U.S. patent application number 10/495428 was filed with the patent office on 2004-12-23 for rear projection screen and method for the production thereof.
Invention is credited to Dickhaut-Bayer, Guenther, Groothues, Herbert, Haering, Helmut, Lorenz, Hans, Parusel, Markus, Scharnke, Wolfgang, Schmidt, Jann.
Application Number | 20040257650 10/495428 |
Document ID | / |
Family ID | 32115318 |
Filed Date | 2004-12-23 |
United States Patent
Application |
20040257650 |
Kind Code |
A1 |
Parusel, Markus ; et
al. |
December 23, 2004 |
Rear projection screen and method for the production thereof
Abstract
The present invention relates to rear-projection screens
encompassing at least one light-scattering polymethyl methacrylate
layer of thickness in the range from 0.05 to 4 mm comprising
spherical particles whose size is in the range from 5 to 35 .mu.m,
at a concentration in the range from 2 to 60% by weight, based on
the total weight of the light-scattering polymethyl methacrylate
layer, the refractive index of the spherical plastics particles
differing from that of the polymethyl methacrylate matrix by a
value in the range from 0.02 to 0.2, wherein the concentration of
the spherical plastics particles c.sub.p, the thickness of the
light-scattering polymethyl methacrylate layer d.sub.s, and the
size of the spherical plastics particles D.sub.p is selected in
such a way that the ratio c.sub.p*d.sub.s/D.sub.p.sup.3 is in the
range from 0.0015 to 0.015% by weight*mm/.mu.m.sup.3 and the ratio
of average surface roughness of the polymethyl methacrylate layer
R.sub.a to the size of the spherical plastics particles D.sub.p is
in the range from 0.05 to 0.4. A feature of the rear-projection
screens is particularly high quality of the images projected onto
the screens.
Inventors: |
Parusel, Markus; (Messel,
DE) ; Schmidt, Jann; (Darmstadt, DE) ;
Groothues, Herbert; (Weiterstadt, DE) ; Scharnke,
Wolfgang; (Darmstadt, DE) ; Lorenz, Hans;
(Darmstadt, DE) ; Haering, Helmut; (Reinheim,
DE) ; Dickhaut-Bayer, Guenther; (Riedstadt,
DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
32115318 |
Appl. No.: |
10/495428 |
Filed: |
May 21, 2004 |
PCT Filed: |
September 27, 2003 |
PCT NO: |
PCT/EP03/10762 |
Current U.S.
Class: |
359/453 |
Current CPC
Class: |
G03B 21/62 20130101 |
Class at
Publication: |
359/453 |
International
Class: |
G03B 021/60 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 2002 |
DE |
102 51 778.9 |
Claims
1. A rear-projection, comprising: at least one light-scattering
polymethyl methacrylate layer of thickness in the range from 0.05
to 4 mm comprising spherical plastic particles whose size is in the
range from 5 to 35 .mu.m at a concentration in the range from 2 to
60% by weight, based on the total weight of the light-scattering
polymethyl methacrylate layer; wherein the refractive index of the
spherical plastic particles differs from that of the polymethyl
methacrylate layer by a value in the range from 0.02 to 0.2;
wherein the concentration of the spherical plastic particles
c.sub.p, the thickness of the light-scattering polymethyl
methacrylate layer d.sub.s, and the size of the spherical plastic
particles D.sub.p are selected in such a way that the ratio
c.sub.p*d.sub.s/D.sub.p.sup.3 is in the range from 0.0015 to 0.015%
by weight*mm/.mu.m.sup.3; and the ratio of average surface
roughness of the polymethyl methacrylate layer R.sub.a to the size
of the spherical plastic particles D.sub.p is in the range from
0.05 to 0.4.
2. A rear-projection screen according to claim 1, wherein the ratio
of concentration of the spherical plastic particles, c.sub.p, to
the thickness of the light-scattering polymethyl methacrylate
layer, d.sub.s, c.sub.p/d.sub.s, is greater than or equal to 2.5%
by weight/mm.
3. A rear-projection screen according to claim 1, wherein the gloss
R85.degree. of the light-scattering polymethyl methacrylate layer
is less than or equal to 60.
4. A rear-projection screen according to claim 1, wherein the ratio
c.sub.p*d.sub.s/D.sub.p.sup.3 is in the range from 0.0025 to 0.009%
by weight*mm/.mu.m.sup.3.
5. A rear-projection screen according to claim 1, wherein the ratio
derived from thickness of the light-scattering polymethyl
methacrylate layer d.sub.s and the size of the spherical plastic
particles D.sub.p is in the range from 5 to 1500.
6. A rear-projection screen according to claim 1, wherein the
spherical plastic particles encompass crosslinked polystyrene
and/or crosslinked poly(meth)acrylates.
7. A rear-projection screen according to claim 1, wherein said
light-scattering polymethyl methacrylate layer has been
coloured.
8. A rear-projection screen according to claim 1, wherein the
light-scattering polymethyl methacrylate layer has a refractive
index in the range from 1.46 to 1.54, measured at the sodium D line
(589 nm) and at 20.degree. C.
9. A rear-projection screen according to claim 1, wherein the
average surface roughness R.sub.a of the light-scattering
polymethyl methacrylate layer is in the range from 0.4 to 6
.mu.m.
10. A rear-projection screen according to claim 1, wherein at least
60% of the spherical plastic particles have a diameter in the range
from 15 .mu.m and at most 30% of the spherical plastic particles
have a diameter of more than 25 .mu.m.
11. A rear-projection screen according to claim 1, wherein at least
60% of the spherical plastic particles have a diameter of at least
15 .mu.m and at most 30% of the spherical plastic particles have a
diameter of more than 22 .mu.m.
12. A rear-projection screen according to claim 1, further
comprising a plastic sheet which has no scattering beads.
13. A rear-projection screen according to claim 12, wherein the
plastic plastics sheet comprises polyacrylic polymers.
14. A rear-projection screen according to claim 1, wherein the
rear-projection screen has a transmittance greater than or equal to
25%.
15. A rear-projection screen according to claim 1, wherein the
rear-projection screen has a yellowness index smaller than or equal
to 12.
16. A rear-projection screen according to claim 1, wherein the
rear-projection screen has a halved-intensity angle greater than or
equal to 0.15.
17. A rear-projection screen according to claim 1, wherein the
rear-projection screen has a scattering power greater than or equal
to 0.15.
18. A process for producing the rear-projection screen according to
claim 1, which comprises: extruding a moulding composition.
19. A process according to claim 18, which further comprises:
non-aggressively incorporating spherical plastic particles using a
twin-screw extruder with side-feed equipment.
20. (Cancelled).
Description
[0001] The present invention relates to rear-projection screens
encompassing at least one light-scattering polymethyl methacrylate
layer and to processes for producing these rear-projection
screens.
[0002] Using the technique of rear projection, information can be
made available to a wide audience. In principle, the structure of
this type of system is composed of an image surface which is
illuminated from the rear by a projector and thus provides the
information.
[0003] Examples of the use of this technique are found in control
rooms (power stations, railways), where they make it easier for
those responsible to gain an overview of the complex processes,
thus permitting avoidance of control errors. Another application is
given by display panels in, for example, sports stadia and at
motor-racing events. Here, the spectators are given information
about progress and events as they occur, even if they are very
distant from the action itself.
[0004] These image surfaces are very large. Constant technical
advances (projector technology) have added other fields of
application over the years.
[0005] For example, this type of information provision is also used
in, for example, TV equipment, large-scale cinemas and home
cinemas, and as a promotional medium at exhibitions, in window
displays, and in shops.
[0006] This technique is moreover also used to provide information
during presentations and in flight simulators, where the virtual
environment is depicted on the cockpit screen with maximum
simulation of reality.
[0007] A source of many advantages of this technique is that the
projector is outside the viewing space. This means that projection
is not interrupted by any observer located in front of the
projection surface, and distracting noises from the projector are
eliminated, and the room can be attractively designed.
[0008] There is now a wide variety of plastic sheets and foils
which are used in rear-projection technology. Sheets are often
modified to give them defined surface structures in the form of
Fresnel lens systems on the rear side and also vertically arranged
lenticular lenses on the observer side. The production of these
rear-projection panels is therefore expensive. The surface
structures can moreover be very sensitive to mechanical load.
Damage causes very great impairment of the appearance of the
projected image.
[0009] There are also known rear-projection sheets and foils which
comprise scattering media, these sheets comprising particles whose
refractive index differs from that of the matrix. The sheets and
foils are likewise suitable for rear projection, but each does not
cover the entire range of requirements, and therefore only some of
the requirements placed upon a screen are met.
[0010] Because of the large number of different possible uses, a
very wide variety of requirements are placed upon the projection
surface. By way of example, in one application the projection
surfaces have to provide a very steady, clear and high-resolution
reproduction of the image, because the observer here has to take in
the information over a prolonged period (example: control rooms,
home cinema, etc.).
[0011] When these projection surfaces are used for presentation and
promotional purposes, for example on exhibition stands, the
surfaces then have to be particularly resistant to mechanical load
and soiling, while the requirements for projection quality are not
so high.
[0012] By way of example, sheets and films which provide a high
light-scattering angle can be produced using known scattering
media, such as barium sulphate and titanium dioxide. The projection
resolution is likewise high. The viewing angle for the image should
likewise be correspondingly high. However, even at low thicknesses,
the image quality on the projection sheets is found to be blurred
and hazy, and achievement, or capability to provide, the other
requirements, such as good surface finish, is found to be absent or
only partial.
[0013] There are also known screens which comprise plastics
particles as scattering media. For example, the document JP11179856
describes multilayer sheets with at least one layer which
encompasses a polymethyl methacrylate matrix and also encompasses
crosslinked polymethyl methacrylate beads as scattering/matting
agent, the proportion of the beads being in the range from 0.5 to
25% by weight. The size of the beads is in the range from 3 to 30
.mu.m, and the examples describe merely sheets of thickness 2 mm
which comprise about 3% by weight of scattering beads whose size is
about 6 .mu.m. Light transmittance and surface gloss are described,
but the imaging properties of the sheet are not ideal.
[0014] The Japanese laid-open specification JP 07234304 describes a
mixture of crosslinked acrylate-styrene beads (14 .mu.m) in a
transparent plastic. No description of surface roughness is given,
but the sheets described in the examples are produced by injection
moulding, and very high pressure is therefore exerted on the
sheets, this pressure generally leading to very low surface
roughness. The sheets produced as in the examples do not have ideal
imaging performance.
[0015] The publication EP-A-0 561 551 describes a multilayer sheet
with a scattering layer of a mixture of a transparent polymer and
spherical particles (2-15 .mu.m). The concentration of the
particles is in the range from 0.1 to 40% by weight. In the
examples a multilayer sheet was produced with a light-scattering
layer of thickness 0.64 mm which encompasses 20% by weight of
particles whose size is about 5 .mu.m. Again, this sheet does not
provide an ideal picture.
[0016] A problem with known rear-projection screens with scattering
media is therefore that their imaging properties are non-ideal. In
particular, the known screens have relatively low image sharpness
or relatively poor brightness distribution. There are also problems
in relation to colour accuracy. In addition, many screens are not
equal to the mechanical requirements, and scratches in particular
here have a disadvantageous optical effect.
[0017] In the light of the prior art stated and discussed herein,
it was therefore an object of the present invention to provide
rear-projection screens which permit particularly high picture
quality. In particular, the screens should permit high image
sharpness and high resolution of the projected picture.
[0018] Furthermore, the images on the rear-projection screens
should have particular colour accuracy.
[0019] Another object of the invention was to provide
rear-projection screens which have particularly uniform brightness
distribution.
[0020] In addition, the rear-projection screens should have maximum
mechanical stability. There should be no, or only slight,
visibility here of scratches on the screen. In particular, damage
should have no, or only slight, effect on the image reproduction
capability of the screen.
[0021] Another object on which the invention was based was to
provide rear-projection screens which are capable of particularly
simple production. In particular, therefore, the rear-projection
screens should be capable of production via extrusion.
[0022] Another object of the present invention, therefore, was to
create rear-projection screens which have high picture steadiness.
This means that the information presented can be observed over a
long period with no fatigue.
[0023] Another object of the present invention was to provide
rear-projection screens whose size and shape can easily be adapted
to the requirements.
[0024] In addition, the images on the rear-projection screens
should have particularly good contrast.
[0025] Another object of the invention was to give the
rear-projection screens high durability, in particular high
resistance to UV irradiation or to weathering.
[0026] Another object on which the present invention was based was
to provide rear-projection screens whose image properties involve
only a slight degree of reflection.
[0027] In addition, the rear-projection screens created should have
low susceptibility to scratching.
[0028] The rear-projection screens described in claim 1 achieve
these objects, and also achieve other objects which, although they
are not specifically mentioned, are obvious or necessary
consequences of the circumstances discussed herein. Useful
modifications of the inventive rear-projection screens are
protected by the subclaims dependent on claim 1.
[0029] Claim 18 achieves the underlying object with respect to the
processes for producing rear-projection screens.
[0030] Rear-projection screens which permit particularly high
picture quality can be provided if the concentration of the
spherical plastics particles c.sub.p, the thickness of the
light-scattering polymethyl methacrylate layer d.sub.s, and the
size of the spherical plastics particles D.sub.p is selected in
such a way that the ratio c.sub.p*d.sub.s/D.sub.p.sup.3 is in the
range from 0.0015 to 0.015% by weight*mm/.mu.m.sup.3 and the ratio
of average surface roughness of the polymethyl methacrylate layer
R.sub.a to the size of the spherical plastics particles D.sub.p is
in the range from 0.05 to 0.4, and if the rear-projection screen
encompasses at least one light-scattering polymethyl methacrylate
layer of thickness in the range from 0.05 to 4 mm comprising
spherical plastics particles whose size is in the range from 5 to
35 .mu.m, at a concentration in the range from 2 to 60% by weight,
based on the total weight of the light-scattering polymethyl
methacrylate layer, the refractive index of the spherical plastics
particles differing from that of the polymethyl methacrylate matrix
by a value in the range from 0.02 to 0.2.
[0031] The inventive measures achieve, inter alia, the following
particular advantages:
[0032] The rear-projection screens of the present invention permit
high picture sharpness and high resolution of the projected
picture.
[0033] The image on the inventive rear-projection screens has
particular colour accuracy and particularly good contrast.
[0034] The rear-projection screens provided according to the
present invention have particularly uniform brightness
distribution.
[0035] In addition, the rear-projection screens of the present
invention have high mechanical stability. Scratches on the screen
here are invisible or only slightly visible.
[0036] Furthermore, pictures projected onto the inventive
rear-projection screens have high picture steadiness. This means
that information presented can be observed over a long period with
no fatigue.
[0037] In addition, the rear-projection screens of the present
invention exhibit a non-glossy, matt surface profile. Where
appropriate, the surface structure can be varied without affecting
the optical parameters other than gloss. This makes it possible to
reduce the extent of reflections which adversely affect the image
on the screen.
[0038] In addition, the rear-projection screens of the present
invention can be produced with particular ease. For example, the
rear-projection screens can in particular be produced via
extrusion.
[0039] The inventive rear-projection sheets exhibit high resistance
to weathering, in particular to UV irradiation.
[0040] The size and shape of the rear-projection screens can be
adapted to the requirements.
[0041] The light-scattering polymethyl methacrylate layer of the
rear-projection screen according to the present invention comprises
from 2 to 60% by weight, in particular from 3 to 55% by weight, and
preferably from 6 to 48% by weight, based on the weight of the
light-scattering polymethyl methacrylate layer, of spherical
plastics particles.
[0042] For the purposes of the present invention, the term
spherical means that the plastics particles preferably have a
spherical shape, but it is clear to the person skilled in the art
that, as a consequence of the methods of production, it is also
possible that plastics particles with some other shape may be
present, or that the shape of the plastics particles may deviate
from the ideal spherical shape.
[0043] The term spherical therefore means that the ratio of the
largest dimension of the plastics particles to the smallest
dimension is not more than 4, preferably not more than 2, each of
these dimensions being measured through the centre of gravity of
the plastics particles. Based on the number of plastics particles,
at least 70% are preferably spherical, particularly at least
90%.
[0044] The average (weight-average) diameter of the plastics
particles is in the range from 5 to 35 .mu.m, preferably in the
range from 8 to 25 .mu.m. 75% of the plastics particles
advantageously lie in the range from 5 to 35 .mu.m.
[0045] The particle size, and also the particle size distribution,
may be determined by means of a laser extinction method. To this
end, use may be made of a Galai-CIS-1 from L.O.T. GmbH, the method
of measurement for particle size determination being found in the
user manual.
[0046] The plastics particles which can be used according to the
invention are not subject to any particular restriction. The nature
of the plastic from which the plastics particles are produced is
therefore substantially non-critical, but refraction of light takes
place at the phase boundary between the plastics beads and the
matrix plastic.
[0047] Accordingly, the refractive index of the plastics particles,
measured for the Sodium D line (589 nm) at 20.degree. C. differs
from the refractive index no of the matrix plastic by from 0.02 to
0.2 units.
[0048] The spherical plastics particles preferably encompass
crosslinked polystyrene and/or crosslinked poly(meth)acrylates.
[0049] The structure of preferred plastics particles comprises:
[0050] b1) from 25 to 99.9 parts by weight of monomers which have
aromatic groups as substituents, for example styrene,
.alpha.-methylstyrene, ring-substituted styrenes, phenyl
(meth)acrylate, benzyl (meth)acrylate, 2-phenylethyl
(meth)acrylate, 3-phenylpropyl (meth)acrylate or vinyl benzoate;
and also
[0051] b2) from 0 to 60 parts by weight of an acrylic and/or
methacrylic ester having 1 to 12 carbon atoms in the aliphatic
ester radical, these being copolymerizable with the monomers b1),
and mention may be made here of the following by way of example:
methyl (meth)acrylate, ethyl (meth)-acrylate, n-propyl
(meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate,
isobutyl (meth)acrylate, tert-butyl (meth)acrylate, cyclo-hexyl
(meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate,
2-ethylhexyl (meth)acrylate, norbornyl (meth)acrylate or isobornyl
(meth)-acrylate;
[0052] b3) from 0.1 to 15 parts by weight of crosslinking
comonomers which have at least two ethylenically unsaturated groups
copolymerizable by a free-radical route with b1) and, where
appropriate, with b2), examples being divinylbenzene, glycol
di(meth)acrylate, 1,4-butanediol di(meth)acrylate, allyl
(meth)acrylate, triallyl cyanurate, diallyl phthalate, diallyl
succinate, pentaerythritol tetra(meth)acrylate or
trimethylolpropane tri-(meth)acrylate, where the amounts of the
comonomers b1), b2) and b3) give a total of 100 parts by
weight.
[0053] Mixtures from which the plastics particles are produced
particularly preferably comprise at least 80% by weight of styrene
and at least 0.5% by weight of divinylbenzene.
[0054] The production of crosslinked plastics particles is known to
the person skilled in the art. For example, the scattering
particles may be produced by emulsion polymerization, for example
as described in EP-A 342 283 or EP-A 269 324, and very particularly
preferably via organic-phase polymerization, for example as
described in the German Patent Application P 43 27 464.1. The
last-mentioned polymerization technique gives particularly narrow
particle size distributions or, in other words, particularly small
deviations of the particle diameters from the average particle
diameter.
[0055] It is particularly preferable to use plastics particles
whose heat resistance extends to at least 200.degree. C., in
particular at least 250.degree. C., with no intended resultant
restriction. The term heat-resistant here means that the particles
are not subject to any substantial thermal degradation. Thermal
degradation causes undesirable discoloration making the plastics
material unusable. Particularly preferred particles are, inter
alia, obtainable from Sekisui with the trade name .RTM.Techpolymer
SBX-6, .RTM.Techpolymer SBX-8 and .RTM.Techpolymer SBX-12.
[0056] In another preferred embodiment of the present invention,
the size of the spherical particles is in the range from 15 to 35
.mu.m. In this embodiment, at least 60% of the spherical particles
particularly preferably have a diameter of at least 15 .mu.m and at
most 30% of the scattering beads particularly preferably have a
diameter of more than 25 .mu.m. According to one particular aspect,
the size of at most 80% of these spherical particles is in the
range from 15 to 25 .mu.m.
[0057] In one particular aspect of the present invention, these
particles have uniform distribution in the plastics matrix, with no
significant aggregation or agglomeration of the particles.
Uniformly distributed means that the concentration of particles is
substantially constant within the plastics matrix.
[0058] The light-scattering layer encompasses not only the
spherical particles but also a plastics matrix which comprises
polymethyl methacrylate (PMMA). The light-scattering polymethyl
methacrylate layer preferably encompasses at least 30% by weight of
polymethyl methacrylate, based on the weight of the
light-scattering layer.
[0059] Polymethyl methacrylates are generally obtained via
free-radical polymerization of mixtures which comprise 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, of methyl methacrylate, based on
the weight of the monomers.
[0060] Alongside this, these mixtures for preparing polymethyl
methacrylates may comprise other (meth)acrylates which are
copolymerizable with methyl methacrylate. The term (meth)acrylates
encompasses methacrylates and acrylates, and also mixtures of the
two.
[0061] These monomers are well known. They include (meth)acrylates
derived from saturated alcohols, for example methyl acrylate, ethyl
(meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate,
tert-butyl (meth)acrylate, pentyl (meth)acrylate and 2-ethylhexyl
(meth)acrylate;
[0062] (meth)acrylates derived from unsaturated alcohols, for
example 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 in each case
the aryl radicals may be unsubstituted or have up to four
substituents;
[0063] 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;
[0064] glycol di(meth)acrylates, such as 1,4-butanediol (meth)
acrylate,
[0065] (meth)acrylates of ether alcohols, for example
tetra-hydrofurfuryl (meth)acrylate, vinyloxyethoxyethyl
(meth)acrylate;
[0066] amides and nitriles of (meth)acrylic acid, for example
N-(3-dimethylaminopropyl)(meth)acrylamide,
N-(diethyl-phosphono)(meth)acr- ylamide,
[0067] 1-methacryloylamido-2-methyl-2-propanol;
[0068] sulphur-containing methacrylates, such as
ethyl-sulphinylethyl(meth- )acrylate,
[0069] 4-thiocyanatobutyl(meth)acrylate,
ethylsulphonylethyl(meth)acrylate- ,
thiocyanatomethyl(meth)acrylate,
[0070] methylsulphinylmethyl(meth)acrylate,
[0071] bis((meth)acryloyloxyethyl) sulphide;
[0072] polyfunctional(meth)acrylates, such as trimethyloyl-propane
tri(meth)acrylate.
[0073] Besides the abovementioned (meth)acrylates, the compositions
to be polymerized may also comprise other unsaturated monomers
copolymerizable with methyl methacrylate and the abovementioned
(meth)acrylates.
[0074] They include 1-alkenes, such as 1-hexene, 1-heptene;
branched alkenes, such as vinylcyclohexane,
3,3-di-methyl-1-propene, 3-methyl-1-diisobutylene,
4-methyl-1-pentene;
[0075] acrylonitrile; vinyl esters, such as vinyl acetate; styrene,
substituted styrenes having an alkyl substituent in the side chain,
e.g. .alpha.-methylstyrene and .alpha.-ethylstyrene, substituted
styrenes having an alkyl substituent on the ring, such as
vinyltoluene and p-methylstyrene, halogenated styrenes, such as
mono-chlorostyrenes, dichlorostyrenes, tribromostyrenes and
tetrabromostyrenes;
[0076] heterocyclic vinyl compounds, such as 2-vinylpyridine,
3-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine,
2,3-dimethyl-5-vinylpyridine, vinyl-pyrimidine, vinylpiperidine,
9-vinylcarbazole, 3-vinyl-carbazole, 4-vinylcarbazole,
1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone,
2-vinyl-pyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine,
N-vinylcaprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran,
vinylthiophene, vinylthiolane, vinyl-thiazoles and hydrogenated
vinylthiazoles, vinyl-oxazoles and hydrogenated vinyloxazoles;
[0077] vinyl and isoprenyl ethers;
[0078] maleic acid derivatives, such as maleic anhydride,
methylmaleic anhydride, maleimide, methylmaleimide; and dienes,
such as divinylbenzene.
[0079] The amount generally used of these comonomers is 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 these compounds may be used individually or in the
form of a mixture.
[0080] The polymerization is generally initiated using known
free-radical initiators. Among the preferred initiators are, inter
alia, the azo initiators well-known to the person skilled in the
art, for example AIBN and 1,1-azobiscyclohexanecarbonitrile, and
also peroxy compounds, such as methyl ethyl ketone peroxide,
acetylacetone peroxide, dilauroyl peroxide, tert-butyl
2-ethylperhexanoate, ketone peroxide, methyl isobutyl ketone
peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl
peroxybenzoate, tert-butylperoxy isopropyl carbonate,
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 not
mentioned but likewise capable of forming free radicals.
[0081] The amount often used of these compounds is from 0.01 to 10%
by weight, preferably from 0.5 to 3% by weight, based on the weight
of the monomers.
[0082] Use may be made here of various poly(meth)acrylates which
differ, for example in their molecular weight or in their monomeric
constitution.
[0083] The matrix of the light-scattering layer may moreover
comprise other polymers in order to modify its properties. Among
these are, inter alia, polyacrylonitriles, polystyrenes,
polyethers, polyesters, polycarbonates and polyvinyl chlorides.
These polymers may be used individually or in the form of a
mixture, and it is also possible here to use copolymers which are
derivable from the abovementioned polymers.
[0084] The weight-average molar mass M.sub.w of the homo- and/or
copolymers to be used as the matrix polymer may vary within a wide
range, the molar mass usually being matched to the intended use and
to the mode of processing of the moulding composition. However, it
is generally in the range from 20 000 to 1 000 000 g/mol,
preferably from 50 000 to 500 000 g/mol and particularly preferably
from 80 000 to 300 000 g/mol, with no intended resultant
restriction.
[0085] In one particular embodiment of the present 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, of polymethyl
methacrylate, based on the weight of the matrix of the
light-scattering layer.
[0086] In one particular aspect of the present invention, the
poly(meth)acrylates of the matrix of the light-scattering layer
have a refractive index in the range from 1.46 to 1.54, measured
for the sodium D line (589 nm) and at 20.degree. C.
[0087] The moulding compositions for preparing the light-scattering
layer may comprise conventional additives of any type. Among these
are antistatic agents, antioxidants, mould-release agents, flame
retardants, lubricants, dyes, flow improvers, fillers, light
stabilizers, UV absorbers and organophosphorous compounds, such as
phosphites or phosphonates, pigments, weathering stabilizers and
plasticizers. However, the amount of additives is restricted in
relation to the intended use. For example, the light-scattering
property of the polymethyl methacrylate layer should not be
excessively impaired by additives, nor should its transparency.
[0088] In one particular aspect of the present invention, the
moulding composition may, where appropriate, be given greater
mechanical stability by an impact modifier. These impact modifiers
for polymethacrylates are well known, and EP-A 0 113 924, EP-A 0
522 351, EP-A 0 465 049 and EP-A 0 683 028, inter alia, describe
the preparation and the structure of impact-modified
polymethacrylate moulding compositions.
[0089] Preferred impact-modified moulding compositions which may be
used to prepare the matrix comprise from 70 to 99% by weight of
polymethyl methacrylates. These polymethyl methacrylates have been
described above.
[0090] In one particular aspect of the present invention, the
polymethyl methacrylates used to prepare impact-modified moulding
compositions are obtained via free-radical polymerization of
mixtures which encompass 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, these
likewise having been listed above. Particularly preferred
comonomers are, inter alia, C.sub.1-C.sub.4-alkyl (meth)acrylates,
in particular methyl acrylate, ethyl acrylate or butyl
methacrylate.
[0091] The average molar mass Mw of the polymethyl methacrylates
which can serve for preparing the impact-modified matrix is
preferably in the range from 90 000 to 200 000 g/mol, in particular
from 100 000 to 150 000 g/mol.
[0092] Preferred impact-resistant moulding compositions which can
serve 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, this being an elastomer phase composed of
crosslinked polymer particles.
[0093] Preferred impact-resistant moulding compositions which can
serve 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, this being an elastomer phase composed of
crosslinked polymer particles.
[0094] The impact modifier may be attained in a manner known per se
via bead polymerization or via emulsion polymerization.
[0095] Preferred impact modifiers are crosslinked particles whose
average particle size is in the range from 50 to 1000 nm,
preferably from 60 to 500 nm and particularly preferably from 80 to
120 nm.
[0096] By way of example, these particles may be obtained via
free-radical polymerization of mixtures which generally comprise 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 also from 0.1 to 2% by weight,
preferably from 0.5 to 1% by weight, of a crosslinking monomer,
e.g. a polyfunctional (meth)acrylate, e.g. allyl methacrylate, and
which comprise comonomers which can be copolymerized with the
abovementioned vinyl compounds.
[0097] Among the preferred comonomers are, inter alia,
C.sub.1-C.sub.4-alkyl (meth)acrylates, such as ethyl acrylate or
butyl methacrylate, preferably methyl acrylate, or other monomers
including vinyl groups capable of polymerization, e.g. styrene. The
mixtures for producing the abovementioned particles may preferably
encompass from 0 to 10% by weight, with preference from 0.5 to 5%
by weight, of comonomers.
[0098] Particularly preferred impact modifiers are polymer
particles which have a two-layer, or particularly preferably a
three-layer, core-shell structure. These core-shell polymers are
described in EP-A 0 113 924, EP-A 0 522 351, EP-A 0 465 049 and
EP-A 0 683 028, inter alia.
[0099] Particularly preferred impact modifiers based on acrylate
rubber have the following structure, inter alia:
[0100] Core: Polymer with at least 90% by weight methyl
methacrylate content, based on the weight of the core.
[0101] Shell 1: Polymer with at least 80% by weight butyl acrylate
content, based on the weight of the first shell.
[0102] Shell 2: Polymer with at least 90% by weight methyl
methacrylate content, based on the weight of the second shell.
[0103] The core may comprise not only the monomers mentioned but
also other monomers, as may each of the shells. These have been
mentioned previously, with particularly preferred comonomers having
a cross-linking action.
[0104] By way of example, a preferred acrylate rubber modifier may
have the following structure:
[0105] Core: copolymer composed of methyl methacrylate (95.7% by
weight) ethyl acrylate (4% by weight) and allyl methacrylate (0.3%
by weight)
[0106] S1: copolymer composed of butyl acrylate (81.2% by weight),
styrene (17.5% by weight) and allyl methacrylate (1.3% by
weight)
[0107] S2: copolymer composed of methyl methacrylate (96% by
weight) and ethyl acrylate (4% by weight).
[0108] The core:shell(s) ratio of the acrylate rubber modifiers may
vary within a wide range. The core:shell ratio C/S is preferably in
the range from 20:80 to 80:20, with preference from 30:70 to 70:30
in the case of modifiers with one shell, or in the case of
modifiers with two shells the core:shell 1:shell 2 ratio C/S1/S2 is
preferably in the range from 10:80:10 to 40:20:40, particularly
preferably from 20:60:20 to 30:40:30.
[0109] The particle size of the core-shell modifier is usually in
the range from 50 to 1000 nm, preferably from 100 to 500 nm and
particularly preferably from 150 to 450 nm, with no intended
resultant restriction.
[0110] Impact modifiers of this type are commercially obtainable
from Mitsubishi with the trade name METABLEN.RTM. IR 441. It is
also possible to obtain impact-modified moulding compositions.
[0111] Particularly preferred moulding compositions for preparing
the plastics matrix are obtainable commercially from Rohm GmbH
& Co. KG.
[0112] The thickness of the light-scattering polymethyl
methacrylate layer is generally in the range from 0.05 to 4 mm.
[0113] According to the invention, the concentration of the
spherical particles c.sub.p, the thickness of the light-scattering
polymethyl methacrylate layer d.sub.s, and also the size of the
spherical particles D.sub.p, is selected in such a way that the
ratio of the product of concentration of the spherical particle
c.sub.p and thickness of the light-scattering polymethyl
methacrylate layer to the third power of the particle size of the
spherical particles c.sub.p*d.sub.s/D.sub.p.sup.3 is in the range
from 0.0015 to 0.015% by weight*mm/.mu.m.sup.3, preferably from
0.0025 to 0.009% by weight*mm/.mu.m.sup.3.
[0114] The ratio of average surface roughness of the polymethyl
methacrylate layer R.sub.a to the particle size of the spherical
particles D.sub.p is in the range from 0.05 to 0.4, in particular
from 0.05 to 0.3 and preferably from 0.06 to 0.2.
[0115] According to one particular embodiment of the screen of the
present invention, the ratio of concentration of the spherical
particles c.sub.p to the thickness of the light-scattering
polymethyl methacrylate layer d.sub.s c.sub.p/d.sub.s is greater
than or equal to 2.5% by weight/mm, in particular greater than or
equal to 4% by weight/mm.
[0116] The gloss R.sub.85.degree. of the light-scattering
polymethyl methacrylate layer is preferably smaller than or equal
to 60, in particular smaller than or equal to 50.
[0117] The ratio of thickness of the light-scattering polymethyl
methacrylate layer d.sub.s and particle size of the spherical
particles D.sub.p d.sub.s/D.sub.p is preferably in the range 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, with no
intended resultant restriction.
[0118] According to one particular embodiment of the present
invention, the average surface roughness R.sub.a of the sheet is
preferably in the range from 0.4 to 6 .mu.m, in particular from 0.4
to 2 .mu.m, preferably from 0.5 to 1.5 .mu.m, in particular from
0.8 to 5 .mu.m, particularly preferably from 1 to 3.5 .mu.m.
[0119] Within this range, the visibility of scratches on the
surface of the light-scattering layer is limited to a particularly
low level. This low susceptibility to scratching may be determined
to DIN 53799 and DIN EN 438 via visual assessment of a damaged
surface, the damage being brought about by a diamond acting on the
surface with varying force.
[0120] The surface roughness R.sub.a of the sheet may be affected
via variation of various parameters, which depend on the production
method. Among these are the temperature of the melt during the
extrusion process, a rougher surface being given by a higher
temperature of the melt. However, a factor which has to be
considered here is that the temperature of the melt depends on the
precise constitution of the moulding composition. The temperature
of the melt is generally in the range from 150 to 300.degree. C.,
preferably in the range from 200 to 290.degree. C. These
temperatures are based on the temperatures of the melt on discharge
from the die.
[0121] The surface roughness may also be affected via the gap
between the rollers used to polish the sheets. For example, if a
polishing stack encompasses three rollers in an L arrangement,
where the moulding composition is conducted from the die into the
gap between roller 1 and roller 2 and as a 60-180.degree. wrap
around roller 2, the gap between roller 2 and roller 3 polishes the
surfaces. If the gap between roller 2 and roller 3 is adjusted to
the thickness of the sheet, the scattering particles on the sheet
surface are pressed into the matrix, making the surface more
polished. To achieve a rougher surface, this gap is generally
adjusted to be somewhat larger than the thickness of the sheet to
be produced, the relevant value being in the range from 0.1 to 2 mm
above the thickness of the sheet, preferably from 0.1 to 1.5 mm
above the thickness of the sheet, with no intended resultant
restriction. The surface roughness is also affected via the
particle size and the thickness of the sheet, the dependencies
being shown in the examples.
[0122] The light-scattering layer may be produced via known
processes, preference being given to thermoplastic shaping
processes. Once the particles have been added, light-scattering
layers can be produced from the moulding compositions described
above via conventional thermoplastic shaping processes.
[0123] According to one particular embodiment, a twin-screw
extruder is used for the extrusion process or for the production of
pellets of moulding compositions comprising scattering beads. In
these processes, the plastics particles are preferably converted
into the melt in the extruder. By this means it is possible to
obtain melts which can give screens whose transmittance is
particularly high.
[0124] The rear-projection screens here may be produced via a
two-stage process in which the extrusion of the foil or sheet in a
single-screw extruder is carried out downstream of an inventive
sidefeeder compounding process in a twin-screw extruder and
intermediate pelletization. The pellets obtained via the twin-screw
extruder may be provided with particularly high proportions of
scattering beads, making it simple to produce projection screens
with varying content of scattering beads via blending with moulding
compositions without scattering beads.
[0125] It is also possible to carry out a single-stage process in
which the compounding of the spherical plastics particles into the
melt takes place as described in a twin-screw extruder which, where
appropriate, has a downstream pressure-increasing unit (e.g. melt
pump) which is immediately followed by the extrusion die, which
extrudes a sheet product. Surprisingly, the means described above
can give rear-projection screens with a particularly low yellowness
index.
[0126] The screens may moreover also be produced by injection
moulding, in which case, however, the selection of the process
parameters or the injection mould is to be such as to give a
surface roughness in the inventive range.
[0127] The compounding of the matrix with the scattering particles
preferably takes place via a twin-screw extruder, and the actual
sheet extrusion can also use a single-screw extruder, with no
intended resultant restriction.
[0128] Depending on the nature of the application, the
light-scattering polymethyl methacrylate layer may be used as a
screen. The relatively thin layers here may be used in the form of
a foil which can be rolled up. Particularly preferred foils are
rendered impact-resistant via the methods described above.
[0129] A thin light-scattering polymethyl methacrylate layer may
moreover be applied to a plastics sheet, in order to increase its
mechanical stability. This plastics sheet generally comprises no
spherical particles. This plastics sheet preferably comprises
polyacrylic polymers.
[0130] According to one particular aspect of the present invention,
the transmittance 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%.
[0131] According to one particular aspect of the present invention,
the moulding composition may be coloured. Surprisingly, this
measure permits improvement of the contrast. Particularly suitable
materials for the colouring process are dyes known per se and/or
carbon black. Particularly preferred dyes are commercially
available. Among these are .RTM.Sandoplast Red G and
.RTM.Sandoplast Yellow 2G, each from Clariant, and .RTM.Macroplex
Green SB and .RTM.Macroplex Violet 3R, each from Bayer. The
concentration of these dyes depends on the desired perceived
colour, and also on the thickness of the sheet. With no intended
resultant restriction, this concentration is generally in the range
from 0 to 0.8% by weight per dye, preferably from 0.000001 to 0.4%
by weight, based on the total weight of the coloured moulding
composition without scattering beads. The sum of the dye
concentrations is preferably in the range from 0 to 1% by weight,
preferably from 0.0001 to 0.6% by weight, based on the total weight
of coloured moulding composition without scattering beads. The loss
of transmittance may at least to some extent be compensated via
more powerful projectors.
[0132] The yellowness index of the screen is preferably smaller
than or equal to 12, in particular smaller than or equal to 10,
with no intended resultant restriction.
[0133] One particular embodiment of the screen of the present
invention has a halved-intensity angle greater than or equal to
15.degree., in particular greater than or equal to 25.degree..
[0134] According to one particular aspect of the present invention,
the screen exhibits a scattering power greater than or equal to
0.15, in particular greater than or equal to 0.35, with no intended
resultant restriction.
[0135] According to one preferred embodiment, the surface of the
inventive polymethyl methacrylate sheets has a matt appearance
under reflected light. Gloss measurement using a reflectometer to
DIN 67530 may be used for characterization. The gloss of the sheets
is preferably below 50, particularly preferably below 40 and very
particularly preferably below 30, with an angle of 850.
[0136] There is no restriction on the size and shape of the
rear-projection screen of the present invention. However, the
screen usually has the shape of a rectangular panel, because it is
the usual format for presenting pictures.
[0137] The length of this type of rear-projection screen is
preferably in the range from 25 to 10 000 mm, with preference from
50 to 3000 mm and particularly preferably from 200 to 2000 mm. The
width of this particular embodiment is generally in the range from
25 to 10 000 mm, preferably from 50 to 3000 mm and particularly
preferably from 200 to 2000 mm. Two or more of these screens may be
brought together in order to provide a particularly large
projection surface.
[0138] According to one particular embodiment, the screen has
particularly high weathering resistance to DIN EN ISO 4892, Part
2--Methods of exposure to laboratory light sources: xenon arc
sources.
[0139] Examples and comparative examples are used below for more
detailed description of the invention, but there is no intention
that the invention be restricted to these examples.
[0140] A) Test Methods
[0141] Average roughness R.sub.a was determined to DIN 4768 using
Taylor Hobson Talysurf 50 test equipment.
[0142] Transmittance .tau..sub.D65/2.degree. was determined to DIN
5036 using Perkin Elmer Lambda 19 test equipment.
[0143] Yellowness index .tau..sub.D65/10.degree. was determined to
DIN 6167 using Perkin Elmer Lambda 19 test equipment.
[0144] R85.degree. gloss was determined at 850 to DIN 67530 using a
laboratory reflectometer from Dr. Lange.
[0145] Scattering power and halved-intensity angle were determined
to DIN 5036 using a GO-T-1500 LMT goniometer test unit.
[0146] The various rear-projection screens were also assessed
visually on the basis of the criteria shown in Table 1.
[0147] The projector used here was an Epson EMP-713. The test
picture was assessed at a distance of about 1-1.5 m from the image
at various angles (0.degree.=perpendicular to the projection
normal, 30.degree. and 60.degree.). The distance of the projector
from the projection sheet was about 85 cm and the image diagonal
was about 50 cm.
[0148] Technical Data for Epson EMP 713 Projector:
[0149] Projection system: dichroitic mirror and lens system,
pixels: 2359296 pixels (1024.times.768)*3, brightness: 1200 ANSI
lumens, contrast: 400:1, picture brilliance: 85%, colour output: 24
bit, 16.7 million colours, H: 15-92 kHz, V: 50-85 Hz, lamp: 150
watt UHE, video resolution: 750 TV lines
1 TABLE 1 Criterion Property Hot spot A hot spot is light
distribution associated with the conical beam of light of the
projection illumination system. A hot spot is therefore a conical
beam of light with substantially greater brightness in the centre
than at the margin of the image. If the hot spot is very
pronounced, the projector lamp is visually detectable. Brightness
Brightness distribution is likewise distribution assessed via the
distribution of light on the image surface and therefore
characterizes the extent to which the illumination of the image
extends from the centre to the margin. Picture sharpness Picture
sharpness is the degree of perceived clarity of the test picture.
Resolution The resolution of the image gives the extent to which
fine structures are distorted on the sheet assessed. Picture
Picture steadiness is the extent to which steadiness the observer
can receive the projected information over a prolonged period
without eye strain.
[0150] The tables indicate very good properties by ++, good
properties by +, satisfactory propeties by 0, unsatisfactory
properties by -, very unsatisfactory properties by -- and
inadequate properties by ---.
[0151] B) Preparation of Plastics Particles
[0152] To prepare the spherical plastics particles, use was made of
an aluminium hydroxide Pickering stabilizer, prepared by
precipitation from aluminium sulphate and soda solution directly
prior to starting the actual polymerization. To this end, 16 g of
Al.sub.2(SO.sub.4).sub.3, 0.032 g of complexing agent (Trilon A)
and 0.16 g of emulsifier (emulsifier K 30 obtainable from Bayer AG;
sodium salt of a C.sub.15 paraffinsulphonate) were first dissolved
in 0.8 l of distilled water. A 1N sodium carbonate solution was
then added, with stirring and at a temperature of about 40.degree.
C., to the aluminium sulphate dissolved in water, the resultant pH
being in the range from 5 to 5.5. This procedure gave a colloidal
dispersion of the stabilizer in the water.
[0153] After the precipitation of the stabilizer, the aqueous phase
was transferred to a glass beaker. 110 g of methyl methacrylate, 80
g of benzyl methacrylate, 10 g of allyl methacrylate, 4 g of
dilauryl peroxide and 0.4 g of tert-butyl 2-ethylperhexanoate were
added into the beaker. This mixture was dispersed by a disperser
(UltraTurrax S50N-G45MF, Janke and Kunkel, Staufen) for 15 minutes
at 7000 rpm.
[0154] Following this exposure to shear, the reaction mixture was
charged to the reactor, which had been preheated to the appropriate
reaction temperature of 80.degree. C., and polymerized with
stirring (600 rpm) at about 80.degree. C. (polymerization
temperature) for 45 minutes (polymerization time). A post-reaction
phase then followed at about 85.degree. C. internal temperature for
1 hour. After cooling to 45.degree. C., the stabilizer was
converted into water-soluble aluminium sulphate by adding 50%
strength sulphuric acid. The beads were worked up by filtering the
resultant suspension through a commercially available textile
filter and drying at 50.degree. C. for 24 hours in a heated
cabinet.
[0155] The size distribution was studied by laser extinction. The
average size V.sub.50 of the particles was 19.66 .mu.m. The beads
had a spherical shape, no fibres being detected. No coagulation
occurred. The resultant particles are termed plastics particles A
below.
C) INVENTIVE EXAMPLES 1-6 AND COMPARATIVE EXAMPLES 1-3
[0156] Various rear-projection screens were produced via extrusion.
To this end, various compounded materials comprising scattering
beads were first prepared from plastics particles A and a PMMA
moulding composition obtainable from Rohm GmbH & Co. KG
(copolymer of 97% by weight of methyl methacrylate and 3% by weight
of methyl acrylate) in a ZSK 30 Werner & Pfleiderer twin-screw
extruder, using side feeder technology=direct feed into the melt
downstream of the vent zone. The pellets obtained form the basis
for the subsequent production of the plastics sheets described in
the examples. The concentrate was used in subsequent processing for
the extrusion-processing of various blends to give varying content
of the scattering particles described. A BREYER .O slashed.60 mm
extruder was used. The temperature of the melt on discharge from
the die was generally 270.degree. C., but the die discharge
temperature was 260.degree. C. in comparative example 2. The
adjustment of the polishing stack was generally, and in particular
in the examples, such as to achieve maximum surface roughness.
[0157] The proportion of plastics particles in the polymethyl
methacrylate matrix is shown in Table 2, as is the thickness of the
sheets. The test results obtained by the abovementioned methods are
given in Tables 3, 4, 5 and 6.
D) INVENTIVE EXAMPLES 7-14 AND COMPARATIVE EXAMPLES 4-6
[0158] The production process described in inventive examples 1-6
was in essence repeated, but .RTM.Techpolymer SBX-8 from Sekisui
and a PMMA moulding composition obtainable from Rohm GmbH & Co.
KG (copolymer of 97% by weight of methyl methacrylate and 3% by
weight of methyl acrylate) were extruded to give plastics
sheets.
[0159] The proportion of plastics particles in the polymethyl
methacrylate matrix is shown in Table 2, as is the thickness of the
sheets. The test results obtained by the abovementioned methods are
given in Tables 3, 4, 5 and 6.
2TABLE 2 Size of plastics Thickness of Content in particles [.mu.m]
sheet [mm] [% by weight] Comp. Ex. 1 20 3 6 Inventive example 1 20
3 12 Inventive example 2 20 3 24 Comp. Ex. 2 20 1 12 Inventive
example 3 20 1 24 Inventive example 4 20 0.5 24 Inventive example 5
20 0.5 48 Comp. Ex. 3 20 0.25 24 Inventive example 6 20 0.25 48
Comp. Ex. 4 8 3 1 Comp. Ex. 5 8 3 3 Comp. Ex. 6 8 1 1 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 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
[0160]
3 TABLE 3 C.sub.p * d.sub.s/D.sub.p.sup.3 [% by weight * R.sub.a
mm/.mu.m.sup.3] [.mu.m] R.sub.a/D.sub.p Comp. Ex. 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 Comp. Ex. 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 5 0.003 4.9 0.245 Comp. Ex. 3 0.00075 4.8 0.24 Inventive
example 6 0.0015 6.6 0.33 Comp. Ex. 4 0.00586 0.24 0.03 Comp. Ex. 5
0.01758 0.29 0.03625 Comp. Ex. 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 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 13 0.00586 1.07
0.13375 Inventive example 14 0.01172 1.48 0.185
[0161]
4TABLE 4 Transmittance Yellowness index Scattering [%] YI
(.tau..sub.D65/10.degree.) power .sigma. Comp. Ex. 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 Comp. Ex. 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 5
78.42 3.18 0.41 Comp. Ex. 3 88.33 0.32 0.19 Inventive example 6
78.04 0.99 0.20 Comp. Ex. 4 60.71 6.75 0.63 Comp. Ex. 5 47.72 5.35
0.88 Comp. Ex. 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 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 13 73.52 5.17 0.56 Inventive example 14 61.33 6.04 0.82
[0162]
5 TABLE 5 R85.degree. gloss Hot Brightness measurement spot
distribution Comp. Ex. 1 35.0 - - Inventive example 1 8.6 + +
Inventive example 2 2.3 ++ ++ Comp. Ex. 2 10.1 - - Inventive
example 3 1.6 0 0 Inventive example 4 1.3 0 0 Inventive example 5
0.5 ++ + Comp. Ex. 3 0.9 --- --- Inventive example 6 0.3 0 0 Comp.
Ex. 4 84.7 ++ ++ Comp. Ex. 5 77.2 ++ ++ Comp. Ex. 6 86.9 --- ---
Inventive example 7 47.2 ++ + Inventive example 8 29.4 ++ ++
Inventive example 9 55.1 + + Inventive example 10 36.9 ++ ++
Inventive example 11 26.4 ++ ++ Inventive example 12 17.6 0 0
Inventive example 13 7.3 ++ + Inventive example 14 2.1 ++ +
[0163]
6 TABLE 6 Picture Picture sharpness Resolution steadiness Comp. Ex.
1 + fine + Inventive example 1 + fine + Inventive example 2 0 fine
+ Comp. Ex. 2 + fine - Inventive example 3 + fine 0 Inventive
example 4 + fine 0 Inventive example 5 + fine + Comp. Ex. 3 0 fine
- Inventive example 6 0 fine - Comp. Ex. 4 - fine + Comp. Ex. 5 --
fine - Comp. Ex. 6 ++ very fine - Inventive example 7 + very fine +
Inventive example 8 0 fine + Inventive example 9 ++ very fine +
Inventive example 10 ++ very fine + Inventive example 11 0 fine +
Inventive example 12 ++ very fine + Inventive example 13 ++ very
fine + Inventive example 14 0 fine +
[0164] Examples of Measurement of Optical Scratch
Susceptibility
[0165] Using the rear-protection screens produced in inventive
examples 1, 4, 5, 6 and 11, the visual susceptibility to scratching
of the extrudates was studied.
[0166] Susceptibility to scratching was tested via the penetration
depth of a diamond t.sub.R=f (load), using the Taber Industries 203
scratch tester, the method being based on DIN 53799 and DIN EN 438:
diamond gouge with 90.degree. cone angle, peak radius 90 .mu.m,
direction of rotation anticlockwise. The loads used are shown in
Table 7.
[0167] A black substrate was used for visual assessment (reflection
test). The tests (roughness, gloss) were carried out on the upper
side of the test extrudates.
[0168] The results obtained are listed in Table 7.
7TABLE 7 Load on diamond Inventive example 1 Inventive example 4
Inventive example 5 Inventive example 6 Inventive example 11 0.4 N
no discernible no discernible discernible damage Discernible damage
no discernible damage damage damage (additional (additional
reflections, reflections, angle-dependent) angle-dependent) 0.7 N
no discernible hardly any discernible damage Discernible damage
hardly any discernible damage discernible damage (additional
(additional reflections, damage (additional (additional
reflections, angle-dependent) reflections, highly angle-
reflections, highly angle-dependent) dependent) angle-dependent)
1.0 N no discernible hardly any discernible damage Discernible
damage slight discernible damage damage discernible damage
(additional (additional reflections, (additional reflections,
(additional reflections, angle-dependent) angle-dependent)
reflections, angle- angle-dependent) dependent) 1.5 N slight
discernible slight discernible discernible damage Discernible
damage slight discernible damage damage (additional damage
(additional (additional (additional reflections, reflections,
highly reflections, angle- reflections, angle-dependent)
angle-dependent) dependent) angle-dependent) 2.0 N slight
discernible discernible discernible Discernible damage discernible
damage damage (additional damage damage reflection, highly
angle-dependent)
[0169] The inventive examples and comparative examples clearly show
that rear-projection screens which provide ideal picture quality
are only obtained from a combination of a certain narrow range for
the relative surface roughness R.sub.a/D.sub.p and the ratio
c.sub.p*d.sub.s/D.sub.p.s- up.3.
[0170] The embodiment where the particles are introduced directly
into the melt may be successfully used to produce pellets or
mouldings which encompass a second component, such as plastics
particles (side feeder process). This technology is therefore not
restricted to this invention.
[0171] A feature of the side feeder process is that the moulding
compositions to be compounded are not fed simultaneously through
the feed zone but that only the parent component passes through the
feed zone, while the 2nd component is fed into the melt after the
parent moulding composition has been melted. The melts are then
homogenized through mixing and shearing sections whose arrangement
--and therefore mode of action --can be adapted so as to avoid any
adverse effect on the material to be mixed.
[0172] The homogenized melt is then processed through strand
pelletization or die-face cutting under water, to give uniformly
sized pellets (see FIG. 1).
[0173] FIG. 1 shows a diagram of compounding via a twin-screw
extruder (side feeder technology). The reference numerals in FIG. 1
indicate:
[0174] 1. addition of the moulding composition through the feed
zone
[0175] 2. molten moulding composition (e.g. a PMMA obtainable from
Rohm GmbH & Co. KG)
[0176] 3. addition of the scattering agents (e.g. Techpolymer SBX8)
to the hot plastics melt
[0177] 4. homogeneous melt of scattering beads in moulding
composition
[0178] 5. extrudate, e.g. 48% strength masterbatch of scattering
beads in a moulding composition (uniformly sized pellets)
[0179] The DF moulding composition serves as starting material in a
second stage for the production of the various products, with only
slight degradation of the 2nd component. This can give substantial
advantages. Among these in the case of beads are a low level of
discoloration of the products, e.g. light-scattering or
light-conducting sheets (yellowness index) and high
transmittance.
[0180] According to one particular embodiment, a twin-screw
extruder is used for the compounding process.
[0181] The side feeder process can moreover also give similarly
good results for the compounding process using single-screw
extruders specifically designed for the processing of powders, and
using side feeder technology.
* * * * *