JPS6111970B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD This invention relates to rubber, and in particular to the reuse of such rubber, including blends of two or more of vulcanized natural rubber and synthetic rubber. The reuse of vulcanized rubber in fine form is well known in the rubber industry. Such materials (known as "crumbs") are usually passed through a two-roll mill to obtain a particle size such that they typically pass through a 40-mesh sieve (i.e., less than 388 microns in diameter). I have it too. It is also well known that when this powder is added to an unvulcanized rubber composition, the tensile properties and other important properties of the rubber obtained by vulcanizing the composition are impaired by a substantial amount. According to the invention, the fine vulcanized natural rubber or rubber reused in the rubber composition is in the form of aggregates of particles, the aggregates are between 10 and 200 microns in size, and the rubber By dispersing it in the composition, it can be separated into particles generally between 2 and 20 microns in size. Preferably at least 90% by weight of the aggregates or particles have a size within the respective ranges described above.
Preferably most of the aggregates have a size of 50-100 microns. Fine vulcanized rubbers include natural rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, polychloroprene, silicone rubber, fluorinated silicone rubber, fluorinated hydrocarbon rubber, chlorosulfonated polyethylene rubber, isobutene-isoprene rubber, and ethylene-propylene. It can be a copolymer or terpolymer or a polyurethane. The invention is particularly advantageous for the reuse of expensive rubber as well as large quantities of vulcanized rubber such as scrap tires. The present invention includes rubber compositions containing finely divided vulcanized rubber, generally having a particle size of 2 to 20 microns.
The composition can contain finely divided vulcanized rubber as the main rubber component or in admixture with unvulcanized rubber. Rubber vulcanizates made from compositions containing finely divided vulcanized rubber as the main rubber component have a tensile strength greater than 9 MN/m ² and a tear strength greater than 55 N/Std. Rubber vulcanizates containing 10-70% by weight of fine vulcanizate have a tensile strength of 23-15 MN/ ^m2 . According to the invention, the vulcanized rubber can be converted into a finely divided vulcanized rubber by a process consisting of grinding it with excess water in a colloid mill of the grinding disc type. According to this method, a fine vulcanized rubber with an effective particle size of 2 to 20 microns is obtained for the purpose of dispersion in a rubber composition, but the fine vulcanized rubber product itself is capable of dispersing these particles in the aforementioned range of sizes. Contained as aggregates. The vulcanized rubber used in the process of the invention is generally insoluble in common rubber solvents such as benzene, chloroform and n-hexane and remains intact when milled. Preferably, the weight ratio of water to vulcanizate in the mill is from 2:1 to 30:1, especially at least 3:1. Vulcanized rubber, eg rubber powder, can be reduced to the required particle size in a colloid mill with a rotor and stator of eg carborundum disks. Preferably, the rotor is housed in a bearing, for example a rubber bearing or a metal spherical bearing, which allows it to rotate under compression. A particularly suitable form of colloid mill is one in which the rubber is fed under pressure to the attritor by a Mono-type pump. The colloid mill milling step is carried out with excess water to reduce the vulcanized rubber to the required particle size.
When using such a mill to grind solid materials it is normal to use just enough water to lubricate the grinder, but when grinding rubber powder this It has been found that an important feature of the process is the preference for using an excess of water. Additionally, it has been found that this water can be removed in a centrifugal dryer and recycled, thereby conserving the entire amount of water needed and reducing drainage problems. Furthermore, using this excess amount of water eliminates the need to use a "dispersing aid." The dispersing aids are inorganic minerals such as various clays that are not easily separated from the rubber powder and have an adverse effect on the physical properties of vulcanizates made from the powder. The use of an excess amount of water in relation to the amount of vulcanized rubber is particularly desirable in the early stages of the milling process. Therefore, the excess amount of water can vary during the milling process;
The maximum excess amount is used in the initial stages of milling. Alternatively, the excess amount can be kept constant during milling. Another highly desirable feature of the present invention to achieve optimal milling is to gradually increase the particle size of the rotor and/or stator during milling. The slurry of vulcanized rubber and water is thus passed continuously through the mill. The water to rubber ratio and/or rotor and/or stator particle size decrease after each successive pass. Advantageously, the rotor and/or rotor particle size is varied by using two or more mills. The slurry of vulcanized rubber and water is therefore passed through a series of multiple attrition disc mills.
The particle size of the rotor and/or rotator decreases with each successive mill. Milling of the vulcanized rubber according to the invention provides a finely divided rubber powder with a highly convoluted surface and thus a high surface area to volume ratio. The higher this ratio, the better the toughening properties of the finely divided rubber powder in the rubber composition, or the lower the amount of finely divided powder required for a given toughening. An important part of the rubber milling process is to keep the temperature of the rubber as low as possible. At temperatures above 100°C, natural rubber molecules decompose, producing inferior materials with lower molecular weights. In the case of synthetic rubbers, the reaction is more complex, in some cases producing substances of low molecular weight, and in other cases after the initial splitting, additional cross-linking occurs to produce substances of very high molecular weight.
In either case the product is inferior to the original material. The invention encompasses a method of making a rubber article comprising incorporating finely divided vulcanized rubber according to the invention into a rubber composition prior to vulcanization and then vulcanizing the composition. The finely divided vulcanizate can be the main rubber component of the composition, but is preferably in the form of a mixture with pre-vulcanized rubber. The rubber composition therefore consists of at least 10 parts by weight, preferably from 40 to 90 parts by weight, of finely divided vulcanized rubber per 100 parts by weight of unvulcanized rubber, such as styrene-butadiene rubber. Recycled rubber or "reclaim" is sometimes used to replace some amount of new rubber in a formulation. It forms as a result of the effect of high temperatures (above 150°C) on the vulcanizate, giving it properties significantly inferior to the original vulcanizate. Commercial recycled rubber, such as fully recycled rubber, is produced in bulk and is less likely to be produced as a powder. This is another drawback of this existing recycled rubber, as there is a current trend towards using powdered rubber and powdered ingredients for automatic metering and processing. The invention is further illustrated by the following examples. Unless otherwise specified, the rubber powders in the examples were obtained from tread buffing. However, it is contemplated that defibrinated whole tire powder containing a small amount of fiber can be used as the starting material for the process of the present invention. In the examples, the fine vulcanized rubber of the present invention is referred to as fine powder. "Premier" in the example
The colloid mill is located in Walton-on-Thurley, England.
It was produced by Premier Colloid Mills Limited, Hashyam Trading Estate, Thomas. EXAMPLE Approximately 15 g of water is fed into the hopper of a "Premier 84" colloid mill sized with an attritor diameter of 3.5 inches (particle size 46). The mill is placed in its tightest clamp setting (-3) and the motor driving the rotor is turned. Therefore,
The attritor rotates under the maximum compression that can be achieved with this mill. The swirl appears directly in the hopper and scatters 40 mesh of vulcanized rubber powder onto the surface of the water at such a rate that 1 kg is fed into the hopper at intervals of 20 to 30 minutes, and at the same time fills the hopper with water. Fulfill. When all the powder has been fed into the hopper, gradually reduce the water level until all the water has passed by one hour after the start of the experiment. During this milling, the powder must not be fed in too quickly. If you feed too quickly, the rotation of the attritor will be uneven, causing a harsh sound.
The mill heats up and coarse particles appear in the effluent. In total, about 30% of the total powder remains after this step;
It must then be discarded as it is unsuitable for further processing by this method. The effluent from this mill is fed directly to a centrifugal dryer containing filter bags. The best material for this bag is a weft of 750 denier;
It was found to be a polyester fabric with a warp of 42 threads per inch, a weight of 11.5 ounces per square yard, and a scarred "M" finish. Suitable materials can be obtained from Richard Hywood & Company Limited, Clewekerne, Somerset, England.
Haywood γ Co. Ltd.). This separates the powder and water and then recirculates the water to the colloid mill. The finely divided rubber powder collected in the bag is passed through the colloid mill again under the same conditions as described above, except that the entire batch can be run through the colloid mill in 20-25 minutes. To compare this fine powder with 40 mesh of powder and whole tire recycled rubber, 83 parts by weight of each of the three materials were mixed with 100 parts of styrene-butadiene rubber (Grade 1500), 3 parts of zinc oxide. , 3 parts stearic acid, 1 part Flectol H, 43 parts HAF Black, 10 parts Dutrex R softener, 0.9 parts cyclohexylbenzthiazylsulfenamide,
Mixed with 0.8 parts diphenylguanidine and 1.75 parts sulfur. A slab of 150 x 150 x 2 mm was press-molded and vulcanized at 150°C for 15 minutes. Similar slabs of this base formulation (ie, without recycled rubber) were also prepared. When tested according to standard methods, the following results were obtained.

[Table] Kuru)
The rubber compound in column (1) did not contain any of the three rubber additives. The rubber formulations in columns (2) and (3) each contained 40 mesh of powder and recycled material, while the rubber formulations in column (4) contained fine particles made according to the invention as described in Example 1. Contains powdered powder. The tensile strength and abrasion resistance of vulcanizate (4) are close to those of (1) and superior to those of vulcanizates (2) and (3). The modulus values indicate that vulcanizate (4) is also harder than vulcanizate (1). EXAMPLE The hopper of a "Premier 200" colloid mill with a rotor and stator having a particle size of 46 and a diameter of 200 mm was filled with 30 g of water. I adjusted the mill to its tightest setting and started the motor. Immediately after, a swirl appeared in the hopper, and 40 mesh of vulcanized rubber powder was sprinkled onto the surface of the water at such a rate that 8 kg was fed into the hopper at intervals of 20 to 30 minutes, and at the same time water was poured into the hopper. Filled. Add at a rate of 4-5 Kg of powder per hour for about 4-5 hours, by which time the production of finely divided powder is greatly reduced. During this milling, the powder must not be fed too quickly. This is because if it is done too quickly, the attritor rotates unevenly, creating a harsh sound, generating heat in the mill, and causing coarse particles to appear in the effluent. After this milling, approximately 30% of the total powder remains in the hopper, which is unsuitable for further processing in this manner and must be discarded. The effluent from this mill is fed directly into a centrifugal dryer containing a filter bag as described in Example 1 to separate the rubber and water. This water can then be recycled to the colloid mill. To compare this product with 40 meshes of whole tire powder and recycled material, formulations were prepared as in the examples with similar results. EXAMPLE No hopper is required in this method. 40
A premixed slurry of mesh vulcanized rubber powder and water is fed directly onto an attritor set to rotate at maximum compression. In the initial pass, the stator preferably has a grain size of 46, while the rotor preferably has a larger grain size, i.e. 24
and can pass through relatively large particles of powder. In subsequent passes, the rotor particle size can be gradually reduced until the entire product is of the required fineness (ie, when all of the material passes through the grain size 46 attritor). As the rotor grain size decreases,
The slurry flow rate also decreases accordingly. The rubber to water concentration in the feed slurry can be increased with successive passes through finer rotors, examples of which are shown in the table below.

Table: To compare this micronized powder product with 40 mesh powder and recycled material, formulations were prepared as in the examples and similar results were obtained. EXAMPLES The potential utility of the fine powders produced as in the examples is best illustrated with respect to two typical commercial applications. Historically, only small amounts of ordinary (40 mesh) powdered rubber have been used in tire tread formulations, and certainly very small amounts of ordinary recycled rubber have been used, if at all. The two formulations listed in the table (labeled Z60 and Z90) contain 25% and 33% finely divided powder, respectively, and the properties in all aspects are within the range of laboratory specifications for passenger car tire treads. It is clear that there are many The data on flexural crack initiation and growth are particularly good. The formulations were used in retread tires and these tires were compared with commercially available tires in short-term, vigorous track tests. After 1500 miles, the following percentage loss of treaded rubber was recorded: Test tire retreaded with a formulation containing 60 parts of finely divided powder...9%, Test tire retreaded with a formulation containing 90 parts of finely divided powder...9%, Commercial retreaded tire ...13%, commercially available front-line tires...8%. All of these tires are of cross-ply construction, but the potential utility is in no way limited to this type of tire, and satisfactory results will be obtained regardless of the construction of the tire.

【table】

Table: Examples The excellent dynamic properties of formulations containing finely divided powders prepared as in the examples can be exploited in rubber fitting applications.
The dynamic modulus and loss factor for a series of formulations (table) containing up to 60 parts of micronized powder are listed in the table.

【table】

【table】

EXAMPLE This example relates to the application of the present invention to an expensive synthetic rubber such as Viton, a copolymer of vinylidene fluoride and hexafluoropropylene manufactured by DuPont. A standard Viiton formulation is prepared to the specifications in the table. This is then cured at 163°C for 30 minutes and post-cured at 250°C for 24 hours. The cured meat is cut into pieces approximately 0.5 inch in size and then soaked in liquid nitrogen to embrittle the material before grinding in a knife mill. The material is ground sufficiently to pass through a 0.05 cm sieve, and the material is then dried.
Colloid mill sieved through a 40 mesh sieve, leaving parts larger than 40 mesh for further grinding, while material smaller than 40 mesh was set at maximum compression setting with water as carrier medium. twice, and the product is filtered and dried in the conventional manner. Four mixtures containing the resulting finely divided powders were prepared. The mixture is a control mixture that does not contain recycled Viaton product. Formulations V2, V3 and V4
were prepared by incorporating 20, 40 and 60 Phr (parts per 100 parts by weight) of fine powder into the original formulation, respectively, on a two roll mill. Formulation V5 contained 20 Phr of micronized powder and other curing agents equal to an additional 10 Phr of rubber hydrocarbon in the formulation. Cure all mixtures at 163°C for 30 minutes, then 250°C
It was cured after 24 hours. Typical properties of vulcanizates are shown in the table.

[Table] The presence of finely divided Viaton powder in the formulation increases the modulus of the vulcanizate and decreases the tensile strength, while the compressive strain of samples V2, V3 and V4 increases due to the presence of recirculated Viaton powder in the formulation. It gradually increases as the amount added increases. By increasing the level of hardener (sample V5), an improvement in tensile strength and compressive strain was observed, indicating that when using fine powder in the Viaton mixture, the amount of hardener with respect to the amount of fine Viaton powder added This suggests that it would be advantageous to adjust the Certain of the rubber compounding components mentioned above are shown in more detail below. Vulcan 3H Carbon Black (HAF) Philblack Carbon Black (ISAF) Dutrex R Carbon Black Aromatic oil Santoflex13 (Ozone anti-ozone agent) N-Phenyl-N'-(1,3-dimethyl)-P-phelenediamine Flectol H ( Antioxidant) Poly-1・2-dihydro-2・
2,4-trimethyl quinoline Nonox ZA (anti-ozone agent) 4-isopropyldiphenylamine CBS (accelerator) N-cyclohexylbenzthiazylsulfenamide DPG (accelerator) Diphenylguanidine SBR Styrene Butadiene Rubber The drawings of the present invention are attached. will be further explained. The colloid mill shown in FIG. 1 consists essentially of two horizontal grinding wheels or stones, an upper wheel A and a lower rotor B. Wheel A
is fixed to top plate C, which is adjusted by screw D to reduce the size of nip E. Tire buffing or whole tire powder, i.e. 40 meshes of rubber powder, which is the defibrinated product from whole tires, is fed with water to a hopper F and drops through a safety grid G into the throat of the mill where the rotor and Due to the centrifugal force generated by the spinner H, the rubber is thrown into the grinding zone between the two attritors and then discharged via the chute H. The rotor B is equipped with a V-belt drive means J. The method illustrated in the flowchart of FIG. 2 is suitable for commercial operation of the invention and can be carried out as follows. A premixed slurry of 40 meshes of vulcanized rubber powder and water at a concentration of 1:7.5 prepared in a small (75 mm) colloid mill was prepared in a large (75 mm) colloid mill with an attritor set to rotate at maximum compression. 200mm) directly into the colloid mill. Stator is grain size
46 carborundum, while the rotor has a grain size of
24 to allow passage of larger particles of powder.
The product comprises a rotor with a grain size of 36 and a stator with a grain size of 46. Sent to similar mills. This product has a particle size
It is sent to a third mill with 46 attritors, then passed over a screen with filter cloth, and the surface water is removed by a centrifugal dryer with filter bags. Final drying is carried out in an oven or in a fluidized bed at 40°C. The water separated in the filter cloth and filter head can be mixed with 40 mesh of powder and recirculated. The product is a fine, free-flowing powder that can be blended alone or with new rubber. Typical formulations and properties are listed in the table. For comparison, ordinary whole tire retread material (WTR)
Or data for formulations containing 40 mesh of powdered feed stock (WTR) are also included.

Table: In commercial operations of this invention, a number of factors must be carefully balanced because excessive heat will soften the rubber and produce small rolls of elastic material rather than true grinding. Must be. Examples of these factors are: (a) the size, type and particle size of the attritor and the feed design; (b) the distance the attritor is separated from each other; (C) the speed of the rotor;
(d) the dilution of the 40 mesh powder, (e) the feed rate of the powder and water slurry, (f) the pressure applied on top of the water to force the slurry through the mill, and (g) the formation of the slurry. and the presence or absence of a wetting agent to facilitate its passage through the mill. As previously mentioned, all materials were considered to pass through each colloid mill sequentially. This is more of a manipulation method than an efficiency one, but there are other methods.
By suitable pipe arrangement, only the finer particles from the first mill pass through the second and third mills, the remainder being recycled in series to the previous mill. Sometimes production is stopped periodically and the mill is briefly flushed with clean water. These mills can also be operated in parallel rather than in series. The particle size of the micronized powder of the present invention is determined by sieving or Coulter Counter.
Counter). FIG. 3 shows a graph produced by a Coulter counter giving the percentage distribution of various particle sizes of the micronized powder. It can be seen that the total particle size ranges from 10 to 200 microns, but most of the particles are present in the 50 to 100 micron range. however,
When such particles are added to light colored crepe rubber and the vulcanizate is examined under an optical microscope, the particle size is clearly much smaller than this, generally in the range of 2 to 20 microns. This is shown in Figure 6, which is at 200x magnification. In contrast, when 40 mesh of powder is subjected to the same milling operation with crepe rubber, vulcanized, and microscopically examined, the particle size present in the rubber is
As shown, the powder is substantially unchanged from the original 40 mesh powder shown in FIG. FIGS. 4 and 5 have the same magnification as FIG. 6. It is therefore clear that the particles represented in FIG. It can be concluded that agglomeration of these particles occurs during the drying process, giving the impression that the product is coarse. This fineness of the particles of the micronized powder produced by the method of the present invention allows the incorporation of large amounts of the micronized powder into the rubber formulation without significantly adversely affecting the properties. In fact, this finely divided powder has a reinforcing effect on the rubber. This is demonstrated by the fact that 120 parts of micronized powder can be incorporated into the pure gum SBR formulation (Table). SBR vulcanizates without finely divided powders are extremely soft and have low tensile and elongation values. Including just 20 parts of micronized powder increases tensile and tear strength by 50% and also increases elongation values. As the level of finely divided powder increases, the tensile strength and tear strength are further enhanced,
The modulus and hardness values are also improved by the addition of finely divided powders.

[Table] Embodiments of the present invention are as follows. 1 in the form of aggregates of particles, which aggregates are generally
A fine vulcanized rubber characterized by having a size of 10 to 200 microns and being dispersed in the rubber composition and separable into particles generally having a size of 2 to 20 microns. 2. The fine vulcanized rubber of 1 above, wherein the aggregates are generally 50 to 100 microns in size. 3. The fine vulcanized rubber of 1 above, in which at least 90% by weight of the aggregates or particles have a size within the specified range. 4 The rubber is natural rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, polychloroprene, silicone rubber, fluorinated silicone rubber, fluorinated hydrocarbon rubber, chlorosulfonated polyethylene rubber, isobutene-isoprene rubber, ethylene-propylene copolymer, or The above 1 which is a terpolymer or polyurethane
The fine vulcanized rubber of any of ~3. 5 Rubber compositions containing fine vulcanized rubber, generally with a particle size of 2 to 20 microns, as the main rubber component. 6 It has the composition listed in 5 above and has a tensile strength of 9MN/m ²
Rubber vulcanizate which is larger. 7. The rubber vulcanizate described in 6 above, which has a tear strength of greater than 55 N/Std. 8. A rubber composition consisting of a mixture of finely divided vulcanized rubber and unvulcanized rubber, generally having a particle size of 2 to 20 microns. 9. A rubber vulcanizate containing 10-70% by weight of fine vulcanizate, typically with a particle size of 2-20 microns and a tensile strength of 23-15 MN/ ^m2 . 10 Fine vulcanization of hot-flow rubber characterized by grinding the vulcanized rubber together with excess water in a grinding disc type colloid mill to obtain the fine rubber according to any one of 1 to 4 above. How to convert it into rubber. 11 The method of 10 above, wherein the weight ratio of water to vulcanized rubber is 2:1 to 30:1. 12 The method of 11 above, wherein the ratio is at least 3:1. 13. The method according to any of 10 to 12 above, wherein the rotor and stator of the colloid mill are grinding disks. 14. Any of the methods 10 to 13 above, in which the rotor of the colloid mill is rotating under compression. 15. The method of any of 10 to 13 above, wherein water and rubber are removed from the colloid mill, and the water is separated from the rubber by centrifugal action and recycled. 16 Any method from 10 to 15 above in which the temperature of the rubber does not exceed 100°C. 17. The method of any of 10 to 16 above, wherein the excess amount of water is varied during the milling and the greatest excess amount is used in the first stage of the milling. 18. The method of any of the above 10 to 17, wherein the particle size of the rotor and/or stator is gradually reduced during the milling process. 19. The method of 17 or 18 above, wherein the slurry of vulcanized rubber and water is passed through a colloid mill in a series of passes, and the water to rubber ratio or rotor and/or stator particle size is reduced after each successive pass. 20. The method of any of 10 to 18 above, wherein the slurry of vulcanized rubber and water is passed sequentially through a plurality of attrition disk mills, and the particle size of the rotor and/or stator is successively reduced from mill to mill. 21 A rubber article comprising the steps of incorporating fine vulcanized rubber produced by any of the methods 10 to 20 above into a rubber composition before vulcanization, and then vulcanizing this composition. Manufacturing method. 22 The method of 21 above, wherein fine vulcanized rubber is the main rubber component of the composition. 23 The method of 21 above, in which fine vulcanized rubber is mixed with unvulcanized rubber before vulcanization. 24. The method of 23 above, wherein at least 10 parts by weight of fine vulcanized rubber is contained per 100 parts by weight of unvulcanized rubber. 25 The method of 23 above, in which 40 to 90 parts by weight of fine vulcanized rubber is contained per 100 parts by weight of unvulcanized rubber. 26 The above 23--wherein the unvulcanized rubber is styrene-butadiene rubber, natural rubber, or a blend thereof.
25 ways. 27 Fine vulcanized rubber made by methods 10 to 20 above. 28 Rubber articles made by the methods 21 to 26 above.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a colloid mill used in the method of the present invention. FIG. 2 is a flow diagram illustrating the method of the present invention. FIG. 3 is a diagram of a Coulter counter for the finely divided powder of the present invention. Fourth
The figure is a micrograph of 40 mesh rubber powder.
Figure 5 is a micrograph of 40 meshes of rubber powder dispersed in the composition. FIG. 6 is a microscopic photograph of the finely divided powder of the present invention dispersed in a rubber composition.

Claims (1)

[Claims] 1 In a grinding disc-type colloid mill with disc elements rotating under compression, the weight ratio of water to vulcanized rubber in the slurry is about 2:1 to 30:1.
The vulcanized rubber is supplied as an aqueous slurry such that at least 90% by weight of the aggregates are generally between 10 and 200 microns in size, and in the rubber composition at least 90% by weight is by dispersion. 1. A process for converting vulcanizate into finely divided vulcanizate, which is characterized by obtaining a finely divided vulcanizate in the form of agglomerates of particles, which can generally be separated into particles with a size of 2 to 20 microns.