Note: Descriptions are shown in the official language in which they were submitted.
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A Lubricant Based on Polyols and its Use
in the Cutting of Elastomers
This invention relates to a lubricant based on aqueous solutions andlor
emulsions of polyols and to its use in the cutting of cured elastomers.
The cutting of elastomers with various tools always involves difficulties
on account of the rubber-elastic behavior of these polymeric compositions. In
modern automotive construction, fixed glass is now directly bonded to the
bodywork. An elastomeric adhesivelsealant, in most cases based on
polyurethane elastomers, is generally used for this purpose. For repair
purposes, the directly bonded glass has to be cut out from the frame using
various tools. Various methods are available for this purpose, including for
example cutting wire, knives and electrical or pneumatic oscillating or
vibrating knives. Such knives are described, for example, in DE-A-38 38 044.
Where vibrating knives are used) so much heat of friction is generated
that decomposition reactions occur after only a very short cutting time) as
immediately reflected in the emission of smoke. This generation of heat is
problematical both on hygiene grounds and on technical grounds. The
hygiene-related or physiological problems are attributable to the emission of
2o smoke gases of which the exact chemical composition is rarely known
because it depends both on the composition of the elastomer and on the
acutely prevailing decomposition temperature. Because the processor
generally has his head relatively close to the point of smoke or gas emission,
the fumes are almost inevitably inhaled. There are generally no safety
2s measures to prevent this and, even where such measures do exist, they are
difficult to put into practice.
The technical problems are attributable to the fact that the knife is
difficult to guide under these conditions and also to the fact that the knives
easily become red hot. As a result of this intensive heating, the knives have
3o very short useful lives. In addition, the intensive heating of the
elastomer in
the cutting zone can lead to serious chemical degradation of the polymer with
the result that both the chemical and the physico-mechanical characteristics
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of the elastomer are seriously affected. The resulting change leads to
significant problems in regard to re-bonding behaviour.
In practice, several hitherto unsatisfactory approaches have been
adopted with a view to solving the problems explained above:
- Cooling of the cutting zone with solvents, particularly benzines. This
method is unsuitable for physiological reasons alone. Besides the
health-related problems caused by exposure of the processor to
solvent vapors, there is also a persistent risk of explosions here on
1o account of the solvent vaporlair mixtures formed. These mixtures can
be ignited both by hot parts of cutting tools and by electrical sparks
from electrically operated cutting tools.
- The cuffing zone cannot be cooledllubricated with water.
- Cooling of the cutting zone while the processor waits. In this case, a
short section is cut until smoke is emitted, after which the blade is
cooled. This method is very time-consuming and is hardly used for this
reason alone.
- One supplier of cuffing tools not only recommends, but actually
stipulates the use of a baby shampoo to reduce friction in the cutting
zone. To this end, a solution of this shampoo in water is sprayed onto
the strand of adhesive before cutting. Around 150 to 200 ml of this
detergent solution are required for spraying the adhesive strand of a
car windscreen. Although this method prevents the generation of heat
in the cutting zone of the adhesive strand, it has a very adverse effect
on the re-bonding behaviour of the remaining strand because residues
of detergent are inevitably left on the cut surface.
In every case where the cut surface of the elastomer is involved in a
rebonding process, the last of the above-mentioned methods cannot be
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applied because the holding strength of the adhesive after rebonding falls to
very low levels on account of the residues remaining on the cut surface.
US-A-4,128,452 describes a knife for separating materials joined by
an adhesive, more particularly self adhesive labels. The blade of this knife
is
accommodated in a sheath with an inner lining of an absorbent material. A
liquid lubricant, for example silicone oil, is uniformly distributed over the
absorbent material of the sheath. When the knife is inserted into or removed
from the sheath, a thin film of lubricant is distributed over all the surfaces
of
the blade. This provides for almost frictionless contact between the knife and
the material to be separated. The liquid lubricant is supposed to prevent the
adhesive cut through from becoming tacky.
Accordingly, the problem addressed by the present invention was to
provide a lubricant and coolant which would enable elastomers to be cut
without much heat of friction being generated. The cut surfaces thus
produced would remain suitable for rebonding of the elastomer parts. This is
particularly important for the repair of directly bonded car glass because,
when damaged glass is replaced) a so-called "residual strand", i.e. an
adhesive layer of variable thickness, remains on the bodywork. Subsequently,
either the adhesive for the replacement glass is directly applied to this cut
2o surface or the cut surface acts as a contact surface for the adhesive
applied
to the new glass. Since bonded-in-place glass, more particularly in the form
of
windscreens and rear windows, is an integral part of the strength and
stiffness
of a car body, car manufacturers specify minimum tensile shear strengths for
such bonds of, generally, at least 3 N/mm2. Standard adhesives generally
achieve bond strengths of more than 5 N/mm2. Accordingly, the same
strength levels also have to be reached in the event of rebonding.
It has now been found that all the disadvantages of known methods
can be avoided by using lubricants based on aqueous solutions andlor
emulsions of polyols. This method enables car glass to be quickly and safely
3o rebonded and is toxically and physiologically safe. The lubricating effect
of the
polyol and the cooling of the blade by the water present are both very good
and have been proven by numerous internal practical tests. The residual
~
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strand is re-bondabie, at least 85% of the tensile shear strength determined
by the adhesive always being achieved. The first-time bonding values
specified by all car manufacturers are thus achieved. In principle, numerous
polyols may be used for the lubricants according to the invention. Polyether
polyols based on linear or branched polyethylene glycols, polypropylene
glycols or copolymers thereof are particularly preferred. The molecular weight
and the OH value and viscosity of the polyether polyols may vary within wide
limits. Preferred ranges for the OH value are 500 to 15 mg KOHIg, OH values
of 50 to 20 mg KOHIg being more particularly preferred. The viscosity of such
polyether polyols at 25~C is between 500 mPa~s and 3,000 mPa~s. The OH
value is determined in accordance with DIN 53240 while viscosity is
determined in accordance with DIN 51550. Although polyether polyols are the
preferred polyols for the purposes of the invention, polytetrahydrofurans)
polyester polyols, hydroxyfunctional polybutadienes and ethoxylation and
~ 5 propoxylation products thereof and other water-miscible or water-
emulsifiable
polyols may also be used. Mixtures of high molecular weight and low
molecular weight polyols and relatively small additions of surfactants or
emulsifiers may be used to support miscibility with water and to guarantee a
stable emulsion. Nonionic surfactants preferably containing at least 2 OH
2o groups per molecule are generally used either individually or in the form
of
mixtures. The alkyl polyglycosides produced and marketed, for example, by
Henkel KGaA are most particularly preferred. Preservatives known per se
may be added to the lubricant according to the invention to increase its
stability in storage.
25 For the actual use at a lubricantlcoolant, it is sufficient for about 2% by
weight of polyether polyol to be present in the solution sprayed onto the
strand of adhesive or elastomer to be cut. However, for more effective
transportation from the point of production to the point of use and in the
interests of better storage, it is advisable initially to prepare a
concentrate
3o which the end user may readily dilute with water.
Accordingly, a typical composition according to the invention for the
lubricant/coolant concentrate contains
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- 15 to 40% by weight of polyether polyoi optionally consisting of a
mixture of several polyether polyols,
- 0. 1 to 3% by weight of nonionic surfactants, preferably alkyl polygly-
cosides,
5 - 0.05 to 0 5% by weight of preservative and
- 56.5 to 84.85% by weight of demineralized water.
The ratio in which such a concentrate is diluted for application is
determined by its polyether polyol content and is of the order of 1:8 to 1:20.
A particularly preferred embodiment of the invention is described in the
following.
Example I
A lubricant concentrate was prepared from the following ingredients:
29% by weight of polyether polyol (Lupranol 2040) a product of BASF,
hydroxyl value ca. 28 mg KOHIg), 0.8% by weight of alkyl polyglycoside
~5 (Henkel KGaA)) 0.2% by weight of Acticid SPX (Thorchemie) and 70% by
weight of demineralized water. The polyol and the surfactant were introduced
first and water was slowly added with intensive stirring using a dissolver. It
is
particularly important to achieve intensive mixing in the highly viscous phase
to ensure that a stable emulsion containing finely dispersed polyol droplets
is
2o formed.
Example 2
In a practical test, the lubricant of Example 1 was diluted with water in
a ratio of 1:15 for application and the resulting liquid was sprayed onto the
adhesive strand of a glazed-in car windscreen. The cured adhesive strand
25 could be cut with a commercial vibrating knife without any generation of
heat.
Example 3, Comparison Example
To determine tensile shear strength after rebonding, glass strips
measuring 25xlOOx4 mm and lacquered steel strips measuring 25x100x1 mm
were pretreated with a primer and bonded with an adhesive strand consisting
30 of the one-component moisture-curing direct glazing adhesive Terostat 8597
(Teroson) so that a layer thickness of 5 mm was formed. The test specimens
were produced and their tensile shear strength was determined in accordance
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with DIN EN 1465. After final curing as directed by the manufacturer, a bond
such as this (referred in the standard as an original bond) develops a tensile
shear strength of 5 to 6 MPa.
To simulate glass removal, the accessible surfaces of the cured
s adhesive strand perpendicular to the cut surface were sprayed with the
lubricant/coolant according to the invention. For comparison) a solution of a
baby shampoo in wafer was prepared as directed by the tool manufacturer
and sprayed onto the adhesive strand. The test specimens were then cut. For
rebonding, new glass strips were pre-cleaned and then pretreated with the
primer Terostat 8510 (Teroson). A corresponding quantity of Terostat 8597
was applied to the primer surface aired as directed by the manufacturer. The
metal strips from the cutting tests still carrying the residual strand which
had
not been pretreated any further were then used to simulate rebonding so that
a layer thickness of 5 mm was again formed.
~5 After the bond had reached its ultimate strength, a tensile strength of
more than 5 Nlmmz was achieved with all the test specimens containing
residual strands which had been cut using the lubricantlcoolant according to
the invention. Test specimens containing residual strands which had been cut
using the baby shampoo developed tensile shear strengths of less than
20 1 NImm2.
It can clearly be seen that, where a recommended lubricantlcoolant
according to the prior art is used, there is a distinct safety risk in regard
to the
tensile shear strength of rebonding whereas, where the lubricantlcoolant
according to the invention is used, tensile shear strengths well above the
25 minimum required by car manufacturers of 3 N/mm2 are achieved in
rebonding.
