heat shrinkable film

Abstract

[Problem] To obtain a heat-shrinkable film which comprises biodegradable resins, is excellent in terms of stretchability, low-temperature shrinkability, flexibility, etc., and is for use in shrink packaging and which has satisfactory interlaminar adhesion.　[Solution] A heat-shrinkable film comprising both outer layers constituted of resin composition A, which comprises a poly(lactic acid)-based resin as a main component, and an interlayer constituted of resin composition B, which comprises an aliphatic / aromatic polyester-based resin as a main component, characterized in that the resin composition A comprises the poly(lactic acid)-based resin and an aliphatic / aromatic polyester-based resin in such a proportion that [poly(lactic acid)-based resin] / [aliphatic / aromatic polyester-based resin]=(70.0-98.0 wt%) / (30.0-2.0 wt%) and the resin composition B comprises a poly(lactic acid)-based resin and the aliphatic / aromatic polyester-based resin in such a proportion that [poly(lactic acid)-based resin] / [aliphatic / aromatic polyester-based resin]=(2.0-20.0 wt%) / (98.0-80.0 wt%).

Description

[Technical Field]

[0001] The present invention relates to a heat-shrinkable film used for shrink packaging and the like, which is biodegradable. [Background technology]

[0002] Heat-shrinkable films have traditionally been widely used in the packaging field. Examples of synthetic resins used in such heat-shrinkable films include polypropylene-based resins, polyethylene-based resins, polyvinyl chloride-based resins, and polystyrene-based resins. However, when heat-shrinkable films made of these synthetic resins are discarded in the natural environment after serving their purpose as packaging materials, they are difficult to decompose due to their chemical stability and remain in the natural environment for long periods of time, thereby contributing to environmental pollution. For this reason, heat-shrinkable films made of biodegradable resins that can be decomposed by the action of microorganisms have attracted attention.

[0003] Patent Document 1 is an invention relating to a biodegradable biaxially stretched film, which is a laminated film having two outer layers made of a polylactic acid resin and an intermediate layer made of an aliphatic-aromatic polyester resin, in which the proportion of polylactic acid resin in all layers is 15 to 55% by weight and the proportion of aliphatic-aromatic polyester resin is 45 to 85% by weight. This biodegradable biaxially stretched film not only has excellent stretchability, but also excellent low-temperature shrinkability and flexibility, making it suitable for shrink packaging. However, the film obtained in this manner has a problem in that the interlayer adhesive strength between the two outer layers made of a polylactic acid resin and the intermediate layer made of an aliphatic-aromatic polyester resin is weak, causing peeling between the layers when the film is folded, resulting in a loss of aesthetic appeal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-15720 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a heat-shrinkable film made of a biodegradable resin that is used for shrink packaging and has excellent stretchability, low-temperature shrinkability, flexibility, etc., and that has good interlayer adhesion. Another objective is to provide a heat-shrinkable film that has good weld-seal strength, elongation, and transparency. [Means for solving the problem]

[0006] The present inventors have conducted extensive research into the resin compositions that form each layer in order to improve the adhesion between layers, and have found that The present invention has been achieved. That is, the present invention provides the following as a means for solving the above problems: A heat-shrinkable film is proposed in [3]. [1] Polylactic acid resin (PLA) Both outer layers are made of a resin composition A having the above as a main component, Condensation polymer of adipic acid, terephthalic acid and 1,4-butanediol (PBAT) and an intermediate layer made of a resin composition B mainly composed of the resin composition A. The PLA and PBAT And, PLA : PBAT = 70.0 to 98.0 wt %: 30.0 to 2.0 wt %, and the resin composition B is The PLA and PBAT And, PLA : PBAT = 2.0 to 20.0% by weight: 98.0 to 80.0% The total thickness of the heat-shrinkable film is 10 to 30 μm, and the thickness ratio of the outer layers to the intermediate layer is outer layer:intermediate layer:outer layer=1:4:1 to 1:8:1. A heat-shrinkable film characterized by: [2] The resin composition A is The PLA and PBAT And, PLA : PBAT = 82.5 to 97.5 wt %: 17.5 to 2.5 wt %, and the resin composition B is The PLA and PBAT And, PLA : PBAT The heat-shrinkable film according to [1], characterized in that it contains 4.0 to 15.0 wt % of hydroxybenzoates and 96.0 to 85.0 wt % of hydroxybenzoates. [Effects of the Invention]

[0007] The heat-shrinkable film of the present invention is made of a biodegradable resin that is decomposed by the action of microorganisms, which reduces its impact on the environment. Furthermore, it not only has excellent stretchability, but also excellent low-temperature shrinkability, flexibility, transparency, etc., making it suitable for use in shrink packaging. Furthermore, the resin composition that forms each layer has been revised, which has increased interlayer adhesion strength and reduced the risk of delamination due to impacts such as bending. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and various embodiments can be adopted within the scope of achieving similar effects. The heat-shrinkable film of the present invention comprises at least two outer layers and an intermediate layer.

[0009] [Both outer layers] Both outer layers are mainly composed of polylactic acid resin (hereinafter abbreviated as PLA as necessary), and further Aliphatic-aromatic polyester resin Fat It consists of resin composition A contained as a secondary component. (Polylactic acid resin (PLA)) PLA is a homopolymer or copolymer of L-lactic acid or D-lactic acid, or a mixture of homopolymers. In the present invention, poly-L-lactic acid having a structural unit of L-lactic acid and poly-L-lactic acid having a structural unit of D-lactic acid are used. Poly(D-lactic acid), a type of lactic acid, and poly(LD-lactic acid), a copolymer of L-lactic acid and D-lactic acid. Alternatively, multiple types can be blended. The proportion of D-lactic acid in PLA is 0. It is preferable that the content of PLA is 5 to 10.0% by weight. Polylactic acid LuminyLX175 manufactured by rbion can be used.

[0010] PLA may be copolymerized with other hydroxycarboxylic acids and may contain small amounts of chain extender residues, provided that the properties of the resin are not impaired. Examples of other hydroxycarboxylic acid units include bifunctional aliphatic hydroxycarboxylic acids such as glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, and 2-hydroxycaproic acid, as well as lactones such as caprolactone, butyrolactone, and valerolactone. It is recommended that such other hydroxycarboxylic acid units be used in an amount of less than 15 mol% in PLA.

[0011] (Aliphatic-aromatic polyester resin fat) Aliphatic-aromatic polyester resin is a polyester obtained by condensation polymerization of an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, and a diol. Aliphatic dicarboxylic acids include succinic acid, adipic acid, suberic acid, sebacic acid, dodecyl alcohol, and the like. Among them, succinic acid or adipic acid is preferred in terms of biodegradability. As the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid, naphthalene Among them, terephthalic acid and isophthalic acid are preferred from the viewpoint of polymerizability. Terephthalic acid is particularly preferred. As the diol component, an aliphatic diol is preferably used. especially ethylene glycol, 1,3-propanediol, and 1,4-butanediol , 1,4-cyclohexanedimethanol, etc. Among them, in consideration of biodegradability, Diols having 2 to 4 carbon atoms are preferred, and ethylene glycol, 1,4-butanediol, Diol is more preferred, and 1,4-butanediol is particularly preferred. Two or more types of acid component, aliphatic diol component and aromatic dicarboxylic acid component are used. You can also be there. Aliphatic-aromatic polyester resin As the polymerizable polymer, for example, "Ecoflex" (registered trademark) manufactured by BASF, which contains a condensation polymer of adipic acid, terephthalic acid, and 1,4-butanediol as its main component, can be used.

[0012] The blending ratio of PLA to PBAT in resin composition (A) is preferably PLA:PBAT=70.0-98.0 wt%:30.0-2.0 wt%, particularly 82.5-97.5 wt%:17.5-2.5 wt%. If the blending ratio of PLA in both outer layers is less than 70 wt%, the transparency of the film will deteriorate. Furthermore, if the blending ratio of PBAT in both outer layers is less than 2.0 wt%, delamination may occur between the outer layers and the intermediate layer when the film is folded. In addition, since BASF's "Ecobio" (registered trademark) contains PLA and PBAT, it is possible to use this resin and further add PLA or PBAT so that the blending ratio of PLA and PBAT falls within the above range.

[0013] [Middle layer] The intermediate layer is made of a resin composition B containing PBAT as a main component and PLA as a secondary component. The PBAT and PLA used in the intermediate layer can be any of the resins described above without any particular limitations. The blending ratio of PLA and PBAT in the resin composition (B) is preferably PLA:PBAT=2.0-20.0% by weight:98.0-80.0% by weight, and more preferably 4.0-15.0% by weight:96.0-85.0% by weight. If the blending ratio of PLA in the intermediate range is less than 2.0% by weight, When the film is folded, delamination may occur between the outer layers and the intermediate layer. Furthermore, if the PBAT content in the intermediate layer is less than 80.0% by weight, the flexibility of the resulting film may decrease. In addition, since BASF's "Ecobio" (registered trademark) contains PLA and PBAT, it is possible to use this resin and further add PLA or PBAT so that the blending ratio of PLA and PBAT falls within the above range.

[0014] [Additives] Resin composition (A) and resin composition (B) may contain, for example, lubricants, antioxidants, ultraviolet absorbers, light stabilizers, antistatic agents, pigments, dyes, surfactants, antiblocking agents, modifying resins, etc., as long as the effects of the present invention are not impaired. It is also desirable to add a compatibilizer to improve the compatibility between PLA and PBAT. Examples of compatibilizers include carboxylic acid anhydrides, such as maleic anhydride, and particularly the aforementioned epoxy-containing copolymers based on styrene, acrylic esters, and / or methacrylic esters. The epoxy-containing units are preferably glycidyl (meth)acrylate. Epoxy-containing copolymers of the aforementioned type are sold, for example, by BASF Resins B.V. under the trade name Joncryl® ADR. A particularly suitable compatibilizer is, for example, Joncryl® ADR 4368. The amount of compatibilizer added is not particularly limited, but it is recommended to add, for example, 0.01 to 2.00 parts by weight per 100 parts by weight of the total of PLA and PBAT.

[0015] [Heat-shrinkable film] The heat-shrinkable film of the present invention has two outer layers made of resin composition A and an intermediate layer made of resin composition B between them, and may have, for example, a three-layer structure consisting of outer layer (resin composition A) / intermediate layer (resin composition B) / outer layer (resin composition A). Alternatively, it may have a five-layer structure consisting of outer layer (resin composition A) / intermediate layer (resin composition B) / intermediate layer (resin composition A) / intermediate layer (resin composition B) / outer layer (resin composition A). In addition to the two outer layers made of resin composition A and the intermediate layer made of resin composition B, the laminate may further include an intermediate layer made of resin composition C containing PLA and PBAT in a ratio of PLA:PBAT=more than 20% to less than 70% by weight:less than 80% to more than 30% by weight. More specifically, the laminate may have a structure such as outer layer (resin composition A) / intermediate layer (resin composition C) / intermediate layer (resin composition B) / intermediate layer (resin composition C) / outer layer (resin composition A), or outer layer (resin composition A) / intermediate layer (resin composition C) / intermediate layer (resin composition B) / outer layer (resin composition A).

[0016] The total thickness of the heat-shrinkable film of the present invention is preferably 10 to 30 μm, more preferably 10 to 25 μm. If the total thickness of the film is less than 10 μm, the strength is insufficient. If the total thickness of the film is more than 25 μm, the flexibility decreases and the amount of resin used increases, which reduces the economic efficiency. When the heat-shrinkable film is a three-layer film having an outer layer / intermediate layer / outer layer in that order, the thickness ratio of each layer is preferably outer layer:intermediate layer:outer layer=1:4:1 to 1:8:1. If the intermediate layer ratio is less than 4, the flexibility of the heat-shrinkable film decreases, and if the intermediate layer ratio exceeds 8, the shrinkage properties deteriorate. Furthermore, if the thickness of the surface layer is less than 1 μm, the transparency of the heat-shrinkable film decreases.

[0017] Furthermore, the heat-shrinkable film of the present invention desirably has a longitudinal and transverse shrinkage rate in glycerin of 30% or more at 90°C and 50% or more at 110°C. A shrinkage rate of 30% or more in glycerin at 90°C, i.e., excellent low-temperature shrinkability, allows the film to be shrink-wrapped at a lower temperature and for a shorter heating time, making it suitable for use in packaging items that are susceptible to deterioration by heat. The shrinkage rate in glycerin at 110°C is close to the film's final shrinkage rate. If this value is less than 50%, the corners of the film may not shrink sufficiently during shrink packaging, resulting in hard protrusions (so-called "horns"), or the area in contact with the packaged item may not shrink sufficiently, resulting in wrinkles, which may prevent the film from producing a beautiful package.

[0018] [Method for manufacturing heat-shrinkable film] The heat-shrinkable film of the present invention can be produced by forming the above-mentioned resin composition into a film using, for example, an inflation film-forming method or a T-die film-forming method, and then uniaxially or biaxially stretching the film using a roll stretching method and / or a tenter stretching method. The heat-shrinkable film of the present invention can also be produced by stretching the film by increasing the blow-up ratio or draw ratio during film formation by inflation film extrusion. Furthermore, the film can also be produced by stretching a tubular film formed by inflation film extrusion by tubular stretching. Other conventionally known methods can also be used to produce the heat-shrinkable film of the present invention. [Example]

[0019] The effects of the present invention will be confirmed below based on Examples and Comparative Examples. The resins used in the Examples and Comparative Examples are as follows:

[0020] The effects of the present invention will now be confirmed based on examples, in which each film was evaluated by the following methods. <Interlayer adhesion strength> The resulting film was cut into a 10 mm wide rectangle. The film was then set on an autograph so that the adhesive strength between the outer and middle layers could be measured. The peel force was measured by peeling at a 180° angle at a peel rate of 500 mm / min. An AGS-500NX made by Shimadzu Corporation was used for the measurement. Note that an interlayer adhesive strength of more than 1 N / 10 mm was considered very good. <Bending peel test> The obtained film is cut in a folded state, and the state of peeling of the outer layer at the cross section of the film is observed under a microscope. If peeling of the outer layer was observed, it was evaluated as ×, and if not, it was evaluated as ◯.

[0021] <Haze> The haze of the obtained film is measured in accordance with JIS K 7136:2000 using an NDH-4000 manufactured by Nippon Denshoku Co., Ltd. A haze of 5% or less can be considered very good. <Fusing seal strength> The resulting film is heat-sealed at a temperature of 190°C for 0.5 seconds, and then cut to a width of 15 mm. The heat-seal strength of the resulting test piece is measured at a tensile speed of 500 mm / min in accordance with JIS Z 1711 8.4 Heat Seal Strength Test. An AG-1 KNISMO tester manufactured by Shimadzu Corporation is used for the measurement. A heat-seal strength of over 11 N / 15 mm is considered very good. <Fusing seal elongation> When measuring the weld seal strength, it is calculated from the distance between the chucks when the seal breaks. Specifically, if the initial distance between the chucks is a and the distance between the chucks when the seal breaks is b, it is calculated as 100 x (ba) / a. Note that weld seal elongation of over 20% can be considered very good.

[0022] [Example 1] Resin composition A for the outer layer and resin composition B for the intermediate layer shown in Table 1 were fed into separate extruders and co-extruded using a T-die to obtain a three-layer film with a thickness of 240 μm: outer layer (resin composition A) / intermediate layer (resin composition B) / outer layer (resin composition A). This was stretched 4 times in both the length and width directions using a biaxial stretching device (Iwamoto Seisakusho Co., Ltd.) to obtain a heat-shrinkable film with a thickness of 15 μm. The thickness ratio of each layer was adjusted to outer layer: intermediate layer: outer layer = 1: 6: 1. The properties of the obtained film are also shown in Table 1. [Examples 2 to 6, Comparative Examples 1 to 4] Each film was obtained in the same manner as in Example 1, except that the resin composition was changed as shown in Table 1 or 2. The evaluation results of the obtained films are also shown in Table 1 and Table 2.

[0023] [Table 1]

[0024] The heat-shrinkable films of Examples 1 to 6 all had high interlayer adhesive strength, and no delamination occurred when the films were folded. In particular, the films of Examples 1 to 3, in which the PLA:PBAT content in both outer layers was within the ranges of 82.5 to 97.5 wt %: 17.5 to 2.5 wt %, and the PLA:PBAT content in the intermediate layer was within the ranges of 4.0 to 15.0 wt %: 96.0 to 85.0 wt %, also had high weld-seal strength. Furthermore, the films of Examples 1 to 4, in which the PLA:PBAT content in the entire heat-shrinkable film was within the ranges of 25.0 to 35.0 wt %: 75.0 to 65.0 wt %, had good weld-seal elongation. Good weld-seal elongation means that the sealed portion is less likely to rupture even when an impact is applied to the sealed portion.

[0025] [Table 2]

[0026] The films of Comparative Examples 1 to 4 all had low interlayer adhesive strength, and delamination of the films was observed when folded. The film of Comparative Example 2 had a problem in that the amount of PBAT in the entire film exceeded 80% by weight, resulting in low weld-seal strength. The films of Examples 5 and 6 and Comparative Example 4 had a PLA amount in the entire heat-shrinkable film of 40% by weight or less, but exceeded the preferred range (35% by weight or less), resulting in low weld-seal elongation.

Claims

1. A heat-shrinkable film having two outer layers made of a resin composition A containing a polylactic acid resin (PLA) as a main component, and an intermediate layer made of a resin composition B containing a condensation polymer of adipic acid, terephthalic acid, and 1,4-butanediol (PBAT) as a main component, the resin composition A contains the PLA and the PBAT in a ratio of PLA:PBAT=70.0 to 98.0% by weight:30.0 to 2.0% by weight, the resin composition B contains the PLA and the PBAT in a ratio of PLA:PBAT=2.0 to 20.0% by weight:98.0 to 80.0%, The total thickness of the heat-shrinkable film is 10 to 30 μm, A heat-shrinkable film characterized in that the thickness ratio of the outer layers to the intermediate layer is outer layer:intermediate layer:outer layer=1:4:1 to 1:8:

1.

2. the resin composition A contains the PLA and the PBAT in a ratio of PLA:PBAT=82.5 to 97.5% by weight:17.5 to 2.5% by weight, 2. The heat-shrinkable film according to claim 1, wherein the resin composition B contains the PLA and the PBAT in a ratio of PLA:PBAT=4.0 to 15.0% by weight:96.0 to 85.0% by weight.

Images