JP2001266407A - Protective film for optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective film easily attachable and detachable to a laser beam incident surface of an optical information recording medium and capable of maintaining signal reproducing performance of the information recording medium by preventing damage or dirt of the incident surface. SOLUTION: A film consisting of a polymer containing alicyclic structure and having a fixed thickness is coated with a strippable pressure sensitive adhesive to be stuck to laser beam incident surface of the optical information recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for protecting a surface of an optical information recording medium such as an optical disk, on which a laser beam for signal reading enters, from scratches, dirt, etc., and a light having the film mounted thereon. More specifically, the present invention relates to a film suitable for protecting a CD-ROM substrate for game software and a CD-R on which the film is mounted.
It relates to an OM substrate.

[0002]

2. Description of the Related Art An optical information recording medium (so-called optical disk) for reading and rewriting information by using a laser beam or the like is used from a compact disk for music (CD) to a magneto-optical disk as an information recording medium of a computer. It is widely used all the way. In recent years, optical disks can be manufactured at a lower cost than before, and in addition to the above-mentioned music CDs and computer recording media, in particular, they are widely used in the form of CD-ROMs (read-only compact disks) as media for home-use game software. Spreading.

However, a CD-RO for the above-mentioned game software is used.
M is often handled by children of relatively young age,
The frequency at which the light incident surface of the laser beam for signal reading is casually touched increases, and the light incident surface is easily scratched or stained, so that there has been a problem that data cannot be read.

Therefore, a protective film has been proposed to prevent the hand or the like of a child or the like from touching the light incident surface to cause scratches or dirt. As the material, polycarbonate (P
Transparent resins such as C), acrylic resin (PMMA), polyethylene terephthalate (PET), and polystyrene are being studied. Characteristics required for such a film are excellent in transparency, that the film itself is not easily damaged,
Although it is possible to attach to and detach from the recording medium surface, the above-mentioned transparent resin does not fully satisfy all the required performances, and even if it can prevent scratches and dirt, signal reading errors increase. Therefore, more suitable materials have been demanded.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a protective film capable of preventing a laser incident surface of an optical information recording medium from being scratched or stained, and capable of maintaining the signal reproduction performance of the medium. An object of the present invention is to provide an optical information recording medium on which the film is mounted.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, by using an alicyclic structure-containing polymer as a material of the film,
It has been found that it is possible to prevent scratches and dirt on the laser incident surface while maintaining the signal reproduction performance of the optical information recording medium,
The present invention has been completed.

Thus, according to the present invention, there is provided a film comprising an alicyclic structure-containing polymer for protecting a light-entering surface of a signal reading laser of an optical information recording medium. Further, according to the present invention, there is provided an optical information recording medium in which the film is mounted on a light incident surface of a signal reading laser.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The protective film of the present invention is intended to prevent scratches and dirt from being attached to the laser light incident surface of an optical information recording medium such as an optical disk by human touch. It is used by attaching to the light incident surface, and is obtained by molding an alicyclic structure-containing polymer.

[0009] alicyclic structure-containing polymer used in the alicyclic structure-containing polymer present invention, the main chain and /
Alternatively, those having an alicyclic structure in the side chain, and those having an alicyclic structure in the main chain are preferable from the viewpoint of mechanical strength, heat resistance and the like.

Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, and a cycloalkane structure is preferred from the viewpoint of mechanical strength and heat resistance. The number of carbon atoms that make up the alicyclic structure is
From the viewpoint of heat resistance and moldability, usually 4 to 30 pieces,
It is preferably in the range of 5 to 20, more preferably 5 to 15. The proportion of the repeating unit having an alicyclic structure is
It is appropriately selected according to the purpose of use, but is usually at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight. It is preferable from the viewpoint of transparency and heat resistance that the proportion of the repeating unit having an alicyclic structure be within this range.

Specific examples of such an alicyclic structure-containing polymer include (1) a norbornene-based polymer, (2) a monocyclic olefin-based polymer, (3) a cyclic conjugated diene-based polymer,
(4) Vinyl alicyclic hydrocarbon polymers and hydrogenated products thereof. Among these, norbornene-based polymers and cyclic conjugated diene-based polymers, and hydrogenated products thereof are preferable, and the norbornene-based polymers are
It is more preferable in terms of heat resistance and mechanical strength.

(1) Norbornene-based polymer The norbornene-based polymer is disclosed in, for example, JP-A-3-1488.
No. 2, JP-A-3-122137, and the like. Specifically, the polymer is a ring-opened polymer of a norbornene-based monomer, a hydrogenated product thereof, and an addition weight of a norbornene-based monomer. And an addition copolymer of a norbornene-based monomer and a vinyl compound.

Specific examples of the norbornene-based monomer used in the polymerization include bicyclo [2,2,1] -hept-2-
Ene (common name: norbornene), 5-methyl-bicyclo [2,2,1] -hept-2-ene, 5,5-dimethyl-bicyclo [2,2,1] -hept-2-ene, 5- Ethyl-bicyclo [2,2,1] -hept-2-ene, 5
-Butyl-bicyclo [2,2,1] -hept-2-ene, 5-hexyl-bicyclo [2,2,1] -hept-
2-ene, 5-octyl-bicyclo [2,2,1] -hept-2-ene, 5-octadecyl-bicyclo [2,
2,1] -hept-2-ene, 5-ethylidene-bicyclo [2,2,1] -hept-2-ene, 5-methylidene-bicyclo [2,2,1] -hept-2-ene, 5 -Vinyl-bicyclo [2,2,1] -hept-2-ene, 5
-Propenyl-bicyclo [2,2,1] -hept-2-
En,

5-methoxy-carbonyl-bicyclo [2,2,1] -hept-2-ene, 5-cyano-bicyclo [2,2,1] -hept-2-ene, 5-methyl-
5-methoxycarbonyl-bicyclo [2,2,1] -hept-2-ene, 5-methoxycarbonyl-bicyclo [2,2,1] -hept-2-ene, 5-ethoxycarbonyl-bicyclo [2,2 , 1] -Hept-2-ene,
5-methyl-5-ethoxycarbonyl-bicyclo [2,
2,1] -hept-2-ene, bicyclo [2,2,1]
-Hept-5-enyl-2-methylpropionate, bicyclo [2,2,1] -hept-5-enyl-2-methyloctanoate, bicyclo [2,2,1] -hept-2
-Ene-5,6-dicarboxylic anhydride, 5-hydroxymethyl-bicyclo [2,2,1] -hept-2-ene,
5,6-di (hydroxymethyl) -bicyclo [2,2,
1] -hept-2-ene, 5-hydroxy-i-propyl-bicyclo [2,2,1] -hept-2-ene, bicyclo [2,2,1] -hept-2-ene, 5,6 -Dicarboxy-bicyclo [2,2,1] -hept-2-ene, bicyclo [2,2,1] -hept-2-ene-5.
6-dicarboxylic imide, 5-cyclopentyl-bicyclo [2,2,1] -hept-2-ene, 5-cyclohexyl-bicyclo [2,2,1] -hept-2-ene, 5
-Cyclohexenyl-bicyclo [2,2,1] -hept-2-ene, 5-phenyl-bicyclo [2,2,1]-
Hept-2-ene,

Tricyclo [4,3,1^2,5,
0^1,6] -Deca-3,7-diene (common name is dicyclope
Antadiene), tricyclo [4,3,1^2,5, 0
^1,6] -Dec-3-ene, tricyclo [4,4,1
^2,5, 0^1,6] -Undeca-3,7-diene
Is tricyclo [4,4,1^2,5, 0^1,6]-Unde
C-3,8-diene, tricyclo [4,4,1^2,5,
0^1,6] -Undec-3-ene, tetracyclo [7,
4,1^10,13, 0^1,9, 0^2,7] -Trideca-
2,4,6-11-tetraene (1,4-methano-1,
4,4a, 9a-tetrahydrofluorene),
Tetracyclo [8,4,1^11,14, 0^1,10, 0
^3,8] -Tetradeca-3,5,7,12-11-tet
Raen (1,4-methano-1,4,4a, 5,10,1
0a-hexahydroanthracene)
A norbornene monomer having no bornan ring;

Tetracyclo [4,4,1^2,5, 1
^7,10, 0] -dodec-3-ene (simply tetracyclo
Dodecene), 8-methyl-tetracyclo [4,
4,1^{2 , 5}, 1^7,10, 0] -dodec-3-ene,
8-methyl-tetracyclo [4,4,1^2,5, 1
^7,10, 0] -Dodeca-3-ene, 8-ethyl-tet
Lacyclo [4,4,1^2,5, 1^7,10, 0] -dode
Car-3-ene, 8-methylidene-tetracyclo [4,
4,1^2,5, 1^7,10, 0] -dodec-3-ene,
8-ethylidene-tetracyclo [4,4,1^2,5, 1
^7,10, 0] -Dodeca-3-ene, 8-vinyl-tet
Lacyclo [4,4,1^2,5, 1^7,10, 0] -dode
Car-3-ene, 8-propenyl-tetracyclo [4,
4,1^2,5, 1^{7, 10}, 0] -dodec-3-ene,
8-methoxycarbonyl-tetracyclo [4,4,1
^2,5, 1^7,10, 0] -dodec-3-ene, 8-me
Tyl-8-methoxycarbonyl-tetracyclo [4,
4,1^2,5, 1^7,10, 0] -dodec-3-ene,
8-hydroxymethyl-tetracyclo [4,4,1
^2,5, 1^{7,1 0}, 0] -dodeca-3-ene, 8-ca
Ruboxy-tetracyclo [4,4,1^{2, 5}, 1
^7,10, 0] -Dodeca-3-ene, 8-cyclopentene
Le-tetracyclo [4,4,1^2,5, 1^7,10,
0] -dodec-3-ene, 8-cyclohexyl-tetra
Cyclo [4,4,1^2,5, 1^7,10, 0] -dodeca
-3-ene, 8-cyclohexenyl-tetracyclo
[4,4,1^2,5, 1^7,10, 0] -dodeca-3-
Ene, 8-phenyl-tetracyclo [4,4,
1^2,5, 1^{7,1 0}, 0] -dodeka-3-ene, pen
Tacyclo [6,5,1^1,8, 1^3,6, 0 ^2,7, 0
^9,13] -Pentadeca-3,10-diene, pentacyclo
Black [7,4,1^3,6, 1^10,13, 0^1,9, 0
^2,7] -Pentadeca-4,11-diene and other norbo
Norbornene-based monomers having a lunan ring are respectively
No.

The above norbornene monomers can be used alone or in combination of two or more.

In the present invention, in addition to the norbornene-based monomer, other monomers copolymerizable with the norbornene-based monomer include, for example, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-hexene,
Methyl-1-butene, 3-methyl-1-pentene, 3-
Ethyl-1-pentene, 4-methyl-1-pentene, 4
-Methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-
1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1
Α-olefins having 2 to 20 carbon atoms, such as hexadecene, 1-octadecene and 1-eicosene; cyclobutene, cyclopentene, cyclohexene, 3,4-dimethylcyclopentene, 3-methylcyclohexene,
-(2-methylbutyl) -1-cyclohexene, cyclooctene, 3a, 5,6,7a-tetrahydro-4,7
-Cycloolefins such as methano-1H-indene;
Non-conjugated dienes such as 1,4-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, and 1,7-octadiene; and the like can be used. These copolymerizable monomers can be used alone or in combination of two or more.

The ring-opening polymer of the above monomer is a catalyst comprising a metal halide such as ruthenium, rhodium, palladium, osmium, iridium, platinum or the like, a nitrate or acetylacetone compound, and a reducing agent as a ring-opening polymerization catalyst. Alternatively, titanium, vanadium, zirconium, tungsten, a metal halide such as molybdenum or an acetylacetone compound, using a catalyst system comprising an organoaluminum compound, in a solvent or without a solvent, usually at -50 ℃ ~ 100 ℃ Polymerization temperature, 0-50k
It can be obtained by ring-opening polymerization at a polymerization pressure of g / cm ² . The hydrogenated norbornene-based polymer can be obtained by a method in which a ring-opened (co) polymer is hydrogenated with hydrogen in the presence of a hydrogenation catalyst according to a conventional method.

The addition copolymer of a norbornene-based monomer and the above-mentioned copolymerizable monomer is, for example, a catalyst system comprising a monomer component in a solvent or without a solvent comprising a titanium, zirconium or vanadium compound and an organoaluminum compound. In the presence of the compound (A), the copolymerization can be usually performed at a polymerization temperature of -50 ° C to 100 ° C and a polymerization pressure of 0 to 50 kg / cm ² .

(2) Monocyclic Cyclic Olefin Polymer Examples of the monocyclic cyclic olefin polymer include monocyclic cycloolefin polymers such as cyclohexene, cycloheptene and cyclooctene disclosed in JP-A-64-66216. Can be used.

(3) Cyclic conjugated diene-based polymer The cyclic conjugated diene-based polymer is described in, for example,
The cyclic conjugated diene-based monomers such as cyclopentadiene and cyclohexadiene disclosed in JP-A-136057 and JP-A-7-258318 are used as 1,2- or 1,2-
4-Polymerized polymers and hydrogenated products thereof can be used.

(4) Vinyl alicyclic hydrocarbon-based polymer Examples of the vinyl alicyclic hydrocarbon-based polymer include vinyl cyclohexene and vinyl cyclohexane disclosed in JP-A-51-59989. Polymers of alicyclic hydrocarbon monomers and hydrogenated products thereof, vinyls such as styrene and α-methylstyrene disclosed in JP-A-63-43910 and JP-A-64-1706. A hydrogenated product of the aromatic ring portion of the polymer of the aromatic monomer can be used. The configuration of these vinyl alicyclic hydrocarbon-based polymers may be any of atactic, isotactic and syndiotactic. For example, any of 0 to 100% in syndiotacticity by dyad display. Can also be used.

The molecular weight of the alicyclic structure-containing polymer used in the present invention is appropriately selected according to the purpose of use, and the gel permeation of a cyclohexane solution (a toluene solution when the polymer is not dissolved) is used. The weight average molecular weight in terms of polyisoprene measured by a chromatographic method is 5,0
00 to 500,000, preferably 8,000 to 20
0000, more preferably 10,000-100,0
When it is in the range of 00, the mechanical strength and the moldability are highly balanced and suitable. The glass transition temperature (Tg) of the alicyclic structure-containing polymer used in the present invention may be appropriately selected according to the purpose of use, but is usually 50 to 300.
° C, preferably 60-200 ° C, more preferably 70-200 ° C.
180 ° C.

Ingredients The alicyclic structure-containing polymer may be added , if desired, to an antioxidant such as a phenolic antioxidant or a phosphorus antioxidant, a benzophenone ultraviolet absorber or a benzotriazole ultraviolet absorber. Various compounding agents such as an ultraviolet absorber, a light stabilizer, an antistatic agent, an ester of an aliphatic alcohol, a partial ester and a partial ether of a polyhydric alcohol may be blended. In addition, other resins, rubbery polymers and the like can be mixed and used as long as the object of the present invention is not impaired.

Protective Film The protective film of the present invention can be obtained by blending the above-mentioned compounding agent with the alicyclic structure-containing polymer, if necessary, to form a film, and then processing it into a specific shape. Examples of the film forming method include an extrusion method, a solution cast method, an inflation method, a calendar method, and the like.From the viewpoint of balancing surface accuracy, productivity, etc., an extrusion method, a cast method, and the like. Is preferred, and an extrusion molding method is more preferred. In the present invention, the thickness of the film is usually 20 to 200 μm, preferably 25 to 80 μm. If the film thickness is too thick, the birefringence value (retardation) of the film will increase and errors will increase. If the film thickness is too thin, the distance between the film outer periphery and the recording medium substrate during signal reading (disk rotation) will be increased. Gaps occur, and errors due to film vibration increase. In addition, the retardation of the film is usually 30 nm or less, preferably 20 nm or less, and more preferably 10 nm or less, in order to be attached to the laser light incident surface. In addition, a resin film other than the alicyclic structure-containing polymer may be laminated on the above-mentioned film and used.

The size and shape of the film are preferably such that the entire area of the optical information recording medium substrate where the signal for laser reading is recorded can be covered with the film and the film does not vibrate. Specifically, it is preferable that the substrate is cut into a ring shape having substantially the same size as the optical information recording medium substrate. Examples of the cutting method include a method such as punching. The ring-shaped film covers almost the entire surface of the optical information recording medium substrate, and the diameter of the central hole is usually 10 to 50 m so as not to protrude.
m, preferably 15 to 45 mm, and the outer diameter is usually 1
It is 10 to 140 mm, preferably 115 to 120 mm.

Since the film of the present invention is used for protecting the laser incident surface of the optical information recording medium substrate from scratches and dirt, if the surface of the film itself is damaged or stained, a new film is obtained. It is preferable that the film can be exchanged. Specifically, it is preferable that the film can be easily removed as needed after the film is mounted on the substrate surface. As a method for mounting the protective film on the laser light incident surface of the optical information recording medium substrate, a method of attaching the film via an adhesive layer, a method by fusion such as heat fusion or ultrasonic fusion, a method of static electricity, Although a method using a suction force and the like can be mentioned, as described above, it is preferable that the adhesive be attached via a peelable adhesive layer in order to facilitate attachment and detachment.

In the present invention, examples of the kind of the adhesive used for the adhesive layer include a pressure-sensitive adhesive and a heat-sensitive adhesive, and it is preferable to use a pressure-sensitive adhesive that is easily removable. Specific examples of the pressure-sensitive adhesive include natural rubber-based, synthetic rubber-based, acrylic resin-based, polyvinyl ether-based, urethane resin-based, and silicone resin-based adhesives. From the viewpoint, an acrylic resin is preferable. The above-mentioned adhesives can be used alone or in combination of two or more. The above-mentioned adhesive may contain, as necessary, an adhesion-imparting agent, a filler, a curing agent, a wax, an antioxidant, an ultraviolet absorber, a crosslinking agent, and the like.

In the present invention, the method for providing the adhesive layer on the protective film is not particularly limited, and various methods can be used. For example, the adhesive is dissolved in an appropriate solvent, and the solution is applied to the protective film. A method of forming an adhesive layer by removing a solvent after coating on the adhesive; dispersing or emulsifying the adhesive in an appropriate medium; applying the liquid on a protective film; and drying the medium to remove the adhesive layer. Method of forming; Method of directly applying an adhesive on a protective film using a calender roll or the like without solvent; Applying and forming an adhesive layer in advance on release paper, and affixing the release paper together with the release paper to the protective film. Thereafter, a method of peeling off the release paper and leaving the adhesive layer on the protective film; a method of applying a double-sided pressure-sensitive adhesive tape obtained by applying an adhesive to both surfaces of the core material sheet, and the like, and the like. The thickness of the adhesive layer is usually 3 to 100 μm.
m, preferably 5 to 40 μm. Further, the adhesive layer may be covered with a release sheet.

The adhesive layer may be provided on the entire surface of the protective film, or may be provided on a part of the film surface. When it is provided in a part, it is preferable to provide an adhesive layer at a portion where the signal for laser reading of the information recording medium substrate is not recorded, that is, at a position where the innermost and / or outermost peripheral portion of the substrate can be adhered. From the viewpoint of easy attachment / detachment of the film and prevention of vibration, it is more preferable to provide the film at a position where it can be bonded to the innermost peripheral portion. Therefore, when the protective film is a ring-shaped film, it is most preferable to provide the adhesive layer on the innermost peripheral portion of the film with a width of about 10 mm.

Optical Information Recording Medium The protective film of the present invention is used to protect a laser light incident surface for reading a signal of an optical information recording medium substrate. Examples include a music compact disc (CD), a read-type optical disc (CD-ROM), and a write-once optical disc (CD
-R), rewritable optical disks such as magneto-optical disks (MO) and phase-change optical disks (PD), mini disks (M
D), a digital video disk (DVD), a laser disk (registered trademark) (LD), and the like.

[0033]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following, “parts” and “%” are based on weight unless otherwise specified. The methods for measuring various physical properties in the following Production Examples, Examples and Comparative Examples are as follows.

Measurement of Physical Properties (1) The weight average molecular weight (Mw) was determined by gel permeation chromatography (GP) using cyclohexane as a solvent.
It was measured as a polyisoprene conversion value by C). (2) The hydrogenation rate was measured by ¹ H-NMR. (3) The glass transition temperature (Tg) was measured based on JIS-K7121. (4) The thickness of the film was measured using a thickness gauge (manufactured by PEACOCK, DIGITAL LINEAR GAUGE MO).
DEL PDN12). (5) The value of the birefringence of the film (retardation)
Micro area automatic birefringence meter (manufactured by Seiko Precision Co., Ltd .: K
OBRA-CCD / X). (6) The data reproduction performance of the information medium was evaluated using a Kenwood CD-ROM analyzer DR-3750. Specifically, when the entire range of the signal recording portion of the information medium substrate is scanned, the number of errors is measured (laser wavelength is 780 nm), the average value is calculated, and reproduction is performed without attaching a film. Was evaluated in comparison with the number of errors.

[Production Example 1] (Production of resin for protective film) Under a nitrogen atmosphere, 8-ethyltetracyclo [4.4.0.1 ^2,5 . ^17,10 ]
15 parts of dodeca-3-ene (hereinafter abbreviated as ETD) and tricyclo [4.3.0.1 ^2,5 ] deca-3,7-
Diene (dicyclopentadiene, hereinafter referred to as DCP)
85 parts were dissolved in 250 parts of dehydrated cyclohexane, 1.8 parts of 1-hexene was added as a molecular weight regulator, polymerized with a known metathesis ring-opening polymerization catalyst, and then hydrogenated by a known method to give ETD / A hydrogenated DCP ring-opening copolymer was obtained. When the copolymerization ratio of each norbornene in the polymer was calculated from the composition of the residual norbornene in the solution after polymerization (by gas chromatography), ET was obtained.
D / DCP = 15/85 was almost equal to the charged composition.
The hydrogenated ETD / DCP ring-opening polymer had a weight average molecular weight (Mw) of 31,000 and a hydrogenation rate of 99.9.
%, Tg was 103 ° C.

An antioxidant (Ilganox 10 manufactured by Ciba-Geigy) was added to 100 parts of the hydrogenated ring-opened polymer.
10) 0.2 parts and 0.2 parts of a soft polymer (ToughTech H1052 manufactured by Asahi Kasei Corporation) were added, and a twin-screw kneader (TEM-35B manufactured by Toshiba Machine Co., screw diameter 37 mm, L / D =
32, screw rotation speed 250 rpm, resin temperature 210
At a feed rate of 10 kg / hour) and extruded into pellets.

Example 1 An extruded film having a thickness of 70 μm was formed from the pellets obtained in Production Example 1 using an extruder equipped with a T-die. Extruder cylinder temperature 220
° C and a T-die temperature of 270 ° C. The birefringence value (retardation) of the obtained film was 4 nm on average. The obtained film is cut into a ring shape of 118 mm in diameter having a hole of 16 mm in the center by punching, and in the range of 9 mm in width of the innermost peripheral portion, in a ring shape,
A pressure-sensitive acrylic adhesive (Nitto Denko) with a thickness of 10μ
m. The ring-shaped film to which the above-mentioned adhesive was applied was stuck so that the center of the circle was overlapped with the laser light incident surface of a polycarbonate (PC) CD-ROM substrate in which game software was stored.

The above-mentioned CD-ROM substrate on which the film is fixed only with the adhesive on the inner peripheral portion is set in a signal reading drive with the film attached side down, and the drive is driven. As a result of the evaluation, no space was formed between the outer peripheral portion of the film and the substrate, the film did not vibrate, and the number of errors was 1.01 times that when the film was not mounted. The results are shown in Table 1.

[0039]

[Table 1]

Example 2 A ring-shaped protective film with an adhesive was produced in the same manner as in Example 1 except that the film thickness was changed to 30 μm. The retardation of the film was 2 nm on average. Thereafter, as in the first embodiment, the CD
-It was mounted on a ROM board and evaluated. Table 1 shows the evaluation results.

[Comparative Example 1] As a material for the protective film,
A 70 μm thick polycarbonate (PC) film was used. Film retardation average 15nm
Met. Thereafter, as in Example 1, a ring-shaped film was manufactured and mounted on a CD-ROM substrate. As a result, the number of errors increased twice as much as when no film was mounted.
The reading performance has decreased. The results are shown in Table 1.

[Comparative Example 2] The thickness of the PC film was 10
A ring-shaped film was manufactured in the same manner as in Comparative Example 1 except that the thickness was changed to μm, and the film was mounted on a CD-ROM substrate and evaluated. Although the retardation of the film was 2.2 nm, a gap was formed between the outermost peripheral portion of the film and the substrate during driving, and the film vibrated. The number of errors increased 2.5 times as compared with the case where no film was mounted, and the reading performance decreased. The results are shown in Table 1.

[Comparative Example 3] The thickness of the PC film was 30
A ring-shaped film was manufactured in the same manner as in Comparative Example 1 except that the thickness was changed to μm, and the film was mounted on a CD-ROM substrate and evaluated. The retardation of the film was 6.5 nm, the number of errors increased 1.6 times that in the case where no film was mounted, and the reading performance was lowered. The results are shown in Table 1.

[0044]

According to the present invention, there is provided a protective film capable of preventing the attachment of scratches and dirt due to hand or the like without increasing the error at the time of signal reading.

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Claims (5)

[Claims] 1. A film comprising an alicyclic structure-containing polymer for protecting a light-entering surface of a signal reading laser of an optical information recording medium. 2. The film according to claim 1, which has a thickness of 20 to 200 μm. 3. The film according to claim 1, further comprising a peelable adhesive layer made of a pressure-sensitive adhesive on a part of the film surface. 4. The film according to claim 3, wherein the film is laminated with a release paper via a peelable adhesive layer. 5. An optical information recording medium, wherein the protective film according to claim 1 is mounted on a light incident surface of a signal reading laser.