Laminated film

Abstract

To provide a multilayer film which can retain the optical characteristics such as wide reflection band and high reflectance for a long period.SOLUTION: A multilayer film including three or more types of different thermoplastic resin layers and having five or more of repetition units formed with the three or more types of different thermoplastic resin layers, is characterized in that a peeling rate of a square in an adhesion test based on a cross-cut method is 10% or less, and when it is assumed, in an optical spectrum in a wavelength band of 300 nm or more and 2500 nm or less with the horizontal axis defined as a wavelength and the vertical axis defined as reflectance, a wavelength band Π1 represents a wavelength band that indicates 20% or higher reflectance successively over 100 nm or more and is located in the longest wavelength band, λ represents a center wavelength in the wavelength band Π1, S represents the area of a region enclosed with the optical spectrum of the wavelength band Π1 and the base line of reflectance, and N represents a total number of layers of the thermoplastic rein layers, then 0.060≤S / (λ N)≤0.300 is satisfied.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laminated film that has optical characteristics of a wide reflection band and a high reflectance over a long period of actual use.

Background Art

[0002] Optical control films that can shield and extract light rays in a specific wavelength band are put into practical use in a wide range of fields for the purpose of preventing the deterioration of the internal environment of products and constituent components from environmental factors such as light and heat rays, or for extracting only light rays in a specific wavelength band to produce a desired color tone. As representative examples, in building materials and automotive applications, an infrared cut film for suppressing the rise in indoor temperature, in industrial material applications, an ultraviolet cut film for absorbing excessive ultraviolet rays during ultraviolet laser surface processing, in the electronic information field, a blue light cut film for shielding harmful blue light rays emitted from a display light source, a brightness improvement film capable of retroreflecting the light of a diffused and lost backlight, and a metallic film that reflects the entire visible light range for imparting a metallic tone in automotive interior materials and mobile housing applications are used. In addition, in fields such as food, medicine, agriculture, and ink, an optical control film is used for the purpose of suppressing the photo-degradation of the contents. In particular, in the electronic information field, the need for optical control films is high, and in accordance with the trend towards thinning of recent curved displays, foldable displays, etc., the demand for thinning of the optical control film, which is one of the constituent members, is also increasing.

[0003] As a method for controlling (shielding) light rays in a specific wavelength band, absorption-type light-controlling films, in which light absorbers such as dyes, pigments, and ultraviolet / heat-absorbing agents are added to the resin constituting the film, are widely used (Patent Document 1). The light absorption characteristics of absorption-type light-controlling films depend on the product of the absorber concentration and the film thickness, so increasing the absorber concentration is necessary to make the film thin. However, depending on the type of light absorber, surface deposition can be significant, leading to problems such as film defects due to contamination during the film-making process and a decrease in cutting performance due to a decrease in the light absorber concentration, resulting in a decline in film quality. Furthermore, it is necessary to select a light absorber according to the wavelength band to be shielded, and if a wide wavelength band is to be shielded, multiple types of light absorbers must be used in combination, requiring a considerable amount of additive concentration. In addition, when dyes or pigments are selected, the former has poor lightfastness, and the latter has a wide absorption range, resulting in a lack of color selectivity.

[0004] To compensate for the shortcomings of such absorption-type optical control films, that is, to sharply block light rays in a specific wavelength band and easily adjust the wavelength band, reflection-type optical control films that utilize interference reflection based on optical interference theory by laminating layers with different refractive indices in the film thickness direction have attracted attention. In particular, many known technologies have been reported for optical control films with an (AB)m configuration (m is a natural number) in which two layers with different refractive indices (layer A and layer B) are alternately laminated. For example, it has been reported that a wide wavelength band of light rays can be reflected by continuously applying a gradient distribution to the layer thickness, and that in order to suppress unwanted reflection bands on the shorter wavelength side (called higher-order reflections) that occur outside the desired wavelength band, techniques such as designing the optical thickness to 1 / 4 of the wavelength (Patent Documents 2, 3) and applying special layer thickness patterning with a ratio of 1:7:1 (Patent Documents 4, 5) have been reported. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-210598 [Patent Document 2] Special Publication No. 2004-503402 [Patent Document 3] Patent No. 4001619 [Patent Document 4] U.S. Patent No. 5360659 [Patent Document 5] Japanese Patent Publication No. 2018-205615 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the reflective type light control film with an (AB)m configuration disclosed in Patent Documents 1 to 5, increasing the number of layers or increasing the refractive index difference between the two types of resin layers is necessary to achieve high reflectivity and a broad reflection band. However, in the former case, the film thickness increases, which goes against the recent trend towards thinner films, and in the latter case, it is necessary to laminate resins with different skeletal structures, which causes delamination at the interface of resin layers with different refractive indices. Therefore, the reflective type light control film with an (AB)m configuration disclosed in Patent Documents 1 to 5 had significant practical problems.

[0007] To address the above-mentioned problems, the present invention aims to provide a laminated film that maintains optical properties of a wide reflectivity band and high reflectivity over a long period of time. [Means for solving the problem]

[0008] The present invention has the following configuration: it is a laminated film having three or more different thermoplastic resin layers, having five or more consecutive repeating units formed by the three or more thermoplastic resin layers, having a grid peel rate of 10% or less in an adhesion test based on the cross-cut method specified in JIS K 5600-5-6:1999, and satisfying 0.060 ≤ S / (λ·N) ≤ 0.300 when, in a spectral spectrum in the wavelength band from 300 nm to 2500 nm with the horizontal axis being wavelength (nm) and the vertical axis being reflectance (%), the wavelength band that shows a reflectance of 20% or more continuously over 100 nm, which is located in the longest wavelength band, is wavelength band Π1, the center wavelength in wavelength band Π1 is λ, the area of ​​the region enclosed by the spectral spectrum of wavelength band Π1 and the baseline of the reflectance is S, and the total number of laminated thermoplastic resin layers is N.

[0009] Furthermore, the present invention can be configured as follows in order to solve the above problems. (1) A laminated film having three or more different thermoplastic resin layers, having five or more consecutive repeating units formed by the three or more thermoplastic resin layers, having a grid peel rate of 10% or less in an adhesion test based on the cross-cut method specified in JIS K 5600-5-6:1999, and satisfying 0.060 ≤ S / (λ·N) ≤ 0.300 when, in a spectral spectrum in the wavelength band from 300 nm to 2500 nm with the horizontal axis being wavelength (nm) and the vertical axis being reflectance (%), the wavelength band Π1 is the wavelength band that shows a reflectance of 20% or more continuously over 100 nm or more, which is located in the longest wavelength band, the center wavelength in the wavelength band Π1 is λ, the area of ​​the region enclosed by the spectral spectrum of the wavelength band Π1 and the baseline of the reflectance is S, and the total number of laminated thermoplastic resin layers is N. (2) The laminated film according to (1), characterized in that it satisfies 35.0 ≤ S / λ ≤ 150.0. (3) The laminated film according to (1) or (2), characterized in that when the wavelength at the short wavelength end of the wavelength band Π1 is λmin and the wavelength at the long wavelength end is λmax, the condition λmin ≥ λmax / 2 is satisfied. (4) The laminated film according to (3), characterized in that when the wavelength band Π2 is defined as a wavelength band of 300 nm or more and λmax / 5 or more and λmin / 2 or less, the average reflectance in the wavelength band Π2 is 25% or less. (5) The laminated film according to any one of (1) to (4), characterized in that when the wavelength band Π3 is defined as the half-wavelength band of the wavelength band Π1, with wavelengths of λmin / 2 to λmax / 2, the average reflectance in the wavelength band Π3 is 25% or less. (6) The laminated film according to any one of (1) to (5), characterized in that there are three types of thermoplastic resin layers. (7) The laminated film according to (6), characterized in that when the thermoplastic resin layers are designated as layer A, layer B, and layer C in order of decreasing refractive index, the laminated film has a repeating configuration of the A / B / C / B layer unit. (8) The laminated film according to (7), characterized in that, in the repeating unit, the stacking ratio of the A layer to the B layer (A / B) is 0.50 or more and 1.10 or less, and the stacking ratio of the C layer to the B layer (C / B) is 0.90 or more and 1.30 or less. (9) A laminated film according to any one of (1) to (8), characterized in that the lightness L* in the transmission color measurement is 70 or less and the haze is 5.0% or less. (10) The laminated film according to any one of (1) to (9), characterized in that N is 100 or more and 901 or less. (11) The laminated film according to any one of (1) to (10), characterized in that the thickness of each layer contained in the repeating unit exhibits a distribution that is monotonically increasing or monotonically decreasing. (12) A laminated film according to any one of (1) to (11), wherein the thermoplastic resin that is the main component of the thermoplastic resin layer with the highest refractive index is polyethylene terephthalate or polyethylene naphthalate. (13) The laminated film according to any one of (1) to (12), characterized in that the thermoplastic resin layer with the lowest refractive index is a layer mainly composed of a thermoplastic resin exhibiting a refractive index of 1.54 or less. A molded article made using the laminated film according to any one of (1) to (13). (15) An image display device comprising the laminated film according to any one of (1) to (13), or the molded article according to (14). (16) A window comprising the laminated film according to any one of (1) to (13), or the molded article according to (14). (17) An exterior material for a transportation vehicle comprising the laminated film according to any one of (1) to (13), or the molded article according to (14). (18) A transportation vehicle comprising the laminated film according to any one of (1) to (13), the molded article according to (14), the window according to (16), or the exterior material for a transportation vehicle according to (17). [Effect of the Invention]

[0010] According to the present invention, it is possible to provide a laminated film having optical characteristics of a wide reflection band and a high reflectance that can be sustained over a long period of time. [Brief Description of the Drawings]

[0011] [Figure 1] It is an example of a cross-sectional view of a laminated film having a repeating unit of (ABCB)m. [Figure 2] It is an example of a cross-sectional view of a laminated film having a repeating unit of (AB)m with an equivalent film configuration. [Figure 3] It is an example of an image diagram of an S-S curve in the peel strength test of the laminated film of the present invention. [Figure 4] It is a schematic diagram showing the area S of the wavelength band Π1, the central wavelength λ, and the reflectance baseline in the spectroscopic spectrum of the laminated sheet according to an embodiment of the present invention. [Figure 5] It is a schematic diagram showing the area S of the wavelength band Π1, the central wavelength λ, and the reflectance baseline in the spectroscopic spectrum of the laminated sheet according to an embodiment of the present invention. [Figure 6] It is a schematic diagram showing the area S of the wavelength band Π1, the central wavelength λ, and the reflectance baseline in the spectroscopic spectrum of the laminated sheet according to an embodiment of the present invention. [Figure 7] This is a schematic diagram showing the baseline in a spectral spectrum indicating a pulsatile reflectance change among the spectral spectra of the laminated sheet according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0012] Hereinafter, the laminated film of the present invention will be described in detail. The laminated film of the present invention has three or more different types of thermoplastic resin layers, and continuously has five or more repeating units formed by the three or more types of thermoplastic resin layers. In an adhesion test based on the cross-cut method defined in JIS K 5600-5-6:1999, the peeling rate of the grid is 10% or less. In a spectral spectrum in a wavelength band of 300 nm or more and 2500 nm or less with the horizontal axis being the wavelength (nm) and the vertical axis being the reflectance (%), a wavelength band showing a reflectance of 20% or more continuously over 100 nm or more located in the longest wavelength band is defined as wavelength band Π1, the central wavelength in the wavelength band Π1 is λ, the area of the region surrounded by the spectral spectrum in the wavelength band Π1 and the reflectance baseline is S, and when the total number of laminated thermoplastic resin layers is N, it satisfies 0.060 ≦ S / (λ·N) ≦ 0.300. It is a laminated film characterized by this.

[0013] The laminated film of the present invention needs to have three or more different types of thermoplastic resin layers from the viewpoint of realizing desired reflection characteristics by interference reflection while improving the interlayer adhesion. In the laminated film of the present invention, the thermoplastic resin layers being "different" means that any of the following cases applies: (1) the compositions are different; (2) in differential scanning calorimetry (DSC), the glass transition temperature and melting point are different; (3) the contrast of the image after staining when observing the cross-section by transmission electron microscopy (TEM) is different.

[0014] "Different composition" means that the conditions for being considered to have "the same composition" as shown below are not met. "Same composition" means that 95 mol% or more of the repeating units of the chemical structure of the thermoplastic resin constituting each thermoplastic resin layer are common, or that when the constituent components of each thermoplastic resin layer are compared, 95% by mass of the components are common.

[0015] For example, regarding the former, polyethylene terephthalate has as its main constituent unit a unit (ethylene terephthalate unit) in which ethylene glycol units and terephthalic acid units are linked by ester bonds. However, if the resin constituting the layers has a common chemical structure of polyethylene terephthalate, such as a layer made of homopolyethylene terephthalate and a layer made of polyethylene terephthalate copolymerized with 10 mol% isophthalic acid, but the amount of copolymerized component exceeds 5 mol%, the two compositions are considered to be different. Similarly, regarding the latter, if the same constituent component is the main component, but 5% of the component differs, such as a layer made only of homopolyethylene terephthalate and a layer containing 90% by mass of homopolyethylene terephthalate with the remaining 10% by mass being other components, the two compositions are considered to be different. The specific composition / chemical structure of each thermoplastic resin layer can be determined by first determining the layer thickness of each thermoplastic resin layer according to the layer configuration method described later in the measurement method, then cutting and extracting the thermoplastic resin layer, or scraping the layer to expose it to the surface, and using infrared spectroscopy (FT-IR or nano-IR), gas chromatography / time-of-flight mass spectrometry (GC-MS), or nuclear magnetic resonance (NMR).

[0016] On the other hand, if it is possible to extract each thermoplastic resin layer but it is difficult to identify the composition by the above method, differential scanning calorimetry (DSC) can be used to determine that the thermoplastic resin layers constituting the laminated film are "different" if they exhibit different melting points and / or glass transition temperatures. In this invention, exhibiting different melting points and different glass transition temperatures means that the melting points and glass transition temperatures differ by 0.1°C or more. In the measurement temperature range of 25°C to 300°C described in the differential scanning calorimetry (DSC) section of the measurement method described later, there may be cases where the thermoplastic resin does not exhibit a glass transition temperature or melting point. However, if one thermoplastic resin layer exhibits a glass transition temperature or melting point and the other thermoplastic resin layer does not, although it cannot be calculated as a temperature difference, the thermal properties of the resins may be interpreted as being different.

[0017] Furthermore, if identification is difficult using the two methods described above, if a layer interface can be confirmed by contrast difference in the cross-sectional image observed using a transmission electron microscope, or if it can be confirmed by the method described later for layer interfaces (contrast difference) that the difference in the average brightness of two adjacent layers is greater than either of the standard deviations of the brightness of the adjacent thermoplastic resin layers, then it may be determined that the adjacent thermoplastic resin layers have "different compositions." Since this contrast is caused by electron beam scattering, crystal diffraction, etc., if the composition of the thermoplastic resin constituting the thermoplastic resin layer differs according to the aforementioned criteria, the crystallinity and electron density state will differ depending on the type and copolymerization amount of each thermoplastic resin, resulting in different staining states. This makes it possible to visualize each layer as a layer structure with contrast differences in the cross-sectional image of the laminated film.

[0018] Typical thermoplastic resins used to form the thermoplastic resin layer of the laminated film of the present invention are shown below, but the thermoplastic resins that can be used in the present invention are not limited to those listed below.For example, polyolefin resins such as polyethylene, polypropylene, poly(1-butene), poly(4-methylpentene), polyisobutylene, polyisoprene, polybutadiene, polyvinylcyclohexane, polystyrene, poly(α-methylstyrene), poly(p-methylstyrene), polynorbornene, polycyclopentene, etc.; polyamide resins such as nylon 6, nylon 11, nylon 12, nylon 66, etc.; vinyl monomer copolymer resins such as ethylene / propylene copolymer, ethylene / vinylcyclohexane copolymer, ethylene / vinylcyclohexene copolymer, ethylene / alkyl acrylate copolymer, ethylene / acrylic methacrylate copolymer, ethylene / norbornene copolymer, ethylene / vinyl acetate copolymer, propylene / butadiene copolymer, isobutylene / isoprene copolymer, vinyl chloride / vinyl acetate copolymer, etc.; acrylic resins such as polyacrylate, polyisobutyl methacrylate, polymethacrylate, polymethyl methacrylate, polybutyl acrylate, polyacrylamide, polyacrylonitrile, etc. Polyester resins such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and polyethylene furanoate; polyether resins such as polyethylene oxide, polypropylene oxide, and polyacrylate glycol; cellulose ester resins such as ethylcellulose, diacetylcellulose, triacetylcellulose, propionylcellulose, butyrylcellulose, acetylpropionylcellulose, and nitrocellulose; polylactic acid and polybutyl succinate. Biodegradable polymers such as those listed above, as well as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyglycolic acid, polycarbonate, polyketone, polyethersulfone, polyetheretherketone, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide, polysiloxane, tetrafluoroethylene resin, trifluoroethylene resin, trifluoroethylene chloride resin, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, etc. can be used.

[0019] These thermoplastic resins may be used individually or as a blend or alloy of two or more polymers. Blending or alloying allows for obtaining physical and chemical properties that cannot be obtained from a single thermoplastic resin, and by placing such polymer blends or alloys between thermoplastic resin layers with significantly different compatibility, interlayer adhesion can be improved. Among these, from the viewpoint of rheological properties related to strength, heat resistance, transparency, and lamination, it is particularly preferable to select from polyolefin resins, polyester resins, acrylic resins, and polycarbonate resins as the thermoplastic resins forming the thermoplastic resin layers.

[0020] The laminated film of the present invention is required to have repeating units formed from three or more different thermoplastic resin layers. Specifically, having three or more different thermoplastic resin layers means that, if the laminated film of the present invention has repeating units consisting of three different thermoplastic resin layers, each thermoplastic resin layer may be formed from three different thermoplastic resins having different skeletal structures, as described above, or two thermoplastic resin layers having different skeletal structures may be used, and the three thermoplastic resin layers may be designed to have different mixing ratios or copolymerization amounts. Similarly, if the laminated film of the present invention has repeating units consisting of four different thermoplastic resin layers, four thermoplastic resin layers with different compositions may be formed by mixing and copolymerizing two thermoplastic resins having two different skeletal structures, or four thermoplastic resin layers with different compositions may be formed by mixing and copolymerizing three thermoplastic resins having three different skeletal structures, or three thermoplastic resin layers having completely different skeletal structures may be used.

[0021] Furthermore, from the viewpoint of achieving desired reflective properties while minimizing the complexity of the manufacturing process, it is preferable that there are three types of thermoplastic resin layers constituting the repeating unit. Hereinafter, the different thermoplastic resin layers will be described as layer A, layer B, layer C, layer D, etc. When the laminated film of the present invention has three different types of thermoplastic resin layers, and the three different types of thermoplastic resin layers are layers A, layer B, and layer C, examples of a certain repeating unit include (ABC)m, (ABCB)m, (ACBC)m, (BACA)m, (ABABC)m, (ACACB)m, (BCBCA)m, (ABCBCB)m, (ACBCBC)m, (BACACA)m, (BCACAC)m, (CABABA)m, (CBABAB)m (where m is a natural number).

[0022] In particular, in order for the laminated film to not delaminate at the interface of the thermoplastic resin layers, it is preferable to have a small number of combinations of adjacent thermoplastic resin layers that form the interface. Specifically, there are three types of interfaces formed from three different thermoplastic resins: AB interface, BC interface, and CA interface. However, within the repeating units, (ABCB)m, (ABCBCB)m, and (CBABAB)m have only two types: AB interface and BC interface; (ACBC)m, (ACBCBC)m, and (BCACAC)m have only two types: AC interface and BC interface; and (BACA)m, (BACACA)m, and (BCACAC)m have only two types: AB interface and AC interface. Therefore, when considering combinations of thermoplastic resin layers to achieve delamination-free laminated films, in this configuration, it is only necessary to consider the interlayer adhesion between one of the A, B, and C layers and the other two layers. For this reason, adopting the above configuration is preferable in that it makes it easier to form laminated films with high interlayer adhesion.

[0023] Furthermore, to improve interlayer adhesion, it is preferable that the difference in compatibility parameters between adjacent thermoplastic resin layers is small. The compatibility parameters referred to here are energy-related parameters specific to thermoplastic resins, and the closer these values ​​are, the easier the resins are to mix with each other.

[0024] In the laminated film of the present invention, in order to obtain high interlayer adhesion, it is preferable that the difference in the absolute value of the solubility parameter (SP value) of adjacent thermoplastic resin layers forming the interface is 1.5 or less. Good compatibility of the thermoplastic resins between adjacent thermoplastic resin layers makes interlayer delamination less likely to occur in the laminated state.

[0025] Compatibility parameters can be estimated by calculation methods such as those of Hansen, Hoy, and Fedors. However, for thermoplastic resins that can be suitably used as organic polymer materials, Fedors' calculation method, which allows calculation based on repeating structural units of the molecular chain, is used. By using this method, the compatibility parameters of thermoplastic resins containing structural units derived from copolymer components can be easily calculated according to the ratio of each structural unit. In Fedors' calculation method, the cohesive energy density and molar molecular volume of molecules, which depend on the type and number of substituents, determine the compatibility parameters, and the compatibility parameters are estimated according to equation (6). Here, E coh (cal / mol) is the cohesive energy, and V is the molar molecular volume (cm³). 3 This represents ( / mol).

[0026]

number

[0027] The compatibility parameter in the laminated sheet of the present invention shall be a value obtained by rounding the estimated value calculated based on Fedor's formula to two decimal places. Typical compatibility parameters for thermoplastic resins include cellulose acetate: 11.0, cellulose: 15.6, polyacrylonitrile: 14.8, polyamide: 13.6, polyisobutylene: 7.7, polyethylene: 8.0, polyethylene terephthalate: 10.7, polyvinyl chloride: 10.1, polyvinyl acetate: 9.5, polycarbonate: 9.9, polystyrene: 9.4, polyvinyl alcohol: 12.6, polyphenylene sulfide: 12.5, polybutadiene: 8.3, polypropylene: 8.1, and polymethyl methacrylate: 9.3.

[0028] When a thermoplastic resin layer contains multiple thermoplastic resins, the compatibility parameter of the thermoplastic resin layer is calculated by multiplying the compatibility parameter of each individual thermoplastic resin by the content ratio of the organic polymer material and summing the results. For example, if polyethylene terephthalate (compatibility parameter: 10.7) and polymethyl methacrylate (compatibility parameter: 9.3) are contained in a 50:50 ratio, the compatibility parameter of the layer will be 10.0, which is the midpoint between the two compatibility parameters.

[0029] Generally, one way to reduce the difference in compatibility parameters between two thermoplastic resin layers is to make the skeletal structure of the thermoplastic resin, which is the main component of the two thermoplastic resin layers, common. For example, to reduce the difference in compatibility parameters between adjacent thermoplastic resin layers, the main components of these thermoplastic resin layers are made of thermoplastic resins having a common skeletal structure, and the difference in compatibility parameters between the two thermoplastic resin layers can be reduced by changing the copolymer components or the type of alloy / blend. When two adjacent thermoplastic resin layers have a common chemical structure, strong intermolecular forces act between the adjacent thermoplastic resins, causing interfacial diffusion of polymers and increasing the thickness region that constitutes the layer interface, thereby improving adhesion.

[0030] In the laminated film of the present invention, it is preferable that both outermost layers consist of the same thermoplastic resin layer. Having both outer layers composed primarily of the same thermoplastic resin eliminates the need to adjust the roll temperature in the manufacturing method described later to prevent adhesion between the roll and the film during roll stretching, in accordance with the thermal properties of the thermoplastic resin layer in contact with the roll. This allows for the acquisition of the laminated film using a film-forming process similar to that used for single-layer films composed primarily of the same thermoplastic resin, in accordance with the thermal properties of the thermoplastic resins constituting the outermost layers.

[0031] Furthermore, it is preferable that the thermoplastic resin constituting the outermost thermoplastic resin layer is a layer mainly composed of crystalline thermoplastic resin. If the outermost thermoplastic resin layer is mainly composed of amorphous resin, when a biaxially oriented laminated film is obtained using the manufacturing method described later, problems may arise such as poor film formation due to adhesion to manufacturing equipment such as rolls and clips, deterioration of the surface condition, or inability to obtain a laminated film with uniform physical and optical properties within the film surface due to insufficient stress during stretching. Crystallinity can be determined by cutting and extracting the thermoplastic resin layer and checking for the presence or absence of enthalpy of fusion using a differential scanning calorimetry (DSC) device.

[0032] It is important that the laminated film of the present invention satisfies the optical properties described below. However, in order for the laminated film to exhibit the effect of reflection due to interference, it is important to increase the refractive index difference of the thermoplastic resin layer. Preferably, the thermoplastic resin constituting the thermoplastic resin layer exhibiting a high refractive index is a crystalline thermoplastic resin whose refractive index can be increased by a stretching process. Considering the film-forming properties mentioned above, it is most preferable that the thermoplastic resin constituting the thermoplastic resin layer located at the outermost layer of the laminated film is mainly composed of a crystalline thermoplastic resin. A low refractive index of the thermoplastic resin layer is often due to the thermoplastic resin constituting the layer being amorphous, which is also disadvantageous from the viewpoint of film-forming properties mentioned above. For convenience, the following description will assume that when a crystalline thermoplastic resin layer is included in the thermoplastic resin layers constituting the laminated film, at least layer A is a crystalline thermoplastic resin layer. In this case, among the laminated films of preferred repeating units having the three types of thermoplastic resin layers, (ABCB)mA and (ABCBCB)mA are preferred repeating unit configurations.

[0033] When a laminated film has four different types of thermoplastic resin layers (layer A, layer B, layer C, and layer D), it is possible to create a laminated film with repeating units such as (ABCD)m, (ABDC)m, (ACBD)m, (ABCDCB)m, (ABDCDB)m, (ACBDBC)m, (ACDBDC)m, (ADBCBD)m, (ADCBCD)m, (BACDCA)m, (BADCDA)m, (BCADAC)m, (BCDADC)m, (BDACAD)m, (BDCACD)m, (CABDBA)m, (CADBDA)m, (CBADAB)m, (CBDADB)m, (CDABAD)m, (CDBABD)m, (DABCBA)m, (DACBCA)m, (DBACAB)m, (DBCACB)m, (DCABAC)m, (DCBABC)m (where m is a natural number).

[0034] Even when the laminated film has four different types of thermoplastic resin layers, it is preferable to have fewer types of interfaces formed by adjacent thermoplastic resin layers in order to provide interlayer adhesion. Therefore, among the repeating units, the (ABCDCB)m and (DCBABC)m repeating units are preferred. Furthermore, as mentioned above, it is preferable from the viewpoint of film-forming properties that the thermoplastic resin layer placed on the outermost layer is made of crystalline thermoplastic resin, so having the (ABCDCB)m repeating unit is even more preferable.

[0035] While the types of layers made of thermoplastic resin used in repeating units and the arrangement of repeating units are not limited to those described above, increasing the number of layer types increases the number of extruders required for simultaneous extrusion. Furthermore, increasing the number of interface types complicates the resin design required to provide and maintain interfacial adhesion. Since thermoplastic resins with different rheological behaviors are laminated at the same temperature, lamination disorder is more likely to occur in the process from lamination equipment to sheet formation with die-cutting. Moreover, the lamination process for merging the resin layers becomes more complicated, making it impractical to use more than five types.

[0036] In order to achieve the broad reflectivity and high reflectivity that are important features of the present invention, it is also important that there are many repeating units (corresponding to m) that generate optical interference reflection. In the relationship between the film design and optical performance of the laminated film of the present invention, high reflectivity can be achieved by having multiple repeating units of similar thickness, and a broad reflectivity can be achieved by giving a gradient to the thickness of these repeating units. Furthermore, within the repeating units, higher-order reflection suppression can be achieved by controlling the refractive index relationship of adjacent thermoplastic resin layers, as described later, and the optical thickness, which is expressed as the product of the refractive index and layer thickness of each thermoplastic resin layer, to a constant relationship. While a large number of different thermoplastic resin layers included in the repeating units enables more advanced optical design, it also increases the complexity of the lamination apparatus because it increases the number of thermoplastic resins with different skeletal structures, and because multiple types of thermoplastic resins with different rheological behaviors are laminated, lamination disorder is more likely to occur, making film formation more difficult. Therefore, it is preferable to use as few types of thermoplastic resin layers as possible to constitute the repeating unit. Specifically, it is preferable that the number of thermoplastic resin layers forming the laminated film be four or fewer, more preferably three types of thermoplastic resin layers. This is because it does not complicate the lamination process, allows for the achievement of the broad reflection band and high reflectivity important in the present invention with as few layers as possible, and conforms to the trend towards thinner films required for optical applications. Furthermore, among the laminated films composed of the three preferred types of thermoplastic resin layers, it is particularly preferable, as shown in Figure 1, to have a laminated structure in which the constituent units of A / B / C / B are repeated, i.e., the repeating unit is A / B / C / B. In Figure 1, reference numerals 1 to 4 represent A layer, B layer, C layer, and the repeating unit, respectively. The same applies to other drawings thereafter.

[0037] In the present invention, a laminated film having a fixed repeating unit can be formed by feeding multiple thermoplastic resins constituting the repeating unit from different channels using an extruder equal to or greater than the number of types of thermoplastic resins, and using a known lamination device such as a multi-manifold type feed block or a static mixer. In particular, when used for optical applications, controlling the layer thickness is extremely important, so in order to obtain the laminated structure of the present invention with high precision and efficiency, a method using a feed block with fine slits is preferred. When forming a laminate using a slit-type feed block, the thickness of each layer and its distribution can be achieved by changing the length and width of the slits to gradient the pressure loss. Here, the length of the slit refers to the length of the comb-shaped portion that forms a channel for flowing each thermoplastic resin layer in a fixed repeating unit within the slit plate.

[0038] In the laminated film of the present invention, the thermoplastic resin layers constituting the repeating units of the laminated film have different crystallinity and electronic states due to their different compositions, and therefore also have different refractive indices, which are important for realizing the optical properties of the laminated film of the present invention. Specifically, a difference in refractive index means that in any of two orthogonal directions arbitrarily selected within the film plane and in a direction perpendicular to the plane, the refractive index of one thermoplastic resin layer differs from that of another thermoplastic resin layer by 0.01 or more. Following this definition, for example, "having three different types of thermoplastic resin layers" also means a configuration in which there are three types of thermoplastic resin layers, and when two of them are selected and their refractive index values ​​are compared, there is a difference of 0.01 or more in both cases.

[0039] By laminating thermoplastic resin layers with different refractive indices, optical interference reflection based on optical theory becomes possible, where light of a specific wavelength can be reflected based on the relationship between the refractive index difference between each layer and the layer thickness. Specifically, when the layer thicknesses of adjacent thermoplastic resin layers separated by an interface are dx and dy (x,y=A,B,C···), and the refractive index difference between adjacent layers is Δn=|ny-nx|, the reflected light wavelength (λ) is roughly determined according to equation (2), and the reflectance (R) is roughly determined according to equation (3) based on the refractive index difference Δnx between adjacent layers (θx and θy refer to the angle of incidence to the layer in question and the angle of incidence when incident on the adjacent layer, as viewed from the direction perpendicular to the surface of the laminated film. k is an arbitrary natural number). Here, when thermoplastic resins with the same refractive index are used for adjacent layers, the numerator of equation (3) representing the reflectance becomes 0, especially for light incident perpendicular to the surface, meaning that interference reflection does not occur at the interface.

[0040]

number

[0041]

number

[0042] The laminated film of the present invention must have five or more repeating units formed from three or more types of thermoplastic resin layers in a continuous sequence. The continuous presence of repeating units facilitates interference reflection, thereby improving the reflectivity and expanding the reflection wavelength band of the laminated film. This contributes to increasing the S / λ ratio, which is a key feature of the laminated film of the present invention and exhibits a wide reflection band and high reflection performance, as described later. From this perspective, the number of continuously included repeating units is preferably 10 or more, more preferably 50 or more, and even more preferably 100 or more. While a larger number of repeating units generally leads to easier interference reflection, this can result in increased manufacturing costs due to larger manufacturing equipment, deterioration of the uniformity of the laminated film in the width direction due to lamination irregularities and widthwise inclination of the lamination ratio resulting from the complexity of the lamination process, and deterioration of handling due to increased film thickness. Therefore, a number of 300 or less is practical.

[0043] Furthermore, the laminated film of the present invention is preferably a laminated film with 101 to 901 layers. By having 101 or more layers, with three or more types of thermoplastic resin layers having a certain repeating unit, interference reflection is easily generated, making it easier to achieve not only high reflectivity but also a wide reflection band. The number of layers in the laminated film is preferably 301 to 701 layers. If the number of layers exceeds 901, it may lead to increased manufacturing costs due to the need for larger manufacturing equipment.

[0044] The laminated film of the present invention can be designed so that the thickness of each thermoplastic resin layer constituting the laminated film increases or decreases monotonically, increases and decreases from one side of the film toward the center, or decreases and increases from one side of the film toward the center. Furthermore, the gradient of the thickness distribution can be designed to change continuously, such as linearly, geometrically, or as a difference sequence, or so, such as having approximately 10 to 50 layers with roughly the same thickness and the thickness changing in a step-like manner.

[0045] The more layers with the same thickness there are, the higher the reflectivity of the laminated film at a particular wavelength. Therefore, to achieve high reflectivity, it is preferable to have a layer thickness distribution with multiple gradient distributions of increasing and decreasing layer thickness. However, when targeting the same wavelength band with the same number of layers, a distribution with multiple gradient distributions requires designing a layer thickness distribution corresponding to the target reflection wavelength band with fewer layers compared to a distribution that shows monotonically increasing / decreasing, resulting in a larger gradient in the layer thickness distribution. This can lead to problems such as broadening of the edges of the reflection band and increased fluctuation in the baseline of reflectivity due to interference reflection distances between multiple gradient distributions, which can result in stronger color unevenness of the laminated film depending on the viewing direction. To avoid these problems, it is preferable that the layer thickness of each thermoplastic resin layer constituting the laminated film exhibits a layer thickness distribution that is either monotonically increasing or monotonically decreasing.

[0046] The reflectance of the laminated film of the present invention in wavelength band Π1 (the wavelength band being defined as the wavelength band showing a continuous reflectance of 20% or more over 100 nm or more in the spectral spectrum in the wavelength band from 300 nm to 2500 nm, where the horizontal axis is wavelength (nm) and the vertical axis is reflectance (%)) is determined by the difference in refractive index between the layer with the highest refractive index and the layer with the lowest refractive index in the repeating unit. For example, if the repeating unit has three types of thermoplastic resin layers with different refractive indices (layer A, layer B, and layer C), and the refractive indices are in the order of A, B, and C, then the difference in refractive index between layer A and layer C will determine the reflectance of the primary reflection of the laminated film. Therefore, it is most important to use a combination of thermoplastic resins that increases the refractive index difference between layer A and layer C, in particular a combination that increases the refractive index difference after the stretching process. The thermoplastic resins that can be preferably used as the layer with the highest refractive index and the layer with the lowest refractive index will be described later.

[0047] In the laminated film of the present invention, a wide reflectivity band can be achieved by providing a continuously sloping layer thickness of the laminated film according to equation (2). Furthermore, the reflectivity band can be expanded by increasing the number of layers, but when interference reflection is utilized as in the laminated film of the present invention, higher-order reflections according to equation (2) may occur in the wavelength band shorter than the primary reflection, which corresponds to the main reflection. For example, in a (AB)m type laminated film in which layers mainly composed of two different thermoplastic resins are alternately laminated, the secondary and tertiary reflections, which correspond to the reflectivity band when the coefficient k of equation (2) is 2 or 3, can be increased or suppressed by controlling the optical thickness, which is the product of the refractive index and the layer thickness. For example, secondary reflections can be suppressed by designing the optical thickness of layer A nA × dA and the optical thickness of layer B nB × dB to be 1 / 4 wavelength of the target wavelength band. This is generally called λ / 4 design. Furthermore, by applying a special equivalent film design, known as optical thickness design, as shown in Figure 2, with A:B:A:B:A:B=1:7:1:1:7:1 as described in Patent Document 4, it is possible to suppress not only secondary reflections but also tertiary reflections simultaneously. However, in the case of (AB)m type laminated films, it is theoretically impossible to simultaneously suppress higher-order reflections up to the fourth order, regardless of the optical thickness design, when the coefficient k in equation (2) is set to 4. Suppressing higher-order reflections up to the fourth order simultaneously is only possible by using three or more thermoplastic resin layers with different refractive indices. Note that the occurrence of these higher-order reflections tends to lead to a decrease in primary reflectance and a narrowing of the reflection bandwidth, so it is preferable to use an optical design that does not cause higher-order reflections, as will be described later.

[0048] For example, in applications such as films that reflect heat rays (near-infrared rays), it is required that the film reflects infrared wavelengths over as wide a reflection band as possible while remaining highly transparent. In the case of a laminated film designed so that the reflection band Π1 is in the near-infrared wavelength band of 800 nm or more, without using optical design to suppress higher-order reflections, higher-order reflections of the second order or higher occur in the visible light band of 400 to 800 nm, which can cause the laminated film to become discolored and lose transparency. To create a laminated film that can reflect heat rays over a wide reflection band without causing reflection in the visible light region, the aforementioned λ / 4 design or equivalent film design can be used to extend the long-wavelength end of the first-order reflection until the long-wavelength end of the generated higher-order reflection is 400 nm or less. However, in a laminated film consisting of two different thermoplastic resin layers, the number of higher-order reflections that can be suppressed is limited to the third order, and there is a limit to the wavelength band in which the first-order reflection wavelength band can be extended while maintaining transparency. Specifically, higher-order reflections of the fourth order or higher occur, so the long-wavelength end of the wavelength band Π1 is limited to 1600 nm. In this case, a sufficient reflection bandwidth and high reflectivity cannot be obtained, making it impossible to increase the value of the area S in the wavelength bandwidth Π1. As a result, S / (λ·N) and S / λ, which are indicators representing the wide reflection bandwidth and high reflectivity of the laminated film of the present invention as described later, cannot satisfy the values ​​required or preferred for the present invention. Therefore, by using three or more types of thermoplastic resins to constitute the repeating units, and designing layers other than those exhibiting high and low refractive indices according to the preferred optical design described later, it is possible to simultaneously suppress up to the fourth-order reflection, thereby extending the primary reflection bandwidth to a maximum of 2000 nm and obtaining a heat-reflective film with a wide reflection wavelength bandwidth without coloring the laminated film.

[0049] The following describes a preferred optical design for a laminated film to suppress higher-order reflections, using a laminated film having three thermoplastic resin layers with different refractive indices as an example. In a laminated film composed of layers mainly made of three different thermoplastic resins, in order to suppress higher-order reflections, it is preferable that the ratios nA / nB and nB / nC at each interface other than the interface between the layer with the highest refractive index and the layer with the lowest refractive index, where nA, nB, and nC are the in-plane average refractive indices of layers A, B, and C in descending order of refractive index, satisfy the relationship given by equation (4). In the optical theory of interference reflection, the presence or absence of interference reflection is influenced not only by the phase overlap of light rays reflected at adjacent interfaces but also by the intensity of light reflected at each interface. Therefore, in order to completely cancel out interference reflections, it is essential that the phases of the interfering waves are reversed and that the intensity of light reflected at each interface is kept constant. Since the magnitude of light reflected at an interface is influenced by the ratio of the refractive indices of the two layers constituting the interface, it is preferable to satisfy the above relationship in order to cancel out interfering light and suppress higher-order reflections.

[0050]

number

[0051] The following describes thermoplastic resins that can be preferably used for the thermoplastic resin layer with the highest refractive index and the thermoplastic resin layer with the lowest refractive index. Here, the thermoplastic resin layer with the highest refractive index will be referred to as layer A.

[0052] In the laminated film of the present invention, the thermoplastic resin layer A, which has the highest refractive index, is preferably a layer mainly composed of a thermoplastic resin that exhibits a high refractive index even in an unstretched state, particularly a thermoplastic resin exhibiting a refractive index of 1.58 or higher. Examples of thermoplastic resins exhibiting a high refractive index of 1.58 or higher include polyethylene terephthalate (1.58), polycarbonate (1.59), polyethylene naphthalate glycol (1.60), polystyrene (1.60), polybutylene naphthalate, polyimide (1.61), polydichlorostyrene (1.62), polysulfone (1.63), polyethylene naphthalate (1.64), polyetherimide (1.66), polyetheretherketone (1.73), and polyphenylene sulfide (the values ​​in parentheses indicate the refractive index). Of course, blends and alloys of these may also be used, and copolymer components that contribute to improving the refractive index and interlayer adhesion may be added to the above-mentioned thermoplastic resin as a base. To improve the refractive index, the thermoplastic resin should preferably contain one or more aromatic rings as its skeletal structure, with the aromatic rings arranged linearly. Most preferably, the thermoplastic resin should contain components such as terephthalic acid, franzicarboxylic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, fluo-orange carboxylic acid, anthracenedicarboxylic acid, pyrenetetracarboxylic acid, paraxylene glycol, naphthalenediol, biphenyldiol, fluo-orangeol, and anthracenediol. Whether a thermoplastic resin exhibits crystalline properties can be determined by whether or not it has a melting enthalpy in differential scanning calorimeter (DSC) measurements (those with a melting enthalpy are considered to exhibit crystalline properties). Among the aforementioned thermoplastic resins, polyethylene terephthalate and polyethylene naphthalate are most preferably selected as crystalline thermoplastic resins that can exhibit a higher in-plane refractive index when stretched and also possess high transparency and versatility suitable for optical applications. In other words, the most preferable embodiment is when the main component of the thermoplastic resin layer with the highest refractive index is polyethylene terephthalate or polyethylene naphthalate. In this context, the main component refers to the component present in the layer at a concentration of more than 50% by mass but not exceeding 100% by mass.

[0053] In the laminated film of the present invention, the thermoplastic resin layer with the lowest refractive index (layer C if there are three types of thermoplastic resin layers) is preferably a layer mainly composed of a thermoplastic resin that exhibits a low refractive index in an unstretched state, particularly a thermoplastic resin exhibiting a refractive index of 1.54 or less. For example, thermoplastic resins that exhibit a low refractive index when used individually include ethylene fluoride-propylene copolymer (1.34), polyvinylidene fluoride (1.42), polybutyl acrylate (1.46), polylactic acid (1.46), polymethylpentene (1.46), polyisobutyl methacrylate (1.48), polymethyl acrylate (1.48), polyethyl methacrylate (1.48), polymethyl methacrylate (1.49), cellulose acetate (1.49), polypropylene (1.50), polybutylene (1.50), polyacrylonitrile (1.51), Ecdel (trademark) (1.52), nylon (1.53), polyethylene (1.54), and others. Of course, blends and alloys of these can also be used, and copolymer components that contribute to improving refractive index and interlayer adhesion may be added to the above-mentioned thermoplastic resins as a base. Furthermore, as long as the final thermoplastic resin satisfies the requirement of having a refractive index of 1.54 or less, it is also possible to use a thermoplastic resin with a refractive index greater than 1.54 as the base and include different components as copolymerization components. The refractive index of the thermoplastic resin that forms the thermoplastic resin layer with the lowest refractive index is preferably 1.51 or less, and more preferably 1.49 or less.

[0054] In particular, the thermoplastic resin layer with the lowest refractive index is preferably composed of an amorphous thermoplastic resin whose refractive index does not change significantly after the stretching process. An amorphous resin refers to a thermoplastic resin that does not exhibit enthalpy of fusion in differential scanning calorimeter (DSC) measurements. Considering transparency, interlayer adhesion, and film-forming properties, it is preferable to use acrylic resins such as polybutyl acrylate, polyisobutyl methacrylate, polymethyl acrylate, polyethyl methacrylate, and polymethyl methacrylate among the above. Alternatively, in order to obtain adhesion with layer A, which is the layer with the highest refractive index, it is also preferable to use an amorphous thermoplastic resin with a refractive index of 1.54 or less by adding copolymer components to a polyester resin that exhibits a high refractive index. For example, in this case, if the total equivalent amount of the components constituting the thermoplastic resin is 100 mol%, it is preferable that the amount of the by-component corresponding to the copolymer component is 25 mol% to 45 mol%. For example, in the case of a copolymer polyester resin whose main component is polyethylene terephthalate, it is preferable that the total amount of dicarboxylic acid components other than terephthalic acid and diol components other than ethylene glycol is between 25 mol% and 45 mol%. By controlling the copolymerization amount within this range, the interlayer adhesion and differences in thermal fluid properties of the laminated film are reduced, making it possible to obtain an amorphous thermoplastic resin with excellent accuracy and uniformity of the thickness of each layer.

[0055] Preferred copolymer components for reducing refractive index include, for example, adipic acid, cyclohexanedimethanol, bisphenol A ethylene oxide, spiroglycol, isophthalic acid, isosorbide, cyclohexanedicarboxylic acid, neopentyl glycol, polyethylene glycol 2000, m-polyethylene glycol 1000, m-polyethylene glycol 2000, m-polyethylene glycol 4000, m-polypropylene glycol 2000, bisphenylethylene glycol fluorene (BPEF), fumaric acid, and acetoxybenzoic acid. Among these, spiroglycol, neopentyl glycol, or polyethylene glycol components exhibiting a three-dimensional skeletal structure are particularly noteworthy. Spiroglycol exhibits a small glass transition temperature difference with polyethylene terephthalate when copolymerized, making it less prone to overstretching during molding and less likely to cause delamination. Polyethylene glycol components enhance hydrophilicity and interlayer adhesion, and can effectively lower the glass transition temperature, resulting in improved co-stretchability.

[0056] The laminated film of the present invention must have a delamination rate of 10% or less in the adhesion test based on the cross-cut method specified in JIS K 5600-5-6:1999. Hereinafter, "delamination rate in the adhesion test based on the cross-cut method specified in JIS K 5600-5-6:1999" may simply be referred to as the delamination rate. Delamination of the laminated film is thought to occur due to both cohesive / material fracture, where rupture occurs within each thermoplastic resin and delamination occurs at the interface between the thermoplastic resin layers, but the cross-cut test can capture delamination caused by both. Neither type of fracture should occur when the laminated film is used for a long period of time, and a delamination rate of 10% or less in the cross-cut test indicates that the laminated film has long-term reliability. If the delamination rate exceeds 10%, fracture may occur at the laminated film interface during long-term use. For example, during processing, lifting due to delamination may occur at the interface while the film is being transported on a roll, or cracks may occur in the cross-section during the cutting process. In such cases, the peel strength of the protective film, which is placed at a different location from the laminated film, may be insufficient, resulting in delamination at the laminated film interface. In applications where repeated bending processes are performed, lifting at the interface can lead to the loss of physical and optical properties derived from the laminated film. From the above viewpoint, the delamination rate is more preferably 3% or less, and most preferably 0%.

[0057] In order to achieve high reflectivity and a wide reflection wavelength band, the laminated film of the present invention may involve laminating thermoplastic resins with different skeletal structures to increase the refractive index difference between a layer exhibiting a high refractive index and a layer exhibiting a low refractive index. However, generally, when resins with different skeletal structures and large differences in compatibility parameters are laminated, interlayer adhesion is poor and delamination occurs. In conventional known examples, there are many descriptions and examples of combining thermoplastic resins with different skeletal structures to exhibit high reflectivity, and descriptions of the optical properties of the resulting laminated film. However, although such laminated films satisfy the optical properties, interlayer delamination often occurs, making practical application difficult. In the present invention, as a method to reduce the delamination rate to 10% or less or within the above preferred range, a method of adjusting the resin design and film design to improve interlayer adhesion can be used, and this method will be described below.

[0058] One preferred resin design for improving interlayer adhesion, as mentioned above, involves copolymerizing, alloying, or blending the thermoplastic resin constituting one side of an adjacent thermoplastic resin layer with the thermoplastic resin constituting the other side. For example, in a laminated film having repeating units of A / B / C / B, this indicates that the thermoplastic resin B layer is a blend or alloy raw material of thermoplastic resin A and thermoplastic resin C. Although this method is the most commonly used and simple method, it results in components with different basic structures coexisting within the thermoplastic resin that mainly constitutes the layer. Depending on the dispersion and mixing state, components with different basic structures may exist as sea-island structures (domains) within the thermoplastic resin that mainly constitutes the layer, increasing turbidity (haze) and impairing the transparency of the laminated film. In particular, when blending / alloying thermoplastic resins with large differences in compatibility parameters, this sea-island structure is likely to occur. Therefore, it is undesirable to apply resins with completely different basic chemical structures to thermoplastic resin A and thermoplastic resin B in order to increase the refractive index difference. To improve the degree of dispersion of thermoplastic resins having different skeletal structures, it is preferable to use a compounding extruder equipped with two or more screws, increase the ratio of screw rotations to the discharge amount during additive compounding, or change the arrangement of the screw segments involved in compounding so that the screws mesh more deeply, thereby increasing the degree of compounding. Alternatively, it is preferable to include an additive having a common skeletal structure that enhances the compatibility of the thermoplastic resins.

[0059] Another aspect of resin design for improving interlayer adhesion involves pre-reacting at least one thermoplastic resin layer with a reactive additive having unreactive functional groups having the same basic structure as an adjacent thermoplastic resin layer, thereby incorporating components with a common structure into both layers and improving compatibility. Specifically, this method involves reacting unreacted end groups contained in the thermoplastic resin constituting the layer whose adhesion is to be improved, or end groups contained in an additive pre-added to the layer whose adhesion is to be improved, with a reactive additive to impart components with the same basic skeletal structure as the adjacent layer, thereby improving compatibility. For example, if the layer whose adhesion is to be improved contains carboxyl group ends, the reactive additive can be an additive containing end groups highly reactive with carboxyl groups, such as phenol groups, epoxy groups, or amino groups. If the layer whose adhesion is to be improved contains alkoxysilyl group ends, the reactive additive can be an additive containing inorganic fillers or metal components. In this method, as with copolymerizing, alloying, or blending thermoplastic resins, problems arise due to increased haze caused by the dispersion state. In addition, if unreacted additives are heated before the lamination process, the reaction may proceed further, changing the rheological properties and causing lamination disorder.

[0060] Furthermore, another aspect of resin design for improving interlayer adhesion involves a formulation in which at least one thermoplastic resin layer contains unreacted functional groups that react with unreacted functional group components contained in the other thermoplastic resin layer whose adhesion is to be improved. In this method, since the thermoplastic resins supplied from individual extruders react during the lamination process within the lamination apparatus, the rheological behavior of the thermoplastic resins constituting each layer is not changed before the lamination process, as in the former method. Therefore, adhesion can be improved without causing lamination disorder, which is preferable. The combination of functional groups described above can be used to achieve such a reaction.

[0061] A preferred film-forming condition that can improve interlayer adhesion is to heat-treat the film at a heat treatment temperature of 180°C or higher after stretching. By undergoing a heat treatment process at a high temperature, the fluidity of the resins at the interface is improved and diffusion occurs, resulting in an interface in which both thermoplastic resin layers are compatible. Therefore, interfacial adhesion can be improved compared to when the heat treatment temperature is low. From the above viewpoint, the heat treatment temperature is preferably 190°C or higher, more preferably 200°C or higher. If the heat treatment temperature is too high, the refractive index may change due to crystal melting depending on the type of thermoplastic resin, and the optical properties may change. For this reason, it is preferable to keep the heat treatment temperature at 230°C or lower. The heat treatment temperature can be determined by the microcrystalline melting temperature (Tmeta) when the thermal properties of the film are measured by heating using a differential scanning calorimeter (DSC).

[0062] Furthermore, interlayer adhesion can also be improved by reducing the number of repeating units and layers that make up the laminated film. This is because a smaller number of repeating units and layers proportionally reduces the number of interfaces where delamination occurs, making delamination less likely in cross-cut tests. This tendency may be particularly pronounced when there is no improvement in adhesion due to chemical interfacial reactions by additives. From the above viewpoint, specifically, the number of layers is preferably 701 or less, more preferably 601 or less, and even more preferably 353 or less.

[0063] Furthermore, it is preferable that the laminated film of the present invention exhibits a peel strength of 1.3 N / 10 mm or more in the T-type peel test specified in JIS K 6854-3:1999. Unlike the cross-cut test method, the T-type peel test allows for the quantification of peel strength focusing solely on interfacial fracture by focusing on a region of the obtained SS curve that shows a constant value. A higher value indicates sufficient interfacial adhesion. If the peel strength is less than 1.3 N / 10 mm, problems due to peeling on the processed surface and practical surface as described above may occur. From the above viewpoint, the peel strength is preferably 2.0 N / 10 mm or more, and more preferably 3.0 N / 10 mm or more. The peel strength due to interfacial peeling is obtained by reading the average value of the region of the obtained SS curve that shows a constant strength (numerical variation within ±10%) over a peel range of 20 mm or more, as shown in Figure 3. In Figure 3, reference numeral 5 indicates the SS curve in the peel strength test, and reference numeral 6 indicates the peel strength.

[0064] The laminated film of the present invention must satisfy the following condition: 0.060 ≤ S / (λ·N) ≤ 0.300 in a spectral spectrum in the wavelength band from 300 nm to 2500 nm, where the horizontal axis is wavelength (nm) and the vertical axis is reflectance (%). The wavelength band Π1 is the wavelength band that shows a continuous reflectance of 20% or more over 100 nm, which is the longest wavelength band. λ is the center wavelength in wavelength band Π1. S is the region enclosed by the spectral spectrum of wavelength band Π1 and the baseline of the reflectance. N is the total number of thermoplastic resin layers in the laminated film. The spectral spectrum described here refers to the spectral spectrum obtained by applying a 10-point averaging process to the reflectance spectral spectrum obtained by measuring at 1 nm intervals using a spectrophotometer in the reflectance-reflection spectral spectrum measurement described later in the examples. As will be explained in detail later, reflectance spectral data from 295 nm to 2505 nm can be obtained by obtaining reflectance data from 295 nm to 2505 nm using a spectrophotometer and averaging 10 consecutive data points.

[0065] The wavelength band Π1, which is located in the longest wavelength range and exhibits a reflectance of 20% or more for a continuous period, will be explained using Figures 4 to 7. In Figures 4 to 7, symbols 7 to 16 represent, respectively, the spectral spectrum, the area S of the wavelength band Π1, higher-order reflectance, the center wavelength λ of wavelength band Π1, λmin of wavelength band Π1, λmax of wavelength band Π1, the maximum reflectance of wavelength band Π1, the midpoint between the maximum reflectance and baseline reflectance of wavelength band Π1, the baseline, and the pulsation of the spectral spectrum. The spectral spectrum with symbol 7 is obtained by performing a 10-point averaging process. The reflectance wavelength band Π1, as shown in Figure 4, refers to the wavelength band located on the longest wavelength side among the wavelength bands that exhibit a reflectance of 20% or more for a continuous period of 100 nm or more in the wavelength range from 300 nm to 2500 nm in the spectral spectrum after the averaging process described above. As shown in Figure 5, if the reflection wavelength band includes even a portion where the reflectance is less than 20%, that region is used as the boundary, and the longer wavelength band where the reflectance is 20% or more is defined as PI1. Furthermore, as shown in Figure 6, if there is a longer wavelength band beyond 2500 nm where the reflectance is 20% or more, the portion included within the wavelength band between 300 nm and 2500 nm that exhibits a reflectance of 20% or more over a period of 100 nm or more is defined as PI1.

[0066] The area S of the region enclosed by the spectral spectrum of wavelength band Π1 and the baseline of the reflectance represents the area of ​​the shaded region shown in Figures 4-7. The numerical value of the area S of this region substantially represents the broadband and high reflectance performance of the laminated film. However, in the case of the laminated film of the present invention, even if the laminated film is manufactured through the same lamination process, the wavelength band shifts depending on the thickness of the laminated film. Therefore, the area of ​​region S alone cannot represent the effect of high reflectance and wide reflectance based on the configuration of the laminated film. In this invention, the area S is divided by the central wavelength λ of the wavelength band to cancel out the effect of wavelength band change due to the thickness of the laminated film and to represent the effect of high reflectance and wide reflectance based on the configuration of the laminated film. The central wavelength λ described here is the intermediate wavelength (Figure 4-6, 10) in the wavelength range of the reflectance band Π1 that shows the median value between the maximum reflectance of the reflectance band Π1 (13 in Figures 4-6) and the baseline (14 in Figures 4-6). The area S of a region can be calculated as follows: for example, a laminated film that reflects 90% of the wavelength band between 800 nm and 1200 nm (assuming a baseline reflectance of 10%) has an area S of (1200-800) nm × (90-10)% = 32000. However, if the thickness of the laminated film is halved, the wavelength band becomes between 400 nm and 600 nm, resulting in an area of ​​(600-400) nm × (90-10)% = 16000. Since the area changes even with the same laminated structure, it is not possible to represent the effect of wide reflectance band and high reflectance based on the laminated film configuration. Therefore, if we divide by the center wavelength λ of the wavelength band, which is 1000 nm for the former and 500 nm for the latter, we get S / λ = 32 in both cases. This makes it possible to compare the effect of wide reflectance band and high reflectance based on the laminated film configuration, even for laminated films that reflect different wavelength bands, without depending on the thickness of the laminated film.

[0067] S / (λ·N) is a value obtained by dividing the area S / center wavelength λ (the area enclosed by the spectral spectrum in wavelength band Π1 and the baseline of the reflectance) by the total number of layers. Therefore, if S / (λ·N) falls within this range, it indicates that a laminated film with high reflectivity and broadband reflection can be obtained with a low number of layers, which cannot be achieved with conventional techniques, especially with (AB)m laminated films that alternately laminate two types of thermoplastic resin layers. If S / (λ·N) is lower than 0.060, it means that the number of layers is excessively large, or that the slope of the layer thickness distribution is small and the reflection band is narrow. In the former case, the thickness of the laminated film becomes excessively large, which does not conform to the recent trend of thinning for optical films used in displays, for example. Furthermore, if the thickness of the laminated film becomes excessively large, it may not satisfy the handling requirements during post-processing or the processability of sputter deposition. In the latter case, the reflection band of the laminated film is insufficient, making it unsuitable for use in the applications described later.

[0068] On the other hand, if S / (λ·N) is higher than 0.300, it means that high reflectivity and a wide reflectivity band can be achieved with a small number of layers. To achieve this, it is necessary to increase the refractive index difference between the thermoplastic resin layers, and for this purpose, it is essential to laminate thermoplastic resin layers made of thermoplastic resins with completely different skeletal structures, which results in poor interlayer adhesion when a laminated film is formed. One method to mitigate the decrease in interlayer adhesion caused by this mechanism is to add a compound (modifier) ​​that has unreacted functional groups that react with unreacted functional group components contained in the other thermoplastic resin layer to which adhesion is to be improved. However, this may lead to a decrease in brightness due to the compatibility of the compound (modifier) ​​with the thermoplastic resin to which it is added. A more preferable range for S / (λ·N) is 0.080 to 0.200, even more preferably 0.080 to 0.150, and particularly preferably 0.090 to 0.130. Furthermore, considering that the laminated film will be used in applications where it is necessary to avoid a decrease in brightness, it is preferable to control S / (λ·N) to a suitable range without using the above-mentioned modifier.

[0069] As a method to set S / (λ·N) to a range satisfying 0.060≦S / (λ·N)≦0.300, or to the preferred range described above, examples include a method in which the laminated film is made by laminating three types of thermoplastic resin layers in a fixed repeating unit, and further, among the three or more types of thermoplastic resin layers, the thermoplastic resin layer with the highest refractive index and the thermoplastic resin layer with the lowest refractive index are combined to satisfy the preferred skeletal structure and refractive index conditions described above, or a method in which the lamination ratio of the three or more types of thermoplastic resin layers is designed to reduce the average reflectance of the wavelength bands Π2 and Π3 described later as optical thickness (lamination ratio).

[0070] The laminated film of the present invention preferably satisfies 35.0 ≤ S / λ ≤ 150.0. In addition to the most important S / (λ·N) range in the present invention, controlling the value of S / λ within the above numerical range indicates that the laminated film has sufficient light-cutting properties for practical use, despite having a low number of layers, high reflectivity, and a wide reflectivity band. If S / λ is 35 or greater, it indicates that the refractive index difference between the layer with the highest refractive index and the layer with the lowest refractive index among the layers constituting the laminated film is sufficient, resulting in high reflectivity, or that there is a sufficient wavelength band of Π1 with high reflectivity, thus achieving the wide reflectivity band targeted by the present invention. The upper limit of S / λ is set at 150 from the standpoint of feasibility.

[0071] The laminated film of the present invention preferably satisfies λmin ≥ λmax / 2, where λmin is the wavelength at the short-wavelength end of the wavelength band Π1 and λmax is the wavelength at the long-wavelength end. λmax and λmin correspond to numbers 11 and 12 in Figures 4-7, respectively, and are represented by the minimum and maximum wavelengths within the wavelength band that represent the midpoint between the maximum reflectance value of the wavelength band Π1 and the baseline reflectance. By satisfying this wavelength relationship, it is possible to design the film so that the primary and secondary reflection bands, and the secondary and quaternary reflection bands, do not completely overlap. If the laminated film is designed to satisfy λmin < λmax / 2, a specific decrease / increase in reflectance occurs in the wavelength band where the reflection bands overlap. As a result, the reflectance becomes lower, making it impossible to obtain sufficient light blocking performance. Furthermore, if the wavelength band where the reflection bands overlap falls within the visible light region, the increased reflectance in the overlapping portion may cause undesirable coloration, reduction in brightness or color tone, and reduction in the reflection effect. Furthermore, a characteristic of laminated films using interference reflection theory is the wavelength band shift at oblique viewing angles, which can sometimes result in undesirable color changes depending on the viewing angle. This wavelength relationship can be altered by changing the number of layers in the laminated film and the slope of the layer thickness distribution, thereby changing the reflection wavelength bandwidth. Specifically, reducing the number of layers, making the slope of the monotonically increasing layer thickness distribution gentler, or making the layer thickness distribution monotonically increasing in two stages can easily achieve λmin≧λmax / 2.

[0072] The laminated film of the present invention is constructed by laminating three or more types of thermoplastic resins in a geometric arrangement to suppress higher-order reflections that cannot be achieved by alternating lamination of two types, and from the viewpoint of realizing a wide reflection band, it is preferable that the average reflectance in the wavelength band Π2, which is 300 nm or more and λmax / 5 or more and λmin / 2 or less, is 25% or less. This wavelength band Π2 corresponds to a wavelength band that includes a portion of the third and fourth-order reflections. Needless to say, this requirement cannot be met unless the λmin of the wavelength band Π1 is 600 nm or more. As mentioned above, the presence of higher-order reflections is effective in improving the average reflectance of the reflection band Π1 and the transparency of the infrared cut film, so it is preferable to suppress higher-order reflections in this wavelength band Π2 as well. From the above viewpoint, the average reflectance in the wavelength band Π2 is more preferably 20% or less, and most preferably, although the numerical value cannot be limited, it is that higher-order reflections are completely suppressed and the average reflectance is the same as the baseline reflectance when calculating the area S in the first-order reflection. By reducing the reflectivity in the higher-order reflection band Π2, which cannot be achieved with conventional laminated films that alternately laminate two types of thermoplastic resin layers, it is possible to further expand the reflection band in the wavelength band Π1 while maintaining the transparency of the laminated film. This makes it possible to further improve the heat-cutting properties of the heat-reflective film.

[0073] To achieve an average reflectance of 25% or less in the wavelength band Π2, it is sufficient to reduce the reflectance of the third and fourth-order reflectors. For example, in a laminated film having a repeating unit of (ABCB)m, this can be achieved by adjusting the lamination ratio of layers mainly composed of different thermoplastic resins. More specifically, this can be achieved by setting the lamination ratio of layer A to layer B (A / B) to 0.50 or more and 1.50 or less (preferably 0.75 or more and 1.50 or less), and the lamination ratio of layer C to layer B (C / B) to 0.75 or more and 1.50 or less. Furthermore, in order to achieve the above, it is preferable to adopt a layer configuration of (ABCB)m when there are three types of layers. Note that the lamination ratio referred to here represents the value obtained by calculating the ratio of the total layer thickness of each thermoplastic resin layer analyzed by the layer thickness analysis evaluation method described later. The lamination ratio will be interpreted similarly below.

[0074] Another method for achieving an average reflectance of 25% or less in the wavelength band PI2 is to add a light absorber having absorption properties in the said wavelength band PI2, or to use a thermoplastic resin that absorbs the said wavelength band. Examples of thermoplastic resins that absorb the latter wavelength band include polyethylene terephthalate that absorbs wavelengths between 300 nm and 320 nm, and polyethylene naphthalate that absorbs wavelengths between 300 nm and 370 nm. However, when the said wavelength is absorbed by a thermoplastic resin, there is a problem that the thermoplastic resin itself will degrade from light during long-term use, causing a change in refractive index and impairing the original optical and mechanical properties of the laminated film. In this case, it is preferable to provide an ultraviolet absorption layer on the outermost surface of the laminated film to protect the thermoplastic resin from ultraviolet rays, or to include an ultraviolet absorber and weather stabilizers (antioxidants, light stabilizers HALS, quenchers) in the thermoplastic resin.

[0075] The laminated film of the present invention preferably has an average reflectance of 25% or less in the wavelength band Π3, which is between λmin / 2 and λmax / 2, corresponding to a half-wavelength band of the wavelength band Π1. This wavelength band Π3 corresponds to the second-order reflection band and a portion of the third-order reflection band relative to the first-order reflection band Π1. As mentioned above, the occurrence of higher-order reflections can lead to a decrease in the reflectance of the first-order reflection, which may impair the high reflectance and wide reflectance band that are characteristics of the laminated film of the present invention. Therefore, it is preferable to have an average reflectance of 25% or less in the wavelength band Π3, so that higher-order reflections of the second and third orders do not occur. From the above viewpoint, the average reflectance in the wavelength band Π3 is more preferably 20% or less. Most preferably, although the numerical value cannot be limited, higher-order reflections are completely suppressed, and the average reflectance is the same as the baseline reflectance when calculating the area S in the wavelength band Π1.

[0076] To achieve an average reflectance of 25% or less in the wavelength band Π3, for example, in a (ABCB)m laminated type, this can be achieved by adjusting the lamination ratio of layers mainly composed of different thermoplastic resins to reduce the reflectance of secondary and tertiary reflections. In particular, by setting the lamination ratio of layer A to layer B to 0.5 or more and 3.0 or less, or the lamination ratio of layer C to layer B to 0.5 or more and 1.5 or less, secondary and tertiary reflections can be suppressed, and the average reflectance of the wavelength band Π3 can be set to 25% or less.

[0077] Furthermore, in the laminated film of the present invention, in the (ABCB)m laminated type, it is preferable that the lamination ratio of layer A to layer B in the repeating unit (A / B) is 0.50 or more and 1.50 or less, and the lamination ratio of layer C to layer B (C / B) is 0.90 or more and 1.30 or less. By satisfying this range of lamination ratios for each layer, it becomes easier to effectively suppress higher-order reflections even when the preferred refractive index condition equation (4) for suppressing higher-order reflections can no longer be satisfied due to fluctuations in lamination ratio conditions such as discharge fluctuations of the extruder during film formation, or fluctuations in refractive index conditions due to fluctuations in process conditions such as stretching ratio, stretching temperature, and heat treatment temperature. In addition, since the thickness of each layer in the laminated film of the present invention is at the nm level, it is not practical to precisely control the thickness of each layer constituting all (ABCB) repeating units included in the laminated film as designed, depending on the design of the lamination apparatus, and slight differences may occur in the ratio of layer thicknesses of the multiple repeating units included in the laminated film. By controlling A / B and C / B within the above ranges, the effects of fluctuations in the layer thickness ratio of repeating units can be reduced, and a laminated film with stable suppression of higher-order reflections can be obtained.

[0078] In particular, the above-mentioned ranges of A / B and C / B are suitable lamination ratios for suppressing higher-order reflections such as secondary and tertiary reflections. From this viewpoint, it is more preferable that the lamination ratio (A / B) is 0.80 or more and 1.10 or less, and the lamination ratio (C / B) is 1.00 or more and 1.30 or less. By controlling the lamination ratio of each layer to the above-preferred range, it is often possible to suppress the average reflectance of the reflection band caused by higher-order reflections such as secondary and tertiary reflections to 20% or less. Therefore, even when these higher-order reflection bands exist in the wavelength band of visible light, it is possible to obtain a laminated film with suppressed coloration and high transparency.

[0079] Furthermore, A / B and C / B can be controlled to a desirable range by adjusting the design of the lamination device, such as the slit gap and length, or by controlling the discharge rate ratio of the extruder that dispenses the thermoplastic resin forming each thermoplastic resin layer.

[0080] The laminated film of the present invention may contain light absorbers (ultraviolet absorbers, dyes, pigments, heat absorbers), antioxidants, light stabilizers, quenchers, heat-resistant stabilizers, weather-resistant stabilizers, organic lubricants, organic or inorganic fine particles, fillers, antistatic agents, nucleating agents, flame retardants, etc., to the extent that they do not degrade the inherent properties of the film. In particular, depending on the type of thermoplastic resin, high-energy ultraviolet light may be absorbed, accelerating degradation; therefore, it is preferable to include an ultraviolet absorber for the purpose of suppressing photodegradation by causing reaction competition. Furthermore, the light absorber itself may be affected by degradation due to heat and oxygen during the resin extrusion process, and by photodegradation due to reaction with ultraviolet light and oxygen. Therefore, it is preferable to add antioxidants to the thermoplastic resin that may degrade, and light stabilizers or quenchers to the thermoplastic resin that may degrade, to address the former.

[0081] When designing the laminated film of the present invention as a metallic-looking film that highly reflects the entire visible light spectrum, it is preferable that the lightness L* in the transmitted color tone measurement is 70 or less and the haze is 5.0% or less. A lightness L* of 70 or less indicates low transparency, and a haze of 5.0% or less indicates no diffuse light, which represents a metallic look that reflects only parallel light rays, rather than the white color associated with light diffusion. When light is absorbed and the color approaches black, the lightness decreases, but in that case, the reflectance also decreases, and therefore the condition 0.060 ≤ S / (λ·N) ≤ 0.300 is usually not satisfied. A lower lightness L* indicates lower transparency and a stronger metallic look, so it is preferable that it be 50 or less. A lower value for lightness L* indicates less light transmission, and therefore exhibits desirable performance as a metallic-looking reflective film, so it is preferable that the lightness L* is 0.1 or higher. A lower haze value indicates lower light diffusion of the film itself, so it is more preferably 3.0% or less, and even more preferably 1.0% or less. A lower haze value means less light diffusion and indicates that the interference reflection characteristics of the present invention are sufficiently present, so it is preferable that it is 0.1% or more.

[0082] To satisfy the aforementioned brightness L* and haze, for example, this can be achieved by controlling the film thickness so that the reflection wavelength band Π1 falls within the visible light region, while maintaining the optical thickness condition that satisfies the aforementioned S / (λ·N). Alternatively, when using higher-order reflection to achieve high reflection in the visible light region, for example, if the repeating unit is (ABC)m, it is effective to satisfy the stacking ratio of layer A / layer B being 1.0 or less and the stacking ratio of layer C / layer B being 0.75 or less, or if the repeating unit is (ABCB)m, satisfying the stacking ratio of layer A / layer B or layer C / layer B being 4 or more.

[0083] The laminated film of the present invention exhibits a wider reflectivity and higher reflectivity than conventional laminated films with a multilayer structure, making it suitable for applications where strong shielding and coloration of ultraviolet light, visible light, and heat rays over a wide range are desired. For example, it can be used as window film in automotive and building materials applications, as a metallic-looking decorative film for exterior and interior use in home appliances, electronic devices, and automobiles, as a film for laminating steel plates for signs and other industrial materials, as a light-cutting film for laser surface processing, as a process and release film for photolithography materials in electronic devices, as an optical film for various image display devices such as smartphones, head-up displays, electronic paper, and digital signage, and in other fields such as food, medical, and ink, as a film for suppressing light degradation of contents. In terms of usage, it can be used by post-application or by in-mold molding or insert molding as a molded body. That is, the molded body of the present invention is made using the laminated film of the present invention.

[0084] The image display device, window, exterior material for transportation vehicles, and transportation vehicle of the present invention will be described below.

[0085] The laminated film and molded article of the present invention can be preferably used as an optical film for an image display device. In other words, the image display device of the present invention comprises the laminated film or molded article of the present invention. Various display methods are used as image display devices, such as liquid crystal display devices, organic EL display devices, quantum dot displays, and digital signage for outdoor use, and various functional films are arranged inside these displays.

[0086] The laminated film of the present invention can be used, for example, as the films shown below in each image display device. In the case of a liquid crystal image display device, examples include polarizer protection films and phase difference films that constitute a polarizing plate, surface treatment films that are bonded to the front of the display to add functionality, brightness enhancement films that are placed directly above the backlight light guide plate, specular reflection films used on the back of the backlight light guide plate, transparent conductive substrate films used for ITO, etc., and ultraviolet protection films for touch sensor components. In the case of an organic EL display device, examples include λ / 4 phase difference films and polarizer protection films that constitute a circular polarizing plate that is placed on the viewing side (above) the light-emitting layer, surface treatment films that are bonded to the front of the display to add functionality, and various optical films that are built in for the purpose of protecting the contents from external light. In the case of a quantum dot display, there are mainly two types: a quantum dot liquid crystal display that includes a liquid crystal panel equipped with a color filter for dimming, and a quantum dot organic EL display that combines a blue organic EL layer with a color filter. These are variations in which the backlight portion of the liquid crystal image display device or the light-emitting layer portion of the organic EL display device has been replaced with a quantum dot structure. Therefore, in these displays as well, the laminated film of the present invention can be used in the same arrangement and application as the liquid crystal image display layer and various films used in organic EL display devices described above. In image display devices such as digital signage used outdoors, it is necessary to suppress deterioration of the inside of the image display device from both heat rays and ultraviolet rays. By using the laminated film of the present invention, which can control higher-order reflections, it is possible to design the film so that Π1 is in the infrared region and specific higher-order reflections are in the ultraviolet region, thereby creating a film that effectively shields both wavelength bands. Furthermore, as an image display device equipped with the molded body of the present invention, for example, an example is in which the laminated film of the present invention is used in the housing as a decorative film that produces a metallic color.

[0087] The window of the present invention comprises the laminated film of the present invention or the molded article of the present invention. For example, by using a laminated film of the present invention having a reflectance band in the near-infrared region for window applications, it is possible to reduce the rise in indoor temperature, improve cooling efficiency, save energy, and improve vehicle fuel efficiency. More preferably, the laminated film has some higher-order reflection occurring in the ultraviolet region, or contains an ultraviolet absorber or the like within the laminated film, so that both near-infrared and ultraviolet rays can be blocked. A window equipped with such a laminated film can effectively reduce not only the rise in indoor temperature but also the burning sensation on the skin caused by sunlight and sunburn caused by ultraviolet rays. Furthermore, there are no restrictions on the color tone of the laminated film or molded article of the present invention, such as color or transparent glass, and a product that has the ability to reflect or block a specific wavelength band can be used as appropriate for applications where it is desired to block specific light.

[0088] In particular, vehicle windows, such as those for automobiles, are subject to strict requirements for high transparency. Therefore, the laminated film of the present invention is preferable because it can achieve high transparency compared to current heat-absorbing window materials that partially block visible light due to the absorption properties of heat-absorbing agents. In vehicle applications, the laminated film of the present invention may be used as an interlayer material for laminated glass in window materials such as front windshields, door windows, side windows, delta windows, rear windows, and sunroofs, and can also be applied to the surface of each of the above windows as an aftermarket part. Furthermore, an example of a molded body incorporating the present invention is a window material that uses a high-strength resin such as polycarbonate as a substitute for glass, in line with recent trends in weight reduction and diverse design possibilities. Such a window material can also be obtained by integrally molding it together with the laminated film of the present invention.

[0089] Windows that can use the laminated film or molded product of the present invention include, in addition to vehicles such as automobiles, windows for building materials and fixtures. In the case of windows for building materials and fixtures, materials that can be combined with the laminated film of the present invention include glass, resin, and other materials, similar to those used for windows in vehicles such as automobiles.

[0090] The exterior material for transportation vehicles of the present invention comprises the laminated film of the present invention or the molded body of the present invention. Transportation vehicles refer to powered vehicles and other means of movement and transport such as vehicles, aircraft, ships, and unmanned aerial vehicles, and exterior material for transportation vehicles refers to materials that can be used on the exterior of transportation vehicles (materials that can be used on the interior are also included if they can be used on the exterior). Specific examples of exterior material for transportation vehicles include emblems, front grilles, and bumpers.

[0091] Examples of using the laminated film or molded body of the present invention for vehicle exterior materials include applying the laminated film of the present invention to automotive exterior materials such as emblems, front grilles, and bumpers, and using a molded body in which the laminated film of the present invention and a high-strength resin such as polycarbonate are integrally molded. Conventionally, metal materials have been used for the above-mentioned automotive exterior materials, but with the spread of autonomous driving technologies using millimeter-wave radar and LIDAR (Light Detection and Ranging), problems have arisen such as the inability to obtain collision prevention effects by recognizing obstacles and vehicles ahead, which should be provided, due to radar reflection loss in metal materials used for vehicle exteriors. In order to solve these problems, it is expected that the above-mentioned automotive exterior materials will be replaced with non-metallic materials that exhibit a metallic appearance, and the laminated film or molded body of the present invention can be preferably used for such applications.

[0092] The transportation system of the present invention comprises the laminated film of the present invention, the molded body of the present invention, the window of the present invention, or the exterior material of the transportation system of the present invention. For example, the laminated film or molded body of the present invention may be used as a material for a heat-shielding window, or as a material for an emblem, front grille, bumper, etc., in order to prevent temperature rise inside the vehicle or housing. For example, as a laminated film of the present invention that can be suitably used as a heat-shielding window material, it is preferable to design the wavelength band Π1 to be in the near-infrared region and suppress higher-order reflections occurring in the visible light region.

[0093] Next, other applications of the laminates and molded articles of the present invention will be described. In applications for automobiles, home appliances, and electronic devices, metallic optical properties can be imparted to molded articles by insert molding or in-mold molding. However, with conventional laminated films, localized elongation during molding can cause changes in the thickness of the laminated film, leading to a shift in the wavelength band and loss of metallic properties due to thinning. The laminated film of the present invention is a broadband reflective laminated film having a reflection band not only in the visible light region but also in the longer wavelength region, making it easy to maintain the metallic properties even after the laminated film has been stretched by molding. In addition, examples of using metallic visible light reflective films or molded articles equipped therewith can be given for decorative applications (garnish materials) in automotive interiors. In this case, by setting the wavelength band Π1 of the laminated film of the present invention to the entire visible light range, it is possible to create a metallic film with a lower number of layers and thinner film thickness than conventional films, while maintaining good adhesion.

[0094] Next, a preferred method for manufacturing the laminated film of the present invention will be described below. Of course, the present invention is not limited to these examples.

[0095] The thermoplastic resins constituting each layer of the laminated film are prepared in the form of pellets or the like. The pellets are dried in hot air or under vacuum as needed and then supplied to separate extruders. If additives are included in the thermoplastic resin, the powdered, granular, or liquid additives may be kneaded and dispersed during the extrusion process, or a master pellet in which the additives have been dispersed in the thermoplastic resin beforehand may be supplied. Inside the extruder, each thermoplastic resin, heated and melted above its melting point, is uniformly extruded using a gear pump or the like, and foreign matter and modified resin are removed through a filter or the like. These thermoplastic resins form the desired laminate via a lamination device and are then extruded from a die in the form of a sheet. The sheet extruded from the die is then pushed onto a cooling body such as a casting drum, cooled and solidified to obtain a cast sheet. At this time, it is preferable to use electrodes such as wire, tape, needle, or knife to rapidly cool and solidify the sheet by making it adhere to the cooling body such as a casting drum using electrostatic force. Furthermore, methods such as blowing air from a slit-shaped, spot-shaped, or surface-shaped device to bring the material into close contact with a cooling body such as a casting drum and rapidly cool and solidify it, or using a nip roll to bring the material into close contact with a cooling body and rapidly cool and solidify it, are also preferred. As an auxiliary measure, a highly wettable liquid such as liquid surfactant water or liquid paraffin can be applied to the surface of the casting drum to provide adhesion.

[0096] Multiple types of thermoplastic resins constituting the laminated film are fed from different channels using more extruders than the number of thermoplastic resin layers, and are sent to a multilayer lamination device before being extruded in sheet form. While multi-manifold dies, feed blocks, and static mixers can be used as the multilayer lamination device, it is particularly preferable to use a feed block with fine slits to efficiently obtain a multilayer laminated structure. Using such a feed block prevents the device from becoming excessively large, resulting in less foreign matter generation due to thermal degradation, and enabling high-precision lamination even with an extremely large number of layers. Furthermore, the lamination accuracy in the width direction is significantly improved compared to conventional technology. In addition, this device allows for adjustment of the thickness of each layer by the shape (length and width) of the slits, making it possible to achieve any desired layer thickness. The molten multilayer laminated sheet formed in this way is then guided to a die, and a cast sheet is obtained as described above.

[0097] The cross-sectional shape of the channel of the single pipe used to guide the laminate to the die preferably has a high aspect ratio, where the ratio of the widthwise length of the channel to the thickness of the channel is 5 or more. When the laminate flows through the single pipe, a difference in flow velocity generally occurs near the wall surface of the single pipe and in the center of the single pipe due to the shear force received by the wall surface. In particular, at the ends in the widthwise direction of the single pipe, the effect of the flow velocity difference due to the wall surface in the widthwise direction of the single pipe is added, resulting in a complex swirling resin flow and lamination turbulence. If a single pipe with a small aspect ratio of the channel cross-section is used, the effect of resin flow turbulence at the widthwise position of the single pipe also affects the area near the center in the widthwise direction, resulting in a laminated film with greater lamination turbulence in the film width direction. Furthermore, in the case of a laminate with three or more types of thermoplastic resin layers, as in the present invention, the viscoelastic behavior of each thermoplastic resin constituting the layer often differs. If a single pipe with a channel cross-section with a low aspect ratio, which is prone to generating resin flow velocity differences, is used, the lamination turbulence may become more pronounced due to the combination of changes in viscoelastic behavior. Therefore, in order to obtain a laminated film with minimal lamination disorder in the film width direction, it is preferable that the cross-sectional shape of the single-pipe channel exhibits the highest possible aspect ratio, more preferably 10 or more, and even more preferably 20 or more. If the aspect ratio of the single-pipe channel cross-section is extremely high, the length of the channel in the width direction becomes very long, leading to an increase in the size of the device in the film width direction, or the thickness of the channel becomes very thin, which can lead to problems such as being strongly affected by the difference in flow velocity on the wall surface of the single pipe, not just at the width direction position of the single pipe, resulting in large lamination thickness disorder in the thickness direction throughout the film. For this reason, it is practical to set the upper limit of the aspect ratio to 100 or less.

[0098] The obtained cast sheet is preferably subsequently biaxially stretched in the longitudinal and width directions. The stretching may be performed sequentially or simultaneously. Furthermore, it may be re-stretched in the longitudinal and / or width directions. Here, the longitudinal direction refers to the direction in which the film travels, and the width direction refers to the direction perpendicular to the longitudinal direction within the film plane.

[0099] First, let's explain the case of sequential biaxial stretching. Here, stretching in the longitudinal direction refers to uniaxial stretching to give the sheet a longitudinal molecular orientation, which is usually done by the difference in peripheral speed of the rolls and may be done in one stage or in multiple stages using multiple pairs of rolls. The stretching ratio varies depending on the type of resin, but is usually preferably 2 to 15 times. For example, when polyethylene terephthalate or polyethylene naphthalate, which are crystalline thermoplastic resins preferably used in the laminated film of the present invention, are used, a stretching ratio of 2 to 7 times is particularly preferred. Furthermore, the stretching temperature is preferably set within the range of the glass transition temperature of the resin with the highest glass transition temperature among the resins constituting the laminated film to the glass transition temperature + 100°C. If the orientation is strongly oriented in the longitudinal stretching process, neck-down in the film width direction occurs, which may result in insufficient film width, and may also lead to greater thickness unevenness and transmission spectrum unevenness in the longitudinal and / or width direction after widthwise stretching.

[0100] The uniaxially stretched laminated sheet obtained in this manner is subjected to surface treatments such as corona treatment, flame treatment, or plasma treatment as needed, and then an easy-adhesion layer with functions such as slipperiness, easy adhesion, and antistatic properties is applied by in-line coating. In the in-line coating process, the easy-adhesion layer may be applied to one side of the laminated film, or it may be applied to both sides of the laminated film simultaneously or sequentially to one side at a time.

[0101] Next, the uniaxially stretched laminated sheet is stretched in the width direction. Stretching in the width direction refers to stretching to give the sheet a width-direction orientation, and is usually performed using a tenter, while gripping both ends of the sheet in the width direction with clips during transport. The stretching ratio varies depending on the type of resin, but is usually 2 to 15 times, and for example, when polyethylene terephthalate or polyethylene naphthalate, which are crystalline thermoplastic resins preferably used in the laminated film of the present invention, is used, a stretching ratio of 2 to 7 times is particularly preferred. Furthermore, the stretching temperature is preferably between the glass transition temperature of the resin with the highest glass transition temperature among the resins constituting the laminated film and the glass transition temperature + 120°C.

[0102] The biaxially stretched laminated film is then subjected to a heat treatment in a tenter, where it is heated above the stretching temperature but below its melting point. After uniform slow cooling, it is cooled to room temperature and wound up. If necessary, a relaxation treatment in the longitudinal and / or widthwise directions may be used in conjunction with the slow cooling after the heat treatment to impart thermal dimensional stability.

[0103] Next, we will explain the case of simultaneous biaxial stretching. In the case of simultaneous biaxial stretching, the obtained cast sheet may be subjected to surface treatments such as corona treatment, flame treatment, or plasma treatment as needed, and then functions such as slipperiness, adhesion, and antistatic properties may be imparted by in-line coating. In the in-line coating process, the adhesion layer may be applied to one side of the laminated film, or it may be applied to both sides of the laminated unit simultaneously or sequentially to one side at a time.

[0104] Next, the cast sheet is guided to a simultaneous biaxial tenter, where it is transported while gripping both ends in the width direction with clips, and stretched simultaneously and / or in stages in the longitudinal and width directions. Simultaneous biaxial stretchers include pantograph type, screw type, drive motor type, and linear motor type, but the drive motor type or linear motor type is preferred because the stretching ratio can be arbitrarily changed and relaxation processing can be performed at any point. The stretching ratio varies depending on the type of resin, but usually an area ratio of 6 to 50 times is preferred, and when polyethylene terephthalate or polyethylene naphthalate, which are crystalline thermoplastic resins preferably used in the laminated film of the present invention, an area ratio of 8 to 30 times is particularly preferred. The stretching speed may be the same speed, or the longitudinal and width directions may be stretched at different speeds. Furthermore, the stretching temperature is preferably between the glass transition temperature of the resin with the highest glass transition temperature among the resins constituting the laminated film and the glass transition temperature + 120°C.

[0105] The sheet, thus simultaneously biaxially stretched, is preferably subjected to further heat treatment in a tenter, above the stretching temperature but below the melting point, in order to impart flatness and dimensional stability. During this heat treatment, it is preferable to instantly loosen the sheet in the longitudinal direction immediately before and / or immediately after entering the heat treatment zone in order to suppress the distribution of the main orientation axis in the width direction. After heat treatment in this manner, the sheet is uniformly cooled slowly and then cooled to room temperature before being wound up. If necessary, loosening may also be performed in the longitudinal and / or width directions during slow cooling after heat treatment. Alternatively, instantaneous loosening may be performed in the longitudinal direction immediately before and / or immediately after entering the heat treatment zone.

[0106] The laminated film obtained in the manner described above is trimmed to the required width via a winding device and wound up in a roll to prevent winding creases. Furthermore, embossing may be applied to both ends of the sheet during winding to improve its appearance.

[0107] The thickness of the laminated film of the present invention is not particularly limited, but is preferably 5 μm to 100 μm. Considering the trend towards thinner films of various functional films and the high-end characteristic of flexibility, it is preferably 80 μm or less, and more preferably 50 μm or less. Although there is no lower limit, in practice, a thickness of 10 μm or more is preferable to ensure stable roll winding and tear-free film formation.

[0108] Furthermore, the outermost surface of the laminated film of the present invention may be laminated with a hard coat layer mainly composed of a curable resin to add functions such as scratch resistance, dimensional stability, and adhesion. When the laminated film is transported by roll-to-roll for mounting to a product, scratches on the surface of the laminated film can be prevented due to friction between the roll and the film. Moreover, even if the resin oligomer components in the laminated film or various additives that can be added to the laminated film may bleed out during high-temperature heat treatment, providing a hard coat layer on the outermost surface allows the hard coat layer with a high crosslink density to exhibit a precipitation suppression effect. In addition, by laminating a curable resin layer, dimensional changes of the film due to heat treatment can be suppressed, and the increase in film thickness due to thermal shrinkage and the resulting changes in optical properties such as the transmission spectrum of the laminated film can be suppressed.

[0109] Since the hard coat layer has superior properties in this laminated film, it is preferable to apply it to at least one side of the laminated film to maintain the film's properties, particularly its dimensions. Although it is possible to apply the hard coat layer to both sides of the laminated film, adhesion between the hard coat layers may worsen the film's slipperiness and, consequently, its roll winding ability. Therefore, it is preferable to apply the hard coat layer to only one side, or, if applied to both sides, to perform surface treatment such as particle addition or atmospheric plasma / vacuum plasma treatment on at least one of the hard coat layers to impart slipperiness.

[0110] The hard coat layer can be laminated directly onto the outermost surface of the laminated film, but it is more preferable to laminate it via an inline coating layer. When there is a large difference in refractive index between the hard coat layer and the thermoplastic resin on the outermost surface of the laminated film, it is preferable to adjust the refractive index of the inline coating layer to improve the adhesion between the two. The refractive index of the inline coating layer is preferably a value between the refractive index of the thermoplastic resin A layer constituting the laminated film and the refractive index of the curable resin constituting the hard coat layer, and more preferably a value between the refractive indices of the two resins (where α is the refractive index of thermoplastic resin A and β is the refractive index of the curable resin constituting the hard coat layer, then 0.98 × (α + β) / 2 or more and 1.02 × (α + β) / 2 or less). For example, when polyethylene terephthalate is used as the thermoplastic resin located on the outermost surface of the laminated film and acrylic resin is used as the curable resin, the refractive index difference is large, with the former having a refractive index of about 1.65 and the latter having a refractive index of about 1.50, which may cause poor adhesion. Therefore, the refractive index of the inline coating layer is preferably 1.50 or more and 1.60 or less, and more preferably 1.55 or more and 1.58 or less.

[0111] The curable resin that can be used for the hard coat layer is preferably highly transparent and durable. For example, acrylic resin, urethane resin, fluororesin, silicone resin, polycarbonate resin, and vinyl chloride resin can be used individually or in combination. In terms of curability, flexibility, and productivity, the curable resin is preferably an active energy ray curable resin such as acrylic resin, represented by polyacrylate resin. Furthermore, when scratch resistance is to be added, the curable resin is preferably a thermosetting urethane resin.

[0112] In this invention, the term "active energy rays" refers to various electromagnetic waves that polymerize acrylic vinyl groups, such as ultraviolet rays, electron beams, and radiation (alpha rays, beta rays, gamma rays, etc.). Practically speaking, ultraviolet rays are the simplest and most preferred. As ultraviolet light sources, ultraviolet fluorescent lamps, low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, xenon lamps, carbon arc lamps, etc., can be used. When curing with an ultraviolet light source, it is preferable to keep the oxygen concentration as low as possible to prevent oxygen inhibition, and curing under a nitrogen atmosphere or an inert gas atmosphere is even more preferable. In the case of the electron beam method, although the equipment is expensive and operation under an inert gas is required, it is advantageous because it does not require the inclusion of photopolymerization initiators or photosensitizers. [Examples]

[0113] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Each characteristic was measured by the following method.

[0114] (Methods for measuring characteristics and evaluating effects) The method for measuring the characteristics and evaluating the effects in this invention is as follows.

[0115] (1) Layer composition The layer thickness distribution of the laminated film was determined by observing samples thinned using an ultramicrotome with a transmission electron microscope (TEM). Specifically, a JEM-1400 Plus transmission electron microscope (manufactured by JEOL Ltd.) was used to observe the cross-section of the laminated film under an acceleration voltage of 100kV. Cross-sectional images were obtained to measure the layer structure (number of layers, repeating unit, layer thickness distribution) and the thickness of each layer. To obtain a large contrast difference between layers, a staining technique using an electron staining agent (such as RuO4) was employed. Furthermore, depending on the thickness of each layer, observations were performed at direct magnifications of 40,000x for thin film layer thicknesses less than 100nm, 20,000x for thin film layer thicknesses between 100nm and 500nm, and 1,000x to 10,000x depending on the thickness for thicknesses of 500nm or more, and the layer thickness distribution was analyzed. Based on the contrast difference of the obtained images, the number of layers, repeating unit, layer thickness of each layer, and layer ratio were determined. The lamination ratio was calculated by determining the total thickness of each thermoplastic resin layer constituting the laminated film relative to the thickness of the layers excluding the outermost layer, and then determining the ratio to a specific thermoplastic resin layer. For example, the lamination ratio of layer A to layer B (A / B) and the lamination ratio of layer C to layer B (C / B) were calculated from the ratio of the total thickness of thermoplastic resin layers A and C to the total thickness of thermoplastic resin layer B included in the laminated film.

[0116] (2) Layer interface (contrast difference) (1) The cross-sectional images obtained from the transmission electron microscope observation were converted into compressed image files (JPEG), and position-luminance data was acquired by line profiling using ImagePro-10 (distributed by Hakuto Co., Ltd.) along the thickness direction of the laminated film. Subsequently, a 5-point moving average was applied to the profile obtained by plotting the relationship between position and luminance using spreadsheet software (Microsoft Excel® 2016). The averaging process was performed by averaging the luminance for five consecutive measurement positions, and then repeating the same calculation by changing the position one point at a time to obtain the averaged position-luminance profile. In the obtained averaged position-luminance profile, the position enclosed by inflection points where the slope changes from positive to negative or from negative to positive was determined to be a single layer. For each layer obtained using this method, position-luminance data was then acquired in the planar direction of the laminated film (direction perpendicular to the thickness direction). After calculating the average value and standard deviation of the luminance obtained for each layer, if the difference between the average values ​​of the luminances of two adjacent layers was greater than either of the standard deviations of the luminances of the adjacent thermoplastic resin layers, it was determined that these two adjacent layers were different. Furthermore, the difference in position (distance) between the inflection points was calculated as the layer thickness of each layer.

[0117] (3) Reflectance and Reflectance Spectroscopic Measurement A 4cm square sample was cut from the center of the laminated film in the width direction, and one side of the laminated film was treated with black lacquer spray to create a black back surface. Three coats of black coating were applied to the back surface to completely block light transmission. A Hitachi High-Tech Science U-4100 spectrophotometer was used to measure the reflectance spectrum of the sample with the untreated side facing the light source and fixed to the opening on the back of the integrating sphere. For the measurement, a standard white aluminum oxide plate (included with the main unit) was attached to the integrating sphere provided with the instrument, and background correction was performed. Reflectance spectra in the wavelength range of 295nm to 2505nm were measured continuously with the slit set to 2nm (visible) / automatic control (infrared), the infrared-visible light source switching wavelength set to 850nm, the gain set to 2, the scan speed set to 600nm / min, and the sampling pitch set to 1nm.

[0118] (4) Averaging of the reflectance spectral data, and calculation of S and λ For the 1nm pitch reflectance spectral data obtained in the reflectance measurement described in (3) above, the average transmittance data of 10 points before and after the peak was calculated. (For example, for data from 295nm to 304nm, the average transmittance data at 299.5nm is calculated. This process is continued up to 2505nm, calculating data at 1nm pitches from 299.5nm to 2500.5nm.) Then, the average of two adjacent points was calculated in sequence (for example, the average transmittance data at 300nm was calculated from the average of 299.5nm and 300.5nm), and by repeating the same calculation, 10-point averaged reflectance spectral data from wavelengths 300nm to 2500nm was obtained. This data was graphed with wavelength in nm on the horizontal axis and reflectance % on the vertical axis, and the area S and center wavelength λ were determined.

[0119] (5) Cross-cut peeling rate The adhesion (cross-cut) test method specified in JIS K 5600-5-6 (1999) was used for evaluation. Using a COTEC CCJ-1 cross-cut guide with 1 mm spacing, 11 orthogonal cuts were made vertically and horizontally at angles of 20-30° using an NT cutter, creating a grid of 100 squares. 24 mm wide Nichiban "Sellotape" (registered trademark) was applied to each square, and the tape was quickly peeled off at an angle of approximately 60°. The number of squares that were completely peeled off was recorded. This process was repeated 10 times, and the peel rate was calculated by averaging the results.

[0120] (6) Peel strength test A strip-shaped sample measuring 200 mm in length and 10 mm in width was cut out. A cutter was used to make an incision at one end of the sample, and approximately 50 mm was peeled off to create a peeling point. A Shimadzu Corporation Autograph AG-IS precision universal testing machine was used as the tensile testing machine, and the peeled portion was fixed by clamping it with upper and lower clips. The distance between the chucks was set to 50 mm and the crosshead movement speed to 100 mm / min. After the sample came to a standstill, the crosshead was moved to obtain the SS curve of the peel strength. From the obtained SS curve, the stress in the region where the strength was stable, as shown in Figure 2, was read and defined as the peel strength. This process was repeated five times, and the average value was taken as the peel strength of the sample.

[0121] (7) Differential scanning calorimetry (DSC) A differential scanning calorimeter EXSTAR DSC6220 manufactured by Hitachi High-Technologies Corporation was used. Measurements and temperature readings were performed in accordance with JIS-K-7122 (1987). Approximately 5 mg of the sample was heated from 25°C to 300°C at a rate of 10°C / min on an aluminum tray. The microcrystalline melting temperature (°C), which shows a small endothermic peak different from the melting point at a temperature higher than the glass transition temperature at the intersection of the baseline when heating from room temperature and the tangent at the inflection point of the step transition portion, was read. The enthalpy of fusion (J / g), which corresponds to the area of ​​the endothermic peak (melting point) observed at the highest temperature when the sample was rapidly cooled with liquid nitrogen after heating and then heated again under the same conditions, was read.

[0122] (8) Transmission color tone measurement A 10cm x 10cm section of the sample was cut from the center of the film width, and the lightness L* of the transmitted color tone of the laminated film was measured using a Konica Minolta Sensing CM3600d spectrophotometer. An LVD attachment with a measuring diameter of 25.4mm was attached, and 0% calibration was performed using the included transmission zero calibration plate CM-A100, followed by 100% calibration using the included white calibration plate. The lightness L* value was then read when the light source was a D65 light source. Five measurements were taken randomly within the 10cm square laminated sample surface, and the average value was used as the measured value.

[0123] (9) Haze measurement A haze meter (HGM-2DP) manufactured by Suga Test Instruments Co., Ltd. was used. A 10cm x 10cm section of the sample was cut from the center of the film width direction, and the total light transmittance and haze value were measured according to the old JIS-K-7105 (1994). Three measurements were taken at equal intervals along the film width direction, and the average value was used as the measurement result.

[0124] (10) Long-term reliability testing A 10 cm square sample was cut from the obtained laminated film, and the sample was placed between two sheets of plain paper and left to stand in a constant temperature and humidity chamber (LHL-114, manufactured by ESPEC Corporation) at 85°C and 85% RH. After standing for 250 hours, the λ and S / λ were calculated by reflection spectral measurement as described in (3) and (4), and the cross-cut peel rate was evaluated as described in (5), and the results were judged as A to D as follows. A: The change in λ was less than 1%, the change in S / λ was less than 1, and the cross-cut peeling rate was 3% or less. B: Not falling under category A, with a change in λ of less than 3%, a change in S / λ of less than 3, and a cross-cut peeling rate of 10% or less. C: Not falling under categories A or B, with a change in λ of less than 5%, a change in S / λ of less than 5, and a cross-cut peeling rate of 20% or less. D: Did not fall under any of categories A-C.

[0125] <Thermoplastic resin> The thermoplastic resin used in the embodiments of the present invention is described below. The refractive index is the refractive index when stretched at the stretching ratio described in the embodiments (measured at a wavelength of 632 nm using SAIRON Technology's SPA-4000). Resin 1: Crystalline polyethylene terephthalate resin with a refractive index of 1.66 and a melting point of 255°C. Resin 2: Crystalline isophthalic acid 4 mol% copolymer polyethylene naphthalate resin with a refractive index of 1.73 and a melting point of 257°C. Resin 3: Crystalline cyclohexanedimethanol 25 mol% copolymer polyethylene terephthalate resin with a refractive index of 1.60 and a melting point of 225°C. Resin 4: Amorphous cyclohexanedimethanol 30 mol% copolymer polyethylene terephthalate resin exhibiting a refractive index of 1.56. Resin 5: 12 mol% copolymer polyethylene terephthalate resin of crystalline isophthalic acid, exhibiting a refractive index of 1.62 and a melting point of 230°C. Resin 6: 15 mol% copolymer polyethylene terephthalate resin of crystalline isophthalic acid, exhibiting a refractive index of 1.61 and a melting point of 220°C. Resin 7: Amorphous spiroglycol 25 mol% and cyclohexanedicarboxylic acid 20 mol% copolymer polyethylene terephthalate resin exhibiting a refractive index of 1.53. Resin 8: Crystalline ethylene copolymer 5 mol% polypropylene resin with a refractive index of 1.51 and a melting point of 140°C. Resin 9: Amorphous polymethylene methacrylate resin exhibiting a refractive index of 1.49 Resin 10: A crystalline polyethylene naphthalate resin with a refractive index of 1.77 and a melting point of 264°C. Resin 11: Amorphous cyclohexanedimethanol 18 mol% copolymer polyethylene terephthalate resin exhibiting a refractive index of 1.59. (Example 1) Resin 1, Resin 3, and Resin 4 were used as the thermoplastic resins constituting layers A, B, and C, respectively. Each of the prepared thermoplastic resins was separately fed into three twin-screw extruders in pellet form and melted and kneaded at 270°C. The kneading conditions were set so that the screw rotation speed was 0.7 relative to the discharge volume. Next, after passing through seven FSS-type leaf disc filters, the materials were metered using a gear pump and merged in a feed block with 601 slits. 601 layers were stacked to form a laminate so that the layering ratio was 1.0 for both layer A / B and layer C / B, the repeating unit in the thickness direction was A / B / C / B, and both surface layers were layer A. Here, the slit length within the feed block was designed to increase monotonically in a stepped manner.

[0126] Subsequently, the laminate that passed through the feed block was supplied to a T-die and formed into a sheet. Then, while applying an electrostatic voltage of 8kV with a wire, it was rapidly cooled and solidified on a casting drum where the surface temperature was maintained at 25°C to obtain an unstretched laminated cast sheet. The obtained laminated cast sheet was heated in a group of rolls set to 90°C, and then rapidly heated from both sides of the film with radiation heaters while being stretched 3.6 times in the longitudinal direction using the difference in roll peripheral speeds, and then cooled. Next, corona discharge treatment was performed on both sides of this laminated uniaxially oriented film in air to set the wetting tension of the base film to 55mN / m. The treated surfaces on both sides of the film were coated with a water-based coating agent containing vinyl acetate / acrylic resin containing 3% by mass of colloidal silica with a particle size of 100nm, which forms a smooth layer using #4 metabar (hereafter, "coating" means the above), forming a transparent, smooth, and easily adhesive layer. Furthermore, this uniaxial laminated film was guided into a tenter, preheated with hot air at 90°C, and then stretched 3.6 times in the film width direction at a temperature of 100°C. Immediately after the stretching was completed, the stretched film was heat-treated with hot air at 180°C in the tenter, followed by a 2% relaxation treatment in the width direction under the same temperature conditions, and then wound up to obtain a laminated film. The thickness of the laminated film was 90 μm, and TEM observation showed an easy-adhesion thickness of approximately 90 nm on both sides. The obtained laminated film had the performance shown in Table 1.

[0127] (Examples 2 and 3) A laminated film was obtained in the same manner as in Example 1, except that the thermoplastic resins constituting each thermoplastic resin layer were as shown in Table 1. The evaluation results of the obtained laminated film are shown in Table 1.

[0128] (Example 4) A laminated film was obtained in the same manner as in Example 3, except that the casting drum speed was adjusted while monitoring the spectral distribution during film formation so that the central wavelength of the wavelength band Π1 was 1200 nm, thereby optimizing the thickness of the laminated film. The evaluation results of the obtained laminated film are shown in Table 1.

[0129] (Examples 5-12) The stacking ratios of layer A / layer B and layer C / layer B were as shown in Tables 1 and 2. The stacked film thickness was optimized by adjusting the casting drum speed while monitoring the spectral distribution during film formation so that the center wavelength of wavelength band Π1 was 1200 nm, except that the procedure was the same as in Example 4. The evaluation results are shown in Tables 1 and 2.

[0130] (Example 13) The thermoplastic resins constituting each thermoplastic resin layer were as shown in Table 2. 2% by mass of an olefin-based modifier to increase the acid value in order to improve adhesion with thermoplastic resin layer B was added to thermoplastic resin 8 constituting thermoplastic resin layer C, and the mixture was fed into an extruder and kneaded at 260°C. The laminated film was then stretched 3.6 times in the longitudinal direction using a roll group set to a stretching temperature of 105°C, matching the glass transition temperature of thermoplastic resin layer A, which is the outermost layer. Furthermore, after being guided to a tenter, the film was preheated with hot air at 100°C and stretched 3.6 times in the film width direction at 105°C to produce a laminated film, except that the process was the same as in Example 4. The evaluation results are shown in Table 2.

[0131] (Example 14) The thermoplastic resins constituting each thermoplastic resin layer were as shown in Table 2. The film was stretched 3.6 times in the longitudinal direction using a group of rolls set to a stretching temperature of 110°C to match the glass transition temperature of thermoplastic resin layer C (100°C). After being guided to a tenter, it was preheated with hot air at 105°C, stretched 3.6 times in the film width direction at a temperature of 110°C, and the heat treatment temperature was set to 190°C. A laminated film was obtained in the same manner as in Example 4. The evaluation results are shown in Table 2.

[0132] (Examples 15-17) A laminated film was obtained in the same manner as in Example 14, except that the number of layers and repeating units of the slit-type feed blocks forming the laminate were as shown in Table 2. The evaluation results are shown in Table 2. The thickness distribution of each thermoplastic resin layer in the final obtained laminated film all showed a monotonically increasing trend, and it was confirmed by transmission electron microscopy that it had repeating units of layer A / layer B / layer C / layer B, with the thickness of the two outermost layers of thermoplastic resin A each being 5 μm, and the number of units being as shown in Table 2.

[0133] (Example 18) A laminated film was obtained in the same manner as in Example 14, except that the heat treatment temperature in the tenter was changed to the temperature shown in Table 2. The evaluation results are shown in Table 2.

[0134] (Example 19) A laminated film was obtained in the same manner as in Example 18, except that a feed block with 301 slits as described in Example 17 was used as the lamination device, and then a mixer mechanism was installed in a single pipe located between the lamination device and the nozzle to divide and stack the laminate at the center in the width direction, resulting in a 601-layer laminated film. The evaluation results are shown in Table 2. Furthermore, it was confirmed by transmission electron microscopy that the layer thickness distribution of each thermoplastic resin layer in the finally obtained laminated film had a two-stage gradient structure, showing a monotonically increasing trend from the surface layer (1st layer) to the intermediate layer (301st layer) on one side, and a monotonically increasing trend from the intermediate layer (302nd layer) to the outermost surface layer on the opposite side, due to the use of the mixer mechanism.

[0135] (Example 20) A laminated film was obtained in the same manner as in Example 18, except that a 601-layer slit-type feed block lamination apparatus was used, which had a two-stage gradient structure in which the thickness of the laminated film monotonically increases from one side of the outermost surface of the film to the center (301st layer), and then monotonically decreases from the center to the other outermost surface of the film. The evaluation results are shown in Table 3.

[0136] (Examples 21, 22) A laminated film was obtained in the same manner as in Example 14, except that 4% by mass of an epoxy-terminated acrylic molecular modifier was added to resin 6 used in the thermoplastic resin B layer in Example 21, and to resin 9 used in the thermoplastic resin C layer in Example 22, in order to improve the interfacial adhesion between the polyester resin and the acrylic resin. The evaluation results are shown in Table 3.

[0137] (Example 23) A laminated film was obtained in the same manner as in Example 18, except that the casting drum speed was increased, the thickness of the laminated film was halved, and the center wavelength of the wavelength band Π1 was set to 600 nm. The performance of the obtained laminated film is shown in Table 3.

[0138] (Examples 24-25) In Example 18, a laminated film was obtained using the same method as in Example 18, except that the extruder discharge rate was adjusted so that the lamination ratios of layer A / layer B and layer C / layer B satisfied the values ​​shown in Table 3. The evaluation results are shown in Table 3.

[0139] (Example 26) In Example 24, a laminated film was obtained in the same manner as in Example 24, except that a laminating apparatus was used in which the monotonically increasing layer thickness distribution gradient of the laminating apparatus was 1.3 times that of the distribution in Example 24. The performance of the obtained laminated film is shown in Table 3.

[0140] (Examples 27-32) In Example 18, a laminated film was obtained using the same method as in Example 18, except that the extruder discharge rate was adjusted so that the layering ratios of layer A / layer B and layer C / layer B satisfied the values ​​shown in Tables 3 and 4. The evaluation results are shown in Tables 3 and 4.

[0141] (Example 33) As a lamination apparatus, the layers were joined in a feed block with 601 slits, where the repeating units in the thickness direction were layers A / B / C, to form a 601-layer laminate with thermoplastic resin A on both surface layers. As thermoplastic resin C, a 4 wt% acrylic molecular modifier used in Example 20 was added. Except for these points, the laminated film was obtained in the same manner as in Example 18. The evaluation results are shown in Table 4.

[0142] (Examples 34-38) A laminated film was obtained in the same manner as in Example 33, except that the stacking ratios of layer A / layer B and layer C / layer B were set to the conditions shown in Table 4. The evaluation results are shown in Table 4.

[0143] (Example 39) The thermoplastic resins used to constitute layers A, B, C, and D were resin 2, resin 1, resin 4, and resin 9, respectively. Each of the prepared thermoplastic resins was separately fed into four twin-screw extruders in pellet form and melted and kneaded at 270°C. The layers were combined in a feed block with 643 slits, and 643 layers were laminated to form a laminate such that the lamination ratio of layer A / B, layer C / B, and layer D / B all showed 1.0, the repeating unit in the thickness direction showed layer A / B / C / D / C / B, and both surface layers were thermoplastic resin layer A. Here, the slit length inside the feed block was designed to increase monotonically in a step-like manner. The film was formed under the same film-forming conditions as in Example 18, and the film thickness was optimized by adjusting the casting drum speed while checking the spectral spectrum during film formation so that the center wavelength of wavelength band Π1 was 1200 nm, thereby obtaining the desired laminated film. The evaluation results are shown in Table 4.

[0144] (Comparative Example 1) Resin 2 and Resin 7 were used as the thermoplastic resins constituting thermoplastic resin layers A and B, respectively. Each of the prepared thermoplastic resins was separately fed into two twin-screw extruders in pellet form, and both were melted and kneaded at 270°C. The mixtures were combined in a feed block with 231 slits to form a 231-layer laminate with a layering ratio of A / B of 1.0, a repeating unit of A / B in the thickness direction, and thermoplastic resin A on both surface layers. Here, the slit length within the feed block was designed to increase monotonically in a stepwise manner. The film thickness was adjusted by changing the casting drum speed so that the center wavelength λ of the wavelength band Π1 was 1200 nm. The laminated film was obtained by forming the film under the same film-forming conditions as in Example 13. The evaluation results are shown in Table 5. The resulting laminated film was confirmed by transmission electron microscopy to have a final laminated structure consisting of alternating A and B repeating units, with 115 repeating units in total. The two outermost thermoplastic resin A layers each had a thickness of 5 μm, while the thickness of the remaining internal layers ranged from 100 nm to 200 nm.

[0145] (Comparative Example 2) In Comparative Example 1, the laminated film was obtained using the same method as described in Comparative Example 1, except that the lamination apparatus used a feed block with 931 slits and an equivalent film design of A:B:A:B:A:B=1:7:1:1:7:1. The evaluation results are shown in Table 5.

[0146] (Comparative Examples 3 and 4) In Comparative Example 1, the thermoplastic resins listed in Table 5 were selected as the thermoplastic resins constituting thermoplastic resin layers A and B. In Comparative Example 3, the film was stretched 3.6 times in the longitudinal direction using a roll group with a stretching temperature set to 110°C to match the glass transition temperature of resin 9 constituting thermoplastic resin layer B. After being guided to a tenter, it was preheated with hot air at 105°C and stretched 3.6 times in the film width direction at 110°C. In Comparative Example 4, the film was stretched 3.6 times in the longitudinal direction using a roll group with a stretching temperature set to 140°C to match the glass transition temperature of resin 10 constituting thermoplastic resin layer A (125°C). After being guided to a tenter, it was preheated with hot air at 130°C and stretched 3.6 times in the film width direction at 145°C. The evaluation results are shown in Table 5.

[0147] (Comparative Example 5) Table 5 shows the evaluation results of Example 13, in which a laminated film was prepared without adding an olefin-based modifier to the C layer to increase the acid value.

[0148] (Comparative Example 6) In Example 14, a laminated film was prepared using a tenter with a heat treatment temperature of 140°C. The evaluation results are shown in Table 5.

[0149] [Table 1]

[0150] [Table 2]

[0151] [Table 3]

[0152] [Table 4]

[0153] [Table 5]

[0154] In each example and comparative example, layers A to D, when judged according to the evaluation criteria described in "(2) Layer Interface (Contrast Difference)," all have a different composition from the other layers. That is, the example having layers A and B has two thermoplastic resin layers with different compositions, the example having layers A to C has three thermoplastic resin layers with different compositions, and the example having layers A to D has four thermoplastic resin layers with different compositions. [Industrial applicability]

[0155] The laminated film of the present invention has a laminated structure in which three or more different thermoplastic resin layers are laminated in a fixed repeating unit. Compared to conventional laminated films in which two types of thermoplastic resins are laminated alternately, even when thermoplastic resins with different skeletal structures are used, interlayer adhesion can be provided by the thermoplastic resin placed in the middle, allowing the laminated film to be used for a long period of time without impairing its original performance. Furthermore, because three or more thermoplastic resin layers with different optical properties are used, optical designs that could not be achieved with conventional laminated films can be realized, and laminated films with a wider reflection band and higher reflectivity than conventional laminated films can be realized with a low number of layers and in a thin film. Such laminated films can be widely used in building materials and automotive applications as window films, in industrial materials applications as films for laminating steel plates for signs, etc., and as light-cutting films for laser surface processing, in electronic device applications as process and release films for photolithography materials, optical films for displays, and in other fields such as food, medical, and ink, as films for suppressing light degradation of contents, and in products that require UV protection. In particular, it can be suitably used in image display devices, windows, exterior materials for transportation vehicles, and transportation applications for purposes such as heat shielding, UV protection, and metallic-like decoration. [Explanation of symbols]

[0156] 1:A layer 2:B layer 3:C layer 4: Repeating Unit 5: SS curve in peel strength test 6: Peel strength 7: Spectroscopic Spectrum 8: Area S of the region in wavelength band Π1 9: Higher-order reflections 10:λ 11:λmin 12:λmax 13: Maximum reflectance in wavelength band PI1 14: Midpoint between the maximum reflectance and baseline reflectance in wavelength band PI1 15: Baseline reflectance 16: Pulsation in the spectral distribution

Claims

1. Having three or more different thermoplastic resin layers, It has five or more repeating units formed of the three or more thermoplastic resin layers described above, The peel rate of the grid in the adhesion test based on the cross-cut method specified in JIS K 5600-5-6:1999 is 10% or less. A laminated film characterized in that, in a spectral spectrum in the wavelength band from 300 nm to 2500 nm, with the horizontal axis representing wavelength (nm) and the vertical axis representing reflectance (%), the wavelength band Π1 is the wavelength band that continuously exhibits a reflectance of 20% or more over 100 nm or more, located in the longest wavelength band; λ is the central wavelength in the wavelength band Π1; S is the area of ​​the region enclosed by the spectral spectrum of the wavelength band Π1 and the baseline of the reflectance; and N is the total number of layers of the thermoplastic resin, the following conditions are met: 0.060 ≤ S / (λ・N) ≤ 0.300; and when the wavelength at the short wavelength end of the wavelength band Π1 is λmin and the wavelength at the long wavelength end is λmax, the following conditions are met: λmin ≥ λmax / 2.

2. The laminated film according to Claim 1, characterized in that when the wavelength band Π2 is defined as a wavelength band of 300 nm or more and λmax / 5 or more and λmin / 2 or less, the average reflectance in the wavelength band Π2 is 25% or less.

3. Having three or more different thermoplastic resin layers, It has five or more repeating units formed of the three or more thermoplastic resin layers described above, The peel rate of the grid in the adhesion test based on the cross-cut method specified in JIS K 5600-5-6:1999 is 10% or less. A laminated film characterized in that, in a spectral spectrum in the wavelength band from 300 nm to 2500 nm, with the horizontal axis representing wavelength (nm) and the vertical axis representing reflectance (%), the wavelength band Π1 is the wavelength band that continuously shows a reflectance of 20% or more over 100 nm or more, which is located in the longest wavelength band; λ is the central wavelength in the wavelength band Π1; S is the area of ​​the region enclosed by the spectral spectrum of the wavelength band Π1 and the baseline of the reflectance; and N is the total number of layers of the thermoplastic resin, the condition 0.060 ≤ S / (λ・N) ≤ 0.300 is satisfied, and when the wavelength band Π3 is the half-wavelength band of the wavelength band Π1, which is from λmin / 2 to λmax / 2, the average reflectance in the wavelength band Π3 is 25% or less.

4. Having three or more different thermoplastic resin layers, It has five or more repeating units formed of the three or more thermoplastic resin layers described above, The peel rate of the grid in the adhesion test based on the cross-cut method specified in JIS K 5600-5-6:1999 is 10% or less. A laminated film characterized in that, in a spectral spectrum in the wavelength band from 300 nm to 2500 nm, with the horizontal axis representing wavelength (nm) and the vertical axis representing reflectance (%), the wavelength band Π1 is the wavelength band that continuously shows a reflectance of 20% or more over 100 nm or more, which is located in the longest wavelength band, the central wavelength in the wavelength band Π1 is λ, the area of ​​the region enclosed by the spectral spectrum of the wavelength band Π1 and the baseline of the reflectance is S, and the total number of layers of the thermoplastic resin is N, the condition 0.060 ≤ S / (λ・N) ≤ 0.300 is satisfied, the thermoplastic resin layer is of three types, and when the thermoplastic resin layers are designated as layer A, layer B, and layer C in order of decreasing refractive index, the laminated structure has a repeating unit of layer A / layer B / layer C / layer B, and in the repeating unit, the stacking ratio of layer A to layer B (A / B) is 0.50 or more and 1.10 or less, and the stacking ratio of layer C to layer B (C / B) is 0.90 or more and 1.30 or less.

5. A laminated film according to any one of claims 1 to 4, characterized in that it satisfies 35.0 ≤ S / λ ≤ 150.

0.

6. The laminated film according to claim 3 or 4, characterized in that when the wavelength at the short wavelength end of the wavelength band Π1 is λmin and the wavelength at the long wavelength end is λmax, the condition λmin ≥ λmax / 2 is satisfied.

7. The laminated film according to claim 6, characterized in that when the wavelength band Π2 is defined as a wavelength band of 300 nm or more and λmax / 5 or more and λmin / 2 or less, the average reflectance in the wavelength band Π2 is 25% or less.

8. The laminated film according to claim 4, characterized in that when the wavelength band Π3 is defined as the half-wavelength band of the wavelength band Π1, with a wavelength band of λmin / 2 to λmax / 2, the average reflectance in the wavelength band Π3 is 25% or less.

9. A laminated film according to any one of claims 1 to 4, characterized in that the lightness L* in a transmittance color measurement is 70 or less and the haze is 5.0% or less.

10. The laminated film according to any one of claims 1 to 4, characterized in that the aforementioned N is 100 or more and 901 or less.

11. The laminated film according to any one of claims 1 to 4, characterized in that the thickness of each layer contained in the repeating unit exhibits a distribution that is monotonically increasing or monotonically decreasing.

12. The laminated film according to any one of claims 1 to 4, wherein the thermoplastic resin that is the main component of the thermoplastic resin layer with the highest refractive index is polyethylene terephthalate or polyethylene naphthalate.

13. The laminated film according to any one of claims 1 to 4, characterized in that the thermoplastic resin layer with the lowest refractive index is a layer mainly composed of a thermoplastic resin exhibiting a refractive index of 1.54 or less.

14. A molded article made using the laminated film described in any one of claims 1 to 4.

15. An image display device comprising a laminated film according to any one of claims 1 to 4.

16. A window comprising a laminated film according to any one of claims 1 to 4.

17. A transport vehicle exterior material comprising a laminated film according to any one of claims 1 to 4.

18. A transportation device comprising a laminated film according to any one of claims 1 to 4.

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