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(11) | EP 0 212 673 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Photographic paper |
| (57) A photographic paper comprising a water-proof support and a photographic emulsion
layer, which is characterized in that another surface of said support is provided
with a printing-retaining layer of gelatin which is hardened with a non-formaldehyde
gelatin hardening agent, said printing-retaining layer dispersively containing an
amorphous inorganic pigment having a mean diameter of 0.1-10 µm and an oil absorption
capacity of not less than 100 cc./10 g. in an amount of 12-80 wt.% based on the amount
of the gelatin and a crystalline inorganic pigment having a mean diameter of 0.1-0.8
µm in an amount of 5-40 wt.% based on the amount of the gelatin. The composition of
the printing-retaining layer can be replaced with a composition comprising a gelatin
having a jelly strength in the range of 130-260 g. which is hardened with a non-formaldehyde
gelatin hardening agent and the inorganic pigment having a high oil absorption capacity. |
BACKGROUND OF THE INVENTION
Field of the invention
[0001] The present invention relates to a photographic paper, more particularly to a photographic paper which is provided with excellent writing characteristics on the back surface.
Description of prior arts
[0002] A photographic paper basically comprises a support, a silver halide emulsion layer (i.e., a photographic emulsion layer) and a protective gelatin layer. In the case of using a paper sheet as the support, the paper sheet is generally coated with a polyolefin resin such as polyethylene on both surfaces thereof to give a water-proof property to the paper.support. In a photographic paper having such polyolefin coated paper sheet, the surface of the side where a photographic emulsion layer is provided is referred to as front surface, and the surface of the side where no photographic emulsion layer is provided is referred to as back surface.
[0003] On the front surface of a photographic paper is formed a visible image. It has been desired to write letters, draw a picture, or print a stamp on the back surface of a photographic paper. A photographic paper having such favorable features can be employed as a post card if the photographic paper is so made as to receive a stamp under adhesion on the back surface. Thus, a photographic paper of this type is employable for various purposes.
[0004] As described above, however, the back surface of a photographic paper is generally coated with a hydrophobic polyolefin layer. Since the polyolefin layer generally has no hygroscopic property (i.e., capacity for absorbing a writing ink, printing ink, etc.), an ink applied to the surface thereof is not rapidly dried, or readily removed by rubbing with fingers or by the similar action even after the ink is dried. Accordingly, it is difficult to put letters or a picture by the use of a pencil, a conte crayon or a fountain pen or to print a stamp on the surface of the polyolefin layer.
[0005] For readily putting letters and pictures or printing a stamp on the back surface of the photographic paper, the polyolefin layer is required to be provided with favorable writing characteristics. The term "writing characteristics" means various features of the photographic paper such as smoothness in writing with a pen, clogging of pen, ink blotting and ink absorption.
[0006] Examples of the processes generally employed for giving favorable writing characteristics to the polyolefin layer on the back surface of the photographic paper include: a process involving providing a large number of fine protrusions and depressions to the polyolefin layer; a process involving subjecting the polyolefin layer to corona discharge treatment; and a process involving coating a layer of surface active agent on the polyolefin layer. A polyolefin layer processed as above shows satisfactory writing characteristics under writing with an oily ink, but shows extremely poor writing characteristics under writing with an aqueous ink.
[0007] Heretofore, a number of methods have been proposed to overcome the above-described drawbacks. For instance, there can be mentioned a method of providing a layer comprising an acid, a polymerizable organic film-forming substance resistant to acid such as polyvinyl alcohol or carboxymethycellulose,. and an aqueous silica solon the polyolefin layer (see: Japanese Patent Publications No. 44(1969)-14884 and No. 50(1975)-36565); a method of providing a hygroscopic painting layer (see: Japanese Utility Model Provisional Publication No. 52(1977)-169426); and a method of providing a layer containing a cationic organic substance and an inorganic pigment on the back surface of a photographic paper (see: Japanese Utility Model Provisional Publication No. 57(1982)-60140).
[0008] Although the photographic papers provided with such layers according to these methods are fairly improved in the writing characteristics, they still have certain drawbacks. For instance, the provided layer is apt to separate from the photographic paper in a developing process, or is soluble in a developing solution. For this reason, such additional layers need to be coated after completion of the development. Further, an ink applied onto the photographic paper varies with a lapse of time to fade out after printing, so that the photographic paper can be hardly employed in the practical use.
[0009] The above-described drawbacks such as the separation of a coated layer from the photographic paper or the dissolution of a coated layer in a developing solution can be improved by providing a gelatin layer containing an inorganic pigment and a hardening agent on the back surface of a photographic paper (see: Japanese Patent Provisional Publication No. 58(1983)-184144). However, the gelatin layer containing such components causes clogging of pen in the course of continuous writing, and further improvement of the photographic papers is desired in view of writing characteristics.
SUMMARY OF THE INVENTION
[0010] It is a principal object of the present invention to provide a photographic paper which shows satisfactory writing characteristics on the back surface and brings about extremely less fading of ink applied onto the back surface.
[0011] The present invention provides an improvement of a photographic paper comprising a water-proof support which comprises a paper sheet coated with a polyolefin resin on both surfaces thereof, and a photographic emulsion layer provided on one surface of said support, the improvement residing in that another surface of said support is provided with a printing-retaining layer of gelatin hardened with a non-formaldehyde gelatin hardening agent, said printing-retaining layer dispersively containing an amorphous inorganic pigment having a mean diameter of 0.1 - 10 µm and an oil absorption capacity of not less than 100 cc./100 g. in an amount of 12 - 80 wt.% based on the amount of the gelatin and a crystalline inorganic pigment having a mean diameter of 0.1 - 0.8 µm in an amount of 5 - 40 wt.% based on the amount of the gelatin.
[0012] The above-mentioned printing-retaining layer can be replaced with a layer of gelatin having a jelly strength in the range of 130 -260 g. which is hardened with a non-formaldehyde gelatin hardening agent, said printing-retaining layer dispersively containing an inorganic pigment having a mean diameter of 0.1 - 10 µm and an oil absorption capacity of not less than 100 cc./100 g. in an amount of 17 - 100 wt.% based on the amount of the gelatin. The jelly strength is a value determined by the known PAGI method.
[0013] In the photographic paper of the invention, the printing-retaining layer provided on the back surface is excellent particularly in the writing characteristics. Further, the printing-retaining layer hardly separates from the photographic paper in a developing process, or is hardly dissolved in a developing solution. In addition to those advantageous features, since the ink fading is brought about at a very low level on the printing-retaining layer, the photographic paper of the invention is very valuable as a commercial product. Accordingly, the photographic paper of the invention can be suitably employed as a post card.
DETAILED DESCRIPTION OF THE INVENTION
[0014] A photographic paper of the invention basically comprises a polyolefin resin coated paper sheet (water-proof support), a photographic emulsion layer provided on one surface of the water-proof support, and a printing-retaining layer provided on another surface (back surface) of the support.
[0015] The paper sheet employable for the preparation of the water-proof support can be selected from materials generally employed for the conventional photographic . papers. Examples of such materials include natural pulp paper, synthetic pulp paper, paper prepared from a mixture of natural pulp and synthetic pulp, and various composite papers. The paper sheet generally has the thickness of 30 - 500 µm.
[0016] The paper sheet may appropriately contain one or more internal additives generally employed in the conventional paper manufacturing art such as a paper strength increasing agent, a fixing agent, a preserving agent, a filler and an antistatic agent. A surface sizing agent can be also applied onto the paper support.
[0017] On the both surfaces of the paper sheet is formed a polyolefin resin-coated layer. Examples of the polyolefin resin include homopolymers of a-olefins such as polyethylene and polypropylene, copolymers of a-olefins such as ethylene and propylene, and mixtures of these polymers. Particularly preferred are high density polyethylene, low density polyethylene and a mixture thereof. There is no specific limitation on the molecular weight of the polyolefin, as far as the polyolefin can be coated by an extrusion coating procedure. However, a polyolefin having a molecular weight in the range of 20,000-200,000 is generally employed.
[0018] The polyolefin layer can be formed by curing a monomer under electron radiation as described in Japanese Patent Provisional Publication No. 57(1982)-49946.
[0019] There is no specific limitation on the thickness of the polyolefin layer, and the thickness can be optionally determined according to the thickness of the polyolefin layer of a conventional photographic support. The thickness generally ranges from 10 to 100 µm, and preferably ranges from 15 to 50 µm.
[0020] The polyolefin layer may contain one or more of additives such as a white pigment, a color pigment, a fluorescent-whitening agent, and an antioxidizing agent. Particularly, a white pigment and a color pigment are preferably incorporated into a polyolefin resin coated layer on which a photographic emulsion layer is to be coated. The kinds, amounts and manners of addition of these additives are described in detail in various publications such as United States Patents No. 3,833,380, No. 4,169,188, No. 3,501,298, No. 3,449,257 and No. 3,499,762.
[0021] The photographic support (water-proof support) having a polyolefin layer on both surfaces thereof comprises a photographic emulsion layer provided on one surface of the support and a printing-retaining layer on another surface (back surface) of the support. For the provision of the photographic emulsion layer and the printing-retaining layer onto the water-proof support, any one of those layers can be coated thereto prior to coating the other layer, or those layers can be coated simultaneously. Generally, a photographic emulsion layer is formed on the water-proof support which has been beforehand provided with a printing-retaining layer. The photographic emulsion layer can be coated on the support according to the conventional method.
[0022] In one aspect according to the present invention, the printing-retaining layer to be coated on the polyolefin layer comprises gelatin which is hardened with a gelatin hardening agent, an amorphous inorganic pigment having a specific mean diameter and a high oil absorption capacity, and a crystalline inorganic pigment having a specific mean diameter, both pigments being dispersed in the gelatin.
[0023] The amorphous pigment having the specific mean diameter and high oil absorption capacity serves for particularly enhancing the ink absorption capacity of the printing-retaining layer. The crystalline inorganic pigment having the specific mean diameter effectively prevents the clogging of pen. In the invention, the excellent writing characteristics can be provided on the printing-retaining layer owing to the synergistic effect of the amorphous inorganic pigment and the crystalline inorganic pigment.
[0024] The amorphous inorganic pigment employable in the invention has the oil absorption capacity of not less than 100 cc./100 g. If the oil absorption capacity is less than 100 cc./100 g., the ink-absorbing rate of the printing-retaining layer is extremely retarded so that the letters put on the layer are readily removed by rubbing with fingers or readily transferred onto another papers placed in contact therewith. For providing the writing characteristics similar to those of an ordinary post card or letter paper on the photographic paper, the printing-retaining layer of the invention is required to contain the amorphous inorganic pigment having the oil absorption of not less than 100 cc./100 g.
[0025] Examples of the amorphous inorganic pigment include amorphous silica, hydrophilic silica, and calcined clay. Those pigments can be employed singly or in combination. The mean particle diameter of the amorphous inorganic pigment employable in the invention needs to be in the range of 0.1 - 10 µm, preferably in the range of 0.2 - 5 µm. If the mean diameter exceeds 10 µm, the coated layer shows unsatisfactory enlarged protrusions and depressions, resulting in deterioration of the writing characteristics. If the mean diameter is less than 0.1 µm, the writing characteristics also deteriorate.
[0026] The oil absorption capacity of the crystalline inorganic pigment employable in the invention is such an extremely low level that the measurement thereof is almost impossible. The mean particle diameter of the crystalline inorganic pigment needs to be in the range of 0.1 - 8 µm, preferably in the range of 0.2 - 5 µm. If the mean diameter exceeds 8 µm, the coated layer shows unsatisfactory protrusions and depressions, sometimes resulting in deterioration of the writing characteristics. If the mean diameter is less than 0.1 µm, the clogging of pen cannot be sufficiently prevented in a procedure of continuous writing with a pen, and occurrence of scratches on the coated layer of the back surface of the photographic paper cannot be restrained in a developing process, whereby the resulting photographic paper is made unsuitable for the practical use. Examples of the crystalline inorganic pigment employable in the invention include crystalline silica, talc and alumina. Those pigments can be employed singly or in combination.
[0027] A gelatin is incorporated into the printing-retaining layer of the invention as a binder. A quite hydrophobic gelatin is unsuitable for the photographic paper of the invention because the printing-retaining layer containing such gelatin is deteriorated in the ink absorption. Most preferred is a hydrophilic gelatin. Examples of the gelatin employable in the invention include lime-treated gelatin, acid-treated gelatin, enzyme-treated gelatin, and gelatin derivatives or denatured gelatins treated or denatured with a reagent containing at least one group reactive with the amino group, imino group, hydroxyl group or carboxyl group contained in a gelatin molecule as the functional group, for instance, phtalated gelatin, citrated gelatin and trimelli- tated gelatin prepared by reactions with phthalic anhydride, succinic anhydride, and trimellitic anhydride, respectively.
[0028] The gelatin employed in the invention preferably has a jelly strength in the range of 130 - 260 g., and more more preferably in the range of 150 - 210 g. The jelly strength of gelatin is determined by the known PAGI method. The gelatin having a jelly strength in the above range can comprise gelatin of one kind or a mixture of two or more gelatin. The mixture of gelatins can be prepared using two or more gelatins having a jelly strength in the above range. Otherwise, a mixture of gelatins, one or more of which have a jelly strength outside of the above range can be employed.
[0029] The aforementioned amorphous inorganic pigment is contained in the printing-retaining layer of the invention in an amount of 12 - 80 wt.% based on the amount of the gelatin, preferably in an amount of 20 - 70 wt.% based on the amount of the gelatin. The writing characteristics are deteriorated in each case that the amount of the amorphous inorganic pigment is less than 12 % by weight, or more than 80 % by weight, based on the amount of gelatin.
[0030] The aforementioned crystalline inorganic pigment is contained in the printing-retaining layer of the invention in an amount of 5 - 40 wt.% based on the amount of the gelatin, preferably in an amount of 5 - 25 wt.% based on the amount of the gelatin. If the amount of the crystalline inorganic pigment exceeds 40 % by weight, the ink absorption of the resulting photographic paper decreases to bring about an occurrence of ink blotting when letters are written with an oily ink or an aqueous ink. If the amount of the crystalline inorganic pigment is excessively small based on gelatin, the clogging of pen occurring in writing using a pen cannot be improved.
[0031] The total amount of the amorphous inorganic pigment and the crystalline inorganic pigment is preferably in the range of 25 - 80 wt.% based on the amount of the gelatin.
[0032] The ratio between the amorphous inorganic pigment and the crystalline inorganic pigment contained in the printing-retaining layer is preferably in the range of 10/1 - 2/1, more preferably 7/1 - 3/1.
[0033] In the invention, a non-formalin hardening agent is incorporated into the above-mentioned gelatin. The incorporation of the hardening agent into the gelatin not only prevents dissolution of gelatin in a developing solution, but also improves the blotting tendency of an applied ink. Formalin and formalin-producing compounds are not appropriate as the gelatin hardening agent to be employed in the invention, because formalin is apt not only to give unfavorable influence to a photographic emulsion layer such as production of fog, but also to cause fading of an applied ink with a lapse of time. Accordingly, aldehyde compounds and their derivatives such as mucochloric acid, mucobromic acid, mucophenoxy- chloric acid, mucophenoxybromic acid, formaldehyde, di- methylolurea, trimethylolmelamine, glyoxal, monomethyl- glyoxal, 2,3-dihydroxy-1,4-dioxane, 2,3-dihydroxy-5-methyl-1,4-dioxanesuccinaldehyde, 2,5-dimethoxytetrahy- drofuran and glutaraldehyde cannot be employed in the invention.
[0034] Examples of the non-formaldehyde gelatin hardening agent employable in the invention include those of active vinyl type, active halogen type, epoxy type, methanesulfonic acid ester type, carbodiimide type, isoxazole type, active ester type, isocyanate type and inorganic type. Examples of the hardening agent of each type are as follows:
Active vinyl type compounds such as divinylsulfone N,N'-ethylenebis(vinylsulfonylacetamide), 1,3-bis(vinyl sulfonyl)-2-propanol, methylenebismaleimide, 5-acetyl-1,3-diacryloyl-hexahydro-S-triazine, 1,3,5-triacryloyl- hexanydro-S-triazine, and 1,3,5-trivinylsulfonyl- hexahyro-S-triazine;
Active halogen type compounds such as 2,4-dichloro-6-hydroxy-S-triazine sodium salt, 2,4-dichloro-6-methoxy-S-triazine, 2,4-dichloro-6-(4-sulfoanilinno)-S-triazine sodium salt, 2,4-dichloro-6-(2-sulfoethylamino) -S-triazine, and N,N-bis(2-chloroethylcarbamyl)-piperazine;
Epoxy type compounds such as bis(2,3-epoxy-propyl)-methylpropylammonium-p-toluenesulfonate, 1,4-bis(2',3'-epoxypropyloxy)butane, 1,3,5-triglycidyl isocyanurate, and 1,3-diglycyl-4-(γ-acetoxy-β-oxypropyl)-isocyanurate;
Ethyleneimino type compounds such as 2,4,6-triethylene-S-triazine, 1,6-hexamethylene-N,N'-bis-ethyleneurea, and bis-β-ethyleneiminoethyl thioether;
Methanesulfonic acid ester type compounds such as 1,2-di(methanesulfonoxy)ethane, 1,4-di(methanesulfonoxy) butane, and 1,5-di(methanesulfonoxy)pentane;
Carbodiimide type compounds such as dicyclo-hexyl- carbodiimide, l-cyclohexyl-3-(3-trimethylamino-propyl)-carbodiimide-p-toluenesulfonate, and l-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride;
Isoxazole type compounds such as 2,5-di-methyl- isoxazol perchlorate, 2-ethyl-5-phenylisoxazole-3'-sulfonate, and 5,5'-(p-phenylene)bisisoxazole;
Inorganic type compounds such as chrome alum and chromium acetate;
Dehydration-condensation peptide type compounds such as N-carboethoxy-2-isopropoxy-1,2-dihydroguinoline, and N-(l-mcrpholinocarboxy)-4-methylpyridinium chloride;
Active ester type compounds such as N,N'-adipoyldi- oxydisuccinimide and N,N'-terephthaloyldioxy-disuccin- imide; and
Isocyanate type compounds such as toluene-2,4-diisocyanate and 1,6-hexamethylenediisocyanate.
[0035] The gelatin hardening agent is contained in the printing-retaining layer in an amount of 0.1 - 3 wt.% based on the amount of the gelatin. The amount of the hardening agent can be appropriately determined according to the employed coating method and the desired hardening degree.
[0036] The printing-retaining layer can be formed on the back surface of the water-proof support by first preparing a coating solution containing a gelatin, an amorphous inorganic pigment, a crystalline inorganic pigment and a hardening agent, then coating the solution onto the back surface of the support, and drying the coated solution.
[0037] As a solvent of the coating solution, water or a mixture of water and an alcohol can be employed. Example of the alcohol employable in the invention include a variety of alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol and butyl alcohol. If a mixture of water and an alcohol is employed, the ratio therebetween can be determined according to the desired drying rate and the employed coating method. If desired, the pH of the coating solution can be varied by selectively employing the hardening agent. For instance, the coating solution can be made alkaline by addition of sodium hydroxide or the like, or made acidic by addition of citric acid or the like.
[0038] The coating solution may contain an antiseptic agent to keep the solution from rotting. Examples of the antiseptic agent employable in the invention include those of metal compound type, organic nitrogen type, organic halogen type, organic nitrogen sulfur type, organic nitrogen halogen type, organic sulfur type, morpholine type, nitrofuran type and thiazoline type; and a chlorine compound oxidizing agent.
[0039] The coating solution may further contain other various additives such as a defoaming agent for removing the possibly produced foams and a surface active agent for enhancing the levelling of the solution so as to prevent production of a coating streak. If desired, an antistatic agent is introduced into the coating solution.
[0040] A surface of the polyolefin layer provided on the back surface of the photographic support is preferably subjected to a surface activation treatment in a conventional manner prior to applying the coating solution for the preparation of a printing-retaining layer thereonto. Examples of the surface activation treatment include etching treatment using an acid, flame treatment using a gas burner, corona discharge treatment and glow discharge treatment. From the viewpoints of cost and simplicity for carrying out the activation treatment, most preferably employed is the corona discharge treatment described in United States Patents No. 2,715,075, No. 2,846,727, No. 3,549,406 and No. 3,590,107.
[0041] The coating solution for the preparation of the printing-retaining layer can be applied according to the known methods such as a dip coating method, air knife coating method, curtain coating method, roller coating method, doctor coating method, wire-bar coating method, slide coating method, gravure coating method, and extrusion coating method employing a hopper described in United States Patent No. 2,681,294. If desired, the layer can be divided into two or more layers and coated simultaneously according to the methods described in United States Patents No. 2,761,791, No. 3,508,947, No. 2,941,898 and No. 3,526,528, and "Coating Technology (in Japanese)" written by Yuji Harazaki (Asakura Shoten, Tokyo, 1973), page 253. An appropriate coating method can be employed according to the desired coating amount and coating rate.
[0042] The amount of the coating solution employed in the invention is generally in the range of 0.5 - 10 g./m2 based on the amount upon dried. If the amount is less than 0.5 g./m2, the coated layer shows poor ink absorption, resulting in increase of ink blotting. If the amount is more than 10 g/m2, various problems are likely brought about, for instance, high production cost, high curling tendency, and deterioration of writing characteristics. From the viewpoints of writing characteristics (e.g., ink absorption, ink blotting and smoothness in writing) and curling tendency, most preferred is in the range of 1.8 - 8 g./m .
[0043] In another aspect according to the invention, the printing-retaining layer is a layer of gelatin having a jelly strength in the range of 130 - 260 g. which is hardened with a non-formaldehyde gelatin hardening agent, said printing-retaining layer dispersively containing an inorganic pigment having a mean diameter of 0.1 - 10 µm and an oil absorption capacity of not less than 100 cc./100 g. in an amount of 17 - 100 wt.% based on the amount of the gelatin. This printing-retaining layer is also effective to provide to the photographic paper the aforementioned advantageous properties.
[0044] The above-mentioned printing-retaining layer can be prepared in a manner similar to the manner described previously with respect to the first aspect of the invention. The inorganic pigment employed in this aspect preferably is the amorphous inorganic pigment described previously.
Example 1
Composition of Coating Solution
[0046]
A coating solution containing the above-described components was prepared. Independently, a paper sheet (support) having been coated with polyethylene on both surfaces was subjected to corona discharge treatment on the back surface. Thus treated surface of the support was then coated with the coating solution prepared as above in an amount of 50 g./m2 (i.e., 7 g./m2 upon dried) through the slide coating method. The support was subsequently dried, and, in turn, coated with a silver gelatin photographic emulsion on the front surface. Thus, a photographic paper of the invention was prepared.
Comparison Examples 1 - 4
[0047] The procedure of Example 1 was repeated except for using crystalline silica having the mean particle diameter set forth in Table 1 in the amount also set forth in Table 1, to prepare a variety of photographic papers.
Comparison Example 5
[0048] The procedure of Example 1 was repeated except that the amorphous silica was replaced with crystalline silica (mean diameter: 2 pm), to prepare a photographic paper.
Comparison Examples 6 - 7
[0049] The procedure of Example 1 was repeated except for using a 40 % formalin solution as a hardening agent (Comparison Example 6), or using no hardening agent (Comparison Example 7), to prepare a photographic paper.
Evaluation of Photographic Paper
[0050] The back surfaces of the photographic papers obtained in the above-described example and comparison examples were evaluated on the writing characteristics, behavior in development and ink fading tendency.
[0051] As the writing characteristics, smoothness in writing by the use of a fountain pen, ink blotting, ink absorption and clogging of pen were evaluated.
[0052] The smoothness in writing was classified into three ranks, namely, A, B and C. A means that a fountain pen moves relatively smoothly; B means that the pen moves simply without difficulty; and C means that the pen moves with difficulty. The photographic paper given A or B is satisfactory in the practical use.
[0053] The ink blotting was evaluated as follows. A printing block on which certain letters and pattern were engraved was prepared. The printing block was pressed onto an ink pad in such condition that the ink was transferred and retained in the same amount for every trial. The printing block was subsequently pressed onto the back surface of the photographic paper to provide reproduction of the letters and pattern of the block under the same conditions for every material. The results were classified into three ranks, namely, A, B and C. A means that the ink blotting was not observed; B means that the ink blotting occurred at a low level; and C means that conspicuous ink blotting was observed. The photographic paper given A or B is satisfactory in the practical use.
[0054] The ink absorption was evaluated by measuring the time required for drying the applied ink in the above-described testing procedure. The results were classified into three ranks, namely, A, B and C. A means that the applied ink dried within 30 seconds; B means that the ink dried within 5 minutes but more than 30 seconds; and C means that the drying of the ink required more than 5 minutes. The photographic paper given A or B is satisfactory in the practical use.
[0055] The clogging of pen was evaluated by the number of test samples (photographic papers) having a size of post card on which continuous writing was carried out by the use of an aqueous felt tipped pen. The results were classified into four ranks, namely, A, B, C and D. A means that 50 or more test samples were written; B means that 30 to 49 test samples were written; C means that 10 to 29 test samples were written; and D means 9 or less test samples were written. The photographic paper given A or B is satisfactory in the practical use.
[0057] Note: As for the photographic paper obtained in Comparison Example 7, the layer on the back surface of the photographic paper (printing retaining layer) was dissolved in a developing solution in the developing process, so that the evaluations on the above characteristics were impossible.
[0058] Subsequently, the photographic papers were evaluated on the behavior in development through eye observation. The photographic paper whose coated layer on the back surface was not dissolved in a developing solution was given A, and the photographic paper whose coated layer on the back surface was dissolved in a developing solution was given C.
[0059] The photographic papers were further evaluated on the ink fading tendency. In detail, the ink transferred onto the photographic papers by the use of a printing block on which certain letters and pattern were engraved was exposed to sunlight for one month, and the ink fading with a lapse of time was evaluated through eye observation. The photographic paper showing no ink fading was given A, and the photographic paper showing ink fading was given C.
[0061] Note: As for the photographic paper obtained in Comparison Example 7, the layer on the back surface of the photographic paper (printing-retaining layer) was dissolved in a developing solution in the developing process, so that the evaluation on the ink fading tendency was impossible.
[0062] The photographic paper of the invention (Example 1) showed satisfactory writing characteristics and excellent behavior in the developing process on its back surface. Further, no ink fading was observed on the back surface of the photographic paper.
[0063] In contrast, other photographic papers prepared for comparison showed at least one unfavorable feature. In more detail, the photographic paper prepared by using crystalline silica having a large mean diameter (Comparison Example 1) was deteriorated in smoothness in writing, resulting being unsatisfactory in the practical use. Both of the photographic paper containing an excessively small amount of crystalline silica (Comparison Example 2) and the photographic paper containing no crystalline silica (Comparison Example 4) brought about clogging of pen, resulting being unsatisfactory in the practical use. The photographic paper containing an excessively large amount of crystalline silica (Comparison Example 3) showed conspicuous ink blotting and low hygroscopicity, resulting also being unsatisfactory in the practical use. The photographic paper containing no amorphous silica (Comparison Example 5) also showed conspicuous ink blotting, and was deteriorated in the hygroscopicity. The photographic paper containing formalin as a hardening agent (Comparison Example 6) had the same results as that of the photographic paper obtained in Example 1 in the writing characteristics and behavior in development, but the ink fading with a lapse of time was conspicuously observed, whereby it was unsuitable for the practical use. The photographic paper containing no hardening agent (Comparison Example 7) was also unsuitable for the practical use because the printing retaining layer thereof dissolved in a developing solution.
Example 2
Composition of Coating Solution
[0065] A coating solution containing the above-described components was prepared. Independently, a paper sheet (support) having been coated with polyethylene on both surfaces was subjected to corona discharge treatment on the back surface. Thus treated surface of the support was then coated with the coating solution prepared as above in an amount of 50 g./m2 (i.e., 7 g./m2 upon dried) through the slide coating method. The support was subsequently dried, and, in turn, coated with a silver gelatin photographic emulsion on the front surface. Thus, a photographic paper of the invention was prepared.
Comparison Examples 8 - 9
[0066] The procedure of Example 1 was repeated except for using as the gelatin only a gelatin of jelly strength of 100 g. (Com. Example 8) and only a gelatin of jelly strength of 280 g. (Com. Example 9) to prepare photographic papers.
Comparison Example 10
[0067] The procedure of Example 1 was repeated except for replacing the amorphous silica with titanium dioxide (mean diameter: 2 µm, oil absorption: 40 cc./100 g.) to prepare a photographic paper.
Evaluation of Photographic Paper
1. In a photographic paper comprising a water-proof support which comprises a paper
sheet coated with a polyolefin resin on both surfaces thereof, and a photographic
emulsion layer provided on one surface of said support, the improvement in which another
surface of said support is provided with a printing-retaining layer of gelatin hardened
with a non-formaldehyde gelatin hardening agent, said printing-retaining layer dispersively
containing an amorphous inorganic pigment having a mean diameter of 0.1 - 10 µm and
an oil absorption capacity of not less than 100 cc./100 g. in an amount of 12 - 80
wt.% based on the amount of the gelatin and a crystalline inorganic pigment having
a mean diameter of 0.1 - 0.8 µm in an amount of 5 - 40 wt.% based on the amount of
the gelatin.
2. The photographic paper as claimed in claim 1, wherein the total amount of said
amorphous inorganic pigment and said crystalline inorganic pigment contained in the
printing-retaining layer is in the range of 25 - 80 wt.% based on the amount of the
gelatin.
3. The photographic paper as claimed in claim 1 or claim 2, wherein said amorphous
inorganic pigment is contained in the printing-retaining layer in an amount of 20
- 70 wt.% based on the amount of the gelatin.
4. The photographic paper as claimed in claim 1 or claim 2, wherein said crystalline
inorganic pigment is contained in the printing-retaining layer in an amount of 5 -
25 wt.% based on the amount of the gelatin.
5. The photographic paper as claimed in claim 1 or claim 2, wherein the ratio between
said amorphous inorganic pigment and said crystalline inorganic pigment contained
in the printing-retaining layer is in the range of 7/1 - 3/1, by weight.
6. The photographic paper as claimed in claim 1 or claim 2, wherein the mean diameter
of said amorphous inorganic pigment is in the range of 0.2 - 5 µm.
7. The photographic paper as claimed in claim 1 or claim 2, wherein the mean diameter
of said crystalline inorganic pigment is in the range of 0.2 - 5 µm.
8. The photographic paper as claimed in claim 1 or claim 2, wherein said amorphous
inorganic pigment is amorphous silica.
9. The photographic paper as claimed in claim 1 or claim 2, wherein said crystalline
inorganic pigment is crystalline silica.
10. The photographic paper as claimed in claim 1 or claim 2, wherein said non-formaldehyde
gelatin hardening agent is selected from the group consisting of those of active vinyl
type, active halogen type, epoxy type, methanesulfonic acid ester type, carbodiimide
type, isoxazole type, active ester type, isocyanate type and inorganic type.
11. The photographic paper as claimed in claim 1 or claim 2, wherein said gelatin
has a jelly strength in the range of 130 - 260 g.
12. In a photographic paper comprising a water-proof support which comprises a paper
sheet coated with a polyolefin resin on both surfaces thereof, and a photographic
emulsion layer provided on one surface of said support, the improvement in which another
surface of said support is provided with a printing-retaining layer of gelatin having
a jelly strength in the range of 130 -260 g. which is hardened with a non-formaldehyde
gelatin hardening agent, said printing-retaining layer dispersively containing an
inorganic pigment having a mean diameter of 0.1 - 10 µm and an oil absorption capacity
of not less than 100 cc./100 g. in an amount of 17 - 100 wt.% based on the amount
of the gelatin.
13. The photographic paper as claimed in claim 12, wherein said gelatin has a jelly
strength in the range of 150 - 210 g.
14. The photographic paper as claimed in claim 12 or claim 13, wherein said inorganic
pigment is contained in the printing-retaining layer in an amount of 30 - 80 wt.%
based on the amount of the gelatin.
15. The photographic paper as claimed in claim 12 or claim 13, wherein the mean diameter
of said inorganic pigment is in the range of 0.2 - 5 µm.
16. The photographic paper as claimed in claim 12 or claim 13, wherein said non-formaldehyde
gelatin hardening agent is selected from the group consisting of those of active vinyl
type, active halogen type, epoxy type, methanesulfonic acid ester type, carbodiimide
type, isoxazole type, active ester type, isocyanate type and inorganic type.