CS231872B1 - Covering agent for typescript retouching - Google Patents

Description

(54) Typewriter retouching cover

BACKGROUND OF THE INVENTION The present invention relates to a liquid composition consisting of chemical individuals which serves as a cover for retouching / correcting / typing or handwriting. drawings on paper or other white backing.

The composition consists of a fine dispersion of titanium dioxide as a white pigment of high opacity, in an organic rapidly evaporating polar ketone type solvent with the addition of water and a dissolved organic film-forming polymeric cellulose-type polymeric substance; it further comprises an alkaline phosphate dispersing agent that dissolves in the aqueous phase present and strongly promotes pigment dispersion and dispersion stability. In use, the covering agent dries quickly to form a smooth elastic film on the substrate, allowing an almost indistinguishable repair. The dispersion is durable and the composition can be diluted with a solvent at any time without sacrificing its quality.

The invention makes it possible to prepare a composition with properties corresponding to the imported preparations using available chemicals used in the paint industry.

The present invention relates to a cover means intended for rapid retouching of machine and handwriting, respectively. drawings on paper or other surface. In office, administrative and drawing work, there is often a need for retouching handwritten or typed text, or drawings and drawings in such a way that the wrong text or pattern is obscured and can be typed or replaced. draw, text or shape new.

Retouching papers coated with a covering pigment on one side are used for typing; the paper is placed with the pigmented side on the wrong text, which is then overwritten with the same / so-called. misspelling / lettering, while the paper releases the release pigment.

The disadvantage of this procedure is that in principle it is only possible to correct text written on a typewriter before the paper has been removed from the machine. When correcting multiple blanks, retouching is made more difficult by the fact that when correcting an error in the original, a hit with a mistaken letter on the retouching paper is transmitted to other copies and there the bold letter becomes even more accentuated, making it difficult to correct the copy.

To eliminate both machine and handwriting errors, ev. In the drawings, a method is also used in which the white pigment can be applied in the form of a slurry with a brush to the repaired area. After the liquid has evaporated, a pigment layer remains on the retouched area, which covers the erroneous text.

However, this layer must be sufficiently coherent to be able to write new text on it. In practice, the rate at which this layer is formed is of great importance and will become coherent to be repaired.

Each coating agent used in the form of a suspension, which is applied to a substrate, generally paper, must meet the following requirements:

and / after the application, completely cover the repaired area so as not to show the wrong characters;

b) create a continuous elastic layer at the repaired place in the shortest possible time, firmly adhering to the substrate and well receiving the color of the tape when correcting the typeface; ink, ink or lead in correcting handwriting or drawing;

o / have a consistency such that it can be easily applied by conventional means, most often with a brush to the repaired area.

Covering of the repaired site is achieved by using a pigment of high opacity, most often titanium white, of the anatase or rutile type, respectively. of another pigment of the same color as the repaired pad.

In order for the coating composition to form a continuous, mechanically resistant layer of desired properties, the pigment used must be incorporated into a carrier film which is formed on the substrate by evaporating the binder solution in which the pigment is dispersed.

The amount of binder sufficient to bond the pigment particles must be kept to a minimum, since only the pigment has a hiding effect, whereas the binder itself does not cover. An important requirement is that the creation of a mechanically resistant cover layer takes as little time as possible, so that the corrected text can be written as soon as possible. to correct the drawing.

This can only be achieved if the rate of total evaporation of the solvent in which the pigment is dispersed and the binder is dissolved is as high as possible. For pure solvents (which do not contain any solute), the rate of evaporation is expressed by so-called relative evaporation.

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The term relative evaporation is often used in paint technology where the ratio between the time required to evaporate a certain amount of the solvent to be investigated and the time to evaporate the same volume of reference liquid, which is a diethylether for volatile substances.

Solvents where the relative evaporation does not exceed 8 are referred to as readily evaporative. This quantity does not fully reflect the rate of evaporation in a complex system such as a coating composition where, in addition to the solvent in which the binder is dissolved, the pigment or the solvent is dispersed. other ingredients are present.

The pigment itself does not greatly affect the evaporation rate, but it could be substantially reduced by the binder if it precipitated on the surface of the evaporating liquid and thereby formed a blank, poorly permeable solvent vapor.

Therefore, it is necessary that the binder be used only in the amount necessary to form, together with the pigment, a covering film of the desired properties.

In preparing the coating composition to be suitable for mechanical application to the repair site, which is generally carried out with a brush, it is particularly necessary to limit the natural tendency of the pigment dispersion to sediment due to the difference in specific gravity of the pigment and the dispersing medium.

This tendency is particularly supported by the fact that the dispersed pigment particles are very easily agglomerated in the dispersing medium and thus their sedimentation is substantially accelerated. The most effective means of preventing particles of inorganic pigments from agglomerating is to impart an electric charge to them, which is counterbalanced by the opposite charge of the ions of the liquid medium.

The particles of the same charge then repel each other under the influence of electrostatic forces and thus prevent agglomeration. These repulsive forces will be retained even if the particles still sediment after prolonged standing; they then cause the sediment to be non-compact and easily dispersed by shaking or other mechanical intervention.

Most of the coating compositions used so far are essentially dispersions of pigment (titanium dioxide) in chlorinated hydrocarbons, especially in 1-, -1-, 1-trichloroethane.

Stabilization of the dispersion, which is necessary for their practical use, must be achieved by other means, most often by the addition of a protective colloid. Although some of these top coatings have proven to work in practice, they have some disadvantages.

Like all organic chlorinated derivatives, are they harmful to health, especially since inhaling them can cause euphoria and can become addictive poison? another disadvantage is that they are relatively expensive and fairly difficult to access.

Polar solvents, which are less harmful to hygiene, much cheaper and more affordable, have also been tested as a dispersion medium; however, it is necessary to obtain a pigment dispersion sufficiently stable for practical use.

The essence of the coating composition according to the invention consists in the preparation of a fine dispersion of titanium dioxide as a white pigment of high opacity in an organic, rapidly evaporating, water-containing ketone-type polar solvent in which an organic cellulose ester type film-forming polymeric substance and an alkaline type dispersant are dissolved. phosphate.

The concentration of the titanium dioxide of the anatase and, preferably, rutile type in the coating composition must be so high that the necessary covering of the text to be corrected is achieved by using a thin film of covering film, the composition being sufficiently fluid.

Satisfactory coverage is achieved with a composition containing at least 25% by weight. Titanium dioxide »with a content of more than 50% by weight the product is already very low in fluidity and is therefore difficult to apply.

The preferred concentration of titanium white in the composition is 30 to 40% by weight. The liquid phase of the composition is based on a ketone type polar organic solvent having a relative permittivity of at least 10 and a relative evaporation of at most 8, which is at least partially miscible with water.

Small amounts of water, up to 5% by weight of the solvent, are added to the solvent, or are already present in the moisture form, to dissolve the inorganic alkaline phosphate dispersant while not appreciably reducing the solubility of the cellulose ester type film-forming polymer.

The organic solvent of the ketone type, preferably butanone, is used in an amount of 43-72% by weight, preferably 55-65% by weight. of the total weight of the coating composition. In order to form a continuous coating layer on the repair text, an organic film-forming polymer of the type of oololose esters well soluble in the polar solvent used, preferably cellulose acetobutyrate, is used as the binder.

The amount of organic polymer sufficient to combine the pigment particles to form a continuous cover film is 20 to 30% by volume of the total cover film volume.

This represents a concentration of organic polymer in the coating composition of 3 to 6% by weight. preferably 4 to 5 Ϊ wt. In order to facilitate the dispersion of the pigment in the liquid phase of the preparation and to increase the stability of the dispersion, an inorganic dispersant of the alkaline phosphate type is used in an amount of 0.3 to 1.0% by weight, whose dissolution under ionization allows the presence of water in the organic solvent.

Linear condensed sodium or potassium phosphates are preferably used, whose dispersion and dissolution in the liquid phase of the dispersion is already achieved during the preparation of the coating composition by intensive homogenization of the starting mixture containing all the individual components.

By the interaction between the dissolved phosphate ions and the hydroxyl ions on the surface of the oxide pigment particles, the coating dispersion is stabilized.

Advantages of the composition according to the invention:

the method of preparation of the coating composition according to the invention is simple and the chemicals required for its preparation are available and are commonly used in the paint industry »

- the pigment sedimentes very slowly in the prepared coating agent (within a few days), after which the coating agent can be easily homogenized again by shaking it so that it is ready for use again »

- When used to correct fonts or drawings, it dries very well and quickly, creating a smooth, matt, elastic film with properties that allow an almost indistinguishable repair »

- the covering agent can be used after its ev. thickening by evaporating a portion of the solvent at any time, as necessary, dilute the solvent used for its preparation without compromising the quality of the composition.

The following are examples of embodiments.

Example 1

Into 320 g of technical butanone was added 190 g of rutile type titanium dioxide, g of cellulose acetobutyrate and 2.7 g of pentasodium cataphosphate. . dilution with butanone (to replace its certain evaporation in the preparation and decantation of the suspension) was ready for use.

Example 2 \

To 600 g of technical butanone was added 350 g of anatase type titanium dioxide, g of cellulose acetobutyrate and 6 g of tetrasodium pyrophosphate; the prepared mixture was homogenized for three hours in a spherical porcelain mill and after the fine and stable coating dispersion / ev. after dilution as in Example 1), it was ready for use.

Claims (1)

SUBJECT OF THE INVENTION Coating means for retouching typefaces or drawings on paper or other white backing, based on a dispersion of titanium dioxide in an organic solvent, with a dissolved organic film-forming substance and a dispersing agent, characterized in that it contains 25 to 50% by weight, preferably 30 to 40 wt. anatase, optionally rutile type titanium dioxide, from 43 to 72 wt.%, preferably 55 to 65 wt. of an organic polar ketone type solvent having a relative permittivity of at least 10 and a relative evaporation of up to 8, preferably butanone, comprising an addition of water in an amount of up to 5% by weight of the solvent; % of an organic film-forming polymer of the cellulose ester type, preferably cellulose acetobutyrate and 0.3 to 1.0 wt. dispersing agents of the alkaline phosphate type, preferably linear condensed sodium or potassium phosphates.