KR20030074579A - Preform for a blow molding and method for manufacturing the preform - Google Patents

Abstract

PURPOSE: A precursor of molded material for bi-directional drawing blow molding formation and its preparation process are provided to increase area to be cooled and cooling efficiency of the precursor made of synthetic resin by simplifying formation of inner sides of the precursor. CONSTITUTION: The precursor(100) consists of PP and prepared by injection molding to have inlet(110) and main body(120). The inlet(100) is coupled to a cap of a bottle by a thread part(112) to open/close inlet of the bottle and a ring(114) formed behind the thread part(112) to fit the precursor(100). The main body(120) is in a hollow form by side wall(125) having a hemispheric bottom end closed to form a cylinder-like shape. The side wall(125) has a thick outer side and cylindrical inner side, and an inner diameter same to that of the inlet(110).

Description

PREFORMING FOR A BLOW MOLDING AND METHOD FOR MANUFACTURING THE PREFORM

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to biaxially oriented blow molding, and more particularly, to a preform for blow molding and a method for producing the preform.

Biaxial stretching blow molding is a method in which a preform or sheet softened by heating is blown with air pressure or the like to be brought into close contact with a mold, and at the same time, the molded article is cooled to obtain a hollow body. Therefore, blow molding is also called blow molding or blow molding, and is generally used for producing water bottles, beverage bottles, and the like.

Mainly used for biaxial stretching blow molding is polyethylene terephthalate (PET or PETE). Usually, the molten thermoplastic plastic is molded by extrusion or injection method to form a tube-shaped preform, and the preform is inserted into a blow molding mold to be softened by heating, and then blown with air into the hollow product to form a hollow product. .

Blow molding can be classified into various methods according to the state molding method of the preform, and typical examples include injection stretch blow molding, injection blow molding, extrusion blow molding, and sheet blow molding. Molding (or sheet parason method), direct blow molding, and needle blow molding.

Polyethylene terephthalate (hereinafter referred to as PET) is a plastic mainly used for biaxially stretch blow molding. PET is a thermoplastic synthetic resin, a kind of saturated polyester, and a polycondensate of terephthalic acid and ethylene glycol. Generally, terephthalic acid and thiomethyl can be used to obtain a polymer through transesterification, and can also be obtained using a direct method.

PET is safe against light and heat, and has high resistance to acids and weak alkalis. In addition, PET is transparent and suitable for use as bottled water or beverage bottles. In fact, most of the soda bottles and bottled water bottles currently in circulation are made of PET. Of course, Yakult bottles use polystyrene (PS) or HI-Impact Poly Styrene (HIPS) and milk bottles mainly use polyethylene (PE), but most of the other transparent beverage bottles use PET. PET can make clear and tough beverage bottles, and most 300 ~ 1800ml bottles are made of PET.

However, this PET also has a disadvantage. That is, acetaldehyde can be produced during the processing of PET. In other words, PET must be melted to make a bottle shape using PET, and a small amount of PET is decomposed when exposed to high temperatures to generate a very small amount of acetaldehyde. The resulting acetaldehyde may remain in the disease, and more than about 3 ppm acetaldehyde may have a harmful effect on the human body as a toxin. Given this, the ability to produce acetaldehyde is a fatal drawback of PET containers.

In addition, PET is difficult to recycle. In order to recycle the PET through the melting process, the water (H ₂ O) must be completely removed. This is because PET is produced by the polycondensation reaction of ethylene glycol (Ethylene Glycol) and terephthalic acid (TPA), so that moisture during the melting process can greatly affect the physical properties of PET.

1 is a cross-sectional view of a preform composed of a conventional PET.

Referring to FIG. 1, the conventional preform 10 is for manufacturing a beverage bottle composed of PET, and includes an inlet 20 and a body 30.

The inlet 20 is a part opened and closed by a cap (not shown) of the beverage bottle, and a male screw is formed to fix the cap, and under the screw portion 22 to fix the beverage bottle and the preform 10. Ring 24 is formed.

In blow molding, the side wall of the body portion 30 is extended along the inside of the mold by a blowing process, wherein the body portion 30 of the preform 10 is stretched horizontally and vertically, i. Form the body. Therefore, since the body portion 30 is extended to form a bottle of a predetermined thickness, the side wall 35 of the preform 10 for manufacturing the bottle should be formed thicker than the thickness of the finished bottle in consideration of the expansion.

Conventional preform 10 is composed of a PET, the outer surface is formed in a cylindrical shape with a constant diameter in the side wall 35 of the body portion 30, the side wall 35 is formed to be thick sailing the inner surface is the inlet portion As you go deeper, the inner diameter decreases or stays. Accordingly, a bending line L is formed on the inner surface of the side wall 35, and the inner diameter of the inner surface gradually decreases from the neck below the ring 24 to the bending line L, and passes through the bending line L. FIG. While the inner surface of the side wall 35 is kept constant.

Accordingly, in order to overcome the above problems, it is an object of the present invention to provide a preform using a material having stable physical properties.

Another object of the present invention is to provide a preform having a structure bonded to the properties of physical properties. For example, polypropylene (PP), which is physically stable, cannot be applied to a conventional injection process as it is, and thus is not properly used in the market. It is to provide a preform of a suitable structure according to the properties of these materials.

Still another object of the present invention is to provide a method for preparing the preform.

1 is a cross-sectional view of a preform composed of a conventional PET.

2 is a view for explaining a draw ratio in biaxial stretching blow molding.

3 is a cross-sectional view of a preform according to an embodiment of the present invention.

4 is a cross-sectional view of a preform according to another embodiment of the present invention.

5 to 8 are schematic views for explaining an injection molding apparatus and a manufacturing method for producing a preform according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100, 200: preform 110, 210: entrance

120, 220: body part 125, 225: side wall

L1: 1st bend line L2: 2nd bend line

300: injection molding apparatus 310: gate mold

320: body mold 330: neck ring mold

340 ： Core 345 ： Cooling tube

According to a preferred embodiment of the present invention for achieving the above object of the present invention, the preform comprises a hollow body portion which is expanded by the inlet and blow molding, where, unlike the conventional body portion, the present invention The body portion includes a side wall thickly formed toward the outside.

In blow molding, the sidewalls extend along the mold interior by a blowing process, wherein the body portion of the preform is stretched horizontally and vertically, ie biaxially, to form the body of the bottle. Therefore, since the body portion is expanded to form a bottle of a certain thickness, the sidewall of the preform should be formed thicker than the thickness of the finished bottle in consideration of expansion.

According to the conventional process using PET, the preform made of PET is formed on the side wall of the body portion of the outer surface is of a substantially cylindrical shape with a constant diameter, the side wall is formed to be thick sailing the inner surface of the inner surface is reduced in depth as it enters from the inlet portion or The reduced inner diameter is maintained. According to this structure, the conventional preform has a narrow inner surface.

However, the structure of this preform may be suitable for PET, but not for polypropylene (PP), which is due to the following properties of polypropylene (PP).

Polypropylene (PP) can be obtained by decomposing petroleum (naphtha) like polyethylene (PE). Alternatively, the polypropylene (PP) is contacted with a Ziegler-Natta catalyst in a solution and polymerized at about 80 ° C. and 3 ~ 10 kg / cm ² at room temperature. It is possible to obtain isotactic polypropylene (IPP) with stereoregularity. In general, polypropylene (PP) commercially available as a molding material is those having a content of stereoregular polypropylene (IPP) of about 90 to 95%.

Polypropylene has a specific gravity of about 0.9 to 0.92, which is the smallest class of all plastics. In addition, compared to high density polyethylene (HDPE), the softening temperature is significantly higher (the melting point of the pure IPP is about 170 ℃), the tensile strength, the bending strength, the rigidity is also large. In addition, when the drawing is applied under suitable conditions, tensile strength, rigidity, impact strength, and the like are further improved, and bending fatigue resistance is remarkably improved. Moreover, the transparency and surface gloss of a molded article are better than polyethylene, and since the molding shrinkage rate is small, it is a suitable material from the point of that external appearance and dimensional stability are favorable. In addition, the transparency of polypropylene and the development of stretching technology have resulted in hollow products, now composed of polypropylene and resistant to transparency and impact.

However, although polypropylene has such excellent physical properties, there is a disadvantage that the cooling rate is slow. The slow cooling characteristics cannot be produced quickly and are disadvantageous for mass production because of the long cycles for forming the preform. Conventional PET has a fast cooling rate, so there is no restriction on the shape of the preform, but a preform composed of polypropylene requires a separate structure to improve the cooling rate because the cooling rate is slow.

Therefore, if the sidewall of the conventional preform is formed thick toward the inner surface, the sidewall of the preform according to the present invention is characterized in that formed thick toward the outer surface.

Specifically, in the preform according to the present invention, the inlet is formed with a screw corresponding to the cap of the bottle, the inner surface of the body side wall is formed with the same inner diameter as the inlet to provide a cylindrical space. Unlike the cylindrical inner surface, the outer surface of the body side wall is formed with a first curved line along the outer periphery, the thickness of the side wall to the first curved line is constantly increased, and the thickness of the side wall is almost constant while passing through the first curved line. Depending on the shape of the finished bottle, the position of the first bend line, the thickness of the side wall, and the like may vary.

According to another preferred embodiment of the present invention, the preform may comprise a second bend line formed at the inner surface of the sidewall as well as the first bend line.

2 is a view for explaining a draw ratio in blow molding.

2, axial stretching ratio (ASR) and circumferential stretching ratio (HSR) are important parameters for blow molding. ASR means the ratio of the length of the bottle to the length of the preform (L / l), and HSR means the diameter of the bottle (D / d) to the diameter of the preform.

If the preform is composed of polypropylene according to the present invention, it is preferred that the ASR is about 2.0-4.0 and the HSR is about 2.5-3.5.

According to a preferred embodiment of the present invention for achieving the above object of the present invention, in order to produce the preform described above, to provide a cavity for forming the inlet and the body portion of the preform, the cavity In the dimension of the portion where the body portion is formed is increased in at least one section is provided with a main molding for forming a thick sidewall formed toward the outer surface. After the main molding part is provided, a core is inserted into the cavity to form the inner surface of the preform, and the molten synthetic resin material is introduced into the space provided by the cavity and the core. The introduced synthetic resin material is cooled between the main molding part and the core to become a preform.

Polypropylene may be used as the synthetic resin material, and polypropylene having a slow cooling rate may be rapidly cooled by passing cooling water inside the core for cooling.

In order to produce the preform, a cavity is provided for forming the inlet and the body of the preform, wherein the dimensions of the portion in which the body is formed are increased in at least one section of the main molding and the main molding. An injection molding apparatus of a preform is provided that includes a core inserted into a cavity provided by a portion to form an inner surface of the preform.

Since the thickness of the side wall increases toward the outer surface, the shape of the body portion is formed to be convex as a whole. Therefore, the cavity of the main molding part for producing such a preform must also be formed concave inside, and the convex portion of the molded preform must be able to be easily separated from the injection apparatus.

To this end, the main molding part includes a gate mold, a neck-ring mold and a body part mold, and each mold is divided into sections to form a main molding part. The gate mold includes a gate into which the molten synthetic resin material is introduced, and forms a low end of the preform. The neck-ring mold is disposed opposite the gate mold, and the neck-ring mold forms the upper portion of the inlet and body of the preform. The body mold is disposed between the gate mold and the neck-ring mold to form the remaining body portion following the neck-ring mold. To provide a thickly formed sidewall towards the outer surface, the body mold forms a concave cavity with the neck-ring mold.

The core may then be inserted into a cavity provided by the gate mold, the neck-ring mold and the body mold through the inlet of the neck-ring mold to form the inner surface of the preform.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited or limited by the embodiments.

3 is a cross-sectional view of the preform 100 according to an embodiment of the present invention.

Referring to FIG. 3, the preform 100 is made of polypropylene (PP) and is manufactured in a structure including an inlet 110 and a body 120 through injection molding.

The inlet 110 includes a threaded portion 112 for opening and closing the inlet of the bottle, which is coupled with a cap (not shown) of the bottle, and can easily pick up the bottle and facilitate the preform 100 in the manufacturing process. A lockable ring 114 is formed below the threaded portion 112.

Body portion 120 is a hollow molded body provided by the side wall 125, the lower end of the side wall 125 is closed in a hemispherical shape having a substantially test tube shape.

The side wall 125 of the body portion 120 is formed thick toward the outer surface. That is, the inner surface of the side wall 125 has a cylindrical shape and has the same inner diameter as that of the inlet portion 110, and the outer surface of the side wall 125 protrudes outward as a whole to have a predetermined thickness or more.

Plastics such as polypropylene (PP) are semi-crystal and have a relatively slow cooling rate compared to PET. Therefore, in the case of the preform 10 thickly formed toward the inner surface as shown in FIG. 1, it takes a considerable time to form the shape of the preform 10 of FIG. 1 from polypropylene (PP).

However, as shown in FIG. 3, the inner diameter of the sidewall 125 of the preform 100 may be maintained the same as the inner diameter of the inlet 110, thereby securing a sufficient area for cooling the inner surface of the sidewall 125. It is possible to secure the polypropylene (PP) necessary for blow molding by forming the side wall 125 thick while sufficiently securing the inner surface of the side wall 125.

In addition, a first bend line L1 is formed along the outer circumference of the outer surface of the sidewall 125. The thickness of the sidewall 125 increases from the neck portion of the lower portion of the ring 114 to the first bend line L1. The thickness of the sidewall 125 is maintained constant below the first bending line L1, and gradually decreases from the lower side of the sidewall 125 so that the lower end of the body portion 120 is formed in a substantially hemispherical shape.

The length from the neck part to the first bend line L1, the angle from the neck part to the first bend line L1, the thickness of the side wall 125, etc. are the shape and use of the finished bottle. It may be changed in various ways according to.

In general, in order to design and manufacture the preform 100, the capacity and use of the bottle should first be determined. The material of the bottle, the design of the bottle, the thickness of the bottle, etc. are determined according to the capacity and use of the bottle, and the weight (wt) of the bottle is determined according to these conditions. The amount of polypropylene (PP) used depends on the weight (wt) of the bottle, and the height and thickness of the preform 100 are determined by the above conditions. Specifically, the height and thickness of the preform 100 depend on ASR (axial stretch ratio = L / l) and HSR (Hoop stretch ratio = D / d).

According to the present invention, in the preform, the ASR is preferably about 2.0 to about 4.0 and the HSR is about 2.5 to about 3.5. This is due to the properties of semicrystalline plastics such as polypropylene (PP).

4 is a cross-sectional view of a preform 200 according to another embodiment of the present invention.

Referring to FIG. 4, the preform 200 is also made of polypropylene (PP), and is manufactured in a structure including an inlet part 210 and a body part 220 through injection molding. The inlet portion 210 includes a threaded portion 212 and a ring 214 formed under the threaded portion 212. The body portion 220 is a hollow molded body provided by the side wall 225, and the lower end of the side wall 225 is closed in a hemispherical shape to have a substantially test tube shape.

The side wall 225 of the body 220 is formed thick toward the outer surface. However, unlike the preform of FIG. 3, the inner surface of the sidewall 225 is formed thick toward the inner surface of the second bending line L2. However, the inner surface of the sidewall 225 is formed thick toward the inner surface under conditions that maintain the cooling rate of the polypropylene (PP) appropriately. Specifically, the inner surface of the side wall 225 is inclined inwardly from the neck portion of the lower portion of the ring 214 to the second bending line L2, thereby increasing the thickness of the side wall 225.

In addition, a first bending line L1 is formed along the outer circumference of the outer surface of the sidewall 225. The thickness of the sidewall 225 increases from the neck portion below the ring 214 to the first bend line L1. The thickness of the sidewall 225 is maintained constant below the first bend line L1, and gradually decreases from the lower side of the sidewall 225 so that the lower end of the body portion 220 has a substantially hemispherical shape.

A second bending line L2 may also be formed on the inner surface of the sidewall 225 to variously adjust the thickness of the sidewall 225. As shown partially enlarged in FIG. 4, the first and second bent lines L1 and L2 are formed at different heights to variously adjust the thickness of the sidewall 225. By adjusting the inclination to the first and second bending lines (L1, L2) it is possible to adjust the sidewall increase rate in two stages.

The length from the neck to each bend line (L1, L2), the angle increasing from the neck to each bend line (L1, L2), the thickness of the sidewall 225, etc., are the shape of the finished bottle. And it can be variously changed according to the use and the like.

5 to 8 are schematic views for explaining an injection molding apparatus and a manufacturing method for producing a preform according to an embodiment of the present invention. The apparatus and method described with reference to FIGS. 5 to 8 is for manufacturing the preform 100 of FIG. 3, with reference to the description and drawings of the previous embodiment with respect to the preform 100, the repeated content of May be omitted.

Referring to FIG. 5, the injection molding apparatus 300 according to the present exemplary embodiment includes a gate mold 310, a body mold 320, a neck-ring mold 330, and a core 340.

The gate mold 310, the body mold 320 and the neck-ring mold 330 are in close contact with each other to form a main molding that provides a cavity. The cavity of the main molding part forms the appearance of the inlet 110 and the body 120 of the preform 100. A gate 315 is formed at the center of the gate mold 310 to introduce polypropylene (PP) in a molten state.

The core 340 may enter and exit through the inlet of the neck-ring mold 330, and the core 340 forms an inner surface of the preform 100. The core 340 is formed to have the same outer diameter except for the upper end of the core 340, and the inner surface of the preform 100 is also formed in a cylindrical shape to have a sufficient cooling area.

The core 340 is supported upward by the support, and the neck-ring mold 330, the body mold 320, and the gate mold 310 are sequentially disposed on the core 340. The core 340 is hollow, and a cooling tube 345 is inserted into the core 340 from the support to block the internal and external paths of the cooling water C.

The molds 310, 320, and 330 are separated from each other before the polypropylene (PP) is introduced into the cavity or after the preform 100 is molded.

Referring to FIG. 6, the gate mold 310, the body mold 320, and the neck-ring mold 330 closely adhere to each other to form a main molding part providing a cavity. In addition, the core 340 is inserted into the inlet of the bottom of the neck-ring mold 330 to be located inside the cavity.

The inner surface of the sidewall 125 of the preform 100 is formed in a cylindrical shape by the core 340, and the outer surface of the sidewall 125 is the gate mold 310, the body mold 320, and the neck-ring mold 330. It is formed thick toward the outer surface. To this end, the inner diameter of the body mold 320 is larger than the inner diameter of the neck-ring mold 330, and a bending line for forming the first bending line L1 is formed on the inner surface of the neck-ring mold 330. It is.

The preform 100 according to the present embodiment is made of polypropylene (PP), and the weight per preform 100 is about 23g, the height is about 92.5mm and the thickness is about 4.74mm.

Referring to FIG. 7, polypropylene (PP) in a molten state is introduced into the cavity through the gate 315 of the gate mold 310. Polypropylene (PP) is introduced into the cavity by injection, and about 23 g of polypropylene (PP) is injected into the cavity for about 3 seconds.

Referring to FIG. 8, after 100% of the polypropylene (PP) is filled in the cavity, the cooling water C is introduced into the core 340 through the cooling tube 345. Cooling water (C) from the support is introduced into the core 340 through the cooling tube 345, the cooling water (C) passing through the top of the core 340 flows between the cooling tube 345 and the core 340, Outflow through the outlet.

In the present invention, the side wall 125 of the preform 100 is formed to be thick toward the outer surface to increase the contact area between the inner surface of the side wall 125 and the core 340 compared to the conventional. In fact, the time to cool one preform is about 13 seconds, which is significantly reduced compared to conventional injection molding methods.

After the preform 100 is considered, as shown in FIG. 5, the molds 310, 320, 330 are separated from each other, and the cooled preform 100 can be separated from the injection molding apparatus 300. have.

According to the structure of the preform according to the present invention, although the conditions of injection molding are difficult, such as polypropylene, it is possible to quickly produce a preform using a material having stable physical properties.

In addition, a preform composed of a crystalline material such as polypropylene can be produced in a short time, which is advantageous for mass production.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art various modifications and variations of the present invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (11)

Inlet; It includes a body portion formed in a hollow form integral with the inlet portion, Preforms, characterized in that the side wall of the body portion is formed thick toward the outside for blow molding. The method of claim 1, The outer surface of the side wall is formed with at least one first bent line formed along the outer periphery of the outer surface, the preform, characterized in that the increasing tendency of the side wall thickness increases or decreases around the first bent line. The method of claim 2, The inner diameter of the side wall of the body portion is the same as the inner diameter of the inlet portion, the preform, characterized in that the lower end of the body portion in the lower end of the body portion. The method of claim 2, At least one second bending line formed along the circumference of the inner surface of the sidewall, and a tendency to increase or decrease the thickness of the sidewall with respect to the second bending line increases or decreases. The method of claim 1, The inlet and the body portion preform, characterized in that consisting of polypropylene (PP). The method of claim 1, Axial stretch ratio (ASR) of the preforms (ASR) is 2 to 4, circumferential stretch ratio (Hoop Stretch Ratio (HSR)) is a preform, characterized in that 2.5 to 3.5. In the method of producing a preform for producing a preform of any one of claims 1 to 6, Providing a cavity for forming the inlet and body of the preform, wherein the dimension of the portion of the body portion in which the body is formed is increased in at least one section; Placing a core in the cavity to mold the inner surface of the preform; Introducing a synthetic resin material in a molten state into a cavity provided by the main molding part and the core; And Cooling the inserted synthetic resin material forming a preform according to the space. The method of claim 7, wherein A gate mold having a gate formed in the cavity of the main molding part, the gate mold for forming a lower end of the preform; A neck-ring mold for forming an inlet portion of the preform and a portion of a body portion of the preform; And a body mold disposed between the gate mold and the neck-ring mold to form the remainder of the body of the preform, the body mold including an inner diameter larger than the inner diameter of the neck-ring mold. After the preform is cooled, the gate mold, the neck-ring mold, and the body mold are separated from each other, thereby providing a space for separating the preform. The method of claim 7, wherein The end of the core is formed in a hemispherical shape, the other body is formed in a cylindrical shape is provided a method of manufacturing a preform. The method of claim 7, wherein Circulating cooling water into the core to cool the preform. The method of claim 7, wherein Axial stretch ratio (ASR) of the preform is a method of producing a preform, characterized in that the range of 2 to 4, the circumferential stretch ratio (HSR) is produced in the range of 2.5 to 3.5.