WO2013151215A1

WO2013151215A1 - Black polyimide film

Info

Publication number: WO2013151215A1
Application number: PCT/KR2012/007228
Authority: WO
Inventors: Kil Nam Lee; Sung Won Kim
Original assignee: Skckolon Pi Inc.
Priority date: 2012-04-06
Filing date: 2012-09-07
Publication date: 2013-10-10
Also published as: CN104169330A; JP6082761B2; KR20130113778A; JP2015509551A; TW201341435A; CN104169330B; TWI454513B

Abstract

There is provided a black polyimide film comprising (a) a polyimide resin; (b) 3.0 to 7.5 wt% of carbon black, wherein said carbon black has 1.5 wt% or less of a high temperature volatile component and is not oxidation treated on its surface; and (c) 0.5 to 1.5 wt% of a shielding agent. The polyimide resin is produced by imidation of a polyamic acid prepared by copolymerization of a dianhydride and a diamine. The film has an optical transmittance of 1.0% or less in the visible light range, a gloss of 60% or less, an elongation of 80% or more, a surface resistivity of 10¹⁵ Ω or more, and a pinhole occurrence of 1/100 m² or less. The film has excellent gloss, shielding, and dielectric properties, as well as a reduced pinhole occurrence.

Description

BLACK POLYIMIDE FILM

FIELD OF THE INVENTION The present invention relates to a black polyimide film useful for shielding purposes.

BACKGROUD OF THE INVENTION Generally, polyimide resins refer to high heat resistant resins, which can be prepared by solution polymerization of an aromatic dianhydride and an aromatic diamine or an aromatic diisocyanate to prepare polyamic acid derivatives, followed by cyclization, dehydration and imidation of the polyamic acid derivatives at high temperatures. In preparation of polyimide resins, examples of commonly used aromatic dianhydrides include pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), and the like; and examples of aromatic diamines include oxydianiline (ODA), p-phenylenediamine (p-PDA), m- phenylenediamine (m-PDA), methylenedianiline (MDA), bisaminophenylhexafluoropropan (HFDA), and the like.

Polyimide resins are insoluble, infusible and very high heat resistant resins used for various applications such as advanced heat resistant materials in automobiles, aircrafts, spacecrafts, and the like, as well as electronic materials such as insulating coating agents, insulating films, semiconductors, electrode protection films of TFT- LCD, and the like, due to their superior mechanical properties including heat oxidation resistance, heat resistance, radiation resistance, low temperature characteristics, chemical resistance, and the like.

Recently, polyimide resins are being widely used as a coverlay in portable electronic and mobile devices. Thus, there is a growing interest in polyimide films for shielding purposes having excellent mechanical properties with good light shielding and insulating functions for security purposes and visual effects.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a black polyimide film for shielding purposes having excellent mechanical properties with good light shielding and insulating functions, and a method for preparing same.

According to one embodiment of the present invention, there is provided a black polyimide film comprising:

(a) a polyimide resin;

(b) 3.0 to 7.5 wt% of carbon black, wherein said carbon black has 1.5 wt% or less of a high temperature volatile component and is not oxidation treated on its surface; and

(c) 0.5 to 1.5 wt% of a shielding agent;

wherein said polyimide resin is produced by imidation of a polyamic acid prepared by copolymerization of a dianhydride and a diamine, and

said film has an optical transmittance of 1.0% or less in the visible light range, a gloss of 60% or less, an elongation of 80% or more, a surface resistivity of 10¹⁵ Ω or more, and a pinhole occurrence of 1/100 m or less.

The carbon black employed for the black polyimide film according to the embodiment of the present invention may have a volume average diameter of 2 μιη or less, a maximum diameter of 10 μιη or less, and a primary particle diameter of 70 to 150 nm.

The shielding agent employed for the black polyimide film according to the embodiment of the present invention may have a volume average diameter of 0.1 to 1.0 μιτι.

The shielding agent employed for the black polyimide film according to the embodiment of the present invention may be Ti0₂.

The diamine employed for the black polyimide film according to the embodiment of the present invention may be phenylenediamine, diaminodiphenylether, or a derivative thereof.

The black polyimide film according to the present invention with good light shielding and insulating functions and excellent mechanical properties is useful for shielding purposes.

DETAILED DESCRIPTION OF THE INVENTION

The black polyimide film according to the present invention is manufactured from a polyimide resin, which is produced by imidation of a polyamic acid prepared by copolymerization of a dianhydride and a diamine. The film comprises, based on total weight of the film, 3.0 to 7.5 wt% of carbon black, wherein said carbon black has 1.5 wt% or less of a high temperature volatile component and is not oxidation treated on its surface; and 0.5 to 1.5 wt% of a shielding agent. The film has an optical transmittance (in the visible light range) of 1.0% or less, a gloss of 60% or less, an elongation of 80% or more, a surface resistivity of 10¹⁵ Ω or more, and a pinhole occurrence of 1/100 m or less.

For the purpose of light shielding, the black polyimide film of the present invention may have an optical transmittance (in the visible light range) of 1.0% or less, preferably 0.1 to 1.0%, and a gloss of 60% or less, preferably 40 to 60%. Once the film having the above optical properties is applied to an article, the film can improve the external aesthetic characteristics of the article and impart security protection to the article.

For the purpose of electrical insulation as a coverlay, the black polyimide film of the present invention may have a surface resistivity of 10¹⁵ Ω or more. The higher the surface resistivity is, the more preferable. When the film having the above properties is used as a coverlay for protecting a flexible printed circuit, it can improve the electrical stability of the electronic device containing such printed circuit. In this regard, the black polyimide film of the present invention may have a breakdown voltage of 80 kV/mm or more, preferably 90 kV/mm or more.

In order for the film to have good mechanical properties together with light shielding and insulating functions, it may have an elongation of 80% or more, preferably 80 to 110%, and a pinhole occurrence of 1/100 m or less. With these properties satisfied, the stability in the manufacture and processing of the film can be improved, and the mechanical reliability of the final product can also be secured.

In order to have the aforementioned mechanical properties, the black polyimide film of the present invention comprises (a) a polyimide resin; (b) 3.0 to 7.5 wt%, preferably 5.0 to 7.0 wt% of carbon black, wherein said carbon black has 1.5 wt% or less of a high temperature volatile component and is not oxidation treated on its surface; and (c) 0.5 to 1.5 wt%, preferably 0.7 to 1.3 wt%, more preferably 0.8 to 1.2 wt% of a shielding agent.

The carbon black is not oxidation treated on its surface for increasing its stability during heat treatment. Preferably, the carbon black has a low amount of a high temperature volatile component, which is 1.5 wt% or less, preferably 0.8 to 1.5 wt%, based on total weight of the carbon black.

The carbon black is employed for imparting black color and gloss to the polyimide film. The amount of carbon black is in the range of from 3.0 to 7.5 wt%, based on total weight of the polyimide film. If the amount is less than 3.0 wt%, it may be difficult to make the film black. If the amount exceeds 7.5 wt%, the corona resistance and insulation properties of the film would deteriorate.

The carbon black may have a volume average diameter of 2 μηι or less, preferably 0.5 to 2 μπι, more preferably 0.6 to 1.6 μιτι, and a maximum diameter of 10 μιτι or less when dispersed in a solvent. Also, the primary particle diameter of the carbon black may be 70 nm or more, preferably 70 to 150 nm. If the primary particle diameter of the carbon black is less than 70 nm, the gloss would increases, which would then make it difficult to impart an extinction property to the film. The black polyimide film according to the present invention comprising carbon black satisfying the size requirements stated above may have an extinction characteristic and uniform color and properties.

Further, the carbon black may have a diameter dispersity (= volume average diameter/number average diameter) of 5 or less, preferably 3 or less. When carbon black particles with low diameter dispersity are employed, they may be well and uniformly dispersed in a resin when admixed with the resin. Consequently, the film thus prepared may have uniform properties (e.g., minimum color variation) throughout the film and a low extent of degradation in the properties of the film. Especially, the elongation of the film can be significantly enhanced. The diameter dispersity of carbon black can also be improved by milling it or employing a dispersing agent. It is preferable to improve the diameter dispersity of carbon black as well as that of a shielding agent by separately milling both carbon black and the shielding agent.

The shielding agent may be employed so as to enhance the processability, heat emission, and shielding properties of the film, wherein the amount employed is 0.5 to 1.5 wt%, based on total weight of the black polyimide film. If the amount is less than 0.5 wt%, the shielding property may be unsatisfactory. On the other hand, if the amount is more than 1.5 wt%, the mechanical properties (especially, elongation) may deteriorate with an increased occurrence of pinholes, resulting in a reduced yield and poor appearance of the film.

Examples of the shielding agent include titanium dioxide (TiO₂), nitride-based particles, and other inorganic particles.

According to an embodiment of the present invention, the shielding agent may be particulate. The volume average diameter of the shielding agent is 0.1 to 1.0 μηι, preferably 0.15 to 0.7 μπι, more preferably 0.2 to 0.6 μηι. If the volume average diameter of the particulate shielding agent falls within the range of 0.1 to 1.0 μιτι, the film thus prepared may have a good shielding property and a minimum extent of deterioration in the mechanical properties of the film.

The black polyimide film according to the present invention may be manufactured by general film deposition methods for polyimide films, which comprise copolymerizing a dianhydride and a diamine to prepare a polyamic acid solution and depositing a film from the polyamic acid solution. Specifically, the polyamic acid solution may uniformly be mixed with carbon black, a shielding agent and a catalyst before it is deposited. The black polyimide film prepared in accordance with the above method may have uniform mechanical, optical, and electrical properties throughout the film.

For uniform mixing, a line mixer may be employed. The polyamic acid solution, carbon black, shielding agent, and catalyst are fed into the line mixer separately, which prevents agglomeration that may otherwise occur if all the ingredients are introduced into an inlet simultaneously. Meanwhile, if the carbon black and the shielding agent are added during the copolymerization step for obtaining the polyamic acid solution, it would be difficult to obtain a uniform solution since the mixing capacity of the reactor may not be sufficient.

The polyamic acid solution may be obtained by copolymerizing a dianhydride and a diamine in an organic solvent. The organic solvent is preferably an amide- based polar aprotic solvent. Examples of the amide-based polar aprotic solvent include N,N'-dimethylformamide, Ν,Ν'-dimethylacetamide, N-methyl-pyrrolidone, and the like, or a mixture of any two thereof, if necessary.

Examples of the dianhydride include biphenylcarboxylic acid dianhydride or its derivatives, and pyromellitic acid dianhydride or its derivatives. Specific examples of the dianhydride may include 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, pyromellitic acid dianhydride, 3,3'4,4'-benzophenonetetracarboxylic acid anhydride, p- phenylene-bis trimellitic dianhydride, and the like, preferably 3,3 ',4,4'- biphenyltetracarboxylic acid dianhydride, pyromellitic acid dianhydride. Particularly, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride or pyromellitic acid dianhydride may reduce deterioration in the mechanical properties of the film prepared, which may otherwise occur due to the employment of the carbon black and shielding agent added for improving light shielding, gloss and capacity resistance.

Examples of the diamine include phenylenediamine, diaminodiphenyl ether, or derivatives thereof. Specific examples of the diamine may include p- phenylenediamine, o-phenylenediamine, m-phenylenediamine, 4,4'- diaminodiphenylether, 3,4-diaminodiphenylether, 2,4-diaminodiphenylether, and the like. Generally, p-phenylenediamine and 4,4'-diaminophenylether are preferred for improving the mechanical properties of the film prepared.

In order to improve the thermal expansion coefficient and modulus, p- phenyleneamine may be employed in an amount of 0.1 to 0.8 mole, based on 1 mole of total diamines. P-phenylene diamine is a monomer with linearity as compared with diaminophenylether, which lowers the thermal expansion coefficient of the film prepared. However, a high amount of p-phenylenediamine may decrease the flexibility and formability of the film.

The carbon black and the shielding agent may be employed in particulate form. But it is preferable to disperse each component in a separate polar aprotic solvent and then feed each solution to the mixer for obtaining a more uniformly admixed solution.

The polyamic acid solution containing the catalyst may be applied on a scaffold.

The catalyst is preferably a dehydration catalyst comprising anhydrides or tertiary amines. Examples of the anhydride include acetic acid anhydride. Examples of the tertiary amine include isoquinoline, β-picoline, pyridine, and the like. Hereinafter, the present invention is further described in Examples and

Comparative Examples.

Example 1 Black polyimide films were prepared in accordance with the composition of ingredients as illustrated in Table 1.

In the copolymerization step for a polyamic acid solution, 181.2 kg of Ν,Ν'- dimethylformamide (DMF) as a solvent was charged in a 300 L reactor under nitrogen atmosphere. The solvent was heated to 30 ^°C , and 20.64 kg of 4,4'- diaminophenyleneether (ODA) was added as a diamine. The mixture was stirred for 30 minutes. After the monomers were completely dissolved, 21.81 kg of pyromellitic acid anhydride (PMDA) was added thereto. The mixture was stirred for 1 hour while the temperature was kept constant to complete the first reaction. Once the first reaction was completed, the temperature of the reactor was raised to 40 ^°C , followed by addition of 0.67 kg of 8% PMDA. The mixture was stirred for 2 hours while the temperature was kept constant. The internal pressure of the reactor was reduced to 1 torr to eliminate any foam entrapped in the solution during the reaction to thereby obtain a polyamic acid solution.

The solid content in the polyamic acid solution after the reaction was 18.5 wt%. The viscosity of the solution was 2,500 poises.

Milling-treated carbon black and a shielding agent were added during the film deposition step while the polyamic acid solution and a catalyst were admixed. For complete mixing, the polyamic acid solution and each solution of carbon black, shielding agent, and catalyst were fed to a line mixer separately.

The amounts of carbon black and TiO₂ employed were 6.0 wt% and 1.2 wt%, respectively, based on total weight of the polyimide film.

The carbon black had a volume average diameter of 0.89 μιη and a primary particle diameter of 95 nm. The shielding agent had a volume average diameter of 0.53 μπι.

The polyamic acid solution and the solutions of carbon black, shielding agent, and catalyst were admixed in a ratio of 2:1 by weight. The solution thus obtained was cast on an Endless belt in a thickness of 100 μιη and then dried at 100 to 200 ^°C . The resulting film was removed from the Endless belt and delivered to a high-temperature tenter. The amounts of catalyst solution, carbon black solution, and shielding agent dispersion solution had been adjusted such that the film had 14.4 wt% of isoquinoline, 44.8 wt% of acetic anhydride, 37.4 wt% of DMF, 1.09 wt% of carbon black, and 0.22% of shielding agent.

The film was heated from 200 to 600 ^°C in the high-temperature tenter, and then cooled and removed from the pin to produce a final film with a thickness of 12 μηι.

The black polyimide film prepared by the above method was tested for its elongation, optical transmittance, corona resistance, gloss, and breakdown voltage. The results are shown in Table 2.

Example 2 The black polyimide film was prepared by repeating Example 1 except that the film had 5.5 wt% of carbon black and 1.2 wt% of shielding agent.

Example 3 The black polyimide film was prepared by repeating Example 1 except that the film had 6.5 wt% of carbon black and 0.8 wt% of shielding agent.

Comparative Example 1 The black polyimide film was prepared by repeating Example 1 except that the film had no shielding agent.

Comparative Example 2 The black polyimide film was prepared by repeating Example 1 except that the film had 8.0 wt% of carbon black. Comparative Example 3

The black polyimide film was prepared by repeating Example 1 except that MA220 (a primary particle diameter of 55 nm and a volume average diameter of 520 nm, Mitsubishi) was used as carbon black.

Comparative Example 4

The black polyimide film was prepared by repeating Example 1 except that the film had 4 wt% of shielding agent.

The black polyimide films prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested according to the following procedures, and the results were given in Table 2.

Elongation The elongations of the films were measured in accordance with ASTM D-882 using Instron 3365SER instrument.

Width and height: 15 mm x 50 mm

Crosshead speed: 200 mm/min

Optical transmittance in the visible light range

Optical transmittances of the films were measured in transmission mode using Hunter Lab CQX3391.

Gloss

Glosses of the films were measure at 60⁰ using a gloss meter.

Instrument: Gloss meter

Model: E406L

Make: Elcometer

Tensile strength and elongation of the films before and after corona treatment

The black polyimide films prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to corona treatment using a corona discharging roller (CT1234, Osaka Katsura) under corona density 250 conditions. After the corona treatment, the films were tested for elongation measurement. The differences in the elongations of the films before and after the corona treatment were calculated according to Formula I below.

[Formula I] Corona resistant = (Elongation before treatment) /(elongation treatment)xlOO

Pinhole occurrence

The pinhole occurrences per 100 m² of the films were measured by running 1,000 m of the film having a width of 0.6 m on a winder equipped with a flaw detector (Wintriss). Surface resistivity

The surface resistivities of the films were measured under 500 V using a high resistance meter (4339B, Agilent Technologies). Breakdown voltage

The breakdown voltages of the corona treated films were measured according to ASTM D149 using a breakdown voltage test equipment (6CC250-5/D149, Phenix Technologies).

As shown in Table 2, the black polyimide films prepared in accordance with Examples 1 to 3 of the present invention had relatively low gloss values and optical transmittances with good shielding properties. They also showed high values of surface resistivity and breakdown voltage with good dielectric properties. Further, the results showed that the films prepared in accordance with Examples 1 to 3 had good mechanical properties including elongation, corona resistant, and low pinhole occurrence.

On the other hand, the film prepared in Comparative Example 1 that had not employed any shielding agent failed to have a desired optical transmittance. In Comparative Example 2, the amount of carbon black was increased instead of employing a shielding agent. Although the film had a desirable optical transmittance, it had poor dielectric property and corona resistance. Further, in Comparative Example 3, the film had high gloss due to the small primary particle diameter of carbon black. In Comparative Example 4, the film had low elongation and high pinhole occurrence due to the high amount of the shielding agent.

Claims

WHAT IS CLAIMED IS:

1. A black polyimide film comprising:

(a) a polyimide resin;

(c) 0.5 to 1.5 wt% of a shielding agent;

said film has an optical transmittance of 1.0% or less in the visible light range, a gloss of 60% or less, an elongation of 80% or more, a surface resistivity of or more, and a pinhole occurrence of 1/100 m or less.

2. The black polyimide film of claim 1, wherein said carbon black has a volume average diameter of 2 μηι or less, a maximum diameter of 10 μηι or less, and a primary particle diameter of 70 to 150 nm.

3. The black polyimide film of claim 1, wherein said shielding agent has a volume average diameter of 0.1 to 1.0 μιη.

4. The black polyimide film of claim 1, wherein said shielding agent is TiO₂.

5. The black polyimide film of claim 1, wherein said diamine is phenylenediamine, diaminodiphenylether, or a derivative thereof.