianhydride component, and the film hardness was high but the elongation was extremely poor. On the contrary, Comparative Example 2 only used BPADA as the dianhydride component, and the elongation was good but the heat resistance was poor. Further, the transparent polyimide film of the present invention, for example, in Examples 1 to 7, after the ratio of the two dianhydride components, it is apparent that both the mechanical properties and the thermal properties can be improved.

Test example 2

Color nature

The color properties of the polyimide films were measured by a spectrophotometer at a temperature of about 25 ° C. The results are shown in Table 3. This color property is represented by "Lab color space", where the L* value defines the color brightness and the b* value defines the color boundary between blue and yellow.

Table 3, colorimetric properties

Compared with the conventional PI film of Comparative Example 3 which is yellow or reddish brown, the a* value and the b* value of the transparent polyimide film of Examples 1-7 both approach 0, indicating that the color is indeed close to colorless. And the brightness L* value is higher. This test showed that the transparent polyimide film of the present invention exhibited a lower yellowing.

Test Example 3

Color stability

In the subsequent application process (for example, LCD, FPC process), the polyimide film needs to be adhered to complete the adhesion of the polyimide film to confirm the color properties of the transparent polyimide film of the present invention. For the stability, Test Example 3 is taken as an illustrative example.

The transparent polyimide film of Example 2 was used as an example to test the b* value under the high temperature condition of the simulated baking process, and the results are shown in Table 4.

Table 4, b* value change of Example 2

As shown in Table 4, the b* value change of the transparent polyimide film of Example 2 was relatively low, and it was confirmed that the transparent polyimide film of the present invention can have stable color properties under thermal stress.

Test Example 4

Optical properties and dielectric properties

Detections include haze (Hz) (expressed in %), full penetration (ie, light transmission, expressed in %), and dielectric constant (expressed in Dk). The Hz and TT detections were performed using NIPPON DENSHOKU NDH-2000 (light source D ₆₅ ) according to JIS-7361 and JIS-7136 specifications. Dk was tested according to ASTM D150-95 using Agilent 4294A, fixture model 16034G. The results are shown in Tables 5 and 6.

Table 5, optical properties

Table 6. Dielectric properties

The results show that the conventional PI film of Comparative Example 3 has a light transmittance of only 72.06% and a haze of 1.11%, while the light transmittance of Examples 1-7 can be more than 90% and the haze is negative. The inventive PI film has quite excellent transparency.

In addition, the dielectric constant values of commercially available PI films are mostly between 3.4 and 3.6, which is also confirmed by Comparative Example 3. The transparent PI film of Examples 1-7 can be as low as 3.0 or less, which does improve the dielectric properties and is more suitable for high frequency substrates.

Test Example 5

UV absorption test

Detection was performed using JASCO V-630 at a speed of 2 nm/sec. The results are shown in Tables 7 and 2.

Table 7, UV absorption test results

Referring to Fig. 2 and Table 7, the transmittance of each polyimide film at different light wavelengths is shown, wherein Comparative Example 4 is fully absorbed at a wavelength of about 430 nm, and the result is also reflected in Comparative Example 3. The film color (yellow), while Comparative Examples 1, 2 and Examples 1-7 were partially absorbed at a wavelength of less than 400 nm, indicating that the film can absorb some of the ultraviolet rays.

From the above Test Examples 1-5, although Comparative Example 1 and Comparative Example 2 have good transparency and dielectric properties, they have great defects in mechanical properties and heat resistance properties, for example, Comparative Example 1 (the dianhydride component contains only BPDA). The elongation rate is extremely poor, while the heat resistance of Comparative Example 2 (the dianhydride component contains only BPADA) is extremely poor. In contrast, the transparent polyimine film of the present invention, after being formulated by the ratio of the two dianhydride components, clearly has a balanced and excellent improvement in various aspects, and can simultaneously achieve high transparency, excellent mechanical properties and heat resistance, and provide Good optical properties and color stability, while absorbing some of the UV rays.

The PI film of the present invention can be applied to flexible circuit boards (FPC), rigid printed boards, liquid crystal displays (LCDs), light emitting diodes (LEDs), photovoltaic cells (photovoltaic cells), liquid crystal displays (TFT- LCD), organic light-emitting diode (OLED), portable communication devices, digital cameras, notebook computers, e-books, tablet PCs and other electronic products. As shown in FIG. 3, the FPC is taken as an example, and includes a substrate layer 11, an electronic component 12, and a low-colority PI film 13 of the present invention. FPC has relatively low requirements for transparency of PI film, but the requirements for other physical properties (such as mechanical properties, thermal properties, flexibility, etc.) are relatively high, and the low chroma polyimine film of the present invention can be formulated by The ratio of dianhydride meets the above physical properties while still having good transparency to meet the current demand for electronic products that are light, thin, flexible, and transparent.

Further, the low chroma polyimine film of the present invention has an absorption amount at a wavelength of 400 nm. Taking the LCD as an example, the low-color polyimine film of the present invention can be used to protect electronic components in the LCD, so that no additional ultraviolet absorbing layer is required in the LCD design, thereby reducing production costs and streamlining the manufacturing process.

The above description of the specific embodiments is intended to be illustrative of the invention, and is not intended to limit the invention. It will be understood by those skilled in the art that various changes or modifications may be made to the present invention without departing from the scope of the appended claims.

11. . . Substrate

12. . . Electronic component

13. . . Low chroma polyimine film

Figure 1 is a flow chart showing the steps of forming a low chroma polyimine film.

Figure 2 is a graph showing the relationship between the wavelengths of different light wavelengths on the polyimide film.

Figure 3 is a schematic illustration of a flexible circuit board using the low chroma polyimine film of the present invention.

Claims (17)

A low chroma polyimine film comprising a polyamidimide polymer consisting of the structures represented by the following formulas (I) and (II): Wherein, the ratio of m: n is 0.15-0.95: 0.85-0.05. The low chroma polyimine film according to claim 1, wherein the diamine component is 2,2'-bis(trifluoromethyl)benzidine. The low chroma polyimine film according to claim 1, wherein the dianhydride component is 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2-dual [ 4-(3,4-Dicarboxyphenoxy)phenyl]propane dianhydride. The low chroma polyimine film according to claim 1, wherein the ratio of m: n is 0.9-0.6: 0.1-0.4. The low chroma polyimine film according to claim 1, wherein the ratio of m: n is 0.75-0.25: 0.25-0.75. A low-color polyimine film composed of a polyamidimide-based polymer characterized by a total transparency of 85% or more and a thermal expansion coefficient of 65 ppm/° C. or less at 100 to 200 ° C. It is between 10% and 60% and absorbs UV rays. The low chroma polyimine film described in claim 6 wherein the L* value is higher than 90, the a* value is between -5 and +5, and the b* value is between -10 and Between 10. The low chroma polyimine film according to claim 6, wherein the difference value (Δb*) of the b* value is 0 to 5 at a temperature range between 250 ° C and 320 ° C. A low chroma polyimine film as described in claim 6 which has a glass transition temperature of from 200 to 300 °C. The low chroma polyimine film according to claim 6, wherein the polyamidimide polymer is a diamine component comprising 2,2'-bis(trifluoromethyl)benzidine. And a dianhydride selected from the group consisting of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride Obtained by component reaction. A method for preparing a low chroma polyimine film, comprising: performing a condensation polymerization reaction with a monomer comprising a diamine and a dianhydride to obtain a solution containing a polyaminic acid; adding a dehydrating agent and a catalyst to the polyfluorene containing a solution of the amine acid to obtain a precursor solution; coating the precursor solution onto a substrate; and baking the coated layer to form a low chroma polyimide film. The method of claim 11, wherein the diamine monomer is 2,2'-bis(trifluoromethyl)benzidine. The method of claim 11, wherein the dianhydride monomer is 3,3',4,4'-biphenyltetracarboxylic dianhydride and 2,2-bis[4-(3,4) -Dicarboxyphenoxy)phenyl]propane dianhydride. The method of claim 11, wherein the baking step is performed at a temperature of from 90 ° C to 350 ° C. The method of claim 11, wherein in the step of adding the dehydrating agent and the catalyst to the solution containing the poly-proline, the molar ratio of the polyglycolic acid: dehydrating agent: catalyst is 1: 2:1. A flexible circuit board comprising the low-color polyimine film as described in claim 1 of the patent application. A flexible circuit board comprising the low-color polyimine film as described in claim 6 of the patent application.