Patent Publication Number: US-2023140576-A1

Title: Component for a nozzle of an injection molding apparatus as well as corresponding nozzle and injection molding apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT International Application No. PCT/IB2021/051726 filed on Mar. 2, 2021, which application claims priority to Italian Patent Application No. 102020000004351 filed on Mar. 2, 2020, the entire disclosures of which are expressly incorporated herein by reference. 
    
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND 
     Field of the Invention 
     The present invention relates to the field of molding plastic containers, for example for making bottle preforms or laboratory test tubes. 
     In particular, the invention relates to a component of a nozzle for an injection apparatus, or molding apparatus, a nozzle comprising such a component, and an injection apparatus comprising such a nozzle. 
     Background Art 
     Processes for molding plastic containers provide for a given amount of molten plastic to be injected into a molding cavity in which the plastic solidifies. 
     The apparatuses for molding preforms comprise one or more nozzles. Each nozzle is associated with a respective molding cavity and a respective shutter. 
     The nozzle serves to inject the molten plastic into the respective molding cavity, and the shutter serves to dose the amount of plastic to be injected. 
     The shutter can indeed slide along an axis in order to open and close the opening, also called inlet point, of the molding cavity. 
     It is important for the shutter to always be aligned with the opening of the molding cavity and therefore it must be suitably guided. 
     The known nozzles provide for the shutter to be guided by a guiding zone at the end portion of the nozzle, which is the portion closest to the inlet point of the molten plastic into the molding cavity. 
     Therefore, when the shutter is in closed position, the guiding zone is also very close to the tip of the shutter. 
     The guiding zone is hot and is in contact with the shutter. Therefore, the tip of the shutter is heated by the guiding zone. 
     This aspect is disadvantageous. Indeed, the heating of the tip of the shutter results in a longer time to allow the plastic to solidify in the molding cavity, in particular at the injection zone. 
     A further disadvantageous aspect of the known molding apparatuses is due to the resistance to the movement of the shutter towards the injection point. The resistance is applied by the molten plastic, in particular by the molten plastic in the guiding zone of the known nozzles. Therefore, there disadvantageously is a need for a significant force to bring the shutter to the closed position. 
     The need is therefore felt for a better nozzle with respect to the prior art. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to make a component of a nozzle and a nozzle capable of effectively guiding the sliding of the shutter and which allows less heat to be transferred to the tip of the shutter with respect to the prior art. 
     It is another object of the present invention to reduce the force required to bring the shutter to the closed position. 
     It is another object of the present invention to avoid or minimize the formation of defects of the molded container. 
     The present invention achieves at least one of such objects, and other objects which will be apparent in light of the present description, by means of a component of a nozzle for injecting molten plastic into a molding cavity of a container, in particular of a test tube or a bottle preform, 
     the component comprising a first body in which a shutter can slide along an axis; 
     wherein the first body defines an end portion of the nozzle and is provided with an opening from which the molten plastic can leave the nozzle, in particular to then enter the molding cavity; 
     wherein the first body has a wall which extends about said axis, 
     wherein said wall is provided with an inner surface having a first zone which is distal from the opening and is adapted to guide the sliding of the shutter along said axis, and a second zone which is proximal to the opening, which delimits a first stretch of a channel for the molten plastic and which delimits said opening; 
     wherein said first body is provided with at least one through hole which crosses said wall transversely to the axis, and which allows the molten plastic to pass through, in particular to enter, said first stretch of the channel; 
     the component comprising a second body which delimits a second stretch of the channel which is distal from the opening; the first body being inserted in the second body so that the molten plastic can pass from the second stretch to the first stretch, passing through said at least one through hole;
         wherein said first zone has a first diameter and said second zone has a second diameter which is greater than the first diameter, or   wherein said second diameter is greater than or equal to the first diameter and the first body is made of a material having a lower thermal conductivity with respect to the material with which the second body is made.       

     The aforesaid component is also called nozzle insert or nozzle tip. 
     The component in particular is an insert. 
     The invention also relates to a nozzle, in particular according to claim  14 ,  15  or  16 . 
     The invention also relates to an injection apparatus, or molding apparatus, in particular according to claim  17 ,  18 ,  19  or  20 . 
     Advantageously, the first zone allows the sliding of the shutter to be guided and to be kept aligned, i.e. centered, with respect to the opening (or injection point) of the molding cavity, in particular during all the steps of the molding process. The diameter of the first zone has a tolerance for obtaining an accurate sliding coupling with the shutter. 
     The first body allows the wear of other components of the molding apparatus to be reduced, in particular the wear of the component which delimits the molding cavity, more specifically the wear of the zone which delimits the injection point, because the shutter is guided by the first zone. 
     Advantageously, the first zone of the first body can guide the shutter both when passing from the closed position to the open position and when passing from the open position to the closed position. 
     In other words, during all the molding steps, the shutter advantageously always remains guided by the first body  1 , in particular by the first zone. 
     The second zone is adapted to be proximal to the molding cavity and the first zone is adapted to be distal from the molding cavity. 
     In this manner, when the shutter is in closed position, the guiding zone (i.e. the first zone) is advantageously far enough from the tip of the shutter, whereby the tip of the shutter is not heated by the heat transmitted from the guiding zone to the shutter, or in any case it is heated much less with respect to the known nozzles. 
     This contrivance allows an improved cooling of the end portion, in particular of the tip, of the shutter during the closing step of the injection point. The time for the plastic in the molding cavity to solidify therefore is reduced and any defects associated with too high a temperature of the tip of the shutter are reduced. 
     In a first variant of the invention, the first body is made of a material having a low thermal conductivity, for example made of steel or titanium alloy or ceramic material, in order to further reduce the heat transmission from the first body to the shutter. In particular, the material of the first body has a lower thermal conductivity than the thermal conductivity of the material of the second body. In this manner, in particular, the second body can transmit heat (provided by heating means) to the molten plastic therein, while the transmission of heat from the first body to the shutter is significantly reduced. In this first variant, the second zone of the first body can have a diameter which is greater than or equal to the diameter of the first zone of said first body. 
     Moreover, it is preferable for the first body to be made of a material which is particularly resistant to wear, in particular having an adequate hardness, such as for example the aforesaid materials. Therefore, it is preferable for the material of the first body to have greater hardness with respect to the material of the second body. 
     Instead, in a second variant of the invention, the second zone of the first body has a greater diameter than the diameter of the first zone, and there is no need to provide materials with different thermal conductivity for the first and second body, respectively. 
     The second zone of the first body has a greater diameter than the outer diameter of the shutter, in particular of the end portion of the shutter. 
     Therefore, advantageously the second zone and the shutter substantially are not in contact with each other, and therefore substantially the second zone does not transmit heat to the shutter. 
     Moreover, the molten plastic can advantageously flow in the annular space between the shutter and the second zone, in particular when the shutter is in the closed position and in the passing from the open position to the closed position. 
     This aspect is advantageous because the molten plastic can flow in a direction away from the molding cavity and possibly pass through the at least one through hole to return in the stretch of channel delimited by the second body of the component. 
     Therefore, the force required to bring the shutter from the open position to the closed position advantageously is reduced. 
     Advantageously the through hole, or the through holes, of the first body also act as filter, thus avoiding contaminants of a given dimension to be incorporated in the molded product. Moreover, since they are obtained in the side wall of the first body, the through holes allow a cleansing action of the end portion of the shutter, removing the possible residual material of the preceding molding operation and decreasing the shadow effect on the tip of the shutter. 
     Preferably, the first stretch and the second stretch of the channel are coaxial to each other and the shutter can slide in the second stretch of the channel. 
     The first body is inserted in the second body, in particular so that the molten plastic can pass from the second stretch to the first stretch of the channel, passing through said at least one through hole. In particular, the first body is inserted in the second body so that said first zone and said at least one through hole are inside said second stretch of the channel. 
     Preferably, the first body and the second body of the component of the invention are coaxial to each other. 
     Further features and advantages of the invention will become more apparent in light of the detailed description of non-exclusive, exemplary embodiments. 
     The dependent claims describe particular embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the description of the invention, reference is made to the accompanying drawings, which are provided by way of non-limiting example, in which: 
         FIG.  1    shows a perspective view of a nozzle according to the invention; 
         FIG.  2    shows a top plan view of a part of the nozzle in  FIG.  1   ; 
         FIG.  3    shows a perspective view of the part in  FIG.  2   ; 
         FIG.  4    shows a cross-section view of the part in  FIG.  2   ; 
         FIG.  5    shows an exploded perspective view of the component of a nozzle according to the invention; 
         FIG.  6    shows the components in  FIG.  5   , assembled to one another; 
         FIG.  7    shows a sectional view of the nozzle in  FIG.  1    and of part of other components of an injection apparatus according to the invention, in a first configuration; 
         FIG.  8    shows an enlarged detail of  FIG.  7   ; 
         FIG.  9    shows an enlarged detail of  FIG.  8   ; 
         FIG.  10    shows a sectional view of the nozzle in  FIG.  1    and of part of other components of an injection apparatus according to the invention, in a second configuration; 
         FIG.  11    shows an enlarged detail of  FIG.  10   . 
     
    
    
     The same elements, or functionally equivalent elements, have the same reference numeral. 
     DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION 
     With reference to the drawings, exemplary embodiments of a component  5  of a nozzle (see in particular  FIGS.  1 ,  5  and  6   ), of a nozzle  100  and of an apparatus according to the invention, are described. 
     Nozzle  100  is in particular a component of an injection apparatus, or injection molding apparatus, for making plastic containers, such as for example bottle preforms or test tubes, in particular laboratory test tubes, for example test tubes for the chemical, pharmaceutical or medical field. The container is, for example made of polyethylene terephthalate (PET). 
     The injection apparatus in particular comprises a molding cavity  9  of a container and a shutter  8 . 
     The injection apparatus can comprise a plurality of nozzles  100 . Each nozzle  100  is associated with a respective shutter  8  and a respective molding cavity  9 . 
     Nozzle  100  serves to inject the molten plastic into the molding cavity  9 , in particular by cooperating with shutter  8  to dose the amount of plastic to be injected. 
     Nozzle  100  delimits a channel for the molten plastic, i.e. a channel for the passage for the molten plastic, which in particular is injected into the molding cavity  9 . 
     Component  5  of the invention is also called nozzle insert or nozzle tip. 
     The component  5  of nozzle  100  in particular is an insert. Component  5  delimits a channel for the molten plastic. The channel delimited by component  5  in particular is a part of the channel delimited by nozzle  100 . 
     Component  5  comprises a body  1 , or first insert, also called first body for descriptive purposes. 
     Shutter  8  can slide in the nozzle  100 , and in particular can slide in the component  5 , and more particularly can slide in the body  1 . The part of shutter  8  which can slide in body  1  in particular is cylindrical, i.e. it has a cylindrical outer surface. 
     Body  1  has a wall  10  ( FIGS.  3  and  4   ), which comprises two zones  11 ,  12  or parts, also called first zone  11  (or guiding zone) and second zone  12  (or discharging zone), respectively, for descriptive purposes. Zone  11  and zone  12  in particular are zones of the inner surface of wall  10 . Wall  10  in particular is a side wall of body  1 . 
     Zone  11  is adapted to guide the sliding of shutter  8 . In particular, the diameter of zone  11  and the outer diameter of shutter  8  are selected so that shutter  8  can slide over the zone  11  of body  1 , which is fixed in position. In other words, the diameter of zone  11  is selected, in particular sized, according to the outer diameter of shutter  8  so that the latter can slide over zone  11 , remaining in contact therewith, preferably with the entire zone  11 . 
     Advantageously, zone  11  allows the sliding of shutter  8  to be guided and to be kept aligned, i.e. centered, with respect to opening  91  (or injection point) of the molding cavity  9 , in particular during all the steps of the molding process. 
     Moreover, body  1 , in particular zone  11 , allows the wear of other components of the molding apparatus to be reduced, in particular of component  90  which delimits the molding cavity  9 , more particularly of the zone which delimits the injection point  91 . 
     The zone  12  of body  1  delimits a first stretch  101 , i.e. a part, of the channel for the molten plastic of nozzle  100 . Said first stretch  101  is an end stretch of the channel, proximal to the opening  19 . 
     The diameter of zone  12  advantageously is greater than or equal to the diameter of zone  11 . 
     The diameter of zone  12  preferably is greater than the diameter of zone  11 , preferably at least 1% greater, for example from 1 to 25% or from 5 to 25%, preferably 5% or about 5% greater than the diameter of zone  11 . In particular, there preferably is a step  110 , preferably an annular step, between zone  12  and zone  11 . 
     Wall  10  extends about an axis X and shutter  8  is adapted to slide along the axis X. 
     Wall  10  delimits a hole, in particular a through hole, of body  1  adapted to be crossed by shutter  8 . In particular, shutter  8  can come out of an opening  19  (indicated in  FIGS.  1  and  6   ) of body  1  delimited by zone  12 . The molten plastic can leave nozzle  100  from the same opening  19 , to then enter the molding cavity  9 . 
     In the configuration shown in  FIGS.  7 ,  8  and  9   , shutter  8  crosses body  1  and comes out thereof, and in particular is in a closed position. 
     Zone  11  and zone  12  are coaxial to each other, i.e. they extend about the same axis X. 
     Zone  11  preferably is cylindrical and/or zone  12  preferably is cylindrical. 
     Zone  11  and zone  12  are distinct from each other. In particular, zone  11  and zone  12  are at a different height from each other along axis X. 
     Preferably, zone  11  is at a lower height along axis X with respect to the height of zone  12  along axis X. 
     Preferably, zone  11  has a height from 1 to 15 mm, for example from 2 to 3 mm, along axis X; and/or zone  12  has a height from 2 to 20 mm, for example from 7 to 8 mm, along axis X. 
     Body  1  is provided with at least one through hole  13 , or opening, which allows the molten plastic to pass through, in particular to enter, in the stretch  101  of the channel for the molten plastic. 
     Said at least one through hole  13  crosses wall  10 , in particular crosses wall  10  transversely to axis X; more particularly, crosses the thickness of wall  10 . 
     In particular, said at least one through hole  13  extends from the inner surface to the outer surface of wall  10 . 
     Said at least one through hole  13  is preferably provided between the two axial ends, considering axis X, of body  1 , one of the two ends of which delimits opening  19  from which the molten plastic can leave. 
     Preferably, said at least one through hole  13  is provided between zone  11  and zone  12 , in particular it is arranged at least partially between zone  11  and zone  12 ; and/or it is at least partially obtained in zone  12 . 
     Preferably, a plurality of through holes  13 , for example four through holes  13 , is provided. Each through hole  13  is in particular made in wall  10 , or side wall, of body  1 . Each through hole  13  is delimited by a respective surface  130  ( FIGS.  3  and  4   ), or wall, which extends about an axis Y which is transverse, preferably substantially orthogonal, with respect to axis X about which wall  10  extends, in particular about which the inner surface of wall  10  extends. Preferably, two through holes  13 , or first through holes, are substantially coaxial to each other (i.e. the respective surfaces  130  extend about a same axis) and the other two through holes  13 , or second through holes, are coaxial to each other. Preferably, the axis about which the surfaces  130  which delimit the two first through holes extend is transverse, preferably substantially orthogonal, to the axis about which the surfaces  130  of the two second through holes  13  extend. 
     Preferably, each through hole  13  has a section from 0.7 to 30 mm 2 . 
     For example, in the case of circular shape, each through hole  13  can have a diameter from 1 to 6 mm. 
     It should be clear that the number of through holes  13  and the shape and the sizes thereof can differ from that described, according to operating needs. 
     Zone  12  of the inner surface of body  1  is proximal to opening  19 , while zone  11  is distal from opening  19 . 
     Therefore, zone  12  is adapted to be proximal to the molding cavity  9  and zone  11  is adapted to be distal from the molding cavity  9 . In particular, when nozzle  100  is assembled with the molding cavity  9  (or more particularly, with component  90  in which the molding cavity  9  is made), zone  12  is proximal to the molding cavity  9  and zone  11  is distal from the molding cavity  9 . In other words, zone  12  is between the molding cavity  9  and zone  11 . 
     Advantageously, in this manner, when shutter  8  is in closed position, zone  11 , or the guiding zone  11 , is far enough from the tip  82  ( FIGS.  8  and  9   ) of shutter  8 , whereby tip  82  of the shutter is not heated by the heat transmitted from the guiding zone  11  to shutter  8 , or in any case it is heated very low. 
     This contrivance allows an improved cooling of the end portion  81 , in particular of tip  82 , of shutter  8  during the closing step of the injection point  91 , thus reducing the solidification time of the plastic in the molding cavity  9  and reducing possible defects associated with too high a temperature of the tip  82  of shutter  8 . 
     In a variant of the invention, body  1  is made of a material having a low thermal conductivity, for example made of steel or titanium alloy or ceramic material, in order to further reduce the heat transmission from body  1  to the shutter. 
     Moreover, it is preferable for body  1  to be made of a material which is particularly resistant to wear, in particular having an adequate hardness, such as for example the aforesaid materials. 
     Preferably, body  1  comprises a cylindrical part  120  ( FIGS.  3  and  4   ), in particular having a cylindrical outer surface and a head  121 , or flange, adjacent to the cylindrical part  120  and projecting radially with respect thereto. 
     Head  121 , in particular the outer surface thereof, is tapered towards the molding cavity  9 . 
     Preferably, the outer surface of head  121  is frustoconical. 
     Preferably, zone  12  is partially obtained in head  121  and partially in the cylindrical part  120 . 
     Preferably, the through holes  13  are made in the cylindrical part  120 . 
     Preferably, the end portion  122  of body  1 , opposite to head  121 , has a tapered outer surface, preferably tapered in the direction distal from opening  19 , and therefore from the molding cavity  9 . The outer surface of the end portion  122  is, for example frustoconical. The tapered shape of the outer surface of the end portion  122  facilitates the flow of the molten plastic towards the through hole(s)  13 . The outer surface of the end portion  122  can alternatively be cylindrical or have another shape. 
     Preferably, zone  11  is obtained in the cylindrical part  120  and/or in the end portion  122 , for example partially in the cylindrical part  120  and partially in the end portion  122 . 
     Component  5  also comprises a body  2 , or second body or insert, which delimits a second stretch  102  of the channel for the molten plastic. Considering the advancement direction of the molten plastic in nozzle  100 , the second stretch  102  is arranged upstream of the first stretch  101 . 
     The first stretch  101  and the second stretch  102  extend along the same axis X. 
     In particular, body  2  has an inner surface  22  which extends about axis X and which delimits said second stretch  102 . 
     Preferably, the first stretch  101  and the second stretch  102  are coaxial to each other. 
     Shutter  8  can slide in body  2 , in particular in the second stretch  102  of the channel, and also in stretch  101  delimited by the zone  12  of body  1 . 
     Body  1  is inserted in body  2 , in particular so that zone  11  and the through holes  13  are in the stretch  102  of the channel, i.e. in the body  2 . 
     Therefore, the molten plastic can leave stretch  102  and be introduced into stretch  101 , passing through the through holes  13 . In other words, stretch  102  is in communication, in particular in fluid communication, with stretch  101  by means of the through holes  13 . 
     Stretch  101  is proximal to opening  19 , and therefore to the molding cavity  9 , and stretch  102  is distal from opening  19 , and therefore distal from the molding cavity  9 . 
     Preferably, body  1  defines an end portion of component  5  and an end portion of nozzle  100 . 
     Preferably, body  1 , in particular zone  12 , projects outside with respect to body  2 . In particular, zone  12  projects towards the molding cavity  9 . Preferably, the part of body  1  which projects with respect to body  2  is the head  121 . 
     Alternatively, body  1  can be non-projecting with respect to body  2 . 
     Body  1  and body  2  are restrained to each other, preferably by interference coupling or by welding. 
     Alternatively, body  1  can be disassembled from nozzle  100 , in particular it can be disassembled from body  2 . 
     Preferably, body  1  and body  2  abut with each other. 
     Preferably, head  121 , in particular a lower surface thereof, of body  1  abuts with a surface, in particular with an upper surface, of body  2 . 
     The through holes  13  face an inner wall or inner surface  22  (in particular, an inner side wall or inner side surface  22 ) of body  2  and are spaced apart from said inner wall of body  2 . 
     Preferably, at least one portion of the cylindrical part  120  which extends between the through holes  13  and head  121  along axis X is surrounded by a wall of body  2 , and preferably is in contact with said wall of body  2 . 
     In a first embodiment of the invention, body  1  and body  2  are made of a different material from each other. Advantageously, the material of body  1  has a lower thermal conductivity than the thermal conductivity of the material of body  2 . 
     Preferably, the material of body  1  has a thermal conductivity comprised between 1 and 50 W m −1  K −1 , preferably between 1 and 49 W m −1  K −1  or between 1 and 45 Wm −1  K −1 , while the material of body  2  has a thermal conductivity comprised between 50 and 400 W m −1 K −1 , preferably comprised between 51 and 400 W m −1  K −1  or between 55 and 400 W m −1  K −1 . 
     In this manner, in particular, body  2  can transmit heat—provided by the heating means- to the molten plastic therein, while the transmission of heat from body  1  to shutter  8  is significantly reduced. In this first embodiment, zone  12  of body  1  can have a diameter which is greater than or equal to the diameter of zone  11  of said body  1 . 
     In particular, it is preferable for body  1  to be made of a material having a greater hardness with respect to the material with which body  2  is made. 
     In particular, the thermal conductivity and the hardness of the two materials are assessed under the same conditions, in particular at the same temperature. 
     Making body  1  with a material having a lower thermal conductivity allows the heat exchange to be reduced between body  1  and shutter  8 , in particular so as to reduce the transfer of heat from zone  11  to the tip  82  of shutter  8  as much as possible. 
     Making body  1  with a material having greater hardness allows the operating life thereof to be lengthened because it is subject to wear due to the sliding of shutter  8  over zone  11 . 
     Preferably, body  1  is made of steel or titanium alloy or ceramic material (as mentioned above), and body  2  is made of copper alloy or copper-beryllium alloy or aluminum alloy or molybdenum alloy or tungsten alloy. 
     Although it is advantageous to make body  1  and body  2  in different materials from each other, alternatively, body  1  and body  2  can be made of a same material, for example of steel or titanium alloy or copper alloy or copper-beryllium alloy or aluminum alloy or molybdenum alloy or tungsten alloy. 
     Indeed, in a second embodiment of the invention, the zone  12  of body  1  has a greater diameter than the diameter of zone  11 , but there is no need to provide materials with different thermal conductivity for body  1  and body  2 , respectively. Nozzle  100  preferably also comprises a body  3  which delimits a third stretch  103  of the channel for the molten plastic. Considering the advancement direction of the molten plastic in nozzle  100 , the third stretch  103  is arranged upstream of the second stretch  102 . 
     Stretch  103  communicates with stretch  102  of the channel, i.e. the molten plastic can pass from stretch  103  to stretch  102 , in particular passing through an opening  21  ( FIG.  7   ) of body  2  delimited by the wall thereof which extends about axis X. 
     Stretch  102  is between stretch  103  and stretch  101 . 
     Stretch  102  and stretch  103  are coaxial to each other. Shutter  8  can slide in body  3 , in particular in stretch  103 . 
     The channel for the molten plastic of nozzle  100  comprises stretch  101 , stretch  102  and stretch  103 , with the through holes  13  of body  1  which put stretch  102  in communication with stretch  101 . 
     The channel for the molten plastic of component  5  comprises stretch  101  and stretch  102 . 
     Body  2  is inserted in body  3 . Preferably, a part, in particular an end part, of body  2  projects outside with respect to body  3 , in particular towards opening  19 , and therefore towards the molding cavity  9 . Preferably, body  1  is restrained to the part of body  2  which projects with respect to body  3 . Preferably, the end edge of body  2  which delimits opening  21  ( FIG.  7   ) abuts with an annular step  321  of the inner wall of body  3 . 
     Body  2  and body  3  are restrained to each other, preferably they are screwed to each other and/or are restrained by means of a ring nut (not shown). 
     Preferably, body  3  comprises a cup or base  31  and a part  32 , in particular a part  32  having a substantially cylindrical outer surface. The width, in particular the maximum width, orthogonally to the axis X of base  31 , is greater than the width, in particular the maximum width, of part  32 . Body  2  in particular is inserted in the part  32  of body  3 . 
     As mentioned, an injection apparatus according to the invention for molding plastic containers comprises one or more nozzles  100 . 
     Each nozzle  100 , defining an axis X, cooperates with a respective shutter  8  and a respective molding cavity  9 . 
     Each nozzle  100  is provided with an inner channel ending with an opening  19  for injecting molten plastic into the molding cavity  9 . 
     Preferably, the molding cavity  9  is provided with a respective opening  91  through which it receives the molten plastic that comes out of nozzle  100 , and therefore out of opening  19 . 
     Shutter  8  slides in the inner channel along axis X from an advanced position, in which opening  19  is closed, to a retracted position, in which opening  19  is open. 
     Advantageously, nozzle  100  includes a component  5  comprising
         a first body  1 , which is coaxial to axis X, defining an end portion of nozzle  100  which includes opening  19  and which delimits a first stretch  101  of the channel proximal to opening  19 ;   and a second body  2 , which is coaxial to axis X and which delimits a second stretch  102  of the channel distal from opening  19 ;       

     wherein the first body  1  is at least partially inserted in the second body  2  so that the second stretch  102  is coaxial with and outside the first stretch  101 ; 
     wherein the first body  1  has a wall  10  which extends about said axis X, 
     wherein said wall  10  is provided with an inner surface having a first zone  11  which is distal from opening  19  and is adapted to guide the sliding of shutter  8  along axis X, and a second zone  12  which is proximal to opening  19 , which delimits said first stretch  101 ; 
     wherein the wall  10  is provided with at least one through hole  13  which is transverse to axis X, whereby the molten plastic passes from the second stretch  102  to the first stretch  101 , passing through said at least one through hole  13  when shutter  8  is in the retracted position; 
     wherein said first zone  11  has a first diameter and said second zone  12  has a second diameter which is greater than the first diameter, or wherein said first zone  11  has a first diameter and said second zone  12  has a second diameter which is greater than or equal to the first diameter, and the first body  1  is made of a first material having a lower thermal conductivity than a second material with which the second body  2  is made. 
     Each nozzle  100  is restrained to a nozzle holder, also called nozzle holder plate  71  (partially shown in  FIG.  7   ). In particular, the body  3  of nozzle  100  is restrained to the nozzle holder plate  71 . More particularly, the base  31  of body  3  is restrained to the nozzle holder plate  71 . 
     Heating means  72 , for example one or more electrical heating elements, are preferably provided around body  3 , in particular around part  32 . The heating means  72  are, for example, fastened to the outer surface of body  3 , in particular of part  32 . The heating means  72  serve to heat or keep at the desired temperature the molten plastic which flows in stretch  102  and/or in stretch  103  of the channel. 
     Component  90 , in which the molding cavity  9  is made, and the molding cavity  9  are partially shown in  FIGS.  7  to  11   . Preferably, component  90  is provided with a cooling system for cooling the plastic in the molding cavity  9 . 
     Body  1  is inserted in component  90 . Body  2  is preferably partially inserted in component  90  and partially extends in component  71 . 
     A heat insulator  73  is preferably provided in component  90 . The heat insulator  73  is preferably made of plastic, for example polyimide (PI), polytetrafluoroethylene (PTFE) or polyetheretherketone (PEEK) and in particular, is resistant to mechanical loads and high temperatures. 
     The heat insulator  73  is arranged between nozzle  100  and component  90 , outside the molding cavity  9 . 
     In particular, the heat insulator  73  covers the outer surface of the head  121  of body  1  and the part of body  2  which comes out of body  3 . Preferably, said part of body  2  comprises a tapered surface portion having a taper angle which is substantially equal to the taper angle of the surface of the head  121  of body  1 . 
     The heat insulator  73  is provided with a hole which is coaxial to axis X, in particular coaxial to the opening  19  of body  1 . The hole of the heat insulator  73  can be crossed by shutter  8  and by the molten plastic. Preferably, the diameter of the hole of the heat insulator  73  is greater than or equal to the diameter of the zone  12  of body  1 . 
     The molding cavity  9  is provided with an opening  91  through which the molten plastic that comes out of nozzle  100  can be introduced into the molding cavity  9 . Opening  91  is also called gate or injection point. Typically, opening  91  is at the part of the molding cavity  9  which molds the bottom of the container. Opening  91  is coaxial to axis X, i.e. is delimited by a surface which extends about axis X. 
     Sliding along axis X, shutter  8  is adapted to switch from a closed position ( FIGS.  7 ,  8  and  9   ) to an open position ( FIGS.  10  and  11   ), and vice versa. 
     In the closed position, shutter  8  prevents the passage of the molten plastic through opening  91  of the molding cavity  9 , and in particular the end portion  81  (which comprises tip  82 ) of shutter  8  obstructs opening  91 . More particularly, shutter  8  prevents the molten plastic both from entering the molding cavity  9  and from leaving the molding cavity  9 . Preferably, also the zone of component  90  which delimits the inlet opening  91  is adapted to guide the sliding of shutter  8 . 
     When shutter  8  is in the open position, the molten plastic can enter the molding cavity  9 . In particular, the molten plastic can pass from stretch  102  to stretch  101  of the channel, passing through the through holes  13 , to then leave from nozzle  100 , and the molten plastic which leaves from nozzle  100  can enter the molding cavity  9 . 
     Advantageously, the apparatus is configured so that shutter  8  is guided by the zone  11  of body  1  both when passing from the closed position to the open position and when passing from the open position to the closed position. 
     In particular, in the open position, the end portion  81  of shutter  8  is surrounded by zone  11 , and more particularly it is not surrounded by zone  12 . In particular, in the open position, the end portion  81  of shutter  8  is in such a retracted position as to leave the outlet section of the through holes  13  at least partially free ( FIG.  11   ). 
     In other words, shutter  8  advantageously always remains guided by body  1 , in particular by zone  11 , during all the molding steps. 
       FIGS.  10  and  11    diagrammatically indicate the path of the molten plastic by arrows. 
     In particular, the molten plastic crosses stretch  102  of the channel of the nozzle and then enters stretch  101  of the channel by passing through the through holes  13 . The molten plastic then leaves body  1 , passes through the hole of the heat insulator  73  (when provided) and enters the molding cavity  9 , passing through opening  91 . 
     As mentioned above, the diameter of zone  12  preferably is greater than the diameter of zone  11 , the latter being adapted to guide the sliding of shutter  8 . Therefore, the diameter of zone  12  is greater than the outer diameter of shutter  8 , in particular of the end portion  81  of shutter  8 . 
     Advantageously, therefore, zone  12  substantially does not transfer heat to shutter  8 , in particular to the tip  82  thereof. 
     Moreover, the molten plastic can advantageously flow in the annular space (i.e. in part of stretch  101 ) between shutter  8  and zone  12 , in particular when shutter  8  is in the closed position and in the switching from the closed position to the open position. 
     This aspect is advantageous because the molten plastic can flow in a direction away from the molding cavity  9  and possibly pass through the through holes  13  to return into stretch  102 . 
     Therefore, the force required to bring shutter  8  from the open position to the closed position advantageously is reduced. 
     Preferably, the diameter of zone  12  is at least 1% greater than the outer diameter of shutter  8 , for example from 1 to 25% or from 5 to 25%, preferably 5% or about 5% greater than the outer diameter of shutter  8 . 
     Advantageously, the through holes  13  of body  1  also act as filter, thus avoiding contaminants of a given dimension to be incorporated in the molded product. Moreover, since the through holes  13  are obtained in the side wall of body  1 , they allow a cleansing action of the end portion  81  of shutter  8 , removing possible residual material of the preceding molding operation and decreasing the shadow effect on the tip  82  of shutter  8 .