JPH0118846B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a heat-deformable plastic bottle, and more particularly to a method for manufacturing a plastic bottle that prevents thermal deformation of the bottle, particularly a decrease in internal volume, when the bottle is hot filled with contents or heated and sterilized after filling with contents. Concerning bottle manufacturing methods. In recent years, tastes in foods and the like have become richer, and as a result, containers have become more diverse. The same is true in the field of plastic bottles, and there is an increasing need for retort-resistant plastic bottles, especially for the purpose of long-term storage during sterilization of foods. Plastic bottles are formed by melt-extruding plastic into a single-layer or multi-layer parison, then blow-molding the extruded parison by injecting fluid into it while it is closed, making it lighter and more impact resistant than glass bottles. However, a major drawback is poor heat resistance. Generally, the sterilization temperature for bottled foods is 115 to 135℃.
Plastic bottles are easily deformed due to the influence of temperature or pressure during sterilization. For example, it has been found that plastic bottles made of polypropylene do not melt or soften at the above-mentioned temperatures, but when sterilized at the above-mentioned temperatures, the inner volume decreases by 2 to 6% due to thermal deformation. The inventors of the present invention have found that when the outer surface of the body of a plastic bottle is made smooth by blow molding, and inward ribs are provided on it at specific dimensions and at specific intervals, thermal deformation during sterilization can be significantly suppressed. I found something to gain. That is, an object of the present invention is to provide a method for manufacturing plastic bottles that significantly suppresses thermal deformation during heat sterilization, particularly a decrease in internal volume. Another object of the present invention is to provide a method for easily manufacturing the above-mentioned sterilization-resistant bottle by making some changes to the extrusion die. According to the present invention, in a method for manufacturing a plastic bottle, which comprises melt-extruding plastic into a parison shape through a die and blow-molding the plastic bottle by blowing a fluid into the closed parison, a die core with a tapered tip and a die shell are formed. and are arranged so that they can be moved relatively in the axial direction and the die lip width can be changed from 1.3 to 4 times the width at the reference position, and when the die core and the die shell are at the reference position, it becomes a body wall part. While extruding the parison portion, the die core and the die shell are moved relatively to extrude the parison portion that becomes the inward rib, and the time when the die core and the die shell are at the reference position is the time when the die core and the die shell are at the relative movement position. There is provided a method for producing a plastic bottle with excellent resistance to heat deformation during sterilization, which is characterized by blow molding a parison with inward ribs formed in this manner for 1.5 to 5 times as long. The invention will be explained in detail below on the basis of the accompanying drawings. In Figures 1-A, 1-B and 1-C showing an example of a plastic bottle molded according to the present invention, this bottle 1 has a neck part 2, a body body, and a neck part 2 integrally formed by blow molding a plastic parison. It consists of a part 3 and a bottom part 4. The plastic body 3 is distinguished by a smooth outer surface 5 and inwardly projecting ribs 6. This inwardly protruding rib 6 may extend in the axial direction as shown in FIG. 1-A, in the circumferential direction as shown in FIG. 2, or as shown in FIG. It may extend in an oblique direction, or it may have a shape in which an axial rib 6a and a circumferential rib 6b are combined, as shown in FIG. The rib 6 of the bottle molded according to the present invention has a thickness t ₁ that is 1.3 to 4 times, most preferably 1.5 to 3.0 times, the thickness t ₂ of the body wall 7, and the rib 6 has a rib width w. They are provided at intervals w ₂ of 1.5 to 5 times ₁ , particularly preferably 2 to 4 times. The rib structure of the bottle molded according to the present invention makes it possible to significantly reduce the amount of thermal deformation of the plastic bottle. That is, in the body 3 of this plastic bottle, its outer surface 5
Regardless of whether the ribs 6 are provided or not, it is smooth and flush, making it the most stable and convenient form in terms of the external shape, that is, the appearance of the container, and the ease of printing and labeling on the container. It is becoming. In addition, the ribs formed by the present invention that protrude inward from the barrel wall have an effect that is completely different from that of ordinary reinforcing ribs, that is, they prevent thermal deformation during heat sterilization. At the same time, it exhibits the effect of preventing a decrease in internal volume. For example, as shown in the example below, when a polypropylene bottle with a uniform body wall thickness and a thickness of t ₁ = t ₂ = 0.8 mm is subjected to retort sterilization at 135°C for 10 minutes, This results in a volume reduction of 5.2%. Similarly, if the thickness of the trunk wall is uniform throughout, and the thickness is twice that of the former, that is, t ₁ =
Polypropylene bottles in the range t ₂ =1.6 mm also show a volume reduction of 4.0% under similar sterilization conditions.
The above-mentioned facts demonstrate that thermal deformation of plastic bottles occurs as a characteristic of plastics, regardless of the mechanical strength of the bottle. However, according to the present invention, in the case of a polypropylene bottle in which the normal body wall part is made t ₂ = 0.8 mm in the former case, and an inward bead with a thickness t ₁ = 1.6 mm is formed as in the latter case, the same retort is used. Under sterilization conditions, the volume decreases by only about 0.2%, and this fact clearly shows that the thickness distribution structure defined by the present invention effectively works to suppress thermal deformation. The reason for this has not yet been fully elucidated, but the inward ribs formed on the inner surface of the body wall act to give firmness to the bottle body, and the thin body wall between the ribs is rather This seems to be because it acts to alleviate thermal deformation. Thickness of ribs of bottle molded according to the present invention
If t ₁ is smaller than 1.3t ₂ , no significant thermal deformation prevention effect will be obtained, while if it is larger than 4t ₂ , significant thermal deformation (heat shrinkage) will occur in the body wall other than the ribs. This is not desirable. In the present invention, the rib width w ₁ is defined as the width of the portion where the inner thickness of the rib is 1/2 (t ₁ −t ₂ ) or more, that is, the half width. That is, the plastic bottle of the present invention is manufactured by blow-molding a plastic parison provided with inward ribs, but during this blow-molding, the thickness is necessarily relaxed at the shoulder portions of the ribs. The definition makes sense. In the present invention, when the ribs are provided at intervals larger than 5w ₁ , it is difficult to obtain a remarkable thermal deformation prevention effect.On the other hand, when the ribs are provided at intervals narrower than 1.5w ₁ , the thickness specified in the present invention is It becomes difficult to create changes in Conventionally, it has been known to form beads on plastic bottles in order to prevent them from being deformed under pressure. However, such a bead is clearly distinguished from the inward bead used in the present invention in that it has the same thickness as the other body wall portions. In addition, such beads tend to be easily deformed and crushed during heat sterilization, making it impossible to expect heat deformation resistance as in the present invention, and also making it difficult to print the entire surface on the outside. There is also. In the present invention, any plastic can be used for the bottle as long as it is thermoformable and can withstand retort sterilization.
For example, olefin resins such as high-density polyethylene, isotactic polypropylene, crystalline propylene-ethylene copolymers, and ionomers; styrene resins such as polystyrene, styrene-butadiene block copolymers, and nitrile-butadiene-styrene resins; Acrylic resins such as polymethyl methacrylate; high nitrile resins; saturated polyester resins; polyamide resins; polycarbonates; ethylene-vinyl alcohol copolymers; vinyl chloride resins or blends thereof can be used. These plastic bottles may have a single layer construction or a multilayer construction such as two layers, three layers, or five layers. A multilayer plastic bottle with good gas barrier properties and therefore storage stability has a layer structure of olefin resin/ethylene-vinyl alcohol copolymer/olefin resin, and between these layers there is an acid or Alternatively, an adhesive layer such as an acid anhydride-modified olefin resin may be interposed. In the present invention, the thickness _t2 of the body wall of the bottle is generally 0.2, although it varies depending on the internal volume of the bottle.
It is desirable that the rib width _w1 is in the range of 5 to 20 mm. As for the shape of the bottle, in order to be resistant to thermal deformation and to enable heat sterilization in a short time, it is advantageous to have a flat shape as shown in Figures 1-A, 2, 3, and 4. The ratio of the maximum dimension to the minimum dimension in the maximum transverse cross section is preferably in the range of 20:1 to 2:1. Molded according to the present invention. Bottles with circumferential or diagonal inward ribs are shown in FIG.
It is manufactured using the die shown in Fig.-A and Fig. 5-B. That is, the die 10 used for parison extrusion in the present invention consists of a die core 12 with a tapered tip 11 and a die shell 13, a die passage 14 is formed between the two, and a die lip 15 is located at the tip. ing. The die passage 14 is the extruder 1
It is connected to the discharge port 17 of No. 6. The die core 12 and the die shell 13 are provided so as to be movable relative to each other in the axial direction. More specifically, the width of the die lip 15 between the die core 12 and the die shell 13 is from the width a ₂ at the reference position shown in FIG. 5-B to the die lip width a ₁ at the relative position shown in FIG. 5-A. The lip width a 1 is variable, with the lip width a ₁ ranging from 1.5a ₂ to 3a ₂ . When the die core 12 and the die shell 13 are extruded from the plastic at the reference position shown in FIG. When the plastic is extruded in the relative movement position shown in FIG. 5-A, the parison portion that becomes the rib 6 is extruded. Moreover, according to the present invention, the time period during which the die core 12 and the die shell 13 are at the reference position shown in FIG. 5-B.
t ₂ , the die core 12 and the die shell 13 are the 5th-A
By setting the time t ₁ at the relative movement position shown in the figure to 1.5 to 5 times, it is possible to form the parison portion that will become the rib 6 and the parison portion that will become the body wall 7 at the ratio specified in the present invention. Become. In the present invention, the die core 12 and the die shell 1
The relative movement with 3 can be performed according to a preset program so that an inward rib of a predetermined shape and size is formed, and the stopping time, moving distance, and moving speed are as follows. For example, everything can be controlled by a computer. The parison with inwardly directed ribs thus formed is introduced into a split mold known per se, the split mold is closed and the bottom is pinched off, and a fluid is blown into the interior to form a predetermined area defined by the split mold cavity. Form into a shaped bottle. Bottles with axial inward ribs formed according to the present invention can also be manufactured using the die shown in FIG. That is, this die 10 has a structure similar to that shown in FIG. 5, but is provided with a groove 17 around the periphery 16 of the die core 12. This groove 17 is spaced apart from the die shell 13.
The depth is such that b ₁ is 1.3 to 4 times the standard spacing b ₂ , and the spacing is 1.5 to 5 times the groove width c _1.
c ₂ spaced apart. Thus, when the plastic is extruded through this gap, the parison portion that becomes the axially inward ribs is extruded from the groove 17, and the parison portion that becomes the shell wall 7 is extruded from the area other than the groove 17. When the plastic is extruded while rotating the die core 12, a parison with diagonal inward ribs is extruded. The parison is formed in the same manner as described above. Furthermore, FIG. 6 shows the die core 12 and die shell 13.
are relatively movable in the axial direction, and the fifth-A
Extrusion of the plastic in both the positions shown in FIG. Example 1 An extruder for inner and outer layers with a built-in full-flight screw with a diameter of 65 mm and an effective length of 1430 mm and a melt channel branched into two flow paths, and a full-flight extruder with a diameter of 40 mm and an effective length of 880 mm. Adhesive layer extruder with a built-in mold screw and a melt channel branched into two channels, and a diameter of 40 mm.
Using an extrusion device that connects a multilayer 5-layer extruder with a built-in full-flight screw with an effective length of 880 mm, the lip width at the standard position is
3.0mm, the lip width corresponding to the thick rib part is 7.5mm
The extrusion time at the reference position was three times the extrusion time at the rib position, and the inner and outer layers were made of polypropylene (MI.1.5, density 0.90), the adhesive layer was made of maleic acid-modified polypropylene, and the middle layer was made of ethylene-vinyl alcohol. A molten parison of three types and five layers made of polymer (ethylene content 30 mol%) with ribs on the inside in the circumferential direction is extruded, and the parison is placed in a blow mold so that the rib part is located on the body wall of the bottle. By placing it in the mold and using the normal blow molding method, it has a fabric weight of 20g and a content of 200g.
A multilayer bottle was molded. The layer composition ratio of the obtained bottle was: inner and outer layers: adhesive layer: intermediate layer = 10:1:1
The thickness of the body wall is 0.6mm, and the thickness of the rib is 1.5mm.
In addition, the width of the rib portion was 10 mm, and the distance between the ribs was 25 mm. Example 2 Using a 65 m/m extruder (L/D = 22), polypropylene resin (MI = 1.5) was heated to a depth of 2 with a die shell and die core interval (gap) of 3 m/m.
The molten parison was extruded by passing the die core through which slit-like grooves with a width of 1 m/m and a width of 1 m/m were provided at intervals of 3 m/m, and the die core was further moved up and down to extrude the molten parison.
A blow molded container of 200 c.c. was obtained. The thickness distribution of this container cross section is 0.7 m/m in the normal part, and 1.3 and 1.2 in the thickest part of the inner rib in the height direction and lateral direction of the container, respectively.
m/m and the width of the ribs were approximately 10 m/m and 8 m/m, respectively. Fill this container with water, seal the mouth,
Retort sterilization at 115-135°C was performed for 10-30 minutes. Table 1 shows the amount of deformation of the container. The surface of this container is smooth, so after retorting,
Printing and labeling were possible without any restrictions. Comparative Example 1 Using a 65 m/m extruder (L/D = 22), polypropylene resin (MI = 1.5) was heated to a depth of 1 with a die shell and die core distance (gap) of 3 m/m.
The molten parison was extruded through a die core in which slit-like grooves of 1 m/m and width 1 m/m were provided at 5 m/m intervals to obtain a blow-molded container with a basis weight of 20 g and 200 cc. The thickness distribution of this container cross section is 0.75m/
The thickest part of the inner rib was 0.95 m/m, and the width of the rib was about 7 m/m. Fill this container with water, seal the mouth,
Retort sterilization at 115-135°C was performed for 10-30 minutes. Table 1 shows the amount of deformation of the container. Comparative Example 2 Using an extruder with a diameter of 65 mm (L/D = 22),
A polypropylene resin (MI=1.5 density 0.90) was extruded to form a molten parison, and the parison was blow molded to obtain a bottle with a basis weight of 40 g and a content capacity of 200 c.c.
The average thickness of the body wall of this bottle is 1.50mm.
There were no ribs. Comparative Example 3 Polypropylene resin (MI=1.5 density 0.90) was extruded using an extruder with a diameter of 65 mm (L/D=22),
A molten parison was formed, and the parison was placed in a blow mold having vertical grooves at equal intervals and blow molded to obtain a bottle with a basis weight of 20 g and a content capacity of 200 c.c.
The wall thickness of the body wall of this bottle was 0.6 mm in both the normal part and the rib part. Since the ribs were convex on the surface of the container, there was almost no printing area, and when the label was attached, it wrinkled and lost its commercial value. The results of measuring the deformation of the container visually and by reducing the content are shown.

【table】

[Table] Contents before retort

[Brief explanation of drawings]

Fig. 1-A is a perspective view of an embodiment according to the present invention, Fig. 1-B is a sectional view taken along line B-B of Fig. 1-A, and Fig. 1-C is a sectional view of Fig. 1-A.
The figure is an enlarged view of the main parts, Figures 2, 3 and 4 are perspective views of other embodiments, Figure 5 is a sectional view of the extruder die, Figures 5-A and 5-B. 6 shows the relative positional relationship between the die core and the die shell, and FIG. 6 shows a sectional view taken along the line CC in FIG. 5. 1 is the bottle, 2 is the neck, 3 is the body, 4 is the bottom,
6 is a rib, 10 is a die, 12 is a die core, and 13 is a die shell, respectively.

Claims (1)

[Claims] 1. A method for manufacturing a plastic bottle, which comprises melt-extruding plastic into a parison through a die and blow-molding the plastic by blowing a fluid into the closed parison, comprising: a die core with a tapered tip; The die core and the die shell are arranged so that they can be moved relative to each other in the axial direction and the die lip width can be changed from 1.3 to 4 times the width at the reference position, and the die core and the die shell are arranged at the reference position and the body wall and At the same time, the die core and the die shell are moved relatively to extrude the parison part that becomes the inward rib, and the time when the die core and the die shell are in the reference position is changed to the relative movement position. 1.5 for some time
A method for producing a plastic bottle having excellent resistance to heat deformation during sterilization, characterized by blow molding a parison having inward ribs formed in this way.