Abstract:
A die for the preparation of a toner resin in an extruder having a housing defining a housing aperture therein and a conveyor for conveying the resin through the housing aperture to form a stream of resin is provided. The die includes a member connected to a first end of the housing. The member defines an opening therethrough. The member includes a splitter disposed adjacent the opening for splitting a stream of resin passing through the opening in a first direction into two separate streams of resin.

Description:
The present invention relates to a method and apparatus for manufacturing resins and reservoir compounds. More particularly, the invention relates to an apparatus and method for extruding resins and reservoir compounds through a die. 
     Cross reference is made to U.S. application Ser. No. 08/624,780, filed Mar. 27, 1996, entitled &#34;Extruder Die Insert Plate System&#34;, by Joseph L. Leonardo et al. 
     BACKGROUND OF THE INVENTION 
     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. 
     Typically, toner may be produced by melt-mixing the 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. 
     The soft polymer and pigment are melt mixed together typically in an extruder which is part of an extruding system. The soft polymer and pigment are translated and mixed in an auger within a cavity of the extruder. A die plate is located on the exit end of the extruder. A conventional die plate has a round hole to enable the extrusion of high viscosity materials and subsequent processing which includes thinning , cooling and crushing. A conventional strand die plate with small holes would be prone to plugging and would generate extremely high back pressure. This would result in vacuum vent flow and other processing problems that create considerable down time to the extruding machine. 
     Often, the die plate has to be removed from the extruder for off-line cleaning, which is a length and labor intensive activity. To avoid the plugging and time consuming off-line cleaning associated with the die plates with small holes, die plates with much larger holes have been used. 
     When large holes are used for the die plate, a large slab of high viscosity extrudate exits from the extruder. This extrudate must be squeezed and spread by nip rolls. This large high viscosity slab often slips when entering the nip rolls. Subsequent processing of this cross sectional slab is very difficult. 
     The following disclosures may be relevant to various aspects of the present invention: 
     U.S. Pat. No. 5,145,762, Patentee: Grushkin, Issue Date: Sep. 8, 1992. 
     U.S. Pat. No. 4,973,439, Patentee: Chang et al. Issue Date: Nov. 27, 1990. 
     U.S. Pat. No. 4,894,308, Patentee: Mahabadi et al. Issue Date: Jan. 16, 1990. 
     U.S. Pat. No. 3,778,287, Patentee: Stansfield et al. Issue Date: Dec. 11, 1973. 
     U.S. Pat. No. 5,227,460, Patentee: Mahabadi et al. Issue Date: Jul. 13, 1993. 
     U.S. Pat. No. 5,376,494, Patentee: Mahabadi et al. Issue Date: Dec. 27, 1994. 
     U.S. Pat. No. 5,468,586, Patentee: Proper et al. Issue Date: Nov. 21, 1995. 
     U.S. Pat. No. 5,650,484, Patentee: Hawkins et al. Issue Date: Jul. 22, 1997. 
     The relevant portions of the foregoing disclosures may be briefly summarized as follows: 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     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. 
     U.S. Pat. No. 5,650,484 (Hawkins et al.) discloses an 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. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a die for the preparation of a toner resin in an extruder having a housing defining a housing aperture therein and a conveyor for conveying the resin through the housing aperture to form a stream of resin. The die includes a member connected to a first end of the housing. The member defines an opening therethrough. The member includes a splitter disposed adjacent the opening for splitting a stream of resin passing through the opening in a first direction into two separate streams of resin. 
     In accordance with another aspect of the present invention, there is provided a method for preparing a toner resin. The method includes the steps of adding base resin and chemical initiator to a toner extruder, mixing the base resin and the chemical initiator within the extruder to form the mixed resin, conveying the mixed resin within the extruder to splitting die, and drawing the mixed resin through the splitting die to form two separate streams of resin. 
    
    
     IN THE DRAWINGS 
     The invention will be described in detail herein with reference to the following Figures in which like reference numerals denote like elements and wherein: 
     FIG. 1 is a perspective view of a die for a toner extruder according to the present invention; 
     FIG. 2 is a schematic elevational view of the toner extruder according to the present invention; 
     FIG. 3 is a schematic elevational view of a toner manufacturing system including a micronization system and the toner extruder of the present invention; and 
     FIG. 4 is an elevational view of a splitter for the die of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The toner that is typically extruded using the extruder die of this invention includes a resin and preferably a charge control additive and other known additives. 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 present invention. 
     The base resin that is typically extruded using the extruder die of this invention is a polymer with a melt viscosity as measured with a mechanical spectrometer at 10 radians per second is from about 5,000 to about 200,000 poise. Such polymers include reactive polymers, preferably a linear reactive polymers such as, for example, linear unsaturated polyester. For example, the base resin may have a degree of unsaturation of about 0.1 to about 30 mole percent, preferably about 5 to about 25 mole percent. The linear unsaturated polyester base resin is typically characterized by number-average molecular weight (Mn) as measured by gel permeation chromatography (GPC) in the range typically from 1000 to about 20,000, and preferably from about 2000 to about 5000, weight-average molecular weight (Mw) in the range typically from 2000 to about 40,000, and preferably from about 4000 to about 15,000. The molecular weight distribution (Mw/Mn) is in the range typically from about 1.5 to about 6, and preferably from about 2 to about 4. Onset glass transition temperature (Tg) as measured by differential scanning calorimetry (DSC) is in the range typically from 50° C. to about 70° C., and preferably from about 51° C. to about 60° C. Melt viscosity as measured with a mechanical spectrometer at 10 radians per second is from about 5,000 to about 200,000 poise, and preferably from about 20,000 to about 100,000 poise, at 100° C. and drops sharply with increasing temperature to from about 100 to about 5000 poise, and preferably from about 400 to about 2,000 poise, as temperature rises from 100° C. to 130° C. 
     Linear unsaturated polyesters used as the base resin are low molecular weight condensation polymers which may be formed by the stepwise reactions between both saturated and unsaturated diacids (or anhydrides) and dihydric alcohols (glycols or diols). The resulting unsaturated polyesters are reactive (e.g., cross-linkable) on two fronts: (i) unsaturation sites (double bonds) along the polyester chain, and (ii) functional groups such as carboxyl, hydroxy, etc. groups amenable to acid-base reactions. Typical unsaturated polyesters useful for this invention are prepared by melt polycondensation or other polymerization processes using diacids and/or anhydrides and diols. Suitable diacids and anhydrides include but are not limited to saturated diacids and/or anhydrides such as, for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, isophthalic acid, terephthalic acid, hexachloroendomethylene tetrahydrophthalic acid, phthalic anhydride, chlorendic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, endomethylene tetrahydrophthalic anhydride, tetrachlorophthalic anhydride, tetrabromophthalic anhydride, and the like and mixtures thereof; and unsaturated diacids and/or anhydrides such as, for example, maleic acid, fumaric acid, chloromaleic acid, methacrylic acid, acrylic acid, iraconic acid, citraconic acid, mesaconic acid, maleic anhydride, and the like and mixtures thereof. Suitable diols include but are not limited to, for example propylene glycol, ethylene glycol, diethylene glycol, neopentyl glycol, dipropylene glycol, dibromoneopentyl glycol, propoxylated bisphenoI-A, 2,2,4-trimethylpentane-1,3-diol, tetrabromo bisphenol dipropoxy ether, 1,4-butanediol, and the like and mixtures thereof, soluble in good solvents such as, for example, tetrahydrofuran, toluene and the like. 
     Preferred linear unsaturated polyester base resins are prepared from diacids and/or anhydrides such as, for example maleic anhydride, fumaric acid, and the like and mixtures thereof, and diols such as, for example, propoxylated bisphenoI-A, propylene glycol, and the like and mixtures thereof. A particularly preferred polyester is poly(propoxylated bisphenol A fumarate). 
     Substantially any suitable unsaturated polyester can be used in the process of the invention, including unsaturated polyesters known for use in toner resins and including unsaturated polyesters whose properties previously made them undesirable or unsuitable for use as toner resins (but which adverse properties are eliminated or reduced by cross-linking them. 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 recently in U.S. Pat. No. 5,227,460. 
     The high density cross-linked microgel particle toner resins may be made by a process that includes a reactive melt mixing process. Such a method of manufacturing that toner and its resin was disclosed in U.S. Pat. No. 5,376,494. 
     Referring first to FIG. 2, a toner preparing apparatus 20 in the form of an extruding system is shown. The toner preparing apparatus 20 includes an extruder 22 for mixing chemical initiator 24 with dry resin 26 and for converting the dry resin 24 into a liquid form having a portion of the toner in gel form. Generally, any extruder, such as a single or twin screw extruder, suitable for preparing electrophotographic toners, may be employed for mixing the chemical initiator 24 with the resin 26. For example, a Werner &amp; Pfleiderer WP-28 extruder is well-suited for melt-blending the resin 26, a chemical initiator 24, and additives. The resin 26 is stored adjacent the extruder 22 in a dry toner resin feeder hopper 62. The resin 26 is uniformly fed from the hopper 62 by an auger 64 to a resin hopper outlet 66. The resin hopper outlet 66 is located adjacent a extruder resin inlet 70 into which the resin 26 is deposited.. After the resin 26 is added to the extruder 22, the chemical initiator 24 is added to the extruder 22. The chemical initiator may be wet or dry. The use of dry initiator will be described herein, but it should be appreciated that the chemical initiator may likewise be in liquid form. 
     The chemical initiator 24 may be any suitable chemical capable of assisting the conversion of an unsaturated toner resin into a partially saturated toner resin. The percentage of conversion preferred may very widely from approximately 40 percent for black toners to approximately 5-7 percent for colored toners. An organic peroxide has been found to be effective in assisting such a conversion from unsaturated toner resin to partially saturated toner resin. The organic peroxide for example may be a benzoyl peroxide. 
     The chemical initiator 24 is stored adjacent the extruder 22 in a chemical initiator feeder hopper 72. The chemical initiator 24 is uniformly fed from the hopper 72 by a valve 74 to a chemical initiator inlet 86. 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. The chemical initiator outlet 86 is located adjacent the extruder resin inlet 70 into which the chemical initiator 24 is deposited. As the chemical initiator 24 is mixed with resin 26, an extrudate 110 is formed which contains the chemical initiator 24 evenly reacted with the resin 26. The screw 36 within the extruder 22 is preferably turned at the fastest rate which allows the molten resin to achieve the desired 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. At the die plate 120, the temperature is raised from approximately 110° C. to above 200° C. temperature to obtain a temperature which thins the extrudate and causes it to flow freely through the aperture 124. The pressure in the preceding mixing zone can be increased by restricting the size of the aperture 124, at the expense of throughput. The aperture 124 is chosen of suitable size to provide flow sufficient to provide for a commercially acceptable process. 
     The extrudate 110 from the extruder 22 is fed between a pair of rolls 126. The rolls 126 are preferably chilled by any suitable means such as by circulating water. The rolls 126 widen, thin and cool the extrudate 110 into a partially cooled extrudate 111. The partially cooled extrudate 111 is fed into a further cooling system represented by a cooling belt 127. At the belt 127, the now brittle extrudate 111 is broken into granules by a cutting machine such a Fitz® mill 128. 
     After the resin has been extruded, the resin mixture is 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. The hammer reduces the toner particles to a size of about 100 microns to about 300 microns. Applicants have found that the invention may be practiced without the use of the hammer mill. 
     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 the pellets 130 into toner particles of an appropriate size, such as four to eight microns. The micronization system 134 is connected to the toner preparing apparatus 20 to form a toner manufacturing system 135. 
     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. 
     The micronization system 134 includes a micronizer 136 which provides for the rapid particle size reduction of the pellets 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. 
     For example, the micronizer 136 may be a Sturtevant 15 inch jet mill having a feed pressure of about 114 psi and a grinding pressure of about 119 psi 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 nozzle. 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 out and collected by a cyclone separator. A further size classification may be performed by an air classifier. 
     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 cutter 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 pellets 130 are propelled toward the feed chamber 138 by any suitable means such as by augers (not shown) or by blowers (not shown). The pellets 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 pellets 130 enter lower portion 150 of the grind chamber 140. 
     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 pellets 130 to accelerate rapidly upwardly within the grind chamber 140. 
     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, pellets 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 pellets 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. 
     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. 
     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. 
     According to the present invention and referring now to FIG. 1, the die plate 120 is shown in greater detail. The die plate 120 is secured to end 210 of the body 28 of the extruder 22. The die plate 120 is located such that the die plate 120 covers the aperture 30 of the body 28 of the extruder 22. A first face 212 of the die plate 120 is secured to the body 28 by any appropriate means, for example, by welding or by fasteners. Preferably, the die plate 120 is secured to the body through the use of fasteners, for example, by socket head cap screws 214 as shown. 
     The die plate 120 may be made of integral construction but, preferably, the die plate 120 is an assembly of several components to ease manufacturing and to permit customizing of the configuration of the die plate as well as to repair and replace worn components. 
     The die plate 120 preferably includes a body 216 which is secured to end 210 of the body 28 of the extruder 22 by cap screws 214 fitted into body holes 220 in the body 216. First face 212 of body 216 is preferably located normal to axis 38 of screw 36 of the extruder 22. First face 212 is further centrally located about axis 38. The body 216 defines opening 122 of the die plate 120. The opening 122 is elongated in a second direction 222 which is normal to axis 38 of the screw 36 of the extruder 32. The opening 122 preferably has a length A in the second direction 222 which is approximately four to ten times as great as height B in third direction 224. Ends 226 of the opening 122 preferably have an arcuate shape, for example, the ends 226 may be defined by radius R 1  which is approximately equal to one half the height B of the opening 122. 
     While the invention may be practiced with an opening 122 of uniform cross section, preferably, the extruder 22 includes insert 230 which serves somewhat as a nozzle to guide the extrudate 110. The insert 230 is secured to the body 216 by any suitable means, for example, by fasteners such as stainless flat head screws 232. It should be appreciated, however, that the insert 230 may be welded or glued to the body 216 or the insert 230 may be made integral to the body 216. 
     According to the present invention, a splitter 240 is located adjacent the opening 122 of the die plate 120. While the invention may be practiced with solitary splitter 240, preferably, a plurality of splitters 240 are used to divide the extrudate 110 into a plurality of streams 244 of extrudate. The splitters 240 may have any suitable shape but preferably have a dimension in second direction 222 which is relatively small in order that the stream of extrudate 110 can be easily divided into streams 244. For example, the splitter 240 may be a blade or similar shape with a width substantially smaller than its length. For example, referring again to FIG. 1, the splitter 240 may be in the shape of a pin. The pin 240 has a diameter D substantially smaller than the height B of the opening 122. The pin 240 may have a straight configuration or, as shown in FIG. 1, be U-shaped with a first pin portion 250 located upstream of a second pin portion 252. The first and second pin portions 250 and 252, respectively, assist in the assembly and disassembly of the pin into the die plate 120 as well as to assist in guiding the extrudate 110 into the streams 244 of resin. 
     While the invention may be practiced with a solitary splitter 240, preferably, the die plate 120 includes a plurality of splitters 240 which preferably are equally spaced in the second direction 222. For example, as shown in FIG. 1, five splitters 240 are equally spaced a distance L from each other. 
     The body 216 is preferably made of any suitable durable material with sufficient strength to withstand the high pressures and temperatures of the extruder 22 as well as of a material non-chemically reactive with the extrudate 110 as well. For example, the body 216 may be made of stainless steel. 
     The splitter pin 240 may be made of any suitable durable material capable of withstanding the pressures and elevated temperatures of the extruder 22 as well as being chemically inert to the extrudate 110. For example, the splitter 240 may be made of stainless steel. 
     Referring now to FIG. 4, the splitter 240 is shown in greater detail. The splitter 240 includes the first pin portion 250 which has a length L 1  which is substantially shorter than length L 2  of second pin portion 252. First and second pin portions 250 and 252 are parallel and spaced apart being interconnected by loop portion 254 interconnecting the first and second pin portions 250 and 252. The loop portion 254 is defined by radius R 2 . 
     The pin 240 is shown assembled into body 216. First pin portion 250 of the splitter pin 240 is slidably fitted into body pin opening 260 of the body 216 while second pin portion 252 is slidably fitted into insert pin opening 262 of the insert 230. The splitter pin 240 is installed from above the die plate 120 with the splitter pin 240 located in upper portion 264 of the body 216 of the die plate 120. First pin portion 250 is engaged in body pin opening 260 both above and below the opening 122 of the body 216. The first pin portion 250 is engaged a distance P below the opening 122 to properly secure the pin in the opening 122. 
     Insert 230 is shown located in position on the body 216. The insert 230 includes a wedge shaped portion 270 and a mounting portion 272. The wedge shaped portion 270 is located within opening 122 while the mounting portion 272 is located on the body 216 and includes openings 274 to which screws 276 are slidably fitted for securing the insert 230 to the body 216. It should be appreciated that the insert 230 may be secured to the body 216 in any suitable manner or may be integrally made therewith. 
     The wedge shaped portion may have any suitable shape which results in a reduction in the cross sectional area of the opening 122 in the direction of arrow 278. The shape of the wedge shaped portion 270 is preferably empirically determined based upon obtaining the proper flow of the streams 244. It has been found that a shape of the wedge shaped portion 270 with a triangular cross section is acceptable. For example, the wedge shaped portion 270 may include a thickness T 1  of a few millimeters near the first face 212 of the body 216 and a thickness T 2  near the splitter pin 240 which thickness T 2  is approximately half the thickness B of the opening 122. The use of the insert 230 serves to permit the flow of extrudate 110 through the die plate 120 with less back pressure than a smaller opening with a uniform cross section. 
     The use of an extruder with a die plate having a splitter provides for a plurality of streams which are spaced apart from each other and would have a smaller cross section than the original stream. The smaller streams of extrudate from the splitter provide for a stream of extrudate which may be more easily compressed through rolls than a single stream of extrudate. The use of the splitter permits each stream of extrudate to have an open end which may permit the widening of the stream of extrudate more easily than one large stream of extrudate. 
     The use of a splitter with a small width permits the for the splitting of the extrudate without a significant increase in the pressure within the extruder. 
     The use of a splitter with a circular cross section permits the use of a small pin with minimal back pressure at maximum strength. 
     The use of a splitter pin with a U-shape provides for a primary and secondary splitting of the stream which prevents the reforming of a solitary stream of extrudate, while minimizing the back pressure within the extruder. 
     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.