Paper testing – Permanent and archival paper (ISO 9706 and ISO 11108)

Background

When talking about archival documents, we refer to documents that can be stored in protected environments for a long time, probably for hundreds of years. Paper that meets the requirements in ISO 9706 is referred to as permanent paper and ISO 11108 is referred to as archival paper (permanent and durable paper). According to the National Archives' technical regulations (RA-FS 2006:4), the paper for permanent documents can be of both types. Archival documents are produced by combining such paper with a permanent writing and printing. Permanent paper is often used as copying paper, while archival paper, which is stronger and made from rag pulp, is used for important documents such as diplomas and certificates. If the documents are expected to be handled in the future, archival paper should be chosen as it is more durable and withstands significantly more handling than permanent paper.

These two types of papers are distinguished from paper tested according to ISO 20494 where the paper stability is intended for general graphic applications. Such paper is not intended for archival storage, and does not have to be permanent, but rather to be durable during its use when used to produce newspapers, brochures etc.

Purpose

The standards are based on providing permanent paper that can be used in the production of archival documents (if the writing and printing is permanent according to ISO 11798)

Method

Permanent paper is evaluated according to ISO 9706 and archival paper (which is permanent and durable) is evaluated according to ISO 11108. RA-FS 2006:4 refers to these two standards for paper testing. The testing includes the following test procedures.

pH - cold water extract 

Acidic paper deteriorates quickly, so pH is an important parameter to measure in paper. Electrolytes are extracted from the paper in a water solution, and the pH value is then measured on this cold water extract.

Alkali reserve 

The formation of acids from air pollutants in the surrounding air or natural ageing is harmful to the paper. Therefore, such paper usually contains some alkaline filler (e.g., calcium carbonate) to prevent acid attacks and neutralize the harmful acids, i.e., the paper has an alkali reserve. The alkali reserve can be measured through a titration process.

Kappa number 

The kappa number indicates the amount of oxidizable material, such as lignin, in the pulp. Since such material can discolor and decompose the paper, the aim is to keep the kappa number low. Accordingly, the paper should only contain a limited amount of oxidizable material. For chemical pulps, the kappa number usually ranges between 1 and 100.

Tear strength 

Tear strength is a measure of the mechanical strength of the paper and indicates the force (mN) required to tear a piece of paper.

Folding strength 

Folding strength is another measure of the mechanical strength of the paper and indicates the strength required to fold a paper strip in a paper folder until it breaks.

Requirements for permanent paper (ISO 9706):

• pH value: between 7.5 and 10.0
• Alkali reserve: at least equivalent to 0.4 mol of acid per kg of paper (at least 2% chalk or equivalent)
• Tear strength: at least 350 mN in the machine and cross direction of the paper
• Kappa number: less than 5

Requirements for archival paper (ISO 11108): 

Archival paper must meet the requirements for permanent paper according to ISO 9706 and additionally;

• Manufacture: must consist of cotton, hemp, or linen but may contain a small amount of bleached chemical pulp
• Grammage: at least 70 g/m²
• Folding strength: at least 2.18 in the machine and cross direction of the paper

Accreditation 

The testing activities for permnent and archival paper maintain high quality through accreditation according to SS-EN ISO/IEC 17025:2018.

Certification 

Certification of durable paper in accordance with RISE certification rules (SPCR 004).

Deliveries

A test report from an accredited laboratory and statement on whether the test results meet the requirements of ISO 9706/ISO 11108 or not.