ISO/TS 23885:2022

TECHNICAL ISO/TS
SPECIFICATION 23885
First edition
2022-06
Paper, board and graphic
technology — Determination of the
coating strength in the inner fold
Papier, carton et technologie graphique — Détermination de la
résistance du revêtement dans le pli intérieur
Reference number
© ISO 2022
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
5.1 Folding device . 2
5.2 Impact device . 2
5.3 Image capturing system . 3
6 Calibration and adjustment of apparatus . 4
6.1 Folding instrument . 4
6.2 Impact device . 4
6.3 Image capturing system . 4
7 Sampling and preparation of test materials . 4
7.1 Sampling . 4
7.2 Conditioning. 4
7.3 Preparation of test materials . 4
7.3.1 Test pieces . 4
7.3.2 Receptors . 5
8 Procedure .5
8.1 General . 5
8.2 Folding. 5
8.3 Separation of particles . 5
8.4 Image capturing . 7
8.5 Image analysis. 7
9 Calculation . 8
9.1 General . 8
9.2 Mean particle area. 8
10 Precision and bias . 8
11 Report .11
Annex A (informative) Impact device .12
Bibliography .16
iii
Foreword
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This document was prepared by Technical Committee ISO/TC 6 Paper, board and pulps, Subcommittee
SC 2, Test methods and quality specifications for paper and board, in collaboration with Technical
Committee ISO/TC 130, Graphic technology.
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iv
Introduction
When folding coated paper during post-press operations, the paper surface can crack in the fold and
coating particles can be separated. In the final printed product, the cracking of coatings can cause
aesthetic and technical disturbances. Separated particles can occur on both sides of the fold but only
remain between sheets of the product, if separated from the inner fold. In case of a good contrast
between particles and the printed surface, aesthetic quality problems result, which can cause customer
complaints. Cracks can also occur on both sides of the fold but can only result in aesthetic quality
problems, if both the fold is still present in the final product and in case of a good contrast between
cracked fold and printed surface. Technical quality problems can occur, e.g. on thread-sewn products, if
weakened coatings disturb the spine-gluing quality.
To improve the folding behaviour of paper and board, creasing is recommended. For woodfree coated
papers (WFC), creasing is typically recommended for grammages of 170 g/m and higher. Thereby, it
should not be neglected that some post-press operations (e.g. folding of signatures) do not allow an
effective creasing, and creasing cannot always achieve the desired improvement.
The coating strength in the fold can be determined both in the inner and outer side of a fold. This
document contains a test method for the inner fold. This method has been developed in a research
[3]
project and is intended to be performed as general paper test to acquire knowledge on a material
property and either as a print finishing quality prognosis or a quality acceptance test.
The test consists of four processes: folding of unprinted paper, separation of particles using an impact
test device, image capturing of separated particles and image analysis.
v
TECHNICAL SPECIFICATION ISO/TS 23885:2022(E)
Paper, board and graphic technology — Determination of
the coating strength in the inner fold
1 Scope
This document specifies a test method for the evaluation of the paper coating strength in the inner fold.
The test method is intended for single or multiple coated papers up to a thickness of 150 µm that can be
folded without creasing.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 187, Paper, board and pulps — Standard atmosphere for conditioning and testing and procedure for
monitoring the atmosphere and conditioning of samples
ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts
images
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
inner fold
fold on the inside of a folded sheet
3.2
coating strength in the inner fold
resistance of a paper coating against cracking and particle separation due to external forces
3.3
machine direction
MD
direction in a paper or a board parallel to the direction of travel of the web on the paper or board
machine
[SOURCE: ISO 4046-3:2016, 3.79]
3.4
cross direction
CD
direction in a plane of the paper perpendicular to the machine direction
[SOURCE: ISO 4046-3:2016, 3.35]
3.5
pressure sensitive adhesive
PSA
type of adhesive which, in a dry state, is permanently tacky at room temperature and adheres readily
when activated by pressure
4 Principle
A test piece of given dimensions is folded with a specified folding pressure using a laboratory folding
device. The folded test piece is inserted into an impact tester to separate loose particles from the fold
onto a carrier. An image of the carrier with the collected particles is then captured followed by an image
analysis. The mean particle area in mm is determined and reported as the test result.
5 Apparatus
5.1 Folding device
The folding device is used to perform folds in a defined and reproducible way. It shall contain two
rotatable rollers made of non-compressible material. One of the rollers shall be equipped with a manual
or automatic drive mechanism, and one of the rollers shall be height adjustable and able to apply a
predetermined line pressure. The adjustment shall be done in two steps: first by adjusting the roller
distance to double paper thickness of the test piece, and second by reducing the roller distance by
applying the selected line pressure. The line pressure scale of the folding device shall include a line
pressure of 80 N/cm.
NOTE 1 The folding device can be constructed in a way such that the non-adjustable roller is on one end of a
beam balance and a spring assembly is on the other end.
NOTE 2 The test result probably depends on the geometric size of the folding device (folding rollers). Thus,
results obtained with different folding devices could not be directly comparable.
1)
NOTE 3 FG II Precision Folding Device and Fogra Folding Instrument FI meet these requirements.
5.2 Impact device
The purpose of the impact device is to separate the loose coating particles from the fold of the sample.
The impact device shall be constructed in a way such that an impulse momentum of (6,8 ± 0,2) Ns is
applied. The basic calculation of the impulse momentum and a construction example of the impact
device are given in Annex A. The impact device consists of a vertically movable insert holder that is able
to execute a guided free fall that stops by reaching the impact plate where an impulse momentum is
applied.
The insert holder is the mount of both the upper and lower insert. The upper insert is for the folded test
piece, the lower insert for the receptor (see 7.3.2). The specified dimensions of both inserts are given in
Figure 1 and Figure 2.
1) FG II Precision Folding Device, a product supplied by prüfbau Dr.-Ing. H. Dürner GmbH, Peissenberg, Germany
and Fogra Folding Instrument FI, a product supplied by Fogra e.V., Aschheim, Germany, are examples of suitable
products available commercially. This information is given for the convenience of users of this document and does
not constitute an endorsement by ISO of the product named. Equivalent products may be used if they can be shown
to lead to the same results.
Dimensions in millimetres with a tolerance of ±0,05 mm
Figure 1 — Plan and front view of the lower insert for the receptor
Dimensions in millimetres with a tolerance of ±0,05 mm
Figure 2 — Plan and front view of the upper insert for the test piece
NOTE The lower insert contains a hole in the base plate in order to simplify the removal of the receptor after
the test. The upper insert contains a notch for the central alignment of the inserts. Upper and lower inserts are
designed to fit to each other and to fix the long edges of the test piece during the test.
5.3 Image capturing system
The image capturing system consists of a digital camera and an illumination unit. It shall ensure the
uniformity of the field of view. The illumination unit shall ensure a homogeneous and reflection-free
illumination of the sample. The irradiation intensity shall be adjusted to the camera system used.
The digital camera shall be able to capture an 8 Bit grey scale image. If a RGB camera is used, the image
shall be converted by the weighted grey level model.
The image capturing system shall be able to detect particles of a minimum size of 12 µm. The contrast
ratio of the captured image shall ensure a good separability of particles and background.
NOTE The image quality of the digital camera depends on the product of the resolution of the camera
sensor, the magnification, and the distortions caused by the lens system. Good results can be achieved using a
monochromatic line camera, having a sensor length of 40,96 mm, a resolution of 4 096 × 1 pixel, a focal length
of 100 mm, and a dynamic range of 50 dB. The use of spacer rings can be necessary to adjust the image area to
the test piece dimensions. The use of a line camera requires a flatbed portal unit with a controlled step function
synchronized with the image capturing. For
...