JP4555846B2 - Optical recording medium - Google Patents

Description

  The present invention relates to an optical recording medium such as a recording / reproducing disk. More specifically, the present invention relates to an optical recording medium that can cope with a change in temperature and a change in environmental humidity and can be used for a high-density optical disk. It is.

  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 required to be small in deformation when the environmental temperature or environmental humidity changes so that information can be stably read and written even if the environmental temperature and humidity change.

  Here, it has been clarified by the present inventors that the deformation of the disk accompanying the environmental temperature change is governed by the elastic modulus of the protective layer. That is, when the elastic modulus of the protective layer is large, the deformation of the disk accompanying the temperature change increases. Conversely, when the elastic modulus of the protective layer is small, the deformation is small. Therefore, it is preferable that the elastic modulus of the protective layer is small from the viewpoint that deformation caused by changes in the environmental temperature is small.

  However, generally, the lower the elastic modulus of the protective layer, the lower the hardness of the hard coat formed on the protective layer. Therefore, from the viewpoint of the hardness of the hard coat layer, that is, the scratch resistance and hardness of the optical recording medium, it is preferable that the elastic modulus of the protective layer is large.

  Further, it is presumed that the deformation of the optical recording medium accompanying the change in the humidity of the environment is dominated by the deformation accompanying the absorption and dehydration of the resin substrate. This can also be seen from the fact that the deformation of the optical recording medium having only the resin substrate and the recording / reproducing functional layer is very large. If a protective layer or a hard coat layer is further formed on the recording / reproducing functional layer, the deformation can usually be reduced. This is considered to be because the deformation accompanying the absorption and dehydration of the protective layer and the hard coat layer cancels out the deformation of the resin substrate existing on the opposite side through a relatively hard layer called the recording / reproducing functional layer. In addition, it is thought that the degree which reduces the said deformation | transformation is dependent on the layer with a thick film thickness, and generally is considered to depend mainly on the elasticity modulus of the protective layer which has a film thickness larger than a hard-coat layer. That is, it is preferable that the elastic modulus of the protective layer is in an appropriate range (relatively high elastic modulus) because the deformation of the disk accompanying the change in environmental humidity becomes small. When the elastic modulus of the protective layer is too small, the deformation due to the absorption and dehydration of the resin substrate due to the change in the environmental humidity cannot be suppressed, and as a result, the deformation of the entire disk due to the change in the environmental humidity may increase. When the elastic modulus of the protective layer is too large, the deformation of the protective layer becomes larger than the deformation of the resin substrate, and the deformation on the side opposite to the resin substrate is increased. Therefore, it is preferable that the elastic modulus of the protective layer is within an appropriate range where the elastic modulus is relatively high, from the viewpoint that deformation due to changes in environmental humidity is small.

  Summarizing the relationship between the elastic modulus of the protective layer and the required performance, (1) From the viewpoint of the surface hardness of the optical recording medium, the protective layer preferably has a high elastic modulus, and (2) the environment. From the viewpoint of deformation accompanying temperature change, the protective layer preferably has a low elastic modulus, and (3) from the viewpoint of deformation accompanying environmental humidity change, it is within an appropriate range having a relatively high elastic modulus. It is preferable.

Here, for example, Patent Document 1 proposes a material that is less deformed with respect to (2) environmental temperature change and (3) environmental humidity change. The above document shows that a composition containing urethane acrylate and other acrylates is suitable as a material for a light transmission layer of an optical information medium. When the material for the transmissive layer is used, there is a possibility that an optical recording medium in which deformation due to environmental temperature and humidity changes does not become so large can be manufactured.
Further, for example, Patent Document 2 proposes a material having (1) high surface hardness and (3) little deformation with respect to changes in environmental humidity.
JP 2003-263780 A JP 2007-131698 A

However, in the optical recording medium using the light transmission layer material described in Patent Document 1, (1) the surface hardness may not be sufficient. In addition, the present inventors have clarified that the optical recording medium using the material described in Patent Document 2 may be deformed with respect to changes in environmental temperature (2). .
In addition, there is no report on (2) optical recording media with little deformation due to changes in environmental temperature and (1) high surface hardness. In view of the above, it is desired to provide an optical recording medium that satisfies all the above requirements, that is, an optical recording medium that is less deformed due to changes in environmental temperature and humidity and that has a higher surface hardness.

  The present invention has been made in view of the above problems. That is, an object of the present invention is to provide an optical recording medium that has a sufficient surface hardness and is less deformed when the environmental temperature and environmental humidity change, and has an excellent balance of characteristics.

  When the present inventors diligently researched an optical recording medium that can satisfy the above-mentioned object, the material of the radiation curable composition for forming the protective layer and the elastic modulus at the time of water absorption of the protective layer are important. I found out. Specifically, the protective layer contains urethane (meth) acrylate (A) and other (meth) acrylate compound (B), and the elastic modulus of the protective layer during normal time and elasticity during water absorption By setting the ratio to the ratio to a predetermined value or more, an optical recording medium having a sufficient surface hardness can be obtained with little deformation when the environmental temperature is changed and immediately after the environmental humidity is changed. And found out that the present invention.

  The first gist of the present invention is a radiation containing a resin substrate, a recording / reproducing functional layer, a urethane (meth) acrylate (A) and a (meth) acrylate compound (B) other than the urethane (meth) acrylate (A). An optical recording medium comprising, in this order, a protective layer that is a cured product of a curable composition and a hard coat layer having a surface hardness of B or more, wherein the tensile elastic modulus of the protective layer at 25 ° C. and 45% humidity In the optical recording medium, the ratio of the tensile elastic modulus at the time of saturated water absorption with respect to is 0.20 or more (claim 1).

  At this time, the water absorption at 25 ° C. of the protective layer is preferably 2 (wt / wt)% or less (Claim 2), and the urethane (meth) acrylate (A) is (a1) polyisocyanate, (A2) a diol having a molecular weight of less than 400, (a3) a polyol having a number average molecular weight of 400 or more and less than 1500, (a4) a polyol having a number average molecular weight of 1500 or more, and (a5) a hydroxyl group-containing (meth) acrylate. A reaction product obtained by reacting is preferred.

  Moreover, it is preferable that (meth) acrylate compounds (B) other than the said urethane (meth) acrylate (A) are alicyclic acrylates (Claim 4), and also (other than said urethane (meth) acrylate (A) ( The (meth) acrylate compound (B) is preferably a monofunctional (meth) acrylate and / or a polyfunctional (meth) acrylate having a molecular weight of 300 or less (Claim 5).

  According to the present invention, it is possible to provide an optical recording medium having a sufficient surface hardness, less deformation when the environmental temperature changes, and less deformation immediately after the environmental humidity changes, and having an excellent balance of characteristics. is there.

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 thereof.
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, urethane (meth) acrylate (A), and the urethane (meth) acrylate. A protective layer, which is a cured product of a radiation curable composition containing a (meth) acrylate compound (B) other than (A), and a hard coat layer having a surface hardness of B or more are provided in this order.

In addition, the optical recording medium of the present invention has a tensile elastic modulus ratio e (hereinafter referred to as “tensile elastic modulus ratio” as appropriate) at the time of saturated water absorption to the tensile elastic modulus at 25 ° C. and 45% humidity of the protective layer represented by the following formula. Is also 0.20 or more.
e = (Tension elastic modulus at saturated water absorption) / (Tension elastic modulus at 25 ° C. and 45% RH)

  The tensile elastic modulus means an elastic modulus when a film having a thickness of 0.1 mm is formed and a tensile test is performed at a tensile speed of 1 mm / min using a tensile strength tester. Further, the tensile elastic modulus at the time of saturated water absorption means an elastic modulus when the above-described tensile test is performed on a film immediately after the film is immersed in water at 25 ° C. for 3 hours.

According to the present invention, the protective layer contains a predetermined material (urethane (meth) acrylate (A) and (meth) acrylate compound (B) other than the urethane (meth) acrylate (A)), The surface hardness of the optical recording medium can be increased, and further, the deformability with respect to the environmental temperature can be reduced.
The reason why the surface hardness and the environmental temperature resistance can be improved is not necessarily clear, but when a predetermined material is used, a material similar to a fine crystal domain derived from the skeleton is formed. While the domain plays a role like an inorganic filler and brings high surface hardness, the crosslinking density itself is reasonably low, and there is a kind of molecular motion buffer, which is presumed to suppress thermal expansion and contraction. The

In the present invention, since the ratio of the tensile elastic modulus of the protective layer is not less than a predetermined value, the deformation immediately after the environmental humidity changes can be reduced. This mechanism is presumed as follows.
As described above, the deformation of the optical recording medium when the environmental humidity changes is dominated by the deformation accompanying the absorption and dehydration of the protective layer and the resin substrate. In the present invention, a protective layer in which the ratio of the tensile elastic modulus during moisture absorption to the normal tensile elastic modulus is within a predetermined range is formed on the recording / reproducing functional layer. A resin material such as a normal radiation curable composition swells and becomes soft at the time of moisture absorption, and its elastic modulus is greatly reduced. A material having such a large decrease will have a small ratio between the tensile elastic modulus at the time of moisture absorption and the tensile elastic modulus at the normal time. In the present invention, the ratio of the elastic modulus at the time of moisture absorption of the protective layer to the elastic modulus at normal time is large, i.e., the elastic modulus is difficult to decrease at the time of moisture absorption. The stress to be applied is increased, and the deformation can be sufficiently suppressed. Therefore, it is considered that the optical recording medium can be hardly deformed even when an environmental humidity change occurs.

From the above, the optical recording medium of the present invention can have a sufficient surface hardness, little deformation when the environmental temperature changes, and little deformation immediately after the environmental humidity changes.
Hereinafter, each member of the optical recording medium of the present invention will be described.

[Protective layer]
First, the protective layer used in the optical recording medium of 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. Such a 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 tensile modulus ratio e in the protective layer is usually 0.2 or more, preferably 0.3 or more, more preferably 0.5 or more, and particularly preferably 0.7 or more. The upper limit is usually 1 or less. If the ratio e of the tensile elastic modulus is too small, the elastic modulus at the time of moisture absorption tends to be small, and when the environmental humidity changes, the deformation of the resin substrate cannot be suppressed, and the deformation of the optical recording medium tends to increase. There is.

The water absorption rate of the protective layer is preferably 2 (wt / wt)% or less, more preferably 1.5 (wt / wt)% or less, still more preferably 1 (wt / wt)% or less, particularly Preferably it is 0.7 (wt / wt)% or less. If the water absorption rate of the protective layer is too high, the tensile modulus ratio e tends to be smaller than the above range, and the optical recording medium may be greatly deformed due to changes in environmental humidity. The water absorption rate is determined by the following method. A 0.1 mm thick film is formed and the initial weight W _o is measured. Next, after immersing the film in a container filled with pure water at 25 ° C. for 3 hours, the film is taken out, the attached pure water is gently wiped with a wiper, and the weight W is measured immediately. It is calculated by obtaining the weight increase after immersion (W−W ₀ ) with respect to the initial weight W _o . That is, the water absorption rate is expressed by the following equation.
Water absorption A (%) = (W−W _o / W _o ) × 100

  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.

  In addition, the protective layer usually exhibits insoluble and infusible properties in solvents and the like, has properties advantageous for the use of optical members even when thickened, and has excellent adhesion and surface curing. Is preferred. 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 hardness of the protective layer is a surface hardness according to a pencil hardness test in accordance with JIS K5400, and is usually about 6B, preferably 4B or more, more preferably 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.

  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.

  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.

  Furthermore, it is preferable that the adhesiveness between the protective layer and the recording / reproducing functional layer described later is high, and it is preferable that the adhesiveness with time is 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 protective layer is a cured product of a radiation curable composition containing urethane (meth) acrylate (A) and a (meth) acrylate compound (B) other than the urethane (meth) acrylate (A). In the said radiation curable composition, materials other than the above may contain suitably as needed.

<Urethane (meth) acrylate (A)>
The radiation curable composition used for forming the protective layer contains urethane (meth) acrylate (A). Thereby, it becomes possible to make the deformation of the optical recording medium with respect to the temperature change small and to make the optical recording medium have a high surface hardness.
The urethane (meth) acrylate (A) is not particularly limited, and is usually obtained by reacting a hydroxyl group-containing compound, polyisocyanate, and a hydroxyl group-containing (meth) acrylate. It can be.

  In the present invention, in particular, the urethane (meth) acrylate (A) is (a1) polyisocyanate, (a2) a diol having a molecular weight of less than 400, (a3) a polyol having a number average molecular weight of 400 or more and less than 1500, (a4) A reaction product obtained by reacting a polyol having a number average molecular weight of 1500 or more and a composition containing (a5) a hydroxyl group-containing (meth) acrylate is preferable.

[(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, and examples thereof include aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanate). Natocyclohexyl) alicyclic diisocyanates such as methane and isophorone diisocyanate; aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, m-phenylene diisocyanate, naphthalene diisocyanate and the like. Moreover, 2 or more types can be used in arbitrary ratios and combinations. Among these, alicyclic such as bis (isocyanatomethyl) cyclohexane, cyclohexane diisocyanate, bis (isocyanatocyclohexyl) methane, and isophorone diisocyanate in that the hue of the urethane (meth) acrylate (A) to be obtained is good. Diisocyanate is preferred.

  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 generally 2 × 10 ⁻⁴ mol / in the sum of the (A) urethane (meth) acrylate and the (B) urethane (meth) acrylate (A) other than the (meth) acrylate compound. g or more, preferably 6 × 10 ⁻⁴ mol / g or more, and usually 22 × 10 ⁻⁴ mol / g or less, preferably 16 × 10 ⁻⁴ mol / g or less.

[(A2) Diol having a molecular weight of less than 400]
A diol having a molecular weight of less than 400 means a compound having a molecular weight of less than 400 containing two hydroxyl groups. The diol having a molecular weight of less than 400 used in the present invention is not particularly limited. For example, 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-hexanediol, 1,8-octanediol 1,9-nonanediol, 2-methyl-1,8-octanediol, 1,2-dimethylolcyclohexane, 1,3-dimethyl Roll cyclohexane, 1,4-dimethylolcyclohexane, alkylenediols such as dicyclopentadienyl dimethanol and the like, one or more of them may be used in optional ratio and combination.

  Among the above, aliphatic diols having 4 to 10 carbon atoms are preferable, specifically 1,4-butanediol, 1,5-pentanediol, 2-methyl-1,5-pentanediol, 1,6-hexane. Diol, 1,8-octanediol, 1,9-nonanediol, and 2-methyl-1,8-octanediol can make the optical recording medium less susceptible to deformation, and the surface hardness of the optical recording medium Is particularly preferable because of a tendency to increase.

  (A2) The molecular weight of the diol having a molecular weight of less than 400 is preferably 250 or less, more preferably 150 or less, and usually 80 or more, preferably from the viewpoint of the balance between deformation of the resin substrate resulting from curing shrinkage and surface hardness. Is 100 or more.

The diol having a molecular weight of less than 400 (a2) is usually 1 × 10 in the sum of the (A) urethane (meth) acrylate and the (B) urethane (meth) acrylate (A) other than the (meth) acrylate compound. ⁻⁴ mol / g or more, preferably 3 × 10 ⁻⁴ mol / g or more, and usually 10 × 10 ⁻⁴ mol / g or less, preferably 8 × 10 ⁻⁴ mol / g or less.

[(A3) polyol having a number average molecular weight of 400 or more and less than 1500]
The polyol having a number average molecular weight of 400 or more and less than 1500 is a compound having a number average molecular weight of 400 or more and less than 1500 and having two or more hydroxyl groups in the molecule.
Examples of the polyol having a number average molecular weight of 400 or more and less than 1500 include, for example, a polyether polyol which is a polymer of (a2) a diol having a molecular weight of less than 400 (hereinafter sometimes referred to as “diol” as appropriate); And polyester polyols having an ester bond by reaction of a polybasic acid with each other, or an ester bond by ring-opening polymerization of a cyclic ester, and polycarbonate polyols having a carbonate bond by reaction of the diol and carbonate.

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

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

  Specific examples of the polycarbonate polyol include the above diol and alkylene carbonates such as ethylene carbonate, 1,2-propylene carbonate, 1,2-butylene carbonate, or diphenyl carbonate, 4-methyldiphenyl carbonate, 4-ethyldiphenyl 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, bischlorophenyl Diaryl carbonates such as carbonate, phenylchlorophenyl carbonate, phenyl naphthyl carbonate, dinaphthyl carbonate, or dimethyl carbonate Reaction with dialkyl carbonates such as sulfonate, 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. Thing etc. are mentioned.

  These polyols may be used individually by 1 type, and may use 2 or more types by arbitrary ratios and combinations. Among the polyols, polyether polyols are preferable, polyalkylene glycol is preferable, and polytetramethylene glycol is particularly preferable.

  The upper limit of the number average molecular weight of the polyol (a3) having a number average molecular weight of 400 or more and less than 1500 is more preferably 1100 or less, still more preferably 900 or less, and particularly preferably 800 or less, in view of improving surface hardness.

The (a3) polyol having a number average molecular weight of 400 or more and less than 1500 is the sum of the (A) urethane (meth) acrylate and the (B) urethane (meth) acrylate (A) (meth) acrylate compound other than Usually 0.1 × 10 ⁻⁴ mol / g or more, preferably 0.5 × 10 ⁻⁴ mol / g or more is used, and usually 2.0 × 10 ⁻⁴ mol / g or less, preferably 1.3 × 10 ^-4 mol / g or less is used.

[(A4) polyol having a number average molecular weight of 1500 or more]
A polyol having a number average molecular weight of 1500 or more is a compound having a number average number average molecular weight of 1500 or more and having two or more hydroxyl groups in the molecule.
Such a polyol having a number average molecular weight of 1500 or more is not particularly limited, and examples thereof include (a3) the polyols exemplified in the column of polyol having a number average molecular weight of 400 or more and less than 1500. Among the above, polyether polyol is preferable, polyalkylene glycol is more preferable, and polytetramethylene glycol is particularly preferable. In addition, the (a4) polyol having a number average molecular weight of 1500 or more may be used alone, or two or more may be used in any ratio and combination.

The lower limit of the number average molecular weight of the polyol (a4) having a number average molecular weight of 1500 or more is preferably 1900 or more in that the decrease in elastic modulus at the time of water absorption of the protective layer is reduced.
The polyol (a4) having a number average molecular weight of 1500 or more is usually the sum of the (A) urethane (meth) acrylate and the (meth) acrylate compound other than the (B) urethane (meth) acrylate (A). 0.05 × 10 ⁻⁴ mol / g or more, preferably 0.1 × 10 ⁻⁴ mol / g or more is used, and usually 1 × 10 ⁻⁴ mol / g or less, preferably 0.5 × 10 ⁻⁴ mol / g or less. / G or less.

(A5) 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 reaction product of glycidyl ether and (meth) acrylic acid. And mono (meth) acrylates of glycols, 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 (a5) 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 (a5) hydroxyl group-containing (meth) acrylate is usually 2 × 10 in the sum of the (A) urethane (meth) acrylate and the (B) urethane (meth) acrylate (A) other than the (meth) acrylate compound. ⁻⁴ mol / g or more, preferably 6 × 10 ⁻⁴ mol / g or more, and usually 21 × 10 ⁻⁴ mol / g or less, preferably 17 × 10 ⁻⁴ mol / g or less.

[(A) Method for producing urethane (meth) acrylate]
(A1) polyisocyanate, (a2) diol having a molecular weight of less than 400, (a3) polyol having a number average molecular weight of 400 or more and less than 1500, (a4) a polyol having a number average molecular weight of 1500 or more, and (a5) hydroxyl group-containing (meta ) A urethane (meth) acrylate compound (A) can be produced by addition reaction of a composition containing acrylate.
It is preferable to adjust so that the isocyanate group and hydroxyl group in the composition containing said (a1)-(a5) may become stoichiometric amount in the case of the said addition reaction.

  Moreover, when manufacturing (A) urethane (meth) acrylate, the weight ratio of the (a4) polyol having a number average molecular weight of 1500 or more to the polyol (a3) having a number average molecular weight of 400 or more and less than 1500, that is, {( The weight of a4)} / {weight of (a3)} is usually 0.05 or more, preferably 0.1 or more, and usually 10 or less, preferably 7 or less. If this ratio is too small, the elastic modulus of the protective layer during water absorption tends to decrease. Conversely, if it is too large, the surface hardness decreases.

  Moreover, the hydroxyl group amount of the (a5) hydroxyl group-containing (meth) acrylate used when producing the urethane (meth) acrylate (A) is (a2) a diol having a molecular weight of less than 400, and (a3) a number average molecular weight. 400 to less than 1500 polyol, (a4) a polyol having a number average molecular weight of 1500 or more, and (a5) a total hydroxyl group content in the hydroxyl group-containing (meth) acrylate is usually 20 mol% or more, Preferably it is 40 mol% or more. Moreover, it is 80 mol% or less normally, Preferably it is 60 mol% or less. Depending on the ratio, it is possible to control the molecular weight of the (A) urethane (meth) acrylate obtained.

  (A1) polyisocyanate, (a2) diol having a molecular weight of less than 400, (a3) polyol having a number average molecular weight of 400 or more and less than 1500, (a4) a polyol having a number average molecular weight of 1500 or more, and (a5) hydroxyl group-containing (meta ) The addition reaction of the acrylate-containing composition can be performed by any known method. For example, (a1) a polyisocyanate, a composition containing (a2) to (a5) (hereinafter also referred to as a hydroxyl group-containing composition) and a mixture containing an addition reaction catalyst are usually 40 ° C. or higher, preferably 50 ° C. In addition, 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) a method of dropping the mixture containing the hydroxyl group-containing composition and the addition reaction catalyst simultaneously or sequentially in the presence of polyisocyanate can be used.

  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)-(a5) 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.

[Properties of urethane (meth) acrylate compound (A)]
As a urethane (meth) acrylate compound (A), a highly transparent thing is preferable, for example, it is preferable that it is a compound which does not have an aromatic ring. When the urethane (meth) acrylate compound has an aromatic ring, the radiation-curable composition having an aromatic ring and the cured product are colored during storage even if the resulting product is a colored product or is not colored. Or coloring (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 (a5). In the present invention, the urethane (meth) acrylate (A) is particularly preferably urethane acrylate from the viewpoint of excellent surface curability as a composition and less stickiness.

  Further, the weight average molecular weight of the urethane (meth) acrylate (A) is usually 1,000 or more, more preferably 1,500 or more from the viewpoint of the balance between viscosity and mechanical properties, and usually 10 ,. 000 or less, more preferably 5,000 or less.

  In the urethane (meth) acrylate (A), two or more types of polyols having different number average molecular weights are used, but two or more types of polyols having different number average molecular weights are urethane (meth) acrylates (A). Whether or not it is contained is determined by analyzing the molecular weight of the polyol using urethane (meth) acrylate (A) in combination with methods such as pyrolysis GC / MS or alkali methylation pyrolysis GC / MS. Judgment is possible. It can also be determined by performing gel permeation chromatography (GPC) analysis and whether the obtained molecular weight distribution profile has two local maximum points.

<(Meth) acrylate compound (B) other than urethane (meth) acrylate compound (A)>
In the radiation-curable composition used for forming the protective layer, a (meth) acrylate compound (B) other than the urethane (meth) acrylate compound (A) (hereinafter referred to as “(meth) acrylate compound (B)” as appropriate. The (meth) acrylate compound (B) serves as a diluent that lowers the viscosity of the urethane (meth) acrylate (A), and enables formation of a smooth and homogeneous protective layer, Helps to develop high surface hardness.

  As said (meth) acrylate (B), monofunctional (meth) acrylate and polyfunctional (meth) acrylate are mentioned. The said monofunctional (meth) acrylate and polyfunctional (meth) acrylate may be used individually by 1 type, and may use 2 or more types by arbitrary ratios and combinations.

  Examples of monofunctional (meth) acrylates include (meth) acrylamides such as N, N-dimethyl (meth) acrylamide; hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and the like. Hydroxyalkyl (meth) acrylates; (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acrylate having a tricyclodecane skeleton, etc. (Meth) acrylates and the like can be mentioned, and among these, alicyclic (meth) acrylates are preferable. Further, for example, one or more carbon atoms of the alicyclic hydrocarbon ring having 5 or more carbon atoms, preferably 5 or more and 7 or less carbon atoms are substituted with a hetero atom such as a nitrogen atom, an oxygen atom, or a sulfur atom. A heteroalicyclic (meth) acrylate having one or more cyclic groups can also be preferably used. Examples of the heteroalicyclic (meth) acrylate include (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, caprolactone-modified tetrahydrofurfuryl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, and the like. Is mentioned.

  In the present invention, among the above, (meth) acryloylmorpholine, tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, alicyclic such as (meth) acrylate having a tricyclodecane skeleton (Meth) acrylates are particularly preferable, and isocyclonyl (meth) acrylate and dicyclopentadienyl (meth) acrylate, which is a (meth) acrylate having a tricyclodecane skeleton, are particularly preferable because the decrease in elastic modulus upon water absorption is small.

Polyfunctional (meth) acrylate compounds include aliphatic poly (meth) acrylates, alicyclic poly (meth) acrylates, aromatic poly (meth) acrylates, and specific examples include 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-polybutylene glycol di (meth) ) Of alkylene oxide adducts such as ethylene oxide, propylene oxide or butylene oxide of bisphenol such as acrylate, polyisobutylene glycol di (meth) acrylate, bisphenol A, bisphenol F, or bisphenol S Di (meth) acrylates of hydrogenated derivatives of bisphenols such as (meth) acrylate, bisphenol A, bisphenol F, or bisphenol S, blocks of various polyether polyol compounds with other compounds, or random copolymer di (meta) ) (Meth) acrylates having a polyether skeleton such as acrylate, and hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, nonanediol di (meth) acrylate, methyloctanediol di (meth) acrylate , Decanediol di (meth) acrylate, 2,2-bis [4- (meth) acryloyloxyphenyl] propane, 2,2-bis [4- (2- (meth) acryloyloxyethoxy) phenyl] propane, bis ( Hydro Methyl) tricyclo [5.2.1.0 ^{2, 6]} decane = di (meth) acrylate, p- bis [beta-(meth) acryloyloxy ethyl thio] xylylene, 4,4'-bis [beta-(meth Trifunctional (meth) acrylates such as bifunctional (meth) acrylates such as) acryloyloxyethylthio] diphenylsulfone, trimethylolpropane tris (meth) acrylate, glycerin tris (meth) acrylate, pentaerythritol tris (meth) acrylate Indefinite polyfunctional (meth) acrylates such as acrylates, tetrafunctional (meth) acrylates such as pentaerythritol tetrakis (meth) acrylate, pentafunctional (meth) acrylates such as dipentaerythritol hexa (meth) acrylate And the like.

Among these, bifunctional (meth) acrylates are preferable from the viewpoint of controllability of the crosslinking formation reaction. As the bifunctional (meth) acrylates, aliphatic poly (meth) acrylates are preferable, and hexanediol di (meth) acrylate, nonanediol di (meth) acrylate, and methyloctanediol di (meth) acrylate are particularly preferable. . Trifunctional or higher functional (meth) acrylates can also be preferably used for the purpose of suppressing deformation accompanying changes in the environmental temperature of the protective layer and improving surface hardness. Examples of the trifunctional or higher functional (meth) acrylates include trimethylolpropane tris (meth) acrylate, pentaerythritol tris (meth) acrylate, dipentaerythritol hexa (meth) acrylate and the like exemplified above and an isocyanurate skeleton. And trifunctional (meth) acrylates.
Among these, alicyclic polyfunctional (meth) acrylates such as bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = di (meth) acrylate are elastic modulus of the protective layer upon water absorption. It is preferable because the decrease is small.

  The molecular weight of the polyfunctional monomer is usually preferably 300 or less, more preferably 280 or less, from the viewpoint of improving curability and surface hardness. On the other hand, it is preferably 200 or more, more preferably 250 or more, from the point of decreasing curing shrinkage.

In addition, in the radiation curable composition used for formation of a protective layer, the said (a3) number with respect to the total weight of the said urethane (meth) acrylate compound (A) and the other (meth) acrylate compound (B). The ratio of the total weight of the polyol having an average molecular weight of 400 or more and less than 1500 and (a4) the polyol having a number average molecular weight of 1500 or more,
{(Weight of (a3) + (a4)} / {weight of (A) + (B)}
Is preferably within a predetermined range. Specifically, the lower limit is usually 0.03 or more, more preferably 0.08 or more, and the upper limit is usually 0.3 or less, more preferably 0.1 or less. If this ratio is too small, when the radiation curable composition is cured, its curing shrinkage rate becomes too large, and the optical recording medium may be deformed. On the other hand, if the ratio is too large, the surface hardness may decrease.

<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, benzyldimethyl 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 normally 0.1 weight part or more with respect to a total of 100 weight part of the said urethane (meth) acrylate compound (A) and the other (meth) acrylate compound (B), Preferably Is 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, and most preferably 4 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.

  In particular, when a benzophenone polymerization initiator is used as the polymerization initiator, the benzophenone polymerization is performed with respect to 100 parts by weight of the total of the urethane (meth) acrylate compound (A) and the other (meth) acrylate compound (B). The initiator is preferably used in an amount of 2 parts by weight or less, more preferably 1 part by weight or less, and usually 0.5 parts by weight or more. This is because if the amount of the benzophenone-based polymerization initiator is large, the volatile components in the protective layer increase, and the film thickness in a high temperature and high humidity environment may decrease.

  In addition, when starting a polymerization reaction with an electron beam as radiation, although the said radical generator can also be used, it is preferable not to use a radical generator and other initiators. This is because sufficient curing can be achieved without using a polymerization initiator. Examples of the polymerization initiator other than the radical generator described above include an oxidizing agent.

  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 includes the urethane (meth) acrylate compound (A), a (meth) acrylate compound (B) other than the urethane (meth) acrylate compound (A), and as necessary. The polymerization initiator and auxiliary components used in the above 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 from the viewpoint of reaction promotion 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 is preferably B or more, more preferably HB or more, further preferably F or more, and most preferably H or more. The surface hardness of the hard coat layer as used in the present invention refers to a pencil conforming to JIS K5400 for the hard coat layer surface of an optical recording medium (a state in which a resin substrate, a recording / reproducing functional layer, a protective layer, and a hard coat layer are laminated). It shall be the surface hardness measured by a hardness test.

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 respect to the 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 function 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.

[Optical recording medium]
As long as the optical recording medium of the present invention has a recording / reproducing functional layer, a protective layer, and a hard coat layer on the resin substrate, its configuration and application are not particularly limited, and other than the above-described layers. In addition, a necessary layer may be appropriately provided. In the present invention, it is particularly preferable that the optical recording medium is a film surface incident type or a next generation high density optical recording medium using a blue laser.
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.

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 A for protective layer)
(A1) 147 g of isophorone diisocyanate and 0.1 g of dibutyltin laurate are placed in a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, heated to 70-80 ° C. in an oil bath, Gently stirred until was constant. When the temperature becomes constant, (a2) 25.5 g of 1,4-butanediol and (a3) 22.5 g of polytetramethylene glycol (number average molecular weight: about 650) and (a4) polytetramethylene glycol (number average molecular weight) : About 2000) 24.7 g of the mixture is added dropwise using a dropping funnel, and the mixture is stirred for 2 hours while maintaining the temperature at 80 ° C. After the temperature is lowered to 70 ° C., a mixture of (a5) 76.7 g of hydroxyethyl acrylate and 0.1 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. An acrylate oligomer (A) was synthesized. To the synthesized urethane acrylate oligomer (A), 174.5 g of tetrahydrofurfuryl acrylate (produced by Osaka Organic Chemical Co., Ltd.), 29 g of 1,6-hexanediol diacrylate (B2) (produced by Kyoeisha Chemical Co., Ltd.), and 1-hydroxycyclohexyl phenyl ketone ( 20 g) (manufactured by Nippon Shibel Hegner) was added and mixed for 5 hours for dilution to prepare a uniform liquid radiation-curable composition A for protective layer. The amounts of (a3) and (a4) were as follows.
{Weight of (a4)} / {weight of (a3)} = 1.10.
{Number of moles of (a4)} / {number of moles of (a3)} = 0.36
{(Weight of (a3) + (a4)} / {weight of (A) + (B)} = 0.094

(Preparation of radiation curable composition B for protective layer)
The urethane acrylate oligomer A was synthesized in the same manner as the preparation of the radiation curable composition A for protective layer. 116.9 g of tetrahydrofurfuryl acrylate (B1) (manufactured by Osaka Organic Chemical Co., Ltd.), 57.6 g of dicyclopentadienyl acrylate (B2) (manufactured by Hitachi Chemical Co., Ltd.), 1,6-hexanediol di Add 29 g of acrylate (B3) (manufactured by Kyoeisha Chemical Co., Ltd.) and 20 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Nippon Siebel Hegner), mix for 5 hours and dilute to prepare a uniform liquid radiation-curable composition B for protective layer. did. The amount of (a3) and (a4) is the same as that of the radiation curable composition A for protective layer.

(Preparation of radiation-curable composition C for protective layer)
The urethane acrylate oligomer A was synthesized in the same manner as the preparation of the radiation curable composition A for protective layer. To the synthesized urethane acrylate oligomer A, 174.5 g of tetrahydrofurfuryl acrylate (B1) (manufactured by Osaka Organic Chemical Co., Ltd.), bis (hydroxymethyl) tricyclo [5.2.1.0 ^2,6 ] decane = diacrylate (B2) ( 9.6 g of Shin-Nakamura Chemical Co., Ltd.), 19.4 g of 1,6-hexanediol diacrylate (B3) (manufactured by Kyoeisha Chemical Co., Ltd.), and 20 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Nippon Siebel Hegner) for 5 hours. Dilution by mixing was performed to prepare a uniform liquid radiation-curable composition C for a protective layer. The amount of (a3) and (a4) is the same as that of the radiation curable composition A for protective layer.

(Preparation of radiation curable composition D for protective layer)
The urethane acrylate oligomer A was synthesized in the same manner as the preparation of the radiation curable composition A for protective layer. 122.2 g of tetrahydrofurfuryl acrylate (B1) (manufactured by Osaka Organic Chemical Co., Ltd.), 29 g of 1,6-hexanediol diacrylate (B2) (manufactured by Kyoeisha Chemical Co., Ltd.), isobornyl acrylate (B3) 52.4 g (manufactured by Osaka Organic Chemical Co., Ltd.) and 20 g of 1-hydroxycyclohexyl phenyl ketone (manufactured by Nippon Siebel Hegner) were added and mixed for 5 hours to dilute to prepare a uniform liquid radiation-curable composition D for protective layer. . The amount of (a3) and (a4) is the same as that of the radiation curable composition A for protective layer.

(Preparation of radiation-curable composition E for protective layer)
In a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, (a1) 146.7 g of isophorone diisocyanate and 0.1 g of dibutyltin laurate were placed, and heated to 70-80 ° C. in an oil bath, Gently stirred until the temperature was constant. When the temperature became constant, a mixture of (a2) 13.8 g of 1,4-butanediol and 42.9 g of (a3) polytetramethylene glycol (number average molecular weight: about 650) was dropped with a dropping funnel, and the temperature was changed. The mixture was stirred for 2 hours while maintaining at 80 ° C. After the temperature is lowered to 70 ° C., (a5) A mixture of 76.6 g of hydroxyethyl acrylate and 0.1 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. An acrylate oligomer (C) was synthesized. To the synthesized urethane acrylate oligomer (C), 195 g of tetrahydrofurfuryl acrylate (B1) (manufactured by Osaka Organic Chemical Co., Ltd.) and 15 g of 1,6-hexanediol diacrylate (B2) (manufactured by Kyoeisha Chemical Co., Ltd.) and 1-hydroxycyclohexyl phenyl ketone ( 20 g) (manufactured by Nippon Shibel Hegner) was added and mixed for 5 hours for dilution to prepare a radiation-curable composition E for a protective layer in a uniform liquid state. The amounts of (a3) and (a4) were as follows.
{Weight of (a4)} / {weight of (a3)} = 0
{Number of moles of (a4)} / {number of moles of (a3)} = 0
{Weight of (a3) + (a4)} / {weight of (C) + (B)} = 0.086

(Preparation of radiation-curable composition F for protective layer)
(A1) 158 g of isophorone diisocyanate and 0.1 g of dibutyltin laurate are placed in a four-necked flask equipped with a stirrer, reflux condenser, dropping funnel and thermometer, and heated to 70-80 ° C. in an oil bath. Gently stirred until constant. When the temperature became constant, a mixture of 28.8 g of (a2) 1,4-butanediol and 23.1 g of (a3) polytetramethylene glycol (number average molecular weight: about 650) was dropped with a dropping funnel, and the temperature was changed. The mixture was stirred for 2 hours while maintaining at 80 ° C. After the temperature is lowered to 70 ° C., a mixture of (a5) 82.6 g of hydroxyethyl acrylate and 0.1 g of methoquinone is added dropwise using a dropping funnel. When the addition is completed, the temperature is kept at 80 ° C. and stirred for 10 hours. An acrylate oligomer (C) was synthesized. To the synthesized urethane acrylate oligomer (C), 172.5 g of tetrahydrofurfuryl acrylate (B1) (produced by Osaka Organic Chemical Co., Ltd.), 35 g of 1,6-hexanediol diacrylate (B2) (produced by Kyoeisha Chemical Co., Ltd.) and 1-hydroxycyclohexylphenyl 20 g of a ketone (manufactured by Nippon Shibel Hegner) was added, mixed and diluted for 5 hours to prepare a uniform liquid radiation-curable composition F for a protective layer. The amounts of (a3) and (a4) were as follows.
{Weight of (a4)} / {weight of (a3)} = 0
{Number of moles of (a4)} / {number of moles of (a3)} = 0
{Weight of (a3) + (a4)} / {weight of (C) + (B)} = 0.046

(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 hard coat composition C (solid content 35% by weight).

Example 1
The radiation curable composition A for protective layer prepared above is applied onto a 100 mm square, 3 mm thick fluorine-coated glass plate with a spin coater, and irradiated with ultraviolet rays with a high pressure mercury lamp at an irradiation intensity of 1 J / cm ^2. This was cured to form a cured coating film having a thickness of 100 μm, and the coating film was carefully peeled off. The same operation was repeated to obtain three release coating films. Of these, 10 strips of 10 mm x 80 mm were cut out from two coated films to make a tensile elastic modulus measurement sample, and an 80 mm square film was cut out from the remaining one coated film to make a water absorption measurement sample. The following evaluation was performed. The results are shown in Table 2.

(Tensile elasticity modulus Eb before water absorption)
Using a Tensilon tensile tester, the elastic modulus Eb was measured by a method according to JIS K7127 at room temperature of 25 ° C.

(Tensile elastic modulus Ea after water absorption)
The sample is immersed in a container containing 1 L of pure water at 25 ° C. for 3 hours, taken out, wiped off with a light drop, and immediately subjected to elasticity using a Tensilon tensile tester at a room temperature of 25 ° C. according to JIS K7127. Ea was measured.
Based on the following definitions, the tensile modulus ratio e was determined.
Tensile modulus ratio e = Ea / Eb

(Create optical recording media)
On the surface of a polycarbonate optical recording medium substrate having a diameter of 120 mm and a thickness of 1.1 mm, an Ag—Cu—Nd reflecting layer having a thickness of 100 nm, a ZnS—SiO ₂ dielectric layer having a thickness of 25 nm, and an Sn—Nb—N layer having a thickness of 15 nm. A recording layer and a ZnS—SiO ₂ dielectric layer having a thickness of 30 nm were formed in this order by sputtering to obtain a recording / reproducing functional layer. On the surface of the outermost dielectric layer of the recording / reproducing functional layer, a radiation curable composition A for protective layer is applied as a protective layer material to a thickness of 100 μm by a spin coater, and a high-pressure mercury lamp (manufactured by Toshiba Harrison; Using Toscure 752), 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 A as a hard coat layer material was applied to the surface of the protective layer with a spin coater, and using a high-pressure mercury lamp (manufactured by JATEC; J-cure 100), the irradiation dose at a wavelength of 365 nm was 400 mJ / cm ^2. Was cured by irradiating with UV rays, and a hard coat layer having a thickness of 2 μm was formed. The same operation was repeated to obtain three optical recording media.
For one of the optical recording media prepared above, the surface hardness of the hard coat surface was evaluated by the following method. Further, water and hexadecane contact angles on the hard coat surface were measured. The results are shown in Table 2.

(Surface hardness evaluation)
The method was performed in accordance with JIS K5400. Specific operations are shown below.
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) were prepared.
Using a pencil hardness measuring device (manufactured by Shinto Kagaku Co., Ltd .; Tribogear Type 18), a hardness of 4B was attached, and the load was crushed by 1 cm at a load of 750 gf and a scratching speed of 30 mm / min. 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.

With respect to the second optical recording medium produced as described above, a humidity-resistant disk deformation evaluation test was performed by the following method. The results are shown in Table 2.

(Humidity disk deformation evaluation test)
The optical recording medium sample was allowed to stand in a constant temperature and humidity chamber, the temperature in the constant temperature and humidity chamber was set to 25 ° C., and the humidity was set to 90% RH and maintained for 100 hours. Thereafter, the disk was taken out, and the deformation of the disk was measured using a displacement sensor (manufactured by Keyence Corporation; LT-9010) in an environment of an air temperature of 25 ° C. and 45% RH. Measurement was performed after 0 hour, 1 hour, 3 hours, 5 hours, 6 hours, 8 hours, 10 hours, and 24 hours, and the change with time was recorded. A graph of the warpage change is shown in FIG. However, the warp value when deformed into a convex shape toward the hard coat layer was negative, and the warp value when deformed into a concave shape toward the hard coat layer was positive.
As shown in FIG. 1, the maximum value of warp deformation was observed after 6 to 8 hours, and the deformation value was 131 μm. This value is shown in Table 2 as the maximum absolute value of deformation against humidity. 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”.

  A humidity resistance disk warpage evaluation test was conducted on the third optical recording medium produced above by the following method. The results are shown in Table 2.

(Vs. temperature disk sled evaluation test)
Disk drive (NEC CD-ROM drive; model PCCD60D) A 40 mm square window is opened on the top of the housing, and a displacement sensor (Keyence Corp .; LT-9010) is fixed above the window, and the disk is inserted into the disk drive. When inserted, a disc deformation detection unit was prepared in which vertical displacement at a position 58 mm from the center of the disc was detected in real time and data could be output to a computer. This unit was installed in the chamber of a thermostat (Hitachi Co., Ltd. Cosmopia; model number EC-10HHP). The outline of this system is shown in FIG. As shown in the figure, 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 to 25 ° C., kept for 20 minutes, and the deformation of the disk was measured. This deformation 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 of the deformation value from the reference value was recorded as the high temperature deformation value.
Next, after changing the setting to 25 ° C. and keeping it for 3 hours, the temperature in the thermostat was changed to 5 ° C. and kept for 1 hour, and the warpage of the disk was measured. The difference of the warp value from the reference value was recorded as the low temperature deformation value.
With the warp reference value as the deformation value 0, 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 absolute value of temperature deformation.
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”.

(Example 2)
In Example 1, it carried out similarly to Example 1 except having used the radiation-curable composition A for protective layers as a material for protective layers, and the composition B for hard-coat layers as a hard-coat material. Table 2 shows the surface hardness of the hard coat, the protective layer Eb, Ea, e, the water absorption, the maximum absolute value of deformation against humidity and the maximum absolute value of deformation against temperature of the optical recording medium.

(Example 3)
In Example 1, it carried out similarly to Example 1 except having used the radiation-curable composition A for protective layers as a material for protective layers, and the composition C for hard-coat layers as a material for hard-coats. Table 2 shows the surface hardness of the hard coat, Eb, Ea, and e of the protective layer, the water absorption, the maximum absolute value of deformation of the optical disk against humidity and the maximum absolute value of deformation against temperature.

Example 4
In Example 1, it carried out like Example 1 except having used radiation curable composition B for protective layers as a material for protective layers, and composition A for hard-coat layers as a material for hard-coats. Table 2 shows the surface hardness of the hard coat, the protective layer Eb, Ea, e, the water absorption, the maximum absolute value of deformation against humidity and the maximum absolute value of deformation against temperature of the optical recording medium.

(Example 5)
In Example 1, it carried out similarly to Example 1 except having used the radiation-curable composition C for protective layers as a material for protective layers, and the composition A for hard-coat layers as a material for hard-coats. Table 2 shows the surface hardness of the hard coat, the protective layer Eb, Ea, e, the water absorption, the maximum absolute value of deformation against humidity and the maximum absolute value of deformation against temperature of the optical recording medium.

(Example 6)
In Example 1, it carried out similarly to Example 1 except having used the radiation-curable composition D for protective layers as a material for protective layers, and the composition A for hard-coat layers as a material for hard-coats. Table 2 shows the surface hardness of the hard coat, the protective layer Eb, Ea, e, the water absorption, the maximum absolute value of deformation against humidity and the maximum absolute value of deformation against temperature of the optical recording medium. In the humidity disk deformation evaluation test, as shown in FIG. 1, a minimum value of deformation was observed after 3 hours, and the deformation value was −98 μm. Table 2 shows the absolute value of 98 μm.

(Comparative Example 1)
In Example 1, it carried out like Example 1 except having used radiation curable composition E for protective layers as a material for protective layers, and composition A for hard coat layers as a material for hard coats. Table 2 shows the surface hardness of the hard coat, the protective layer Eb, Ea, e, the water absorption, the maximum absolute value of deformation against humidity and the maximum absolute value of deformation against temperature of the optical recording medium. In the deformation test for humidity disk, as shown in FIG. 1, the maximum value of deformation was observed after 8 hours, and the deformation value was 194 μm.

（評価）
表２から明らかなように、本発明を用いた実施例１から実施例６までの光記録媒体では、対湿度ディスク変形最大絶対値及び対温度変形最大絶対値が好ましい値を示しており、耐湿度性及び耐温度性に優れているといえる。また表面硬度についても十分なものであった。
一方、比較例１の光記録媒体では、対湿度変形最大絶対値が大きく、耐湿度性が十分ではなかった。また比較例２は、対湿度変形最大絶対値、及び対温度変形最大絶対値が大きく、耐湿度性及び耐温度性が十分ではなかった。 (Comparative Example 2)
In Example 1, it carried out like Example 1 except having used radiation curable composition F for protective layers as a material for protective layers, and composition A for hard coat layers as a material for hard coats. Table 2 shows the surface hardness of the hard coat, the protective layer Eb, Ea, e, the water absorption, the maximum absolute value of deformation against humidity and the maximum absolute value of deformation against temperature of the optical recording medium. In the test for evaluating deformation of the disk against humidity, a maximum value of deformation was observed after 8 hours, and the deformation value was 177 μm. In the temperature disk sled evaluation test, as shown in FIG. 2, the deformation value at low temperature was as large as −200 μm.

(Evaluation)
As is apparent from Table 2, in the optical recording media of Examples 1 to 6 using the present invention, the maximum absolute value of deformation against humidity disk and the maximum absolute value of deformation against temperature show preferable values. It can be said that it is excellent in humidity and temperature resistance. Also, the surface hardness was sufficient.
On the other hand, in the optical recording medium of Comparative Example 1, the maximum absolute value of deformation against humidity was large and the humidity resistance was not sufficient. In Comparative Example 2, the maximum absolute value of deformation against humidity and the maximum absolute value of deformation against temperature were large, and the humidity resistance and temperature resistance were not sufficient.

  The optical recording medium of the present invention can cope with changes in environmental temperature and humidity, and is excellent in wear resistance and protection of the recording protective layer. 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 graph which shows the result of the anti-humidity disk deformation | transformation test of Examples 1 and 6 and Comparative Example 1. It is a graph which shows the result of the temperature disk deformation | transformation evaluation test of Example 1 and Comparative Example 2 with respect to temperature. It is a figure which shows the outline | summary of the system of a vs. temperature disk deformation | transformation evaluation test.

Claims (5)

A cured product of a radiation curable composition containing a resin substrate, a recording / reproducing functional layer, a urethane (meth) acrylate (A) and a (meth) acrylate compound (B) other than the urethane (meth) acrylate (A). An optical recording medium comprising a protective layer and a hard coat layer having a surface hardness of B or more in this order,
An optical recording medium, wherein a ratio of a tensile elastic modulus at the time of saturated water absorption to a tensile elastic modulus at 25 ° C. and a humidity of 45% of the protective layer is 0.20 or more. 2. The optical recording medium according to claim 1, wherein the protective layer has a water absorption at 25 ° C. of 2 (wt / wt)% or less. The urethane (meth) acrylate (A) is (a1) polyisocyanate, (a2) a diol having a molecular weight of less than 400, (a3) a polyol having a number average molecular weight of 400 or more and less than 1500, and (a4) a number average molecular weight of 1500 or more. 3. The optical recording medium according to claim 1, wherein the reaction product is a reaction product obtained by reacting a polyol composition and a composition containing (a5) a hydroxyl group-containing (meth) acrylate. The optical recording medium according to any one of claims 1 to 3, wherein the (meth) acrylate compound (B) other than the urethane (meth) acrylate (A) is an alicyclic acrylate. The (meth) acrylate compound (B) other than the urethane (meth) acrylate (A) is a monofunctional (meth) acrylate and / or a polyfunctional (meth) acrylate having a molecular weight of 300 or less. Item 5. The optical recording medium according to any one of Items 1 to 4.

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