Pressure-sensitive adhesive composition

Abstract

A pressure-sensitive adhesive composition is provided. The pressure-sensitive adhesive composition shows stable antistatic performance, and in particular, stably maintains its antistatic performance even when the pressure-sensitive adhesive composition is kept for an extended time under extreme conditions or conditions in which environmental changes are severe, and also has excellent general physical properties such as pressure-sensitive adhesive properties, durability and workability.

Claims

1. A pressure-sensitive adhesive composition, satisfying the following General Formula 1 and General Formula 2, and comprising: an acrylic polymer comprising, as polymerized units, 59.5-79.9 parts by weight of (meth)acrylic acid ester monomer, 10 to 20 parts by weight of monomer comprising hydroxyl group, 0.1 to 0.8 parts by weight of monomer comprising carboxyl group and 10 to 20 parts by weight of monomer having an alkylene oxide unit, relative to 100 total parts by weight of said monomers; an antistatic agent, the antistatic agent comprises bis(trifluoromethanesulfonyl)imide anion; and a silane coupling agent selected from the group consisting of a compound represented by the following Formula 5 and Formula 6:
0.35≦ΔSRA=log SR2−log SR1≦0.72  General Formula 1 wherein SR1 is a surface resistance measured after curing the pressure-sensitive adhesive composition and then maintaining it under the conditions of 23° C. and 50% relative humidity for 24 hours, and SR2 is a surface resistance measured after curing the same pressure-sensitive adhesive composition as used for the measurement of SR1, maintaining it under the conditions of 60° C. and 90% relative humidity for 500 hours, and then maintaining it under the conditions of 23° C. and 50% relative humidity for 24 hours,
0.13≦ΔSRB=log SR3—log SR1≦0.25  General Formula 2 wherein SR1 is the same as defined in the General Formula 1, and SR3 is a surface resistance measured after curing the same pressure-sensitive adhesive composition as used for the measurement of SR1, maintaining it under condition of 80° C. for 500 hours, and then maintaining it under conditions of 23° C. and 50% relative humidity for 24 hours,
(R.sub.11).sub.nSi(R.sub.12).sub.(4−n)  Formula 5
(R.sub.13).sub.nSi(R.sub.12).sub.(4−n)  Formula 6 wherein R.sub.11 represents a β-cyanoacetyl group, R.sub.13 represents an acetoacetyl group or an acetoacetylalkyl group, R.sub.12 represents an alkoxy group, and n represents an integer ranging from 1 to 3.

2. The pressure-sensitive adhesive composition of claim 1, wherein the (meth)acrylic acid ester monomer is alkyl (meth)acrylate.

3. The pressure-sensitive adhesive composition of claim 1, wherein the monomer having the alkylene oxide unit is represented by the following Formula 1: ##STR00004## wherein R represents hydrogen or an alkyl group, A represents an alkylene, R.sub.1 represents an alkyl group or an aryl group, and n is in the range from 1 to 12.

4. The pressure-sensitive adhesive composition of claim 1, wherein the antistatic agent comprises at least one selected from the group consisting of a metal salt and an ionic compound that is in a liquid phase at room temperature.

5. The pressure-sensitive adhesive composition of claim 4, wherein the ionic compound is an organic salt.

6. The pressure-sensitive adhesive composition of claim 5, wherein the organic salt comprises at least one cation selected from the group consisting of quaternary ammonium, phosphonium, pyridinium, imidazolium, pyrrolidinium and piperidinium.

7. The pressure-sensitive adhesive composition of claim 6, wherein the quaternary ammonium is represented by the following Formula 3: ##STR00005## wherein R.sub.7 to R.sub.10 each independently represent hydrogen, alkyl, alkoxy, alkenyl or alkynyl.

8. The pressure-sensitive adhesive composition of claim 7, wherein R.sub.7 to R.sub.10 each independently represent linear or branched alkyl having 1 to 12 carbon atoms, with the proviso that R.sub.7 to R.sub.10 are not an alkyl having the same numbers of carbon atoms at the same time.

9. The pressure-sensitive adhesive composition of claim 4, wherein the metal salt comprises an alkaline metal cation or an alkaline earth metal cation.

10. The pressure-sensitive adhesive composition of claim 1, wherein the antistatic agent comprises a metal salt and an ionic compound that is in a liquid phase at room temperature.

11. The pressure-sensitive adhesive composition of claim 1, wherein the antistatic agent is comprised in an amount of 0.1 to 20 parts by weight, relative to 100 parts by weight of the acrylic polymer.

12. The pressure-sensitive adhesive composition of claim 1, further comprising a multifunctional cross-linking agent.

13. The pressure-sensitive adhesive composition of claim 12, wherein the multifunctional cross-linking agent is an isocyanate cross-linking agent.

14. The pressure-sensitive adhesive composition of claim 1, which has a gel fraction after being cured of 50 to 90 weight%.

15. The pressure-sensitive adhesive composition of claim 1, which a peel strength that is measured after attaching on glass in the form of a pressure-sensitive adhesive, and then peeling it with a peel angle of 180 degrees and a peel rate of 0.3 m/min is in the range of 150 gf/25 mm or more.

16. The pressure-sensitive adhesive composition of claim 1, wherein the acrylic polymer comprises 12 to 20 parts by weight of the monomer comprising hydroxyl group.

17. The pressure-sensitive adhesive composition of claim 1, wherein the antistatic agent is present in the composition in an amount of 2 to 5 parts by weight, relative to 100 parts by weight of the acrylic polymer.

18. The pressure-sensitive adhesive composition of claim 1, wherein the antistatic agent comprises both trioctylmethylammonium-bis(trifluoromethanesulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

19. The pressure-sensitive adhesive composition of claim 1, wherein the (meth)acrylic acid ester monomer comprises at least one of n-butyl (meth)acrylate or ethyl (meth)acrylate, the monomer comprising hydroxyl group comprises 2-hydroxyethyl (meth)acrylate, the monomer comprising carboxyl group comprises (meth)acrylic acid, and the monomer having an alkylene oxide unit comprises at least one of methoxy ethyleneglycol acrylate or ethoxyethoxyethyl acrylate.

20. The pressure-sensitive adhesive composition of claim 19, wherein the (meth)acrylic acid ester monomer comprises both n-butyl (meth)acrylate and ethyl (meth)acrylate.

21. The pressure-sensitive adhesive composition of claim 19, wherein the monomer having an alkylene oxide unit comprises both methoxy ethyleneglycol acrylate and ethoxyethoxyethyl acrylate.

22. A polarizing plate comprising: a polarizer; and a pressure-sensitive adhesive layer which is formed on one or both sides of the polarizer, and comprises a cured product of the pressure-sensitive adhesive composition defined of claim 1, the pressure-sensitive adhesive layer being for attaching the polarizing plate to a liquid crystal panel.

23. A liquid crystal display (LCD) device comprising: a liquid crystal panel; and the polarizing plate of claim 22 which is attached to one or both sides of the liquid crystal panel.

Description

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(1) Hereinafter, illustrative embodiments of the present application will be described in detail. However, the present application is not limited to the embodiments stated below and can be implemented in various forms. The following embodiments are described in order to enable those of ordinary skill in the art to embody and practice the present application.

PREPARATIVE EXAMPLE 1

Preparation of Acrylic Polymer (A)

(2) 69.7 parts by weight n-butyl acrylate (n-BA), 20 parts by weight methoxy ethyleneglycol acrylate (MEA). 18 parts by weight hydroxyethyl acrylate (HEA) and 0.3 parts by weight acrylic acid (AA) were put into a 1 L reactor, through which nitrogen gas was refluxed and with which a cooling device to facilitate the temperature control was equipped. 120 parts by weight ethyl acetate (EAc) was added as a solvent, and the reactor was purged with nitrogen gas for 60 minutes to remove oxygen. Subsequently, 0.05 parts by weight azobisisobutyronitrile (AIBN) was added as a reaction initiator while maintaining a temperature of 60° C., 0.01 parts by weight n-dodecylmercaptan (n-DDM) was then added, and the resulting mixture was reacted for approximately 8 hours. After the reaction, the mixture was diluted with EAc so that a solid content of the mixture could amount to approximately 25 weight %, thereby preparing an acrylic polymer (A) having a molecular weight (Mw) of 1,200,000 and a molecular weight distribution of 4.2.

PREPARATIVE EXAMPLES 2 to 9

Acrylic Polymers (B) to (I)

(3) Acrylic polymers were prepared in the same manner as in Preparative Example 1, except that the polymerization conditions were adjusted as listed in the following Table 1 in consideration of a weight ratio and desired molecular weight (Mw) of a monomer during polymerization (in the case of Preparative Example 9, however, n-dodecyl mercaptan was not used).

(4) TABLE-US-00001 TABLE 1 Preparative Examples 1 2 3 4 5 6 7 8 9 A B C D E F G H I n-BA 69.7 64.9 69.5 79.9 65 84 79.7 99 94 EA — 5 — — 5 — 5 — — MEA 20 — 10 10 — 15 — — — ECA — 15 5 15 — — — — AA 0.3 0.1 0.5 0.1 0.8 — 0.3 — 6 2-HEA 18 15 15 10 10 1 15 1 — EAc 120 120 120 120 120 120 120 120 120 M.sub.w 120 130 125 132 125 122 132 135 185 (×10,000) Molecular 4.2 4.5 4.4 3.8 4.8 3.9 4.2 4.7 4.9 weight distribution Content unit: part(s) by weight n-BA: n-butyl acrylate EA: ethyl acrylate MEA: methoxy ethyleneglycol acrylate ECA: ethoxyethoxyethyl acrylate 2-HEA: 2-hydroxyethyl acrylate AA: acrylic acid EAc: ethyl acetate

EXAMPLE 1

Preparation of Pressure-sensitive Adhesive Composition

(5) 1.0 parts by weight of an XDI-based isocyanate cross-linking agent (D110N commercially available from Mitsui Takeda Chemicals, Inc. Japan) and 1 part by weight trioctylmethylammonium bis(trifluorosulfonyl)imide were blended relative to 100 parts by weight of the solid content of the acrylic polymer (A) prepared in Preparative Example 1, 1 part by weight lithium bis(trifluoromethanesulfonyl)imide and 0.2 parts by weight of a (3-cyanoacetyl group-containing silane coupling agent (M812 commercially available from LG Chem. Ltd.) were further blended, and solid concentration in the resulting mixture was adjusted to 15 weight % to prepare a pressure-sensitive adhesive composition.

Preparation of Pressure-sensitive Adhesive Polarizing Plate

(6) The prepared pressure-sensitive adhesive composition was coated onto a release agent-treated surface of a 38 μm-thick PET film (MRF-38 commercially available from Mitsubishi Corporation) release-treated as a release sheet so that a coating layer can have a thickness after drying of approximately 25 μm, and dried at 110° C. for 3 minutes in an oven to form a pressure-sensitive adhesive layer. Thereafter, the pressure-sensitive adhesive layer was laminated onto one surface of an iodine-based polarizing plate to prepare a pressure-sensitive adhesive polarizing plate.

EXAMPLES 2 to 7 and COMPARATIVE EXAMPLES 1 to 4

(7) Pressure-sensitive adhesive compositions and pressure-sensitive adhesive polarizing plates were prepared in the same manner as in Example 1, except that components and weight ratios were adjusted during preparation of the pressure-sensitive adhesive composition as listed in the following Tables 2 and 3.

(8) TABLE-US-00002 TABLE 2 Examples 1 2 3 4 5 6 7 Polymer A 100 100 100 Polymer B 100 Polymer C 100 Polymer D 100 Polymer E 100 TOMA- 2 1 TFSi LiTFSi 2 2 2 2 2 0.5 5 Cross- 1.0 1.0 1.0 1.0 1.0 1.0 1.0 linking agent M812 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Content unit: part(s) by weight TOMA-TFSi: trioctylmethylammonium-bis(trifluoromethanesulfonyl)imide LiTFSi: lithium bis(trifluoromethanesulfonyl)imide Cross-linking agent: XDI-based isocyanate cross-linking agent (D110N commercially available from Mitsui Takeda Chemicals, Inc., Japan) M812: β-cyanoacetyl group-containing silane coupling agent (LG Chem. Ltd.)

(9) TABLE-US-00003 TABLE 3 Comparative Examples 1 2 3 4 5 Polymer F 100 100 Polymer G 100 Polymer H 100 Polymer I 100 TOMA-TFSi 5 LiTFSi 2 2 2 2 5 Cross-linking agent 1.0 1.0 1.0 1.0 T-743L 3.0 M812 0.2 0.2 0.2 0.2 0.2 Content unit: part(s) by weight TOMA-TFSi: trioctylmethylammonium bis(trifluormethanesulfonyl)imide LiTFSi: lithium bis(trifluoromethanesulfonyl)imide Cross-linking agent: XDI-based isocyanate cross-linking agent (D110N commercially available from Mitsui Takeda Chemicals, Inc., Japan) T-743L: epoxy cross-linking agent(Sosken Electronc Co. Ltd., Japan) M812: β-cyanoacetyl group-containing silane coupling agent (LG Chem. Ltd.)

(10) The physical properties of the pressure-sensitive adhesive polarizing plates were evaluated according to the following evaluation method.

(11) 1. Measurement of Gel Fraction//

(12) A pressure-sensitive adhesive layer was maintained in a constant temperature/humidity chamber (23° C. and 60% relative humidity (R.H.)) for approximately 7 days, and then 0.3 g (A) of the pressure-sensitive adhesive was taken and put into a 200-mesh stainless wire net, and then immersed in 100 mL of ethyl acetate, and maintained at room temperature for 3 days in a dark room. A pressure-sensitive adhesive that was not dissolved in ethyl acetate after the storage was collected, and then dried at 70° C. for 4 hours. Thereafter, a weight (B) of the non-dissolved pressure-sensitive adhesive was measured, and a gel fraction was then measured by applying the measured weight (B) to the following Equation 1.
Gel fraction (%)=B/A×100  Equation 1

(13) In Equation 1, A represents a weight (0.3 g) of the pressure-sensitive adhesive before being immersed in ethyl acetate, and B represents a dry weight (units: g) of the non-dissolved parts.

(14) 2. Evaluation of Pressure-sensitive Adhesive Strength

(15) A pressure-sensitive adhesive polarizing plate was cut into pieces having a width of 25 mm and a length of 100 mm, a releasable PET film was then removed, and the polarizing plate was then attached to an alkaline-free glass using a laminator. The attachment was performed according to JIS Z 0237 using a 2 kg roller. Thereafter, the polarizing plate was treated in an autoclave (50° C., 5 atm) for approximately 20 minutes, and stored for 24 hours under constant temperature/humidity conditions (23° C., 50% R.H.). The peel strength was evaluated using measuring equipment (Texture analyzer commercially available from Stable Micro Systems Ltd., G.B.) by peeling the polarizing plate from the glass at a peel rate of 300 mm/min and a peel angle of 180 degrees.

(16) 3. Evaluation of Durability/Reliability

(17) A pressure-sensitive adhesive polarizing plate was cut into pieces having a width of 180 mm and a length of 250 mm to prepare samples. The samples were attached to a 19-inch commercially available panel using a laminator, treated in an autoclave (50° C. and 5 atm) for approximately 20 minutes, and then stored for 24 hours under constant temperature/humidity conditions (23° C. and 50% R.H.) to prepare samples.

(18) The heat/humidity resistant durability was evaluated according to the following evaluation criteria by keeping the prepared sample under heat/humidity resistant conditions (60° C. and 90% R.H. for 500 hours) and observing the appearance of bubbles and peels, and the heat-resistant durability was evaluated according to the following evaluation criteria by keeping the samples under a heat-resistant condition (80° C. for 500 hours) and observing the appearance of bubbles and peels. Also, the durability was evaluated by keeping the samples under a heat-resistant or heat/humidity condition and storing the samples at room temperature for 24 hours.

(19) <Evaluation Criteria for Durability>

(20) ∘: Bubbles and peels are not generated.

(21) Δ: Bubbles and/or peels are slightly generated.

(22) ×: Bubbles and/or peels are highly generated.

(23) 4. Measurement of Time-Dependent Changes in Surface Resistance and Surface Resistance

(24) A pressure-sensitive adhesive polarizing plate having a pressure-sensitive adhesive formed thereon was cut into pieces having a width of 50 mm and a length of 50 mm to prepare samples. Thereafter, releasable PET films of the test samples attached to the pressure-sensitive adhesive layer were removed, and their surface resistance was then measured.

(25) The surface resistance was measured according to the manufacturer's manual using MCP-HT 450 equipment (commercially available from Mitsubishi chemical, Japan).

(26) The surface resistance (SR1) before a durability test was measured after maintaining the cut test samples for 24 hours under 23° C. and 50% R.H. conditions, removing the releasable PET film from the polarizing plate and then applying a voltage of 500 Volt to the polarizing plate for 1 minute.

(27) The surface resistance (SR2) after the heat/humidity resistant durability test and surface resistance (SR3) after the heat-resistant durability test were measured after maintaining the polarizing plates under the heat/humidity conditions (60° C. and 90% R.H. for 500 hours) or heat-resistant conditions (80° C. for 500 hours), respectively, and then maintaining it again at 23° C. and 50% R.H. for 24 hours, removing the releasable PET film, and then applying a voltage of 500 Volt to the polarizing plates for 1 minute.

(28) 5. Measurement of Transparency

(29) Each of the pressure-sensitive adhesive compositions prepared in Examples or Comparative Examples was coated onto a release agent-treated surface of a 38 μm-thick PET film (MRF-38 commercially available from Mitsubishi Corporation) release-treated as a release sheet so that a coating layer could have a thickness after drying of approximately 25 μm, and dried at 110° C. for 3 minutes in an oven to form a pressure-sensitive adhesive layer. A release agent-treated surface of another PET film was laminated onto the pressure-sensitive adhesive layer formed after the drying process, and aged for 7 days under the conditions of 25° C. and 50% R.H. Thereafter, the pressure-sensitive adhesive layer was observed with the naked eye, and the transparency was evaluated according to the following evaluation criteria.

(30) <Evaluation Criteria for Transparency>

(31) ∘: A pressure-sensitive adhesive layer is observed as a colorless and transparent layer.

(32) Δ: Slight haze is generated in a pressure-sensitive adhesive layer.

(33) ×: Turbid and/or condensed matter is observed on a pressure-sensitive adhesive layer.

(34) The measured physical properties are listed in the following Tables 4 and 5.

(35) TABLE-US-00004 TABLE 4 Examples 1 2 3 4 5 6 7 Gel fraction (%) 79 82 83 79 80 81 80 Pressure-sensitive 750 830 810 870 900 755 845 adhesive strength (gf/25 mm) Heat-resistant ∘ ∘ ∘ ∘ ∘ ∘ ∘ durability Damping durability ∘ ∘ ∘ ∘ ∘ ∘ ∘ Surface resistance 2.2 3.8 4.5 5.9 4.3 2.3 0.3 (×10.sup.9 Ω/□) Δ SR.sub.B (Heat 0.15 0.22 0.2 0.25 0.2 0.13 0.2 resistance) Δ SR.sub.A (Damping) 0.4 0.47 0.48 0.72 0.58 0.35 0.42 Transparency ∘ ∘ ∘ ∘ ∘ ∘ ∘

(36) TABLE-US-00005 TABLE 5 Comparative Examples 1 2 3 4 5 Gel fraction (%) 81 80 82 78 79 Pressure-sensitive 350 780 380 950 230 adhesive strength (gf/25 mm) Heat-resistant durability ◯ ◯ ◯ ◯ Δ Damping durability ◯ ◯ Δ ◯ ◯ Surface resistance 8.9 9.7 58 49 2.5 (×10.sup.9 Ω/□) Δ SR.sub.B (Heat resistance) 0.96 1.02 1.3 1.2 1.3 Δ SR.sub.A (Damping) 1.6 1.5 1.8 1.9 1.8 Transparency ◯ ◯ ◯ ◯ X

(37) According to the present application, a pressure-sensitive adhesive that shows stable antistatic performance, and in particular stably maintains its antistatic performance even when the pressure-sensitive adhesive is kept for an extended time under extreme conditions or conditions in which environmental changes are severe, and also has excellent general physical properties such as pressure-sensitive adhesive properties, durability and workability, may be provided.