The importance of product quality
This note seeks to explain the importance of number plate component quality and the requirement of correct matching of components to give Quality performance assurance to the motorist and the supplying outlet, as required within the British Standard.
The British Standard for number plates (BS AU 145d, soon to be replaced with BS Au 145e) is designed to ensure that number plates give value for money for the motorist and compatibility with ANPR requirements. It covers performance criteria for plates which must be met not just when plates are new but also when subjected to a testing regime which simulates conditions likely to be met during the life of the plate.
It is important to be aware of the responsibilities and dangers of using components that are of substandard quality or are mismatched. BNMA Number Plate manufacturers carry out extensive test procedures to eliminate components which may lead to number plates failing to meet the required standard - the failure of a plate against any aspect of the British Standard means that the plate is not just sub-standard and illegal but will give practical problems in service
(1) THE IMPORTANCE OF QUALITY COMPONENTS
With a Number Plate being an item subject to legislation product performance and durability is important to give the motorist the assurance of quality – this is the main driver of any British Standard.
A number plate that passes just the initial BS photometric tests should be treated with caution, as this does not indicate conformance with the standard. The British Standard is formalised to give the consumer adequate protection that the number plate can perform satisfactorily for its design life of 5 years. BS tests (9 through 15 in BS AU 145e) address this aspect of number plate quality and are key to assure number plate durability.
The challenging environment experienced by the number plate (particularly the front plate in adverse weather conditions) is reflected in the testing regime. It is important that components of the correct specifications are used, and this applies particularly to the Impact Resistance and UV Stabilisation qualities of all materials. If inferior components are used this has the consequence of weakening the performance of the construction and may lead to the breakdown of the number plate construction.
Number Plates break down prematurely either due to poor quality components or the incompatibility of components (see also “The Importance of Matched Components” below). A major risk area is the use of inferior quality adhesives which bond optically clear front face type products (often referred to generically but incorrectly as “acrylic”) with retro reflective products. Components used by BNMA members are designed and tested specifically for this application.
In general standard “off the shelf” products have tested as unsuitable by BNMA members who only use components which have been designed and specifically approved by suppliers for number plate construction.
Poor quality components give the following effects:
Inferior raw materials and / or inferior quality moulded components or incorrect lamination procedures of components can create stresses. When these materials are exposed to typical summer temperatures they can stress release and warp and bend as shown below:
This warping and internal stress can rapidly lead to “tunnelling” which is where a portion of the reflective material separates from the acrylic creating a tunnel that runs from top to bottom of the plate allowing moisture and dirt ingress. This is accelerated in winter conditions in particular when roads are treated with salt.
Below are images of a tunnelled plate both in daylight and under ANPR NIR.
CRACKING, CRAZING AND FADING
Number Plates made from materials with insufficient impact strength will crack or break in normal service. Cracks are particularly detrimental as the plate is unlikely to be replaced immediately but left on the vehicle. These fractures will let in moisture and dirt, causing delamination and problems for ANPR systems. Number Plates that break completely while driving can lead to hazards such as large plastic parts being left on the carriageway as well as extra cost for the motorist.
Components of the correct specification are therefore critical to avoid this, and sub-standard materials here can also lead to changes in the optical properties of these materials by reducing light transmittance and increasing the ‘haze’ value.
It is well known that inferior quality adhesive and incorrect UV stabilisation (see below) of a clear front face type product will increase the risk of cracking, crazing and fading.
Printing ribbons/toners are also important here. When poor print materials have been substituted premature character, breakdown has resulted which again gives a poor plate readability and subsequent problems for ANPR.
This is often most apparent during high temperatures where poor quality high wax content ribbons will effectively ‘melt’ in hot weather allowing the reflective to show through the character - see example below:
The UV stability of components is important. Almost all plastic and printed products that are exposed to sunlight will degrade substantially if the polymers and inks that are used are not UV stable. In the case of polymers UV damage can cause brittleness, crazing and loss of strength. It is not uncommon for some non-UV stabilised clear acrylic products to turn a “milky white” after even relatively short exposure which would have significant impact on ANPR. Similarly, toners or thermal ribbons that are not UV stabilised will quickly fade making the characters appear to be grey rather than black.