Method for Use of Light Colored Undeveloped Photographic Element

The invention relates to an element for forming photographic images. It particularly relates to sensitizing and absorbing dyes for color paper.

In the manufacture of color photographic paper it is critical to maintain the activity of the photographic components such that the photographic response does not change during the course of manufacturing. To ensure a consistent outcome is obtained, it is necessary to monitor photographic activity in the process of manufacturing. During the course of manufacturing, many incidental changes can occur and impact photographic response characteristics such as photographic speed. These speed changes can be measured during the manufacturing process, and adjustments can be made to maintain a consistent response. It is of enormous benefit to the process of manufacturing photographic materials if adjustments to the levels of the components bear a linear response to the speed value. Additionally, it is obvious that if less material is utilized in obtaining the desired photographic effect, cost advantages can be accrued.

Advantages gained in the manufacture of color paper cannot be realized if photographic performance is jeopardized. Therefore, it is desired that manufacturing gains be made concomitantly with gains in photographic performance. It is known that visual sharpness of the photographic material is critical to its acceptability for use, and that changes in sharpness or detail can occur when changes are made in the process of manufacturing; thus, it is highly desirable that manufacturing changes do not degrade sharpness, and it is even more desirable that such changes lead to improved sharpness.

It is intended that color photographic paper satisfy the desires of photographers in the practice of their art. In the hands of the photographer it is common practice to regulate the exposure of photographic material under conditions where some areas of the print may receive greater light exposure than a normal exposure to "burn in" the desired image to a greater degree. Alternatively, it is also the practice to shield some areas of the print from normal exposure to light, and by "dodging" the light in this way create the desired image. In practicing the techniques of dodging and burning, the photographer or enlarger operator is hindered by the present color photographic material that has a dark color content prior to exposure. Color papers also vary in their undeveloped color from batch to batch, as different absorber dyes are added to adjust their properties. This makes the dodging and burning more difficult, as the paper looks different during exposure as the undeveloped paper color is different.

There remains a need for a color paper on which it is easier for a photographer to see the exposing image during dodging and burning processes in printing. There is also a need for photographic paper that is more easily adjusted to control speed and sensitivity during manufacturing without sharpness loss.

It is an object of the invention to overcome disadvantages of prior photographic elements.

It is a further object of the invention to provide a color paper that is easier for the printer operator to accurately dodge and burn during printing.

A further object of the invention is to provide a color paper that has the sensitometric and speed properties adjusted during manufacturing without significantly changing the color of the undeveloped paper.

An additional object of the invention is to provide lower manufacturing cost for color papers.

These and other objects generally are accomplished by providing a method of improved burning and dodging comprising providing a color photographic element that prior to development has CIELAB coordinates such that L* is greater than 71, exposing said paper, wherein during exposure burning and dodging is carried out.

In the invention there is also provided a color photographic paper wherein said paper prior to development has spectral photometric properties wherein the CIELAB coordinates are selected such that L* is greater than 71, a* is greater than 18, b* is greater than 2.8, and c* is greater than 18.

An advantage of the invention is that color papers are produced that are easier to control as to sensitivity and speed during manufacturing. Another advantage is that in printing photographs on the elements of the invention, the printer can more easily dodge and burn as the paper is light colored, and this light color does not vary significantly from batch to batch.

FIG. 1 is the dye sensitivity comparison of the spectral dye and absorber dyes such as in the prior art.

FIG. 2 is the dye sensitivity comparison of a spectral dye and absorber dyes in accordance with the invention.

The invention has numerous advantages over prior photographic elements. The photographic elements of the invention are low cost manufacture, as absorber dye and sensitizing dye have the same peak response, less chemicals are needed to adjust the overall sensitivity of the photographic element. Further, the adjustment is more accurate. Since less absorbing dye is needed to make adjustments, the paper is lighter in color, as well as varying less in color between batches as different adjustments are made. There is a cost savings as less chemicals are utilized for adjusting the paper properties during manufacturing. Further, there is greater customer satisfaction as the paper always looks the same. Customers previously were uneasy in that the color of unexposed paper would vary even though the pictures developed from the paper were very uniform. These and other advantages of the invention will be apparent from the detailed description below.

In the manufacture of color paper and other photographic products such as color negative film, it is known to adjust the speed of the paper by the use of absorber dyes. These absorber dyes allow the photographic elements to be sold with a fixed speed over a period of time even though the speed of the photographic emulsions may vary somewhat in manufacture over time. By the use of the dyes, the speed is adjusted to a constant over time.

In the invention the absorber dyes are selected to have similar response to light as the spectral sensitizing dyes for the emulsions. While absorber dyes have been used in the art, there is no recognition of the benefits of adjusting the band absorption of the absorber dyes to be generally the same as those of the spectral sensitizing dyes. It has been found that to obtain the benefits of the invention that the peak responses of the spectral sensitizing dye and the absorber dye should overlap for at least 75% of the spectral envelope of the spectral sensitizing dye. Spectral envelope is the area underneath the spectral sensitization curve of the particular spectral sensitizing dye. The spectral sensitization curve is determined by the sensitivity of the silver halide to different wavelengths of light for a particular sensitizing dye. This is done by using a standard wedge spectrophotometer. It is preferred that the absorber dye overlap at least 90% of the spectral envelope of the spectral sensitizing dye for the easiest adjustment of speed with the use of the least absorbing dye and best maintaining of the sharpness of the photographic element.

The invention may be utilized to match spectral sensitization and absorber dye in any color photographic product. The dye adjustment of peak sensitivity may be used in the red, blue, or green sensitive layer. A preferred use has been found to be in the red sensitive layer, as addition of the absorbing dyes in this layer results in a darker photographic element that makes printing more difficult, as dodging and burning is more difficult to carry out on the dark color, and presently used dyes are wide apart in peak sensitivity. Linear adjustment of speed values during manufacturing is possible when the absorber and spectral dyes have the same peak as in the invention.

Any red spectral sensitizing dye may be utilized in the red light sensitive layer of a photographic element. Suitable for use in color paper are the red sensitizer dyes symmetrical or unsymmetrical benzothiazoledicarbocyanines, benzoxazole dicarbocyanines, benzothiazole-benzoxazole dicarbocyanines, for example, those sensitizing dyes described in Research Disclosure #38957, September 1996. Preferred for use in color paper are sensitizer dyes symmetrical or unsymmetrical benzothiazoledicarbocyanines. Preferred materials are those of Class A and Class B.

Class A dyes have structure I (and substituents W.sub.1 -W.sub.8 are chosen such that J is .gtoreq.0.0, where J is defined as the sum of the Hammett s.sub.p values of W.sub.1-8, or, alternatively, Class A dyes can also have the structure II provided substituents W.sub.1 -W.sub.8 are chosen such that J is .gtoreq.0.24;

Class B dyes have structure II and substituents W.sub.1 -W.sub.8 are chosen independently such that J is .ltoreq.0.10, or, alternatively, Class B dyes can also have structure I provided substituents W.sub.1 -W.sub.8 are chosen such that J is .ltoreq.-0.14 ##STR1## where, R.sub.1 and R.sub.2 each independently represents an alkyl group or a substituted alkyl group;

X is a counterion, if needed, to balance the charge of the dye;

Z is a hydrogen or halogen atom or an alkyl group or a substituted alkyl group;

Z.sub.1 and Z.sub.2 is each independently a 1-8 carbon alkyl group;

A preferred sensitizing dye is ##STR2##

Any red absorber dye may be used in the invention. Suitable red absorber dyes are ##STR3## wherein: G is oxygen, substituted nitrogen, or C(CN).sub.2 ;

R.sup.1, R.sup.1 ', R.sup.2, R.sup.2 ', independently represent H or a substituent, or R.sup.1 and R.sup.2, R.sup.1 ' and R.sup.2 ' may form a ring;

R.sup.3 is an alkyl, aryl, alkyloxy, aryloxy, amino, or heterocyclic, any of which may be substituted or unsubstituted;

m is 0, 1, 2, or 3;

all of the L together define a methine chain, each L representing a methine any of which may be substituted or unsubstituted; and

M.sup.+ is a cation.

Preferred red absorber dyes have a peak sensitivity the same as the peak sensitivity of the preferred sensitizing dyes. Preferred absorber dye is D-7.

The selection of pairs of absorber and sensitizing dyes having the same peak sensitivites for the green sensitive and blue sensitive layers also may be carried out.

The spectral envelope of a dye may be determined by several techniques. A suitable technique is absorbance spectrophotometry.

The lightness of a color paper desired by professional printers has been determined by surveying the printer operators to determine how light the paper should be in order to provide them improved control of the burning and dodging process. The burning and dodging process is easier if the paper is light in color, as the printer operator can effectively determine the shades of gradation of the image projected by the enlarger onto the color paper. If the paper is dark, the gradations of the image as projected are not clear, and it is more difficult for the printer operator to effectively burn and dodge. This leads to trial and error which wastes time and paper material. A suitable lightness of color paper is one that is within the color space wherein L* is greater than 71. In a preferred form, values for L* are greater than 76. The meaning of spectral photometric data relating to a*, b*, c*, and L* is well known in the photographic art. These color coordinates are well-known metrics in the CIE System (Commission International de l'Eclairage), and their derivation is discussed at length in many texts on color science. One such example is PRINCIPLES OF COLOR TECHNOLOGY, 2nd Edition, authored by Fred W. Billmeyer, Jr. and Max Saltzman, which is published by John Wiley and Sons, New York with pages 25-66 being of particular interest.

Accordingly, the metrics, a* and b* are measures of the color of an object. The value of a* are generally thought of as a measure of the amount of redness or greenness of an object. An object with a positive value for a* is increasingly red while a negative value for a* indicates the degree of greenness in the object. Likewise for b*, a positive value indicates more yellowness; while negative b* values indicate increasing blueness.

An objects lightness or darkness is measured using the term L*. An L* value of 100 indicates that the object is perfectly white; while an L* value of 0 indicates that the object is perfectly black. Values of L* between 0 and 100 indicate intermediate lightness. Chroma, or color saturation, is calculated as c* using the equation described below. In black and white imaging systems it has little meaning since it is derived from the a* and b* terms which are both near zero indicating no color. In black and white photographs, c* is also near zero. For an object to be rendered neutral, it should have a very small values for a* and b*. In fact, the closer that a* and b* are to zero, the lesser amount of color in the object and the more neutral appearing the object will be rendered. In the examples below, L* describes the lightness of the sample patch and does not relate to the color of the patch.

Illustrated in FIG. 1 attached are figures illustrating the overlapping of the spectral sensitivity of the red sensitizing dye and red absorbing dye of a representative prior art paper. As can be seen, the spectral red absorber dye curve A does not closely match the spectral sensitizing dye curve B of the absorbing dye. The area underneath the curves above the horizontal axis is referred to as the spectral envelope with a dye. As can be seen in the drawing of FIG. 1, the overlap is at about 50% The failure of the dye to have the same peak sensitivity means that more of the absorbing dye needs to be added to control the response of the sensitizing dye than if the peaks were the same. This leads to the following disadvantages. The color paper is darker and, therefore, more difficult for a printer to burn and dodge. Also, sharpness can only be obtained at high and expensive amounts of absorber dyes.

In FIG. 2, there is shown a pair of red sensitizing dye 8 (curve D) and red absorbing dye 7 (curve C) curves of dyes of the invention. As shown in FIG. 2, these dyes have a peak sensitivity that overlaps at about 90% of their spectral envelope. This leads to the advantage that less dye is needed to change the sensitivity to the same degree. Further, sharpness is not deteriorated because control is now linear and further sharpness can be achieved with less absorber dye than in FIG. 1.

The invention may be suitably practiced in any photographic material. Suitable for use of the invention are transparency materials, reversal transparency materials, movie internegative film, and movie film. The invention also is suitable for color negative film. The invention finds its most preferred use in negative working color paper where the advantage for burning and dodging is achieved. The invention may be utilized with any silver halide grains and color couplers conventionally utilized in color papers and color negative film. Further, it may be utilized with any conventional spectral sensitizing dyes for which a spectral envelope matching absorbing dye is available. Typical of materials suitable for the invention are those found in Research Disclosure 38957, September 1996, p. 592. Color paper materials suitable for the invention may be found in Research Disclosure 37038, February 1995, p. 79-115.

The following examples illustrate the practice of this invention. They are not intended to be exhaustive of all possible variations of the invention. Parts and percentages are by weight unless otherwise indicated.

Preparation of emulsion E1. A high chloride silver halide emulsion was precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a reactor vessel containing a gelatin peptizer and a thioether ripener. An osmium dopant was added during the silver halide grain formation for most of the precipitation followed by shelling without dopant. The resultant emulsion contained cubic shaped grains of 0.76 mm in edgelength size. The emulsion was optimally sensitized by the addition of a colloidal suspension of aurous sulfide followed by a heat ramp, and addition of sensitizing dye, D-1,1-(3-acetamidophenyl)-5-mercaptotetrazole and potassium bromide. In addition, iridium and ruthenium dopants were added during the sensitization process.

Preparation of emulsion E2. A high chloride silver halide emulsion was precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a reactor vessel containing a gelatin peptizer and a thioether ripener. An osmium dopant was added during the silver halide grain formation for most of the precipitation followed by shelling without dopant. The resultant emulsion contained cubic shaped grains of 0.30 mm in edgelength size. The emulsion was optimally sensitized by the addition of a colloidal suspension of aurous sulfide followed by a heat ramp, and addition of an iridium dopant, Lippmann bromide and 1-(3-acetamidophenyl)-5-mercaptotetrazole, sensitizing dye, D-2, and further 1-(3-acetamidophenyl)-5-mercaptotetrazole.

Preparation of emulsion E3. A high chloride silver halide emulsion was precipitated by adding approximately equimolar silver nitrate and sodium chloride solutions into a reactor vessel containing a gelatin peptizer and a thioether ripener. The resultant emulsion contained cubic shaped grains of 0.40 mm in edgelength size. The emulsion was optimally sensitized by the addition of a colloidal suspension of aurous sulfide followed by a heat ramp, and addition of 1-(3-acetamidophenyl)-5-mercaptotetrazole, potassium bromide and red sensitizing dye, D-3. In addition, iridium and ruthenium dopants were added during the sensitization process.

The emulsions were combined with dispersions using techniques known in the art and the resulting light-sensitive silver halide components were applied to polyethylene resin coated paper support as described in coating format 1 to provide Example 1. The amount of absorber dye in Example 1 was adjusted as shown in Table 1 to give samples 101-106.

Example 2 was prepared as described in Example 1 except that D-6 was replaced by D-7 in coating format 1. The amount of absorber dye in Example 2 was adjusted as shown in Table 1 to give samples 201-206.

Example 3 was prepared as described in Example 1 except that D-3 was replaced by D-8 in coating format 1. The amount of absorber dye in Example 3 was adjusted as shown in Table 2 to give samples 301-303.

Example 4 was prepared as described in Example 2 except that D-3 was replaced by D-8 in coating format 1. The amount of absorber dye in Example 4 was adjusted as shown in Table 2 to give samples 401-403. ##STR4##

Table 1 shows that increasing amounts of the inventive dye lead to continued sharpness improvements, whereas the comparative dye reaches a maximum value in sharpness and further quantities do not provide any further sharpness improvements. It is also evident from Table 1 that the in-process speed will continue to decrease with increased amounts of the inventive dye, that is, it exhibits a linear relationship. The comparative dye fails to continue to decrease speed with increased amount of dye and exhibits a non-linear relationship. The inventive dye has the advantage of being useful over a greater range of adjustment during manufacturing. Further, it is apparent from Table 1 that a lesser amount of the inventive dye can be used to obtain the speed and sharpness position of the comparative dye. Additionally, using less of the inventive dye provides for a lighter material that is easier to dodge and burn.

Table 2 shows that the sensitivity to ambient temperature changes can be controlled by the inventive combination of absorber and sensitizing dyes which leads to greatly reduced sensitivity at the same laydown of absorber dye.

These four samples were exposed with dodging and burning. Examples 2 and 4, the invention were found by the photographer to have a noticeable advantage in the easy and accuracy of dodging and burning. The four papers then were tested as follows to determine the spectral photometric properties of the color papers. The test batch was removed from each undeveloped paper and tested as follows:

In our calorimetric calculations, we assume a color temperature of D5500 and have used the 1931 CIE 2 degree standard observer.

In the coated example described above, the colorimetry results for the test patch produced an a* value of -1.15 and a b* of 1.23 with a lightness L* of 38.2. Both the a* and b* values are close to zero indicating neutrality was achieved. As added confirmation, the sample patch when viewed under the appropriate D5500 illumination appeared visually neutral with no evidence of a color bias.

The calculation of the colorimetric values for a*, b*, L* and c* is straightforward and is discussed in detail in the reference noted above. However, to further clarify their calculation, the following derivations are given for the four terms.

First it is necessary to know the spectral power distribution of the light source used as the viewing illuminant. For these calculations we have chosen a daylight source with a color temperature of 5500.degree. Kelvin (D5500). The spectral power distribution, P(lambda), of this source is well known and we have chosen to use the spectral range of 340 nm to 800 nm in 10 nm increments. Secondly, it is necessary to know the reflectance spectrum, R(lambda), of the object being observed. These data are conveniently obtained by using any commercial reflectance spectrophotometer. The wavelength range measured is 340 nm to 800 nm. Lastly, it is necessary to know the 1931 CIE 2.degree. standard observer functions x(lambda), y(lambda) and z(lambda). These values are also conveniently obtained over the necessary wavelength range from the reference text cited above.

Once the above values are obtained, they are spectrally multiplied together as a function of wavelength and the individual values for x(lambda), y(lambda) and z(lambda) are summed to obtain the tristimulus values X, Y and Z. Once obtained, the tristimulus values are used to calculate the calorimetric values of a*, b*, L* and c* using the equations given below:

In these equations, X.sub.n, Y.sub.n and Z.sub.n represent the tristimulus values for the reference white.

The measured results of the tests are shown in Table 3 below.

As can be seen from evaluation of the values in Table 3, the invention Examples 2 and 4 have values that show a lightness that enables the photographic print to better burn and dodge during printing.

In Table 3, measurements are provided for the four examples.

The measurements were read off the paper raw-stock surface. Two sets of readings were made in each example.

1) The first set are readings taken using a Spectrodensitometer providing CIELAB coordinates L*, a*, b*, and c*.

The higher the value of L*, the lighter the appearance of the sample in each example. The a*, b* coordinates represent the color of the sample. The c* value is the square root of [(a*)(a*)+(b*)(b*)] and represents the color saturation level at a given lightness level (L*).

In the plot below of a* versus b* are shown the four quadrants and preferences in each and where the preferred invention region is located. ##STR6##

In the plot below of L* versus c* are shown the preference regions and where the preferred invention region is located.

The higher the value of L*, the more preferred the sample appearance. However, L* less than 71 is not a preferred region. The L* of 71 to 76 is acceptable. L* values of greater than 76 are preferred invention regions. ##STR7##

2) The second set of readings are taken using a status A densitometer providing Red (R), Green (G), and Blue (B) values. As can be seen, the higher the red reading (keeping the other two G, B about the same) implies more red density, hence more Cyan look to the sample. Example 2 has a R=20 which is redder compared to Example 1 which is Cyaner (R=39). Comparing Examples 3 and 4 show a much larger red/cyan difference compared to Examples 1 and 2, but also shows that the green and blue densities of the inventive dye are lower as well. When all three densities are lower, the sample will appear lighter. The set of R, G, and B values are correlated to the L*, a*, b*, and c* values. Both the R, G, B values and the CIELAB values indicate a redder sample color in Example 2 and a cyaner sample color in Example 1. Additionally, both values indicate a redder and lighter sample color in Example 4 and a cyaner and darker color in Example 3.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.