Polyamide-imide resin film

Abstract

There is provided a polyamide-imide resin film including a polyamide-imide block copolymer having a specific structure and having a predetermined retardation.

Claims

1. A polyamide-imide resin film comprising a polyamide-imide block copolymer containing a first repeating unit represented by Chemical Formula 1, a second repeating unit represented by Chemical Formula 2, and a third repeating unit represented by Chemical Formula 3, wherein a molar ratio of the second repeating unit to the third repeating unit is 40:60 to 45:55, wherein a molar ratio between the first repeating unit the total sum of the second repeating unit and the third repeating unit is 3:7 to 4:6, wherein the polyamide-imide block copolymer has a weight average molecular weight of 10,000 to 1,000,000 g/mol, and wherein retardation (Rth) in the thickness direction with respect to the polyamide-imide resin film, as measured at a wavelength of 400 nm to 800 nm is 8000 nm or less: ##STR00015## wherein, in the Chemical Formula 1, each R .sup.1 is the same as or different from each other in each repeating unit, and each is independently a single bond, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O).sub.2—, —Si(CH.sub.3).sub.2—, —(CH.sub.2).sub.p—(wherein 1≤p≤10), —(CF.sub.2).sub.q—(wherein 1≤q≤10), —C(CH.sub.3).sub.2—, —C(CF.sub.3).sub.2—, —C(═O)NH—, or a divalent aromatic organic group having 6 to 30 carbon atoms; each R.sup.2 is the same as or different from each other in each repeating unit, and each is independently —H, —F, —Cl, —Br, —I, —CF.sub.3, —CCl.sub.3, —CBr.sub.3, —Cl.sub.3, —NO.sub.2, —CN, —COCH.sub.3, —CO.sub.2CH.sub.2C.sub.2H5, a silyl group having three aliphatic organic groups having 1 to 10 carbon atoms, an aliphatic organic group having 1 to 10 carbon atoms, or an aromatic organic group having 6 to 20 carbon atoms; n1 and m1 are each independently n integer of 0 to 3; each Y.sup.1 is the same as or different from each other in each repeating unit, and each independently includes a divalent aromatic organic group having 6 to 30 carbon atoms including at least one trifluoromethyl group (—CF.sub.3) the aromatic organic group exists alone, or two or more aromatic organic groups are bonded to each other to form a divalent condensed ring, or two or more aromatic organic groups are linked by a single bond, a fluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O).sub.2—, —Si(CH.sub.3).sub.2—, —(CH.sub.2).sub.p—(wherein 1≤p≤10), —(CF.sub.2).sub.q—(wherein 1≤q≤10), —C(CH.sub.3).sub.2—, —C(CF.sub.3).sub.2—, or —C(═O)NH—; and each E.sup.1 is independently a single bond or —NH—, ##STR00016## wherein, in the Chemical Formulae 2 and 3, Y.sup.2 and Y.sup.2′ are the same as or different from each other in each repeating unit, and each is independently a divalent aromatic organic group having 6 to 30 carbon atoms and containing at least one trifluoromethyl group (—CF.sub.3), the aromatic organic group exists alone, or two or more aromatic organic groups are bonded to each other to form a divalent condensed ring, or two or more aromatic organic groups are linked by a single bond, a fluorenylene group, —O—, —S—, —C(═O)—, —CH(OH)—, —S(═O).sub.2—, —Si(CH.sub.3).sub.2—, —(CH.sub.2).sub.p—(wherein 1≤p≤10), —(CF.sub.2).sub.q—(wherein 1≤q≤10), —C(CH.sub.3).sub.2—, —C(CF.sub.3).sub.2—, or —C(═O)NH—; and E.sup.2, E.sup.2′, E.sup.3, E.sup.3′, E.sup.4, and E.sup.4′ are each independently a single bond or —NH—.

2. The polyamide-imide resin film according to claim 1, wherein the retardation (Rth) in the thickness direction with respect to the polyamide-imide resin film, as measured at a wavelength of 400 nm to 800 nm is 4500 to 7500 nm, and the polyamide-imide resin film is anisotropic.

3. The polyimide-imide resin film according to claim 1, wherein the first repeating unit includes a repeating unit represented by Chemical Formula 1-1: ##STR00017## wherein, in Chemical Formula. 1-1, R.sup.1, R.sup.2, n1, and m1 are as defined in Chemical Formula 1.

4. The polyamide-imide resin film according to claim 1, wherein the second repeating unit includes a repeating unit represented by Chemical Formula 2-1: ##STR00018##

5. The polyimide-imide resin film according to claim 1, wherein the third repeating unit includes a repeating unit represented ley Chemical Formula 3-1: ##STR00019##

6. The polyamide-imide resin film according to claim 1, wherein the polyamide-imide: resin film has a thickness of 10 to 100 μm.

7. The polyamide-imide resin film according to claim 1, wherein a stretching ratio in the transverse direction (TD direction) of the polyamide-imide resin film is 1% to 10%.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) Hereinafter, preferred examples are presented to facilitate understanding of the present invention. However, the following examples are given for illustrative purposes only, and the scope of the present invention is not intended to be limited to or by these examples.

Examples 1 to 5 and Comparative Example 1: Preparation of Polyamide-Imide Copolymer

Example 1

(2) 2,2′-bis(trifluoromethyl)benzidine, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, and dimethylacetamide were placed in a 500 mL round flask (reactor) equipped with a Dean-Stark apparatus and a condenser, and the reaction was initiated at room temperature. The reaction mixture was stirred in an ice bath at 0° C. for 4 hours under a nitrogen atmosphere.

(3) After 4 hours, the reaction product was taken out and raised to room temperature, and 2,2′-bis(trifluoromethyl)benzidine, isophthaloyl dichloride (IPC), 4,4′-biphenyldicarbonyl chloride (BPC), and dimethylacetamide were added thereto, and the reaction was initiated at room temperature (25° C.±3° C.) under a nitrogen atmosphere.

(4) After the formation of a polyamic acid polymer by the reaction for 4 hours, acetic anhydride and pyridine were added to the reaction mixture, and the mixture was stirred in an oil bath at 40° C. for 15 hours to carry out a chemical imidization reaction.

(5) After completion of the reaction, the reaction product was precipitated with water and ethanol (1:1 (v/v)) to obtain a polyimide-imide block copolymer A-1 having a first repeating unit, a second repeating unit, and a third repeating unit of the following structure (weight average molecular weight: about 200,000 g/mol).

(6) The obtained copolymer had a molar ratio ({circle around (1)}) of the first repeating unit to the total sum of the second repeating unit and third repeating unit of 50:50, and a molar ratio ({circle around (2)}) of the second repeating unit to the third repeating unit of 20:80.

(7) [First Repeating Unit]—Imide Repeating Unit

(8) ##STR00011##

(9) [Second Repeating Unit]—Amide Repeating Unit (Derived from IPC)

(10) ##STR00012##

(11) [Third Repeating Unit]—Amide Repeating Unit (Derived from BPC)

(12) ##STR00013##

Examples 2 to 5

(13) A polyamide-imide copolymer was prepared by adjusting the addition ratios of the respective monomers so as to satisfy the molar ratios ({circle around (1)} and {circle around (2)}) described in the following Table 1 in Example 1.

Comparative Example 1

(14) A copolymer including the following 2-2 repeating unit instead of the second repeating unit was prepared by using terephthaloyl dichloride (TPC) instead of isophthaloyl dichloride in Example 5.

(15) In the case of such copolymer, gelation occurred, and thus the weight average molecular weight was not confirmed.

(16) [2-2 Repeating Unit]—Amide Repeating Unit (Derived from TPC)

(17) ##STR00014##

(18) The compositions of the monomers used in Examples 1 to 5 and Comparative Example 1 and the weight average molecular weights of the produced copolymers are shown in Table 1 below.

(19) TABLE-US-00001 TABLE 1 Amide repeating Weight average unit ratio - {circle around (2)} molecular weight of Category Imide:Amide -{circle around (1)} kind ratio copolymer Example 1 50:50 IPC:BPC 20:80 520,000 Example 2 50:50 IPC:BPC 30:70 490,000 Example 3 40:60 IPC:BPC 20:80 420,000 Example 4 40:60 IPC:BPC 30:70 360,000 Example 5 40:60 IPC:BPC 40:60 270,000 Comparative 40:60 BPC:TPC 40:60 Gelation Example 1 * Imide: Amide {circle around (1)} represents a molar ratio of the first repeating unit to the total sum of the second repeating unit and the third repeating unit. * Amide repeating unit ratio {circle around (2)} represents a molar ratio of the second repeating unit (or the 2-2 repeating unit) to the third repeating unit (or the 2-2 repeating unit).

Examples 6 to 9 and Reference Example 1

(20) The polyamide-imide copolymer obtained in Example 5 was dissolved in dimethylacetamide to prepare an approximate 10 wt % solution.

(21) The solution was casted on a glass plate through a bar coater. At this time, the drying temperature was controlled sequentially to 80° C. and then 140° C.

(22) As a result, polyamide-imide films of the examples and comparative examples having a thickness of 50 μm were prepared.

(23) After the polyamide-imide film was subjected to the primary heat treatment at the temperature and time described in Table 2 below, and the stretching was carried out by applying the stretching temperature, stretching speed, and stretching ratio shown in Table 2 below, annealing was carried out to provide a stretched polyamide-imide resin film (Examples 6 to 9/Reference Example 1 was not subjected to primary heat treatment and stretching).

(24) TABLE-US-00002 TABLE 2 Primary heat Stretching Conditions treatment Stretching ratio Stretching for annealing Category temperature/time temperature (MD*TD) speed in nitrogen gas Example 6 175° C./60 s  .sup.  175° C. 1.05*1.05 0.1%/s Example 7 200/60 s 200 1.05*1.05 0.1%/s 250° C./60 s Example 8 200/60 s 200 1.05*1.05 0.1%/s 250° C./60 s Example 9 250/60 s 250 1.05*1.05 0.1%/s 250° C./60 s Reference Example 1

Experimental Example

(25) The physical properties of the polymer films prepared in the examples and comparative examples were evaluated by the following methods, and the results are shown in Table 2 below.

(26) 1. Mechanical Properties

(27) The elastic modulus (EM, GPa), the ultimate tensile strength (TS, MPa), and the tensile elongation (TE, %) of a film having a thickness of 30±2 μm were measured according to ASTM D 882 using a universal testing machine.

(28) 2. Retardation (Rth) in Thickness Direction

(29) The retardation (Rth) in the thickness direction was determined by directly using the polymer film (a length of 76 mm, a width of 52 mm, and a thickness of 13 μm) prepared in each of the examples and comparative examples as a measuring sample, using a measuring apparatus manufactured by AXOMETRICS, Inc. under the trade name of “AxoScan”, inputting a value of a refractive index (the refractive index at a wavelength of 589 nm of the film obtained by the measurement of the refractive index described above) of each polymer film into the measuring apparatus, measuring the thickness-direction retardation by using light at a wavelength of 590 nm under conditions of a temperature of 25° C. and humidity of 40%; and then converting the measured value of the thickness-direction retardation thus obtained (the value was measured according to the automatic measurement of the measuring apparatus) into a retardation value per 10 μm of the thickness of the film.

(30) 3. Measurement of Folding Endurance (MIT)

(31) The folding endurance was measured using an MIT Folding Endurance Tester (manufactured by Cometech).

(32) Specifically, the produced film was cut into test pieces of a width 1 cm×length 7 cm and then repeatedly bent at an angle of 135° according to ISO 5626, a radius of curvature of 0.8 mm, a load of 250 g, and a speed of 175 rpm, and the number of cycles required for breakage was measured.

(33) The measurement was performed by dividing each of the TD direction in which stretching was performed and the MD direction in which stretching was not performed.

(34) TABLE-US-00003 TABLE 3 Thickness- Elastic Tensile Tensile Folding direction modulus strength elongation endurance retardation Category (GPa) (MPa) (%) (cycle) (Rth) Example 6 4.26 161.76 23.83 4227 4771 Example 7 4.08 145.91 26.91 5627 5093 Example 8 4.41 156.58 23.59 6783 5100 Example 9 4.70 172.77 16.41 7500 6517 Reference 4.58 167.76 15.33 2274 4065 Example 1

(35) It was confirmed that the polyamide-imide resin films obtained in Examples 6 to 9 had a low yellowness index and haze and thus had colorless and transparent appearance characteristics, and further had excellent mechanical properties, particularly significantly improved folding endurance, while having a feature that the retardation (Rth) in the thickness direction measured at 400 nm to 800 nm was 4500 to 7500 nm as can be seen from Table 3.