Optical information recording medium
This is a continuation-in-part of application Ser. No. 544,747 filed Oct. 24, 1983, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a recording medium, in particular relates to an optical information recording medium for use in writing and reading with a high density energy beam such as laser beam. 
     (b) Description of the Prior Art 
     A great number of optical information recording mediums for use in writing and reading with a high density energy beam (for instance, such as laser beam) have hitherto been proposed. 
     As one typical example of such recording mediums there is known an optical information recording medium which comprises a substrate, a metal reflective film and a translucent coloring layer containing a coloring matter. This recording medium is designed so that the laser beam entering the coloring matter-containing translucent coloring layer reaches the metal reflective film and is reflected therefrom so as to detect the reflected beam with ease, wherein said metal reflective film is provided for the purpose of supplementing the deficient amount of the beam reflected from the coloring layer alone. However, the provision of the metal reflective film is defective in that it causes the complicated construction of the information recording medium as well as high costs. 
     In view of this, it has recently been proposed to eliminate the above mentioned defects by using a high-reflective and bronze-lustered organic coloring matter-containing monolayer film. In particular, when using, as a recording film, a highly light absorptive cyanine coloring matter and making said recording film have a thickness of 300 Å to 600 Å, there can be obtained a light absorption reflective film which exhibits metal luster (reflective index: 20 to 30%) and further which permits to effect recording with laser beam and reflective reading with laser beam. In particular, the use of semiconductor laser with wavelength of 750 to 850 nm as the laser source, is advantageous in that a means (an information recording regenerating means which functions to write and read the information by exposing a rotating disk-shaped information recording medium to laser beam radiation) may be minimized. 
     SUMMARY OF THE INVENTION 
     The first object of the present invention is to provide an optical information recording medium which, in spite of containing a cyanine coloring matter in a light absorption reflective film (recording layer), exhibits a superior stability to light radiation and further displays a high reflective index thereto. 
     The second object of the present invention is to provide an optical information recording medium which is uniform in quality and further is high in the S/N (signal to noise ratio). 
     The inventors of this application have carried out various studies and investigations for the purpose of achieving the above objects to find that the coexistence of a specific transition metal complex with a cyanine coloring matter improves especially the stability to light radiation of the resulting optical information recording medium and moreover there is no inconvenience to be caused by the coexistence of said transition metal complex. The present invention has been completed on the basis of this finding. 
     That is, the present invention is related to an optical information recording medium comprising a substrate and a recording layer (light absorption reflective layer) provided thereon, characterized in that said recording layer is consisted essentially of a cyanine coloring matter and a transition metal complex which exhibits a more superior absorbability to light in the long wavelength range than said coloring matter does. 
     The present invention permits the provision of a protective layer on the recording layer and an adhesive layer under the recording layer (namely, between the substrate and the recording layer) as occasion demands. 
     The optical information recording medium according to the present invention will be explained in more detail hereinafter. 
     The recording layer is suitable to have such a metal-like reflection as the coloring matter displays at a specific light wavelength region, in practice to have a reflection index of 20% or more, preferably about 30%, against the wavelength of laser used for writing and reading. This reflection is different from said metal-like reflection because the former has a particular color, but is permitted to have a high reflection index against the wavelength of laser beam used in recording and regenerating, whereby the amount of light for use in information reading and accordingly the S/N of reading signal can be enhanced. 
     The cyanine coloring matter used in the present invention is generally known as the coloring matter for sensitizing the spectral sensitivity of silver halide. As the especially desirable example thereof there can be enumerated the compounds represented by the following general formulas I and II: ##STR1## 
     B is nitrogenous heterocycle which will be exemplified hereinafter: ##STR2## group, or an alkyl, alkoxy, hydroxy, acetyl, aryl or halogen substituent thereof, in which R 2  is an alkyl, alkoxyalkyl, hydroxyalkyl, aralkyl, carboxyalkyl, carboxylato alkyl bonded with an alkali metal cation, sulfoalkyl or sulfonatoalkyl group. 
     A is a nitrogenous heterocycle having a positive charge, which will be exemplified hereinafter: ##STR3## group, or an alkyl, alkoxy, hydroxy, acetyl, aryl or halogen substituent thereof, in which R 2  is the same as in said B and X is a counter ion, for instance, such as halogen. 
     Z is H, --OH, --COOH, halogen, C 1  -C 5  alkyl, phenyl, N-substituted amino, N-substituted alkyl, substituted or unsubstituted aryl, or --COOR&#39; (wherein R&#39; is C 1  -C 5  alkyl, phenyl or substituted phenyl group) group, and said Z, when plural, may be same or different, and m and n are each an integer of 0, 1, 2 or 3 with the proviso m+n≦3. 
     In this connection, it is to be noted that the cyanine coloring matters disclosed in U.S. Pat. Nos. 1,846,301; 1,846,302; 1,990,507; 2,112,140; 2,739,964; 2,503,776; 2,519,001; 2,666,761; 2,734,900; 2,739,149 and 3,690,891 Specifications may be used in the present invention. In particular, the cyanine coloring matter with indole or naphthoindole neucleus is high in light stability and so used suitably. 
     These suitable cyanine coloring matters are represented by the following general formula III: ##STR4## (wherein, R 3 , R 4  and R 5  may be the same or different, and each stands for C 1  -C 6  alkyl; X stands for halogen, perhalogenate, boron tetrafluoride, toluenesulfonic acid or alkylsulfonic acid; E stands for a benzene ring or a naphthyl ring and a substituent such as alkyl, alkoxy, hydroxy, carboxyl, halogen, allyl or alkylcarboxyl may be or may be not present on each ring; and l is an integer of 1-3.). 
     Of the above enumerated cyanine coloring matter represented by the general formula III, the especially usable one for the present invention is the one represented by the following general formula IV: ##STR5## (wherein, R 3 , R 4  and R 5  are the same as defined above and D stands for a halogen atom.), and the more especially usable cyanine coloring matter is the one represented by the following general formula V: ##STR6## (wherein, D stands for a halogen atom selected from fluorine, chlorine, bromine and iodine.). 
     The cyanine coloring matter represented by this general formula V is especially superior in thermal resistance and light resistance. Although the reason has not been fully elucidated yet, it may be considered that those superior properties have been caused through the influence of the large ion radius of a counter ion and the electron attractive effect of a halogen on an indole ring. 
     As the cyanine coloring matter especially usable for the present invention (namely, the cyanine coloring matter represented by the general formula V), there may be enumerated as follows: 1-methyl-2-[7-(1-methyl-3,3-dimethyl-5-chloro-2-indolinylidene)-1,3,5-heptatrienyl]-3,3-dimethyl-5-chloro-indolium perchlorate, 1-methyl-2-[7-(1-methyl-3,3-dimethyl-5-bromo-2-indolinylidene)-1,3,5-heptatrienyl]-3,3-dimethyl-5-bromo-indolium perchlorate, 1-methyl-2-[7-(1-methyl-3,3-dimethyl-5-iodo-2-indolinylidene)-1,3,5-heptatrienyl]-3,3-dimethyl-5-iodo-indolium perchlorate. 
     Whilst, the transition metal complexes used in the present invention may be those represented by the following structural formula or their quaternary ammonium salts: ##STR7## (wherein, M is a transition metal selected from the group consisting of nickel, platinum and palladium, R 6  and R 7  may be the same or different, R 6  and R 7  each is an alkyl group, a phenyl group, an alkyl-substituted phenyl group, an alkoxy-substituted phenyl group or a dialkylaminophenyl group or R 6  and R 7  may cooperate to form a ring.). 
     As the transition metal complexes referred to above there can be enumerated bis(4-diethylaminodithiobenzyl)nickel, bis(4-dimethylaminodithiobenzyl)nickel, bis(3,4,5,6-tetrachloro-1,2-dithiophenyl)nickel, tetrabutylammonium, bis(4-chloro-1,2-dithiophenyl)nickel tetrabutylammonium, bis(1,4-dimethyl-2,3-dithiophenyl)nickel tetrabutylammonium, bis(1,2-dithiophenyl)nickel tetrabutylammonium, bis(3,4,5,6-tetrachloro-1,2-dithiophenyl)platinum tetrabutylammonium, bis(1,4-dimethyl-2,3-dithiophenyl)palladium tetrabutylammonium, and the like. The bis(4-diethylaminodithiobenzyl)nickel is known to be a substance which is absorbent of light in the vicinity of about wavelength 1000 nm. 
     The substrate materials used in the present invention may be those well known to the ordinary worker in this art and may be either transparent or opaque to the laser beam used. However, when writing record is effected from the substrate side with laser beam, the substrate material must be transparent to writing laser beam. On the other hand, when writing record is effected from the side opposite to the substrate, namely from the surface of the recording layer, there is no necessity that the substrate material should be transparent to writing laser beam. However, when reading regeneration is carried out with a transmitted light, the substrate material must be transparent to reading laser beam, while when reading regeneration is carried out with a reflected light, the substrate material may be either transparent or opaque to reading laser beam. Referring to the quality of the substrate material, there may be employed the supports generally used for recording elements made of glass, quartz, ceramics, plastics, paper, plate-like or foil-like metal and the like. Among them, plastics are especially suitable in the points of safety, improved recording sensitivity, flatness, light weight, workability and the like. The typical plastics include vinyl chloride resin, vinyl acetate resin, acrylic resin, methacrylic resin, polyester resin, nitrocellulose, polyethylene resin, polypropylene resin, polyamide resin, polystyrene resin, polycarbonate resin, epoxy resin and the like. 
     The recording layer used in the present invention can be formed by preparing a solution which has dissolved the essential material, namely the cyanine coloring matter and the transition metal complex, and together with a binder and/or an addition agent in case of necessity, in an organic solvent and by coating the substrate with the resulting solution. 
     As the organic solvent there can be used such, for instance, as methanol, methylenedichloride, 1,2-dichloroethane and the like. Coating is carried out in a usual manner such as spraying, roller coating, dipping, rotary coating and the like. Of these coating methods, spinning is most preferable. As example of binder there can be enumerated polyvinyl butyral, cellulose acetate, polyvinyl acetate, acrylic or methacrylic resin, polyester resin, polyamide resin or the like, but it is desirable that such binders should not be used. 
     Said addition agent is also an optional component. As the example of this addition agent there can be enumerated an antioxidant (for instance, phenol resin). 
     The mixing ratio of the cyanine coloring matter and the transition metal complex in the recording layer is that the latter (transition metal complex) is 1 to 80 parts by weight, preferably 4 to 40 parts by weight against 100 parts by weight of the former (cyanine coloring matter). When the latter is more than 80 parts by weight against 100 parts by weight of the former it is not preferable because the sensitivity deteriorates and the S/N is lowered. On the other hand, when the latter is less than 1 part by weight it is not preferable because the stability to light radiation is lost. And, when the optional components (binder, antioxidant and the like) are contained in this recording layer, the amounts of these optional components should be less than 70% by weight of the total amount of the recording layer. 
     The cyanine coloring matter and the transition metal complex each may be used either alone or in mixture of two kinds or more. In the formation of the recording layer, however, the keenest attention should be paid to the fact that the transition metal complex used herein should be absorbent of the light in the wavelength range longer than the wavelength range of which the cyanine coloring matter used herein is absorbent. If this condition is not satisfied, there will be brought about such a disadvantage that the effect of the stability to light radiation rendered to the cyanine coloring matter is diminished. The reason why said effect is brought about is not always clarified, but is considered to consist in that the excited energy of the cyanine coloring matter is received by the transition metal complex and escaped. That is, it may be considered that since the transition metal complex is more absorptive to short wavelength light than the cyanine coloring matter, transfer of said energy is difficult to take place in the former. 
     In any case, there is no positive necessity of the recording medium of the present invention being provided with a reflective layer because the recording layer of the present invention comprising the cyanine coloring matter and the transition metal complex exhibits a superior index of reflection. 
     The thickness of the recording layer is in the range of 100-1000 Å, preferably 300-600 Å, more preferably 300-500 Å. 
     The adhesive layer (undercoat layer), as stated above, is provided between the substrate and the recording layer as occasion demands. 
     Taking the thermal conductivity into consideration, this adhesive layer may be formed using a heat insulating resin material or an inorganic material in a conventional manner such as vapordeposition coating or the like. 
     As the resins used herein there can be enumerated vinyl chloride resin, vinyl acetate resin, acrylic or methacrylic resin, polyester such as polyethylene terephthalate, celluloses such as nitro-cellulose, polyamide, polycarbonate, epoxy resin, polyimide, polysulfone, and the like. And, as the inorganic compounds used herein there can be enumerated SiO, SiO 2 , TiO 2  and the like. The use of polyimide and polysulfone is particularly preferable. The thickness of the adhesive layer is in the range of about 0.05 to 10 μm, preferably in the range of about 0.1 to 0.5 μm. 
     The protective layer, as stated above, is formed on the recording layer as occasion demands. This layer may be formed by using the usual method of vapor deposition, coating or the like, and its thickness is suitably in the range of about 0.1 to 10 μm, preferably in the range of about 0.5 to 1.0 μm. The materials used in the formation of the protective layer may be either organic or inorganic so far as the thin recording layer is protected thereby. 
     The concrete examples of organic materials are disclosed in Japanese Laid Open Patent Application No. 96716/1974 Specification, Japanese Laid Open Patent Application No. 59626/1976 Specification, Japanese Laid Open Patent Application No. 75523/1976 Specification, Japanese Laid Open Patent Application No. 88024/1976 Specification, Japanese Laid Open Patent Application No. 134633/1976 Specification, and the like. Among them, polystyrene, polyethylene terephthalate and ethylene-vinyl acetate copolymer are used profitably. As the concrete examples of inorganic materials, on the other hand, there may be enumerated Al 2  O 3 , SiO 2 , SiO, MgO, ZnO, MgF 2 , CuF 2  and the like. 
     The lasers used in the optical information recording medium according to the present invention include N 2 , He-Cd, Ar, He-Ne, ruby, semi-conductor, dye lasers. Among them, the semi-conductor laser is suitable especially from the viewpoints of light weight, easiness of handling, compactness and the like. 
     The recording medium according to the present invention is of a superior lightproofing preservability while maintaining the sensitivity and the S/N at high levels, which is evident from Examples and Comparative Example referred to afterwards. 
    
    
     EXAMPLES 
     EXAMPLE 1 
     As the cyanine coloring matter there was employed NK 2014 produced by Nihon Kanko Shikiso K. K. and represented by the following structural formula: ##STR8## 
     And, a 1,2-dichloroethane solution containing NK 2014 (1.25% by weight) and bis(4-diethylaminodithiobenzyl)nickel (0.05% by weight) was applied on an acryl substrate (ACRYRITE produced by Mitsubishi Rayon K. K.) by rotary coating. Thus, an about 500 Å-thick recording film was formed and a recording medium was prepared. In this connection, it is to be noted that the above mentioned structural formula, in fact, is sometimes represented as follows: ##STR9## 
     COMPARATIVE EXAMPLE 1 
     In order to make a comparison with Example 1, an about 500 Å-thick recording film was formed of the coloring matter NK 2014 alone, and thus a control recording medium was prepared. 
     EXAMPLE 2 
     A recording medium was prepared according to the exactly same procedure as Example 1 except that bis(4-dimethylaminodithiobenzyl)nickel was employed as the nickel complex. 
     EXAMPLE 3 
     As the cyanine coloring matter there was employed NK 125  produced by Nihon Kanko Shikiso K. K. and represented by the following structural formula: ##STR10## 
     And, a 1,2-dichloroethane solution containing NK 125 (1.25% by weight) and bis(1,4-dimethyl-2,3-dithiophenyl)nickel tetrabutylammonium (0.1% by weight) was rotary coated on an acryl substrate (ACRYRITE L produced by Mitsubishi Rayon K. K.) provided with a light setting resin guide groove to form an about 450 Å-thick recording film. Thus, a recording medium was prepared. 
     EXAMPLE 4 
     A recording medium was prepared by repeating the exactly same procedure as Example 1 except that NK 1666 produced by Nihon Kanko Shikiso K. K. and represented by the following structural formula: ##STR11## was employed as the cyanine coloring matter and bis(3,4,5,6-tetrachloro-1,2-dithiophenyl)platinum tetrabutylammonium was employed as the metal complex. 
     EXAMPLE 5 
     The coating solution of Example 1 was admixed further with 0.1% by weight of polyvinyl butyral resin as a binder. This solution was applied on an acryl substrate (ACRYRITE AR produced by Mitsubishi Rayon K. K.) by rotary coating to form a recording film which is about 550 Å thick, and thus a recording medium was prepared. 
     EXAMPLES 6 TO 20 
     By using the cyanine coloring matters (each 1.25% by weight) shown in the following table-1 and bis(4-diethylaminodithiobenzyl)nickel (0.05% by weight) there were prepared coating solutions. These solutions were applied on substrates by rotary coating to form recording films. Thus, recording mediums were prepared. 
     
                                           TABLE 1                                 
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Ex-                                                  Film                 
ample                                                thickness            
No. Coloring matter                            Solvent                    
                                                     (μm)              
                                                          Substrate       
__________________________________________________________________________
     ##STR12##                                 methanol                   
                                                     0.4  glass           
7                                                                         
     ##STR13##                                 methylene dichloride       
                                                     0.8  acrylic resin   
8                                                                         
     ##STR14##                                 methylene dichloride       
                                                     0.04 acrylic resin   
9                                                                         
     ##STR15##                                 methylene dichloride       
                                                     0.05 acrylic resin   
10                                                                        
     ##STR16##                                 methylene dichloride       
                                                     0.04 acrylic resin   
11                                                                        
     ##STR17##                                 ethanol                    
                                                     0.06 acrylic resin   
12                                                                        
     ##STR18##                                 ethanol                    
                                                     0.06 acrylic resin   
13                                                                        
     ##STR19##                                 methylene dichloride       
                                                     0.06 acrylic resin   
14                                                                        
     ##STR20##                                 ethanol                    
                                                     0.05 acrylic resin   
15                                                                        
     ##STR21##                                 methylene dichloride       
                                                     0.06 acrylic resin   
16                                                                        
     ##STR22##                                 methylene dichloride       
                                                     0.05 acrylic resin   
17                                                                        
     ##STR23##                                 methylene dichloride       
                                                     0.04 acrylic resin   
18                                                                        
     ##STR24##                                 methylene dichloride       
                                                     0.05 acrylic resin   
19                                                                        
     ##STR25##                                 methylene dichloride       
                                                     0.03 acrylic resin   
20                                                                        
     ##STR26##                                 methylene dichloride       
                                                     0.04 acrylic         
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                                                          resin           
 
    
     EXAMPLES 21 TO 23 
     By using the cyanine coloring matters (each 1.25% by weight) shown in the following table-2 and bis(3,4,6-trichloro-1,2-dithiophenyl)nickel tetrabutylammonium (0.05% by weight) there were prepared coating solutions. These solutions were applied on substrates by rotary coating to form recording films. Thus, recording mediums were prepared. 
     
                                           TABLE 2                                 
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                                          Film                            
Example                                   thickness                       
No.  Coloring matter                 Solvent                              
                                          (μm)                         
                                               Substrate                  
__________________________________________________________________________
21                                                                        
      ##STR27##                      1,2-di- chloro ethane                
                                          0.05 acrylic resin              
22                                                                        
      ##STR28##                      1,2-di- chloro ethane                
                                          0.05 acrylic resin              
23                                                                        
      ##STR29##                      1,2-di- chloro ethane                
                                          0.05 acrylic resin              
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     These samples were recorded and regenerated using the HeNe laser beam (wavelength: 630 nm) or the semi-conductor laser beam (wavelength: 790 nm) each stopped down to 1.54 μm under the conditions: laser power 4 mW, recording frequency 0.6875 and pit distance 1.8 μm (pit length 0.9 μm). These regenerated signals were subjected to spectral analysis at the scanning filter band width of 30 KHz by means of Tracking scope TR4110 manufactured by Takeda Riken to measure the S/N (1). At the same time, both the reflection percentage (1) and the absorption percentage (1) were measured. 
     Furthermore, these samples were measured with reference to the S/N (2), the reflection percentage (2) and the absorption percentage (2) after 120 hours&#39; exposure to the radiation of the 54,000-lux light from a tungsten lamp. 
     The thus obtained results were as shown in Table-3. 
     
                       TABLE 3                                                     
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                     Reflection    Absorption                             
                     percentage    percentage                             
        S/N (dB)     (%)           (%)                                    
        (1) (2)      (1)    (2)    (1)  (2)                               
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Example                                                                   
        1     50    50     28   20     60   58                            
        2     50    50     28   21     60   57                            
        3     49    49     29   24     57   55                            
        4     49    49     28   22     56   53                            
        5     50    50     27   20     53   51                            
        6     49    49     28   20     57   55                            
        7     50    50     26   20     58   56                            
        8     52    52     28   21     60   57                            
        9     51    51     29   22     62   60                            
       10     49    49     27   21     59   57                            
       11     52    52     28   21     58   55                            
       12     51    51     26   20     60   58                            
       13     51    51     26   19     58   55                            
       14     50    50     28   21     56   54                            
       15     53    53     27   21     62   60                            
       16     53    53     28   22     61   58                            
       17     49    49     26   19     52   48                            
       18     49    49     29   21     59   57                            
       19     52    52     29   20     60   58                            
       20     50    50     27   20     58   54                            
       21     53    53     28   26     62   61                            
       22     52    52     26   23     60   59                            
       23     52    52     26   23     62   61                            
Comparative                                                               
          50    48       28   16     60   52                              
example 1                                                                 
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 Note (1) The samples of Examples 6, 8, 9, 10, 11, 15, 18 and 19 were     
 recorded and regenerated using the HeNe laser beam (wavelength: 630 nm). 
 Note (2) The samples other than the aforesaid samples were recorded and  
 regenerated using the semiconductor laser beam (wavelength: 790 nm).