JPH03232134A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain such an optical recording medium having good workability, no slipping of disks at high temp. disks, or no increase of defect by using a specified reactive hot-melt adhesive for an adhesive to bond optical recording medium bodies. CONSTITUTION:Two substrates each having a recording layer, reflecting layer and org. protective layer, etc., are stuck together with a reactive hot-melt adhe sive. Namely, this adhesive is a reactive hot-melt type one essentially comprising urethane prepolymers having isocyanate groups at the molecule end. The adhe sive is prepared by the reaction of polyisocyanate and a polyol component comprising 95 - 50 wt.% polyhydroxy hydrocarbon polymers having 600 - 20000 number average mol. weight, 1 - 8 average hydroxyl groups in one molecule, and <100 iodine number and 5 - 50 wt.% diols having <600 mol.wt. Thereby, the obtd. medium is excellent in adhesion property, long-term stability, workability, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium. Specifically, the present invention relates to an optical recording medium having a structure in which transparent substrates having a recording layer are bonded together and having excellent adhesive properties, stability over time, workability, etc.

[Conventional technology]

Optical recording media such as optical video discs, optical audio discs, and writable optical discs have a metal recording layer, a dye recording layer, a magneto-optical recording layer, etc. on a plastic substrate. Known types include a drilling type that uses melting and sublimation with a light beam, a type that uses phase transition between crystal and amorphous, and a magneto-optical type that uses magneto-optic effects. In either type, in order to prevent dust from adhering to the recording layer and to prevent scratches, etc., the optically transparent substrate on which the recording layer and other auxiliary layers are provided is placed so that these layers face each other on the inside. The structure is such that recording and reproduction is performed through the substrate. As the adhesive used for this bonding, a hot melt type adhesive is known, which is solvent-free, has no adverse effect on the recording layer, and is easy to process.

The properties required for adhesives used in optical recording media include:
It is required to have contradictory properties such as low coating temperature during operation and good heat resistance when using the medium so as not to adversely affect the recording layer.Furthermore, it is required to have sufficient initial adhesion strength, excellent mechanical properties, and Characteristics such as low film transparency are desired.

True-melt adhesives are heated and melted using an applicator and applied to an adherend (optical recording medium), and after bonding and bonding, they are cooled and solidified to perform adhesion.

This hot-melt adhesive has the characteristics of obtaining initial adhesive strength and good workability, but on the other hand, the adhesive strength decreases at high temperatures and softens, causing disc displacement and peeling, which limits the range of use. There is a limit. True melt adhesives are generally EVA-based and polyolefin-based (LDPE).
, APP, etc.) floc copolymer systems (SBS, SIS, 5
EBS, etc.) butyl rubber, polyamide, polyester, etc. are commercially available. In particular, polyamide-based and polyester-based materials have relatively high heat resistance, but the coating temperature must be set high due to their melt viscosity, and they cannot be used for optical recording media that use heat-sensitive resin substrates.

On the other hand, reactive adhesives have the advantage of maintaining adhesive strength even when used at high temperatures. However, generally well-known reactive adhesives such as epoxy, urethane, and acrylic have extremely low initial adhesive strength during operation, and it takes a long time for reaction curing to proceed and adhesive strength is obtained, resulting in poor workability.

For this reason, adhesives that have both the initial adhesive strength of a hot-melt type and the heat resistance of a reactive type are also being considered.

In this case, heating, oxidation, energy irradiation, moisture/humidity, two-liquid, etc. have been proposed as reaction methods, but the simplest and most practical method is one that cures with moisture/humidity. As such, reactive hot-melt adhesives are known which have as a main component a urethane prepolymer having an isocyanate c (NGO) group at the molecular end.

For example, in Japanese Patent Publication No. 51-47735, polypropylene glycol (PPG) and toluene diisocyanate (TDI
), etc., a reactive hot melt adhesive whose main component is an NGO-terminated urethane prepolymer has been disclosed.
Urethane having a polyether structure as a backbone, such as PPG, has poor heat resistance and is inconvenient for practical use.

In addition, JP-A No. 63-251415 discloses a reactive hot melt adhesive whose main components are an NGO-terminated urethane prepolymer consisting of polycaprolactone polyol, a polyester polyol obtained from adipic acid and hexanediol, and diphenylmethane diisocyanate (MDI). Although disclosed, urethane having a polyester structure as a skeleton has poor hydrolysis resistance and is problematic in practice.

Furthermore, JP-A No. 64-54089 discloses a reactive real-melt adhesive whose main component is an NC○-terminated urethane prepolymer made of polyalkylene diol or polyalkylene triol and isocyanate, but this adhesive has poor heat resistance. Although improvements have been made, the strength of the adhesive itself is only 30 kg/aj (~430 psi) or less, and its mechanical properties are unsatisfactory.

[Problem to be solved by the invention]

An object of the present invention is to improve the adhesive used for bonding, and to provide an optical recording medium that is free from practical problems.

[Means to solve the problem]

The inventors of the present invention have made intensive studies to solve the above-mentioned problems with optical recording media, and have found that the problems can be solved by bonding with a special adhesive, and have completed the present invention.

That is, the gist of the present invention is an optical recording medium having a structure in which substrates each having a recording layer or one substrate and another substrate are bonded to each other with an adhesive, and the adhesive has a The average number of hydroxyl groups is 1 to 8 and the number average molecular weight is 6.
95-5ON amount% of a polyhydroxy hydrocarbon polymer in the range of 00-20,000 and an iodine value of 100 or less
It is characterized by being a reactive photomelt adhesive whose main component is a urethane prepolymer having an isocyanate group at the end of the molecule, which is obtained by reacting a polyol component consisting of 5 to 50% by weight of a diol with a molecular weight of less than 600 with a polyisocyanate. It exists in an optical recording medium. The present invention will be explained in more detail below.

In the present invention, the substrate is polycarbonate resin,
A resin substrate such as acrylic resin is used.

As the recording layer, one having a layer structure generally used for optical recording can be used.

In the case of the magneto-optical recording layer, a layer structure of a known magneto-optical recording layer is used. For example, TbFe TbFeCo,
Amorphous magnetic alloys of rare earth and transition metals such as TbCo and DyFeCo, MnB1. A polycrystalline perpendicular magnetization film such as MnCuB1 is used.

As the magneto-optical recording layer, a single layer may be used, or CdT
Two or more recording layers may be stacked, such as bFe/TbFe.

An interference layer can also be provided between the substrate and the recording layer.

This layer uses the light interference effect of a transparent film with a high refractive index.
This is to reduce noise and improve the C/N ratio by lowering the reflectance.

Metal oxides and metal nitrides are used as the interference layer.

Metal oxides include metal oxides such as Afz 03 and Taz Os alone or a mixture thereof, or Al.
-Ta-00 composite oxide and the like.

Furthermore, other elements such as Si and Ti may be added to these.

Zr, W, Mo, Yb, etc. alone or in the form of oxides
j2. It may be combined with Ta to form an oxide.

Specifically, metal tinides include metal tinides such as silicon, aluminum, and germanium, or two of these metals.
More than one species of composite tinides or composite tinides of these with niobium and tantalum (e.g., 5iNbN, 5iTaN, etc.)
can be mentioned. Among them, a tinide containing Si gives good results.

The appropriate thickness of this interference layer is about 300 to 1500 λ.

It is desirable to provide a dielectric layer made of the aforementioned metal oxide or metal nitride on the surface of the recording layer opposite to the interference layer. In media with a structure in which a reflective layer is provided, a highly reflective metal (for example, AI!,
, Cu, etc.) or an alloy thereof is provided as a reflective layer.

It is also possible to provide an organic protective film on the outer layer of the reflective layer to prevent scratches and oxidation. This organic protective film is preferably a compound containing multiple acrylate or methacrylate groups that can be cured by radiation such as ultraviolet rays, and is coated uniformly by a coating method such as a spin coater, spray roll coater, or flow coater. It should be hardened.

The radiation irradiated to the coating film includes ultraviolet rays and electron beams, but ultraviolet rays are preferable.

In the present invention, the substrate having the recording layer, reflective layer, organic protective layer, etc. obtained as described above is adhered to each other with a reactive hot melt adhesive.

The reactive hot melt adhesive has an average number of hydroxyl groups per molecule of 1 to 8 and a number average molecular weight of 600 to 8.
20,000 and an iodine value of 100 or less and a polyol component consisting of 95 to 50% by weight of a polyhydroxy hydrocarbon polymer having an iodine value of 100 or less and 5 to 50% by weight of a diol having a molecular weight of less than 600, and a polyisocyanate. It is a reactive real-melt adhesive mainly composed of a urethane prepolymer having an isocyanate group at the molecular end. ``The number of hydroxyl groups j) is 1 to 8,
Those having a number average molecular weight in the range of 600 to 20,000 and an iodine value of 100 or less are used. There are no particular restrictions on the manufacturing method of such polyhydroxy hydrocarbon polymers, and various vinyl monomers and diene monomers are polymerized by known polymerization methods such as radical polymerization, anionic polymerization, and cationic polymerization, and the terminals are converted into hydroxyl groups. If necessary, hydrogenation may be carried out by a known method.

Other manufacturing methods include isobutylene-diene monomer copolymers or olefins (e.g. ethylene,
For example, a method involving oxidative decomposition and reduction of a propylene, etc.)-nonconjugated diene (or conjugated diene) copolymer can be mentioned.

Among these, hydrogenated products of polyhydroxydiene polymers are preferred.

The polyhydroxydiene polymer is a conjugated diene or
A well-known method using conjugated diene and vinyl monomer as raw materials,
For example, it is produced by a radical polymerization method, an anionic polymerization method, etc. In the case of radical polymerization, if the polymerization is carried out using hydrogen peroxide as a polymerization initiator, a conjugated diene polymer or copolymer having a hydroxyl group at the terminal can be obtained directly, but in the case of anionic polymerization, an alkali metal is first added to the terminal using an anionic polymerization catalyst. It can be produced by producing a glued polymer with a bonded structure, and then reacting with a monoepoxy compound, formaldehyde, etc., and hydrolyzing it. As the raw material conjugated diene, isobutylene, chloroprene, etc. can also be used, but 1,3-butadiene is preferable. Examples of the copolymerization component include vinyl monomers such as styrene, acrylonitrile, methyl (meth)acrylate, and vinyl acetate. The amount of the copolymer component used is preferably 30% by weight or less of the total monomer amount.

In addition, polyhydroxydiene polymers are hydrogenated as necessary to improve heat resistance, but this reaction is carried out using a catalyst such as nickel, cobalt, platinum, palladium, ruthenium, or rhodium alone or with a carrier. The reaction may be carried out in a hydrogen atmosphere by a conventional method.

Here, in order to obtain sufficient heat resistance, it is desirable that the double bonds contained in the polymer have an iodine value of 100 or less, preferably 50 or less, and more preferably 20 or less.

In addition, in the present invention, a part of the polyhydroxy hydrocarbon polymer can also be replaced with another polyol. Examples of other polyols include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; polyester polyols such as polycaprolactone polyol and castor oil polyol; lower polyols such as ethylene glycol and trimethylolpropane; Examples include those obtained by adding propylene oxide or the like to lower polyols. The amount that can be substituted is 0 of the polyhydroxy hydrocarbon polymer.
~49% by weight. If it exceeds this range, it is not preferable because the heat resistance and hydrolysis resistance, which are characteristics of polyhydroxy hydrocarbon polymers, will be poor.

Next, the reason why a diol having a molecular weight of less than 600 is used in the present invention is to improve the mechanical properties of the resulting adhesive by increasing the molecular weight of the urethane prepolymer and increasing the urethane group concentration. JP-A No. 64-54089 describes that a small amount of low molecular weight polyol can be added together with polyalkylene diol, but this is a method to reduce the volatility of diisocyanate monomer and does not meet the gist of the present invention. are completely different.

Diols with a molecular weight of less than 600 used in the present invention include ethylene glycol, propylene glycol,
1,3-propanediol, 1,2 butanediol, 1
．． 3-butanediol, 1°4-butanediol, 2.
3-butanediol, 1,5-bentanediol, 1,
6-hexanediol, 2.5-hexanediol, 2
-Methyl-2,4-bentanediol, 3-methyl-2
゜4-bentanediol, 3-methyl-1,5-bentanediol, 1,7-hebutanediol, ■.

8-octanediol, 2-ethyl-1,3-hexanediol, 1,9-nonanediol, 1゜10-decanediol, α-olefin glycol having 6 to 38 carbon atoms, hydroxymethylstearyl alcohol, dimer acid hydrogenation Molecular weight of alkylene diols such as reduced diols, diethylene glycol, triethylene glycol, etc. 60
Polyethylene glycols with a molecular weight of less than 0, polypropylene glycols with a molecular weight of less than 600, polytetramethylene glycols with a molecular weight of less than 600, castor oil-based diols,
Examples include ester diols having a molecular weight of less than 600, such as polycaprolactone diol. Among these, preferred are alkylene diols, and particularly preferred are 1
．． 2-butanediol, 3-methyl-1,5-bentanediol, 2-ethyl-1,3-hexanediol, α-olefin glycol having 6 to 38 carbon atoms, hydroxymethylstearyl alcohol, dimer acid hydrogenated reduced diol, etc. It is a diol having a branched chain. The amount of these diols having a molecular weight of less than 600 is 5 to 50% by weight of the polyol component.

If it is less than 5% by weight, the effect of increasing the urethane group concentration of the urethane prepolymer is small, so only a product with low 100% tensile stress can be obtained, and conversely, if it is more than 50% by weight, flexibility is lost and only a product with low elongation can be obtained. I won't be able to do it.

Note that a part of these diols can also be replaced with a trifunctional triol. Examples of triols include glycerin, trimethylolpropane, and triols with a molecular weight of less than 600, which are obtained by adding propylene oxide or the like to these, but the amount that can be substituted is determined by the molecule! 60
0 to 49% by weight of less than 0 diols. If it exceeds this range, gelation tends to occur during urethane prepolymer synthesis, which is undesirable.

Next, the polyisocyanates used in the present invention include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) and its derivatives, naphthylene diisocyanate, tolydine diisocyanate,
Isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated MDI, xylylene diisocyanate, and dimers and trimers of these diisocyanates can be used. Among these, preferred is TD
Examples include I and MDI.

There are no particular restrictions on the method of reaction between the polyol component and polyisocyanate, and either a one-shot method or a two-step method can be adopted, but the equivalent ratio of functional groups is determined by
Since it is necessary to leave a group, NCO group 10H group = 1.01
-4, preferably 1.05-3. Further, a catalyst such as dibutyltin dilaurate may be used if necessary.

Furthermore, in the present invention, 20 to 70% by weight, preferably 30 to 60% by weight of a terpene-based, petroleum resin-based, or almost completely hydrogenated tackifier of these is added to the adhesive as an additive.
It is preferable to mix about % by weight.

Furthermore, 0 to 50% by weight, preferably 10 to 40% by weight of a plasticizer consisting of process oil, carboxylic acid ester, etc.
It is also good to soften the adhesive layer and improve adhesiveness by adding it.

Furthermore, styrene-ethylene-butadiene-styrene elastomer (SEBS), styrene-butadiene-styrene elastomer (SBS), styrene-isoprene-styrene elastomer (SIS), etc. can also be added to improve the initial strength.

The reactive hot melt adhesive with the above composition is heated to 70 to 100°C.
Can be applied at temperatures as low as less than 1, but in some cases
It may be applied by heating to about 20''C.

As a coating device, it is preferable to use various roll coaters and applicators.

Hereinafter, the present invention will be explained in more detail by showing specific examples of the present invention, but the present invention is not limited by the following examples unless it exceeds the gist thereof.

[Example-1] A substrate with a diameter of 130 cm with a hole of 151 m11 in the center
A circular flat polycarbonate injection molded substrate with a guide groove having a thickness of 1.2 mm was used, and a film having the following layer structure was formed thereon as a magneto-optical recording medium using a continuous sputtering apparatus.

Substrate / 5iNx (750 people) / TbFeCo (300 people) / AfSi (400 people) / SiNx (350 people)
Polyol HA (trade name, hydroxyl equivalent: 0.877 m eq / g, number average molecular weight: 2000, iodine value: 4.2) was then applied to the side with the recording film using a roll coater as a reactive hot melt adhesive. Polyhydroxy hydrocarbon polymer) (manufactured by Mitsubishi Kasei ■) and AφGX68 (trade name, hydroxyl equivalent: 5.529 m e q/g, carbon number: 16)
and 18 α-olefin glycol) (manufactured by Daicel Chemical Co., Ltd.) and l5onate 12
5M (trade name, diphenylmethane diisocyanate),
An adhesive having the composition shown in Table 1, whose main component was a urethane prepolymer having an isocyanate group at the end of the molecule, was applied at the melting temperature of IQOoC. Thereafter, they were bonded together by applying pressure using a cold press machine so that the recording film was on the inside.

The initial adhesive strength of the obtained optical recording medium of the present invention was 55.4
kg/c+fl and 85°C-85%RH-
After 500 hours, there was no disc peeling or disc shift, and no increase in defects was observed.

[Examples 2 to 14] When the same substrates and the like as in Example 1 were bonded using an adhesive having the composition shown in Table 1, the results shown in Table 1 were observed.

[Comparative Example-1] A recording layer was formed on a polycarbonate substrate in the same manner as in Example-1, and when bonding was carried out in the same manner, Super, manufactured by Hirodyne Co., Ltd., which is commercially available as a polyurethane-based reactive hot melt adhesive, was used. Grip 2000 was used. In this case, the disk was easily peeled off because its ability as an adhesive was low and the initial adhesive force was extremely small.

[Comparative Example 2] In the same manner as in Comparative Example 1, a polyether-based urethane prepolymer Hibon 4810 manufactured by Hitachi Chemical Polymers Co., Ltd. was used as a reactive hot melt adhesive. There was initial adhesive strength, but there was no heat resistance and the temperature was 85°C - 85%.
In the -500 hr atmosphere, the disk was slightly distorted, corrosion occurred in the recording layer, and the number of defects increased by more than 10 times.

[Comparative Example-3] Using the same method as in Comparative Example-1, Kanebo N was used as a reactive hot melt adhesive using a urethane prepolymer consisting of a low molecular weight polymer of polyisocyanate and an ethylenically unsaturated monomer.
Bondmaster 70-7254 manufactured by SC Corporation was used. The initial adhesion was good, and there was no disc displacement after 500 hours at 85°C and 85%, but the moisture permeability of the adhesive was 150g/r.
The increase in defects was as high as rr・24hr, and the increase in defects was more than double.

〔Effect of the invention〕

The present invention is an adhesive used for bonding optical recording media, which has an average number of hydroxyl groups per molecule of 1 to 8, a number average molecular weight of 600 to 20,000, and an iodine value of 10.
0 or less polyhydroxy hydrocarbon polymer 95-5
A reactive hot melt adhesive whose main component is a urethane prepolymer having an isocyanate group at the end of the molecule, which is obtained by reacting a polyol component consisting of 0% by weight and 5 to 50% by weight of a diol with a molecular weight of less than 600 with a polyisocyanate. By doing so, it is possible to obtain an extremely good optical recording medium with good workability and no disc shift at high temperatures and no increase in defects.

Claims (1)

[Claims] (1) An optical recording medium having a structure in which substrates having a recording layer or the substrate and another substrate are bonded facing each other with an adhesive, and the adhesive has an average number of hydroxyl groups per molecule. 1 to 8 molecules, and the number average molecular weight is 600 to 20,00
95 to 50% by weight of a polyhydroxy hydrocarbon polymer with an iodine value of 100 or less and a molecular weight of 6
A reactive hot melt adhesive whose main component is a urethane prepolymer having an isocyanate group at the end of the molecule, which is obtained by reacting a polyol component consisting of 5 to 50% by weight of a diol less than 0.00 with a polyisocyanate. optical recording medium.