JP2009048743A - Optical recording medium - Google Patents

Abstract

The present invention provides an excellent optical recording medium that has a sufficient surface hardness, undergoes little deformation when the environmental temperature changes, and does not cause blocking during storage.
A resin substrate, a recording / reproducing functional layer formed on the resin substrate, a protective layer formed on the recording / reproducing functional layer, a hard layer formed on the protective layer and having a surface hardness of B or more. An optical recording medium having a coating layer and / or a back layer having a film thickness of 50 μm or less formed on the surface of the resin substrate opposite to the recording / reproducing functional layer, wherein the optical recording medium has a constant time in an environment of 25 ° C. The optical recording medium after standing for 1 hour in an environment at 5 ° C. after standing, and the optical recording medium after standing for 1 hour in an environment at 55 ° C. after standing for a fixed time in an environment at 25 ° C. When the amount of displacement in the vertical direction of the surface of the back layer at the position farthest from the center of the recordable / reproducible region of the optical recording medium is measured, the amount of displacement is 150 μm or less in all cases.
[Selection] Figure 1

Description

  The present invention relates to an optical recording medium such as a recording / reproducing disk, and more particularly to an optical recording medium that can cope with a change in environmental temperature and can be used for a high-density optical disk or the like.

  In recent years, optical information media such as read-only optical discs and optical recording discs have been widely used as information recording media for recording or storing vast amounts of information such as moving image information. As one of them, for example, a high-density optical disc (so-called Blu-ray disc, hereinafter also referred to as “Blu-ray disc” as appropriate) using a laser beam having a wavelength of 400 nm has been proposed (see Patent Document 1). The Blu-ray Disc is an optical recording medium having a resin substrate, a recording / reproducing functional layer, a protective layer, and a hard coat layer in this order. The hard coat layer is required to have scratch resistance and hardness. On the other hand, the entire disk is stored at a high temperature and high humidity for a certain period of time so that information can be read and written stably even if the environment such as temperature and humidity changes. In other words, the deformation of the disk is small, and the deformation of the disk after being stored for a certain period of time at high and low temperatures is required.

  Patent Document 2 discloses a radiation curable composition (a radiation curable composition containing urethane acrylate) that is excellent in transparency, abrasion resistance, recording film protection, mechanical properties, and also excellent in heat resistance and moisture deformation resistance. ) Has been reported, and an optical recording medium using this radiation-curable composition has been proposed. In the above document, it is reported that the optical recording medium undergoes little deformation after being stored at high temperature and high humidity for a long time and then returned to room temperature and stored for a long time. However, in the optical recording medium, it is required to further improve the surface hardness. When this surface hardness is improved, for example, the disc is warped after being stored for a certain period of time in a high or low temperature environment. Deformation (hereinafter also referred to as “temperature tilt” as appropriate) may occur.

Japanese Patent Laid-Open No. 11-273147 JP 2003-263780 A

  Therefore, as a method for improving the temperature tilt, for example, a method of forming a thick back layer on the surface of the resin substrate opposite to the surface on which the recording / reproducing functional layer is formed has been proposed. However, when the thickness of the back layer is increased, the optical recording media may be blocked due to stacking when storing the optical recording media.

  The present invention has been made in view of the above problems. That is, an object of the present invention is an optical recording medium that is less deformed and has a high surface hardness even when the environmental temperature is changed. An object of the present invention is to provide an optical recording medium that is less likely to be blocked.

  As a result of intensive research on optical recording media that can satisfy the above-mentioned objectives, the inventors have formed a back layer with a relatively thin film thickness on the surface opposite to the recording / reproducing functional layer of the resin substrate, and By setting the surface hardness of the hard coat layer to a predetermined value or higher, the surface hardness is high, and even when the environmental temperature changes, it is possible to reduce the deformation of the optical recording medium, and It has been found that even when stacked and stored, an optical recording medium in which blocking is less likely to occur can be obtained. Furthermore, by keeping the amount of displacement of the optical recording medium in the vertical direction after being stored at a predetermined temperature for a certain time within a predetermined range, the optical recording medium can be stabilized even when the environmental temperature changes. As a result, the present invention has been found.

  The gist of the present invention is a resin substrate, a recording / reproducing functional layer formed on the resin substrate, a protective layer formed on the recording / reproducing functional layer, formed on the protective layer, and having a surface hardness of B or more. An optical recording medium having a hard coat layer and / or a back layer having a thickness of 50 μm or less formed on the surface of the resin substrate opposite to the recording / reproducing functional layer, in an environment of 25 ° C. After standing for a certain time, after standing for 1 hour in a 5 ° C. environment, and after standing for a certain time in a 25 ° C. environment and for 1 hour in a 55 ° C. environment. Regarding the optical recording medium, when the amount of displacement in the vertical direction of the back layer surface at the position farthest from the center of the recordable / reproducible region of the optical recording medium is measured, the displacement amount is 150 μm or less in all cases. (1).

In the optical recording medium, the protective layer comprises (A) urethane (meth) acrylate 10 to 85% by weight, (B) monofunctional (meth) acrylate 10 to 80% by weight, and (C) polyfunctional (meth). A cured product of a radiation curable composition containing 0 to 30% by weight of acrylate is preferable (Claim 2).
Further, the elastic modulus at 25 ° C. of the protective layer is preferably in the range of 500 to 1300 MPa (Claim 3), and the (A) urethane (meth) acrylate is (a1) polyisocyanate, (a2) A reaction product obtained by reacting a polyether polyol and a composition containing (a3) a hydroxyl group-containing (meth) acrylate is preferred (Claim 4).
Furthermore, the (B) monofunctional (meth) acrylate is preferably an alicyclic (meth) acrylate (Claim 5), and the (C) polyfunctional (meth) acrylate is an aliphatic polyfunctional ( It is preferable that it is a meth) acrylate (Claim 6).

  According to the present invention, an excellent optical recording medium that has a sufficient surface hardness, can be used stably even when the environmental temperature changes, and does not cause blocking when stacked and stored. Is possible.

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description, and various modifications can be made within the scope of the gist of the present invention.
The present invention relates to an optical recording medium such as a recording / reproducing disk. The optical recording medium of the present invention includes a resin substrate, a recording / reproducing functional layer, a protective layer, and a hard coat layer having a surface hardness of B or more. Are provided in this order, and if necessary, a back layer having a thickness of 50 μm or less is provided on the surface of the resin substrate opposite to the recording / reproducing functional layer.

  In the present invention, since the back layer is formed and / or the surface hardness of the hard coat layer is not less than a predetermined value B, the surface hardness is high and the environmental temperature is changed. However, the deformation of the optical recording medium can be reduced. The surface hardness of the hard coat layer referred to in the present invention is the state of the optical recording medium, that is, the hard coat in a state where a resin substrate, a recording / reproducing functional layer, a protective layer, a hard coat layer, and / or a back layer are laminated. The surface hardness of the layer surface measured by a pencil hardness test in accordance with JIS K5400 is used. Generally, the surface hardness of the hard coat layer does not depend only on the hardness of the hard coat layer, but also depends on the hardness and type of the protective layer. In the present invention, since the protective layer and the hard coat layer capable of realizing the surface hardness of the hard coat layer are used, optical recording is performed when the environmental temperature changes even if the back layer is thin. The deformation of the medium can be reduced.

The mechanism by which the temperature change resistance can be improved by using a material capable of achieving the above surface hardness is not necessarily clear, but the surface hardness of the composite layer of the protective layer and the hard coat layer is high. That is, it is considered that the composite layer is rigid and hardly deformed, and the rigid composite layer is an optical recording medium when the temperature of the environment changes, particularly a resin substrate having a large thickness and a high elastic modulus. It is estimated that the deformation is suppressed.
In addition, when the back layer is formed, the film thickness is within the above range, so even if the optical recording media are stacked and stored, the optical recording media are less likely to stick to each other. It can be.

  The optical recording medium is allowed to stand for a certain period of time in an environment of 25 ° C., and is then allowed to stand for one hour in an environment of 5 ° C. With respect to the optical recording medium after standing for 1 hour in an environment of 55 ° C., when the amount of displacement in the vertical direction is measured, the amount of displacement is all within a predetermined range. By setting the amount of displacement within a predetermined range, the optical recording medium can be stably used even when the environmental temperature changes.

From the above, in the optical recording medium of the present invention, the surface hardness is sufficient, and even when the environmental temperature changes, it can be used stably, and even when stacked and stored, It is possible to reduce the occurrence of blocking.
Hereinafter, the measurement of the amount of displacement in the vertical direction and the recording medium of the present invention will be described.

1. Measurement of displacement in the vertical direction Measurement of the displacement in the vertical direction will be described. FIG. 1 shows an outline of a temperature disk deformation measurement system used for measuring the amount of displacement in the vertical direction. In FIG. 1, a device for detecting deformation of the optical recording medium (hereinafter also referred to as “optical recording medium deformation detection device”) is installed in the thermostatic chamber. However, the present invention is not limited to the above. An optical recording medium deformation detection device may be formed outside the thermostat. FIG. 1 is used for convenience to explain the outline of the system of the optical recording medium deformation detection apparatus, and any changes can be made without departing from the gist of the present invention.

  The measurement in the optical recording medium deformation detection apparatus is performed by fixing the central portion of the optical recording medium with a fixed weight. The method for fixing the optical recording medium is not particularly limited, and is appropriately selected depending on the shape of the optical recording medium. Usually, since the optical recording medium is formed in a planar annular shape, for example, a method of passing a central hole of the optical recording medium through an axis provided in the optical recording medium deformation detecting device and fixing with a fixed weight, etc. can do.

Next, with respect to the optical recording medium fixed by the fixed weight, a displacement sensor is used, and the position farthest from the center of the optical recording medium in the recordable / reproducible area of the optical recording medium (hereinafter also referred to as “measurement point” as appropriate) Measure the spatial position of the back layer surface. In the present invention, the recordable / reproducible area of the optical recording medium refers to an area used for recording / reproduction when the optical recording medium is used in various recording / reproducing apparatuses.
Data obtained by the above measurement is transmitted to a computer connected to the displacement sensor, and the amount of displacement in the vertical direction is calculated by comparing the reference time data with the measurement data. The reference time data is data obtained by measuring the spatial position of the measurement point on an optical recording medium at 25 ° C. In the present invention, the vertical direction is a direction perpendicular to the back layer surface of the optical recording medium in an environment of 25 ° C. The measurement is usually performed multiple times and the maximum value is adopted.

In the present invention, a specific method for measuring the amount of displacement in the vertical direction using the optical recording medium deformation detection device will be described below.
First, the optical recording medium is usually allowed to stand for about 1 hour in a thermostatic chamber set at 25 ° C. At this time, the humidity in the thermostat is usually 45% RH. The standing method is not particularly limited as long as it is a method in which no load is applied to the optical recording medium.
Thereafter, the spatial position of the measurement point is measured by the optical recording medium deformation detection device installed in the thermostat or outside the thermostat. At this time, the measured data is used as a reference value.

  Subsequently, the temperature of the thermostat is changed to 55 ° C. or 5 ° C., and the optical recording medium is left in the thermostat and stored for 1 hour. The conditions such as the humidity of the thermostatic chamber at this time are the same as those at the time of 25 ° C. setting. The constant temperature bath set at 25 ° C. and the constant temperature bath set at 55 ° C. or 5 ° C. may be the same or different.

After storing for 1 hour at the temperature, usually within 5 minutes, the optical recording medium deformation detector measures the spatial position of the measurement point, compares the obtained data with reference data, The amount of displacement (absolute value) in the vertical direction is calculated.
In addition, as shown in FIG. 1, when the optical recording medium is concavely deformed toward the protective layer and the hard coat layer, the deformation value is negative, and when the optical recording medium is convexly deformed toward the protective layer and the hard coat layer, the deformation is deformed. It is also possible to distinguish the values as positive. The above plus / minus can be reversed.

  In the present invention, the amount of displacement in the vertical direction (absolute value) after standing at 55 ° C. for 1 hour, and the amount of displacement in the vertical direction after standing at 5 ° C. for 1 hour, obtained by the above measurement. Any of the (absolute values) is usually 150 μm or less, preferably 130 μm or less, more preferably 120 μm or less. This is because the optical recording medium can be used stably even when the environmental temperature changes.

2. Next, the optical recording medium of the present invention will be described. The optical recording medium of the present invention comprises a recording / reproducing functional layer, a protective layer, and a hard coat layer in this order on a resin substrate, and further, if necessary, a back layer on the surface opposite to the recording / reproducing functional layer of the resin substrate. If it is formed, the structure, use, etc. will not be specifically limited, In addition to each said layer, you may have a required layer suitably.
As such an optical recording medium, in the present invention, the optical recording medium is particularly preferably a next generation high density optical recording medium using a blue laser or a film surface incident type next generation high density optical recording medium. The next generation high density optical recording medium means an optical recording medium using laser light having a wavelength of 380 to 800 nm, preferably laser light having a wavelength of 380 to 450 nm.

The optical recording medium of the present invention may be used as a single plate or may be used by bonding two or more sheets. Moreover, a hub may be attached if necessary and used by being incorporated into a cartridge.
Hereinafter, each layer of the optical recording medium of the present invention will be described.

[Protective layer]
The protective layer used in the present invention will be described. The protective layer used in the present invention is provided in contact with a later-described recording / reproducing functional layer, and can usually have a planar annular shape. The protective layer is formed of a material that can transmit laser light used for recording and reproduction.
The physical properties of the protective layer used in the optical recording medium of the present invention, the material of the protective layer, and the formation method will be described below.

(Physical properties of the protective layer)
The protective layer used in the optical recording medium of the present invention usually exhibits insoluble and infusible properties in a solvent or the like, and has properties that are advantageous for the use of optical members even when it is thickened. It is preferable that the degree of curing is excellent. Specifically, low optical distortion (low birefringence), high light transmittance, mechanical strength, dimensional stability, high adhesion, high surface hardness, and a certain level of heat and humidity resistance, low shrinkage It is preferable to show. In addition, it is sufficiently transparent to laser light in the vicinity of the wavelength used for recording / reproducing of optical recording media, and the recording / reproducing functional layer formed on the resin substrate described later is protected from water and dust to prevent deterioration. It is desirable to have such properties.

  The elastic modulus at 25 ° C. of the protective layer is usually 500 MPa or more, preferably 700 MPa or more, more preferably 900 MPa or more. Moreover, it is 1300 MPa or less normally, Preferably it is 1200 MPa or less, More preferably, it is 1150 MPa or less. As a result, it is possible to reduce the deformation of the optical recording medium when the environmental temperature changes. The elastic modulus means an elastic modulus when a 0.1 mm thick film is formed and a tensile test is performed at a tensile speed of 1 mm / min using a tensile strength tester.

  The thickness of the protective layer is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, further preferably 70 μm or more, particularly preferably 85 μm or more, and usually 300 μm or less, preferably 130 μm or less, more preferably 115 μm or less. Thereby, the balance between the influence on the reading and writing of information due to dust and the like and the transmittance can be improved.

  The light transmittance of the protective layer is usually 80% or more, preferably 85% or more, and more preferably 89% or more per light path length of 0.1 mm at a wavelength of 550 nm. Moreover, there is no upper limit and it is so preferable that it is near 100%. When the light transmittance is too low, the transparency of the protective layer is poor. Accordingly, errors tend to increase when reading recorded information in an optical recording medium. Further, the light transmittance per optical path length of 0.1 mm at a wavelength of 400 nm is preferably 80% or more, more preferably 85% or more, and particularly preferably 89% or more.

  The light transmittance of the protective layer is usually 80% or more, preferably 85% or more, and more preferably 89% or more at the wavelength of light used for recording / reproduction. Within such a range, loss due to absorption of recording / reproducing light can be minimized. On the other hand, the light transmittance is particularly preferably 100%, but is usually 99% or less in view of the performance of the material used. The light transmittance can be measured at room temperature by a known method using, for example, an HP8453 ultraviolet / visible absorptiometer manufactured by Hewlett-Packard Company.

  In order to make the light transmittance of a protective layer into the said range, it is preferable to use what has a high light transmittance as each component which comprises the radiation-curable composition mentioned later. Specifically, in order not to reduce the light transmittance in the visible light region, it is preferable that the amount of impurities such as colored substances and decomposed substances in each component is small. Moreover, it is preferable that there is little catalyst amount at the time of manufacturing each component. In order not to reduce the light transmittance in the ultraviolet region, it is preferable to select an aliphatic or alicyclic skeleton that does not contain an aromatic ring in each component.

  Moreover, the hardness of the said protective layer is the surface hardness by the pencil hardness test based on JISK5400, and is 6B or more normally, Preferably it is 4B or more, More preferably, it is 3B or more. As a result, the surface hardness of the hard coat layer, which will be described later, can be increased, and an optical recording medium excellent in wear resistance and recording film protection can be obtained.

  Furthermore, it is preferable that the adhesiveness between the protective layer and the recording / reproducing functional layer described later is high, and the adhesiveness with time is also high. Specifically, the ratio of the adhesion area between the protective layer and the recording / reproducing functional layer after being placed in an environment of 80 ° C. and 80% RH for 100 hours, more preferably 200 hours, is 50% or more of the initial adhesion area. It is preferably held, more preferably 80% or more, and particularly preferably 100%.

(Protective layer material)
The material of the protective layer is not particularly limited, and a known material can be used as a protective layer material for a general optical recording medium. In the present invention, the protective layer is particularly preferably (A It is preferably a cured product of a radiation curable composition containing urethane (meth) acrylate, (B) monofunctional (meth) acrylate, and (C) polyfunctional (meth) acrylate. This is because the deformation of the optical recording medium when the environmental temperature changes can be reduced, and the surface hardness can be increased.
Hereinafter, each component will be described.

<Urethane (meth) acrylate (A)>
The (A) urethane (meth) acrylate compound is usually obtained by reacting (a1) polyisocyanate, (a2) a compound containing a hydroxyl group, and (a3) a hydroxyl group-containing (meth) acrylate compound. As the (A) urethane (meth) acrylate compound used in the present invention, a urethane acrylate compound is more preferable from the viewpoint of excellent surface curability as a composition and less stickiness.

[(A1) Polyisocyanate]
A polyisocyanate is a compound having two or more isocyanate groups in the molecule. The polyisocyanate used in the present invention is not particularly limited. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, Examples include isophorone diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, naphthalene diisocyanate, and the like. One of these may be used alone, or two or more may be used in any ratio and combination. It may be used. Among these, bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate are preferable in that the hue of the resulting urethane oligomer is good.

  The molecular weight of (a1) polyisocyanate is usually 100 or more, preferably 150 or more, from the viewpoint of the balance between the strength and elastic modulus of the protective layer. Moreover, it is 1000 or less normally, Preferably it is 500 or less.

The (a1) polyisocyanate is usually 2 × 10 ⁻⁴ in the sum of the (A) urethane (meth) acrylate, the (B) monofunctional (meth) acrylate, and the (C) polyfunctional (meth) acrylate. Mol / g or more, preferably 6 × 10 ⁻⁴ mol / g or more is used, and usually 22 × 10 ⁻⁴ mol / g or less, preferably 16 × 10 ⁻⁴ mol / g or less.

[(A2) Compound containing hydroxyl group]
As the compound containing a hydroxyl group, polyols containing two or more hydroxyl groups are preferable, and specific examples thereof include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl- 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 3-methyl-1,5 -Pentanediol, 2,3,5-trimethyl-1,5-pentanediol, 1,6-hexanediol, 2-ethyl-1,6-hexanediol, 2,2,4-trimethyl-1,6-hexane Diol, 1,8-octanediol, trimethylolpropane, pentaerythritol, sorbitol, mannitol, Examples include alkylene polyols such as lysine, 1,2-dimethylolcyclohexane, 1,3-dimethylolcyclohexane, 1,4-dimethylolcyclohexane, 1,9-nonanediol, and 2-methyl-1,8-octanediol. It is done.

  Among these, the polyol is a polyether polyol compound having an ether bond for forming a multimer or the like, a polyester polyol compound having an ester bond by reaction with a polybasic acid or an ester bond by ring-opening polymerization of a cyclic ester. And a polycarbonate polyol compound having a carbonate bond by reaction with carbonate.

  Specific examples of the polyether polyol compound include polytetramethylene glycol as a ring-opening polymer of a cyclic ether such as tetrahydrofuran in addition to the multimers of the polyols, and ethylene oxide, propylene oxide of the polyols, Examples include adducts of alkylene oxides such as 1,2-butylene oxide, 1,3-butylene oxide, 2,3-butylene oxide, tetrahydrofuran and epichlorohydrin.

  Specific examples of the polyester polyol compound include a reaction product of the polyol and a polybasic acid such as maleic acid, fumaric acid, adipic acid, sebacic acid, and phthalic acid, and ring opening of a cyclic ester such as caprolactone. Examples include polycaprolactone as a polymer.

  Specific examples of the polycarbonate polyol compound include the polyols and alkylene carbonates such as ethylene carbonate, 1,2-propylene carbonate, and 1,2-butylene carbonate, diphenyl carbonate, 4-methyldiphenyl carbonate, 4- Ethyl diphenyl carbonate, 4-propyl diphenyl carbonate, 4,4′-dimethyl diphenyl carbonate, 2-tolyl-4-tolyl carbonate, 4,4′-diethyl diphenyl carbonate, 4,4′-dipropyl diphenyl carbonate, phenyl toluyl carbonate , Diaryl carbonates such as bischlorophenyl carbonate, phenylchlorophenyl carbonate, phenylnaphthyl carbonate, dinaphthyl carbonate, or Dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, di-n-butyl carbonate, diisobutyl carbonate, di-t-butyl carbonate, di-n-amyl carbonate, diisoamyl carbonate, etc. Examples include reactants.

  These polyols may be used individually by 1 type, and may be used in combination of 2 or more type. Among these polyols, polyether polyol is preferable, among which polyalkylene glycol is more preferable, and polytetramethylene glycol is particularly preferable.

  The molecular weights of these polyols can be low water absorption and low hygroscopicity when (A) urethane (meth) acrylate is used, and corrode the metal layer when used as an optical recording medium as a protective layer. The number average molecular weight is preferably 5 mol% or more, more preferably 10 mol% or more, and particularly preferably 15 mol% or more of all polyols contained in the composition from the viewpoint that they can be difficult. Is preferably 200 or more, more preferably 400 or more, and is preferably 1500 or less, and more preferably 800 or less.

  From the above, the compound (a2) containing a hydroxyl group used in the present invention is preferably a polyalkylene glycol having a number average molecular weight of 800 or less, and particularly preferably a polytetramethylene glycol having a number average molecular weight of 800 or less.

  The molecular weight of the compound (a2) containing a hydroxyl group is preferably 3000 or less, more preferably 2000 or less, and usually 80 or more, in terms of the balance between the deformation of the substrate derived from curing shrinkage and the surface hardness. Preferably it is 100 or more.

In addition, the compound containing the (a2) hydroxyl group is usually the sum of the (A) urethane (meth) acrylate, the (B) monofunctional (meth) acrylate, and the (C) polyfunctional (meth) acrylate. 1 × 10 ⁻⁴ mol / g or more, preferably 3 × 10 ⁻⁴ mol / g or more is used, and usually 12 × 10 ⁻⁴ mol / g or less, preferably 10 × 10 ⁻⁴ mol / g or less.

(A3) Hydroxyl group-containing (meth) acrylate Hydroxyl group-containing (meth) acrylate is a compound having both a hydroxyl group and a (meth) acryloyl group. The hydroxyl group-containing (meth) acrylate is not particularly limited. For example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, addition of glycidyl ether and (meth) acrylic acid Examples include reactants, glycol mono (meth) acrylates, etc., and one of these may be used alone, or two or more may be used in any ratio and combination.

  In addition, the molecular weight of the (a3) hydroxyl group-containing (meth) acrylate is preferably 40 or more, more preferably 80 or more, and is preferably 800 or less, and more preferably 400 or less.

The (a3) hydroxyl group-containing (meth) acrylate is usually the sum of the (A) urethane (meth) acrylate, the (B) monofunctional (meth) acrylate, and the (C) polyfunctional (meth) acrylate. 2 × 10 ⁻⁴ mol / g or more, preferably 6 × 10 ⁻⁴ mol / g or more is used, and usually 21 × 10 ⁻⁴ mol / g or less, preferably 17 × 10 ⁻⁴ mol / g or less.

[(A) Method for producing urethane (meth) acrylate]
(A) Urethane (meth) acrylate compound is produced by addition-reacting the composition containing (a1) polyisocyanate, (a2) hydroxyl group-containing compound, and (a3) hydroxyl group-containing (meth) acrylate. can do. In that case, it is preferable to charge so that an isocyanate group and a hydroxyl group may become a stoichiometric amount. In addition, diols are used as the compound containing a hydroxyl group, and the (A) urethane (meth) acrylate compound having a (meth) acryloyl group further has adhesion and surface hardness as a cured product of the resulting composition. There is an advantage that increases further.

  Moreover, when manufacturing (A) urethane (meth) acrylate compound, the usage-amount of (a3) hydroxyl group containing (meth) acrylate compound is used for (a2) hydroxyl group containing compound and (a3) hydroxyl group containing (meta ) The total amount of hydroxyl group-containing compounds combined with the acrylate compound is usually 20% by weight or more, preferably 40% by weight or more. Further, it is usually 80% by weight or less, preferably 60% by weight or less. Depending on the ratio, the molecular weight of the (A) urethane (meth) acrylate compound obtained can be controlled.

  The addition reaction of the composition containing (a1) polyisocyanate, (a2) a compound containing a hydroxyl group, and (a3) a hydroxyl group-containing (meth) acrylate can be carried out by any known method. For example, (a1) polyisocyanate, (a2) a compound containing a hydroxyl group, (a3) a hydroxyl group-containing (meth) acrylate, and a mixture containing an addition reaction catalyst are usually 40 ° C. or higher, preferably 50 ° C. or higher. Also, the mixing is usually performed at a temperature of 90 ° C. or lower, preferably 75 ° C. or lower. As a mixing method at that time, (a1) the above mixture can be dropped simultaneously or sequentially in the presence of polyisocyanate.

  In this case, as the addition reaction catalyst used, for example, dibutyltin laurate, dibutyltin dioctoate, dioctyltin dilaurate, and dioctyltin dioctoate are preferable, and one of these may be used alone, Two or more kinds may be used in any ratio and combination.

  In addition, when manufacturing (A) urethane (meth) acrylate, as above-mentioned, you may contain components other than (a1)-(a3) by 1 type (s) or 2 or more types and arbitrary ratios and combinations. In addition, (A) urethane (meth) acrylate usually has a high viscosity, and workability may be lowered. Therefore, in order to improve workability, a low viscosity liquid compound such as (meth) acrylate described later is mixed. Thus, the viscosity can be reduced.

[(A) Properties of urethane (meth) acrylate compound]
(A) As a urethane (meth) acrylate compound, a highly transparent thing is preferable, for example, it is preferable that it is a compound which does not have an aromatic ring. (A) When the urethane (meth) acrylate compound has an aromatic ring, the radiation-curable composition having an aromatic ring and the cured product thereof are preserved even if the resulting product is a colored product or is not colored at first. It may be colored inside or strengthened (so-called yellowing). This is considered to be caused by the double bond portion forming the aromatic ring irreversibly changing its structure by energy rays. For this reason, the (A) urethane (meth) acrylate compound has a structure that does not have an aromatic ring, so that the hue does not deteriorate and the light transmittance does not decrease. The (A) urethane (meth) acrylate having no aromatic ring can be produced by selecting those having no aromatic ring as the above (a1) to (a3).

  The amount of (A) urethane (meth) acrylate in the radiation curable composition is usually 10% by weight or more, preferably 30% by weight or more, and usually 85% by weight or less, preferably 70% by weight or less. . (A) If the content of the urethane (meth) acrylate compound is too small, the moldability and mechanical strength when forming the protective layer tend to decrease and cracks tend to occur. There is a tendency to rise.

<(B) Monofunctional (meth) acrylate>
Specific examples of the (B) monofunctional (meth) acrylate compound used in the radiation curable composition include (meth) acrylamides such as N, N-dimethyl (meth) acrylamide, hydroxyethyl (meth) acrylate, hydroxy Hydroxyalkyl (meth) acrylates such as propyl (meth) acrylate and hydroxybutyl (meth) acrylate; (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, tri Examples thereof include alicyclic (meth) acrylates such as (meth) acrylate having a cyclodecane skeleton, and one of these may be used alone, or two or more thereof may be used in any ratio and combination. Also good.

  Of these, alicyclic (meth) acrylates are preferable, and tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, and tricyclodecane skeleton having high hydrophobicity are preferred (meth). Acrylate is preferred.

  The molecular weight of the (B) monofunctional (meth) acrylate is usually 50 or more, preferably 100 or more, from the viewpoint of the balance between the viscosity of the radiation curable composition and the curing shrinkage. Moreover, it is 1000 or less normally, Preferably it is 500 or less.

  The content of (B) monofunctional (meth) acrylate is usually 10% by weight or more, preferably 15% by weight or more, more preferably 25% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less. . (B) When there is too little content of monofunctional (meth) acrylate, there exists a tendency for the viscosity of a radiation-curable composition to become high, and when too large, there exists a tendency for the mechanical physical property as hardened | cured material to fall.

<(C) Polyfunctional (meth) acrylate>
Examples of the (C) polyfunctional (meth) acrylate used in the present invention include alicyclic poly (meth) acrylates, alicyclic poly (meth) acrylates, and aromatic poly (meth) acrylates. Specifically, polyethylene glycol di (meth) acrylate, 1,2-polypropylene glycol di (meth) acrylate, 1,3-polypropylene glycol di (meth) acrylate, polytetramethylene glycol di (meth) acrylate, 1,2 Dialkylene adducts such as polybutylene glycol di (meth) acrylate, polyisobutylene glycol di (meth) acrylate, bisphenol A, bisphenol F, or bisphenol S, such as ethylene oxide, propylene oxide, or butylene oxide. Di (meth) acrylates of hydrogenated derivatives of bisphenol such as (meth) acrylate, bisphenol A, bisphenol F, or bisphenol S, various polyether polyols (Meth) acrylates having a polyether skeleton such as a block of a compound and another compound or a random low molecular weight copolymer di (meth) acrylate, and hexanediol di (meth) acrylate, nonanediol di ( (Meth) acrylate, decanediol di (meth) acrylate, 2,2-bis [4- (meth) acryloyloxyphenyl] propane, 2,2-bis [4- (2- (meth) acryloyloxyethoxy) phenyl] propane Bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = dimethacrylate, p-bis [β- (meth) acryloyloxyethylthio] xylylene, 4,4′-bis [β- ( And bifunctional (meth) acrylates such as (meth) acryloyloxyethylthio] diphenylsulfone. .

Of these, aliphatic polyfunctional (meth) acrylates, that is, alicyclic poly (meth) acrylates, alicyclic poly (meth) acrylates, and the like are preferable from the viewpoint of control of the cross-linking formation reaction. Furthermore, hexanediol di ( Preferred are (meth) acrylate, nonanediol di (meth) acrylate, bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = dimethacrylate.
These polyfunctional acrylates may be used alone or in combination of two or more in any ratio and combination.

  In the present invention, trifunctional or higher (meth) acrylates may be used as the polyfunctional (meth) acrylate for the purpose of improving the heat resistance of the crosslinked structure of the cured product and improving the surface hardness. Specific examples thereof include trimethylolpropane tris (meth) acrylate, pentaerythritol tris (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and trifunctional (meth) acrylate having an isocyanurate skeleton. It is done.

  The molecular weight of the (C) polyfunctional (meth) acrylate is usually 50 or more, preferably 100 or more, from the viewpoint of the balance between the viscosity of the radiation curable composition and the curing shrinkage. Moreover, it is 1000 or less normally, Preferably it is 500 or less.

  The content of (C) polyfunctional (meth) acrylate is preferably 1% by weight or more, more preferably 2% by weight or more, and usually 30% by weight or less, more preferably 10% by weight or less. (C) If the content of the polymonofunctional (meth) acrylate is too small, the surface hardness of the protective layer tends to decrease, while if too large, curing shrinkage increases and the optical recording medium tends to be deformed. .

<Others>
The radiation curable composition used for forming the protective layer further contains a polymerization initiator, auxiliary components, etc. for initiating a polymerization reaction that proceeds by radiation (for example, active energy rays, ultraviolet rays, electron beams, etc.). May be.

(Polymerization initiator)
As the polymerization initiator, a radical generator that is a compound having a property of generating radicals by light is common, and any known radical generator can be used as long as the effects of the present invention are not significantly impaired. Furthermore, a combined system of a radical generator and a sensitizer may be used.

  Specific examples of such radical generators include benzophenone, 2,4,6-trimethylbenzophenone, 4,4-bis (diethylamino) benzophenone, 4-phenylbenzophenone, methylorthobenzoylbenzoate, thioxanthone, diethylthioxanthone, and isopropylthioxanthone. Chlorothioxanthone, 2-ethylanthraquinone, t-butylanthraquinone, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, benzoin methyl ether, Benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, methylbenzoylformate, 2-methyl-1- [ -(Methylthio) phenyl] -2-morpholinopropan-1-one, 2,6-dimethylbenzoyldiphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis (2,6-dimethoxybenzoyl) -2, 4,4-trimethylpentylphosphine oxide, bis (2,4,6-trimethylbenzoyl) phenylphosphine oxide, 2-hydroxy-1- [4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] -Phenyl] -2-methyl-propan-1-one and the like.

  Among these, since the curing speed is high and the crosslinking density can be sufficiently increased, benzophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2, 4, 6-trimethylbenzoyldiphenylphosphine oxide and 2-hydroxy-1- [4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] -phenyl] -2-methyl-propan-1-one 1-hydroxycyclohexyl phenyl ketone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and 2-hydroxy-1- [4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] -Phenyl] -2-methyl-propan-1-one is more preferred Arbitrariness.

  In the case where the optical recording medium of the present invention is used in an apparatus using a laser having a wavelength of 380 to 800 nm as a light source, radicals are used so that the laser light necessary for reading sufficiently passes through the protective layer. It is preferable to select and use the type and amount of the generator. In this case, it is particularly preferable to use a short wavelength photosensitive radical generator that hardly absorbs laser light in the radiation curable composition.

  Among the above radical generators, such short wavelength photosensitive radical generators include benzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, methylorthobenzoylbenzoate, diethoxyacetophenone, 2-hydroxy -2-methyl-1-phenylpropan-1-one, benzyl dimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, methyl benzoyl formate, etc. Among them, those having a hydroxyl group such as 1-hydroxycyclohexyl phenyl ketone are particularly preferable.

  One of these radical generators may be used alone, or two or more thereof may be used in any ratio and combination. Moreover, the usage-amount of a radical generator is 0 normally with respect to a total of 100 weight part of said (A) urethane (meth) acrylate, (B) monofunctional (meth) acrylate, and (C) polyfunctional (meth) acrylate. .1 part by weight or more, preferably 1 part by weight or more, more preferably 2 parts by weight or more, and usually 10 parts by weight or less, preferably 7 parts by weight or less, more preferably 5 parts by weight or less. If the amount used is too small, the radiation curable composition tends to be unable to be cured sufficiently, while if too large, the polymerization reaction proceeds rapidly, causing not only an increase in optical distortion but also a hue. There is a tendency to get worse.

  In addition to these radical generators, for example, a known sensitizer such as methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, amyl 4-dimethylaminobenzoate, 4-dimethylaminoacetophenone, etc. is used in combination. May be. A sensitizer may be used individually by 1 type, and may be used 2 or more types by arbitrary ratios and combinations.

  One of these polymerization initiators may be used alone, or two or more thereof may be used in any combination and ratio.

[Auxiliary ingredients]
In addition, the radiation curable composition used for forming the protective layer may contain auxiliary components such as additives as necessary, as long as the effects of the present invention are not significantly impaired. Specific examples of the auxiliary components include stabilizers such as antioxidants, heat stabilizers, or light absorbers; glass fibers, glass beads, silica, alumina, zinc oxide, titanium oxide, mica, talc, kaolin, metal fibers, fillers metal powders and the like; carbon fiber, carbon black, graphite, carbon nanotube, a carbon material such as fullerene such as C ₆₀ (fillers, referred to as an inorganic component are collectively a carbon material such.); charge Modifiers such as inhibitors, plasticizers, mold release agents, antifoaming agents, leveling agents, anti-settling agents, surfactants, thixotropy imparting agents; colorants such as pigments, dyes, hue modifiers; monomers and And / or oligomers thereof, or curing agents, catalysts, curing accelerators, and the like necessary for the synthesis of the inorganic component. These auxiliary components may be used alone or in combination of two or more. of It may be used at a rate and in combination. The content of these auxiliary components is usually 20% by weight or less, preferably 10% by weight or less, more preferably 5% by weight or less of the radiation curable composition.

  Among these, silica as fillers will be described in detail. Silica used in the radiation curable composition refers to silicon oxide in general, and it does not matter whether the ratio of silicon and oxygen is crystalline or amorphous. Examples of the silica particles include industrially produced silica particles dispersed in a solvent, or powdered silica particles; silica particles derived and synthesized from raw materials such as alkoxysilanes, and the like. Can do. Among these, when used in the radiation curable composition, silica particles dispersed in a solvent or silica particles derived and synthesized from a raw material such as alkoxysilane are preferable because of easy mixing and dispersion. .

  Although the particle diameter of the silica particles is arbitrary, the number average particle diameter measured by morphological observation using a TEM (transmission electron microscope) or the like is preferably 0.5 nm or more, more preferably 1 nm or more, Further, it is preferably 50 nm or less, more preferably 40 nm or less, still more preferably 30 nm or less, particularly preferably 15 nm or less, and more preferably 12 nm or less. The silica particles are preferably ultrafine particles, but if they are too small, the cohesiveness of the ultrafine particles is extremely increased, and the transparency and mechanical strength of the cured product tend to be extremely decreased. This is because the characteristics tend not to be remarkable.

(Method for forming protective layer)
The radiation-curable composition used for forming the protective layer is the above (A) urethane (meth) acrylate, (B) monofunctional (meth) acrylate, (C) polyfunctional (meth) acrylate, and used as necessary. The polymerization initiator, auxiliary components, and the like are prepared by stirring and mixing uniformly in a state where radiation is blocked. The order of mixing the components at that time is not particularly limited, but it is preferable to add a high viscosity liquid component and / or a solid component to a low viscosity liquid component and stir. The polymerization initiator is preferably added last.

  Moreover, the stirring conditions in that case are not specifically limited. The stirring temperature is usually normal temperature, but may be heated to a temperature of usually 90 ° C. or lower, preferably 70 ° C. or lower. The stirring speed is usually 100 rpm or more, preferably 300 rpm or more, and usually 1000 rpm or less. The stirring time is usually 10 seconds or more, preferably 3 hours or more, and usually 24 hours or less.

  The protective layer is so-called “radiation-cured” in which the radiation-curable composition is applied onto a recording / reproducing functional layer, which will be described later, and a polymerization reaction is started by irradiation with radiation (active energy rays or electron beams). Can be obtained. There is no restriction | limiting in the said coating method, For example, it can be set as general methods, such as a spin coat method.

  Moreover, there is no restriction | limiting in the form of the polymerization reaction of the said radiation-curable composition, For example, well-known polymerization forms, such as radical polymerization, anionic polymerization, cationic polymerization, and coordination polymerization, can be used. Among these examples of polymerization modes, a particularly preferable polymerization mode is radical polymerization. The reason is not clear, but it is presumed to be due to the homogeneity of the product due to the initiation of the polymerization reaction being homogeneous and proceeding in a short time within the polymerization system.

  Here, the radiation refers to an electromagnetic wave (gamma ray, X-ray, ultraviolet ray, visible ray, infrared ray, which acts on a polymerization initiator that initiates a necessary polymerization reaction and generates a chemical species that initiates the polymerization reaction. Microwave, etc.) or particle beam (electron beam, α-ray, neutron beam, various atomic beams, etc.). An example of the radiation preferably used in the present invention is preferably ultraviolet rays, visible rays, and electron beams, and particularly preferably ultraviolet rays and electron beams because energy and a general-purpose light source can be used.

  When ultraviolet rays are used as radiation, it is preferable to use a photo radical generator that generates radicals by ultraviolet rays as the polymerization initiator. At this time, you may use a sensitizer together as needed. The wavelength of the ultraviolet ray is usually 200 nm or more, preferably 240 nm or more, and usually 400 nm or less, preferably 350 nm or less.

  As a device for irradiating ultraviolet rays, a known device such as a high-pressure mercury lamp, a metal halide lamp, or an ultraviolet lamp having a structure for generating ultraviolet rays by microwaves can be preferably used. The output of the apparatus is usually 10 W / cm or more, preferably 30 W / cm or more, and usually 200 W / cm or less, preferably 180 W / cm or less. The apparatus is usually 5 cm or more, preferably Is preferably set at a distance of 30 cm or more, and usually 80 cm or less, preferably 60 cm or less, because there is little light deterioration, thermal deterioration, thermal deformation, etc. of the irradiated object.

  The radiation curable composition can be cured preferably by an electron beam, and a cured product having excellent mechanical properties, particularly tensile elongation properties, can be obtained. When an electron beam is used, the light source and the irradiation device are expensive, but there are advantages that the use of a polymerization initiator can be omitted and that the polymerization is not hindered by oxygen and therefore the surface hardness is good. An electron beam irradiation apparatus used for electron beam irradiation is not particularly limited, and examples thereof include a curtain type, an area beam type, a broad beam type, and a pulse beam type. The acceleration voltage upon electron beam irradiation is usually 10 kV or more, preferably 100 kV or more, and usually 1000 kV or less, preferably 200 kV or less.

These radiation, the irradiation intensity, usually 0.1 J / cm ² or more, preferably 0.2 J / cm ² or more, and generally 20 J / cm ² or less, preferably 10J / cm ² or less, more preferably 5 J / Irradiation is performed at cm ² or less, more preferably 3 J / cm ² or less, and particularly preferably ² J / cm ² or less. If irradiation intensity is in this range, it can select suitably by the kind of radiation-curable composition.

  The irradiation time of radiation is usually 1 second or longer, preferably 10 seconds or longer, and usually 3 hours or shorter, and preferably 1 hour or shorter in terms of reaction acceleration and productivity. When the irradiation energy or irradiation time of radiation is extremely small, the heat resistance and mechanical properties of the protective layer may not be sufficiently exhibited due to incomplete polymerization. On the other hand, when the amount is excessively large, deterioration such as hue deterioration due to light such as yellowing may occur.

  The irradiation with the radiation may be performed in one stage or may be performed in a plurality of stages. As the radiation source, a diffusion radiation source in which radiation spreads in all directions is usually used. The irradiation of radiation is usually carried out with the radiation source fixed and stationary in a state where the disk coated with the radiation curable composition is fixed and stationary or conveyed by a conveyor.

[Hard coat layer]
In the optical recording medium of the present invention, a hard coat layer is formed on the protective layer. The type of the hard coat layer is not particularly limited as long as the surface hardness is HB or more, and a known hard coat layer can be used as a hard coat layer in a general optical recording medium. In the present invention, the surface hardness measured by the method described above is preferably B or more, more preferably HB or more, still more preferably F or more, and particularly preferably H or more. As described above, the surface hardness is JIS K5400 for the surface of the hard coat layer in a state where it is used as an optical recording medium, that is, a state where a resin substrate, a recording / reproducing functional layer, a protective layer, a hard coat layer, and / or a back layer is laminated. The surface hardness measured by a pencil hardness test in accordance with the above.

The hard coat layer preferably has a light transmittance at a wavelength of 550 nm of 80% or more, more preferably 85% or more, and further preferably 89% or more. The measurement of the light transmittance is the same as the method for measuring the light transmittance of the protective layer described above.
Moreover, it is preferable that the contact angle with respect to water is 90 degrees or more, More preferably, it is 100 degrees or more. Thereby, the antifouling property of the optical recording medium can be increased. The measurement of the contact angle with respect to water can be carried out by a known method using a contact angle meter or the like.

  The film thickness of the hard coat layer is usually 0.5 μm or more, preferably 1 μm or more, more preferably 1.5 μm or more. Further, it is usually 5 μm or less, preferably 3 μm or less, more preferably 2 μm or less.

The hard coat layer of the present invention preferably has antifouling properties such as a high contact angle with water.
Hard coating materials with antifouling properties include radiation curing that contains silicone compounds and fluorine compounds as antifouling agents and contains inorganic components such as polyfunctional (meth) acrylate monomers, epoxy compounds, and inorganic nanoparticles. The composition is preferably used. Specific examples of the stain resistance imparting agent include a polymer having a silicone skeleton such as an organopolysiloxane skeleton, a radiation curable compound having a silicone skeleton and an acrylic group, a silicone compound such as a silicone surfactant, and a fluorine atom. , Fluorine-containing compounds such as a radiation curable compound having a fluorine atom and an acryl group, and a fluorine-based surfactant.

  However, in the case of a high recording density medium such as an optical recording medium using a blue laser, since the laser spot diameter is small, it is sensitive to dirt such as fingerprints, dust, and dust. In particular, dirt containing organic matter such as fingerprints may cause serious effects such as laser recording / playback errors if the dirt adheres to the surface of the optical recording medium on the laser beam incident side, and it may be removed. It is preferable to pay attention to these points because they may be difficult.

The antifouling hard coat layer forming material that can be used in the present invention is basically limited as long as it is basically an active energy ray-curable hard coat agent containing a polysiloxane or a stain resistance imparting agent containing a fluorine-containing group. However, it is preferable that the contamination resistance imparting agent is imparted with active energy ray curability. Specific examples include the following.
(1) An active energy ray-curable hard coat agent containing a polysiloxane compound having an active energy ray-curable group at the terminal and / or a fluorine compound and not containing an inorganic component.
(2) An active energy ray-curable hard coating agent containing an active energy ray-curable group and a polymer containing a polysiloxane unit and / or an organic fluorine group unit.
(3) An active energy ray-curable hard coating agent containing a polysiloxane compound having an active energy ray-curable group in the side chain and / or a fluorine compound.

Below, said (1)-(3) is explained in full detail.
The active energy ray-curable hard coat agent (1) comprises 0.01 to 10 parts by weight of a polysiloxane compound and / or fluorine compound having an active energy ray-curable group at the terminal, in one molecule. 88 parts by weight or more and 99.5 parts by weight or less of (meth) acrylate composition containing 30% by weight or more of (meth) acrylate having the above (meth) acryloyl groups, and 0.1 parts by weight or more of photopolymerization initiator. It is preferable to contain 10 parts by weight or less (100 parts by weight in total) as an essential component. Further, if necessary, an organic solvent capable of dissolving these essential components may be added in order to adjust the viscosity, coating property and the like.

The polysiloxane compound having an active energy ray-curable group at the end is not particularly limited as long as it is a polysiloxane having an acryloyl group or a methacryloyl group at one end or both ends, one type alone, or two or more types Can be used in any ratio and combination. Among these, polydimethylsiloxane having a number average molecular weight of 500 or more and 10,000 or less and having (meth) acryloyl groups at both ends is preferable.
Examples of the fluorine compound having an active energy ray group at the terminal include perfluoroalkyl compounds, perfluoroalkylene compounds, perfluoroalkylene polyether compounds having an acryloyl group or a methacryloyl group at one or both terminals. These can be used alone, or two or more can be used in any ratio and combination.

A (meth) acrylate composition containing 30% by weight or more of (meth) acrylate having 3 or more (meth) acryloyl groups in one molecule is one or more and 2 or less (meta) in one molecule. ) A (meth) acrylate having an acryloyl group may be included.
Examples of (meth) acrylate having three or more (meth) acryloyl groups in one molecule include pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate. , Polyester acrylates, polyfunctional urethane acrylates, polyepoxy acrylates, triethoxy acrylate having an isocyanurate ring (for example, manufactured by Toagosei Co., Ltd., Aronix M315, M313, etc.). More than one type can be used in any ratio and combination. Of course, it is needless to say that the present invention is not limited to these.

  Examples of (meth) acrylate compounds having one (meth) acryloyl group per molecule include alkyl (meth) acrylates such as butyl methacrylate and stearyl acrylate, and alicyclic (meth) acrylates such as cyclohexyl acrylate and isobornyl methacrylate. Examples include acrylates, heteroatom-containing cyclic structure-containing acrylates such as tetrahydrofurfuryl acrylate, etc., but other (meth) acrylates having an aromatic ring, (meth) acrylates having a hydroxy group, polyalkylene glycol chains ( A (meth) acrylate or the like can also be preferably used. These can be used singly or in combination of two or more in any ratio and combination. Of course, nothing other than these is not excluded.

  Examples of the (meth) acrylate compound having two (meth) acryloyl groups in one molecule include aliphatic or cycloaliphatic di (meth) acrylates such as hexanediol diacrylate, and polyalkylenes such as polyethylene glycol diacrylate. Glycol di (meth) acrylate, polyester diacrylate, polyurethane diacrylate, bifunctional epoxy acrylate, and the like are preferable, and these can be used alone or in combination of two or more in any ratio and combination. Of course, nothing other than these is not excluded.

  As the photopolymerization initiator, known ones can be widely used, but preferably an alkylphenone type compound (α-hydroxyacetophenone type, α-aminoacetophenone type, benzyl ketal type), acylphosphine oxide type compound, oxime ester compound. Oxyphenyl acetates, benzoin ethers, phenyl formates, ketone / amine compounds, and the like. Specifically, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin butyl ether, diethoxyacetophenone, benzyldimethyl ketal, 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, benzophenone, 2, 4,6-trimethylbenzoindiphenylphosphine oxide, 2-methyl- [4- (methylthio) phenyl] -2-morpholino-1-propanone, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl)- Butan-1-one, methylbenzoylformate, Michler's ketone, isoamyl N, N-dimethylaminobenzoate, 2-chlorothioxanthone, 2,4-diethylthioxanthone and the like are preferable. Two or more of these photopolymerization initiators can be used in combination as appropriate.

  When diluted with a solvent, alcohols (ethanol, isopropanol, isobutanol, etc.), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), alcohols having an alkoxy group (methoxyethanol, ethylene glycol monoethyl ether, propylene glycol monomethyl) Ethers), ethers (ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.), ether esters (propylene glycol monomethyl ether acetate, 2-ethoxyethyl acetate, etc.), aromatic hydrocarbons (toluene, xylene, etc.), esters (acetic acid, etc.) Ethyl, propyl acetate, etc.) are preferable examples, and these are used alone or in combination of two or more in any ratio and combination. To be able to use. In addition, it is preferable to select suitably what is excellent in compatibility with other components and / or uniform dispersibility.

  The active energy ray-curable hard coating agent (2) containing a polymer containing an active energy ray-curable group and a polysiloxane unit and / or an organic fluorine group unit comprises an active energy ray-curable group and a polysiloxane unit and / or 0.1 to 20 parts by weight of a polymer containing an organic fluorine group unit contains 30% by weight or more of (meth) acrylate having 3 or more (meth) acryloyl groups in one molecule (meth) It is preferable that 79.8 parts by weight or more and 99.5 parts by weight or less of the acrylate composition, and 0.1 to 10 parts by weight (total 100 parts by weight) of the photopolymerization initiator are included as essential components. In addition, an organic-inorganic hybrid type (meth) acrylate may be added so as to include inorganic (oxide) fine particles such as silica or the like within a range not exceeding 50% by weight of the entire (meth) acrylate composition. Further, if necessary, an organic solvent capable of dissolving these essential components may be added in order to adjust the viscosity, coating property and the like.

  The polymer containing an active energy ray-curable group and a polysiloxane unit and / or an organic fluorine group unit is not particularly limited. For example, dimercaptosilicon and / or perfluoroalkyl (meth) acrylate and an epoxy group-containing (meth) A preferred example is a polymer obtained by copolymerizing acrylate as an essential component and adding a carboxylic acid having a (meth) acryloyl group to the epoxy group of the copolymer, but of course it is limited to this. It is not done.

  The active energy ray-curable hard coating agent (3) comprises 0.01 parts by weight or more and 10 parts by weight or less of a polysiloxane compound and / or a fluorine compound having an active energy ray-curable group in the side chain. 88 parts by weight or more and 99.5 parts by weight or less of (meth) acrylate composition containing 30% by weight or more of (meth) acrylate having at least one (meth) acryloyl group, and 0.1% by weight of photopolymerization initiator It is preferable to contain 10 parts by weight or more and 100 parts by weight or less (total 100 parts by weight) as an essential component. An organic / inorganic hybrid type (meth) acrylate may be added so as to include inorganic (oxide) fine particles such as silica within a range not exceeding 50% by weight of the total (meth) acrylate composition. Further, if necessary, an organic solvent capable of dissolving these essential components may be added in order to adjust the viscosity, coating property and the like.

  Although it does not specifically limit as a polysiloxane compound and / or a fluorine compound which have an active energy ray hardening group in a side chain, When some preferable examples are illustrated, two or more (meth) acryloyl per molecule will be in a side chain. Containing poly (dimethylsiloxane-methyl (meth) acryloyloxyalkylsiloxane) or poly (dimethylsiloxane-methyl (meth) acryloylsiloxane, poly (dimethylsiloxane-methyl (meth) acryloyloxyalkyloxysiloxane), List polyperfluoroalkylene polyether, perfluoroalkyl mercaptan end-capped polyglycidyl methacrylate oligomer (meth) acrylic acid modified products having two or more (meth) acryloyl groups per molecule in the side chain, etc. Can, and it can be used singly or two or more in optional ratio and combination.

  Moreover, the application | coating method of the radiation curable composition for hard-coat layer formation at the time of forming the said hard-coat layer is not specifically limited, For example, it can be set as general application methods, such as a spin coat method. Moreover, it does not specifically limit about the radiation used for hardening of the said radiation curable composition for hard-coat layer formation, For example, it can be made to be the same as that of the radiation used in the case of formation of the said protective layer.

[Resin substrate]
There is no restriction | limiting about the resin substrate used for this invention, A well-known thing can be used arbitrarily as a resin substrate of an optical recording medium. The shape of the resin substrate of the optical recording medium is arbitrary, but is usually formed in a disc shape.

  Further, the material of the resin substrate is not limited as long as it is a light transmissive material. That is, it can be formed of any material that can transmit light having a wavelength used for recording and reproducing optical information. Specific examples thereof include thermoplastic resins such as polycarbonate resin, polymethacrylate resin, and polyolefin resin. Among these, polycarbonate resin is particularly widely used in CD-ROMs and the like, and is particularly preferable because it is inexpensive. In addition, the material of a resin substrate may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

Further, the dimensions of the resin substrate are not limited and are arbitrary. However, the thickness of the resin substrate is usually 0.1 mm or more, preferably 0.3 mm or more, more preferably 0.5 mm or more, and usually 20 mm or less, preferably 15 mm or less, more preferably 3 mm or less. Among them, a resin substrate having a thickness of about 1.2 ± 0.2 mm is often used. The outer diameter of the resin substrate is generally about 120 mm.
Moreover, although there is no restriction | limiting in the manufacturing method of a resin substrate, it is arbitrary, For example, it can manufacture by injection molding of a light transmissive resin, etc.

[Recording / playback layer]
In the recording / reproducing functional layer used in the present invention, the optical recording medium of the present invention is a reproduction-only medium (ROM medium) or a write-once medium (Write Once medium) that can be recorded only once. In addition, depending on the case of a rewritable medium (Rewriteable medium) in which recording and erasing can be repeated, a layer structure corresponding to each purpose can be adopted. For example, in a read-only medium, the recording / playback functional layer is usually composed of a single layer containing a metal such as Al, Ag, or Au. In addition, in a write-once medium or a rewritable medium, the recording / reproducing functional layer is usually composed of a reflective layer, a dielectric layer, a recording layer, and the like. For example, a recording / reproducing functional layer in a rewritable optical recording medium includes a reflective layer formed of a metal material directly provided on a resin substrate, a recording layer formed of a phase change material, and a recording layer from above and below. It can be composed of two dielectric layers provided so as to be sandwiched.

As the reflection layer, for example, various materials such as Ag, Ag alloy, Al, Al alloy, Au, and Au alloy can be used. One of these may be used alone, or two or more may be combined in any combination. And may be used in combination in a ratio. More preferably, pure Ag, an alloy containing elements such as Ti, Mg, Au, Cu, Nd, or Pd in pure Ag, and an alloy containing elements such as Ta, Ti, Cr, or Mo in Al are used. As the dielectric layer, oxides such as SiO ₂ , ZnO, Al ₂ O ₃ , Ta ₂ O ₅ and Nb ₂ O ₅ , nitrides such as GeN, SiN, GeN and TaN, carbides such as SiC, MgF ₂ Fluorides such as CaF ₂ and sulfides such as ZnS and Y ₂ O ₂ S are preferably used. Among these, ZnS—SiO ₂ , SiN, Ta ₂ O ₅ , and Y ₂ O ₂ S are particularly preferable because they have a high film formation rate and a low film stress.

  As the recording layer, a material composed of an inorganic element or a material composed of an organic compound such as an organic dye can be used. Examples of the material composed of an inorganic element include a material containing both a substance that decomposes when heated and a thermally stable substance. Specific examples of the substance that decomposes when heated include nitrides of elements selected from the group consisting of Cr, Mo, W, Fe, Ge, Sn, and Sb, and elements selected from the group consisting of Ir, Au, Ag, and Pt. And the like. Specific examples of thermally stable materials include nitrides of elements selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Al and Si, and Zn, Al, Y, Zr, Ti, Nb, Examples thereof include oxides of elements selected from the group consisting of Ni, Mg, and Si. In the recording layer, one of these may be used alone, or two or more may be used in any combination and ratio.

[Back layer]
In the optical recording medium of the present invention, a back layer may be formed on the surface of the substrate opposite to the recording / reproducing functional layer.
The back layer used in the present invention preferably has an elastic modulus at 25 ° C. within a predetermined range. Specifically, the upper limit is 2000 MPa or less, preferably 1500 MPa or less. Moreover, although there is no restriction | limiting in a minimum, it is preferable that it is higher than the elasticity modulus of a protective layer. If the elastic modulus of the back layer is too high, the deformation of the optical recording medium with respect to temperature changes may become too large. The method for measuring the elastic modulus can be the same as the method for measuring the elastic modulus of the protective layer.

  The upper limit of the film thickness of the back layer is usually 50 μm or less, preferably 30 μm or less, more preferably 20 μm or less, and further preferably 15 μm or less. If the film thickness of the back layer is too large, when the optical recording media are stacked and stored, the optical recording media are likely to come into contact with each other, and the appearance may be impaired, and an error may easily occur during reading of the recording.

  The material used for forming the back layer is not particularly limited, and generally known materials can be used for the back layer, for example, the same material as the protective layer described above can be used. However, it is particularly preferable to selectively use one that can obtain the above elastic modulus. In particular, a radiation curable composition is preferably used as such a material. Examples of the resin contained in the radiation curable composition used for forming the back layer include unsaturated bonds at the molecular ends or side chains of alkyl (meth) acrylate, urethane (meth) acrylate, polyester (meth) acrylate, and the like. And a resin composition containing as a main component a compound. Among the above main components, urethane (meth) acrylate is preferable from the viewpoint that the back layer can be formed without curing shrinkage or without solvent. Specific examples of urethane (meth) acrylate include, for example, (A) urethane (meth) acrylate used for the formation of a protective layer. One of these may be used alone, or two or more may be used in any ratio and combination. Can be used.

  Moreover, it is preferable to use monofunctional (meth) acrylate as a component used by mixing with the main component. Examples of monofunctional acrylate include (meth) acrylamides such as N, N-dimethyl (meth) acrylamide, Hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate; (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate And cycloaliphatic (meth) acrylates such as cyclohexyl (meth) acrylate and (meth) acrylate having a tricyclodecane skeleton. One of these may be used alone, or two or more may be used in any ratio and combination.

  Among these, from the point that the elastic modulus of the back layer can be increased, isobornyl (meth) acrylate, cyclopentane (meth) acrylate, dicyclopentadienyl (meth) acrylate and the like containing an alicyclic structure. Functional acrylates are preferred.

  The content of urethane (meth) acrylate in the radiation curable composition used for forming the back layer is preferably 1%, with the total content of urethane (meth) acrylate and monofunctional (meth) acrylate being 100% by weight. It is at least 10 wt%, more preferably at least 30 wt%, more preferably at most 70 wt%, more preferably at most 60 wt%.

  Moreover, polyfunctional (meth) acrylate can be used in the radiation curable composition for forming the back layer as long as the elastic modulus is not lowered. As said polyfunctional (meth) acrylate, the thing similar to (C) polyfunctional (meth) acrylate used for formation of a protective layer, for example is mentioned. One of these may be used alone, or two or more may be used in any ratio and combination.

  In addition, in the radiation curable composition for forming the back layer, a polymerization initiator for initiating a polymerization reaction that proceeds by radiation (for example, active energy rays, ultraviolet rays, electron beams, etc.) You may contain an auxiliary component etc. Specific examples include polymerization initiators and auxiliary components used in the radiation curable composition used for forming the protective layer. These can be used alone, or two or more can be used in any ratio and combination.

  Moreover, the application | coating method of the radiation-curable composition for back layer formation at the time of forming the said back layer is not specifically limited, For example, it can be set as general coating methods, such as a spin coat method. Moreover, it does not specifically limit about the radiation used for hardening of the said radiation curable composition for hard-coat layer formation, For example, it can be made to be the same as that of the radiation used in the case of formation of the said protective layer.

  The optical recording medium of the present invention is provided on the surface opposite to the recording / reproducing functional layer of the resin substrate in place of the above-described back layer or the above back layer for the purpose of suppressing deformation of the optical recording medium with respect to temperature change. In addition, a thin film such as an inorganic layer may be formed by a technique such as sputtering, but it is preferably not formed from the viewpoint of cost.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to a following example, unless it deviates from the summary.

[Preparation of radiation curable composition for protective layer]
(Preparation of radiation curable composition A for protective layer)
A four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer was charged with 147.3 g of isophorone diisocyanate and 60 mg of dibutyltin laurate and heated to 70-80 ° C. in an oil bath to keep the temperature constant. Gently stirred until When the temperature became constant, a mixture of 27.6 g of 1,5-pentanediol and 43.1 g of polytetramethylene glycol (number average molecular weight: about 650) was dropped with a dropping funnel, and the temperature was kept at 80 ° C. Stir for 2 hours. After the temperature is lowered to 70 ° C., a mixture of 77.0 g of hydroxyethyl acrylate and 0.3 g of methoquinone is dropped with a dropping funnel, and when the dropping is completed, the temperature is kept at 80 ° C. and stirred for 10 hours to obtain a urethane acrylate oligomer. Was synthesized. After lowering the temperature to 50 ° C., 190 g of tetrahydrofurfuryl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 15 g of 1,6-hexanediol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), and 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals Co., Ltd.) 20 g was added, and the mixture was further stirred for 3 hours to obtain a uniform liquid radiation-curable composition A for a protective layer.

(Preparation of radiation curable composition B for protective layer)
Into a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer, 148.0 g of isophorone diisocyanate and 60 mg of dibutyltin laurate are placed, and heated to 70-80 ° C. in an oil bath to keep the temperature constant. Gently stirred until When the temperature became constant, a mixture of 27.0 g of 1,5-pentanediol and 47.7 g of polytetramethylene glycol (number average molecular weight: about 650) was dropped with a dropping funnel, and the temperature was kept at 80 ° C. Stir for 2 hours. After the temperature is lowered to 70 ° C., a mixture of 77.3 g of hydroxyethyl acrylate and 0.3 g of methoquinone is added dropwise with a dropping funnel, and when the addition is completed, the temperature is kept at 80 ° C. and stirred for 10 hours. Was synthesized. After the temperature was lowered to 50 ° C., 175 g of tetrahydrofurfuryl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 25 g of 1,6-hexanediol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), and 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals Co., Ltd.) ) 20 g was added, and the mixture was further stirred for 3 hours to obtain a uniform liquid radiation-curable composition B for a protective layer.

(Preparation of radiation-curable composition C for protective layer)
A four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer is charged with 143.5 g of isophorone diisocyanate and 60 mg of dibutyltin laurate and heated to 70-80 ° C. in an oil bath, and the temperature becomes constant. Gently stirred until. When the temperature became constant, a mixture of 31.3 g of 1,5-pentanediol and 45.3 g of polytetramethylene glycol (number average molecular weight: about 2000) was dropped with a dropping funnel, and the temperature was kept at 80 ° C. Stir for 2 hours. After the temperature is lowered to 70 ° C., a mixture of 75.0 g of hydroxyethyl acrylate and 0.3 g of methoquinone is dropped with a dropping funnel, and when the dropping is completed, the temperature is kept at 80 ° C. and stirred for 10 hours to obtain a urethane acrylate oligomer. Was synthesized. After lowering the temperature to 50 ° C., 190 g of tetrahydrofurfuryl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 15 g of 1,6-hexanediol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), and 1-hydroxycyclohexyl phenyl ketone (manufactured by Ciba Specialty Chemicals Co., Ltd.) 15 g was added, and the mixture was further stirred for 3 hours to obtain a uniform liquid radiation-curable composition C for a protective layer.

(Preparation of radiation curable composition D for protective layer)
A four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer is charged with 155.6 g of isophorone diisocyanate and 60 mg of dibutyltin laurate and heated to 70 to 80 ° C. in an oil bath to keep the temperature constant. Gently stirred until When the temperature became constant, a mixture of 32.9 g of 1,5-pentanediol and 22.8 g of polytetramethylene glycol (number average molecular weight: about 650) was dropped with a dropping funnel, and the temperature was kept at 80 ° C. Stir for 2 hours. After the temperature is lowered to 70 ° C., a mixture of 81.3 g of hydroxyethyl acrylate and 0.3 g of methoquinone is dropped with a dropping funnel, and when the dropping is finished, the temperature is kept at 80 ° C. and stirred for 10 hours to obtain a urethane acrylate oligomer. Was synthesized. After the temperature was lowered to 50 ° C., 172.5 g of tetrahydrofurfuryl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.), 35 g of 1,6-hexanediol diacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), and 1-hydroxycyclohexyl phenyl ketone (Ciba Specialty Chemicals) 20 g) was added and stirred for 3 hours to obtain a uniform liquid radiation-curable composition D for a protective layer.

[Preparation of composition for hard coat layer]
(Preparation of composition A for hard coat layer)
Dipentaerythritol (hexa / penta) acrylate (trade name: Kayarad DPHA (manufactured by Nippon Kayaku Co., Ltd.)) 99.5 g as a curable composition for a hard coat layer, TEGO (water repellent / oil repellent / low friction agent) (Registered trademark) Rad2200N (manufactured by Degussa, polydimethylsiloxane containing an acrylic group in the side chain) 0.5 g, 2 g of hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, 50 g of propylene glycol monomethyl ether (PGM), and 1- 103 g of acetoxy-2-methoxypropane (PGMA) was stirred in the dark / room temperature for 2 hours to prepare composition A for hard coat layer (solid content: 40% by weight).

(Preparation of composition B for hard coat layer)
90 g of dipentaerythritol (hexa / penta) acrylate (trade name: Kayalad DPHA (manufactured by Nippon Kayaku Co., Ltd.)) as a curable composition for a hard coat layer, and methyl methacrylate (water repellent / oil repellent / low friction agent) MMA), perfluorooctylethyl methacrylate, X-22-167B (both end mercapto polydimethylsiloxane, manufactured by Shin-Etsu Chemical Co., Ltd.) and glycidyl methacrylate (GMA) 25/40/5/30 (weight ratio) copolymer 28.57 g of an acrylic acid adduct (35% PGM solution) and 2 g of hydroxycyclohexyl phenyl ketone as a photopolymerization initiator were added, and PGMA was added in an amount corresponding to a solid content of 40% by weight. It stirred for 2 hours and the composition B for hard-coat layers was prepared.

(Preparation of composition C for hard coat layer)
75 g of dipentaerythritol (hexa / penta) acrylate (trade name: Kayarad DPHA (manufactured by Nippon Kayaku Co., Ltd.)) as the curable composition for the hard coat layer, PMA-ST (manufactured by Nissan Chemical Industries, average particle size) as the inorganic component Dipenta to 20/1 (weight ratio) reaction product of 30% concentration 1-acetoxy-2-methoxypropane dispersion of 12 nm colloidal silica) and KBE9007 (manufactured by Shin-Etsu Chemical Co., Ltd., 3-isocyanatopropyltriethoxysilane) Erythritol pentaacrylate adduct 20g, LMA (lauryl methacrylate), perfluorooctylethyl methacrylate and X-22-167B (both end mercapto polydimethylsiloxane, manufactured by Shin-Etsu Chemical Co., Ltd.) ) And glycidyl methacrylate (GMA) 20/40/3 Add 27.57g of acrylic acid adduct (35% PGM solution) to 37 (weight ratio) copolymer, 1g of hydroxycyclohexyl phenyl ketone as photopolymerization initiator, and mix 1/1 (weight ratio) of PGM / PGMA The solvent was added in an amount corresponding to a solid content of 35% by weight and stirred for 2 hours in the dark / room temperature to prepare composition C for hard coat layer (solid content of 35% by weight).

[Preparation of radiation curable composition for back layer]
In a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer, 191.4 g of isophorone diisocyanate, 125.0 g of polytetramethylene glycol (number average molecular weight: about 650), and 39.9 g of neopentyl glycol The mixture was allowed to react for 8 hours while being heated at 95 ° C. in an oil bath. After cooling to 65 ° C., 0.06 g of dioctyltin dilaurate, 0.13 g of methoquinone, 90.0 g of tetrahydrofurfuryl acrylate (Osaka Organic) were added, and the reaction was started by dropping 70.1 g of hydroxyethyl acrylate. . The reaction was performed for 10 hours while heating at 70 ° C. in an oil bath, and the progress of the reaction was confirmed by disappearance of the peak derived from the NCO group by IR (infrared spectrophotometer). Thereafter, 431.3 g of dicyclopentanyl acrylate (manufactured by Hitachi Chemical Co., Ltd.), 42.7 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Nippon Siebel Hegner), 4.7 g of benzophenone, and 4.7 g of antifoaming agent are added. A radiation curable composition was obtained.

<Example 1>
(Production of optical recording medium)
On the surface of a polycarbonate resin substrate having a diameter of 120 mm and a thickness of 1.1 mm on which a stack ring having a height of 0.18 mm, a diameter of 35 mm, and a width of 1 mm is formed, an Ag—Cu—Nd reflective layer having a thickness of 100 nm, ZnS having a thickness of 25 nm -SiO ₂ dielectric layer, 15nm Sn-Nb-N recording layer with a thickness of the ZnS-SiO ₂ dielectric layer of 30nm thickness was formed by sputtering in this order to obtain a recording and reading layer.
The radiation curable composition A for protective layer is applied to the surface of the outermost dielectric layer of the recording / reproducing functional layer with a spin coater so as to have a thickness of 100 μm, and a high-pressure mercury lamp (manufactured by Toshiba Harrison; Toscure 752) is used. Then, the protective layer was formed by curing by irradiating with ultraviolet rays having a dose of 100 mJ / cm ² at a wavelength of 365 nm. The amount of ultraviolet irradiation was measured with a UV meter (USHIO Corporation; UIT-250).
Next, the hard coat layer composition was applied to the surface of the protective layer with an A spin coater, and using a high-pressure mercury lamp (manufactured by JATEC Corporation; J-cure 100), ultraviolet rays with a dose of 400 mJ / cm ^{2 at} a wavelength of 365 nm were irradiated. And cured to form a hard coat layer having a thickness of 2 μm.
Next, the radiation curable composition for the back layer was applied to the surface of the polycarbonate resin substrate opposite to the surface on which the hard coat layer was formed with a spin coater so as to have a thickness of 15 μm. A back layer was formed by irradiating with an ultraviolet ray with a dose of 80 mJ / cm ^{2 at} a wavelength of 365 nm using a Harrison (Toscure 752) to form a back layer, thereby producing an optical recording medium. The same operation was repeated to obtain 52 optical recording medium disks.

(Temperature disk deformation evaluation test)
Disk drive (manufactured by NEC; model number PCCD60D) A 40 mm square window is opened on the top surface of the housing, a displacement sensor (manufactured by Keyence; model number "LT-9010") is fixed above the window, and the disk is inserted into the disk drive. In this case, a disc deformation detection unit was prepared in which the vertical displacement at a position 58 mm from the center of the disc was detected in real time, and the data could be output to a computer. This unit was installed in a chamber of a thermostatic chamber (Humidator Cosmopia manufactured by Hitachi; model number EC-10HHP). The outline of this system is shown in FIG. As shown in FIG. 1, the deformation value was negative in the case of concave deformation on the protective layer / hard coat side, and the deformation value was positive in the case of convex deformation on the protective layer / hard coat side.
One optical recording medium produced as described above was inserted into a disk drive, and the thermostatic chamber was sealed. Then, the temperature in the thermostatic chamber was set at 25 ° C. and maintained for 1 hour, and the deformation of the disk was measured. The obtained value was used as a deformation reference value.
Next, the temperature in the thermostatic chamber was changed to 55 ° C., kept for 1 hour, and the deformation of the disk was measured. The difference between this measured value and the reference value was recorded as the deformation value at high temperature. Next, the temperature in the thermostatic chamber was changed to 25 ° C. and kept for 3 hours, then changed to 5 ° C. and kept for 1 hour, and the deformation of the disk was measured. The difference between this measured value and the reference value was recorded as the low temperature deformation value.
The deformation value at high temperature and the deformation value at low temperature are plotted in FIG. As seen in FIG. 2, the high temperature deformation value was positive and the low temperature deformation value was negative. The higher absolute value of the high temperature deformation value and the low temperature deformation value is shown in Table 2 as the maximum temperature deformation value. If the absolute value of the deformation value is larger than 150 μm, an appropriate working distance cannot be secured when using a lens with a representative lens of NA = 0.85 and a diameter of 3 mm. The cases other than were determined as “good”.

(Stack test)
For each of the 50 optical recording media produced above, the optical recording media are slowly stored one by one in a spindle case of 50 internal volumes having a stainless steel stack pole with a diameter of 14.8 mm in the center, for a total of 50 sheets. Stacked and stored. After this spindle case is left in an environment of 25 ° C. and 45% RH for 7 days, the optical recording medium is slowly taken out one by one from the upper part of the stack, and there is sticking of the disks due to deformation and sticking marks due to the sticking. It was observed visually. Table 2 shows the number of discs on which sticking marks were observed.

(Surface hardness evaluation)
The surface hardness of each optical recording medium produced as described above was evaluated by a method based on JIS K5400. The results are shown in Table 2.
Specifically, pencils of hardness 4B, 3B, 2B, B, HB, F, and H (manufactured by Mitsubishi Pencil Co., Ltd .; part number UNI, Nikko inspection completed, for pencil scratch value test) are prepared, and a pencil hardness measuring device ( A hardness of 4B was first attached using Shinto Kagaku Co., Ltd .; Tribogear Type 18), and 1 cm running was performed at a weight of 750 gf and a scratching speed of 30 mm / min, and the presence or absence of running traces was visually confirmed. When no running trace was observed, the pencil was replaced with a one-step hard pencil and the same operation was repeated.
The results are organized as follows.

<Example 2>
In Example 1, it carried out like Example 1 except having used composition B for hard-coat layers as a composition for hard-coat layers. Table 2 shows the surface hardness, the maximum temperature deformation, and the stack test sticking trace.

<Example 3>
In Example 1, it carried out like Example 1 except having used composition C for hard coat layers as a composition for hard coat layers. Table 2 shows the surface hardness, the maximum temperature deformation, and the stack test sticking trace.

<Example 4>
In Example 1, it carried out similarly to Example 1 except having used the radiation-curable composition B for protective layers as a radiation-curable composition for protective layers, and having formed the back layer with the thickness of 30 micrometers. Table 2 shows the surface hardness, the maximum temperature deformation, and the stack test sticking trace.

<Comparative Example 1>
In Example 1, it carried out similarly to Example 1 except having used the composition C for protective layers as a composition for protective layers, and having formed the back layer material by the thickness of 30 micrometers. Table 2 shows the surface hardness, the maximum temperature deformation, and the stack test sticking trace.

<Comparative example 2>
In Example 1, it carried out similarly to Example 1 except having used the radiation-curable composition D for protective layers as a radiation-curable composition for protective layers, and having formed the back layer with the thickness of 30 micrometers. Table 2 shows the surface hardness, the maximum temperature deformation, and the stack test sticking trace. Further, the high temperature deformation value and the low temperature deformation value are shown in FIG.

<Comparative Example 3>
In Example 1, it carried out similarly to Example 1 except having used the radiation-curable composition D for protective layers as a radiation-curable composition for protective layers, and having formed the back layer with the thickness of 70 micrometers. Table 2 shows the surface hardness, the maximum temperature deformation, and the stack test sticking trace.

<Evaluation>
As shown in Table 2, when the maximum temperature deformation value was larger than 150 μm, an appropriate working distance could not be ensured as described above, and thus the determination was “x”. Further, Comparative Example 1 had a low surface hardness and had sticking marks. In Comparative Example 2, the surface hardness was low and no sticking trace was made, but the temperature deformation was large and the disk was not recognized. In Comparative Example 3, the surface hardness was high and the temperature deformation determination was a good result, but adhesion marks were easily formed and the storage stability was low.
On the other hand, in Examples 1 to 4, the maximum temperature deformation value was 150 μm, the deformation was small with respect to the temperature change, and the surface hardness was high. Furthermore, even if it is a case where it accumulates and preserve | saves, it could be set as the thing which does not produce blocking.

  The optical recording medium of the present invention can cope with environmental temperature changes, and is excellent in wear resistance and recording protective layer protection. In addition, blocking or the like hardly occurs during storage. Therefore, the present invention can be suitably used for optical recording media including next-generation high-density optical recording media such as Blu-ray discs.

It is a figure which shows the outline | summary of the system of a vs. temperature disk deformation | transformation evaluation test. It is a graph which shows the result of the disk deformation characteristic with respect to temperature of Example 1 and Comparative Example 2.

Claims (6)

A resin substrate, a recording / reproducing functional layer formed on the resin substrate, a protective layer formed on the recording / reproducing functional layer, a hard coat layer formed on the protective layer and having a surface hardness of B or more, and An optical recording medium having a back layer having a thickness of 50 μm or less formed on the surface of the resin substrate opposite to the recording / reproducing functional layer,
The optical recording medium after standing for 1 hour in an environment of 5 ° C. after standing for a certain time in an environment of 25 ° C., and for 1 hour in an environment of 55 ° C. after standing for a certain time in an environment of 25 ° C. About the optical recording medium after placing
When the amount of displacement in the vertical direction of the surface of the back layer at the position farthest from the center of the recordable / reproducible region of the optical recording medium is measured, the amount of displacement is 150 μm or less in all cases. Medium. The protective layer comprises (A) urethane (meth) acrylate 10 to 85% by weight, (B) monofunctional (meth) acrylate 10 to 80% by weight, and (C) polyfunctional (meth) acrylate 0 to 30% by weight. 2. The optical recording medium according to claim 1, wherein the optical recording medium is a cured product of a radiation curable composition. The optical recording medium according to claim 1 or 2, wherein the protective layer has an elastic modulus at 25 ° C in a range of 500 to 1300 MPa. The (A) urethane (meth) acrylate is a reaction product obtained by reacting a composition containing (a1) polyisocyanate, (a2) polyether polyol, and (a3) hydroxyl group-containing (meth) acrylate. The optical recording medium according to any one of claims 1 to 3. The optical recording medium according to any one of claims 1 to 4, wherein the (B) monofunctional (meth) acrylate is an alicyclic (meth) acrylate. The optical recording medium according to any one of claims 1 to 5, wherein the (C) polyfunctional (meth) acrylate is an aliphatic polyfunctional (meth) acrylate.

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