Method for manufacturing semifinished products from a mixture of rubber and rubber-like plastic materials by shock cooling to increase tackiness

A method for manufacturing calendered and/or extruded semifinished products with increased surface tackiness from a mixture of rubber and rubber-like plastic materials employs a shock-cooling step for cooling the hot semifinished products at a maximum shock cooling temperature of 0.degree. C.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for manufacturing calendered 
and/or extruded semifinished products with increased surface tackiness 
made from a mixture of rubber and rubber-like plastic materials as well as 
a device for performing the method. 
With semifinished products of rubber mixtures, for example, with components 
for the construction of tires, it is often important that the surface of 
these articles be provided with high tackiness so that during assembly a 
good adhesion to neighboring layers can be achieved. A plurality of 
methods for increasing the surface tackiness of semifinished products of 
rubber mixtures are known. For example, in an additional working step 
solutions are applied by pasting to the surface and generate the required 
surface tackiness. 
It is an object of the present invention to provide a more favorable 
manufacturing process for semifinished products of the aforementioned kind 
which furthermore can be directly integrated into the conventional 
manufacturing process of the semifinished products.

SUMMARY OF THE INVENTION 
According to the inventive method for manufacturing calendered and/or 
extruded semifinished products with increased surface tackiness made from 
a mixture of rubber and rubber-like plastic materials, the hot 
semifinished products are shock cooled at a maximum temperature of 
0.degree. C. The invention is based on the finding that the surface 
tackiness of a semifinished product is substantially increased when the 
hot article is subjected to a shock cooling step, i.e., a cooling with a 
great cooling speed. This can be achieved by providing a cooling 
temperature of 0.degree. C. or less, preferably below -100.degree. C. 
Due to the strong increase of the tackiness at the surface of the 
semifinished products the invention has the advantage that during assembly 
of the rubber end product a substantially increased adhesion to other 
rubber parts is achieved. By avoiding solutions that have to be applied 
the release of respective gases is prevented so that the inventive method 
is environmentally safe. 
Even though the cooling effect according to the present invention primarily 
occurs at the surface of the semifinished products it is however so 
effective that for somewhat thin profiles a conventional cooling, for 
example, in a water bath at room temperature can be completely dispensed 
with. The invention is also suitable for such components in which 
conventionally additional rubber strips, for example, so-called 
underplates during manufacture of tire tread strips for pneumatic vehicle 
tires, must be used for increasing the tackiness. 
In a preferred embodiment of the present invention the shock cooling step 
is carried out with liquified gas, for example, with liquid nitrogen. In 
theory it is possible to guide the semifinished product of a rubber 
mixture through an open bath of liquid nitrogen; however, this would 
result in great losses of nitrogen gas. Therefore, the invention is 
preferably performed with closed cooling drums in which the liquid 
nitrogen is contained. The semifinished product is guided about at least 
one cooling drum at a peripheral angle extending over a great portion of 
the outer surface of the cooling drum so that a great cooling effect in a 
short period of time can be achieved. It is preferred that a temperature 
decrease by 70.degree. to 90.degree. C. occurs in less than 30 seconds, 
preferably in 10 to 20 seconds. 
For increasing the cooling effect in a short period of time and thus 
improving the shock cooling effect, it is also possible to use a plurality 
of cooling drums horizontally arranged one after another and/or vertically 
stacked one above the other. With two vertically stacked cooling drums it 
is possible to guide the semifinished product in an S-configuration or a 
mirror-symmetrical S-configuration about two cooling drums so that the 
underside as well as the upper side of the semifinished product are 
subjected to a cooling effect. In a preferred embodiment the cooling drums 
are provided with inlet lines for the liquid gas as well as with outlet 
lines for the spent gas so that the spent gas can be recycled. 
It is also possible to subject the semifinished product to an additional 
cooling step in a liquid bath. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention will now be described in detail with the aid of 
several specific embodiments utilizing FIGS. 1 and 2. 
FIG. 1 shows a conventional duplex extruder 1 for generating a strip 2 for 
tread strips of pneumatic vehicle tires. The strip 2 is comprised of two 
different rubber mixtures which are introduced into the hoppers of the 
duplex extruder 1. The strip 2 is guided to a cooling drum 4 supported on 
a frame 3 and is partially guided about it. The height adjustable guide 
rollers 5 serve to compensate for different velocities. The shock-cooled 
strip 2 can then be transported by the conveyor belt 6 to a further 
conventional treatment step. This further treatment can be in the form of 
a conventional liquid cooling bath into which the strip 2 is submerged 
which may be comprised of, for example, an aqueous salt solution at room 
temperature. The cutting of the strip 2 into tire tread strips for 
pneumatic vehicle tires of a desired length is then carried out according 
to conventional methods. 
The cooling drum 4 in the shown example has a diameter of 1550 mm and a 
width of 500 mm. The circumferential length of the strip on the cooling 
drum is approximately 2 m. The cooling drum 4 is driven by a 
frequency-regulated motor. The cooling drum 4 is filled with liquid 
nitrogen to about 1/3 or 1/2 of its volume. The liquid nitrogen is 
introduced via an inlet line in the axle of the cooling drum 4. The 
cooling drum 4 is also provided with a non-represented outlet opening for 
removing the spent nitrogen gas which is recycled and, for example, 
returned into an inert gas heating system of the vulcanization process. 
The strip 2 exits the extruder 1 at a velocity of approximately 9.5 mm per 
minute so that for a circumferential length of 2 m on the cooling drum 4 a 
contacting time of approximately 20 seconds results. While the liquid 
nitrogen cools the cooling drum at least in the beginning to approximately 
-195.degree. C., at the underside of the strip 2 directly behind the 
cooling drum 4 temperatures of 25.degree. C. have been measured. Since the 
strip 2 leaves the extruder 1 at a temperature of approximately 
105.degree. C. this results within the limits of the shock cooling step in 
a temperature reduction of 80.degree. C. in 20 seconds. It should be noted 
that it is advantageous to use cooling drums of a greater diameter, for 
example, of a diameter of 2.5 to 3 mm. Furthermore, it is possible to use 
a plurality of cooling drums that are sequentially arranged in order to 
improve the shock cooling effect. 
FIG. 2 shows schematically a device in which with the extruder 7 a thin 
endless or continuous profile 8 is produced from a rubber mixture. The 
endless or continuous profile 8 is guided in a mirror-symmetrical 
S-configuration about two cooling drums 4 arranged atop one another and is 
then further transported by the conveyor belt 6 to further treatment steps 
or a winding station. By using two cooling drums 4 and the aforedescribed 
S-configuration for guiding the strip through the cooling drums the 
endless profile 8 is shock-cooled at its underside as well as at its upper 
side so that both sides are provided with a surface of an increased 
tackiness. With this cooling method a further cooling step in a 
conventional liquid bath is in general obsolete. 
The present invention is, of course, in no way restricted to the specific 
disclosure of the specification and drawings, but also encompasses any 
modifications within the scope of the appended claims.