JP6966847B2 - Method for manufacturing transparent polyimide film - Google Patents

Description

The present invention relates to a method for producing a transparent polyimide film, particularly a method for producing a transparent polyimide film useful as a resin substrate material having high transparency, low thermal expansion coefficient, high heat resistance, and laser lift-off characteristics.

The performance of electronic devices is rapidly increasing, and the weight and thickness are increasing. Along with this, the components used in electronic devices and the boards on which they are mounted are also required to have higher performance. Is increasing. Glass substrates are used as the base material for display panels in thin displays and touch panel applications, but they are made thinner, lighter, more flexible, and the processing cost is reduced by the Roll-to-Roll process. Resin substrate materials have been developed to achieve this. However, since resins are generally inferior in dimensional stability, transparency, heat resistance, etc., as compared with glass, various studies have been made.

Examples of display applications include large displays such as televisions and small displays such as mobile phones, personal computers, and smartphones. For example, a glass substrate is used as a support substrate on which various elements such as thin film transistors (TFTs) are mounted in an organic EL device. Is used. Similarly, in touch panel applications, there is a strong demand for resin substrate materials that can replace glass substrates, and in that case, the coefficient of thermal expansion (CTE) is also required to be low, for example, 45 ppm / K or less. It is desired from the viewpoint of preventing the occurrence of

As such a resin substrate material, polyimide is one of the promising materials because it is excellent in heat resistance and dimensional stability.

In recent years, in order to obtain a thin polyimide substrate, a glass substrate is used as a supporting base material, a polyimide film is once formed on the supporting base material, and then electronic components are mounted, and then the polyimide film is peeled off from the glass substrate as the supporting base material. It is also proposed to do. For example, Patent Document 1 is a polyimide precursor resin composition for forming a flexible device substrate, which is manufactured by peeling from a carrier substrate, and has a glass transition temperature of 300 ° C. or higher and a coefficient of thermal expansion of 20 ppm / K or lower. To disclose. However, no studies have been made on transparency and the like. Patent Document 2 is a laminate composed of a polyimide film and an inorganic substrate obtained by casting a polyimide precursor solution having a specific structure on an inorganic substrate, drying and imidizing it, and has high light transmittance and outgas. Disclosure less. However, since the coefficient of thermal expansion (CTE) of polyimide exceeds 45 ppm / K, the difference from the coefficient of thermal expansion of glass substrate of 10 ppm / K or less is large, and the shape stability is inferior.

Further, Patent Document 3 discloses that the transmittance of a diamine or a tetracarboxylic dianhydride used as a raw material is strictly controlled in order to reduce the coloring of polyimide. Patent Document 4 specifies a diamine-derived structure and a tetracarboxylic acid dianhydride-derived structure in order to produce a colorless and transparent, low-CTE polyimide film, and is derived from a specific alicyclic tetracarboxylic acid dianhydride. Disclosed is a polyimide precursor and a resin composition having an imidization ratio of 10 to 100% of an amide bond. In addition, Patent Document 5 describes a diamine compound and a compound containing three or more amino groups to react with tetracarboxylic acid dianhydride, and Patent Document 6 describes a polymer solution containing fine particles in a polyimide-based precursor. It is proposed to be used to form a fine particle-containing layer.
However, the reality is that there are still expectations for the development of a transparent polyimide film manufacturing method that can replace glass substrates and is useful as a practical heat-resistant transparent resin substrate material that satisfies the required characteristics such as dimensional stability. Is.

Japanese Unexamined Patent Publication No. 2010-20729 Japanese Unexamined Patent Publication No. 2012-40836 Japanese Unexamined Patent Publication No. 2013-23583 International release 2015/122032 Japanese Unexamined Patent Publication No. 2014-210896 Japanese Unexamined Patent Publication No. 2013-209498

Under such circumstances, the present invention produces a transparent polyimide film that is excellent in dimensional stability, transparency, and heat resistance, and is useful as a heat-resistant transparent resin substrate material that can be easily peeled off from a supporting substrate to obtain a thin polyimide film. The purpose is to provide a method.

The present invention is a step of applying a polyimide precursor or a resin solution thereof on the surface of a support, and a step of heating the polyimide precursor or the resin solution thereof to imidize and forming a polyimide layer on the surface of the support. A method for producing a polyimide film comprising the steps of peeling the polyimide layer from the support to obtain a polyimide film, wherein the polyimide precursor is 2,2'-bis (trifluoromethyl)-. From 4,4'-diaminobiphenyl (also known as 2,2'-bis (trifluoromethyl) benzidine) and 2,2'-dimethyl-4,4'-diaminobiphenyl (also known as 2,2'-dimethylbenzidine) It is obtained by reacting a diamine containing one or two selected kinds with an acid dianhydride containing 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, and the polyimide film is A method for producing a transparent polyimide film, characterized in that the thermal expansion coefficient is 45 ppm / K or less, the light transmittance is 5% or less in a light beam of 308 nm, and 70% or more in a light beam of 400 nm.

It is desirable that the method for producing a transparent polyimide film of the present invention satisfies any one or more of the following.
1) Contains 50 mol% or more of the diamine selected from 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl and 2,2'-dimethyl-4,4'-diaminobiphenyl. Moreover, it contains 70 mol% or more of 1,2,3,4-cyclobutanetetracarboxylic dianhydride.
2) Does the total diamine contain 1 to 50 mol% of diamines other than 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl or 2,2'-dimethyl-4,4'-diaminobiphenyl? Or, an acid dianhydride other than 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride shall be contained in 1 to 30 mol% of the total acid dianhydride.
3) The yellowness of the obtained polyimide film is 6 or less.
4) Irradiate the interface between the polyimide layer and the support with laser light to peel off the polyimide layer from the support substrate.

Another aspect of the present invention is the above-mentioned method for producing a transparent polyimide film, which comprises a step of forming a functional layer on the polyimide layer and then peeling the polyimide layer with the functional layer from the support. This is a method for manufacturing a transparent polyimide film with a layer.
In this case, the functional layer is a group consisting of a transparent conductive layer, a wiring layer, a conductive layer, a gas barrier layer, a thin film, an electrode layer, a light emitting layer, an adhesive layer, an adhesive layer, a transparent resin layer, a color filter resist, and a hard coat layer. It is preferable that the layer is any one or more selected from the above.

According to the manufacturing method of the present invention, a thin transparent polyimide film having excellent dimensional stability, transparency, heat resistance, and excellent film peelability (laser lift-off characteristic) from a supporting substrate can be easily obtained. The transparent polyimide film obtained by the present invention can be substituted for a glass substrate in display and touch panel applications by utilizing these characteristics, and is suitable as a practical flexible heat-resistant transparent resin substrate material satisfying required characteristics such as dimensional stability. Available.

In the method for producing a transparent polyimide film of the present invention, a polyimide precursor is applied onto a support (supporting base material), imidized to form a polyimide layer, and then the polyimide layer is peeled off from the supporting base material, preferably. It is suitable for producing a polyimide film used as a transparent resin substrate material having a thickness of 30 μm or less, more preferably 20 μm or less, still more preferably 15 μm or less.

As is well known, the polyimide precursor can be represented by the following general formula (1).
[-OCX (COOH) ₂ CO-HN-Y-NH-] (1)
Further, the polyimide obtained by imidizing the polyimide precursor can be represented by the following general formula (2).
[-N (OC) ₂ X (CO) ₂ NY-] (2)
In formulas (1) and (2), X is a tetravalent residue formed by taking two acid anhydride groups from an acid dianhydride, and Y is a tetravalent residue formed by taking two amino groups from a diamine. It is a residue of valence.

A diamine and a tetracarboxylic acid dianhydride are used for the synthesis of the polyimide precursor (polyamic acid). In the production method of the present invention, the diamine is represented by the following formula (3a), 2,2'-bis. (Trifluoromethyl) -4,4'-diaminobiphenyl (abbreviation: TFMB) or 2,2'-dimethyl-4,4'-diaminobiphenyl (abbreviation: m-TB) represented by the following formula (3b) Use a diamine containing one or two selected species.

In the production method of the present invention, TFMB or m-TB is used as an essential component as a diamine. By using TFMB or m-TB in an amount of 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more of the total diamine, the structural unit derived from TFMB or m-TB can be converted into a structure derived from the total diamine. It will be included in the unit in the corresponding ratio. It is preferable to use TFMB or m-TB in the above range because the light transmittance of the visible light of the polyimide is excellent and the transparency of the flexible substrate is improved.

In the production method of the present invention, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (abbreviation: CBDA) represented by the following formula (4) is used as an essential component as the tetracarboxylic dianhydride. ..

When CBDA is used in an amount of 70 mol% or more, preferably 80 mol% or more of the total acid dianhydride, the structural unit derived from CBDA is contained in the structural unit derived from the total acid dianhydride in a corresponding ratio. Become. If CBDA is used in the above range, the CTE of the obtained polyimide will be low. This improves the dimensional stability of the flexible substrate using polyimide and makes it possible to suppress the warp of the flexible device.

In the production method of the present invention, the polyimide precursor can be obtained by reacting a diamine containing one or two selected from TFMB or m-TB with a tetracarboxylic dianhydride containing CBDA. It is preferable that the total diamine contains TFMB or m-TB in an amount of preferably 50 mol% or more. Further, it is preferable that the total acid dianhydride contains CBDA in an amount of preferably 70 mol% or more.

However, not only TFMB or m-TB and CBDA, but also the acid dianhydride component may contain a tetracarboxylic dianhydride component other than CBDA in the range of 1 to 30 mol%, and / or as a diamine component. , 1-50 mol%, preferably 1-40 mol%, more preferably 1-30 mol%, preferably containing a diamine component other than TFMB or m-TB. Within this range, the light transmittance of the polyimide obtained by imidizing the polyimide precursor at 308 nm is lowered, and the peelability (laser lift-off characteristic) is improved, which is preferable. When a diamine component other than TFMB or m-TB is contained, the polyimide obtained by imidizing the polyimide precursor by simultaneously containing a tetracarboxylic acid dianhydride component other than CBDA has a low light transmittance of 308 nm and 400 nm. It is more preferable because the light transmittance of the above is high and the CTE is low.

As a result, a polyimide precursor having a structural unit consisting of a structure derived from TFMB or m-TB and a structure derived from CBDA, and then imidizing this to obtain a polyimide having a structural unit represented by the following formula (6). Obtainable. In the formulas (5) and (6), the diamine-derived structure shows the case where TFMB is used as a raw material, and when m-TB is used as a raw material, the trifluoromethyl group (CF ₃ ) is eventually used. Also becomes a methyl group (CH ₃ ), and when the two are used together, these become a coexisting structure depending on the amount used.

The polyimide precursor used in the production method of the present invention may contain the structural unit represented by the formula (5) in the polyimide precursor in an amount of preferably 50 to 97 mol%, more preferably 70 to 97 mol%. .. Similarly, the polyimide used in the production method of the present invention obtained by imidizing this polyimide precursor also contains the structural unit represented by the formula (6) in the polyimide, preferably 50 to 97 mol%, more preferably. It is preferable to contain 70 to 97 mol%.

In addition to TFMB or m-TB, diamines used for copolymerization include, for example, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether. , 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomethicylene, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2, 6-xylidine, 4,4'-methylene-2, 6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diamino Diphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,2-bis [4- (4-aminophenoxy) ) Phenyl] Propane 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylether, 3, 3-Diaminodiphenyl ether, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4'-diamino Biphenyl, 3,3'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-p-tel Phenyl, 3,3'-diamino-p-terphenyl, bis (p-β-amino-t-butylphenyl) ether, bis (p-β-methyl-δ-aminopentyl) benzene, p-bis (2-bis) Methyl-4-aminopentyl) benzene, p-bis (1,1-dimethyl-5-aminopentyl) benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis (β-amino-) t-butyl) Toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylene diamine, p-xylylene diamine, 2,6-diamino Examples thereof include pyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine and the like.

Among these diamines, 5-amino-2- (4-aminophenyl) benzimidazole (AAPBZI) or 5-amino-2- (4-aminophenyl) benzoxazole (AAPBZO) is exemplified as a suitable one.

When these diamine components other than TFMB or m-TB are used in combination, the ratio of the diamine component to be used is preferably 1 to 50 mol%, more preferably 1 to 30 mol% with respect to the total diamine.

In addition to CBDA, tetracarboxylic acid dianhydride used for copolymerization includes, for example, 4,4'-(2,2'-hexafluoroisopropridene) diphthalic acid dianhydride ("bis (3,4)". -Dicarboxyphenyl) Hexafluoropropane dianhydride ", or abbreviated as" 6FDA "), naphthalene-2,3,6,7-tetracarboxylic acid dianhydride, naphthalene-1,2,5,6 -Tetracarboxylic acid dianhydride, naphthalene-1,2,6,7-tetracarboxylic acid dianhydride, pyromellitic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride 3 , 3', 4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 2,3,3', 4'-benzophenone tetracarboxylic dianhydride Anhydride, naphthalene-1,2,5,6-tetracarboxylic acid dianhydride, naphthalene-1,2,4,5-tetracarboxylic acid dianhydride, naphthalene-1,4,5,8-tetracarboxylic acid Dianhydride, Naphthalene-1,2,6,7-Tetracarboxylic Acid Dianhydride, 4,8-Dimethyl-1,2,3,5,6,7-Hexahydronaphthalene-1,2,5,6 -Tetracarboxylic acid dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-2,3,6,7-tetracarboxylic acid dianhydride, 2,6-dichloro Naphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic acid dianhydride, 2,3,6,7-tetrachloronaphthalene -1,4,5,8-Tetracarboxylic acid dianhydride, 1,4,5,8-Tetrachloronaphthalene-2,3,6,7-Tetracarboxylic acid dianhydride, 2,2', 3, 3'-biphenyltetracarboxylic acid dianhydride, 2,3,3', 4'-biphenyltetracarboxylic acid dianhydride, 3,3'',4,4''-p-terphenyltetracarboxylic acid dianhydride , 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,3,3', 4'-p-terphenyltetracarboxylic dianhydride, 2,2- Bis (2,3-dicarboxyphenyl) -propane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -propane dianhydride, bis (2,3-dicarboxyphenyl) ether dianhydride , Bis (2,3-dicarboxyphenyl) methane dianhydride, Bis (3.4-dicarboxyphenyl) methane dianhydride Water, bis (2,3-dicarboxyphenyl) sulfonate dianhydride, bis (3,4-dicarboxyphenyl) sulfonate dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride , 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, perylene-2,3,8,9-tetracarboxylic acid dianhydride, perylene-3,4,9,10-tetracarboxylic Acid dianhydride, perylene-4,5,10,11-tetracarboxylic acid dianhydride, perylene-5,6,11,12-tetracarboxylic acid dianhydride, phenanthrene-1,2,7,8-tetra Carboxydic dianhydride, phenanthrene-1,2,6,7-tetracarboxylic acid dianhydride, phenanthrene-1,2,9,10-tetracarboxylic acid dianhydride, cyclopentane-1,2,3,4 -Tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4, 5-Tetracarboxylic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, (trifluoromethyl) pyromellitic acid dianhydride, di (trifluoromethyl) pyromellitic acid dianhydride, di (heptafluoropropyl) ) Piromellitic dianhydride, pentafluoroethyl pyromellitic dianhydride, bis {3,5-di (trifluoromethyl) phenoxy} pyromellitic dianhydride, 2,2-bis (3,4-di) Carboxyphenyl) Hexafluoropropane dianhydride, 5,5'-bis (trifluoromethyl) -3,3', 4,4'-tetracarboxybiphenyl dianhydride, 2,2', 5,5'-tetrakis (Trifluoromethyl) -3,3', 4,4'-tetracarboxybiphenyl dianhydride, 5,5'-bis (trifluoromethyl) -3,3', 4,4'-tetracarboxydiphenyl ether dianhydride Thing, 5,5'-bis (trifluoromethyl) -3,3', 4,4'-tetracarboxybenzophenone dianhydride, bis {(trifluoromethyl) dicarboxyphenoxy} benzene dianhydride, bis {( Trifluoromethyl) dicarboxyphenoxy}, trifluoromethylbenzene dianhydride, bis (dicarboxyphenoxy) trifluoromethylbenzene dianhydride, bis (dicarboxyphenoxy) bis (trifluoromethyl) benzene dianhydride, bis (dicarboxyphenoxy) Dicarboxyphenoxy) Tetrax (trifluoromethyl) benzene Anhydride Water, 2,2-bis {(4- (3,4-dicarboxyphenoxy) phenyl} hexafluoropropane dianhydride, bis {(trifluoromethyl) dicarboxyphenoxy} biphenyl dianhydride, bis {(tri) Fluoromethyl) dicarboxyphenoxy} bis (trifluoromethyl) biphenyl dianhydride, bis {(trifluoromethyl) dicarboxyphenoxy} diphenyl ether dianhydride, bis (dicarboxyphenoxy) bis (trifluoromethyl) biphenyl dianhydride And so on.

Among these tetracarboxylic dianhydrides, 3,3', 4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA) or 6FDA are exemplified as suitable ones. ..

When these tetracarboxylic acid dianhydride components other than CBDA are used in combination, the ratio of use thereof is preferably 1 to 30 mol%, preferably 1 to 28 mol%, more preferably, based on the total tetracarboxylic acid dianhydride component. Is 1 to 20 mol%, more preferably 1 to 10 mol%.

In the production method of the present invention, the polyimide precursor (polyamic acid) is known to polymerize in an organic polar solvent using a diamine and an acid dianhydride in a molar ratio of 0.9 to 1.1 (substantially equimolar). It can be manufactured by the method of. Specifically, after dissolving the diamine in an aprotic amide solvent such as N, N-dimethylacetamide and N-methyl-2-pyrrolidone under a nitrogen stream, acid dianhydride is added, and the temperature is 3 to 3 at room temperature. It is obtained by reacting for about 20 hours. At this time, the molecular terminal may be sealed with an aromatic monoamine or an aromatic monocarboxylic acid anhydride. Examples of the solvent include dimethylformamide, 2-butanone, diglyme, xylene, γ-butyl lactone and the like, and one type or two or more types can be used in combination.

Then, in the production method of the present invention, the polyimide precursor thus obtained is imidized by a thermal imidization method or a chemical imidization method. For thermal imidization, a polyimide precursor was applied to any support substrate material such as glass, metal, resin (polyimide film, etc.) using an applicator, and pre-dried at a temperature of 130 ° C. or lower for 3 to 60 minutes. After that, it is usually carried out by heat treatment at a temperature of about room temperature to 360 ° C. for about 30 minutes to 24 hours for solvent removal and imidization. In chemical imidization, a dehydrating agent and a catalyst are added to a polyimide precursor (also referred to as "polyamic acid") solution, and the mixture is chemically dehydrated at 30 to 60 ° C. Acetic anhydride is exemplified as a typical dehydrating agent, and pyridine is exemplified as a catalyst. For thermal imidization, if a combination of acid dianhydride, diamine type, and solvent type is selected, imidization can be completed in a relatively short time, and heat treatment including preheating can be performed within 60 minutes. be. It is also possible to use both thermal imidization and chemical imidization in combination. When the polyimide precursor is applied, it may be applied as a polyimide precursor solution in which the polyimide precursor is dissolved in a known solvent. The thickness of the supporting base material may be, for example, about 0.02 to 1.0 mm. When the polyimide precursor is applied, it may be applied as a polyimide precursor solution in which the polyimide precursor is dissolved in a known solvent.

The preferred degree of polymerization of the polyimide precursor and the polyimide in the production method of the present invention is 1,000 to 40,000 cP as the viscosity of the polyimide precursor solution measured by an E-type viscometer, preferably in the range of 3,000 to 5,000 cP. .. The molecular weight of the polyimide precursor can be determined by the GPC method. The preferred molecular weight range (polystyrene equivalent) of the polyimide precursor is preferably in the range of 15,000 to 250,000 for the number average molecular weight, 30,000 to 800,000 for the weight average molecular weight, and preferably 50,000 to 300,000 for the weight average molecular weight. Not all polyimides outside the range cannot be used. The molecular weight of polyimide is also in the same range as the molecular weight of its precursor.

In the production method of the present invention, various fillers and additives may be added to the polyimide precursor or polyimide as needed, as long as the object of the present invention is not impaired. For example, inorganic fine particles such as silica, alumina, boron nitride, and aluminum nitride may be added for the purpose of improving slipperiness and thermal conductivity.

The polyimide laminate having the polyimide layer formed on the surface of the support (support base material) is then peeled from the support to obtain a polyimide film. Since the suitable means for this peeling differs depending on the type of the support, the suitable means is adopted. If the support is a copper foil or the like, there is a means for dissolving it with an acid. When the support is a resin (polyimide) film, a polyimide having a thickness of 25 μm or more and a heat resistance of 400 ° C. or more is suitable. If the support is made of a transparent material such as a glass substrate, the laser lift-off (LLO) method is suitable. In the LLO method, laser light is irradiated from the glass substrate side. If the laser light has a wavelength in the ultraviolet region, preferably in the near-ultraviolet region around 308 μm, it is efficiently absorbed by the polyimide film obtained by the present invention to generate heat, and at the same time, between the glass substrate and the polyimide layer. A gap is created in the surface to facilitate or enable peeling.

Further, the polyimide film obtained by the production method of the present invention may be composed of not only a single layer but also a plurality of layers of polyimide.

By the production method of the present invention, a thin polyimide layer (film) can be formed on a supporting substrate, and a transparent polyimide film exhibiting excellent performance in transparency, dimensional stability, heat resistance, and ease of peeling from the supporting substrate can be obtained. be able to. That is, the light transmittance of 400 nm is 70% or more, preferably 80% or more, and the coefficient of thermal expansion (CTE) is 45 ppm / K or less, preferably 35 ppm / K or less, and more preferably 30 ppm / K or less. , It can be easily peeled off from the supporting substrate by a known method. In particular, in the production method of the present invention, the light transmittance of the polyimide is 5% or less, preferably 3% or less in the wavelength range of the laser beam (for example, 308 nm), and unlike the glass substrate of the supporting base material, the laser beam emits light. Since it is absorbed without being transmitted, it easily peels off at the interface with the supporting base material (glass substrate), has excellent peelability (laser lift-off: LLO) from the supporting base material by laser light irradiation, and has a thickness of 30 μm or less. It is more preferable to obtain a thin transparent polyimide film having a thickness of 20 μm or less, more preferably 15 μm or less.

Here, the coefficient of thermal expansion (CTE) is a coefficient of linear expansion when the temperature is changed from 250 ° C. to 100 ° C. unless otherwise specified, and the polyimide in the production method of the present invention is the coefficient of thermal expansion of glass (10 ppm). Since the difference from (/ K or less) is not large, the shape stability is excellent when glass is used as the supporting base material. For example, when manufacturing a flexible device such as a TFT substrate for an organic EL device having a bottom emission structure or a top emission structure, a touch panel substrate, a color filter, etc., such as stacking functional layers, the warp of the substrate can be suppressed and the manufacturing yield of the flexible device is excellent. .. Then, it is possible to absorb the light rays in the invisible light region and increase the transmittance in the visible light region. Within this range, 308 nm laser light (excimer laser) can be absorbed while maintaining the transparency of the visible light region. As a result, by irradiating a flexible substrate such as a substrate for an organic EL device, a touch panel substrate, and a color filter substrate with a laser, the polyimide layer (film) can be removed from the glass without damaging the display device on the transparent polyimide layer. It can be peeled off and suitably manufactured by a laser lift-off method. The degree of yellowness (YI) is preferably 6 or less, preferably 4 or less. Within this range, it can be suitably used for substrates that are required to be transparent or colorless, such as TFT substrates for organic EL devices, touch panel substrates, and color filter substrates. In addition, from the viewpoint of heat resistance, the glass transition temperature is 300 ° C. or higher, preferably 350 ° C. or higher, more preferably 380 ° C. or higher, and the pyrolysis temperature (Td1) is 340 ° C. or higher, preferably 380 ° C. or higher. be.

The polyimide film obtained by the production method of the present invention is suitable as a practical flexible heat-resistant transparent resin substrate material that replaces a glass substrate, which is an existing material, and satisfies required characteristics such as dimensional stability in applications such as thin displays and touch panels. Can be used for. That is, a polyimide film can be used as a substrate material, and a functional layer such as an element having various functions can be formed on the surface thereof. For example, not only main display devices such as liquid crystal displays, organic EL display devices, touch panels, and electronic papers, but also related components such as thin film transistors (TFTs), color filters, conductive films, gas barrier films, and flexible circuit boards. , Adhesive film and the like can also be formed.
In this case, the polyimide film may be composed of not only a single layer but also a plurality of layers of polyimide.

As for the method of forming the functional layer, the forming conditions are appropriately set according to the target device, but generally, after forming a metal film, an inorganic film, an organic film or the like on a polyimide film, the film is formed. It can be obtained by using a known method such as patterning into a predetermined shape or heat treatment as needed. That is, the means for forming these display elements is not particularly limited, and for example, sputtering, vapor deposition, CVD, printing, exposure, immersion, etc. are appropriately selected, and if necessary, in a vacuum chamber. These process processes may be performed by such as. Then, after the functional layer is formed on the polyimide film, the supporting base material and the polyimide film with the functional layer may be separated immediately after the functional layer is formed through various process treatments, or for a certain period of time. It may be integrated with the support base material after a lapse of time, and may be separated and removed immediately before being used as a display device, for example.

In the production method of the present invention, the polyimide layer (film) formed on the supporting base material further forms a functional layer on the polyimide layer (film), and then the polyimide film is peeled off from the supporting base material together with the functional layer. For example, after the assembly manufacturing process of various electronic components forming the functional layer on the polyimide film is completed, the polyimide film with the functional layer on the obtained support substrate is irradiated with laser light to form the polyimide layer with the functional layer. The (film) is peeled off from the supporting substrate. As described above, if the interface between the supporting base material (glass) and the polyimide film is irradiated with an excimer laser (wavelength 308 nm), the polyimide film with the functional layer can be easily peeled off from the supporting base material.

When the polyimide film is peeled from the supporting base material together with the functional layer, if the polyimide film is stretched, the retardation becomes large. Therefore, a method of peeling so that the stress applied to the polyimide film at the time of peeling is reduced is preferable. In order to prevent the polyimide film from stretching, a stretch-preventing layer such as an adhesive is formed on the supporting base material, a polyimide layer (film) is formed on the layer, and a functional layer is further formed on the polyimide layer (film). , A method is preferable in which the polyimide film is peeled off together with the stretch prevention layer and the functional layer, and the stress required for the peeling is dispersed in the other layers.

Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples. The present invention is not limited to these examples.

The abbreviations of the raw materials used in the examples are shown below.
・ TFMB: 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl ・ m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl ・ AAPBZI: 5-amino-2- (4-Aminophenyl) benzoimidazole ・ AAPBZO: 5-amino-2- (4-aminophenyl) benzoxazole ・ CBDA: 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride ・ PMDA: dipyromellitic acid Anhydride ・ BPDA: 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride ・ 6FDA: 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride ・ NMP: N -Methyl-2-pyrrolidone

The measurement method and evaluation method of each physical property in Examples and the like are shown below.
[Light transmittance and yellowness (YI)]
The light transmittance (T308, T 355, T 400, T 430) of the polyimide film (50 mm × 50 mm, thickness 10 to 15 μm) at 308 nm, 355 nm, 400 nm and 430 nm was determined by a SHIMADZU UV-3600 spectrophotometer. In addition, YI (yellowness) was calculated based on the following formula.
YI = 100 × (1.2879X-1.0592Z) / Y
X, Y, Z are specified in JIS Z 8722, which is the tristimulus value of the test piece.

[Coefficient of thermal expansion (CTE)]
A polyimide film having a size of 3 mm × 15 mm was heated from 30 ° C. to 280 ° C. at a constant heating rate (10 ° C./min) while applying a load of 5.0 g using a thermomechanical analysis (TMA) device, and then. The temperature was lowered from 250 ° C. to 100 ° C., and the coefficient of thermal expansion was measured from the amount of elongation (linear expansion) of the polyimide film at the time of lowering the temperature.

[Glass transition temperature (Tg)]
The dynamic viscoelasticity when the polyimide film (5 mm × 70 mm) was heated from 23 ° C to 500 ° C at 5 ° C / min with a dynamic thermomechanical analyzer was measured, and the glass transition temperature (tan δ maximum value: ° C) was measured. ) Was asked.

[Pyrolysis temperature (Td1)]
Measure the weight change when a polyimide film weighing 10 to 20 mg is heated from 30 ° C to 550 ° C at a constant speed with a thermogravimetric analysis (TG) device TG / DTA6200 manufactured by SEIKO under a nitrogen atmosphere. Then, based on the weight at 200 ° C., the temperature when the weight loss rate was 1% was defined as the thermal decomposition temperature (Td1).

[Removability: LED]
^{Laser irradiation energy density (mJ / cm 2} ) until the polyimide layer and the supporting base material (glass substrate) can be peeled off (abbreviation: LED). The irradiation conditions are the same as those of "Removability: Laser Lift Off (LLO)" described in the next paragraph "0048". The higher the energy density, the harder it is to peel off. Considering the life of the laser irradiation device, one having a small irradiation energy density is preferable. The upper limit of measurement is 300 mJ / cm ² , and those that cannot be peeled off at 300 mJ / cm ^{2 or less are marked with "x".}

[Removability: Laser lift-off (LLO)]
Using an excimer laser processing machine (wavelength 308 nm), a laser with a beam size of 14 mm × 1.2 mm, a moving speed of 6 mm / s, and an overlap rate of 80% is irradiated from the support base material (glass) side, and the support base material and polyimide are irradiated. When the layer is completely separated (determine the peeling range with a cutter, make one round of the cut, and then the polyimide film naturally peels from the glass), "○" indicates that the coating substrate and the polyimide layer are completely or partially separated. The state in which the above was not possible or the polyimide layer was discolored was designated as "x".

Synthesis example 1
To synthesize the polyimide precursor, 8.57 g of TFMB was dissolved in 85 g of NMP in a 100 ml separable flask under a nitrogen stream. Then 0.67 g of AAPBZI was added to this solution. After stirring for 10 minutes, 5.76 g of CBDA was added. The molar ratio of the diamine component to the tetracarboxylic dianhydride component was 0.99 (substantially equimolar). Then, this solution was stirred at room temperature for 24 hours to carry out a polymerization reaction to obtain polyamic acid A (viscous colorless solution) having a high degree of polymerization (Mw 80,000 or more and viscosity 5,000 cP or more).

Synthesis Examples 2-18
Polyamide acid solutions were prepared in the same manner as in Synthesis Example 1 except that the diamine and tetracarboxylic dianhydride were changed to the compositions shown in Tables 1 and 2, to obtain polyamic acids B to R.

In Tables 1 and 2, the unit of the amount of diamine and tetracarboxylic dianhydride is g, and the numerical value in parentheses indicates the mol% in the diamine component or the tetracarboxylic dianhydride component.

Example 1
Solvent NMP was added to the polyimide precursor solution A obtained in Synthesis Example 1 to dilute it so that the viscosity became 4000 cP, and then a glass substrate (E-XG manufactured by Corning, size = 150 mm × 150 mm, thickness = 0). .7 mm) was coated with a spin coater so that the cured polyimide had a thickness of about 15 μm. Subsequently, heating was performed at 100 ° C. for 15 minutes. Then, in a nitrogen atmosphere, the temperature was raised from room temperature to 300 ° C. (360 ° C. in Comparative Example 4) at a constant temperature rise rate (3 ° C./min), held at 130 ° C. for 10 min on the way, and 150 mm × on a glass substrate. A 150 mm polyimide layer (polyimide A) was formed to obtain a polyimide laminate A.

Examples 2-11, Comparative Examples 1-7
The operation was carried out in the same manner as in Example 1 except that the polyimide precursor A was replaced with any of the polyimide precursors B to R to obtain polyimide laminated bodies B to R. The symbols of the polyimide precursor and the polyimide laminated body correspond to each other, which means that the polyimide laminated body B is obtained from the polyimide precursor B, and the same applies to the reference numerals C and below.

The obtained polyimide laminates A to R were measured for laser lift-off (LLO) and LED. The results are shown in Tables 3 and 4.

For measurements other than the above, the polyimide film was peeled off from the laminate, but in this case, the laminate was prepared according to the above except that a 75 μm polyimide film was used as the substrate instead of the glass substrate. .. The detailed creation conditions are shown below.
Solvent NMP was added to the polyamic acid solutions A to R obtained in Synthesis Examples 1 to 15, diluted to a viscosity of 3000 cP, and then placed on a 75 μm polyimide film (Upilex-S) substrate. Painted. Subsequently, heating was performed at 100 ° C. for 15 minutes. Then, the temperature was raised from room temperature to 300 ° C. (360 ° C. in Comparative Example 4) at a constant temperature rise rate (3 ° C./min) in a nitrogen atmosphere, and the temperature was maintained at 130 ° C. for 10 min on the way to obtain a polyimide laminated film. .. Then, the polyimide base material (Upilex-S) was peeled off, and the polyamide acid solutions A to R were imidized to obtain polyimide films A to R as a single body. The above peeling was performed by making one cut of the formed polyimide layer with a cutter to determine the peeling range, and then peeling from the base material with tweezers. The thickness of these films is shown in the section of thickness.

The obtained polyimide films A to R were evaluated in various ways such as CTE, light transmittance, YI, Td1 and Tg, respectively. The results are shown in Tables 3 and 4.

Claims (5)

A step of applying the polyimide precursor or its resin solution on the surface of the support, a step of heating the polyimide precursor or the resin solution thereof to imidize, and a step of forming a polyimide layer on the surface of the support, and the polyimide. A method for producing a polyimide film, comprising a step of peeling a layer from the support to obtain a polyimide film.
The polyimide precursor contains one or two selected from 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl and 2,2'-dimethyl-4,4'-diaminobiphenyl. It is obtained by reacting a diamine with an acid dianhydride containing 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, and is obtained by reacting 2,2'-bis (trifluoromethyl) -4,4'-diaminobiphenyl. It contains 50 mol% or more of the total diamine, and has a structural unit represented by the following formula (6) in the polyimide.

A method for producing a transparent polyimide film, wherein the polyimide film has a coefficient of thermal expansion of 45 ppm / K or less, a light transmittance of 3.0% or less in a light beam of 308 nm, and 70% or more in a light beam of 400 nm. ..
However, the polyimide does not contain any of the structural units represented by the following formula (A1) or (A2) or the structural units represented by the following formula (B).

The method for producing a transparent polyimide film according to claim 1, wherein the yellowness is 6 or less. The method for producing a transparent polyimide film according to claim 1, wherein the interface between the polyimide layer and the support is irradiated with laser light to peel off the polyimide layer from the support. The method for producing a transparent polyimide film according to any one of claims 1 to 3 is characterized by comprising a step of forming a functional layer on the polyimide layer and then peeling the polyimide layer with the functional layer from the support. A method for manufacturing a transparent polyimide film with a functional layer. The functional layer is selected from the group consisting of a transparent conductive layer, a wiring layer, a conductive layer, a gas barrier layer, a thin film transistor, an electrode layer, a light emitting layer, an adhesive layer, an adhesive layer, a transparent resin layer, a color filter resist, and a hard coat layer. The method for producing a transparent polyimide film with a functional layer according to claim 4 , wherein the layer is one or more of the above-mentioned layers.