JPH0155120B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the use of certain ketone dye compositions in optical recording elements. This ketone dye has a high extinction coefficient at 488 nm, exhibits good solubility in organic solvents, and can be mixed with common binders. The invention thus relates to an optical recording element having a layer of an amorphous material comprising a binder and a dye as described above.

Elements are known that record information by thermally changing the physical structure of a material. One such element consists of a layer of plastic material applied onto a support. The plastic material can be thermally deformed by a writing beam (usually a laser beam) such that a portion of the plastic material is displaced in the area illuminated by the beam. This deformed pattern retains its shape after irradiation with the writing beam is stopped. The resulting deformation pattern can be read by projecting this pattern onto a viewing screen.

More recently, elements and methods have been provided for quickly recording large amounts of digital information in a small area. These elements provide a way to record video information that can be read out with a high signal-to-noise ratio (SNR). These elements use a thin recording layer of a metallic or organic material that is vacuum deposited onto a support. Recording is accomplished by high energy density radiation such as laser light. Typically, a laser beam is focused onto the surface of the recording layer of the element. The irradiated areas of the recording layer are such that they absorb energy from the laser beam and small parts of the layer burn, evaporate, or otherwise are pushed away from these parts. This technique is commonly referred to as "ablative recording." There is usually continuous movement between the laser and the layer, and when the laser is pulsed or modulated, independent pits or holes of different sizes are created in the layer. The size and spacing of these holes constitute the encoded information. One element of this type is commonly referred to in the art as a "video disk."

Ablative video discs can be read using a laser beam similar to that used to record the element. In conventional ablative video discs, the reading beam must also be absorbed significantly by the recording layer. A successive read beam is focused onto the recording layer and the difference in optical density between the pitted and unpitted areas is detected by a photodetector. It will be readily seen that if physical damage to the recording is to be avoided, the recording layer must absorb significantly less energy from the reading beam than it absorbs from the recording beam. This is usually accomplished by using a reading beam that is much less powerful than the recording beam.

If the deformations formed in the recording layer are of a certain type, the information represented by these deformations can be read using a reading beam that is not absorbed by the recording layer. It has been found that by using a layer of amorphous material with extremely high light absorption, it is possible to form a deformation with sharply defined ridges. It is theorized that the ability to read with a laser that is not absorbed by the recording layer is the result of light scattering from the sharp-confined ridges or phase transfer. For whatever reason, it is now possible to use a more powerful laser reading beam, thereby providing a higher signal to noise ratio (SNR) output. Recording elements and reading methods are described in International Application No. 404 by Thomas and Wrbel, published July 12, 1979.

In the Thomas and Lobel method described above, it is desirable to provide a recording layer with as high an extinction coefficient as possible at the recording wavelength. It has been determined that an extinction coefficient of 20 or more is required to create a deformation that can be read by the reading beam that is not absorbed by the recording layer. The extinction coefficient is defined as the product of the weight percent of the dye contained in the dye-binder composition divided by the molecular weight (MW) of the dye and the molecular extinction coefficient of the dye at the wavelength of the recording beam (ελ). . Absorption coefficients are given in liters/gram-centimeter. Thus, the maximum extinction coefficient of a particular dye-binder amorphous recording composition is limited by both the molecular extinction coefficient and the miscibility of the dye with the binder.
One source of high energy density radiation is an argon laser that emits at about 488 nm. When recording with this laser, it is desirable that the dye in the amorphous composition has a very high molecular extinction coefficient at this wavelength. Furthermore, it is desirable that the dye be miscible with the binder in high concentrations. Although the materials shown in the Thomas and Lobel U.S. patent applications cited in the previous section provide extinction coefficients high enough to form the type of deformation required, there are materials that provide even higher extinction coefficients. continues to be pursued.

Dyes have been discovered that have properties that are particularly useful in video disc recording elements. These dyes are
It has an extremely high molecular extinction coefficient at 488 nm and has excellent solvent properties against ordinary organic solvents.
These dyes can be mixed in high concentrations with binders useful in video disc recording layers and can be used in these layers to provide extremely high extinction coefficients.

This dye is a (4-dialkylaminobenzylidene) ketone compound. More specifically, this dye has the structural formula: It is expressed as where n is an integer from 0 to 5 and each R independently represents a straight chain and a branched chain of 1 to 6 carbon atoms, such as methyl, ethyl, isopropyl, t-butyl groups, and the like. selected from the group consisting of branched alkyl groups. (When n=0, both compounds derived from acetone and compounds derived from cyclopropanone are included.) In the present invention, a layer of an amorphous composition consisting of a binder and a paint is A recording element is provided comprising a support coated thereon. Where: the amorphous material described above has an extinction coefficient of 20 or more at 488 nm, and the dye described above is a (4-dialkylaminobenzylidene) ketone as described above.

The recording of information in the elements of the present invention is achieved through a number of variations in the layer of the amorphous dye and binder composition as described above. These deformities have a size smaller than 1.5 microns and consist of depressions surrounded by sharply defined ridges.
These deformations are such that they can be detected using high energy density radiation that is not absorbed by the amorphous composition.

Dyes useful according to the invention have the structural formula: It is expressed as

These dyes have very high molecular extinction coefficients at 488 nm, typically around
It has a molecular extinction coefficient of over 65,000. Additionally, these dyes are miscible at relatively high concentrations with conventional binders, making them useful for use in video disc applications. These dyes are soluble in common solvents such as cyclohexanone, acetone, benzene, xylene and the like.

Each R in the above structural formula is an alkyl group as described above. For the purposes of the present invention, for example:
Dyes having substituted alkyl groups, such as halogen-substituted alkyl, such as chloromethyl, bromoethyl and the like, are considered equivalent. Furthermore, the benzylidene group may be substituted with groups other than aminoalkyl groups at other positions, as long as these substituents do not adversely affect the chromophore. When a cyclic ketone ring is present, it may be similarly substituted. Useful substituents include, for example, halogen and lower alkyl groups. however,
These substituents increase the molecular weight and therefore ελ/
In order to reduce the MW value, dyes without these substitutions are preferred.

The above dyes can be prepared by reacting acetone or a cyclic ketone such as cyclopentanone with dialkylaminobenzaldehyde. Starting materials for making dyes useful in this invention are well known in the art. This dye is produced by condensing an aldehyde and a ketone in an alkaline solution containing an organic solvent. The solution can be made alkaline by adding a suitable base such as potassium hydroxide, sodium hydroxide and the like. Useful organic solvents include methanol and ethanol. This reaction solution can be heated under reflux to produce the desired product.

Examples of dyes made in this way include: 2,5-bis(4-diethylaminobenzylidene)cyclopentanone 2,6-bis(4-diethylaminobenzylidene)cyclohexanone 1,3-bis(4-diethylaminobenzylidene)acetone is included.

Other useful dyes include: 2,3-bis(4-dimethylaminobenzylidene)cyclopropanone 2,5-bis[4-(N-t-butyl-N-methylamino)benzylidene]cyclopentanone It will be done.

The dyes described above are miscible with binders useful in making laser recording element elements. "miscibility"
After applying and drying a layer of this dye and binder, the binder is applied in a sufficient concentration that this dye, without crystallization, gives the required extinction coefficient, e.g. an extinction coefficient of 20 or more. It means that it can be mixed with. Although higher concentrations and thereby higher extinction coefficients are possible, typically
The dyes described above are miscible in dye-binder compositions containing at least 50 percent dye by weight. Due to the high molecular extinction coefficients of the dyes of the invention at 488 nm and their excellent miscibility with common binders, these dyes can be used over a very wide concentration range while retaining extinction coefficients above 20. can be included in the composition. This facilitates optimal efficiency of the elements.

Useful binders include all film-forming materials that can be deformed by exposure to high energy density radiation such as laser light. Useful binders include cellulose acetate butyrate, polystyrenes, polysulfonamides, polycarbonates, cellulose nitrate, poly(ethyl methacrylate) poly(vinyl butyral), and the like. Combinations of multiple binders can also be used. Cellulose nitrate is the preferred binder.

Useful laser recording elements consist of a support on which is coated a layer of dye contained in the binder. Depending on the desired element reading style,
The support can be either reflective or transparent. In the case of a reflective support, both sides of the support can be reflective and recording layers can be made on both sides. The support can be any of a number of materials including glass, a self-supporting polymeric film such as poly(ethylene terephthalate) or cellulose acetate, or metal. This support must have a relatively high melting point to avoid deformation of the support during recording. It is desirable that the support be very smooth to minimize noise and dropouts. In one preferred embodiment, the support is coated with a smoothing layer prior to application of the reflective surface and the dye-binder composition.

The composition used as a smoothing layer preferably comprises:
A low viscosity, polymeric fluid that can be applied onto the surface of a support. Following application, polymerization of this fluid produces a very smooth surface on the support. The support can also be made reflective by vacuum deposition of a smooth surface. In a preferred embodiment, the polymerizable fluid comprises photopolymerizable monomers. Preferably, the monomer or mixture of monomers is a low viscosity fluid in the absence of a solvent. Useful polymerizable fluid compositions are described in US Pat. Nos. 4,092,173 and 4,171,979.

The recording layer consisting of the above dye and binder is
It can be applied by many different methods. Most conveniently, the dye and binder are applied from a conventional solvent or, alternatively, from a mixture of miscible solvents. The dye-binder composition can be applied by spray coating, air knife coating, spin coating, or by other suitable methods. The thickness of the recording layer according to the invention is not critical; however, best results are obtained when the layer thickness is about 0.1 to 10 microns.

The recording composition described above is capable of producing depressions or holes surrounded by sharply defined ridges. This type of deformation can be read out using a reading beam that is poorly absorbed by the recording layer. A "sharply defined ridge" is defined by the fact that the ridge and the hole/indentation have pronounced boundaries, and that the width of the ridge is the width of the hole indentation when measured in a plane containing the undeformed outer surface of the layer. means less than or equal to. These dimensions can be determined from electron micrographs.

The following examples are presented.

Preparation Example 1: Preparation of 2,5-bis(4-diethylaminobenzylidene)cyclopentanone Approximately 110 g of p-diethylaminobenzaldehyde were dissolved in a solution of 80 g of potassium hydroxide in 1000 ml of methanol. Approximately 26 g of cyclopentanone was added with stirring and the reaction mixture was heated at reflux on a steam bath for 3 hours. After cooling in the freezer, the solid precipitate was collected, washed with alcohol, and recrystallized from a mixture of alcohol and acetonitrile. The NMR spectrum confirmed the title compound. This dye has a concentration of 488/MW188/g·cm at 100%.

Example 1: Video Recording Element This example is based on the method of Howe, cited above.
and the examples in the Wrobel US patent application.

Apply a large amount of smoothing composition to the glass support at low rpm (approximately 80-100 rpm), then reduce the speed to approximately
The surface smoothing composition was spin coated onto a circular glass support of 110 mm diameter by increasing the speed to 500 rpm to ensure uniform application. The surface smoothing composition consisted of: 20 g pentaerythritol tetraacrylate 20 g low viscosity urethane acrylate monomer (UV-curable Topcoat 874-C-2002,
Fuller O'Brien) 2-ethoxyethanol 60 g Tamarin sensitizer composition 3 g Surfactant 3 drops The applied and dried surface smoothing composition was irradiated with a 3000 watt pulsed xenon arc lamp at 18 inches for 4 minutes. It was cured by

The surface of the support smoothed in this way was then coated with a 500 Å thick reflective layer of aluminum by vapor deposition.

The recording layer was spin coated over the reflective layer by applying a large amount of the dye-binder composition to the reflective layer at low rpm and then uniformizing the coating at about 1300 rpm. A dye-binder composition was formed by dissolving 1 g of cellulose nitrate and 1 g of the dye prepared in Preparation 1 in 60 g of cyclohexanone.

After drying, the extinction coefficient of the recording layer was 94/g·cm, and the disc was ready for use.

Tracks were recorded in the recording layer of the disk using an argon-ion laser beam (488 nm) focused with a numerical aperture NAg = 0.525 while the disk was rotating at 1800 rpm. (NAg”
represents the numerical aperture of a beam with a focused Gaussian intensity distribution, measured for its e ^-2 radiator diameter. ) The recorded tracks are then
Approximately 1m above the disk surface, similarly focused
It was read out using a helium-xenon laser beam (633 nm) with a power of W. For an incident recording power of about 10 mW, the readout
The SNR was approximately 50. In comparison, the dye is 3,
The recording layer, which is identical to that of this example except that it is 3'-carbonylbis(7-diethylaminocoumarin), requires an incident write power of approximately 15 mW to form a record that can be read at an SNR of 50. And so.

Although the invention has been described in considerable detail with particular reference to preferred embodiments thereof, various changes and modifications can be made within the spirit and scope of the invention.

Claims (1)

Claims: 1. An element for recording encoded information in high energy density radiation at a wavelength of 488 nm, the element comprising a layer of an amorphous composition comprising a binder and a selectively absorbing dye. a support coated thereon, the amorphous composition having an extinction coefficient at 488 nm of at least 20/g·cm, and the dye having the formula: (wherein n is an integer 0-5, and each R is independently a linear or branched alkyl group having 1-6 carbon atoms) element. 2. A recording element according to claim 1, wherein the support is reflective. 3. A recording element according to claim 1, wherein the binder is cellulose nitrate. 4. The dye is selected from the group consisting of: 2,5-bis(4-diethylaminobenzylidene)cyclopentanone, 2,6-bis(4-diethylaminobenzylidene)cyclohexanone and 1,3-bis(4-diethylaminobenzylidene)acetone Claim 2
Recording elements described in Section.