JP7553890B1 - Polylactic acid film and laminated film - Google Patents

Abstract

The present invention provides a polylactic acid film having excellent elastic modulus and heat resistance, which is derived from a biomass raw material and is biodegradable. The polylactic acid film is made of a resin composition containing polylactic acid. In this polylactic acid film, the tensile elastic modulus Ea in the longitudinal direction and the tensile elastic modulus Eb in the transverse direction satisfy the formula "Ea + Eb > 8.0 GPa", the crystallinity is 40% to 90%, and when heated at 150°C for 30 minutes, the thermal shrinkage rate in the longitudinal direction and the thermal shrinkage rate in the transverse direction are each 10.0% or less. In the polylactic acid film, the weight ratio of L-lactic acid/D-lactic acid is preferably 100/0 to 85/15.

Description

The present invention relates to a polylactic acid film made of a resin composition containing polylactic acid, and a laminate film containing the same.

Films made of polylactic acid (hereinafter sometimes referred to as "PLA") resin are derived from biomass raw materials and are biodegradable, so they are being developed as an alternative to conventional fossil raw materials. However, compared to polyethylene terephthalate, nylon, polyolefins, and other materials commonly used in industry, polylactic acid films made of polylactic acid resin have a low elastic modulus and low heat resistance. For this reason, when used for industrial purposes, PLA films have problems such as dimensional changes and appearance defects such as wrinkles during processing.

To solve these problems, methods have been proposed that improve the film-forming conditions of PLA films. For example, Patent Document 1 discloses a method of improving heat resistance without impairing formability by dividing the stretching into two or more steps in the longitudinal direction, followed by stretching in the width direction, with the second stretching step in the longitudinal direction being performed at a temperature lower than the first stretching temperature.

JP 2004-359948 A

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

The above-mentioned conventional techniques have been unable to improve the tensile modulus in the longitudinal and transverse directions and at the same time obtain good heat resistance.
An object of the present invention is to provide a polylactic acid film having excellent elastic modulus and heat resistance, which is produced by using polylactic acid derived from a biomass raw material and has biodegradability, and a laminate film containing the same.

As a result of extensive research by the inventors of the present application on polylactic acid films, the inventors have found that by stretching the polylactic acid film multiple times in multiple stages at a high temperature near the melting point of polylactic acid, it is possible to suppress the stretching stress of the internal molecular chains and improve the total stretching ratio, thereby achieving a crystallinity within a predetermined range and successfully improving the elastic modulus and heat resistance of the polylactic acid film of the present invention.
That is, in order to solve the above problems, the present invention has the following configuration.

1. A polylactic acid film made of a resin composition containing polylactic acid,
A polylactic acid film having a longitudinal tensile modulus Ea and a transverse tensile modulus Eb that satisfy the formula Ea + Eb > 8.0 GPa, a crystallinity of 40% or more and 90% or less, and a longitudinal heat shrinkage rate and a transverse heat shrinkage rate each of which are 10.0% or less when heated at 150°C for 30 minutes.
2. The polylactic acid film according to 1. above, which has a thermal shrinkage rate of 3.0% or less in both the longitudinal direction and the transverse direction when heated at 120° C. for 30 minutes.
3. The polylactic acid film according to 1. or 2. above, wherein the weight ratio of L-lactic acid/D-lactic acid is 100/0 to 85/15.
4. The polylactic acid film according to any one of 1. to 3. above, which has a total light transmittance of 75% or more and a haze of 3% or less.
5. A laminated film having a base layer and a release layer, the base layer comprising the polylactic acid film according to any one of 1. to 4. above.
6. The laminated film according to the above item 5, which is a release film for use in producing a ceramic green sheet, and the release layer is made of a composition containing a silicone release component.
7. The laminate film according to 5. or 6. above, wherein the maximum projection height (P) of the surface of the release layer is 200 nm or less, and the arithmetic mean roughness (Sa) of the surface of the release layer is 10 nm or less.

The polylactic acid film of the present invention has excellent elastic modulus and heat resistance. Therefore, it has good dimensional stability during processing at high temperatures and high rigidity, making it suitable for industrial applications such as release film applications and optical applications. Furthermore, since it is made from biomass-derived raw materials and is biodegradable, it is possible to provide an excellent polylactic acid film and a laminated film containing the same that take into consideration the recent SDGs.

The polylactic acid film of the present invention is a polylactic acid film made of a resin composition containing polylactic acid. In this polylactic acid film, the longitudinal tensile modulus Ea and the transverse tensile modulus Eb satisfy the formula "Ea + Eb > 8.0 GPa", the crystallinity is 40% to 90%, and when heated at 150 ° C for 30 minutes, the longitudinal heat shrinkage rate and the transverse heat shrinkage rate are each 10.0% or less. In addition, the laminated film of the present invention is a laminated film containing this polylactic acid film, and is preferably a laminated film containing a polylactic acid film in a substrate layer and further having a release layer on one or both surfaces of the substrate layer.

(Polylactic acid)
The polylactic acid preferably used in the present invention is obtained by ring-opening polymerization of lactide using a compound having a hydroxyl group as an initiator in the presence of a specific catalyst. The specific catalyst is, for example, tin, aluminum, etc. The polylactic acid can contain an L-lactic acid component and a D-lactic acid component as a copolymer component or a blend component. In the polylactic acid film and resin composition, the weight ratio of L-lactic acid (hereinafter L-form)/D-lactic acid (hereinafter 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 L-form)/D-lactic acid (hereinafter D-form) is 100/0 to 85/15, high crystallinity is obtained, which is preferable. In the present invention, the preferred glass transition point is 40 to 70°C, the preferred melting point is 150 to 180°C, and it is also preferable that oriented crystallization is possible. The glass transition point and melting point can be measured by a differential scanning calorimeter (DSC), etc. The presence or absence of crystallinity can be confirmed by the presence or absence of a crystallization peak in the heating process or in the cooling process after melting in a DSC.

The reduced viscosity (ηsp/c) of the resin composition used in the present invention is preferably in the range of 1.0 dl/g or more and 3.0 dl/g or less. When the reduced viscosity is 1.0 dl/g or more, the polylactic acid film can be prevented from tearing. When the reduced viscosity is 3.0 dl/g or less, the increase in filtration pressure is small, making it easier to perform high-precision filtration.

The reduced viscosity (ηsp/c) of the polylactic acid film of the present invention is preferably in the range of 1.0 dl/g or more and 2.5 dl/g or less. When the reduced viscosity is 1.0 dl/g or more, it is preferable because not many breaks occur during the stretching process. When the reduced viscosity is 2.5 dl/g or less, it is preferable because the cuttability is good when cutting to a specified product width and dimensional defects do not occur.

The resin composition used in the present invention may contain one or more of various additives, such as inert particles such as inorganic particles, heat-resistant polymer particles, and crosslinked polymer particles, fluorescent brighteners, ultraviolet inhibitors, infrared absorbing dyes, heat stabilizers, surfactants, and antioxidants, depending on the purpose of use. As the antioxidant, an aromatic amine-based or phenol-based antioxidant can be used. As the stabilizer, a phosphorus-based stabilizer such as phosphoric acid or a phosphoric acid ester-based stabilizer, a sulfur-based stabilizer, or an amine-based stabilizer can be used.

(Method of manufacturing polylactic acid film)
The polylactic acid film of the present invention is preferably an oriented film, more preferably a biaxially oriented film, from the standpoints of mechanical strength, chemical resistance, heat resistance, and the like.

The resin composition of the present invention can be processed into an unstretched sheet by various methods, and then biaxially stretched to obtain a polylactic acid film. In addition to the solution casting method, the melt extrusion method can be used to manufacture the unstretched sheet. The melt extrusion method is preferred in the present invention.

The melting temperature of the resin composition is preferably in the range of 150 to 250°C, more preferably 180 to 240°C. A temperature of 150°C or higher is preferable because it provides an appropriate melt viscosity and increases productivity. A temperature of 250°C or lower is preferable because it suppresses thermal degradation of the polylactic acid resin.

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

The polylactic acid film of the present invention can be manufactured according to a general polyester film manufacturing method. For example, a method can be used in which a polyester resin is melted, and the unoriented polyester extruded into a sheet is stretched in the longitudinal direction at a temperature equal to or higher than the glass transition temperature by utilizing the speed difference between rolls, and then stretched in the transverse direction by a tenter and heat-treated. Specifically, for example, in the longitudinal stretching process in the longitudinal direction, the film is heated and stretched 1.1 to 6 times between two or many rolls having different peripheral speeds. The heating means at this time may be a method using a heated roll or a method using a non-contact heating medium, or these may be used in combination. In this case, it is preferable to set the temperature of the film in the range of (Tg-10°C) to (Tg+50°C). Next, it is preferable to introduce the uniaxially stretched film into a tenter and stretch it 1.1 to 10 times in the width direction at a temperature of (Tg-10°C) to Tm or less.

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

It is preferable that the heat setting temperature is in the range of 90 to 180°C. If the heat setting temperature is 90°C or higher, sufficient dimensional stability due to heat of the film can be obtained, which is preferable. If it is 180°C or lower, the phenomenon of holes being formed in the film due to heat can be suppressed, which is preferable.

(Physical properties of polylactic acid film)
The thickness of the 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 polylactic acid film has a minimum rigidity and is easy to handle. When the thickness of the polylactic acid film is 500 μm or less, the transportability of the film when transporting the film with multiple rolls and the handleability of the produced film are improved, making it easy to handle.

The sum of the tensile modulus Ea in the MD direction and the tensile modulus Eb in the TD direction of the polylactic acid film is preferably 8.0 GPa or more. The preferred lower limit of the sum of the tensile modulus is 8.2 GPa, more preferably 8.4 GPa, even more preferably 8.6 GPa, even more preferably 8.8 GPa, even more preferably 9.0 GPa, particularly preferably 9.5 GPa, and most preferably 10.0 GPa or more. When the sum of the tensile modulus is 8.0 GPa or more, the rigidity of the film is sufficient, and the occurrence of wrinkles and warping of the film can be suppressed, which is preferable. In consideration of manufacturing points, the upper limit of the sum of the tensile modulus is considered to be 15.0 GPa.

The breaking strength of the polylactic acid film is preferably 75 MPa or more in both the MD and TD directions. The preferred lower limit of the breaking strength is 100 MPa, more preferably 150 MPa, even more preferably 200 MPa, and even more preferably 220 MPa. A breaking strength of 75 MPa or more is preferable because the mechanical strength of the film is sufficient and the occurrence of problems such as elongation and displacement during the film processing process can be suppressed. Taking manufacturing considerations into account, the upper limit of the breaking strength is considered to be 1000 MPa.

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

In the case of a polylactic acid film, when heated at 150°C for 30 minutes, the heat shrinkage rate in the MD direction and the heat shrinkage rate in the TD direction are each preferably 10.0% or less. When heated at 150°C for 30 minutes, the upper limit of each of the heat shrinkage rate in the MD direction and the heat shrinkage rate in the TD direction is more preferably 8.0% or less, even more preferably 6.0% or less, even more preferably 4.0% or less, particularly preferably 3.0% or less, and most preferably 2.0% or less. A small heat shrinkage rate makes it easier to carry out processing such as coating, and can suppress poor appearance due to deformation of the film under high heat. Although it is preferable that the heat shrinkage rate is low, 0.01% is considered to be the lower limit from a manufacturing standpoint.

In the case of a polylactic acid film, when heated at 120°C for 30 minutes, the heat shrinkage rate in the MD direction and the heat shrinkage rate in the TD direction are preferably 3.0% or less. When heated at 120°C for 30 minutes, the upper limit of each of the heat shrinkage rates in the MD direction and the TD direction is more preferably 2.0% or less, even more preferably 1.6% or less, even more preferably 1.4% or less, particularly preferably 1.2% or less, and most preferably 1.0% or less. A small heat shrinkage rate makes it easier to carry out processing such as coating, and can suppress poor appearance due to deformation of the film under high heat. Although it is preferable that the heat shrinkage rate is low, 0.01% is considered to be the lower limit from a manufacturing standpoint.

The total light transmittance of the polylactic acid film is preferably 75% or more. In order to improve the accuracy of detection of internal foreign bodies that are defects of the film, high transparency is preferable. Therefore, the total light transmittance of the film of the present invention is preferably 75% or more, more preferably 80% or more, even more preferably 85% or more, even more preferably 88% or more, particularly preferably 91% or more, and most preferably 93% or more. In order to improve the accuracy of detection of internal foreign bodies that are defects of the film, the higher the total light transmittance, the better, but it is technically difficult to achieve a total light transmittance of 100%. From a manufacturing standpoint, it is preferable that the total light transmittance is less than 100%.

The surface of the polylactic acid film of the present invention is preferably smooth, and when used as a release film for producing ceramic green sheets, it is preferable that the haze is small. 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 as low as possible, but it may be 0.1% or more, or 0.3% or more. In order to reduce the haze, it is better for the film surface to not have too much unevenness, but in order to provide a certain degree of slipperiness from the viewpoint of handling against a rotating roll, it is preferable to form a certain degree of unevenness on at least one surface.

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

In addition, when a smooth release layer or the like is formed on the surface of the polylactic acid film, it is preferable that at least one surface of the polylactic acid film is also smooth. For the smooth surface of the polylactic acid film, it is preferable that the arithmetic mean roughness (Sa) 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 surface is 10 nm or less and the maximum protrusion height is 150 nm or less, more preferably that the arithmetic mean roughness of the surface is 10 nm or less and the maximum protrusion height is 120 nm or less, and even more preferably that 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 may be 0.3 nm or more. Furthermore, the maximum projection height (P) on the surface may be 1 nm or more, or may be 3 nm or more.

(Laminated film)
The laminated film of the present invention is a laminated film having a base layer and a release layer, the base layer containing the polylactic acid film as described above. The release layer can be provided on one or both sides of the base layer, and is preferably provided on the outermost surface.
The substrate layer may be made of a polylactic acid film, but may further include other layers such as other polyester layers, an easy-adhesion layer, an antistatic layer, and an easy-slip layer.
The laminated film of the present invention can be used for the production or transfer of ceramic green sheets, various resin sheets, and optical films, and as a release film for pressure sensitive adhesive sheets, adhesive sheets, and the like.
(Release Layer)
The resin constituting the release layer is not particularly limited, and may be a silicone resin, a fluororesin, an alkyd resin, various waxes, an aliphatic olefin, etc., and each resin may be used alone or in combination of two or more kinds. The release layer preferably contains a silicone release component such as a silicone resin or a silicone oil.

For example, silicone resin is a resin that has a silicone structure in the molecule, and examples include cured silicone, silicone graft resin, and modified silicone resin such as alkyl modified, but from the viewpoint of migration, it is preferable to use reactive cured silicone resin. Examples of reactive cured silicone resins that can be used include addition reaction type, condensation reaction type, and ultraviolet or electron beam cured type. More preferably, low-temperature curing addition reaction type that can be processed at low temperature, and ultraviolet or electron beam cured type are good. By using these silicone resins, it is possible to process at low temperature when coating polyester film. Therefore, there is little heat damage to the polyester film during processing, and a polyester film with high flatness can be obtained, and defects such as pinholes can be reduced even when manufacturing thin sheets such as ceramic green sheets.

An example of an addition reaction silicone resin is one in which polydimethylsiloxane with vinyl groups at the end or side chain is reacted with hydrogen siloxane using a platinum catalyst to harden it. In this case, it is more preferable to use a resin that can be hardened within 30 seconds at 120°C, as this allows processing at low 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.) manufactured by Dow Toray Co., Ltd., 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.) manufactured by Shin-Etsu Chemical Co., Ltd.

An example of a condensation reaction type silicone resin is one in which a polydimethylsiloxane having an OH group at its terminal and a polydimethylsiloxane having an H group at its terminal are subjected to a condensation reaction using an organotin catalyst to create a three-dimensional crosslinked structure.

Examples of UV-curable silicone resins include, as their most basic type, those that utilize the same radical reaction as normal silicone rubber crosslinking, those that introduce unsaturated groups and photocure, those that use UV light to decompose onium salts to generate strong acids that then cleave epoxy groups to crosslink, and those that crosslink by an addition reaction of thiols to vinyl siloxanes. Electron beams can also 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 the resin to be used include UV-curable silicones manufactured by Shin-Etsu Chemical Co., Ltd. (X62-7028A/B, X62-7052, X62-7205, X62-7622, X62-7629, X62-7660, etc.), UV-curable silicones manufactured by Momentive Performance Materials, Inc. (TPR6502, TPR6501, TPR6500, UV9300, UV9315, XS56-A2982, UV9430, etc.), and UV-curable silicones manufactured by Arakawa Chemical Co., Ltd. (Silicolease UV POLY200, POLY215, POLY201, KF-UV265AM, etc.).

As the above UV-curable silicone resin, acrylate-modified or glycidoxy-modified polydimethylsiloxane can also be used. Good release performance can also be achieved by mixing these modified polydimethylsiloxanes with multifunctional acrylate resins or epoxy resins and using them in the presence of an initiator.

Other examples of resins that can be used include alkyd resins and acrylic resins with long-chain alkyl groups, such as stearyl- or lauryl-modified resins, and alkyd-based resins, acrylic-based resins, and olefin-based resins obtained by reactions such as methylated melamine. When molding sheets for use in electronic components, etc., release agents that do not contain silicone are also preferred.

Examples of amino alkyd resins and amino acrylic resins obtained by reactions such as those described above with methylated melamine include the Tesfine series manufactured by Showa Denko Materials Co., Ltd.

When the above resins are used in the release layer of the present invention, one type may be used, or two or more types may be mixed. When two or more types are mixed, two or more types of silicone-based resins may be used, and it is also preferable to mix multiple different resin types, such as a binder resin and a silicone-based resin.

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

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

Examples of resins having reactive functional groups that can be used preferably include polyester resins, polyacrylic resins, polyurethane resins, and polyolefin resins. These resins preferably have at least one reactive functional group selected from the group consisting of carboxyl groups, hydroxyl groups, epoxy groups, and amino groups.

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

The release layer of the present invention may contain particles having a particle size of 1 μm or less, but from the viewpoint of preventing the occurrence of pinholes, it is preferable that the layer does not substantially contain any particles or other substances that form protrusions.

In order to adjust the release force, additives such as light release additives and heavy release additives, as well as additives such as adhesion improvers and antistatic agents may be added to the release layer of the present invention. In order to improve adhesion to the base layer, it is also preferable to perform pretreatment such as anchor coating, corona treatment, plasma treatment, and atmospheric pressure plasma treatment on the surface of the polylactic acid film before providing the release coating layer.

In the present invention, the thickness of the release layer may be set according to the purpose of use, and is not particularly limited, but is preferably in the range of 0.005 to 2.0 μm after curing. If the thickness of the release layer is 0.005 μm or more, the peeling performance is maintained, which is preferable. In addition, if the thickness of the release layer is 2.0 μm or less, the curing time is not too long, and there is no risk of uneven thickness of the sheet due to a decrease in the flatness of the release film, which is preferable. In addition, since the curing time is not too long, there is no risk of the resin constituting the release layer agglomerating, and there is no risk of forming protrusions, which is preferable because pinhole defects in the sheet are unlikely to occur.

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

The lower limit of the surface free energy of the release layer provided in the release film of the present invention is preferably 8 mJ/ ^m2 or more. More preferably, it is 10 mJ/m2 or ^more , and even more preferably, it is 12 mJ/m2 or ^more . If it is 8 mJ/ ^m2 or more, it is preferable because repelling and the like are unlikely to occur when a dissolving solution of the sheet is applied.

The upper limit of the surface free energy of the release layer provided on the release film of the present invention is preferably 45 mJ/m2 or ^less . More preferably, it is 40 mJ/m2 ^or less, and even more preferably, it is 35 mJ/m2 ^or less. If it is 45 mJ/m2 or ^less , the releasability of the molded sheet is good, so it is preferable.

In the present invention, the method of forming the release layer is not particularly limited, and a method is used in which a coating liquid in which a releasing resin is dissolved or dispersed is spread on one side of the base layer by coating, etc., and the solvent, etc. is removed by drying, followed by heating, drying, heat curing, or ultraviolet curing. At this time, the drying temperature during solvent drying and heat curing is preferably 180°C or less, more preferably 150°C or less, and most preferably 120°C or less. The heating time is preferably 30 seconds or less, more preferably 20 seconds or less. When it is 180°C or less, the flatness of the film is maintained and there is little risk of causing unevenness in the thickness of the sheet, which is preferable. When it is 120°C or less, it can be processed without impairing the flatness of the film, and there is a further reduction in the risk of causing unevenness in the thickness of the sheet, which is particularly preferable.

In the present invention, the surface tension of the coating liquid when applying the release layer is not particularly limited, but is preferably 30 mN/m or less. By setting the surface tension as described above, the wettability after application is improved and the unevenness of the coating film surface after drying can be reduced.

In the present invention, the coating liquid used to apply the release layer is not particularly limited, but it is preferable to add a solvent with a boiling point of 90°C or higher. By adding a solvent with a boiling point of 90°C or higher, bumping during drying can be prevented, the coating film can be leveled, and the smoothness of the coating film surface after drying can be improved. The amount of the solvent added is preferably about 10 to 80% by mass of the entire coating liquid.

Examples of methods for applying the coating liquid include roll coating methods such as gravure coating and reverse coating, bar coating methods such as wire bars, die coating, spray coating, and air knife coating.

(Ceramic green sheets and ceramic capacitors)
In general, a multilayer ceramic capacitor has a rectangular parallelepiped ceramic body. Inside the ceramic body, first internal electrodes and second internal electrodes are alternately provided along the thickness direction. The first internal electrodes are exposed at a first end face of the ceramic body. A first external electrode is provided on the first end face. The first internal electrode is electrically connected to the first external electrode at the first end face. The second internal electrode is exposed at a second end face of the ceramic body. A second external electrode is provided on the second end face. The second internal electrode is electrically connected to the second external electrode at the second end face.

The release film for producing ceramic green sheets of the present invention is used to produce such a multilayer ceramic capacitor. For example, it is produced 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 the first or second internal electrode is printed on the applied and dried ceramic green sheet. A mother laminate is obtained by appropriately stacking and pressing a ceramic green sheet, a ceramic green sheet on which a conductive layer for forming the first internal electrode is printed, and a ceramic green sheet on which a conductive layer for forming the second internal electrode is printed. The mother laminate is divided into a plurality of pieces to produce a raw ceramic body. The raw ceramic body is fired to obtain a ceramic body. Then, a first and second external electrodes are formed to complete a multilayer ceramic capacitor.

Next, the effects of the present invention will be explained using examples and comparative examples. First, the evaluation method of the characteristic values used in the present invention is shown below.

[Evaluation method]

(1) Thickness The thickness of the polylactic acid film was measured using a TH-104 manufactured by Tester Sangyo Co., Ltd.

(2) Crystallinity: Measured using a differential scanning calorimeter (DSC214Polyma) manufactured by Netsch Japan Co., Ltd. Using 10 mg of sample, measurements were made in the range from 25°C to 250°C at a heating rate of 10°C/min, and the endothermic heat of the melting peak observed during heating was divided by the theoretical heat of fusion (93.6 J/g) of perfect crystals of polylactic acid to determine the crystallinity (%) of the polylactic acid film.

(3) Tensile modulus The tensile modulus of the polylactic acid film was measured in accordance with JIS K 7127. A sample was cut into a strip of 200 mm in length and 15 mm in width in the MD and TD directions of the film using a single-edged razor, and two parallel marks were made at a distance of 50 mm in the center of the test piece. Next, the strip-shaped sample was clamped with a chuck distance of 100 mm using an autograph AGS-X manufactured by Shimadzu Corporation, and pulled at a speed of 0.5 mm/min, and the tensile modulus (GPa) in each direction was obtained from the obtained load-strain curve of 0.1 to 0.3%. The value of strain was measured using the distance between the marks.

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

(5) Heat shrinkage The heat shrinkage of the polylactic acid film was measured in accordance with JIS C 2318. The laminated film was cut to a width of 10 mm and a length of 190 mm in the direction to be measured, and marks were made at 150 mm intervals, and the intervals (A) between the marks were measured. Next, the film was placed in an oven in an atmosphere of 150°C, and heat-treated at 150±3°C for 30 minutes under no load, and the intervals (B) between the marks were measured. The heat shrinkage at 150°C was then calculated using the following formula. In addition, the film cut out in the same manner as above was placed in an oven in an atmosphere of 120°C, and heat-treated at 120±3°C for 30 minutes under no load, and the intervals (C) between the marks were measured, and the heat shrinkage at 120°C was calculated using the following formula.
150°C heat shrinkage rate (%) = (A-B)/A x 100
120°C heat shrinkage rate (%) = (A - C) / A x 100

(6) Haze The haze (%) of the polylactic acid film was measured according to JIS K 7136 using a haze meter NDH-7000 II type manufactured by Nippon Denshoku Industries Co., Ltd.

(7) Total Light Transmittance The total light transmittance (%) of the polylactic acid film was measured according to JIS K 7136 using a haze meter NDH-7000 II type manufactured by Nippon Denshoku Industries Co., Ltd.

(8) Reduced viscosity (ηsp / c)
0.1 g of polylactic acid was dissolved in 15 mL of a mixed solvent of phenol/1,1,2,2-tetrachloroethane (75/25 (weight ratio)), and the viscosity was measured using an Ostwald viscometer at 30° C. The unit is dl/g.

(9) Surface Roughness Using a non-contact surface shape measurement system (VertScan R550H-M100), the arithmetic mean roughness (Sa) and maximum projection height (P) were measured as the average roughness of the area surface under the following conditions. The arithmetic mean roughness (Sa) was calculated by averaging five measurements, and the maximum projection height (P) was calculated by measuring seven times and using the maximum value of the five measurements excluding the maximum and minimum values.
(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

Example 1
(1) Preparation of Polylactic Acid Resin Poly-L-lactic acid PLA L175 (weight ratio of L-lactic acid/D-lactic acid: 99/1) manufactured by Total Corbion was used as the polylactic acid resin.

(2) Production of polylactic acid film Poly-L-lactic acid (L175) was dried under reduced pressure (1 Torr) at 120°C for 6 hours, and then fed to an extruder. It was melted at a temperature of 220°C and melt-extruded from a die into a sheet shape. A gear pump was used to control the thickness to 400 μm. In addition, a filter medium (initial filtration efficiency: 95%) made of stainless steel sintered body with a filtration particle size of 10 μm was used for the filter.

The extruded resin was cast onto a cooling drum with a surface temperature of 50°C and adhered to the surface of the cooling drum using an electrostatic application method, allowing it to cool and solidify, creating an unstretched film with a thickness of 400 μm.

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

The uniaxially stretched film was then held with clips and stretched transversely at a temperature of 75° C. and a transverse stretch ratio of 4.96.
Next, a heat treatment was carried out at 150° C. for 15 seconds.

The biaxially stretched film that had been stretched in the TD direction was again held with clips and stretched transversely. The transverse stretching temperature was 170°C, and the transverse stretching ratio was 1.01 times. Next, heat treatment was performed at 160°C for 15 seconds to obtain a polylactic acid film with a thickness of 40 μm. The physical properties of the obtained film of Example 1 are shown in Table 2. The sum of the crystallinity and tensile modulus of elasticity of the obtained polylactic acid film was high, and the thermal shrinkage rate was low, so that in Example 1, a film with excellent modulus of elasticity and heat resistance was obtained.

(Examples 2 and 3)
In Examples 2 and 3, polylactic acid films were obtained in the same manner as in Example 1, except that the conditions were changed as shown in Table 1. The physical properties of the obtained films of Examples 2 and 3 are shown in Table 2. In Example 2, a higher elastic modulus was obtained by increasing the second stretching ratio in the TD direction. In Example 3, a relaxation treatment (160°C, relaxation rate 5%) was performed after TD stretching, thereby suppressing heat shrinkage in the TD direction and maintaining a high elastic modulus. The films of Examples 2 and 3 had a high sum of the crystallinity and the tensile elastic modulus, and a low thermal shrinkage rate, and therefore, it was shown that films excellent in elastic modulus and heat resistance were obtained in Examples 2 and 3.

Example 4
(1) Preparation of Polylactic Acid Resin As the polylactic acid resin, poly-L-lactic acid PLA LX175 (weight ratio of L-lactic acid/D-lactic acid: 96/4) manufactured by Total Corbion was used.

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

The extruded resin was cast onto a cooling drum with a surface temperature of 50°C and adhered to the surface of the cooling drum using an electrostatic application method, allowing it to cool and solidify, creating an unstretched film with a thickness of 400 μm.

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

The uniaxially stretched film was then held with clips and stretched transversely at a temperature of 75° C. and a transverse stretch ratio of 4.96.
Next, a heat treatment was carried out at 150° C. for 15 seconds.

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

Example 5
In Example 5, a polylactic acid film was obtained in the same manner as in Example 3, except that an unstretched sheet was introduced into a simultaneous biaxial stretching machine, and while the ends of the film were held with clips, the sheet 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., and then the sheet was held again with clips and stretched laterally. The physical properties of the film obtained in Example 5 are shown in Table 2. The polylactic acid film obtained had a high sum of the crystallinity and the tensile modulus and a low thermal shrinkage, indicating that a film excellent in modulus and heat resistance was obtained in Example 5.

From the above, the films obtained in Examples 1 to 5 have excellent elastic modulus and heat resistance, good dimensional stability during processing at high temperatures, and can obtain high rigidity. Furthermore, the films obtained in Examples 1 to 5 have a maximum projection height (P) of 200 nm or less and an arithmetic mean roughness (Sa) of 10 nm or less, so that when a release layer is formed on the surface of the film, it is possible to obtain a maximum projection height (P) of 200 nm or less and an arithmetic mean roughness (Sa) of 10 nm or less on that surface.

(Comparative Examples 1 and 2)
In Comparative Examples 1 and 2, polylactic acid films were obtained in the same manner as in Examples 1 and 4, except that the conditions were changed as shown in Table 1. The physical properties of the obtained films of Comparative Examples 1 and 2 are shown in Table 2. Comparative Examples 1 and 2 are outside the scope of the present invention because they have a low tensile modulus and a 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, the modulus and heat resistance were poor.

(Comparative Example 3)
In Comparative Example 3, a biaxially stretched film was obtained in the same manner as in Comparative Example 1, except that the conditions were changed to those shown in Table 1. In Comparative Example 3, the stretch ratio in the TD direction was set high in the commonly used sequential biaxial stretching, but stretching breakage occurred, and a polylactic acid film could not be obtained.

The polylactic acid film and laminate film of the present invention are suitable for use, for example, as release films for producing ceramic green sheets.

Claims (7)

A laminated film having a base layer and a release layer on one or both sides of the base layer,
The substrate layer includes a polylactic acid film made of a resin composition containing polylactic acid,
The polylactic acid film has a longitudinal tensile modulus Ea and a transverse tensile modulus Eb that satisfy the formula Ea+Eb>8.0 GPa, a crystallinity of 40% or more and 90% or less, and when heated at 150° C. for 30 minutes, each of the longitudinal heat shrinkage rate and the transverse heat shrinkage rate is 10.0% or less,
The release layer has a surface having a maximum projection height (P) of 200 nm or less and an arithmetic mean roughness (Sa) of 10 nm or less . 2. The laminated film according to claim 1, wherein the polylactic acid film has a thermal shrinkage rate of 3.0% or less in both the longitudinal direction and the width direction when heated at 120° C. for 30 minutes. 2. The laminated film according to claim 1, wherein the polylactic acid film has a weight ratio of L-lactic acid/D-lactic acid of 100/0 to 85/15. The laminated film according to claim 1 , wherein the polylactic acid film has a total light transmittance of 75% or more and a haze of 3% or less. 2. The laminated film according to claim 1, wherein the polylactic acid film has at least one surface forming the release layer having an arithmetic mean roughness (Sa) of 10 nm or less and a maximum projection height (P) of 200 nm or less. 2. The laminate film of claim 1 , wherein the release layer comprises a composition containing a silicone release component. The laminate film according to any one of claims 1 to 6, which is a release film for producing a ceramic green sheet.