Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-11-23
2001-07-17
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S302000, C430S944000, C430S945000, C101S453000, C101S467000, C008S659000, C008S690000
Reexamination Certificate
active
06261737
ABSTRACT:
INDUSTRIAL FIELD OF APPLICATION
The present invention relates to a novel polymethine compound, a method of producing the same and a near infrared absorber comprising the same. The polymethine compound of the present invention has an absorption region in the near infrared region of 750-900 nm and can be utilized as a near infrared absorber for use in image recording utilizing laser beams, for instance, as a near infrared absorber in plate making utilizing laser beams or in producing laser heat-sensitive recording media. It can further be utilized as a spectral sensitization dye in electrophotography or silver halide photography, or a dye for optical disks, for instance.
PRIOR ART
In recent years, with the progression of laser technology, image recording systems utilizing laser beams have been explored in high-speed recording or high-density, high-image-quality recording. Thus, for example, image forming systems using laser heat-sensitive recording materials or laser thermal transfer recording materials have been studied in recording systems where a laser beam is converted to heat. Furthermore, the spread of computers, the rapid progress in electronics, and improvements in digital image processing technology have formed the backdrop for attempts to develop the so-called computer-to-plate technique (CTP plate making technique), which makes printing plates directly from digital data possible.
In the system of recording images through conversion of laser beams to heat (laser thermal recording system), a light absorber appropriate to the laser wavelength is used, and the light absorbed is converted to heat to form images. However, unless the laser output is increased to a considerable extent, the heat energy required for image formation cannot hardly be obtained. Therefore, the advent of a light absorber with good light-to-heat conversion efficiency is desired. In laser thermal recording materials, semiconductor lasers are generally used which have a light emitting region in the near infrared region of 750 nm to 900 nm. Near infrared absorbers appropriate to such laser wavelengths generally absorb light in the visible region as well and tend to disadvantageously cause coloration of the plain ground. Thus, a near infrared absorber that absorbs less light in the visible region is desired.
In the CTP plate making technology, known plate making methods are classifiable into the one comprising irradiating with a laser beam, the one comprising writing by means of a thermal head, the one comprising partially applying a voltage by means of a pin electrode, the one comprising forming an ink-repelling or ink-receiving layer with an ink jet, and so forth. Among them, the method which uses a laser beam is superior in resolution and in rate of plate making to other techniques, so that various image forming techniques have been investigated for said method.
Further, recently, small-sized, high-output inexpensive semiconductor lasers having a light emitting region in the near infrared region (750 nm to 900 nm) have become readily available and are becoming useful as exposure light sources in plate making.
There are two types of direct plate making utilizing laser beams, namely the photosensitive type and heat-sensitive type. As the photosensitive type plate material, there are known the electrophotographic system using an organic semiconductor (OPC), the silver salt system using a silver salt, and so on. These plate materials require a large-size and expensive apparatus for the manufacture thereof and are relatively expensive as compared with the conventional PS plates. There is also the problem of waste developer treatment.
Heat-sensitive plate materials are disadvantageous in that they are low in sensitivity as compared with the photosensitive type plate materials. Nevertheless, they have been intensively investigated since they can be handled in ordinary rooms (lighted rooms) and the corresponding apparatus are small in size and are inexpensive.
The heat-sensitive plate materials all require a light-to-heat conversion layer for converting light to heat. This light-to-heat conversion layer contains a light-to-heat conversion agent, for example a near infrared absorber. It is essential for this light-to-heat conversion agent to absorb the laser beam used and, for attaining improved sensitivity, it is necessary that the ability thereof to absorb the laser beam used and the light-to-heat conversion efficiency be higher.
The light-to-heat conversion agent includes pigment type and dye type substances. Carbon black is generally used as a pigment type substance. While various substances have been proposed as dye type ones, polymethine compounds are in general use. With carbon black, there is a wide selection of lasers to choose from. However, car bon black is generally less capable of absorbing laser beams as compared with dy e type substances, so that it is necessary to increase the amount thereof. A high-level dispersion technique is also required.
In cases where a dye type substance is used, it is necessary that it be highly capable of absorbing the laser beam used and that it be compatible with other components such as the image forming component and resin binder or soluble in the solvent employed.
Polymethine compounds have a methine chain linked by conjugated double bonds within the molecule and have absorption bands within the broad region from the visible to the near infrared region (340 to 1,400 nm) and have a high extinction coefficient at the absorption maximum. For these and other reasons, they are used in various fields, for example as photosensitive dyes for silver salt photography, photosensitive dyes for electrophotography, dyes for laser recording, or dyes for laser beam generation.
Although the polymethine compounds are high ly capable of absorbing laser beams, they are problems: matching with the laser beam to be used is necessary and known compounds are generally poor in light stability and poorly compatible with image forming substances and binder resins, among others.
A number of such polymethine compounds are already known. For instance, the compound A shown below is described in JP Kokai S63-319191 (page 3, Compound 9 as a specific example), and the compound B shown below is described in JP Kokai H02-229865 (page 6, Production Example 3).
However, the compounds A and B both have a maximum absorption wavelength within the range of 785 to 795 nm and are insufficiently sensitive to small-size, high-output lasers having a light emission region at 820 to 870 nm, which are currently under investigation as most likely candidates for use. As compared with the compound B, the compound A has improved light stability as a result of the introduction of a ring structure into the methine chain but it has drawbacks, such as poor solubility in solvents and poor compatibility with resins and therefore the range of choice of binder resin is restricted.
Accordingly, the primary object of the present invention is to provide a polymethine compound which is less absorptive in the visible region of light and is highly sensitive to beams from semiconductor lasers having light emission regions in the near infrared region (750 nm-900 nm) and is suited for use as a near infrared absorber or for use in the light-to-heat conversion layers of laser thermal recording media or original plates for direct plating for printing.
SUMMARY OF THE INVENTION
As a result of investigations made in an attempt to solve the problems such as mentioned above, the present inventors found that the novel polymethine compounds specified below are less absorptive in the visible region, highly sensitive to beams from semiconductor lasers having light emission regions in the near infrared region (750 nm-900 nm) and highly efficient in light-to-heat conversion and can be used as near infrared absorbers readily processible for various applications. Based on these findings, the present invention has now been completed.
In a first aspect, the present invention provides a polymethine compound represented by the genera l formula (I):
Fujita Shigeo
Iwasaki Yasuhisa
Sasaki Nobuaki
Birch & Stewart Kolasch & Birch, LLP
Gilmore Barbara
Le Hoa Van
Yamamoto Chemicals Inc.
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