EP1920275A1 - Light-scattering moulded body with a high level of light transmission - Google Patents

Abstract

The invention relates to a solid plate consisting of a composition of a transparent polycarbonate with a molar mass of Mw of between 16,000 and 21,000 g/mol and an MFR of between 50 and 80 cm3/(10 min) (3000C; 1.2 kg), and transparent polymer particles having an optical density which is different from that of matrix materials. The invention also relates to the use of one such solid plate as a diffuser plate in flat-panel monitors.

Description

Light-scattering shaped bodies with high light transmission

The present invention relates to a multilayer solid plate whose base material consists of a composition of a readily flowing transparent polycarbonate, and transparent polymeric particles having a different optical density from matrix material and optionally one or more cover layers, which are coextruded onto the

Solid plate be applied either one-sided or two-sided.

When using diffuser plates in the so-called backlight circuits (BLUs) of flat screens, it depends on a very high luminance of this system, so that the brightness of the image of the flat screen is as high as possible. Basically, a Backhght-Umt (Direct Light System) on the structure described below. It usually consists of a housing m, depending on the size of the backlight Umt a different number of fluorescent tubes, so-called CCFL (CoId Cathode Fluorescent Lamp) are arranged. The inside of the housing is equipped with a light-reflecting surface. On this illumination system, the diffuser plate has a thickness of 1 to 3 mm, preferably a thickness of 2 mm. On the diffuser plate is a set of films which may have the following functions. Light scattering (Diffuserfohen), Circularpalansatoren, focusing of the light in the forward direction by so-called BEF (Bπghtness Enhancmg film) and Lmearpolansatoren. The linearly polarizing film is directly under the LCD display above.

Light-diffusing translucent products made of polycarbonate with various light-scattering additives and moldings produced therefrom are already known from the prior art.

For example, EP-A 634 445 discloses phosphorus scattering compositions containing vinyl acrylate-based polymeric particles having a core / shell morphology in combination with TiO ₂

The use of light-diffusing polycarbonate foils m flat screens is. in US

2004/0066645 describe. Polyacrylate, PMMA, polytetrafluoroethylene, Polyalkyltπalkoxysiloxane and mixtures of these components are mentioned here as the light-scattering component

JP 03078701 describes light-scattering PC boards which have calcium carbonate and titanium dioxide as scattering pigments and have a light transmission of about 40%.

JP 05257002 describes light-scattering PC boards with scattering pigments from Sihca. JP 10046022 describes PC plates with scattering pigments of polyorganosiloxanes.

JP 2004/029091 describes PC diffuser plates containing 0.3 to 20% scattering pigment and 0.0005 to 0.1% optical brightener.

In these documents, however, usually the molecular weight of the polycarbonate is not further specified.

JP 10046018 describes a PC board containing 0.01 to 1% cross-linked spherical polyacrylates.

In order to assess the suitability of the light-diffusing plates for so-called backlight units for LCD flat screens, in particular the brightness (brightness) of the entire system must be considered, ie the entire BLU, not just the diffuser plates for themselves. The from the

Diffuser plates known from the prior art exhibit unsatisfactory color constancy with simultaneously high brightness (brightness).

In this invention it has now been found that the viscosity of the polycarbonate base resin used has a decisive influence on the performance of the diffuser plates. Polycarbonate resins having a low viscosity (low molecular weight) in use as a diffuser plate surprisingly show a significantly higher luminance than polycarbonate resins having a higher viscosity (higher molecular weight) even though the optical properties of the base resins used in the examples are equal to the light transmission of the base resin are. Polycarbonate resins having a molecular weight of M _w = 16,000 to 21,000 g / mol or a MFR = 50 to 80 cm ³ / (10 min) (300 ^° C., 1.2 kg) have proved to be particularly advantageous.

A first subject of the present invention is therefore a solid sheet comprising a composition

80 to 99.99 wt .-% of a transparent polycarbonate having a molecular weight of M _w = 15,000 to 21,000 g / mol, preferably 15,000 to 21,000 with the exception of 18,000, more preferably 18,100 to 21,000, most preferably 18,500 to 20,000 g / mol or a MFR of 50 to 80 cm ³ / (10 min) (300 ⁰ C, 1.2 kg) and

0.01 to 20 wt .-% transparent polymeric particles having a different optical density of the polycarbonate.

The solid sheets according to the invention have a high light transmission at the same time high light scattering and can, for example, in the lighting systems of flat screens (LCD screens) are used. Here a high light scattering with simultaneous high light transmission is of crucial importance. The illumination system of such flat screens can be done either with lateral light coupling (Edgelight system) or larger screen sizes, in which the lateral light coupling is no longer sufficient, via a backlight unit (BLU), in which the direct illumination behind the diffuser plate through this as evenly as possible must be distributed (Direct Light System).

Furthermore, the solid plate described here (possibly multi-layered) by a high color consistency over a longer period of time at the same time undiminished luminance (brightness) in the operation of the flat panel displays.

Another object of this invention is the use of the erfϊndungsgemäßen

Solid sheets as diffuser panels of flat screens, especially in the backlighting of LCD displays.

Suitable polycarbonates for the production of the solid sheets according to the invention are all known polycarbonates. These are homopolycarbonates, copolycarbonates and thermoplastic polyestercarbonates.

The suitable polycarbonates have average molecular weights M _{w of} from 15,000 to 21,000, determined by measuring the relative solution viscosity in dichloromethane or in mixtures of equal amounts by weight of phenol / o-dichlorobenzene calibrated by light scattering. Preferably, the average molecular weight is 15,000 to 21,000, with the exception of 18,000, more preferably 18,100 to 21,000, most preferably 18,500 to 20,000.

For example, for preparing polycarbonates, see "Rapid, Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York, London, Sydney 1964" and "DC PREVORSEK, BT DEBONA and Y. RESTEN, Corporate Research Center, Allied Chemical Corporation, Moristown, New Jersey 07960, 'Synthesis of Poly (ester) Carbonate Copolymer' in Journal of Polymer Science, Polymer Chemistry Edition,

Vol. 19, 75-90 (1980) ", and JD Freitag, U. Grigo, PR Müller, N. Nouvertne, BAYER AG, 'Polycarbonates' in Encyclopaedia of Polymer Science and Engineering, Vol. 1988, pages 648-718 "and finally to" Dres. U. Grigo, K. Kircher and PR Müller 'polycarbonates' in Becker / Braun, Plastics Handbook, Volume 3/1, polycarbonates, polyacetals, polyesters, cellulose esters, Carl Hanser Verlag Munich, Vienna 1992, pages 117-299 "referenced. The polycarbonates are preferably prepared by the phase boundary process or the melt transesterification process and will be described below by way of example by the phase boundary process.

Preferred compounds to be used as starting compounds are bisphenols of the general formula

HO-Z-OH, in which

Z is a divalent organic radical of 6 to 30 carbon atoms containing one or more aromatic groups.

Examples of such compounds are bisphenols belonging to the group of dihydroxydiphenyls,

Bis (hydroxyphenyl) alkanes, indanebisphenols, bis (hydroxyphenyl) ethers, bis (hydroxyphenyl) sulfones, bis (hydroxyphenyl) ketones, and α, α'-bis (hydroxyphenyl) diisopropylbenzenes.

Particularly preferred bisphenols belonging to the aforementioned linking groups are bisphenol-A, tetraalkylbisphenol-A, 4,4- (meta-phenylenediisopropyl) diphenol (bisphenol M), 4,4- (para-phenylenediisopropyl) -diphenol, 1,1 Bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane

(Bisphenol TMC) and mixtures thereof.

Preferably, the bisphenol compounds to be used according to the invention are reacted with carbonic acid compounds, in particular phosgene, or with diphenyl carbonate or dimethyl carbonate in the melt transesterification process.

Polyestercarbonates are preferably obtained by reacting the abovementioned bisphenols, at least one aromatic dicarboxylic acid and optionally carbonic acid equivalents. Suitable aromatic dicarboxylic acids are, for example, phthalic acid, terephthalic acid, isophthalic acid, 3,3'- or 4,4'-diphenyldicarboxylic acid and benzophenone dicarboxylic acids. A portion, up to 80 mole%, preferably from 20 to 50 mole%, of the carbonate groups in the polycarbonates may be replaced by aromatic dicarboxylic acid ester groups.

Inert organic solvents used in the interfacial process are, for example, dichloromethane, the various dichloroethanes and chloropropane compounds, tetrachloromethane, trichloromethane, chlorobenzene and chlorotoluene, preferably chlorobenzene or dichloromethane or mixtures of dichloromethane and chlorobenzene are used.

The interfacial reaction can be catalyzed by catalysts such as tertiary amines, in particular

N-alkylpiperidines or onium salts are accelerated. Preference is given to tributylamine, Tπethylarrun and N-Ethylpipeπdm used. In the case of the melt transesterification process, preference is given to using the catalysts mentioned in DE-A 42 38 123.

The polycarbonates can be deliberately and controlled by the use of small amounts of branching Some suitable branching agents are: Phloroglucm, 4,6-dimethyl-2,4,6-tπ- (4-hydroxyphenyl) -hepten-2, 4,6-dimethyl -2,4,6-tπ- (4-hydroxyphenyl) heptane; 1,3,5-Tπ-

(4-hydroxyphenyl) -benzene, 1,1,1-Tπ- (4-hydroxyphenyl) -ethane; Tπ- (4-hydroxyphenyl) -phenylmethane; 2,2-bis [4,4-bis (4-hydroxyphenyl) -cyclohexyl] -propane; 2,4-Bis- (4-hydroxyphenyl-isopropyl) -phenol, 2,6-bis- (2-hydroxy-5'-methyl-benzyl) -4-methylphenol, 2- (4-hydroxyphenyl) -2 - (2,4-dihydroxyphenyl) -propane; Hexa- (4- (4-hydroxyphenyl-isopropyl) -phenyl) -orthoterephthalate; Tetra (4-hydroxyphenyl) methane; Tetra- (4- (4-hydroxyphenyl-isopropyl) -phenoxy) -methane; α, α ', α "-Tπs- (4-hydroxyphenyl) -1, 3,5-tπisopropylbenzol, 2,4-dihydroxybenzoic acid; Tπmesm- acid, cyanurchloπd; 3,3-bis (3-methyl-4-hydroxyphenyl ) -2-oxo-2,3-dihydromdole, 1,4-bis- (4 ', 4 "-dihydroxytiphenyl) -methyl) -benzene, and in particular: 1, l, l-Tπ- (4-hydroxyphenyl) -ethane and bis (3-methyl-4-hydroxyphenyl) -2-oxo-2,3-dihydromdole.

The optionally used 0.05 to 2 mol%, based on diphenols, to

Branching or mixtures of the branching agents can be used together with the diphenols but can also be added at a later stage of the synthesis.

The chain terminators used are preferably phenols such as phenol, alkylphenols such as cresol and 4-tert-butylphenol, chlorophenol, bromophenol, cumylphenol or mixtures thereof in amounts of 1-20 mol%, preferably 2-10 mol% per mol of bisphenol. Preference is given to phenol, 4-tert.

Butylphenol or cumylphenol.

Chain terminators and branching agents may be added separately or together with the bisphenol to the syntheses.

The preparation of the polycarbonates after the melt transesterification process is described by way of example in DE-A 42 38 123.

Polycarbonates which are preferred according to the invention are the homopolycarbonate based on bisphenol A, the homopolycarbonate based on 1,1-bis (4-hydroxyphenyl) -3,3,5-t-methylcyclohexane and the copolycarbonates based on the two monomers bisphenol A and I, l Bis (4-hydroxyphenyl) -3,3,5-t-methylcyclohexane and the copolycarbonates based on the two monomers bisphenol A and 4,4'-dihydroxydiphenyl (DOD)

The homopolycarbonate based on bisphenol A is particularly preferred. Suitable transparent polymeric particles having an optical density different from the polycarbonate are, for example, those based on acrylate having a core-shell morphology, preferably those disclosed in EP-A 634,445.

These polymeric particles have a core of a rubbery vinyl polymer. The rubbery vinyl polymer may be a homo- or copolymer of any of

Monomers which have at least one ethylenically unsaturated group and which are known to those skilled in the art addition polymerization under the conditions of emulsion polymerization in an aqueous medium. Such monomers are listed in US 4,226,752, column 3, lines 40-62.

The rubbery vinyl polymer preferably contains at least 15%, more preferably at least 25%, most preferably at least 40% of a polymerized acrylate, methacrylate, monovinylarene or optionally substituted butadiene and from 0 to 85%, more preferably from 0 to 75%, most preferably from 0 to 60% of one or more copolymerized vinyl monomers, based on the total weight of the rubbery vinyl polymer.

Preferred acrylates and methacrylates are alkyl acrylates or alkyl methacrylates which preferably contain from 1 to 18, more preferably 1 to 8, most preferably 2 to 8 carbon atoms in the alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n- Butyl, sec-butyl or tert-butyl or hexyl, heptyl or octyl groups. The alkyl group may be branched or linear. The preferred alkyl acrylates are ethyl acrylate, n-butyl acrylate, isobutyl acrylate or 2-ethylhexyl acrylate. The most preferred alkyl acrylate is butyl acrylate.

Other suitable acrylates are, for example, 1,6-hexanediol diacrylate, ethylthioethyl methacrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-phenoxyethyl acrylate, glycidyl acrylate, neopentyl glycol diacrylate, 2-ethoxyethyl acrylate, t-butylaminoethyl methacrylate, 2-methoxyethyl acrylate, glycidyl methacrylate or benzyl methacrylate.

Preferred monovinylarenes are styrene or α-methylstyrene optionally substituted on the aromatic ring with an alkyl group such as methyl, ethyl or tertiary butyl or with a halogen such as chlorostyrene.

When substituted, the butadiene is preferably substituted with one or more alkyl groups containing from 1 to 6 carbon atoms or with one or more halogens, most preferably substituted with one or more methyl groups and / or one or more chlorine atoms.

Preferred butadienes are 1,3-butadiene, isoprene, chlorobutadiene or 2,3-dimethyl-1,3-butadiene. The rubbery vinylmolypolymer may contain one or more (co) polymerized acrylates, methacrylates, monovinylarenes and / or optionally substituted butadienes. These monomers may be copolymerized with one or more other copolymerizable vinyl polymers, such as diacetone acrylamide, vinylnaphthalene, 4-vinylbenzyl alcohol, vinylbenzoate, vinyl propionate, vinylcaproate, vinylmethyl, vinyl oleate, dimethyl maleate, malemic anhydride, dimethyl fumarate, vinylsulfonic acid, vinylsulfonamide, methylvylsulfonate. N-vinylpyrrolidone, vinylpyridine, divmylbenzene, vinyl acetate, vinylsatate, acrylic acid, methacrylic acid, N-methylmethacrylamide, Acrylmtπl, Methacrylnitπl, acrylamide or N- (isobutoxymethyl) acrylamide.

One or more of the aforementioned monomers are optionally 0 to 10%, preferably 0 to 5%, of a copolymerizable polyfunctional crosslinker and / or 0 to 10%, preferably 0 to 5%, of a copolymerizable polyfunctional graft crosslinker, based on When the crosslinking monomer is used, it is preferably used at a content of 0.05 to 5%, more preferably 0.1 to 1%, based on the total weight of the core monomers. Crosslinking monomers are well known in the art and generally have a polyethylene-like unsaturation in which the ethylenically unsaturated groups have approximately the same reactivity as divmylbenzene, t-methylbenzene, 1,3- or 1,4-triacrylates or methacrylates, glycol di- or -tπ- methacrylates or acrylates, such as ethylene glycol dimethacrylate or diacrylate, propylene glycol dimethacrylate or diacrylate, 1,3- or 1,4-butylene glycol dimethacrylate or, most preferably, 1,3- or 1,4-butylene glycol diacrylate. If a graft-crosslinking monomer is used, it is preferably used at a content of 0.1 to 5%, more preferably 0.5 to 2.5%, based on the total weight of the core monomers. Graftlinking monomers are well known in the art, and generally they are polyethylenically unsaturated monomers which have sufficient mediocre reactivity of the unsaturated groups to allow for significant residual unsaturation present in the nucleus in the

Connection to his Polymeπsation remains. Preferred graft crosslinkers are copolymerizable allyl, methallyl or crotyl esters of α, β-ethylenically unsaturated carboxylic acids or dicarboxylic acids, such as allyl methacrylate, allyl acrylate, diallyl maleate and allyl acryloxypropionate, most preferably allyl methacrylate.

Most preferably, the polymeric particles contain a rubbery core

Alkyl acrylate polymers wherein the alkyl group has from 2 to 8 carbon atoms, optionally copolymerized with from 0 to 5% crosslinker and from 0 to 5% graft crosslinker, based on the total weight of the core. The rubbery alkyl acrylate is preferably copolymerized with up to 50% of one or more copolymerizable vinyl monomers, for example those mentioned above. Suitable crosslinking and graftlinking monomers are those skilled in the art - -

are well known in the art, and are preferably those described in EP-A 0 269 324.

The core of the polymeric particles may contain residual oligomeric material used in the polymerization process to swell the polymer particles, however, such oligomeric material has sufficient molecular weight to prevent its diffusion or to prevent it from being generated during processing or the use is extracted.

The polymeric particles contain one or more coats. This one coat or coats are preferably made from a vinyl homo- or copolymer. Suitable monomers for the preparation of the sheath (s) are disclosed in US Pat. 4,226,752, column 4,

Lines 20-46, reference being made to the information hereof. One or more coats are preferably a polymer of a methacrylate, acrylate, vinylarene, vinyl carboxylate, acrylic acid and / or methacrylic acid.

Preferred acrylates and methacrylates are alkyl acrylates or alkyl methacrylates, which preferably have 1 to 18, more preferably 1 to 8, most preferably 2 to 8 carbon atoms in the

Alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl, 2-ethylhexyl or the hexyl, heptyl or octyl groups. The alkyl group may be branched or linear. The preferred alkyl acrylate is ethyl acrylate. Other useful acrylates and methacrylates are those previously reported for the core, preferably 3-hydroxypropyl methacrylate. The most preferred alkyl methacrylate is methyl methacrylate.

Preferred vinylarenes are styrene or α-methylstyrene optionally substituted on the aromatic ring with an alkyl group such as methyl, ethyl or tert-butyl or with a halogen such as chlorostyrene.

A preferred vinyl carboxylate is vinyl acetate.

The sheath (s) preferably contains at least 15%, more preferably at least

25%, most preferably at least 40% of a polymerized methacrylate, acrylate or monovinylarene and 0 to 85%, more preferably 0 to 75%, most preferably 0 to 60% of one or more vinyl comonomers such as other alkyl methacrylates, aryl methacrylates, alkyl acrylates, Aryl acrylates, alkyl and aryl acrylamides, acrylonitrile, methacrylonitrile, maleimide and / or alkyl and aryl acrylates and methacrylates, which contain one or more

Substituents such as halogen, alkoxy, alkylthio, cyanoalkyl or amino are substituted. Examples of suitable vinyl comonomers are given above. Two or more monomers may be copolymerized.

The shell polymer may contain a crosslinker and / or a graft crosslinker of the type previously set forth with reference to the core polymer.

The shell polymers preferably make from 5 to 40%, more preferably from 15 to 35% of

Total particle weight off.

The polymeric particles contain at least 15%, preferably from 20 to 80%, more preferably from 25 to 60%, most preferably from 30 to 50% of a polymerized alkyl acrylate or methacrylate, based on the total weight of the polymer. Preferred alkyl acrylates and methacrylates are given above. The alkyl acrylate or alkyl methacrylate component may be present in the core and / or in the sheath (s) of the polymeric particles. Homopolymers of an alkyl acrylate or methacrylate in the core and / or sheath (s) are useful, however, an alkyl (meth) acrylate is preferably copolymerized with one or more other types of alkyl (meth) acrylates and / or one or more other vinyl polymers , preferably with the ones listed above. Most preferably, the polymeric particles contain a core of a poly (butyl acrylate) and one or more shells of poly (methyl methacrylate).

The polymeric particles are useful to impart light scattering properties to the polycarbonate. The refractive index n of the core and the cladding / cladding of the polymeric particles is preferably within +/- 0.25 units, more preferably within +/- 0.18 units, most preferably within +/- 0.12 units of the refractive index of the polycarbonate. The refractive index n of the core and the sheath (s) is preferably not closer than +/- 0.003 units, more preferably not closer than +/- 0.01 units, most preferably not closer than +/- 0.05 units in the Refractive index of the polycarbonate. The refractive index is measured in accordance with ASTM D 542-50 and / or DIN 53 400.

The polymeric particles generally have an average particle diameter of at least 0.5 microns, preferably at least 2 microns, more preferably from 2 to 50 microns, most preferably from 2 to 15 microns. Preferably, at least 90%, most preferably at least 95% of the polymeric particles have a diameter of greater than 2 microns The polymeric particles are preferably a free flowing powder. _ _

The polymeric particles can be prepared in a known manner. Generally, at least one monomer component of the core polymer is subjected to emulsion polymerization to form emulsion polymer particles. The emulsion polymer particles are swollen with the same or one or more other monomer components of the core polymer, and the monomer (s) are polymerized within the emulsion polymer particles.

The steps of swelling and polymerisation can be repeated until the particles have grown to the desired core size. The core polymer particles are suspended in a second aqueous monomer emulsion and a polymer shell of the monomer (s) is polymerized onto the polymer particles in the second emulsion. One or more coats may be polymerized on the core polymer. The production of

Core / shell polymer particles are described in EP-A 0 269 324 and in U.S. Patents 3,793,402 and 3,808,180.

Furthermore, it is surprisingly found that the brightness values can be further increased by using a small amount of optical brightener.

As optical brighteners compounds of the following classes can be used:

a) bis-benzoxazoles of the following structure:

where R ¹ , R ² , R ⁵ and R ⁶ independently of one another are H, alkyl, aryl, heteroaryl or halogen and X can be the following groups:

T hiophen: Naphthalene:

with R ¹ and R ^{2 are} independently H, alkyl, aryl, heteroaryl or halogen.

For example, Uvitex® OB from Ciba Specialty Chemicals of the formula

or Hostalux KCB from Clariant GmbH of the formula

b) Phenylcoumarins of the following structure:

c) where R ¹ and R ² independently of one another may be H, alkyl, aryl, heteroaryl or halogen. - -

For example, Leukopur® EGM from Clariant GmbH of the formula:

d) Bis-styryl-biphenyls of the following structure:

where R ¹ and R ² independently of one another may be H, alkyl, aryl, heteroaryl or halogen.

A preferred embodiment of the invention therefore represents a solid sheet according to the invention, which additionally contains 0.001 to 0.2 wt .-%, preferably about 1000 ppm of an optical brightener of the class bis-benzoxazoles, Phenylcoumarine or bis-Styrylbiphenyle. A particularly preferred optical brightener is Uvitex OB, from Ciba Specialty Chemicals.

The solid sheets according to the invention can be produced either by injection molding or by extrusion. If these are large-area solid plates production by injection molding for technical reasons can not be economical. In these cases, the extrusion process is preferable. For extrusion, a polycarbonate granules are fed to the extruder and melted in the plasticizing system of the extruder. The

Plastic melt is pressed through a slot die and thereby deformed, brought in the nip of a smoothing calender in the desired final shape and formfϊxiert by mutual cooling on smoothing rolls and the ambient air. The polycarbonates of high melt viscosity used for extrusion are usually processed at melt temperatures of 230 to 320 ⁰ C, according to the cylinder temperatures of the plasticizing and die temperatures are set.

The solid sheet according to the invention may additionally comprise one or more coextruded layers (coextrusion layers). By using one or more side extruders and suitable melt adapters in front of the slot die, polycarbonate melts can be produced superimpose different composition and thus produce multilayer solid plates (see, for example, EP-A 0 110 221 and EP-A 0 110 238).

Both the base layer and the optionally present coextrusion layer (s) of the solid sheet according to the invention may additionally contain additives such as, for example, UV absorbers and other customary processing aids, in particular defoaming agents and flow agents, and the stabilizers customary for polycarbonates, in particular heat stabilizers and also antistatic agents, optical brighteners. In each layer different additives or concentrations of additives may be present. In particular, the coextrusion layer may contain UV absorbers and defogging agents.

In a preferred embodiment, the composition of the solid plate additionally contains 0 to 0.5 wt .-% of a UV absorber of the classes benzotriazole derivatives, dimer benzotriazole derivatives, triazine derivatives, dimer triazine derivatives, Diarylcyanoacrylate.

Preferably, the UV protective layer consists of at least one coextrusion layer with at least one UV absorber in a proportion of 0.1 to 20 wt .-% based on the coextrusion layer.

The solid plate according to the invention preferably has a thickness of 0, 1 to 4.0 mm, more preferably from 1.0 to 2.0 mm, in particular about 2 mm.

Optionally present coextrusion layers preferably have a thickness of 10 to 100 .mu.m, particularly preferably from 20 to 60 .mu.m.

Suitable stabilizers are, for example, phosphines, phosphites or Si-containing stabilizers and further compounds described in EP-A 0 500 496. Exemplary

Triphenyl phosphites, diphenyl alkyl phosphites, phenyl dialkyl phosphites, tris (nonylphenyl) phosphite, tetrakis (2,4-di-tert-butylphenyl) -4,4'-biphenylene diphosphonite, bis (2,4-dicumylphenyl) petaerythritol diphosphite and triaryl phosphite called. Particularly preferred are triphenylphosphine and tris (2,4-di-tert-butylphenyl) phosphite.

Suitable mold release agents are, for example, the esters or partial esters of monohydric to hexahydric alcohols, in particular of glycerol, pentaerythritol or guerbet alcohols.

Monohydric alcohols are, for example, stearyl alcohol, palmityl alcohol and Guerbet alcohols, a dihydric alcohol is, for example, glycol, a trihydric alcohol is, for example, glycerol, tetrahydric alcohols are, for example, pentaerythritol and mesoerythritol, pentavalent alcohols are, for example, arabitol, ribitol and xylitol, hexahydric alcohols are, for example

Mannitol, glucitol (sorbitol) and dulcitol. The esters are preferably the monoesters, diesters, triesters, tetraesters, pentaesters and hexaesters or mixtures thereof, in particular random mixtures, of saturated, aliphatic Cio to C ₃₆ -monocarboxylic acids and optionally hydroxy-monocarboxylic acids, preferably with saturated, aliphatic C ₁₄ to C ₃₂ Monocarboxylic acids and optionally hydroxy-monocarboxylic acids.

The commercially available fatty acid esters, in particular of pentaerythritol and of glycerol, may contain <60% of different partial esters as a result of the preparation.

Saturated, aliphatic monocarboxylic acids having 10 to 36 carbon atoms are, for example, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, hydroxystearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid and montan acids.

Preferred saturated, aliphatic monocarboxylic acids having 14 to 22 carbon atoms are, for example, myristic acid, palmitic acid, stearic acid, hydroxystearic acid, arachic acid and behenic acid.

Particularly preferred are saturated, aliphatic monocarboxylic acids such as palmitic acid, stearic acid and hydroxystearic acid.

The saturated, aliphatic C ₁ to C ₃₆ carboxylic acids and the fatty acid esters are either known from the literature or can be prepared by processes known from the literature. Examples of pentaerythritol fatty acid esters are those of the particularly preferred monocarboxylic acids mentioned above.

Particularly preferred are esters of pentaerythritol and glycerol with stearic acid and

Palmitic acid.

Also particularly preferred are esters of Guerbet alcohols and of glycerol with stearic acid and palmitic acid and optionally hydroxystearic acid.

Examples of suitable antistatic agents are cationic compounds, for example quaternary ammonium, phosphonium or sulfonium salts, anionic compounds, for example

Alkyl sulfonates, alkyl sulfates, alkyl phosphates, carboxylates in the form of alkali metal or alkaline earth metal salts, nonionic compounds, for example polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters, ethoxylated fatty amines. Preferred antistatic agents are nonionic compounds. - -

Suitable UV absorbers are, for example

a) Benzotriazole derivatives of the formula (I):

Formula (I)

In formula (I), R and X are the same or different and are H or alkyl or alkylaryl.

Tinuvin 329 with X = 1,1,3,3-tetramethylbutyl and R = H is preferred

Tinuvin 350 with X = tert-butyl and R = 2-butyl

Tinuvin 234 with X = R = 1,1-dimethyl-1-phenyl

b) Dimer Benzotriazole Derivatives of Formula (II):

Formula (H)

In formula (II) R ¹ and R ² are identical or different and denote H, halogen, Ci-Ci ₀ - A Allkkyyll ,, --CC CC _{55 1100} --CCyyCcloalkyl, C ₇ -C ₁₃ aralkyl, C ₆ - Ci ₄ -alkyl, -OR ⁵ or - (CO) -OR ⁵ with R ⁵ = H or C ₁ -C ₄ -alkyl.

In formula (II), R ³ and R ^{4 are} also identical or different and are H, C _r C ₄ -alkyl, Cs-Cβ-cycloalkyl, benzyl or C ₆ -C ₄ -aryl.

In formula (II), m is 1,2 or 3 and n is 1,2,3 or 4. - -

Tinuvin 360 with R ¹ = R ³ = R ⁴ = H is preferred here; n = 4; R ² = 1,1,3,3-tetramethylbutyl; m = 1

bl) Dimer benzotriazole derivatives according to formula (DI):

Formula (EI)

wherein the bridge

O O

- (CHR ³ ) _p - C - O (Y - OL C (CHR ⁴ ) _p -

means

R, R, m and n have the meaning given for formula (II),

and wherein p is an integer from 0 to 3,

q is an integer from 1 to 10,

Y is -CH ₂ -CH ₂ -, - (CH ₂ ) ₃ -, - (CH ₂ ) ₄ -, - (CH ₂ ) ₅ -, - (CH ₂ ) ₆ -, or CH (CH ₃ ) -CH ₂ -ist and

R ³ and R ^{4 have} the meaning given for formula (II).

Preference is given to Tinuvin 840 with R ¹ = H; n = 4; R ² = tert-butyl; m = 1; R ² is attached ortho to the OH group; R ³ = R ⁴ = H; p = 2; Y = - (CH ₂ ) ₅ -; q = 1 - -

c) Triazine derivatives according to formula (IV):

Formula (IV)

wherein R ¹ , R ² , R ³ , R ⁴ in formula (IV) are the same or different and are H or aryl or alkyl or CN or halogen and X is alkyl.

Preference is given to Tinuvin 1577 with R ¹ = R ² = R ³ = R ⁴ = H; X = hexyl as well

Cyasorb UV-1164 with R ¹ = R ² = R ³ = R ⁴ = methyl; X = octyl

d) triazine derivatives of the following formula (IVa)

Formula (TVa)

embedded image in which

R ¹ is C _r alkyl to C ₁₇ alkyl,

R ² is H or C 1 -alkyl to C ₄ -alkyl and

n is 0 to 20.

e) Dimer triazine derivatives of the formula (V):

Formula (V)

embedded image in which

R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ in formula (V) may be the same or different and denote H or alkyl or CN or halogen, and

X is alkyl or - (CH ₂ CH ₂ -O-) n C (= O>.

Diaryl cyanoacrylates of the formula (VI):

Formula (VI)

wherein R ¹ to R ^{40 may be the} same or different and denote H, alkyl, CN or halogen. Uvinul 3030 with R ¹ to R ⁴⁰ = H is preferred

The abovementioned UV absorbers are generally known to the person skilled in the art and in some cases commercially available, or can be prepared according to known processes.

The following examples are intended to illustrate the invention without, however, limiting it.

_ _

Examples

The 2 mm solid sheets listed in Examples 1 to 6 were prepared as follows:

1. Preparation of the compound with conventional twin-screw compounding extruders (e.g., ZSK 32) at processing temperatures of 250 to 33 ° C common for polycarbonate.

2. The machines and apparatus used to produce the coextruded 2 mm solid sheets include:

the main extruder with a screw of length 33 D and a diameter of

70 mm with degassing - a coextruder for applying the top layer with a screw of length 25

D and a diameter of 35 mm a special coextrusion slot die with a width of 450 mm a smoothing calender a roller conveyor - a take-off device a cutting device (saw) a storage table.

The polycarbonate granules of the base material were fed to the hopper of the main extruder. In the plasticizing cylinder / screw, the melting and conveying of the respective material took place. The other facilities served the transport,

Cutting and depositing the extruded sheets.

For the examples described below, the following types of polycarbonate were used:

• Makrolon® 3100 (Mw about 32,000, light transmittance according to DIN 5036-1 at 4 mm = 89.8%, yellowness index according to ASTM E313 = 1.94) from Bayer MaterialScience.

• Makrolon® 2800 (Mw about 29,000, light transmittance according to DIN 5036-1 at 4 mm =

89.8%, yellowness index according to ASTM E313 = 1.65) from Bayer MaterialScience.

• Makrolon CD 2005® (Mw about 19,000 light transmittance according to DUST 5036-1 at 4 mm =

89.9%, yellowness index according to ASTM E313 = 1.19) from Bayer MaterialScience. example 1

A compound of the following composition was prepared:

• Makrolon 3100 polycarbonate with 97.5% by weight

Core-shell particles with a butadiene / styrene core and a methyl methacrylate shell Paraloid EXL 5137 from Rohm & Haas with a particle size of 2 to 15 μm and an average particle size of 8 μm with a content of 2.4% -%.

• Thermostabilizer triphenylphosphine in a proportion of 0.1% by weight.

From this compound, a 2 mm solid plate without coextrusion layer was extruded.

Example 2

A compound of the following composition was prepared:

• Makrolon 3100 polycarbonate with a 96.9% share

Core-shell particles with a butadiene / styrene core and a methyl methacrylate shell Paraloid EXL 5137 from Rohm & Haas with a particle size of 2 to 15 μm and an average particle size of 8 μm with a content of 3.0% -%.

• Thermostabilizer triphenylphosphine in a proportion of 0.1% by weight.

From this compound, a 2 mm solid plate without coextrusion layer was extruded.

Example 3

A compound of the following composition was prepared:

• Makrolon 2800 polycarbonate with a 97.5% share

Core-shell particles with a butadiene / styrene core and a methyl methacrylate

Shell Paraloid EXL 5137 from Rohm & Haas with a particle size of 2 to 15 μm and an average particle size of 8 μm with a content of 2.4% by weight.

• Thermostabilizer triphenylphosphine in a proportion of 0.1% by weight.

From this compound, a 2 mm solid plate without coextrusion layer was extruded. Example 4

A compound of the following composition was prepared:

• Makrolon 3100 polycarbonate with a 96.9% share

Core-shell particles with a butadiene / styrene core and a methyl methacrylate shell Paraloid EXL 5137 from Rohm & Haas with a particle size of 2 to 15 μm and an average particle size of 8 μm with a content of 3.0% -%.

• Thermostabilizer triphenylphosphine in a proportion of 0.1% by weight.

From this compound, a 2 mm solid plate without coextrusion layer was extruded.

Example 5 ( ^' according to the invention ^' )

A compound of the following composition was prepared:

• Polycarbonate Makrolon CD 2005 with a share of 97.5 w-%

Core-shell particles with a butadiene / styrene core and a methyl methacrylate shell Paraloid EXL 5137 from Rohm & Haas with a particle size of 2 to 15 μm and an average particle size of 8 μm with a content of 2.4% -%.

• Thermostabilizer triphenylphosphine in a proportion of 0, 1 w%.

From this compound, a 2 mm solid plate without coextrusion layer was extruded.

Example 6 (according to the invention)

A compound of the following composition was prepared:

• Polycarbonate Makrolon CD 2005 with a share of 96.9% w

Core-shell particles with a butadiene / styrene core and a methyl methacrylate

Shell Paraloid EXL 5137 from Rohm & Haas with a particle size of 2 to 15 μm and an average particle size of 8 μm with a proportion of 3.0% by weight.

• Thermostabilizer triphenylphosphine in a proportion of 0.1% by weight.

From this compound, a 2 mm solid plate without coextrusion layer was extruded. The 2 mm solid plates listed in Examples 1 to 6 were examined for their optical properties according to the following standards and with the following measuring devices:

To determine the light transmission (Ty (D6510 ⁰ )) and the light reflection (Ry (D6510 ⁰ ) over a white background), an Ultra Scan XE from Hunter Associates Laboratory, Inc. was used. In addition, yellowness index YI (D65, C2 °), ASTM E313), x, y color values (D65, C2 °, CIE standard color chart) and L, a, b color values were measured with this instrument (D65, C2 °, CIELAB color system, DIN 6174). For the Haze determination (according to ASTM D 1003), a Hazegard Plus from Byk-Gardner was used.

The brightness measurements were taken on a backlight unit (BLU) of the company DS LCD, (LTA170WP, 17 "LCD TV Panel) with the help of a Luminance Meter LS100 from the company Minolta, where the standard diffuser plate was removed and each replaced by the 2 mm solid plates produced in Examples 1 to 6. The BLU comprises four films and is constructed in the arrangement of light source diffuser plate films (circular, polarizer, diffuser foil, prismatic fibers / BEF, linear polarizer) LCD display.

The results of the measurements are summarized in the following Table 1.

Table 1 Optical data of the 2 mm solid sheets

, ,

In Examples 1 to 6 are described from base resins of different viscosity but the same additive composition plates that show a significant dependence on the viscosity of the base resin in their performance when used as diffuser plates m backlight units

The optical properties with respect to light transmission according to DIN 5036-1 at 4 mm are more or less the same for the three polycarbonate viscosities used with Ty = 89.8 to 89.9%. Thus, in Examples 1 and 2, respectively, a high molecular weight polycarbonate is used (Makrolon 3100), the litter additive content being 2.4 or 3.0% by weight. It is noteworthy that the critical value of brightness is independent of the amount of scattering additive. The luminance is increased in the forward direction by overlaying the film system (see Table 1, last and penultimate lines.) The differences between Examples 1 and 3 are in the range of Measurement accuracy of the luminance determination

In Examples 3 and 4, the difference from Examples 1 and 2 is only in the base material used, in these examples Makrolon 2800. The optical properties of the base material are the same as those of Makrolon 3100 and the luminance measurements of Examples

3 and 4 also give the same values as in Examples 1 and 2.

Surprisingly, however, are the values of the luminance measurements in Examples 5 and 6. Although the luminances without film set are initially the same as in the examples before, but surprisingly here is the significant jump in the luminance when using the film package, ie in the manufacture BLU. The luminance levels here are about 15 to 18% higher than the previous examples, which was not to be expected considering the same optical data of the basic CD 2005 used.

Claims

claims

1. Solid sheet of a composition containing 80 to 99.99 wt .-% of a transparent polycarbonate having a molecular weight of M _w = 15,000 to 21,000 g / mol and 0.01 to 20 wt .-% transparent polymeric particles having a different optical density of the polycarbonate ,

2. Solid sheet according to claim 1, wherein the transparent polycarbonate has a molecular weight of M _w = 18,500 to 20,000 g / mol.

The solid sheet according to claims 1 or 2, wherein the transparent polymeric particles having a different optical density from the polycarbonate are acrylate-based polymeric particles having a core-shell morphology with a particle size of between 1 and 2

100 microns are.

4. Solid sheets according to claims 1 to 3, characterized in that they additionally comprise at least one coextrusion layer.

5. Solid sheets according to claim 4, characterized in that at least one coextruded layer contains a UV absorber.

6. Solid sheets according to claim 4 or 5, characterized in that at least one coextrusion layer contains a lubricant.

7. Solid sheets according to one of claims 4 to 6, characterized in that it comprises a coextrusion layer on both sides.

8. Solid sheets according to claims 5 to 8, characterized in that each

Coextrusion layer has a thickness of 10 to 100 microns.

9. Solid sheets according to claims 1 to 8, characterized in that it has a thickness of 0.1 to 4.0 mm.

10. Use of a solid plate according to one of claims 1 to 9 as a diffuser plate in flat screens.

A solid plate according to claim 1, wherein the light transmission is below 70%.

12. Solid sheet according to claim 1, wherein the particles are organic.

3. Solid sheet according to claim 1, wherein the molecular weight is between 15,000 and 18,000 g / mol.