JPH0431286B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a heat-resistant multilayer stretched polyester container, and more specifically, a method for producing a heat-resistant multilayer stretched polyester container, and more specifically, a container made of a layer made of a thermoplastic polyester such as polyethylene terephthalate and a gas barrier resin. The present invention relates to a method for producing a multilayer stretched polyester container having excellent heat resistance and heat shrinkage resistance.

Prior Art and Technical Problems of the Invention Stretched bottles made of polyethylene terephthalate (PET) have transparency, impact resistance (drop strength), light weight, hygiene, appropriate gas barrier properties such as oxygen and carbon dioxide, and It has excellent pressure resistance and can be 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. Widely used.

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 mouth and neck part) and the stretched parts (for example, the body part) of the polyester bottle are subjected to heat treatment (heat setting). In this case, the stretched portion is heat-treated in the stretch-blowing step, but the non-stretched portion is normally heat-treated separately from the stretch-blowing step.

First, conventional single-layer PET bottles have moderate gas barrier properties, but considering the current state of technology and economical considerations, the type of content,
This is still not completely satisfactory due to the distribution format. A multilayer method has been proposed to improve the gas barrier properties of polyester, but it has not yet been put into practical use. It is not proposed.

Next, when heat treatment is performed in the stretch blowing process,
The blow mold temperature is maintained at a high temperature, and the polyester bottle wall that has been stretch-blown comes into contact with the blow mold and is heat treated, so the polyester bottle after heat treatment is at a high temperature, so even if it is removed from the mold immediately. The bottle cannot maintain its normal shape. That is, when manufacturing heat-treated polyester bottles using conventional methods, the blow mold
Since stretch blowing is performed while maintaining the temperature at ℃, the temperature of the molded product after stretch blow molding is high, so even if it is removed from the blow mold in that state, it will shrink so much that it will not be able to maintain its shape. It is.

Therefore, in order to mold a bottle of normal shape, the blow mold heated to a high temperature must be heated to a temperature at which the molded product can be taken out, for example, 60° C. or lower.

For this reason, after stretching and blow molding a preform (preformed product) that has been heated to the appropriate temperature for stretching while maintaining the blow mold at a temperature of 85 to 210°C, the compressed air for blowing after blow molding is used at a low temperature when taking out the molded product. Air, especially cooling air (e.g. -40 to -20℃
The molded product can be cooled by cooling the blow mold by passing cooling water into the mold to cool the molded product to a temperature at which it can be removed from the blow mold. By taking it out, a predetermined heat-treated polyester bottle is obtained.

However, in the above-mentioned heat treatment method, heat treatment and internal cooling are performed in the same blow mold, and each has its own required treatment time. This requires 2 to 4 times longer molding time than normal stretch blow molding of polyester bottles, resulting in a significant drop in production efficiency and an increase in manufacturing costs. Furthermore, if the heat treatment temperature is increased, it takes a longer time to cool down 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, resulting in bottles with low heat resistance and heat shrinkage resistance. become.

OBJECTS OF THE INVENTION An object of the present invention is to provide a multilayer stretched container that has excellent gas barrier properties and heat resistance, and has low thermal deformability.

Furthermore, another object of the present invention is to solve the contradictory processing methods of heat treatment and cooling within one blow mold in stretch blow molding of polyester containers.

Structure and Effects of the Invention According to the present invention, a multilayer parison (preform) including at least one layer made of thermoplastic polyester, at least one layer made of gas barrier resin, and optionally an adhesive layer is provided. This is a method of manufacturing multilayer containers by performing stretch blow molding and heat-resistant treatment (heat setting) in a blow mold.The method separates heat treatment and cooling, and uses a heated blow mold and a cooling mold. Heat-resistant treatment and cooling are performed separately, i.e., the polyester stretch blow molded product (primary molded product) is heated to 85 to 230°C.
Heat treatment is performed in a primary blow mold that is heated to a desired heat treatment temperature, and then the temperature of the primary molded product is controlled to a temperature below the glass transition point of polyester, preferably 5 to 30°C. By performing cooling within the secondary mold, the respective heat treatment effects and cooling effects can be efficiently exerted, thereby improving the productivity of polyester containers with excellent heat resistance and heat shrinkage resistance.

In the present invention, as the thermoplastic polyester, polyethylene terephthalate, a copolyester mainly containing ethylene terephthalate units, and also containing a small amount of a known modifying ester unit, etc. are used for the purpose of the present invention. This polyester may also 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, polyester-ether adhesives, epoxy-modified thermoplastics, acid-modified thermoplastics, and the like 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 threaded part on the outer periphery is 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 first forms a first inner layer preform, then transfers it to a second mold, injects an intermediate layer, and then sequentially injects an outer layer in a third mold. It is also possible to obtain a multilayer preform by transferring a multistage mold to a mold.

In order to impart heat resistance to the preform obtained in this way, the mouth and neck parts including the threaded parts, fitting parts, support rings, etc. may be crystallized and whitened by heat treatment at the preform stage, while the biaxial stretching described below After the blowing process is completed and the bottle is formed, the unstretched mouth and neck area may crystallize and turn white.

Using the heat given to the preform of the prepared multilayer preform injection machine, that is, preheating, the temperature range is
Adjust the temperature to 85 to 110°C, or reheat in the case of a cold parison, and preheat to the same temperature range of 85 to 110°C, and perform biaxial stretching with the primary blow mold at 85 to 230°C. The mold is heated preferably at 115 to 210° C., and heat treatment (heat setting) is started at the same time as the PET on the wall of the stretch-blown multilayer preform comes into contact with the inner surface of the mold. After a predetermined time, when the stretching blow in the same mold is released, the multilayer container shrinks and deforms slightly due to the heat. The deformed preform is transferred to a second blow mold or cooling mold cooled to a temperature below the glass transition point of the thermoplastic polyester, preferably from 5 to 30°C, and in the second blow mold. Blow mold again. The second blow-molded container is cooled and solidified at a temperature below the temperature at which heat shrinkage deformation occurs, and the container no longer loses its shape even when taken out from the mold.

In biaxial stretch blow molding of multilayer parison,
Heat treatment is performed in the first blowing step, cooling is performed in the second blowing step, and by separating the heat treatment and cooling, it is recognized that the heat setting effect and production efficiency are improved.

The stretched polyester container, which is a secondary molded product formed in this manner, has improved heat resistance and heat shrinkage resistance by minimizing its thermal properties.

For heat treatment (heat setting) of the container during biaxial stretching blowing, only one blow mold is provided, and that mold is used as a heating mold to biaxially stretch the preform. There is also a method of cooling the container wall with cooling air, etc., and removing it from the mold at a temperature that does not cause deformation.
Such a method is unreasonable in terms of molding efficiency because it requires both heat setting and cooling of the container in one mold.

That is, the temperature of the preform is adjusted to a temperature suitable for stretching polyester, and stretch blowing is performed in the primary blow mold, and the wall of the primary molded product is heated to a desired temperature in the cavity of the primary blow mold. The heat setting effect progresses as the contact time with the mold progresses, but from the viewpoint of productivity, the normal blowing time is 5 to 20 seconds, so the mold is heated within this blowing time. During the contact time, when the blow molding is completed and the product is removed from the mold, the temperature of the primary molded product molded from the preform is quite high, causing shrinkage. The amount of shrinkage varies depending on the temperature of the mold, blowing time, stretching ratio, etc. That is, the higher the temperature of the mold and the longer the blowing time, the smaller the amount of shrinkage.
As long as blow molding is performed for a limited time of about 20 seconds, the primary molded product will inevitably shrink after being removed from the mold.

Therefore, the present inventors proposed that heat treatment and cooling in the stretch blowing process be performed separately using a primary blow mold and a secondary blow mold, and further,
A primary blow mold for heat setting is prepared in which the primary blow mold cavity is set to a volume ratio of 80 to 110% of the secondary blow mold cavity, and pre-blowing (stretch blowing) is performed within the mold. If the obtained primary molded product is further blown and cooled in a secondary blow mold, production efficiency is improved.
Moreover, the present invention was achieved by discovering that the heat resistance and heat shrinkage resistance of the final molded product (secondary molded product) are also improved.

Embodiments of the Invention Next, a method for manufacturing a thermoplastic polyester bottle according to the present invention will be described with reference to the drawings.

FIG. 1 shows a multilayer preform molded by co-extrusion molding or co-injection molding, and the preform 1 consists of a neck part 2, a threaded part 3, a support ring (neck ring) 4, a long cylinder part 5, and a bottom part 6. There is.

FIG. 2 shows a cross section of the wall of a multilayer preform, which includes an inner layer 7 and an outer layer 8 made of thermoplastic polyester, an intermediate layer 9 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. 1 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 85-120℃,
Preferably it is 90-110°C.

Next, the first stretch blowing step (heat treatment step) will be explained using FIGS. 3 and 4.

The mouth and neck of the preform 1 are held in lip cavities 11a and 11b, and the other parts of the preform 1 are held in a primary blow mold 13a, which has a built-in heater 12 to heat it to a desired heat treatment temperature.
The stretching rod 1 is placed in the cavities 14a, 14 of the preform 13b, and the stretching rod 1
A mandrel 16 with 5 is inserted. The stretching rod 15 is vertically movable, and a blowing fluid passage 17 is provided between the stretching rod 15 and the mandrel 16.

In the present invention, the primary blow mold 13a, 1
3b is heated to a desired heat treatment temperature of 85 to 230°C, and the preform 1 whose temperature has been adjusted to the drawing temperature is set in this mold, and while the tip of the drawing rod 15 is applied to the inside of the bottom of the preform 1. While stretching in the axial direction, compressed air is blown into the preform through the fluid passage 17 to expand and stretch it in the circumferential direction to form a primary molded product 18.

This primary molded product 18 is immediately inserted into cavities 20 of secondary blow molds 19a and 19b shown in FIG.
a, 20b. Secondary blow mold 19
A and 19b are provided with a cooling water passage 21, and the temperature is controlled to be below the glass transition point of polyester, particularly at a temperature of 5 to 30°C. Further, a lower portion forming mold 22 is arranged at the lower end.

The primary molded product 18 placed in the secondary blow molds 19a, 19b is again stretched in the axial direction by the stretching rod 15, and expanded and stretched in the circumferential direction by blowing, resulting in a final molded product, a multilayer stretched bottle. 23 is molded.

The gas barrier resin used in the present invention includes:
Ethylene-vinyl alcohol copolymer, high nitrile resin, vinylidene resin, polyamide,
High gas barrier polyester and the like can be suitably used.

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.

Application of the Invention The container according to the present invention is a hot-pack product at a high temperature of 80°C or higher, and contains carbon dioxide such as fruit juice or lager beer whose shelf life is to be extended, and requires heat treatment (pastelization). It is particularly useful as a packaging container for contents that require pressure resistance and heat resistance.

Example The invention is illustrated by the following examples.

Example 1 Polyethylene terephthalate (PET), 30 mol% ethylene, vinyl alcohol by coextrusion method
Using 70% ethylene-vinyl alcohol copolymer (EVOH) and a copolymer of nylon 6 and nylon 66 (6-6 nylon 22
mol%, 6 nylon 78 mol% copolymer) to form a multilayer pipe, forming the bottom neck and weighing 59
A multilayer preform of g was obtained.

The thickness ratio of the layers during pipe forming is: PET (outer layer) / AD / EVOH / AD / PET (inner layer) = 10 / 0.2 / 1 / 0.2 / 5, where AD means the adhesive layer.

It was hot.

The multilayer preform was preheated to 100℃ and then heated to 145℃.
The pre-blown preform was cooled to 20°C and had an internal volume of 1500 c.c. The pre-blown preform was then heated to 20°C and had an internal volume of 1500 c.c. The bottle was transferred to the second blow mold shown in c. and stretched and blown again for 9 seconds to obtain a bottle with an internal volume of 1500 c.c.

Gas permeability The oxygen permeability _QO2 of the bottle of the present invention is 0.4cc/
m ²・day・atm (storage conditions: 100% RH inside the bottle, 60% RH outside the bottle, temperature 22°C) (Reference QO ₂ of a single-layer PET bottle with the same weight, same volume, and same conditions is 4.4cc/
^m2・day・atm).

Heat Resistance The internal volume of a bottle according to the present invention with an internal volume of 1500 c.c. was measured in advance (V ₀ ml), filled with hot water at 85°C, left to cool to room temperature, and the internal volume of the bottle was measured again ( (V ₁ ml) Bottle heat shrinkage rate S = V ₁ -V ₀ /V ₀ ×100, S was -0.3%.

Also, no deformation was observed in terms of shape.

Example 2 Polyethylene terephthalate (PET) with an intrinsic viscosity of 0.75 is supplied to the main injection machine, ethylene vinyl alcohol copolymer (EVOH) containing 70 mol% of vinyl alcohol is supplied to the sub-injection machine, and a multilayer preform is co-injection molded. Approximately from the main injection machine at first
Primary injection is performed for 1.3 seconds at a pressure of 60Kg/ ^cm2 , then 0.1
After stopping the injection of the PET for 1.4 seconds after starting the injection of the PET, a predetermined amount of molten EVOH is injected from the sub-injection machine in 0.8 seconds at a pressure higher than the primary injection pressure of the PET (approximately 100Kg/cm ² ). Inject and further
After a delay of 0.05 seconds from the end of EVOH injection, the pressure is lower than the primary injection pressure (approximately 30Kg/cm ² ) from the main extruder.
A multilayer preform of two types and three layers with a wall thickness of 5 mm was molded by injecting PET. The EVOH content was approximately 59g and was 3.5% by weight.

A bottle with an internal volume of 1500 c.c. was obtained under the same conditions as the multilayer preform Example 1.

Gas permeability The oxygen permeability QO ₂ of the bottle according to the invention is 1.2
cc/m ²・day・atm (storage conditions: 100% RH in bottle)
60% RH temperature outside the bottle 22℃)
QO ₂ was 4.4cc/ ^m2・day・atm).

Heat Resistance The internal volume of a bottle according to the present invention with an internal volume of 1500 c.c. was measured in advance (V ₀ ml), filled with hot water at 85°C, left to cool to room temperature, and the internal volume of the bottle was measured again ( (V ₁ ml) Bottle shrinkage rate S=V ₁ −V ₀ /V ₀ ×100, S was 0.3%.

Also, no deformation was observed in terms of shape.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the preform used in the present invention, Fig. 2 is a sectional view of the wall of the preform shown in Fig. 1, and Figs. Cross-sectional views before and after blow molding, and FIG. 5 is a cross-sectional view of final blow molding in the second stretch blowing (stretch blowing/cooling) step. Reference number 1 is preform (preformed product), 1
1a, 11b are lip cavities, 13a, 13
b is a primary blow mold, 15 is a drawing rod, 18 is a primary molded product, 19a and 19b are secondary blow molds, 22 is a bottom forming mold, and 23 is a bottle.

Claims (1)

[Scope of Claims] 1. At least one layer made of polyester mainly containing ethylene terephthalate units, and at least one layer made of gas barrier resin;
The multilayer preform, including the adhesive layer, is heated to 85°C
Preheat the polyester stretching temperature to 110°C and heat the preheated multilayer preform to 85°C to 230°C.
Biaxial stretch blow molding is performed in the primary blow mold maintained at a temperature range of °C, and the blow molded product is heat treated, and the heat treated blow molded product taken out from the primary blow mold is It is characterized by stretch-blowing and cooling the blow-molded product in a secondary blow mold maintained at a temperature range of 5°C to 30°C, and taking the formed container out of the secondary mold. A method for manufacturing a heat-shrinkable stretched polyester container. 2 The primary blow mold is 80-110% of the secondary mold.
The method for producing a heat-shrinkable stretched polyester container according to claim 1, wherein the volume ratio is .