JP2003170560A - Polylactate biaxially stretched laminated film having heat sealability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polylactate biaxially stretched laminated film having excellent transparency, mechanical characteristics and slipperiness and heat sealability, and to provide a method for manufacturing the same. <P>SOLUTION: The laminated film comprises a base layer (A) made of a polylactate polymer, and a heat sealing layer (B) obtained by blending an anti- blocking agent with a specific biodegradable resin having a void suppressing effect. Alternatively, the laminated film comprises the base layer (A), and the heat sealing layer (B) obtained by blending a surface-treated specific anti- blocking agent with the biodegradable resin and laminated on the layer (A). In the laminated film, the presence ratio of the number of voids having a size of 5 μm or more per 100 of the anti-blocking agents as seen from the section of the film is 10% or less, and a haze is 10% or less. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polylactic acid-based biaxially stretched laminated film having a heat-sealing property and a method for producing the same, and particularly to a heat-sealing property excellent in transparency, mechanical properties and slipperiness. The present invention relates to a polylactic acid-based biaxially stretched laminated film.

[0002]

2. Description of the Related Art Conventionally, polyethylene terephthalate and polypropylene have been known as materials excellent in mechanical strength, heat resistance and dimensional stability, and stretched films using these are widely used in the industrial world.

However, when these plastic films are incinerated when they are disposed of after use, the amount of heat generated during incineration is high, so the incinerator may be damaged during the incineration process, and they are discarded by landfill. Upon processing, these plastics remain with little degradation due to chemical and biological stability. Therefore, with the increasing social demand for environmental protection in recent years, a film made of a resin having biodegradability that can be decomposed by microorganisms and that can be composted by compost is demanded. There is. Among the biodegradable resins, polylactic acid is a plant-derived raw material obtained by polymerizing lactic acid obtained by fermenting various starches and sugars, and finally becomes carbon dioxide gas and water again and is environmentally recycled on a global scale. It has begun to be used for various purposes as an ideal polymer raw material.

However, polylactic acid has a property of being hard and brittle, and an unstretched film or sheet made of polylactic acid has low strength and elongation and is poor in impact resistance.
As it is, the practicality as a molded body is insufficient.

Therefore, in order to improve the brittleness of polylactic acid, a method of uniaxially or biaxially stretching and orienting is known, and generally, in order to improve or improve mechanical strength and impact strength. A film is formed by a biaxial stretching process. By subjecting the polylactic acid resin to biaxial stretching,
The effect is great depending on the draw ratio and the thickness accuracy is improved, but when an anti-blocking agent is added to give the stretched film the slip property, the heat of fusion is 20 J / g or more. When a highly crystalline polylactic acid-based resin is biaxially stretched, large voids are generated around the anti-blocking agent depending on the type of the anti-blocking agent to be mixed, so-called voids are generated, and as a result, the film There is a problem that transparency is lowered and haze unevenness is caused.

The polylactic acid biaxially stretched laminated film is used for information recording materials (magnetic cards), industrial packages,
It has been applied to agricultural mulch film, etc., and part of it has been put to practical use, but in the future, it is expected to expand to fields mainly for food packaging applications.

When a polylactic acid-based biaxially stretched laminated film is applied to food packaging, heat sealing is often employed as a method for sealing the contents. Sex is strongly required.
Therefore, Japanese Unexamined Patent Publication No. 10-100353 discloses a film obtained by laminating a non-stretched film as a sealant material on a stretched film made of polylactic acid via an adhesive to impart heat sealability. However,
Although this film has satisfactory heat-sealing properties, there is a problem in that the reduction of impact strength due to the brittleness of the unstretched film and the reduction of transparency due to the different polymer blend are unavoidable, and the application is likely to be limited. In addition, since the manufacturing process is complicated, a large energy loss occurs from the viewpoint of energy saving and resource saving such as film loss.

In addition to the above, Japanese Patent Laid-Open No. 32394/1996
No. 6, JP-A-10-151715 and the like disclose biaxially stretched films having heat sealability. The biaxially stretched film described in Japanese Patent Application Laid-Open No. 8-323946 has a biaxially stretched film made of a polylactic acid polymer as a base material layer, and a low melting point different material as a heat seal layer is formed on the base material layer as an outer layer. As for the multi-layer film laminated as above, since the crystalline low melting point resin is used, the transparency is lowered due to its characteristics, and the compatibility and stretchability of the base material layer and the heat seal layer are greatly different. It is difficult to obtain good thickness accuracy. In addition, JP-A-10
Japanese Patent Publication No. 151715 discloses a biaxially stretched film in which a heat-sealing layer is made of amorphous polylactic acid, but the stretching ratio which affects the mechanical properties of the film is 4
Since it is twice as low, there is a problem that mechanical properties are inferior. Further, there is no description about the slipperiness required for the film. As described above, any biaxially stretched film has mechanical properties that can withstand practical use, and does not have the transparency required for packaging applications.

[0009]

The present invention solves the above problems and provides a polylactic acid-based biaxially stretched laminated film having excellent heat resistance and transparency, mechanical properties and slipperiness, and a method for producing the same. It is provided.

[0010]

The present inventors have achieved the present invention as a result of intensive studies to solve the above problems. That is, the present invention is a biaxially stretched laminated film having at least two layers of a base material layer (A) and a heat seal layer (B) which is the outermost layer, and the base material layer (A) is L
-The ratio of lactic acid to D-lactic acid is (L-lactic acid) / (D-lactic acid) = 100/0 to 94/6 (mol%), and is composed of a polylactic acid-based polymer mainly composed of polylactic acid, In the seal layer (B), L-lactic acid and D-lactic acid are (L-lactic acid).
/ (D-lactic acid) = 94/6 to 70/30 (mol%) of poly DL-lactic acid copolymerized at a ratio of 60% by mass or more and 100
When the amount is less than 40% by mass, the content of at least one polymer selected from aliphatic-aromatic polyesters, polyester carbonates and aliphatic polyesters is more than 40% by mass.
It is contained at a ratio of not more than 10% by mass and is 10 ° C. higher than the melting point or softening point of the polylactic acid-based polymer constituting the base material layer (A)
The biodegradable resin has a low melting point or softening point and has an average particle size of 0.1 to 5.0.
An anti-blocking agent of μm is contained in an amount of 0.01 to 1% by mass, and the presence of the number of voids having a diameter of 5 μm or more per 100 anti-blocking agents is 10% or less when the film cross section is viewed. The gist is a polylactic acid-based biaxially stretched laminated film having a heat-sealing property, which has a haze of 10% or less.

Further, the present invention is a biaxially stretched laminated film having at least two layers of a base material layer (A) and a heat seal layer (B) which is the outermost layer, wherein the base material layer (A) is L-
The heat-sealing is made of a polylactic acid-based polymer mainly composed of polylactic acid in which the ratio of lactic acid and D-lactic acid is (L-lactic acid) / (D-lactic acid) = 100/0 to 94/6 (mol%). The layer (B) is composed of a biodegradable resin mainly composed of polylactic acid having a melting point or softening point lower by 10 ° C. or more than the melting point or softening point of the polylactic acid-based polymer constituting the base material layer (A), In the biodegradable resin, silica having an average particle size of 0.1 to 5.0 μm in which surface hydroxyl groups are blocked is 0.1.
It is contained in an amount of 01 to 1% by mass, and when the film cross section is viewed, the diameter is 5 μ per 100 anti-blocking agents.
The gist of the present invention is a polylactic acid-based biaxially stretched laminated film having a heat-sealing property, in which the existence ratio of the number of voids of m or more is 10% or less and the haze is 10% or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The polylactic acid-based biaxially stretched laminated film having a heat-sealing property of the present invention has at least two layers of a base material layer (A) and a heat-sealing layer (B) as an outermost layer. It is a biaxially stretched laminated film. Since a biaxially stretched film is required to have slipperiness, it is necessary to blend an anti-blocking agent, but a so-called void called a void is generated around the anti-blocking agent during biaxial stretching, which reduces the transparency of the film. Easier to do. Therefore, in the present invention, the heat seal layer (B) is formed of a biodegradable resin having a void suppressing effect, or a special anti-blocking agent is added to the biodegradable resin forming the heat seal layer (B). Thus, when the anti-blocking agent is contained in the outermost heat seal layer (B) without substantially blending the anti-blocking agent in the base material layer (A), the cross section of the film is The occurrence of voids is suppressed so that the existence ratio of voids having a diameter of 5 μm or more per 100 anti-blocking agents (hereinafter, referred to as “void content”) is 10% or less, and the haze is 10% or less. It realizes a certain laminated film with excellent transparency.

Hereinafter, a laminated film in which the heat seal layer (B) is composed of a biodegradable resin having an effect of suppressing voids is blended into the first laminated film and the heat seal layer (B) with a special anti-blocking agent. The laminated film will be described in detail as a second laminated film.

The base material layer (A), which has a common structure to the first laminated film and the second laminated film, comprises L-lactic acid and D-lactic acid.
-The ratio with lactic acid is (L-lactic acid) / (D-lactic acid) = 10
It must be composed of a polylactic acid-based polymer mainly composed of polylactic acid of 0/0 to 94/6 (mol%). When the content of D-lactic acid in polylactic acid exceeds 6 mol%,
The polylactic acid-based polymer does not show a clear melting point and has poor crystallinity. As a result, the accuracy of the thickness during stretching is significantly deteriorated, and the oriented crystallization due to heat setting after stretching does not proceed, resulting in problems such as insufficient mechanical strength and difficulty in controlling the heat shrinkage rate. Further, L-lactic acid may be used alone, but when D-lactic acid is blended, crystallinity is relaxed and a film-forming property is obtained. Therefore, in the present invention, L-lactic acid and D-lactic acid are (L-lactic acid) / (D-lactic acid) = 99 /
It is more preferable to be blended in the range of 1 to 97/3 (mol%). The L-lactic acid and D-lactic acid may be a copolymer or a blend as long as they are blended in the above proportions.

A urethane bond, an amide bond, an ether bond or the like can be introduced into the polylactic acid-based polymer forming the base material layer (A) as long as the biodegradability is not affected. The number average molecular weight of the polylactic acid-based polymer is 5
It is preferably in the range of 10,000 to 300,000, and more preferably in the range of 80,000 to 150,000. When the number average molecular weight is less than 50,000, the resulting film has poor mechanical strength,
Cutting in the stretching process and the winding process also frequently occurs, resulting in deterioration of operability. On the other hand, when the number average molecular weight exceeds 300,000, the fluidity at the time of heating and melting becomes poor and the film formability deteriorates.

In order to improve the slipperiness, the base material layer (A) may be blended with an organic lubricant represented by an anti-blocking agent or stearic acid amide described below within a range that does not impair the characteristics. In order to suppress the formation of voids and improve transparency, it is preferable not to contain an antiblocking agent.

Next, the heat seal layer (B) arranged as the outermost layer will be described. The heat seal layer (B) that constitutes the first laminated film is formed of a biodegradable resin having a void suppressing effect. This biodegradable resin needs to have a melting point or softening point lower by 10 ° C. or more than the melting point or softening point of the polylactic acid-based polymer constituting the base material layer (A). When the difference between the melting point or softening point of the biodegradable resin and the melting point or softening point of the polylactic acid-based polymer constituting the base material layer (A) is less than 10 ° C, mechanical strength is obtained but heat sealing is possible. As the temperature rises, the heat sealability deteriorates.

The biodegradable resin having a void suppressing effect is, specifically, L-lactic acid and D-lactic acid are (L-lactic acid) / (D-lactic acid) = 94/6 to 70/30. (Mol%)
And at least one polymer selected from the group consisting of an aliphatic polyester other than polylactic acid, an aliphatic polyester carbonate, and an aliphatic-aromatic polyester (hereinafter, referred to as "specific polyester").
Called. ) Is a biodegradable resin blended in a specific ratio. The poly-DL-lactic acid copolymerized in the above proportion is a low-crystalline polylactic acid, which does not exhibit a substantially clear melting point and easily flows, so that it is possible to improve heat sealability at low temperature. , A high void suppression effect comes to be expressed. Further, by further adding a specific polyester to this low crystalline poly DL-lactic acid, the crystallinity of the polylactic acid can be more relaxed, and a high void suppressing effect and an improvement in heat sealability can be achieved. However, if the specific polyester is blended in an excessively large amount, not only the adhesiveness with the base material layer (A) is lowered, but also the transparency tends to be lowered, so that the blending ratio of the low crystalline poly DL-lactic acid is high. Of 60% by mass or more and less than 100% by mass, and the blending ratio of the specific polyester is more than 0% by mass and 40% by mass or less.

The low-temperature heat-sealing property in the present invention means a good heat-sealing property when the films are stuck together at a temperature of 100 to 140 ° C., more preferably a heat of 3 N / cm or more. It has heat sealability with sealing strength. A material having such a heat-sealing property can be suitably used for packaging a lightweight product centering on overlapping.

The biodegradable resin having the effect of suppressing voids configured as described above has an average particle size of 0.1 to 5.0.
The μm antiblocking agent must be contained in the range of 0.01 to 1% by mass. If the average particle size of the anti-blocking agent is less than 0.1 μm, not only sufficient slip properties and abrasion resistance cannot be obtained, but also the compounded anti-blocking agent may drop off from the film. When the average particle diameter of the above exceeds 5.0 μm, the film surface becomes extremely rough and the transparency is lowered. Therefore, the average particle size of the anti-blocking agent is 0.5 to 3 μm.
More preferably, it is in the range of m. Further, if the blending ratio of the antiblocking agent is less than 0.01% by mass, sufficient slipperiness and abrasion resistance cannot be obtained, and if the blending ratio of the antiblocking agent exceeds 1% by mass, the film surface is It becomes extremely rough and the transparency is reduced. Therefore, the blending ratio of the anti-blocking agent is more preferably in the range of 0.05 to 0.5 mass%.

As the anti-blocking agent in the present invention, stable metal oxides such as silica, titanium dioxide and alumina, stable metal salts such as calcium carbonate, calcium phosphate and barium sulfate, or polylactic acid type resins inactive organic Examples thereof include so-called organic beads coated with a resin, and silica is particularly preferably used. These antiblocking agents may be used alone or in combination of two or more.

Examples of the aliphatic polyester other than polylactic acid in the present invention include polyethylene succinate, polyethylene adipate, polyethylene suberate, polyethylene sebacate, polyethylene decane dicarboxylate, polybutylene succinate, polybutylene adipate, polybutylene. Examples include sebacate and copolymers thereof. Among them, polybutylene succinate and polybutylene succinate adipate are preferably used. In the present invention, it is also possible to use a block copolymer of a polylactic acid-based polymer and an aliphatic polyester (including a partial transesterification product thereof and a product containing a small amount of a chain extender residue). it can. This block copolymer can be prepared by any method.

The aliphatic-aromatic polyester in the present invention may be any one having an aliphatic component and an aromatic component, and examples thereof include hydroxycaproic acids such as lactic acid, glycolic acid, hydroxybutyric acid and hydroxycaproic acid, and caprolactone. , Butyrolactone, lactide, cyclic lactones such as glycolide, ethylene glycol, butanediol, cyclohexanedimethanol, bis-hydroxymethylbenzene, toluenediol and other diols, succinic acid, adipic acid, suberic acid, sebacic acid,
Examples thereof include copolymers containing dicarboxylic acids such as terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid, cyclic acid anhydrides and oxiranes as components and having an aliphatic component and an aromatic component. Among them, a copolyester having 1,4-butanediol and adipic acid as an aliphatic component and terephthalic acid as an aromatic component is preferable. Further, a urethane bond, an amide bond, an ether bond or the like can be introduced as long as it does not affect the biodegradation.

As the polyester carbonate in the present invention, those obtained by reacting a dihydroxy compound with a dicarboxylic acid or an alkyl ester thereof, or a dihydroxy compound with a carbonic acid diester can be used.

Examples of the dihydroxy compound include ethylene glycol, trimethylene glycol, tetramethylene glycol, butanediol, pentanediol, propylene glycol, hexamethylene glycol, neopentyl glycol, toluene diol and bis-hydroxymethylbenzene. Among them, 1,
It is preferable to use 4-butanediol as one of the components. Examples of the dicarboxylic acid include malonic acid, glutaric acid, adipic acid, azelaic acid, terephthalic acid,
Isophthalic acid, naphthalenedicarboxylic acid and the like can be appropriately used in combination. Above all, it is preferable to use succinic acid as one of the components. The dihydroxy compound and dicarboxylic acid may be esters or acid anhydrides thereof. Further, the dihydroxy compound and the dicarboxylic acid can be used alone or as a mixture and can be combined in a desired manner, but in the present invention, they have appropriate biodegradability and realize practical heat resistance. A high melting point is preferable. The dihydroxy compound preferably contains 1,4-butanediol and succinic acid as the dicarboxylic acid. Examples of the carbonic acid diester include dimethyl carbonate, diethyl carbonate, diisopropyl carbonate, dibutyl carbonate, diphenyl carbonate, ditolyl carbonate, bis (chlorophenyl) carbonate, and m-cresyl carbonate. Among them, diphenyl carbonate is particularly preferable.

The heat-sealing layer (B) constituting the second laminated film comprises a biodegradable resin and a special anti-blocking agent. The biodegradable resin here means
In order to exhibit good heat-sealing property and to secure the adhesion with the base material layer (A), the melting point or softening point of the polylactic acid-based polymer constituting the base material layer (A) is 10 ° C. or more. The biodegradable resin mainly having polylactic acid having a low melting point or softening point is not particularly limited.

As a special anti-blocking agent to be added to this biodegradable resin, silica having surface hydroxyl groups blocked is used, and particularly silica having surface hydroxyl groups blocked with a silane coupling agent is preferably used. . Silica is preferably 20% or more of surface hydroxyl groups blocked with a silane coupling agent, but when the blocking rate of surface hydroxyl groups exceeds 80%, the silane coupling agent is present in the film in a free state. The upper limit is preferably set to 80%, because the ratio tends to increase and white turbidity of the film and fish eyes tend to occur.

The silane coupling agent used in the present invention is a compound represented by the chemical formula YRSiX ₃ . Here, Y is an organic functional group such as an epoxy group, an amino group, a methacryl group, and a vinyl group, R is an alkyl group, X is a hydrolyzable group such as an alkoxy group, an acetoxy group, and a chloro group,
Specifically, γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, vinyltrichlorosilane, and the like.
The surface treatment method of the silica with the silane coupling agent is not particularly limited, and known methods such as a transfer method, a slurry method, a pretreatment method such as a spray method, and an integral blend method can be adopted. A pretreatment method capable of uniformly treating the surface of silica is preferable.

The silica having surface hydroxyl groups blocked has an average particle size of 0.1 to 5.0 μm and a compounding ratio of 0.0
It should be 1 to 1% by mass. When the average particle size of silica is smaller than 0.1 μm, sufficient slipperiness and abrasion resistance cannot be obtained, and the compounded silica may fall off from the film. The average particle size of silica is 5.0.
When it exceeds μm, the film surface becomes extremely rough and the transparency is lowered. Therefore, the average particle diameter of the surface-treated silica is more preferably in the range of 0.5 to 3 μm. Further, when the blending ratio of the surface-treated silica is less than 0.01% by mass, sufficient slip properties and abrasion resistance cannot be obtained, and when the blending ratio of silica exceeds 1% by mass, the film is The surface becomes extremely rough and the transparency decreases. Therefore, the blending ratio of silica having surface hydroxyl groups blocked is more preferably in the range of 0.05 to 0.5 mass%.

As described above, the surface-treated silica is used as an anti-blocking agent, and is mixed with the biodegradable resin forming the heat-sealing layer (B) to obtain the anti-blocking agent and the heat-sealing layer (B). ) Or the affinity with the resin constituting the base material layer (A) is further enhanced, and the stretching followability at the time of performing the stretching treatment is improved as described below,
The amount of void formation can be further suppressed.

In the first and second laminated films of the present invention, the method of incorporating the antiblocking agent into the biodegradable resin is not particularly limited, and known methods can be adopted. For example, a method in which a biodegradable resin and an anti-blocking agent are kneaded in a twin-screw extruder to a high concentration to form a masterbatch, and a biodegradable resin containing no anti-blocking agent is blended and diluted during extrusion. To be A method of incorporating an anti-blocking agent at the time of polymerizing the biodegradable resin is also applicable. 2 biodegradable resins
When more than one species are mixed, either one may contain an anti-blocking agent, or it may be contained in advance in each resin. The average particle size and the addition amount of the anti-blocking agent to be blended are appropriately adjusted according to the required performance such as the thickness of the heat seal layer (B), transparency, and slipperiness.

Base layer (A) of the first and second laminated films
In addition, pigments, antioxidants, plasticizers, ultraviolet absorbers, lubricants, crystal nucleating agents, antistatic agents and the like may be added to the heat seal layer (B) as long as the characteristics are not impaired.

In the first and second laminated films, the base material layer (A) and the heat seal layer (B) configured as described above are prepared by, for example, T-die method, inflation method,
A method of separately producing by a calendering method and thermocompression-bonding the obtained stretched film via an adhesive may be considered, but since the cost is high, the base material layer and the heat-sealing layer are formed using a plurality of extruders. Extrude by stacking them in a die,
It is preferably produced by a so-called coextrusion method.

The first and second laminated films have a two-layer structure (A / B) of a base material layer (A) and a heat seal layer (B).
Alternatively, any form of a three-layer structure (B / A / B) may be used, but a three-layer structure is preferable. A three-layer structure is advantageous in both application and seal strength because both outermost layers are heat-sealing layers, and sufficient slipperiness is obtained even if the base layer does not contain an anti-blocking agent. Therefore, it is preferable in terms of transparency and cost.

The thickness of the first and second laminated films is not particularly limited and may be set appropriately depending on the intended use, required performance, price, etc.
A thickness of about m is suitable.

In addition to the base material layer (A) and the outermost heat seal layer (B), the first and second laminated films are made of, for example, polyvinyl alcohol or the like for imparting gas barrier properties. May be provided.

Further, the film surfaces of the first and second laminated films may be subjected to surface treatment such as corona treatment, plasma treatment and flame treatment. The surface treatment of the film not only improves printability but also heat seal. It is also an effective means for sex.

A method for producing the heat-sealable polylactic acid-based biaxially stretched laminated film of the present invention by the coextrusion method will be described below with reference to an example. When manufactured by the T-die method, a polylactic acid-based polymer that constitutes the base material layer (A) and a biodegradable resin containing an anti-blocking agent that constitutes the heat seal layer (B) are mixed, for example, at a cylinder temperature. 180-260 ℃, T-die temperature 200-25
It is melted and kneaded by heating with an extruder set to 0 ° C., and melt-casting is performed by coextrusion with the heat seal layer (B) as the outermost layer. And it cools with the cooling roll controlled by 20-40 degreeC, and the 100-500-micrometer-thick unstretched sheet is obtained.

The biaxially stretching method of the unstretched sheet may be either a coaxial biaxial stretching method by a tenter system or a sequential biaxial stretching method by a roll and a tenter. For example, when the unstretched film is formed into a laminated stretched film by the sequential biaxial stretching method, the unstretched sheet is stretched in the machine direction at a roll surface temperature of 50 to 80 ° C. according to the rotation speed ratio of a driving roll, and then continuously. Stretching is performed in the transverse direction at a stretching temperature of 70 to 100 ° C. The stretching ratio is not particularly limited, but considering the mechanical properties and transparency, the stretching ratio is such that the longitudinal stretching ratio and the transverse stretching ratio are each 2.5 times or more, and Is preferably 8 times or more and biaxially stretched. If the longitudinal stretching ratio and the lateral stretching ratio are less than 2.5 times, sufficient mechanical strength cannot be obtained,
It becomes inferior in practicality. The upper limits of the longitudinal stretching ratio and the transverse stretching ratio are not particularly limited, but if the ratio exceeds 8 times, film breakage is likely to occur, so the longitudinal stretching ratio and the lateral stretching ratio are 2.5 times or more and 8 times or more. The stretching ratio is preferably 2.5 times to 5.0 times, and the transverse stretching ratio is more preferably 2.5 times to 8.0 times.

After the above stretching treatment is performed, the temperature is set to 100.
Heat treatment is performed at ˜150 ° C., and heat relaxation treatment is performed under the condition of a relaxation rate of 2 to 8%. In this way, the heat seal layer (B) is composed of a low crystalline polylactic acid resin having a void suppressing effect, or the heat seal layer (B)
By containing a small amount of a specific anti-blocking agent in the above and producing a laminated film by coextrusion, the voids formed in the film surface can be extremely reduced until the void content becomes 10% or less. . As a result, a laminated film having a haze of 10% or less and less haze unevenness can be obtained.

The outermost heat-sealing layer (B) is the main polylactic acid resin even if it is stretched together with the base material layer (A) and heat-set for oriented crystallization of the base material layer (A). Since it is difficult to be oriented and crystallized, the heat sealability is never impaired.

Therefore, the obtained polylactic acid-based biaxially stretched laminated film having heat sealability is transparent, slippery, and
It is possible to obtain a laminated film which is excellent in heat sealability and mechanical properties and requires a small amount of antiblocking agent, and is also advantageous in terms of cost.

The polylactic acid-based biaxially stretched laminated film having such heat-sealing property is used for food packaging materials such as confectionery bags, packaging materials for medicines, individual packaging such as magnetic tapes and magnetic disks, or integrated packaging. It can be suitably used as a suitable packaging material for overwrapping applications. Other than that, it is a bag for packaging garbage, a window sticking film for envelopes, a wrapping material for electric and electronic parts, an agricultural film, a print laminated film laminated with paper, etc. Can be suitably used as.

[0044]

EXAMPLES Next, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In addition, the measurement of various physical property values in Examples and Comparative Examples was carried out by the following methods. (1) Void content (%): The cross section of the film was observed with an electron microscope, and the size of voids formed around the antiblocking agent was read on a photograph. Then, the existence rate of the number of voids having a diameter of 5 μm or more per 100 anti-blocking agents was defined as the void content rate. In the present invention, those having a void content of 10% or less were regarded as good. (2) Haze (%): Measured using a fully automatic haze meter (TC-H 111DPK manufactured by Tokyo Denshoku Co., Ltd.) and calculated based on the following formula.

Haze (%) = (Td / Tt) × 100 where Td is diffuse transmittance (%) and Tt is total light transmittance (%). In the present invention, those having a haze of 10% or less are considered to have good transparency. (3) Tensile strength (MPa): Measured with a sample having a length of 100 mm and a width of 10 mm according to the measuring method of ASTM-D882. In the present invention, both MD and TD directions are 13
The case where it exceeded 0 MPa was regarded as good. (4) Coefficient of dynamic friction: It is an index of slipperiness, and J
According to the method described in IS K-7125, the dynamic friction coefficient of each film was measured. And the dynamic friction coefficient is 0.6
Those having a value of 0 or less were considered to have good slipperiness. (5) Heat seal strength (N / 15mm): width 15m
m, a film sample cut into a length of 150 mm,
Using a heat sealer manufactured by Tester Sangyo, width 10 mm
The seal bar was heated at 100 ° C., 120 ° C., 140 ° C. under the condition of 0.1 MPa × 1 second, and the two sides of the film were superposed and heat-sealed. The heat-sealed sample thus obtained was measured according to the method described in JIS K-6854 to 30
A T-type peel test was performed at a peel speed of 0 mm / min, and the maximum stress during peeling was taken as the heat seal strength. Then, those having a heat seal strength of 3 N / 15 mm or more were considered to have excellent heat sealability. (6) Blockage rate (%) of silica hydroxyl group: Silica was reduced with lithium and aluminum hydride, and the amount of hydrogen generated was calculated by a gas chromatography method.

Hydroxyl blockage rate (%) = (amount of hydroxyl group after treatment / amount of hydroxyl group before treatment) × 100 Example 1 As a polymer constituting the base material layer (A), the melting point is 166.
Polylactic acid (manufactured by Cargill Dow Polymer Co., Ltd.) having L-lactic acid / D-lactic acid = 99/1 (mol%) at 0 ° C. was used.

As the polymer constituting the heat seal layer (B), polylactic acid having a melting point of 130 ° C. and L-lactic acid / D-lactic acid = 92/8 (mol%) (manufactured by Cargill Dow Polymer Co., Ltd.) ) 90% by mass and an aliphatic polyester having a melting point of 115 ° C. (Bionore # 190 manufactured by Showa High Polymer Co., Ltd.)
3) 10% by mass was used. As an anti-blocking agent, an amorphous silica having an average particle diameter of 1.4 μm (manufactured by Fuji Silysia Chemical Ltd., Sylysia 310P) was added to this polymer.
A polymer containing 1% by mass was used.

Then, each polymer is melted and coextruded at a T-die temperature of 220 ° C. so that the heat-sealing layers (B) are formed on both sides of the base material layer (A).
A cast roll whose temperature was controlled to 5 ° C. was brought into close contact with it and rapidly cooled to prepare an unstretched sheet having a thickness of 360 μm. The extruded amount of the polymer is such that the film thickness is finally the heat seal layer (B) / base material layer (A) / in consideration of the stretching ratio described later.
The heat seal layer (B) was adjusted to 5/20/5 (μm).

The obtained unstretched sheet is successively fed to a biaxial stretching machine and stretched 3.5 times in the machine direction under the conditions of a preheating roll of 60 ° C. and a stretching roll of 75 ° C., and subsequently a stretching roll of 80 ° C. Under these conditions, the film was stretched 4.5 times in the transverse direction. After that, heat treatment is performed at 125 ° C. with a lateral relaxation rate of 4%, and one surface is subjected to corona treatment to obtain a thickness of 30%.
A laminated stretched film of μm was obtained.

Table 1 shows the physical properties and the like of the obtained laminated film.

[0051]

[Table 1] Example 2 Polylactic acid having a melting point of 130 ° C. and L-lactic acid / D-lactic acid = 92/8 (mol%) as a polymer forming the heat-sealing layer (B) (manufactured by Cargill Dow Polymer Co.)
80% by mass and 20% by mass of polyester carbonate (IUPEC 550 manufactured by Mitsubishi Gas Chemical Co., Inc.) having a melting point of 97 ° C. were used. In addition, the stretching ratio during stretching is 4.
0 times and 5.0 times in the lateral direction. A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 1 shows the physical properties and the like of the obtained laminated film. Example 3 As a polymer constituting the base material layer (A), the melting point was 151.
Polylactic acid (manufactured by Cargill Dow Polymer Co., Ltd.) having L-lactic acid / D-lactic acid = 96/4 (mol%) at C was used.
Further, as the polymer forming the heat seal layer (B), the melting point is 130 ° C., and L-lactic acid / D-lactic acid = 92/8.
(Mol%) 70% by mass of polylactic acid (manufactured by Cargill Dow Polymer) and 30% by mass of aliphatic-aromatic copolyester (BASF Co., Ecoflex F) having a melting point of 105 ° C. A blocking agent containing 0.05% by mass of amorphous silica having an average particle size of 3.0 μm (manufactured by Fuji Silysia Chemical Ltd., Sylysia 730) was used. Further, the stretching ratio during stretching is 4.
0 times and 5.0 times in the lateral direction. A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 1 shows the physical properties and the like of the obtained laminated film. Example 4 As a polymer constituting the base material layer (A), the melting point was 151.
Polylactic acid (manufactured by Cargill Dow Polymer Co., Ltd.) having L-lactic acid / D-lactic acid = 96/4 (mol%) at C was used.
The anti-blocking agent contained in the heat-sealing layer (B) has a hydroxyl group of γ-glycidoxypropyltrimethoxysilane of amorphous silica (Silysia 310P manufactured by Fuji Silysia Chemical Ltd.) having an average particle diameter of 1.4 μm. In 5
Silica that had been capped with 0% was used. Further, the stretching ratio during stretching was 4.0 times in the longitudinal direction and 5.0 times in the lateral direction.
A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 1 shows the physical properties and the like of the obtained laminated film. Example 5 As an anti-blocking agent to be added to the heat-sealing layer (B), a hydroxy group of amorphous silica having an average particle size of 1.4 μm (manufactured by Fuji Silysia Chemical Ltd., Sylysia 310P) was γ-.
Silica 100% capped with glycidoxypropyltrimethoxysilane was used, and the compounding ratio was 0.05% by mass. A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 1 shows the physical properties and the like of the obtained laminated film. In Examples 1 to 3, the base material layer (A) was L-lactic acid and D-.
Biodegradability which is formed by polylactic acid-based polymer mixed with lactic acid in a specific ratio, and has a void-suppressing effect in which a heat-seal layer (B) is mixed with polylactic acid having low crystallinity and a specific polyester Since the heat-sealing layer (B) was formed of a resin and contained the anti-blocking agent having the average particle diameter of the present invention in a ratio within the range of the present invention, both had a void content of 10% or less. The haze was 10% or less, the transparency was excellent, and the slipperiness was good. The heat seal layer (B) is
The base layer (A) and the heat seal layer (B) are formed of a biodegradable resin having a melting point of 10 ° C. or more lower than the melting point of the polylactic acid-based polymer forming the base layer (A). The base material layer (A) was laminated by coextrusion and stretched at a suitable stretch ratio in the present invention.
The adhesiveness between the heat-sealing layer (B) and the heat-sealing layer (B) was improved, mechanical strength was excellent, and a laminated film having excellent heat-sealing strength was obtained.

Further, instead of the constitution of the heat seal layer (B) of Examples 1 to 3, the heat seal layer (B) is formed of a biodegradable resin containing surface-treated silica as an anti-blocking agent. Also in Examples 4 and 5, the same effects as those of the above Examples were obtained. In addition, Example 5
Since the treatment rate of the surface hydroxyl groups of silica was higher than the preferred range in the present invention, bleed-out of the surface treatment agent was slightly generated to increase the haze, but it did not affect the transparency. Comparative Example 1 The polymer constituting the base material layer (A) has a melting point of 130.
Polylactic acid (manufactured by Cargill Dow Polymer Co., Ltd.) having L-lactic acid / D-lactic acid = 92/8 (mol%) at C was used.
Further, as a polymer constituting the heat seal layer (B), the melting point is 166 ° C. and L-lactic acid / D-lactic acid = 99/1.
Polylactic acid (manufactured by Cargill Dow Polymer Co.), which is (mol%), was used. A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 2 shows the physical properties and the like of the obtained laminated film.

[0058]

[Table 2] Comparative Example 2 The blending ratio of the anti-blocking agent blended in the heat seal layer (B) was set to 2% by mass, which was higher than that of the present invention.
A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 2 shows the physical properties and the like of the obtained laminated film. Comparative Example 3 The blending ratio of the antiblocking agent blended in the heat seal layer (B) was set to 0.005% by mass, which was less than the proportion of the present invention. A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 2 shows the physical properties and the like of the obtained laminated film. Comparative Example 4 As the polymer constituting the base material layer (A), the melting point was 115.
An aliphatic polyester (Bionole # 1903, manufactured by Showa High Polymer Co., Ltd.) at a temperature of ℃ was used. A laminated stretched film was produced in the same manner as in Example 1 except for the above.

Table 2 shows the physical properties and the like of the obtained laminated film. In Comparative Example 1, since the melting point of the heat seal layer (B) was higher than that of the base material layer (A), the heat seal strength was inferior and it could not withstand actual use. Further, the heat seal layer (B) had a high crystallinity, a high void content, a high haze value, and poor transparency.

In Comparative Example 2, since the blending ratio of the antiblocking agent was higher than the range of the present invention, the void content was high, the haze value was high and the transparency was poor. In Comparative Example 3, since the blending ratio of the anti-blocking agent was less than the range of the present invention, the coefficient of dynamic friction was high and the slipperiness was poor.

Comparative Example 4 was inferior in transparency and tensile strength because the base material layer (A) was formed of an aliphatic polyester rather than a polylactic acid type polymer.

[0064]

As described above, according to the polylactic acid-based biaxially stretched laminated film having a heat-sealing property of the present invention, a laminated film comprising a base material layer (A) and a heat-sealing layer (B) is used as a base material. The material layer (A) is formed of polylactic acid-based polymer,
The film obtained by forming the heat-sealing layer (B) with a low-crystalline biodegradable resin having a void suppressing effect has an anti-blocking agent 1 when the cross section of the film is observed.
The existence ratio of the number of voids having a diameter of 5 μm or more per 100 is 10
% Or less and a haze of 10% or less gives a laminated film having excellent transparency. Further, since the compounding amount of the anti-blocking agent is small, it is possible to obtain a laminated film which is advantageous in terms of cost.

Alternatively, instead of the structure of the heat-sealing layer (B) described above, the heat-sealing layer (B) is formed by blending biodegradable resin with silica having surface hydroxyl groups blocked as an anti-blocking agent. In addition, a laminated film having an effect of suppressing voids, excellent transparency, mechanical strength, heat sealability, and slipperiness can be obtained.

Such a laminated film can be preferably used as a food packaging material such as a confectionery bag, a packaging material for pharmaceuticals, an overlapping packaging material suitable for individual packaging or integrated packaging of magnetic tapes, magnetic disks and the like.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 69:00) B29K 67:00 B29K 67:00 B29L 7:00 B29L 7:00 9:00 9:00 F-term (reference) 4F100 AA20B AA20C AK41A AK41B AK41J AK42B AK42C AK43B AK43C AK45B AK45C AL01B AL05A AL05B AL05C AR00B AR00C AT00A BA02 BA03 BA06 BA10B BA10C BA16 CA17B CA17C DE01B DE01C EH20 EJ38 EJ55 JA04B JA04C JC00B JC00C JK01 JK16 JL12 JL12B JL12C JN01 JN01B JN01C YY00A YY00B YY00C 4F210 AA24 AA28 AB07 AB17 AG01 AG03 QC05 QC06 QG01 QG15 QG18 QW12 4J002 CF032 CF042 CF181 CG042 GA01 GG02 GS01

Claims (2)

[Claims] 1. A biaxially stretched laminated film having at least two layers of a base material layer (A) and a heat seal layer (B) which is the outermost layer, wherein the base material layer (A) is L-lactic acid. The ratio with D-lactic acid is (L-lactic acid) / (D-lactic acid) = 100/0.
The heat seal layer (B) is composed of a polylactic acid-based polymer whose main component is polylactic acid of about 94/6 (mol%).
-Lactic acid and D-lactic acid are (L-lactic acid) / (D-lactic acid) =
PolyDL-lactic acid copolymerized at a ratio of 94/6 to 70/30 (mol%) in an amount of 60% by mass or more and less than 100% by mass, and at least 1 selected from aliphatic-aromatic polyesters, polyester carbonates and aliphatic polyesters. The polymer contains one or more kinds of polymers in a proportion of more than 0% by mass and 40% by mass or less, and has a melting point or softening point lower by 10 ° C. or more than the melting point or softening point of the polylactic acid-based polymer constituting the base material layer (A). It is made of a biodegradable resin, and the biodegradable resin contains 0.01 to 1% by mass of an anti-blocking agent having an average particle size of 0.1 to 5.0 μm. The heat-sealing property is characterized in that the existence ratio of the number of voids having a diameter of 5 μm or more per 100 anti-blocking agents is 10% or less and the haze is 10% or less. Polylactic acid biaxially stretched laminated film. 2. A biaxially stretched laminated film having at least two layers of a base material layer (A) and a heat seal layer (B) which is the outermost layer, wherein the base material layer (A) is L-lactic acid. The ratio with D-lactic acid is (L-lactic acid) / (D-lactic acid) = 100/0.
To 94/6 (mol%) of polylactic acid-based polymer mainly composed of polylactic acid, and the heat-sealing layer (B) is the melting point or softening point of the polylactic acid-based polymer constituting the base material layer (A). Made of biodegradable resin mainly composed of polylactic acid having a melting point or softening point lower by 10 ° C or more than
The biodegradable resin contains 0.01 to 1% by mass of silica having a surface hydroxyl group blocked and an average particle diameter of 0.1 to 5.0 μm. A polylactic acid-based biaxially stretched laminated film having a heat-sealing property, wherein the existence ratio of the number of voids having a diameter of 5 μm or more per 100 is 10% or less and the haze is 10% or less.