JP2016172410A - Multilayer structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer structure having an ethylene-vinyl ester-based copolymer saponified product layer in which occurrence of a poor appearance is reduced, even when multilayer co-extrusion molding is applied, while keeping long run property.SOLUTION: There is provided a multilayer structure formed by laminating a thermoplastic resin layer other than an ethylene-vinyl ester-based copolymer saponified product on at least one surface of a layer containing the ethylene-vinyl ester-based copolymer saponified product through an adhesive resin layer. In the multilayer structure, a thickening ratio originated in a lamination interface reaction between the ethylene-vinyl ester-based copolymer saponified product and the adhesive resin is 0.1-8% per surface of the interface.SELECTED DRAWING: None

Description

  The present invention relates to an ethylene-vinyl ester copolymer via an adhesive resin layer on at least one surface of a layer containing a saponified ethylene-vinyl ester copolymer (hereinafter sometimes referred to as “EVOH”). The present invention relates to a multilayer structure in which a thermoplastic resin layer other than a saponified copolymer is laminated, and more particularly to a multilayer structure with reduced appearance defects even when multilayer coextrusion molding is applied. .

EVOH is mainly used as a food packaging material because it has excellent gas barrier properties and transparency. Also, as a trend of food packaging materials in recent years, since there is a strong demand for security in the contents in recent years, packaging materials with high visibility (transparency) tend to be preferred so that the contents can be confirmed even from the outside. is there.
Sheets, films, and containers as packaging materials can be produced by EVOH alone, but usually other than EVOH through an adhesive resin layer to increase water resistance, strength, and other functions. It is used as a multilayer structure in which the above thermoplastic resins (other thermoplastic resins) are laminated.

  However, since EVOH is a resin that is difficult to stretch as compared with other thermoplastic resins, there is a problem that appearance defects occur when a film, sheet, container, or the like is accompanied by a heat stretching process. Therefore, it is necessary to improve the stretchability of EVOH so that the elongation of other thermoplastic resins can be followed.

  In general, EVOH tends to have better stretchability as the content of ethylene structural units (hereinafter simply referred to as “ethylene content”) is higher. On the other hand, as the ethylene content increases, the gas barrier property increases. descend. In order to achieve both gas barrier properties and stretchability, it has been proposed to use EVOH having a low ethylene content and EVOH having a high ethylene content.

  For example, Patent Document 1 discloses an EVOH composition containing two types of EVOH having a difference in ethylene content of 3 to 20 mol% and having a specific boron concentration. And it is disclosed that even when the laminated film in which the EVOH composition is used as an intermediate layer and a polypropylene layer is laminated via an adhesive resin layer is stretched by heating, no stretching unevenness such as whitening and stripes is observed. .

JP-A-8-311276

Multi-layer coextrusion molding of a multilayer structure having a layer containing EVOH (hereinafter sometimes abbreviated as EVOH layer) is performed by laminating an adhesive resin layer and another thermoplastic resin layer on the EVOH layer. However, in general, when an EVOH layer is used as an intermediate layer of a multilayer structure and an adhesive resin layer and other thermoplastic resin layers are subjected to multilayer coextrusion molding, EVOH and its adjacent adhesive resin are chemically bonded. Thus, the mechanical strength (adhesive strength) of the multilayer structure is exhibited.
However, the resin composition containing two types of EVOH and a specific boron concentration disclosed in Patent Document 1 has advanced technology in recent years, such as diversification of feed block and die shapes and enhancement of functions of molding apparatuses. As a result of this process, when multi-layer coextrusion molding is performed, there are problems such as the appearance of the resulting multi-layer structure, especially the transparency of the multi-layer structure, due to insufficient moldability. I came.
This is because the degree of chemical bonding at the laminate interface between the EVOH layer and the adhesive resin layer differs depending on the combination of the EVOH and the adjacent adhesive resin, and the multilayer coextrusion flow behavior becomes complicated. This is probably because the transparency of the structure deteriorated.

Conventionally, the evaluation of the transparency of the multilayer structure has been performed visually. However, with the recent advancement of technology, the multilayer structure obtained by multilayer coextrusion molding has no problem in visual transparency evaluation, but is not sufficient to meet the recent demand for high transparency. Sometimes it was enough.
Therefore, in the present invention, as an evaluation of transparency more suitable for practicality, image sharpness, that is, whether an optical image obtained by separating a film is clear is used as an index.

  In view of the above, the present invention is a multilayer structure in which a thermoplastic resin layer other than EVOH is laminated on at least one surface of an EVOH layer via an adhesive resin layer, and has a long run property. An object of the present invention is to provide a multilayer structure having an EVOH layer which is excellent in moldability even when multilayer coextrusion molding is applied while maintaining, and the occurrence of poor appearance is reduced, and in particular, there is little decrease in image definition. Is.

  However, as a result of intensive studies in view of such circumstances, the present inventor has obtained a multilayer structure in which a thermoplastic resin layer other than EVOH is laminated on at least one surface of the EVOH layer via an adhesive resin layer. Focusing on the fluidity of the laminate interface between the EVOH layer and the adhesive resin layer, for example, in the case of multilayer coextrusion molding, the interface between the EVOH layer / adhesive resin layer is chemically bonded within the feed block so that the laminate interface is When the viscosity increases and the fluidity changes locally, by controlling the resin fluidity at the EVOH layer / adhesive resin layer interface, the interface roughness generated at the EVOH layer / adhesive resin layer laminate interface The present inventors have found that a multilayer structure having a reduced appearance defect caused by the above-mentioned, and in particular a reduction in image sharpness can be obtained.

  That is, the gist of the present invention is a multilayer structure in which a thermoplastic resin layer other than EVOH is laminated on at least one surface of an EVOH-containing layer via an adhesive resin layer, the EVOH and the EVOH The present invention relates to a multilayer structure having a viscosity increase rate of 0.1 to 10% per one surface of the interface due to the lamination interface reaction of the adhesive resin.

  A multilayer structure in which a thermoplastic resin layer other than EVOH is laminated on at least one surface of the EVOH layer of the present invention via an adhesive resin layer is an EVOH layer / adhesive resin layer while maintaining a long run property. Occurrence of poor appearance due to interface roughness generated at the interface is reduced, and a multilayer structure having excellent appearance and particularly excellent image definition is obtained.

  Hereinafter, although it demonstrates in detail about the structure of this invention, these show an example of a desirable embodiment and are not specified by these content.

In the multilayer structure of the present invention, a thermoplastic resin layer other than EVOH is laminated on at least one surface of the EVOH layer via an adhesive resin layer.
In the present invention, the greatest feature is that the rate of increase in viscosity resulting from the lamination interface reaction between the EVOH and the adhesive resin is 0.1 to 10% per surface of the interface. A preferable range of such a thickening rate is 0.3 to 8%, particularly 0.5 to 6%, per surface of the interface. When the thickening rate derived from the reaction of the lamination interface between the EVOH layer and the adhesive resin layer becomes large, when such a multilayer structure is subjected to multilayer coextrusion molding, poor appearance due to the rough interface generated at the EVOH layer / adhesive resin layer interface Is likely to occur. On the other hand, if the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer is too small, the mechanical strength (adhesive strength) of the multilayer structure cannot be maintained at a practical level.
In addition, when there are a plurality of laminated interfaces between the EVOH layer and the adhesive resin layer, the average value of the thickening ratios may be in the above range.
Moreover, the thickening rate derived from the lamination | stacking interface reaction of an EVOH layer and an adhesive resin layer is measured as follows.

<Thickening rate derived from the reaction at the interface between the EVOH layer and adhesive resin layer>
In the present invention, the viscosity increase rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer was measured using a rotary rheometer, and the shear viscosity (Pa) of the EVOH, the adhesive resin, and the EVOH layer / adhesive resin layer laminate was measured. -It is calculated from S).

[EVOH, adhesive resin, and shear viscosity (Pa · S) of EVOH layer / adhesive resin layer laminate]
The shear viscosity (Pa · S) of EVOH, adhesive resin, and EVOH layer / adhesive resin layer laminate in the present invention is a value measured under the following conditions using a rotary rheometer.
(Measurement condition)
Atmosphere: Under nitrogen atmosphere, temperature: 210 [° C.], strain: 5 [%], frequency: 3 [rad / s], measuring jig; φ25 mm parallel-parallel plate, preheating time: 10 [min]
* The measurement conditions are clearly defined in the specification, and the conditions in the claims are eliminated.

[Thickening rate derived from the reaction of lamination interface between EVOH layer and adhesive resin layer]
Depending on the number of layers of the multilayer structure, the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer can be expressed by formulas (1), (2), or formulas (3), (4), (5). Can be used to evaluate.

<Repetitive multilayer structure of EVOH and adhesive resin (even layer)>

<Repetitive multilayer structure (odd layer) of EVOH and adhesive resin>

For example, in the case of a two-layer sample of EVOH and an adhesive resin, the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer is expressed as follows by substituting n = 2 in the formulas (1) and (2). It is requested as follows.
<In the case of a two-layer sample of EVOH layer and adhesive resin layer>
The thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer can be evaluated using the following formula.

In addition, when the time-dependent change of the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer was evaluated under the above measurement conditions, if the heating time was within 1 hour, it was derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer. The thickening rate of the film hardly changes.
Therefore, the multilayer structure used for the evaluation of the thickening rate derived from the reaction of the lamination interface between the EVOH layer and the adhesive resin layer may be, for example, a multilayer structure produced by multilayer coextrusion molding or may be laminated in advance. It is also possible to use a single material film or sheet obtained by laminating individual material films or sheets on a rotary rheometer.
In the present invention, the viscosity increase rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer was evaluated using a laminate obtained by laminating the EVOH sheet and the adhesive resin sheet on a rotary rheometer.
Hereinafter, the multilayer structure will be described in order.

<EVOH>
EVOH used in the present invention is a resin obtained by saponifying a copolymer of ethylene and a vinyl ester monomer (ethylene-vinyl ester copolymer), and is a water-insoluble thermoplastic resin. is there. The polymerization method can also be carried out using any known polymerization method such as solution polymerization, suspension polymerization, and emulsion polymerization. Generally, solution polymerization using a lower alcohol such as methanol as a solvent is used. Saponification of the obtained ethylene-vinyl ester copolymer can also be performed by a known method. EVOH produced in this manner mainly comprises ethylene-derived structural units and vinyl alcohol structural units, and contains a slight amount of vinyl ester structural units remaining without being saponified.

  As the vinyl ester monomer, vinyl acetate is typically used because it is easily available from the market and has good impurity treatment efficiency during production. Examples of other vinyl ester monomers include vinyl formate, vinyl propionate, vinyl valelate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl versatate, etc. Examples include aliphatic vinyl esters, aromatic vinyl esters such as vinyl benzoate, and the like. Usually, aliphatic vinyl esters having 3 to 20 carbon atoms, preferably 4 to 10 carbon atoms, and particularly preferably 4 to 7 carbon atoms are used. Can do. These are usually used alone, but a plurality of them may be used simultaneously as necessary.

  The ethylene content in EVOH is a value measured based on ISO 14663, and is usually 20 to 60 mol%, preferably 25 to 50 mol%, and particularly preferably 25 to 35 mol%. When the content is too low, the gas barrier property and melt moldability under high humidity tend to decrease, and when it is too high, the gas barrier property tends to decrease.

  The saponification degree of the vinyl ester component in EVOH is a value measured based on JIS K6726 (however, EVOH is a solution uniformly dissolved in water / methanol solvent), and is usually 90 to 100 mol%, preferably 95 to 100 mol%, particularly preferably 99 to 100 mol%. When the degree of saponification is too low, gas barrier properties, thermal stability, moisture resistance and the like tend to decrease.

  Moreover, the melt flow rate (MFR) (210 ° C., load 2,160 g) of the EVOH is usually 0.5 to 100 g / 10 minutes, preferably 1 to 50 g / 10 minutes, and particularly preferably 3 to 35 g / minute. 10 minutes. If the MFR is too large, the film forming property tends to be lowered, and if it is too small, the melt viscosity becomes too high and melt extrusion tends to be difficult.

  In addition to ethylene structural units and vinyl alcohol structural units (including unsaponified vinyl ester structural units), EVOH used in the present invention may further include structural units derived from the following comonomer. . Examples of the comonomer include α-olefins such as propylene, isobutene, α-octene, α-dodecene, α-octadecene; 3-buten-1-ol, 4-penten-1-ol, 3-butene-1, Hydroxyl group-containing α-olefins such as 2-diols and hydroxy group-containing α-olefin derivatives such as esterified products and acylated products thereof; unsaturated carboxylic acids or salts thereof, partial alkyl esters, fully alkyl esters, nitriles, amides or anhydrous Unsaturated sulfonic acid or its salt; Vinyl silane compound; Vinyl chloride; Styrene.

  Furthermore, “post-modified” EVOH-based resins such as urethanization, acetalization, cyanoethylation, oxyalkyleneation, and the like can also be used.

  Among the modified products as described above, EVOH in which a primary hydroxyl group is introduced into a side chain by copolymerization is preferable from the viewpoint of good secondary formability such as stretching treatment and vacuum / pressure forming, among which 1,2- EVOH having a diol structure in the side chain is preferred.

  In the EVOH used in the present invention, in the range that does not inhibit the effect of the present invention, a compounding agent generally blended with EVOH, for example, a heat stabilizer, an antioxidant, an antistatic agent, a colorant, an ultraviolet absorber, Lubricant, plasticizer, light stabilizer, surfactant, antibacterial agent, drying agent, antiblocking agent, flame retardant, crosslinking agent, curing agent, foaming agent, crystal nucleating agent, antifogging agent, biodegradation additive, silane A coupling agent, an oxygen absorbent, etc. may be contained.

  Examples of the heat stabilizer include organic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, and behenic acid or the like for the purpose of improving various physical properties such as heat stability during melt molding. Alkali metal salts (sodium, potassium, etc.), alkaline earth metal salts (calcium, magnesium, etc.), zinc salts, etc .; or inorganic acids such as sulfuric acid, sulfurous acid, carbonic acid, phosphoric acid, boric acid, or the like Examples include alkali metal salts (such as sodium and potassium), alkaline earth metal salts (such as calcium and magnesium), and zinc salts.

  The EVOH used in the present invention may be a mixture with other different EVOH. Examples of such other EVOH include those having different ethylene contents, those having different saponification degrees, and melt flow rates (MFR). ) (210 ° C., load 2,160 g), other copolymer components are different, and the amount of modification is different (for example, the content of 1,2-diol structural units is different). it can.

  In particular, in the present invention, it is preferable to use two or more types of EVOH having different ethylene contents in the EVOH layer. Even when multi-layer coextrusion molding is applied while maintaining long run properties, the EVOH layer / adhesive resin layer It is possible to more efficiently obtain a multilayer structure having an EVOH layer in which occurrence of poor appearance due to interface roughness occurring at the interface is reduced, and in particular, there is little reduction in image sharpness.

In particular, the difference (ΔEt) between the one having the highest ethylene content of the ethylene structural unit and the lowest one (ΔEt) of two or more types of EVOH having different ethylene contents is preferably 10 to 25 mol%, more preferably It is 10-23 mol%, Most preferably, it is 10-20 mol%. If the difference in ethylene content is too small, it tends to be difficult to maintain a balance between moldability and gas barrier properties, and if it is too large, the compatibility with each other decreases. There is a tendency that streaks are likely to occur during secondary molding using a multilayer structure as a raw material, and a transparent molded product tends to be difficult to obtain.
In the following, the case where two types of EVOH are used will be described. In the case of three or more types, the ethylene content of the ethylene structural unit is the highest and the ethylene content of the ethylene unit other than the lowest is the same. It can be suitably used within the range.
Hereinafter, for example, a case where two types of EVOH are used will be described.

  The two types of EVOH used in the present invention are combinations of EVOH selected from EVOH as described above. In particular, a combination of EVOHs having an ethylene content difference (ΔEt) of 10 to 25 mol%, preferably 10 to 23 mol%, particularly preferably 10 to 20 mol%. If the difference in ethylene content is too small, it tends to be difficult to maintain a balance between moldability and gas barrier properties, and if it is too large, the compatibility with each other decreases. There is a tendency that streaks are likely to occur during secondary molding using a multilayer structure as a raw material, and a transparent molded product tends to be difficult to obtain.

  Specifically, a combination of EVOH (low ethylene EVOH) (A1) having a lower ethylene content and EVOH (high ethylene EVOH) (A2) having a higher ethylene content is preferably used.

  The low ethylene EVOH (A1) has an ethylene content of 20 to 40 mol%, preferably 22 to 38 mol%, particularly preferably 25 to 33 mol%. If the ethylene content is too low, the decomposition temperature and melting point tend to be too close, making melt molding of the resin composition difficult, and conversely if too high, the effect of imparting gas barrier properties due to low ethylene EVOH (A1) can be obtained. There is a tendency to decrease.

  The degree of saponification of the vinyl ester component in the low ethylene EVOH (A1) is usually 90 mol% or more, preferably 95 to 99.99 mol%, particularly preferably 98 to 99.99 mol%. When the degree of saponification is too low, the gas barrier property imparting effect due to the low ethylene EVOH (A1) tends to decrease.

  Furthermore, the melt flow rate (MFR) (210 ° C., load 2,160 g) of the low EVOH (A1) is usually 1 to 100 g / 10 minutes, preferably 3 to 50 g / 10 minutes, particularly preferably 3 to 10 g. / 10 minutes. If the MFR is too large, the mechanical strength of the molded product tends to decrease, and if it is too small, the extrudability tends to decrease.

  On the other hand, the ethylene content of the high ethylene EVOH (A2) is usually 40 to 60 mol%, preferably 42 to 56 mol%, particularly preferably 44 to 53 mol%. When the ethylene content is too low, the effect of improving the stretchability by the high ethylene EVOH (A2) is small. As a result, the secondary formability tends to decrease. In order to make it within the predetermined range, the ethylene content of the low ethylene EVOH (A1) must be increased, and as a result, the gas barrier property of the EVOH layer tends to be lowered.

  Moreover, the saponification degree of the vinyl ester component in the high ethylene EVOH (A2) is usually 90 mol% or more, preferably 93 to 99.99 mol%, particularly preferably 98 to 99.99 mol%. When the saponification degree is too low, the gas barrier property of the high ethylene EVOH (A2) tends to decrease.

  Furthermore, the melt flow rate (MFR) (210 ° C., load 2,160 g) of the high ethylene EVOH (A2) is usually 1 to 100 g / 10 minutes, preferably 3 to 50 g / 10 minutes, particularly preferably 3 to 3 g. 30 g / 10 minutes. If the MFR is too large, the mechanical strength of a molded product made from the multilayer structure of the present invention tends to be reduced, and if it is too small, the extrusion processability tends to be reduced.

  The blending ratio (A1 / A2) (weight ratio) of the low ethylene EVOH (A1) and the high ethylene EVOH (A2) is usually 90/10 to 60/40, preferably 85/15 to 65/35, particularly Preferably it is 80 / 20-70 / 30. When the ratio of the low ethylene EVOH (A1) is too small, the gas barrier property of the composition layer tends to decrease, and when it is too large, the stretching improvement effect due to the high ethylene EVOH (A2) tends to decrease. .

<Adhesive resin>
The adhesive resin used in the present invention will be described.
What is necessary is just to use a well-known thing as adhesive resin. Such an adhesive resin varies depending on the type of base resin, and may be appropriately selected. Typically, an unsaturated carboxylic acid or its anhydride is chemically bonded to a polyolefin resin by an addition reaction or a graft reaction. The modified olefin resin containing the carboxyl group obtained can be mentioned. Among these, maleic anhydride-modified polyolefin is preferable as the adhesive resin, and a combination of polyolefin, particularly linear low density polyethylene or polypropylene, is preferable as the base resin.

  Examples of maleic anhydride-modified polyolefin include maleic anhydride graft-modified polyethylene, maleic anhydride graft-modified polypropylene, maleic anhydride graft-modified ethylene-propylene (block and random) copolymers, maleic anhydride graft-modified ethylene-ethyl acrylate A copolymer, a maleic anhydride graft-modified ethylene-vinyl acetate copolymer, and the like, and one or a mixture of two or more selected from these are preferable. These adhesive resins can be blended with EVOH other than EVOH that forms the EVOH layer used in the present invention, rubber / elastomer components such as polyisobutylene and ethylene-propylene rubber, and polyolefin resins. is there. In particular, blending a polyolefin resin that is different from the polyolefin resin of the base of the adhesive resin is useful because the adhesion may be improved.

<Other thermoplastic resins>
Another thermoplastic resin used in the present invention will be described. In the present invention, the other thermoplastic resin may be any thermoplastic resin other than EVOH.

  Examples of other thermoplastic resins used herein (referred to as “base resin”) include polyethylenes such as linear low density polyethylene, low density polyethylene, ultra low density polyethylene, medium density polyethylene, and high density polyethylene. , Polypropylene, ethylene-propylene (block and random) copolymers, propylene-α-olefin (α-olefins having 4 to 20 carbon atoms) copolymers, polyolefins such as polybutene and polypentene; Grafted polyolefins graft-modified with acids or esters thereof; ethylene-vinyl compound copolymers such as ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers; polyesters Resin; polyamide Resin (including copolyamide); Halogenated polyolefin such as polyvinyl chloride, polyvinylidene chloride, chlorinated polyethylene, chlorinated polypropylene; Vinyl ester resin; Elastomer such as polyester elastomer and polyurethane elastomer; Acrylic resin; Polystyrene; Aromatic or aliphatic polyketones, and polyalcohols obtained by reducing them are listed. From the viewpoint of practicality such as physical properties (particularly strength) of the multilayer structure, polyolefin resins and polyamide resins are preferred. In particular, polyethylene and polypropylene are preferably used.

  These base resins may appropriately contain conventionally known antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, ultraviolet absorbers, waxes and the like.

<Multilayer structure>
The layer structure of the multilayer structure is such that the EVOH layer is a (a1, a2,...), The adhesive resin layer is b (b1, b2,...), And the thermoplastic resin layer is c (c1, c2,. )), A / b / c, a1 / b / a2, c1 / b / a / c2, c / a1 / b2 / a2, c1 / b1 / a / b2 / c2, c1 / a1 / Arbitrary combinations such as b / a2 / c2, c1 / b1 / a1 / b2 / a2 / b3 / c2, and the like are possible. In addition, a recycling layer containing a mixture of EVOH, an adhesive resin, and a thermoplastic resin, which is obtained by recovering edges and defective products generated in the process of manufacturing the multilayer structure and again melt-molding the R (R1 , R2,..., C / R / b / a, c / R / a1 / b / a2, c1 / R / a / b / c2, R1 / a1 / b / a2 / R2, c1 / R1 / b1 / a / b2 / R2 / c2, c1 / R1 / a1 / b / a2 / R2 / c2, etc. are also possible.

  The thickness of the EVOH layer, thermoplastic resin layer and adhesive resin layer of the multilayer structure is appropriately selected depending on the layer structure, type of EVOH, type of thermoplastic resin, type of adhesive resin, application and packaging form, required physical properties, etc. Is done.

The thickness of the EVOH layer varies depending on the required gas barrier property and the like, but is usually 0.1 to 500 μm, preferably 0.1 to 250 μm, and particularly preferably 0.1 to 100 μm. If the thickness is too thin, sufficient gas barrier properties tend not to be obtained. Conversely, if the thickness is too thick, the flexibility of the film tends to decrease.
The thickness of the thermoplastic resin layer is usually 0.1 to 5000 μm, preferably 1 to 1000 μm, and the thickness of the adhesive resin layer is usually 0.1 to 500 μm, preferably 1 to 250 μm.

Furthermore, the ratio of the thickness of the EVOH layer to the thermoplastic resin layer in the multilayer structure (EVOH layer / thermoplastic resin layer) is usually 1/99 in the ratio of the thickest layers when there are a plurality of layers. -50/50, preferably 5/95 to 45/55, particularly preferably 10/90 to 40/60. Moreover, the thickness ratio (EVOH layer / adhesive resin layer) of the EVOH layer and the adhesive resin layer in the multilayer structure is usually 10/90 to 99/1 in the ratio of the thickest layers when there are a plurality of layers. , Preferably 20/80 to 95/5, particularly preferably 30/70 to 90/10.
The thickness ratio of the thermoplastic resin layer to the adhesive resin layer in the multilayer structure (thermoplastic resin layer / adhesive resin layer) is usually 99/1 in the ratio of the thickest layers when there are a plurality of layers. -50/50, preferably 95 / 5-55 / 45, particularly preferably 90 / 10-60 / 40.

  Lamination | stacking of an EVOH layer, an adhesive resin layer, and a thermoplastic resin layer can be performed by a well-known method. For example, the lamination of the EVOH layer and the adhesive resin layer can be performed by multilayer coextrusion molding in the apparatus. Specifically, a method in which a feed block is used to develop the product width in the die after joining the layers, a method in which the multi-manifold die is used to join the layers after development to the product width, and the EVOH layer and the adhesive resin by the above method Examples include a method in which a layer is laminated and then spread on a base material made of another resin layer. Considering from the viewpoint of cost and environment, a method of multilayer coextrusion molding of the entire EVOH layer, adhesive resin layer, and thermoplastic resin layer is preferable.

  In the present invention, the greatest feature is that the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer is 0.1 to 10% per one surface of the interface. In particular, when producing a multilayer structure by multilayer coextrusion molding, it is important to satisfy the physical properties of the above thickening rate.

Although there is no particular limitation in order to satisfy such a thickening rate derived from the reaction of the lamination interface reaction of the EVOH layer / adhesive resin layer within a predetermined range, it can be achieved by appropriately combining the following methods.
(1) In the EVOH layer, a method for adjusting the thickening rate derived from the reaction of the laminated interface reaction of the EVOH layer / adhesive resin layer. For example, the molecular weight of EVOH, especially the MFR, ethylene content, saponification degree, It can adjust by using EVOH together. However, in these methods, other characteristics such as moldability and gas barrier properties may be greatly changed. Therefore, when such a method is applied, it is necessary to consider other characteristics. In that case, a method that does not affect other characteristics by using a trace amount of an additive having a large effect on the thickening rate derived from the reaction of lamination of the EVOH layer / adhesive resin layer is preferable.
Examples of such additives include blending the following.
(I) A polyamide resin which is a reaction resin is blended with EVOH.
(Ii) Adhesive resin which is a reaction resin for EVOH (typically a carboxyl group obtained by chemically bonding an unsaturated carboxylic acid or an anhydride thereof to a polyolefin resin by an addition reaction or a graft reaction) A modified olefin polymer containing styrene, a modified ethylene vinyl acetate copolymer (EVA), etc.). Specific examples include maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester and the like. is there.
(Iii) A non-reactive compatibilizing agent (for the purpose of lowering interfacial tension; for example, styrene thermoplastic elastomer (SBS), hydrogenated styrene thermoplastic elastomer (SEBS), etc.) is blended.
(IV) Reaction system compatibilizer (for the purpose of lowering the interfacial tension; polymers having functional groups that react with hydroxyl groups in EVOH, such as acid anhydride groups, carboxylic acid groups, epoxy groups, oxazoline groups, or co-polymers containing them Blend).
(V) Ionomer is added.
(Vi) Acids such as acetic acid, boric acid and phosphoric acid, and metal salts thereof such as alkali metals, alkaline earth metals and transition metals are contained.
(Vii) A higher fatty acid metal salt such as a higher fatty acid zinc salt is blended.

(2) Regarding the method of adjusting the thickening rate derived from the reaction at the EVOH layer / adhesive resin layer lamination interface in the adhesive resin layer For example, the degree of acid modification is changed by blending adhesive resins having different molecular weights or resins having different compositions And so on.
In addition, a small amount of an additive having a large effect on the thickening rate derived from the EVOH layer / adhesive resin layer lamination interface reaction can be added to the adhesive resin.
Examples of such additives include blending the following.
(I) EVOH
(Ii) A polyamide resin which is a reaction resin is blended with EVOH.
(Iii) Adhesive resin which is a reaction resin to EVOH (typically a carboxyl group obtained by chemically bonding an unsaturated carboxylic acid or an anhydride thereof to a polyolefin resin by an addition reaction or a graft reaction) And a modified olefin polymer containing a modified ethylene vinyl acetate copolymer (EVA)). Specific examples include maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester and the like. is there.
(IV) A non-reactive compatibilizing agent (for the purpose of lowering the interfacial tension; for example, styrene thermoplastic elastomer (SBS), hydrogenated styrene thermoplastic elastomer (SEBS), etc.) is blended.
(V) Reaction system compatibilizer (for the purpose of reducing interfacial tension; polymer having a functional group that reacts with a hydroxyl group in EVOH, such as an acid anhydride group, a carboxylic acid group, an epoxy group, an oxazoline group, or a co-polymer containing them. (Vi) Ionomer is blended.
(Vii) An acid such as acetic acid, boric acid or phosphoric acid or a metal salt thereof such as an alkali metal, alkaline earth metal or transition metal is blended. (Viii) A higher fatty acid metal salt such as a higher fatty acid zinc salt is blended.

  Especially among these, about the method of adjusting the thickening rate derived from the lamination | stacking interface reaction of EVOH layer / adhesive resin layer, 2 or more types of different EVOH whose difference (ΔEt) in ethylene content is 10 to 25 mol% are used. By adding a relatively large amount of a higher fatty acid metal salt, particularly a higher fatty acid zinc salt, as an additive to such an EVOH composition, the viscosity increase rate derived from the interfacial reaction of the target EVOH layer / adhesive resin layer is predetermined. It is preferable to be within the range.

  Examples of the higher fatty acid used in the higher fatty acid metal salt include fatty acids having 8 or more carbon atoms, preferably 12 to 30 carbon atoms, and more preferably 12 to 20 carbon atoms. Examples thereof include lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadecanoic acid, oleic acid, capric acid, behenic acid, linoleic acid and the like. Among these, stearic acid, oleic acid, and lauric acid are preferably used.

By using such a higher fatty acid metal salt, the multilayer coextrusion moldability of the resin composition in which EVOH, in particular, two types of EVOH having an ethylene content difference (ΔEt) of 10 to 25 mol% coexist is improved. Reduction in sharpness can be reduced. In addition, when the multilayer structure is vacuum-compressed, the tension varies depending on the part, and even when the tension is applied from all directions such as diameter expansion processing, the generation of streaks is reduced. A molded product can be obtained.
Although the reason is not clear, the higher fatty acid metal salt moderately suppresses the thickening rate derived from the reaction between the EVOH layer / adhesive resin layer and the minute interface roughness that occurs during multilayer coextrusion molding with other resins. It is thought to reduce.

  As a compounding quantity of a higher fatty acid metal salt, when mix | blending with EVOH, it is 350-800 ppm normally with respect to EVOH, Preferably it is 400-750 ppm, Most preferably, it is 450-700 ppm. When the amount of the higher fatty acid metal salt is too small, the effect of reducing the appearance defect tends to be reduced, and in some cases, the transparency of the multilayer structure may be impaired. On the other hand, the metal salt of higher fatty acid generally promotes decomposition of EVOH in a molten state. Therefore, if the concentration of the higher fatty acid metal salt is too high, gas is generated due to decomposition of EVOH, and a multilayer formed by melt molding or coextrusion. May adversely affect the manufacture of the structure.

[Other additives]
In the EVOH layer used in the multilayer structure of the present invention, a plasticizer, a filler, an antiblocking agent, an antioxidant, a colorant in addition to the above components, as long as the gist of the present invention is not impaired (for example, 1% by weight or less). In addition, known additives such as an antistatic agent, an ultraviolet absorber and a lubricant can be appropriately blended.

<Method for Preparing EVOH Composition>
Regarding the method of blending the higher fatty acid metal salt with EVOH used in the multilayer structure of the present invention, for example, EVOH and the higher fatty acid metal salt may be blended at a predetermined ratio, and blended by melt kneading or the like. The components may be only dry blended at a predetermined ratio.
Moreover, the blending method by dry blending is preferable from the viewpoint of suppressing decomposition by a higher fatty acid metal salt with respect to molten EVOH. That is, the EVOH composition is preferably in a state where a higher fatty acid metal salt is attached to the surface of each EVOH by dry blending.

As a dry blending method, a higher fatty acid metal salt may be blended with EVOH by dry blending. When two or more types of EVOH are used, for example, a higher fatty acid metal salt may be blended with a dry blend of different EVOH, or a higher fatty acid metal salt may be added to a compound of two or more types of EVOH mixture prepared in advance. May be blended. Two or more types of EVOH and higher fatty acid metal salts may be blended in a dry blend.
Further, any EVOH and higher fatty acid metal salt may be dry blended and the remaining EVOH may be blended, or the remaining EVOH may be added to a compound of any EVOH and higher fatty acid metal salt prepared in advance. You may mix | blend. Further, a dry blend of any EVOH and higher fatty acid metal salt may be blended with a dry blend of the remaining EVOH and higher fatty acid metal salt, or any EVOH and higher fatty acid metal prepared in advance. You may mix | blend the compound of the remaining EVOH and the higher fatty-acid metal salt produced previously in the compound with a salt.

<Use of multilayer structure>
The multilayer structure having the above configuration is usually used after being subjected to a heat stretching treatment. Since the EVOH layer of the present invention has excellent gas barrier properties as a gas barrier layer and the interface roughness at the lamination interface is reduced, various known heat stretching processes can be applied.

Specifically, for example, uniaxial stretching or biaxial stretching that grasps and widens both ears of the multilayer structure; draw forming that heats and softens the multilayer structure and forms a bottomed container using a press or the like; vacuum suction Alternatively, vacuum forming, pressure forming, vacuum pressure forming, etc., in which the multilayer structure is brought into close contact with the mold by blowing compressed air, etc .; a preformed multilayer structure such as a parison is processed by a tubular drawing method, a drawing blow method, or the like. A method is mentioned.
The multilayer structure having EVOH of the present invention has reduced disturbance at the interface with adjacent layers and has excellent heat stretchability, so only uniaxial stretching and biaxial stretching that sequentially stretches in different directions. In addition, it is also suitable for stretch molding or blow molding by close contact with a mold that is stretched in the radial direction at the same time.

  The temperature at which the heat-stretching is performed is selected from the range of about 40 to 300 ° C., preferably about 50 to 160 ° C., which is the temperature of the multilayer structure (temperature near the multilayer structure). A draw ratio is 2-50 times normally by an area ratio, Preferably it is 2-10 times.

  The multilayer structure is preferably heated uniformly by a hot air oven, a heater-type oven, or a combination of both, and is appropriately selected depending on the type of stretch molding method.

  The multilayer structure obtained by multilayer coextrusion molding, and further by heat stretching treatment, may be extrusion coated with another substrate, or a film or sheet of another substrate may be laminated using an adhesive. Good. As such a base material, not only the thermoplastic resin described above as a base resin but also a base material having poor stretchability (paper, metal foil, woven fabric, non-woven fabric, metallic cotton, wood, etc.) can be used. Further, an inorganic layer made of metal or metal oxide may be formed on the multilayer structure by vapor deposition or the like.

  Films obtained as described above, sheets, molded products such as bags and cups made of stretched film, cups, trays, tubes, bottles, etc., in addition to general foods, seasonings such as mayonnaise, dressing, It is useful as fermented foods such as miso, fat and oil foods such as salad oil, various packaging materials such as beverages, cosmetics and pharmaceuticals, packaging containers and lids.

[Manufacture of secondary molded products by vacuum forming and pressure forming]
The multilayer structure of the present invention is suitable as a raw material for producing secondary molded products, particularly bottomed containers such as cups and trays, by vacuum molding or pressure molding. Since the multilayer structure of the present invention has a small turbulence in the resin flow at the lamination interface, a secondary molded product having an excellent appearance can be obtained.

  The shape of the bottomed container is not particularly limited. A cylindrical bottomed container, a rectangular bottomed container, a modified bottomed container, and a conical bottom with a diameter reduced from the opening toward the bottom. Containers, pyramid-bottomed containers whose bottom area is smaller than the opening area, hemispherical containers, stepped bottomed containers whose bottom is smaller in two stages from the opening, and flanges and projections on these containers It may be formed.

  When a molded product having a drawing ratio (depth of molded product (mm) / maximum diameter of molded product (mm)) of usually 0.1 to 3, such as cups and trays, is particularly a rapid stretching treatment. However, it is difficult to produce a molded product with an excellent appearance because the tension applied to the resin is different between the cup side surface and the bottom surface when vacuum pressure forming is performed. . However, in the multilayer structure of the present invention, a molded product having an excellent appearance without impairing gas barrier properties even when subjected to cup-shaped molding by a vacuum / pressure forming method, in which the tension applied during molding differs depending on the part. Can be obtained.

  The heating temperature in the heat softening step is the temperature of the multilayer structure (the temperature in the vicinity of the multilayer structure), and is usually selected from the range of about 40 to 300 ° C, preferably about 50 to 170 ° C, and more preferably about 60 to 160 ° C. If the heating temperature is too low, softening is insufficient, and there is a tendency that a molded article having an excellent appearance cannot be obtained.If it is too high, the balance of the melt viscosity of each layer is lost, and a molded article having an excellent appearance is obtained. May not be obtained.

  The heating time is a time during which the multilayer structure temperature can be heated to such an extent that a necessary and sufficient softening state can be achieved, and the layer structure of the multilayer structure, the component composition of each layer forming the multilayer structure, It is appropriately set depending on the heater temperature used for heating.

  The drawing ratio of vacuum / pressure forming (depth of molded product (mm) / maximum diameter of molded product (mm)) depends on the shape of the intended bottomed container, but is usually 0.1 to 3, preferably 0. .2 to 2.5, particularly preferably 0.3 to 2. When this value is too large, cracks and the like of the EVOH composition layer tend to enter, and when it is too small, uneven thickness tends to occur in the wall thickness.

The thickness of the EVOH layer of the multilayer structure after the secondary molding as described above varies depending on the required gas barrier properties, but is usually 0.1 to 500 μm, preferably 0.1 to 250 μm, particularly preferably. 0.1 to 100 μm. If the thickness is too thin, sufficient gas barrier properties tend not to be obtained. Conversely, if the thickness is too thick, the flexibility of the film tends to decrease.
The thickness of the thermoplastic resin layer is usually 0.1 to 5000 μm, preferably 1 to 1000 μm, and the thickness of the adhesive resin layer is usually 0.1 to 500 μm, preferably 1 to 250 μm.

  Furthermore, the thickness ratio between the EVOH layer and the adhesive resin layer, the total thickness of the EVOH layer and the total thickness of the thermoplastic resin layer does not change greatly before and after the heat stretching, and is the same value as in the case of the multilayer structure described above. It becomes.

  In the multilayer structure of the present invention, appearance defects, particularly a decrease in image definition, are reduced. This is presumably because the roughness at the interface between the EVOH layer of the multilayer structure and the adjacent adhesive resin layer is reduced, and the minute interface roughness that causes the appearance defect is reduced. Therefore, it is useful as a raw material for various food packaging containers such as seasonings such as mayonnaise and dressing, fermented foods such as miso, fats and oils such as salad oil, beverages, cosmetics and pharmaceuticals in addition to general foods.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the description of the examples unless it exceeds the gist. In the examples, “part” means a weight basis.

[EVOH No. Production of 1-7]
EVOH was prepared by selecting from the following four types of EVOH, blending EVOH and a higher fatty acid zinc salt shown in Table 1 at the concentrations shown in Table 1, and dry blending.
EVOH1: ethylene content 29 mol%, saponification degree 99.6 mol%, MFR 4.0 g / 10 min (210 ° C., load 2160 g), boron content 90 ppm
EVOH2: ethylene content 44 mol%, saponification degree 98.5 mol%, MFR 4.0 g / 10 min (210 ° C., load 2160 g), boron content 70 ppm
EVOH3: ethylene content 25 mol%, saponification degree 99.7 mol%, MFR 4.2 g / 10 min (210 ° C., load 2160 g), boron content 80 ppm
EVOH4: ethylene content 38 mol%, saponification degree 99.7 mol%, MFR 4.1 g / 10 min (210 ° C., load 2160 g), boron content 250 ppm

[Manufacture of multilayer structures]
EVOH, linear low-density polyethylene (LLDPE) prepared above (“UF240” manufactured by Nippon Polyethylene Co., Ltd.), adhesive resin (“PLEXAR PX3236” manufactured by LyondellBasell) And a multilayer structure (film) having a three-kind five-layer structure of LLDPE layer / adhesive resin layer / EVOH layer / adhesive resin layer / LLDPE layer was obtained by multilayer coextrusion molding under the following conditions. The thickness (μm) of each layer of the multilayer structure was 37.5 / 5/15/5 / 37.5. The die temperature of the molding apparatus was all set to 210 ° C.
(Multi-layer coextrusion molding conditions)
Intermediate layer extruder (EVOH): 40 mmφ single screw extruder (barrel temperature: 210 ° C.)
・ Upper and lower layer extruder (LLDPE): 40mmφ single screw extruder (barrel temperature: 210 ° C)
・ Middle upper and lower layer extruder (adhesive resin): 32mmφ single screw extruder (barrel temperature: 210 ° C)
-Die: 3 types, 5 layers feed block type T die (die temperature: 210 ° C)
・ Taking speed: 14m / min ・ Roll temperature: 50 ℃

[Thickening rate derived from the reaction of lamination interface between EVOH layer and adhesive resin layer]
The shear viscosity (Pa · S) of the EVOH, adhesive resin, and EVOH layer / adhesive resin layer laminate prepared above was measured using a rotary rheometer (“MCR301” manufactured by Anton Paar) under the following conditions. did.

(Measurement sample preparation)
The EVOH adjusted as described above and the adhesive resin are hot press molded at 210 ° C. using a compression molding machine (NSF-37) manufactured by Shinto Metal Industry Co., Ltd., and single-layer sheets having a thickness of 1 mm and 0.5 mm are obtained. Manufactured.
A single-layer sheet having a thickness of 1 mm is used for measuring the shear viscosity of EVOH and adhesive resin, and a single-layer sheet having a thickness of 0.5 mm is used for measuring the shear viscosity of the EVOH layer / adhesive resin layer laminate. A two-layer sheet laminated on a meter was used.

(Measurement condition)
Atmosphere: Under nitrogen atmosphere, temperature: 210 [° C.], strain: 5 [%], frequency: 3 [rad / s], measuring jig; φ25 mm parallel-parallel plate, preheating time: 10 [min]

(Calculation of the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer)
Moreover, the viscosity increase rate derived from the lamination | stacking interface reaction of an EVOH layer and an adhesive resin layer was computed from the obtained measurement result using the formula described below.

[Evaluation of image clarity]
The image definition of the multilayer structure was measured by the transmission method in accordance with JIS K 7374 “Plastics: Determination of image definition”. The film test piece was measured with the film machine direction as the vertical direction. An ICM-1 type image clarity measuring device manufactured by Suga Test Instruments Co., Ltd. was used as the measuring device. Optical combs of 0.5, 1.0, and 2.0 mm were used.

[Evaluation of long run properties]
Torque change was measured when 55 g of EVOH adjusted as described above was kneaded at 50 rpm and 250 ° C. using a plastograph EC-plus (manufactured by Brabender). The torque after 5 minutes from the start of kneading was measured, and the time until the torque value reached 20% of the torque after 5 minutes was measured. The longer this time, the smaller the change in melt viscosity and the better the long run property.
A: 45 minutes or more B: 35 minutes or more and less than 45 minutes C: 25 minutes or more and less than 35 minutes D: Less than 25 minutes

・ΔＥｔ＝エチレン含有率差（モル％）
・高級脂肪酸亜鉛塩：ステアリン酸亜鉛
・※1：増粘率の測定温度：２００℃

-ΔEt = ethylene content difference (mol%)
・ Higher fatty acid zinc salt: Zinc stearate * 1: Thickness measurement temperature: 200 ° C

  From the above results, the multilayer structure produced by making the thickening rate derived from the reaction of the lamination interface between the EVOH layer and the adhesive resin layer within a predetermined range reduces the occurrence of poor appearance while maintaining the long run property, In particular, it can be seen that the decrease in image definition is reduced.

  The multilayer structure of the present invention reduces the occurrence of poor appearance, and in particular, the decrease in image sharpness is reduced. This is presumably because the roughness at the interface between the EVOH layer of the multilayer structure and the adjacent adhesive resin layer is reduced, and the minute interface roughness that causes the appearance defect is reduced. Therefore, the multilayer structure of the present invention is used for various packaging material containers such as seasonings such as mayonnaise and dressing, fermented foods such as miso, fats and oils such as salad oil, beverages, cosmetics, and pharmaceuticals in addition to general foods. Useful as a raw material.

That is, the gist of the present invention is a multilayer structure in which a thermoplastic resin layer other than EVOH is laminated on at least one surface of an EVOH-containing layer via an adhesive resin layer, the EVOH and the EVOH The present invention relates to a multilayer structure having a viscosity increase rate of 0.1 to 8 % per one surface of the interface due to the lamination interface reaction of the adhesive resin.

In the multilayer structure of the present invention, a thermoplastic resin layer other than EVOH is laminated on at least one surface of the EVOH layer via an adhesive resin layer.
In the present invention, the greatest feature is that the thickening rate derived from the reaction of the lamination interface between the EVOH and the adhesive resin is 0.1 to 8 % per one surface of the interface. A preferable range of such a thickening rate is 0.3 to 8%, particularly 0.5 to 6%, per surface of the interface. When the thickening rate derived from the reaction of the lamination interface between the EVOH layer and the adhesive resin layer becomes large, when such a multilayer structure is subjected to multilayer coextrusion molding, poor appearance due to the rough interface generated at the EVOH layer / adhesive resin layer interface Is likely to occur. On the other hand, if the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer is too small, the mechanical strength (adhesive strength) of the multilayer structure cannot be maintained at a practical level.
In addition, when there are a plurality of laminated interfaces between the EVOH layer and the adhesive resin layer, the average value of the thickening ratios may be in the above range.
Moreover, the thickening rate derived from the lamination | stacking interface reaction of an EVOH layer and an adhesive resin layer is measured as follows.

[Shear viscosity (Pa · S) of EVOH, adhesive resin, and EVOH layer / adhesive resin layer laminate] The shear viscosity (Pa · S) of EVOH, adhesive resin, and EVOH layer / adhesive resin layer laminate in the present invention is The value measured under the following conditions using a rotary rheometer.
(Measurement condition)
Atmosphere: Under nitrogen atmosphere, temperature: 210 [° C.], strain: 5 [%], frequency: 3 [rad / s], measuring jig; φ25 mm parallel-parallel plate, preheating time: 10 [min ]

In the present invention, the greatest feature is that the thickening rate derived from the lamination interface reaction between the EVOH layer and the adhesive resin layer is 0.1 to 8 % per one surface of the interface. In particular, when producing a multilayer structure by multilayer coextrusion molding, it is important to satisfy the physical properties of the above thickening rate.

Claims (4)

  A multilayer in which a thermoplastic resin layer other than the saponified ethylene-vinyl ester copolymer is laminated on at least one surface of the saponified ethylene-vinyl ester copolymer layer via an adhesive resin layer It is a structure, and the thickening rate derived from the lamination interface reaction between the layer containing the saponified ethylene-vinyl ester copolymer and the adhesive resin layer is 0.1 to 10% per one surface of the interface A multilayer structure characterized by.   2. The multilayer structure according to claim 1, wherein the saponified ethylene-vinyl ester copolymer is a mixture of two or more types of saponified ethylene-vinyl ester copolymers having different ethylene structural unit contents. body.   Among the saponified products of two or more types of ethylene-vinyl ester copolymers, the difference (ΔEt) between the highest ethylene content of the ethylene structural unit and the lowest ethylene structural unit is 10 to 25 mol%. The multilayer structure according to claim 2.   The layer containing the saponified ethylene-vinyl ester copolymer contains 350 to 800 ppm of a higher fatty acid zinc salt with respect to the saponified ethylene-vinyl ester copolymer. The multilayer structure according to any one of claims 1 to 3.