Pressure-sensitive adhesive composition

Abstract

The present invention relates to a pressure sensitive adhesive composition, a polarizer and a liquid crystal display device. The present invention may provide a pressure sensitive adhesive which can have excellent stress relaxation characteristic to effectively inhibit light leakage by dimension change of optical films such as polarizing plates. In addition, a pressure sensitive adhesive having excellent physical properties such as adhesion durability and workability may be provided.

Claims

1. A polarizing plate comprising a polarizing element; and a pressure sensitive adhesive layer for attaching the polarizing plate to a liquid crystal panel, being formed on one or both sides of said polarizing element, and including a pressure sensitive adhesive composition in a cured state, wherein the pressure sensitive adhesive composition has a viscosity of 3,000 cP to 10,000 cP at room temperature and a solid content of at least 20% by weight to 40% by weight, and comprises a crosslinkable acrylic polymer having a weight average molecular weight of more than 500,000 and 700,000 or less, a non-crosslinkable acrylic polymer having a weight average molecular weight of more than 500,000 and 700,000 or less, a multifunctional acrylate and a multifunctional crosslinker, wherein an interpenetrating polymer network structure comprising a cross-linked structure formed by the crosslinkable acrylic polymer cross-linked with the multifunctional crosslinker, and a cross-linked structure formed by the polymerized multifunctional acrylate, is embodied in a cured state, the multifunctional crosslinker being different from the multifunctional acrylate, wherein the multifunctional acrylate is included in an amount of more than 5 parts by weight and less than 15 parts by weight, relative to 100 parts by weight of the crosslinkable acrylic polymer, wherein a gel content as represented by General Formula 2 is at least 80% by weight:
Gel content (% by weight)=B/A100[General Formula 2] wherein A represents a mass of said pressure sensitive adhesive and B represents a dry mass of insoluble fractions in said pressure sensitive adhesive after depositing it in ethyl acetate at room temperature for 48 hours, and wherein a ratio of the non-crosslinkable acrylic polymer to the crosslinkable acrylic polymer, by weight, is 0.1 to 0.5.

2. The polarizing plate according to claim 1, wherein the crosslinkable acrylic polymer comprises 80 to 99.8 parts by weight of a (meth)acrylic acid ester monomer; and 0.01 to 10 parts by weight of a crosslinkable monomer as a polymerized unit.

3. The polarizing plate according to claim 1, wherein the multifunctional crosslinker is one or more selected from a group consisting of an isocyanate compound, an epoxy compound, an aziridine compound and a metal chelate compound.

4. The polarizing plate according to claim 1, wherein the multifunctional crosslinker is included in an amount of 0.01 to 10 parts by weight relative to 100 parts by weight of the crosslinkable acrylic polymer.

5. The polarizing plate composition according to claim 1, wherein the multifunctional acrylate comprises a ring structure in the molecular structure thereof.

6. The polarizing plate according to claim 1, the pressure sensitive adhesive composition further comprises a photoinitiator.

7. The polarizing plate according to claim 1, the pressure sensitive adhesive composition further comprises a silane coupling agent or a tackifier.

8. A liquid crystal display device comprising a liquid crystal panel that the polarizing plate according to claim 1 is attached to one or both sides.

Description

DETAILED DESCRIPTION FOR CARRYING OUT THE INVENTION

(1) The present invention is explained in more detail through examples according to the present invention and comparative examples not according to the present invention below, but the scope of the present invention is not restricted by the following examples.

Preparation Example 1

Preparation of Crosslinkable Acrylic Polymer (A)

(2) In a 1 L reactor with nitrogen gas refluxed and installing a refrigerator to easily regulate a temperature, 98 parts by weight of n-butyl acrylate (n-BA) and 2 parts by weight of hydroxyethyl methacrylate (HEMA) were poured. Subsequently, 120 parts by weight of ethyl acetate (EAc) as a solvent was introduced thereto and nitrogen gas was purged for 60 minutes to remove oxygen. Then, 0.03 parts by weight of azobisisobutyronitrile (AIBN) was introduced thereto with maintaining the reactor at 60 C. and reacted for 8 hours to prepare a crosslinkable acrylic polymer (A) having a weight average molecular weight of about 700,000. The weight average molecular weight herein was measured by general gel permeation chromatography (GPC) method.

Preparation Examples 2 to 8

Preparation of Crosslinkable and Non-Crosslinkable Acrylic Polymers

(3) Crosslinkable and non-crosslinkable acrylic polymers were prepared by a method based on Preparation Example 1, except for monomer composition and weight average molecular weights of the prepared polymers to be regulated as the following tables 1 and 2.

(4) TABLE-US-00001 TABLE 1 Copoly- Copoly- Copoly- Copoly- mer (A) mer (B) mer (C) mer (D) Monomer n-BA/HEMA n-BA n-BA/AA n-BA/HEMA Composition (98/2) (100) (97/3) (99/1) (part by weight) M.sub.w (10,000) 70 70 70 150 n-BA: n-butyl acrylate HEMA: 2-hydroxyethyl methacrylate AA: acrylic acid M.sub.w: weight average molecular weight

(5) TABLE-US-00002 TABLE 2 Copoly- Copoly- Copoly- Copoly- mer (E) mer (F) mer (G) mer (H) Monomer n-BA n-BA/HEMA n-BA n-BA/HEMA Composition (100) (99/1) (100) (98/2) (part by weight) M.sub.w (10,000) 150 120 120 40 n-BA: n-butyl acrylate HEMA: 2-hydroxyethyl methacrylate AA: acrylic acid M.sub.w: weight average molecular weight

Example 1

Preparation of Pressure Sensitive Adhesive Composition

(6) 12 parts by weight of tris(acryloxyethyl)isocyanulate (molecular weight: 423, trifunctional, aronix M-315), 1.59 parts by weight of 1-hydroxycyclohexyl phenyl ketone (Irg 184, manufactured by Ciba) as a photoinitiator and 0.01 parts by weight of trimethylol modified tolylene diisocyanate (coronate L) as a crosslinker were formulated, relative to 100 parts by weight of the crosslinkable acrylic polymer (A), to prepare a pressure sensitive adhesive composition.

(7) Preparation of Pressure Sensitive Adhesive Polarizer

(8) The above prepared pressure sensitive adhesive composition was coated on a PET film (manufactured by Mitsubishi, MRF-38) having a thickness of 38 m and treated with a release sheet to have a thickness of 25 m after drying, and dried in an oven at 110 C. for 3 minutes. Subsequently, the dried coating layer was stored in a constant temperature and humidity room (23 C., 55% RH) for about 24 hours, and then laminated on a wide view (WV) liquid crystal layer of the polarizing plate coated on one side therewith. Then, the laminated plate was subjected to ultraviolet irradiation under the following condition to prepare a pressure sensitive adhesive polarizing plate.

(9) <Condition for Irradiating Ultraviolet>

(10) Ultraviolet irradiator: high pressure mercury lamp

(11) Irradiation condition: Illuminance=600 mW/cm.sup.2, Light quantity=150 mJ/cm.sup.2

Examples 2 to 4 and Comparative Examples 1 to 6

(12) The pressure sensitive adhesive polarizing plates were prepared by the method based on Example 1, except for composition of the pressure sensitive adhesive compositions to be changed as represented in the following tables 3 and 4.

(13) TABLE-US-00003 TABLE 3 Examples 1 2 3 4 Crosslinkable Kind A A C C copolymer Part by weight 100 100 100 100 Non- Kind B B crosslinkable Part by weight 25 25 polymer Non-crosslinkable: Crosslinkable 0 0.25 0 0.25 MFA Kind M315 M315 M315 M315 Part by 12 12 12 12 weight Photoinitiator Kind Irg184 Irg184 Irg184 Irg184 Part by 1.59 1.59 1.59 1.59 weight Crosslinker Kind Coro- Coro- Coro- Coro- nate L nate L nateL nate L Part by 0.01 0.07 0.04 0.07 weight M315: tris(acryloxyethyl)isocyanulate (Mw: 423, 3-functional Irg184: 1-hydroxycyclohexyl phenyl ketone (Irg184, Ciba) Crosslinker: trimethylol modified tolylene diisocyanate (coronate L) Crosslinkable: Non-crosslinkable = Part by weight of Non-crosslinkable acrylic copolymer/Part by weight of Crosslinkable acrylic polymer

(14) TABLE-US-00004 TABLE 4 Comparative Examples 1 2 3 4 5 6 Crosslinkable Kind D D F F A H copolymer Part by 100 100 100 100 100 100 weight Non- Kind E G crosslinkable Part by 400 400 polymer weight Non-crosslinkable: 4 0 4 0 0 0 crosslinkable MFA Kind M315 M315 M315 Part by 12 12 12 weight Photoinitiator Kind Irg184 Irg184 Irg184 Part by 1.59 1.59 1.59 weight Crosslinker Kind Coronate L Coronate L Coronate L Coronate L Coronate L Coronate L Part by 0.04 0.04 0.04 0.04 0.06 weight M315: tris(acryloxyethyl)isocyanulate (Mw: 423, 3-functional Irg184: 1-hydroxycyclohexyl phenyl ketone (Irg184, Ciba) Crosslinker: trimethylol modified tolylene diisocyanate (coronate L) Crosslinkable: Non-crosslinkable = Part by weight of Non-crosslinkable acrylic copolymer/Part by weight of Crosslinkable acrylic polymer

(15) For the pressure sensitive adhesive polarizing plates prepared in Examples and Comparative Examples, physical properties were measured by the following methods and their results were summarized in Tables 5 and 6 below.

(16) 1. Evaluation of Curl Property in Liquid Crystal Panel

(17) The pressure sensitive adhesive polarizing plates prepared in Examples and Comparative Examples were each attached to both sides of general liquid crystal panels as top and bottom polarizing plates. Then, the liquid crystal panels, to which the polarizing plates were attached, were left in an oven at 80 C. for 72 hours, and removed from the oven to measure a degree of curling along four edges of the liquid crystal panels within 5 minutes and to evaluate curl property depending on the following standard.

(18) <Evaluation Standard>

(19) : no occurrence of curl in liquid crystal panel

(20) : slight occurrence of curl in liquid crystal panel

(21) : some occurrence of curl in liquid crystal panel

(22) x: frequent occurrence of curl in liquid crystal panel

(23) 2. Evaluation of Endurance Reliability

(24) The pressure sensitive adhesive polarizing plates prepared in Examples and Comparative Examples were tailored in a size of 90 mm170 mm to prepare specimens, which were then attached to both sides of glass substrates (110 mm190 mm0.7 mm) in a state of crossed optical absorption axes to prepare samples. Here, the applied presser was about 5 Kg/cm.sup.2, and the above procedures were carried out in a clean room to cause no bubbles or foreign materials. To identify humidity and heat resistance of the prepared samples, the samples were left at a temperature of 60 C. and under a 90% relative humidity condition for 1,000 hours and observed of whether bubbles or peel-off were present. In addition, for heat resistance, the samples were left at a temperature of 80 C. for 1,000 hours and then observed of whether bubbles or peel-off were present. The state of specimens was evaluated after being left at room temperature for 24 hours shortly before evaluation. Evaluation standards for reliability are as follows.

(25) <Evaluation Standard>

(26) : no occurrence of bubbles or peel-off phenomenon

(27) : slight occurrence of bubbles or peel-off phenomenon

(28) x: frequent occurrence of bubbles or peel-off phenomenon

(29) 3. Evaluation of Light Transmission Uniformity (Light Leakage)

(30) Light transmission uniformity was measured using the same specimens as those for evaluating endurance reliability. The above specimens were irradiated with backlight and observed of whether a portion of light leakage in a dark room was present. Specifically, the light transmission uniformity was evaluated by a method of attaching pressure sensitive adhesive polarizing plates (200 mm200 mm) to both sides of glass substrates (210 mm210 mm0.7 mm) in a state crossed at 90 degrees and observing them. Evaluation standards for light transmission uniformity are as follows.

(31) <Evaluation Standard>

(32) : it is difficult to identify a non-uniformity phenomenon in light transmission by the naked eye

(33) : slight presence of a non-uniformity phenomenon in light transmission

(34) x: large presence of a non-uniformity phenomenon in light transmission

(35) Each physical property measured in the above was summarized in the following tables 5 and 6.

(36) TABLE-US-00005 TABLE 5 Examples 1 2 3 4 Re-detachability Endurance Heat resistant Reliability condition Humidity and heat resistant condition Light transmission uniformity

(37) TABLE-US-00006 TABLE 6 Comparative Examples 1 2 3 4 5 6 Re-detachability X X Endurance Heat resistant X X Reliability condition Humidity and heat X X resistant condition Light transmission uniformity X X X

(38) As could be known from results of the above tables 5 and 6, in cases of Examples 1 to 4 according to the present invention, re-detachability, endurance reliability and light transmission uniformity of the pressure sensitive adhesives were maintained all outstandingly. However, in cases of Comparative Examples 1 and 3 using polymers having a molecular weight of 1,000,000 or more, it was identified to highly reduce re-detachability and light transmission uniformity, although the IPN structures were embodied in the pressure sensitive adhesives. Furthermore, in case of Comparative Example 6 using a polymer having a molecular weight of 500,000 or less, stress relaxation characteristic was secured to a certain degree, but durability was highly lowered.

(39) Also, in cases of Comparative Examples 2 and 4 using polymers having a molecular weight of 1,000,000 or more and embodying no IPN structure in the pressure sensitive adhesives, it could be identified that at least one physical property of re-detachability, durability and control capability of light leakage control capability was lowered and its balance was poor. In addition, in case of Comparative Example 5 embodying no IPN structure in the pressure sensitive adhesive, it was also identified that durability of the pressure sensitive adhesive was highly lowered.