PRESSURE-SENSITIVE ADHESIVE LAYER

Abstract

The present application provides a pressure-sensitive adhesive layer comprising at least first and second regions having different physical properties, wherein the difference in physical properties, such as an elastic modulus or creep strain rate is maintained relatively large for each region, and the difference in physical properties, such as a peel force or recovery rate is maintained relatively small for each region.

Claims

1. A pressure-sensitive adhesive layer, comprising: a first region and a second region, wherein an absolute value of a difference in creep strain rates of the first and second regions according to Equation 1 below is 20% or more, and wherein an absolute value of a difference in recovery rates of the first and second regions according to Equation 2 below is 15% or less:
D.sub.C60=100×(C.sub.60.1−C.sub.60.2)/C.sub.60.2  [Equation 1]
D.sub.R60=100×(R.sub.60.1−R.sub.60.2)/R.sub.60.2  [Equation 2] wherein D.sub.C60 is the difference in the creep strain rates, C.sub.60.1 is a creep strain rate of the first region at 60° C., and C.sub.60.2 is a creep strain rate of the second region at 60° C.; and D.sub.R60 is the difference in the recovery rates, R.sub.60.1 is a recovery rate of the first region at 60° C., and R.sub.60.2 is a recovery rate of the second region at 60° C.

2. The pressure-sensitive adhesive layer according to claim 1, wherein the creep strain rate of the second region at 60° C. is 100% or more.

3. The pressure-sensitive adhesive layer according to claim 1, wherein the difference in creep strain according to Equation 1 is a negative number.

4. The pressure-sensitive adhesive layer according to claim 1, wherein the recovery rate of the first region at 60° C. is 80% or more.

5. The pressure-sensitive adhesive layer according to claim 1, wherein the difference in recovery rate according to Equation 2 is a positive number.

6. The pressure-sensitive adhesive layer according to claim 1, wherein an absolute value of a difference in creep strain rates according to Equation 3 below is 5% or more:
D.sub.CM20=100×(C.sub.M20.1−C.sub.M20.2)/C.sub.M20.2  [Equation 3] wherein D.sub.CM20 is the difference in the creep strain rates, C.sub.M20.1 is a creep strain rate of the first region at −20° C., and C.sub.M20.2 is a creep strain rate of the second region at −20° C.

7. The pressure-sensitive adhesive layer according to claim 6, wherein the creep strain rate of the second region at −20° C. is 30% or more.

8. The pressure-sensitive adhesive layer according to claim 6, wherein the difference in creep strain rates according to Equation 3 is a negative number.

9. The pressure-sensitive adhesive layer according to claim 6, wherein an absolute value of a difference in recovery rates according to Equation 4 below is 20% or less:
D.sub.RM20=100×(R.sub.M20.1−R.sub.M20.2)/R.sub.M20.2  [Equation 4] wherein D.sub.RM20 is the difference in the recovery rates, R.sub.M20.1 is a recovery rate of the first region at −20° C., and R.sub.M20.2 is a recovery rate of the second region at −20° C.

10. The pressure-sensitive adhesive layer according to claim 9, wherein the recovery rate of the first region at −20° C. is 70% or more.

11. The pressure-sensitive adhesive layer according to claim 9, wherein the difference in recovery rates according to Equation 4 is a positive number.

12. The pressure-sensitive adhesive layer according to claim 1, comprising a crystalline acrylic copolymer.

13. The pressure-sensitive adhesive layer according to claim 1, comprising an acrylic copolymer having a melting point of −20° C. or less.

14. A pressure-sensitive adhesive film, comprising: a base film; and the pressure-sensitive adhesive layer of claim 1 formed on one side or both sides of the base film.

15. An optical laminate, comprising: an optical film; and the pressure-sensitive adhesive layer of claim 1 formed on one side or both sides of the optical film.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0188] FIG. 1 is an exemplary diagram for explaining deformation according to stress generated upon folding in a foldable device.

[0189] FIGS. 2 to 5 are diagrams exemplarily showing the formation form of first and second regions in a pressure-sensitive adhesive layer.

[0190] FIGS. 6 to 8 are diagrams schematically expressing an electromagnetic wave irradiation process for forming a pressure-sensitive adhesive layer.

[0191] FIG. 9 is a diagram exemplarily expressing a graph used in a process of measuring creep strain rates and recovery rates.

[0192] FIG. 10 is a diagram showing the structure of a specimen applied in a dynamic folding test.

[0193] FIG. 11 is a diagram showing a process in which a dynamic folding test is performed.

[0194] Hereinafter, the present application will be described in detail through Examples, but the scope of the present application is not limited by Examples below.

[0195] 1. Evaluation of Storage Elastic Modulus

[0196] The storage elastic modulus was evaluated using ARES G2 (Advanced Rheometric Expansion System G2) (TA). A specimen was prepared by cutting a pressure-sensitive adhesive layer having a thickness of about 0.8 mm or so into a circle having a diameter of about 8 mm or so. The pressure-sensitive adhesive layer was prepared by overlapping the pressure-sensitive adhesive layer having a thickness of about 25 μm or so to a thickness of about 0.8 mm or so. The storage elastic modulus at the measurement temperature was evaluated for the specimen using a parallel plate fixture having a diameter of about 8 mm. Upon the evaluation, the evaluation conditions were a frequency of 1 Hz and a strain of 5%.

[0197] 2. Evaluation of Creep Strain Rate and Recovery Rate

[0198] The creep strain rate and recovery rate were evaluated in the following manner. A specimen was prepared by cutting a pressure-sensitive adhesive layer having a thickness of about 0.8 mm or so into a circle having a diameter of about 8 mm or so. The pressure-sensitive adhesive layer was prepared by overlapping the pressure-sensitive adhesive layer having a thickness of about 25 μm or so to a thickness of about 0.8 mm or so.

[0199] Using ARES G2 (Advanced Rheometric Expansion System G2) (TA) equipment, the specimen was mounted on a parallel plate fixture having a diameter of about 8 mm, and a stress of about 10,000 Pa or so in the shear direction was applied to the specimen for 600 seconds, and the strain rate after removing the stress was confirmed as shown in FIG. 9 and evaluated.

[0200] In the graph of FIG. 9, the x-axis is an axis showing the lapse of time that the time point when the stress starts to be applied is set to 0 seconds, and the y-axis is an axis showing the strain (%) of the pressure-sensitive adhesive layer, where the stain is a result of calculation according to Equation A below.

Stain(unit:%)=100×(L.sub.a−L.sub.i)/L.sub.i  [Equation A]

[0201] In Equation A, La is the length (unit: mm) after deformation of the pressure-sensitive adhesive layer in the deformation direction (direction to which stress is applied), and Li is the initial thickness (unit: mm) of the pressure-sensitive adhesive layer before deformation.

[0202] The maximum strain (10 in FIG. 9) of the pressure-sensitive adhesive layer confirmed by such evaluation was designated as the creep strain rate value.

[0203] In addition, the recovery rate was designated according to Equation B below.

R%=100×(C−S)/C  [Equation B]

[0204] In Equation B, R % is the recovery rate, C is the creep strain rate value (Creep, maximum strain rate), and S is the strain rate (e.g., 20 in FIG. 9) of the specimen at the time that the stress of about 10,000 Pa has been applied to the specimen for 600 seconds and then the stress has been removed, and again 600 seconds have elapsed.

[0205] 3. Peel Force Evaluation

[0206] A specimen was prepared by cutting the pressure-sensitive adhesive film (the structure of the release film/pressure-sensitive adhesive layer/base film) to be measured into a rectangle having a width of about 25 mm or so and a length of about 100 mm or so. Subsequently, the release film was peeled off, and the pressure-sensitive adhesive layer was attached to soda lime glass or a polyimide film using a roller of 2 kg according to the regulations of JIS Z 0237 and left at room temperature for 1 day. Thereafter, the peel force was measured while peeling the pressure-sensitive adhesive layer at a peel angle of 180 degrees and a peel rate of 0.3 m/min at room temperature using a TA (Texture Analyzer) equipment (Stable Micro System).

[0207] 4. Evaluation of Melting Point and Glass Transition Temperature

[0208] The melting point and glass transition temperature of the copolymer were measured according to a measurement method using a conventional DSC (differential scanning calorimeter) equipment. As the equipment, DSC-STAR3 equipment (Mettler Toledo) was used. About 10 mg of the sample (copolymer) was sealed in a dedicated pan, and the melting point and the like were measured by checking the endothermic and calorific values according to the temperature under a temperature increase condition of 10° C./min.

[0209] 5. Evaluation of Weight Average Molecular Weight

[0210] The weight average molecular weight (Mw) of the copolymer was measured using GPC (gel permeation chromatograph), and the measurement conditions were as follows. When measuring the weight average molecular weight, standard polystyrene (manufactured by Agilent System) was used to prepare the calibration curve, and the measurement results were converted.

[0211] <GPC Measurement Conditions>

[0212] Measuring instrument: Agilent GPC (Agilent 1200 series, U.S.)

[0213] Column: Connecting two PL Mixed B

[0214] Column temperature: 40° C.

[0215] Eluent: Tetrahydrofuran (THF)

[0216] Flow rate: 1.0 μL/min

[0217] Concentration: ˜1 mg/mL (100 μl injection)

[0218] 6. Dynamic Folding Test

[0219] The dynamic folding test was performed by preparing a specimen as shown in FIG. 10. As the specimen shown in FIG. 10, a laminate prepared by sequentially laminating a polyimide film (200) having a thickness of about 50 μm or so, in which a hard coating layer (100) was formed on both sides, a pressure-sensitive adhesive layer (300), a polarizing plate (400), a pressure-sensitive adhesive layer (300) and a display panel (500) was cut in a rectangular shape having a horizontal length of about 7.8 cm and a vertical length of about 17 cm or so to prepare a specimen. Subsequently, as shown in FIG. 11, the folding that the specimen was sandwiched between parallel plates at an interval of 5 mm and folded was repeated 200,000 times at 25° C., and after collecting the sample, defects such as occurrence of bubbles and occurrence of lifting/peeling in the sample, and crack occurrence of the hard coating layer were visually observed. The case where even one of the above defects occurred was evaluated as NG, and the case where all of the above defects did not occur was evaluated as PASS.

Preparation Example 1. Preparation of Copolymer (A)

[0220] 2-ethylhexyl acrylate (2-EHA), lauryl acrylate (LA), 4-hydroxybutyl acrylate (HBA) and 4-benzoylphenyl methacrylate (BPMA) were introduced into ethyl acetate as a solvent in a reactor in a weight ratio (2-EHA:LA:HBA:BPMA) of 50:40:10:0.05, about 500 ppm of a radical initiator (2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile)) was added thereto, and then, the mixture was polymerized at about 50° C. for about 8 hours to prepare a polymer substance (copolymer (A)).

[0221] In addition, the copolymer (polymer substance) (A) had a glass transition temperature (Tg) of about −60° C. or so and a melting point of about −40° C. or so.

Preparation Examples 2 to 16. Preparation of Copolymers

[0222] Copolymers (polymer substances) were prepared in the same manner as in Preparation Example 1, except that the weight ratios of the applied monomers and the weight average molecular weights of the polymer substances (copolymers) were as shown in Table 1 below.

TABLE-US-00001 TABLE 1 Co- poly- 2- mer EHA LA HBA BPMA Mw Tg Tm Preparation A 50 40 10 0.05 1990000 −60 −40 Example 1 Preparation B 40 40 20 0.01 1970000 −60 −44 Example 2 Preparation C 40 40 20 0.03 1890000 −56 −44 Example 3 Preparation D 40 40 20 0.05 2030000 −61 −43 Example 4 Preparation E 40 40 20 0.1 1990000 −54 −44 Example 5 2-EHA: 2-ethylhexyl acrylate LA: lauryl acrylate HBA: 4-hydroxybutyl acrylate BPMA: 4-benzoylphenyl methacrylate Mw: weight average molecular weight (unit: g/mol) Tg: glass transition temperature (unit: ° C.) Tm: melting point (unit: ° C.)

Example 1

[0223] A pressure-sensitive adhesive composition was prepared by formulating about 0.3 parts by weight of an isocyanate cross-linking agent (xylylene diisocyanate) relative to 100 parts by weight of the copolymer (polymer substance) (A) of Preparation Example 1. The prepared pressure-sensitive adhesive composition was applied on a base film (PET (poly(ethylene terephthalate)) with a comma coater, and maintained at 130° C. for about 3 minutes or so to form a pressure-sensitive adhesive layer having a thickness of about 25 μm or so.

Example 2

[0224] A pressure-sensitive adhesive layer was formed in the same manner as in Example 1, except that the copolymer (polymer substance) (B) of Preparation Example 2 was used instead of the copolymer (polymer substance) (A) of Preparation Example 1.

Example 3

[0225] A pressure-sensitive adhesive layer was formed in the same manner as in Example 1, except that the copolymer (polymer substance) (C) of Preparation Example 3 was used instead of the copolymer (polymer substance) (A) of Preparation Example 1.

Example 4

[0226] A pressure-sensitive adhesive layer was formed in the same manner as in Example 1, except that the copolymer (polymer substance) (D) of Preparation Example 4 was used instead of the copolymer (polymer substance) (A) of Preparation Example 1.

Example 5

[0227] A pressure-sensitive adhesive layer was formed in the same manner as in Example 1, except that the copolymer (polymer substance) (E) of Preparation Example 5 was used instead of the copolymer (polymer substance) (A) of Preparation Example 1.

Test Example 1. Evaluation of Creep Strain Rate and Recovery Rate

[0228] For the pressure-sensitive adhesive layers, creep strain rates and recovery rates in the case where ultraviolet rays were irradiated and the case where ultraviolet rays were not irradiated were evaluated, respectively, and the results were described in Tables 2 and 3 below.

[0229] Here, the irradiation of ultraviolet rays in the above was performed by irradiating the pressure-sensitive adhesive layer with ultraviolet rays at a light quantity of about 3,600 mJ/cm.sup.2 or so as a light source of Fusion D-bulb equipment.

TABLE-US-00002 TABLE 2 Region not irradiated Region irradiated with ultraviolet rays with ultraviolet rays Creep Recovery Creep Recovery strain rate rate strain rate rate (60° C.) (60° C.) (60° C.) (60° C.) (%) (%) (%) (%) Example 1 378.1 92.4 107.1 96.7 Example 2 360.3 93.9 183.8 95.4 Example 3 515.2 91.9 131.2 93 Example 4 510.9 93.4 101 97.4 Example 5 490.4 93.2 74.7 98.4

TABLE-US-00003 TABLE 3 Region not irradiated Region irradiated with ultraviolet rays with ultraviolet rays Creep Recovery Creep Recovery strain rate rate strain rate rate (−20° C.) (−20° C.) (−20° C.) (−20° C.) (%) (%) (%) (%) Example 1 116.4 84.1 81.1 90.5 Example 2 68.2 84.8 61.3 86.4 Example 3 70.2 83.2 59.3 87.6 Example 4 68.5 83 55.7 88.7 Example 5 74.4 82.4 52 90.5

[0230] In the case of Examples 1 to 5, the difference in creep strain rates according to Equations 1 and 3 and the difference in recovery rates according to Equations 2 and 4 are as summarized in Table 4 below.

TABLE-US-00004 TABLE 4 Creep Creep Recovery Recovery strain rate strain rate rate rate difference difference difference difference (Equation 1) (Equation 3) (Equation 2) (Equation 4) D.sub.C60 (60° C.) D.sub.CM20 (−20° C.) D.sub.R60 (60° C.) D.sub.RM20 (−20° C.) (%) (%) (%) (%) Example 1 −71.7 −30.3 4.7 7.6 Example 2 −49 −10.1 1.6 1.9 Example 3 −74.5 −15.5 4.5 5.2 Example 4 −80.2 −18.7 4.3 6.9 Example 5 −84.8 −30.1 5.6 9.8

[0231] From the results of Tables 2 to 4, it can be confirmed that the pressure-sensitive adhesive layer according to the present application shows a relatively large difference in creep strain rates in the region irradiated with ultraviolet rays and in the other region, and simultaneously the difference in recovery rates is controlled to be relatively small. Accordingly, it can be confirmed that for example, when the pressure-sensitive adhesive layer of the present application is applied to a pattern exposure technique with a mask applied as disclosed in Patent Document 1, it can form a multi-region pressure-sensitive adhesive layer in which the difference in recovery rates is maintained relatively small while the difference in creep strain rates is maintained large.

Test Example 2. Evaluation of Storage Elastic Modulus and Peel Force

[0232] For the pressure-sensitive adhesive layers of Examples and Comparative Examples, the storage elastic moduli and peel force in the case where ultraviolet rays were irradiated and the case where they were not irradiated were evaluated, respectively, and the results were described in Tables 5 and 6 below. Here, the irradiation of ultraviolet rays was performed in the same manner as in Test Example 1. In the following, the unit of storage elastic modulus is Pa.

TABLE-US-00005 TABLE 5 Storage elastic Storage elastic Storage elastic modulus (−20° C.) modulus (30° C.) modulus (60° C.) Ultraviolet No ultraviolet Ultraviolet No ultraviolet Ultraviolet No ultraviolet irradiation irradiation irradiation irradiation irradiation irradiation Example 1 68674 65169 23260 20628 16658 12795 Example 2 117571 119014 27735 26268 19469 17429 Example 3 125143 112915 28547 24963 20760 16464 Example 4 133564 115601 29438 25475 22275 16375 Example 5 105493 113616 27904 24070 22571 15239

TABLE-US-00006 TABLE 6 Peel force to glass Peel force to glass (gf/inch) (gf/inch) Ultraviolet No ultraviolet Ultraviolet No ultraviolet irradiation irradiation irradiation irradiation Example 1 1138 1168 1028 1279 Example 2 1197 1227 1149 1213 Example 3 1210 1426 1152 1258 Example 4 1167 1397 1085 1287 Example 5 1030 1410  982 1259

[0233] Differences in storage elastic moduli of the first and second regions in the pressure-sensitive adhesive layer of Examples 1 to 5 according to Equations 5 to 7 according to Equations 5 to 7 are as summarized in Table 7 below, and differences of peel force according to Equations 8 and 9 are as summarized in Table 8 below.

TABLE-US-00007 TABLE 7 Storage elastic modulus difference Equation 4, Equation 5, Equation 6, D.sub.M60 (60° C.) D.sub.M30 (30° C.) D.sub.M20 (−20° C.) (%) (%) (%) Example 1 30.2 12.8 5.4 Example 2 11.7 5.6 −1.2 Example 3 26.0 14.4 10.8 Example 4 36.0 15.6 15.5 Example 5 48.1 15.9 −7.1

TABLE-US-00008 TABLE 8 Difference of peel force Equation 8, Equation 9, D.sub.PG (%) D.sub.PI (%) Example 1 −2.6 −19.6 Example 2 −2.4 −5.3 Example 3 −15.1 −8.4 Example 4 −16.4 −15.7 Example 5 −27.0 −22.0

[0234] From the results of Tables 5 to 8, it can be confirmed that the pressure-sensitive adhesive layer according to the present application shows a relatively large difference in storage elastic moduli in the region irradiated with ultraviolet rays and in the other region, and simultaneously the difference in peel force is controlled to be relatively small. Accordingly, it can be confirmed that for example, when the pressure-sensitive adhesive layer of the present application is applied to a pattern exposure technique with a mask applied as disclosed in Patent Document 1, it can form a multi-region pressure-sensitive adhesive layer in which the difference in peel force is maintained relatively small while the difference in storage elastic moduli is maintained large.

Test Example 3. Dynamic Folding Test

[0235] The first region (1000) and the second region (2000) as shown in FIG. 2 were formed on each pressure-sensitive adhesive layer of Examples by ultraviolet irradiation via a mask, and a dynamic folding test was performed in the above-described manner. In the dynamic folding test, the folding axis (3000) overlapped the center of the second region (2000) as shown in FIG. 2. As a result, in the case of all the pressure-sensitive adhesive layers of Examples, no defect appeared after repeated folding, and no folding mark was observed after folding.