Multilayer film

Abstract

To provide a multilayer film which includes heat resistance, in which curl is suppressed and which has an asymmetric structure.SOLUTION: A multilayer film comprises a polyamide layer and a polyolefin layer and has an asymmetric structure. In the multilayer film, the polyamide layer comprises a polyamide resin composition, consisting of a crystalline nylon having a melting point of 205°C or higher and an amorphous nylon, as a main component, and a weight ratio of the crystalline nylon to the amorphous nylon (the crystalline nylon):(the amorphous nylon) is (51-99):(1-49), and the polyolefin layer contains a propylene homopolymer or a propylene block-copolymer as a main component.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for preventing curling in a multilayer film having an asymmetric structure. [Background technology]

[0002] In packaging and industrial applications, multilayer films with an asymmetric structure, in which the outer layer is made of a polyamide resin and the inner layer is made of a polyolefin resin, are used. It is known that such multilayer films are prone to curling due to their asymmetric structure. Various methods have been proposed to prevent curling, such as Patent Document 1.

[0003] Patent Document 1 describes a method for producing an asymmetric multilayer unstretched film by an air-cooled multilayer inflation method, in which the outermost layer is made of a polyamide resin, the innermost layer is made of a polyolefin-based resin, and an adhesive layer is provided between the two layers, and describes that curling can be prevented by using the polyamide resin as a. a crystalline copolyamide resin, or a combination of this with b. an amorphous polyamide resin or another crystalline copolyamide resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-175543 A Summary of the Invention [Problem to be solved by the invention]

[0005] Meanwhile, the above-mentioned polyamide resin / polyolefin resin multilayer film is often used for lamination in press molding. In press molding, a heating step of about 200 to 210°C is performed, and the multilayer film is required to have heat resistance. The multilayer film of Patent Document 1 could not withstand the heat molding in the above-mentioned heating step, and had insufficient heat resistance.

[0006] Therefore, an object of the present invention is to provide a multilayer film having an asymmetric structure that is heat resistant and suppressed from curling. [Means for solving the problem]

[0007] In response to the above problem, the present inventors have investigated whether it is possible to impart heat resistance to a polyamide resin / polyolefin resin multilayer film by using nylon having a melting point of 205° C. or higher as the polyamide resin, but in this case, it is difficult to suppress curling. As a result of extensive investigation, the present inventors have arrived at the present invention.

[0008] That is, as a means for solving the above problems of the present invention, (1) A multilayer film having a polyamide layer and a polyolefin layer and having an asymmetric structure, wherein the polyamide layer is mainly composed of a polyamide resin composition composed of a crystalline nylon having a melting point of 205°C or more and an amorphous nylon, and the weight ratio of the crystalline nylon to the amorphous nylon is crystalline nylon:amorphous nylon=51-99:1-49, and the polyolefin layer is mainly composed of a propylene homopolymer or a propylene block copolymer; (2) The multilayer film according to (1), wherein the crystalline nylon is nylon 6; (3) The multilayer film according to (1) or (2), which is a coextruded film; (4) The multilayer film according to any one of (1) to (3), characterized in that the weight ratio of the polyamide resin composition is crystalline nylon: amorphous nylon=80-95:5-20; (5) A multilayer film according to any one of (1) to (4), characterized in that it comprises two layers, a polyamide layer and a polyolefin layer; (6) The multilayer film according to any one of (1) to (4), which comprises three layers of the polyamide layer / the adhesive resin layer / the polyolefin layer, and the adhesive resin layer contains a polypropylene-based acid-modified adhesive resin; (7) The multilayer film according to any one of (1) to (6), characterized in that the multilayer film has a thickness of 70 μm or less; The gist of this paper is as follows. Effect of the Invention

[0009] According to the present invention, in an asymmetric multilayer film, since the outer layer has a polyamide layer mainly composed of crystalline nylon having a melting point of 205°C or more, the multilayer film has heat resistance, and since the inner layer has a polyolefin layer, the multilayer film can be heat-sealed to itself or to other members. Furthermore, since the polyamide layer mainly contains a polyamide resin composition having a crystalline nylon: amorphous nylon ratio of 51-99:1-49, and the polyolefin layer mainly contains a propylene homopolymer or a propylene block copolymer, a multilayer film with reduced curl can be obtained. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic top view showing a cut portion in the method for measuring curl of a multilayer film according to the present invention. [Diagram 2] FIG. 2 is an explanatory diagram showing an evaluation method in the curl measurement method for the multilayer film according to the present invention. [Diagram 3] FIG. 2 is a schematic diagram showing a curl state in the method for measuring curl of a multilayer film according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail. The multilayer film according to the present invention is an asymmetric multilayer film having a polyamide layer and a polyolefin layer, wherein the polyamide layer is mainly composed of a polyamide resin composition consisting of crystalline nylon and amorphous nylon having a melting point of 205°C or higher, and the weight ratio of the crystalline nylon to the amorphous nylon is crystalline nylon:amorphous nylon=51-99:1-49, and the polyolefin layer contains a propylene homopolymer or a propylene block copolymer as a main component. The term "multilayer film having an asymmetrical structure" refers to a film having an asymmetrical laminated structure in which the resin components used in the outer layer and the inner layer of the laminated film are different.

[0012] The multilayer film according to the present invention may be any multilayer film having a polyamide layer and a polyolefin layer and having an asymmetric structure in the thickness direction, for example, a film having a two-layer structure of polyamide layer / polyolefin layer, or a film having a three-layer structure of polyamide layer / intermediate layer / polyolefin layer, in which the outermost layer is a polyamide layer and the innermost layer is a polyolefin layer. A film structure of three or more layers may also be used. Examples of film configurations with three or more layers include polyamide layer / intermediate layer 1 / intermediate layer 2 / polyolefin layer, outermost layer / polyamide layer / intermediate layer / polyolefin layer, polyamide layer / intermediate layer / polyolefin layer / innermost layer, and outermost layer / polyamide layer / intermediate layer / polyolefin layer / innermost layer.

[0013] The multilayer film according to the present invention is preferably a coextruded film produced by a coextrusion method. Examples of the coextruded film include a coextruded inflation film produced by an inflation method and a coextruded cast film produced by a casting method using a T-shaped die. Examples of the coextruded inflation film include a coextruded air-cooled inflation film produced by an air-cooled inflation method and a coextruded water-cooled inflation film produced by a water-cooled inflation method, and among these, a coextruded air-cooled inflation film is preferred. Incidentally, an unstretched multi-layer film obtained by the inflation method or the cast method can be made into a stretched film by tubular stretching or tenter stretching.

[0014] The multilayer film according to the present invention has a polyamide layer on the outer layer side. The polyamide layer contains crystalline nylon in a polyamide resin composition as a main component. Since the polyamide layer contains crystalline nylon having a melting point of 205°C or more as a main component, the multilayer film has heat resistance when used for press processing, etc., and can be used without melting during processing. The proportion of the polyamide resin composition in the polyamide layer is 50% by weight or more of the entire layer, preferably 80% by weight or more, more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

[0015] The polyamide resin composition in the polyamide layer in the present invention contains crystalline nylon: amorphous nylon in a weight ratio of 51-99:1-49. When the polyamide resin composition contains amorphous nylon in a ratio (weight ratio) of 1 to 49, curling can be suppressed when a multilayer film having an asymmetric structure including a polyamide layer and a polyolefin layer is produced. The weight ratio of crystalline nylon to amorphous nylon is preferably crystalline nylon:amorphous nylon=70-97:3-30, more preferably 80-95:5-20, and particularly preferably 85-93:7-15.

[0016] The melting point of the crystalline nylon is preferably 205° C. to 270° C., and particularly preferably 210° C. to 250° C. from the standpoints of both heat resistance and film formability. Examples of crystalline nylons having a melting point of 205° C. or higher include nylon 6 and nylon 66. From the viewpoints of heat resistance and film-forming properties, nylon 6 is particularly preferred.

[0017] Amorphous nylon means nylon that does not have a clear melting point, specifically, nylon having a crystalline melting enthalpy ΔHm of 5 J / g or less, preferably 3 J / g or less, more preferably 1 J / g or less. The crystalline melting enthalpy is obtained by differential scanning calorimetry (DSC) in accordance with JIS K7121 and JIS K7122.

[0018] As the amorphous nylon, an amorphous semi-aromatic nylon having two or more types of structural units derived from an aromatic dicarboxylic acid is preferred, and a nylon having, as the dicarboxylic acid component, a structural unit derived from isophthalic acid and a structural unit derived from terephthalic acid, and, as the diamine component, a structural unit derived from an aliphatic diamine is more preferred.

[0019] In the amorphous semi-aromatic nylon, the proportion of the constitutional units derived from isophthalic acid in 100 mol % of the constitutional units derived from dicarboxylic acid is preferably 40 mol % or more and 98 mol % or less, more preferably 50 mol % or more and 80 mol % or less, and the proportion of the constitutional units derived from terephthalic acid is preferably 2 mol % or more and 60 mol % or less, more preferably 20 mol % or more and 50 mol % or less. The above proportions can be measured by NMR.

[0020] In the amorphous semi-aromatic nylon, the total proportion of the constituent units derived from isophthalic acid and the constituent units derived from terephthalic acid in 100 mol% of the constituent units derived from dicarboxylic acids is preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, particularly preferably 90 mol% or more, 95 mol% or more, or 98 mol% or more. The amorphous semi-aromatic nylon may have constituent units derived from dicarboxylic acids other than isophthalic acid and terephthalic acid (e.g., adipic acid) as necessary.

[0021] The amorphous semi-aromatic nylon preferably has a structural unit derived from hexamethylenediamine as a diamine component. In the amorphous semi-aromatic nylon, the proportion of the structural units derived from hexamethylenediamine in 100 mol% of the structural units derived from diamine is preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, particularly preferably 90 mol% or more, 95 mol% or more, or 98 mol% or more. The amorphous semi-aromatic nylon may have a structural unit derived from a diamine other than hexamethylenediamine as necessary. The amorphous semi-aromatic nylon is preferably PA6I / 6T.

[0022] The glass transition temperature (Tg) of the amorphous semi-aromatic nylon is, for example, 90° C. or more and 180° C. or less, preferably 95° C. or more and 160° C. or less, and more preferably 100° C. or more and 150° C. or less. Tg is measured by differential scanning calorimetry (DSC) in accordance with JIS K7121.

[0023] The polyamide layer may contain other resins as appropriate within the limits that do not affect the performance. The polyamide layer may contain one or more additives, such as crosslinking agents, antiblocking agents, slip agents, antioxidants, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, dyes, and modifying resins.

[0024] The multilayer film according to the present invention has, on the inner layer side, a polyolefin resin layer having a melting point lower than that of the crystalline nylon. By providing the polyolefin layer on the inner layer side, the multilayer film can be heat-sealed to itself or to another member.

[0025] In the present invention, the polyolefin layer contains a propylene homopolymer or a propylene block copolymer as a main component, and may be a blend of a propylene homopolymer and a propylene block copolymer. A propylene homopolymer is a polymer consisting of only propylene. A propylene block copolymer is a copolymer having a polymer block consisting of propylene and a polymer block consisting of an ethylenically unsaturated monomer other than propylene (e.g., an α-olefin such as ethylene, 1-butene, or 4-methyl-1-pentene). In the present invention, by using a propylene homopolymer or a propylene block copolymer as the main component of the polyolefin layer, curling of the multilayer film having a polyamide layer and a polyolefin layer and an asymmetric structure in the thickness direction can be suppressed. Among these, the use of a propylene block copolymer in particular can further reduce curling of the multilayer film.

[0026] From the viewpoint of film-forming property and processability, the MFR of the propylene homopolymer or propylene block copolymer is preferably 0.1 g / 10 min to 50 g / 10 min, more preferably 0.3 g / 10 min to 30 g / 10 min. The MFR of polypropylene is measured at a temperature of 230° C. and a load of 2.16 kg in accordance with ASTM D1238.

[0027] The polyolefin layer may contain a resin other than the propylene homopolymer and the propylene block copolymer as appropriate, provided that the resin does not affect the performance. The total amount of the propylene homopolymer and the propylene block copolymer in the polyolefin layer is 50% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, and particularly preferably 95% by weight or more of the entire layer. The polyolefin layer may contain one or more additives, such as crosslinkers, antiblocking agents, slip agents, antioxidants, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, dyes, and modifying resins.

[0028] The multilayer film according to the present invention may have an intermediate layer between the polyamide layer and the polyolefin layer. The intermediate layer is preferably an adhesive resin layer containing an adhesive resin capable of improving the adhesion between the polyamide layer and the polyolefin layer. Examples of the adhesive resin include polyolefin and modified polyolefin. Examples of the modified polyolefin include modified polyolefins, particularly acid modified polyolefins. Examples of the modified polyolefin include graft modified polyolefins with unsaturated carboxylic acids such as maleic acid and fumaric acid, or their acid anhydrides, esters, or metal salts. Among these, modified polypropylene is particularly preferred.

[0029] From the viewpoint of film-forming property and processability, the melt flow rate (MFR) of the modified polyolefin is preferably 0.1 g / 10 min to 50 g / 10 min, more preferably 0.3 g / 10 min to 30 g / 10 min, further preferably 0.5 g / 10 min to 10 g / 10 min, and particularly preferably 0.5 g / 10 min to 5.0 g / 10 min. The adhesive resin layer can contain one or more adhesive resins.

[0030] The multilayer film according to the present invention may have another layer on the outer layer side of the polyamide layer, for example, a coating layer that imparts heat resistance, or a resin layer made of heat-resistant polyethylene terephthalate.

[0031] Furthermore, the multi-layer film according to the present invention may have another layer provided on the inner layer side of the polyolefin layer, for example, a resin layer made of polyethylene having a lower melting point than polypropylene resin.

[0032] The total thickness of the multilayer film according to the present invention is preferably 5 to 100 μm, 10 to 80 μm, 20 to 70 μm, or 30 to 50 μm. The thickness of the polyamide layer is preferably 1 to 50 μm, 3 to 40 μm, 5 to 30 μm, or 10 to 20 μm. The thickness of the polyolefin layer is preferably 1 to 50 μm, 3 to 40 μm, 5 to 30 μm, or 10 to 20 μm. The thickness of the adhesive resin layer is preferably 1 to 50 μm, 3 to 40 μm, 5 to 30 μm, or 10 to 20 μm. In addition, the thickness ratio between the polyamide layer and the polyolefin layer in the multilayer film according to the present invention is preferably polyamide layer:polyolefin layer=1:2 to 2:1.

[0033] The multilayer film according to the present invention preferably has a curl of 180° or less in at least the direction perpendicular to the flow direction of the multilayer film (TD direction) as measured by the curl measurement method described in the Examples. Suppression of curl in the TD direction of the multilayer film allows stable processing when processing is performed by a roll-to-roll method. Furthermore, it is particularly preferred that the curl in both the machine direction (MD) and TD of the multilayer film is 180° or less, as measured by the curl measurement method described in the Examples. EXAMPLES

[0034] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples as long as they do not depart from the gist of the invention. In the following examples and comparative examples, curl measurement and heat resistance evaluation were carried out as follows.

[0035] <Curl measurement method> As shown in Figure 1, the multilayer film was placed with the polyolefin layer side up, and two diagonal cuts were made in a 100 mm square along the MD of the multilayer film. The multilayer film was left for 1 hour in an environment with a temperature of 23°C and a humidity of 50%, and then the curl of test pieces (a) and (b) facing each other in the MD and test pieces (c) and (d) facing each other in the TD shown in Figure 1 was measured. The curl was measured by distinguishing between cases where the curl of the test piece was within 180° (see Figure 2) and cases where the curl of the test piece exceeded 180° (i.e., the apex of the test piece was curled more than halfway around, see Figure 3), and when the curl of the test piece was within 180°, the apex angle α was measured using a protractor as shown in Figure 2. The evaluation criteria were as follows: (Evaluation Criteria) ◎: Both test pieces facing each other in the MD or TD direction have a curl angle of 40° or less ○: Both of the test pieces facing each other in the MD or TD direction have a curl angle of 180° or less. At least one of the test pieces facing each other in the MD or TD direction has a curl angle of more than 40° and less than 180°. △: At least one of the test pieces facing each other in the MD or TD direction has a curl angle of more than 180°, and the other has a curl angle of 180° or less ×: Both test pieces facing each other in the MD or TD direction have a curl angle of more than 180°

[0036] <Heat resistance evaluation> The obtained multilayer film and a PET-based nonwoven fabric were laminated and heated at 200° C. for 1 minute, and then molded in a cold press. The evaluation criteria were as follows. (Evaluation Criteria) ○: The mold could be formed without any resin adhering to the mold of the cold press. ×: Resin was attached to the die of the cold press machine.

[0037] [Example 1] A polyamide resin composition obtained by mixing 90% by weight of 6 nylon shown in Table 1 and 10% by weight of amorphous nylon shown in Table 1 for the polyamide layer, an adhesive resin composition obtained by mixing 50% by weight of a propylene block copolymer shown in Table 1 and 50% by weight of a polypropylene-based acid-modified adhesive resin shown in Table 1 for the adhesive resin layer, and 100% by weight of a propylene block copolymer shown in Table 1 for the polyolefin layer were co-extruded and air-cooled inflation molded at a circular die temperature of 230°C to 250°C to obtain a multilayer film. The thickness configuration of the obtained multilayer film was polyamide layer / adhesive resin layer / polyolefin layer=20μm / 10μm / 10m. The curl and heat resistance of the resulting multilayer film were evaluated, and the results are shown in Table 2.

[0038] [Example 2] Except for using 95% by weight of nylon 6 and 5% by weight of amorphous nylon in the polyamide layer, a multilayer film was obtained in the same manner as in Example 1. The curl measurement evaluation and heat resistance evaluation results of the obtained multilayer film are shown in Table 2.

[0039] [Example 3] A multilayer film was obtained in the same manner as in Example 1, except that the adhesive resin layer was made of 50% by weight of a propylene homopolymer shown in Table 1 and 50% by weight of a polypropylene-based acid-modified adhesive resin shown in Table 1, and the resin in the polyolefin layer was 100% by weight of a propylene homopolymer shown in Table 1. The results of curl measurement and heat resistance evaluation of the obtained multilayer film are shown in Table 2.

[0040] [Comparative Example 1] A multilayer film was obtained in the same manner as in Example 1, except that the adhesive resin layer was made of 50% by weight of a propylene random copolymer shown in Table 1 and 50% by weight of a polypropylene-based acid-modified adhesive resin shown in Table 1, and the resin in the polyolefin layer was 100% by weight of a propylene random copolymer shown in Table 1. The curl measurement evaluation and heat resistance evaluation results of the obtained multilayer film are shown in Table 2.

[0041] [Comparative Example 2] A polyamide resin composition containing 90% by weight of 6 / 6,6 copolymer nylon (melting point: 195°C) shown in Table 1 and 10% by weight of amorphous nylon shown in Table 1 was used for the polyamide layer, an adhesive resin composition containing 50% by weight of linear low-density polyethylene shown in Table 1 and 50% by weight of a polyethylene-based acid-modified adhesive resin shown in Table 1 was used for the adhesive resin layer, and 100% by weight of linear low-density polyethylene shown in Table 1 was used for the polyolefin layer, and a multilayer film was obtained in the same manner as in Example 1. The results of curl measurement evaluation and heat resistance evaluation of the obtained multilayer film are shown in Table 2.

[0042] [Comparative Example 3] A multilayer film was obtained in the same manner as in Comparative Example 2, except that the polyamide layer was made of 90% by weight of 6 nylon and 10% by weight of amorphous nylon shown in Table 1. The results of curl measurement and heat resistance evaluation of the obtained multilayer film are shown in Table 2.

[0043] [Comparative Example 4] A multilayer film was obtained in the same manner as in Comparative Example 3, except that the adhesive resin layer was made of 50% by weight of low-density polyethylene shown in Table 1 and 50% by weight of a polyethylene-based acid-modified adhesive resin shown in Table 1, and the resin in the polyolefin layer was made of 100% by weight of low-density polyethylene shown in Table 1. The results of curl measurement and heat resistance evaluation of the obtained multilayer film are shown in Table 2.

[0044] [Comparative Example 5] A multilayer film was obtained in the same manner as in Comparative Example 3, except that the adhesive resin layer was made of 50% by weight of high-density polyethylene shown in Table 1 and 50% by weight of a polyethylene-based acid-modified adhesive resin shown in Table 1, and the resin in the polyolefin layer was made of 100% by weight of high-density polyethylene shown in Table 1. The results of curl measurement and heat resistance evaluation of the obtained multilayer film are shown in Table 2.

[0045] [Table 1]

[0046] [Table 2]

[0047] As shown in Comparative Example 2 in Table 2, a multilayer film using copolymer nylon, which is a crystalline nylon having a melting point of less than 205°C, and amorphous nylon as the polyamide layer and linear low-density polyethylene as the polyolefin layer was not only poor in heat resistance but also poor in curl measurement evaluation. Also, as shown in Comparative Examples 3 to 5, the heat resistance evaluation was good when nylon 6 and amorphous nylon, which have a melting point of 205°C or more, were used as the polyamide layer, but the curl measurement evaluation was poor in all cases when polyethylene resin (linear low-density polyethylene, low-density polyethylene, high-density polyethylene) was used as the polyolefin layer. Furthermore, as seen from Comparative Example 1, when nylon 6 and amorphous nylon were used as the polyamide layer and a propylene random copolymer was used as the polyolefin layer, the curl measurement evaluation was also poor.

[0048] On the other hand, in Examples 1 to 3, when nylon 6 and amorphous nylon were used as the polyamide layer and a propylene homopolymer or a propylene block copolymer was used as the polyolefin layer, the heat resistance was excellent and the curl measurement evaluation was also favorable. Furthermore, when the data of Example 1 and Example 3 are compared, when a propylene block copolymer was used as the polyolefin layer, the curl measurement evaluation was particularly excellent. Furthermore, when the data of Example 1 and Example 2 are compared, a weight ratio of 90:10 between nylon 6 and amorphous nylon in the polyamide layer was more effective in reducing curling than a weight ratio of 95:5. [Explanation of symbols]

[0049] 10 Multilayer film

Claims

1. A multilayer film having a polyamide layer and a polyolefin layer, the multilayer film having an asymmetric configuration, The polyamide layer is mainly composed of a polyamide resin composition composed of crystalline nylon and amorphous nylon having a melting point of 205° C. or more, and the weight ratio of the crystalline nylon to the amorphous nylon is crystalline nylon:amorphous nylon=51 to 99:1 to 49. The multilayer film is characterized in that the polyolefin layer contains a propylene homopolymer or a propylene block copolymer as a main component.

2. 2. The multilayer film of claim 1, wherein the crystalline nylon is nylon 6.

3. 3. The multilayer film according to claim 1, which is a coextruded film.

4. 3. The multilayer film according to claim 1, wherein the weight ratio of said polyamide resin composition is said crystalline nylon: said amorphous nylon=80-95:5-20.

5. 3. The multilayer film according to claim 1, which comprises two layers, a polyamide layer and a polyolefin layer.

6. 3. The multilayer film according to claim 1, which comprises three layers: the polyamide layer / the adhesive resin layer / the polyolefin layer, and the adhesive resin layer contains a polypropylene-based acid-modified adhesive resin.

7. 3. The multilayer film according to claim 1, wherein the multilayer film has a thickness of 70 μm or less.

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