DE2262478A1 - PAPER FOR ELECTROSTATIC IMAGE GENERATION AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Description

Electrostatic imaging paper and method for making the same

The invention relates to an electrostatic image recording paper, which consists of an electrically conductive paper base "which is on one side with a contiguous dielectric coating is coated, as well as a method for producing such a paper.

Such paper is used for electrostatic imaging is used, whereby an electrical charge pattern, e.g. a stylus, applied to the dielectric coating and then with the help of a so-called toner, which is either as dry powder or as a powder dispersion in a non-aqueous liquid is made visible. The visible pattern is then made permanent by fixing

Various methods of making such a paper are already known, and the dielectric sheet becomes common by extrusion of a polymer layer onto an electrically conductive paper base or by coating

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ten an electrically conductive paper base with a solution a polymer prepared in a non-aqueous solvent.

It is also known to "coat the dielectric covering" an electrically conductive paper base with an aqueous solution or with an aqueous dispersion (e.g. a Latex) of the polymer. The application of the coating from aqueous solution or dispersion is because of the low Cost and simplicity preferred; have the known methods of coating from aqueous solution or dispersion but the disadvantage that the paper produced in this way shows a less favorable behavior in use as paper, the covering of which is produced in the usual way by extrusion or by coating from non-aqueous solution has been.

A dielectric covering is required to be preferably paper-based with conventional coating equipment can be applied in the form of a smooth, cohesive film, and the dielectric properties of the covering should be independent of the humidity of the environment, i.e. the covering should be resistant to Be water vapor. Furthermore, the covering should be at all temperatures that can be expected during use, be non-sticky and non-yellowing and when used it is said to produce an intense, sharp image that does not have any background discolouration caused by excessive amount of toner being absorbed during processing are.

According to one feature, the subject matter of the invention is a paper for electrostatic imaging, consisting of an electrically conductive paper base on one side has a cohesive dielectric covering, which is characterized in that the dielectric covering consists of

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a polymer "consists of an aqueous dispersion has been deposited with a minimum film formation temperature of not more than 30 ° C.

The dielectric coating preferably contains an inorganic pigment in amounts of up to about 20 percent by weight, based on on the dry polymer.

The addition of an inorganic pigment, such as titanium dioxide, barium sulfate, silicon dioxide, clay or zinc oxide, is reduced the stickiness of the dielectric coating.

According to another feature, the subject matter of the invention is a / Process for the production of a paper for electrostatic imaging which consists of an electrically conductive paper base ", which has a continuous dielectric coating on one side. The method consists of in that one is on one side of an electrically conductive paper base an aqueous Polyroerisat & ispersion with a Minimum film formation temperature of not more than 30 ° C and by drying the coated paper base a coherent polymer coating produced on the same.

An advantage offered by the use of a polymer made from an aqueous dispersion with a minimum film-forming temperature of 30 ° C or less is due to the fact that the migration of the in the paper base conductivity agent contained in the dielectric Coating when applying the latter is limited to a minimum and therefore the specific electrical resistance of the dielectric Surface is not affected too much.

The important properties that the dielectric covering has are meant to be smooth and coherent. The smoothness is desirable so that the coating does not take up too much toner during processing, and the continuity of the

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Covering, e.g. the absence of sand holes, is desirable, about the discharge of an applied electrical charge pattern to prevent these interruptions to the electrically conductive paper base, and also, to prevent liquid toner from penetrating through these interruptions and discoloring the paper base.

The method according to the invention can therefore comprise, as a further method step, the measure that after the Drying of the coating obtained from the first aqueous dispersion, a second polymer dispersion is applied to it.

If the paper is to be used in a printing machine that makes use of a dry toner, the paper has to be used preferably a second coating that is non-sticky so that less toner is picked up by the background.

The second aqueous dispersion is used for this purpose preferably a minimum film forming temperature of more than 30 ° C, e.g. from 60 to 120 ° C.

According to the invention, the aqueous dispersion or each of the both aqueous dispersions contain a pigment.

Various im Commercially available polymers whose selection for the particular application is not so much based on the electrical ones Properties that are generally similar, such as the required physical properties and the Direct costs. Typical polymers which can be used according to the invention are the polyolefins and the substituted polyolefins as well as the polycondensation products such as polyester and phenolic resins. When the imaging paper is very If high humidity is to be used, the polymer should, if possible, not be ionized or ionizable

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Contain groups and have the lowest possible affinity for Have water.

Various commercially available pigments can also be used in the context of the invention.

About the settling of the pigment in the aqueous polymer dispersion To avoid this, a pigment dispersant may be required. "Most known pigment dispersants but are ionic and would therefore preserve the dielectric Impair the covering against moisture. It has been found that ammonium salts, e.g. the ammonium salt of a Polycarboxylic acid, suitable as a pigment dispersant, because when such salts are heated, the ammonia is driven off and a non-ionic dispersant remains in the dielectric coating.

example 1

A dispersion for applying a dielectric coating is prepared according to the following procedure:

Styrene-acrylic polymer dispersion with a minimum film-forming temperature of 27 ° C ("Vinacryl 7170" from Vinyl Products Ltd.) - 154 kg

Silica pigment with a high specific surface area ("Gasil 16" from J. Grosfield &

Sons Ltd.). * 1.5.6 kg

Antifoam agents ("lOamaster B" der - Nopeο Hess Ltd.) 750 ml

Water . - 30 kg

The silica is slurried in 26.4 kg of water and the slurry is then added to the remaining ingredients. The aqueous dispersion is in a dispersing device

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direction (Hydrisperser).

The mixture is on an electrically conductive paper base with the help of an air knife coating machine in densities, corresponding to covering densities between 5 and 10 g / m 2, and the coatings are dried at 100 ° C.

Example 2

A first aqueous dispersion is prepared according to the following procedure:

Styrene-acrylic polymer dispersion with a Minimum film formation temperature of 27 G

("Vinacryl 7170"), as in Example 1 40 kg

Silica pigment ("Gasil 16"),

as in example 1 5 kg

Antifoam agents ("Nopco 8034" der

Nopco Hess Ltd.) 60 ml

Pigment dispersant in the form of an ammonium salt of a polycarboxylic acid ("Dispex A 40" from Allied Colloids Manufacturing Co. Ltd.) 67 ml

Water 93 kg

A second aqueous dispersion is made according to the following procedure manufactured:

Styrene-acrylic polymer dispersion

("Vinacryl '7170") as in Example 1 13.6 kg

Polystyrene dispersion with a minimum film formation temperature between 100 and 120 ° C ("Vinamul 7700" from Vinyl Products Ltd.) 27.2 kg

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Silica pigment ("Gasil 16"),

as in example 1 '3 - 6 kg

Antifoam agents ("Nopco 8034"),

as in the first mixture 60 ml

Pigment dispersant ("Dispex A40"),

as in the first mixture ■ 48 ml

Water . 15.6 kg

The first mixture is made on an electrically conductive paper base according to example, 1 in one density, accordingly

a covering density of 7 g / m 2, applied and the covering dried at 100.degree.

The second mixture is made according to the procedure of Example T. on the dried first covering in a density corresponding to

accordingly a covering density of 5 g / m 2, applied and dried at 120 ° C.

Example 3

In this example, as in Example 2, two coatings are applied; however, the polymer dispersions have both a minimum film-forming temperature for the first as well as for the second coating below 30 ° C. The first aqueous coating dispersion is prepared according to the following instructions:

Acrylic polymer dispersion with a minimum film formation temperature from 20 ° C ("Acronal 290D" from Badische .Anilin- & Soda-I'abrik AG) 50 kg;

Barium sulfate 4.39 kg

Anti-foaming agent ("Hopco 8034"),

as in example 1 75 ml

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42222 ρ

Pigment dispersant ("Dispex A40 ^H ) i

as in example 2 55 ml

Water 19 * 2 kg

The second aqueous coating dispersion is produced according to the following procedure: _φ ■

Styrene-acrylic polymer dispersion with a minimum film melting temperature of 27 ° C ("Vinacryl 7170"), as in

Example 1 24 kg

Kaolin 12 kg

Pigment dispersant ("Dispex A40"),

as in Example 2 150 ml

Antifoam agents ("Nopco 8034") »

as in example 1 36 ml

Water 24 kg

The first mixture is, as in Examples 1 and 2, on an electrically conductive paper base in a density

corresponding to a covering density of 3 g / m 2, applied and the coating "dried at 100 ° C.

The second mixture is, as described in Examples 1 and 2, on the dried first covering in a density corresponding to a coating density of 3 g / ra, applied and at 120 ° C dried.

The electrostatic image recording paper obtained in the above examples is tested by comparing its behavior with the behavior of commercially available solvent-coated examined and found to be satisfactory.

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Claims (5)

Wiggins Teape Research & Development Limited 42,222 claims 1. Paper for electrostatic imaging, 'consisting of an electrically conductive paper base, which is on a Side with one; coherent dielectric coating "coated is, characterized in that the dielectric coating consists of a polymer "which consists of a aqueous dispersion with a minimum film-forming temperature of 30 ° C or "less has been deposited. 2. Paper for electrostatic imaging according to claim 1 :, characterized in that the dielectric coating also contains an inorganic pigment in amounts of up to about 20 percent by weight, based on the dry polymer. · 3. A process for the production of paper for electrostatic imaging according to claim 1, characterized in that that on an electrically conductive paper base on one side an aqueous polymer dispersion with a Minimum film formation temperature of 30 ° C or less and by drying the coated paper base a coherent polymer coating produced on the same. 4. The method according to claim 3, characterized in that after drying the aqueous dispersion layer on the dried covering, a second aqueous polymer satdispersion applies. ■ " - 9. 309828/0756 42222 5. The method according to claim 4, characterized in that a second aqueous dispersion is applied, its minimum film melting temperature is above 30 ° C. - 10 - 309828/0756