CA1301743C

CA1301743C - Mixing apparatus employing a cavity transfer mixer

Info

Publication number: CA1301743C
Application number: CA000535742A
Authority: CA
Inventors: Elwyn G. Huddleston
Original assignee: Kendall Co
Current assignee: Kendall Co
Priority date: 1986-04-29
Filing date: 1987-04-28
Publication date: 1992-05-26
Anticipated expiration: 2009-05-26
Also published as: FR2597763B1; FR2597763A1; GB8710169D0; GB2195093B; GB2195093A; IT1205847B; DE3714162A1; IT8747892A0

Abstract

ABSTRACT

TITLE: NOVEL MIXING APPARATUS EMPLOYING A CAVITY TRANSFER
MIXER

Novel system for providing a homogeneous mixtures of materials comprising an internal mixer, an extruder, a cavity transfer mixer, means for discharging a mix from the internal mixer directly into the extruder, said extruder and cavity transfer mixer being juxtaposed in fluid-tight arrangement whereby material traversing the length of the extruder passes directly into the cavity transfer mixer, means for injecting material into the cavity transfer mixer for admixture with material traversing therethrough from the extruder, output means for removing the resulting homogeneous mix from the cavity transfer mixer, and motor means for operating said internal mixer, extruder and cavity transfer mixer, said motor means comprising means for separately driving and varying the speed of said cavity transfer mixer, whereby said cavity transfer mixer is adapted for operation at varying speeds higher than said extruder.

Description

BACKGROUND_O~_THE INVEN~ION

The present invention is directed to novel apparatus including a cavity transfer mixer ~or preparing homog~neous mixtures of materials and, more particularly, for commercial preparation of such mixtures, 2 . g . to the manufacture of ru~ber-based compositions, adhesive formulations and other mixtures of solid materials.
Cavity transfer mixers are per se old and have been employed in various mixing operations.
In general, they are a form of extruder mixer wherein material is fed into one end and exits through an extruder die at the opposed end. They consist essentially of a hollow cylindrical stator member and a cylindrical rotor member which is rotatable therewithin. The facing cylindrical surfaces on the rotor and stator carry respective pluralities of rows of grooves or cavities positioned so as to cause a mixing as the material traverses the mixer.
British Specification No. 930,339 describes a cavity transfer mixer of this description wherein the grooves are elongate and longitudinally extending. The rows of grooves on each member extend peripherally around the member and are spaced apart axially, the rows on one member being axially ~set ~f~ e ro~s ~ ~he other member so as to provide an axial overlap of the grooves in adjacent rows on the stator and rotor. Because of this arrangement o~ overlapping closed cavities on the rotor and stator, material passing through this mixer mu~t travel a path which alt~rnates - 2 - ~

~L3@~3l7~3 between rotor and stator cavitie whQrQ a cavity on one member happen~ to be opposite a land on the other member, the material to be admixed i3 subjected to simpl~ shear so that it i5 cut in half before being displaced approximately at right angles to its original direction as it passes into the next cavity.
U.S. Patent No. 4,419,014 relates to an lmproved cavity transfer mixer which is particularly efficacious in the practice of the present invention. In accordance with this patent, the rotor and skator cavities are formed as hemispheres arranged in a special con~iguration.
Specifically, these hemispherical cavities are arranged in parallel rows on the rotor and stator such that: (a) khe cavities in adjacent rows on the strator are circumferentially offset; (b) the cavities in adjacent rows on the rotor are circumferentially of~set; and (c) the rows of cavities on the stator and rotor are axially offset~
whereby an overall increase in mixing capacity for the same surface area can be obtained while achieving a desired exponential mixing characteristic which simple shear mixing is repeatedly interrupted by cutting and turning stages.
The cavity transfer mixer disclosed in the aforementioned U.S. Patent is appreciably more efficient than that described in the British Patent. Specifically, the mixing capacity for the surface area is considerably increased. Moreover, other signi~icant advantages are obtained. The configuration of hemispherical cavities can be arranged so that overlaps occur between three cavities at any give time so that extra mixing or blending is obtained by repeated division of the melt streams. The hemis~herical shape of the cavities provides excellent streamlining so that, for example, stagnation will not occur. Other advantages arQ described in Col. 3.

~ ~3~7~L3 73~62 U.S. Patent No. ~,750,~2 clescri.bes ancl clalms a novel system for incorporatiny a rubbér crosslinki.n~ agellt. ln a ruhher-based adhesive formulation wherein the crosslinklnq agent is admlxed with the aclhesive formulatio.n in a cavity transfer mixer (CTM), e.g. a CTM of the type disclos&d in the aforementioned U.S.P. ~,41~,014, thereby providing siynificant manufacturing advantages. Preferably the crosslinker is incorporated in an oil or plastisizer vehicle. As described in the copending application, a premix of the rubber and other components is first formed in a Banbury in a batch operation.
The premix is then transported to the input end of -the extruder, -to the output end of which the CTM is positioned.
The CTM is provided near its leading end with an injection port through which -the crosslinking agent is fed. As is discussed, the CTM may he threaded on-to -the exit end of the extruder or otherwise secured to the extruder. Alternatively, it may be a separately driven~ variable speed CTM mounted or secured contiguous with the exit port of the extruder, e.g. by clamping means. In the latter embodiment, the CTM may have a diameter significantly yreater than the extruder, thereby providing greater surface area for mixing in the CTM, which in turn allows the addition of laryer quantities of additives, i.e.
increases output.
Preferably, the process is operated as a continuous one where the premix from the ~anbury drops directly into a continuously operating extruder and metered amounts of crosslinker are automatically fed into the CTM with the aid of per se known microprocessors. In other words, since the amount of premix exiting from the Banbury in a given batch time, e.g.
10 minutes is known, as is the rate of passage of the premix through the extruder, the required amount of crosslinker to be 132G~-~0 admixec1 can be c1eterminec1 and autonlatically metered into the CTM as the premix is continuously ied therethroucJil.
In -this manner, employing a CTM in lieu of the 8~
inch two-roll mill, a homogeneous adhesive mixture containing the crosslinker is i.nstaneously obtained and this premix may be immediately conveyed to a calendar where the adhesive is applied to a suitable backing material to form an adhesive -tape.
The copending Canadian application of Elwyn G.
Huddleston (instant Applicant) and Richard J. Lacana, S.N.
543,519 filed July 31, lg87 describes and claims another process for preparing rubber compositions employing a cavity transfer mixer. As described therein, a CT~1 is employed to incorporate tackifying resins into rubber compositions, including adhesive formulations.
In the preferred embodiments, as is described in this copending application, all of the components of the adhesive formulation except for the required amount of tackifier are first admixed in an internal mixer, most preferably a aanbury, in per se known manner to provide a substantially homogeneous molten premix of the rubber ancl other components (filler, antioxidant, etc.) The mol-ten premix is then transported from the Banbury or other internal mixer to the CTM for the addition of the tackifier. Preferably, this is accomplished in a continuous rather than a batch operation wherein the premix is dropped from the internal mixer discharge hopper directly into the input end of a conventional extruder~ Tlle CT~1 is mounted or secured adjacent to the output end of the extruder so that the premix is conveyed to the CTM via the extruder.
In theory, the CTM may be threacled onto the output ``` ~ 3~

end of the extruder. Theoretically, the CTM may also be provicled with a single port through which the resin is introduced. Both of these clesigns have utility for purposes of this invention. ~lowever, the usefulness of either or both o-f these constructions i.s limited from a manufacturing standpoint and consequently they are not preferred, at least with most adhesive systems which are con-templated.
Canadian S.N. 543,519 further discloses that, experiments have shown that when a 6 row CTM was fitted directly with a Davis Standard 16:1 cold feed extruder, a maximum amount of about 5-6 percent resin can be incorporated.
While this percentage of tackifier may be entirely adec~uate ~or some adhesives, higher amounts of this aclditive to the premix are required for adhesive formulations ~enerally envisioned.
As is further disclosed in Canadian S.N. 543,519 the CTM is preferably detached from the extruder, and is independently driven so as to be capable of operating at variable speeds, including speeds appreciably higher ~han the extruder. In this manner, much greater quantities of resin may be incorporated, i.e. cluantities typical of these commonly employed in the contemplated adhesives. It will of course be appreciated that where the CTM is detached and separately driven (as distinyuished from being threaded to the extruder), it should nevertheless be mounted in juxtc-position with the extruder (by any per se known mechanical means) so that the molten mass of premix passes directly from tlle extruder to the CTM.
It is also disclosed to have been found that optimum results may be obtained by increasing the length of the CTM, e.g. to provide a nine row CTM. This may be accomplished simply by providing a single nine row CTM. Alternatively, it (. -may be by means of a variahle l.encJth C'T~I, e.rJ. two or more separate units ln seal.ed relationshiu t.o preverlt escclpe of material travellincJ downstream from one CTM to -the next.
~ y way of i.l:Lustration, a three row CrrM may be fitted directly to a cold feed extruder, e.g. -to the output end of a 2-1~" extruder. A 6 row variable speed, separately driven CTM
may be placed in sealed relationship with the 3 row CTM.
While -the CTM may theoretically be provided with a single en-try port for feeding the resin, in the preferred embodiment multiple ports are provicled along the path (length) of the CTM. By way of illustration, in the embodimen-t just described employing a 9 row CT~I, excel:Lent results were obtained employing two entry ports for the resin. For example, with a nine row CT~I in which the last six rows were driven independently, e.g. a 3-4 times the speed of the main extruder, two injection ports were found to be adecluate for the addition of up to 23% hot resin.
Preferably, however, a 9 row unit which is entirely driven independently, will be provided with three spaced ports for injecting the resin, e.g. a first one just before the CTM, a second one a-t the 3 row posltion, and a third one at -the six row position. It should be however noted, that it will not always be necessary -to inject at all three positions.
Neverthelessr -the use of three ports will provide greater flexibility for -the system.
BRIEF DESCRIPTION OF THE INVENTION
The present invention is directed to a novel apparatus for use in manufacturing processes for preparing compositions such as those described in the aforetnentioned copending applications, the essence of the invention being the combination of elements described therein including an internal 732G2~20 mixer, an extruder ancl a variable speecl separately drl.ven CT~I
arranged so that a premix of materials prepared i.n the internal mixer is transportecl direc!tly in~o the ~xtruder and from there to the CT~I where aclditional ingredients are introcluced into the premix.
According to a broad aspect of the invention there ls provided a sys~em for providing a homogeneous mix~ure of materials comprising an internal mixer including input means for inserting materials to be admixed, mixing means for admixing said materials inser-ted in said internal mixer, and output means for removiny said mixture from said internal mixer; an extruder having an input means through which material is introduced, an output means through which material exits and motor means for driving said extruder; and a cavity transfer mixer having an input means for introducing material for admixture, an output means through which material exits from said cavity transfer mixer, motor means for driving said cavity transfer mixer and means for varying the speed for driving said cavity transfer mixer, said input means of said extruder being arranged with respect to said internal mixer so that said mix discharged from said internal mixer may be introduced into said input means of said extruder, said input means of said cavi.ty transfer mixer being in fluid-tight position ~ith respect to the output means of said extruder whereby material in said extruder is discharged directly into said cavity transfer mixer, said extruder and said cavity transfer mixer being separately driven by said respective mo-tor means.
According to another broad aspect of the invention there is provided a system for admixing solid materials to form a substantially homogeneous mixture thereof wherein a premix of components thereof is first formed in a first mixing operation and at leas~ one aclclitiQnal componerlt of sa:Lcl m:i..xture ls thereafter lncolporated in saicl ~remix irl a seconcl mixing operation, said system comprl.s:Lng: a Banbury mlxer including neans for introducincJ said premix componen~;s for adrnixture arld a drop chute -through which sald premix is clis~harged from Banbury mixer; an extruder haviny a throat at one encl for receiving material and outpu-t means at the opposed end through which traversing said extrucler is discharged, said throat o~
said extruder being positioned beneath said drop ehutes of said Banbury mixer, whereby said premix discharged from said Banbury mixer is fed by gravity into the thxoat of said extruder; a cavity -transfer mixer comprising a hollow cylindrical stator member and a cylindrical rotor member rotatable therewithin, said cavity transfer mixer having an input end for feeding material and an output end for discharging said material, said cavity transfer mixer or said extruder further including at least one injection port for introducing an additive for admixture with material traversing therethrough, said input end of said cavity transfer mixer being contiguouos with said output means of said extruder and in fluid-tight relationship therewith, whereby said premix passing through said extruder is fed directly in-to sa:id cavity transfer mixer; Inotor means for separately driving said extruder and cavity transfer mixer; and means for varying the speed of sa:id cavity transfer mixer whereby said cav:ity transfer mixer can operate at variahle revolutions per minute the same or greater than those of said extruder.

7b gL3~ 3 BRIEF_D ~

The figure is a schematic ~iew illu~tratlng the combination o~ elements of thi~ invention.

DETAILED DESCRIPTION OF THE INVENTIQN

A~ previously mentioned, the novel mixing system of this invention consists essentially of three mixing elements each of which is per se kno~n and heretofore us~d in the rubber industry, namely (a) an internal mixex; (b) an extruder; and ~c) a cavity transfer mixer, e.g. of the type described and claimed in the aforementioned U.S.P.
4,419,014. For a full appreciation of the nature and objects of the invention, it is appropriate to consider a brief history of the rubber manufacturing art.
In the early manufacture, the rubber was first cut and then placed in a mill that first masticated and then compounded it. In general, a mill consists of two parallel metal rolls 50 adjusted that the rubber could be ground and sheared between them. Mixing mills may typically vary from 20 to 84 inches in length and ~rom 16 to 28 inchas in diameter. 84 inch rolls, generally regarded as the mechanical limit, are capable of handling a batch o~ 300 pounds of rubber in 25 to 40 minutes. The rolls are water-cooled internally. The tremendous power of these two rolls, operating at different speeds (the back roll turns faster than the front one; speed ratios ~rom 1.2:1 to 1.5:1 are customary) coupled with slight oxidation and the heat e~erated by the resulting friction, eventually reduces the chunks o~ cold rubber into a plastisized shPet that adheres to one of the cylinders. A two roll mill of this descrip~ion is re~erred to as an external mixer.

`` ~3~ 3 As demands for manufacturing rubber product~ increased, a need was felt ~or larger, ~aster and more power~ul machines. Today, nearly all rubber is proces~d initially in internal mixers such as the ~anbury. These maahineæ, which work by internal pressure and rotating parts, have a capacity which may typically range ~rom 150 to 1000 pounds.
As compared with the 25 to 40 minutes generally required with a two-roll mill for handling 1~0 to 300 pounds of rubber, the internal mixers may reduce this to, say 5 to 8 minutes. In addition to saving time, a Banbury will produce a much more uniform or homogeneous product than that dependent upon hand operations on the external mill.
On the other hand, the high power requirements and the fact that the Banbury process is essentially batch-type mixing rather than continuous flow led to the development of mixer-extruders.
In a typical manufacturing process as employed in the rubber-based adhesive industry, the rubber whether natural or synthetic, and most of the other ingredients are mixed in the Banbury to form what may be termed a "premix". This premix is discharged from the Banbury drop chute and then transported to an extruder which shapes it into strips or tubes. In general, an extruder for this purpose is a device for forcing the heat-softened rubber premix through orifices or dies. The rubber is ground in the extruder and forced through a heated die by means of a screw. The extruded material, which retains the shape of the die and may be circular or rectangular in cross section and having a diameter varying from 1 to 8 inches, is then transported, e.g. on a conveyer, to the two-roll mill where the remaining ingredients, which could not be added under ~anbury processing conditions, are-then scooped or shoveled onto the milling premix. Following th~ milling operation, the resulting rubbsr-based composition is then transported to ~.3~74~

the remaining manufacturing steps, e.g calendering, slitting, rol~ing up on cores and packaging.
Most recently, the cavity trans~er mixer came lnto existence. The CTM, which may be considered to be a state of the art form o~ an extruder-mixer, is only several inches in length and provides significant advantages, including those heretofore mentioned, over a milling operation.
However, it lacks the capacity of and thus cannot replace the Banbury.
In any event, prior to the present invention, the processes for preparing rubber compositions was of ~he batch type wherein a premix was ~ormed in the Banbury (or other internal mixer) and the resulting premix was then transported to a two-roll mill and/or CTM for preparation of the final composition. As is understood by those skilled in the art, a batch operation has certain inherent disadvantages, chief of which are the manpower requirements, time, energy consumption, and lack o~ precise controls in product formulations.
The present invention is directed to a continuous operation which therefore obviates the above-noted problems of batch operation-and permits precise and uniform formulations.
In accordance with the present invention, the premix formed in the internal mixer in per se known manner, is deposited from the drop chute of the internal mixer directly into the throat of the extruder of known type such as a Davis Standard 16:l cold feed extruder. The premix exiting from the die at the output end of the extruder passes d;r~ v ;~ CTM ~rovided with at least one port for introducing metered amounts of the material, e.g. tackifying resin, crosslinking agent or the like to be incor~orated into the premix to form the desired composition.

~3~ 3 ~hile the input end o~ the CTM could be khreaded onto the output en~ of the extruder and the resultiny combination then driven by a single motor, an essential part o~ this invention, as previously mentioned, is that the CTM is separately driven and possessas a variable speed, i.e. can be driven at higher speeds than the extruder in order to obtain material increases in output.
In the preferred embodiments, per se known microprocessors are employed to determine the amount of the premix and rate of flow through the extruder and thereby in turn to cause precise metered amounts of additive material to be introduced into ~he injection port or ports of the CTM. Also, as previously mentioned, in the preferred embodiments, a plurality of injection ports are providedO
In lieu of having the first such injection port adjacent the input end of the CTM, it may, if desired, be provided just prior to the output end of the juxtaposed extruder, so that at least a portion of the additive is introduced just before the premix enters the CTM. One or more additional injection ports may be positioned at spaced intervals along the path of the CTM.
As will be appreciated, the CTM is positioned adjacent or contiguous with the extruder where it is maintained in fluid-tight arrangement with the extruder by suitable connecting means in order to preclude escape or exudation of material traversing therethrough.
The invention will be further understood by reference to the accompanying drawing.
As shown in the illustrative drawing, the essential components of the novel mixing system of this invention are an internal mixer 10, an extruder 30, and a separately driven variable speed CTM 44.
Mixer 10 is illustrated to be a conventional Banbury mixer seated on a bas~ 12 supported by column~ or I-beams ~ 30~3 14. In a t~pical m~nufacturing facility, base 12 would ~e the flooring ~ one levQl of the facility and the extruder and CTM would be on a lower level. Mixer 10 is operated by a motor 16 mounted on block 18. The mixer includes an inlet hopper 20 ~or feeding raw materials to be admixed and a drop chute 22 for discharging the mix. As is known, a Banbury mixer, as illustrated in the drawing, will also include a ram 24 driven by air pressure from a source (not shown) sntering the mixer through air inlet pipe 26.
Drop chute 22 feeds the mix discharged ~rom mixer 10 directly into the throat or input end 28 of extruder 30 mounted to and supported by end block 32 and support block 34. Extruder 30 is driven by motor 36 seated on block 38.
The output end 40 of extruder 30 is positioned in fluid-tight manner to the input end 42 of CTM 44 by means of clam-shell connector 46 so that material in the mix leaving the extruder is discharged without leakage directly into the CTM.
The CTM 44 is separately driven by means of motor 48 which, for purposes of illustration, is shown to be seated on trolley 50 having wheels 52 so that it is readily movable to and from the extruder. A gear box 54 is provided to enable the speed for driving the CTM to be variable, e.g. so that the CTM may be driven at variable speeds higher (faster) than the extruder.
The CTM has one or more injection ports 56 for introducing material into the moving mass in the CTM. For purposes of illustration, two such ports are shown. Other similar ports may be provided at varying distances along the path lenqth ~f th~ CT~ if found desirable or expedient to do so, as will be discussed in more detail hereina~ter.
The output end 58 of CTM 44 i5 shown to have a discharge pipe 60 from which ~he mix from the CTM is discharg~d onto an endless moving conveyor bel~ 62 for ~.3~L7~3 transport to the next manufacturing station, e.g.. a packaging sta ion, a calendering operation for coating onto a backing material to prepare tapes containing a layer of the mix, a~c. As will be appreciated, intermediate stations may be provided for sampling the mix ~or ~uality control, etc.
While the essential elements o~ the invention have been shown for purposes of illustration, it will be appreciated that other elements performing speci~ic desired functions ma~ and usually will be provided. For example, in the preferred contemplated use of the novel arrangement of elements, microprocessors of per se known description will be provided to determine the amount and rate o~ flow of material in the extruder which will in turn cause precise metered amounts of material to be introduced for admixture into the CTM via the injection port(s) 56. If the material to be injected is not sufficiently liquid or flowable for injection at room temperature, heating means may be provided to facilitate its introduction.
It will also be appreciated that the material entering the internal mixer lO may be fed manually, e.g. by an operator stationed on a platform adjacent inlet hopper 20 or, alternatively, means (not shown) may be provided for automatically feeding mixer lO.
From the foregoing description and illustrative drawing, the operation of the novel system of this invention will be apparent.
A supply of material to be introduced into the CTM is provided along with suitable metering valves and conduit n~ to the injection ports. As previously mentioned, if the material is not suitably fluid or flowable at room temperature, heating means is also provided to render it fluid for introduction through the injection port.
~ /3 ~

~L30~ 7D~3 The motors for the respective elements are activated and the rubber and other components of the premix are f~d into th~ Banbury. This may b~ ~one manually or by au~omatic means which would be readily apparent for those ~killed in t~e art and per se comprises no part of thi~ invention. In like manner, the additive mat~rial may be introduced manually into the CTM. However, in the preferred system, this is done automatically with the aid of per se known microprocessors, as previously described.
Material exiting the die of the CTM may be transported, as described, to the final manufacturing stations, e.g.
calendering, packaging, etc.
The following examples show by way o~ illustration and not by way of limitation the practice of this invention.

EXAMPLEI

The following ingredients were incorporated into a Banbury to provide a substantially homogeneous natural rubber premix:

Natural Rubber (Smoked Sheet) 193.0 lbs.

White Pigment (Titanox 2010) 5.0 lbs.

Black Pigment (Butex) 7.0 ozs.

Phenolic Resin Crosslinker B.O ozs.
(SPl055) Kaolin Soft Clay (McNamee Clay~ i6~`.0 ~s, Filler Antioxidant 2.5 lbs.
~odified Tall Oil Rosin Tackifier 68.0 lbs.
Zinc Oxide 9.0 lbs.

7~3 Approx. 44Z.0 lbs.

An existing 3 Row CTM was ~itted directly with a Davis Standard 16:1 cold feed extruder. An existing 6 Row CTM was then fitted to a drive shaft capable of being driven from a 2 1/2" Prodex extruder. An exit sleeve was constructed between the 6 Row CTM and the Prodex barrel. An injection port was provide~ just prior to the output end of the 2-1/2"
extruder, i.e. just before the 3 Row CTM; and a second injection port was provided between the 3 Row and 6 Row CTMs. The extruder and CTM's were set for 160C (320F).
The speed of the 2-1/2l' extruder was set at about 10 RPM;
and the speed of the separately driven 6 Row CT~ was set at about 80-90 RPM. The premix from the Banbury was fed into the extruder and resin STA TAC B (trademark of Reichhold Co.
for a polymerized petroleum hydrocarbon tackifier) was pumped into the two injection ports at a speed of about 137 g./min. to provide a natural adhesive mix output at the rate of 36 kg/hr and which contained about 22.9% by weiyht.

The following ingredients were incorporated in a Banbury to provide a substantially homogeneous butyl rubber premix comprising:

Butyl Rubber 76.0 lbs.

~e~ ~ 145.0 lbs.

Indopol HlO0 63.5 lbs.
(polybutene tackifier) ~ /5 ~3~74L3 McNamee Clay 220.0 lb~.

Antioxidant 2.5 lbs.
(Agerite Stalite S) ApproxO507.0 lbs.

An extruder, 3 Row CTM and 6 Row CTM construction as described in Example 1 was emp}oyed. However, the 2-1/2"
extruder was set at 14 RPM and the separately driven 6 Row CTM at 50 RPM (approximately 3.S times faster than the extruder.) The butyl premix was fed into the extruder and Piccopale 100 (trademark of Hercules Co., for a aliphatic hydrocarbon tackifier resin) was pumped into the two injection ports at a speed of about 115 g/min to provide a butyl rubber adhesive mix output at the rate of 40.4 kg/hr and which contained about 17% resin by weight~
In the foregoing illustrative examples, it will be seen that, in each instance, a portion of the desired amount of tackifier was incorporated in the Banbury, the remainder being added in the CTM. It is to be noted, however, that it is entirely possible to incorporate substantially all of the resin and plasticizer via the CTM. In order to do so, a somewhat longer CTM may be needed. As will be appreciated by those skilled in the art, however, it may be expedient or advisable to incorporate at least plastisizing amounts of resin in the Banbury mix.
The adhesive formulations prepared above were .... .
~; ~ - calendered onto backings in known manner to p~epare adhesive tapes which were then compared to adhesive properties with control tapes of similar formulations prepared in th~
conventional (prior) manner. ~he adhesive properties of the ~13~7~3 test tapes were comparable and well within the prsscribed limits.
From the foregoing illustrative examples it will be seen that the present invention provides an elegant manu~acturing process for preparing rubber-based adhesives comparable in adhesive characteristics to those prepared by the prior art systems commonly employed. In other words, the adhesives so produced by the present invention are not necessarily better. However, the manufacturing process is vastly superior.
The aforementioned parent application, S.N. 869,692 cohtains illustrative examples for introducing a crosslinking agent into a rubber premix via a CTM. However, in those examples, the CTM was not a variable speed separately driven one, but was instead fitted with a plain screw onto the outflow end of the extruder. In view of the foregoing description, it will be appreciated that the apparatus of this invention will be particularly useful in the processed described in the parent application.
It will also be apparent that the usefulness of the present invention is not restricted to the rubber industry, but may find use in other industries as well, e.g. in the manufacturing of various solid or semi-liquid products containing a homogeneous mixture of dispersion of particulate matter.
Since certain changes may be made without departing from the scope of the invention herein described, it is intended that all matter contained in the foregoing description, including the drawing, shall be taken as t i~ ~ 3j~iting sense.

Claims

1. System for providing a homogeneous mixture of materials comprising an internal mixer including input means for inserting materials to be admixed, mixing means for admixing said materials inserted in said internal mixer, and output means for removing said mixture from said internal mixer; an extruder having an input means through which material is introduced, an output means through which material exits and motor means for driving said extruder;
and a cavity transfer mixer having an input means for introducing material for admixture, an output means through which material exits from said cavity transfer mixer, motor means for driving said cavity transfer mixer and means for varying the speed for driving said cavity transfer mixer, said input means of said extruder being arranged with respect to said internal mixer so that said mix discharged from said internal mixer may be introduced into said input means of said extruder, said input means of said cavity transfer mixer being in fluid-tight position with respect to the output means of said extruder whereby material in said extruder is discharged directly into said cavity transfer mixer, said extruder and said cavity transfer mixer being separately driven by said respective motor means.

2. A system as defined in Claim 1 wherein at least one of said extruder and said cavity transfer mixer includes an entry port for introducing an additive for admixture with material passing therethrough.

3. A system as defined in Claim 2 wherein said entry port is positioned on said extruder adjacent the output means thereof.

4. A system as defined in Claim 2 wherein said cavity transfer mixer contains at least two of said entry ports at spaced intervals between the input and the output means thereof.

5. A system as defined in Claim 1 wherein said internal mixer is a Banbury mixer.

6. A system as defined in Claim 5 wherein the output means of said internal mixer comprises a drop chute.

7. A system as defined in Claim 6 wherein the input means of said extruder comprises an opening positioned directly below said drop chute, whereby material exiting said drop chute is gravity fed into said opening of said extruder.

8. A system as defined in Claim 1 wherein said cavity transfer mixer consists essentially of a hollow cylindrical stator member and a cylindrical rotor member rotatable therewithin, the facing cylindrical surfaces on said rotor and stator carrying respective pluralities of cavities positioned so as to cause a mixing as the material traverses the mixer from the entry port thereof to the exit port thereof, said cavities being hemispherical and arranged in parallel rows on said rotor and stator such that: (a.) the cavities in adjacent rows on said stator are circumferentially offset; (b.) the cavities in adjacent rows on said rotor are circumferentially offset, and (c.) the rows of the cavities on said rotor and stator are axially offset, whereby an overall increase in mixing capacity for the same surface area is obtainable while achieving a desired exponential mixing characteristic in which simple shear mixing is repeatedly interrupted by cutting and turning stages.

9. A system for admixing solid materials to form a substantially homogeneous mixture thereof wherein a premix of components thereof is first formed in a first mixing operation and at least one additional component of said mixture is thereafter incorporated in said premix in a second mixing operation, said system comprising:
a Banbury mixer including means for introducing said premix components for admixture and a drop chute through which said premix is discharged from Banbury mixer;
an extruder having a throat at one end for receiving material and output means at the opposed end through which traversing said extruder is discharged, said throat of said extruder being positioned beneath said drop chutes of said Banbury mixer, whereby said premix discharged from said Banbury mixer is fed by gravity into the throat of said extruder;
a cavity transfer mixer comprising a hollow cylindrical stator member and a cylindrical rotor member rotatable therewithin, said cavity transfer mixer having an input end for feeding material and an output end for discharging said material, said cavity transfer mixer or said extruder further including at least one injection port for introducing an additive for admixture with material traversing therethrough, said input end of said cavity transfer mixer being contiguous with said output means of said extruder and in fluid-tight relationship therewith, whereby said premix passing through said extruder is fed directly into said cavity transfer mixer:
motor means for separately driving said extruder and cavity transfer mixer; and means for varying the speed of said cavity transfer mixer whereby said cavity transfer mixer can operate at variable revolutions per minute the same or greater than those of said extruder.

10. A system as defined in Claim 9 wherein said extruder is a cold feed extruder.

11. A system as defined in Claim 9 wherein said means for varying the speed of said cavity transfer mixer comprises gear means.

12. A system as defined in Claim 9 wherein said cavity transfer mixer has at least two said injection ports.

13. A system as defined in Claim 9 wherein each of said extruder and cavity transfer mixer are cylindrical in shape.

14. A system as defined in Claim 13 wherein the diameter of said cavity transfer mixer is greater than the diameter of said extruder.