CS251376B1 - Heat-sensitive paper with reduced tack and reduced tendency to clog the printing elements - Google Patents

Abstract

The heat-sensitive paper used in thermal printers melts at the recording point and tends to stick to the printing element when it cools. This phenomenon impairs the movement of the platen in the printer and is the reason for clogging of the printing elements. To eliminate this disadvantage, the heat-sensitive layer is coated with a base coat containing a non-filamentous binder and a pigment whose surface has adhesive properties. This pigment anchors the melted heat-sensitive layer and thus prevents it from sticking to the printing element.

Description

The invention relates to heat-sensitive recording paper for ternoprinters and ternographic recording devices.

Many heat-sensitive paper systems have been known to date. Recently, the system utilizing the reaction between a bioreactor (electron donor) and a color developing substance (electron acceptor), which leads to intensely colored compounds, has undergone the greatest expansion ». e.g., U.S. Pat. No. 3,539,375, U.S. Pat. No. 3,451,338.

The coloring agent (BIL) and the color developing agent (BVL) are contained in a heat-sensitive layer applied to paper or other suitable lining material. In the heat-sensitive layer, BTL and BVL are present in very fine particle forms (less than 5 µm). A prerequisite for a bervo-forming reaction between BTL and BVL is that at least one of these substances is molten on recording.

In addition to BTL and BVL, the heat-sensitive layer includes a binder and other auxiliaries that adjust the temperature sensitivity, improve shelf life and prevent unwanted discolouration, especially when smoothing the surface of the heat-sensitive layer, which is necessary for good contact with the recording element.

Examples of BVL are phenolic compounds and have a melting point above 70 ° C of acidic clay minerals, mineral and organic acids and their acid-reacting salts, organic sulfonic acids (see, e.g., U.S. Pat. Nos. 3,666,525, 3,884,0153).

Examples of BTL are leuko dyes based on derivatives of triphenylethane, fluoro, phenothiazine, auramine and spiropyran. A detailed list thereof can be found in the patent literature, eg US 3451338, US 4341403, and is well known to those skilled in the art.

Examples of binders are polyvinyl alcohol, carboxymethylcellulose, methyl vinyl ether, maleic acid copolymers, hydroxyethylcellulose, gelatin, acacia, dispersion binders based on butadiene-styrene copolymers, oxidized starches, and mixtures thereof. Examples of temperature-sensing and friction-reducing substances are amides and salts of fatty acids, waxes, etc.

At the point where the heat-sensitive layer is heated to the melting point, the aforementioned 1 bore-forming reaction occurs between molten BVL and molten or molten BTL. For high-quality recording, it is essential that the melt with the resulting dye remains in the place where the recording element acts, i.e. that the molten heat-sensitive layer does not stick to the recording element when cooled, and further that the colored melt diffuses into the environment. The bonding of the heat-sensitive layer makes it difficult to move the heat-sensitive material, clogging the recording element, thereby impairing the sharpness and intensity of the recording.

For this reason, various inorganic pignents, such as calcium carbonate (CaCO3), kaolin, titanium dioxide (TiOg), or organic pigments, such as the condensation product of urea and formaldehyde, are added to the coating composition when applying the heat-sensitive layer, as disclosed in the patent literature e.g. US 3674535, US 4243716, US 4355070.

The disadvantage of this process is a considerable reduction in the color intensity when using such amounts of pigment as to prevent the sticking of the recording elements.

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The above drawbacks are overcome by the solution according to the invention. To significantly improve the properties of the heat-sensitive layer in terms of bonding to the printing element and its fouling, this can be achieved by priming the substrate with a primer, the main components of which are a suitable pigment and a non-film-forming binder.

The base coat is applied with a heat-sensitive layer of the usual composition, either as a single coat containing all the necessary components (BIL, BVL, flux, binder, sensitizing agents, antifoams β, etc.), or as two coats, usually using BIL and BVL separately. Another possibility is that some or all of the BVL is added to the primer.

The function of the primer is to anchor the molten heat-sensitive composition, which is facilitated by the free surface of the pigment in the primer. From this point of view, it is obvious that the most effective is the pignent having a large inherent surface which binds and anchors a relatively large amount of the molten phase and does not require the amount of pigment to achieve the desired effect. In order to avoid closure of the large surface of the pigment used, it is necessary to use non-film-forming binders when applying the primer.

Such binders are, for example, disperse synthetic binders with high bonding strength.

Suitable pigments with a high surface area are seolites (natural and synthetic), bentonites, acid-activated bentonites, synthetic alumosilicates (eg alumosilicate pigment according to PV 7288-81, AO 229557).

To achieve this effect, the amount of pigment in the primer may be in the range of 5 to 200% based on the fusible fraction of the heat-sensitive deposit, but an amount in the range of 5 to 30% is practically sufficient.

The weight fraction of the dispersion binder and pigment in the primer is 1: 3 to 1: 7. The content of the aesthetic components in the heat-sensitive layer ae is as follows: BTL 5 to 30% BVL 30 to 70%, heat-sensitive layer binder 10 to 30% up to 30%.

The following examples illustrate the invention and its effects.

Example 1

First (primer): 10 parts of acid-activated bentonite Copisil (trade name of Sud Chemie), 20 parts of BVL (2,2-bis (p-hydroxyphenyl) propane) are dispersed in a pearl mill in 250 parts of water until it reaches size particles less than 5 µm. Then 5 parts of styrene-butadiene dispersion (containing 50% dry matter) are added and the suspension is applied to a paper substrate of a fertile weight of 50 g / m ² so that the basis weight of the coating is 3 g / m 2.

Second coat: 10 parts BTL (TH-107 fluoride black dye leukoform, Japanese trade name Hodogaya), 10 parts calcium stearate, 10 parts PVA is dispersed in a pearl mill in 200 parts defect and then applied to the primer in a surface layer weight 2 g / m ² .

Example 2

First coat: 10 parts urea-formaldehyde condensate organic pigment, 20 parts BVL (2,2-bis (p-hydroxyphenyl) propane), 3 parts PVA, 200 parts water is dispersed in a bead mill under the same conditions as in Example 1, including applying the resulting suspension.

Second coat: same as in Example 1.

Example 3

The same embodiments as in Example 1, but in the first (primer) coating, there are 15 parts of acid-activated bontonite Copisil.

> 376

Example 4

Same embodiment as in Example 1, but crystal violet lactone is used as BTL.

Example 5 (for example with 4) parts of acid-activated bentenite Copis11, 20 parts of BVL (2,2-bis (p-hydroxyphenyl) propane), 3 parts of PVA is dispersed in 250 parts of water with the same conditions as in the example. The resulting suspension is labeled A. Next, disperse > 0 parts BTL (crystal violet lactate), > 0 parts calcium stearate, > 0 parts PVA in 200 parts water equal to > In the resulting suspension we denote B.

Mix the suspension A and B in a ratio of 3: 2 and apply to the same substrate as in the example> as a layer with a weight of 5 g / m ² .

Example 6 parts of acid-activated bentonite Copis11, 20 parts of BVL (2,2-bis (p-hydrozyphenyl) propane), 1.5 parts of PVA ee dispersed as in Example>, then 1.5 parts of styrene-butadiene dispersion (containing 50%) are added. dry matter) and applied to the floor in a layer of 3 g / m ² .

The second coating is carried out as in Example>.

Example 7

The embodiment is the same as in Example 1, but in the first (high-quality) coating there are 10 parts of synthetic alumosilicate prepared according to AO 229557.

The heat-sensitive papers according to the above examples are evaluated in the following overview. The tendency of the molten heat-sensitive layer to adhere to a cold metal surface is evaluated according to the following criteria, indicated by the numbers 0, 1, 2, 3, where 0 - does not stick, 1 - slightly glues, 2 - glues. - strongly bonded (when the metal surface is removed, the heat-sensitive layer is also torn off).

Example:

2 3 4 5 6 7

Adhesion criteria:

3 0 0 2 0 0

The achieved effect of the solution according to the invention results in reduced stickiness and increased strength of the heat-sensitive layer under teraographic recording conditions, as exemplified by the above examples.

Use of the subject invention is possible in the manufacture of paper for thermal printers and recording devices.

Claims (5)

SUBJECT OF THE INVENTION CLAIMS 1. A thermosensitive paper having a reduced tack and a reduced tendency to clog printing elements, characterized in that the heat-sensitive layer is applied to a base coat of a paper composed of a non-film-forming binder and a pigment. . 2. The heat-sensitive paper of claim 1, characterized in that a color developing component is contained in the basic aatir. 3. The heat-sensitive paper of claim 1 or claim 1 wherein the pigment in the primer is acid-activated bentonite. 4. The heat-sensitive paper of claim 1 or 1 and 2, wherein the pigment in the primer is a synthetic active aluminosilicate. 5. The heat-sensitive paper of claim 1 or claim 2 wherein the binder in the primer is styrene-butadiene latex or acrylate latex.