Multilayer film, and laminates and packaging bags using the same.

Abstract

The present invention provides a multilayer film having sufficient adhesion between layers and primarily composed of a biodegradable polyester resin, as well as laminates and packaging bags using the same. [Solution] The multilayer film (F) consists of a resin layer (A) / barrier layer (B) / resin layer (A), where the resin layer (A) is a layer containing a mixture of a biodegradable polyester resin and a carbodiimide-modified isocyanate, and the barrier layer (B) is a layer containing a modified polyvinyl alcohol resin having a butenediol structure.

Description

Technical Field

[0001] The present invention relates to a multilayer film, a laminate using the same, and a packaging bag.

Background Art

[0002] In recent years, as a countermeasure against environmental problems, multilayer films using biodegradable resins have been proposed. In Patent Document 1, a multilayer film composed only of a biodegradable resin is developed, which has layers made of a biodegradable resin such as polybutylene succinate on both surface layers and a barrier layer made of a modified polyvinyl alcohol resin having a 1,2-diol structure in the intermediate layer. In Patent Document 2, a multilayer resin sheet is developed, which has a base material layer made of a mixture of polylactic acid and polybutylene succinate, an adhesive layer made of a biodegradable resin-based adhesive such as a biodegradable acid-modified polyester resin, and an oxygen barrier layer made of a biodegradable oxygen barrier resin such as butanediol-modified polyvinyl alcohol resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Although the technology described in Patent Document 1 achieves a multilayer structure consisting solely of biodegradable resin, the adhesive strength between the polybutylene succinate layer and the modified polyvinyl alcohol resin layer is weak. As a result, delamination easily occurs when the film is bent or stored in a high-humidity environment, and sufficient barrier properties cannot be maintained. Delamination is particularly likely to occur in high-temperature and high-humidity environments. Furthermore, the thickness of the intermediate layer, which consists of modified polyvinyl alcohol resin, accounts for 20-80% of the total thickness, and a higher proportion of the intermediate layer thickness makes it prone to swelling. In addition, because modified polyvinyl alcohol resin is highly water-soluble, the barrier layer dissolves after swelling, and the barrier layer cannot be maintained. In the technology described in Patent Document 2, the maleic anhydride-modified polyester resin used as an adhesive is prone to a decrease in adhesive properties due to water absorption, and therefore is not suitable for use in high-humidity environments.

[0005] The present invention provides a multilayer film having sufficient adhesion between layers and mainly composed of a biodegradable polyester resin, as well as a laminate and packaging bag using the same. [Means for solving the problem]

[0006] The present invention includes the following embodiments. [1] A multilayer film comprising a resin layer (A) / barrier layer (B) / resin layer (A), wherein the resin layer (A) is a layer containing a mixture of a biodegradable polyester resin and a carbodiimide-modified isocyanate, and the barrier layer (B) is a layer containing a modified polyvinyl alcohol resin having a butenediol structure. [2] The multilayer film according to [1], characterized in that the thickness of the barrier layer (B) is 5 to 40% of the total thickness of the multilayer film consisting of a resin layer (A) / barrier layer (B) / resin layer (A), which is 100% of the total thickness of the multilayer film. [3] The multilayer film according to [1] or [2], characterized in that the resin layer (A) is composed of 96 to 99.9% by mass of the biodegradable polyester resin and 0.1 to 4% by mass of the carbodiimide-modified isocyanate, based on 100% by mass of the mixture. [4] A multilayer film according to any one of [1] to [3], characterized in that a resin layer (A) / barrier layer (B) / resin layer (A) is manufactured by co-extrusion. [5] A laminate characterized in that a biodegradable resin is laminated on at least one side of a multilayer film as described in any one of [1] to [4]. [6] A packaging bag formed using the laminate described in [5]. [Effects of the Invention]

[0007] Although polyester resins do not adhere to polyvinyl alcohol resins, the present invention makes it possible to laminate polyester resins and polyvinyl alcohol resins without providing an adhesive layer between them. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing an example of a multilayer film. [Figure 2] This is a cross-sectional view showing an example of a laminate. [Modes for carrying out the invention]

[0009] The present invention will be described below based on preferred embodiments.

[0010] Figure 1 shows an example of a multilayer film (F) according to this embodiment. The multilayer film (F) consists of a resin layer (A) / barrier layer (B) / resin layer (A). Here, the " / " between resin layer (A) and barrier layer (B) means that the multilayer film (F) is laminated without an adhesive layer between resin layer (A) and barrier layer (B).

[0011] The resin layer (A) consists of a layer containing a mixture of a biodegradable polyester resin and a carbodiimide-modified isocyanate. The barrier layer (B) consists of a layer containing a modified polyvinyl alcohol resin having a butenediol structure. This makes it possible to laminate a multilayer film (F) without providing an adhesive layer between the resin layer (A) containing the polyester resin and the barrier layer (B) containing the polyvinyl alcohol resin.

[0012] The resin layer (A) contains a biodegradable polyester resin as an essential resin component. Specific examples of biodegradable polyester resins include, for example, polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polyhydroxyalkanoate (PHA), and polybutylene adipate terephthalate (PBAT). From the viewpoint of moldability, it is preferable to use a thermoplastic biodegradable polyester resin having an appropriate melting point (Tm) and melt flow rate (MFR) as the raw material.

[0013] The resin layer (A) may use only one type of biodegradable polyester resin as its resin component, or it may use a blend of two or more different biodegradable polyester resins. When a blend of two or more is used, the following blending ratio is the sum of the two or more biodegradable polyester resins.

[0014] The blending ratio of biodegradable polyester resin in resin layer (A) is preferably 96 to 99.9% by mass, and more preferably 97 to 99% by mass. If the blending ratio of biodegradable polyester resin in resin layer (A) is less than 96% by mass, the crosslinking reaction may become excessive, making it impossible to form a film. A higher blending ratio of biodegradable polyester resin in resin layer (A) is advantageous for the biodegradability of the multilayer film (F) and is therefore preferable.

[0015] The resin layer (A) contains a carbodiimide-modified isocyanate as an essential crosslinking component. Specific examples of the carbodiimide-modified isocyanate include, for example, Carbodilite (registered trademark) of Nisshinbo Chemical, Millionate (registered trademark) MTL of Tosoh Corporation, and the like.

[0016] As the crosslinking component, the resin layer (A) may use only one kind of carbodiimide-modified isocyanate, or two or more different carbodiimide-modified isocyanates may be blended and used. When using a blend of two or more kinds, the following blending ratio is the total of two or more kinds of carbodiimide-modified isocyanates.

[0017] The blending ratio of the carbodiimide-modified isocyanate in the resin layer (A) is preferably 0.1 to 4% by mass, more preferably 1 to 3% by mass. When the blending ratio of the carbodiimide-modified isocyanate in the resin layer (A) is less than 0.1% by mass, there is almost no effect of imparting adhesiveness. When the blending ratio exceeds 4% by mass, the crosslinking reaction of the polyester-based resin may become excessive and there is a risk that film formation may not be possible. The blending ratio of the carbodiimide-modified isocyanate in the resin layer (A) may be added in an appropriate amount from the viewpoint of obtaining the effect of imparting adhesiveness by crosslinking. However, from the viewpoints of maintaining the biodegradability of the multilayer film (F) and facilitating film formation, it is preferable not to make the blending ratio excessive.

[0018] The barrier layer (B) contains a modified polyvinyl alcohol resin having a butanediol structure as an essential resin component. The barrier layer (B) has gas barrier properties, particularly oxygen gas barrier properties. The modified polyvinyl alcohol resin having a butanediol structure preferably has water solubility in addition to biodegradability. By dissolving the barrier layer (B) by water washing, separation from the resin layer (A) becomes possible and the recyclability is improved.

[0019] Specific examples of the modified polyvinyl alcohol resin having a butanediol structure include, for example, Nichigo G-Polymer (registered trademark) of Mitsubishi Chemical, and the like.

[0020] In a modified polyvinyl alcohol resin having a butenediol structure, the butenediol structure content is preferably 1 to 20 mol%, more preferably 2 to 18 mol%, and even more preferably 3 to 16 mol%. This improves melt moldability. It is preferable that the modified polyvinyl alcohol resin having a butenediol structure does not contain any modifications that could inhibit the biodegradability and water solubility of the barrier layer (B). From this viewpoint, it is preferable that the vinyl alcohol structure content in the modified polyvinyl alcohol resin is sufficiently high, for example, that the content of repeating structural units other than the 1,2-diol structure and vinyl alcohol structure is zero or minimal.

[0021] The preferred method for forming the multilayer film (F) molded article of this embodiment is to melt-extrude adjacent layers simultaneously using a co-extrusion method, thereby forming the film without a stretching process. The type of extruder used in the co-extrusion method is not particularly limited, but examples include T-die molding and inflation molding.

[0022] The mixture used for molding the resin layer (A) is a resin composition containing a biodegradable polyester resin and a carbodiimide-modified isocyanate. As described above, it is preferable that the biodegradable polyester resin accounts for 96 to 99.9% by mass and the carbodiimide-modified isocyanate accounts for 0.1 to 4% by mass per 100% by mass of the mixture. Alternatively, a masterbatch containing a high concentration of the carbodiimide-modified isocyanate compound may be prepared in advance, and the additive may be diluted during extrusion molding to form the resin layer (A). The resin composition for the resin layer (A) may optionally contain other resins or other additives, as long as the effect of the resin layer (A) is not impaired.

[0023] The resin used for molding the barrier layer (B) is a resin composition containing a modified polyvinyl alcohol resin having a butenediol structure. This resin composition may contain only one or more modified polyvinyl alcohol resins having a butenediol structure. The resin composition for the barrier layer (B) may optionally contain other resins or appropriate additives, as long as they do not impair the effect of the barrier layer (B).

[0024] It is even more effective to heat-treat the multilayer film (F) with a cooling roll after T-die molding. In the case of inflation molding, the multilayer film (F) may be air-cooled by blowing in cold air, etc.

[0025] The thickness ratio in the multilayer film (F) can be set as appropriate, but the thickness of the barrier layer (B) is preferably 5 to 40% of the total thickness of the multilayer film (F), and more preferably 10 to 35%. If the ratio of the barrier layer (B) thickness is higher than this upper limit (40%), the barrier layer will swell due to moisture absorption, causing delamination between the surface layer and the barrier layer, which may result in a decrease in barrier function or the introduction of wrinkles. If the ratio of the barrier layer (B) thickness is lower than the lower limit (5%), depending on the total thickness of the multilayer film (F) and the thickness of the barrier layer (B), it may not be possible to provide sufficient barrier function.

[0026] The multilayer film (F) of this embodiment may be used with each resin layer (A) serving as a surface layer, or it may be used with other resin layers laminated on at least one side. When other resin layers are laminated on both sides of the multilayer film (F), the same type of resin layer may be laminated on each surface, or different resin layers may be laminated. When other resin layers are laminated on the multilayer film (F), it is preferable to laminate a biodegradable resin.

[0027] The thickness of the multilayer film (F) in this embodiment is not particularly limited, but the total thickness may be, for example, about 10 to 1000 μm. If it is desired to reduce the amount of resin used for packaging applications, etc., the thickness may be, for example, 300 μm or less.

[0028] Figure 2 shows a laminate (L) in which a biodegradable resin (C) is laminated on at least one side of a multilayer film (F). In the illustrated example of laminate (L), the biodegradable resin (C) is laminated on the surface of the resin layers (A) on both sides of the multilayer film (F).

[0029] The biodegradable resin (C) laminated on at least one side of the multilayer film (F) consisting of a resin layer (A) / barrier layer (B) / resin layer (A) is not particularly limited to biodegradable polyesters, and any desired biodegradable resin (C) can be laminated. For example, polylactic acid (PLA) can be used as the biodegradable resin (C) for the substrate. Examples of biodegradable resins (C) for the sealant layer include polylactic acid (PLA), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polyhydroxyalkanoate (PHA), polybutylene adipate terephthalate (PBAT), and acetylcellulose. From the viewpoint of moldability, a thermoplastic biodegradable resin (C) having an appropriate melting point (Tm) and melt flow rate (MFR) is preferred.

[0030] When the biodegradable resin (C) is laminated on both sides of the multilayer film (F), the same type of biodegradable resin (C) may be laminated with a similar thickness. Different biodegradable resins (C) may be laminated on both sides of the multilayer film (F). Biodegradable resins (C) may be laminated on both sides of the multilayer film (F) with different thicknesses. The biodegradable resin (C) for the sealant layer described above may be laminated on the resin layers (A) on both sides.

[0031] Furthermore, the method for manufacturing the laminate (L) is not particularly limited, and each layer constituting the laminate (L) may be appropriately laminated by extrusion lamination, dry lamination, co-extrusion, or a combination thereof. For example, a resin layer (A) / barrier layer (B) / resin layer (A) of a multilayer film (F) may be laminated by co-extrusion, and then a biodegradable resin (C) may be laminated on top of the resin layer (A) of the multilayer film (F). Alternatively, four layers of resin layer (A) / barrier layer (B) / resin layer (A) / biodegradable resin (C) or five layers of biodegradable resin (C) / resin layer (A) / barrier layer (B) / resin layer (A) / biodegradable resin (C) may be laminated together by co-extrusion.

[0032] As is clear from the above explanation, the present invention provides the following effects. By dissolving the barrier layer (B) through water washing, separation from the resin layer (A) becomes possible, improving recyclability. By making all layers constituting the multilayer film (F) and laminate (L) biodegradable, the environmental impact can be reduced. Applications for multilayer films (F) and laminates (L) include food packaging films and agricultural films. Laminates (L) in particular can be used in the manufacture of packaging bags.

[0033] The reason why the interlayer adhesion between the resin layer (A) and the barrier layer (B) improves is not entirely clear, but it is possible that reactivity is involved, such as the formation of chemical bonds between the components contained in the resin layer (A) and the components contained in the barrier layer (B).

[0034] The uses of packaging bags are not particularly limited and include disposable, refillable, storage, and storage of goods. Specific examples of packaging bag structures include flat bags such as three-sided sealed bags and four-sided sealed bags, as well as pillow bags, gusset bags, and standing pouches. The shape of the packaging bag is not particularly limited and may be a polygon such as a square, a flat shape including curves such as a circle, ellipse, or egg, or a three-dimensional shape such as a prism, pyramid, cylinder, or cone. [Examples]

[0035] The present invention will be specifically described below with reference to examples.

[0036] (Sample preparation method) (Melting extruded film) The films of the examples and comparative examples were prepared using a T-die extruder with resins and additives in the proportions (mass ratios) shown in the "Composition of Resin Layer (A)" column of Table 1. The resin layer (A) of Examples 1 to 5 is a blend of biodegradable polyester resin (PEs):carbodiimide-modified isocyanate compound (Add-1).

[0037] Furthermore, the "(A) / (B) / (A)" column in Table 1 shows the layer thickness ratio (%) in the film. The films of Examples 1-5 and Comparative Examples 1-7 consist of three-layer co-extruded films. The films of Comparative Examples 8 and 9 are single-layer extruded films. The total thickness of the films was set to 100 μm.

[0038] [Table 1]

[0039] The meanings of the abbreviations used for the resin layer (A) in Table 1 are as follows: "PEs-1" Luminy (registered trademark) LX930...Polylactic acid (PLA), ρ=1.24g / cm 3 Tm=130℃, MFR=8g / 10min (190℃, 2.16kg), manufactured by Total Corbion PLA. "PEs-2" BioPBS (registered trademark) FZ71... Polybutylene succinate (PBS), ρ = 1.26 g / cm³ 3 Tm=115℃, MFR=22g / 10min (190℃, 2.16kg), PTT MCC Biochem "PEs-3" Luminy (registered trademark) LX175...Polylactic acid (PLA), ρ=1.24g / cm 3 Tm=155℃, MFR=3g / 10min (190℃, 2.16kg), manufactured by Total Corbion PLA. "Add-1" Carbodilite (registered trademark) LA-1...Carbodiimide-modified isocyanate, manufactured by Nisshinbo Chemical Co., Ltd. "Add-2" Carbodilite (registered trademark) HMV-5CA-LC...Polyvalent carbodiimide, manufactured by Nisshinbo Chemical Co., Ltd. "Add-3" SCONA (registered trademark) TPPL 1112PA... Maleic anhydride-modified polylactic acid, manufactured by BYK.

[0040] Furthermore, the barrier layer (B) was formed using the following resin. Nichigo G-Polymer (registered trademark) BVE8049P... Butenediol-modified polyvinyl alcohol resin, ρ = 1.29 g / cm³ 3 Tm=188℃, MFR=4.3g / 10min (210℃, 2.16kg), manufactured by Mitsubishi Chemical Corporation.

[0041] (Sample evaluation method) The multilayer films of Examples 1-5 and Comparative Examples 1-7, as well as the single-layer films of Comparative Examples 8 and 9, were evaluated using the following method.

[0042] (1)(Membrane adhesion strength) Using the ring method, a sample of the target film cut to 25.4 mm x 200 mm was examined. The surface layer was clamped with a gripper at a peeling distance of 30 mm and a peeling speed of 5 mm / min, and the film adhesion strength between the resin layer (A) and the barrier layer (B) in the flow direction (MD direction) was measured.

[0043] (2) (Oxygen gas permeability) The oxygen gas permeability of the prepared film was measured in accordance with JIS K 7126-2, and the unit was cm. 3 / (m 2 The pressure was converted to (24h·atm). Here, 1 atm represents 101325 Pa. The measurement conditions were a temperature of 30°C and a humidity of 70% RH.

[0044] Table 2 shows the evaluation results.

[0045] [Table 2]

[0046] As shown in Table 2, according to the present invention (Examples 1-5), by mixing the resin composition for the resin layer (A) within a predetermined blending range, a desirable result was obtained in which the film adhesion strength with the barrier layer (B) exceeds 1 N / 25.4 mm.

[0047] When the resin layer (A) was made of polyester resin alone (Comparative Examples 1 and 2), the film adhesion strength was very low at 0.1 N / 25.4 mm in both cases, indicating that there was almost no adhesion. When a carbodiimide compound other than carbodiimide-modified isocyanate (Add-2) was used in the resin layer (A) (Comparative Examples 3-5), the film adhesion strength was improved compared to polyester resin alone (Comparative Examples 1, 2), but it was lower than that of the present invention (Examples 1-5). Even when polylactic acid (Add-3) having maleic anhydride groups that are reactive with vinyl alcohol resin was mixed with the resin layer (A) to impart adhesion (Comparative Examples 6, 7, 8), the film adhesion strength did not improve.

[0048] Furthermore, regarding oxygen permeability (gas barrier properties), the present invention (Examples 1-5) showed a desirable result of approximately 1 / 100th of the oxygen permeability (gas barrier properties) in single-layer films without butendiol-modified polyvinyl alcohol resin in the barrier layer (B) (Comparative Examples 9, 10). [Explanation of Symbols]

[0049] A... Resin layer, B... Barrier layer, C... Biodegradable resin, F... Multilayer film, L... Laminate.

Claims

1. It is a multilayer film consisting of a resin layer (A) / barrier layer (B) / resin layer (A), The above resin layer (A) consists of a layer containing a mixture of a biodegradable polyester resin and a carbodiimide-modified isocyanate. A multilayer film characterized in that the barrier layer (B) comprises a layer containing a modified polyvinyl alcohol resin having a butenediol structure.

2. The multilayer film according to claim 1, characterized in that the thickness of the barrier layer (B) is 5 to 40% of the total thickness of the multilayer film consisting of a resin layer (A) / barrier layer (B) / resin layer (A), which is 100% of the total thickness of the multilayer film.

3. The multilayer film according to claim 1, characterized in that the resin layer (A) comprises 96 to 99.9% by mass of the biodegradable polyester resin and 0.1 to 4% by mass of the carbodiimide-modified isocyanate, based on 100% by mass of the mixture.

4. The multilayer film according to claim 1, characterized in that a resin layer (A) / barrier layer (B) / resin layer (A) is manufactured by co-extrusion.

5. A laminate characterized in that a biodegradable resin is laminated on at least one side of a multilayer film according to any one of claims 1 to 4.

6. A packaging bag formed using the laminate described in claim 5.

Images