JPH02236838A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve the resistance to heat, corrosion, moisture and weather by using a moisture curing type hot melt adhesive agent which has polyester as its main chain and consists of a prescribed urethane prepolymer. CONSTITUTION:The hot melt type adhesive agent which has the polyester structure as its main chain and consists of the urethane prepolymer having isocyanate groups at both terminals of the molecule is of the type in which the curing is progressed by the moisture in the air. This adhesive agent has 5,000 to 12,000cps viscosity at 120 deg.C. The adhesion with this adhesive agent is, therefore, easily executed by applying the adhesive agent on the magneto-optical recording layer on a resin substrate without adding a tackiness imparting resin or plasticizer to the adhesive agent. The resistance to heat, corrosion, moisture and weather is improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magneto-optical recording medium, and particularly to a magneto-optical recording medium used for optical recording.

[Conventional technology Among optical memory devices, magneto-optical recording is at the closest stage to practical use for erasable memory, which allows additional recording and erasing. Currently, thin films of rare earth and transition metals are often used as the recording layer of magneto-optical recording media, considering their overall characteristics. Since such a recording layer is generally very susceptible to oxidation, a protective layer made of metal oxide, metal nitride, etc. is provided on the recording layer. Furthermore, it is common to apply a resin coating as a protective layer in the case of single-panel specifications, and as an adhesive layer that also serves as a protective layer in the case of double-sided lamination specifications. The resin used for the organic protective layer and adhesive layer made of this resin coat has a high shearing force, does not cause warping of the bonded substrates, and has good mechanical, chemical, and optical properties. Excellent heat resistance, moisture resistance, and weather resistance.
It is required that the reliability of the properties as a magneto-optical recording medium does not deteriorate over time. Conventionally, adhesives such as (1) rubber adhesive, (2) epoxy adhesive, (2) acrylic adhesive, and (2) hot melt adhesive have been used as resins for the organic protective layer and adhesive layer. Among these, JP-A-62-264
No. 456 describes a reactive hot-melt adhesive containing a urethane prepolymer having isocyanate groups at both ends of a polyether main chain, a tackifier resin, and a plasticizer. [Problems to be Solved by the Invention] However, the rubber adhesive described in (2) above has a problem in that it takes a very long time to cure. The problem with the epoxy adhesive (2) is that the recording layer is oxidized (corroded) due to the presence of acid contained in the epoxy adhesive. Furthermore, the above acrylic adhesive has the problem that it hydrolyzes under high temperature conditions and generates organic acids, which oxidizes the recording layer. Furthermore, since the hot-melt adhesive described in (2) above contains a thermoplastic resin as its main component, it softens due to a rise in temperature after bonding, resulting in a decrease in adhesive strength.
For this reason, when magneto-optical recording media are stored at high temperatures,
The adhesive layer between the two substrates deforms, causing the substrate to shift, distort,
Warpage and the like are likely to occur, and in severe cases, the substrate may peel off.

Furthermore, since the reactive hot melt adhesive disclosed in JP-A-62-264456 contains a plasticizer, if there are even a few holes in the recording layer, the plasticizer will reach the substrate through the holes, causing the plasticizer to form a plasticizer. Deteriorates resin substrates such as carbonate. Deterioration of the substrate impairs information recording and reproducing functions, resulting in a serious problem of lowering the reliability of the magneto-optical recording medium.

The present invention solves the above conventional problems and improves heat resistance, corrosion resistance,
The purpose is to provide highly reliable magneto-optical recording media with excellent moisture resistance and weather resistance. [Means for Solving the Problems] The magneto-optical recording medium of the present invention is formed by adhering a pair of substrates facing each other with an adhesive, and a recording layer is formed on at least one of the opposing surfaces of the substrates. In the magneto-optical recording medium, the adhesive is a moisture-curable hot melt adhesive that is made of a urethane brebolymer having a polyester main chain and isocyanate groups at both ends of the molecule, and does not substantially contain a plasticizer. It is characterized by having That is, the present inventors have made extensive studies to provide a magneto-optical recording medium that overcomes the drawbacks of conventional magneto-optical recording media using the adhesives described in (1) to (3) above. As an adhesive, it is made of urethane polymer with a polyester structure in the main chain and isocyanate groups at both ends of the molecule, and is moisture-curable (with virtually no plasticizer).
It has been discovered that the above-mentioned problems can be solved by using a hot-melt adhesive (reactivity), and a high-performance magneto-optical recording medium with excellent heat resistance, corrosion resistance, moisture resistance, weather resistance, etc. can be obtained, and the present invention has been developed. It was completed.

The present invention will be explained in detail below. Examples of the substrate used in the present invention include resin substrates such as polycarbonate resin, acrylic resin, and polyolefin resin. The thickness of this substrate is generally about 1 to 2 mm. Examples of the magneto-optical recording layer formed on such a resin substrate include TbFe, TbFeCo, TbCo, and DyFe.
Non-quality magnetic alloys of rare earths such as Co and transition metals, MnB
A polycrystalline perpendicularly magnetized film such as i, MnCuBi, etc. is used. As the magneto-optical recording layer, a layer may be used, or a G layer may be used.
Two or more recording layers may be stacked and used, such as dTbFe/TbFe. An interference layer may also be provided between the substrate and the magneto-optical recording layer. This layer reduces noise by lowering the reflectance due to the light interference effect of a transparent film with a high refractive index.
This is to improve the /N ratio. The interference layer may be a single layer or a multilayer. Metal oxides and metal nitrides are used as constituent materials for the interference layer. As a metal oxide, Aj2203. Ta205. SiO
Examples include metal oxides such as 2, Sin and TiO2 alone or mixtures thereof, and composite oxides such as AIL-Ta-0. Furthermore, these oxides may contain other elements such as T.
i, Zr, W, Mo, Yb, etc. may be used alone in the form of oxides, or may be combined with Aλ, Ta to form oxides. The interference layer made of these metal oxides is dense and can prevent moisture and oxygen from entering from the outside, and has high corrosion resistance and low reactivity with the reflective layer described below. Furthermore, when a resin substrate is used as the substrate, it has excellent adhesion to the resin that makes up the substrate. Examples of metal nitrides include silicon nitride and aluminum nitride. Among these metal nitrides, it is preferable to use silicon nitride because it is particularly dense and has an excellent effect of preventing moisture and oxygen from entering from the outside.

The optimal thickness of the interference layer made of such a metal oxide or metal nitride varies depending on its refractive index, but it is usually 4.
It is appropriate to set it to about 00 to 1500A, especially about 500 to IOOOA.

It is desirable to provide a protective layer made of a telephone body made of the same material as the interference layer, that is, a telephone body layer, on the surface of the recording layer opposite to the interference layer. The thickness of this dielectric layer is usually 500~
It should be about 1500A.

In a medium having a structure in which a reflective layer is provided, a high reflectance metal (for example, Al) is used in contact with the recording layer or through several hundred dielectric layers.
1, Cu, etc.) or an alloy thereof is provided as a reflective layer. It is also possible to further provide a Hokuden body layer on top of the reflective layer. In addition, in the present invention, it is also possible to provide an organic protective layer on the reflective layer depending on the case. However, it is usually not necessary to provide this because it complicates the process. In the present invention, a substrate (hereinafter sometimes referred to as a "medium") provided with the recording layer, a protective layer, a reflective layer, and a telephone body layer is further provided with a polyester main chain skeleton as an outer layer. Then, an adhesive layer is formed by melt-coating a moisture-curable hot-melt adhesive that is made of urethane brebolymer having isocyanate groups at both ends of the molecule and does not substantially contain a plasticizer, and is applied to the substrate. It is made by adhering it to the opposite substrate. In this case, the pair of substrates to be bonded does not necessarily have to have a recording layer on both opposing surfaces, but may have a recording layer or the like formed only on one opposing surface.

The hot melt adhesive used in the present invention is composed of a urethane urethane polymer (hereinafter referred to as r-polyester-terminated isocyanate urethane prepolymer) that has a polyester structure as the main chain skeleton and has isocyanate groups at both molecular ends. This type of adhesive is moisture curable, that is, it cures due to moisture in the air.
The adhesive has a viscosity of 1.5 s, so that it can be easily applied onto a magneto-optical recording layer on a resin substrate without adding a tackifying resin or plasticizer.

As the polyester-based isocyanate-terminated urethane urethane polymer according to the present invention, preferably used is a brevolimer obtained by addition polymerization of a polyisocyanate and a polyester, particularly a diisocyanate and a polyester oligomer. Examples of the diisocyanate include 2.4-}lylene diisocyanate, 4.4'-diphenylmethane diisocyanate, ethylene diisocyanate, phenylene diisocyanate, tetramethylene diisocyanate,
Hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and the like may be used singly or as a mixture thereof. Examples of polyester include oligomers obtained by esterification reaction between dicarboxylic acid or dicarboxylic acid anhydride and diol, or transesterification reaction between half ester or dialkyl ester and diol. Here, as the dicarboxylic acid, saturated aliphatic dicarboxylic acid, alicyclic dicarboxylic acid, aromatic dicarboxylic acid, or anhydride thereof can be used. Among these, saturated aliphatic dicarboxylic acid is represented by the following general formula. It is preferable that the R H O O C +C H }T-C O O H Alicyclic dicarboxylic acids include tetrahydrophthalic acid, 3.
Examples of the aromatic dicarboxylic acids include 6-endomethylenetetrahydrophthalic acid and anhydrides thereof, and aromatic dicarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, and phthalic anhydride. These compounds may be used alone or in mixtures. In addition, as diols, ethylene glycol, brobylene glycol, 1,4-butanediol,
1.4-Butynediol! #mer or polymer, polytetramethylene ether glycol, etc., and these can be used singly or as a mixture.

As for the oligomer production conditions, the molar ratio of diol and dicarboxylic acid is preferably 0.8 to 1.5, and the oligomer obtained by reacting at normal pressure in the presence of a catalyst,
By the addition reaction of the diisocyanate, a moisture-curable hot-melt adhesive made of a urethane prepolymer having a main chain with a polyester structure and incyanate groups at both ends of the molecule can be obtained.

This hot melt adhesive can be used as it is, but it may cause a decrease in adhesive strength, coloration, change in viscosity, etc., so it is desirable to add an appropriate antioxidant to prevent thermal deterioration of the hot melt.

The polyester-terminated isocyanate urethane polymer of the moisture-curable hot melt adhesive used in the present invention has a molecular weight in the range of 20,000 to 40,000 and a viscosity of 50,000 to 1,200 at 120°C.
0 0 c p s and a softening point of 110
℃ or higher, preferably 120℃ or higher is suitably used. The hot melt adhesive of the present invention can be applied at a low temperature of 70 to 100°C, but in some cases it can be applied at a temperature of 100 to 100°C.
There is no problem in applying it by heating it to 40℃, for example, about 120℃. Examples of commercially available adhesives used in the present invention include the product name "Hybon 4830J" marketed by Hitachi Chemical Polymer ■. A hot melt coater or a hot melt applicator can be employed, and it is particularly advantageous to use a roll coater.

The thickness of the adhesive layer to be formed is usually 1 to 200 μm.
, preferably about 3 to 100 μm.

In the present invention, methods for forming each layer such as an interference layer, a recording layer, a reflective layer, and a contact layer on a substrate include a physical vapor deposition method (PvD) such as sputtering, and a chemical vapor deposition method such as plasma CVD. (CvD) etc. are applied. Furthermore, a method using ion brating is also considered.

To form interference layers, magneto-optical recording layers, reflective layers, telephone body layers, etc. using the PVD method, each layer is deposited on a substrate by electron beam evaporation or sputtering using a target with a predetermined composition. The usual method is to do this. If the film deposition rate is too fast, it will increase the film stress, and if it is too slow, the productivity will decrease, so it is usually appropriately determined in the range of about 0.1 to IOOA/See.

[Function] The adhesive used in the present invention has a temperature of 5,000 to 5,000 at 120°C, for example.
Since it can have a viscosity suitable for coating, such as 1 to 2000 cps, there is no need to specifically add a conventionally used tackifier and/or plasticizer to obtain a suitable coating viscosity.

Since the adhesive of the present invention does not contain an adhesive resin or a plasticizer, even if the adhesive reaches the resin substrate through a pinhole in the recording layer, there is no risk of damaging the resin substrate, and the adhesive can be used under high temperature and high humidity conditions. will not react with the recording layer or substrate and cause their deterioration over time.

Magneto-optical recording media, which consist of a pair of media or substrates bonded together with an adhesive, have water-absorbing properties in the adhesive layer, which has the effect of, for example, eliminating moisture from the recording layer, allowing long-term recording. The layer can be stably held, the optical properties can be stabilized, and the adhesive layer itself has the effect of increasing adhesive strength by using this moisture.

The adhesive used in the present invention has the advantage of not causing any deterioration in adhesive strength or elasticity even if left in an environment of 120 tons and saturated steam pressure for a long time. There is no peeling of the medium that occurs when melt adhesives or other adhesives are used.

For this reason, the magneto-optical recording medium of the present invention provides an optical information recording medium that has excellent heat resistance, moisture resistance, weather resistance, corrosion resistance, etc., and is highly reliable.

[Examples] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Example 1 ■ Production of adhesive A mixture of 0.9 mol of dimethyl terephthalate, 0.05 mol of dimethyl isocyanate, 0.05 mol of dimethyl phthalate and 1.5 mol of ethylene glycol was heated at 150 to 225°C in the presence of a cobalt acetate catalyst. The reaction was carried out at atmospheric pressure for 4 to 8 hours, and the obtained oligomer was subjected to addition polymerization with diphenylmethane diisocyanate to obtain a urethane brebolymer having a main chain having a polyester structure and having isocyanate groups at both ends.

The urethane brevolomer had a molecular weight of 25,000, a viscosity of 8,000 cps at 120°C, and a softening point of 120°C or higher.

(2) Preparation of recording medium A polycarbonate substrate of 130 mmφ was introduced into a sputtering apparatus, and the air was first evacuated to below 8xlO-'torr, and Ar was introduced at 20 seconds and 5 sccm of %02, and the pressure was adjusted to 0.8 Pa. In this state, a 4 inch φ Ta target was subjected to DC sputtering with a power of 500 W, and a tantalum oxide interference layer was sputtered at a rate of 80 OA at a speed of 4 A/sec.
formed to a thickness. Then Tb target and Fe9. C
Perform simultaneous sputtering of O Io target,
T b23 (F egoc Ola) on top of the interference layer
A tt recording layer was formed to a thickness of 30 OA. Furthermore, Ta
Sputtering was performed in Ar gas using an AJ2 target equipped with a chip, and Aλ. , T a 3, and a thickness of 300 A was formed. A dielectric layer of tantalum oxide was further formed on this reflective layer to a thickness of 30 OA using the same method as for the interference layer. ■ Adhesive application and bonding The two media obtained in ■ are taken out of the sputtering device, the adhesive produced in step ■ is heated and melted at 120°C, and coated on each medium to a thickness of 30 μm using a roll coater. The two media were pressure-bonded together facing each other with an oven time of 10 seconds to produce the intended magneto-optical recording medium.

■ Environmental test (heat resistance, moisture resistance test) Using Yamato Scientific Autoclave RSD-41,
Prepare tap water in advance, set the magneto-optical recording medium prepared in step (3) in the gas phase, and heat to raise the temperature. At this time, in order to achieve saturated water vapor pressure, open the purge piping valve and
The temperature is raised until 20't:.

When the temperature reaches 120℃, close the valve, and at 120℃
After holding for a certain period of time, it was cooled and taken out for visual inspection. The results are shown in Table 1. Example 2 In Example 1, a commercially available moisture-curing hot-melt adhesive (manufactured by Hitachi Chemical Polymer ■, trade name "Hybon 4830J," molecular weight 30,000, viscosity 120t,
700 C p s% Softening point 120°C or higher. ) A magneto-optical recording medium was fabricated in the same manner except that it was adhered using a bonding agent. The results are shown in Table 1.

Comparative Examples 1 and 2 Using a Botmelt adhesive (manufactured by Diabond Kogyo ■, trade name "Meltron 3S42J" or "Meltron 3S49") containing thermoplastic rubber as the main component, 16
A magneto-optical recording medium was prepared in the same manner as in Example 1, except that it was bonded by heating and melting at 0° C., and was subjected to an environmental test. The results are shown in Table 1. Table 1 An optical information recording medium with excellent environmental test results, excellent repeat recording characteristics, and high reliability is provided.

Claims (1)

[Claims] (1) In a magneto-optical recording medium in which a pair of substrates are faced and bonded together with an adhesive, and a recording layer is formed on at least one of the opposing surfaces of the substrates, the adhesive is a polyester main chain. What is claimed is: 1. A magneto-optical recording medium characterized by using a moisture-curable hot melt adhesive which is made of a urethane prepolymer having isocyanate groups at both molecular ends and which does not substantially contain a plasticizer.