WO2000067976A1

WO2000067976A1 - Method for adding particles to raw rubber and other polymers

Info

Publication number: WO2000067976A1
Application number: PCT/NO2000/000148
Authority: WO
Inventors: Lars Erik BÖNAA; Torbjörn BERG
Original assignee: TROMS DEKK AS
Current assignee: TROMS DEKK AS
Priority date: 1999-05-10
Filing date: 2000-05-04
Publication date: 2000-11-16
Anticipated expiration: 2001-11-10
Also published as: NO310648B1; NO992253D0; AU4439100A; NO992253L

Abstract

Method of dosage and mixing of solid particles to non-vulcanized rubber or other polymeric materials. A stud extruder is utilized as a mixing unit, wherein the quantity of rubber or polymer added is measured continuously, and the particle quantity supplied to the extruder is measured continuously in relation to the consecutive quantity of rubber or polymer added. The method is particularly applicable to the addition of abrasive particles to rubber for the production of friction tyres or antiskid soles for shoes.

Description

Method for adding particles to raw rubber and other polymers.

The present invention relates to a method of dosing and adding a desired quantity of solid particles into initially non-vulcanized rubber or other polymers.

Background

From several patents it is known that the friction between a tyre, the sole of a shoe, and a slippery base such as ice and snow, increase when the matrix material has been intermixed with abrasive particles. This is caused by increased surface roughness because particles detached from the surface leave open pores in the surface. A further increase in friction is achieved if the particles are securely held within the matrix material, thus forming hard projections.

Several patents suggest the particles are to be coated with a primer prior to mixing with the matrix material. Such primers can be commercial chemicals developed for rubber coating of metallic materials. Said patents are based upon the fact that the final intermix of the particles into the matrix material is to be performed by standard rubber mixers. However, for fear of exposing valuable mixers to substantial abrasive wear, the industry normally aviods such blending methods. Moreover, blending methods of this type involve wear of any primer coating on the particles. The present inventors have made a test production of tyres of premixed friction rubber as disclosed in NO Patent 177048. In view of this method mineral particles are mixed with rubber in a common roller mill, whereupon the friction rubber is machined into strips in accordance with directions disclosed in said patent. However, the experience from this method is that the composition can be inconsistent, and the cross section of the strip varied both in width and thickness. The circumstances made it impossible to produce tyres having a uniform quality with regard to balance and roundness, including lateral and radial eccentricity.

Object Accordingly, an object of the present invention is to provide a method of dosing and adding a desired quantity of solid particles into a predetermined quantity of initially non- vulcanized rubber or other polymers, thus achieving a homogenous mixture of particles and rubber or other polymers. Another object of the invention is to perform the method above to limit and control the degree of abrasive wear of the production equipment by the particles as far as possible.

Yet another object is to utilise said method for the addition of abrasive particles to rubber or other polymer compositions in the manufacture of friction tyres, antiskid soles, etc.

The objects above are achived by the method of the present invention.

Invention The invention relates to a method of dosing and adding solid particles into non- vulcanized rubber or other polymers, wherein the method is characterized by mixing the components with a stud extruder, performing a continuous measurement of the rubber or polymer added, and continuously dosing the particle quantity into the stud extruder in relation to the quantity of rubber or polymer being added as defined by patent claim 1. Preferred embodiments appears from the dependent claims.

The challenge from which the present invention originated is bipartite. Firstly it was necessary to find a method limiting the wear damage to the production equipment, particularly from abrasive particles, or at least simplify repair of such damage. This is achieved by using a stud extruder where the internal surface is substantially limited in relation to conventional mixers, decreasing preplacement or repair of wear components similarly.

By the use of an extruder of this type, the particles are given a short travel distance from dosing to complete blending. This type of machine is known as having a very satisfactory mixing effect and to provide a fast plastification of the rubber after dosage. The extruder turns the mass back to the dosage inlet as a paste during kneading, since the machine is operated in a particular manner dependent on screw speed and heat supply. For that reason extruders of this type always exhibit a top mounted inlet opening. Then, the powder material to be blended can be dropped directly down into the inlet opening where the powder is kneaded into the plastified rubber paste. The second challenge consisted in achieving a homogenous mixture of rubber or polymer and particles regardless of the variations in polymer addition occuring naturally with commonly used crude polymers in the form of strips or similar. This is achieved by the use of a dosage system for the particles which are subjected to a continuous control in relation to the quantity of polymer being supplied. A dosage system of this type may per se comprise prior art measuring units, weighing units and dosage units, as exemplified below.

The method of the present invention is simple and flexible, in addition to reducing wear and resulting maintenance costs to an acceptable level. In this manner friction rubber and tyres can be manufactured in an economically acceptable manner. Moreover, the present method is so simple to rearrange that it offers full freedom in tailoring the production in view of rubber quality, component portions and, last but not least, the components per se. The accompanying figure illustrates schematically a stud extruder with accompanying accesories for rubber/polymer and particles.

The stud extruder 1 exhibits an inlet 2 for rubber/polymer, which also is used for supply of particles, and an outlet (extruder die) 3 for blended material. The interior of the extruder is not illustrated. The system further comprises a tachogenerator 5, a container 7 for particles and a cell dispenser 8 or a similar particle weighing system, and a computer (PC) 9.

The quantity or rubber supplied into the extruder 1 is monitored by a tachogenerator 5 rolling unrestrained on the rubber strip 4 as the latter is drawn across a tilted board provided with lateral guiding means. The tachogenerator 5 produces electrical voltage pulses timed with the speed of the rubber strip 4, and the pulses are preferably logged by a PC 9 as a measure of the rotational speed of the tachometer wheel. Between the tachometer wheel 5 and the rubber strip 4 there is a high friction level, and accordingly, no slip should occur. The circumference of the wheel is preferably stored as a constant in the software. Rubber strip width and thickness can be established as static variables in the software. Moreover, the specific gravity of the rubber/polymer material can be established as a constant multiplier. By online measurement of the strip speed the system is able to perform a continuous calculation of the quantity of rubber being supplied into the machine and to control the speed of the cell dispenser in view of the former, thus retaining a constant weight distribution between the particles and the matrix material (polymer).

The total weight of the container 7 with particles 6 is logged regularly. The system will raise a message when refill of the container 7 is required and perform weighing of the quantity of particles 6 being refilled. If desirable, the system is also able to refill the container 7 from a bin (not illustrated) automaticically. The output is controlled by means of the speed of the cell dispenser 8. Each cell ejects a known volume, and the specific gravity of the particle material to be ejected can be established as a constant multiplier in the software. Ready-mixed material is ejected from the extruder die 3, and the cross-sectional profile can be selected in a common manner.

By using a computer and a loss weighing system having a cell dispenser it is also possible to establish functions for automatic halt and starting, which occur at regular intervals in production. The system can handle several types of powder materials. The specific gravity of each material in question can be established as constants in the software. In production the operator selects the number of the desired material to be intermixed. The main purpose of the invention is to mix friction promoting particles in the tread of snow tyres, but it is also applicable for blending granulated rubber from recycled tyres. Thus it is possible to save considerable amounts of fresh rubber in the production of tyres by recycling vulcanized rubber from old tyres.

With regard to the software mentioned above for controlling the supply of particles, the software does not exhibit algorithms or constructions departing from the technical field within control engineering. Accordingly, the software is not described in further detail here.

The present inventors developed the invention on a Marangoni Compact 100, which is a combined extruder and tyre construction machine. It has shown to be particularly useful as it is applicable to both construction of tyres for sale and for production of semifinished products formed as camelback or strips for other tyre manufacturers. The inventors also conducted experiments with types of minerals other than those disclosed in NO Patent 177 048. As is common in any grinding or gluing process, it is desirable that the particles to be intermixed are clean and dust-free. This has been verified by mixing washed un-primed mineral particles having a size of 0,2-1,2 mm. Particles of this category are shown to exhibit a substantially improved adhesion to rubber than the primed and dust containing particles of NO Patent 177048. Rubber er se is an adhesive material having a high degree of adhesion, and accordingly the inventors have stated that priming of clean porous surfaces is not necessary. The bonding strength between the particles and the matrix material can also be increased by breaking down or removing the oxide layer on the particle surface immediately prior to mixing. Such breakdown of the oxide layer is achievable from mechanical strain such as agitation or pneumatic transport or from acid-wash (etching) followed by drying. Subsequent to a treatment of this type the particles must be mixed within a short period of time to prevent formation of a new oxide layer, or the particles must be kept within an oxygen- free environment, e.g., by displacing the air from the sand container with an inert gas such as argon.

An alternative method of increasing the bonding strength is to heat the sand particles to at least 20-30°C above the rubber vulcanization temperature. Subsequent kneading of the particles into the rubber will initiate vulcanization of rubber contacting the particles, but the process is gradually halted with the heat loss from the particles.

Claims

1. Method of dosing and blending solid particles and non-vulcanized rubber or other polymers, characterized by

- using a stud extruder as mixing means,

- performing a continuous measurement of the quantity of rubber or polymer added, and

- effecting a continuous mass feed of particles to the stud extruder in relation to the quantity of rubber or polymer added.

2. Method in accordance with claim 1, characterized by supplying the rubber or polymer as continuous bands or strips, and using a tachogenerator for continuous measurement of rubber or polymer added.

3. Method in accordance with claim 1, characterized by weighing and feeding the particles by an electronic weighing means and a cell dispenser.

4. Method in accordance with claim 2 or 3, characterized by the tachogenerator and the cell dispenser being connected to a computer, said computer provided with suitable software controlling the supply of particles from the cell dispenser to the stud extruder.

5. Method in accordance with claim 1, characterized by the particles having a particle size from 0,1 to 5,0 mm.

6. Method in accordance with claim 1, characterized by supplying rubber or polymer in the form of commercially available materials having up to 100% natural rubber.

7. Method in accordance with claim 1, characterized by subjecting the particles to a mechanical or chemical purification immediately before the mixing step to remove dust, fat or oxide layer, thus improving the adhesion to the polymer material.

8. Method in accordance with claim 1, characterized by preheating said particles to a temperature of the vulcanization temperature of the polymer material or higher prior to mixing to form a thin layer of vulcanized polymer material adhered to the particles already within the mixing step, whereupn the particles are cooled and the process is halted.

9. Method in accordance with claim 1, characterized by storing purified or preheated particles in an oxygen-free atmosphere until mixing to prevent formation of new oxide layer.

10. Method in accordance with claim 1, characterized by applying a primer to particles not exhibiting a porous surface, such as metallic particles.

11. Method in accordance with claim 1 , characterized by using particles comprising abrasive particles suitable for incorporation into friction tyres and antiskid sole for shoes.