EP0697622A1 - Base paper for photographic supports - Google Patents

Abstract

Base paper for photographic base is made from a paper compsn. contg. hydrophobising size(s) and wt-proofing cationic resin(s), which also contains a starch (I) contg. alkylammonium gps. and opt. phosphate gps.. Also claimed is a method for making the paper.

Description

The invention relates to a base paper for photographic supports, which is formed from a paper pulp which contains at least one hydrophobizing sizing agent and at least one wet-strengthening cationic resin, and to a process for producing the base paper.

It is known to use paper coated on both sides with hydrophobic resin layers as a carrier material for wet-to-develop photographic layers. Such a carrier material consists of a base paper with polyolefin resin coatings applied to both surfaces, of which the coating initially lying on the photographic layers usually contains at least one light-reflecting pigment, such as TiO 2.

The polyolefin coating protects the paper surface against the ingress of water or aqueous photographic treatment liquids.

To prevent these liquids from penetrating the edges of the coated paper, the base paper is sized. Both reactive substances, for example alkyl ketene dimers, and non-reactive substances, for example higher fatty acids, are known as glues for photographic base papers. Reactive glue is usually used together with a cationic resin processed neutral, while non-reactive glue with acid addition of aluminum ions are processed. There is also a combination of these two sizing processes.

The hydrophobizing glues are added to the fiber suspension and deposited on the surface of the fibers by adding the auxiliary agents. Such an aid is in the case of acid sizing, for example an aluminum salt, in the case of neutral sizing, for example, a cationic polyamide-polyamine-epichlorohydrin resin, which is mainly used together with C₁₆ to C₁₈ alkyl ketene dimer. However, other cationic substances such as cationic polyacrylamides, cationized starches or polyethyleneimines are also suitable in certain cases for improving the retention and for fixing reactive sizing agents in the paper sheet.

Due to the addition of the glue to the surface of the pulp fibers, the bond between the fibers is weaker in a sized paper than in a non-sized paper. In order to improve the paper strength, further auxiliaries are added to the paper pulp. These include water-soluble resins such as polyvinyl alcohol, anionic polyacrylamide and various starch derivatives. DE-OS 32 10 621 describes, for example, the use of anionic polyacrylamide together with cationic starch and DE-OS 33 28 463 describes a combination of cationic resin with anionic starch phosphoric acid ester.

A disadvantage of hard sizing of the base paper is not only the loss of strength, but also that the use of flocculent additives adversely affected sheet formation. This is due to the fact that the addition of cationic substances not only retains the glue on the fiber surface, but also creates more flakes of fiber because the repulsive negative charges on the fibers are largely neutralized by the cationic substances and fiber-fiber bridging is facilitated.

The fiber flakes have different sizes and distributions in the paper sheet, depending on the materials used and mechanical engineering devices, and determine the homogeneity and surface quality of the base paper (formation).

The combined use of cationic and anionic water-soluble resins to reduce bath penetration at the cut edges has been e.g. described in DE-OS 32 10 621 and DE-PS 36 06 806.

In neutral sized papers, the combined use of anionic and cationic resins causes the formation to deteriorate.

Good paper formation is particularly important for photographic base papers, since there is a connection between the fiber distribution of the paper base and the so-called "mottle" of the photographic image developed later.

"Mottle" denotes fluctuations in the optical density (density) in the photographic image. The surface of the carrier material is decisive for this phenomenon. Uneven surfaces lead to flow phenomena in the layer, even with an absolutely even layer application, which become visible in the finished image as a "mottle". The unevenness of a paper is largely determined by the fiber structure of the pulp and by the formation of pulp flakes during sheet formation. This also has an effect on coated papers.

In addition to the formation deterioration mentioned above, the structural strength of the paper sheet often declines because isolated flakes of anionic and cationic resin are formed which are embedded in the paper structure without a strengthening effect.

To avoid flocculation problems, attempts have been made to add nonionic polymers, e.g. Add polyvinyl alcohol, starch. This leads to a certain improvement in sheet formation and surface quality; however, the retention of these substances is significantly poorer, which leads to contamination of the sewage system and deposits in the paper machine.

It is therefore an object of the present invention to provide a base paper for photographic supports which does not have the disadvantages described.

In addition, it is an object of the present invention to propose a method for producing a base paper, according to which the above-mentioned properties are improved and a better retention and thus clean circulation can be achieved.

The object is achieved in that the base paper is formed from a paper pulp which, in addition to at least one hydrophobizing sizing agent and at least one wet-strengthening resin, contains a starch containing alkylammonium groups or a starch containing alkylammonium groups and phosphate groups.

Reactive sizing agents such as dimerized alkylketenes, epoxidized fatty acid amides or fatty acid anhydrides as well as non-reactive sizing agents such as higher fatty acids and salts of higher fatty acids have proven to be suitable hydrophobizing sizing agents. A particularly preferred dimerized alkyl ketene consists of at least 50% behenyl ketene or another alkyl ketene with more than 18 carbon atoms in the alkyl radical. However, two or more hydrophobizing sizing agents can also be contained in the paper. Reactive sizing agents can be combined with non-reactive ones.

A cationic resin is any resin with cationic groups commonly used in papermaking as a wet strength agent. They are usually used for wet consolidation and for the retention of reactive sizing agents. However, they can be used both in combination with reactive and with non-reactive sizing agents. In a preferred embodiment, the cationic resin is an epichlorohydrin modified polyamine or polyamide amine resin. Other suitable resins include urea / formaldehyde resins, melamine / formaldehyde resins, polyethyleneimines and polyethyleneimine derivatives.

The starch contained as a further component in the paper pulp is an alkylammonium group or a starch containing alkylammonium and phosphate groups.

An amphoteric or cationic corn or potato starch is particularly suitable. The content of ammonium groups in the starch according to the invention is 0.9 to 2.5 mol%. The content of phosphate groups can be up to 0.3 mol%.

The amount of the starch according to the invention used in the paper pulp is preferably 0.5 to 2.0% by weight, based on cellulose (dry). However, an amount of 1 to 1.5% by weight is particularly preferred.

A colloidal silica, a colloidal aluminum-modified silica or a colloidal aluminum-modified silicate are particularly suitable as anionic inorganic particles.

The amount of anionic inorganic particles in the paper pulp is preferably up to 0.2% by weight, based on the dry cellulose fibers. In a particularly preferred embodiment of the invention, the anionic inorganic particles are used in an amount of 0.02 to 0.1% by weight.

The base papers according to the invention are produced in a known manner using a paper machine. In addition to cellulose fibers, the paper pulp can also contain synthetic fibers, mineral or organic fillers, white pigment, Contain dye or color pigment, optical brighteners, antioxidants and / or other additives customary in the production of photographic paper supports.
In the context of the method according to the invention, the various components can be added to the pulp suspension in different orders and at various locations known to the paper manufacturer.

In order to achieve optimal results, in a preferred embodiment of the invention the starch according to the invention is mixed into the fiber suspension in the order before the anionic inorganic particles. The anionic inorganic particles are preferably fed to the so-called thin material before the headbox.

The paper can also be surface sized, e.g. with polyvinyl alcohol, starch, gelatin and the like, and after finishing and smoothing is coated on both sides with synthetic resin in the usual way.

The synthetic resin coating can be carried out as an extrusion coating from the melt, as a dispersion coating, as a coating of radiation-curing mixtures or in another known manner. The resin-coated paper serves, if necessary also after the application of further layers and after application of an adhesion-improving pretreatment, as a support for any photographic layers.

The invention is explained in more detail in the examples below.

example 1

A mixture of 100% by weight hardwood sulfate pulp was ground at a consistency of 4% to a freeness of 35 ° SR. Sizing agents, starch according to the invention and other auxiliaries according to Table 1 were then added to the pulp suspension and an approximately 170 g / m 2 base paper was produced therefrom. The paper was surface-sized and smoothed in a known manner with an aqueous solution containing 3.33% by weight polyvinyl alcohol and 3.33% by weight CaCl₂. Table 1 Glue * sample 1a 1b 1c 1d 1e 1f Corn starch with alkyl ammonium groups 0.9 mol% - - - - 1.5 - 1.7 mol% 0.5 1.0 1.2 2.0 - - 2.5 mol% - - - - - 1.5 Polyamide / polyamine epichlorohydrin resin 0.7 0.7 0.7 0.7 0.7 0.7 Alkyl ketene dimer 0.5 0.5 0.5 0.5 0.5 0.5 Epoxy fatty acid amide 0.05 0.05 0.05 0.05 0.05 0.05 Whitener 0.05 0.05 0.05 0.05 0.05 0.05 * All quantities in this table are% by weight, based on the fiber

Example 2

Analogous to Example 1, base papers weighing 170 g / m 2 were produced with the substances listed in Table 2 and then analyzed. Table 2 Glue * sample 2a 2 B 2c Potato starch with 1.7 mol% ammonium groups and 0.2 mol% phosphate groups 1.50 1.50 1.50 Polyamide / polyamine epichlorohydrin resin 0.40 0.40 0.40 Alkyl ketene dimer 0.50 0.50 0.50 Epoxy. Fatty acid amide 0.05 0.05 0.05 anion. silicate 0.05 0.10 0.20 Whitener 0.05 0.05 0.05 * Quantities in% by weight, based on the fiber

Example 3

Sizing agents and starch according to the invention in accordance with Table 3 were added to a cellulose suspension composed of 50% by weight hardwood sulfate pulp and 50% by weight hardwood sulfite pulp, and base papers of approximately 190 g / m 2 were made therefrom. Table 3 Glue * sample 3a 3b 3c Corn starch with 1.7 mol% alkylammonium groups 0.9 0.6 0.3 Polyamide / polyamine epichlorohydrin resin 1.2 1.2 1.2 Alkyl ketene dimer 0.5 0.5 0.5 Epoxy. Fatty acid amide 0.05 0.05 0.05 Whitener 0.05 0.05 0.05 * Quantities in% by weight, based on the fiber

Comparative Example V1

The following substances were added to a cellulose suspension composed of 100% by weight hardwood sulfate pulp: Anionic starch (Emcoat KPS) 1.50% by weight Alkyl ketene dimer 0.50% by weight Polyamide / polyamine epichlorohydrin resin 0.70% by weight Epoxy. Fatty acid amide 0.05% by weight Whitener 0.05% by weight A 170 g / m² base paper was made from it.

Comparative example V2

The following substances were added to a cellulose suspension composed of 50% by weight hardwood sulfite pulp and 50% by weight hardwood sulfate pulp: Polyacrylamide 0.3% by weight Alkyl ketene dimer 0.5% by weight Polyamide / polyamine epichlorohydrin resin 1.2% by weight Epoxy. Fatty acid amide 0.05% by weight Whitener 0.05% by weight A 190 g / m² base paper was made from it.

Examination of the base papers produced according to the examples and comparative examples

One part of the paper samples produced was left uncoated and tested, another part was coated on both sides with polyethylene in a known manner and subjected to a test in this form. The following test methods were used for the evaluation:

Internal strength (structural strength)

The structural strength was determined in accordance with TAPPI RC 308 using a Scott Bond splitting strength tester (Internal Bond Impact Tester Model B). The figures in the following tables are mean values from 5 individual measurements.
The readings are expressed in 1/1000 feet x pounds (ft.lb/1000).

Developer Edge Penetration (KE)

The paper samples coated with polyethylene were immersed in the required sample size for 14 minutes in a commercially available color developer bath (T = 30 ° C.). After intermediate rinsing, treatment with a commercially available fixing solution and final rinsing, the samples were dried and the penetration depth (mm) of the developer solution was measured at the cut edge using a measuring magnifier. The zone of developer penetration can be seen as a brown discolored edge strip.

Stiffness

The stiffness values of the base papers were determined with the bending stiffness tester from Lorentzen & Wettre, according to standard SCAN-P 29.69. The measured values are given in mN.

formation

The formation is assessed in an internal test on the basis of comparative samples using a grading scale from 1 to 5, with grade 1 for a very uniform and grade 5 for a very "cloudy" appearance of the paper structure in transmitted light.

Retention

The retention (total retention,%) was determined according to the "Britt" dynamic drainage year method (DDJ method) developed by Paper Research Materials, Inc.

Other properties of the base paper, such as surface number, tear strength, adhesion of the polyethylene layers and photochemical properties, were also routinely tested. However, the results are within the known framework and were not used to evaluate the invention.

The test results are summarized in Table 4. The entirety of the properties tested should be used to evaluate the invention.

As can be seen from Table 4, it was possible to achieve a significant improvement in the formation and thereby surface quality while maintaining the required strengths and stiffnesses (see cf. V1 and Ex. 1-3).
An increase in the total retention and thereby a cleaner circulation can also be achieved with the sizing according to the invention.

Claims (13)

Base paper for photographic supports, which is formed from a paper pulp which contains at least one hydrophobizing sizing agent and at least one wet-strengthening cationic resin, characterized in that the paper pulp also contains a starch containing alkylammonium groups or a starch containing alkylammonium groups and phosphate groups contains. Base paper according to Claim 1, characterized in that the content of ammonium groups in the starch is 0.9 to 2.5 mol%. Base paper according to claim 1, characterized in that the content of phosphate groups in the starch is up to 0.3 mol%. Base paper according to claims 1 to 3, characterized in that the paper pulp additionally contains anionic inorganic particles. The base paper according to claim 4, characterized in that the anionic inorganic particles are selected from colloidal silicas, colloidal aluminum-modified silicas or colloidal aluminum-modified silicates. Base paper according to Claims 1 to 5, characterized in that the amount of starch is 0.5 to 2% by weight, but in particular 1 to 1.5% by weight, based on the cellulose fiber content. Base paper according to Claims 4 to 6, characterized in that the amount of the anionic inorganic particles is up to 0.2% by weight, but in particular 0.02 to 0.1% by weight, based on the cellulose fiber content. The base paper of claim 1 to 7, characterized in that the surface of the core paper is additionally coated with a dissolved or dispersed in water binder. Process for the production of a base paper for photographic supports, characterized in that a pulp suspension consisting of cellulose and optionally further additives comprises at least one hydrophobizing sizing agent, at least one wet-strengthening cationic resin and at least one starch containing alkylammonium groups or an alkylammonium group and phosphate groups containing starch are added and a paper is made from this suspension. Process according to Claim 9, characterized in that anionic inorganic particles are additionally added to the paper stock suspension. A method according to claim 10, characterized in that the anionic inorganic particles is a colloidal silica, a colloidal aluminum-modified silica or a colloidal aluminum-modified silicate. The method of claim 10 and 11, characterized in that the anionic inorganic particles are always added to the thin stock and just before the headbox. The method of claim 9 to 12, characterized in that the surface of the paper is additionally coated with a dissolved or dispersed in water binder.