Polarizer protective film, polarizing plate and method for preparing polarizing plate

Abstract

The present invention relates to a polarizer protective film comprising a binder resin layer in which a poly(C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer and a bifunctional or higher polyfunctional (meth)acrylate-based compound form a cross-linked bond, a polarizing plate comprising the polarizer protective film and a method for preparing a polarizing plate comprising forming the polarizer protective film.

Claims

1. A polarizer protective film comprising a binder resin layer in which a poly(C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer and a bifunctional or higher polyfunctional (meth)acrylate-based compound form a cross-linked bond, wherein the weight ratio of the bifunctional or higher polyfunctional (meth)acrylate-based compound to the poly(C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer is from 1.1 to 1.20, and wherein the poly(C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer has a trifunctional or higher functional urethane bond and is bound to each poly(C.sub.2-4 alkylene glycol)-modified (meth)acrylate-based compound via the urethane bond, and at least two poly(C.sub.2-4 alkylene glycol)-modified (meth)acrylate-based compounds bound to each urethane bond comprises poly(C.sub.2-4 alkylene glycol) repeating units whose numbers of repetitions are different from each other.

2. The polarizer protective film of claim 1, wherein the difference of the number-average molecular weight between at least two poly(C.sub.2-4 alkylene glycol)-modified (meth)acrylate-based compounds bound to the urethane bond is 100 to 500.

3. The polarizer protective film of claim 1, wherein the poly(C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer comprises at least one selected from the group consisting of a polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based polymer and a polypropylene glycol-modified polyfunctional urethane (meth)acrylate-based polymer.

4. The polarizer protective film of claim 1, wherein the poly(C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer is a reactant between a trifunctional or higher functional polyvalent isocyanate-based compound; and at least two poly(C.sub.2-4 alkylene glycol)- modified (meth)acrylate-based compounds including poly (C.sub.2-4 alkylene glycol) repeating units whose numbers of repetitions are different from each other.

5. The polarizer protective film of claim 4, wherein the polyvalent isocyanate-based compound is selected from the group consisting of an oligomer of a diisocyanate compound, a polymer of a diisocyanate compound, a cyclic polymer of a diisocyanate compound, hexamethylene diisocyanate isocyanurate, isophorone diisocyanate isocyanurate, toluene 2,6-diisocyanate isocyanurate, a triisocyanate compound and an isomer thereof.

6. The polarizer protective film of claim 4, wherein each of the at least two poly (C.sub.2-4 alkylene glycol)-modified (meth)acrylate-based compounds including poly (C.sub.2-4 alkylene glycol) repeating units whose numbers of repetitions are different from each other has a number-average molecular weight of 200 to 1000.

7. The polarizer protective film of claim 1, wherein the binder resin layer further includes a polycarbonate-modified bifunctional urethane (meth)acrylate-based polymer.

8. The polarizer protective film of claim 7, wherein the polycarbonate-modified bifunctional urethane (meth)acrylate-based polymer has a bifunctional or higher functional urethane bond and is bound to each polycarbonate-modified (meth)acrylate-based compound via the urethane bond.

9. The polarizer protective film of claim 1, wherein the bifunctional or higher polyfunctional (meth)acrylate-based compound includes at least one selected from the group consisting of polyfunctional urethane acrylate, 9-ethylene glycol diacrylate (9-EGDA), bisphenol A epoxy acrylate, polyether triacrylate, pentaerythritol tri/tetraacrylate(PETA), dipentaerythritol hexa-acrylate DPHA), trimethylolpropane triacrylate (TMPTA) and hexamethylene diacrylate (HDDA).

10. The polarizer protective film of claim 1, wherein the weight ratio of the bifunctional or higher polyfunctional (meth)acrylate-based compound relative to the poly (C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer is from 1.5 to 1.15.

11. A polarizing plate comprising a polarizer and the polarizer protective film of claim 1.

12. The polarizing plate of claim 11, further comprising an adhesive layer positioned between the polarizer and the protective film.

13. The polarizing plate of claim 11, further comprising a second polarizer protective film formed on one side of the polarizer.

14. The polarizing plate of claim 11, wherein the thickness of the polarizer protective film is 1 m to 100 m, and the thickness of the polarizer is 5 m to 300 m.

15. A method for preparing a polarizing plate, comprising forming a polarizer protective film by photocuring a coating composition including a poly (C.sub.2-4alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer; a bifunctional or higher polyfunctional (meth)acrylate-based compound; and a photo-initiator; and laminating and adhering the polarizer protective film to one surface of a polarizer, wherein the weight ratio of the bifunctional or higher polyfunctional (meth)acrylate-based compound to the poly (C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer is from 1.1 to 1.20, and wherein the poly(C.sub.2-4 alkylene glycol)-modified polyfunctional urethane (meth)acrylate-based polymer has a trifunctional or higher functional urethane bond and is bound to each poly(C.sub.2-4 alkylene glycol)-modified (meth)acrylate-based compound via the urethane bond, and at least two poly(C.sub.2-4 alkylene glycol)-modified (meth)acrylate-based compounds bound to each urethane bond comprises poly(C.sub.2-4 alkylene glycol) repeating units whose numbers of repetitions are different from each other.

16. The method for preparing a polarizing plate of claim 15, wherein the coating composition further includes an organic solvent; or at least one additive selected from the group consisting of an inorganic nanoparticle, a surfactant, a leveling agent and a dispersion stabilizer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows FT-IR spectra before and after carrying out a urethane reaction for preparing the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder in Preparation Example 1, by comparison.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) Hereinafter, the present invention will be described in more detail by way of Examples. However, these Examples are given for illustrative purposes only, and the scope of the invention is not intended to be limited by these Examples.

PREPARATION EXAMPLES

Preparation Example 1

Preparation of Polyethylene Glycol-modified Polyfunctional Urethane (Meth)Acrylate-based Binder

(3) DN980S manufactured by AEKYUNG Chemical, which is an HDI-based trimer, was used as a trifunctional or higher functional polyvalent isocyanate-based compound, and as polyethylene glycol-modified (meth)acrylate-based compounds, a polyethylene glycol monoacrylate (Mn=300) and a polyethylene glycol monoacrylate (Mn=500) having different number-average molecular weights and including polyethylene glycol repeating units whose numbers of repetitions are different from each other were respectively used.

(4) 40 g of the polyvalent isocyanate-based compound, 30 g of the polyethylene glycol monoacrylate (Mn=300) and 30 g of the polyethylene glycol monoacrylate (Mn=500) were mixed with 0.1 g of DBTDL (dibutyl tin dilaurate) and 200 g of methyl ethyl ketone, and the mixture was stirred at 60 C. for about 5 hours to carry out a urethane reaction.

(5) After completion of the urethane reaction, a polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder of Preparation Example 1 was prepared. The progress of the urethane reaction and the formation of the binder were confirmed via FT-IR. For reference, the FT-IR spectra before and after the urethane reaction are shown in FIG. 1. Referring to FIG. 1, it was confirmed that the peak derived from the isocyanate group (NCO) appearing at the position of about 2268.5 cm.sup.1 disappeared, thereby confirming the progress of the urethane reaction and the formation of the binder.

Preparation Example 2

Preparation of Polypropylene Glycol-modified Polyfunctional Urethane (Meth)Acrylate-based Binder

(6) DN980S manufactured by AEKYUNG Chemical, which is an HDI-based trimer, was used as a trifunctional or higher functional polyvalent isocyanate-based compound, and as polypropylene glycol-modified (meth)acrylate-based compounds, a polypropylene glycol monoacrylate (Mn=400) and a polypropylene glycol monoacrylate (Mn=600) having different number-average molecular weights and including polypropylene glycol repeating units whose numbers of repetitions are different from each other were each used.

(7) 40 g of the polyvalent isocyanate-based compound, 40 g of the polypropylene glycol monoacrylate (Mn=400) and 40 g of the polypropylene glycol monoacrylate (Mn=600) were mixed with 0.15 g of DBTDL (dibutyl tin dilaurate) and 300 g of methyl ethyl ketone, and the mixture was stirred at 60 C. for about 5 hours to carry out a urethane reaction.

(8) After completion of the urethane reaction, a polypropylene glycol-modified polyfunctional urethane (meth)acrylate-based binder of Preparation Example 2 was prepared. The progress of the urethane reaction and the formation of the binder were confirmed by the disappearance of the peak derived from the isocyanate group (NCO) appearing at the position of about 2268.5 cm.sup.1 via FT-IR, in the same manner as in Preparation Example 1.

Comparative Preparation Example 1

Preparation of Polyethylene Glycol-modified Polyfunctional Urethane (Meth)Acrylate-based Binder

(9) 40 g of DN980S (trifunctional or higher functional polyvalent isocyanate-based compound) manufactured by AEKYUNG Chemical, which is an HDI-based trimer, and 70 g of polyethylene glycol monoacrylate (Mn=300) were mixed with 0.1 g of DBTDL (dibutyl tin dilaurate) and 200 g of methyl ethyl ketone, and the mixture was stirred at 60 C. for about 5 hours to carry out a urethane reaction.

(10) After completion of the urethane reaction, a polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder of Comparative Preparation Example 1 was prepared. The progress of the urethane reaction and the formation of the binder were confirmed via FT-IR, in the same manner as in Preparation Example 1.

Comparative Preparation Example 2

Preparation of Polyethylene Glycol-modified Polyfunctional Urethane (Meth)Acrylate-based Binder

(11) 40 g of DN980S (trifunctional or higher functional polyvalent isocyanate-based compound) manufactured by AEKYUNG Chemical, which is an HDI-based trimer, and 80 g of polypropylene glycol monoacrylate (Mn=600) were mixed with 0.15 g of DBTDL (dibutyl tin dilaurate) and 300 g of methyl ethyl ketone, and the mixture was stirred at 60 C. for about 5 hours to carry out a urethane reaction.

(12) After completion of the urethane reaction, a polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder of Comparative Preparation Example 2 was prepared. The progress of the urethane reaction and the formation of the binder were confirmed via FT-IR, in the same manner as in Preparation Example 1.

Comparative Preparation Example 3

Preparation of Polyethylene Glycol-modified Polyfunctional Urethane (Meth)Acrylate-based Binder

(13) 40 g of DN980S (trifunctional or higher functional polyvalent isocyanate-based compound) manufactured by AEKYUNG Chemical, which is an HDI-based trimer, and 80 g of polypropylene glycol monoacrylate (Mn=200) were mixed with 0.15 g of DBTDL (dibutyl tin dilaurate) and 300 g of methyl ethyl ketone, and the mixture was stirred at 60 C. for about 5 hours to carry out a urethane reaction.

(14) After completion of the urethane reaction, a polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder of Comparative Preparation Example 3 was prepared. The progress of the urethane reaction and the formation of the binder were confirmed via FT-IR, in the same manner as in Preparation Example 1.

Comparative Preparation Example 4

Preparation of Polyethylene Glycol-modified Polyfunctional Urethane (Meth)Acrylate-based Binder

(15) 40 g of DN980S (trifunctional or higher functional polyvalent isocyanate-based compound) manufactured by AEKYUNG Chemical, which is an HDI-based trimer, and 80 g of polypropylene glycol monoacrylate (Mn=1000) were mixed with 0.15 g of DBTDL (dibutyl tin dilaurate) and 300 g of methyl ethyl ketone, and the mixture was stirred at 60 C. for about 5 hours to carry out a urethane reaction.

(16) After completion of the urethane reaction, a polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder of Comparative Preparation Example 4 was prepared. The progress of the urethane reaction and the formation of the binder were confirmed via FT-IR, in the same manner as in Preparation Example 1.

EXAMPLES

Preparation of Polarizer Protective Films and Polarizing Plates

Example 1

(17) (1) Preparation of Composition for Forming Polarizer Protective Film

(18) The polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Preparation Example 1 and dipentaerythritol hexaacrylate (DPHA), as a bifunctional or higher polyfunctional (meth)acrylate-based compound, were mixed at a weight ratio of 1:8 to prepare a composition for forming a binder.

(19) Then, a coating composition of Example 1 was prepared by mixing 2 parts by weight of a UV initiator (Irgacure 184), 5 parts by weight of a leveling agent (tego glide 270 manufactured by Evonik) and 35 parts by weight of methyl ethyl ketone based on 100 parts by weight of the composition for forming a binder.

(20) (2) Preparation of Polarizer Protective Film

(21) The coating composition of Example 1 was coated on a PET release film to have a thickness of 30 m, dried in an oven at 60 C. for 2 minutes and irradiated with ultraviolet rays with an intensity of 100 mJ/cm.sup.2 to prepare a polarizer protective film having a self-healing property.

(22) (3) Preparation of Polarizing Plate

(23) The polarizer protective film prepared above was laminated and adhered to a polyvinyl alcohol (PVA) film using an acryl-based adhesive (thickness: about 1 m), and the PET release film was peeled off. Then, a triacetyl cellulose (TAC) film having a thickness of 60 m was laminated and adhered to the other side of the polyvinyl alcohol (PVA) film to which the polarizer protective film is not adhered using an acryl-based adhesive (thickness: about 1 m) to prepare a polarizing plate.

Example 2

(24) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Preparation Example 2 was used.

Example 3

(25) (1) Preparation of Composition for Forming Polarizer Protective Film

(26) A coating composition was prepared in the same manner as in Example 1.

(27) (2) Preparation of Polarizer Protective Film

(28) The coating composition prepared above was coated on a PET release film to have a thickness of 60 m, dried in an oven at 60 C. for 2 minutes and irradiated with ultraviolet rays with an intensity of 100 mJ/cm.sup.2 to prepare a polarizer protective film having a self-healing property.

(29) (3) Preparation of Polarizing Plate

(30) The polarizer protective film prepared above was laminated and adhered to a polyvinyl alcohol (PVA) film using an acryl-based adhesive (thickness: about 1 m), and the PET release film was peeled off. Then, a triacetyl cellulose (TAC) film having a thickness of 60 m was laminated and adhered to the other side of the polyvinyl alcohol (PVA) film to which the polarizer protective film is not adhered using an acryl-based adhesive (thickness: about 1 m) to prepare a polarizing plate.

Example 4

(31) (1) Preparation of Composition for Forming Polarizer Protective Film

(32) The polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in preparation Example 1, the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Preparation Example 2 and dipentaerythritol hexaacrylate (DPHA), as a bifunctional or higher polyfunctional (meth)acrylate-based compound, were mixed at a weight ratio of 1:1:10 to prepare a composition for forming a binder.

(33) Then, a coating composition of Example 4 was prepared by mixing 2 parts by weight of a UV initiator (Irgacure 184), 5 parts by weight of a leveling agent and 35 parts by weight of methyl ethyl ketone based on 100 parts by weight of the composition for forming a binder.

(34) (2) Preparation of Polarizer Protective Film and Polarizing Plate

(35) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that the coating composition of Example 4 was used.

COMPARATIVE EXAMPLES

Comparative Example 1

(36) A triacetyl cellulose (TAC) film [polarizer protective film] having a thickness of 60 m was laminated and adhered to a polyvinyl alcohol (PVA) film using an acryl-based adhesive (thickness: about 1 m). Then, a triacetyl cellulose (TAC) film having a thickness of 60 m was laminated and adhered to the other side of the polyvinyl alcohol (PVA) film using an acryl-based adhesive (thickness: about 1 m) to prepare a polarizing plate.

Comparative Example 2

(37) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Comparative Preparation Example 1 was used.

Comparative Example 3

(38) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Comparative Preparation Example 2 was used.

Comparative Example 4

(39) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that a composition for forming a binder was prepared by mixing the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Preparation Example 1 and dipentaerythritol hexaacrylate (DPHA), as a bifunctional or higher polyfunctional (meth)acrylate-based compound, at a weight ratio of 2:1.

Comparative Example 5

(40) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that a coating composition was prepared by mixing 2 parts by weight of a UV initiator (Irgacure 184), 5 parts by weight of a leveling agent (tego glide 270 manufactured by Evonik) and 35 parts by weight of methyl ethyl ketone based on 100 parts by weight of dipentaerythritol hexaacrylate (DPHA).

Comparative Example 6

(41) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Comparative Preparation Example 3 was used.

Comparative Example 7

(42) A composition for forming a polarizer protective film, polarizer protective film and polarizing plate were prepared in the same manner as in Example 1, except that the polyethylene glycol-modified polyfunctional urethane (meth)acrylate-based binder obtained in Comparative Preparation Example 4 was used.

EXPERIMENTAL EXAMPLES

(43) 1. Measurement of Scratch Resistance

(44) The surface of each polarizer protective film of Examples and Comparative Examples was reciprocatively rubbed 10 times by applying a constant load to a brightness-enhancing diffusion film, and then the load at which the scratches were generated on the surface of the polarizer protective film was compared.

(45) [OK: no scratch generated at the relevant load/NG: scratch generated at the relevant load]

(46) 2. Measurement of Scratch Self-healing Property Using Copper Wire Brush

(47) After generating the scratches on the surface of the polarizer protective films of Examples and Comparative Examples using a copper wire brush, a period of time during which the scratches were restored was measured.

(48) Specifically, a black PET film was laminated on the back surface of the polarizer protective film, and then dust on the surface of the film was removed using a nitrogen breeze. Then, a scratch was generated by a copper wire brush on the surface of the film under a three-wavelength lamp, and the time until the scratch disappeared was measured. Herein, the generation of the scratch was determined by whether the light of the three-wavelength lamp was reflected on the scratch and the scratch was observed with the naked eye, and the disappearance of the scratch was also determined by whether the light of the three-wavelength lamp was observed with the naked eye.

(49) 3. Measurement of Pencil Hardness

(50) Using a pencil hardness tester (Chungbuk Tech), the pencil hardness of the surface of the polarizer protective films of Examples and Comparative Examples was measured under a constant load of 500 g. Specifically, the hardness was measured using a standard pencil (Mitsubishi Inc.) having a hardness of 6B to 9H, and the measurement was repeated five times with a measurement length of 3 cm. Herein, scratches (0.5 cm) in the early stage of the measurement may not allow force to act uniformly on the part where the load starts to be applied, and thus, the surface hardness was determined by using scratches (2.5 cm) in the second half of the measurement.

(51) 4. Thermal Shock Test

(52) The polarizing plates obtained in Examples and Comparative Examples were laminated on a glass plate with an adhesive and then placed in a light-shielded room at room temperature for 24 hours to complete the adhesion. In this way, six test samples were prepared for each polarizing plate.

(53) Then, a temperature change condition was applied in which the process of exposing these test samples to a temperature of 80 C. for 30 minutes, followed by exposure to 30 C. for 30 minutes and back to 80 C. is one cycle, and the process was repeated 100 cycles.

(54) After repeating for 100 cycles, the samples were observed to evaluate the deformation of the polarizer, the occurrence of a crack and the adhesion state of the film. Herein, the deformation of the polarizer was determined by whether the axis of the polarizer was warped, the occurrence of a crack was determined by whether a gap was generated in the polarizer and the light was transmitted therethrough, and the adhesion state of the film was determined by whether a bubble was generated or a phenomenon where the film is detached from the edge had occurred.

(55) When any of the problems of the deformation of the polarizer, the occurrence of a crack and the adhesion state of the film occurred, it was evaluated as NG, and when none of the problems occurred, it was evaluated as OK.

(56) The results of the physical properties measured above are summarized and shown in the following Tables 1 and 2.

(57) TABLE-US-00001 TABLE 1 Example1 Example2 Example3 Example4 Scratch 700 g 600 g 700 g 700 g Resistance OK OK OK OK Load Scratch 1 second 1 second 1 second 1 second Self-Healing or less or less or less or less Property Using Copper Wire Brush Pencil HB HB HB HB Hardness (500 g) Thermal OK OK OK OK Shock Test

(58) TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Scratch 10 g OK 700 g 10 g OK 50 g OK 700 g 700 g 10 g OK Resistance 50 g NG OK 50 g NG 100 g NG OK OK 50 g NG Load Scratch Not 3 1 1 Not 5 1 Self- healed seconds second second healed seconds second Healing or more or less or less or more or less Property Using Copper Wire Brush Pencil B HB B B 3H HB B Hardness (500 g) Thermal OK NG NG NG NG NG NG Shock Test (crack) (bubble) (bubble) (crack) (crack) (bubble)

(59) As shown in the Tables 1 and 2, it was confirmed that the polarizer protective films obtained from Examples can prevent the deterioration of physical and optical properties caused by abrasion or scratches on the surface while having a high scratch resistance, and exhibits a self-healing property on the surface when a scratch is generated, compared to the polarizer protective films of the Comparative Examples.

(60) In addition, it was confirmed that the polarizer protective films of Examples not only exhibit an excellent pencil hardness, but also exhibit excellent stability in which the problem in the adhesion of the film, which occurs repeatedly, does not occur even under a large temperature change or the internal and external shapes and structures are not deformed.