EP1660935A1

EP1660935A1 - Diffuser disk for lcd applications, method for the production and use thereof

Info

Publication number: EP1660935A1
Application number: EP04732288A
Authority: EP
Inventors: Markus Parusel; Jann Schmidt; Herbert Groothues
Original assignee: Roehm GmbH Darmstadt
Current assignee: Roehm GmbH Darmstadt
Priority date: 2003-08-04
Filing date: 2004-05-12
Publication date: 2006-05-31
Also published as: TW200523645A; JP2007501425A; ZA200601021B; US20060240200A1; RU2006106618A; AU2004269463B2; MXPA06001067A; NZ545549A; AU2004269463A1; CN100541283C; WO2005022245A1; US7629041B2; KR20060056365A; CA2534538A1; DE10336130A1; BRPI0413302A; RU2359298C2; HK1094044A1; CN1829936A

Abstract

The invention relates to diffuser disks for LCD applications, comprising at least one light-diffusing polymethylmethacrylate layer, which has a polymethylmethacrylate matrix and 0.5 % by weight to 59.5 % by weight, with regard to the weight of the light-diffusing polymethylmethacrylate layer, of spherical diffusing particles (A), which have an average particle size V50 ranging from 0.1 to 40 µm and a refractive index difference from the polymethylmethacrylate matrix ranging from 0.02 to 0.2, and 0.5 % by weight to 59.5 % by weight, with regard to the weight of the light-diffusing polymethylmethacrylate layer, of spherical particles (B), which have an average particle size V50 ranging from 10 to 150 µm and a refractive index difference from the polymethylmethacrylate matrix ranging from 0 to 0.2, whereby the total concentration of the spherical diffusing particles (A) and particles (B) ranges from 1 to 60 % by weight with regard to the weight of the light-diffusing polymethylmethacrylate layer, and the spherical diffusion particles (A) and the spherical particles (B) have a different average particle size V50, whereby the diffuser disks have a transmission ranging from 20 % to 70 % and a diffusion coefficient factor greater than 0.3, and the ratio of the square of the average surface roughness of the polymethylmethacrylate layer Rz to the cube of the particle size of the spherical particles (B) RZ<2> /DPB <3> ranges from 0.0002 µm<-1> to 0.1300 µm<-1>.

Description

Diffuser for LCD applications, process for their production and use

The present invention relates to lenses for LCD applications comprising at least one light-scattering polymethyl methacrylate layer, process for producing these lenses and use.

Monitors based on liquid crystal technology have been known for some time. These LCDs (Liquid Crystal Displays) are often used as a display medium on computers. Recently, this technology has also been offered in television sets. In addition, LCDs are also used for the graphic display of navigation data in automobiles, aircraft and ships. The requirements for these monitors are correspondingly diverse. Many LCDs have one lighting unit in common, which is attached behind the actual LCD cell with the polarizing foils. Diffusers are often used between the lighting unit and the LCD cell, which distributes the light necessary for the display evenly over the LCD cell.

Disks suitable for this purpose, which comprise mixtures of particles, are known per se. JP 4-134440 describes rear projection screens which comprise particles with different refractive indices. As a result, the color tone is reproduced better.

In addition, JP 8-198976, JP 5-51480 and JP 2000-296580, for example, describe such panes which can be used for lighting applications. The plates mentioned above, which have scattering media, can in principle be used as a scattering disc. However, known plates do not show a balanced property profile.

For example, the brightness distribution achieved by known plates equipped with scattering media is often not optimal.

Furthermore, many have a relatively high yellow index, which can lead to color falsification. Furthermore, many scatter plates show a transmission that is too high or too low and that the turbidity is too great.

In addition, the optical properties, such as scattering power or intensity half-value angle or yellowness index, of many known impact-modified scattering plates have a temperature dependency. The temperature dependency may be negligible in some applications. However, it should be borne in mind that the dashboards of automobiles are subject to strong temperature fluctuations. Among other things, measurable inhomogeneities occur at high temperatures. Despite these strong fluctuations, the spreading disc should ensure that the properties are as constant as possible.

Furthermore, many scatter plates are very sensitive to scratches. This property may appear relatively negligible when installed. However, increased precautionary measures must be taken during the assembly of the screens to avoid scratches. Visually visible scratches lead to inhomogeneities in the light scattered on the LCD cell.

In view of the state of the art specified and discussed herein, it was therefore an object of the present invention to provide lenses for LCD applications that have a particularly balanced Enable property profile. In particular, the spreading discs should allow a high light yield with a very high scattering effect.

In addition, the lenses should allow a particularly neutral scattered light without color shift. The colors generated by the LCD cells should only change slightly due to temperature fluctuations.

Another object of the present invention was to provide diffusing screens for LCD applications which have a particularly uniform brightness distribution.

In addition, the spreading discs should have the highest possible mechanical stability. Scratches on the plastic plate should not be visible or only slightly. In particular, damage should have little or no influence on the brightness distribution of the monitor provided with a lens.

Furthermore, the invention was based on the object of providing diffusers for LCD applications which can be produced particularly easily. For example, the spreading disks should be able to be produced in particular by extrusion.

In addition, it was therefore an object of the present invention to provide spreading disks whose property profile has only a low sensitivity to temperature. This provides LCDs that can be used, for example, in automobiles.

Another object of the present invention was to provide diffusers which are simple in size and shape Requirements can be adjusted. For example, the spreading disks should be able to be processed using very cost-effective methods, for example using laser cutting systems.

Another object of the invention was that the lenses have a high durability, in particular a high resistance to UV radiation or weathering.

These tasks are solved as well as others, which are not named literally, but which can be derived as a matter of course from the contexts discussed here, or which inevitably result from these, by means of the lenses described in claim 1. Expedient modifications of the lenses according to the invention are protected in the subclaims which refer back to claim 1.

With regard to the methods for the production of spreading discs, claim 24 provides a solution to the underlying problem.

Since the ratio of the square of the average surface roughness of the polymethyl methacrylate layer R _z to the third power of the particle size of the spherical particles (B) Rz ² / D _PB ^{3 is} in the range from 0.0002 μm ^" to 0.1300 μm ^'1 , Surprisingly, it is possible for diffusing screens for LCD applications to comprise at least one light-scattering polymethyl methacrylate layer, a polymethyl methacrylate matrix and 0.5% by weight to 59.5% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, of spherical scattering particles (A) which have an average particle size V ₅₀ in the range from 0.1 to 40 μm and a refractive index difference to the polymethyl methacrylate matrix in the range from 0.02 to 0.2, and 0.5% by weight to 59.5 % By weight, based on the weight of the light-scattering polymethyl methacrylate layer, of spherical particles (B), an average particle size V ₅ o microns in the range of 10 to 150 and a refractive index difference of the polymethyl methacrylate matrix is in the range of 0 have to 0.2, wherein the total concentration of the spherical scattering particles (A) and particles (B) in the range of 1 to 60% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, and the spherical scattering particles (A) spherical particles (B) have a different mean particle size V ₅₀ , the scattering discs having a transmission in the range from 20% to 70 % and have a scattering capacity greater than 0.2, which provide a very good, balanced property profile.

The measures according to the invention include achieved the following advantages in particular:

> The lenses of the present invention can be adapted to individual needs without the brightness distribution and / or the sensitivity to scratching being impaired as a result.

> The spreading discs of the present invention allow high transmission and good spreading power.

> The display on the lenses according to the invention enables LCDs that provide particularly true color images.

> The spreading disks made available according to the present invention have a particularly uniform brightness distribution.

> In addition, the lenses of the present invention show high mechanical stability. In this case, scratches, which may be present on the pane, have no or only a slight effect on the image generated by the LCD cell. In addition, the lenses of the present invention can also be used in LCDs which are exposed to a particularly high temperature fluctuation. Here, these temperature fluctuations have only a minor effect on the brightness distribution, the transmission or the scattering power of the lenses.

> Furthermore, the lenses of the present invention can be manufactured particularly easily. The spreading disks can be produced in particular by extrusion.

> The spreading discs according to the invention show a high resistance to weathering, in particular to UV radiation.

> The size and shape of the spreading discs can be adapted to the needs.

The light-scattering polymethyl methacrylate layer of the lens according to the present invention has 1 to 60% by weight, in particular 3 to 55% by weight and preferably 6 to 48% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, of spherical scattering particles (A) and spherical particles (B).

The scattering particles (A) and the particles (B) are spherical. In the context of the present invention, the term spherical denotes that the particles preferably have a spherical shape, it being obvious to the person skilled in the art that, due to the production methods, particles with a different shape may also be present, or that the shape of the particles may deviate from the ideal spherical shape , Accordingly, the term spherical means that the ratio of the largest dimension of the particles to the smallest dimension is a maximum of 4, preferably a maximum of 2, these dimensions being measured in each case by the center of gravity of the particles. At least 70, particularly preferably at least 90%, based on the number of particles, is preferably spherical.

The scattering particles (A) have an average particle size V ₅₀ in the range from 0.1 to 40 μm, in particular from 0.5 to 30 μm and particularly preferably 1 to 15 μm.

The light-scattering PMMA layer comprises 0.5 to 59.5% by weight, preferably 1 to 20% by weight and particularly preferably 1.5 to 10% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, spherical Scattering particles (A).

Such particles are known per se and can be obtained commercially. These include in particular plastic particles as well as particles that comprise inorganic materials.

The scattering particles which can be used according to the invention are not particularly restricted, the light refraction taking place at the phase boundary of the scattering particles (A) with the matrix plastic.

Accordingly, the refractive index of the scattering particles (A) has a refractive index n ₀ measured at the Na-D line (589 nm) and at 20 ° C., which differs from the refractive index n _{0 of} the matrix plastic by 0.02 to 0.2 units ,

The spherical scattering particles (A) preferably comprise crosslinked polystyrene, polysilicon and / or crosslinked poly (meth) acrylates. A group of preferred plastic particles that are used as scattering agents contain silicones. Such particles are obtained, for example, by hydrolysis and polycondensation of organotrialkoxysilanes and / or tetraalkoxysilanes, which have the formulas

R ¹ Si (OR ² ) ₃ and Si (OR ² ) ₄

in which R ^{1 represents,} for example, a substituted or unsubstituted alkyl group, an alkenyl group or a phenyl group, and the radical R ^{2 of} the hydrolyzable alkoxy group represents an alkyl group such as methyl, ethyl or butyl or an alkoxy-substituted hydrocarbon group such as 2-methoxyethyl or 2 Represents ethoxyethyl. Exemplary organotrialkoxysilanes are methyltrimethoxysilane, methyltriethoxysilane, methyl-n-propoxysilane, methyltriisopropoxysilane and methyltris (2-methoxyethoxy) silane.

The aforementioned silane compounds and processes for producing spherical silicone particles are known to those skilled in the art and are described in documents EP 1 116 741, JP 63-077940 and JP 2000-186148.

Spreading agents made of silicone that are particularly preferably used in the present invention are available from GE Bayer Silicones under the trade names TOSPEARL® 120 and TOSPEARL® 3120.

Another group of preferred plastic particles are composed of: b1) 25 to 99.9 parts by weight of monomers which have aromatic groups as substituents, such as styrene, methylstyrene, ring-substituted styrenes, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-phenylethyl (meth) acrylate, 3-phenylpropyl (meth) acrylate or vinyl benzoate; and b2) 0 to 60 parts by weight of an acrylic and / or methacrylic acid ester having 1 to 12 carbon atoms in the aliphatic ester residue, which with the Monomers b1) can be copolymerized, examples being: methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i- Butyl (meth) acrylate, tert-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 3,3,5-trimethylcyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, norbomyl (meth) acrylate or isobornyl (meth) acrylate; b3) 0.1 to 15 parts by weight of crosslinking comonomers which have at least two ethylenically unsaturated groups which can be free-radically copolymerized with b1) and optionally with b2), such as, for example, divinylbenzene, glycol di (meth) acrylate, 1,4-butanediol di (meth ) acrylate, allyl (meth) acrylate, triallyl cyanurate, diallyl phthalate, diallyl succinate, pentaerythritol tetra (meth) acrylate or trimethylolpropane tri (meth) acrylate, the comonomers b1), b2) and b3) being added to 100 parts by weight.

Mixtures from which the plastic particles are produced particularly preferably have at least 80% by weight of styrene and at least 0.5% by weight of divinylbenzene.

The production of cross-linked plastic particles is known in the specialist world. For example, the scattering particles can be produced by emulsion polymerization, as described, for example, in EP-A 342 283 or EP-A 269 324, very particularly preferably by polymerization in the organic phase, as described, for example, in German patent application P 43 27 464.1, with the latter Polymerization technology particularly narrow particle size distributions or, in other words, particularly small deviations of the particle diameter from the average particle diameter occur.

Plastic particles are particularly preferably used which have a temperature resistance of at least 200 ° C., in particular of Have at least 250 ° C, without this being intended to be a limitation. Here, the term temperature-resistant means that the particles are essentially not subject to thermal degradation. Thermal degradation undesirably leads to discoloration, making the plastic material unusable.

Particularly preferred particles are available from Sekisui, among others, under the trade names © Techpolymer SBX-6, ®Techpolymer SBX-8 and ® Techpolymer SBX-12.

The inorganic materials from which the scattering particles (A) can also be produced include aluminum hydroxide, aluminum-potassium silicate (mica), aluminum silicate (kaolin), barium sulfate (BaSO ₄ ), calcium carbonate, magnesium silicate (talc). Of these materials, BaSO _{4 is} preferred.

Of the above-mentioned scattering particles, particles comprising inorganic materials are preferred.

The previously described scattering particles (A) can be used individually or as a mixture of two or more types.

The light-scattering PMMA layer comprises 0.5 to 59.5% by weight, preferably 5 to 40% by weight and particularly preferably 8 to 25% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, spherical particles ( B).

The particles (B) to be used according to the invention have an average particle size V ₅₀ in the range from 10 to 150 μm, preferably 15 to 70 μm and particularly preferably 30 to 50 μm, the refractive index of the particles being one of the sodium D line (589 nm ) and measured at 20 ° C Have refractive index n ₀ , which differs by 0 to 0.2 units from the refractive index n _{0 of} the matrix carbon.

The particles (B) can also be obtained commercially. These particles can be made from the same materials as the scattering particles (A). Plastic particles are preferably used here.

The spherical particles (B) preferably comprise crosslinked polystyrene, polysilicon and / or crosslinked poly (meth) acrylates.

The particles (B) described above can be used individually or as a mixture of two or more types.

The ratio of the weight average of the scattering particles (A) to the particles (B) is in the range from 1: 00 to 10: 1, in particular 1:50 to 7.5: 1, particularly preferably 1:25 to 5: 1 and entirely particularly preferably 1:10 to 3: 1.

The difference between the mean particle size V _{50 of} the scattering particles (A) and the particles (B) is preferably at least 5 μm, in particular at least 10 μm, the particles (B) being larger than the scattering particles (A).

The particle size and the particle size distribution can be determined using a laser extinction method. A Galay-CIS from L.O.T. GmbH are used, the measurement method for determining the particle size and the particle size distribution is contained in the user manual.

The particle size of inorganic particles can be determined by means of an X-ray graph. A MICROSCAN Il device from Quantachrome can be used. The MICROSCAN II is an automatic measuring device for determining the particle size distribution of powders in suspensions with a measuring range from 0.1 to 300 μm. The measuring principle of the MICROSCAN II is sedimentation with X-ray detection. For this purpose, the particles are dispersed homogeneously in a liquid with the help of a built-in hose pump or ultrasonic treatment. The particle size determination is determined according to Stokes' law depending on the density of particles and dispersing liquid, the viscosity of the liquid and the sinking speed of the particles

The average particle size of V ₅₀ results from the median of the weight average, 50% by weight of the particles being less than or equal to and 50% by weight of these particles being greater than or equal to this value.

According to a special aspect of the present invention, these particles are present in the plastic matrix in a uniformly distributed manner without any significant aggregation or aggregation of the particles occurring. Evenly distributed means that the concentration of particles within the plastic matrix is essentially constant.

In addition to the spherical particles, the light-scattering layer comprises a plastic matrix which has polymethyl methacrylate (PMMA). The light-scattering polymethyl methacrylate layer preferably comprises at least 30% by weight, in particular at least 40% by weight and particularly preferably at least 50% by weight, based on the weight of the light-scattering layer, of polymethyl methacrylate.

Polymethyl methacrylates are generally obtained by radical polymerization of mixtures containing methyl methacrylate. In general, these mixtures contain at least 40% by weight, preferably at least 60% by weight and particularly preferably I o

at least 80% by weight, based on the weight of the monomers, of methyl methacrylate.

In addition, these mixtures for the production of polymethyl methacrylates can contain further (meth) acrylates which can be copolymerized with methyl methacrylate. The term (meth) acrylates encompasses methacrylates and acrylates and mixtures of the two.

These monomers are well known. These include, among others

(Meth) acrylates derived from saturated alcohols, such as, for example, methyl acrylate, ethyl! (Meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate and

2-ethylhexyl (meth) acrylate;

(Meth) acrylates derived from unsaturated alcohols, such as. B.

Oleyl (meth) acrylate, 2-propynyl (meth) acrylate, allyl (meth) acrylate,

Vinyl (meth) acrylate;

Aryl (meth) acrylates, such as benzyl (meth) acrylate or

Phenyl (meth) acrylate, where the aryl radicals can in each case be unsubstituted or substituted up to four times;

Cycloalkyl (meth) acrylates, such as 3-vinylcyclohexyl (meth) acrylate,

Bornyl (meth) acrylate;

Hydroxylalkyl (meth) acrylates such as

3-hydroxypropyl (meth) acrylate,

3,4-dihydroxybutyl (meth) acrylate,

2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate;

Glycol di (meth) acrylates, such as 1,4-butanediol (meth) acrylate,

(Meth) acrylates of ether alcohols, such as

Tetrahydrofurfuryl (meth) acrylate, vinyloxyethoxyethyl (meth) acrylate;

Amides and nitriles of (meth) acrylic acid, such as

N- (3-dimethylaminopropyl) (meth) acrylamide,

N- (diethylphosphono) (meth) acrylamide,

1-Methacryloylamido-2-methyl-2-propanol; sulfur-containing methacrylates, such as Ethylsulfinylethyl (meth) acrylate,

4-Thiocyanatobutyl (meth) acrylate,

Ethylsulfonylethyl (meth) acrylate,

Thiocyanatomethyl (meth) acrylate,

Methylsulfinylmethyl (meth) acrylate,

Bis ((meth) acryloyloxyethyl) sulfide; polyvalent (meth) acrylates, such as

Trimethyloylpropantri (meth) acrylate.

In addition to the (meth) acrylates set out above, the compositions to be polymerized can also have further unsaturated monomers which are copolymerizable with methyl methacrylate and the aforementioned (meth) acrylates.

These include 1-alkenes such as 1-hexene, 1-heptene; branched alkenes such as vinylcyclohexane, 3,3-dimethyl-1-propene, 3-methyl-1-diisobutylene, 4-methylpentene-1;

acrylonitrile; Vinyl esters such as vinyl acetate;

Styrene, substituted styrenes with an alkyl substituent in the side chain, such as. B. α-methylstyrene and α-ethylstyrene, substituted styrenes with an alkyl substituent on the ring, such as vinyltoluene and p-methylstyrene, halogenated styrenes such as monochlorostyrenes, dichlorostyrenes, tribromostyrenes and tetrabromostyrenes;

Heterocyclic vinyl compounds, such as 2-vinylpyridine, 3-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine, 2,3-dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine, 9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole, 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone, 2-vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine, N-vinylcaprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran, vinylthiophene, vinylthiophene, vinylthiolthene hydrogenated vinyl thiazoles, vinyl oxazoles and hydrogenated vinyl oxazoles; Vinyl and isoprenyl ether;

Maleic acid derivatives, such as maleic anhydride, methyl maleic anhydride, maleimide, methyl maleimide; and dienes such as divinylbenzene.

In general, these comonomers are used in an amount of 0 to 60% by weight, preferably 0 to 40% by weight and particularly preferably 0 to 20% by weight, based on the weight of the monomers, the compounds being used individually or can be used as a mixture.

The polymerization is generally started with known radical initiators. The preferred initiators include, among others, the azo initiators well known in the art, such as AIBN and 1, 1-azobiscyclohexane carbonitrile, and also peroxy compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, methyl isobutyl ketone peroxide, and cyclohexyl peroxide , tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, 2,5-bis (2-ethylhexanoyl-peroxy) -2,5-dimethylhexane, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5- trimethylhexanoate, dicumyl peroxide, 1,1-bis (tert-butylperoxy) cyclohexane, 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, cumyl hydroperoxide, tert-butyl hydroperoxide, bis (4-tert.- butylcyclohexyl) peroxydicarbonate, mixtures of two or more of the abovementioned compounds with one another and mixtures of the abovementioned compounds with compounds not mentioned which can likewise form free radicals.

These compounds are often used in an amount of from 0.01 to 10% by weight, preferably from 0.5 to 3% by weight, based on the weight of the monomers.

Various poly (meth) acrylates can be used here, which differ, for example, in molecular weight or in the monomer composition. Furthermore, the matrix of the light-scattering layer can contain further polymers in order to modify the properties. These include polyacrylonitriles, polystyrenes, polyethers, polyesters, polycarbonates and polyvinyl chlorides. These polymers can be used individually or as a mixture, copolymers also being derivable from the aforementioned polymers.

The weight average molecular weight M _{w of} the homopolymers and / or copolymers to be used according to the invention as matrix polymers can vary within wide limits, the molecular weight usually being matched to the intended use and the processing mode of the molding composition. In general, however, it is in the range between 20,000 and 1,000,000 g / mol, preferably 50,000 to 500,000 g / mol and particularly preferably 80,000 to 300,000 g / mol, without any intention that this should impose a restriction.

According to a particular embodiment of the present invention, the matrix of the light-scattering polymethyl methacrylate layer has at least 70, preferably at least 80 and particularly preferably at least 90% by weight, based on the weight of the matrix of the light-scattering layer, of polymethyl methacrylate.

According to a particular aspect of the present invention, the poly (meth) acrylates of the matrix of the light-scattering layer have a refractive index measured at the Na-D line (589 nm) and at 20 ° C. in the range from 1.46 to 1.54.

The molding compositions for producing the light-scattering layer can contain customary additives of all kinds. These include, among others, antistatic agents, antioxidants, mold release agents, flame retardants, lubricants, dyes, flow improvers, fillers, light stabilizers, UV absorbers and organic phosphorus compounds such as phosphites or phosphonates, pigments, weathering protection agents and plasticizers. However, the amount of additives is limited to the application. The light-scattering property of the polymethyl methacrylate layer and its transmission should not be adversely affected by additives. In particular, only small amounts of additives should be added, the optical properties of which depend on the temperature. For example, the lens should only contain a small amount of impact modifier, which are described, for example, in EP-A 0 113 924, EP-A 0 522 351, EP-A 0 465049 and EP-A 0 683 028. The content of impact modifier in the lenses is limited to a maximum of 20% by weight, preferably 10% by weight and particularly preferably 4% by weight. According to a particular aspect of the present invention, diffusing disks of the present invention particularly preferably do not comprise any impact modifiers.

Particularly preferred molding compositions for the production of the plastic matrix are commercially available from Röhm GmbH & Co. KG.

The thickness of the light-scattering polymethyl methacrylate layer is generally in the range from 1 to 100 mm, preferably in the range from 1 to 10 mm and particularly preferably in the range from 2 to 5 mm.

According to a particular aspect of the present invention, the concentration of the spherical scattering particles (A) C _PA , the thickness of the light-scattering polymethyl methacrylate layer d _s and the particle size of the spherical scattering particles (A) D _PA are chosen such that the ratio of the product of concentration the spherical scattering particle (A) c _PA and the thickness of the light-scattering polymethyl methacrylate layer to the third power of the particle size of the spherical scattering particle (A) CpA * ds / Dp _A ³ preferably in the range from 0.0001 to 0.5% by weight * mm / μm ³ , in particular 0.0025 to 0.3% by weight * mm / μm ³ . If plastics particles are o used with a particle size of V ₅ in the range 6 to 30 microns as the scattering media, then there is the relationship of the product of concentration of the spherical scattering particles (A) c _PA and thickness of the light-scattering polymethyl methacrylate layer to the cube of particle size the spherical scattering particle (A) c _PA * ds / D _PA ³ according to a particular aspect of the present invention preferably in the range from 0.0015 to 0.09% by weight * mm / μm ³ , particularly preferably 0.0025 to 0, 06% by weight * mm / μm ³ and very particularly preferably in the range from 0.005 to 0.04% by weight * mm / μm ³ .

If inorganic particles with a particle size V ₅₀ in the range from 0.1 to 5 μm are used as scattering media as scattering media, then the ratio of the product of the concentration of the spherical scattering particles (A) C _PA and the thickness of the light-scattering polymethyl methacrylate layer to third power of particle size of the spherical scattering particle

(A) c _PA * ds / D _PA ³ according to a particular aspect of the present invention, preferably in the range from 0.015 to 0.5% by weight * mm / μm ³ , in particular 0.025 to 0.3% by weight * mm / μm ³ .

The concentration of the spherical particles (B) O _B , the thickness of the light-scattering polymethyl methacrylate layer d _s and the particle size of the spherical particles (B) D _PB can be chosen such that the ratio of the product of the concentration of the spherical scattering particles (B) C _PB and thickness of the light-scattering polymethyl methacrylate layer to the third power of the particle size of the spherical scattering particles

(B) Cp _B * ds / D _PB ³ preferably in the range from 0.000005 to 0.04% by weight * mm / μm ³ , in particular 0.00005 to 0.02% by weight * mm / μm ³ % by weight .-% * mm / μm ³ .

The ratio of the square of the average surface roughness of the polymethyl methacrylate layer Rz to the third power of the particle size of the spherical particles (B) R _Z ² / D _PB ³ can preferably be in the range from 0.0002 μnrϊ ¹ to 0.1300 μm ^"1 , preferably 0.0009 μm ^{" 1} to 0.0900 μm ^"1 , in particular 0.0006 μm ^{" 1} to 0.0800 μm ^"1 and preferably 0.0008 μm ^{" 1} up to 0.0400 μm ^"1 .

According to a particular embodiment of the pane of the present invention, the ratio of the concentration of the spherical scattering particles (A) C _PA to the thickness of the light-scattering polymethyl methacrylate layer ds C _PA ΛJ _{S is} in the range from 0.2% by weight / mm to 20% by weight. % / mm, in particular from 0.5% by weight / mm to 10% by weight / mm.

According to a special aspect of the lens of the present invention, the ratio of the concentration of the spherical particles (B) C _PB to the thickness of the light-scattering polymethyl methacrylate layer d _s cpß / ds is greater than or equal to 2.5% by weight / mm, in particular greater than or equal 4 wt% / mm.

The ratio of the thickness of the light-scattering polymethyl methacrylate layer ds and the particle size of the spherical scattering particles DP _A s / Dp _A is preferably in the range from 5 to 1500, in particular 10 to 1000 and particularly preferably 100 to 600, without any intention that this should impose a restriction.

The light-scattering polymethyl methacrylate layer preferably has a gloss Rδ5 ° of less than or equal to 60, in particular less than or equal to 40 and particularly preferably less than 30.

The lenses of the present invention, in particular the light-scattering polymethyl methacrylate layer, have a particularly low sensitivity to scratching. According to a particular aspect of the present invention are scratches with a force of at most 0.4 N, in particular of at most 0.7 N and particularly preferably of at most 1.0 N are generated on the disk, not visually recognizable, without this being intended to impose a restriction.

This scratch resistance can be determined in accordance with DIN 53799 and DIN EN 438 by a visual assessment of a damaged surface, the damage being caused by a diamond that acts on the surface with different forces.

According to a particular embodiment of the present invention, the average surface roughness R _{z of} the plate is preferably in the range from 5 μm to 50 μm, in particular 5 to 25 μm, preferably 6 to 35 μm and particularly preferably 6 μm to 30 μm.

The average surface roughness Rz can be determined in accordance with DIN 4768 using a Talysurf 50 measuring device from Taylor Hobson, where Rz is the average roughness depth that results from the mean values of the individual roughness depths of five successive individual measuring sections in the roughness profile.

The surface roughness R _{z of} the plate generally results from the choice of the particles (B). In addition, this value can be influenced by varying various parameters, which depend on the type of manufacture.

These include the temperature of the melt during extrusion, with a higher temperature of the melt resulting in a rougher surface. However, it should be noted that the temperature of the melt depends on the exact composition of the molding compound. The temperature of the melt is generally in the range from 150 to 300 ° C., preferably in the range from 200 to 290 ° C. This Temperatures refer to the temperatures of the melt at the nozzle outlet.

Furthermore, the surface roughness can be influenced via the gap between the rollers used to smooth the plates. If a calender comprises, for example, 3 rolls in an L arrangement, the molding compound being guided from the nozzle onto the nip between roll 1 and roll 2 and looping around the roll 2 by 60-180 °, the gap between roll 2 and roll 3 smoothes the surfaces. If the gap between roller 2 and roller 3 is set to plate thickness, the scattering particles on the plate surface are pressed into the matrix, as a result of which the surface is smoother. In general, this gap is set somewhat larger than the plate thickness of the plate to be produced in order to achieve a rougher surface, this value often being in the range from 0.1 to 2 mm above plate thickness, preferably 0.1 to 1.5 mm above plate thickness, without that this should result in a restriction. Furthermore, the surface roughness is influenced by the particle size and the plate thickness, the exemplary embodiments setting out the dependencies.

The light-scattering layer can be produced by known processes, thermoplastic molding processes being preferred. After the addition of the particles, light-scattering layers can be produced from the molding compositions described above by conventional thermoplastic molding processes.

According to a particular embodiment, a twin-screw extruder is used for the extrusion or for the production of molding compound granules containing scattering pearls. Here, the plastic particles are preferably transferred to the melt in the extruder. By this measure, melts can be obtained from which Plates can be provided that have a particularly high transmission.

Here, the spreading disks can be produced in a two-stage process, in which a sidefeeder compounding according to the invention on a twin-screw extruder and intermediate granulation is followed by extrusion of the film or plate on a single-screw extruder. The granules obtained via the twin-screw extruder can contain particularly high proportions of scattering pearls, so that by mixing with molding compositions without scattering pearls, scattering discs with different scattering pearls content can be produced in a simple manner.

Furthermore, a one-step process can also be carried out, in which the spherical plastic particles are compounded into the melt as described on a twin-screw extruder, which may be followed by a pressure-increasing unit (e.g. melt pump), to which the extrusion nozzle is directly connected, with which a flat product is formed. Spreading disks with a particularly low yellow index can surprisingly be obtained by the measures described above.

Furthermore, the spreading disks can also be produced by injection molding, but the process parameters or the mold must be selected such that a surface roughness is achieved in the area according to the invention.

The matrix is preferably compounded with the scattering particles by means of a twin-screw extruder; a single-screw extruder can also be used in the actual plate extrusion, without any intention that this should impose a restriction. The lens of the present invention has a transmission in the range from 30% to 70%, in particular in the range from 40% to 70% and particularly preferably in the range from 40 to 65%.

The lens preferably shows a yellowness index of less than or equal to 12, in particular less than or equal to 10, without this being intended to impose a restriction.

A special embodiment of the lens of the present invention has an intensity half-value angle greater than or equal to 15 °, in particular greater than or equal to 25 °.

The spreading disc of the present invention has a scattering power greater than or equal to 0.3, in particular greater than or equal to 0.45 and particularly preferably greater than or equal to 0.6.

According to a preferred embodiment, the surface of the lenses according to the invention have a matt appearance in reflection. The characterization can be carried out by measuring the gloss with a reflectometer according to DIN 67530. The gloss of the plates is preferably at an angle of 85 ° below 60, particularly preferably below 40 and very particularly preferably below 30.

The size and shape of the lenses of the present invention are not limited. In general, however, the lens has a rectangular, tabular shape, since LCDs usually have such a format.

According to a special embodiment, the lens has a particularly high weather resistance according to DIN EN ISO 4892, part 2 - Artificially proven or irradiated in devices, filtered xenon arc radiation.

The lenses according to the invention are generally very resistant to weathering. The weather resistance according to DIN 53387 (Xenotest) of preferred spreading disks is at least 5000 hours.

The molded body preferably has an elastic modulus according to ISO 527-2 of at least 1500 MPa, in particular at least 2000 MPa, without this being intended to impose a restriction.

In accordance with a particular aspect of the present invention, preferred spreading disks have a continuous use temperature of at least 60 ° C., in particular at least 70 °. The continuous use temperature results in particular from the materials from which the lenses were made. The continuous use temperature characterizes the temperature at which the lenses show no deformation even after several hours.

In this case, these panes preferably have a low thermal expansion, so that by heating them to at least 20 ° C., in particular at least 40 ° C., they experience an elongation of at most 0.55%, in particular at most 0.3%.

The diffusing screens according to the invention can be used for other lighting applications, for example as rear projection screens. The invention is explained in more detail below by means of examples and comparative examples, without the invention being restricted to these examples.

A) Measurement methods

The average roughness R _z was determined in accordance with DIN 4768 using a Talysurf 50 measuring device from Taylor Hobson.

The transmission τo65 _/ 2 ° was determined in accordance with DIN 5036 using a Lambda 19 measuring device from Perkin Elmer.

The yellowness index X _D65 / _IO ^O was determined in accordance with DIN 6167 using a Lambda 19 measuring device from Perkin Elmer.

The gloss R85 ° was measured at 85 ° according to DIN 67530 with a Dr. Long laboratory reflectometer from Dr. For a long time.

The scattering power and the intensity half-value angle were determined in accordance with DIN 5036 using an LMT goniometer measuring station GO-T-1500 from LMT.

B) Production of plastic particles

Plastic particles B1)

An aluminum hydroxide Pickering stabilizer was used to produce spherical plastic particles, which was prepared by precipitation from aluminum sulfate and soda solution immediately before the actual polymerization started. For this purpose, 16 g of Al ₂ (SO ₄ ) ₃ , 0.032 g of complexing agent (Trilon A) and 0.16 g of emulsifier were initially used (Emulsifier K 30 available from Bayer AG; sodium salt of a C ₁₅ paraffin sulfonate) dissolved in 0.81 distilled water. A 1N sodium carbonate solution was then added to the aluminum sulfate dissolved in water with stirring at a temperature of about 40 ° C., the pH then being in the range from 5 to 5.5. This procedure resulted in a colloidal distribution of the stabilizer in the water.

After the stabilizer had precipitated, the aqueous phase was transferred to a beaker. 110 g of methyl methacrylate, 80 g of benzyl methacrylate and 10 g of allyl methacrylate, 4 g of dilauryl peroxide and 0.4 g of tert-butyl per-2-ethylhexanoate were added. This mixture was dispersed for 15 minutes at 7000 rpm using a disperser (Ultra-Turrax S50N-G45MF, from Janke and Kunkel, Stauten).

Following the shear, the reaction mixture was poured into the reactor, which was preheated to the appropriate reaction temperature of 80 ° C., and polymerized at about 80 ° C. (polymerization temperature) for 45 minutes (polymerization time) with stirring (600 rpm). This was followed by a post-reaction phase of 1 hour at an internal temperature of approx. 85 ° C. After cooling to 45 ° C., the stabilizer was converted into water-soluble aluminum sulfate by adding 50% sulfuric acid. To work up the beads, the suspension obtained was filtered through a commercially available filter cloth and dried in a heating cabinet at 50 ° C. for 24 hours.

The size distribution was examined by laser extinction methods. The particles had an average size V50 of 18.6 μm. The beads had a spherical shape, with no fibers being found. Coagulation did not occur. The particles obtained in this way are referred to below as plastic particles B1 Plastic particles B2)

Plastic particles according to DE 3528165 C2 were produced, the particles having essentially the same composition as the plastic particles B1) set out above.

The size distribution was examined by laser extinction methods. The particles had an average size V ₅₀ of 40.5 μm. The beads had a spherical shape, with no fibers being found. Coagulation did not occur. The particles obtained in this way are referred to below as plastic particles B2

C) Examples 1 to 6

Various spreading discs were produced by extrusion. At the beginning, various scattering pearl compounds made of plastic particles B1, plastic particles B2, plastic particles based on styrene with a particle size V ₅₀ of approximately 8.4 μm, which are commercially available from Sekisui under the trade name © Techpolymer SBX-8, and BaSO particles with a particle size median value d50 (Sed.) Of approx. 5 μm, which are available from Sachtleben under the name P63 barium sulfate, VELVOLUX M, and one available from Röhm GmbH & Co. KG PMMA molding compound (copolymer of 97% by weight methyl methacrylate and 3% by weight methyl acrylate) extruded to plastic sheets, the molding compounds containing 0.05% by weight Tinuvin P, a UV stabilizer available from Ciba. An extruder 060 mm from BREYER was used. The temperature of the melt at the nozzle outlet was generally 270 ° C. The smoothing system was generally adjusted so that the surface was as rough as possible. The proportion of particles in the polymethyl methacrylate matrix and the thickness of the plates are shown in Table 1.

Table 1

Table 1 (continued)

The spreading disks obtained were examined in accordance with the measurement methods described above, the measurement results obtained being shown in Table 2.

Table 2

Table 2 (continued)

Claims

claims

1.Spreading disc for LCD applications comprising at least one light-scattering polymethyl methacrylate layer which comprises a polymethyl methacrylate matrix and 0.5% by weight to 59.5% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, spherical scattering particles ( a) ₅ o micron average particle size V is in the range of 0.1 to 40 and have a refractive index difference of the polymethyl methacrylate matrix is in the range of 0.02 to 0.2, and 0.5 wt .-% to 59.5 % By weight, based on the weight of the light-scattering polymethyl methacrylate layer, spherical particles (B) which have an average particle size V5 ₀ in the range from 10 to 150 μm and a refractive index difference to the polymethyl methacrylate matrix in the range from 0 to 0.2 , wherein the total concentration of the spherical scattering particles (A) and particles (B) is in the range from 1 to 60% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, and the spherical scattering type icles (A) spherical particles (B) have a different mean particle size V ₅₀ , the diffusing screen having a transmission in the range from 20% to 70% and a scattering power greater than 0.3, characterized in that the ratio of the square of medium Surface roughness of the polymethyl methacrylate layer R _z to the third power of the particle size of the spherical particles (B) Rz ² / D _PB ^{3 is} in the range from 0.0002 μm ^"1 to 0.1300 μm ^{" 1} .

2. Diffuser according to claim 1, characterized in that the ratio of the square of the average surface roughness of the polymethyl methacrylate layer R _z to the third power of the particle size of the spherical particles (B) Rz / D _PB ³ in the range from 0.0009 μm ^"1 to 0.0900 μm ^"1 yes.

3. Diffuser according to claim 1 or 2, characterized in that the ratio of the concentration of the particles (B) Cp _B to the thickness of the light-scattering polymethyl methacrylate layer d _s c _PB / ds is greater than or equal to 2.5% by weight / mm ,

4. Diffuser according to one of the preceding claims, characterized in that the light-scattering polymethyl methacrylate layer has a gloss R85 ° less than or equal to 40.

5. Diffuser according to one of the preceding claims, characterized in that the ratio c _PA * ds / D _PA ^{3 is} in the range from 0.0025 to 0.3% by weight * mm / μm ² .

6. Diffuser according to one of the preceding claims, characterized in that the ratio c _PB * d _s / D _PB ^{3 is} in the range from 0.00005 to 0.02% by weight * mm / μm ² .

7. Diffusing screen according to one of the preceding claims, characterized in that the light-scattering polymethyl methacrylate layer has a thickness in the range from 1 to 10 mm.

8. Diffuser according to one of the preceding claims, characterized in that the spherical particles (B) comprise cross-linked polystyrene, polysilicon and / or cross-linked poly (meth) acrylates.

9. Diffuser according to one of the preceding claims, characterized in that the scattering particles (A) comprise BaSO ₄ .

10. Diffuser according to one of the preceding claims, characterized in that the matrix of the light-scattering polymethyl methacrylate layer has a refractive index measured at the Na-D line (589 nm) and at 20 ° C in the range from 1.46 to 1.54 ,

11. Diffuser according to one of the preceding claims, characterized in that the average surface roughness R _{z of} the plate is in the range from 6 to 30 μm.

12. Diffuser according to one of the preceding claims, characterized in that the average particle size V5 _{0 of} the spherical particles (B) is at least 5 microns larger than the average particle size of the scattering particles (A).

13. Spreading disc according to one of the preceding claims, characterized in that the spherical scattering particles (A) have an average size V ₅₀ in the range from 2 to 15 μm.

14. Diffuser according to one of the preceding claims, characterized in that the spherical particles (B) have an average particle size V ₅₀ in the range from 15 to 70 microns.

15. Diffuser according to one of the preceding claims, characterized in that the scratches that were generated with a force of at most 0.7 N on the disc are not visually recognizable.

16. Diffuser according to one of the preceding claims, characterized in that the disc has a continuous use temperature of at least 60 ° C.

17. Spreading disc according to one of the preceding claims, characterized in that the disc has an elastic modulus of at least 2000 MPa.

18. Diffuser according to one of the preceding claims, characterized in that the disc has a longitudinal expansion of at most 5% by heating at least 20 ° C.

19. Spreading disc according to one of the preceding claims, characterized in that the disc has a weathering resistance according to DIN 53 387 of at least 5000 hours.

20. Diffuser according to one of the preceding claims, characterized in that the disc has a transmission in the range from 40 to 65%.

21. Diffuser according to one of the preceding claims, characterized in that the disc has a yellow value less than or equal to 12.

22. Diffuser according to one of the preceding claims, characterized in that the disc has an intensity half-value angle greater than or equal to 15 °.

23. Spreading disc according to one of the preceding claims, characterized in that the disc has a scattering capacity greater than or equal to 0.45.

24. A process for producing a diffuser according to one of claims 1 to 23, characterized in that a molding compound comprising polymethyl methacrylate, spherical scattering particles (A) and spherical particles (B) is extruded.

25. Use of a diffusing screen according to one of claims 1 to 23 in lighting applications.

26. Use according to claim 25 as a rear projection screen.