Multilayer polylactic acid film and release film

Abstract

The present invention relates to a first stretched polylactic acid film formed from a first film-forming material containing polylactic acid, and a multilayer polylactic acid film including a particle-containing layer, wherein the tensile modulus Ea in the longitudinal direction and the tensile modulus Eb in the width direction of the multilayer polylactic acid film satisfy the formula Ea + Eb > 8.0 GPa, the degree of crystallinity is 40% or more and 90% or less, and when the multilayer polylactic acid film is heated at 150°C for 30 minutes, both the thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the width direction are 10.0% or less. According to the present invention, it is possible to provide a multilayer polylactic acid film with excellent elastic modulus and heat resistance using polylactic acid derived from iomass raw materials and which is biodegradable.

Description

[Technical Field]

[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 containing a particle-containing layer, and a release film containing the same. [Background technology]

[0002] Films made from polylactic acid (PLA) resin are being developed as a substitute for conventional fossil fuels because they are derived from biomass raw materials and are biodegradable. However, compared to polyethylene terephthalate, nylon, and polyolefins, which are commonly used as industrial materials, polylactic acid films made from polylactic acid resin have a low elastic modulus and low heat resistance. Therefore, when PLA films are used for industrial purposes, problems such as dimensional changes and appearance defects such as wrinkles occur during processing.

[0003] To solve these problems, methods have been proposed to improve the film formation conditions of PLA films. For example, Patent Document 1 discloses a manufacturing method in which the longitudinal stretching is divided into two or more stages, followed by the widthwise stretching, and the temperature of the second longitudinal stretching is lower than that of the first stretching, thereby improving heat resistance without impairing moldability. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2004-359948 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, although the polylactic acid film produced by the manufacturing method described in Patent Document 1 has improved heat resistance, it suffers from the problem of having a low elastic modulus because the second stretching temperature in the longitudinal direction is low, which prevents setting a high stretching ratio in the subsequent width direction.

[0006] The conventional technologies described above were unable to improve the tensile modulus in the longitudinal and width directions while also achieving good heat resistance. The present invention aims to provide a multilayer polylactic acid film containing a polylactic acid film with excellent elastic modulus and heat resistance, using biomass-derived and biodegradable polylactic acid. Furthermore, it aims to provide a multilayer polylactic acid film with excellent slipperiness. Moreover, it aims to provide a release film using the multilayer polylactic acid film. [Means for solving the problem]

[0007] As a result of diligent research by the inventors of the present invention regarding polylactic acid films, they discovered that by stretching a polylactic acid film multiple times in multiple stages 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 stretching ratio can be improved. Furthermore, they added a layer containing particles. As a result, the degree of crystallinity is within a predetermined range, and the multilayer polylactic acid film of the present invention succeeds in improving the elastic modulus, heat resistance, and slipperiness. In other words, the present invention has the following configuration in order to solve the above problems. [Section 1] A first stretched polylactic acid film formed from a first film-forming material containing polylactic acid, and a multilayer polylactic acid film including a particle-containing layer, A multilayer polylactic acid film in which the tensile modulus Ea in the longitudinal direction and the tensile modulus Eb in the width direction satisfy the formula Ea + Eb > 8.0 GPa, the degree of crystallinity is 40% or more and 90% or less, and when the multilayer polylactic acid film is heated at 150°C for 30 minutes, both the thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the width direction are 10.0% or less. [Section 2] A multilayer polylactic acid film as described in item 1, wherein the thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the width direction are both 3.0% or less when heated at 120°C for 30 minutes. [Section 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. [Section 4] The multilayer polylactic acid film according to any one of claims 1 to 3, wherein the particle-containing layer is the outermost layer of at least one surface of the multilayer polylactic acid film. [Section 5] The multilayer polylactic acid film according to claim 3 or 4, wherein the outermost layer of one side of the multilayer polylactic acid film is the particle-containing layer, and the outermost layer of the other side is the particle-free layer. [Section 6] A multilayer polylactic acid film according to any one of items 3 to 5, comprising two layers: the particle-containing layer and the particle-free layer. [Section 7] The multilayer polylactic acid film is the multilayer polylactic acid film according to item 5 or 6, wherein the coefficient of dynamic friction (μd) when the particle-containing layer on the outermost surface of one side and the particle-free layer on the outermost surface of the other side are superimposed is 0.65 or less. [Section 8] A multilayer polylactic acid film according to any one of items 1 to 7, wherein the mass ratio of L-lactic acid to D-lactic acid of the polylactic acid is 100 / 0 to 85 / 15. [Section 9] A multilayer polylactic acid film according to any of items 1 to 8, having a total light transmittance of 75% or more and a haze of 3% or less. [Section 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 an aqueous resin and lubricant particles. [Section 11] The multilayer polylactic acid film according to claim 10, wherein the resin layer is formed by an in-line coating method. [Section 12] The multilayer polylactic acid film according to item 10 or 11, wherein the surface free energy γs of the resin layer is 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 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 layer The release film according to Item 15, which is provided on the side of the first stretched polylactic acid film, which is the outermost particle-free layer in the multilayer polylactic acid film. [Item 17] The Release layer The release film according to Item 15 or 16, which is formed from a release layer-forming material containing a silicone release component. [Item 18] The release film according to any one of Items 15 to 17, wherein the release film is for manufacturing a ceramic green sheet. [Item 19] The release film according to any one of Items 15 to 18, wherein the maximum protrusion height (P) of the surface of the release layer is not more than 200 nm and the arithmetic mean roughness (Sa) of the surface of the release layer is not more than 10 nm. [Advantages of the Invention]

[0008] The multilayer polylactic acid film of the present invention is excellent in elastic modulus and heat resistance. Therefore, it has good dimensional stability during processing at high temperatures and high rigidity, and is suitable for industrial applications such as release film applications and optical applications. Furthermore, since it is a biomass-derived raw material and has biodegradability, it takes into account the recent SDGs. In addition to the elastic modulus and heat resistance, the multilayer polylactic acid film of the present invention also has excellent slipperiness. Therefore, due to the good slipperiness, good conveyance during the film winding and processing steps is possible.

Best Mode for Carrying Out the Invention

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

[0010] (Aspect 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. As one aspect of the particle-containing layer, for example, a resin layer formed from a forming material containing an aqueous resin and lubricant particles can be mentioned. Hereinafter, this is also referred to as the particle-containing layer (a), and when the particle-containing layer (a) is used, it is also referred to as the multilayer polylactic acid film (A). Also, as one aspect of the particle-containing layer, for example, a second stretched polylactic acid film formed from a second film-forming material containing polylactic acid and lubricant particles can be mentioned. Hereinafter, this is also referred to as the particle-containing layer (b), and when the particle-containing layer (b) is used, it is also referred to as the multilayer polylactic acid film (B). Further, the multilayer polylactic acid film of the present invention can also be used in a mode 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 predetermined catalyst. The predetermined catalyst is, for example, tin or aluminum. The polylactic acid may contain L-lactic acid and D-lactic acid components as copolymer components or blended 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. When the ratio of L-lactic acid (hereinafter referred to as L-form) to D-lactic acid (hereinafter referred to as D-form) is 100 / 0 to 85 / 15, high crystallinity is obtained, making it easier to improve the properties of the film, such as increasing the physical properties of the film and decreasing the thermal shrinkage rate, which is preferable. Polylactic acid may also contain copolymerized hydroxy acid components other than lactic acid. Examples of hydroxy acid components other than lactic acid include glycolic acid, 3-hydroxypropionic acid, and 6-hydroxycaproic acid (ε-caprolactone). Of the total components of polylactic acid (total amount of hydroxycarboxylic acid components, dicarboxylic acid components, and glycol components), the lactic acid component is preferably 85 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, particularly preferably 97 mol% or more, and may also be 99 mol% or more, or even 100 mol%.

[0013] In the present invention, the preferred glass transition temperature of polylactic acid is 40 to 70°C, the preferred melting point is 150 to 180°C, and the ability to undergo oriented crystallization is also preferred. The glass transition temperature and melting point can be obtained by differential scanning calorimeter (DSC) or the like. The presence or absence of crystallinity can be confirmed by the presence or absence of crystallization peaks during the heating process or the cooling process after melting using DSC.

[0014] The reduced viscosity (ηsp / c) of the first film-forming material containing polylactic acid used in this invention is preferably in the range of 1.0 dl / g to 3.0 dl / g, and more preferably 1.5 to 2.8 dl / g. When the reduced viscosity is 1.0 dl / g or higher, the first stretched polylactic acid film can be prevented from tearing. When the reduced viscosity is 3.0 dl / g or lower, the increase in filtration pressure is reduced, making high-precision filtration easier.

[0015] The reduced viscosity (ηsp / c) of the first stretched polylactic acid film (the same applies to multilayer polylactic acid films) used in the present invention is preferably in the range of 1.0 dl / g to 2.5 dl / g, and more preferably 1.2 to 2.3. When the reduced viscosity is 1.0 dl / g or higher, it is preferable because breakage does not occur frequently during the stretching process. When the reduced viscosity is 2.5 dl / g or lower, it is preferable because the cutability is good when cutting to a predetermined product width and dimensional defects do not occur. Since the reduced viscosity of polylactic acid tends to decrease when melted, it is preferable to reduce the decrease in reduced viscosity during film 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 may contain resin components other than polylactic acid as a resin component, but the polylactic acid content 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 100% by mass. In other words, the resin component may consist only of polylactic acid. Furthermore, the first film-forming material may consist only 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 completely free of particles; it may contain inert particles such as lubricant particles, heat-resistant polymer particles, or crosslinked polymer particles described in the particle-containing layers (a) and (b) below, in amounts that do not affect the surface roughness or slipperiness of the film. The amount of lubricant particles that may be included is determined by the first stretched polylactic acid film. ム( The amount of the first film-forming material is preferably less than 100 ppm by mass, more preferably less than 50 ppm, even more preferably less than 30 ppm, particularly preferably less than 10 ppm, and may also be less than 5 ppm.

[0018] The first film-forming material constituting the first stretched polylactic acid film of the present invention may further contain one or more additives, such as fluorescent whitening agents, ultraviolet inhibitors, infrared absorbing dyes, heat stabilizers, surfactants, and antioxidants, depending on the purpose of use. As antioxidants, aromatic amine-based and phenol-based antioxidants can be used. As stabilizers, phosphorus-based (such as phosphoric acid and phosphate esters), sulfur-based, and amine-based stabilizers can be used.

[0019] (Method for producing the first stretched polylactic acid film) The first stretched polylactic acid film of the present invention is preferably an oriented film, and more preferably a biaxially oriented film, from the viewpoint of mechanical strength, chemical resistance, and heat resistance.

[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 processes such as biaxial stretching to obtain the first stretched polylactic acid film. As a method for producing the unstretched sheet, a solution casting method or a melt extrusion method can be used. 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, and more preferably in the range of 180 to 240°C. A melting temperature of 150°C or higher is preferable because it results in a suitable melt viscosity and high productivity. A melting temperature of 250°C or lower is preferable because it suppresses thermal degradation of polylactic acid.

[0022] The die temperature during melt extrusion is the same as described above, but 150 to 300°C is preferred, 170 to 290°C is more preferred, and the range of 180 to 240°C is even more preferred. When the die temperature during melt extrusion is 150°C or higher, the melt viscosity is within a suitable range, and stable extrusion is possible. 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 manufactured according to a general method for manufacturing polyester films. For example, a method can be used in which a non-oriented polyester, obtained by melting polyester resin and extruding it into a sheet, is stretched longitudinally using a difference in roll speed at a temperature above the glass transition temperature, then stretched transversely by a tenter, and then heat-treated. Specifically, for example, in the longitudinal stretching step in the longitudinal direction, the film is heated and stretched 1.1 to 6 times between two or more rolls with different peripheral speeds. The heating means at this time may be a method using a heating roll or a method using a non-contact heating medium, or a combination of these may be used. In this case, it is preferable to set the temperature of the film in the range of (Tg-10℃) to (Tg+50℃). Next, it is preferable to introduce the uniaxially oriented film into a tenter and stretch it 1.1 to 10 times in the width direction at a temperature of (Tg-10℃) to Tm or less.

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

[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 preferable because it allows for sufficient dimensional stability of the film due to heat. A temperature of 180°C or lower is preferable because it suppresses the phenomenon of holes forming in the film due to heat.

[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 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 transporting the film on multiple rolls and the handlingability of the manufactured film are improved, making it easier to handle.

[0027] (Particle-containing layer (a): resin layer) The resin layer in this invention is laminated on one side of the first stretched polylactic acid film. The resin layer forming material in this invention includes an aqueous resin and lubricant particles. The presence of the resin layer maintains the high transparency that is a characteristic of the multilayer polylactic acid film of this invention, while also providing smoothness during film roll production.

[0028] The aqueous resin is not particularly limited, but (from the viewpoint of controlling the surface free energy γs of the resin layer described later) it is preferable that it be mainly composed of at least one of polyester resin, polyurethane resin, or acrylic resin. Here, "main component" refers to a component that accounts for 50% by mass or more of the solid components constituting 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 of resins to improve adhesion. For example, to achieve both adhesion and heat and humidity resistance, two or more different resins may be used in combination, such as polyester resin and urethane resin, polyester resin and acrylic resin, or urethane resin and acrylic resin. Alternatively, two or more polyester resins with different glass transition temperatures may be used.

[0030] In this invention, a crosslinking agent may be included in the resin layer forming material to form a crosslinked structure in the resin layer. By including a crosslinking agent, it is possible to further improve adhesion under high temperature and high humidity conditions. Examples of crosslinking agents include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based agents. Among these, melamine-based, isocyanate-based, oxazoline-based, and carbodiimide-based agents are preferred due to their long-term stability of the coating solution and their effect on improving adhesion under high temperature and high humidity treatment. Furthermore, catalysts and the like may be used as needed to promote the crosslinking reaction.

[0031] The crosslinking agent content in the resin layer is preferably 1% by mass or more and 50% by mass or less of the total solid components. More preferably 5% by mass or more and 30% by mass or less. A content of 5% by mass or more increases the strength of the resin in the resin layer and its adhesion under high temperature and high humidity conditions, while a content of 5% by mass or more increases the flexibility of the resin in the resin layer and helps to suppress the decrease in adhesion under room temperature, high temperature, and high humidity conditions.

[0032] The lubricant particles may be inorganic particles or organic particles, or a combination of both. The inorganic particles are not particularly limited, but examples include silica, kaolinite, talc, light calcium carbonate, heavy calcium carbonate, zeolite, alumina, barium sulfate, carbon black, zinc oxide, zinc sulfate, zinc carbonate, titanium dioxide, zirconium dioxide, tin oxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, aluminum hydroxide, hydrated halloysite, magnesium carbonate, and magnesium hydroxide.

[0033] The organic particles are not particularly limited, but examples include particles of polystyrene, melamine resin, acrylic, acrylic-styrene, silicone, benzoguanamine resin, benzoguanamine-formaldehyde condensate resin, polycarbonate, polyethylene, etc., and it is preferable that these resin particles are three-dimensionally crosslinked.

[0034] By incorporating lubricant particles, slipperiness can be imparted, which can suppress wrinkle formation when winding the film during film manufacturing processes, and blockage (film sticking together due to tightening over time) when wound film rolls are stored for long periods.

[0035] The average particle size of the lubricant particles is not particularly limited, but from the viewpoint of maintaining the transparency of the film, an average particle size of 1 to 500 nm is preferred, and 1 to 100 nm is more preferred. The average particle size is the average particle size measured by dispersing the particles in a solvent that does not cause swelling using a Coulter counter (Beckman Coulter, Multisizer Type II). Two or more types of lubricant particles with different average particle sizes may be used, and any combination of inorganic particles, organic particles, or inorganic and organic particles may be used.

[0036] The content of the lubricant particles in the resin layer is preferably 0.1 parts by mass to 30 parts by mass, and more preferably 1 part by mass to 20 parts by mass, per 100 parts by mass of the aqueous resin. A content of 0.1 parts by mass or more makes it easier to obtain sufficient blocking resistance and improve scratch resistance. A content of 0.1 parts by mass or less makes it easier to increase the transparency and coating strength of the resin layer.

[0037] The resin layer forming material may also contain a surfactant to improve leveling during coating and to degas the coating liquid. The surfactant can be cationic, anionic, or nonionic, but silicone-based, acetylene glycol-based, or fluorine-based surfactants are preferred. These surfactants are preferably included in the resin layer to an extent that does not impair adhesion with the functional layer laminated on the resin layer.

[0038] In order to impart other functionalities to the resin layer forming material, various additives may be included to the extent that they do not impair adhesion to the functional layer. Examples of such additives include fluorescent dyes, fluorescent whitening agents, plasticizers, ultraviolet absorbers, pigment dispersants, antifoaming agents, defoaming agents, preservatives, and antistatic agents.

[0039] (Method for manufacturing multilayer polylactic acid film (A)) The multilayer polylactic acid film (A) of the present invention can be manufactured by forming a resin layer which is a particle-containing layer (a) on a first stretched polylactic acid film. In the present invention, a method for providing a resin layer on a first stretched polylactic acid film is to apply a resin layer forming material (coating solution) containing a solvent, lubricant particles, and an aqueous resin to the polylactic acid film and then dry it. From the viewpoint of environmental issues, water or a mixture of water and a water-soluble organic solvent is preferred as the solvent, and the amount of aqueous solvent in the coating solution is preferably 50 to 95% by mass, and particularly preferably 60 to 90% by mass.

[0040] In the present invention, the solid content concentration in the resin layer forming material (coating liquid) that forms the resin layer is preferably 0.5 to 35% by mass, and particularly preferably 1.0 to 15% by mass.

[0041] Any known method can be used to apply the coating solution to the polylactic acid film. Examples include the reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, curtain coating method, and the like. These methods can be used individually or in combination for coating.

[0042] The method for forming the resin layer is not particularly limited, and conventionally known methods such as coating methods can be used. Among coating methods, preferred methods include coating after manufacturing the stretched polylactic acid film substrate (offline coating method) and coating during the manufacturing process of the stretched polylactic acid film substrate (in-line coating method). However, the in-line coating method is preferred because it provides better adhesion between the substrate film and the resin layer, and reduces deterioration of the mechanical properties of the substrate film during manufacturing and minimizes thermal wrinkles. In the case of the in-line coating method performed in the manufacturing process of the first stretched polylactic acid film, the drying and heat treatment conditions during coating depend on the coating thickness and the conditions of the equipment, but it is preferable to immediately send the film to the stretching process in a perpendicular direction after coating and dry it in the preheating zone or stretching zone of the stretching process, and in such cases, it is usually preferable to set the temperature to around 50 to 120°C. Furthermore, although the heat treatment process after stretching depends on the required mechanical properties of the first stretched polylactic acid film and the conditions of the equipment, it is preferable to perform the heat treatment at a temperature of 130°C or higher from the viewpoint of improving the adhesive strength between the 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 solution to an unstretched or uniaxially stretched polylactic acid film, drying it, stretching it at least uniaxially, and then performing a heat treatment.

[0044] In the present invention, the thickness of the final resin layer is preferably 20 nm or more and 500 nm or less. A resin layer thickness of 20 nm makes it easier to obtain the high lubricity effect required in the present invention. On the other hand, a resin layer thickness of 500 nm or less makes it easier to suppress the increase in haze and the decrease in transparency.

[0045] In the present invention, it is preferable that the surface free energy γs of the final resin layer is 40 mN / m or more. Since polylactic acid film has poorer wettability than general polyester film, setting the surface free energy γs to 40 mN / m or more improves the coatability of the aqueous resin, makes it easier to achieve uniform thickness when laminating the resin layer, suppresses uneven coating and repelling which result in poor coating appearance, and also suppresses localized reduction in lubricity by unevenly distributing the lubricant particles contained in the resin layer, making it less likely for wrinkles to occur when winding the film. Furthermore, it is preferable that the above surface free energy γs be as large as possible in terms of manufacturing, but since a larger value increases hydrophilicity and makes the surface of the resin layer more susceptible to moisture absorption, it is preferable that it be 80 mN / m or less. The above 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 in the present invention is laminated on one side of the first stretched polylactic acid film. The second stretched polylactic acid film in 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 and improve its 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 that constitutes the first stretched polylactic acid film. Furthermore, the polylactic acid content in the second film-forming material can be within the same range as that in the first film-forming material. The additives can also be those exemplified in the first film-forming material.

[0048] Furthermore, the lubricant particles may be inorganic particles or organic particles, or a combination of both. Examples of inorganic and organic particles include those used in the resin layer forming material described above.

[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. A size greater than or equal to the above can provide high slipperiness. 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. A size less than or equal to the above can suppress the increase in film haze and improve transparency.

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

[0051] Furthermore, the content of 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 setting it to the above or higher, good slipperiness 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 setting it to the above or lower, the 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 was determined by scanning electron microscopy (SEM). 100 non-aggregated lubricant particles were randomly selected and observed, and the average value was used as the mean particle size. The particle size was calculated as the equivalent circle diameter. The equivalent circle diameter was calculated by dividing the area of ​​the observed lubricant particle by π, calculating the square root, and multiplying by 2. The area-to-equivalent circle diameter was calculated using an image analyzer. The particle size in the film can be determined by embedding the film in epoxy resin, cutting out a section, observing the section with a scanning electron microscope (SEM), randomly selecting 100 lubricant particles, calculating the area-equivalent diameter of the circle, and using the average value (average of 100 particles) as the average particle size. Alternatively, the film can be dissolved in a solvent such as HFIP, filtered through a membrane filter, and the particle size of the particles remaining on the filter can be measured 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 consist of two or more layers. Furthermore, the first stretched polylactic acid film of the multilayer polylactic acid film (B) can be applied as a particle-free layer or as a particle-containing layer, but it is preferable that the first stretched polylactic acid film be a particle-free layer. Furthermore, the multilayer polylactic acid film (B) of the present invention preferably has at least one surface that is a particle-containing layer (b), and both surfaces may be particle-containing layers (b). By making at least one surface a particle-containing layer (b), slipperiness can be provided, which can suppress the occurrence of wrinkles when winding the film in the film manufacturing process, and blocking, where the films stick together due to tightening over time when the wound film roll is stored for a long period of time.

[0054] Furthermore, a preferred configuration is one surface being a particle-containing layer (b) and the other surface being a particle-free layer. By making one surface a particle-free layer, when a release layer, as described later, is provided on the particle-free resin-free layer surface of the multilayer polylactic acid film (B), it is possible to maintain high smoothness of the release layer surface while providing ease of slippage during film roll production.

[0055] The thickness of the particle-containing layer (b) is preferably 0.5 μm or more, and more preferably 1.0 μm or more. Furthermore, the thickness of the particle-containing layer (b) is preferably determined considering the thickness of the multilayer polylactic acid film (B). Using the thickness of the multilayer polylactic acid film (B) (X μm) as a reference, 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 is preferably (X-15) μm or less.

[0056] The following shows an example of the layer structure of a typical multilayer polylactic acid film (B). In the layer configurations (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 (2) above, 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 size of the added lubricant particles is different. In (3) above, it is preferable that the first particle-containing layer (b) and the second particle-containing layer (b) use materials with different compositions as the second film-forming material, and it is particularly preferable that they have different content amounts 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 higher, but it is preferable that the lubricant particle content of the first particle-containing layer (b) is higher. The second particle-containing layer (b) may be made from recovered resin such as gripping material from a tenter that is generated when a multilayer polylactic acid film (B) is manufactured. In (4) above, it is preferable that the thickness of the first particle-free layer and the second particle-free layer differs, and that at least one of the layers is thin enough that surface irregularities are created by the particles of the particle-containing layer (b), ensuring slipperiness. 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 shown in the layer configuration of (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) refers to the case where the first stretched polylactic acid film also contains lubricant particles. In the above (5), it is preferable that the particle size of the added lubricant particles differs between the first particle-containing layer (first stretched polylactic acid film) and the second particle-containing layer (first stretched polylactic acid film), and the average particle size of the lubricant particles in one of the layers is preferably 0.1 μm or less, or less than 0.1 μm, and preferably 0.08 μm or less.

[0058] Note that the above layer configuration is the layer configuration during the film manufacturing process, and if in-line coating is performed during the film manufacturing process, the in-line coating layer is not included in this layer configuration. In other words, it is the layer configuration at the point when the first film-forming material and the particle-containing layer (b)-forming material of the first stretched polylactic acid film are extruded in multiple layers from the die onto a cooling roll.

[0059] When the multilayer polylactic acid film (B) of the present invention includes 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 achieving the above levels or higher, stable slipperiness, film-forming properties, and thickness ratio can be ensured. From the viewpoint of suppressing the increase in haze of the multilayer polylactic acid film (B) and improving 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, most preferably 40% or less, and may also be 30% or less, 25% or less, or 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] In the multilayer polylactic acid film (B), the first film-forming material and the second film-forming material can be processed into unstretched sheets by various methods, and then subjected to stretching processes such as biaxial stretching to obtain the first stretched polylactic acid film and the second stretched polylactic acid film. As a method for producing the unstretched sheets, a solution casting method and a melt extrusion method can be used. The melt extrusion method is preferred in the present invention. Furthermore, during melt extrusion, the first film-forming material and the second film-forming material can be melted using multiple extruders in accordance with the first film-forming material and the second film-forming material, and the molten resin composition can be introduced into a die for multilayer co-extrusion to produce 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 conditions as those described in the method for producing the first stretched polylactic acid film.

[0063] (Physical properties of multilayer polylactic acid films) 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 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 transporting the film on multiple rolls and the handlingability of the manufactured 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 higher. The preferred lower limit of the sum of tensile moduli is 8.2 GPa, a more preferred lower limit is 8.4 GPa, an even more preferred lower limit is 8.6 GPa, an even more preferred lower limit is 8.8 GPa, an even more preferred lower limit is 9.0 GPa, a particularly preferred lower limit is 9.5 GPa, and the most preferred lower limit is 10.0 GPa or higher. A sum of tensile moduli of 8.0 GPa or higher is preferable because it provides sufficient rigidity to the film and suppresses the occurrence of wrinkles and warping. Considering manufacturing points, the upper limit of the sum of tensile moduli is considered to be 15.0 GPa.

[0065] The tensile modulus Ea in the MD direction is preferably between 3 GPa and 5 GPa, with a more preferable lower limit of 3.3 GPa, an even more preferable lower limit of 3.5 GPa, a more preferable upper limit of 4.7 GPa, and an even more preferable upper limit of 4.5 GPa. The tensile modulus Eb in the TD direction is preferably between 4 GPa and 6.5 GPa, with a more preferable lower limit of 4.3 GPa, an even more preferable lower limit of 4.5 GPa, a more preferable upper limit of 6.2 GPa, and an even more preferable upper limit of 6 GPa.

[0066] In the layer structure of a multilayer polylactic acid film, when the outermost layer of one side is the particle-containing layer and the outermost layer of the other side is the particle-free layer, the preferred upper limit of the coefficient of dynamic friction (μd) when the particle-containing layer of the outermost layer of one side and the particle-free layer of the outermost layer of the other side are overlapped and slid is 0.65, more preferred upper limit is 0.60, even more preferred upper limit is 0.55, and even more preferred upper limit is 0.50. A coefficient of dynamic friction (μd) of 0.65 or less is preferable because it ensures sufficient slipperiness of the film and improves winding characteristics that affect wrinkles during film winding. The preferred lower limit of the coefficient of dynamic friction is 0.30, and more preferred lower limit is 0.35. A value above the above makes it less likely for the film to shift laterally when winding it into a roll or when transporting the roll.

[0067] The breaking strength of the multilayer polylactic acid film is preferably 75 MPa or higher in both the MD and TD directions. The preferred lower limit of the breaking strength is 100 MPa, a more preferred lower limit is 150 MPa, an even more preferred lower limit is 200 MPa, and an even more preferred lower limit is 220 MPa. A breaking strength of 75 MPa or higher is preferable because it provides sufficient mechanical strength for the film, suppressing defects such as elongation and slippage during the film processing process. Considering manufacturing considerations, the upper limit of the breaking strength is considered to be 1000 MPa.

[0068] The elongation at break of the multilayer polylactic acid film is preferably 5% or more in both the MD and TD directions. An elongation at break of 5% or more is preferable because it provides sufficient mechanical elongation of the film, suppressing defects such as cracking and tearing during the film processing process. Considering manufacturing points, the upper limit of the elongation at break is considered to be 300%. More preferably, the upper limit of the elongation at break is 150%, even more preferably 100%, and even more preferably 80%.

[0069] In multilayer polylactic acid films, it is preferable that the thermal shrinkage rate in the MD direction and the TD direction are both 10.0% or less when heated at 150°C for 30 minutes. When heated at 150°C for 30 minutes, the upper limits of the thermal shrinkage rate in the MD direction and the TD direction are more preferably 8.0% or less, even more preferably 6.0% or less, even more preferably 4.0% or less, particularly preferably 3.0% or less, and most preferably 2.0% or less, independently for the MD direction and the TD direction, respectively. A low thermal shrinkage rate facilitates processing such as coating and suppresses appearance defects due to deformation of the film under high heat. While a low thermal shrinkage rate is preferable, from a manufacturing standpoint, 0.01% is considered the lower limit.

[0070] In multilayer polylactic acid films, it is preferable that the thermal shrinkage rate in the MD direction and the TD direction are both 3.0% or less when heated at 120°C for 30 minutes. When heated at 120°C for 30 minutes, the upper limits of the thermal shrinkage rate in the MD direction and the TD direction are more preferably 2.0% or less, even more preferably 1.6% or less, even more preferably 1.4% or less, particularly preferably 1.2% or less, and most preferably 1.0% or less, independently for the MD direction and the TD direction, respectively. A low thermal shrinkage rate facilitates processing such as coating and suppresses appearance defects due to deformation of the film under high heat. While a low thermal shrinkage rate is preferable, from a manufacturing standpoint, 0.01% is considered the lower limit.

[0071] The total light transmittance of the multilayer polylactic acid film is preferably 75% or higher. High transparency is preferable in order to improve the accuracy of detecting internal foreign matter, which is a drawback of the film. Therefore, the total light transmittance of the film of the present invention is preferably 75% or higher, more preferably 80% or higher, even more preferably 85% or higher, even more preferably 88% or higher, particularly preferably 91% or higher, and most preferably 93% or higher. In order to improve the accuracy of detecting internal foreign matter, which is a drawback of the film, the higher the total light transmittance, the better, but a total light transmittance of 100% is technically difficult to achieve. From a manufacturing standpoint, it is preferable that the total light transmittance is 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 manufacturing ceramic green sheets, low haze is preferable. 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 better the smaller, but it may be 0.1% or more, or 0.3% or more. For the purpose of reducing haze, it is better not to have too much unevenness on the film surface, but from the viewpoint of handling on a rotating roll, it is preferable to form a certain degree of unevenness on at least one surface to give it a certain degree of slipperiness.

[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 modulus of elasticity. The crystallinity of the multilayer polylactic acid film (B) is measured by cutting a small piece from the film that includes all layers of the polylactic acid film (B) using a differential scanning calorimeter.

[0074] Furthermore, when forming a smooth release layer or the like 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 surface roughness of the multilayer polylactic acid film on which the release layer is formed is preferably such that the arithmetic mean roughness (Sa) is 10 nm or less and the maximum protrusion height (P) is 200 nm or less. More preferably, the arithmetic mean roughness of the surface is 10 nm or less and the maximum protrusion height is 150 nm or less; even more preferably, the arithmetic mean roughness of the surface is 10 nm or less and the maximum protrusion height is 120 nm or less; and still preferably, the arithmetic mean roughness of the surface is 8 nm or less and the maximum protrusion height is 120 nm or less. If the arithmetic mean roughness of the surface is 10 nm or less and the maximum protrusion height is 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 0.3 nm or more. Furthermore, the maximum surface protrusion height (P) may be 1 nm or more, or 3 nm or more.

[0075] As the smooth surface described above, the surface of the particle-free layer of a multilayer polylactic acid film is preferred, where 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. However, the surface roughness of the particle-free layer may be affected by the particles of the underlying particle-containing layer. To suppress the influence of the underlying particles and keep the surface roughness of the particle-free layer below the above-mentioned level, the thickness of the particle-free layer on the side where the release layer is provided 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. Furthermore, the surface layer on the surface where the release layer is provided may be a particle-containing layer, but it is preferable that the average particle diameter of the contained particles is small. Specifically, the average particle diameter is preferably 0.1 μm or less, and preferably 0.08 μm or less.

[0076] If the surface roughness of the multilayer polylactic acid film exceeds the aforementioned roughness parameters, a particle-free coating layer may be provided on the surface, and a release layer may be provided on the outermost surface, which has a roughness level equal to or less than the aforementioned roughness parameters. In this case, the surface on which the particle-free coating layer is provided may be 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 a multilayer polylactic acid film. Preferably, the release layer is provided on the side of the first stretched polylactic acid film on the outermost surface of the multilayer polylactic acid film that is free of particles. The release layer may be laminated directly onto the particle-free layer of the multilayer polylactic acid film, or it 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 manufacture and transfer of ceramic green sheets, various resin sheets, and optical films, as well as for adhesive sheets and other adhesive sheets.

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

[0079] For example, silicone resin refers to a resin having a silicone structure within its molecule. Examples include curable silicone, silicone graft resin, and modified silicone resin such as alkyl-modified silicone. However, from the viewpoint of migration properties, it is preferable to use a reactive curable silicone resin. Reactive curable silicone resins can include those that use addition reactions, condensation reactions, or ultraviolet or electron beam curing. More preferably, low-temperature curable addition reaction resins that can be processed at low temperatures, and ultraviolet or electron beam curing resins are preferred. By using these silicone resins, processing can be done at low temperatures when coating polyester films. Therefore, there is less thermal damage to the polyester film during processing, a polyester film with high flatness can be obtained, and defects such as pinholes can be reduced when manufacturing thin films such as ceramic green sheets.

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

[0081] Examples of silicone resins used in condensation reactions include those in which polydimethylsiloxane with OH groups at the ends and polydimethylsiloxane with H groups at the ends are condensed using an organotin catalyst to create a three-dimensional crosslinked structure.

[0082] Examples of UV-curable silicone resins include, as the most basic type, those that utilize the same radical reaction as conventional silicone rubber crosslinking, those that introduce unsaturated groups for photocuring, those that decompose onium salts with UV light to generate strong acids which then cleave epoxy groups for crosslinking, and those that crosslink through the addition reaction of thiols to vinylsiloxane. In addition, electron beams can be used instead of UV light. Electron beams have more energy than UV light, and it is possible to carry out a radical crosslinking reaction without using an initiator as in the case of UV curing. Examples of resins used include UV-curing silicones from Shin-Etsu Chemical Co., Ltd. (X62-7028A / B, X62-7052, X62-7205, X62-7622, ​​X62-7629, X62-7660, etc.), UV-curing silicones from Momentive Performance Materials Inc. (TPR6502, TPR6501, TPR6500, UV9300, UV9315, XS56-A2982, UV9430, etc.), and UV-curing silicones from Arakawa Chemical Corporation (Silicolise UV POLY200, POLY215, POLY201, KF-UV265AM, etc.).

[0083] As the UV-curing silicone resins mentioned above, acrylate-modified or glycidoxy-modified polydimethylsiloxanes can also be used. Good mold release properties can also be obtained by mixing these modified polydimethylsiloxanes with polyfunctional acrylate resins or epoxy resins and using them in the presence of an initiator.

[0084] Other suitable resins include alkyd resins and acrylic resins having long-chain alkyl groups such as stearyl-modified and lauryl-modified resins, or alkyd resins, acrylic resins, and olefin resins obtained by reactions such as methylated melamine. When molding sheets used in electronic components, silicone-free release agents are also preferred.

[0085] Examples of amino alkyd resins and amino acrylic resins obtained through the above-mentioned reaction of methylated melamine include the Tesfine series manufactured by Showa Denko Materials.

[0086] When using the above-mentioned resin or other release components as a release layer forming material, one type of release component may be used, or two or more types may be mixed. When mixing two or more types, two or more types of silicone resins may be used, or it is preferable to mix multiple different types of resins, such as a binder resin and a silicone resin.

[0087] In particular, when molding thin film sheets such as ceramic green sheets, it is preferable that the release layer does not deform during peeling, and therefore it is preferable that the release layer is crosslinked and hardened. For this reason, it is preferable that the release layer forming material contains not only silicone-based release agents but also binder components and crosslinking agents.

[0088] The binder component included in the release layer forming material preferably consists of a crosslinkable component that increases the crosslinking density of the release layer and improves its durability and solvent resistance. Therefore, the binder component is preferably formed by the reaction of a resin having a reactive functional group with a crosslinking agent. It is also preferable that the reactive functional group or the crosslinking agent alone self-crosslinks. However, the present invention does not exclude embodiments in which the binder component consists only of a resin having a reactive functional group or a crosslinking agent.

[0089] Suitable resins having reactive functional groups include, for example, polyester resins, acrylic resins, polyurethane resins, and polyolefin resins. These resins preferably have at least one reactive functional group selected from carboxyl groups, hydroxyl groups, epoxy groups, amino groups, and the like.

[0090] The release layer forming material may also preferably contain a crosslinking agent. Preferred crosslinking agents include, for example, melamine-based, isocyanate-based, carbodiimide-based, oxazoline-based, and epoxy-based agents. One or more crosslinking agents may be used in combination. Particularly preferred are crosslinking agents that react with the reactive functional groups introduced into the binder component.

[0091] The release layer forming material may contain particles with an average particle diameter of 1 μm or less, but from the viewpoint of pinhole generation, it is preferable to substantially omit materials that form protrusions such as particles.

[0092] To adjust the release force, additives such as light release additives and heavy release additives, as well as adhesion enhancers and antistatic agents, may be added to the release layer forming material. Furthermore, to improve adhesion to the substrate layer, it is preferable to pre-treat the surface of the polylactic acid film with an anchor coat, corona treatment, plasma treatment, atmospheric pressure plasma treatment, etc., before applying the release coating layer.

[0093] The thickness of the release layer can be set according to its intended use and is not particularly limited, but preferably, the thickness of the release layer after curing is in the range of 0.005 to 2.0 μm. A release layer thickness of 0.005 μm or more is preferable because it maintains release performance. Furthermore, a release layer thickness of 2.0 μm or less is preferable because the curing time does not become too long, and there is no risk of uneven sheet thickness due to a decrease in the flatness of the release film. In addition, because the curing time is not too long, there is no risk of the resin constituting the release layer agglomerating and forming protrusions, so it is preferable that pinhole defects in the sheet do not 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 in order to prevent defects from occurring in the sheet coated and molded on the outer surface of the film. It is preferable that the arithmetic mean roughness (Sa) of the release layer surface is 10 nm or less and the maximum protrusion height (P) is 200 nm or less. Furthermore, it is more preferable that the arithmetic mean roughness of the release layer surface is 10 nm or less and the maximum protrusion height is 100 nm or less, and even more preferable that 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, it is preferable that defects such as pinholes do not occur during sheet formation and the yield is good. 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 also be said that the smaller the maximum protrusion height (P), the better, 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 on the release film is 8 mJ / m 2 Preferably, it is 10 mJ / m³. More preferably, 10 mJ / m³. 2 That is all. 12 mJ / m 2 The above is even more preferable. 8mJ / m 2 This is preferable because it reduces the likelihood of the sheet dissolving solution being repelled when applied.

[0096] The upper limit of the surface free energy of the release layer provided on the release film is 45 mJ / m 2 Preferably, it is less than 40 mJ / m³. More preferably, 40 mJ / m³. 2 The following is true: 35 mJ / m 2 The following is even more preferable: 45 mJ / m 2 The following is preferable because it provides good peelability of the molded sheet.

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

[0098] The surface tension of the release agent (coating liquid) when applying it is not particularly limited, but is preferably 30 mN / m or less. By setting the surface tension as described above, the wettability after coating is improved, and the surface irregularities of the coating film after drying can be reduced.

[0099] When applying the release layer forming agent (coating liquid), the coating liquid is not particularly limited, but it is preferable to add a solvent with a boiling point of 90°C or higher. Adding a solvent with a boiling point of 90°C or higher prevents bumping during drying, levels the coating film, and improves the smoothness of the coating film surface after drying. The amount of solvent added is preferably about 10 to 80% by mass of the total coating liquid.

[0100] Examples of application methods for the above-mentioned coating liquid include roll coating methods such as gravure coating and reverse coating, bar coating methods such as wire bar coating, die coating, spray coating, and air knife coating.

[0101] (Ceramic green sheet and ceramic capacitor) Generally, multilayer ceramic capacitors have a rectangular parallelepiped-shaped ceramic body. Inside the ceramic body, first internal electrodes and second internal electrodes are alternately arranged along the thickness direction. The first internal electrodes are exposed on the first end face of the ceramic body. A first external electrode is provided on the first end face. The first internal electrodes are electrically connected to the first external electrode at the first end face. The second internal electrodes are exposed on the second end face of the ceramic body. A second external electrode is provided on the second end face. The second internal electrodes are 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 manufacturing ceramic green sheets for manufacturing such multilayer ceramic capacitors. For example, it can be manufactured as follows: First, the release film of the present invention is used as a carrier film, and 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 laminating the ceramic green sheet, the ceramic green sheet with the conductive layer for forming the first internal electrode printed on it, and the ceramic green sheet with the conductive layer for forming the second internal electrode printed on it, and pressing them. The mother laminate is divided into multiple parts to produce raw ceramic bodies. Ceramic bodies are obtained by firing the raw ceramic bodies. After that, a multilayer ceramic capacitor can be completed by forming the first and second external electrodes. [Examples]

[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 Method] 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 comparative examples were measured and evaluated in the same manner. In addition, 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, regarding the tensile modulus, degree of crystallinity, thermal shrinkage coefficient, breaking strength, and elongation at break of the film properties described below, 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 (or any effect will be only within the range of measurement error). By measuring the first stretched polylactic acid film, the tensile modulus of the multilayer polylactic acid film (A) can be measured.

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

[0107] (2) Degree of crystallinity Measurements were taken using a differential scanning calorimeter (DSC214Polyma) manufactured by Netch Japan. Using a 10 mg sample, measurements were taken in the range from 25°C to 250°C at a heating rate of 10°C / min. The degree of crystallinity (%) of the multilayer polylactic acid film was determined by dividing the endothermic amount of the melting peak observed during heating by the theoretical heat of fusion of a perfect polylactic acid crystal (93.6 J / g). The sample used was obtained by cutting the film so that all layers of the multilayer polylactic acid film were included.

[0108] (3) Tensile modulus The tensile modulus of the multilayer polylactic acid film was measured in accordance with JIS K 7127. Strips of 200 mm in length and 15 mm in width were cut from the film in both the MD and TD directions, respectively, using a single-edged razor. Two parallel gauge marks were marked 50 mm apart in the center of each specimen. Next, the strips were clamped in a Shimadzu Autograph AGS-X with a 100 mm chuck distance and pulled at a speed of 0.5 mm / min. The tensile modulus (GPa) in each direction was determined from the resulting load-strain curves for 0.1-0.3%. The strain value was measured using the distance between the gauge marks.

[0109] (4) Thermal shrinkage The heat shrinkage rate of multilayer polylactic acid film was measured in accordance with JIS C 2318. A 10 mm wide, 190 mm long strip of laminated film was cut in the direction to be measured, marked at 150 mm intervals, and the interval between the marks (A) was measured. Next, the film was placed in an oven in a 150°C atmosphere and heated at 150 ± 3°C for 30 minutes without load, and the interval between the marks (B) was measured. The heat shrinkage rate at 150°C was then calculated using the following formula. Similarly, a film cut in the same manner as above was placed in an oven in a 120°C atmosphere and heated at 120 ± 3°C for 30 minutes without load, and the interval between the marks (C) was measured, and the heat shrinkage rate at 120°C was calculated using the following formula. Heat shrinkage rate at 150°C (%) = (AB) / A × 100 Heat shrinkage rate at 120°C (%) = (AC) / A × 100

[0110] (5) Breaking strength, breaking elongation The breaking strength and elongation at break of the multilayer polylactic acid film were measured in accordance with JIS C 2318. Samples were cut into strips of 120 mm in length and 10 mm in width in the MD and TD directions of the film, respectively, using a single-edged razor. Next, the strips were clamped in a Shimadzu Autograph AG-IS with a chuck distance of 100 mm and pulled at a speed of 100 mm / min. The breaking strength (MPa) and elongation at break (%) in each direction were determined from the resulting load-strain curves.

[0111] (6) Hayes In accordance with JIS K 7136, the haze (%) of multilayer polylactic acid film was measured using an NDH-7000 Type 2 turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd.

[0112] (7) Total light transmittance In accordance with JIS K 7136, the total light transmittance (%) of multilayer polylactic acid film was measured using an NDH-7000 Type 2 turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd.

[0113] (8) Coefficient of kinetic friction The coefficient of dynamic friction of the multilayer polylactic acid film was measured in accordance with JIS-K-7125. A piece of film measuring 70 mm in width and 200 mm in length was cut out (sample A) with the longitudinal direction as the length direction, and sample A was fixed to a table with the lubricant-free layer facing upwards. On the other hand, sample B measuring 50 mm in width and 50 mm in length was prepared from the film, and the lubricant-free layer of sample B was attached to a sliding stand (50 mm in width and 50 mm in length). Next, the film surface of sliding stand B was placed on sample A on the table so that the length direction of the film was parallel, and the coefficient of dynamic friction (μd) was determined by using an AND (A&D) Tensilon universal tester RGT-1210, applying a load of 4.4 kg to the sliding stand, and sliding the sliding stand along the length direction of sample A against the surface of the film at a speed of 200 mm / min.

[0114] (9) Surface free energy γs of the resin layer After leaving multilayer polylactic acid films in an atmosphere of 50% relative humidity for 24 hours, the contact angles of distilled water and diiodomethane were measured one minute after dropping them onto the resin layer using a FACE contact angle meter (Kyowa Interface Chemical Co., Ltd., CA-X type). Each sample was measured five times, 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 then calculated from the contact angles of distilled water and diiodomethane.

[0115] (10) Appearance of the resin layer coating The surface of a multilayer polylactic acid film with a laminated resin layer was illuminated using a bromine light (VIDEOLIGHT VLG301 100V 300W, manufactured by LPL) and a fluorescent lamp (Panasonic Palook, FL 15EX-N 15W, 3-wavelength daylight white) at an angle of approximately 10° to 45° relative to the film surface, and the appearance of the resin layer coating was judged by visual observation according to the following criteria. A: Both the bromine light and the fluorescent light showed no unevenness in the coating, no streaks, or defects, resulting in a uniform coating surface. B: Under bromlight, coating irregularities, streaks, and imperfections can be observed, but they are not visible under fluorescent light. C: Both bromite and fluorescent lighting show uneven coating, streaks, and paint defects. Coatings with a grade of A or B were judged to have a good coating appearance, and those with a grade of A were judged to have a particularly good appearance.

[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 surface roughness of the region under the following conditions. For the arithmetic mean roughness (Sa), the average of 5 measurements was adopted, and for the maximum protrusion height (P), the maximum value of 5 measurements was used after excluding the maximum and minimum values ​​from 7 measurements. (Measurement conditions) • Measurement mode: WAVE mode • Objective lens: 10x 0.5x Tube Lens ·Measurement area 936μm x 702μm (Analysis conditions) • Surface correction: 4th order correction • Interpolation process: Full interpolation

[0117] (12) Reduced viscosity (ηsp / c) A solution prepared by dissolving 0.1 g of the sample in 15 mL of a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (75 / 25 (mass ratio)) was measured at 30°C using an Ostwald viscometer. The unit is dl / g. For polylactic acid samples, the polylactic acid used as a film-forming material was crushed chips and used, while for multilayer polylactic acid films, the film was cut with scissors. The solution was filtered before measurement to remove particles and other contaminants.

[0118] (Example 1) (1) Preparation of polylactic acid As the polylactic acid, we used Total Corbion's poly-L-lactic acid PLA L175 (L-lactic acid / D-lactic acid mass ratio of 99 / 1, reduced viscosity of 2.0 dl / g).

[0119] (2) Preparation of aqueous resin to be used in the 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 reaction vessel in a stainless steel autoclave equipped with a stirrer, thermometer, and partial reflux condenser, and a transesterification reaction was carried out at 180°C for 3 hours. Next, 5-sodium sulfoisophthalic acid (6.0 parts by mass) was added, and an esterification reaction was carried out at 240°C for 1 hour, followed by a polycondensation reaction at 250°C under reduced pressure (10-0.2 mmHg) for 2 hours to obtain copolymer polyester resin (A) with a number average molecular weight of 19,500 and a softening point of 60°C. In a reactor equipped with a stirrer, thermometer, and reflux device, 30 parts by mass of the copolymerized polyester resin (A) and 15 parts by mass of ethylene glycol n-butyl ether were placed and heated at 110°C, and the resin was stirred to dissolve it. After the resin was completely dissolved, 55 parts by mass of water were gradually added to the polyester solution while stirring. After the addition, the liquid was cooled to room temperature while stirring to prepare a milky white aqueous dispersion of polyester resin with a solid content of 30% by mass.

[0120] (3) Preparation of coating liquid (resin layer forming material) for resin layer formation The following coating agents were mixed to create coating solution A. (Coating solution A) Water 46.89% by mass Isopropanol 30.00% by mass Polyester resin aqueous dispersion 20.00% by mass MP4540M 0.08% by mass (Manufactured by Nissan Chemical Industries, solid content concentration 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 concentration 100% by mass)

[0121] (4) Manufacturing of multilayer polylactic acid film Poly-L-lactic acid (L175) was dried under reduced pressure at 120°C for 6 hours (1 Torr) and then fed into an extruder. It was melted at 220°C and extruded in sheet form through a die. A gear pump was used to control the thickness to 6400 μm. For the filters, stainless steel sintered material with a filtration particle size of 10 μm (initial filtration efficiency: 95%) was used.

[0122] The extruded resin was cast onto a cooling drum with a surface temperature of 50°C, and cooled and solidified using an electrostatic application method to ensure close contact with the surface of the cooling drum, thereby creating an unstretched film with a thickness of 600 μm.

[0123] The obtained unstretched film was heated to 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, coating solution A, used to form the resin layer, was applied to one side of the obtained uniaxially oriented film, adjusting the amount applied using the fountain coat method so that the resin layer thickness would be 50 nm. Next, the inline-coated uniaxially oriented film was held with clips and dried at 60°C for 20 seconds, after which it was stretched in the transverse direction (TD direction). The transverse stretching temperature was 75°C, and the transverse stretching ratio was 4.96 times. Subsequently, it was heat-treated at 150°C for 15 seconds.

[0125] The biaxially oriented film, which 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, a 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 sum of the degree of crystallinity and tensile modulus of elasticity of the obtained multilayer polylactic acid film was high, and the thermal shrinkage rate was low, indicating that a multilayer polylactic acid film with excellent elastic modulus and heat resistance can 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 solution B. In Example 2, a multilayer polylactic acid film was obtained in the same manner as in Example 1, except that coating solution A used for forming the resin layer was changed to coating solution B described below. The film properties of the multilayer polylactic acid film obtained in Example 2 are shown in Table 2. (Coating solution B) Water 52.25% by mass Isopropanol 30.00% by mass Nikazol RX-2035A 13.64% by mass (Acrylic resin aqueous dispersion, manufactured by Nippon Carbide Co., Ltd., solids content 44% by mass) MP4540M 0.08% by mass (Manufactured by Nissan Chemical Industries, solid content concentration 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 concentration 100% by mass)

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

[0128] (Example 3) The following coating agents were mixed to prepare coating solution C. Example 3 was conducted in the same manner as in Example 1, except that coating solution A used to form the resin layer was changed to coating solution C described below. The film properties of the multilayer polylactic acid film obtained in Example 3 are shown in Table 2. (Coating solution 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, solids content 23% by mass) MP4540M 0.08% by mass (Manufactured by Nissan Chemical Industries, solid content concentration 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 concentration 100% by mass)

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

[0130] (Examples 4 and 5) Examples 4 and 5 were conducted in the same manner as Example 1, except that the stretching conditions were changed as shown in Table 1, to obtain multilayer polylactic acid films. In Example 5, the unstretched film thickness was adjusted by changing the extruder discharge rate to achieve the film thickness shown in Table 2. The film properties of the multilayer polylactic acid films obtained in Examples 4 and 5 are shown in Table 2. In Example 4, a higher modulus of elasticity was obtained by improving the second stretching ratio in the TD direction. In Example 5, thermal shrinkage in the TD direction was suppressed and a high modulus of elasticity was maintained by performing a relaxation treatment (160°C, relaxation rate 5%) after TD stretching. The multilayer polylactic acid films of Examples 4 and 5 had a high sum of crystallinity and tensile modulus of elasticity, and a low thermal shrinkage rate, demonstrating that multilayer polylactic acid films with excellent modulus of elasticity and heat resistance can be obtained in Examples 4 and 5. In addition, the coating appearance of the resin layer was particularly good.

[0131] (Example 6) (1) Preparation of polylactic acid As the polylactic acid, we used Total Corbion's poly-L-lactic acid PLA LX175 (with a mass ratio of L-lactic acid to D-lactic acid of 96 / 4).

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

[0133] The extruded resin was cast onto a cooling drum with a surface temperature of 50°C, and cooled and solidified using an electrostatic application method to ensure close contact with the surface of the cooling drum, thereby creating an unstretched film with a thickness of 600 μm.

[0134] The obtained unstretched film was heated to 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, coating solution A, used for forming the resin layer, was applied to one side of the obtained uniaxially oriented film using the fountain coat method, adjusting the amount applied so that the resin layer thickness was 50 nm. Next, the inline-coated uniaxially oriented film was held with clips, 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, a heat treatment was performed at 150°C for 15 seconds.

[0136] The biaxially oriented film, which 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 of 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 sum of the degree of crystallinity and tensile modulus of elasticity of the obtained multilayer polylactic acid film was high, and the thermal shrinkage rate was low, indicating that a multilayer polylactic acid film with excellent elastic modulus and heat resistance can be obtained in Example 6. In addition, the coating appearance of the resin layer was particularly good.

[0137] (Example 7) In Example 7, an unstretched film was prepared in the same manner as in Example 1, except that the extrusion rate of the extruder was changed to adjust the thickness of the unstretched film so that it matched the film thickness shown in Table 2. On one side of the unstretched film, coating liquid A, used for forming the resin layer, was applied using the fountain bar coating method, with the amount adjusted so that the resin layer thickness was 50 nm, and then dried at 60°C for 20 seconds. Next, the inline-coated unstretched film was guided to a simultaneous biaxial stretcher, and while the ends of the film were held with clips, it was stretched 3.0 times in the longitudinal direction and 5.0 times in the width direction in a hot air zone at a temperature of 75°C. Then, after being held with clips again, transverse stretching was performed under the same stretching conditions as in Example 5, followed by a relaxation treatment (160°C, relaxation rate of 5%) to obtain a multilayer polylactic acid film. Table 2 shows the film properties of the multilayer polylactic acid film obtained in Example 7. The sum of the degree of crystallinity and tensile modulus of the obtained multilayer polylactic acid film was high, and the thermal shrinkage rate was low. Therefore, Example 7 demonstrated that a multilayer polylactic acid film with excellent elastic modulus and heat resistance can be obtained. In addition, the coating appearance of the resin layer was good.

[0138] (Comparative Examples 1 and 2) Comparative Example 1 yielded a multilayer polylactic acid film in the same manner as Example 1, except that the extrusion rate was changed to adjust the unstretched film thickness to achieve the film thickness shown in Table 2, and the stretching conditions were changed to those shown in Table 1. Comparative Example 2 yielded a multilayer polylactic acid film in the same manner as 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 are outside the scope of the present invention because they have low tensile modulus and high thermal shrinkage. Comparative Examples 1 and 2 were stretched using the commonly used sequential biaxial stretching or simultaneous biaxial stretching method, and because the stretching ratio was low, their elastic modulus and heat resistance were inferior.

[0139] (Comparative Example 3) Comparative Example 3 followed the same procedure as in Example 1, except that the unstretched film thickness was adjusted by changing the extrusion rate of the extruder to achieve the film thickness shown in Table 2, and the stretching conditions were changed to those shown in Table 1. In Comparative Example 3, although the stretching ratio in the TD direction was set high in the commonly used sequential biaxial stretching, 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 solution D. Example 8 was conducted in the same manner as in Example 1, except that coating solution A used for forming the resin layer was changed to coating solution D described below. The film properties of the multilayer polylactic acid film obtained in Example 8 are shown in Table 2. (Coating solution D) Water 42.89% by mass Isopropanol 30.00% by mass Zicen L 24.00 mass% (Polyolefin resin aqueous dispersion, manufactured by Sumitomo Seika Chemicals Co., Ltd., solid content 25 mass%) MP4540M 0.08 mass% (Manufactured by Nissan Chemical Industries, Ltd., solid content concentration 40 mass%, average particle diameter 450 nm) Snowtex ST-XL 3.00 mass% (Manufactured by Nissan Chemical Industries, Ltd., solid content 30 mass%, average particle diameter 45 nm) Surfactant 0.03 mass% (Silicone-based, solid content concentration 100 mass%)

[0141] The sum of the crystallinity and tensile modulus of the multilayer polylactic acid film obtained in Example 8 was high, and the thermal shrinkage rate was low, indicating that a film excellent in 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, solid content concentration 100 mass%) and 1 part by mass of a curing catalyst bis(alkylphenyl)iodonium hexafluoroantimonate were diluted with a toluene / methyl ethyl ketone / heptane (=3:5:2) solution to prepare a solution of a release layer forming material with a solid content of 1 mass%. This solution of the release layer forming material was applied onto 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 that the thickness after drying would be 0.05 μm, and then dried with hot air at 90 °C for 30 seconds. Immediately thereafter, ultraviolet irradiation (300 mJ / cm 2 ) was performed using an electrodeless lamp (H bulb manufactured by Fusion Co., Ltd.) 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 excellent in modulus and heat resistance, had good dimensional stability during processing at high temperatures, and could obtain high rigidity, and the coating appearance of the resin layer was also good. Table 2 shows the evaluation results of the surface of the release layer of the release films obtained in Examples 1 to 8. Since the maximum protrusion height (P) was 200 nm or less and the arithmetic mean roughness (Sa) was 10 nm or less, it was suitable as a release film for the manufacture of ceramic green sheets.

[0144] [Table 1]

[0145] [Table 2]

[0146] (Example 11) (1) Preparation of polylactic acid As the polylactic acid, we used Total Corbion's poly-L-lactic acid PLA L175 (with a mass ratio of L-lactic acid to D-lactic acid of 99 / 1). Poly-L-lactic acid (L175) was used as raw material A1 for the particle-free layer. (2) Preparation of forming material to be used in the particle-containing layer As inorganic particles (lubricant particles), SYLYSIA310P (average particle size 2.7 μm) manufactured by Fuji Silysia Chemical Co., Ltd. was used. 0.5 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 mass%. Next, L-175 was dry-blended with 0.67% by mass of lubricant masterbatch raw materials to prepare raw material B1 for the granular lubricant-containing layer.

[0147] (3) Manufacturing of multilayer polylactic acid film Poly-L-lactic acid (L175) was used as raw material A1 for the particle-free layer. It was dried under reduced pressure at 120°C for 6 hours (1 Torr), then supplied to extruder A and melted at 220°C. Similarly, raw material B1 for the particle-containing layer was dried and supplied to extruder B, where it was also melted at 220°C. The molten resin from each extruder was fed into a die, where raw materials A1 and B1 were layered and melt-extruded into a sheet. The sheet thickness was controlled using a gear pump. For the filters, stainless steel sintered material with a filtration particle size of 10 μm (initial filtration efficiency: 95%) was used in both cases.

[0148] The multilayer co-extruded resin was cast onto a cooling drum with a surface temperature of 50°C, and cooled and solidified using an electrostatic application method to ensure close contact with the drum surface. Two layers of two types of unstretched films with the layer thickness ratios shown in Table 3 were prepared. The thickness of the unstretched film was 600 μm.

[0149] The obtained unstretched film was heated to 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] Next, the obtained uniaxially oriented film was guided to a tenter, held with clips, and stretched in the transverse direction (TD direction). The transverse stretching temperature was 75°C, and the transverse stretching ratio was 4.96 times. Next, a heat treatment was performed at 150°C for 15 seconds.

[0151] The biaxially oriented film, which 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, a 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 sum of the degree of crystallinity and tensile modulus of elasticity of the obtained multilayer polylactic acid film was high, and the thermal shrinkage rate was low, indicating that a film with excellent elastic modulus and heat resistance can be obtained in Example 1. The reduced viscosity of the obtained film was 1.8 dl / g.

[0152] (Examples 12 and 13) Examples 12 and 13 were conducted in the same manner as Example 11, except that the stretching conditions were changed as shown in Table 1. In Example 13, the extruder discharge rate was adjusted to achieve the film thickness shown in Table 4. The film properties of the multilayer polylactic acid films obtained in Examples 12 and 13 are shown in Table 2. In Example 12, a higher modulus of elasticity was obtained by improving the second stretching ratio in the TD direction. In Example 13, thermal shrinkage in the TD direction was suppressed and a high modulus of elasticity was maintained by performing a relaxation treatment (160°C, relaxation rate 5%) after TD stretching. The multilayer polylactic acid films of Examples 12 and 13 had a high sum of crystallinity and tensile modulus of elasticity, and a low thermal shrinkage rate. Therefore, Examples 12 and 13 demonstrated that multilayer polylactic acid films with excellent modulus of elasticity and heat resistance can be obtained.

[0153] (Example 14) (1) Preparation of the forming material to be used for the polylactic acid and particle-containing layer As polylactic acid, we prepared Total Corbion's poly-L-lactic acid PLA LX175 (with a mass ratio of L-lactic acid to D-lactic acid of 96 / 4). In Example 11, 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.

[0154] (2) Manufacturing of 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. The obtained multilayer unstretched film was heated to 70°C using a group of heated rolls, and then stretched to 3.0 times its length in the longitudinal direction using a group of rolls with different peripheral speeds.

[0155] Next, the obtained uniaxially oriented film was grasped with a clip and stretched in the transverse direction (TD direction). The transverse stretching temperature was 75°C and the transverse stretching ratio was 4.96 times. Next, a heat treatment was performed at 150°C for 15 seconds.

[0156] The biaxially oriented film, which 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 of 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 sum of the degree of crystallinity and tensile modulus of elasticity of the obtained multilayer polylactic acid film was high, and the thermal shrinkage rate was low, indicating that Example 4 shows that a multilayer polylactic acid film with excellent elastic modulus and heat resistance can be obtained.

[0157] (Example 15) In Example 15, an unstretched film prepared in the same manner as in Example 13 was introduced into a simultaneous biaxial stretcher, except that Total Corbion's poly-L-lactic acid PLA LX175 (L-lactic acid / D-lactic acid mass ratio of 96 / 4) was used as the polylactic acid. The film was held at the ends with clips and stretched 3.0 times in the longitudinal direction and 5.0 times in the width direction in a hot air zone at 75°C. Then, the film was held again with clips and transversely stretched under the same stretching conditions as in Example 13, followed by a relaxation treatment (160°C, relaxation rate of 5%) to obtain a multilayer polylactic acid film. Table 2 shows the film properties of the multilayer polylactic acid film obtained in Example 15. The sum of the degree of crystallinity and tensile modulus of the obtained multilayer polylactic acid film is high, and the thermal shrinkage rate is low, indicating that Example 15 yielded a film with excellent elastic modulus and heat resistance.

[0158] (Example 16) In the production of the multilayer polylactic acid film of Example 11, the remaining raw materials A1 and B1 generated at the clip gripping section were recovered, pelletized, and used as raw material C. After drying raw materials A1, B1, and C, they were supplied 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 die, and raw materials A / C / B were layered within the die and melt-extruded into a sheet. The sheet thickness was controlled using a gear pump. In addition, a stainless steel sintered filter material with a filtration particle size of 10 μm (initial filtration efficiency: 95%) was used for all filters.

[0159] The multilayer co-extruded resin was cast onto a cooling drum with a surface temperature of 50°C and cooled and solidified using an electrostatic application method to ensure close contact with the surface of the cooling drum, thereby creating three unstretched films of three types and three layers with the layer thickness ratios shown in Table 3. The obtained unstretched films were subjected to the same stretching conditions as in Example 11 to obtain multilayer polylactic acid films.

[0160] (Comparative Examples 11 and 12) Comparative Example 11 was obtained in the same manner as Example 11, except that only raw material A1 for the particle lubricant-free layer was used, and it was melt-extruded into a single layer sheet with a thickness of 450 μm, and the stretching conditions were changed as shown in Table 3. Comparative Example 12 was obtained in the same manner as Example 15, except that only raw material A1 for the particle lubricant-free layer was used, and it was melt-extruded into a single layer sheet with a thickness of 450 μm, and the stretching conditions were changed as shown in Table 3. Table 3 shows the film properties of the single-layer stretched polylactic acid films obtained in Comparative Examples 11 and 12. 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 the commonly used sequential biaxial stretching or simultaneous biaxial stretching method, and because the stretching ratio was low, their elastic modulus and heat resistance were inferior.

[0161] (Comparative Example 13) Comparative Example 13 followed the same procedure as Example 11, except that only raw material A1 for the particle lubricant-free layer was used, and it was melt-extruded into a single layer sheet with a thickness of 450 μm, and the stretching conditions were changed as shown in Table 3. In Comparative Example 13, although the stretching ratio in the TD direction was set high in the sequential biaxial stretching which is commonly used, stretching fracture occurred, and a single layer of stretched polylactic acid film could not be obtained.

[0162] <Lamination of release layer (2)> A solution of the release layer forming material was prepared in the same manner as described in <Lamination of release layer (1)>. This release layer-forming material was applied to the lubricant-free layer on the multilayer polylactic acid film obtained in Examples 11-16 using a reverse gravure coater to a thickness of 0.05 μm after drying. Then, it was dried with hot air at 90°C for 30 seconds, and immediately irradiated with ultraviolet light (300 mJ / cm²) using an electrodeless lamp (H-bulb manufactured by Fusion Co., Ltd.). 2 A release layer was formed by the above procedure to obtain a release film. A release layer was also formed in the same manner to obtain a release film for the single-layer stretched polylactic acid films obtained in Comparative Examples 11 and 12.

[0163] Based on the above, the multilayer polylactic acid films obtained in Examples 11 to 16 are films with excellent elastic modulus and heat resistance, 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 had a maximum protrusion height (P) of 200 nm or less and an arithmetic mean roughness (Sa) of 10 nm or less, making them suitable, for example, as release films for the manufacture of ceramic green sheets.

[0164] [Table 3]

[0165] [Table 4] [Industrial applicability]

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

Claims

1. A release film having a release layer on at least one surface of a multilayer polylactic acid film, The multilayer polylactic acid film 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. The tensile modulus Ea in the longitudinal direction and the tensile modulus Eb in the width direction of the multilayer polylactic acid film satisfy the formula Ea + Eb > 8.0 GPa, the degree of 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 thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the width direction are both 10.0% or less. A release film having a maximum protrusion height (P) of the surface of the release layer of 200 nm or less, and an arithmetic mean roughness (Sa) of the surface of the release layer of 10 nm or less.

2. The release film according to claim 1, wherein the thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the width direction are both 3.0% or less when heated at 120°C for 30 minutes.

3. The release film according to claim 1, wherein the first stretched polylactic acid film is a particle-free layer that does not contain particles, or whose particle content relative to the total amount of the first stretched polylactic acid film is less than 100 ppm by mass and is substantially particle-free.

4. The release film according to claim 1, wherein the particle-containing layer is the outermost layer of at least one surface of the multilayer polylactic acid film.

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

6. The release film according to claim 3, wherein the multilayer polylactic acid film has a two-layer structure consisting of the particle-containing layer and the particle-free layer.

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

8. The release film according to claim 1, wherein the mass ratio of L-lactic acid to D-lactic acid of the polylactic acid is 100 / 0 to 85 / 15.

9. The release film according to claim 1, wherein the multilayer polylactic acid film has a total light transmittance of 75% or more and a haze of 3% or less.

10. The release film according to claim 1, wherein the particle-containing layer is a resin layer formed from a resin layer-forming material containing an aqueous resin and lubricant particles.

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

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

13. The release film according to claim 1, 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 release film according to claim 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 the first film-forming material and the second film-forming material.

15. The release layer is located on the first stretched polylactic acid film side, which is the outermost particle-free layer of the multilayer polylactic acid film, according to claim 1.

16. The release film according to claim 1, wherein the release layer is formed from a release layer forming material containing a silicone release component.

17. The release film according to any one of claims 1 to 16, wherein the release film is for manufacturing ceramic green sheets.

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