Method for producing mixed resin film

Abstract

In this method for producing a mixed resin film that includes a polyimide and a solvent-soluble resin other than a polyimide, when a mixed resin solution that includes the polyimide and the solvent-soluble resin other than a polyimide in a ratio of 2:98 to 98:2 is prepared, a crushed product of a film including the polyimide and the solvent-soluble resin is dissolved in a solvent. This mixed resin solution is flow cast on a support body, the result is dried to form a resin film, and the resin film is peeled away from the support body and then dried, whereby a mixed resin film is obtained. The dried film may be stretched.

Description

Method for manufacturing mixed resin films

[0001] The present invention relates to a method for producing a mixed resin film containing polyimide and a solvent-soluble resin other than polyimide.

[0002] Display devices such as liquid crystal displays, organic EL displays, and electronic paper, as well as electronic devices such as solar cells and touch panels, are required to be thinner, lighter, and more flexible. By replacing the glass materials used in these devices with film materials, flexibility, thinning, and weight reduction can be achieved. Transparent polyimide film has been developed as a glass substitute material and is used in display substrates and cover films, etc.

[0003] As a method for producing polyimide films with high transparency, it has been proposed to use polyimide soluble in organic solvents (for example, Patent Document 1). By using solvent-soluble polyimide, high-temperature heating for imidization after film formation is not required, and a polyimide film with less coloration can be obtained.

[0004] International Publication No. 2020 / 004236

[0005] Solvent-soluble polyimides often contain organofluorine compounds as monomer components, and from the perspective of reducing environmental impact, waste reduction is desired. To reduce waste, it is conceivable to re-dissolve and recycle off-cut portions (trimmed off during product manufacturing) and films that are substandard. However, recycling polyimide films can lead to problems such as a decrease in quality and variations in properties.

[0006] In view of the above, the present invention aims to provide a method for manufacturing film that exhibits less deterioration in quality and less variation in properties when recycled.

[0007] The present invention relates to a method for producing a mixed resin film containing polyimide and a solvent-soluble resin other than polyimide. The method for producing a mixed resin film comprises, in order: a solution preparation step of preparing a mixed resin solution containing polyimide and a solvent-soluble resin other than polyimide in a ratio of 2:98 to 98:2; a resin film formation step of casting the mixed resin solution onto a support and drying it to form a resin film; a peeling step of peeling the resin film from the support; and a drying step of drying the resin film after peeling it from the support.

[0008] The glass transition temperature of the mixed resin film is 100 to 250°C. The mixed resin film may also have a yellowness of 3.0 or less and a haze of 10% or less.

[0009] The solution preparation step includes dissolving crushed film containing polyimide and solvent-soluble resin in a solvent. In addition to the crushed film, unused resin may also be dissolved in the solvent during the solution preparation step.

[0010] The mixed resin solution may contain a bluing agent and / or an ultraviolet absorber. A pigment is preferred as the bluing agent.

[0011] In the drying process, it is preferable to dry the resin film so that the amount of residual solvent is 10% by weight or less.

[0012] In each of the solution preparation step, resin film formation step, peeling step, and drying step, it is preferable that the maximum temperature is 250°C or lower.

[0013] After the drying process, a stretching process may be carried out to stretch the obtained film. The heating temperature (stretching temperature) in the stretching process is preferably 250°C or lower.

[0014] As for solvent-soluble resins, those with a glass transition temperature 50°C or more lower than polyimide are preferred. Examples of solvent-soluble resins include acrylic resins, polyesters, polycarbonates, and polyarylates.

[0015] Mixed resin films containing polyimide and other solvent-soluble resins, with a glass transition temperature of 100-250°C, exhibit minimal changes in properties such as color (yellowness) and mechanical strength even when heated to temperatures near the glass transition temperature. Films produced by re-melting and recycling crushed film materials have the same quality as films produced using only unused resin as raw materials, and show less quality degradation and variation in properties due to recycling.

[0016] The present invention relates to a method for producing a mixed resin film containing polyimide and a solvent-soluble resin other than polyimide (hereinafter sometimes referred to as "other resin"), characterized by dissolving and recycling the crushed film material.

[0017] [Mixed Resin Film] The mixed resin film contains polyimide and other resins in a ratio of 2:98 to 98:2. The ratio of polyimide to other resins may be 95:5 to 10:90, or 90:10 to 15:85.

[0018] Resin compositions containing polyimide and other resins, and mixed resin films formed from such resin compositions, preferably have a single glass transition temperature in differential scanning calorimetry (DSC) and / or dynamic viscoelasticity measurement (DMA). When a resin composition containing polyimide and other resins, and a mixed resin film, have a single glass transition temperature, the polyimide and other resins can be considered to be perfectly miscible.

[0019] The glass transition temperature of the mixed resin film is 100 to 250°C. The glass transition temperature of the mixed resin film may also be 120 to 240°C, 130 to 230°C, 140 to 220°C, or 150 to 210°C. Increasing the proportion of other resins tends to lower the glass transition temperature of the mixed resin film. A low glass transition temperature of the mixed resin film allows for film processing, such as stretching, to be performed at low temperatures, thus reducing degradation and volatilization of resins and additives, and ensuring uniformity and reproducibility of properties when the film is recycled.

[0020] Polyimide is not particularly limited as long as it is soluble in organic solvents and compatible with other resins. The compatibility of polyimide with other resins causes the mixed resin film to exhibit transparency. Examples of other resins include acrylics, polyesters, polycarbonates, and polyarylates. Two or more resins other than polyimide may also be used as the other resins. In the following, unless otherwise specified, the polyimide, other resins, and various additives constituting the mixed resin film may be used individually or in combination of two or more types.

[0021] Specific examples of polyimides and other resins will be described later. For combinations of polyimides and other resins that exhibit compatibility, and for mixed resin films containing such resin compositions, refer to disclosures such as WO2021 / 132279, JP 2023-159875, JP 2023-155614, JP 2023-31196, WO2023 / 249079, WO2023 / 149435, WO2023 / 132310, WO2023 / 085325, and WO2023 / 026982.

[0022] The mixed resin film may contain various additives in addition to polyimide and other resins. Examples of additives include UV absorbers, bluing agents, dyes and / or pigments other than bluing agents, surfactants, leveling agents, plasticizers, fine particles, and sensitizers. Polymer compounds such as epoxy resins may also be included as additives.

[0023] Examples of UV absorbers include triazine-based UV absorbers, benzotriazole-based UV absorbers, benzophenone-based UV absorbers, cyanoacrylate-based UV absorbers, and hydroxybenzoate-based UV absorbers. Among these UV absorbers, triazine-based UV absorbers and benzotriazole-based UV absorbers are preferred because they provide good light resistance, and benzotriazole-based UV absorbers are particularly preferred because they produce less discoloration.

[0024] When the mixed resin film contains an ultraviolet absorber, the amount of ultraviolet absorber is preferably 0.1 to 10 parts by weight, more preferably 1 to 8 parts by weight, and may also be 3 to 8 parts by weight or 5 to 6 parts by weight, per 100 parts by weight of polyimide in the film. The more ultraviolet absorber there is, the better the light resistance of the film tends to be. On the other hand, if the amount of ultraviolet absorber is excessively high, the yellowness (YI) of the film tends to increase.

[0025] Blueing agents are additives (pigments or dyes) that absorb long-wavelength light (red, orange, yellow) in the visible light spectrum to adjust color. Examples include organic pigments such as phthalocyanine blue, inorganic pigments such as ultramarine, Prussian blue, and cobalt blue, anthraquinone derivatives, indigo compounds, and organic dyes such as methylene blue.

[0026] Blueing agents alter the color tone of a film with the addition of even small amounts. When recycled mixed resin films, if the blueing agent volatilizes or degrades due to heat during the film manufacturing process, variations in film YI (Yield Indication) between lots occur, impairing the stability of quality. Therefore, it is preferable that the blueing agent has high heat resistance. The temperature at which the blueing agent loses 1% of its weight is preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 250°C or higher. Due to their low volatility and high heat resistance, organic or inorganic pigments such as phthalocyanine blue, ultramarine, Prussian blue, and cobalt blue are preferred as blueing agents.

[0027] The amount of bluing agent in the mixed resin film can be adjusted as appropriate according to the required yellowness (YI) of the film. From the viewpoint of uniformly coloring the film, the amount of bluing agent in the film is preferably 10 to 1000 ppm by weight, more preferably 20 to 500 ppm, and may also be 30 to 200 ppm or 50 to 100 ppm.

[0028] [Method for Manufacturing a Mixed Resin Film] In the method for manufacturing a mixed resin film of the present invention, the following steps are carried out in order: preparing a mixed resin solution containing polyimide and another resin (solution preparation step); casting the mixed resin solution onto a support and drying it to form a resin film (resin film formation step); peeling the resin film from the support (peeling step); and drying the resin film after peeling it from the support (drying step). Furthermore, a step of stretching the film (stretching step) may be carried out after the drying step.

[0029] <Solution Preparation Process> In the solution preparation process, a mixed resin solution containing polyimide and other resins is prepared. As mentioned above, the ratio of polyimide to other resins by weight is 2:98 to 98:2, and may also be 95:5 to 10:90, or 90:10 to 15:85. The higher the proportion of polyimide, the higher the elastic modulus of the film tends to be, resulting in superior mechanical strength. The higher the proportion of other resins, the less coloration the film tends to have, and the higher its transparency tends to be.

[0030] The solvent for the resin solution is not particularly limited as long as it is soluble in both polyimide and other resins. Examples of solvents include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; ether solvents such as tetrahydrofuran and 1,4-dioxane; ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, cyclopentanone, cyclohexanone, and methylcyclohexanone; and alkyl halogen solvents such as chloroform, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, dichlorobenzene, and methylene chloride.

[0031] In terms of the solubility of polyimide and the compatibility of polyimide with other resins in solution, amide solvents are preferred. On the other hand, in terms of the ease of solvent removal during film production, low-boiling non-amide solvents are preferred, and ketone solvents and alkyl halide solvents are preferred because they have excellent solubility for both polyimide and other resins and have low boiling points.

[0032] In this invention, during the solution preparation process, crushed film containing polyimide and other resins is dissolved in a solvent, and the film is recycled for reuse.

[0033] In the industrial production of long rolls of film, the ends in the width direction that are not suitable for the final product are cut off. Furthermore, if the film has cosmetic defects (scratches, dents, air bubbles, or other deformations) or if its thickness or other specifications are outside of the standard, substandard products that cannot be used as finished products may be produced. These non-product portions are generally discarded, but by reusing them as crushed material, the amount of waste is reduced, the environmental impact is minimized, and the film manufacturing costs can be lowered.

[0034] The method of shredding the film is not particularly limited and can include cutting with a cross shredder or crushing. From the perspective of improving solubility during recycling, the area of ​​the shredded film should be 30 cm². ２ The following is preferable: 25 cm ２ The following is preferable: 20 cm ２ Below, 15cm ２ less than or 10 cm ２ The following is also acceptable.

[0035] The film to be shredded (film to be recycled) is not particularly limited as long as it contains polyimide and other resins in a weight ratio of 2:98 to 98:2, but it is preferable that it has substantially the same composition as the film to be manufactured. Specifically, it is preferable that the film to be shredded and the film to be manufactured have the same types of polyimide and other resins, and that the difference in their ratios is within ±5%. The difference in glass transition temperature between the film to be shredded and the film to be manufactured is preferably 5°C or less, more preferably 3°C or less, and may be 1°C or less or 0°C.

[0036] In the solution preparation step, a solution may be prepared by dissolving only crushed products of a film containing polyimide and another resin in a solvent, or in addition to the crushed products, unused (i.e., not yet formed into a film) resin (and additives) may be dissolved in the solvent. When an unused resin is dissolved in a solvent in addition to the crushed film product, the order of adding the crushed film product and the unused resin into the solvent is not particularly limited, and both may be added at the same time. When an unused resin is dissolved in a solvent in addition to the crushed film product, the ratio of the crushed film product to the unused resin is not particularly limited. The ratio of the crushed film product to the total of the crushed film product and the unused resin (i.e., the total amount of resin components in the solution) may be 0.5% or more, 1% or more, 3% or more, 5% or more, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 97% or more, or 99% or more.

[0037] <Resin film forming step, peeling step and drying step> After the solution preparation step, the film manufacturing step may be carried out according to a conventional method. In the resin film forming step, the above solution is applied onto a support, and the solvent is removed by drying. As a method for applying the solution, a method using a bar coater, a comma coater, or the like, or a known method such as die coating can be applied.

[0038] As the support, a glass substrate, a metal substrate such as SUS, a metal drum, a metal belt, a plastic film, or the like can be used. From the viewpoint of improving productivity, it is preferable to use an endless support such as a metal drum or a metal belt, or a long plastic film or the like as the support, and manufacture the film by roll-to-roll processing. When a plastic film is used as the support, a material that is insoluble in the solvent of the polyimide-based resin solution (dope) containing polyimide resin and a soluble resin may be appropriately selected.

[0039] The temperature for drying the solvent on the support (primary drying) is not particularly limited as long as the solvent can be removed to such an extent that the resin film can be peeled from the support, and is appropriately set at approximately room temperature to 250°C. The temperature for primary drying may be 50°C to 220°C. The temperature for primary drying may be increased stepwise.

[0040] The resin film after primary drying still has residual solvent therein. The mixed resin film can be obtained by peeling this resin film from the support, further drying the resin film to remove residual solvent (secondary drying). The temperature of secondary drying is not particularly limited as long as the solvent can be removed, and is appropriately set at approximately 50 to 300°C. The temperature of secondary drying may be increased stepwise. The residual solvent content of the resin film (mixed resin film) after secondary drying is preferably 10% by weight or less, more preferably 5% by weight or less, and may be 3% by weight or less or 1% by weight or less. It is preferable to set the secondary drying conditions such that the residual solvent content falls within the above range.

[0041] Secondary drying is preferably performed at a higher temperature than primary drying. The maximum temperature of secondary drying is preferably 60°C or higher, more preferably 80°C or higher, and may be 100°C or higher or 120°C or higher. A higher secondary drying temperature enables efficient removal of the solvent in a shorter time. However, excessively high temperatures may cause yellowing of the film or decomposition and volatilization of additives. Therefore, the maximum temperature of secondary drying is preferably 250°C or lower, and may be 220°C or lower or 200°C or lower. The secondary drying temperature is preferably not higher than the glass transition temperature (Tg) of the mixed resin film plus 10°C, more preferably not higher than Tg, and may be not higher than Tg minus 10°C or not higher than Tg minus 20°C.

[0042] <Stretching Step> The film after secondary drying may be stretched in at least one direction. Stretching orients polymer chains in the stretching direction, which improves the in-plane strength of the film and tends to suppress the occurrence of cracks in the film. In particular, the tensile modulus of elasticity in the stretching direction increases, which tends to improve flex resistance accordingly.

[0043] The film stretching method is not particularly limited and may be either free-end stretching or fixed-end stretching. Free-end stretching includes a method of stretching the film in the transport direction while transporting it with two pairs of nip rolls at different peripheral speeds (longitudinal stretching). Fixed-end stretching includes a method of stretching the transported film in a direction perpendicular to the transport direction using a tenter clip device (lateral stretching), and a method of stretching in a direction perpendicular to the transport direction while also stretching in the transport direction (simultaneous biaxial stretching and oblique stretching). Sequential biaxial stretching may also be performed by performing lateral stretching after longitudinal stretching.

[0044] By biaxial stretching a film, the strength in any direction within the film plane can be increased. In biaxial stretching, the stretching ratio in one direction and the stretching ratio in the direction perpendicular to it may be the same or different. When there is a difference in stretching ratios, the mechanical strength tends to be relatively higher in the direction with the larger stretching ratio. When using a biaxially oriented film with anisotropic stretching ratios in a foldable device, it is preferable to position the direction with the larger stretching ratio perpendicular to the folding axis.

[0045] The stretching ratio is not particularly limited and is generally around 1-200%. The stretching ratio may also be 5-150%, 10-120%, or 20-100%. The larger the stretching ratio, the greater the tensile modulus in the stretching direction tends to be. On the other hand, if the stretching ratio is excessively large, the mechanical strength in the direction perpendicular to the stretching direction tends to decrease, which may reduce the handling properties of the film.

[0046] The stretching temperature is not particularly limited, but is usually around the glass transition temperature (Tg) of the film ± 40°C, preferably Tg ± 30°C, and may also be Tg ± 20°C or Tg ± 10°C. The stretching temperature may be 100°C or higher, 120°C or higher, 130°C or higher, or 150°C or higher. The stretching temperature is preferably 250°C or lower, and may also be 230°C or lower, 220°C or lower, 210°C or lower, or 200°C or lower.

[0047] Films containing only polyimide as the resin component have a high glass transition temperature, making stretching difficult below 250°C. On the other hand, stretching at temperatures above 250°C can easily lead to discoloration (increased yellowness) and a decrease in mechanical strength due to degradation and volatilization of the resin and additives, reducing their practical usability. Furthermore, when manufacturing films using recycled crushed film materials that have undergone processes above 250°C, the resulting films may have inferior transparency and mechanical strength compared to films made using only unused resin (and developing agent) as raw materials, because the crushed film materials, which are the raw material components, have already undergone thermal degradation. Thus, films containing only polyimide as the resin component have a high glass transition temperature, resulting in poor processability such as stretching and poor recyclability.

[0048] On the other hand, in the present invention, by mixing polyimide with other resins, the glass transition temperature of the resin composition and film is set to 250°C or lower. Therefore, each step of solution preparation, resin film formation (primary drying), peeling, and drying (secondary drying) can be carried out at 250°C or lower, and furthermore, stretching can also be carried out at 250°C or lower. In other words, it is possible to set the maximum temperature of all steps in the manufacturing process of the mixed resin film to 250°C or lower. The maximum temperature of all steps in the manufacturing process of the mixed resin film is preferably 250°C or lower, and more preferably 230°C or lower.

[0049] Because the mixed resin film of polyimide and other resins has a glass transition temperature of 250°C or lower, it is possible to lower the temperature of the film manufacturing process, resulting in a film with less coloration (low yellowness) and high mechanical strength. Furthermore, because the film undergoes little thermal degradation, even when film is made using recycled film fragments, there is little difference in properties compared to films made using only unused resin (and developing agent) as raw materials, resulting in excellent recyclability and the ability to be recycled multiple times. In other words, the mixed resin film of the present invention, made using recycled film fragments, can be recycled again as fragments. Thus, even after multiple recycling uses, the uniformity and reproducibility of the film's properties can be ensured.

[0050] [Characteristics and Applications of Mixed Resin Film] The thickness of the mixed resin film is not particularly limited and can be set appropriately according to the application. The thickness of the mixed resin film is, for example, 5 to 300 μm, and from the viewpoint of achieving both self-supporting properties and flexibility, the thickness of the mixed resin film is preferably 10 μm to 200 μm, and may be 30 μm to 150 μm, 40 μm to 100 μm, or 50 μm to 80 μm. When the film is stretched, it is preferable that the thickness after stretching is within the above range.

[0051] The yellowness (YI) of the mixed resin film is not particularly limited, but is preferably 10 or less, more preferably 5.0 or less, even more preferably 3.0 or less, and may be 2.0 or less, 1.0 or less, or 0.0 or less.

[0052] The haze of the mixed resin film is preferably 10% or less, more preferably 5% or less, even more preferably 4% or less, and may be 3.5% or less, 3% or less, 2% or less, or 1% or less. As described above, since polyimide and soluble resins are compatible, a film with low haze and high transparency can be obtained.

[0053] The total light transmittance of the mixed resin film is preferably 85% or higher, more preferably 86% or higher, even more preferably 87% or higher, particularly preferably 88% or higher, and may also be 89% or higher or 90% or higher.

[0054] The tensile modulus of the mixed resin film is not particularly limited, but from the viewpoint of strength, the tensile modulus at room temperature is preferably 2.0 GPa or higher, more preferably 3.0 GPa or higher, and even more preferably 4.0 GPa or higher. The tensile modulus may be anisotropic, and the tensile modulus in at least one direction may be 4.0 GPa or higher, 5.0 GPa or higher, 5.5 GPa or higher, 6.0 GPa or higher, 6.5 GPa or higher, or 7.0 GPa or higher.

[0055] The pencil hardness of the mixed resin film is preferably 6B or higher, preferably 4B or higher, and may also be 2B or higher, F or higher, or 2H or higher.

[0056] Mixed resin films containing polyimide and other resins are suitable for use as display materials because they exhibit low coloration and high transparency, even when using recycled materials. In particular, films with high mechanical strength can be applied to surface components such as display cover windows. For practical use, mixed resin films may be provided with an antistatic layer, an easy-adhesion layer, a hard coat layer, an anti-reflective layer, etc., on their surface.

[0057] [Preferred Form of Mixed Resin] As mentioned above, specific examples of combinations of polyimide and solvent-soluble resins other than polyimide (other resins) that constitute the mixed resin film can be found in the disclosures of WO2021 / 132279, JP 2023-159875, JP 2023-155614, JP 2023-31196, WO2023 / 249079, WO2023 / 149435, WO2023 / 132310, WO2023 / 085325, WO2023 / 026982, etc., but below specific examples of preferred forms of polyimide and other resins will be shown.

[0058] <Polyimide> (Structure of Polyimide) In this specification, the term "polyimide" refers to polyimide in a broad sense, including polyamideimide.

[0059] In the narrow sense, "polyimide" is a polymer obtained by dehydrating and cyclizing polyamic acid, which is obtained by addition polymerization of tetracarboxylic dianhydride (hereinafter sometimes referred to as "acid dianhydride") and diamine, and is a polymer having an imide structural unit represented by general formula (I).

[0060] Polyamide-imide is a polymer having imide structural units represented by general formula (I) and amide structural units represented by general formula (II) and / or amide-imide structural units represented by general formula (III).

[0061]

[0062] In general formulas (I) to (III), X is a tetravalent organic group, Y and Z are divalent organic groups, and W is a trivalent organic group. Y is a diamine residue, which is an organic group obtained by removing two amino groups from the diamine represented by general formula (V) below. X is a tetracarboxylic dianhydride (hereinafter sometimes referred to as "acid dianhydride") residue, which is an organic group obtained by removing two anhydrous carboxyl groups from the tetracarboxylic dianhydride represented by general formula (IV) below. Z is a dicarboxylic acid residue, which is an organic group obtained by removing two carboxyl groups from the dicarboxylic acid represented by general formula (VI) below. W is a tricarboxylic acid anhydride residue, which is an organic group obtained by removing anhydrous carboxyl groups from the tricarboxylic acid anhydride represented by general formula (VII) below.

[0063]

[0064] In other words, polyamide-imide includes a diamine-derived structure represented by the following general formula (Va) and a tetracarboxylic dianhydride-derived structure represented by the following general formula (IVa), and further includes one or more structures selected from the group consisting of a dicarboxylic acid-derived structure represented by the following general formula (VIa) and a tricarboxylic acid anhydride-derived structure represented by the following general formula (VIIa). The diamine-derived structure (Va) and the tetracarboxylic dianhydride-derived structure (IVa) form an imide bond to constitute an imide structural unit represented by general formula (I), the diamine-derived structure (Va) and the dicarboxylic acid-derived structure (VIa) form an amide bond to constitute an amide structural unit represented by general formula (II), and the anhydride carboxyl group portion and carboxyl group portion of the tricarboxylic acid anhydride-derived structure (VIIa) form an imide bond and an amide bond, respectively, with the diamine-derived structure (Va), to constitute an amide-imide structural unit represented by general formula (III).

[0065]

[0066] Polyimides are generally obtained by synthesizing polyamic acids using diamines and tetracarboxylic dianhydrides as monomers, and then dehydrating and cyclizing the amidic acid at the bond between the tetracarboxylic acid and the diamine. Polyimides can also be synthesized by decarboxylation of tetracarboxylic dianhydrides and diisocyanates, but in either synthesis method, the resulting polyimides have structures derived from acid dianhydrides (tetracarboxylic dianhydride residues) X, which are obtained by removing four carboxyl groups from tetracarboxylic dianhydrides, and structures derived from diamines (diamine residues) Y, which are obtained by removing two amino groups from diamines. Therefore, even if the starting materials used in the synthesis of polyimides are not tetracarboxylic dianhydrides or diamines, the structures corresponding to tetracarboxylic dianhydride residues contained in the polyimide are referred to as "acid dianhydride components," and the structures corresponding to diamine residues are referred to as "diamine components."

[0067] In the synthesis of polyamide-imides, polybasic acid derivatives such as dicarboxylic acid dichlorides and tricarboxylic acid anhydride chlorides are used in addition to diamines and tetracarboxylic dianhydrides. The resulting polyamide-imides have a structure Z (dicarboxylic acid residue) obtained by removing two carboxyl groups from a dicarboxylic acid, or a structure W (tricarboxylic acid residue) obtained by removing three carboxyl groups from a tricarboxylic acid. Therefore, even when the starting material used in the synthesis of polyamide-imides is a polybasic acid derivative, the structure corresponding to the polybasic acid residue is expressed as the "polybasic acid component."

[0068] (Composition of polyimide) Examples of polyimides that are soluble in solvents and compatible with other resins include: 1) those containing a benzidine derivative having a fluorine-containing substituent at least one of the 2, 2', 3, and 3' positions of benzidine as a diamine component; and 2) those containing a diamine and / or acid dianhydride having a fluorene structure as a diamine and / or acid dianhydride component.

[0069] Examples of benzidine derivatives having a fluorine-containing substituent at least one of the 2, 2', 3, and 3' positions of benzidine include those in which the fluorine-containing substituent is a trifluoromethyl group (trifluoromethyl-substituted benzidines). Specific examples of trifluoromethyl-substituted benzidines include 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, and 2,3'-bis(trifluoromethyl)benzidine.

[0070] Benzidine derivatives in which the fluorine-containing substituent is a trifluoromethoxy group, a difluoromethyl group, or a difluoromethoxy group do not have a perfluoroalkyl group bonded to the carbon atoms constituting the aromatic ring, and therefore have higher degradability and lower environmental impact compared to trifluoromethyl-substituted benzidines. Specific examples of these benzidine derivatives include 2,2'-bis(trifluoromethoxy)benzidine, 3,3'-bis(trifluoromethoxy)benzidine, 2,3'-bis(trifluoromethoxy)benzidine, 2,2'-bis(difluoromethyl)benzidine, 3,3'-bis(difluoromethyl)benzidine, 2,3'-bis(difluoromethyl)benzidine, 2,2'-bis(difluoromethoxy)benzidine, 3,3'-bis(difluoromethoxy)benzidine, and 2,3'-bis(difluoromethoxy)benzidine.

[0071] In the polyimide of type 1) described above, the amount of the benzidine derivative relative to the total amount of the diamine component is preferably 10 mol% or more, more preferably 30 mol% or more, even more preferably 50 mol% or more, and may be 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more, or even 100 mol%.

[0072] Specific examples of diamines having a fluorene structure include 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(3-amino-4-hydroxyphenyl)fluorene, and 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene. Among these, 9,9-bis(4-aminophenyl)fluorene is particularly preferred.

[0073] Specific examples of tetracarboxylic dianhydrides having a fluorene structure include 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride, spiro[11H-difluoro[3,4-b:3',4'-i]xanthene-11,9'-fluorene]-1,3,7,9-tetraone, 5,5'-[9H-fluorene-9-ylidenebis(2-methyl-4,1-phenylene)]bis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), 5,5'-spiro[9H-fluorene-9,9'-[9H]xanthene]-3',6'-diylbis(1,3-dihydro-1,3-dioxo-5-isobenzofurancarboxylate), and the like. Among these, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride is particularly preferred.

[0074] In the polyimide of type 2) above (excluding those corresponding to type 1) above), it is preferable that the amount of diamine having a fluorene structure relative to the total amount of diamine components is 30 mol% or more, and / or the amount of tetracarboxylic dianhydride having a fluorene structure relative to the total amount of acid dianhydride components is 30 mol% or more. From the viewpoint of improving solubility in the solvent, it is particularly preferable that the amount of diamine having a fluorene structure relative to the total amount of diamine components is 30 mol% or more, and the amount of tetracarboxylic dianhydride having a fluorene structure relative to the total amount of acid dianhydride components is 30 mol% or more.

[0075] The amount of diamine having a fluorene structure relative to the total amount of diamine components may be 50 mol% or more, 70 mol% or more, or 90 mol% or more, and may also be 100 mol%. The amount of tetracarboxylic dianhydride having a fluorene structure relative to the total amount of acid dianhydride components may be 50 mol% or more, 70 mol% or more, or 90 mol% or more, and may also be 100 mol%.

[0076] Preferred examples of diamines other than those mentioned above (diamines used in combination with the above diamines) include diaminodiphenylsulfones such as 3,3'-diaminodiphenylsulfone and 4,4'-diaminodiphenylsulfone; and alicyclic diamines such as isophoronediamine and 1,4-diaminocyclohexane.

[0077] Preferred examples of tetracarboxylic dianhydrides other than those mentioned above (tetracarboxylic dianhydrides used in combination with the above tetracarboxylic dianhydrides) include: tetracarboxylic dianhydrides having a bisphenol derivative structure such as 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic acid anhydride; bis(trimellitic anhydride) esters such as 1,4-phenylenebis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate) and 2,2',3,3',5,5'-hexamethylbiphenyl-4,4'-diylbis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate); 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetra Examples include alicyclic tetracarboxylic acid dianhydrides such as carboxylic acid dianhydrides, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, and 1,1'-bicyclohexane-3,3',4,4'tetracarboxylic acid-3,4:3',4'-dianhydride, tetracarboxylic acid dianhydrides having ether links such as 3,4'-oxydiphthalic acid anhydride and 4,4'-oxydiphthalic acid anhydride; and tetracarboxylic acid dianhydrides having perfluoroalkyl groups such as 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride and 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}-1,1,1,3,3,3-hexafluoropropane dianhydride.

[0078] In the polyimide of type 2) described above, if the diamine component contains a diamine having a fluorene structure and the acid dianhydride component does not contain a tetracarboxylic dianhydride having a fluorene structure, it is preferable that the acid dianhydride component contains one or more from the above-mentioned tetracarboxylic dianhydride having a bisphenol derivative structure, bis(trimellitic anhydride) ester, alicyclic tetracarboxylic dianhydride, and tetracarboxylic dianhydride having an ether linkage.

[0079] The polyimide may contain diamines other than those listed above as a diamine component, as long as it exhibits solubility in the solvent and compatibility with other resins, and may also contain tetracarboxylic dianhydrides other than those listed above as an acid dianhydride component.

[0080] (Polybasic Acids) As described above, by using dicarboxylic acids and / or tricarboxylic anhydrides as polybasic acid components in addition to the diamine and acid dianhydride components, polyamide imides containing a dicarboxylic acid-derived structure represented by general formula (VIa) and / or a tricarboxylic anhydride-derived structure represented by general formula (VIIa) can be obtained.

[0081] Examples of dicarboxylic acids include aliphatic dicarboxylic acids such as adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2-chloroterephthalic acid, 2-methylterephthalic acid, 5-methylisophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-oxybisbenzoic acid, 4,4'-biphenyldicarboxylic acid, and 2-fluoroterephthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-hexahydroterephthalic acid, hexahydroisophthalic acid, 1,3-cyclopentanedicarboxylic acid, and bi(cyclohexyl)-4,4'-dicarboxylic acid; and heterocyclic dicarboxylic acids such as 2,5-thiophenedicarboxylic acid and 2,5-franzicarboxylic acid.

[0082] Examples of tricarboxylic acid anhydrides include trimellitic anhydride, 2-fluorotrimellitic anhydride, 5-fluorotrimellitic anhydride, 6-fluorotrimellitic anhydride, 2,5-difluorotrimellitic anhydride, 2,6-difluorotrimellitic anhydride, 5,6-difluorotrimellitic anhydride, and 2,5,6-trifluorotrimellitic anhydride, as well as other trimellitic anhydride derivatives.

[0083] From the viewpoint of solubility, preferred polybasic acids are aromatic dicarboxylic acids, alicyclic dicarboxylic acids, and trimellitic anhydride, with aromatic dicarboxylic acids being particularly preferred. Among aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, 4,4'-biphenyldicarboxylic acid, and 4,4'-oxybisbenzoic acid are preferred, with terephthalic acid and isophthalic acid being particularly preferred, and terephthalic acid being particularly preferred. Among alicyclic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid and bi(cyclohexyl)-4,4'-dicarboxylic acid are preferred, with 1,4-cyclohexanedicarboxylic acid being particularly preferred.

[0084] In the preparation of polyamide-imides and polyamic acids as precursors, polybasic acid derivatives such as dicarboxylic acid dichlorides, dicarboxylic acid esters, dicarboxylic acid anhydrides, and tricarboxylic acid anhydride chlorides may be used instead of polybasic acids.

[0085] Preferably, the polyamide-imide contains 90 to 110 mole parts of the total structure derived from a tetracarboxylic dianhydride represented by general formula (IVa), a dicarboxylic acid represented by general formula (VIa), and a tricarboxylic acid anhydride represented by general formula (VIIa), with respect to 100 mole parts of the diamine-derived structure represented by general formula (Va).

[0086] The ratio of the structure of general formula (VIa) to the total of the structure of general formula (VIIa) to the total of the structure of general formula (VIIa) is preferably 1 to 99 mol%, and may be 5 mol% or more, 10 mol% or more, 20 mol% or more, 30 mol% or more, 40 mol% or more, or 50 mol% or more, and may be 80 mol% or less, 75 mol% or less, 70 mol% or less, 65 mol% or less, or 60 mol% or less.

[0087] <Other Resins> As mentioned above, other resins are preferably solvent-soluble and compatible with polyimide. Solvent solubility is defined as being soluble at a concentration of 1% by weight or more at 23°C in one or more solvents selected from amide solvents such as N,N-dimethylformamide (DMF), N-methylpyrrolidone, and N,N-dimethylacetamide, alkyl halide solvents such as methylene chloride, and cyclic ether solvents such as dioxolane. Solvent-soluble resins are preferably soluble at a concentration of 1% by weight or more in both DMF and methylene chloride, and more preferably soluble at a concentration of 5% by weight or more.

[0088] Other resins include acrylic resins, polycarbonates, polyesters, polyarylates, polyamides, polyethers, cellulose resins, silicone resins, and cyclic polyolefins. Among these, acrylic resins, polyester resins, polycarbonate resins, and polyarylate resins are preferred as alternative resins due to their high transparency and compatibility with polyimide. Acrylic resins, polyesters, and polycarbonates are preferred, with acrylic resins and polyesters being particularly preferred, because mixing them with polyimide has a high effect in lowering the glass transition temperature of the mixed resin film.

[0089] As mentioned above, the glass transition temperature (Tg) of other resins is the same as the glass transition temperature (Tg) of polyimide. ＰＩ It is preferable that the Tg of other resins is 50°C or more lower than (Tg). ＰＩ (Tg) °C or lower is more preferable. ＰＩ (Tg) 70°C or lower is more preferable.ＰＩ more preferably (Tg - 80)°C or lower ＰＩ may be (Tg - 90)°C or lower, or (Tg ＰＩ - 100)°C or lower.

[0090] The Tg of the other resin may be room temperature or higher, 60°C or higher, 80°C or higher, or 100°C or higher. The Tg of the other resin is preferably 220°C or lower, more preferably 200°C or lower, and may be 180°C or lower, 160°C or lower, or 150°C or lower.

[0091] (Acrylic resin) Examples of the acrylic resin include poly(meth)acrylic acid esters such as polymethyl methacrylate, methyl methacrylate-(meth)acrylic acid copolymers, methyl methacrylate-(meth)acrylic acid ester copolymers, methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers, and methyl (meth)acrylate-styrene copolymers. The stereoregularity of the polymer is not particularly limited, and any of isotactic, syndiotactic, and atactic structures may be used.

[0092] From the viewpoints of transparency, compatibility with polyimide, and mechanical strength of the film, the acrylic resin is preferably one having methyl methacrylate as a main structural unit. The amount of methyl methacrylate relative to the total amount of monomer components in the acrylic resin is preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The acrylic resin may be a homopolymer of methyl methacrylate.

[0093] The acrylic resin may have imide structures or lactone ring structures introduced into it. Such modified polymers are preferably acrylic polymers in which methyl methacrylate content is within the above range, and imide structures or lactone ring structures are introduced into them. That is, in acrylic resins modified by the introduction of imide structures or lactone ring structures, the total amount of methyl methacrylate and the modified methyl methacrylate structure is preferably 60% by weight or more, and may be 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The modified polymer may be a homopolymer of methyl methacrylate in which imide structures or lactone ring structures are introduced.

[0094] Acrylic resins having a glutarimide structure can be obtained, for example, by heating and melting polymethyl methacrylate resin and treating it with an imidizing agent, as described in Japanese Patent Application Publication No. 2010-261025. Commercially available products such as EVONIK's "PLEXIMID TT70" and "PLEXIMID 8805" can also be used as imide-modified polymethyl methacrylate.

[0095] From the viewpoint of heat resistance, the glass transition temperature of the acrylic resin is preferably 100°C or higher, more preferably 110°C or higher, and may be 115°C or higher or 120°C or higher.

[0096] From the viewpoint of solubility in organic solvents, compatibility with the above-mentioned polyimide, and film strength, the weight-average molecular weight (polystyrene equivalent) of the acrylic resin is preferably 5,000 to 5,000,000, more preferably 10,000 to 2,000,000, and may also be 30,000 to 1,000,000 or 50,000 to 500,000.

[0097] (Polyester) Polyester is a condensate of dicarboxylic acid and diol, and has a structure derived from both dicarboxylic acid and diol. The dicarboxylic acid and diol components of polyester are not particularly limited, but amorphous polyester is preferred from the viewpoint of solubility in organic solvents. Polyethylene terephthalate (PET), a typical polyester, is a condensate of ethylene glycol and terephthalic acid, and has high crystallinity and low solubility in organic solvents, whereas amorphous polyester is soluble in organic solvents and shows high compatibility with the above-mentioned polyimides.

[0098] Examples of amorphous polyesters include those containing one or more diol components selected from the group consisting of diols having a chain-like alkylene group with 3 or more carbon atoms, diols having a chain-like alkenylene group with 3 or more carbon atoms that may be branched, polyalkylene glycols, and diols having a cyclic structure.

[0099] Examples of diols having a chain-like alkylene structure with 3 or more carbon atoms, which may be branched, include propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, and 1,6-hexanediol. Among these, diols having a chain-like alkylene structure with 5 or more carbon atoms are preferred, and among these, diols having branched alkylene groups such as neopentyl glycol are preferred. Examples of diols having a chain-like alkenylene group with 3 or more carbon atoms, which may be branched, include 2-butene-1,4-diol.

[0100] Examples of polyalkylene glycols include diethylene glycol, triethylene glycol, dipropylene glycol, and polytetramethylene ether glycol.

[0101] Examples of diols having a cyclic structure include diols having a cycloalkylene structure such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol; diols having a cyclic ether structure such as isosorbide; diols having a fluorene structure; and diols having a bisphenol derivative structure.

[0102] Among these, butanediol, neopentyl glycol, polytetramethylene ether glycol, diols having a fluorene structure, and diols having a bisphenol derivative structure are preferred from the viewpoint of polyester solubility and compatibility with polyimide.

[0103] Specific examples of diols having a fluorene structure include 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis[4-(2-hydroxypropoxy)phenyl]fluorene, and 9,9-bis[4-(2-hydroxyethoxy)-3-phenylphenyl]fluorene. Specific examples of diols having a bisphenol derivative structure include ethylene oxide adducts of bisphenol A, ethylene oxide adducts of bisphenol S, and ethylene oxide adducts of bisphenol Z.

[0104] From the viewpoint of ensuring the mechanical strength of the film, the weight-average molecular weight of the polyester is preferably greater than 10,000, more preferably 15,000 or more, even more preferably 20,000 or more, and may be 30,000 or more. From the viewpoint of ensuring compatibility with polyimide and moldability of the film, the weight-average molecular weight of the polyester is preferably 200,000 or less, more preferably 150,000 or less, even more preferably 100,000 or less, and may be 80,000 or less.

[0105] From the viewpoint of heat resistance and moldability of the film, the glass transition temperature of polyester is preferably -25 to 200°C, more preferably 15 to 180°C, even more preferably 40 to 150°C, and may be around 60 to 130°C.

[0106] Examples of commercially available amorphous polyesters include "OKP4HT" and "OKP4" from Osaka Gas Chemical, the "Elitel" series from Unitika (product numbers: UE3200G, UE3210, UE3240, UE3500, UE3510, UE3600, UE3690, UE9100, UE9200, UE9800, UE9900, etc.), and the "Pylon" series from Toyobo (product numbers: 200, 240, 290, 600, etc.).

[0107] (Polycarbonate) Polycarbonate is a polymer in which monomer units are linked together by carbonate bonds (-O-(C=O)-O-). Preferred monomer units for polycarbonate are bisphenols such as bisphenol A, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C, bisphenol E, bisphenol F, bisphenol G, bisphenol M, bisphenol S, bisphenol P, bisphenol PH, bisphenol TMC, and bisphenol Z, and it is more preferable that bisphenol A is present. It is preferable that 50 mol% or more of the monomer units of polycarbonate are bisphenols.

[0108] From the viewpoint of ensuring the mechanical strength of the film, as well as compatibility with polyimide and moldability of the film, the weight-average molecular weight of the polycarbonate is preferably 5,000 to 200,000, more preferably 10,000 to 150,000, and may also be 50,000 to 100,000.

[0109] From the viewpoint of the heat resistance of the film, the glass transition temperature of polycarbonate is preferably 100°C or higher, and more preferably 120°C or higher. From the viewpoint of lowering the glass transition temperature of the mixed resin film, the glass transition temperature of polycarbonate is preferably 220°C or lower, and may be 200°C or lower, 180°C or lower, 160°C or lower, or 150°C or lower.

[0110] Commercially available polycarbonate products include Teijin's "Panlight" series (product numbers: AD-5503, K-1300Y, L-1225L, L-1225LM, L-1225Y, L-1225Z100, L-1225Z100M, L-1225ZL100, L-1250Y, L-1250Z100, LD-1000RM, LN-1010RM, LN-2250Y, LN-2250Z, LN-2520A, LN-2520HA, LN-2525Z A, LN-3000RM, LN-3050RM, LS-2250, LV-2225L, LV-2225Y, LV-2225Z, LV-2250Y, Examples include the LV-2250Z, MN-4800, MN-4800Z, MN-4805Z, etc., the "Yupilon" series from Mitsubishi Engineering Plastics (product numbers: K4100, ML200, ML300, ML400, etc.), the "APEC" series from Covestro (product numbers: 1695, 1697, 1795, 1797, 1895, 1897, 2095, 2097, 9351, 9371, etc.), and the "Yupizeta" series from Mitsubishi Gas Chemical (product numbers: PCZ-200, FPC-0820, FPC-0220, FPC-8225, FPC-2136, FPC-0330, FPC-F124, etc.).

[0111] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0112] [Preparation of Polyimide Resin] Dimethylformamide (DMF) was placed in a pressure-resistant reaction vessel and stirred under a nitrogen atmosphere. 100 moles of 2,2'-bis(trifluoromethyl)benzidine (TFMB) as the diamine, 60 moles of 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride (6FDA) as the tetracarboxylic dianhydride, and 40 moles of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) were added. The mixture was stirred under a nitrogen atmosphere for 5 to 10 hours to react and obtain a polyamic acid solution with a solid content of 18% by weight.

[0113] To 100 parts by weight of a polyamic acid solution, 5.5 parts by weight of pyridine was added as an imidization catalyst and completely dispersed. Then, 8 parts by weight of acetic anhydride was added as a dehydrating agent, and the mixture was stirred at 90°C for 3 hours to carry out imidization.

[0114] After cooling the imidized solution to room temperature, 2-propyl alcohol (hereinafter referred to as IPA) was added while stirring to precipitate polyimide. Another 150 parts by weight of IPA were added, and after stirring for about 30 minutes, the mixture was filtered by suction. The obtained solid was washed with IPA and then dried in a vacuum oven at 120°C for 12 hours to obtain polyimide resin (glass transition temperature 295°C).

[0115] [Manufacturing Example 1] <Preparation of Resin Solution> The above polyimide resin and a commercially available acrylic resin (Kuraray's "Parapet G"; a copolymer of methyl methacrylate / methyl acrylate (monomer ratio 87 / 13), glass transition temperature 109°C) were dissolved in methylene chloride in a weight ratio of polyimide resin:acrylic resin = 55:45. 5.5 parts by weight of a triazine-based ultraviolet absorber (ADEKA's "ADEKA Stab LA-31RG") and 0.02 parts by weight of a phthalocyanine-based bluing agent (Dainichi Seika's "ET 4B403") were added to 100 parts by weight of the total resin to prepare a resin solution with a solid content of 15% by weight.

[0116] <Preparation of mixed resin film> The resin solution was applied to a PET film (Toray's "Lumirror U40") as a support using a roll-to-roll coating and drying equipment. Primary drying was performed by passing the film through a drying oven set to gradually increase the temperature from 30°C to 45°C, and a resin film with a residual solvent content of 10-15% by weight was prepared.

[0117] The resin film was peeled from the support (PET film) and dried by passing it through a drying oven set to gradually increase the temperature from 90°C to 150°C (secondary drying), thereby obtaining a mixed resin film A1 with a residual solvent content of approximately 1% by weight and a thickness of 50 μm.

[0118] [Manufacturing Example 2] <Film Crushing> The mixed resin film A1 obtained in Manufacturing Example 1 was crushed into pieces smaller than 5 cm square to obtain film crushed material.

[0119] <Preparation of Resin Solution and Fabrication of Mixed Resin Film> A resin solution with a solid content of 15% by weight was prepared by dissolving the crushed mixed resin film A1 in methylene chloride. Except for using this resin solution, the process was the same as in Production Example 1, and coating, primary drying, peeling, and secondary drying were performed to obtain mixed resin film A2 (first recycling) with a thickness of 50 μm.

[0120] [Manufacturing Examples 3 and 4] In Manufacturing Example 3, a mixed resin film A3 (second recycling) with a thickness of 50 μm was obtained in the same manner as in Manufacturing Example 2, except that crushed mixed resin film A2 was used instead of crushed mixed resin film A1. In Manufacturing Example 4, a mixed resin film A4 (third recycling) with a thickness of 50 μm was obtained using crushed mixed resin film A3.

[0121] [Manufacturing Example 5] A resin solution was prepared in the same manner as in Example 1, except that the amounts of polyimide resin, acrylic resin, ultraviolet absorber, and bluing agent were changed so that the solid content concentration was 7.5% by weight. Crushed mixed resin film A1 was dissolved in this resin solution to prepare a resin solution with a solid content concentration of 15% by weight. Coating, primary drying, peeling, and secondary drying were performed in the same manner as in Manufacturing Example 1, except that this resin solution was used, to obtain a mixed resin film A5 with a thickness of 50 μm.

[0122] [Manufacturing Example 6] Film A1 obtained in Manufacturing Example 1 was heated in an air atmosphere at 263°C (corresponding to Tg + 60°C) for 30 minutes to obtain a mixed resin film A6.

[0123] [Manufacturing Example 7] A mixed resin film A7 with a thickness of 50 μm was obtained in the same manner as in Manufacturing Example 2, except that crushed mixed resin film A6 was used instead of crushed mixed resin film A1.

[0124] [Manufacturing Example 8] Without using an acrylic resin, 100 parts by weight of polyimide resin, 5.5 parts by weight of ultraviolet absorber, and 0.02 parts by weight of bluing agent were dissolved in methylene chloride to prepare a resin solution with a solid content concentration of 15% by weight. Except for using this resin solution, the process was carried out in the same manner as in Manufacturing Example 1, including coating, primary drying, peeling, and secondary drying, to obtain a polyimide film B1 with a thickness of 50 μm.

[0125] [Production Example 9] Film B1 obtained in Production Example 8 was heated in an air atmosphere at 305°C (corresponding to Tg + 10°C) for 30 minutes to obtain polyimide film B2.

[0126] [Production Example 10] Film B1 obtained in Production Example 8 was heated in an air atmosphere at 355°C (corresponding to Tg + 60°C) for 30 minutes to obtain polyimide film B3.

[0127] [Manufacturing Example 11] A polyimide film B4 with a thickness of 50 μm was obtained in the same manner as in Manufacturing Example 2, except that crushed polyimide film B2 was used instead of crushed mixed resin film A1.

[0128] [Evaluation] <Glass Transition Temperature> The glass transition temperature (Tg) of the film was determined by dynamic viscoelasticity measurement (Hitachi High-Tech "DMA7100"). A sample cut into strips 9 mm wide was fixed to the apparatus with a gripping distance of 10 mm and heated to 450°C in tensile mode under a nitrogen atmosphere at a heating rate of 3°C / min. The temperature at the maximum point of the loss tangent (tanδ) observed at a frequency of 5 Hz was defined as the glass transition temperature.

[0129] <Haze> Haze was measured using a haze meter (Suga Test Instruments, Model: HZ-V3) with a D65 light source.

[0130] <Yellowness> Using a UV-Vis spectrophotometer (JASCO "V650"), the transmittance in the wavelength range of 200 to 800 nm was measured in 1 nm increments. Based on the transmission spectra obtained, the yellowness (YI) was calculated by performing color calculations with a D65 light source and a 10-degree field of view.

[0131] <Elongation at Breaking> A 10 mm wide strip of film was cut and left to humidify at 23°C / 55% RH for one day to prepare the sample for measurement. A tensile test was performed using a tensile testing machine (Shimadzu Corporation "AUTOGRAPH AGS-X") with a grip distance of 100 mm and a tensile speed of 20.0 mm / min to measure the elongation at breaking.

[0132] <Heating Test> Films A1, A4, A5, A7, and B1, B4 were heated in an air atmosphere at glass transition temperature + 10°C (213°C for films A1, A4, A5, A7, and 305°C for films B1, B4) for 30 minutes. This heating simulates the temperature used during stretching and the highest temperature used throughout the entire film manufacturing process. The yellowness and elongation at break of the heated films were measured to confirm whether or not there were any changes in properties due to heating.

[0133] Table 1 shows the resin composition of the films produced in the manufacturing examples, the ratio of film crushed material, and the evaluation results of the films. Note that since film A6 was produced by heating film A1 at 263°C (Tg + 60°C) for 30 minutes, in Table 1, the YI and elongation at break of film A6 are listed as the YI and elongation at break of film A1 after heating at Tg + 60°C. Similarly, the YI and elongation at break of film B3, which was produced by heating film B1 at 355°C (Tg + 60°C) for 30 minutes, are listed as the YI and elongation at break of film B1 after heating at Tg + 60°C. In all of the films obtained in the above manufacturing examples, the residual solvent content was less than 5% by weight.

[0134]

[0135] Polyimide film B1, which contains only polyimide as a resin component and no other resins, showed a significant increase in YI and a significant decrease in elongation at break when heated to Tg + 10°C (film B2). This indicates that films made of polyimide resin alone have a high glass transition temperature, and therefore require high processing temperatures for stretching and other processes, making them susceptible to changes in properties due to heating during the process.

[0136] On the other hand, in mixed resin film A1 containing polyimide and acrylic resin as resin components, when heated to Tg + 10°C, which is a temperature typically reached in processes such as stretching, the YI and elongation at break were the same as before heating.

[0137] Films A2 to A4, which were produced by repeatedly recycling (re-melting of crushed resin film A1), and film A5, which was produced by mixing unused resin with crushed film A1, maintained the same good optical properties (low YI, low haze) and mechanical properties (elongation at break) as before recycling (film A1). Furthermore, films A4 and A5, like film A1, maintained the same YI and elongation at break as before heating even when heated at Tg + 10°C, and no decrease in transparency or mechanical strength was observed. These results indicate that mixed resin films containing polyimide and other resins are suitable for recycling, as they do not suffer from problems such as deterioration or variation in properties even after repeated recycling.

[0138] Film A6, produced by heating film A1 at Tg + 60°C, showed an increase in YI and a decrease in elongation at break compared to before heating. Film A7, produced by remelting the crushed material of film A6, had YI and elongation at break equivalent to film A6, indicating that the properties degraded by heating were not recovered even after remelting the film. Similar results were observed when comparing film B2 with film B4, produced by remelting its crushed material. These results indicate that when the process temperature is high (especially above 250°C), the properties of the film deteriorate, making recycling difficult.

[0139] From these results, it can be seen that by mixing a solvent-soluble resin with polyimide to control the glass transition temperature to 250°C or lower, and thereby reducing the maximum temperature of the manufacturing process, a film with less degradation and variation in properties can be obtained even when recycled.

[0140] In the above embodiment, it was shown that a mixed resin film containing a polyimide having a composition of TFMB / / 6FDA / CBDA = 100 / / 60 / 40 and an acrylic resin (Parapet G) copolymerized with methyl methacrylate / methyl acrylate = 87 / 13 did not undergo significant changes in properties even when heated to Tg + 10°C, and was recyclable.

[0141] The same applies to other combinations of polyimides and solvent-soluble resins. Specifically, it has been confirmed that mixed resin films containing polyimides and solvent-soluble resins of the following compositions (i) to (iii) show no significant change in properties even when heated to Tg + 10°C, and are therefore recyclable.

[0142] Composition (i): A combination of a polyimide containing 2,2'-bis(difluoromethoxy)benzidine (TFMOB), 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), and CBDA in a ratio of TFMOB / / BPAF / CBDA = 100 / / 70 / 30, and an acrylic resin (Parapet G) copolymerized with methyl methacrylate / methyl acrylate = 87 / 13.

[0143] Composition (ii): A combination of polyimide and polyester (Unitika's "Elitel UE3600", weight-average molecular weight 60,000, Tg: 75°C) with a composition of TFMOB / / BPAF / CBDA = 100 / / 70 / 30.

[0144] Composition (iii): A combination of polyimide containing 9,9-bis(4-aminophenyl)fluorene (BAFL) and 4,4'-(4,4'-isopropylidene diphenoxy)diphthalic anhydride (BPADA) in a ratio of BAFL / / BPADA = 100 / / 100, and polyester (Osaka Gas Chemical's "OKP4HT", weight-average molecular weight 38,000, glass transition temperature 142°C).

Claims

1. A method for producing a mixed resin film containing polyimide and a solvent-soluble resin other than polyimide, comprising: a solution preparation step of preparing a mixed resin solution containing polyimide and a solvent-soluble resin other than polyimide in a ratio of 2:98 to 98:2; a resin film formation step of casting the mixed resin solution onto a support and drying it to form a resin film; a peeling step of peeling the resin film from the support; and a drying step of drying the resin film after peeling it from the support, wherein the solution preparation step includes a step of dissolving crushed film containing the polyimide and the solvent-soluble resin in a solvent, and the glass transition temperature of the mixed resin film is 100 to 250°C.

2. A method for producing a mixed resin film according to claim 1, comprising a stretching step of stretching the obtained film after the drying step.

3. The method for producing a mixed resin film according to claim 2, wherein the heating temperature in the stretching step is 250°C or less.

4. The method for producing a mixed resin film according to any one of claims 1 to 3, wherein the drying step is performed such that the amount of residual solvent in the resin film is 10% by weight or less.

5. A method for producing a mixed resin film according to any one of claims 1 to 3, wherein the maximum temperature in each of the solution preparation step, the resin film formation step, the peeling step, and the drying step is 250°C or less.

6. A method for producing a mixed resin film according to any one of claims 1 to 3, wherein the glass transition temperature of the solvent-soluble resin is 50°C or more lower than the glass transition temperature of the polyimide.

7. A method for producing a mixed resin film according to any one of claims 1 to 3, wherein the solvent-soluble resin comprises one or more selected from the group consisting of acrylic resins, polyesters, polycarbonates, and polyarylates.

8. A method for producing a mixed resin film according to any one of claims 1 to 3, wherein the mixed resin solution contains a bluing agent.

9. The method for producing a mixed resin film according to claim 8, wherein the bluing agent is a pigment.

10. A method for producing a mixed resin film according to any one of claims 1 to 3, wherein the mixed resin solution contains an ultraviolet absorber.

11. A method for producing a mixed resin film according to any one of claims 1 to 3, wherein the mixed resin film has a yellowness of 3.0 or less and a haze of 10% or less.

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