JP6534151B2 - Multilayer structure - Google Patents

Description

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

EVOH is mainly used as a food packaging material because it has excellent gas barrier properties and transparency. In addition, since a sense of security is particularly strongly demanded in recent years as a trend of food packaging materials, packaging materials with high visibility (transparency) are preferred so that the contents can be confirmed from the outside. is there.
Sheets, films, and containers as packaging materials can be produced with EVOH alone, but usually, except for EVOH, through an adhesive resin layer, for the purpose of enhancing water resistance, increasing strength, and imparting other functions. Is used as a multilayer structure in which thermoplastic resins (other thermoplastic resins) are laminated.

  However, since EVOH is a resin which is difficult to stretch as compared with other thermoplastic resins, there is a problem that appearance defects occur when the heat stretching process is involved in forming a film, a sheet, a container, and the like. Therefore, it is necessary to improve the stretchability of EVOH so as to be able to follow the stretch of other thermoplastic resins.

  Generally, EVOH tends to be excellent in stretchability as the content of ethylene structural units (hereinafter simply referred to as "ethylene content") increases, but on the other hand, the higher the ethylene content, the better the gas barrier properties. descend. In order to achieve both gas barrier properties and stretchability, it has been proposed to use together 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. Then, it is disclosed that, in the laminated film in which the EVOH composition is used as an intermediate layer and the polypropylene layer is laminated via the adhesive resin layer, no stretching unevenness such as whitening or streaks is recognized even if heat drawing is performed. .

JP-A-8-311276

Multilayer coextrusion 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 adhesive resin layer and another thermoplastic resin layer are co-extrusion molded using an EVOH layer as an intermediate layer of a multilayer structure, the EVOH and its adjacent adhesive resin are chemically bonded to each other. And mechanical strength (adhesive strength) as a multilayer structure is exhibited.
However, resin compositions containing two types of EVOH and a specific boron concentration disclosed in Patent Document 1 are, for example, advanced in recent technology such as diversification of feed block / die shapes, high functionalization of molding apparatus, etc. In the process of co-extrusion, there are problems such as the appearance of the resulting multilayer structure, in particular, the transparency of the multilayer structure being insufficient, because the moldability is insufficient when co-extrusion molding is performed. It has
This is because the degree of chemical bonding at the laminated interface of the EVOH layer and the adhesive resin layer differs depending on the combination of EVOH and the adjacent adhesive resin, and their multilayer coextrusion flow behavior becomes complicated, and depending on molding conditions, multilayer It is considered that the transparency of the structure deteriorated.

In addition, conventionally, transparency evaluation of the multilayer structure was performed by visual observation. However, with the recent advancement of technology, multilayer structures obtained by multilayer co-extrusion molding have no problem in visual transparency evaluation, but can not meet the recent high transparency requirements. It might have been enough.
Therefore, in the present invention, as an evaluation of the transparency more suitable for practicality, the image sharpness, that is, whether the optical image obtained by separating the film is clear is used as an index.

  Therefore, under such a background, the present invention is 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, and long run property is obtained. An object of the present invention is to provide a multilayer structure having an EVOH layer which is excellent in moldability even when multi-layer co-extrusion molding is applied and in which generation of appearance defects is reduced and in which the decrease in image definition is small. It is a thing.

However, as a result of intensive investigations conducted by the present inventor under such circumstances, 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. In the case of multi-layer co-extrusion molding, for example, the interface of the EVOH layer / adhesive resin layer is chemically bonded to each other in the feed block by focusing on the fluidity of the laminated interface of the EVOH layer and the adhesive resin layer. While the viscosity increases and the fluidity changes locally, the interface roughness generated at the laminated interface of the EVOH layer / adhesive resin layer is controlled by controlling the resin fluidity at the EVOH layer / adhesive resin layer interface. appearance caused defects is reduced to, in particular, decreased less food image clarity, seasonings, fermented foods, fat foods, beverages, cosmetics, various packaging material containers for multi-layer structure of a medicament is obtained Heading the door, and have completed the present invention.

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 a layer containing EVOH via an adhesive resin layer, and the EVOH and the EVOH are different. Multilayer for various packaging material containers of food, seasoning, fermented food, fat and oil food, beverage, cosmetics, and pharmaceuticals whose thickening ratio derived from the adhesive layer reaction of adhesive resin is 0.5 to 5.2% per one surface of the interface It relates to a structure.

A multilayer structure in which a thermoplastic resin layer other than EVOH is laminated via an adhesive resin layer on at least one surface of the EVOH layer of the present invention is an EVOH layer / adhesive resin layer while maintaining long run properties. Various packaging materials of food, seasoning, fermented food, fat and oil food, beverage, cosmetics, and pharmaceuticals which are reduced in appearance defects due to interface roughening generated at the interface and excellent in appearance, particularly excellent in image definition It becomes a multilayer structure for containers .

  Hereinafter, although the configuration of the present invention will be described in detail, these show one example of the preferred embodiments, and are not specified in the contents.

The multilayer structure of the present invention is obtained by laminating a thermoplastic resin layer other than EVOH on at least one surface of the EVOH layer via an adhesive resin layer.
And, in the present invention, the greatest characteristic is that the thickening rate derived from the laminated interface reaction of the EVOH and the adhesive resin is 0.5 to 5.2% per one surface of the interface . Or the hunt EVOH layer and the thickening rate from laminated interface reaction of the adhesive resin layer is increased, such multilayer structure when the multilayer coextrusion appearance due to rough surface generated in the EVOH layer / adhesive resin layer interface Defects are likely to occur. On the other hand, when the thickening rate derived from the reaction of the laminated interface of the EVOH layer and the adhesive resin layer is too small, the mechanical strength (adhesive strength) of the multilayer structure can not be maintained at a practical level.
In addition, when there exist multiple lamination | stacking interfaces of an EVOH layer and an adhesive resin layer, the average value of the viscosity rate should just be the said 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 reaction at the laminated interface of EVOH layer and adhesive resin layer>
In the present invention, the viscosity ratio derived from the interfacial reaction between the EVOH layer and the adhesive resin layer is the shear viscosity of the EVOH, the adhesive resin, and the EVOH layer / adhesive resin layer laminate measured using a rotary rheometer (Pa • Calculated from S).

[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 This is a value measured under the following conditions using a rotary rheometer.
(Measurement condition)
Atmosphere; under a nitrogen atmosphere, temperature; 210 [° C.], Strain; 5 [%], the frequency; 3 [rad / s], the measuring jig; 25mm parallel - parallel plate, preheating time; 10 [min]

[Thickening rate derived from reaction at the laminated interface of EVOH layer and adhesive resin layer]
Depending on the number of layers in the multilayer structure, the thickening rate derived from the reaction at the laminated interface of the EVOH layer and the adhesive resin layer is represented by the formula (1), (2) or the formulas (3), (4), (5) It can be used for evaluation.

<In the case of repeated multi-layered structure (even layer) of EVOH and adhesive resin>

<In the case of repeated multilayer structure of EVOH and adhesive resin (odd layer)>

For example, in the case of a two-layer sample of EVOH and an adhesive resin, the thickening ratio derived from the reaction at the laminated interface of the EVOH layer and the adhesive resin layer is as follows by substituting n = 2 in formulas (1) and (2): It is asked according to.
<In the case of a two-layer sample of an EVOH layer and an adhesive resin layer>
The thickening rate derived from the interfacial reaction between the EVOH layer and the adhesive resin layer can be evaluated using the following equation.

In addition, when the time-dependent change of the thickening rate derived from the lamination | stacking interface reaction of an EVOH layer and an adhesive resin layer was evaluated on the said measurement conditions, if a heating time is less than 1 hour, the lamination interface reaction origin of an EVOH layer and an adhesion resin layer is derived. The thickening rate of is almost unchanged.
Therefore, for example, a multilayer structure produced by multilayer coextrusion may be used as the multilayer structure used in the evaluation of the thickening rate derived from the interfacial reaction between the EVOH layer and the adhesive resin layer, or lamination is performed in advance. It is also possible to use one of them, or one obtained by laminating single films or sheets of each material on a rotary rheometer.
In the present invention, using a laminate of an EVOH sheet and an adhesive resin sheet on a rotary rheometer, the thickening rate derived from reaction at the interface between the EVOH layer and the adhesive resin layer was evaluated.
Hereinafter, the multilayer structure will be described in order.

<EVOH>
EVOH used in the present invention is usually a resin obtained by saponifying a copolymer of ethylene and a vinyl ester-based monomer (ethylene-vinyl ester-based copolymer), and is a water-insoluble thermoplastic resin is there. The polymerization method can also be carried out using any known polymerization method, for example, solution polymerization, suspension polymerization, emulsion polymerization, but 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 carried out by a known method. The EVOH thus produced is mainly composed of a structural unit derived from ethylene and a vinyl alcohol structural unit, and contains a slight amount of vinyl ester structural unit remaining without being saponified.

  As the above-mentioned vinyl ester-based monomer, vinyl acetate is typically used from the viewpoint of easy availability from the market and good efficiency of treatment of impurities at the time of production. Other vinyl ester monomers include, for example, vinyl formate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl versatate and the like. Aliphatic vinyl esters, aromatic vinyl esters such as vinyl benzoate and the like can be mentioned, and 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. These are usually used alone, but two or more species may be used simultaneously as required.

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

  The saponification degree of the vinyl ester component in EVOH is a value measured based on JIS K 6726 (wherein EVOH is a solution uniformly dissolved in water / methanol solvent), and is usually 90 to 100 mol%, preferably 95 to 100 It is 100 mol%, particularly preferably 99 to 100 mol%. If the degree of saponification is too low, the gas barrier properties, thermal stability, moisture resistance and the like tend to decrease.

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

  The EVOH used in the present invention may further contain structural units derived from comonomers shown below, in addition to ethylene structural units and vinyl alcohol structural units (including unsaponified vinyl ester structural units). . Examples of the comonomer include α-olefins such as propylene, isobutene, α-octene, α-dodecene, α-octadecene and the like; 3-buten-1-ol, 4-penten-1-ol, 3-butene-1, Hydroxy group-containing α-olefins such as 2-diol and the like, and hydroxy group-containing α-olefin derivatives such as esters and acylates thereof; unsaturated carboxylic acids or salts thereof, partial alkyl esters, complete alkyl esters, nitriles, amides or anhydrides Unsaturated sulfonic acids or salts thereof; vinyl silane compounds; vinyl chloride; styrene and the like.

  Furthermore, it is also possible to use “post-modified” EVOH resins such as urethanization, acetalization, cyanoethylation, oxyalkylenation and the like.

  Among the modified products as described above, EVOH in which the primary hydroxyl group is introduced into the side chain by copolymerization is preferable in that the secondary formability such as stretching and vacuum / pressure forming becomes good, and above all, 1,2-OH Preference is given to EVOH having a diol structure in the side chain.

  In the EVOH used in the present invention, compounding agents generally added to the EVOH as long as the effects of the present invention are not impaired, such as a heat stabilizer, an antioxidant, an antistatic agent, a colorant, an ultraviolet absorber, Lubricants, plasticizers, light stabilizers, surfactants, antibacterial agents, desiccants, antiblocking agents, flame retardants, crosslinking agents, curing agents, foaming agents, nucleating agents, antifogging agents, additives for biodegradation, silanes A coupling agent, an oxygen absorbent, etc. may be contained.

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

  In addition, EVOH used in the present invention may be a mixture with another different EVOH, and as such other EVOH, one having a different ethylene content, one having a different degree of saponification, a melt flow rate (MFR) ) (210 ° C., load: 2,160 g) different, other copolymerization components different, modification amounts different (eg, content of 1,2-diol structural units different), etc. it can.

  In particular, in the present invention, it is preferable to use two or more types of EVOH having different ethylene content in the EVOH layer, and EVOH layer / adhesive resin layer is also applied when multilayer coextrusion molding is applied while maintaining long run property. It is possible to more efficiently obtain a multilayer structure having an EVOH layer in which the occurrence of appearance defects due to interface roughening occurring at the interface of the above is reduced, and in particular, the decrease in image sharpness is small.

In particular, it is preferable that the difference (ΔEt) between the highest ethylene content of the ethylene structural unit and the lowest ethylene content among two or more types of EVOH having different ethylene contents is 10 to 25 mol%, more preferably It is 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 balance between moldability and gas barrier properties, and if it is too large, the mutual compatibility decreases, and the difference in elongation rate There is a tendency that streaks tend to be generated during secondary molding using a multilayer structure as a raw material, and that a transparent molded article tends to be difficult to obtain.
In addition, although the case where two types of EVOH are used below is demonstrated, in the case of three or more types, that whose ethylene content rate of the ethylene structural unit is the highest, and that of the ethylene content other than the lowest are those. It can use suitably within the limits.
Hereinafter, for example, the case of using two types of EVOH will be described.

  The two types of EVOH used in the present invention are combinations of EVOH selected from the above EVOHs. In particular, it is a combination of EVOH in which the ethylene content difference (ΔEt) is 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 balance between moldability and gas barrier properties, and if it is too large, the mutual compatibility decreases, and the difference in elongation rate There is a tendency that streaks tend to be generated during secondary molding using a multilayer structure as a raw material, and that a transparent molded article tends to be difficult to obtain.

  Specifically, a combination of EVOH (low ethylene EVOH) (A1) having a lower ethylene content as described below 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%. When the ethylene content is too low, the decomposition temperature and the melting point tend to be too close and melt molding of the resin composition tends to be difficult. Conversely, when it is too high, the gas barrier property imparting effect by low ethylene EVOH (A1) There is a tendency to decline.

  In addition, 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 by the low ethylene EVOH (A1) tends to decrease.

  Furthermore, the melt flow rate (MFR) (210 ° C., load 2,160 g) of low EVOH (A1) is usually 1 to 100 g / 10 min, preferably 3 to 50 g / 10 min, particularly preferably 3 to 10 g It is 10 minutes. When the MFR is too large, the mechanical strength of the molded article tends to decrease, and when it is too small, the extrusion processability 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 improvement effect of stretchability by high ethylene EVOH (A2) is small, and as a result, there is a tendency for secondary formability to decrease, and conversely, when it is too high, ethylene content difference In order to be within the predetermined range, the ethylene content of low ethylene EVOH (A1) has to be increased, and as a result, the gas barrier properties of the EVOH layer tend to be lowered.

  Moreover, the saponification degree of the vinyl ester component in high ethylene EVOH (A2) is 90 mol% or more normally, Preferably it is 93-99.99 mol%, Especially preferably, it is 98-99.99 mol%. If the degree of saponification is too low, the gas barrier properties of the high ethylene EVOH (A2) tend to decrease.

  Furthermore, the melt flow rate (MFR) (210 ° C., load: 2,160 g) of high ethylene EVOH (A2) is usually 1 to 100 g / 10 min, preferably 3 to 50 g / 10 min, particularly preferably 3 to 3 g It is 30 g / 10 minutes. When the MFR is too large, the mechanical strength of a molded product using the multilayer structure of the present invention as a raw material tends to decrease, and when too small, the extrusion processability tends to decrease.

  The blending ratio (A1 / A2) (weight ratio) of the low ethylene EVOH (A1) to 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 low ethylene EVOH (A1) is too small, the gas barrier properties of the composition layer tend to decrease, and when too large, the effect of improving the elongation by high ethylene EVOH (A2) tends to decrease. .

<Adhesive resin>
The adhesive resin used in the present invention will be described.
A known adhesive resin may be used. Such an adhesive resin may be selected as appropriate depending on the type of base resin, but typically, an unsaturated carboxylic acid or an anhydride thereof is chemically bonded to a polyolefin resin by an addition reaction, a grafting reaction or the like. The modified olefin resin containing the carboxyl group obtained can be mentioned. Among them, as the adhesive resin, maleic anhydride-modified polyolefin is preferable, and as the base resin, a combination with polyolefin, particularly, linear low density polyethylene or polypropylene is preferable.

  As maleic anhydride modified polyolefin, for example, maleic anhydride graft modified polyethylene, maleic anhydride graft modified polypropylene, maleic anhydride graft modified ethylene-propylene (block and random) copolymer, maleic anhydride graft modified ethylene-ethyl acrylate It is a copolymer, a maleic anhydride graft modified ethylene-vinyl acetate copolymer, etc., and 1 type, or 2 or more types of mixtures chosen from these are preferable. These adhesive resins can also be blended with rubber-elastomer components such as EVOH other than EVOH forming the EVOH layer used in the present invention, polyisobutylene, ethylene-propylene rubber, and polyolefin resins. is there. In particular, by blending a polyolefin-based resin different from the base polyolefin-based resin of the adhesive resin, the adhesion may be improved, which is useful.

<Other thermoplastic resin>
The other thermoplastic resins 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 (referred to as "base resin") used herein include polyethylenes such as linear low density polyethylene, low density polyethylene, ultra low density polyethylene, medium density polyethylene, high density polyethylene, etc. , Polypropylenes, ethylene-propylene (block and random) copolymers, propylene-α-olefins (α-olefins of 4 to 20 carbon atoms) copolymers, polyolefins such as polybutene and polypentene; Grafted polyolefins grafted with an acid or an ester thereof; ethylene-vinyl compound copolymers such as ionomers, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylate copolymers, etc .; polyesters Resin; Polyamide Resins (including copolyamides); Halogenated polyolefins such as polyvinyl chloride, polyvinylidene chloride, chlorinated polyethylene and chlorinated polypropylene; Vinyl ester resins; Elastomers such as polyester elastomers and polyurethane elastomers; Acrylic resins; Polystyrenes Although aromatic or aliphatic polyketones and polyalcohols obtained by reducing these may be mentioned, polyolefin resins and polyamide resins are preferable from the viewpoint of practicality such as physical properties (particularly strength) of the multilayer structure. In particular, polyethylene and polypropylene are preferably used.

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

<Multilayer structure>
The layer structure of the multilayer structure is a (a1, a2, ...) of the EVOH layer, b (b1, b2, ...) of the adhesive resin layer, c (c1, c2, ...) of the thermoplastic resin layer. ···) if a / b / c, a1 / b / a2, c1 / b / a / c2, c / a1 / b2 / a2, c1 / b1 / a / b2 / c2, c1 / a1 / 1 Any combination of b / a2 / c2, c1 / b1 / a1 / b2 / a2 / b3 / c2, etc. is possible. In addition, a recycling layer containing a mixture of EVOH, an adhesive resin and a thermoplastic resin, which is obtained by recovering the end portion or defective product generated in the process of producing the multilayer structure, and re-melting it is R (R1 , R2,..., C / R / b / a, c / R / a1 / b / a2, c1 / R / a / b / c2, R1 / a1 / b / a2 / R2, c1 It is also possible to use / R1 / b1 / a / b2 / R2 / c2, c1 / R1 / a1 / b / a2 / R2 / c2, etc.

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

The thickness of the EVOH layer varies depending on the required gas barrier properties 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. When the thickness is too thin, sufficient gas barrier properties tend not to be obtained, and when 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 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. The thickness ratio of the EVOH layer to the adhesive resin layer (EVOH layer / 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.
In addition, 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 to 50, preferably 95/5 to 55/45, particularly preferably 90/10 to 60/40.

  The lamination of the EVOH layer, the adhesive resin layer, and the thermoplastic resin layer can be performed by a known method. For example, the lamination of the EVOH layer and the adhesive resin layer can be performed by multi-layer co-extrusion of in-apparatus merging. Specifically, a method of expanding to a molded product width in a die after joining each layer using feed blocks, a method of joining layers after expanding to a product width using a multi-manifold die, EVOH layer and adhesive resin by the above method The method etc. which are spread on the base material which consists of another resin layer after a layer is laminated | stacked are mentioned. From the viewpoint of cost and environment, a method in which all layers of the EVOH layer, the adhesive resin layer, and the thermoplastic resin layer are multi-layer co-extrusion is preferable.

In the present invention, the greatest characteristic is that the thickening rate derived from the reaction of the laminated interface of 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, it is important to satisfy the physical properties of the above-mentioned thickening rate.

There is no particular limitation on satisfying the viscosity increasing ratio derived from the laminated interface reaction of the EVOH layer / adhesive resin layer within a predetermined range, but it is possible by combining the following methods and the like as appropriate.
(1) A method of adjusting the thickening rate derived from the laminated interface reaction of the EVOH layer / adhesive resin layer in the EVOH layer For example, changing the molecular weight of EVOH, especially MFR, ethylene content, saponification degree, or a plurality of It can adjust by using EVOH together. However, since other properties such as moldability and gas barrier properties may greatly change in these methods, it is necessary to consider other properties in the case of applying such a method. In such a case, it is preferable to use a small amount of an additive that has a large effect on the thickening rate derived from the laminated interface reaction of the EVOH layer / adhesive resin layer, without affecting other properties.
As such an additive, for example, blending the following may be mentioned.
(I) The polyamide resin which is a reaction system resin is blended to EVOH.
(Ii) Adhesive resin which is a reaction system 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, a grafting reaction, etc. And a modified ethylene-vinyl acetate copolymer (EVA), etc.). Specifically, maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, monomethyl ester of maleic acid, monoethyl ester of maleic acid, diethyl ester of maleic acid and the like can be mentioned, and in particular, maleic anhydride is preferable. is there.
(Iii) A non-reactive system compatibilizer (in order to lower the interfacial tension; for example, a styrene-based thermoplastic elastomer (SBS), a hydrogenated styrene-based thermoplastic elastomer (SEBS), etc.) is blended.
(IV) Compatibilizer for reaction system (in order to reduce 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, etc., or copolymer containing them Combine).
(V) blend an ionomer.
(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) In the adhesive resin layer, a method of adjusting the thickening rate derived from the reaction at the laminated interface of the EVOH layer / adhesive resin layer For example, blending adhesive resins having different molecular weights or resins having different compositions changes the degree of acid modification And the like.
In addition to this, it is possible to add a trace amount of an additive having a large effect on the thickening rate derived from the laminated interface reaction of the EVOH layer / adhesive resin layer to the adhesive resin.
As such an additive, for example, blending the following may be mentioned.
(I) EVOH
(Ii) Blending a polyamide resin which is a reaction system resin with EVOH.
(Iii) Adhesive resin which is a reaction system 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, a grafting reaction, etc. And a modified ethylene-vinyl acetate copolymer (EVA), etc.). Specifically, maleic acid, fumaric acid, itaconic acid, maleic anhydride, itaconic anhydride, monomethyl ester of maleic acid, monoethyl ester of maleic acid, diethyl ester of maleic acid and the like can be mentioned, and in particular, maleic anhydride is preferable. is there.
(IV) Compatibilizers for non-reactive systems (in order to lower interfacial tension; for example, styrene thermoplastic elastomer (SBS), hydrogenated styrene thermoplastic elastomer (SEBS), etc.) are blended.
(V) Compatibilizer for reaction system (in order to reduce 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, etc., or copolymer containing them Blending (Vi) Blend the ionomer.
(Vii) Acids such as acetic acid, boric acid and phosphoric acid and metal salts thereof such as alkali metals, alkaline earth metals and transition metals thereof are blended. (Viii) higher fatty acid metal salts such as zinc of higher fatty acids are blended.

  Among these, with regard to the method of adjusting the thickening rate derived from the laminated interface reaction of the EVOH layer / adhesive resin layer, two or more different EVOHs having an ethylene content difference (ΔEt) of 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, it is possible to set the thickening rate derived from the interfacial reaction between layers of the desired EVOH layer / adhesive resin layer. It is preferred to be in the range.

  Examples of higher fatty acids used for higher fatty acid metal salts include fatty acids having 8 or more carbon atoms, preferably 12 to 30 carbon atoms, and more preferably 12 to 20 carbon atoms. Specifically, for example, Lauric acid, tridecyl acid, myristic acid, pentadecyl acid, palmitic acid, heptadecyl acid, stearic acid, nonadecanoic acid, oleic acid, capric acid, behenic acid, linoleic acid and the like can be mentioned. Among these, stearic acid, oleic acid and lauric acid are preferably used.

By using such a higher fatty acid metal salt, the multilayer coextrusion formability of a 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, ie, an image The reduction in sharpness can be reduced. In addition, when the multilayer structure was vacuum pressure formed, the tension applied was different depending on the part, and the generation of streaks was reduced even when subjected to processing such as diameter expansion processing in which tension was applied from all directions. An article can be obtained.
Although the reason is not clear, the higher fatty acid metal salt moderately suppresses the thickening rate derived from the laminated interface reaction of the EVOH layer / adhesive resin layer, and micro interface roughening occurs during multilayer coextrusion molding with other resins To reduce the

  The blending amount of the higher fatty acid metal salt is usually 350 to 800 ppm, preferably 400 to 750 ppm, and particularly preferably 450 to 700 ppm based on EVOH when blended in EVOH. When the content of the higher fatty acid metal salt is too small, the effect of reducing appearance defects tends to be reduced, and in some cases, the transparency of the multilayer structure may be impaired. On the other hand, metal salts of higher fatty acids generally promote decomposition of EVOH in the molten state, so if the concentration of higher fatty acid metal salts is too high, decomposition of EVOH generates gas, and multilayers by melt molding or coextrusion It may adversely affect the production of the structure.

[Other additives]
In the EVOH layer used for the multilayer structure of the present invention, a plasticizer, a filler, an antiblocking agent, an antioxidant, a coloring agent in addition to the above components in a range (for example, 1 wt% or less) Well-known additives, such as an antistatic agent, an ultraviolet absorber, and a lubricant, can be suitably blended.

<Method of Preparing EVOH Composition>
With regard to 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 etc. The components may only be dry blended at a predetermined ratio.
Moreover, the compounding method by dry blending is preferable from the viewpoint of suppressing the decomposition of higher fatty acid metal salt to EVOH in a molten state. That is, in the EVOH composition, it is preferable that the higher fatty acid metal salt be adhered and present on the surface of each EVOH by dry blending.

As a method of dry blending, a higher fatty acid metal salt may be blended with EVOH as a dry blend. 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 compound of two or more types of EVOH prepared in advance may be a higher fatty acid metal salt. May be blended. Two or more types of EVOH and higher fatty acid metal salts may be blended in a dry blend.
In addition, the remaining EVOH may be blended into a dry blend of any EVOH and higher fatty acid metal salt, or the remaining EVOH may be added to a previously prepared compound of any EVOH and higher fatty acid metal salt. You may mix | blend. Furthermore, 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 The compound with the salt may be compounded with the remaining prepared EVOH and the higher fatty acid metal salt compound.

<Application of Multilayer Structure>
The multilayer structure having the above constitution is usually subjected to a heat drawing treatment and used. 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, so that various known heat drawing treatments can be applied.

Specifically, for example, uniaxial stretching and biaxial stretching in which both ears of the multilayer structure are grasped and widened; heat softening of the multilayer structure; draw forming processing of forming 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 a mold by blowing compressed air, etc., are processed by tubular drawing method, stretch blow method etc. The method is mentioned.
The multilayer structure having the EVOH of the present invention has reduced thermal disturbance at the interface with the adjacent layer and has excellent heat stretchability, so uniaxial stretching, only biaxial stretching that stretches sequentially in different directions It is also suitable for stretch processing and blow molding by die adhesion which is simultaneously stretched in the radial direction.

  The temperature at which the heat drawing is performed is selected from the range of about 40 to about 300 ° C., preferably about 50 to about 160 ° C., as a temperature of the multilayer structure (temperature near the multilayer structure). The stretching ratio is usually 2 to 50 times, preferably 2 to 10 times in area ratio.

  Moreover, it is preferable to heat a multilayer structure uniformly by a hot-air oven, a heating heater type | mold oven, or both combined use etc., and it selects it suitably according to the kind of stretch molding method.

  Another substrate may be extrusion coated onto the multilayer structure obtained by multi-layer coextrusion molding or thermal stretching treatment, or films, sheets, etc. of other substrates may be laminated using an adhesive. Good. As the base material, not only the thermoplastic resin described above as the base material resin, but also a base material having poor stretchability (paper, metal foil, woven fabric, non-woven fabric, metallic cotton, wood, etc.) can be used. Furthermore, an inorganic material layer made of metal or metal oxide may be formed on the multilayer structure by vapor deposition or the like.

  Molded articles such as bags and cups made of films, sheets and stretched films, and containers made of cups, trays, tubes, bottles, etc. obtained as described above are seasonings such as mayonnaise and dressings, as well as general foods. It is useful as fermented foods such as miso, fats and oils such as salad oil, various packaging materials such as beverages, cosmetics, and pharmaceuticals, packaging containers and lids.

[Production of secondary molded articles by vacuum molding / pressure forming]
The multilayer structure of the present invention is suitable as a raw material for the production of secondary molded articles, particularly bottomed containers such as cups and trays, by vacuum molding or pressure forming. The multilayer structure of the present invention can obtain a secondary molded article having an excellent appearance because the resin flow disorder at the laminated interface is small.

  The shape of the bottomed container is not particularly limited, and a cylindrical bottomed container, a rectangular cylinder bottomed container, or an irregularly shaped bottomed container, a conical bottomed member whose diameter is reduced or enlarged from the opening to the bottom Container, a pyramidal bottomed container having a bottom area smaller than the opening area, a hemispherical container, a stepped bottomed container whose bottom is reduced in two steps from the opening, and further, a flange or a convex portion is formed on these containers It may be formed.

  In particular, when the object is 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, in particular, rapid drawing processing In the case of vacuum pressure forming, it is difficult to produce a molded product having an excellent appearance because the magnitude of the tension applied to the resin is different between the side portion and the bottom portion of the cup. . However, in the multilayer structure of the present invention, a molded article having an excellent appearance without impairing the gas barrier properties even when it is subjected to cup-like molding by a vacuum pressure forming method, the tension applied during molding processing varies depending on the part. You can get

  The heating temperature in the heat softening step is selected from the range of about 40 to 300 ° C., preferably 50 to 170 ° C., particularly preferably about 60 to 160 ° C., as the temperature of the multilayer structure (temperature near the multilayer structure). If the heating temperature is too low, the softening tends to be insufficient and a molded article having an excellent appearance can not be obtained. If the heating temperature is too high, the melt viscosity balance of each layer is lost, and a molded article having an excellent appearance is obtained. There is a possibility that it can not be obtained.

  The heating time is a time in which the temperature of the multilayer structure can be heated to such an extent that a sufficient softening state necessary for molding can be achieved, and the layer configuration of the multilayer structure, the component composition of each layer forming the multilayer structure, It is suitably set by the heater temperature etc. which are used for heating.

  The drawing ratio of vacuum pressure air forming (depth of molded product (mm) / maximum diameter of molded product (mm)) is usually 0.1 to 3, preferably 0, although it depends on the shape of the target bottomed container. 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 be easily formed, and when too small, uneven thickness tends to easily occur in the wall thickness.

The thickness of the EVOH layer of the multilayer structure after secondary molding as described above varies depending on the required gas barrier properties and the like, but is usually 0.1 to 500 μm, preferably 0.1 to 250 μm, particularly preferably It is 0.1 to 100 μm. When the thickness is too thin, sufficient gas barrier properties tend not to be obtained, and when 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 of the EVOH layer to the adhesive resin layer, and the total thickness ratio of the EVOH layer to the total thickness ratio of the thermoplastic resin layer do not greatly change before and after heat drawing, and the same values as in the case of the multilayer structure described above It becomes.

  The multilayer structure of the present invention is one in which the occurrence of appearance defects, in particular, the decrease in image sharpness is reduced. It is considered that this is because the roughness at the interface between the EVOH layer of the multilayer structure and the adjacent adhesive resin layer is reduced and the micro interface roughness that causes the appearance defect is reduced. Therefore, it is useful as a general food, as well as seasonings such as mayonnaise and dressing, fermented foods such as miso, oil and fat foods such as salad oil, various packaging materials containers such as beverages, cosmetics and pharmaceuticals.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the description of the examples unless the gist is exceeded. In the examples, "part" means weight basis.

[EVOH No. Production of 1-7]
The EVOH was prepared by selecting from the four types of EVOH shown below, blending the EVOH and the higher fatty acid zinc salt shown in Table 1 at the concentrations shown in Table 1, and dry blending.
EVOH 1: 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%, degree of saponification 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
EVOH 4: ethylene content 38 mol%, saponification degree 99.7 mol%, MFR 4.1 g / 10 min (210 ° C., load 2160 g), boron content 250 ppm

[Production of multilayer structure]
Three types, five layers, multilayer coextrusion cast film film forming apparatus, EVOH prepared above, linear low density polyethylene (LLDPE) ("UF240" manufactured by Japan Polyethylene Corporation), adhesive resin ("PLEXAR PX3236" manufactured by LyondellBasell) Were supplied, and a multilayer structure (film) of 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 molding apparatus die temperatures were all set at 210.degree.
(Multilayer coextrusion molding conditions)
・ Interlayer extruder (EVOH): 40 mmφ single screw extruder (barrel temperature: 210 ° C)
Upper and lower layer extruder (LLDPE): 40 mm φ single screw extruder (barrel temperature: 210 ° C.)
・ Middle upper and lower layer extruder (adhesive resin): 32 mmφ single screw extruder (barrel temperature: 210 ° C)
・ Die: 3-layer 5-layer feed block type T die (die temperature: 210 ° C)
-Take-up speed: 14 m / min-Roll temperature: 50 ° C

[Thickening rate derived from reaction at the laminated interface of EVOH layer and adhesive resin layer]
The shear viscosity (Pa · S) of the EVOH, the adhesive resin, and the EVOH layer / adhesive resin layer laminate prepared as described above is measured using a rotary rheometer ("MCR301" manufactured by Anton Paar Co., Ltd.) under the following conditions did.

(Preparation of measurement sample)
The EVOH prepared above and the adhesive resin are heat-pressed at 210 ° C. using a compression molding machine (NSF-37) manufactured by Kamitoko Kogyosho Co., Ltd. to obtain single-layer sheets of 1 mm and 0.5 mm in thickness. Manufactured.
A single-layer sheet with a thickness of 1 mm is used to measure the shear viscosity of the EVOH and the adhesive resin, and a single-layer sheet with a thickness of 0.5 mm is used to measure 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 reaction at the interface between the EVOH layer and the adhesive resin layer)
Further, from the obtained measurement results, the thickening rate derived from the reaction of the laminated interface of the EVOH layer and the adhesive resin layer was calculated using the equation described below.

[Evaluation of image definition]
The image definition of the multilayer structure was measured by the transmission method according to JIS K 7374 "Plastic-Determination of image definition". The film test pieces were measured with the film machine direction as the vertical direction. As a measuring instrument, an ICM-1 image clarity measuring instrument manufactured by Suga Test Instruments Co., Ltd. was used. The optical comb used 0.5, 1.0, and 2.0 mm.

[Evaluation of long run property]
A change in torque was measured when 55 g of the above-prepared EVOH was kneaded at 50 rpm and 250 ° C. using Plastograph EC-plus (manufactured by Brabender). The torque 5 minutes after the start of kneading was measured, and the time until the torque value became 20% of the torque 5 minutes after that 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: Measurement of thickening rate Temperature: 200 ° C

  From the above results, the multilayer structure manufactured by setting the thickening rate derived from the interfacial reaction between the EVOH layer and the adhesive resin layer within a predetermined range reduces the occurrence of appearance defects while maintaining 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 appearance defects, and in particular, the decrease in image sharpness is reduced. It is considered that this is because the roughness at the interface between the EVOH layer of the multilayer structure and the adjacent adhesive resin layer is reduced and the micro interface roughness that causes the appearance defect is reduced. Therefore, the multi-layered structure of the present invention can be used not only for general foods but also for seasonings such as mayonnaise and dressings, fermented foods such as miso, fats and oils such as salad oil, various packaging materials containers such as beverages, cosmetics and pharmaceuticals. It is useful as a raw material.

Claims (4)

A multilayer comprising a thermoplastic resin layer other than a saponified ethylene-vinyl ester copolymer laminated on at least one surface of a layer containing a saponified ethylene-vinyl ester copolymer via an adhesive resin layer. It is a structure, and the thickening rate derived from the layer-to-layer interface reaction between the layer containing the ethylene-vinyl ester copolymer saponified product and the adhesive resin layer is 0.5 to 5.2% per one surface of the interface. A multilayer structure for various packaging material containers of food, seasoning, fermented food, fat and oil food, beverage, cosmetics, and pharmaceuticals characterized in that they are characterized by the following. The food according to claim 1, wherein the ethylene-vinyl ester-based copolymer saponified product is a mixture of two or more ethylene-vinyl ester-based copolymer saponified products having different ethylene structural unit contents . Multilayer structure for various packaging material containers for seasonings, fermented foods, fats and oils, beverages, cosmetics, and pharmaceuticals . It is characterized in that the difference (ΔEt) between the highest ethylene content of the ethylene structural unit and the lowest ethylene structural unit among the two or more ethylene-vinyl ester copolymer saponifications is 10 to 25 mol%. A multi-layered structure for packaging material containers according to claim 2, wherein the food, the seasoning, the fermented food, the fat and oil food, the beverage, the cosmetic and the medical drug . A layer containing a saponified ethylene-vinyl ester copolymer is characterized in that it contains 350 to 800 ppm of a higher fatty acid zinc salt relative to the saponified ethylene-vinyl ester copolymer. The multi-layered structure for various packaging material containers according to any one of claims 1 to 3, wherein the food, the seasoning, the fermented food, the fat and oil food, the beverage, the cosmetic and the pharmaceutical product .