Laminated films and films for packaging materials

Abstract

To provide a laminate film having excellent mechanical strength while having high transparency and flexibility, and a film for a packaging material having the laminate film.SOLUTION: A laminate film has a laminate in which a second layer is arranged on one surface or both surfaces of a first layer, wherein the first layer is a layer containing a polylactic resin having a D body percentage content of 0.1 mass% or more and 5 mass% or less, the second layer is a layer containing a polylactic resin having a D body percentage content of 0.1 mass% or more and less than 12 mass%, the laminate has a glass transition temperature of 32-49°C, and the laminate has a content ratio of a D body of 0.1 mass% or more and 5.5 mass% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a laminated film and a film for packaging materials.

Background Art

[0002] Resin films are excellent in various properties such as moisture resistance, water resistance, and oil resistance, and have good mechanical strength. Therefore, they are widely applied to various uses such as packaging materials for foods and pharmaceuticals, and protective films for displays, etc., and are functional materials with high utility value.

[0003] On the other hand, in recent years, various problems have been raised, such as the increasing amount of plastic materials discarded, and concerns about global warming caused by carbon dioxide generated during the incineration of plastic materials. For this reason, biomass plastics having biodegradability have been attracting great attention from the viewpoints of consideration for the global environment and the human body. For example, various material developments have been actively promoted by combining biomass plastics such as polylactic acid with general-purpose resins (for example, see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, films using conventional biodegradable resins such as polylactic acid have high transparency and flexibility, but have a problem that their mechanical strength (for example, tensile strength and tear strength) is not sufficient, so their uses are likely to be limited. In particular, in laminated films, flexibility (texture) and mechanical strength are in a trade-off relationship with each other, so it has never been easy to provide a laminated film having both.

[0006] The present invention has been made in view of the above, and aims to provide a laminated film that possesses high transparency and flexibility (texture) while also having excellent mechanical strength, and a packaging film equipped with the laminated film. [Means for solving the problem]

[0007] As a result of diligent research to achieve the above objective, the inventors of the present invention have found that the above objective can be achieved by using a laminate containing a polylactic acid resin containing a specific amount of the D-isomer and having a glass transition temperature within a predetermined range, and have completed the present invention.

[0008] In other words, the present invention encompasses, for example, the subject matter described in the following sections. Item 1 A laminated film comprising a laminate in which a second layer is arranged on one or both sides of a first layer, The first layer is a layer containing polylactic acid resin having a D-isomer content of 0.1% by mass or more and 5% by mass or less. The second layer is a layer containing polylactic acid resin having a D-isomer content of 0.1% by mass or more and less than 12% by mass, The laminated body is The glass transition temperature is measured under the following [glass transition temperature measurement conditions]. The glass transition temperature is 32-49°C. The laminate has a D-isomer content of 0.1% by mass or more and 5.5% by mass or less. A laminated film in which the plasticizer content in the second layer is 7% by mass or less. [Glass transition temperature measurement conditions] In the DSC curve of the laminate, the glass transition temperature of the laminate is defined as the midpoint glass transition temperature specified in JIS-K7121 9.3(1). The DSC curve is obtained by heating 5 mg of the laminate from 0°C to 230°C at a rate of 20°C / min under a nitrogen flow, holding at 230°C for 5 minutes, cooling to 0°C at 20°C / min, holding at 0°C for 5 minutes, and then heating again to 230°C at 20°C / min. Section 2 The first layer further contains a plasticizer, The laminated film according to item 1, wherein the second layer does not contain a plasticizer. Section 3 The content of the plasticizer in the first layer is 6% by mass or more and less than 16% by mass, The laminated film according to item 2, wherein the content of the plasticizer in the laminate is 5% by mass or more and less than 12% by mass. Section 4 The following formula (1) S(N / μm)=A / d (1) (In formula (1), A is JIS K 7128-2 to This shows the average value (N) of the Elmendorff tear strength in the MD direction and the Elmendorff tear strength in the TD direction of the laminated film measured according to the standard, where d represents the film thickness (μm). A laminated film according to any one of items 1 to 3, wherein the S value represented by is 5 N / μm or greater. Section 5 A laminated film according to any one of items 1 to 3, wherein the average value of the tensile strength in the MD direction (MPa) and the tensile strength in the TD direction (MPa) is 65 MPa or more. Section 6 The elastic modulus in at least one direction on the film surface is 1.5 to 3.5 G P a, which is a, the laminated film described in any one of items 1 to 3. Section 7 A packaging film comprising a laminated film as described in any one of items 1 to 3. [Effects of the Invention]

[0009] The laminated film of the present invention possesses high transparency and flexibility (texture) while also having excellent mechanical strength. Specifically, the laminated film of the present invention has high transparency and flexibility while also possessing excellent tear strength and tensile strength. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below. In this specification, the expressions "containing" and "including" include the concepts of "containing," "including," "substantially consisting of," and "consisting only of."

[0011] The laminated film of the present invention comprises a laminate in which a second layer is disposed on one or both sides of a first layer. In particular, in the laminated film of the present invention, the first layer is a layer containing a polylactic acid resin having a D-form content of 0.1% by mass or more and 5% by mass or less, the second layer is a layer containing a polylactic acid resin having a D-form content of 0.1% by mass or more and 12% by mass or less, the laminate has a glass transition temperature of 32 to 49°C, the laminate has a D-form content ratio of 0.1% by mass or more and 5.5% by mass or less, and the content ratio of the plasticizer in the second layer is 7% by mass or less.

[0012] By being configured as described above, the laminated film of the present invention has high transparency and flexibility (texture), while having excellent tear strength, tensile strength, elastic modulus, and elongation at break. Therefore, the laminated film of the present invention is suitable for packaging materials that require all of transparency, flexibility, tensile strength, tear strength, elastic modulus, and elongation at break, and can be preferably applied, for example, to fields such as agricultural mulch films and food packaging for packaging vegetables and the like.

[0013] (First layer) In the laminated film of the present invention, the first layer is a layer containing a polylactic acid resin and is the core layer of the laminated film. The polylactic acid resin contained in this first layer has a D-form content of 0.1% by mass or more and 5% by mass or less. The first layer contains, for example, 80% by mass or more of the polylactic acid resin, preferably 90% by mass or more, and more preferably 94% by mass or more.

[0014] In this specification, the D-form in the polylactic acid resin means the D-lactic acid (D-form) unit among the lactic acid units constituting the polylactic acid resin. Therefore, the D-form content in the polylactic acid resin means the content ratio (mass%) of the D-form unit with respect to the total mass of the polylactic acid resin.

[0015] Hereinafter, the polylactic acid resin contained in the first layer is referred to as polylactic acid resin (1).

[0016] The type of polylactic acid resin (1) is not particularly limited as long as the D-isomer content is within the above range, and a wide range of known polylactic acids can be mentioned, such as polylactic acid obtained by condensation polymerization of lactic acid components as raw material monomers. Since the polylactic acid resin (1) has a D-isomer content of 0.1% by mass or more and 5% by mass or less, it has L-lactic acid as its main constituent unit.

[0017] The laminated film of the present invention, by including a polylactic acid resin (1) with a D-isomer content within the above range in the first layer, can have high transparency and flexibility while also possessing excellent tear strength and tensile strength. When the D-isomer content of the polylactic acid resin (1) is less than 0.1% by mass, it has high crystallinity, a high melting point, and is prone to generating unmelted material. When it exceeds 5% by mass, it has the problem of reduced tensile strength of the film.

[0018] The polylactic acid resin (1) preferably has a D-isomer content of 0.15% by mass or more, particularly preferably 0.2% by mass or more, and the polylactic acid resin (1) preferably has a D-isomer content of less than 5.0% by mass, more preferably 4.5% by mass or less, even more preferably 4% by mass or less, and particularly preferably 3% by mass or less.

[0019] The mass-average molecular weight of the polylactic acid resin (1) is not particularly limited, but is preferably 50,000 or more, more preferably 75,000 or more, and particularly preferably 100,000 or more. Furthermore, the mass-average molecular weight of the polylactic acid resin (1) is preferably 300,000 or less, more preferably 250,000 or less, and even more preferably 200,000 or less.

[0020] The method for producing the polylactic acid resin (1) is not particularly limited, and for example, known methods for producing polylactic acid can be widely used. Furthermore, the polylactic acid resin (1) can also be obtained from commercially available products. Representative commercially available polylactic acid resins (1) include, for example, Luminy "L175", "LX575", "LX175", "LX975", "L130", "LX530", "LX930", "LX105", "D120", and "D070" from TotalCorbion, Inc., Ingeo from NatureWorks, Inc., and REVODE from Zhejiang Haizheng Biomaterials, Inc.

[0021] The polylactic acid resin (1) contained in the first layer may be a single type or two or more types.

[0022] The first layer may contain a plasticizer in addition to the polylactic acid resin (1). The inclusion of a plasticizer in the first layer makes it easier to adjust the glass transition temperature of the laminate to a specific range, and as a result, the laminated film of the present invention can have excellent flexibility and a good texture.

[0023] The plasticizer is not particularly limited as long as it has the property of providing a plasticizing effect to the resin, and for example, a wide range of known plasticizers can be mentioned. For example, a plasticizer for biodegradable resins can be preferably applied as the plasticizer for the first layer, and a plasticizer known as polylactic acid resin can be more preferably applied as the plasticizer for the first layer.

[0024] The plasticizer preferably has a boiling point of 220°C or higher at atmospheric pressure, more preferably 250°C or higher. Alternatively, the plasticizer preferably has a boiling point of 170°C or higher at 5 to 10 torr, more preferably 180°C or higher. Furthermore, from the viewpoint of compatibility with polylactic acid resin, the solubility parameter (SP value) of the plasticizer is preferably in the range of 9.0 to 11.0.

[0025] In particular, as a plasticizer, various plasticizers known as polyester plasticizers can be mentioned, and among them, it is preferable that it be one selected from the group consisting of mixed dibasic acid esters (e.g., benzyl methyl diglycol adipate), adipic acid esters, phthalic acid esters, trimellitic acid esters, aliphatic dibasic acid esters, orthophosphate esters, ricinoleic acid esters, acetate esters, citrate esters, sulfonamides, and natural oils and fats and their derivatives, with mixed dibasic acid esters (e.g., benzyl methyl diglycol adipate) being more preferable.

[0026] Specific examples of the aforementioned natural oils and fats and their derivatives include soybean oil, epoxidized soybean oil, castor oil, tung oil, and rapeseed oil.

[0027] If the first layer contains a plasticizer, its content is not particularly limited. The content of the plasticizer in the first layer is preferably 6% by mass or more and less than 16% by mass, as this facilitates adjusting the glass transition temperature of the laminate to a specific range and provides excellent flexibility to the laminated film. More preferably, the content of the plasticizer in the first layer is 7% by mass or more, even more preferably 8% by mass or more, and particularly preferably 9% by mass or more. Furthermore, the content of the plasticizer in the first layer is more preferably less than 16.0% by mass, even more preferably 15% by mass or less, and particularly preferably 14% by mass or less.

[0028] The first layer may contain other components in addition to the polylactic acid resin (1) and a plasticizer as needed. These other components can broadly include components found in known packaging films, etc. In the first layer, the other components are present in an amount of, for example, 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, relative to the total mass of the first layer. The first layer may be formed solely of the polylactic acid resin (1).

[0029] The first layer preferably contains a polylactic acid resin (1) and the plasticizer, and more preferably consists only of the polylactic acid resin (1) and the plasticizer. In this case, it is easy to provide a laminated film that has high transparency and flexibility while having excellent tear strength and tensile strength.

[0030] The thickness of the first layer is not particularly limited and can be set appropriately depending on the application. The thickness of the first layer is preferably 5 to 50 μm, and more preferably 10 to 30 μm.

[0031] (2nd layer) In the laminated film of the present invention, the second layer is a layer containing polylactic acid resin, and is laminated to one or both sides of the second layer. The polylactic acid resin contained in this second layer has a D-isomer content of 0.1% by mass or more and less than 12% by mass. For example, the second layer contains 80% by mass or more of polylactic acid resin, preferably 90% by mass or more, more preferably 94% by mass or more, and even more preferably 99% by mass or more.

[0032] Hereafter, the polylactic acid resin contained in the second layer will be referred to as polylactic acid resin (2).

[0033] The type of polylactic acid resin (2) is not particularly limited as long as the D-isomer content is within the above range, and a wide range of known polylactic acids can be mentioned, such as polylactic acid obtained by condensation polymerization of lactic acid components as raw material monomers. Since the D-isomer content of polylactic acid resin (2) is 0.1% by mass or more and 12% by mass or less, L-lactic acid is the main constituent unit.

[0034] The laminated film of the present invention, by including a polylactic acid resin (2) in the second layer with a D-isomer content within the above range, can have high transparency and flexibility while also possessing excellent tear strength and tensile strength. When the D-isomer content of the polylactic acid resin (2) is less than 0.1% by mass, it has high crystallinity, a high melting point, and is prone to generating unmelted material. When it is 12% by mass or more, it is prone to blocking and is prone to a decrease in tensile strength.

[0035] The polylactic acid resin (2) preferably has a D-isomer content of 0.15% by mass or more, and particularly preferably 0.2% by mass or more. The polylactic acid resin (1) preferably has a D-isomer content of less than 12.0% by mass, more preferably 11% by mass or less, even more preferably 10% by mass or less, and particularly preferably 9% by mass or less.

[0036] The mass-average molecular weight of the polylactic acid resin (2) is not particularly limited, but is preferably 50,000 or more, more preferably 75,000 or more, and particularly preferably 100,000 or more. Furthermore, the mass-average molecular weight of the polylactic acid resin (2) is preferably 300,000 or less, more preferably 250,000 or less, and even more preferably 200,000 or less.

[0037] The method for producing the polylactic acid resin (2) is not particularly limited, and for example, known methods for producing polylactic acid can be widely used. In addition, the polylactic acid resin (1) can be obtained from commercially available products. Representative commercially available polylactic acid resins (1) include, for example, Luminy "L175", "LX575", "LX175", "LX975", "L130", "LX530", "LX930", "LX105", "D120", and "D070" from Total Cobion, Inc., Ingeo from NatureWorks, Inc., and REVODE from Zhejiang Haizheng Biomaterials, Inc.

[0038] The polylactic acid resin (2) contained in the second layer can be a single type or two or more types.

[0039] The plasticizer content in the second layer is 7% by mass or less. That is, the plasticizer content in the second layer is 7% by mass or less of the total content of the second layer, and the second layer does not need to contain plasticizer (it may be 0% by mass). By having a plasticizer content of 7% by mass or less in the second layer, the mechanical strength of the laminated film, especially the tensile strength, tends to increase, and the transparency also tends to improve.

[0040] If the second layer contains a plasticizer, the type of plasticizer can be the same as that of the plasticizer that may be included in the first layer. If the second layer contains a plasticizer, the plasticizer included in the first layer and the plasticizer included in the second layer may be the same or different.

[0041] The second layer preferably does not contain a plasticizer. When the second layer does not contain a plasticizer, the laminated film is more likely to have excellent tear strength and tensile strength, and as a result, it is easier to provide a laminated film that has excellent tear strength and tensile strength while also having high transparency and flexibility.

[0042] The second layer may contain other components in addition to the polylactic acid resin (2). These other components can be broadly categorized into components found in known packaging films, such as antiblocking agents. In the second layer, the other components are present in an amount of, for example, 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, relative to the total mass of the second layer. The second layer may also be formed solely from the polylactic acid resin (2).

[0043] The thickness of the second layer is not particularly limited and can be set appropriately depending on the application. The thickness of the second layer is preferably 0.1 to 6.0 μm, and more preferably 1.0 to 4.0 μm.

[0044] When the second layer is bonded to both sides of the first layer, the second layers of each layer may be identical or different.

[0045] (Laminated structure) The laminate of the laminated film of the present invention comprises a second layer arranged on one or both sides of a first layer. Preferably, the laminate consists only of the first and second layers. Preferably, the first and second layers are directly bonded together. Furthermore, preferably, the second layer is directly bonded to both sides of the first layer. Of course, other layers may be interposed between the first and second layers as long as the effects of the present invention are not hindered.

[0046] The laminate has a glass transition temperature of 32 to 49°C. As a result, the laminated film of the present invention can have excellent tear strength and tensile strength while possessing high transparency and flexibility. If the glass transition temperature is below 32°C, the mechanical strength of the laminated film (especially high tensile strength and elastic modulus) decreases, and if the glass transition temperature exceeds 49°C, flexibility decreases, making it difficult to obtain a good texture, and the S value also decreases, as does the tensile strength.

[0047] The laminate preferably has a glass transition temperature of 33°C or higher, more preferably 35°C or higher, even more preferably 37°C or higher, and preferably 48°C or lower, more preferably 46°C or lower, and even more preferably 45°C or lower.

[0048] The method for adjusting the glass transition temperature of the laminate is not particularly limited, and for example, known methods can be widely employed. Among these, methods for adjusting the glass transition temperature of the laminate by selecting the types of polylactic acid resin (1) and polylactic acid resin (2) contained in the first and second layers, and methods for adjusting the glass transition temperature by adding a predetermined amount of a predetermined plasticizer to the first layer are preferred. In this case, the glass transition temperature of the laminate is easy to adjust, and it is easy to form a laminated film that has high transparency and flexibility while having excellent tear strength and tensile strength.

[0049] The laminate has a D-isomer content of 0.1% by mass or more and 5.5% by mass or less. This makes it easy to form a laminated film that has high transparency and flexibility, as well as excellent tear strength and tensile strength. If the D-isomer content of the laminate is less than 0.1% by mass, problems arise such as high crystallinity, a high melting point, and a tendency for unmelted material to occur. If it exceeds 5.5% by mass, problems arise such as a decrease in the tensile strength of the film.

[0050] For the sake of clarity, the term "D-form" here refers to the D-form lactic acid units of polylactic acid resin (1) and polylactic acid resin (2) contained in the first and second layers, respectively.

[0051] In the laminate, it is preferable that the first layer contains the plasticizer and the second layer does not contain the plasticizer. In this case, it is easy to form a laminated film that has high transparency and flexibility while having excellent tear strength and tensile strength.

[0052] From this viewpoint, it is preferable that in the laminate, the content of the plasticizer in the first layer is 6% by mass or more and less than 16% by mass, and the content of the plasticizer in the laminate is 5% by mass or more and less than 12% by mass.

[0053] In terms of easily imparting excellent flexibility to the laminated film, the content of the plasticizer in the first layer of the laminate is more preferably 7% by mass or more, even more preferably 8% by mass or more, particularly preferably 9% by mass or more, more preferably less than 16.0% by mass, even more preferably 15% by mass or less, and particularly preferably 14% by mass or less.

[0054] Furthermore, in terms of easily imparting excellent mechanical strength (especially high elastic modulus and tensile strength) to the laminated film, the content of the plasticizer in the laminate is more preferably 5.5% by mass or more, even more preferably 6% by mass or more, particularly preferably 7% by mass or more, more preferably less than 12.0% by mass, even more preferably 11.5% by mass or less, and particularly preferably 11% by mass or less.

[0055] Furthermore, the thickness of the laminate is not particularly limited and can be set appropriately depending on the application. The thickness of the laminate is preferably 10 to 50 μm, and more preferably 15 to 35 μm.

[0056] (Laminated film) The laminated film of the present invention comprises the laminate. Preferably, the laminate has a second layer arranged on both sides of the first layer. In this case, the first layer is a so-called core layer, and the second layer is a so-called skin layer.

[0057] The laminated film of the present invention may be formed solely of the laminate, or it may include other layers as long as the effects of the present invention are not hindered. Examples of other layers include a heat seal layer, and other layers having one or more functions such as antifogging, antistatic properties, tackiness, smoothness, gloss, printability, antiblocking properties, slipperiness, strength-granting properties, gas barrier properties such as oxygen gas and ethylene gas, water vapor barrier properties, odor component barrier properties, prevention of component migration of packaged contents, antibacterial properties, and antifungal properties.

[0058] The laminated film of the present invention is, for example, the following formula (1) S(N / μm)=A / d (1) (In formula (1), A is JIS K 7128-2 to This shows the average value (N) of the Elmendorff tear strength in the MD direction and the Elmendorff tear strength in the TD direction of the laminated film measured according to the standard, where d represents the film thickness (μm). The S value, expressed as , is 5 N / μm or higher. This allows the laminated film to have superior tear strength.

[0059] The S value is preferably 6 N / μm or higher, more preferably 7 N / μm or higher, even more preferably 8 N / μm or higher, and particularly preferably 10 N / μm or higher. A S value of 11 N / μm or higher is preferable in that it maintains the excellent flexibility of the laminated film and facilitates moderate moldability.

[0060] The laminated film of the present invention has, for example, an average tensile strength (MPa) in the MD direction and the tensile strength (MPa) in the TD direction of 65 MPa or more. As a result, the laminated film can have superior tensile strength.

[0061] The average value of the tensile strength in the MD direction (MPa) and the tensile strength in the TD direction (MPa) is preferably 70 MPa or higher, and more preferably 75 MPa or higher. In order to maintain the excellent flexibility of the laminated film and to easily obtain moderate moldability, the average value of the tensile strength in the MD direction (MPa) and the tensile strength in the TD direction (MPa) is preferably 80 MPa or higher.

[0062] The laminated film of the present invention has, for example, an elastic modulus of 1.5 to 3.5 G in at least one direction on the film surface. P a. This allows the laminated film to have better flexibility. The laminated film of the present invention has, for example, an elastic modulus of 2 to 3.5 G in at least one direction on the film surface. P It is more preferable that it be a. Here, one direction on the film surface is not particularly limited, and may be, for example, the MD direction of the film or the TD direction of the film. Preferably, the modulus of elasticity in at least one of the MD direction and the TD direction is 1.5 to 3.5 G. P a (more preferably 2-3.5G) P a) and more preferably, the modulus of elasticity in both the MD and TD directions is 1.5 to 3.5 G P a (more preferably 2-3.5G) P a) is correct.

[0063] The laminated film of the present invention can have a haze of 16% or less, for example. In this case, the laminated film can have excellent transparency. The haze of the laminated film is preferably 15% or less, more preferably 14% or less, and particularly preferably 13% or less. The lower limit of the haze can be, for example, 0.5% in order to avoid having to make the film extremely thin. The haze of the laminated film is a value measured in accordance with JIS-K7361 using a haze meter NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0064] The laminated film of the present invention is preferably transparent or translucent, and preferably transparent (i.e., preferably a transparent laminated film).

[0065] The laminated film of the present invention is preferably a stretched film. That is, the laminated film of the present invention is preferably formed by stretching a raw material sheet (raw material sheet). In particular, the laminated film of the present invention is preferably a biaxially oriented film. In this case, the laminated film of the present invention tends to have particularly high mechanical strength and transparency.

[0066] When the laminated film of the present invention is a stretched film, the stretching ratio is not particularly limited and is, for example, 4 to 16 times. The stretching ratio refers to the value obtained by multiplying the stretching ratio in the MD direction and the stretching ratio in the TD direction of the raw sheet used to obtain the laminated film (i.e., stretching ratio in the MD direction × stretching ratio in the TD direction). The stretching ratio in the MD direction is preferably 2 to 4 times, and the stretching ratio in the TD direction is preferably 2 to 5 times.

[0067] Conventionally, in laminated films, flexibility and mechanical strength (especially tear strength and tensile strength) have been in a trade-off relationship. However, in the present invention, by employing the specific laminate described above, all of these properties can be within the desired range. In particular, by making the first layer a layer containing polylactic acid resin (1) and a specific amount of the plasticizer, and the second layer a layer containing polylactic acid resin (2) but without the plasticizer, it is easy to form a laminated film that has high transparency and flexibility while also having excellent tear strength and tensile strength.

[0068] The laminated film of the present invention can be suitably used for packaging, food packaging, pharmaceutical packaging, decoration (including fashion), labels, tape substrates, printing substrates, stationery, home appliances, poster paper, thermal paper substrates, recording paper substrates, interior and exterior applications for houses, automobiles, and the like.

[0069] In particular, laminated films are especially suitable for use in packaging films. Since packaging films incorporate the laminated film of the present invention, they can possess excellent transparency, flexibility, and impact resistance. As long as a packaging film incorporates the laminated film of the present invention, it can have a similar structure to, for example, known packaging films.

[0070] (Method of manufacturing laminated film) The method for manufacturing the laminated film of the present invention is not particularly limited, and for example, known manufacturing methods can be widely employed. For example, the method for manufacturing the laminated film of the present invention comprises the step of obtaining a laminate in which a second layer is formed on one or both sides of a first layer.

[0071] The method for forming the laminate is not particularly limited; for example, co-extrusion, lamination, heat sealing, etc., can be used, and these methods can be used individually or in combination.

[0072] For example, a laminated film can be obtained by preparing raw materials for forming the first layer and raw materials for forming the second layer, co-extruding these raw materials by co-extrusion to obtain a raw material sheet, and then stretching this raw material sheet. Alternatively, a laminate can be obtained by preparing the first and second layers separately and laminating them together. In addition, a laminate can be obtained by stretching a multilayer unoriented film obtained by bonding unoriented first and second layers, which have been extruded as single layers, together.

[0073] Examples of the aforementioned co-extrusion methods include pre-die lamination, in which molten resin is brought into contact within a feed block in front of the mold; in-die lamination, in which contact occurs within a path inside the mold, such as a multi-manifold die; and off-die lamination, in which the molten resin is extruded and brought into contact from multiple concentric lips. For example, in the in-die lamination method, a three-layer structure can be achieved by using a multi-layer die such as a three-layer multi-manifold die.

[0074] Lamination methods include the extrusion lamination method, which uses the equipment for the molten extrusion molding method used in the T-die method to directly extrude a film of molten resin onto another film to form a laminated film.

[0075] Heat sealing methods include external heating methods, in which a heated metal object is pressed against multiple films to be bonded together from the outside of the films, and the conducted heat melts and bonds the films, and internal heating methods, in which heat is generated in the films using high-frequency radio waves or ultrasound to bond them.

[0076] The raw material for forming the first layer (hereinafter abbreviated as "raw material 1") contains at least the polylactic acid resin (1) and may optionally contain the plasticizer. The content of the plasticizer in raw material 1 is preferably 6% by mass or more and less than 16% by mass. The content of the plasticizer in raw material 1 is more preferably 7% by mass or more, even more preferably 8% by mass or more, and particularly preferably 9% by mass or more. Furthermore, the content of the plasticizer in raw material 1 is more preferably less than 16.0% by mass, even more preferably 15% by mass or less, and particularly preferably 14% by mass or less. Raw material 1 may consist only of polylactic acid resin (1) and a plasticizer.

[0077] The raw material for forming the second layer (hereinafter abbreviated as "raw material 2") includes at least the polylactic acid resin (2). In addition, various additives such as antiblocking agents may be included as needed. Raw material 2 may consist only of polylactic acid resin (2).

[0078] The preparation methods for raw material 1 and raw material 2 are not particularly limited and can be the same as known preparation methods. For example, a method of dry blending polylactic acid resin pellets or powder using a batch-type mixing device such as a tumbler or mixer, or a continuous weighing-type mixing device; or a method of supplying pellets or powder together with pellets or powder of other resins and / or additives as needed to a kneader and melt-kneading to obtain a melt-blended resin composition. Among these, it is preferable to prepare each raw material by melt-kneading.

[0079] For the melt-mixing process, a known mixer can be used, and a single-screw type, a twin-screw type, or a multi-screw type with more than one screw may be used. Furthermore, in the case of a twin-screw type, either co-direction rotation or opposite-direction rotation may be used. The mixing temperature for melt-mixing is preferably in the range of 150°C to 260°C, and more preferably 180°C to 240°C. To prevent deterioration of the resin during melt-mixing, an inert gas such as nitrogen may be purged. The melt-mixed resin can be pelletized to an appropriate size using a generally known granulator to obtain melt-blend resin composition pellets.

[0080] Using raw materials 1 and 2, a base sheet for obtaining a laminate can be obtained. Specifically, each raw material is supplied to its respective extruder, heated and melted, and if necessary, minute foreign matter is removed using a filter or the like. Then, the base sheet is obtained by melt-extruding it into a sheet shape through a T-die.

[0081] The extruder used to obtain the raw material sheet can be any known extruder. There are no restrictions on the screw type of the extruder; a single-screw type, a twin-screw type, or a multi-screw type with more than one screw may be used. When the resin raw material is prepared using the dry blend described above, using a twin-screw type or a multi-screw type with more than one screw tends to provide better mixing and dispersibility. The extrusion temperature is preferably in the range of 200°C to 300°C, and more preferably 220°C to 280°C. To prevent thermal degradation of the resin during extrusion, purging with an inert gas such as nitrogen can be performed.

[0082] The melt-extruded raw material sheet is obtained as a raw material sheet by known methods, such as pressing it onto at least one metal drum set to a temperature of 25 to 120°C using an air knife, other rolls, or static electricity. A more preferred temperature for the metal drum is 30 to 80°C.

[0083] As for the method of stretching the raw material sheet, known methods such as stretching between rolls with a difference in peripheral speed, the tenter method, and the tubular method can be used. As for the stretching direction, uniaxial stretching, biaxial stretching, and diagonal biaxial stretching are possible, and for stretching with two or more axes, both sequential stretching and simultaneous stretching are applicable. Of these, the simultaneous biaxial stretching method using the tenter method, the sequential biaxial stretching method using the tenter method, and the sequential biaxial stretching method, in which longitudinal (flow, MD) stretching is performed between rolls with a difference in peripheral speed and then transverse (width, TD) stretching is performed using the tenter method are preferred because they make it easier to obtain the desired stretched film. The method for obtaining the stretched film of the present invention by the sequential biaxial stretching method will be described below, but is not limited thereto.

[0084] In the sequential biaxial stretching method, it is preferable to adjust the stretching temperature and stretching ratio according to the melting point and glass transition temperature of the resin used. First, the resin sheet (raw material sheet) is kept at a temperature of preferably 30 to 90°C, more preferably 50 to 70°C, and stretched to a desired multiple in the longitudinal direction (MD direction) by passing it between rolls with a difference in peripheral speed, or by the tenter method. Subsequently, the stretched film is stretched to a desired multiple in the transverse direction (TD direction) by the tenter method at a temperature of preferably 40 to 130°C, more preferably 50 to 120°C, and then heat-set, relaxed, and heat-set before being wound up.

[0085] The wound film can be aged in an atmosphere of approximately 20-45°C before being cut to the desired product width. [Examples]

[0086] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to the embodiments of these examples.

[0087] The raw materials used in each example and comparative example are as follows. [Polylactic acid resin (1) and (2)] Resin A: Luminy® LX175 (manufactured by Total Corbion PLA, polylactic acid, D-isomer content 4.0% by mass) Resin B: Luminy (registered trademark) L175 (manufactured by Total Corbion PLA, polylactic acid, D-isomer content 0.2% by mass) Resin C: Luminy (registered trademark) L975 (manufactured by Total Corbion PLA, polylactic acid, D-isomer content 12.0% by mass)

[0088] [Plasticizer] Plasticizer A: DAIFATTY(registered trademark)-101 (manufactured by Daihachi Chemical Industry Co., Ltd.) Plasticizer B: Tirabazole VR-01 (manufactured by Taiyo Kagaku Co., Ltd.) Plasticizer C: Tirabazole VR-17 (manufactured by Taiyo Kagaku Co., Ltd.)

[0089] [Streetblocking agent] Antiblocking agent A: Silicea 310P (manufactured by Fuji Silicea Chemical Co., Ltd.)

[0090] (Example 1) A laminate was obtained in which a second layer was arranged on one or both sides of a first layer by the following procedure. First, a raw material 1 containing 6% by mass of plasticizer A was prepared by mixing resin A and plasticizer A. Raw material 1 was used as a raw material for forming the first layer. Next, a raw material 2 containing 0.1% by mass of antiblocking agent A was prepared by mixing resin A and antiblocking agent A. Raw material 2 was used as a raw material for forming the second layer.

[0091] The obtained raw material 1 was fed from a hopper into a device consisting of a twin-screw extruder (L / D=25) equipped with a strand die, connected to a Laboplast Mill (registered trademark) (Model 4C150) manufactured by Toyo Seiki Seisakusho Co., Ltd., and melt-kneaded at a set temperature of 230°C. After water cooling the strand obtained by this melt-kneading, it was cut into pellets using a strand cutter to obtain pellet 1. Pellet of raw material 2 was also prepared in the same manner as pellet 1, and obtained as pellet 2.

[0092] Pellet 1 was fed from a hopper into a single-screw extruder a, and pellet 2 was fed from a hopper into a separate single-screw extruder b. Pellet 1 and pellet 2 were melted and laminated in a three-layer configuration inside a three-layer multi-manifold die, and extruded as a three-layer laminated resin layer (layer of pellet 2 - layer of pellet 1 - layer of pellet 2). The ratio of the amount of resin extruded from single-screw extruder a to single-screw extruder b was set to 2:1. The extruded resin layer was cooled and solidified on a cooling drum controlled at 45°C while being pressed with air pressure using an air knife to obtain a raw material sheet.

[0093] The obtained raw material sheets were stretched using a Bruckner KARO batch-type biaxial stretcher. The stretching method was a sequential biaxial stretching method, where the sheets were stretched longitudinally and then transversely. The film was preheated in an oven at a set temperature of 75°C until the film temperature (Ts) reached 65°C, and then stretched longitudinally to 2.5 times its original thickness at a stretching speed of 0.5 times / second. Next, it was stretched transversely to 4.3 times its original thickness at a stretching speed of 0.5 times / second, and then preheated in an oven at a set temperature of 120°C until the film temperature reached 110°C. The transverse direction was relaxed to 4 times its original thickness at a relaxation speed of 0.5 times / second, and then heated for 12 seconds before being removed from the oven and cooled to room temperature to obtain a laminate with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick).

[0094] (Example 2) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 1, except that the content of plasticizer A in raw material 1 was changed to 10% by mass.

[0095] (Example 3) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 1, except that the content of plasticizer A in raw material 1 was changed to 15% by mass.

[0096] (Example 4) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 1, except that the resin A in raw material 1 was changed to the resin B, the content of plasticizer A in raw material 1 was changed to 10% by mass, and the polylactic acid resin in raw material 2 was changed to the resin B.

[0097] (Example 5) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 4, except that the resin B in raw material 2 was changed to resin A.

[0098] (Example 6) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 2, except that the resin A in raw material 2 was changed to a mixture of resin A and resin C (mass ratio A:C = 4:6).

[0099] (Example 7) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 2, except that plasticizer A was added to raw material 2, and the content of plasticizer A in raw material 2 was set to 2% by mass.

[0100] (Example 8) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 2, except that plasticizer A was added to raw material 2, and the content of plasticizer A in raw material 2 was set to 6% by mass.

[0101] (Comparative Example 1) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 1, except that the content of plasticizer A in raw material 1 was changed to 0% by mass (i.e., no plasticizer was used).

[0102] (Comparative Example 2) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 1, except that the content of plasticizer A in raw material 1 was changed to 5% by mass.

[0103] (Comparative Example 3) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 1, except that the content of plasticizer A in raw material 1 was changed to 16% by mass.

[0104] (Comparative Example 4) A laminated film with a thickness of 29 μm (the first layer was 23 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 2, except that the resin A in raw material 2 was changed to the resin C.

[0105] (Comparative Example 5) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 2, except that the resin A in raw material 1 was replaced with resin C.

[0106] (Comparative Example 6) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 1, except that plasticizer A was added to raw material 2 and the content of plasticizer A was changed to 10% by mass.

[0107] (Comparative Example 7) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 2, except that plasticizer A in raw material 1 was changed to plasticizer B.

[0108] (Comparative Example 8) A laminated film with a thickness of 24 μm (the first layer was 18 μm thick, and the second layer was 3 μm thick) was obtained in the same manner as in Example 2, except that plasticizer A in raw material 1 was changed to plasticizer C.

[0109] (Evaluation method) The laminated films (laminated structures) obtained in each example and comparative example were evaluated by the following method. [thickness] The thickness of the laminated film was measured using a Citizen Seimitsu Co., Ltd. paper thickness measuring instrument MEI-11, in accordance with JIS-C2330.

[0110] [Hayes] The haze of the laminated film was measured using a haze meter NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd., in accordance with JIS-K7361.

[0111] [Total light transmittance] Three measurements were performed in accordance with JIS K 7361-1, and the average value was used as the total light transmittance value. An integrating sphere type light transmittance measuring device (NDH-5000, manufactured by Nippon Denshoku Industries Co., Ltd.) was used for the measurements.

[0112] [Modulus of elasticity, stress at fracture, and elongation at fracture] The films obtained in each example and comparative example were cut into strips of 150 mm in length and 15 mm in width in the MD and TD directions to prepare tensile test samples. The samples were placed in a Tensilon universal testing machine (manufactured by Orientec Co., Ltd.) and pulled at a speed of 300 mm / min until the sample broke. The stress (tensile strength) and elongation at the breaking point were measured, and the (tensile) modulus of elasticity in the MD and TD directions was calculated from the slope of the rising SS curve and the cross-sectional area (width × thickness) of the sample.

[0113] [Tear strength] The tear strength of the films obtained in each example and comparative example is as follows: JIS K 7128-2 to The measurement was performed in accordance with JIS7128-2. Specifically, let A be the average value (N) of the Elmendorff tear strength in the MD direction and the Elmendorff tear strength in the TD direction of the laminated film measured in accordance with JIS7128-2, and let d be the thickness of the laminated film (μm). The following formula (1) was used. S(N / μm)=A / d (1) The S value was calculated using this method.

[0114] [Melting point and glass transition temperature of resins] The following procedure was used to calculate the melting point and glass transition temperature using a PerkinElmer input-compensated DSC, DiamondDSC. 5 mg of resin was weighed out, placed in an aluminum sample holder, and set in the DSC instrument. The temperature was increased from 0°C to 230°C at a rate of 20°C / min under a nitrogen flow, held at 230°C for 5 minutes, cooled to 0°C at 20°C / min, and held at 0°C for 5 minutes. The melting point and glass transition temperature were then determined from the DSC curve obtained when the temperature was increased again to 230°C at 20°C / min. The melting point was defined as the melting peak (the largest melting peak if multiple melting peaks were observed) as defined in JIS-K7121 9.1(1), and the glass transition temperature was defined as the midpoint glass transition temperature as defined in JIS-K7121 9.3(1).

[0115] [Film texture (flexibility)] The sound produced when shaking the films obtained in each example and comparative example was checked, and the texture was judged according to the following criteria based on the presence or absence of a brittle sound. ○: It had no crackling sound and a superior texture. △: It made a slightly crackling sound and did not have the desired texture. ×: The crisp, crackling sound was clearly audible, and the texture was poor.

[0116] [Percentage of D-isomer content in the laminate] The percentage of D-isomer in the laminate was calculated based on the proportion of D-isomer contained in the polylactic acid resin used to form the first and second layers, and the ratio of the thicknesses of the first and second layers.

[0117] [Percentage of plasticizer content in laminates] The percentage of plasticizer content (by mass) in the laminate was calculated based on the proportion of plasticizer contained in the first and second layers and the proportion of the thicknesses of the first and second layers.

[0118] [Table 1]

[0119] Table 1 shows that the laminated films obtained in each example possessed high transparency and flexibility, as well as excellent mechanical properties (tear strength, tensile strength, modulus of elasticity, and elongation at break). On the other hand, the laminated films obtained in the comparative examples had a glass transition temperature of the laminate that was outside the specified range, resulting in inferiority in at least one of the following: transparency, flexibility (texture), tear strength, and tensile strength.

Claims

1. A laminated film comprising a laminate in which a second layer is disposed on one or both sides of a first layer, wherein the first layer is a layer containing polylactic acid resin having a D-isomer content of 0.1% by mass or more and 5% by mass or less. The second layer is a layer containing polylactic acid resin having a D-isomer content of 0.1% by mass or more and less than 12% by mass, The aforementioned laminate has a glass transition temperature of 32 to 49°C, as measured under the following [glass transition temperature measurement conditions]. The laminate has a D-isomer content of 0.1% by mass or more and 5.5% by mass or less. A laminated film in which the plasticizer content in the second layer is 7% by mass or less. [Glass transition temperature measurement conditions] In the DSC curve of the laminate, the glass transition temperature of the laminate is defined as the midpoint glass transition temperature specified in JIS-K7121 9.3(1). The aforementioned DSC curve is obtained by heating 5 mg of the laminate from 0°C to 230°C at a rate of 20°C / min under a nitrogen stream, holding at 230°C for 5 minutes, cooling to 0°C at 20°C / min, holding at 0°C for 5 minutes, and then heating again to 230°C at 20°C / min.

2. The first layer further contains a plasticizer, The laminated film according to claim 1, wherein the second layer does not contain a plasticizer.

3. The content of the plasticizer in the first layer is 6% by mass or more and less than 16% by mass, The laminated film according to claim 2, wherein the content of the plasticizer in the laminate is 5% by mass or more and less than 12% by mass.

4. The following formula (1) S (N / μm)=A / d (1) (In formula (1), A represents the average value (N) of the Elmendorff tear strength in the MD direction and the Elmendorff tear strength in the TD direction of the laminated film, measured in accordance with JIS K7128-2, and d represents the thickness of the film (μm).) A laminated film according to any one of claims 1 to 3, wherein the S value represented by is 5 N / μm or more.

5. A laminated film according to any one of claims 1 to 3, wherein the average value of the tensile strength (MPa) in the MD direction and the tensile strength (MPa) in the TD direction is 65 MPa or more.

6. A laminated film according to any one of claims 1 to 3, wherein the elastic modulus in at least one direction on the film surface is 1.5 to 3.5 GPa.

7. A film for packaging materials comprising a laminated film according to any one of claims 1 to 3.

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