Pressure-sensitive adhesive composition

Abstract

The present application is relates to a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition of the present application may form a pressure-sensitive adhesive having excellent durability and reliability, stress relaxation and reworkability. In addition, when the pressure-sensitive adhesive composition is used collaterally, for example, a coating process may be efficiently performed even when a coating solid content is high, thereby maintaining excellent productivity and forming a pressure-sensitive adhesive having excellent uniformity in thickness. The pressure-sensitive adhesive composition may be used for an optical film such as a polarizing plate.

Claims

1. A pressure-sensitive adhesive composition, comprising: a block copolymer having 5 to 50 parts by weight of a first block having a glass transition temperature of 50° C. or more; and 50 to 95 parts by weight of a second block having a glass transition temperature of −10° C. or less, and comprising a crosslinkable functional group; and a silane coupling agent selected from the group consisting of compounds represented by Formula 1, wherein the crosslinkable functional group is not comprised in the first block but in the second block, wherein the first block comprises a polymerized unit derived from a methacrylic acid ester monomer, wherein the block copolymer has a polydispersity index of 1.9 to 2.5, wherein the block copolymer has a number average molecular weight of 90,000 to 300,000, wherein the pressure-sensitive adhesive composition has a coating solid content of 20 to 50 wt %, and wherein a coating viscosity is 500 cP to 3,000 cP at 25° C.:
(R.sub.1).sub.nSi(R.sub.2).sub.(4−n)  [Formula 1] in Formula 1, R.sub.1 is a β-cyanoacetyl group or a β-cyanoacetylalkyl group, R.sub.2 is an alkoxy group, and n is a number of 1 to 3.

2. The pressure-sensitive adhesive composition of claim 1, where the crosslinkable functional group is a hydroxyl group.

3. The pressure-sensitive adhesive composition of claim 1, wherein the second block comprises a polymerized unit derived from 90 to 99.9 parts by weight of an acrylic acid ester monomer and 0.1 to 10 parts by weight of a copolymerizable monomer having a crosslinkable functional group.

4. The pressure-sensitive adhesive composition of claim 1, wherein the first block has a number average molecular weight of 2,500 to 150,000.

5. The pressure-sensitive adhesive composition of claim 1, wherein the block copolymer is a diblock copolymer having the first and second blocks.

6. The pressure-sensitive adhesive composition of claim 1, further comprising: a crosslinking agent having at least two functional groups capable of reacting with the crosslinkable functional group.

7. The pressure-sensitive adhesive composition of claim 6, wherein the crosslinking agent is comprised at 0.01 to 10 parts by weight, relative to 100 parts by weight of the block copolymer.

8. The pressure-sensitive adhesive composition of claim 1, wherein a gel fraction after a crosslinked structure is embodied is 80 wt % or less.

9. A pressure-sensitive adhesive optical laminate, comprising: an optical film; and a pressure-sensitive adhesive layer present on one or both surfaces of the optical film and formed from the pressure-sensitive adhesive composition of claim 1.

10. A pressure-sensitive adhesive polarizing plate, comprising: a polarizing film; and a pressure-sensitive adhesive layer present on one or both surfaces of the polarizing film and formed from the pressure-sensitive adhesive composition of claim 1.

11. The pressure-sensitive adhesive polarizing plate of claim 10, wherein the pressure-sensitive adhesive composition is comprised into the pressure-sensitive adhesive layer in state of formed a crosslinked structure.

12. A display device, comprising: the pressure-sensitive adhesive optical laminate of claim 9 attached to one or both surfaces of a liquid crystal panel or the pressure-sensitive adhesive polarizing plate of claim 10.

Description

MODE FOR INVENTION

(1) Hereinafter, the pressure-sensitive adhesive composition will be described in detail with reference to Examples and Comparative Examples, but the scope of the pressure-sensitive adhesive composition is not limited to the following Examples.

(2) 1. Evaluation of Weight-average Molecular Weight

(3) A weight-average molecular weight(M.sub.n) and polydispersity index(PDI) were measured using GPC according to the following conditions. To draw a calibration curve, standard polystyrene produced by Agilent System was used, and the measurement results were converted.

(4) <Measurement Conditions>

(5) Measurer: Agilent GPC (Agilent 1200 series, U.S.)

(6) Column: connected two PL Mixed B

(7) Column temperature: 40° C.

(8) Eluent: tetrahydrofuran (THF)

(9) Flow Rate: 1.0 ml/min

(10) Concentration: ˜1 mg/mL (100 μL injection)

(11) 2. Coating Solid Content

(12) Coating solid contents were evaluated by the following method:

(13) <Order of Measuring Coating Solid Content>

(14) 1) A weight(A) of an aluminum dish was measured.

(15) 2) A pressure-sensitive adhesive composition (sample that was not dried) from Example or Comparative Example was harvested in an amount of 0.3 g or 0.5 g and put into the aluminum dish.

(16) 3) A polymerization inhibitor (hydroquinone) solution dissolved in ethyl acetate (concentration:0.5 wt %) was added to an extremely small amount of the pressure-sensitive adhesive composition using a pipette.

(17) 4) The resulting product was dried in an oven at 150° C. for 30 minutes to remove the solvent.

(18) 5) The resulting product was cooled at room temperature for 15 to 30 minutes, and subjected to measurement of a weight of a residual component(weight of the sample after drying).

(19) 6) A coating solid content was evaluated by the following equation according to the measurement result.
Coating solid content (unit:%)=100×(DS−A)/(S+E)  <Equation>

(20) DS: the weight(A) of the aluminum dish+the weight of the sample after drying (unit: g)

(21) A: the weight of the aluminum dish(unit:g)

(22) S: the weight of the sample before drying(unit:g)

(23) E: the weight of the removed components(solvent,etc.)(unit:g)

(24) 3. Evaluation of Viscosity

(25) A viscosity of the pressure-sensitive adhesive composition was evaluated by the following method using a Brookfield digital viscometer(DV-I+, DV-II+Pro).

(26) <Order of Measuring Viscosity>

(27) 1) 180 ml of a pressure-sensitive adhesive composition (sample) was put into a beaker and left under constant temperature/constant humidity (23° C./50% relative humidity) for 1 hour to remove bubbles.

(28) 2) A spindle was obliquely put into the sample without bubbles such that a liquid surface of the pressure-sensitive adhesive composition (sample) was not at a lower level than a groove of the spindle.

(29) 3) The spindle was connected to the viscometer to fit the liquid surface of the sample in the groove of the spindle.

(30) 4) An RPM of the spindle was selected by pressing a set speed key.

(31) 5) The viscometer was operated by pressing a motor on/off key.

(32) A value was obtained after a viscosity number shown on a screen stabilized. Fixation of RPM was performed when an RPM having a confidence interval of approximately 10% or more was selected on the display, and a viscosity was measured.

(33) 4. Evaluation of Coating Property

(34) Coating property of the pressure-sensitive adhesive composition prepared in each of the Examples and Comparative Examples was evaluated according to the following criteria by coating the compositions and observing a coating layer with the naked eye.

(35) <Evaluation Criteria>

(36) A: No bubbles and lines on the coating layer were observed with the naked eye.

(37) B: Bubbles and/or lines on the coating layer were vaguely observed with the naked eye.

(38) C: Bubbles and/or lines on the coating layer were clearly observed with the naked eye.

(39) 5. Evaluation of Durability

(40) A specimen was manufactured by cutting a polarizing plate formed in an Example or Comparative Example to have a width of approximately 180 mm and a length of approximately 320 mm, and attached to a 19-inch commercially available panel. Afterward, the panel was stored in an autoclave (50° C., 5 atm) for approximately 20 minutes, thereby preparing a sample. Humidity and heat resistance durability of the prepared sample was evaluated according to the following criteria by leaving the sample under conditions of a temperature of 60° C. and a relative humidity of 90% for 500 hours and observing the occurrence of bubbling and peeling at a pressure-sensitive adhesive interface. The heat resistance durability was evaluated according to the following criteria by maintaining the sample at 80° C. for 500 hours and observing the occurrence of bubbling and peeling.

(41) <Evaluation Criteria>

(42) A: No Bubbling and peeling occurred

(43) B: Bubbling and/or peeling slightly occurred

(44) C: Bubbling and/or peeling considerably occurred.

(45) 6. Calculation of Glass Transition Temperature

(46) Glass transition temperatures(Tg) of respective blocks of a block copolymer were calculated according to the following equation.
1/Tg=ΣWn/Tn  <Equation>

(47) In this equation, Wn was a weight fraction of a monomer used in each block, and Tn was a glass transition temperature obtained when the used monomer forms a homopolymer.

(48) That is, in this equation, the right side represented a result obtained by summarizing values(Wn/Tn) obtained by dividing the weight fraction of the used monomer with the glass transition temperature obtained when the used monomer formed a homopolymer by monomers.

(49) 7. Measurement of Conversion Rate and Composition Ratio

(50) The conversion rate in a polymerization process between methyl methacrylate(MMA), which was a main monomer for forming a first block, and butyl acrylate(BA), which was a main monomer for forming a second block, in a block copolymer of Example or Comparative Example, and the composition ratio in the block copolymer, were calculated by the following Equation according to 1H-NMR results.

(51) <Conversion Rate of MMA>
MMA conversion rate(%)=100×B/(A+B)

(52) Here, A is an area of a peak (in the vicinity of 3.4 ppm to 3.7 ppm) derived from a methyl group derived from MMA included in a polymer, and B is an area of a peak (in the vicinity of 3.7 ppm) derived from a methyl group of unpolymerized MMA. That is, the conversion rate of the monomer was calculated in consideration of a shift position of the metal peak in the structure of the MMA.

(53) <Conversion Rate of BA>
BA conversion rate(%)=100×C/(C+D)

(54) Here, D is an area of a peak (in the vicinity of 5.7 ppm to 6.4 ppm) derived from ═CH.sub.2 at a terminal end of a double bond, and C is an area of a peak (in the vicinity of 3.8 ppm to 4.2 ppm) derived from —OCH.sub.2— present in a polymer formed by polymerization of BA. That is, a relative values of the ═CH.sub.2 peak and the —OCH.sub.2— peak of the polymer were calculated, thereby measuring the conversion rate of BA.

(55) <Calculation of Composition Ratio>

(56) A ratio of the first and second blocks of the block copolymer was estimated by the following formula, based on a ratio of MMA to BA, which were the main monomers used to form the first and second blocks.
Content of MMA in block copolymer(%)=100×MMA peak area/BA peak area  <Equation>

(57) Here, the MMA peak area is an area value per 1H proton of the peak (peak observed by —CH.sub.3 derived from MMA) in the vicinity of 3.4 to 3.7 ppm in 1H-NMR, and a BA peak area is an area value per 1H proton of the peak (peak observed by —OCH.sub.2— present in the polymer formed by BA) in the vicinity of 3.8 to 4.2 ppm in 1H-NMR.

(58) That is, a weight ratio of the first and second blocks was estimated by calculating a relative value of the —CH.sub.3 peak in the MMA structure and the —OCH.sub.2-present in the polymer formed by BA.

PREPARATION EXAMPLE 1

Preparation of Block Copolymer (A)

(59) 0.1 g of ethyl 2-bromoisobutyrate(EBiB) and 14.2 g of methyl methacrylate(MMA) were mixed with 6.2 g of ethyl acetate(EAc). A flask containing the resulting mixture was sealed with a rubber layer, purged with nitrogen and stirred at about 25° C. for about 30 minutes, and subjected to removal of dissolved oxygen through bubbling. Afterward, 0.002 g of CuBr.sub.2, 0.005 g of tris(2-pyridylmethyl)amine (TPMA) and 0.017 g of (2,2′-azobis(2,4-dimethyl valeronitrile) (V-65) were put into the oxygen-removed mixture, and immersed in a reaction vessel at approximately 67° C. to initiate a reaction (polymerization of the first block). At the time when the conversion rate of MMA was approximately 75%, a mixture of 155 g of butyl acrylate (BA), 0.8 g of hydroxybutyl acrylate (HBA) and 250 g of ethyl acetate (EAc) which was previously bubbled with nitrogen was input in the presence of nitrogen. Afterward, 0.006 g of CuBr.sub.2, 0.012 g of TPMA and 0.05 g of V-65 were put into a reaction flask and a chain extension reaction was performed (polymerization of the second block). When the conversion rate of the monomer(BA) approached 80% or more, the reaction mixture was exposed to oxygen and diluted with a suitable solvent to terminate the reaction, thereby preparing a block copolymer (In this process, V-65 was suitably divided and input until a reaction termination time, in consideration of its half-life).

PREPARATION EXAMPLES 2 to 7

Preparation of block copolymers (A2 to A4 and B1 to B3)

(60) A block copolymer was prepared by the same method as described in Preparation Example 1, except that kinds of ingredients and additives used in the polymerization of the first block were controlled as shown in Table 1, and kinds of ingredients and additives used in the polymerization of the second block were controlled as shown in Table 2.

(61) TABLE-US-00001 TABLE 1 Ingredient MMA BMA HPMA EBiB EA CuBr.sub.2 TPMA V-65 Block A1 14.2 — — 0.1 6.2 0.002 0.005 0.017 copolymer A2 11.2 2.8 — 0.08 6.1 0.002 0.005 0.016 A3 9.4 6.3 — 0.07 6.8 0.002 0.005 0.016 A4 35.8 15.3  — 0.1 22 0.008 0.016 0.055 B1 11.6 2.4 0.4 0.08 6.2 0.002 0.005 0.016 B2 11.6 2.4 0.4 0.08 6.2 0.002 0.005 0.016 B3 5.8 — — 0.1 2.5 0.001 0.002 0.007 Content unit: g MMA: methyl methacrylate (homopolymer Tg: about 110° C.) BMA: butyl methacrylate(homopolymer Tg: about 27° C.) HPMA: 2-hydroxypropyl methacrylate (homopolymer Tg: about 26° C.) EBiB: ethyl 2-bromoisobutyrate EA: Ethyl acetate TPMA: tris(2-pyridylmethyl)amine V-65: 2,2′-azobis(2,4-dimethyl valeronitrile)

(62) TABLE-US-00002 TABLE 2 Ingredient BA HBA EA CuBr.sub.2 TPMA V-65 Block A1 115 0.8 250 0.006 0.01 0.05 copolymer A2 151 4.7 250 0.006 0.01 0.05 A3 146 9.3 250 0.006 0.01 0.05 A4 113 5.9 234 0.0002 0.0004 0.047 B1 156 — 250 0.006 0.01 0.05 B2 151 4.7 250 0.006 0.01 0.05 B3 163 0.8 250 0.006 0.01 0.05 Content unit: g BA: butyl acrylate (homopolymer Tg: about −45° C.) HBA: 4-hydroxybutyl acrylate (homopolymer Tg: about −80° C.) EA: Ethyl acetate TPMA: tris(2-pyridylmethyl)amine V-65: 2,2′-azobis(2,4-dimethyl valeronitrile)

(63) Characteristics of the block copolymers prepared by the above-described methods are shown in Table 3.

(64) TABLE-US-00003 TABLE 3 Block copolymer A1 A2 A3 A4 B1 B2 B3 First MMA ratio 100 80 60 70 81 81 100 block BMA ratio 0 20 40 30 16 16 0 HPMA ratio 0 0 0 0 3 3 0 Tg(° C.) 110 90 72 80 90 90 110 Mn(×10000) 1.9 2.3 2.9 3.8 2.3 2.3 0.8 PDI 1.27 1.34 1.38 1.41 1.36 1.36 1.18 Second BA ratio 99.5 97.0 94.0 95.0 100.0 97.0 99.5 block HBA ratio 0.5 3.0 6.0 5.0 0.0 3.0 0.5 Tg(° C.) −47 −46.2 −47.5 −47.0 −45 −46.2 −47.0 Block Mn(×10000) 10.6 12.3 14.1 10.4 12.4 12.2 10.1 copolymer PDI 1.7 1.8 2.1 2.1 1.8 1.8 1.6 First block: 10.5:89.5 10.1:89.9 11.2:88.8 34.7:65.3 10.1:89.9 10.1:89.9 4.2:95.8 Second block (weight ratio) monomer ratio unit: parts by weight BA: butyl acrylate (homopolymer Tg: about −45° C.) HBA: 4-hydroxybutyl acrylate (homopolymer Tg: about −80° C.) MMA: methyl methacrylate (homopolymer Tg: about 110° C.) BMA: butyl methacrylate(homopolymer Tg: about. 27° C.) HPMA: 2-hydroxypropyl methacrylate (homopolymer Tg: about. 26° C.) Tg: glass transition temperature Mn: number average molecular weight (Mn) PDI: polydispersity index

PREPARATION EXAMPLE 8

Preparation of Random Copolymer (B4)

(65) 10 parts by weight of MMA, 87.3 parts by weight of n-butyl acrylate and 2.7 parts by weight of 4-hydroxybutyl acrylate were put into a 1 L reactor equipped with a cooling system refluxed with a nitrogen gas and facilitating temperature control, 200 ppm of n-dodecyl mercaptan was added as a molecular weight was controlled, and 120 parts by weight of ethyl acetate was input. Subsequently, to control oxygen, purging with a nitrogen gas was performed for 60 minutes, 0.05 parts by weight of azobisisobutyronitrile(AIBN) was input as a reaction initiator while the temperature was maintained at 60° C. and reacted for approximately 8 hours, thereby preparing a random copolymer. A number average molecular weight(M.sub.n) of the prepared random copolymer(B4) was about 132,000, and a polydispersity index (PDI) thereof was about 4.6.

EXAMPLE 1

Preparation of Coating Solution(Pressure-sensitive Adhesive Composition)

(66) 0.04 parts by weight of a crosslinking agent (Coronate L, NPU, Japan), 0.1 parts by weight of dibutyltin dilaurate (DBTDL) and 0.2 parts by weight of a silane coupling agent having a β-cyanoacetyl group were mixed, relative to 100 parts by weight of the block copolymer(A1) prepared in Preparation Example 1, and ethyl acetate was blended as a solvent to control a coating solid content to be approximately 33 wt %, thereby preparing a coating solution(pressure-sensitive adhesive composition).

Preparation of Pressure-sensitive Adhesive Polarizing Plate

(67) The prepared coating solution was coated on a release-treated surface of a releasing poly(ethylene terephthalate)(PET) (MRF-38, Mitsubishi) having a thickness of 38 μm to have a dry thickness of approximately 23 μm, and maintained in an oven at 110° C. for about 3 minutes. The coating layer formed on the releasing PET layer was laminated on a WV liquid crystal layer of a polarizing plate (a laminate structure of TAC/PVA/TAC: TAC=triacetylcellulose, PVA=polyvinylalcohol-based a polarizing film), one surface of which was coated with the wide view(WV) liquid crystal layer, thereby preparing a pressure-sensitive adhesive polarizing plate.

EXAMPLES 2 AND 3 AND COMPARATIVE EXAMPLES 1 TO 4

(68) A pressure-sensitive adhesive composition(coating solution) and a pressure-sensitive adhesive polarizing plate were manufactured by the same methods as described in Example 1, except that components and ratios thereof were controlled as shown in Table 4 in preparation of the pressure-sensitive adhesive composition(coating solution).

(69) TABLE-US-00004 TABLE 4 Example Comparative Example 1 2 3 4 1 2 3 4 Acryl Kind A1 A2 A3 A4 B4 B1 B2 B3 polymer Content 100 100 100 100 100 100 100 100 Content of crosslinking agent 0.04 0.07 0.2 0.2 0.07 0.07 0.07 0.07 Content of DBTDL 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Content of SCA 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Content of coating solid 33 30 28 23 25 30 30 35 Viscosity of coating 1860 1760 1700 1690 1900 1650 1920 1770 solution (23° C.) Content unit: parts by weight Crosslinking agent: coronate L, NPU, Japan) DBTDL: dibutyltin dilaurate SCA: silane coupling agent having β-cyanoacetyl group (M812, LG Chem., Ltd.) Unit of coating solid content: wt % Unit of viscosity of coating solution: cP

(70) Evaluation results of physical properties of Examples or Comparative Examples are shown in Table 5.

(71) TABLE-US-00005 TABLE 5 Example Comparative Example 1 2 3 4 1 2 3 4 Coatability A A A A A A A A Heat resistance A A A A C C B C durability Humidity and heat A A A A B C B C resistance durability