JPH0223344B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention has excellent oxygen barrier properties, interlayer adhesion,
The present invention aims to provide a laminate that has oil resistance, heat sealability, and transparency, and is particularly suitable for oil-based food packaging materials. Packaging of oil-based foods such as ham, meat, fish, mayonnaise, and edible oil requires packaging materials that both protect the contents and are suitable for packaging. Protecting the contents means preventing the packaged items from spoiling due to contact with oxygen, and for this purpose, the packaging material is required to have oxygen barrier properties. Also, packaging suitability refers to transparency so that the contents can be seen from the outside, oil resistance so that the packaging material is not attacked by oil exuding from the contents, and heat sealability to seal the contents. . Heat sealability here refers to the heat sealing strength after the base material is sealed with a heat sealer and the sealed part is completely solidified, and the heat generated when peeling force is applied to the sealing surface immediately after sealing and before the sealed part hardens. Refers to both sealability and sealability. However, there is currently no single plastic packaging material that has all of these properties. For example, although low-density polyethylene film, which is widely used as a packaging material, has many advantages, it is unsuitable as an oil-based food packaging material due to its gas permeability and oil resistance. (EVA) has transparency, heat sealability,
In particular, it has excellent low-temperature heat-sealing properties, but it has poor oil resistance. On the other hand, saponified ethylene-vinyl acetate copolymer (EVOH) is an excellent packaging material with oxygen barrier properties, oil resistance, and transparency properties necessary for oil-based food packaging materials, but it also has heat sealability. It cannot be used alone because it does not have EVOH, but it is used in combination with a material that has excellent heat sealability and does not inhibit the aforementioned characteristics of EVOH, such as an ionomer resin. [Problems to be solved] Generally, when making a laminate from multiple resins, an extrusion lamination method or dry lamination method is used, in which an anchor coating agent or liquid adhesive is applied onto one resin film and bonded to the other resin. There is a co-extrusion method in which each resin is extruded in a molten state and thermally fused together, but the co-extrusion method produces a laminate in one step without using adhesives or solvents.
It is advantageous in terms of economy and health and safety. However, since EVOH does not directly thermally bond to ionomer resins, which are suitable as laminated partners for oil-based food packaging materials, it is possible to use a multilayer coextrusion method using maleic anhydride-modified polyolefin, which has thermal adhesive properties to both resins, as an intermediate adhesive layer. It was layered. However, when the number of constituent layers increases in the coextrusion lamination method, the advantages of the coextrusion method are largely lost in terms of equipment and manufacturing. Therefore, as an improvement measure, we added resin for the intermediate adhesive layer.
Efforts have been made to reduce the number of constituent layers by blending EVOH with ionomer resins, but in this case, the blending reduces oxygen barrier properties, transparency, and heat sealability, making it impossible to achieve the intended purpose. . Therefore, there was a need for a resin that could be co-extruded with EVOH to form a strong thermal bond, and also had excellent packaging suitability such as heat sealability. [Prior Art] It has been known that graft modification of polyethylene or EVA with maleic anhydride increases thermal adhesion to both EVOH and ionomer resins. However, when the ionomer resin is graft-modified with maleic anhydride, the effect of imparting thermal adhesion to EVOH is not exhibited at all. Furthermore, a blend of an ionomer resin and a maleic anhydride graft-modified resin not only does not provide thermal adhesion to EVOH, but also significantly impairs the excellent heat sealability of the ionomer resin. in this way,
Conventionally, as a means to obtain a laminate that shares the excellent oxygen barrier properties of EVOH and the excellent heat sealability of ionomer resins, an intermediate adhesive layer such as maleic anhydride-grafted modified polyethylene, which has thermal adhesion properties to both resins, has been used. 3 interposed between the two
The only method available was coextrusion of layers or more. On the other hand, it is known that ethylene-ethylenically unsaturated carboxylic acid copolymer (EA), which is the base of ionomer resin, has excellent thermal adhesion to polar substrates such as metals and nylon. The heat adhesion to EVOH is poor, and the heat sealability is also inferior to that of ionomer resins. Due to these circumstances, conventional oil-based food packaging materials
For EVOH, ionomer resins have been bonded with adhesives or laminates made by coextrusion with an intermediate adhesive layer interposed have been used. However, surprisingly, when EA, which is the base of the ionomer resin, is graft-modified with maleic anhydride, this copolymer (called EAMA)
It was discovered that not only the heat adhesion to EVOH was significantly improved, but also the heat sealability was improved, and the present invention was completed based on this knowledge. [Structure] That is, the present invention comprises: (a) an EVOH layer with an ethylene content of 10 to 75 mol% and a saponification degree of 90 mol% or more; (b) an ethylene content of 50 to 99 mol% and an ethylenically unsaturated carboxylic acid content of 1.0 ~10 mol% ethylene
The gist is a laminate consisting of an EAMA layer made of an ethylenically unsaturated carboxylic acid copolymer and an EAMA layer grafted with maleic anhydride at a ratio of 0.05 to 5.0% by weight, and this laminate is suitable for oil-based food packaging. Various properties required for the material, namely oxygen barrier properties,
It satisfies all of oil resistance, transparency, and heat sealability, and also has sufficient interlayer adhesive strength. This laminate can be obtained by thermally bonding the films molded from the above two types of resins.
For example, it is industrially advantageous to manufacture by coextrusion using a multilayer inflation method, and this is also one of the features of the present invention. [Details of configuration conditions] In the present invention, one layer of the laminate is
As EVOH, from the viewpoint of the balance between oxygen barrier properties and moldability, those having an ethylene content of 10 mol% or more and 75 mol% or less and a saponification degree of 90 mol% or more are used. In addition, EA, which is the base of EAMA, has an ethylene content of 50 mol% for ease of manufacture and moldability.
~99 mol%, ethylenically unsaturated carboxylic acid content 1.0 for heat sealability, oil resistance, and adhesion
~10 mol% is suitable. Examples of ethylenically unsaturated carboxylic acids include acrylic acid, methacrylic acid, and methyl hydrogen maleate. EA does not necessarily have to be two components, and can include acrylic acid alkyl esters, methacrylic acid alkyl esters, vinyl acetate, etc. as a third component in addition to ethylene and ethylenically unsaturated carboxylic acid. In particular, it contains acrylic esters and methacrylic esters.
EAMA is preferable because it has excellent thermal adhesion with EVOH. EA is synthesized by high-pressure polymerization using a radical catalyst such as an organic peroxide. The grafting amount of maleic anhydride is suitably 0.05 to 5% by weight based on the base copolymer. If it is less than 0.05% by weight, thermal adhesion with EVOH will be insufficient, and if it exceeds 5% by weight, thermal stability will be poor and practical processing will be difficult. Graft modification with maleic anhydride can be carried out by various methods, but in the present invention, a method in which maleic anhydride is reacted with the base copolymer in the coexistence of a radical generator such as a peroxide is preferred from the viewpoint of efficacy. The reaction can be carried out by a solution method in which the base copolymer is reacted in a state dissolved in a solvent, or a melt method in which the reaction is carried out using an extruder, and either method can be used. As the laminate forming method for carrying out the present invention, normal laminate forming methods such as heat fusion method, dry lamination method, Sand-German lamination method, extrusion coating method, coextrusion method, etc. can be adopted. The coextrusion method is most preferred from the economic point of view. Further, there are many known coextrusion methods such as an inflation method, a T-die method, and a blow molding method, and the present invention is applicable to any of these methods. Moreover, the present invention
It is sufficient that the EVOH layer and the EAMA layer are in direct contact with each other to form a laminate, and there is no hindrance to adding a printing layer or the like to either layer. The thickness of each layer varies depending on the purpose of use, but
For oil-based food packaging materials, which are typically used,
Generally, EVOH layer 10~100μm, EAMA layer 20~
A range of 150 μm is suitable. [Examples and Effects] The present invention will be explained below with reference to Examples. Note that the measurements in the Examples are based on the following method. Γ Adhesive force measurement (interlayer adhesive strength) Measuring device: Autograph Measuring method: 90° peel adhesive strength, test piece 15 mm width, tensile speed 300 mm/min Γ Heat sealing strength Heat sealing conditions: 1 second, pressure 0.4 Mpa, seal bar width Heat-compression bonded at 25mm Measurement method: 90° peel adhesive strength, test piece 10mm width, tensile speed 300mm/min Γ Hot sealability Film sealing pressure 0.2Mpa, sealing time 05
90g/10 on the sealing surface immediately after heat sealing in seconds
A mm-wide force is applied at 90° in the peeling direction, and the peeling distance of the sealing surface is measured. The shorter the peeling distance, the better the hot sealing properties and the better the packaging workability. Γ Melt index (MI) Measurement temperature 190°C according to JIS K-6760 Example 1 Reference example 1 Ethylene-methacrylic acid copolymer pellets 100
Parts by weight, 1 part by weight of maleic anhydride, and 0.05 parts by weight of 2,5-dimethyl-2,5bis(t-butylperoxy)hexyne-3 were dry blended in advance, and an extruder (screw diameter 65 mm, L/D=
26) at a rate of 30 kg/h to perform graft modification. Temperature at the middle part of the extruder during graft modification
It was kept at 250℃. When the grafting rate of the modified resin was measured, it was confirmed that 80 to 90% of the supplied maleic anhydride was grafted as shown in Table 1. This maleic anhydride graft-modified copolymer and maleic anhydride graft-modified low-density polyethylene conventionally used for adhesives were molded into a 0.1 mm thick film by inflation molding.
0.1mm of EVOH (EVAL EP-F manufactured by Kuraray Co., Ltd.)
This maleic anhydride graft-modified resin film was sandwiched between thick films and adhered from both sides by heat sealing. When the adhesive strength between the two resins was measured using a peel method, the maleic anhydride-grafted modified ethylene-methacrylic acid copolymer showed good adhesion, similar to the conventionally used maleic anhydride-grafted modified low-density polyethylene. . The results are shown in Table 1. Comparative Example 1 The thermal adhesion between the ethylene-methacrylic acid copolymer used in Example 1 and the ionomer resin containing them as a base polymer and EVOH was measured in the same manner as in Example 1. Adhesion was poor in all cases. The results are shown in Table 1. Comparative Example 2 An ionomer was synthesized by ionizing the maleic anhydride-modified ethylene-methacrylic acid copolymer used in Example 1 to 20% with Zn ⁺⁺ ions. of this
The thermal adhesion with EVOH was measured in the same manner as in Example 1. Adhesion was poor. The results are shown in Table 1.

[Table] Example 2 Comparative Example 3 The maleic anhydride grafted modified ethylene-methacrylic acid copolymer listed in Table 2 and the unmodified ethylene-methacrylic acid copolymer as a comparative example were used as the inner layer, and EVOH (Kuraray Co., Ltd.) Eval EP-F) manufactured by Eval EP-F) was supplied to each of the two extruders so as to form the outer layer, and melt-extruded at the same time. Both of these resins were adhered within the die using a two-layer die, and a two-layer inflation film was formed by a known air cooling method. The temperature of each resin in the die was set to 200°C, and the thickness of the coextruded film was set to 25 μm for the outer layer and 55 μm for the inner layer. The interlayer adhesive strength of the obtained film and the heat seal strength using a layer of a maleic anhydride grafted modified ethylene-methacrylic acid copolymer or an unmodified ethylene-methacrylic acid copolymer as a heat seal layer were measured. The maleic anhydride graft-modified product showed higher values for both interlayer adhesion and heat seal strength than the unmodified product. The results are shown in Table 2.

[Table] Example 3 Comparative Example 4 Reference Example 2 EVOH, a maleic anhydride graft modified ethylene-methacrylic acid copolymer, and a maleic anhydride graft modified low density polyethylene as a comparative example were coextruded in the same manner as in Example 2. A two-layer laminate was obtained by molding. In addition, as a reference example, a three-layer coextruded film was molded having an intermediate adhesive layer of maleic anhydride graft-modified low-density polyethylene, an inner layer of ionomer, and an outer layer of EVOH. When the heat seal strength and hot sealability of each laminated film were measured, it was found that when the maleic anhydride graft modified ethylene-methacrylic acid copolymer was used, the heat seal was as good as when the ionomer of the reference example was used. Although it showed strength and hot sealability,
Laminated films with maleic anhydride-grafted modified low-density polyethylene as the heat-sealing layer were poor in both heat-sealing strength and hot-sealability.
The results are shown in Table 3.

[Table] Reference Example 3 Maleic anhydride graft modified ethylene-methacrylic acid copolymer, the same ethylene-methacrylic acid-isobutyl acrylate copolymer, the same low-density polyethylene and unmodified ethylene-methacrylic acid copolymer, ionomer resin Sachets were made from blown film each having a thickness of 30 μm and filled with lard. This lard-filled sachet was left at room temperature, and the oil resistance was measured by measuring the time it took for the lard contents to seep through the bag and onto the surface. Maleic anhydride-modified ethylene-methacrylic acid copolymer, ethylene-methacrylic acid-isobutyl acrylate copolymer, and ionomer resin did not cause oil leaching, but unmodified ethylene-methacrylic acid copolymer and maleic anhydride Oil seepage was observed in acid-graft modified low-density polyethylene.
The results are shown in Table 4.

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Claims (1)

[Claims] 1 (a) Ethylene content 10 to 75 mol%, saponification degree 90
(b) an ethylene-vinyl acetate copolymer saponified layer having an ethylene content of 50 to 99 mol% and an ethylenically unsaturated carboxylic acid content of 1.0 to 10 mol%;
A laminate comprising a maleic anhydride-grafted modified ethylene-ethylenically unsaturated carboxylic acid copolymer layer in which maleic anhydride is grafted onto an ethylenically unsaturated carboxylic acid copolymer in a proportion of 0.05 to 5.0% by weight. 2. In claim 1, the maleic anhydride graft-modified ethylene-ethylenically unsaturated carboxylic acid copolymer is a copolymer containing one or more of acrylic ester, methacrylic ester, and vinyl acetate as a copolymerization component. The laminate according to claim 1, which is a polymer. 3. The laminate according to claim 1, obtained by coextruding a saponified ethylene-vinyl acetate copolymer layer and a maleic anhydride graft-modified ethylene-ethylenically unsaturated carboxylic acid copolymer layer.