PRESSURE-SENSITIVE ADHESIVE COMPOSITION

Abstract

The present invention relates to a pressure-sensitive adhesive composition, a protective film, an optical element, and a display device. A pressure-sensitive adhesive sheet formed using the pressure-sensitive adhesive composition according to the present invention can have proper high-speed and low-speed peel strengths and simultaneously can exhibit an excellent balance between the high-speed and low-speed peel strengths. The pressure-sensitive adhesive sheet formed using the pressure-sensitive adhesive composition according to one exemplary embodiment of the present invention exhibits a proper level of surface resistance and excellent electrostatic discharge characteristics, and has no contaminants with respect to an adherend even when the pressure-sensitive adhesive sheet is peeled from the adherend after the pressure-sensitive adhesive sheet is attached to the adherend for a long period of time. Such a pressure-sensitive adhesive sheet formed using the pressure-sensitive adhesive composition according to one exemplary embodiment of the present invention can be applied to various fields of applications. For example, the pressure-sensitive adhesive sheet can be used as a protective film for optical members such as polarizing plates.

Claims

1. A pressure-sensitive adhesive composition comprising: a compound represented by Formula 1 at 0.1 to 5 parts by weight; a polymer comprising a nitrogen-containing reactive compound at 1 to 30 parts by weight of, a first monomer at 0.1 to 15 parts by weight and a second monomer at 0.1 to 5 parts by weight as monomer components, the first monomer being represented by Formula 2, A and B of which represent an alkylene group having 1 to 3 carbon atoms, and the second monomer being represented by Formula 2, A and B of which represent an alkylene group having 4 to 8 carbon atoms; and an ionic compound: ##STR00006## wherein Q represents hydrogen or an alkyl group, U represents an alkylene group, Z represents hydrogen, an alkyl group, or an aryl group, m is a number ranging from 1 to 2, A and B each independently represent an alkylene group, and n is a number ranging from 0 to 10.

2. The pressure-sensitive adhesive composition of claim 1, wherein U in Formula 1 is an alkylene group having 1 to 4 carbon atoms.

3. The pressure-sensitive adhesive composition of claim 1, wherein the nitrogen-containing reactive compound is a dialkyl (meth)acrylamide.

4. The pressure-sensitive adhesive composition of claim 3, wherein the dialkyl (meth)acrylamide contain an alkyl group having 1 to 4 carbon atoms.

5. The pressure-sensitive adhesive composition of claim 1, wherein a ratio (A/B) of a weight (A) of the first monomer and a weight (B) of the second monomer is in a range of 1 to 5.

6. The pressure-sensitive adhesive composition of claim 1, further comprising an aliphatic isocyanate cross-linking agent.

7. The pressure-sensitive adhesive composition of claim 6, wherein the aliphatic isocyanate cross-linking agent comprises at least one selected from the group consisting of an aliphatic cyclic isocyanate compound and an aliphatic non-cyclic isocyanate compound.

8. The pressure-sensitive adhesive composition of claim 7, wherein the aliphatic cyclic isocyanate compound comprises at least one selected from the group consisting of an isocyanate compound such as isophorone diisocyanate, methylene dicyclohexyl diisocyanate, or cyclohexane diisocyanate, a dimer or trimer of the isocyanate compound, and a reaction product of the isocyanate compound and a polyol.

9. The pressure-sensitive adhesive composition of claim 7, wherein the aliphatic non-cyclic isocyanate compound comprises at least one selected from the group consisting of an alkylene diisocyanate compound having 1 to 20 carbon atoms, a dimer or trimer of the isocyanate compound, and a reaction product of the isocyanate compound and a polyol.

10. The pressure-sensitive adhesive composition of claim 6, wherein the aliphatic isocyanate cross-linking agent is included at a content of 0.01 parts by weight to 10 parts by weight, based on 100 parts by weight of the polymer.

11. A surface protective film comprising: a base layer for surface protection; and a pressure-sensitive adhesive layer formed at one or both surfaces of the base layer and comprising the pressure-sensitive adhesive composition of claim 1 in a cross-linked state.

12. The surface protective film of claim 11, wherein a peel strength of the pressure-sensitive adhesive layer is in a range of 1 gf/25 mm to 40 gf/25 mm, as measured at a peel angle of 180° and a peel rage of 0.3 m/min with respect to an adherend having a surface energy of 30 mN/m or less.

13. The surface protective film of claim 11, wherein a peel strength of the pressure-sensitive adhesive layer is in a range of 10 gf/25 mm to 180 gf/25 mm, as measured at a peel angle of 180° and a peel rage of 30 m/min with respect to an adherend having a surface energy of 30 mN/m or less.

14. An optical element having the surface protective film of claim 11 detachably attached to a surface thereof.

15. The optical element of claim 14, wherein a surface energy of the surface of the optical element to which the surface protective film is attached is less than or equal to 30 mN/m.

16. A display device comprising the optical element defined in claim 14.

Description

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0121] Hereinafter, the pressure-sensitive adhesive composition will be described in detail with reference to the following Examples and Comparative Examples. However, it should be understood that the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention.

[0122] 1. Measurement of Surface Resistance

[0123] A pressure-sensitive adhesive sheet was cut into pieces having a width of 150 mm and a length of 50 mm, and a release poly(ethylene terephthalate) (PET) film was peeled from a pressure-sensitive adhesive layer at a constant rate. Thereafter, three arbitrary points were determined on a surface of the release PET film or the pressure-sensitive adhesive layer from which the release PET film was peeled off, the surface resistance was measured at the three arbitrary points, and the average of the obtained surface resistance values was calculated. The surface resistance was measured according to the manufacturer's manual using a high-resistance resistance meter (MCP-HT 450 commercially available from Mitsubishi Chemical Corp.).

[0124] 2. Measurement of Low-Speed Peel Strength

[0125] Each of the pressure-sensitive adhesive sheets prepared in the Examples and the Comparative Examples was attached to a glare shielding film (Trade Name: ASG5 commercially available from LG Chem. Ltd.) using a 2 kg roller according to the JIS Z 0237 standard. Thereafter, the glare shielding film to which the protective film was attached was cut to a width of 25 mm and a length of 100 mm to prepare test samples, and then kept at a temperature of 23° C. and a relative humidity of 65% for 24 hours. Then, peel strengths of the test samples were measured at room temperature using a tensile tester (Texture Analyzer commercially available from Stable Micro Systems Ltd.) while horizontally peeling each of the pressure-sensitive adhesive sheets from the glare shielding film at a peel angle of 180° and a peel rate of 0.3 m/min. The peel strength was determined by measuring two identical test samples in duplicate and averaging the measured values.

[0126] 3. Measurement of High-Speed Peel Strength

[0127] Each of the pressure-sensitive adhesive sheets prepared in the Examples and the Comparative Examples was attached to a glare shielding film (Trade Name: ASG5 commercially available from LG Chem. Ltd.) using a 2 kg roller according to the JIS Z 0237 standard. Thereafter, the glare shielding film to which the protective film was attached was cut to a width of 25 mm and a length of 250 mm to prepare test samples, and then kept at a temperature of 23° C. and a relative humidity of 65% for 24 hours. Then, peel strengths of the test samples were measured at room temperature using a tensile tester (Texture Analyzer commercially available from Stable Micro Systems Ltd.) while horizontally peeling each of the pressure-sensitive adhesive sheets from the glare shielding film at a peel angle of 180° and a peel rate of 30 m/min. The peel strength was determined by measuring two identical test samples in duplicate and averaging the measured values.

[0128] 4. Measurement of Electrostatic Discharge (ESD) Voltage

[0129] Each of the pressure-sensitive adhesive sheets prepared in the Examples and the Comparative Examples was cut to a width of 220 mm and a length of 250 mm Thereafter, each of the cut pressure-sensitive adhesive sheets was attached to a glare shielding film (Trade Name: ASG5 commercially available from LG Chem. Ltd.) using a 2 kg roller according to the JIS Z 0237 standard. Then, each of the pressure-sensitive adhesive sheets was peeled from the glare shielding film at a temperature of 23° C., a relative humidity of 65%, a peel angle of 180°, and a peel rate of 40 m/min Immediately after peeling, ESD voltage was measured at a distance of 40 mm from a surface of the glare shielding film using an electrostatic potential analyzer (KSD-200). The ESD voltage was determined by measuring two identical test samples in duplicate and averaging the measured values. The evaluation criteria for ESD voltage were as follows.

[0130] <Evaluation Criteria for ESD Voltage>

[0131] A: ESD voltage is less than or equal to 0.5 kV

[0132] B: ESD voltage is greater than 0.5 kV

[0133] 6. Evaluation of Contamination Level

[0134] Each of the pressure-sensitive adhesive sheets prepared in the Examples and the Comparative Examples was cut to a width of 150 mm and a length of 250 mm Thereafter, each of the cut pressure-sensitive adhesive sheets was attached to a glare shielding film (Trade Name: ASG5 commercially available from LG Chem. Ltd.) using a 2 kg roller according to the JIS Z 0237 standard. Then, a black pressure-sensitive adhesive film was attached to a surface of the glare shielding film to which the pressure-sensitive adhesive sheet was not attached, and kept at a temperature of 50° C. for 24 hours. Subsequently, a protective film was peeled, and bubbles were intentionally injected between the pressure-sensitive adhesive layer and the glare shielding film by repeatedly performing this attachment process. The resulting stacked body into which the bubbles were incorporated was again kept at room temperature for 24 hours. Then, the protective film was removed, and the presence of contaminants formed at a bubble position was checked by illuminating the glare shielding film with a Xenon HID lamp (commercially available from Polarion. Co., Ltd.). The contamination level was evaluated according to the following evaluation criteria.

[0135] <Evaluation Criteria for Contamination Level>

[0136] A: Contaminants are not observed

[0137] B: Contaminants are slightly observed

[0138] C: A large amount of contaminants are observed

Preparative Example 1: Preparation of Acrylic Copolymer A

[0139] 2-Ethylhexyl acrylate (2-EHA), 4-hydroxybutyl acrylate (4-HBA), 2-hydroxyethyl acrylate (2-HEA), N,N-dimethyl acrylamide, and 2-(2-ethoxyethoxy)ethyl acrylate (EOEOEA) were put at a weight ratio of 86:3:3:4:4 (2-EHA:4-HBA:2-HEA:DMAA:EOEOEA) into a 3-L reactor equipped with a cooling device to facilitate the reflux of nitrogen gas and easily adjust the temperature, and 100 parts by weight of ethyl acetate (EAc) was added, based on 100 parts by weight of the solid content of a monomer. Thereafter, the reactor was purged with nitrogen gas for an hour to remove oxygen, and then maintained at a temperature of 60° C. Then, a reaction initiator (azobisisobutyronitrile (AIBN)) and a molecular weight modifier (n-dodecyl mercaptan (n-DDM)) were put at a proper amount into the reactor, and reacted for approximately 8 hours. After the reaction, the reaction product was diluted with ethyl acetate (EAc) to prepare an acrylic copolymer A having a solid content of 44% by weight and a weight average molecular weight (M.sub.w) of approximately 350,000.

Preparative Examples 2 to 15: Preparation of Acrylic Copolymers B to L

[0140] Acrylic copolymers were prepared in the same manner as in Preparative Example 1, except that the contents of the monomers used to prepare polymers were altered as listed in the following Tables 1 and 2.

TABLE-US-00001 TABLE 1 Preparative Examples 1 2 3 4 5 6 Polymer A B C D E F 2-EHA 86  83  80 78 87  55  HBA 3 3  3  3 3 3 HEA 3 6  6 15 3 3 DMAA 4 4 — — 3 35  EOEOEA 4 4 — — — 4 FM-401 — — 11  4 4 — Unit of proportion: part(s) by weight 2-EHA: 2-ethylhexylacrylate HBA: 4-hydroxybutylacrylate HEA: 2-hydroxyethylacrylate DMAA: N,N-dimethylacrylamide EOEOEA: 2-(2-ethoxyethoxy)ethyl acrylate FM-401: polyethylene glycol monomethylether methacrylate (added ethylene oxide unit mole number: 9 moles)

TABLE-US-00002 TABLE 2 Preparative Examples 7 8 9 10 11 12 13 Polymer G H I J K L M 2-EHA 75  65  77  86  83  69  79  HBA 3 3 3 3 3 3 10  HEA 3 3 12  3 3 20  3 DMAA 15  25  4 4 4 4 4 EOEOEA 4 4 4 — 7 4 4 EOEOEOEA — — — 4 — — — Unit of proportion: part(s) by weight 2-EHA: 2-ethylhexylacrylate HBA: 4-hydroxybutylacrylate HEA: 2-hydroxyethylacrylate DMAA: N,N-dimethylacrylamide EOEOEA: 2-(2-ethoxyethoxy)ethyl acrylate EOEOEOEA: 2-[2-(2-ethoxyethoxy)ethoxy]ethyl acrylate

Example 1: Preparation of Pressure-Sensitive Adhesive Composition

[0141] 6 parts by weight of a mixture of an isophorone diisocyanate-based cross-linking agent and a hexamethylene diisocyanate-based cross-linking agent (MHG-80B commercially available from Asahi Kasei Chemicals Corp.) as a cross-linking agent, 2 parts by weight of lithium bis(trifluoromethanesulfonyl)imide (LiTFSi), and 3 parts by weight of acetylacetone were also mixed homogeneously, based on 100 parts by weight of the acrylic polymer A prepared in Preparative Example 1. In consideration of coatability, the resulting mixture was then diluted to a proper concentration to prepare a pressure-sensitive adhesive composition.

[0142] Preparation of Pressure-Sensitive Adhesive Sheet

[0143] One surface of a PET film (thickness: 38 μm) was coated with the prepared pressure-sensitive adhesive composition, and dried to form a coating layer (i.e., a pressure-sensitive adhesive layer) having a uniform thickness of approximately 20 μm. Thereafter, a release PET film was stacked on the coating layer, and aged at approximately 50° C. for approximately 3 days to prepare a pressure-sensitive adhesive sheet (i.e., a protective film).

Examples 2 to 4 and Comparative Examples 1 to 8

[0144] Pressure-sensitive adhesive compositions were prepared in the same manner as in Example 1, except that the components and contents of the pressure-sensitive adhesive compositions were altered as listed in the following Tables 3 and 4.

TABLE-US-00003 TABLE 3 Examples 1 2 3 4 5 6 7 8 Polymer Type A A A A B G H I Proportion 100 100 100 100 100 100 100 100 Cross- Proportion 6 7 6 7 5 7 8 6 linking agent Metal A Proportion 2 1 1 1 1.5 2 2 2 Metal B Proportion 0.5 Organic Proportion 0.5 Unit of proportion: part(s) by weight Cross-linking agent: Mixture of isophorone diisocyanate-based cross-linking agent and hexamethylenediisocyanate-based cross-linking agent (Asahi Kasei Chemicals Corp.) Metal A: Lithium bis(trifluoromethanesulfonyl)imide (LiTFSi) Metal B: PEL-20A (Japan Carlit Co., Ltd.) Organic: Tributylmethyl ammonium bistrifluoromethane sulfonimide (3M)

TABLE-US-00004 TABLE 4 Comparative Examples 1 2 3 4 5 6 7 8 9 10 Polymer Type C C D E E F J K L M Proportion 100 100 100 100 100 100 100 100 100 100 Cross- Proportion 5 5 6 5 5.5 5 5 5 5 5 linking agent Metal A Proportion 0.1 0.5 0.5 1 1 Metal B Proportion 0.5 0.5 0.5 0.5 0.5 0.5 Organic Proportion 0.5 1 0.5 0.5 0.5 0.5 Unit of proportion: part(s) by weight Cross-linking agent: Mixture of isophorone diisocyanate-based cross-linking agent and hexamethylenediisocyanate-based cross-linking agent (Asahi Kasei Chemicals Corp.) Metal A: Lithium bis(trifluoromethanesulfonyl)imide (LiTFSi) Metal B: PEL-20A (Japan Carlit Co., Ltd.) Organic: Tributylmethyl ammonium bistrifluoromethane sulfonimide (3M)

[0145] Physical properties of the respective pressure-sensitive adhesive compositions prepared in Examples and Comparative Examples were evaluated. The evaluation results are summarized and listed in the following Tables 5 and 6.

TABLE-US-00005 TABLE 5 Examples 1 2 3 4 5 6 7 8 Surface 2 3.1 2.7 2.4 2.1 2.3 2.1 2.2 resistance L-peel 6.3 4.5 2.6 5.4 7.0 10.7 15.6 10.2 H-peel 65 51 46 62 80 121 178 111 H/L 10.3 11.3 17.7 11.5 11.4 11.3 11.4 10.9 ESD A A A A A A A A Contamination A A A A A A A A L-peel: Low-speed peel strength (unit: gf/25 mm) H-peel: High-speed peel strength (unit: gf/25 mm) H/L: Ration of high-speed peel strength (H) and low-speed peel strength (L) ESD: ESD voltage Surface resistance: Surface resistance (×10.sup.11) of pressure-sensitive adhesive (unit: Ω/□)

TABLE-US-00006 TABLE 6 Comparative Examples 1 2 3 4 5 6 7 8 9 10 Surface 0.55 3.2 2.6 0.76 1.8 1.9 2.1 1.8 2.9 2.6 resistance L-peel 2.7 4.7 7.1 4.4 4.9 15 5.4 3.8 17.2 9.3 H-peel 56 77 92 53 70 223 61 59 198 116 H/L 20.7 16.4 13 12.1 14.3 14.9 11.3 15.5 14.8 12.5 ESD A A A A A B A B A B Contamination C C C C B B C B C B L-peel: low-speed peel strength (Unit: gf/25 mm) H-peel: high-speed peel strength (Unit: gf/25 mm) H/L: Ratio of high-speed peel strength (H) and low-speed peel strength (L) ESD: ESD voltage Surface resistance: Surface resistance (×10.sup.11) of pressure-sensitive adhesive (unit: Ω/□)

[0146] As listed in Tables 5 and 6, it was revealed that the pressure-sensitive adhesive sheets prepared in the Examples had proper low-speed and high-speed peel strengths and simultaneously exhibited an excellent balance between the low-speed and high-speed peel strengths. Also, it was revealed that the pressure-sensitive adhesive layers exhibited excellent surface resistance and high ESD voltage, and had no contaminants with respect to the adherend when each of the pressure-sensitive adhesive sheets were peeled from the adherend.

[0147] On the other hand, it could be seen that the balance between the low-speed and high-speed peel strengths was poor, and the adherend was severely contaminated when a large amount of the monomer having a high added ethylene oxide unit mole number was used in the case of Comparative Examples 1 and 2.

[0148] Also, it could be seen that the adherend was contaminated when the monomer having a high added ethylene oxide unit mole number was included in the polymer in the case of Comparative Example 3.

[0149] In addition, it could be seen that the adherend was severely contaminated when the monomer having a high added ethylene oxide unit mole number was used in the case of Comparative Examples 4 and 5. Also, it was revealed that a large amount of the nitrogen-containing reactive compound was used, and thus the high-speed peel strength was very low, and increased contamination of the adherend and an increase in ESD voltage were observed in the case of Comparative Example 6.

[0150] Further, it was confirmed that the adherend was severely contaminated in the case of Comparative Example 7 even when the composition was prepared under the same conditions as in Example 1, except for a slight difference in added ethylene oxide unit mole numbers of the monomers. Also, it was confirmed that the peel strengths highly increased at the same time that the contamination of the adherend increased to a high level in the case of Comparative Examples 8 and 9, and that simultaneous increases in the peel strengths and the ESD voltage, and increased contamination of the adherend were observed in the case of Comparative Example 10.