Pressure-sensitive adhesive composition

Abstract

Provided is a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition may be applied as a light diffusing or scattering material to various display devices or lighting apparatuses.

Claims

1. A pressure-sensitive adhesive composition, comprising: a photocurable syrup which comprises: monomer components that comprise a linear or branched alkyl (meth)acrylate; (meth)acrylic acid; and a compound of any one of Formulas 1 to 3; or a polymer component that comprises the monomer components as a polymerization unit; and a blue dye, wherein, in the photocurable syrup, the linear or branched alkyl (meth)acrylate is included in an amount of 55 to 75 parts by weight of the photocurable syrup, the (meth)acrylic acid is included in an amount of 1 to 15 parts by weight of the photocurable syrup, the compound of any one of Formulas 1 to 3 is included in an amount of 5 to 30 parts by weight of the photocurable syrup: ##STR00003## wherein R is hydrogen or an alkyl group, A, B, T, U and W are each independently an alkylene or alkylidene group, Q is an alkyl group or aryl group, and n is a number of 0 to 5, and wherein the pressure-sensitive adhesive composition has a “b*” value on a CIE coordinate system of −2 to 3 and a yellow index (YI) value of −8.0 to 7.5 after being cured.

2. The composition according to claim 1, wherein the monomer components further comprises a compound of Formula 4: ##STR00004## wherein R is hydrogen or an alkyl group, and P is a monovalent moiety derived from an aliphatic saturated cyclic hydrocarbon compound.

3. The composition according to claim 1, wherein the monomer components or the polymer component is a partially polymerized product of a mixture comprising a linear or branched alkyl (meth)acrylate; (meth)acrylic acid; and the compound of any one of the Formulas 1 to 3.

4. The composition according to claim 1, wherein the “b*” value on the CIE coordinate system is from −1 to 3 after being cured.

5. The composition according to claim 1, wherein the YI value is from 0 to 7.5 after being cured.

6. The composition according to claim 1, wherein the monomer or polymer component has a viscosity at 25° C. of 1,500 to 4,000 cps.

7. The composition according to claim 1, further comprising a particle having a difference in refractive index with the pressure-sensitive adhesive of 0.05 to 1.0.

8. The composition according to claim 7, wherein the particle is an acrylic resin particle, a styrene resin particle, a urethane resin particle, a melamine resin particle, a benzoguanamine resin particle, an epoxy resin particle, a silicon resin particle, a silica particle, a titanium dioxide particle, a magnesium fluoride particle, a zirconium oxide particle, an aluminum oxide particle or a glass particle.

9. The composition according to claim 1, further comprising a photoinitiator.

10. The composition according to claim 1, further comprising an antioxidant or a reworkability improving agent.

11. A pressure-sensitive adhesive pad comprising a pressure-sensitive adhesive layer that comprises the pressure-sensitive adhesive composition of claim 1 in a cured state.

12. The pad according to claim 11, further comprising a plastic sheet treated by roughening or a plastic sheet having printed light shielding patterns, the plastic sheet being formed on one or both surfaces of the pressure-sensitive adhesive layer.

13. A light source for an optical or lighting apparatus comprising the pressure-sensitive adhesive pad of claim 11 as a light diffusing member.

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 adhered drawings, in which:

(2) FIGS. 1 to 3 are cross-sectional views illustrating various examples of a pressure-sensitive adhesive pad; and

(3) FIGS. 4 and 5 are diagrams illustrating a backlight unit.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

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

EXAMPLE 1

(5) Preparation of First Pressure-Sensitive Adhesive Pad

(6) A monomer mixture was prepared by mixing 75 parts by weight of ethylhexyl acrylate, 15 parts by weight of acrylic acid and 10 parts by weight of hydroxyethyl acrylate. As an initiator, a suitable amount of di(2-ethylhexyl) peroxydicarbonate (EHPDC) was added to the monomer mixture, and the mixture was bulk-polymerized to have a viscosity at 25° C. in a range of approximately 2,000 to 2,500 cps, thereby preparing a photocurable syrup. With respect to 100 parts by weight of the syrup, 0.7 parts by weight of a photoinitiator (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, TPO), 0.3 parts by weight of 1,6-hexanediol diacrylate (HDDA), 15 parts by weight of scattering particles (refractive index: 1.59, average diameter: 4,000 nm, polystyrene-based beads, HR-59-40, Sunjin Chemicals Co., Ltd.) and 1 ppm of a dye (Blue dye, MACROLEX Blue RR Gran, Lanxess) were mixed, thereby preparing a pressure-sensitive adhesive composition. The prepared pressure-sensitive adhesive composition was coated on a PET sheet, and UV rays were irradiated as a light source for approximately 6 minutes under the state where a distance between a black light source and a layer of the coated pressure-sensitive adhesive composition was maintained at 15 cm, thereby preparing a pressure-sensitive adhesive layer, that is, a first pressure-sensitive adhesive pad, which had a thickness of 0.8 mm.

(7) Preparation of BLU

(8) A pressure-sensitive adhesive pad 32 as shown in FIG. 4 was formed as a second pressure-sensitive adhesive pad on a PCB (PCB for 47-inch BLU, thickness: approximately 500 μm) on which an LED was arranged. Specifically, a pressure-sensitive adhesive composition which was the same as one used in the preparation of the pressure-sensitive adhesive layer of the first pressure-sensitive adhesive pad was prepared, but a ratio of a scattering particle 322 was changed to 0.01 parts by weight with respect to 100 parts by weight of syrup. The pressure-sensitive adhesive pad 32 having a thickness of approximately 1.45 mm was attached on the entire top surface of the PCB, thereby forming the second pressure-sensitive adhesive pad 32. Afterward, the prepared first pressure-sensitive adhesive pad was attached at a position of the pressure-sensitive adhesive pad 2 in FIG. 4, thereby preparing a light source.

EXAMPLE 2

(9) A monomer mixture was prepared by mixing 70 parts by weight of ethylhexyl acrylate, 10 parts by weight of acrylic acid, 10 parts by weight of hydroxyethyl acrylate and 10 parts by weight of 2-(2-ethoxyethoxy)ethyl acrylate, and bulk polymerization was performed by the substantially same method as described in Example 1 to prepare a photocurable syrup. In the above, polymerization conditions were controlled for the syrup to have a viscosity at 25° C. in a range of approximately 3,000 to 3,500 cps. With respect to 100 parts by weight of the syrup, 0.7 parts by weight of a photoinitiator (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, TPO), 0.2 parts by weight of 1,6-hexanediol diacrylate (HDDA), 15 parts by weight of scattering particles (refractive index: 1.59, average diameter: 4,000 nm, polystyrene-based beads, HR-59-40, Sunjin Chemicals Co., Ltd.) and 0.6 ppm of a dye (Blue dye, MACROLEX Blue RR Gran, Lanxess) were mixed, thereby preparing a pressure-sensitive adhesive composition. Afterward, a first pressure-sensitive adhesive pad having a pressure-sensitive adhesive layer 11 with a thickness of 0.8 mm was prepared by the same method as described in Example 1 using the pressure-sensitive adhesive composition. The prepared first pressure-sensitive adhesive pad was attached on the second pressure-sensitive adhesive pad, which was the same as the one used in Example 1, of a PCB, thereby preparing a light source.

EXAMPLE 3

(10) A monomer mixture was prepared by mixing 60 parts by weight of ethylhexyl acrylate, 10 parts by weight of acrylic acid, 10 parts by weight of hydroxyethyl acrylate, 10 parts by weight of 2-(2-ethoxyethoxy)ethyl acrylate and 10 parts by weight of isobornyl acrylate, and bulk polymerization was performed by the substantially same method as described in Example 1 to prepare a photocurable syrup. In the above, polymerization conditions were controlled for the syrup to have a viscosity at 25° C. in a range of approximately 3,000 to 3,500 cps. With respect to 100 parts by weight of the syrup, 0.7 parts by weight of a photoinitiator (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, TPO), 0.3 parts by weight of 1,6-hexanediol diacrylate (HDDA), 12.5 parts by weight of scattering particles (refractive index: 1.59, average diameter: approximately 3,000 to 4,000 nm, polystyrene-based bead, GS-0459S-6, Granz) and 1 ppm of a dye (Blue dye, MACROLEX Blue RR Gran, Lanxess) were mixed, thereby preparing a pressure-sensitive adhesive composition. Afterward, a first pressure-sensitive adhesive pad having a pressure-sensitive adhesive layer 11 with a thickness of 0.8 mm was prepared by the same method as described in Example 1 using the pressure-sensitive adhesive composition. The prepared first pressure-sensitive adhesive pad was attached on the second pressure-sensitive adhesive pad, which is the same as the one used in Example 1, of a PCB, thereby preparing a light source.

COMPARATIVE EXAMPLE 1

(11) A monomer mixture was prepared by mixing 85 parts by weight of ethylhexyl acrylate, 10 parts by weight of acrylic acid and 5 parts by weight of hydroxyethyl acrylate, and bulk polymerization was performed by the substantially same method as described in Example 1 to prepare a photocurable syrup. In the above, polymerization conditions were controlled for the syrup to have a viscosity at 25° C. in a range of approximately 2,000 to 2,500 cps. With respect to 100 parts by weight of the syrup, 0.7 parts by weight of a photoinitiator (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, TPO), 0.1 parts by weight of 1,6-hexanediol diacrylate (HDDA) and 15 parts by weight of scattering particles (refractive index: 1.59, average diameter: approximately 4 μm, polystyrene-based beads, HR-59-40, Sunjin Chemicals Co., Ltd.) were mixed, thereby preparing a pressure-sensitive adhesive composition. Afterward, a first pressure-sensitive adhesive pad having a pressure-sensitive adhesive layer 11 with a thickness of 0.8 mm was prepared by the same method as described in Example 1 using the pressure-sensitive adhesive composition, and a light source was prepared in the same manner as described above.

COMPARATIVE EXAMPLE 2

(12) A monomer mixture was prepared by mixing 70 parts by weight of ethylhexyl acrylate and 30 parts by weight of isobornyl acrylate. A photocurable syrup was prepared by adding a suitable amount of di(2-ethylhexyl) peroxydicarbonate (EHPDC) as an initiator to the monomer mixture and performing bulk polymerization so as for the syrup to have a viscosity at 25° C. in a range of approximately 2,000 to 2,500 cps. With respect to 100 parts by weight of the syrup, 0.7 parts by weight of a photoinitiator (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, TPO), 0.07 parts by weight of 1,6-hexanediol diacrylate (HDDA), 15 parts by weight of scattering particles (refractive index: 1.59, average diameter: 4,000 nm, polystyrene-based beads, HR-59-40, Sunjin Chemicals Co., Ltd), 0.3 parts by weight of an antioxidant (Songnox 2450Pw) and 1 ppm of a dye (Blue dye, MACROLEX Blue RR Gran, Lanxess) were mixed, thereby preparing a pressure-sensitive adhesive composition. Afterward, a first pressure-sensitive adhesive pad having a pressure-sensitive adhesive layer 11 with a thickness of 0.8 mm was prepared by coating the prepared pressure-sensitive adhesive composition on a PET sheet and irradiating UV rays from the light source for approximately 6 minutes under the state where a distance between the black light source and the coated layer of the pressure-sensitive adhesive composition was maintained at 15 cm, and a light source was prepared in the same manner as described in Example 1.

COMPARATIVE EXAMPLE 3

(13) A monomer mixture was prepared by mixing 75 parts by weight of ethylhexyl acrylate, 10 parts by weight of isobornyl acrylate and 15 parts by weight of acrylic acid. A photocurable syrup capable of being cured by being irradiated with an active energy ray was prepared by adding a suitable amount of di(2-ethylhexyl) peroxydicarbonate (EHPDC) as an initiator to the monomer mixture and performing bulk polymerization so as for the syrup to have a viscosity at 25° C. in a range of approximately 2,000 to 2,500 cps. With respect to 100 parts by weight of the syrup, 0.7 parts by weight of a photoinitiator (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, TPO), 0.1 parts by weight of 1,6-hexanediol diacrylate (HDDA), 0.15 parts by weight of an antioxidant (Songnox 2450Pw) and 15 parts by weight of scattering particles (refractive index: 1.59, average diameter: 4,000 nm, polystyrene-based beads, HR-59-40, Sunjin Chemicals Co., Ltd) were mixed, thereby preparing a pressure-sensitive adhesive composition. A first pressure-sensitive adhesive pad having a pressure-sensitive adhesive layer with a thickness of 0.8 mm was prepared by coating the prepared pressure-sensitive adhesive composition on a PET sheet and irradiating UV rays from the light source for approximately 6 minutes under the state where a distance between the black light source and the coated layer of the pressure-sensitive adhesive composition was maintained at 15 cm, and a light source was prepared in the same manner as described in Example 1.

COMPARATIVE EXAMPLE 4

(14) A monomer mixture was prepared by mixing 73 parts by weight of ethylhexyl acrylate, 20 parts by weight of isobornyl acrylate and 7 parts by weight of hydroxyethyl acrylate. A photocurable syrup capable of being cured by being irradiated with an active energy ray was prepared by adding a suitable amount of di(2-ethylhexyl) peroxydicarbonate (EHPDC) as an initiator to the monomer mixture and performing bulk polymerization so as for the syrup to have a viscosity at 25° C. in a range of approximately 2,000 to 2,500 cps. With respect to 100 parts by weight of the syrup, 1 part by weight of a photoinitiator (2,4,6-trimethylbenzoyl diphenyl phosphine oxide, TPO), 0.5 parts by weight of 1,6-hexanediol diacrylate (HDDA), 0.2 parts by weight of an antioxidant (Songnox 2450Pw) and 15 parts by weight of scattering particles (refractive index: 1.59, average diameter: 4,000 nm, polystyrene-based beads, HR-59-40, Sunjin Chemicals Co., Ltd) were mixed, thereby preparing a pressure-sensitive adhesive composition. A first pressure-sensitive adhesive pad having a pressure-sensitive adhesive layer with a thickness of 0.8 mm was prepared by coating the prepared pressure-sensitive adhesive composition on a PET sheet and irradiating UV rays from the light source for approximately 6 minutes under the state where a distance between the black light source and the coated layer of the pressure-sensitive adhesive composition was maintained at 15 cm, and a light source was prepared in the same manner as described in Example 1.

EXPERIMENTAL EXAMPLE 1

Durability Test

(15) Heat-resistant durability and humidity/heat-resistant durability were evaluated with respect to each of the light sources prepared in Examples and Comparative Examples (samples) (each having a width of 10 cm and a length of 30 cm). The heat-resistant durability was evaluated by leaving the sample at 80° C. for 240 hours and observing the generation of bubbles, and the occurrence of lift-off and peeling with the naked eyes, and the humidity/heat-resistant durability was evaluated by leaving the sample at 60° C. and a relative humidity of 90% for 240 hours and observing the generation of bubbles, and the occurrence of lift-off and peeling with the naked eyes. Criteria for each evaluation were as follows.

(16) <Evaluation for Generation of Bubbles>

(17) ◯: In case where no bubbles were generated in the pressure-sensitive adhesive and at an interface, or where bubbles could not be observed with the naked eyes since they had an excessively small size

(18) ×: In case where a single bubble or a group of bubbles was observed with the naked eyes in the pressure-sensitive adhesive and/or at an interface

(19) <Evaluation of Lift-off and Peeling>

(20) ◯: In case where neither lift-off nor peeling occurred at an interface between the pressure-sensitive adhesive and the adherent

(21) ×: In case where lift-off, partial peeling or complete peeling occurred at an interface between the pressure-sensitive adhesive and the adherent

EXPERIMENTAL EXAMPLE 2

Evaluation of Curling Property

(22) The samples used in Experimental Example 1 were left under a heat resistant condition, and then whether curling occurred or not was evaluated. Specifically, the samples were left standing in a vertical direction at 80° C. for 240 hours, and slowly cooled at room temperature for approximately 30 minutes. Afterward, the samples standing in a vertical direction were disposed to face and be in contact with a flat glass substrate, and the longest distance between the glass substrate, which was the reference, and the sample was measured by a tape measurer, thereby evaluating the occurrence of curling.

(23) The measurement results are summarized and listed in Table 1.

(24) TABLE-US-00001 TABLE 1 Examples Comparative Examples 1 2 3 1 2 3 4 Dura- Bubbles Heat ◯ ◯ ◯ ◯ X ◯ X bility Resistance Test Test Humidity/ ◯ ◯ ◯ ◯ X ◯ X Heat Resistance Test Lift- Heat ◯ ◯ ◯ ◯ X X X Off/ Resistance Peeling Test Humidity/ ◯ ◯ ◯ ◯ X X X Heat Resistance Test Curling Test (cm) ◯ ◯ ◯ ◯ — — —

(25) From the results of Table 1, it is confirmed that the light sources having the excellent durability and curling properties were obtained in Examples. However, in Comparative Examples 2 and 4, bubbles were excessively generated after the humidity/heat resistance test and thus a haze was observed. In addition, in Comparative Examples 2 to 4, the pressure-sensitive adhesive layer was peeled off during the heat or humidity/heat resistance test, and thus the curling property could not be evaluated.

EXPERIMENTAL EXAMPLE 3

Measurement of Optical Property

(26) To evaluate the optical property of the pressure-sensitive adhesive according to the presence or absence of a dye, b* and YI on the CIE coordinate system for the pressure-sensitive adhesives in Examples 1 to 3 and Comparative Example 1 were evaluated, and the results are listed in the following Table 2. In Table 2, the reference value (Ref) is a value for a diffuser plate produced by Kolon, which is generally used in BLUs.

(27) <Measurement of CIE Color Coordinate System and YI>

(28) Right after the preparation of the pressure-sensitive adhesive layers, the prepared pressure-sensitive adhesives were left in an oven at 80° C. for 240 hours (heat resistance test) and left at 60° C. and a relative humidity of 90% for 240 hours (humidity/heat resistance test), L*, a*, b*, x and y values and YI on the CIE color coordinate system for the pressure-sensitive adhesive layers prepared in Examples 1 to 3 and Comparative Example 1 were measured using a measurer (UV-vis-NIR Spectrophotometer (SolidSpec-3700, Shimadzu)) (In Table 2, the values for the pressure-sensitive adhesive measured right after the preparation are listed.)

(29) TABLE-US-00002 TABLE 2 Examples *C. Example Ref* 1 2 3 1 CIE L* 64.31 66.82 65.86 64.20 66.41 Coordinate a* −0.45 −0.54 −0.47 −0.45 −0.37 system b* 2.49 2.29 2.42 2.49 3.16 x* 0.3154 0.3147 0.3152 0.3154 0.3171 y* 0.3230 0.3223 0.3227 0.3230 0.3244 Yellowness 6.32 5.58 6.05 6.32 7.98 Index *Ref indicates an optical property of the diffuser plate produced by Kolon. *C. Example: Comparative Example

(30) As seen from Table 2, it is confirmed that, in the case of the pressure-sensitive adhesive pads in Examples 1 to 3, b* and YI equal to the diffuser plate currently applied to BLUs were shown, and the ranges were maintained after the heat resistance and humidity/heat resistance tests and thus the pressure-sensitive adhesive pads were suitable for an optical use. However, in Comparative Example 1 which did not include a dye, excessively high b* and YI values were measured, and these values mean that significant yellowing was shown in the pressure-sensitive adhesive, and thus the application of the pressure-sensitive adhesive to an optical use is highly limited.

(31) An exemplary pressure-sensitive adhesive composition of the present invention can be applied to various optical and lighting devices as a light diffusing material. Since the pressure-sensitive adhesive composition is used as a light diffusing material, the curling or bubble generation does not occur under a high temperature or high temperature and humidity condition. In addition, since the pressure-sensitive adhesive composition can be applied to an optical or lighting apparatus in a form of a pressure-sensitive adhesive pad, an air gap is removed or reduced from the device and thus light loss can be minimized. In addition, another optical material such as a prism sheet can also be attached to a device without using a separate pressure-sensitive adhesive, and effective in configuration of a flexible device. The pressure-sensitive adhesive composition cannot cause whitening or yellowing after being applied to an optical or lighting apparatus, and an excellent optical property can be stably maintained for a long time.