Method of manufacturing a randomly patterned floor covering from a preform of rubber

A method of manufacturing a randomly patterned floor covering having contrastingly-colored zones from a preform of rubber in which the preform is cut in pieces, each of which are molded into a blank having projections extending from a top side of the blank in relief-like fashion, solidified by vulcanization and then machined by cutting only in the region of the projections. The rubber forming the contrastingly-colored zones is mixed with contrastingly-colored particles in an amount of at least ten percent by weight. These particles are substantially free of flat surfaces and are in, at least, an advanced state of vulcanization. The particles located in the projections extending from the top side of the blank are exposed during the cutting step.

BACKGROUND OF THE INVENTION 
The invention relates generally to a method of manufacturing a randomly 
patterned floor covering having contrastingly-colored zones from a preform 
of rubber and, more particularly, to an improved method in which the 
preform is cut into pieces, which are molded into the shape of blanks 
having projections extending from the top side thereof in a relief-like 
fashion, solidified by vulcanization and then machined by cutting only in 
the region of the projections. 
This type of method is disclosed in DE-OS2836642 in which a thick lower 
layer and a thin upper layer are placed into a forming tool and pressed 
together. Randomly placed recesses in the forming tool are used to form 
projections in a relief-like fashion at the side of the blank that 
eventually is exposed for viewing. The projections are ground off this 
side after vulcanization in such a manner that the upper flat portion is 
completely removed at this point and the contrastingly-colored lower flat 
portion becomes visible. The upper and the lower portions require separate 
production and processing, which results in considerable costs. 
In U.S. Pat. No. 1,816,822, a method for producing a rubber floor covering 
is disclosed in which contrastingly-colored, vulcanized rubber particles 
are distributed in an unvulcanized rubber mixture. The ensuing 
conglomerate mass is subsequently drawn into a sheet after which a 
semi-curing process, in which the conglomerate mass is partly vulcanized, 
occurs. Next the upper side of the sheet is sanded or buffed to cut back 
the outer surface and expose the particles. Finally, the vulcanization 
process is completed. The contrastingly-colored zones, which are 
determined by the location of the particles, are related to each other by 
a statistical distribution. An observer viewing a floor covering made 
according to this method will receive an overall impression of a speckled 
or marblized appearance. A floor covering having a pattern of a defined 
shape cannot be obtained with this method. 
SUMMARY OF THE INVENTION 
One of the problems to which the invention is directed is provision of a 
method of manufacturing a rubber floor covering that can be carried out 
simply and generates contrastingly-colored zones that appear in randomly, 
predeterminately patterned, regions on the surface of the covering. The 
invention solves this problem by providing a method of manufacturing a 
randomly patterned floor covering having contrastingly-colored zones from 
a preform of rubber in which the zones are formed by uniformly mixing a 
rubber mixture of one color With contrastingly-colored particles of 
another color in an amount of at least ten percent by weight. The 
particles are substantially free of flat surfaces and are in at least an 
advanced state of vulcanization. After complete mixing of the particles, a 
preform is drawn by appropriate processing in a rolling mill or calendar. 
The preform then is cut into pieces, which are placed in a pressing tool 
to form projections in the top surface of the pieces. Each piece is 
simultaneously vulcanized to form to a blank. The tops of the projections 
of the vulcanized blank then are cut off such that the particles located 
within the projections become visible. 
Particularly advantageous results can be achieved when the 
contrastingly-colored particles are mixed in amounts between ten and fifty 
percent by weight, with an amount of thirty percent by weight being 
preferred. The most advantageous particle diameter lies in the range of 
1.2-1.4 mm. 
As discussed above, the projections may be formed in a pressing tool. A 
particularly good pattern can be obtained if the blank is vulcanized with 
the eventual top side facing downward The cutting off of the tops of the 
projections may be carried out by a grinding or splitting machine and the 
entire projection, rather than just the top, may be removed. 
Further features, advantages and embodiments of the invention are apparent 
from consideration of the following detailed description, drawings and 
appended claims.

DETAILED DESCRIPTION 
The rubber mixture and the particles used in the mixing step of the 
invention are dyed differently to have contrasting colors. The rubber 
material forming the particles is in, at least, an advanced state of 
vulcanization compared to the rubber mixture. The particles thereby are 
inhibited during vulcanization of the blank from softening with the rubber 
mixture, which precludes mutual mixing of the dyes contained in the 
particles and in the rubber. In this manner, the particles in the floor 
covering made according to the invention are precisely delineated from the 
surrounding rubber mixture. This same effect can be achieved if the 
particles are only in an initially vulcanized state and the rubber is in 
an unvulcanized state when mixed. 
The particles are substantially free of any flat surface areas, which 
ensures that during mixing with the rubber mixture the particles are 
covered on all sides with the rubber mixture. Thus, after being molded 
into the form of the blank, the particles are no longer visible at the 
outer surfaces of the blank. Hence, after the blank has been vulcanized, 
it has substantially the same color as the color of the rubber mixture 
employed. 
The amount of Contrastingly-colored particles is relatively high; with at 
least ten percent by weight compared to the weight of the blank, the 
overall color impression of the blank is substantially determined by the 
particles, which are exposed by cutting off the tops of the projections. 
The tops of the projections of the finished floor covering aesthetically 
appear as patterned zones, which are clearly delineated from the 
surrounding unmachined area of the upper side of the floor covering. The 
floor covering made according to the invention is distinguished by its 
patterned projections and particularly high durability. One advantage of 
the method of the invention is that the floor covering retains its 
original appearance to a large degree, even after intensive use and a long 
period of time has passed. 
The maximum amount of contrastingly-colored particles that should be used 
is fifty percent by weight to ensure that the particles are completely 
incorporated, when being mixed, into the rubber mixture. As a higher 
amount of particles is used, the danger of seeing individual particles 
shining through the floor covering in the region of the unprocessed flat 
zones at the top side becomes increasingly prevalent. If this occurs, the 
overall pattern obtained can be adversely affected. A minimum content of 
contrastingly-colored particles of twenty percent by weight and, more 
advantageously, of thirty percent by weight is preferred, while the upper 
limit of fifty percent by weight should be observed. 
The particles should have a diameter that is smaller than the thickness of 
the floor covering, but large enough to let the particles appear 
distinctly when viewed at a distance from the human eye of 2 to 3 m. 
Mixing-in of dust waste is as equally unsuitable as the mixing-in of 
particles having a thickness larger than the thickness of the floor 
covering at the thinnest point. Under normal conditions, it is 
advantageous to use particles having a mean diameter of 1.2 to 1.4 mm, 
With the amount of particles in dust form (having a diameter of less than 
0.5 mm) being less than 2 percent by weight. A regular curvature of the 
surface of the particles is not necessary, as long as the presence of 
basically flat, particle surfaces is predominately precluded. The most 
advantageous benefits of the invention can be obtained if the presence of 
flat surfaces is completely eliminated. 
As noted above, the projections may be formed in the blank, which is in the 
pre-vulcanized plastic state, by means of a pressing tool. Depending on 
the form of the particular pressing tool used, the location of the 
projections can be randomly set in desired patterns, which are permanently 
fixed during the subsequent vulcanization of the blank. 
The use of a pressing tool results in a particularly precise formation of 
the projections in a relief-like manner. During the cutting process, the 
projections may be removed entirely. A particularly good pattern can be 
obtained if the blank is vulcanized with the top side facing down. In this 
manner, the contrastingly-colored particles are incorporated and fixed 
into the region of what later becomes the top side of the covering with a 
particular degree of uniformity. 
The machining of the cutting process may be performed by means of a 
grinding or splitting machine in which a linear cut is generally applied. 
This type of operation is simple to carry out on a large scale, and 
ensures a great amount continuity of the end products obtained. 
Specific examples made in accordance with the method of the invention are 
discussed below. 
EXAMPLE 1 
In this example, 100 parts by weight of a rubber mixture of color 1 are 
mixed in an internal rubber mixer with 20 parts by weight of an already 
vulcanized rubber milling material of color 2 having a grain size of 1.2 
to 1.4 mm, until complete mixing is achieved. From this mixture, a preform 
having a thickness of 5 mm is drawn in a rolling mill or a calendar. 
Pieces are cut from the preform and transported to a pressing tool, which 
is bounded on one side by a flat forming surface. The other side of the 
pressing tool is bounded by a square base having a side length of 35 mm 
and a forming surface that has depressions in the shape of truncated 
cones. The cones have a depth of 1.5 mm and a maximum diameter of 25 mm. 
The two forming surfaces are pressed against mutually opposite sides of a 
preform piece in such a manner that the piece is molded into the shape of 
the forming surfaces, thereby converting the piece into the shape of the 
blank shown in FIG. 1. The shape of the blank is permanently fixed by the 
simultaneously occurring vulcanization process. 
The upstanding ends of the projections 2 of the blank are cut off in a 
manner shown in FIG. 1. In the cutting process, the particles located 
within the projections are exposed These particles substantially determine 
the overall color impression received when viewing the end faces of the 
projections 2. The surrounding unprocessed zones 3, on the other hand, 
continue to have the color 1 of the rubber mixture used. 
EXAMPLE 2 
In this example, 100 parts by weight of a rubber mixture of color 1 are 
mixed in a rubber mixer with 20 parts by weight of an already vulcanized 
rubber milling material of color 2 having an average diameter of 1.3 to 
1.4 mm, until complete homogenization of the mixture is achieved. From 
this mixture, a preform with a thickness of 5 mm is drawn by means of a 
rolling mill, calendar or extruder. 
Pieces of suitable size are cut from the preform and are molded in a 
pressing tool comprising a flat lower die part and an upper die part 
having depressions formed therein. The depressions are distributed in a 
pattern to form the projections in the surface of the molded piece. The 
rubber milling material particles of color 2 admixed to the rubber mixture 
of color 1 are almost completely surrounded by the rubber mixture. The 
blank obtained after vulcanization is suitably processed at the vicinity 
of the end faces of the relief-like projections such that the particles of 
the rubber milling material are exposed. These particles substantially 
determine the overall color impression of the end faces of the projections 
2, while between the projections, the color 1 of the rubber mixture 2 is 
essentially preserved.