Patent Abstract:
A toner extruder for the preparation of a toner resin extrudate from a resin is provided. The extruder includes a housing defining a housing aperture and a resin inlet opening in the housing. The extruder also includes a conveyor for conveying the resin through the housing aperture. A lead-in gap at the resin inlet opening collects prematurely melted base resin and holds it for take-up by the conveyor, thus preventing fusing of the resin on the conveyor and avoiding clumping. The extruder can further include a member adjacent the resin inlet opening for inhibiting the heat transfer from the housing and/or the conveyor to the resin at the opening. The flow of resin adjacent the opening is thus improved.

Full Description:
BACKGROUND OF INVENTION  
         [0001]    In the process of electrophotographic printing, a photoconductive surface has an electrostatic latent image recorded therein. Toner particles are attracted from carrier granules to the latent image to develop the latent image. Thereafter, the toner image is transferred from the photoconductive surface to a sheet and fused thereto.  
           [0002]    Typically, toner may be produced by melt-mixing the soft polymer and pigment whereby the pigment is dispersed in the polymer. The polymer having the colorant dispersed therein is then pulverized. Recently in U.S. Pat. No. 5,227,460 (Mahabadi et al.), incorporated herein by reference, a low melt toner resin with minimum fix temperature and wide fusing latitude containing a linear portion and a cross-linked portion containing high density cross-linked microgel particles, but substantially no low density cross linked polymer was disclosed. A method of manufacturing that toner and its resin was disclosed in U.S. Pat. No. 5,376,494 (Mahabadi et al.), incorporated herein by reference. The method of fabricating the low fix temperature toner resins includes a reactive melt mixing process wherein polymer resins are cross-linked at high temperature and high shear. The resins are particularly suitable for high speed fusing, show excellent offset resistance and wide fusing latitude and superior vinyl offset properties.  
           [0003]    The base resin and pigment are melt mixed together typically in an extruder, which is a part of an extruding system. The soft polymer and pigment are translated and mixed in an auger within a cavity of the extruder.  
           [0004]    The polyester base resins of the present invention are typically in the form of soft polymers. These base resins have an extremely low melting temperature. The melting temperature of these polyester based toners are about 90° C. A typical extruder is maintained at high temperature by jacket heaters on the extruder body. On top of this, as the base resin is extruded in an extruder, a significant amount of heat is generated which is result of high shear energy of the extruding. The heat from the extruding process raises the temperature of both the body of the extruder and the screw within the extruder. The entire extruder is at an elevated temperature above ambient. The polymer base resin is added to the extruder through a feed opening in the inlet end of the extruder.  
           [0005]    When utilizing the low melt polymer based resins, the heat from the screws and body of the extruder tend to melt the base resin at the open feed barrel at which the resin is added to the extruder. The premature melting of the toner affects the productivity of the extruder. If the premature melting is severe enough, the extruder must be shut down and cleaned of the melted extruder before the process may continue.  
           [0006]    Furthermore, the use of a commercially available extruder to manufacture the polyester base resins requires that the input area of feed barrel be redesigned to have a shape between the screws of the extruder and the body of the extruder which has increased clearance in order to optimize conveying base resin into the extruder. The requirement for increased clearance between the body and the screws when utilizing the polyester based resin, necessitates that the feed barrel of the extruder be changed from a standard feed barrel to a specially designed feed barrel when manufacturing such resin. This process is very time and labor intensive and results in a loss of productivity.  
           [0007]    The following disclosures may be of note:  
           [0008]    U.S. Pat. No. 5,145,762 (Grushkin) discloses a process for the preparation of toner compositions. The process comprises melt blending toner resin particles, magnetic particles, wax, and charge additives. The process further comprises adding a coupling component to the aforementioned mixture, injecting water therein, and cooling.  
           [0009]    U.S. Pat. No. 4,973,439 (Chang et al.) discloses an apparatus for obtaining toner particles with improved dispersion of additive components therein comprised of a toner extrusion device containing therein a blending chamber, a mixing screw, a heater, a toner supply, and an injector for injecting additive components including charge control agents into the extrusion device enabling a decrease in the melting temperature of the toner resin particles contained therein.  
           [0010]    In U.S. Pat. No. 4,894,308 (Mahabadi et al.), a process for preparing an electrophotographic toner is disclosed, which comprises premixing and extruding a pigment, a charge control additive and a resin. The pigment and the charge control additive may be premixed prior to being added to the extruder with the resin; alternatively, the pigment and charge control additive may be premixed by adding them to the extruder via an upstream supply means and extruding them, and subsequently adding the resin to the extruder via a downstream supply means.  
           [0011]    In U.S. Pat. No. 3,778,287 (Stansfield et al.) dispersions of inorganic pigments, lakes or toners in organic liquids containing polyesters dissolved therein having acid values up to 100 derived from certain hydroxy-containing, saturated or unsaturated aliphatic carboxylic acids are described. While liquid colorants offer the distinct advantage of being more readily incorporated into the medium to be colored than dry pigments, their commercial significance is seriously limited due to the problems of handling and storing potentially hazardous liquid chemicals. Thus, from an economic and safety standpoint, it is desirable to have the colorants in a dry, storage stable form which is readily dispersible in a wide variety of coating media without detriment to any of the desirable properties of coating produced therefrom.  
           [0012]    U.S. Pat. No. 5,227,460 (Mahabadi et al.) discloses a low melt toner resin with minimum fix temperature and wide fusing latitude containing a linear portion and a cross-linked portion containing high density cross-linked microgel particles, but substantially no low density cross linked polymer.  
           [0013]    U.S. Pat. No. 5,376,494 (Mahabadi et al.) discloses a method of fabricating low fix temperature toner resins by a reactive melt mixing process wherein polymer resins are cross-linked at high temperature and high shear. The resins are particularly suitable for high speed fusing, show excellent offset resistance and wide fusing latitude and superior vinyl offset properties.  
           [0014]    U.S. Pat. No. 5,468,586 (Proper et al.) discloses an apparatus for the preparation of a mixture of toner resin and a liquid colorant. The apparatus includes a toner extruder having the resin being conveyed therethrough and a colorant feeder for adding the colorant to the toner resin in the toner extruder to form the toner mixture. The color of the extrudate is measured, compared to a standard and the amount of colorant added is modified accordingly.  
           [0015]    U.S. Pat. Nos. 5,650,484 and 5,750,909 (Hawkins et al.) disclose apparatus for the preparation of a mixture of toner resin and initiator, to form a toner resin or toner mixture including cross-linked microgel particles is provided. The apparatus includes a toner extruder having the resin being conveyed therethrough and an adder for adding the initiator to the toner resin in the toner extruder to form the toner resin or mixture. The apparatus also includes a measurer for measuring the cross-linked microgel particles in the toner mixture substantially immediately after mixing in the toner extruder and transmitting a signal indicative of the quantity of cross-linked microgel particles in the toner resin or mixture. The apparatus also includes a controller for controlling the addition rate of initiator in response to the signals from the measurer.  
           [0016]    U.S. Pat. No. 5,686,219 (Higuchi) discloses a Toner Extruder Feed Port Insert that overcomes many of the problems associated with the prior art. The insert provides cooling to the extruder feed port, reducing premature melt of the resin. However, toner resin can still melt prematurely, fusing on the crest of a screw element and forming clumps of fused material that can cause material backup.  
         SUMMARY OF THE INVENTION  
         [0017]    In embodiments, a lead in gap is provided at the feed port end of a toner extruder used for the preparation of a toner resin extrudate from a resin. The lead-in gap can collect prematurely melted resin, allowing the screws to carry the melt away with a lower incidence of clumping. Embodiments also provide enhanced cooling capability on one or both of a downwardly traveling screw feed port wall and downstream feed port wall. This extra cooling of the walls reduces adhesion of the fused resin on the cooled surfaces. The greater the temperature difference between the walls and the fused base resin, the less likely the fused base resin will be to adhere on the walls.  
           [0018]    Embodiments can include a housing defining a housing aperture and a resin inlet opening in the housing. The extruder can also include a conveyor for conveying the resin through the housing aperture. The extruder further includes a member adjacent the resin inlet opening for inhibiting the heat transfer from the housing and/or the conveyor to the resin at the opening. The flow of resin adjacent the opening is thus improved.  
           [0019]    In additional embodiments, there is provided a method for preparing a toner resin. The method includes conveying the base resin to an aperture in the housing of a toner extruder, the housing surrounding a conveyor, inhibiting the heat transfer from the extruder to the base resin at the aperture, adding chemical initiator to a toner extruder, mixing the base resin and the chemical initiator within the extruder to form the mixed resin, and conveying the mixed resin within the extruder to an extruding die. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0020]    Embodiments will be described herein with reference to the following Figures in which like reference numerals denote like elements and wherein:  
         [0021]    [0021]FIG. 1 is a schematic perspective view of a toner extruder feed port with a toner extruder feed port insert according to embodiments.  
         [0022]    [0022]FIG. 2 is a schematic elevational view of the toner extruder according to embodiments.  
         [0023]    [0023]FIG. 3 is a schematic elevational view of a toner manufacturing system including a micronization system and the toner extruder of embodiments.  
         [0024]    [0024]FIG. 4 is a schematic perspective view of the toner extruder feed port of FIG. 1.  
         [0025]    [0025]FIG. 5 is a schematic perspective view of a toner extruder feed port insert of FIG. 1.  
         [0026]    [0026]FIG. 6 is a schematic of embodiments with no lead-in gap.  
         [0027]    [0027]FIG. 7 is a schematic of embodiments with no lead-in gap and illustrating backup of prematurely melted resin.  
         [0028]    [0028]FIG. 8 is a schematic of embodiments with a lead-in gap.  
         [0029]    [0029]FIG. 9 is a schematic of embodiments with no lead-in gap and illustrating reduction of backup of prematurely melted resin by the presence of the lead-in gap. 
     
    
     DETAILED DESCRIPTION  
       [0030]    According to embodiments, the toner created by the subject process comprises a resin and preferably a charge control additive and other known additives and, some times, very fine toners for reclaim purpose. The manufacture of black toners will be discussed henceforth. It should be readily apparent that the manufacture of colored toner may likewise include the process of the embodiments described as well as variations within the capabilities of one of skill in the art.  
         [0031]    In a process of an embodiment, polyester resins with associated additives are fed to a melt mixing apparatus. Dispensing and mixing of additives are carried out at high temperature and high shear to produce a toner in extrudate form for the next process.  
         [0032]    Referring first to FIG. 2, a toner preparing apparatus  20  in the form of an extruding system is shown. The toner preparing apparatus  20  include an extruder  22  for mixing prepared resin mix with additives including very fine toner  26  and converting the prepared resin mix into a liquid form having a portion of the toner. Generally, any extruder, such as a single or twin screw extruder, suitable for preparing electrophotographic toners, may be employed for the melt mixing of prepared resin mix  26 . For example, a Werner &amp; Pfleiderer ZSK-58SC extruder is well-suited for melt-mixing the prepared resin mix  26 .  
         [0033]    The prepared resin mix is stored adjacent the extruder  22  in a dry resin feeder hopper  62 . The extruder  22  typically includes a body  28  which defines a centrally located aperture  30  therethrough. A feed and mixing mechanism  36  is located in the aperture  30 . Preferably the feed mechanism is in the form of a screw rotatably located in the aperture  30 . The screw  36  rotates within aperture  30  about its axis. The extruder  22  for simplicity is described with a single screw, but many commercial extruders include twin screws, parallel to each other and closely spaced from each other. As the prepared resin mix is mixed, an extrudate  110  is formed which contains the additives evenly distributed within the raw resin. The screw  36  within the extruder  22  is preferably turned at the predetermined rate which allows the molten resin to achieve the desired melt-mixing and temperatures. The extrudate continues to pass through the extruder  22  to a die plate  120  located at an outlet  122  of the extruder  22 . The die plate  120  includes a large rectangular aperture  124  through which the extrudate  110  exits the extruder  22 . The aperture  124  is chosen of suitable size to provide flow sufficient to provide for a commercially acceptable process.  
         [0034]    The extrudate  110  from the extruder  22  is cooled and squeezed to form a thin, preferably 1 to 2 mm, sheet by a pair of squeeze rolls  126  to form a thin sheet  111 . This thin sheet  111  is further cooled by belt  127 , preferably by double water cooled metal belts, prior to crushing the sheet  111  with a rotary pin breaker  128  or other suitable means.  
         [0035]    After the resin has been cooled and crushed, resin particles are reduced in size by any suitable method including those known in the art. An important property of toners is brittleness which causes the resin to fracture when impacted. This allows rapid particle size reduction in attritors, other media mills, or even jet mills used to make dry toner particles. It should be appreciated that the particle size reduction may possibly include the use of a pulverizer (not shown). The pulverizer may be a hammer mill such as, for example, an Alpine® hammer mill or FitzMill® rotary mill. The hammer reduces the toner particles to a size of about 300 microns to about 3 mm.  
         [0036]    Referring now to FIG. 3, a micronization system  134  is shown in use with the toner preparing apparatus  20  to form a toner manufacturing system  135 . The micronization system  134  serves to reduce the particle size of milled particles or material  130  into toner particles of an appropriate size, such as four to ten microns. The micronization system  134  is connected to the toner preparing apparatus  20  to form a toner manufacturing system  135 .  
         [0037]    As earlier stated, an important property of toners is brittleness, which causes the resin to fracture when impacted. This allows rapid particle size reduction in aerators, other media mills, or even jet mills to make dry toner particles.  
         [0038]    The micronization system  134  includes a micronizer  136  which provides for the rapid particle size reduction of the particles  130  into toner particles. Preferably, the micronizer is a jet-type micronizer such as a jet mill. Jet mills containing a milling section into which water vapor jets or air jets are blown at high speeds and the solid matter to be micronized is brought in across an injector by a propellant. Compressed air or water vapor is usually used as the propellant in this process. The introduction of the solid matter into the injector usually occurs across a feeding hopper or entry chute.  
         [0039]    For example, the micronizer  136  may be a Sturtvant 36 inch jet mill having a feed pressure of about 115 psig and a grinding air pressure of about 120 psig may be used in the preparation of the toner resin particles. The nozzles of this jet mill are arranged around the perimeter of a ring. Feed material is introduced by a pneumatic delivery device and transported to the injector nozzles. The particles collide with one another and are attrited. These particles stay in the grinding zone by centrifugal force until they are small enough to be carried and collected by a cyclone separator. A further size classification may be performed by an air classifier.  
         [0040]    Preferably, however, the micronizer  136  is in the form of an AFG-800 grinder. The AFG-800 grinder is a fluidized air mill made by AFG (Alpine Fliebbertt-Gegenstrahlmuhle). The micronizer  136  includes a feed chamber  138  and a grind chamber  140 . A pipe or tube  142  connects the rotary mill  128  with the feed chamber  138 . The pipe  142  is made of any suitable durable material which is not interactive with the toner composition, such as stainless steel. The milled material  130  are propelled toward the feed chamber  138  by any suitable means such as by augers (not shown) or by blowers (not shown). The milled material  130  accumulated in the feed chamber  138  are extracted from the feed chamber  138  by a screw  144  located in a tube or pipe  146  interconnecting the feed chamber  138  with the grind chamber  140 . The screw  144  and the pipe  146  are made of any suitable durable material which is not chemically interactive with the toner, such as stainless steel. The milled material  130  enter lower portion  150  of the grind chamber  140 .  
         [0041]    A pressurized fluid, preferably in the form of compressed air is added to the grind chamber  140  in a lower central portion  152  of the grind chamber  140 . The compressed air is supplied by any suitable compressed air source  154 , such as an air compressor. Compressed air conduit  156  interconnects the compressed air source with a ring  162  located around the grind chamber  140 . Extending inwardly from the ring  162  are a series of inwardly pointing nozzles (not shown) through which the compressed air enters the grind chamber  140 . The compressed air causes the particles  130  to accelerate rapidly inwardly within the grind chamber  140 .  
         [0042]    In an upper portion  178  of the grind chamber  140  a series of rotating classifier wheels (not shown) set the toner air mixture into rapid rotation. The classifier wheels (not shown) include fins (not shown) along the periphery of the classifier wheels. The wheels cause the larger particles, milled material  130 , to be propelled to inner periphery  184  of the grind chamber  140  and to return to the lower portion  150  of the grind chamber  140 . The milled material  130  impact each other and the components of the micronizer  136  and thereby micronize the toner into micronized toner  188 . The micronized toner  188 , on the other hand, is permitted to move upwardly within the grind chamber  140  into manifold  186 .  
         [0043]    A long connecting pipe  190  is connected on one end thereof to manifold  186  and on the other end thereof to a product cyclone  192 . The long connecting pipe  190  serves to provide a conduit between the grind chamber  140  and the product cyclone  192  for the micronized toner  188 . The long connecting pipe  190  may be of any suitable durable material, such as stainless steel.  
         [0044]    The product cyclone  192  is designed to separate particles from the air stream in which they are carried. The product cyclone  192  may be any suitable commercially available cyclone manufactured for this purpose and may, for example, include a (quad) cyclone which consists of four cyclones combined. Within the product cyclone  192 , the micronized toner  188  circulates in a spinning manner about inner periphery  194  of the cyclone  192 . The larger micronized toner  188  has a greater mass and is thereby propelled to the inner periphery  194  of the cyclone  192 , falling into lower portion  196  of the product cyclone  192 . Air and very small dust particles  200  having a lesser mass and a particle size of, perhaps, less than 1 microns are drawn upwardly through upper opening  202  of the cyclone  192  into dust collector  204 . The micronized toner  188  collects in the lower portion  196  of the cyclone  192  and is extracted therefrom.  
         [0045]    According to the present invention and referring to FIG. 1, a toner extruder feed port insert  210  is shown in position ready for assembly into toner extruder feed port  212 . The toner extruder feed port  212  is in the form of a housing aperture within feed barrel  214  of extruder  22 . The feed barrel  214  represents one section or portion of the body  28  of the extruder  22 . While the invention may be practiced with extruders  22  having only a singular screw  36 , preferably, the extruder  22  includes a twin screws  216  and  220 . The first and second screws  216  and  220 , respectively, are located proximate each other. Preferably, the first screw  216  has a first screw axis  222  which is parallel to second screw axis  224  of the second screw.  
         [0046]    The feed barrel  214  includes a feed barrel body or housing  230  which defines the housing aperture or port  212 . The feed barrel housing  230  includes a lower portion  232  which closely conforms with the screws  216  and  220  as well as an upper portion  234  which includes the central opening or port  212 . The upper portion  234  of the feed barrel housing  230  may have any suitable shape, for example, as shown in FIG. 1, the upper portion  234  has a generally rectangular shape with four vertically extending walls which define the upper portion  234 . These four walls include a downstream wall  236  located in the direction of flow  240  of the extrudate  110 . Opposed to the downstream wall  236  is an upstream wall  242 . Located normal to the walls  236  and  242  are downwardly traveling screw wall  244  and upwardly traveling screw wall  246 .  
         [0047]    In prior art extruders, the entire feed barrel  214  would require removal when converting from conventional toner to polyester based resin toner. This is because the clearance between the screws  216  and  220  and the feed barrel  214  need to be altered or increased at initial meeting clearances when using the polyester based resin.  
         [0048]    Heat from the extruding process propagates from the extrudate  110  to the body  28  of the extruder in a first direction  250  opposite a second direction  252  of flow of the extrudate  110 . Since the heat propagates in the first direction  250 , wall  236  of the feed barrel  214  receives the most heat.  
         [0049]    Furthermore, the intensive melt-mixing utilizes very high shear energy which results into heat. This heat is conducted throughout the screws  36  including the portion of screws  216  and  220  in the feed port  214 . Applicants have found that it is at the downstream wall  236  and side wall  244  where the base resin  24  is most likely to melt and the most of scrapping of melted resin occur and cause damage to the extruder as well as to reduce its productivity and require downtime. The base resin  24  is most likely to melt at crests of the two screws  216  and  220 ; it is at downstream wall  236  and side wall  244  where the melted resin on the crests is scraped and form lumps. These lumps can keep growing and could eventually fill the feed port cavity, causing major machine downtime. Since the second screw  220  rotates in direction of arrow  254 , the base resin  24  is urged between the screw  220  and the downwardly traveling screw wall  244 . Between the downstream wall  236  and the two screws  216  and  220 , the base resin  24  is also likely to melt.  
         [0050]    Referring again to FIG. 1, toner extruder feed port insert  210  is shown. The insert  210  serves three main purposes. The first of these purposes is to isolate the heat from the extrusion process from the base resin  24 . This isolation of the heat of the screws and the extruder from the base resin  24  serves to reduce the likelihood of the base resin melting and the associated problems therewith. The second of these benefits is enhanced cooling of the two vertical walls  264 , which greatly reduces adhesion the melted resin to the cooled surfaces. The melted resin is repelled by the walls and pushed back into the remaining resin, keeping the wall surfaces clear from melted resin. The third purpose of the insert is establishing the greater clearance between the screws  216  and  220  and both walls  264  of the insert  210  that is required for the polyester base resin  24 .  
         [0051]    While the insert  210  may have any suitable shape, preferably the insert  210  includes a top ring or rim  260  which when assembled into the feed barrel  214  rests upon upper face  262  of the feed barrel  214 . Extending downward from the top rim  260  are vertical walls  264  which separate the feed barrel housing  230  from the base resin  24 . It should be appreciated that the invention may be practiced with as few as a single vertical wall  264 , but preferably includes an insert downstream wall  266  as well as an downwardly traveling screw insert wall  270 . Downstream wall  266  and downwardly traveling screw insert wall  270  are included in that they correspond with downstream wall  236  and downwardly traveling screw wall  244  of the feed barrel  214 , respectively. The heat from walls  236  and  244  are thus isolated from the base resin  24  by the walls  266  and  270 .  
         [0052]    Since the insert  210  serves to isolate the heat from the extruder  22  and keep the surfaces of the two vertical walls  264  and the base resin  24  cold, it is preferable that the insert  210  be ineffective in transferring heat from the housing  230  of the feed barrel  214 .  
         [0053]    There are several ways of curing the ineffective heat transfer desired between the insert  210  and the feed barrel  214 . First, a water cooling may be practiced by running a fluid  275  through the walls of the insert  264 . The passage of the fluid  275  is to be a number of conduits  306  drilled throughout both walls  264 . The cooling fluid  275  may be utility water supply, however, circulating chilled water is preferred.  
         [0054]    Furthermore, pads  272  may be placed on outer surface  274  of the walls  270  and  266  to assure the spacing between the walls  266  and  270  and the feed barrel  214 . In fact, these pads may be made of an insulative material to improve the heat insulating properties even further.  
         [0055]    The insert  210  may be made of any suitable durable material which is chemically non-reactive with the base resin  24 . While the invention may be practiced with an insert  210  made of steel or other somewhat conductive material, preferably, the insert  210  is made of an somewhat thermally non-conductive material, such as an insulative material, for example, a ceramic or a carbon graphic material, or a suitable plastic material.  
         [0056]    Referring now to FIG. 4, the feed barrel  214  is shown in greater detail. The first screw  216  as well as the second screw  220  rotate within aperture  30  along axis  222  and  224 , respectively. First screw  216  has a periphery  276  defined by radius R S1 , while second screw  220  has a periphery  278  defined by radius R S2 . The aperture  30  is defined by radius R B1  at the first screw  216  and by radius R B2  at the second screw  220 . Radius R S1  and R S2 , are typically identical and are slightly smaller than radius R B2  and R B1 .  
         [0057]    The walls of the feed barrel  214  have any suitable width capable of withstanding the pressures, temperatures, and other environment factors of the extruder  22  but typically have a thickness T of approximately one inch. The walls of the feed barrel define the housing aperture  212  which has a length L 1  and a width W 1 .  
         [0058]    Referring now to FIG. 5, the insert  210  is shown in greater detail. The insert  210  includes the top rim  260  as well as downwardly traveling screw insert wall  270  and downstream insert wall  266  which extend vertically downward from the top rim  260 . It should be appreciated that a third and fourth wall may be added to the insert and still remain within the scope of the invention. The applicant, however, has found that a third or fourth wall (not shown) are not required for the effective implementation of the invention.  
         [0059]    Referring again to FIG. 5, insert  210  is shown. To accommodate the polyester base resin which has a lower melt temperature than standard resins, the gap between the barrel and the screws need to be increased. This is accomplished with the use of the insert  210 . For the use of the low melt base resin  24 , the distance between at upstream end of the first screw downstream wall bore  280  and the first screw  216  as well as the distance between the second screw downstream wall bore  282  and the second screw  220  is more than the corresponding distance at the downstream end of the bores. Furthermore, the distance between the entering end of the downwardly traveling screw insert wall  284  and the second screw  220  is more than that distance at the other end of the downwardly traveling screw insert wall  284  and the second screw  220 .  
         [0060]    Because of the intense heat of the extruding process, the extruder  22  (see FIG. 2) may generate sufficient heat that when the low melt base resin toner  24  contacts the screws  216  and  220  (see FIG. 4), the base resin  24  may melt even with the use of the insert  210 . The applicant has found by providing surface  284  with clearances between the surface  284  and the screw  220 , which clearance is increased in the direction opposite to the direction of rotation of the screws  36 , the prematurely melted base resin  24  will be conveyed away by the screws  36  and not be scrapped along the periphery  278  of the screw  220 . The applicant has also found that by providing surfaces  280  and  282  with clearances between the surfaces  280  and  282 , and the screws  216  and  220 , which clearances are decreased in the direction of flow of the extrudate  110 , the prematurely melted base resin  24  will be conveyed away by the screws  36  and not be scrapped along the peripheries  276  and  278  of the screws  216  and  220 , respectively.  
         [0061]    Increasing the clearance of the insert  210  to the screws  36  may be accomplished in any suitable way. For example, again referring to FIG. 5, the first screw downstream wall bore  280  may be defined by radius R i1.  The radius R i1  extends from axis  290  of the insert  210 . Axis  290  is parallel and concentric with the axis  222  of the screw  216  when the insert  210  is assembled into the feed barrel  214 . Radius R i1  is slightly larger than radius R S1  of the first screw  216  at first end  292  of bore  280 . The radius R i1  decreases steadily in the direction of material flow  301  such that the radius R i1  at second end  293  of bore  280  is slightly smaller than the radius R i1  at first end  292 , typically 2 to 3 mm.  
         [0062]    Second screw downstream wall bore  282  is defined by radius R i2  which extends from axis  298  of insert  210 . Axis  298  is parallel and concentric with second screw axis  224  of the second screw  220  when the insert  210  is assembled into the feed barrel  214 . The radius R i2  is slightly larger than radius R S2  of the second screw  220  at the entering end  295  of the bore  282 . Radius R i2  decreases steadily in the direction of material flow  301 . At second end  297  of the bore  282 , the radius R i2  is slightly smaller than the radius R i2  at the entering end  295 .  
         [0063]    Downwardly traveling screw insert wall surface  284  is defined by radius R i3  which extends from axis  298  of insert  210 . The radius R i3  increases steadily in size in the direction of arrow  294  which is opposite arrow  296  of the screws  36 . Radius R i3 a t position  300  is slightly larger than radius R S2  of the second screw  220  while radius R i3  at position  302  is significantly larger than radius R S2  of the second screw  22  and slightly larger than radius R i3  at position  302 .  
         [0064]    As seen, for example, in FIG. 5, the cooling feature  304  includes a chamber  306  within the insert  210  is shown. The chamber  306  may be in the form of a conduit. The conduit  306  may be positioned anywhere within the insert, and may, for example, extend around the top rim  260  of the insert  210 . An inlet  310  as well as an outlet  312  are operatively connected to the conduit  306 . A cooling source  314  is connected to the inlet  310  as well as to the outlet  312 . It should be appreciated that the cooling feature  304  may be accomplished by an external conduit (not shown) attached to the insert  210  as well as by an internal conduit within the insert  310 .  
         [0065]    It should be appreciated that the bores  280  and  282  may, like wall surface  284 , have a profile that provides for a decrease in clearance between the screws  36  and the insert  210  in the direction of rotation  296  of the screws  36 .  
         [0066]    The fluid  275  is circulated through the conduit  306  of the cooling feature. The fluid  275  may be air or, preferably, water or ethylene glycol. The cooling source may be tap water or a tank of fluid. The fluid may be propelled through the conduit in any suitable fashion, for example, by a pump (not shown). The cooling feature  304  serves to remove the heat from the insert  210  making it more effective.  
         [0067]    The feed port insert described above isolates the extruder heat from the resin to reduce the melting of resin at the feed port. This reduction of heat of the resin reduces melting of the resin at the feed port insert and the associated problems with melted toner at the feed port. However, even this arrangement can suffer premature melting of the toner resin  24  on the screws, resulting in lump formation.  
         [0068]    As another approach to overcome premature resin melt, referring to FIGS. 8 and 9 in particular, embodiments can include a lead-in gap  300  that accepts prematurely melted resin on the screws. Where the resin might ordinarily accumulate, cool, and form lumps, the lead-in gap smoothes and eventually squeezes the excess material to the sides of the screws to await take-up. In embodiments, the lead-in gap  300  is located near the point at which resin enters the conveyor. While the lead-in gap could be used in conjunction with the insert disclosed above, the combination is not required.  
         [0069]    An advantageous variation of the lead-in gap  300  can be variable in size and shape. For example, the portion of the inner surface of the housing could be movable to allow the gap  300  to grow or shrink as required for particular rates of flow of base resin into the conveyor. A more simple approach could include a slidable section of the housing wall that would slide longitudinally to expose more or less of the lead-in gap  300  as required.  
         [0070]    While the invention has been described with reference to the structures and embodiments disclosed herein, it is not confined to the details set forth, and encompasses such modifications or changes as may come within the purpose of the invention.

Technology Classification (CPC): 1