HK1093100A

HK1093100A - Scratch-resistant rear projection screen and method for producing the same

Info

Publication number: HK1093100A
Application number: HK06113814.1A
Authority: HK
Inventors: M．帕鲁泽尔; J.施密特; H．格罗特许斯; C．克罗默尔; G．迪克豪特-拜尔
Original assignee: Evonik Röhm Gmbh
Priority date: 2003-08-04
Filing date: 2004-03-12
Publication date: 2007-02-23

Description

Scratch-resistant rear projection screen and production method thereof

The invention relates to a scratch-resistant rear projection screen comprising at least one light-scattering polymethyl methacrylate layer, to a method for producing said rear projection screen and to the use thereof.

Using backprojection techniques, information is available to a wide range of viewers. In principle, the structure of this type of system consists of an image surface, which is illuminated from the back by a projector and thus provides information.

This technique can be used, for example, for controlling observation stations (power stations, rail traffic) in order to make it easier for the person in charge to visit complex processes, so that control errors can be avoided. Another application is display panels in for example stadiums and in motor sports games. Here, the viewer is conveyed about the progress and status of the event that occurred, even if they stay at a greater distance from the true venue.

Which is a very large image surface. Due to the continuous further development of technical aspects (projector technology), further fields of application have increased over the last years.

This type of information transfer is also used, for example, in TV equipment, large movie theaters and home theaters, and as a promotional medium for exposition shows, for showcases and shops.

Furthermore, this technology is also used to convey information during the presentation and for flight simulators, where the virtual environment is depicted as close to realism as possible on the cockpit plate.

Many of the advantages of this technique are achieved by: the projector is outside the viewing space. Thereby, the projection is not obstructed by any observer located in front of the projection surface and disturbing noise from the projector is avoided, and thereby also an attractive spatial design can be made.

During this time there are a variety of plastic sheets and films used in rear projection technology. The sheet is often modified as follows: so that they have a defined structure in the form of a fresnel lens system on the rear side and also a vertically arranged lenticular lens on the viewer side. The production of such rear projection panels is therefore associated with high costs. Furthermore, the surface structure is sensitive to mechanical loads. The projected apparent image is also greatly impaired due to breakage.

Rear projection sheets and films comprising a scattering medium are also known, wherein the sheet comprises particles having a refractive index different from the matrix. The sheet and film are equally suitable for rear projection but do not provide uniform overall span width of the desired distribution and therefore only meet a portion of the requirements for the screen.

Due to the large number of different application possibilities, various requirements are placed on the projection surface. For example, in one of these applications, the projection surface must have a very smooth, sharp and high resolution image reproduction, since the viewer must then receive information over a long period of time (e.g., control the viewing station, home theater, etc.).

If the projection surface is used for display and promotional purposes, for example on a exposition display counter, the surface must be particularly resistant to mechanical loads and soiling, without the requirements on the quality of the projection being too high.

For example, sheets and films having a high light scattering angle can be produced using known scattering media, such as barium sulfate and titanium dioxide. The projection resolution is also high. Therefore, the viewing angle of the image should be correspondingly high. However, it has been shown that even the image sharpness of the projection sheet is less than ideal, wherein other requirements, such as scratch sensitivity, do not meet many requirements.

Screens comprising plastic particles as scattering medium are also known. For example, document JP11179856 describes a multilayer sheet having at least one layer comprising a polymethyl methacrylate matrix and comprising crosslinked polymethyl methacrylate beads as scattering/matting agent, the proportion of the beads being 0.5 to 25% by weight. The size of the beads is 3-30 μm, of which only sheets with a thickness of 2mm comprising about 3% by weight of scattering beads with a size of about 6 μm are described in the examples. The scratch sensitivity of the screen is problematic.

Japanese publication JP 07234304 describes mixtures of crosslinked acrylate-styrene beads (14 μm) in transparent plastics. A disadvantage of the screen is that scratches are visually noticeable.

Plates comprising a mixture of particles are also known (Scheiben). Publication JP 4-134440 describes the use of a mixture of two types of particles, wherein the particle size and the difference in refractive index relative to the matrix must be coordinated with one another, with the result that the wavelength-selective scattered light on the particles cancels one another out (smaller particles scatter blue light more strongly and larger particles scatter red light more strongly). Accordingly, the scattering sheet has a neutral hue.

Plates which can be used for optical technical applications are also known. For example, the plates are described in JP8-198976, JP 5-51480 and JP 2000-296580.

The disadvantage of the above-mentioned sheet is firstly that it is not as good as the desired image quality in combination with the high scratch sensitivity of the screen.

Publication EP- ｃA-0561551 describes ｃA multilayer sheet having ｃA scattering layer consisting of ｃA mixture of transparent polymers and spherical particles (2-15 μm). These screens are also very scratch sensitive.

A problem associated with known rear projection screens provided with a scattering medium is therefore that their image performance in terms of scratch sensitivity is not ideal. In particular, the known screens have a lower image sharpness or a less favorable brightness distribution. There are sometimes problems with color authenticity. In addition, many screens do not meet the mechanical requirements, where scratches in particular have disadvantageous optical effects.

In accordance with the prior art described and discussed herein, it is therefore an object of the present invention to provide a rear projection screen which enables particularly high image quality to be achieved and at the same time has a low susceptibility to scratching. In particular, the screen should allow to provide a high image definition and a high resolution of the projected image.

Furthermore, the image on the rear projection screen should have a particularly high color fidelity.

It is a further object of the invention to provide a rear projection screen having a particularly uniform brightness distribution.

In addition, the rear projection screen should have as high a mechanical stability as possible. Here, no, or only slightly visible scratches should be present on the screen. In particular, the breakage should have no or only a low influence on the visualization capacity of the screen.

Another object on which the invention is based is to provide a rear projection screen which can be produced particularly simply. For example, rear projection screens should be able to be produced in particular by extrusion.

It is another object of the present invention to produce a rear projection screen having high image smoothness. Thus, the presented information can be observed over a long period of time without fatigue.

It is another object of the present invention to provide a rear projection screen that is easily adjustable in size and shape as desired.

In addition, the image on the rear projection screen should have a particularly good contrast.

It is a further object of the invention that the rear projection screen has a high durability, in particular a high resistance to UV radiation or weathering.

Another object on which the invention is based is to provide a rear projection screen on the basis of which the image properties are only reflected to a low extent.

In addition, the size of the screen should be adjustable to the respective requirements. In particular, the thickness of the rear projection screen should be adjustable to any desired requirements without this impairing the image quality or the susceptibility to scratching.

The above object is achieved, as well as other objects which, although not specifically mentioned, are obvious from the context discussed herein or are necessarily derived therefrom, by a rear projection screen as claimed in claim 1. Advantageous developments of the rear projection screen according to the invention are protected in the dependent claims dependent on claim 1.

Claim 24 provides a solution to the object on which the invention is based with regard to a method for producing a rear projection screen.

A rear projection screen which achieves particularly high image quality and low optical scratch sensitivity is successfully provided by: concentration c of spherical scattering particles (A)_PAThickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical scattering particles (A)_PABy applying such a ratio c_PA*d_S/D_PA ³0.001-0.015 wt% mm/mum³Is selected in such a way that the concentration c of the spherical particles (B)_PBThickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical particles (B)_PBBy applying such a ratio c_PB*d_S/D_PB ³0.000005-0.002 wt% mm/mum³Is selected and the average surface roughness R of the polymethyl methacrylate layer_ZThe square of (A) and the cube of the particle size of the spherical particles (B)_Z ²/D_PB ³0.0002 to 0.1300 mu m^-1Wherein the rear projection screen comprises at least one light-scattering polymethyl methacrylate layer comprising a polymethyl methacrylate matrix and having different mean particle sizes V₅₀The spherical scattering particles (A) and the spherical particles (B) of (1), wherein the spherical scattering particles (A) have an average particle size V₅₀0.1 to 40 μm, the difference between the refractive index of the spherical scattering particles (A) and the refractive index of the polymethyl methacrylate matrix being 0.02 to 0.2, wherein the spherical particles (B) have an average particle size V₅₀10 to 150 μm, the difference between the refractive index of the spherical particles (B) and the refractive index of the polymethyl methacrylate matrix being 0 to 0.2, and wherein the total concentration of the spherical scattering particles (A) and particles (B) is 1 to 60% by weight, based on the weight of the light-scattering polymethyl methacrylate layer.

The measures according to the invention achieve, in particular, the following advantages:

the rear projection screen of the invention can be adjusted to individual requirements without this being the caseThe image quality and/or scratch sensitivity is now deteriorated.

□ the rear projection screen of the invention allows the production of projected images with high image definition and resolution.

□ the image on the rear projection screen of the invention has particularly high color realism and high contrast.

□ a rear projection screen is provided according to the invention having a particularly uniform brightness distribution.

□ in addition, the rear projection screen of the invention has high mechanical stability. The scratches on the screen are not visible or are only slightly visible here.

□ in addition, the image projected onto the rear projection screen of the present invention has high image smoothness. The display information can be observed for a long time without fatigue.

In addition, the rear projection screen according to the invention has a non-luminous, matt surface contour. Where appropriate, the properties of the surface structure can be adjusted differently without affecting optical parameters other than gloss. Thereby serving to reduce the degree of reflectivity which adversely affects the image on the screen.

□ the rear projection screen according to the invention can be produced in a particularly simple manner. For example, rear-projection screens can be produced in particular by extrusion.

□ the rear projection screen of the invention has high weatherability, especially resistance to UV radiation.

□ the size and shape of the rear projection screen can be adjusted as desired.

The light-scattering polymethyl methacrylate layer of the rear projection screen according to the invention comprises from 1 to 60% by weight, in particular from 3 to 55% by weight, and preferably from 6 to 48% by weight, of spherical scattering particles (a) and spherical particles (B), based on the weight of the light-scattering polymethyl methacrylate layer.

The scattering particles (a) and particles (B) are spherical. For the purposes of the present invention, the term "spherical" means that the particles preferably have a spherical shape, it being obvious to the person skilled in the art that, for reasons of the production method, particles having other shapes may also be present, or the shape of the particles may deviate from the ideal spherical shape.

The term "spherical" therefore means that the ratio of the largest dimension to the smallest dimension of the particles, each measured by the center of gravity of the particle, is at most 4, preferably at most 2. Preferably at least 70% of the particles are spherical, particularly preferably at least 90%, based on the number of particles.

Average particle size V of the scattering particles (A)₅₀From 0.1 to 40 μm, in particular from 1 to 35 μm, preferably from 2 to 30 μm, more preferably from 3 to 25 μm, in particular from 4 to 2O μm, and particularly preferably from 5 to 15 μm.

Such particles are known per se and are commercially available. Wherein the particles comprise, in particular, plastic particles and consist of inorganic materials, such as aluminum hydroxide, potassium aluminum silicate (mica), aluminum silicate (kaolin), barium sulfate (BaSO)₄) Calcium carbonate, magnesium silicate (talc). Among them, particles made of plastic are particularly preferable.

The plastic particles that can be used according to the invention are not particularly limited. For example, the type of plastic used for producing the plastic particles is essentially unimportant, where refraction of light occurs at the phase interface between the plastic bead and the matrix plastic.

The refractive index of the plastic particles thus has a refractive index n determined at 20 ℃ under the sodium D line (589nm)₀Refractive index n of the base plastic₀The difference is 0.02-0.2 units.

The spherical scattering particles (a) preferably comprise crosslinked polystyrene, silicone polymers and/or crosslinked poly (meth) acrylates.

One preferred group of plastic particles for use as scattering agents comprises silicone resins. Particles of this type are obtained, for example, by hydrolysis and polycondensation of organotrialkoxysilanes and/or tetraalkoxysilanes described by the following formulae

R¹Si(OR²)₃And Si (OR)²)₄

Wherein R is¹Radicals R which are, for example, substituted or unsubstituted alkyl, alkenyl or phenyl, and hydrolyzable alkoxy²Is an alkyl group, such as methyl, ethyl or butyl, or an alkoxy-substituted hydrocarbon group, such as 2-methoxyethyl or 2-ethoxyethyl. Examples of organotrialkoxysilanes are methyltrimethoxysilane, methyltriethoxysilane, methyl-n-propoxysilane, methyltriisopropoxysilane and methyltris (2-methoxyethoxy) silane.

The above silane compounds and methods for producing spherical silicone polymer particles are known in the art and are described in the documents EP 1116741, JP 63-077940 and JP 2000-186148.

Particularly preferred scattering agents for use in the present invention that are composed of silicone polymers are available from GE Bayer Silicones under the trade names tospearll * 120 and tospearll * 3120.

Another preferred group of plastic particles consists of the following monomers:

b1)25 to 99.9 parts by weight of a monomer having an aromatic group as a substituent, such as styrene, α -methylstyrene, ring-substituted styrene, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-phenylethyl (meth) acrylate, 3-phenylpropyl (meth) acrylate or vinyl benzoate; and

b2) from 0 to 60 parts by weight of acrylic and/or methacrylic esters having from 1 to 12 carbon atoms in the aliphatic ester group, which are copolymerizable with the monomers b1), and there may be mentioned, for example: methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 3, 5-trimethylcyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, norbornyl (meth) acrylate or isobornyl (meth) acrylate;

b3)0.1 to 15 parts by weight of a crosslinking comonomer containing at least two ethylenically unsaturated groups which can be copolymerized by free radical route with b1) and, where appropriate, b2), examples being divinylbenzene, diol 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, where the amounts of comonomers b1), b2) and b3) add up to 100 parts by weight.

The mixture for producing the plastic particles particularly preferably comprises at least 80% by weight of styrene and at least 0.5% by weight of divinylbenzene.

The production of crosslinked plastic particles is known in the art. For example, the scattering particles can be produced by emulsion polymerization, as described, for example, in EP-A342283 or EP-A269324, and more particularly preferably by polymerization in the organic phase, as described, for example, in German patent application P4327464.1, in the polymerization techniques mentioned at the end of which ｃA particularly narrow particle size distribution is obtained or, in other words, ｃA particularly small deviation of the particle diameter from the average particle diameter.

It is particularly preferred to use plastic particles having a heat resistance of at least 200 c, in particular at least 250 c, without this being limiting. Herein, the term "heat-resistant" means that the particles do not substantially undergo degradation caused by heat. The degradation caused by heat causes undesirable discoloration, rendering the plastic material unusable.

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

The scattering particles (a) described above may be used alone or in the form of a mixture of two or more types.

The particles (B) used according to the invention have an average particle size V₅₀Is 10 to 150 μm, preferably 15 to 70 μm, and particularly preferably 30 to 50 μm, the refractive index of the particles here having a refractive index n determined at 20 ℃ for the sodium D line (589nm)₀Refractive index n of the base plastic₀The difference is 0-0.2 units.

Particles (B) are likewise commercially available. These particles can be produced from the same material as the scattering particles (a), and here, it is also preferred to use plastic particles.

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

The above particles (B) may be used alone or in the form of a mixture of two or more types.

The weight ratio of scattering particles (A) to particles (B) is preferably from 1: 10 to 10: 1, in particular from 1: 5 to 5: 1, particularly preferably from 1: 3 to 3: 1, and very particularly preferably from 1: 2 to 2: 1.

Average particle size V of the scattering particles (A) and particles (B)₅₀The difference is preferably at least 5 μm, in particular at least 10 μm, where the particles (B) are larger than the scattering particles (A).

The particle size and the particle size distribution can be determined by means of laser extinction. Galay-CIS, available from L.O.T.GmbH, can be used here, and the measurement methods used here for determining the particle size and the particle size distribution are contained in the user manual. Average particle size, V₅₀As derived from the weight average median value, wherein 50% by weight of the particles have a value less than or equal to said value and 50% by weight of the particles have a value greater than or equal to said value.

According to a particular aspect of the invention, the particles are homogeneously distributed in the plastic matrix without significant aggregation or agglomeration of the particles. By uniformly distributed is meant that the concentration of particles within the plastic matrix is substantially constant.

In addition to the spherical particles, the light-scattering layer also comprises a plastic matrix comprising 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, of polymethyl methacrylate, based on the weight of the light-scattering layer.

Polymethyl methacrylate is generally obtained via radical polymerization of a mixture comprising methyl methacrylate. The mixture generally comprises 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 to this, the above-mentioned mixtures for preparing polymethyl methacrylate may also comprise other (meth) acrylates copolymerizable with methyl methacrylate. The term "(meth) acrylate" includes methacrylates and acrylates and mixtures of the two.

These monomers are well known. They include in particular (meth) acrylates derived from saturated alcohols, such as methyl acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate and 2-ethylhexyl (meth) acrylate; (meth) acrylates derived from unsaturated alcohols, such as oleyl (meth) acrylate, 2-propynyl (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate;

aryl (meth) acrylates, for example benzyl (meth) acrylate or phenyl (meth) acrylate, where the aryl radical may in each case be unsubstituted or have up to 4 substituents;

cycloalkyl (meth) acrylates such as 3-vinylcyclohexyl (meth) acrylate, bornyl (meth) acrylate;

hydroxyalkyl (meth) acrylates such as 3-hydroxypropyl (meth) acrylate, 3, 4-dihydroxybutyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate;

diol di (meth) acrylates, for example 1, 4-butanediol (meth) acrylate,

(meth) acrylic esters of ether alcohols such as tetrahydrofurfuryl (meth) acrylate, ethyleneoxyethoxyethoxyethyl (meth) acrylate;

amides and nitriles of (meth) acrylic acid, such as N- (3-dimethylaminopropyl) (meth) acrylamide, N- (diethylphosphono) (meth) acrylamide, 1-methacrylamido-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;

polyfunctional (meth) acrylates, such as trimethylolpropane tri (meth) acrylate.

In addition to the above-mentioned (meth) acrylic esters, the composition to be polymerized may also contain other unsaturated monomers copolymerizable with methyl methacrylate and the above-mentioned (meth) acrylic esters.

They include in particular 1-olefins, such as 1-hexene, 1-heptene; branched olefins such as vinylcyclohexane, 3-dimethyl-1-propene, 3-methyl-1-diisobutylene, 4-methyl-1-pentene;

acrylonitrile; vinyl esters, such as vinyl acetate;

styrene, substituted styrenes having an alkyl substituent in the side chain, such as α -methylstyrene and α -ethylstyrene, substituted styrenes having an alkyl substituent in the ring, such as vinyltoluene and p-methylstyrene, halogenated styrenes, such as monochlorostyrene, dichlorostyrene, tribromostyrene and tetrabromostyrene;

heterocyclic vinyl compounds, for example 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 (oxolan), vinylfuran, vinylthiophene, vinylthiolane, vinylthiazoline, vinyl and hydrogenated vinyl thiazoles, vinyl oxazoles and hydrogenated vinyl oxazoles;

vinyl ethers and isoprenyl ethers;

maleic acid derivatives such as maleic anhydride, methylmaleic anhydride, maleimide, methylmaleimide; and dienes such as divinylbenzene.

The comonomers are generally used in amounts of from 0 to 60% by weight, preferably from 0 to 40% by weight, and particularly preferably from 0 to 20% by weight, based on the weight of the monomers, and the compounds mentioned here can be used individually or in the form of mixtures.

The polymerization is generally initiated using known free radical initiators. The preferred initiators include in particular the azo initiators known in the art, such as AIBN and 1, 1-azobiscyclohexanecarbonitrile, and peroxy compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxides, methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butylperoxyisopropyl carbonate, 2, 5-bis (2-ethylhexanoylperoxy) -2, 5-dimethylhexane, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3, 5, 5-trimethylhexanoate, dicumyl peroxide, 1-bis (tert-butylperoxy) cyclohexane, 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 are likewise capable of forming free radicals.

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

Here, various different poly (meth) acrylates can be used, for example, which differ in molecular weight or monomer composition.

In addition, the matrix of the light scattering layer may comprise other polymers to improve its properties. These other polymers are, in particular, polyacrylonitrile, polystyrene, polyethers, polyesters, polycarbonates and polyvinyl chloride. These polymers may be used alone or in the form of a mixture, and copolymers derivable from the above polymers may also be used here.

The weight-average molecular weight M of the homopolymers and/or copolymers used as matrix polymers according to the invention_wCan be varied within wide limits, the molecular weight generally being adapted to the intended use and to the mode of processing of the molding compositions. However, without intending to be limiting, the weight average molecular weight is generally 20000-.

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

In a particular aspect of the invention, the poly (meth) acrylate of the matrix of the light-scattering layer has a refractive index of 1.46 to 1.54, measured at 20 ℃ and under the sodium D line (589 nm).

The molding composition used for the preparation of the light-scattering layer may comprise any type of conventional additives. They include, in particular, antistatics, antioxidants, mold-release agents, flame retardants, lubricants, dyes, flow improvers, fillers, light stabilizers, UV absorbers, and organophosphorus compounds, such as phosphites or phosphonates, pigments, weathering stabilizers and plasticizers. However, the amount of the additive is limited by the purpose of use. For example, neither the light scattering properties of the polymethyl methacrylate layer nor its transparency should be impaired too strongly by the additives.

According to a particular aspect of the invention, the molding compositions can, where appropriate, be given greater mechanical stability by means of impact modifiers. Impact modifiers for polymethacrylates of this type are well known, for example the preparation and structure of impact-modified polymethacrylate molding compositions are described in particular in EP-A0113924, EP-A0522351, EP-A0465049 and EP-A0683028.

Preferred impact-resistant molding compositions which can be used for preparing the matrix comprise from 50 to 99% by weight, in particular from 70 to 98% by weight, of polymethyl methacrylate, based on the weight of the molding composition in the absence of scattering particles (A) and particles (B). The polymethyl methacrylate is described above.

In a particular aspect of the invention, the polymethyl methacrylate used for the preparation of the impact-modified molding compositions is obtainable by free-radical polymerization of a mixture comprising 80 to 100% by weight, preferably 90 to 98% by weight, of methyl methacrylate and, where appropriate, 0 to 20% by weight, preferably 2 to 10% by weight, of other comonomers capable of free-radical polymerization, which comonomers have also been listed above. Particularly preferred comonomers are, in particular, (meth) acrylic acid-C₁-C₄Alkyl esters, in particular methyl acrylate, ethyl acrylate or butyl methacrylate.

Average molecular weight M of polymethyl methacrylate useful for preparing impact-modified matrices_wPreferably 90000-200000 g/mol, especially 100000-150000 g/mol.

Preferred impact molding compositions which can be used for preparing the matrix comprise from 0.5 to 55% by weight, preferably from 1 to 45% by weight, particularly preferably from 2 to 40% by weight, in particular from 3 to 35% by weight, of impact modifiers, based on the weight of the molding composition in the absence of scattering particles (A) and particles (B), which impact modifiers are an elastomeric phase composed of crosslinked polymer particles.

The impact modifiers can be obtained by bead polymerization or by emulsion polymerization by methods known per se.

Preferred impact modifiers are crosslinked particles having an average particle size of from 50 to 1000nm, preferably from 60 to 500nm, and particularly preferably from 80 to 120 nm.

Such particles are obtained, for example, by free-radical polymerization of a mixture which generally comprises at least 40% by weight, preferably from 50 to 70% by weight, of methyl methacrylate, from 20 to 80% by weight, preferably from 25 to 35% by weight, of butyl acrylate, and from 0.1 to 2% by weight, preferably from 0.5 to 1% by weight, of a crosslinking monomer, for example a polyfunctional (meth) acrylate such as allyl methacrylate, and a comonomer copolymerizable with the vinyl compounds mentioned above.

Preferred comonomers include in particular (meth) acrylic acid-C₁-C₄Alkyl esters, in particular ethyl acrylate or butyl methacrylate, preferably methyl acrylate, or other monomers capable of vinyl polymerization, such as styrene. The mixture used for producing the above-mentioned particles may preferably contain from 0 to 10% by weight, preferably from 0.5 to 5% by weight, of comonomers.

Particularly preferred impact modifiers are polymer particles having a core-shell structure with two layers, or particularly preferably three layers. Such core-shell polymers are described in particular in EP-A0113924, EP-A0522351, EP-A0465049 and EP-A0683028.

Particularly preferred impact modifiers based on acrylate rubbers have in particular the following structure:

and (3) nucleus: a polymer having a methyl methacrylate content of at least 90 wt.%, based on the weight of the core.

Shell 1: a polymer having a butyl acrylate content of at least 80% by weight, based on the weight of the shell 1.

A shell 2: a polymer having a methyl methacrylate content of at least 90% by weight, based on the weight of the shell 2.

The core and the shell may each comprise other monomers in addition to the monomers. These monomers have already been mentioned above, and particularly preferred comonomers here have a crosslinking action.

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

and (3) nucleus: copolymer composed of methyl methacrylate (95.7 wt%), ethyl acrylate (4 wt%) and allyl methacrylate (0.3 wt%)

S1: copolymer of butyl acrylate (81.2 wt%), styrene (17.5 wt%) and allyl methacrylate (1.3 wt%)

S2: a copolymer composed of methyl methacrylate (96 wt%) and ethyl acrylate (4 wt%).

Core of acrylate rubber modifier: the shell ratio can vary within wide limits. Preferably, in the case of modifiers having a shell, the core-shell weight ratio K/S is from 20: 80 to 80: 20, preferably from 30: 70 to 70: 30; or in the case of modifiers having two shells, the ratio K/S1/S2 of core to shell 1: shell 2 is from 10: 80: 10 to 40: 20: 40, particularly preferably from 20: 60: 20 to 30: 40: 30.

Without intending to be limiting, the particle size of the core-shell modifier is generally from 50 to 1000nm, preferably 100-500nm, and particularly preferably 150-450 nm.

Impact modifiers of the above type are commercially available from Mitsubishi under the trade name METABLEN * IR 441. Impact-modified molding compositions can also be obtained.

Particularly preferred molding compositions for the preparation of plastic substrates are commercially available from the company R * hm GmbH & Co.

The thickness of the light-scattering polymethyl methacrylate layer is usually 0.05 to 5mm, preferably 0.05 to 2mm, and particularly preferably 0.1 to 1 mm.

According to the invention, the concentration c of the spherical scattering particles (A) is adjusted_PAThickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical scattering particles (A)_PAIs selected such that the concentration c of the spherical scattering particles (A)_PAAnd the cubic ratio c of the product of the thickness of the light-scattering polymethyl methacrylate layer and the particle size of the spherical scattering particles (A)_PA*d_S/D_PA ³0.001-0.015 wt% mm/mum³Preferably 0.0025-0.009 wt% mm/μm³。

The concentration c of the spherical particles (B)_PBThickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical particles (B)_PBIs selected such that the concentration c of the spherical scattering particles (B)_PBAnd the cubic ratio c of the product of the thickness of the light-scattering polymethyl methacrylate layer and the particle size of the spherical scattering particles (B)_PB*d_S/D_PB ³0.000005-0.002 wt% mm/mum³Preferably 0.00004-0.0015 wt% mm/μm³。

Average surface roughness R of polymethyl methacrylate layer_ZThe square of (A) and the cube of the particle size of the spherical particles (B)_Z ²/D_PB ³Can be 0.0002-0.1300 μm^-1In particular 0.0009-0.0900 μm^-1And preferably 0.00025 to 0.0600 μm^-1And particularly preferably 0.0025 to 0.0600 μm^-1。

In a particular embodiment of the screen according to the invention, the concentration c of spherical scattering particles (A)_PAThickness d of light-scattering polymethyl methacrylate layer_SRatio of c_PA/d_SGreater than or equal to 2.5 wt%/mm, in particular greater than or equal to 4 wt%/mm.

In a particular aspect of the screen according to the invention, the concentration c of spherical particles (B)_PBThickness d of light-scattering polymethyl methacrylate layer_SRatio of c_PB/d_SGreater than or equal to 2.5 wt%/mm, in particular greater than or equal to 4 wt%/mm.

Without intending to be limiting, the thickness d of the light-scattering polymethyl methacrylate layer_sAnd the particle size D of the spherical scattering particles_PACalculated ratio d_S/D_PAPreferably 1 to 500, in particular 1 to 250, preferably 2.5 to 250 and particularly preferably 2.5 to 150.

Gloss R of light-scattering polymethyl methacrylate layer₈₅. Preferably less than or equal to 60, in particular less than or equal to 40 and particularly preferably less than 30.

The rear projection screen, in particular the light-scattering polymethyl methacrylate layer, according to the invention has a particularly low susceptibility to scratching. In a particular aspect of the invention, scratches on the screen which are produced using a force of up to 0.4N, in particular up to 0.7N, and particularly preferably up to 1.0N, are not discernible by visual inspection, but are not intended to be limiting thereby.

The scratch resistance can be determined by visual evaluation of the damaged surface according to DIN 53799 and DIN EN438, in which damage is caused by diamonds acting on the surface with different forces.

According to a particular embodiment of the invention, the average surface roughness R of the sheet_ZPreferably 5 to 50 μm, in particular 5 to 25 μm, preferably 6 to 35 μm, in particular 15 to 50 μm, particularly preferably 6 to 30 μm.

Average surface roughness R_ZCan be determined in accordance with DIN 4768 using a Talysurf50 measuring instrument from Taylor Hobson, where R is_ZThe average roughness depth is calculated from the average of the individual roughness depths of five successive individual measurement runs within the roughness profile.

Surface roughness R of sheet_ZUsually by selection of the particles (B). Furthermore, the value may be affected by variations in various parameters depending on the type of production method.

Said parameters are in particular the temperature of the melt during extrusion, wherein higher melt temperatures result in rougher surfaces. However, a factor which has to be taken into account here is that the temperature of the melt depends on the exact composition of the molding composition. The temperature of the melt is typically 150 ℃ to 300 ℃, preferably 200 ℃ to 290 ℃. The temperature is based on the temperature of the melt as it exits the die.

The surface roughness may also be affected by the gap between the rollers used to polish the sheet. If the polishing mechanism comprises, for example, three rolls arranged in an L-shape, wherein the molding composition is guided from the die to the gap between roll 1 and roll 2 and wound around roll 2 at 60-180 deg., the surface is polished through the gap between roll 2 and roll 3. If the gap between the rollers 2, 3 is adjusted to the thickness of the sheet, the scattering particles on the surface of the sheet are pressed into the matrix, which makes the surface smoother. In order to obtain a rougher surface, such a gap is usually adjusted to be slightly larger than the sheet thickness of the sheet to be produced, where this value usually exceeds the sheet thickness by 0.1-2mm, preferably by 0.1-1.5mm, without this being limiting. The surface roughness is also influenced by the grain size and sheet thickness, the correlation being given in the examples.

The light-scattering layer can be produced by known methods, thermoplastic forming being preferred here. Once the particles have been added, the light-scattering layer can be produced from the molding compositions described above by conventional thermoplastic shaping methods.

According to a particular embodiment, a twin-screw extruder is used for extrusion or for producing pellets of the molding composition comprising scattering beads. In these processes, the plastic particles are preferably converted into a melt in an extruder. By this measure a melt can be obtained which can be used to provide a screen with a particularly high transmission.

Here, rear projection screens can be produced by a two-step process, wherein the extrusion of a film or sheet on a single screw extruder is carried out downstream of the side-feeder compounding process and intermediate pelletization of the present invention on a twin screw extruder. Pellets obtained by means of a twin-screw extruder make it possible to obtain a particularly high proportion of scattering beads, which makes it possible to produce projection screens having different contents of scattering beads by simply blending into the molding composition without scattering beads.

It is also possible to carry out a single-stage process in which the process of compounding the spherical plastic particles into the melt is carried out as described above for a twin-screw extruder, where appropriate with a set of pressure-increasing devices (e.g.melt pumps) downstream of the extruder, which is then directly connected to an extrusion die for shaping the flat product. Surprisingly, rear projection screens having a particularly low yellowness index are also obtainable by the above-described process.

Furthermore, the screen can also be produced by injection moulding, but in this case the process parameters or the injection mould must be selected such that a surface roughness within the scope of the invention is achieved.

The compounding of the matrix with the scattering particles is preferably carried out by means of a twin-screw extruder, and a single-screw extruder can likewise be used in the case of true sheet extrusion, without this being intended to be limiting.

Depending on the type of application, a light-scattering polymethyl methacrylate layer can be used as the screen. Here, the thinner layer may be used in the form of a film that can be wound. Particularly preferred films are provided with impact resistance by the methods described above.

Furthermore, a thin light-scattering polymethyl methacrylate layer can be applied to the plastic sheet in order to increase its mechanical stability. The above-mentioned plastic sheets used as carrier layer preferably have a strength 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 contains no or only a small amount of spherical particles having a scattering effect. The plastic sheet preferably comprises a poly (meth) acrylate.

Preferably, the surface of the carrier layer has a gloss at an angle of 60 ° 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.

According to a preferred embodiment, the carrier layer has an average surface roughness R_ZPreferably 2 to 45 μm, in particular 3 to 40 μm, preferably 5 to 35 μm. In this way, spatial reflections of the image projected onto the screen can be avoided without impairing the image quality.

According to a particular aspect of the invention, the transmission of the screen is greater than or equal to 25%, in particular greater than or equal to 40%, and particularly preferably greater than or equal to 55%, the values described herein being obtained in particular by a screen which does not contain a dye which improves the contrast.

According to a particular aspect of the invention, the molding compositions can be colored. Surprisingly, the contrast can be improved by this method. Suitable materials for coloring are in particular dyes and/or carbon black known per se. Particularly preferred dyes are commercially available. The dyes include in particular * Sandoplast red G and * Sandoplast yellow 2G, both available from Clariant, and * Macrolex green 5B and * Macrolex violet 3R, both available from Bayer. The concentration of the dye depends on the desired color impression and the thickness of the sheet. Without intending to be limiting, the concentration of each dye is generally from 0 to 0.8% by weight, preferably from 0.000001 to 0.4% by weight, based on the total weight of the colored molding composition in the absence of the scattering particles (a) and particles (B). The sum of the dye concentrations is preferably from 0 to 1% by weight, preferably from 0.0001 to 0.6% by weight, based on the total weight of the colored molding composition in the absence of scattering particles (A) and particles (B). The loss of transmissivity can be at least partially compensated for by a more powerful projector.

Preferably, the yellowness index of the screen display is less than or equal to 12, in particular less than or equal to 10, without this being intended to be limiting.

A particular embodiment of the screen of the 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 invention, the scattering power of the screen display is greater than or equal to 0.15, in particular greater than or equal to 0.35, without this being limitative.

According to a preferred embodiment, the surface of the polymethylmethacrylate sheet of the invention shows a matt appearance in reflection on a diffuser plate. Gloss measurements using a reflectometer according to DIN67530 may be used for characterization. The gloss of the sheet at an angle of 85 ° is preferably less than 60, particularly preferably less than 40, and very particularly preferably less than 30.

The size and shape of the rear projection screen of the present invention is not limited. However, the screen typically has a rectangular, panel-like shape, as images are typically displayed in this format.

The length of such a rear projection screen is preferably from 25 to 10000 mm, preferably from 50 to 3000mm and particularly preferably from 200 to 2000 mm. The width of this particular embodiment is generally from 25 to 10000 mm, preferably from 50 to 3000mm, and particularly preferably from 200 to 2000 mm. In order to provide a particularly large projection surface, a plurality of such screens can be combined.

According to a particular embodiment, the screen has a particularly high resistance to weathering according to DIN EN ISO 4892, part 2 (artificially exposed or irradiated in the instrument, filtered xenon arc radiation).

The rear projection screen of the present invention can be used in other optical technology applications, such as a diffuser plate in an LCD monitor.

The present invention will be illustrated in more detail below by way of examples and comparative examples, but the present invention is not limited to the examples.

A) Measuring method

Average roughness R_ZMeasured according to DIN 4768 using a Talysurf50 measuring instrument from Taylor Hobson.

Transmittance tau_D65/2°Measured according to DIN 5036 using a Lambda19 measuring instrument from Perkin Elmer.

Yellowness index τ_D65/10°Measured according to DIN 6167 using a Lambda19 measuring instrument from Perkin Elmer.

R85 ° gloss was determined at 85 ° according to DIN67530 using a dr. lange laboratory reflectometer from dr. lange company as measuring instrument.

The scattering power and the half-value angle of intensity were determined according to DIN 5036 using the LMT goniometer measuring platform GO-T-1500 from LMT.

The various rear projection screens were also evaluated visually according to the criteria shown in table 1.

For this purpose an Epson EMP-713 projector is used. The test images were evaluated at a distance of about 1-1.5m from the image at a number of angles (0 ° -perpendicular to the projection normal, 30 ° and 60 °). At an image diagonal of about 50cm, the distance of the projector from the projection sheet was about 85 cm.

Technical data of Epson projector EMP 713:

a projection system: dichroic mirror and lens system, image unit: 2359296 pixels (1024 × 768) × 3, luminance: 1200ANSI lumens, contrast: 400: 1, image luminance: 85%, color reproduction: 24 bits, at 16.7 million colors, H: 15-92kHz, V: 50-85Hz, lamp: 150 watt UHE, video resolution: 750TV line

TABLE 1

Standard of merit	Performance of
Standard of merit	Performance of	Hot Spot (Hot Spot)	Hot spots refer to the light distribution due to the conical beam of the projection illumination system. The hot spot is thus a conical beam with a significantly higher intensity at its center than at the edges of the image. If the hot spot is very noticeable, the projector lamp can be visually distinguished.
Distribution of brightness	The brightness distribution is also evaluated by the distribution of light over the image surface andthus characterizing the extent to which the image is illuminated from the center to the edge.	Hot Spot (Hot Spot)
Distribution of brightness		Image sharpness	Image sharpness is the degree to which the test image is clearly perceived.
Resolution ratio	The image resolution describes the degree to which the fine structure on the evaluated sheet is distorted.	Image sharpness
Resolution ratio		Image stationarity	Image smoothness refers to the degree to which an observer can receive projected information over a long period of time without subjecting his eyes to intense stress.

In the table + + indicates good performance, with 0 indicates satisfactory performance, with-indicates poor performance, with-indicates very poor performance and with-indicates insufficient performance.

B) Preparation of Plastic particles

Plastic particle B1

For the preparation of spherical plastic particles, use was made of an aluminum hydroxide-Pickering-stabilizer prepared by precipitation directly from aluminum sulfate and soda solution before the start of the actual polymerization. For this purpose, first 16g of Al are added₂(SO₄)₃0.032g of complex former (Trilon A) and 0.16g of emulsifier (emulsifier K30 from Bayer AG; C)₁₅Sodium salt of paraffin sulfonic acid) was dissolved in 0.8l of distilled water. The 1N sodium carbonate solution is then added to the aluminium sulphate dissolved in water, with stirring and at a temperature of about 40 ℃, at which pH value is then 5-5.5. The colloidal distribution of the stabilizer in water is achieved by this procedure.

After the stabilizer had precipitated, the aqueous phase was transferred to a glass beaker. To this end, 110g of methyl methacrylate, 80g of benzyl methacrylate and 10g of allyl methacrylate are added, as well as 4g of dilauryl peroxide and 0.4g of tert-butyl per 2-ethylhexanoate. The mixture was dispersed by means of a disperser (UltraTurrax S50N-G45MF, Jankeund Kunkel, Staufen) at 7000rpm for 15 minutes.

After the shearing process, the reaction mixture was passed into a reactor which had been preheated to the corresponding reaction temperature of 80 ℃ and allowed to polymerize under stirring (600rpm) at about 80 ℃ (polymerization temperature) for 45 minutes (polymerization duration). The post-reaction phase was then carried out at an internal temperature of about 85 ℃ for 1 hour. After cooling to 45 ℃, the stabilizer is converted into water-soluble aluminium sulphate by adding 50% strength sulphuric acid. The beads were treated by filtering the resulting suspension through a commercial filter cloth and drying in a heated oven at 50 ℃ for 24 hours.

The particle size distribution was investigated by laser extinction. Average size V of particles₅₀It was 18.6 μm. The beads had a spherical shape, where no fibers could be detected. No coagulation occurred. The resulting particles are referred to below as plastic particles B1.

Plastic particle B2

For the preparation of spherical plastic particles, an aluminum hydroxide-Pickering-stabilizer prepared by precipitation directly from aluminum sulfate and soda solution (1N sodium carbonate solution) before the start of the actual polymerization was used. For this purpose, first of all N is passed through a heat exchanger with baffles, Ni-Cr-Ni thermocouples and a circulating heating system₂A rinsed 100L V4A kettle was used with an impeller stirrer under stirring (330rpm) to form an initial charge of 38L of deionized water, 400g of aluminum sulfate, and 8g of a complex forming agent (Trilon A). 1760g of soda solution are then added to precipitate the aluminium hydroxide, and emulsifier K30 dispersing aid (4g) (C15 paraffin sulphonic acid sodium salt) commercially available from Bayer AG and polymer wax 5000/6000(4g) (polyethylene glycol with a molecular weight of 5000-6000) commercially available from H * chst are added, both dissolved in 240ml of deionized water. The pH after precipitation was about 5.3, thus giving a colloidal distribution of the dispersant in water.

Then, a monomer mixture consisting of 6900g of methyl methacrylate, 3000g of styrene, 100g of ethylene glycol dimethacrylate, 200g of dilauroyl peroxide, 20g of tert-butyl per 2-ethylhexanoate and 50g of 2-ethylhexyl thioglycolate was added at room temperature likewise.

The heating phase is carried out until the temperature is 80 ℃ at which the reactor is pressure-sealed at a temperature of 40 ℃ inside the kettle and the N is switched off₂And (4) introducing. Within the next 115 minutes, the internal temperature was raised to about 87 ℃ and the pressure was raised from 0.70 to 0.92 bar. After the temperature maximum, the reaction mixture was heated to about 87-88 ℃ and stirring was continued at this temperature for about 1 hour, where the stirrer speed was reduced to 200 rpm. After the reaction mixture had cooled down, the pressure was relieved at a pot temperature of 46 ℃ and then 400ml of 50% strength sulfuric acid were added, whereby the aluminum hydroxide was converted into soluble aluminum sulfate and whereby the suspension polymer precipitated out. For the treatment of the beads, the suspension obtained is filtered through a ceramic suction filter with filter cloth, washed until neutral and dried in a heating oven at 50 ℃ for about 20 hours.

The size distribution was studied by laser extinction. Average size V of particles₅₀And 40.5 μm. The beads had a spherical shape, where no fibers could be detected. No coagulation occurred. The resulting particles are referred to below as plastic particles B2.

C) Examples 1 to 4

Various rear projection screens are produced by extrusion. For this purpose, the coating composition initially comprises a mixture of B1 plastic particles, B2 plastic particles, based on styrene and having a particle size V₅₀Various scattering bead compounds consisting of plastic particles (all available from Sekisui under the name * Teehpolymer SBX-8) of about 8.4 μm, and from R * hm GmbH&Kg company PMMA moulding composition (copolymer consisting of 97 wt% methyl methacrylate and 3 wt% methyl acrylate) was extruded to give a plastic sheet. A60 mm phi extruder from BREYER was used. The temperature of the melt as it exits the die is typically 270 ℃. Generally, and in particular embodiments, the polishing mechanism is adjusted to achieve as rough a surface as possible.

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

TABLE 2

	Example 1	Example 2	Example 3	Example 4
	Example 1	Example 2	Example 3	Example 4	Thickness [ mm ]]	0.5	0.5	0.5	0.5
PMMA matrix [ weight%]	88	82	88	82	Thickness [ mm ]]	0.5	0.5	0.5	0.5
PMMA matrix [ weight%]	88	82	88	82	* SBX8[ wt. ]]	6	6	6	6
Plastic particles B1[ wt.%]	0	0	6	12	* SBX8[ wt. ]]	6	6	6	6
Plastic particles B1[ wt.%]	0	0	6	12	Plastic particles B2[ wt.%]	6	12	0	0

The obtained rear projection screen was investigated according to the measurement method described above, and the measurement results obtained here are shown in table 3.

TABLE 3

	Example 1	Example 2	Example 3	Example 4
	Example 1	Example 2	Example 3	Example 4	Transmittance [% ]]	71.4	73.14	71.95	71.34
Yellowness index G (τ)_D65/10°)	5.36	4.86	5.2	5.3	Transmittance [% ]]	71.4	73.14	71.95	71.34
Yellowness index G (τ)_D65/10°)	5.36	4.86	5.2	5.3	Scattering power σ	0.6	0.56	0.6	0.6
Intensity half angle gamma deg]	49	43	49	49	Scattering power σ	0.6	0.56	0.6	0.6
Intensity half angle gamma deg]	49	43	49	49	R_Z[μm]	15.0	25.4	6.1	7.6
R85 ℃ gloss measurement	14.8	4.6	25.3	8.6	R_Z[μm]	15.0	25.4	6.1	7.6
R85 ℃ gloss measurement	14.8	4.6	25.3	8.6	c_PA*d_S/D_PA ³[ wt%. mm/. mu.m³]	0.00505	0.00505	0.00505	0.00505
c_PB*d_S/D_PB ³[ wt%. mm/. mu.m³]	0.000045	0.000090	0.000466	0.00093	c_PA*d_S/D_PA ³[ wt%. mm/. mu.m³]	0.00505	0.00505	0.00505	0.00505
c_PB*d_S/D_PB ³[ wt%. mm/. mu.m³]	0.000045	0.000090	0.000466	0.00093	R_Z ²/D_PB ³	0.00338	0.00968	0.00263	0.00416
Hot spot	++	++	++	++	R_Z ²/D_PB ³	0.00338	0.00968	0.00263	0.00416
Hot spot	++	++	++	++	Distribution of brightness	++	++	++	++
Image sharpness	+	+	+/++	++	Distribution of brightness	++	++	++	++
Image sharpness	+	+	+/++	++	Resolution ratio	Fine-very fine	Fine-very fine	Is very fine	Is very fine
Image stationarity	+	0/+	+	+	Resolution ratio	Fine-very fine	Fine-very fine	Is very fine	Is very fine

Visual scratch sensitivity of the extrudates was also investigated.

Sensitivity of scratching by penetration depth t of diamond_RF (load), using a scratch tester model 203 from taber industries, which method is in accordance with DIN 53799 and DIN EN 438: the diamond graver having a taper angle of 90 deg. had a tip radius of 90 μm and a rotation direction of counterclockwise. The loads used are listed in table 4.

Visual evaluation (reflection test) was performed on a black substrate. The tests (roughness, gloss) on the test extrudates were carried out on the upper surface.

The results obtained are shown in Table 4.

TABLE 4

DiamondLoad of	Example 1	Example 2
DiamondLoad of	Example 1	Example 2	0.4N	Damage is indistinguishable	Damage is indistinguishable
0.7N	Damage is indistinguishable	Damage is indistinguishable	0.4N	Damage is indistinguishable	Damage is indistinguishable
0.7N	Damage is indistinguishable	Damage is indistinguishable	1.0N	Damage is indistinguishable	Damage is indistinguishable
1.5N	Damage is indistinguishable	Damage is indistinguishable	1.0N	Damage is indistinguishable	Damage is indistinguishable
1.5N	Damage is indistinguishable	Damage is indistinguishable	2.0N	Lesions are hardly discernible (extra reflection (ausspiegeln), strong angle dependence)	Lesions are hardly discernible (extra reflections, strong angle dependence)
3.0N	Damage is discernible	Damage is discernible (extra reflection)	2.0N

TABLE 4 continuation

Load of diamond	Example 3	Example 4
Load of diamond	Example 3	Example 4	0.4N	Damage is indistinguishable	Damage is indistinguishable
0.7N	Damage is indistinguishable	Damage is indistinguishable	0.4N	Damage is indistinguishable	Damage is indistinguishable
0.7N	Damage is indistinguishable	Damage is indistinguishable	1.0N	Damage is indistinguishable	Damage is indistinguishable
1.5N	Lesions are hardly discernible (extra reflections, strong angle dependence)	Lesions are hardly discernible (extra reflections, strong angle dependence)	1.0N	Damage is indistinguishable	Damage is indistinguishable
1.5N			2.0N	Lesions are hardly discernible (extra reflections, strong angle dependence)	Lesions are hardly discernible (extra reflections, strong angle dependence)
3.0N	Damage is discernible	Damage is discernible	2.0N

D) Examples 5 and 6

The production process described in examples 1 to 4 above was substantially repeated, but here an impact modifier (* Metablen IR 441, available from Mitsubishi) was additionally added. In addition, colored rear-projection screens are produced, which are likewise provided with impact resistance. The dye consisted of a mixture of 52.66 wt% * Sandoplast red G, 0.84 wt% * Sandoplast yellow 2G (both available from Clariant) and 39.22 wt% * Macrolex green 5B and 7.28 wt% * Macrolex violet 3R (both available from Bayer).

The proportion of plastic particles in the polymethyl methacrylate matrix and the thickness of the sheet are given in Table 5.

TABLE 5

	Example 1	Example 5	Example 6
	Example 1	Example 5	Example 6	Thickness [ mm ]]	0.5	0.5	0.5
PMMA matrix [ parts by weight]	88	53	53	Thickness [ mm ]]	0.5	0.5	0.5
PMMA matrix [ parts by weight]	88	53	53	* SBX8[ wt.%]	6	6	6
Plastic particles B1[ wt.%]	0	0	0	* SBX8[ wt.%]	6	6	6
Plastic particles B1[ wt.%]	0	0	0	Plastic particles B2[ wt.%]	6	6	6
* Metablen IR 441[ parts by weight]	0	35	35	Plastic particles B2[ wt.%]	6	6	6
* Metablen IR 441[ parts by weight]	0	35	35	Dye [ parts by weight]	0	0	0.02142

The obtained rear projection screen was investigated according to the measurement method described above, and the measurement results obtained here are shown in table 6.

The mechanical properties of rear projection screens have also been investigated. Tensile strength, elongation at break and modulus of elasticity were determined according to ISO 527-2 and reflectance according to DIN 5036.

TABLE 6

	Example 1	Example 5	Example 6
	Example 1	Example 5	Example 6	Transmittance [% ]]	71.4	73.43	39.74
Yellowness index G (τ)_D65/10°)	5.36	4.88	-	Transmittance [% ]]	71.4	73.43	39.74
Yellowness index G (τ)_D65/10°)	5.36	4.88	-	Scattering power σ	0.6	0.56	0.59
Intensity half angle gamma deg]	49	43	48	Scattering power σ	0.6	0.56	0.59
Intensity half angle gamma deg]	49	43	48	Reflectance (ρ)_D65/2°)[％]	26.72	25.26	11.21
Tensile Strength (sigma-M; 5 mm-min)[MPa]	64.6	34.5	33.8	Reflectance (ρ)_D65/2°)[％]	26.72	25.26	11.21
Tensile Strength (sigma-M; 5 mm-min)[MPa]	64.6	34.5	33.8	Modulus of elasticity (1mm/min) [ MPa ]]	3258	1642	1621
Elongation at break (. epsilon. -B; 5mm/min) [% ]]	3.4	23.6	17.1	Modulus of elasticity (1mm/min) [ MPa ]]	3258	1642	1621
Elongation at break (. epsilon. -B; 5mm/min) [% ]]	3.4	23.6	17.1	R_Z[μm]	15.0	16.0	20.1
R85 ℃ gloss measurement	14.8	9.9	5.4	R_Z[μm]	15.0	16.0	20.1
R85 ℃ gloss measurement	14.8	9.9	5.4	Hot spot	++	++	++
Distribution of brightness	++	++	++	Hot spot	++	++	++
Distribution of brightness	++	++	++	Image sharpness	+	+	+
Resolution ratio	Fine-very fine	Fine-very fine	Coarse-very fine	Image sharpness	+	+	+
Resolution ratio	Fine-very fine	Fine-very fine	Coarse-very fine	Image stationarity	+	+	+

Rear projection screen for 3D projection

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

In 3D projection methods, as image source, in each case two projections are superimposed, which in principle transmit the same image content, but which are received blended in within a certain distance, for example within the distance between the eyes. An example of a frequently used principle is polarization. With projectors operated with polarized light, two received lights having different polarization arrangements are irradiated onto a rear projection screen.

The observer observes the image through glasses each equipped with a corresponding polarization filter for the right eye and the left eye separately. The human brain processes these two different image impressions to give a three-dimensional image perception.

For 3D projection, the rear projection screen according to the invention can preferably be produced from extruded polymethyl methacrylate plastic in the form of a sheet or film comprising at least one light-scattering layer of extruded polymethyl methacrylate plastic, the total optical path difference here being at most 25nm, preferably at most 15nm, particularly preferably at most 5nm, owing to optical birefringence.

It must be noted here that the extrusion process always causes a certain orientation of the molecular chains in the extrusion direction. This orientation leads to a birefringent behavior which partially depolarizes the two projected polarized light, which is of course undesirable.

Extruded polymethylmethacrylate plastics which are designed for rear projection screens for 3D projection are therefore particularly preferably subjected to a thermal post-treatment after extrusion. During the thermal post-treatment, a reversion of the polymer molecules occurs, which essentially eliminates the orientation of the polymer molecules again. The result is a substantial reduction in the birefringence properties initially present in the material.

Depending on the composition of the material and the material thickness, the thermal aftertreatment of the extruded polymethyl methacrylate plastic in the form of films or sheets, designed for rear projection screens for 3D projection, can be carried out, for example, at 190 ℃ at 110-. Which can be easily optimized by the person skilled in the art. The heat-induced recovery process can be carried out with materials that lie flat or preferably hang.

Measurement methods suitable for measuring optical path differences due to optical birefringence are known to the person skilled in the art. For example, the optical path difference can be measured with the aid of a polarization microscope in combination with an Ehringhaus relaxation oscillation compensator.

Claims

1. Rear projection screen comprising at least one light-scattering polymethyl methacrylate layer comprising a polymethyl methacrylate matrix and having different mean particle sizes V₅₀The spherical scattering particles (A) and the spherical particles (B) of (1), wherein the spherical scattering particles (A) have an average particle size V₅₀0.1 to 40 μm and the difference between the refractive index of the spherical scattering particles (A) and the refractive index of the polymethyl methacrylate matrix is 0.02 to 0.2, wherein the spherical particles (B) have an average particle size V₅₀10 to 150 μm, and the refractive index of the spherical particles (B) and the refractive index of the polymerThe difference in the refractive index of the methyl methacrylate matrix is from 0 to 0.2 and the total concentration of spherical scattering particles (A) and spherical particles (B) is from 1 to 60% by weight, based on the weight of the light-scattering polymethyl methacrylate layer, characterized in that the concentration c of the spherical scattering particles (A)_PAThickness dS of light-scattering polymethyl methacrylate layer and particle size D of spherical scattering particles (A)_PAIs selected such that the ratio c_PA*d_S/D_PA ³0.001-0.015 wt% mm/mum³Concentration c of spherical particles (B)_PBThickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical particles (B)_PBIs selected such that the ratio c_PB*d_S/D_PB ³0.000005-0.002 wt% mm/mum³And the average surface roughness R of the polymethyl methacrylate layer_ZThe square of (A) and the cube of the particle size of the spherical particles (B)_Z ²/D_PB ³0.0002 to 0.1300 mu m^-1。

2. A rear projection screen according to claim 1, characterized in that the polymethyl methacrylate layer has an average surface roughness R_ZThe square of (A) and the cube of the particle size of the spherical particles (B)_Z ²/D_PB ³Is 0.0025-0.0600 μm^-1。

3. A rear projection screen according to claim 1 or 2, characterized in that the concentration c of the particles (B)_PBThickness d of light-scattering polymethyl methacrylate layer_SRatio of c_PB/d_SGreater than or equal to 2.5 wt%/mm.

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

5. A rear projection screen according to any one of the preceding claims, characterized in that the ratio c is_PA*d_S/D_PA ³0.0025-0.009 wt% mm/μm³。

6. A rear projection screen according to any one of the preceding claims, characterized in that the ratio c is_PB*d_S/D_PB ³Is 0.00004-0.0015 wt% mm/μm³。

7. A rear projection screen according to any one of the preceding claims, characterized in that the light-scattering polymethylmethacrylate layer of the rear projection screen has a thickness of 0.05 to 1 mm.

8. A rear-projection screen according to any one of the preceding claims, characterized in that the spherical scattering particles (a) and/or the spherical particles (B) of the rear-projection screen comprise crosslinked polystyrene, silicone polymers and/or crosslinked poly (meth) acrylates.

9. A rear projection screen according to any one of the preceding claims, characterized in that the light-scattering polymethylmethacrylate layer is coloured.

10. A rear projection screen according to any one of the preceding claims, characterized in that the matrix of the light-scattering polymethyl methacrylate layer has a refractive index, measured at sodium D-line (589nm) and at 20 ℃, of 1.46 to 1.54.

11. A rear projection screen according to any one of the preceding claims, characterized in that the average surface roughness R of the sheet material_ZIs 4-50 μm.

12. A rear-projection screen according to any one of the preceding claims, characterized in that the spherical particles (B) have an average particle size V₅₀Is at least 5 μm larger than the average particle size of the scattering particles (A).

13. Back according to any of the preceding claimsScreen, characterized in that the spherical scattering particles (A) have an average particle size V₅₀Is 5-20 μm.

14. A rear-projection screen according to any one of the preceding claims, characterized in that the spherical particles (B) have an average particle size V₅₀Is 15-60 μm.

15. A rear projection screen according to any one of the preceding claims, characterized in that scratches produced on the screen with a force of at most 0.7N are visually indistinguishable.

16. A rear projection screen according to any one of the preceding claims, characterized in that the screen additionally comprises a carrier layer having a half-value angle of strength of less than 6.5 °.

17. A rear projection screen according to claim 16, characterized in that the carrier layer has an average surface roughness R_ZIs 3-40 μm.

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

19. A rear-projection screen according to any one of the preceding claims, characterized in that the thickness of the rear-projection screen is 0.05-5 mm.

20. A rear projection screen according to any one of the preceding claims, characterized in that the transmission of the screen is greater than or equal to 25%.

21. A rear projection screen according to any one of the preceding claims, characterized in that the screen has a yellowness index of less than or equal to 12.

22. A rear projection screen according to any one of the preceding claims, characterized in that the intensity half-value angle of the screen is greater than or equal to 15 °.

23. A rear projection screen according to any one of the preceding claims, characterized in that the scattering power of the screen is greater than or equal to 0.15.

24. A rear projection screen according to any one of the preceding claims, characterized in that the screen consists of an extruded polymethylmethacrylate plastic having an optical path difference of at most 25nm due to optical birefringence.

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

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

27. Use of a rear projection screen according to any of claims 1 to 24 for optical technical applications.

28. Use according to claim 27 as a diffuser plate in an LCD monitor.

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