EP1652001A1 - Scratch-resistant rear projection screen and method for producing the same - Google Patents

Abstract

The invention relates to a rear-projection screen comprising at least one light-diffusing polymethylmethacrylate layer, including a polymethylmethacrylate matrix and spherical diffusion particles (A) and spherical particles (B) having different average particle sizes V50. The spherical diffusion particles (A) have an average particle size V50 ranging between 0.1 and 40 µm and a difference in refractive index relative to the polymethylmethacrylate matrix ranging between 0.02 to 0.2. The spherical particles (B) have an average particle size V50 ranging between 10 and 150 µm and a difference in refractive index relative to the polymethylmethacrylate matrix ranging between 0 and 0.2. The overall concentration of the spherical diffusion particles (A) and particles (B) ranges between 1 and 60 % by weight relative to the weight of the light-diffusing polymethylmethacrylate layer. The concentration of the spherical diffusion particles (A) cPA, the thickness of the light-diffusing polymethylmethacrylate layer dS and the particle size of the spherical diffusion particles (A) DPA are selected such that the ratio cPA<*>dS/DPA<3> ranges between 0.001 and 0.015 % by weight<*>mm/µm<3>, the concentration of the spherical particles (B) cPB, the thickness of the light-diffusing polymethylmethacrylate layer dS and the particle size of the spherical particles (B) DPB are selected such that the ratio cPB<*>dS/DPB<3> ranges between 0.000005 and 0.002 % by weight<*>mm/µm<3> and the ratio of the second power of the average surface roughness of the polymethylmethacrylate layer RZ to the third power of the particle size of the spherical particles (B) RZ<2>/DPB<3> ranges between 0.0002 µm-<1> and 0.1300 µm<-1>.

Description

Scratch-resistant rear projection screen and method for its production

The present invention relates to scratch-resistant rear projection screens comprising at least one light-scattering polymethyl methacrylate layer, process for producing these rear projection screens and use.

Back projection technology can be used to make information accessible to a wide audience. In principle, the construction of such a system consists of an imaging surface that is illuminated from the back with a projector and thus provides the information.

This technique takes place e.g. Use in control rooms (power plants, rail traffic) to make it easier for those responsible to keep track of the complex processes so that control errors can be avoided. Another application is scoreboards in e.g. Sports stadiums and motor racing races. Here, the course and status of the event is communicated to the viewers, even if they are at a greater distance from the actual events.

These were very large image areas. Due to the constant further development in the technical sector (projector technology), further fields of application have been added over the years.

This type of information transfer is also used in, for example, TV sets, open-plan and home cinemas, but also as an advertising medium at trade fairs, in shop windows and shops. Furthermore, this technology is also used to transmit information in presentations and in flight simulators, where the virtual environment is mapped as realistically as possible on the cockpit panes.

Many advantages of this technology are achieved when the projector is outside the viewing area. A viewer in front of the projection surface does not cover the projection, disturbing noises of the projector are avoided and an appealing interior design is possible.

There are now a large number of plastic plates and foils that are used in rear projection technology. Plates are often modified in such a way that they have defined surface structures in the form of Fresnel lens systems on the back and additionally vertically arranged lenticular lenses on the observer side. The production of these rear projection panels is therefore associated with a high outlay. The surface structures can also be very sensitive to mechanical stress. As a result of damage, the appearance of the projection is very badly affected.

Furthermore, rear projection panels and foils are known which have scattering media, such panels containing particles with a refractive index different from the matrix. The panels and foils are also suitable for rear projection, but do not combine the entire range of the requirement profile, so that only a part of the requirements for a screen are met.

Due to the large number of different possible uses, a wide variety of requirements are placed on the projection surface. In one application, the projection surfaces must, for example, have a very quiet, clear and high-resolution image reproduction because the viewer has to record the information over a longer period of time (example: control room, home cinema, etc.).

If these projection surfaces are used for presentation and advertising on exhibition stands, for example, then the surfaces must be particularly insensitive to mechanical stress and dirt, while the requirements for the projection quality are not so high.

For example, known scattering media such as barium sulfate and titanium dioxide can be used to produce plates and foils which have a high light scattering angle. The resolution of the projection is also high. Accordingly, the viewing angle of the image should also be correspondingly high. However, it turns out that even the image sharpness of the projection plates are suboptimal, with the other requirements, for example scratch sensitivity, not meeting many requirements.

Umbrellas are also known which contain plastic particles as scattering media. Document JP11179856 describes multilayer boards with at least one layer which comprises a polymethyl methacrylate matrix and crosslinked polymethyl methacrylate beads as scattering / matting agents, the proportion of the beads being in the range from 0.5 to 25% by weight. The beads have a size in the range from 3 to 30 μm, with only 2 mm thick plates being described in the examples, which contain about 3% by weight of scattering beads with a size of about 6 μm. The problem with these screens is their scratch sensitivity.

Japanese laid-open specification JP 07234304 describes a mixture of crosslinked acrylate / styrene beads (14 μm) in a transparent plastic. A disadvantage of these umbrellas is that scratches are very noticeable visually. In addition, disks are known which comprise mixtures of particles. JP 4-134440 describes plates in which two types of particles are used, the particle size and refractive index difference of the matrix having to be coordinated with one another, as a result of which the wavelength-selective scattered light (small particles scatter blue light more strongly, large particles red light) on the particles is canceled out. The scatter plates are characterized by a neutral color.

Furthermore, panes are known which can be used for lighting applications. Such discs are set out, for example, JP 8-198976, JP 5-51480 and JP 2000-296580.

A disadvantage of the previously described plates is, on the one hand, their suboptimal image quality and a high scratch sensitivity of the screen.

The document EP-A-0 561 551 describes a multilayer plate with a scattering layer made of a mixture of a transparent polymer and spherical particles (2-15 μm). These umbrellas are also very sensitive to scratching.

A problem with known rear projection screens provided with scattering media is therefore that their imaging properties are not optimal with regard to their scratch sensitivity. In particular, the known screens have a relatively low image sharpness or a relatively unfavorable brightness distribution. In addition, there are sometimes problems with color fastness. Furthermore, many umbrellas do not meet the mechanical requirements, scratches in particular having an optically disadvantageous effect. In view of the prior art specified and discussed herein, it was therefore an object of the present invention to provide rear projection screens which enable a particularly high image quality with low scratch sensitivity. In particular, the screens should allow high definition and resolution of the projected image.

In addition, the images on the rear projection screens should be particularly true to color.

Another object of the present invention was to provide rear projection screens which have a particularly uniform brightness distribution.

In addition, the rear projection screens should have the highest possible mechanical stability. Scratches on the screen should not be visible or only slightly. In particular, damage should have little or no influence on the imaging ability of the screen.

Furthermore, the invention was based on the object of providing rear projection screens which can be produced particularly easily. For example, the rear projection screens should be able to be produced in particular by extrusion.

In addition, it was therefore an object of the present invention to provide rear projection screens which have a high level of image smoothness. As a result, displays can be viewed without fatigue over a long period of time. Another object of the present invention was to provide rear projection screens which can be easily adapted in size and shape to the requirements.

In addition, the images on the rear projection screens should be particularly rich in contrast.

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

The present invention was also based on the object of providing rear projection screens which, based on their imaging properties, only reflect to a small extent.

In addition, the size of the screens should be able to be adapted to the respective requirements. In particular, the thickness of the rear projection screens should be able to be adapted to any requirements without the image quality and the scratch sensitivity being adversely affected thereby.

These tasks 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 necessarily result from these, are solved by the rear projection screens described in claim 1. Expedient modifications of the rear projection screens according to the invention are protected in the subclaims which refer back to claim 1.

With regard to the methods for producing rear projection screens, claim 24 provides a solution to the underlying problem. Because the concentration of the spherical scattering particles (A) c _PA , the thickness of the light-scattering polymethyl methacrylate layer ds and the particle size of the spherical scattering particles (A) DA SO are selected, the ratio c _PA * ds / Dp _A ^{3 is} in the range of 0.001 to 0.015% by weight ^* mm / μm ³ , the concentration of the spherical particles (B) c _PB , the thickness of the light-scattering polymethyl methacrylate layer ds and the particle size of the spherical particles (B) DPB is chosen so that the ratio cp _B * ds Dp _B ³ in the range from 0.000005 to 0.002% by weight * mm / μm ³ and 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 is} in the range from 0.0002 μm ^"1 to 0.1300 μm ^{" 1} , the rear projection screen comprising at least one light-scattering polymethyl methacrylate layer which comprises a polymethyl methacrylate matrix and spherical scattering Particles (A) and spherical particles (B) with different mean particle size V ₅₀ , the spherical scattering particles (A) having a mean 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, the spherical particles (B) having a mean particle size V ₅₀ 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, the total concentration of the spherical scattering particles (A ) and particles (B) in the range from 1 to 60% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, it is possible to provide rear projection screens which have both a particularly high image quality and a very low optical scratch sensitivity enable.

The following advantages in particular are achieved by the measures according to the invention: > The rear projection screens of the present invention can be adapted to individual needs without the image quality and / or the scratch sensitivity being impaired thereby.

D The rear projection screens of the present invention allow high definition and resolution of the projected image.

D The images on the rear projection screens according to the invention are particularly true to color and rich in contrast.

□ The rear projection screens made available according to the present invention have a particularly uniform brightness distribution.

D Furthermore, the rear projection screens of the present invention show high mechanical stability. Scratches are not or only slightly visible on the screen.

D Furthermore, images projected onto the rear projection screens according to the invention are very quiet. As a result, displays can be viewed without fatigue over a long period of time.

> In addition, the rear projection screens of the present invention show a non-glossy, matt surface profile. The shape of the surface structure can be adjusted differently without affecting the optical parameters, apart from the gloss. This can reduce reflections that adversely affect the image on the screen. D Furthermore, the rear projection screens of the present invention can be manufactured particularly easily. The rear projection screens can be produced in particular by extrusion.

D The rear projection panels according to the invention show a high resistance to weathering, in particular to UV radiation.

D The size and shape of the rear projection screens can be adapted to the needs.

The light-scattering polymethyl methacrylate layer of the rear projection screen 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. The term spherical in the context of the present invention 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 differ 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 1 to 35 μm, preferably 2 to 30 μm, preferably 3 to 25 μm, in particular 4 to 20 μm and particularly preferably 5 to 15 μm.

Such particles are known per se and can be obtained commercially. These include, in particular, plastic particles and particles made of inorganic materials, such as aluminum hydroxide, aluminum-potassium silicate (mica), aluminum silicate (kaolin), barium sulfate (BaSO ₄ ), calcium carbonate, magnesium silicate (talc). Of these, plastic particles are particularly preferred.

The plastic particles that can be used according to the invention are not particularly limited. The type of plastic from which the plastic particles are produced is largely uncritical, with the light refraction taking place at the phase boundary of the plastic beads with the matrix plastic.

Accordingly, the refractive index of the plastic particles 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, α-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 with 1 to 12 carbon atoms in the aliphatic ester radical, which can be copolymerized with the monomers b1), examples of which are: methyl (meth) acrylate, ethyl ( meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, partly. Butyl (meth) acrylate, cyclohexyl (meth) acrylate, 3,3,5-trimethylcyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, norbomyl (meth) acrylate or isobomyl (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 at least 250 ° C., without this being intended to impose a restriction. Here, the term temperature-resistant means that the particles are essentially not subject to thermal degradation. Thermal degradation leads to undesirable discoloration, so that the plastic material is unusable.

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

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

The used according to invention particles (B) have an average particle size V ₅ o in the range of 10 to 150 microns, preferably 15 to 70 microns, and more preferably 30 to 50 .mu.m, wherein the refractive index of the particles have a sodium D line (589 nm) and the refractive index n ₀ measured at 20 ° C, which differs by 0 to 0.2 units from the refractive index no of the matrix carbon.

The particles (B) can also be obtained commercially. These particles can be produced from the same materials as the scattering particles (A), plastic particles also preferably being used.

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 weight ratio of the scattering particles (A) to the particles (B) is preferably in the range from 1:10 to 10: 1, in particular 1: 5 to 5: 1, particularly preferably 1: 3 to 3: 1 and very particularly preferably 1: 2 to 2: 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 LOT GmbH can be used for this, the measurement method for determining the particle size and the particle size distribution being contained in the user manual. 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 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, 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) acrylic! At, A! Lyl (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,

Bomyl (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,

Ethylsuifonylethyl (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 a

Alkyl substituents 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-vinylbutyrol Vinyl oxolane, vinyl furan, vinyl thiophene, vinyl thiolane, vinyl thiazoles and 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 the azo initiators well known in the art, such as AIBN and 1, 1-azobiscyclohexane carbonitrile, and peroxy compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, methyl isobutyl ketone peroxide, and peroxide compounds , tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, 2,5-bis (2 ~ ethylhexanoyl-peroxy) -2,5-dimethylhexane, tert-butyl peroxy-2-ethylhexanoate, part-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 ranges, 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 other things, 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 transparency should not be adversely affected by additives.

According to a particular aspect of the present invention, the molding composition can optionally be given a mechanically more stable finish by means of an impact modifier. The impact modifier for polymethacrylate plastics is well known, so the manufacture and construction of impact modified polymethacrylate molding compositions are described, inter alia, in EP-A 0 113 924, EP-A 0 522 351, EP-A 0 465 049 and EP-A 0 683 028.

Preferred impact-resistant molding compositions which can be used to produce the matrix have 50-99% by weight, in particular 70-98% by weight, of polymethyl methacrylates, based on the weight of the molding composition without scattering particles (A) and particles (B). These polymethyl methacrylates have been previously described. According to a particular aspect of the present invention, the polymethyl methacrylates used to produce impact-modified molding compositions are obtained by radical polymerization of mixtures which contain 80 to 100% by weight, preferably 90 to 98% by weight, methyl methacrylate and optionally 0 to 20% by weight. %, preferably 2-10% by weight of further free-radically polymerizable comonomers, which were also listed above. Particularly preferred comonomers include C 1 -C 4 -alkyl (meth) acrylates, in particular methyl acrylate, ethyl acrylate or butyl methacrylate.

The average molecular weight M _{w of} the polymethyl methacrylates which can be used to produce the impact-modified matrix is preferably in the range from 90,000 g / mol to 200,000 g / mol, in particular 100,000 g / mol to 150,000 g / mol.

Preferred impact-resistant molding compositions which can be used to prepare the matrix contain 0.5 to 55, preferably 1 to 45, particularly preferably 2 to 40, in particular 3 to 35% by weight of an impact modifier, based on the weight of the molding composition without scattering particles ( A) and particles (B), which is an elastomer phase made of crosslinked polymer particles.

The impact modifier can be obtained in a manner known per se by bead polymerization or by emulsion polymerization.

Preferred impact modifiers are crosslinked particles with an average particle size in the range from 50 to 1000 nm, preferably 60 to 500 nm and particularly preferably 80 to 120 nm. Such particles can be obtained, for example, by the radical polymerization of mixtures which generally have at least 40% by weight, preferably 50 to 70% by weight, of methyl methacrylate,

20 to 80 wt .-%, preferably 25 to 35 wt .-% butyl acrylate and

0.1 to 2, preferably 0.5 to 1 wt .-% of a crosslinking monomer, e.g. B. a multifunctional (meth) acrylate, such as. B. allyl methacrylate and

Comonomers that can be copolymerized with the aforementioned vinyl compounds.

The preferred comonomers include, among others, -C-alkyl (meth) acrylates, such as ethyl acrylate or butyl methacrylate, preferably methyl acrylate, or other vinyl-polymerizable monomers such as, for. B. styrene. The mixtures for producing the abovementioned particles can preferably comprise 0 to 10, preferably 0.5 to 5% by weight of comonomers.

Particularly preferred impact modifiers are polymer particles which have a two, particularly preferably a three-layer core-shell structure. Such core-shell polymers are described, inter alia, in EP-A 0 113 924, EP-A 0 522 351, EP-A 0 465 049 and EP-A 0 683 028.

Particularly preferred impact modifiers based on acrylate rubber have the following structure, among others:

Core: polymer with a methyl methacrylate content of at least 90% by weight, based on the weight of the core.

Shell 1: polymer with a butyl acrylate content of at least 80% by weight, based on the weight of the first shell. Shell 2: polymer with a methyl methacrylate content of at least 90% by weight, based on the weight of the second shell.

The core and the shells can each contain other monomers in addition to the monomers mentioned. These were set out above, with particularly preferred comonomers having a crosslinking effect.

For example, a preferred acrylate rubber modifier can have the following structure:

Core: copolymer of methyl methacrylate (95.7% by weight), ethyl acrylate (4% by weight) and allyl methacrylate (0.3% by weight) S1: copolymer of butyl acrylate (81.2% by weight), styrene (17.5% by weight) and allyl methacrylate (1.3% by weight) S2: copolymer of methyl methacrylate (96% by weight) and ethyl acrylate (4% by weight)

The ratio of core to shell (s) of the acrylate rubber modifiers can vary within wide ranges. The weight ratio core to shell K / S is preferably in the range from 20:80 to 80:20, preferably from 30:70 to 70:30 to modifiers with one shell or the ratio of core to shell 1 to shell 2 K / S1 / S2 in the range from 10:80:10 to 40:20:40, particularly preferably from 20:60:20 to 30:40:30 for modifiers with two shells.

The particle size of the core-shell modifiers is usually in the range from 50 to 1000 nm, preferably 100 to 500 nm and particularly preferably from 150 to 450 nm, without any intention that this should impose a restriction. Such impact modifiers are commercially available from Mitsubishi under the trade name METABLEN® IR 441. In addition, impact-modified molding compounds can also be obtained.

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 0.05 to 5 mm, preferably in the range from 0.05 to 2 mm and particularly preferably in the range from 0.1 to 1 mm.

According to the invention, the concentration of the spherical scattering particles (A) CPA, the thickness of the light-scattering polymethyl methacrylate layer ds and the particle size of the spherical scattering particles (A) DPA SO are chosen such that the ratio of the product of the concentration of the spherical scattering particles (A) Cp _A and Thickness of the light-scattering polymethyl methacrylate layer to the third power of the particle size of the spherical scattering particles (A) cpA ^* ds / D _PA ³ in the range from 0.001 to 0.015% by weight * mm / μm ³ , preferably 0.0025 to 0.009% by weight * mm / μm ³ .

The concentration of the spherical particles (B) CPB, the thickness of the light-scattering polymethyl methacrylate layer ds and the particle size of the spherical particles (B) DPB is chosen so that the ratio of the product of the concentration of the spherical scattering particles (B) CPB and the thickness of the light-scattering polymethyl methacrylate layer for the third power of the particle size of the spherical scattering particles (B) cps * s / DpB ³ in the range from 0.000005 to 0.002% by weight * mm / μm ³ , preferably 0.00004 to 0.0015% 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 μm ^"1 to 0.1300 μm ^{" 1} , in particular 0.0009 μm ^"1 to 0.0900 μm ^{" 1} and preferably 0.00025 μm ^"1 to 0.0600 μm ^{" 1} and particularly preferably 0.0025 μm ^"1 to 0.0600 μm ^{" 1} .

According to a particular embodiment of the screen of the present invention, the ratio of the concentration of the spherical scattering particles (A) CPA to the thickness of the light-scattering polymethyl methacrylate layer ds cp _A / ds is greater than or equal to 2.5% by weight / mm, in particular greater than or equal to 4 wt .-% / mm.

According to a particular aspect of the screen of the present invention, the ratio of the concentration of the spherical particles (B) CPB to the thickness of the light-scattering polymethyl methacrylate layer ds Cp _B / ds is greater than or equal to 2.5% by weight / mm, in particular greater than or equal to 4 wt .-% / mm.

The ratio of the thickness of the light-scattering polymethyl methacrylate layer ds to the particle size of the spherical scattering particles D _PA ds / D _PA is preferably in the range from 1 to 500, in particular 1 to 250, preferably 2.5 to 250 and particularly preferably 2.5 to 150, without any limitation.

The light-scattering polymethyl methacrylate layer preferably has a gloss R ₈₅ ° of less than or equal to 60, in particular less than or equal to 40 and particularly preferably less than 30.

The rear projection screens of the present invention, in particular the light-scattering polymethyl methacrylate layer, show a particularly low sensitivity to scratching. According to a particular aspect of the present According to the invention, scratches which are generated on the screen 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 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 which acts on the surface with different forces.

According to a particular embodiment of the present invention, the average surface roughness Rz 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, in particular 15 μm to 50 μm, particularly preferably 6 μm to 30 μm ,

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

The surface roughness Rz 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. These 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, which makes the surface appear 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 can be obtained from which screens can be provided, which have a particularly high transmission.

Here, the rear projection screens can be produced using a two-stage process, in which a sidefeeder compounding according to the invention is connected to 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 projection screens with different scattering pearls content can be produced in a simple manner by mixing with molding compositions without scattering pearls.

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. Surprisingly, rear projection screens with a particularly low yellow index can be obtained by the measures described above.

Furthermore, the screens 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. Depending on the type of use, the light-scattering polymethyl methacrylate layer can be used as a screen. The thinner layers can be used as a rollable film. Particularly preferred films are made impact resistant by the methods set out above.

Furthermore, a thin light-scattering polymethyl methacrylate layer can be applied to a plastic plate in order to increase its mechanical stability. This plastic plate, which serves as a carrier layer, preferably has an intensity half-value angle of less than 6.5 °, in particular less than or equal to 6 °, preferably less than or equal to 5 ° and particularly preferably less than or equal to 3 °. Accordingly, the carrier layer comprises no or only a small amount of spherical particles which have a scattering effect. This plastic sheet preferably has poly (meth) acrylates.

The surface of the carrier layer preferably has a gloss of less than or equal to 70, preferably less than or equal to 60, in particular less than or equal to 40, particularly preferably less than or equal to 30 and very particularly preferably less than or equal to 15 at an angle of 60 °.

According to a preferred embodiment, the carrier layer has an average surface roughness Rz in the range from preferably 2 μm to 45 μm, in particular 3 to 40 μm, preferably 5 to 35 μm. In this way, reflections of the image projected on the screen into the room can be avoided without the image quality being impaired.

According to a particular aspect of the present invention, the screen has a transmission greater than or equal to 25%, in particular greater than or equal to 40% and particularly preferably greater than or equal to 55%, these values can be achieved in particular from screens without contrast-enhancing dyes.

According to a particular aspect of the present invention, the molding composition can be colored. This measure can surprisingly improve the contrast. Dyes and / or soot known per se are particularly suitable for coloring. Particularly preferred dyes are commercially available. These include, among others, © Sandoplast Rot G and © Sandoplast Gelb 2G each from Clariant and © Macrolex Grün 5B and © Macrolex Violett 3R each from Bayer. The concentration of these dyes depends on the desired color impression and the thickness of the plate. Without being restricted thereby, this concentration per dye is generally in the range from 0 to 0.8% by weight, preferably 0.000001 to 0.4% by weight, based on the total weight of the colored molding composition without scattering particles (A) and particles (B). The sum of the dye concentrations is preferably in the range from 0 to 1% by weight, preferably 0.0001 to 0.6% by weight, based on the total weight of the colored molding composition without scattering particles (A) and particles (B). The loss of transmission can at least partially be compensated for by stronger projectors.

The screen 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 screen of the present invention has an intensity half-value angle greater than or equal to 15 °, in particular greater than or equal to 25 °. According to a particular aspect of the present invention, the screen has a scattering power greater than or equal to 0.15, in particular greater than or equal to 0.35, without this being intended to impose a restriction.

According to a preferred embodiment, the surface of the polymethyl methacrylate plates according to the invention have a matt appearance when reflected on the lens. 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 rear projection screen of the present invention is not limited. In general, however, the screen has a rectangular, tabular shape, since images are usually displayed in this format.

Such a rear projection screen preferably has a length in the range from 25 mm to 10000 mm, preferably from 50 to 3000 mm and particularly preferably from 200 to 2000 mm. The width of this particular embodiment is generally in the range from 25 to 10000 mm, preferably from 50 to 3000 mm and particularly preferably from 200 to 2000 mm. In order to provide a particularly large projection area, several of these screens can be combined.

According to a special embodiment, the screen has a particularly high weather resistance in accordance with DIN EN ISO 4892, Part 2 -Artificial weathering or irradiation in devices, filtered xenon arc radiation. The rear projection screens according to the invention can be used for other lighting applications, for example as diffusing screens in LCD monitors.

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 Rz was determined in accordance with DIN 4768 using a Talysurf 50 measuring device from Taylor Hobson.

The transmission XD ₆ 5/2 ° was determined in accordance with DIN 5036 with a Lambda 19 measuring device from Perkin Elmer.

The yellowness index τ _D65 / -ιo ° was determined in accordance with DIN 6167 with 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.

The various rear projection screens were also assessed visually according to the criteria set out in Table 1. A projector of the brand Epson EMP-713 was used for this. At a distance of approximately 1-1.5 m from the image, the test image was assessed at several angles (0 ° = perpendicular to the projection normal, 30 ° and 60 °). The distance between the projector and the projection screen was approx. 85 cm with an image diagonal of approx. 50 cm.

Technical data Epson projector EMP 713:

Projection system: dichroic mirror and lens system, picture elements: 2359296 pixels (1024x768) * 3, brightness: 1200 ANSI lumens, contrast: 400: 1, image illumination: 85%, color rendering: 24 bit with 16.7 million colors, H: 15-92 kHz, V: 50-85 Hz, lamp: 150 watt UHE, video resolution: 750 TV lines

Table 1

In the tables, very good properties were marked with ++, good properties with +, satisfactory properties with 0, poor properties with -, very poor properties with - and insufficient properties with -.

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) ₃ , 0.032 g of complexing agent (Trilon A) and 0.16 g of emulsifier (emulsifier K 30 available from Bayer AG; sodium salt of a C ₅ -paraffin sulfonate) in 0.81 distilled water were first solved. A 1 N 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 was precipitated, the aqueous phase was placed in a beaker transferred. 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, Staufen).

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 V ₅₀ 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

An aluminum hydroxide Pickering stabilizer was used to produce spherical plastic particles, which was prepared by precipitation from aluminum sulfate and sodium carbonate solution (1N sodium carbonate solution) immediately before the actual polymerization started. For this purpose, 38 ions were initially used. Water, 400 g of aluminum sulfate and 8 g of complexing agent (Trilon A) with stirring (330 rpm) using an impeller stirrer in a mixture with N ₂ rinsed 100 L V4A boiler with breakwater, Ni-Cr-Ni thermocouple and circulation heating. This is followed by the addition of 1760 g of sodium carbonate solution for the precipitation of the aluminum hydroxide, as well as the addition of auxiliary distributors emulsifier K30 (4 g) available from Bayer AG (sodium salt of a C15 paraffin sulfonate) and polywax 5000/6000 (4 g) available from from Höchst (polyethylene glycol with a molecular weight in the range of 5000-6000), each dissolved in 240 ml of deion. Water. After the precipitation, the pH was about 5.3, which resulted in a colloidal distribution of the stabilizer in the water.

A monomer mixture consisting of 6900 g of methyl methacrylate, 3000 g of styrene, 100 g of glycol dimethacrylate, 200 g of dilauroyl peroxide, 20 g of tert-butyl per-2-ethylhexanoate and 50 g of 2-ethylhexylthioglycolate is then also added at room temperature.

The heating phase takes place up to a temperature of 80 ° C., the reactor being sealed pressure-tight at an internal boiler temperature of 40 ° C. and the N _{2 introduction being} shut off. Over the next 115 minutes the internal temperature rises to approx. 87 ° C and the pressure increases from 0.70 to 0.92 bar. After the maximum temperature, the reaction mixture was heated to about 87-88 ° C. and stirred at this temperature for about an hour, the stirring speed being reduced to 200 rpm. After the reaction mixture had been cooled, the kettle was let down at a temperature of 46 ° C. and then 400 ml of 50% strength sulfuric acid were added, as a result of which the aluminum hydroxide is converted into the soluble aluminum sulfate and the suspension polymer thereby precipitates out. To work up the beads, the suspension obtained was filtered through a stoneware filter with a filter cloth, washed neutral and dried at 50 ° C. in an oven for about 20 hours. 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 4

Various rear projection screens were manufactured by extrusion. For this purpose, 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 extruded a PMMA molding compound (copolymer of 97 wt .-% methyl methacrylate and 3 wt .-% methyl acrylate) from Röhm GmbH & Co. KG to plastic sheets. An extruder 060 mm from BREYER was used. The temperature of the melt at the nozzle outlet was generally 270 ° C. In general, especially in the examples, the smoothing mechanism was adjusted in such a way that the surface was as rough as possible.

The proportion of plastic particles in the polymethyl methacrylate matrix and the thickness of the plates are shown in Table 2. Table 2

The rear projection screens obtained were examined in accordance with the measurement methods described above, the measurement results obtained being shown in Table 3.

Table 3

Furthermore, the visual scratch sensitivity of the extrudates was examined.

The scratch sensitivity was checked by the penetration depth of a diamond t * = f (load) with the scratch test device Model 203 from Taber Industries, based on DIN 53799 and DIN EN 438: diamond stylus with cone angle 90 °, tip radius 90 μm, counter-clockwise rotation. The loads used are set out in Table 4.

The visual assessment was carried out on a black background (reflection test). The tests (roughness, gloss) on the test extrudates were carried out on the top.

The results obtained are shown in Table 4. Table 4

D) Examples 5 and 6

The manufacturing process previously described in Examples 1 to 4 was essentially repeated, but with additional impact modifiers (© Metablen IR 441, available from Mitsubishi) added. In addition, a colored rear projection screen was manufactured, which was also equipped with an impact-resistant finish. The dye consisted of a mixture of 52.66% by weight © Sandoplast Rot G, 0.84% by weight © Sandoplast Gelb 2G (each available from Clariant) and 39.22% by weight © Macrolex Grün 5B and 7 , 28% by weight © Macrolex Violett 3R (each available from Bayer). The proportion of plastic particles in the polymethyl methacrylate matrix and the thickness of the plates are shown in Table 5.

Table 5

The rear projection screens obtained were examined in accordance with the measurement methods described above, the measurement results obtained being shown in Table 6. The mechanical properties of the rear projection screens were also examined. The tensile strength, the elongation at break and the modulus of elasticity were determined in accordance with ISO 527-2 and the reflection in accordance with DIN 5036.

Table 6

Rear projection screens for 3D projection.

The rear projection screen according to the invention can also be used for the 3D projection of images or films.

In the 3D projection method, two projections are superimposed as image sources, which in principle transmit the same image content, but which is at a certain distance, e.g. B. were added at eye relief. A commonly used principle is e.g. B. the polarization process. By means of projectors that work with polarized light, the light from both images is emitted onto the rear projection screen with different polarization orientations.

The viewer views the image through glasses which are each equipped with appropriate polarization filters for the right and left eyes. The human brain processes the two different image impressions into a three-dimensional image perception.

For the purposes of 3D projection, the rear projection screens according to the invention can preferably be made from extruded polymethyl methacrylate plastic in the form of a plate or film comprising at least one light-scattering layer from extruded polymethyl methacrylate plastic, the path difference due to the optical birefringence overall being at most 25 nm, preferably at most 15, particularly preferably at most 5 nm.

It should be noted here that the extrusion process always causes a certain orientation of the molecular chains in the extrusion direction. This alignment leads to birefringence properties which partially depolarize the polarized light of the two projections, which is of course undesirable. The extruded polymethyl methacrylate plastic for rear projection screens which are intended for 3D projection is therefore particularly preferably subjected to a thermal aftertreatment after the extrusion. During thermal aftertreatment, shrinkage occurs, which largely negates the alignment of the polymer molecules. The result is that the birefringence property originally present in the material is greatly reduced.

The thermal aftertreatment of extruded polymethyl methacrylate plastic in the form of foils or plates which are provided for rear projection screens for 3D projection can, for. B. in the range of 110 to 190, preferably 120 to 160 ° C for 5 minutes to 24 hours, preferably 10 minutes to 2 hours, depending on the material composition and material thickness. One skilled in the art can easily optimize this. The thermally induced shrinking process can be carried out with material lying or preferably hanging.

Suitable measuring methods for measuring the path difference due to the optical birefringence are known to the person skilled in the art. The path difference can e.g. B. be measured using a polarization microscope in combination with an Ehringhaus tilt compensator.

Claims

claims

1. A rear projection screen comprising at least one light-scattering polymethyl methacrylate layer comprising a polymethyl methacrylate matrix and spherical scattering particles (A) and spherical particles (B) with different average particle size V ₅ o, wherein the spherical scattering particles (A) have an average particle size V ₅₀ in 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, the spherical particles (B) having a mean particle size V ₅₀ in the range from 10 to 150 μm and a refractive index difference Having a polymethyl methacrylate matrix in the range from 0 to 0.2, the total concentration of the spherical scattering particles (A) and particles (B) being in the range from 1 to 60% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, characterized in that the concentration of the spherical scattering particles (A) CPA, the thickness of the light scattering Polymethyl methacrylate layer ds and the particle size of the spherical scattering particles (A) D _PA is chosen so that the ratio CpA * ds / D _A ³ in the range from 0.001 to 0.015% by weight * mm / μm ³ , the concentration of the spherical particles (B) CPB, the thickness of the light-scattering polymethyl methacrylate layer ds and the particle size of the spherical particles (B) DB SO is chosen such that the ratio Cp _B * ds / Dp _B ^{3 is} in the range from 0.000005 to 0.002% by weight * mm / μm ³ and 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) R _Z ² / D _PB ³ in the range from 0.0002 μm ^"1 to 0.1300 μm ^"1 lies.

2. Rear projection screen 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) R _Z ² / D _PB ³ in the range of 0.0025 μm ^{" 1} to 0.0600 μm ^"1 yes.

3. Rear projection screen 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 ds cpe / d _{s is} greater than or equal to 2.5% by weight / mm.

4. Rear projection screen 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. Rear projection screen according to one of the preceding claims, characterized in that the ratio cp _A ^* ds / Dp _A ^{3 is} in the range from 0.0025 to 0.009% by weight * mm / μm ² .

6. Rear projection screen according to one of the preceding claims, characterized in that the ratio Cp _B ^* ds / Dp _B ^{3 is} in the range from 0.00004 to 0.0015% by weight * mm / μm ³ .

7. Rear projection screen according to one of the preceding claims, characterized in that the light-scattering polymethyl methacrylate layer of the rear projection screen has a thickness in the range from 0.05 to 1 mm.

8. Rear projection screen according to one of the preceding claims, characterized in that the spherical scattering particles (A) and / or spherical particles (B) comprise crosslinked polystyrene, polysilicon and / or crosslinked poly (meth) acrylates.

9. rear projection screen according to one of the preceding claims, characterized in that the light-scattering polymethyl methacrylate layer is colored.

10. Rear projection screen 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. rear projection screen according to one of the preceding claims, characterized in that the average surface roughness R _{z of} the plate is in the range of 4 to 50 microns.

12. rear projection screen according to one of the preceding claims, characterized in that the average particle size V _{50 of} the spherical particles (B) is at least 5 microns larger than the average particle size of the scattering particles (A).

13. Rear projection screen 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 5 to 20 μm.

14. Rear projection screen 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 60 μm.

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

16. Rear projection screen according to one of the preceding claims, characterized in that the screen additionally comprises a carrier layer which has an intensity half-value angle less than 6.5 °.

17. rear projection screen according to claim 16, characterized in that the carrier layer has an average surface roughness Rz in the range of 3 microns to 40 microns.

18. rear projection screen according to claim 16 or 17, characterized in that the carrier layer comprises poly (meth) acrylates.

19. Rear projection screen according to one of the preceding claims, characterized in that the rear projection screen has a thickness in the range from 0.05 to 5 mm.

20. Rear projection screen according to one of the preceding claims, characterized in that the screen has a transmission greater than or equal to 25%.

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

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

23. Rear projection screen according to one of the preceding claims, characterized in that the screen has a scattering power greater than or equal to 0.15.

24. Rear projection screen according to one of the preceding claims, characterized in that the screen consists of extruded polymethyl methacrylate plastic with a path difference due to the optical birefringence of at most 25 nm.

25. A method for producing a rear projection screen according to one of claims 1 to 24, characterized in that a molding compound comprising polymethyl methacrylate, spherical scattering particles (A) and spherical particles (B) is extruded.

26. The method according to claim 25, characterized in that a sheet or film is extruded and the extruded sheet or film is then heated at 110 to 190 ° C for 5 minutes to 24 hours.

27. Use of a rear projection screen according to one of claims 1 to 24 in lighting applications.

28. Use according to claim 27 as a lens in LCD monitors.

29. Use of a rear projection screen according to claim 24 for the 3D projection.