JP4092925B2 - Optical disc protective film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk protective film (sheet) that is attached to the surface of an optical disk substrate and used to protect an optical recording layer. In particular, the present invention relates to a protective film that is optimally used for protecting an optical disk for high density optical recording for DVD Blue using a blue laser beam as light.
[0002]
[Prior art]
[0003]
[Prior art]
In recent years, the optical disk substrate has been used rapidly because it can record at high density and large capacity, but on the other hand, scratches and foreign materials smaller than the wavelength on the recording surface are not particularly problematic in error processing. If there is a large defect or foreign matter in comparison with the wavelength of the laser beam used, there is a problem that an error occurs during writing or reading.
[0004]
Therefore, a surface protective film is used on these optical disk substrates so as not to get dust and scratches. As the polymer material, a solution-cast polycarbonate (PC) film is mainly used.
[0005]
[Problems to be solved by the invention]
However, according to the knowledge of the present inventors, such a PC film has no antistatic property, so it is easy to adsorb dust, and since there is no surface hardness, the surface is easily damaged, and the water absorption rate is large. In addition, there is a problem that PC deteriorates by hydrolysis under high temperature and high humidity and becomes mechanically brittle, microcracks enter inside, optical transmittance decreases, and a recording error occurs. Since the foundation value was large, there were many problems such as errors during writing and reading, and poor adhesion due to poor adhesion to the optical disk substrate.
[0006]
Moreover, since PC had to use the solvent called methylene chloride at the time of manufacture, it had the problem that examination with respect to an environment etc. was also needed.
[0007]
Therefore, in JP-A No. 13-266407, etc., it is proposed to use a water-resistant thermoplastic alicyclic norbornene resin instead of PC. However, the above-mentioned problems such as antistatic performance and scratch resistance are proposed. In particular, the surface layer is apt to be damaged, which is a major problem, and foreign matter, base stripes and thickness unevenness are large, reading and recording errors are likely to occur, UV light is easily deteriorated, and It has poor adhesiveness, and there is no protective sheet with excellent mechanical properties and environmental suitability without altering the optical recording / reproducing characteristics over a long period of time. Therefore, there is no excellent optical disk protective film. It is.
[0008]
The present invention is intended to provide an optical disk protective film that improves the above-mentioned drawbacks.
[0009]
[Means for Solving the Problems]
That is, the optical disk protective film of the present invention is an optical disk protective film using an amorphous polyolefin , and the amorphous polyolefin is an alicyclic polyolefin copolymer (COC) , hydrogenated polyethylene, poly- 4- methylpentene- 1 , And a non-crystalline thermoplastic polymer selected from those modified products, and has a surface specific resistance value of at least one surface of 10 ¹¹ Ω / □ at 25 ° C. and 65 RH%, preferably 10 ⁹ at 25 ° C. and 40 RH%. It is Ω / □ or less, and the surface hardness of the surface is 3H or more.
[0010]
Further, as a specific embodiment of the optical disk protective film of the present invention, an optical disk protective film characterized in that the surface tension on the surface opposite to the one side is preferably 40 dyn / cm or more, more preferably 45 dyn / cm or more. is there.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the optical disk protective film of the present invention will be described.
[0013]
The optical disk protective film of the present invention is typically used by being attached to the light incident surface side in order to prevent dirt and scratches from adhering to the laser light incident surface of an optical information recording medium such as an optical disk. It is a protective film.
[0014]
The optical disk protective film of the present invention has a good antistatic performance as its function. Specifically, the surface specific resistance value on the surface of at least one side is 10 at 25 ° C. and 65 RH%. ¹¹ Ω / □ or less, preferably 10 ⁹ Ω / □ or less under conditions of 25 ° C. and 40 RH%.
[0015]
Since at least the surface on one side has such a surface resistivity characteristic, the optical disk protective film of the present invention has a good effect in preventing dust and foreign matters from being brought close to each other with good antistatic performance. That is, since the film of the present invention is used in a dry optical disc apparatus, antistatic performance is particularly important in a low humidity state.
[0016]
Furthermore, the optical disk protective film of the present invention has an antistatic function and the surface of the protective film is hard and not easily damaged. In particular, the one-side surface having the above-mentioned surface specific resistance characteristic has a pencil hardness of 3H as the surface hardness. It is what has the above, Preferably it is 5H or more.
[0017]
The surface hardness of this level (3H or more) may be used for a normal use as an optical disk protective film. However, in order to reduce the size of the scratch to the wavelength used, especially when the disk is rotated and contacted with foreign matter. A surface hardness is required, and in particular, the pencil hardness of 6H or more is most preferable in the present invention.
[0018]
In addition, it is important for prevention of reading / writing errors in recording that the retardation Rd value in the in-plane direction and the thickness direction of the protective film is preferably 8 nm or less, more preferably 3 nm or less. . Further, the photoelastic modulus H of the protective film is preferably 20 (10 ⁻¹³ cm ² / dyn) or less, more preferably 8 (10 ⁻¹³ cm ² / dyn) or less. This is because even if a small retardation Rd film is prepared, the retardation may be increased by an external force in a process such as laminating or coating.
[0019]
Further, the water vapor transmission rate W is preferably 40 (g / m ² · day · 0.1 mm) or less, more preferably 10 (g / m ² · day · 0.1 mm) or less. When the rate is preferably 88% or more, more preferably 92% or more, a protective film excellent in durability, moisture resistance and heat resistance can be realized.
[0020]
In order to bond the protective film to the recording surface of the optical disk, a pressure-sensitive adhesive such as acrylic with the optical recording surface may be applied to the surface opposite to the surface having antistatic properties and hard coat properties. For this reason, the surface tension of the opposite surface is preferably 40 dyn / cm or more, more preferably 45 dyn / cm or more. As a surface treatment method used for this purpose, a treatment in which the surface is not charged by the surface treatment such as a flame treatment, a plasma treatment, an anchor coating treatment or the like is necessary.
[0021]
As a preferred polymer material for the protective film, typically, an amorphous polyolefin material having a water absorption of 0.1% by weight or less and a glass transition temperature of 120 ° C. or more can be used . and a polymer compound consisting of non-crystalline polyolefin, alicyclic olefin copolymer (COC), polystyrene hydrogenated, poly 4-methylpentene-1, and amorphous thermoplastic polymer selected from modified compounds thereof and Use . In the present invention, an alicyclic olefin copolymer (COC) that is transparent, has a low photoelastic modulus, and has a high glass transition temperature (Tg) is particularly preferable. Here, the alicyclic olefin copolymer (COC) is a high-Tg polyolefin having a norbornene skeleton having a Tg of 120 ° C. or higher, a tetracyclododecene derivative or an unsaturated cyclic compound copolymerizable with the tetracyclododecene. And a polymer obtained by hydrogenating a polymer obtained by metathesis polymerization. JP-A-60-168708, JP-A-62-252406, JP-A-62-2252407, Examples thereof include JP-A-63-145324, JP-A-63-264626, JP-A-2-133413, JP-A-1-240517, and JP-B-57-8815.
[0022]
Those having a moderately polar group such as — (CH ₂ ) _n COOR in the side chain of cyclic COC, for example, those having about 1 polar group in 2 to 5 norbornene groups are preferred, but all norbornene groups are preferred. When there are many polar groups such as all having polar groups, the water vapor transmission rate exceeds 40 (g / m ² · day · 80 μm sheet), and the water absorption rate and humidity expansion coefficient β also increase. Since the characteristic as a protective function may be impaired, it is not preferable. These protective films can be used in combination with various additives such as ultraviolet absorbers, sliding materials, stabilizers, antioxidants, viscosity modifiers, antistatic agents, water absorbing materials and the like.
[0023]
In the present invention, the surface specific resistance value of at least one surface of the protective film is 10 ¹¹ Ω / □ or less at 25 ° C. and 65 RH%, preferably 10 ⁹ Ω / □ or less at 25 ° C. and 40 RH%, In addition, the optical disk protective film has a surface hardness of 3H or more, and the surface tension of the surface opposite to the surface is preferably 40 dyn / cm or more, more preferably 45 dyn / cm or more. More preferably, it is an optical disk protective film using an amorphous polyolefin material that satisfies the above-described characteristics.
[0024]
In the present invention, the film thickness is not particularly limited, but a film thickness of preferably about 40 to 150 μm, more preferably about 75 to 120 μm is preferable because of excellent handleability. However, if the thickness unevenness of the protective film is not strictly managed, an error may occur during recording / reproduction. Therefore, the thickness variation value is preferably 3 μm or less, more preferably 1 μm or less. is important.
[0025]
An example of a method for producing the optical disk protective film of the present invention is shown below, but the film of the present invention is not limited to this.
[0026]
That is, the amorphous polyolefin resin A and the polymer resin B that can be peeled from the resin A are separately melted by a conventionally known uniaxial, biaxial, or tandem type extruder, etc. Each melted resin flow is laminated in a three-layer merger before the die called a feed block to form a three-layer laminated structure, and the three-layer molten laminated structure laminated sheet made of BAB is closely cooled to a moving cooling medium such as a drum. Solidify to obtain a cast sheet. At this time, the resin A to be melted easily undergoes oxidative decomposition or oxidation reaction, especially an amorphous high Tg resin called COC, in order to minimize oxygen at the time of melting, the resin is previously dried in a vacuum. It is important to completely deaerate, vacuum extrude, nitrogen displacement extrusion to prevent the oxidation reaction of the resin, and to add an antioxidant to the resin. If such measures are not taken, the resin will undergo an oxidation reaction when melted, the resin will be modified to oxidize and gelate, and the molten resin will become very sticky to metal materials such as a die. Fixed streaks, called streaks, are likely to occur and may not be available for optical applications. For this reason, the material in contact with the molten resin is preferably not a normal chrome plating or nitrided steel, but a ceramic material having excellent releasability such as TiN or WC or a SUS material.
[0027]
As the peelable polymer resin B, the molten resin stacked in three layers in the “BAB” laminated structure is brought into close contact with the cooling drum and solidified by cooling. Therefore, it is good for thickness unevenness to cast so as to land on the drum at the same time. For this purpose, it is important to select the resin for the B layer and to control the mutual melt viscosity and cooling drum temperature.
[0028]
Further, when the molten sheet slides on the cooling drum, molecular orientation occurs, so that the retardation becomes 10 nm or more, and it is not optically isotropic. For this purpose, when the three-layer laminate BAB is brought into close contact with the cooling drum and cooled, the sheet is air knife, air chamber, press roll method, liquid paraffin coating method, static electricity application method, high temperature drum adhesion method, etc. It is important to cast by means of improving adhesion such as a method selected from In particular, it is preferable that the electrical specific resistance value at the time of melting of the protective layer B on the surface layer is set to be about two orders of magnitude smaller than the layer A on the drum side. Further, when melt extrusion is performed with three BAB layers, a high adhesion amount can be obtained by taking a laminated form in which both surface layers B wrap around the inner layer A.
[0029]
Further, as the casting position, the direction of polymer flow in the base land portion for extruding the three-layer laminate BAB is the horizontal direction, and the first contact point with the cooling drum is near the top position of the cooling drum. Although it is most preferable, even if it is not necessarily such a casting position, the flow direction of the so-called land in the base and the traveling direction of the sheet extruded under the atmosphere are almost the same, or the flowing direction and the traveling direction This is because a surface defect called a base stripe is less likely to occur over time when the narrow angle formed by is within 30 degrees. In addition, the surface roughness Ry of the moving cooling medium is preferably 0.4 μm or less, more preferably 0.2 μm or less in a mirror surface roll, and it is important to improve adhesion and smoothness of the sheet. . However, when it is desired to cast at a high speed, the surface roughness Ry obtained by applying a reverse electric field to chrome plating to form a microcrack drum may be a rough surface roll of about 1 to 4 μm. The total thickness of these three-layer laminates can be measured by β-ray, IR absorption method, etc., but in order to measure the thickness of only the A layer, the thickness is obtained by optical interference or absorption such as infrared rays. Is possible. Since the polymer resin layer A thus obtained is covered on both sides with the B layer, a sheet with less surface oxidative modification is obtained, and furthermore, the surface is free of defects and excellent in optical isotropy, as well as thickness uniformity. It becomes a sheet excellent in surface smoothness.
[0030]
The B layer on one side of this three-layer laminate sheet is peeled off, and the peeled A side is subjected to non-electrical surface activation treatment such as corona treatment, plasma treatment, flame treatment, or anchor treatment, and the surface tension is 40 dyn / cm or more. After coating the surface, the surface is coated with an antistatic agent having antistatic properties and hard coat properties, dried and cured by irradiating with ultraviolet rays to provide hard coat properties and antistatic functions, and the coating surface A protective film with olefin-based adhesiveness is applied to protect the film.
[0031]
Further, an acrylic pressure sensitive adhesive (adhesive) is applied to the optical recording layer on the surface A opposite to the surface A having the antistatic and hard coat, and silicon is applied. A release PET film is applied.
[0032]
The optical disk protective film thus obtained is a five-layer film comprising a protective film layer / hard coat / antistatic layer / optical isotropic layer / pressure-sensitive adhesive layer / PET release film layer. The mold layer is peeled off and the surface thereof is adhered to the optical recording layer to obtain an optical disk protective film. Thus, at the time of actual use, the protective film stuck on the surface layer is peeled off and used. By doing so, the optical disc is free from recording errors due to dust and scratches, and the reliability is further improved.
[0033]
[Measurement method of physical properties]
A method for measuring physical properties used in the present invention will be described below.
1. Unevenness of film thickness:
Using a film thickness tester “KG601A” manufactured by Anritsu Corporation, the thickness of a film sampled 30 mm wide and 10 m long in the longitudinal direction of the film is continuously measured. The conveyance speed of the film was 3 m / min.
[0034]
R = Tmax−Tmin is obtained from the maximum thickness Tmax (μm) and the minimum value Tmin (μm) at a length of 10 m, and the thickness unevenness (%) = R / Tave from R and the average thickness Tave (μm) of the length of 10 m. It calculated | required as x100.
2. Thermal properties (Tm, Tg, Tmc):
Using a DSC-II type measuring device manufactured by PerkinElmer, Inc., the sample was heated at a rate of 20 ° C./min under a nitrogen stream, and the temperature at which baseline deviation started was increased to Tg. The exothermic peak when heated was Tcc, and the endothermic peak temperature accompanying crystal melting was the melting point Tm. After maintaining at Tm + 20 ° C. for 1 minute, the melt was cooled at a cooling rate of 20 ° C./min, and the exothermic peak temperature based on crystallization was defined as Tmc.
3. Water vapor transmission rate:
According to JIS-K7129 B method, it measured at 40 degreeC and 90RH%. The unit is g / m 2 · 24 hours · sheet. A PERMATRAN-WIA manufactured by MOCON was used.
4). Light transmittance:
Using a spectrophotometer U-3410 (manufactured by Hitachi, Ltd.), the total light transmittance of visible light in the wavelength range of 300 to 700 nm was measured, and the light transmittance at 550 nm was adopted.
5. Retardation:
A sample was set under a polarizing microscope, a 45 ° sample was rotated from the extinction position, and the value at which the polarization interference color was erased with a compensator was defined as retardation. The unit is nm.
6). Adhesive strength (kg / cm):
It is a value obtained by dividing the strength (kg) required for peeling obtained by the T peel peeling test according to JIS Z0237 by the width of the test piece.
7). Surface roughness Ra:
Using a high-precision thin film level gauge ET-10 manufactured by Kosaka Laboratory, measured with a stylus tip radius of 0.5 μm, a needle pressure of 5 mg, a measurement length of 1 mm, and a cut-off of 0.08 mm, and centerline average roughness according to JISB-601 Ra was determined.
8). Surface tension γ:
It measured according to JIS K-6788.
9. Photoelastic modulus H:
A weight F (dyn / cm ² ) is applied to the measurement sheet at room temperature, and it is obtained from Δn / F from birefringence Δn generated when the sheet is stretched, and the unit is expressed as 10 ⁻¹³ cm ² / dyn.
10. Surface resistivity:
The sample was allowed to stand for 24 hours at 25 ° C. and 65 RH%, and then measured using a three-terminal electrode at an applied voltage of 100 V using a digital ultrahigh resistance / microammeter (advantest R8340A) in that atmosphere. The unit is Ω / □ and measured according to JIS K6911.
[0035]
The surface specific resistance value at 25 ° C. and 40 RH% was measured in the same manner under the conditions of 25 ° C. and 40 RH%.
11. Surface pencil hardness:
According to JIS K5400, when a pencil of various hardness is pressed against the film at an angle of 90 degrees and scratched with a load of 1 kg, the display is made with the hardest pencil hardness when no scratch is generated.
[0036]
【Example】
In order to make the present invention easier to understand, examples and comparative examples are shown below.
[0037]
Example 1
As compound A of the polymer sheet, cyclic olefin copolymer COC (“ZEONOR” 1600, manufactured by Nippon Zeon Co., Ltd., Tg: 165 ° C.), which is a norbornene-based resin, was used. After deaeration of oxygen, the raw material hopper to the extruder were supplied to a 150 mm vacuum extruder purged with nitrogen and melted at 280 ° C. On the other hand, after being vacuum-dried polyethylene terephthalate PET resin (inherent viscosity: 0.75, Tg: 70 ° C., melt resistivity value 10 ⁶ Ω) as resin B laminated so as to surround the periphery of the resin A , Fed to a 65 mm melt extruder, melted at 285 ° C., passed through a filter that removes foreign matters of 15 μm or more, and then formed into three layers of B / A / B in the thickness direction, and the lamination After laminating to surround the A layer so that only the resin B layer is laminated at the end of the sheet, the 1200 mm wide crow die-shaped T die die (set so that the resin flow direction is horizontal) to the LD As the top of the cast drum at a distance of 50 mm.
[0038]
At this time, the narrow angle formed between the resin flow direction and the molten resin sheet in the base land portion was 0 degree. In order to increase the adhesion between the drum and the resin sheet, a positive charge of 10 kv and 5 mA was applied from the non-drum surface side with a 0.15 mm wire of tungsten just before the grounding point to bring the melt sheet to 40 ° C. It was made to adhere and cool and solidify at a speed | rate of 50 m / min on the mirror surface chromium plating drum (drum diameter: 1800 mm, surface maximum roughness Rt: 0.1 micrometer) kept.
[0039]
The three-layer cast film thus obtained has a laminated structure of B / A / B and each layer thickness is 5/100/5 μm and has a total thickness of 110 μm. When the thickness unevenness of 100 μm was measured, it was as small as 1% or less in both the longitudinal direction and the width direction, and even if the frequency analysis of the thickness unevenness of the A layer was performed, the thickness unevenness caused by the landing vibration of 3 to 10 Hz was obtained. A 100 μm sheet of amorphous 100 μm that is completely isotropic, with no retardation, craters, streaks, etc. there were.
[0040]
Further, the sheet was a transparent and completely amorphous sheet having excellent optical isotropy, with no variation in width at the edges and light transmittance of 90% or more in the range of 400 to 700 nm.
[0041]
After the B layer was peeled off, the one side A layer surface was corona-treated in a sealed state shut off from the outside to make it easy to adhere, and then 40% exhaled liquid of Kayanova KAS-205 manufactured by Nippon Kayaku Co., Ltd. was used with isopropyl alcohol. Diluted to 30%, coated with Metabar # 10 to a coating thickness of 4.5 g / m ² , dried at 80 ° C., and then irradiated with ultraviolet rays at 200 mJ / m ² .
[0042]
The surface specific resistance value of the surface thus obtained was 10 ⁸ Ω / □ at 25 ° C. and 40 RH%, and had an excellent antistatic function and a hard coat property with a pencil hardness of 4H. A protective film was affixed to the coated surface to prevent contamination.
[0043]
An acrylic pressure-sensitive adhesive was applied to the surface opposite to the A surface, and after drying, a silicon release PET film was superposed and wound.
[0044]
The obtained optical disk protective film is a five-layer film comprising a protective film layer / hard coat / antistatic layer / optical isotropic layer / pressure-sensitive adhesive layer / PET release film layer, The layer was peeled off and the surface was adhered to the optical recording layer to form an optical disk protective film. In actual use, the protective film affixed to the surface layer is peeled off and used, so that the optical disc is free from recording errors due to dust and scratches, and the reliability is further improved.
Comparative Example 1
Stop coating the resin A surface layer used in Example 1 with a hard coat and a layer having an antistatic function, and peel off one side B layer of the BAB 3 layer film as in Example 1 and apply a pressure sensitive adhesive. A release PET film was affixed to produce a protective film mainly having a thickness of 100 μm so as to have a laminated structure of B / A / adhesive layer / release layer.
[0045]
As described above, when the surface of the resin A does not have an antistatic function and a hard coat performance, even if it is used as a protective film for an optical disk, it does not show any effect, and dust adheres to it or the surface is scratched. And cannot be used as an optical protective film.
[0046]
【The invention's effect】
The optical disk protective film of the present invention is affixed to the surface of an optical disk substrate, and can favorably protect the optical recording layer of the optical disk.
[0047]
In particular, a high-density optical recording disk for DVD Blue using a blue laser beam as light requires a high level of protection of the optical recording layer. According to the film of the present invention, the protection can be easily performed. It can be achieved well.

Claims (3)

An optical disk protective film comprising amorphous polyolefin, wherein the amorphous polyolefin is selected from alicyclic polyolefin copolymer (COC) , hydrogenated polyethylene, poly- 4- methylpentene- 1 , and modified products thereof. An optical disk protective film, which is a crystalline thermoplastic polymer, having a surface specific resistance value of at least one surface at 25 ° C. and 65 RH% of 10 ¹¹ Ω / □ or less, and a surface hardness of the surface of 3 H or more in pencil hardness. The optical disk protective film according to claim 1 , wherein the optical disk protective film has a thickness of 40 to 150 μm . The optical disk protective film according to claim 1 or 2 , wherein a thickness fluctuation value of the optical disk protective film is 3 µm or less .