Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
. ~ " ~ Le A 33 570-Foreign Countries Gi/ngb/NT
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Polycarbonate sheets
The present invention relates to polycarbonate sheets, the use thereof to
produce
glazing and said glazing. ,.
Polycarbonate sheets are used to produce glazing, for example. In this case,
it is
desirable to use sheets with as high as possible light transmissions and as
lo~.v as
possible yellowness indexes. Although it is possible to reduce the yellowness
index
by adding of blue pigments, this is achieved at the expense of light
transmission and
greying of the sheets. During weathering of the sheets, it is important that
the
mechanical properties of the sheets are kept at the highest possible level.
Even after
weathering, the sheets must retain a high resistance to mechanical influences
e.g.
hail.
Polycarbonates may be produced by the so-called interfacial polycondensation
process. In said process, dihydroxydiarylalkanes (also known as bisphenols)
are
reacted in the form of their alkali salts in aqueous solution with phosgene in
the
heterogeneous phase in the presence of inorganic bases such as sodium
hydroxide
solution and an organic solvent, in which the product polycarbonate is readily
soluble.
More details relating to the interfacial polycondensation process for
producing poly-
carbonates are disclosed in Schnell, "Chemistry and Physics of
Polycarbonates",
Polymer Reviews, Volume 9, Interscience Publishers, New York, London, Sydney
1964.
The polycarbonate sheets known from the prior art exhibit the disadvantage
that they
do not adequately meet the above-mentioned requirements of high light
transmission,
low yellowness index and good retention of mechanical properties on
weathering.
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The object of the present invention is therefore to produce polycarbonate
sheets
which do not exhibit the above-mentioned disadvantages of the prior art.
This object is achieved according to,the invention by polycarbonate sheets,
wherein
S the polycarbonate is produced by the interfacial polycondensation process
and the
aqueous solution of an alkali salt of a bisphenol used therein has a content
of
dissolved oxygen of less than 150 ppb.
The content of dissolved oxygen in the aqueous solution of the alkali salt of
bisphenol is <150 ppb, preferably <100 ppb, particularly preferably <50 ppb.
The invention thus provides polycarbonate sheets, wherein the polycarbonate is
produced by the interfacial polycondensation process and the aqueous solution
of an
alkali salt of a bisphenol used therein has a content of dissolved oxygen of
less than
150 ppb.
In addition, the present invention also provides glazing, for example for
automobiles
or buildings, in particular for greenhouses, winter gardens, bus shelters,
advertising
panels, signboards, protective screens, automotive glazing, windows or
roofing.
The polycarbonates are produced according to the invention in that the other
raw
materials apart from the aqueous solution of the alkali salt of bisphenol do
not
contain a noteworthy amount of oxygen. In addition, production is performed
with
the exclusion of oxygen, as described for example in DE-A 4 227 272.
For example, in a reaction vessel and tubular reactor configuration, the
forced
circulation loop and the tubular reactors are flooded and the reaction vessel
is
blanketed with nitrogen, to ensure the exclusion of oxygen.
The polycarbonate sheets according to the invention are, for example, solid
sheets,
hollow sheets (also known as mufti wall sheets e.g: twin wall sheets, triple
wall
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sheets...) or corrugated sheets, which are e.g. used as glazing materials. The
sheets
may be produced in a manner known in principle to the person skilled in the
art, for
example by extrusion or by injection moulding.
S Subsequent processing of the sheets, such as thermoforming or surface
modification,
such as application of scratch-proof lacquers, water-dispersing layers and the
like, is
also possible. The patent also relates to the moulded articles produced by
these
processes.
To produce the polycarbonate for the sheets according to the invention,
aqueous
solutions of an alkali salt of a bisphenol with a content of dissolved oxygen
<150 ppb, preferably <100 ppb, particularly preferably <50 ppb are used, which
may
preferably be obtained by reacting bisphenols with a dissolved oxygen content
<10 ppb with an aqueous alkali hydroxide solution with a dissolved oxygen
content
<100 ppb under oxygen exclusion.
Preferred alkali salts are the sodium salts of bisphenols.
Bisphenols which may be used according to the invention are those which may be
obtained by reacting ketones with aromatic hydroxy compounds which are not
substituted in the para position and do not contain any second order
substituents,
such as cyano, carboxy or nitro groups, for example phenol, o- and m-cresol,
2,6-
dimethylphenol, o-tert.-butylphenol, 2-methyl-6-tert.-butylphenol, o-
cyclohexyl-
phenol, o-phenylphenol, o-isopropylphenol, 2-methyl-6-cyclopentylphenol, o-
and
m-chlorophenol, 2,3,6-trimethylphenol, preferably phenol, o- and m-cresol, 2,6-
dimethylphenol, o-tert.-butylphenol and o-phenylphenol. Phenol is particularly
preferred. Ketones with at least one aliphatic group on the carbonyl function
are
preferred, for example acetone, methyl ethyl ketone, methyl propyl ketone,
methyl
isopropyl ketone, diethyl ketone, acetophenone, cyclohexanone, cyclopentanone,
methyl-, dimethyl- and trimethylcyclohexanones, which may also comprise
geminal
methyl groups, e.g. 3,3-dimethyl-5-methylcyclohexanone (hydroisophorone).
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Acetone, acetophenone, cyclohexanone and the homologues thereof bearing methyl
groups are very particularly preferred. Acetone is the most preferable. By
providing
an intensive inert nitrogen atmosphere throughout the production process, it
is
ensured that the residual content of dissolved oxygen in the bisphenols is
less than
10 ppb.
Bisphenols which may be used according to the invention are, additionally: 3-
(4-
hydroxyphenyl)-1,1,3-trimethylindan-5-ol; 1,3-di-(2-(4-hydroxyphenyl)-2-
propyl)-
benzene and 1,4-di-(2-(4-hydroxyphenyl)-2-propyl)benzene.
Bisphenols which are particularly preferred are 2,2-bis(4-
hydroxyphenyl)propane
(i.e. bisphenol A) and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.
The bisphenols or the mixtures thereof are preferably reacted, with the
exclusion of
oxygen (e.g. by providing an inert nitrogen atmosphere), with aqueous alkali
hydroxide solution having a dissolved oxygen content <100 ppb, preferably <20
ppb.
The concentration of aqueous alkali hydroxide solution is preferably such that
the
concentration of the resultant aqueous solutions of an alkali salt of a
bisphenol is as
close as possible to the solubility limit, i.e. in the range of from 15 to 20
wt.%,
preferably 16.5 to 18.5 wt.%. The molar ratio of alkali hydroxide to bisphenol
is in
particular from 1.8:1 to 2.5:1, preferably 1.9:1 to 2.4:1, particularly
preferably 2.0:1
to 2.3:1. The bisphenol may be dissolved as a solid in aqueous alkali
hydroxide
solution. However, it is preferable for it to be added to the aqueous alkali
hydroxide
solution directly as a melt at temperatures of from 20°C to
90°C, preferably 30°C to
70°C, without its having to pass through the solid state.
The virtually oxygen-free aqueous alkali hydroxide solution used to produce
the
aqueous solutions of an alkali salt of a bisphenol may be produced by
electrolysis.
After production, the aqueous alkali hydroxide solution should be stored and
transported under inert gas. For use in the process according to the
invention, the
concentration of aqueous alkali hydroxide solution ~ obtained during
electrolysis is
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generally reduced by dilution with virtually oxygen-free, fully deionised
water.
Oxygen is removed from the fully deionised water in a manner known in
principle,
e.g. catalytically, by degassing or by inert gas stripping.
,.
The aqueous solutions thus obtained of an alkali salt of a bisphenol exhibit
particularly low colour indexes, which are naturally also dependent on the
colour
index of the bisphenol used. If a bisphenol is used which has a colour index
<10
Hazen (measured according to ASTM D 1686), colour indexes of <1.5 Hazen,
preferably <1.0 Hazen may be achieved.
The polycarbonates may be branched deliberately and in a controlled manner by
the
use of small amounts of branching agent. Examples of suitable branching agents
are:
phloroglucinol, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-2-heptene; 4,6-
dimethyl-
2,4,6-tri-(4-hydroxyphenyl)heptane; 1,3,5-tri-(4-hydroxyphenyl)benzene; 1,1,1-
tri-
1 S (4-hydroxyphenyl)ethane; tri-(4-hydroxyphenyl)phenylmethane; 2,2-bis-[4,4-
bis(4-
hydroxyphenyl)cyclohexyl]propane; 2,4-bis(4-hydroxyphenylisopropyl)phenol; 2,6-
bis(2-hydroxy-5'-methylbenzyl)-4-methylphenol; 2-(4-hydroxyphenyl)-2-(2,4-dihy-
droxyphenyl)propane; hexa-(4-(4-
hydroxyphenylisopropyl)phenyl)orthoterephthalic
acid ester; tetra-(4-hydroxyphenyl)methane; tetra-(4-(4-
hydroxyphenylisopropyl)-
20- phenoxy)methane); a,a',a"-tris-(4-hydroxyphenyl)-1,3,5-
triisopropylbenzene; 2,4-
dihydroxybenzoic acid; trimesic acid; cyanuric chloride; 3,3-bis(3-methyl-4-
hydroxyphenyl)-2-oxo-2,3-dihydroindole; 1,4-bis(4',4"-
dihydroxytriphenyl)methyl)-
benzene. 1,1,1-tri-(4-hydroxyphenyl)ethane and bis-(3-methyl-4-hydroxyphenyl)-
2-
oxo-2,3-dihydroindole (= isatinbiscresol).
The branching agents or mixtures of branching agents which may optionally also
be
used, preferably in an amount of 0.05 to 2 mol-% relative to the bisphenols
used,
may be introduced together with the bisphenols or added at a later stage of
the
synthesis.
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Chain terminators may be used according to the invention. The chain
terminators
used according to the invention are preferably phenols such as phenol,
alkylphenols
such as cresol and 4-tert.-butylphenol, chlorophenol, bromophenol, cumylphenol
or
mixtures thereof. Phenol, 4-tert.-l~.utylphenol or cumylphenol are
particularly
preferred.
Chain terminators and branching agents may be added to the reaction mixture as
a
separate solution or together with the bisphenolate, wherein care must be
taken to
ensure that the solutions have the same low oxygen content according to the
invention as the aqueous solutions of an alkali salt of a bisphenol.
Other additives which may be used according to the invention and which may be
added to the polycarbonate from which the sheets according to the invention
are
produced, are mentioned in EP-A 0 500 496 and WO 96/15102. According to the
invention, mixtures of these additives may also be introduced into the
polycarbonate.
Additives which are particularly preferred are UV absorbers such as the
compounds
described in WO 99/05205 of formula (I)
~Rt~n
~ SRO"
~N H R3 Ra H
-N
N-N, ~ ~ ~ ~N
(I)
~R2~"' \(Ry)m
in which
R' and R2 are the same or different and mean H, halogen, C,-Clo alkyl, CS-Clo
cycloalkyl, CrC~3 aralkyl, C6-Ct4 aryl, -ORS or -(CO)-O-RS, with RS
being H or C1-C4 alkyl,
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R3 and Ra are also the same or different and mean H, C~-C4 alkyl, C6
cycloaikyl,
benzyl or C6-C~4 aryl,
m is l, 2 or 3 and ,.
n is 1, 2, 3 or 4,
and also those of formula (II)
(R~~n (Rt)n
I \N N/
N ~ _'-
N / Bridge \ N .
HO
OH (II)
(R2)n
(R2)n
in which the bridge means
O O
(CHR3)P C-O-(Y-O)q CI-(CHR4)p
RI, R2, m and n have the meaning stated in relation to formula (I),
in which, moreover, p is a whole number from 0 to 3,
q is a whole number from 1 to 10,
Y is -CH2-CHZ-, -(CHZ)s-, -(CH2~4-, -(CHZ)5-, -(CH2)s-, or CH(CH3)-CH2
and
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_g_
R3 and R4 have the meaning stated in relation to formula (I).
Other suitable UV absorbers are those comprising substituted triazines, such
as 2,4-
bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-n-octyloxyphenyl)-1,3,5-triazine
(CYASORB~ UV-
1164) or 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol (Tinuvin~
1577).
The UV absorber which is particularly preferred is 2,2-methylene bis(4-
(1,1,3,3-
tetramethylbutyl)-6-(2H-benzotriazol-2-yl)phenol), which is sold commercially
under the names Tinuvin~ 360 or Adeka Stab~ LA 31. The W absorber Uvinul
3030, made by BASF AG and obtained in accordance with Example 1 of WO
96/15102, is also suitable, as are the UV absorbers given in EP 0 500 496 A1.
Other suitable UV absorbers are 5'-methyl-, 3',S'-di-tert.-butyl-, 5'-tert.-
butyl-, 5'-
(1,1,3,3-tetramethylbutyl)-, (= Tinuvin 329), S-chloro-3',5'-di-tert.-butyl-,
S-chloro-
3'-tert.-butyl-5'-methyl-, 3'-sec.-butyl-5'-tert.-butyl, 4'-octoxy-, 3',5'-di-
tert.-amyl-,
3',5'-bis(a,a-dimethylbenzyl)-, mixture of 5-chloro-3'-tert.-butyl-5'-(2-
octyloxycarb-
onylethyl)- and 5-chloro-3'-tert.-butyl-5'-[2-(2-ethylhexyloxy)carbonylethyl]-
, 5-
chloro-3'-tert.-butyl-5'-(2-methoxycarbonylethyl)-, 3'-tert.-butyl-5'-(2-
methoxycarb-
onylethyl)-, 3'-tert.-butyl-S'-(2-octyloxycarbonylethyl)-, 3'-tert.-butyl-S'-
[2-(2-ethyl-
hexyloxy)-carbonylethyl]-, 3'-dodecyl-5'-methyl- and 3'-tert.-butyl-5'-(2-
isooctyl-
oxycarbonylethyl)-2'-hydroxyphenyl-2H-benzotriazole(2), 2,2'-methylenebis[4-
(1,1,3,3-tetramethylbutyl)-6-benzotriazol-2-yl-phenol] together with 3'-sec.-
butyl-5'-
(1,1,3,3-tetramethylbutyl-2'-hydroxyphenyl-2H-benzotriazole (= Tinuvin 350)
and 2-
[2'-hydroxy-3',5'-bis(1,1-dimethylbenzyl)phenyl]-2H-benzotriazole (= Tinuvin
234)
and 2-hydroxybenzophenones, such as for example 4-hydroxy-, 4-methoxy-, 4-
octoxy-, 4-decyloxy-, 4-dodecyloxy-, 4-benzyloxy-, 4,2',4-trihydroxy-, 2'-
hydroxy-
4,4'-dimethoxy derivative, ethyl-2-cyano-3,3-diphenyl acrylate (= Uvinul 3035)
made by BASF AG, 2-ethylhexyl-2-cyano-3,3-diphenyl acrylate (= Uvinul 3039)
made by BASF AG.
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Examples of suitable stabilisers, which may be used as additives according to
the
invention, are phosphines, phosphites or Si-containing stabilisers and other
compounds described in EP-A 0 500 496. Triphenyl phosphites, diphenylalkyl
phosphites, phenyldialkyl phosphites, tris(nonylphenyl) phosphite, triphenyl
phosphine, tetrakis(2,4-di-tert.-butylphenyl)-4,4'-biphenylene diphosphonite
and tri-
arylphosphite may be cited by way of example. Triphenylphosphine and tris(2,4-
di-
tert.-butylphenyl)phosphite are particularly preferred.
The polycarbonates, from which the sheets according to the invention are
produced,
may additionally contain additives to improve the surface slip
characteristics, for
example esters of polyhydric alcohols with long-chain fatty acids, such as for
example pentaerythritol tetrastearate/-palmitate, glycerol monostearate/-
palmitate,
glycerol tristearate/-palmitate. Furthermore, the addition of flame
retardants,
pigments, colorants, finely divided minerals, optical brighteners and other
additives
is also possible.
All the feed materials and solvents used for synthesis may be contaminated
with
impurities from the production and storage thereof, wherein the aim is to work
with
starting materials which are as clean as possible.
Glazing according to the invention comprises, in particular, glazing for
automobiles
or buildings, for example glazing for greenhouses, winter. gardens, bus
shelters,
advertising panels, signboards, protective screens, automotive glazing,
windows or
roofing.
Subsequent processing of the sheets according to the invention, such as
thermoforming or surface modification, such as application of scratch-proof
lacquers,
water-dispersing layers and the like, is possible.
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Examples
In the following Examples, the colour indexes were determined according to
ASTM
D 1686 by measuring absorption up to 400 nm over an irradiation length of 50
cm.
Weathering of these sheets (according to ISO 4892-2A) was performed in a
Weatherometer made by Atlas, USA, using a 6.5 W xenon lamp and a cycle
involving 102 mins of exposure to light and 18 mins of spraying with deionised
water together with light exposure. The maximum black body temperature was
60°C
(~ 5°C). After 1000 hours, samples of the sheets were taken and
toughness was
tested under practical conditions using a modified falling dart test which was
developed for mufti-walled sheets on the basis of DIN 53 443. The fracture
energy
WS being measured using a 5 mm diameter puncture body intended to cause
biaxial
stress similar to that caused by a falling hailstone. At room temperature, a
falling
mass of 36 kg falling from a height of 0.2 m struck the samples, which lay
freely on a
supporting ring with an internal diameter of 20 mm.
Testing was performed with the weathered side of the sample in the compression
zone. The fracture appearance (BB) was characterised by numbers: 1 =
splintered, 2
= smooth crack, 3 = ductile/brittle, 4 = ductile.
The yellowness index determined according to ASTM E 313 was stated as
Yellowness Index YI.
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Example 1
To produce 1.022 t/h of a 15% aqueous NaBPA solution, 867.5 kg/h of a 6.5%
aqueous sodium hydroxide solution,. and 154.5 kg/h of bisphenol A melt were
S combined continuously. The entire process was performed under an inert
atmosphere
of nitrogen. The 6.5% aqueous sodium hydroxide solution comprised an oxygen
content of 10 ppb. The Hazen colour index of the resultant 15% aqueous sodium
bisphenolate solution amounted to 0.5 Hazen. This sodium bisphenolate solution
was
used to produce polycarbonate by the interfacial polycondensation process.
Comparative Example 2
To produce 1.022 t/h of a 15 % aqueous sodium bisphenolate solution, 867.5
kg/h of
a 6.5% aqueous sodium hydroxide solution and 154.5 kg/h of bisphenol A melt
were
combined continuously. The entire process was performed under an inert
atmosphere
of nitrogen. The 6.5% aqueous sodium hydroxide solution comprised an oxygen
content of 250 ppb. The Hazen colour index of the resultant 15% aqueous sodium
bisphenolate solution amounted to 2 Hazen. This sodium bisphenolate solution
was
used to produce polycarbonate by the interfacial polycondensation process.
Example 3
A polycarbonate with phenol end groups, a melt flow index (MFR) of 3 (measured
according to ISO 1133), a branching agent content of 0.3 mol% isatinbiscresol
and a
UV absorber content of 0.25% Tinuvin~ 350 (3'-sec.-butyl-5'-(1,1,3,3-
tetramethyl-
butyl-2'-hydroxyphenyl-2H-benzotriazole) was produced from the sodium bis-
phenolate solution obtained in Example 1. This polycarbonate was processed in
the
following plant to produce 10 mm coextruded twin-wall sheets:
- main extruder having a screw of length 33D and a diameter of 70 mm with
venting
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- coextruder for applying the outer layer having a screw of length 25D and a
diameter of 30 mm
- special sheet die with a width of 350 mm
- calibrator ,.
- roller conveyor
- take-off unit
- cutting device (saw)
- stacking table.
The polycarbonate obtained from Example 1 was fed introduced into the
coextruder.
Coextrusion as such is known in the art (see for example EP-A 110 221 and EP-A
110 238). In the present instance, the process was performed as follows:
Extruders for producing the core layer and the outer layers) were connected to
a
coextrusion adapter. The adapter was designed that the melt forming the outer
layer
was applied as a thin layer adhering to the core layer melt.
The mufti-layer melt strand thereby produced was then given the desired form
(twin-
walled sheet) in the die connected downstream. The melt was then cooled in a
known
way under controlled conditions by means of vacuum calibration and
subsequently
sawn into pieces 1 metre in length.
Comparative Examine 4
A polycarbonate with phenol end groups, a melt flow index (MFR) of 3 (measured
according to ISO 1133), a branching agent content of 0.3 mol% isatinbiscresol
and a
L1V absorber content of 0.25% Tinuvin~ 350 (3'-sec.-butyl-S'-(1,1,3,3-
tetramethyl-
butyl-2'-hydroxyphenyl-2H-benzotriazole) was produced from the sodium bis-
phenolate solution obtained in Example 2. This polycarbonate was processed in
the
same plant and under the same conditions as in Example 3 to produce 10 mm
coextruded twin-wall sheets.
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Example 5
A polycarbonate with phenol end groups and a melt flow index (MFR) of 3
(according to ISO 1133) was produced from the sodium bisphenolate solution
obtained in Example 1. This polycarbonate was processed in the same plant and
under the same conditions as in Example 3 to produce 10 mm coextruded twin-
wall
sheets.
A compound of the polycarbonate obtained from Example 1 and 5% of a benzo
triazole UV absorber (Tinuvin~ 360 = 2,2-methylenebis-(4-(1,1,3,3-tetramethyl
butyl)-6-(2H-benzotriazol-2-yl)phenol) was introduced into the coextruder.
This
compound was produced in the following manner: the IIV absorber was mixed into
the polycarbonate in a twin-screw extruder (ZSK 32, Werner & Pfleiderer) at
280°C
and 80 rev/min and the extrudate was then pelletised.
Comparative Example 6
A polycarbonate with phenol end groups and a melt flow index (MFR) of 3
(according to ISO 1133) was produced from the sodium bisphenolate solution
obtained in Example 2. This polycarbonate was processed in the same plant and
under the same conditions as in Example 3 to produce 10 mm coextruded double-
wall sheets.
A compound of the polycarbonate obtained from Example 1 and 5% of a benzo
triazole UV absorber (Tinuvin~ 360 = 2,2-methylenebis-(4-(1,1,3,3-tetramethyl
butyl)-6-(2H-benzotriazol-2-yl)phenol) was introduced into the coextruder.
This
compound was produced in the following manner: the UV absorber was mixed into
the polycarbonate in a double-shaft extruder (ZSK 32, Werner & Pfleiderer) at
280°C
and 80 rev/min and the extrudate was then pelletised.
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Example 7
A polycarbonate with phenol end groups, a melt flow index (MFR) of 3 (measured
according to ISO 1133) and a W absorber content of 0.3% Tinuvin~ 350 (3'-sec.-
butyl-5'-(1,1,3,3-tetramethylbutyl-2'-hydroxyphenyl-2H-benzotriazole) was
produced
from the sodium bisphenolate solution obtained in Example 1. This
polycarbonate
was processed by injection moulding to produce colour chips 3 mm thick.
Comparative Example 8
A polycarbonate with phenol end groups, a melt flow index (MFR) of 3 (measured
according to ISO 1133) and a W absorber content of 0.3% Tinuvin~ 350 (3'-sec.-
butyi-5'-{1,1,3,3-tetramethylbutyl-2'-hydroxyphenyl-2H-benzotriazole) was
produced
from the sodium bisphenolate solution obtained in Example 2. This
polycarbonate
was processed by injection moulding to produce colour chips 3 mm thick.
The sheets obtained were then subjected to colorimetric assessment, using the
following measuring methods:
1. Transmission (on the basis of standard ASTM D 1003)
Apparatus: Pye-Unicam (measuring. geometry: 0°/diffuse, calculated
accord-
ing to illuminant C)
2. Yellowness index YI according to ASTM E 313
3. Weathering of these sheets was performed according to ISO 4892-2A in the
Weatherometer made by Atlas, USA using a 6.5 W xenon lamp and a cycle
involving 102 mins of exposure to light and 18 mins of spraying with
deionised water together with light exposure. The maximum black body
temperature was 60°C (t 5°C). After 1000 hours, samples of the
sheets were
taken and toughness was tested under practical conditions using a modified
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falling dart test developed for mufti wall sheets on the basis of DIN 53 443,
the fracture energy WS being measured using a 5 mm diameter puncture body
intended to cause biaxial stress similar to that caused by a falling
hailstone.
At room temperature, a falling mass of 36 kg falling from a height of 0.2 m
struck the samples, which lay freely on a supporting ring with an internal
diameter of 20 mm.
Testing was performed with the weathered side of the sample in the
compression zone. The fracture appearance (BB) was characterised by
numbers: 1 = splintered, 2 = smooth crack, 3 = ductile/brittle, 4 = ductile.
The yellowness index determined according to ASTM E 313 was stated as
Yellowness Index YI.
Results:
Transmission (%) Yellowness Index
Example 3 79.5 1.2
Comparative Example77.4 2.7
4
Example 7 87.3 3.0
Comparative Example84.0 5.5
8
Appearance Appearance of fractureAppearance
of of
fracture (0 (4000 hours weatheringfracture (5000
hours as
weathering stated) hours weathering
as as
stated) stated
Example 4x4 4x4 4x4
3
Comparative
4x4 4x3 4x3
example
4
Example 4x4 4x4 4x4
5
Comparative
4x4 3x4, 1x3 3x4, 1x3
example
6
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The results show that sheets produced according to the invention have higher
transmission values together with lower Yellowness Index values and better
mechanical stability after weathering than the sheets according to comparative
tests.
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