METHOD FOR MANUFACTURING POLYIMIDE-BASED FILM AND POLYIMIDE-BASED FILM MANUFACTURE

Abstract

The present invention relates to a method for manufacturing a polyimide-based film and a polyimide-based film manufactured thereby and, particularly, to a method for manufacturing a polyimide-based film and a polyimide-based film manufactured thereby, wherein the polyimide-based film is useful as a cover substrate for a flexible electronic device since flexure characteristics thereof, represented by yield elongation, are excellent.

Claims

1. A polyimide-based film manufactured by a roll-to-roll manner, the roll-to-roll manner comprising: conducting first heat treatment (S1) on a polyimide-based film obtained as a gel state formed by being cast on a support while elongating the polyimide-based film at an elongation percentage of more than 100% and less than 135% in a machine direction (MD) and shrinking the polyimide-based film at a shrinkage percentage of more than 75% and less than 100% in a transverse direction (TD); and conducting second heat treatment (S2) on the first heat-treated polyimide-based film while further elongating the polyimide-based film in the machine direction (MD) at a tension not less than 30 N/mm.sup.2 and less than 160 N/mm.sup.2, wherein a maximum heating temperature during the first heat treatment is 250° C. to 330° C., and the second heat treatment is performed for 200 seconds or longer at a temperature within −10° C. to +30° C. of the maximum heating temperature reached during the first heat treatment.

2. The polyimide-based film according to claim 1, wherein, in step (S1), the elongation percentage in the machine direction is 105% to 130%.

3. The polyimide-based film according to claim 1, wherein, in step (S1), the elongation percentage in the machine direction is 115% to 130%.

4. The polyimide-based film according to claim 1, wherein, in step (S1), the shrinkage percentage in the traverse direction is 80% to 100%.

5. The polyimide-based film according to claim 4, wherein, in step (S1), the shrinkage percentage in the transverse direction is 80% to 95%.

6. The polyimide-based film according to claim 1, wherein, in step (S2), the time for second heat treatment is not less than 200 seconds and less than 1,500 seconds.

7. The polyimide-based film according to claim 1, wherein, in step (S2), the tension is 30 N/mm.sup.2 to 150 N/mm.sup.2.

8. The polyimide-based film according to claim 1, wherein the polyimide-based film has a yield strain in a uniaxial direction of 3% or more.

9. The polyimide-based film according to claim 1, wherein the polyimide-based film has a pencil hardness of 1H or more based on ASTM D3363 measurement, and a yellowness of 5.0 or less and a light transmittance of 85% or more at 550 nm based on measurement with a CM-3700D produced by Konica Minolta, Inc.

10. A polyimide-based film having a yield strain in a uniaxial direction of 3% or more, a pencil hardness of 1H or more based on ASTM D3363 measurement, and a yellowness of 5.0 or less and a light transmittance of 85% or more at 550 nm based on measurement with a CM-3700D produced by Konica Minolta, Inc.

Description

EXAMPLE

[0061] Hereinafter, the present disclosure will be described in more detail with reference to Examples. The examples are provided only for better understanding of the present disclosure, and should not be construed as limiting the scope of the present disclosure.

Preparation Example 1. Preparation of Polyimide-Based Resin

[0062] 832 g of N,N-dimethylacetamide (DMAc) was charged in a 1 L reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller and a cooler, as a reactor, while passing nitrogen through the reactor, the temperature of the reactor was adjusted to 25° C., 6.4646 g (0.2 mol) of bistrifluoromethyl benzidine (TFDB) was dissolved therein, and the solution was maintained at 25° C. 31.09 g (0.07 mol) of 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 8.83 g (0.03 mol) of biphenyl tetracarboxylic dianhydride (BPDA) were added to the solution and dissolved and allowed to react while stirring for a predetermined period of time. At this time, the temperature of the solution was maintained at 25° C. Then, 20.302 g (0.1 mol) of terephthaloyl chloride (TPC) was added to the solution to obtain a polyamic acid solution having a solid content of 13% by weight.

[0063] 25.6 g of pyridine and 33.1 g of acetic anhydride were added to the polyamic acid solution, the resulting mixture was stirred for 30 minutes and then further stirred at 70° C. for 1 hour, cooled to room temperature and precipitated with 20 L of methanol, the precipitated solid was filtered, pulverized and dried under vacuum at 100° C. for 6 hours to obtain 111 g of polyimide-amide as a solid powder.

Example 1

[0064] 0.03 g (0.03 wt %) of amorphous silica particles having an OH group bonded to the surface thereof was added to N,N-dimethylacetamide (DMAc) at a dispersion concentration of 0.1% and sonicated until the solvent became transparent. Then, 100 g of the polyamide-imide obtained as the solid powder in Preparation Example 1 was dissolved in 670 g of the N,N-dimethylacetamide (DMAc) in which the silica particles were dispersed, to obtain a 13 wt % solution. The solution thus obtained was applied to a stainless steel plate, cast to 200 μm and dried with hot air of 130° C. for 30 minutes, and then the film was peeled off from the stainless steel plate and fixed to the frame with a pin. At this time, the film fixed to the frame was elongated at 115% in the machine direction and shrunk at 85% in the transverse direction.

[0065] Then, the frame, on which the film was fixed, was placed in a vacuum oven, slowly heated from 100° C. to 300° C. for 2 hours (first heat treatment) and then slowly cooled, and then a polyimide-based film was obtained by separation from the frame. Subsequently, the film was subjected to heat treatment again at 310° C. for 300 seconds, as a final heat treatment (second heat treatment). At this time, a tension of 80 N/mm.sup.2 was applied in the machine direction during the final heat treatment to perform further elongation and heat setting in the machine direction.

[0066] At this time, the thickness of the produced polyimide-based film was 50 μm.

Example 2

[0067] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was elongated at 105% in the machine direction and shrunk at 85% in the transverse direction.

Example 3

[0068] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was elongated at 130% in the machine direction and shrunk at 85% in the transverse direction.

Example 4

[0069] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was elongated at 115% in the machine direction and shrunk at 95% in the transverse direction.

Example 5

[0070] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was elongated at 115% in the machine direction and shrunk at 80% in the transverse direction.

Example 6

[0071] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed at 300° C.

Example 7

[0072] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed at 320° C.

Example8

[0073] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed at 290° C.

Example 9

[0074] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed for 200 seconds.

Example 10

[0075] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed for 400 seconds.

Example 11

[0076] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed for 1,000 seconds.

Example 12

[0077] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed for 1,500 seconds.

Example 13

[0078] A polyimide-based film was produced in the same manner as in Example 1, except that a tension of 30 N/mm.sup.2 was applied in the machine direction during the final heat treatment to perform further elongation and heat setting in the machine direction.

Example 14

[0079] A polyimide-based film was produced in the same manner as in Example 1, except that a tension of 70 N/mm.sup.2 was applied in the machine direction during the final heat treatment to perform further elongation and heat setting in the machine direction.

Example 15

[0080] A polyimide-based film was produced in the same manner as in Example 1, except that a tension of 100 N/mm.sup.2 was applied in the machine direction during the final heat treatment to perform further elongation and heat setting in the machine direction.

Example 16

[0081] A polyimide-based film was produced in the same manner as in Example 1, except that a tension of 150 N/mm.sup.2 was applied in the machine direction during the final heat treatment to perform further elongation and heat setting in the machine direction.

Example 17

[0082] A polyimide-based film was produced in the same manner as in Example 1, except that the frame, on which the film was fixed, was placed in a vacuum oven, slowly heated from 100° C. to 320° C. for 2 hours (first heat treatment) and then slowly cooled, and then a polyimide-based film was obtained by separation from the frame.

Comparative Example 1

[0083] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was shrunk at 85% only in the transverse direction.

Comparative Example 2

[0084] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was elongated at 135% in the machine direction and shrunk at 85% in the transverse direction.

Comparative Example 3

[0085] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was elongated at 115% in the machine direction and shrunk at 75% in the transverse direction.

Comparative Example 4

[0086] A polyimide-based film was produced in the same manner as in Example 1, except that the fixed frame was elongated at 115% only in the machine direction.

Comparative Example 5

[0087] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed at 280° C.

Comparative Example 6

[0088] A polyimide-based film was produced in the same manner as in Example 1, except that the final heat treatment was performed for 150 seconds.

Comparative Example 7

[0089] A polyimide-based film was produced in the same manner as in Example 1, except that a tension of 25 N/mm.sup.2 was applied in the machine direction during the final heat treatment to perform further elongation and heat setting in the machine direction.

Comparative Example 8

[0090] A polyimide-based film was produced in the same manner as in Example 1, except that a tension of 160 N/mm.sup.2 was applied in the machine direction during the final heat treatment to perform further elongation and heat setting in the machine direction.

Comparative Example 9

[0091] A polyimide-based film was produced in the same manner as in Example 1, except that neither elongation nor shrinkage was performed in step (S1) and no tension was applied in step (S2).

Measurement Example

[0092] Physical properties were measured in the following manner and the results are shown in FIG. 1.

[0093] (1) Light transmittance (%): optical transmittance at 550 nm was measured using a spectrophotometer (CM-3700D, Konica Minolta Inc.) in accordance with the standard ASTM E313.

[0094] (2) Yellowness: yellowness was measured using a spectrophotometer (CM-3700D, Konica Minolta Inc.) in accordance with the standard ASTM E313.

[0095] (3) Pencil hardness: a 50 mm line was drawn 5 times using a pencil (UNI, produced by Mitsubishi) at a speed of 180 mm/min with a load of 1 kg and a pencil hardness causing no scratch on the surface thereof was measured using an electric pencil hardness tester (in the case where a coating layer was formed, in the direction of formation of the coating layer) in accordance with the standard ASTM D3363.

[0096] Yield strain (%): yield strain was measured at a cross head speed of 5 mm/min and a grip distance of 100 mm using a universal tester (UTM, Instron) in accordance with the standard (ASTM D882).

TABLE-US-00001 TABLE 1 First heat Second heat MD TD treatment Second heat Second heat treatment Trans- Pencil Item elongation shrinkage maximum treatment treatment MD mittance Yellow- hard- Yield strain (%) (50 μm) (%) (%) temperature temperature time tension (%) ness ness MD TD Ex. 1 115 85 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 2H 6 2 Ex. 2 105 85 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 2H 5 2 Ex. 3 130 85 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 3H 8 1 Ex. 4 115 85 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 2H 5 2 Ex. 5 115 80 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 2H 6.2 2.0 Ex. 6 115 85 300° C. 330° C. 300 s 80 N/mm.sup.2 88 7.5 2H 6 2 Ex. 7 115 85 300° C. 320° C. 300 s 80 N/mm.sup.2 88 5.0 2H 8 2 Ex. 8 115 85 300° C. 290° C. 300 s 80 N/mm.sup.2 88 4.0 2H 6 2 Ex. 9 115 85 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 2H 5.8 2.0 Ex. 10 115 85 300° C. 310° C. 1000 s 80 N/mm.sup.2 88 4.0 2H 6.2 2.0 Ex. 11 115 85 300° C. 310° C. 1500 s 80 N/mm.sup.2 87 4.5 2H 8 2 Ex. 12 115 85 300° C. 310° C. 300 s 80 N/mm.sup.2 85 6.0 2H 6 2.0 Ex. 13 115 85 300° C. 310° C. 300 s 30 N/mm.sup.2 88 4.0 2H 5 2 Ex. 14 115 85 300° C. 310° C. 300 s 70 N/mm.sup.2 88 4.0 2H 6 2.0 Ex. 15 115 85 300° C. 310° C. 300 s 100 N/mm.sup.2 88 4.0 2H 7 2.0 Ex. 16 115 85 300° C. 310° C. 300 s 150 N/mm.sup.2 88 4.0 2H 10 1 Ex. 17 115 85 300° C. 320° C. 300 s 80 N/mm.sup.2 83 6.2 2H 7 2 Comp. No 85 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 2H 2 1 Ex. 1 elongation Comp. 135 85 300° C. 310° C. 300 s 80 N/mm.sup.2 Production impossible due to breakage Ex. 2 Comp. 115 75 300° C. 310° C. 300 s 80 N/mm.sup.2 Production impossible due to breakage Ex. 3 Comp. 115 No 300° C. 310° C. 300 s 80 N/mm.sup.2 88 4.0 2H 2 2 Ex. 4 shrinkage Comp. 115 85 300° C. 280° C. 300 s 80 N/mm.sup.2 88 4.0 2H 2 2 Ex. 5 Comp. 115 85 300° C. 310° C. 150 s 80 N/mm.sup.2 88 4.0 2H 2 1 Ex. 6 Comp. 115 85 300° C. 310° C. 300 s 25 N/mm.sup.2 88 4.0 2H 2 1 Ex. 7 Comp. 115 85 300° C. 310° C. 300 s 160 N/mm.sup.2 Production impossible due to breakage Ex. 8 during final heat treatment Comp. No No 300° C. 310° C. 300 s No further 88 4.0 1H 2 2 Ex. 9 elongation shrinkage elongation

[0097] As can be seen from the results shown in Table 1, Examples 1 to 5, wherein the polyimide-based films were produced through elongation in the machine direction and shrinkage in the transverse direction, exhibited great improvement in yield strain in the machine direction compared to Comparative Examples 1 and 4 wherein such elongation/shrinkage was not performed. In addition, Examples 6 to 12 wherein the second heat treatment was performed for 200 seconds or longer at a temperature within −10° C. (290° C.) to +30° C. (330° C.) of the first heat treatment temperature (300° C.), exhibited great improvement in yield strain in the machine direction, compared to Comparative Examples 5 and 6 wherein such second heat treatment was not performed. In addition, Examples 13 to 16 wherein a tension of 30 to 150 N/mm.sup.2 was applied under the same conditions during the second heat treatment secured sufficient yield strains compared to Comparative Examples 7 and 8 wherein the tension was excessively low or high.

[0098] On the other hand, in Comparative Example 2, a film could not be obtained due to breakage resulting from excessive elongation in the machine direction in the production of the polyimide-based film, and in Comparative Example 3 wherein excessive shrinkage occurred in the transverse direction in the production of the polyimide-based film, the film sagged, was broken due to friction with the floor and thus could not be obtained. In addition, in Comparative Example 8 wherein excessive tension was applied during the final heat treatment, a film could not be obtained due to breakage. In other words, Comparative Examples 1 to 8 exhibited no great change in physical properties and caused breakage of the film, unlike Comparative Example 9 wherein no treatment was performed.

[0099] These results indicate that the polyimide-based film of the present disclosure has excellent bending characteristics such as yield strain and is thus advantageous for use as a substrate for various applications of flexible display electronic devices, more particularly, foldable and rollable display electronic devices having a radius of curvature of 1 mm (1R) or less.