JP6935477B2 - Thermoformed container and its manufacturing method - Google Patents

Description

The present invention relates to a thermoformed container and a method for producing the same.

Ethylene-vinyl alcohol copolymer (hereinafter, also referred to as "EVOH") is widely used as a material that can be melt-molded and has excellent gas barrier properties. Specifically, EVOH is used as a material for a film or sheet formed by, for example, melt molding. The EVOH layer made of this sheet or the like is used as a packaging material by being laminated with a thermoplastic resin layer containing a polyolefin resin or the like as a main component. A packaging material containing such an EVOH layer is used as a packaging container by thermoforming. Since such a packaging container has an excellent oxygen barrier property because it contains an EVOH layer, it is widely used in various fields such as foods, cosmetics, medical chemicals, toiletries, etc., where oxygen barrier properties are required.

However, the EVOH layer generally lacks thermoformability as compared with the thermoplastic resin layer containing a polyolefin resin or the like as a main component. Therefore, the packaging material containing the EVOH layer tends to have defects such as pinholes and cracks during thermoforming, and the packaging container tends to have a poor appearance. Further, since the packaging material containing the EVOH layer tends to have uneven thickness after thermoforming, it tends to cause inconveniences such as a decrease in gas barrier property and mechanical strength of the packaging container.

In order to improve such inconvenience, a method of adding a plasticizer to a resin composition for forming a sheet or the like containing EVOH as a main component (Japanese Patent Laid-Open Nos. 53-088067 and 59-020345). (See), a method of blending a polyamide (see Japanese Patent Application Laid-Open No. 52-141785), and the like have been studied, but all of them have a large decrease in gas barrier property. Therefore, it has not been possible to obtain a thermoformed container having excellent appearance and sufficient strength by suppressing the occurrence of defects in thermoforming while maintaining the original characteristics of EVOH.

Japanese Unexamined Patent Publication No. 53-088067 JP-A-59-020345 Japanese Unexamined Patent Publication No. 52-141785

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a thermoformed container which suppresses the occurrence of defects in thermoforming, has excellent appearance, and has sufficient strength. Furthermore, an object of the present invention is to provide a thermoformed container having such characteristics and to provide a manufacturing method excellent in long-running property.

The invention made to solve the above problems contains an ethylene-vinyl alcohol copolymer (hereinafter, also referred to as "EVOH (I)") obtained by saponifying a copolymer of ethylene and vinyl ester as a main component. A gel permeation chromatograph comprising a first layer (hereinafter, also referred to as "layer (1)"), wherein the EVOH (I) includes a differential refractometer detector and an ultraviolet visible absorbance detector. The heat-molded container is characterized in that the molecular weight measured after heat treatment at 220 ° C. for 50 hours in a nitrogen atmosphere satisfies the condition represented by the following formula (1).
(Ma-Mb) / Ma <0.45 ... (1)
Ma: Molecular weight converted to polymethylmethacrylate at the maximum value of the peak measured by the differential refractive index detector Mb: Converted to methylpolymethacrylate at the maximum value of the absorption peak at a wavelength of 220 nm measured by the ultraviolet-visible absorbance detector. Molecular weight

The thermoformed container includes a layer (1) containing EVOH (I) as a main component that satisfies the above specific conditions. The layer (1) is formed, for example, by melt-molding a resin composition containing EVOH (I) as a main component that satisfies the above specific conditions. In this melt molding, since the resin composition contains EVOH (I) satisfying the above specific conditions as a main component, its action is not clear, but defects such as gel-like lumps and streaks are generated, and fine pins are generated. It is possible to suppress the generation of holes and cracks and coloring. Therefore, the thermoformed container provided with the layer (1) obtained from the resin composition has excellent appearance and sufficient strength. In addition, the thermoformed container is also excellent in self-purging property in the manufacturing process, so that the manufacturing cost can be reduced.

The molecular weight of EVOH (I) measured after heat treatment at 220 ° C. for 50 hours in a nitrogen atmosphere using a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector is expressed by the following formula (2). It is preferable that the conditions represented are further satisfied.
(Ma-Mc) / Ma <0.45 ... (2)
Mc: Molecular weight in terms of polymethylmethacrylate at the maximum value of the absorption peak at a wavelength of 280 nm measured by an ultraviolet-visible absorbance detector.

As described above, when EVOH (I) further satisfies the above conditions, the generation of defects such as gel-like lumps and streaks, the generation of fine pinholes and cracks, and coloring can be further suppressed, and as a result, the appearance and strength can be further suppressed. Can be improved. In addition, the manufacturing cost can be further reduced by further improving the self-purging property in the manufacturing process.

The layer (1) may further contain an alkali metal salt of an organic acid. The content of the alkali metal salt is preferably 1 ppm or more and 1,000 ppm or less in terms of metal. As described above, when the layer (1) further contains the above-mentioned specific amount of the alkali metal salt, the interlayer adhesive strength can be improved and the long-running property in the manufacturing process can be improved.

The vinyl ester is preferably vinyl acetate. In this case, the content of acetaldehyde in vinyl acetate is preferably less than 100 ppm. As described above, the vinyl ester is vinyl acetate, and the content of acetaldehyde in the vinyl acetate is within the above-mentioned specific range, so that the appearance is improved by further reducing the occurrence and coloring of defects such as gel-like lumps. Can be improved further.

The thermoformed container is arranged on one surface side and the other surface side of the layer (1), and the solubility parameter (SP value) calculated from the polyolefin formula is 11 (cal / cm ³ ) ^1/2 or less. A pair of second layers (hereinafter, also referred to as "(2) layers") containing a certain thermoplastic resin as a main component, and carboxylic acid modification arranged between the above (1) layer and the pair of (2) layers. It is preferable to further include a pair of third layers (hereinafter, also referred to as “(3) layer”) containing polyolefin as a main component.

As described above, the thermoformed container is further provided with the above-mentioned resin-based (2) layer and (3) layer to improve gas barrier property, oil resistance, impact resistance and the like under high humidity. be able to.

The thermoformed container is preferably formed by thermoforming a multilayer body including the above (1) layer, (2) layer, and (3) layer. The thermoformed container thus obtained is excellent not only in gas barrier property, oil resistance and the like, but also in appearance.

The thermoformed container may further include a fourth layer (hereinafter, also referred to as “(4) layer”) containing the above EVOH (I), the above thermoplastic resin, and the above carboxylic acid-modified polyolefin. As described above, when the thermoformed container is further provided with the layer (4), the gas barrier property, impact resistance, etc. under high humidity can be further improved.

The thermoformed container can be suitably used as a cup-shaped container or a tray-shaped container.

The present invention includes a step of forming a layer (1) using a resin composition containing an ethylene-vinyl alcohol copolymer as a main component, and a step of thermoforming a layer structure containing the layer (1). The molecular weight of the ethylene-vinyl alcohol copolymer measured after heat treatment at 220 ° C. for 50 hours in a nitrogen atmosphere using a gel permeation chromatograph equipped with a differential refractometer detector and an ultraviolet visible absorbance detector is the above formula ( Includes a manufacturing method that satisfies the conditions represented by 1). According to the method for producing a thermoformed container, it is possible to obtain a thermoformed container having excellent appearance in which defects such as gel-like lumps and streaks are suppressed and coloring is suppressed. Further, in the thermoformed container, the resin composition is excellent in self-purging property, so that the manufacturing cost can be reduced.

The thermoformed container of the present invention has sufficient gas barrier properties and oil resistance as the characteristics of EVOH, and the layer (1) contains EVOH (I) satisfying the above specific conditions, so that the thermoforming container can be used in thermoforming. The occurrence of defects is suppressed, the appearance is excellent, and the strength is sufficient. Further, in the thermoformed container, since the layer (1) contains EVOH (I) satisfying the above-mentioned specific conditions, the self-purge property in the manufacturing process is excellent, so that the manufacturing cost can be reduced. Therefore, the thermoformed container is used for various purposes. The method for producing the thermoformed container can provide the thermoformed container and is excellent in long-running property.

The relationship between the molecular weight of EVOH (logarithmic value), the signal value (RI) measured by the differential refractive index detector, and the absorbance (UV) measured by the absorbance detectors (measurement wavelengths 220 nm and 280 nm) is schematically shown. It is a graph. It is a schematic perspective view which shows the cup-shaped container which is one Embodiment of the thermoformed container of this invention. It is a schematic cross-sectional view of the cup-shaped container of FIG. It is a schematic cross-sectional view which shows the main part of the cup-shaped container of FIG. It is a schematic diagram for demonstrating the manufacturing method of the cup-shaped container of FIG. It is a schematic diagram for demonstrating the manufacturing method of the cup-shaped container of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. Further, as for the illustrated materials, unless otherwise specified, one type may be used alone, or two or more types may be used in combination.

<Thermoforming container>
The thermoformed container is used in various fields such as foods, cosmetics, medical chemicals, toiletries, etc., where oxygen barrier properties are required. The thermoformed container is formed as having an accommodating portion by, for example, thermoforming a multilayer body.

[Accommodation]
The storage part is a part that stores the contents such as food. The shape of the accommodating portion is determined according to the shape of the contents. Specifically, the thermoformed container is formed as, for example, a cup-shaped container, a tray-shaped container, a bag-shaped container, a bottle-shaped container, a pouch-shaped container, or the like.

The form of the accommodating portion can be represented by the aperture ratio (S) as one index. Here, the drawing ratio (S) is a value obtained by dividing the depth of the deepest part of the container by the diameter of the circle having the maximum diameter inscribed in the opening of the container. That is, the aperture ratio (S) means that the larger the value, the deeper the bottom of the container, and the smaller the value, the shallower the bottom of the container. For example, when the thermoformed container has a cup shape, the drawing ratio (S) is large, and when the thermoformed container has a tray shape, the drawing ratio (S) is small. The diameter of the circle having the maximum diameter inscribed in the opening of the container is, for example, the diameter of the circle when the opening of the accommodating portion is circular, the minor diameter (minor axis length) when the opening is elliptical, and the rectangle. In some cases, it is the length of the short side.

The drawing ratio (S) has a suitable value depending on whether the multilayer body for forming the thermoforming container is a film or a sheet, that is, the thickness of the multilayer body. When the thermoforming container is a film formed by thermoforming, the lower limit of the drawing ratio (S) is preferably 0.2, more preferably 0.3, and even more preferably 0.4. On the other hand, when the thermoformed container is a molded sheet, the lower limit of the drawing ratio (S) is preferably 0.3, more preferably 0.5, and even more preferably 0.8. The film means a film having an average thickness of less than 0.2 mm and being soft, and the sheet means a film having an average thickness larger than that of the film, for example, a film having a thickness of 0.2 mm or more and being soft.

[Multilayer]
The multilayer body includes a layer (1) containing EVOH (I) as a main component, and another layer is laminated on one surface of the layer (1) and at least one surface side of the other surface. .. Here, in the thermoformed container, one surface is the inner surface side of the accommodating portion when the multilayer body is used as the thermoformed container, and the other surface is the outer surface side of the accommodating portion. The multilayer body may be in a film-like form or a sheet-like form.

The thickness ratio (I) of the total average thickness I of the other layers laminated on one surface side of the layer (1) and the total average thickness O of the other layers laminated on the other surface side of the layer (1). As the lower limit of / O), 1/99 is preferable, and 30/70 is more preferable. As the upper limit of the thickness ratio (I / O), 70/30 is preferable, and 55/45 is more preferable. The thickness of all layers or a single layer of the multilayer body is an average value of the thickness measured by optical microscope observation for a sample cut out from a plurality of places of the multilayer body using a microtome, and is the average value of all layers or a single layer of the thermoforming container. Substantially matches the thickness of the layer.

The lower limit of the overall average thickness of the thermoformed container is preferably 300 μm, more preferably 500 μm, and even more preferably 700 μm. On the other hand, the upper limit of the overall average thickness of the thermoformed container is preferably 10,000 μm, more preferably 8,500 μm, and even more preferably 7,000 μm. The overall average thickness of the thermoformed container refers to the thickness of all layers in the housing portion of the thermoformed container, and the measuring method is the same as the case of measuring the thickness of all layers of the multilayer body. If the overall average thickness of the thermoformed container is too large, the manufacturing cost may increase. On the other hand, if the overall average thickness of the thermoformed container is too small, the rigidity cannot be maintained and the thermoformed container may be easily broken. Therefore, it is important to set the overall average thickness of the thermoformed container according to the capacity and application.

Examples of other layers laminated on the (1) layer include a (2) layer, a (3) layer, and a (4) layer as a recovery layer. The thermoformed container preferably further includes a layer (2) and a layer (3). When the thermoformed container includes the (2) layer and the (3) layer, it is more preferable to further include the (4) layer. Hereinafter, the (1) layer, the (2) layer, the (3) layer and the (4) layer will be described in detail.

[(1) layer]
The layer (1) is a layer containing EVOH (I) as a main component. Further, the layer (1) preferably contains an alkali metal salt of an organic acid. Further, the layer (1) may contain other optional components as long as the effects of the present invention are not impaired. Here, the "main component" means the most abundant component on a mass basis. When the content of each component is represented by "ppm", this "ppm" means the mass ratio of the content of each component, and 1 ppm is 0.0001 mass%. Hereinafter, each component will be described in detail.

(EVOH (I))
EVOH (I) is a saponified copolymer of ethylene and vinyl ester.

The copolymerization method of ethylene and vinyl ester is not particularly limited, and known methods such as solution polymerization, suspension polymerization, emulsion polymerization, and bulk polymerization can be used. Further, the above-mentioned copolymerization method may be either a continuous method or a batch method.

The lower limit of the ethylene content of EVOH (I) is preferably 10 mol%, more preferably 20 mol%, still more preferably 25 mol%. On the other hand, the upper limit of the ethylene content of EVOH (I) is preferably 60 mol%, more preferably 55 mol%, further preferably 50 mol%, and particularly preferably 40 mol%. If the ethylene content is less than the above lower limit, the thermal stability during melt extrusion is lowered and gelation is likely to occur, and defects such as gel-like lumps and streaks are likely to occur. In particular, if the operation is performed for a long time under conditions of high temperature or high speed than the conditions at the time of general melt extrusion, the possibility of gelation increases. On the other hand, if the ethylene content exceeds the above upper limit, the gas barrier property and the like are lowered, and there is a possibility that the advantageous characteristics of EVOH (I) cannot be sufficiently exhibited.

As the vinyl ester, vinyl acetate is preferably used from the viewpoint of industrial availability and the like. This vinyl acetate usually contains a small amount of acetaldehyde as an unavoidable impurity. The acetaldehyde content of this vinyl acetate is preferably less than 100 ppm. The upper limit of the acetaldehyde content of vinyl acetate is more preferably 60 ppm, further preferably 25 ppm, and particularly preferably 15 ppm. By setting the acetaldehyde content of vinyl acetate in the above range, it becomes easy to prepare EVOH (I) satisfying the formula (1) described later.

EVOH (I) may contain other structural units derived from monomers other than ethylene and vinyl esters. Examples of the monomer giving such another structural unit include vinylsilane-based compounds and other polymerizable compounds. The content of the other structural units is preferably 0.0002 mol% or more and 0.2 mol% or less with respect to all the structural units of EVOH (I).

The lower limit of the degree of saponification of the structural unit derived from the vinyl ester of EVOH (I) is usually 85 mol%, preferably 90 mol%, more preferably 98 mol%, still more preferably 98.9 mol%. If the degree of saponification is less than the above lower limit, the thermal stability may be insufficient.

The lower limit of the content of EVOH (I) in the layer (1) is usually 95% by mass, preferably 98.0% by mass, more preferably 99.0% by mass, and even more preferably 99.5% by mass. By setting the content of EVOH (I) to the above lower limit or more, the gas barrier property, oil resistance, etc. of the thermoformed container can be further improved.

(Peak top molecular weight (Ma))
The peak top molecular weight (Ma) is determined by separating EVOH (I) after heat treatment at 220 ° C. for 50 hours under a nitrogen atmosphere using gel permeation chromatography (hereinafter referred to as “GPC”), and elution from the column at this time. This is a value corresponding to the maximum value of the main peak of the signal (“RI” in FIG. 1) measured by the differential refractive index detector as schematically shown in FIG. 1 of the EVOH (I). The peak top molecular weight (Ma) in the present invention is a value of polymethyl methacrylate conversion (hereinafter, also referred to as “PMMA conversion”) calculated using a calibration curve prepared by the method described later.

As the lower limit of the peak top molecular weight (Ma), 30,000 is preferable, 35,000 is more preferable, 40,000 is further preferable, and 50,000 is particularly preferable. On the other hand, as the upper limit of the peak top molecular weight (Ma), 100,000 is preferable, 80,000 is more preferable, 65,000 is further preferable, and 60,000 is particularly preferable.

(Absorption peak molecular weight (Mb) and (Mc))
As shown schematically in FIG. 1, the absorption peak molecular weights (Mb) and (Mc) are measured by separating EVOH (I) by GPC under the same conditions as the measurement of the peak top molecular weight (Ma) and measuring with an ultraviolet-visible absorbance detector. It is a value corresponding to the maximum value of the absorption peak of the signal (“UV” in FIG. 1) at a specific wavelength. The absorption peak molecular weights (Mb) and (Mc) are molecular weights in terms of polymethylmethacrylate. The molecular weight of the absorption peak at a wavelength of 220 nm is expressed as “Mb”, and the molecular weight of the absorption peak at a wavelength of 280 nm is expressed as “Mc”.

As the lower limit of the absorption peak molecular weight (Mb), 30,000 is preferable, 35,000 is more preferable, 40,000 is further preferable, and 50,000 is particularly preferable. On the other hand, the upper limit of the absorption peak molecular weight (Mb) is preferably 75,000, more preferably 60,000, and even more preferably 55,000.

As the lower limit of the absorption peak molecular weight (Mc), 35,000 is preferable, 40,000 is more preferable, 45,000 is further preferable, and 48,000 is particularly preferable. On the other hand, the upper limit of the absorption peak molecular weight (Mc) is preferably 75,000, more preferably 55,000, and even more preferably 50,000.

(Creation of calibration curve)
The calibration curve is, for example, a monodisperse PMMA (peak top molecular weight: 1,944,000, 790,000,467,400, 271,400, 144,000, 79,250, 35,300) manufactured by Agilent Technologies as a standard. , 13,300,7,100,1,960,1,020,690), and prepare for each of the differential refractive index detector and the absorbance detector. It is preferable to use analysis software to create the calibration curve. In the PMMA measurement of this measurement, for example, a column capable of separating peaks between standard samples having both molecular weights of 1,944,000 and 271,400 is used.

(Molecular weight correlation of EVOH (I))
EVOH (I) satisfies the condition represented by the following formula (1).

(Ma-Mb) / Ma <0.45 ... (1)

The left side (Ma-Mb) / Ma of the formula (1) is preferably less than 0.40, more preferably less than 0.30, and even more preferably less than 0.10. Here, the smaller the difference between the Ma and Mb (Ma-Mb), the main peak (P _RI) and the absorption peak obtained from ultraviolet-visible absorbance detector (P _UV obtained from the differential refractive index detector in FIG. 1 (220 nm)) means that they are in close proximity. On the contrary, when the value of the molecular weight difference (Ma-Mb) becomes large, it means that these two peaks ( _PRI and _PUV (220 nm)) are separated from each other. That is, _{when the value of the molecular weight difference (Ma-Mb) of both peaks (PRI} , _PUV (220 nm)) is large, it means that there are many components having a relatively low molecular weight that absorb ultraviolet rays having a wavelength of 220 nm. do. Therefore, when EVOH (I) does not satisfy the above formula (1), it means that there are many components having a relatively low molecular weight that absorb ultraviolet rays having a wavelength of 220 nm. Then, in this case, during thermoforming using the resin composition containing EVOH (I), EVOH (I) is thermally deteriorated and defects are generated and coloring becomes apparent, and as a result, the strength of the thermoformed container is lowered. Tend to do.

The effect of satisfying the above equation (1) is considered to occur for the following reasons. That is, EVOH causes thermal deterioration such as dehydration to generate carbon-carbon double bonds and carbonyl groups in the molecule that absorb ultraviolet rays having a wavelength of 220 nm, and these groups promote gelation of the resin composition. .. The gelation-promoting action depends on the molecular weight of the heat-deteriorated EVOH. When the molecular weight of the heat-deteriorated EVOH is large, the promoting action is weak, and the smaller the molecular weight, the stronger the promoting action. Therefore, when EVOH satisfies the above formula (1), that is, when a relatively high molecular weight can be maintained even if it is thermally deteriorated, it is considered that the decrease in strength of the thermoformed container can be suppressed.

EVOH (I) preferably satisfies the condition of the following formula (2).

(Ma-Mc) / Ma <0.45 ... (2)

The left side (Ma-Mc) / Ma of the formula (2) is more preferably less than 0.40, further preferably less than 0.30, and particularly preferably less than 0.15. Here, if the value of the left side (Ma-Mc) / Ma of the equation (2) becomes large, the main peak ( _PRI ) obtained from the differential refractive index detector and the absorption peak (P) obtained from the ultraviolet-visible absorbance detector _{It is separated from UV} (280 nm)), and a large number of components absorb ultraviolet rays having a wavelength of 280 nm in a component having a relatively low molecular weight. In this case, EVOH is thermally deteriorated during thermoforming, and defects and coloring become apparent, and as a result, the strength of the thermoformed container tends to decrease.

The effect of satisfying the above equation (2) is considered to occur for the following reasons. That is, EVOH has a conjugated double bond in the molecule that absorbs ultraviolet rays having a wavelength of 280 nm due to further thermal deterioration after a carbon-carbon double bond or a carbonyl group is generated in the molecule due to the above-mentioned thermal deterioration. This conjugated double bond promotes yellowing of the resin composition. Similar to the above-mentioned gelation promoting action, the above-mentioned yellowing promoting action depends on the molecular weight of the heat-deteriorated EVOH, and when the heat-deteriorated EVOH has a large molecular weight, the above-mentioned promoting action is weak and the molecular weight is small. Indeed, the above-mentioned promoting action becomes stronger. Therefore, when EVOH satisfies the above formula (2), that is, when the relatively high molecular weight can be maintained even if the thermal deterioration progresses, it is considered that the decrease in the strength of the thermoformed container can be further suppressed.

(Method of preparing EVOH (I) satisfying the condition represented by the formula (1))
As a method for preparing EVOH (I) satisfying the condition represented by the formula (1), in the conventional preparation of EVOH ,
In the preparation of the copolymer of (B) the raw material ethylene and vinyl ester, how such a specific amount of impurities contained in the vinyl ester used in the radical polymerization like et be.

((B) In the preparation of a copolymer of ethylene and vinyl ester as a raw material, a method of setting an impurity contained in the vinyl ester used for radical polymerization to a specific amount)
As the lower limit of the total content of impurities contained in the vinyl ester used for radical polymerization, 1 ppm is preferable, 3 ppm is more preferable, and 5 ppm is further preferable. The upper limit of the total content of the impurities is preferably 1,200 ppm, more preferably 1,100 ppm, still more preferably 1,000 ppm.

Examples of the impurities include aldehydes such as acetaldehyde, crotonaldehyde and achlorein; acetals such as acetal aldehyde dimethyl acetal, crotonaldehyde dimethyl acetal and achlorein dimethyl acetal in which this aldehyde is acetalized by alcohol as a solvent; ketones such as acetone; methyl acetate and acetic acid. Examples thereof include esters such as ethyl.

Of the above impurities, acetaldehyde is likely to be generated in the production of vinyl acetate and the like, and it is easy to prevent EVOH (I) from satisfying the formula (1). Therefore, in this method, it is particularly preferable to reduce the content of acetaldehyde.

(Melting viscosity of EVOH (I) (melt flow rate))
The lower limit of the melt flow rate of EVOH (I) is preferably 0.5 g / 10 min, more preferably 1.0 g / 10 min, and even more preferably 1.4 g / 10 min. On the other hand, the upper limit of the melt flow rate of EVOH (I) is preferably 30 g / 10 min, more preferably 25 g / 10 min, further preferably 20 g / 10 min, particularly preferably 15 g / 10 min, still more preferably 10 g / 10 min. Most preferably 1.6 g / 10 min. If the melt flow rate of EVOH (I) is less than the above lower limit or exceeds the above upper limit, the moldability and appearance may be deteriorated.

The melt flow rate is a value measured at a temperature of 190 ° C. and a load of 2,160 g in accordance with JIS-K7210 (1999).

(Alkali metal salt of organic acid)
The alkali metal constituting the alkali metal salt of the organic acid may be a single metal species or may be composed of a plurality of metal species. Examples of the alkali metal of the organic acid include lithium, sodium, potassium, rubidium, cesium and the like, but sodium and potassium are more preferable from the viewpoint of industrial availability. (1) When the layer contains an alkali metal salt of an organic acid, the long-running property and the interlayer adhesive strength when formed into a multilayer body are improved.

Examples of the organic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, heptic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, palmitic acid, stearic acid, succinic acid, linoleic acid and oleic acid. And other aliphatic carboxylic acids; aromatic carboxylic acids such as benzoic acid, salicylic acid and phthalic acid; hydroxycarboxylic acids such as lactic acid, tartaric acid, citric acid and malic acid; Sulfuric acid and the like. Among these, the organic acid is preferably a carboxylic acid, more preferably an aliphatic carboxylic acid, and even more preferably acetic acid.

The alkali metal salt of the organic acid is not particularly limited, and examples thereof include aliphatic carboxylic acid salts such as lithium, sodium and potassium, and aromatic carboxylic acid salts. Specific examples of the alkali metal salt of the organic acid include sodium acetate, potassium acetate, sodium stearate, potassium stearate, sodium salt of ethylenediamine tetraacetic acid and the like. Of these, sodium acetate and potassium acetate are preferable as the alkali metal salt of the organic acid.

(1) When the layer contains an alkali metal salt of an organic acid, the lower limit of the content of the alkali metal salt of the organic acid is preferably 1 ppm, more preferably 5 ppm, further preferably 10 ppm, and 80 ppm in terms of metal. Especially preferable. On the other hand, the upper limit of the content of the alkali metal salt of the organic acid is preferably 1,000 ppm, more preferably 800 ppm, further preferably 550 ppm, particularly preferably 250 ppm, and even more preferably 150 ppm in terms of metal. If the content of the alkali metal salt of the organic acid is less than the above lower limit, the interlayer adhesiveness may decrease. On the contrary, when the content of the alkali metal salt of the organic acid exceeds the above upper limit, it becomes difficult to reduce the coloring of the layer (1), and the appearance may be deteriorated.

(Other optional ingredients)
Other optional components include antioxidants, UV absorbers, plasticizers, antioxidants, lubricants, colorants, fillers, polyvalent metal salts of higher aliphatic carboxylic acids, hindered phenolic compounds and hindered amine compounds. Examples thereof include heat stabilizers such as, other resins such as polyamide and polyolefin, and hydrotalcite compounds. The total content of the other optional components of the resin composition is usually 1% by mass or less.

Examples of the filler include glass fiber, ballast night, calcium silicate, talc, montmorillonite and the like.

Examples of the polyvalent metal salt of the higher aliphatic carboxylic acid include calcium stearate and magnesium stearate.

As a measure against gelation, for example, a hindered phenol-based compound and a hindered amine-based compound exemplified as the above-mentioned heat stabilizer, a polyvalent metal salt of the above-mentioned higher aliphatic carboxylic acid, a hydrotalcite compound and the like are added to the layer (1). You may. (1) When a compound for preventing gelation is added to the layer, the amount of the compound added is usually 0.01% by mass or more and 1% by mass or less.

(Method for preparing EVOH-containing resin composition)
The layer (1) can be formed by an EVOH-containing resin composition containing each component. Examples of the method for producing this EVOH-containing resin composition include a method of mixing and kneading an alkali metal salt and other optional components together with EVOH (I) pellets, if necessary, and EVOH (I) pellets. Examples thereof include a method of immersing in a solution containing components. For mixing the pellets with other components, for example, a ribbon blender, a high-speed mixer conider, a mixing roll, an extruder, an intensive mixer, or the like can be used.

(Melting viscosity (melt flow rate) of EVOH-containing resin composition)
The lower limit of the melt flow rate of the EVOH-containing resin composition is preferably 0.5 g / 10 min, more preferably 1.0 g / 10 min, and even more preferably 1.4 g / 10 min. On the other hand, the upper limit of the melt flow rate of the EVOH-containing resin composition is preferably 30 g / 10 min, more preferably 25 g / 10 min, further preferably 20 g / 10 min, particularly preferably 15 g / 10 min, and even more preferably 10 g / 10 min. , 1.6 g / 10 min is most preferable. If the melt flow rate of the EVOH-containing resin composition is less than the above lower limit or exceeds the above upper limit, the moldability and appearance may be deteriorated.

(1) The lower limit of the average thickness of the layers is not particularly limited, but is preferably 0.5% and 1.0% with respect to the average thickness of all layers from the viewpoint of barrier properties and mechanical strength. Is more preferable, and 1.5% is further preferable. (1) The upper limit of the average thickness of the layers is not particularly limited, but is preferably 5.0% and 4.5% with respect to the average thickness of all layers from the viewpoint of barrier properties and mechanical strength. Is more preferable, and 4.1% is further preferable.

[(2) layer]
The layer (2) is mainly composed of a thermoplastic resin which is arranged on the inner surface side and the outer surface side of the layer (1) and whose solubility parameter calculated from the Fedors equation is 11 (cal / cm ³ ) ^{1/2 or less.} It is a layer to do. A thermoplastic resin having a solubility parameter calculated by this formula of 11 (cal / cm ³ ) ^1/2 or less is excellent in moisture resistance. The solubility parameter calculated from the Fedors equation is a value represented by ^{(E / V) 1/2.} In the above formula, E is the molecular aggregation energy (cal / mol) and is represented by E = Σei. Note that ei is evaporation energy. Further, V has a molecular volume (cm ³ / mol) and is represented by V = Σvi (vi: molar volume).

(2) The thermoplastic resin that is the main component of the layer is not particularly limited as long as it is a thermoplastic resin having a solubility parameter of 11 (cal / cm ³ ) ^1/2 or less, but is, for example, polyethylene (linear). Low density polyethylene, low density polyethylene, medium density polyethylene, high density polyethylene, etc.), ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, polypropylene, propylene and co-weight of α-olefin with 4 to 20 carbon atoms Combined, homopolymers or copolymers of olefins such as polybutene and polypentene, polystyrene, polyvinyl chloride, polyvinylidene chloride, acrylic resin, vinyl ester resin, polyurethane elastomer, polycarbonate, chlorinated polyethylene, chlorinated polypropylene, etc. Can be mentioned. Of these, polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, and polystyrene are preferable, and high-density polyethylene is more preferable.

The lower limit of the density of the high-density polyethylene is preferably 0.93 g / cm ^{3 and} more ^{preferably 0.95 g / cm 3} from the viewpoints of rigidity, impact resistance, moldability, drawdown resistance, gasoline resistance and the like. Preferably, 0.96 g / cm ³ is even more preferable. The upper limit of the density of the high-density polyethylene is preferably ^{0.98 g / cm 3} from the viewpoints of rigidity, impact resistance, moldability, drawdown resistance, gasoline resistance and the like.

The lower limit of the melt flow rate (MFR) of the high-density polyethylene under a load of 190 ° C. and 2,160 g is preferably 0.01 g / 10 minutes. On the other hand, the upper limit of the MFR is preferably 0.5 g / 10 minutes, more preferably 0.1 g / 10 minutes.

The high-density polyethylene can be used by appropriately selecting it from commercially available products. Further, the layer (2) may contain other optional components similar to the layer (1) as long as the effects of the present invention are not impaired.

(2) The lower limit of the average thickness of the layers is not particularly limited, but is preferably 5%, more preferably 8%, and even more preferably 10% with respect to the average thickness of all layers. (2) The upper limit of the average thickness of the layers is not particularly limited, but is preferably 70%, more preferably 60%, and even more preferably 50% with respect to the average thickness of all layers.

[(3) layer]
The layer (3) is arranged between the layer (1) and the layer (2) and contains a carboxylic acid-modified polyolefin as a main component. The layer (3) can function as an adhesive layer between the layer (1) and another layer such as the layer (2). The carboxylic acid-modified polyolefin has a carboxy group or an anhydride group thereof obtained by chemically bonding an ethylenically unsaturated carboxylic acid or an anhydride thereof to an olefin polymer by an addition reaction, a graft reaction, or the like. It refers to an olefin polymer.

Examples of the ethylenically unsaturated carboxylic acid and its anhydride include monocarboxylic acid, monocarboxylic acid ester, dicarboxylic acid, dicarboxylic acid monoester, dicarboxylic acid diester, and dicarboxylic acid anhydride. Specific examples thereof include maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester, and fumaric acid monomethyl ester. Of these, dicarboxylic acid anhydrides such as maleic anhydride and itaconic anhydride are preferable, and maleic anhydride is more preferable.

Examples of the olefin-based polymer to be the base polymer include polyolefins such as low-density, medium-density or high-density polyethylene, linear low-density polyethylene, polypropylene, and boribten;
Examples thereof include a copolymer of an olefin such as an ethylene-vinyl acetate copolymer and an ethylene-ethyl acrylate copolymer and a comonomer. The comonomer is not particularly limited as long as it is a monomer copolymerizable with an olefin, and examples thereof include vinyl ester and unsaturated carboxylic acid ester. Examples of the olefin polymer include linear low-density polyethylene, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5% by mass or more and 55% by mass or less, and an ethyl acetate content of 8% by mass or more and 35% by mass or more. An ethylene-ethyl acrylate copolymer having a mass% or less is preferable, and a linear low-density polyethylene and an ethylene-vinyl acetate copolymer having a vinyl acetate content of 5% by mass or more and 55% by mass or less are more preferable.

The carboxylic acid-modified polyolefin is subjected to an addition reaction or a graft reaction of the ethylenically unsaturated carboxylic acid or its anhydride to the olefin polymer in the presence of a solvent such as xylene and a catalyst such as a peroxide. It is obtained by introducing by. At this time, the lower limit of the amount of carboxylic acid or its anhydride added to the olefin polymer or the amount of graft (modification degree) is preferably 0.01% by mass, preferably 0.02% by mass, based on the olefin polymer. % Is more preferable. On the other hand, the upper limit of the degree of modification is preferably 15% by mass, more preferably 10% by mass, based on the olefin polymer.

The layer (3) may contain other optional components similar to the layer (1) in addition to the carboxylic acid-modified polyolefin as long as the effects of the present invention are not impaired.

(3) The lower limit of the average thickness of the layers is not particularly limited, but is preferably 0.3%, more preferably 0.6%, and further 1.2% with respect to the average thickness of all layers. preferable. (3) The upper limit of the average thickness of the layers is not particularly limited, but is preferably 12%, more preferably 9%, and even more preferably 6% with respect to the average thickness of all layers. If the average thickness of the layer (3) as the adhesive resin layer is less than the above lower limit, the adhesiveness may decrease. Further, if the average thickness of the layer (3) exceeds the above upper limit, the cost may increase.

[(4) layer]
The layer (4) is a layer containing EVOH (I), the thermoplastic resin, and the carboxylic acid-modified polyolefin. Further, the layer (4) is preferably formed by using the recovered products of the layer (1), the layer (2) and the layer (3) in the manufacturing process of the thermoformed container. Examples of the recovered product include burrs generated in the manufacturing process of the thermoformed container, products that have failed the certification, and the like. By further having the layer (4) as such a recovery layer in the thermoforming container, such burrs, products that have failed the certification, etc. can be reused, and a resin used in the manufacture of the thermoforming container. Loss can be reduced.

The layer (4) can be used as a substitute for the layer (2) described above, but in general, the mechanical strength of the layer (4) is often lower than that of the layer (2). It is preferable to use the 2) layer and the (4) layer in a laminated manner. When the thermoformed container receives an impact from the outside, stress is concentrated in the container, and compressive stress against the impact acts on the inner layer side of the container at the stress concentration part, which may cause damage, so the strength is weak. The layer (4) is preferably arranged on the outer layer side of the layer (1). Further, when it is necessary to recycle a large amount of resin, such as when a large amount of burrs are generated, layers (4), which are recovery layers, can be arranged on both sides of the layer (1).

The upper limit of the content of EVOH (I) in the layer (4) is preferably 9.0% by mass. If the content of EVOH (I) in the layer (4) exceeds the above upper limit, cracks are likely to occur at the interface with the layer (2), and the entire thermoformed container may be destroyed starting from the cracks. be. The lower limit of the EVOH (I) content in the layer (4) is, for example, 3.0% by mass.

(4) The lower limit of the average thickness of the layers is not particularly limited, but is preferably 10%, more preferably 20%, and even more preferably 30% with respect to the average thickness of all layers. (4) The upper limit of the average thickness of the layers is not particularly limited, but is preferably 60%, more preferably 55%, and even more preferably 50% with respect to the average thickness of all layers.

The thermoformed container is preferably one obtained by thermoforming a multilayer body including the (1) layer, the (2) layer and the (3) layer. This multilayer body may further include the (4) layer.

[Manufacturing method of multilayer body used for thermoforming container]
The multilayer body used for the thermoforming container can be formed by using a coextrusion molding apparatus. The multilayer body is, for example, the above-mentioned EVOH-containing resin composition forming the (1) layer, the resin composition forming the (2) layer, the resin composition forming the (3) layer, and the resin forming the (4) layer. The composition can be formed as having a predetermined layer structure by charging the composition into separate extruders and co-extruding with these extruders.

Extrusion molding of each layer is performed by operating an extruder equipped with a uniaxial screw at a predetermined temperature. (1) The temperature of the extruder that forms the layer is, for example, 170 ° C. or higher and 240 ° C. or lower. The temperature of the extruder that forms the layer (2) is, for example, 200 ° C. or higher and 240 ° C. or lower. Further, the temperature of the extruder forming the layer (3) is set to, for example, 160 ° C. or higher and 220 ° C. or lower. Further, the temperature of the extruder for forming the layer (4) is set to, for example, 200 ° C. or higher and 240 ° C. or lower.

(Thermoforming)
The thermoformed container can be formed by heating and softening a multilayer body such as a film or a sheet, and then molding it into a mold shape. As the thermoforming method, for example, vacuum or compressed air is used, and if necessary, a plug is also used to form a mold shape (straight method, drape method, air slip method, snapback method, plug assist method, etc.), press molding. How to do it. Various molding conditions such as molding temperature, degree of vacuum, pressure of compressed air, and molding speed are appropriately set according to the shape of the plug, the shape of the mold, the properties of the raw material film and the sheet, and the like.

The molding temperature is not particularly limited as long as the resin can be softened sufficiently for molding, and the suitable temperature range varies depending on the configuration of the multilayer body such as a film or a sheet.

When the film is thermoformed, it is desirable that the temperature is not so high that the film is melted by heating or the unevenness of the metal surface of the heater plate is transferred to the film, but the temperature is not so low that the shaping is not sufficient. The lower limit of the specific heating temperature of the film is usually 50 ° C., preferably 60 ° C., more preferably 70 ° C. The upper limit of the heating temperature of the film is usually 120 ° C., preferably 110 ° C., more preferably 100 ° C.

On the other hand, when the sheet is thermoformed, it may be possible to form the sheet even at a higher temperature than the case of the film. The heating temperature of the sheet is, for example, 130 ° C. or higher and 180 ° C. or lower.

<Manufacturing method of thermoformed container>
The thermoforming container includes a step of forming a layer (1) using a resin composition containing EVOH as a main component and a step of thermoforming a layer structure containing the layer (1). Production in which the molecular weight measured after heat treatment at 220 ° C. for 50 hours under a nitrogen atmosphere using a gel permeation chromatograph equipped with a differential refractometer detector and an ultraviolet visible absorbance detector satisfies the condition represented by the above formula (1). It is preferably produced by the method.

<Layer structure of thermoformed container>
The thermoformed container may be provided with at least the layer (1), and may be composed of a single layer or a plurality of layers. When the thermoforming container has a plurality of layers, the layer structure may be appropriately set according to the application and the like.

When the thermoforming container is composed of a plurality of layers, it is preferable to arrange the layer (2) on the outermost layer. That is, from the inner surface to the outer surface of the accommodating portion, the (2) layer / (3) layer / (1) layer / (3) layer / (2) layer (hereinafter, "(inner surface) (2) / (3) / (1) / (3) / (2) (outer surface) ”) is preferable from the viewpoint of impact resistance. The layer structure when the recovery layer (4) is included is, for example, (inner surface) (2) / (3) / (1) / (3) / (4) / (2) (outer surface). ),
(Inner surface) (2) / (4) / (3) / (1) / (3) / (4) / (2) (Outer surface),
(Inner surface) (4) / (3) / (1) / (3) / (4) (outer surface) and the like. In these layer configurations, a layer configuration may include a layer (4) instead of the layer (2). Among these, the layer structure of the thermoformed container includes (inner surface) (2) / (3) / (1) / (3) / (4) / (2) (outer surface) and (inner surface). Surface) (2) / (4) / (3) / (1) / (3) / (4) / (2) (outer surface) is preferable. When a plurality of layers (1) to (4) are used, the resins constituting each layer may be the same or different.

[Cup-shaped container]
Next, the thermoformed container of the present invention will be specifically described by taking the cup-shaped container shown in FIGS. 2 and 3 as an example. However, the cup-shaped container is only an example of a thermoformed container, and the following description of the cup-shaped container does not limit the scope of the present invention.

The cup-shaped container 1 of FIGS. 2 and 3 includes a cup body 2 as an accommodating portion and a flange portion 3. The cup-shaped container 1 is used by accommodating the contents in the cup body 2 and sealing the lid 7 on the flange portion 3 so as to close the opening 4 of the cup body 2. Examples of the seal include a resin film, a metal foil, a metal resin composite film, and the like, and among these, a metal resin composite film in which a metal layer is laminated on the resin film is preferable. Examples of the resin film include a polyethylene film and a polyethylene terephthalate film. The metal layer is not particularly limited, but a metal foil and a metal vapor deposition layer are preferable, and an aluminum foil is more preferable from the viewpoint of gas barrier property and productivity.

The cup-shaped container 1 can be obtained by thermoforming a multilayer body such as a film or a sheet. It is preferable that the multilayer body includes at least the (1) layer, and another layer is laminated on the (1) layer. Examples of other layers include (2) layer, (3) layer, (4) layer and the like.

As the layer structure of the cup-shaped container 1, the structure shown in FIG. 4 is preferable. In the layer structure shown in FIG. 4, the layer 12 is laminated on one surface side of the layer 11 (the inner surface 5 side of the cup body 2 of the cup-shaped container 1) via the layer 13 (3). The layer structure is such that the (4) layer 14 and the (2) layer 12 are laminated via the (3) layer 13 on the other surface side (the outer surface 6 side of the cup body 2 of the cup-shaped container 1).

[Manufacturing method of cup-shaped container]
As shown in FIG. 5, the cup-shaped container 1 is manufactured by heating a continuous multilayer body 20 in the form of a film, a sheet, or the like with a heating device 30 to soften it, and then thermoforming it using a mold device 40. NS.

(Heating device)
The heating device 30 includes a pair of heaters (heater 31 and heater 32), and the continuous multilayer body 20 can pass between these heaters 31 and the heater 32. As the heating device 30, one that is heated by a hot press can also be used.

(Mold device)
The mold device 40 is suitable for thermoforming by the plug assist method, and includes a lower mold 50 and an upper mold 51 housed in a chamber (not shown). The lower die 50 and the upper die 51 can be individually moved in the vertical direction, and the continuous multilayer body 20 can pass between the lower die 50 and the upper die 51 in a separated state. The lower mold 50 has a plurality of recesses 52 for forming a housing portion of the cup-shaped container 1. The upper die 51 includes a plurality of plugs 53 projecting toward the lower die 50. The plurality of plugs 53 are provided at positions corresponding to the plurality of recesses 52 of the lower mold 50. Each plug 53 can be inserted into the corresponding recess 52.

(Thermoforming)
First, as shown in FIGS. 5 and 6 (A), the continuous multilayer body 20 softened by the heating device 30 is brought into close contact with the lower mold 50 by moving the lower mold 50 upward, and the continuous multilayer body 20 is brought into close contact with the lower mold 50. Is slightly lifted to give tension to the continuous multilayer body 20. Next, as shown in FIG. 6B, the plug 53 is inserted into the recess 52 by moving the upper mold 51 downward.

Subsequently, as shown in FIG. 6C, the upper die 51 is moved upward to separate the plug 53 from the recess 52, and then the inside of the chamber (not shown) is evacuated to draw the continuous multilayer body 20 into the recess 52. Adhere to the inner surface. After that, the shape is fixed by cooling the molded portion by injecting air. Subsequently, as shown in FIG. 6D, a primary molded product is obtained by opening the chamber (not shown) to the atmosphere and moving the lower mold 50 downward to release the lower mold 50. By cutting this primary molded product, the cup-shaped container 1 shown in FIGS. 2 and 3 can be obtained.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. In the following, "%" and "part" represent "mass%" and "part by mass", respectively, unless otherwise specified.

[Synthesis of EVOH]
[Synthesis Example 1] (Synthesis of EVOH pellets)
(Polymerization of ethylene-vinyl acetate copolymer)
83 kg of vinyl acetate and 14.9 kg of methanol were charged in a 250 L pressurized reaction tank equipped with a jacket, a stirrer, a nitrogen inlet, an ethylene inlet and an initiator addition port, and the temperature was raised to 60 ° C., and then nitrogen was added to the reaction solution. The gas was bubbled for 30 minutes to replace the inside of the reaction vessel with nitrogen. Next, ethylene was introduced so that the reaction vessel pressure (ethylene pressure) was 4.0 MPa. After adjusting the temperature in the reaction vessel to 60 ° C., use 12.3 g of 2,2'-azobis (2,4-dimethylvaleronitrile) ("V-65" from Wako Pure Chemical Industries, Ltd.) as an initiator. It was added as a methanol solution to initiate polymerization. During the polymerization, the ethylene pressure was maintained at 4.0 MPa and the polymerization temperature was maintained at 60 ° C. After 5 hours, when the polymerization rate of vinyl acetate reached 40%, the mixture was cooled to terminate the polymerization. Ethylene was exhausted from the reaction vessel, and nitrogen gas was bubbled into the reaction solution to completely remove ethylene. Then, after removing unreacted vinyl acetate under reduced pressure, an ethylene-vinyl acetate copolymer (hereinafter referred to as EVAc) was obtained. As the vinyl acetate used for the synthesis, acetaldehyde having the content shown in Table 1 below was added.

(Saponification)
Methanol was added to the obtained EVAc solution to prepare a methanol solution of EVAc having a concentration of 15% by mass. To 253.4 kg of a methanol solution of EVAc (38 kg of EVAc in the solution), 76.6 L of a methanol solution containing 10% by mass of sodium hydroxide (molar ratio 0.4 to vinyl acetate unit in EVAc) was added. EVAc was saponified by stirring at 60 ° C. for 4 hours. Six hours after the start of the reaction, 9.2 kg of acetic acid and 60 L of water were added to neutralize the above reaction solution, and the reaction was stopped.

(Washing)
The neutralized reaction solution was transferred from the reactor to a drum can and left at room temperature for 16 hours to be cooled and solidified into a cake. Then, the cake-shaped resin was deflated using a centrifuge (“H-130” manufactured by Japan Centrifuge Co., Ltd., rotation speed 1200 rpm). Next, the central portion of the centrifuge was washed while continuously supplying ion-exchanged water from above, and the above resin was washed with water for 10 hours. The conductivity of the cleaning liquid 10 hours after the start of cleaning was 30 μS / cm (measured with “CM-30ET” of Toa Denpa Kogyo Co., Ltd.).

(Granulation)
The powdery EVOH thus obtained was dried at 60 ° C. for 48 hours using a dryer. 20 kg of dry powdery EVOH was dissolved in 43 L of a mixed water / methanol solution (mass ratio: water / methanol = 4/6) at 80 ° C. for 12 hours with stirring. Next, the stirring was stopped, the temperature of the dissolution tank was lowered to 65 ° C., and the mixture was left for 5 hours to defoam the above-mentioned EVOH water / methanol solution. Then, it is extruded from a gold plate having a circular opening with a diameter of 3.5 mm into a water / methanol mixed solution (mass ratio: water / methanol = 9/1) at 5 ° C. to precipitate in a strand shape and cut. A hydrous EVOH pellet having a diameter of about 4 mm and a length of about 5 mm was obtained.

(purification)
The obtained pellets were deliquescented with a centrifuge, and the operation of adding a large amount of water to deliquesce was repeated to wash the pellets to obtain EVOH pellets. The degree of saponification of the obtained EVOH was 99 mol%.

20 kg of the obtained EVOH pellets were washed with an aqueous acetic acid solution and ion-exchanged water, and then immersed in an aqueous solution containing sodium acetate. The aqueous solution for dipping treatment and the resin composition chip are separated and deliquescented, then placed in a hot air dryer and dried at 80 ° C. for 4 hours, and further dried at 100 ° C. for 16 hours to obtain Synthetic Example 1. An EVOH-containing resin composition (dried EVOH pellets) was obtained. Using these dried EVOH pellets, the saponification degree, ethylene content, alkali metal content and the like of EVOH shown in Table 1 were measured by the method described below.

[Synthesis Examples 2-4 and Comparative Synthesis Example 1]
The EVOH-containing resin compositions of Synthesis Examples 2 to 4 are the same as in Synthesis Example 1 except that the acetaldehyde content of vinyl acetate, the degree of saponification of EVOH (I), and the alkali metal salt content are as shown in Table 1. Was synthesized.

[Ethylene content and saponification of EVOH]
The dried EVOH pellets were pulverized by freeze milling. The obtained pulverized EVOH was sieved with a sieve having a nominal size of 1 mm (standard flue standard JIS-Z8801 compliant). 5 g of EVOH powder that had passed through this sieve was immersed in 100 g of ion-exchanged water, stirred at 85 ° C. for 4 hours, and then deliquesed and dried twice. Using the obtained powdered EVOH after washing, ¹ H-NMR measurement was carried out under the following measurement conditions, and the ethylene content and saponification degree were determined by the following analysis method.

(Measurement condition)
Device name: Superconducting nuclear magnetic resonance device ("Lambda500" from JEOL Ltd.)
Observation frequency: 500MHz
Solvent: DMSO-d ₆
Polymer concentration: 4% by mass
Measurement temperature: 40 ° C and 95 ° C
Number of integrations: 600 Pulse delay time: 3.836 seconds Sample rotation speed: 10Hz to 12Hz
Pulse width (90 ° pulse): 6.75 μsec

(analysis method)
In the measurement at 40 ° C., a hydrogen peak in the water molecule was observed around 3.3 ppm, which overlapped with the 3.1 ppm to 3.7 ppm portion of the peak of methine hydrogen in vinyl alcohol unit of EVOH. On the other hand, in the measurement at 95 ° C., although the overlap generated at 40 ° C. is eliminated, the hydrogen peak of the hydroxyl group of the vinyl alcohol unit of EVOH present in the vicinity of 4 ppm to 4.5 ppm is the methine of the vinyl alcohol unit of EVOH. It overlapped with the 3.7 ppm to 4 ppm portion of the hydrogen peak. That is, regarding the quantification of methine hydrogen (3.1 ppm to 4 ppm) in vinyl alcohol units of EVOH, 95 for the portion of 3.1 ppm to 3.7 ppm in order to avoid duplication with the hydrogen peak of water or hydroxyl group. The measurement data at ° C. was adopted, and the measurement data at 40 ° C. was adopted for the portion of 3.7 ppm to 4 ppm, and the total amount of the methine hydrogen was quantified as the total value of these. It is known that the peak of hydrogen of water or a hydroxyl group shifts to the high magnetic field side by raising the measurement temperature. Therefore, the analysis was performed using the measurement results of both 40 ° C. and 95 ° C. as follows. From the above spectrum measured at 40 ° C., the integrated value (I ₁ ) of the peak of the chemical shift of 3.7 ppm to 4 ppm and the integrated value (I ₂ ) of the peak of the chemical shift of 0.6 ppm to 1.8 ppm were obtained. ..

On the other hand, from the spectrum measured at 95 ° C., the integral value _{of the chemical shift peak of 3.1 ppm to 3.7 ppm (I 3} ), the integral value of the chemical shift peak of 0.6 ppm to 1.8 ppm (I ₄ ), and _{The integral value (I 5} ) of the peak of the chemical shift of 1.9 ppm to 2.1 ppm was determined. Here, the peak of the chemical shift of 0.6 ppm to 1.8 ppm is mainly derived from methylene hydrogen, and the peak of the chemical shift of 1.9 ppm to 2.1 ppm is in the unsaponified vinyl acetate unit. It is derived from methyl hydrogen. From these integrated values, the ethylene content was calculated by the following formula (3), and the saponification degree was calculated by the following formula (4).

[Alkali metal content]
The alkali metal content was measured using a spectroscopic analyzer. Specifically, 0.5 g of dried EVOH pellets was added to a pressure-resistant container made of Teflon (registered trademark) manufactured by Actac, and 5 mL of nitric acid (for precision analysis by Wako Pure Chemical Industries, Ltd.) was added. After leaving for 30 minutes, cover the container with a cap lip with a rupture disc, and use a microwave high-speed decomposition system (Actac's "Speedwave MWS-2") at 150 ° C for 10 minutes, then 180 ° C for 10 minutes. Treatment was performed to decompose the dried EVOH pellets. When the decomposition of the dried EVOH pellets was not completed in the above treatment, the treatment conditions were appropriately adjusted. The obtained decomposition product was diluted with 10 mL of ion-exchanged water, the whole solution was transferred to a 50 mL volumetric flask, and the volume was adjusted with ion-exchanged water to obtain a decomposition solution. The alkali metal content was measured by quantitatively analyzing the decomposition solution at a Na wavelength of 589.592 nm using an ICP emission spectrophotometer (“Optima 4300 DV” manufactured by PerkinElmer Japan Co., Ltd.).

[Melting viscosity (melt flow rate)]
The melt viscosity (melt flow rate) was measured at a temperature of 190 ° C. and a load of 2,160 g in accordance with JIS-K7210 (1999).

[Measurement of molecular weight of EVOH]
(Preparation of measurement sample)
The measurement sample was prepared by heating EVOH at 220 ° C. for 50 hours in a nitrogen atmosphere.

(GPC measurement)
GPC measurement was performed using "GPCmax" manufactured by VISCOTECH. The molecular weight was calculated based on the signal intensity detected by the differential refractive index detector and the ultraviolet-visible absorbance detector. As the differential refractive index detector and the ultraviolet-visible absorbance detector, "TDA305" and "UV Detector 2600" manufactured by VISCOTECH were used. As the detection cell of this absorbance detector, a cell having an optical path length of 10 mm was used. As the GPC column, "GPC HFIP-806M" manufactured by Showa Denko KK was used. Further, as the analysis software, "OmniSEC (Version 4.7.0.406)" attached to the apparatus was used.

(Measurement condition)
A measurement sample was taken and dissolved in hexafluoroisopropanol (hereinafter referred to as "HFIP") containing 20 mmol / L of sodium trifluoroacetate to prepare a 0.100 wt / vol% solution. For the measurement, a solution filtered through a 0.45 μm polytetrafluoroethylene filter was used. The measurement sample was dissolved by allowing it to stand overnight at room temperature.

As the mobile phase, HFIP containing 20 mmol / L sodium trifluoroacetate was used. The flow rate of the mobile phase was 1.0 mL / min. The sample injection amount was 100 μL, and the measurement was performed at a GPC column temperature of 40 ° C.

(Creation of calibration curve)
As a standard, polymethyl methacrylate (hereinafter abbreviated as "PMMA") manufactured by Agilent Technologies (hereinafter abbreviated as "PMMA") (peak top molecular weight: 1,944,000, 790,000,467,400, 271,400, 144,000, 79, 250, 35, 300, 13, 300, 7,100, 1,960, 1,020 or 690) to measure the elution volume for each of the differential index detector and the absorbance detector. The calibration curve of was created. The above analysis software was used to create each calibration curve. In this measurement, a column capable of separating peaks between standard samples having both molecular weights of 1,944,000 and 271,400 was used in the measurement of PMMA.

The peak intensity obtained from the differential refractive index detector is represented by "mV", and as a standard sample, American Polymer Standard Corp. When a PMMA sample (PMMA85K: weight average molecular weight 85,450, number average molecular weight 74,300, intrinsic viscosity 0.309) was used as a concentration of 1.000 mg / mL, the peak intensity was 358.31 mV.

The peak intensity obtained from the ultraviolet-visible absorbance detector was represented by the absorbance (absorbance unit), and the absorbance of the ultraviolet-visible absorbance detector was converted to 1 absorption unit = 1,000 mV in the analysis software.

<Making a thermoformed container>
[ Reference Examples 1 and 2, Examples 1 and 2 and Comparative Example 1]
[Preparation of coextrusion film formation]
Using a coextrusion molding apparatus, homopolypropylene (“PY220” manufactured by Mitsubishi Noblen Co., Ltd.) for forming a layer (2), EVOH resin compositions of Synthesis Examples 1 to 4 and Comparative Synthesis Example 1 for forming a layer (1), ( 3) Carboxylic acid-modified polyolefin (“QF-500” manufactured by Mitsui Chemicals Admer Co., Ltd.) forming a layer was charged into separate extruders, and (2): 425 μm / (3): 50 μm / (1): 50 μm / (3). ): 50 μm / (2): A multilayer sheet having a layer structure of 425 μm and having an average thickness of 1,000 μm was produced. For extrusion molding, the temperature of an extruder equipped with a uniaxial screw having a diameter of 65 mm and L / D = 22 is 200 ° C to 240 ° C for homopolypropylene, and the temperature is 40 mm for an EVOH resin composition and uniaxial with L / D = 26. Feed block with an extruder equipped with a screw at a temperature of 170 ° C. to 240 ° C., and an extruder having a diameter of 40 mm and an L / D = 26 uniaxial screw at a temperature of 160 ° C. to 220 ° C. for carboxylic acid-modified polyolefin. This was carried out by operating the mold die (width 600 mm) at 255 ° C.

[Thermoforming]
The multilayer sheet obtained by the co-extrusion molding device (collected 30 minutes and 24 hours after the start-up of the co-extrusion molding device) was cut into 15 cm squares and used by Asano Seisakusho's batch thermoforming tester. Under the condition of sheet temperature 150 ℃, thermoformed into a cup shape (die shape 70φ × 70mm, drawing ratio S = 1.0) (pressure air: 5kg / cm ² , plug: 45φ × 65mm, syntax foam, plug temperature: A thermoformed container was produced by heating at 150 ° C. and mold temperature: 70 ° C.).

<Evaluation>
The obtained resin composition, multilayer sheet and thermoformed container were evaluated for motor torque fluctuation, appearance and impact resistance according to the method described below. The evaluation results are shown in Table 2.

[Evaluation of motor torque fluctuation]
The torque change when 60 g of EVOH pellets were kneaded at 100 rpm and 260 ° C. with a lab plast mill (“20R200” biaxially different direction of Toyo Seiki Seisakusho Co., Ltd.) was measured. The motor torque was evaluated by measuring the torque 5 minutes after the start of kneading and evaluating it as the time until the torque value became 1.5 times the torque 5 minutes later. The longer this time is, the smaller the change in viscosity is, and the better the long-running property is.

(criterion)
A: 60 minutes or more B: 40 minutes or more and less than 60 minutes C: 20 minutes or more and less than 40 minutes

[Evaluation of appearance of thermoformed container]
Streak and coloring of the thermoformed container formed by using the multilayer sheet obtained 30 minutes and 6 hours after the start-up of the coextrusion molding apparatus were visually evaluated according to the following criteria.

(Streak evaluation criteria)
A (good): No streak was observed.
B (slightly good): Streak was confirmed.
C (defective): Many streaks were confirmed.

(Evaluation criteria for coloring)
A (good): colorless B (slightly good): yellowing C (poor): markedly yellowing

[Impact resistance evaluation]
250 mL of ethylene glycol was placed in a thermoformed container formed from a multilayer sheet 20 minutes, 40 minutes, and 10 hours after the start-up of the coextrusion molding apparatus, and the opening was a film having a three-layer structure (polyethylene 40 μm /). It was heat-sealed with aluminum foil 12 μm / polyethylene terephthalate 12 μm) and covered. This thermoformed container was cooled at −40 ° C. for 3 days, 10 thermoformed containers were dropped from a height of 6 m so that the opening was on top, and the number of broken thermoformed containers was evaluated. The impact resistance 20 minutes after the start-up of the coextrusion molding apparatus is an index of self-purgeability.

(Evaluation criteria for impact resistance)
A (good): less than 3 B (slightly good): 3 or more and less than 6 C (bad): 6 or more

As shown in Table 2, the thermoformed containers of Examples 1 and 2 were superior in appearance as compared with the thermoformed containers of Comparative Example 1 in that streak generation and coloring were suppressed. Further, the thermoformed containers of Examples 1 and 2 were excellent in impact resistance even if they were molded 20 minutes after the start-up of the coextrusion molding apparatus. From the above, since the thermoforming containers of Examples 1 and 2 use the EVOH-containing resin composition having excellent self-purgeability, the impact resistance is lowered in a short time from the start-up of the coextrusion molding apparatus. It was found that the generation of gel-like lumps was suppressed.

The thermoformed container of the present invention has sufficient gas barrier properties and oil resistance as the characteristics of EVOH, and the layer (1) contains EVOH (I) satisfying the above specific conditions, so that the thermoforming container can be used in thermoforming. The occurrence of defects is suppressed, the appearance is excellent, and the strength is sufficient. Further, since the layer (1) contains EVOH (I) satisfying the above-mentioned specific conditions, the thermoformed container is excellent in self-purging property in the manufacturing process, so that the manufacturing cost of the thermoformed container can be reduced. can. Therefore, the thermoformed container is used for various purposes.

1 Cup-shaped container 2 Cup body 3 Flange part 4 Opening 5 Inner surface 6 Outer surface 7 Lid 11 (1) Layer (layer containing EVOH as the main component)
12 (2) Layer (thermoplastic resin layer)
13 (3) Layer (polyolefin layer)
14 (4) Layer (recovery layer)
20 Continuous multilayer body 30 Heating device 31, 32 Heater 40 Mold device 50 Lower mold 51 Upper mold 52 Recessed 53 Plug

Claims (10)

A thermoformed container provided with a first layer containing an ethylene-vinyl alcohol copolymer as a main component, which is obtained by saponifying a copolymer of ethylene and vinyl ester.
The above ethylene-vinyl alcohol copolymer
Using a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector, the molecular weights measured after heat treatment at 220 ° C. for 50 hours in a nitrogen atmosphere are the following formulas (1), (i) and (ii). Satisfy the conditions represented by
The first layer further contains an alkali metal salt of an organic acid,
A thermoformed container characterized in that the content of the alkali metal salt in the first layer is 10 ppm or more and 250 ppm or less in terms of metal.
(Ma-Mb) / Ma <0.10 ... (1)
Mb ≧ 50,000 ・ ・ ・ (i)
Mc ≧ 48,000 ・ ・ ・ (ii)
Ma: Molecular weight converted to polymethylmethacrylate at the maximum value of the peak measured by the differential refractive index detector Mb: Converted to methylpolymethacrylate at the maximum value of the absorption peak at a wavelength of 220 nm measured by the ultraviolet-visible absorbance detector. Molecular weight Mc: Molecular weight in terms of polymethyl methacrylate at the maximum value of the absorption peak at a wavelength of 280 nm measured by an ultraviolet-visible absorbance detector. The above ethylene-vinyl alcohol copolymer
Using a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector, the molecular weight measured after heat treatment at 220 ° C. for 50 hours in a nitrogen atmosphere further satisfies the condition represented by the following formula (2). The thermoformed container according to claim 1.
(Ma-Mc) / Ma <0.45 ... (2) The thermoformed container according to claim 1 or 2, wherein the content of the alkali metal salt in the first layer is 10 ppm or more and 150 ppm or less in terms of metal. The thermoformed container according to claim 1, claim 2 or claim 3, wherein the vinyl ester is vinyl acetate, and the content of acetaldehyde in the vinyl acetate is less than 100 ppm. A pair containing a thermoplastic resin as a main component, which is arranged on one surface side and the other surface side of the first layer and has a solubility parameter of 11 (cal / cm ³ ) ^{1/2 or less calculated from the polyolefin formula.} The second layer of the above, and any of claims 1 to 4, further comprising a pair of third layers arranged between the first layer and the pair of second layers and containing a carboxylic acid-modified polyolefin as a main component. The thermoformed container according to item 1. The thermoformed container according to claim 5, wherein the multilayer body including the first layer, the second layer, and the third layer is thermoformed. The thermoformed container according to claim 5 or 6, further comprising a fourth layer containing the ethylene-vinyl alcohol copolymer, the thermoplastic resin, and the carboxylic acid-modified polyolefin. The thermoformed container according to any one of claims 1 to 7, which is a cup-shaped container. The thermoformed container according to any one of claims 1 to 7, which is a tray-shaped container. A step of forming a first layer using a resin composition containing an ethylene-vinyl alcohol copolymer as a main component, which is obtained by saponifying a copolymer of ethylene and vinyl ester.
A step of thermoforming a layer structure including the first layer is provided.
The above ethylene-vinyl alcohol copolymer
Using a gel permeation chromatograph equipped with a differential refractive index detector and an ultraviolet-visible absorbance detector, the molecular weights measured after heat treatment at 220 ° C. for 50 hours in a nitrogen atmosphere are the following formulas (1), (i) and (ii). Satisfy the conditions represented by
The resin composition further contains an alkali metal salt of an organic acid,
A method for producing a thermoformed container in which the content of the alkali metal salt in the resin composition is 10 ppm or more and 250 ppm or less in terms of metal.
(Ma-Mb) / Ma <0.10 ... (1)
Mb ≧ 50,000 ・ ・ ・ (i)
Mc ≧ 48,000 ・ ・ ・ (ii)
Ma: Molecular weight converted to polymethylmethacrylate at the maximum value of the peak measured by the differential refractive index detector Mb: Converted to methylpolymethacrylate at the maximum value of the absorption peak at a wavelength of 220 nm measured by the ultraviolet-visible absorbance detector. Molecular weight Mc: Molecular weight in terms of polymethyl methacrylate at the maximum value of the absorption peak at a wavelength of 280 nm measured by an ultraviolet-visible absorbance detector.

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