JP2001072032A - Pressure-proof polyester bottle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure-proof polyester bottle having a self-standing type structure in which foot segments and valley segments are alternatively installed therein and some contents producing self-generative pressure are filled, and bottom cracking and latent bottom cracking are prevented from being produced even in a long-period storage under a high temperature and high humidity condition. SOLUTION: There is provided a pressure-proof polyester bottle in which foot segments and valley segments are alternatively arranged at its bottom segment 4, the valleys have a curved surface with a substantial uniform radius of curvature in a height direction, density of the valley within a radius corresponding to 40% of a radius of barrel from the center of the bottom segment is lower than 1.34 g/cm3 and the valleys have no substantial single-axial orientation in a circumferential direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-resistant polyester bottle, and more particularly, to a self-standing structure in which a bottom portion of a bottle has a foot portion and a valley portion arranged alternately.
It has a unique shape and orientation characteristics and is resistant to environmental stress cracking (ES
C) It relates to a polyester bottle excellent in properties, impact resistance, pressure resistance, appearance characteristics and the like.

[0002]

2. Description of the Related Art Stretch-blow molded plastic containers, particularly polyester containers, are nowadays commonplace. Due to their excellent transparency and moderate gas barrier properties, liquid detergents,
In addition to liquid products such as shampoo, cosmetics, soy sauce and sauce, carbonated beverages such as beer, cola and cider, fruit juice,
It is widely used in other beverage containers such as mineral water, dessert cups, miso containers, cup products and the like.

[0003] As the bottom structure of the polyester bottle,
A two-piece structure with a separate base cup fitted to the bottom of the round bottom and a one-piece structure with feet and valleys alternately arranged at the bottom are known. In terms of point and productivity, the latter one-piece type has become the mainstream.

However, the latter bottle having a one-piece bottom has a problem that it is not always easy to achieve both pressure resistance and self-sustainability, and in addition to this, the bottom of this type of bottle has environmental stress cracks. (ES
C) easily occurs, and various means for preventing environmental stress cracking (ESC) have been studied.

[0005] Japanese Patent Application Laid-Open No. 5-246416 discloses a self-standing bottle made of synthetic resin formed by biaxial stretching blow molding.
A point that is a predetermined distance away from the center of the bottom is defined as a change point of the bottom shape, and reaches the ground portion through an inclined portion that extends obliquely downward in the radial direction outward from the change point. An inner substantially circular region having three or more provided leg portions and having a predetermined radius having a length exceeding the change point from the center is formed by an unstretched or low-stretched thick portion, Synthetic resin characterized in that at least the outer region including the ground portion is formed of a thin portion that is extended, and a thickness transition portion that connects the thick portion and the thin portion is formed in the middle of the inclined portion. A self-contained bottle is described, and it is also described that in this self-contained bottle, occurrence of stress cracking can be prevented while ensuring internal pressure resistance.

Japanese Patent Application Laid-Open No. 11-43127 discloses that in a plastic bottle manufactured by biaxial stretch blow molding, a plurality of legs whose bottoms swell downward from the bottom surface of a hemispherical curved surface are formed substantially in the circumferential direction. Are arranged at equal intervals,
(A) polyethylene terephthalate and (B) polyethylene naphthalate in an ethylene naphthalate component ratio of 5 to 15 mol% with respect to the total of (A) and (B), an ester exchange rate of 5 to 30%, and Intrinsic viscosity is 0.
A self-supporting bottle characterized by being made of a polyester resin composition of 70 (dl / g) or more is described. In this self-standing bottle, deformation due to heat sterilization treatment is reduced without performing crystallization treatment. It also describes what can be done.

[0007]

SUMMARY OF THE INVENTION Environmental stress cracking (ES)
C) is also called simply stress cracking,
In general, cracks occur when a polymer material is placed under a certain atmosphere, such as when it comes into contact with certain chemicals while being subjected to stress or strain during processing remains. It means a phenomenon that occurs.

[0008] In a polyester bottle, particularly a polyester bottle having a self-standing bottom structure, when contents filled with autogenous pressure, such as carbonated beverages, are filled and stored, it is often recognized that stress cracking occurs at the bottom.

[0009] As a factor for the occurrence of stress cracking in a PET bottle, an extremely large number of factors are known. Even if stress cracking does not occur with one factor, it is possible that defects coexist with several factors at the same time. Are known. These factors include, for example, the intrinsic viscosity of the polyester, the proportion of repro and the dimensions of the pellets, the conditions of injection and blow molding, the degree of stretching, the distribution of the material, the degree of crystallinity of the surface, and the sharp changes in the thickness at the bottom. , Surface finish, inclusions, elapsed time since bottle production, high temperature, high humidity, ventilation of pallets for filled products, storage of filled products beyond the shell life of containers, solvents, incorrect line lubricants, filling Excessive foam in the line, high gas volumes, etc. are known.

[0010] The present inventors have intensively studied the causes of bottom cracks that occur when contents having autogenous pressure are filled and stored in a pressure-resistant polyester bottle having feet and valleys alternately at the bottom. did. As a result, the bottom cracks that occur are all along the circumferential direction of the bottom, and near the bottom crack occurrence position, uniaxial orientation occurs in the circumferential direction. It was concluded that stress was concentrated and cracking occurred.

Thus, an object of the present invention is to provide a pressure-resistant polyester bottle for filling contents having a self-standing structure having a foot portion and a valley portion alternately at the bottom portion and having a self-generated pressure. An object of the present invention is to provide a polyester bottle in which occurrence of bottom cracks or potential bottom cracks is prevented even under long-term storage under humid conditions.

[0012]

According to the present invention, in a pressure-resistant polyester bottle, a foot portion and a valley portion are alternately provided on a bottom portion, and the valley portion has a substantially single radius of curvature in the height direction. On a curved surface, the density of the valleys within a radius equivalent to 40% of the body radius from the center of the bottom is less than 1.34 g / cm ³ , and the valleys have substantially no uniaxial orientation in the circumferential direction. Is provided. In the pressure-resistant polyester bottle of the present invention: 1. 90% or more of the valleys in the height direction are curved surfaces having a single radius of curvature; The crystallinity of the valley within a radius equivalent to 40% of the body radius from the center of the bottom is 2θ = 0 ° to 10 by X-ray diffraction.
2. 3% or less as measured in a range of 0 °; It is preferable that the surface area (S ₁ ) of the valley is 16 to 25% with respect to the surface area (S ₀ ) of the bottom.

[0013]

FIG. 1 shows an example of the polyester bottle of the present invention. The bottle has a neck portion 1 formed by biaxial stretch blow molding of a thermoplastic polyester, a shoulder portion 2 connected to the neck portion, It consists of a body 3 and a bottom 4. The bottom 4 has a self-supporting structure and is composed of feet 5 and valleys 6 arranged alternately.

In the polyester bottle of the present invention, I.I. The valley 6 is constituted by a curved surface having a substantially single radius of curvature in the height direction; II. A valley within a radius equivalent to 40% of the body radius from the bottom center has a density of less than 1.34 g / cm ³ , and III. The valley portion has substantially no uniaxial orientation in the circumferential direction, which is a remarkable feature. Thereby, even during long-term storage under high-temperature and high-humidity conditions, generation of bottom cracks can be effectively prevented. .

In the polyester bottle of the present invention, the valley portion is constituted by a curved surface having a substantially single radius of curvature in the height direction (the requirement I). Thereby, stress concentration on a specific portion of the bottom portion is prevented, and bottom cracks during storage can be effectively prevented. See the example below. That is, in a polyester bottle in which a valley portion is composed of three curvature radii, in an alkali immersion test (accelerated bottom cracking test), bottom cracking occurs 18 minutes after the start of immersion, and the bottom cracking occurrence rate is 23%. On the other hand, in a bottle having a valley portion composed of a substantially single radius of curvature, the bottom crack generation time was 23 minutes after the start of immersion in a similar alkali immersion test. It is clear that the length is extended and the incidence of bottom cracks is suppressed to 5.6% (see Example 1 described later).

In the present invention, the fact that the valley portion is constituted by a curved surface having a substantially single radius of curvature in the height direction means, of course, that the entire valley portion is constituted by a curved surface having a single radius of curvature. This means that most of the valleys may be constituted by a curved surface having a single radius of curvature, and a very limited small portion may be constituted by a curved surface having a different radius of curvature. In general, it is preferable that 90% or more of the valley in the height direction is a curved surface having a single radius of curvature. In this configuration, stress concentration at a specific portion of the valley, a bottom crack or a potential bottom due to the stress concentration. The generation of cracks can be effectively prevented.

In the present invention, the radius of the torso is 40 from the center of the bottom.
% Of the valley within a radius of 1.34 g
/ Cm ³ (Requirement II) and substantially no uniaxial orientation in the circumferential direction (Requirement III). Thereby, it is possible to prevent the generation of a brittle portion that causes a bottom crack. For example, as shown in an example to be described later, a valley having a density of 1.34 g / cm ³ or more within a radius corresponding to 40% of the body radius from the bottom center (Comparative Example 2 to be described later), In the case where uniaxial orientation substantially occurs (Comparative Example 2 described later), in the same accelerated bottom cracking test as described above, bottom cracks occur 2 minutes after the start of immersion,
In addition, the rate of occurrence of bottom cracks reaches 48.0%,
In a bottle configured to have a valley density of less than 1.34 g / cm ³ and to have substantially no uniaxial orientation in the circumferential direction, in a similar alkaline immersion test, the bottom crack generation time was 20 minutes after the start of immersion. And the rate of occurrence of bottom cracks can be suppressed to 8% or less.

In the present invention, the problem of the density of valleys and the presence or absence of uniaxial orientation within a radius equivalent to 40% of the radius of the trunk from the center of the bottom is caused by the self-standing type in which the feet and valleys are alternately arranged. In the structure of pressure-resistant polyester bottle,
The portion where the bottom crack occurs after filling the content is a valley within a radius equivalent to 40% of the body radius from the center of the bottom, and when the density at this portion is within the above range and there is substantially no uniaxial orientation. This is because bottom cracks are effectively avoided.

The density of the polyester was determined by preparing an n-heptane-carbon tetrachloride density gradient tube (Ikeda Rika Co., Ltd.)
The density of the sample can be determined under the condition of 20 ° C. This density increases with oriented and thermal crystallization of the polyester. In the case of polyethylene terephthalate, it is known that the amorphous density (ρam) is 1.335 g / cm ³ and the crystal density (ρc) is 1.455 g / cm ³ , and the density (ρ) and crystallinity of the sample are known. The relationship with (Xc) is given by the following equation (1): Crystallinity Xc = (ρc / ρ) × [(ρ−ρam) / (ρc−ρam)] × 100 ‥‥ (1)

On the other hand, the uniaxial orientation in the valley in the circumferential direction can be detected by X-ray diffraction as an oriented mesophase in the circumferential direction.

It is known that a thermoplastic polyester represented by polyethylene terephthalate (PET) has an oriented mesophase in addition to an amorphous phase and a crystalline phase (Journal of the Textile Society, Vol. 40). No. 6 (1984) pp. 49-56). That is, in the crystal phase of PET, regularity is also observed in the arrangement of benzene rings in the molecule. In this oriented intermediate layer, the arrangement of benzene rings is not regular, but unlike the amorphous phase. In addition, a structure having a certain periodicity is recognized in the orientation in the fiber axis direction. In the case of the oriented fiber, this periodic structure has a characteristic characteristic of uniaxial orientation that is superimposed on an amorphous X-ray diffuse scattering peak in X-ray diffraction. The peak due to the orientation is detected separately.

Also in the polyester bottle of the present invention, a transmission X-ray diffractometer is used to make X-rays perpendicularly incident on the sample in the valley and to reduce the Bragg angle (2θ) in the direction perpendicular to the circumferential direction from 0 to 0. The diffraction intensity is measured by changing the angle in the range of 100 °, and the orientation crystallinity (Doc) can be obtained from the following equation (2). Doc = [(I ₁ −I ₀ ) / I ₁ ] × 100 {2} where I ₁ is the diffraction peak area of the valley sample at 2θ = 0 to 100 °, and I ₀ is the valley sample. Diffraction peak area of 2θ = 0 to 100 ° although completely amorphized by melting and quenching.

In the present invention, if the degree of orientational crystallinity (Doc) obtained from the above formula (2) is 3% or less, it can be said that there is substantially no uniaxial orientation causing bottom cracks.

In the self-supporting pressure-resistant polyester bottle of the present invention, when the density of the valleys is less than 1.34 g / cm ³ and the uniaxial orientation in the circumferential direction is substantially absent, bottom cracks are prevented. The fact can be said to be truly unexpected from conventional knowledge. Because, as already pointed out, the bottom crack in the pressure-resistant polyester bottle is a typical environmental stress crack (ESC), and it is believed that provision of molecular orientation is effective in preventing this environmental stress crack. However, in the self-supporting polyester bottle of the present invention, the crystallization of the valley is suppressed to a low level, and the uniaxial orientation in the circumferential direction is also suppressed, thereby suppressing the occurrence of bottom cracks and the pressure resistance. It has succeeded in improving the preservability of the contents as well as the storability.

[Polyester] In the present invention, any polyester material which can be stretch blow-molded and thermally crystallized can be used. In particular, an ethylene terephthalate thermoplastic polyester is advantageously used.
Of course, other polyesters such as polybutylene terephthalate and polyethylene naphthalate, or a blend with polycarbonate, arylate resin and the like can also be used.

The ethylene terephthalate-based thermoplastic polyester used in the present invention contains most of ester repeating units,
In general, the ethylene terephthalate unit accounts for 70 mol% or more, particularly 80 mol% or more, and has a glass transition point (Tg) of 50 to 90 ° C., particularly 55 to 80 ° C., and a melting point (Tm) of 200 to 275 ° C. Especially 220 to 27
Thermoplastic polyesters at 0 ° C. are preferred.

Homopolyethylene terephthalate is preferred in terms of heat and pressure resistance, but copolymerized polyesters containing a small amount of ester units other than ethylene terephthalate units may also be used.

Examples of dibasic acids other than terephthalic acid include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; succinic acid, adipic acid, sebacic acid and dodecane One or a combination of two or more aliphatic dicarboxylic acids such as diacids, and diol components other than ethylene glycol include propylene glycol,
1,4-butanediol, diethylene glycol, 1,
One or more of 6-hexylene glycol, cyclohexane dimethanol, an ethylene oxide adduct of bisphenol A and the like can be mentioned.

A composite material obtained by blending about 5% to 25% of ethylene terephthalate-based thermoplastic polyester with, for example, polyethylene naphthalate, polycarbonate or polyarylate having a relatively high glass transition point can be used. Material strength at high temperatures can be increased. Further, polyethylene terephthalate and the above-mentioned material having a relatively high glass transition point can be laminated and used.

The ethylene terephthalate-based thermoplastic polyester used should have at least a molecular weight sufficient to form a film, and an injection grade or an extrusion grade is used depending on the application. Its intrinsic viscosity (IV) is generally 0.6 to 1.4 dL / g,
In particular, those in the range of 0.63 to 1.3 dL / g are desirable.

[Bottle and Production Thereof] The pressure-resistant polyester bottle of the present invention has valleys and feet alternately at the bottom, and the valleys have the characteristics described above. The trough has a curved surface with a substantially single radius of curvature (R) in the height direction, and the radius of curvature (R) is equal to the radius of the bottle body (R).
d), but generally Rd of 0.9-1.
It is preferably in the range of 2 times, particularly 0.95 to 1.05 times.

If the radius of curvature (R) of the valley is larger than the above range, the pressure resistance of the bottle becomes unsatisfactory, and the valley and the center of the bottom or the body are separated from each other by a considerably high radius. Unless provided over the entire surface, it tends to be difficult to make a smooth connection. On the other hand, the radius of curvature of the valley (R)
Is smaller than the above range, the independence of the bottle is reduced, or the moldability of the foot tends to be reduced, and furthermore, the valley and the bottom center and the trunk are formed with valleys having different radii of curvature. Unless provided over a considerable height, smooth connection tends to be difficult.

In the polyester bottle of the present invention, the surface area (S ₁ ) of the valley is 16 to 25%, particularly 18 to 23%, relative to the surface area (S ₀ ) of the bottom. It is preferable in terms of balance with the properties. That is, when the surface area ratio of the valleys falls below the above range, the pressure resistance decreases, or there is a tendency that bottom cracks and the like during filling storage tend to occur, while when the surface area ratio of the valleys exceeds the above range, Independence tends to decrease, and the formability of the foot tends to decrease.

On the other hand, the foot portion has a ground contact portion at the lowest position. The horizontal radius of curvature (Rg) of the contact portion differs depending on the bottle body radius (Rd).
0.69 to 0.74 times, particularly preferably 0.71 to 0.735 times. When the radius (Rg) of the ground contact portion falls below the above range, the tendency for the self-sustained stability to be impaired increases. On the other hand, when the radius (Rg) exceeds the above range, the foot becomes overstretched and becomes whitened or cracked. And the pressure resistance tends to decrease.

It is preferable that the lower portion of the inside of the foot portion, which is inside the ground contact portion, has an upwardly convex curved surface in terms of pressure resistance and self-sustainability, and the radius of curvature (Rl) of this curved surface is 1.3 to 1.8 times the body radius (Rd), especially 1.4 to
It is preferably in the range of 1.65 times.

A bottom center portion which is substantially flat and is smoothly connected to the foot portion and the valley portion can be provided on the inner side of the foot portion and the valley portion. 0.14 to 0.16 times the part radius (Rd), especially 0.1
It is preferably in the range of 45 to 0.155 times.

The height from the grounding portion to the center of the bottom generally has a height of 4 to 5 mm, particularly 4.3 to 4.7 mm. preferable. The number of feet provided on the bottom is generally 4 to 6, particularly 5 to 6, from the viewpoint of self-sustainability.

The body of the pressure-resistant bottle of the present invention is preferably highly biaxially oriented. In general, the density of the body is between 1.355 and 1.39 g / cm ³ , in particular 1.36.
It is preferably in the range of from 1.39 g / cm ^{3 to} 1.39 g / cm ³ in terms of pressure resistance.

The mouth-and-neck portion of the pressure-resistant bottle of the present invention includes a screw for fastening the cap, a support ring for supporting the bottle, and a jaw or ratchet for locking the tamper-evidence band of the cap. A mechanism known per se is provided.

The pressure-resistant bottle of the present invention generally has a thickness of 0.2 to 3.5 mm, especially 0.25 mm, except for the aforementioned mouth and neck.
To 3.4 mm in thickness. At the valley within a radius equivalent to 40% of the body radius from the bottom center, the uniaxial orientation in the circumferential direction is suppressed, so that the valley is relatively thick,
Its thickness is generally 1.1 to 3.2 mm.

In the pressure-resistant bottle of the present invention, a bottomed preform of a polyester in a substantially amorphous state is produced, and the bottomed preform is heated to a stretching temperature and then stretch blow-molded in a specific mold. It is manufactured by The mold used (cavity type) naturally has an inner surface corresponding to the valley and the foot, but the inner surface of the mold for forming the valley is a curved surface having a substantially single radius of curvature in the height direction. Must be configured. Further, in a valley portion within a radius equivalent to 40% of the body portion radius from the center of the bottom portion, it is necessary to perform stretch blow molding under conditions in which uniaxial orientation in the circumferential direction is suppressed.

For molding the polyester into a preform, injection molding can be used. That is, the polyester is melt-injected into a cooled injection mold to form a supercooled amorphous polyester preform.

As the injection machine, a known injection machine equipped with an injection plunger or a screw is used, and the polyester is injected into an injection mold through a nozzle, a sprue, and a gate. As a result, the polyester flows into the injection mold cavity and is solidified to form a preform for stretch blow molding.

As the injection mold, one having a cavity corresponding to the shape of the container is used, but it is preferable to use a one-gate or multi-gate injection mold. Injection temperature is 270 ~ 310 ℃, pressure is 28 ~ 110kg / c
about m ² is preferred.

The stretching temperature of the preform is generally from 85 to 135 ° C., preferably from 90 to 130 ° C., and the heating is performed by means known per se such as infrared heating, hot air heating furnace, and dielectric heating. be able to.

For stretch blow molding from a preform, a method of performing stretch blow molding following preform molding by utilizing heat given to a preform molded article to be molded, ie, residual heat, can also be used. However, in general, it is preferable to produce a preform molded article in a supercooled state, and then heat the preform to the above-mentioned stretching temperature to carry out stretch blow molding.

The preform preheated to the stretching temperature is fed into a stretch blow molding machine known per se, set in the mold described above, and stretched in the axial direction by pushing in a stretching rod. Blow stretch molding is performed in the circumferential direction by blowing fluid.

The stretching ratio in the final bottle is suitably 5 to 18 times in area ratio, and among these, the axial stretching ratio is 2 to 4 times, and the circumferential stretching ratio is 2.5 to 4 times.
It is better to double.

[0049]

EXAMPLES The present invention will be specifically described by the following examples.
The present invention is not limited by these examples.

The measurement was performed as follows. 1) Oriented crystallinity The ratio of the oriented crystal peak in the range of 2θ = 0 to 100 ° was determined by a transmission X-ray diffractometer and defined as the oriented crystallinity. 2) Alkaline immersion test Ten bottles of each example were subjected to 1 at a temperature of 40 ° C and a humidity of 90%.
After humidification for 2 hours, fill with carbonated water, adjust the filling liquid in the bottle with warm water of 30 ° C to 20 to 22 ° C, immerse in a 0.2% NaOH aqueous solution of 20 to 22 ° C for 60 minutes, The crack occurrence rate and the shortest time at which bottom cracks occurred were examined.

3) Alkali drop test Each of 20 bottles of each example was subjected to a temperature of 40 ° C. and a humidity of 90% for 1 bottle.
After humidification for a period of time, the solution is filled with carbonated water, the temperature of the filling solution in the bottle is adjusted to 20 to 22 ° C. with warm water at 30 ° C., and the bottle is immersed in a 0.1% aqueous NaOH solution at 20 to 22 ° C. for 5 minutes. Then 0.
It was dropped three times from a height of 8 m or 1.2 m.

Example 1 By biaxial stretching blow of PET
Make a container with five legs and a valley separating them
Was. The valley is substantially a single radius of curvature (R = 46.34)
And a bottom valley having a radius equivalent to 35% of the body radius is zero.
% Oriented crystallinity and 1.336 g / cm ³With a density of
Then S₁/ S₀= 0.192. Example
The dimensions of the container No. 1 are shown in FIG. In FIG.
The unit is mm, φ is the diameter, and R is the radius of curvature.
You.

Example 2 In Example 1, the orientation crystallinity was 2.65%, the density was 1.338 g / cm ³ , and S ₁ /
A container similar to that of Example 1 except that S ₀ = 0.172.

Example 3 In Example 1, the orientation crystallinity was 2.50%, and the density was 1.338 g / cm.
It is _^3, except that the S ₁ / S 0 = 0.226 is the same container as in Example 1.

Example 4 The trough has a substantially single radius of curvature (R = 45.7), and the bottom trough having a radius equivalent to 40% of the body radius has 0% oriented crystallinity. 1.33
A container having a density of 6 g / cm ³ and S ₁ / S ₀ = 0.196.

Example 5 In Example 1, the orientation crystallinity was 2.71%, and the density was 1.339 g / cm.
It is _^3, except that the S ₁ / S 0 = 0.244 is the same container as in Example 1.

COMPARATIVE EXAMPLE 1 The procedure of Example 1 was repeated except that the three radiuses of curvature (R = 82.5, 40, 25) were almost equal, and that S ₁ / S ₀ = 0.276. A container similar to the example.

Comparative Example 2 Three radii of curvature (R = 70.3, 40, 55) having approximately the same distribution, and a bottom valley of 4.1.
A container having 5% oriented crystallinity, a density of 1.350 g / cm ³ , and S ₁ / S ₀ = 0.147.

Table 1 shows the results of the alkali immersion test on these carbonated beverage PET bottles, and Table 2 shows the results of the alkali drop test.

[0060]

Table 1 Result of alkali immersion test Rate of occurrence of bottom cracks (%) Minimum time for bottom cracks to occur (min.) Example 1 5.6 23 Example 2 8.0 23 Example 30-Example 4 7.8 20 Example 50 0-Comparative Example 1 23.3 18 Comparative Example 2 48.0 2 In a bottle satisfying a single radius and a low degree of crystallization, the rate of occurrence of bottom cracks is suppressed to about 10%, and the shortest time is obtained. It is more than 20 minutes and has clearly excellent stress cracking resistance. Comparative Example 2 having three radii of curvature and having the highest degree of oriented crystallinity has the lowest stress cracking resistance.

[0061]

Table 2 Results of alkali drop test Breakage height and number of drops 0.8 m 1.2 m 1 2 3 1 2 3 Comparative Example 1 1 2 1 Comparative Example 2 1 Example 2 Implementation of a single radius of curvature and low crystallinity Only Example 2 has not failed.

[0062]

According to the present invention, in a pressure-resistant polyester bottle having a foot portion and a valley portion alternately on the bottom portion, the valley portion is formed with a curved surface having a substantially single radius of curvature in the height direction. The density of the valleys within a radius equivalent to 40% of the body radius from the center is less than 1.34 g / cm ³ , and the valleys have substantially no uniaxial orientation in the circumferential direction, so that they are stable. In addition to the fact that the self-standing structure is maintained, the generation of bottom cracks or potential bottom cracks can be effectively prevented even when the contents having autogenous pressure are filled and stored for a long time under high temperature and high humidity conditions. is there.

[Brief description of the drawings]

FIG. 1 is a side view of a pressure-resistant polyester bottle of the present invention.

FIG. 2 is an explanatory diagram showing various dimensions of the bottle of Example 1.

Claims (4)

[Claims] In a pressure-resistant polyester bottle, a foot portion and a valley portion are alternately provided at a bottom portion, and the valley portion is a curved surface having a substantially single radius of curvature in a height direction, and a radius of a body portion radius from a center of the bottom portion. 4
The density of valleys within a radius equivalent to 0% is 1.34 g / c.
less than m ^3, and pressure resistance polyester bottle, characterized in that the valleys are not substantially have a uniaxial orientation in the circumferential direction. 2. The pressure-resistant polyester bottle according to claim 1, wherein 90% or more of the valleys in the height direction are curved surfaces having a single radius of curvature. 3. The crystallinity of a valley within a radius corresponding to 40% of the body radius from the center of the bottom is 2θ = 0 by X-ray diffraction.
3. The pressure-resistant polyester bottle according to claim 1, wherein the content is 3% or less when measured in a range of from 100 ° to 100 °. 4. 4. The pressure-resistant polyester bottle according to claim 1, wherein the surface area (S ₁ ) of the valley is 16 to 25% of the surface area (S ₀ ) of the bottom.