Method for Producing Long Optical Film Containing Polyimide-Based Resin

Abstract

The present invention relates to a method for producing a long optical film, the method comprising a step for preparing a varnish by dissolving a polyimide-based resin in a solvent, wherein the polyimide-based resin contains a constitutional unit derived from an aliphatic diamine, and a moisture absorption speed per unit area of the solvent is 25% by mass/h.Math.m.sup.2 or less as determined by a Karl Fischer method.

Claims

1. A method for producing a long optical film, the method comprising a step of preparing a varnish by dissolving a polyimide-based resin in a solvent, wherein the polyimide-based resin comprises a constitutional unit derived from an aliphatic diamine, and a moisture absorption speed per unit area of the solvent is 25% by mass/h.Math.m.sup.2 or less determined by a Karl Fischer method.

2. The method according to claim 1, wherein the solvent comprises at least one selected from a group consisting of cyclohexanone and cyclopentanone.

3. The method according to claim 1, wherein the long optical film has a glass transition temperature Tg of higher than 180° C.

4. The method according to claim 1, wherein the long optical film has an optical transmittance at 350 nm of 10% or less.

5. The method according to claim 1, wherein the long optical film has an optical transmittance at 500 nm of 90% or more.

6. The method according to claim 1, wherein the long optical film has a tensile strength of more than 86 MPa.

7. A long optical film comprising a polyimide-based resin, wherein the polyimide-based resin comprises a constitutional unit derived from an aliphatic diamine, and the long optical film has a maximum height roughness Rz defined by JIS B-0601: 2013 of 2.0 μm or less on at least one surface thereof.

8. A long optical film comprising a polyimide-based resin, wherein the polyimide-based resin comprises a constitutional unit derived from an aliphatic diamine, and the long optical film has a maximum height roughness Rz defined by JIS B-0601: 2013 of 2.0 μm or less on a surface which has not been in contact with a substrate of the long optical film.

9. The long optical film according to claim 7, wherein the long optical film has a thickness retardation Rth of 100 nm or less.

10. The long optical film according to claim 7, wherein the long optical film has a solvent content of 3.0% by mass or less based on a mass of the long optical film.

11. The long optical film according to claim 7, wherein the polyimide-based resin comprises a constitutional unit represented by Formula (1) ##STR00011## wherein X represents a divalent aliphatic group, Y represents a tetravalent organic group, and * represents a bonding hand.

12. The long optical film according to claim 11, wherein the constitutional unit represented by Formula (1) comprises, as Y, a structure represented by Formula (2) ##STR00012## wherein R.sup.2 to R.sup.7 each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, the hydrogen atoms contained in R.sup.2 to R.sup.7 may be each independently substituted by a halogen atom, V represents a single bond, —O—, —CH.sub.2—, —CH.sub.2—CH.sub.2—, —CH(CH.sub.3)—, —C(CH.sub.3).sub.2—, —C(CF.sub.3).sub.2—, —SO.sub.2—, —S—, —CO—, or —N(R.sup.8)—, R.sup.8 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which is optionally substituted with a halogen atom, and * represents a bonding hand.

13. The long optical film according to claim 11, wherein the polyimide-based resin contains a fluorine atom.

Description

EXAMPLES

[0099] Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to the following Examples. First, methods of measurement and evaluation will be described.

<Moisture Absorption Speed Per Unit Area of Solvent>

[0100] A solvent (40 mL) was put in a plastic container with a volume of 100 mL (bottom diameter: 45 mm, opening diameter: 50 mm) and held for 30 minutes or 60 minutes in an environment with a temperature of 22.0° C. and a relative humidity of 30% RH. After holding for a prescribed time, the entire solvent was stirred with a spatula for 1 to 2 seconds, and the stirred solvent was transferred to a glass bottle having a volume of 10 mL to fill the glass bottle, and the glass bottle was sealed to afford a solvent sample. Under the same atmosphere as described above, a moisture absorption speed per one hour (% by mass/h) and a moisture absorption speed per one minute Vs (% by mass/min) were determined from water amounts at 30 minutes and 60 minutes determined by a volumetric titration method using a vaporizable Karl Fischer moisture titrator (“831”, “832” (manufactured by Metrohm Corporation)). The value obtained by dividing the moisture absorption speed per hour by the unit area of the opening of the plastic container was defined as the moisture absorption speed per unit area.

<Glass Transition Temperature Tg>

[0101] The glass transition temperature Tg was measured using DSC Q200 manufactured by TA Instruments under the conditions of a measurement sample amount: 5 mg, a temperature range: from room temperature to 400° C., and a temperature raising rate: 10° C./min.

<Optical Transmittance>

[0102] As the optical transmittance, the transmittance with respect to light of 200 to 800 nm was measured using a UV-Visible/NIR spectrophotometer V-670 manufactured by JASCO Corporation.

<Tensile Strength>

[0103] The tensile strength was measured using Autograph AG-IS manufactured by Shimadzu Corporation. A strip-shaped optical film substrate having a width of 10 mm and a length of 100 mm was prepared as a test piece from a long optical film. A tensile test was carried out under the conditions of a chuck distance of 50 mm and a tensile speed of 20 mm/min, and the tensile strength was measured.

<Thickness Retardation Rth>

[0104] The thickness retardation Rth was measured using a retardation measuring device (trade name: KOBRA) manufactured by Oji Scientific Instruments Co., Ltd. Specifically, the thickness retardation Rth is calculated by the following equation, where the refractive index in one direction in the film plane is Nx, the refractive index in a direction orthogonal to Nx is Ny, the refractive index in the thickness direction of the film is Nz, and the thickness of the film is d (nm). Nx is a refractive index in the slow axis direction, Ny is a refractive index in the fast axis direction, and these satisfy Nx>Ny.

Rth={(Nx+Ny)/2−Nz}×d(nm)

<Solvent Content>

(Thermogravimetry-Differential Thermal Analysis (TG-DTA) Measurement)

[0105] The residual solvent amount of each of the long optical films obtained in Examples and Comparative Examples was measured using a TG-DTA measuring apparatus (“TG/DTA 6300”, manufactured by Hitachi High-Tech Science Corporation).

[0106] About 20 mg of sample was obtained from the optical film. The sample was heated from room temperature to 120° C. at a temperature raising rate of 10° C./min and held at 120° C. for 5 minutes, and then the mass change of the sample was measured while raising the temperature (heating) to 400° C. at a temperature raising rate of 10° C./min.

[0107] From the results of TG-DTA measurement, the mass loss ratio S (% by mass) from 120° C. to 250° C. was calculated according to the following Equation (1).

S(% by mass)=100−(W1/W0)×100  (1)

[In Equation (1), W0 is the mass of the sample after holding at 120° C. for 5 minutes, and W1 is the mass of the sample at 250° C.].

[0108] The mass loss ratio S calculated was defined as a residual solvent amount S (% by mass) in the long optical film.

<Thickness>

[0109] The thickness of the long optical film was measured at n=3 using a contact type digital thickness meter (manufactured by Mitutoyo Corporation).

<Viscosity>

[0110] The viscosity of a varnish was measured using an E-type viscometer (“HBDV-II+P CP” manufactured by Brookfield) was used. Using 0.6 cc of the varnish as a sample, the viscosity was measured under the conditions of 25° C. and a rotation speed of 3 rpm.

<Maximum Height Roughness Rz>

[0111] A laser displacement meter CL-3050 and a sensor head CL-PT010 manufactured by KEYENCE CORPORATION were used. The measurement was carried out by randomly scanning the front and back surfaces of a 10 cm×10 cm optical film with a measurement width of 1 cm. Five points were measured for each surface (10 times in total), and the average value of the measurements was defined as Rz.

<Appearance Evaluation>

[0112] The appearance such as the surface irregularities of a long optical film was observed under a fluorescent lamp and judged according to the following criteria.

(Evaluation Criteria)

[0113] ∘ . . . No appearance abnormality such as surface irregularities is observed.
Δ . . . Appearance abnormality such as surface irregularities is slightly observed.
x . . . An appearance abnormality such as surface irregularities is clearly observed.

Synthesis Example 1: Preparation of Polyimide-Based Resin

[0114] A polyimide-based resin (6FDA-DAB) composed of a constitutional unit derived from 6FDA and a constitutional unit derived from 1,4-DAB was produced by the method described in WO 2019/156717 A.

[Production of Long Optical Film]

Example 1

[0115] The polyimide obtained in Synthesis Example 1 was dissolved in cyclohexanone (CH: moisture absorption speed per unit area: 19% by mass/h.Math.m.sup.2) such that the solid content concentration was 12% by mass. 2 phr of Sumisorb 340 was added as a UVA to prepare a polyimide-based varnish (varnish viscosity: 26 Pa s). Next, the polyimide-based varnish was applied in a width of 50 cm and a length of 10 m to a PET roll substrate using a coater facility installed in a thermostatic chamber (temperature: 22° C., humidity: 50% RH), the PET substrate was conveyed into a drying furnace of the coater facility, and the coating film was heated at 30° C. for 2 minutes and then at 140° C. for 8 minutes. Thereafter, the dried polyimide film was peeled off from the PET substrate, and further heated at 220° C. for 10 minutes under the condition of a draw ratio of 1.0 using a small tenter facility, thereby affording a long polyimide-based film having a thickness of 25 μm and the aforementioned dimensions. The results are shown in Table 1.

Comparative Example 1

[0116] A polyimide-based film having a thickness of 25 μm was produced in the same manner as in Example 1 except that γ-butyrolactone (GBL: moisture absorption speed per unit area: 28% by mass/h.Math.m.sup.2) was used as a solvent in varnish production. The results are shown in Table 1.

Comparative Example 2

[0117] A polyimide-based film having a thickness of 25 μm was produced in the same manner as in Example 1 except that dimethylacetamide (DMAc: moisture absorption speed per unit area: 40% by mass/h.Math.m.sup.2) was used as a solvent in varnish production. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Solvent (moisture Optical Solvent absorption transmittance Tensile content speed [% by Tg [%] strength Rth [% by Rz Appearance mass/h .Math. m.sup.2]) [° C.] 350 nm 500 nm [MPa] [nm] mass] [μm] characteristics Example 1 CH(19) 181 1.1 90.5 90 55.6 1.2  0.3 ◯ Comparative GBL(28) 181 1.2 90.3 89 53.5 1.2 25   X Example 1 Comparative DMAc(40) 180 1.4 90.4 90 54.0 1.3 19   Δ Example 2

[0118] As shown in Table 1, it was confirmed that the long optical films produced by the production methods of Examples had superior smoothness and good appearance because the Rz values of the surfaces of the films were small. On the other hand, the long optical films produced by the production methods of Comparative Examples were found to have irregularities in the appearance of the films and have poor appearance.

INDUSTRIAL APPLICABILITY

[0119] The long optical film produced by the method of the present invention has high smoothness and good appearance. Therefore, the long optical film can be suitably used for various applications, for example, a substrate for a touch sensor, a material for a flexible display device, a protective film, a film for bezel printing, a semiconductor application, a speaker diaphragm, and an IR cut filter.