ROLLERS AND METHOD FOR THE PREPARATION THEREOF

ROULEAUX ET METHODE DE PREPARATION

English Abstract

The rollers consist of a metal core with a coating of an elastomeric material
and have a layer of plastic, i.e., a polyurea, between the metal core and the
elastomeric material, which polyurea can be obtained from the components
isocyanate and a diamine. The exposed metal portions of the metal core are
preferably also coated with polyurea.

Claims

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CLAIMS:
1. Rollers consisting of a metal core with a coating of an elastomeric
material and a layer of plastic between the metal core and the elas-
tomeric material, characterized in that said layer of plastic is a poly-
urea, which polyurea can be obtained from the components isocy-
anate and a diamine.
2. The rollers according to claim 1, characterized in that the exposed
metal portions not coated with the elastomeric material additionally
bear a layer of polyurea throughout or in part.
3. A method for the preparation of rollers consisting of a metal core and
a coating of an elastomeric material and a layer of plastic, character-
ized in that at least the portions to be coated of the metal core are
previously coated with a polyurea which can be obtained from the
components isocyanate and a diamine.

Description

CA 02329158 2000-12-20
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Rollers and Method for the Preparation Thereof
The present invention relates to rollers consisting of a metal core with a
coating of an elastomeric material and a layer of plastic, and to a method
for the preparation thereof.
The elastomeric coating of the metal core of rollers consisting of rubber or
polyurethane must be replaced from time to time. Thus, these layers are
burned off, peeled off or ground off, which may occasionally result in
damage to the metal core. At least, the peeling cutters are damaged when
coming into contact with the metal core.
From DE-A-30 35 117, rollers are known in which the roller core is not
made of metal, but of a material prepared by pressing a mixture of a
plastic, graphite and glass fibers or carbon fibers, which material can
withstand a temperature of 200 °C without becoming deformed. These
rollers have a significantly lower weight than conventional rollers have, and
in addition, they possess a better heat resistance. Figure 3 shows a roller
which has still a small metal core at its ends. However, the major length of
the roller core is made of this hardened mixture.
From DE-C-195 11 153, there are known calender rollers, especially for
paper treatment, which consist of a thin-walled tube to which a thicker
layer of fiber-reinforced plastic is applied and which has in turn a thin
layer
of silicone rubber as the outermost layer. For stabilization, the epoxy layer
reinforced by carbon fibers is fixed by long fiber strands which have deflec-

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tion members at the front ends of the tube. Thus, this is a very sophisti-
Gated special construction for calender rollers.
From DE-A-18 07 331, it is known to provide metal cores, which are coated
with polyurethane rubber, first with a thin layer of hard rubber or with a
layer formed from fibers impregnated with a thermosetting resin solution by
winding on the peripheral surface of the metallic roller core. As the fibers,
there are employed glass fibers, nylon fibers and polyester fibers soaked in
a solution of thermosetting synthetic resin, such as epoxy, polyester or
diallyl phthalate. Although this intermediate layer improves the adhesion of
the polyurethane rubber to the metal core of the roller and thus the risk of
detachment during operation is reduced, this method is also cumbersome
and does not always lead to the desired success.
DE-C-30 29 288 describes some improvement of the properties by the
impregnation of the thermosetting resin additionally containing a fine
inorganic powder. Such rollers have not proven useful in practice either.
Instead, elastomeric coatings with a good adhesion to the metal due to
their composition are mainly applied directly to the metal core. These may
also be burned off, peeled off or ground off without difficulties, but with
occasional damage to the metal core and/or the peeling cutters when
coming into contact with the metal core.
US-A-4,038,731 describes a method for coating a metal core with elas-
tomeric material wherein an adhesive is to be employed between the core
and the elastomeric coating. Suitable adhesives are mentioned in column 4,
lines 33 to 53. As a hot curing adhesive, urea-formaldehyde is mentioned.
This adhesive is a thermosetting plastic, cf. Rompp Chemielexikon, 9th
Edition, page 1425.
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Thus, it has been the object of the invention to simplify the removal of used
rubber or polyurethane layers from the metal core and increase the safety,
especially when said removal is effected by peeling or grinding.
This object is achieved by the rollers having a layer of polyurea between the
metal core and the elastomeric material, which polyurea can be obtained
from the components isocyanate and a diamine.
Especially in the metal, textile, wood as well as plastics and paper process-
ing industries, the rollers are exposed to aggressive media which often also
attack the metal core of the rollers. The elastomer-coated materials of the
rollers are protected against such attacks, but the other exposed portions of
the metal core are not. It has been another object of the invention to also
protect these portions of the metal core from aggressive media.
According to the invention, this is achieved by the exposed metal portions
not coated with the elastomeric material additionally bearing a layer of the
polyurea throughout or in part.
Such coatings of the polyurea are preferably applied with the aid of two-
component high-pressure spraying machines, the pot life of the composi-
tions being set to short values, namely within a range of a few seconds. The
processing of such mixtures can be done at room temperature or at tem-
peratures of up to about 100 °C. The layers formed thereby are
generally
stable to about 150 °C and are not or hardly attacked by aggressive
media.
These layers of the polyurea are clearly harder than the elastomeric layers
on the rollers so that only these elastomeric layers are removed in the
mechanical removal by cutting or grinding.
Once these tools reach the polyurea layer, no or but very little material of
the polyurea is removed. However, the peeling cutters or grinding tools are
not damaged.

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The adhesion of the elastomeric layer to the polyurea layer is virtually the
same as to the surface of the metal core. The mechanical properties of such
rollers are virtually the same as when the elastomeric layer is directly
applied to the metal core. Especially when the exposed metal portions of
the metal core not coated with the elastomeric material are additionally
coated with the polyurea, these portions are also excellently protected from
aggressive media.
In the following Example, a typical preparation of a roller according to the
invention is described.
A conventional roller core of steel is coated using a two-component high-
pressure spraying machine at temperatures of between 80 and 90 °C. The
components are isocyanate and a diamine. The mixing ratio of the compo-
nents is about 1:1 (by volume). The pot life is only a few seconds. The layer
of the polyurea has a hardness in the range of between 55 and 60 Shore D
according to DIN 53505. To this layer is conventionally applied the elas-
tomeric layer of rubber or polyurethane. The properties of the finished
rollers are absolutely identical with those having no intermediate layer of
the polyurea. Since the exposed metal portions of the roller are also coated
with the polyurea, the overall rollers are resistant to aggressive media to
which the finished rollers are normally exposed, for example, in the metal,
textile, plastics, wood and paper processing industries.
As with conventional rollers, the elastomeric layer can be removed by
peeling or grinding, wherein the harder layer of the polyurea is virtually not
attacked at all so that a recoating of the metal core with the polyurea is not
necessary or only so after many recoatings with elastomeric material.
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