JP4186431B2 - Stretch blow molded container - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a stretch blow molded container which is formed by biaxial stretch blow molding of a thermoplastic polyester and has excellent heat resistance and heat pressure resistance to withstand heat sterilization such as hot filling.
[0002]
[Prior art]
A biaxial stretch blow molded container of thermoplastic polyester such as polyethylene terephthalate (PET) has excellent transparency and surface gloss, as well as impact resistance, rigidity and gas barrier properties required for bottles. It is used as a bottled container for various liquids, that is, a bottle.
[0003]
In general, in the manufacture of bottled products, in order to enhance the shelf life of the contents, the contents such as fruit juice and tea are hot-filled or filled with contents such as carbonated beverages containing fruit juice, and then heat-sterilized or sterilized. It is necessary to. However, polyester bottles have the disadvantage of poor heat resistance, causing hot deformation of the contents or heat deformation during heat sterilization or sterilization, and shrinkage deformation of the volume. (Heat setting) is being performed.
[0004]
Japanese Examined Patent Publication No. 6-22862 discloses a heat-resistant pressure-resistant container having a hemispherical bottom and is provided with a base cup to obtain self-supporting properties. In this container manufacturing method, a preform whose bottom and mouth and neck are spheroidized by heating is used, and the preform is biaxially stretch blow-molded to remove the spherulized part and increase the entire container. Stretching can be performed at a stretch ratio. In particular, by carrying out stretch blow molding while constraining the spherulite portion at the bottom of the preform with a stretching rod, it is possible to reduce the thickness in a sufficiently stretched state to the periphery of the bottom central spherulite portion. A container with a hemispherical bottom that has been thinned in a highly stretched state is excellent in heat and pressure resistance, filled with contents that require sterilization, such as carbonated beverages containing fruit juice, and internal pressure is applied. It can sufficiently withstand the heat sterilization treatment (10 minutes or more at 65 ° C. for legal reasons).
[0005]
Japanese Patent Application Laid-Open No. 5-42586 describes a method of manufacturing a synthetic resin bottle having a self-supporting bottom by a two-stage blow molding method including primary and secondary biaxial stretch blow molding. In the embodiment, it is described that the thickness of the bottom can be 1.6 mm at the center of the bottom and 1.16 to 0.36 mm from the center of the bottom to the body.
[0006]
In Japanese Patent No. 29178851 proposed by the present applicant, a preform molded body heated to a stretching temperature is blow-molded, and the bottom portion is composed of a plurality of feet and valleys, and the valley is substantially hemispherical. In a method for producing a heat-resistant and pressure-resistant self-supporting plastic container forming a part, the preform molded body is biaxially stretch blow-molded, and the portion to be the bottom of the final container has a surface area larger than the surface area of the hemispherical surface And forming a secondary molded body having a generally dome-shaped bottom portion that is thinned to a thickness of 1 mm or less in a relatively high stretch excluding the center of the bottom, and at the bottom and bottom of the secondary molded body A portion of the continuous body portion is opposed to the infrared radiator, the opposite portion is heated and shrunk, and the portion to be the bottom of the final container is sized to fit within the hemispherical surface, and the hemispherical surface thereof Relatively close to A biaxial excellent in heat and pressure resistance, comprising: a step of forming a tertiary molded body, and a step of performing secondary blow molding of the tertiary molded body in a heated state into a final product in a mold A method for producing stretched plastic bottles is described.
[0007]
[Problems to be solved by the invention]
Containers with a hemispherical bottom that has been thinned by stretching, especially where the center of the bottom is crystallized, have excellent heat and pressure resistance, and are filled with contents to which internal pressure such as carbonated beverages containing fruit juice is applied. Although it can sufficiently withstand the heat sterilization process (more than 10 minutes at 65 ° C in the method) in which hot water is poured, the base cup must be manufactured separately from the container and fixed to the container by bonding or the like. There is. In addition, a container with a crystallized center at the bottom is inferior in aesthetics and may give the consumer the misunderstanding that the contents are precipitated.
[0008]
A plastic bottle that has multiple legs and valleys arranged alternately and is highly stretched and thinned except for the center of the bottom is also excellent in heat and pressure resistance and independence after heat sterilization. However, the problem is that the degree of stretching at the center of the bottom is still insufficient or the degree of crystallization is not sufficient, and there are limits to its heat resistance and pressure resistance. Yes, the improvement is left as an important issue.
[0009]
In the stretch blow molded container made of polyester, the present inventors can introduce a pseudo-crystal structure independent of the original crystal of the polyester at least in the center of the bottom, and by introducing this pseudo-crystal structure, Improves heat resistance at temperatures below the melting temperature, thereby significantly improving the self-sustainability of the container after sterilization, especially in the case of a container comprising a plurality of feet and valleys at the bottom. I found out.
[0010]
[Means for Solving the Problems]
According to the present invention, in a container formed by stretch blow molding of a preform containing thermoplastic polyester as a main component, the trunk portion, the bottom portion and the shoulder portion are stretched and oriented, and at least the bottom center portion is a differential. In a scanning calorimeter (DSC) measurement, it has an endothermic peak (B) accompanying the disappearance of pseudo crystals in a temperature range higher than the glass transition point of the polyester and lower than the crystal melting start temperature of the polyester. In addition, in the differential scanning calorimeter (DSC) measurement, the shoulder also has an endothermic peak (S) associated with the disappearance of pseudo crystals in a temperature range higher than the glass transition point of the polyester and lower than the crystal melting start temperature of the polyester. Have A stretch blow molded container is provided.
In the stretch blow molded container of the present invention,
1. The endotherm of the endothermic peak (B) accompanying the disappearance of the pseudo-crystal is 8% or more of the melting endotherm of the crystal, particularly 10 to 20%,
2. The endotherm of the endothermic peak (S) accompanying the disappearance of the pseudo crystal has a heat quantity of 5% or more, particularly 7 to 15% of the melting endotherm of the crystal,
3. In the temperature range higher than the glass transition point of the polyester and lower than the crystal melting start temperature of the polyester, the endothermic amount of the endothermic peak (B) accompanying the disappearance of the pseudo crystal is the largest at the bottom center and the second at the shoulder. Large and the smallest in the torso,
4). The container is formed by primary blow molding of a preform, heat treatment including the bottom, body and shoulder of the primary blow molded product, and secondary blow molding of the heat treated product;
5. The bottom portion is composed of feet and valleys alternately arranged in the circumferential direction, and the valley has a self-supporting structure located on a virtual curved surface convex downward in the container axis direction;
Is preferred.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1 for explaining a row of stretch blow molded containers according to the present invention, the container comprises a mouth neck 1, a shoulder 2, a trunk 3 and a bottom 4 formed by biaxial stretch blow molding of resin. The bottom portion 4 has a bottom center portion 5 at the center thereof, and alternately has a plurality of valley portions 6 and a plurality of foot portions 7 on the periphery. The valley portion 6 is located on a virtual curved surface that is convex in the bottom direction, and the foot portion 7 located between the valley portions is provided so as to protrude in the bottom direction from the valley portion 6. The foot 7 has a grounding portion at the tip 8 extending radially outward and off-axis from the center of the center.
The shoulder 2, body 3, and bottom 4 of the container are stretch oriented.
[0012]
These shoulder part 2, body part 3 and bottom part 4 have the crystal structure of the polyester used for the production of the container, but at least the bottom center part 5 has pseudo crystals in addition to the above crystals.
The presence of the crystal of the polyester is observed as an endothermic peak (A) accompanying the melting of the crystal in the differential scanning calorimeter (DSC) measurement. The presence of the pseudo crystal is also the same in the differential scanning calorimeter measurement. It is observed as an endothermic peak (B) accompanying the disappearance of.
In the differential scanning calorimeter, the sample was heated at a rate of 20 ° C. to 10 ° C./min.
At least at the center 5 at the bottom of the stretch blow molded container of the present invention, this endothermic peak (B) is in a temperature range higher than the glass transition point (Tg) of the polyester and lower than the crystal melting start temperature (Tm ′) of the polyester. )have.
[0013]
FIG. 2 of the accompanying drawings is a measurement curve of a differential scanning calorimeter of polyester in the center of the bottom (the gate remainder) of the container of the present invention. In addition to the endothermic peak (A) accompanying the melting of the crystal, the lower temperature side Has an endothermic peak (B) accompanying the melting of the pseudocrystal.
On the other hand, FIG. 5 is a measurement curve of a differential scanning calorimeter of a polyester at the bottom center part (gate remainder) of a normal biaxially stretched blow-molded container, and an endothermic peak (A) accompanying the melting of the crystal is observed, The endothermic peak (B) accompanying the melting of the pseudo crystal is not observed.
[0014]
Generally, polyester crystals include oriented crystals and thermal crystals. In these crystals, the molecular state is in a low energy state as in the case of ordinary crystals, and the structure is stable in this state. .
By the way, in the orientation crystal of the polyester other than the lamellar crystal, as described later, the degree of crystallinity is about 40% at most, and the remaining polyester exists in an amorphous state, which is the cause of the inhibition of heat resistance. It has become.
[0015]
In the present invention, as described above, it is possible to introduce a pseudo crystal structure independent of the original crystal of the polyester at least at the center of the bottom, and a temperature equal to or lower than the melting temperature of the pseudo crystal by the introduction of the pseudo crystal structure. It has been found that, in this case, in the case of a container composed of a plurality of feet and valleys, the self-sustainability of the container after sterilization can be remarkably improved. Is. That is, in the container of the present invention, at least the amorphous polyester at the center of the bottom forms a pseudo-crystal structure, so that the energy is lower than that of mere amorphous polyester and is stabilized, and the pseudo-crystal disappears. The heat resistance at a temperature lower than the temperature to be improved is improved.
[0016]
In the container of the present invention, it must be emphasized that the polyester in the center of the bottom forms pseudo crystals. In particular, in a container having a self-supporting structure in which feet and valleys are alternately arranged, the bottom center is the lowest position except for the feet protruding downward, and the bottom center is creep. If the protrusion is deformed downward, the self-supporting stability of the container is impaired. However, in the container of the present invention, this creep deformation is prevented by the generation of the pseudo crystal described above, and the heat resistance, heat pressure resistance and self-supporting stability are reduced. The property is improved.
[0017]
The endothermic amount of the endothermic peak (B) at least in the center of the bottom of the container of the present invention is 8% or more, particularly 10 to 20% of the endothermic amount of the melting endothermic peak (A) of the crystal of the present invention. Preferred for the purpose.
When the endothermic amount of the endothermic peak (B) at the center of the bottom is below the above range, the heat resistance, the heat pressure resistance and the self-supporting stability tend to be lower than in the above range.
On the other hand, there is a limit to the generation of pseudo crystals, and if the endothermic amount of the endothermic peak (B) is too large, the crystallinity is relatively lowered, which is not preferable in terms of container strength and heat resistance. In the above range, it is preferable.
[0018]
The melting point (Tm) required as the peak temperature of the melting endothermic peak (A) of the polyester crystal constituting the container of the present invention varies depending on the type of polyester and the degree of stretching, but is generally 200 to 280 ° C., particularly 220. It is the range of thru | or 270 degreeC.
On the other hand, although the peak temperature of the endothermic peak (B) accompanying the disappearance of the pseudo crystal is in the range already pointed out, the preferred range is a balance with the temperature of the heat sterilization of the container, and the disappearance of the pseudo crystal occurs during the heat sterilization. In the case of hot filling or hot water sterilization generally adopted, it is preferably in the range of 90 to 180 ° C.
[0019]
The biaxially stretched blow molded container of the present invention may be formed by the usual single-stage biaxially stretched blow molding, but preferably the primary blow molding of the preform and the bottom, body and shoulders of the primary blow molded product. And a secondary blow molding of the heat-treated product.
In this manufacturing process, the heat treatment performed between the primary blow molding and the secondary blow molding affects the generation of pseudo crystals, that is, the endothermic peak (B), and the strain in the secondary blow molding is also the endothermic peak (B). Affects the size of the.
[0020]
In the container of the present invention, in relation to the above manufacturing operation, the shoulder of the container is also a temperature higher than the glass transition point of the polyester and lower than the crystal melting start temperature of the polyester in the differential scanning calorimeter (DSC) measurement. The region has an endothermic peak (S) accompanying the disappearance of the pseudocrystal.
[0021]
FIG. 3 is a measurement curve of a differential scanning calorimeter of polyester on the shoulder of the container of the present invention. In addition to the endothermic peak (A) accompanying the melting of the crystal, the endotherm accompanying the melting of the pseudo crystal on the lower temperature side. peak (S) have.
The fact that pseudo-crystals are formed on the shoulder portion also improves the heat resistance and heat pressure resistance at the container shoulder portion, for example, prevents deformation of the shoulder portion during hot filling, hot water sterilization process or cooling process thereof. Helps improve the appearance characteristics of bottling products.
[0022]
From the above viewpoint, it is preferable that the endothermic amount of the endothermic peak (S) accompanying the disappearance of the pseudo-crystal of the polyester on the shoulder of the container is 5% or more, particularly 7 to 15% of the melting endotherm of the crystal.
[0023]
In the stretch blow molded container of the present invention, the polyester in the container body does not have an endothermic peak (D) associated with the disappearance of pseudo crystals, or the endothermic peak (D) is considerably small.
The reason seems to be that the pseudo-crystal generated in the heat treatment process was broken in the body portion due to the stretching of the secondary blow molding.
[0024]
FIG. 4 is a measurement curve of the differential scanning calorimeter of the polyester of the body of the container of the present invention. In addition to the endothermic peak (A) accompanying the melting of the crystal, the endotherm accompanying the melting of the pseudo crystal on the lower temperature side. peak (D) However, its peak area (endothermic amount) is considerably small.
[0025]
In the container of the present invention, the endothermic peak endotherm accompanying the disappearance of pseudo crystals in the temperature range higher than the polyester glass transition point and lower than the polyester crystal melting start temperature is the largest at the bottom center, It has the feature that it is next largest at the part and smallest at the body part.
That is, the endothermic amount of the endothermic peak at the center of the bottom is H. _B , The endothermic amount of the endothermic peak at the shoulder is H _S And the endothermic amount of the endothermic peak of the body portion is H _D Then, these relationships are generally expressed by the following formula (1)
H _B > H _S > H _D (1)
It is in the relationship represented by.
[0026]
The container having the above-mentioned polyester pseudo-crystal distribution has an advantage that it is particularly excellent in the balance of heat resistance and heat pressure resistance as the whole container. In the center of the bottom, which has the smallest degree of molecular orientation and is most important in terms of self-supporting stability, the degree of quasi-crystallization is large, and in the body part where the degree of molecular orientation is the largest, the degree of quasi-crystallization is small, In the shoulder where the degree is in the middle, the degree of pseudo-crystallization is also in the middle.
[0027]
When the present invention is a one-piece self-supporting container having legs and valleys alternately arranged in the circumferential direction at the bottom, and the valleys are located on a virtual curved surface convex downward in the container axial direction. There is a particularly excellent effect.
In this type of container, the center of the bottom is located on the lowermost position on the virtual curved surface, but according to the present invention, by suppressing deformation due to creep or the like of the center of the bottom during heat sterilization, the container is self-supporting. Or the stability thereof can be prevented from being impaired.
[0028]
[Container wall structure]
In the present invention, a thermoplastic polyester that can be stretch blow molded and thermally crystallized, particularly an ethylene terephthalate thermoplastic polyester, is advantageously used as a constituent material of the container. Of course, polybutylene terephthalate, polyethylene naphthalate, etc. Other polyesters or blends with polycarbonate or arylate resin can also be used.
Further, the constituent material of the container may be a single layer within a range where the main material is polyester, or may be a multilayer structure of two or more layers.
[0029]
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.
[0030]
Homopolyethylene terephthalate is preferable in terms of heat resistance and heat pressure resistance, but a copolyester containing a small amount of ester units other than ethylene terephthalate units can also be used.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
In the container of the present invention, the above-described ethylene terephthalate-based polyester can be used as an inner and outer layer, and a recycled polyester layer, a gas barrier resin layer, an oxygen-absorbing resin layer, or the like can be interposed as an intermediate layer.
As the recycled polyester layer, a polyester crushed product recovered as a used PET bottle is washed and regenerated as necessary.
Examples of gas barrier resins include ethylene vinyl alcohol copolymers, particularly ethylene vinyl alcohol copolymers having an ethylene content of 20 to 60 mol%, polyamide resins, particularly nylon 6, nylon 6,6, and polyxylylene adipa. Mid (MXD6) or the like is used.
Any known oxygen-absorbing resin composition may be used as the oxygen absorbent layer, but typical examples include polyamide resins, especially MXD6 blended with transition metal catalysts, especially cobalt carboxylates, etc. Is used.
[0035]
[Containers and their production]
The stretch blow molded container of the present invention is preferably formed by primary blow molding of a preform, heat treatment including the bottom, trunk and shoulder of the primary blow molded product, and secondary blow molding of the heat treated product.
[0036]
In FIG. 6 for explaining the manufacturing process, first, in the preliminary heating process, the preform 10 formed of the above-described polyester is supported by a mandrel 11 and stretched by using a heating apparatus 12 such as an infrared heating apparatus. Heat to temperature.
Next, in the primary blow molding process, the heated preform 10 is put into a blow mold 13 that can be opened and closed, the preform is pulled and stretched in the axial direction by the stretching rod 14, and through the mouth and neck held by the mandrel 11. The preform is blown and stretched in the circumferential direction by blowing gas. In this primary blow molding, a bottom mold 16 and a press bar 17 can be used to make the bottom shape of the primary blow molded product 15 into a predetermined shape.
[0037]
Next, heat treatment including the bottom portion, the trunk portion, and the shoulder portion of the primary blow-molded product 15 is performed. That is, the infrared heating apparatus for heat treatment includes an infrared heating unit 18a for bottom heating, an infrared heating unit 18b for body heating, and an infrared heating unit 18c for shoulder heating, and the primary blow is performed by this heating. The bottom part, the body part, and the shoulder part of the molded product shrink, and the heat-treated product 19 is heat-set.
Finally, in the secondary blow molding process, the heat-treated product 19 is placed in a secondary blow mold 21 that includes a bottom mold 20 and can be opened and closed, and pressurized gas is supplied from the neck of the heat-treated product 19 held by the mandrel 11. Is blow-drawn to form the final container 9.
In the above manufacturing process, the infrared heating apparatus for heat treatment may be composed of an infrared heating section 18a for bottom heating and an infrared heating section 18d in the vicinity thereof as shown in FIG.
[0038]
In the stretch blow molded container of the present invention, as already pointed out, at least the center of the bottom has a pseudo crystal that appears as an endothermic peak in the differential scanning calorimeter analysis, and the pseudo crystal at the bottom is subjected to the heat treatment described above. Although produced, it tends to disappear or be destroyed by secondary blow molding.
Therefore, it is important that the pseudo crystal is effectively generated at the center of the bottom at the time of heat treatment, and that the degree of blow stretching at the center of the bottom is kept low in the secondary blow molding.
[0039]
(1) Preform:
A bottomed cylindrical preform is used for forming the container of the present invention. The preform used in the present invention consists of a mouth and neck, a cylindrical trunk and a closed bottom, and the mouth and neck are provided with a lid fastening mechanism such as a screw and a support ring for holding a container, The mouth / neck portion of the preform is the mouth / neck portion of the final container. This neck and neck can be thermally crystallized in order to improve heat resistance and increase its sealing accuracy.
[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.
For injection molding of the multilayer preform, a number of screws or plungers corresponding to the type of the resin layer may be used, and co-injection molding or sequential injection molding may be performed through multilayer multiple nozzles.
[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, polyester or the like flows into the injection mold cavity and is solidified to form 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.
Injection temperature is 270 to 310 ° C, pressure is 28 to 110 kg / cm ² The degree is preferred.
[0043]
If necessary, thermal crystallization of the mouth and neck of the preform can be performed by selectively heating these parts by means known per se. Since thermal crystallization of polyester or the like occurs remarkably at a specific crystallization temperature, generally a corresponding portion of the preform may be heated to the crystallization temperature. Heating can be performed by infrared heating, dielectric heating, or the like. In general, it is preferable to perform selective heating by blocking a body portion to be stretched from a heat source with a heat insulating material.
[0044]
The above thermal crystallization may be performed simultaneously with the preheating to the stretching temperature of the preform or may be performed separately. Mouth thermal crystallization can be performed by heating the preform bottom and mouth in a temperature of generally 140 to 220 ° C., particularly 160 to 210 ° C., in a state of being thermally insulated from the other portions. The crystallinity of the preform mouth is preferably 25% or more.
[0045]
The preform can be molded by compression molding.
In this case, an almost fixed amount of molten lump formed by cutting an extrudate such as polyester is supplied into the female mold (cavity mold) without substantially lowering the temperature, and the supplied molten lump is immediately put into the mold ( Compression molding with a core mold). At the time of compression molding, it is preferable to perform compression molding on a preform having a bottomed body portion and a mouth portion while promptly discharging residual air in the mold.
In the production of preforms by compression molding, it is possible to produce a preform having no gate residue at the bottom, and the preform can be molded at a relatively low pressure, and the occupation time of the mold in the preform mold is short. There are advantages.
[0046]
The preform stretching temperature is generally 85 to 135 ° C, particularly 90 to 130 ° C. In this case, it is preferable that the heating temperature difference between the bottom and the body of the preform is within 10 ° C.
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 (cold parison method) in which a preform molded product in a supercooled state is once manufactured, and this preform is heated to the above-described stretching temperature to perform stretch blow molding.
The heating can be performed by means known per se such as infrared heating, hot air heating furnace, dielectric heating and the like. In general, it is desirable to support the neck and neck of the preform with a core mold, hold it under rotation in a heating device (heating furnace) equipped with an infrared source, and uniformly heat the trunk and bottom to the stretching temperature. .
[0047]
The stretching ratio is preferably 2 to 5 times, particularly 2.2 to 4 times in the axial direction, and 2.5 to 6.6 times, particularly 3 to 6 times in the circumferential direction. The axial stretch ratio is determined by the axial length of the preform and the stroke length of the stretch rod, but the circumferential stretch ratio is determined by the preform diameter and the mold cavity diameter. . As the pressure fluid, room temperature or heated air, and other gases such as nitrogen, carbon dioxide or water vapor can be used, and the pressure is usually 10 to 40 kg / cm. ² Gauge, especially 15-30kg / cm ² It should be in the gauge range.
The temperature of the primary blow mold is generally preferably in the range of 15 ° C to 100 ° C.
[0048]
In the primary blow molding process, the preform is held in a cavity formed by a pair of split molds with the mouth and neck portions supported by a core mold. On the opposite side of the mandrel, a bottom mold that defines the bottom shape of the primary blow-molded product is also disposed.
A stretch rod is inserted into the preform, the tip is pressed against the center of the bottom of the preform, the preform is pulled and stretched in the axial direction, and a fluid is blown into the preform so that the preform moves in the circumferential direction. Expand and stretch.
[0049]
The stretching ratio is preferably 2 to 5 times, particularly 2.2 to 4 times in the axial direction, and 2.5 to 6.6 times, particularly 3 to 6 times in the circumferential direction. The axial stretch ratio is determined by the axial length of the preform and the stroke length of the stretch rod, but the circumferential stretch ratio is determined by the preform diameter and the mold cavity diameter. .
As the pressure fluid, room temperature or heated air, and other gases such as nitrogen, carbon dioxide or water vapor can be used, and the pressure is usually 10 to 40 kg / cm. ² Gauge, especially 15-30kg / cm ² It should be in the gauge range.
[0050]
In the primary blow molding, a press bar is arranged on the bottom die side coaxially with the stretching rod, and at the time of tensile stretching, the center of the bottom of the preform is held between the stretching rod and the pressing rod, and the bottom of the preform It is preferable that the position is regulated so that the center portion of the center is accurately positioned at the center of the primary blow-molded product.
Further, the bottom mold preferably has a generally dome shape with a large radius of curvature in order to promote high stretching of the bottom portion of the secondary molded product, and in particular, a flat portion is provided at the bottom center portion. It is also effective.
[0051]
In the primary blow molding, it is preferable to maintain the temperature drop of the sandwiched portion at the bottom of the preform within 40 ° C., more preferably within 30 ° C., until the end of the stretching process. The bottom of the product can be thinned in a relatively high stretched state, except for the bottom center which is the sandwiched portion.
The means for preventing the temperature drop at the sandwiched portion at the bottom of the preform is not particularly limited. For example, a heat insulating member, for example, a polytetrafluoroethylene gripping portion is attached to the end of the stretching rod, and the bottom center by heat conduction The temperature drop of the part can be made as small as possible. For the same purpose, a heat insulating member such as a gripping part made of polytetrafluoroethylene can be attached to the tip of the press bar.
[0052]
Desirably, the bottom of the obtained primary blow-molded product is oriented and crystallized in a relatively high stretched state so that the degree of orientation crystallinity is 20% or more, more preferably 25% or more, excluding the bottom center part. It is preferable to reduce the thickness to 1 mm or less, more preferably 0.8 mm or less.
[0053]
In the heat treatment step of the primary blow-molded product, the primary blow-molded product is supported by a mandrel, and the bottom, body, and shoulder of the primary blow-molded product face the infrared heating body while rotating. As a result, the primary blow-molded product is heated by the infrared rays of the infrared heating body at the bottom, body, and shoulder, contracted in the height direction and radial direction, and accommodated in the secondary blow mold corresponding to the final container shape. It becomes a shape.
[0054]
According to the present invention, by this heat treatment, crystallization of polyester on the molecularly oriented vessel wall and relaxation of stretching strain by primary blow molding are performed simultaneously with generation of pseudo crystals. The generation of the pseudo crystal is confirmed by the differential scanning calorimeter (DSC) measurement as described above.
The endothermic peak temperature (Tp) accompanying the disappearance of the pseudo crystal is closely related to the temperature at the time of heat treatment, and generally has a tendency for a peak to appear at or near the heat treatment temperature. When the heat treatment temperature is Tt, the endothermic peak temperature (Tp) is generally in the range of Tt-100 ° C. to Tt + 40 ° C.
[0055]
The heat treatment conditions vary depending on the type of polyester and the conditions of the primary blow molding, but generally speaking, a temperature of 150 to 220 ° C., particularly 160 to 200 ° C., and a treatment of 5 to 15 seconds, particularly 7 to 10 seconds. From the time, the degree of generation of the pseudocrystal in the final container is determined to be in the above-described range.
It is advantageous to suppress the degree of contraction of the bottom center portion by this heat treatment as much as possible as compared with the body portion and the shoulder portion. This is because if the degree of this shrinkage is large, the degree of stretch blow tends to increase in the subsequent secondary blow molding, and the degree of disappearance of the pseudo crystals increases.
[0056]
Since the heating from the infrared radiator is non-contact heating, the bottom part, the trunk part, and the shoulder part are contracted without restriction, and the infrared ray irradiated to the surface of the primary blow molded product is a part thereof. Is absorbed by the vessel wall, and the remaining part passes through the vessel wall and reaches the inner surface on the opposite side opposite to the irradiation site, and heating by infrared rays from the inner and outer surfaces is extremely efficient and even within a short time. There is an advantage of being done.
[0057]
In the secondary blow molding process, the heat-treated molded product is inserted into the secondary blow mold with the neck supported by the core mold. A bottom mold that defines the bottom shape of the final container is also inserted on the opposite side of the core mold. The split mold is closed and fluid is blown into the heat-treated product, and the heat-treated product is subjected to secondary blow molding to form a final container having a predetermined shape.
[0058]
In this secondary blow molding, the heat-treated product to be blown has an increased elastic modulus due to crystallization by heat treatment, so it is preferable to perform blow molding using a high fluid pressure, and generally 15 to 45 kg / cm. ² It is preferable to use a pressure of
At the time of secondary blow molding, the mold temperature may be maintained at a temperature of 5 to 135 ° C., and cooling may be performed immediately after molding, or cooling is performed by flowing cold air or the like in the final molded product. May be performed.
[0059]
In the secondary blow molding, the pseudo crystal generated by the heat treatment tends to be destroyed or disappeared in a portion where the stretch blow is large.
In the container of the present invention, during secondary blow molding, the extent of stretch blow at the center of the bottom is the smallest, so the degree of residual pseudo crystals is the largest, and the extent of stretch blow is the largest in the barrel, The degree of residual pseudo crystal is the smallest, and the degree of residual pseudo crystal at the shoulder is intermediate between the center of the bottom and the body.
[0060]
At the time of secondary blow molding, it is preferable that the shape of the center of the bottom of the heat-treated product be as close as possible to the center of the bottom of the secondary blow mold, thereby increasing the degree of residual pseudo crystals and reducing the stretching strain. Can do. Further, it is possible to easily form the foot portion of the final product.
[0061]
In the container of the present invention, the crystallinity obtained by the density method should be in the range of 40 to 50% at the center of the bottom, 35 to 45% at the body, and 30 to 40% at the shoulder. Desirable in terms of pressure resistance.
The crystallinity (Xc) by the density method is the sample density (ρ) and the amorphous density (ρam, 1.335 g / cm). ³ ) And crystal density (ρc, 1.455 g / cm ³ ) And the following formula.
Xc = (ρc / ρ) × [(ρ−ρam) / (ρc−ρam)]
[0062]
The bottom of the container of the present invention preferably has feet and valleys alternately arranged in the circumferential direction, but the number of feet is 6 to 4, particularly preferably 6 to 5. Is preferable in terms of self-supporting stability.
Further, the valley portion is located on a virtual curved surface projecting downward, including the bottom center portion, for example, a substantially spherical surface or a spheroidal surface, and the curvature radius of this curved surface is 0.9 to 1.2 of the trunk portion radius. It is desirable to be in the double range.
[0063]
【Example】
The present invention is further illustrated by the following examples, but the present invention is in no way limited to the following examples.
[0064]
Example 1
First, the mouth of a preform made of polyethylene terephthalate resin is crystallized by appropriate means, and then the preform is heated to 110 ° C. above the glass transition point, and the mold temperature is 60 ° C. Performs a biaxial stretch blow molding of 3.0 times in length, 3.0 times in width and 9 times in area, and is a primary molded product having a barrel diameter of 64.3 mm and a height of 253.6 mm, which is larger than the polyester bottle of the final molded product. did.
Next, the bottom part, the body part and the shoulder part of the obtained primary molded product are heated in a heating oven at 800 ° C. for 5 seconds so that the surface temperature becomes 150 ° C. on the average to be thermally contracted. The next molded product was obtained. Next, the heat-shrinked secondary molded product was biaxially stretched and blow molded with a secondary mold having a mold temperature of 60 ° C., and a cross-sectional shape having a barrel diameter of 64.3 mm, a height of 207.2 mm, and an internal volume of 500 ml. Made a round polyester bottle. Fig. 2 shows the measurement curve of the differential scanning calorimeter at the center of the bottom of the container (the remainder of the gate), Fig. 3 shows the measurement curve of the differential scanning calorimeter at the shoulder, and Fig. 3 shows the measurement curve of the differential scanning calorimeter at the trunk. 4 respectively.
This polyester bottle was filled with hot water at 85 ° C. at high temperature and sealed with a plastic cap made of polypropylene. Subsequently, after leaving still for 10 minutes, it cooled to room temperature. The volume shrinkage at this time was 1.83%, which was within the allowable range for heat-resistant bottle use.
Moreover, after filling with carbonated water of 5 ° C. and 2.6 GV, it was immersed in a warm bath at 70 ° C. for 32 minutes and cooled to room temperature.
Therefore, the bottle of the first embodiment can be applied to heat resistance and heat pressure application.
[0065]
Comparative Example 1
In Example 1, a biaxial stretch blow molding was performed only with a primary mold with a mold temperature of 150 ° C., and a barrel diameter of 69.2 mm with a stretch ratio of 3 times, width 3 times, and area 9 times high. A polyester bottle having a circular cross section of 209.4 mm was obtained.
The polyester bottle thus obtained was filled with 85 ° C. hot water at a high temperature and sealed with a plastic cap made of polypropylene. Subsequently, after leaving still for 10 minutes, it cooled to room temperature. The volumetric shrinkage at this time was 0.023%.
However, after being filled with carbonated water at 5 ° C. and 2.6 GV, it was immersed in a warm bath at 70 ° C. for 32 minutes and cooled to room temperature, and lost its independence due to protruding deformation at the bottom.
Therefore, although the bottle of this comparative example 1 can be applied to a heat resistant use, it is not applicable to a heat resistant pressure use.
[0066]
【The invention's effect】
According to the present invention, in a stretch blow molded container from polyester, it can be seen that a pseudo crystal structure independent of the original crystal of polyester can be introduced at least in the center of the bottom. This improves the heat resistance at a temperature below the melting temperature of the glass, and thereby makes the container self-supporting after sterilization significantly in the case of a container comprising a plurality of feet and valleys at the bottom or heat resistance. Can be improved.
[Brief description of the drawings]
FIG. 1 is a side view for explaining a stretch blow molded container according to the present invention.
FIG. 2 is a measurement curve of a differential scanning calorimeter of polyester at the center of the bottom (remaining gate) of the container of the present invention.
FIG. 3 is a measurement curve of a differential scanning calorimeter of polyester on the shoulder of the container of the present invention.
FIG. 4 is a measurement curve of a differential scanning calorimeter of polyester in the body of the container of the present invention.
FIG. 5 is a measurement curve of a differential scanning calorimeter of polyester at the center of the bottom (remaining gate) of a normal biaxial stretch blow molded container.
FIG. 6 is an explanatory view showing a production process of the biaxially stretched blow molded container of the present invention.
FIG. 7 is a diagram showing another example of an infrared heating device in the manufacturing process of the biaxially stretched blow molded container of the present invention.

Claims (6)

In a container formed by stretch blow molding of a preform containing thermoplastic polyester as a main component, the body, bottom and shoulder are stretched and oriented, and at least the bottom center is a differential scanning calorimeter (DSC). In the measurement, the shoulder has a differential scanning calorimeter (B) having an endothermic peak (B) accompanying the disappearance of pseudo crystals in a temperature region higher than the glass transition point of the polyester and lower than the crystal melting start temperature of the polyester. In the DSC) measurement, the stretch blow molded container has an endothermic peak (S) accompanying the disappearance of pseudo crystals in a temperature range higher than the glass transition point of the polyester and lower than the crystal melting start temperature of the polyester. .   The stretch blow-molded container according to claim 1, wherein the endothermic peak (B) has an endotherm of 8% or more of the melting endotherm accompanying the disappearance of the pseudo crystal. The stretch blow molded container according to claim 1 or 2 , wherein the endothermic peak (S) accompanying the disappearance of the pseudo crystal has a heat quantity of 5% or more of the melting endothermic quantity of the crystal. In the temperature range higher than the glass transition point of the polyester and lower than the crystal melting start temperature of the polyester, the endothermic amount of the endothermic peak (B) accompanying the disappearance of the pseudo crystal is the largest at the bottom center and the second at the shoulder. The stretch blow-molded container according to any one of claims 1 to 3 , wherein the stretch blow molded container is large in size and smallest in the body portion. 2. The container is formed by primary blow molding of a preform, heat treatment including a bottom portion, a body portion and a shoulder portion of the primary blow molded product, and secondary blow molding of the heat treated product. The stretch blow molding container in any one of thru | or 4 . Claims 1 to 5, characterized in that it has a self-supporting structure located at the bottom circumferential foot portion arranged alternately and valleys from it and the valley portions on the convex virtual curved axial direction of the container downward A stretch blow molded container according to any one of the above.

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