JP2002079570A - Method for manufacturing biaxially stretched polyester container of which bottom part is prevented from whitening - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the whitening of a bottom part and the generation of white stripes in the bottom part, in a method for manufacturing a biaxiallty stretched polyester container using an injection machine equipped with a nozzle tip with a valve stem. SOLUTION: The method for manufacturing the biaxiallty stretched polyester container of which the bottom part is prevented from whitening consists of a process for injection-molding polyester to form a bottomed preform having a substantially amorphous side wall part and a process for subjecting the bottomed preform to biaxial stretch blow molding in the stretching temperature region of polyester. A bottomed preform injection mold, equipped with a straight cylindrical part and a gate part comprising a taper part increased in its diameter toward the cavity connected to the cylindrical part, is used in this manufacturing method and the injection machine, which is fitted with the nozzle tip having a valve stem capable of being fitted in the cylindrical part in a reciprocally movable manner, is used. A ratio (D/L) of the diameter (D) of the cylindrical part and the land length (L) of the gate part is set to 0.3-0.8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a biaxially oriented polyester container in which bottom whitening is prevented.
More specifically, the present invention relates to a method for producing a biaxially stretched polyester container which prevents whitening and white streaks at the bottom, has excellent appearance characteristics, and has excellent commercial value.

[0002]

2. Description of the Related Art Stretch blow-molded containers, especially polyester containers, have become popular today, and due to their excellent transparency and moderate gas barrier properties, liquid detergents, shampoos,
In addition to liquid products such as cosmetics, soy sauce, and sauces, it is widely used in carbonated beverages such as beer, cola, and cider, and in other beverage containers such as fruit juice and mineral water.

[0003] In molding a polyester container, a bottomed preform, which is considerably smaller in size than the final container and in which the polyester is amorphous, is stretched axially in a blow mold at the stretching temperature by injection molding of the polyester. And a method of blow-stretching in the circumferential direction is adopted.

[0004] The shape of the preform with a bottom is a bottle having a mouth and neck portion, for example, a mouth and neck portion comprising an opening end for sealing, a screw for engaging a lid, a support ring, and the like, and having an overall shape of a test tube. General.

[0005] Polyethylene terephthalate has a temperature range from its glass transition point to just below its melting point, generally from 120 to 15 ° C.
It tends to crystallize at a temperature of 0 ° C. and whiten due to the formation of spherulites. Injection molding of polyester into a preform is performed by cooling the mold and shortening the passage time of the above crystallization temperature to suppress crystallization of polyester, but inject molten resin from the bottom center. Therefore, the bottom is the longest in the above-mentioned temperature range, and it is inevitable that the center (gate portion) of the bottom of the preform is slightly whitened.

[0006] As described above, a slight turbidity is unavoidable at the bottom of a container obtained by stretch-blow-molding a preform having a slight turbidity at the bottom, and it cannot always be sufficiently satisfied from the appearance characteristics of the container. At the same time, there is a problem in that the purchaser of the bottled product has a fear that the deposit of the contents may be generated and the contents may be degraded, thereby lowering the commercial value.

[0007] To prevent the whitening tendency of the bottom of the preform
It is already known, and in Japanese Patent Publication No. 5-21055
Is a polymer mainly composed of ethylene terephthalate units.
Tell injected into bottomed preform with substantially amorphous sidewalls
Molding step, and the bottomed preform is made of polyester.
From the process of biaxial stretch blow molding in the stretching temperature range
In the production of biaxially stretched polyester containers
As a reforming injection mold, the diameter toward the bottom cavity
And the land length (l) is 5 mm
30mm and the inclination angle (θ) of the tapered part is 2 to 8
And a diameter of the gate exit (D
₀) And bottom inner diameter (D₁) And the ratio (D ₀/ D₁)But
It is in the range of 0.10 to 0.50,
Radius of curvature (R₁) Is 4-8mm and gate
The radius of curvature of the cavity mold at the outlet (R₂)But
Within the range of 0.3 to 2.0 mm and maximum height roughness
(Rmax, JISB-0601) is 0.8 μm or less
Using an injection mold with a surface finish
Injection molding of polyester into preform with bottom
Biaxially stretched polyester with bottom whitening prevented
It describes the method of making the container.

[0008]

The above-mentioned proposal is to prevent the bottom of the preform from being whitened by setting the shape and dimensions of the gate portion of the preform injection mold within a specific range. It is observed that injection molding of a preform using a nozzle tip with a stem still causes whitening at the center (gate) of the bottom of the preform.

The valve stem opens and closes the mold gate and cuts the preform gate. The valve stem closed by the mold gate is retracted by the air cylinder and opened, and at the same time the injection piston advances. Then, the polyester resin is injected into the mold, and is closed again at the end of the injection to cut the preform gate.

According to the research of the present inventor, the cause of whitening of the preform gate in the injection molding using the nozzle tip with the valve stem is that the valve stem which comes into contact with the mold gate in the closed state is in the open state. Thus, it was found that the cooling or slow cooling of the resin progressed by contact with the molten polyester resin in the nozzle tip, and the resin passed through the crystallization temperature range of the resin, so that the crystallization progressed. It was also found that the crystallized portion adhered to the cavity surface and the core surface around the gate was the whitened portion at the bottom, and the one that flowed with the resin was white streaks.

Accordingly, an object of the present invention is to provide a step of injection-molding a polyester into a bottomed preform having a substantially amorphous side wall portion, and a biaxial stretch blow molding of the bottomed preform in a polyester stretching temperature range. The present invention is to provide a method for producing a biaxially stretched polyester container using an injection machine equipped with a nozzle tip with a valve stem as an injection machine, in which whitening at the bottom and generation of white stripes are prevented.

[0012]

According to the present invention, there is provided a step of injection-molding a polyester into a bottomed preform having a substantially amorphous side wall portion, and forming the bottomed preform in a polyester stretching temperature range. And a process of forming a biaxially stretched polyester container comprising a step of axially stretch blow molding, wherein a preform injection mold with a bottom has a straight cylindrical portion and a tapered portion whose diameter increases toward a cavity connected to the cylindrical portion. A nozzle having a nozzle tip provided with a valve stem that can be fitted to the cylindrical portion so as to be reciprocally movable is used as an injection machine, and the diameter (D) of the cylindrical portion of the preform gate and A method for producing a biaxially stretched polyester container in which whitening at the bottom is prevented, wherein the ratio (D / L) to the land length (L) of the gate portion is 0.3 to 0.8. Further, in the present invention, it is preferable that the inclination angle of the tapered portion is in a range of 1 to 5 degrees.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Operation] In the present invention, similarly to the conventional method, a step of injection-molding a polyester into a bottomed preform having substantially amorphous side walls, The biaxially stretched polyester container is manufactured by the process of biaxially stretch blow-molding in the stretching temperature range described above, but the whitening of the bottom of the final container is prevented in the injection molding step of the bottomed preform.

As an injection machine for forming a preform, an injection machine having a nozzle tip with a valve stem is used. In connection with this, a straight cylindrical portion as a bottomed preform injection mold and the cylindrical portion are used. A nozzle having a gate portion comprising a tapered portion whose diameter increases toward a cavity connected to the nozzle, and a nozzle having an injecting machine reciprocally provided with a valve stem capable of being fitted to the cylindrical portion. Use the one with a tip.

The fitting of the cylindrical portion of the mold gate to the valve stem is indispensable for cutting the preform gate. At the same time, this fitting cools the valve stem, and the resin by the valve stem. Cooling or slow cooling,
This causes the resin to crystallize.

According to the present invention, the shape of the gate portion of the preform is made thin and long, that is, the diameter (D) of the cylindrical portion and the land length (L) of the gate portion when the preform gate is cut.
The ratio (D / L) to 0.3 to 0.8 prevents cooling of the valve stem, which causes whitening and white streaks, eliminates slowly cooled crystals, and whitens at the gate. By absorbing, whitening and white streaks at the bottom of the preform can be effectively prevented. Further, by setting the inclination angle of the tapered portion in a range of 1 to 5 degrees,
The occurrence of whitening and white streaks can be prevented more effectively.

That is, when the ratio (D / L) of the diameter (D) of the cylindrical portion to the land length (L) of the gate portion is out of the above range, the cooling or slow cooling of the resin is caused by the influence of the mold and the valve stem. Occurs, the whitening cannot be absorbed in the gate portion, and the tendency of whitening and white streaks to occur at the bottom of the preform increases.

According to the present invention, as described above, the occurrence of whitening or white streaks at the bottom of the preform is achieved by a simple means of setting the ratio between the diameter of the cylindrical portion and the land length of the gate portion within a certain range. Can be effectively prevented, the appearance characteristics of the biaxially stretch blow-molded container can be improved, and the commercial value can be increased.

[Injection Molding Apparatus] In FIG. 1 showing a schematic structure of an injection molding apparatus used in the present invention, this injection mold is
A cavity mold 10 and a gate mold 20 are provided.
The cavity mold 10 has a cavity surface 11 that defines the outer surface of the preform body. The gate mold 20 has a bottom forming surface 21 that defines the outer surface of the preform bottom, and has a gate 22 at the center thereof. Although not shown, the cavity mold 10 and the gate mold 2
0, a core mold is coaxially inserted therein, and the core mold (not shown), the cavity mold 1
A polyester resin is injected into a cavity defined by the gate mold 20 and the gate mold 20 to form a preform.

On the other hand, the nozzle tip 30 attached to the tip of an injection machine (not shown) has a hollow cylindrical shape with the tip 31 narrowed, and a solid cylindrical valve stem 32 reciprocates at its axis. It is movably provided. Nozzle tip 3
A resin passage 33 for flowing the resin is formed between the inner surface of the valve stem 32 and the outer surface of the valve stem 32. However, when the valve stem 32 is advanced, the outer surface of the nozzle tip 31 and the outer surface of the valve stem 32 are formed. Are contacted in a liquid-tight state, and the resin passage 33 is closed. When the valve stem 32 is retracted, the resin passage is opened.

A band heater 34 is provided around the nozzle tip 30 to keep the resin in the resin passage 33 warm.
In addition, a heat insulating material layer 35 for preventing the cooling of the nozzle tip 31 is provided on the outer surface of the tapered tip 31.

On the opposite side of the bottom forming surface 21 of the gate mold 20, a recess 23 for receiving the nozzle tip 30 is formed, and the valve stem 32 and the gate portion 22 are fitted to each other, and the tip of the nozzle tip is formed. The portion 31 and the concave portion 23 can come into contact with each other via a heat insulating material layer 35.

In FIG. 2 for explaining the shapes and dimensions of the gate mold 20 and the valve stem 32, the gate 2
2 has a straight cylindrical portion 23 and a tapered portion 24 whose diameter increases toward a cavity connected to the cylindrical portion. The exit side of the tapered portion 24 is the curvature portion 2.
5 (radius of curvature: R) and is in contact with the bottom molding surface 21.

As shown in FIG. 2, the cylindrical portion 23 of the gate portion
Has a axial dimension L ₁ diameter D, whereas the tapered portion 24 and an inclined angle θ and an axial dimension L _2.
The axial dimension of the tapered portion 24 means the distance from the root of the cylindrical portion 23 to the virtual curved surface including the bottom forming surface 21 of the gate mold. On the other hand, the diameter of the cylindrical portion is given by D, and the land length of the gate portion is given by L. In the present invention, D / L
Is set in the range of 0.3 to 0.8 described above.

During injection molding of a preform, molten polyester is stored in an injection machine (not shown). At the start of injection, the valve stem 32 is retracted from the advanced position shown in FIG. 1 (moves rightward in FIG. 1) by driving an air cylinder (not shown) or the like, and the nozzle tip 31 opens. At the same time, the injection piston (not shown) in the injection machine moves forward (moves rightward in FIG. 1), and the molten resin in the injection machine passes through the resin passage 33 of the nozzle chip and the gate portion 22, and the injection mold 10, Inject into the cavity in 20. At the end of injection molding, the valve stem 32 moves forward, cutting the preform gate and closing the tip 31 of the nozzle tip 30. The cavity mold 10 and the gate mold 20 are forcibly water-cooled together with the core mold, and the injection molten resin is supercooled to an amorphous state, and the preform is formed.

In FIG. 3 showing an example of a preform formed by the method of the present invention, a preform 40 is integrally formed of an amorphous thermoplastic polyester,
A body 41, a closed bottom 42, and a mouth 43 are provided, and a support ring 44 and a screw 45 for fastening the lid are provided on the outer periphery of the mouth.
Is provided.

In order to prevent whitening of the bottom of the preform, it is important that the polyester constituting the bottom pass through the thermal crystallization temperature region in as short a time as possible. Making the shape thinner and longer makes it easier and faster for the resin to flow into the cavity from the gate part of the gate mold, so that the molten resin is not affected by cooling at the gate part. It is effective in preventing bottom whitening.

For this purpose, the fitting amount of the valve stem is advantageously in the range from 0.2 to 0.9 mm. The radius of curvature R at the gate exit is preferably in the range of 0.5 to 2 mm. Further, the length L ₁ of the gate portion cylindrical portion 23 is a fitting of the valve stem in the shortest, and set to be longer than the fitting amount, that keep the adjustable fitting of the valve stem preferable. This is because the cutability of the preform gate varies depending on the type of resin and the injection conditions, but with the above-described setting of the length of the gate cylindrical portion, the gate is reliably cut. .

[Polyester Resin] In the present invention, a stretchable blow moldable thermoplastic polyester, particularly an ethylene terephthalate thermoplastic polyester, is advantageously used as the polyester resin. Of course, polybutylene terephthalate, polyethylene naphthalate, etc. Blends with other polyesters, polycarbonates, and polyarylate resins.
Further, the material configuration of the container may be a single layer or a multilayer configuration of two or more layers as long as the main material is polyester. 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, and has a glass transition point (Tg) of 50 to 90. C., especially 55 to 80 ° C., melting point (Tm) 200 to 275 ° C., especially 220 to 27
Thermoplastic polyesters at 0 ° C. are preferred.

Homopolyethylene terephthalate is preferred in terms of pressure resistance, heat resistance and heat and pressure resistance, but a copolymerized polyester 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 acid 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 ethylene terephthalate-based thermoplastic polyester with about 5% to 25% of a relatively high glass transition point, for example, polyethylene naphthalate, polycarbonate or polyarylate, can be used. The material strength at a relatively high temperature 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 to be 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 use. 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.

Further, in the container according to the present invention, the above-mentioned ethylene terephthalate-based polyester is used as an inner and outer layer, and this is used as an intermediate layer, and a recycled polyester layer, a gas barrier resin layer, an oxygen-absorbing resin layer and the like are interposed. it can. As the recycled polyester layer, a product obtained by washing and regenerating a crushed polyester product collected as a used PET bottle as necessary is used.
As the gas barrier resin, an ethylene-vinyl alcohol copolymer, in particular, an ethylene content of 20 to 60 mol%
And a polyamide resin, especially nylon 6, nylon 6,6, polyxylene adipamide (MXD6), and the like. As the oxygen absorbent layer, any known oxygen-absorbing resin composition may be used, and typical examples thereof include polyamide resins, particularly those obtained by blending a transition metal catalyst, particularly cobalt carboxylate with MXD6. Is used.

[Production of preform] The production of the preform is carried out under the conditions known per se, except that the above-described injection machine equipped with the nozzle tip and the gate mold are used, and that the conditions that can prevent the whitening at the bottom are used. Can be done with

As the injection mold, it is preferable to use a mold having a large thermal conductivity and a small surface roughness in order to prevent whitening at the bottom. For this reason, it is preferable to use a copper-beryllium alloy as the mold, and the surface of the mold is finished to a maximum height roughness (Rmax, JIS B-0601) of 3.2 μm or less, particularly 0.8 μm or less. Preferably, one is used.

The injection temperature and injection pressure also have certain conditions for preventing bottom whitening. That is, when the temperature of the resin to be injected is high, a long time is required for cooling the resin, and the time for passing through the crystallization temperature region also becomes long. On the other hand, when the resin temperature is lowered, the share increases at the time of molding, and a trouble in molding occurs. For this reason, the injection molding temperature is preferably in the range of 280 to 320 ° C, particularly 290 to 310 ° C. On the other hand, the injection pressure is 60 to 130 kg
/ Cm ² is preferable.

Further, when the temperature of the injection mold is lowered, the time required to pass through the crystallization temperature range can be shortened. Therefore, it is desirable to lower the temperature of the gate mold (bottom mold) as much as possible.
On the other hand, if the temperature is too low, the problem of an increase in the shear occurs as described above. Therefore, it is preferable to maintain the temperature of the gate mold (bottom mold) at 10 to 20 ° C.

[Preparation of Biaxially Stretched Blow Molding Container] The preform obtained by the above method is heated to a stretching temperature, the heated preform is stretched in the axial direction and stretched in the circumferential direction by blowing a pressure fluid. Blow stretching is performed to obtain a biaxially stretched blow molded container. This stretch blow molding may be performed in one stage, or may be performed in two stages called two-stage blow. Further, the container subjected to the biaxial stretch blow molding may be heat-fixed by a known means. Furthermore, in the two-stage blow molding method, a heat treatment step may be provided between the primary blow and the secondary blow.

Prior to stretch blow molding, the preform is preheated to a suitable stretching temperature by means such as hot air, an infrared heater, or high frequency induction heating. Its temperature range is 85
The temperature is preferably in the range of from 120 to 120 ° C, particularly from 95 to 110 ° C.

The stretching ratio in the final container is suitably 4 to 10 times in area ratio, and among these, the axial stretching ratio is 1 to 3 times and the circumferential stretching ratio is 3 to 5 times. Good. The axial stretching ratio is determined by the axial length of the preform molded article and the stroke length of the stretching rod, while the circumferential stretching ratio is determined by the diameter of the preform and the diameter of the mold cavity. . As the pressure fluid, room temperature or heated air or other gas such as nitrogen, carbon dioxide or water vapor can be used, and its pressure is usually 10 to 40 kg / cm ² gauge, particularly 15 to 30 kg / g. It should be in the range of cm ² gauge.

The mouth of the preform used in the present invention serves as the mouth of the final container, and this mouth may be subjected to thermal crystallization in order to improve heat resistance and sealing accuracy. it can. The thermal crystallization of the mouth of the preform, which is performed as necessary, can be performed by selectively heating these portions by a means known per se. Since thermal crystallization of polyesters and the like occurs remarkably at an inherent crystallization temperature, generally, the corresponding portion of the preform may be heated to the crystallization temperature. Heating can be performed by infrared heating, dielectric heating, or the like. Generally, it is preferable to selectively heat the body to be stretched by shielding the body from a heat source with a heat insulating material. The above-mentioned thermal crystallization may be performed simultaneously with or separately from the preheating of the preform to the stretching temperature.
Mouth thermal crystallization is generally carried out at 140-220 ° C., especially 16 ° C., with the preform mouth thermally insulated from other parts.
It can be performed by heating to a temperature of 0 to 210 ° C. The crystallinity at the mouth of the preform is preferably at least 25%.

The bottom of the container according to the invention preferably has a free-standing structure. An example of a self-supporting bottom portion is a bottom portion formed from a surrounding ground portion and a top portion in which an inner portion rises upward from the ground portion, and the top bottom has ribs for reinforcing the bottom. May be provided radially.

A self-standing container of this type is disclosed in Japanese Patent No. 301
As described in Japanese Patent No. 1058, in a preform for stretch blow molding comprising a trunk, a mouth-and-neck portion provided at one end of the trunk, and a closed bottom provided at the other end of the trunk, Is a cylindrical or tapered shape and the bottom is substantially hemispherical, and is smoothly connected on the inner surface side and is tapered on the outer surface side so that the outer diameter decreases toward the bottom. connected to the bottom through the cross-sectional shape of the tapered portion is straight, the ratio between the thickness of the bottom thickness of the body portion _{(d 1) (d 2)} (d 1 / d 2) is to 1.1 Using a preform for stretch blow molding in the range of 1.5, at the time of blow molding, the preform is stretched in the axial direction so that the hemisphere portion is at the bottom center and the outer diameter reducing taper portion is at the bottom periphery. And stretch in the circumferential direction, Ide and bottomed out the bottom center, as well as with the outer size reduction bottom portion of the ground portion and the outer peripheral than the small tapered portion is manufactured by molding inside the upper base above ground portion of the hemispherical portion.

At least the body of the molded container is brought into contact with the surface of a mold maintained at a temperature of 110 to 170 ° C., or a heated fluid having a temperature of 200 to 300 ° C. is blown into the container to form a biaxial shaft. The oriented polyester can be heat-set to improve heat resistance.

Another example of the self-supporting bottom structure is a structure in which a plurality of feet and valleys are alternately formed around the bottom. This type of stretch blow molded container is generally a first-stage blow molding of a preform, and a heat treatment including a bottom, a body and a shoulder of the first-stage blow molded product,
It is formed by second-stage blow molding of a heat-treated product. The first-stage blow molding is performed under the conditions described above.

In the heat treatment step of the first-stage blow-molded product, the bottom, body, and shoulder of the first-stage blow-molded product are heated by infrared while the core is rotated. Face your body. As a result, the first-stage blow-molded product has its bottom, body, and shoulder heated by the infrared rays of the infrared heater, shrinks in the height direction and the radial direction, and has the final container shape. The shape fits in the mold. The heat treatment conditions vary depending on the type of polyester and the conditions of the first-stage blow molding, but generally, 9
0 to 120 ° C., especially 95 to 115 ° C. and 20
The processing time is set to be in the range of from 120 seconds to 120 seconds, particularly from 30 seconds to 90 seconds, so that the degree of generation of pseudocrystals in the final container is in the range described above.

In the second-stage blow molding step, the heat-treated molded product is inserted into the second-stage blow mold with its neck supported by the core mold. On the opposite side of the core mold, a bottom mold that defines the bottom shape of the final container is also inserted.
The split mold is closed, a fluid is blown into the heat-treated product, and the heat-treated product is subjected to second-stage blow molding to form a final container having a predetermined shape. In this second-stage blow molding, the heat-treated product to be blown has an increased elastic modulus due to crystallization by heat treatment.
Blow molding is preferably performed using a high fluid pressure, and it is generally preferable to use a pressure of 15 to 45 kg / cm ² . At the time of the second stage blow molding, the temperature of the mold may be maintained at a temperature of 5 to 135 ° C., and cooling may be performed immediately after molding, or cold air may be flowed through the final molded product. Cooling may be performed.

A container bottom of the above type has feet and valleys alternately arranged in the circumferential direction, but the number of feet is preferably 6 to 4, more preferably 6 to 5 independence. It is preferable in terms of stability. Also, the valley, including the bottom center,
Although it is located on a downwardly convex virtual curved surface, for example, a substantially spherical surface or a spheroidal surface, it is desirable that the radius of curvature of this curved surface be in the range of 0.5 to 1 times the radius of the body.

[0050]

The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.

[Example 1] The diameter D of the cylindrical portion at the time of cutting the preform gate of the mold gate portion was 3.00 mm, the land length L of the gate portion was 8.0 mm (D / L = 0.375), and the taper was tapered. A polyethylene terephthalate is injection-molded with a mold having an angle θ of 4.0 ° to form a preform, which is blow-molded in a conventional manner to obtain a capacity of 500 parts.
ml of a biaxially stretched blow bottle was prepared. When the bottom of the prepared container was visually observed, no whitening was observed.

[Example 2] The diameter D of the cylindrical portion at the time of cutting the preform gate of the mold gate portion was 4.03 mm, and the land length L of the gate portion was 5.09 mm (D / L = 0.791).
7) Polyethylene terephthalate is injection-molded into a preform using a mold having an angle θ of the tapered portion of 3.0 °, and the preform is blow-molded by a conventional method to obtain a biaxially stretched blow bottle having a capacity of 500 ml. Was prepared. When the bottom of the prepared container was visually observed, no whitening was observed.

[Example 3] The diameter D of the cylindrical portion at the time of cutting the preform gate of the mold gate portion was 4.03 mm, the land length L of the gate portion was 7.0 mm (D / L = 0.5757),
A preform is manufactured by injection molding polyethylene terephthalate using a mold having an angle θ of the tapered portion of 2.0 °, and is blow molded by a conventional method to obtain a capacity of 50%.
A 0 ml biaxially stretched blow bottle was prepared. When the bottom of the prepared container was visually observed, no whitening was observed.

[Comparative Example 1] The diameter D of the cylindrical portion at the time of cutting the preform gate of the mold gate portion was 4.20 mm, and the land length L of the gate portion was 4.49 mm (D / L = 0.935). Using a mold, polyethylene terephthalate was injection-molded to produce a preform, which was blow-molded by a conventional method to produce a 500-ml biaxially stretched blow bottle. When the bottom of the produced container was visually observed, whitening was observed.

[Comparative Example 2] The diameter D of the cylindrical portion at the time of cutting the preform gate of the mold gate portion was 3.00 mm, and the land length L of the gate portion was 11.0 mm (D / L = 0.273). Using a mold, polyethylene terephthalate was injection-molded to produce a preform, which was blow-molded by a conventional method to produce a 500-ml biaxially stretched blow bottle. When the bottom of the produced container was visually observed, whitening was observed.

[0056]

According to the present invention, a step of injection-molding a polyester into a bottomed preform having substantially amorphous side walls, and biaxially stretch-blowing the bottomed preform in a polyester stretching temperature range. In the method for producing a biaxially stretched polyester container comprising a step of performing, a gate having a straight cylindrical portion as a bottomed preform injection mold and a tapered portion having a diameter increasing toward a cavity connected to the cylindrical portion is provided. An injection machine with a nozzle tip equipped with a reciprocatingly movable valve stem that can be fitted into the cylindrical portion is used. The diameter (D) of the cylindrical portion when cutting the preform gate and the gate portion Land length (L) ratio (D /
By setting L) to 0.3 to 0.8, it is possible to effectively prevent whitening and white streaks at the bottom of the container, improve the appearance characteristics of the container, and increase the commercial value.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of an injection molding apparatus used in the present invention.

FIG. 2 is an enlarged sectional view showing the shape and dimensions of a gate type used in the present invention.

FIG. 3 is a cross-sectional view of an example of a preform.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4F202 AA24 AH55 CA11 CB01 CK06 4F208 AA24 AH55 LA04 LA08 LB01 LG29 LG34

Claims (2)

[Claims] 1. A method comprising the steps of: injection-molding a polyester into a bottomed preform having substantially amorphous side walls; and biaxially stretch-blowing the bottomed preform in a polyester stretching temperature range. In the manufacturing method of the axially stretched polyester container, using a preform injection mold with a bottom having a gate portion composed of a straight cylindrical portion and a tapered portion whose diameter increases toward the cavity connected to the cylindrical portion, An injection machine with a nozzle tip provided with a reciprocating valve stem capable of fitting into the cylindrical portion is used. The diameter (D) of the cylindrical portion and the land length (L) of the cylindrical portion when the preform gate is cut. Wherein the ratio (D / L) is from 0.3 to 0.8. 2. The method for producing a biaxially stretched polyester container according to claim 1, wherein the inclination angle of the tapered portion is in a range of 1 to 5 degrees.