Title: "GRAIN AND PRODUCTION METHOD THEREOF."

TECHNICAL FIELD

The present invention relates to a devulcanized rubber granule, a method of treating vulcanized rubber and a use of such treatment method.

BACKGROUND OF THE INVENTION

Synthetic or natural rubber is the basic component in the manufacture of tires. Rubber undergoes a vulcanization process, which makes it suitable for tire manufacture.

The vulcanization process is almost irreversible and substantially prevents recovery of tires, e.g. scrap tires, into the production cycle.

Scrap tires are typically destroyed by disgregation, whereupon the granules obtained from disgregation are used as a second rate raw material and cannot be reused, due to vulcanization, in the manufacture of new tires, unless in very small amounts.

Many attempts have been made to obtain tire devulcanization: for an overview of existing devulcanization technologies, see "Evaluation of Waste Tire Devulcanization Technologies", a report written in 2004 upon request of the "INTEGRATED WASTE MANAGEMENT BOARD" of California government.

It will be apparent that important parameters for evaluating a devulcanization process are both the devulcanization amount, e.g. defined by ASTM D 6814, e.g. the 2002 issue (ASTM D 6814:2002), and the energy (and thus money cost) required to achieve a given result.

A third important parameter for evaluating the devulcanization process is its ability to avoid physical or chemical alterations to the rubber material, which should be ideally devulcanized without being affected by any further change. In the light of the above prior art, the object of the present invention is to provide a devulcanization process that is improved as compared with the prior art, in terms of percent devulcanization and/or energy cost and/or monetary cost and/or process yield and/or changes to the devulcanized rubber.

Furthermore, the present invention affords advantages in terms of simple fabrication, greater strength, more compact design and/or higher versatility of the devulcanization process and/or the devulcanized rubber.

SUMMARY OF THE INVENTION

According to the present invention, this object is fulfilled by a treatment method as defined in claim 1 , a granule as defined in claim 8 or a use as defined in claim 15.

DETAILED DESCRIPTION

The characteristics and the advantages of the invention will appear from the following detailed description of one practical embodiment, which is given by way of non-limiting example:

Although this is not expressly shown, the individual features described with reference to each embodiment shall be intended as auxiliary and/or interchangeable with other features, as described with reference to other embodiments.

It shall be further noted that the claims shall not cover what will be found to be known or obvious to the skilled person before the priority date (which will be intended as disclaimed).

As used herein, the term "rubber" may be intended to designate the unvulcanized raw material, the vulcanized material or the material at the end of the devulcanization process; likewise, the term "devulcanization process" shall be intended to apply to any type of vulcanized material, regardless of its origin.

While reference shall be made hereinafter, for simplicity, to scrap tires, it shall be understood that other types of vulcanized rubber may undergo the devulcanization process.

The present invention provides both a devulcanization process and a devulcanized rubber element, hereinafter briefly designated as "granule".

As used herein any reference to the degree (or percent) of devulcanization will relate to the values obtained by application of ASTM D 6814, namely ASTM D 6814:2002.

Particle size measurement as intended herein shall be performed according to CEN-TS 14243.

Nevertheless, the skilled person may easily appreciate that equivalent methods may be also used, instead of those mentioned above, for implementation of the present invention and/or its principles.

Reference shall be made herein to sizes (or parameter values) and size (or value) ranges. The sizes (or parameter values) may be expressed in the metric system or the British system.

Although this is not expressly mentioned, each size (or value) indicated herein, whether expressed in the metric or British system, shall be deemed to be an explicit disclosure of the corresponding standard size (or standard value), expressed in the British or metric system respectively.

This is because any skilled person is able to recognize the standard sizes and values of a system and adapt them to the closest standard sizes and values of the other system.

For instance, 0.8 mm corresponds to 0.031496 in, but the closest standard size is 0,0325 in, corresponding to 0,8255 mm. Therefore, both 0.8 mm and 0.0325 shall be intended to be disclosed herein, even by mentioning one of the two numbers only.

The rubber granule of the present invention has a high devulcanization degree: such devulcanization degree is equal to or higher than 16%, advantageously equal to or higher than 18%, 21 %, 24%, 27%, 30%, 34%, 38%, 42%, 47%, 52%, 57%, 63%, 69%, 76%, \'82% or 91 %.

It was experimentally found that the degree of devulcanization may not be exactly 100%, but it may be lower than 99%, 97% or 94%. In certain cases, it may also be lower than 88%, 83%, 78%, 74%, 71 %, 64%, 58%, 53%, 48%, 43%, 39% or 36%.

The degree of vulcanization of rubber may depend on particle size.

A first particle size classification of rubber may be based on that, in the market, rubber granules, possibly devulcanized, may be divided into more valuable and less valuable particle size granules.

The limit L between the two particle size ranges, according to each particular market, may be set to 1 mm or 0.8 mm, or 0.9 mm, or 1.1 mm, or 0.7 mm, or 0.45 mm.

Therefore, in this first classification, particle size classes may be expressed as larger than (and possibly equal to) L and smaller than (and possibly equal to) L.

Furthermore, it will be possible to only consider granules having a particle size lower than an upper limit S. Such upper limit S may be, for instance, 6 mm, 5.5 mm, 5 mm, 4.6 mm, 4.2 mm, 4 mm or 3.5 mm.

In a preferred embodiment, in which rubber granules are obtained from disgregation of a particularly large element (such as a tire), S may be selected so that the overall weight of rubber having a particle size exceeding S is equal or about equal to or less than 10% the weight of rubber with lower particle size.

In a preferred embodiment of the present invention, the upper limit S is 5 mm.

The particle size class lower than L may be further divided, e.g. into particle sizes higher and lower than a F value, that may be selected from the group comprising approximately or exactly the following values: 30%, 33%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 66% or 70% the L value , or 0.33 mm, 0.35 mm, 0.38 mm, 0.4 mm, 0.42 mm, 0.45 mm, 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm.

A greater number of particle sizes lower than L may be also defined, by setting multiple values F1 , F2 ... Fn (with n=2, 3, 4 or 5), and assigning to each value of F1 , F2 ... Fn one of the values mentioned above with respect to F. In a preferred embodiment of the present invention, a single F value is provided, i.e. 0.45 mm.

Two or more particle size classes may be also set between L and S, and be defined by particle size values C1 , C2 ... Cn (for instance with n=1 , 2, 3, 4, 5, 6, 7, 8, 9 or 10), in which each of the values C1 , C2 ... Cn may be selected from the group comprising approximately or exactly the following values: 15%, 20%, 25%, 30%, 33%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, l'80%, l'85% or 90% the S value, or 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.7 mm, 2 mm, 2.3 mm, 2.5 mm, 3 mm, 3.3 mm or 3.5 mm.

In a preferred embodiment, four values are considered: C1=1 mm, C2=1.7 mm, C3=2 mm and C4=2.5 mm.

In one aspect of the present invention, devulcanization occurs by submitting vulcanized rubber to a high pressure water treatment, known as water jet.

It should be noted that in the prior art no devulcanization system or method has ever used water jet treatments.

For instance, the water jet treatment may be directly used on rubber yielded from scrap tires, solid rubber tires, crawlers or other rubber elements.

For example, a scrap tire treatment plant may comprise one or more of the following work areas:

1. Storage area for the rubber to be treated (such as tires, trolley wheels, etc.)

2. Sorting area for sorting rubber to be treated by classes;

3. Preparation area, in which the rubber to be treated is prepared for devulcanization and transferred and/or loaded into the devulcanization chambers;

4. Devulcanization area;

5. Collection and/or drying area, for collecting and drying rubber granules after devulcanization;

6. Sorting area for sorting the devulcanized rubber by particle size;

7. Storage area for the devulcanized rubber;

8. Process water recovery area.

The areas 1 and 2 are advantageous if the rubber to be treated is not homogeneous in terms of size, weight, shape and/or composition and may be as known in the art, e.g. equipped with lifting and conveyor equipment and/or suitable instruments, and will not be described in further detail.

The area 3, herein defined for treatment of scrap tires, comprises systems for cutting tire shoulders and treads, or for special preparation of solid rubber tires or tires of non-standard sizes. These systems do not fall within the scope of the present invention and will not be described in further detail.

The area 4 is where water jet treatment is performed for devulcanization, as better described hereinafter.

The areas 5, 6 and 7 include automatic (or in certain cases, manual) systems for collecting and drying devulcanized rubber, for removing residual metal parts, for sorting devulcanized rubber by its particle size and for storing it. Unless otherwise stated in the present application, the methods to achieve the above are known and do not fall within the scope of the invention, and will not be described in further detail.

The area 8 comprises a water recovery and recirculation system, which is useful to reduce the environmental impact of water jet treatment for devulcanization.

The water jet treatment according to one aspect of the present invention is performed by exposing the rubber to be treated to a water jet. Preferably, the water jet is directed toward a reference surface, which provides support to the rubber to be treated.

Therefore, the rubber to be treated is interposed between the water jet nozzle and the reference surface.

According to the invention, such treatment is used to obtain at least partial devulcanization of the rubber to be treated.

The reference surface may be formed with a mesh, a net, sectors or rollers and may be made of metal or other materials. In one aspect of the present invention, the reference surface is formed by rollers, upon which the rubber to be treated is fed.

Water jet treatment is performed by a water jet emitted by one or more nozzles mounted to a water jet head. Water jet heads are known in the art and will not be discussed in further detail.

The water jet treatment is defined by certain independent parameters, such as working pressure P, water flow rate Q, water jet nozzle diameter D, rotation speed Ω of the water jet head, distance between the nozzle and the surface to be treated, speed of the water jet head relative to the rubber to be treated, in the two dimensions of the reference surface, temperature and composition of water jets.

Optionally, granule devulcanization may be influenced by the drying procedure that the granules undergo after water jet treatment.

According to one embodiment of the present invention, the working pressure P may be equal to or lower than a value P _max , selected from the group comprising approximately or exactly the following values: 4000 bar, 3800 bar, 3500 bar, 3300 bar, 3100 bar, 3000 bar, 2900 bar, 2800 bar, 2700 bar, 2600 bar, 2500 bar, 2400 bar, 2350 bar, 2300 bar, 2250 bar, 2200 bar, 60000 psi, 50000 psi, 45000 psi, 40000 psi, 38000 psi, 37000 psi, 36000 psi, 35000 psi, 34000 psi, 33000 psi, 32000 psi.

According to one embodiment of the present invention, the working pressure P may be equal to or higher than a value P _max , selected from the group comprising approximately or exactly the following values: 1000 bar, 1200 bar, 1400 bar, 1500 bar, 1600 bar, 1800 bar, 1900 bar, 1950 bar, 2000 bar, 2050 bar, 2100 bar, 2150 bar, 2200 bar, 2250 bar, 2300 bar, 2350 bar, 20000 psi, 25000 psi, 27000 psi, 28000 psi, 29000 psi, 30000 psi, 31000 psi, 31500 psi, 32000 psi, 32500 psi, 33000 psi, 33500 psi, 34000 psi.

For instance, the working pressure P may range from 30000 psi to 36000 psi, preferably from 31000 psi to 35000 psi, more preferably from 32000 psi to 34000 psi, and be for instance about 33000 psi.

According to one embodiment of the present invention, the working flow rate Q of water of each water jet head may be equal to or higher than a value Qmin, selected from the group comprising approximately or exactly the following values: 8 l/min, 9 l/min, 10 1/min, 11 l/min, 11 ,5 1/min, 12 l/min, 12,5 l/min, 13 l/min.

According to one embodiment of the present invention, the working flow rate Q of water of each water jet head may be equal to or lower than a value Qmax, selected from the group comprising approximately or exactly the following values: 16 l/min, 15 l/min, 14 l/min, 13 l/min, 12.5 l/min, 12 l/min, 11.5 Umin, 11 l/min.

For example, the working flow rate Q of water of each water jet head may range from 10 to 14 l/min, preferably from 11 to 13 l/min, and be for instance about 12 l/min.

According to one embodiment of the present invention, the diameter D of water jet nozzles may be equal to or higher than a value D _m i _n , selected from the group comprising approximately or exactly the following values: 8 mils (milli-inch), 9 mils, 10 mils, 11 mils, 12 mils, 13 mils, 14 mils, 15 mils, 16 mils, 17 mils.

According to one embodiment of the present invention, the diameter D of water jet nozzles may be equal to or lower than a value D _max , selected from the group comprising approximately or exactly the following values: 22 mils, 21 mils, 20 mils, 19 mils, 18 mils, 17 mils, 16 mils, 15 mils, 14 mils, 13 mils.

For instance, the diameter D of water jet nozzles may range from 10 to 20 mils.

The water jet heads typically include multiple nozzles and may rotate about one axis, typically parallel to the average direction of water jets emitted by the water jet head (which jets are balanced about such axis, for minimized vibration), to change the angular position of each nozzle relative to the axis of rotation.

According to one embodiment of the present invention, the rotation speed Ω of the water jet head may be equal to or higher than a value _mm , selected from the group comprising approximately or exactly the following values: 1000 rpm, 1300 rpm, 1500 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 1950 rpm, 2000 rpm, 2050 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm.

According to one embodiment of the present invention, the rotation speed Ω of the water jet head may be equal to or lower than a value Q _max , selected from the group comprising approximately or exactly the following values: 3500 rpm, 3200 rpm, 3000 rpm, 2800 rpm, 2700 rpm, 2600 rpm, 2550 rpm, 2500 rpm, 2450 rpm, 2400 rpm, 2300 rpm, 2200 rpm, 2100 rpm.

For example, the rotation speed Ω may range from 2000 rpm and

3000 rpm, preferably from 2200 rpm and 2700 rpm, and be for instance about 2500 rpm.

Advantageously, in order that the water jet heads can treat the whole vulcanized rubber, the water jet heads are displaced relative to the latter.

If the reference surface is, for instance, a flat surface, the material to be treated will be also laid over a plane. In this case, the relative motion may have two translational components, so that the whole material to be treated can be effectively hit by the water jet.

If the reference surface has, for instance, a cylindrical shape, the relative motion may have a translational component along the axis of the cylinder and a rotational component about the axis of the cylinder, for treatment of the entire material.

The reference surface that is actually exposed to water jets is the surface on which, in operation, the rubber to be vulcanized is to lie.

If it is flat, it will have a given width, substantially smaller than length, if it has a cylindrical shape, it will have a given height and a given circumferential development. For the purposes of the following description, which is given with reference to a flat reference surface, the relative motion along the width of the reference surface (hereinafter referred to as lateral movement) will be equivalent (or comparable, or corresponding) to the relative movement along the height of the reference surface when it has a cylindrical shape, and the relative movement along the width of the reference surface (hereinafter referred to as longitudinal movement) will be equivalent (or comparable, or corresponding) to the relative movement along the circumferential development of the reference surface, when it has a cylindrical shape.

In the case of a flat reference surface, the water jet head may have a lateral, e.g. translational, e.g. reciprocating motion, relative to the material to be treated/devulcanized, which is interposed between the water jet head and the reference surface.

While the lateral movement may be actuated by the detection of the material to be treated/devulcanized, for the purposes of the present invention, the relative movement will be considered with respect to a fixed reference, such as the reference surface itself.

In the case of a flat reference surface, the water jet head may have a longitudinal motion, relative to the material to be treated, which is interposed between the water jet head and the reference surface.

Advantageously, the longitudinal movement occurs as a feeding motion of the material to be treated, without requiring any displacement of the water jet head. Nevertheless, a longitudinal movement may be imparted to the water jet head, in addition to the longitudinal movement of the material to be treated, but such movement will be advantageously a periodic, e.g. harmonic movement.

However, in the case of a cylindrical reference surface, the longitudinal movement is a relative circumferential movement and may be obtained by rotating the water jet head and/or the material to be vulcanized relative to the axis of the cylindrical reference surface.

The relative movement, which is a vector sum of the lateral movement and the longitudinal movement, may either have a speed v which is substantially constant in modulus (obviously excluding any transient value caused by direction reversal of lateral movement), or a speed v whose advantageously modulus changes in a periodic, e.g. harmonic manner.

The lateral movement shall have such a speed, relative to the longitudinal movement, as to allow treatment of all incoming vulcanized rubber. Therefore, the track of the water jets on the rubber to be treated will be such that the lateral movement can effectively treat substantially all the incoming rubber.

In one embodiment, the relative speed v is higher than or equal to a minimum speed v _min , selected from the group comprising exactly or approximately the following values: 0.5 m/min, 0.7 m/min, 1 m/min, 1.1 m/min, 1.2 m/min, 1.3 m/min, 1.4 m/min, 1.45 m/min, 1.5 m/min, 1.55 m/min, 1.6 m/min.

In one embodiment, the relative speed v is lower than or equal to a maximum speed v _max , selected from the group comprising approximately or exactly the following values: 5 m/min, 3.8 m/min, 3 m/min, 2.7 m/min, 2.5 m/min, 2.2 m/min, 2 m/min, 1.8 m/min, 1.7 m/min, 1.6 m/min, 1.55 m/min, 1.5 m/min, 1.45 m/min, 1.4 m/min.

For instance, the relative speed v may range from 1 m/min to 2.5 m/min, preferably from 1.2 m/min to 2 m/min, and be for instance about 1.5 m/min.

The above relative speed values v may be intended as average values or maximum values of the speed modulus, if the lateral speed periodically changes with time.

The speed V of the longitudinal movement may be higher than or equal to a minimum value V _min and or lower than or equal to a maximum value V _max :

V _min may be selected from the group comprising exactly or approximately the following values: 0.5 m/min, 0.7 m/min, 1 m/min, 1.1 m/min, 1.2 m/min, 1.3 m/min, 1.4 m/min, 1.45 m/min, 1.5 m/min, 1.55 m/min, 1.6 m/min.

V _max may be selected from the group comprising exactly or approximately the following values: 5 m/min, 3.8 m/min, 3 m/min, 2.7 m/min, 2.5 m/min, 2.2 m/min, 2 m/min, 1.8 m/min, 1.7 m/min, 1.6 m/min, 1.55 m/min, 1.5 m/min, 1.45 m/min, 1.4 m/min.

The lateral speed may be higher than the longitudinal movement speed V.

The distance d between the nozzle and the rubber to be devulcanized may e higher than or equal to a value d _m in and/or lower than or equal to a value dmax-

The distance d is the distance between the ideal profile of the material to be devulcanized and the water jet head nozzle. By way of indication, the distance d may be approximated to the distance between the plane of the nozzle parallel to the reference plane and the average plane, still parallel to the reference plane, of the upper surface of the rubber to be treated, or the plane substantially tangent thereto, on the side facing toward the nozzles.

For instance, the undeformed condition of the rubber to be treated may be considered, i.e. it will be possible to disregard the deformations induced by water jet treatment, which increase in practice the actual distance d.

The distance d _m i _n may be selected from the group comprising exactly or approximately the following values: 1 mm, 2 mm, 3 mm, 4 mm, 4.5 mm, 5 mm, 5.5 mm, 6 mm, 7 mm, 10 mm, 15 mm.

The distance d _max may be selected from the group comprising exactly or approximately the following values: 15 mm, 18 mm, 20 mm, 22 mm, 24 mm, 25 mm, 26 mm, 28 mm, 30 mm, 35 mm, 40 mm, 50 mm.

The distance d may range from 2 mm to 45 mm, preferably from 4 mm to 30 mm, e.g. from 5 mm to 25 mm.

The temperature T^ of water used for water jet treatment may be lower than or equal to, e.g. always lower than or equal to a maximum temperature T^ _ma x selected from the group comprising exactly or approximately the following values: 95°C, 85°C, 75°C, 65°C, 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C. For example, ambient temperature water may be used.

The water used for water jet treatment may advantageously include chemical additives, such as petroleum-derived solvents (such as toluene), thiol-amine reagents, hydroxides, disulfide or chlorinated hydrocarbons. More effectively, it can be simply drinking water, possibly filtered as required for water jet pumps.

Then, the rubber granules yielded from water jet treatment are freed from residual water and may later be sorted into the different particle size classes.

Granules may be dried while being maintained at a temperature T ^a lower than or equal to, preferably always lower than or equal to a maximum temperature T ^a _max , selected from the group comprising approximately or exactly the following values: 110°C, 100°C, 95°C, 85°C, 75°C, 65°C, 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C.

Drying is obtained by exposing granules to a preferably dry air airflow, for the time required to change the water content x ^H2 ° to a value lower than or equal to a maximum value x ^H2 °max selected from the group comprising exactly or approximately the following values: 10%, 7%, 6%, 5%, 4%, 3%, 2.5%, 2%, 1.5%, 1.2%, 1%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%.

Experimentally, it has been found that the water content x ^H2 ° may be higher than or equal to a minimum value x ^H2 ° _m in selected from the group comprising exactly or approximately the following values: 0.001%, 0.01 %, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% 0.8%, 0.9%.

The above described water jet treatment may yield the result of a particularly advantageous particle size distribution in the treated rubber.

Particle size distribution might have two distinct peaks, for instance one above and one below the limit value L.

These two distinct peaks may appear, for instance, from at least one cumulative particle size curve having an irregular profile, i.e. with an additional concavity/convexity (or flex point) with respect to a cumulative curve like that related to normal distribution.

Considering two particle size classes, percent devulcanization may be higher for the finer particle size class. Assume for instance a first particle size class A1 and a second particle size class A2, where A1 is finer than A2. For instance, A1 may be finer than any one of the above mentioned values and A2 may be higher than any one of the above mentioned values. For instance, the value selected for A1 may be equal to the value selected for A2. For instance, this value may be 4.2 mm.

For instance, granules having a particle size below 4.2 mm may have a devulcanization above 30%, 35%, 40%, 45%, 50%, 52%, 53% or 54%. For instance, granules having a particle size below 4.2 mm may have a devulcanization below 95%, 85%, 80%, 75%, 70%, 65%, 63%, 60%, 58% or 56%.

For instance, granules having a particle size above 4.2 mm may have a devulcanization above 10%, 15%, 20%, 23%, 25%, 26%, 27% or 28%.

For instance, granules having a particle size above 4.2 mm may have a devulcanization below 95%, 85%, 75%, 65%, 55%, 45%, 40%, 35%, 33%, 31% or 29%.

Those skilled in the art will clearly appreciate that a number of changes and variants may be made to the arrangements as described hereinbefore to meet incidental and specific needs.

Particularly, should a metric size be mentioned in a claim, the scope of the invention shall be intended to extend to equivalents, at least to the closest standard size in the British system, and vice versa, as already stated in the beginning of the present description.

All of these variants and changes fall within scope of the invention, as defined in the following claims.