JPH0948061A - Biaxially stretched polypropylene blow molded bottle with transparent bottom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a biaxially stretched polypropyrene blow-molded bottle with a bottom of excellent transparency by making the bottom of the bottle thin and unevenly shaped through the elongation of the bottom. SOLUTION: An annular recessed part 12, an annular projecting part 13, an annular recessed part 14 and a center projecting part 15 are provided in an annular projecting part 11. The number of concentrical recessed parts and projecting parts is not particularly limited. However, the total number should be 3-10 and preferably be about 4-8. The recessed part and the projecting part should not necessarily be formed in such an order that the recessed part and the projecting part come alternately one after another. In this case, the stretchability of the bottom is improved by making the bottom surface of the bottle uneven, and besides, the bottom has high transparency. Consequently, the strength of the bottom is increased. That is, it is possible to sufficiently elongate the bottom by the formation of an uneven surface on the bottom and increase the strength of the bottom by the structural reinforcement of the bottom with the uneven shape, which contributes to the enhancement of the strength of the entire bottle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene biaxially stretched blow bottle, and more specifically, it is stretch blow-molded by a cold parison method to obtain transparency,
The present invention relates to a polypropylene biaxially stretched blow bottle which is excellent in gloss, falling strength, and the like, and has excellent transparency not only in the body but also in the bottom.

[0002]

2. Description of the Related Art In stretch blow molding, a preform (parison) is made from a thermoplastic resin, and a glass transition point or higher is obtained.
This is a method of manufacturing a container such as a bottle by blowing compressed air in a predetermined mold at a temperature equal to or lower than the melting point and expanding and stretching. The stretch blow bottle obtained by stretch blow molding generally has improved strength, rigidity, barrier property, smoothness, transparency and the like due to the stretch orientation, as compared with an unstretched product. The molding of the preform includes an injection molding method and an extrusion pipe method. The injection molding method is a method of directly injecting a molten resin into a mold to form a bottomed parison.In the hot parison method, a solidified bottomed parison is continuously heated and stretched, while in the cold parison method, After molding the bottomed parison, it is reheated and stretched in another independent blow molding process. In the extrusion pipe method, a pipe obtained by extrusion molding is cooled, cut into a certain length, and reheated to a stretching temperature near the melting point to prepare a heated parison, and then blow molding is performed in a mold.

It is a known technique to produce polypropylene (PP) biaxially stretched blow bottles by stretch blow molding. PP biaxial stretching blow method,
Known are (1) a pipe extrusion method typified by Hercules In-line method, and (2) a hot parison method typified by Nissei ASB Company. However, PP tends to form spherulites, and it is difficult to obtain a PP biaxially stretched blow bottle having high quality and excellent transparency even by biaxially stretch blow molding.

That is, the pipe extruding method (1) is a method of cutting the extruded pipe after adjusting the drawing temperature, or heating by blowing after adjusting the temperature, but the optimum processing temperature of the parison is strictly controlled. However, it was not possible to obtain a PP biaxially stretched blow bottle which was complicated and difficult, and which was satisfactory in terms of transparency. The hot parison method of (2) is also called an injection blow method, and is a method of molding a preform by injection, rotating a turret, adjusting the temperature in the next step, and then blow molding. It is difficult to strictly maintain the required optimum preform processing temperature, and it is difficult to reach a high quality of the product.

[0005] Heretofore, several proposals have been made for an improved method of a PP biaxially stretched blow bottle. For example, in Japanese Examined Patent Publication No. 4-3727, the ethylene content is 1 to 6% by weight and the melt flow index (MFI) is 4 to 50 g.
/ 10 minutes propylene-ethylene random copolymer is used to mold a bottomed parison by injection molding, and then preliminary blow, stretching temperature adjustment, and stretch blowing are performed to obtain excellent transparency and blow without uneven thickness. A method of manufacturing a molded container has been proposed. Specifically, this method is a hot parison method using a blow molding machine manufactured by Nissei ASB. And, according to this method, it is said that a blow container having excellent transparency can be obtained. However, according to the study result of the present inventor, the stretching ratio (length 1.8 times, width 1.2 times) is Since it is low, transparency and strength are still insufficient, and there is a problem that uneven thickness is large.

Recently, as a method for producing a PP biaxially stretched blow bottle, a Bekum Reheat Cold Parison method of Bekum Co. has been used.
nProcess) has been proposed. In this method, the bottomed parison formed by injection molding is taken out from the storage and reheated before the blow molding process.
It is characterized by improving the reheat treatment method to uniformly heat the cold parison to the optimum treatment temperature in a short time. Specifically, in this method, a bottomed cold parison made of injection-molded partially crystalline synthetic resin is placed on a holding metal core and rotated while being conveyed by a conveyor chain. Along the heating / cooling section to alternate between heating and cooling to prevent the outer surface of the parison from overheating and reach a temperature suitable for blow molding. It is raised and then exposed to the hot air in a substantially closed space to completely equalize the temperature over the entire cross section of the parison (JP-A-6-63940). This method is a two-stage injection stretch blow molding method (Two-Stage Injection Str).
etch Blow-Moulding Procedures
It is also called s).

According to this cold parison method, PP
The cold parison consisting of can be raised to a temperature suitable for blow molding in a short time without overheating. Further, according to this method, for example, the vertical axis is 3.0.
The biaxially stretched blow bottle having better transparency than that of the conventional product can be obtained by biaxially stretching at a high degree of 4.0 times (12 times in total) on the horizontal axis. However, according to this cold parison method, although a PP biaxially stretched blow bottle having a transparent barrel can be obtained by devising conditions such as selecting a resin material, milk derived from spherulites is present at the bottom thereof. There is a problem that the product value is impaired because the turbid state remains and the bottom is opaque or translucent. PP2 with opaque or translucent bottom
If the axially stretched blow bottle is used as a transparent liquid container, the commercial value of the contents will be impaired. Also,
If the stretchability of the bottom portion is insufficient, the strength of that portion becomes low, and there is a problem that it is easily damaged by impact.

[0008]

The object of the present invention is to obtain excellent transparency, luster, strength, uniformity of wall thickness, etc. from the cold parison of polypropylene by biaxial stretch blow molding and to improve the transparency of the bottom. It is to provide an excellent biaxially stretched blow bottle. As described above, according to the reheat / cold parison method of Bekm Co., PP cold parison can be uniformly heated in a short time to a temperature suitable for blow molding without overheating of the outer surface.
The stretching ratio can be set high. However, even with this method, it was difficult to obtain a bottle having excellent bottom transparency. The present inventor, as a result of investigating the cause thereof, the bottle body has good transparency because the stretching is sufficiently performed, while the bottom has a spherulite due to insufficient stretching. I thought that the emulsion remained and became opaque or translucent. As a result of further study, it was found that a PP biaxially stretched blow bottle having excellent transparency not only in the barrel but also in the bottom can be obtained by forming the bottom of the bottle into an uneven shape that is easy to stretch. The present invention has been completed based on these findings.

[0009]

According to the present invention, in a polypropylene biaxially stretched blow bottle obtained by biaxially stretch blow molding a polypropylene cold parison, the bottom of the bottle has an uneven shape which is thinned by stretching. A polypropylene biaxially stretched blow bottle having a transparent bottom is provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The PP used in the present invention may be any of a homopolymer, a random copolymer, a block copolymer and a random block copolymer. In addition, syndiotactic PP obtained using a recently developed metallocene (ie, single site) catalyst can also be used. Among these, carbon numbers 2 to 1
A random copolymer having 0-α-olefin as a comonomer is preferable, and among them, in terms of transparency, rigidity, strength, and uniformity of wall thickness, the content of α-olefin in the comonomer exceeds 6% by weight, 15% by weight. % Or less of PP random copolymer is particularly preferred. Ethylene and 1-butene are preferable as the α-olefin. P used in the present invention
Melt flow index of P (g / 10 minutes) (JIS
-Measurement according to K6758: MFI) is usually 3 to 40, preferably 5 to 3 from the viewpoint of transparency, processability and the like.
It is 0, more preferably 7 to 20. If the MFI is less than 3, it becomes difficult to obtain sufficient transparency, and conversely, it is 4
If it exceeds 0, uneven thickness increases, and it becomes difficult to stably obtain a high-quality biaxially stretched blow bottle.

If desired, various additives such as an antioxidant, a clarifying agent, a lubricant, an ultraviolet absorber and an antistatic agent can be added to PP. As the antioxidant, phenol-based compounds, phosphorus-based compounds and other known compounds can be used.
The amount of the antioxidant added is usually 300 to 3000 ppm. As a clarifying agent, sorbitol type, especially NC
-4 (manufactured by Mitsui Toatsu Co., bis p-ethylbenzylidene type) and Millard 3988 (manufactured by Milliken Chemical Co., Ltd., sorbitol acetal type), so-called third-generation clearing agents are preferable. The amount added is usually 100 to 5000 ppm. If the amount of the clarifying agent added is less than 100 ppm, the effect is small, and if it exceeds 5000 ppm, the effect is saturated. A polymer nucleating agent such as a vinylcycloalkane polymer may be used as the clarifying agent. With a polymeric nucleating agent, 100
A good transparency effect can be obtained even with a small amount of about ppm. When the PP biaxially stretched blow bottle of the present invention is used for food, it is desirable to use an additive that does not cause a problem in terms of organoleptic (functionality) such as taste and smell. The selection can be made by a sensory (organoleptic) test for each application.

As a PP biaxially stretched blow bottle producing apparatus of the present invention, an apparatus adopting a two-stage injection stretch blow method from a cold parison represented by the reheat cold parison method of Bekum (RBU445 machine of Bekum). Etc.) are preferred. In the cold parison method, PP is injection-molded to form a bottomed parison. FIG. 1 shows an external view of an example of a parison. In order to make a thick parison 1 and to secure room for the extension rod to work, usually the meat 2 on the outside cavity side.
Serve. In the present invention, in order to improve the stretchability of the bottom portion, the thickness of the parison bottom portion 3 may be made thinner than that of the body portion, and further, the tip portion 4 of the parison bottom portion may be formed into a pointed hat shape or a conical shape. is important. The bottomed parison is stored at low temperature and is called a cold parison. Reheating of the cold parison is carried out, for example, by using an RBU molding machine (trade name) manufactured by Bekum Co., and by the reheat cold parison method, an infrared radiation heating furnace in which an infrared radiation heating rod is arranged, and heating and cooling are alternately performed. It is desirable to carry out and uniformly heat up to the stretching temperature (120 to 160 ° C.). Immediately after adjusting the cold parison to the drawing temperature, blow molding is carried out in the mold with the help of a drawing rod.

In the present invention, it is desirable to carry out biaxial stretch blow molding in a total of 8 or more in the vertical and horizontal directions (vertical axis magnification × horizontal axis magnification = total magnification). A biaxially stretched blow bottle having a high degree of transparency and gloss can be obtained by using the specific PP random copolymer and performing biaxially stretch blow molding at a high magnification of 8 times or more in total. The total draw ratio is preferably about 10 to 15 times. For example, biaxially stretching at a total draw ratio of 12 times, 3.0 times on the vertical axis and 4.0 times on the horizontal axis, increases strength and rigidity, improves low temperature impact resistance and surface condition, and improves transparency. A blow bottle having improved properties can be obtained. Total draw ratio is 8
A PP biaxially stretched blow bottle with a high stretch ratio of ~ 15 times is
Although the body has good transparency, strength, rigidity, etc., if the bottom is molded into a flat shape, stretching of that part is not sufficient, so satisfactory transparency, strength, rigidity, etc. can be obtained. Can not. Therefore, in the present invention, the bottom of the bottle is molded so as to have an uneven shape that is thinned by stretching.

As the uneven shape of the bottom of the bottle, a method of providing radial ribs or a method of providing concentric unevenness (ribs) can be mentioned. The uneven shape referred to here is
It maintains a thin state such as a corrugated cross section. More specifically, a bottom portion provided with radial unevenness 8 as shown in FIG. 3 can be mentioned. That is, FIG. 3 is a front view of the bottom of the bottle, in which there is a concave portion 7 in the annular convex portion 6, and the concave portion 7 further has a concave radial concave portion 8 in which Is provided with an annular concave portion 9 and a central convex portion 10. The number of radial ribs is not particularly limited, but is generally 3 to 10, preferably 4 to 8.
It is about a book. Further, FIG. 4 shows a front view of a bottom portion provided with concentric concavo-convex shapes. An annular concave portion 12, an annular convex portion 13, and an annular concave portion 1 in the annular convex portion 11.
4 and a central convex portion 15 are provided. The number of concentric concave portions and convex portions is not particularly limited, but is 3 to in total.
The number is about 10, preferably about 4 to 8.

The convex portion and the concave portion may be provided, for example, in the order of convex portion-concave portion-convex portion-concave portion .. It may not be formed in order. In the present invention, by providing such a concavo-convex shape on the bottom portion of the bottle, the stretchability of the bottom portion is improved and transparency is imparted, but this can also increase the strength of the bottom portion. That is, since the bottom portion is sufficiently stretched due to the formation of the concavities and convexities, and the concavo-convex shape is structurally reinforced, the strength of the bottom portion is increased, and thus the strength of the entire bottle is improved. P of the present invention
The shape of the P2-axially stretched blow bottle includes a round shape, a square shape, a cylindrical shape, an oval (egg shape), and other shapes. FIG. 2 shows an external view of an example of the PP biaxially stretched blow bottle 5 of the present invention.

[0016]

The present invention will be described below more specifically with reference to examples and comparative examples. In addition, the measuring method of physical properties is as follows. (1) Transparency of bottom part The bottom part of the biaxially stretched blow bottle was visually observed, and the transparent part was regarded as good, and the emulsion part (opaque or translucent) was regarded as poor. (2) Dropping body strength After filling a biaxially stretched blow bottle with water and capping it,
After storing at 2 ℃ for 20 hours, 2m on a stainless steel plate
It was dropped from the height of the bottom to the bottom. Those that did not break were rated as good, and those that break were rated as bad. (3) Body thickness The body of a biaxially stretched blow bottle was cut and the thickness was measured.

Examples 1 and 2, Comparative Example 1 PP having an ethylene content of 7% by weight and an MFI of 7 (g / 10 minutes)
Ethylene-propylene random copolymer of
A cold parison having a characteristic shape as shown in FIG. 1 (unit weight: 30 g) was molded by an injection molding machine. Then, this cold parison is RBU4 of Bekum (Germany)
45 molding machine alternately heats / cools to reheat uniformly and adjusts the stretching temperature, then with the help of a stretching rod, the vertical axis is 3.0 times the horizontal axis is 4.0 times total Biaxial stretch blow molding was performed at a draw ratio of 12 times to prepare a rectangular blow bottle having an internal volume of 1000 ml, a height of 275 mm, and an 81 mm square with a shape shown in FIG. Blow air pressure is 18b
ar. Example 1: A structure provided with radial ribs as shown in FIG. Example 2 Concentric concavo-convex (rib) as shown in FIG.
What provided. Comparative Example 1: A flat bottom without ribs. Phenol-based antioxidants (1500 ppm) and sorbitol-based clarifying agents (NC-
4, manufactured by Mitsui Toatsu Co., Ltd., 2000 ppm) was used. The results are shown in Table 1.

[0018]

[Table 1]

The PP biaxially stretched blow bottles of the present invention (Examples 1 and 2) have excellent transparency not only in the bottle body but also in the bottom, and have good drop strength. On the other hand, when the bottom portion was not provided with irregularities (Comparative Example 1), the transparency of the bottom portion was poor and the drop strength was not good.

[0020]

INDUSTRIAL APPLICABILITY According to the present invention, PP2 having a high degree of transparency and gloss, good strength, and excellent transparency at the bottom by biaxial stretch blow molding from a cold parison (preform). An axial stretch blow bottle is provided.

[Brief description of drawings]

FIG. 1 is an external view of an example of a PP cold parison used in the present invention.

FIG. 2 is an external view of an example of a PP biaxially stretched blow bottle of the present invention.

FIG. 3 is a front view showing an example of an uneven shape (radial ribs) on the bottom of the bottle.

FIG. 4 is a front view showing an example of an uneven shape (concentric ribs) on the bottom of the bottle.

[Explanation of symbols]

 1: Parison (preform) 2: Body part 3: Bottom part 4: Tip part of the bottom part 5: PP biaxially stretched blow bottle 6: Annular convex part 7: Concave part 8: Radial rib 9: Convex part 10: Concave part 11: Annular convex part Part 12: Annular recess 13: Annular projection 14: Annular recess 15: Projection

Claims (1)

[Claims] 1. A polypropylene cold parison containing 2 parts.
A polypropylene biaxially stretched blow bottle having a transparent bottom, characterized in that the polypropylene biaxially stretched blow bottle obtained by axial stretch blow molding has an uneven shape in which the bottom of the bottle is thinned by stretching.