Note: Descriptions are shown in the official language in which they were submitted.
CA 02037713 1999-12-07
ROLLS HAVING SYNTHETIC COATINGS,
AND PROCESS FOR MANUFACTURING SAME
Rolls having synthetic coatings are employed for
many different user, and are manufactured according to
many different processes. Typical synthetic coatings
consist of rubber, polyamides, polyurethanes, polyesters,
polyester amides, epoxide resins, silicone resins, phenol
resins, polyacetate~ resins, polyamide resins, melamine
resins and the like. Depending on use and requirements,
said coatings are modified in known manner by inorganic
fillers, flexibilizers, impact modifiers, and other
additives with respect to hardness, abrasion resistance,
impact resistance, temperature resistance, as well as
resistance to solvents and chemicals. Generally,
manufacture is carried out by casting, extruding or
winding the synthetic coating onto the roll shell being
optionally provided with an adhesive layer. With
thermoplastics, final curing is effected by cooling, and
with other syr.thetic:s, by subsequent cross-linking.
One disadvantage of most synthetic coatings being
used hitherto, .is their relatively low temperature
resistance. For example, although coatings made of
silicone and fluorine rubber, respectively, do have high
temperature resistance, they do not have the hardness
required for certain uses. The trend towards faster
production and hence higher rotational speed increasingly
requires better resistance to high temperatures, as well
as rapidly changing temperatures and short-termed local
overheating.
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Thus, it is an object of the invention, to develop
rolls having such synthetic coatings which are resistant
to high tempenature;~, and which, in addition, are able to
be adjusted variably with respect to hardness, abrasion
resistance, impact resistance, resistance to solvents and
chemicals and otherwise required physical properties.
It has :zow been found that this problem can be
solved by using coatings made of poly-2-oxazolidinones.
Here, said poly-2--oxazolidinones may be admixed with
certain amounts of isocyanurates. Furthermore, they may
be modified by admixing or incorporating other
components.
Poly-2-ox:azoli<~inones are formed, for example, in
the catalyzed reaction of diepoxides with diisocyanates
at temperatures a~>ove 120 C. Since under these conditions
isocyanates also self-react to form isocyanurates, the
thus produced synthetic coatings generally contain more
or less large quantities of isocyanurates. However, it is
possible by varying the conditions of the process,
selecting catalysts, and by other modifying additives to
suppress or enhance formation of isocyanurates, thereby
modifying the properties of the final synthetic coating.
Moreover, of c:our~~e not only diepoxides and diisocyanates
may be used, but. also other multifunctional epoxides
and/or isocyar.ates.
Linking epox:ides to isocyanates with formation of
oxazolidinone structures is known per se, but hitherto
said linking is hardly utilized technically on a large
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scale. See, Bec:ker/Braun, Kunststoff Handbuch 10,
"Duroplaste", page 111. Known hitherto above all are
oligomeric polye~>o:~ides containing oxazolidinone, and
which are made of bisepoxides and diisocyanates according
to EP-A-0 296 450.-These oligomers have been admixed in
particular wii~h other liquid or solid epoxide resins or
reactive diluents, and have been cured by means of usual
curing agents such as polyamines, acid anhydrides or
polyisocyanates. 'fhf~ thus obtained products show enhanced
tensile strength, breaking elongation, impact resistance,
ball indentation hardness, and deflection temperature.
However, unti7_ now they have not been used to self-react
with only relatively small quantities of a catalyst and
then cured. Here, this can be attributed to the formation
of very hard and brittle products, and hence ultimately
unusable products. It has now been found that it is
possible, howeverr to cure such oligomeric pre-polymers
having isocya:zurate moieties by means of catalysts and
relatively small quantities of flexibilizers to obtain
products being excellently suitable for use as hard
synthetic coatings for rolls. Furthermore, it has been
confirmed that it is easily possible to react said
diepoxides and diisocyanates being used in the
manufacture, with a catalyst and a flexibilizer to obtain
products, which, depending on reaction conditions,
contain a substantially smaller amount of isocyanurate
moieties.
Furthermore, it has been found that by varying said
multifunctional epo:~ides used, on the one hand, and said
multifunctional isocyanates, on the other, the properties
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of the synthetic may be varied considerably, and thus may
be adjusted to any required property of a synthetic
coating for rolls. Likewise, it is possible to vary and
modify such synthet_Lcs by means of inorganic fillers.
However, all such synthetic coatings according to
the invention when compared to synthetics used hitherto
show substant:iall.y higher temperature resistance and
resistance to temperature fluctuations, and nevertheless
are sufficiently flexible.
This should be attributed to the fact that both the
oxazolidinone strucaure and the isocyanurate structure
are very insensitive to temperature stress. Since pure
poly-2-oxazoli.dinones, as well as their mixtures with
isocyanurates, are very brittle, particularly when
manufactured from diepoxides based on bisphenol A, and
diisocyanates based on diphenylmethane, this group of
synthetics has received little attention. Thus, it was
not to be foreseen that these synthetics could be further
developed to ~=xcellent synthetic coatings for rolls with
only slight modification, in particular by using
flexibilizers.
According to the invention, however, bisepoxides
generally can be used, not only those based on bisphenol
A, but also ot=her commercial bisepoxides having been used
as epoxide components in synthetics. A summary of such
epoxides is j=ound in Becker/Braun, Kunststoff Handbuch
10, "Duroplaste", pp. 115-118. In addition, components
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having three or more epoxide moieties, may likewise be
used.
Similarly, all industrially available diisocyanates
may in principle be considered as diisocyanate
components. Furthermore, substances having three or more
isocyanate moieties, are likewise possible.
Most di_=ferent product groups are possible as
catalysts for the addition of epoxides to isocyanates.
Suitable are, for instance, tertiary bases such as
pyridine, tribenzylamine, N-methyldibenzylamine, but also
Lewis acids such a:~ zinc chloride, iron chloride, boron
trifluoride; alkali and alkaline earth alcoholates such
as calcium and magnesium ethylate; and aluminum
isopropylate. Other catalysts are lithium chloride,
tetramethylam~r~onium iodide, and phosphonium salts.
Substances which are candidates for flexibilizers
include those in which the functional groups are joined
together within th.e molecule at a wide distance via
principally aliphatic structural elements. Typical
flexibilizers are p~zlypropylene glycol diglycidyl ethers,
oligoesters, oligoether esters having terminal carboxy
groups, amine groups or hydroxy groups being able to
react, at least <~t elevated temperatures, with epoxide
groups or isocyanate groups left, leading to
flexibilizing cross-linking. Thus, also flexibilized
epoxides, polybutad:iene, polyisoprene, and polybutadienes
having terminal epoxide or hydroxy groups, have good
flexibilizing properties.
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In princ:~ple, all known inorganic fillers that are
used already now as fillers for synthetics, and, in
particular, for synthetic coatings of rolls, may be used
as inorganic fillers in the invention. For instance,
aluminum oxide, ;silicon dioxide, silicon carbide, and
granite powder, are well suited where hard, wear-
resistant coatings having good grip are desired.
The manufacture of said synthetic coatings on the
rolls is like;aise carried out in known per se and usual
manner. For this purpose, the roll shell is usually
degreased and sandblasted. It is often convenient to
apply an adh~=sine layer as a primer, for instance a
phenol resin. Fux_thermore, it is convenient with hard
rolls to apply <~ polyurethane layer, onto which the
synthetic coating of poly-2-oxazolidinone according to
the invention is coated as a stress relaxating factor
between the shell and the synthetic coating. This can be
carried out ai. temperatures of up to 100 C. Final curing
is then carried out at temperatures above 120 C.
Preferably, said c:u:ring is carried out at temperatures of
between 130 ,end 180 C. In order to obtain synthetic
coatings free of bubbles, it is advisable to degas and
homogenize the lie~u:id components in a vacuum. If a higher
proportion of isocyanurate structures is desired, the
diisocyanate component, for instance, may be heated in
advance with catalysts such as alkali and alkaline earth
alcoholates to a temperature at which the isocyanurate
structure is formed. Another possibility for raising the
proportion of said isocyanate structure is the use of
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oligomeric pre-polymers, as described, for instance, in
EP-A-0 296 450.
The objects of the present invention is therefore not
the production of rolls having a synthetic coating in
general, or the process for their manufacture, but the
use of poly-2-oxaz:olidinones, optionally admixed with
isocyanurates as well as flexibilizers, fillers, and
other additives, as material for roll covers. Another
object of the in~Tention is the use of oligomeric pre-
polymers containing oxazolidinone moieties, and being
made of diepo:~ides and diisocyanates, in the manufacture
of roll covers..
Several embodiments of rolls according to the
invention, and the process for manufacturing them, are
described in t:he f=ollowing examples. Properties, however,
can conveniently be varied in a wide range, depending on
purpose of application and use.
EXAMPLE 1
20 parts by weight of diepoxide based on bisphenol A
(Lekutherm X 18) are mixed with 80 parts by weight of a
diisocyanate (mixture of 4,4- and 4,2-diisocyanatodi-
phenylmethane (MDI),, Baymidur VP 50021, and mixed with 5
parts by weight of :N-methyldibenzylamine (as a catalyst),
and 10-30 parts b~~ weight of polybutadiene (R 20 LM with
terminal hydroxy groups ) . To the mixture is added 160 to
220 parts by weight silicon carbide. The mixture,
degassed at 80 C and homogenized, is cast onto a roll
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shell pre-coated with an adhesive layer and a
polyurethane .Layer. being about 1 mm thick, and cured at
130 C. The thus c>btained synthetic coating shows all
required physical. properties, and, in addition, is
resistant to nigh temperatures.
EXAMPLE 2
In an analogous manner, as described in example 1,
100 parts by weight of a pre-polymer having been prepared
from 20 parts by weight of the same diepoxide and the
same diisocy<~natE~ are used, the pre-polymer still
containing about 20% free isocyanate groups, and,
additionally, isocyanurate groups to a considerable
extent (BlendL.r I-VF? KU 3-4516, from Bayer AG) .
EXAMPLE 3
In an analogous manner, as described in example 2,
100 parts by weight: of the same pre-polymer (Blendur KU
3-4516) are mixed with 15 parts by weight of diepoxide
based on bisphenol A (Epikote 828), 15 parts by weight of
hexamethylene di:isocyanate having isocyanate groups
(Desmodur N 3300), and 10 parts by weight of N-methyl-
dibenzylamine as <~ catalyst. Further admixed are 160 to
200 parts b_~ w.=fight silicon carbide. The mixture,
degassed at 80 C and homogenized, is cast onto a roll
shell pre-coated with an adhesive layer and a
polyurethane =~ayer being about 1 mm thick, and cured at
130 C. The thus obtained synthetic coating shows all
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required physical properties, and, in addition, is
resistant to high temperatures.
EXAMPLE 4
In an analogous manner, as described in example 3,
100 parts by weight of the pre-polymer (Blendur KU 3-
4516) are mixed with 12 parts by weight of butane-1,4-
diol-diglycidyl ether (Araldit DY 026 SP), 9 parts by
weight of hexamethylene diisocyanate (Desmodur N 3200),
parts by weight of N-methyl-dibenzylamine, and 160 to
220 parts by weight: silicon carbide, and processed to a
roll cover. The thus obtained synthetic coating shows all
required phy:~ical_ properties, and, in addition, is
resistant to nigh temperatures.
EXAMPLE 5
In an analogous manner, as described in example 1,
100 parts by weight of butane-1,4-diol-diglycidyl ether
(Araldit DY 02.6 Sf), are mixed with 80 parts by weight of
hexamethylene diisocyanate (Desmodur N 3200), 18 parts by
weight of N-methyl-dibenzylamine, and up to 220 parts by
weight fillers, and processed to a roll cover. This
coating is relatively soft, and has a relatively low
hardness (about 50 Shore A). Thus, it is possible to
blend this formulation with harder formulations to adjust
the desired hardnes:~.
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