US2637657A - Thermosensitive papers and compositions therefor - Google Patents

Description

Patented May 5, 1953 UNETED PATENT? OFFICE r Ep osE su vE PARERS; AND

Q I'Q manages,

N o Drawing.- Application lune 10, ,1946, SeriaLNo. 675 8};

materials sensitive to light and toiexpos er them,

to light before subjection to bean-which required, quite a high temperature andfldid not give as satisfactory a trace in color and permanency as would be desired.

Many of these papers require complicated and delicate mechanism effectively; to apply ,the heat to the composition or coated-paper aud to obtain the desired record and; subsequently reg-i, quire special handling or afterdevelopingandin all cases are very sensitive totemperatureand-Q humidity changes of the surrounding atmospheres,

t is among the objects of the present invention to provide improved thermosensitive recording papers and compositions therefor which are more sensitive to heat than other known compoundsfi or compositions and which may be readily utilized without specific treatment beforehand or development afterward and which will be highly stable regardless of varying temperature and humidity, and upon heat inscription thereorpwillgim give a trace or record of desirable dark color, and,- contrast which will have superior permanency.

Another object is to procure a coating com position which may be readily applied to a recording sheet of paper or other fabric, which will 35 be non-cracking and which will fiex .;,with, the paper and not flake or peel ofi, which after application will readily dry without efflorescence, hygroscopicity of deliquescence and may be readily handled, and which will produce non-smudgin g w and non-fading recordings of high permanency regardless of exposure to atmosphere, prolonged, storage under ordinary conditions,

A further object is to prepare an improved inexpensive thermosensitive recording paper upon 45 which recordings may be readily produced with out expensive or delicate mechanisms and without elaborate controls and whi h maybe-ppm ated upon by a heated stylus, by rfocused inira red rays, by high voltage spark discharge or by (o1. mpu s p ssing current through a conducting or grainy,

ite'd,,shet, byponcentrated blasts of hot ener y superheated steam or otherheat sources,

Afurther object is to provide thermosen'sitive, recording paper, devoid of wax, whichwill make satisfactory non-smudging dark recordings of desired contrast to a white background at a rlatively low temperature without loss of all the fine detail of the recording, which'paper will not be sensitive to varying atmospheric temperatures and humidities.

Still further objects and advantages will appear in the more detailed description set forth below, it being understood, however, that this more detailed description is given by way of illustration and explanation only, and not by, way of limitation, 'since various changes therein may be made by those skilled in the art without departing from the scope and spirit of the present invention.

It has been foundrithat certain metal salts, particularly heavy .metalsalts which are stable at ordinary temperatures, may be decomposed at high temperatures to forma marking or recording of the metal or metal oxide, but these high temperatures cannotnormally be attained by the recording instruments employed for. marking thermosen'sitive recording sheets. Lead formate'? has been found to be the most effective heavy" metal salt, although other heavy metal salts, such as mercury salts, iron fsalts, lead salts, zinc ,salts silve gsalts and titanium -salts may also be eme. q edr It 'has been discovered, however, that. when... these metal salts are mixed with other salts or; compounds which decompose at a lower tempera-Y ture ,Within the effective heat range of a record ing instrument, the heat given off by the'dtpni position of said lastmen'tioned salt or compound", addedto that, applied by the recording mare-1f; ment will result in effective decomposition of'the" first mentioned salt giving the recordationl The last mentioned. salt or compound giving rise to. the .,exothermic decomposition may Or may not give a yisiblerecording on. decomposition, but. m5; the preierred, form the; decomposition products of both salts or compounds. give rise to thefde sired recordationpr mark ng.v

Forexample although a heated recording in; strument may actually have a temperature of 350 C. to 550 C. due to the speed of the instrument, conditions of contact and conductivity of the recording sheet, a much lower decomposition temperature will be produced in the body of the decomposable salt or compound on the recording sheet. Actually, often effective temperatures of between 100 C. and 250 C. will be produced upon and in the recording sheet. On the other hand, the most satisfactory record producing salts or compounds may not decompose at temperature below 250 C. and may require temperatures of between 260 C. to 300 C.

A feature of the present invention resides in the provision of a mixture of high temperature (e. g. 250 C. to 300 C.) decomposable trace producing salts, such as lead salts with low'temperature (e. g. 150 C. to 250 C.) decomposable heat producing salts, such as mercury or iron salts. factory to use a synergistic mixture of relatively heavy metal salts, and desirably of monobasic Generally it has been found most satis or dibasic-carboxylic acids, which apparently will sensitize each other and which individually will not be satisfactory in obtaining a recording of desired density and permanency.

Generally a mixture of mercury organic acid As mercury salts, it is possible to employ:

Mercuric oxalate (preferred) Mercurous oxalate Mercuric acetate Mercurous acetate Mercuric thiocyanate. Mercuric benzoate Mercuric citrate Mercuric formate Mercuric tartrate Mercuric oxide may also be used in lieu of the mercury salts stated.

For example, in connection with the above preferred salts, lead formate will decompose at about 250 C., while mercuric oxalate will decompose at 200 to 250 C. It will be noted that the preferred acids are organic acids, or inorganic acids which are not stable particularly when heated.

The best combination is lead formate and. mere cury oxalate and it has been found that this combination will not only result in a most permanent dense non-fading dark recording, but will satisfactorily adhere to sulphite paper or bond paper.

The preferred combinations should include a relatively small amount (e. g. 1% to 25%) of a lead or mercury salt which will decompose exothermically on heating and produce sufficient heat to catalyze the reduction or decomposition of a relatively large amount of another trace or record producing salt to similar condition, the

60 to 80% of lead formate; 5 to 30% of mercuric oxalate; 2 to of ethyl cellulose.

The mercury salt is the preferred sensitizer or activator and usually should be present in minor proportion-say, for example, from 1% to of the lead salt and both salts should be present in astate of subdivision of less than 20' microns and desirably from 2 to 10 microns.

Zinc sulphide and titanium oxide in amounts from 2% to 10% may be added to improve the color and background of the material.

To give several examples:

' Example 1 One gram of ethyl cellulose is dissolved in 100 cc. of carbon tetrachloride and 10 grams of finely ground lead formate are added. Then 1 gram of finely ground mercuric oxalate is added. The mixture is brushed or caused to flow upon a strip of sulphite or rag bond paper. Cellophane, plastic strips and metal foil may also be used as a sheet carrier. The paper or carrier may be graphite filled where passage of electric current supplies the heat. When the paper is to be used for marking with a heated stylus, the thickness of the coating may be 0.00020 to 0.00100 inch.

Example 2 Example 3 Adecomposable salt composition composed of the following may be used:

Preferred Range Lead thiosulphate 10 to Lead formate 60 to 70 Mercury oxalate 10 5 to 15 All parts by weight.

Example 4 As another decomposable salt composition:

Preferred Range Lead'formate 45 to Lead oxalate 10 5 to 15 Mercurous oxalate. 5 0 to 15 Mercuric formate- 5 0 to 15 Lead thiosulphat 20 0 to 30 Zinc sulphide 5 0 to 10 All parts by weight.

Titanium oxide may be used instead of zinc sulphide. Mercuric salts generally are preferred to mercurous salts and give better results.

Example As a most satisfactory composition:

All parts by weight.

As other decomposable salt compositions which may be employed:

Example 6 Parts by weight Lead formate 45 Lead oxalate 45 Mercuric oxalate Example 7 Parts by weight Lead formate 90 Mercuric oxalate 5 Mercuric acetate 5 Example 8 Parts by weight Lead formate 90 Mercurous acetate 10 Example 9 Parts by weight Lead oxalate 75 Mercuric thiocyanate 25 Example 10 Parts by weight Lead thiosulfate 80 Mercuric acetate 20 Example 11 Parts by weight Lead formate 90 Lead oxalate l0 In the above examples, the salts present in smaller quantity may be regarded as the low temperature decomposable heat producing salts, while the salts present in large quantity may be regarded as the high temperature decomposable trace producing salts.

Examples 3, 4 and 6 to 11 above omit the binder.

In these compositions a medium viscosity grade of ethyl cellulose, as a binder, may be used up to 10% by weight, and zinc sulphide or titanium oxide may be used up to 10% by weight. These salts may be placed in the paper pulp when the paper is being made.

Although silver oxalate may be added to the lead and mercury combination, this is not preferred since the lead and mercury decomposition products produce a superior trace in the absence of silver.

Although monobasic and dibasic carboxylates are preferred, tribasic carboxylic acid salts may be used.

The above compositions give much more desirable results than dark colored blue or black wax coated recording papers, in which case the hot stylus will melt the wax into the paper. These wax coated papers are susceptible to varying atmospheric temperatures and humidities and will frequently smudge very badly and in any case will usually not show fine detail. By exothermic as used in the present specification and claims, the applicant includes salts which give oil" heat upon being decomposed.

As many changes could be made in the above composition and methods of making the same, and many widely varying embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A thermosensitive salt composition, useful in the form of a thin adherent surfacing provided with a binder to hold it on a flexible carrier sheet and capable of recording a permanent contrasting colored trace when locally heated to an elevated temperature, said composition including a binder and comprising to parts by weight of lead formate 5 to 30 parts by weight of mercuric oxalate 2 to 15 parts by weight of ethyl cellulose.

2. As a thermosensitive composition, a major proportion of lead formate and a minor proportion of mercuric oxalate to sensitize the lead formate.

3. A thermosensitive recording sheet coated with a mixture of a minor proportion of mercuric oxalate and a major proportion of lead formate.

4. A coating composition for a thermosensitive recording paper comprising 1 gram ethyl cellulose, cc. carbon tetrachloride, 10 grams lead formate and 1 gram mercuric oxalate.

5. A coating composition for a thermosensitive recording paper comprising ethyl cellulose, carbon tetrachloride, lead formate and mercuric oxalate, the amount of the mercuric oxalate ranging between 1% to 25% of the lead formate.

6. A thermosensitive composition for surfacing a recording paper comprising one part by weight of ethyl-cellulose, ten parts by weight of finely divided lead formate and one part by weight of finely ground mercuric oxalate.

KARLIS V. OZOLS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 150,722 Smith May 12, 1874 423,530 Raymond Mar. 18, 1890 1,434,432 Donohue Nov. '7, 1922 1,515,495 Kolle et al Nov. 11, 1924 1,685,715 Molz Sept. 25, 1928 1,689,8 12 Pauschenberg Oct. 30, 1928 1,693,369 Cochran Nov. 27, 1928 1,939,232 Sheppard et al. Dec. 12, 1933 2,046,823 Johnson et al. July 7, 1936 2,137,456 Palm Nov. 22, 1938 2,210,565 Asher Aug. 6, 1940 2,251,742 Kline Aug. 5, 1941 2,294,150 Kline Aug. 25, 1942

Claims (1)

1. A THERMOSENSITIVE SALT COMPOSITION, USEFUL IN THE FORM OF A THIN ADHERENT SURFACING PROVIDED WITH A BINDER TO HOLD IT ON A FLEXIBLE CARRIER SHEET AND CAPABLE OF RECORDING A PERMANENT CONTRASTING COLORED TRACE WHEN LOCALLY HEATED TO AN ELEVATED TEMPERATURE, SAID COMPOSITION INCLUDING A BINDER AND COMPRISING 60 TO 80 PARTS BY WEIGHT OF LEAD FORMATE 5 TO 30 PARTS BY WEIGHT OF MERCURIC OXALATE 2 TO 15 PARTS BY WEIGHT OF ETHYL CELLULOSE.