WO2010096106A1 - Cyclic block copolymer composition and thin wall guide plate made thereof - Google Patents

Abstract

A cyclic block copolymer composition that comprises a cyclic block copolymer resin with a pre-hydrogenation polymerized vinyl aromatic monomer content within a range of from 75 wt% to 90 wt%, based upon total pre-hydrogenation vinyl aromatic-conjugated diene block copolymer weight, a Mw within a range of from 30,000 g/M to 125,000 g/M, a shear viscosity at a shear rate of 1000 sec^-1 and a temperature of 280 °C of less than 50 pascal seconds (Pa-s), an unnotched Izod toughness (ASTM D256)) at room temperature ≥ 1.8 foot-pounds per inch (315.2 newtons per meter), and a tensile modulus (ASTM D638) ≥ 280,000 psi (1930.5 MPa) yields a variety of articles of manufacture, especially a thin wall light guide panel that has a diagonal measure ≥ 13.3 inches (33.8 cm).

Description

CYCLIC BLOCK COPOLYMER COMPOSITION AND THIN WALL GUIDE PLATE MADE THEREOF

This application is a non-provisional application claiming priority from the U.S. Provisional Patent Application No. 61/154,017, filed on February 20, 2009, entitled "THIN WALL LIGHT GUIDE PLATE," the teachings of which are incorporated by reference herein, as if reproduced in full hereinbelow.

As described more fully below, this invention relates to certain cyclic block copolymer (CBC) resin compositions and their use in fabricating a thin wall light guide panel (LGP). "CBC" refers to a substantially fully hydrogenated vinyl aromatic-conjugated diene block copolymer. "Thin" and "thin wall" mean a thickness of less than or equal to (<) 0.7 millimeters (mm). The thin wall light guide panel may have any diagonal measure, e.g. greater than (>) one inch (2.54 cm). The CBC resin compositions are particularly useful in fabricating a thin wall light guide panel with a diagonal measurement of at least (>) 13.3 inches (in.) (33.8 centimeters (cm)).

A LGP is part of a back light unit (BLU) of a display such as a liquid crystal display (LCD). The LGP desirably functions as a means to guide light from a source, e.g. a light emitting diode (LED) to a display device (e.g. a notebook computer or a LCD monitor) and uniformly distribute that light for illumination of the display device. Display manufacturers increasingly emphasize a need for thin and light weight LGPs.

Thin wall LGP fabrication usually occurs via injection molding. An alternate technique involves an extrusion process with surface patterning using a patterning roller. In both cases, manufacturers focus their attention on providing a LGP or light guide film (LGF) (a thickness of < 0.7 mm) with one flat and smooth surface and one featured or patterned surface. The featured surface can be designed for either light reflection or light extraction. Irrespective of specific surface design, manufacturers desire as complete a replication of the surface patterns as possible to maximize both homogeneous distribution of light and light output. They also desire a LGP that has all of several characteristics including sufficient toughness and stress crack resistance to avoid breakage, optical clarity with little, preferably no discernible yellowness to minimize and preferably avoid light absorbance with consequent loss of luminance at distal ends of a LGP or LGF or color shift across the LGP or LGF, sufficient surface hardness to minimize, preferably avoid, scratching during LGP handling or assembly, and dimensional stability or lack of warping, especially in humid environments. They further desire a polymer composition that provides all of these characteristics and has sufficient fluidity to completely fill mold cavities of an injection molding device.

Several polymers fail to deliver one or more of the above characteristics or lack sufficient fluidity to completely fill mold cavities used to fabricate LGPs that have a thickness of < 0.7 mm and a diagonal measurement of > 33.8 cm. Polymethylmethacryalte (PMMA) compositions tend to lack sufficient fluidity to completely fill such mold cavities and suffer warping in humid environments. Polycarbonate (PC) compositions exhibit high yellowness that leads, in turn, to non-uniform luminance and large color shift (e.g. Δx > 0.015 or Δy > 0.015, where Δx and Δy represents the chromaticity difference measured on a LGP between its light inlet end and its distal end) in a LGP when it is used in a medium-to- large size display (e.g., diagonal measurement > 33.8 cm). Compositions based on a cyclic olefin polymer (COP) or a cyclic olefin copolymer (COC) either lack sufficient fluidity to completely fill such mold cavities or enough toughness and stress crack resistance to avoid breakage when they do fill the mold cavities. Co-pending provisional application number 61/122931, filed 16 December

2008, discloses CBC compositions comprising a CBC with an elongation strain at break of more than (>) 30% and a modulus within a range of from > 150,000 pounds per square inch (psi) (1034 MPa) to less than (<) 270,000 psi (1862 MPa). The CBC is preferably results from hydrogenation of a SBSBS-based pentablock copolymer with a pre-hydrogenation styrene content that is > 50 wt% to less than (<) 70 wt%, more preferably from 55 wt% to 65 wt%. each wt% being based upon total pentablock copolymer weight prior to hydrogenation.

European Patent (EP) 1 189 988 Bl (Donald et al.) teaches compositions comprising a rigid hydrogenated block copolymer that has at least two distinct blocks of hydrogenated polymerized vinyl aromatic monomer and at least one block of hydrogenated polymerized conjugated diene monomer. In paragraph [0179], Donald et al. discusses injection molded articles and lists more than thirty categories or illustrations of such articles, one of which is a light guide. See also counterpart United States Patent (USP) 6,815,475.

USP 6,633,722 (Kohara et al.) discloses a LGP made of a polymeric resin having an alicyclic structure.

-^")- USP 7,357,973 (Obuchi et al.) relates to a flat plate made of a COP that has utility as a LGP and comprises at least 30 wt%, based on the COP, of repeating units having an alicyclic structure.

USP 6,835,440 (Konishi et al.) teaches LGP fabrication by melt molding a thermoplastic resin having a melt flow rate (MFR) of at least 50 grams per 10 minutes (g/10 min.) under a load of 2.16 kilogram force (kgf) at a temperature of 28O⁰C. The thermoplastic resin may be any of a number of resins including polymethyl methacrylates, polymethyl acrylates, and polymers having an alicyclic structure.

In some aspects, this invention is a CBC composition, the composition comprising a CBC resin that has a shear viscosity at a shear rate of 1000 reciprocal seconds (sec ¹) and a temperature of 280 degrees centigrade (⁰C) of less than 50 pascal seconds (Pa- s), and, when formed into a tensile test bar having a thickness of 1/8 in. (0.3 cm), an unnotched Izod toughness (American Society for Testing and Materials (ASTM) test D256)) at room temperature (nominally 25°C) > 1.8 foot-pounds per inch (ft-lb/in.) (315.2 newtons per meter (N/m)), and a tensile modulus (ASTM D638) > 280,000 pounds per square inch (psi) (1930.5 megapascals (MPa)). The CBC resin preferably has a pre-hydrogenation polymerized vinyl aromatic monomer content within a range of from 75 percent by weight (wt%) to 90 wt%, based upon total pre-hydrogenation vinyl aromatic-conjugated diene block copolymer weight, and a weight average molecular weight (Mw) within a range of from 30,000 grams per mole (g/M) to 125,000 g/M.

The CBC compositions can be used to fabricate light guides (LGPs and LGFs) useful for LCD devices or other display devices that require a waveguide. The light guide can be fabricated by any known thermoplastic polymer processing technique such as injection molding, extrusion roll molding, extrusion blow molding, blown film, melt casting, and compression molding. For LGPs and LGFs in particular, at least one side thereof bears a surface pattern for light extraction. This can be achieved either during fabrication or with a subsequent printing (e.g. ultraviolet imprinting) or embossing (e.g. thermal embossing) step.

While particularly suited for use in fabricating thin LGPs and thin LGFs, the CBC compositions have utility in fabricating thicker LGPs (e.g. a thickness within a range of from 1 mm to 5 mm) such as those designed for use in large (diagonal measure of 27 inches (68.6 cm) panels for LED television back light units. In some aspects, this invention is an article of manufacture fabricated from such a hydrogenated CBC composition, especially a thin LGP, particularly one that has a diagonal measure > 13.3 inches (33.8 cm).

When ranges are stated herein, as in a range of from 2 to 10, both end points of the range (e.g. 2 and 10) and each numerical value, whether such value is a rational number or an irrational number, are included within the range unless otherwise specifically excluded.

"Substantially fully hydrogenated" means that > 90 percent (%) of vinyl aromatic (e.g. styrene) double bonds and > 90%, preferably > 95% of conjugated diene (preferably butadiene) double bonds are hydrogenated.

CBC resins suitable for use in various aspects of this invention preferably have, prior to hydrogenation, a pentablock architecture with alternating styrene (S) blocks and butadiene (B) blocks. Representative pre-hydrogenation pentablock copolymers include

SBSBS pentablock copolymers. The styrene (S) blocks may, but need not be of equal length. Similarly, the butadiene (B) blocks may, but need not be of equal length.

SBSBS-based CBC resins have a pre-hydrogenation styrene content that is preferably from greater than or equal to (>) 75 wt% to less than or equal to (<) 90 wt%, more preferably within a range of from > 80 wt% to < 90 wt%, each wt% being based upon total pentablock copolymer weight prior to hydrogenation. The pentablock copolymers have a pre-hydrogenation Mw that is preferably within a range of from 30,000 g/M to 125,000 g/M, more preferably within a range of from 40,000 g/M to 90,000 g/M, and even more preferably within a range of from 45,000 g/M to 75,000 g/M.

When formed into a tensile test bar having a thickness of 1/8 in (0.3 cm), the hydrogenated, SBSBS-based CBC pentablock copolymers have an unnotched Izod toughness (ASTM test D256) at room temperature that is preferably at least 1.8 ft-lb/in. (315.2 N/m), more preferably > 2 ft-lb/in. (350.2 N/m), and still more preferably > 2.2 ft- lb/in. (385.3 N/m) The tensile test bars also have a tensile modulus (ASTM D638) that is preferably > 280,000 psi (1930.5 MPa), more preferably > 300,000 psi (2068.4 MPa).

While sequentially polymerized pentablock copolymers may be preferred, satisfactory results also occur with use of multi-armed or coupled block copolymers. The multi- armed and coupled block copolymers contain a residue from a coupling agent. Such coupled block copolymers may be represented as, for example, X(BS)_n where n is > 2 and X represents a chain coupling agent. The coupled block copolymers preferably have the same styrene content and hydrogenation percentage as the sequential SBSBS pentablock copolymers but a broader Mw range that is preferably from 30,000 g/M to 200,000 g/M, more preferably from 40,000 g/M to 150,000 g/M and even more preferably from 45,000 g/M to 125,000 g/M.

Block copolymers suitable for use in various aspects of this invention have a pre-hydrogenation vinyl aromatic polymerized monomer content that is preferably from 75 wt% to 90 wt%, more preferably from 80 wt% to 90 wt%, and still more preferably from 80 wt% to 87 wt%. Each wt% is passed upon total pre-hydrogenated block copolymer weight. CBC compositions suitable for use in various aspects of this invention may include one or more conventional additives including, but not limited to antioxidants, hindered amine light stabilizers (HALS), processing aids or lubricants, and mold release agents. Illustrative antioxidants include hindered phenols (e.g. IRGANOX™ 1010, Ciba Geigy). Illustrative HALS include poly[[6-[(l,l,3,3-tetramethylbutyl)amino]-s-triazine-2,4- diyl]-[(2,2,6,6-tetramethyl-4-piperidyl)imino]-hexamethylene-[(2,2,6,6-tetramethyl-4- piperidyDimino]] (CHMASSORB™ 944, Ciba Geigy), bis (2,2,6,6,-tetramethyl-4- piperidyl) sebacate (Tinuvin® 770, Ciba Geigy). Illustrative mold release agents (MRAs) include glycerol monostearate (e.g., GMS-90, Danisco Inc.), pentaerythritol tetrastearate, amides wax, poly(oxyethylene)nonylphenyl ether, etc. Illustrative processing aids include fluorinated polymers (e.g., Kynar Flex® PPA, Arkema), aliphatic amide type of processing aids (e.g., INT-33UDK, Axel Plastics Research Laboratory), etc.

CBC compositions that include a mold release agent (MRA), a processing aid or both, preferably do so at a loading level for each of the MRA and processing aid of from 200 parts by weight per million parts by weight (ppm) of CBC to 5,000 ppm, more preferably from 300 ppm to 3,000 ppm, and still more preferably from 300 ppm to 2,000 ppm.

CBC compositions that include an antioxidant do so at a loading level that is preferably from 300 ppm to 5,000 ppm, more preferably from 500 ppm to 3,000 ppm, and still more preferably from 750 ppm to 2,000 ppm. A loading of 1000 ppm produces very satisfactory results.

CBC compositions suitable for use in some aspects of this invention optionally include one or more of a second CBC resin or a soft polymer such as styrene- ethylene butylene-styrene (SEBS) polymers and styrene-ethylene propylene-styrene (SEPS) polymers. In such aspects, an amount of < one wt% but > 500 ppm improves molding of the compositions. The incorporation of soft polymer in such an amount appears to effectively eliminate development of stress whitening spots that might otherwise occur during extended use of molded panels or plates in a humid environment. Addition of a larger amount of soft polymer, e.g. two wt% or more adversely affects optical transparency of articles fabricated from such CBC compositions.

If desired, an article fabricated from a CBC composition may have an abrasion-resistant or hardness coating applied to one or more of the article's external surfaces. Suitable coatings may include, for example, ultraviolet (UV) light curable acrylic coating and aliphatic urethane coatings.

CBC compositions of various aspects of this invention have utility as a LGP.

The LGP preferably has at least one flat surface with a diagonal measurement of at least

13.3 in. (33.8 cm) and a thickness of 0.7 mm or less, preferably from 0.2 mm to 0.7 mm, and more preferably from 0.3 mm to less than 0.7 mm.

Examples

The following examples illustrate, but do not limit, the present invention.

All parts and percentages are based upon weight, unless otherwise stated. AU temperatures are in ⁰C. Examples (Ex) of the present invention are designated by Arabic numerals and Comparative Examples (Comp Ex or CEx) are designated by capital alphabetic letters.

Unless otherwise stated herein, "room temperature" and "ambient temperature" are nominally 25⁰C.

Table 1 below lists six pentablock (SBSBS-based) CBC resins (CBC-I,

CBC-2, CBC-3, CBC-4, CBC-5 and CBC-6), one triblock (SBS-based) CBC (CBC-7), one cyclic olefin copolymer (COC) (TOPAS™ 5013, Ticona Polyplastics), two cyclic olefin polymers (COP-I (ZEONOR™ 1060R, Zeon Chemical) and COP-2 (ZEONOR™ 1430R,

Zeon Chemical)), and a polymethylmethacrylate (Parapet™ GH-1000S, Kuraray Co., Ltd.).

For the CBCs, Table 1 includes their respective Mw, and wt% styrene (based on total block copolymer weight before hydrogenation). Table 1 also includes physical performance data in terms of shear viscosity at 1000 sec^"1 and 28O⁰C, unnotched Izod Impact ((ft- lbs/in.)(/N/m)) (ASTM D256), Tensile Modulus (psi times 1000 or kpsi/MPa) (ASTM

D638), and Pencil Hardness (ASTM D3363-05). Use a capillary rheometer such as a Rheograph™ 2003, commercially available from Gottfert, to measure apparent shear viscosity (η) at an apparent shear rate of 1000 s^"1 and a melt temperature of 280° C with a capillary die with a length of 20 millimeters (mm) and a diameter of one (1) mm, to measure shear viscosity (η).

Table 1

"nd" means not determined

Conduct molecular weight analysis of a hydrogenated vinyl aromatic- conjugated diene block copolymer by subjecting the block copolymer, prior to its hydrogenation, to gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a solvent for the block copolymer. Calibrate GPC columns using narrow molecular weight polystyrene standards from Polymer Labs, Inc. The molecular weight of the standards ranges from 580 g/M to 3,900,000 g/M. Prepare six standard mixtures that have three or four standards per mixture, each standard in the mixture differing in molecular weight from others in the mixture by a factor of approximately ten. Determine peak elution volume of each standard and generate a column calibration of molecular weight versus elution volume by fitting the narrow standard data with a 5th order polynomial fit. Report Mw of pre- hydrogenated block copolymers as polystyrene-equivalent values. Ex 1-3 and CEx A-G Prepare a series of LGPs, each of which has a diagonal measure of 13.3 inches (33.8 cm) and a thickness as shown in Table 2 below using a 450 ton (4.082 x IO⁵ kilograms (kg)), high speed injection molding machine (Model: SE450HY, Sumitomo Heavy Industries, Ltd.) and processing temperature and mold temperature as shown in Table 2. Use a nitrogen purge through molding and keep the injection time constant at 1 second with the holding pressure maintained at 360 tons (326,586 kg) for 0.2 second (sec), followed by a holding pressure of 300 tons (272,155 kg) for 0.3 sec and finally a holding pressure of 400 tons (362,874 kg) for 1.2 seconds. Set the mold cooling time at 30 sec.

Table 2

G = Good - complete filling of mold and good surface texture replication on light reflective surface. Product quality deemed commercially acceptable

P = Partial - at least five percent (5%) of LGPs evidence incomplete mold filling and/or < 80% surface texture replication on light reflective surface Characterize surface texture replication for injection molded panels using a 3D profilometer scan of the featured surface in terms of average surface height of the micro-structure over a panel area of 30 mm x 30 mm. The average surface height of nine micro-structures evenly spaced 10 mm apart in both vertical and horizontal directions must differ from a desirable surface height by < 20% in order to be commercially acceptable as < 80% surface replication or surface texture replication tends to cause an inhomogeneous light distribution or a light output that is too low to meet industry demands.

B = Brittle - injection molded panels are brittle and easy to crack or crack during de-molding, handling or assembly.

F= Fail - cannot fill the mold as the flow length of polymer melt is too short

The data presented in Table 2 above demonstrate that certain CBC compositions allow one to fabricate a thin wall (< 0.7 mm thick) LGP molding when the

LGP molding has a diagonal measurement of 13.3 inches (33.8 cm). Other CBC compositions, cyclic olefin copolymers (COCs), the PMMA and the COPs do not allow one to make such moldings at all in some instances (e.g. CEx A at 0.4 mm and 0.45 mm) or have them be useful once fabricated as in CEx A. The COC, the COPs and the PMMA allow one to make a LGP that receives a subjective "good" rating at a thickness of 0.7 mm, but not at a lower thickness such as 0.6 mm while the CBC compositions of Ex 1-3 achieve the subjective "good" rating at a thickness of 0.6 mm, and Ex 1 does so at a thickness of

0.45 mm. Similar results are expected with CBC-I and some LGPs with a diagonal measurement in excess of 13.3 inches (33.8 cm).

Claims

WHAT IS CLAIMED IS:

1. A cyclic block copolymer composition, the composition comprising a cyclic block copolymer resin that has a shear viscosity at a shear rate of 1000 reciprocal seconds and a temperature of 280 degrees centigrade of less than 50 pascal-seconds, and, when formed into a tensile test bar having a thickness of 1/8 in. (0.3 cm), an unnotched Izod toughness (American Society for Testing and Materials (ASTM) test D256)) at room temperature of at least 1.8 foot-pounds per inch (315.2 newtons per meter), and a tensile modulus (ASTM D638) of at least 280,000 pounds per square inch (1930.5 megapascals).

2. The composition of Claim 1, wherein the cyclic block copolymer resin has a pre-hydrogenation polymerized vinyl aromatic monomer content within a range of from 75 percent by weight to 90 weight percent, based upon total pre-hydrogenation cyclic block copolymer weight, and a weight average molecular weight within a range of from 30,000 grams per mole to 125,000 grams per mole.

3. The composition of Claim 1 or Claim 2, wherein the cyclic block copolymer resin, prior to hydrogenation, is a pentablock copolymer.

4. The composition of Claim 3, wherein the pentablock copolymer is a styrene-butadiene-styrene-butadiene-styrene-based pentablock copolymer with a pre- hydrogenation molecular weight within a range of from 45,000 g/M to 75,000 g/M.

5. An article of manufacture fabricated from the composition of any of Claims 1 through 4, the article of manufacture being a thin light guide panel.

6. The article of manufacture of Claim 5, wherein the thin light guide panel has a diagonal measure of 13.3 inches (33.8 centimeters) or larger.

7. The article of manufacture of Claim 5 or Claim 6, wherein the thin light guide panel has a thickness of less than or equal to 0.7 millimeters.