JP2005059332A - Biaxially oriented multilayer laminated film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reflective biaxially oriented multilayer laminated film showing a sharp developed color, having large color shift, excellent in interlaminar adhesion and hard to tear. <P>SOLUTION: The biaxially oriented multilayer laminated film is constituted by alternately laminating first and second layers so that the total number of layers becomes 11 or above and biaxially stretching the formed laminate. The thicknesses of the first and second layers are 0.05-0.5 μm and the first layer is constituted of a polyester composition while the second layer is constituted of a polyester composition different from the polyester composition of the first layer and the refractive index of the second layer is different from that of the first layer. The maximum reflectivity of light in a wavelength range of 350-2,000 nm is higher than the base line of reflectivity, which is obtained from a light reflectivity curve within the wavelength range of 350-2,000 nm, by 20% or above. The half value width of the light reflectivity curve in the maximum reflectivity is 10-100 nm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a multilayer laminated film that selectively reflects light in an arbitrary wavelength band according to the difference in refractive index between layers and the thickness of each layer, in which layers having a low refractive index and layers having a high refractive index are alternately and regularly arranged. About.

  In recent years, forgery-preventing hologram stickers and the like have become widespread in order to prevent unauthorized copying, but the hologram technology itself has already been imitated, and new anti-counterfeiting measures are being searched for.

  The multilayer laminated film is obtained by alternately laminating a plurality of layers having a low refractive index and a layer having a high refractive index, and is an optical interference film that selectively reflects or transmits light of a specific wavelength by structural optical interference between the layers. be able to. Such a multilayer laminated film can be made into a pearly luster film that is excellent in design, for example, looks like iridescent, due to structural color development, if the wavelength of light that is selectively reflected or transmitted is in the visible light region. Moreover, the design properties obtained here are due to the structural color development of the multilayer laminated film, so that there are few problems of fading unlike the color development with dyes.

As these multilayer laminated films, multilayer multilayer films using thermoplastic resins of different materials such as polyethylene terephthalate and polymethyl methacrylate have been proposed in JP-A-56-99307. Further, in Japanese Patent Laid-Open No. 9-506837 and WO01 / 47711, a multilayer stretched film using a layer made of polyethylene 2,6-naphthalenedicarboxylate as a layer having a high refractive index has been proposed.
JP-A-56-99307 Japanese National Patent Publication No. 9-506837 WO01 / 47711

  Unlike general holograms, multilayer laminated films are promising as a novel anti-counterfeit sealing material from the viewpoint that they can be differentiated from holograms because the reflected light differs depending on the incident angle. A material that shows a large color shift depending on the angle has not yet been realized.

  The refractive index difference of each layer of the conventional multilayer stretched film is derived from the refractive index difference of the resin constituting each layer. For example, as described in JP-A-56-99307, polyethylene terephthalate is used for a layer having a high refractive index, and a resin having a low refractive index such as polymethacrylate is used for a layer having a low refractive index. Has been used. However, according to the conventional concept of providing a difference in refractive index between layers depending on the refractive index of the resin, it is necessary to select resins having different compositions for each layer, and the adhesion between the layers is inferior. It was not obtained. Furthermore, since the multilayer laminated film described in JP-A-56-99307 has a large difference in resin characteristics, the film thickness uniformity is not maintained, and random hue spots are observed. It was not suitable for various uses.

  In Japanese Patent Publication No. 9-506837 and WO01 / 47711, polyethylene 2,6-naphthalenedicarboxylate (hereinafter sometimes referred to as PEN) having a high refractive index is used for a layer having a high refractive index. Biaxially stretched film using a thermoplastic elastomer for the low refractive index layer, PEN having a high refractive index for the high refractive index layer, and PEN copolymerized with 30 mol% of isophthalic acid for the low refractive index layer. The uniaxially stretched multilayer stretched film used is illustrated. These multilayer laminated films make the layer with a low refractive index substantially amorphous.

  However, such a film is useful for use as a mirror because the difference in refractive index between the layers is too large and becomes reflected light in a wide wavelength band, but it is insufficient in terms of color shift. In addition, even if such a multilayer laminated film is subjected to stretching treatment, sufficient interlayer adhesion cannot be obtained, biaxial stretching treatment cannot be performed uniformly in the surface direction, and the film quality becomes non-uniform. There was a potential problem. From such a background, a material satisfying interlayer adhesion and optical property homogeneity while having a large color shift has not been put into practical use.

  As a problem common to the multilayer laminated film described above, in order to increase the refractive index difference between the layers, a resin having a different composition is combined, so the adhesion between each layer is weak and the delamination phenomenon tends to occur. Since different resins are combined, it is difficult to uniformly stretch the film, and it is easy to form a film with insufficient strength and easy to tear.

  SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and to obtain a multilayer laminate film having a large color shift that is not found in conventional multilayer laminate films, and having high interlayer adhesion and solving the above-mentioned problems, and is difficult to tear. To do.

  The biaxially stretched multilayer laminate film of the present invention is a multilayer laminate film in which the first layer and the second layer are alternately laminated so that the total number of layers is 11 or more, and biaxially stretched. The first layer and the second layer have a thickness in the range of 0.05 to 0.5 μm, the first layer is composed of a polyester composition, and the second layer is composed of the first layer. The maximum reflectance of light in the wavelength range of 350 to 2000 nm is obtained from the light reflectance curve in the wavelength range of 350 to 2000 nm. It is characterized by being 20% or more higher than the reflectance baseline, and the half-value width of the reflectance curve at the maximum reflectance is 10 to 100 nm.

  In the present invention, the optical design of a multilayer stretched film having a large color shift is optimized according to the viewing angle of the observer, and a multilayer laminated film that overcomes the above-mentioned problems has been intensively studied. In order to produce a large color shift, the design of the reflected light hue to be as close to the primary color as possible, and intensive studies to realize a multilayer laminated film in which the reflection peak wavelength is shifted more greatly with respect to the incident angle And at least one of the layers exhibits a large birefringence, and the other layer has a birefringence as small as possible, and the refractive index difference is adjusted to an appropriate difference, leading to the present invention. . That is, in the present invention, by adjusting the interlayer refractive index difference and suppressing the half width of the reflection peak of the multilayer stretched film to 10 nm or more and 100 nm or less, a hue closer to the primary color is realized, and as a result, a large color shift is realized. It came to.

  Furthermore, even if the resin composition constituting the high refractive index layer and the low refractive index layer is close to the limit, the melting point of the resin constituting the low refractive index layer is lower than that of the resin constituting the high refractive index layer. In addition, by relaxing the molecular orientation of the layer made of the resin having a low melting point after the biaxial stretching treatment, the biaxial stretching processability is excellent and the interlayer adhesion is excellent while expressing the refractive index difference between the layers. The inventors have found that a multilayer stretched film can be obtained, and have reached the present invention. That is, the present invention employs a combination of resins having a very close composition, which has conventionally been difficult to express a difference in refractive index between layers, as a combination of resins constituting each layer, and has sufficient strength for a multilayer laminated film. Surprisingly, the difference in refractive index between the layers is sufficiently provided while the adhesion between the layers is provided.

  The preferred embodiments of the present invention include the following. In the wavelength range of 350 to 2000 nm, the difference between the maximum reflectance wavelength for light with an incident angle of 5 degrees and the maximum reflectance wavelength for light with an incident angle of 50 degrees is 50 nm or more. The ratio of the ethylene terephthalate component in the film is 80 mol% or more based on all repeating units of the polyester. 1.5 to 20 mol% of all repeating units are isophthalic acid or 2,6-naphthalenedicarboxylic acid component. The polyester constituting the first layer is a crystalline polyester, 90 mol% or more of all repeating units are ethylene terephthalate components, the polyester constituting the second layer is a crystalline polyester, and all repeating 75 to 97 mol% of the unit is an ethylene terephthalate component.

  The biaxially stretched multilayer laminated film of the present invention not only has excellent design properties such as an iridescent color due to structural coloration, but also exhibits a bright reflected color, has a large color shift, and excellent interlayer adhesion Because of its high properties and high breaking strength, its industrial value such as anti-counterfeit seals and various labels is high.

  The biaxially stretched multilayer laminated film of the present invention includes a first layer having a thickness of 0.05 to 0.5 μm made of a polyester composition and a second layer having a thickness of 0.05 to 0.5 μm also made of a polyester composition. 11 layers are alternately stacked. The polyester composition constituting the first layer and the second layer has a very close composition but needs to have a different composition. If the number of layers is less than 11, selective reflection due to multiple interference is small, and sufficient reflectance cannot be obtained. The upper limit of the number of stacked layers is preferably at most 501 from the viewpoint of productivity. The first layer and the second layer each have a thickness of 0.05 to 0.5 μm in order to selectively reflect light by optical interference between layers. The selective reflection exhibited by the multilayer laminated film of the present invention can be realized by appropriately adjusting the layer thickness in the range of ultraviolet light, visible light, and near infrared light. When the thickness of each layer is less than 0.05 μm, the reflected light cannot be reflected due to absorption of the polyester composition. On the other hand, if the thickness exceeds 0.5 μm, the light selectively reflected by the light interference between layers reaches the infrared light region, and the usefulness as an optical characteristic cannot be obtained. For convenience of explanation, a layer having a high refractive index is hereinafter referred to as a first layer, and a layer having a low refractive index is hereinafter referred to as a second layer.

  In the biaxially stretched multilayer laminated film of the present invention, the maximum light reflectance is 20% or more higher than the baseline of the reflectance curve in the wavelength range of 350 to 2000 nm. The difference between the maximum reflectance and the baseline reflectance is preferably 30% or more, more preferably 50% or more. FIG. 1 shows an example of the reflectance curve of the biaxially stretched multilayer laminated film of the present invention. In FIG. 1, 1 is the difference between the maximum reflectance and the baseline of reflectance, 2 is the baseline of reflectance, and 3 is the full width at half maximum at the portion where the reflectance curve is the reflectance peak. If the biaxially stretched multilayer laminated film does not have a reflection peak whose maximum reflectance is 20% or more higher than the baseline of reflectance, it cannot be used as an optical interference film that selectively reflects or transmits light of a specific wavelength.

  Furthermore, in the biaxially stretched multilayer laminated film of the present invention, it is necessary that the half-value width wavelength of the reflection peak at a wavelength at which the maximum reflectance is obtained within the wavelength range is 10 nm or more and 100 nm or less. The half value of the reflection peak is not a simple half value of the maximum reflectance, but a half value based on the baseline reflectance. If the half-value wavelength width is larger than 100 nm, the intermediate color is also reflected, so that a hue close to a bright primary color cannot be exhibited. Moreover, since it can reflect only a very partial wavelength range as it is 10 nm or less, sufficient hue cannot be exhibited. A preferred upper limit is 80 nm, a more preferred upper limit is 60 nm, and a preferred lower limit is 20 nm, more preferably 30 nm. In order to achieve the half width as described above, the refractive index difference between the layers is preferably in the range of 0.03 to 0.20 in at least one direction in the in-plane direction after biaxial stretching. Preferably, it is 0.05-0.15. Although it is difficult to measure the refractive index of each layer of the multilayer film in the laminated state, it can be determined from the refractive index of the film in a sufficiently optically thick state.

  Moreover, in this invention, it is preferable that the difference of the reflection peak wavelength of 5 degree incidence and 50 incidence in the said wavelength range is 50 nm or more. If the difference in reflection peak wavelength is less than 50 nm, the color shift is not sufficient, and different colors cannot be visually recognized at different angles. The preferable lower limit of the difference in the reflection peak wavelength is 70 nm or more, more preferably 90 nm or more. The upper limit is about 300 nm at most from the refractive index of the resin.

  By the way, in this invention, sufficient refractive index difference is given to the 1st layer and 2nd layer which comprise a biaxial stretching multilayer laminated film by the above-mentioned thickness structure without depending on the refractive index difference of the conventional resin. doing. In order to give a sufficient refractive index difference to the first layer and the second layer constituting the biaxially stretched multilayer laminated film without depending on the refractive index difference of the resin, for example, the refractive index difference is given by heat treatment after stretching. The method of doing is mentioned. That is, the first layer resin having a high melting point is oriented by stretching and exhibits a high refractive index, and the second layer resin having a low melting point is rendered non-oriented by heat treatment, thereby providing a refractive index. Decreases. As a result, a sufficient difference in refractive index can be imparted even in a combination of resins having substantially the same refractive index as the resin. The refractive index difference obtained here is preferably 0.03 or more, and more preferably 0.05 or more. Although it is difficult to measure the refractive index of each layer of the multilayer film in the laminated state, it can be determined from the refractive index of the film in a sufficiently optically thick state.

  In the biaxially stretched multilayer laminated film of the present invention, a resin having a very similar composition can be selected as a resin constituting the first layer and the second layer, and the adhesion between the layers can be determined by selecting a resin having a similar composition. Is a dramatic improvement. Therefore, in the biaxially stretched multilayer laminated film of the present invention, 80 mol% or more of all repeating units are made of polyester having an ethylene terephthalate component. When the ethylene terephthalate component is less than 80 mol% of all repeating units, the adhesion between the layers is lowered. The copolymer component other than the ethylene terephthalate component is preferably a 2,6-naphthalenedicarboxylic acid component or an isophthalic acid component because the melting point is easily lowered. The copolymerization ratio of the 2,6-naphthalenedicarboxylic acid or isophthalic acid component is in the range of 1.5 to 20 mol% based on the repeating unit. If the number of moles of the 2,6-naphthalenedicarboxylic acid or isophthalic acid component is less than the lower limit, it is difficult to give a sufficient refractive index difference between the first layer and the second layer, while 2,6-naphthalene When the number of moles of the dicarboxylic acid or isophthalic acid component is larger than the upper limit, the composition of the polyester constituting the first layer and the second layer is greatly different, and the adhesion between the layers tends to be lowered.

[First layer]
In a preferred example of the present invention, the resin constituting the first layer is a polyester whose main repeating unit is an ethylene terephthalate component. Preferably, homopolyethylene terephthalate or copolymer polyethylene terephthalate in which 95 mol% or more of repeating units are composed of an ethylene terephthalate component can be maintained at a higher melting point than the polyester constituting the second layer described later. When the number of moles of the ethylene terephthalate component is less than 95% by mole of the repeating unit, the melting point is lowered, and it is difficult to obtain a difference in melting point from the polyester constituting the second layer to be described later. It is difficult to give a large difference in refractive index. Among these, homopolyethylene terephthalate is preferable because the melting point can be maintained at a high level. Examples of copolymer components other than the ethylene terephthalate component include other aromatic carboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid; adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid Aliphatic dicarboxylic acids such as acids; Acid components such as alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; Aliphatic diols such as butanediol and hexanediol; Glycol components such as alicyclic diols such as cyclohexanedimethanol Can be preferably mentioned.

  By the way, the melting point of the resin constituting the first layer is preferably in the range of 250 to 260 ° C., since the difference in melting point from the resin constituting the second layer described later can be relatively large. When the melting point of the resin constituting the first layer is lower than the lower limit, the melting point difference from the resin constituting the second layer is reduced, and as a result, a sufficient refractive index difference is imparted to the resulting multilayer stretched film. It becomes difficult. In addition, the melting point of non-copolymerized polyethylene terephthalate is usually around 256 ° C.

[Second layer]
In a preferred example of the present invention, the resin constituting the second layer is a polyester whose main repeating unit is an ethylene terephthalate component. In particular, from the viewpoint of film forming property in biaxial stretching, a crystalline polyester is preferable. Further, since the melting point can be made lower than that of the polyester constituting the first layer, 75 to 97 mol% of the repeating units are composed of an ethylene terephthalate component, and 3 to 25 mol% is a copolymer composed of other copolymer components. Polymerized polyethylene terephthalate. When the number of moles of the ethylene terephthalate component is less than 75 mol% of the repeating unit or the number of moles of the copolymer component exceeds 25 mol%, the polymer is substantially amorphous and film-forming properties by biaxial stretching And the composition of the polyester constituting the first layer is greatly different, and the adhesion between the layers tends to decrease. On the other hand, if the number of moles of the ethylene terephthalate component exceeds 97 mol% of the repeating unit or the number of moles of the copolymer component is less than 3 mol%, the melting point difference from the polyester constituting the first layer is reduced, As a result, it becomes difficult to give sufficient reflectivity to the multilayer stretched film. Examples of copolymer components other than the ethylene terephthalate component include other aromatic carboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid; adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid Aliphatic dicarboxylic acids such as acids; acid components such as alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; aliphatic diols such as butanediol and hexanediol; glycol components such as alicyclic diols such as cyclohexanedimethanol Can be preferably mentioned. Among these, 2,6-naphthalenedicarboxylic acid or isophthalic acid is preferable because it is relatively easy to lower the melting point while maintaining stretchability.

  By the way, the melting point of the resin constituting the second layer is preferably in the range of 200 to 245 ° C., since the difference in melting point from the resin constituting the first layer can be relatively large. When the melting point of the resin constituting the second layer is higher than the upper limit, the melting point difference from the resin constituting the first layer is reduced, and as a result, a sufficient refractive index difference is imparted to the resulting multilayer stretched film. It becomes difficult. On the other hand, in order for the melting point of the resin constituting the second layer to be lower than the lower limit, the composition with the resin constituting the first layer will be greatly changed, which is sufficient for the obtained biaxially stretched multilayer laminated film. It becomes difficult to provide adhesion between layers. Note that the melting point of the resin constituting the second layer does not need to be low from the stage before forming the film, and may be low after the stretching treatment. For example, it will be easily understood that homopolyethylene terephthalate and other polyesters other than that may be prepared and transesterified at the time of melt kneading.

[Biaxially stretched multilayer laminated film]
The biaxially stretched multilayer laminated film of the present invention is obtained by alternately laminating at least 11 layers of the above-mentioned first layer and second layer. In addition, as mentioned above, the biaxially stretched multilayer laminate film of the present invention needs to be stretched in the biaxial direction from the viewpoint of having sufficient mechanical strength.

  In particular, the biaxially stretched multilayer laminated film of the present invention exhibits crystallinity in both the first layer and the second layer from the viewpoint of ensuring adhesion between layers and film forming properties of biaxial stretching. The resin of the second layer is preferably at least partially melted after stretching. The biaxially stretched multilayer laminated film thus obtained preferably has two or more melting points measured by DSC (differential scanning calorimeter), and their melting points are preferably different by 5 ° C. or more. Here, it can be easily imagined that the measured melting point is the first layer exhibiting a high refractive index on the high melting point side, and the second layer exhibiting the low refractive index on the low melting point side. . More preferably, since the second layer is at least partially melted after stretching, the crystallization peak measured by DSC is preferably in the range of 100 ° C. to 190 ° C. When the crystallization peak is 100 ° C. or lower, one layer is rapidly crystallized when the film is stretched, and the film-forming property at the time of film formation tends to be lowered, and the homogeneity of the film quality is likely to be lowered. Spots of hue may occur. On the other hand, when the crystallization peak is 190 ° C. or higher, when the second layer is melted by heat setting, crystallization occurs at the same time, making it difficult to express a sufficient refractive index difference.

  As described above, the biaxially stretched multilayer laminated film of the present invention is obtained by stretching the resin of the first layer and the resin of the second layer, both of which exhibit crystallinity, to obtain a film having a uniform film quality and stretching. By melting the second layer after the process, the interlayer adhesion can be improved and simultaneously the reflection performance can be improved. Therefore, in the biaxially stretched multilayer laminate film of the present invention, a crystal peak by DSC is present at 100 ° C. to 190 ° C., and two or more melting peaks having a melting point difference of 5 ° C. or more are observed. Is preferred.

  The biaxially stretched multilayer laminated film of the present invention preferably has a breaking strength in the stretched direction of 50 MPa or more. When the breaking strength is less than 50 MPa, the handleability during processing of the multilayer stretched film is lowered, and the durability when it is made into a product is lowered. In addition, when the breaking strength is 50 MPa or more, there is an advantage that the film becomes firm and the winding property is improved. The preferred breaking strength is 80 MPa or more in the longitudinal direction, particularly 100 MPa or more, and 80 MPa or more, particularly 100 MPa or more in the transverse direction. In addition, the strength ratio in the longitudinal direction and the transverse direction is preferably 3 or less because tear resistance can be sufficiently obtained. In particular, the strength ratio in the longitudinal direction and the transverse direction is preferably 2 or less because tear resistance can be further improved. The upper limit of the breaking strength is not particularly limited, but is preferably at most 500 MPa from the viewpoint of maintaining the stability of the stretching process.

  Further, the biaxially stretched multilayer laminated film of the present invention is characterized by high thermal dimensional stability, and heat shrinkage when treated at 150 ° C. for 30 minutes in the stretched direction (film forming direction and width direction). Each rate is preferably 3.0% or less. More preferably, it is 2.5% or less, and further preferably 2.0% or less. Moreover, when the biaxially stretched multilayer laminated film of the present invention is treated at 200 ° C. for 10 minutes, the thermal shrinkage in the film forming direction and the width direction is preferably 5.0% or less, respectively. A more preferable heat shrinkage rate is 4.0% or less, and a still more preferable heat shrinkage rate is 3.0% or less. Since the thermal dimensional stability is high, it can be said that the biaxially stretched multilayer laminated film of the present invention is excellent in process suitability such as bonding with a PVC sheet and embossing.

In the biaxially stretched multilayer laminated film of the present invention, it is preferable that the resins constituting the first layer and the second layer are both crystalline resins. If both the resin constituting the first layer and the second layer are crystalline resins, the treatment such as stretching is unlikely to be uneven, and as a result, the thickness unevenness of the film can be reduced. A preferable range of thickness unevenness is a thickness variation rate represented by the following formula of less than 10%, preferably less than 5%, more preferably less than 3%. When the variation rate of the film thickness is 10% or more, the color of the reflected light changes and appears as a color spot.
Variation rate of thickness (%) = {(T _max −T _min ) / T _ave } × 100
Here, T _ave in the above formula is an average thickness, T _max is a maximum thickness, and T _min is a minimum thickness.

  In order to improve the rollability of the film, the biaxially stretched multilayer laminated film of the present invention has inert particles having an average particle diameter of 0.01 μm to 2 μm in at least one of the first layer and the second layer. The content is preferably 0.001% by weight to 0.5% by weight based on the weight of the multilayer stretched film. If the average particle size of the inert particles is smaller than the lower limit or the content is less than the lower limit, the effect of improving the winding property of the multilayer stretched film tends to be insufficient, while the content of the inert particles is When the upper limit is exceeded or the average particle diameter exceeds the upper limit, the deterioration of the optical properties of the multilayer stretched film due to the particles becomes remarkable. Preferred average particle diameter of the inert particles is in the range of 0.05 to 1 μm, particularly 0.1 to 0.3 μm. Moreover, content of a preferable inert particle is the range of 0.005-0.2 weight%.

  Examples of the inert particles contained in the biaxially stretched multilayer laminated film include inorganic inert particles such as silica, alumina, calcium carbonate, calcium phosphate, kaolin, and talc, silicone, crosslinked polystyrene, and styrene-divinylbenzene copolymer. Such organic inert particles can be mentioned. These inert particles are spherical particles whose ratio of major axis to minor axis is 1.2 or less, and further 1.1 or less (hereinafter sometimes referred to as true spherical particles). And optical properties can be maintained at a high level. Further, these inert particles preferably have a sharp particle size distribution. For example, those having a relative standard deviation of less than 0.3, more preferably less than 0.2 are preferable. When particles having a large relative standard deviation are used, the frequency of coarse particles increases, which may cause optical defects.

Here, the average particle size and the particle size ratio of the inert particles are based on an image obtained by first sputtering a metal for imparting conductivity on the particle surface very thinly and expanding 10,000 to 30,000 times with an electron microscope. The major axis, the minor axis, and the area equivalent circle diameter are obtained, and then these are applied to the following equation.
Average particle diameter = total sum of area equivalent circle diameters of measured particles / measured particle number particle diameter ratio = average long diameter of particles / average short diameter of the particles Further, the relative standard deviation is calculated based on the result.

  The biaxially stretched multilayer laminated film of the present invention preferably has a haze of 10% or less. If the haze is 10% or less due to light scattering by inert particles, the film itself becomes whitish and loses gloss.

[Method for producing biaxially stretched multilayer laminated film]
The biaxially stretched multilayer laminated film of the present invention is stretched more than polyester (for the first layer) having an ethylene terephthalate component having a melting point of 250 to 260 ° C. as a main repeating unit and the polyester constituting the first layer. A polyester (second layer) having a melting point of at least 10 ° C. lower than that of the ethylene terephthalate component as a main repeating unit is extruded in a molten state and alternately laminated in at least 11 layers. It is set as a stretched film (process made into a sheet-like material). The polyester constituting the first layer and the second layer is the same as that described for the first layer and the second layer. When the melting point of the first layer polyester is less than 250 ° C., the difference in melting point from the second layer polyester is not sufficiently applied, and as a result, a sufficient refractive index difference cannot be imparted between the layers of the resulting multilayer stretched film. On the other hand, since the melting point of homopolyethylene terephthalate is around 256 ° C., the upper limit of the melting point of the first layer polyester is about 260 ° C. at most. In addition, when the melting point of the second layer polyester is not lower by 15 ° C. or more than the first layer polyester, the difference in melting point from the second layer polyester is not sufficient, and as a result, the resulting multilayer stretch A sufficient refractive index difference cannot be imparted between the layers of the film. The upper limit of the melting point difference between the first layer polyester and the second layer polyester is preferably at most 50 ° C. from the viewpoint of maintaining the adhesion between the two layers.

  The multilayer unstretched film thus obtained is stretched in the biaxial direction (the direction along the film surface) in the film forming direction and the width direction perpendicular thereto. The stretching temperature is preferably in the range of the glass transition temperature (Tg) to Tg + 50 ° C. of the polyester of the first layer. The area magnification at this time is preferably 5 to 50 times. The larger the draw ratio, the smaller the variation in the plane direction in the individual layers of the first layer and the second layer is reduced by thinning by stretching, that is, the optical interference of the multilayer stretched film becomes uniform in the plane direction. Therefore, it is preferable. The stretching method for stretching in two directions may be sequential biaxial stretching or simultaneous biaxial stretching.

  The multilayer film thus stretched is heat-treated at a temperature in the range from 10 ° C. lower than the melting point of the second layer polyester to 15 ° C. lower than the melting point of the first layer polyester. The purpose is to relax the orientation of the molecular chains in the layer and to lower the refractive index of the second layer. When the temperature of the heat treatment is lower than the melting point of the polyester for the second layer by more than 10 ° C., the effect of reducing the refractive index by relaxing the molecular chain orientation in the second layer is obtained and obtained. A sufficient refractive index difference cannot be imparted to the multilayer stretched film. On the other hand, if the temperature of the heat treatment is not lower by 10 ° C. or more than the melting point of the polyester for the first layer, the orientation of molecular chains in the first layer is relaxed and the refractive index is lowered, and the resulting multilayer stretched film Cannot provide a sufficient difference in refractive index. A preferable heat treatment temperature is 6 ° C. lower than the melting point of the second layer polyester, 16 ° C. lower than the melting point of the first layer polyester, and 2 more than the melting point of the second layer polyester. The temperature is lower by 18 ° C. than the melting point of the first layer polyester. The heat treatment time is preferably 1 to 60 seconds.

  Further, by changing the temperature and time of this heat treatment, the refractive index of the second layer can be adjusted without changing the resin composition, that is, the multilayer stretched film without changing the resin composition. The reflection characteristics can be changed.

[Evaluation methods]
In Examples and Comparative Examples described later, the physical properties and characteristics of films were measured or evaluated by the following methods.

(1) Melting point and glass transition point (Tg) of polyester resin
10 mg of a polyester resin sample is sampled, and the melting point is measured at a temperature increase rate of 20 ° C./min using DSC (trade name: DSC2920, manufactured by TA Instruments).

(2) Thickness of each layer A sample is cut into triangles, fixed to an embedded capsule, and then embedded in an epoxy resin. And the embedded sample was cut | disconnected along the film forming direction and thickness direction with the microtome (ULTRACUT-S, manufacturer: Reichert), and it was set as the thin film slice | slice of thickness 50nm. The obtained thin film slices were observed and photographed at an accelerating voltage of 100 kV using a transmission electron microscope (manufacturer: JEOL Ltd., trade name: JEM2010), and the thickness of each layer was measured from the photograph.

(3) Optical characteristics (reflectance, reflection wavelength)
Using a spectrophotometer (manufactured by Shimadzu Corp., MPC-3100), the relative specular reflectance with the aluminum-deposited mirror at each wavelength is measured in the wavelength range of 350 nm to 2000 nm. The maximum reflectance among the measured reflectances is defined as the maximum reflectance, and the wavelength thereof is defined as the maximum reflection wavelength.

(4) Optical characteristics (total light transmittance and haze)
According to JIS K7105-1981, a total light transmittance Tt (%) and a scattered light transmittance Td (%) were measured using a haze measuring machine (NDH-20, manufactured by Nippon Denshoku Industries Co., Ltd.). The haze H (%) is calculated from the equation “H = (Td / Tt) × 100”.

(5) Reflection peak wavelengths at 5 and 50 degrees Relative to spectrophotometer (manufactured by Shimadzu Corp., MPC-3100) with variable angle unit and aluminum deposited mirror at each wavelength at 5 and 50 degrees The specular reflectance is measured in the wavelength range of 350 nm to 2000 nm. The maximum reflectance among the measured reflectances is defined as the maximum reflectance, and the wavelength thereof is defined as the peak reflection wavelength.

(6) Adhesion between layers Adhesive tape of 24 mm width (made by Nichiban Co., Ltd., trade name: cello tape) is attached to both surfaces of a sample film (10 mm × 50 mm), peeled off at a peeling angle of 185 degrees, and then peeled off. Observe. This was performed for each 10 samples, and the number of delaminations was counted.

(7) Color spots Prepare 10 sheets of A4 size sample film, overlay each sample film on white plain paper, and visually observe the color spots of the transmitted color in the sample film under 30 lux illumination. evaluated. In addition, 10 A4-size sample films were prepared, and the back surface of each sample film was colored with a black spray. Then, under the illumination of 30 lux, the reflected color spots in the sample film were visually observed. evaluated.
Then, the color spots of the transmitted color and the reflected color were synthesized and judged according to the following evaluation criteria.
○: There is no visible color spot in the sample.
Δ: Part of the sample with a different color is observed.
X: Color spots that clearly appear as spots or streaks can be confirmed.

[Example 1]
Polyethylene terephthalate (PET) having an intrinsic viscosity of 0.62 (orthochlorophenol, 35 ° C.) is used as the first layer polyester, and 12 mol% of isophthalic acid is copolymerized as the second layer polyester. Copolymerized polyethylene terephthalate (IA12PET) of chlorophenol (35 ° C.) and true spherical silica particles (average particle size: 1.5 μm, ratio of major axis to minor axis: 1.02, average deviation of particle size: 0.1. Among them, a type to which 0.10% by weight of type “A” was added was prepared. The first layer polyester and the second layer polyester are each dried at 170 ° C. for 3 hours and then supplied to an extruder, heated to 280 ° C. to be in a molten state, and the first layer polyester is 101. After the polyester for the second layer and the second layer are branched into 100 layers, a multilayer feedblock device in which the first layer and the second layer are alternately stacked is used, and the die is maintained while maintaining the stacked state. Then, the film was cast on a casting drum to produce a total of 201 unstretched multilayer laminated films in which the first layer and the second layer were alternately laminated so that the thickness of each layer was equal. At this time, the extrusion amount of the first layer and the second layer was adjusted to be 1: 1, and the both end layers were laminated so as to be the first layer. This multilayer unstretched film was stretched 3.6 times in the film forming direction at a temperature of 90 ° C., further stretched 3.9 times in the width direction at a temperature of 95 ° C., and heat-fixed at 230 ° C. for 3 seconds. . Table 2 shows the physical properties of the obtained biaxially stretched multilayer laminated film.

[Examples 2-3]
A biaxially stretched multilayer laminated film was produced in the same manner as in Example 1 except that the thickness conditions of each layer were changed as shown in Table 1. The properties of the obtained multilayer stretched film are shown in Table 2.

[Comparative Example 1]
Polyethylene 2,6-naphthalenedicarboxylate (PEN) with intrinsic viscosity 0.62 (orthochlorophenol, 35 ° C.) and true spherical silica particles (average particle size: 0.20 μm, ratio of major axis to minor axis: 1.02 Average deviation of particle size: 0.1. In the table, 0.10% by weight of the type “I” is added to make polyester for the first layer and 12 mol% of isophthalic acid is copolymerized. .65 (orthochlorophenol, 35 ° C.) copolymerized polyethylene terephthalate (IA12PET) was prepared as the second layer polyester. Then, the first layer polyester and the second layer polyester are each dried at 170 ° C. for 5 hours, then supplied to an extruder, heated to 300 ° C. to be in a molten state, and the first layer polyester is 101. After the polyester for the second layer and the second layer are branched into 100 layers, a multilayer feedblock device in which the first layer and the second layer are alternately stacked is used, and the die is maintained while maintaining the stacked state. Then, the film was cast on a casting drum to produce a total of 201 unstretched multilayer laminated films in which the first layer and the second layer were alternately laminated so that the thickness of each layer was equal. At this time, the extrusion amount of the first layer and the second layer was adjusted to be 1: 1, and the both end layers were laminated so as to be the second layer. This multilayer unstretched film was stretched 3.6 times in the film forming direction at a temperature of 115 ° C., further stretched 4.0 times in the width direction at a temperature of 120 ° C., and heat-set at 200 ° C. for 3 seconds. .

  The obtained multilayer stretched film was a film with severe color spots and inferior peeling properties between layers. The physical properties are shown in Table 2.

[Comparative Examples 2 to 4]
The same operation as in Comparative Example 1 was repeated except that the production conditions were changed as shown in Table 1. The films obtained in Comparative Examples 2 and 3 were inferior in reflection performance. Similar to Comparative Example 1, the film obtained in Comparative Example 4 was a film with severe color spots and inferior peeling properties between layers. The physical properties are shown in Table 2.

  “IA3PET” indicating the resin type in the table is polyethylene terephthalate having an intrinsic viscosity of 0.65 (orthochlorophenol, 35 ° C.) obtained by copolymerizing 3 mol% of isophthalic acid. “NDC10PET” is polyethylene terephthalate having an intrinsic viscosity of 0.70 (orthochlorophenol, 35 ° C.) obtained by copolymerization of 10 mol% of 2,6-naphthalenedicarboxylic acid.

  The film of the present invention can be preferably applied to decorative applications such as clothing and packaging because it is excellent in design as a forgery prevention seal utilizing the angle dependence of reflected light wavelength and structural color development.

The light reflectance curve graph of a film.

Explanation of symbols

1 Difference between maximum reflectance and baseline of reflectance 2 Baseline of reflectance 3 Half width at maximum reflectance

Claims (6)

  A multilayer laminated film in which the first layer and the second layer are alternately laminated so that the total number of layers is 11 or more, and biaxially stretched, wherein the first layer and the second layer are The thickness is in the range of 0.05 to 0.5 μm, the first layer is composed of a polyester composition, the second layer is composed of a polyester composition having a composition different from that of the first layer, and the first layer The maximum reflectance of light in the wavelength range of 350 to 2000 nm is 20% or more higher than the reflectance baseline obtained from the light reflectance curve in the wavelength range of 350 to 2000 nm. And the half value width of the reflectance curve in the maximum reflectance is 10-100 nm, The biaxially stretched multilayer laminated film characterized by the above-mentioned.   The biaxially stretched multilayer laminated film according to claim 1, wherein the first layer and the second layer have a refractive index difference of 0.03 to 0.20.   The difference between the maximum reflectance wavelength for light with an incident angle of 5 degrees and the maximum reflectance wavelength for light with an incident angle of 50 degrees is 50 nm or more in a wavelength range of 350 to 2000 nm. The biaxially stretched multilayer laminated film according to any one of the above.   The ratio of the ethylene terephthalate component in the film of a biaxially stretched multilayer laminated film is 80 mol% or more based on the total repeating units of the polyester. Stretched multilayer laminated film.   The biaxially oriented multilayer laminated film according to any one of claims 1 to 4, wherein 1.5 to 20 mol% of all repeating units is an isophthalic acid or 2,6-naphthalenedicarboxylic acid component.   The polyester constituting the first layer is a crystalline polyester, 90 mol% or more of all repeating units are ethylene terephthalate components, the polyester constituting the second layer is a crystalline polyester, and all repeating 75-97 mol% of a unit is an ethylene terephthalate component, The biaxially-stretched multilayer laminated film in any one of Claims 1-5 characterized by the above-mentioned.

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