JP6759828B2 - A polylactic acid-based film, a heat-shrinkable film using the film, a molded product or a heat-shrinkable label using the heat-shrinkable film, and a container using the molded product or having the label attached. - Google Patents

Description

The present invention relates to a polylactic acid-based film having excellent transparency and rigidity. Further, the present invention relates to a heat-shrinkable film using the film, which has excellent shrinkage characteristics and excellent transparency and rigidity.

Polylactic acid-based resin is a plant-derived raw material made from lactic acid obtained by fermentation of starch, and is attracting attention from the viewpoints of measures against global warming and replacement of petroleum resources that are expected to be depleted in the future. While this polylactic acid-based resin has features such as excellent transparency and rigidity, it has a limitation in that it has a slow crystallization rate and is inferior in heat resistance when it is crystallized and used for a molded product or the like. Further, when used as a film, the glass transition temperature is relatively low, so that there is a limit to using it for heat-resistant applications. Various technical studies have been conducted on the modification of such polylactic acid-based resins.

On the other hand, cellulose derivatives such as cellulose and cellulosic esters are the most produced biomass materials on the earth, and are attracting attention from the same viewpoint as the above-mentioned polylactic acid-based resins. For example, a method of melt spinning by adding a water-soluble plasticizer such as polyethylene glycol to cellulose acetate is known, but the use of a highly hygroscopic plasticizer such as polyethylene glycol has limited applications. Therefore, a more general-purpose method was expected.

By the way, at present, most beverages such as tea, juice and coffee are sold in a container such as a PET bottle, and in recent years, PET bottle sales of alcoholic beverages such as wine have been seen. .. With this increasing variety, the importance of heat-shrinkable labels that are attached to differentiate products from other products and improve product visibility is increasing. Heat-shrinkable labels are used not only for beverages but also for various purposes such as foods, toiletries, medical products, chemical products, and industrial products.

This heat-shrinkable label is usually printed on the back side of the film in order to prevent the printed matter from slipping due to rubbing or scratching between containers, so high transparency is required for the raw film for heat-shrinkable labels. Will be done. Therefore, as the material of the film, a polyvinyl chloride resin, a polystyrene resin, an aromatic polyester resin, a polylactic acid resin and the like are used, and among them, the polylactic acid resin is used for the above viewpoints and the like. , Is also attracting attention as a material for heat-shrinkable films.

In addition, polylactic acid-based resins have high tensile elastic modulus and tensile strength, and can be thinned, so they are attracting attention in terms of environmental consideration. As the importance of environmentally friendly products will continue to increase, further improvement in the rigidity of polylactic acid is required.

By the way, a method of improving the characteristics of each resin by a polymer blend of a polylactic acid-based resin and a cellulose ester is known. For example, Patent Document 1 proposes a resin composition having flexibility and heat resistance by adding a natural product to a resin composition composed of a polymer component composed of polylactic acid and an aliphatic polyester and a plasticizer. .. Further, Patent Document 2 proposes a method for improving moldability by mixing an aliphatic polyester such as polylactic acid with a cellulose ester. Further, Patent Documents 3 and 4 propose resin compositions having transparency, mechanical properties, and heat resistance by mixing a polylactic acid resin, a cellulose ester, and a compatibilizer.

Japanese Unexamined Patent Publication No. 11-241008 Japanese Unexamined Patent Publication No. 2003-82160 WO2004 / 087812 Japanese Unexamined Patent Publication No. 2004-204217

However, the technique of Patent Document 1 includes starch, chitin, chitosan, and celluloses as natural products, and only acetyl cellulose is exemplified as the celluloses, and there is no specific example of actually blending them. Further, the technique of Patent Document 2 is only shown to improve the moldability of the cellulose ester, and does not mention the technique of improving the properties of polylactic acid. Further, Patent Documents 3 and 4 show that heat resistance is improved by a compatibilizer of polylactic acid, cellulose ester, and the polymer blend of polylactic acid and cellulose ester provides rigidity while maintaining transparency. There is no example showing the improvement of the above, and the technology having the property as a heat-shrinkable label is not mentioned.
As described above, in the prior art, it has not been studied so far to improve the rigidity of the polylactic acid-based resin and obtain a film having high transparency and a heat-shrinkable film.

The present invention has been made in view of the above problems, that is, an object of the present invention is to provide a polylactic acid-based film having excellent transparency and rigidity. Among them, it is an object of the present invention to provide a polylactic acid-based heat-shrinkable film having excellent shrinkage characteristics, high rigidity, and excellent transparency, which is suitable for applications such as shrinkage packaging, shrinkage binding packaging, and shrinkage label.

The present inventor has completed the following invention as a result of diligent studies to solve the problems of the prior art.
That is, the subject of the present invention is a mixed resin composition of a polylactic acid-based resin (A) and a cellulose ester (B) having an acetyl group content of 10 to 25% by mass and a butyryl group content of 25 to 45% by mass. At least one layer containing the above as a main component is provided, and the mixing ratio of (A) and (B) in the mixed resin composition is (A) / (B) = 92/8 to 55/45% by mass. , A polylactic acid-based film characterized by an internal haze value of 15% or less according to JIS K7136.

According to the present invention, a polylactic acid-based film having high transparency and rigidity can be obtained. Further, it is possible to obtain a heat-shrinkable film having excellent shrinkage characteristics, high rigidity and excellent transparency. Since the heat-shrinkable film has excellent shrinkage characteristics, high rigidity and transparency, it can be suitably used for applications such as shrinkage packaging, shrinkage binding packaging and shrinkage labels.

Hereinafter, a film as an example of an embodiment of the present invention (hereinafter referred to as “the film of the present invention”), a heat-shrinkable film of the present invention, a molded product of the present invention, a label of the present invention, and a container of the present invention will be described. To do. However, the scope of the present invention is not limited to the embodiments described below.

In addition, in this specification, "the main component" means that it is allowed to contain other components as long as it does not interfere with the action / effect of the resin contained as the main component. Further, although the term does not limit the specific content, it is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and 100% by mass or less of the total components. It is a component that occupies the range of.

<Film of the present invention>
The film of the present invention contains a polylactic acid-based resin (A) and a cellulose ester (B) as a resin composition.

<Polylactic acid resin (A)>
The polylactic acid-based resin (A) used in the present invention is a homopolymer of D-lactic acid or L-lactic acid, or a copolymer thereof, and specifically, poly (specifically, the structural unit is D-lactic acid. D-lactic acid), poly (L-lactic acid) whose structural unit is L-lactic acid, poly (DL-lactic acid) which is a copolymer of L-lactic acid and D-lactic acid, and D-lactic acid A mixed resin of a plurality of the above copolymers having different copolymerization ratios with L-lactic acid is also included.

The copolymer of L-lactic acid and D-lactic acid has a copolymerization ratio of D-lactic acid and L-lactic acid (hereinafter abbreviated as "D / L ratio"), preferably from "1/99". It is "10/90" or "90/10" to "99/1", more preferably "1/99" to "9.5 / 90.5" or "90.5 / 9.5" to "90.5 / 9.5". It is "99/1", more preferably "1/99" to "9/91" or "91/9" to "99/1".
When the D / L ratio is higher than 99 or less than 1, it exhibits high crystallinity, has a high melting point, and tends to be excellent in heat resistance and mechanical properties. However, when it is used as a heat-shrinkable film, it usually involves printing and a bag making process using a solvent, so that the crystallinity of the constituent material itself can be appropriately lowered in order to improve printability and solvent sealability. You will need it. Further, when the crystallinity is excessively high, orientation crystallization proceeds during stretching, and the film shrinkage characteristics during heating tend to deteriorate. Further, even if the film suppresses crystallization by adjusting the stretching conditions, crystallization proceeds before shrinkage due to heating during heat shrinkage, and as a result, uneven shrinkage and insufficient shrinkage tend to occur. ..

On the other hand, when the D / L ratio is less than 90 and higher than 10, the crystallinity is almost completely lost, and as a result, when the labels collide with each other after heat shrinkage, they are fused by heat. Trouble may occur. Further, in the stretching process, it tends to be difficult to make the thickness uniform in the width direction, and it is difficult to impart surface smoothness, which tends to impair transparency.
By adjusting the D / L ratio within the above range, it is possible to obtain a heat-shrinkable film having excellent shrinkage characteristics without causing such a problem. In the film of the present invention, it is also possible to blend polylactic acid-based resins having different D / L ratios. It is preferable to blend polylactic acid-based resins having different D / L ratios because the D / L ratio of the polylactic acid-based resin can be adjusted relatively easily. In this case, the average value of the D / L ratios of the plurality of lactic acid-based polymers may be within the above range. By blending two or more types of polylactic acid-based resins having different D / L ratios and adjusting the crystallinity according to the intended use, heat resistance and heat shrinkage characteristics can be balanced.

Further, the polylactic acid-based resin (A) is a non-aliphatic dicarboxylic acid other than lactic acid, such as α-hydroxycarboxylic acid and terephthalic acid, as a small amount of copolymerization component as long as the essential properties are not impaired. At least one selected from the group consisting of an aliphatic dicarboxylic acid such as acid and succinic acid, a non-aliphatic diol such as an ethylene oxide adduct of bisphenol A, and an aliphatic diol such as ethylene glycol can be used. Further, for the purpose of increasing the molecular weight, a small amount of chain extender, for example, a diisocyanate compound, an epoxy compound, an acid anhydride or the like can be used.

Specific examples of α-hydroxycarboxylic acid other than lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, and 2-hydroxy-. Examples thereof include bifunctional aliphatic hydroxycarboxylic acids such as 3-methylbutyric acid, 2-methyllactic acid and 2-hydroxycaproic acid, and lactones such as caprolactone, butyrolactone and valerolactone.
Specific examples of the dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid and the like, and examples of the diol include ethylene glycol, 1,4-butanediol and 1, Examples thereof include 4-cyclohexanedimethanol.

The copolymerization ratio of lactic acid and a copolymer of α-hydroxycarboxylic acid other than lactic acid, diol, or dicarboxylic acid [lactic acid / (α-hydroxycarboxylic acid other than lactic acid, diol, or dicarboxylic acid)] is particularly limited. However, in terms of mass ratio, it is preferably "100/0" to "50/50", more preferably "100/0" to "60/40", and even more preferably "100/0" to "70/30". Is. When the copolymerization ratio is within the above range, a film having a good balance of physical properties such as rigidity, transparency and impact resistance can be obtained. In addition, examples of the structures of these copolymers include random copolymers, block copolymers, and graft copolymers, and any structure may be used. However, from the viewpoint of impact resistance and transparency of the film, block copolymers or graft copolymers are preferable.

The weight average molecular weight of the polylactic acid-based resin (A) is 20,000 or more, preferably 40,000 or more, more preferably 60,000 or more, and considering the upper limit, 400,000 or less, preferably 400,000 or more. It is 350,000 or less, more preferably 300,000 or less. When the weight average molecular weight is 20,000 or more, an appropriate resin cohesive force can be obtained, and it is possible to suppress insufficient strength and elongation of the film and brittleness. On the other hand, when the weight average molecular weight is 400,000 or less, the melt viscosity can be lowered, which is preferable from the viewpoint of improving production and productivity. The weight average molecular weight can be measured by gel permeation chromatography (hereinafter referred to as "GPC").

As the polymerization method of the polylactic acid-based resin (A), a known method such as a condensation polymerization method or a ring-opening polymerization method can be adopted. For example, in the case of the condensation polymerization method, D-lactic acid, L-lactic acid, or a mixture thereof can be directly dehydrated and condensed to obtain a polylactic acid-based resin having an arbitrary composition. Further, in the ring-opening polymerization method, a poly having an arbitrary composition is obtained by ring-opening polymerization of lactide, which is a cyclic dimer of lactic acid, in the presence of a predetermined catalyst while using a polymerization modifier or the like as necessary. A lactic acid-based resin can be obtained. The above-mentioned lactide includes DL-lactide, which is a dimer of L-lactic acid, and these can be mixed and polymerized as necessary to obtain a polylactic acid-based resin having an arbitrary composition and crystallinity. it can.

As a representative of the polylactic acid-based resin (A), "Nature Works" manufactured by Nature Works LLC and the like can be mentioned as commercially available ones. Further, as a specific example of a random copolymer of a polylactic acid resin, a diol and a dicarboxylic acid, for example, "GS-Pla" (manufactured by Mitsubishi Chemical Corporation) can be mentioned.

<Cellulose ester (B)>
Generally, as the cellulose ester, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cellulose diacetate, cellulose triacetate, cellulose acetate phthalate and the like are known, but in the present invention, cellulose acetate butyrate is used. It was found that good results were obtained in terms of compatibility with polylactic acid-based resins, improvement of film transparency and rigidity, and balance of shrinkage characteristics of heat-shrinkable films.

It is important that the acetyl group content of the cellulose ester (B) is 10 to 25% by mass. The acetyl group content is preferably 12 to 20% by mass, more preferably 13.5 to 17.5% by mass. When the acetyl group content is within the above range, the compatibility with the polylactic acid-based resin is excellent, and the obtained film is excellent in the balance between transparency and rigidity, moldability and the like.

Further, it is important that the butyryl group content of the cellulose ester (B) is 25 to 45% by mass. The butyryl group content is preferably 30-40% by mass. When the butyryl group content is within the above range, the compatibility with the polylactic acid-based resin is excellent, and the obtained film is excellent in the balance between transparency and rigidity, moldability and the like.

The cellulose ester (B) preferably has a hydroxyl group content of 0.5 to 5.0%. In order to obtain good compatibility with polylactic acid, it is more preferably 1.0 to 4.5%, and even more preferably 1.0 to 3.5%.

The number average molecular weight of the cellulose ester (B) is not particularly limited, but the lower limit is preferably 8,000 or more, more preferably 10,000 or more, and even more preferably 12,000 or more. The upper limit is preferably 100,000 or less, more preferably 90,000 or less, and even more preferably 80,000 or less.

Examples of commercially available products of the cellulose ester (B) include [CA] "CAB" and "CAP" series manufactured by Eastman Chemical Company, which are commercially available. These cellulose esters (B) may be used alone or in combination of two or more having different compositions.

<Mixing ratio>
It is important that the mixing ratio of the polylactic acid resin (A) and the cellulose ester (B) is (A) / (B) = 92/8 to 55/45% by mass.
The lower limit of the mixing ratio of the cellulose ester (B) is preferably 10% by mass or more, and the upper limit is preferably 40% by mass or less. The lower limit of the mixing ratio of the polylactic acid resin (A) is preferably 60% by mass or more, and the upper limit is preferably 90% by mass or less.
When the lower limit of the mixing ratio of the cellulose ester (B) is in the above range, the rigidity of the film is sufficient. Further, if the upper limit of the mixing ratio of the cellulose ester (B) is in the above range, transparency can be satisfied.

<Other ingredients>
The mixed resin composition of the present invention may contain the polylactic acid-based resin (A) and a resin other than the cellulose ester (B) as long as the effects of the present invention are not impaired.
Specific examples of other resins include (meth) acrylic acid ester resin, (meth) acrylic acid resin, polyolefin resin, polystyrene resin, polyvinyl chloride resin, polyvinylidene chloride resin, and chlorinated polyethylene resin. Resin, polyester resin other than polylactic acid resin, polycarbonate resin, polyamide resin, polyacetal resin, ethylene vinyl acetate copolymer, polymethylpentene resin, polyvinyl alcohol resin, cyclic olefin resin, polybutylene succin Nate resin, polyacrylonitrile resin, polyethylene oxide resin, cellulose resin, polyimide resin, rigid polyurethane resin, polyphenylene sulfide resin, polyphenylene ether resin, polyvinyl acetal resin, polybutadiene resin, polybutene resin, Polyamideimide-based resin, polyamide bismaleimide-based resin, polyarylate-based resin, polyetherimide-based resin, polyether ether ketone-based resin, polyether ketone-based resin, polyether sulfone-based resin, polyketone-based resin, polysulfone-based resin, aramid Examples thereof include based resins and silicone-based resins, and examples thereof include copolymers containing these resins as main components, core-shell type multilayer structure polymers, and modified products thereof.
Of these, (meth) acrylic acid ester-based resins, ethylene vinyl acetate copolymers, polybutylene succinate-based resins, polyethylene oxide-based resins, and polyvinyl acetal-based resins have excellent compatibility with polylactic acid-based resins. It is effective for adjusting the glass transition temperature, which affects shrinkage characteristics by blending with a polylactic acid-based resin, and for imparting further break resistance by being finely dispersed in the polylactic acid-based resin.

Further, in addition to the other components described above, additives generally blended in the resin composition can be appropriately added to the mixed resin composition of the present invention as long as the effects of the present invention are not significantly impaired. The additives include recycled resins generated from trimming loss of ears and the like, which are added for the purpose of improving and adjusting molding processability, productivity and various physical properties of porous films, silica, talc, kaolin, and calcium carbonate. Inorganic particles such as calcium, pigments such as titanium oxide and carbon black, flame retardants, weather resistance stabilizers, heat stabilizers, antistatic agents, melt viscosity improvers, cross-linking agents, lubricants, nucleating agents, plasticizers, antiaging agents , Antioxidants, light stabilizers, UV absorbers, neutralizers, antifogging agents, antiblocking agents, slip agents, colorants and other additives.

<Transparency: Internal haze value>
It is important that the film of the present invention has an internal haze value of 15% or less measured in accordance with JIS K7136. The internal haze value is more preferably 10% or less, and even more preferably 8% or less. When the internal haze value is 15% or less, the transparency of the film is sufficient, and the visibility of the covering body and the back surface printing when attached as a label or the like can be sufficiently obtained.
The internal haze value can be adjusted by adopting the above-mentioned types, compositions, and blending amounts of the polylactic acid-based resin (A) and the cellulose ester (B) in the mixed resin composition of the present invention. it can.

<Heat shrinkable film of the present invention>
The heat-shrinkable film of the present invention is formed by stretching the film of the present invention in at least one direction.

<Heat shrinkage rate>
The heat-shrinkable film of the present invention preferably has a heat-shrinkage rate of 20% or more and 80% or less in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds, and the lower limit is 30% or more. More preferably, the upper limit is 70% or less.
In order to keep the heat shrinkage within the above range, the stretching speed, stretching temperature, stretching ratio in the stretching step in the method for producing a heat shrinkable film of the present invention, which will be described later, and the temperature and time in the heat treatment and relaxation treatment. It can be adjusted by stretching conditions such as relaxation rate.

As will be described later, the "heat shrinkage rate" in the present invention represents the ratio of the amount of shrinkage to the actual size before shrinkage in% values in the vertical direction or the horizontal direction. Further, the "main contraction direction" means the larger of the longitudinal direction and the lateral direction in the stretching direction, and is, for example, a direction corresponding to the outer peripheral direction when the bottle is mounted on a bottle.

The heat shrinkage rate in the main shrinkage direction is an index for determining adaptability to a shrinkage processing process in a relatively short time (about several seconds to a dozen seconds) such as for shrink label applications of PET bottles. Currently, the shrinkage processing machine most often used industrially for labeling PET bottles is generally called a steam shrinker that uses steam as a heating medium for shrinkage processing. Further, the heat-shrinkable film needs to be sufficiently heat-shrinked at a temperature as low as possible from the viewpoint of the influence of heat on the object to be coated. However, in the case of a film that is highly temperature-dependent and has an extremely different shrinkage rate depending on the temperature, parts with different shrinkage behavior are likely to occur with respect to temperature spots in the steam shrinker, so shrinkage spots, wrinkles, avatars, etc. occur. The shrinkage finish tends to deteriorate the appearance. From the viewpoint of including these industrial productivity, if the heat shrinkage rate in the main shrinkage direction of the film when immersed in warm water at 80 ° C. for 10 seconds is 20% or more, the film is sufficiently adhered to the object to be coated within the shrinkage processing time. It is preferable because it can be formed and a good shrinkage finished appearance can be obtained without causing spots, wrinkles, and avatars, and the upper limit of the heat shrinkage rate in the main shrinkage direction of the film when immersed in warm water at 80 ° C. for 10 seconds is set. It is preferably 80% or less in order to suppress abrupt shrinkage of the film.

When the heat-shrinkable film of the present invention is used as a heat-shrinkable label, the heat-shrinkability in the direction orthogonal to the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds is -10% or more. % Or less (a negative shrinkage rate indicates that the film has expanded after immersion in warm water, and in the case of a uniaxially stretched film, it may be observed in the measurement of the heat shrinkage rate in the direction orthogonal to the main shrinkage direction. ), More preferably −8% or more and 8% or less, and further preferably −6% or more and 6% or less. If the film has a heat shrinkage rate of -10% or more and 10% or less in the direction orthogonal to the main shrinkage direction, the dimensional change in the direction orthogonal to the main shrinkage direction after shrinkage is small, and the printed pattern and characters are distorted after shrinkage. Also, it is preferable because the vertical shrinkage phenomenon does not easily occur when the product is mounted on a container.

<Tensile modulus>
The heat-shrinkable film of the present invention has a tensile elastic modulus in both the vertical direction and the horizontal direction of 4000 MPa or more, which is measured under the conditions of an atmospheric temperature of 23 ° C. and a tensile speed of 5 mm / min in accordance with JIS K7127. Is preferable. The tensile elastic modulus is more preferably 4200 MPa or more, still more preferably 4500 MPa or more. When the tensile elastic modulus is 4000 MPa or more, the elasticity of the entire film can be increased, and problems such as meandering of the film during processes such as printing and bag making of heat-shrinkable labels are less likely to occur, which is preferable. Even when the thickness of the film is reduced, when the film made in a bag such as a PET bottle is covered with a labeling machine or the like, the film tends to be covered diagonally or the yield tends to decrease due to the film bending. It is preferable because points are less likely to occur. The upper limit is not particularly limited, but the higher the tensile elastic modulus, the thinner the label thickness tends to be.

<Difference in storage modulus (ΔE')>
The heat-shrinkable film of the present invention has a storage elastic modulus difference (ΔE') of 2. Is preferably 0. hereinafter. The storage elastic modulus difference is more preferably 1.8 or less, still more preferably 1.5 or less. The difference in storage elastic modulus in the present invention means that a test piece having a width of 4 mm and a length of 60 mm is subjected to a vibration frequency of 10 Hz and a strain of 0.1% using a viscoelastic spectrometer DVA-200 (manufactured by IT Measurement Co., Ltd.). Storage elastic modulus at 90 ° C when dynamic viscoelasticity is measured in the lateral direction in the measurement temperature range of -100 ° C to 150 ° C under the conditions of a temperature rise rate of 3 ° C / min and a chuck distance of 2.5 cm. E _'90 and the storage modulus at 60 ° C. E' ₆₀ difference ΔE of '= log E' is a representation in _{90 -logE '60.} The difference in storage elastic modulus is 2. If it is 0 hereinafter, the rigidity change of the film from the glass transition temperature (Tg) of more than before shrinkage temperature becomes gentle, it is possible to suppress the shrinkage unevenness of the film, it is possible to reduce the occurrence of wrinkles, preferred. The lower limit is not particularly limited, but if the film retains a sufficient heat shrinkage rate, the smaller the value, the better the shrinkage finish.

<Layer structure>
The film of the present invention may have at least one layer containing the mixed resin composition of the present invention as a main component, and may have a single-layer structure or a laminated structure.
As the laminated structure, a plurality of layers (1) containing the composition of the present invention as a main component may be laminated, or may be laminated with other layers (2) containing a resin as a main component. Specific examples include (1) / (1), (1) / (1) / (1), (1) / (2), (1) / (2) / (1), (2) / ( 1) / (2), (1) / (2) / (1) / (2) / (1), etc. can be mentioned, but in addition to the above, what kind of film is required according to the required film quality. Even a combination can be adopted.
In the laminated structure, when a layer containing the mixed resin composition of the present invention as a main component is used as the front and back layers, it is preferable because the most transparent and rigidity improving effect can be expected among the various layer structures. Further, when it is used for the intermediate layer, the same effect can be expected, which is preferable.

Examples of the method for forming the laminated structure include a coextrusion method, a method of forming a film of each layer and then laminating and heat-sealing, and a method of joining with an adhesive or the like.

The total thickness of the film of the present invention is not particularly limited regardless of whether it is a single layer or a laminated film, but it is preferably thin from the viewpoint of transparency, shrinkage processability, raw material cost and the like. Specifically, the total thickness of the stretched film is preferably 100 μm or less, more preferably 80 μm or less, and further preferably 60 μm or less. The lower limit of the total thickness of the film is not particularly limited, but it is preferably about 10 μm in consideration of the handleability of the film.

<Method for producing a film of the present invention>
The method for producing the film of the present invention is not particularly limited, and the film can be produced by a conventionally known method. Specifically, for example, a film can be obtained by an inflation method, a tubular method, a T-die method, or the like. The film of the present invention can also be uniaxially or biaxially stretched. The stretching method is not particularly limited, and conventionally known methods such as a roll method, a tenter method, and a tubular method can be adopted. Further, the film of the present invention may be surface-treated for the purpose of imparting various functions. Specific examples of the surface treatment include corona treatment, plasma treatment, acid treatment, coating treatment, and the like, which can be appropriately selected and performed as necessary.

<Method for Producing Heat Shrinkable Film of the Present Invention>
The production method when the film of the present invention is a heat-shrinkable film is not particularly limited, and can be produced by a known method. Specifically, the resin is melted using an extruder, extruded from a T-die, cooled and solidified by a cooling roll, rolled in the vertical direction (film flow direction), and in the horizontal direction (film flow direction). It is stretched in at least one direction by tenter stretching in the vertical direction). Further, the simultaneous biaxial stretching machine may simultaneously stretch in the vertical direction and the horizontal direction. Further, the tubular film may be radially stretched by the internal pressure by the tubular method, and a method of cutting open the tubular object stretched by the tubular method to make it flat may also be mentioned. The form of the film may be either flat or tubular, but the flat shape is preferable from the viewpoint of productivity (several pieces can be taken as a product in the width direction of the raw film) and printing is easy.

The stretching ratio in the above stretching is 2 times or more and 10 times or less in the vertical direction, 2 times or more and 10 times or less in the horizontal direction, preferably 3 times or more and 6 times in the vertical direction in applications such as for overlapping and shrinking in two directions. Hereinafter, the lateral direction is about 3 times or more and 6 times or less. On the other hand, in applications such as heat-shrinkable labels that shrink mainly in one direction, the direction corresponding to the main shrinkage direction is 2 times or more and 10 times or less, preferably 3 times or more and 8 times or less, and more preferably 3 times or more and 7 times. It is less than or equal to, and the direction orthogonal to the main contraction direction is 1 times or more and 2 times or less (1 time means a case where it is not stretched), preferably 1.01 times or more and 1.50 times or less, substantially. It is desirable to select a magnification ratio that is in the category of uniaxial stretching. A film stretched at a stretching ratio within the above range does not have an excessively large heat shrinkage in the direction orthogonal to the main shrinkage direction, and is also a film in the height direction of the container when attached to a container as a shrinkage label, for example. Is preferable because it can suppress the so-called vertical shrinkage phenomenon.

The stretching temperature needs to be adjusted according to the glass transition temperature of the resin used and the characteristics required for the heat-shrinkable film, but is generally 60 ° C. or higher, preferably 70 ° C. or higher, and the upper limit is 100 ° C. or lower, preferably 90 ° C. It is controlled in the range of ° C or less.

Next, the stretched film is subjected to heat treatment or relaxation treatment at a temperature of about 50 ° C. or higher and 100 ° C. or lower for the purpose of reducing the natural shrinkage rate or improving the heat shrinkage characteristics, if necessary, and then the molecular orientation is changed. It cools quickly within a non-relaxing time, resulting in a heat shrinkable film.

The heat-shrinkable film of the present invention is subjected to surface treatment and surface treatment such as corona treatment, printing, coating and thin film deposition, as well as bag making and perforation processing using various solvents and heat seals, as necessary. Can be done.

The heat-shrinkable film of the present invention can be processed from a flat shape to a cylindrical shape or the like depending on the object to be packaged and used for packaging. For cylindrical containers such as PET bottles that require printing, first print the required image on one side of a wide flat film wound on a roll, and then cut this to the required width while the printed side is inside. It may be folded so as to form a cylinder by center-sealing (the shape of the seal is a so-called envelope). As the center sealing method, a method using an organic solvent, a method using a heat seal, a method using an adhesive, and a method using an impulse sealer can be considered. Among these, the bonding method using an organic solvent is preferably used from the viewpoint of productivity and appearance.

<Molded article of the present invention, label of the present invention, and container of the present invention>
The use of the heat-shrinkable film of the present invention is not particularly limited, but a bottle can be formed by laminating a printing layer, a vapor-deposited layer, and other functional layers as necessary using this as a base material. It can be used as various molded products such as (blow bottles), trays, lunch boxes, delicatessen containers, and dairy products containers.

Further, the heat-shrinkable film of the present invention can be used as a base material for a heat-shrinkable label for food containers (for example, PET bottles for soft drinks or foods, glass bottles, preferably PET bottles). In this case, even a complicated shape (for example, a cylinder with a constricted center, a quadrangular prism with a corner, a pentagonal prism, a hexagonal prism, etc.) can be adhered to the shape, and it is beautifully mounted without wrinkles or avatars. It becomes a label. Then, the food container equipped with the label can be used as a container. The molded product and the container can be manufactured by using a normal molding method.

The heat-shrinkable film of the present invention is extremely different from the heat-shrinkable film of the present invention in terms of heat expansion rate, water absorption, etc., in addition to the heat-shrinkable label material used for plastic molded products that deform when heated to a high temperature. From different materials such as metal, porcelain, glass, paper, polyethylene, polypropylene, polybutene and other polyolefin resins, polymethacrylic acid ester resins, polycarbonate resins, polyethylene terephthalates, polybutylene terephthalates and other polyester resins, polyamide resins It can also be suitably used as a heat-shrinkable label material for a package (container) using at least one selected material as a constituent material.

In addition to the above resins, the materials constituting the plastic package include polystyrene, rubber-modified impact-resistant polystyrene (HIPS), styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, and styrene-maleic anhydride copolymer. Combined, acrylonitrile-butadiene-styrene copolymer (ABS), (meth) acrylic acid-butadiene-styrene copolymer (MBS), polyvinyl chloride resin, phenol resin, urea resin, melamine resin, epoxy resin, unsaturated Examples thereof include polyester resin and silicone resin. These plastic packages may be a mixture of two or more kinds of resins or a laminate.

The use of the composition of the present invention has been described above with a heat-shrinkable film as a typical example, but the use of the film of the present invention is not limited to the heat-shrinkable film, and for example, various packaging films, containers, and various industries. It is also useful as a base material for parts, various injection molded products, medical materials, building materials, electric / electronic machine members, films for information recording, sheet materials, labels, adhesive tapes, and the like.

Examples are shown below, but the present invention is not limited thereto.

<Evaluation method>
The measurements and evaluations shown in the examples were performed as follows. In the embodiment, the take-up (flow) direction of the film is described as the "vertical" direction (or "MD"), and the direction perpendicular to the direction is described as the "horizontal" direction (or "TD").

(1) Heat Shrinkage Rate The obtained film was cut into a size of 10 mm in length and 200 mm in width, immersed in a hot water bath at 80 ° C. for 10 seconds, and the amount of shrinkage was measured. For the heat shrinkage rate, the ratio of the amount of shrinkage to the actual size before shrinkage was expressed as a% value.

(2) Tensile elastic modulus With respect to the obtained film, the temperature of the No. 1 test piece (total length 200 mm, width 10 mm to 25 mm strip, distance between marked lines 100 mm, distance between grippers 150 mm) according to JIS K7127 is 23. The tensile elastic modulus was measured in the direction (MD) orthogonal to the main contraction direction at ° C.
◯: When the tensile modulus of elasticity is 4000 MPa or more ×: When the tensile elongation at break is less than 4000 MPa

(4) Internal haze value With respect to the obtained film, the internal haze value was measured in accordance with JIS K7136 and judged according to the following criteria.
◯: When the internal haze value is 15% or less ×: When the internal haze value exceeds 15%

(5) Difference in storage elastic modulus With respect to the obtained film, a test piece having a width of 4 mm and a length of 60 mm was used with a viscoelastic spectrometer DVA-200 (manufactured by IT Measurement Co., Ltd.) at a vibration frequency of 10 Hz and a strain of 0.1. %, Heating rate 3 ° C / min, storage at 90 ° C when measuring dynamic viscoelasticity in the lateral direction in the measurement temperature range of -100 ° C to 150 ° C under the conditions of chuck spacing 2.5 cm. calculates a difference _{ΔE '= logE' 90 -logE '} 60 ₆₀ elastic modulus E' the storage modulus E at ₉₀ and 60 ° C. ', was judged by the following criteria.
◯: When ΔE'is 2.0% or less ×: When ΔE'is more than 2.0%

<Material used>
(Polylactic acid resin (A))
-Manufactured by Nature Works LLC, trade name: Nature Works4060D, D body / L body mass = 12/88, abbreviated as "A-1".
-Manufactured by Nature Works LLC, trade name: Nature Works4043D, D body / L body mass = 4/96, abbreviated as "A-2".

(Cellulose ester (B))
-Manufactured by Eastman Chemical Company, trade name: CAB381-0.1, acetyl group content 13.5%, butyryl group content 38%, hydroxyl group content 1.3%, number average molecular weight 20,000, abbreviated as "B-1" To do.
-Manufactured by Eastman Chemical Company, trade name: CAB321-0.1, acetyl group content 17.5%, butyryl group content 17.5%, hydroxyl group content 1.3%, number average molecular weight 12,000, "B-2" Abbreviated as.
-Manufactured by Eastman Chemical Company, trade name: CAB171-15, acetyl group content 29.5%, butyryl group content 17%, hydroxyl group content 1.1%, number average molecular weight 65,000, abbreviated as "B-3".
-Manufactured by Eastman Chemical Company, trade name: CAB551-0.2, acetyl group content 2.0%, butyryl group content 52%, hydroxyl group content 1.8%, number average molecular weight 30,000, abbreviated as "B-4" To do.

(Example 1)
Polylactic acid-based resin (A-1) is blended in a proportion of 45% by mass, polylactic acid-based resin (A-2) in a proportion of 45% by mass, and cellulose ester (B-1) in a proportion of 10% by mass. It is put into a screw diameter of 25 mmφ), melt-kneaded at a set temperature of 200 ° C., shaped into a sheet with a T-die, and then cooled and solidified with a cast roll set at 50 ° C. to obtain an unstretched sheet having a thickness of 200 μm. Obtained. Next, this unstretched sheet was stretched 5 times in the width direction of the unstretched sheet using a film tenter (manufactured by Kyoto Machinery Co., Ltd.) set to a preheating temperature of 82 ° C., a stretching temperature of 82 ° C., and a heat treatment temperature of 82 ° C. to obtain a thickness. A heat shrinkable film of 40 μm was obtained. The evaluation results of the obtained film are shown in Table 1.

(Example 2)
A heat-shrinkable film was obtained by the same method as in Example 1 except that the mixing ratio of the polylactic acid resin and the cellulose ester was changed. The evaluation results of the obtained film are shown in Table 1.

(Example 3)
A heat-shrinkable film was obtained by the same method as in Example 1 except that the cellulose ester was changed to (B-2). The evaluation results of the obtained film are shown in Table 1.

(Example 4)
A heat-shrinkable film was obtained by the same method as in Example 3 except that the blending ratio of the polylactic acid resin and the cellulose ester (B-2) was changed. The evaluation results of the obtained film are shown in Table 1.

(Example 5)
A heat-shrinkable film was obtained by the same method as in Example 3 except that the blending ratio of the polylactic acid resin and the cellulose ester (B-2) was changed. The evaluation results of the obtained film are shown in Table 1.

(Comparative Example 1)
A heat-shrinkable film having a thickness of 40 μm was prepared by blending a polylactic acid-based resin (A-1) in a proportion of 50% by mass and a polylactic acid-based resin (A-2) in a proportion of 50% by mass in the same manner as in Example 1. Obtained. Table 2 shows the evaluation results of the obtained film.

(Comparative Example 2)
A heat-shrinkable film was obtained by the same method as in Example 1 except that the mixing ratio of the polylactic acid resin and the cellulose ester was changed. Table 2 shows the evaluation results of the obtained film.

(Comparative Example 3)
A film collection was attempted by the same method as in Comparative Example 1 except that the mixing ratio of the polylactic acid resin and the cellulose ester was changed. Although it was possible to make a sheet, it was difficult to collect a film because the sheet was broken in the process of stretching the sheet 5 times.

(Comparative Example 4)
Polylactic acid-based resin (A-1) was blended in a proportion of 45% by mass, polylactic acid-based resin (A-2) in a proportion of 45% by mass, and cellulose ester (B-3) in a proportion of 10% by mass, as in Example 1. I tried to make a sheet by the method of. There was a difference in the melting temperature of the polylactic acid resin and the cellulose ester (B-3), and it was difficult to form a sheet.

(Comparative Example 5)
The polylactic acid-based resin (A-1) was blended in a proportion of 45% by mass, the polylactic acid-based resin (A-2) in a proportion of 45% by mass, and the cellulose ester (B-4) in a proportion of 10% by mass, as in Example 1. A heat-shrinkable film having a thickness of 40 μm was obtained by the above method. Table 2 shows the evaluation results of the obtained film.

As shown in the results shown in Table 1, when the film of the present invention is a heat-shrinkable film, it can be a film having excellent shrinkage characteristics, rigidity at room temperature, and excellent transparency.
On the other hand, as shown in the results shown in Table 2, when the cellulose ester is not blended (Comparative Example 1) or outside the scope of the present invention (Comparative Examples 2 to 5), film formation is difficult or the rigidity is low. The film was not improved or had poor shrinkage characteristics.

The polylactic acid-based film of the present invention is excellent in transparency and rigidity, and can be suitably used for films for packaging and industrial applications. Although the film of the present invention has a wide range of applications, it can be particularly preferably used for a heat-shrinkable film, a heat-shrinkable label, and the like.

Claims (7)

A layer containing a mixed resin composition of a polylactic acid resin (A) and a cellulose ester (B) having an acetyl group content of 10 to 25% by mass and a butyryl group content of 25 to 45% by mass as a main component. It has at least one layer, and the mixing ratio of (A) and (B) in the mixed resin composition is (A) / (B) = 92/8 to 55/45 mass%, and the inside conforms to JIS K7136. A polylactic acid-based film having a haze value of 15% or less. The film according to claim 1 is stretched in at least one direction and has a heat shrinkage rate of 20 to 80% in the main shrinkage direction when immersed in warm water at 80 ° C. for 10 seconds. the film. The heat-shrinkable film according to claim 2, wherein the tensile elastic modulus in both the vertical direction and the horizontal direction, which is measured in accordance with JIS K7127, is 4000 MPa or more. Lateral storage modulus of the heat-shrinkable film using a viscoelasticity spectrometer, 'the storage modulus at _90, 60 ° C. E' the storage modulus E at 90 ° C. as measured by a vibration frequency 10 Hz ₆₀ Then, the storage elastic modulus difference (ΔE') represented by the following relational expression is 2. Heat-shrinkable film according to claim 2 or 3, characterized in that a 0 hereinafter.
Storage modulus difference _{(ΔE ') = logE' 90} -logE '60 A molded product using the heat-shrinkable film according to any one of claims 2 to 4 as a base material. A heat-shrinkable label using the heat-shrinkable film according to any one of claims 2 to 4 as a base material. A molded product according to claim 5 or a container equipped with the heat shrinkable label according to claim 6.