JP2632960B2 - Biaxial stretch blow molding method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for producing a polyester container by a biaxial stretch blow molding method.

[Conventional technology]

The biaxially stretched blow-molded container made of a saturated polyester resin represented by polyethylene terephthalate has extremely excellent transparency and surface gloss, is beautiful, has excellent gas barrier properties and moisture impermeability, and has excellent content resistance. It has many advantages such as excellent storage stability, no generation of toxic gas in additives such as plasticizers and stabilizers, and low heat generation during combustion and no damage to the furnace. Therefore, it is widely used for various drinking water, seasonings, alcoholic beverages and other food containers.

However, biaxially stretch blow molded containers made of saturated polyester resin have the disadvantage of causing container changes due to heat shrinkage or shrinkage over time. For this reason, for applications such as sake, mirin, vinegar, sauces, and juices that are heat-sterilized at, for example, about 65 to 95 ° C. and then filled at high temperatures, the use of polyester containers by ordinary biaxial stretch blow molding is restricted. It has been.

In order to solve the problems associated with the molding and heat treatment of the biaxially stretched blow-molded container made of a saturated polyester resin as described above, by heating the container from the inside with radiant energy in a temperature-adjusting mold, It has been found that a heat-resistant container having excellent shape uniformity can be produced by heat treatment, and a few methods have been previously proposed (Japanese Patent Application Laid-Open No. 54-102377).
No., JP-A-55-95521).

[Problems to be Solved by the Invention] However, it has been found that even if heat treatment is performed after biaxial stretch blow molding, there is a problem that there is residual stress in the molded container and transparency of the container is poor.

[Means for solving the problem]

In view of the above problems, as a result of diligent research, the present inventor has found that after biaxial stretch blow molding, by rapidly cooling the molded container in a mold, it is possible to obtain a polyester container having little residual stress and without accompanying whitening phenomenon. I discovered what I could do. For this purpose, a flow path for pressurized gas, a heater provided in the flow path, and a flow path for cooling fluid are provided in the blow mandrel, and the supply of pressurized gas and cooling fluid is biaxially stretched. It has been discovered that a configuration in which switching is performed in accordance with the blow molding cycle is sufficient.

Therefore, the method of the present invention for producing a polyester container by biaxial stretch blow molding comprises the steps of (a) blowing a pressurized air of 3 to 40 kg / cm ² into a parison while heating it to 30 ° C. or more in a blow mandrel. Perform biaxial stretch blow molding,
(B) After holding the blown heated air for 3 to 50 seconds, the air is evacuated from the flow path in the blow mandrel, and (c) a cooling fluid is supplied from a stretching rod into a container obtained by biaxial stretching blow molding. The container is rapidly cooled by blowing, and (c) the container is released from the mold.

Further, the apparatus of the present invention for producing a polyester container by biaxial stretch blow molding comprises a mold, a blow mandrel mounted on the mold, and a biaxial stretch blow molding attached to the center of the blow mandrel. A blow rod inserted into the parison, wherein the blow mandrel is provided with a pressurized air flow path, a pressurized air heating heater, and a separate pressurized air flow path for cooling fluid exhaust. Having a flow path, heating and pressurizing air is blown into the parison by causing the heater to generate heat, and after forming is completed, the pressurized air is evacuated and a cooling fluid is caused to flow to rapidly cool the forming container. Equipment to do.

[Action]

By quenching with a cooling fluid after the biaxial stretch blow molding, the residual stress in the molding container is remarkably reduced, whereby the whitening phenomenon of the heat insulating bottle can be prevented and the transparency can be improved.

〔Example〕

 The present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an example of a preform (parison) to which the biaxial stretch blow molding method of the present invention can be applied. The multilayer preform comprises a mouth 1, a body 2, and a bottom 3. The mouth 1 has a thread 11, a locking ring 12, and a support ring 13. In this embodiment, the mouth 1 has three heat-resistant resin layers 14, and each heat-resistant resin layer 14 is located alternately with the polyester layer 15. The opening end 16 is entirely covered with a heat-resistant resin layer.

On the other hand, the body 2 is composed of only the polyester layer 20. The bottom 3 has at least one heat-resistant resin layer 23.

FIG. 2 is a sectional view showing another example of the preform (parison). In this embodiment, the heat-insulating resin layer 24 is also present in the trunk together with the polyester layer 25.

The present invention is not limited to the preforms shown in FIGS. 1 and 2, and can be applied to multilayer preforms having various layer structures.

The polyester resin used for these preforms is a thermoplastic resin comprising a saturated dicarboxylic acid and a saturated dihydric alcohol. As the saturated dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, naphthalene-1,4- or
Aromatic dicarboxylic acids such as 2,6-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid, diphenyldicarboxylic acids, diphenoxyethanediethanedicarboxylic acids, adipic acid, sebacic acid, azelaic acid, decane-
Aliphatic dicarboxylic acids such as 1,10-dicarboxylic acid and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid can be used. Examples of the saturated dihydric alcohol include fats such as ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, hexamethylene glycol, dotecamethylene glycol, and neopentyl glycol. Aliphatic glycols, alicyclic glycols such as cyclohexanedimethanol, 2,2-bis (4'-β-hydroxyethoxyphenyl) propane,
Other aromatic diols and the like can be used.
A preferred polyester is polyethylene terephthalate consisting of terephthalic acid and ethylene glycol.

The polyester resin used in the present invention has an intrinsic viscosity of 0.5
It has a value in the range of ~ 1.5, preferably 0.55-0.8. Such polyesters are also produced by melt polymerization,
Those subjected to a reduced pressure treatment or a heat treatment in an inert gas atmosphere at a temperature of up to 250 ° C., or those in which the content of oligomers and acetaldehyde, which are low molecular weight compounds, is reduced by solid phase polymerization are preferred.

Further, as the heat-resistant resin, a U polymer (manufactured by Unitika, a blend polymer of polyarylate and polyethylene terephthalate), polycarbonate, a blend polymer of polycarbonate and polyethylene terephthalate, a blend polymer of polyarylate, polycarbonate and polyethylene terephthalate, and the like can be used.

In the polyester resin or the heat-resistant resin used in the present invention, a stabilizer as long as the object of the present invention is not impaired,
Pigments, antioxidants, thermal degradation inhibitors, UV degradation inhibitors,
Additives such as antistatic agents and antibacterial agents and other resins can be added in appropriate amounts.

FIG. 3 is a sectional view schematically showing an apparatus for performing the biaxial stretch blow molding method of the present invention. The apparatus includes a mold 30 including a body mold 31, a mouth mold 32, and a bottom mold 33;
A blow mandrel 34 that can be hermetically mounted on the blow mandrel 32, and an extension rod 35 attached to the lower end of the blow mandrel 34
And a fixed block 36 attached to the upper end, and an extended rod fixed block 37. The extension rod 35 is positioned at the center of the blow mandrel 34 by the extension rod slide sleeve 42.

An elongate rod 35 extends through the center of the bromandrel 34, around which there are channels 38 and 39. A sheath heater 40 is provided in the channel 38, and a separating sleeve 39 'is provided between the channels 38 and 39. Further, the stretching rod 35 is formed in a tubular shape, through which a cooling fluid can flow, and a plurality of holes 41 for blowing out gas are provided in portions protruding into the mold. The extension rod 35 has an opening 43 in the fixed block 37,
The flow paths 38 and 39 are each provided with an opening 4 in the fixed block 37.
Has 5,44. Both the heated and pressurized air and the cooling fluid are discharged from the holes of the sleeve 42 through the exhaust passage 39.

FIG. 4 is a schematic diagram showing a pipeline system for injecting and discharging pressurized air and cooling fluid to and from the apparatus of FIG. In this embodiment, the opening 43 is connected to a cooling fluid source 51 via a pipe 46, the opening 44 is connected to a relief valve _VR1 via a pipe 47, and the opening 45 is connected to a pipe 48. , 49 and 50 to a pressurized air source 52. Note The pipe 46 is provided with a valve V _1, the pipe 47 valve
V ₂ and V ₆ are provided, and the pipe 49 has a valve V ₃ and a pressure reducing valve R
_R2 is provided, the valve V ₄ is provided on the pipe 50. The pipe 48 has a valve at the position after branching off with the pipe 50.
V ₅ is provided.

With such a pipeline system, heated and pressurized air and a cooling fluid are supplied and discharged into the parison P installed in the mold as described below.

With the primary blow valves V ₁ and V ₂ closed, V ₃ is opened, and pressurized air flows from the pressurized air source 52 into the flow path 38.

With the secondary blow valves V ₁ and V ₂ closed, V ₄ is opened, and pressurized air flows from the pressurized air source 52 into the flow path 38.

Primary air vent valve V _1, V _3, to close the V ₄ to open the valve V _2, the relief valve V _R1
The heated and pressurized air is exhausted through the. It should be noted that it may be open to V ₅ at the same time.

Closed cooling blow valve _{V 3, V 4, V 5} , opening valve V _1, V _2, a source of cooling fluid
From 51, the cooling fluid flows into the flow path in the extension rod 35. This Saiben V ₂ is opened, the pressure of the cooling fluid quenching the molded container by the relief valve _R1 is kept at a constant level.

Close the cooling fluid degassing valves _{V 1, V 3, V 4} , V 5 opens the valve V _2, V _6, to discharge the cooling fluid.

The above steps 1 to 3 are performed for each cycle of the biaxial stretch blow molding.

In the process, when performing biaxial stretch blow molding of the parison, the pressurized air is supplied to the flow path 38 in the blow mandrel 35.
Is heated to a predetermined temperature by the sheath heater 40 that is passing through. The temperature of heated and pressurized air for biaxial stretch blow molding is 30
℃ or more, preferably about 70 to 300 ℃, the pressure is 3 to 4
It is 0 kg / cm ² .

In this embodiment, the pressure of the primary blow is 3 to 10 kg / cm ²
Relatively low, the pressure of the secondary blow is at the above level.

During biaxial stretch blow molding, each part of the mold is kept at a predetermined temperature. Specifically, the die of the die 30
32 contacts the parison mouth which is hardly stretched, the barrel mold 31 contacts the stretched portion of the parison, and the bottom mold 33 contacts the parison bottom having a low stretch ratio. According to the stretching ratio of each parison, the temperature of the mouth mold 32 is equal to or lower than the glass transition temperature Tg of the polyester, and the temperature of the bottom mold 33 is the glass transition temperature.
Tg ± 15 ° C, and the temperature of the body mold 31 is the glass transition temperature Tg ~
Preferably it is the crystallization temperature. In particular, when the bottle is biaxially stretch blow-molded with polyethylene terephthalate resin (PET), the mouth mold 32 is 20 to 60 ° C, and the bottom mold 33 is 50 to 80 °.
C., the temperature of the body mold 31 is preferably 90 to 130C.

As the cooling fluid, either cooling air or liquid nitrogen or a gas obtained by vaporizing the same can be used. In the case of cooling air, the temperature may be 70 ° C. or less, and may be room temperature. The cooling air is pressurized to about 5 to ²⁰ kg / cm ² and flows into the flow path in the stretching rod 35. As mentioned above, the extension rod
Since a large number of holes are provided at the tip of 35 (inserted into the parison P), the cooling air is discharged into the molding container to rapidly cool the molding container. In the case of cooling air, the extension rod 35 does not need to be a double pipe, and can be exhausted from the opening 44 through the cooling air discharge channel 39. Since the exhaust pipe 47 is provided with the relief valve _VR1 , the pressure of the cooling air in the molding container is kept constant.

Next, in the case where the cooling fluid is nitrogen gas obtained by vaporizing liquid nitrogen, the extending rod has a double-pipe structure from the viewpoint of heat insulation with the sheath heater 40, the discarded heating pressurized air, and the like. Further, a vacuum is provided between the double tubes to further improve the heat insulation. In order to further enhance the quenching effect, the liquid nitrogen is allowed to flow into the stretching rod 35 in a liquid state without being vaporized, and the hole 41
It is more preferable to adopt a method of vaporizing and expanding when discharged into a molding container. In any case, the pressure of the nitrogen gas discharged into the molding container is generally preferably about 5 to 10 kg / cm ² . In the case of nitrogen gas, similarly, the relief valve V
_The pressure is kept constant from _R1 .

After the cooling fluid is discharged into the forming container, it is discharged through the flow path 39 in the mandrel 34, so that the forming container is always in contact with the fresh cooling fluid and is rapidly cooled. Usually, the cooling time is about 10 seconds for cooling air and about 1 to 5 seconds for liquid or vaporized nitrogen gas. The temperature of the molding container is cooled down to about 60 to 90 ° C. by rapid cooling. After quenching, the molded container is released from the mold.

〔The invention's effect〕

As described in detail above, the biaxially stretched blow-molded container is rapidly cooled with a cooling fluid before it is released from the mold, so that the residual stress of the container can be significantly reduced. Thereby, even if it is a multilayer polyester container having a heat-resistant resin layer, a container having good transparency can be manufactured without causing a whitening phenomenon. In addition, since the quenching is performed after the molding until the release, the cycle of the biaxial stretch blow molding can be shortened, and the productivity is improved.

Further, the apparatus of the present invention has a blow air flow path and a cooling fluid exhaust flow path separated and independent by a sleeve in a blow mandrel for such a purpose, and further has a cooling liquid or liquid flow path. Having a stretching rod at the center of the blow mandrel. Since the heating and pressurizing air and the cooling gas have a structure in which the heating and pressurizing air and the cooling gas are insulated and discharged in an adiabatic manner, a heater is provided in the blow air flow path to heat the heater in accordance with the blow air inflow timing, and If the cooling liquid is allowed to flow after degassing, the cycle of blow molding, heating and rapid cooling can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a preform to which the biaxial stretch blow molding method of the present invention can be applied. FIG. 2 is a sectional view of a preform to which the biaxial stretch blow molding method of the present invention can be applied. FIG. 3 is a sectional view showing another example, FIG. 3 is a schematic sectional view showing an apparatus for carrying out the biaxial stretch blow molding method of the present invention, and FIG. FIG. 2 is a schematic diagram showing a pipeline system for feeding the water. 1 ... mouth 2 ... trunk 3 ... bottom 14,24 ... heat insulating resin layer 15, 25 ... polyester layer 30 ... mold 34 ... blow mandrel 35 ... stretch rod 36 ... fixed blow mandrel Block 37 ... Extension rod fixing lock 38,39 ... Flow path 40 ... Sheater 41 ... Hole 43,44,45 ... Opening 46,47,48,49,50 ... Pipe 51 ... Cooling fluid Source 52… Pressurized air V _{1 to} V ₆ … Valve V _R1 … Relief valve V _R2 … Reducing valve

Claims (8)

(57) [Claims] 1. A method for producing a polyester container by biaxial stretch blow molding, comprising: (a) applying 3 to 40 kg / cm ² of pressurized air in a blow mandrel;
Blowing into a parison while heating to 30 ° C. or higher to perform biaxial stretch blow molding. (B) After holding the blown heated air for 3 to 50 seconds, bleed air from the flow path in the blow mandrel; A) a cooling fluid is blown from a stretching rod into a container obtained by biaxial stretch blow molding to rapidly cool the container; and (c) releasing the container. 2. The method according to claim 1, wherein said cooling fluid is cooling air at 70 ° C. or less. 3. The method according to claim 1, wherein the cooling fluid is liquid nitrogen or nitrogen gas obtained by vaporizing the liquid nitrogen. 4. The method according to claim 1, wherein the cooling fluid is blown into the container.
A method comprising evacuating said cooling fluid through a relief valve from an exhaust passage in said blow mandrel via a relief valve, thereby quenching said container by constantly supplying fresh cooling fluid into said container. 5. The method according to claim 1, wherein the temperature of a mold portion in contact with the mouth of the container is equal to or lower than the glass transition temperature Tg of the polyester, and the mold in contact with the bottom of the container. A temperature of a mold in contact with the body of the container is adjusted to be equal to or higher than the glass transition temperature Tg and equal to or lower than the crystallization temperature of the polyester. 6. An apparatus for producing a polyester container by biaxial stretch blow molding, comprising: a mold, a blow mandrel mounted on the mold, and a biaxial stretch blow molding attached to a center portion of the blow mandrel. A blow rod inserted into the parison, and the blow mandrel includes a flow path for pressurized air, a heater for heating pressurized air provided in the flow path for pressurized air, and a flow path for pressurized air. The passage has a separate cooling fluid exhaust passage, and the heater is heated to blow heated pressurized air into the parison, exhaust the pressurized air after the molding is completed, and allow the cooling fluid to flow. An apparatus characterized by rapidly cooling a molded container. 7. The apparatus according to claim 6, wherein a cooling fluid inflow passage is provided in the extension rod in an adiabatic structure, and a cooling fluid discharge passage is provided outside the blow mandrel. An apparatus characterized in that: 8. The apparatus according to claim 7, wherein a portion of the extension rod in the blow mandrel has a double tube structure, and a vacuum is formed in the double tube wall. And equipment.