Patent Description:
Conventionally, as one of resin containers for containing various liquids therein, a polyethylene container is known. Polyethylene (PE), in particular high-density polyethylene (HDPE), is excellent in chemical resistance, waterproofness, impact resistance and insulation properties. Therefore, the polyethylene container is suitable for containing, for example, drugs, bleach, milk, kerosene, or the like.

As manufacturing methods for manufacturing resin containers, for example, a method called a direct blow molding method, in which blow air is blown into a cylindrical parison to shape the parison, or a method called an injection stretch blow molding (ISBM) process, in which a bottomed cylindrical preform formed by injection molding is shaped by stretching the preform by a stretching rod while blowing blow air therein, is known (see Patent Literatures <NUM> and <NUM>).

<CIT> discloses a manufacturing method for manufacturing a resin container made of polyethylene using an injection stretch blow molding method, the manufacturing method comprising:an injection molding step of forming a bottomed preform by injection molding;anda stretch blow molding step of stretching the preform by pressing a bottom portion of the preform by a stretching rod while introducing blow air into the preform, wherein the stretch blow molding step comprises: a first step of stretching the preform by introducing preliminary blow air which has a pressure lower than final blow air into the preform in a state;a second step of stretching the preform by moving the stretching rod at a predetermined set speed and pressing the bottom portion of the preform by the stretching rod while introducing the preliminary blow air into the preform, the second step being performed after the first step; anda third step of stretching the preform by introducing the final blow air into the preform, the third step being performed after the second step.

<CIT> discloses a process for producing tube-like bodies and tube-like bodies.

<CIT> discloses an injection stretch blow-molding process for the preparation of polyethylene containers.

<CIT> discloses a method of forming a container by blowing and filling.

<CIT> discloses a method and device for molding.

<CIT> discloses a method for production of hollow articles from injection molded preforms.

As compared with the direct blow molding method, the injection stretch blow molding method has advantages that it is possible to manufacture a container which has a higher dimensional accuracy and has physical properties improved due to a biaxial stretching effect by the stretching rod and the blow air.

However, resin containers made of polyethylene (PE) could be molded by the injection stretch blow molding method only for relatively small sized ones. That is, resin containers made of polyethylene have been mainly molded by the direct blow molding method for the reasons of the material properties described below.

Polyethylene (PE) has a property (physical property) that it is relatively soft. For example, polyethylene is a soft material as compared with polyethylene terephthalate (PET), polypropylene (PP), and the like. Therefore, unlike PET and the like, PE does not have a strain fixing property, and there is a problem that it is difficult to adjust a thickness thereof by stretching with a rod.

Herein, the strain fixing property means a property that after the weakest portion (usually the hottest portion) of the preform first reaches a yield point, strength of a preform is increased by orientation during a stretching process, until the next weakest portion reaches a level of strength at which the next weakest portion starts to be stretched. This procedure is repeated until each portion of the preform has been stretched by substantially the same amount. Therefore, in a case of a PET preform, if a shape or temperature thereof is appropriately adjusted, it is easy to shape a container having a substantially uniform thickness and to obtain a container having an increased strength by a stretch orientation effect.

On the contrary, in a case of a PE preform, there is no strain fixing property as described above. Accordingly, it is difficult to adjust a thickness of a container by stretching with a rod. Also, it is difficult to obtain a PE container having sufficient and appropriate strength, rigidity and appearance. In addition, PE has a property that a crystallization speed is faster than that of PET, PP, and the like. Accordingly, a preform formed by injection molding is easily solidified. Therefore, there is a problem that it is difficult to appropriately inflate the PE preform by stretch blow molding.

For example, in order to appropriately inflate a PE preform, it is necessary to raise a temperature of the preform to a temperature close to a melting point thereof during stretch blow molding. This makes it difficult to control the temperature. Further, since the PE preform in a high temperature state is very soft, there is also a problem that puncture or rupture easily occurs due to the contact of the stretching rod therewith or a pressure of the blow air. In particular, if a small-mouthed PE container is blow-molded, it is necessary to use a stretching rod having a small diameter suitable for the small-mouthed container. Accordingly, defects, such as puncture or rupture as described above, are more likely to occur.

Further, PE has a property that a thermal shrinkage rate thereof is also larger than that of PET, PP, and the like. Therefore, the PE preform formed by injection molding is subject to significant shrinkage and deformation before stretch blow molding. Accordingly, it is difficult to appropriately adjust an amount of lowering of the stretching rod and an amount of the blow air to be introduced in consideration of an amount of deformation of the preform.

Further in the case of PE, a temperature range suitable for blow molding is very narrow and also an allowable range of longitudinal and transverse stretch ratios is narrow.

For these reasons, the present situation is that the resin containers made of polyethylene is mainly molded by the direct blow molding method.

The present invention has been made in view of the above problems and an object thereof is to provide a manufacturing method for manufacturing a resin container, in which it is possible to satisfactorily form a resin container made of polyethylene using the injection stretch blow molding method.

One aspect of the present invention solving the above object is a manufacturing method for manufacturing a resin container made of polyethylene using an injection stretch blow molding method, the manufacturing method including:.

According to the present invention, it is possible to satisfactorily form a resin container made of polyethylene (PE) using the injection stretch blow molding method.

First, an example of a shape of a hollow container (resin container) manufactured by a manufacturing method for manufacturing a resin container according to the present embodiment will be described.

As shown in <FIG>, the hollow container <NUM> includes a tubular neck portion <NUM> having an opening <NUM> on one end side thereof (upper end side); a tubular body portion <NUM> connected to the neck portion <NUM>; and a bottom portion <NUM> continuous from the body portion <NUM>. The hollow container (resin container) <NUM> is made of a relatively soft resin material, specifically polyethylene (PE), preferably high-density polyethylene (HDPE), and is excellent in chemical resistance, waterproofness, impact resistance and insulation properties. The hollow container <NUM> is suitable to be filled with, for example, drugs, bleach, milk, kerosene, or the like as contents.

The hollow container <NUM> is formed by injection-molding a bottomed preform as an intermediate molded product and then stretch blow-molding the preform. That is, the hollow container <NUM> is formed by the injection stretch blow molding (ISBM) method. Although it is sufficient if the material of the hollow container <NUM> (the material of the preform) is polyethylene, it is preferable to employ polyethylene having a melt flow rate (MFR) of <NUM> to <NUM>/<NUM>, more preferably <NUM> to <NUM>/<NUM>, further more preferably <NUM> to <NUM>/<NUM>.

As shown in <FIG>, the preform <NUM> for forming the hollow container <NUM> includes a neck portion <NUM> having an opening <NUM> on one end side (upper end side), a body portion <NUM> continuous from the neck portion <NUM>, and a bottom portion <NUM> continuous from the body portion <NUM>.

The neck portion <NUM> is formed in substantially the same shape as the neck portion <NUM> of the hollow container <NUM>. Also, the bottom portion <NUM> of the preform <NUM> is preferably formed to be thinner than the body portion <NUM>. For example, a thickness t1 of the bottom portion <NUM> of the preform <NUM> is preferably <NUM>/<NUM> or less of a thickness t2 of the body portion <NUM>. Further, a length of the body portion <NUM> of the preform <NUM> is preferably <NUM>/<NUM> or less of a length of the body portion <NUM> of the hollow container <NUM>, in particular <NUM>/<NUM> to <NUM>/<NUM> of the length of the body portion <NUM> of the hollow container <NUM>.

In the following a manufacturing method for manufacturing the hollow container (resin container) <NUM> will be described. First, a schematic configuration of an injection stretch blow molding apparatus which is a manufacturing apparatus for manufacturing the hollow container <NUM> will be described.

As shown in <FIG>, the injection stretch blow molding apparatus <NUM> is a so-called hot parison type (one-step type) apparatus and has, on a machine base <NUM>, an injection molding part (injection molding device) <NUM>, a temperature adjustment part (temperature adjustment device) <NUM>, a stretch blow molding part (stretch blow molding device) <NUM>, and a take-out part (take-out device) <NUM>.

Also, a rotation plate <NUM> is provided above the injection molding part <NUM>, the temperature adjustment part <NUM>, the stretch blow molding part <NUM>, and the take-out part <NUM>. The rotation plate <NUM> is configured to intermittently rotate relative to the machine base <NUM>, for example, counterclockwise as viewed from above. A neck mold (lip mold) <NUM> is provided at four positions on the rotation plate <NUM> along a circumferential direction. Accordingly, the preform <NUM> and the hollow container <NUM> can be sequentially conveyed to a predetermined device by intermittent rotation of the rotation plate <NUM> while being held by the neck mold <NUM>.

As shown in <FIG>, the injection molding part <NUM> is configured to allow a molten resin material (polyethylene or the like) injected from an injection unit (injection device) <NUM> to be introduced into a space of an injection molding mold <NUM> defining an outer shape of the preform, thereby molding a preform <NUM> having a shape as described above (injection molding step). The injection-molded preform <NUM> is released from the injection molding mold <NUM> and then conveyed to the temperature adjustment part <NUM> (first conveying step). The temperature adjustment part <NUM> is configured to perform a temperature adjustment treatment to the injection-molded preform <NUM> using a temperature adjustment mold <NUM>, thereby adjusting a temperature of the preform <NUM> to an appropriate temperature (temperature adjustment step). The temperature-adjusted preform <NUM> is conveyed to the stretch blow molding part <NUM> (second conveying step).

While the preform <NUM> is conveyed from the injection molding part <NUM> to the stretch blow molding part <NUM>, the preform <NUM> is temperature-adjusted (cooled) and shrunk to a predetermined size. In other words, the temperature adjustment (cooling) for the preform <NUM> is performed between the injection molding part <NUM> and the stretch blow molding part <NUM> such that when being brought into the stretch blow molding part <NUM>, the preform <NUM> has a size shrunk to the predetermined size.

Specifically, the temperature adjustment is performed such that a length in a longitudinal axis direction of the preform <NUM> at the time of being brought into the stretch blow molding part <NUM> via the first conveying step, the temperature adjustment step, and the second conveying step is considerably shrunk by at least <NUM>% or more, more preferably by about <NUM>% to <NUM>%, of a length in the longitudinal axis direction of the preform <NUM> at the time of being injection-molded in the injection molding part <NUM>. Due to such a shrinkage phenomenon, temperature equalization of the preform <NUM> progresses and thus an effect that a temperature variation therein is eliminated is achieved, thereby enhancing formability.

Also, the injection molding step includes a filling step of introducing a molten resin material into the space, which is formed in the injection molding mold (including an injection core mold and an injection cavity mold) <NUM>, defining the outer shape of the preform <NUM> (including an injection step and a pressure maintaining step), and a cooling step of cooling the introduced resin material inside the injection molding mold <NUM>. The injection molding mold <NUM> is supplied with a cooling medium (temperature adjustment medium) and a temperature of the injection molding mold <NUM> is set to <NUM> to <NUM>, preferably <NUM> to <NUM>. It is preferable that a temperature of the injection core mold is set lower than a temperature of the injection cavity mold by setting a temperature of the injection core mold to <NUM> to <NUM> (preferably <NUM> to <NUM>) and a temperature of the injection cavity mold to <NUM> to <NUM> (preferably <NUM> to <NUM>).

In a case where the resin material is polyethylene, if the preform <NUM> is not maintained at a high temperature (for example, <NUM>) close to a melting point (for example, <NUM>) until stretch blow molding is performed, solidification by crystallization is promoted, and the preform <NUM> cannot be properly inflated. Therefore, in the injection molding step, it is preferable that an inside layer (core layer) of the preform <NUM> is formed to be thicker and an outer surface-side layer (skin layer) of the preform <NUM> is formed to be thinner, thereby ensuring that the preform <NUM> has a higher residual heat. In order to realize this state, it is preferable to shorten a duration of cooling; for example, it is preferable to set a duration of the cooling step to <NUM>/<NUM> or less of a duration of the filling step.

Also, the temperature adjustment step is preferably performed such that the shrinkage phenomenon of the preform <NUM> is almost ended by the temperature adjustment mold <NUM> (a heating pot mold which is not in contact with the preform <NUM> and a heating rod mold which is not in contact with the preform <NUM> (or a temperature adjustment rod mold which is in contact with the preform <NUM>)), and the second conveying step is preferably performed such that the preform <NUM> which hardly shrinks can be conveyed to the blow molding mold <NUM>. As a result, it is possible to appropriately adjust a position of a stretching rod during stretch blow molding, thereby avoiding puncture or rupture of the bottom portion <NUM> of the preform <NUM> due to inadvertent contact of the stretching rod therewith during stretch blow molding. Therefore, in the temperature adjustment step, it is preferable that decrease in temperature of the preform <NUM> is reduced by radiant heat from the heating pot, and it is preferable that the temperature adjustment rod, which has a length considering an amount of shrinkage of the preform <NUM> during the first conveying step and the temperature adjustment step, is inserted into the preform <NUM> to adjust the temperature of the preform <NUM>. The heating pot mold and the heating rod mold is set to a temperature of, for example, <NUM> to <NUM> and heats the preform <NUM> from inside and outside by radiant heat. The temperature adjustment rod mold is appropriately set in a range of, for example, <NUM> to <NUM>.

Also, in the stretch blow molding part (stretch blow molding device) <NUM>, the preform <NUM> brought therein at an appropriate stretching temperature is received in the blow molding mold (a pair of blow split molds and one bottom mold) and is stretched (inflated) in the longitudinal axis direction by a rod and in a transversal axis direction by a high pressure fluid (blow air). That is, by stretch-blow-molding the preform <NUM>, the hollow container <NUM> which is a final molded product is formed (stretch blow molding step). The blow molding mold is supplied therein with a cooling medium, and a temperature of the blow molding mold is set to <NUM> to <NUM>. The hollow container <NUM> formed as described above is conveyed to the take-out part <NUM> and then is taken out from the take-out part <NUM> to the outside (take-out step).

Also, the present embodiment is characterized in the manufacturing method for manufacturing the hollow container (resin container) <NUM> using the injection stretch blow molding apparatus <NUM> as described above, in particular, in the stretch blow molding step performed in the stretch blow molding part (stretch blow molding device) <NUM>.

In the following, the stretch blow molding method in the manufacturing method for manufacturing the hollow container (resin container) <NUM> will be described in detail with reference to <FIG>.

In the stretch blow molding part <NUM>, the hollow container (resin container) <NUM> is formed by stretch-blow-molding the preform <NUM>. As shown in <FIG>, the stretch blow molding part <NUM> includes a blow molding mold <NUM> and a stretching rod <NUM>. The blow molding mold <NUM> includes an openable blow molding split mold <NUM>, a blow core mold <NUM>, and a blow bottom mold <NUM>. The blow core mold <NUM> has an insertion hole <NUM> through which the stretching rod <NUM> is inserted to be movable in a vertical direction. Also, although not shown, the stretch blow molding part <NUM> includes a supply unit for supplying a pressurized gas through the insertion hole <NUM> of the blow core mold <NUM>.

In the stretch blow molding part <NUM>, the preform <NUM> disposed in the blow molding mold <NUM> is stretched in the longitudinal axis direction by the stretching rod <NUM> and also stretched in a radial direction by the pressurized gas (blow air) supplied from the supply unit until the preform <NUM> comes into contact with an inner wall surface of the blow molding mold <NUM>. As a result, the hollow container (resin container) <NUM> which is a final molded product is formed.

Specifically, the stretch blow molding step performed in the stretch blow molding part <NUM> includes first to third steps.

In the first step, blow air (preliminary blow air) having a pressure (for example, <NUM> MPa or less) lower than a predetermined set pressure Pa (for example, <NUM> to <NUM> MPa) of final blow air (blow air for strongly pressing the preform <NUM> against the blow molding mold <NUM> to shape the preform <NUM> into the shape of the hollow container <NUM>) is introduced into the preform <NUM> disposed in the blow molding mold <NUM> in a state where the stretching rod <NUM> is not in contact with the bottom portion <NUM> of the preform <NUM>, thereby slightly stretching the preform <NUM> in the longitudinal axis direction and the transversal axis direction. That is, in the first step, the preform <NUM> is slightly inflated by introducing low pressure blow air into the preform <NUM> ((a) of <FIG>). As a result, it is possible to prevent puncture or rupture of the bottom part <NUM> of the preform <NUM> even if a thin (small diameter) stretching rod is used as in blow molding of a small mouth container.

Here, although it is sufficient if the set pressure Pa in the first step is set lower than at least a pressure of the blow air to be introduced in the third step described below, it is preferable to set the set pressure Pa as low as possible (for example, <NUM> MPa or less). That is, it is preferable that the pressure of the blow air introduced in the first step is as low as possible but enough to inflate the preform <NUM>. Further, it is preferable that a flow velocity of the blow air (preliminary blow air) in the first step is set lower than a flow velocity of the blow air (final blow air) in the third step described below.

Also, in the first step, it is sufficient if the preform <NUM> is slightly inflated, and a size of the preform <NUM> after inflation is not particularly limited. For example, it is sufficient if the preform <NUM> is inflated to such an extent that the body portion <NUM> of the preform <NUM> does not come into contact with the inner surface of the blow molding mold <NUM>.

Next, the second step is performed. In the second step, blow air having a pressure lower than the set pressure Pa is introduced into the preform <NUM> like the first step, and the stretching rod <NUM> is moved (lowered) at a predetermined set speed Va. As a result, the preform <NUM> arranged in the blow molding mold <NUM> is stretched in the radial direction by low pressure blow air and also stretched in the longitudinal axis direction by the stretching rod <NUM>, thereby inflating the preform <NUM> to a size bringing it into contact with the inner surface of the blow molding mold <NUM> ((b) of <FIG>).

The set speed Va in the second step is preferably set at a speed as slow as possible such that the stretching rod <NUM> can follow inflation of the preform <NUM> by the blow air. That is, in the second step, it is preferable that the set speed Va is set as slow as possible to such an extent that the stretching rod <NUM> can press the bottom portion <NUM> of the preform <NUM>.

Also, although the pressure of the blow air in the second step is preferably set lower than the set pressure Pa, it is not necessarily for the pressure to be set lower than the set pressure Pa. The pressure of the blow air in the second step may be properly determined to such an extent that the preform <NUM> is not ruptured or the like. Specifically, it is sufficient if the pressure is lower than the pressure of the blow air (final blow air) in the third step, which is the next step.

Next, the third step is performed. In the third step, blow air (final blow air) having a pressure higher than the set pressure Pa is introduced into the preform <NUM>, which has been inflated in the second step, thereby further stretching the preform <NUM>. That is, in the third step, the preform <NUM> is brought into close contact with the inner surface of the blow molding mold <NUM> by introducing high pressure blow air into the preform <NUM>. As a result, the hollow container <NUM> having a predetermined appearance is formed ((c) of <FIG>).

Then, the hollow container <NUM> is released from the blow molding mold <NUM>, is conveyed from the stretch blow molding part <NUM> to the take-out part <NUM>, and is taken out of the apparatus through the take-out part <NUM>.

As described above, according to the present embodiment, the stretch blow molding step of stretch-blow-molding the preform <NUM> to form the hollow container <NUM> includes; a first step of stretching the preform <NUM> by low pressure blow air (preliminary blow air); a second step of stretching the preform <NUM> by low pressure blow air having a pressure, which is equal to or higher than that in the first step and lower than that in a third step (described below), and by pressing the preform <NUM> using the stretching rod <NUM>; and a third step of stretching the preform by high pressure blow air (final blow air). As a result, it is possible to satisfactorily form the hollow container (resin molded product) <NUM> made of polyethylene (PE). For example, even if the hollow container <NUM> is made of high-density polyethylene, the hollow container <NUM> can be satisfactorily formed.

Also, by stretching the preform <NUM> through the stretch blow molding step including the first to third steps, it is possible to satisfactorily form the hollow container <NUM> without causing puncture or rupture even if polyethylene (including high-density polyethylene) which is a relatively soft resin material is employed. Further, it is possible to make a thickness of the hollow container <NUM> uniform or to make a surface of the hollow container <NUM> good.

Further, according to the present embodiment, a thickness t1 of the bottom portion <NUM> of the preform <NUM> formed by injection molding is set to be <NUM>/<NUM> or less of a thickness t2 of the body portion <NUM>. Accordingly, the bottom portion <NUM> of the preform <NUM> is more likely to be hardened than the body portion <NUM> (the temperature is easily decreased). That is, in the stretch blow molding part <NUM>, a ratio of a skin layer in the bottom portion <NUM> of the preform <NUM> becomes higher than that in the body portion <NUM>. Therefore, it is possible to more reliably prevent puncture or rupture from occurring in the bottom portion <NUM> of the preform <NUM> due to contact of the stretching rod <NUM> therewith while the stretch blow molding step is performed.

Further, according to the present embodiment, the preform <NUM> is released from the injection molding part <NUM> in a high temperature state where a surface temperature of the body portion <NUM> after the releasing becomes high in a short time; for example, in a high temperature state where the preform <NUM> has such a high residual heat that a temperature of the skin layer of the body portion <NUM> becomes <NUM> lower than a temperature of the melting point of the resin material within <NUM> seconds after the releasing. Then, the preform <NUM> formed by injection molding is temperature-adjusted and conveyed. Accordingly, it is possible to equalize the temperature and eliminate a variation in temperature of the preform <NUM> brought into the stretch blow molding part <NUM>. As a result, it is possible to achieve a uniform distribution in thickness of the hollow container <NUM> formed by stretch-blow-molding the preform <NUM>.

Here, the first conveying step, the temperature adjustment step, and the second conveying step as described in the foregoing embodiment may be performed according to another aspect (hereinafter, a modified aspect) as described below. <FIG> is a schematic view showing the modified aspect of the first conveying step, the temperature adjustment step, and the second conveying step. In the modified aspect, (a) of <FIG> shows the first conveying step, (b) and (c) of <FIG> shows the temperature adjustment step, and (d) of <FIG> shows the second conveying step. A temperature adjustment part and a temperature adjustment mold in the modified aspect will be referred to as a temperature adjustment part <NUM> and a temperature adjustment mold <NUM>, respectively, in order to distinguish them from the foregoing embodiment, and the other members will be described using the same reference numerals.

In the first conveying step according to the modified aspect, the injection-molded preform <NUM> is released from the injection molding mold <NUM> and conveyed to the temperature adjustment part <NUM>. In the second conveying step according to the modified aspect, the preform <NUM> whose temperature has been adjusted in the temperature adjustment step is conveyed to the blow molding mold <NUM>. At this time, for reasons similar to those described in the forgoing embodiment, it is preferable that shrinkage phenomenon of the preform <NUM> is almost ended in the temperature adjustment step, and the preform <NUM> which hardly shrinks is conveyed to the blow molding mold <NUM>.

The temperature adjustment step according to the modified aspect includes a heating step of heating the preform <NUM> in the temperature adjustment mold <NUM> immediately after moving the preform <NUM> from the injection molding mold <NUM> to the temperature adjustment part <NUM>. Specifically, a temperature adjustment rod of the temperature adjustment mold <NUM> is inserted into an inner portion of the preform <NUM>, and the preform <NUM> is received in a heating pot of the temperature adjustment mold <NUM>, thereby reheating inner and outer skin layers of the preform <NUM> ((b) of <FIG>).

After the heating step, the preform <NUM> is released from the temperature adjustment mold <NUM>, and then the preform <NUM> is shrunk in the longitudinal axis direction in the temperature adjustment part <NUM>, thereby performing a temperature equalization treatment. During the temperature equalization treatment, the preform <NUM> is deformed in a direction intersecting the longitudinal axis direction of the preform <NUM> ((c) of <FIG>). The preform <NUM> follows a procedure, in which the preform is bent and deformed (deformation from (b) of <FIG> of <FIG>) and then as the bending and deforming is relieved (reduced or ended), the preform returns to a state where there is substantially no bending (deformation from to (c) of <FIG> of <FIG>). That is, the temperature adjustment step according to the modified aspect includes; a first step of shrinking the preform <NUM> in the longitudinal axis direction while bending and deforming the preform (deforming accompanied by horizontal swaying); and a second step of shrinking the preform <NUM> in the longitudinal axis direction while relieving (reducing or ending) the bending and deforming of the preform <NUM>.

In a case of a <NUM>-station type one-step molding machine, the temperature adjustment step is not performed. Accordingly, it is not possible to spend a period of time to equalize the temperature of the preform <NUM> before blow molding, or it is necessary to spend a period of time in the blow molding part before blow molding, thereby reducing a period of time required for blowing. According to the manufacturing method for manufacturing the resin container including the temperature adjustment step as described above, the preform <NUM> is bent and deformed due to a variation in temperature of the preform <NUM> (residual heat being asymmetrically present along a circumferential direction) resulting from injection molding. During bending deformation, heat in a core layer of the preform <NUM> is transferred to a skin layer thereof, thereby achieving temperature equalization. Accordingly, the bending deformation is relieved and thus bending is substantially eliminated. Before the stretch blow molding step, a period of time required to deform the preform <NUM> and equalize the temperature thereof is secured in the temperature adjustment step. Accordingly, the preform <NUM> can be stretched in a state suitable for the stretch blow molding step. In addition, when shaping a preform using HDPE, temperature equalization accompanied by the deformation described above progresses favorably.

The heating step in the temperature adjustment step described above is not an essential step. However, by reheating the inner and outer skin layers of the preform <NUM> through the heating step, it is possible to facilitate shrinkage of the preform <NUM> accompanied by bending deformation and thus to appropriately perform temperature equalization. Therefore, it is preferable to include the heating step. In addition, an amount of shrinkage of the preform <NUM> in the modified aspect may be the same as that described in the foregoing embodiment.

Claim 1:
A manufacturing method for manufacturing a resin container (<NUM>) made of polyethylene using an injection stretch blow molding method, the manufacturing method comprising:
an injection molding step of forming a bottomed preform (<NUM>) by injection molding; and
a stretch blow molding step of stretching the preform (<NUM>) by pressing a bottom portion of the preform (<NUM>) by a stretching rod (<NUM>) while introducing blow air into the preform (<NUM>),
wherein the stretch blow molding step comprises:
a first step of stretching the preform (<NUM>) by introducing preliminary blow air which has a pressure lower than final blow air into the preform (<NUM>) in a state where the stretching rod (<NUM>) is not in contact with the bottom portion of the preform (<NUM>);
a second step of stretching the preform (<NUM>) by moving the stretching rod (<NUM>) at a predetermined set speed and pressing the bottom portion of the preform (<NUM>) by the stretching rod (<NUM>) while introducing the preliminary blow air into the preform (<NUM>), the second step being performed after the first step; and
a third step of stretching the preform (<NUM>) by introducing the final blow air into the preform (<NUM>), the third step being performed after the second step.