JP6860778B2 - Preform cover, composite preform, container manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a preform cover, a composite preform, and a container.

As a molding method for a plastic container (bottle), a biaxial stretch blow molding method in which an injection-molded preform is set in a mold and air is blown into the mold to form the shape of the mold cavity is known. There is.

In recent years, in the field of plastic containers, various functions and performances are often required, and ingenuity is required for the materials and molding methods used. For example, when gas barrier properties, light shielding properties, heat retention properties, etc. are required, the material used is made to have gas barrier properties, or a colorant or an ultraviolet absorber is added to a plastic material.

However, there is a limit to the device of the material, and various functions are given by making the plastic container multi-layered. By optimizing the constituent materials of each layer, it is expected that a plastic container having multiple functions, such as a light-shielding container having excellent gas barrier properties, can be realized.

In order to mold a multi-layer plastic container, it is considered that a multi-layer preform is injection-molded and then biaxially stretch-blow-molded, and various methods for forming the multi-layer preform have been proposed. However, molding of a multi-layer preform requires advanced technology, and a large amount of capital investment is required for the molding apparatus, and there are problems in terms of cost and the like.

Under such circumstances, it has been proposed to superimpose a separately molded preform cover on the outside of the preform to form a composite preform, and to form the container by biaxially stretching blow molding (Patent Document). See 1st grade). By using the preform cover, it is not necessary to mold the multi-layer preform, which is considered to lead to cost reduction and the like.

Japanese Unexamined Patent Publication No. 2016-097669

By the way, the present inventor has been diligently studying to develop a preform cover having an EVOH layer having a gas barrier property in order to impart gas barrier property by the preform cover. , I noticed that the EVOH layer is not uniformly stretched, and a portion where the EVOH layer is excessively thin may be formed in the container obtained by biaxial stretching blow molding.

The present invention has been made in view of such circumstances, and provides a preform cover capable of uniformly stretching an EVOH layer.

According to the present invention, the preform cover is provided with an EVOH layer made of an EVOH resin, and the EVOH resin has a maximum uniaxial extensional viscosity of 3.0 × 10 measured at a ^{temperature of 180 ° C. and a strain rate of 10s-1. A} preform cover of 4 (Pa · s) or higher is provided.

The present inventor investigated the reason why the EVOH layer contained in the preform cover may not be uniformly stretched in the biaxial stretching blow molding of the composite preform. It has been found that biaxial blow molding is usually performed at a temperature suitable for the preform resin, and that the temperature is not suitable for the EVOH resin, so that the stretching of the EVOH layer becomes non-uniform. Therefore, it was subjected to further examine the EVOH resin of the EVOH layer, when the maximum value of the uniaxial elongation viscosity with EVOH resin is ^{3.0 × 10 4 (Pa · s} ) or more, the preform It has been found that the EVOH layer can be uniformly stretched even when biaxial stretching blow molding is performed under conditions suitable for the above, and the present invention has been completed.

Hereinafter, various embodiments of the present invention will be illustrated. The embodiments shown below can be combined with each other.
Preferably, the EVOH resin has an ethylene content of 32 mol% or less.
Preferably, the EVOH resin has an MFR of 6 g / 10 min or less as measured under the conditions of a temperature of 210 ° C. and a load of 2.16 kg.
Preferably, the EVOH layer is sandwiched between a pair of polyolefin layers.
Preferably, the EVOH layer has a thickness of 0.3 to 1 mm.
According to another aspect of the present invention, a composite preform comprising a preform and a preform cover superimposed on the preform, wherein the preform cover is the preform cover described above, is provided by the composite preform. Will be done.
According to still another aspect of the present invention, there is provided a method for manufacturing a container including a step of biaxially stretching blow molding the above composite preform.

The first embodiment of the present invention is shown, (a) shows the preform 1 and the preform cover 11 in a separated state, and (b) is a composite plastic obtained by superimposing the preform cover 11 on the preform 1. Reform 10 is shown. The second embodiment of the present invention is shown, (a) shows the preform 1 and the preform cover 11 in a separated state, and (b) is a composite plastic obtained by superimposing the preform cover 11 on the preform 1. Reform 10 is shown. 6 is a graph showing the relationship between the elapsed time from the start of measurement and the uniaxial extensional viscosity of the EVOH resin used in Examples and Comparative Examples.

Hereinafter, embodiments of the present invention will be described. The various features shown in the embodiments shown below can be combined with each other. In addition, the invention is independently established for each feature.

1. 1. 1st Embodiment FIG. 1 shows a 1st embodiment of the present invention, (a) shows a preform 1 and a preform cover 11 in a separated state, and (b) shows a preform 1 and a preform cover 11 in a separated state. The composite preform 10 obtained by stacking the above is shown.

The preform 1 includes a tubular (preferably cylindrical) body 2. A mouth portion 3 is provided at one end of the body portion 2, and an engaging portion 3a for attaching a cap (not shown) is provided at the mouth portion 3. The cap may be attached by a plug type or may be attached by a screw type. The other end of the body portion 2 is an insertion end 4 to be inserted into the preform cover 11, and the insertion end 4 is the bottom portion 5 of the preform 1. The bottom portion 5 has a hemispherical shape in one example, but the shape is not particularly limited. The preform 1 can be formed by injection molding a resin material. As the resin material, it is preferable to use a thermoplastic resin, particularly PE (polyethylene), PP (polypropylene), PET (polyethylene terephthalate), PEN (polyethylene terephthalate), and PC (polyethylene).

The preform cover 11 includes a tubular (preferably cylindrical) body portion 12. An inserted end 13 is provided at one end of the body portion 12, and the preform 1 is inserted into the preform cover 11 through the inserted end 13. The other end of the body portion 12 is the opposite end 14, which is the opposite end of the inserted end 13, and the opposite end 14 is the bottom portion 15 of the preform cover 11. The bottom portion 15 has a hemispherical shape in one example, but the shape is not particularly limited. The method for forming the preform cover 11 is not particularly limited, but in one example, the preform cover 11 is formed by extrusion molding in which a molten resin is extruded into a cylindrical shape to be cooled and solidified, or direct blow molding in which a cylindrical parison in a molten state is blow molded as it is. In the case of extrusion molding, one end of a cylindrical molded product can be welded to make it closed. The resin material for forming the preform cover 11 may be the same as or different from that of the preform 1.

The preform cover 11 includes an EVOH layer made of an EVOH resin (ethylene-vinyl alcohol copolymer). In general, the EVOH layer has a property of being easily stretched non-uniformly depending on the molding conditions because the stretchability is not good. Therefore, for example, when the preform 1 made of PET and the preform cover 11 having an EVOH layer are overlapped and biaxially stretch-blow molded, the biaxial at a molding temperature suitable for PET is 100 to 120 ° C. When stretch blow molding is performed, the EVOH layer of the preform cover 11 is non-uniformly stretched, and there is a problem that a portion where the EVOH layer is excessively thin is easily formed in the container obtained by biaxial stretch blow molding. In order to solve such a problem, in the present embodiment, the maximum value of the uniaxial extensional viscosity measured at a ^{temperature of 180 ° C. and a strain rate of 10s-1 is 3.0 × 10 4} (Pa · s) or more. The EVOH layer is formed by using an EVOH resin. When such an EVOH layer is used, the stretchability of the EVOH layer during biaxial stretching blow molding becomes good, and even when biaxial stretching blow molding is performed at a temperature suitable for the material of Preform 1. The EVOH layer is likely to be uniformly stretched. The uniaxial extensional viscosity can be measured based on the time course of the load when the test piece is elongated and deformed at a temperature of 180 ° C. and a strain rate of 10 s- ^{1, and the uniaxial extensional viscosity is measured and shown in FIG.} Such a graph showing the relationship between the elapsed time and the uniaxial extensional viscosity can be obtained. The measurement of uniaxial extensional viscosity is continued until the test piece is cut, and the maximum value of uniaxial extensional viscosity observed during the measurement is the "maximum value of uniaxial extensional viscosity" within the scope of claims.

The maximum value of the uniaxial extensional viscosity is, for example, 3.0 × 10 ^{4 to} 3.0 × 10 ⁶ (Pa · s), and specifically, for example, 3.0 × 10 ⁴ , 4.0 × 10 ⁴ , 5.0 × 10 ⁴ , 6.0 × 10 ⁴ , 7.0 × 10 ⁴ , 8.0 × 10 ⁴ , 9.0 × 10 ⁴ , 1.0 × 10 ⁵ , 2.0 × 10 ⁵ , 3, It is 0.0 × 10 ⁵ and 3.0 × 10 ⁶ (Pa · s), and may be within the range between any two of the numerical values exemplified here.

The ethylene content of the EVOH resin constituting the EVOH layer is not particularly specified, and is, for example, 25 to 50 mol%. The smaller the ethylene content of the EVOH resin, the higher the gas barrier property of the EVOH resin tends to be. Therefore, the ethylene content of the EVOH resin is preferably 32 mol% or less, more preferably 30 mol% or less. Specifically, the ethylene content is, for example, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 40, 45, 50 mol%, and any of the numerical values exemplified here. It may be within the range between the two.

The smaller the ethylene content of the EVOH resin, the higher the rigidity and the poorer the secondary processability. However, the ethylene content is 32 mol% or less and the maximum value of the uniaxial extensional viscosity is 3.0 × 10 ⁴ ( By using an EVOH resin having Pa · s) or higher, both good gas barrier properties and stretchability can be achieved.

The EVOH resin constituting the EVOH layer preferably has an MFR (melt flow rate) of 6 g / 10 min or less as measured under the conditions of a temperature of 210 ° C. and a load of 2.16 kg. In this case, the EVOH layer is likely to flow appropriately and be uniformly stretched. The MFR of this EVOH resin is, for example, 2 to 6 g / 10 min, and specifically, for example, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 g / 10 min. Yes, it may be within the range between any two of the numerical values exemplified here.

The preform cover 11 may have a single-layer structure of an EVOH layer or a multi-layer structure including an EVOH layer. In the case of a multi-layer structure, a structure in which the EVOH layer is sandwiched between a pair of polyolefin layers is preferable. The EVOH layer tends to have a reduced gas barrier property when it absorbs moisture, and the EVOH layer can be suppressed from absorbing moisture by being sandwiched between a pair of polyolefin layers. Examples of the polyolefin constituting the polyolefin layer include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene copolymer and a mixture thereof. The polyolefin layer may have a laminated structure of a repro layer and a virgin layer. Here, the repro layer refers to a layer used by recycling burrs generated during the molding of a container, and the virgin layer refers to a layer formed of a virgin material. When the polyolefin layer contains a repro layer, the layers constituting the innermost surface and the outermost surface of the preform cover 11 are preferably virgin layers.

When the EVOH layer is sandwiched between a pair of polyolefin layers, the ratio of the thickness of the outer surface side and the thickness of the polyolefin layer on the inner surface side to the thickness of the EVOH layer is preferably 0.5 to 3, respectively. In this case, it is possible to make the EVOH layer sufficiently thick so that the EVOH layer exhibits gas barrier properties while preventing the EVOH layer from absorbing moisture by the polyolefin layer. This ratio is specifically, for example, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, It is 2.7, 2.8, 2.9, and 3, and may be within the range between any two of the numerical values exemplified here. It may be within the range between any two of the numerical values exemplified here.

It is preferable to provide an adhesive layer between the EVOH layer and the polyolefin layer in order to increase the adhesive strength between the two. The adhesive layer is, for example, an acid-modified polyolefin in which a carboxyl group is introduced into the above-mentioned polyolefin (eg, maleic anhydride-modified polyethylene), or an ethylene-vinyl acetate copolymer (EVA). An example of the adhesive layer 13c is a mixture of low-density polyethylene or linear low-density polyethylene and acid-modified polyethylene.

The thickness of the EVOH layer is preferably 0.3 to 1 mm, more preferably 0.4 to 0.7 mm. This is because such a thickness ensures a sufficient thickness to exhibit the gas barrier property even when the preform cover 11 is stretched five times or more.

As shown in FIGS. 1A to 1B, the preform cover 11 is preformed by inserting the insertion end 4 of the preform 1 into the preform cover 11 from the inserted end 13 of the preform cover 11. It can be mounted so as to overlap with 1. The preform cover 11 may be formed so as to cover the entire preform 1, but in the present embodiment, the preform cover 11 partially covers the preform 1 (specifically, a large body portion 2). It is configured to cover the portion and the bottom 5).

The inner surface shape of the preform cover 11 is substantially the same as the outer surface shape of the preform 1, and when the preform 1 is inserted into the preform cover 11, substantially the entire inner surface of the preform cover 11 is the outer surface of the preform 1. The preform 1 and the preform cover 11 are integrated in appearance.

The composite preform 10 obtained by superimposing the preform cover 11 on the preform 1 is set in the mold and biaxially stretched and blow-molded to become a container corresponding to the cavity shape inside the mold. The composite preform 10 is biaxially stretch blow-molded in a state of being heated and softened before or after being set in the mold. In the present embodiment, since the maximum value of the uniaxial elongation viscosity of the EVOH resin constituting the EVOH layer included in the preform cover 11 is ^{3.0 × 10 4 (Pa · s} ) or higher, the EVOH layer is uniformly stretched As a result, a container having excellent gas barrier properties can be obtained. The thickness of the EVOH layer after stretching is not particularly specified, but is, for example, 40 μm or more, preferably 50 μm or more. The draw ratio is not particularly specified, but is, for example, 5 to 10 times.

2. Second Embodiment The second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the preform cover 11 has a pipe shape having only the body portion 12. In the present embodiment, since the preform cover 11 has a pipe shape, it can be manufactured at low cost by extrusion molding or the like.

<Measurement of maximum uniaxial extensional viscosity>
Pellets made of EVOH resin (both manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) shown in Table 1 are heated on a hot plate at 230 ° C., and the pellets are pressed with a hot plate to prepare a sheet having a thickness of 500 μm. By cutting into 18 mm × 10 mm, a test piece of 18 mm × 10 mm × 0.5 mm was prepared. This test piece was set in an MCR rheometer (model: MCR302, manufactured by Anton Pearl Co., Ltd.), melted at 200 ° C., lowered to 180 ° C., and measured for uniaxial extensional viscosity at ^{a strain rate of 10s-1.} A graph showing the relationship between the elapsed time shown in (1) and the uniaxial extensional viscosity was obtained, and the maximum value of the uniaxial extensional viscosity was obtained for each EVOH resin. The obtained values are shown in Table 1.

<Evaluation of stretchability>
Using the EVOH resin shown in Table 1, polypropylene layer (thickness 125 μm) / adhesive layer (thickness 10 μm) / EVOH layer (thickness 50 μm) / adhesive layer (thickness 10 μm) / repro layer (thickness) in this order from the outside. A preform cover 11 having a layer structure of (200 μm) / polypropylene layer (105 μm in thickness) was formed by direct blow molding. The preform cover 11 is superposed on the PET preform 1 to form the composite preform 10, and the composite preform 10 is heated to 100 ° C. and biaxially stretched and blow molded so that the stretching ratio becomes about 7 times. Got to form a container. The thickness of the EVOH layer was measured at eight points evenly spaced in the circumferential direction at the center of the obtained container in the height direction, and stretched based on the thickness ratio determined by the maximum thickness / minimum thickness. Gender was evaluated according to the following criteria.
⊚: Thickness ratio is less than 1.5 ○: Thickness ratio is 1.5 or more and less than 2.0 ×: Thickness ratio is 2.0 or more

<Discussion>
As shown in Table 1, in the examples in which the maximum value of the uniaxial extensional viscosity is 3.0 × 10 ⁴ (Pa · s) or more, the stretchability is excellent and the EVOH layer is uniformly stretched in the biaxial stretching blow molding. However, in the comparative example in which the maximum value of the uniaxial extensional viscosity ^{is less than 3.0 × 10 4} (Pa · s), the stretchability is poor and the EVOH layer is unevenly stretched in the biaxial stretching blow molding. It was.

1: Preform 2: Body 3: Mouth 3a: Engagement 4: Insertion end 5: Bottom 10: Composite preform 11: Preform cover 12: Body 13: Inserted end 13c: Adhesive layer 14: Opposite Edge 15: Bottom

Claims (6)

A preform cover having an EVOH layer made of EVOH resin.
The EVOH resin temperature of 180 ° C., Ri der maximum uniaxial elongation viscosity measured at a strain rate of ^{10s -1} is ^{3.0 × 10 4 (Pa · s} ) or more,
The EVOH resin temperature of 210 ° C., measured MFR of Ru der following 6 g / 10min under a load of 2.16 kg, preform the cover. The preform cover according to claim 1, wherein the EVOH resin has an ethylene content of 32 mol% or less. The preform cover according to claim 1 or 2 , wherein the EVOH layer is sandwiched between a pair of polyolefin layers. The preform cover according to any one of claims 1 to 3 , wherein the EVOH layer has a thickness of 0.3 to 1 mm. A composite preform with a preform and a preform cover overlaid on it,
The preform cover is a composite preform which is the preform cover according to any one of claims 1 to 4. A method for manufacturing a container, comprising a step of biaxially stretching blow molding the composite preform according to claim 5.

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