JP3748739B2 - Pressure-resistant polyester bottle and package using the same - Google Patents

Description

【００５３】
［実験例２］
延伸シートを作成し、エンタルピー緩和量、配向結晶化度、脆性破壊の割合を測定した。その結果を表２に示す。
【表２】

【００５４】
［実験例３］
二軸延伸ブローにより二軸延伸自立型耐圧ポリエステルボトルを作成し、底中心より胴部半径の３５％相当半径の底谷部のエンタルピー緩和量、配向結晶化度の測定および充填試験を行った。その結果を表３に示す。
【表３】

【００５５】
［実験例4］
押し出しフィルムを作成し、温度・湿度履歴により種々のエンタルピー緩和量を持たせた。これらフィルムの引張り試験（ｎ＝７〜１０）により脆性破壊を示した試料の割合を求めた。その結果を表４に示す。
【表４】

【００５６】
［実験例５］
延伸シートを作成し、温度・湿度履歴により種々のエンタルピー緩和量を持たせた。これらフィルムの引張り試験（ｎ＝７〜１０）により脆性破壊を示した試料の割合と、配向結晶化度を求めた。その結果を表５に示す。
【表５】

【００５７】
［実験例６］
二軸延伸ブローにより二軸延伸自立型耐圧ポリエステルボトルを作成したのち、温度・湿度履歴により種々のエンタルピー緩和量を持たせ、底中心より胴部半径の３５％相当半径の底谷部のエンタルピー緩和量、配向結晶化度の測定および充填試験を行った。その結果を表６に示す。
【表６】

【００５８】
【発明の効果】
本発明によれば、底部に足部と谷部とを交互に有する耐圧性ポリエステルボトルにおいて、底部中心より胴部半径の４０％相当半径以内の少なくとも谷部における一軸配向結晶化度とエンタルピー緩和量とを特定の範囲に設定することにより、自生圧力を有する内容物を充填した際の脆性破壊を有効に防止でき、耐圧性を向上させると共に、内容物の保存性をも向上させることができる。
【図面の簡単な説明】
【図１】本発明の耐圧性ポリエステルボトルの側面図である。
【図２】一軸配向結晶化度及びエンタルピー緩和量と脆性破壊との関係を示すグラフである。
【図３】示差走査熱量計によるエンタルピー緩和量の求め方を示すグラフである。
【図４】一軸配向を有するポリエステルのＸ線回折像を示すグラフである。
【図５】無配向のポリエステルのＸ線回折像を示すグラフである。[0001]
[Industrial application fields]
The present invention relates to a pressure-resistant polyester bottle and a package using the same. More specifically, the bottle bottom has a self-standing structure in which feet and valleys are alternately arranged, and is excellent in brittle fracture resistance. The present invention relates to a polyester bottle and a package using the same.
[0002]
[Prior art]
Stretch blow molded plastic containers, especially polyester containers, are now commonplace, and because of their excellent transparency and moderate gas barrier properties, beer is used in addition to liquid products such as liquid detergents, shampoos, cosmetics, soy sauce and sauces. It is widely used in carbonated beverages such as cola and cider, other beverage containers such as fruit juice and mineral water, dessert cups, miso containers and cup products.
[0003]
The bottom structure of polyester bottles is known as a two-piece structure with a separate base cup fitted to the bottom of a round bottom and a one-piece structure with alternately foot and troughs on the bottom. However, the latter one-piece type has become the mainstream in terms of resource reuse and productivity.
[0004]
However, the bottle with the bottom of the latter one-piece structure has the problem that it is not always easy to achieve both pressure resistance and self-supporting properties. In addition, the bottom of this type of bottle is filled with contents and stored. In this case, brittle fracture often occurs.
[0005]
In Japanese Patent Laid-Open No. 5-246416, in a self-supporting cage made of synthetic resin that has been biaxially stretched and blow molded, 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 outward in the radial direction from this change point. The bottom part has three or more legs provided at almost equal central angles through an inclined part extending obliquely downward to a grounding part, and has a length beyond the change point from the center. An inner substantially circular region having a predetermined radius is formed of an unstretched or low-stretched thick portion, and at least an outer region including the grounding portion is composed of a stretched thin portion, and the thick portion and the thin portion A synthetic resin self-supporting scissors characterized in that a thick-walled transition portion is formed in the middle of the inclined portion. In this self-supporting scissors, stress cracking is ensured while ensuring internal pressure resistance. It is also noted that the occurrence of It is.
[0006]
In JP-A-11-43127, in a plastic bottle manufactured by biaxial stretch blow molding, a large number of leg portions whose bottom portions bulge downward from the bottom surface of a hemispherical curved surface are arranged at substantially equal intervals in the circumferential direction. And comprises (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), and a transesterification rate of 5 to 30 %, And a self-supporting bottle characterized by comprising a polyester resin composition having an intrinsic viscosity of 0.70 (dl / g) or more is described, and the self-supporting bottle is subjected to a crystallization treatment. No, it is also described that deformation due to heat sterilization can be reduced.
[0007]
[Problems to be solved by the invention]
It is known that biaxially stretched polyester bottles, especially one-piece self-supporting bottles, undergo brittle fracture when stored under high temperature and humidity conditions. This brittle fracture occurs because the inherently ductile polyester has a rapid decrease in elongation at break due to aging. This is because the polyester in the melt equilibrium state is rapidly cooled, It is said that the structure changes to an equilibrium state (pseudo-crystallization state) at room temperature.
It is also known that the degree of this structural change is obtained as enthalpy relaxation (ΔE), and can be actually measured by, for example, a differential scanning calorimeter.
[0008]
In order to prevent this brittle fracture, it is known that highly biaxially oriented polyester is effective, and in fact, the conventional biaxially stretched polyester bottle has such a conventional knowledge. Is accepted as is.
However, in an actual pressure-resistant self-supporting polyester bottle, brittle fracture occurs at the bottom of the bottle, and so much knowledge has not been obtained on how to prevent brittle fracture at the bottom of the bottle.
[0009]
The present inventors have found that the brittle fracture that occurs at the bottom of the bottle is closely related to the uniaxial crystallinity and the amount of enthalpy relaxation in at least the valley within a radius equivalent to 40% of the radius of the barrel from the center of the bottom. It was found that the brittle fracture at the bottom of the bottle can be prevented by controlling to a certain range.
[0010]
That is, an object of the present invention is to provide a one-piece structure self-standing polyester bottle having a foot portion and a trough portion alternately on the bottom portion, in which brittle fracture at the bottom portion is prevented.
[0011]
[Means for Solving the Problems]
According to the present invention, in a biaxially stretched self-supporting pressure-resistant bottle made of polyester having a foot and a valley alternately on the bottom, uniaxial orientation in at least a valley within a radius equivalent to 40% of the trunk radius from the center of the bottom A pressure-resistant polyester bottle is provided in which the degree of crystallinity and the amount of enthalpy relaxation satisfy the following formulas (1) and (2):
Y ≦ (2.5 × 10 ⁻⁴ ) × (X-10.5) ⁴ (1)
0 ≦ X <10.5 (2)
In the formula, Y is an enthalpy relaxation amount obtained as an endothermic peak (J / g) measured in the range of Tg to Tg + 25 ° C. measured by a differential scanning calorimeter, and X is 2θ = 0 ° by X-ray diffraction method. The orientation crystallinity (%) measured in the range of up to 100 ° is expressed.
According to the present invention, there is also provided a package characterized in that the pressure-resistant polyester bottle is filled with a content having a self-generated pressure and sealed.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1 which shows an example of the polyester bottle of the present invention, this bottle comprises a mouth neck 1 formed by biaxial stretch blow molding of thermoplastic polyester, a shoulder 2 connected to the mouth neck, a trunk 3 and a bottom 4. Consists of. The bottom 4 has a self-supporting structure,
It consists of legs 5 and valleys 6 arranged alternately.
[0013]
In the polyester bottle of the present invention, the uniaxial crystallinity (X) and the enthalpy relaxation amount (Y) in at least a valley portion within a radius equivalent to 40% of the trunk radius from the center of the bottom are expressed by the following formulas (1) and (2). ,
Y ≦ (2.5 × 10 ⁻⁴ ) × (X-10.5) ⁴ (1)
0 ≦ X <10.5 (2)
In the formula, Y is an enthalpy relaxation amount determined as an endothermic peak (J / g) measured in a range of Tg to Tg + 25 ° C. measured by a differential scanning calorimeter,
X represents the orientation crystallinity (%) measured by X-ray diffraction method in the range of 2θ = 0 ° to 100 °,
If the relationship satisfies the above, brittle fracture can be effectively prevented.
[0014]
Please refer to FIG. 2 of the accompanying drawings. FIG. 2 plots the relationship between the uniaxial crystallinity and the amount of enthalpy relaxation for various polyester sheets and bottles. For the bottles, valleys within a radius equivalent to 40% of the trunk radius from the bottom center. The measured values for the parts are shown.
In the marks in the figure, the black-colored ones indicate brittle fracture, and the white ones indicate no brittle fracture.
The curve in the figure is the following formula (1a)
Y = (2.5 × 10 ⁻⁴ ) × (X-10.5) ⁴ (1a)
The curve is shown.
According to these results, it is clear that brittle fracture occurs in the region above the curve (1a), whereas brittle fracture is prevented in the curve and the region below the curve.
[0015]
That is, as already pointed out, it was already known that the structural change from the melt equilibrium state to the room temperature equilibrium state was measured as the amount of enthalpy relaxation, but to what extent to prevent brittle fracture at the bottom of the bottle It is not known at all whether the amount of enthalpy relaxation is allowed, and it was unclear to what extent the enthalpy relaxation amount is allowed in relation to the situation and uniaxial crystallinity. In the invention, it has been found that there exists an amount range of an enthalpy relaxation amount that prevents brittle fracture in relation to the uniaxial crystallinity.
Explaining this point, when the uniaxial crystallinity is 0%, the allowable enthalpy relaxation amount is the largest, and the upper limit is about 3 J / g, whereas the uniaxial crystallinity increases. As the amount of enthalpy relaxation allowed decreases as a quartic function, brittle fracture occurs regardless of the amount of enthalpy relaxation when the uniaxial crystallinity is 10.5% or more.
[0016]
In the present invention, the problem of the enthalpy relaxation amount and uniaxial crystallinity of the valley within a radius equivalent to 40% of the trunk radius from the center of the bottom is that the legs and valleys are alternately arranged. In the pressure-resistant polyester bottle with the structure, the part where brittle fracture occurs after filling the contents is a valley part within a radius equivalent to 40% of the trunk part radius from the center of the bottom, and the enthalpy relaxation amount and uniaxial crystallinity at this part This is because this brittle fracture is effectively avoided when the above-described equations (1) and (2) are satisfied.
In the claims, it is essential that the portion within the radius corresponding to 40% of the radius of the body portion from the center of the bottom portion is at least a valley portion. This valley portion must satisfy the above formulas (1) and (2). This is essential, but the feet within the above radius may also satisfy the expressions (1) and (2).
[0017]
The amount of enthalpy relaxation that is a problem in the present invention is determined as an endothermic peak area in the range of Tg (glass transition point) to Tg + 25 ° C. in a differential scanning calorimeter.
FIG. 3 shows a differential scanning calorimetry curve of a polyester having an enthalpy relaxation amount of 1.028 J / g.
[0018]
On the other hand, the uniaxial crystallinity in the valley can be detected by X-ray diffractometry as an oriented mesophase in the circumferential direction.
[0019]
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 Fiber Society, Vol. 40, No. 6). (1984) p49-56).
In other words, in the crystal phase of PET, regularity is also observed in the arrangement of benzene rings in the molecule, but in this oriented intermediate layer, there is no regularity in the arrangement of benzene rings, but unlike the amorphous phase. In the orientation in the fiber axis direction, a structure having a certain periodicity is recognized. In the case of an oriented fiber, this periodic structure has a peak peculiar to uniaxial orientation superimposed on the amorphous X-ray diffuse scattering peak in X-ray diffraction, and this amorphous peak and uniaxial The peak due to orientation is detected separately.
[0020]
Even in the polyester bottle of the present invention, a transmission X-ray diffractometer is used to allow X-rays to be incident perpendicularly to the sample at the valley, and the Bragg angle (2θ) is 0 to 100 ° perpendicular to the circumferential direction. By varying the range, the diffraction intensity is measured, and the orientation crystallinity (Doc) can be obtained from the following formula (2).
Doc = [(I ₁ −I ₀ ) / I ₁ ] × 100 (2)
In the formula, I ₁ is a diffraction peak area of 2θ = 0 to 100 ° of the valley sample, and I ₀ is a diffraction of 2θ = 0 to 100 ° of the valley sample which is completely amorphized by melting and quenching. It is the peak area.
[0021]
FIG. 4 of the accompanying drawings is an X-ray diffraction image of a polyester bottle valley having uniaxial orientation, and FIG. 5 is an X-ray diffraction image of non-oriented polyester.
[0022]
According to the present invention, as described above, the uniaxial crystallinity and the amount of enthalpy relaxation in at least the valley within the radius corresponding to 40% of the trunk radius from the center of the bottom satisfy the above formulas (1) and (2). By filling the self-supporting pressure-resistant polyester bottle having the above-mentioned relationship with the content having the self-generated pressure, brittle fracture at the bottom can be prevented, the pressure resistance can be improved, and the preservability of the content can be improved.
[0023]
[polyester]
In the present invention, any polyester material that can be stretch blow molded and crystallized may be used, but ethylene terephthalate-based thermoplastic polyesters are particularly advantageously used. Of course, polybutylene terephthalate, polyethylene Other polyesters such as phthalate, or blends with polycarbonate or arylate resin can also be used.
[0024]
The ethylene terephthalate-based thermoplastic polyester used in the present invention occupies most of the ester repeating units, generally 70 mol% or more, particularly 80 mol% or more of ethylene terephthalate units, and has a glass transition point (Tg) of 50 to 90. Thermoplastic polyesters having a melting point (Tm) of 200 to 275 ° C., particularly 220 to 270 ° C., at 55 ° C., in particular 55 to 80 ° C., are preferred.
[0025]
Homopolyethylene terephthalate is preferred in terms of pressure resistance, but a copolyester containing a small amount of ester units other than ethylene terephthalate units can also be used.
[0026]
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, dodecanedioic acid, etc. 1 type or combination of 2 or more types of diol components other than ethylene glycol include propylene glycol, 1,4-butanediol, diethylene glycol, 1,6-hexylene glycol, cyclohexane di 1 type, or 2 or more types, such as methanol and the ethylene oxide adduct of bisphenol A, are mentioned.
[0027]
Also, it is possible to use a composite material in which ethylene terephthalate-based thermoplastic polyester is blended with about 5% to 25% of polyethylene naphthalate, polycarbonate, polyarylate, etc. having a relatively high glass transition point, so that it can be used at a relatively high temperature. The material strength can be increased.
Further, polyethylene terephthalate and the above-mentioned material having a relatively high glass transition point can be laminated and used.
[0028]
The ethylene terephthalate-based thermoplastic polyester to be used should have at least a molecular weight sufficient to form a film, and an injection grade or extrusion grade is used depending on the application. The intrinsic viscosity (IV) is generally in the range of 0.6 to 1.4 dL / g, particularly 0.63 to 1.3 dL / g.
[0029]
[Bottle and its production]
The pressure-resistant polyester bottle of the present invention is alternately provided with valleys and legs at the bottom, and the valleys have the characteristics described above.
The valley portion may be a spherical surface or a curved surface close to a spherical surface as a whole in a vertical section, but it is preferable that the valley portion is a curved surface having a substantially single curvature radius (R) in the height direction. The radius of curvature (R) varies depending on the bottle barrel radius (Rd), but is generally 0.9 to 1.2 times, particularly 0.95 to 1.05 times Rd.
[0030]
If the curvature radius (R) of the valley is larger than the above range, the pressure resistance of the bottle is unsatisfactory, and the valley, the bottom center, and the body are provided with portions having different curvature radii over a considerable height. Unless it is, it tends to be difficult to connect smoothly.
On the other hand, if the curvature radius (R) of the valley is smaller than the above range, the bottle's independence tends to be lowered, and the moldability of the foot tends to be lowered. There is a tendency that smooth connection is difficult unless the valleys having different curvature radii are provided over a considerable height.
[0031]
Further, in the polyester bottle of the present invention, the surface area (S ₁ ) of the valley portion is 16 to 25%, particularly 18 to 23% with respect to the surface area (S ₀ ) of the bottom portion. It is preferable in terms of balance.
That is, if the surface area ratio of the valley is less than the above range, the pressure strength is reduced, or bottom cracks during filling storage tend to occur, whereas the surface area ratio of the valley exceeds the above range, There is a tendency that the independence is lowered and the moldability of the foot part is lowered.
[0032]
On the other hand, the foot portion has a ground contact portion at the lowermost portion, and the radius of curvature (Rg) in the horizontal direction of the ground contact portion differs depending on the radius of the bottle body portion (Rd), but generally 0.69 of Rd. It is preferable to be in the range of ~ 0.74 times, particularly 0.71 to 0.735 times.
When the radius (Rg) of the ground contact portion is less than the above range, the tendency to lose the self-supporting stability is increased. On the other hand, when the radius (Rg) exceeds the above range, the foot portion is overstretched and whitening or cracking occurs. Will occur and the pressure strength tends to decrease.
[0033]
Of the legs, the lower part inside the grounding part is preferably a curved surface convex upward from the viewpoint of pressure resistance and self-supporting property, and the radius of curvature (Rl) of this curved surface is the radius of the bottle body It is preferable to be in the range of 1.3 to 1.8 times (Rd), particularly 1.4 to 1.65 times.
[0034]
A bottom center portion that 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, and the radius (Rc) of the bottom center portion is the bottle trunk radius ( Rd) is preferably 0.14 to 0.16 times, particularly preferably 0.145 to 0.155 times.
[0035]
In addition, the height from the ground contact portion to the bottom center portion is generally 4 to 5 mm, and particularly preferably 4.3 to 4.7 mm, from the standpoint of self-supporting stability in the content-filled state.
Further, the number of feet provided on the bottom is generally 4 to 6, particularly 5 to 6 in terms of self-standing stability.
[0036]
It is desirable that the body of the pressure-resistant bottle of the present invention is highly biaxially oriented. In general, the density of the body portion is preferably in the range of 1.355 to 1.39 g / cm ³ , particularly 1.36 to 1.39 g / cm ³ , in view of pressure resistance.
The density of the polyester can be determined by preparing an n-heptane-carbon tetrachloride-based density gradient tube (Ikeda Rika Co., Ltd.) and measuring the density of the sample at 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. The relationship with the degree of conversion (Xc) is expressed by the following formula (3)
Crystallinity Xc = (ρc / ρ) × [(ρ−ρam) / (ρc−ρam)] × 100 (3)
Given in.
[0037]
The mouth-and-neck portion of the pressure-resistant bottle of the present invention is known per se, such as a screw for fastening a cap, a support ring for supporting the bottle, and a jaw or ratchet for locking a tamper-evident band of the cap. It is equipped with the mechanism. The mouth-and-neck portion may be in an uncrystallized state as formed or may be spherulized by heating.
[0038]
The pressure-resistant bottle of the present invention generally has a thickness of 0.2 to 3.5 mm, particularly 0.25 to 3.4 mm, excluding the aforementioned mouth and neck. In the valley portion within a radius equivalent to 40% of the trunk radius from the center of the bottom, since the uniaxial orientation in the circumferential direction is suppressed, it is relatively thick, and the thickness is generally 1.1 to 3.2 mm. .
[0039]
The pressure-resistant bottle of the present invention is produced by producing a bottomed preform of a substantially amorphous polyester, heating the bottomed preform to a stretching temperature, and then stretch-blow-molding in a specific mold. Is done.
Of course, the mold used (cavity mold) has an inner surface corresponding to the valley and the foot.
Further, in the valley portion within the radius equivalent to 40% of the trunk radius from the center of the bottom, the uniaxial orientation in the circumferential direction is suppressed, that is, the uniaxial orientation crystallinity is less than 10.5%, particularly 6% or less. It is necessary to perform stretch blow molding so that
[0040]
Injection molding can be used for molding the polyester into a preform. That is, polyester is melt-injected into a cooled injection mold to form a supercooled amorphous polyester preform.
[0041]
As the injection machine, a known one having an injection plunger or 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 solidifies into a preform for stretch blow molding.
[0042]
As the injection mold, a mold having a cavity corresponding to the container shape is used, but a one-gate or multi-gate injection mold is preferably used.
The injection temperature is preferably 270 to 310 ° C., and the pressure is preferably about 28 to 110 kg / cm ² .
[0043]
The preform stretching temperature is generally 85 to 135 ° C., particularly 90 to 130 ° C., and the heating can be performed by means known per se such as infrared heating, hot air heating furnace, dielectric heating and the like. .
[0044]
In addition, for stretch blow molding from a preform, a method of performing stretch blow molding subsequent to preform molding using heat applied to the preform molded product to be molded, that is, residual heat, can be generally used. Is preferably a method in which a preform molded product once in a supercooled state is produced, and this preform is heated to the aforementioned stretching temperature and stretch blow molding is performed.
[0045]
The preform preheated to the stretching temperature is supplied into a publicly known stretch blow molding machine, set in the above-described mold, stretched in the axial direction by pushing the stretching rod, and fluid blown. Is blow stretched in the circumferential direction.
[0046]
The draw ratio in the final bottle is suitably 5 to 18 times in terms of area magnification. Among these, the axial draw ratio is 2 to 4 times, and the circumferential draw ratio is 2.5 to 4.5 times. Is good.
[0047]
[Packaging]
In the present invention, the self-standing pressure resistance in which the uniaxial crystallinity and the amount of enthalpy relaxation in at least a valley portion within a radius equivalent to 40% of the trunk radius from the center of the bottom have a relationship satisfying the expressions (1) and (2). A polyester bottle is filled with contents having self-generated pressure and sealed to form a package.
The uniaxially oriented crystallinity of the valley is unique to the bottle, but the amount of enthalpy relaxation greatly depends on the aging and storage conditions of the bottle after molding, and generally the longer the storage time, There is a tendency that the higher the temperature during storage and the higher the humidity during storage, the higher the value.
In the present invention, the uniaxial crystallinity and the amount of enthalpy relaxation are reduced by adopting means such as shortening the storage time of the empty bottle after molding, and making the storage atmosphere a dry atmosphere with the lowest possible temperature. Is maintained in a relationship satisfying the above formulas (1) and (2), and the contents are filled with this to prevent brittle fracture at the bottom of the bottle.
[0048]
Examples of the content having a self-generated pressure include carbonated beverages such as beer and sparkling liquor, carbonated beverages such as cola, cider, and carbonated synthetic beverages.
After the contents are cold-filled at about 5 ° C., the cap is stoppered and sealed, and if necessary, the product is subjected to hot water spraying treatment to prevent bottle condensation. In general, this treatment is preferably performed at a temperature of 30 to 45 ° C. for about 10 to 20 minutes.
[0049]
【Example】
The present invention will be specifically described by the following examples, but the present invention is not limited to these examples.
[0050]
Samples were prepared in the following manner and used for experiments.
-Extruded sheet A polyethylene terephthalate sheet having a thickness of 200 to 350 μm was prepared with a small extruder (Laboplast Mill; manufactured by Toyo Seiki Co., Ltd.). The extrusion temperature setting was 270 ° C.
-An injection sheet having a stretched sheet thickness of 2 mm was prepared, and this was stretched with a biaxial stretching machine to prepare a sample. The stretching temperature is 100 ° C., and the stretching ratio is 2 × 1.4, 3 × 1.3, 3.7 × 1.2.
[0051]
The measurement was performed as follows.
1) Using an enthalpy relaxation amount differential thermal analyzer from 20 ° C to 10 ° C / min. The endothermic peak area from the glass transition point (Tg) to (Tg + 25) ° C. when the temperature was raised at a rate of was calculated as the enthalpy relaxation amount.
2) Oriented crystallinity The ratio of crystal peaks in the range of 2θ = 0 to 100 ° was determined by a transmission X-ray diffractometer to obtain the oriented crystallinity.
3) The tensile test sheet is cut into a dumbbell shape, and the tensile speed is 30 mm / min. The test was conducted. The ratio of brittle fracture was determined from the measurement of n = 7-10.
4) Filling test A biaxially stretched self-supporting pressure resistant polyester bottle was prepared by biaxial stretching blow, and carbonated water was filled to 4.5 GV using sodium bicarbonate and citric acid. Thereafter, the bottom was impregnated with an aqueous solution of 4.5 vol% slider (Ecolabo Saniclens PET), stored at a temperature of 25 ° C. or 37 ° C. for one month, and the bottom was observed. The bottom crack generation bottle was ranked as C, the case where crazes with a length of 2 cm or more were generated was classified as B, and the others were ranked as A.
[0052]
[Experimental Example 1]
Extruded films were prepared, and the enthalpy relaxation, orientation crystallinity, and brittle fracture ratio were measured. The results are shown in Table 1.
[Table 1]

[0053]
[Experiment 2]
A stretched sheet was prepared, and the amount of enthalpy relaxation, orientation crystallinity, and the ratio of brittle fracture were measured. The results are shown in Table 2.
[Table 2]

[0054]
[Experiment 3]
A biaxially stretched self-supporting pressure-resistant polyester bottle was prepared by biaxial stretch blow, and the enthalpy relaxation amount, orientation crystallinity, and filling test of the bottom valley portion having a radius corresponding to 35% of the trunk radius from the bottom center were performed. The results are shown in Table 3.
[Table 3]

[0055]
[Experiment 4]
Extruded films were prepared and given various enthalpy relaxations depending on the temperature and humidity history. The ratio of the sample which showed the brittle fracture by the tensile test (n = 7-10) of these films was calculated | required. The results are shown in Table 4.
[Table 4]

[0056]
[Experimental Example 5]
Stretched sheets were prepared and given various enthalpy relaxation amounts depending on the temperature and humidity history. The ratio of the sample which showed the brittle fracture by the tensile test (n = 7-10) of these films, and the orientation crystallinity were calculated | required. The results are shown in Table 5.
[Table 5]

[0057]
[Experimental Example 6]
After making biaxially stretched self-supporting pressure resistant polyester bottles by biaxial stretch blow, various enthalpy relaxation amounts are given depending on the temperature and humidity history, and enthalpy relaxation at the bottom valley with a radius equivalent to 35% of the trunk radius from the bottom center. The amount and orientation crystallinity were measured and a filling test was performed. The results are shown in Table 6.
[Table 6]

[0058]
【The invention's effect】
According to the present invention, in the pressure-resistant polyester bottle having the foot and the valley alternately on the bottom, the uniaxial crystallinity and the amount of enthalpy relaxation in at least the valley within the radius equivalent to 40% of the trunk radius from the center of the bottom. Can be effectively prevented from brittle fracture when the contents having a self-generated pressure are filled, the pressure resistance can be improved, and the storability of the contents can be improved.
[Brief description of the drawings]
FIG. 1 is a side view of a pressure-resistant polyester bottle of the present invention.
FIG. 2 is a graph showing the relationship between uniaxially oriented crystallinity, enthalpy relaxation, and brittle fracture.
FIG. 3 is a graph showing how to determine the amount of enthalpy relaxation by a differential scanning calorimeter.
FIG. 4 is a graph showing an X-ray diffraction image of polyester having uniaxial orientation.
FIG. 5 is a graph showing an X-ray diffraction image of non-oriented polyester.

Claims (2)

In a biaxially-stretched self-supporting pressure-resistant bottle made of polyester having a foot and a trough alternately at the bottom, uniaxial crystallinity and enthalpy relaxation at least in the trough within a radius equivalent to 40% of the trunk radius from the center of the bottom The pressure-resistant polyester bottle characterized in that the amount satisfies the following formulas (1) and (2):
Y ≦ (2.5 × 10 ⁻⁴ ) × (X-10.5) ⁴ (1)
0 ≦ X <10.5 (2)
In the formula, Y is an enthalpy relaxation amount obtained as an endothermic peak (J / g) measured in the range of Tg to Tg + 25 ° C. measured by a differential scanning calorimeter, and X is 2θ = 0 ° by X-ray diffraction method. The orientation crystallinity (%) measured in the range of up to 100 ° is expressed. The pressure-resistant polyester bottle according to claim 1 is filled with a content having a self-generated pressure and sealed.

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