Laminated polylactic acid film

Abstract

The present invention relates to a laminated polylactic acid film having a stretched polylactic acid film substrate and a resin layer on at least one surface of the stretched polylactic acid film substrate, wherein the stretched polylactic acid film substrate substantially does not contain a lubricant, the resin layer is formed of a resin layer forming material containing an aqueous resin and lubricant particles, the tensile modulus of the stretched polylactic acid film substrate is 4.0 GPa or more in both the MD and TD directions, and the resin layer forming material may contain an antistatic agent. According to the present invention, it is possible to provide a laminated polylactic acid film that is easy to print and process and has excellent transparency.

Description

[Technical Field]

[0001] This invention relates to a laminated polylactic acid film with good printability and processability. More specifically, it relates to a laminated polylactic acid film that is easy to print on roll-to-roll and also has high transparency. Furthermore, it relates to a laminated polylactic acid film that can suppress static electricity during film transport. [Background technology]

[0002] Generally, plastics such as polyolefins, polyesters, and polyamides are used as base materials for packaging materials and functional films used in food, pharmaceuticals, industrial products, etc. However, in recent years, due to growing environmental awareness, the development of polylactic acid films, which are made from non-petroleum raw materials and are biodegradable, has been progressing. Compared to general polyester and polyamide films, polylactic acid films have lower mechanical strength and heat resistance. This has led to problems such as wrinkles forming when the film is wound during the film manufacturing process, and blocking occurring when the wound film rolls are stored for long periods, causing the films to stick together due to tightening over time.

[0003] Therefore, as a method to suppress wrinkles that occur when winding film during film manufacturing processes, a method of adding lubricants or antiblocking agents to polylactic acid film has been proposed. (See, for example, Patent Documents 1 and 2) However, although both methods can suppress wrinkles, the presence of lubricants and antiblocking agents in the polylactic acid film causes light scattering within the film, reducing the transparency inherent in the polylactic acid film.

[0004] Furthermore, methods have been proposed to improve the mechanical strength and heat resistance of polylactic acid films, as well as to impart lubricity, by adjusting the composition ratio of L-lactic acid and D-lactic acid in the polylactic acid, or by adding biodegradable resins other than polylactic acid. (See, for example, Patent Documents 3 and 4.) However, because transparency was not considered, whitening occurred due to crystallization within the film and due to the compatibility of polylactic acid with the added biodegradable resin, resulting in unsatisfactory performance.

[0005] Therefore, a method has been proposed to improve transparency and impart lubricity by laminating a coating layer containing various resins and lubricants onto the surface of a polylactic acid film. (See, for example, Patent Documents 5 and 6.) However, because blocking occurs when the wound film roll is stored for a long period of time, there are practical limitations. To resolve this, it has been proposed to increase the surface roughness of the coated layer by including a large amount of particles, but this causes light scattering on the surface of the coated layer, resulting in high haze and reduced transparency, and satisfactory performance has not been achieved.

[0006] Furthermore, polylactic acid film is prone to static electricity due to its high electrical insulation properties. The generation of static electricity can often lead to problems during printing and other processes, such as dust adhesion and poor handling due to film-to-film adhesion caused by triboelectric charging.

[0007] Therefore, a method has 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 7-9) However, while all of them exhibited antistatic properties that could improve processability, none of them possessed high transparency. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2004-331860 [Patent Document 2] Japanese Patent Publication No. 2002-146064 [Patent Document 3] Japanese Patent Publication No. 2004-010900 [Patent Document 4] Japanese Patent Publication No. 2003-170560 [Patent Document 5] Japanese Patent Application Publication No. 10-120811 [Patent Document 6] Japanese Patent Publication No. 2005-212242 [Patent Document 7] Japanese Patent Publication No. 2006-347009 [Patent Document 8] Patent No. 5292949 [Patent Document 9] Japanese Patent Publication No. 2011-148915 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The object of the present invention is to solve the above-mentioned problems, namely, to provide a laminated polylactic acid film that is easy to print on and process, and also has excellent transparency, by using a film roll. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors diligently conducted research and finally completed the present invention. That is, the present invention is as follows. [Section 1] A laminated polylactic acid film comprising a stretched polylactic acid film substrate and a resin layer on at least one surface of the stretched polylactic acid film substrate, wherein the stretched polylactic acid film substrate substantially contains no lubricant, the resin layer is formed of 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. [Section 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 direction and the TD direction is 1.0 GPa or less. [Section 3] The laminated polylactic acid film according to claim 1 or 2, wherein the resin layer is formed of a resin layer forming material containing an aqueous resin, lubricant particles, and an antistatic agent. [Claim 4] The laminated polylactic acid film according to claim 3, wherein the antistatic agent is an anionic antistatic agent. [Claim 5] The laminated polylactic acid film according to claim 3 or 4, wherein in the resin layer forming material, the content of the antistatic agent is 12 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the aqueous resin. [Claim 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. [Claim 7] The 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 the average particle diameter (a) to the resin layer thickness (b) of 0.45 or more and 1.5 or less. [Claim 8] As the lubricant particles contained in the resin layer forming material, two or more types of particles having different average particle diameters are used, and the lubricant particles include one or more types of lubricant particles (p1) having a ratio (a / b) of the average particle diameter (a) to the resin layer thickness (b) of 0.45 or more and 1.5 or less, and include one or more types of lubricant particles (p2) having a ratio (a / b) of the average particle diameter (a) to the resin layer thickness (b) of more than 1.5 and 15 or less. The laminated polylactic acid film according to any one of claims 1 to 6. [Claim 9] The laminated polylactic acid film according to 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 with respect to 100 parts by mass of the aqueous resin. [Claim 10] The laminated polylactic acid film according to 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 with respect to 100 parts by mass of the aqueous resin. [Claim 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. [Section 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. [Section 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. [Section 14] A laminated polylactic acid film roll consisting of a laminated polylactic acid film as described in any of items 1 to 13. [Effects of the Invention]

[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 having a predetermined tensile modulus and being substantially free of lubricants. Due to the combination of the above configuration, it has excellent transparency and can be formed into film rolls, making printing and processing easy. It can be suitably used as a packaging material for food, pharmaceuticals, and industrial products, replacing conventional plastic films. Since the laminated polylactic acid film is made from non-petroleum raw materials and biodegradable materials, it makes a significant contribution to reducing the burden on the global environment. Furthermore, by including an antistatic agent in the resin layer, the laminated polylactic acid film can be given antistatic properties, suppressing static charge during film transport. [Best Mode for Carrying Out the Invention]

[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 predetermined catalyst. The predetermined catalyst is, for example, tin or aluminum. The polylactic acid preferably has a mass ratio of L-lactic acid (hereinafter referred to as L-form) to D-lactic acid (hereinafter referred to as D-form) 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. When the ratio of L-lactic acid (hereinafter referred to as L-form) to D-lactic acid (hereinafter referred to as D-form) is 100 / 0 to 85 / 15, high crystallinity can be obtained, making it easier to improve the film's properties, such as increasing the physical properties of the film and decreasing the thermal shrinkage rate, which is preferable. Polylactic acid may also contain copolymerized hydroxy acid components other than lactic acid. Examples of hydroxy acid components other than lactic acid include glycolic acid, 3-hydroxypropionic acid, and 6-hydroxycaproic acid (ε-caprolactone). Of the total components of polylactic acid (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 also be 99 mol% or more, or even 100 mol%.

[0014] In the present invention, the preferred glass transition temperature of polylactic acid is 40 to 70°C, the preferred melting point is 150 to 180°C, and the ability to undergo oriented crystallization is also preferred. The glass transition temperature and melting point can be obtained by differential scanning calorimeter (DSC) or the like. The presence or absence of crystallinity can be confirmed by the presence or absence of crystallization peaks during the heating process or the cooling process after melting using DSC.

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

[0016] The reduced viscosity (ηsp / c) of the stretched polylactic acid film (and laminated polylactic acid film) of the present invention is preferably in the range of 1.0 dl / g to 2.5 dl / g, and more preferably 1.2 to 2.3. When the reduced viscosity is 1.0 dl / g or higher, it is preferable because breakage does not occur frequently during the stretching process. When the reduced viscosity is 2.5 dl / g or lower, it is preferable because the cutability is good when cutting to a predetermined product width and dimensional defects do not occur. Since the reduced viscosity of polylactic acid tends to decrease when melted, it is preferable to reduce the decrease in reduced viscosity during film manufacturing 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 may contain resin components other than polylactic acid as a resin component, but it is preferable that the polylactic acid content in the total resin components of the film-forming material be 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 100% by mass. In other words, the film-forming material may consist only of polylactic acid.

[0018] The stretched polylactic acid film substrate used in the present invention preferably does not contain substantially lubricating particles (hereinafter also simply referred to as lubricants). Substantially lubricant-free does not necessarily mean that it does not contain any lubricants at all, and may contain lubricants in an amount that does not affect the surface roughness or slipperiness of the film. The amount of lubricant that may be included 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, and may also be 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 diameter of 0.01 to 10 μm, and more preferably an average particle diameter of 0.05 to 5 μm.

[0019] The film-forming material constituting the stretched polylactic acid film substrate used in the present invention may contain one or more additives, such as fluorescent whitening agents, ultraviolet inhibitors, infrared absorbing dyes, heat stabilizers, surfactants, and antioxidants, depending on the purpose of use. As antioxidants, aromatic amine-based and phenol-based antioxidants can be used, and as stabilizers, phosphorus-based (such as phosphoric acid and phosphate esters), sulfur-based, and amine-based stabilizers can be used.

[0020] The stretched polylactic acid film substrate used in the present invention is obtained by processing a film-forming material containing polylactic acid into an unstretched sheet using various methods, and then stretching it. 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 longitudinal or transverse, and more preferably a biaxially oriented film stretched in two directions, the MD direction (longitudinal) and the TD direction (transverse). Any stretching method can be used for the biaxially oriented film, such as simultaneous biaxial stretching or sequential biaxial stretching. One preferred method for sequential biaxial stretching is to stretch the unstretched film in the MD direction at a stretching ratio of 1.1 to 6.0 times at a temperature of 50 to 110°C using a roll-type stretcher, then stretch it in the TD direction at a stretching ratio of 1.1 to 10.0 times at a temperature of 60 to 140°C using a tenter-type stretcher, and after stretching, to perform a longitudinal relaxation treatment of 0.5 to 10% and a transverse relaxation treatment at a temperature of 90 to 180°C. Furthermore, it is preferable to employ an in-line coating method as the process for forming the resin layer described later, but in the sequential biaxial stretching process described above, the resin layer can be coated onto the film before stretching or the film after stretching in the MD direction, and then the film can be continuously guided to a tenter-type stretcher for stretching in the TD direction and heat treatment.

[0021] The stretched polylactic acid film substrate used in the present invention may be a single-layer 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 and other plastic films (which may be two or more types) are laminated together. Furthermore, it may be a laminated film having multiple polylactic acid layers with different compositions of additives, etc. In the case of a laminated film, the type of laminate is not particularly limited as long as there are polylactic acid layers, and the number of layers, lamination method, etc., can be arbitrarily selected from known methods depending on the purpose.

[0022] (Physical properties of stretched polylactic acid film substrates) 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 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 on multiple rolls and the handlingability of the manufactured 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 modulus of elasticity.

[0024] The tensile modulus of the stretched polylactic acid film substrate of the present invention is preferably 4.0 GPa or higher in both the MD and TD directions, and more preferably the difference between the tensile modulus of the MD and TD directions is 1.0 GPa or less. If the tensile modulus of either the MD or TD direction is less than 4.0 GPa, the rigidity of the film is insufficient, resulting in reduced lubricity when winding the film, and making it prone to blocking when the wound film roll is stored for a long period of time. The structure of the laminated polylactic acid film of the present invention ensures the lubricity of the film by creating protrusions on the surface of the resin layer due to lubricant particles contained in the resin layer. By increasing the tensile modulus of either the MD or TD direction of the stretched polylactic acid film substrate, 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 pushed towards the stretched polylactic acid film substrate, thus ensuring high lubricity and resistance to blocking.

[0025] Furthermore, if the difference in tensile modulus between the MD and TD directions exceeds 1.0 GPa, when a wound film roll is stored for a long period, wrinkles and localized blocking are likely to occur due to tightening over time. Also, when unwinding a blocked film roll, peeling of the resin layer, detachment of lubricant particles, and reduction of surface irregularities in the resin layer may occur, reducing the slipperiness of the film in those areas and making it easier for the film to unwind. Moreover, if the resin layer, as described later, contains an antistatic agent, the antistatic agent contained in the resin layer may migrate to the back, reducing its antistatic function. This can lead to increased dust adhesion during film transport and a reduced effectiveness in suppressing problems such as poor unwinding due to adhesion between films caused by triboelectric charging. Furthermore, poor film handling refers to a phenomenon where, during the printing and distribution of individual sheets of film, the sheets become misaligned or overlap while being fed. This can result in not only unprinted film sheets but also machine problems such as jams, wrinkles, and folds in the film. By appropriately controlling the tensile modulus of the stretched polylactic acid film substrate, the amount of lubricant particles and antistatic agents added to the resin layer (described later) can be suppressed, enabling high transparency. This tensile modulus can be arbitrarily 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 higher in both the MD and TD directions. The preferred lower limit for the breaking strength in the MD and TD directions is 100 MPa, a more preferred lower limit is 150 MPa, an even more preferred lower limit is 200 MPa, and an even more preferred lower limit is 220 MPa. A breaking strength of 75 MPa or higher is preferable because it provides sufficient mechanical strength for the film, suppressing defects such as elongation and slippage during the film processing process. Considering manufacturing considerations, the upper limit is considered to be 1000 MPa.

[0027] The elongation at break of the stretched polylactic acid film substrate is preferably 5% or more in both the MD direction and the TD direction. An elongation at break of 5% or more in both the MD and TD directions is preferable because it ensures sufficient mechanical elongation of the film, thereby suppressing defects such as cracking and tearing during the film processing process. Considering manufacturing considerations, the upper limit is considered to be 300%. The upper limit is more preferably 150%, even more preferably 100%, and even more preferably 80%.

[0028] For stretched polylactic acid film substrates, it is preferable that the thermal shrinkage rate in the MD direction and the TD direction are both 10.0% or less when heated at 150°C for 30 minutes. When heated at 150°C for 30 minutes, the upper limits of the thermal shrinkage rate in the MD direction and the TD direction are 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, independently for the MD direction and the TD direction, respectively. A low thermal shrinkage rate facilitates processing such as printing and suppresses appearance defects due to deformation of the film under high heat. While a low thermal shrinkage rate is preferable, from a manufacturing standpoint, 0.01% is considered the lower limit.

[0029] For stretched polylactic acid film substrates, it is preferable that the thermal shrinkage rate in the MD direction and the TD direction are both 3.0% or less when heated at 120°C for 30 minutes. When heated at 120°C for 30 minutes, the upper limits of the thermal shrinkage rate in the MD direction and the TD direction are 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, independently for the MD direction and the TD direction, respectively. A low thermal shrinkage rate facilitates processing such as coating and suppresses appearance defects due to deformation of the film under high heat. While a low thermal shrinkage rate is preferable, from a manufacturing standpoint, 0.01% is considered the lower limit.

[0030] The total light transmittance of the stretched polylactic acid film substrate is preferably 80% or higher. High transparency is preferable in order to improve the accuracy of detecting internal foreign matter, which is a drawback of the film. Therefore, the total light transmittance of the film of the present invention is preferably 85% or higher, and particularly preferably 90% or higher. By setting it to 80% or higher, it is possible to improve the accuracy of detecting internal foreign matter, which is a drawback of the functional film and can lead to a decrease in the design quality of printed materials.

[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 it at 0.3% or less, it is possible to improve the accuracy of detecting internal foreign matter, which can lead to a decrease in the design quality of printed materials and a drawback of functional films.

[0032] (Resin layer) The resin layer in this invention is laminated on at least one side of a stretched polylactic acid film substrate. The resin layer in this invention is formed from a resin layer forming material containing an aqueous 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 it mainly consists of at least one of polyester resin, polyurethane resin, or acrylic resin. Here, "main component" refers to a component that makes up 50% by mass or more of the solid components constituting 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 of resins to improve adhesion. For example, to achieve both adhesion and heat and humidity resistance, two or more different resins may be used in combination, such as polyester resin and urethane resin, polyester resin and acrylic resin, or urethane resin and acrylic resin. Alternatively, two or more polyester resins with different glass transition temperatures may be used.

[0035] In this invention, a crosslinking agent may be included in the resin layer forming material to form a crosslinked structure in the resin layer. By including a crosslinking agent, it is 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 agents. Among these, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based agents are preferred due to their long-term stability of the coating solution and their effect on improving adhesion under high temperature and high humidity treatment. Furthermore, catalysts and the like may be used as needed to promote the crosslinking reaction.

[0036] The crosslinking agent content in the resin layer forming material is preferably 1% by mass or more and 50% by mass or less of the total solid components. More preferably, it is 5% by mass or more and 30% by mass or less. A content of 5% by mass or more increases the strength of the resin in the resin layer and its adhesion under high temperature and high humidity conditions. A content of 5% by mass or more increases the strength of the resin in the resin layer and its adhesion under high temperature and high humidity conditions. A content of 5% by mass or more increases the flexibility of the resin in the resin layer and makes it easier to suppress the decrease in adhesion under room temperature and high temperature and high humidity conditions.

[0037] The lubricant particles may be inorganic particles or organic particles, or a combination of both. The inorganic particles are not particularly limited, but examples 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 include particles of polystyrene, melamine resin, acrylic, acrylic-styrene, silicone, benzoguanamine resin, benzoguanamine-formaldehyde condensate resin, polycarbonate, polyethylene, etc., and it is preferable that these resin particles are three-dimensionally crosslinked.

[0039] By incorporating lubricant particles, slipperiness can be imparted, which can suppress wrinkle formation when winding the film during film manufacturing processes, and blockage (film sticking together due to tightening over time) when wound film rolls are stored for long periods.

[0040] The average particle size of the lubricant particles is not particularly limited, but from the standpoint of maintaining the transparency of the film, an average particle size of 1 to 500 nm is preferred, and 1 to 100 nm is more preferred. The average particle size is measured using a Coulter counter (Beckman Coulter, Multisizer Type II) after dispersing the particles in a solvent that does not cause swelling.

[0041] The lubricant particles preferably include lubricant particles (p1) whose ratio (a / b) of average particle diameter (a) to resin layer thickness (b) is 0.45 or more and 1.5 or less, preferably 0.5 or more, and more preferably 1.3 or less. The presence of lubricant particles (p1) with an average particle diameter within the range of the above ratio in the resin layer reduces the amount of particles added that cause a decrease in transparency due to surface roughness, and provides sufficient lubricity. By setting the ratio (a / b) of lubricant particles (p1) to 0.45 or more, sufficient lubricity is ensured, while setting it to 1.5 or less suppresses a decrease in lubricity due to the lubricant particles (p1) falling off the resin layer. Both of these factors make it easier to suppress the occurrence of wrinkles when winding the film and the occurrence of blocking when the film roll is stored for a long period of time.

[0042] The lubricant particles may consist of two or more types of particles with different average particle diameters. The lubricant particle (p1) having a ratio (a / b) of 0.45 to 1.5, or 0.45 to 1.3, is preferably the lubricant particle with the smallest average particle diameter among the two or more types of particles with different average particle diameters used. When two or more types of particles with different average particle diameters 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) whose ratio (a / b) of average particle diameter (a) to resin layer thickness (b) is greater than 1.5. The ratio (a / b) related to the lubricant particles (p2) is more preferably 3 or greater, and even more preferably 5 or greater. The presence of the lubricant particles (p2) together with the lubricant particles (p1) in the resin layer can contribute to transparency and lubricity. High lubricity can be ensured by making the ratio (a / b) related to the lubricant particles (p2) greater than 1.5. On the other hand, from the viewpoint of preventing particle detachment, the ratio (a / b) related to the lubricant particles (p2) is preferably 15 or less, and more preferably 10 or less.

[0043] Furthermore, when using two or more types of particles with different average particle sizes as lubricant particles, any combination of inorganic particles, organic particles, or a combination of inorganic and organic particles may be used.

[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 per 100 parts by mass of the aqueous resin, with a lower limit of 5 parts by mass or more, and even more preferably 10 parts by mass or more. On the other hand, the upper limit may be 25 parts by mass or less.

[0045] In particular, the content of lubricant particles (p1) such that 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 per 100 parts by mass of the aqueous resin, with a lower limit of 12 parts by mass or more and an upper limit of 25 parts by mass or less. By setting it to above, sufficient blocking resistance can be easily obtained. Also, scratch resistance can be improved. By setting it to below above, the transparency of the resin layer and the strength of the coating film can be increased.

[0046] Furthermore, when using the lubricant particles (p1) and lubricant particles (p2) in combination, it is preferable that the total amount of lubricant particles (p1) and lubricant particles (p2) is within 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, the lower limit may be 0.1 parts by mass or more, or 0.2 parts by mass or more, and the upper limit may be 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 content of the lubricant particles (p1), the lower limit may be 1 part by mass or more, and the upper limit may be 5 parts by mass or less.

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

[0048] The resin layer forming material may contain various additives to impart other functionalities, provided that these additives do not impair adhesion to the functional layer. Examples of such additives include fluorescent dyes, fluorescent whitening agents, plasticizers, ultraviolet absorbers, pigment dispersants, antifoaming agents, defoaming agents, preservatives, and antistatic agents.

[0049] An antistatic agent is preferred as an additive to be included in the resin layer forming material. By including an antistatic agent in the resin layer forming material, static charge during film transport in the printing process can be reduced, thereby suppressing dust adhesion and poor handling due to film adhesion caused by triboelectric charging.

[0050] While there are no particular limitations on the antistatic agent, it is preferable to use one that can suppress migration to other articles in contact with the resin layer or to the back surface of the film itself. Examples include nonionic types such as sorbitan, ether, ester, sorbitol, and glucose types; cationic types such as quaternary ammonium salts, quaternary ammonium resins, imidazoline, Arcover, and Solomin A types; anionic types such as alkyl sulfates, alkyl phosphates, phosphate esters, and sulfate esters; and amphoteric surfactant types or polymer types such as betaine, amino acid, and aminosulfate esters. Since aqueous resins used in the resin layer are generally used as aqueous dispersions, anionic antistatic agents are preferred due to their dispersibility and stability in the coating solution.

[0051] The amount of antistatic agent contained in the resin layer is preferably 12 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the aqueous resin of the resin layer forming material. The antistatic agent reduces static charge on the surface of the resin layer, thereby suppressing problems during printing. The amount of 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 increasing the amount of antistatic agent above the above, the required antistatic properties can be achieved, and problems during printing such as appearance defects can be suppressed. Furthermore, by decreasing the amount of antistatic agent below the above, the wettability of the resin layer surface can be appropriately controlled, and back-printing and blocking on the film roll due to excessive addition can be suppressed. The resin layer will contain the antistatic agent in the amount within the above range.

[0052] In the present invention, a method for providing a resin layer on a stretched polylactic acid film substrate is to apply a resin layer forming material (coating solution) containing a solvent, lubricant particles, and an aqueous resin to the polylactic acid film substrate and dry it. From the viewpoint of environmental issues, water or a mixture of water and a water-soluble organic solvent is preferred as the solvent, and the amount of aqueous solvent in the coating solution 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) that forms 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 solution to the polylactic acid film substrate. Examples include the reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, and the like. These methods can be used individually or in combination for coating.

[0055] The method for forming the resin layer is not particularly limited, and conventionally known methods such as coating methods can be used. Among coating methods, preferred methods include coating after manufacturing the stretched polylactic acid film substrate (offline coating method) and coating during the manufacturing process of the stretched polylactic acid film substrate (in-line coating method). However, the in-line coating method is preferred because it provides better adhesion between the substrate film and the resin layer, and minimizes deterioration of the mechanical properties of the substrate film during manufacturing and reduces thermal wrinkling. In the case of the in-line coating method performed during the manufacturing process of the stretched polylactic acid film substrate, the drying and heat treatment conditions during coating depend on the coating thickness and the conditions of the equipment, but it is preferable to immediately send the film to the stretching process in a perpendicular direction after coating and dry it in the preheating zone or stretching zone of the stretching process, and in such cases, it is usually preferable to set the temperature to around 50 to 120°C. Furthermore, although the heat treatment process after stretching depends on the required mechanical properties of the stretched polylactic acid film substrate and the conditions of the equipment, it is preferable to perform 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 solution to an unstretched or uniaxially stretched polylactic acid film, drying it, stretching it at least uniaxially, and then performing a heat treatment.

[0057] In the present invention, the thickness of the final resin layer is preferably 20 nm or more and 150 nm or less, 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 on the lubricity required in the present invention is almost lost. On the other hand, if the thickness of the resin layer exceeds the above, haze increases and transparency decreases.

[0058] In the present invention, it is preferable that the diffusion component γd of the surface free energy of the final resin layer is 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 when the resin layer is laminated, causing uneven coating and repelling, and resulting in a poor coating appearance. In addition, the lubricant particles contained in the resin layer become unevenly distributed, causing a partial decrease in lubricity, which is undesirable as it makes it easier for wrinkles to occur when winding the film and blocking to occur when the film roll is stored for a long period of time. Furthermore, it is preferable that the diffusion component γd of the surface free energy be as large as possible in terms of manufacturing, but as it becomes larger, the hydrophilicity increases and the surface of the resin layer becomes more susceptible to moisture absorption, so it is preferable that it be 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. Furthermore, the diffusion component γd of the surface free energy is larger in the resin layer containing an antistatic agent compared to the resin layer without an antistatic agent.

[0059] Furthermore, if the resin layer contains an antistatic agent, the antistatic properties of the laminated polylactic acid film of the present invention are such that the surface resistivity of the resin layer surface is 1.0 × 10⁻⁶. 13 It is preferable that the density is Ω / sq or less, and 1.0 × 10 12 A ratio of Ω / sq or less is even more preferable, and 1.0 × 10 11 A value of Ω / sq or less is most preferable. By keeping it below this level, static charge during film transport in the printing process can be reduced, and problems such as dust adhesion and poor handling due to film-to-film adhesion caused by triboelectric charging can be suppressed. The surface resistivity of the resin layer surface is 1.0 × 10⁻⁶. 9Preferably, the Ω / sq is greater than or equal to 5.0 × 10 9 A density of Ω / sq or higher is even more preferable, and 1.0 × 10 10 The Ω / sq or higher is also acceptable. By increasing the density to this level, it becomes less likely for the antistatic agent to bleed out, etc.

[0060] (Laminated polylactic acid film) The laminated polylactic acid film of the present invention can be used with 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 to 500 μm, more preferably 15 μm to 400 μm, and even more preferably 20 μm to 250 μm. If the thickness is too thin, handling is likely to be poor. On the other hand, if the thickness is too thick, not only are there cost issues, but when stored wound in a roll, poor flatness due to curling is likely to occur.

[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 quality of the printed material deteriorates, and the accuracy of detecting internal foreign matter, which is a drawback of the functional film, decreases.

[0062] The static and dynamic friction coefficients of the laminated polylactic acid film of the present invention are preferably both 0.40 or more and 0.70 or less. If the coefficient is less than 0.40, misalignment is likely to occur when the film roll is transported. On the other hand, if it exceeds 0.70, the slipperiness decreases, and wrinkles are more likely to occur when the film is wound up.

[0063] (Laminated polylactic acid film roll) A laminated polylactic acid film roll formed by winding the laminated polylactic acid film of the present invention is also a preferred embodiment of the present invention. Since the resin layer of the present invention has good blocking resistance due to the addition of lubricant particles, 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 made into a roll, the length and width of the roll are appropriately determined depending on the intended use of the film roll. The length of the film roll is preferably 1500m or more, and more preferably 1800m or more. The upper limit of the length is preferably 5000m. The width of the film roll is preferably 150mm or more, and more preferably 200mm. The upper limit of the width of the film roll is preferably 2000mm.

[0065] As described above, the laminated polylactic acid film of the present invention is made from non-petroleum raw materials and biodegradable materials, thus contributing to the reduction of environmental impact. Furthermore, it has printability and processability on film rolls similar to general plastics such as polyolefins, polyesters, and polyamides, making it easily replaceable. It can be suitably used as a packaging material or a base material for functional films used in food, pharmaceuticals, industrial products, etc. [Examples]

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

[0068] Furthermore, regarding the following film characteristic (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 will not be affected by the resin layer (or will be affected only to the extent of measurement error), and by measuring the laminated polylactic acid film, the stretched polylactic acid film substrate (substrate film) can be measured. If the resin layer of the laminated polylactic acid film is thick enough to affect the measurement results, the resin layer can be scraped off with a razor or the like before measuring the following film characteristic (1): tensile modulus.

[0069] (1) Tensile modulus The tensile modulus of the laminated polylactic acid film was measured in accordance with JIS K 7127. Strips of 200 mm in length and 15 mm in width were cut from the film in both the MD and TD directions, respectively, using a single-edged razor. Two parallel gauge marks were marked 50 mm apart in the center of each specimen. Next, the strips were clamped in a Shimadzu Autograph AGS-X with a 100 mm chuck distance and pulled at a speed of 0.5 mm / min. The tensile modulus (GPa) in each direction was determined from the resulting load-strain curves for 0.1-0.3%. The strain value was measured using the distance between the gauge marks.

[0070] (2) Thickness of the resin layer Samples were prepared using the following method and observed with a transmission electron microscope. First, the obtained laminated polylactic acid film was cut perpendicular to the film's flow direction and embedded in epoxy resin. The epoxy resin used was a well-mixed mixture of Luavec 812, Luavec NMA (both from Nacalai Tesque), and DMP30 (from TAAB) in a mass ratio of 100:89:3. After embedding the sample film in epoxy resin, it was left in an oven adjusted to 60°C for 16 hours to cure the epoxy resin and obtain an embedded block. The obtained embedded blocks were mounted on a Hitachi Sangyo UltraCut N to prepare ultrathin sections. First, a glass knife was used to trim the film until the cross-section of the portion to be observed was visible on the resin surface. Next, a diamond knife (Sumitomo Electric Industries, SumiKnife SK2045) was used to cut out the ultrathin sections. After collecting the cut ultrathin sections on a mesh, a thin layer of carbon deposition was applied. Electron microscopy observations were performed using a JEOL JEM-2010 under an acceleration voltage of 200kV. The thickness of the resin layer was measured from the images obtained by electron microscopy of the film cross-section. Tables 1 and 2 show the ratio (a / b) of the average particle size (a) of the lubricant particles with the smallest average particle size 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 samples in an atmosphere of 50% relative humidity for 24 hours, the contact angles of distilled water and diiodomethane were measured one minute after dropping them onto the resin layer using a FACE contact angle meter (Kyowa Interface Chemical Co., Ltd., CA-X type). 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 the surface free energy was then calculated from the contact angles of distilled water and diiodomethane.

[0072] (4) Haze of stretched polylactic acid film substrate and laminated polylactic acid film The turbidity was measured using a turbidimeter (NDH2000, manufactured by Nippon Denshoku) in accordance with JIS K7136. Laminated polylactic acid films with a turbidity of 2.0% or less were considered transparent, and those with a turbidity of 1.0% or less were judged to have particularly good transparency. For stretched polylactic acid film substrates, the haze was measured by taking film samples using the preparation methods of each example and comparative example without laminating the resin layer.

[0073] (5) Coefficient of friction A film was cut out to an area of 8 cm × 5 cm to create a sample. For convenience, one surface of the sample was designated as surface A and the opposite surface as surface B. This was fixed to the bottom surface of a metal rectangular parallelepiped with a weight of 4.4 kg and a bottom surface size of 6 cm × 5 cm such that surface A faced outward. At this time, the 5 cm width direction of the sample was aligned with the 5 cm width direction of the metal rectangular parallelepiped, and one side in the longitudinal direction of the sample was bent and fixed to the side surface of the metal rectangular parallelepiped with adhesive tape. Next, a sample was cut out from the same film to an area of 20 cm × 10 cm, and the longitudinal ends were fixed with adhesive tape with surface B facing up on a flat metal plate. The sample was placed so as to contact the measurement surface of the metal rectangular parallelepiped to which the sample was attached, and the static friction coefficient (μs) and dynamic friction coefficient (μd) were measured at 23°C and 65% RH with a pulling speed of 200 mm / min. For the measurement, RTM-100 manufactured by Toyo BALDWIN was used, and the static friction coefficient (μs) and dynamic friction coefficient (μd) were calculated in accordance with JIS K-7125. Those with both the static friction coefficient (μs) and dynamic friction coefficient (μd) being 0.30 or more and 0.70 or less were considered to have lubricity, and in particular, those with both being 0.40 or more and 0.60 or less were judged to have good lubricity. In addition, if there were traces of blocking on the film unwound from the roll, the sample was cut out from the part with traces of blocking on the film unwound from the roll.

[0074] (6) Blocking resistance The front and back surfaces of two film samples were overlapped, and a pressure of 1 kgf / cm 2 was applied for 24 hours in an atmosphere of 40°C and then peeled off, and the peeling state was judged according to the following criteria. A: Those with no transfer of the coating layer and can be peeled off easily A - : Those with slight peeling noise but no transfer of the coating layer and can be peeled off B: Those with peeling noise and partial transfer of the coating layer to the opposite surface C: Those where the two films are stuck and cannot be peeled off, or those where the base film is split even if peeled off The rank of this blocking resistance is A, A -Alternatively, those with a B rating were considered to have blocking resistance, and those with a rank of A were judged to be particularly good.

[0075] (7) Antistatic properties Surface resistivity Five 5.0 cm squares of laminated polylactic acid film were cut out and used as samples. The surface of the resin layer of each of the five samples was measured using a surface resistance meter (Nitto Seiko Analytic, Highresta MCP-HT800) at 23°C and 65% humidity with an applied voltage of 500V, in accordance with JIS K6911, and the average value was taken as the surface resistivity. If this surface resistivity is 1.0 × 10⁻⁶ 13 Materials with a density of Ω / sq or less are considered to have antistatic properties, especially 1.0 × 10⁻⁶. 12 Samples with a resistance of Ω / sq or less were judged to have good antistatic properties. If there were blocking marks on the film unwound from the roll, the sample was cut from the portion of the film showing these blocking marks.

[0076] (8) Reduced viscosity (ηsp / c) A solution prepared by dissolving 0.1 g of the 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 polylactic acid samples, the polylactic acid used as a film-forming material was crushed chips, and for laminated polylactic acid films, the film was cut with scissors. The solution was filtered before measurement to remove particles and other contaminants.

[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 deionized water so that the lubricant particle content in the dispersion was 0.05% by mass, and measuring the particle size distribution using a laser diffraction particle size analyzer (SALD-7500, Shimadzu Corporation). The average value of this particle size distribution was calculated and defined as the average particle size.

[0078] (I-1: Water-based 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 reaction vessel in a stainless steel autoclave equipped with a stirrer, thermometer, and 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 (10-0.2 mmHg) for 2 hours to obtain copolymer polyester resin (A) with a number average molecular weight of 19,500 and a softening point of 60°C. In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by mass of the copolymerized polyester resin (A) and 15 parts by mass of ethylene glycol n-butyl ether were placed and heated at 110°C, and the resin was stirred to dissolve it. After the resin was completely dissolved, 55 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white polyester aqueous dispersion (I-1) with a solid content of 30% by mass. (E-2: Water-based acrylic resin) Nikazol RX-2035A (manufactured by Nippon Carbide Co., Ltd., solid content 44% by mass) (E-3: Aqueous ethylene copolymer resin) Hi-Tech S-9201 (manufactured by Toho Chemical Industry Co., Ltd., solid content 20% by mass)

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

[0080] (Examples 1-8, Comparative Examples 1 and 2) For the polylactic acid used in the polylactic acid film substrate, we used poly-L-lactic acid PLA L175 manufactured by Total Corbion (mass ratio of L-lactic acid to D-lactic acid is 99 / 1, reduced viscosity is 2.0 dl / g). Poly-L-lactic acid (L175) was dried under reduced pressure at 120°C for 6 hours (1 Torr), then melted at 220°C using an extruder. The molten resin was extruded from a T-die into a sheet and brought into close contact with a cooling roll maintained at 50°C to obtain an unstretched sheet with a thickness of 500 μm. The obtained unstretched sheet was guided into a roll-type stretcher, and stretched 3.0 times in the MD (longitudinal) direction at 80°C using the difference in peripheral speed of the rolls. On one side of the obtained uniaxially oriented film, the coating solution used to form the resin layer (the values ​​for aqueous resin and lubricant particles in Table 1 are all mass % of the solution) prepared in the proportions listed in Table 1 was applied by the fountain coat method at a rate of 5.0 g / m². 2 It was adjusted to the desired consistency and then applied. Subsequently, the inline-coated uniaxially oriented film was continuously fed into a tenter-type stretcher, preheated to 70°C, stretched in the TD (transverse) direction at 75°C at the magnifications shown in Table 1, heat-set at 140°C, followed by a 3% relaxation treatment at 120°C, trimmed at both ends with shear blades, and the laminated film was wound around a 6-inch diameter cylindrical core made of polypropylene to obtain the laminated polylactic acid films of Examples 1-8 and Comparative Examples 1-2. The stretching ratio in the TD (transverse) 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 fabricated laminated polylactic acid film are shown in Table 1.

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

[0082] On the other hand, while Comparative Examples 1 and 2 satisfied the blocking resistance requirement, they failed to satisfy the lubricity requirement.

[0083] Furthermore, the antistatic properties (surface resistivity) of Examples 1 to 8 and Comparative Examples 1 and 2, as described in (7) above, were all 1.0 × 10⁻⁶. 14 It was incredible.

[0084] [Table 1]

[0085] (Examples 11-20, Comparative Examples 11-12) A laminated polylactic acid film was 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 values ​​for 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 11-20 satisfied the requirements for lubricity, blocking resistance, and antistatic properties, with Examples 1, 4-7 showing particularly good results.

[0087] On the other hand, while Comparative Examples 1 and 2 satisfied the requirements for blocking resistance and antistatic properties, they failed to satisfy the requirement for lubricity.

[0088] [Table 2] [Industrial applicability]

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

Claims

1. A laminated polylactic acid film having a stretched polylactic acid film substrate and a resin layer on at least one surface of the stretched polylactic acid film substrate, wherein the stretched polylactic acid film substrate substantially does not contain a lubricant, the resin layer is formed of 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. The resin layer forming material contains a laminated polylactic acid film comprising lubricant particles (p1) such that the ratio (a / b) of the average particle diameter (a) to the resin layer thickness (b) is 0.45 or more and 1.5 or less.

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

3. The laminated polylactic acid film according to claim 1, wherein the resin layer is formed of a resin layer forming material comprising an aqueous 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. The laminated polylactic acid film according to claim 3, 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 claim 1, wherein the thickness of the resin layer is 20 nm or more and 150 nm or less.

7. The resin layer forming material contains two or more types of lubricant particles with different average particle sizes, and the lubricant particles are It contains one or more types of lubricant particles (p1) whose ratio (a / b) of average particle diameter (a) to resin layer thickness (b) is 0.45 or more and 1.5 or less, The laminated polylactic acid film according to claim 1, comprising one or more lubricant particles (p2) having an average particle diameter (a) to resin layer thickness (b) ratio (a / b) of more than 1.5 and less than or equal to 15.

8. The laminated polylactic acid film according to claim 1, 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.

9. The laminated polylactic acid film according to claim 7, 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.

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

11. The laminated polylactic acid film according to claim 1, wherein the haze of the laminated polylactic acid film is 2.0% or less.

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

13. A laminated polylactic acid film roll comprising the laminated polylactic acid film according to any one of claims 1 to 12.

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