Multilayer polylactic acid film and release film

Abstract

The present invention is a multilayer polylactic acid film including a particle-containing layer and a first stretched polylactic acid film formed from a first film-forming material containing polylactic acid. The multilayer polylactic acid film has a tensile elastic modulus Ea in the longitudinal direction and a tensile elastic modulus Eb in the width direction that satisfy the formula Ea + Eb > 8.0 GPa and a crystallinity of 40-90%, and when heated at 150°C for 30 minutes, exhibits both a thermal shrinkage rate in the longitudinal direction and a thermal shrinkage rate in the width direction of 10.0% or less. According to the present invention, it is possible to provide a multilayer polylactic acid film having excellent elastic modulus and heat resistance by using polylactic acid being derived from a biomass raw material and having biodegradability.

Description

Multilayer polylactic acid film and release film

[0001] The present invention relates to a stretched polylactic acid film formed from a film-forming material containing polylactic acid, a multilayer polylactic acid film including a particle-containing layer, and a release film including the same.

[0002] Films made of polylactic acid (hereinafter sometimes referred to as "PLA") resin are derived from biomass materials and are biodegradable, and therefore are being developed as an alternative to conventional fossil fuels. However, compared to polyethylene terephthalate, nylon, polyolefin, and other commonly used industrial materials, polylactic acid films made of polylactic acid resin have a low modulus of elasticity and low heat resistance. Therefore, when used for industrial purposes, PLA films have problems such as dimensional changes and appearance defects such as wrinkles during processing.

[0003] To solve these problems, methods have been proposed that improve the film-forming conditions of PLA films. For example, Patent Document 1 discloses a production method in which longitudinal stretching is performed in two or more separate steps, followed by transverse stretching, and the second longitudinal stretching is performed at a temperature lower than the first stretching temperature, thereby improving heat resistance without impairing formability.

[0004] Japanese Patent Application Laid-Open No. 2004-359948

[0005] However, although the polylactic acid film produced by the method of Patent Document 1 has improved heat resistance, the second longitudinal stretching temperature is low, so the subsequent widthwise stretching ratio cannot be set high, resulting in a problem of low elastic modulus.

[0006] The above-mentioned conventional techniques have not been able to improve the tensile modulus in the longitudinal and transverse directions while also achieving good heat resistance. The present invention aims to provide a multilayer polylactic acid film, including a polylactic acid film, which is made using biomass-derived, biodegradable polylactic acid and has excellent modulus and heat resistance. Another object of the present invention is to provide a multilayer polylactic acid film that also has excellent slip properties. A further object of the present invention is to provide a release film using the multilayer polylactic acid film.

[0007] As a result of extensive research into polylactic acid films, the present inventors discovered that by multistage stretching a polylactic acid film multiple times at a high temperature near the melting point of polylactic acid, the stretching stress of the internal molecular chains can be suppressed and the total stretch ratio can be increased, and further, a particle-containing layer was provided. As a result, the crystallinity falls within a predetermined range, and the multilayer polylactic acid film of the present invention has been successfully improved in elastic modulus, heat resistance, and slip properties. That is, in order to solve the above problems, the present invention has the following configuration. [Item 1] A multilayer polylactic acid film comprising a first stretched polylactic acid film formed from a first film-forming material containing polylactic acid, and a particle-containing layer, wherein the multilayer polylactic acid film has a longitudinal tensile modulus Ea and a transverse tensile modulus Eb satisfying the formula Ea + Eb > 8.0 GPa, a crystallinity of 40% to 90%, and a heat shrinkage rate of 10.0% or less in both the longitudinal and transverse directions when heated at 150°C for 30 minutes. [Item 2] The multilayer polylactic acid film according to Item 1, wherein the heat shrinkage rate of 3.0% or less in both the longitudinal and transverse directions when heated at 120°C for 30 minutes. [Item 3] The multilayer polylactic acid film according to Item 1 or 2, wherein the first stretched polylactic acid film is a particle-free layer that is substantially free of particles. [Item 4] The multilayer polylactic acid film according to any one of Items 1 to 3, wherein the particle-containing layer is the outermost layer on at least one side of the multilayer polylactic acid film. [Item 5] The multilayer polylactic acid film according to Items 3 or 4, wherein the particle-containing layer is the outermost layer on one side of the multilayer polylactic acid film and the particle-free layer is the outermost layer on the other side of the multilayer polylactic acid film. [Item 6] The multilayer polylactic acid film according to any one of Items 3 to 5, wherein the multilayer polylactic acid film has a two-layer structure of the particle-containing layer and the particle-free layer. [Item 7] The multilayer polylactic acid film according to Items 5 or 6, wherein the dynamic friction coefficient (μd) when the particle-containing layer on the outermost side of one side and the particle-free layer on the outermost side of the other side are superimposed is 0.65 or less. [Item 8] The multilayer polylactic acid film according to any one of Items 1 to 7, wherein the mass ratio of L-lactic acid / D-lactic acid in the polylactic acid is 100 / 0 to 85 / 15.[Item 9] The multilayer polylactic acid film according to any one of Items 1 to 8, having a total light transmittance of 75% or more and a haze of 3% or less. [Item 10] The multilayer polylactic acid film according to any one of Items 1 to 9, wherein the particle-containing layer is a resin layer formed from a resin layer-forming material containing an aqueous resin and lubricant particles. [Item 11] The multilayer polylactic acid film according to Item 10, wherein the resin layer is formed by an in-line coating method. [Item 12] The multilayer polylactic acid film according to Items 10 or 11, wherein the resin layer has a surface free energy γs of 40 mN / m or more. [Item 13] The multilayer polylactic acid film according to any one of Items 1 to 9, wherein the particle-containing layer is a second stretched polylactic acid film formed from a second film-forming material containing polylactic acid and lubricant particles. [Item 14] The multilayer polylactic acid film according to Item 13, wherein the first stretched polylactic acid film and the second stretched polylactic acid film are stretched products of a laminate formed by multilayer co-extrusion of a first film-forming material and a second film-forming material. [Item 15] A release film having a release layer on at least one surface of the multilayer polylactic acid film according to any one of Items 1 to 14. [Item 16] The release film according to Item 15, wherein the release layer is provided on the first stretched polylactic acid film side, which is the outermost particle-free layer of the multilayer polylactic acid film. [Item 17] The release film according to Item 15 or 16, wherein the release layer is formed from a release layer-forming material containing a silicone release component. [Item 18] The release film according to Items 15 to 17, wherein the release film is used for producing a ceramic green sheet. [Item 19] The release film according to any one of Items 15 to 18, wherein the surface of the release layer has a maximum protrusion height (P) of 200 nm or less, and the surface of the release layer has an arithmetic mean roughness (Sa) of 10 nm or less.

[0008] The multilayer polylactic acid film of the present invention has excellent elastic modulus and heat resistance. Therefore, it has good dimensional stability during processing at high temperatures and high rigidity, making it suitable for industrial applications such as release film and optical applications. Furthermore, since it is made from biomass-derived raw materials and is biodegradable, it takes into consideration the recent SDGs. Furthermore, the multilayer polylactic acid film of the present invention has excellent slip properties in addition to elastic modulus and heat resistance. Therefore, its excellent slip properties enable smooth transport during winding and processing of the film.

[0009] The multilayer polylactic acid film of the present invention is a multilayer polylactic acid film comprising a first stretched polylactic acid film formed from a first film-forming material containing polylactic acid, and a particle-containing layer, wherein the tensile modulus Ea in the longitudinal direction (hereinafter also referred to as MD) and the tensile modulus Eb in the width direction (hereinafter also referred to as TD) satisfy the formula "Ea + Eb > 8.0 GPa," the crystallinity is 40% to 90%, and when heated at 150°C for 30 minutes, the heat shrinkage rates in both the longitudinal direction and the width direction are 10.0% or less. Furthermore, the multilayer polylactic acid film can be used as a release film having a release layer on at least one side.

[0010] (Embodiments of Multilayer Polylactic Acid Film) The multilayer polylactic acid film of the present invention includes a particle-containing layer in addition to the first stretched polylactic acid film. One embodiment of the particle-containing layer is, for example, a resin layer formed from a forming material containing an aqueous resin and lubricant particles. Hereinafter, this is also referred to as particle-containing layer (a), and when the particle-containing layer (a) is used, it is also referred to as multilayer polylactic acid film (A). Another embodiment of the particle-containing layer is, for example, a second stretched polylactic acid film formed from a second film-forming material containing polylactic acid and lubricant particles. Hereinafter, this is also referred to as particle-containing layer (b), and when the particle-containing layer (b) is used, it is also referred to as multilayer polylactic acid film (B). The multilayer polylactic acid film of the present invention can also be used in an embodiment in which the particle-containing layer (a) and the particle-containing layer (b) are combined with the first stretched polylactic acid film.

[0011] (First Stretched Polylactic Acid Film) The first stretched polylactic acid film of the present invention is formed from a first film-forming material containing polylactic acid.

[0012] (Polylactic Acid) The polylactic acid preferably used as the first film-forming material in the present invention 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. Polylactic acid can contain an L-lactic acid component and a D-lactic acid component as copolymer or blend components. In polylactic acid films and resin compositions, the mass ratio of L-lactic acid (hereinafter referred to as L-form) to D-lactic acid (hereinafter referred to as D-form) is preferably 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) to D-lactic acid (hereinafter referred to as D-form) of 100 / 0 to 85 / 15 is preferred because it provides high crystallinity, improves film physical properties, reduces heat shrinkage, and facilitates improvements in film properties. 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%.

[0013] 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.

[0014] The reduced viscosity (ηsp / c) of the first film-forming material containing polylactic acid 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 first stretched 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.

[0015] The reduced viscosity (ηsp / c) of the first stretched polylactic acid film (similarly for the multilayer polylactic acid film) used in the present invention 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 tends to lose its reduced viscosity when melted, so it is preferable to minimize the loss of reduced viscosity during film production by thoroughly drying the film-forming material containing polylactic acid and shortening the residence time in the molten state.

[0016] The first film-forming material constituting the first stretched polylactic acid film of the present invention can contain a resin component other than polylactic acid as a resin component, but the content of polylactic acid in the first 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. That is, the resin component may be composed solely of polylactic acid. Furthermore, the first film-forming material may be composed solely of polylactic acid.

[0017] Furthermore, the first stretched polylactic acid film is preferably a particle-free layer that is substantially free of particles. Substantially free of particles does not necessarily mean that it is completely free of particles, but may contain inactive particles such as lubricant particles, heat-resistant polymer particles, or crosslinked polymer particles, as described in the particle-containing layers (a) and (b) below, in an amount that does not affect the surface roughness or slipperiness of the film. The amount of lubricant particles 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, and even less than 5 ppm, relative to the first stretched polylactic acid film substrate (total amount of first film-forming material).

[0018] The first film-forming material constituting the first stretched polylactic acid film of the present invention may further contain one or more of various additives, such as fluorescent whitening agents, ultraviolet inhibitors, infrared absorbing dyes, heat stabilizers, surfactants, and antioxidants, depending on the intended use. Examples of antioxidants that can be used include aromatic amine-based and phenol-based antioxidants. 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.

[0019] (Method for Producing First Stretched Polylactic Acid Film) The first stretched polylactic acid film of the present invention is preferably an oriented film, more preferably a biaxially oriented film, from the viewpoints of mechanical strength, chemical resistance, heat resistance, etc.

[0020] The first film-forming material containing polylactic acid in the present invention can be processed into an unstretched sheet by various methods, and then subjected to stretching such as biaxial stretching to obtain a first stretched polylactic acid film. As a method for producing the unstretched sheet, a melt extrusion method can be used in addition to a solution casting method. The melt extrusion method is preferred in the present invention.

[0021] The melting temperature of the first film-forming material is preferably in the range of 150 to 250°C, more preferably 180 to 240°C. A temperature of 150°C or higher is preferred because it provides an appropriate melt viscosity and increases productivity. A temperature of 250°C or lower is preferred because it can suppress thermal degradation of polylactic acid.

[0022] The die temperature during melt extrusion is the same as described above, but is preferably 150 to 300°C, more preferably 170 to 290°C, and even more preferably 180 to 240°C. When the die temperature during melt extrusion is 150°C or higher, the melt viscosity falls within an appropriate range, allowing stable extrusion. When the temperature is 300°C or lower, thermal decomposition of the resin can be suppressed.

[0023] The first stretched polylactic acid film of the present invention can be produced according to a typical polyester film manufacturing method. For example, a polyester resin is melted and extruded into a sheet of unoriented polyester. The resulting sheet is stretched longitudinally at a temperature above its glass transition temperature using a roll speed differential, then stretched transversely using a tenter and heat-treated. Specifically, in the longitudinal stretching step, the film is heated and stretched 1.1 to 6 times between two or more rolls with different peripheral speeds. The heating method may involve the use of a heated roll or a non-contact heating medium, or a combination of these. In this case, the film temperature is preferably maintained within a range of (Tg - 10°C) to (Tg + 50°C). The uniaxially stretched film is then introduced into a tenter and stretched 1.1 to 10 times in the width direction at a temperature of (Tg - 10°C) to Tm.

[0024] Furthermore, after the stretching is completed, in order to reduce the thermal shrinkage rate of the film, it is preferable to carry out a heat setting treatment within 30 seconds, preferably within 10 seconds, in the heat setting step, and to carry out a longitudinal relaxation treatment and a transverse relaxation treatment of 0.5 to 10%.

[0025] The heat setting temperature is preferably in the range of 90 to 180° C. A heat setting temperature of 90° C. or higher is preferred because sufficient dimensional stability of the film due to heat can be obtained, while a heat setting temperature of 180° C. or lower is preferred because the phenomenon of holes being formed in the film due to heat can be suppressed.

[0026] The thickness of the first stretched polylactic acid film 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 first stretched polylactic acid film is 2 μm or more, the first stretched polylactic acid film has a minimum rigidity and is easy to handle. Furthermore, when the thickness of the first stretched polylactic acid film is 500 μm or less, the transportability of the film when transported between multiple rolls and the handleability of the produced film are improved, making it easier to handle.

[0027] (Particle-containing layer (a): Resin layer) The resin layer in the present invention is laminated on one side of the first stretched polylactic acid film. The resin layer-forming material in the present invention contains an aqueous resin and lubricant particles. The presence of the resin layer imparts easy lubricity for producing a film roll while maintaining the high transparency that is a characteristic of the multilayer polylactic acid film of the present invention.

[0028] The aqueous resin is not particularly limited, but preferably contains at least one of polyester resin, polyurethane resin, or acrylic resin as a main component (from the viewpoint of controlling the surface free energy γs of the resin layer, which will be described later). 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 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.

[0029] 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.

[0030] 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.

[0031] The content of the crosslinking agent in the resin layer 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 can be increased, and by making the content below this range, it is easier to suppress a decrease in the flexibility of the resin in the resin layer and a decrease in adhesion under normal temperature and high temperature and high humidity.

[0032] 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.

[0033] 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.

[0034] 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 wound film rolls are stored for long periods of time.

[0035] 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 the average particle size measured using a Coulter Counter (Multisizer II, manufactured by Beckman Coulter) after dispersing the particles in a solvent that does not swell the particles. The lubricant particles may be two or more types of particles with different average particle sizes, and may be any of a combination of inorganic particles, a combination of organic particles, or a combination of inorganic particles and organic particles.

[0036] The content of the lubricant particles in the resin layer is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 1 part by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the aqueous resin. By using an amount equal to or more than this amount, sufficient blocking resistance can be easily obtained and scratch resistance can be easily improved. By using an amount equal to or less than this amount, the transparency of the resin layer and the coating strength can be easily improved.

[0037] 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.

[0038] 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.

[0039] (Method for producing multilayer polylactic acid film (A)) The multilayer polylactic acid film (A) of the present invention can be produced by forming a resin layer, which is the particle-containing layer (a), on a first stretched polylactic acid film. In the present invention, an example of a method for providing a resin layer on a first stretched polylactic acid film is to apply a resin layer-forming material (coating liquid) containing a solvent, lubricant particles, and an aqueous resin to the polylactic acid film and dry it. 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, particularly preferably 60 to 90% by mass.

[0040] 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.

[0041] Any known method can be used to apply the coating liquid to the polylactic acid film. Examples include 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.

[0042] 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 thermal wrinkles. In the case of the in-line coating method performed in the process of producing the first stretched polylactic acid film, 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 process after stretching depends on the required mechanical properties of the first stretched polylactic acid film 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 first stretched polylactic acid film and the resin layer.

[0043] 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.

[0044] In the present invention, the thickness of the resin layer finally obtained is preferably 20 nm or more and 500 nm or less. By making the resin layer thickness 20 nm, it becomes easier to obtain a high effect on the lubricity required in the present invention. On the other hand, by making the resin layer thickness 500 nm or less, it becomes easier to suppress an increase in haze and a decrease in transparency.

[0045] In the present invention, the surface free energy γs of the final resin layer is preferably 40 mN / m or more. Since polylactic acid films have poorer wettability than general polyester films, a surface free energy γs of 40 mN / m or more improves the coatability of the aqueous resin, making it easier to achieve a uniform thickness when the resin layer is laminated, and making it easier to prevent coating unevenness and cissing, which can lead to poor coating appearance. It also prevents the uneven distribution of lubricant particles contained in the resin layer, which can prevent partial reduction in lubrication and reduce the occurrence of wrinkles when the film is wound up. Furthermore, the surface free energy γs is preferably as high as possible within manufacturing limits. However, since a higher surface free energy γs increases hydrophilicity and makes the resin layer surface more susceptible to moisture absorption, it is preferably 80 mN / m or less. The surface free energy γs may be 70 mN / m or less, 60 mN / m or less, 55 mN / m or less, or 50 mN / m or less.

[0046] (Particle-containing layer (b): Second stretched polylactic acid film) The second stretched polylactic acid film of the present invention is laminated on one side of the first stretched polylactic acid film. The second stretched polylactic acid film of the present invention is formed from a second film-forming material containing polylactic acid and lubricant particles. The lubricant particles can impart irregularities to the film surface, improving slipperiness.

[0047] The polylactic acid used in the second film-forming material can be the same as that used in the first film-forming material constituting the first stretched polylactic acid film. The content of polylactic acid in the second film-forming material can be in the same range as the content of polylactic acid in the first film-forming material. The additives exemplified for the first film-forming material can also be used.

[0048] The lubricant particles may be either inorganic particles or organic particles, or a combination of these may be used. Examples of the inorganic particles and organic particles include those used in the resin layer-forming material.

[0049] The average particle size of the lubricant particles used in the second film-forming material is preferably 0.01 μm or more, more preferably 0.1 μm or more, even more preferably 0.5 μm or more, particularly preferably 1.0 μm or more, and most preferably 1.5 μm or more. By making it above the above range, high slip properties can be imparted. The average particle size of the particles is preferably 10 μm or less, more preferably 5.0 μm or less, even more preferably 4.0 μm or more, particularly preferably 3.5 μm or more, and most preferably 3.0 μm or less. By making it above the above range or less, an increase in haze of the film can be suppressed and transparency can be increased.

[0050] It is also preferable to use two or more types of lubricant particles in combination. When using two or more types in combination, it is preferable to use two or more types with different average particle sizes.

[0051] Furthermore, the content of the lubricant particles in the second film-forming material constituting the layer is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and particularly preferably 0.2% by mass or more. By having a content above this level, good slip properties can be imparted. The content is preferably 2% by mass or less, more preferably 1.7% by mass or less, even more preferably 1.5% by mass or less, particularly preferably 1.2% by mass or less, and most preferably 1.0% by mass or less. By having a content above this level or less, an increase in haze of the multilayer polylactic acid film (B) can be suppressed and transparency can be improved.

[0052] The average particle size of the lubricant particles in the second film-forming material is measured by the following method. The particle size of the particles added to polylactic acid is measured by photographing them with a scanning electron microscope (SEM), randomly selecting 100 unagglomerated lubricant particles, and observing them. The average particle size is calculated as the average particle size. The particle size is calculated as the equivalent circle diameter. The equivalent circle diameter is calculated by dividing the area of ​​the observed lubricant particle by π, calculating the square root, and then multiplying it by two. The equivalent circle diameter is calculated using an image analyzer. The particle diameter in the film can be measured by embedding the film in epoxy resin, cutting out a cross section, observing the cross section with an SEM, randomly selecting 100 lubricant particles, determining the equivalent circle diameter, and averaging the results (average of 100 particles) to determine the average particle size. Alternatively, the film can be dissolved in a solvent such as HFIP, filtered through a membrane filter, and measuring the particle size of the particles remaining on the filter in the same manner.

[0053] (Layer Structure of Multilayer Polylactic Acid Film (B)) The multilayer polylactic acid film (B) of the present invention has a particle-containing layer (b) as a second stretched polylactic acid film on a first stretched polylactic acid film. The particle-containing layer (b) may be two or more layers. Furthermore, the first stretched polylactic acid film of the multilayer polylactic acid film (B) can be used as a particle-free layer or as a particle-containing layer, but the first stretched polylactic acid film is preferably a particle-free layer. Furthermore, the multilayer polylactic acid film (B) of the present invention preferably has at least one surface formed as a particle-containing layer (b), and both surfaces may be particle-containing layers (b). By forming at least one surface as a particle-containing layer (b), lubricity can be imparted, which can prevent wrinkles from occurring when the film is wound up during the film production process, etc., and can also prevent blocking, in which films stick to each other due to tightness over time when the wound film roll is stored for a long period of time.

[0054] In addition, it is also a preferred embodiment that one surface is a particle-containing layer (b) and the other surface is a particle-free layer. By making one surface a particle-free layer, when a release layer described below is provided on the particle-free layer surface of the multilayer polylactic acid film (B), it is possible to impart easy slipperiness during the production of a film roll while maintaining high smoothness of the release layer surface.

[0055] The thickness of the particle-containing layer (b) is preferably 0.5 μm or more, more preferably 1.0 μm or more. The thickness of the particle-containing layer (b) is preferably determined taking into consideration the thickness of the multilayer polylactic acid film (B), and based on the thickness (X μm) of the multilayer polylactic acid film (B), if the thickness of the multilayer polylactic acid film (B) is 15 μm or more, the thickness of the particle-containing layer (b) is preferably (X-2) μm or less, and if the thickness of the multilayer polylactic acid film (B) is 20 μm or more, the thickness of the particle-containing layer (b) is preferably (X-15) μm or less.

[0056] Representative examples of the layer structure of the multilayer polylactic acid film (B) are shown below. In the layer structures (1) to (4) below, it is preferable to use a first stretched polylactic acid film that is substantially free of particles as the particle-free layer. (1) Particle-containing layer (b) / particle-free layer (2) First particle-containing layer (b) / particle-free layer / second particle-containing layer (b) (3) First particle-containing layer (b) / second particle-containing layer (b) / particle-free layer (4) First particle-free layer / particle-containing layer (b) / second particle-free layer In the above structure (2), the first particle-containing layer (b) and the second particle-containing layer (b) may be formed from the same second film-forming material, or they may be different. If the second film-forming materials are different, it is preferable that the average particle diameters of the added lubricant particles be different. In the above (3), the first particle-containing layer (b) and the second particle-containing layer (b) preferably use second film-forming materials with different compositions, particularly with different contents of added lubricant particles. In this case, either the particle content of the first particle-containing layer (b) or the lubricant particle content of the second particle-containing layer (b) may be high, but the lubricant particle content of the first particle-containing layer (b) is preferred. The second particle-containing layer (b) may use recycled resin from the tenter gripping portion or the like generated during the production of the multilayer polylactic acid film (B). In the above (4), the first particle-free layer and the second particle-free layer preferably have different thicknesses, and at least one of the layers is preferably thin enough to ensure smoothness by creating surface irregularities due to the particles in the particle-containing layer (b). Specifically, the thickness of at least one particle-free layer is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, and particularly preferably 2 μm or less.

[0057] Furthermore, as in the layer structure (5) below, a first stretched polylactic acid film can be used as the first particle-containing layer. (5) First particle-containing layer (first stretched polylactic acid film) / second particle-containing layer (b) The above (5) is a case where lubricant particles are also contained in the first stretched polylactic acid film. In the above (5), the particle diameters of the lubricant particles added to the first particle-containing layer (first stretched polylactic acid film) and the second particle-containing layer (first stretched polylactic acid film) are preferably different, and the average particle diameter of the lubricant particles in one layer is preferably 0.1 μm or less or less than 0.1 μm, and preferably 0.08 μm or less.

[0058] The layer structure described above is the layer structure during the film formation process, and does not include the in-line coating layer when in-line coating is performed during the film formation process. In other words, it is the layer structure at the time when the first film-forming material of the first stretched polylactic acid film and the material for forming the particle-containing layer (b) are extruded in multiple layers from a die onto a cooling roll.

[0059] When the multilayer polylactic acid film (B) of the present invention comprises a particle-containing layer (b) and a particle-free layer, the thickness of the particle-containing layer (b) is preferably 1% or more, more preferably 3% or more, even more preferably 5% or more, and particularly preferably 7% or more of the total thickness of the multilayer polylactic acid film (B). By making it greater than the above, stable slip properties, film-forming properties, and thickness ratio can be ensured. From the viewpoint of suppressing an increase in haze of the multilayer polylactic acid film (B) and increasing transparency, the thickness of the particle-containing layer (b) is preferably 75% or less, more preferably 70% or less, even more preferably 60% or less, particularly preferably 50% or less, and most preferably 40% or less, and may be 30% or less, 25% or less, or even 20%.

[0060] (Method for Producing Multilayer Polylactic Acid Film (B)) The multilayer polylactic acid film (B) of the present invention can be obtained, for example, by laminating a second stretched polylactic acid film prepared in the same manner as the first stretched polylactic acid film.

[0061] The first and second film-forming materials in the multilayer polylactic acid film (B) can be processed into unstretched sheets by various methods, and then subjected to stretching such as biaxial stretching to obtain the first and second stretched polylactic acid films. As a method for producing the unstretched sheets, melt extrusion methods can be used in addition to solution casting. Melt extrusion methods are preferred in the present invention. Furthermore, during melt extrusion, multiple extruders can be used to melt the first and second film-forming materials, and the molten resin composition can be introduced into a multilayer coextrusion die to form a multilayer unstretched sheet.

[0062] The melting temperatures of the first and second film-forming materials, the stretching conditions of the unstretched sheet, the heat-setting process after stretching, and the heat-setting temperature can be the same as those described in the first method for producing a stretched polylactic acid film.

[0063] (Physical Properties of Multilayer Polylactic Acid Film) The thickness of the multilayer polylactic acid film 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 polylactic acid film is 2 μm or more, the multilayer polylactic acid film has a minimum rigidity and is easy to handle. Furthermore, when the thickness of the multilayer polylactic acid film is 500 μm or less, the transportability of the film when transported with multiple rolls and the handleability of the produced film are improved, making it easier to handle.

[0064] The sum of the tensile modulus Ea in the MD direction and the tensile modulus Eb in the TD direction of the multilayer polylactic acid film is preferably 8.0 GPa or more. The preferred lower limit of the sum of the tensile moduli is 8.2 GPa, more preferably 8.4 GPa, even more preferably 8.6 GPa, even more preferably 8.8 GPa, even more preferably 9.0 GPa, particularly preferably 9.5 GPa, and most preferably 10.0 GPa or more. A sum of the tensile moduli of 8.0 GPa or more is preferable because the film has sufficient rigidity and can suppress the occurrence of wrinkles and warping of the film. Considering manufacturing considerations, the upper limit of the sum of the tensile moduli is considered to be 15.0 GPa.

[0065] The tensile modulus Ea in the MD direction is preferably 3 GPa or more and 5 GPa or less, more preferably 3.3 GPa or more, even more preferably 3.5 GPa or less, and more preferably 4.7 GPa or more, even more preferably 4.5 GPa or less. The tensile modulus Eb in the TD direction is preferably 4 GPa or more and 6.5 GPa or less, more preferably 4.3 GPa or more, even more preferably 4.5 GPa or less, and more preferably 6.2 GPa or more, even more preferably 6 GPa or less.

[0066] In the layer structure of a multilayer polylactic acid film, when the outermost layer on one side is the particle-containing layer and the outermost layer on the other side is the particle-free layer, the upper limit of the dynamic friction coefficient (μd) when the particle-containing layer on one side and the particle-free layer on the other side are overlapped and slid is preferably 0.65, more preferably 0.60, even more preferably 0.55, and even more preferably 0.50. By making the dynamic friction coefficient (μd) 0.65 or less, the film's slipperiness is sufficient, and winding characteristics that affect wrinkles during film winding are improved, which is preferable. The lower limit of the dynamic friction coefficient is preferably 0.30, more preferably 0.35. By making it above the above limit, lateral slippage of the film when wound into a roll and lateral slippage of the film during roll transportation are less likely to occur.

[0067] The breaking strength of the multilayer polylactic acid film is preferably 75 MPa or more in both the MD and TD directions. The lower limit of the breaking strength 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. Considering manufacturing considerations, the upper limit of the breaking strength is considered to be 1000 MPa.

[0068] The breaking elongation of the multilayer polylactic acid film is preferably 5% or more in both the MD and TD directions. A breaking elongation of 5% or more is preferable because the mechanical elongation of the film is sufficient, preventing defects such as cracking and tearing during the film processing process. In consideration of manufacturing, the upper limit of the breaking elongation is thought to be 300%. The upper limit of the breaking elongation is more preferably 150%, even more preferably 100%, and even more preferably 80%.

[0069] When heated at 150°C for 30 minutes, the multilayer polylactic acid film preferably has a heat shrinkage rate of 10.0% or less in both the MD and TD directions. When heated at 150°C for 30 minutes, the upper limits of the heat shrinkage rates 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 low heat shrinkage rate facilitates processing such as coating, and can suppress poor appearance due to deformation of the film under high heat. A low heat shrinkage rate is preferred, but from a manufacturing standpoint, a lower limit of 0.01% is considered.

[0070] When heated at 120°C for 30 minutes, the multilayer polylactic acid film preferably has a heat shrinkage rate of 3.0% or less in both the MD and TD directions. When heated at 120°C for 30 minutes, the upper limits of the heat shrinkage rates 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 low 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, a lower limit of 0.01% is considered appropriate.

[0071] The total light transmittance of the multilayer polylactic acid film is preferably 75% 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 75% or more, more preferably 80% or more, even more preferably 85% or more, even more preferably 88% or more, particularly preferably 91% or more, and most preferably 93% or more. To improve the accuracy of detecting internal foreign matter, which can be a defect in the film, the higher the total light transmittance, the better, but achieving a total light transmittance of 100% is technically difficult. From a manufacturing standpoint, the total light transmittance is preferably less than 100%.

[0072] At least one surface of the multilayer polylactic acid film of the present invention is preferably smooth, and when used as a release film for producing ceramic green sheets, it preferably has a low haze. The haze is preferably 3% or less, more preferably 2% or less, and most preferably 1% or less. The lower limit of the haze is the better, but it may be 0.1% or more, or even 0.3% or more. In order to reduce the haze, it is preferable that the film surface does not have too much unevenness. However, in order to provide a certain degree of slipperiness from the viewpoint of handling ease against a rotating roll, it is preferable to form a certain degree of unevenness on at least one surface.

[0073] The crystallinity of the multilayer polylactic acid film 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. The crystallinity of the multilayer polylactic acid film (B) is measured using a differential scanning calorimeter by cutting a small piece from the film so as to include all layers of the polylactic acid film (B).

[0074] Furthermore, when a smooth release layer or the like is formed on the surface of a multilayer polylactic acid film, it is preferable that at least one surface of the multilayer polylactic acid film is also smooth. The roughness of the surface on which the release layer of the multilayer polylactic acid film is provided is preferably an arithmetic mean roughness (Sa) of 10 nm or less and a maximum protrusion height (P) of 200 nm or less. Furthermore, the arithmetic mean roughness of the surface is more preferably 10 nm or less and a maximum protrusion height of 150 nm or less, even more preferably 10 nm or less and a maximum protrusion height of 120 nm or less, and even more preferably 8 nm or less and a maximum protrusion height of 120 nm or less. If the arithmetic mean roughness of the surface is 10 nm or less and a maximum protrusion height of 200 nm or less, the surface of the release layer or the like formed on the surface can be smoothed to the same degree. The arithmetic mean roughness (Sa) of the surface of the polylactic acid film may be 0.1 nm or more, or may be 0.3 nm or more. Furthermore, the maximum protrusion height (P) on the surface may be 1 nm or more, or may be 3 nm or more.

[0075] The smooth surface is preferably the surface of a particle-free layer of a multilayer polylactic acid film in which the first stretched polylactic acid film of the multilayer polylactic acid film has a particle-free layer as its outermost surface, which is substantially free of particles. The surface roughness of the particle-free layer may be affected by particles in the underlying particle-containing layer. To suppress the influence of particles in the underlying layer and maintain the surface roughness of the particle-free layer at or below the above-mentioned level, the thickness of the particle-free layer on the release layer side is preferably 5 μm or more, more preferably 8 μm or more, even more preferably 10 μm or more, particularly preferably 12 μm or more, and most preferably 15 μm or more. The surface layer on the surface on which the release layer is to be formed may be a particle-containing layer, but the average particle diameter of the particles contained therein is preferably small. Specifically, the average particle diameter is preferably 0.1 μm or less, and more preferably 0.08 μm or less.

[0076] When the surface roughness of the multilayer polylactic acid film exceeds the above-mentioned roughness parameters, a particle-free coating layer may be provided on the surface, and a release layer may be provided on the outermost surface whose roughness is equal to or less than the above-mentioned roughness parameters. In this case, the surface on which the particle-free coating layer is provided may be either a particle-containing layer or a particle-free layer.

[0077] (Release Film) The release film of the present invention has a release layer on at least one surface of the multilayer polylactic acid film. The release layer is preferably provided on the particle-free layer side of the first stretched polylactic acid film, which is the outermost surface of the multilayer polylactic acid film. The release layer may be laminated directly on the particle-free layer of the multilayer polylactic acid film, or may be laminated via a functional layer. Examples of functional layers include an easy-adhesion layer, an antistatic layer, a barrier layer, and an ultraviolet absorbing layer. The release film of the present invention can be used as a release film for the production and transfer applications of ceramic green sheets, various resin sheets, and optical films, as well as for pressure-sensitive adhesive sheets and adhesive sheets.

[0078] (Release Layer) The release layer is formed from a release layer-forming material containing a release component. The release component resin constituting the release layer is not particularly limited, and silicone resin, fluororesin, alkyd resin, various waxes, aliphatic olefin, etc. can be used, and each resin can be used alone or in combination of two or more types. It is preferable that the release layer-forming material contains a silicone release component such as silicone resin or silicone oil.

[0079] For example, a silicone resin is a resin having a silicone structure within the molecule, and examples thereof include curable silicones, silicone graft resins, and modified silicone resins such as alkyl-modified silicones. However, from the viewpoint of migration, it is preferable to use a reactive curable silicone resin. Examples of reactive curable silicone resins that can be used include addition reaction-based resins, condensation reaction-based resins, and ultraviolet or electron beam curable resins. Low-temperature curable addition reaction-based resins that can be processed at low temperatures, and ultraviolet or electron beam curable resins are more preferable. The use of these silicone resins allows for low-temperature processing when coating polyester films. Therefore, heat damage to the polyester film during processing is reduced, resulting in a polyester film with high flatness. This also reduces defects such as pinholes when producing thin sheets such as ceramic green sheets.

[0080] Examples of silicone resins that use addition reactions include those that are cured by reacting polydimethylsiloxane, which has vinyl groups introduced into the terminals or side chains, with hydrogen siloxane using a platinum catalyst. In this case, it is more preferable to use a resin that can be cured within 30 seconds at 120°C, as this allows for processing at low temperatures. Examples include low-temperature addition cure types (LTC1006L, LTC1056L, LTC300B, LTC303E, LTC310, LTC314, LTC350G, LTC450A, LTC371G, LTC750A, LTC755, LTC760A, etc.) and thermal UV cure types (LTC851, BY24-510, BY24-561, BY24-562, etc.) manufactured by Dow-Toray Industries, and solvent addition + UV cure types (X62-5040, X62-5065, X62-5072T, KS5508, etc.) and dual cure cure types (X62-2835, X62-2834, X62-1980, etc.) manufactured by Shin-Etsu Chemical Co., Ltd.

[0081] An example of a condensation reaction silicone resin is one in which a three-dimensional crosslinked structure is formed by condensing a polydimethylsiloxane having an OH group at its terminal with a polydimethylsiloxane having an H group at its terminal using an organotin catalyst.

[0082] Examples of UV-curable silicone resins include, for example, the most basic type that utilizes the same radical reaction as normal silicone rubber crosslinking, those that introduce unsaturated groups to cause photocuring, those that use UV light to decompose onium salts to generate strong acids that then cleave epoxy groups to cause crosslinking, and those that crosslink via an addition reaction of thiol to vinyl siloxane. Electron beams can also be used instead of UV light. Electron beams have stronger energy than UV light, making it possible to carry out a radical-based crosslinking reaction without using an initiator as in UV curing. Examples of resins that can be used include UV-curable silicones manufactured by Shin-Etsu Chemical Co., Ltd. (X62-7028A / B, X62-7052, X62-7205, X62-7622, ​​X62-7629, X62-7660, etc.), UV-curable silicones manufactured by Momentive Performance Materials (TPR6502, TPR6501, TPR6500, UV9300, UV9315, XS56-A2982, UV9430, etc.), and UV-curable silicones manufactured by Arakawa Chemical Industries, Ltd. (SilicoLease UV POLY200, POLY215, POLY201, KF-UV265AM, etc.).

[0083] The UV-curable silicone resin may be an acrylate-modified or glycidoxy-modified polydimethylsiloxane, etc. Good release properties can also be achieved by mixing such modified polydimethylsiloxane with a polyfunctional acrylate resin or epoxy resin, etc., and using the mixture in the presence of an initiator.

[0084] Other suitable resins include stearyl-modified, lauryl-modified, and other long-chain alkyl group-containing alkyd and acrylic resins, as well as alkyd-based resins, acrylic resins, and olefin-based resins obtained by reactions such as methylated melamine. When molding sheets for use in electronic components, etc., release agents that do not contain silicone are also preferred.

[0085] Examples of the aminoalkyd resins and aminoacrylic resins obtained by the reaction of methylated melamine include the Tesfine series manufactured by Showa Denko Materials Co., Ltd.

[0086] When a release component such as the resin described above is used in the release layer-forming material, the release component may be used alone or in a mixture of two or more. When two or more types are mixed, two or more types of silicone-based resins may be used, and it is also preferable to mix a plurality of different resin types, such as a binder resin and a silicone-based resin.

[0087] In particular, when molding a thin film sheet such as a ceramic green sheet, it is preferable that the release layer does not deform when peeled off, so it is preferable that the release layer is crosslinked and hardened. Therefore, it is also preferable that the release layer-forming material contains a binder component, a crosslinking agent, etc. in addition to the silicone-based release agent.

[0088] The binder component contained in the release layer-forming material is preferably a crosslinked component that can be crosslinked to increase the crosslink density of the release layer and improve the durability and solvent resistance of the release layer. Therefore, the binder component is preferably formed by reacting a resin having a reactive functional group with a crosslinking agent. It is also preferable that either the reactive functional group or the crosslinking agent is self-crosslinked. However, the present invention does not exclude an embodiment in which the binder component is formed solely from a resin having a reactive functional group or a crosslinking agent.

[0089] Suitable examples of resins having a reactive functional group include polyester resins, acrylic resins, polyurethane resins, polyolefin resins, etc. These resins preferably have at least one reactive functional group selected from the group consisting of carboxyl groups, hydroxyl groups, epoxy groups, amino groups, etc.

[0090] It is also preferable that the release layer-forming material contains a crosslinking agent. Examples of preferred crosslinking agents include melamine-based, isocyanate-based, carbodiimide-based, oxazoline-based, and epoxy-based agents. One type of crosslinking agent may be used alone, or two or more types may be used in combination. Particularly preferred is a crosslinking agent that reacts with the reactive functional group introduced into the binder component.

[0091] The release layer forming material may contain particles having an average particle size of 1 μm or less, but from the viewpoint of preventing pinholes, it is preferable that the material does not substantially contain particles that form protrusions.

[0092] To the release layer-forming material, additives such as a light release additive or a heavy release additive, or additives such as an adhesion improver or an antistatic agent may be added in order to adjust the release force. Furthermore, in order to improve adhesion to the substrate layer, it is also preferable to subject the surface of the polylactic acid film to pretreatment such as anchor coating, corona treatment, plasma treatment, or atmospheric pressure plasma treatment before providing the release coating layer.

[0093] The thickness of the release layer may be set depending on the intended use and is not particularly limited, but is preferably in the range of 0.005 to 2.0 μm after curing. A release layer thickness of 0.005 μm or more is preferable because release performance is maintained. Furthermore, a release layer thickness of 2.0 μm or less is preferable because the curing time is not too long and there is no risk of uneven thickness of the sheet due to a decrease in the flatness of the release film. Furthermore, because the curing time is not too long, there is no risk of the resin constituting the release layer agglomerating and forming protrusions, which is preferable because pinhole defects in the sheet are less likely to occur.

[0094] The outer surface of the film on which the release layer is formed (i.e., the outer surface of the release layer) is preferably flat so as not to cause defects in the sheet to be coated and molded on the outer surface of the film. The arithmetic mean roughness (Sa) of the release layer surface is preferably 10 nm or less and the maximum protrusion height (P) is preferably 200 nm or less. Furthermore, the arithmetic mean roughness of the release layer surface is more preferably 10 nm or less and the maximum protrusion height is 100 nm or less, and even more preferably the arithmetic mean roughness of the release layer surface is 10 nm or less and the maximum protrusion height is 30 nm or less. If the arithmetic mean roughness of the release layer surface is 10 nm or less and the maximum protrusion height is 200 nm or less, defects such as pinholes do not occur during sheet formation, and the yield is good, which is preferable. It can be said that the smaller the arithmetic mean roughness (Sa) of the release layer surface, the better, but it may be 0.1 nm or more, or 0.3 nm or more. It can be said that the smaller the maximum protrusion height (P), the more preferable it is, but it may be 1 nm or more, or 3 nm or more.

[0095] The lower limit of the surface free energy of the release layer provided on the release film is 8 mJ / m ２ More preferably, it is 10 mJ / m or more. ２ or more, and 12 mJ / m ２ More preferably, it is 8 mJ / m or more. ２ If the thickness is more than this, repelling or the like is less likely to occur when the sheet dissolving solution is applied, which is preferable.

[0096] The upper limit of the surface free energy of the release layer provided on the release film is 45 mJ / m ２ It is preferably 40 mJ / m or less. More preferably, it is 40 mJ / m ２ less than 35 mJ / m ２ More preferably, it is 45 mJ / m ２ If it is less than this, the releasability of the molded sheet is good, which is preferable.

[0097] The method for forming the release layer is not particularly limited, and a method is used in which a coating liquid (release layer-forming material) in which at least a release component resin is dissolved or dispersed is spread on one side of the multilayer polylactic acid film by coating, etc., and the solvent is removed by drying, followed by heat drying, heat curing, or ultraviolet curing. In this case, the drying temperature during solvent drying and heat curing is preferably 180°C or less, more preferably 150°C or less, and most preferably 120°C or less. The heating time is preferably 30 seconds or less, more preferably 20 seconds or less. At 180°C or less, the flatness of the film is maintained and there is little risk of causing uneven thickness of the sheet, which is preferable. At 120°C or less, the film can be processed without impairing the flatness of the film, and there is a further reduction in the risk of causing uneven thickness of the sheet, which is particularly preferable.

[0098] The surface tension of the coating liquid when applying the release layer-forming material (coating liquid) is not particularly limited, but is preferably 30 mN / m or less. By adjusting the surface tension to the above range, the wettability after application can be improved and the unevenness of the coating film surface after drying can be reduced.

[0099] Although not particularly limited, it is preferable to add a solvent having a boiling point of 90° C. or higher to the coating liquid when applying the release layer-forming material (coating liquid). By adding a solvent having a boiling point of 90° C. or higher, bumping during drying can be prevented, the coating film can be leveled, and the smoothness of the coating film surface after drying can be improved. The amount of solvent added is preferably about 10 to 80% by mass of the total coating liquid.

[0100] Examples of the method for applying the coating liquid include roll coating methods such as gravure coating and reverse coating, bar coating using a wire bar, die coating, spray coating, and air knife coating.

[0101] (Ceramic Green Sheet and Ceramic Capacitor) Generally, a multilayer ceramic capacitor has a rectangular parallelepiped ceramic body. First internal electrodes and second internal electrodes are alternately provided inside the ceramic body along the thickness direction. The first internal electrodes are exposed at a first end face of the ceramic body. A first external electrode is provided on the first end face. The first internal electrode is electrically connected to the first external electrode at the first end face. The second internal electrode is exposed at a second end face of the ceramic body. A second external electrode is provided on the second end face. The second internal electrode is electrically connected to the second external electrode at the second end face.

[0102] The release film of the present invention is useful as a release film for producing ceramic green sheets for producing such multilayer ceramic capacitors. For example, it can be produced as follows. First, using the release film of the present invention as a carrier film, a ceramic slurry for forming a ceramic body is applied and dried. A conductive layer for forming a first or second internal electrode is printed on the applied and dried ceramic green sheet. A mother laminate is obtained by appropriately stacking and pressing a ceramic green sheet, a ceramic green sheet on which a conductive layer for forming a first internal electrode is printed, and a ceramic green sheet on which a conductive layer for forming a second internal electrode is printed. The mother laminate is then divided into multiple pieces to produce green ceramic bodies. The green ceramic bodies are then fired to obtain ceramic bodies. Then, first and second external electrodes are formed to complete the multilayer ceramic capacitor.

[0103] Next, the effects of the present invention will be explained using examples and comparative examples, but the present invention is not limited to the following examples. Examples 1 to 8 relate to multilayer polylactic acid film (A), and Examples 11 to 16 relate to multilayer polylactic acid film (B).

[0104] [Evaluation Methods] The film properties of the multilayer polylactic acid films and release films obtained in each Example were measured and evaluated by the following methods (1) to (8), (11), and (12). The same measurements and evaluations were also carried out for the Comparative Examples. Note that for Examples 1 to 8 and Comparative Examples 1 to 4, the following methods (9) and (10) were also measured and evaluated. The results are shown in Tables 2 and 4.

[0105] Furthermore, with regard to the following film properties, tensile modulus, crystallinity, heat shrinkage, breaking strength, and breaking elongation, if the thickness of the resin layer of the multilayer polylactic acid film (A) is 0.5 μm or less, the measurement results will not be affected by the resin layer (even if they are affected, it will be to the extent of measurement error). The tensile modulus of the multilayer polylactic acid film (A) can be measured by measuring the first stretched polylactic acid film.

[0106] (1) Thickness The thickness of the multilayer polylactic acid film was measured using a TH-104 manufactured by Tester Sangyo Co., Ltd. The thickness of each layer in Examples 11 to 16 relating to the multilayer polylactic acid film (B) was measured by embedding the multilayer polylactic acid film in epoxy resin, cutting out a cross section, and observing and measuring the cross section with a microscope.

[0107] (2) Crystallinity: Measurement was performed using a differential scanning calorimeter (DSC214Polyma) manufactured by Netsch Japan Co., Ltd. Using 10 mg of sample, measurements were performed over a range from 25°C to 250°C at a heating rate of 10°C / min, and the endothermic heat of the melting peak observed during heating was divided by the theoretical heat of fusion of fully crystalline polylactic acid (93.6 J / g) to determine the crystallinity (%) of the multilayer polylactic acid film. The sample used was a film cut so as to include all layers of the multilayer polylactic acid film.

[0108] (3) Tensile Modulus The tensile modulus of the multilayer 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 from 0.1 to 0.3%. The strain value was measured using the distance between the benchmark lines.

[0109] (4) Heat Shrinkage Rate The heat shrinkage rate of the multilayer polylactic acid film was measured in accordance with JIS C 2318. A 10 mm wide, 190 mm long piece of laminated film was cut in the direction to be measured, and marks were made at 150 mm intervals. The distance between the marks (A) was measured. The film was then placed in an oven at 150°C and heat-treated at 150±3°C for 30 minutes without load, after which the distance between the marks (B) was measured. The heat shrinkage rate at 150°C was calculated using the following formula. Similarly, a film cut out in the same manner as above was placed in an oven at 120°C and heat-treated at 120±3°C for 30 minutes without load, after which the distance between the marks (C) was measured, and the heat shrinkage rate at 120°C was calculated using the following formula: 150°C Heat Shrinkage Rate (%) = (A-B) / A×100 120°C Heat Shrinkage Rate (%) = (A-C) / A×100

[0110] (5) Breaking Strength and Breaking Elongation The breaking strength and breaking elongation of the multilayer polylactic acid film were measured in accordance with JIS C 2318. A sample was cut into a strip shape with a length of 120 mm and a width of 10 mm in the MD and TD directions of the film using a single-edged razor. The strip-shaped sample was then clamped with a chuck distance of 100 mm using an Autograph AG-IS manufactured by Shimadzu Corporation and pulled at a rate of 100 mm / min. The breaking strength (MPa) and breaking elongation (%) in each direction were determined from the obtained load-strain curve.

[0111] (6) Haze The haze (%) of the multilayer polylactic acid film was measured in accordance with JIS K 7136 using a turbidity meter NDH-7000 Type 2 manufactured by Nippon Denshoku Industries Co., Ltd.

[0112] (7) Total Light Transmittance The total light transmittance (%) of the multilayer polylactic acid film was measured in accordance with JIS K 7136 using a turbidity meter NDH-7000 Type 2 manufactured by Nippon Denshoku Industries Co., Ltd.

[0113] (8) Dynamic Friction Coefficient The dynamic friction coefficient of the multilayer polylactic acid film was measured in accordance with JIS-K-7125. A 70 mm wide, 200 mm long sample (Sample A) was cut out of the film with the machine direction as the length direction, and the lubricant-free layer of Sample A was attached to a table with the surface facing up. Separately, Sample B, 50 mm wide and 50 mm long, was prepared from the film, and the lubricant-free layer of Sample B was attached to a slide (50 mm wide, 50 mm long). Next, the film surface of Slide B was placed parallel to Sample A on the table in the longitudinal direction of the film. Using an AND (A & D) Tensilon Universal Testing Machine RGT-1210 as the measuring device, a 4.4 kg load was applied to the slide, and the slide was slid along the length of Sample A against the surface of the film at a speed of 200 mm / min to determine the dynamic friction coefficient (μd).

[0114] (9) Surface Free Energy γs of Resin Layer After leaving the multilayer polylactic acid film 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 γs of the surface free energy was calculated from the contact angles of distilled water and diiodomethane.

[0115] (10) Coating appearance of resin layer The surface of the multilayer polylactic acid film on which the resin layer was laminated was irradiated with light from a bromine light source (VIDEOLIGHT VLG301 100V 300W, manufactured by LPL) and a fluorescent lamp (Panasonic Paluk, F.L 15EX-N 15W, three-wavelength daylight white) at an angle of approximately 10° to 45° relative to the film surface, and the coating appearance of the resin layer was judged by visual observation according to the following criteria: A: No coating unevenness, coating streaks, or repelling was observed under either bromine light or fluorescent light, resulting in a uniform coating surface. B: Coating unevenness, coating streaks, repelling, etc. were observed under bromine light but not under fluorescent light. C: Coating unevenness, coating streaks, repelling, etc. were observed under both bromine light and fluorescent light. Coating appearances ranked A or B were judged to be good, and coating appearances ranked A were judged to be particularly good.

[0116] (11) Evaluation of the surface of the release layer Using a non-contact surface shape measurement system (VertScan R550H-M100), the arithmetic mean roughness (Sa) and maximum protrusion height (P) were measured as the average roughness of the area surface under the following conditions. The arithmetic mean roughness (Sa) was the average value of five measurements, and the maximum protrusion height (P) was the maximum value of the five measurements, excluding the maximum and minimum values, measured seven times. (Measurement conditions) Measurement mode: WAVE mode Objective lens: 10x, 0.5x Tube lens Measurement area: 936 μm x 702 μm (Analysis conditions) Surface correction: 4th order correction Interpolation processing: Full interpolation

[0117] (12) 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 multilayer polylactic acid film, the film was cut with scissors and used. The solution was filtered before measurement to remove particles and the like.

[0118] Example 1 (1) Preparation of Polylactic Acid 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 was used as polylactic acid.

[0119] (2) Preparation of aqueous resin used in resin layer 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, 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. After that, a polycondensation reaction was carried out at 250 ° C. under reduced pressure (10 to 0.2 mmHg) for 2 hours to obtain a copolymer polyester resin (A) having a number average molecular weight of 19,500 and a softening point of 60 ° C. A reactor equipped with a stirrer, a thermometer, and a reflux device was charged with 30 parts by mass of the copolymerized polyester resin (A) and 15 parts by mass of ethylene glycol n-butyl ether, 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 prepare a milky white polyester resin aqueous dispersion with a solids content of 30% by mass.

[0120] (3) Preparation of coating liquid (resin layer forming material) for forming resin layer The following coating agents were mixed to prepare coating liquid A. (Coating liquid A) Water 46.89% by mass Isopropanol 30.00% by mass Polyester resin water dispersion 20.00% by mass MP4540M 0.08% by mass (manufactured by Nissan Chemical Industries, Ltd., solid content 40% by mass, average particle size 450 nm) Snowtex ST-XL 3.00% by mass (manufactured by Nissan Chemical Industries, Ltd., solid content 30% by mass, average particle size 45 nm) Surfactant 0.03% by mass (silicone-based, solid content 100% by mass)

[0121] (4) Production of multilayer polylactic acid film Poly-L-lactic acid (L175) was dried under reduced pressure (1 Torr) at 120°C for 6 hours and then fed to an extruder. It was melted at 220°C and melt-extruded into a sheet from a die. A gear pump was used to control the thickness to 6,400 μm. The filters used were stainless steel sintered filter media with a filtration particle size of 10 μm (initial filtration efficiency: 95%).

[0122] The extruded resin was cast onto a cooling drum having a surface temperature of 50° C., and adhered to the surface of the cooling drum using an electrostatic application method, followed by cooling and solidification to form an unstretched film having a thickness of 600 μm.

[0123] The obtained unstretched film was heated to a film temperature of 75° C. using a group of heated rolls, and then stretched 3.0 times in the longitudinal direction (MD direction) using a group of rolls with different peripheral speeds.

[0124] Next, one side of the obtained uniaxially stretched film was coated with coating solution A used to form the resin layer by a fountain bar coating method, adjusting the coating amount so that the resin layer thickness was 50 nm. Subsequently, this in-line coated uniaxially stretched film was held with a clip, dried at 60 ° C for 20 seconds, and then stretched in the transverse direction (TD direction). The transverse stretching temperature was 75 ° C, and the transverse stretching ratio was 4.96 times. Next, it was heat-treated at 150 ° C for 15 seconds.

[0125] The biaxially stretched film that had been stretched in the TD direction was again gripped with clips and transversely stretched. The transverse stretching temperature was 170°C, and the transverse stretching ratio was 1.01 times. Next, heat treatment was performed at 160°C for 15 seconds to obtain a multilayer polylactic acid film with a thickness of 40 μm. The film properties of the multilayer polylactic acid film obtained in Example 1 are shown in Table 2. The obtained multilayer polylactic acid film had a high sum of the crystallinity and tensile modulus and a low thermal shrinkage rate, indicating that a multilayer polylactic acid film with excellent modulus and heat resistance could be obtained in Example 1. In addition, the coating appearance of the resin layer was particularly good. The reduced viscosity of the obtained multilayer polylactic acid film was 1.8 dl / g.

[0126] (Example 2) The following coating agents were mixed to prepare coating liquid B. In Example 2, a multilayer polylactic acid film was obtained in the same manner as in Example 1, except that coating liquid A used to form the resin layer was changed to coating liquid B below. The film properties of the multilayer polylactic acid film obtained in Example 2 are shown in Table 2. (Coating liquid B) Water 52.25% by mass Isopropanol 30.00% by mass Nikazol RX-2035A 13.64% by mass (acrylic resin water dispersion, manufactured by Nippon Carbide Corporation, solid content 44% by mass) MP4540M 0.08% by mass (manufactured by Nissan Chemical Industries, solid content 40% by mass, average particle size 450 nm) Snowtex ST-XL 3.00% by mass (manufactured by Nissan Chemical Industries, solid content 30% by mass, average particle size 45 nm) Surfactant 0.03% by mass (silicone-based, solid content 100% by mass)

[0127] The multilayer polylactic acid film obtained in Example 2 had a high sum of the crystallinity and the tensile modulus, and a low thermal shrinkage, indicating that a multilayer polylactic acid film excellent in modulus and heat resistance could be obtained in Example 2. In addition, the coating appearance of the resin layer was particularly good.

[0128] (Example 3) The following coating agents were mixed to prepare Coating Liquid C. In Example 3, a multilayer polylactic acid film was obtained in the same manner as in Example 1, except that Coating Liquid A used to form the resin layer was changed to Coating Liquid C below. The film properties of the multilayer polylactic acid film obtained in Example 3 are shown in Table 2. (Coating Liquid C) Water 40.80% by mass Isopropanol 30.00% by mass Hydran AP-201 26.09% by mass (polyurethane resin aqueous dispersion, manufactured by DIC Corporation, solid content 23% by mass) MP4540M 0.08% by mass (manufactured by Nissan Chemical Industries, solid content 40% by mass, average particle size 450 nm) Snowtex ST-XL 3.00% by mass (manufactured by Nissan Chemical Industries, solid content 30% by mass, average particle size 45 nm) Surfactant 0.03% by mass (silicone-based, solid content 100% by mass)

[0129] The multilayer polylactic acid film obtained in Example 3 had a high sum of the crystallinity and the tensile modulus and a low thermal shrinkage, indicating that a multilayer polylactic acid film excellent in modulus and heat resistance could be obtained in Example 3. In addition, the coating appearance of the resin layer was particularly good.

[0130] Examples 4 and 5 In Examples 4 and 5, multilayer polylactic acid films were obtained in the same manner as in Example 1, except that the stretching conditions were changed as shown in Table 1. In Example 5, the unstretched film thickness was adjusted by changing the extruder output to obtain the film thickness shown in Table 2. The physical properties of the multilayer polylactic acid films obtained in Examples 4 and 5 are shown in Table 2. In Example 4, a higher elastic modulus was obtained by increasing the second stretch ratio in the TD direction. In Example 5, a relaxation treatment (160°C, relaxation rate 5%) was performed after TD stretching, thereby suppressing thermal shrinkage in the TD direction and maintaining a high elastic modulus. The multilayer polylactic acid films of Examples 4 and 5 had a high sum of the crystallinity and tensile modulus and a low thermal shrinkage, demonstrating that multilayer polylactic acid films with excellent elastic modulus and heat resistance could be obtained. Furthermore, the coating appearance of the resin layer was particularly good.

[0131] Example 6 (1) Preparation of Polylactic Acid Poly-L-lactic acid PLA LX175 (mass ratio of L-lactic acid / D-lactic acid: 96 / 4) manufactured by Total Corbion was used as polylactic acid.

[0132] (2) Production of polylactic acid film Poly-L-lactic acid (LX175) was dried under reduced pressure (1 Torr) at 120°C for 6 hours and then fed to an extruder. It was melted at 220°C and extruded into a sheet from a die. A gear pump was used to control the thickness to 400 μm. The filters used were stainless steel sintered filter media with a filtration particle size of 10 μm (initial filtration efficiency: 95%).

[0133] The extruded resin was cast onto a cooling drum having a surface temperature of 50° C., and adhered to the surface of the cooling drum using an electrostatic application method, followed by cooling and solidification to form an unstretched film having a thickness of 600 μm.

[0134] The obtained unstretched film was heated to a film temperature of 70° C. using a group of heated rolls, and then stretched 3.0 times in the longitudinal direction (MD direction) using a group of rolls with different peripheral speeds.

[0135] Next, one side of the obtained uniaxially stretched film was coated with coating solution A used to form the resin layer by a fountain bar coating method, adjusting the coating amount so that the resin layer thickness was 50 nm. Subsequently, this in-line coated uniaxially stretched film was held with a clip, dried at 60 ° C for 20 seconds, and then stretched in the transverse direction (TD direction). The transverse stretching temperature was 75 ° C, and the transverse stretching ratio was 4.96 times. Next, it was heat-treated at 150 ° C for 15 seconds.

[0136] The biaxially stretched film that had been stretched in the TD direction was again gripped with clips and transversely stretched. The transverse stretching temperature was 150°C, and the transverse stretching ratio was 1.01 times. Next, a relaxation treatment (relaxation rate: 3%) was performed at 140°C for 15 seconds to obtain a multilayer polylactic acid film with a thickness of 40 μm. The film properties of the multilayer polylactic acid film obtained in Example 6 are shown in Table 2. The multilayer polylactic acid film obtained had a high sum of the crystallinity and tensile modulus and a low thermal shrinkage, indicating that a multilayer polylactic acid film with excellent modulus and heat resistance could be obtained in Example 6. Furthermore, the coating appearance of the resin layer was particularly good.

[0137] Example 7 In Example 7, the unstretched film was prepared in the same manner as in Example 1, except that the extruder output was changed to adjust the thickness of the unstretched film to the film thickness listed in Table 2. Coating Solution A used to form the resin layer was applied to one side of the unstretched film using the fountain bar coating method, adjusting the coating amount to achieve a resin layer thickness of 50 nm, and then dried at 60°C for 20 seconds. Subsequently, this in-line coated unstretched film was introduced into a simultaneous biaxial stretching machine, and while holding the film edges with clips, it was stretched 3.0 times in the longitudinal direction and 5.0 times in the transverse direction in a hot air zone at a temperature of 75°C. Next, the film was again held with clips and transversely stretched under the same stretching conditions as in Example 5, followed by relaxation treatment (160°C, relaxation rate 5%) to obtain a multilayer polylactic acid film. The film properties of the multilayer polylactic acid film obtained in Example 7 are shown in Table 2. The resulting multilayer polylactic acid film had a high sum of the crystallinity and the tensile modulus and a low thermal shrinkage, demonstrating that a multilayer polylactic acid film with excellent modulus and heat resistance could be obtained in Example 7. In addition, the coating appearance of the resin layer was good.

[0138] (Comparative Examples 1 and 2) In Comparative Example 1, a multilayer polylactic acid film was obtained in the same manner as in Example 1, except that the unstretched film thickness was adjusted by changing the extruder output rate to obtain the film thickness shown in Table 2, and that the stretching conditions were changed to those shown in Table 1. In Comparative Example 2, a multilayer polylactic acid film was obtained in the same manner as in Example 7, except that the stretching conditions were changed to those shown in Table 1. Table 2 shows the film properties of the multilayer polylactic acid films obtained in Comparative Examples 1 and 2. Comparative Examples 1 and 2 have low tensile modulus and high heat shrinkage, and are therefore outside the scope of the present invention. Comparative Examples 1 and 2 were stretched using the commonly used sequential biaxial stretching or simultaneous biaxial stretching method, and the stretch ratio was low, so that the modulus and heat resistance were poor.

[0139] (Comparative Example 3) In Comparative Example 3, the same operations as in Example 1 were carried out, except that the unstretched film thickness was adjusted by changing the extruder discharge rate so as to obtain the film thickness shown in Table 2, and the stretching conditions were changed to those shown in Table 1. In Comparative Example 3, in the commonly used sequential biaxial stretching, the stretching ratio in the TD direction was set high, but stretching fracture occurred, and a multilayer polylactic acid film could not be obtained.

[0140] (Example 8) The following coating agents were mixed to prepare coating liquid D. In Example 8, a multilayer polylactic acid film was obtained in the same manner as in Example 1, except that coating liquid A used to form the resin layer was changed to coating liquid D below. The film properties of the multilayer polylactic acid film obtained in Example 8 are shown in Table 2. (Coating liquid D) Water 42.89% by mass Isopropanol 30.00% by mass ZAIKSEN L 24.00% by mass (polyolefin resin water dispersion, manufactured by Sumitomo Seika Chemicals Co., Ltd., solid content 25% by mass) MP4540M 0.08% by mass (manufactured by Nissan Chemical Industries, Ltd., solid content 40% by mass, average particle size 450 nm) Snowtex ST-XL 3.00% by mass (manufactured by Nissan Chemical Industries, Ltd., solid content 30% by mass, average particle size 45 nm) Surfactant 0.03% by mass (silicone-based, solid content 100% by mass)

[0141] The multilayer polylactic acid film obtained in Example 8 had a high sum of the crystallinity and the tensile modulus and a low thermal shrinkage, indicating that a film with excellent modulus and heat resistance could be obtained; however, the coating appearance of the resin layer was poor.

[0142] <Lamination of Release Layer (1)> 100 parts by mass of a UV-curable silicone resin (UV9300 manufactured by Momentive, solids concentration 100% by mass) and 1 part by mass of the curing catalyst bis(alkylphenyl)iodonium hexafluoroantimonate were diluted with a toluene / methyl ethyl ketone / heptane (=3:5:2) solution to prepare a release layer-forming material solution with a solids content of 1% by mass. This release layer-forming material solution was applied to the polylactic acid film side of the multilayer polylactic acid films obtained in Examples 1 to 8 and Comparative Examples 1 and 2 using a reverse gravure coater so as to have a thickness of 0.05 μm after drying. Then, the film was dried with hot air at 90° C. for 30 seconds and immediately irradiated with ultraviolet light (300 mJ / cm ) using an electrodeless lamp (H bulb manufactured by Fusion Corporation). ２) was carried out to form a release layer, and a release film was obtained.

[0143] From the above, the multilayer polylactic acid films obtained in Examples 1 to 8 were films with excellent elastic modulus and heat resistance, had good dimensional stability during processing at high temperatures, and were able to obtain high rigidity, and the coating appearance of the resin layer was also good. Furthermore, the evaluation results of the surfaces of the release layers of the release films obtained in Examples 1 to 8 are shown in Table 2. Since the maximum protrusion height (P) was 200 nm or less and the arithmetic mean roughness (Sa) was 10 nm or less, they were suitable as release films for producing ceramic green sheets.

[0144]

[0145]

[0146] (Example 11) (1) Preparation of Polylactic Acid: Poly-L-lactic acid (PLA L175) manufactured by Total Corbion (L-lactic acid / D-lactic acid mass ratio: 99 / 1) was used as the polylactic acid. Poly-L-lactic acid (L175) was used as raw material A1 for the particle-free layer. (2) Preparation of Forming Material Used in Particle-Containing Layer: SYLYSIA310P (average particle diameter: 2.7 μm) manufactured by Fuji Silysia Chemical Ltd. was used as the inorganic particles (lubricant particles). 0.5% by mass of SYLYSIA310P was added to L-175 and pelletized to prepare a lubricant masterbatch raw material with a lubricant particle concentration of 0.45% by mass. Next, 0.67% by mass of the lubricant masterbatch raw material was dry-blended with L-175 to prepare raw material B1 for the particle-lubricant-containing layer.

[0147] (3) Production of Multilayer Polylactic Acid Films: Poly-L-lactic acid (L175) was used as raw material A1 for the particle-free layer, and the raw material A1 was dried under reduced pressure (1 Torr) at 120°C for 6 hours, then fed to extruder A and melted at 220°C. Meanwhile, raw material B1 for the particle-containing layer was similarly dried and then fed to extruder B and melted at 220°C. The molten resin from each extruder was sent to a metal nozzle, and raw materials A1 and B1 were laminated in the nozzle and melt-extruded into a sheet. The thickness of the sheet was controlled using a gear pump. Furthermore, a stainless steel sintered filter medium with a filtration particle size of 10 μm (initial filtration efficiency: 95%) was used for the filter.

[0148] The multilayer co-extruded resin was cast onto a cooling drum with a surface temperature of 50°C and adhered to the surface of the cooling drum using an electrostatic application method, followed by cooling and solidification to produce a two-kind, two-layer unstretched film with the layer thickness ratio shown in Table 3. The thickness of the unstretched film was 600 μm.

[0149] The obtained unstretched film was heated to a film temperature of 75° C. using a group of heated rolls, and then stretched 3.0 times in the longitudinal direction (MD direction) using a group of rolls with different peripheral speeds.

[0150] The uniaxially stretched film was then introduced into a tenter, held with clips, and stretched in the transverse direction (TD) at a temperature of 75°C and a stretch ratio of 4.96. The film was then heat-treated at 150°C for 15 seconds.

[0151] The biaxially stretched film that had been stretched in the TD direction was again gripped with clips and transversely stretched. The transverse stretching temperature was 170°C, and the transverse stretching ratio was 1.01 times. Next, heat treatment was performed at 160°C for 15 seconds to obtain a multilayer polylactic acid film with a thickness of 40 μm. The film properties of the multilayer polylactic acid film obtained in Example 1 are shown in Table 4. The multilayer polylactic acid film obtained had a high sum of the crystallinity and tensile modulus and a low thermal shrinkage, indicating that a film with excellent modulus and heat resistance was obtained in Example 1. The reduced viscosity of the obtained film was 1.8 dl / g.

[0152] Examples 12 and 13 In Examples 12 and 13, multilayer polylactic acid films were obtained in the same manner as in Example 11, except that the stretching conditions were changed as shown in Table 1. In Example 13, the extruder output was adjusted to obtain the film thickness shown in Table 4. The physical properties of the multilayer polylactic acid films obtained in Examples 12 and 13 are shown in Table 2. In Example 12, a higher elastic modulus was obtained by increasing the second stretch ratio in the TD direction. In Example 13, a relaxation treatment (160°C, relaxation rate 5%) was performed after TD stretching, thereby suppressing thermal shrinkage in the TD direction and maintaining a high elastic modulus. The multilayer polylactic acid films of Examples 12 and 13 had a high sum of the degree of crystallinity and the tensile modulus and a low thermal shrinkage, demonstrating that multilayer polylactic acid films with excellent elastic modulus and heat resistance could be obtained.

[0153] Example 14 (1) Preparation of forming materials for polylactic acid and particle-containing layer Poly-L-lactic acid PLA LX175 (mass ratio of L-lactic acid / D-lactic acid: 96 / 4) manufactured by Total Corbion was prepared as polylactic acid. Raw material A2 for the particle-free layer and raw material B2 for the particle-containing layer were prepared in the same manner as in Example 11, except that LX175 was used instead of L-175 in Example 11.

[0154] (2) Production of a multilayer polylactic acid film An unstretched film was obtained in the same manner as in Example 11, except that raw material A2 for the particle-free layer and raw material B2 for the particle-containing layer were used instead of raw material A1 for the particle-free layer and raw material B2 for the particle-containing layer in Example 11. The obtained multilayer unstretched film was heated to 70°C using a group of heated rolls, and then stretched 3.0 times in the longitudinal direction using a group of rolls with different peripheral speeds.

[0155] The uniaxially stretched film was then stretched in the transverse direction (TD) at a temperature of 75°C and a stretch ratio of 4.96 times, followed by heat treatment at 150°C for 15 seconds.

[0156] The biaxially stretched film that had been stretched in the TD direction was again gripped with clips and transversely stretched. The transverse stretching temperature was 150°C, and the transverse stretching ratio was 1.01 times. Next, a relaxation treatment (relaxation rate: 3%) was performed at 140°C for 15 seconds to obtain a multilayer polylactic acid film with a thickness of 40 μm. The film properties of the multilayer polylactic acid film obtained in Example 4 are shown in Table 2. The multilayer polylactic acid film obtained had a high sum of the crystallinity and the tensile modulus and a low thermal shrinkage, indicating that a multilayer polylactic acid film with excellent modulus and heat resistance could be obtained in Example 4.

[0157] Example 15 In Example 15, an unstretched film was prepared in the same manner as in Example 13, except that poly-L-lactic acid PLA LX175 (mass ratio of L-lactic acid / D-lactic acid: 96 / 4) manufactured by Total Corbion was used as the polylactic acid. The unstretched film was introduced into a simultaneous biaxial stretching machine, and while the edges of the film were held with clips, it was stretched 3.0 times in the longitudinal direction and 5.0 times in the transverse direction in a hot air zone at a temperature of 75°C. The film was then again held with clips and stretched transversely under the same stretching conditions as in Example 13, followed by a relaxation treatment (160°C, relaxation rate: 5%) to obtain a multilayer polylactic acid film. The physical properties of the multilayer polylactic acid film obtained in Example 15 are shown in Table 2. The resulting multilayer polylactic acid film had a high sum of the crystallinity and tensile modulus and a low thermal shrinkage, demonstrating that a film with excellent modulus and heat resistance was obtained in Example 15.

[0158] Example 16: In the production of the multilayer polylactic acid film of Example 11, the remainder of raw materials A1 and B1 generated at the clip gripping portion was recovered and pelletized to form raw material C. Raw materials A1, B1, and C were dried and then fed to extruders A, B, and C, respectively, and melted at a temperature of 220°C. The molten resin from each extruder was sent to a metal nozzle, and raw materials A, C, and B were laminated in the nozzle and melt-extruded into a sheet. The thickness of the sheet was controlled using a gear pump. Furthermore, a stainless steel sintered filter medium with a filtration particle size of 10 μm (initial filtration efficiency: 95%) was used for the filter.

[0159] The multilayer co-extruded resin was cast onto a cooling drum with a surface temperature of 50°C and adhered to the surface of the cooling drum using an electrostatic application method, followed by cooling and solidification to prepare an unstretched film of three types and three layers with the layer thickness ratios shown in Table 3. The unstretched film obtained was subjected to the same stretching conditions as in Example 11 to obtain a multilayer polylactic acid film.

[0160] Comparative Examples 11 and 12 In Comparative Example 11, a single-layer stretched polylactic acid film was obtained in the same manner as in Example 11, except that only raw material A1 for the particulate lubricant-free layer was melt-extruded into a single-layer sheet having a thickness of 450 μm, and the stretching conditions were changed to those shown in Table 3. In Comparative Example 12, a single-layer stretched polylactic acid film was obtained in the same manner as in Example 15, except that only raw material A1 for the particulate lubricant-free layer was melt-extruded into a single-layer sheet having a thickness of 450 μm, and the stretching conditions were changed to those shown in Table 3. The physical properties of the single-layer stretched polylactic acid films obtained in Comparative Examples 11 and 12 are shown in Table 3. Comparative Examples 11 and 12 are outside the scope of the present invention because they have low tensile modulus and high thermal shrinkage. Comparative Examples 11 and 12 were stretched using commonly used sequential biaxial stretching or simultaneous biaxial stretching methods, and the stretch ratio was low, resulting in poor modulus and heat resistance.

[0161] Comparative Example 13 In Comparative Example 13, the same operation as in Example 11 was carried out, except that only raw material A1 for the particulate lubricant-free layer was used, and melt-extruded into a single-layer sheet having a thickness of 450 μm, and the stretching conditions were changed to those shown in Table 3. In Comparative Example 13, in the commonly used sequential biaxial stretching, the stretching ratio in the TD direction was set high, but stretching fracture occurred, and a single-layer stretched polylactic acid film could not be obtained.

[0162] <Lamination of Release Layer (2)> A solution of the release layer-forming material similar to that described in <Lamination of Release Layer (1)> was prepared. This release layer-forming material was applied to the surface of the lubricant-free layer on the multilayer polylactic acid film obtained in Examples 11 to 16 using a reverse gravure coater so that the thickness after drying would be 0.05 μm. Then, after drying with hot air at 90° C. for 30 seconds, the film was immediately irradiated with ultraviolet light (300 mJ / cm ) using an electrodeless lamp (H bulb, manufactured by Fusion Co., Ltd.). ２For the single-layer stretched polylactic acid films obtained in Comparative Examples 11 and 12, release layers were formed in the same manner as above, and release films were obtained.

[0163] From the above, the multilayer polylactic acid films obtained in Examples 11 to 16 were films with excellent elastic modulus and heat resistance, and were able to obtain good dimensional stability during processing at high temperatures and high rigidity. Furthermore, the surface roughness of the release layer of the release films obtained in Examples 11 to 16 was such that the maximum protrusion height (P) was 200 nm or less and the arithmetic mean roughness (Sa) was 10 nm or less, making them suitable as release films for producing ceramic green sheets, for example.

[0164]

[0165]

[0166] The multilayer polylactic acid film of the present invention is suitable for various uses, and when used as a release film, it is suitable for use, for example, as a release film for producing ceramic green sheets.

Claims

1. A multilayer polylactic acid film comprising a first stretched polylactic acid film formed from a first film-forming material containing polylactic acid, and a particle-containing layer, wherein the longitudinal tensile modulus Ea and the transverse tensile modulus Eb of the multilayer polylactic acid film satisfy the formula Ea + Eb > 8.0 GPa, the crystallinity is 40% or more and 90% or less, and when the multilayer polylactic acid film is heated at 150°C for 30 minutes, the longitudinal heat shrinkage rate and the transverse heat shrinkage rate are both 10.0% or less.

2. The multilayer polylactic acid film according to claim 1, which has a thermal shrinkage rate of 3.0% or less in both the longitudinal and transverse directions when heated at 120°C for 30 minutes.

3. The multilayer polylactic acid film according to claim 1 or 2, wherein the first stretched polylactic acid film is a particle-free layer that is substantially free of particles.

4. The multilayer polylactic acid film according to any one of claims 1 to 3, wherein the particle-containing layer is the outermost layer on at least one side of the multilayer polylactic acid film.

5. The multilayer polylactic acid film according to claim 3 or 4, wherein the outermost layer on one side of the multilayer polylactic acid film is the particle-containing layer, and the outermost layer on the other side is the particle-free layer.

6. The multilayer polylactic acid film according to any one of claims 3 to 5, which has a two-layer structure consisting of the particle-containing layer and the particle-free layer.

7. The multilayer polylactic acid film according to claim 5 or 6, wherein the coefficient of dynamic friction (μd) when the particle-containing outermost layer on one side and the particle-free outermost layer on the other side are superimposed is 0.65 or less.

8. The multilayer polylactic acid film according to any one of claims 1 to 7, wherein the mass ratio of L-lactic acid / D-lactic acid in the polylactic acid is 100 / 0 to 85 / 15.

9. The multilayer polylactic acid film according to any one of claims 1 to 8, which has a total light transmittance of 75% or more and a haze of 3% or less.

10. The multilayer polylactic acid film according to any one of claims 1 to 9, wherein the particle-containing layer is a resin layer formed from a resin layer-forming material containing a water-based resin and lubricant particles.

11. The multilayer polylactic acid film according to claim 10, wherein the resin layer is formed by an in-line coating method.

12. The multilayer polylactic acid film according to claim 10 or 11, wherein the surface free energy γs of the resin layer is 40 mN / m or more.

13. The multilayer polylactic acid film according to any one of claims 1 to 9, wherein the particle-containing layer is a second stretched polylactic acid film formed from a second film-forming material containing polylactic acid and lubricant particles.

14. The multilayer polylactic acid film according to claim 13, wherein the first stretched polylactic acid film and the second stretched polylactic acid film are stretched laminates formed by multilayer coextrusion of a first film-forming material and a second film-forming material.

15. A release film having a release layer on at least one surface of the multilayer polylactic acid film according to any one of claims 1 to 14.

16. The release film according to claim 15, wherein the release layer is provided on the first stretched polylactic acid film side, which is the outermost particle-free layer of the multilayer polylactic acid film.

17. The release film according to claim 15 or 16, wherein the release layer is formed from a release layer-forming material containing a silicone release component.

18. The release film according to claims 15 to 17, which is used for producing ceramic green sheets.

19. The release film according to any one of claims 15 to 18, wherein the maximum protrusion height (P) of the surface of the release layer is 200 nm or less, and the arithmetic mean roughness (Sa) of the surface of the release layer is 10 nm or less.

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