Abstract:
To solve a problem associated with formation of a transparent window portion in a biaxially stretch blow molded container by a nozzle structure of an injection molding apparatus, provided is a biaxially stretch blow molded container formed with a clearly transparent window portion in longitudinal strip shape by effectively preventing mixture of colored resin to window portion. Injection molding apparatus includes in nozzle portion a longitudinal groove flow path, wherein a transparent B resin flows. By, for example, reducing and increasing, respectively, the width and depth of the longitudinal groove flow path on the downstream side, and engraving slits in an inner mandrel and even in a front end portion of a stopper pin, flowability of the B resin in a horizontal direction is enhanced.

Description:
[0001]    This is a Divisional application of U.S. application Ser. No. 14/646,785 filed May 22, 2015, which is a 371 of international application PCT/JP2013/082299, Filed Nov. 30, 2013, which claims priority to foreign application No. JP 2012-263131, filed Nov. 30, 2012 in Japan. The disclosure of the prior applications is hereby incorporate by reference herein in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to a biaxially stretch blow molded synthetic resin container including a translucent or semi-translucent window portion through which an amount of a remaining content may be identified from an outside, a test-tube-shaped preform that is a precursor of the container, and an injection molding apparatus used for molding the preform. 
       BACKGROUND 
       [0003]    Conventionally, blow molded containers made of synthetic resins are widely used in applications such as beverages, foods, detergents, cosmetics, and chemicals. Such a container often conceals the content for the purpose, for example, of protecting the content against ultraviolet rays and improving appearance and design quality. 
         [0000]    Examples of ways of concealing the content from an outside view includes opaquing the container itself with a colored resin, opaquing an outer surface of the container by painting, and applying an overcoat of a shrink film, which is opaque or with opaque printing on a surface thereof, onto the outer surface of the container. 
         [0004]    However, concealing the content from the outside view as such poses a problem that the amount of the remaining content may not be identified from the outside, and this leads to inconvenience and anxiety in use. Another problem arising when filling the content again for use is that too much content might be added to cause it to overspill due to invisibility of how much content is filled. 
         [0005]    One possible way to overcome the aforementioned problems is to form a window portion, by masking a part of a container which is transparent or semi-transparent (hereinafter, collectively referred to as transparent) and painting the container and by peeling the masking after the painting. In a case of the shrink film, such a window portion may be formed by leaving a portion of the shrink film unprinted and transparent to allow the amount of the remaining content to be identified from the outside. 
         [0006]    Furthermore, as described in Patent Literature 1, a blow molded container produced by blow molding an extrusion molded cylindrical parison, that is to say, by direct blow molding, may be relatively easily formed with a transparent window portion in a longitudinal strip shape after the blow molding, by coloring, during the extrusion molding of the parison, a majority of the parison to make the parison opaque while flowing an uncolored transparent resin into a portion of a cylindrical flow path formed in a dice used for the extrusion molding. 
       CITATION LIST 
     Patent Literature 
       [0007]    PTL 1: JP2005153901A 
       SUMMARY 
       [0008]    As described above, the container produced by the direct blow molding may be formed with a transparent window portion in the longitudinal strip shape relatively easily. 
         [0000]    On the other hand, a biaxially stretch blow molded container made of polyethylene terephthalate (hereinafter, abbreviated as PET) that is formed by biaxially stretch blow molding an injection molded preform faces problems such as mixture of a colored resin into a portion of such a transparent window portion and deterioration in the transparency, even when a transparent window portion in the longitudinal strip shape is desired to be formed in the container. 
         [0009]    This disclosure has been conceived to solve the aforementioned problems associated with the formation of a window portion in the biaxially stretch blow molded container by a nozzle structure of an injection molding apparatus. It could be helpful to provide a biaxially stretch blow molded container that is formed with a clearly transparent window portion in the longitudinal strip shape by effectively preventing the mixture of the colored resin. 
         [0010]    This disclosure relates to the biaxially stretch blow molded synthetic resin container with a window, the test-tube-shaped preform which is the precursor of the container, and the injection molding apparatus used for molding the preform. For convenience of description, a description is given below of the injection molding apparatus, the preform, and the container with a window, in the stated order. 
         [0011]    Firstly, one aspect of this disclosure resides in an injection molding apparatus that injection molds a test-tube-shaped preform that is subjected to biaxial stretch blow molding, the preform including a circumferential wall having a longitudinal strip-shaped portion that is made of a B resin and that is formed in a longitudinal strip shape in a circumferentially predetermined position in the circumferential wall over a predetermined height range, a remaining portion of the circumferential wall excluding the longitudinal strip-shaped portion being made of an A resin. 
         [0000]    The injection molding apparatus includes:
 
a nozzle portion that supplies the A resin and the B resin which are molten along a circumferential direction; and a mold that is located in a front end of the nozzle portion.
 
The nozzle portion includes:
 
a cylindrical inner mandrel; an outer mandrel that is arranged coaxially with the inner mandrel; and a columnar shut-off pin that is inserted and arranged in the inner mandrel and that serves to release and shut off flows of the molten resins in a front end portion of the nozzle portion.
 
Between the inner mandrel and the outer mandrel, a cylindrical flow path and a reduced-diameter flow path are formed in the stated order in a direction toward a downstream side, the reduced-diameter flow path being configured by a cylindrical flow path tapered to have a reduced diameter toward downstream, and on downstream of the reduced-diameter flow path, a columnar joining flow path is formed in which the molten resins in cylindrical forms join into a columnar form, and a longitudinal groove flow path is further formed to interrupt the cylindrical flow path and the reduced-diameter flow path in a circumferential direction,
 
the longitudinal groove flow path has a flow path width that is reduced on a downstream side below a predetermined position than on an upper stream side thereof and a flow path depth that is increased on the downstream side below the predetermined position than on the upper stream side thereof, and
 
the molten B resin is supplied to the longitudinal groove flow path, and the molten A resin is supplied to the cylindrical flow path excluding the longitudinal groove flow path, and the molten resins that have joined into the columnar form are injected and filled into a cavity of the mold via the joining flow path of the nozzle portion and a pin gate located in a position of the cavity of the mold that corresponds to a middle of a bottom wall of a bottom portion of the preform.
 
         [0012]    In the above regard, assume that, similarly to the dice used in the direct blow molding of the parison as described above, merely the cylindrical flow path is arranged in the nozzle portion included in the injection molding apparatus and that the B resin is caused to flow in a longitudinal strip shape in a portion of the A resin to flow the A resin and the B resin along the circumferential direction into a cylindrical form. 
         [0000]    However, in the case of the injection molding of the test-tube-shaped parison, the cylindrically formed molten resins do not remain in the cylindrical forms but are joined into a columnar form in the front end of the nozzle portion, and the joined molten resins in the columnar form are injected and flowed to be filled into the test-tube-shaped cylindrical cavity via the pin gate. 
         [0013]    In the sectional plan view, the cylindrically joined and formed parison which is used in the direct blow molding includes the A resin in an annular form and the B resin that completely interrupts the A resin in the radial direction. On the other hand, in the sectional plan view, the molten resins joined and formed in the columnar form in the front end portion of the nozzle portion as described above include the A resin in the columnar form and the B resin that is laminated in the columnar A resin, in the form of a slit extending from a peripheral edge portion to a center position of the columnar A resin. 
         [0014]    Accordingly, upon the joining, the A resin and the B resin collide with each other in the vicinity of a center position of the columnar flow path. At this collision time, the A resin might push the B resin to a peripheral direction and prevent the B resin from being laminated to the center position of the columnar flow path. In this situation, even when a window portion in the longitudinal strip shape is desired to be formed in the circumferential wall of the container by using a transparent resin as the B resin, various problems arise, such as the mixture of the colored resin into a portion of the transparent window portion, for example, a portion of the transparent window portion that is located on an inner circumferential surface side, and the deterioration in transparency in the portion of the window portion as described above. 
         [0000]    On the other hand, when the B resin is laminated in the form of a slit extending beyond the center position of the columnar flow path, even though the transparent B resin might mix into the inner circumferential surface side of the circumferential wall made of the colored A resin, the transparent B resin is covered by the colored A resin, and therefore, appearance properties will not be deteriorated. 
         [0015]    The structure of the injection molding apparatus according to the above aspect has been conceived based on a result of analysis of a phenomenon of how the B resin is laminated in the form of a slit in the A resin in the columnar flow path in which the resins have been joined from the cylindrical form into the columnar form. 
         [0000]    The basic technical idea resides in that the flow path of the B resin in the nozzle portion is designed to allow the B resin, being joined into the columnar form in the front end portion of the nozzle portion, to be laminated in the columnar flow path, in the form of a slit extending sufficiently to reach at least the center position in the direction from the peripheral edge to the center position, and even in the form of a slit extending from the peripheral edge to and beyond the center position in consideration of variation in the position in which the B resin is laminated due to a slight variance in conditions of the injection molding and in consideration of possible fluctuations in flow behavior of the molten resins injected from the pin gate. 
         [0016]    According to the injection molding apparatus with the above structure, preferably, the structure of the nozzle portion provides the following advantageous effects. 
         [0000]    Firstly, by forming the longitudinal groove flow path to interrupt the cylindrical flow path and the reduced-diameter flow path in the circumferential direction, segmentation between the A resin and the B resin is clarified in the circumferential direction.
 
Secondly, by reducing and increasing, respectively, the flow path width and the flow path depth of the longitudinal groove flow path on the downstream side below the predetermined position than on the upper stream side thereof, a decrease in pressure of the B resin flowing in the longitudinal groove flow path is prevented, and the flow of the B resin is directed further to the horizontal direction, that is to say, to a central axis of the nozzle portion.
 
As a result, upon the joining in the front end portion of the nozzle portion, the B resin provides force to push the A resin toward a peripheral direction in the vicinity of the center position of the columnar flow path. Accordingly, the B resin is laminated in the form of a slit extending sufficiently to reach at least the center position, and even beyond the center position.
 
         [0017]    Additionally, in the above structure, the A resin and the B resin are used for convenience of differentiation of the two resins. The A resin and the B resin may be differentiated in terms of the kinds of the synthetic resins or may be the same kind of two synthetic resins that are differentiated in terms of whether the synthetic resins are colored or uncolored. 
         [0000]    For example, to form the longitudinal strip-shaped transparent window portion in the container, the same two synthetic resins, one for the A resin that is colored to make it opaque and the other one for the B resin that is left uncolored and transparent, may be used.
 
Furthermore, in the description of the above structure and in the description below, terms, e.g., the longitudinal groove flow path, implying directions such as the longitudinal and horizontal directions are used for convenience. Herein, the longitudinal direction corresponds to the central axis direction of the nozzle portion, and the horizontal direction corresponds to the direction that is perpendicular to the central axis direction.
 
Moreover, although the above structure includes, as the structural requirements, the “longitudinal groove flow path having a flow path width that is reduced on a downstream side below a predetermined position (in a predetermined range) than on an upper stream side thereof and a flow path depth that is increased on the downstream side below the predetermined position than on the upper stream side thereof”, the flow path width and the flow path depth do not necessarily need to be respectively reduced and increased in the same predetermined range, and the flow path width and the flow path depth may be respectively reduced and increased in different ranges as appropriate.
 
         [0018]    Another aspect of this disclosure resides in the injection molding apparatus according to the above aspect, wherein, in the cylindrical flow path and the reduced-diameter flow path, a pair of guiding ribs in the form of longitudinal ridges is arranged in line to partition the cylindrical flow path and the reduced-diameter flow path in the circumferential direction, and the longitudinal groove flow path is formed between the pair of guiding ribs. 
         [0019]    The above structure is specifically designed to form the longitudinal groove flow path interrupting the cylindrical flow path and the reduced-diameter flow path in the circumferential direction, and such a structure may be formed by leaving portions of the inner mandrel unprocessed when cutting the inner mandrel to form the flow paths. 
         [0020]    Yet another aspect of this disclosure resides in the injection molding apparatus according to the above aspect, wherein the longitudinal groove flow path has a flow path width that is reduced from a position of a lower end portion of the cylindrical flow path. 
         [0021]    With the above structure, the flow path width of the longitudinal groove flow path is reduced before the longitudinal groove flow path reaches the reduced-diameter flow path. As a result, the pressure of the flow of the B resin along the taper in the reduced-diameter flow path is increased, and flowability of the B resin in the horizontal direction is enhanced. This further ensures that the B resin may be laminated in the form of a slit extending sufficiently to reach at least the center position in the columnar flow path, and even in the form of a slit extending beyond the center position. 
         [0022]    Yet another aspect of this disclosure resides in the injection molding apparatus according to the above aspect, wherein the inner mandrel forming the reduced-diameter flow path is engraved with a slit having an inclination angle that is greater than an inclination angle that the tapered reduced-diameter flow path forms with respect to a central axis of the nozzle portion, in order to increase a flow path depth of the longitudinal groove flow path. 
         [0023]    With the above structure, flowability of the B resin in the horizontal direction is further enhanced, and this further ensures that the B resin may be laminated in the form of a slit extending sufficiently to reach at least the center position in the columnar flow path, and even in the form of a slit extending beyond the center position. 
         [0024]    Yet another aspect of this disclosure resides in the injection molding apparatus according to the above aspect, wherein, in a release position of the shut-off pin, the slit engraved in the inner mandrel is further extended into the shut-off pin to engrave a slit in a portion of the shut-off pin that is located from a circumferential wall to a front end surface thereof, the slit having the same inclination angle as the slit engraved in the inner mandrel. 
         [0025]    Yet another aspect of this disclosure resides in the injection molding apparatus according to the above aspect, wherein, in the front end surface of the shut-off pin, the slit is engraved from a peripheral edge toward a center and beyond a center position of the front end surface. 
         [0026]    According to the above two structures, the slit forming the longitudinal flow path is extended from the inner mandrel into the shut-off pin, and this further ensures that the B resin may be stably laminated in the form of a slit extending sufficiently to reach at least the center position in the columnar flow path, and even in the form of a slit extending beyond the center position. 
         [0027]    Secondly, a description is given of a structure of the preform according to this disclosure. The preform with a structure such as the following may be molded by the injection molding apparatus described above. 
         [0000]    One aspect of this disclosure resides in an injection molded test-tube-shaped preform that is subjected to biaxial stretch blow molding.
 
The preform includes a circumferential wall including a longitudinal strip-shaped portion that is made of a transparent or a semi-transparent resin and that is formed in a longitudinal strip shape in a circumferentially predetermined position in the circumferential wall over a predetermined height range.
 
         [0028]    The aforementioned injection molding apparatus is capable of providing the preform in which the clear longitudinal strip-shaped portion, which is made of the transparent B resin, is formed to interrupt the circumferential wall, which is generally made of the opaque A resin, in the circumferential direction, by effectively preventing the mixture of the A resin to the longitudinal strip-shaped portion. 
         [0000]    Additionally, the aforementioned injection molding apparatus may be configured to form the longitudinal strip-shaped portion over an entire height range of the preform. However, by, for example, shutting off and starting the supply of the B resin to the longitudinal groove flow path at appropriate timing by arranging a check valve or other means on the upstream side, the longitudinal strip-shaped portion may also be formed over a predetermined height range of the preform excluding, for example, the mouth tubular portion. 
         [0029]    Another aspect of this disclosure resides in the preform according to the above aspect, further including a bottom portion, wherein the longitudinal strip-shaped portion is formed over an entire height range measured from a bottom wall of the bottom portion. Such a preform in which the clear longitudinal strip-shaped portion made of a transparent resin is formed over the entire height range would be difficult to achieve conventionally. 
         [0030]    Yet another aspect of this disclosure resides in the preform according to the above aspect, wherein, in the bottom wall of the bottom portion, the longitudinal strip-shaped portion is arranged from a peripheral edge toward a center and beyond a center position of the bottom wall. A preform with such a structure would be difficult to achieve conventionally. 
         [0031]    Thirdly, a description is given of the biaxially stretch blow molded synthetic resin container with a window according to this disclosure. The container with a structure such as the following may be molded by biaxially stretch blow molding the preform described above. 
         [0000]    One aspect of this disclosure resides in a synthetic resin container with a window that is produced by biaxially stretch blow molding a test-tube-shaped preform, the synthetic resin container with a window including a circumferential wall including a longitudinal strip-shaped portion that is made of a transparent or a semi-transparent resin and that is formed in a longitudinal strip shape in a circumferentially predetermined position in the circumferential wall over a predetermined height range, the longitudinal strip-shaped portion serving as a window portion. 
         [0032]    The container with a window with the above structure may be produced by biaxially stretch blow molding the aforementioned preform in which the clear longitudinal strip-shaped portion, which is made of the transparent B resin, is formed by effectively preventing the mixture of the opaque A resin to the longitudinal strip-shaped portion. Accordingly, a container formed with the clearly transparent window portion in the longitudinal strip shape is achieved. 
         [0033]    Another aspect of this disclosure resides in the container with a window according to the above aspect, further including a bottom portion, wherein the longitudinal strip-shaped portion is formed over an entire height range measured from a bottom wall of the bottom portion. Such a biaxially stretch blow molded container with a window in which the clear longitudinal strip-shaped portion made of the transparent resin is formed over the entire height range would be difficult to achieve conventionally. 
         [0000]    Of course, the longitudinal strip-shaped portion does not necessarily need to be formed over the entire height range as described above and may be formed over a predetermined height range determined in advance in accordance with the intended use. 
         [0034]    Yet another aspect of this disclosure resides in the container with a window according to the above aspect, wherein, in the bottom wall of the bottom portion, the longitudinal strip-shaped portion is arranged from a peripheral edge toward a center and beyond a center position of the bottom wall. A biaxially stretch blow molded container formed with such a structure could not be achieved conventionally. 
         [0000]    In the above regard, although the longitudinal strip-shaped is preferably arranged beyond the center position of the bottom wall as described above, the extent of the longitudinal strip-shaped may also reach at most the center position or to reach the vicinity of the center position. 
         [0035]    With the above structures, the injection molding apparatus, the preform, and the container with a window according to this disclosure provide the following advantageous effects. 
         [0000]    The injection molding apparatus is capable of forming the longitudinal groove flow path, in which the B resin in the nozzle portion flows, in a shape that enhances flowability of the B resin in the horizontal direction, by, for example, reducing and increasing, respectively, the width and depth of the longitudinal groove flow path on the downstream side, and engraving the slits in the inner mandrel and even in the front end portion of the stopper pin. As a result, it is ensured that the B resin may be laminated in the form of a slit extending sufficiently to reach at least the center position in the columnar flow path, and even in the form of a slit extending beyond the center position. 
         [0036]    The injection molding apparatus is also capable of injection molding the test-tube-shaped preform in which the clear longitudinal strip-shaped portion, which is made of the transparent B resin, is formed to interrupt the circumferential wall, which is generally made of the opaque A resin, in the circumferential direction, by effectively preventing the mixture of the A resin to the longitudinal strip-shaped portion. 
         [0000]    Furthermore, biaxial stretch blow molding of the above preform provides the container with a window including the longitudinal strip-shaped clearly transparent window portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    In the accompanying drawings: 
           [0038]      FIG. 1  is a perspective view illustrating a container with a window according to one embodiment; 
           [0039]      FIG. 2A  is a sectional plan view taken along a line A-A in  FIG. 1 , and 
           [0040]      FIG. 2B  is a bottom view of  FIG. 1 ; 
           [0041]      FIG. 3  is a perspective view of a preform according to one embodiment; 
           [0042]      FIG. 4A  is a sectional plan view of the preform taken along a line B-B in  FIG. 3 ; 
           [0043]      FIG. 4B  is a bottom view of the preform illustrated in  FIG. 3 ; 
           [0044]      FIG. 5  is a schematic longitudinal sectional view taken along a line C-C in  FIG. 6 , illustrating a part of an injection molding apparatus according to one embodiment; 
           [0045]      FIG. 6  is a plan view of the injection molding apparatus illustrated in  FIG. 5 ; 
           [0046]      FIG. 7  is an enlarged longitudinal sectional view of a part of the vicinity of a nozzle portion of the injection molding apparatus illustrated in  FIG. 5 ; 
           [0047]      FIG. 8  is a bottom view of an inner mandrel and a shut-off pin illustrated in  FIG. 5 ; 
           [0048]      FIG. 9  is a developed view of an outer circumferential surface of an inner mandrel; 
           [0049]      FIG. 10A  is a sectional plan view taken along a line N 1 -N 1  in  FIG. 7 ; 
           [0050]      FIG. 10B  is a sectional plan view taken along a line N 2 -N 2  in  FIG. 7 ; 
           [0051]      FIG. 10C  is a sectional plan view taken along a line N 3 -N 3  in  FIG. 7 ; 
           [0052]      FIG. 10D  is a sectional plan view taken along a line N 4 -N 4  in  FIG. 7 , each of which illustrates a laminated state of an A resin and a B resin in the nozzle portion; 
           [0053]      FIG. 10E  is sectional view of a comparative example in which the A resin pushes the B resin toward the peripheral portion and prevents a tip of the slit-shaped B resin Rb portion from reaching the center position Cx; 
           [0054]      FIG. 11A  is an overall perspective view of a container with a window according to another embodiment; 
           [0055]      FIG. 11B  is a bottom view of the container of  FIG. 11A ; and 
           [0056]      FIG. 12A  is an overall perspective view of a preform according to another embodiment; and 
           [0057]      FIG. 12B  is a bottom view of the preform of  FIG. 12A . 
       
    
    
     REFERENCE SIGNS LIST 
       [0000]    
       
           1  mold 
           2  cavity 
           3  pin gate 
           11  nozzle portion 
           12   a  introduction path (of A resin) 
           12   b  introduction path (of B resin) 
           13   a  supply start position (of A resin) 
           13   b  supply start position (of B resin) 
           14  manifold 
           15  cylindrical flow path 
           16  reduced-diameter flow path 
           17  longitudinal groove flow path 
           19  joining flow path 
           20  shut-off pin 
           20   s  slit 
           21  inner mandrel 
           21   s  slit 
           21   g  guiding rib 
           21   r  eccentricity prevention rib 
           22  outer mandrel 
           101  preform 
           102  mouth tubular portion 
           103  neck ring 
           105  trunk portion 
           106  bottom portion 
           107  gate mark 
           112  longitudinal strip-shaped portion 
           201  container 
           202  mouth tubular portion 
           203  neck ring 
           204  shoulder portion 
           205  trunk portion 
           206  bottom portion 
           212  longitudinal strip-shaped portion 
           212   w  window portion 
         An 1 , An 2  inclination angle 
         Ax central axis 
         Cx center position 
         Hab parallel region 
         Hc cylindrical region 
         Ht tapered region 
         Ra A resin 
         Rb B resin 
         Sa resin supply unit (of A resin) 
         Sb resin supply unit (of B resin) 
         W 1 , W 2  flow path width 
       
     
       DETAILED DESCRIPTION 
       [0104]    A biaxially stretch blow molded synthetic resin container with a window, a preform, and an injection molding device according to embodiments will be described below with reference to the drawings. 
         [0000]      FIGS. 1 and 2  illustrate one embodiment of the container with a window.  FIG. 1  is an overall perspective view of the container,  FIG. 2A  is a sectional plan view taken along a line A-A in  FIG. 1 , and  FIG. 2B  is a bottom view of  FIG. 1 .
 
A container  201  is made of a PET resin and has a bottle shape formed by biaxial stretch blow molding. The container  201  includes a mouth tubular portion  202 , a shoulder portion  204  having a tapered tubular shape, a trunk portion  205  having a cylindrical shape, and a bottom portion  206 . The mouth tubular portion  202  is provided on a circumference thereof with a neck ring  203 .
 
         [0105]    The container  201  is formed with the A resin Ra, which is obtained by coloring a PET resin opaque white, and the B resin Rb, which is an uncolored PET resin. Substantially the entire container  201  is made of the opaque A resin Ra, and a longitudinal strip-shaped portion  212 , which is made of the transparent B resin Rb, is located in a circumferentially predetermined position in a circumferential wall of the container  201  over the entire height range measured from un upper end of the mouth tubular portion  202  to a bottom wall of the bottom portion  206 . The longitudinal strip-shaped portion  212  is utilized as a window portion  212   w  through which an inside of the container  201  is visible and through which the amount of a remaining content is identified. 
         [0106]    In the sectional plan view as illustrated in  FIG. 2A , substantially the entire circumferential wall is made of the A resin Ra, and the longitudinal strip-shaped portion  212  made of the B resin Ra is laminated in the form of a slit along the circumferential direction in such a manner as to interrupt the A resin Ra portion. 
         [0000]    The longitudinal strip-shaped portion  212  has a horizontal width that varies according to respective stretch (draw) ratios of portions in the horizontal direction. 
         [0107]    With reference to a bottom view in  FIG. 2B , as illustrated in the figure, in the bottom wall of the bottom portion  206 , the longitudinal strip-shaped portion  212  extends from a peripheral edge to a center position Cx, and further to a position beyond the center position Cx. 
         [0000]    The longitudinal strip-shaped portion  212  also has a fan shape arising from an increased width from the center position to the peripheral edge as a result of the biaxial stretch blow molding. 
         [0108]    Next,  FIGS. 3 and 4  illustrate a preform according to one embodiment. A preform  101  is a precursor of the container  201  according to the above embodiment.  FIG. 3  is a perspective view,  FIG. 4A  is a sectional plan view taken along a line B-B in  FIG. 3 , and  FIG. 4B  is a bottom view of  FIG. 3 . 
         [0000]    The preform  101  is made of a PET resin and has a test tubular shape formed by injection molding. The preform  101  includes a mouth tubular portion  102 , a trunk portion  105  having a cylindrical shape, and a bottom portion  106 . The mouth tubular portion  102  is provided on a circumference thereof with a neck ring  103 . 
         [0109]    The preform  101  is formed with the A resin Ra, which is obtained by coloring the PET resin opaque white, and the B resin Rb, which is the uncolored PET resin. Substantially the entire preform  101  is made of the opaque A resin Ra, and a longitudinal strip-shaped portion  112 , which is made of the transparent B resin Rb, is formed in a circumferentially predetermined position in a circumferential wall of the preform  101  over the entire height range measured from un upper end of the mouth tubular portion  102  to a bottom wall of the bottom portion  106 . 
         [0110]    In the sectional plan view as illustrated in  FIG. 4A , substantially the entire circumferential wall is made of the A resin Ra, and the longitudinal strip-shaped portion  112  made of the B resin Ra is laminated in the form of a slit along the circumferential direction in such a manner as to interrupt the A resin Ra portion. 
         [0111]    With reference to a bottom view in  FIG. 4B , as illustrated in the figure, in the bottom wall of the bottom portion  106 , the longitudinal strip-shaped portion  112  extends from a peripheral edge to the center position Cx, and further to a position beyond the center position Cx. There is also a gate mark  107  located in a middle of the bottom wall. 
         [0112]    Next,  FIGS. 5 to 9  illustrate an injection molding apparatus according to one embodiment. The injection molding apparatus is used for injection molding the preform  101  according to the above embodiment. 
         [0000]      FIG. 5  is a longitudinal sectional view taken along a line C-C in  FIG. 6 ,  FIG. 6  is a plan view,  FIG. 7  is a longitudinal sectional view of a part of the vicinity of a nozzle portion  11  illustrated in  FIG. 5 ,  FIG. 8  is a bottom view of an inner mandrel and a shut-off pin illustrated in  FIG. 5 , and  FIG. 9  is a developed view of an outer circumferential surface of an inner mandrel  21  illustrated in  FIG. 5 . 
         [0113]    The injection molding apparatus includes resin supply units Sa and Sb that supply the A resin and the B resin in their molten states, a nozzle portion  11  that laminates these resins in the circumferential direction, and a mold  1  that shapes the preform. 
         [0000]    A basic structure of the nozzle portion  11  includes the cylindrical inner mandrel  21  and an outer mandrel  22  that are coaxially arranged, and a columnar shut-off pin  20  that is inserted and arranged in the inner mandrel  21  in a manner such that the shut-off pin  20  may slidably move forward and backward. The shut-off pin  20  serves to release and shut off flows of the molten resins in a front end portion of the nozzle portion  11 .
 
As illustrated in  FIG. 7 , the inner mandrel  21  and the outer mandrel  22  each include a cylindrical region Hc and a tapered region Ht. In the tapered region Ht, a tapered surface forms an inclination angle An 1  of 30° with respect to a central axis Ax of the nozzle portion  11 .
 
         [0114]    Between the inner mandrel  21  and the outer mandrel  22 , a cylindrical flow path  15  is formed in the cylindrical region Hc, and a reduced-diameter flow path  16  is formed in communication with the cylindrical flow path  15  in the tapered region. The reduced-diameter flow path  16  is configured by a cylindrical flow path tapered to have a reduced diameter toward downstream. Furthermore, the reduced-diameter flow path  16  has a front end that is formed with a columnar joining flow path  19  in which the molten resins in cylindrical forms join into a columnar form. 
         [0115]    There is also formed a longitudinal groove flow path  17  having a longitudinal strip shape that extends to interrupt the cylindrical flow path  15  and the reduced-diameter flow path  16  in the circumferential direction. 
         [0000]    As illustrated in  FIGS. 7 and 8 , in order to increase a flow path depth of the longitudinal groove flow path  17  in the tapered region Ht, a slit  21   s  is engraved in a manner such that the tapered surface of the inner mandrel  21  forms an inclination angle An 2  of 45° with respect to the central axis Ax of the nozzle portion  11 . The slit  21   s  is further extended into the shut-off pin  20  to form a slit  20   s  in a portion of the shut-off pin  20  that is located from a circumferential wall to a front end surface thereof beyond a center Cx of the front end surface. 
         [0116]    The flow paths described above are formed by cutting the outer circumferential surface of the inner mandrel  21 . 
         [0000]      FIG. 9  is a developed view of the outer circumferential surface of the inner mandrel  21  in the cylindrical region Hc. In the figure, a circumferential position in which the longitudinal groove flow path  17  is formed is defined as 0°, and regions with different depths of the cutting are filled differently to clarify the differences. In the figure, a region that is left white indicates a region where the cutting does not occur, that is to say, an unprocessed region which is in internal contact with an inner circumferential surface of the outer mandrel  22 .
 
A blotted region indicates a region where the flow path having a flow path depth of 1 mm is formed. A crosshatched region indicates a flow path, i.e., a manifold, that is circumferentially formed in the form of a slant groove to distribute the A resin across the cylindrical flow path, and the depth of this flow path is 1.5 mm in a position of 90° where the A rein is supplied and the depth gradually changes to 1 mm along the circumferential direction.
 
The figure also illustrates an eccentricity prevention rib  21   r  located in three positions of 90°, −90°, and 180° (refer also to  FIG. 8 ). The eccentricity prevention rib  21   r  serves to prevent eccentricity between the inner mandrel  21  and the outer mandrel  22 .
 
         [0117]    As illustrated in  FIG. 9 , the longitudinal groove flow path  17  has a flow path width that is reduced on a downstream side than on an upper stream side thereof. In the present embodiment, the flow path width W 1  on the upstream side is set 2 mm, and the flow path width W 2  on the downstream side is set 0.5 mm, and the flow path width W 2  is also maintained in the tapered region Ht. 
         [0000]    Furthermore, as illustrated in  FIG. 9 , in a parallel region Hab, the longitudinal groove flow path  17 , in which the B resin flows, and the cylindrical flow path  15 , in which the A resin flows, are lined up. In the parallel region Hab, portions of the inner mandrel  21  are left unprocessed to form a pair of guiding ribs  21   g  and  21   g  in the form of longitudinal ridges arranged in line, thereby partitioning the cylindrical flow path  15 , in which the A resin flows, in the circumferential direction. The guide ribs  21   g  and  21   g  also extend in the tapered region Ht (refer to  FIG. 8 ). 
         [0118]    To sum up the shapes of the flow paths, the cylindrical flow path  15  and the reduced-diameter flow path  16 , in which the A resin flows, each have a flow path depth of 1 mm. The longitudinal groove flow path  17 , in which the resin B flows, has the flow path width that is reduced in the vicinity of a lower end portion of the cylindrical region Hc, and the flow path width is 2 mm on the upstream side and is 0.5 mm on the downstream side. The longitudinal groove flow path  17  has a flow path depth of 1 mm in the cylindrical region Hc and also has a gradually increased flow path depth downward of the cylindrical region Hc due to the presence of the slit  20   s  and the slit  21   s  described above. 
         [0119]    In the following, a description is given of molding processes of the preform  101  illustrated in  FIGS. 3 and 4  using the injection molding apparatus (refer to  FIGS. 5 to 9 ). 
         [0000]    Firstly, the A resin, which is obtained by coloring the PET resin white, is supplied from the resin supply unit Sa to an A resin introduction path  12   a  and caused to flow into the cylindrical flow path  15  via a supply start position  13   a  and the manifold  14 . On the other hand, the B resin, which is the uncolored PET resin, is supplied from the resin supply unit Sb to a B resin introduction path  12   b  and caused to flow to the longitudinal groove flow path  17  via a supply start position  13   b.  
 
The supply start position  13   b  of the B resin is located further upstream of the supply start position of the A resin.
 
As the resin supply units Sa and Sb, various devices, such as a screw extruder or an accumulator including a plunger attached to a front end of an extruder, may be used.
 
         [0120]    The molten A resin is shaped into a cylindrical form by the cylindrical flow path  15 , and the molten B resin flows across the longitudinal groove flow path  17  to interrupt the A resin portion shaped in the cylindrical form in the circumferential direction. However, in the region where the A resin and the B resin flow in parallel, the flow path of the A resin portion is partitioned by the pair of guiding ribs  21   g  and  21   g  in the circumferential direction, and therefore, the A resin is prevented from mixing with the B resin in the flow path. 
         [0000]    After passing through the reduced-diameter flow path  16 , the molten resins, including the A resin and the B resin formed in reduced-diameter cylindrical forms, join in the front end of the reduced-diameter flow path  16  and pass through the columnar joining flow path  19  to be shaped into a columnar form.
 
Thus obtained columnar molten resins including the A resin and the B resin that is laminated into the A resin in the form of a slit are injected and filled into a cavity  2  via a pin gate  3  located in a position of the cavity  2  of the mold  1  that corresponds to the middle of the bottom portion of the preform (refer to  FIG. 5 ).
 
         [0121]      FIG. 10  schematically illustrates changes in the plane sectional shapes of the molten resins from the upstream side to the downstream side of the nozzle portion  11  illustrated in  FIG. 7 .  FIG. 10A  is a sectional plan view taken along a line N 1 -N 1  in  FIG. 7 ,  FIG. 10B  is a sectional plan view taken along a line N 2 -N 2  in  FIG. 7 ,  FIG. 10C  is a sectional plan view taken along a line N 3 -N 3  in  FIG. 7 , and  FIG. 10D  is a sectional plan view taken along a line N 4 -N 4  in  FIG. 7 .  FIG. 10A  is the sectional plan view in the cylindrical flow path  15 , in which the longitudinal groove flow path  17  has a flow path width of 0.5 mm.  FIG. 10B  is the sectional plan view in a middle height position in the reduced-diameter flow path  16 , and  FIG. 10C  is the sectional plan view in the front end position of the reduced-diameter flow path  16 , and  FIG. 10D  is the sectional plan view of the columnar form shaped in the joining flow path  19 . 
         [0000]      FIGS. 10E and 10D  are sectional views of comparative examples. 
         [0122]    As can be seen from  FIGS. 10A to 10D , while the molten resins in the plane sectional shapes are in a ring form (as in  FIGS. 10A to 10C ), the B resin Rb remains laminated in the form of a slit to interrupt the ring-shaped A resin Ra in the circumferential direction. Eventually, however, the B resin Rb is shaped into a columnar form in the joining flow path  19 . 
         [0000]    Upon such joining, the A resin and the B resin collide with each other in the vicinity of a center position of the columnar flow path. At this collision time, the A resin sometimes pushes the B resin to a direction of the peripheral portion and prevents a tip of the slit-shaped B resin Rb portion from reaching the center position Cx as illustrated in  FIG. 10E . 
         [0123]    When the molten resins in the state as illustrated in  FIG. 10E  are injected and filled into the cavity  2  via the pin gate  3  of the mold  1  to inject mold the preform  1  illustrated in  FIGS. 3 and 4 , the A resin, which is colored white, mixes into a portion of the longitudinal strip-shaped portion  112 , which is made of the transparent B resin Rb, for example, a portion of the longitudinal strip-shaped portion  112  that is located on an inner circumferential surface side. Accordingly, when the preform  1  is biaxially stretch blow molded into the container  1  with a window as illustrated in  FIGS. 1 and 2 , various problems of defects such as a portion of the window portion  112   w  being colored white and a border between the window portion  212   w  and the adjacent white circumferential wall being unclear. As a result, usability of the container  1  as a product is ruined. 
         [0124]    In view of the above, the injection molding apparatus of the present embodiment is mainly characterized by the nozzle portion  11 , preferably, the flow path shape of the longitudinal groove flow path  17 , having the following structures (1) to (4). 
         [0000]    (1) In the region where the A resin and the B resin flow in parallel, the pair of guiding ribs  21   g  and  21   g  in the form of longitudinal ridges ensures that the cylindrical flow path in which the A resin flows is partitioned in the circumferential direction.
 
(2) The shape of longitudinal groove flow path  17  has a flow path width that is reduced (to ¼ in the present embodiment) on the downstream side in order to prevent a decrease in pressure of the B resin.
 
(3) The inner mandrel  21 , which is tapered to have a reduced diameter to form the reduced-diameter flow path  16 , is engraved with the slit  21   s  having the inclination angle An 2  that is greater than the inclination angle An 1  of the reduced-diameter flow path  16  in order to increase the flow path depth of the longitudinal groove flow path  17 .
 
(4) The slit  21   s  is further extended to form the slit  20   s  in the shut-off pin  20  in order to extend the longitudinal groove flow path  17  to the front end surface of the shut-off pin  20 .
 
         [0125]    The structural requirements of the flow path shape of the longitudinal groove flow path  17  described in (1) to (4) provide an advantageous effect of enhancing flowability of the B resin in the horizontal direction, and ultimately, allowing the B resin Rb portion to be laminated in the form of a slit extending sufficiently to reach the center position Cx, or even in the form of a slit extending beyond the center position Cx, in the columnar joining flow path  19  of the nozzle portion  11  as illustrated in the sectional view of  FIG. 10D . 
         [0000]    The above structural requirements also prevent the A resin, which is colored white, from mixing into a portion of the longitudinal strip-shaped portion  112 , which is made of the transparent B resin Rb, during the molding of the preform.
 
Furthermore, biaxial stretch blow molding of the preform provides the container  201  with a window including the longitudinal strip-shaped clearly transparent window portion  212   w  as illustrated in  FIGS. 1 and 2 .
 
         [0126]    Additionally, when, as illustrated in  FIG. 10D , the B resin Rb portion in the form of a slit extends beyond the center position Cx, injection molding of the preform  1  illustrated in  FIGS. 3 and 4  might result in mixture of the transparent B resin into the inner circumferential surface side of the circumferential wall made of the opaque white A resin in a region that is located axisymmetrical to the longitudinal strip-shaped portion  112 . In this situation, however, the transparent B resin will be covered by the opaque white A resin, and therefore, an appearance problem does not occur. 
         [0127]    Although the synthetic resin container with a window, the preform, and the injection molding apparatus of the preform according to the embodiments have been described above, this disclosure is not limited to these embodiments. For example, although in the above embodiments the container is a round bottle made of a PET resin, any other synthetic resin such as a polypropylene resin that may be subjected to biaxial stretch blow molding may be used. Furthermore, the shape of the container may be any other shape such as a square. 
         [0000]    Moreover, as the resin material of the window portion  212   w , a colored transparent resin may also be used. 
         [0128]    The shape of the longitudinal groove flow path  17  of the nozzle portion  11  is described to have the structures (1) to (4) in the present embodiments. However, the flow path may be determined as appropriate in consideration of melt viscosity or the like of the resin used, if only the flow path width is reduced and the flow path depth is increased in a predetermined range on the downstream side compared with those on the upstream side. 
         [0000]    Moreover, in the above embodiment of the container with a window (refer to  FIGS. 1 and 2 ), the window portion  212   w  formed in the trunk portion  205  has a straight shape having a constant width over the entire height range. However, depending on the shape of the longitudinal groove flow path  17  and the injection pressure of the B resin, as illustrated in  FIG. 12 , for example, the preform  101  including the strip-shaped portion  112  whose width is increased downward in a lower end portion of the trunk portion  105  may be molded. By biaxially stretch blow molding such a preform  101 , as in the container  201  with a window illustrated in  FIG. 11 , the width of the window portion  212   w  may be increased downward in the lower end portion of the trunk portion  205 . 
       INDUSTRIAL APPLICABILITY 
       [0129]    The container with a window that is produced by biaxially stretch blow molding the preform molded by the injection molding apparatus according to this disclosure includes a longitudinal strip-shaped clearly transparent window portion that is conventionally considered difficult to form, and such a container is expected to be used in a wide range of applications.