BLOW MOLDING METHOD AND BLOW MOLDING APPARATUS

Abstract

A blow molding method and blow molding device are provided that can improve the degree of thickness unevenness in each part of a hollow container. [Solution] This is a blow molding method in which a resin preform (10) is subjected to a primary blow to form an intermediate molded product (30), and then the intermediate molded product (30) is subjected to a final blow to form the final molded product, a hollow container. At least one of the steps of performing the primary blow and the final blow includes a thinning step in which the target preform (10) or primary molded products (20a-20c) is stretched by blowing, and the stretched portions of the target primary molded products (20a-20c) are contracted by exhausting the blown air, and this blow molding method is configured to include a thinning step in which these steps are repeated continuously within a predetermined time.

Description

[Technical field]

[0001] The present invention relates to a blow molding method and a blow molding apparatus. [Background technology]

[0002] Conventionally, hollow containers (bottles) made of thermoplastic resin materials are widely used in society because they are lightweight, durable, easy to handle, and easy to maintain the desired aesthetic appearance. One example of this type of hollow container is a PET bottle that can be filled with liquids such as beverages.

[0003] Such hollow containers are usually molded by the so-called blow molding method. Representative blow molding methods include a hot parison method in which the heat remaining in an injection-molded preform is retained in the preform and the preform is blown at an appropriate temperature for blowing to be stretched, and a cold parison method in which a preform that has been injection-molded and cooled to room temperature is separately prepared, heated to an appropriate temperature for blowing, and then blown to be stretched (see, for example, Patent Document 1).

[0004] Also, various blow molding methods have been proposed for the purpose of improving the heat resistance of hollow containers. For example, there is a method having a step of blow molding a resin preform into a primary blow molded product, a step of holding the primary blow molded product in a heated mold and heat treating it, a step of heat treating an intermediate molded product outside the mold after being removed from the mold and shrinking, and a step of blow molding the intermediate molded product heat treated outside the mold into a final molded product in a final blow molding die (see Patent Document 2). There is also a method that omits the step of heat treatment outside the mold as described above (see Patent Document 3). The inventions of Patent Document 2 and Patent Document 3 attempt to promote crystallization of the resin by heat treatment, thereby improving heat resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-107391 A [Patent Document 2] Patent No. 3760045 [Patent Document 3] Patent No. 3907494 Summary of the Invention [Problem to be solved by the invention]

[0006] Here, in the above-mentioned hot parison and cold parison blow molding methods, the ease with which each part (shoulder, body, bottom, etc.) is stretched varies depending on the wall thickness of the preform. For this reason, regardless of which method is used, there is a risk that variations in wall thickness will occur in the hollow container, which is the final molded product. Variations in wall thickness can lead to a decrease in various performance characteristics of the hollow container, such as the handleability, rigidity, drop resistance, and top load resistance of the hollow container, and can also be a factor in impairing the aesthetics, quality, and commercial value of the hollow container. For this reason, it is desirable to make the wall thickness of the hollow container as uniform as possible. In particular, in the hot parison blow molding method, Even if the wall thickness of the reform is the same, temperature deviations caused by injection molding can occur, making it even more difficult to mold a hollow container with a uniform (neat) wall thickness.

[0007] In addition, when a heat-resistant container is formed by promoting the crystallization of a resin by heat treatment as in the inventions of Patent Documents 2 and 3, if the thickness distribution is uneven in each part of the intermediate molded product, the temperature distribution in each part will also become uneven. As a result, it becomes difficult to manufacture a heat-resistant container with a uniform thickness. Furthermore, if the thickness of the heat-resistant container is not uniform (uniform), the difference in the amount of deformation between the thin and thick parts is likely to become significant when the container is filled with high-temperature (for example, about 85 to 95°C) contents, and the container as a whole is likely to become distorted. In particular, in the hot parison blow molding method, the temperature unevenness caused by the injection molding occurs in the preform, so the degree of unevenness in the thickness (unevenness in the thickness distribution) in each part of the intermediate molded product is likely to become even greater.

[0008] The present invention has been made in view of the above circumstances, and has an object to provide a blow molding method and a blow molding apparatus that can improve the degree of wall thickness unevenness in each portion of a hollow container. [Means for solving the problem]

[0009] One aspect of the present invention that solves the above-mentioned problems is a blow molding method in which a resin preform is subjected to a primary blow to form an intermediate molded product, and then the intermediate molded product is subjected to a final blow to form a final molded product, characterized in that at least one of the steps of performing the primary blow and the final blow includes a thinning step in which a step of stretching an object by blowing, and a step of contracting each stretched portion of the object by exhausting the blown air are continuously repeated within a predetermined time.

[0010] Here, it is preferable that the thinning step includes at least a first step of stretching each portion of the object by blowing, a second step of evacuating the gas introduced into the object in the first step and shrinking each stretched portion of the object, a third step of stretching each portion of the object by blowing after the second step, and a fourth step of evacuating the gas introduced into the object in the third step and shrinking each stretched portion of the object.

[0011] Furthermore, it is preferable that the time for performing the first step, the second step, the third step, and the fourth step is within 2 seconds, respectively. It is also preferable that the second step is performed in a shorter time than the fourth step.

[0012] Furthermore, when the step of performing the primary blow includes the thinning step, in the first step, it is preferable that each part is stretched while pressing the bottom part inside the preform, which is the object, with a stretch rod.

[0013] In the thinning step, it is preferable that the stretching rod is maintained in contact with a bottom portion inside the object after the blowing in the first step.

[0014] In addition, in the step of performing the primary blow, it is preferable to form the intermediate molded product by utilizing the amount of heat remaining in the preform after injection molding.

[0015] The primary blow is a heat treatment blow, and it is preferable that the crystallization of the resin of the intermediate molded product is promoted by carrying out the primary blow.

[0016] Another aspect of the present invention is a blow molding apparatus including a molding means for molding an intermediate molded product by performing a primary blow on a resin preform in a blow molding die, and further performing a final blow on the intermediate molded product in a final blow molding die, the molding means comprising: The blow molding apparatus is characterized in that, when performing at least one of the final blows, stretching of each part of the object by blowing and contraction of the stretched parts of the object by exhausting the blown gas are continuously repeated within a predetermined time. Effect of the Invention

[0017] According to the blow molding method of the present invention, it is possible to improve the degree of thickness unevenness in each part, and in particular to provide a hollow container with a thin-walled bottom part.

[0018] Furthermore, the blow molding apparatus of the present invention can provide a hollow container that can improve the unevenness in thickness of each part, particularly the thinning of the bottom part. [Brief description of the drawings]

[0019] [Figure 1] 1A to 1C are views for explaining a blow molding method according to the first embodiment. [Diagram 2] FIG. 2 is a diagram for explaining a thinning step (Stp) of the blow molding method according to the first embodiment. [Diagram 3]FIG. 1 is a diagram showing a schematic configuration of a blow molding device according to a first embodiment. [Figure 4] 1A to 1C are diagrams illustrating a blow molding method and a blow molding apparatus according to a first embodiment. [Diagram 5] 1A to 1C are diagrams illustrating a blow molding method and a blow molding apparatus according to a first embodiment. [Figure 6] FIG. 6 is a diagram showing a schematic configuration of a blow molding device according to a second embodiment. [Figure 7] 5A to 5C are diagrams illustrating a blow molding method and a blow molding apparatus according to a second embodiment. [Figure 8] FIG. 11 is a diagram showing a schematic configuration of a blow molding device according to a third embodiment. [Figure 9] FIG. 2 is a diagram showing an example of a hollow container formed by blow molding. [Figure 10] FIG. 2 is a diagram showing an example of a hollow container formed by blow molding. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present embodiment will be described with reference to the drawings. The following embodiment is one aspect of the present invention, and can be modified as desired within the scope of the present invention. In each drawing and description, the same members are given the same reference numerals, and duplicated descriptions will be omitted.

[0021] (Embodiment 1) 1 and 2 are diagrams for explaining the blow molding method according to the present embodiment. Fig. 1 is a diagram showing the overall flow of the blow molding method, and Fig. 2 is a diagram showing the flow of the thinning step (Stp) included in the blow molding method.

[0022] 1 and 2, the blow molding method according to this embodiment is a method of molding an intermediate molded product 30 with improved thickness unevenness by performing a primary blow including a plurality of blow steps on a resin preform 10, and then performing a final blow (secondary blow) on the intermediate molded product 30 to form a hollow container 40. As will be described in detail later, in this method, the intermediate molded product 30 is formed from the preform 10 formed by injection molding via primary molded products 20 (20a to 20c), and the intermediate molded product 30 is then subjected to a final blow (secondary blow) to form the hollow container 40, which is the final molded product.

[0023] The blow molding method according to this embodiment is a so-called hot parison method in which the preform 10 adjusted to an appropriate blowing temperature is blown by utilizing the heat remaining in the preform 10 after injection molding. Since the preform 10 here is made of polyethylene terephthalate (PET), various blowing temperatures are appropriately adjusted based on the crystallization temperature and softening point of PET. However, the resin material constituting the preform 10 is not limited to PET, and may be other resin materials including PET or different from PET.

[0024] The intermediate molded product 30 is formed by the primary blow (heat treatment blow in this embodiment) as described above. 20a to 20c) are also formed by the primary blow.

[0025] Specifically, the primary blow (heat treatment blow) includes a thinning step in which a predetermined blow step and a predetermined exhaust step are repeated several times in succession within a predetermined time. In the blow step, each part of the target object such as the preform 10 or the primary molded article 20 is stretched. In the exhaust step, each stretched part of the primary molded article 20 is contracted by exhausting the blown gas (e.g., air), that is, by discharging the blown gas from the target object, the primary molded article 20. Note that each part referred to in this embodiment is, for example, the shoulder part, the body part, the bottom part, etc. of the primary molded article 20.

[0026] In general, in a hot parison type blow molding method, the ease with which each part of a preform is stretched is determined by the thickness of each part. That is, the thicker the part of the preform (such as the body), the higher the heat retention and the easier it is to stretch. In other words, the thinner the part of the preform (such as the bottom), the lower the heat retention and the harder it is to stretch. For this reason, for example, when a hollow container is formed from a preform using a hot parison type blow molding method, the part of the hollow container 40 that corresponds to the thick part of the preform (such as the body) tends to be relatively thin, and the part of the hollow container 40 that corresponds to the thin part of the preform (such as the bottom) tends to be relatively thick.

[0027] However, by carrying out the thinning step as described above, the thick parts (particularly the bottom) can be stretched each time the blowing step is repeated. Therefore, the bottom of the hollow container 40, which tends to be thick, can be suitably thinned. In addition, the thickness of each part can be stretched in a well-balanced manner throughout the thinning step. In other words, such a thinning step can improve the degree of unevenness in the thickness of the hollow container 40, which is the final molded product. In other words, the thickness of the hollow container 40 can be made uniform.

[0028] In this embodiment, the thinning step includes at least a first blow step (first step), a first exhaust step (second step), a second blow step (third step), and a second exhaust step (fourth step). In this way, in the thinning step, the blow step and the exhaust step are performed alternately within a predetermined time. These steps are each performed consecutively within a predetermined time (e.g., 2 seconds).

[0029] In the thinning step, a primary molded product 20 (20a) is formed in the first blow step, a primary molded product 20 (20b) is formed in the first exhaust step, and a primary molded product 20 (20c) is formed in the second blow step, and then an intermediate molded product 30 is formed in the second exhaust step.

[0030] The hollow container 40, which is the final molded product, is a container (a so-called PET bottle) that can be filled with liquid such as beverages. A recess 42 is formed in the body 41 of this hollow container 40, for example, in the circumferential direction, corresponding to the shape of the final blow molding mold when the final blow is performed (see FIG. 1). Moreover, the hollow container 40 has an upper bottom portion 44 formed on its bottom 43, which protrudes in a convex manner toward the inside of the container, and a base portion 45 (heel portion) is formed at the base of the upper bottom portion 44, which surrounds the upper bottom portion 44 in the circumferential direction (see FIG. 2).

[0031] Similarly to the hollow container 40, the primary molded product 20 obtained in the process of forming the hollow container 40 from the preform 10 has an upper bottom portion 24 formed on its bottom portion 23 so as to protrude inwardly of the molded product, and a base portion (heel portion) 25 formed at its base portion so as to circumferentially surround the upper bottom portion 24. Similarly, the intermediate molded product 30 has an upper bottom portion 34 and a base portion (heel portion) 35 formed on its bottom portion 33.

[0032] FIG. 3 is a diagram showing a schematic configuration of a blow molding apparatus 100 according to this embodiment. As shown in FIG. 3, the blow molding apparatus 100 is an apparatus (intermittent rotation conveying type) that sequentially rotates the preform 10, the primary molded product 20, the intermediate molded product 30, and the hollow container 40 intermittently and conveys them to the next process, and has five stations on the machine base, including an injection molding section 120 to which an injection device 110 is connected, a temperature control section 130, a blow molding section (intermediate molding section: primary blow molding section) 140, a final molding section (secondary blow molding section) 150, and a removal section 160. A rotating plate (transfer plate) (not shown) is rotatably provided above these five stations, and the rotating plate supports a neck mold (described later) for holding and conveying the molded product. Among these, the above-mentioned thinning step is performed mainly around the blow molding section (intermediate molding section) 140. The blow molding section 140 and the final molding section 150 are slidably installed on the machine base, and are moved alternately relative to the neck mold supported by the rotating plate.

[0033] 4 and 5 are diagrams for explaining the configuration and operation of the blow molding apparatus 100, and the blow molding method according to this embodiment. Fig. 4 is a diagram corresponding to the overall flow of the blow molding method, and Fig. 5 is a diagram corresponding to the thinning step (Stp) included in the blow molding method.

[0034] The injection molding section 120 injection molds a preform using PET injected from the injection device 110 (FIG. 4(a)). The injection molding section 120 is equipped with an injection molding die 121 connected to the injection device 110. The injection molding die 121 is equipped with an injection cavity die 122 that defines the outer surface of the body of the preform 10, and a core die 123 that defines the inner surface of the preform 10. An upper portion of the injection molding die 121 is provided with a neck die 124 consisting of a split die that can be opened and closed in the horizontal direction, which defines the outer wall surface of the neck part of the preform 10, which is a molded product.

[0035] In this injection molding section 120, the raw material PET is filled into the injection cavity mold 122 through a gate 125 provided in the center of the bottom of the injection cavity mold 122, thereby forming the preform 10. The injection-molded preform 10 is transported to the temperature adjustment section 130 while being held by the neck mold 124.

[0036] In the temperature adjustment section 130, the temperature of the preform 10 is adjusted before blow molding in the blow molding section (intermediate molding section) 140 (temperature adjustment step: FIG. 4(b)). The temperature adjustment section 130 is equipped with, for example, a temperature adjustment pot 131 that contains the preform 10, and this temperature adjustment pot 131 adjusts the temperature to an appropriate temperature for stretching PET (for example, about 80 to 90°C) while utilizing the heat remaining in the preform 10 after injection molding. The preform 10 that has been adjusted (heated) to the predetermined appropriate stretching temperature is then transported to the blow molding section 140.

[0037] The blow molding section 140, together with the subsequent final molding section 150, constitutes the molding means according to this embodiment. The blow molding section 140 is a section for performing a primary blow (heat treatment blow in this embodiment), and molds the intermediate molded product 30 from the preform 10 via the primary molded product 20 (FIGS. 4(c) and (d)). The blow molding section 140 includes a blow molding die 141, which includes a pair of blow molding split dies 142 that can be opened and closed, a stretch rod 143, and a blow bottom die 144. Note that, in this embodiment, a heat treatment blow is performed as the primary blow, but the primary blow may be a blow without heat treatment.

[0038] The stretch rod 143 is movable in the vertical direction (up and down direction) through a blow core 145 fitted into the mouth portion 12 of the preform 10. The blow molding section 140 also includes a supply section (not shown) that supplies air (pressurized gas) through the blow core 145.

[0039] In the blow molding section 140, the bottom of the preform 10 arranged in a blow molding die 141, which is a primary blow die (heat treatment blow die), is pressed from the inside of the container by a stretching rod 143, thereby stretching the preform 10 in the vertical axis direction. The preform 10 is stretched in the radial direction until it comes into contact with the inner wall surfaces of the blow molding die 141 and the blow bottom die 144 which are heated to a temperature equal to or higher than the crystallization temperature of PET (for example, about 180° C. to 200° C.).

[0040] This forms a primary molded product 20 (20a) larger in size than the hollow container 40 (first blow step: FIG. 5(a)). In such a first blow step, the residual stress of the PET can be relaxed, and the crystallization density of the PET can be improved.

[0041] As described above, the ease of stretching of each part varies depending on the thickness of the preform 10. That is, the thicker the part of the preform 10, the greater the heat retention and the easier it is to stretch in the first blow step. For this reason, the body part of the preform 10 tends to stretch first in the first blow step, while the bottom part tends to stretch later. That is, in the first blow step, the body part of the preform 10 is stretched relatively greatly, but the amount of stretching of the bottom part is relatively small. Therefore, in the primary molded product 20a formed in the first blow step, the bottom part 23 is relatively thicker than the body part.

[0042] In this embodiment, the height from the base 45 to the upper bottom 44 of the hollow container 40, which is the final molded product, is lower than the height from the base 25 to the upper bottom 24 of the primary molded product 20a. In other words, the primary molded product 20a is formed with a higher bottom than the hollow container 40. As a result, the bottom 23 (particularly the upper bottom 24) of the primary molded product 20a is not fully stretched by a single blow process (first blow step) alone, and tends to become thicker than the body.

[0043] After the first blow step, the blow molding section 140 exhausts the air blown in the first blow step through the blow core 145, causing each stretched portion of the primary molded article 20a to shrink (first exhaust step: FIG. 5(b)). Note that exhaust can be performed by opening an exhaust valve (not shown) on the upper part of the blow core 145.

[0044] The degree of shrinkage at this time is relatively large, and the amount by which the skirt portion 25 surrounding the upper bottom portion 24 in the circumferential direction in the primary molded product 20a is pulled toward the mouth portion 22 is greater than the amount by which the portion of the upper bottom portion 24 that the stretch rod 143 abuts against is pulled toward the mouth portion 22. At the same time, each portion other than the skirt portion 25 also shrinks. As a result, a primary molded product 20b smaller in size than the primary molded product 20a is obtained (FIG. 5(b)). Also, at this time, the resin of the upper bottom portion 24, which is thick and has a large heat retention capacity, is pulled toward the skirt portion 25. Therefore, in the upper bottom portion 24, the difference in thickness between the central region in contact with the stretch rod 143 and the peripheral region not in contact with the stretch rod 143 becomes small. The heat retention capacity of the skirt portion 25 and the body portion of the primary molded product 20a, which has been highly stretched by the first blow step, is relatively lower than that of the upper bottom portion 24.

[0045] After exhaust in the first exhaust step, the blow molding section 140 continues to heat-treat the primary molded product 20b while supplying air from the supply section through the blow core 145 to the mouth 22 of the primary molded product 20b. This stretches each part of the primary molded product 20b to form the primary molded product 20c (second blow step: FIG. 5(c)). At this time, the bottom part 23 (upper bottom part 24) is particularly stretched. This is because the bottom part 23 (upper bottom part 24) was stretched to a low degree in the first blow step and maintained relatively thick, and therefore retains a larger amount of heat than other parts in the second blow step.

[0046] According to the second blow step, the bottom 23 is further stretched in the blow molding die 141, thereby thinning the bottom 23. The thickness d2 of the bottom 23 of the primary molded product 20c is thinner than the thickness d1 of the bottom 23 in the primary molded product 20a.

[0047] The thickness d1 of the bottom 23 of the primary molded product 20a and the thickness d2 of the bottom 23 of the primary molded product 20c are located between the central region of the upper bottom 24 that is in contact with the stretch rod 143 and the skirt portion 25, and indicate the thickness of the outer peripheral region of the upper bottom 24 that is not in contact with the stretch rod 143. Although not as much as the bottom 23, each part other than the bottom 23 (shoulder part, body part, etc.) is also stretched twice, thereby forming the primary molded product 20c with a balanced wall thickness of each part. In addition, the second blow step as well as the first blow step relieves the residual stress of the PET and improves its crystallization density, so that the heat resistance of the hollow container 40 finally obtained can be improved.

[0048] After the second blow step, the blow molding section 140 exhausts the air blown in the second blow step through the blow core 145, causing each stretched portion of the primary molded product 20c to shrink (second exhaust step: FIG. 5(d)). This forms an intermediate molded product 30 that is smaller in size than the hollow container 40. The intermediate molded product 30 is also formed to be slightly larger in size than the primary molded product 20b.

[0049] In the steps following the first blow step, i.e., the first exhaust step, the second blow step, and the second exhaust step, the blow molding section 140 holds the stretch rod 143 in a position pressed down in the vertical axis direction. This maintains the stretch rod 143 in contact with the inner wall surfaces of the bottom 23 of the primary molded product 20 and the bottom 33 of the intermediate molded product 30. This reliably prevents the axial misalignment of the bottom 23 with respect to the central axis of the primary molded product 20 and the axial misalignment of the bottom 33 with respect to the central axis of the intermediate molded product 30 when the primary molded product 20 is blow molded or shrunk.

[0050] 5(d), the center line L1 of the intermediate molded product 30 (the stretch rod 143) and the center line L2 of the convexly protruding upper bottom portion 34 are shown to be substantially aligned with each other. By preventing the axial misalignment between the two, it becomes easier to improve the uneven thickness of the hollow container 40.

[0051] In the thinning step, blowing and exhausting are continuously repeated, and as the thick portions of the primary molded article 20 are thinned and the overall unevenness in thickness is improved, the heat retention of each portion of the primary molded article 20 decreases, and the degree of stretching and shrinkage of the primary molded article 20 due to blowing and exhausting decreases. For example, since the bottom portion 23 in particular is thinned in the second blowing step, the degree of shrinkage of the bottom portion 23 in the second exhausting step is smaller than that in the first exhausting step.

[0052] The intermediate molded product 30 obtained by the second evacuation step must be smaller in size than the hollow container 40 so that it can be held in the subsequent final blow molding die 151. At the same time, it is preferable that the intermediate molded product 30 is close in size to the hollow container 40, which is the final molded product. This makes it possible to keep the degree of stretching of the intermediate molded product 30 small during the final blow (secondary blow), and to reduce stress that may remain in the hollow container 40 molded by the final blow. As a result, for example, the hollow container 40 can be made in a manner that makes it possible to suitably suppress deformation due to heat.

[0053] As described above, through the thinning step mainly performed in the blow molding section 140, the preform 10 becomes the intermediate molded article 30 that is slightly smaller than the final molded product, the hollow container 40. The intermediate molded article 30 is transported to the final molding section 150 while being held by the neck mold 124.

[0054] The final molding section 150, together with the blow molding section 140, constitutes a part of the molding means according to this embodiment. In the final molding section 150, the intermediate molded product 30 is blow molded to form a hollow container 40 (final molding step: FIG. 4(e)). The final molding section 150 includes a final blow molding die 151, which includes an openable and closable final blow molding split die 152 and a final blow bottom die 153.

[0055] The final blow molding split mold 152 has an inner wall surface that conforms to the outer shape of the hollow container 40. This inner wall surface is provided with a protrusion 154 that protrudes inward at a position corresponding to the recess 42 of the hollow container 40, and the final molding section 150 also includes a supply section that supplies air (pressurized gas) via the blow core mold.

[0056] Then, air is supplied from a supply section through a blow core into the intermediate molded product 30 placed in the final blow molding mold 151, and the intermediate molded product 30 is stretched in the vertical and radial directions until it comes into contact with the inner wall surface of the final blow molding split mold 152 heated to a predetermined temperature (for example, about 100°C to 120°C), and then cooled by circulation of blow air. In this way, a hollow container 40 is formed. The hollow container 40 is then transported to a removal section 160 and removed from the removal section 160 to the outside of the apparatus.

[0057] According to the blow molding method and blow molding apparatus 100 described above, in the thinning step in the blow molding section 140, the blow step and the exhaust step are repeated continuously within a predetermined time. In the first blow step, the body part of the preform 10 is mainly stretched, so that the bottom part 23 of the primary molded product 20a remains thicker than the body part. Even after shrinkage in the next first exhaust step, the bottom part 23 of the primary molded product 20b remains thick. As a result, in the next second blow step, the bottom part 23, which is relatively thick and has a large heat retention, is suitably stretched and thinned, and the thickness of the bottom part 23 of the primary molded product 20c becomes relatively uniform.

[0058] Furthermore, the second blow step stretches each portion other than the bottom portion 23 again, although not as much as the bottom portion 23, so that the thickness of each portion of the primary molded product 20c is balanced. As the thick portions are thinned and the overall degree of thickness unevenness is improved, the heat retention of each portion of the primary molded product 20c also decreases, so that large shrinkage of the primary molded product 20c accompanying the next second exhaust step is also avoided.

[0059] In this way, according to the blow molding method and the blow molding apparatus 100, the above-mentioned thinning step is performed, so that the degree of thickness unevenness of the intermediate molded product 30 can be improved. In addition, the degree of thickness unevenness of the hollow container 40 obtained by final blowing of this intermediate molded product 30 can be improved. In particular, the bottom 43 of the hollow container 40 can be highly elongated and thinned, and the thickness of the bottom 43 can be made uniform. Furthermore, by performing a heat treatment blow as the primary blow in the molding process, crystallization of the resin can be promoted, and the heat resistance of the obtained hollow container 40 can be improved.

[0060] In this embodiment, the time for each of the blowing and exhausting steps performed intermittently in the thinning step is short, for example, within 2 seconds. Therefore, even if such blowing and exhausting are repeated, the overall manufacturing time does not become significantly longer. Therefore, this embodiment is suitable for mass production, and can meet the expectations for excellent manufacturing efficiency and container quality in response to the increasing opportunities for using hollow containers in recent years.

[0061] The time for performing the first blow step in the thinning step described above is, for example, 0.7 to 0.8 seconds. The time for performing the first blow step can be appropriately adjusted based on the degree to which the preform 10 is stretched, the time sufficient to perform heat treatment on the PET (primary molded product 20a), and the like.

[0062] The time for performing the first exhaust step in the thinning step is, for example, about 0.5 to 0.6 seconds. The time for performing the first exhaust step can be appropriately adjusted based on the time required to exhaust the blown air, etc. From the viewpoint of optimally thinning the bottom 23 of the primary molded product 20b in the subsequent second blow step, it is preferable to make the time shorter. As a guideline, it is preferable to perform the first exhaust step for a shorter time than, for example, the subsequent second exhaust step. is better.

[0063] The time for performing the second blow step is, for example, about 1.2 seconds to 1.3 seconds. The time for performing the second blow step can be appropriately adjusted based on the degree to which each portion of the preform 10 is stretched, the time sufficient to perform a heat treatment on the PET (primary molded product 20b), and the like.

[0064] The time for performing the second evacuation step is, for example, about 0.9 seconds to 1.1 seconds. The time for performing the second evacuation step is longer than the first evacuation step even though they are the same evacuation steps. By ensuring a relatively long time for performing the second evacuation step, the degree of contraction accompanying the second evacuation step can be kept as small as possible.

[0065] Incidentally, the times for performing these steps can be adjusted by calculating backwards from the sizes of the hollow container 40 and the intermediate molded product 30. As described above, it is preferable that the intermediate molded product 30 obtained by the primary blow molding (thinning step) is close in size to the hollow container 40, which is the final molded product. For this reason, the times for performing these steps are adjusted so that an intermediate molded product 30 close in size to the hollow container 40 is obtained, taking into consideration the degree of stretching of each part of the primary molded product 20 etc. accompanying the blow step and the degree of shrinkage of each part of the primary molded product 20 accompanying the evacuation step.

[0066] The blow molding method and the blow molding apparatus 100 adopt a hot parison type. In the hot parison type blow molding method, the temperature of the preform is adjusted (temperature adjustment process) before the primary blow (heat treatment blow) is performed, but when priority is given to removing temperature deviation and making the temperature uniform, it is often the case that a suitable temperature distribution cannot be given to the bottom region of the preform, and conventionally, it is often difficult to thin the bottom of the hollow container. In contrast, according to the present embodiment, even if such a hot parison type blow molding method is adopted, the bottom 43 of the hollow container 40 can be thinned by increasing the degree of elongation, and the degree of thickness deviation can be improved. As a result, the thicknesses of the body and bottom of the hollow container 40 can be reduced to be approximately equal, and the heat resistance and rigidity of the hollow container 40 can be improved and the weight can be reduced. In addition, as a result of increasing the degree of elongation of the bottom 43 of the hollow container 40, the crack resistance (drop resistance) of the bottom 43 against a drop can also be improved.

[0067] The blow molding method and the blow molding apparatus 100 according to the present embodiment are not limited to the hot parison type, but can be suitably implemented even in the cold parison type. Furthermore, the thinning step is not limited to the heat treatment blowing, but can be performed during the final blowing.

[0068] (Embodiment 2) The blow molding method and blow molding apparatus according to this embodiment have basically the same structure as in embodiment 1, but the configuration of the blow molding section is different. The following description will focus on the differences.

[0069] Fig. 6 is a diagram showing a schematic configuration of a blow molding apparatus 100A according to this embodiment. As shown in Fig. 6, the blow molding apparatus 100A is a rotary conveying type apparatus, in which the injection molding section 120, the temperature adjustment section 130, the blow molding section 170, and the removal section 160 are arranged around the conveying mechanism along the conveying direction. The injection molding section 120, the temperature adjustment section 130, and the removal section 160 are as described in the first embodiment. The blow molding section 170 is a station that also functions as the blow molding section 140 and the final molding section 150 described in the first embodiment.

[0070] 7 is a diagram for explaining the configuration and operation of the blow molding apparatus 100A, and the blow molding method according to this embodiment. Note that the process indicated by Stp in the diagram corresponds to the thinning step described in the first embodiment.

[0071] The blow molding section 170 includes a blow molding die 171. The blow molding die 171 includes a blow molding split die 172 that can be opened and closed, a stretch rod 173, and a blow bottom die 174. The blow molding split mold 172 has an inner wall surface provided with a protrusion 175 corresponding to the recess 42 of the hollow container 40. The stretch rod 173 is movable in the vertical axis direction through a blow core 176 fitted into the mouth 12 of the preform 10. The blow molding section 140 also has a supply section that supplies air (pressurized gas) through the blow core 176.

[0072] In the blow molding method and blow molding apparatus 100A according to this embodiment, the preform 10 is injection molded in the injection molding section 120, and after the preform 10 is heated in the temperature control section 130, the preform 10 is transported to the blow molding section 170 and placed in the blow molding mold 171.

[0073] In the blow molding section 170, first, the preform 10 arranged in the blow mold 171 is stretched in the vertical axis direction by the stretch rod 173 (FIG. 7(c)). Then, the preform 10 is stretched in the radial direction by air supplied from the supply section until it contacts the inner wall surface of the blow mold 171 set at a predetermined temperature (primary blow). This forms a primary molded product 20 of the same size as the hollow container 40 (first blow step: FIG. 7(c)). Note that the blow mold 171 (blow mold split mold 172 and blow bottom mold 174) is desirably set to a temperature at which PET crystallizes or higher (for example, about 80°C to 100°C), but may be set to room temperature (for example, about 20°C).

[0074] Thereafter, evacuation, blowing, and evacuation are each performed intermittently within a predetermined time period by the first evacuation step, the second blow step, and the second evacuation step described in embodiment 1, using the blow molding mold 171. Each part of the primary molded product 20 shrinks due to evacuation in the second evacuation step, and an intermediate molded product 30 that is slightly smaller in size than the hollow container 40, which is the final molded product, is formed (FIG. 7(d)).

[0075] The intermediate molded product 30 is then further blow molded in this blow molding die 171 to form a hollow container 40 (FIG. 7(e)). In this embodiment, the stretch rod 173 is kept inserted in the intermediate molded product 30 during the final blow, but the stretch rod 173 can also be removed. Thereafter, as in the first embodiment, the hollow container 40 is transported to the removal section 160 and removed from the removal section 160 to the outside of the apparatus.

[0076] According to the present embodiment described above, as in the first embodiment, the degree of thickness unevenness can be improved, and in particular, the thickness of the bottom can be made thinner. Furthermore, by setting the temperatures of the blow molding die 171 and the blow bottom die 174 to a temperature lower than that of the first embodiment but equal to or higher than the crystallization temperature of the resin, the heat resistance of the obtained hollow container 40 can be improved. Furthermore, as a result of increasing the degree of elongation of the bottom 43 of the hollow container 40, the crack resistance (drop resistance) of the bottom 43 when dropped can also be improved.

[0077] Furthermore, according to this embodiment, it is possible to simplify the equipment used to manufacture the hollow container 40, in that molding by primary blow (improving the thickness unevenness by the thinning step) and molding by final blow (final shaping into the hollow container 40) are performed within one blow molding die 171. Therefore, like the first embodiment, this embodiment is also suitable for mass production, and can meet the expectations for excellent manufacturing efficiency and container quality in response to the increasing opportunities for using hollow containers in recent years.

[0078] (Embodiment 3) The blow molding method and blow molding apparatus according to this embodiment differ from those of the first embodiment in that a cold parison system is adopted. The following description will focus on the differences.

[0079] FIG. 8 is a diagram showing a schematic configuration of a blow molding apparatus 100B according to this embodiment.

[0080] In this embodiment, a preform that has been injection molded and then cooled to room temperature is prepared separately, and then heated to an appropriate temperature for blowing with a heater or the like, and the preform is stretched by blowing. Therefore, the blow molding method according to this embodiment does not include the step of injection molding the preform as described in the first embodiment.

[0081] As shown in FIG. 8, the blow molding apparatus 100B of this embodiment includes a temperature control section (heating section) 130, a blow molding section 140, a final molding section 150, and a removal section 160, but does not include the injection molding section 120 as described in embodiment 1.

[0082] The temperature adjustment section (heating section) 130 includes a plurality of rod-shaped heaters arranged at a predetermined interval in the longitudinal direction of the preform 10, and heats a separately prepared preform at room temperature to adjust the temperature to a suitable temperature for blow molding (temperature adjustment process / heating process). Thereafter, as in the first embodiment, a thinning step is performed mainly in the blow molding section 140, and a final blow is performed to obtain the hollow container 40, which is the final molded product.

[0083] According to the present embodiment described above, even in the case of the cold parison type, the thinning step is performed in the same manner as in the first embodiment, so that the degree of unevenness in the thickness of the hollow container 40 can be improved, and particularly the bottom part can be thinned. In addition, by performing a heat treatment blow as the primary blow in the blow molding section 140, the crystallization of the resin can be promoted, and the heat resistance of the obtained hollow container 40 can be improved.

[0084] In addition, the blow molding apparatus 100B of this embodiment, like embodiment 1, is also suitable for mass production, and can meet the expectations for excellent manufacturing efficiency and container quality in response to the ever-increasing use of hollow containers in recent years.

[0085] (Other embodiments) Although one aspect of the blow molding method and blow molding device according to this embodiment has been described above, the present invention is not limited to any of the above-mentioned embodiments 1 to 3. Moreover, the above-mentioned embodiments 1 to 3 can be combined with each other within the scope of the present invention.

[0086] For example, the shape of the hollow container formed by the blow molding method and blow molding apparatus according to the above-described embodiments is not particularly limited.

[0087] 9 and 10 are diagrams showing another example of a hollow container formed by blow molding, where (a) is a front view, (b) is a bottom view, and (c) is a cross-sectional view of the bottom. In the above-mentioned embodiment, the body part 41 of the hollow container 40 is formed in a shape that functions as a vacuum absorption panel part, but for example, as shown in Figs. 9 and 10, the hollow container 40 may be formed so that its bottom part 43 functions as a vacuum absorption panel part. The vacuum absorption panel part is formed in a shape that is more easily deformed than other parts, and is a part that deforms with the internal pressure reduction when the hollow container 40 is cooled after being filled with high-temperature contents and sealed with a lid. The hollow container 40 in Figs. 9 and 10 is in a state before being filled with high-temperature contents, that is, in a state where no deformation due to the pressure reduction occurs.

[0088] The bottom 43 of the hollow container 40 shown in Figures 9 and 10 is composed of an upper bottom 44 and a foot (heel) 45, and the upper bottom 44 functions as a vacuum absorption panel. The upper bottom 44 also has an inclined portion 44a, an intermediate wall 44b, and a recessed portion 44c. The inclined portion 44a is provided so as to continue from the vertical wall 45a of the foot 45 and to be inclined toward the outside (lower side) of the hollow container 40. The intermediate wall 44b is provided so as to be substantially parallel to the ground surface and to connect the inside of the inclined portion 44a and the outside of the recessed portion 44c. The recessed portion 44c is provided so as to continue from the inside of the intermediate wall 44b and is formed in a recessed shape toward the inside (upper side) of the hollow container 40.

[0089] Furthermore, a plurality of ribs 46 are formed on the inclined portion 44a of the outer periphery of the upper bottom portion 44, protruding toward the outside (lower side) of the hollow container 40. These ribs 46 are formed intermittently in a plurality of rows around the circumference of the hollow container 40, and are arranged in at least two rows in the radial direction of the hollow container 40. Each rib 46 is formed in a substantially elliptical shape in a plan view. The length of the rib 46 increases as it is arranged toward the outside in the radial direction of the hollow container 40. Furthermore, the cross-sectional shape of the rib 46 is a circular arc that protrudes in a curved manner toward the outside (lower side) of the hollow container 40. Of course, the shape of each rib 46 is not particularly limited.

[0090] In this way, by providing an upper bottom portion 44 that functions as a vacuum absorption panel portion on the bottom 43 of the hollow container 40 and providing a plurality of ribs 46 on the inclined portion 44a of the upper bottom portion 44, it is possible to suppress any deterioration in the aesthetic appearance of the upper bottom portion 44.

[0091] Generally, it is difficult to adjust the thickness of each part of the hollow container with high precision. For example, it is difficult to make the thickness of the upper bottom part uniform. For this reason, in a conventional hollow container without ribs on the inclined part of the upper bottom part, when the upper bottom part deforms due to the internal pressure reduction, the upper bottom part may develop streaks at the boundary between the easily deformed part and the less easily deformed part, and the entire upper bottom part may become uneven. As a result, the aesthetic appearance of the hollow container may be significantly deteriorated, and the commercial value may be reduced.

[0092] However, by providing a plurality of ribs 46 on the inclined portion 44a of the hollow container 40 as described above, the occurrence of such streaks can be suppressed, and even if streaks do occur, they are hard to see because they are formed between the plurality of ribs 46. In addition, the decorative effect of the ribs 46 makes it hard to distinguish the unevenness of the entire upper bottom portion 44, which functions as a vacuum absorption panel portion.

[0093] Therefore, deterioration in the aesthetic appearance of the surface of the upper bottom portion 44 after vacuum absorption, that is, deterioration in the commercial value of the hollow container 40, can be suppressed, and accordingly, deterioration in consumer purchasing motivation can also be suppressed.

[0094] In the above embodiment, the thinning step is performed during the primary blow, but it is also possible to perform the thinning step during the final blow (secondary blow). When the thinning step is performed during the final blow, the thinning step is performed on an intermediate molded product that has been heat-treated and is at a high temperature. This also makes it possible to thin the bottom and improve the degree of thickness unevenness in each part. The thinning step can also be performed both during the primary blow and the final blow.

[0095] Furthermore, in the above embodiment, the resin material constituting the preform 10 is PET, and the hollow container which is the final molded product is a so-called PET bottle, but the resin material is not limited to PET. It is possible to adjust the temperature, time, etc. of the thinning step depending on the selected resin material (e.g., polyethylene (PP) or polyethylene (PE)).

[0096] In the above embodiment, the thinning step consisting of the first blow step, the first exhaust step, the second blow step, and the second exhaust step has been described, but the thinning step may include further blow steps and exhaust steps thereafter. The blow steps after the second exhaust step (e.g., the third blow step (fifth step), the fourth exhaust step (seventh step), etc.) can be performed in the same manner as the first blow step and the second blow step, and the exhaust steps after the second exhaust step (e.g., the third exhaust step (sixth step), the fourth exhaust step (eighth step), etc.) can be performed in the same manner as the first exhaust step and the second exhaust step.

[0097] Moreover, the devices of the first and second embodiments may be of a linear conveying type, in place of the intermittent rotary conveying type, in which the intermediate molded products and hollow containers are conveyed successively along a straight line.

[0098] As described above, according to the present invention, it is possible to provide a blow molding method and a blow molding apparatus that can improve the degree of wall thickness unevenness in each portion of a hollow container. [Industrial Applicability]

[0099] The present invention can be utilized in industrial fields related to blow molding methods and blow molding apparatuses. [Explanation of symbols]

[0100] 10 preform, 12 mouth, 20 primary molded product, 22 mouth, 23 bottom, 24 upper bottom, 25 bottom (heel), 30 intermediate molded product, 33 bottom, 34 upper bottom, 35 bottom (heel), 40 hollow container, 41 body, 42 recess, 43 bottom, 44 upper bottom, 44a inclined portion, 44b intermediate wall, 44c recess, 45 bottom (heel), 46 rib, 100 blow molding device, 100A blow molding device, 100B blow molding device, 110 injection device, 120 injection molding part, 121 injection molding mold, 122 injection cavity mold, 123 core mold, 124 neck mold, 125 gate, 130 Temperature control section, 131 temperature control pot, 140 blow molding section (intermediate molding section), 141 blow molding mold, 142 blow molding split mold, 143 stretch rod, 144 blow bottom mold, 145 blow core, 150 final molding section, 151 final blow molding mold, 152 final blow molding split mold, 153 final blow bottom mold, 154 convex section, 160 removal section, 170 blow molding section, 171 blow molding mold, 172 blow molding split mold, 173 stretch rod, 174 blow bottom mold, 175 convex section, 176 blow core

Claims

1. A hollow container formed of a resin material, A body portion that defines an internal space; The hollow container has a bottom that is deformable in response to a pressure reduction that occurs in the internal space when the sealed hollow container is cooled after the internal space is filled with a high-temperature content, The bottom portion is An upper base portion protruding upward; A skirt portion is located between the upper bottom and the body portion and has a ground contact surface; Contains The base portion has a vertical wall portion extending upward from the ground contact surface, The upper base portion is A concave portion; an inclined portion located between the recessed portion and the vertical wall portion; an intermediate wall portion located between the recessed portion and the inclined portion; Contains In a state where no deformation due to the decompression occurs, The inclined portion is inclined downward from an upper end of the vertical wall portion toward the intermediate wall portion, The intermediate wall portion extends substantially parallel to the ground surface, The recessed portion is recessed upward, Among the inclined portion, the intermediate wall portion, and the recessed portion, a plurality of ribs extending along a circumferential direction of the hollow container are formed only on the inclined portion, The plurality of ribs are formed in a substantially elliptical shape in a plan view, The plurality of ribs are formed to be aligned along a radial direction of the hollow container, The plurality of ribs are formed discontinuously in the circumferential direction, a length dimension along the circumferential direction of one of the plurality of ribs located on an outer side in the radial direction is longer than a length dimension along the circumferential direction of one of the plurality of ribs located on an inner side in the radial direction, A cross section of each of the ribs along the radial direction has an arc shape that protrudes downward in a curved manner. Hollow container.

2. A recess extending along the circumferential direction of the hollow container is formed in the body portion.

2. The hollow vessel according to claim 1.

3. The resin material is polyethylene terephthalate.

3. The hollow vessel according to claim 1 or 2.

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