GB1593820A

GB1593820A - Dustless free flowing rubber additives

Info

Publication number: GB1593820A
Application number: GB2137078A
Authority: GB
Original assignee: Goodyear Tire and Rubber Co
Current assignee: Goodyear Tire and Rubber Co
Priority date: 1978-05-23
Filing date: 1978-05-23
Publication date: 1981-07-22
Also published as: DE2822459C2; DE2822459A1

Description

(54) DUSTLESS FREE FLOWING RUBBER ADDITIVES (71) We, THE GOODYEAR TIRE & RUBBER COMPANY, a corporation organised under the laws of the State of Ohio, United States of America, of 1144 East Market Street, Akron, Ohio, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process of agglomerating normally dusty, finely divided materials with rubber latex or partially prevulcanized rubber latex and thereby improving dispersibility of such agglomerates used as compounding ingredients in rubber compositions.More specifically, this invention relates to a method for preparing a mixture of finely divided particles comprising a rubber latex and a finely divided material to obtain the free-flowing agglomerate.

The use of finely divided materials in compounding of both natural and synthetic rubber presents certain problems to the rubber goods manufacturers. The finely divided nature of these materials causes them to be blown into the air during production operations such as milling or other mixing. This results in an increase in the cost of production and in the possible contamination of other materials.

In addition, the nature of some finely divided compounding ingredients makes uniform dispersion in rubber difficult since finely divided materials, particularly powders, tend to form lumps or cakes which may stick or cake on the mill roll or remain undispersed in internal mixers such as Banburys thus increasing the time, effort and expense required to form an intimate dispersion in the rubber. Such lumping and caking makes the use of automatic weighing and mixing equipments unfeasible.

Efforts have been made to reduce the objectionable features of finely divided materials by converting such finely divided materials into agglomerates. The prior art discloses that in order to form such agglomerates, an agglomerating agent must be added to the finely divided material for the agglomerate to remain stable. Frequently this agglomerating agent has been a material which was objectionable when mixed into a rubber compound with which the finely divided material was used. Also, some of the prior art agglomerates were cohesive and thus not free flowing. Such compositions do not lend themselves to either normal handling and weighing procedures or automatic handling and weighing procedures.

Some agents previously employed for preparing agglomerates were used in such large amounts that the rubber ingredient was excessively diluted. Such diluted ingredients can form agglomerates which do not disperse readily in rubber during mixing operations or are not sufficiently stable to be transported from the manufacturer to the user.

The prior art teaches that when manufacturing agglomerates from a finely divided material which may be in a damp filter cake form, said finely divided material is reduced to a paste, forced through an extruder into rod or L shaped form, dried, and then ground or chopped to the desired size. Such products tend to become finely divided again during shipping due to settling that occurs when containers of these materials are handled.

It is an object of this invention to provide a method for converting finely divided materials to an agglomerate of such a nature that individual agglomerates do not break down but remain an agglomerate during normal warehousing and weighing operations, yet disperse uniformly into rubber during mixing operations. Another object of this invention is to make an agglomerate of finely divided material and rubber latex which lends itself to use in automated weighing and mixing equipment. Other objects will become apparent to those skilled in this art as the description proceeds.

The finely divided materials to which this invention relates are materials as hereinafter specified which are in or susceptible to being made into finely divided state whereby they may be agglomerates with latices of rubber.

The process of this invention comprises (1) forming a damp mass or cake of at least one finely divided material selected from the group hereinafter specified, said damp mass or cake having a dry solids content of from 6() percent to 95 percent by weight of the total weight of the cake, (2) placing said damp mass or cake into a gas suspension apparatus which divides and crumbles the damp mass or cake into small particles while suspending said particles in a gaseous medium and (3) slowly adding to the gaseous suspension an amount of a finely divided spray of a rubber latex having a solids content of from 9 percent to 7() percent by weight of total weight of the latex to provide from 1 to 30 parts dried rubber for l()() parts of dry finely divided material and (4) mixing the particles of latex and particles of damp mass or cake while both are suspended in said gaseous medium for a time sufficient to allow the particles of latex spray to collide with the small particles of the damp finely divided material and form composite particles or agglomerates comprising rubber and said small particles of damp finely divided material said composite particles having an average diameter of from ().()()3 inch to ().l() inch, and (5) drying said composite particles at a temperature and time sufficient to drive off excess moisture and to provide a dustless, free flowing agglomerite of rubber and the initially finely divided material.

For some materials it is necessary to discharge the composite particles into a screening apparatus which free screens out the smaller of the composite particles and then force screens the balance of the composite particles to the desired agglomerate size before drying.

Representative examples of rubber latices useful in the practice of this invention are latices of normally rubbery polymers such as: polybutadiene latex, the latices of rubbery copolymers of butadiene and styrene, the latices of rubbery copolymers of butadiene and acrylonitrile the laíices of polychloroprenes, the latices of rubbery copolymers of isobutylene and isoprene, and natural rubber latex. The latices of the rubbery copolymers of butadiene and styrene and the latices of rubbery copolymers of butadiene and acrylonitrile are preferred for most finely divided materials.

As already indicated, a sufficient amount of rubber latex is used to provide from 1 to 30 parts (dry weight) of rubber per l()() parts of dry finely divided material. Preferably an amount is used to provide from I to l() parts of rubber (dry weight) to 100 parts of dry finely divided material. Some of these finely divided materials require only an amount to provide from 1 to 2 parts of rubber (dry weight) to l()() parts of dry finely divided materials.

The finely divided materials of the group hereinafter specified which are most easily agglomerated by the process of this invention are those produced and finished in an aqueous medium. Other finely divided materials of the group hereinafter specified can also be treated using the process of this invention but require first to be moistened with water to the desired level; they thus require additional handling. Some materials of the group hereinafter specified can also be reduced to a finely divided state, dampened, and then agglomerated using the process of this invention in order to improve dispersibility in rubber compounds. The damp finely divided material must be high enough in total solids content to crumble easly when placed inside a gas suspension apparatus and low enough in total solids content to remain dustless.

The group of finely divided materials which can be used in the process of this invention comprises 2-mercapto-benzothiazole, 2,2'-dithiobis(benzothiazole), 2 (morpholinodithio)benzothiazole, zinc 2-benzothiazolyl mercaptide, copper 2benzothioazolyl mercaptide zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, copper (ill) dimetyldithiocarbamate, copper (ill) diethyldithiocarbamate, cadmium diethyldithiocarbamate, lead diethyldithiocarbamate, tetramethylthiuram disulfide, tetramethylthiuram monosulfide, tetraethylthiuram disulfide, mixtures of tetraethylthiuram disulfide and tetramethylthiuram disulfide, N-cyclohexyl-2benzothioazolesulfenamide, N-t-butyl-2-benzothiazolesulfenamide, N-(3 methylcyclopentamethylene)-2-benzothiazolesulfenamde, 2-(N-hexamethyleneiminothio)benzothiazole, morpholine disulfide, mixtures of 2-mercaptobenzothiazole and tetramethylthiuram disulfide 4-morpholino-2-benzothiazyl disulfide asbestos. sulfur.

monoastral blue, phthalo green and pyrazolone red.

The following are examples of useful specific procedures falling within the scope of the present invention: (a) A process according to the invention wherein the finely divided material is 2-(morpholinodithio)benzothiazole, the rubber latex is a latex of rubbery copolymers of butadiene and sytrene having a total solids content from 10 to 50 percent. and the agglomerates formed have a total dry rubber content from 1.00 to 10.00 parts by weight pet hundred parts of dry 2-(morpholinothio)benzothiazole.

(b) A process according to the invention wherein the finely divided material is 4-morpholino-2-benzothiazyl disulfide, the rubber latex is a latex of rubbery copolymers of butadiene and styrene having a total solids content of from 25 to 45 percent, and the agglomerates formed have a total dry rubber content of from 1.00 to 2.00 parts per hundred parts of dry 4-morpholino-2-benzothiazyl disulfide.

(c) A process according to the invention wherein the finely divided material is asbestos, the rubber latex is a copolymer of butadiene and acrylonitrile having a total solids conent of from 10 to 30 percent, and the agglomerate formed has a total dry rubber content of from 1.00 to 10 parts per hundred parts of dry asbestos.

(d) A process according to the invention wherein the finely divided material is asbestos, the rubber latex is a copolymer of butadiene and styrene having a total solids content of from 25 to 45 percent, and the agglomerate formed has a total dry rubber content of from 1.00 to 10 parts per hundred parts of dry asbestos.

It is advisable that natural rubber latex should be used to agglomerate only those finely divided materials containing no metals such as copper, iron and manganese which are normally deleterious to natural rubber.

The equipment used for mixing the finely divided latex spray droplets and the damp finely divided material is a kind that will suspend the damp finely divided material in a gaseous medium such as air and in which the latex can be injected into the interior of the apparatus in a finely divided spray at a slow rate and mixed with the damp finely divided material. The time of mixing should be sufficient for the latex spray and the particles of damp finely divided material to collide and form composite particles having an average diameter ranging from 0.003 inch to 0.10 inch. The amount of latex used and the time of the actual mixing can be varied.

Free screening can be accomplished by moving the damp free-flowing agglomerate across a vibrating sieve. The sieve used for free screening is usually flat or a rotating drum moving at a slight angle from the horizontal. Various methods of free screening are known in the art and can be used with the materials of this invention.

In force screening the unscreened material is placed on a rotating sieve of the desired screen opening size and forced against a roller rotating in the opposite direction from the sieve's rotation. The roller is adjusted near the surface of the sieve, normally at a distance less than the diameter of the sieve opening to force the particles through the openings of the sieve. The roller used is normally large enough in diameter to contain the rolling unscreened material on one side. Various methods of force screening are known in the art and can be used with the materials of this invention.

The time and temperature of drying can be varied over a wide range. Usually the slighly damp agglomerated particles are tumble dried between 1500 F. and 1600 F. for a time ranging from 2 to 4 hours. Pan drying of the agglomerated particles can be used if desired and can be carried out in an oven for 30 to 60 minutes at a temperature of from 1500 F. to 1600 F. The time needed is dependent upon the thickness of the damp crumb in the drying pan. Another drying method that can be used is the hot air flotation drying, known as fluid bed drying, where the small agglomerates are placed in an apparatus and warm air in fine streams is blown through the small particles. The warm air suspends the particles and carries away moisture.

A Patterson-Kelly V shell blender or a Littleford-Lodige precision mixer are convenient types of equipment that can be used for suspending the finely divided damp rubber additive in a gaseous medium.

The examples below illustrate the invention and show use of the process of this invention to produce dustless, free-flowing agglomerated rubber additives comprising rubber and asbestos. The equipment used for Examples 1 to 3 was a Patterson-Kelly liquid-solids twin shell v-shaped blender, which is well known to those skilled in this art.

Example I A Patterson-kelly 8-U.S. quart internal volume liquid-solids blender was charged to two-thirds of its internal volume with 2870 grams of 80 percent total solids content asbestos flock. The blender was started while running 460 grams of 25 percent total solids content styrene/butadiene (SBR) latex was metered into the blender chamber and distributed on the asbestos flock. The blender was allowed to run for a short period after latex addition was complete. The batch was discharged into a pan as a damp agglomerate or crumb. The rubber-asbestos flock agglomerate was pan dried in a circulating air oven at 70 C. or 158 F. for a period of about four hours.

Example 2 The procedure used was the same as described in Example 1 above except 460 grams of 25 percent total solids content acrylonitrile/butadiene (NBR) latex was used in place of the SBR latex.

Example 3 The procedure used was the same as that described in Example 1 above except that the latex used was 460 grams of 25 percent total solids content natural rubber (NR) latex was used in place of the SBR latex.

Table I below shows the particle size obtained using 80 percent total solids content asbestos flock agglomerated with various latices having 25 percent total solids content (TSC) in a Patterson-Kelly liquid-solids blender as opposed to nonagglomerated asbestos.

The "mesh" in Table I is U.S. Standard mesh.

TABLE I Control 1 2 3 (No Latex) Parts by Weight, Dry Asbestos Flock 100 100 100 100 SBR Latex 25% T.S.C. 5 NBR Latex 25% T.S.C. 5 Natural Rubber Latex 25% T.S.C. 5 Particle Size, % on 20 mesh 52.5 52.2 50.0 94.3 Through 20 mesh to 40 mesh 35.5 38.9 36.0 5.0 Through 40 mesh to 60 mesh 2.2 6.5 8.0 .4 Through 60 mesh to 100 mesh 9.8 2.4 6.0 0.3 Through 100 mesh 4.1 0.7 1.8 0.2 Bulk Density (grams/cubic centimeter) .32 .63 .64 .64 4-morpholino-2-benzothiazyl disulfide was treated with 1.25 parts SBR latex (dry weight) per 100 parts of said disulfide using latex having different total solids content. The materials were agglomerated in a Littleford-Lodige high speed internal mixer having a four cubic foot internal capacity. As the total solids content of the disulfide was increased, a lower total solids content SBR latex was used yielding a more uniform particle size. The data are shown in Examples 4 to 6.

Table II shows below the effect of variation of latex total solids content (TSC) on the particle size of the finished product and a comparison with the particle size of unagglomerated powder. These data reveal that the water content of the mixing system as a whole is an important factor.

TABLE II 100 Parts of 82% TSC 4-Morpholino 2-Benzothiazyl Disulfide Cake Treated with 1.25 parts/1OO SBR Latex Containing Different TSC of Rubber Control 82% 4 5 6 4-Morpholino Latex Latex Latex 2-Benzothiazyl 13.7% TSC 25% TSC 45% TSC Disulfide Cake (no latex) On 20 mesh screen 61.9% 31.6% 15% 4.3% Through 20 on 40 mesh 23.9% 37.4% 28.4% 5.6% Through 40 on 100 mesh 13.1% 30.6 56.2 14.1% Through 100 mesh on 200 1.1 0.4 0.4 29.1 Through 200 mesh 46.9 In carrying out the process the total solids content of the latex is adjusted according to the solids content of the damp finely divided material being agglomerated. When the finely divided material is low in total solids content (from 60 to 70So) a higher total solids content latex is used.The preferred latex total solids contents is from 25 to 45 percent. When the total solids content of the finely divided material and the total solids content of the rubber latex are combined produce a total solids content for the entire system in the range of from 60 to 95 percent total solids content, the particle size of the agglomerate produced is small enough to eliminate both free screening and force screening with some materals. It was found that at least 1.25 parts of SBR per 100 parts of finely divided material was required to obtain good properties of dustlessness and flowability.

In Examples 4 to 6, 4-morpholino-2-benzothiazyl disulfide was free screened as it came from the mixer. Twelve, ten and six mesh screens were used, producing a more uniform particle size in the treated material. A portion of the wet latex coated 4-morpholino-2benzothiazyl disulfide could not be free screened through twelve mesh. This portion was force screened through 12 mesh screen. When high total solids content latex was used, the amount of material needing to be force screened was low. For example, using 45 percent total solids content latex, 12 percent of the batch was force screened through 12 mesh screen. At 25 percent total solids latex, 20 percent of the batch was force screened through 12 mesh screen, and with a 13 percent total solids content latex, 67 percent of the batch was force screened through 12 mesh screen.In con-trast, free screening untreated material through a 12 mesh screen left 10 percent to be force screened. While the examples described herein illustrate the invention with respect to a single finely divided material, two or more such finely divided materials can be combined or added together and a mixed agglomerate formed.

The agglomerates prepared according to Examples 1 through 6 are stable, nondusting and free flowing. When these free flowing agglomerates were mixed with rubber in accordance with normal practices in a Banbury internal mixer or on a mill, the agglomerates dispersed rapidly and uniformly.

While certain representative embodiments and details have been shown for the purpose of illustrating this invention, it will be apparent to those skilled in this art that various changes and modifications may be made herein without departing from the scope of the invention.

It is to be understood that the invention includes not only a process as indicated in the foregoing description but also a vulcanized rubber composition product derived from a vulcanizable rubber composition containing at least one finely divided compounding ingredient which has been blended with a rubber in latex form by a process according to the invention.

WHAT WE CLAIM IS: 1. A process for forming dustless free flowing agglomerates consisting essentially of (1) forming a damp mass or cake of at least one finely divided material selected from the group consisting of 2-mercaptobenzothiazole, 2,2'-dithiobis(benzothiazole), 2 (morpholinodithio)benzothiazole, zinc 2-benzothiazolyl mercaptide, copper 2benzothiazolyl mercaptide, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, copper (II) dimethyldithiocarbamate, copper (II) dieth

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

TABLE II

100 Parts of 82% TSC 4-Morpholino 2-Benzothiazyl Disulfide Cake Treated with 1.25 parts/1OO SBR Latex Containing Different TSC of Rubber Control 82%

4 5 6 4-Morpholino Latex Latex Latex 2-Benzothiazyl 13.7% TSC 25% TSC 45% TSC Disulfide Cake (no latex) On 20 mesh screen 61.9% 31.6% 15% 4.3% Through 20 on 40 mesh 23.9% 37.4% 28.4% 5.6% Through 40 on 100 mesh 13.1% 30.6 56.2 14.1% Through 100 mesh on 200 1.1 0.4 0.4 29.1 Through 200 mesh 46.9 In carrying out the process the total solids content of the latex is adjusted according to the solids content of the damp finely divided material being agglomerated. When the finely divided material is low in total solids content (from 60 to 70So) a higher total solids content latex is used.The preferred latex total solids contents is from 25 to 45 percent. When the total solids content of the finely divided material and the total solids content of the rubber latex are combined produce a total solids content for the entire system in the range of from 60 to 95 percent total solids content, the particle size of the agglomerate produced is small enough to eliminate both free screening and force screening with some materals. It was found that at least 1.25 parts of SBR per 100 parts of finely divided material was required to obtain good properties of dustlessness and flowability.

In Examples 4 to 6, 4-morpholino-2-benzothiazyl disulfide was free screened as it came from the mixer. Twelve, ten and six mesh screens were used, producing a more uniform particle size in the treated material. A portion of the wet latex coated 4-morpholino-2benzothiazyl disulfide could not be free screened through twelve mesh. This portion was force screened through 12 mesh screen. When high total solids content latex was used, the amount of material needing to be force screened was low. For example, using 45 percent total solids content latex, 12 percent of the batch was force screened through 12 mesh screen. At 25 percent total solids latex, 20 percent of the batch was force screened through 12 mesh screen, and with a 13 percent total solids content latex, 67 percent of the batch was force screened through 12 mesh screen.In con-trast, free screening untreated material through a 12 mesh screen left 10 percent to be force screened. While the examples described herein illustrate the invention with respect to a single finely divided material, two or more such finely divided materials can be combined or added together and a mixed agglomerate formed.

The agglomerates prepared according to Examples 1 through 6 are stable, nondusting and free flowing. When these free flowing agglomerates were mixed with rubber in accordance with normal practices in a Banbury internal mixer or on a mill, the agglomerates dispersed rapidly and uniformly.

While certain representative embodiments and details have been shown for the purpose of illustrating this invention, it will be apparent to those skilled in this art that various changes and modifications may be made herein without departing from the scope of the invention.

It is to be understood that the invention includes not only a process as indicated in the foregoing description but also a vulcanized rubber composition product derived from a vulcanizable rubber composition containing at least one finely divided compounding ingredient which has been blended with a rubber in latex form by a process according to the invention.

WHAT WE CLAIM IS: 1. A process for forming dustless free flowing agglomerates consisting essentially of (1) forming a damp mass or cake of at least one finely divided material selected from the group consisting of 2-mercaptobenzothiazole, 2,2'-dithiobis(benzothiazole), 2 (morpholinodithio)benzothiazole, zinc 2-benzothiazolyl mercaptide, copper 2benzothiazolyl mercaptide, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, copper (II) dimethyldithiocarbamate, copper (II) dieth

yldithiocarbamate, cadmium diethyldithiocarbamate, lead diethyldithiocarbamate, tetramethylthiuram disulfide, tetramethylthiuram monosulfide, tetraethylthiuram disulfide, mixtures of tetraethylthiuram disulfide and tetramethylthiuram disulfide, N-cyclohexyl-2benzothiazolesulfenamide, N-t-butyl-2-benzothiazolesulfenamide, N-(3- methylcyclopentamethylene)-2-benzothiazolesulfenamide, 2-(N-hexamethyleneiminothio)benzothiazole, morpholine disulfide, mixtures of 2-mercaptobenzothiazole and tetramethylthiuram disulfide, 4-morpholino-2-benzothiazyl disulfide, asbestos, sulfur, monastral blue, phthalo green and pyrazolone red, said damp mass or cake of finely divided materials having a dry solids content of from 60 to 95 percent by weight of said finely divided material, (2) placing said damp mass or cake in a gas suspension apparatus which divides and crumbles the damp mass or cake into small particles while suspending said particles in a gaseous medium and (3) slowly adding to the gaseous suspension an amount of a finely divided spray of a rubber latex having a solids content of from 9 percent to 70 percent by weight of total weight of the latex to provide from 1 to 30 parts dried rubber for 100 parts of dry finely divided material and (4) mixing the particles of latex and particles of damp mass or cake while both are suspended in said gaseous medium for a time sufficient to allow the particles of latex spray to collide with the small particles of the damp finely divided material and form composite particles or agglomerates comprising rubber and said small particles of damp finely divided material, said composite particles having an average diameter of from 0.003 inch to 0.10 inch, and (5) drying said composite particles at a temperature and time sufficient to drive off excess moisture and to provide a dustless, free flowing agglomerate of rubber and the initially finely divided material.
2. A process according to claim 1 wherein the finely divided material is asbestos.
3. A process according to claim 1 wherein the rubber latex is selected from the group consisting of polybutadiene latex, the latices of rubbery copolymers of butadiene and styrene, the latices of rubbery copolymers of butadiene and acrylonitrile, the latices of polychloroprenes, the latices of rubbery copolymers of isobutylene and isoprene, and natural rubber latex.
4. A process according to claim 3 in which the rubber latex is selected from the group consisting of latices of rubbery copolymers of butadiene and styrene and the latices of rubbery copolymers of butadiene and acrylonitrile.
5. A process according to claim 3 wherein the finely divided material is 2 (morpholinodithio)benzothiazole, the rubber latex is a latex of rubbery copolymers of butadiene and styrene having a total solids content from 10 to 50 percent, and the agglomerates formed have a total dry rubber content from 1.00 to 10.00 parts by weight per hundred parts of dry 2-(morpholinothio)benzothiazole.
6. A process according to claim 1 wherein the finely divided material is 4-morpholino-2 benzothiazyl disulfide, the rubber latex is a latex of rubbery copolymers of butadiene and styrene having a total solids content of from 25 to 45 percent, and the agglomerates formed have a total dry rubber content of from 1.00 to 2.00 parts per hundred parts of dry 4-morpholino-2-benzothiazyl disulfide.
7. A process according to claim 1 wherein the finely divided material is asbestos, the rubber latex is a copolymer of butadiene and acrylonitrile having a total solids content of from 10 to 30 percent, and the agglomerate formed has a total dry rubber content of from 1.00 to 10 parts per hundred parts of dry asbestos.
8. A process according to claim 1 wherein the finely divided material is asbestos, the rubber latex is a copolymer of butadiene and styrene having a total solids content of from 25 to 45 percent, and the agglomerate formed has a total dry rubber content of from 1.00 to 10 parts per hundred parts of dry asbestos.
9. A process according to claim 1, substantially as described in respect of any of the foregoing Examples 1 to 6.
10. An agglomerate formed by a process according to any one of claims 1 to 9.
11. A vulcanized rubber composition product derived from a vulcanizable rubber composition containing at least one finely divided compounding ingredient which can be blended with a rubber in latex form by a process according to any of claims 1 to 9.