JP2002067128A - Bottom structure of preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To thin and equalize a bottom thickness of a bottle to be molded by smoothly thinning the bottom by constituting the bottom of a preform of a spherical surface and a flat surface. SOLUTION: Inner and outer bottoms 4a and 4b of the preform 1 are formed in parallel spherical surfaces having equal radii to those of inner and outer wall surfaces of a body continued with a peripheral wall of the bottom. The outer bottom 4b is formed in the flat surface so as to satisfy Γ=t2/(R2-R1), t2=Γ (R2-R1), Γ=0.4 to 0.5, wherein t2 is a thickness of the center of the bottom, R1 is a radius of the inner bottom, R2 is a radius of the outer bottom.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bottom structure of a preform used for stretch blow molding of a thin bottle or the like made of a thermoplastic resin.

[0002]

As a packaging container such as a thin bottle made of a thermoplastic resin, one made by stretch blow molding is known. The main ones are made of polyester, polypropylene, polycarbonate and the like, and in particular, beverage bottles made of polyethylene terephthalate are generally widely known as PET bottles.

In this stretch blow molding, first, a preform consisting of a neck portion and a bottomed body is injection-molded, and the preform is stretched with a stretch rod in a blow mold at a temperature not lower than a glass transition temperature. Normally, it is stretched and expanded in the axial direction and the radial direction by blow air to form a bottle or the like.

In the above stretch blow molding, the preform is transported or stretch blown by grasping the neck portion with a holding die. Also, since the blow core is inserted into the preform opening at the time of stretch blow, the stretch blow molding is performed. The heat loss due to the heat transfer of the continuous upper part of the body is larger than that of the lower part of the body, so that the temperature of the upper part of the body is lowered and a temperature difference is likely to occur.

In such a temperature condition, when the stretching rod is extended to the bottom of the cavity and air blow is performed, due to the temperature difference, the stretching of the upper part of the barrel becomes insufficient compared with the lower part, and the bottle shoulder formed by the upper part of the barrel is formed. Is formed thick from the connection portion of the neck portion, which impairs the appearance as a packaging container, is not only unfavorable as a product image, but may even be handled as a defective molded product.

Therefore, the connecting portion between the neck portion of the preform and the upper portion of the trunk is formed thick to increase the retained heat and facilitate the extension of the upper portion, or the stretching rod is stepwisely extended so that the upper portion of the trunk is stretched ahead. Although the thickness of the shoulder of the bottle is prevented by operating or controlling the blow timing of the air, if the upper part of the body is easily extended, the extension stroke of extending the lower part of the body to the bottom of the cavity is shortened, In addition, since the air inlet is in the neck, expansion by air blow is performed from the upper part of the trunk, and the lower part of the trunk, especially around the center of the bottom is insufficiently stretched, so it is called a meat pool. It becomes thicker.

As a means for improving the wall thickness, attempts have been made to improve the bottom structure of the preform. However, in the preform, since the inner bottom surface is pressed by the leading end of the stretching rod by the stretching rod, the bottom surface is in contact with the trunk. If the same amount of heat is retained, the bottom portion is punched out by the extension force of the rod, making molding impossible, so the bottom surface is formed thinner than the body. Due to this reduction in thickness, the bottom surface of the preform during injection molding is cooled faster than the body portion, and is less likely to expand than the body portion, and withstands the pressing force of the stretching rod.

[0008] The thin bottom can be easily formed by forming the inner and outer bottoms in parallel, but in this case, the wall thickness suddenly changes around the intersection of the trunk and the bottom, and this suddenly changing portion is formed. Unnecessary meat puddles are formed at the bottom of the bottle or cause uneven wall thickness.

The inner bottom surface is made closer to the outer bottom surface by forming the inner bottom surface with a curvature smaller than that of the outer bottom surface, or by forming the inner and outer bottom surfaces as non-parallel spherical surfaces. However, in such a design, the difference in wall thickness between the periphery and the center of the bottom surface becomes too large, and the thickness at the center of the bottom surface becomes extremely thin, so that it can withstand the extension force of the rod. There is a problem that can not be.

The present invention has been conceived in order to solve the problem of increasing the thickness of the bottom of the bottle, particularly the thickness of the periphery of the center, and an object of the invention is to make the bottom of the preform a spherical surface and a flat surface. , The thickness of the bottom of the bottle is gently reduced, and the thickness of the bottom surface of the bottle and the like formed thereby is thinner than before, and the whole is uniformly molded without accumulation of meat. It is to provide a new preform bottom structure that can be used.

[0011]

According to the present invention, the inner and outer bottom surfaces of the preform are formed as parallel spherical surfaces having the same radius as the inner and outer wall surfaces of a body portion having a continuous bottom peripheral wall, and the outer bottom surface has a thickness t2 at the center of the bottom surface. Are the inner bottom radius R1 and the outer bottom radius R2
Γ = t2 / (R2-R1) where t2 = {(R2-R1)} = 0.4-0.5.

The present invention also provides a preform in which a sprue is formed at the center of the outer bottom surface by reducing the thickness of the central portion of the inner bottom surface in the sprue projection plane according to the sprue length. It is also.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings, reference numeral 1 denotes a preform having a bottom.
A neck portion 2 forming an open end, a cylindrical body portion 3 connected to a lower portion thereof, and a bottom portion 4 having a peripheral wall connected to the body portion 3, a screw 5 and a support ring 6 are provided on the outer periphery of the neck portion 2. Is integrally molded.

The inner and outer bottom surfaces 4a and 4b of the bottom portion 4 are formed as parallel spherical surfaces having the same radius as the inner and outer wall surfaces 3a and 4b of the body portion 3 having a continuous bottom peripheral wall with a common fulcrum on the center line of the preform. The bottom surface 4b is formed as a flat surface, and the thickness t2 at the center of the bottom surface is formed to be approximately half of the body thickness t1.

The thickness t2 is obtained by the following relational expression. Inner bottom radius: R1, Outer bottom radius: R2 Γ = t2 / (R2-R1) t2 = {(R2-R1)} = 0.4-0.5

In the preform 1 in which the sprue 7 is formed in the center of the outer bottom surface 4b as shown in FIG.
The center of the bottom surface is formed thicker than the surrounding bottom surface by the sprue 7, whereby the central portion in the sprue projection plane is more easily extended than the surrounding bottom surface, and the central portion of the bottle bottom surface is formed thin. Therefore, a depression 8 having a depth corresponding to the sprue length is formed in the inner bottom surface 4a in the sprue projection plane so that the sprue 7 does not substantially increase in thickness even if it is present. The sprue 7 prevents the center of the bottom of the bottle from being thinned.

FIG. 3 shows a bottle 10 formed by stretching and blowing the preform 1 by ordinary means. The bottle neck portion 12 is formed by the neck portion 2 of the preform 1, a thin body portion 13 connected thereto, and a body portion. 13, a thin bottom surface 11 which is continuous with the lower portion and a bottom portion 14 having a truncated cone shape.

In the preform bottom 4 having the above structure, the inner bottom surface 4a and the outer bottom surface 4b of the parallel spherical surface are formed as flat surfaces, and the thickness t2 at the center of the bottom surface is formed thinner than the body thickness t1. The peripheral bottom surface of the outer bottom surface 4b is formed into a spherical surface together with the inner bottom surface 4a until it intersects with the flat surface, so that the thickness t3 of the bottom peripheral wall is the same as the body thickness t1, and the thickness increases from there toward the center of the bottom surface. As the thickness gradually decreases, even if the bottom is thinned, the center of the bottom is not extremely thinned, and the wall thickness, which causes uneven wall thickness during bottle molding, is unlikely to occur. In addition, the entire preform bottom portion 4 is uniformly expanded and expanded, and the bottom surface 11 of the bottle 10 can be formed thinner than before.

FIGS. 4 and 5 show a bottle A of the above-mentioned embodiment formed from a preform according to the following embodiment having the same form as that of the preform 1 of FIG. 1, and a sudden change in wall thickness at the bottom peripheral wall with parallel inner and outer bottom surfaces. FIG. 4 is a comparison diagram of the result of actually measuring the thickness of the bottom (peripheral wall and bottom surface) of the bottle B with the conventional preform at the measurement points shown in FIG. 3.

FIG. 4 shows the thickness of the bottom peripheral wall, and FIG. 5 shows the thickness of the bottom surface. As is clear from these two comparison diagrams, in the bottle B using the conventional preform, the portions c and e around the center of the bottom face are difficult to stretch, and are formed much thicker than the center portion d, and the drawing is not performed. It will remain in sufficient condition.

On the other hand, in the bottle A formed by the preform 1 according to the present invention, the thickness of the bottom portion (periphery and bottom surface) is generally significantly reduced as compared with the conventional case, and the inner bottom surface is spherical and the outer bottom surface is Due to the bottom surface structure of the bottom surface being a flat surface, the thickness of the peripheral portions c and e at the center of the bottom surface of the bottle A is
The thickness of the bottle B is significantly thinner than that of the same portion, and there is almost no difference from the bottom center portion d. As a result, the bottom thickness is also uneven from the peripheral portions c and e to the peripheral portions a and g. , So that it is sequentially formed into a thin wall.

Since the bottom surface of the bottle formed without any sudden change in the thickness is unlikely to cause distortion, the bottom portion of the bottle is excellent in heat resistance and pressure resistance, and there is no unnecessary thick portion. It also prevents material waste.

The preform of the present invention may be a hot parison method in which the injection-molded preform is stretch blow-molded immediately or by controlling the temperature, or an injection-molded preform is stocked and then heated to stretch blow-molding. It can be adopted in any of the cold parison systems.

[0024]

[Example] Preform material Polyethylene terephthalate Length (excluding neck) 7.56 mm Thickness of body (t1) 3.8 mm Radius of inner wall of body 8.2 mm Radius of outer wall of body 11. 9mm Radius of inner bottom (R1) 8.2mm Radius of outer bottom (R2) 11.9mm Thickness of bottom center (t2) 1.9mm Temperature (body) 105-110 ° C Weight 29.8g

Molding conditions Extension stroke 95 mm Blow air pressure 24 Kgf

Molded product (beverage bottle capacity: 500 ml) Height (excluding neck) 185 mm Outer diameter of body (φ) 68.8 mm Thickness distribution around bottom surface See FIG. 4 (A) Thickness distribution at bottom surface See 5 (A)

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a preform having a bottom structure according to the present invention.

FIG. 2 is an enlarged sectional view of a main part of the above.

FIG. 3 is a diagram showing a contour of a bottle and a preform molded from the same preform and a wall thickness measuring point at the bottom of the bottle.

FIG. 4 is a comparison diagram of the thickness around the bottom surface of a bottle formed from the preform of the present invention and a bottle formed from a conventional preform.

FIG. 5 is a comparison diagram of the bottom wall thickness.

[Description of Signs] 1 Preform 2 Neck 3 Body 4 Bottom 4a Inner Bottom 4b Outer Bottom 7 Sprue 8 Depression for Thin Wall 10 Bottle 11 Bottom 14 Bottom

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shin Yoshizawa 4963, Nanjo, Nanjo-cho, Hanashi-gun, Nagano-gun, Japan F-term in the Aoki Solid Research Institute (reference) 4F201 AA11 AA24 AG07 AG23 AG25 AG26 AH55 AR12 BA03 BC02 BC12 BC21 BC29 BD04 BD06 BM05 BM12 BN18 4F202 AA11 AA24 AG07 AG23 AG25 AG26 AH55 AR12 CA11 CB01 CK02 CK11 4F208 AA11 AA24 AG07 AG23 AG25 AG26 AH55 AR12 LA02 LA08 LB01 LG01 LG03 LG15 LG29 LH03 LH06

Claims (2)

[Claims] 1. The inner and outer bottom surfaces of a preform are parallel spherical surfaces having the same radius as the inner and outer wall surfaces of a trunk portion having a continuous bottom peripheral wall, and the outer bottom surface has a thickness t2 at the center of the bottom surface, an inner bottom radius R1, and an outer bottom radius. The preform is formed on a flat surface such that, when R2, Γ = t2 / (R2-R1) t2 = Γ (R2-R1) Γ = 0.4-0.5. Bottom structure. 2. A preform in which a sprue is formed at the center of the outer bottom surface, wherein a thickness of a central portion of the inner bottom surface in a sprue projection plane is reduced according to a sprue length. The bottom structure of the preform according to claim 1.