JP2004256795A - Polylactic acid film and laminate using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film having excellent hand-cutting properties, in particular one having good transparency which is suitably applicable to an easy-openable packaging material for foodstuffs, medicines, etc., to provide an adhesive tape having excellent hand-cutting properties, and to provide, in addition, a material which is favorable in sanitation from the aspect of having a fungicidal property, antibacterial activity and the like. <P>SOLUTION: The film is a polylactic acid film wherein haze is ≤20%, a melting point is ≥150°C and the value of breaking strength (MPa)×thickness (μm) is in the range of 100-2,100. A laminate comprising at least two layers consisting of a layer A composed of the polylactic acid film and a sealant layer (layer B), and having 50-700 g tear starting strength, is also provided. The packaging film and the adhesive tape are obtained by using the polylactic acid film. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention is a film partially using a polylactic acid composed of non-petroleum raw material and a laminated structure using the film, particularly a packaging film having good hand-cutting properties, and an adhesive tape having good hand-cutting properties. It has features that are favorable in terms of hygiene such as environmental friendliness, easy-opening properties, hand-cutting properties, transparency, as well as mold resistance and antibacterial properties.

  In recent years, packaging materials have been increased in strength from the viewpoint of protection of contents, while various proposals have been made with a focus on easy opening.

  For example, there is a packaging film having good hand-cutting properties, in which paper or aluminum is combined with a polyester film, and a sealant is further provided (see Patent Documents 1 and 2). However, in these examples, since a polyethylene terephthalate-based film having excellent strength is used, it is insufficient in hand-cutting properties, and further improvement in hygiene such as mold resistance is desired. Met.

  Patent Literatures 3 to 5 are mentioned as examples focusing on the hand-cutting property of the polylactic acid film, but the examples described in these literatures have the following problems.

  That is, in Patent Document 3, a laminated type film mainly using polylactic acid having a low melting point for expressing hand-cutting properties is cited as a specific example (for example, Example 2). In this example, there is a defect that heat resistance is inferior, and it is inferior in processing such as heat loss during processing, so that it is insufficient as an easily openable packaging material in which a sealant is laminated as intended in the present invention.

  Patent Literatures 4 and 5 disclose examples of a film having good hand-cutting properties obtained by blending polyester (copolymerized polyethylene terephthalate, crystalline aliphatic polyester) with polylactic acid. In the examples shown in these figures, hand-cutting properties are exhibited by making the polyester finely dispersed in polylactic acid. Since light scattering is caused by the finely dispersed polyester, transparency is extremely poor in any of the examples shown in these documents. Therefore, the film intended by the present invention is not sufficient as a film requiring transparency.

On the other hand, there are examples in which a sealant layer and the like are laminated on polylactic acid (Patent Documents 6 to 8), but in these examples, the hand-cutting property is not considered, and thus the problem of the present invention cannot be solved. Was.
JP 2001-162753 A JP-A-2002-104496 JP 2001-191407 A JP 2001-64413 A JP 2000-198913 A JP 2003-11287 A JP 2001-58372 A JP-A-8-267640

  An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a film having good hand-cutting properties, particularly, a film which can be easily opened and is suitably used as a packaging material for foods, medicines and the like. It is in. Another object of the present invention is to provide a pressure-sensitive adhesive tape which is easy to cut.

  The present invention has the following configuration to solve the above problems. That is, the polylactic acid-based film of the present invention has a haze of 20% or less, a melting point of 150 ° C. or more, and a value of breaking strength (MPa) × thickness (μm) in the range of 100 to 2100.

  Further, the laminated structure of the present invention is composed of at least two layers, that is, the layer A composed of the polylactic acid-based film and the sealant layer (layer B), and has a tear initiation strength of 50 to 700 g.

  The packaging film and the adhesive tape of the present invention use the above-mentioned polylactic acid-based film.

  The polylactic acid-based film of the present invention is excellent in transparency, hygiene and hand-cutting properties, and can be suitably used as a packaging material for foods, medicines and the like, which can be easily opened especially when taking out the contents. Moreover, the laminated structure of the present invention is obtained by disposing a sealant layer on the polylactic acid-based film of the present invention, and can be suitably used for various packaging materials. The packaging film and the pressure-sensitive adhesive tape of the present invention use a polylactic acid-based film and have excellent hand-cutting characteristics.

  Examples of the polylactic acid-based resin used in the polylactic acid-based film of the present invention include polylactic acid or a polymer composed of lactic acid such as L-lactic acid and D-lactic acid, or a copolymer with another hydroxycarboxylic acid. Representative examples of other hydroxycarboxylic acids include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, and 6-hydroxylcaproic acid. Here, the polylactic acid-based resin may be used alone, or may be a mixture of two or more kinds.

  In addition, in terms of sanitary properties such as antibacterial properties and fungicidal properties, the polylactic acid-based film of the present invention is a polymer of lactic acid or a polymer composed of lactic acid such as L-lactic acid or D-lactic acid with respect to the entire polylactic acid-based resin. The proportion is preferably at least 90 mol%, and further, from the viewpoint of having high heat resistance, long-term stability of physical properties, and being able to control such physical properties in a wide range, the proportion of L-lactic acid is preferably 95%. It is preferably at least mol%.

  Further, the resin component in the polylactic acid-based film of the present invention is preferably a polylactic acid-based resin in an amount of 70 to 100% by weight based on the entire resin component excluding a lubricant such as inorganic particles. It is more preferably 85 to 100% by weight, and further preferably 95 to 100% by weight. When the content of the polylactic acid-based resin is large, it is preferable from the viewpoint of heat resistance and also from the viewpoint of hygiene such as antibacterial property and mold resistance.

  In the present invention, the polylactic acid-based film needs to have a melting point of 150 ° C. or more. In particular, the melting point of the polylactic acid-based film is more preferably 160 ° C. or more, and particularly preferably 165 ° C. or more, in terms of appropriate processing such as lamination and printing generally required as a packaging material. If the melting point is low, heat resistance is poor, and problems such as generation of wrinkles in a drying step during processing and the like occur. The melting point has no particular upper limit, but is preferably 250 ° C. or lower.

  In the polylactic acid-based film of the present invention, a plasticizer, a lubricant, an inorganic particle, an organic particle, an antioxidant, and an antistatic agent are preferably contained in a range of 20% by weight or less, particularly preferably in a range of 5% by weight or less. And various additives and modifiers such as an ultraviolet absorber and a coloring inhibitor, and a known polymer such as an aliphatic polyester, an aromatic polyester and a polyolefin.

  The polylactic acid-based film is preferably a uniaxially stretched film or a biaxially stretched film in order to exhibit easy opening properties. The method for producing these stretched films is not particularly limited, but an example is shown below.

  The addition concentration of the lubricant is 0.01 to 0.1% of the polylactic acid-based resin and the lubricant master pellet (the polylactic acid-based resin containing a high concentration (about 2 to 50% by weight) of a lubricant such as silicon oxide in advance by a twin screw extruder or the like). After diluting and mixing to about 0.5% by weight, drying at an appropriate temperature (for example, a temperature of about 60 to 140 ° C.) to sufficiently remove water (300 ppm or less, preferably 100 ppm or less), extrusion Melting is carried out in a machine under suitable conditions of about 180 to 250 ° C. to form a polymer stream. The molten polymer is passed through a filter having a filtration accuracy of about 5 to 50 μm to filter the polymer and remove coarse foreign substances. The polymer after filtration is extruded into a sheet shape from a slit-shaped die, and is adhered to a casting drum controlled at a temperature of about 10 to 50 ° C. by a method such as an electrostatic application method to be cooled and solidified to prepare an unstretched film. The film is continuously stretched by heating about 2 to 5 times in the longitudinal direction, and then introduced into a tenter and stretched by 2 to 6 times in the transverse direction while being gripped with clips. Heat treatment is performed at a temperature to obtain a stretched film.

  The polylactic acid-based film of the present invention needs to have a haze of 20% or less. It is preferably at most 10%, particularly preferably at most 3%. If the haze is low, the transparency is good, so that it can be preferably used in applications that require printing from the back surface or where transparency is required for confirming the contents. In order to set the haze in the above range, it is preferable to suppress the addition amount of additives and modifiers having a size and a dispersion diameter of 0.1 μm or more used for the film, and an incompatible heterogeneous polymer. It is preferable that the addition amount is 1% by weight or less based on the polylactic acid-based resin. The lower limit is not particularly limited, but the lower limit is about 0.001% by weight.

  The polylactic acid-based film of the present invention needs to have a value of breaking strength (MPa) × thickness (μm) in the range of 100 to 2100. It is more preferably in the range of 500 to 1800, and particularly preferably in the range of 800 to 1200.

  In the present invention, attention has been paid to the fact that the effect of the breaking strength and the thickness is great on the easy tearing property (hand tearability). For example, even if the breaking strength is high, tearing is difficult if the film thickness is large, and even if the film thickness is small, tearing is difficult if the breaking strength is high. Therefore, in the present invention, it has been found that when the value obtained by multiplying the breaking strength by the film thickness exceeds the above-mentioned range, the easy tearing property is insufficient. On the other hand, if the value is less than the above range, it is easily broken, so that it is not particularly suitable as a packaging material or an adhesive tape in terms of proper processing or practical use.

  The film thickness is not particularly limited as long as the index of the above-mentioned breaking strength (MPa) × thickness (μm) is within the range, but is usually about 4 to 100 μm, more preferably about 5 to 30 μm, and particularly preferably. It is about 6 to 15 μm. If the thickness of the film is less than the above range, the film is not flexible, and the workability such as wrinkles and elongation during printing or laminating is deteriorated, which is not preferable. On the other hand, when the thickness is more than this range, not only the deterioration of the easy-cutting property becomes remarkable, but also the stiffness becomes too strong and the flexibility is lost, so that it is not suitable for a packaging material or an adhesive tape.

  In order for the thickness of the polylactic acid-based film to be in the above-mentioned range, it is preferable to include a step of filtering the molten polymer with a filter in the step of producing the film. Filtration by a filter sufficiently removes coarse foreign substances and modified polymer, and not only prevents coarse projections and fish eyes, which are problematic in film quality, but also reduces breakage in the production process and enables stable film formation.

  The elongation at break is preferably in the range of 100 to 300%. It is more preferably in the range of 100 to 200%, particularly preferably 100 to 150%. If the lower limit is not more than the lower limit, particularly when used as a packaging material, there is a problem in the protection of contents, or when used as a material on which a vapor-deposited layer or an aluminum foil layer is arranged, it causes a decrease in gas barrier properties. It is not preferable because there are some cases. In addition, when the amount is equal to or more than the above upper limit, it is not preferable because the easy-opening property may be deteriorated. Means for setting the elongation at break within this range are not particularly limited. For example, additives such as a lubricant to be added to the polylactic acid-based resin, modifiers, minimizing the content of different polymers, and stretching. In particular, the stretching temperature during film formation is set to a range of Tg (glass transition temperature) +5 to 30 ° C., and the stretching ratio is set to an area ratio (longitudinal ratio × horizontal ratio) of 2 And a range of up to 16 times.

  The heat shrinkage of the polylactic acid film of the present invention when heated at 120 ° C. for 30 minutes is preferably in the range of −5 to 5% in both the longitudinal direction (MD direction) and the width direction (TD). And more preferably in the range of -1 to 3%. If the heat shrinkage ratio is large, the film shrinks greatly at the time of film processing, which causes printing distortion and wrinkles, which is not preferable. On the other hand, if it is smaller than this range, the film is stretched at the time of heat processing, and the film is easily deformed by winding tension, and winding becomes difficult. The method for setting the heat shrinkage of the film in the above range is not particularly limited, but is relatively high, for example, about 120 to 160 ° C. while preliminarily relaxing the film by about 0.5 to 10% in the film manufacturing process. Examples thereof include a method of performing a heat treatment (thermal fixing) at a temperature and a method of performing a heat treatment at a temperature of about 120 to 160 ° C. while relaxing a once wound film in a heating oven.

The polylactic acid-based film of the present invention preferably has at least one surface resistivity in the range of 10 ² to 10 ¹³ Ω / □. More preferably, it is in the range of 10 ⁶ to 10 ¹² Ω / □. If the surface specific resistance is higher than this, in the packaging material, at the time of enclosing the content, there may be a problem such as scattering of the content due to static electricity. In particular, for packaging materials such as powders and dried products, the surface resistivity is preferably not more than the upper limit value. Even in the case of the pressure-sensitive adhesive tape, static electricity may be generated at the time of peeling, and it is preferable that the surface resistivity is not more than the upper limit value. When the surface resistivity is less than the lower limit of the above-mentioned preferable surface resistivity, no problem occurs in characteristics, but it is not preferable because it leads to an increase in cost.

  As a method for controlling the surface resistivity to the above range, a method of forming a film using a polylactic acid-based resin to which an antistatic agent is added, or a method of laminating polylactic acid in which a layer to which an antistatic agent is added is laminated on at least one surface And a method for forming a base film.

  In particular, as a preferred method of forming a layer to which an antistatic agent is added, a coating liquid in which a mixture of a binder resin including an acrylic resin, a polyester resin, and a polyurethane resin and an antistatic agent is dispersed in water or an organic solvent is formed. A method in which the film is applied to an intermediate film or a film after film formation by an existing method such as a gravure roll method, a metalling bar method, or a spray method, and dried by hot air or the like. At this time, the coating thickness is preferably about 0.01 to 2 μm.

  In the above-mentioned coating film, a crosslinking agent can be added as necessary. For example, a melamine-based crosslinking agent, an oxazoline-based crosslinking agent, an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, various silane couplings can be used. Agents, various titanate-based coupling agents, and the like.

  Furthermore, in the coating film, within the range where the effect of the present invention is not impaired, various additives, for example, antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, Organic or inorganic fine particles, fillers, antistatic agents, nucleating agents and the like may be blended.

  Regarding these techniques, as documents which specifically describe compounds which can be preferably used for a coating film and preferable coating methods, for example, JP-A-60-141525 and JP-A-6-145394 (Charging Method of adding an inhibitor to a polyester film), JP-A-2-283733, JP-A-4-28728, and JP-A-2-110141 (a method of applying a compound having a sulfonate group to a polyester film) JP-A-7-81015 (method of forming a coating layer containing a phosphate group on a polyester film) and JP-A-6-172562 (coating a compound having an ionized nitrogen atom on a polyester film) Method).

  Further, the laminated structure of the present invention is composed of at least two layers of the layer A composed of the polylactic acid-based film and the sealant layer (layer B).

  Here, the resin for the sealant used for the sealant layer (B layer) is not particularly limited as long as the object of the present invention is not hindered. For example, low-density polyethylene, linear low-density polyethylene, metallocene polyethylene, ionomer-based polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer And the like. Of these, low-density polyethylene, which is thermally stable and has few additives, and a linear low-density polyethylene having flexibility can be preferably used.

  Still further, it is possible to use a biodegradable heat-adhesive resin for the B layer, for example, polybutylene succinate, porobutylene succinate adipate, polyhydroxybutyrate, polylactic acid, or starch-derived denaturation. Polymer resins, shellac resins, and derivatives of these resins can be mentioned.

  The method of arranging the layer B includes a method by dry lamination, a method by extrusion lamination, and a method by coating, but any method may be used as long as the object of the present invention is not hindered. In particular, a method using dry lamination and a method using extrusion lamination are preferable from the viewpoint of improving the adhesion at the interface of the layer B and producing a packaging bag excellent in protecting contents.

  The thickness of the polylactic acid-based film (layer A) in the laminated structure of the present invention is preferably in the range of 4 to 15 μm in order to achieve the object of the present invention. It is more preferably in the range of 5 to 12 μm, particularly preferably in the range of 6 to 10 μm, in terms of easy tearing and proper processing.

  The thickness of the layer B can be arbitrarily set within a range that does not interfere with the heat adhesion and the easy tearing property, but is usually in the range of 0.01 to 50 μm.

  The preferred thickness ratio of the A layer and the B layer (A layer thickness / B layer thickness) is in the range of 10 to 0.1, and more preferably 2 to 0. 3 is within the range.

  Although the laminated structure of the present invention is composed of two or more layers, it is preferable that at least one surface of the adhesive interface of the B layer has a peel strength of 50 g / 15 mm or more. More preferably, it is 80 g / 15 mm, and particularly preferably in a state where it is tightly adhered to such an extent that it cannot be measured due to material destruction. If the peel strength is less than this range, it is not preferable because when used as a packaging bag, the strength is insufficient and the tearing property may be deteriorated.

  In order to improve the adhesiveness of the interface, it is preferable that a surface treatment such as a corona treatment is previously performed on the surface of the layer A or the layer B before the adhesion, and the adhesiveness can be further improved by an anchor coat treatment.

  The laminated structure of the present invention may be further provided with another layer according to the purpose. For example, a gas barrier layer typified by a vapor-deposited film formed of aluminum foil or an inorganic compound, a printing ink layer, an easy-adhesion layer, an adhesive layer, a heat seal layer, an anchor coat layer for improving adhesion between layers, paper And the like.

  For example, it is preferable to dispose an aluminum foil layer (C layer) in applications that require properties such as high gas barrier properties and dead hold properties. In addition, when a deposited film (D layer) made of an inorganic compound is provided, there is an improvement in gas barrier properties. Examples of such an inorganic compound include aluminum, copper, silver, gold, tin, cobalt, nickel, chromium, and oxide compounds such as aluminum oxide and silicon oxide. Among them, a vapor-deposited film composed of silicon oxide and aluminum oxide In this case, since transparency can be exhibited, it can be preferably used as a packaging material in which the contents can be confirmed. In order to impart light-shielding properties, metallic luster, and the like, aluminum deposition can be preferably performed. In addition, when a layer (E layer) made of paper such as kraft paper, high-quality paper, pure white, feng shing paper, glassine, rayon paper, synthetic fiber paper, etc. is arranged, dead hold properties, lightweight properties, etc. can be imparted, and hand cutting properties are particularly good. Because of this, it can be preferably used as an easy-open packaging material. A / B for applications that require visibility of the contents, A / D / B for applications that require gas barrier properties, dead-hold properties in which the opening is bent and used in addition to the gas barrier properties For necessary applications, an A / C / E configuration or an A / E / C / B configuration is preferably exemplified. Further, another layer may be provided between each layer as long as the effects of the present invention are not impaired.

  The thickness of each of the above layers can be arbitrarily set as long as the object of the present invention is not hindered. For example, the thickness of the aluminum foil layer is about 3 to 200 μm, and the thickness of the layer made of paper is about 5 to 1000 μm.

  The tear strength of the laminated structure using the polylactic acid-based film of the present invention needs to be in the range of 50 to 700 g. The weight is more preferably 50 to 500 g, and particularly preferably 50 to 300 g. If the tear initiation strength is within this range, the hand-cutting property is good, and it is preferable. On the other hand, from the viewpoint of protection of the contents, it is necessary that the weight is 50 g or more.

  The polylactic acid-based film of the present invention and a laminated structure using the same are used as packaging materials for articles such as pillows, side seals, three-sided, four-sided seals, solids, liquids, viscous materials, foods, and pharmaceuticals. Since it is suitable and can be easily torn by hand, it is particularly suitable as a packaging material that is easy to open when taking out the contents. In addition, since the plant-derived biodegradable resin polylactic acid is used, it is environmentally friendly and has excellent features of fungicide and antibacterial properties.

  The pressure-sensitive adhesive tape of the present invention uses at least one layer of the polylactic acid-based film of the present invention, and has a characteristic of easy tearing. Preferable configurations include a layer (F layer) made of a non-stretched or stretched film such as polyethylene and polypropylene, and an adhesive layer (G layer) as A / F / G, A / F / A / G, and A / E / G. And the like, but another layer may be provided between each layer as long as the effects of the present invention are not impaired.

  Hereinafter, the present invention will be further described with reference to examples.

[Method of measuring characteristics]
(1) Melting point A 5 mg film sample was collected and measured at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC2, manufactured by Perkin-Elmer Co.), and the melting peak temperature was taken as the melting point.

(2) Breaking strength and breaking elongation A sample was cut out to a width of 10 mm and a length of 150 mm, and the sample was subjected to an initial length of 50 mm, a tensile speed of 300 mm / min, and a temperature of 23 ° C. using a tensile tester manufactured by Orientec according to JISZ1702. A tensile test was performed under the conditions, and the breaking strength (MPa) and the breaking elongation (%) were measured.

  In addition, these measured values were obtained by averaging five samples in the longitudinal direction and five points in the width direction of the film, for a total of 10 samples.

(3) Haze Haze (all haze) was measured using a haze meter manufactured by Suga Test Instruments in accordance with JIS-K7105.

(4) Number of Defects A film having a size of about 15 cm × 15 cm was prepared, and the number of foreign matters, defects, and fish eyes observed when passing through a polarizing plate for a total area of 1 m ² was counted. / M ² ) was recorded.

(5) Tearing Start Strength A sample was cut out to a size of 50 mm × 50 mm, and a 19 mm-wide polyester adhesive tape was adhered from both sides in the shape of FIG. A cut is made in the polyester adhesive tape in the longitudinal direction, and both ends (A and B in FIG. 1) are gripped with a chuck, and a tensile tester manufactured by Orientec Co., Ltd. is pulled at a pulling speed of 300 mm / min. Recorded as tear onset strength.

  In addition, these measured values were obtained by averaging five samples in the longitudinal direction and five points in the width direction of the film, for a total of 10 samples.

(6) Peeling strength A sample having a width of 15 mm and a length of 150 mm was cut out, and the sealant layer was peeled off to an appropriate length using an organic solvent such as alcohol or ethyl acetate. The peeled both ends were pulled and peeled at 23 ° C. at a pulling speed of 300 mm / min by a tensile tester manufactured by Orientec, and the maximum peel strength was recorded. The measurement results were determined based on the following criteria. In this evaluation, ◎ and ○ are for practical use.
：: Good adhesion, not peelable

(The adhesion is strong and the film breaks.)
：: Peeling at a peel strength of 50 g / 15 mm or more
X: Peel strength is less than 50 g / 15 mm.

(7) Hand-cutting property A sample of a polylactic acid film alone and a laminate using the polylactic acid film was cut out in a shape of 50 mm in the longitudinal direction and 50 mm in the width direction, and was completely folded in half and overlapped. The state when the sheet was torn by hand from the center from the bent side without making a cut was determined as follows. In this evaluation, ◎ and ○ indicate practical use.
：: easily torn by hand, no elongation / deformation at the beginning of tearing.
：: tears easily by hand, but there is a slight elongation / deformation at the start of tearing.
×: Does not tear by hand. It is accompanied by large elongation and deformation at the tearing start part.

(8) Hygiene In accordance with JIS Z 2801 (antibacterial processed product-antibacterial test method and antibacterial effect), the mold preventive property of the surface of layer A, which is the surface of the packaging material, was evaluated.
：: No growth of bacteria was observed.
×: Growth of bacteria is observed.

(9) Suitability of film processing In the processing steps of extrusion lamination, dry lamination, and vapor deposition processing, it was visually confirmed whether wrinkles or the like due to heat were generated or heated.
：: The processing state is good.
X: Wrinkles or heat scattering due to heat occur.

(10) Surface Specific Resistance After standing for 24 hours in a normal state (23 ° C., 65% relative humidity), an applied voltage of 100 V was applied using a digital ultra-high resistance / microammeter R8340A (manufactured by Advantest Corporation) in that atmosphere. After applying for 2 seconds, the measurement was performed. The unit is Ω / □.

  In addition, the surface (surface opposite to the corona treated surface) to be the surface of the laminate was measured.

[Preparation of packaging film]
Example 1 (film name: F-1):
Polylactic acid A (weight average molecular weight: about 150,000, L-lactic acid component: 98.5%, D-lactic acid component: 1.5%, melt viscosity: 200 Pa · s (240 ° C., shear rate: 100 sec ⁻¹ ), melting point: 168 ° C. ) And polylactic acid B (silica particles having an average particle diameter of 1.6 μm with respect to polylactic acid A (Mizukasil P-527 manufactured by Mizusawa Chemical Industry Co., Ltd.) at 210 ° C. using a twin screw extruder to obtain a silica concentration of 5%. % By weight) were mixed at a weight ratio of polylactic acid A: polylactic acid B = 99: 1, and dried at 120 ° C. under a vacuum condition of 2 KPa or less for 5 hours.

The dried resin was supplied to a single-screw extruder having a screw diameter of 50 mm, and was melted at an extruder cylinder temperature of 230 ° C. The molten polymer was passed through a sintered disk filter having a filtration accuracy of 20 μm, extruded into a film at a die temperature of 220 ° C., and cast on a drum cooled to 30 ° C. to form an unstretched film. After continuously stretching the film between the heating rolls at 83 ° C. three times in the longitudinal direction, gripping the end of the film with a clip, guiding the film into a tenter, and stretching the film 3.5 times in the lateral direction while heating at a temperature of 75 ° C. A heat treatment was performed at 145 ° C. for 10 seconds while relaxing 2% in the width direction to obtain a 6 μm-thick polylactic acid-based film (F-1). The obtained polylactic acid-based film was subjected to a corona treatment on one side. Table 1 shows the properties of the obtained film, which was very good as the polylactic acid-based film of the present invention.
F-1 was evaluated for processing suitability in Example 5 described later, and very good results were obtained as the polylactic acid-based film of the present invention.

Example 2 (F-2), Example 3 (F-3):
In the same manner as in Example 1, an 8 μm-thick polylactic acid-based film (F-2) and a 10 μm-thick polylactic acid-based film (F-3) were obtained. The obtained polylactic acid-based films (F-2, F-3) were subjected to a corona treatment on one side. Table 1 shows the properties of the obtained films, all of which were favorable as the polylactic acid-based film of the present invention.

  F-2 was evaluated in Examples 7 and 10 and F-3 was evaluated in Examples 6 and 9, and good results were obtained.

Example 4 (F-4):
A 12 μm polylactic acid-based film (F-4) was obtained in the same manner except that a 400-mesh stainless steel wire mesh was provided instead of the filter used in Example 1. The obtained polylactic acid-based film was subjected to a corona treatment on one side. The film-forming stability of the film tended to be poor as compared with Example 3, and some defects (fish eyes) were observed. However, as shown in Table 1, the polylactic acid-based film of the present invention was relatively It was good.
F-4 was evaluated for processing suitability in Example 8, but relatively good results were obtained.

Comparative Example 1 (F-5):
Polylactic acid C (weight average molecular weight 170,000, L-lactic acid component 94.9%, D-lactic acid component 5.1%, melt viscosity 200 Pa · s (240 ° C, shear rate 100 sec ^-1 ), melting point 147 ° C) And polylactic acid B (silica particles having an average particle size of 1.6 μm with respect to polylactic acid C (Mizukasil P-527 manufactured by Mizusawa Chemical Industry Co., Ltd.) at 190 ° C. using a twin screw extruder to obtain a silica concentration of 5 wt. % Mixed) at a weight ratio of polylactic acid A: polylactic acid B = 99: 1 and dried under vacuum conditions of 100 ° C. and 2 KPa or less for 5 hours. The dried resin was placed in a single screw extruder having a screw diameter of 50 mm. The mixture was fed and melted at an extruder cylinder temperature of 200 ° C. The molten polymer was passed through a sintered disk filter having a filtration accuracy of 20 μm, extruded into a film at a die temperature of 200 ° C., and cast on a drum cooled to 30 ° C. to produce an unstretched film. After continuously stretching three times in the longitudinal direction between the heating rolls at 75 ° C., the end of the film is gripped with a clip, guided into a tenter, and stretched 3.2 times in the lateral direction while heating at a temperature of 70 ° C. A heat treatment was performed at 120 ° C. for 10 seconds while relaxing 2% in the width direction to obtain a 6 μm-thick polylactic acid-based film (F-5). The obtained polylactic acid-based film was subjected to corona treatment on one side.The obtained polylactic acid-based film was subjected to dry lamination, vapor deposition, etc. Inferior, although the film alone had hand-cutting properties, it was not evaluated as a packaging material.

Comparative Example 2 (F-6):
A polylactic acid-based film (F-6) having a thickness of 20 μm was obtained in the same manner as in Example 1. The obtained polylactic acid-based film was subjected to a corona treatment on one side.

  F-6 was evaluated for processing suitability in Comparative Example 5. The workability was good, but the hand-cutting properties of the film alone were insufficient.

Example 12 (F-7):
During the film formation in Example 3, a polylactic acid-based film having an antistatic coating film was formed. After the antistatic coating film is stretched in the longitudinal direction, one surface of the film is subjected to corona discharge treatment, and an aqueous coating solution (solid content concentration: 4%) having the following composition is applied to the treated surface at 9 μm using a metaling bar. Was gripped with a clip and guided into a tenter. Other conditions were the same as in Example 3 to prepare a 10 μm polylactic acid-based film. The surface opposite to the surface on which the antistatic coating film was formed was subjected to corona treatment.

Aqueous coating liquid: A mixture of (A) / (B) shown below in a solid content weight ratio of 30/70, and diluted with water to a solid content concentration of 4% by weight.
(A) Antistatic agent: aqueous dispersion of ammonium polystyrene sulfonate (molecular weight = about 40,000)
(B) Binder resin: acrylic emulsion (acryl component: methyl methacrylate / butyl acrylate / acrylic acid / N-methylolacrylamide = 60/38/1/1 (weight%) copolymer)

[Preparation of laminated structure using polylactic acid-based film]
Example 5:
The corona-treated surface of the polylactic acid-based film (F-1, 6 μm) prepared in Example 1 and the corona-treated surface of a linear low-density polyethylene film (manufactured by Toray Synthetic Film, type 4801, 30 μm) were dry-laminated to form polylactic acid. Table 2 shows the properties of the processed product, and the obtained laminate has good hand-cutting properties and good hygiene, and is very good as the laminate of the present invention. Was.

Example 6:
A transparent laminated structure of polylactic acid / polyethylene was prepared in the same manner as in Example 5 except that the polylactic acid-based film (F-3, 10 μm) prepared in Example 3 was used instead of F-1. Although the properties of the product were shown, it was good as the laminated structure of the present invention.

Example 7:
The corona-treated surface of the polylactic acid-based film (F-2, 8 μm) prepared in Example 2 and an aluminum foil (7 μm) were dry-laminated, and a polylactic acid / aluminum foil was laminated. Furthermore, the aluminum foil surface of polylactic acid / aluminum foil and the corona-treated surface side of a linear low-density polyethylene film (manufactured by Toray Synthetic Film, type 4801, 30 μm) are dry-laminated to form a laminated structure of polylactic acid / aluminum foil / polyethylene. did.

  Table 2 shows the properties of the processed product. The processed product was excellent in hand-cutting properties and was very good as the laminated structure of the present invention.

Example 8:
A laminated structure of polylactic acid / aluminum foil / polyethylene was prepared in the same manner as in Example 7 except that the polylactic acid-based film (F-4, 12 μm) prepared in Example 4 was used instead of F-2. Shows the properties of the processed product, but the hand-cutting property was also relatively good, and was good as the laminated structure of the present invention.

Example 9:
The corona-treated surface of the polylactic acid-based film (F-3, 10 μm) prepared in Example 3 and pure white paper were dry-laminated, and further, an aluminum foil, a linear low-density polyethylene film (manufactured by Toray Synthetic Film, type 4801, 30 μm) ) Was laminated by dry lamination to form a laminated structure of polylactic acid / paper / aluminum foil / polyethylene. Table 2 shows the properties of the processed product. It was a good body.

Example 10:
An anchor coat treatment was performed on the corona-treated surface of the polylactic acid-based film (F-3, 10 μm) prepared in Example 3, and silicon oxide was deposited on the treated surface. An anchor coat was further applied to the surface of the vapor-deposited layer, and a laminate (20 μm) of polyethylene (Mooretec 1018D manufactured by Idemitsu Petrochemical) was extruded and laminated to form a transparent laminated structure of polylactic acid / polyethylene. Despite the characteristics, the hand-cutting property was relatively good, and the laminated structure of the present invention was good.

Example 11:
F-1 was further bonded to the polylactic acid-based film (F-1) prepared in Example 5 by dry lamination. Further, one side thereof was coated with a pressure-sensitive adhesive to prepare a laminated structure of PLA / polyethylene / PLA / pressure-sensitive adhesive. The peel strength was measured for both polyethylene / PLA interfaces, and both were good. Table 2 shows the properties of the processed product. It was suitable for use.

Comparative Example 3:
A laminated structure of PET / polyethylene was prepared in the same manner as in Example 5 except that a polyethylene terephthalate film (PET film “Lumirror” type P60, 12 μm manufactured by Toray) was used instead of the polylactic acid-based film. However, it has no hand-cutting property and is inferior in hygiene, so that the object of the present invention has not been achieved.

Comparative Example 4:
A laminated structure of PET / aluminum foil / polyethylene was prepared in the same manner as in Example 3 except that a polyethylene terephthalate film (PET film “Lumirror” type P375, 6.5 μm, manufactured by Toray) was used instead of the polylactic acid-based film. Table 2 shows the characteristics of the processed product. Although the processed product had hand-cutting properties, the hygiene was insufficient and the object of the present invention was not achieved.

Comparative Example 5:
A polylactic acid / polyethylene laminated structure was prepared in the same manner as in Example 5 except that the polylactic acid-based film (F-6, 20 μm) prepared in Comparative Example 2 was used instead of F-1. The processed product had no hand-cutting property and did not achieve the object of the present invention.

Comparative Example 6:
A laminated structure of polylactic acid / polyethylene was prepared in the same manner as in Example 6 except that the adhesive surface of F-3 was a non-corona-treated surface. There was no hand-cutting property and the object of the present invention was not achieved.

Example 13:
A polylactic acid / aluminum foil / polyethylene laminated structure was prepared in the same manner as in Example 7, except that the polylactic acid-based film (F-7, 10 μm) prepared in Example 12 was used instead of F-2. Created.

  Table 2 shows the properties of the processed product. The processed product is excellent in hand-cutting properties, is good as a laminated structure of the present invention, and has good antistatic properties, so that it can be used without difficulty in packaging dry foods. Was something.

The front view and sectional drawing which show the sample preparation method at the time of the measurement of a tear starting load.

Explanation of reference numerals

Reference Signs List 1 Measurement sample 2 Polyester adhesive tape 3 Cut A, B Grasping part in tensile test

Claims (10)

A polylactic acid-based film having a haze of 20% or less, a melting point of 150 ° C. or more, and a value of breaking strength (MPa) × thickness (μm) in the range of 100 to 2100. The polylactic acid-based film according to claim 1, wherein the elongation at break is in the range of 100 to 300%. The polylactic acid-based film according to claim 1, wherein the surface specific resistance of at least one surface is in a range of 10 ² to 10 ¹³ Ω / □. A laminated structure comprising at least two layers of the layer A comprising the polylactic acid-based film according to claim 1 and a sealant layer (layer B), and having a tear initiation strength of 50 to 700 g. The laminated structure according to claim 4, wherein the peel strength at the B layer adhesive interface is 50 g / 15 mm or more. The laminated structure according to claim 4 or 5, further comprising an aluminum foil layer. The laminated structure according to any one of claims 4 to 6, further comprising a deposited film made of an inorganic compound. The laminated structure according to claim 4, further comprising a layer made of paper.   A packaging film using the polylactic acid-based film according to claim 1.   An adhesive tape using the polylactic acid-based film according to claim 1.

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