Paints and varnishes - Scratch test
1 Scope
1.1 This standard is one of a series of standards dealing with the sampling and testing of paints, varnishes and related products.
This standard specifies a test method for determining under defined conditions the resistance of a single coating or a multi-coat system of paint, varnish or related product to penetration by scratching with a hemispherically tipped needle. Penetration of the needle is to the substrate, except in the case of a multi-coat system, where the penetration of the needle may be either to the substrate or to an intermediate coat.
1.2 The method is intended for application as follows:
a) either as a pass/fail test, by testing with a single specified load applied to the needle to assess compliance with a particular specification;
b) or by applying increasing loads to the needle to determine the minimum load at which the coating is penetrated.
2 Normative references
The following normative documents contain provisions which, through reference in this standard, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrections), or revisions, of any of these publications do not apply to this standard. However, parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies.
GB/T 3186-2006 Paints, varnishes and raw materials for paints and varnishes - Sampling (ISO 15528:2000, IDT)
GB/T 9271 Paints and varnishes - Standard panels for testing (GB/T 9271-1988, eqv ISO 1514:1984)
GB 9278 Paints and varnishes and their raw materials - Temperatures and humidities for conditioning and testing (GB 9278-1988, eqv ISO 3270:1984)
GB/T 13452.2 Paints and varnishes - Determination of film thickness (GB/T 13452.2-1992, eqv ISO 2808:1974)
GB/T 20777-2006 Paints and varnishes - Examination and preparation of test samples (ISO 1513:1992, IDT)
3 Required supplementary information
For any particular application, the test method specified in this standard needs to be completed by supplementary information. The items of supplementary information are given in Annex A.
4 Apparatus
4.1 Scratch apparatus, the principle of which is illustrated in Figure 1; other arrangements which give a similar performance can be used, however. This apparatus consists essentially of a horizontally sliding test panel holder (1) driven by a constant-speed motor (2) at a rate of 30mm/s to 40mm/s beneath the point of a scratching needle (3), which is perpendicular to the test panel. The needle is fixed in a chuck, directly above which is a holder capable of carrying weights up to a mass of 2kg. The maximum load for which the apparatus is designed shall be marked on the test apparatus.
The apparatus is adjusted so that the needle comes smoothly into contact with the film, i.e. before the stop (4) reaches the bottom of the sloping ramp, to form a straight scratch not less than 60mm in length. A ramp with an angle of 10° to 15° to the horizontal has been found to be satisfactory. The panel holder can be designed to allow a lateral movement of test pieces so that more than one scratch test can be carried out on the same test piece.
Foreword i
1 Scope
2 Normative references
3 Required supplementary information
4 Apparatus
5 Sampling
6 Test panels
7 Procedures
8 Precision
9 Test report
Annex A (Normative) Required supplementary information
Annex B (Informative) Procedure found to be convenient for manufacture and re-tipping of scratch test needles
