Patent Publication Number: US-2022234272-A1

Title: Preform, resin-made container, and manufacturing method therefor

Description:
TECHNICAL FIELD 
     The present invention relates to a preform, a resin-made container, and a manufacturing method for manufacturing the preform and the resin-made container. 
     BACKGROUND ART 
     Patent Literature 1 discloses a plastic bottle having a two-layer structure in which an inner layer is made of virgin plastic and an outer layer is made of recycled plastic. Patent Literature 2 discloses a manufacturing method for a laminated resin molded product including: an outer layer molding process of molding a tubular outer layer material using a recycled resin; and an inner layer molding process of laminating and molding, on an inner surface side of the outer layer material, a tubular inner layer material using a virgin resin that is thinner than the outer layer material. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP-2002-103429-A 
     Patent Literature 2: JP-2002-104362-A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In recent years, marine pollution caused by plastic waste is seen as a problem seriously, and measures of 3R (reduce, reuse, recycle) of plastics have been activated internationally. For a food/beverage/medicine bottle (food container), there has been developed a method of blow molding a preform that is injection-molded in an inner and outer two-layer structure, in which a virgin material is used for a portion (inner layer) to come into contact with content, and a recycled material is used for a non-contact portion (outer layer). However, with a two-layer molding method in the related art, the haze (turbidity) of the bottle tends to be large. It is difficult to manufacture a bottle having sufficient transparency, and commercialization (practical use) has not progressed. 
     An object of the present invention is to provide a preform from which a resin-made container having a two-layer structure and having high transparency even when a use ratio of a recycled material is large can be formed, a resin-made container having a two-layer structure and having high transparency even when a use ratio of a recycled material is large, and manufacturing methods for manufacturing the preform and the resin-made container. 
     Solution to Problem 
     An aspect of the present invention that can solve the above problem is a preform including: 
     an opening portion; 
     a body portion; and 
     a bottom portion, the preform having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material, 
     in which a weight ratio of the recycled material to a total weight of the preform is 50% by weight or more, 
     in which a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more, and 
     in which a haze of a body portion of a container molded from the preform is 1.8% or less. 
     Another aspect of the present invention that can solve the above problem is a manufacturing method for manufacturing a preform, the preform including an opening portion, a body portion, and a bottom portion, and the preform having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material, the manufacturing method including: 
     a first injection molding process of injecting the virgin material or the recycled material into a first mold to injection mold an inner layer material or an outer layer material; and 
     a second injection molding process of accommodating the inner layer material or the outer layer material molded in the first injection molding process in a second mold, and injecting the recycled material to an outer side of the inner layer material to injection mold an outer layer material or injecting the virgin material to an inner side of the outer layer material to injection mold an inner layer material, 
     in which the inner layer material and the outer layer material are molded such that a weight ratio of the recycled material to a total weight of the preform is 50% by weight or more and a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more. 
     Another aspect of the present invention that can solve the above problem is a resin-made container including: 
     an opening portion; 
     a body portion; and 
     a bottom portion, the resin-made container having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material, 
     in which a weight ratio of the recycled material to a total weight of the resin-made container is 50% by weight or more, 
     in which a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more, and 
     in which a haze of the body portion is 1.8% or less. 
     Another aspect of the present invention that can solve the above problem is a manufacturing method for manufacturing a resin-made container, the manufacturing method including: 
     an injection molding process of injection molding a preform, the preform including an opening portion, a body portion, and a bottom portion, and the preform having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material; 
     a temperature adjustment process of adjusting a temperature of the preform; and 
     a blow molding process of blow molding the preform to mold a resin-made container, 
     in which the injection molding process includes
         a first injection molding process of injecting the virgin material or the recycled material into a first mold to injection mold an inner layer material or an outer layer material, and   a second injection molding process of accommodating the inner layer material or the outer layer material molded in the first injection molding process in a second mold, and injecting the recycled material to an outer side of the inner layer material to injection mold an outer layer material, or injecting the virgin material to an inner side of the outer layer material to injection mold an inner layer material, and       

     in which in the injection molding process, the inner layer material and the outer layer material are molded such that a weight ratio of the recycled material to a total weight of the preform is 50% by weight or more and a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a preform from which a resin-made container having a two-layer structure and having high transparency even when a use ratio of a recycled material is large can be formed, a resin-made container having a two-layer structure and having high transparency even when a use ratio of a recycled material is large, and manufacturing methods for manufacturing the preform and the resin-made container. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a preform according to an embodiment. 
         FIG. 2  is a cross-sectional view illustrating a resin-made container according to the embodiment. 
         FIG. 3  is a flowchart illustrating a manufacturing process of the preform according to the embodiment. 
         FIG. 4  is a cross-sectional view illustrating a mode of injection molding of the preform according to the embodiment. 
         FIG. 5  is a cross-sectional view illustrating a mode of cooling the preform according to the embodiment. 
         FIG. 6  is a cross-sectional view illustrating another mode of cooling the preform according to the embodiment. 
         FIG. 7  is a flowchart illustrating a manufacturing process of the resin-made container according to the embodiment. 
         FIG. 8  is a schematic view illustrating a manufacturing device of the resin-made container according to the embodiment. 
         FIG. 9  is a flowchart illustrating a manufacturing process of a resin-made container according to a modification of the embodiment. 
         FIG. 10  is a schematic view illustrating a manufacturing device of the resin-made container according to the modification of the embodiment. 
         FIG. 11  is a cross-sectional view illustrating a mode of injection molding of a preform according to the modification of the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that, for convenience of description, the dimensions of the respective members illustrated in the drawings may be different from the actual dimensions of the respective members. 
     First, a preform  10  according to an embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a cross-sectional view of the preform  10 . The preform  10  is a tubular resin-molded product including an opening portion  12 , a neck portion  14  that is continuous with the opening portion  12 , a body portion  16  that is continuous with the neck portion  14 , and a bottom portion  18  that is continuous with the body portion  16 . The body portion  16  and the bottom portion  18  have a two-layer structure including an inner layer  22  and an outer layer  24 . The inner layer  22  is made of a virgin material that is an unused resin material. The outer layer  24  is made of a recycled material prepared by recycling a used resin material. As a base material of the virgin material and the recycled material, a thermoplastic resin (crystalline plastic) having transparency in an amorphous state is used, such as a polyethylene terephthalate (PET) resin. 
     The preform  10  is used to mold a resin-made container  30  to be described later. 
     A weight ratio of the recycled material to a total weight of the preform  10  is 50% by weight or more. The weight ratio is preferably 60% by weight or more from the viewpoint of a recycling rate of a resin material, and is preferably 70% by weight or less from the viewpoint of transparency of a container to be molded. A ratio of a thickness th 2  of the outer layer  24  to a thickness th 1  of the inner layer  22  in the body portion  16  is 1.5 or more. The ratio is preferably 3.0 or less from the viewpoint of transparency of the container to be molded. 
     Gate marks  22   a  and  24   a  formed by injection molding exist in the inner layer  22  and the outer layer  24  in the bottom portion  18  of the preform  10 , respectively. A height he 1  of the gate mark  22   a  of the inner layer  22  is smaller than a thickness th 3  of the outer layer  24  in the bottom portion  18 . 
     Next, the container  30  according to the embodiment will be described with reference to  FIG. 2 .  FIG. 2  is a cross-sectional view of the container  30 . The container  30  is a bottle-like resin-made container obtained by blow molding the preform  10 . The container  30  includes the neck portion  14  that is continuous with the opening portion  12 , a body portion  36  that is continuous with the neck portion  14 , and a bottom portion  38  that is continuous with the body portion  36 . Similarly to the preform  10 , the body portion  36  and the bottom portion  38  have a two-layer structure including an inner layer  42  made of a virgin material and an outer layer  44  made of a recycled material. 
     A weight ratio of the recycled material to a total weight of the container  30  and a ratio of a thickness th 12  of the outer layer  44  to a thickness th 11  of the inner layer  42  in the body portion  36  are the same as the weight ratio of the recycled material to the total weight of the preform  10  and the ratio of the thickness th 2  of the outer layer  24  to the thickness th 1  of the inner layer  22  in the body portion  16 , respectively, and thus a description thereof will be omitted. 
     A haze of the body portion  36  of the container  30  is 1.8% or less, more preferably 1.4% or less, still more preferably 1.0% or less. Although not particularly limited, a lower limit of the haze may be 0.1%. The haze mentioned here represents an average value of values obtained by selecting and measuring  10  arbitrary portions of the body portion  36 . The haze is measured using a haze meter (haze meter) in accordance with “Plastics: determination of haze for transparent materials (JIS-K7136: 2000)”. The container  30  is a resin-made container of a two-layer structure having high transparency even in a case of a large use ratio of the recycled material, and can achieve a high recycling rate of a plastic material while being highly practical. 
     Next, a manufacturing method for the preform  10  will be described with reference to  FIGS. 3 to 6 .  FIG. 3  is a flowchart illustrating a manufacturing process of the preform  10 .  FIG. 4  is a diagram illustrating a mode of injection molding of the preform  10 .  FIGS. 5 and 6  are diagrams illustrating modes of cooling after injection molding of the preform  10 . 
     As shown in  FIG. 3 , the manufacturing method for manufacturing the preform  10  according to the present embodiment includes an inner layer material molding process S 1  and an outer layer material molding process S 2 , which are two steps of injection molding process. Here, each process will be described with reference to  FIG. 4 . In the inner layer material molding process S 1 , a virgin material is injected into a cavity defined by a first mold  50 , which includes a first cavity mold  52 , a first injection core mold  54 , and a neck mold  56   m , via a first gate  58 . The first mold  50  includes a first hot runner mold  59 . The first hot runner mold  59  has a valve pin  59   a  that is movable toward the first gate  58  in a flow path through which a resin material in a molten state (for example, a PET resin in a molten state at about 255° C.) flows. That is, the first gate  58  of the first mold  50  is configured as a valve gate. When filling of the virgin material into the cavity is completed, mold clamping of the first mold  50  is maintained for a predetermined period of time, and thereafter the first mold  50  is opened, so that an inner layer material  60  is molded. A circuit (medium flow hole or medium flow groove) through which a cooling medium (fluid) for cooling the inner layer material  60  flows is provided in the first cavity mold  52  and the first injection core mold  54 , and the cooling medium is appropriately set in a range of, for example, about 5° C. to about 20° C. 
     The molded inner layer material  60  is lifted together with the first injection core mold  54  and the neck mold  56 , and is separated from the first cavity mold  52 . Further, the first injection core mold  54  is further lifted and is separated from the inner layer material  60 . Then, the inner layer material  60  is rotated together with the neck mold  56  by a rotation part (not shown) in a state of being held by the neck mold  56 , and is disposed above a second cavity mold  72 . In the outer layer material molding process S 2 , the neck mold  56  that holds the inner layer material  60  is clamped to a second injection core mold  55  and the second cavity mold  72 , so that the inner layer material  60  is accommodated in a second mold  70  that includes the second cavity mold  72 , the second injection core mold  55 , and the neck mold  56 . Then, a recycled material in a molten state is injected to a portion on an outer side of the inner layer material  60  in a cavity defined by the second mold  70  via a second gate  78 . The second mold  70  includes a second hot runner mold  79 . The second hot runner mold  79  may have a valve pin that is movable toward the second gate  78  in a flow path through which a resin material flows. That is, the second gate  78  of the second mold  70  may be configured as a valve gate. When filling of the recycled material into the cavity is completed, mold clamping of the second mold  70  is maintained for a predetermined period of time, and thereafter the second mold  70  is opened, so that the preform  10  including an outer layer material  80  and the inner layer material  60  is molded. In the present embodiment, the inner layer material molding process S 1  of the next preform  10  is performed during the outer layer material molding process S 2  of the previous preform  10 . In addition, in the second cavity mold  72  and the second injection core mold  55 , a circuit through which a cooling medium for cooling the outer layer material  80  and the inner layer material  60  flows is provided, and the cooling medium is appropriately set within a range of, for example, about 5° C. to about 20° C. Note that, the temperature of the cooling medium, that is, a cooling intensity may be different in the first mold  50  and the second mold  70  (for example, the temperature of the cooling medium of the second mold  70  is set to be lower than that of the first mold  50 ). Further, even in the second mold  70 , the cooling intensity may differ in the second cavity mold  72  and in the second injection core mold  55  (for example, the temperature of the cooling medium of the second cavity mold  72  is set to be lower than that of the second injection core mold  55 ). 
     In the inner layer material molding process S 1  and the outer layer material molding process S 2 , the inner layer material  60  and the outer layer material  80  are molded by using the first mold  50  and the second mold  70  designed so that the weight ratio of the recycled material (the outer layer material  80 ) to the total weight of the preform  10  is 50% by weight or more and the ratio of the thickness of the outer layer  24  (the outer layer material  80 ) to the thickness of the inner layer  22  (the inner layer material  60 ) in the body portion  16  of the preform is 1.5 or more. Here, a length le 1  of the first gate  58  in the first mold  50  is smaller than the thickness th 3  of the outer layer  24  (the outer layer material  80 ) in the bottom portion  18  of the preform  10 . 
     When the manufacturing method for manufacturing the preform  10  according to the present embodiment includes a cooling process S 3  of cooling the preform after the outer layer material molding process S 2 , cooling time of the injection molding process can be shortened, which is preferable from the viewpoint of production efficiency ( FIG. 3 ). The cooling process S 3  mentioned here does not include the process in which the preform  10  is cooled with the second mold  70  when the mold clamping of the second mold  70  is maintained. Here, a mode of the cooling process S 3  will be described with reference to  FIGS. 5 and 6 . 
       FIG. 5  is a diagram illustrating a state of a mode of the cooling process S 3 . In the cooling process S 3  illustrated in  FIG. 5 , the preform  10  released from the second mold  70  is accommodated in a third cavity mold  100 , and an air introduction member  110  is brought into contact with the preform  10  airtightly. The air introduction member  110  includes a rod member  112  that is hollow and provided with an air flow hole inside, and a fitting core (blow core member)  114 . The rod member  112  is accommodated inside the fitting core  114  so as to be movable up and down. An inner-side flow port  116  through which air can be jetted or sucked is provided in a tip of the rod member  112 . A temperature of the air is appropriately set within a range of, for example, about 0° C. to about 20° C. (normal temperatures) according to a thickness of the preform  10  or the container  30 . The fitting core  114  is configured to be fitted into (brought into close contact with) the neck portion  14  when the air introduction member  110  is inserted into the preform  10  (when the air introduction member  110  is brought into contact with the perform  10  airtightly). Accordingly, it is possible to prevent the air inside the preform  10  from leaking from the neck portion  14  to the outside of the fitting core  114 . A gap between the rod member  112  and the fitting core  114  is an air flow path for supplying and discharging air to and from the preform  10 . A gap formed by a tip of the fitting core  114  and the rod member  112  constitutes an outer-side flow port  118  through which air can be jetted or sucked. The inner-side flow port  116  and the outer-side flow port  118  may be an air-blowing port and a discharge port respectively. For example, air is fed into the preform  10  from the air-blowing port of the air introduction member  110 , and air is discharged from the discharge port of the air introduction member  110  to the outside of the preform  10 , thereby cooling the preform  10 . In addition, a circuit for a cooling medium for cooling the outer layer material  80  is also provided in the third cavity mold  100 , and the fluid medium is appropriately set in a range of, for example, about 5° C. to about 80° C., more preferably 10° C. to 70° C., and still more preferably 20° C. to 65° C. 
       FIG. 6  is a diagram illustrating a state of another mode of the cooling process S 3 . In the cooling process S 3  illustrated in  FIG. 6 , the preform  10  released from the second mold  70  is accommodated in a fourth cavity mold  120 , and the preform  10  is sandwiched between the fourth cavity mold  120  and a core mold  130  configured to be movable up and down, thereby cooling the preform  10 . The fourth cavity mold  120  and the core mold  130  are also provided with a circuit through which a cooling medium set in a range of, for example, about 5° C. to about 80° C., more preferably 10° C. to 70° C., and still more preferably 20° C. to 65° C. flows. 
     Next, a manufacturing method for manufacturing the container  30  will be described with reference to  FIGS. 4 to 7 .  FIG. 7  is a diagram illustrating a manufacturing process of the container  30 . As illustrated in  FIG. 7 , the manufacturing method for manufacturing the container  30  according to the present embodiment includes an injection molding process S 11  of injection molding the preform  10 , a temperature adjustment process S 12  of adjusting a temperature of the preform  10 , and a blow molding process S 13  of blow molding the preform  10  to mold the container  30 . 
     First, the injection molding process S 11  will be described. The injection molding process S 11  includes the inner layer material molding process S 1  and the outer layer material molding process S 2  described in the manufacturing method for manufacturing the preform  10 . In the injection molding process S 11 , as described in the inner layer material molding process S 1  and the outer layer material molding process S 2  of the preform  10 , the inner layer material  60  and the outer layer material  80  are molded such that the weight ratio of the recycled material (the outer layer material  80 ) to the total weight of the preform  10  is 50% by weight or more and the ratio of the thickness of the outer layer  24  (the outer layer material  80 ) to the thickness of the inner layer  22  (the inner layer material  60 ) in the body portion  16  of the preform is 1.5 or more. The first mold  50  used in the inner layer material molding process S 1 , the second mold  70  used in the outer layer material molding process S 2 , and other modes adopted in the injection molding process S 11  are similar to those described in the manufacturing method for the preform  10  ( FIG. 4 ), and thus a description thereof will be omitted. 
     Next, the temperature adjustment process S 12  will be described. The temperature adjustment process S 12  is a process of adjusting a temperature of the injection-molded preform  10  to a temperature range suitable for blow molding. In the temperature adjustment process S 12 , the temperature of the preform  10  is adjusted by using a temperature adjustment pod, a temperature adjustment core, an infrared heater, or the like. In addition, in the temperature adjustment process S 12 , the modes ( FIGS. 5 and 6 ) described in the cooling process S 3  of the manufacturing method for the preform  10  may be adopted, and the temperature may be adjusted while cooling the preform. When the temperature adjustment process S 12  adopts the modes described in the cooling process S 3  of the manufacturing method for the preform  10 , the production efficiency of the container  30  is improved, which is preferable. In particular, when performing the manufacturing of the preform  10  and the container  30  continuously in a hot parison type manufacturing device of a resin-made container shown in  FIG. 8  that will be described later, the production efficiency of the container  30  is improved, which is preferable. In addition, when performing the injection molding and blow molding of a two-layer preform continuously using a hot parison type blow molding method, a boundary portion between the inner layer  22  and the outer layer  24  is insufficiently cooled (gradually cooled), and the haze is likely to increase. However, when the modes ( FIGS. 5 and 6 ) described in the cooling process S 3  are adopted in the temperature adjustment process S 12 , the cooling efficiency of the boundary portion can be improved while the amount of heat required in the blow molding is maintained, and the haze of the container  30  can be reduced. When the cooling process S 3  is adopted in the temperature adjustment process S 12 , the temperatures of the cooling medium flowing through the third cavity mold  100 , the fourth cavity mold  120 , and the core mold  130  are appropriately set in a wider range of, for example, about 10° C. to about 65° C. 
     Next, the blow molding process S 13  will be described. In the blow molding process S 13 , the preform  10  is accommodated in a blow cavity mold. Subsequently, while the preform  10  is optionally stretched by a stretching rod, the preform  10  is inflated to a shape of the container  30  by introducing blow air from a blow core mold, and the container  30  is manufactured. Thereafter, the container  30  is released from the mold. The container is manufactured according to the above procedure. 
     Here, a manufacturing device  150  of the container  30  according to the present embodiment will be described with reference to  FIG. 8 .  FIG. 8  is a functional block diagram of the manufacturing device  150  of the container  30 . The manufacturing device  150  includes an injection molding part  152  for manufacturing the preform  10 , a temperature adjustment part  154  for adjusting the temperature of the manufactured preform  10 , a blow molding part (an example of a blow device)  156  for blowing the preform  10  to manufacture the container  30 , and a taking-out part  158  for taking out the manufactured container  30 . The preform  10  and the container  30  are conveyed by a conveying part (not illustrated) in an order of the injection molding part  152 , the temperature adjustment part  154 , the blow molding part  156 , and the taking-out part  158  in the manufacturing device  150 . As modes of the injection molding part  152 , the temperature adjustment part  154 , and the blow molding part  156 , configurations of the modes ( FIGS. 4 to 6 ) described in the manufacturing method for the preform  10  and the manufacturing method for the container  30  are adopted. The manufacturing device  150  is a hot parison type manufacturing device of a resin-made container, and continuously performs the manufacturing of the preform  10  and the container  30 . 
     In the meantime, during the international activation of the measures of  3 R of plastics, various recycling measures are taken with an ultimate goal of the “Bottle-to-Bottle” recycling even in the field of a PET container. For example, a detergent/toner PET bottle (non-food container) is often manufactured using a blended material of a flake material obtained by pulverizing a used PET bottle or a recycled pellet material and a virgin material. On the other hand, a food/beverage/medicine PET bottle (food container) is manufactured using a virgin material, and a recycled material is seldom used. This is because this type of PET bottle is required to have high safety on sanitation. Therefore, there has been developed a method of blow molding a preform that is injection-molded in an inner and outer two-layer structure, in which a virgin material is used for a portion (inner layer) to come into contact with the content, and a recycled material is used for a non-contact portion (outer layer). 
     However, with a two-layer molding method in the related art, the haze (turbidity) of the bottle tends to be large. It is difficult to manufacture a bottle having sufficient transparency, and commercialization (practical use) has not progressed. In addition, also in the case of using a blended material, considering the transparency of the bottle, a use ratio (weight ratio) of a recycled pellet material is limited to about 30% by weight at most, and further improvement is required. 
     According to the preform  10  having the above configuration, it is possible to form the resin-made container  30  having a two-layer structure and having high transparency even when the use ratio of the recycled material is large. Specifically, it is possible to form a resin-made container having transparency equivalent to that of a container formed from a two-layer preform made of a blended material containing 30% by weight of a recycled pellet material. 
     In addition, in the preform  10 , since the height “he 1 ” of the gate mark  22   a  is smaller than the thickness “th 3 ” of the outer layer  24  in the bottom portion  18 , an occurrence that the virgin material melts and mixes with the recycled material at the time of injecting the recycled material can be suppressed. Accordingly, it is possible to provide the preform  10  in which whitening in the bottom portion  18  thereof can be suppressed and from which the resin-made container  30  that has a two-layer structure and has high transparency can be formed. 
     In addition, the recycled material has a higher crystallization rate and is likely to whiten as compared with the virgin material. In order to suppress whitening of the recycled material, the inner layer material  60  made of the virgin material was molded first, and then the outer layer material  80  made of the recycled material was molded. However, the following was found: a phenomenon occurs that, due to injection of the recycled material, the virgin material is reheated in a temperature range (for example, at about 150° C. in the case of the PET resin) in which the virgin material is likely to crystalize and is cooled gradually, and whitening (crystallization) is likely to occur in a boundary surface between the virgin material and the recycled material. Accordingly, the cooling efficiency of the inner layer  22  by the first mold  50  and the second mold  70  (second injection core mold  55 ) is increased by lowering a weight ratio of the virgin material to the total weight of the preform  10  and reducing the thickness of the inner layer  22  with respect to the outer layer  24 , so that the whitening in the boundary surface between the virgin material and the recycled material can be successfully suppressed. That is, according to the above-described manufacturing method for manufacturing the preform  10 , the inner layer material  60  made of the virgin material is molded and thereafter the outer layer material  80  made of the recycled material is molded, and the inner layer material  60  and the outer layer material  80  are molded such that the weight ratio of the recycled material to the total weight of the preform  10  is 50% by weight or more and the ratio of the thickness th 2  of the outer layer  24  to the thickness th 1  of the inner layer  22  in the body portion  16  is 1.5 or more. Accordingly, it is possible to provide the preform  10  capable of forming the resin-made container  30  that has a two-layer structure and has high transparency even when the use ratio of the recycled material is large. 
     In addition, in the above-described manufacturing method for manufacturing the preform  10 , since the length le 1  of the first gate  58  from which the virgin material is injected is smaller than the thickness th 3  of the outer layer  24  in the bottom portion  18 , the height he 1  of the gate mark  22   a  formed in the inner layer material  60  is reduced, and it is possible to prevent the virgin material from melting and mixing with the recycled material at the time of injecting the recycled material. Accordingly, it is possible to provide the preform  10  in which whitening caused by crystallization or the like in the bottom portion  18  thereof can be suppressed and from which the resin-made container  30  that has a two-layer structure and has high transparency can be formed. 
     In addition, in the above-described manufacturing method for manufacturing the preform  10 , since the cooling process S 3  of cooling the preform  10  after the outer layer material molding process S 2  is provided, it is possible to shorten the cooling time of the preform  10  at the time of injection molding. Accordingly, molding of the next preform  10  can be started during the cooling of the preform  10 , and the production efficiency can be improved. 
     In addition, since the preform  10  is cooled by sending and discharging air in the cooling process S 3  of the above-described manufacturing method for manufacturing the preform  10 , it is possible to accelerate the cooling of the preform  10 . Accordingly, it is possible to provide the preform  10  from which the resin-made container  30  which has a two-layer structure and is more excellent in transparency can be formed, while improving the production efficiency of the preform  10 . 
     In addition, since the preform  10  is sandwiched between the fourth cavity mold  120  and the core mold  130  in the cooling process S 3  of the above-described manufacturing method for manufacturing the preform  10 , it is possible to accelerate the cooling of the preform  10 . Accordingly, it is possible to provide the preform  10  from which the resin-made container  30  which has a two-layer structure and is more excellent in transparency can be formed, while improving the production efficiency of the preform  10 . 
     In addition, according to the above-described manufacturing method for manufacturing the container  30 , the outer layer material  80  of the preform  10  is molded after the inner layer material  60  of the preform  10  is molded, and the inner layer material  60  and the outer layer material  80  of the preform  10  are molded such that the weight ratio of the recycled material to the total weight of the preform  10  is 50% by weight or more and the ratio of the thickness th 2  of the outer layer  24  to the thickness th 1  of the inner layer  22  in the body portion  16  is 1.5 or more. Accordingly, it is possible to provide the container  30  having a two-layer structure and having high transparency even when a use ratio of the recycled material is large. In addition, regarding the hot parison type two-layer molding method in the related art, since the haze of the container tends to become large and it is difficult to manufacture a bottle having sufficient transparency, commercialization (practical use) has not progressed. According to the above method, in particular, in the hot parison type two-layer molding method, it is possible to provide the container  30  having a two-layer structure and having high transparency even when the use ratio of the recycled material is large. 
     In addition, since the injection molding process S 11  and the temperature adjustment process S 12  in the above-described manufacturing method for manufacturing the container  30  adopt the modes described in the manufacturing method for manufacturing the preform  10 , it is possible to form a resin-made container having a two-layer structure and being more excellent in transparency, it is possible to shorten cycle time of container molding, and it is possible to improve the production efficiency. 
     Although a mode is described in the above embodiment in which the outer layer material molding process S 2  is performed after the inner layer material molding process S 1 , the present invention is not limited to this mode.  FIG. 9  is a flowchart illustrating a manufacturing process of a resin-made container according to a modification of the above embodiment. As shown in  FIG. 9 , a first injection molding process S 31 , a first temperature adjustment process S 32 , a second injection molding process S 33 , a second temperature adjustment process S 34 , and a blow molding process S 35  may be performed in this order to manufacture a resin-made container. In molding a preform, the first injection molding process S 31 , the first temperature adjustment process S 32 , the second injection molding process S 33 , and the second temperature adjustment process S 34  may be performed in this order. 
     The first injection molding process S 31  in this modification is a process of molding any one of an inner layer material and an outer layer material of a preform, and the second injection molding process S 33  is a step of molding one of the inner layer material and the outer layer material of the preform that is not molded in the first injection molding process S 31  to mold the preform. The first temperature adjustment process S 32  is a process of adjusting a temperature of the inner layer material or the outer layer material of the preform molded in the first injection molding process S 31 . The first temperature adjustment process S 32  may be a step of cooling the inner layer material or the outer layer material of the preform. In the first temperature adjustment process S 32  between the first injection molding process S 31  and the second injection molding process S 33 , the inner layer material or the outer layer material of the preform that is first molded is subjected to post-cooling (in particular, a surface on which a resin material is to be laminated in the second injection molding process S 33  is subjected to post-cooling), so that haze reduction of the two-layer preform (haze reduction by suppressing whitening in a boundary surface between the inner layer material and the outer layer material) and molding cycle shortening can be realized. The second temperature adjustment process S 34  is a process of adjusting a temperature of the preform molded in the second injection molding process S 33 . The second temperature adjustment process S 34  may be a process of cooling the preform. The blow molding process S 35  is a process of blow molding the preform whose temperature is adjusted in the second temperature adjustment process S 34  to obtain the resin-made container. 
       FIG. 10  is a schematic diagram illustrating a manufacturing device  350  for a resin-made container according to a modification of the above-described embodiment. As illustrated in  FIG. 10 , the manufacturing device  350  is a six-station type manufacturing device including: a first injection molding part  352  that includes a first injection device  362 ; a first temperature adjustment part  354 ; a second injection molding part  353  that includes a second injection device  363 ; a second temperature adjustment part  355 ; a blow molding part  356 ; and a taking-out part  358 . In the manufacturing device  350 , the preform and the resin-made container are conveyed in a direction of arrows shown in the drawing by a conveying device  370  including a rotary disk or the like, and are molded in accordance with the manufacturing process described above. As specific modes of the stations, the modes of the above-described embodiment can be adopted as appropriate. 
     Although a mode is described in the above-described embodiment in which the two-step injection molding process of performing the outer layer material molding process S 2  after the inner layer material molding process S 1  is included, a mode in which an inner layer material is molded after an outer layer material is firstly molded may be adopted. Hereinafter, a modification of the present embodiment will be described with reference to  FIG. 11 .  FIG. 11  is a cross-sectional view illustrating a mode of injection molding of a preform  210  according to the modification of the above-described embodiment. 
     Hereinafter, the present modification will be described based on a manufacturing device that molds the preform  210  and molds a resin-made container from the preform  210 . The manufacturing device according to the present modification is similar to the manufacturing device  150  and the manufacturing device  350  described in the above-described embodiment and modification except that a configuration of the injection molding part is different. The injection molding part of the manufacturing device of the present modification includes a first mold  250  that molds an outer layer material  280  and a second mold  270  that molds an inner layer material  260  on an inner side of the outer layer material  280  (see  FIG. 11 ). 
     The first mold  250  includes a first cavity mold  252 , a first injection core mold  254 , and a neck mold  256 . The first mold  250  is configured to form the outer layer material  280  by pouring a recycled material into a cavity defined by mold clamping of these molds. The recycled material is supplied from a first hot runner mold  259  and poured into the cavity via a first gate  258 . 
     The first hot runner mold  259  has a valve pin  259   a  movable toward the first gate  258  in a flow path through which the recycled material flows. The valve pin  259   a  is configured to move to a position close to the first injection core mold  254  through the first gate  258  after the recycled material is filled in the cavity. Accordingly, a thin film portion  281  having a thickness smaller than that of a peripheral portion is formed in a central portion of a bottom portion of the outer layer material  280 . 
     The second mold  270  includes a second cavity mold  272 , a second injection core mold  255 , and a neck mold  256 . The neck mold  256  is a common neck mold that moves to a position of the second mold  270  in a state of holding the outer layer material  280  molded by the first mold  250 . A core diameter of the second injection core mold  255  is smaller than a core diameter of the first injection core mold  254  by a thickness of the layer of the inner layer material  260 . In addition, a size (diameter) of a recess in a top view of the second cavity mold  272  is the same as a size (diameter) of a recess in a top view of the first cavity mold  252 . The second mold  270  is configured to form the inner layer material  260  on the inner side of the outer layer material  280 , which is molded by the first mold  250 , by pouring a virgin material into a cavity defined by mold clamping of these molds. 
     The virgin material is supplied from a second hot runner mold  279  and is poured into the cavity via a second gate  278 . The thin film portion  281  formed in the outer layer material  280  is broken by the flow of the virgin material and thus the virgin material is poured into the cavity. When the thin film portion  281  of the outer layer material  280  is broken, an opening portion  282  is formed in a bottom portion  218  of the preform  210  (the bottom portion of the outer layer material  280 ). The virgin material poured into the cavity is filled into the cavity via the opening portion  282 . 
     In the present modification, a two-step injection molding process is adopted in which the outer layer material molding process of molding the outer layer material  280  by the first mold  250  is performed, and thereafter the inner layer material molding process of molding the inner layer material  260  on the inner side of the outer layer material  280  by the second mold  270  is performed. In the present modification, the preform  210  is molded such that a weight ratio of the recycled material to a total weight of the preform  210  formed by the two-step injection molding process and a ratio of a thickness of the outer layer with respect to a thickness of the inner layer in the body portion are similar to those in the above-described embodiment. In addition, in the present modification, the container is molded such that the haze of the body portion of the container formed from the preform  210  is similar to that in the above-described embodiment. 
     In the present modification, unlike the method (see  FIG. 7 ) in which the outer layer material molding process S 2  is performed after the inner layer material molding process S 1 , no gate mark is formed in the outer layer material  280  (recycled material) that is first molded in the first injection molding process. Therefore, the possibility that the virgin material and the recycled material are melted and mixed in a bottom region of the preform  210  is further lowered, and whitening (crystallization or the like) of the bottom portion can be more reliably suppressed. An injection amount of the inner layer material  260  (virgin material) injected in the second injection molding process is smaller than an injection amount of the outer layer material  280  (recycled material) injected in the first injection molding process, and a degree of reheating of the first molded outer layer material  280  is also reduced. Therefore, a phenomenon that whitening (crystallization) occurs in a boundary surface between the virgin material and the recycled material is unlikely to occur. As a result, in the present modification, the preform  210  from which a resin-made container having a two-layer structure and having high transparency can be formed can be manufactured and provided more easily. 
     The present modification is preferably performed by the manufacturing method of  FIG. 9  and the manufacturing device  350  of  FIG. 10 . This is because the thick outer layer material  280  of the preform  210  made of the recycled material can be additionally cooled (subjected to post-cooling) in the first temperature adjustment process S 32  (first temperature adjustment part  354 ) in addition to being cooled in the first injection molding process S 31  (first mold  250 ). Accordingly, it is possible to sufficiently cool the thick outer layer material  280  of the preform  210  to decrease the temperature thereof, and thus it is possible to suppress a temperature rise (reheating) of the outer layer material  280  due to the injection of the virgin material in the second injection molding process S 33  (second mold  270 ). Therefore, whitening of the preform  210  can be further reduced, and a container having a lower value of haze can be manufactured. 
     EXAMPLE 
     Hereinafter, an example of the present embodiment will be described. Note that the technical scope of the present invention is not limited to the present example. The technical scope of the present invention is defined in the claims or in a scope equivalent thereto. 
     By using the manufacturing device  150  described in the present embodiment and changing the resin material used in the injection molding of the preform, manufacturing tests of resin-made containers having a two-layer structure of Example 1, Example 2, and Example 3 were performed. 
     The container of Example 1 was formed from a preform having a structure shown in  FIG. 1  that includes an inner layer made of a PET virgin material (BK-2180, manufactured by Mitsubishi Chemical Co., Ltd.) and an outer layer made of a PET recycled material (LCG-1810, manufactured by Mexico Pet One Co., Ltd.). A weight ratio of the virgin material to a total weight was 38%, and a weight ratio of the recycled material to the total weight was 62%. A thickness of the inner layer in a body portion of the preform was 1.8 mm, and a thickness of the outer layer in the body portion of the preform was 2.98 mm 
     The container of Example 2 was formed from a preform having a structure shown in  FIG. 1  including an inner layer and an outer layer that are made of a blended material of a virgin material and a recycled material (a mixture of BK-2180 manufactured by Mitsubishi Chemical Co., Ltd. and LCG-1810 manufactured by Mexico Pet One Co., Ltd.), in which a proportion of the recycled material to a total weight was 30%. A weight ratio of the virgin material to the total weight was 70%. A thickness of the inner layer in a body portion of the preform was 1.8 mm, and a thickness of the outer layer in the body portion of the preform was 2.98 mm 
     The container of Example 3 was formed from a preform having a structure shown in  FIG. 1  including an inner layer and an outer layer that are made of a recycled material (LCG-1810, manufactured by Mexico Pet One Co., Ltd.). A thickness of the inner layer in a body portion of the preform was 1.8 mm, and a thickness of the outer layer in the body portion of the preform was 2.98 mm 
     Hazes in the body portions of the containers of Examples 1 to 3 were measured using a haze meter (NDH-300, manufactured by Nippon Denshoku Industries Co., Ltd.). Average values calculated from values obtained by selecting and measuring  10  arbitrary portions of the body portions of the containers of Examples 1 to 3 were 1.74%, 1.75%, and 2.69%, respectively. When conversion was performed by setting the thickness of the body portion to 0.5 mm, values of the hazes in Examples 1 to 3were respectively 1.36%, 1.49%, and 2.13%. It was found that in the containers of Examples 1 and 2, the hazes were lower than that of the container of Example 3 in which only the recycled material was used, and the transparency was good. In addition, it was found that the container of Example 1 exhibited a haze value equivalent to that of the container of Example 2 even though a use ratio of the recycle material in the container of Example 1was higher than that of the container of Example 2, and that the container of Example 1 was excellent in transparency while having a high recycling rate. 
     The present invention is not limited to the above embodiment and may be modified or improved as appropriate. Materials, shapes, dimensions, numerical values, forms, numbers, arrangement places, and the like of components in the above embodiment are optional and not limited as long as the present invention can be achieved. 
     For example, although a mode is described in the above-described embodiment in which the virgin material and the recycled material use a PET resin as a base material, a material using a PE resin, a PP resin, or the like as a base material may be used. However, in the mode of the present embodiment, the PET resin is preferable. 
     Hereinafter, aspects extracted from the above-described embodiment and modifications thereof will be listed.
     [1] A preform including:   

     an opening portion; 
     a body portion; and 
     a bottom portion, the preform having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material, 
     in which a weight ratio of the recycled material to a total weight of the preform is 50% by weight or more, 
     in which a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more, and 
     in which a haze of a body portion of a container molded from the preform is 1.8% or less.
     [2] The preform according to [1],   

     in which a height of a gate mark of the inner layer in the bottom portion is smaller than a thickness of the outer layer in the bottom portion.
     [3] A manufacturing method for manufacturing a preform, the preform including an opening portion, a body portion, and a bottom portion, and the preform having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material, the manufacturing method including:   

     a first injection molding process of injecting the virgin material or the recycled material into a first mold to injection mold an inner layer material or an outer layer material; and 
     a second injection molding process of accommodating the inner layer material or the outer layer material molded in the first injection molding process in a second mold, and injecting the recycled material to an outer side of the inner layer material to injection mold an outer layer material or injecting the virgin material to an inner side of the outer layer material to injection mold an inner layer material, 
     in which the inner layer material and the outer layer material are molded such that a weight ratio of the recycled material to a total weight of the preform is 50% by weight or more and a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more.
     [4] The manufacturing method for manufacturing a preform according to [3], in which the first injection molding process is an inner layer material molding process of injecting the virgin material into the first mold to injection mold the inner layer material, and in which the second injection molding process is an outer layer material molding process of accommodating the inner layer material in the second mold, and injecting the recycled material to the outer side of the inner layer material to injection mold the outer layer material.   [5] The manufacturing method for manufacturing a preform according to [4], in which a length of a gate in the first mold from which the virgin material is injected is smaller than a thickness of the outer layer in the bottom portion of the preform.   [6] The manufacturing method for manufacturing a preform according to [3],   

     in which the first injection molding process is an outer layer material molding process of injecting the recycled material into the first mold to injection mold the outer layer material, and 
     in which the second injection molding process is an inner layer material molding process of accommodating the outer layer material in the second mold, and injecting the virgin material to the inner side of the outer layer material to injection mold the inner layer material.
     [7] The manufacturing method for manufacturing a preform according to any one of [3] to [6], further including:   

     a cooling process of cooling the preform after the second injection molding process.
     [8] The manufacturing method for manufacturing a preform according to [7],   

     in which in the cooling process,
         the preform is accommodated in a cavity mold,   an air introduction member is airtightly brought into contact with the preform, and   the preform is cooled by sending air from an air-blowing port of the air introduction member into the preform and discharging the air from a discharge port of the air introduction member to an outside of the preform.       [9] The manufacturing method for manufacturing a preform according to [7],   

     in which in the cooling process, the preform is cooled by sandwiching the preform between a cavity mold and a core mold.
     [10] The manufacturing method for manufacturing a preform according to any one of [3] to [6], further including:   

     a first cooling process of cooling the inner layer material or the outer layer material after the first injection molding process; and 
     a second cooling process of cooling the preform after the second injection molding process.
     [11] The manufacturing method for manufacturing a preform according to [10],   

     in which in the first cooling process and the second cooling process,
         the preform is accommodated in a cavity mold,   an air introduction member is airtightly brought into contact with the preform, and   the preform is cooled by sending air from an air-blowing port of the air introduction member into the preform and discharging the air from a discharge port of the air introduction member to an outside of the preform.       [12] The manufacturing method for manufacturing a preform according to [10],   

     in which in the first cooling process and the second cooling process, the preform is cooled by sandwiching the preform between a cavity mold and a core mold.
     [13] A resin-made container including:   

     an opening portion; 
     a body portion; and 
     a bottom portion, the resin-made container having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material, 
     in which a weight ratio of the recycled material to a total weight of the resin-made container is 50% by weight or more, 
     in which a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more, and 
     in which a haze of the body portion is 1.8% or less.
     [14] A manufacturing method for manufacturing a resin-made container, the manufacturing method including:   

     an injection molding process of injection molding a preform, the preform including an opening portion, a body portion, and a bottom portion, and the preform having a two-layer structure in which the body portion and the bottom portion include an inner layer made of a virgin material and an outer layer made of a recycled material; 
     a temperature adjustment process of adjusting a temperature of the preform; and 
     a blow molding process of blow molding the preform to mold a resin-made container, 
     in which the injection molding process includes:
         a first injection molding process of injecting the virgin material or the recycled material into a first mold to injection mold an inner layer material or an outer layer material; and   a second injection molding process of accommodating the inner layer material or the outer layer material molded in the first injection molding process in a second mold, and injecting the recycled material to an outer side of the inner layer material to injection mold an outer layer material or injecting the virgin material to an inner side of the outer layer material to injection mold an inner layer material, and       

     in which in the injection molding process, the inner layer material and the outer layer material are molded such that a weight ratio of the recycled material to a total weight of the preform is 50% by weight or more and a ratio of a thickness of the outer layer to a thickness of the inner layer in the body portion is 1.5 or more.
     [15] The manufacturing method for manufacturing a resin-made container according to [14],   

     in which the first injection molding process is an inner layer material molding process of injecting the virgin material into the first mold to injection mold the inner layer material, and 
     in which the second injection molding process is an outer layer material molding process of accommodating the inner layer material in the second mold, and injecting the recycled material to the outer side of the inner layer material to injection mold the outer layer material.
     [16] The manufacturing method for manufacturing a resin-made container according to [15],   

     in which a length of a gate in the first mold from which the virgin material is injected is smaller than a thickness of the outer layer in the bottom portion of the preform.
     [17] The manufacturing method for manufacturing a resin-made container according to [14],   

     in which the first injection molding process is an outer layer material molding process of injecting the recycled material into the first mold to injection mold the outer layer material, and 
     in which the second injection molding process is an inner layer material molding process of accommodating the outer layer material in the second mold, and injecting the virgin material to the inner side of the outer layer material to injection mold the inner layer material.
     [18] The manufacturing method for manufacturing a resin-made container according to any one of [14] to [17],   

     in which the preform molded in the injection molding process is cooled in the temperature adjustment process.
     [19] The manufacturing method for manufacturing a resin-made container according to [18],   

     in which in the temperature adjustment process,
         the preform is accommodated in a cavity mold,   an air introduction member is airtightly brought into contact with the preform, and   the preform is cooled by sending air from an air-blowing port of the air introduction member into the preform and discharging the air from a discharge port of the air introduction member to an outside of the preform.       [20] The manufacturing method for manufacturing a resin-made container according to [18],   

     in which in the temperature adjustment process, the preform is cooled by sandwiching the preform between a cavity mold and a core mold.
     [21] The manufacturing method for manufacturing a resin-made container according to any one of [14] to [17],   

     in which the temperature adjustment process includes a first temperature adjustment process and a second temperature adjustment process, 
     in which the first temperature adjustment process is a process of cooling the inner layer material or the outer layer material after the first injection molding process, and 
     in which the second temperature adjustment process is a process of cooling the preform after the second injection molding process.
     [22] The manufacturing method for manufacturing a resin-made container according to [21],   

     in which in the first cooling process and the second cooling process,
         the preform is accommodated in a cavity mold,   an air introduction member is airtightly brought into contact with the preform, and   the preform is cooled by sending air from an air-blowing port of the air introduction member into the preform and discharging the air from a discharge port of the air introduction member to an outside of the preform.       [23] The manufacturing method for a resin-made container according to [21],   

     in which in the first cooling process and the second cooling process, the preform is cooled by sandwiching the preform between a cavity mold and a core mold. 
     The present application is based on Japanese Patent Application No. 2019-109558 filed on Jun. 12, 2019, the entire contents of which are incorporated herein by reference. Further, all references cited here are entirely incorporated. 
     REFERENCE SIGNS LIST 
       10 ,  210 : preform,  12 : opening portion,  14 : neck portion,  16 : body portion,  18 ,  218 : bottom portion,  22 : inner layer,  24 : outer layer,  22   a ,  24   a : gate mark,  30 : container,  36 : body portion,  38 : bottom portion,  42 : inner layer,  44 : outer layer,  50 ,  250 : first mold,  52 ,  252 : first cavity mold,  54 ,  254 : first injection core mold,  55 ,  255 : second injection core mold,  56 ,  256 : 
     neck mold,  58 ,  258 : first gate,  59 ,  259 : first hot runner mold,  59   a ,  259   a : valve pin,  60 ,  260 : inner layer material,  70 ,  270 : second mold,  72 ,  272 : second cavity mold,  78 ,  278 : second gate,  79 ,  279 : second hot runner mold,  80 ,  280 : outer layer material,  282 : opening portion,  100 : third cavity mold,  110 : air introduction member,  120 : fourth cavity mold,  130 : core mold,  150 ,  350 : manufacturing device,  152 : injection molding part,  154 : temperature adjustment part,  156 ,  356 : blow molding part,  158 ,  358 : taking-out part,  352 : first injection molding part,  353 : second injection molding part,  354 : first temperature adjustment part,  355 : second temperature adjustment part,  362 : first injection device,  363 : second injection device,  370 : 
     conveying device