Extracts from DIN 6738, Classification of Paper and Board According to Life Span

(Papier und Karton; Lebensdauer-Klassen)

Reprinted with permission (see introductory paragraph)

3. Requirements

3.1 Minimum requirements

The minimum requirements for the following properties (for the purposes of this standard, referred to collectively as "MA") shall be as follows:

a) the tensile strength, F_B, determined in the cross direction, shall be 5 N;

b) the stretch at break, e_B, determined in the machine direction, shall be 0.5%;

c) the tearing resistance, W_i (E), determined in the machine direction, shall be 50 mN.

NOTE: These minimum requirements are of relevance to, for example, archivists and librarians, in order that older documents may be used and stored properly. In other words, the values specified are absolute and refer neither to unaged paper nor to paper of a certain thickness (caliper) or grammage.

3.2 Residual properties

After accelerated aging and subsequent conditioning, the residual properties of the paper (for the purposes of this standard, referred to collectively as "RE") shall comply with the following, in relation to the minimum requirements for the properties specified in subclause 3.1:

    RE >= MA + fL(AE - MA) (1)

where

MA	is the value of one of the properties specified in subclause 3.1;
AE	is the original value of the relevant property, i.e. that determined on the conditioned paper, before it has been subjected to accelerated aging;
fL	is the life expectancy factor.

5. Determination of life expectancy factor

The original value of the properties of test pieces which have only been conditioned (for the purposes of this standard, referred to collectively as "AE"), and the residual properties of test pieces which have been subjected to accelerated aging (RE), shall be taken as the mean value from all measurements made. Using the minimum requirements specified in subclause 3.1 (MA), the life expectancy factor, f_L ,shall be determined for each of the three relevant properties, using the following equation:

    fL=(RE - MA) : (AE - MA) (2)