JP2006273346A - Thermally shrinkable film for container lid material, and container lid material using thermally shrinkable film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally shrinkable film for a container lid material which has a superior low-temperature high shrinkability, prevents the shrinking deformation of a container even after subjecting the container to a shrinkage process, and provides superior unsealability, and also to provide the container lid material using the film. <P>SOLUTION: The thermally shrinkable film is mainly composed of a lactic acid polymer. The film shows a shrinkage rate of 25% or higher to less than 50% in both machine direction (MD) and transverse direction (TD) of the film when soaked in warm water of 80°C for 10 minutes, a shrinkage stress of less than 4 MPa in both machine direction (MD) and transverse direction (TD) of the film after having been soaked in silicon oil of 80°C for 1 minute, and a haze value (JIS K 7105) of 5% or higher. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a heat-shrinkable film mainly composed of a lactic acid-based polymer. It is a film for container lids such as inner lids, and it is difficult for the container to deform during shrinkage processing, and the opening opening is less shrinkage-deformed after processing, has excellent openability, and is heat-shrinkable for this application The present invention relates to a heat-shrinkable film for container lids and a lid using the same.

In recent years, heat-shrinkable lids have been printed on stretched films made of polyester resin for lids for aluminum containers such as pot-baked udon and miso soup and plastic containers such as PSP (polystyrene paper) sold at convenience stores. Is used.
These are pre-printed on a stretched film and then heat-shrinked into an aluminum or plastic container and displayed as a product. And after a user purchases this, it opens from the opening opening provided in a part of container lid | cover material, and uses it.

In addition, a heat-shrinkable cover material obtained by printing on a stretched film made of a polyester resin by the same processing method is used as a cover material for a container for cosmetics and toiletries.
Many of these cosmetic / toiletry-related inner lid materials are plain and may not have an opening.

  By the way, when heat-shrinkable films made of these polyester-based resins are discarded in the natural environment after use, they 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.

  In addition, since the container lid material using a polyester heat-shrinkable film has a large shrinkage stress, the container is easily deformed during processing, and the opening of the V notch or the like is greatly deformed during the shrinking process and is difficult to open. There's a problem.

On the other hand, many researches and developments have been conducted on materials composed of biodegradable polymers that do not cause these environmental problems and decompose under the environment. An example of the biodegradable polymer is polylactic acid. It is known that this polylactic acid is naturally hydrolyzed in the soil, remains in its original form in the soil, and then becomes a harmless decomposition product by microorganisms.
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 1).

JP 2002-46116 A

As described above, the polyester-based heat-shrink film currently used has a very high shrinkage stress when the shrinkage rate is increased, so that the container is easily deformed during processing. There is a problem that the opening is greatly deformed during shrinkage and is difficult to open.
Thus, in order to suppress the shrinkage stress, a contrivance such as setting the shrinkage rate low is made. However, when the shrinkage rate is low, it is necessary to increase the shrinking processing temperature or lengthen the processing time in order to cover it cleanly. As a result, the container may be deformed or the opening property (opening opening remains after processing). Or the contents of the container are affected. As described above, it is difficult for polyester-based heat-shrinkable films to make shrinkage processability, container deformation and unsealing properties compatible and difficult to use.

  In addition, from the viewpoint of environmental suitability, Patent Document 1 discloses that a lunch box or a sheet-like material made of a lactic acid polymer is used as a binding band for a container. There is no disclosure about the required quality of the.

  Therefore, the present invention has been made to solve these problems, that is, the object of the present invention is to have excellent low-temperature high-shrinkage properties, and to prevent container deformation due to shrinkage even after shrinkage processing. And the heat-shrinkable film for container lid materials which has the outstanding openability, and a container lid material using the same are provided.

(1) The heat-shrinkable film for a container lid material of the present invention is a heat-shrinkable film mainly composed of a lactic acid-based polymer, and the shrinkage rate in 10 seconds when immersed in warm water at 80 ° C. The film drawing direction (MD) and its perpendicular direction (TD) are both 25% or more and less than 50%, and the shrinkage stress after 1 minute in 80 ° C. silicone oil is the film drawing direction (MD) and its perpendicular direction. The direction (TD) is less than 4 MPa, and the haze value (JIS K 7105) is 5% or less.
(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) The heat-shrinkable film for container lid material of the present invention can be used as a lid material for aluminum or plastic containers.
(4) The container lid material of the present invention is characterized by using any one of the above-described heat-shrinkable films for a container lid material, and further provided with a notch for opening.

  According to the present invention, it has excellent low-temperature and high-shrinkage properties, and even after shrinkage processing, it has the ability to prevent food container deformation due to shrinkage and has excellent openability, and is further excellent in environmental suitability. Film and a container lid using the same 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 a range that does not impair the function of the lactic acid-based polymer. The meaning that it may contain is 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.

The present invention will be described in detail below.

(Container processing process)
A processing process for food containers, which is one of the applications in which the present invention can be used, will be described.
First, the stretched film is printed and cut according to the shape and size of the product with a cutting machine. At this time, a notch for opening such as a V notch and a W notch is provided on one surface. This is manually attached to a plastic container such as aluminum or PSP containing the product, and the container for each film is poured on the belt conveyor sandwiched between the upper and lower sides, and heated air is blown out from the hot air nozzle built in the side, By shrinking the film, the film is wrapped around the edge of the container. Furthermore, it is a general processing method to give the film a tight feeling by applying heated air to the upper part after being released from the upper sandwiching conveyor.

  The cutting pattern for opening is generally V-notch, W-notch or the like, but depending on the product, a U-shaped protrusion may be provided on the contrary to form an opening. The reason why the heat-shrinkable film of the present invention is suitable for a container lid provided with an opening cut is that the shrinkage stress is low and the tearability is good. This is because if the shrinkage stress is low, the opening notch is less likely to be deformed even during heat shrinkage during shrinkage processing, and if tearing is good, smooth opening can be realized.

(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 too high, stretch orientation crystallization proceeds at the time of stretching, so it becomes difficult to adjust the heat shrinkage rate. Even if a film in a 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-hydroxy-3, 3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycapron 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, and 1,4-cyclohexanedimethanol.
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 weight average molecular weight of 10,000 to 400,000, preferably 50,000 to 300,000, and more preferably 100,000 to 300,000. 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 low temperature high shrinkage and low shrinkage stress properties to the heat shrinkable film.

  Since the content of the aliphatic polyester is an application for which transparency is required, it is preferably about 5 to 15% by weight in the layer containing the aliphatic polyester. If it is 5% by weight or more, sufficient low-temperature high shrinkage and low shrinkage stress properties can be obtained, and if it is 15% by weight or less, transparency can be sufficiently secured.

(Plasticizer)
The heat-shrinkable film for container lid materials of the present invention can contain a plasticizer. By including a plasticizer, it is possible to impart appropriate low temperature and high shrinkage and low shrinkage stress properties while maintaining transparency. 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 used in the present invention has an SP value of the aliphatic polyester whose solubility parameter (SP value) is higher than the SP value of the lactic acid polymer and the intermediate value of the SP value of the aliphatic polyester (excluding the lactic acid polymer). It is preferably close to the value. 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, it is possible to increase the low-temperature high-shrinkage and low-shrinkage stress properties of the film while reducing the amount of aliphatic polyester, and to minimize the decrease in transparency. Can do. The reason why such an effect is obtained is not clear, but can be considered as follows. That is, the addition of an aliphatic polyester to a lactic acid polymer improves low-temperature high-shrinkage and low-shrinkage stress properties. However, if the amount of the added aliphatic polyester is large, the transparency inherent in the lactic acid polymer is impaired. End up. Therefore, it is preferable to plasticize the aliphatic polyester with a plasticizer to plasticize the aliphatic polyester to increase its low-temperature shrinkage so that the shrinkage 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 difference in refractive index between the lactic acid-based polymer and the aliphatic polyester is reduced, and the low-temperature high-shrinkage and low-shrinkage stress properties can be improved while maintaining transparency.

  The content of the plasticizer is preferably 3 to 10 parts by mass, and more preferably 5 parts by mass with respect to 100 parts by mass of the total amount of the lactic acid polymer and the aliphatic polyester resin. If the addition amount is 3 parts by weight or more, sufficient low temperature shrinkage can be obtained.

(Laminated structure)
The heat-shrinkable film for container lid materials of the present invention can be composed not only of a single layer but also of a laminated structure. For example, a central layer containing a lactic acid polymer and an aliphatic polyester resin or plasticizer other than the lactic acid polymer is provided, and an outer layer containing 90% by mass or more of the lactic acid polymer is laminated on the outside thereof. It can also be the composition which consists of.

  The outer layer preferably contains a lactic acid-based polymer as a main component from the viewpoint of improving transparency. 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.

  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 weight of the outermost resin layer.

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

A lactic acid polymer, an aliphatic polyester, and other components are blended and mixed. At this time, for the purpose of adjusting various physical properties, 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 as necessary. 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. In the use of the film of the present invention, it is preferably stretched in two directions. At this time, the stretching temperature needs to be adjusted according to the required use of the heat-shrinkable film such as the mixing ratio and the crystallinity of polylactic acid, but may be controlled in the range of about 70 to 95 ° C. The draw ratio needs to be adjusted according to the specific required use of the heat-shrinkable film for container lids, such as the mixing ratio and the crystallinity of polylactic acid, but is generally 1.5 to 6 times in the main shrinkage direction. What is necessary is just to determine suitably in the range.

(Shrinkage rate and shrinkage stress)
The heat shrinkable film for container lids of the present invention has a heat shrinkage rate of 25% or more and less than 50% for 10 seconds in 80 ° C hot water in both the film take-off direction (MD) and its orthogonal direction (TD). The shrinkage stress after 1 minute in silicon oil must be less than 4 MPa in both the film take-up direction (MD) and its orthogonal direction (TD). That is, when the shrinkage rate in 10 seconds when immersed in warm water at 80 ° C. is less than 25%, sufficient shrinkage characteristics cannot be obtained. If the shrinkage rate in 10 seconds when immersed in warm water at 80 ° C exceeds 50%, or if the shrinkage stress after 1 minute in 80 ° C silicone oil exceeds 4 MPa, the deformation of the container and the opening of the opening can be suppressed. I can't. The shrinkage rate range is more preferably 30% or more to cope with recent protection of contents and high processing speed, and 48% or less in consideration of suppressing the probability of container deformation and opening deformation. preferable. The shrinkage stress is more preferably 3 MPa or less.

(Haze)
As for transparency, it is necessary to make the contents look beautiful. Therefore, the haze value (JIS K 7105) needs to be 5% or less. Especially, it is preferable to set it as 3.5% or less especially. When the haze value is 5% or less, there is no problem with the design because the film does not feel cloudy with the naked eye.

(Processing method for container lid)
The printed film is cut individually according to the shape and size of the product using a cutting machine. The shape at this time is generally an octagonal shape. In addition, the octagonal surface is cut into a shape such as a V-notch and a W-notch with a dedicated cutting blade.

(Biodegradation)
The heat-shrinkable film for a container lid material and the container lid material using the same according to the present invention can be decomposed by microorganisms when disposed in landfills, and various problems associated with disposal do not occur. The aliphatic polyester resin mainly composed of a lactic acid polymer is hydrolyzed by microorganisms and 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 ratio of MD / TD of film The 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 MD and TD into a width of 10 mm and a length of 70 mm, chucked at 50 mm, and fixed to 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) Shrinkability, container deformation, openability
A 500 g weight is placed in an aluminum container having a radius of about 200 mm and a height of about 50 mm, and an octagonal film slightly larger than the container is placed on top. A V-notch is made on one side of the octagon as an opening for the film. First, an iron plate is put on the upper part so that hot air does not hit, and the container on which the iron plate is put is passed to a caterpillar Hanagata hot air shrinker: type T-350 so that hot air hits the side of the container. After passing through a hot air temperature of 190 ° C. for 5 seconds, the iron plate is removed, and it is made to flow again into the shrinker under the same conditions to shrink the top part and give a tight feeling. The condition of the coated container and film was compared.
(4-1) Shrinkage workability ○: The lid is tightly covered without opening.
X: Wrinkles due to opening of the lid or insufficient contraction on the top are observed.
(4-2) Container deformation ○: Container is not deformed.
X: The container is slightly warped in the upper part.
(4-3) Openability ○: The V-notch for opening remains clean and the lid is easy to open.
X: V-notch for opening is deformed by contraction, and it is difficult to open the lid.

[Example 1]
A lactic acid polymer (“Nature Works 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, weight 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 3 times at 62 ° C. in the longitudinal direction, and then stretched 3.5 times at 85 ° C. by a tenter in the width direction to obtain a heat-shrinkable film of about 25 μm. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Example 2]
Lactic acid-based polymer (“NatureWorks 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, weight average molecular weight: 200,000) 100% by mass as an intermediate layer, the lactic acid-based polymer The outer layer raw material is 100% by mass of resin to which 0.15% of alumina silica having a particle size of 1.6 μm is added, and the intermediate layer and outer layer raw materials are kneaded at 190 ° C. to 210 ° C. in separate extruders, Di (2-ethylhexyl) azelate (DOZ: SP value 8.96) is added from 5 parts by mass vent groove to 100 parts by mass of the mixed resin constituting the intermediate layer, and merged in a T die at 200 ° C. The melt composed of two types / three layers of / intermediate layer / back layer was quenched with a casting roll at about 36 ° C. to obtain an unstretched sheet. This unstretched sheet was roll-stretched 3 times at 62 ° C. in the longitudinal direction, then stretched 3.5 times at 82 ° C. in the width direction, and a heat-shrinkable film having a thickness of 25 μm (lamination ratio: 2.5 μm / 20 μm / 2) 0.5 μm) was obtained. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Example 3]
90% by mass of a lactic acid polymer (“NatureWorks 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, weight average molecular weight: 200,000), polycaprolactone (“Selgoulin, manufactured by Daicel Chemical Industries, Ltd.) PH-7 ”, melting point: 61 ° C., glass transition temperature: −58 ° C.) 10% by mass of resin as an intermediate layer, 0.15% alumina silica having a particle size of 1.6 μm is added as the lactic acid polymer. 100% by mass of the resin used as the outer layer raw material, the intermediate layer and the mixed raw material of the outer layer are kneaded at 190 ° C. to 210 ° C. in separate extruders and merged in a T die at 200 ° C., and the surface layer / intermediate layer / The melt composed of the two-layered three-layer structure of the back layer was quenched with a casting roll at about 36 ° C. to obtain an unstretched sheet. This unstretched sheet is stretched 3.0 times in the longitudinal direction at 62 ° C., then stretched 3.5 times in the width direction at 82 ° C., and a heat-shrinkable film having a thickness of 25 μm (lamination ratio: 2.5 μm / 20 μm). /2.5 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 1 in the same manner. This unstretched sheet is roll-stretched 3.0 times in the longitudinal direction at 62 ° C., then stretched 3.5 times in the width direction at 80 ° C., and a heat-shrinkable film having a thickness of 25 μm (lamination ratio: 2.5 μm / 20 μm) /2.5 μm). Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 2]
An unstretched sheet was obtained from the resin having the same structure as in Example 2 in the same manner. This unstretched sheet is roll-stretched 3.0 times in the longitudinal direction at 62 ° C., then stretched 3.5 times in the width direction at 78 ° C., and a heat-shrinkable film having a thickness of 25 μm (lamination ratio: 2.5 μm / 20 μm) /2.5 μm). Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 3]
Lactic acid-based polymer (“NatureWorks 4050” manufactured by Cargill Dow, L-lactic acid / D-lactic acid = 94.5 / 5.5, weight average molecular weight: 200,000) 80% by mass, polycaprolactone (manufactured by Daicel Chemical Co., Ltd. PH-7 ”, melting point: 61 ° C., glass transition temperature: −58 ° C.) Using 20% by mass of resin as an intermediate layer, 0.15% of alumina silica having a particle size of 1.6 μm is added as the lactic acid polymer. 100% by mass of the resin used as the outer layer raw material, the intermediate layer and the mixed raw material of the outer layer are kneaded at 190 ° C. to 210 ° C. in separate extruders and merged in a T die at 200 ° C., and the surface layer / intermediate layer / The melt composed of the two-layered three-layer structure of the back layer was quenched with a casting roll at about 36 ° C. to obtain an unstretched sheet. This unstretched sheet is stretched 3.0 times in the longitudinal direction at 62 ° C., then stretched 3.5 times in the width direction at 82 ° C., and a heat-shrinkable film having a thickness of 25 μm (lamination ratio: 2.5 μm / 20 μm). /2.5 μm). Table 1 shows the evaluation results of the obtained heat-shrinkable film.

[Comparative Example 4]
The following copolymer polyester resin and polybutylene terephthalate resin are mixed at a ratio of 85:15 to obtain a raw material resin, kneaded at 250 ° C. by an extruder, melt-extruded from a T-die at 250 ° C., and the melt is about The sheet was quenched with a 36 ° C. casting roll to obtain an unstretched sheet. This unstretched sheet was roll-stretched 4 times at 72 ° C. in the longitudinal direction and then stretched 5 times at 75 ° C. by a tenter in the width direction to obtain a heat-shrinkable film of about 25 μm. Table 1 shows the evaluation results of the obtained heat-shrinkable film.
<Copolymerized polyester resin>
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 1,4-cyclohexanedimethanol 19.2 mol% (total diol It was prepared by adding 0.3% by weight of amorphous silica (“Silysia 320” manufactured by Fuji Silysia) having an average particle size of 2.4 μm to the copolyester resin as a ratio to the component.

[Comparative Example 5]
An unstretched sheet was obtained from the resin having the same configuration as that of Comparative Example 4 by the same method. This unstretched sheet was 4.0 times roll-stretched at 72 ° C. in the longitudinal direction, then stretched 5 times at 90 ° C. in the width direction, and a heat-shrinkable film having a thickness of 25 μm (lamination ratio: 2.5 μm / 20 μm / 2) 0.5 μm) was obtained. Table 1 shows the evaluation results of the obtained heat-shrinkable film.

As is clear from Table 1, Examples 1, 2, and 3 all have excellent low-temperature and high-shrinkage properties, and even after shrinkage processing, they have food container deformation prevention due to shrinkage and excellent openability. Yes.
According to the present invention, the food container lid material has excellent low-temperature and high-shrinkability, has a food container deformation prevention due to shrinkage, has excellent openability even after shrinkage processing, and has excellent environmental suitability. A lactic acid heat-shrinkable film can be obtained.

On the other hand, Comparative Example 1 has a high shrinkage stress, and Comparative Example 2 has a high shrinkage rate. Therefore, deformation of the container and deformation of the opening portion were observed. Comparative Example 3 had excellent processability but high haze. Since the comparative example 4 had high shrinkage stress, the container deformation | transformation and the deformation | transformation of the opening part were seen. In Comparative Example 5, since the shrinkage rate was low, wrinkles due to insufficient shrinkage were observed in the top part although the lid was not opened.

Claims (4)

A heat-shrinkable film mainly composed of a lactic acid-based polymer, which has a shrinkage rate of 10 seconds when immersed in warm water at 80 ° C., in both the film take-up direction (MD) and its orthogonal direction (TD). 25% or more and less than 50%, the shrinkage stress after 1 minute in 80 ° C. silicone oil is less than 4 MPa in both the film take-up direction (MD) and its orthogonal direction (TD), and the haze value (JIS) A heat-shrinkable film for container lid materials, wherein K 7105) is 5% or less. 2. The heat shrinkage for a container lid 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. Sex film. The heat-shrinkable film for a container lid according to any one of claims 1 and 2, which is used as a lid for an aluminum or plastic container. A container lid material comprising the heat-shrinkable film for a container lid material according to any one of claims 1 to 3, and further provided with a notch for opening.