JP2005339727A - Photoreactive adhesive for optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoreactive adhesive for an optical disk by which coating can be performed on an optical disk base material with uniform thickness and adhesive layers can be formed in a uniform thickness in the optical disk formed by bonding a plurality of optical disk base materials. <P>SOLUTION: The photoreactive adhesive for the optical disk contains a cationically polymerizable substance, a cationic polymerization initiator and favorably an organic filler and/or an inorganic filler and has a thixotropic value of 2.0 to 15.0. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photoreactive adhesive for optical discs used for optical discs in which a plurality of optical disc base materials are bonded together.

In recent years, optical recording media (hereinafter referred to as optical disks) such as CDs (Compact Disks), DVDs (Digital Versatile Disks), Blu-ray Discs (Blu-Ray Disks) have become widespread as information recording media.
In order to increase the recording capacity of information, for example, an optical disc in which two optical disc substrates are bonded is known. In such an optical disc, it is required that the optical disc bases are strongly bonded with high precision by an adhesive. Conventionally, radical polymerization type ultraviolet curable compositions have been used as optical disk adhesives.

  When using a radical polymerization type ultraviolet curable composition, first, it coats on the adhesive surface of an optical disk base material by a spin coat method, a screen printing method, etc. Next, the optical disk substrate coated with the radical polymerization type ultraviolet curable composition is bonded to another optical disk substrate. Thereafter, by irradiating with ultraviolet rays, the radical polymerization type ultraviolet curable composition is cured to obtain an optical disc in which two optical disc substrates are bonded together.

  However, when the optical disk substrate has a low ultraviolet transmittance, the radical polymerization type ultraviolet curable composition is not easily cured even when irradiated with ultraviolet rays. Therefore, it is necessary to lengthen the irradiation time of ultraviolet rays or use a large-capacity lamp.

  Accordingly, a cationic polymerization type ultraviolet curable composition has attracted attention as a photoreactive adhesive for optical disks.

  When a cationic polymerization type ultraviolet curable composition is used, the coated cationic polymerization type ultraviolet curable composition is irradiated with ultraviolet rays after the adhesive is applied and before the optical disk is bonded. After irradiating with ultraviolet rays, the two optical disk substrates are bonded together. In this case, the curing reaction proceeds by a dark reaction even after the irradiation of ultraviolet rays is stopped. Therefore, even when optical disk base materials with low ultraviolet transmittance are used, the optical disk base materials are firmly bonded to each other.

  In Patent Document 1 below, a cationic polymerization type ultraviolet ray having a viscosity at 25 ° C. in the range of 200 to 1000 mPa · s and an increase rate of the complex viscosity 3 minutes after irradiation with the ultraviolet ray is 300% or less. A curable composition is disclosed.

  When this cationic polymerization type ultraviolet curable composition is used, first, the cationic polymerization type ultraviolet curable composition is applied in a ring shape on one surface of at least one optical disk substrate of the two optical disk substrates. Next, the applied cationic polymerization type ultraviolet curable composition is irradiated with ultraviolet rays. After irradiating with ultraviolet rays, the two optical disk substrates are bonded together, and the cationic polymerization type ultraviolet curable composition is spread by pressing or dead weight. According to this method, it is said that the cationic polymerization type ultraviolet curable composition does not protrude from the end face of the optical disk after being bonded, and no coating failure or spreading failure occurs.

  Patent Document 2 below discloses a cationic polymerization type ultraviolet curable composition having an viscosity at 25 ° C. in the range of 80 to 800 mPa · s and containing an additive for reducing the surface tension such as silicone oil. Has been.

When using this cationic polymerization type ultraviolet curable composition, first, a cationic polymerization type ultraviolet curable composition is apply | coated to a part of at least 1 optical disk base material among two optical disk base materials. Next, the applied cationic polymerization type ultraviolet curable composition is irradiated with ultraviolet rays. After irradiating with ultraviolet rays, the two optical disk substrates are bonded together, and the cationic polymerization type ultraviolet curable composition is spread by centrifugal force action by high-speed rotation. According to this method, it is said that the cationic polymerization type ultraviolet curable composition does not protrude from the end face of the optical disk during spreading, and can be spread over the entire adhesive surface.
JP 2000-344872 A JP 2003-30910 A

  However, in the configuration described in Patent Document 1, when the photoreactive adhesive for optical discs is spread, the thickness of the adhesive layer may not be uniform. That is, the photoreactive adhesive applied to the optical disk substrate in a ring shape is spread when the optical disk substrate is bonded. Therefore, when a uniform amount of the photoreactive adhesive cannot be accurately applied in a ring shape, the adhesive layer cannot be formed in a uniform thickness.

  On the other hand, the configuration described in Patent Document 2 requires a step of spreading after bonding the optical disk base material. That is, it is necessary to spread the optically reactive adhesive for optical disk applied to a part of the optical disk substrate by using centrifugal force action by high speed rotation.

  In order to form an adhesive layer having a uniform thickness on an optical disc, a photoreactive adhesive is applied in advance to the entire adhesive surface of the optical disc substrate so that the thickness is uniform, and then the optical disc substrate is bonded. Good. In this case, a step of spreading the photoreactive adhesive is not required when the optical disk substrate is bonded or after that.

  However, when the photo-reactive adhesive for optical disks described in Patent Document 1 and Patent Document 2 is applied to an optical disk substrate by spin coating, the thickness depends on the distance from the center on the optical disk substrate. Tend to change. In particular, when the viscosity of the photoreactive adhesive is low, the photoreactive adhesive tends to rise slightly at the end of the optical disk substrate.

  Therefore, in order to bond the two optical disk base materials to form an adhesive layer with a uniform thickness, the coated photoreactive adhesive must be flattened, and the above-described bulging portion is eliminated. Needed to be processed. Furthermore, when a photoreactive adhesive is applied by spin coating, the photoreactive adhesive tends to scatter. Therefore, the excess photoreactive adhesive had to be recovered. In addition, a solvent may be required to adjust the viscosity of the photoreactive adhesive, and a step of drying the solvent may also be required.

  An object of the present invention is to provide a uniform adhesive layer in an optical disc that can be applied to an optical disc substrate with a uniform thickness in view of the current state of the prior art described above, and in which a plurality of optical disc substrates are bonded together. An object of the present invention is to provide a photoreactive adhesive for optical discs that can be formed in a suitable thickness.

  The photoreactive adhesive for optical disks according to the present invention includes a cationic polymerizable substance and a cationic polymerization initiator, and has a thixotropic value of 2.0 to 15.0.

In a specific aspect of the present invention, the photoreactive adhesive for optical disks further contains an organic filler and / or an inorganic filler.

  In still another specific aspect of the photoreactive adhesive for optical discs according to the present invention, the inorganic filler is an inorganic particle having a primary particle diameter of 1 to 300 nm, and based on 100 parts by weight of the cationic polymerizable substance. 1 to 30 parts by weight.

  In still another specific aspect of the photoreactive adhesive for optical discs according to the present invention, when the cured sheet has a thickness of 50 μm, the light transmittance at a wavelength of 400 nm is 80% or more.

  In still another specific aspect of the photoreactive adhesive for optical discs according to the present invention, the cationically polymerizable substance contains an aliphatic and / or alicyclic glycidyl ether compound at 80% by weight or more.

  The photoreactive adhesive for optical disks according to the present invention contains a cationically polymerizable substance and a cationic polymerization initiator and has a thixotropy value in the range of 2.0 to 15.0. When the optical disk substrate is coated by, for example, the coating thickness variation is small. Therefore, in the bonded optical disk, the adhesive layer can be formed with a uniform thickness.

  Since the photoreactive adhesive for optical discs of the present invention has good thixotropy, no solvent is required for coating. Therefore, no solvent drying step is required. Further, since no solvent is used, the yield can be improved.

  In the photoreactive adhesive for optical disks of the present invention, when an organic / or inorganic filler is further contained, the temperature sensitivity is lowered, and the change in viscosity due to a change in temperature is reduced. Therefore, strict temperature control is not required when applying the photoreactive adhesive.

  When the inorganic filler is an inorganic particle having a primary particle diameter of 1 to 300 nm and is contained in an amount of 1 to 30 parts by weight with respect to 100 parts by weight of the cationic polymerizable substance, a photoreactive adhesive for optical discs Has good thixotropic properties.

  When the photoreactive adhesive for optical disc is a cured sheet having a thickness of 50 μm, when the light transmittance at a wavelength of 400 nm is 80% or more, the optical disc forms an adhesive layer with excellent transparency. Difficult to read recorded information.

  In the photoreactive adhesive for optical discs of the present invention, when the cationic polymerizable substance contains 80% by weight or more of an aliphatic and / or alicyclic glycidyl ether compound, it is strongly bonded with high precision. Optical disc. Furthermore, when the glycidyl ether compound is used, an optical disk is formed with an adhesive layer having excellent transparency, and it is difficult to cause trouble in reading recorded information.

  In the method for producing an optical disk of the present invention, the photoreactive adhesive for optical disk of the present invention is applied to the optical disk substrate using a coating apparatus, and therefore, the photoreactive adhesive is not coated at the end of the optical disk substrate. No processing is required to eliminate the bulge. Furthermore, since a photoreactive adhesive having good thixotropy is used, it is not necessary to use an extra photoreactive adhesive, and the photoreactive adhesive need not be recovered after coating.

  Details of the present invention will be described below.

  The cationically polymerizable substance used in the present invention is not particularly limited as long as it has at least one reactive group selected from a cyclic ether group and a vinyl ether group. In order to obtain sufficient adhesive strength when bonded by irradiation with active energy rays, the cationic polymerizable substance is polyfunctional containing two or more polymerizable groups in one molecule and has an epoxy equivalent of 100 to 200. It is preferable that at least one monomer or oligomer is included. Furthermore, a monomer having an epoxy equivalent of 100 to 200 and having four or more glycidyl groups in one molecule is more preferably used.

  Examples of the cationically polymerizable substance having a cyclic ether group include, but are not limited to, those having an epoxy group, an alicyclic epoxy group, or an oxetanyl group.

  Examples of the cationic polymerizable substance having an epoxy group include bisphenol A diglycidyl ether, novolak type epoxy resins, trisphenol methane triglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, Examples include glycerin triglycidyl ether, trimethylolpropane triglycidyl ether, and propylene glycol diglycidyl ether.

  Examples of the cationic polymerizable substance having an alicyclic epoxy group include 2,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis (3,4-epoxycyclohexylmethyl) adipate, and 2- (3,4-epoxy. Cyclohexyl-5,5-spiro-3,4-epoxy) cyclohexanone-meta-dioxane, bis (2,3-epoxycyclopentyl) ether, EHPE-3150 (manufactured by Daicel Chemical Industries, Ltd., alicyclic epoxy resin), etc. Can be mentioned.

  As cationically polymerizable substances having an oxetanyl group, 1,4-bis [(3-ethyl-3-oxetanylmethoxy) methyl] benzene, 1,3-bis [(3-ethyl-3-oxetanylmethoxy) methyl] propane , Ethylene glycol bis (3-ethyl-3-oxetanylmethyl) ether, trimethylolpropane tris (3-ethyl-3-oxetanylmethyl) ether, pentaerythritol tetrakis (3-ethyl-3-oxetanylmethyl) ether, dipentaerythritol Examples include hexakis (3-ethyl-3-oxetanylmethyl) ether, ethylene oxide-modified bisphenol A bis (3-ethyl-3-oxetanylmethyl) ether, and the like.

  As the cationically polymerizable substance, a compound having a vinyl ether group can also be used. As cationically polymerizable substances having a vinyl ether group, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, trimethylolpropane trivinyl ether, cyclohexane-1,4-dimethylol divinyl ether, 1,4-butanediol divinyl ether, polyester Examples thereof include divinyl ether and polyurethane polyvinyl ether.

In the present invention, an aliphatic compound or an alicyclic compound is preferably used as the cationic polymerizable substance in order to increase the adhesive strength. When using an aliphatic compound or an alicyclic compound, only 1 type may be used and 2 or more types may be used together. As the aliphatic compound or alicyclic compound, an adhesive glycidyl ether compound or an alicyclic glycidyl ether compound is more preferable because adhesive strength can be further increased. When the cationic polymerizable substance contains 80% by weight or more of an aliphatic and / or alicyclic glycidyl ether compound, an optical disk with higher accuracy and higher adhesive strength can be obtained. When an aliphatic and / or alicyclic glycidyl ether compound is used, an adhesive layer having excellent transparency is formed on the optical disk.

  In the photoreactive adhesive for optical disks, a radical polymerizable substance may be used in combination with the cationic polymerizable substance. The radically polymerizable substance is not particularly limited as long as it has one or more radically polymerizable unsaturated double bonds in the molecule. For example, a compound having a (meth) acryloyl group or a vinyl group Can be used.

  Examples of the radical polymerizable substance having the (meth) acryloyl group include trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (methacrylate), dipentaerythritol hexa (meth) acrylate, triethylene glycol di (meth) acrylate, Bis (2-hydroxyethyl) isocyanurate di (meth) acrylate and the like can be mentioned.

  Examples of the radical polymerizable substance having a vinyl group include divinylbenzene, ethylene glycol divinyl ether, diethylene glycol divinyl ether, and triethylene glycol divinyl ether.

  When using a radically polymerizable substance, only 1 type mentioned above may be used, and 2 or more types may be used together.

  In the present invention, the cationic polymerizable substance contained in the photoreactive adhesive for optical disks does not inhibit curing by oxygen. On the other hand, when a radically polymerizable substance is included, it is necessary to control the oxygen concentration in the active energy ray irradiation atmosphere. In the case of a cationically polymerizable substance, active species are easily deactivated by moisture, amine compounds, and alkali compounds, so care must be taken not to mix these components.

  As the cationic polymerization initiator used in the present invention, known photocationic polymerization initiators, thermal polymerization cationic curing initiators, and the like are used. When a photocationic polymerization initiator is used, the photoreactive adhesive for optical disks is cured by irradiating active energy rays.

  As the cationic polymerization initiator, an onium salt such as a diazonium salt, a sulfonium salt or an iodonium salt can be used, and an aromatic onium salt is particularly preferable. In addition, iron-arene complexes such as ferrocene derivatives, arylsilanol-aluminum complexes, and the like can be preferably used, and may be appropriately selected from these. Specifically, Syracure UVI-6970, Syracure UVI-6974, Syracure UVI-6990 (all manufactured by Dow Chemical Co., USA), Irgacure 264 (manufactured by Ciba Specialty Chemicals), CIT-1682 (manufactured by Nippon Soda) It is done. If the content of the photocationic initiator is too small, curing will be poor, and if it is too large, the pot life will be shortened. Therefore, the photoreactive adhesive composition (as a solid content) is preferably 0.5 to About 5% by weight.

  In the photoreactive adhesive for optical discs, when a radical polymerizable substance is used in combination with a cationic polymerizable substance, it is preferable to have a radical polymerization initiator simultaneously with a cationic polymerization initiator. Examples of the radical polymerization initiator include Darocur 1173, Irgacure 651, Irgacure 184, Irgacure 907 (all manufactured by Ciba Specialty Chemicals), and those having high purity are preferably used. If the content of the radical polymerization initiator is too small, curing will be poor, and if it is too much, the effect will not change. Therefore, preferably, the photoreactive adhesive composition (as a solid content) is 0.5 to 5 in the whole. It is about wt%.

The photoreactive adhesive for optical discs may preferably contain an organic filler and / or an inorganic filler, whereby good thixotropy can be expressed. Moreover, when an organic filler and / or an inorganic filler are contained in the photoreactive adhesive, the temperature dependency of the viscosity of the photoreactive adhesive is reduced.

  Examples of the organic filler include acrylic particles and acrylic hollow particles.

  Examples of the inorganic filler include silica, alumina, zirconia, titania and the like. In order to increase the transparency of the adhesive layer of the optical disk, inorganic particles having a primary particle diameter of preferably 1 to 300 nm, more preferably 5 to 100 nm, and most preferably 5 to 50 nm are used as the inorganic filler.

  In order to increase the adhesive strength, the surface of the inorganic filler is preferably modified with a compound having an active energy ray polymerizable group.

  Examples of the inorganic filler having a primary particle size of 50 nm or less and whose surface is modified with a compound having an active energy ray polymerizable group include JP-A-11-60235, JP-A-9-100111, and The reactive silica particle | grains described in Kaikai 2001-187812 are mentioned, It can use preferably in this invention.

  The silica particles described in JP-A-11-60235 contain a cation-reactive oxetanyl group as a reactive group. The silica particles described in JP-A-9-100111 contain a radical reactive (meth) acryloyl group as a reactive group. The silica particles described in JP-A No. 2001-187812 simultaneously have a radical reactive unsaturated double bond such as a (meth) acryloyl group and a cation reactive group such as an epoxy group. By adding such an inorganic filler to the photoreactive adhesive composition, the adhesive strength of the photoreactive adhesive can be further increased.

  The content of the inorganic filler is preferably 1 to 30 parts by weight with respect to 100 parts by weight of the cationic polymerizable substance. When the inorganic filler content is 1 to 30 parts by weight with respect to 100 parts by weight of the cationic polymerizable substance, the thixotropic value of the photoreactive adhesive can be easily set to 2.0 to 15.0. . More preferably, it is 2 to 10 parts by weight.

  When the inorganic filler is contained in an amount of more than 30 parts by weight with respect to 100 parts by weight of the cationic polymerizable substance, the adhesive strength of the photoreactive adhesive may be weakened, and the coating is difficult due to the increased viscosity. May be. When the inorganic filler is less than 1 part by weight with respect to 100 parts by weight of the cationic polymerizable substance, the effect of developing good thixotropy and the effect of reducing the temperature dependence of the viscosity of the photoreactive adhesive are not sufficient. There is.

  The optically reactive adhesive for optical disks according to the present invention further contains a sensitizer, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a leveling agent, a pigment, and the like as necessary. It doesn't matter if it goes out. Some sensitizers cannot irradiate light having a wavelength suitable for the catalyst depending on the type of ultraviolet lamp, and those having a specific absorption wavelength are excluded when they interfere with laser reading of an optical disk.

  When an adhesive layer is formed on an optical disc, transparency of the adhesive layer may be required from the viewpoint of reading recorded information. That is, in an optical disc having an adhesive layer with excellent transparency, it is difficult to cause trouble even when the adhesive layer is used to read data recorded on one optical disc substrate. For example, in an optical disc in which two optical disc base materials are bonded together, an adhesive layer can also be used to read data from a recording layer of one optical disc base material through another optical disc base material and an adhesive layer. The trouble of reading by is unlikely to occur.

  This transparency shows transparency at a visible light wavelength of 380 to 800 nm, considering optical devices and display elements, and the light transmittance is preferably 80% or more in the wavelength region. In the present invention, when the photoreactive adhesive applied to the optical disk substrate is a cured sheet having a thickness of 50 μm, the light transmittance at a wavelength of 400 nm is preferably 80% or more.

  The thixotropy value of the photoreactive adhesive for optical disks according to the present invention is 2.0 to 15.0, preferably 2.0 to 10.0. When the thixotropy value is smaller than 2.0, the thickness of the photoreactive adhesive after coating is not uniform, and when the thixotropy value is larger than 15.0, the coating property is deteriorated.

  The thixotropy value is measured using a viscoelasticity measuring device, and is indicated by the value of viscosity at 25 ° C. (1 rpm) / viscosity at 25 ° C. (10 rpm).

  In order to easily make the thixotropy value in the range of 2.0 to 15.0, the photoreactive adhesive preferably contains, for example, ultrafine silica with respect to the cationic polymerizable substance.

  Hereinafter, an example of an optical disk using the photoreactive adhesive for optical disks according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a side view of an optical disk 1 in which two optical disk substrates are bonded together using the optically reactive adhesive for optical disks according to the present invention.

  In the optical disk 1, a disk-shaped optical disk substrate 2 and a disk-shaped optical disk substrate 3 are bonded together by an adhesive layer 4.

  In addition to the CD, DVD, and Blu-ray discs described above, there are various types of optical discs such as CD-ROMs, DVD-ROMs, MDs, and MOs, depending on the application. A photoreactive adhesive can be used.

  The optical disk substrates 2 and 3 are usually made of polycarbonate, but may be made of other materials such as polyethylene terephthalate (PET) and polymethyl methacrylate as long as the substrate performance is satisfied, and is not particularly limited.

  A photoreactive adhesive for optical disc is applied to the upper surface 2 a of the optical disc base 2. The applied photoreactive adhesive is irradiated with active energy rays. Thereafter, it is bonded to another optical disk substrate 3 to form an adhesive layer 4.

  In the present invention, a photoreactive adhesive may be applied to the upper surface 2 a of the optical disk substrate 2 and the lower surface 3 a of the optical disk substrate 3. An active energy ray is irradiated to the photoreactive adhesive applied to the two optical disk substrates 3 and 4. Thereafter, the optical disk substrate 2 and the optical disk substrate 3 are bonded together to form the adhesive layer 4.

  Three or more optical disk substrates can be bonded together using the photoreactive adhesive for optical disks of the present invention.

  Examples of the coating method include a dip coating method, a clavia coating method, a roll coater, a comma coater, a shim, a press, and the like. Among these, an appropriate method is used.

  In the case where the photoreactive adhesive is applied to the optical disc bases 2 and 3, it is preferable to use an apparatus capable of applying a uniform mirror surface state at a low speed. Examples of such an apparatus include a roll coat, a bar coat, and a T die.

  In the coating process, if the temperature is too high, the optical disk substrates 2 and 3 may be damaged, and the reaction of the cationic polymerization initiator may proceed. If the temperature is too low, the viscosity of the photoreactive adhesive is increased, which may make coating difficult. Accordingly, the coating temperature is preferably 15 to 80 ° C. However, the coating temperature is adjusted by the reactivity of the cationic polymerizable substance selected and the cationic polymerization initiator.

  In the present invention, as the active energy ray for curing the photoreactive adhesive for optical discs, an appropriate one such as ultraviolet ray, electron beam, visible light may be selected and used.

In the case of using ultraviolet rays, the appropriate ultraviolet irradiation amount is, for example, 1 to 500 mJ / cm ² , preferably 1 to 200 mJ / cm ² . In the case of irradiation with an electron beam, the electron beam irradiation amount is, for example, 1 to 30 Mrad, preferably 1 to 10 Mrad. In both cases of ultraviolet irradiation and electron beam irradiation, the irradiation amount depends on the type and amount of the reactive group of the cationic polymerizable substance used, and the thickness of the photoreactive adhesive applied to the optical disk substrates 2 and 3. The catalyst amount during the reaction and the additives such as fillers to be contained may be adjusted.

  The thickness of the adhesive layer 4 is not particularly limited, and is appropriately set depending on the type and use of the optical disc 1. For example, in a DVD or the like that is recorded and reproduced by light, the thickness of the adhesive layer 4 is preferably 1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less. If it is less than 1 μm, the strength of the adhesive layer 4 may not be sufficient, and if it exceeds 10 μm, cracks in the adhesive layer 4 tend to occur and warpage of the optical disk bases 2 and 3 tends to increase.

  Hereinafter, the present invention will be described in more detail by giving specific examples and comparative examples using the photoreactive adhesive for optical disks according to the present invention.

(Example 1)
100 parts by weight of 1,6-hexanediol diglycidyl ether (Denacol EX212: manufactured by Nagase ChemteX), 8 parts by weight of ultrafine silica (R805: manufactured by Nippon Aerosil Co., Ltd., primary particle size: 12 nm), and cationic polymerization start 3 parts by weight of an agent (Syracure UVI-6990: manufactured by Dow Chemical Co., Ltd.) was stirred and kneaded to prepare a photoreactive adhesive.

(Example 2)
100 parts by weight of bisphenol A diglycidyl ether (Epicoat 825: manufactured by Japan Epoxy Resin Co., Ltd.), 8 parts by weight of ultrafine anhydrous silica (HDK T-40: manufactured by Asahi Kasei Wacker Co., Ltd., primary particle size: 7 nm), and cationic polymerization start 3 parts by weight of an agent (Syracure UVI-6990: manufactured by Dow Chemical Co., Ltd.) was stirred and kneaded to prepare a photoreactive adhesive.

(Comparative Example 1)
100 parts by weight of 1,6-hexanediol diglycidyl ether (Denacol EX212: manufactured by Nagase ChemteX Corp.) and 3 parts by weight of a cationic polymerization initiator (Syracure UVI-6990: manufactured by Dow Chemical Co., Ltd.) are stirred and kneaded to produce a photoreaction. An adhesive was prepared.

(Evaluation)
The photoreactive adhesive for optical disks described in Examples 1 and 2 and Comparative Example 1 was prepared. First, the prepared photoreactive adhesive was applied to the upper surface 2a of the optical disk substrate 2 made of polycarbonate resin by a roll coater method so as to have a thickness of 50 μm. Next, the applied photoreactive adhesive was irradiated with ultraviolet rays in the atmosphere. A high pressure mercury lamp was used as the light source, and the irradiation amount was 70 mW / cm ² for 15 seconds.

  The condition of the coating end on the upper surface 2a of the optical disk substrate 2 was visually evaluated. Furthermore, the light transmittance of the adhesive layer 2 after curing and the thixotropy value of the photoreactive adhesive were measured or evaluated.

  The light transmittance was measured by measuring the light transmittance at a wavelength of 400 nm using a spectrophotometer for a sheet prepared by preparing a hot melt hard coat composition to a thickness of 50 μm and irradiating it with ultraviolet rays.

  The results are shown in Table 1.

  In the evaluation of the state of the coating end on the upper surface 2a of the optical disk substrate 2, in Examples 1 and 2, there was no swell and the thickness was uniform. This is because the photoreactive adhesive contains a cationically polymerizable substance and a cationic polymerization initiator and has a good thixotropy value. Therefore, the process of eliminating the raised portion of the coating end portion of the photoreactive adhesive is unnecessary, and the process can be simplified. Further, when the upper surface 2 a of the optical disk substrate 2 and the lower surface 3 a of the optical disk substrate 3 are bonded together, the adhesive layer 4 having a uniform thickness can be formed on the optical disk 1.

  The photoreactive adhesive of Comparative Example 1 had low thixotropy, and therefore was not applied to a uniform thickness, and the coating end of the photoreactive adhesive was raised. Therefore, in order to form the adhesive layer 4 having a uniform thickness when the optical disk equipments 2 and 3 are bonded together, it is necessary to perform processing for eliminating the raised portion of the coating end portion of the photoreactive adhesive. .

  In Comparative Example 1, since the photoreactive adhesive does not contain an inorganic filler, the thixotropy is low, and it is considered that the coating end of the photoreactive adhesive was raised.

The side view of the optical disk by which two optical disk base materials are bonded together.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical disk 2 ... Optical disk base material 2a ... Upper surface 3 ... Optical disk base material 3a ... Lower surface 4 ... Adhesive layer

Claims (5)

  A photoreactive adhesive for optical disks, comprising a cationically polymerizable substance and a cationic polymerization initiator, and having a thixotropic value of 2.0 to 15.0.   The photoreactive adhesive for optical disks according to claim 1, further comprising an organic filler and / or an inorganic filler.   The optical disk according to claim 1, wherein the inorganic filler is an inorganic particle having a primary particle diameter of 1 to 300 nm and is contained in an amount of 1 to 30 parts by weight with respect to 100 parts by weight of the cationic polymerizable substance. Photoreactive adhesive for use.   4. The photoreactive adhesive for optical discs according to claim 1, wherein when the cured sheet has a thickness of 50 μm, the light transmittance at a wavelength of 400 nm is 80% or more. 5. The photoreactive adhesive for optical disks according to any one of claims 1 to 4, wherein the cationically polymerizable substance contains 80% by weight or more of an aliphatic and / or alicyclic glycidyl ether compound.

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