JP6270384B2 - Curl-free multilayer film - Google Patents

Description

  The present invention relates to a multilayer film that does not curl to the extent that it becomes a practical impediment, and a method for producing the same. Specifically, the present invention relates to a curl-free multilayer film having a core layer (B), an outer skin layer (E), and an inner skin layer (F) having specific structures and obtained by an extrusion water-cooled inflation method.

  When producing a multilayer film by the coextrusion water cooling inflation method, a highly hygroscopic resin layer made of layers of different resins, for example, a saponified product of nylon or ethylene-vinyl acetate copolymer (abbreviated as “EVOH”), and a polyolefin When a low hygroscopic resin layer such as the above is laminated, the obtained multilayer inflation film (hereinafter sometimes abbreviated as “multilayer inflation film”) is often curved (hereinafter abbreviated as “curl”). ).

  For example, a multi-layer tubular film (sometimes abbreviated as “film A”) composed of at least two layers of polyethylene (F) and polyethylene (E) and 6-nylon (E) is coextruded with water-cooled inflation. When manufactured by this method, curling occurs in a curved shape on the outside of the tubular film. This phenomenon is particularly remarkable at the open end (mouth) of the tubular body.

  In such a phenomenon, when the generated curl is larger than a certain degree, it becomes a significant hindrance in the bag making process using the co-extruded water-cooled inflation tube or the step of filling the bag with the encapsulated material, etc. The big problem of practical use still remains.

  In order to solve such a problem, the present applicant has proposed a curl-free multilayer film and a method for producing the same in Patent Document 1 (Japanese Patent No. 3227301).

Japanese Patent No. 3227301

  The multilayer film in Patent Document 1 certainly has no curling property. In recent years, multilayer films have been used for food preservation and the like, and in this case, it is desired to reduce curling properties at low temperatures.

  As a result of intensive studies to solve such problems in view of such technical demands, in order to reduce curling even under low temperature conditions, a limited polyamide is used as the outer skin layer, and the thickness is within a specific range. By limiting, it discovered that the said subject could be solved and came to complete this invention.

The configuration of the present invention is as follows.
[1] An endothelium layer (F), a core layer (B), and an outer skin layer (E) are laminated in this order, and are composed of at least three layers.
Highly hygroscopic nylon in which the core layer (B) is at least one selected from 6-nylon, 66-nylon, a mixture of 6-nylon and 66-nylon, and a cocondensate of 6-nylon and 66-nylon Consists of
The outer skin layer (E) is made of 610-nylon,
Endothelial layer (F) consists of a single polyolefin resin or two or more polyolefin resins,
When the thickness of the multilayer film is 100%, the thickness of the outer skin layer is 2% or more and 8% or less,
A curl-free multi-layer film produced by a coextrusion water-cooled inflation method.

[2] The polyolefin resin of the endothelial layer is
A polyethylene resin having a density of 0.88 to 0.97 g / cc, MI (190 ° C .; 2.16 kgf) of 0.1 to 30 g / 10 min and a melting point (Tm) of 90 to 138 ° C. A mixture of two or more, or
[1] non-curling multilayer film which is a polypropylene resin having a MFR (230 ° C .; 2.16 kgf) of 0.5 to 45 g / 10 min and a melting point (Tm) of 125 to 165 ° C. or a mixture of two or more of these resins. .

  According to the present invention, the outer layer is made of 610-nylon, and the thickness of the outer layer is in a specific range, so that the curl can be reduced even under low temperature conditions and the multilayer film has excellent oxygen barrier properties. Is obtained. The multilayer film obtained by co-extrusion water-cooled inflation molding with the above layer structure is rich in a high-class feeling having high gloss and high transparency, which are the advantages of nylon, despite being non-curl.

It is a sketch which shows a curvature radius typically. (ap) is a plan view showing the position, direction and length of the cut for generating the curl on the sample film, (bp) is a plan view of the state after the cut is made on the sample film, and (br) is (bp) ) Is a sketch of the state of FIG.

Hereinafter, the present invention will be described, but the present invention should not be construed as being limited thereto.
Curled Multilayer Film The curled multilayer film according to the present invention is formed by laminating an endothelial layer (F), a core layer (B), and an outer skin layer (E) in this order.

・ Core layer (B)
The core layer (B) is made of highly hygroscopic nylon.
(1) Highly hygroscopic nylon for the core layer (B) is 6-nylon, 66-nylon (6,6-nylon), a mixture of 6-nylon and 66-nylon, or 6-nylon and 66-nylon Highly hygroscopic nylon such as a cocondensate.
Here, “highly hygroscopic” means that the water absorption rate (according to ASTM D570) is 1% or more, preferably 1.4% or more.
These may be used alone or in combination of two or more.

・ Skin layer (E)
The outer skin layer is composed of 610-nylon. Commercially available 610-nylon can be used without particular limitation.

・ Endothelial layer (F)
Polyolefin Resin for Endothelial Layer (F) The polyolefin resin is a resinous material obtained by polymerizing (including copolymerization) one or more 1-olefins having about 2 to 10 carbon atoms. Polyethylene, which is the most frequently used polyolefin resin, includes not only ethylene homopolymers but also copolymers of ethylene and 1-olefins of propylene or more (3 or more carbon atoms). In general, in a polyethylene resin, the amount of comonomer contained is about 15 mol% or less.

  Polyethylene resins are also divided into high density, medium density and low density resins. Among these, the low-density polyethylene resin has a preferable property as a film that is excellent in heat sealability in addition to being most transparent and flexible. For the purposes of the present invention, low density polyethylene resin is most preferred. Of course, a high density polyethylene resin may be employed for special applications. In particular, it is more suitable than low density polyethylene resin for applications that are required to withstand high temperatures, high tension, and the like.

  As the polyethylene resin suitable for the present invention, MI (190 ° C .; 2.16 kgf) is usually 0.1 to 30 g / 10 min, preferably 1 to 5 g / min, and density is usually 0.91 to 0.965 g / cc, preferably 0. 0.92 to 0.95 g / cc and a melting point (Tm) of usually 90 to 138 ° C, preferably 100 to 130 ° C.

  Polypropylene resin is widely used for mold applications taking advantage of its higher melting point, higher transparency, higher rigidity, higher tensile strength, and the like than polyethylene, but is not used as much as polyethylene for film applications. The polypropylene resin used for the endothelial layer in the present invention is MFR (230 ° C .; 2.16 kgf) usually 0.5 to 45 g / 10 min, preferably 2 to 12 g / 10 min and melting point (Tm) usually 125 to 165 ° C., preferably 130. ~ 150 ° C. A wide variety of copolymers are also commercially available for polypropylene resins, and examples include propylene-ethylene copolymers and propylene-1-butene copolymers. An appropriate one can be selected from these according to the application.

-Adhesive layer For applications requiring strong interlayer adhesion to the highly hygroscopic nylon layer forming the core layer (B), an appropriate amount of an adhesive modified polyolefin resin is blended in the polyolefin resin, or An adhesive layer made of an adhesive polyolefin resin may be provided.

-Layer thickness The layer thickness (outer layer thickness + core layer thickness + endothelial layer thickness) of the curl-free multilayer film of the present invention is usually in the range of 50 to 110 μm, preferably 60 to 90 μm. The core layer thickness is usually in the range of 10 to 50 μm, preferably 15 to 30 μm, and the endothelial layer thickness is usually in the range of 30 to 80 μm, preferably 40 to 70 μm.

  In the present invention, the thickness of the outer skin layer is 2% or more and 8% or less of the total layer thickness. By forming a specific skin layer within this thickness range, a film having high oxygen barrier properties and less curling can be obtained.

  When an outer skin layer made of a specific material is provided as in the present invention, the curling property at a low temperature is improved. However, if the outer skin layer is too thick, the oxygen barrier property is lowered. On the other hand, when the outer skin layer is too thin, the curling property is not improved sufficiently, and the curling property is not improved particularly at low temperatures.

There is no restriction | limiting in particular in the number of the layers which comprise the multilayer film of this invention. In addition, the “skin layer (E)” which is an essential layer, the “skin layer (B)” and the core layer (B) which are located on the inner side and firmly adhere to the skin layer (E) and are protected from curling. There are no particular restrictions on the configuration or order of the other layers except for the point constituted by the hydrophobic endothelial layer (F) located on the inner side, the properties and order of each layer. Each constituent layer may be a mixture of two or more of the same type of resin, or may be formed of two or more layers.
The adhesion between the outer skin layer (E) and the core layer (B) is extremely strong and practically inseparable. The endothelium layer (F) exists in a state of being sufficiently strongly laminated on the inner side of the core layer (B).

-Definition of curl-freeness The term "curl-free" in this specification is not necessarily a complete curl-free state, that is, not only a state in which the radius of curvature of the test piece curl is infinite. The case where the curl stays at a level that does not become a hindrance in practice is also included in the “curl-free” of the present invention. Specifically, it is a comprehensive expression in the case where a value of at least 1.5 cm can be maintained as the radius of curvature (r) in the curl measurement method under the conditions used.

  Fig. 1 shows the measurement of the radius of curvature. FIG. 1 (br) is a view of the curled state as viewed from the direction (lateral direction) perpendicular to the long axis of the bag, and clearly shows that the two triangles 31 and 33 facing each other are curled. Can be seen. An arrow r from the center of the arc formed by both triangles to the arc represents the radius of curvature of the arc. When r is large, the degree of curling of the bag is low (slow), and when it is small, the degree of curling is high (violent).

When the curl is large, there are problems such as a significant hindrance during processing into a bag or in a process of filling an object to be encapsulated.
In the present invention, the presence or absence of curl at the bag mouth portion is greatly influenced by the direction parallel to the take-up direction (MD, that is, 31 and 33 in FIG. 1). For this reason, evaluation is performed using the measured radius of curvature in the MDs 31 and 33 in FIG.

  The curl-free multilayer film of the present invention is produced by a coextrusion water-cooled inflation molding method. Such a molding method is a method of coextrusion inflation molding the material constituting each of the above layers from, for example, a concentric annular die. In this case, a method of rapidly cooling the multilayer inflation tube through an aqueous cooling medium bath is called co-extrusion water cooling inflation. Here, the aqueous cooling medium is usually water (including hot water), but also includes those in which various additives are blended depending on the use of the product.

In the method for producing a curl-free multilayer film of the present invention,
Core layer (B) made of 6-nylon, 66-nylon, a mixture of 6-nylon and 66-nylon, and one or more highly hygroscopic nylon selected from 6-nylon and 66-nylon cocondensates Materials,
610-nylon outer layer (E) material,
An endothelium layer (F) material composed of a single polyolefin resin or two or more polyolefin resins,
The inner layer (F), the core layer (B), and the outer skin layer (E) are laminated in this order. When the thickness of the multilayer film is 100%, the outer skin layer thickness is 2% or more and 8% or less. Thus, co-extrusion is performed from a concentric annular die to form a multilayer tube. For applications that require strong interlayer adhesion to the highly hygroscopic nylon layer forming the core layer (B), an appropriate amount of an adhesive modified polyolefin resin is blended in the polyolefin resin, or an adhesive polyolefin It is also possible to adopt a form in which a resin adhesive layer is interposed. At the time of molding, the multilayer inflation tube is rapidly cooled by passing it through an aqueous cooling medium such as water. The rapid cooling treatment with a liquid refrigerant is beneficial for improving the dimensional accuracy and transparency of the multilayer film. The temperature of the liquid coolant is usually set to 10 to 60 ° C., and the passing linear velocity in the coolant is usually set to 5 to 80 m / min.

In addition, the compounding component, thickness, etc. of each layer are as having mentioned above.
Such a multilayer film according to the present invention is suitably used for industrial products such as electronic components, food packaging such as ham and sausage, and the like. In particular, since the end portion does not curl, there is no trouble in filling and packaging. Moreover, since it is excellent also in haze, transparency is also high and the visibility of the content is also excellent.

[Example]
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

Also, legends for resin abbreviations are as follows:
6-NY: 6-nylon [relative viscosity 3.6; degree of polymerization 250; molecular weight 28000; water absorption (ASTM D570) 1.3 to 3.5% (24 h)];
610-NY: 610-nylon [relative viscosity 2.7; degree of polymerization 160; molecular weight 18 × 10 ³ ; water absorption (ASTM D570) 0.3 to 1.5% (24 h)];
L-LDPE: linear low density polyethylene [MI (190 ° C; 2.16 kgf) 1.0 g / 10 min];

<Layer configuration, coextrusion inflation molding and quenching operations and conditions>
Endothelial layer (F): L-LDPE
・ Core layer (B): 6-nylon ・ Outer layer (E): 610-nylon (Example)
-Extrusion equipment: Co-extrusion water-cooled inflation equipment-Extrusion temperature: 210 ° C (L-LDPE),
Extrusion temperature: 250 ° C (6-NY), 250 ° C (610-NY),
-Swelling ratio: about 1;
Cooling water temperature (° C.): 10 to 60 (in the case of outer 610-NY / core 6-NY / inner L-LDPE);
-Passing linear velocity in cooling water bath (m / sec): 5-80 (same as above).

<Measurement and evaluation of curls>
As shown in FIG. 1, a square (5 cm on a side) having two sides of an original fabric take-up direction and a direction perpendicular thereto is drawn on a sample multilayer film, and cuts (× mark shape) are formed on both diagonal lines. Further, the radius of curvature (r) appearing at the curved portions of the four petal-like pieces is measured and obtained as an arithmetic average value thereof.

  The measurement is performed under conditions of a temperature of 25 ° C., a relative humidity of 60% and 5 ° C., and a relative humidity of 13%. Here, the smaller the numerical value of the “curl radius of curvature r (cm)”, the stronger the curl.

<Oxygen permeability>
Evaluation is performed using an oxygen permeability measuring machine (manufactured by MOCON) according to JIS K7126.

[Examples 1 and 2]
A combination of various resin types, layer thicknesses and layer configurations exemplified in Table 1 is selected to form the outer skin layer (E), the core layer (B) and the inner skin layer (F) with the above-mentioned molding equipment and molding conditions, respectively. Were made and evaluated.

[Comparative Examples 1 and 2]
A laminated film was prepared in the same manner as in Example 1 except that the outer skin layer and the core layer in the embodiment of Example 1 were changed as shown in Table 1.

上記表より、外皮層と芯層を所定の厚さとすることで、酸素透過度が低く、特に低温下での無カール性の高い積層フィルムが得られることが判明した。

From the above table, it was found that by setting the outer skin layer and the core layer to a predetermined thickness, it is possible to obtain a laminated film having a low oxygen permeability and a particularly high anti-curl property at a low temperature.

31 Parts separated by cuts provided in the sample film (upper side in the figure)
32 Parts separated by cuts provided in the sample film (left side of the figure)
33 Parts separated by cuts provided in the sample film (bottom side of the figure)
34 Parts separated by cuts in the sample film (right side of the figure)

Claims (2)

Endothelial layer (F), core layer (B), and outer skin layer (E) are composed of at least three layers laminated in this order,
Highly hygroscopic nylon in which the core layer (B) is at least one selected from 6-nylon, 66-nylon, a mixture of 6-nylon and 66-nylon, and a cocondensate of 6-nylon and 66-nylon Consists of
The outer skin layer (E) is made of 610-nylon,
Endothelial layer (F) consists of a single polyolefin resin or two or more polyolefin resins,
When the thickness of the multilayer film is 100%, the thickness of the outer skin layer is 2% or more and 4% or less,
A curl-free multi-layer film produced by a coextrusion water-cooled inflation method The polyolefin resin of the endothelium layer
A polyethylene resin having a density of 0.88 to 0.97 g / cc, MI (190 ° C .; 2.16 kgf) of 0.1 to 30 g / 10 min, and a melting point (Tm) of 90 to 138 ° C. A mixture of two or more, or
2. A polypropylene resin having a MFR (230 ° C .; 2.16 kgf) of 0.5 to 45 g / 10 min and a melting point (Tm) of 125 to 165 ° C., or a mixture of two or more of these resins. The curl-free multilayer film as described.

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