Solid material comminution or disintegration – Processes – By operations other than force of contact with solid surface
Reexamination Certificate
2001-03-08
2003-07-01
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Processes
By operations other than force of contact with solid surface
C241S005000, C241S018000, C241S021000, C241S022000, C241S023000
Reexamination Certificate
active
06585176
ABSTRACT:
The invention relates to a process for the comminution of bulk materials consisting of synthetic polymers which do not have an elastomeric behavior by mechanical, thermal or electromagnetic loading of the bulk materials.
The invention also relates to a process for the comminution of bulk materials comprising synthetic polymers which have an elastomeric behavior.
The invention relates to a process for increasing the effectiveness of the comminution of bulk materials, in particular for increasing the throughput, reducing the requisite comminution work and/or achieving particle sizes which, without this process, can only be achieved with high energy consumption, or not at all.
For many applications, it is necessary for the solids to have certain degrees of fineness. Defined particle sizes are necessary, for example, for the setting of a dissolution rate, for binding fillers in films, for the preparation of stable suspensions or for facilitating downstream processes (for example drying, mixing or conveying). One way of setting defined degrees of fineness is comminution of relatively coarse particle sizes of the solid. This is frequently also the only possibility using the means of mechanical process engineering, since the bulk material is only present in relatively coarse particle sizes owing to the production process or the genesis.
Bulk materials can only be comminuted to the requisite degrees of fineness with high energy expenditure. This is as a result of the general laws of fracture mechanics and consequently the material behavior of solids. Thus, plastic deformations increasingly occur if the particle size of the loaded particles decreases. This is due to the reduction in the number of fracture-initiating flaws which occurs with increasing fineness. During comminution, this results in the achievement of shear stresses, which result only in plastic deformation, rather than tensile stresses, which can result in brittle fractures. With decreasing particle size, plastic and/or elastic deformations increasingly also occur in substances having a material behavior which is very brittle in macroscopic terms. This phenomenon also occurs if relatively large particles are loaded in very small volume regions (microplasticity). In the case of very fine particles, there is a limit below which only plastic deformation occurs. This limit is known by the term grindability limit. Quartz exhibits this behavior at about 1 &mgr;m and calcite at about 3-5 &mgr;m under room conditions. The grindability limit under room conditions is shifted significantly toward relatively coarse particles for substances having a viscous material behavior (for example polymers). The comminution of such substances thus represents a technical problem.
Various proposals have been made for processes for the comminution of substances of this type.
In so-called cryogenic comminution, polymers are comminuted at below their glass transition temperature. The material behavior changes here from elastic-plastic to brittle. This causes a significant reduction in the grindability limit and thus in the comminution energy required. The limits of this process are in the energy consumption for cooling and in that certain substances do not exhibit a transition in the material behavior from elastic-plastic to brittle at the temperatures which can be managed in industry and are economically acceptable.
The material behavior of bulk materials changes with the load rate in comminution machines. Substances having inelastic deformation components exhibit a greater tendency toward brittle fracture at high rates. This behavior is utilized in comminution machines which stress the particles at high rates. Examples thereof are jet mills and high-speed impact mills or impact disk mills. Due to the high speeds and thus also the accelerations, the power input is, however, generally relatively high based on the throughput in such mills.
A further possibility is the use of comminution machines which enable loading of the solid by multiaxial stress states. Under certain prerequisites, multiaxial stress states can result in a change in the material behavior of the solid. The solid then exhibits brittle behavior, in contrast to elastic-plastic behavior in the case of uniaxial stress states. The use of multiaxial stress states is used in moldings or very coarse particles for recycling. In the case of smaller particles, it is not technically possible to produce multiaxial stress states. This method thus remains closed for the production of very fine particles.
In certain comminution processes, grinding auxiliaries are added to the substances to be comminuted. These grinding auxiliaries cause more effective comminution, resulting in greater degrees of fineness or a lower energy demand for the comminution. Grinding auxiliaries are only used in comminution machines which load the particles as a material bed. Use in machines in which the conditions of single-particle comminution prevail (for example hammer mills, jet mills, impact mills and impact disk mills) does not result in an improvement in the comminution action. The grinding auxiliaries influence the flow properties of the particulate system in the comminution machines. This is achieved by a change in the interaction forces (van der Waals forces, electrostatic forces and capillary adhesive forces) between the particles through adsorption of the substances at the surface of the bulk materials to be comminuted. Examples of grinding auxiliaries are stearic acid, alcohols, amines and carboxylates in the case of dry grinding and polyacrylamides, polyacrylic acids and sodium silicate in the case of wet grinding.
So-called reactive grinding is employed for facilitating or accelerating chemical reactions. The action of reactive grinding is based on the fact that freshly fractured surfaces of solids can have increased chemical activities. If a surface of this type is brought into contact with a reaction partner, reactions can proceed more quickly or be better controlled compared with a surface which has not been freshly fractured. The aim of reactive grinding is controlled generation of defined chemical compounds with a certain yield by known chemical reactions. Reactive grinding does not have the aim of achieving certain degrees of fineness.
The document RU 2060882 C1 describes the digestion of used, metal-reinforced rubber products for recycling. A feature of the process described therein is the use of ozone. The aim of the process described is the separation of metal and rubber and not the generation of a certain degree of fineness of the end product.
The processes introduced for the generation of large degrees of fineness each have specific disadvantages for the comminution of materials having a viscous material behavior. The invention therefore had the object of increasing the effectiveness of the comminution of bulk materials. This applies both to the generation of particle sizes which cannot be generated using other processes and the increase in the throughput together with a reduction in the requisite comminution work.
This object is achieved in accordance with the invention by treating the bulk materials to be comminuted, before or during the loading, with oxidants which have an oxidation potential of greater than or equal to 1.5 V or subjecting them to corona, UV or plasma treatment. During this treatment, the bulk materials can be stationary or agitated.
The invention therefore relates to a process for the comminution of bulk materials comprising synthetic polymers which do not have an elastomeric behavior by mechanical, thermal or electromagnetic loading of the bulk materials, which comprises treating the bulk materials, before and/or during the loading, with oxidants which have a redox potential of greater than 1.5 V or subjecting them to corona, UV or plasma treatment without complete oxidation of the synthetic polymers taking place.
The invention likewise relates to a process for the comminution of bulk materials comprising synthetic polymers which have an elastomeric behavior by mechanical, t
Bauer Ulrich
Drögemeier Raimo
Gursky Helmut
Mientkewitz Olaf
Müller Hubert
Connolly Bove & Lodge & Hutz LLP
Rosenbaum Mark
Siemens Axiva GmbH & Co. KG
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