Injection mold, injection stretch blow molding machine, and manufacturing method of hollow molded body

Abstract

To obtain an aesthetically pleasing hollow molded body with a well-defined bottom, so that no transfer marks of the roughened surface are produced on the bottom of the hollow molded body, when manufacturing a hollow molded body using a preform that is formed with a thin-walled bottom while taking advantage of roughening the outer surface of the injection core mold.SOLUTION: The outer surface of the tip of the injection core mold 12 corresponds to the preform bottom 10 and the bottom end 14a of the preform body 14, with the surface corresponding to the preform bottom 10 and the bottom end 14a of the preform body 14 being mirror-finished surfaces 20 and the preform corresponding surfaces other than the mirror-finished surface being rough-finished surfaces 15.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an injection molding die for molding a preform, an injection stretch blow molding machine equipped with this injection molding die for producing a hollow molded article from the preform, and a method for producing a hollow molded article. [Background technology]

[0002] Patent Document 1 points out the problem that the preform has a small taper and is long and slender, making it difficult to remove the injection core from the injection molding die used to mold the preform. As a countermeasure, it is shown that even if the outer surface of the injection core is mirror-polished to simply make it easier to remove, the air cannot escape and traces of trapped air are left.

[0003] Patent Document 1 also mentions forming fine irregularities such as a leather pattern or a matte pattern on the outer surface of the injection core mold by etching. It also shows that this technology can be used to perform embossing and blasting on the outer surface of the injection core mold to roughen the surface and create an air layer between the injected resin and the core mold, allowing air to flow toward the core tip. In the case of blasting, fine projection material particles are sprayed onto the surface to roughen it and create fine irregularities on the surface, and the molten resin does not transfer the uneven pattern but forms an air layer, which is explained to improve the suitability for removal from the mold.

[0004] Furthermore, Patent Document 1 discloses a technology in which the surface of the area corresponding to the inner surface of the preform near the tip of the preform mouth and the surface facing the inner surface of the preform opposite protrusions such as flanges and couplers are mirror-finished, and the other surfaces are textured, showing a technique in which the core mold and preform are in close contact at the mirror-finished parts, cooling the resin of the preform and preventing sink marks.

[0005] Patent Document 2 also discloses a technique for making it easier to remove the injection core mold from the injection-molded preform, in which a groove is formed on the surface of the body defining portion of the injection core mold, extending from the body defining portion to the neck defining portion, and the circumferential center line average roughness of the portion of the surface of the body defining portion of the injection core mold where the groove is formed is set to be 0.2 μm or more and 15 μm or less.

[0006] Patent Document 3 also shows that, as a way to make it easier to remove the injection core mold from the injection-molded preform, a large number of fine depressions are formed in the surface layer below the mouth molding part of the injection core mold, and that these depressions allow air to remain in the depressions during preform molding, causing an air layer to remain intermittently between the soft preform and the injection core mold, and that the depressions in the injection core mold cause partial contact between the inner surface of the soft preform and the outer surface of the injection core mold, thereby reducing frictional resistance when the injection core mold is pulled out.

[0007] Patent Document 4 does not disclose a technique for improving the release from the preform, but it does disclose the formation of a textured pattern formed of a rough surface formed with fine projections and recesses on the hemispherical surface at the tip of the injection core mold. The invention of Patent Document 4 itself aims to effectively generate foaming when the bottle is opened, and discloses a technique for transferring a pattern from the injection core mold to the bottom of the injection molded preform. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6326790 [Patent Document 2] Patent No. 6780155 [Patent Document 3] Japanese Patent Application Publication No. 04-085007 [Patent Document 4] JP 2017-088209 A Summary of the Invention [Problem to be solved by the invention]

[0009] A molding machine that molds hollow molded bodies such as PET bottles using the hot parison method includes an injection molding section in which molten resin is injected from an injection device to injection mold a preform, a blow molding section in which the high-temperature preform transferred from the injection molding section is stretched and gas is blown into it to blow mold a hollow molded body, and an ejection section that sends the hollow molded body out of the molding machine.

[0010] The injection molding section, the blow molding section, and the ejection section are provided so as to be positioned in order along the rotation direction of the rotating plate. The rotating plate rotates at predetermined angles, and the lip mold moves to the injection molding section, the blow molding section, and the ejection section while being positioned correspondingly thereto in order. In the injection molding section, the injection core mold and the injection cavity mold of the injection molding die provided in the injection molding section, and the lip mold are combined with these, and molten resin is injected into the injection molding section to injection mold a preform.

[0011] The injection molded preform is transported to the blow molding section by the lip mold, and the lip mold is combined with a split blow molding die to place the preform in the mold. In the blow molding section, the bottom of the preform is pushed down by a stretching rod to stretch it in the height direction, and gas is blown in to blow the preform into a hollow molded body.

[0012] The blow-molded hollow body is then transported to the removal section by a lip mold that moves with the rotation of the rotating plate. At the removal section, the lip mold opens the mouth of the hollow body so that the hollow body is sent out of the molding machine. The lip mold that has released the hollow molded body is moved to the injection molding section by the rotation of the rotating plate, where the lip mold is incorporated into the injection molding die as described above so that the preform can be injection molded.

[0013] In an injection stretch blow molding machine, shortening the molding cycle of a preform increases the production efficiency of a hollow molded body. Therefore, as described above, the outer surface of the injection core mold is roughened to improve releasability, thereby shortening the molding cycle of a preform.

[0014] In addition, by speeding up the timing of releasing the preform from the injection molding die, the molding cycle of the preform can be shortened and it can be transferred to the blow molding die earlier for blow molding, thereby improving the production efficiency of hollow molded bodies.

[0015] When the preform is released from the mold earlier and the preform is blow molded in a high temperature state in a blow molding die, if the bottom of the preform is as thick as the body of the preform, it will retain heat to a high degree and will be easily broken through by the stretch rod. Therefore, the bottom of the preform is designed to be thin so that it can be cooled more easily in the injection molding die, and the strength of the bottom of the preform is increased.

[0016] For example, the thickness of the bottommost part of the preform is 1.0 mm (excluding the gate portion), and the thickness of the preform body, which forms the body portion including the shoulder position of the hollow molded body (bottle), is 2.1 to 2.2 mm, and the shape of the preform is often set so that the ratio of the thickness of the preform bottom to the thickness of the preform body is about 1:2.

[0017] By roughening the outer surface of the injection core mold to improve the demoldability of the preform, and by reducing the thickness of the bottom of the preform, the timing of demolding of the preform can be accelerated without causing breakage during stretching, thereby shortening the molding cycle of the preform and increasing the production efficiency of hollow molded bodies.

[0018] However, since the outer surface of the injection core mold is roughened (roughened) over the entire surface that corresponds to the preform, there is a problem in that the roughening marks are transferred to the bottom surface of the blow-molded hollow molding and appear stretched. That is, in the preform body, the stretching and spreading is large when it is shaped into the molded body, so the roughening marks transferred from the injection core mold spread and disappear, but in the preform bottom, the stretching and spreading is small because the preform is stretched while a certain degree of hardness is ensured, and the transferred roughening marks remain and spread over the entire bottom surface.

[0019] Therefore, the bottom of the hollow molded body may be formed with traces of roughening remaining, which may impair the appearance of the hollow body.

[0020] In view of the above circumstances, the present invention aims to obtain a hollow molded body having a beautifully designed bottom by taking advantage of the advantages of roughening the outer surface of an injection core mold while preventing traces of roughening from appearing on the bottom of the hollow molded body when manufacturing the hollow molded body using a preform which is molded with a thin bottom. [Means for solving the problem]

[0021] The present invention has been made in consideration of the above problems, and provides an injection molding die that includes an injection core die and an injection cavity die, and that molds a preform whose bottom portion is thinner than its body portion, comprising: The above-mentioned problems are solved by providing an injection molding die, characterized in that the outer surface of the tip of the injection core die corresponds to the bottom of the preform and the lower end of the preform body to which the preform bottom is connected, the surfaces corresponding to the preform bottom and the lower end of the preform body are mirror-finished surfaces, and the preform-corresponding surfaces of the injection core die other than the mirror-finished surfaces are rough surfaces. A mirror surface is a surface finish state that corresponds to a surface roughness (triangular symbols ▽▽▽▽ in the old notation) that is, for example, an arithmetic mean roughness Ra of 0.2 μm or less and a maximum height Rz of 0.8 μm or less in JIS B 0601:2001. However, it is not limited to these values.

[0022] In the above-mentioned injection molding die of the present invention, the rough surface is preferably a machined surface obtained by roughening the outer surface of the injection core mold so as to form vertical fine grooves along the height direction of the injection core mold.

[0023] Another invention is an injection molding unit having an injection molding die for injection molding a preform; a blow molding section that stretches the injection-molded preform and blow molds a hollow molded body; Equipped with The injection molding die of the injection molding section includes an injection core mold and an injection cavity mold, An injection molding die for molding a preform in which a bottom portion of the preform is thinner than a body portion of the preform, The object of the present invention is to provide an injection stretch blow molding machine in which the outer surface of the tip of the injection core mold corresponds to the bottom of the preform and the lower end of the preform body to which the preform bottom is connected, the surfaces corresponding to the preform bottom and the lower end of the preform body are mirror-finished surfaces, and the preform-corresponding surfaces of the injection core mold other than the mirror-finished surfaces are rough surfaces.The object of the present invention is to provide an injection stretch blow molding machine in which the above-mentioned problems are solved.

[0024] In the above-mentioned injection stretch blow molding machine, the rough surface is preferably a processed surface that has been roughened so as to form vertical fine grooves along the height direction of the injection core mold.

[0025] Further, another invention relates to a method for producing a hollow molded body, comprising an injection molding step of injection molding a preform, and a blow molding step of stretching the preform obtained in the injection molding step and blowing a gas into the preform to blow mold the hollow molded body, The injection molding process is performed by injection molding a preform having a bottom part thinner than a body part of the preform using an injection molding die having an injection core die and an injection cavity die, This is a method for producing a hollow molded body, characterized in that the outer surface of the tip of the injection core mold corresponds to the bottom of the preform and the lower end of the preform body to which the preform bottom is connected, the surface corresponding to the preform bottom and the lower end of the preform body is a mirror-finished surface, and the preform-corresponding surface of the injection core mold other than the mirror-finished surface is a rough surface, and by providing this method for producing a hollow molded body, the above-mentioned problems are solved.

[0026] In the above-mentioned method for producing a hollow molded body, it is preferable that during the blow molding step, the bottom of the hollow molded body and a rising portion continuing from the bottom of the hollow molded body toward the body of the hollow molded body are formed by the preform bottom and the lower end of the preform body of the preform that correspond to the mirror-finished surface of the injection core mold.

[0027] Furthermore, the rough surface is preferably a machined surface that has been roughened so as to form vertical fine grooves along the height direction of the injection core mold on the outer surface of the injection core mold. Effect of the Invention

[0028] The injection molding die of the present invention is a die for molding a preform in which the bottom of the preform is thinner than the body of the preform, and since the outer surface of the tip of the injection core die corresponding to the bottom of the preform and the lower end of the preform body is a mirror-finished surface, the surface shape of the mirror-finished surface is transferred to the portion (inner surface) extending from the lower end of the preform body to the bottom of the preform.

[0029] Furthermore, the portions of the preform-compatible surface of the injection core mold other than the mirror-finished surface are rough, so that the injection core mold can be smoothly released from the preform, and the preform, which is in a soft state at high temperatures, does not lose its shape when released.

[0030] Furthermore, at the injection molding stage, cooling proceeds easily because the area from the lower end of the preform body to the bottom of the preform is thin, and even when the process proceeds to the blow molding stage, breakage of the bottom of the preform is prevented, resulting in the appropriate production of a hollow molded body. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of an injection stretch blow molding machine of the present invention. [Diagram 2] FIG. 1 is an explanatory diagram showing an injection molding die in the considered technology. [Diagram 3] FIG. 13 is an explanatory diagram showing a blow molding die according to the considered technique. [Figure 4] FIG. 2 is an explanatory diagram showing an example of an injection molding die. [Diagram 5] FIG. 2 is an explanatory diagram showing both a state in which a preform is placed in a blow molding die and a state in which a hollow molded body has been blow molded. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] In the figure, reference numeral 1 generally denotes an injection stretch blow molding machine for producing hollow molded articles made of synthetic resin, such as PET bottles and wide-mouth bottles.

[0033] (Injection stretch blow molding machine) Injection stretch blow molding machine 1 is a machine for manufacturing hollow molded bodies using the hot parison method, and as shown in Fig. 1, an injection molding section 3 into which molten resin is pumped from an injection device 2, a blow molding section 4 which blow molds the hollow molded body, and an ejection section 5 which sends the hollow molded body out of the molding machine are arranged in this order in the rotation direction of a rotating plate (not shown) having a lip mold 8. The movement marked with an arrow in Fig. 1 indicates the rotation direction of the rotating plate and the movement direction of the lip mold 8.

[0034] The following describes the technology studied to arrive at the present invention and the embodiment of the present invention. Note that the injection stretch blow molding machine 1 in the studied technology and the embodiment of the present invention have the same basic configuration as shown in Figure 1.

[0035] (Technology under consideration) First, in the technology under consideration, a preform 6 is injection molded using an injection molding die 7 shown in FIG. 2, the preform 6 is stretched in the convex direction, and gas is blown in to blow mold a wide-mouthed cup-shaped container A.

[0036] The injection molding die 7 used in the technology under consideration consists of a dome-shaped injection core die 12 that is convex downwards and a mortar-shaped injection cavity die 13 that opens upwards, and is configured by combining it with a lip die 8 when performing injection molding.

[0037] The preform 6 that is injection molded by the injection molding die 7 is shaped like a mortar that opens upward as shown in FIG. 3, and is made up of a preform bottom 10 and a preform body 14 that extends upward from the preform bottom 10 in an umbrella-like shape and is provided with a mouth at the upper edge.

[0038] Furthermore, the preform 6 has a shape in which the thickness of the preform bottom 10 is smaller than the thickness of the preform body 14. As a specific example, the thickness of the preform bottom 10 is 1.2 mm, and the thickness of the preform body (opening portion) is 2.0 mm.

[0039] In this injection molding die 7, the preform 6 is injection molded with the thickness of the preform bottom 10 being thinner than the thickness of the preform body 14, so that the cooling of the preform bottom 10 can proceed easily. By making the cooling of the preform bottom 10 proceed easily, the preform bottom 10 remains hard even when it is released from the injection molding die 7 and placed in the blow molding die 9, so that it will not break even when a stretching operation is performed.

[0040] 3 shows a state in which a mortar-shaped preform 6 is placed in a blow molding die 9 in an injection stretch blow molding machine 1 configured as the considered technology, and a blow-molded cup-shaped container A. In the blow molding die 9, the preform bottom 10 is thin and hard as described above, so that it expands in the radial direction of the preform 6 (the direction perpendicular to the height direction of the preform 6) by being stretched and blown with air or the like, forming the container bottom B of the cup-shaped container A.

[0041] On the other hand, the preform body 14 is thicker than the preform bottom 10 and maintains a soft state, so that it is stretched vertically and radially by drawing and blowing to form the container body C.

[0042] In this technology, the outer peripheral surface of the lower end of the injection core mold 12, which corresponds to the preform bottom 10, is a roughened surface 15, which is provided with many vertical fine grooves extending upward from the lowest end position along the core mold surface. A specific example of the processing is to roughen the surface vertically using sandpaper of the required grit size.

[0043] The outer surface of the injection core mold 12 corresponding to the preform body 14 is provided as a mirror-finished surface 20, which is a mirror surface formed by polishing with an abrasive, polishing paste, etc. so as to form a smooth surface with a predetermined surface roughness or less. In Fig. 3, the outer periphery of the preform bottom 10 and the outer periphery of the container bottom B are connected by a dashed line, making it easy to understand the degree to which the preform bottom 10 spreads when it forms the container bottom B.

[0044] According to this technology, it has been confirmed that by forming the preform bottom 10 of the injection molding die 7 that molds the mortar-shaped preform 6 with a thin wall thickness, it is possible to prevent the preform bottom 10 from breaking when the preform 6 is blow molded.

[0045] Furthermore, the provision of the roughened surface 15 at the bottom end of the injection core mold 12 is intended to ensure smooth demolding by preventing the occurrence of a problem in which air gets into the preform core layer due to a tearing force being applied to the preform 6 when the mold is opened. It was also found that the injection core mold 12 could be separated from the preform 6 without any problems even if the timing of demolding was brought forward by setting the thickness of the preform bottom 10 to be thin.

[0046] Next, an embodiment of the present invention will be described with reference to Figures 4 and 5. As described above, the basic configuration of the injection stretch blow molding machine 1 is the same as that described in the technology under review.

[0047] The injection molding section 3 in the injection stretch blow molding machine 1 of the embodiment has an injection molding die 7 that injection molds a preform 6 with molten resin from the injection device 2. The preform 6 is supported by a lip mold 8 that is combined with the injection molding die 7 and is provided so as to move away from the injection molding die 7 and to the blow molding section 4.

[0048] The blow molding section 4 has a split blow molding die 9, and a lip mold 8 is combined with the blow molding die 9 to place the preform 6 inside the blow molding die 9. After that, a stretching rod (not shown) enters the inside of the preform 6 to press down the bottom part 10 of the preform to perform stretching, and gas is blown in to blow-mold a hollow molded body 11 from the preform 6.

[0049] The blow-molded hollow body 11 is moved from the blow molding section 4 to the removal section 5 by the movement of the lip mold 8 away from the blow molding die 9. The lip mold 8 that has moved to the removal section 5 opens and releases the hold of the hollow body 11 on the mouth portion, and the hollow body 11 is sent out of the molding machine.

[0050] The lip mold 8 is arranged to close again and move to the injection molding section 3. The lip mold 8 moved to the injection molding section 3 is combined with the injection molding die 7, and as described above, the molten resin is fed into the injection molding die 7 to injection mold the preform 6.

[0051] (Method for manufacturing hollow molded body) In this way, the production of hollow molded bodies by the injection stretch blow molding machine 1 involves an injection molding process in the injection molding section 3, in which the preform 6 is injection molded, a blow molding process in the blow molding section 4, in which the preform 6 obtained in the injection molding section 3 is stretched and blow molded into a hollow molded body 11 by blowing, and an ejection section process in which the hollow molded body 11 blown in the blow molding section 4 reaches the ejection section 5 from which it is sent out of the molding machine, and the hollow molded body 11 is obtained by proceeding in order through the injection molding process, blow molding process, and ejection process.

[0052] The movement of the lip mold 8 is achieved by rotating the rotating plate at predetermined angles. When moving from the injection molding process to the blow molding process, the lip mold 8 moves while supporting the preform 6 in its mouth, and when moving from the blow molding process to the removal process, the lip mold 8 similarly moves while supporting the hollow molded body. Furthermore, when moving from the removal process to the injection molding process, only the lip mold 8 that has released the hollow molded body moves to the injection molding section.

[0053] In this way, the lip mold 8 moves in order from the injection molding section 3 to the blow molding section 4, from the blow molding section 4 to the removal section 5, and from the removal section 5 to the injection molding section 3, thereby continuously carrying out the injection molding process, the blow molding process, and the removal process to manufacture the hollow molded body 11. The rotating plate is provided with lip molds 8 in three locations corresponding to the injection molding section 3, the blow molding section 4, and the removal section 5, and the manufacturing of the hollow molded body proceeds with the above-mentioned process being different for each of the three lip molds 8.

[0054] (Injection mold) 4, the injection molding die 7 of the injection molding section 3 is equipped with an injection core die 12 and an injection cavity die 13, and molten resin is injected by combining the lip die 8. The injection molding die 7 consisting of the injection core die 12, injection cavity die 13, and lip die 8 is molded so that the preform bottom part 10 is thinner than the preform body part 14, and gradually becomes thinner from the lower end 14a of the preform body part 14 to the lowest end 10a of the preform bottom part 10.

[0055] By molding the preform so that it becomes gradually thinner from the lower end 14a of the preform body 14 to the lowest end 10a of the preform bottom 10, the cooling of the preform bottom 10 from the lower end 14a of the preform body 14 in the injection molding die 7 is accelerated, increasing the hardness around the preform bottom 10, and preventing the stretching rod from breaking through the preform bottom 10 side when stretching is performed in the blow molding section 4.

[0056] As described above, the injection molding die 7 shown in Fig. 4 is designed to injection mold a preform 6 that is gradually thinner from the lower end 14a of the preform body 14 to the bottom end 10a of the preform bottom 10 and is thinnest at the bottom end 10a. Note that the thin state of the bottom end 10a is explained without including the gate portion.

[0057] (Injection core type) Furthermore, in the injection molding die 7 according to the embodiment of the present invention, the outer surface of the injection core die 12 is provided with a roughened surface 15, except for a portion described below. The roughened surface 15 is a surface obtained by roughening the outer surface of the injection core die 12, which has been polished to a predetermined surface roughness that provides a mirror finish, vertically to form fine grooves that run along the height direction of the preform 6.

[0058] (roughened surface) The roughened surface 15 is processed to improve the flow of molten resin fed into the injection molding die 7 and to facilitate the removal of the injection core die 12 when demolded, and is finished to a surface roughness suitable for this purpose.

[0059] The specific position of the roughened surface 15 is shown as the diagonally lined area in Figure 4, and the portion corresponding to the roughened surface 15 in the preform 6 is shown in Figure 5, with the roughened surface 15 having been subjected to vertical roughening at the locations corresponding to the inner surface of the preform mouth portion 16 of the preform 6 and the inner surface of the general portion 14b of the preform body portion 14 which will become the shoulder portion 17, body portion 18 and skirt starting end 19 when made into the hollow molded body 11.

[0060] (Mirror polished surface) On the other hand, the tip of the outer surface of the injection core mold 12 (the lower end portion of the injection core mold) is a mirror-finished surface 20 that is not roughened but is mirror-finished. The mirror-finished surface 20 corresponds to the inner surface from the lower end 14a of the preform body 14 to the inner surface of the lowermost end 10a of the preform bottom 10 of the preform 6, and the mirror state of the mirror-finished surface 20 is transferred to these inner surfaces.

[0061] During the blow molding process, the portion from the lower end 14a of the preform body 14 to the lowest end 10a of the preform bottom 10, onto which the mirror-finished state of the mirror-finished surface 20 has been transferred, is formed as a rising portion 23 that expands in diameter from the bottom 21 of the hollow molded body 11 and the ground contact portion (thread tail) 22, which is the outer periphery of this bottom 21, toward the preform body 14, and continues to the starting end 19 of the bottom hem.

[0062] In Figure 5, the outer peripheral portion of the lower end 14a of the preform body 14 and the outer peripheral portion of the raised portion 23 of the hollow molded body 11 are connected by a dotted line, making it easy to understand the degree of expansion when the area up to the lower end 14a of the preform body 14 becomes the area up to the raised portion 23 of the hollow molded body 11.

[0063] As shown in Figures 4 and 5, the mirror-finished surface 20 of the injection core mold 12 is transferred to the region from the lowest end 10a of the preform bottom 10 to the lower end 14a of the preform body 14, so that no roughening marks are transferred to the bottom 21 and raised portion 23 of the hollow molded body 11, and a hollow molded body 11 is obtained that does not mar the aesthetic appearance of the bottom.

[0064] In the present invention, the finishing method for forming the mirror-finished surface 20 is not limited. As described above, the surface condition of the mirror-finished surface 20 can be expressed as a surface finish state equivalent to a surface roughness having an arithmetic mean roughness Ra of 0.2 μm or less or a maximum height Rz of 0.8 μm or less according to JIS B 0601:2001, but is not limited to the numerical values ​​indicating the roughness. [Explanation of symbols]

[0065] 1…Injection stretch blow molding machine 3…Injection molding section 4…Blow molding section 5…Removal section 6…Preform 7…Injection mold 8…Lip type 9…Blow molding mold 10…Bottom of preform 10a…Lowest end of the preform bottom 11...Hollow molded body 12…Injection core mold 13…Injection cavity mold 14…Preform body 14a…Lower end of preform body 14b…General part of preform body 15…Roughened surface 16…Preform mouth 17...Shoulder 18...Torso 19…Beginning of hem 20…Mirror finish surface 21…Bottom 22...Grounding part 23…Rising part

Claims

1. An injection molding die for molding a preform having a bottom part thinner than a body part of the preform, the injection molding die comprising an injection core die and an injection cavity die, An injection molding die characterized in that the outer surface of the tip of the injection core mold corresponds to the bottom of the preform and the lower end of the preform body to which the preform bottom is continuous, the surface corresponding to the preform bottom and the lower end of the preform body is a mirror-finished surface, and the preform-corresponding surface of the injection core mold other than the mirror-finished surface is a rough surface.

2. 2. The injection molding die according to claim 1, wherein the rough surface is a machined surface which is roughened so as to form fine vertical grooves along the height direction of the injection core die on the outer surface of the injection core die.

3. an injection molding section having an injection molding die for injection molding a preform; a blow molding section that stretches the injection-molded preform and blow molds a hollow molded body; Equipped with The injection molding die of the injection molding section includes an injection core mold and an injection cavity mold, An injection molding die for molding a preform in which a bottom portion of the preform is thinner than a body portion of the preform, an outer surface of a tip of an injection core mold corresponds to a bottom of a preform and a lower end of a body of a preform to which the bottom of the preform is continuous, the surface corresponding to the bottom of the preform and the lower end of the body of the preform is a mirror-finished surface, and the surface of the injection core mold corresponding to the preform other than the mirror-finished surface is a rough surface.

4. 4. The injection stretch blow molding machine according to claim 3, wherein the rough surface is a processed surface which is roughened so as to form vertical fine grooves along the height direction of the injection core mold on the outer surface of the injection core mold.

5. A method for producing a hollow molded body, comprising an injection molding step of injection molding a preform, and a blow molding step of stretching the preform obtained in the injection molding step and blowing a gas into the preform to form a hollow molded body, The injection molding process is performed by injection molding a preform having a bottom part thinner than a body part of the preform using an injection molding die having an injection core die and an injection cavity die, A method for producing a hollow molded body, characterized in that the outer surface of the tip of the injection core mold corresponds to the bottom of the preform and the lower end of the preform body to which the preform bottom is connected, the surfaces corresponding to the preform bottom and the lower end of the preform body are mirror-finished surfaces, and the surfaces of the injection core mold corresponding to the preform other than the mirror-finished surfaces are rough surfaces.

6. 6. The method for producing a hollow molded body according to claim 5, wherein during the blow molding process, the bottom of the hollow molded body and the lower end of the preform body of the preform corresponding to the mirror-finished surface of the injection core mold form a bottom of the hollow molded body and a rising portion that continues from the bottom of the hollow molded body toward the body of the hollow molded body.

7. 7. The method for producing a hollow molded article according to claim 5 or 6, wherein the rough surface is a machined surface which is roughened so as to form fine vertical grooves along the height direction of the injection core mold on the outer surface of the injection core mold.

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