JPS60157826A - Manufacture of multilayer drawn bottle - Google Patents

Abstract

PURPOSE:To obtain the resin bottle excellent in gas barrier-property by biaxially-oriented blow molding the multilayer pipe formed by coextruding a polyester family resin with a specified ethylene-vinyl alcohol copolymer. CONSTITUTION:Ethylene-vinyl alcohol copolymer having ethylene component equal to or less than 50mol% is used as a gas barrier resin layer, and polyester family resin mainly consisting of ethylene terephthalate unit is used as an inner layer, an outer layer or an inner and outer layers which are to become a base material. If necessary, an adhesive resin is caused to intervene between said layers. A multilayer pipe is formed, coextruding said layers in the range of 1.1:1-5:1 by the ratio of the inner layer to the outer layer. One end of said pipe is sealed, and a neck part is formed at other end thereof. Thus, a preform is made. The preform is blow molded into a bottle at 80-120 deg.C. Preferably, the nozzle 1 provided with the path 2 for a polyester inner layer, an adhesive path 3a, a gas barrier resin path 4, an adhesive path 3b and the part 5 for a polyester outer layer, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer stretched bottle, and more specifically, it is provided with a polyester layer and an ethylene-vinyl alcohol copolymer layer, and has excellent temperature resistance and gas permeability (gas barrier). The present invention relates to a method for manufacturing a multilayer stretched bottle with excellent properties.

As is well known, polyester stretch-blow-molded bottles have long been used for containers for carbonated beverages such as beer, wine, and whiskey due to their characteristics such as toughness, lightness, transparency, pressure resistance, and gas barrier properties. It has also come to be widely used as packaging containers for sauces, detergents, cola, cider, beer, etc. However, polyester bottles, which are said to have excellent gas barrier properties among plastic containers, have a significantly inferior gas barrier when compared to metal cans, glass bottles, etc. when it comes to preserving carbonated beverages and fruit juice drinks. The reality is that you can't get it. In other words, metal can walls and glass bottle walls have zero performance in terms of gas permeation, but polyester is superior from a gas barrier standpoint.

It has some gas permeability such as oxygen gas and carbon dioxide gas. Therefore, although the newly appeared stretched polyester bottles have characteristics not found in other materials, such as transparency, light weight, toughness, and pressure resistance, they cannot necessarily be said to be excellent materials in terms of gas barrier properties, so the contents, such as those containing carbon dioxide, cannot be said to be excellent materials. The shelf life of products packaged with beverages, beer, fruit juice, etc. is limited by the expiration date, and storage conditions are limited to large containers with mild storage conditions, so containers cannot be considered satisfactory when distributing products in the market. be.

However, the demand for improved gas barrier properties for this type of polyester container inevitably arises, and if this cannot be satisfied with a single-layer polyester container, a better method is needed to improve the gas barrier property. - It becomes necessary to give gender.

Examples of ways to improve the gas barrier properties of single-layer polyester containers include coating the container surface with gas-impermeable aluminum foil or glass foil, coating the inner and outer surfaces of the container with gas-barrier resin paint, and other gas barrier coatings. Multi-layering by co-injection (multi-stage injection molding method) or co-extrusion method using a thermoplastic resin can be considered.

The present invention employs, among the aforementioned methods for improving the gas barrier properties of polyester bottles, a method in which a gas barrier resin and a polyester resin are coextruded to form a pipe, and then stretch blow molding is performed.

With the method of covering the surface of polyester bottles with aluminum foil, etc., it is difficult to cover the neck, shoulders, and bottom of the bottle, and depending on the shape of the container (e.g., spherical), there are drawbacks such as significantly damaging the appearance. Furthermore, with the method of coating the inner and outer surfaces of the bottle with gas barrier resin, it is difficult to coat the gas barrier resin layer sufficiently thickly, and the gas barrier resin layer may peel, craze, or crack. There was a drawback that this occurred.

Further, in the co-injection molding method, there is a complicated molding operation in that injection must be performed for each resin layer while changing the mold.

The present invention relates to a method for manufacturing a multilayer stretched bottle that eliminates the above-mentioned drawbacks and is suitable for accommodating an inner container containing a large amount of water, and basically involves stretching and molding a multilayer polyester with improved gas barrier properties. Since the purpose is to form a bottle, it is necessary to obtain a multilayer preform as an intermediate product necessary for stretch molding, and to make a multilayer pipe, which is a product in the pre-stage of the preform, with an ethylene vinyl alcohol copolymer as the middle layer and an outer layer. It is formed with a five-layer structure in which the inner layer is made of polyester and an adhesive layer is interposed therebetween, and this preform is heated to a stretching temperature and biaxially stretch blow molded.
More specifically, it is a method for producing a multilayer stretched bottle, in which a layer to be a gas barrier resin layer is made of an ethylene-vinyl alcohol copolymer (EVO) containing 50 mol% or less of ethylene.
H), a polyester resin mainly composed of ethylene terephthalate units is used for the inner layer, outer layer, or inner and outer layers that are to be the base, and if necessary, an adhesive resin (A) is used between them.
D), a multilayer pipe is formed by coextrusion with the ratio of the inner layer and the outer layer in the range of 1.1:l to 5:l, this pipe is formed, and one end of this pipe is fused and closed. At the same time, the other end is formed at the bottom part, and the other end is formed at the neck and neck part.The obtained preform is heated to an appropriate stretching temperature of 80 to 120"C, and then biaxially stretched in the axial direction and the circumferential direction in the blow molding mold. The present invention relates to a method for producing a multilayer stretched bottle characterized by stretch blow molding.

According to the present invention, an advantage is achieved in that the gas barrier properties of the multilayer stretched polyester bottle having the above structure can be economically improved.

The improvement in gas barrier properties of the multilayer stretched polyester bottle according to the present invention is mainly due to the excellent gas barrier properties of the ethylene-vinyl alcohol copolymer, but this ethylene-vinyl alcohol copolymer also has humidity dependence. The disadvantage is that it is large. That is, in general, the higher the vinyl alcohol content of the ethylene-vinyl alcohol copolymer pair, the higher the gas barrier properties, but the greater the humidity dependence.
Conversely, the higher the ethylene content, the lower the gas barrier properties, but the lower the humidity dependence. Here, we have selected a material with a low ethylene content and high gas barrier properties, so in order to maintain the gas barrier properties, the ethylene-vinyl alcohol copolymer layer must be included in the polyester multilayer layer. Therefore, it is desirable to keep the relative humidity as low as possible.

On the other hand, if we consider the humidity conditions inside the body wall of a multi-layered polyester bottle filled with soft drink and sealed, the relative humidity at the point in contact with the water-based beverage on the inside of the bottle is considered to be 100%, while the outside surface of the bottle is exposed to outside air. Humidity varies depending on the season, weather, and storage location conditions, but on average it is approximately 60% RIB.
(relative humidity). Suppose the inner wall of the bottle is 100% R.
Assuming that the outer wall of the H bottle is 60%, experiments have shown that the relative humidity within the bottle wall is determined approximately linearly depending on the position within the thickness between the inner and outer layers. That is, if the barrier layer is located exactly in the middle of the bottle wall, there will be approximately 80% RH, with higher relative humidity further inward and lower relative humidity outside this.

As the relative humidity changes depending on the position of the bottle wall, the gas barrier properties (blocking properties against oxygen, carbon dioxide, etc.) of the ethylene-vinyl alcohol copolymer used as the intermediate gas barrier layer also change depending on the position within the bottle wall. .

The gist of the present invention is to maintain the extremely excellent gas barrier properties of the ethylene-vinyl alcohol copolymer (ethylene content: 50 mol% or less) by selecting the lowest possible relative humidity for multilayer polyester. More specifically, the layer structure of the bottle wall is composed of outer layer polyester/AD/EVOH/AD/inner layer polyester, where outer layer; inner layer = 1: 1.1.
The ratio should be from 1:5 to 1:5, preferably from 1:2 to 1:3, and a multilayer pipe that will be the primary molded product should be formed with such a ratio (the layer ratio of the pipe and the layer ratio of the stretched blow bottle should be on average There is no particularly large difference).

In the thus formed multilayer stretched polyester bottle, the middle layer of ethylene-vinyl alcohol copolymer in the wall is closer to the outer layer, and when the content is an aqueous beverage, the relative humidity is lower than that of the inner layer, and the relative humidity is lower than that of the inner layer. It has been experimentally revealed that the gas barrier properties of EVOH can be maintained by lowering the amount of gas. From this point of view, it is logical that it is better for the intermediate EVOH layer to be located at or as close to the outer surface as possible from the beginning, but this position may impede the cooling effect during pipe forming or cause temporary cracks in the multilayer stretch blower. In the present invention, the intermediate layer EVO
Such a layer position of H is not selected.

In particular, placing ethylene-vinyl alcohol copolymer on the outer surface or in a position in contact with the outer surface during pipe forming impairs the cooling effect of the pipe, so it is necessary to increase the number of natural cooling layers without increasing the length of the pipeline. This results in unavoidable drawbacks. On the other hand, placing the intermediate ethylene-vinyl alcohol copolymer layer inside the middle position of the bottle wall will impair the excellent gas barrier properties of EVOH as mentioned above, so it is necessary to avoid increasing the thickness of the EVOH layer. Therefore, it is not economical, so to speak.

As explained in the examples below, the polyester outer layer:
When the ratio of the inner layer was 1:2 and 2:1, a difference in oxygen gas barrier property of 6 to 2 times was observed, and the oxygen permeability was clearly lower in the outer layer. This tendency was also the same for carbon dioxide gas barriers.

In the present invention, as the polyester constituting the inner and outer layers, polyethylene terephthalate, a copolyester mainly containing ethylene terephthalate units, and a small amount of a known modifying ester unit, etc. are used for the purpose of the present invention. Ru. This polyester only needs to have a molecular weight sufficient to form a film.

In addition, regarding the ethylene-vinyl alcohol copolymer used as the gas barrier intermediate layer, as mentioned above, the gas barrier property is less affected by the relative humidity depending on the layer position with the vinyl alcohol copolymer with a large ethylene component. Although it is clear that even if the humidity dependence is large, an ethylene-vinyl alcohol copolymer with a low ethylene component and a low absolute value of gas permeability is preferable in terms of providing I\gas barrier properties. It is particularly advantageous in the present invention to use an ethylene-vinyl alcohol copolymer with a low ethylene component and low gas permeability. A copolymer obtained by saponifying a polymer is used, and considering moldability and barrier properties, the ethylene content is 15 to 50 mol%.
Particularly, those having a saponification degree of 25 to 45 mol% and a saponification degree of 96% or more are advantageously used. The molecular weight of this copolymer may be any as long as it has film-forming ability.

To enhance the adhesion between the polyester layer and the ethylene-vinyl alcohol copolymer layer, any adhesive known per se can be used.

Copolyester adhesives, polyester-ether adhesives, epoxy-modified thermoplastics, acid-modified thermoplastics, and the like are used for this purpose.

Polyester substrate (PET), ethylene-vinyl alcohol copolymer (EVOI), adhesive layer (AD) can be used in various layer configurations, PET/EVOH/P
E.T.

It can be used in a layered structure such as PET/AD/EVOH/AD/PET.

The thickness of the layer can vary, but generally PET:
A thickness ratio of EVOH=2:1 to 30:1, especially 4:1 to 15:1 is preferable, and when an adhesive layer is used, PET:AD=5:1 to 10:1, especially 1
The thickness ratio is preferably in the range of O:l to 50:l.

The present invention will be explained in detail below based on specific examples shown in the accompanying drawings.

In FIG. 1 showing the overall arrangement of the molding machine used in the method of the present invention and FIG. 2 showing the detailed structure of the die, the multilayer die 1 has a polyester inner layer passage in order from the center outward. 2. An adhesive passage 3a, a gas barrier resin passage 4, an adhesive passage 3b, and a polyester outer layer passage 5 are provided. The polyester inner and outer layer passages 2 and 5 are connected to a polyester extruder (main extruder) 6 via a gear pump 7 and a branch channel 8. In addition, the adhesive passages 3a and 3b are connected to an adhesive extruder (
The sub-extruder 4ilA) 9 and the gas barrier resin passage 4 are connected to an extruder for gas barrier resin (sub-extruder B) io, respectively.

The resin supplied into the die from each resin passage is laminated within the die in the order of polyester inner layer/adhesive layer/gas barrier resin intermediate layer/adhesive layer/polyester outer layer, and passes through the die orifice 11 into the shape of a multilayer pipe 12. is pushed out. This resin pipe 12 is guided into a sizing former 13, its diameter is adjusted to a predetermined size, and then guided into a cooling tank 14 containing cooling water, where the molten pipe is cooled and solidified. The pipe is pulled out of the cooling tank by a pulling machine 15, and cut into a predetermined size by a cutter 16 to become a pipe for forming a preform.

In the present invention, an inert gas or an inert gas containing water spray is actively passed into the pipe to be melt-extruded. For this purpose, in FIG. 2, an inert gas supply pipe 17 and a water supply pipe 18 are provided on the central axis of the die l so as to pass through the die. In the specific example shown in Figure 2,
The pipe 17 and the pipe 18 are coaxially provided, and the small diameter pipe 17 serves as an inert gas passage, and the annular space between the large diameter pipe 18 and the pipe 17 serves as a water passage. Pipe 17 and pipe 18 are connected at opposite ends of die orifice 11 to a source 18 of an inert gas such as nitrogen and a source 20 of water.
The pipe 18 at the other end is narrowed to a small diameter to form a nozzle 21. Thus, when the water supply source 0 is closed and gas from the inert gas source 19 is supplied to the pipe 17, the inert gas is filled into the resin pipe 12 from the nozzle 21, and the inert gas The resin pipe 12 is cooled from the inner surface by the gas. Similarly, water supply source 20
When both are supplied from the inert gas source 19,
The resin pipe 12 is filled with inert gas containing water spray through the nozzle 21, and the resin pipe 12 is cooled from the inner surface side more efficiently.

FIG. 3 shows a preferred multilayer pipe 21 made in accordance with the present invention, comprising inner and outer layers 22 and 25 of polyester, an intermediate layer 24 and a rear layer 24 of ethylene-vinyl alcohol copolymer. Adhesive layer 23a interposed between these.

23b.

It has already been pointed out that it is important to manufacture pipes by coextrusion, but in order to prevent the polyester from becoming opaque, extruded pipes are rapidly cooled by immersion in water, etc., and an inert material is added inside the pipe. As already pointed out, it is important to allow gas to pass through.

After cutting this pipe to a certain size, one end of the pipe is heated and melted, and then pressed with a male and female mold having a cavity and protrusion corresponding to an arbitrary bottom shape, such as a semicircular shape, as shown in Fig. 4. A bottom portion 26 is formed as shown.

Next, the other end of this pipe 2 is also heated and subjected to pressing, stretching, blow molding, etc. in a desired mold to form an opening 27 at the upper end and a neck ring ( A preform 30 having a fitting portion, a screwing portion, and a locking portion for fitting with a lid such as a support ring 29 is formed.

The order of forming these preforms does not matter, and they may be carried out in the above order or in the reverse order, or may be carried out simultaneously.

The method described above has the feature that no excess resin is generated when a preformed product is obtained from a multilayer pipe.

In the next process, the above preformed product is heated using hot air, an infrared heater,
The multilayer preform is preheated to the appropriate temperature for stretching using high-frequency dielectric heating or the like. In this case the temperature range is 85''~120℃
It is preheated to the stretching temperature of the polyester resin, preferably between 95°C and 110°C.

6 and 7 for explaining the stretch blow molding operation, a mandrel 31 is inserted into the mouth of a preform 30, and the mouth is inserted into a pair of split molds 32a, 32b.
Hold it between the two. A vertically movable stretching rod 33 is provided coaxially with the mandrel 31, and between this stretching rod 33 and the mandrel 31 there is an annular passage 34 for the injection of fluid.

The tip 35 of this stretching rod 33 is attached to the bottom 2 of the preform 30.
6 and moves the stretching rod 33 downward to stretch it in the axial direction, and at the same time blow fluid into the preform 30 through the passage 34, and use this fluid pressure to stretch the preform in the circumferential direction. Expand and stretch.

By performing axial stretching and circumferential stretching at the same time or almost simultaneously using a pipe manufactured by the uninvented method, even if the ethylene-vinyl alcohol copolymer layer has a high vinyl alcohol content, it is possible to A multilayer container that can be stretched at low temperatures and has excellent transparency can be obtained.

This means that even ethylene-vinyl alcohol copolymers containing high vinyl alcohol are extremely difficult to stretch.
In stretching a film, even if the stretching temperature is appropriate, if the film is stretched sequentially in the vertical axis and then in the horizontal axis, the film will burst in the middle as described above. Furthermore, in stretch blow molding of multilayer pipes made of polypropylene and ethylene-vinyl alcohol copolymer, it is finally possible to stretch the ethylene-vinyl alcohol copolymer layer within the multilayer at a fairly high temperature range of 140' to 165°C. Considering the fact that polyester resin temperature range 856~1200C5, 95''~11
It is surprising that an ethylene-vinyl alcohol copolymer can be biaxially stretched in a temperature range as low as 0°C.

The reason for this is that co-stretching is performed with the ethylene-vinyl alcohol copolymer layer placed on the polyester layer.
Moreover, it is presumed that this is because delamination between both resin layers is suppressed during co-stretching, and biaxial stretching is performed simultaneously and in a well-balanced manner.

The thus obtained multi-layer stretched polyester bottle 36 shown in FIG. 8 has gas barrier properties that are superior to other plastic bottles with excellent transparency and are still much higher than polyester (stretched PET) single bottles. Its gas barrier properties can be adjusted5) accordingly, and the bottle also has pressure resistance, making it extremely easy to fill and store carbonated beverages, such as beer, cola, and citrus. Yes, even when used containers are disposed of and incinerated, the gas generated is almost only carbon dioxide and water, and no harmful gases are generated.They are easily incinerated, and have a transparency comparable to that of glass bottles, and a gas barrier. The present invention provides an ideal container that is lightweight and wave-resistant while having high pressure resistance.

Furthermore, the multilayer stretched polyester bottle according to the present invention can be applied in any of colored, uncolored, transparent, and opaque forms.

Examples will be described below.

Example: 90mm main extruder, its attached gear pump, and 40mm main extruder
mm auxiliary extrusion I! 3 types and 5 using 2 extruders, total of 3 extruders
Each resin is merged into a polycyclic shape using a die head for forming layered pipes, the molten pipe is extruded, passed through a sizing former to determine the dimensions, passed through a cooling tank where the outer surface of the pipe is cooled with a water stream, and a take-off machine, and then cut to a fixed size with a cutter. A pipe forming machine was used to cut the pipe.

The main extruder was filled with PET having an intrinsic viscosity (IV value) of 1.0, and the auxiliary extruder 1 was filled with an ethylene-vinyl alcohol copolymer (trade name: EVAL) containing approximately 30 mol% ethylene. From No. 2, the ester adhesive was supplied to each multilayer die via a gear pump, and the layer ratio was changed from the outer layer side to PET/AD/EVOH/AD/PET 50:5:
The pipes were formed with an average ratio of 15:5:100 and 100:5:15:5:50. The obtained pipes each had an outer diameter of 30 mm.

Inner diameter 23a+m, thickness 3. ? This is a multi-layer regular pipe with a weight of 59 g.

The lower end of each pipe is heated to fuse and close the pipe into a semicircular sphere, the other end is heated and formed into a neck and neck part with a threaded connection, and the obtained preform is preheated to about 98°C, Stretch and blow vertically and horizontally using a blowing mold to create a volume of 1.51.
A cylindrical bottle was obtained.

The average wall thickness of the body of the same bottle was about 290 JL, the average wall thickness of the middle layer ethylene-vinyl alcohol copolymer was 24 pL, and the thickness of each adhesive layer was about 8 JL.

The relative humidity of these two types of bottles was set to 60% RH,
The amount of oxygen permeation when the storage condition was 35°C was as follows.

n73 In other words, the oxygen permeation rate of the EVOH layer closer to the outer surface is 2/3 to 1/2 lower than that of the EVOH layer closer to the inner surface.If EVOH is placed closer to the outer surface, the thickness of the intermediate layer may be made thinner. The result was obtained.

In addition, when the same bottle as above was filled with water containing 4.0 gas porium and sealed and the carbon dioxide loss was measured under storage conditions of 22°C, the period (shelf life) during which the carbon dioxide loss was 15% was It was as shown in the table below.

This clearly shows that the carbon dioxide gas loss is slower in the case where EVOH is placed closer to the outer surface.

[Brief explanation of the drawing]

Fig. 1 is a plan view of the multilayer pipe forming apparatus, Fig. 2 is a sectional view of the multilayer die, Fig. 3 is a sectional view of the multilayer pipe used in the present invention, and Figs. 4 and 5 are the bottom and A cross-sectional view of a preformed product with a neck formed therein; FIGS. 6 and 7 are a cross-sectional view of the preformed product held in a blow mold; a cross-sectional view before blow molding; and a cross-sectional view after blow molding; FIG. is a multilayer stretched bottle formed according to the present invention. Reference number 1 is a multilayer die, 6 is a main extruder, 9°10 is a sub-extruder, 12 is a multilayer pipe, 13 is a sizing former, 114 is a cooling tank, 16 is a cutter, 17 is an inert gas supply pipe, 18 is Water supply pipe, 21 is a pipe, 26
27 represents the bottom, 27 represents the open end, 30 represents the preform, and 36 represents the multilayer stretched bottle. Patent applicant: Toyo Seikan Co., Ltd. Figure 3 Figure 5

Claims (1)

[Claims] A method for manufacturing a multilayer stretched bottle, which comprises using an ethylene-vinyl alcohol copolymer with an ethylene component of 50 mol% IFF in the layer that is to become the gas barrier resin layer, and ethylene terephthalate units in the inner layer, outer layer, or inner and outer layers that are to become the base material. Multilayer pipes are produced by coextrusion using polyester resin as the main material, with an adhesive resin interposed between them as necessary, and with a ratio of the inner layer to the outer layer ranging from 1.1:1 to 5:1. One end of this pipe is fused and closed to form the bottom part, and the other end is formed as the neck and neck part.The obtained preform is heated to an appropriate stretching temperature of 80 to 120°C to form a blow molding mold. A method for manufacturing a multilayer stretched bottle, characterized by biaxial stretching blow molding in the axial direction and circumferential direction within a mold.