JP2005190529A - Polyester film for process paper of high density dvd light transmission protection layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film being excellent in running and smoothing, and being suitable for a process paper used when a high density DVD light transmission protection layer is prepared. <P>SOLUTION: This film is the laminating polyester film used for the process paper of the high density DVD light transmission protection layer, and average roughness of a center plane (SRa(A)) of one film plane (A plane) is 20 nm or less, and average roughness of a center plane (SRa(C)) of the other film plane (C plane) is larger than SRa(A). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a base film used for process paper used in the production of a thinned light-transmitting protective layer necessary for increasing the density of a DVD.

  As a high-density recording medium for recording various types of information for computers, audio, etc., optical discs that perform reproduction and recording by light irradiation, and DVD among them, are attracting attention as one of the three new treasures. In order to cope with digital broadcasting and high-definition broadcasting, there is an increasing demand for larger capacity.

  The conventional DVD has a structure in which two substrates having a thickness of 600 μm are bonded together. However, as one means for increasing the capacity, the thinner the light transmission layer through which laser light passes, the more advantageous the thickness is. A disc having a structure in which a 100 μm optical film is bonded to a substrate via an adhesive and a signal is read from the film side is under development.

  Another important technique for increasing the capacity is to shorten the wavelength of laser light used in the optical pickup section. Currently, red laser light having a wavelength of about 650 nm is used for DVD, but application of a blue laser having a wavelength of 405 nm is also under development. However, the shorter the wavelength, the more easily affected by fine thickness variations on the surface of the recording medium, and noise is more likely to occur when signal characteristics are evaluated, so surface smoothness is particularly required.

  The substrate is mainly made by injection molding. However, when forming a thin film by injection molding, optical unevenness is likely to occur due to cooling unevenness during molding, so it is suitable for making sheets and films of 300 μm or less. Not. Therefore, film formation by a solution casting method in which a resin is dissolved in a solution and coating and drying are being used in a method for manufacturing an optical film (light transmission protective layer). This is because the solution method is excellent in terms of optical uniformity and has a low viscosity, so that foreign matters can be easily removed by filtration or the like.

In the case of forming an optical film by this solution casting method, a case where a metal endless belt or drum is used as a support and a case where a plastic or metal film or sheet is used are generally used. The method using a plastic film as a support is particularly preferred because it has excellent flexibility and has no joint step characteristic of an endless belt. Furthermore, a PET (polyethylene terephthalate) film has been preferably used because of its high rigidity, good chemical resistance and low cost. Furthermore, in order to smooth the surface of the PET film, a film having one surface hard-coated has been used. However, a base film with a smooth surface was used because the smoothness of the hard coat surface was emphasized. However, the running property of the film was poor, there was a signal error in part, and the situation was not practical (Patent Literature). 1, 2).
JP 2003-326542 A JP 2003-326543 A JP 2002-238706 A

  The present invention is intended to solve such problems, and the problem to be solved is as a process paper that is excellent in runnability and smoothness, and used in the production of a light-transmitting protective layer for high-density DVDs. The object is to provide a suitable polyester film.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be easily solved by a film having a specific configuration, and have completed the present invention.

  That is, the gist of the present invention is a polyester film used as a process paper for a high-density DVD light transmission protective layer, and the average roughness (SRa (A)) of one film surface (A surface) is 20 nm. The present invention resides in a laminated polyester film characterized in that the center plane average roughness (SRa (C)) of the other film surface (C surface) is larger than SRa (A).

Hereinafter, the present invention will be described in detail.
The polyester referred to in the present invention refers to a polymer containing an ester group obtained by polycondensation from dicarboxylic acid and diol or from dicarboxylic acid and hydroxycarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, succinic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and the diol includes ethylene. Glycol, 1,3-propanediol, 1,6-hexanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, etc. as hydroxycarboxylic acids Can be exemplified by p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and the like.

  Typical examples of such polymers include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. These polymers may be homopolymers or may be a copolymer of the third component.

  As the film of the present invention, a biaxially stretched film is preferably used from the viewpoint of excellent strength and dimensional stability, but a polyester film that has not been stretched or stretched at least in one direction can also be used.

  In the polyester film of the present invention, SRa (A) on one surface (A surface) is 20 nm or less, preferably 10 nm or less, more preferably 5 nm or less. Surface A is the surface to be the cast film installation surface. When SRa (A) of surface A is larger than 20 nm, the smoothness of the surface in contact with the cast film support becomes insufficient when the cast film is installed. It is not preferable.

  Furthermore, in the film of the present invention, the center surface average roughness SRa (C) of the opposite surface (C surface) of the A surface is larger than SRa (A), that is, it needs to be a rough surface, particularly 10 to 50 nm. Furthermore, it is preferable that it is 15-30 nm. When SRa (C) is less than 10 nm, problems such as generation of blocking and deterioration of the transportability of the cast film may occur when the film is wound with the cast film. Further, when SRa (C) exceeds 50 nm, there is a risk of transfer of surface protrusions to the cast film surface, so-called show-through, and when SRa (C) is the same as or smaller than SRa (A), Is not preferable.

  In order to bring the SRa of the polyester film of the present invention into the above-mentioned range, inert fine particles such as silica, calcium carbonate, kaolin, titanium oxide, aluminum oxide, barium sulfate, inorganic particles such as zeolite, or silicone resin, crosslinked polystyrene, It is preferable to mix organic particles such as acrylic resin alone or in a mixture in the film. In this case, the average particle size, the amount added, and the particle size distribution of the particles used are not particularly limited as long as they do not depart from the gist of the present invention, but the average particle size is 0.1 to 4.0 μm. It is preferable that the range and addition amount are in the range of 0.01 to 3.0% by weight, and that the particle size distribution has a small dispersion.

  The polyester film of the present invention needs to be a multilayer film in which a plurality of layers are laminated. In order to maintain the blocking resistance by making one side extremely smooth, finally smoothing the cast film, and at the same time roughening the opposite surface of the smooth surface, for example, 2 types 2 layers or 3 types 3 layers It is necessary to have different roughness on the front and back sides in such a configuration. Furthermore, for example, by adopting a film configuration in which an intermediate layer such as three types and three layers and two surface layers can be blended with different raw materials, fine particles can be added only to the surface layer, even without adding fine particles to the intermediate layer. There are cases where the gist of the present invention is satisfied only by addition, and it is possible to reduce foreign substances caused by fine particles, reduce production costs, and the like, which is more desirable (for example, described in Patent Document 3).

  The optical film produced using the film of the present invention is usually an optical film that is formed into a film by a solution casting method using an amorphous thermoplastic composition. The center surface average roughness SRa of the support-side surface of the optical film thus obtained is preferably in the range of 0.1 to 1.0 nm. The above range is preferable because a blue laser is used to increase the capacity of the recording medium and extreme smoothness is required to cope with the advancement of lenses.

  In the present invention, the average thickness of the produced optical film is 20 to 300 μm, preferably 50 to 150 μm, more preferably 60 to 110 μm, which is suitable for use as a light transmission layer of an optical recording medium. It is.

  In the present invention, polycarbonate is preferably used as the amorphous thermoplastic resin composition used as a raw material for the optical film. This is because polycarbonate is inexpensive and soluble in solvents such as methylene chloride, and is currently used in large quantities as a material for CDs and DVDs. In order to prevent warping or distortion due to a difference in dimensional change rate, it is preferable that the light transmission layer and the substrate on which the light transmission layer is bonded are made of the same material.

  In the present invention, the aromatic polycarbonate resin that can be preferably used in the optical film is not particularly limited, but as an example, the main constituent is 2,2-bis (4-hydroxyphenyl) propane (bisphenol A). The aromatic polycarbonate comprised by the repeating unit which becomes is preferable. The main component here refers to a repeating component composed of a compound that accounts for 50 mol% or more of the dihydroxy compound that is a raw material of polycarbonate. Therefore, even if 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) is used alone, other dihydroxy compounds may be added or copolymerized or mixed within a range not exceeding 50%. Can do. The repeating unit of bisphenol A is preferably 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 100 mol% (that is, alone).

  In the present invention, when the optical film cast on the polyester film of the support is wound up, the surface opposite to the cast film surface of the support film may be wound up as it is unless it is transferred to the cast film. Although it is good, as a precaution, it is preferable to attach a protective film on the surface of the cast film and wind it up. Although it does not specifically limit as a protective film, It is preferable to use the protective film of PET film with comparatively high surface smoothness, and what carried out the fine adhesion process on the surface of PET film is preferable. The slight adhesion in this case means that the protective film once bonded can be peeled without damaging the optical film and without the adhesive remaining on the optical film.

  Hereinafter, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the effect of this invention is satisfied, this invention is not specifically limited to the following illustrations.

  A polyester chip dried by a known method is supplied to an extruder for melt lamination and heated to a temperature equal to or higher than the melting point of each polymer to melt. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. That is, using two or three or more extruders, two or more manifolds or a merge block, a film layer constituting the outermost layer and a film layer constituting the intermediate layer are laminated, and two or more sheets are formed from the die. Extruded and cooled with a casting roll to form an unstretched film. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In this case, it is preferable to perform high-precision filtration in order to remove foreign substances contained in the resin during melt extrusion. The filter medium used for high-precision filtration is preferably a stainless sintered body.

  The sheet thus obtained is stretched in the biaxial direction to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 2 to 90 to 160 ° C. in the lateral direction. It is preferable to perform ~ 6 times stretching and heat treatment at 150 to 240 ° C for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  Furthermore, since the film of the present invention dislikes the generation of scratches, it is also preferable to stretch using a simultaneous biaxial stretching apparatus. Any apparatus may be used as long as it is a simultaneous biaxial stretching apparatus, but an apparatus that travels with a linear motor is preferably used.

  In addition, the polyester film of the present invention has a length that does not impair the effects of the present invention. After the stretching, a so-called in-line coating method in which coating is performed before the entrance of the tenter for lateral stretching and drying in the tenter may be performed. Various coatings may be performed by offline coating after film production. Such a coat may be either single-sided or double-sided. The coating material may be either water-based and / or solvent-based for offline coating, but is preferably water-based or water-dispersed for in-line coating.

  Furthermore, other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate can be mixed in the polyester film of the present invention as long as the effects of the present invention are not impaired. Further, an ultraviolet absorber, an antioxidant, a surfactant, a pigment, a fluorescent brightening agent, and the like can be mixed.

  In the present invention, as a method for further increasing the smoothness of the optical film, a method of coating another resin on the smooth surface side of the film of the present invention, a method of depositing or plating a metal on the surface, an adhesive, etc. A method of laminating another sheet or film or a metal plate, a method of polishing, a method of smoothing by physical or chemical treatment, etc., but a method of coating a resin whose surface property is relatively easy to control Is preferred.

  Furthermore, it is preferable that the coating layer has a high surface hardness (for example, an index such as pencil hardness) so that the coating layer is hardly damaged even when the support is conveyed. As a method of forming such a coating layer, a method of forming a hard coat layer using a known resin can be used.

  The support film thus obtained is cast using a solution casting method typified by a solution coating method or a solution casting method. At that time, it is preferable to dry the resin solution, and attach a protective film on the surface opposite to the support to wind it. Using the optical film thus obtained, a DVD can be produced by processing it into a disc so as to form a light transmission layer.

  ADVANTAGE OF THE INVENTION According to this invention, the polyester film which has the outstanding effect when it uses as process paper at the time of the light transmission layer preparation for DVD can be provided, The industrial value is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. Various physical properties and characteristics are measured or defined as follows. In the examples, “%” means “% by weight”.

(1) Measurement of center plane average roughness Non-contact type three-dimensional roughness meter (manufactured by Micromap) using Al deposition on the surface of a 3 cm square film sample and using direct phase detection interferometry, so-called two-beam interferometry 512), the average surface roughness SRa of the A plane and the C plane in the measurement area of 232 μm × 177 μm is 50 points from the projection height distribution curve under the conditions of the measurement wavelength: 554 nm and the objective lens magnification: 20 times. The SRa value of the film was calculated by averaging the 50 SRa values.

(Polyester chip manufacturing method)
Take 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, and 0.07 part of calcium acetate monohydrate in a reactor, heat up and evaporate methanol to conduct transesterification, and take about 4 and a half hours after starting the reaction. The temperature was raised to 230 ° C. to substantially complete the transesterification reaction. Next, 0.04 part of phosphoric acid and 0.035 part of antimony trioxide were added and polymerized in accordance with a conventional method. That is, the reaction temperature was gradually raised to finally 280 ° C., while the pressure was gradually reduced to finally 0.05 mmHg. After 4 hours, the reaction was completed, and a chip was obtained according to a conventional method to obtain polyester A.

  When manufacturing the said polyester A, 20000 ppm of calcium carbonate with an average particle diameter of 0.7 micrometer was added, and the polyester B was obtained.

  Furthermore, when manufacturing the said polyester A, 20000 ppm of amorphous silica with an average particle diameter of 2.4 micrometers was added, and the polyester C was obtained.

  Furthermore, when manufacturing the said polyester A, 20000 ppm of aluminum oxide with an average particle diameter of 0.2 micrometer was added, and the polyester D was obtained.

(Manufacture of polyester film)
The mixed raw material 1 in which the polyesters A and D are mixed at a ratio of 50% and 50%, respectively, is used as the raw material for the A layer, and the mixed raw material 2 in which the polyesters A and C are mixed at a ratio of 95% and 5%, respectively. Each is supplied to two extruders as raw materials, melted at 285 ° C each, and then the layer configuration of two types and two layers on a casting drum in which the A layer and the C layer are cooled to the outermost layer (surface layer) 20 ° C Were coextruded and cooled and solidified to obtain a non-oriented sheet. Next, the film was stretched three times in the longitudinal direction at 90 ° C., then subjected to a preheating step in a tenter, transversely stretched four times at 100 ° C., and subjected to heat treatment at 230 ° C. for 10 seconds. The thickness unevenness was actually measured while scanning in the horizontal direction with a non-contact type on-line thickness meter, the interval between the caps was adjusted according to the measured thickness pattern, and a 125 μm polyester film with controlled thickness unevenness was obtained. The thickness and surface roughness of each layer were as shown in Table 1 below.

  An acrylic resin was applied to the smooth surface of the obtained polyester film and cured by ultraviolet irradiation to provide a 5 μm hard coat layer. Next, using a dichloromethane as a solvent, a 20% by weight solution of polycarbonate was prepared, the polycarbonate solution was applied to the support, dried, and wound with a protective film sandwiched between the surface opposite to PET. When a DVD was prepared using the optical film of 100 μm thus obtained as a light transmission layer and the signal characteristics were examined, good characteristics were obtained.

(Examples 2-3)
In the same manner as in Example 1 except that the raw material composition in Example 1 was changed as shown in Table 1 and the thickness unevenness was controlled by the same method as in Example 1 to obtain the thickness unevenness in Table 1. A 125 μm polyester film was obtained. The obtained polyester film showed the results as shown in Table 1. When it was made into a DVD as in Example 1, it showed good characteristics.

Example 4
After preparing the mixed raw material of each layer by the raw material composition shown in Table 1, supplying each to three extruders and melting each at 285 ° C., the A layer and the C layer are the outermost layer (surface layer), and the B layer is As an intermediate layer, a polyester film was produced in the same manner as in Example 1 except that a non-oriented sheet was obtained by coextrusion and solidification on a casting drum cooled to 20 ° C. in a three-layer / three-layer structure. Got. The thickness of each layer of the polyester film was as shown in Table 1. Good characteristics as in Example 1 were exhibited.

(Comparative Examples 1-2)
A polyester film was obtained in the same manner as in Example 4 except that the raw material composition of layer A, layer B and layer C, and thickness unevenness were as shown in Table 2 below. A DVD was produced in the same manner as in Example 1. However, in Comparative Example 1, the surface irregularities were large and good signal characteristics could not be obtained. On the other hand, in Comparative Example 2, wrinkles occurred and the film could not be wound well.

  The film of the present invention can be suitably used for process papers used in the production of a thinned light-transmitting protective layer necessary for increasing the density of DVD.

Claims (1)

A polyester film used as a process paper for a high-density DVD light-transmitting protective layer, wherein one film surface (A surface) has a center surface average roughness (SRa (A)) of 20 nm or less, and the other film. A laminated polyester film characterized in that the center surface average roughness (SRa (C)) of the surface (C surface) is larger than SRa (A).