JPH0443499B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a heat-resistant multilayer stretched polyester container, and more specifically, it includes a layer made of a thermoplastic polyester such as polyethylene terephthalate and a layer made of a gas barrier resin. This invention relates to a method for efficiently manufacturing a multilayer stretched polyester container with excellent heat resistance and heat shrinkage resistance using only one type of mold. (Prior technology) Stretched bottles made of polyethylene terephthalate (PET) have advantages such as transparency, impact resistance (drop resistance), lightness, hygiene, appropriate gas barrier properties against oxygen and carbon dioxide, and pressure resistance. Widely used as packaging containers for soy sauce, sauces, dressings, edible oils, carbonated drinks such as beer, cola, and cider, fruit juice drinks, mineral water, shampoo, detergents, cosmetics, wine, mustard, aerosol products, etc. There is. However, since stretched polyester bottles are also made of plastic, gas permeability can be considered to be zero for completely sealed items such as glass bottles and metal cans, whereas stretched polyester bottles are free from oxygen, carbon dioxide gas, etc. However, it has a slight permeability to water, making it inferior to cans and glass bottles in terms of food filling and preservation, causing a loss of carbon dioxide gas in the case of carbonated beverages, and in beer, cola, cider, etc. There is a clear shelf life limit, and fruit juice-containing beverages are also subject to shelf life limitations due to the permeation of oxygen from the outside. In addition, stretched polyester bottles are significantly superior to other plastic bottles in terms of transparency, gas barrier properties, and pressure resistance against gas-filled beverages, but the stretching and forming temperature is relatively low (80 to 110°C). In addition, since it has non-stretched parts or low-stretched parts, it has no heat resistance, so when hot-packing, it cannot be put to practical use unless the filling temperature is 65°C or lower, and it has the disadvantage of losing its shape retention. In order to eliminate this drawback, a method has already been proposed in which the non-stretched parts (for example, the neck and neck) and the stretched parts (for example, the body) of the polyester bottle are heat-treated (heat-set). This heat treatment method involves a so-called one-mold process in which a mold for stretch blow molding is maintained at a high temperature for heat treatment, heat treatment is performed within this mold following stretch blow molding, and the mold is cooled and removed from the mold. law (e.g. Tokkosho
59-6216), a mold for stretch blow molding is maintained at a high temperature for heat treatment, heat treatment is performed in this mold following stretch blow molding, the blow molded product is taken out, and then placed in a cooling mold. The so-called two-mold method (for example, Japanese Patent Application Laid-Open No. 57-53326) is known, in which the mold is expanded and then cooled in a secondary mold. (Problem to be solved by the invention) However, although conventional single-layer PET bottles have moderate gas barrier properties, considering the current state of technology and economic efficiency, The shape is still not completely satisfactory. A multilayer method has been proposed to improve the gas barrier properties of polyester, but it has not yet been put into practical use. has not been proposed. In addition, when heat treatment is performed in the stretch blowing process,
The molded product is cooled by passing cooling water into the mold to cool the blow mold, and the temperature of the molded product is cooled to a temperature at which it can be taken out from the blow mold. A heat-treated polyester bottle is obtained. However, in the former heat treatment method, heat treatment and internal cooling are performed in the same blow mold, and each has its own processing time, so the time occupied in one mold becomes long. This method requires 2 to 4 times longer molding time than normal stretch blow molding of polyester bottles, resulting in a significant decrease in production efficiency and an increase in manufacturing costs. Furthermore, when the heat treatment temperature is increased, it takes longer to cool the molded product to a temperature at which it can be removed from the mold, so there is a tendency to lower the natural heat treatment temperature.
This means that only bottles with low heat resistance and heat shrinkage resistance can be obtained. In addition, in the latter heat treatment method, two types of molds and two
This requires multiple stages of blowing, which increases the number of steps and equipment costs. The dimensions of the product must be smaller than the dimensions of the final molded product, taking into account the safety factor, and for this reason some expansion and stretching by secondary blowing must be performed. It is easy to cause corresponding thermal contraction. Furthermore, in this two-mold method,
There is also the problem that it is difficult to faithfully reproduce the shape of the mold cavity surface on the surface of the blow-molded product during secondary blowing. Therefore, the technical problem of the present invention is to overcome the above-mentioned drawbacks in the conventional method for manufacturing biaxially stretched heat-set polyester containers, use only one type of mold, and reduce the occupation time of the blow-molded product in the mold. The object of the present invention is to provide a method for producing a biaxially oriented polyester container having an excellent combination of heat shrinkage resistance and gas barrier properties at a high production rate while making the container as short as possible. (Means for Solving the Problems) According to the present invention, a multilayer preformed product is provided which includes inner and outer layers made of polyester mainly containing ethylene terephthalate units and at least one intermediate layer made of a gas barrier resin. The temperature is preheated or adjusted to the appropriate temperature for stretching, and the preform is subjected to biaxial stretch blow molding in a mold maintained within the heat-setting temperature range, and the blow molded product is heat treated, and then processed for blow molding. Switch the pressurized fluid to an internal cooling fluid, and cool the blow-molded article while keeping it in contact with the mold cavity surface to a temperature at which the blow-molded article will not lose its shape even when taken out of the mold, and then take the molded article out of the mold. As a result, a biaxially oriented polyester container having an excellent combination of heat shrinkage resistance and gas barrier properties can be manufactured at a high production rate and with a small number of steps. (Function) The present invention is characterized in that the gas barrier resin intermediate layer in the multilayer blow molded product acts as a heat insulating layer during heat treatment and cooling removal of the blow molded product, and the blow molded product is cooled from the inside with a cooling fluid. This is based on the new finding that the shape retention required for removal can be quickly obtained. In FIG. 1 for explaining the principle of the present invention, a multilayer blow-molded article 1 consists of a polyester inner layer 2, a polyester outer layer 3, and a gas barrier resin intermediate layer 4 located between these layers. At the stage of cooling after heat treatment, the polyester outer layer 3 is in contact with the mold 5 heated to the heat setting temperature and is heated, while the polyester inner layer 2 is in a cooled state in contact with the cooling fluid 6. In the present invention, since the gas barrier resin intermediate layer 4 acts as a heat transfer barrier layer, the temperature at which the polyester inner layer 2 can be taken out of the mold without losing its shape is maintained.
While generally cooled quickly to temperatures below 60°C,
An advantage is obtained that the temperature of the polyester outer layer 3 and the mold 5 in contact with it does not drop much by this inner layer cooling operation. Table 1 below shows the thermal conductivity of various resins.

[Table] From this result, gas barrier resins such as ethylene-vinyl alcohol copolymer (EVOH) have low thermal conductivity, and in particular, only 1/2 to 1/3 of the thermal conductivity of polyethylene terephthalate (PET). It becomes clear that there is no. That is, the ethylene-vinyl alcohol copolymer not only has gas barrier properties, but also acts as a heat conduction barrier. According to the present invention, the polyester inner layer is quickly cooled for removal from the mold so that it has sufficient shape retention, and the temperature of the mold surface required for heat treatment is not significantly lowered. ,
A single mold can be used to quickly heat treat and cool a stretch blow molded product for removal. (Operations and Effects of the Invention) According to the present invention, since only one type of mold and a single blowing operation are required, heat-set biaxial stretch blow molding can be performed with a small number of steps and a small equipment cost. In addition to being able to manufacture containers, the heat treatment time in the mold and the cooling time for removal from the mold are significantly shortened, the time occupied in the mold is significantly reduced, and heat shrinkage resistance and gas barrier properties are improved. Biaxially oriented polyester containers with excellent combinations can be produced at high production rates. Moreover, since the container obtained is produced using a one-stage blowing method, it has excellent surface shape reproducibility and also has excellent appearance characteristics such as aesthetic appearance and commercial value. In particular, in the two-mold method, two parting lines are placed on each side of the final container corresponding to the two split molds used, but according to the present invention, only one parting line is placed on the left and right sides, and the appearance characteristics are It is also excellent. (Description of preferred embodiments of the invention) In the present invention, thermoplastic polyesters include polyethylene terephthalate and copolyesters containing mainly ethylene terephthalate units and a small amount of modifying ester units that are known per se. used for the purpose of the invention. This polyester only needs to have a molecular weight sufficient to form a film. In addition, as a gas barrier resin, a copolymer obtained by saponifying a copolymer of ethylene and a vinyl ester such as vinyl acetate is used, and considering moldability and barrier properties, the ethylene content is 15%. Those having a saponification degree of 96% or more with a content of 50 to 50 mol%, particularly 25 to 45 mol% are advantageously used. Other resins that can be used include vinylidene chloride resin, high nitrile resin, xylylene group-containing polyamide resin, and high barrier polyester. Although not required, any adhesive known per se can be used to enhance the adhesion between the polyester layer and the gas barrier resin layer. Copolyester adhesives, polyamide adhesives, polyester-ether adhesives, epoxy-modified thermoplastic resins, acid-modified thermoplastic resins, etc. are used for this purpose. Next, as a method for manufacturing a multilayer parison including a thermoplastic polyester layer and a gas barrier resin layer, one method is to use a gas barrier resin as an inner layer and an outer layer, or a polyester resin as an inner and outer layer, respectively, and if necessary, use a polyester resin in both layers. A pipe is formed by coextrusion with an adhesive layer interposed between the resin layers, the multilayer pipe is cut to an appropriate length, one end of the pipe is fused and closed to form the bottom, and the top of the other end is sealed. A mouth and neck part having an opening and a fitting part or a screw part on the outer periphery are formed in the preform to form a multilayer preform. In addition, using a co-injection molding machine equipped with two or more injection machines and a co-injection mold, the inner and outer layers are made of polyester resin, and one or more layers of barrier resin are inserted in the middle to cover the inner and outer layers. A multilayer preform having a bottom and an opening can be obtained depending on the shape of the preform mold. In addition, a multi-stage injection machine equipped with three or more injection machines is used to first form a first inner layer preform, then transfer it to a second mold, inject an intermediate layer, and then inject an outer layer in a third mold. A multilayer preform can also be obtained by sequentially transferring multistage molds. In order to impart heat resistance to the preform obtained in this manner, the neck and neck portions having threaded portions, fitting portions, support rings, etc. may be crystallized and whitened by heat treatment at the preform stage, while biaxial stretching blowing described below After completing bottle molding, the unstretched portion of the mouth and neck may crystallize and turn white. The heat applied to the preform of the prepared multilayer preform injection machine, that is, the residual heat, is used to increase the temperature range to 85
The stretching temperature is adjusted to ~115°C or, in the case of a cold parison, reheated and preheated to the same stretching temperature range of 85-115°C. When biaxially stretching with a blow mold, the temperature of the blow mold is 120-230℃, preferably 130-230℃.
Heat treatment (heat setting) begins at the same time as the outer layer PET on the wall of the stretch-blown multilayer preform comes into contact with the inner surface of the mold in a heated mold at 210°C. After a predetermined heat treatment time, the blowing fluid is switched to the internal cooling fluid to start cooling the inner layer PET. The heat treatment time varies depending on the thickness and temperature of the blow molded article, but is generally on the order of 1.5 to 30 seconds, particularly 2 to 20 seconds. On the other hand, the cooling time
Although it varies depending on the heat treatment temperature and the type of cooling fluid, it is generally on the order of 1 to 30 seconds, particularly 2 to 20 seconds. Cooling fluids include various types of cooled gases, such as nitrogen, air, and carbon dioxide at -40°C to +10°C, as well as chemically inert liquefied gases such as liquefied nitrogen gas, liquefied carbon dioxide, and liquefied carbon dioxide. Trichlorofluoromethane gas, liquefied dichlorodifluoromethane gas, other liquefied aliphatic hydrocarbon gases, etc. are also used. This cooling fluid may also contain a liquid mist having a large heat of vaporization, such as water. By using the cooling fluids described above, significantly greater cooling rates can be obtained. The outer layer of the blow-molded product taken out from the mold is cooled by cooling or by blowing cold air.
Cools PET. In the present invention, the gas barrier intermediate layer should have an average thickness of at least 5 μm when used as a container in terms of blocking heat transfer, but it should not exceed 300 μm.
If it exceeds this, stretch formability tends to decrease. Generally, a range of 20 to 80 μm is preferred. In terms of shape retention during cooling and removal, the PET inner layer should also have a thickness of at least 25 μm,
A range of 25 to 70 μm is suitable. The inner layer/outer layer thickness ratio is preferably in the range of 1/3 to 1/1. However, this may not apply depending on the manufacturing method. Next, a method for manufacturing a thermoplastic polyester bottle according to the present invention will be explained with reference to the drawings. FIG. 2 shows a multilayer preform molded by co-extrusion molding or co-injection molding.
It consists of FIG. 3 shows a wall section of a multilayer preform, which includes an inner layer 2 and an outer layer 3 made of thermoplastic polyester, an intermediate layer 4 made of a gas barrier resin such as ethylene-vinyl alcohol copolymer, and an intervening layer between these layers. It consists of adhesive layers 10a and 10b. The preform shown in FIG. 2 is heated by hot air heating, infrared heating, high frequency heating, etc. to a temperature suitable for stretching. In this case the temperature range is 85-115℃,
Preferably it is 90-110°C. Next, the stretch blowing process (heat treatment process) will be explained using FIGS. 4 and 5. The mouth and neck of the preform 11 are held by lip cavities 21a and 21b, and the preform 11
The other parts are blow molds 23a, 2, which have a built-in heater 22 for heating to the desired heat treatment temperature.
The stretching rod 2 is placed in the cavities 24a and 24b of the preform 11, and
A mandrel 26 with 5 is inserted. The stretching rod 25 is vertically movable and a fluid passage 17 is provided between the stretching rod 25 and the mandrel 26. In the present invention, the blow molds 23a and 23b are
The preform 21, which has been heated to a desired heat treatment temperature of 110 to 230°C and whose temperature has been adjusted to the drawing temperature, is set in this mold, and while the tip of the drawing rod 25 is applied to the inside of the bottom of the preform 21, the preform 21 is drawn in the axial direction. At the same time, compressed gas is blown into the preform through the fluid passage 27 to expand and stretch it in the circumferential direction to form a blow-molded product 28 (FIG. 4). The stretching ratio is not particularly limited, but is approximately 1.5 to 3 times in the axial direction and 3 to 5 times in the circumferential direction. The molded blow-molded body continues to be molded onto the cavity surface 24 while the internal pressure of the compressed fluid is applied.
A and 24b are contacted and heat treatment is performed. Next, the compressed blowing fluid is switched to the cooling fluid, and the inside 29 of the molded body is filled with the cooling fluid through the fluid passage 27 to perform cooling for removal. The final molded product obtained in this way is, for example,
Even when hot-filled at high temperatures of 80°C or higher, there is no heat deformation or shrinkage, and a multilayer bottle with heat resistance, heat shrinkage resistance, and excellent transparency and gas barrier properties can be obtained. (Applications of the Invention) The container according to the present invention is a hot-packed product at a high temperature of 80°C or higher, contains carbon dioxide such as fruit juice or lager beer whose shelf life is desired to be extended, and is heat-treated (pastelized). It is particularly useful as a packaging container for contents that require pressure resistance and heat resistance. (Example) The present invention will be explained by the following example. Example 1 Polyethylene terephthalate (PET, temperature conductivity = 5.55×10 ^-4 m ² /hr.) was produced by coextrusion method.
and an ethylene-vinyl alcohol copolymer (EVOH, temperature conductivity = 2.00×10 ^-4 with an ethylene content of 30 mol% and a vinyl alcohol content of 70 mol%)
m ² /hr・), and a copolymer of 6 nylon and 66 nylon (66 nylon is 22
mol%, copolymer with 78 mol% of nylon 6, thermal conductivity = 2.85×10 ^-4 m ² /hr・) to form a multilayer pile, form a bottom neck, and have a weight of 59
A multilayer preform of g was obtained. The thickness ratio of the layers during pipe forming was PET (outer layer)/AD/EVOH/AD/PET (inner layer) = 10/0.2/1/0.2/5. However, AD
means adhesive layer. After preheating the multilayer preform to 100°C,
The inner volume of the cavity is heated to 145℃.
1580c.c.． After biaxial stretching blowing and heat setting for 12 seconds in the blowing mold, the blowing fluid was switched to internal cooling fluid (air adjusted to +5℃), fluid pressure was applied again for 9 seconds, and immediately By taking it out and letting it cool, the internal volume becomes 1500.
cc. molded into a bottle. Gas permeability The oxygen permeability _QO2 of the bottle of the present invention is 0.2cc/
^m2・day・atm・(Storage conditions: Humidity inside the bottle is 100
%RH・, the humidity outside the bottle was 60%RH., and the storage temperature was 22℃・). For comparison, a molded single-layer PET bottle (same weight, same internal volume) was measured under the same conditions as above, and the oxygen permeability QO was 4.4 cc/m ² ·day · atm ·. Heat resistance The internal volume according to the present invention is 1500c.c. The internal volume of the bottle was measured in advance (V ₀ ml), filled with 85°C hot water, cooled to room temperature, and the internal volume of the bottle was measured again (V ₁ ml). When the heat shrinkage rate of the bottle, S, is defined as S=(V ₁ /V ₀ −1)×100, S was −0.2%. Moreover, no change was observed in terms of shape. Example 2 Polyethylene terephthalate (PET, the temperature conductivity is the same as in Example 1) with an intrinsic viscosity of 0.75 was supplied to the main injection machine, and metaxylylene adipamide resin (SM/nylon manufactured by Toyobo Co., Ltd.) was supplied to the sub-injection machine. , temperature conductivity = 2.45×10 ^-4 m ² /hr・) and co-injected the multilayer preform, first, primary injection was performed for 1.3 seconds at a pressure of about 60 Kg/cm ² from the main injection machine.
Then, after stopping the injection of the PET for 0.1 seconds,
1.4 seconds after the start of PET injection, a predetermined amount of molten SM/nylon is injected in 0.8 seconds from the sub-injection machine at a pressure higher than the primary injection pressure of PET (approximately 100Kgcm ² ), and further SM/nylon is injected. from the end of
After a delay of 0.05 seconds, PET is injected from the main injection machine at a pressure lower than the primary injection pressure (approximately 30 kg/cm ² ), and the wall thickness is approximately 5 mm. A multilayer preform was molded. The weight of this refohm is approximately 59g, of which SM
Nylon was approximately 4.5% by weight. The multilayer preform was subjected to biaxial stretching blowing in the same mold under the same conditions as in Example 1, and was simultaneously heat set and cooled to have an internal volume of 1500 c.c.
Got a bottle of. Gas permeability The oxygen permeability, QO ₂ , of the bottle according to the invention is:
The concentration was 0.9 cc/m ² ·day · atm (storage conditions were the same as in Example 1). The QO ₂ of a single-layer PET bottle (same weight, same internal volume) tested for comparison was 4.4cc/m ²・day・
It was ATM・). Heat Resistance A heat resistance test (bottle shrinkage rate measurement) was performed using the same method as in Example 1 using a bottle according to the present invention having an internal volume of 1500 c.c. Bottle shrinkage rate (S)
was -0.1%. Moreover, no deformation was observed in terms of shape.

[Brief explanation of drawings]

FIG. 1 is an explanatory view showing the principle of the manufacturing method of the present invention, FIG. 2 is a side cross-sectional view of a preform used in the present invention, and FIG. 3 is an enlarged cross-sectional view showing the cross-sectional structure of the preform of FIG. FIG. 4 is a side sectional view for explaining the stretch-blowing process, and FIG. 5 is a side sectional view for explaining the heat-setting and cooling steps. 1 is a multilayer blow molded product, 2 is a polyester inner layer, 3 is a polyester outer layer, 4 is a gas barrier resin intermediate layer, 5 is a heated mold, 6 is a cooling fluid, 11 is a preform, 22 is a heater, 23
a and 23b are molds, 25 is a drawing rod, and 27 is a passage for blowing fluid and cooling fluid.

Claims (1)

[Claims] 1. Preheating or controlling the temperature of a multilayer preformed product containing inner and outer layers made of polyester mainly composed of ethylene terephthalate units and at least one intermediate layer made of a gas barrier resin to an appropriate stretching temperature of 85 to 115°C, The preform is subjected to biaxial stretch blow molding in a mold maintained at a heat-setting temperature range, and the blow molded body is heat treated, after which the pressurized fluid for blow molding is switched to an internal cooling fluid. , wherein the blow-molded body is brought into contact with the mold cavity surface and cooled to a temperature at which the blow-molded body does not lose its shape even when taken out from the mold, and then the molded body is taken out from the mold. Manufacturing method for stretched containers.