Note: Descriptions are shown in the official language in which they were submitted.
WO 98/05499 ~ PCT/EP97/03855
Multilayered, colored sheet of a crystallizable thermoplastic, a process for
its production and its use.
The invention relates to an amorphous, colored sheet of a crystallizable
thermoplastic, the thickness of which is in the range from 1 to 20 mm. The
invention furthemmore relates to a process for the production of this sheet
and to its use.
Multilayered sheets of plastics materials are known per se.
Such sheets of branched polycarbonates are described in EP-A-
0 247 480, EP-A-320 632 and US-A 5,108,835.
UV-stabilized polycarbonate shaped articles which are built up from
polydiorganosiloxane-polycarbonate block copolymers are known from
DE-A-34 14 116 and US-A 4,600,632.
Multilayered sheets of plastic with layers of polydiorganosiloxane-
polycarbonate block copolymers which comprise UV absorbers are known
from US-A 5,137,949. UV-stabilized, branched polycarbonates from
specific diphenols are known from EP-A-0 416 404. It is mentioned that
such polycarbonates can be employed for the production of sheets or
multiwall sheets.
All these sheets are made of polycarbonate, an amorphous thermoplastic
which cannot be crystallized. Polycarbonate sheets have the disadvantage
that they often lead to blooming in the form of white specks and surface
deposits, especially in the UV-stabilized embodiment (cf. EP-A-0 649 724).
According to EP-A-0 649 724, for example, evaporative loss of the UV
absorber is linked to a high degree to the average molecular weight.
These PC sheets, furthermore, are readily flammable and therefore
CA 02262~34 1999-01-29
require the addition of flameproofing agents so that they can be employed
for certain purposes, such as for interior applications. Tedious predrying
times and relativeiy long processing times at high temperatures are
necessary for further processing of these sheets to moldings. Devolatilizing
5 extruders must furthermore be used during sheet production for the
purpose of withdrawing moisture, which means that the additives added to
the raw material can also be removed at the same time, especially if low
molecular weight, relatively volatile additives are employed.
10 Single-layered, colored amorphous sheets having a thickness in the range
from 1 to 20 mm which comprise, as the main constituent, a crystallizable
thermoplastic, such as, for example, polyethylene terephthalate, and an
organic and/or inorganic pigment as a colorant have already been
described by the Applicant (German Patent Applications No. 19519577.9,
19522119. 2 and 19528333.3). These sheets can have a standard
viscosity of 800-6000 and comprise a UV stabilizer.
EP-A-0 471 528 describes a process for shaping an object from a
polyethylene terephthalate (PET) sheet. The PET sheet is heat-treated on
both sides in a thermoforming mold in a temperature range between the
20 glass transition temperature and the melting temperature. The shaped PET
sheet is removed from the mold when the extent of crystallization of the
shaped PET sheet is in the range from 25 to 50%. The PET sheets
disclosed in EP-A-0 471 528 have a thickness of 1 to 10 mm. Since the
thermoformed shaped article produced from this PET sheet is partly
25 crystalline and therefore no longer transparent and the surface properties
of the shaped article are determined by the thermoforming process and the
temperatures and shapes given by this, the optical properties (for example
gloss, clouding and light transmission) of the PET sheets employed are
unimportant. As a rule, the optical properties of these sheets are poor and
30 in need of optimization. These polyethylene terephthalate sheets also have
a single-layer construction and are not colored.
AMENDED SHEET
CA 02262~34 1999-01-29
-~ -re~ui~ ~he addition of f!ameproofin~ agents so that they can h~ l~mp~oy
for certain purposes, such as for interior applications. Tedious predrying
times and relatively long processing times at high temperatures are
necessary for further processing of these sheets to moldings. Devolatilizing
5 extruders must furthermore be used during sheet production for,the
purpose of withdrawing moisture, which means that the additi~es added to
the raw material can also be removed at the same time, es~Decially if low
molecular weight, relatively volatile additives are employefd.
!'
10 Single-layered, colored amorphous sheets having afthickness in the range
from 1 to 20 mm which comprise, as the main co,nstituent, a crystallizable
thermoplastic, such as, for example, polyethyle~e terephthalate, and an
organic and/or inorganic pigment as a colora~t have already been
described by the Applicant (German Patent Applications No.19519577.9,
19522116. 2 and 19528333.3). These s~eets can have a standard
viscosity of 800-6000 and comprise a UV stabilizer.
EP-A-0 471 528 describes a process for shaping an object from a
polyethylene terephthalate (PET) sheet. The PET sheet is heat-treated on
20 both sides in a thermoforming mold in a temperature range between the
glass transition temperature and the melting temperature. The shaped PET
sheet is removed from the mold when the extent of crystallization of the
shaped PET sheet is,in the range from 25 to 50%. The PET sheets
disclosed in EP-A-0 471 528 have a thickness of 1 to 10 mm. Since the
25 thermoformed s~aped article produced from this PET sheet is partly
crystalline an~therefore no longer transparent and the surface properties
of the shap~d article are determined by the thermoforming process and the
temperat~res and shapes given by this, the optical properties (for example
gloss,~louding and light transmission) of the PET sheets employed are
30 uni~portant. As a rule, the optical properties of these sheets are poor and
i~/need of optimization. These polyethylene terephthalate sheets also have
fa single-layer construction and are not cQIored.
US-A-3 496 143 describes vacuum thermoforming of a 3 mm thick PET
CA 02262~34 1999-01-29
sheet, the crystallization of which should be in the range from 5 to 25%.
The crystallinity of the themmoformed shaped article is greater than 25%.
On these PET sheets also, no requirements are imposed in respect of
optical properties. Since the crystallinity of the sheets employed is already
5 between 5% and 25%, these sheets are cloudy and nontransparent. These
partly crystalline PET sheets are also single-layered.
Austrian Patent Specification No. 304 086 describes a process for the
production of transparent shaped articles by the thermoforming process, a
10 PET sheet or film having a degree of crystallinity of less than 5% being
employed as the starting material.
The sheet or film used as the starting material is single-layered and has
been produced from a PET having a crystallization temperature of at least
1 60~C. From this relatively high crystallization temperature it follows that
15 the PET here is not a PET homopolymer but a glycol-modified PET, called
PET-G for short, which is a PET copolymer. In contrast to pure PET, PET-
G shows an extremely low tendency toward crystallization and is usually
present in the amorphous state because of the glycol units additionally
incorporated .
The object of the present invention is to provide a multilayered,
amorphous, colored sheet having a thickness of 1 to 20 mm which is
distinguished by good mechanical and homogeneous optical properties.
25 The homogeneous optical properties include, for example, a homogeneous
light transmission and a high surface gloss.
The good mechanical properties include, inter alia, a high impact strength
and a high fracture strength.
Furthermore, the sheet according to the invention should be recyclable, in
particular without loss of the mechanical properties, and poorly
combustible, so that, for example, it can also be used for interior
applications and in exhibition construction.
CA 02262~34 1999-01-29
This object is achieved by a multilayered, colored amorphous sheet having
a thickness of 1 to 20 mm which comprises, as the main constituent, at
least one crystallizable thermoplastic, wherein the sheet has at least one
core layer and at least one covering layer, the standard viscosity of the
5 cryst~lli7~hle thermoplastic of the core layer being higher than the standard
viscosity of the crystallizable themmoplastic of the covering layer, and
wherein at least one layer comprises at least one organic and/or inorganic
pigment as a colorant.
10 Amorphous sheet in the context of the present invention is understood as
meaning those sheets which are noncrystalline, although the crystallizable
thermoplastic employed has a crystallinity of between 5 and 65%.
Noncrystalline, i.e. essentially amorphous, means that the degree of
crystallinity is in general below 5%, preferably below 2%, and particularly
15 preferably is 0%, and that the sheet essentially shows no orientation.
According to the invention, crystallizable thermoplastic is understood as
meaning
- crystallizable homopolymers,
20 - crystallizable copolymers,
- crystallizable compounds,
- crystallizable recycled material and
- other variations of crystallizable thermoplastics.
25 Examples of suitable thermoplastics are polyalkylene terephthalates with a
C1 to C1 2-alkylene radical, such as polyethylene terephthalate and
polybutylene terephthalate, polyalkylene naphthalate with a C1 to
C12-alkylene radical, such as polyethylene naphthalate and polybutylene
naphthalate, and crystallizable cycloolefin polymers and cycloolefin
30 copolymers, it being possible for the thermoplastic or thermoplastics for the core iayer(s) (also called the base layer) and the thermoplastic or
thermoplastics for the covering layer(s) to be identical or different.
Polyolefins have also proved to be suitable for the covering layer.
CA 02262~34 1999-01-29
- Thermoplastics having a crystallite melting point Tm~ measured by DSC
(differential scanning calorimetry) with a heating-up rate of 10~C/minute, of
220~C to 260~C, preferably 230~C to 250~C, a crystallization temperature
range Tc of between 75~C and 260~C, a glass transition temperature Tg of
5 between 65~C and 90~C and a density, measured in accordance with DIN
53479, of 1.30 to 1.45 g/cm3 and a crystallinity of between 5% and 65%
are preferred polymers for the core layer and the covering layer as starting
materials for production of the sheet.
10 A thermoplastic having a cold (after-)crystallization temperature TCC of 120
to 158~C, in particular 130 to 158~C, is particularly preferred for the
purpose according to the invention.
The bulk density, measured in accordance with DIN 53466, is preferably
between 0.75 kg/dm3 and 1.0 kg/dm3, and particularly preferably between
0.80 kg/dm3 and 0.,90 kg/dm3.
The polydispersity MW/Mn of the thermoplastic, measured by means of
GPC, is preferably between 1.5 and 6.0, and particularly preferably
20 between 2.0 and 5Ø
A particularly preferred crystallizable thermoplastic for the core layer(s) and
the covering layer(s) is polyethylene terephthalate. The polyethylene
terephthalate preferably used according to the invention essentially
25 comprises monomer units of the following formula
O O
ECH2-CH2-O C~C O3
30 It is essential to the invention that the themmoplastic or thermoplastics of
the core layer(s) has or have a higher standard viscosity than the
thermoplastic OrllhC~ O~d~nCS Ot Ille ~ rin~ ~y~r~s) The~ st~a,J
viscosilies ~f th~ th~rmoplastics ~f ~ari~us cor~ af.d/or ~vel n ~y ~ayers of a~multila~crccl pl~tc 3an d~er.
CA 02262~34 1999-01-29
thermoplastics of the covering layer(s). The standard
viscosities of the thermoplastics of various core and/or covering layers of a
multilayered plate can differ.
AMENDED SHEET
CA 02262534 1999-01-29
The standard viscosity SV (DCA) of the crystallizable thermoplastic of the
core layer or base layer, measured in dichloroacetic acid in accordance
with DIN 53728, is preferably between 800 and 5000, and particularly
preferably between 1000 and 4500.
The standard viscosity SV (DCA) of the crystallizable thermoplastic of the
covering layer, measured in dichloroacetic acid in accordance with DIN
53728, is preferably between 500 and 4500, and particularly preferably
between 700 and 4000.
The intrinsic viscosity IV (DCA) can be calculated from the standard
viscosity SV (DCA) as follows:
IV (DCA) = 6.67 x 10-4 SV (DCA) + 0.118
The amorphous, multilayered sheet according to the invention furthermore
comprises at least one organic and/or inorganic pigment. The pigment or
also a mixture of pigments can be added to one or more of the layers. The
concentration of the colorant is preferably in the range from 0.1 to 30% by
weight, based on the weight of the thermoplastic in the layer treated with
pigment.
Organic and inorganic pigments which are suitable for the invention are
described in the abovementioned German Patent Applications No.
195 195 77.9, 195 221 19.2 and 195 283 33.3. By citation, these
Applications are valid as belonging to the disclosure of the present
Application .
When considering colorants, a distinction is made in accordance with DIN
55944 between dyestuffs and pigments. Pigments are virtually insoluble in
the polymer under the respective processing conditions, whereas dyestuffs
are soluble (DIN 55949).
AMENDED SHEET
CA 02262~34 1999-01-29
Th_ ~Id"darJ ~ ;usty ~V ~DCA) ef Ih~: ~,ly~lalllzable thermoplastic a~he
core layer or base layer, measured in dichloroacetic acid in accorda,7ce
with DIN 53728, is preferably between 800 and 5000, and particu,~rly
preferably between 1000 and 4500.
The standard viscosity SV (DCA) of the crystallizable thermf~plastic of the
covering layer, measured in dichloroacetic acid in accord~nce with DIN
53728, is preferably between 500 and 4500, and parti~fiarly preferably
between 700 and 4000.
The intrinsic viscosity IV (DCA) can be calculate~from the standard
viscosity SV (DCA) as follows: /
IV (DCA) = 6.67 x 10-4 SV (DCA) + 0.118/
The amorphous, multilayered sheet af~cording to the invention furthemmore
comprises at least one organic and)6r inorganic pigment. The pigment or
also a mixture of pigments can bfl'added to one or more of the layers. The
concentration of the colorant i~fpreferably in the range from 0.1 to 30% by
weight, based on the weight~6f the thermoplastic in the layer treated with
pigment.
Organic and inorgan~/pigments which are suitable for the invention are
described in the a)7~ovementioned German Patent Applications No.
195 195 77.9,1~5 221 19.2 and 195 283 33.3. By citation, these
Applications~e valid as belonging to the disclosure of the present
Applicatio~
When/~onsidering colorants, a distinction is made in accordance with DIN
559~4 between dyestuffs and pigments. Pigments are virtually insoluble in
th,~ polymer under the respective processing conditions, whereas dyestuffs
e s~l~o (DIN 55Dq9~¦ The coloring action of the pigments is brought
about by the particles themselves. The term pigment is generally linked to
a particle size of 0.01 to 1.0,um. According to DIN 53206, when defining
CA 02262~34 l999-0l-29
pigment particles a distinction is made between primary particles,
aggregates and agglomerates.
Primary particles such as are generally obtained in the preparation
5 possess a pronounced tendency to aggregate as a result of their extremely
small particle size. This produces, by areal aggregation of the primary
particles, the aggregates, which thus have a smaller surface area than that
corresponding to the sum of the surface areas of their primary particles. As
a result of the agglomeration of primary particles and/or aggregates at
10 comers and edges, agglomerates are formed, the total surface areas of
which differ only little from the sum of the individual areas. If pigment
particle size is referred to - without more detailed indications - this refers to
the aggregates such as are essentially present after coloration.
15 In pulverulent pigments, the aggregates have always come together to
forrn agglomerates, which, during coloration, must be divided up, wetted by
the polymer and homogeneously distributed. These simultaneously
occurring processes are called dispersion. In the case of coloring with
dyestuffs, on the other hand, the process is a solution process, as a result
20 of which the dye is present in molecularly dissolved form.
In contrast to the inorganic pigments, in the case of individual organic
pigments there is no complete insolubility, especially not in the case of
pigments of simple composition having low molecular weights.
Dyestuffs are adequately described by their chemical structure. Pigments
which are in each case of identical chemical composition, however, can be
prepared in and exist in different crystal modifications. A typical example of
this is the white pigment titanium dioxide, which can exist in the rutile form
30 and in the anatase foml.
In the case of pigments, it is possible by coating, i.e. by aftertreatment of
the pigment particle surface, using organic or inorganic agents, to achieve
an improvement in the use properties. This improvement lies in particular
CA 02262~34 1999-01-29
in facilitating dispersion and in raising the light stability and resistance to
weathering and chemicals. Typical coating agents for pigments are, for
example, fatty acids, fatty acid amides, siloxanes and aluminum oxides.
5 Examples of suitable inorganic pigments are the white pigments titanium
dioxide, zinc sulfide and tin sulfide, which may be coated with organic
and/or inorganic substances.
The titanium dioxide particles can comprise anatase or rutile, but
10 preferably rutile, which, in comparison to anatase, has a higher covering
power. In a preferred embodiment, at least 95% by weight of the titanium
dioxide particles consist of rutile. They can be prepared by a customary
process, for example by the chloride or the sulfate process. The mean
particle size is relatively low and is preferably in the range from 0.10 to
0.30 ~m.
By using titanium dioxide of the type described, no vacuoles form within the
polymer matrix during production of sheets.
20 The titanium dioxide particles can have a coating of inorganic oxides as is
usually employed as a coating for TiO2 white pigment in papers or coating
compositions, to improve the light fastness. TiO2 is known to be
photoactive. Under the action of UV rays, free radicals form on the surface
of the particles. These free radicals may migrate to the film-forming
25 constituents of the coating composition, leading to degradation reactions
and yellowing. Particularly suitable oxides include the oxides of aluminum,
silicon, zinc or magnesium, or mixtures of two or more of these
compounds. TiO2 particles having a coating of several of these compounds
are described, for example, in EP-A-0 044 515 and EP-A-0 078 633. The
30 coating can also comprise organic compounds having polar and nonpolar
groups. During production of the sheet by extrusion of the polymer melt,
the organic compounds must be of sufficient heat stability. Examples of
polar groups are -OH, -OR and -COOX (X = R, H or Na, R = alkyl having 1
to 34 carbon atoms). Preferred organic compounds are alkanols and fatty
CA 02262~34 1999-01-29
acids having 8 to 30 carbon atoms in the alkyl group, in particular fatty
acids and primary n-alkanols having 12 to 24 carbon atoms, and also
polydiorganosiloxanes and/or polyorganohydridosiloxanes, such as, for
example, polydimethylsiloxane and polymethylhydridosiloxane.
The coating on the titanium dioxide particles usually comprises 1 to 12, in
particular 2 to 6 g of inorganic oxides and 0.5 to 3, in particular 0.7 to 1.5 gof organic compound, based on 100 g of titanium dioxide particles. The
coating is applied to the particles in aqueous suspension. The inorganic
10 oxides are precipitated in the aqueous suspension from water-soluble
compounds, for example alkali metal, in particular sodium, aluminate,
aluminum hydroxide, aluminum sulfate, aluminum nitrate, sodium silicate
(water-glass) or silicic acid.
15 Inorganic oxides, such as Al2O3 and SiO2, are also to be understood as
meaning the hydroxides or various dehydration stages thereof, such as, for
example, oxide hydrates, without the precise composition and structure
thereof being known. The oxide hydrates, for example of aluminum and/or
silicon, are precipitated onto the TiO2 pigment after calcining and grinding
20 in aqueous suspension, and the pigments are then washed and dried. This
precipitation can therefore take place directly in a suspension as is
obtained in the preparation process following calcining and the subsequent
wet grinding. The precipitation of the oxides and/or oxide hydrates of the
respective metals takes place from the water-soluble metal salts within the
25 known pH range; for aluminum, for example, aluminum sulfate in aqueous
solution (pH less than 4) is employed, and the oxide hydrate is precipitated
by addition of aqueous ammonia solution or sodium hydroxide solution in
the pH range between 5 and 9, preferably between 7 and 8.5. If a water-
glass or alkali metal aluminate solution is used as the starting substance,
30 the pH of the initially introduced TiO2 suspension should be in the strongly
alkaline range (pH greater than 8). The precipitation is then extracted by
addition of mineral acid, such as sulfuric acid, in the pH range from 5 to 8.
After precipitation of the metal oxides, the suspension is stirred for a further15 minutes to about 2 hours, during which the precipitated layers undergo
CA 02262~34 1999-01-29
ageing. The coated product is separated off from the aqueous dispersion
and, after washing, is dried at elevated temperature, in particular at 70 to
1 1 O~C.
5 Typical inorganic black pigments are carbon black modifications, which
may likewise be coated, carbon pigments which differ from the carbon
black pigments by a higher ash content, and black oxide pigments, such as
iron oxide black and copper, chromium and iron oxide mixtures (mixed
phase pigments).
Suitable inorganic colored pigments are colored oxide pigments, hydroxyl-
containing pigments, sulfide pigments and chromates.
Examples of colored oxide pigments are iron oxide red, titanium dioxide-
15 nickel oxide-antimony oxide mixed phase pigments, titanium dioxide-
chromium oxide-antimony oxide mixed phase pigments, mixtures of oxides
of iron, zinc and titanium, chromium oxide-iron oxide brown, spinels of the
system cobalt-aluminum-titanium-nickel-zinc oxide, and mixed phase
pigments based on other metal oxides.
Examples of typical hydroxyl-containing pigments are oxide hydroxides of
trivalent iron, such as FeOOH.
Examples of sulfide pigments are calcium sulfide selenides, cadmium-zinc
25 sulfides, and sodium aluminum silicate containing sulfur bonded in a
polysulfide form in the lattice.
Examples of chromates are the lead chromates, which can exist in the
crystal forms monoclinic, rhombic and tetragonal.
All colored pigments, like the white and black pigments, can be either
uncoated or coated with inorganic and/or organic substances.
The organic colored pigments are as a rule divided into azo pigments and
CA 02262~34 1999-01-29
11
so-called non-azo pigments.
The characteristic feature of the azo pigments is the azo (-N=N-) group.
Azo pigments can be monoazo pigments, diazo pigments, diazo
5 condensation pigments, salts of azo dye acids and mixtures of the azo
pigments.
In specific embodiments, the amorphous, multilayered sheet can also
comprise mixtures of inorganic and/or organic pigments and additionally
10 soluble dyestuffs in the core layer and/or covering layer.
The concentration of the soluble dyestuff here is preferably in the range
from 0.01 to 20% by weight, particularly preferably in the range from 0.5 to
10% by weight, based on the weight of the crystallizable thermoplastic.
Among the soluble dyestuffs, those dyestuffs which are soluble in fats and
aromatic substances are preferred. These are azo and anthraquinone
dyestuffs.
20 Suitable soluble dyestuffs for the present invention are mentioned in
German Patent Applications No.195 195 78.7,195 221 20.6 and
195 283 34.1. By citation, these Applications belong to the disclosure
content of the present application.
The crystallizable thermoplastics used according to the invention can be
25 obtained by customary processes known to the expert. In general,
thermoplastics such as are used according to the invention can be
obtained by polycondensation in the melt or by a two-stage
polycondensation. The first step here is carried out up to a moderate
molecular weight - corresponding to a moderate intrinsic viscosity IV of
30 about 0.5 to 0.7 - in the melt, and the further condensation is carried out by
means of solid condensation. The polycondensation is usually carried out
in the presence of known polycondensation catalysts or catalyst systems.
In the solid condensation, chips of the thermoplastic are heated at
temperatures in the range from 180 to 320~C under reduced pressure or
CA 02262~34 1999-01-29
under an inert gas until the desired molecular weight is reached.
For example, the preparation of polyethylene terephthalate, which is
particularly preferred according to the invention, is described in detail in a
large number of patent applications, such as in JP-A-60-139 717, DE-C-2
429 087, DE-A-27 07 491, DE-A-23 19 089, DE-A-16 94 461, JP-63-41
528, JP-62-39 621, DE-A-41 17 825, DE-A-42 26 737, JP-60-141 715, DE-
A-27 21 501 and US-A-5 296 586.
Polyethylene terephthalates having particularly high molecular weights can
be prepared, for example, by polycondensation of dicarboxylic acid-diol
precondensates (oligomers) at elevated temperature in a liquid heat
transfer medium in the presence of customary polycondensation catalysts
and, if appropriate, cocondensable modifying agents, if the liquid heat
transfer medium is inert and free from aromatic structural groups and has a
boiling point in the range from 200 to 320~C, a weight ratio of dicarboxylic
acid-diol precondensate (oligomer) employed to liquid heat transfer
medium is in the range from 20:80 to 80:20, and the polycondensation is
carried out in a boiling reaction mixture in the presence of a dispersion
stabilizer.
The multilayered, colored, amorphous sheets according to the invention
can furthermore be treated with suitable additives, if desired. These
additives can be added, as required, to one or more layers of the sheet
individually or as a mixture, it also being possible for the layers to be those
with a colorant.
Examples of suitable additives are UV stabilizers and antioxidants, such as
are described in German Patent Application No.195 221 19.2 and
Application by the same Applicant, attached at the same time, entitled
'Polyethylene terephthalate sheet of improved stability to hydrolysis'. By
citation, these applications are valid as a constituent of the disclosure
content of the present application.
As stated above, the multilayered, colored, amorphous sheet can
CA 02262~34 1999-01-29
- 13
additionally comprise at least one UV stabilizer as a light stabilizer in the
covering layer(s) and/or the core layer(s).
Light, in particular the ultraviolet portion of solar radiation, i.e. the
wavelength range from 280 to 400 nm, initiates degradation processes in
thermoplastics, as a consequence of which not only does the visual
appearance change, owing to a change in color or yellowing, but also the
mechanical-physical properties are adversely influenced.
Inhibition of these photooxidative degradation processes is of considerable
industrial and economic importance, since otherwise the possible uses of
numerous thermoplastics are limited drastically.
A high UV stability means that the sheet is not damaged or is damaged
only extremely little by sunlight or other UV radiation, so that the sheet is
suitable for exterior applications and/or critical interior applications, and
shows no or only slight yellowing even after several years of external use.
Polyethylene terephthalates, for example, already start to absorb UV light
below 360 nm, and their absorption increases considerably below 320 nm
and is very pronounced below 300 nm. The maximum absorption is
between 280 and 300 nm.
In the presence of oxygen, chiefly chain splitting reactions but no
crosslinking reactions are observed here. Carbon monoxide, carbon
dioxide and carboxylic acid are the predominant photooxidation products in
terms of amount. In addition to direct photolysis of the ester groups,
oxidation reactions which likewise result in the formation of carbon dioxide
via peroxide radicals must also be taken into consideration.
The photooxidation of polyethylene terephthalates can also lead, via
splitting off of hydrogen in the ~-position of the ester groups, to
hydroperoxides and decomposition products thereof and to associated
chain splitting reactions (H. Day, D. M. Wiles: J. Appl. Polym. Sci 16,1972,
page 203).
CA 02262~34 1999-01-29
14
UV stabilizers, also called light stabilizers or UV absorbers, are chemical
compounds which can intervene in the physical and chemical processes of
light-induced degradation.
5 Certain pigments, such as, for example, carbon black, can also partly have
the effect of light protection. However, these substances are unsuitable for
the colored sheets according to the invention, since they lead to
discoloration or a change in color. Only those UV stabilizers, for example,
from the class of organic and organometallic compounds which bring about
10 very, very little or no color or change in color in the themmoplastic to be
stabilized are expediently used for the amorphous sheets according to the
nventlon.
Examples of UV stabilizers which are suitable for the present invention are
15 2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organonickel
compounds, salicylic acid esters, cinnamic acid ester derivatives,
resorcinol monobenzoate, oxalic acid anilides, hydroxybenzoic acid esters,
sterically hindered amines and triazines, 2-hydroxybenzotriazoles and
triazines being preferred.
20 Mixtures of several UV stabilizers can also be employed.
The UV stabilizer is expediently present in a layer in a concentration of
0.01% by weight to 8% by weight, preferably 0.01 to 5% by weight, based
on the weight of the themmoplastic in the layer treated with the stabilizer.
25 However, if the UV stabilizer is added to a core layer, a concentration of
0.01% by weight to 1% by weight, based on the weight of the
thermoplastic, in the core layer treated with the stabilizer is in general
sufficient.
According to the invention, several layers can be treated simultaneously
30 with UV stabilizer. In general, however, it is sufficient for the layer on which
the UV radiation impinges to be treated.
The core layer(s) can be treated in order to prevent UV radiation impairing
the underlying core layer in the event of possible damage to the covering
CA 02262~34 1999-01-29
layer.
In a particularly preferred embodiment, the colored, amorphous sheet
according to the invention comprises, as the main constituent, a
5 crystallizable polyethylene terephthalate for the core layer and covering
layer and 0.01% by weight to 8.0% by weight of 2-(4,6-diphenyl-1,3,5-
triazin-2-yl)-5-(hexyl)oxyphenol or 0.01% by weight to 8.0% by weight of
2,2'-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1 ,1 ,3,3-
tetramethylbutyl)phenol in the covering layer.
10 A mixture of these compounds and a mixture of at least one of these
compounds with at least one other UV stabilizer can of course also be
used.
The sheet according to the invention can also be treated with at least one
1 5 antioxidant.
Antioxidants are chemical compounds which can delay the oxidation and
hydrolysis phenomena and the resulting aging.
Antioxidants which are suitable for the sheet according to the invention can
20 be classified as follows:
Additive group Substance class
Primary antioxidants Sterically hindered phenols and/or
secondar,v aromatic amines
Secondary antioxidants Phosphites and phosphonites, thioethers,
carbodiimides, zinc dibutyl-dithiocarbamate
Mixtures of primary and secondary antioxidants and/or mixtures of
secondary and/or primary antioxidants with UV stabilizers can furthermore
be used. It has been found, surprisingly, that such mixtures show a
synergistic effect.
In a preferred embodiment, the amorphous sheet according to the
CA 02262~34 1999-01-29
invention comprises a phosphite and/or a phosphonite and/or a
carbodiimide as a hydrolysis and oxidation stabiliser.
Examples of antioxidants used according to the invention are 2-[(2,4,8,10-
tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxa-phosphepin-6-yl]oxy)-
ethyl]ethanamine and tris-(2,4-di-tert-butylphenyl) phosphite.
The antioxidant is usually present in a concentration of 0.01 to 6% by
weight, based on the weight of the thermoplastic of the layer treated with
1 0 this.
The thickness of the multilayered sheet according to the invention varies
between 1 mm and 20 mm, it being possible for the thickness of the
covering layer(s) to be between 10 ~m and 1 mm, depending on the sheet
thickness. The covering layers preferably each have a thickness of
between 400 and 500 ~m.
As already stated, the sheet according to the invention can have several
core and covering layers which are laid one on top of the other like a
sandwich. However, the sheet can also consist of only one covering layer
and one core layer.
A structure having two covering layers and a core layer Iying between the
covering layers is particularly preferred according to the invention.
The individual covering and core layers can comprise different or identical
crystallizable themmoplastics as the main constituents, as long as the
thermoplastic of a core layer has a higher standard viscosity than the
thermoplastic of the covering layers directly adjacent to this core layer. A
layer can also comprise a mixture of crystallizable thermoplastics.
If desired, the colored, amorphous, multilayered sheet according to the
invention, which optionally comprises one or more additives, can be
provided with a scratch-resistant surface on one side or several sides.
CA 02262~34 1999-01-29
17
Possible coating systems and materials for the scratch-resistant surface
(coating) are all the systems and materials known to the expert.
Suitable coating systems and materials are described, in particular, in
German Patent Application No. 196 255 34.1, to the full contents of which
5 reference is made for the present invention.
From the large number of possible coating systems and materials, some
are mentioned as examples below.
(1) US-A-4822828 discloses aqueous, radiation-curable coating
compositions which comprise, in each case based on the weight of the
dispersion, (A) from 50 to 85% of a silane having vinyl groups, (B) from 15
to 50% of a multifunctional acrylate and, if appropriate, (C) 1 to 3% of a
photoinitiator.
(2) Inorganic/organic polymers, so-called ormocers (organically
modified ceramics), which combine the properties of ceramic materials and
polymers, are also known. Ormocers are employed, in particular, as hard
and/or scratch-resistant coatings on polymethyl methacrylate (PMMA) and
20 polycarbonate (PC). The hard coatings are bonded on the basis of Al2O3,
ZrO2, TiO2 or SiO2 as network formers and epoxide or methacrylate
groups with Si by --Si-C- compounds.
(3) Coating compositions for acrylic resin plastics and polycarbonate
25 based on silicone resins in aqueous-organic solution which have a
particularly high storage stability are described, for example, in EP-A-0 073
362 and EP-A-0 073 911. This technique uses the condensation products
of partly hydrolyzed organosilicon compounds as coating compositions,
above all for glass, and in particular for acrylic resin plastics and PC.
(4) Acrylic-containing coatings are also known, such as, for example,
the Uvecryl coatings from UCB Chemicals. One example is Uvecryl 29203,
which is cured with UV light. This material comprises a mixture of urethane
acrylate oligomers with monomers and additives. Constituents are about
CA 02262~34 1999-01-29
18
81% of acrylate oligomer and 19% of hexanediol diacrylate. These
coatings are likewise described for PC and PMMA.
(5) CVD or PVD coating technologies with the aid of a polymerizing
5 plasma and diamond-like coatings are also described in the literature
(Dunnschichttechnologie [Thin-layer technology], edited by Dr.Hartmut
Frey and Dr. Gerhard Kienel, VDI Verlag, Dusseldorf, 1987~. These
technologies are used here in particular for metals, PC and PMMA.
10 Other commercially obtainable coatings are, for example, Peeraguard from
Peerless, Clearlite and Filtalite from Charvo, coating types such as, for
example, the UVHC series from GE Silicones, Vuegard such as the 900
series from TEC Electrical Components, Highlink OG series from Société
Francaise Hoechst, PPZ~ products marketed by Siber Hegner (produced
15 by Idemitsu) and coating materials from Vianova Resins, Toagoshi,
Toshiba or Mitsubishi. These coatings are also described for PC and
PMMA.
Coating processes known from the literature are, for example, offset
20 printing, pouring on, dipping processes, flow-coating processes, spray
processes or atomizing processes, knife-coating or rolling.
Coatings applied by the processes described are then cured, for example
by means of UV radiation and/or heat. For the coating processes, it may be
25 advantageous to treat the surface to be coated with a primer, for example
based on acrylate or an acrylic latex, before application of the coating.
Other known processes are, for example:
CVD processes and vacuum plasma processes, such as, for example,
30 vacuum plasma polymerization, PVD processes, such as coating with
electron beam vaporization, resistance-heated vaporizer sources or
coating by conventional processes under a high vacuum, such as in the
case of a conventional metallization.
CA 02262~34 1999-01-29
Literature on CVD and PVD is, for example: Modeme
Beschichtungsverfahren [Modern coating processes] by H.-D. Steffens and
W. Brandl. DGM Infomlationsgesellschaft Verlag Oberursel. Other
literature on coatings: Thin Film Technology by L. Maissel, R. Glang,
5 McGraw-Hill, New York (1983).
Coating systems which are particularly suitable for the purpose of the
present invention are systems (1), (2), (4) and (5), coating system (4) being
particularly preferred.
Suitable coating processes are, for example, also the pouring, the
spraying, the atomizing, the dipping and the offset process, the atomizing
process being preferred for coating system (4).
15 For coating the amorphous sheets, curing with UV radiation and/or at
temperatures which preferably do not exceed 80~C can be carried out, UV
curing being preferred.
The coating according to system (4) has the advantage that no
20 crystallization which could cause clouding occurs. Furthermore, the coating
shows an outstanding adhesion, outstanding optical properties and a very
good resistance to chemicals and causes no impairment of the intrinsic
color.
25 The thickness of the scratch-resistant coating is in general between 1 and
50 ,um.
The amorphous sheet according to the invention, which comprises a
crystallizable thermoplstic, such as, for example, PET, as the main
30 constituent, has outstanding mechanical and optical properties. Thus,
when the impact strength an according to Charpy (measured in accordance
with ISO 179/1 D) is measured on the sheet, preferably no fracture occurs.
Furthermore, the notched impact strength ak according to Izod (measured
in accordance with ISO 180/1A) of the plate is preferably in the range from
CA 02262~34 1999-01-29
2.0 to 8.0 kJ/m2, particularly preferably in the range from 4.0 to 6.0 kJ/m2.
The surface gloss, measured in accordance with DIN 67530 (measurment
angle 20~) is preferably greater than 100, and the light transmission,
measured in accordance with ASTM D 1003, is preferably less than 60%.
Weathering tests have shown that even after 5 to 7 years of exterior use,
the UV-stabilized sheets according to the invention show no visible
yellowing and no visible loss of gloss, as well as no visible surface defects.
Furthermore, the sheet according to the invention is poorly flammable and
produces non-buming drips with very little evolution of smoke, so that it is
also particularly suitable for interior applications and in exhibition
construction.
The sheet according to the invention furthermore can recycled without
problems, without pollution of the environment and without loss in the
mechanical properties, which means that it is suitable, for example, for the
production of short-lived advertising signs or other advertising articles.
Outstanding and economical thermoforming properties (heat forming and
vacuum forming properties) have in addition completely unexpectedly been
found. Surprisingly, in contrast to polycarbonate sheets, it is not necessary
to predry the sheet according to the invention before thermoforming. For
25 example, polycarbonate sheets must be predried at about 1 25~C for 3 to
50 hours before thermoforming, depending on the sheet thickness.
Furthermore, the sheet according to the invention can be obtained with
very low thermoforming cycle times and at low temperatures during the
30 thermoforming. On the basis of these properties, shaped articles can be
produced economically and with a high productivity from the sheet
according to the invention on customary thermoforming machines.
The production of the multilayered, colored, amorphous sheet according to
CA 02262~34 1999-01-29
21
the invention, which has been treated, if appropriate, with one or more
additives, can be carried out, for example, by the coextrusion process
known per se in an extrusion line.
5 Coextrusion as such is known from the literature (cf., for example,
EP-1 10 221 and EP-1 10 238, which are expressly referred to here).
In this case, an extruder for plasticizing and producing the core layer and a
further extruder per covering layer are each connected to a coextruder
10 adapter. The adapter is constructed such that the melts which form the
covering layers are applied as thin layers adhesively to the melt of the core
layer. The multilayered melt strand thus produced is then shaped in the
downstream die and sized, polished and cooled in the polishing stack,
before the sheet is cut to size.
The process for the production of the sheets according to the invention is
described generally below.
If necessary, the thermoplastic polymer can be dried before the
coextrusion.
Drying can expediently be carried out at temperatures in the range from
1 10 to 1 90~C over a period of 1 to 7 hours. The main drier is associated
with the main extruder, and, per covering layer, a drier is associated with a
coextruder.
Thereafter, the thermoplastic or the thermoplastics for the core layer(s) and
the covering layer(s) are melted in the main extruder and in the
coextruders. The temperature of the melt is preferably in the range from
230 to 330~C, it then being possible for the temperature of the melt to be
30 established essentially both by the temperature of the extruder and by the
residence time of the melt in the extruder.
If polyethylene terephthalate, which is preferred according to the invention
as the thermoplastic, is used, drying is usually carried out at 160 to 1 80~C
CA 02262~34 1999-01-29
for 4 to 6 hours and the temperature of the melt is established in the range
from 250 to 320~C.
The colorant and, if appropriate, the additive, such as a UV stabilizer
5 and/or an antioxidant, can be metered into the themmoplastic of the
corresponding layer by the actual manufacturer of the raw material, or can
be metered into the extruder during sheet production.
Addition of the colorant and the additives via masterbatch technology or via
the solid pigment preparation is particularly preferred. In this case, the
10 colorant and, if appropriate, the additives are dispersed completely in a
solid carrier material. Possible carrier materials are certain resins, the
thermoplastic itself, or else other polymers which are sufficiently
compatible with the thermoplastic.
15 It is important that the particle size and bulk density of the masterbatch are
similar to the particle size and bulk density of the therrnoplastic, so that
homogeneous distribution and thus a homogeneous effect of the colorant
and additives, such as, for example, homogeneous coloration and
stabilization to UV and hydrolysis, can be achieved.
As already stated, the main extruder for producing the core layer and the
coextruder(s) are connected to a coextruder adapter such that the melts
forming the covering layers are applied as thin layers adhesively to the
melt of the core layer. The multilayered melt strand thus produced is
25 shaped in a die connected to the line. This die is preferably a slot die.
The multilayered melt strand shaped by a slot die is then sized by polishing
calender rolls, i.e. cooled intensively and polished. The calender rolls used
can be arranged, for example, in an 1-, F-, L- or S-shape.
The material can then be after-cooled on a roller conveyor, trimmed to size
at the edges, cut to length and stacked.
The thickness of the resulting sheet is essentially determined by the take-
CA 02262~34 1999-01-29
23
off, which is positioned at the end of the cooling zone, by the cooling
(polishing) rolls coupled to this in temms of speed, and by the conveying
speed of the extruder on the one hand and the distance between the rolls
on the other hand.
Both single-screw and twin-screw extruders can be employed as the
extruders.
The slot die preferably comprises the dismountable die body, the lips and
10 the restrictor bar for flow regulation via the width. For this, the restrictor bar
can be bent by tension and pressure screws. The thickness is set by
adjusting the lips. It is important to ensure that the multilayered melt strand
and the lip have a uniform temperature, since otherwise the melt strand
flows out in different thicknesses as a result of the different flow paths.
The sizing die, i.e. the polishing calender, gives the melt strand the shape
and the dimensions. This is effected by freezing to below the glass
transition temperature by means of cooling and polishing. Shaping should
no longer take place in this state, since otherwise surface defects would
20 form because of the cooling which has taken place. For this reason, the
calender rolls are preferably driven jointly. The temperature of the calender
rolls must be lower than the crystallite melting temperature in order to avoid
sticking of the melt strand. The melt strand preferably leaves the slot die
with a temperature of 240 to 300~C. The first polishing/cooling roll has a
25 temperature between 50~C and 80~C, depending on the output and sheet
thickness. The second, somewhat cooler roll cools the second or other
surface.
To obtain a uniform thickness in the range from 1 to 20 mm, with good
30 optical properties, it is essential for the temperature of the first polishing roll
to be 50 to 80~C.
While the sizing device freezes the surfaces of the sheet as smoothly as
possible and cools the profile to the extent that it is dimensionally stable,
CA 02262~34 1999-01-29
24
the after-cooling device lowers the temperature of the sheet to virtually
room temperature. After-cooling can take place on a roller board.
The speed of the take-off should be coordinated precisely with the speed
5 of the calender rolls in order to avoid defects and variations in thickness.
As additional devices, the extrusion line for production of the sheets
according to the invention can comprise a separating saw as a device for
cutting to length, the edge trimmer, the stacking unit and a control station.
10 The edge or margin trimmer is advantageous, since under certain
circumstances the thickness in the margin region may be nonuniform. The
thickness and visual properties of the sheet are measured at the control
station.
15 As a result of the surprisingly large number of excellent properties, the
colored, amorphous sheet according to the invention is outstandingly
suitable for a large number of various uses, for example for interior
panelling, for exhibition construction and exhibition articles, as displays, forsigns, in the illumination sector, in shopfitting and shelf construction, as
20 advertising articles, as menu stands, as basketball target boards, as room
dividers, as aquaria, as information boards, as brochure and magazine
stands, and also for external applications, such as, for example,
greenhouses, roofing, exterior paneling, coverings, for applications in the
building sector, illuminated advertising profiles, balcony paneling and roof
25 patios.
The invention is illustrated in more detail in the following with the aid of
embodiment examples, without being limited by these.
30 Measurement of the individual propeties is carried out here in accordance
with the following standards or methods.
CA 02262~34 1999-01-29
- 25
Measurement methods
Surface gloss:
5 The surface gloss is determined in accordance with DIN 67 530. The
reflector value is measured as the optical parameter for the surface of a
sheet. In accordance with the standards ASTM-D 523-78 and ISO 2813
the angle of incidence was set at 20~. Under the angle of incidence set, a
ray of light strikes the flat test surface and is reflected or scattered by it.
10 The rays of light incident on the photoelectronic receiver are indicated as aproportional electrical value. The measurement value is dimensionless and
must be stated together with the angle of incidence.
Whiteness
The whiteness is detemmined with the aid of the electrical remission
photometer"ELREPHO" from Zeiss, Oberkochem (DE), standard light
source C, 2~ normal observer. The whiteness is defined as
W = RY + 3RZ - 3RX.
W = whiteness, RY, RZ, RX = corresponding reflexion factors when using
Y-, Z- and X-color measurement filter. The white standard used is a
compression molding of barium sulfate (DIN 5033, Part 9).
Surface defects:
The surface defects are determined visually.
Charpy impact strength an:
30 This value is determined in accordance with ISO 179/1 D.
Izod impact strength ak:
The Izod notched impact strength or resistance ak is measured in
accordance with ISO 180/1A.
CA 02262534 1999-01-29
26
Density:
The density is determined in accordance with DIN 53479.
SV (DCA), IV (DCA):
5 The standard viscosity SV (DCA) is measured in dichloroacetic acid in
accordance with DIN 53728.
The intrinsic viscosity is calculated as follows from the standard viscosity
IV (DCA) = 6.67 x 10-4 SV (DCA) + 0.118
Themmal properties:
The thermal properties, such as crystallite melting point Tm~ crystallization
temperature range Tc, (after-(cold)crystallization temperature TCC and
15 glass transition temperature Tg are measured by means of differential
scanning calorimetry (DSC) at a heating-up rate of 10~C/minute.
Molecular weight, polydispersity:
The molecular weights Mw and Mn and the resulting polydispersity MW/Mn
20 are measured by means of gel permeation chromatography.
Weathering (both sides), UV stability:
The UV stability is tested as follows in accordance with test specification
ISO 4892
Test apparatus : Atlas Ci 65 Weather Ometer
Test conditions : ISO 4892, i.e. simulated weathering
lu~ v~ e ; 1000 h~ r5 (C-ersi-
Irradiati~ : 0.5 W/m2, 340 nm
30 Temperature \: 63~C
Relative atmospheric hum~ %
Xenon lamp : int~xternal filter of borosilicate
Irradiation cycles : 102 minutes U~ liy~,t, th~n 1~ minutes
UV light ~ith ~r~yinS~ t~f th~ 3~6im
CA 02262~34 1999-01-29
s ~
1o
I rradiation time : 1 000 hou rs (per side)
Irradiation : 0.5 Wlm2, 340 nm
Temperature : 63~C
Relative atmospheric humidity: 50 %
Xenon lamp : internal and external filter of borosilicate
Irradiation cycles : 102 minutes UV light, then 18 minutes
UV light with spraying of the specimens
AMENDED SHEET
CA 02262~34 1999-01-29
with water, then 102 minutes UV light
again and so on.
In the following examples and comparison examples, the sheets are in
5 each case colored sheets of different thickness produced on the extrusion
line described.
Example 1:
A 4 mm thick, multilayered, colored, amorphous polyethylene terephthalate
10 sheet having the layer sequence A-B-A is produced by the coextrusion
process described, B representing the base layer and A the covering layer.
The base layer B is 3.5 mm thick and the two covering layers, which coat
the base layer, are each 0.250 mm thick.
15 The polyethylene terephthalate employed for the base layer B has the
following properties:
SV (DCA) : 1100
IV (DCA) 0.85 dl/g
Density : 1.38 g/cm3
Crystallinity 44 %
Crystallite melting point Tm : 245~C
Crystallization temperature range Tc : 82 to 245~C
After-(cold)crystallization temperature range TCG : 152~C
Polydispersity MW/Mn : 2.02
Glasstransition temperature : 82~C
~ ~~
I
AMENDED SHEET
CA 02262~34 1999-01-29
with water, then 102 minutes UV light
again and so on.
I;i~f~ following exampies and comparison examples, the shee~re in
5 each case colored sheets of different thickness produced o,~e extrusion
line described. f
Example 1: ~
A 4 mm thick, multilayered, colored, amorpho~polyethylene terephthalate
10 sheet having the layer sequence A-B-A is ~oduced by the coextrusion
process described, B representing the ~se layer and A the covering layer.
The base layer B is 3.5 mm thick and~the two covering layers, which coat
the base layer, are each 250 mmt~thick.
15 The polyethylene terephtha~e employed for the base layer B has the
following properties:
~r~
SV (DCA) ff : 1100
IV (DCA) ,tAf 0.85 dl/g
Density ~ : 1.38 g/cm3
Crystallinity/ : 44 %
Crystallitymelting pointTm : 245~C
Crysta~tzation temperature range Tc : 82to 245~C
Afte~(cold)crystallization temperature range TCC : 152~C
P~ydispersity M~NJMn : 2.02
s t~nsiti~n tel~p~r~lur~ : 8~C
The base layer comprises the polyethylene terephthalate described, as the
main constituent, and 8% by weight of titanium dioxide.
The titanium dioxide is of the rutile type and is coated with an inorganic
coating of Al2O3 and with an organic coating of polydimethylsilane. The
titanium dioxide has an average particle diameter of 0.2 ~m.
CA 02262534 1999-01-29
28
The titanium dioxide is added in the form of a masterbatch. The
masterbatch is composed of 40% by weight of the titanium dioxide
described, as the active compound component, and 60% by weight of the
polyethylene terephthalate described, as the carrier material.
The polyethylene terephthalate from which the covering layers are
produced has a standard viscosity SV (DCA) of 1010, which corresponds
to an intrinsic viscosity IV (DCA) of 0.79 dl/g. The moisture content is
~ 0.2% and the density (DIN 53479) is 1.41 g/cm3. The crystallinity is 59%,
10 the crystallite melting point, according to DSC measurements, being
258~C. The crystallization temperature range Tc is between 83~C and
258~C, the after-crystallization temperature (also the cold crystallization
temperature) TCC being 144~C. The polydispersity MW/Mn of the
polyethylene terephthalate polymer is 2.14.
15 The glass transition temperature is 83~C.
Before the coextrusion, 80% by weight of the polyethylene terephthalate
for the base layer and 20% by weight of the masterbatch are mixed and
the mixture is dried at 170~C for 5 hours in the main dryer, which is
20 associated with the main extruder.
The polyethylene terephthalate for the base or core layer and the
masterbatch are melted in the main extruder and the polyethylene
terephthalate for the covering layers is melted in the coextruders. The
25 extrusion temperature of the main extruder for the core layer is 281 ~C.
The extrusion temperatures of the two coextruders for the covering layers
are 294~C. The main extruder and the two coextruders are connected to a
coextruder adapter, which is constructed such that the melts which form
30 the covering layers are applied as thin layers adhesively to the melt of the
core layer. The multilayered melt strand thus produced is shaped in the
slot die, connected to the line, and polished on a polishing calender, the
rolls of which are arranged in an S-shape, to give a three-layered sheet
4 mm thick.
CA 02262~34 1999-01-29
29
The first calender roll has a temperature of 65~C and the subsequent rolls
each have a temperature of 58~C. The speed of the take-off is
4.2 m/minute.
5 After the after-cooling, the three-layered colored sheet is trimmed at the
edges with separating saws, cut to length and stacked.
The white-colored, amorphous three-layered PET sheet produced has the
following properties profile:
- Layer build-up : A-B-A
- Totalthickness : 4 mm
- Thickness of the base layer : 3.5 mm
- Thickness of the covering layers : 0.25 mm each
- Surface gloss 1 st side : 152
(Measurement angle 20~) 2nd side : 148
- Light transmission : o %
- Whiteness : 1 18
- Coloration : white, homogeneous
- Surface defects : none
(specks, bubbles, orange peel and the like)
- Charpy impact strength an : no fracture
- Izod notched impact strength ak : 5.1 kJ/m2
- Crystallinity : o %
- Roll deposits after 2 hours of
production : none
Example 2:
A three-layered colored sheet is produced analogousiy to Example 1, a
30 polyethylene terephthalate which has the following properties being used
for the core layer:
SV (DCA) : 2717
IV (DCA) 1.9 dl/g
CA 02262~34 1999-01-29
- 30
Density : 1.38 g/cm3
Crystallinity : 44 %
Crystallite melting point Tm : 245~C
Crystallization temperature range Tc : 82 to 245~C
Cold crystallization temperature TCC : 154 ~C
Mw : 175 640 g/mol
Mn : 49 580 g/mol
Polydispersity MW/Mn : 2.02
Glass transition temperature : 82~C
The titanium dioxide masterbatch is composed of 40% by weight of the
titanium dioxide described under Example 1 and 60% by weight of the
polyethylene terephthalate of this example.
15 The extrusion temperature is 280~C. The first calender roll has a
temperature of 56~C and the subsequent rolls have a temperature of 50~C.
The speed of the take-off and of the calender rolls is 2.9 m/minute.
The three-layered PET sheet produced has the following properties:
- Layer build-up : A-B-A
- Total thickness : 6 mm
- Thickness of the base layer : 5.5 mm
- Thickness of the covering layers : 0.25 mm each
- Surface gloss 1st side : 149
(Measurement angle 20~) 2nd side : 143
- Light transmission : 0 %
- Whiteness : 125
- Coloration : white, homogeneous
- Surface defects : none
(specks, bubbles, orange peel and the lime)
- Charpy impact strength an : nofracture
- Izod notched impactstrength ak : 5.2 kJ/m2
- Crystallinity : 0 %
CA 02262~34 1999-01-29
- Roll deposits after 2 hours of
production : none
Example 3:
5 A three-layered, white-colored PET sheet is produced analogously to
Example 1. 50% by weight of the polyethylene terephthalate from Example
1 are mixed with 30% by weight of recycled material from the sheets of
Example 1 and 20% by weight of the titanium dioxide masterbatch and the
mixture is dried and coextruded analogously to Example 1.
The three-layered, colored PET sheet produced has the following
properties:
- Layer build-up : A-B-A
- Total thickness : 4 mm
- Thickness of the base layer : 3.5 mm
- Thickness ofthe covering layers : 0.25 mm each
- Surface gloss 1st side : 150
(measurement angle 20~) 2nd side : 144
- Lighttransmission : 0 %
- Whiteness : 127
- Coloration : white, homogeneous
- Surface defects : none
(specks, bubbles, orange peel and the like)
25 - Charpy impactstrength an : nofracture
- Izod notched impact strength ak : 4.9 kJ/m2
- Crystallinity : 0%
- Roll deposits after 2 hours of production: none
30 Example 4:
A three-layered PET sheet is produced analogously to Example 1. The
base layer comprises the polyethylene terephthalate described in Example
1, as the main constituent, and 1.0% by weight of the titanium dioxide from
Example 1. The titanium dioxide is incorporated into the polyethylene
CA 02262~34 1999-01-29
32
terephthalate for the base layer directly by the manufacturer of the raw
material.
The two covering layers comprise the polyethylene terephthalate of the
5 covering layers from Example 1, as the main constituent, and 0.5% by
weight of the titanium dioxide for the base layer. The titanium dioxide is
metered in directly by the manufacturer of the raw material. Drying,
coextrusion and sheet production are carried out analogously to
Example 1.
The three-layered PET sheet produced has the following properties:
- Layer build-up : A-B-A
- Total thickness : 4 mm
- Thicknessofthe base layer : 3.5 mm
- Content of TiO2 in the base layer : 1.0% by weight
- Thickness of the covering layers : 0.25 mm each
- Content of TiO2 in the covering layers : 0.5% by weight
- Surface gloss 1st side : 121
(measurement angle 20~) 2nd side : 118
- Lighttransmission : 36 %
- Coloration : opal, white
- Surface defects : none
(specks, bubbles, orange peel and the like)
25 - Charpyimpact strength an : no fracture
- Izod notched impact strength ak : 4.8 kJ/m2
- Crystallinity : 0 %
Example 5:
30 A three-layered sheet is produced analogously to Example 2. The sheet is
colored green, not white. The base layer comprises the polyethylene
terephthalate from Example 2, as the main constituent, and 9% by weight
of Pigment Green 17. Pigment Green 17 is a chromium oxide (Cr2O3) from
BASF (C~9Sicopalgrun 9996).
CA 02262~34 1999-01-29
The chromium oxide is added in the form of a masterbatch. The
masterbatch is composed of 45% by weight of chromium oxide and 55%
by weight of the polyethylene terephthalate from Example 2.
5 The two covering layers comprise the polyethylene terephthalate from
Example 2, as the main constituent, and 2% by weight of chromium oxide,
the chromium oxide being metered in directly by the manufacturer of the
raw material.
10 Drying, coextrusion and sheet production are carried out analogously to
Example 2.
The three-layered PET sheet produced has the following properties:
- Layer build-up : A-B-A
- Total thickness : 6 mm
- Thickness of the base layer : 5.5 mm
- Content of Cr2O3 in the base layer : 9% by weight
- Thickness of the covering layers : 0.25 mm each
- Content of Cr2O3 in the covering layers: 2% by weight
- Surface gloss 1 st side : 1 16
(measurement angle 20~) 2nd side : 114
- Light transmission : 0 %
- Coloration : opaquegreen,
homogeneous
- Surfacedefects : none
(steps, bubbles, orange peel and the like)
- Charpyimpactstrength an : nofracture
- Izod notched impact strength ak : 5.3 kJ/m2
30 - Crystallinity : 0%
- Roll deposits after 2 hours of production: none
Example 6:
A three-layered, white-colored, amorphous PET sheet is produced
CA 02262~34 1999-01-29
34
analogously to Example 2.
The two covering layers comprise the polyethylene terephthalate from
Example 2, as the main constituent, and 2.5% by weight of the UV
stabilizer 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol ('9Tinuvin
t577 from Ciba Geigy). Tinuvin 1577 has a melting point of 1 49~C and is
stable to heat up to about 330~C.
2.5% by weight of the UV stabilizer are incorporated into the polyethylene
terephthalate directly by the manufacturer of the raw material.
The drying, coextrusion and process parameters are chosen as in
Example 2.
The three-layered PET sheet produced has the following properties:
- Layer build-up : A-B-A
- Total thickness : 6 mm
- Thickness of the base layer : 5.5 mm
- Thickness of the covering layers : 0.25 mm each
- Surface gloss 1st side : 138
(measurement angle 20~) 2nd side : 134
- Lighttransmission : 0 %
- Whiteness : white, homogeneous
- Surface defects : none
(specks, bubbles, orange peel and the like)
- Charpyimpactstrength an : nofracture
- Izod notched impact strength ak : 5.1 kJ/m2
- Crystallinity : 0 %
- Roll deposits after 2 hours of production: none
After 1000 hours of weathering on each side with the Atlas Ci 65 Weather
Ometer, the PET sheet has the following properties:
- Surface gloss 1st side : 126
CA 02262~34 1999-01-29
(measurement angle 20~) 2nd side : 125
- Light transmission : 0 %
- Whiteness : 120
- Coloration : white, homogeneous
- Surface defects : none
(specks, bubbles, orange peel and the like)
- Charpyimpact strength an : nofracture
- Izod notched impact strength ak : 4.6 kJ/m2
- Crystallinity : o %
Example 7:
A three-layered sheet is produced analogously to Example 1.
The covering layers comprise 3.5% by weight of the UV stabilizer
2,2'-methylenebis(6-(2H-benzotriazol-2-yl)4-(1,1,3,3-tetramethylbutyl)-
phenol (~DTinuvin 360 from Ciba Geigy), based on the weight of the
covering layer.
Tinuvin 360 has a melting point of 195~C and is stable to heat up to about
250~C.
As in Example 6, 3.5% by weight of the UV stabilizer are incorporated
directly into the polyethylene terephthalate by the manufacturer of the raw
material.
25 The three-layered PET sheet produced has the following properties:
- Layer build-up : A-B-A
- Totalthickness : 4 mm
- Thickness of the base layer : 3.5 mm
- Thickness of the covering layers : 0.25 mm each
- Surface gloss 1st side : 146
(measurement angle 20~) 2nd side : 142
- Lighttransmission : 0 %
- Whiteness : 116
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36
- Coloration : white, homogeneous
- Surface defects : none
(specks, bubbles, orange peel and the like)
- Charpy impactstrength an : no fracture
5 - Izod notched impact strength ak : 4.9 kJ/m2
- Crystallinity : 0 %
After 1000 hours of weathering on each side of the Atlas Ci 65 Weather
Ometer, the PET sheet has the following properties:
- Surface gloss 1st side : 138
(Measurement angle 20~) 2nd side : 134
- Lighttransmission : o %
- Whiteness : 1 13
- Coloration: : white, homogeneous
- Surface defects : none
(specks, bubbles, orange peel and the like)
- Charpy impact strength an : nofracture
- Izod notched impact strength ak : 4.6 kJ/m2
20 - Crystallinity : 0 %
Comparison Example
A colored sheet is produced analogously to Example 1. The polyethylene
25 terephthalate employed for the core layer has a standard viscosity SV
(DCA) of 760, which corresponds to an intrinsic viscosity IV (DCA) of
0.62 dVg. The other properties are identical to the properties of the
polyethylene terephthalate from Example 1 in the context of measurement
accuracy. The titanium dioxide masterbatch, the covering layers, the
3~ process parameters and the temperature are chosen as in Example 1.
Because of the low viscosity, no sheet production is possible. The stability
of the melt is inadequate. The emerging melt strand shows a number of
flow streams and inhomogeneities.
CA 02262~34 1999-01-29
