Volume 13, Number 8
Dec 1989

A Short Research Project into the Permanence of Thermal Fax Papers

Printed with the permission of the Australian Archives, from the AICCM National Newsletter, June 1989, p. 10-11.

Introduction

In response to a series of public enquiries on the stability of facsimile documents, a short testing project on thermal facsimile papers was carried out in the Conservation Laboratory at Australian Archives, ACT Regional Office.

The papers were tested for paper content, reaction to prolonged high humidity, washing and drying and exposure to ultraviolet light. The image was tested for sensitivity to common solvents and reagents and to heat.

The tests were carried out on unknown brands of fax paper but, on inquiry, it was found that there are only two thermal fax paper technologies, both of which are vary similar to each other. Therefore it is probably safe to conclude that any thermal fax paper would react in much the same way to the tests in this project.

Only thermal fax paper was tested in this project. Facsimilies that use plain paper and a heat activated liftoff ribbon were not tested. These papers would have a longer life than thermal fax paper if high quality paper was used, but the stability and longevity of the image is still not known.

Manufacturer's information for a thermal paper known as Kanzaki Thermal Paper was obtained from the supplier of fax paper to Archives, ACT Regional Office. This information suggests that even in optimum conditions (20°C, 50% RH and in the dark), the papers will only last five years.

Structure of Thermal Fax Paper

Thermal fax papers consist of a base paper with a thin color forming layer on the top surface. This color forming layer is made up of a colorless dye and a color-forming agent suspended in a binder. Color appears once heat is applied, presumably by initiating a reaction or by breaking the particles open and allowing the reaction to occur (Figure 1).

Testing

Paper content. Paper content was determined using standard spot tests for lignin, alum, rosin, starch and calcium carbonate filler. The pH was tested using Universal Indicator, flat head electrode and cold extraction. All the tests were done in triplicate and with a control.

Figure 1. Structure of thermal fax paper.

Solubility tests. The image was tested for solubility in common organic and inorganic solvents and reagents. The chemicals were selected as ones that may be used in the treatment of damaged records. Samples were spot tested with toluene, acetone, 1,1,1-trichlorethane, petroleum spirits (100°-120°c BP) and acetic acid. Other samples were immersed in ethanol, 50% aqueous ethanol, deionized water, calcium hydroxide and ammonia solutions to pH 8.5 and ammonia. Acetic acid, hydrochloric acid and sulphuric acid to pH 3.5 were used to see how fax papers would respond to acidic vapors.

Exposure to high humidity. Samples of thermal fax paper were placed in a cool, high humidity environment for periods of up to 10 days because prolonged high humidity is a common cause of damage to records. It was thought that the corrosion of iron fastenings on records may catalyse some reaction within the paper. Two sets of samples were placed in the chamber, one set with staples and paperclips ad one without. Both sets were exposed to high humidity for the sane periods of time.

Exposure to UV light. Samples were placed in a closed chamber and exposed to short wave length UV (254 nm). The tests were not meant to simulate exposure to UV in a working environment but only to see if any image fading or paper discoloration occurred with maximum exposure. The samples were exposed to UV for up to six days.

Washing and drying. Several sheets were washed in deionized water and dried separately in Reemay and blotters to check the image quality after washing and drying. Two stacks of sheets were dried unseparated to see if blocking would occur.

Heat sensitivity. The final series of tests was carried out to see at what temperature the thermal layer was activated. Heat was applied to three strips using a heated spatula with temperatures set from 30°c to 100°c.

Boiling water was poured on the paper to simulate a desk top disaster.

Results

Paper content. These tests indicated a fairly poor quality wood pulp paper. The presence of lignin, alum and rosin would normally indicate an acidic paper, but the calcium carbonate filler, or possibly the coating, boosted the pH to around 8.5. The presence of lignin, alum and rosin limit the life of the paper.

Solubility tests. All the reagents used for spot tests, except for petroleum spirits and ammonia solutions, blackened the thermal layer completely. The reagents went black and the discoloration transferred to adjacent pages.

The ethanol used to immerse the papers turned the thermal layer black and appeared to wash the layer off the paper completely. No image remained. The aqueous ethanol reduced the intensity of the image and made it extremely difficult to read. All the acids produced a green tinge to the paper but the information was still readable. The water and the calcium hydroxide solution did not noticeably affect the image.

Exposure to humidity. The samples exposed to high humidity suffered image fading after 24 hours. The fading became progressively worse over prolonged exposure (up to 10 days).

The paper in contact with the metal fastenings began to darken very slightly after 24 hours and the image had started to fade slightly also. The 10-day sample had larger areas of darkening around the staples and paper clip and rust had started to form, but the image was still quite readable.

Exposure to UV. After 10 hours the samples had yellowed slightly but no image fading had occurred. On the full five days' exposure the paper was almost the color of brown paper but the image had still not faded, although it was more difficult to read.

The discoloration was most severe on the face of the paper (which was exposed to the UV source). The discoloration was worse where there were finger prints.

Washing and drying. The sheets that were washed and dried separately did not appear to suffer any damage. The image had not faded nor had the thermal layer discolored. The sheets that had been washed and dried in a block, stuck together.

Heat sensitivity. Slight darkening was noticed at 70° c, then up to complete darkening at 100°c. The darkening did not transfer to blotter when the paper was heated from the back.

The boiling water blackened the thermal layer and appeared to wash the layer off the paper completely.

Conclusions

From the results of the paper content testing, it can be seen that the calcium carbonate filler will slow down the acid deterioration of the paper, but the acidic pulp and sizing will always cause the paper to degrade. The content of the thermal layer is still unknown and, therefore, its effect on the lifespan of the paper is unknown.

Although the exposures to UV were far greater than could be expected in a normal working environment, it can be seen that UV light will cause some degree of damage to thermal facsimile papers.

The washing and drying tests showed that if the sheets were damaged by water and allowed to dry without being separated, they would block and be difficult to separate.

The final series of tests showed that if thermal papers were exposed to a heat source (below combustion point), e.g. radiation from a fire, the heat could blacken the paper completely and render it useless.

Any treatments involving the damaging reagents used in this project, e.g. tape removal, oily stain removal, or treatment of mold with ethanol, could not be carried out. Anything beyond routine washing and drying would be difficult.

The results of the testing reinforce the manufacturer's statement that thermal facsimile papers have a very limited life span even in a normal working environment and without taking mishaps or disasters into consideration.

If the papers are exposed to less than optimum conditions, an even shorter life span should be expected.

A staff member at Australian Archives had a thermal fax on file against a PVC cover, under conditions of normal office light, temperature and humidity. The fax was dated May 1987 ad it had faded to a pale brown image over a period of only 18 months. This may have been the result of damaging vapors emitted from the PVC cover.

Recommendations

From the results of the tests and from the information obtained from the manufacturer, the following recommendations can be made:

• Store papers in a cool place away from excess light (illumination and UV), humidity and heat, e.g. lamps, heaters and hot liquids.
• Do not use solvent based adhesives or adhesive tapes, as they will darken the image as well as stain the paper in the usual way. (Aqueous adhesives can be used with safety.)
• Do not use solvent based inks. Highlighters and other solvent based felt pens are known to cause darkening of the image and may dissolve the thermal layer. Aqueous inks, felt tip pens or pencil should be used.
• Do not store the papers with diazo type duplicates, or expose them to alkaline (or acid) vapors from any source, as these are known to effect the image.
• Do not touch the papers with sweaty or oily hands, as oils and organic acids may darken the image.
• Do not scratch, rub, erase on, or fold the papers, as the friction may cause darkening of the image.
• Do not store the papers in PVC folders. Polyethylene, polypropylene or polyester folders are suitable.
• Do provide optimum storage conditions (20°C and 50% RH) to obtain the full five-year life span. Or ideally, Photocopy the information onto good quality paper to retain the information for longer, and discard the facsimile.

If anyone would like more information on this project, a more extensive report is available from Cheryl Jackson, Preservation Services, Australian Archives ACT Regional Office, P0 Box 447, Belconnen, ACT 2617, Australia.