Pressure sensitive adhesive composition

Abstract

Provided are a pressure-sensitive adhesive composition, a pressure-sensitive adhesive optical laminate, a pressure-sensitive adhesive polarizing plate and a display device. The pressure-sensitive adhesive composition offers a pressure-sensitive adhesive that has excellent durability and processability in manufacturing due to increased hardness even when the pressure-sensitive adhesive layer is formed thinner than a typical adhesive composition, and that can prevent a pressure mark and leakage of the pressure-sensitive adhesive, as well as a bending problem generated when applied on an optical member such as a polarizing plate, etc.

Claims

1. A pressure-sensitive adhesive composition, consisting of: a pressure-sensitive adhesive polymer including a polymerization unit of a first monomer which forms a homopolymer having a glass transition temperature of less than 0° C., a polymerization unit of a second monomer which forms a homopolymer having a glass transition temperature of 0° C. or more, and a polymerization unit of a cross-linking monomer, and having an acid value of 1 mgKOH/g or less; a cross-linking agent at 0.01 to 10 parts by weight, relative to 100 parts by weight of the pressure-sensitive adhesive polymer; a cross-linking catalyst in an amount of 1 to 40 ppm; optionally at least one of other monomers for copolymerization; optionally a silane coupling agent; optionally a tackifier; and optionally one or more additives selected from the group consisting of a curing agent, a UV light stabilizer, an antioxidant, a coloring agent, a reinforcing agent, a filler, an antifoaming agent, a surfactant and a plasticizer, wherein the pressure sensitive adhesive composition has a storage elastic modulus at 30° C. and 1 rad/sec ranging from 0.01 MPa to 0.5 MPa in a state in which a cross-linked structure is formed.

2. The pressure-sensitive adhesive composition of claim 1, wherein the homopolymer formed of the first monomer has a glass transition temperature ranging from −100° C. to −20° C.

3. The pressure-sensitive adhesive composition of claim 1, wherein the homopolymer formed of the second monomer has a glass transition temperature ranging from 5° C. to 200° C.

4. The pressure-sensitive adhesive composition of claim 1, wherein the second monomer is an acyclic monomer.

5. The pressure-sensitive adhesive composition of claim 1, wherein the pressure-sensitive adhesive composition has a glass transition temperature ranging from −50° C. to 50° C. in a state in which a cross-linked structure is formed.

6. The pressure-sensitive adhesive composition of claim 1, wherein the cross-linking catalyst is at least one selected from the group consisting of trialkylaminoalkylethanol amine, N,N,N′,N′-tetraalkylhexanediamine, trialkylamine, imidazole, naphthenic acid cobalt, dialkyltin diacetate, dialkyltin diacetylacetonate, trialkyltin hydroxide, dialkyltin dilaurate, and a combination thereof.

7. A pressure-sensitive adhesive optical laminate comprising: an optical film; and a pressure-sensitive adhesive layer formed on either or both sides of the optical film, and containing the pressure-sensitive adhesive composition of claim 1 which is cross-linked.

8. A pressure-sensitive adhesive polarizing plate comprising: a polarizer film; and a pressure-sensitive adhesive layer formed on either or both sides of the polarizer film, and containing the pressure-sensitive adhesive composition of claim 1 which is cross-linked.

9. A display device comprising the optical laminate of claim 7.

10. A display device comprising the polarizing plate of claim 8.

11. The pressure-sensitive adhesive composition of claim 1, wherein the silane coupling agent is a compound of Formula 1 or Formula 2:
(R.sub.1).sub.nSi(R.sub.2).sub.(4-n)  [Formula 1]
(R.sub.3).sub.nSi(R.sub.2).sub.(4-n)  [Formula 2] wherein R.sub.1 is a beta-cyanoacetyl group or a beta-cyanoacetylalkyl group, R.sub.3 is an acetoacetyl group or an acetoacetylalkyl group, R.sub.2 is an alkoxy group and n is an integer of 1 to 3.

12. The pressure-sensitive adhesive composition of claim 1, wherein the silane coupling agent is acetoacetylpropyl trimethoxysilane, acetoacetylpropyl triethoxysilane, beta-cyanoacetylpropyl trimethoxysilane, or beta-cyanoacetylpropyl triethoxysilane.

13. The pressure-sensitive adhesive composition of claim 1, wherein the tackifier is selected from the group consisting of hydrocarbon resins, hydrogenated hydrocarbon resins, rosin resins, hydrogenated rosin resins, rosin ester resins, hydrogenated rosin ester resins, terpene resins, hydrogenated terpene resins, terpene phenol resins, hydrogenated terpene phenol resins, polymerized rosin resins, polymerized rosin ester resins, and a combination thereof.

14. The pressure-sensitive adhesive composition of claim 1, wherein the at least one of other monomers is selected from the group consisting of a styrene-based monomer and a monomer containing a glycidyl group.

15. The pressure-sensitive adhesive composition of claim 13, wherein the styrene-based monomer is methyl styrene.

16. The pressure-sensitive adhesive composition of claim 14, wherein the monomer containing a glycidyl group is glycidyl (meth)arylate.

17. The pressure-sensitive adhesive composition of claim 1, wherein the pressure-sensitive adhesive composition has a gel fraction of 70 wt % to 80 wt % calculated using the following Equation 1 after forming a cross-linked structure:
Gel fraction (%)=B/A×100  [Equation 1] wherein in Equation 1, A is a mass of the pressure-sensitive adhesive composition forming a cross-linked structure, B is a dry mass of the insoluble fraction which is obtained by depositing the pressure-sensitive adhesive composition having a mass of A in ethyl acetate for 24 hours, in the state in which the pressure-sensitive adhesive composition is laid in the mesh having a size of 200 meshes at room temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic view illustrating a bending evaluation method of polarizing plates to which the pressure-sensitive adhesive prepared according to Examples and Comparative Examples of the present invention is applied; and

(3) FIG. 2 is a picture illustrating peeling of the pressure-sensitive adhesive on the polarizing plates prepared according to Example 1, Comparative Example 1 and Comparative Example 4 of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(4) Exemplary embodiments of the pressure-sensitive adhesive composition of the present invention will be described in detail below with reference to the following Examples and Comparative Examples. However, it will be apparent to those skilled in the art that the scope of the pressure-sensitive adhesive composition is not limited by the following Examples and Comparative Examples.

(5) 1. Evaluation of Pressure-Sensitive Adhesive Peeling

(6) The polarizing plate prepared in Examples or Comparative Examples was aged for 3 days after being produced, and the release film thereon was removed, such that a pressure-sensitive adhesive layer was exposed. A powerful adhesive tape with a thickness of 50 mm (consumable adhesive masking tape, manufactured by TAPEX) was attached to the pressure-sensitive adhesive layer and stripped therefrom, and then the residue of the pressure-sensitive adhesive on the tape was observed. The degree of the pressure-sensitive adhesive peeling was evaluated based on the below standard.

(7) <Evaluation Standard>

(8) A: no residue with a diameter of 1 mm or more was observed

(9) B: residue with a diameter of 2 mm or more in 5 places or less

(10) C: residue with a diameter of 2 mm or more in 6 places or more

(11) 2. Measurement of Gel Fraction

(12) 0.2 g of the pressure-sensitive adhesive was collected from the polarizing plate prepared in each of Examples and Comparative Examples, and was deposited in 100 g of the solvent (ethyl acetate). After 24 hours, an insoluble fraction (gel) was filtered out using a mesh with a size of 200 meshes and the amount of the obtained gel was substituted into the following Equation 1 to calculate the gel fraction. The evaluation standard based on the calculated gel fraction is as follows.
Gel fraction (%)=100×the weight of the insoluble fractions filtered by a mesh (unit: g)/0.2  [Equation 1]

(13) <Evaluation Standard>

(14) A: gel fraction was 70% or more and less than 80%

(15) B: gel fraction was 60% or more and less than 70%

(16) C: gel fraction was less than 60%

(17) 3. Evaluation of Durability

(18) The polarizing plates prepared in Examples and Comparative Examples were cut to a size of 180 mm×320 mm (width×length) to prepare specimens, and such obtained specimens were attached to 19-inch commercial panels. Thereafter, the panels with the polarizing plates were left in an autoclave (50° C., 5 atm) for about 20 minutes such to produce test samples. The test samples were left at 80° C. for 500 hours, during which the formation of bubbles and peeling was observed, and then the heat resistance durability was evaluated based on the following standard. Further, the test samples were left for 500 hours under conditions of 60° C. and a relative humidity of 90%, during which the formation of bubbles and peeling at the pressure-sensitive adhesive interface was observed, and then the water resistance durability was also evaluated based on the following standard.

(19) <Evaluation Standard>

(20) A: no bubbles, peeling or lifting was observed

(21) B: bubbles, peeling and/or lifting were observed slightly

(22) C: bubbles, peeling and/or lifting were observed substantially

(23) 4. Evaluation of Bending

(24) The polarizing plates prepared in Examples and Comparative Examples were cut to a size of 180 mm×320 mm (width×length) and attached to glass substrates (0.7T) with a size of 200 mm×400 mm (width×length) to be matched to the center part of the glass substrates, and then were aged for 72 hours in a chamber at 60° C. Positions 1-8 of polarizing plates attached to a glass substrate are demonstrated by numberals 1-8 in FIG. 1. Subsequently, the glass substrates taken out of the chamber were left for 4 hours at room temperature. Thereafter, a center position 4 and a center position 5 of polarizing plates attached to a glass substrate shown in FIG. 1 were laid on a flat floor and the difference in the distances in which an end position 1 and an end position 8 of polarizing plates attached to a glass substrate shown in FIG. 1 rose from the flat floor was measured to evaluate the degree of bending based on the following standard.

(25) <Evaluation Standard>

(26) A: the difference between the distances in which the end position 1 and the end position 8 in FIG. 1 rose from the flat floor was less than 3 mm

(27) B: the difference between the distances in which the end position 1 and the end position 8 in FIG. 1 rose from the flat floor was 3 mm or more and less than 5 mm

(28) C: the difference between the distances in which the end position 1 and the end position 8 in FIG. 1 rose from the flat floor was 5 mm or more

(29) 5. Measurement of Acid Value

(30) The polymerization solutions prepared in each Preparation Example were fully dried to form the polymer samples, and 0.5 g of each of the obtained samples was dissolved in 50 g of a solvent of toluene and 2-propanol mixed at a weight ratio of 1:1. The proper amount of a phenolphthalein indicator which contains acrylic acid having a molecular weight of 72.06 was added into the resulting solution, and a prepared base solution (0.1 M, KOH) was further put dropwise into the transparent sample solution with stirring, until an equivalence point, at which the color of the sample solution turned red, was reached. Thereafter, when the base solution was put dropwise into the sample solution so that an equivalence point was almost reached, the sample solutions were observed for color changes for about 10 seconds, and then the volume of the base solution which was added dropwise just prior to the change of the color was measured. The acid value was calculated by substituting such measured volume into the following Equation.
A=(X×Y×72.06)/M  [Equation]

(31) A: an acid value (mgKOH/g)

(32) X: a mol concentration of KOH (M)

(33) Y: a volume of the base solution put dropwise into the samples (ml)

(34) M: a weight of the polymer samples (=0.5 g)

(35) 6. Measurement of Storage Modulus

(36) A storage modulus of the pressure-sensitive adhesives prepared in Examples and Comparative Examples were measured using Advanced Rheometric Expansion System (ARES; manufactured by TA Instruments). Specifically, the cross-linked pressure-sensitive adhesives were cut to a diameter of 8 mm and a thickness of 1 mm to produce the samples. The frequency sweep was carried out for the obtained samples using a parallel plate fixture, under conditions of 10% strain and a frequency of 0.1 Hz to 500 Hz, and a storage modulus of the pressure-sensitive adhesive composition in the Examples and the Comparative Examples was measured under conditions of 30° C. and 1 rad/s.

(37) 7. Measurement of Glass Transition Temperature

(38) 5 mg of the sample of the polymerization solution prepared in each of Preparation Examples was measured with the glass transition temperatures within the range of −70° C. to 50° C., using a Differential Scanning calorimetry (DSC; manufactured by TA Instruments) with a heating rate of 10° C. per minute.

Preparation Example 1. Preparation of Polymerization Solution A1

(39) A monomer mixture composed of n-butyl acrylate (BA) forming a homopolymer with a glass transition temperature of −45° C., tert-butyl acrylate (t-BA) forming a homopolymer with a glass transition temperature of 118° C., and 4-hydroxybutyl acrylate (HBA) forming a homopolymer with a glass transition temperature of −80° C. at the weight ratio of 79:20:1 and ethyl acetate as a solvent were put into a reactor equipped with a cooling device for the regulation of temperature and the reflux of nitrogen gas. Subsequently, the reactor was purged with nitrogen gas for 1 hour in order to remove oxygen from the reactor and the proper amount of azobisisobutylonitrile (AIBN) was added therein as a reaction initiator for polymerization. After polymerization, the reactants were diluted with ethyl acetate (EAc) and thereby a polymerization solution A1 with a weight average molecular weight of about 1,800,000 and with a distribution of molecular weight of about 3.8 was obtained.

Preparation Examples 2 to 4. Preparation of Polymerization Solutions A2, B1 and B2

(40) The polymerization solutions A2, B1, and B2 were prepared in the same manner as in Preparation Example 1 except that the type and ratio of the monomers were adjusted as shown in Table 1 below.

(41) TABLE-US-00001 TABLE 1 BA t-BA HBA MA AA Polymer- A1 79 20 1 — — ization A2 79 — 1 20 — solution B1 99 — 1 — — B2 96 — — — 4 Content unit: parts by weight BA: butyl acrylate (glass transition temperature (Tg) of homopolymer: about −45° C.) t-BA: tert-butyl acrylate (Tg of homopolymer: about 43° C. to 107° C.) HBA: 4-hydroxybutyl acrylate (Tg of homopolymer: about −32° C.) MA: methyl acrylate (Tg of homopolymer: about 10° C.) AA: acrylic acid (Tg of homopolymer: about 105° C.)

Example 1

(42) Preparation of Coating Solution (Pressure-Sensitive Adhesive Composition)

(43) 0.1 parts by weight of a cross-linking agent (T-39M; manufactured by Soken Chemical & Engineering Co., Ltd.) based on 100 parts by weight of the solid fractions of the polymerization solution A1 prepared in Preparation Example 1, and 8 ppm of a catalyst (DBTDL, dibutyltin dilaurate) were mixed in a solvent (EAc, ethyl acetate) and thereby a coating solution (pressure-sensitive adhesive composition) was prepared.

(44) Preparation of Pressure-Sensitive Adhesive Polarizing Plate

(45) The prepared coating solution was laid on a release-processed surface of the release polyethylene terephthalate (PET) film with a thickness of 38 μm (MRF-38, manufactured by Mitsubishi Chemical Corporation) and was stored for about 3 minutes at 120° C. so as to form a coating layer having a thickness of about 23 μm after drying. After drying, the pressure-sensitive adhesive layer formed on the release film was laminated on a wide view (WV) liquid crystal layer of a polarizing plate (laminated structure: TAC/PVA/TAC, TAC=triacetyl cellulose, PVA=polyvinyl alcohol-based polarizer film), one side of which was coated with the WV liquid crystal layer. Thereby, the pressure-sensitive adhesive polarizing plate sequentially including a polarizing plate, a pressure-sensitive adhesive layer, and a release PET film was prepared.

Examples 2 to 3 and Comparative Examples 1 to 5

(46) The pressure-sensitive adhesive composition (coating solution) and the adhesive polarizing plate were prepared in the same manner as in Example 1, except that the composition and ratio of each pressure-sensitive adhesive composition (coating solution) were adjusted as shown in Table 2 below when prepared.

(47) TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 3 1 2 3 4 5 Polymerization Type A1 A1 A2 A1 A1 B1 B2 A1 solution Content 100 100 100 100 100 100 100 100 Cross-linking Type (1) (1) (1) (1) (1) (1) (1)/(2) (1) agent Content 0.1 0.1 0.1 0.1 0.1 0.1 1.36/0.01 0.2 DBTDL content 8 10 8 50 — 50 — 50 Content unit: parts by weight (polymerization solution is measured with its solid fraction/content unit of DBTDL: ppm) Cross-linking agent (1): T-39M, Soken Chemical & Engineering Co., Ltd. Cross-linking agent (2): T-743, Soken Chemical & Engineering Co., Ltd. DBTDL: dibutyltin dilaurate

(48) The property evaluation results in accordance with each of the Examples and the Comparative Examples are shown in Table 3.

(49) TABLE-US-00003 TABLE 3 Example Comparative Example 1 2 3 1 2 3 4 5 Pressure-sensitive A A A C A B C A adhesive peeling Gel fraction A A A A C A A A Durability A A A A C B A A Bending A A A A A A B C evaluation Acid value 0.12  0.12  0.15  0.13  0.12  0.16  11 0.13  (mgKOH/g) Storage modulus 0.053 0.053 0.051 0.053 0.052 0.043 0.078 0.055 (MPa)

(50) As described above, the comparison results of Examples and Comparative Examples show that the pressure-sensitive adhesive composition in accordance with an exemplary embodiment of the present invention offers a pressure-sensitive adhesive that has increased durability and processability in manufacturing by increasing a hardness, even when the pressure-sensitive adhesive layer is formed to be thinner than a typical pressure-sensitive adhesive composition, and that can prevent a pressure mark and peeling of the pressure-sensitive adhesive, as well as a bending problem generated when applied on an optical member such as a polarizing plate, etc.