JPS629423B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a polyethylene composition layer and an ethylene composition layer.
The present invention relates to a multilayer laminate structure comprising a vinyl alcohol copolymer layer. Ethylene-vinyl alcohol copolymers with an ethylene content of 15 to 60% have excellent transparency and gas permeation resistance, high rigidity, and good heat resistance, making them suitable for packaging films and containers for foods, pharmaceuticals, etc. It has properties. However, ethylene-vinyl alcohol copolymers have the disadvantages of high moisture permeability, low impact strength, and poor heat-sealing properties, so they are often used in practical applications as laminated structures with polyolefins. . In such a laminated structure, the problem is how firmly the layers can be bonded together, and this is particularly important when the laminated structure is used after being boiled, such as in retort food packaging materials. One method for obtaining a laminated structure is coextrusion, but polyolefins and ethylene-vinyl alcohol copolymers have poor affinity and do not adhere to each other using normal coextrusion methods. As a method for adhering a laminated structure consisting of polyolefin and ethylene-vinyl alcohol copolymer by coextrusion method, for example, polyolefin and/or ethylene-vinyl alcohol copolymer are combined with an ionomer resin and an ethylene content of 60%. mol% or more of ethylene-vinyl acetate copolymer or its saponified product, chlorinated polyethylene,
A method of mixing chlorosulfonated polyethylene, ethylene-ethyl acrylate copolymer, etc. is known. (JP-A-49-4772, JP-A-49-
35482, Japanese Unexamined Patent Publication No. 49-37984, etc.) However, as a result of studies by the present inventors, the interlayer adhesion strength of the laminated structure obtained by the above method was found to be good at most.
g/cm, and delamination easily occurs due to decreased adhesion during long-term storage or boiling, so it could hardly be used as a packaging material for retort food. The present applicant discovered that polyethylene partially or wholly grafted with an unsaturated carboxylic acid or its derivative has good adhesion to ethylene-vinyl alcohol copolymer, and previously proposed (Japanese Unexamined Patent Publication No. 50-1999 No. 77485). Although this method is superior to the method using an ethylene polymer, the long-term adhesion and the adhesion when used under severe conditions, such as boiling water, are still insufficient. An object of the present invention is to provide a multilayer laminate structure comprising a polyethylene layer and an ethylene-vinyl alcohol copolymer layer, which has further improved interlayer adhesion and interlayer adhesion when immersed in boiling water. Another object of the present invention is to provide a multilayer laminated structure having excellent resistance to water vapor permeation and gas permeation, and high mechanical strength and rigidity. That is, the present invention provides crystallinity grafting which is partially or entirely grafted with at least one monomer selected from unsaturated carboxylic acids or derivatives thereof.
99 to 51 parts by weight of polyethylene of 65% or more, 1 to 49 parts by weight of an ethylene-α-olefin random copolymer having a crystallinity of 5 to 30% and an ethylene content of 85 to 95 mol% (100 parts by weight in total), and A multilayer laminate structure consisting of a polyethylene composition layer comprising up to 20 parts by weight of an ethylene-vinyl alcohol copolymer if necessary, and an ethylene-vinyl alcohol copolymer layer having an ethylene content of 15 to 60 mol%. It is. The ethylene-vinyl alcohol copolymer layer used in the present invention is a polymer with a degree of saponification of 90 to 100% obtained by saponifying an ethylene-vinyl acetate copolymer with an ethylene content of 15 to 60 mol%. . Ethylene-vinyl alcohol copolymers with an ethylene content of less than 15 mol % are difficult to mold because the moldable temperature approaches the decomposition temperature. Ethylene content
When it exceeds 60 mol%, gas permeation resistance, which is an excellent property of ethylene-vinyl alcohol copolymer,
The mechanical properties are poor and the effect of forming a laminated structure is lost. Ethylene-vinyl alcohol copolymers with a degree of saponification of less than 90% are unfavorable in practical terms because of their poor mechanical properties, oil resistance, and water resistance. The ethylene-vinyl alcohol copolymer used in the present invention may further include other polymers such as nylon, polyester,
Polyolefin, polycarbonate, ionomer resin, polyvinyl acetate, polystyrene, ABS
It may be a mixture of resins, acrylic resins, vinyl chloride resins, etc., or it may be modified with epoxy compounds, isocyanate compounds, etc. Furthermore, the ethylene-vinyl alcohol copolymer contains additives such as antioxidants, ultraviolet absorbers, antistatic agents, pigments, dyes, nucleating agents, fillers, slip agents, lubricants, flame retardants, plasticizers, etc. may be included to the extent that it does not defeat the purpose of the Polyethylene with a crystallinity of 65% or more, which is a raw material for the modified polyethylene used in the present invention, is a homopolymer of ethylene or ethylene and other α-olefins such as propylene, 1-butene, 3-methyl-1-butene, -methyl-1-butene, 1-
A copolymer with hexene, 4-methyl-1-pentene, etc. with a crystallinity of 65% or more, preferably 70% or more. In addition, the crystallinity degree in the present invention is
This refers to the value measured by X-ray diffraction on a sample prepared under ASTM D-618 conditions. In the present invention, polyethylene with a degree of crystallinity of 65% or more is partially or completely graft-modified. Derivatives are used. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. Derivatives of unsaturated carboxylic acids include acid anhydrides, esters, amides, imides, metal salts, etc., such as maleic anhydride, citraconic anhydride, itaconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate,
Ethyl methacrylate, butyl acrylate, butyl methacrylate, glycidyl acrylate, glycidyl methacrylate, monoethyl maleate, diethyl maleate, monomethyl fumarate, dimethyl fumarate, monomethyl itaconate, diethyl itaconate , acrylamide, methacrylamide, maleic acid monoamide, maleic acid diamide, maleic acid-N-monoethylamide, maleic acid-N・N-diethylamide, maleic acid-N
-monobutylamide, maleic acid-N/N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monoethylamide, fumaric acid-N/N-diethylamide, fumaric acid-N-monobutylamide, Fumaric acid-N・N-dibutylamide, maleimide, N-butylmaleimide, N-
Examples include phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, and the like. Among these graft monomers, maleic anhydride is most preferably used. Various known methods can be used to graft the graft monomer onto polyethylene. This is carried out, for example, by heating polyethylene, a grafting monomer, at high temperatures in the presence or absence of a solvent, with or without the addition of a radical initiator. Other vinyl monomers such as styrene may be present during the reaction. The amount of graft monomer grafted onto polyethylene (hereinafter referred to as grafting ratio) is preferably adjusted so that the grafting ratio of the entire composition is in the range of 10 ^-4 to 5% by weight. From an industrial manufacturing point of view, modified polyethylene with a graft ratio of 10 ^-2 to 10% by weight is produced in advance, and then this modified polyethylene is mixed with unmodified polyethylene to appropriately adjust the concentration of the graft monomer in the composition. Although this is a preferred method because it can be adjusted, a predetermined amount of graft monomer may be added to polyethylene from the beginning for grafting. In the present invention, the ethylene-α-olefin random copolymer blended into polyethylene with a crystallinity of 65% or more refers to a copolymer with a crystallinity of 5 to 30% and an ethylene content of 85 to 95 mol%, such as ethylene. and propylene, 1-butene, 3-methyl-
It refers to a copolymer with one or more α-olefins such as 1-butene, 1-hexene, 3-methyl-1-pentene, and 4-methyl-1-pentene. These polymers may be subjected to various modifications such as oxidation, chlorination, chlorosulfonation, or grafting with an epoxy compound or a carboxyl group-containing compound. Among these, when an ethylene-1-butene random copolymer with an ethylene content of 85 to 95 mol% and a crystallinity of 5 to 30% is used, it is possible to improve the transparency, impact resistance, adhesion, and boiling water resistance of modified polyethylene. This is most preferred because it improves both adhesive properties. The ethylene-α-olefin random copolymer has a melt index (ASTM-D-1238, 190
°C) is preferably in the range of 0.1 to 50. The present invention is based on (a) a polyethylene with a crystallinity of 65% or more, which is partially or entirely grafted with at least one monomer selected from unsaturated carboxylic acids or derivatives thereof, and (b) an ethylene-α-olefin random copolymer. Crystallinity level is 65 by adding coalescence.
It has been found that the adhesion of modified polyethylene to ethylene-vinyl alcohol copolymer is improved by more than 10%, and such an effect has not been previously known. That is, first, polyethylene with a crystallinity of 65% or more must be modified as described in (a) above, and unmodified polyethylene with a crystallinity of 65% or more must be modified with a polymer as described in (b) above. Even when mixed, it does not adhere at all. Furthermore, even the modified polyethylene alone as in (a) above does not have sufficient adhesion to the ethylene-vinyl alcohol copolymer, as shown in Comparative Example 4 below. As shown in Comparative Examples 14 to 16, unmodified high-pressure polyethylene, ethylene-vinyl acetate copolymers, etc. hardly adhere to ethylene-vinyl alcohol copolymers. Also, modified resins do not have sufficient adhesion. Ethylene polymers with a crystallinity of less than 64% are listed above.
By blending with modified polyethylene having a crystallinity of 65% or more as shown in (a), initial adhesion to ethylene-vinyl alcohol copolymer and boiling water resistant adhesion are improved in Comparative Examples 1 to 3 and Examples 1 to 3. and Comparative Example 8~
However, by using the ethylene-α-olefin random copolymer (b) with a crystallinity of 5 to 30% of the present invention, the crystallinity is significantly improved as shown in Figure 12.
As is clear from the comparison between Examples 1 to 3 and Comparative Examples 1 to 3 and Comparative Examples 8 to 12, it is clear that the initial adhesion and boiling water resistant adhesion are further improved compared to those with a concentration of more than 30%. be. The polyethylene composition used in the present invention comprises (a) 99 to 51 parts by weight, preferably 99 to 51 parts by weight of polyethylene with a crystallinity of 65% or more, which is partially or wholly grafted with an unsaturated carboxylic acid or a derivative thereof;
70 parts by weight, (b) 1 to 49 parts by weight of ethylene-α-olefin random copolymer, preferably 1 to 49 parts by weight
The main component is a composition consisting of 30 parts by weight (100 parts by weight in total). (b) If the amount of the ethylene-α-olefin random copolymer is less than 1% by weight, the effect of the blending will be insufficient, and if it exceeds 49% by weight, heat deformation resistance, rigidity, and mechanical strength will be impaired, and the retort It cannot be used for any purpose. Furthermore, the adhesive strength also decreases. The polyethylene composition used in the present invention may further contain up to 20% by weight of an ethylene-vinyl alcohol copolymer, if necessary. Polyethylene to which a partially or completely unsaturated carboxylic acid or its derivative is grafted has better miscibility with ethylene-vinyl alcohol copolymer than unmodified polyethylene; Even if they are mixed, there are almost no drawbacks caused by the mixture, such as a decrease in water vapor permeation resistance, a decrease in transparency, and delamination. The polyethylene composition may further contain antioxidants, ultraviolet absorbers, pigments, dyes, fillers, nucleating agents, and antiblocking agents within the range that does not impair the object of the present invention. Various known methods can be used to prepare the polyethylene composition used in the present invention.
For example, after mixing each component with a ribbon blender, V-type blender, tumbler, Henschel mixer, etc.,
A method of melting and kneading with a kneader or the like, or a method of dissolving each component in a solvent, stirring and mixing well, and then adding a poor solvent to precipitate the components can be used. As a method for manufacturing a laminated structure consisting of a polyethylene composition layer and an ethylene-vinyl alcohol copolymer layer of the present invention, (1) a method of manufacturing each film and sheet in advance and bonding them together by thermocompression; , (2) a method of extruding and laminating a molten polyethylene composition onto an ethylene-vinyl alcohol copolymer layer, and (3) a method of melting each in separate extruders and coextruding from the same die. . In methods (1), (2), and (3) above, the polyethylene resin temperature during molding is 140℃ to 300℃, especially 150℃.
A range of 0.degree. C. to 250.degree. C. is preferred. The resin temperature of the ethylene-vinyl alcohol copolymer in methods (1) and (3) is 170°C to 250°C, especially 180°C to 230°C.
A range of 0.degree. C. is preferred. The laminated structure comprising a polyethylene composition layer and an ethylene-vinyl copolymer of the present invention may have a two-layer structure with a polyethylene composition layer and an ethylene-vinyl alcohol copolymer layer as an inner layer or an outer layer. In the case of a three-layer structure in which one layer is an intermediate layer and another layer is sandwiched, or a polymer having adhesive properties with either a polyethylene composition or an ethylene-vinyl alcohol copolymer, for example, a polyethylene composition, the above structure is used. ,
Polypropylene, polyethylene, ethylene-α-
In the case of an ethylene-vinyl alcohol copolymer such as an olefin copolymer, a laminated structure in which layers of nylon, polyester resin, etc. are laminated, such as polyethylene/polyethylene composition defined in the present invention/ethylene-vinyl alcohol copolymer Union, three-layer structure of polyethylene composition/ethylene-vinyl alcohol copolymer/nylon, polyethylene/polyethylene composition/ethylene-vinyl alcohol copolymer/polyethylene composition, polyethylene/
In addition to those with a four-layer structure of polyethylene composition/ethylene-vinyl alcohol copolymer/nylon, five-layer structure of polyethylene/polyethylene composition/ethylene-vinyl alcohol copolymer/polyethylene composition/polyethylene, etc. Various combinations are possible within the laminated structure comprising the constituent elements of /ethylene-vinyl alcohol copolymer. In these laminated structures, any of the layers may be uniaxially or biaxially oriented. A laminated structure comprising a polyethylene composition layer and an ethylene-vinyl alcohol copolymer layer of the present invention can be put to practical use as a film, sheet, pipe, hollow bottle, etc. A laminated structure consisting of the polyethylene composition and ethylene-vinyl alcohol copolymer of the present invention,
The interlayer adhesion and the interlayer adhesion after boiling water treatment have been further improved, and the conventional problem of peeling of the laminate during use has been resolved. Therefore, by taking advantage of the high rigidity, mechanical strength, boiling water resistance, gas permeation resistance, water vapor permeation resistance, etc. of polyethylene/ethylene-vinyl alcohol copolymer laminates, vegetables,
It can be suitably used as packaging materials for meat and dairy products, packaging containers for seasonings, edible oils, pharmaceuticals, etc., and packaging materials for retort foods such as curry and stew. Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples as long as the gist thereof is not exceeded. Comparative Examples 1 to 5 High density polyethylene (melt index 12,
A modified polyethylene consisting of modified polyethylene (hereinafter abbreviated as modified PE) with 2.5% by weight of maleic anhydride (crystallinity 78%) grafted with high density polyethylene (melt index 1, crystallinity 76%, hereinafter abbreviated as HDPE). Component (hereinafter abbreviated as modified HDPE component) and high-pressure low density polyethylene (product name: Mirason M-50, manufactured by Mitsui Polychemicals, melt index 1.9, crystallinity 59%, hereinafter LDPE)
) were mixed in a tumbler blender according to the weight parts listed in Table 1, and then granulated at 210°C in an extruder.
Pellets of this composition are melted in one extruder,
The resin is supplied to a composite inflation molding die at a temperature of 210°C. Meanwhile, in another extruder, ethylene-vinyl alcohol copolymer (ethylene content 31 mol%,
Saponification degree of 99%) is melted and supplied to the die at a resin temperature of 210°C to form an inflation film (with a polyethylene composition layer) consisting of a polyethylene composition layer on the inside and an ethylene-vinyl alcohol copolymer layer on the outside. The thickness of the ethylene-vinyl alcohol layer was 70μ and the thickness of the ethylene-vinyl alcohol layer was 30μ. Width 15 from this film
After cutting a test piece of mm in diameter and partially peeling off the polyethylene composition layer and ethylene-vinyl alcohol copolymer layer, the peel strength of both layers was measured using an Instron measuring machine at a chuck speed of 100 mm/min. I asked for it. Further, a film taken out after being immersed in boiling water at 98° C. for 1 hour was also tested in the same manner. The measurement results are shown in Table 1.

[Table] Examples 1 to 3 Low density polyethylene was replaced with ethylene-1-butene random copolymer (ethylene content 90 mol%, melt index 1.0, crystallinity 15%, hereinafter abbreviated as EBC) and blending ratio Comparative Example 1 was carried out in the same manner as in Comparative Example 1, except that the composition was used in the parts by weight shown in Table 2. The results are shown in Table 2.

[Table] From Tables 1 and 2, it can be seen that modified HDPE components with a crystallinity of 65% or more have a crystallinity of 64% or less (LDPE of Comparative Examples 1 to 3 is 59%, EBC of Example 1 is 15%)
It is clear that when the olefin polymer of It can be seen that by blending the olefin polymer with a crystallinity of 30% or less, the initial adhesion and boiling water resistance are further improved compared to the olefin polymer with a crystallinity of 59%. Comparative Examples 6 and 7 Medium-density polyethylene (melt index 2.0, crystallinity 68%, hereinafter abbreviated as MDPE) was used instead of high-density polyethylene, which is one of the modified HDPE components, and the compounding ratio was as shown in Table 3. The same procedure as in Comparative Example 1 was conducted except that the weight parts shown were used. Comparative Examples 8 to 11 Ethylene-vinyl acetate copolymer (vinyl acetate content 8% by weight, melt index 1.7, crystallinity 43%, hereinafter abbreviated as EVA) was used instead of low-density polyethylene, and the blending ratio was The same procedure as in Comparative Example 1 was conducted except that the weight parts shown in Table 3 were used. The results are shown in Table 3.

[Table] Comparative Examples 12 to 14 The same procedure as Comparative Example 1 was conducted except that each of HDPE, LDPE, and EVA used in Comparative Examples 1 and 8 was used alone. The results are shown in Table 4.

【table】

Claims (1)

[Claims] 1 99 to 51 parts by weight of polyethylene with a crystallinity of 65% or more, partially or wholly grafted with at least one monomer selected from unsaturated carboxylic acids or derivatives thereof, crystallinity 5 to 30%;
Ethylene-α with an ethylene content of 85 to 95 mol%
- a polyethylene composition layer consisting of 1 to 49 parts by weight of an olefin random copolymer (100 parts by weight in total) and, if necessary, further up to 20 parts by weight of an ethylene-vinyl alcohol copolymer, with an ethylene content of 15 to 49 parts by weight; A multilayer laminated structure consisting of a 60 mol% ethylene-vinyl alcohol copolymer layer.