Method of producing adhesive resin particles

Adhesive resin particles of adhesive resin having a plasticizing range between 60.degree. and 120.degree. C., as well as a method of producing the particles. To prevent the particles from sticking together or caking during storage, they are in the form of coated particles, with at least one polyethylene hard wax having a solidification point of .gtoreq.90.degree. C. being added to the adhesive resin to coat the same.

BACKGROUND OF THE INVENTION 
The present invention relates to adhesive resin particles of adhesive resin 
having a softening or plasticizing range between 60 and 120.degree. C., 
especially for the manufacture of rubber. The present invention also 
relates to a method of producing such particles. 
The adhesive resin additives of rosin and tall oil resins are used during 
the manufacture of rubber. In this connection, the rosin is customarily 
delivered in metal drums, whereas tall oil resin is present in bags in the 
form of large pieces or clumps. When the drums are broken open, the 
drawback exists that metal particles can enter the rubber mixtures. 
However, the primary drawback with both rosin and tall oil resins is that 
both adhesive resins, as additives for a rubber mixture, can be weighed 
only by hand. Furthermore, it is already known to produce adhesive resins 
having higher plasticizing temperatures, for example phenol resins and 
hydrocarbon resins, in bead or tablet form. 
With a view toward automating the production of rubber mixtures, it is 
desirable to have all of the adhesive resins present in such a form that 
they can be automatically weighed. 
It is therefore an object of the present invention to provide adhesive 
resin particles that can be weighed automatically, and also to provide a 
method of producing the same. 
SUMMARY OF THE INVENTION 
Pursuant to the present invention, this object is realized in that the 
particles are in the form of coated particles, and in that added to the 
adhesive resin to coat the same is at least one polyethylene hard wax 
having a solidification point of .gtoreq.90.degree. C. One method of 
producing such adhesive resin particles is characterized primarily by 
adding t molten adhesive resin, in an inert gas atmosphere, a polyethylene 
hard wax, conveying the thus-formed material to a bead or tablet-forming 
apparatus, and producing coated adhesive resin in tablet form with the 
tablet-forming apparatus, accompanied by cooling of the material comprised 
of adhesive resin and polyethylene hard wax. 
The primary advantage of the inventive coating of the adhesive resin 
particles is that even after long storage periods of the particles, even 
during higher temperatures, such as in the summertime, the particles no 
longer adhere to one another or cake together, thus assuring an exact 
automatic weighing of the particle additives during the manufacture of a 
rubber mixture. Even where increased pressures are encountered due to the 
fact that the bags are stacked one above another on a plurality of 
pallets, no caking of the particles in the bottom bags occurs. In contrast 
with the state of the art, where the hard and brittle rosin produces dust 
problems and the danger of fire when it is broken up, the inventive coated 
rosin particles can be handled without difficulty in the plant. A further 
advantage of the present invention is that there no longer takes place a 
reduction in size or crushing of the rosin or tall oil resin accompanied 
by an increase in surface area and the thereby resulting oxidation, i.e. a 
reduction of the adhesive effect.

EXAMPLE 
The following is one exemplary embodiment for explaining in detail the 
method of producing adhesive resin particles. First, rosin having a 
plasticizing range of between 60.degree. and 120.degree. C. is melted in 
an inert gas atmosphere, for example a nitrogen atmosphere, which prevents 
oxidation, at temperatures between 100.degree. and 140.degree. C. While 
stirring, polyethylene hard wax having a solidification point of 
.gtoreq.90.degree. C. is subsequently added in an amount of about 2% by 
weight, with this polyethylene hard wax being dissolved in the molten 
material. Subsequently, the thus obtained material is conveyed to a bead 
or tablet-forming apparatus with which, accompanied by cooling, coated 
adhesive resin tablets are produced. By changing the pressure and 
viscosity, the desired size of the tablets can be set. In this connection, 
the viscosity of the molten material is controlled by the temperature. The 
particles of material are pressed through openings in the outer wall of 
the tablet-forming apparatus and fall onto a cooled stainless steel band, 
at the end of which coated adhesive resin tablets are present that have 
been cooled down to about 50.degree. C. During the cooling process on the 
band, the polyethylene hard wax that is present in the material is 
deposited on the surface of the tablets, thus reliably preventing a later 
caking of the tablets. The tablets have a diameter of about 8 mm and a 
thickness of about 4 mm. With such small particles sizes, the rosin can be 
especially precisely automatically weight as an additive for a rubber 
mixture. 
The described production method can analogously also be used for the 
production of adhesive resin particles on a tall oil resin base, of 
hydrocarbon resins (C5- or Cg base), and phenol resins, in each case with 
a plasticizing range between 60.degree. and 120.degree. C. The additives 
are linear or branched polyethylene hard waxes in an amount of from 0.5 to 
6% by weight. The tabletizing is effected at temperatures of between 
90.degree. and 140.degree. C. In order to assure an automated weighing 
with a weighing precision of only a few grams, the adhesive resin 
particles should have an average particle size of less than 15 mm. 
Pursuant to a further inventive production method, the molten material 
comprised of the adhesive resin and the polyethylene hard wax that has 
been added thereto are poured onto a cooled metal band, resulting in a 
thin layer having a coated surface. By subsequently breaking up the 
material, adhesive resin particles in so-called flake form are obtained. 
Tests have shown that the inventively produced coated adhesive resin 
particles show no sign of caking together even when stored for a long 
period of time under pressure and under temperatures of 50.degree. C. Also 
when used to produce a rubber mixture, the inventive adhesive resin 
particles showed no drawbacks with regard to adhesion and vulcanisate 
characteristics. 
The present invention is, of course, in no way 
ed to the specific disclosure of the specification and example, but also 
encompasses any modifications within the scope of the appended claims.