EP0002762B1 - Method of hardening multicolour photographic silver-halide emulsion layers - Google Patents

Description

It is known to harden protein layers, especially photographic gelatin layers. This considerably increases the stability of these layers against mechanical injuries during processing.

From DT-PS 872 153 triaryl formal (1,3,5-triacrylhexahydro-1,3,5-triazine) is known as a hardening agent for gelatin, which has proven itself for the hardening of color coupler-containing photographic gelatin layers, since it contains the color components and other emulsion additives in contrast to many other hardening agents, e.g. Formalin, not responding. The main disadvantage of triacyl formal hardening is the slow reaction rate of the hardening reaction with gelatin. The hardening reaction can be accelerated by a higher dosage of the hardening agent.

It is also known that the simultaneous use of polyhydric alcohols and certain hardening agents, including triacryl formal, can increase the hardening speed of gelatin layers.

From DT-OS 2 354 336 it is known to incorporate a hardening agent from the group of the aldehydes, triazine compounds or the compounds containing active vinyl groups together with a polyhydric alcohol into photographic materials and thus to determine the effect of the hardening agent on a specific layer of the material. In this way, individual layers of a photographic multilayer material can be selectively hardened. A layer structure treated in this way can then be easily separated at the interface between the hardened and non-hardened layer; a way of working that e.g. is used in the silver salt diffusion process.

This method of selective layer hardening is unsuitable for the hardening of color photographic multilayer materials, which should be machinable and which have to go through a series of baths, possibly at elevated bath temperatures, whose individual layers must have perfect adhesion.

Furthermore, a silver halide photographic material is described in DT-OS 2 359 345, the physical properties of which contain glyoxal, a water-soluble salt of 2,4-dichloro-6-hydroxy-5-triazine and a polyhydric alcohol with at least 2 hydroxyl groups in one Silver halide emulsion layer or an auxiliary layer can be improved.

Finally, it is known from GB-PS 1 111 930 to improve the physical and photographic properties of photographic gelatin-containing silver halide emulsion layers by incorporating a trihydric alcohol which contains three methylol groups bonded to a carbon atom, e.g. 1,1,1-trimethylol propane.

Chemical Abstracts 65 (1966), Unit 19505 c, describes the hardening of photographic emulsions with a triazine hardener containing acryloyl groups, optionally in the presence of polyethylene glycol, the pH of the emulsion being equal to that of Na _Z CO ₃ and NaH CO 0 ₃ existing solution is buffered. The sensitometric problems which arise when curing multilayer photographic materials which contain paper laminated on both sides with a polyolefin layer, as described below, cannot be solved with this method.

When observing the hardening behavior of gelatin layers it should be noted that the hardening rate is generally dependent on the pH and on the relative humidity to which the gelatin layer is exposed during storage. Higher relative humidities (over 60% RH) accelerate the hardening reaction significantly. However, photographic layers cannot be handled technically in this moisture range, since the gelatin layers become sticky and the sensitometric properties of the silver halide emulsion layers are adversely affected, particularly with regard to their sensitivity.

Recently, polyolefin-coated papers have gained considerable importance as a base for photographic supervisory materials. For color photographic papers in particular, polyolefin-coated papers are used almost exclusively as layer supports because of the advantages that these documents offer during processing.

When polyolefin-coated papers are used as the substrate, the dependency of the curing rate of triacryl formal as hardener-containing silver halide emulsion layers on the moisture content of the layer is of particular importance. At the same water vapor partial pressure, the cellulose inner paper contains about nine times the amount of water compared to the water content of the silver halide emulsion layer. Since the polyolefin layer between the photographic gelatin layer and the cellulose felt is permeable to water vapor, the equilibrium moisture content of the inner paper determines the relative humidity of the gelatin layer during storage. As already mentioned, the hardening speed depends on the equilibrium moisture, and therefore with a double-sided polyolefin-coated paper base (PE base), which is in equilibrium with 40% RH at 23 ° C, a higher amount of hardening agent triacrylformal, based on gelatin, can be applied to approximately equal curing speeds achieve than is necessary with a PE underlay whose inner paper is in equilibrium with 60% RH.

Maintaining the same moisture values in the inner paper is difficult in the technical manufacturing process and is only possible with certain fluctuations over the web length and width. The amount of hardening agent can only be adjusted to an average moisture value when the layers are applied to such webs, and the layer locations of the web which deviate from this value will also differ in the degree of hardening. The parts of the coated web with the higher moisture content of the inner paper show the stronger curing and vice versa. The sensitometric values, in particular the sensitivity and gradation of the yellow coupler-containing layer of a color photographic material, show a clear dependence on the degree of hardening and differences in hardening lead to fluctuations in these sensitometric values.

The invention is therefore based on the object of eliminating the curing fluctuations caused by different water contents of the inner paper of a paper base coated on both sides with polyolefin of color photographic recording materials.

The invention relates to a method for curing light-sensitive, color component-containing silver halide gelatin emulsion layers and non-sensitive auxiliary gelatin layers of a color photographic multilayer recording material which, as a layer support, contains paper provided on both sides with a polyolefin layer and which has been subjected to a corona discharge, with a triazine compound, the process thereby is characterized in that the casting solutions of the layers, based on gelatin, 0.4 to 0.8 wt .-% 1,3,5-triacrylhexahydro-1,3,5-triazine as a hardening agent and 2 to 20 times the amount by weight a polyhydric aliphatic alcohol having 3 to 10 carbon atoms, based on the hardening agent, are added and the casting solutions are then applied to the corona-irradiated surface of the support.

The method of the invention enables the sensitometric fluctuations in gradation and sensitivity caused by hardening fluctuations in color photographic papers on PE substrates, the inner paper of which has equilibrium moisture contents of 30-60% RH. to avoid.

Under the conditions of the method according to the invention, the amount of triacryl formal can surprisingly be kept constant, regardless of the moisture content of the inner paper, which is an essential prerequisite for eliminating the sensitometric fluctuations. In spite of the relatively small amounts of triacrylic formal, sufficient curing speeds are achieved regardless of the moisture content of the inner paper. It has proven useful to use the polyhydric alcohol in about 2 to 20 times the amount by weight, based on the hardening agent.

Examples of polyhydric alcohols which are suitable for the process of the invention are glycerol, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, 1,1,1-trimethylol isobutane, 1,1,1-trimethylolhexane , of which glycerol and trimethylolpropane are preferred.

The order of addition to the layers in a multi-layer color photographic material has no influence. The polyhydric alcohol can be distributed evenly over the casting solutions of all layers of the multilayer material, or it can be added to a single, for example the last, casting solution in the dosage corresponding to the total content of hardening agent. The polyhydric alcohol is apparently able to exert an accelerating effect on the course of the hardening reaction between triacryl formal and gelatin and thereby eliminate the dependence of the hardening rate on the water content in the gelatin layer.

The amounts of triacryl formal used for curing color photographic silver halide gelatin emulsion layers are generally 0.4 to 0.8% by weight, based on the gelatin weight of the casting solution, and also apply to the process of the invention.

The inner paper of the support with the polyolefin surface is one of the types customary in the photographic industry, which are expediently sized so that the adhesion of the polyolefin layers is not adversely affected and that they tolerate the treatments to which photographic paper is subjected. The paper must inherently have good strength and dimensional stability and have a calendered surface.

Preferred polyolefins for the double-sided coating of the base paper referred to as inner paper are polypropylene, polyethylene or mixtures of both polymers, which are extruded onto the two sides of the base paper in a known manner.

In order to improve the adhesion of the aqueous emulsion layers, the surface of the polyolefin film intended for the accommodation of the silver halide emulsion layers is hydrophilized by a corona discharge treatment by likewise known methods (e.g. DT-OS 22 63 863). The treatment can be carried out at a voltage of approximately 72,000 to 200,000 volts and a web speed of 50 to 75 m / min. 450 kH can serve as a reference point for the frequency.

The color photographic multilayer materials can contain the usual color couplers, which are usually incorporated into the silver halide layers. For example, the red-sensitive layer contains a non-diffusing color coupler for producing the blue-green partial color image, generally a coupler of the phenol or a-naphthol type. The green-sensitive layer contains at least one non-diffusing color coupler for producing the purple partial color image, color couplers of the 5-pyrazolone or indazolone type usually being used. Finally, the blue-sensitive layer unit contains at least one non-diffusing color coupler for producing the yellow partial color image, usually a color coupler with an open-chain ketomethylene grouping. Color couplers of this type are known in large numbers and are described in a large number of patents. Examples include the publication "Farbkuppler" by W. Pelz in "Mitteilungen aus der Forschungslaboratorien der Agfa, Leverkusen / München", Volume 111 (1961) and K. VENKATARAMAN in "The Chemistry of Synthetic Dyes", Vol. 4, 341 to 387 Academic Press, 1971. Of course, so-called 2-equivalent or 4-equivalent couplers as well as white couplers can also be used as non-diffusing color couplers.

In addition, the layers of the photographic materials can contain the additives customary for such layers, such as natural or synthetic binders, chemical or optical sensitizers such as those e.g. in Belgian patents 493 464, 568 687, 547 323, the article by R. Koslowsky in Z.Wiss.Phot. 46, 65-72, (1951), Belgian patent 537 278, British patent 727 982 or in the work of F.M. Hamer, "The Cyanine Dyes and related Compounds", (1964). The usual stabilizers can also be included.

Multilayer color photographic materials as may be made by the process of the invention can be machined. This is to be understood in such a way that the gelatin layer has achieved such mechanical strength through the crosslinking that neither the mechanical stress on the material during transport over rollers nor bath temperatures above 30 ° C. lead to layer damage in the material.

The layer melting points given in the following examples were determined according to the following procedure: A sample is immersed in water at room temperature and pH = 5. The temperature of the water is then heated to the boiling point at a rate of 1 ° per minute. The melting point is defined by the water temperature at which the gelatin layer peels off. For samples that reach the boiling point, the cooking time is determined until the layer comes off.

Unless otherwise described, percentages in the examples mean percentages by weight.

example 1 Layer structure A1

• 1. Eine für rotes Licht sensibilisierte, einen Blaugrünkuppler enthaltende Chlorbromsilber-Gelatineemulsion mit pH=6,5, die pro kg Gießlösung 0,1 Mol Silberhalogenid, 8 g Kuppler und 54 g Gelatine und 0,35 g Triacrylformal enthielt, wurde mit 40 g Naßauftrag pro m² vergossen und getrocknet. Der Blaugrünkuppler hat die Formel
  
• 2. Über dieser Schicht wurde eine Gelatinetrennschicht angeordnet, indem 35 g einer 3%igen wäßrigen Gelatinelösung (pH=6,5) die pro Liter 0,21 g Triacrylformal enthielt, aufgetragen und getrocknet wurden.
• 3. Nun wurde eine für grünes Licht sensibilisierte, einen Purpurkuppler enthaltende Chlorbromsilbergelatineemulsion, entsprechend der Mengenangabe von 1., aufgetragen und getrocknet. Der Purpurkuppler hat die Formel
  
• 4. als nächste Schicht folgte ein Guß, entsprechend der unter 2. beschriebene Schicht.
• 5. Hierauf wurde eine für blaues Licht empfindliche, einen Gelbkuppler enthaltende Bromsilberemulsion aufgetragen. Dabei wurden wiederum die Mengenverhältnisse wie bei 1. eingehalten. Der
  
• 6. Als oberste Schicht wurde wiederum eine Schicht entsprechend 2. aufgetragen.

The following layers were applied to a substrate made of corona-irradiated polyethylene-coated paper, the inner paper (170 g / m ^z ) is in equilibrium with 60% relative humidity at 23 ° C and the polyethylene layers are 35 / u thick:

• 1. A chlorobromosilver gelatin emulsion, pH = 6.5, sensitized to red light and containing a cyan coupler and containing 0.1 mol of silver halide, 8 g of coupler and 54 g of gelatin and 0.35 g of triacryl formalal per kg of casting solution, was mixed with 40 g Pour wet application per m ² and dry. The cyan coupler has the formula
  
• 2. A gelatin separation layer was placed over this layer by applying 35 g of a 3% aqueous gelatin solution (pH = 6.5) containing 0.21 g of triacryl formal per liter and drying it.
• 3. A chlorobromosilver gelatin emulsion, sensitized to green light and containing a purple coupler, was then applied and dried in accordance with the quantity given in 1. The purple coupler has the formula
  
• 4. The next layer was a cast, corresponding to the layer described under 2.
• 5. A bromine silver emulsion sensitive to blue light and containing a yellow coupler was then applied. The quantitative ratios as in 1. were again observed. The
  
• 6. A layer corresponding to 2. was again applied as the top layer.

At the end of the drying process, the cast was heated to 60% RH for 4 minutes. Air-conditioned at 23 ° C and packed moisture-proof.

Layer structure B1

A layer structure analogous to that of A1 was made on polyethylene-coated paper, the inner paper of which was 50% RH. was in equilibrium at 23 ° C.

Layer structure C1

A layer structure similar to that of A1 was made on polyethylene-coated paper, the inner paper of which was 35% RH. was in equilibrium at 23 ° C.

Layer structure D1

A layer structure analogous to A1 was produced on a cellulose acetate film filled with TiO ₂ pigment.

Layer structure E1

A layer structure analogous to that of A1 was produced with TiO ₂ pigmented polyethylene terephthalate backing.

From samples A1 to E1, samples were cut, stored in a light-tight and moisture-tight manner at room temperature, and the hardening state was determined at regular intervals after the coating by determining the water temperature at which the gelatin layers detached. The results are shown in the table below:

While samples A1, D1, and E1 show the desired increase in hardening and can be processed by machine from 30 days at a developer temperature of 35 °, the hardening of samples B1 and C1 is inadequate and unusable for machine processing even after 70 days.

Example 2

In a further row A2 to E2, a layer structure was produced in the manner described there on the same documents which were also used for A1 to E1, but 0.95% hardening agent triacryl formal was added based on gelatin.

The curing results are shown in the following table.

Due to the higher amount of hardening agent e) sample B2 now achieves the mechanical strength required for machine processing without impairing the sensitometric values. samples A2, D2, and E2, on the other hand, harden too much. Under these conditions, the swelling in the developer was already too low after 70 days of storage, and the sensitivity e.g. the blue-sensitive layer decreased by 0.2 Ig lt units with a simultaneous loss of gradation of 25%. Sample C2 was still not suitable for machine processing.

Example 3

In a third row A3-E3, the same substrates that were used for A1 to E1 were provided with the same layers, but the amount of triacryl formal was increased to 1.25% based on gelatin.

The curing results are shown in the following table.

After 40 days, the material of sample C3 now also achieved the mechanical strength required for machine processing at an elevated processing temperature. Samples A3, D3 and E3 showed such low swelling values with these hardener amounts that the blue sensitivity is 0.3 Ig It units less than for A1, D1 and E1 and the gradation was 40% lower than the target value.

From the results it can be seen that colored papers, the paper base of which is made waterproof on both sides with water vapor-permeable polyolefin layers, give unsatisfactory mechanical and sensitometric results when cured with triacryl formal due to technically unavoidable fluctuations in moisture.

Example 4

A layer structure A4 to E4 with the bases and casting solutions from A1 ― E1 was produced. All casting solutions, based on the amount of hardener, were added 5 times the amount of glycerin. The melting points obtained during the storage of these tests are summarized in the following table.

The hardening differences that occurred in the A1-E1 series between the PE substrates A1, B1 and C1 have practically disappeared, and the melting points rise more quickly.

All samples achieve the mechanical strength required for machine processing. The sensitometric values for all specimens are also mutually uniform in terms of sensitivity and gradation as well as in corresponding target values.

Example 5

The casting solutions described in Example 1 were poured onto the supports A1 to E1, but trimethylolpropane was added to each casting solution, namely seven times the amount, based on the curing agent. The melting points of the samples are summarized in the following table.

In this series too, all samples, irrespective of the moisture content of the inner paper of the PE backing, achieve the mechanical strength required for machine processing with the same small amount of hardening agent and sensitometric properties that are in accordance with the target value.

Claims (2)

1. A process for hardening, by means of a triazine compound, light sensitive silver halide gelatin emulsion layers which contain colour components and light insensitive auxiliary gelatin layers of a colour photographic multi-layered recording material which contains, as substrate layer, a paper which is laminated with a layer of polyolefin on both sides and which has been subjected to corona discharge, characterised in that from 0.4 to 0.8% by weight, based on gelatin, of 1,3,5-triacrylohexadhydro-1,3,5-triazine as hardener, and 2 to 20 times this quantity by weight of a polyhydric aliphatic alcohol with from 3 to 10 carbon atoms, based on the quantity of hardener are added to the casting solutions for the layers and the casting solutions are then applied to the corona irradiated surface of the substrate layer.

2. A process according to claim 1, characterised in that the polyhydric alcohol is glycerol or 1,1,1-trimethylol propane.