Layered polylactic acid film

Abstract

The present invention is a layered polylactic acid film that includes a stretched polylactic acid film substrate and a resin layer that is on at least one surface of the stretched polylactic acid film substrate. The stretched polylactic acid film substrate does not substantially include a lubricant, and the resin layer is formed from a resin layer formation material that includes an aqueous resin and lubricant particles. The tensile modulus of the stretched polylactic acid film substrate is at least 4.0 GPa in both the MD direction and the TD direction, and the resin layer formation material can include an antistatic agent. The present invention makes it possible to provide a layered polylactic acid film that facilitates printing and has excellent transparency.

Description

Laminated polylactic acid film

[0001] The present invention relates to a laminated polylactic acid film having good printability and processability. More specifically, the present invention relates to a laminated polylactic acid film that is easy to print on by roll-to-roll processing and has high transparency. Furthermore, the present invention relates to a laminated polylactic acid film that can suppress static electricity during film transport.

[0002] Generally, plastics such as polyolefin, polyester, and polyamide are used as the base materials for packaging materials and functional films used in foods, pharmaceuticals, industrial products, etc., but in recent years, growing environmental awareness has led to the development of polylactic acid film, a non-petroleum-based, biodegradable material. Compared to common polyester and polyamide films, polylactic acid film has lower mechanical strength and heat resistance, which has led to problems such as wrinkles occurring when the film is wound up during the film manufacturing process, and blocking, in which films stick to each other due to tightening over time when wound film rolls are stored for long periods of time.

[0003] Therefore, methods of adding a lubricant or an antiblocking agent to a polylactic acid film have been proposed as a method of suppressing wrinkles that occur when the film is wound up during the film production process, etc. (See, for example, Patent Documents 1 and 2.) However, although both methods can suppress wrinkles, the lubricant or antiblocking agent contained in the polylactic acid film causes light scattering in the film, which reduces the transparency of the polylactic acid film.

[0004] Furthermore, methods have been proposed for improving the mechanical strength and heat resistance of polylactic acid films and imparting lubricity by adjusting the composition ratio of L-lactic acid to D-lactic acid in the polylactic acid or by adding a biodegradable resin other than polylactic acid (see, for example, Patent Documents 3 and 4). However, because no consideration is given to transparency, whitening occurs due to crystallization inside the film or due to the compatibility between the polylactic acid and the added biodegradable resin, and fully satisfactory performance has not been achieved.

[0005] Therefore, as a method for improving transparency and imparting lubricity, a method of laminating a coating layer containing various resins and lubricants on the surface of a polylactic acid film has been proposed (see, for example, Patent Documents 5 and 6). However, since no consideration is given to blocking that occurs when a wound film roll is stored for a long period of time, there is a problem that practical limitations arise. To solve this problem, it has been proposed to increase the surface roughness of the coating layer by incorporating a large amount of particles, but light scattering occurs on the coating layer surface, resulting in high haze and reduced transparency, and fully satisfactory performance has not been obtained.

[0006] Furthermore, polylactic acid film is highly electrically insulating, so it easily becomes charged. This static electricity can often cause problems during printing, such as dust adhesion due to charging during various processes, or poor separation due to adhesion of films to each other due to frictional charging.

[0007] Therefore, methods have been proposed to suppress the generation of static electricity by incorporating an antistatic agent into a coating layer laminated on the surface of a polylactic acid film (for example, Patent Documents 7 to 9). However, although all of these methods exhibit antistatic properties that can improve processability, none of them have high transparency.

[0008] Japanese Patent Application Laid-Open No. 2004-331860 Japanese Patent Application Laid-Open No. 2002-146064 Japanese Patent Application Laid-Open No. 2004-010900 Japanese Patent Application Laid-Open No. 2003-170560 Japanese Patent Application Laid-Open No. 10-120811 Japanese Patent Application Laid-Open No. 2005-212242 Japanese Patent Application Laid-Open No. 2006-347009 Japanese Patent No. 5292949 Japanese Patent Application Laid-Open No. 2011-148915

[0009] The object of the present invention has been made to solve the above-mentioned problems, namely, to provide a laminated polylactic acid film that can be used in a film roll, making it easy to print on and also having excellent transparency.

[0010] The present inventors conducted extensive research to solve the above-mentioned problems, and finally completed the present invention. Specifically, the present invention is as follows: [Item 1] A laminated polylactic acid film having a stretched polylactic acid film substrate and a resin layer on at least one side of the stretched polylactic acid film substrate, wherein the stretched polylactic acid film substrate is substantially free of lubricant, the resin layer is formed from a resin layer-forming material containing an aqueous resin and lubricant particles, and the stretched polylactic acid film substrate has a tensile modulus of 4.0 GPa or more in both the MD and TD directions. [Item 2] The laminated polylactic acid film according to Item 1, wherein the difference in tensile modulus of the stretched polylactic acid film substrate between the MD and TD directions is 1.0 GPa or less. [Item 3] The laminated polylactic acid film according to Item 1 or 2, wherein the resin layer is formed from a resin layer-forming material containing an aqueous resin, lubricant particles, and an antistatic agent. [Item 4] The laminated polylactic acid film according to Item 3, wherein the antistatic agent is an anionic antistatic agent. [Item 5] The laminated polylactic acid film according to Item 3 or 4, wherein the content of the antistatic agent in the resin layer-forming material is 12 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the aqueous resin. [Item 6] The laminated polylactic acid film according to any one of Items 1 to 5, wherein the thickness of the resin layer is 20 nm or more and 150 nm or less. [Item 7] The laminated polylactic acid film according to any one of Items 1 to 6, wherein the lubricant particles contained in the resin layer-forming material include lubricant particles (p1) having a ratio (a / b) of an average particle diameter (a) to a resin layer thickness (b) of 0.45 to 1.5. [Item 8] The laminated polylactic acid film according to any one of Items 1 to 6, wherein the resin layer-forming material contains two or more types of lubricant particles having different average particle sizes, and the lubricant particles include one or more types of lubricant particles (p1) having a ratio (a / b) of average particle size (a) to resin layer thickness (b) of 0.45 to 1.5, and one or more types of lubricant particles (p2) having a ratio (a / b) of average particle size (a) to resin layer thickness (b) of more than 1.5 to 15. [Item 9] The laminated polylactic acid film according to Items 7 or 8, wherein the content of the lubricant particles (p1) in the resin layer-forming material is 10 parts by mass to 30 parts by mass per 100 parts by mass of the aqueous resin.[Item 10] The laminated polylactic acid film according to Item 8 or 9, wherein the content of the lubricant particles (p2) in the resin layer-forming material is 0.05 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the aqueous resin. [Item 11] The laminated polylactic acid film according to any one of Items 1 to 10, wherein the diffusion component γd of the surface free energy of the resin layer is 33 mN / m or more. [Item 12] The laminated polylactic acid film according to any one of Items 1 to 11, wherein the haze of the stretched polylactic acid film substrate is 0.3% or less. [Item 13] The laminated polylactic acid film according to any one of Items 1 to 12, wherein the resin layer is formed by an in-line coating method. [Item 14] A laminated polylactic acid film roll comprising the laminated polylactic acid film according to any one of Items 1 to 13.

[0011] The laminated polylactic acid film of the present invention has a resin layer formed from a resin layer-forming material containing an aqueous resin and lubricant particles on a stretched polylactic acid film substrate that has a predetermined tensile modulus and is substantially free of lubricants. This combination of components provides excellent transparency and allows for the formation of film rolls, facilitating printing processes. It can be used as a suitable replacement for conventional plastic films, for example, as packaging materials for food, pharmaceuticals, and industrial products. Because the laminated polylactic acid film is made from non-petroleum-derived, biodegradable materials, it significantly contributes to reducing the burden on the global environment. Furthermore, by incorporating an antistatic agent into the resin layer, the laminated polylactic acid film can be made antistatic, suppressing static buildup during film transport.

[0012] The present invention will be described in detail below.

[0013] (Stretched Polylactic Acid Film Substrate) The stretched polylactic acid film substrate used in the present invention is formed from a film-forming material containing polylactic acid. The polylactic acid is obtained by ring-opening polymerization of lactide using a compound having a hydroxyl group as an initiator in the presence of a specific catalyst. Examples of the specific catalyst include tin and aluminum. The polylactic acid preferably has an L-lactic acid (hereinafter referred to as L-form) / D-lactic acid (hereinafter referred to as D-form) mass ratio of 100 / 0 to 85 / 15, more preferably 100 / 0 to 90 / 10, even more preferably 100 / 0 to 90 / 10, and particularly preferably 100 / 0 to 95 / 5. A ratio of L-lactic acid (hereinafter referred to as L-form) / D-lactic acid (hereinafter referred to as D-form) of 100 / 0 to 85 / 15 is preferred because it provides high crystallinity and facilitates improvements in film properties such as improved film physical properties and reduced heat shrinkage. Polylactic acid may be copolymerized with a hydroxy acid component other than lactic acid, and examples of the hydroxy acid component other than lactic acid include glycolic acid, 3-hydroxypropionic acid, 6-hydroxycaproic acid (ε-caprolactone), etc. Of all the components of polylactic acid (the total amount of hydroxycarboxylic acid components, dicarboxylic acid components, and glycol components), the lactic acid component is preferably 85 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, particularly preferably 97 mol% or more, and may be 99 mol% or more, or even 100 mol%.

[0014] The polylactic acid of the present invention preferably has a glass transition point of 40 to 70°C, a melting point of 150 to 180°C, and is preferably capable of orientation crystallization. The glass transition point and melting point can be measured by a differential scanning calorimeter (DSC), etc. The presence or absence of crystallinity can be confirmed by the presence or absence of a crystallization peak during the heating process or the cooling process after melting in DSC.

[0015] The reduced viscosity (ηsp / c) of the polylactic acid-containing film-forming material used in the present invention is preferably in the range of 1.0 dl / g to 3.0 dl / g, more preferably 1.5 to 2.8 dl / g. When the reduced viscosity is 1.0 dl / g or more, tearing of the polylactic acid film can be prevented. When the reduced viscosity is 3.0 dl / g or less, the increase in filtration pressure is small, facilitating high-precision filtration.

[0016] The reduced viscosity (ηsp / c) of the stretched polylactic acid film of the present invention (similarly for the laminated polylactic acid film) is preferably in the range of 1.0 dl / g or more and 2.5 dl / g or less, more preferably 1.2 or more and 2.3 or less. A reduced viscosity of 1.0 dl / g or more is preferable because it prevents frequent breakage during the stretching process. A reduced viscosity of 2.5 dl / g or less is preferable because it provides good cuttability when cutting to a specified product width and prevents dimensional defects. Note that polylactic acid is prone to a decrease in reduced viscosity when melted, so it is preferable to minimize the decrease in reduced viscosity during film production by thoroughly drying the film-forming material containing polylactic acid and shortening the residence time in the molten state.

[0017] The film-forming material constituting the stretched polylactic acid film substrate used in the present invention can contain resin components other than polylactic acid as resin components, but the content of polylactic acid in all resin components in the film-forming material is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 98% by mass or more, or even 100% by mass. In other words, the film-forming material may be composed only of polylactic acid.

[0018] The stretched polylactic acid film substrate used in the present invention preferably does not substantially contain lubricant particles (hereinafter simply referred to as lubricant). "Substantially free of lubricant" does not necessarily mean that the film is completely free of lubricant, but may contain a lubricant in an amount that does not affect the surface roughness or slipperiness of the film. The amount of lubricant that may be contained is preferably less than 100 ppm by mass, more preferably less than 50 ppm, even more preferably less than 30 ppm, particularly preferably less than 10 ppm, or even less than 5 ppm, relative to the stretched polylactic acid film substrate (total amount of film-forming material). Furthermore, the lubricant preferably has an average particle size of 0.01 to 10 μm, more preferably 0.05 to 5 μm.

[0019] The film-forming material constituting the stretched polylactic acid film substrate used in the present invention can contain one or more of various additives, such as fluorescent brighteners, ultraviolet inhibitors, infrared absorbing dyes, heat stabilizers, surfactants, and antioxidants, depending on the purpose of use. Examples of antioxidants that can be used include aromatic amine-based and phenol-based antioxidants, and examples of stabilizers that can be used include phosphorus-based, sulfur-based, and amine-based stabilizers, such as phosphoric acid and phosphate ester-based stabilizers. Examples of stabilizers that can be used include phosphorus-based, sulfur-based, and amine-based stabilizers, such as phosphoric acid and phosphate ester-based stabilizers.

[0020] The stretched polylactic acid film substrate used in the present invention can be obtained by processing a film-forming material containing polylactic acid into an unstretched sheet using various methods and then stretching the sheet. From the viewpoint of imparting mechanical strength, the stretched polylactic acid film substrate used in the present invention is preferably a stretched film stretched in at least one direction, either the longitudinal or transverse direction, and more preferably a biaxially stretched film stretched in two directions, the MD direction (longitudinal direction) and the TD direction (transverse direction). Any stretching method, such as simultaneous biaxial stretching or sequential biaxial stretching, can be used for the biaxially stretched film. A preferred embodiment of the stretching method in successive biaxial stretching involves stretching an unstretched film in the MD direction at a stretch ratio of 1.1 to 6.0 times at a temperature of 50 to 110° C. using a roll-type stretching machine, then stretching in the TD direction at a stretch ratio of 1.1 to 10.0 times at a temperature of 60 to 140° C. using a tenter-type stretching machine, and after stretching, subjecting the film to a longitudinal relaxation treatment, transverse relaxation treatment, or the like of 0.5 to 10% at a temperature of 90 to 180° C. In addition, it is preferable to employ an in-line coating method as the step of forming the resin layer described below, and in the step of successive biaxial stretching, a resin layer can be coated on the film before stretching or on the film after stretching in the MD direction, and then the film can be continuously introduced into a tenter-type stretching machine to be stretched in the TD direction and heat-treated.

[0021] The stretched polylactic acid film substrate used in the present invention may be a monolayer film (hereinafter also referred to as a polylactic acid layer) formed from a film-forming material containing polylactic acid, or a laminated film in which the polylactic acid layer is laminated with other plastic films (which may be two or more types). It may also be a laminated film having multiple polylactic acid layers with different compositions, such as additives. When forming a laminated film, the type of laminate is not particularly limited as long as there is a polylactic acid layer, with respect to the number of layers, lamination method, etc., and can be arbitrarily selected from known methods depending on the purpose.

[0022] (Physical properties of stretched polylactic acid film substrate) The thickness of the stretched polylactic acid film substrate of the present invention is preferably 2 μm or more and 500 μm or less, more preferably 15 μm or more and 400 μm or less, and even more preferably 20 μm or more and 250 μm or less. When the thickness of the stretched polylactic acid film substrate is 2 μm or more, the stretched polylactic acid film substrate has a minimum rigidity and is easy to handle. Furthermore, when the thickness of the stretched polylactic acid film substrate is 500 μm or less, the transportability of the film when transporting the film with multiple rolls and the handleability of the produced film are improved, making it easier to handle.

[0023] The crystallinity of the stretched polylactic acid film of the present invention is preferably 40% to 90%, more preferably 50% to 85%, and even more preferably 55% to 80%. A crystallinity in the range of 40% to 90% is preferable because it improves strength and provides a high elastic modulus.

[0024] The tensile modulus of the stretched polylactic acid film substrate of the present invention is preferably 4.0 GPa or more in both the MD and TD directions, and more preferably the difference between the tensile modulus in the MD and TD directions is 1.0 GPa or less. If the tensile modulus in either the MD or TD direction is less than 4.0 GPa, the film will have insufficient rigidity, resulting in reduced lubrication when wound up, and blocking is likely to occur when the wound film roll is stored for a long period of time. The laminated polylactic acid film of the present invention is configured so that the lubricant particles contained in the resin layer create protrusions on the surface of the resin layer to ensure the film's lubrication. By increasing the tensile modulus in either the MD or TD direction of the stretched polylactic acid film substrate, it is thought that when force is applied to the surface of the laminated polylactic acid film, the lubricant particles in the resin layer are less likely to be pressed into the stretched polylactic acid film substrate, thereby ensuring high lubrication and anti-blocking properties.

[0025] Furthermore, if the difference in tensile modulus between the MD and TD directions exceeds 1.0 GPa, the wound film roll is likely to develop wrinkles and localized blocking due to tight winding over time when stored for a long period of time. Furthermore, when a blocked film roll is unwound, peeling of the resin layer, shedding of lubricant particles, and deterioration of the surface irregularities of the resin layer occur, resulting in a decrease in the film's slipperiness in those areas and a tendency for poor separation to occur. Furthermore, if the resin layer (described below) contains an antistatic agent, the antistatic agent contained in the resin layer may cause offset, reducing its electrostatic function, making the film more susceptible to dust adsorption during film transport and reducing the effectiveness of preventing poor separation due to adhesion of films to each other due to frictional charging. Poor separation refers to the phenomenon in which films are misaligned or overlapped when printed or distributed on a sheet-by-sheet basis. This not only results in unprinted sheets of film, but can also cause mechanical problems such as jams, film wrinkles, and folds. By optimizing the tensile modulus of the stretched polylactic acid film substrate, it is possible to reduce the amount of lubricant particles and antistatic agent added to the resin layer (described later), thereby achieving high transparency. This tensile modulus can be freely controlled by the stretching conditions and the relaxation treatment after stretching.

[0026] The breaking strength of the stretched polylactic acid film substrate is preferably 75 MPa or more in both the MD and TD directions. The lower limit of the breaking strength in the MD and TD directions is preferably 100 MPa, more preferably 150 MPa, even more preferably 200 MPa, and even more preferably 220 MPa. A breaking strength of 75 MPa or more is preferable because the mechanical strength of the film is sufficient and problems such as elongation and slippage during the film processing process can be suppressed. In consideration of manufacturing, the upper limit is considered to be 1000 MPa.

[0027] The breaking elongation of the stretched polylactic acid film substrate is preferably 5% or more in both the MD and TD directions. A breaking elongation of 5% or more in both the MD and TD directions is preferable because the mechanical elongation of the film is sufficient, preventing problems such as cracking and tearing during the film processing process. Considering manufacturing considerations, the upper limit is thought to be 300%. The upper limit is more preferably 150%, even more preferably 100%, and even more preferably 80%.

[0028] When heated at 150°C for 30 minutes, the stretched polylactic acid film substrate preferably has a heat shrinkage rate in both the MD and TD directions of 10.0% or less. When heated at 150°C for 30 minutes, the upper limits of the heat shrinkage rate in the MD and TD directions are, independently, more preferably 8.0% or less, even more preferably 6.0% or less, even more preferably 4.0% or less, particularly preferably 3.0% or less, and most preferably 2.0% or less. A small heat shrinkage rate facilitates processing such as printing and can suppress poor appearance due to film deformation under high heat. A low heat shrinkage rate is preferred, but from a manufacturing standpoint, a lower limit of 0.01% is considered.

[0029] When heated at 120°C for 30 minutes, the heat shrinkage rate in both the MD and TD directions of a stretched polylactic acid film substrate is preferably 3.0% or less. When heated at 120°C for 30 minutes, the upper limits of the heat shrinkage rate in the MD and TD directions are, independently, more preferably 2.0% or less, even more preferably 1.6% or less, even more preferably 1.4% or less, particularly preferably 1.2% or less, and most preferably 1.0% or less. A small heat shrinkage rate facilitates processing such as coating, and can suppress poor appearance due to film deformation under high heat. A low heat shrinkage rate is preferred, but from a manufacturing standpoint, 0.01% is considered to be the lower limit.

[0030] The total light transmittance of the stretched polylactic acid film substrate is preferably 80% or more. High transparency is preferable to improve the accuracy of detecting internal foreign matter, which can be a defect in the film. Therefore, the total light transmittance of the film of the present invention is preferably 85% or more, and particularly preferably 90% or more. By making it 80% or more, it is possible to improve the accuracy of detecting internal foreign matter, which can reduce the design of printed matter and cause defects in functional films.

[0031] The haze of the stretched polylactic acid film substrate is preferably 0.3% or less, more preferably 0.2% or less, and particularly preferably 0.1% or less. By keeping the haze at 0.3% or less, it is possible to improve the accuracy of detecting internal foreign matter, which can cause a deterioration in the design of printed matter and defects in functional films.

[0032] (Resin Layer) The resin layer in the present invention is laminated on at least one surface of the stretched polylactic acid film substrate and is formed from a resin layer-forming material containing a water-based resin and lubricant particles.

[0033] The aqueous resin is not particularly limited, but from the viewpoint of adhesion to the stretched polylactic acid film substrate, it is preferable that the resin contains at least one of polyester resin, polyurethane resin, or acrylic resin as the main component. Here, "main component" refers to a component that accounts for 50% by mass or more of the solid components that make up the resin layer. The resin layer-forming material (coating liquid) used to form the resin layer of the present invention is preferably an aqueous coating liquid containing at least one of water-soluble or water-dispersible copolymer polyester resin, acrylic resin, and polyurethane resin.

[0034] The aqueous resin of the present invention may contain two or more types to improve adhesiveness. For example, to achieve both adhesion and moist heat resistance, two or more different resins, such as a combination of a polyester resin and a urethane resin, a polyester resin and an acrylic resin, or a urethane resin and an acrylic resin, may be used. Furthermore, two or more polyester resins with different glass transition temperatures may be used.

[0035] In the present invention, a crosslinking agent may be contained in the resin layer-forming material to form a crosslinked structure in the resin layer. By containing a crosslinking agent, it becomes possible to further improve adhesion under high temperature and high humidity conditions. Examples of crosslinking agents include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based crosslinkers. Among these, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based crosslinkers are preferred in terms of the stability of the coating liquid over time and the effect of improving adhesion under high temperature and high humidity treatment. Furthermore, a catalyst or the like may be used as needed to promote the crosslinking reaction.

[0036] The content of the crosslinking agent in the resin layer-forming material is preferably 1% by mass or more and 50% by mass or less of the total solid components, and more preferably 5% by mass or more and 30% by mass or less. By making the content above this range, the strength of the resin in the resin layer and the adhesion under high temperature and high humidity conditions can be increased, and by making the content below this range, a decrease in the flexibility of the resin in the resin layer can be suppressed, and a decrease in adhesion under normal temperature and high temperature and high humidity conditions can be easily suppressed.

[0037] The lubricant particles may be either inorganic particles or organic particles, and may be used in combination. The inorganic particles are not particularly limited, and examples thereof include silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, titanium dioxide, zirconium dioxide, tin oxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrated halloysite, magnesium carbonate, and magnesium hydroxide.

[0038] The organic particles are not particularly limited, but examples thereof include particles of polystyrene, melamine resin, acrylic, acrylic-styrene, silicone, benzoguanamine resin, benzoguanamine-formaldehyde condensation resin, polycarbonate, polyethylene, etc., and it is preferable that the particles of these resins are three-dimensionally crosslinked.

[0039] The inclusion of lubricant particles can impart lubricity, thereby suppressing the occurrence of wrinkles when the film is wound up during the film manufacturing process, etc., and blocking, in which films stick to each other due to tightening over time when the wound film roll is stored for a long period of time.

[0040] The average particle size of the lubricant particles is not particularly limited, but from the viewpoint of maintaining the transparency of the film, the average particle size of the lubricant particles is preferably 1 to 500 nm, and more preferably 1 to 100 nm. The average particle size is measured by dispersing the particles in a solvent that does not swell them using a Coulter counter (Multisizer II, manufactured by Beckman Coulter).

[0041] The lubricant particles preferably contain lubricant particles (p1) having a ratio (a / b) of the average particle size (a) to the resin layer thickness (b) of 0.45 or more and 1.5 or less, and the ratio (a / b) is preferably 0.5 or more and more preferably 1.3 or less. The presence of lubricant particles (p1) having an average particle size within the above ratio range in the resin layer reduces the amount of particles added that cause a decrease in transparency due to surface roughness, and can impart sufficient lubricity. The lubricant particles (p1) ensure sufficient lubricity by making the ratio (a / b) 0.45 or more, while making it 1.5 or less prevents the lubricant particles (p1) from falling off the resin layer, thereby making it easier to prevent wrinkles from occurring when the film is wound up and blocking from occurring when the film roll is stored for a long period of time.

[0042] The lubricant particles may be two or more types of particles with different average particle sizes. The lubricant particles (p1) having the ratio (a / b) of 0.45 to 1.5 or 0.45 to 1.3 are preferably the lubricant particles with the smallest average particle size among the two or more types of particles with different average particle sizes. When two or more types of particles with different average particle sizes are used as the lubricant particles, it is preferable to include one or more types of lubricant particles (p1) and one or more types of lubricant particles (p2) having a ratio (a / b) of the average particle size (a) to the resin layer thickness (b) of greater than 1.5. The ratio (a / b) for the lubricant particles (p2) is more preferably 3 or greater, and even more preferably 5 or greater. The presence of the lubricant particles (p2) in the resin layer together with the lubricant particles (p1) can contribute to transparency and lubrication. High lubricity can be ensured by setting the ratio (a / b) of the lubricant particles (p2) to more than 1.5. On the other hand, the ratio (a / b) of the lubricant particles (p2) is preferably 15 or less, and more preferably 10 or less, from the viewpoint of preventing particles from falling off.

[0043] When two or more types of particles having different average particle sizes are used as lubricant particles, they may be a combination of inorganic particles, a combination of organic particles, or a combination of inorganic particles and organic particles.

[0044] The content of the lubricant particles in the resin layer-forming material is preferably 0.5 parts by mass or more and 30 parts by mass or less relative to 100 parts by mass of the aqueous resin, the lower limit is more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, and the upper limit may be 25 parts by mass or less.

[0045] In particular, the content of the lubricant particles (p1) in which the ratio (a / b) is 0.45 or more and 1.5 or less, or 0.45 or more and 1.3 or less, or 0.5 or more and 1.5 or less, or 0.5 or more and 1.3 or less, is preferably 10 parts by mass or more and 30 parts by mass or less relative to 100 parts by mass of the aqueous resin, and the lower limit may be 12 parts by mass or more and the upper limit may be 25 parts by mass or less. By making it equal to or more than the above range, sufficient blocking resistance can be easily obtained. In addition, scratch resistance can be improved. By making it equal to or less than the above range, the transparency of the resin layer and the coating strength can be increased.

[0046] Furthermore, when the lubricant particles (p1) and the lubricant particles (p2) are used in combination, it is preferable that the total amount of the lubricant particles (p1) and the lubricant particles (p2) is used in a range of 30 parts by mass or less per 100 parts by mass of the aqueous resin. The content of the lubricant particles (p2) is preferably 0.05 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the aqueous resin, with the lower limit being 0.1 parts by mass or more or 0.2 parts by mass or more and the upper limit being 2 parts by mass or less or 1 part by mass or less. Alternatively, the content of the lubricant particles (p2) is preferably 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the lubricant particles (p1), with the lower limit being 1 part by mass or more and the upper limit being 5 parts by mass or less.

[0047] The resin layer-forming material may contain a surfactant to improve leveling during coating and to defoam the coating solution. The surfactant may be cationic, anionic, or nonionic, but silicone, acetylene glycol, or fluorine-based surfactants are preferred. These surfactants are preferably contained in the resin layer to an extent that does not impair adhesion with the functional layer laminated on the resin layer.

[0048] In order to impart other functionality to the resin layer-forming material, various additives may be added to the resin layer-forming material to the extent that the adhesion to the functional layer is not impaired. Examples of the additives include fluorescent dyes, fluorescent brighteners, plasticizers, ultraviolet absorbers, pigment dispersants, foam inhibitors, antifoaming agents, preservatives, and antistatic agents.

[0049] The additive to be contained in the resin layer-forming material is preferably an antistatic agent, which reduces static electricity when the film is transported during printing, and can suppress dust adsorption and separation defects caused by adhesion of films to each other due to frictional charging.

[0050] The antistatic agent is not particularly limited, but is preferably one that can suppress migration to the back surface of other articles that the resin layer comes into contact with or the film itself. Examples include nonionic antistatic agents whose functional groups are sorbitan, ether, ester, sorbitol, glucose, etc.; cationic antistatic agents such as quaternary ammonium salt, quaternary ammonium resin, imidazoline, Arcobel, Solomine A, etc.; anionic antistatic agents such as alkyl sulfate, alkyl phosphate, phosphoric acid ester salt, and sulfuric acid ester salt; and amphoteric surfactant or polymer antistatic agents such as betaine, amino acid, and aminosulfate. Since aqueous resins used in the resin layer are generally used as aqueous dispersions, anionic antistatic agents are preferred in terms of dispersion stability in the coating liquid.

[0051] The content of the antistatic agent contained in the resin layer is preferably 12 to 45 parts by mass relative to 100 parts by mass of the aqueous resin of the resin layer-forming material. The antistatic agent reduces static charge on the resin layer surface, thereby suppressing problems during printing. The content of the antistatic agent is more preferably 15 parts by mass or more, and even more preferably 18 parts by mass or more. The upper limit may be 40 parts by mass or less. By making the content of the antistatic agent greater than the above range, the required antistatic properties can be achieved, and printing problems such as poor appearance can be suppressed. Furthermore, by making the content of the antistatic agent less than the above range, the wettability of the resin layer surface can be appropriately controlled, and offset and blocking in a film roll due to excessive addition can be suppressed. The antistatic agent is contained in the resin layer in an amount within the above range.

[0052] In the present invention, a method for providing a resin layer on a stretched polylactic acid film substrate includes coating a resin layer-forming material (coating liquid) containing a solvent, lubricant particles, and an aqueous resin onto the polylactic acid film substrate and drying the coating liquid. From the viewpoint of environmental concerns, the solvent is preferably water or a mixture of water and a water-soluble organic solvent, and the water solvent in the coating liquid is preferably 50 to 95% by mass, and particularly preferably 60 to 90% by mass.

[0053] In the present invention, the solid content concentration in the resin layer forming material (coating liquid) for forming the resin layer is preferably 0.5 to 35% by mass, and particularly preferably 1.0 to 15% by mass.

[0054] Any known method can be used to apply the coating liquid to the polylactic acid film substrate, such as reverse roll coating, gravure coating, kiss coating, die coater, roll brush, spray coating, air knife coating, wire bar coating, pipe doctor coating, impregnation coating, curtain coating, etc. These methods can be used alone or in combination.

[0055] The method for forming the resin layer is not particularly limited, and conventional methods such as coating methods can be used. Among the coating methods, preferred are those in which the film surface is coated after the production of a stretched polylactic acid film substrate (offline coating method) and those in which the film is coated during the production process of a stretched polylactic acid film substrate (in-line coating method). In-line coating is preferred because it improves adhesion between the substrate film and the resin layer and reduces deterioration of the mechanical properties of the substrate film during production and heat wrinkles. In the case of an in-line coating method performed during the production process of a stretched polylactic acid film substrate, the drying and heat treatment conditions during coating vary depending on the coating thickness and the equipment conditions, but it is preferable to feed the film to a stretching process in the perpendicular direction immediately after coating and dry it in the preheating zone or stretching zone of the stretching process. In such cases, a temperature of about 50 to 120°C is usually preferred. Furthermore, the heat treatment step after stretching depends on the required mechanical properties of the stretched polylactic acid film substrate and the conditions of the equipment, but it is preferable to carry out the heat treatment at a temperature of 130°C or higher from the viewpoint of improving the adhesive strength between the stretched polylactic acid film substrate and the resin layer.

[0056] In the in-line coating method, the resin layer is formed by applying the coating liquid to an unstretched or uniaxially stretched polylactic acid film, drying the film, stretching the film at least uniaxially, and then heat-treating the film.

[0057] In the present invention, the thickness of the resin layer finally obtained is preferably 20 nm to 150 nm, more preferably 120 nm or less, and even more preferably 100 nm or less. If the thickness of the resin layer is less than 20 nm, the effect of the lubrication required in the present invention is almost lost. On the other hand, if the thickness of the resin layer exceeds the above range, the haze increases and the transparency decreases.

[0058] In the present invention, the diffusion component γd of the surface free energy of the final resin layer is preferably 33 mN / m or more. If the diffusion component γd of the surface free energy is less than 33 mN / m, the wettability of the polylactic acid film substrate is poor, resulting in uneven thickness during lamination of the resin layer, resulting in uneven coating and cissing, and poor coating appearance. In addition, the lubricant particles contained in the resin layer are unevenly distributed, resulting in a partial decrease in lubrication, which is undesirable because it is prone to wrinkles when the film is wound up and blocking when the film roll is stored for a long period of time. Furthermore, the diffusion component γd of the surface free energy is preferably as large as possible within manufacturing limits, but since a larger value increases hydrophilicity and makes the resin layer surface more susceptible to moisture absorption, it is preferably 80 mN / m or less. The diffusion component γd of the surface free energy may be 70 mN / m or less, 60 mN / m or less, 50 mN / m or less, or 45 mN / m or less. The diffusion component γd of the surface free energy is larger in a resin layer containing an antistatic agent than in a resin layer not containing an antistatic agent.

[0059] In addition, when the resin layer contains an antistatic agent, the antistatic property of the laminated polylactic acid film of the present invention is such that the surface resistivity of the resin layer surface is 1.0 × 10 １３ It is preferably Ω / sq or less, and 1.0×10 １２ Ω / sq or less is more preferable, and 1.0 × 10 １１ By setting the surface resistivity at or below this level, charging during film transport during printing processing can be reduced, and separation defects due to adhesion of dust and films to each other due to frictional charging can be suppressed. The surface resistivity of the resin layer surface is 1.0 × 10 ９ It is preferably 5.0×10 Ω / sq or more. ９ More preferably, Ω / sq or more, and 1.0×10 １０ By making it equal to or greater than the above range, bleeding out of the antistatic agent can be made less likely to occur.

[0060] (Laminated Polylactic Acid Film) The laminated polylactic acid film of the present invention can have any thickness depending on the desired purpose and application, such as mechanical strength and transparency. The thickness is not particularly limited, but is preferably 2 μm or more and 500 μm or less, more preferably 15 μm or more and 400 μm or less, and even more preferably 20 μm or more and 250 μm or less. If the thickness is too thin, handling tends to be poor. On the other hand, if the thickness is too thick, not only is there a cost problem, but when wound into a roll and stored, poor flatness is likely to occur due to curling.

[0061] The haze of the laminated polylactic acid film of the present invention is preferably 2.0% or less, more preferably 1.5% or less, and most preferably 1.0% or less. If it is 2.0% or more, the design of the printed matter will be deteriorated and the accuracy of detecting internal foreign matter, which is a defect in the functional film, will be reduced.

[0062] The static and dynamic friction coefficients of the laminated polylactic acid film of the present invention are both preferably 0.40 or more and 0.70 or less. If they are less than 0.40, the film roll is likely to slip during transport. On the other hand, if they exceed 0.70, the film has reduced lubricity and is likely to wrinkle during winding.

[0063] (Laminated polylactic acid film roll) A laminated polylactic acid film roll obtained by winding the laminated polylactic acid film of the present invention is also a preferred embodiment of the present invention. The resin layer of the present invention has good blocking resistance due to the addition of lubricant particles, so it can be suitably used even when formed into a roll body to improve productivity.

[0064] When the laminated polylactic acid film of the present invention is formed into a roll, its winding length and width are appropriately determined depending on the intended use of the film roll. The winding length of the film roll is preferably 1,500 m or more, more preferably 1,800 m or more. The upper limit of the winding length is preferably 5,000 m. The width of the film roll is preferably 150 mm or more, more preferably 200 mm. The upper limit of the width of the film roll is preferably 2,000 mm.

[0065] The laminated polylactic acid film of the present invention as described above can contribute to reducing the environmental load because it is made from non-petroleum-derived, biodegradable materials, and can easily be substituted for general plastics such as polyolefins, polyesters, and polyamides because it has the same printability and processability in film rolls as general plastics such as polyolefins, polyesters, and polyamides. It can also be suitably used as a packaging material for food, pharmaceuticals, industrial products, etc., or as a substrate for functional films.

[0066] The present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0067] (Evaluation Methods) The film properties of the laminated polylactic acid films obtained in Examples 1 to 8 and Comparative Examples 1 and 2 were measured and evaluated by the following methods (1) to (6). The results are shown in Table 1. The film properties of the laminated polylactic acid films obtained in Examples 11 to 20 and Comparative Examples 11 and 12 were measured and evaluated by the following methods (1), (2), and (4) to (7). The results are shown in Table 2.

[0068] Furthermore, with regard to the following film property (1): tensile modulus, if the thickness of the resin layer of the laminated polylactic acid film is 0.5 μm or less, the measurement results are not affected by the resin layer (even if there is an effect, it is within the range of measurement error), and the stretched polylactic acid film substrate (substrate film) can be measured by measuring the laminated polylactic acid film. Note that if the resin layer of the laminated polylactic acid film is so thick that it affects the measurement results, the resin layer can be scraped off with a razor or the like before measuring the following film property (1): tensile modulus.

[0069] (1) Tensile Modulus The tensile modulus of the laminated polylactic acid film was measured in accordance with JIS K 7127. A sample was cut into a strip of 200 mm long and 15 mm wide in both the MD and TD directions of the film using a single-edged razor, and two parallel benchmark lines 50 mm apart were marked in the center of the test piece. Next, the strip-shaped sample was clamped with a chuck distance of 100 mm using an Autograph AGS-X manufactured by Shimadzu Corporation and pulled at a rate of 0.5 mm / min. The tensile modulus (GPa) in each direction was determined from the resulting load-strain curves of 0.1 to 0.3%. The strain value was measured using the distance between the benchmark lines.

[0070] (2) Resin Layer Thickness: Samples were prepared using the following method and observed using a transmission electron microscope. First, the resulting laminated polylactic acid film was cut perpendicular to the film's flow direction and embedded in epoxy resin. The epoxy resin used was a mixture of Luabec 812, Luabec NMA (both manufactured by Nacalai Tesque), and DMP30 (manufactured by TAAB) in a mass ratio of 100:89:3. The sample film was embedded in the epoxy resin and then left in an oven at 60°C for 16 hours to cure the epoxy resin and obtain an embedded block. The resulting embedded block was mounted on a Nissei Sangyo Ultracut N to prepare ultrathin sections. First, a glass knife was used to trim the film until the cross section of the desired area for observation appeared on the resin surface. Next, ultrathin sections were cut using a diamond knife (Sumitomo Electric Industries, Sumiknife SK2045). The cut ultrathin sections were then collected on a mesh and thinly carbon-coated. Electron microscope observation was performed using a JEOL JEM-2010 microscope at an acceleration voltage of 200 kV. The resin layer thickness was measured from the electron microscope image of the film cross section. Tables 1 and 2 also show the ratio (a / b) of the average particle size (a) of the smallest average particle size lubricant particles used in the coating solution for forming the resin layer to the resin layer thickness (b). The ratios (a / b) in Tables 1 and 2 are rounded values.

[0071] (3) Diffusion component γd of surface free energy After leaving the laminated polylactic acid film sample in an atmosphere of 50% relative humidity for 24 hours, the contact angles of distilled water and diiodomethane were measured 1 minute after dropping them onto the resin layer using a FACE contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., CA-X model). Five measurements were taken for each sample, and the average of the three measurements excluding the maximum and minimum values ​​was used as the contact angle. The diffusion component γd of surface free energy was calculated from the contact angles of distilled water and diiodomethane.

[0072] (4) Haze of stretched polylactic acid film substrate and laminated polylactic acid film: Measured using a turbidity meter (NDH2000, manufactured by Nippon Denshoku) in accordance with JIS K7136. Laminated polylactic acid films with a haze of 2.0% or less were considered to be transparent, and those with a haze of 1.0% or less were considered to have good transparency. The haze of the stretched polylactic acid film substrate was measured by preparing films without laminating a resin layer using the production method of each example and comparative example.

[0073] (5) Coefficient of Friction A sample was prepared by cutting the film into an area of ​​8 cm x 5 cm. For convenience, one surface of the sample was designated as side A and the other surface as side B. This was fixed to the bottom of a 4.4 kg metal rectangular parallelepiped with a base measuring 6 cm x 5 cm, with side A facing outward. The 5 cm width of the sample was aligned with the 5 cm width of the metal rectangular parallelepiped, and one longitudinal edge of the sample was bent and fixed to the side of the metal rectangular parallelepiped with adhesive tape. Next, a sample was cut from the same film into an area of ​​20 cm x 10 cm, and the longitudinal end was fixed to a flat metal plate with side B facing up with adhesive tape. The metal rectangular parallelepiped with the sample attached was placed on top of the sample so that the measurement surface was in contact with the metal rectangular parallelepiped. The static friction coefficient (μs) and dynamic friction coefficient (μd) were measured at a pulling speed of 200 mm / min at 23°C and 65% RH. For the measurements, an RTM-100 manufactured by Toyo Baldwin Co., Ltd. was used, and the static friction coefficient (μs) and dynamic friction coefficient (μd) were calculated in accordance with JIS K-7125. A film having both a static friction coefficient (μs) and a dynamic friction coefficient (μd) of 0.30 or more and 0.70 or less was deemed to have good lubricity, and a film having both a static friction coefficient (μs) and a dynamic friction coefficient (μd) of 0.40 or more and 0.60 or less was deemed to have good lubricity. If there were traces of blocking on the film unwound from the roll, a sample was cut out from the portion of the film unwound from the roll where there were traces of blocking.

[0074] (6) Blocking Resistance Two film samples were stacked on top of each other, and a pressure of 1 kgf / cm ２ After the pressure was applied for 24 hours in an atmosphere of 40°C, the film was peeled off, and the peeling state was evaluated according to the following criteria: A: The coating layer was not transferred and the film could be easily peeled off. －A: A slight peeling noise is generated, but the coating layer is not transferred and the film can be peeled off. B: A peeling noise is generated and the coating layer is partially transferred to the other surface. C: The two films are stuck together and cannot be peeled off, or the film can be peeled off but the base film has cleaved. The blocking resistance is ranked as A or A. － Those ranked A or B were judged to have blocking resistance, and those ranked A were judged to be particularly good.

[0075] (7) Antistatic Surface Resistivity Value Five 5.0 cm square pieces were cut out of the laminated polylactic acid film to prepare samples. The resin layer surfaces of the samples were measured using a surface resistance measuring instrument (Hiresta MCP-HT800, manufactured by Nitto Seiko Analic) at 23°C and 65% humidity with an applied voltage of 500 V in accordance with JIS K6911 for each of the five pieces, and the average value was taken as the surface resistivity value. When the surface resistivity value was 1.0 × 10 １３ Those with a resistance of 1.0×10 Ω / sq or less are considered to have antistatic properties, and １２ When the film had a resistance of 0.01 Ω / sq or less, the antistatic property was judged to be good. If there were any traces of blocking on the film unwound from the roll, a sample was cut out from the part of the film unwound from the roll where there were traces of blocking.

[0076] (8) Reduced Viscosity (ηsp / c) A solution prepared by dissolving 0.1 g of a sample in 15 mL of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (75 / 25 (mass ratio)) was measured at 30°C using an Ostwald viscometer. The unit is dl / g. For the polylactic acid sample, the polylactic acid used as the film-forming material was crushed into chips and used, and for the laminated polylactic acid film, the film was cut with scissors and used. The solution was filtered before measurement to remove particles and the like.

[0077] The aqueous resin, lubricant particles, and antistatic agent used in the resin layer-forming material are as follows. The average particle size of the lubricant particles was determined by diluting the dispersion containing the lubricant particles with ion-exchange water so that the content of the lubricant particles in the dispersion was 0.05% by mass, and measuring the particle size distribution using a laser diffraction particle size distribution analyzer (SALD-7500, manufactured by Shimadzu Corporation). The average value of the particle size distribution was calculated, and this was taken as the average particle size.

[0078] (A-1: Aqueous Polyester Resin) Dimethyl terephthalate (95 parts by mass), dimethyl isophthalate (95 parts by mass), ethylene glycol (35 parts by mass), neopentyl glycol (145 parts by mass), zinc acetate (0.1 parts by mass), and antimony trioxide (0.1 parts by mass) were charged into a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, and a transesterification reaction was carried out at 180°C for 3 hours. Next, 5-sodium sulfoisophthalic acid (6.0 parts by mass) was added, and an esterification reaction was carried out at 240°C for 1 hour, followed by a polycondensation reaction at 250°C under reduced pressure (10 to 0.2 mmHg) for 2 hours to obtain a copolymerized polyester resin (A) having a number average molecular weight of 19,500 and a softening point of 60°C. 30 parts by mass of the copolymer polyester resin (A) and 15 parts by mass of ethylene glycol n-butyl ether were placed in a reactor equipped with a stirrer, a thermometer, and a reflux device, and the mixture was heated to 110°C and stirred to dissolve the resin. After the resin was completely dissolved, 55 parts by mass of water was gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to produce a milky white polyester water dispersion (A-1) with a solids content of 30% by mass. (A-2: Water-based acrylic resin) Nikazol RX-2035A (manufactured by Nippon Carbide Corporation, solids content 44% by mass) (A-3: Water-based ethylene copolymer resin) Hitec S-9201 (manufactured by Toho Chemical Industry Co., Ltd., solids content 20% by mass)

[0079] (Lo-1: Silica particles) Snowtex ST-30L (manufactured by Nissan Chemical Industries, Ltd., solid content 30% by mass) Using the evaluation method described above, the average particle diameter of the lubricant particles was 45 nm. (Lo-2: Silica particles) MP4540M (manufactured by Nissan Chemical Industries, Ltd., solid content 40% by mass) Using the evaluation method described above, the average particle diameter of the lubricant particles was 450 nm. (Ha-1: Anionic antistatic agent) TB702 (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., solid content 50% by mass)

[0080] (Examples 1 to 8, Comparative Examples 1 and 2) The polylactic acid used for the polylactic acid film substrate was poly-L-lactic acid PLA L175 (mass ratio of L-lactic acid / D-lactic acid: 99 / 1, reduced viscosity: 2.0 dl / g) manufactured by Total Corbion. Poly-L-lactic acid (L175) was dried under reduced pressure (1 Torr) at 120°C for 6 hours, then melted at 220°C using an extruder. The molten resin was extruded into a sheet from a T-die and brought into close contact with a cooling roll temperature-controlled at 50°C to obtain an unstretched sheet with a thickness of 500 μm. The resulting unstretched sheet was introduced into a roll-type stretching machine and stretched 3.0 times in the MD (machine direction) direction at 80°C using the difference in peripheral speed of the rolls. The coating solution used to form the resin layer, prepared in the proportions shown in Table 1 (the numerical values ​​for the aqueous resin and lubricant particles in Table 1 are all % by mass of the solution), was applied to one side of the obtained uniaxially stretched film by a fountain coat method in an amount of 5.0 g / m ２ The in-line coated uniaxially stretched film was then continuously introduced into a tenter-type stretching machine, preheated at 70°C, and stretched in the transverse (TD) direction at 75°C to the stretching ratios shown in Table 1. The film was then heat-set at 140°C, relaxed at 120°C by 3%, and both ends were trimmed with a shear blade. The laminated film was then wrapped around a 6-inch diameter cylindrical polypropylene core to obtain laminated polylactic acid films of Examples 1 to 8 and Comparative Examples 1 and 2. The stretching ratio in the transverse (TD) direction, the haze of the stretched polylactic acid film substrate, the composition of the coating solution used to form the resin layer, and the properties of the resulting laminated polylactic acid films are as shown in Table 1.

[0081] The laminated polylactic acid films of Examples 1 to 8 satisfied the lubricity and blocking resistance, with Examples 1 to 6 being particularly good. The reduced viscosity of the laminated polylactic acid film obtained in Example 1 was 1.8 dl / g.

[0082] On the other hand, Comparative Examples 1 and 2 were satisfactory in terms of blocking resistance but were unable to satisfy the lubricity requirement.

[0083] In Examples 1 to 8 and Comparative Examples 1 and 2, the antistatic properties (surface resistivity) of (7) above were all less than 1.0 × 10 １４ It was super.

[0084]

[0085] (Examples 11 to 20, Comparative Examples 11 and 12) Laminated polylactic acid films were obtained in the same manner as in Example 1, except that the TD (transverse) stretching ratio and the composition of the coating solution used to form the resin layer (the numerical values ​​for the aqueous resin, lubricant particles, and antistatic agent in Table 2 are all in mass % of the solution) were changed as shown in Table 2. The haze of the stretched polylactic acid film substrate is also shown in Table 2.

[0086] The laminated polylactic acid films of Examples 11 to 20 satisfied the requirements for lubricity, anti-blocking property, and antistatic property, and Examples 1 and 4 to 7 were particularly good.

[0087] On the other hand, Comparative Examples 1 and 2 were satisfactory in terms of anti-blocking property and anti-static property, but were unable to satisfy the requirement for lubricity.

[0088]

[0089] The laminated polylactic acid film of the present invention is made from non-petroleum-derived, biodegradable materials, and therefore contributes to reducing the environmental impact. Furthermore, it has the same printability and processability in film rolls as common plastics such as polyolefins, polyesters, and polyamides, making it an easy substitute for them. It can be suitably used as a packaging material for food, pharmaceuticals, industrial products, etc., or as a base material for functional films.

Claims

1. A laminated polylactic acid film having a stretched polylactic acid film substrate and a resin layer on at least one side of the stretched polylactic acid film substrate, wherein the stretched polylactic acid film substrate is substantially free of lubricants, the resin layer is formed from a resin layer forming material containing an aqueous resin and lubricant particles, and the tensile modulus of the stretched polylactic acid film substrate is 4.0 GPa or more in both the MD direction and the TD direction.

2. The laminated polylactic acid film according to claim 1, wherein the difference in tensile modulus between the MD and TD directions of the stretched polylactic acid film substrate is 1.0 GPa or less.

3. The laminated polylactic acid film according to claim 1 or 2, wherein the resin layer is formed from a resin layer-forming material containing a water-based resin, lubricant particles, and an antistatic agent.

4. The laminated polylactic acid film according to claim 3, wherein the antistatic agent is an anionic antistatic agent.

5. A laminated polylactic acid film as described in claim 3 or 4, wherein the content of the antistatic agent in the resin layer forming material is 12 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the aqueous resin.

6. The laminated polylactic acid film according to any one of claims 1 to 5, wherein the thickness of the resin layer is 20 nm or more and 150 nm or less.

7. A laminated polylactic acid film according to any one of claims 1 to 6, wherein the lubricant particles contained in the resin layer forming material include lubricant particles (p1) having a ratio (a / b) of average particle diameter (a) to resin layer thickness (b) of 0.45 or more and 1.5 or less.

8. A laminated polylactic acid film according to any one of claims 1 to 6, wherein the resin layer forming material contains two or more types of lubricant particles having different average particle sizes, and the lubricant particles include one or more types of lubricant particles (p1) having a ratio (a / b) of average particle size (a) to resin layer thickness (b) of 0.45 or more and 1.5 or less, and one or more types of lubricant particles (p2) having a ratio (a / b) of average particle size (a) to resin layer thickness (b) of more than 1.5 and 15 or less.

9. A laminated polylactic acid film as described in claim 7 or 8, wherein the content of the lubricant particles (p1) in the resin layer forming material is 10 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the aqueous resin.

10. A laminated polylactic acid film as described in claim 8 or 9, wherein the content of the lubricant particles (p2) in the resin layer forming material is 0.05 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the aqueous resin.

11. The laminated polylactic acid film according to any one of claims 1 to 10, wherein the diffusion component γd of the surface free energy of the resin layer is 33 mN / m or more.

12. The laminated polylactic acid film according to any one of claims 1 to 11, wherein the haze of the stretched polylactic acid film substrate is 0.3% or less.

13. The laminated polylactic acid film according to any one of claims 1 to 12, wherein the resin layer is formed by an in-line coating method.

14. A laminated polylactic acid film roll comprising the laminated polylactic acid film according to any one of claims 1 to 13.

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