HK1073155B

HK1073155B - Rear projection screen and method for the production thereof

Info

Publication number: HK1073155B
Application number: HK05105786.2A
Authority: HK
Inventors: M．帕鲁塞尔; J.施米特; H．格鲁瑟斯; W．沙恩克; H．洛伦佐; H．哈林; G．迪克豪特-拜尔
Original assignee: Evonik Röhm Gmbh
Priority date: 2002-11-05
Filing date: 2003-09-27
Publication date: 2009-06-05

Description

Rear projection screen and method for producing the same

The invention relates to rear projection screens comprising at least one light-scattering polymethyl methacrylate layer and to a method for producing these rear projection screens.

Information is available to a large audience using rear projection technology. In principle, the structure of such a system consists of an image surface which is illuminated from behind by a projector and thus provides information.

This technique is used, for example, in control rooms (power stations, railroads) so that a person in charge can observe complex processes more easily, which can avoid control errors. Another use is for example a display board for stadiums and in motorcycle racing. Here, the spectators get information about the progress and things that have occurred, even if they are far from the event itself.

These image surfaces are very large. Other applications have increased over the past years through constant technological advances (projector technology).

Such information transfer is also used, for example, in TV equipment, large movie theaters and home theaters, and as an advertising medium at the time of exhibition, in window displays, and in shops.

The technology is also used for providing information during the presentation and for flight simulators, where the virtual environment is depicted on the cockpit screen in the case of a maximum reality simulation.

A source of many of the advantages of this technique is that the projector is outside the viewing space. This means that the projection is not obstructed by any observer located in front of the projection surface and disturbing noise from the projector is eliminated and the venue can be attractive designed.

There are various plastic sheets and foils used in rear projection technology. The sheeting is usually modified in such a way that they have a defined surface structure in the form of a fresnel lens system on the rear and a vertically aligned biconvex lens on the viewer side. These rear projection panels are therefore expensive to produce. The surface structure is also sensitive to mechanical loads. The result of the damage is a great impairment of the appearance of the projected image.

Rear projection sheets and foils comprising a scattering medium are also known, these sheets comprising particles having a refractive index different from the matrix. The sheets and foils are equally suitable for rear projection but neither of these meets all the requirements and therefore only some of the requirements for screens.

Due to the large number of different possible uses, there are various requirements for the projection surface. For example, in one scenario, the projection surface must provide, for example, very stable, transparent and high resolution image reproduction, since the viewer must then receive the information over a long period of time (e.g., control room, home theater, etc.).

If these projection surfaces are used for display and advertising purposes, for example on a display table, the surfaces must therefore be particularly resistant to mechanical loads and contamination, without the requirements for projection quality being too high.

For example, sheets and films that provide high light scattering angles can be made using known scattering media, such as barium sulfate and titanium dioxide. The projection resolution is equally high. The viewing angle of the image should likewise be correspondingly high. It has been found that even at low thicknesses, the image quality on the projection sheet is hazy and hazy, and that other requirements, such as good surface properties, cannot be or are only partially fulfilled or provided.

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 bead size is 3-30 μm and the examples only describe a sheet with a thickness of 2mm containing about 3% by weight of scattering beads whose size is about 6 μm. Light transmittance and surface gloss are described, but the imaging properties of the sheet are not ideal.

Japanese laid-open publication JP 07234304 describes mixtures of crosslinked acrylate-styrene beads (14 μm) in transparent plastics. The surface roughness is not described, but the sheets described in the examples are made by injection moulding and therefore very high pressures are applied to the sheets, which generally result in very low surface roughness. The sheet material made as in the examples did not have the desired imaging properties.

Publication EP- ｃA-0561551 describes ｃA multilayer sheet having ｃA scattering layer of ｃA mixture of transparent polymers and spherical particles ( 2-15 μm). The concentration of the particles is 0.1-40% by weight. In the examples, the multilayer sheet was made using a light scattering layer having a thickness of 0.64mm, the latter comprising 20% by weight of particles having a size of about 5 μm. Also, the sheet cannot provide a desired image.

A problem associated with known rear projection screens having a scattering medium is therefore that their imaging performance is not ideal. In particular, the known screens have a relatively low image sharpness or a relatively poor brightness distribution. There is also a problem in color accuracy. In addition, many screens do not adapt to mechanical requirements, wherein scratches especially produce adverse optical effects.

In view of the prior art described and discussed herein, it is therefore an object of the present invention to provide a rear projection screen which enables a particularly high image quality to be obtained. In particular, the screen should be able to obtain a projected image with high image definition and high resolution.

In addition, the image on the rear projection screen should have a special color accuracy.

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

In addition, the rear projection screen should have maximum mechanical stability. There should be no, or only a slight visible scratch on the screen. In particular, the impairment should have no or only a slight influence on the imaging capacity of the screen.

It is a further object of the invention to provide a rear projection screen which can be produced particularly simply. Therefore, rear projection screens should be able to be produced in particular by extrusion.

It is therefore a further object of the invention to obtain a rear projection screen with high image stability. This means that 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 whose size and shape can be easily adjusted as desired.

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

It is another object of the present invention to provide a rear projection screen having high durability, especially high resistance to UV radiation or to weathering.

It is another object of the present invention to provide a rear projection screen whose image performance is only slightly reflective.

In addition, the resulting rear projection screen should have low scratch sensitivity.

The rear projection screen described in claim 1 achieves these objects, as well as other objects which, although not specifically mentioned, are obvious or necessary results of the situation described herein. Useful variants of the rear projection screen of the invention are protected by the dependent claims depending on claim 1.

The following object is achieved in respect of a method for producing a rear projection screen as claimed in claim 18.

If the concentration c of spherical plastic particles_PThickness d of light-scattering polymethyl methacrylate layer_SAnd size D of spherical plastic particles_PIs selected such that the ratio c_P＊d_S/D_P ³Is 0.0015-0.015% by weight mm/mum³And the average surface roughness R of the polymethyl methacrylate layer_aWith size D of spherical plastic particles_PWherein the rear projection screen comprises at least one light-scattering polymethylmethacrylate layer having a thickness of 0.05 to 4mm, wherein spherical plastic particles having a size of 5 to 35 μm are contained in a concentration of 2 to 60% by weight, based on the total weight of the light-scattering polymethylmethacrylate layer, the refractive index of the spherical plastic particles differing from the refractive index of the polymethylmethacrylate matrix by a value of 0.02 to 0.2, a rear projection screen producing a particularly high image quality is provided.

The following special advantages are achieved in particular by the measures according to the invention:

the rear projection screen of the present invention produces a projected image of high image definition and high resolution.

The image on the rear projection screen of the invention has special color accuracy and particularly good contrast.

The rear projection screen provided according to the invention has a particularly uniform brightness distribution.

In addition, the rear projection screen has high mechanical stability. Scratches on the screen are here not visible or only slightly visible.

In addition, the image projected onto the rear projection screen of the present invention has high image stability. This means that the presented information can be observed over a long period of time without fatigue.

In addition, the rear projection screen of the present invention has a non-glossy, matte surface profile. If appropriate, the surface structure can be varied without affecting optical parameters other than gloss. This makes it possible to reduce the degree of reflection that adversely affects the image on the screen.

In addition, the rear projection screen of the present invention can be made particularly easily. For example, rear projection screens can be made, inter alia, by extrusion.

The rear projection sheet of the present invention has high resistance to weathering, especially 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 contains 2 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 plastic particles.

For the purposes of the present invention, the term spherical means that the plastic granules preferably have a spherical shape, but it is obvious to the person skilled in the art that, for reasons of the production method, plastic granules having some other shape may also be present, or that the shape of the plastic granules may deviate from the ideal spherical shape.

The term spherical thus means that the ratio of the largest dimension to the smallest dimension of the plastic particles, which is determined in each case by the center of gravity of the plastic particles, does not exceed 4, preferably 2. At least 70%, in particular at least 90%, based on the number of plastic particles, are preferably spherical.

The mean (weight-average) diameter of the plastic particles is from 5 to 35 μm, preferably from 8 to 25 μm. 75% of the plastic particles are advantageously 5-35 μm.

The particle size and particle size distribution can be determined using a laser extinction method. For this purpose, Galai-CIS-1 from L.O.T.GmbH can be used, wherein the measurement methods for particle size determination are found in the user manual.

The plastic granules which can be used according to the invention are not subject to any particular restrictions. The properties of the plastic used for producing the plastic particles are therefore essentially unimportant, wherein refraction of light takes place at the phase boundary between the plastic bead and the matrix plastic.

The refractive index of the plastic particles and the refractive index n of the matrix plastic, determined at 20 ℃ from the sodium D line (589nm), are therefore₀The difference is 0.02-0.2 units.

The spherical plastic particles preferably comprise crosslinked polystyrene and/or crosslinked poly (meth) acrylate.

Preferred plastic particles have a structure comprising:

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 the following 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 monomer having at least two ethylenically unsaturated groups copolymerizable via the free radical route with b1) and, if 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 used to produce 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 to the person skilled 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 very particularly preferably by organic-phase polymerization, as described, for example, in German patent application P4327464.1, wherein in the polymerization technique mentioned at the end a particularly narrow particle size distribution or, in other words, a particularly small deviation of the particle diameter from the average particle diameter is obtained.

It is particularly preferred to use plastic particles whose heat resistance is at least 200 c, in particular at least 250 c, without being restricted thereby. The term heat resistance herein means that the particles do not undergo any significant thermal degradation. Thermal degradation causes undesirable discoloration, rendering the plastic material unusable. Particularly preferred particles are especially under the trade nameTechpolymer SBX-6，Techpolymer SBX-8 andtechpolymer SBX-12 was obtained from Sekisui.

In another preferred embodiment of the invention, the spherical plastic particles have a size of 15 to 35 μm. In this embodiment, it is particularly preferred for at least 60% of the spherical plastic particles to have a diameter of at least 15 μm and for at most 30% of the spherical plastic particles (used as scattering beads) to have a diameter of more than 22 μm, preferably more than 25 μm. According to a particular aspect, up to 80% of these spherical plastic particles have a size of 15-25 μm.

In a particular aspect of the invention, the particles have a uniform distribution in the plastic matrix without significant agglomeration or aggregation of the particles. By uniformly distributed is meant that the concentration of particles is substantially constant within the plastic matrix.

The light scattering layer comprises not only spherical particles but also a plastic matrix comprising polymethyl methacrylate (PMMA). The light-scattering polymethylmethacrylate layer preferably comprises at least 30% by weight of polymethylmethacrylate, based on the weight of the light-scattering layer.

Polymethyl methacrylate is generally obtained by free-radical polymerization of a mixture comprising methyl methacrylate. These mixtures generally comprise 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.

Furthermore, these mixtures for preparing polymethyl methacrylates may comprise further (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) acrylic esters derived from unsaturated alcohols, such as oleyl (meth) acrylate, 2-propynyl (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate;

aryl (meth) acrylates, such as benzyl (meth) acrylate or phenyl (meth) acrylate, where the aryl groups may in each case be unsubstituted or have up to four 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, such as 1, 4-butane diol (meth) acrylate,

(meth) acrylic esters of ether alcohols such as tetrahydrofurfuryl (meth) acrylate, vinyloxyethoxyethoxyethyl (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-thiocyanato butyl (meth) acrylate,

ethyl sulfonyl ethyl (meth) acrylate,

thiocyanato methyl (meth) acrylate,

methyl methylsulfinylmethyl (meth) acrylate,

bis ((meth) acryloyloxyethyl) sulfide;

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

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

They include, in particular, 1-olefins, such as 1-hexene, 1-heptene; branched olefins, such as vinylcyclohexane, 3, 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, such as 2-vinylpyridine, 3-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine, 2, 3-dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine, 9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole, 1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone, 2-vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine, N-vinylcaprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran, vinylthiophene, vinylthiolane, vinyl thiazoles and hydrogenated vinyl thiazoles, vinyl oxazoles and hydrogenated vinyl oxazoles;

vinyl and isopentenyl ethers;

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

These 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, where these compounds can be used individually or in the form of mixtures.

The polymerization is generally initiated using known free radical initiators. Preferred initiators are, in particular, azo initiators which are known to the person skilled in the art, such as AIBN and 1, 1-azobiscyclohexanecarbonitrile, and also peroxy compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauroyl peroxide, tert-butyl 2-ethylperoxyhexanoate, ketone peroxide, methyl isobutyl ketone peroxide, cyclohexanone peroxide, benzoyl peroxide, tert-butyl perbenzoate, tert-butylperoxyisopropyl carbonate, tert-butyl 2, 5-bis (2-ethylhexanoylperoxy) -2, 5-dimethylhexane, tert-butyl 2-ethylperoxyhexanoate, tert-butyl 3, 5, 5-trimethylperoxyhexanoate, 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 also mixtures of the abovementioned compounds with compounds which are not mentioned but 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.

Various poly (meth) acrylates which differ, for example, in their molecular weight or in their monomer composition can be used here.

The matrix of the light scattering layer may additionally comprise other polymers to modify its properties. Among these are, inter alia, polyacrylonitrile, polystyrene, polyethers, polyesters, polycarbonates and polyvinyl chloride. These polymers may be used individually or in the form of mixtures, where copolymers which can be derived from the abovementioned polymers may also be used here.

The weight-average molecular weight Mw of the homo-and/or copolymers used according to the invention as matrix polymers can vary within wide limits, the molecular weight generally being adapted to the intended use and to the mode of processing of the molding compositions. However, it is generally 20000 to 1000000g/mol, preferably 50000 to 500000g/mol and particularly preferably 80000 to 300000g/mol, without being restricted thereto.

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

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

The moulding compositions used for the production of the light-scattering layer may comprise any type of conventional additives. Among these are, inter alia, 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. But the amount of additive is limited according to the intended use. For example, the light scattering properties of the polymethyl methacrylate layer and its transparency should not be unduly impaired by the additives.

In a particular aspect of the invention, the molding compositions, if appropriate, can be given greater mechanical stability by means of impact modifiers. These impact modifiers for polymethacrylate plastics are known for a long time, and EP-A0113924, EP-A0522351, EP-A0465049 and EP-A0683028 describe, inter alia, the preparation and construction of impact-modified polymethacrylate molding compositions.

Preferred impact-resistant molding compositions useful for preparing the matrix comprise from 70 to 99% by weight of polymethyl methacrylate. These polymethyl methacrylates have already been described above.

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

The polymethyl methacrylates which can be used for the preparation of the impact-modified substrates preferably have an average molecular weight Mw of 90000 to 200000g/mol, in particular 100000 to 150000 g/mol.

Preferred impact-resistant molding compositions which can be used for preparing the matrix comprise from 1 to 30% by weight, preferably from 2 to 20% by weight, particularly preferably from 3 to 15% by weight, in particular from 5 to 12% by weight, of an impact modifier, which is an elastomeric phase composed of crosslinked polymer particles.

Preferred impact-resistant 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 an impact modifier, which is an elastomeric phase composed 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 whose average particle size is from 50 to 1000nm, preferably from 60 to 500nm and particularly preferably from 80 to 120 nm.

For example, these particles can be obtained by radical polymerization of a mixture generally comprising 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, such as a polyfunctional (meth) acrylate, for example allyl methacrylate, and a comonomer copolymerizable with the vinyl compounds mentioned above.

Preferred comonomers are, in particular, (meth) acrylic acid C₁-C₄Alkyl esters, such as ethyl acrylate or butyl methacrylate, preferably methyl acrylate, or other vinyl-polymerizable monomers, such as styrene. The mixture used for producing the above-mentioned particles may preferably comprise 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 two-layer, particularly preferably three-layer core-shell structure. These 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% by weight, 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 first shell.

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

The core as well as the shell may comprise not only the monomers mentioned but also further monomers. These substances have already been mentioned previously, with particularly preferred comonomers having a crosslinking action.

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

and (3) nucleus: copolymer consisting of methyl methacrylate (95.7% by weight), ethyl acrylate (4% by weight) and allyl methacrylate (0.3% by weight)

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

S2: a copolymer consisting of methyl methacrylate (96% by weight) and ethyl acrylate (4% by weight).

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

The particle size of the core-shell modifier is generally from 50 to 1000nm, preferably from 100 to 500nm and particularly preferably from 150 to 450nm, without this being intended to be limiting.

Such impact modifiers may be available under the trade name METABLENIR 441 was purchased from Mitsubishi. Impact-modified molding compositions are also obtainable.

Particularly preferred molding compositions for the preparation of plastic substrates are available fromGmbH& Co.KG。

The thickness of the light-scattering polymethyl methacrylate layer is generally 0.05 to 4 mm.

According to the invention, the concentration c of the spherical particles_PThickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical particles_PThe concentration c of the spherical particles is selected such that_PAnd the ratio c of the product of the thickness of the light-scattering polymethyl methacrylate layer and the third power of the particle size of the spherical particles_P＊d_S/D_P ³Is 0.0015-0.015% by weight mm/mum³Preferably 0.0025 to 0.009% by weight mm/. mu.m³。

Average surface roughness R of polymethyl methacrylate layer_aParticle size D with spherical particles_PThe ratio of (A) is 0.05 to 0.4, in particular 0.05 to 0.3 and preferably 0.06 to 0.2.

According to a particular embodiment of the screen according to the invention, the concentration c of spherical particles_PThickness d of light-scattering polymethyl methacrylate layer_SRatio c of_P/d_SGreater than or equal to 2.5% weight/mm, in particular greater than or equal to 4% weight/mm.

Gloss R of light-scattering polymethyl methacrylate layer₈₅Preferably less than or equal to 60, especially less than or equal to 50.

Thickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical particles_PRatio d of_S/D_PPreferably from 5 to 1500, in particular from 5 to 500, preferably from 5 to 250, particularly preferably from 5 to 150 and from 10 to 300, without this being intended to be limiting.

According to a particular embodiment of the invention, the average surface of the sheet is roughRoughness R_aPreferably from 0.4 to 6 μm, in particular from 0.4 to 2 μm, preferably from 0.5 to 1.5 μm, in particular from 0.8 to 5 μm, particularly preferably from 1 to 3.5. mu.m.

In this range, the visibility of scratches on the surface of the light scattering layer is limited to a particularly low level. This susceptibility to scratching can be determined by visual evaluation of the damaged surface according to DIN 53799 and DIN EN438, where damage is caused by the diamond acting on the surface with varying forces.

Surface roughness R of sheet_aCan be influenced by variations in various parameters depending on the production process. Among these are, in particular, the temperature of the melt during the extrusion process, wherein rougher surfaces result from the higher melt temperature. One factor that must be taken into account here is, however, that the temperature of the melt depends on the exact composition of the molding composition. The temperature of the melt is generally from 150 to 300 ℃ and preferably from 200 to 290 ℃. These temperatures are 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. For example, if the polishing group comprises three rolls arranged in L, wherein the molding composition is guided by a die to the gap between roll 1 and roll 2 and wound around roll 2 at 60-180, the gap between roll 2 and roll 3 thus polishes the surface. If the gap between the rollers 2 and 3 is adjusted to the thickness of the sheet, scattering particles on the surface of the sheet are pressed into the matrix, so that the surface becomes brighter. In order to achieve a rougher surface, the gap is generally adjusted to be slightly greater than the thickness of the sheet to be produced, wherein the corresponding value exceeds the thickness of the sheet by 0.1 to 2mm, preferably by 0.1 to 1.5mm, without this being limitative. The surface roughness is also influenced by the particle size and the thickness of the sheet, wherein these dependencies are given in the examples.

The light scattering layer can be produced by known processes, with a thermoplastic molding process being preferred. Once the particles have been added, the light-scattering layer can be produced from the molding compositions described above by means of conventional thermoplastic shaping processes.

According to a particular embodiment, the twin-screw extruder is used in an extrusion process or for producing pellets of a molding composition comprising scattering beads. In these processes, the plastic granules are preferably converted into a melt in an extruder. This makes it possible to obtain a screen whose transparency is particularly high from the melt obtained.

The rear projection screen can be produced here by a two-step process, in which the extrusion of the foil or sheet in a single-screw extruder takes place downstream of the inventive side-feeder compounding process and intermediate pelletization in a twin-screw extruder. The pellets obtained by means of the twin-screw extruder can have a particularly high proportion of scattering beads, so that projection screens having varying levels of scattering beads can be produced simply by blending with molding compositions without scattering beads.

It is also possible to carry out a single-stage process in which the spherical plastic granules are compounded to a melt as described in a twin-screw extruder which, if appropriate downstream, has a pressure-increasing unit (e.g.melt pump) immediately before the extrusion die for extruding the sheet product. The above measures surprisingly result in a rear projection screen with a particularly low yellowness index.

The screen may alternatively be made by injection moulding, but wherein the process parameters or the injection mould are selected such that a surface roughness within the scope of the invention is obtained.

The compounding of the matrix with the scattering particles is preferably carried out by means of a twin-screw extruder, wherein a single-screw extruder can also be used for the actual sheet extrusion, without this being limitative.

Depending on the nature of the application, the light scattering polymethylmethacrylate layer may be used as a screen. The thinner layer can be used here in the form of a rollable foil. Particularly preferred foils are impact resistant by the above method.

A thin light scattering polymethylmethacrylate layer may additionally be applied onto the plastic sheet, which increases its mechanical stability. The plastic sheet is generally free of spherical particles. The plastic sheet preferably comprises a polyacrylic acid polymer.

According to a particular aspect of the invention, the screen has a light transmission greater than or equal to 25%, in particular greater than or equal to 40% and particularly preferably greater than or equal to 55%.

According to a particular aspect of the invention, the molding compositions can be colored. This measure surprisingly enables an improvement of the contrast. Particularly suitable materials for the coloring process are dyes and/or carbon black known per se. Particularly preferred dyes are commercially available. Among which are from Clariant respectivelySandoplast Red G andsandoplast Yellow 2G, and from Bayer, respectivelyMacroplex Green 5B andmacroplex Violet 3R. The concentration of these dyes depends on the desired perceived color, as well as on the thickness of the sheet. Without being restricted thereto, 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 pigmented molding composition without scattering beads. 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 pigmented molding composition without scattering beads. The loss of light transmission can be compensated, at least to some extent, by a more powerful projector.

The yellowness index of the screen is preferably less than or equal to 12, in particular less than or equal to 10, without this being limitative.

A particular embodiment of the screen according to the invention has a half-intensity angle greater than or equal to 15 °, in particular greater than or equal to 25 °.

According to a particular aspect of the 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 limitative.

According to a preferred embodiment, the surface of the polymethylmethacrylate sheet of the invention has a matt appearance under reflected light. Gloss measurements using a reflectometer to DIN 67530 can be used for characterization. The gloss of the sheet at an angle of 85 ° is preferably less than 50, 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. But the screen usually has the shape of a rectangular plate because the image is usually presented in this form.

The length of such rear projection screens is preferably from 25 to 10000mm, with 50 to 3000mm being preferred and 200 to 2000mm being particularly preferred. The width of this particular embodiment is generally from 25 to 10000mm, preferably from 50 to 3000mm and particularly preferably from 200 to 2000 mm. Two or more of these screens can be combined together to provide a particularly large projection surface.

According to a particular embodiment, the screen has a particularly high resistance to weathering, in accordance with DIN EN ISO4892, part 2-method of exposure to a laboratory light source, xenon arc source.

The following examples and comparative examples are intended to describe the invention in more detail, but the invention is not intended to be limited to these examples.

A) Test method

Average roughness R_aDetermined according to DIN 4768 using a Talysurf 50 test apparatus from Taylor Hobson.

Transmittance of light_D65/2Determined according to DIN 5036 using a Lambda 19 test apparatus from Perkin Elmer.

Yellowing index_D65/10Measured according to DIN 6167 using a Lambda 19 test apparatus from Perkin Elmer.

R85 ° gloss was determined at 85 ° according to DIN 67530 using a laboratory reflectometer from dr. lange.

The scattering power and the half-intensity angle were determined in accordance with DIN 5036 using the GO-T-1500LMT goniometer test unit of LMT.

The various rear projection screens were additionally visually evaluated on the basis of the criteria shown in table 1.

The projector used here is Epson EMP-713. The test images were evaluated at various angles (0 ° -normal to the projection, 30 ° and 60 °) at a distance of about 1-1.5m from the image. The distance from the projector to the projection sheet was about 85cm and the image slope was about 50 cm.

Technical data for the Epson EMP 713 projector:

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

TABLE 1

Standard of merit	Performance of
Standard of merit	Performance of	Hot spot	The hot spot is the light distribution associated with the conical beam of the projection illumination system. The hot spot is thus a conical beam of light having a substantially greater intensity in the center of the image than at the edges. If the hot spot is very noticeable, the projector light can be visually detected.
Distribution of brightness	The brightness distribution is likewise evaluated by the distribution of light over the image surface and thus characterizes the extent to which the illumination of the image extends from the center to the edges.	Hot spot
Distribution of brightness		Image sharpness	Image sharpness is the degree to which the test image is clearly perceived.
Resolution ratio	The resolution of the image indicates the degree to which the fine structure is distorted on the evaluated sheet.	Image sharpness
Resolution ratio		Image stabilization	Image stability is the degree to which the viewer can accept projected information over a long period of time without eye strain.

In the table, very good performance is represented by ++, good performance is represented by +, satisfactory performance is represented by 0, unsatisfactory performance is represented by-, - -very unsatisfactory performance is represented by-and unsuitable performance is represented by-.

B) Preparation of plastic granules

For the preparation of spherical plastic particles, an aluminum hydroxide Pickering stabilizer prepared by precipitation from aluminum sulfate and sodium carbonate solution just before the start of the actual polymerization reaction was used. For this purpose, 16g of Al₂(SO₄)₃0.032g of complexing agent (Trilon A) and 0.16g of emulsifier (emulsifier K30, available from Bayer AG; C)₁₅Sodium salt of paraffin sulfonate) was first 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 c, resulting in a pH of 5-5.5. This procedure results in a colloidal dispersion of the stabilizer in water.

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

After such shearing, the reaction mixture was charged into a reactor which had been preheated to a suitable reaction temperature of 80 ℃ and polymerized under stirring (600rpm) at about 80 ℃ (polymerization temperature) for 45 minutes (polymerization time). The post-reaction phase was then carried out at a temperature of about 85 ℃ for 1 hour. After cooling to 45 ℃, the stabilizer is converted into water-soluble aluminum sulfate by adding 50% strength sulfuric acid. The beads were processed by filtering the resulting suspension through a commercial textile filter and drying in a heating cabinet at 50 ℃ for 24 hours.

The size distribution was studied by the laser extinction method. Average size V of the particles₅₀It was 19.66. mu.m. The beads had a spherical shape and no fibers were detected. No agglomeration occurred. The resulting granules are referred to below as plastic granules A.

C) Inventive examples 1-6 and comparative examples 1-3

Various rear projection screens are made by extrusion. For this purpose, various scattering bead compounds are first prepared from plastic particles A and those available fromGmbH &KG PMMA moulding composition (copolymer of 97% by weight of methyl methacrylate and 3% by weight of methyl acrylate) on ZSK 30Werner&In a Pfleiderer twin-screw extruder, using a side feeder technique (i.e. feeding directly into the melt downstream of the venting zone). The resulting pellets form the basis for the subsequent production of the plastic sheets described in the examples. From this concentrate, various blends were subjected to an extrusion process in a subsequent treatment, resulting in varying contents of the scattering particles.Using BREYERA mm extruder. The temperature of the melt as it exits the die was typically 270 c, but the die exit temperature was 260 c in comparative example 2. The polishing set is generally adjusted, particularly in embodiments, such that maximum surface roughness is achieved.

The proportion of plastic particles in the polymethyl methacrylate matrix and the thickness of the sheet are given in table 2. The test results obtained by the above method are given in tables 3, 4, 5 and 6.

D) Inventive examples 7 to 14 and comparative examples 4 to 6

The production process described in inventive examples 1 to 6 was substantially repeated, but extrusion from SekisuiTechpolymer SBX-8 and is obtainable fromGmbH &Kg (co) to give a plastic sheet.

The proportion of plastic particles in the polymethyl methacrylate and the thickness of the sheet are given in table 2. The test results obtained by the above method are given in tables 3, 4, 5 and 6.

TABLE 2

	Size of the Plastic particles [ mu ] m]	Thickness of sheet [ mm ]]	Content [% by weight]
	Size of the Plastic particles [ mu ] m]	Thickness of sheet [ mm ]]	Content [% by weight]	Comparative example 1	20	3	6
Inventive example 1	20	3	12	Comparative example 1	20	3	6
Inventive example 1	20	3	12	Inventive example 2	20	3	24
Comparative example 2	20	1	12	Inventive example 2	20	3	24
Comparative example 2	20	1	12	Inventive example 3	20	1	24
Inventive example 4	20	0.5	24	Inventive example 3	20	1	24
Inventive example 4	20	0.5	24	Inventive example 5	20	0.5	48
Comparative example 3	20	0.25	24	Inventive example 5	20	0.5	48
Comparative example 3	20	0.25	24	Inventive example 6	20	0.25	48
Comparative example 4	8	3	1	Inventive example 6	20	0.25	48
Comparative example 4	8	3	1	Comparative example 5	8	3	3
Comparative example 6	8	1	1	Comparative example 5	8	3	3
Comparative example 6	8	1	1	Inventive example 7	8	1	3
Inventive example 8	8	1	6	Inventive example 7	8	1	3
Inventive example 8	8	1	6	Inventive example 9	8	0.5	3
Inventive example 10	8	0.5	6	Inventive example 9	8	0.5	3
Inventive example 10	8	0.5	6	Inventive example 11	8	0.5	12
Inventive example 12	8	0.25	6	Inventive example 11	8	0.5	12
Inventive example 12	8	0.25	6	Inventive example 13	8	0.25	12
Inventive example 14	8	0.25	24	Inventive example 13	8	0.25	12

TABLE 3

	c＊d/DMm/mum [% by weight]	R[μm]	R/D
	c＊d/DMm/mum [% by weight]	R[μm]	R/D	Comparative example 1	0.00225	0.9	0.045
Inventive example 1	0.0045	1.5	0.075	Comparative example 1	0.00225	0.9	0.045
Inventive example 1	0.0045	1.5	0.075	Inventive example 2	0.009	2.5	0.125
Comparative example 2	0.0015	0.8	0.04	Inventive example 2	0.009	2.5	0.125
Comparative example 2	0.0015	0.8	0.04	Inventive example 3	0.003	2.5	0.125
Inventive example 4	0.0015	3.2	0.16	Inventive example 3	0.003	2.5	0.125
Inventive example 4	0.0015	3.2	0.16	Inventive example 5	0.003	4.9	0.245
Comparative example 3	0.00075	4.8	0.24	Inventive example 5	0.003	4.9	0.245
Comparative example 3	0.00075	4.8	0.24	Inventive example 6	0.0015	6.6	0.33
Comparative example 4	0.00586	0.24	0.03	Inventive example 6	0.0015	6.6	0.33
Comparative example 4	0.00586	0.24	0.03	Comparative example 5	0.01758	0.29	0.03625
Comparative example 6	0.00195	0.18	0.0225	Comparative example 5	0.01758	0.29	0.03625
Comparative example 6	0.00195	0.18	0.0225	Inventive example 7	0.00586	0.4	0.05
Inventive example 8	0.01172	0.62	0.0775	Inventive example 7	0.00586	0.4	0.05
Inventive example 8	0.01172	0.62	0.0775	Inventive example 9	0.00293	0.48	0.06
Inventive example 10	0.00586	0.66	0.0825	Inventive example 9	0.00293	0.48	0.06
Inventive example 10	0.00586	0.66	0.0825	Inventive example 11	0.01172	0.81	0.10125
Inventive example 12	0.00293	0.8	0.1	Inventive example 11	0.01172	0.81	0.10125
Inventive example 12	0.00293	0.8	0.1	Inventive example 13	0.00586	1.07	0.13375
Inventive example 14	0.01172	1.48	0.185	Inventive example 13	0.00586	1.07	0.13375

TABLE 4

	Transmittance [% ]]	Yellowness index YI (°)	Scattering force
	Transmittance [% ]]	Yellowness index YI (°)	Scattering force	Comparative example 1	90.75	3.16	0.25
Inventive example 1	75.22	9.16	0.48	Comparative example 1	90.75	3.16	0.25
Inventive example 1	75.22	9.16	0.48	Inventive example 2	60.62	10.74	0.65
Comparative example 2	93.78	0.81	0.16	Inventive example 2	60.62	10.74	0.65
Comparative example 2	93.78	0.81	0.16	Inventive example 3	86.73	3.81	0.35
Inventive example 4	88.81	1.64	0.26	Inventive example 3	86.73	3.81	0.35
Inventive example 4	88.81	1.64	0.26	Inventive example 5	78.42	3.18	0.41
Comparative example 3	88.33	0.32	0.19	Inventive example 5	78.42	3.18	0.41
Comparative example 3	88.33	0.32	0.19	Inventive example 6	78.04	0.99	0.20
Comparative example 4	60.71	6.75	0.63	Inventive example 6	78.04	0.99	0.20
Comparative example 4	60.71	6.75	0.63	Comparative example 5	47.72	5.35	0.88
Comparative example 6	88.65	2.35	0.11	Comparative example 5	47.72	5.35	0.88
Comparative example 6	88.65	2.35	0.11	Inventive example 7	69.05	5.82	0.62
Inventive example 8	58.06	6.55	0.84	Inventive example 7	69.05	5.82	0.62
Inventive example 8	58.06	6.55	0.84	Inventive example 9	82.04	3.73	0.35
Inventive example 10	71.62	5.35	0.61	Inventive example 9	82.04	3.73	0.35
Inventive example 10	71.62	5.35	0.61	Inventive example 11	61.82	6.05	0.81
Inventive example 12	83.64	3.43	0.31	Inventive example 11	61.82	6.05	0.81
Inventive example 12	83.64	3.43	0.31	Inventive example 13	73.52	5.17	0.56
Inventive example 14	61.33	6.04	0.82	Inventive example 13	73.52	5.17	0.56

TABLE 5

	RGloss measurement	Hot spot	Distribution of brightness
	RGloss measurement	Hot spot	Distribution of brightness	Comparative example 1	35.0	-	-
Inventive example 1	8.6	+	+	Comparative example 1	35.0	-	-
Inventive example 1	8.6	+	+	Inventive example 2	2.3	++	++
Comparative example 2	10.1	-	-	Inventive example 2	2.3	++	++
Comparative example 2	10.1	-	-	Inventive example 3	1.6	0	0
Inventive example 4	1.3	0	0	Inventive example 3	1.6	0	0
Inventive example 4	1.3	0	0	Inventive example 5	0.5	++	+
Comparative example 3	0.9	---	---	Inventive example 5	0.5	++	+
Comparative example 3	0.9	---	---	Inventive example 6	0.3	0	0
Comparative example 4	84.7	++	++	Inventive example 6	0.3	0	0
Comparative example 4	84.7	++	++	Comparative example 5	77.2	++	++
Comparative example 6	86.9	---	---	Comparative example 5	77.2	++	++
Comparative example 6	86.9	---	---	Inventive example 7	47.2	++	+
Inventive example 8	29.4	++	++	Inventive example 7	47.2	++	+
Inventive example 8	29.4	++	++	Inventive example 9	55.1	+	+
Inventive example 10	36.9	++	++	Inventive example 9	55.1	+	+
Inventive example 10	36.9	++	++	Inventive example 11	26.4	++	++
Inventive example 12	17.6	0	0	Inventive example 11	26.4	++	++
Inventive example 12	17.6	0	0	Inventive example 13	7.3	++	+
Inventive example 14	2.1	++	+	Inventive example 13	7.3	++	+

TABLE 6

	Image sharpness	Resolution ratio	Image stabilization
	Image sharpness	Resolution ratio	Image stabilization	Comparative example 1	+	Thin and thin	+
Inventive example 1	+	Thin and thin	+	Comparative example 1	+	Thin and thin	+
Inventive example 1	+	Thin and thin	+	Inventive example 2	0	Thin and thin	+
Comparative example 2	+	Thin and thin	-	Inventive example 2	0	Thin and thin	+
Comparative example 2	+	Thin and thin	-	The inventionExample 3	+	Thin and thin	0
Inventive example 4	+	Thin and thin	0	The inventionExample 3	+	Thin and thin	0
Inventive example 4	+	Thin and thin	0	Inventive example 5	+	Thin and thin	+
Comparative example 3	0	Thin and thin	-	Inventive example 5	+	Thin and thin	+
Comparative example 3	0	Thin and thin	-	Inventive example 6	0	Thin and thin	-
Comparative example 4	-	Thin and thin	+	Inventive example 6	0	Thin and thin	-
Comparative example 4	-	Thin and thin	+	Comparative example 5	--	Thin and thin	-
Comparative example 6	++	Is very thin	-	Comparative example 5	--	Thin and thin	-
Comparative example 6	++	Is very thin	-	Inventive example 7	+	Is very thin	+
Inventive example 8	0	Thin and thin	+	Inventive example 7	+	Is very thin	+
Inventive example 8	0	Thin and thin	+	Inventive example 9	++	Is very thin	+
Inventive example 10	++	Is very thin	+	Inventive example 9	++	Is very thin	+
Inventive example 10	++	Is very thin	+	Inventive example 11	0	Thin and thin	+
Inventive example 12	++	Is very thin	+	Inventive example 11	0	Thin and thin	+
Inventive example 12	++	Is very thin	+	Inventive example 13	++	Is very thin	+
Inventive example 14	0	Thin and thin	+	Inventive example 13	++	Is very thin	+

Examples of optical scratch sensitivity measurements

The rear projection screens made in inventive examples 1, 4, 5, 6 and 11 were used to study the visual sensitivity of the extrudates to scratching.

Scratch sensitivity through the penetration depth t of the diamond_RF (load), measured using a taber industries model 203 scratch tester, based on DIN 53799 and DIN EN 438: diamond gouge with a cone angle of 90 deg., peak radius 90 μm, direction of rotation counter clockwise. The loads used are given in table 7.

The black substrate was used for visual evaluation (reflection test). The tests (roughness, gloss) were carried out on top of the test extrudates.

The results obtained are listed in table 7.

TABLE 7

Load on diamond	Inventive example 1	Inventive example 4	Inventive example 5
Load on diamond	Inventive example 1	Inventive example 4	Inventive example 5	0.4N	No discernible damage	No discernible damage	Discernible impairment (extra reflection, angle dependence)
0.7N	No discernible damage	Hardly any discernible damage (extra reflection, high angle dependence)	Discernible impairment (extra reflection, angle dependence)	0.4N	No discernible damage	No discernible damage	Discernible impairment (extra reflection, angle dependence)
0.7N	No discernible damage		Discernible impairment (extra reflection, angle dependence)	1.0N	No discernible damage	Hardly any discernible damage (extra reflection, angle dependence)	Discernible impairment (extra reflection, angle dependence)
1.5N	Slightly discernible impairment (extra reflection, highly angle-dependent)	Slightly discernible impairment (extra reflex, dependence on the base of the corner)	Discernible impairment (extra reflection, angle dependence)	1.0N	No discernible damage		Discernible impairment (extra reflection, angle dependence)
1.5N			Discernible impairment (extra reflection, angle dependence)	2.0N	Slightly discernible impairment (extra reflection, highly angle-dependent)	Discernible lesions	Discernible lesions

Table 7 (continue)

Load on diamond	Inventive example 6	Inventive example 1
Load on diamond	Inventive example 6	Inventive example 1	0.4N	Discernible impairment (extra reflection, angle dependence)	No discernible damage
0.7N	Discernible impairment (extra reflection, angle dependence)	Hardly any discernible damage (extra reflection, highly angle-dependent)	0.4N	Discernible impairment (extra reflection, angle dependence)	No discernible damage
0.7N	Discernible impairment (extra reflection, angle dependence)		1.0N	Discernible impairment (extra reflection, angle dependence)	Slightly discernible impairment (extra reflection, angle dependence)
1.5N	Discernible lesions	Slightly discernible Damage (Extra inverse)Dependence of beam on angle)	1.0N	Discernible impairment (extra reflection, angle dependence)
1.5N	Discernible lesions		2.0N	Discernible lesions	Discernible lesions

The examples according to the invention and the comparative examples clearly show a narrow range of relative surface roughness R_a/D_PAnd the ratio c_P＊d_S/D_P ³The combination of (a) and (b) provides a rear projection screen of desired image quality.

The embodiment in which the particles are introduced directly into the melt can be successfully used to produce pellets or moldings comprising a second component, such as plastic particles (side-feeder process). The technique is therefore not limited to the invention.

The side-feeder process is characterized in that the molding composition to be compounded is not fed simultaneously through the feed zone, but only the base component is passed through the feed zone, while the second component is fed into the melt after the base molding composition has been melted. The melt is subsequently homogenized by means of mixing and shearing sections whose alignment-and hence mode of action-matches the mixing material.

The homogenized melt is then processed under water by strand granulation or die face granulation to give uniform sized pellets (see fig. 1).

Figure 1 gives a diagram of compounding by means of a twin-screw extruder (side-feeder technique). Reference numerals in fig. 1 denote:

1. introduction of the moulding composition via the introduction zone

2. Melt molding compositions (e.g. obtainable from)GmbH &PMMA of Co.KG)

3. Adding a scattering agent (e.g., Techpolymer SBX8) to the thermoplastic melt

4. Homogeneous melt of scattering beads in a molding composition

5. Extrudates, e.g. master batches (uniform-sized pellets) with a concentration of 48% of scattering beads in the moulding compositions

The DF molding compositions were used as starting materials in the second stage for the production of various products, in which the second component was only slightly degraded. This can result in significant advantages. In the case of beads, low levels of products such as light scattering or light guide sheet discoloration (yellowness index) and high light transmittance are included.

According to a particular embodiment, a twin-screw extruder is used for the compounding process.

The side feeder process also gave equally good results for compounding processes using a single screw extruder designed specifically for handling powders, and using side feeder technology.

Claims

1. Rear projection screen comprising at least one light-scattering polymethylmethacrylate layer with a thickness of 0.05 to 4mm, which layer comprises 2 to 60% by weight, based on the total weight of the light-scattering polymethylmethacrylate layer, of spherical plastic particles with a particle size of 5 to 35 μm, wherein the refractive index of the spherical plastic particles differs from the refractive index of the polymethylmethacrylate matrix by a value of 0.02 to 0.2, characterized in that the concentration c of the spherical plastic particles is selected_PThickness d of light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical plastic particles_PSo that the ratio c_P＊d_S/D_P ³Is 0.0015-0.015% by weight mm/mum³And the average surface roughness R of the polymethyl methacrylate layer_aParticle size D of spherical plastic particles_pThe ratio of (A) is 0.05-0.4.

2. Rear projection screen according to claim 1, characterized in that the concentration c of spherical plastic particles_PThickness d of light-scattering polymethyl methacrylate layer_SRatio c of_P/d_SGreater than or equal to 2.5% weight/mm.

3. Rear projection screen according to claim 1 or 2, characterized in that the gloss R of the light-scattering polymethyl methacrylate layer_85°Less than or equal to 60.

4. Rear projection screen according to claim 1 or 2, characterized in that the ratio c_P＊d_S/D_P ³Is 0.0025 to 0.009 wt.% mm/mum³。

5. Rear projection screen according to claim 1 or 2, characterized in that the thickness d of the light-scattering polymethyl methacrylate layer_SAnd the particle size D of the spherical plastic particles_PIs 5-500.

6. Rear projection screen according to claim 1 or 2, characterized in that the spherical plastic particles comprise crosslinked polystyrene and/or crosslinked poly (meth) acrylate.

7. Rear projection screen according to claim 1 or 2, characterized in that the light-scattering polymethylmethacrylate layer has been coloured.

8. Rear projection screen according to claim 1 or 2, characterized in that the matrix of the light-scattering polymethylmethacrylate layer has a refractive index of 1.46 to 1.54 measured at the sodium D-line at a wavelength of 589nm and at 20 ℃.

9. Rear projection screen according to claim 1 or 2, characterized in that the average surface roughness R of the sheet material_aIs 0.4 to 6 μm.

10. Rear projection screen according to claim 1 or 2, characterized in that the spherical plastic particles have a size of 15-35 μm.

11. Rear projection screen according to claim 1 or 2, characterized in that at least 60% of the spherical plastic particles have a diameter of at least 15 μm and at most 30% of the spherical plastic particles have a diameter of more than 22 μm.

12. Rear projection screen according to claim 1 or 2, characterized in that the screen further comprises a plastic sheet which does not comprise scattering beads.

13. The rear projection screen according to claim 12, characterized in that the plastic sheet comprises a polyacrylic polymer.

14. Rear projection screen according to claim 1 or 2, characterized in that the screen has a transmittance of greater than or equal to 25%.

15. Rear projection screen according to claim 1 or 2, characterized in that the screen has a yellowness index of less than or equal to 12.

16. Rear projection screen according to claim 1 or 2, characterized in that the screen has a half-intensity angle greater than or equal to 15 °.

17. Rear projection screen according to claim 1 or 2, characterized in that the screen has a scattering power of greater than or equal to 0.15.

18. Process for producing a rear projection screen according to any one of claims 1 to 17, characterized in that the molding composition is extruded.

19. The process as claimed in claim 18, characterized in that a twin-screw extruder with a side-feeding device is used for the intact introduction of the spherical plastic particles into the molding composition.

20. Use of spherical plastic particles having a size of 5-35 μm for the production of a rear projection screen according to any of claims 1-17.