Alkaline Paper Advocate

Volume 9, Number 1
May 1996

Some Properties of Permanent Paper Made in Slovakia

by Jozef Hanus
National Archives of the Slovak Republic, Drotárska 42, 817 01 Bratislava, SK (Fax: + 42-7-580 12 47)

[Editor's note: This report of permanence tests done on four papers is significant because detailed test results like these are rarely published, and because the papers not only met but far exceeded the requirements of permanence standards used in the U.S. and abroad.]

Problems of acid paper degradation are well known and have been documented by a large number of research and general publications, in conferences, seminars, and elsewhere. It is also very obvious that use of permanent paper for documents and books is the best way to preserve the printed and written cultural heritage of today for the future. For this reason, some commercial papers from several paper mills in the Slovak and Czech republics were thoroughly tested to determine their aging resistance [1-5].

This large research program was developed at the National Archives of the Slovak Republic in the beginning of 1980. Its aim was to test writing and printing paper available on the market from different producers--all of them state enterprises in the former Czecho-Slovak Republic at that time--for their permanence and durability. Nowadays, there are three large paper manufacturers in Slovakia. Only one of them, however, produces alkaline paper.

North Slovakian Pulp and Paper Mills (Severoslovenské celulózky a papierne, Ruzomberok) is the largest papermaker in the Slovak Republic, with three alkaline mills, one of which (the Celpap mill) has its own kraft pulp mill. A brief description of this company and its mills appeared in the November 1993 Alkaline Paper Advocate [6]. It produces over 90% of the total printing and writing paper production in Slovakia, which could cover all needs of a home market and moreover, a large part of their production has been exported. The prices are very competitive with those of "good quality" acid paper (5% to 15% more expensive).

Most of the Celpap papers were tested in laboratories of the National Archives in Bratislava for permanence and durability. Their compliance with the international and U.S. permanence standards, ISO 9706 and ANSI Z39.48-1984 was also evaluated. (At the time of this research the most recent draft of ISO 9706 and the 1984 edition of Z39.48 were used.) [7]. The test results and the relevant specifications of each standard are presented here.

Common Required Characteristics of ISO 9706 and ANSI Z39.48-1984

1. pH

2. Alkaline Reserve

3. Tear Resistance

Basis Weight of Paper

Minimum Average MD Tear Resistance





















Different Required Characteristics

1. Folding Endurance

2. Paper Stock (Resistance to Oxidation)

Materials and Methods

Paper Samples

Composition of the papers used in tests is shown in Table 1. All samples--xerographic (XE), laser (LA), offset (OF) and writing paper (WP)--were produced on Paper Machine no. 8 in the Celpap mill.

Table 1
Composition of Tested Papers





Bleached softwood kraft pulp(%)





Bleached hardwood kraft pulp (%)





CaCO3 (%)





Aquapel internal size





Starch surface size





Basis weight (gsm)





pH measurements

pH was measured by the cold extraction method according to ISO 6588.

Alkaline reserve

Alkaline reserve of samples was determined as specified in Finnish Standard SFS 4465, since ISO 10716 for determination of alkaline reserve was still in preparation at the time of our investigation.

Tearing resistance

Tearing resistance tests were performed on an Elmendorf testing machine according to ISO 1974, on samples cut in the machine and cross direction (MD, CD).

Folding endurance

Schopper folding endurance was determined in accordance with CSN 50 0345 on the equipment Doppelfalzgerät, DFP, WEB Werkstoffprüfmaschinen, Leipzig, in machine and cross direction at a maximal tension of 10.0 N. It is expressed as number of double folds.

Resistance to oxidation

Kappa number was measured by ISO 302, with the modification given in Annex A of ISO 9706.

Results and Discussion

pH of aqueous extract

The pH of all four papers was 9.3. This is within the range given in ISO 9706 and above the minimal value of 7.5 given in ANSI Z39.48-1984.

Alkaline reserve

Despite Note 3 in ISO 9706, which permits the calculation of alkaline reserve as "about 20 g of CaCO3 per kg of paper" instead of moles of acid per kilogram (as specified in ISO 10716), we also determined alkaline reserve according to Finnish standard SFS 4465, as ISO 10716 had not been finished at the time of our measurements.

All four papers easily met the requirement of both the ISO and the ANSI standard for a 2% alkaline reserve.

Percent CaCO3









Tearing resistance

Despite a slight difference between the specifications for tear resistance in the two standards (about 370 mN vs. 350 mN for 70 gsm basis weight), it can be seen, from the test results below, that all of the papers easily meet the specifications.

Tearing resistance (mN)

(70 gsm)

(70 gsm)

(80 gsm)

(80 gsm)











Folding endurance

Although folding endurance is not included in ISO 9706 as a property to be tested or recommended, ANSI Z39.48-1984 requires a minimum cross direction folding endurance. The use of folding endurance is widespread in paper permanence testing, because it is very sensitive to paper aging. It changes more rapidly during the aging process than other mechanical or chemical properties [8]. Therefore the paper samples were aged at 103°C (Czecho-Slovak Standard CSN 50 0375) and changes in folding endurance were followed and evaluated.

The initial values of MD and CD double folds and changes during accelerated aging at 103°C are shown in Figures 1 and 2.

It can be seen from the measured results that the values of double folds even after 24-day accelerated aging greatly exceed the value of 30 double folds at 1 kg tension required by ANSI Z39.48-1984.

Fig 1.
Figure 1. Changes in folding endurance during accelerated aging at 103°C (MD)

Fig 2.
Figure 2. Changes in folding endurance during accelerated aging at 103°C (CD)

Paper stock (Resistance to oxidation)

It can be seen from Table 1 that none of the papers includes groundwood or unbleached pulp. Therefore, they meet the paper stock requirement of ANSI Z39.48-1984.

None of the papers had a kappa number over 3. Since ISO 9706 calls for a maximum kappa number of 5, indicating resistance to oxidation, all of the papers meet the ISO requirement as well.

Statement and symbol of compliance

A symbol of compliance in the form of the mathematical symbol for infinity set inside a circle was developed by NISO, the U.S. National Information Standards Organization. It was introduced in ANSI Z39.48-1984, and is also part of ANSI/NISO Z39.48-1992. The symbol is used in ISO 9706 with the permission of NISO.

Since the four papers tested meet the requirements of both of the above standards, they are marked with the symbol of compliance with this standard. The symbol is one-sided multiprinted on one side of every sheet of A4 in white printing ink, trade name Bianco Acquagem HSL/B, produced by the German company BASF:



Alkaline papers produced by the North Slovakian Pulp and Paper Mill in Ruzomberok were thoroughly tested in laboratories of the National Archives of the Slovak Republic in Bratislava for permanence and durability. On the basis of the results it can be stated that these papers meet the requirements of ISO 9706 and ANSI Z39.48-1984 for permanence; their aging resistance is very high; and their properties are suitable for documents destined for retention and long-term storage.


1. Hanus, J.: Stúdium starnutia papiera z hl'adiska ochrany archívnych dokumentov (Study of paper ageing as it relates to preservation of archival documents). Ph.D. thesis, Chemical-Technological Faculty, Slovak Technical University, Bratislava 1987, 130 pp.

2. Krkoska, P., and J. Hanus. "Description of paper ageing by zero-span tensile strength." Cellulose Chemistry and Technology, 22 (6) 633 (1988).

3. Hanus, J., P. Krkoska and M. Komorníková: "Zmenyoptickych vlastností niektorych papierov pri urychlenom starnutí" (Changes in optical properties of some papers during accelerated ageing). Pap'r a celul-za 43 (12) 1988, pp. 251-253.

4. Hanus, J., ed.: Degradation of Archives and Library Materials vs. Permanent and Durable Paper for Archives. Proceedings of the International Seminar, SNA Bratislava, 22-23 April 1993, 79 pp.

5. Hanus, J., and M. Komorníková: "The Application of Statistical Analysis in Evaluation of Changes in Some Properties of Aged Papers." Archives et Bibliothques de Belgique 1-2, 1987, p. 161-182.

6. Hanus, J.: "Alkaline Papermaking in Slovakia." Alkaline Paper Advocate, Nov. 1993, v.6, p. 38.

7. Hanus, J. and J. Mináriková: Stúdium stálosti a trvanlivosti niektorych druhov papiera z produkcie Severoslovenskych celulózok a papierní v Ruzomberku (Study of permanence and durability of some types of paper from the production of the North Slovakian Pulp and Paper Mills in Ruzomberok). Záverecná vyskumná práca (Final research report). National Archives of the Slovak Republic, Bratislava 1993, 40 pp.

8. Browning, B.L.: "The Application of Chemical and Physical Tests in Estimating the Potential Permanence of Paper and Papermaking Materials." In: Preservation of Paper and Textiles of Historic and Artistic Value. (Advances in Chemistry Series 164) American Chemical Society, Washington, DC 1977, p. 275-285.

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