JP2011201107A - Resin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem wherein when different resin is used for an outer layer and a core layer of a three-layer resin film, curls are generated in the film having irregularity formed thereon.SOLUTION: The same resin is used for outer layers on the surface and back face. A index ratio of a moment of inertia of the cross section between the both outer layers to which irregularities are applied is set to be ≥0.8 and ≤1.2.

Description

  The present invention relates to a resin film in which at least one surface has an uneven shape.

  A resin film with a three-layer structure formed by differentiating the characteristics of the outer layer constituting the front and back surfaces and the core layer sandwiched between the front and back outer layers is a film that can obtain characteristics that cannot be obtained with a single-layer film. Widely used industrially.

  For example, biaxially stretched polyethylene terephthalate film and polycarbonate film having high mechanical strength and high heat resistance are known, but their surface processability is also poor due to their high strength and heat resistance. Therefore, by forming a resin layer with excellent workability such as copolymer polyester and low Tg polymer alloy on the surface, it should be a film with excellent surface processability while maintaining high mechanical strength and high heat resistance. Can do.

  Moreover, the film which provided the unevenness | corrugation on the surface is known as a film, an optical functional film, etc. which are excellent in slipperiness.

  As the optical functional film, a light diffusing film, a prism sheet, a microlens film, an antireflection film, a wire grid polarizing film, and the like used for a backlight of a liquid crystal display are known. For example, a prism sheet is formed on the surface with a concave-convex shape such that a large number of fine triangular prisms having a substantially right-angled isosceles triangle cross section are arranged without gaps with one side on the long side parallel to the film surface. It is a thing.

  Such a film was prepared by applying a photocurable resin on a transparent substrate to form a prism pattern (Patent Document 1), and was prepared by hot pressing a mold on a sheet made of a thermoplastic resin. (Patent Document 2, Patent Document 3).

JP 62-144102 A Japanese Patent Laid-Open No. 9-21908 JP-A-9-323354

  However, when different resins are used for the outer layer and the core layer of the three-layer resin film, curling occurs in the film with irregular shapes, causing problems during transportation and use, and uneven brightness in the optical film There was a problem of doing. In particular, the curl becomes conspicuous when the overall thickness is thin or the uneven shape is large. Accordingly, the present invention provides a three-layer resin film having a concavo-convex shape that suppresses the occurrence of curling even when it is thin and has a large concavo-convex shape on the surface.

The present invention employs the following means in order to solve such problems. That is,
A resin film in which at least one surface of the outer layer of a three-layer structure composed of at least a front and back outer layer made of the same resin and a core layer sandwiched between the front and back outer layers has an uneven shape, and has the largest thickness When the thickness of the part is T, and the average depth of each outer layer surface shape is Da, Db from the larger one,
(Da + Db) /T≧0.07
A resin film having a cross-sectional second moment index ratio of both outer layers of 0.8 or more and 1.2 or less,
It is.

  According to the present invention, different resins are used for the outer layer and the core layer of the three-layer resin film, and even when the three-layer configuration is such that the outer layer and the core layer have different thermal linear expansion coefficients, plane orientation coefficients, glass transition points, etc. Moreover, although the three-layer resin film is thin, the occurrence of curling can be suppressed even when a large uneven shape is applied.

It is a figure which shows thickness T of the largest part. It is a figure which shows the example of the uneven | corrugated shape formed in the resin film surface of this invention. It is a figure which shows the cross-sectional shape in a direction perpendicular | vertical with respect to the longitudinal direction of an uneven | corrugated shape. It is a figure which shows the example of the method of forming several uneven | corrugated shape in the outer layer of the resin film of this invention. It is a figure which shows the cut surface of the 3 layer resin film which gave uneven | corrugated shape. It is a figure showing the position of a centroid. It is a figure which shows the metal mold | die which has a stripe shape.

The resin film of the present invention is a resin film in which at least one surface of the outer layer of a three-layer structure composed of at least an outer layer made of the same resin and a core layer sandwiched between the outer layers of the front and back surfaces has an uneven shape. .
The resin film of the present invention has a thickness of the thickest portion as T (FIG. 1), and when the average depth of each outer layer surface shape is Da, Db from the larger one,
(Da + Db) /T≧0.07
It satisfies the relationship. That is, the shape shaped with respect to the whole thickness has a certain size or more. When the value of (Da + Db) / T is smaller than 0.07, the curl problem hardly occurs.
The example of the uneven | corrugated shape formed in the resin film surface of this invention is shown in FIG. 2A to 2E are perspective views schematically showing the uneven shape. As an arrangement structure within the surface of the concavo-convex shape formed on the surface of the outer layer, a stripe pattern (a plurality of concavo-convex shapes extending in one direction as shown in FIGS. 2A to 2C) As an example, a pattern in which shapes such as a dome shape and a pyramid shape are spread as shown in FIGS. 2D and 2E can be given. The stripe pattern illustrated in FIGS. 2A to 2C will be described. FIG. 3 shows a cross-sectional shape in a direction perpendicular to the longitudinal direction of the concavo-convex shape. The cross-sectional shape of each stripe is an isosceles triangle, equilateral triangle, right-angled isosceles triangle, a modified triangle (FIG. 3A), a semicircle, a semi-ellipse, or an arc shape obtained by deforming them (see FIG. 3). 3 (b)), waveform shapes such as regular sine curves and random curves (FIG. 3D), and the like.
Further, as shown in FIGS. 3 (a) and 3 (b), each of the cross-sectional shapes may be a repeating pattern having the same shape, or as shown in FIG. 3 (d), a regular or random array pattern having different sized shapes. Alternatively, as shown in FIG. 3E, regular or random patterns having different shapes are also preferable embodiments.
Further, as shown in FIG. 3F, a shape in which flat portions are formed between adjacent patterns in the cross section of each stripe is also used. However, since the light incident on the flat portion is likely to pass through without being subjected to angle conversion, as shown in FIGS. 3A to 3E, flat portions are formed between adjacent patterns. Shapes that are not done are preferred.

  Further, the cross-sectional shape of each stripe may be a uniform stripe having the same shape and size when observed in the longitudinal direction of the stripe, or may be the same shape but different in size (that is, the height fluctuates). A stripe) or a stripe whose shape changes.

  Furthermore, when the stripes are observed from the normal direction of the film, the individual stripes may be completely straight, or may be used when the stripes are not straight, for example, wavy. Therefore, the distance (pitch) between individual stripes is also used regularly and randomly.

  Next, as shown in FIGS. 2D and 2E, a pattern in which shapes such as a dome shape and a pyramid shape are spread will be described. Preferable shapes can be roughly divided into a hemispherical shape such as a dome shape and a polygonal pyramid shape such as a pyramid shape.

  In the case of a hemispherical shape, a hemisphere, a shape obtained by expanding and contracting the hemisphere in the height direction (semi-spheroid), and the like may be mentioned, and the shape may be anisotropic in the film plane. In the case of anisotropy, anisotropy can be optically induced by aligning the major axis directions of the individual shapes. As for the arrangement in the hemispherical film plane, a regular arrangement (such as closest packing) and a random arrangement are preferably used.

  In the case of a polygonal pyramid shape, a triangular pyramid, a quadrangular pyramid, a hexagonal pyramid, an octagonal pyramid, and the like are given as examples. Also in this case, the arrangement in the film plane is preferably a regular arrangement or a random arrangement. These shapes may be uniform patterns having the same shape in the film plane, or may be composite shapes in which other types of shapes are arranged.

For example, when a stripe pattern as shown in FIGS. 2A to 2C is formed on the surface, anisotropy corresponding to the direction of the stripe may occur particularly with respect to curling. The effect by is great.
In the present invention, the average depth of the outer layer surface shape is
Da / Db ≧ 5
It is preferable to satisfy the relationship.
That is, when there is a difference in the size of the concavo-convex shape, curling is particularly likely to occur, and the effects of the present invention are more exhibited.

  The resin film of the present invention has a three-layer structure consisting of at least front and back outer layers made of the same resin and a core layer sandwiched between the front and back outer layers.

  Here, the resin constituting the outer layer and the core layer is not particularly limited. For example, polyethylene terephthalate, polyethylene-2, 6-naphthalate, polypropylene terephthalate, polybutylene terephthalate, cyclohexanedimethanol copolymer polyester resin, isophthalic acid Polyester resins such as copolyester resins, spiroglycol copolyester resins, fluorene copolyester resins, polyolefin resins such as polyethylene, polypropylene, polymethylpentene, cyclic polyolefin copolymer resins, acrylic resins such as polymethyl methacrylate, Polycarbonate, polystyrene, high impact polystyrene, styrene / acrylonitrile copolymer, methyl methacrylate / styrene copolymer, methyl methacrylate Heat-resistant styrene resin obtained by copolymerization of acrylate / butadiene / styrene copolymer, styrene / maleic anhydride copolymer, styrene / methacrylic acid copolymer, α-methylstyrene or maleimide, and styrene / acrylonitrile series Copolymer resin, α-methylstyrene / acrylonitrile copolymer resin, polyphenylene ether resin, polyamide, polyether, polyester amide, polyether ester, polyvinyl chloride, and a copolymer containing these as a component, or a mixture of these resins And other thermoplastic resins.

  Of these, cyclic polyolefin-based, polyester-based, polycarbonate-based, and polystyrene-based resins are more preferably used in terms of mechanical strength, heat resistance, dimensional stability, and surface formability.

  The core layer and the outer layer of the present invention have different characteristics in mechanical strength, heat resistance, chemical resistance, environmental resistance, and the like according to characteristics required according to the application. The outer layer has the characteristics of the outer layer, and the core layer has the characteristics of the core layer, so that the resin film can be made multifunctional. For example, a rigid and easy-to-mold resin film can be obtained by imparting mechanical characteristics to the easily molded layer and the core layer as the outer layer.

As a method of making the properties of the core layer and the outer layer different, a method of making the glass transition point different by making the resin composition different, a molecular weight different, etc., a method of making the molecular orientation state of the outer layer and the core layer different, an outer layer and a core There is a method of varying the crystallinity of the layer.
Here, the molecular orientation state can be expressed by a plane orientation coefficient. The plane orientation coefficient represents the strength of polymer orientation in the film plane. The larger the plane orientation coefficient, the higher the orientation state. When the plane orientation coefficient is 0, the surface orientation coefficient is random. Indicates that there is.

When making the crystallinity different, it is preferable that the crystallinity of the core layer is larger than the crystallinity of the outer layer. Accordingly, the core layer can be given mechanical and thermal strength by crystallization, and the outer layer can be made excellent in moldability by suppressing crystallization.
In the present invention, the crystallinity refers to the weight fraction crystallinity Xc and is defined by the following formula 1. Note that the density of the sample, the density of the crystal, and the density of the amorphous are ρ, ρc, and ρa, respectively.
The crystallinity of the three-layer laminate film can be determined by using Raman spectroscopy to obtain the density from the measurement of the Raman spectrum, and then performing line analysis to obtain the crystallinity in each laminate.

As an example of a preferable combination of the core layer and the outer layer of the resin film of the present invention, for example, the glass transition point may be obtained by changing some molecular components or changing the molecular weight while having the same kind of molecular skeleton in the core layer and the outer layer. A combination of resins having different values can be given.

  Even with such approximate resins, the difference in thermal expansion coefficient causes curling when a three-layer resin film is formed.

  Here, the thermal linear expansion coefficient is an expansion coefficient indicating the rate at which the length of an object expands due to an increase in temperature per 1K.

  Further, as another example of the combination of the core layer and the outer layer, naphthalenedicarboxylic acid copolymerized PET (hereinafter, referred to as the core layer is a biaxially stretched polyethylene terephthalate (hereinafter sometimes abbreviated as “PET”) and the outer layer is relaxed in orientation. An example of “PET / N” may also be given.

  In such a case, since the orientation of the core layer is fixed during biaxial stretching, the core layer is in a highly oriented state and has high strength, but the outer layer is in a state in which the orientation is relaxed, so that the plane orientation coefficient is In contrast, it is considered that the difference in the amount of dimensional change due to environmental changes causes curling.

  In the present invention, in order to suppress the occurrence of curling even though it is a three-layer resin film having a concavo-convex surface, attention is paid to the sectional second moment index ratio of each outer layer, and curling is controlled by controlling this to a specific range. It has been found that it can be completely suppressed.

  In the present invention, the cross-sectional secondary moment index is a value obtained by approximating the cross-sectional secondary moment, and the cross-sectional secondary moment is determined by the cross-sectional shape dimensions of the material and has a small area element. The dA is defined as the product of the distance from a certain axis (the second moment of area) added to the entire figure (Reference 1).

  In order to control the cross-sectional secondary moment index ratio from 0.8 to 1.2, the cross-sectional secondary moment index ratio calculated from the surface shape to be formed is calculated in advance, and the thickness configuration of the resin film is designed from here. In some cases, the average thickness of the outer layer is changed by 5% or more of the total thickness.

  Here, the average thickness of the outer layer is a thickness when the outer layer having the uneven shape is averaged flat, and is equal to the thickness of the outer layer before the uneven shape is applied to the outer layer. Further, the total thickness is the thickest portion of the film having a concavo-convex shape. Ten points of the film are selected at random, the thickness is measured, and the maximum value is taken as the total thickness.

  A more preferable cross-sectional second moment index ratio of both outer layers is 0.9 or more and 1.1 or less. By setting it in such a range, not only the initial curl but also the curl after the wet heat resistance test can be suppressed.

  When the shape of the shaped shape relative to the overall thickness is small, the influence of the shape on the secondary moment index of the cross section becomes small, and curling does not occur even if the average thickness of the outer layer is equal, but the shape is shaped to the overall thickness. When the size of the shape is large, the change in the sectional secondary moment index due to shaping increases, and when the thickness of the outer layer is made equal, the difference in the sectional secondary moment index of the outer layer increases and curling occurs.

  Here, the average depth of the outer layer surface shape is an average value of the shape depth in a cross section cut by a plane orthogonal to the stripe, that is, the thickness of 10 points from the highest height in each outer layer portion is D1, D2, D3,... D10, where 10 points from the smallest are d1, d2, d3,..., D10, the average value of D1-d1, D2-d2,. To tell. In addition, when the shape is not a stripe shape, the average value of the shape depth means that 20 points are sampled randomly in the film surface, and the thicknesses of 10 points from the largest height are D1, D2, D3,. When 10 points from the smallest are d1, d2, d3,..., D10, the average value of D1-d1, D2-d2,.

As a method for producing a three-layer laminate in the resin film of the present invention, a method for producing a laminate without using an adhesive as described below is preferable.
(I) A method in which the resin constituting the support layer and the resin constituting the outer layer are separately charged into two extruders, melted and coextruded onto a cast drum cooled from the die, and processed into a sheet (coextrusion) Law)
(ii) A method in which a resin constituting the outer layer is put into an extruder and melt-extruded and laminated while being extruded from a die on a sheet of a support layer produced by a single film (melt lamination method)
(iii) A method in which a support layer sheet and an outer layer sheet made of a single film are separately prepared and thermocompression bonded by a heated roll group (thermal lamination method)
(Iv) In addition, a method (coating method) in which the outer layer sheet is dissolved in a solvent, and the solution is applied onto the support layer sheet and dried.

  The use of an adhesive is not preferable because the number of work steps increases and the cost increases. Among these, the coextrusion method of coextrusion and processing into a sheet shape is a preferable method in that a laminate can be produced with high accuracy in a single step.

Laminates by the coextrusion method have the excellent feature that the number of processes and therefore the cost is low, but the interface of each layer is in direct contact, so the stress when the dimensional change of each layer is different does not disperse the curl. There is a drawback that is likely to occur. For this reason, the resin film of the present invention has a great effect of suppressing curling.
When a crystalline resin such as polyester is used for the outer core layer, the melting endothermic peak temperature (Tm ₁ ) of the resin constituting the support layer is equal to or higher than the melting endothermic peak temperature (Tm ₁ ) of the resin constituting the molding layer after biaxial stretching. ₂ ) Heat treatment is performed at a temperature below. By performing such heat treatment, the resin constituting the molding layer becomes in an amorphous state, and the resin constituting the support layer can maintain the orientation state without melting and improve the mechanical strength. That is, by setting the heat treatment temperature after biaxial stretching within this range, it is possible to obtain a film having both formability and mechanical strength in a consistent film forming process by coextrusion. The heat treatment temperature may be at least the melting endothermic peak temperature Tm _{1 of} the resin constituting the molding layer, but it is preferably at least 5 ° C, more preferably at least 10 ° C, particularly preferably at least 20 ° C. It is. By increasing the heat treatment temperature by 5 ° C. or more from the melting endothermic peak temperature Tm _{1 of} the resin constituting the molding layer, the orientation relaxation of the resin constituting the molding layer proceeds and the moldability is improved by increasing the amorphous part. Therefore, it is preferable. In addition, an amorphous resin or the like in which Tm is not observed is preferably heat-treated at a temperature of (Tg + 100 ° C.) to (Tg + 150 ° C.) from the viewpoint of an increase in amorphous contributing to moldability and relaxation of the tension state of the molecular chain.
Here, the melting endothermic peak temperature Tm is obtained by the following procedure.
Using DSC as a DSC robot “DSC220” manufactured by Seiko Electronics Industry Co., Ltd. and as a data analysis device using the company's disk station “SSC / 5200”, 5 mg of the composition or film sample was filled into an aluminum tray, and this sample was used. Heat from room temperature to 300 ° C. at a rate of temperature increase of 20 ° C./min to melt for 5 minutes, and measure the temperature (Tm) of the melting endothermic peak observed in this process.

  An example of a method for forming a plurality of uneven shapes on the outer layer of the resin film of the present invention will be described with reference to FIG. Both the resin film of the present invention before forming the concavo-convex shape on the outer layer and the mold having a shape obtained by inverting the pattern to be transferred, the glass transition temperature Tg of the entire resin constituting the outer layer, Tg + 60 ° C. or lower In the temperature range (FIG. 4A). Next, the outer layer of the resin film and the concavo-convex surface of the mold are brought close to each other (FIG. 4B), pressed as it is at a predetermined pressure, and held for a predetermined time (FIG. 4C). Next, the temperature is lowered while maintaining the pressed state. Finally, the press pressure is released to release the resin film from the mold (FIG. 4D).

  As a pattern forming method for the outer layer, in addition to a method of pressing a flat plate as shown in FIG. 4 (flat plate pressing method), a roll-shaped mold having a pattern formed on the surface is used to form a roll-shaped film. The roll-to-roll continuous molding may be performed to obtain a roll-shaped molded body. The flat plate pressing method is excellent in that a finer and higher aspect ratio pattern can be formed. The roll-to-roll continuous forming is superior to the flat plate pressing method in terms of productivity. Furthermore, in the case of roll-to-roll continuous molding, since the core layer is present in the resin film of the present invention, the film itself is firmer than the single film made of the resin constituting the outer layer, so that the moldability is high. Is excellent.

Below, the measuring method and evaluation method of each Example and a comparative example are demonstrated. In each of the following measurements, each sample was evaluated with an average value of values obtained by performing the measurement three times. The following measurements were all performed under conditions of room temperature of 23 ° C. and humidity of 65%.

(Measurement and evaluation method)
A. Measurement of curl amount A sample having a concavo-convex shape of 50 mm × 50 mm size was placed on a desk with the surface on which the convex shape was formed facing up. The curl amount (height from the film installation surface) of the four corners of the sample was measured, and the average value was taken as the curl amount. In addition, a curl amount of ± 3.0 mm or less was defined as low curl. If the sample is 50 mm × 50 mm or less, the curl amount is measured after cutting the sample into as large a square as possible.

B. A laminate thickness measurement sample is cut in a direction perpendicular to the film surface using a microtome or the like, and the cut surface is observed with a scanning electron microscope (hereinafter referred to as SEM) to measure the laminate thickness. In SEM observation, when the contrast between the core layer and the outer layer is low and it is difficult to observe the interface, a thin film slice is prepared from the cut surface and observed with a transmission electron microscope (hereinafter referred to as TEM). Measure. Further, in TEM observation, when the contrast between the core layer and the outer layer is low and it is difficult to observe the interface, a means for enabling the interface to be observed by staining or the like is taken. These observation magnifications are maximized within a range in which the thickness direction of the sample is entirely within the observation field. For example, when a three-layer film having a total thickness of 50 μm is used, it is possible to measure at a magnification of 1000 times in TEM observation.
The cutting direction is not particularly specified when the surface unevenness is a random shape, but when the unit shape is repeated, cutting is performed in a direction perpendicular to the repeated arrangement direction. That is, in the case of a stripe arrangement shape, cutting is performed in a direction parallel to the longitudinal direction of the stripe unit.

C. Sectional moment index ratio calculation of outer layer (back surface layer with respect to molding layer) (1) For each sample, 100 sections are created. At this time, the cutting direction is not particularly specified when the surface unevenness is a random shape, but when the unit shape is repeated, the cutting direction is repeatedly cut in a direction perpendicular to the arrangement direction. That is, in the case of a stripe arrangement shape, cutting is performed in a direction parallel to the longitudinal direction of the stripe unit.
(2) Cross-sectional SEM observation of each of the 100 cut surfaces is performed in the same manner as in (B.) above, and an image capable of measuring the laminated thickness is obtained. A substantially rectangular figure having a width B in the direction parallel to the boundary line between the core layer and the outer layer is cut out from the cross-sectional observation image. Here, in the substantially rectangular figure, both outer layers are the outer layer 1 and the outer layer 2, the thickness of the outer layer 1 is h1, the thickness of the outer layer 2 is h2, the thickness of the core layer is hc, and the width of the cut surface is B.
Here, when the outer layer is not rectangular and the thickness is not constant in the cross-sectional figure, the outer layer in the observation visual field is equally divided into 11 in the direction parallel to the boundary line of the outer core layer, and 10 dividing lines and the outer core layer are divided. The average value of the thicknesses at the 10 intersections of the boundary line is the thickness of the outer layer. (Fig. 5)
(3) As shown in FIG. 6, the center of gravity of the entire cross-section is centroid c, the center of gravity of the outer layer 1 is centroid 1, and the center of gravity of the outer layer 2 is centroid 2. At this time, the y coordinate of the centroid c when the lower left of the outer layer 1 is the origin is Yc, the y coordinate of the centroid 1 is Y1, and the y coordinate of the centroid 2 is Y2.
(4) I1 and I2 are calculated according to Equations 2 to 6, and the sectional secondary moment exponent ratio in each sectional image is calculated according to Equation 7. At this time, if I1 <I2 in Expression 7, the obtained sectional second moment index ratio is I1 / I2.
(5) The above-mentioned (1) to (3) are carried out on 100 cut surfaces, and all are averaged to obtain the sectional second moment index ratio of the entire film.

D. Thermal linear expansion coefficient As heat / stress / strain measurement (TMA), measurement was performed using an apparatus “EXSTAR TMA / SS6000” manufactured by SII Nano Technology Co., Ltd. A film sample having a longitudinal direction of 20 mm and a lateral direction of 4 mm was set in a sample tube. Subsequently, it heated with the temperature increase rate of 10 degree-C / min from -40 degreeC to 95 degreeC on the conditions of load 49.0mN. And after keeping constant at 95 degreeC for 15 minutes, it cooled to -40 degreeC on the conditions of temperature-fall rate 10 degree-C / min. Under such conditions, the change in length of the sample in the longitudinal direction was measured.
In the case of a three-layer film, a resin for each of the outer layer and the core layer is prepared, and the film is measured under the same film forming conditions.
The thermal expansion coefficient was calculated according to the following formula in the following temperature range when the temperature was lowered, and the average value was defined as the thermal expansion coefficient of each layer (−40 to −30, −20 to −30,..., 70 to 80 80-90 ° C).
Thermal expansion coefficient calculation formula:
Thermal linear expansion coefficient = Change in length at each temperature range (every 10 ° C.) / 10 / Length at the initial temperature drop in each temperature range.

E. Measurement of the plane orientation coefficient A film sample having both the longitudinal direction and the short side direction of 40 mm is prepared, the layer for measuring the plane orientation coefficient is adhered to the glass surface, and then the sodium D line (wavelength 589 nm) is used as a light source, The methylene iodide was used as a refractive index in the longitudinal direction, the width direction, and the thickness direction (Nx, Ny, and Nz, respectively) using an Abbe refractometer. In the case of a three-layer film, a resin for each of the outer layer and the core layer is prepared, and the film is measured under the same film forming conditions.
The plane orientation coefficient fn was obtained by calculating fn = (Nx + Ny) / 2−Nz.

F. Tg (glass transition temperature) measurement As a differential scanning calorimetry (DSC), a robot DSC “RDSC220” manufactured by Seiko Denshi Kogyo Co., Ltd. is used, and as a data analysis device, a disk station “SSC / 5200” manufactured by the same company is used. Fill the saucer with 5 mg of composition or film sample. This sample is heated from room temperature to 300 ° C. at a temperature rising rate of 20 ° C./min and melted for 5 minutes. Then it is quenched with liquid nitrogen. Further, it is heated from room temperature to 300 ° C. at a temperature rising rate of 20 ° C./min and melted for 5 minutes. The glass transition temperature was measured in this process, that is, the second temperature raising process.

[Example 1]
Cyclic polyolefin resin 1 (ZEONOR1420R, Tg 136 ° C., manufactured by Nippon Zeon Co., Ltd.) as the resin constituting the core layer, and cyclic polyolefin resin 2 (ZEONOR1020R, Tg 102 ° C., manufactured by Nippon Zeon Co., Ltd.) as the resin constituting the outer layer ) Was prepared.
These were dried at 100 ° C. for 6 hours and then melted in a separate extruder at a temperature of 240 ° C. Next, the laminated resin extruded from the molten three-layer coextrusion die was extruded into a sheet shape on a metal drum maintained at 100 ° C. By winding the metal drum at a speed of 25 m / min, the thickness of the outer layer 1 / core layer / outer layer 2 is 11.7 μm / 29.6 μm / 7.7 μm, respectively, and the total is 49 μm. (The difference in thermal linear expansion coefficient of the outer core layer was 6 ppm / ° C., and the plane orientation coefficient of the outer layer was fn = 0).
Next, using a 2 ton vacuum heater press machine (MKP-150TV-WH, manufactured by Mikado Technos Co., Ltd.), the following mold 1 having a pitch P of 25 μm between adjacent patterns and a height of d12.5 μm and the laminated sheet 1 are 142 ° C. The mold 1 and the laminated sheet 1 were hot-pressed for 30 seconds at a pressure of 2.34 MPa while maintaining 142 ° C. for 1 minute. Subsequently, the heat press was released, the mold was cooled to 87 ° C., and then the laminated sheet was released from the mold, thereby reversing the shape of the following mold 1 on the surface of the outer layer 1 of the laminated sheet 1. An optical sheet 1 having a pattern was obtained. The thickness of outer layer 1 / core layer / outer layer 2 of optical sheet 1 was 18.0 μm / 29.6 μm / 7.7 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 55.3 μm. In addition, the cross-sectional second moment index ratio of the outer layer at this time was 0.839. The curl amount of this optical sheet 1 was −1 mm.
(Mold 1)
In-plane pattern: Striped (Figure 7)
Individual shape: right-angled isosceles triangle (height d: 12.5 μm)
Pitch between adjacent patterns (p): 25 μm
Size: 100 mm × 100 mm (pattern area).

[Example 2]
An optical sheet 2 was obtained in the same manner as in Example 1 except that the following mold 2 having a pitch P of 15 μm between adjacent patterns and a height of d7.5 μm was used. The thicknesses of the outer layer 1 / core layer / outer layer 2 of the optical sheet 2 were 15.5 μm / 29.6 μm / 7.7 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 52.8 μm. At this time, the sectional second moment index ratio of the outer layer was 0.806. The curl amount of this optical sheet 2 was −1.6 mm.
(Mold 2)
In-plane pattern: Striped (Figure 7)
Individual shape: right-angled isosceles triangle (height d: 7.5 μm)
Pitch between adjacent patterns (p): 15 μm
Size: 100 mm × 100 mm (pattern area).

Example 3
Polyester resin 1 (PET Toray Co., Ltd.) as the resin that constitutes the core layer, and polyester resin 2 (8 mol of 2,6-naphthalenedicarboxylic acid having an intrinsic viscosity of 0.65 dl / g) as the resin that constitutes the outer layer % Copolymerized PET, Tg: 86 ° C. manufactured by Toray Industries, Inc.). These were dried at 180 ° C. for 3 hours and then melted in a separate extruder at a temperature of 240 ° C. Subsequently, the laminated resin extruded from the molten three-layer coextrusion die was closely cooled and solidified while applying an electrostatic charge to a cooling drum maintained at 25 ° C. Next, the cast film was stretched 3.3 times in a longitudinal direction at 90 ° C. by a roll type stretching machine. Next, this film was introduced into a tenter, and after transverse stretching at 110.degree. C. by 3.2 times, heat treatment was performed in a temperature zone controlled to 240.degree. C., followed by 4% relaxation treatment at 170.degree. C. in the width direction. Thereafter, the sheet is cooled to room temperature and wound up to obtain a three-layer laminated sheet 2 having a thickness of 7.5 μm / 28.9 μm / 8.6 μm and a total of 45 μm (difference in thermal linear expansion coefficient of outer core layer: 19 ppm / ° C., outer layer The plane orientation coefficient fn = 0.084) was obtained.
An optical sheet 3 was obtained in the same manner as in Example 1 except that such a three-layer laminated sheet 2 was used. The thickness of outer layer 1 / core layer / outer layer 2 of optical sheet 3 was 13.8 μm / 28.9 μm / 8.6 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 51.3 m. In addition, the cross-sectional second moment index ratio of the outer layer at this time was 1.075. The curl amount of the optical sheet 3 was −2.4 mm.

Example 4
An optical sheet 4 was obtained in the same manner as in Example 3 except that the following mold 3 having a pitch P of 24 μm between adjacent patterns and a height of d12 μm was used. The thickness of the outer layer 1 / core layer / outer layer 2 of the optical sheet 4 was 13.5 μm / 28.9 μm / 8.6 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 51.0 mm. Further, the cross-sectional second moment index ratio of the outer layer at this time was 1.057. The curl amount of this optical sheet 4 was −2.3 mm.
(Mold 3)
In-plane pattern: Striped (Figure 7)
Individual shape: right-angled isosceles triangle (height d: 12 μm)
Pitch between adjacent patterns (p): 24 μm
Size: 100 mm × 100 mm (pattern area).

Example 5
An optical sheet 5 was obtained in the same manner as in Example 3 except that the following mold 4 having a pitch P of 18 μm between adjacent patterns and a height of d9 μm was used. The thickness of the outer layer 1 / core layer / outer layer 2 of the optical sheet 5 was 12.0 μm / 28.9 μm / 8.6 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 49.5 mm. In addition, the cross-sectional second moment index ratio of the outer layer at this time was 0.983. The curl amount of this optical sheet 5 was −0.3 mm.
(Mold 4)
In-plane pattern: Striped (Figure 7)
Individual shape: right-angled isosceles triangle (height d: 9 μm)
Pitch between adjacent patterns (p): 18 μm
Size: 100 mm × 100 mm (pattern area).

Example 6
Polycarbonate resin 1 (Iupilon S3000, Tg 150 ° C., manufactured by Mitsubishi Engineering Plastics Co., Ltd.) is used as the resin constituting the core layer, and polycarbonate resin 1 and polyester resin 3 (PCTG5445, manufactured by Eastman Chemical Company) are used as the resin constituting the outer layer. , Tg: manufactured at 86.5 ° C.), the three-layer laminated sheet 3 having a thickness of 16.0 μm / 124.1 μm / 14.9 μm and a total of 154.9 μm, respectively, in the same manner as in Example 1. (The difference in thermal linear expansion coefficient of the outer core layer was 15 ppm / ° C., and the plane orientation coefficient of the outer layer was fn = 0.002). Next, the optical sheet 6 was obtained in the same manner as in Example 1 using the mold 1. The thickness of the outer layer 1 / core layer / outer layer 2 of the optical sheet 6 was 22.3 μm / 124.1 μm / 14.9 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 161.2 mm. At this time, the sectional second moment index ratio of the outer layer was 0.988. The curl amount of this optical sheet 6 was −1.0 mm.

Example 7
As in Example 1, using the above-described mold 1 having a pitch P of 25 μm between adjacent patterns and a height of d12.5 μm, an optical having a pattern obtained by reversing the shape of the following mold 1 on the surface of the outer layer 1 of the laminated sheet 1 Sheet 1 was obtained. Further, when the optical sheet 1 is turned upside down on the following mold 5 having a pitch P of 5 μm between adjacent patterns and a height of d2.5 μm, the stripe direction of the outer layer 1 and the stripe direction of the mold 5 are equal. And heated at 142 ° C. for 1 minute using a 2 ton vacuum heater press (MKP-150TV-WH, manufactured by Mikado Technos Co., Ltd.) and maintained at 142 ° C. with a pressure of 2.34 MPa, The optical sheet 1 was hot-pressed for 30 seconds. Subsequently, the heat press is released, the mold is cooled to 87 ° C., and then the optical sheet 1 is released from the mold, thereby reversing the shape of the following mold 1 on the surface of the outer layer 2 of the optical sheet 1. An optical sheet 7 having the pattern thus obtained was obtained. The thickness of outer layer 1 / core layer / outer layer 2 of optical sheet 7 was 18.0 μm / 29.6 μm / 9.0 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 56.6 μm. At this time, the sectional second moment index ratio of the outer layer was 0.831. The curl amount of this optical sheet 7 was −0.4 mm.
(Mold 5)
In-plane pattern: Striped (Figure 7)
Individual shape: right-angled isosceles triangle (height d: 2.5 μm)
Pitch between adjacent patterns (p): 5 μm
Size: 100 mm × 100 mm (pattern area).

[Comparative Example 1]
The three-layer laminated sheet 4 (thermal expansion of the outer core layer) was carried out in the same manner as in Example 1, except that the thickness of the outer layer 1 / core layer / outer layer 2 was 7.7 μm / 29.6 μm / 11.7 μm, respectively, and the total thickness was 49 μm. A coefficient difference of 6 ppm / ° C. and an outer layer plane orientation coefficient fn = 0) were obtained.
Next, the optical sheet 8 was obtained in the same manner as in Example 1 using the mold 1. The thickness of outer layer 1 / core layer / outer layer 2 of optical sheet 8 was 14.0 μm / 29.6 μm / 11.7 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 55.3 mm. In addition, the cross-sectional second moment index ratio of the outer layer at this time was 1.588. The curl amount of this optical sheet 8 was 7.0 mm.

[Comparative Example 2]
An optical sheet 9 was obtained in the same manner as in Comparative Example 1 except that the above mold 2 having a pitch P of 15 μm between adjacent patterns and a height of d7.5 μm was used. The thickness of the outer layer 1 / core layer / outer layer 2 of the optical sheet 9 was 11.5 μm / 29.6 μm / 11.7 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 52.8 mm. At this time, the cross-sectional second moment index ratio of the outer layer was 1.341. The curl amount of the optical sheet 9 was 5.9 mm.

[Comparative Example 3]
The three-layer laminated sheet 5 (outer core layer) was formed in the same manner as in Example 3 except that the thickness of the outer layer 1 / core layer / outer layer 2 was 7.5 μm / 20.6 μm / 8.0 μm, respectively, and the total thickness was 36.1 μm. The difference in thermal expansion coefficient was 19 ppm / ° C., and the plane orientation coefficient fn of the outer layer was 0.084). Next, the optical sheet 10 was obtained in the same manner as in Example 1 using the mold 1. The thicknesses of the outer layer 1 / the core layer / the outer layer 2 of the optical sheet 10 were 13.8 μm / 20.6 μm / 8.0 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 42.4 mm. Further, the cross-sectional second moment index ratio of the outer layer at this time was 1.297. The curl amount of this optical sheet 10 was −7.3 mm.

[Comparative Example 4]
An optical sheet 11 was obtained in the same manner as in Comparative Example 3 except that the above-described mold 3 having a pitch P of 24 μm between adjacent patterns and a height of d12.0 μm was used. The thickness of the outer layer 1 / core layer / outer layer 2 of the optical sheet 11 was 13.5 μm / 20.6 μm / 8.0 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 42.1 mm. At this time, the cross-sectional secondary moment exponent ratio of the outer layer was 1.256. The curl amount of the optical sheet 11 was −4.5 mm.

[Comparative Example 5]
Three-layer laminated sheet 6 (outer core layer) was formed in the same manner as in Example 3 except that the thickness of outer layer 1 / core layer / outer layer 2 was 7.5 μm / 28.9 μm / 8.6 μm, respectively, and the total thickness was 45.0 μm. The difference in thermal expansion coefficient was 19 ppm / ° C., and the plane orientation coefficient fn of the outer layer was 0.084). Next, the optical sheet 12 was obtained in the same manner as in Example 1 using the mold 3. The thickness of outer layer 1 / core layer / outer layer 2 of optical sheet 12 was 13.5 μm / 28.9 μm / 8.6 μm, respectively, and the total thickness (from the top of the shaping surface to the back surface) was 51.0 mm. Further, the cross-sectional second moment index ratio of the outer layer at this time was 1.356. The curl amount of the optical sheet 12 was −8.0 mm.

  1 Resin sheet

  As an optical functional film, it can be suitably used as a light diffusive film, prism sheet, microlens film, antireflection film, wire grid polarizing film, etc. used for a backlight of a liquid crystal display.

Claims (5)

A resin film in which at least one surface of the outer layer of a three-layer structure composed of at least a front and back outer layer made of the same resin and a core layer sandwiched between the front and back outer layers has an uneven shape, and has the largest thickness When the thickness of the part is T, and the average depth of each outer layer surface shape is Da, Db from the larger one,
(Da + Db) /T≧0.07
A resin film in which the cross-sectional second moment index ratio of both outer layers is 0.8 or more and 1.2 or less. The resin film according to claim 1, wherein the average thickness of each outer layer differs by 5% or more of the thickness T of the thickest portion. Average depth of each outer layer surface shape is Da / Db ≧ 5
The resin film of Claim 1 or Claim 2 which has the relationship of these. The resin film according to any one of claims 1 to 3, wherein the outer layer and the core layer are made of different resins, and the thermal expansion coefficients of the outer layer and the core phase are different by 5 ppm / ° C or more. The resin film according to claim 1, wherein the core layer has a larger plane orientation coefficient than the outer layer.

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