JP2006160788A - Heat-shrinking film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-shrinking film having a good shrinking characteristics even on re-heating after its heat shrink-packaging, and especially in the case of being used as a binding belt of a container heated together with its content in a microwave oven, capable of showing both of a good primary processability and the crush prevention of the container jointly. <P>SOLUTION: This heat-shrinking film consisting mainly of a lactic acid-based polymer has ≥30 and <60 % shrinking rate in at least one direction on immersing it in 80°C warm water for 10 sec, and <5 MPa shrinking stress after 1 min in 80°C silicone oil. Also, the lactic acid-based polymer may have (98:2)-(85:15) or (2:98)-(15:85) constitution ratio of D-lactic acid to L-lactic acid. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a heat-shrinkable film mainly composed of a lactic acid-based polymer, and particularly suitable for applications in which reheating is performed after shrink wrapping, such as a cable tie for a container heated together with contents in a microwave oven. Relates to a heat shrinkable film.

  In recent years, the use of a heat-shrinkable binding band obtained by printing a stretched film made of a polyester resin and making a bag for binding lunch boxes sold at convenience stores and the like is increasing. However, since the polyester-based heat-shrinkable film has a large shrinkage stress, there is a problem that the lunch box is crushed by shrinkage of the film when the lunch is heated with a microwave oven or the like.

  For this reason, the technique which makes a shrinkage stress less than 5 Mpa by reducing a shrinkage rate to less than 30%, and prevents crushing of the lunch box at the time of microwave oven heating is proposed (patent document 1).

  On the other hand, heat-shrinkable films made of these polyester-based resins, when discarded in the natural environment after use, remain in the natural world without being decomposed due to their high stability, which may cause damage to the landscape. There is concern that it may contaminate the living environment of fish, wild birds and other living organisms, and may cause various environmental problems.

  Therefore, as a natural material container excellent in environmental suitability, especially the lid part of the container, the window part, the surface moisture-proof layer part of the container, the constituent layer part of the laminate forming the container, the binding band part of the container, the overlapping wrapping sheet shape It has been proposed to use a lactic acid polymer sheet for a product, an adhesive label, etc. (Patent Document 2).

JP 2004-67203 A JP 2002-46116 A

  Lunch boxes sold at convenience stores and the like are previously bundled by heating and shrinking a binding band obtained by printing a stretched film and making a bag. And when a user uses, in order to warm the contents, the lunch box with the binding band is heated in a microwave oven. As described above, the binding band of the lunch box is subjected to heat treatment for contracting the binding band and applying it to the lunch box as primary heating (hereinafter also referred to as “primary processing”, which is referred to as “primary workability”). Further, as secondary heating, heating by a microwave oven is added when the contents are warmed.

Here, the polyester-based heat-shrinkable film of Patent Document 1 is designed so that the shrinkage stress is less than 5 MPa by reducing the shrinkage rate to less than 30%, thereby preventing the lunch box from being crushed during microwave heating. However, it has been found that when the shrinkage rate is less than 30%, it is difficult to perform primary processing when bundling the lunch box, that is, the shrinkage rate is too low to be bundled cleanly. In order to bind them more neatly, if the temperature of the primary heating is increased or the treatment time is increased, the contents of the lunch box are affected.
On the other hand, if the shrinkage rate is increased to facilitate the primary processing, the lunch box can be bundled cleanly, but the shrinkage stress increases, so that the lunch box is crushed during secondary heating by microwave heating. As described above, the conventional polyester heat-shrink film is difficult to balance because it is difficult to balance the primary workability when the lunch box is bundled with the prevention of the collapse of the lunch box when heating the microwave oven.

  In addition, Patent Document 2 discloses that a sheet-like material made of a lactic acid-based polymer is used as a binding band for a container such as a lunch box, but the primary workability and the influence of microwave heating, etc. No specific required quality is disclosed.

  The present invention has been made to solve these problems. That is, the object of the present invention is to provide a heat-shrinkable film having good shrinkage characteristics even when reheating is performed after shrink-wrapping. A heat-shrinkable film that can achieve both good primary processability and prevention of container collapse, especially when used as a binding band for containers heated with contents in a microwave oven. Is to provide.

(1) The heat-shrinkable film of the present invention is a heat-shrinkable film mainly composed of a lactic acid-based polymer, and has a shrinkage rate of 30 in 10 seconds when immersed in 80 ° C. warm water in at least one direction. % And less than 60%, and the shrinkage stress after 1 minute in 80 ° C. silicone oil is less than 5 MPa.
(2) In the lactic acid polymer, the constituent ratio of D lactic acid and L lactic acid may be 98: 2-85: 15 or 2: 98-15: 85.
(3) In the present invention, a central layer containing a lactic acid polymer, an aliphatic polyester resin other than the lactic acid polymer, and a plasticizer is provided, and 90% by mass or more of the lactic acid polymer is provided on the outside thereof. The structure which laminates | stacks the outer layer to contain can be provided.
(4) Furthermore, it is preferable that the aliphatic polyester resin has at least one glass transition temperature at 0 ° C. or lower, and its content in the central layer is 10 to 25% by mass.
(5) The heat-shrinkable film of the present invention can be reheated after shrink-wrapping.
(6) Moreover, the heat-shrinkable film of this invention can be used as a binding band of the container heated with a content with a microwave oven.
(7) Furthermore, the container may be a food container.

  According to the present invention, even when reheating is performed after shrink packaging, it has excellent shrinkage characteristics, can prevent the adherend such as a container from being crushed by shrinkage, and has excellent thermal suitability. Can be obtained.

The present invention will be described in detail below. In the present invention, even when referred to as “film”, “sheet” is included, and even when referred to as “sheet”, “film” is included.
“Lactic acid-based polymer as a main component” means that one of the components that determine the main function of the heat-shrinkable film is a lactic acid-based polymer, and other components within the range of not inhibiting the function of the lactic acid-based polymer. It is intended to include that components may be included. In general, the content of the lactic acid polymer in the heat-shrinkable film is at least 50% or more, preferably 80% or more.
Note that the upper and lower limits of the numerical range in the present invention are equivalent to the present invention as long as they have the same effects as those in the numerical range even if they are slightly outside the numerical range specified by the present invention. The intention to include in the range is included.

(Primary processing)
A primary processing (primary heating) step when the heat-shrinkable film of the present invention is used as a binding band for food containers such as lunch boxes will be described. First, the heat-shrinkable film is printed, and the film that has been solvent-sealed in a cylindrical shape by a bag making machine is cut into individual sheets for each container. This is manually attached to a container such as a lunch box, the container for each film is poured on a belt conveyor sandwiched between the upper and lower sides, heated air is blown out from a hot air nozzle built in the side, and the film on the side of the container is shrunk to the container. It is common to bind. Therefore, in this case, the primary heating means contraction heating of the binding band on the side surface portion of the container.

(Heat shrinkage)
It is important that the heat shrinkable film of the present invention has a heat shrinkage rate of 30% or more and less than 60% in hot shrink water at 80 ° C. for 10 seconds in the main shrink direction (TD). By setting the thermal shrinkage rate to 30% or more, sufficient shrinkage characteristics can be provided, and particularly when used as a binding band for a container, it is possible to realize good primary workability. Furthermore, it is more preferable that the thermal shrinkage rate is 35% or more in order to meet the recent demand for the container tie band such as protection of contents and speeding up. Moreover, if the heat shrinkage rate is less than 60%, problems such as crushing and cutting of the container will not occur during the primary processing. Further, considering the suppression of the occurrence probability of container collapse, it is more preferable to set it to 50% or less.

  On the other hand, it is preferable that the longitudinal shrinkage rate is low, but it may be preferable to slightly shrink in order to eliminate lateral wrinkles during shrinkage. Generally, as described above, the shrinkage rate for 10 seconds in 80 ° C. hot water is 10% or less, more preferably 7% or less, and still more preferably 5% or less. If it is 10% or more, the shrinkage in the vertical direction of the film is more conspicuous than necessary, and the shrinkage finish may be deteriorated. In order to keep the longitudinal shrinkage ratio low, it is preferable that the longitudinal stretching ratio is about 1.01 to 1.20.

(Shrinkage stress)
Moreover, it is important for the heat-shrinkable film of the present invention that the shrinkage stress after 1 minute in 80 ° C. silicone oil is less than 5 MPa. By setting the shrinkage stress to 5 MPa, the influence on the adherend such as a container can be suppressed during reheating, especially when used as a binding band for a container heated together with contents in a microwave oven. It is possible to prevent the container from being crushed. Furthermore, the shrinkage stress is preferably 4.0 MPa or less, and particularly preferably 3 MPa or less.

  As described above, by setting the heat shrinkage rate and shrinkage stress in appropriate ranges, even when reheating is performed after shrink wrapping, a heat shrinkable film having good shrinkage properties can be obtained, In particular, when used as a tying band for a container that is heated together with the contents in a microwave oven, it becomes possible to satisfy both different characteristics of maintaining good primary workability and preventing the container from collapsing. .

(Lactic acid polymer)
The lactic acid polymer of the present invention refers to a homopolymer of D-lactic acid or L-lactic acid or a copolymer thereof. That is, poly (L-lactic acid) whose structural unit is L-lactic acid, poly (D-lactic acid) whose structural unit is D-lactic acid, or poly (DL-) whose structural units are L-lactic acid and D-lactic acid. Lactic acid), or a mixture or copolymer of two or more of these.

  The DL constituent ratio of the lactic acid-based polymer is preferably such that the constituent ratio of D-lactic acid and L-lactic acid is 98: 2-85: 15 or 2: 98-15: 85, and more preferably 95: 5-85: 15 or 5 : 95-15: 85 is preferable. A lactic acid polymer in which the constituent ratio of D-lactic acid and L-lactic acid is 100: 0 or 0: 100 becomes a very high crystalline resin, has a high melting point, and tends to have excellent heat resistance and mechanical properties. . However, when used as a heat-shrinkable film, if the crystallinity is very high, stretching and orientation crystallization proceeds at the time of stretching, making it difficult to adjust the heat shrinkage rate. Even if a film in a crystalline state is obtained, crystallization proceeds due to heat at the time of shrinkage, and shrinkage finish performance is lowered. In the case of a DL-lactic acid copolymer, it is known that the crystallinity decreases as the proportion of the optical isomer increases. Therefore, when a lactic acid polymer is used as the material of the heat-shrinkable film, it is preferable that the crystallinity is appropriately reduced within the range of the DL composition ratio described above. In addition, for the purpose of adjusting the D-form and the L-form, it is also possible to blend two or more types of lactic acid polymers having different constituent ratios of D-lactic acid and L-lactic acid.

The lactic acid-based polymer of the present invention may be a copolymer of any of the above lactic acids and other hydroxycarboxylic acid units, or a copolymer of an aliphatic diol or an aliphatic dicarboxylic acid. Also good. The above-mentioned “other hydroxy-carboxylic acid units” copolymerized with a polylactic acid polymer include optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid). Lactic acid), glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxyn-butyric acid, 2-hydroxy3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycaprone Examples thereof include bifunctional aliphatic hydroxy-carboxylic acids such as acids and lactones such as caprolactone, butyrolactone, and valerolactone.
Examples of the “aliphatic diol” copolymerized with the lactic acid-based polymer include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like.
Examples of the “aliphatic dicarboxylic acid” copolymerized with the polylactic acid polymer include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid.

  Further, if necessary, copolymerization may be carried out using a non-aliphatic dicarboxylic acid such as terephthalic acid and / or a non-aliphatic diol such as an ethylene oxide adduct of bisphenol A as a small amount copolymerization component. A small amount of a chain extender such as a diisocyanate compound, an epoxy compound, or an acid anhydride can be copolymerized for the purpose of increasing the molecular weight.

  As a polymerization method for the lactic acid-based polymer, a condensation polymerization method, a ring-opening polymerization method, and other known polymerization methods can be employed. For example, in the condensation polymerization method, L-lactic acid, D-lactic acid, or a mixture thereof can be directly dehydrated and condensation polymerized to obtain a lactic acid polymer having an arbitrary composition. In addition, in the ring-opening polymerization method, lactide, which is a cyclic dimer of lactic acid, is subjected to ring-opening polymerization in the presence of a predetermined catalyst and using a lactic acid series having an arbitrary composition, if necessary, using a polymerization regulator or the like. A polymer can be obtained. In this case, lactide includes L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, or DL-lactide composed of L-lactic acid and D-lactic acid. By mixing and polymerizing as necessary, a lactic acid-based polymer having an arbitrary composition and crystallinity can be obtained.

  The preferred range of the weight average molecular weight of the lactic acid polymer used in the present invention is 50,000 to 400,000, more preferably 100,000 to 250,000. If the molecular weight is 50,000 or more, suitable practical physical properties are exhibited, and if it is 400,000 or less, good moldability is exhibited without the melt viscosity being too high. Representative examples of the polylactic acid-based polymer include the Lacty series manufactured by Shimadzu Corporation, the Lacia series manufactured by Mitsui Chemicals, and the Nature Works series manufactured by Cargill Dow.

(Aliphatic polyester)
In the present invention, an aliphatic polyester other than the lactic acid polymer can be blended. The aliphatic polyester used is obtained by condensing a biodegradable aliphatic polyester excluding a lactic acid polymer, for example, polyhydroxycarboxylic acid excluding a lactic acid polymer, an aliphatic diol and an aliphatic dicarboxylic acid. Examples thereof include aliphatic polyesters, aliphatic polyesters obtained by ring-opening polymerization of cyclic lactones, synthetic aliphatic polyesters, and aliphatic polyesters biosynthesized in cells. The aliphatic polyester used in the present invention is an aliphatic polyester as a polymer having a mass average molecular weight of 10,000 to 400,000, preferably 50,000 to 300,000, more preferably 100,000 to 300,000, and as a plasticizer. A distinction is made from the low molecular weight aliphatic polyesters used. The difference between the two appears in the presence or absence of a decrease in the glass transition temperature (Tg) of the lactic acid resin to be blended.

  As the above “polyhydroxycarboxylic acid” other than the lactic acid polymer, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy- Examples thereof include homopolymers and copolymers of hydroxycarboxylic acids such as 3-methylbutyric acid, 2-methyllactic acid, and 2-hydroxycaproic acid.

  As the aliphatic polyester obtained by condensing an aliphatic diol and an aliphatic dicarboxylic acid, one or two or more kinds of aliphatic diols and aliphatic dicarboxylic acids described below are selected and condensed, or If necessary, it can be jumped up with an isocyanate compound or the like to obtain a desired polymer (polymer). Examples of the “aliphatic diol” in this case include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like, and examples of the “aliphatic dicarboxylic acid” include succinic acid. Typical examples include acids, adipic acid, suberic acid, sebacic acid and dodecanedioic acid. An aromatic aliphatic polyester copolymerized with an appropriate amount of an aromatic dicarboxylic acid is also included in these categories. In order to develop biodegradability in the aromatic aliphatic polyester, it is necessary that an aliphatic chain exists between the aromatics. As the aromatic dicarboxylic acid component at this time, for example, isophthalic acid, Examples include terephthalic acid and 2,6-naphthalenedicarboxylic acid.

  Typical examples of the aliphatic polyester obtained by ring-opening condensation of cyclic lactones include ε-caprolactone, δ-valerolactone, β-methyl-δ-valerolactone, and the like, which are cyclic monomers, and one or more of them. Can be obtained by polymerization.

  Examples of synthetic aliphatic polyesters include cyclic acid anhydrides and oxiranes, such as copolymers of succinic anhydride with ethylene oxide, propion oxide, and the like.

  Examples of the aliphatic polyester biosynthesized in the fungus body include an aliphatic polyester biosynthesized with acetylcoenteam A (acetyl CoA) in the fungus body, such as Alkaline genus eutrophus. This aliphatic polyester is mainly poly-β-hydroxybutyric acid (poly-3HB). In order to improve practical properties as a plastic, valeric acid unit (HV) is copolymerized to produce poly (3HB-CO-3HV). It is industrially advantageous to use a copolymer of Generally, the HV copolymerization ratio is 0 to 40%. Further, a long-chain hydroxyalkanoate may be copolymerized.

  The aliphatic polyester used in the present invention preferably has at least one glass transition temperature (Tg) of 0 ° C. or less, more preferably −20 ° C. or less. This makes it possible to impart appropriate fracture resistance to the heat-shrinkable film. The melting point (Tm) of the aliphatic polyester is not particularly limited, but by including an aliphatic polyester having a melting point of 100 ° C. or higher, the direction perpendicular to the main shrinkage direction (MD, take-up direction, or longitudinal direction). )) Can be reduced. This is particularly effective for applications where longitudinal shrinkage is to be suppressed as much as possible. The reason for this is not clearly understood, but since the aliphatic polyester is crystallized in the pre-shrink film, this is not the case in the temperature range where the lactic acid polymer shrinks (range of 60 ° C. to 100 ° C.). The aliphatic polyester maintains a crystalline state even during shrinkage, and as a result, it can be considered that longitudinal shrinkage is suppressed by acting as a column. The aliphatic polyester used in the present invention may be a copolymer. For example, an aliphatic aliphatic polyester having an aromatic dicarboxylic acid component or an aliphatic polyester carbonate having a carbonate group (for example, a structure having a carbonate group in a 14-butanediol / succinic acid polymer), an aliphatic having biodegradability Any polyester may be used.

  In the case where the transparency is required, the content of the aliphatic polyester is preferably about 10% by mass to 40% by mass in the layer containing the aliphatic polyester. On the other hand, when the transparency is required to be very high, the content is preferably 10% by mass to 25% by mass, more preferably 10% by mass to 20% by mass. If it is 10% by mass or more, sufficient fracture resistance can be obtained, and if it is 25% by mass or less, transparency can be sufficiently secured.

(Plasticizer)
The heat-shrinkable film of the present invention can contain a plasticizer. By including a plasticizer, the fracture resistance can be improved. In particular, when a lactic acid polymer and an aliphatic polyester (excluding a lactic acid polymer) are used together, it is preferable to include a plasticizer exhibiting a specific solubility parameter (SP value).

  The plasticizer that can be used in the present invention has an aliphatic parameter whose SP is less than the intermediate value between the SP value of the lactic acid polymer and the SP value of the aliphatic polyester (excluding the lactic acid polymer). It is preferably close to the SP value of polyester. That is, since the SP value of a lactic acid polymer is usually (in theory) higher than that of an aliphatic polyester (excluding a lactic acid polymer), it is preferably a value lower than the intermediate value. , Not between the SP value of the lactic acid polymer and the SP value of the aliphatic polyester (excluding the lactic acid polymer), but in a range exceeding the SP value of the aliphatic polyester (excluding the lactic acid polymer), That is, it is more preferable that the value is lower than the SP value of the aliphatic polyester (excluding the lactic acid polymer).

  Specifically, the SP value of a lactic acid polymer is generally 11.12 (cal / cm 3) 1/2, and when polycaprolactone is used as the aliphatic polyester, the SP value is 10.18 (cal / Cm3) 1/2, the plasticizer SP value is preferably lower than the intermediate value of 10.65, and more preferably lower than 10.18. The SP value of other aliphatic polyesters, such as polybutylene succinate, is 10.87, and the SP value of polybutylene succinate / adipate varies with the ratio of succinate to adipate, but the SP value of polybutylene succinate is 10. In view of the fact that it is lower than 87, the range of the SP value of the plasticizer that can be used in the present invention is preferably 8.5 to 9.5 (cal / cm3) 1/2. Examples of plasticizers having an SP value in the range of 8.5 to 9.5 (cal / cm 3) 1/2 include dibutyl adipate, diisobutyl adipate, diisononyl adipate, diisodecyl adipate, di (2-ethylhexyl) adipate, Di (n-octyl) adipate, di (n-decyl) adipate, dibutyl diglycol adipate, dibutyl sebacate, di (2-ethylhexyl) sebacate, di (n-hexyl) azelate, di (2-ethylhexyl) azelate, di Fatty acid ester plasticizers such as (2-ethylhexyl) dodecanedionate, phthalic acid ester plasticizers such as diisononyl phthalate, diisodecyl phthalate, di (2-ethylhexyl) phthalate, and trimellitic acid such as tri (2-ethylhexyl) trimellitate ester And the like can be mentioned plasticizer is not limited thereto. In addition, said SP value is Fedors method [Polym. Eng. Sci. 14 (2) 152, (1974)].

  By adding a plasticizer having an SP value in the above range, the rupture resistance of the film can be increased while reducing the amount of aliphatic polyester, and a decrease in transparency can be minimized. The reason why such an effect is obtained is not clear, but can be considered as follows. That is, the impact resistance is improved by adding an aliphatic polyester to the lactic acid polymer, but if the amount of the aliphatic polyester to be added is large, the transparency inherent in the lactic acid polymer is impaired. Therefore, it is preferable to plasticize the aliphatic polyester with a plasticizer to plasticize the aliphatic polyester to enhance its impact resistance improving ability so that the fracture resistance can be improved with a smaller amount. However, in a mixed system of a lactic acid polymer and an aliphatic polyester (other than a lactic acid polymer), a so-called sea-island structure in which the islands of the aliphatic polyester are dispersed in the sea phase formed by the lactic acid polymer. Depending on the type of plasticizer to be added, the lactic acid polymer phase (sea phase) shifts to lower the glass transition temperature of the lactic acid polymer phase (sea phase) and the aliphatic polyester phase (island Phase) may not be plasticized. On the other hand, if it is said specific plasticizer, since SP value is close to SP value of aliphatic polyester (except a lactic acid polymer) and compatibility is high, transfer to a sea phase is suppressed. The transition to the island phase is advanced, the decrease in the glass transition temperature of the sea phase is suppressed, the softness of the aliphatic polyester forming the island phase can be improved, and the refractive index can be lowered. It can be considered that the refractive index difference between the lactic acid-based polymer and the aliphatic polyester becomes small, and the fracture resistance can be improved while maintaining transparency. In addition, when SP value is too lower than the minimum value (8.5) of this prescription | regulation, it will become difficult to transfer to an aliphatic polyester phase, and it will be difficult to acquire the effect of an improvement in fracture resistance.

  The content of the plasticizer is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the total amount of the lactic acid polymer and the aliphatic polyester resin. In particular, it is more preferably 2 to 5 parts by mass. If it is an addition amount of 15 parts by mass or less, the glass transition temperature of the mixed resin part can be secured in a range that can be used as a heat shrinkable film.

(Laminated structure)
The heat-shrinkable film of the present invention can have a laminated structure. In particular, a central layer containing a lactic acid polymer, an aliphatic polyester resin other than the lactic acid polymer, and a plasticizer is provided, and an outer layer containing 90% by mass or more of the lactic acid polymer is laminated on the outside thereof. The structure formed is preferable.

  The outer layer preferably contains a lactic acid-based polymer as a main component in applications where transparency is required. Lactic acid polymers and aliphatic polyesters have different deformation behaviors when stretched, so when stretching a mixture of both resins, surface roughness may occur and haze increases significantly, resulting in loss of transparency. There is sex. This is because the haze increases due to the diffusion of transmitted light and the transparency is lowered. However, by laminating an outer layer mainly composed of a highly transparent lactic acid polymer on the surface of the central layer, it is possible to suppress the diffusion of transmitted light and ensure transparency.

  The content of the lactic acid polymer in the outer layer is 90% by mass or more, preferably 95% by mass or more, and more preferably 100% by mass. When the amount of the polylactic acid polymer is 90% by mass or more, the surface roughness during stretching is small, and the role as the outer layer can be sufficiently achieved. Further, the lactic acid polymer of the outer layer may be the same lactic acid polymer as the lactic acid polymer constituting the central layer or may be different. Although not particularly limited, crystallinity may be imparted to some extent in order to prevent the film from fusing and forming holes by contacting the film while it is covered in a hot state. preferable.

  The outer layer is preferably formed so as to be thicker than the average height of the rough surface roughness of the center layer surface. Specifically, it is preferable to form 1 μm or more, preferably 2 μm or more. When the outer layers are formed on both outer sides of the central layer, it is preferable from the viewpoints of shrinkage characteristics and curling prevention that the both outer layers have the same thickness and the same composition, but it is not necessarily limited thereto.

  Even if the outer layer is not provided on both outer sides of the central layer, other layers may be present further outside the outer layer as long as the characteristics of the present invention are not impaired.

(Inorganic particles)
In addition, inorganic particles can be added to the outer layer for the purpose of improving the slipperiness between films. Such inorganic particles move to the surface during stretching and have a function of imparting slipperiness by roughening the surface.

  Specific examples of inorganic particles include inorganic particles such as silica, talc, and kaolin. The average particle size is preferably about 0.5 to 5 μm. The addition amount is preferably 0.01 parts or more and 5.0 parts or less, and more preferably 0.05 parts or more and 3.0 parts or less, with respect to 100 parts by mass of the outermost resin layer.

(Production method)
Next, although the manufacturing method of the heat-shrinkable film of this invention is demonstrated concretely, the manufacturing method of the heat-shrinkable film of this invention is not limited to the following manufacturing method.

A lactic acid polymer and, if necessary, an aliphatic polyester and other components are blended in a predetermined manner. At this time, a heat stabilizer, a light stabilizer, a light absorber, a lubricant, a plasticizer, an inorganic filler, a colorant, a pigment, and the like can be added for the purpose of adjusting various physical properties. This mixture (mixture) is melted by an extruder, and a predetermined amount of a plasticizer is added by extrusion from a vent groove or an injection groove in the middle of the extruder and extruded. However, a plasticizer may be mixed with the aliphatic polyester in advance.
In extruding, an existing method such as a T-die method or a tubular method can be arbitrarily employed. At that time, it is necessary to set the temperature in consideration of a decrease in molecular weight due to decomposition.

The melt-extruded resin is cooled with a cooling roll, air, water, etc., and then reheated by a suitable method such as hot air, hot water, infrared rays, microwaves, etc., and uniaxially by a roll method, a tenter method, a tubular method, etc. Or it extends to biaxial. At this time, the stretching temperature needs to be adjusted according to the required application of the heat-shrinkable film such as the mixing ratio and the crystallinity of the lactic acid-based polymer, but may be controlled in the range of about 70 to 95 ° C. The draw ratio needs to be adjusted according to the required application of the heat-shrinkable film, such as the mixing ratio and the crystallinity of the lactic acid-based polymer, but is determined appropriately in the range of 1.5 to 6 times in the main shrinkage direction. do it. Whether to use uniaxial stretching or biaxial stretching may be determined depending on the intended use of the product.
In general, it is most preferable to suppress longitudinal shrinkage by lateral uniaxial stretching, but in this case, the direction perpendicular to the lateral uniaxial direction is in an unstretched state, and thus the fracture resistance is insufficient. Sometimes. For this reason, it is preferable to stretch in the vertical direction. For example, by adding the above-mentioned specific plasticizer, both the vertical shrinkage and the breakage resistance in the vertical direction can be achieved, and only the horizontal stretching or the minimum Fracture resistance can be imparted by only limited longitudinal stretching.

(Haze)
Further, the transparency is not particularly limited in the present invention. However, in the case of usage in which transparency is important, the haze value (JIS K 7105) is 10% or less, particularly 7% or less, and especially 5%. The following is preferable.

(Hydrolysis inhibitor)
In the heat-shrinkable film according to the present invention, a hydrolysis inhibitor can be added for the purpose of imparting durability at high temperature and high humidity.

Examples of the hydrolysis inhibitor preferably used in the present invention include carbodiimide compounds. Preferred examples of the carbodiimide compound include those having a basic structure represented by the following general formula.

-(N = C = N-R-) _n-

In the formula, n represents an integer of 1 or more, and R represents an organic bond unit. For example, R can be either aliphatic, alicyclic, or aromatic. In addition, n is generally an appropriate integer selected from 1 to 50.

  Specifically, for example, bis (dipropylphenyl) carbodiimide, poly (4,4′-diphenylmethanecarbodiimide), poly (p-phenylenecarbodiimide), poly (m-phenylenecarbodiimide), poly (tolylcarbodiimide), poly ( Examples of the carbodiimide compound include diisopropylphenylenecarbodiimide), poly (methyl-diisopropylphenylenecarbodiimide), poly (triisopropylphenylenecarbodiimide), and the like. These carbodiimide compounds may be used alone or in combination of two or more.

  In this invention, it is preferable to add 0.1-3.0 mass parts of carbodiimide compounds with respect to 100 mass parts of resin which has a lactic acid polymer as a main component which comprises a film. If the addition amount of the carbodiimide compound is 0.1 parts by mass or more, the hydrolysis resistance improving effect is sufficiently exhibited in the obtained film. Moreover, if the addition amount of a carbodiimide compound is 3.0 mass parts or less, there will be little coloring of the film obtained and sufficient durability improvement can be aimed at.

(Biodegradation)
The heat-shrinkable film of the present invention can be decomposed by microorganisms when disposed in landfills, and does not cause various problems associated with disposal. The aliphatic polyester resin mainly composed of a lactic acid polymer is hydrolyzed by microorganisms or the like in the soil after the ester bond is hydrolyzed in the soil and the molecular weight is reduced to about 1,000.

  On the other hand, aromatic polyester-based resins such as polyethylene terephthalate have high intramolecular bond stability, and hydrolysis of ester bond portions hardly occurs. Therefore, even if the aromatic polyester resin is buried in the soil, the molecular weight does not decrease and biodegradation by microorganisms or the like does not occur. As a result, there are problems such as remaining in the soil for a long time, promoting the shortening of the landfill site for waste disposal, and damaging the natural landscape and the living environment of wild animals and plants.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples, and various applications are possible without departing from the technical idea of the present invention. In addition, the measured value and evaluation which are shown to an Example were performed as shown below. Here, the film take-up (flow) direction is indicated by MD, and its orthogonal direction is indicated by TD.

(Measurement and evaluation method)

(1) Shrinkage rate in the TD direction of the film A film was cut into a size of 70 mm in the measurement direction and 10 mm in the direction perpendicular to the measurement direction to prepare a sample. And the marked line of 50 mm space | interval was attached | subjected to the sample measurement direction, it was immersed in the 80 degreeC warm water bath for 10 second, and it calculated | required by the following formula. In the formula, L represents a marked line interval (unit: mm) after contraction.

Shrinkage rate = [(50−L) / 50] × 100 (%)

(2) Shrinkage stress Each film was cut into a width of 10 mm and a length of 70 mm in the TD direction, chucked at 50 mm, and fixed in a load cell so that there was no sagging. Then, the sample piece was immersed in a silicon bath at 80 ± 0.5 ° C., and the stress after 1 minute was measured. The shrinkage stress was calculated by applying the following formula.

Shrinkage stress (MPa) = stress applied to load cell (N) / cross-sectional area of sample piece (mm 2)

(3) Haze Haze was measured according to JIS K7105.

(4) Primary workability A lunch box made of polystyrene having a length of 22 cm, a width of 14.5 cm, and a depth of 3.5 cm is filled with 500 g of white rice, and has a width of 8 cm and a folding diameter (length when folded into two) of 18.4 cm. A cable tie made of each film was placed in the center of the lunch box, and an iron plate was placed on top to prevent hot air from hitting it.
And the container which put the iron plate was flowed so that a hot air might hit the side of a container to the hot air shrinker (form T-350) made from a caterpillar type Nagata. A hot air temperature of 190 ° C. was passed for 5 seconds, and the condition of whether or not the lunch box lid was tightly bound without opening was compared.
○: The lunch box lid is tightly bound without opening.
Δ: The lunch box lid does not open, but the film is likely to come off.
× (+): The lunch box was crushed.
X (-): The lunch box cover is slightly empty and insufficiently contracted.

(5) Lunch box crushing Polystyrene lunch box 22cm long, 14.5cm wide, 3.5cm deep is packed with 500g of white rice, 8cm wide and folded (length when folded into two) 18.4cm A binding band made of each film was placed on the center of the lunch box and heated by a heat gun from the side of the lunch box to shrink only the side of the lunch box. Then, it heated for 4 minutes with the 500W microwave oven, and the crushing condition of the lunch box was compared. Evaluation was performed in three stages shown in the following table.
○: The lunch box did not collapse.
X: The lunch box was crushed.

[Example 1]
Lactic acid polymer 1 (Cargill Dow “Nature Works 4050”, L-lactic acid / D-lactic acid = 94.5 / 5.5, mass average molecular weight: 200,000) 50% by mass, lactic acid polymer 2 (Cargill “NatureWorks 4060” manufactured by Dow, L-lactic acid / D-lactic acid = 88.0 / 12.0, mass average molecular weight 200,000, 30% by mass, polycaprolactone (“Serguline PH-7” manufactured by Daicel Chemical Industries, Ltd., melting point: 61 C., glass transition temperature: -58.degree. C.) 12% by mass, polybutylene succinate (Showa Polymers "Bionore 1010", melting point: 114.degree. C., glass transition temperature: -32.degree. C.) 8% by mass of resin As a layer, a mixed resin containing 50% by mass of the lactic acid polymer 1 and 50% by mass of the lactic acid polymer 2 (0.15% of alumina silica having a particle diameter of 1.6 μm was added). The intermediate layer and the mixed raw material of the outer layer are kneaded in a separate extruder at 190 ° C. to 210 ° C., and the di (2- Ethylhexyl) azelate (DOZ: SP value 8.96) is added from 3 parts by mass vent groove, and merged in a T die at 200 ° C., and a melt composed of a two-layer three-layer structure of surface layer / intermediate layer / back layer is obtained. The sheet was quenched with a casting roll at about 36 ° C. to obtain an unstretched sheet. This unstretched sheet was roll-stretched 1.08 times at 60 ° C. in the longitudinal direction, then stretched 3.5 times at 65 ° C. in the width direction, and a heat-shrinkable film having a thickness of 50 μm (lamination ratio: 5 μm / 40 μm / 5 μm) ) Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Example 2]
Lactic acid-based polymer 1 (“Nature Works 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, mass average molecular weight: 200,000) 25% by mass, lactic acid-based polymer 2 (Cargill “NatureWorks 4060” manufactured by Dow, L-lactic acid / D-lactic acid = 88.0 / 12.0, mass average molecular weight 200,000, 55% by mass, polycaprolactone (“Serguline PH-7” manufactured by Daicel Chemical Industries, Ltd., melting point: 61 C., glass transition temperature: -58.degree. C.) 12% by mass, polybutylene succinate (Showa Polymers "Bionore 1010", melting point: 114.degree. C., glass transition temperature: -32.degree. C.) 8% by mass of resin As a layer, a mixed resin containing 40% by mass of the lactic acid polymer 1 and 60% by mass of the lactic acid polymer 2 (0.15% of alumina silica having a particle diameter of 1.6 μm was added). The intermediate layer and the mixed raw material of the outer layer are kneaded in a separate extruder at 190 ° C. to 210 ° C., and the di (2- Ethylhexyl) azelate (DOZ: SP value 8.96) is added from a 5 mass part vent groove, and merged in a T-die at 200 ° C., and a melt comprising a surface layer / intermediate layer / back layer two-layer / three-layer structure is obtained. The sheet was quenched with a casting roll at about 36 ° C. to obtain an unstretched sheet. This unstretched sheet was roll-stretched 1.02 times at 60 ° C. in the longitudinal direction, and then stretched 3.5 times at 65 ° C. in the width direction to give a heat-shrinkable film having a thickness of 50 μm (lamination ratio: 5 μm / 40 μm / 5 μm). ) Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Example 3]
Lactic acid-based polymer 1 (“Nature Works 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, mass average molecular weight: 200,000) 45% by mass, lactic acid-based polymer 2 (Cargill “NatureWorks 4060” manufactured by Dow, L-lactic acid / D-lactic acid = 88.0 / 12.0, weight average molecular weight 200,000) 45% by mass, polybutylene succinate / adipate which is an aliphatic polyester (trade name: Bionore #) 3003: manufactured by Showa High Polymer Co., Ltd.) 10% by weight of mixed resin is kneaded at 190 to 210 ° C. with an extruder, melt extruded from a T die at 200 ° C., and the melt is rapidly cooled with a casting roll at about 36 ° C. An unstretched sheet was obtained. This unstretched sheet was roll-stretched 1.02 times at 60 ° C. in the longitudinal direction, and then stretched 4.0 times at 75 ° C. by a tenter in the width direction to obtain a heat-shrinkable film of about 50 μm. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Example 4]
A lactic acid-based polymer (“Nature Works 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, mass average molecular weight: 200,000) was kneaded at 190 to 210 ° C. with an extruder. The melt was extruded through a T-die at 200 ° C., and the melt was quenched with a casting roll at about 36 ° C. to obtain an unstretched sheet. This unstretched sheet was roll-stretched 1.02 times at 60 ° C. in the longitudinal direction, and then stretched 4.0 times at 78 ° C. by a tenter in the width direction to obtain a heat-shrinkable film of about 50 μm. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 1]
An unstretched sheet was obtained from the resin having the same structure as in Example 2 in the same manner. This unstretched sheet was roll-stretched 1.02 times at 60 ° C. in the longitudinal direction and then stretched 5.0 times at 63 ° C. in the width direction, and a heat-shrinkable film having a thickness of 50 μm (lamination ratio: 5 μm / 40 μm / 5 μm) ) Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 2]
Lactic acid-based polymer 1 (“Nature Works 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, mass average molecular weight: 200,000) 45% by mass, lactic acid-based polymer 2 (Cargill “NatureWorks 4060” manufactured by Dow, L-lactic acid / D-lactic acid = 88.0 / 12.0, mass average molecular weight 200,000) 45% by mass, polybutylene succinate / adipate which is an aliphatic polyester (manufactured by Showa Polymer “ (Bionole 3003), melting point: 94 ° C., glass transition temperature: −45 ° C.) 10% by mass of resin as an intermediate layer, the lactic acid polymer 1 is 40% by mass, and the lactic acid polymer 2 is 60% by mass. The mixed resin (0.15% of alumina silica having a particle size of 1.6 μm added) was used as an outer layer raw material, and the intermediate layer and outer layer mixed raw materials were 190 ° C. in separate extruders. Kneaded at 210 ° C, merged in a T-die at 200 ° C, and rapidly melted the melt composed of two layers and three layers of surface layer / intermediate layer / back layer with a casting roll at about 36 ° C, Obtained. This unstretched sheet was roll-stretched 1.02 times at 60 ° C. in the longitudinal direction, and then stretched 4 times at 76 ° C. in the width direction to obtain a heat-shrinkable film having a thickness of 50 μm (lamination ratio: 6 μm / 38 μm / 6 μm). Obtained. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 3]
An unstretched sheet was obtained from the resin having the same structure as that of Comparative Example 2 in the same manner. This unstretched sheet was roll-stretched 1.02 times at 60 ° C. in the longitudinal direction, then stretched 3.0 times at 76 ° C. in the width direction, and a heat-shrinkable film having a thickness of 50 μm (lamination ratio: 6 μm / 38 μm / 6 μm) ) Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 4]
Starting from 32.4 kg of terephthalic acid, 14.5 kg of ethylene glycol and 12.5 kg of polytetramethylene ether glycol (number average molecular weight 1000), as a catalyst and a co-catalyst, 3.2 g of tetrabutoxytitanate, 1.3 g of normal phosphoric acid, Copolymer polyester resin was prepared by direct polycondensation at 270 ° C. and 400 Pa using 10.0 g of cobalt acetate and 50 g of amorphous silica having an average particle size of 2.4 μm (“Silysia 320” manufactured by Fuji Silysia). Obtained. The copolyester resin was extracted in the form of a strand from the polycondensation tank, cooled, and then cut with a pelletizer to be recovered in a pellet form. The copolymerized polyester resin thus obtained had an intrinsic viscosity of 0.79 and a polytetramethylene ether glycol copolymerization amount of 19.8% by mass. And with the extruder, said resin was extruded from the T-die mouthpiece on the cooling roll, pulling a vacuum vent, and the sheet | seat of width 150mm thickness 0.20mm was obtained. Thereafter, the above sheet was transferred to T.W. M.M. Using a “Film Stretcher” manufactured by Long as standard specifications, the film was stretched 4 times in the direction perpendicular to the casting extrusion direction at a stretching temperature of 56 ° C. and a stretching speed of 3000% / min. A film was obtained. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 5]
The following copolymerized polyester resin A and copolymerized polybutylene terephthalate resin B were mixed at a ratio of 75:25 to form a raw material resin, and a sheet was formed in the same manner as in Comparative Example 4 except that the stretching temperature was changed to 60 ° C. The film was stretched to obtain a heat-shrinkable film. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

<Copolymerized polyester resin A>
The dicarboxylic acid component is terephthalic acid, the diol component is ethylene glycol, the copolymer component is 10.8 mol% isophthalic acid (ratio to the total dicarboxylic acid component), and 19.2 mol% 1,4-cyclohexanedimethanol (total diol It was prepared by adding 0.3% by mass of amorphous silica (“Silysia 320” manufactured by Fuji Silysia) having an average particle diameter of 2.4 μm to the copolyester resin, which is a ratio to the component.

<Copolymerized polybutylene terephthalate resin B>
The dicarboxylic acid component is terephthalic acid, the diol component is 1,4-butanediol, the copolymerization component is 7.5 mol% isophthalic acid (ratio to the total dicarboxylic acid component), and polytetramethylene ether glycol (number average molecular weight 1000). It is 8 mass% (ratio to the total diol component).

As can be seen from Table 1, Examples 1, 2, 3 and 4 all had good primary workability and the lunch box was not crushed by microwave heating. In Examples 1, 2, and 4, the haze was low and the transparency was excellent.
In particular, in Examples 1 and 2, even when heated in a 1000 W microwave oven for 3 minutes, the lunch box was not crushed at all and was superior to Examples 3 and 4.

On the other hand, since the shrinkage rate of Comparative Example 1 was high, the lunch box was crushed during the primary processing. In Comparative Example 2, the primary processing could be performed without any problem, but because the shrinkage stress was high, the lunchbox collapse occurred during the microwave processing. Since the shrinkage rate of Comparative Example 3 was low, the film was likely to fall off during the primary processing. In Comparative Example 4, although the collapse of the lunch box did not occur, the rate of shrinkage was low, so that the lunch box lid was open during the primary processing. In Comparative Example 5, the primary workability was good, but the lunch box was crushed because the shrinkage stress was high.

Claims (7)

  A heat-shrinkable film having a lactic acid polymer as a main component, and having a shrinkage rate of 30% or more and less than 60% in 10 seconds when immersed in hot water at 80 ° C in at least one direction. A heat-shrinkable film, wherein the shrinkage stress after 1 minute in oil is less than 5 MPa.   The heat-shrinkable film according to claim 1, wherein the lactic acid polymer has a constituent ratio of D lactic acid and L lactic acid of 98: 2 to 85:15 or 2:98 to 15:85.   A central layer containing a lactic acid polymer, an aliphatic polyester resin other than the lactic acid polymer, and a plasticizer is provided, and an outer layer containing 90% by mass or more of the lactic acid polymer is laminated on the outside thereof. The heat-shrinkable film according to claim 1, further comprising:   4. The heat according to claim 3, wherein the aliphatic polyester resin has at least one glass transition temperature at 0 ° C. or lower, and its content in the central layer is 10 to 25 mass%. Shrink film.   The heat-shrinkable film according to any one of claims 1 to 4, wherein the film is reheated after shrink-wrapping.   The heat-shrinkable film according to any one of claims 1 to 5, wherein the heat-shrinkable film is used as a binding band for a container heated together with contents in a microwave oven. The heat-shrinkable film according to claim 6, wherein the container is a food container.