JPH05334721A - Optical recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To provide the optical recording medium by which its recording part is not limited two-dimensionally, and the recording density per unit area can be increased, and also, its manufacturing method. CONSTITUTION:A built-up film containing a photochromic organic molecule whose anisotropy is displayed by the immersion direction of a substrate 3 is formed on the substrate by an LB method. Also, by executing accumulation of plural layers by varying the immersion direction, plural recording layers are formed. At the time of writing information, it is recorded by selecting a write-in light lambda1 by a filter 1, and selecting the recording layer consisting of a specific LB film by a polarizing plate 2. At the time of reading the information, it is detected by selecting a read light lambda2 by the filter 1, selecting the recording layer consisting of the specific LB film by the polarizing plate 2, and also, converting light intensity of a transmission light to an electric signal by a photoelectric multiplier 7, and binarizing this intensity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of writing, reproducing and erasing information at high density using light and a method for manufacturing the same.

[0002]

BACKGROUND OF THE INVENTION Langmuir-Blodgett films (herein referred to as LB films) containing photochromic materials prepared by the Langmuir-Blodgett method (referred to herein as the LB method) have a high density. It is expected as an optical recording medium. Specifically, by irradiating the optical recording medium with writing light, the light absorption spectrum is changed, and then by irradiating reading light,
The changed absorbance or reflectance is detected, and the recorded information is erased by erasing light (heat in some cases).

For example, Japanese Unexamined Patent Publication (Kokai) No. 2-102253 proposes a photosensitive LB film containing a photochromic material having an azobenzene moiety having an increased free space and a method for producing the same. According to this technique, by the irradiation of light, trans-formation occurs in the azobenzene moiety of the photochromic material existing in the LB film in the light-irradiated portion.
It has been found that a cis photoisomerization reaction occurs and a change occurs in the light absorption spectrum or the light reflection spectrum. Then, this photosensitive LB film is expected to be applied to a photochromic material such as an ultrahigh density optical memory or an optical switching device.

[0004]

However, in the conventional photosensitive LB film containing a photochromic material, the recording surface is only one layer which is flat with respect to one substrate, and one recording pixel is an optical layer. Is limited to the spread of about the wavelength. Therefore, in the conventional LB film, the recording portion is mainly limited two-dimensionally, and there is a problem that there is a limit in increasing the recording density per unit area of the optical recording medium.

Further, the suggestion of the multiple recording by the hetero LB film constitution composed of a plurality of layers of photochromic materials different from each other has been suggested in the past, for example, "LB film and electronics".
(Kiyosei Fukuda et al., CMC, 1986), but there is no specific explanation there. Then, in reality, the multiple recording by the LB film structure composed of a plurality of layers of the photochromic material has not yet been realized based on the specific photochromic material.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical recording medium capable of increasing the recording density per unit area without limiting the recording area two-dimensionally, and a manufacturing method thereof.

[0007]

In order to achieve the above object, the present invention provides a plurality of LB films containing photochromic organic molecules, which exhibit anisotropy depending on the dipping direction of the substrate, on the substrate in anisotropic form. An optical recording medium is characterized in that a recording layer is formed by accumulating in different directions.

Further, according to the present invention, a cumulative film containing a photochromic organic molecule exhibiting anisotropy depending on the dipping direction of the substrate is formed on the substrate by the LB method, and the dipping direction of the substrate is changed to carry out multiple layer accumulation. Thus, the method for producing an optical recording medium is characterized by forming a recording layer. In the method of manufacturing an optical recording medium of the present invention, LB
The immersion speed of the substrate for forming the film is selected so that the anisotropy is exhibited.

Further, writing, reproducing and erasing information are
For the optical recording medium of the present invention, light having a polarization direction corresponding to the molecular arrangement of each layer is used. The Applicant has noted that among the LB film molecules, photochromic organic molecules are arranged in the same direction as the dipping direction of the substrate, and the arranged photochromic organic molecules exhibit anisotropy. It has been found that, for example, a long-chain derivative of azobenzene capable of accumulating an LB film can be applied to such photochromic organic molecules exhibiting anisotropy.

Therefore, in the production of an LB film containing photochromic organic molecules whose anisotropy is exerted depending on the dipping direction of the substrate, for example, when two recording layers are formed, the dipping directions of the substrates should be different from each other. It can be formed by making a 90 degree difference. The angle of the dipping direction for forming each layer is not limited to 90 degrees, and may be any number as long as a clear difference is produced in the anisotropy of both layers. Further, the number of layers having different dipping directions is not limited to two, and the dipping directions can be shifted by a smaller angle to form a plurality of recording layers having three or more dipping directions, and multiple recording of three or more is also possible. Is.

Further, in forming a monomolecular film of photochromic organic molecules by the LB method, the immersion speed of the substrate is one of the conditions for producing anisotropy in the LB film to be obtained. You need to consider speed. Further, similarly to the case of writing and reading, it is possible to erase each layer independently by using polarized erase light. In this case, it can be performed by increasing the intensity of light of the wavelength used for reading and irradiating. Further, by heating the optical recording medium of the present invention, it is possible to simultaneously erase the recording in all recording layers of the LB film.

Similar to other known optical recording media, by providing a large number of pixels in the recording surface of the optical recording medium of the present invention,
A medium capable of multiple recording of information for each pixel can be used. Further, in order to improve the response speed of writing and erasing, the free space of the azobenzene site is increased by increasing the free space of the azobenzene site by including a polydimethyldiallylammonium salt that forms a polyion complex with a molecule containing the azobenzene site in the lower layer water. -The cis photoisomerization can be easily caused. Similarly, in order to improve the response speed of writing and erasing, inclusion of an azobenzene molecule in cyclodextrin increases the free space of the azobenzene site and facilitates trans-cis photoisomerization. be able to.

The substrate used in the present invention includes, for example, a quartz glass substrate, plastic, calcium fluoride, silicon wafer and the like, but is not particularly limited to these materials.

[0014]

In the optical recording medium of the present invention, the photochromic organic molecules are oriented according to the dipping direction of the substrate, so that each layer of the LB film exhibits anisotropy depending on the dipping direction. Since the LB film is formed on the substrate in a plurality of layers and the layers are accumulated in the directions of different anisotropies, the polarized light corresponding to the molecular arrangement of each layer is recorded, read, and erased. Recording, reading, and erasing can be performed on a specific layer of the LB film by selectively irradiating light having a direction. Specifically, it can be performed on a specific layer simply by rotating the polarizing plate. As described above, since recording, reading and erasing can be separately performed on each layer of the LB film, the recording density per unit area can be increased.

[0015]

Example 1 Production of LB Membrane 4-octyl-4 ′-(5-carboxypentamethyleneoxy) azobenzene (hereinafter simply referred to as azobenzene molecule) having an azobenzene moiety was used as a photochromic molecule, and ion-exchanged water was used as the lower layer water. Cadmium ion is contained at 4 × 10 ^-4 M, and a solution of azobenzene molecules dissolved in chloroform at a concentration of 0.5 mM is developed on the water surface, and the water surface is compressed to form a monomolecular film on the water surface. Then, the LB film was accumulated on the quartz glass substrate by a known LB film manufacturing method.

A vertical dipping method in which the temperature of the water tank is controlled to 20 ° C., the pH is adjusted to 6.5, and the surface pressure of the monomolecular film on the water surface is controlled to 20 mN / m, and the substrate is vertically moved to the monomolecular film surface. Thus, 20 layers of monomolecular film were accumulated on the substrate. The substrate is made by accumulating three layers of arachidic acid monolayer in advance,
The one having a hydrophobic surface was used. The substrate immersion rate was 3 cm / min. As a result, a so-called Y-type LB film in which the film adheres to both the upper and lower sides of the substrate could be produced with a good film-forming property with a cumulative rate of about 1.

Confirmation of Anisotropy Development by Immersion Direction Light is incident from the normal direction of the prepared LB film surface, and the angle between the polarization plane of the incident light and the immersion direction at the time of preparing the LB film is changed,
The light absorption spectrum of the LB film was measured. The result is shown in the graph of FIG. The solid line in FIG. 1 is the light absorption spectrum when the plane of polarization of the incident light is parallel to the immersion direction during the production of the LB film, and the broken line is the case where the plane of polarization of the incident light is orthogonal to the immersion direction during the production of the LB film. Is an absorption spectrum of. As shown in FIG. 1, there is a clear difference in absorbance between the two, and it can be seen that the azobenzene molecules are anisotropically arranged along the dipping direction of the substrate.

In order to investigate the anisotropy with respect to the immersion direction in more detail, the absorbance of the LB film at a wavelength of 310 nm was plotted against the angle formed by the polarization direction and the immersion direction, and the results are shown in the graph of FIG. It was This is the white circle in FIG. Incidentally, the black circles shown in the figure are the results when the immersion speed of the substrate was set to 1/10 of this experimental example, that is, 0.3 cm / min as a comparative example, and almost no anisotropy was observed. ..

As shown in FIG. 2, in order to obtain a large anisotropy, it is necessary to optimize the manufacturing conditions such as the immersion speed of the LB film. Examples of the optical recording medium of the present invention: The azobenzene moiety changed from a trans form to a cis form when irradiated with ultraviolet light in the vicinity of 360 nm.
The absorption corresponding to 0 nm of transazobenzene is decreased and the absorption of 400 to 500 nm corresponding to the cis form is increased. Further, it is changed from a cis form to a trans form by irradiation with visible light near 450 nm or by heat. An example in which such a change in absorption spectrum is used for multiple recording of information will be described below.

As described in the section of accumulation of LB film, 20
After accumulating azobenzene molecules of one layer on the quartz glass substrate, rotating the dipping direction of the substrate by 90 degrees, and further accumulating 20 layers to form an LB film containing two layers of azobenzene molecules having dipping directions different from each other by 90 degrees. A laminated optical recording medium was manufactured. Here, the 20 layers accumulated first are the a layers,
Subsequently, the accumulated 20 layers will be referred to as b layer.

FIG. 3 shows a block diagram of an apparatus for confirming the multiple recording of the optical recording medium of the present invention. 1 is a filter for selecting and passing a specific wavelength.
By exchanging, the writing light λ ₁ and the reading light λ ₂ can be selected. Reference numeral 2 is a polarizing plate arranged between the filter 1 and the substrate. 3 is a substrate, and as described above, the LB including the a layer 4 and the b layer 5 on the substrate 3
Membranes are stacked. Reference numeral 6 is a filter for selecting light that has passed through the substrate 3. Reference numeral 7 is a photomultiplier tube for converting the light intensity of the light passing through the filter into an electric signal. Reference numeral 8 is a comparator circuit for making a change in absorbance into a digital signal of 0 or 1.

For the LB film accumulated in a single immersion direction, the polarization direction of the writing light λ ₁ which can change the light absorption spectrum most is represented by ζ with respect to the immersion direction of the substrate 3. The read light lambda ₂ which can best detect a change in light absorption spectrum by irradiation of the writing light lambda ₁
The polarization direction of is represented by η with respect to the dipping direction of the substrate 3. The writing light λ ₁ and the reading light λ ₂ are selected by changing the type of the filter 1, and the information writing and reading modes are selected. Further, by rotating the polarizing plate 2, the polarization directions of the writing light λ ₁ and the reading light λ ₂ are selected,
A layer made of a specific LB film of the a layer 4 or the b layer 5 can be selected and irradiated.

At the time of writing information, the writing light λ ₁ is selected by the filter 1, and the layer made of a specific LB film is selected by the polarizing plate 2. At this time, the filter 6 causes the writing light λ
_It prevents the transmission of ₁ and reaches the photomultiplier tube 7. When reading information, the filter 1 selects the read light λ ₂ and the polarizing plate 2 selects the layer made of a specific LB film. Further, the read light λ ₂ passes through the filter 6 and reaches the photomultiplier tube 7. After the light intensity of the light received by the photomultiplier tube 7 is converted into an electric signal, the change in the light intensity is detected as a digital signal of 0 or 1 by comparing it with a reference voltage by a comparator circuit 8. The reference voltage is set to an appropriate value so that the change in light intensity can be measured in advance using an LB film formed in advance and binarization is possible.

According to the present invention, in the apparatus having the above-mentioned structure, writing is performed by changing the polarization direction of the writing light λ _{1 in} the same initial state. Next, Table 1 below shows the results of reading by changing the polarization direction of the reading light λ ₂ . Here, the polarization directions ζ and η are based on the dipping direction of the a layer 4, and therefore ζ + 90 ° and η + 90 ° are polarization directions suitable for the b layer 5, respectively.

[0025]

[Table 1]

From Table 1, it is understood that information can be recorded and read out independently on the a layer 4 and the b layer 5 by selecting the polarization directions of λ ₁ and λ ₂ .

[0027]

As described in detail above, according to the present invention, a plurality of LB films made of photochromic molecules capable of exhibiting anisotropy depending on the dipping direction are accumulated on the substrate by changing the dipping direction. , Information can be recorded, read, and erased in each layer independently.

Therefore, different information can be recorded in each layer of the multiple LB films having anisotropy in the same plane of the LB film of the optical recording medium, and an optical recording medium capable of multiple recording of information is provided. be able to.

[Brief description of drawings]

FIG. 1 shows an optical absorption spectrum of an optical recording medium of the present invention.

FIG. 2 shows the relationship between the absorbance of the optical recording medium of the present invention at a wavelength of 310 nm and the angle formed by the polarization direction and the immersion direction.

FIG. 3 shows the configuration of an apparatus for confirming multiplex recording on an optical recording medium used in the present invention.

[Explanation of symbols]

 1 filter 2 polarizing plate 3 substrate 4 a layer 5 b layer 6 filter 7 photomultiplier tube 8 comparator circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minoru Saito 1-7-12 Toranomon, Minato-ku, Tokyo Inside Oki Electric Industry Co., Ltd. (72) Masaichi Kato 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (2)

[Claims] 1. A recording layer is formed by accumulating a plurality of LB films containing photochromic organic molecules, which exhibit anisotropy depending on the dipping direction of the substrate, on the substrate in different anisotropy directions. An optical recording medium characterized by: 2. A cumulative film containing a photochromic organic molecule exhibiting anisotropy depending on the dipping direction of the substrate is formed on the substrate by the LB method, and the dipping direction of the substrate is changed to carry out multiple layer accumulation. A method of manufacturing an optical recording medium, which comprises forming a recording layer.