Abstract:
An apparatus for forming a parison is described. The apparatus has a mandrel housing. The housing has an axially aligned hollow mandrel channel therein and a side channel substantially transverse to the mandrel channel. A mandrel is also provided. The mandrel has an axially oriented notch in an exterior surface. The notch is in fluid communication with two fluid channels that extend continuously downwardly around the mandrel to meet one another on an opposite side of the mandrel from the notch. When the mandrel is installed within the mandrel channel, a first radial gap and a second radial gap, both between the mandrel and the mandrel housing, are formed.

Description:
RELATED APPLICATIONS 
   This application claims the benefit, under 35 U.S.C. 119(e), of U.S. patent application Ser. No. 60/878,593, filed on Jan. 3, 2007 under 35 U.S.C. 111 (b), which is incorporated in its entirety by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to a method and apparatus for forming a parison. 
   BACKGROUND OF THE INVENTION 
   Current or standard practice for making a composite stream is that each material is given its own separate channel for polymer flow all the way through to a point just before the exit of material from the head. One departure of the device disclosed herein from the prior art is that the composite stream is fully formed before the material even enters the head. The designed channels described below then ensure that the fully formed composite stream is then distributed around the head to form the parison. 
   SUMMARY OF THE INVENTION 
   An assembly for forming a parison has at least a mandrel housing and a mandrel. The mandrel housing has an axially aligned hollow mandrel channel therein and a side channel substantially transverse to the mandrel channel. The mandrel has an axially oriented notch in an exterior surface. The notch is in fluid communication with two fluid channels that extend continuously downwardly around the mandrel to meet one another on an opposite side of the mandrel from the notch. Each of the fluid channels has at least one flow restrictor forming a sloped transition from the fluid channels to the exterior surface of the mandrel. When the mandrel is installed within the mandrel channel, a first radial gap and a second radial gap, both between the mandrel and the mandrel housing, are formed. The first radial gap is less than the second radial gap. The first radial gap being on the side of the notch and the second gap being opposite the notch. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic perspective view of an assembly of components for forming a parison; 
       FIG. 2  is another schematic perspective view of the assembly of  FIG. 1  from another angle; 
       FIG. 3  is a schematic plan view of an alternative arrangement of extruders and feed adapators; 
       FIG. 4  is a schematic side view of a portion of  FIG. 3 ; 
       FIG. 5  depicts various perspective, top, side, bottom and internal views of a component of  FIG. 1 ; 
       FIG. 6  depicts various perspective, top, side, bottom and internal views of another component of  FIG. 1 ; 
       FIG. 7  depicts a schematic, cut-away side view of an assembly of certain components of the present invention; and 
       FIG. 8  depicts a schematic plan view of an alternative arrangement of extruders, feed blocks, melt pipes and extrusion heads. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   It is to be understood that the device described herein may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. 
   Referring now to  FIGS. 1 and 2 , melt pipes  10  are shown connected to a feed block  12 .  FIGS. 1 and 2  depict three melt pipes  10 , arranged in a substantially horizontal plane, that are connected to the feed block  12  at one end. The opposite end of each melt pipe  10  is connected to an extruder (not shown in  FIGS. 1 and 2 ). 
   Additional extruders as well as feed adaptors are permissible. For example,  FIG. 3  schematically depicts a first and a second extruder  14 ,  16  connected by first and second melt pipes  18 ,  20 , respectively, to a first feed block  22 . A third and a fourth extruder  24 ,  26  are connected by third and fourth melt pipes  28 ,  30 , respectively, to a second feed block  32 . The feed blocks are connected to an accumulator head  34 , or mandrel housing, described in more detail below. 
     FIG. 4  depicts a portion of  FIG. 3  in that only the first and second extruders  14 ,  16  and the first and second melt pipes  18 ,  20  are depicted feeding the feed first block  22 .  FIG. 4  demonstrates that the extruders, as well as the melt pipes, need not be in the same substantially horizontal plane. 
   As known by those skilled in the art, polymeric melt streams from the extruder flow through the melt pipes to the feed block. Referring now back to  FIGS. 1 and 2 , the feed block  12  assembles the melt streams from each melt pipe  10  into a composite stream. Feed blocks  12  and methods of assembly, such as depicted and described in U.S. Pat. Nos. 3,557,265 and 3,884,606, whose disclosures are incorporated by reference, can be used. The feed block  12  can be heated by heater lines  36 , as shown in  FIGS. 1 and 2 . 
   The melt streams can be diverse. By diverse it is meant one stream can comprise a matrix material, another stream can comprise an adhesive, another stream can be a compatibilizer and another stream can be a functional polymeric material. While exemplary streams are discussed above, the present invention is not limited to these types of streams. The resulting composite stream can consist of anywhere from 2 layers and 2 different materials up to 100 layers and 10 dissimilar materials. 
   The composite stream is preferably comprised of primarily a thermoplastic material, which makes up the majority percentage of the final composite stream. The simplest structure is one material and two layers. The two layers are obviously compatible since they are the same material but the two layers are differentiated by color or regrind content or similar difference. In the case of two layers and two materials the materials must be compatible in order to stick to each other, e.g. they must be from the same polymeric family. An example may be such as a layer of HDPE and a layer of LDPE. The materials are compatible hence they do not require an adhesive or compatibilizing layer. 
   When combining two dissimilar polymers, an adhesive or compatibilizer is required, necessitating the use of a third layer. A compatibilizer is a thermoplastic that ties two other thermoplastics together by a reactive (covalent or dipole-dipole) bond or a non-reactive means (chain entanglement) means. 
   All materials from the family of polyolefins suitable for a defined blow molding operation can be used in this invention. The polyolefins category may comprise polyethylene and polypropylene. 
   The present method and apparatus can also be used with barrier resins. A barrier resin is a thermoplastic material that has a low gas and/or water vapor transmission rate and a high barrier to odorants and essential flavorant oils. 
   As an example, one embodiment may comprise a five layer structure 
                                               Location in the final product   Material   Percentage                           Outside Layer   HDPE   20-69%           Compatibilizer   Mitsui Admer   1.5%           Barrier Layer   EVOH     3%           Compatibilizer   Mitsui Admer   1.5%           Inside Layer   HDPE   Minimum  25%                        
Another example may comprise the following structure:
 
                                               Location in the final product   Material   Percentage                           Outside Layer   HDPE      20-69%           Regrind   Regrind   30%-60%           Compatibilizer   Mitsui Admer   1.5%           Barrier Layer   EVOH     3%           Compatibilizer   Mitsui Admer   1.5%           Inside Layer   HDPE   Minimum  25%                        
Another example comprises the following structure:
 
   
     
       
             
             
             
           
         
             
                 
                 
             
             
                 
               Location in the final product 
               Material 
             
             
                 
                 
             
           
           
             
                 
               Matrix Polymer Layer 
               HDPE 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Barrier Layer 
               EVOH 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Matrix Polymer Layer 
               HDPE 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Barrier Layer 
               EVOH 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Matrix Polymer Layer 
               HDPE 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Barrier Layer 
               EVOH 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Matrix Polymer Layer 
               HDPE 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Barrier Layer 
               EVOH 
             
             
                 
               Compatibilizer 
               Mitsui Admer 
             
             
                 
               Matrix Polymer Layer 
               HDPE 
             
             
                 
                 
             
           
        
       
     
   
   With continued reference to  FIGS. 1 and 2 , the feed block  12  is attached to a transfer pipe  38  which compresses and shapes the composite stream. The transfer pipe  38  has a substantially polygonal entrance that is relatively thin and wide. The entrance leads to a substantially polygonal channel that gradually tapers down to an exit that has a shape that is slightly taller and thicker than the entrance. Heat, through a heater line  36 , may be added to the transfer pipe  38 . 
   Optionally, an interfacial surface generator, such as the devices described in U.S. Pat. Nos. 5,202,074, 5,380,479, 5,540,878 and 5,628,950, which are incorporated by reference, may be located anywhere after the feed block  12  but preferably before the entrance of the mandrel housing (described in more detail below). The generator acts as a layer multiplier, as know by those skilled in the art. 
   Attached to the outlet of the transfer pipe  38  is a flow insert  40 , as seen in  FIGS. 1 and 2 . The flow insert  40  has a tube  42  with a substantially circular exterior  44  and a hollow interior in the shape of a substantially polygonal channel  46 . The tube  42  terminates in a concave end wall  48 . The composite stream flows through the substantially polygonal channel  46 . 
   The flow insert  40  is attached to a mandrel housing  50  which is best seen in  FIG. 5 . The mandrel housing  50  has a side channel  52  for receiving the tube  42  from the flow insert  40 . The side channel  52  is substantially circular to accommodate the tube  42 . The side channel  52  extends substantially horizontally into a mandrel channel  54  within the mandrel housing  50 . The mandrel channel  54  extends substantially transverse to the side channel  52 . 
   The mandrel channel  54  has an upper portion  56  and a lower portion  58 . The upper portion  56  has a substantially constant inner diameter. The lower portion  58  may have any number of sections. 
   A tubular mandrel  66 , such as depicted in  FIG. 6 , is located within the mandrel housing  50 . The mandrel  66  has a first portion  68  with a plurality of threads. The threads can be engaged with a system for blowing air through the mandrel  66 , as known by those skilled in the art. 
   Beneath the first portion  68 , a substantially cylindrical second portion  70  is provided. A notch  72 , having a complementary shape to the tube  42  of the flow insert  40 , is provided in the second portion  70 . Two channels  74  in the mandrel  66  connect to the notch  72 . The channels  74  extend downwardly and around the mandrel  66  until they meet approximately 180 degrees from the notch  72 . The channels  74  are defined by flow restrictors  76 . The flow restrictors  76  preferably have a sloped surface. 
   Connected below the second portion  70  may be any number of sections having any number of shapes. 
   While the figures depict the tube  42  of the flow insert  40  being substantially perpendicular to the mandrel channel  54 , other orientations are possible. For example, the flow insert  40  can be at almost any angle with respect to the mandrel channel  54 . 
   As shown in  FIG. 7 , when the mandrel  66  is located within the mandrel channel  54 , the notch  72  of the mandrel  66  is aligned with the tube  42  of flow insert  40 . Additionally, when the mandrel  66  is located in the mandrel channel  54 , a first gap  88 , located between a first portion  90  of the mandrel  66  and a first portion  92  of the housing  50 , is less than a second gap  94 , located between a second portion  96  of the mandrel  66  and a second portion  98  of the housing  50 . The first gap  88  is preferably on the same side as the notch  72  in the mandrel  66 . The second gap  94  of is preferably located approximately 180 degrees from the notch  72 . The circumferential gap between the mandrel  66  and the mandrel channel  54  is a smooth transition from the minimum at the first gap  88  to the maximum at the second gap  94 . 
   The composite stream flows through the insert  40  into the side channel  52  of the mandrel housing  52 . The composite stream flows into the notch  72  of the mandrel  66 . The notch  72  re-directs the composite stream approximately 90 degrees from its original direction. The composite stream then begins to follow the channels  74  downwardly along the mandrel  66 . The sloped surfaces of the flow restrictors  76 , as well as a pressure gradient (described below), assist in maintaining the integrity of the layered nature of the composite stream fully around the mandrel  66 . 
   The pressure gradient results from the composite stream entering the mandrel channel  54  and encountering the flow restrictors  76 , as well as the first gap  88  and the second gap  94 . The smaller clearance of the first gap  88  results in a localized high pressure area in the first gap  88 . The larger clearance of the second gap  94  results in a lower pressure in the second gap  94 , as compared to the pressure in gap  88 . The higher pressure in the first gap  88  urges the composite stream to flow toward the lower pressure in the second gap  94 . The pressure gradient achieved is a function of many factors including, but not limited to, the make-up of the composite stream, the viscosity of the material, the input and output rate of the composite stream into and out of the mandrel housing and/or the temperature of the composite stream. 
   The composite stream then preferentially fills the space above (upstream of) the first gap  88 . The composite stream then flows downwardly producing an annular tube called a parison, as known by those skilled in the art. The parison is formed with the distinct layers of the composite stream still substantially intact. The parison can then be molded into a useful article such as a container. The container can be of any configuration achievable with known blow molding technology. 
   It is within the scope of the present invention to use the above-described method and apparatus with typical secondary operations for the blow molding process such as parison programming, blowing through a blow pin and blowing through a needle. As known by those skilled in the art, blow pin technology allows the blow air to enter the parison from the top or bottom between the mold halves and blow needle technology allows the blow air to enter the parison by puncturing the parison from the side. 
   The methods and apparatus described herein can also be applied to other plastics processes such as sheet extrusion and thermoforming, compression molding, blown film extrusion and injection molding. 
   Blow molding is mentioned above. Blow molding can be defined as the extrusion of a substantially circular parison of melted material followed by the capture of the parison between two cooled mold halves and the subsequent blowing, with air or other gas, of the plastic parison within the mold, forming the final part. Within the category of blow molding there are a number of commercially available machines that are characterized by the method used to extrude the parison. These different blow molding machines form sub-categories such as continuous extrusion, reciprocating screw extrusion, accumulator head, injection blow and stretch blow. 
   As known by those skilled in the art, continuous extrusion can be characterized by the continuous extrusion of the parison. Reciprocating screw extrusion can be characterized by the extrusion of a polymer into a chamber inside the extruder. The melted polymer is then injected into the blow mold head. Accumulator head can be characterized by the extrusion of a polymer into a chamber inside the blow mold head. The melted polymer is then injected into the parison by means of an annular ram pushing down. Injection blow can be characterized by the extrusion of a polymer into a chamber inside the extruder. The melted polymer is then injected into a cavity making a “pre-form” which is then quickly transferred to another station and blown into a useful part. Stretch blow can be characterized by the injection of a pre-form. The pre-form is then re-heated and then blown into a useful part. 
   The method and apparatus described above can also comprise the device depicted in  FIG. 8 .  FIG. 8  depicts multiple extruders  100 ,  102 ,  104  connected to a feed block  106  with multiple melt pipes  108 ,  110 ,  112 . The melt pipes all feed into a single mold or feed block. The mold block may be connected to multiple extrusion heads  114 ,  116 ,  118 ,  120 , each which function as the single extrusion head described above. 
   In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.