JPS60147317A - Manufacture of multilayer orientation polypropylene bottle - Google Patents

Abstract

PURPOSE:To improve gas barrier property of a polypropylene bottle by forming one end of a pipe made of a specific composition in a bottom, the other end in a neck portion, preliminarily heating it at the specific orientation suitable temperature, and molding in a blowing mold. CONSTITUTION:A pipe 1 is molded by using ethylene-vinyl alcohol copolymer containing 50mol% of ethylene component for a layer to become a gas barrier resin layer, polyproplene resin for inner and outer layers to become a base, by interposing an adhesive layer between the both resin layers, and by coextrusion method. The pipe is cut in a suitable length, fused and closed at one end to form a bottom 6, formed at the other end with a hole at the upper end and a neck 7 having a connecting portion on the outer periphery. The obtained preliminarily molded product 10 is preliminarily heated at suitable orienting temperature of 125 to 165 deg.C, and blow-molded axially and circumferentially in the blowing mold. The multilayer orientation polypropylene bottle obtained in this manner has excellent transparency and high gas barrier property.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a multilayer stretched polypropylene bottle, and more specifically, the bottle is made of a gas barrier layer of ethylene-vinyl alcohol copolymer and a base layer of polypropylene resin, and the container wall is This invention relates to a method for producing a bottle with improved gas barrier properties whose molecules are biaxially oriented by stretching.

Molding of stretched polypropylene bottles is common today,
The resulting molded containers are used for infusions, liquids, body cleansers, shampoos, cosmetics, etc. due to their excellent transparency, heat resistance, and toughness. However, stretched polypropylene resin bottles are used for glass bottles,
For completely sealed items such as metal cans, gas permeability can be considered to be zero, but stretched polypropylene bottles are permeable to oxygen, carbon dioxide, etc. It has poor filling storage stability, and cannot be expected to be used as a storage container for food, etc.

Methods for improving the gas barrier properties of stretched polypropylene bottles In 1-1, an improvement by coextrusion of stretched polypropylene bottles with an ethylene vinyl alcohol copolymer has already been put to practical use.

Candidates for gas barrier resins for this type of coextrusion are hot plastic resins such as vinylidene chloride resins, acrylonitrile resins, and vinyl alcohol resins, but in any case, the properties and processing of each resin are different. It must be selected in relation to gender.

The present inventor used polypropylene resin as a base and ethylene vinyl alcohol copolymer as a gas barrier layer,
When manufacturing a multi-layer stretched polypropylene bottle, combining pipe forming by coextrusion, cutting the pipe and thermoforming the bottom, thermoforming the mouth and neck, and then biaxially stretching blow molding in this order improves gas barrier properties. We have also found that a multilayer stretched polypropylene bottle with excellent molecular orientation can be obtained economically.

According to the present invention, there is provided a method for manufacturing a multilayer stretched polypropylene bottle, in which an ethylene-vinyl alcohol copolymer having an ethylene content of 50 mol or less is applied to a layer to be a gas barrier resin layer, an inner layer to be a base material, and an outer layer to be a base material. Alternatively, a pipe or tube is formed by co-extrusion using polypropylene resin for the inner and outer layers, an adhesive layer is interposed between the two fecal fat layers, and the pipe or tube is cut to an appropriate length. One end of this tube or tube is fused and closed to form a bottom part, and the other end is formed into a neck part having an opening at the upper end and a fitting part or a threaded part on the outer periphery, and the obtained preformed product is obtained. Provided is a method for producing a multilayer stretched polypropylene bottle, which comprises preheating the bottle to a suitable stretching temperature of 125 to 165C, and performing biaxial stretching blow molding almost simultaneously in the axial and circumferential directions in a blow molding mold. Ru.

As already mentioned, the purpose of the present invention is to improve the gas barrier properties of stretched polypropylene bottles. Use a copolymer. As is already known, polyvinyl alcohol is not thermoplastic unless special processing methods are used, but in the case of ethylene-vinyl alcohol, the melting point decreases and the thermoplasticity increases as the ethylene content increases. . Since the ethylene-vinyl alcohol copolymer is stretch blown together with the polypropylene resin as described below, normally it would be assumed that the melting point is as low as possible and the temperature at which it can be stretched is as low as possible, but here, the melting point and Ethylene-vinyl alcohol copolymerization, which has a high stretching temperature, is selected. The first reason is that the ethylene component is 5
If it exceeds 0 molt, the melting point will be low and the temperature at which it can be stretched will be low, which is convenient for co-stretching with a polypropylene resin layer, but if the ethylene content increases, the gas barrier properties will rapidly decrease, so The second reason is that there is no point in making the system resin multilayered.The second reason is that even if the ethylene-vinyl alcohol copolymer is low in ethylene content and high in vinyl alcohol content, it can be processed by the method of the present invention. For example, as will be detailed later, it was discovered that it is possible to stretch an ethylene-vinyl alcohol copolymer layer in the form of a multilayer structure with a polypropylene resin even at the appropriate stretching temperature for the polypropylene resin. The ethylene-vinyl alcohol copolymer used in the multilayer structure of the invention was selected to have an ethylene component of 50 mole or less, that is, a high vinyl alcohol content.

Conventionally, stretch blow molding of plastics such as polypropylene involves extruding polypropylene into a pipe shape, cutting it to a certain length, preheating it to a certain temperature, holding it between a pair of clamps and stretching it in the axial direction. A method of blow-stretching in the circumferential direction by blowing fluid into the material, that is, a sequential stretching method is known.

However, when this method is applied to a multilayer parison of polypropylene and ethylene-vinyl alcohol copolymer, it has been found that certain drawbacks arise in terms of stretchability and interlayer adhesion.

Part F, Part -JC shows that the ethylene-vinyl alcohol copolymer has stretchability at the appropriate temperature for stretching polypropylene.
In particular, there is a problem that biaxial stretchability is significantly lacking. That is, when a coextruded multilayer pipe of polypropylene and ethylene-vinyl alcohol copolymer is held with clamps and stretched in the axial direction, and then stretched in the circumferential direction by blowing (sequential stretching method), the ethylene-vinyl alcohol copolymer There is a tendency for a large number of fissures or latent cracks to occur in the axial direction in the combined layer. This is thought to be because a phenomenon similar to fibrillation occurs in the ethylene-vinyl alcohol copolymer layer during axial stretching, and cracks, etc. occur during the subsequent circumferential stretching operation. This tendency is more severe for ethylene-vinyl alcohol copolymers containing less ethylene (having gas barrier properties).

In addition, -2, when both ends of a multilayer pipe are held together with clamps, cracks are generated as unformed joints, including the clamp parts, and the resulting scraps are returned to the extruder to be returned to the product, and are used for pipe forming, stretching, etc. Molding it will impair the transparency of the intended product. This means that the returned material is a mixture of polypropylene, ethylene vinyl alcohol copolymer, and adhesive, and when this is mixed with virgin resin as a polypropylene layer, the transparency is reduced.

The first feature of the present invention is that polypropylene and an ethylene-vinyl alcohol copolymer are first coextruded into a pipe or tube.

That is, in coextrusion, molten polypropylene and molten ethylene-vinyl alcohol copolymer are combined in a die,
This is done by extruding through a ring-shaped orifice, but since these two types of resin are in contact for a period of time while both are in a molten state, good mixing of the resins occurs at the interface between the two, and the thermal adhesion between the two becomes strong. It is something that is done.

This is exactly the same even when an adhesive resin is interposed between polypropylene and ethylene-vinyl alcohol copolymer.

The second feature is that after cutting this co-extruded multilayer pipe or tube to a certain length, one end is fused and closed with Eve's own plastic to form the bottom part. That is, by forming a preform with a bottom,
While pressing the stretching rod against the preheated preform,
It becomes possible to perform blow stretching in the circumferential direction at the same time or almost simultaneously with the axial stretching, which eliminates the occurrence of cracks or potential cracks in the ethylene-vinyl alcohol copolymer layer that are observed in the case of sequential stretching. It's something. In addition, the sixth feature is that since the pipe is closed in a molten semicircle made of the pipe's own plastic, no excess resin is generated during molding of the preform. As a copolymer, a copolymer obtained by saponifying a copolymer of ethylene and a vinyl ester such as vinyl acetate is used.
In consideration of molding workability and barrier properties, those having an ethylene content of 15 to 50 moles, particularly 25 to 45 moles, and a saponification degree of 96 moles or more are advantageously used. The molecular weight of this copolymer may be any as long as it has film-forming ability.

As the polypropylene, a propylene homopolymer, a block copolymer random copolymer of propylene and ethylene, etc. are used. This polypropylene resin may also have a molecular weight sufficient to form a film.

In order to enhance the adhesion between the polyfluorhylene layer and the ethylene-vinyl alcohol copolymer layer, any adhesive known per se can be used, such as acid-modified polyolefins being used for this purpose.

The polypropylene substrate (PP), ethylene-vinyl alcohol copolymer (EVOH), and adhesive layer (AD) can be used in various layer configurations, for example, with the outer layer on the left and the inner layer on the right, PP/EVOH, EVOH/PP PP/AD/EVOH,EVOH/AD/PPPP/E
It can be used in layer configurations such as VOH/PP, PP/AD/EVOH/AD/PP, etc.

The thickness of the layer can vary, but generally PP:EV
The thickness ratio is preferably in the range of OH=2:1 to 3n:1, especially 5:1 to 20:1, and when an adhesive layer is used, PP:AD=5:1 to 100:1, especially 1.
The thickness ratio is preferably in the range of 0:1 to 50:1.

FIG. 1 shows a multilayer pipe 1 which is particularly suitable for the purposes of the invention, comprising an inner layer 2 and an outer layer 3 of polypropylene, an intermediate gas barrier layer 4 of ethylene-vinyl alcohol copolymer, and It consists of adhesive layers 5α and 5h interposed therebetween.

It has already been pointed out that it is important to manufacture pipes and tubes in seconds by coextrusion, but extruded pipes
In order to prevent crystallization of polypropylene, it is important to rapidly cool it, such as by immersing it in water.

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 semi-circular shape, as shown in Fig. 2. A bottom portion 6 is formed as shown.

Next, the other end of this pipe 1 is also subjected to heating 12, pressing, stretching, blow molding, etc. in a desired mold, and as shown in Fig. A preform 10 having a fitting part, a screwing part, and a locking part for a lid such as a neck ring (support ring) 9 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 characteristic that no excess resin is generated when a preformed product is obtained from a multilayer pipe or tube. This is extremely important for economically forming multilayer molded products.Next, in the third step, the above preform is heated to the appropriate temperature for stretching the multilayer preform using hot air, infrared heaters, high frequency dielectric heating, etc. Preheat until hot. In this case, the temperature range is 125C ~
The polypropylene resin is preheated to a stretching temperature of 165C, preferably 145 to 155C.

In FIGS. 4 and 5 for explaining the stretch blow molding operation, a mandrel 11 is inserted into the mouth of a preform 10, and the mouth is inserted into a pair of split molds 12α, 12b.
hold it in place. A vertically movable stretching rod 13 is provided coaxially with the mandrel 11, and between this stretching rod 13 and the mandrel 11 there is an annular channel 14 for the injection of fluid.

In the present invention, the tip 15 of this stretching rod 13 is applied to the inside of the bottom part 6 of the preform 10, and this stretching rod 13
is moved downward to stretch it in the axial direction, and at the same time, fluid is blown into the preform 10 through the passage 14, and the fluid pressure causes the preform to expand and stretch in the circumferential direction.

According to the present invention, by performing axial stretching and circumferential stretching simultaneously or almost simultaneously, even if the ethylene-vinyl alcohol copolymer layer has a high vinyl alcohol content, the melting point of the ethylene-vinyl alcohol copolymer layer can be lowered. It was discovered that it is also possible to stretch at relatively low temperatures.

This is because even ethylene-vinyl alcohol copolymers containing high vinyl alcohol are extremely difficult to stretch.
This is surprising because when a film is stretched at the appropriate stretching temperature, the film ruptures during stretching as described above when the film is stretched sequentially in the vertical axis and then in the horizontal axis.

In addition, in stretch blow molding of multilayer pipes made of polypropylene and ethylene-vinyl alcohol copolymer, '140'
Even in a fairly high temperature range of ~155C, in the sequential stretching method, the ethylene-vinyl alcohol copolymer layer in the multilayer has an ethylene content of about 40 mol/kg or more, and stretching is finally possible. Taken together, it is a surprising fact that multilayer bodies using high vinyl alcohol content ethylene-vinyl alcohol copolymers can be biaxially stretched with this method.

The reason for this is that co-stretching is performed with the ethylene-vinyl alcohol copolymer layer placed on the polypropylene layer.
However, it is presumed that the delamination between the two phase resin layers is suppressed during the main stretching and that the biaxial stretching is carried out simultaneously and in a well-balanced manner.

The thus obtained multilayer stretched polypropylene bottle 16 shown in FIG. 6 has not only excellent transparency but also extremely high gas barrier properties compared to other plastic bottles, and in this case, the gas barrier properties can be adjusted as necessary. Moreover, this bottle is also heat resistant, making it extremely easy to fill and store fruit juice drinks, mineral water, etc. at high temperatures.The container is hygienic, and almost no gas is generated when used containers are incinerated. It is characterized by being easily incinerated even though it generates noxious gases because it only uses carbon dioxide and water.It has transparency, gas barrier properties, and pressure resistance comparable to glass bottles, yet is lightweight and wave-resistant, making it an ideal bottle. A container is provided.

Example 1 Using an extruder for the inner and outer layers with a diameter of 90 m+, an extruder for the intermediate layer and an extruder for the adhesive layer with a diameter of 40 mm, and a 5-layer ring-shaped die, the inner and outer layers' had melt indexes of CM and I. ) 1
．． 0 polypropylene (Mitsui Norprene), the middle layer is vinyl alcohol-containing 70 mol ethylene-vinyl alcohol copolymer a (EVAL), and the adhesive layer is epoxidized octyl oleate 10.0 OOP blended maleic anhydride graph and modification. A laminated pipe of three types and five layers made of high-density polyethylene is extruded from a die into water and cooled. The outer diameter of this pipe is 31 mm, the inner diameter is 17 m, and the thickness is 7.
rm, and the thickness of each layer, the inner layer is 2.1! , the outer layer is 4
．． 2n+m.

Each adhesive layer is 0.14 m thick and the middle layer is 0.42 m long, and the pipe has fixed dimensions (length 82 m + weight 4 m).
1v) and heat one end of the pipe to about 240C.
Close the bottom of the semi-circular sphere l-1 and heat the other end to 155C to form the threaded part and neck ring, total height F12111
Seven 11 preforms were obtained.

This preformed product was heated to 1550° C., and while it was stretched in the vertical axis direction in a blow mold, it was stretched in the horizontal direction with a blow 1-, so that it was almost simultaneously biaxially stretched and blow molded to have an internal volume of 1040 C.
The oxygen permeability of this bottle was approximately 4.5cc/m'・2477-aim (37"C).
), and there was no damage when dropped onto concrete from a height of 120 t-In, and no peeling occurred between the layers. In addition, since this bottle is heat resistant, the bottle body and neck did not deform even when filled with 96C liquid and sealed.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the multilayer/< Eve used in the present invention, Figs. 2 and 3 are cross-sectional views of the preform with the bottom and neck formed, and Figs. 4 and 5 are the preform. is held in a blow mold, and FIG. 6 shows a cross-sectional view before blow molding and a cross-sectional view after blow molding, which shows a multilayer stretched bottle molded according to the present invention. 1...Pipe, 6...Bottom, 7...
... Opening end, 10 ... Preformed product, 16.
...Multilayer stretched bottle. Patent applicant: Toyo Seikan Co., Ltd. Figure 1 Figure 3

Claims (2)

[Claims] (1) A method for manufacturing a multilayer stretched polypropylene bottle, in which the layer to be the gas barrier resin layer contains 50% ethylene component.
Ethylene-vinyl alcohol copolymer of less than molti,
Polypropylene resin is used for the inner layer, outer layer, or inner and outer layers that are to be the base, and an adhesive layer is interposed between both phase resin layers, and a pipe or tube is formed by coextrusion method, and the pipe or tube is Cut the pipe or tube to an appropriate length, fuse and close one end of the pipe or tube to form a bottom part, and form the other end into a mouth and neck part with an opening at the top and a fitting or threaded part on the outer periphery. □ A multilayer stretched polypropylene bottle characterized by preheating the obtained preform to a suitable stretching temperature of 1'25C to 165C, and biaxially stretching and blow molding it in the axial direction and circumferential direction in a blow molding mold. manufacturing method. (2) A stretching rod is pressed against the bottom of the preheated preform to harden it in the axial direction, and at the same time or almost simultaneously with this, blow stretching is performed in the local direction. The method described in paragraph 1.