stiffness. This can be measured as follows:
A single Large Letter should be placed on a flat surface with the shortest edge of the Large Letter overhanging a straight edge of a flat surface by a horizontal distance of 100mm. The leading edge of the Large Letter is then released and allowed to bend down under its own weight. If the leading edge drops to 40mm or more, then the stiffness is less than 8N.mm and the large letter is unmachineable. 5.4 Separation The large letter must not be stuck together and must be capable of separating to allow them to be effectively processed. When placed on a slope of 65? to the horizontal, the items must be capable of separating, by sliding one from another, under the force of gravity. 5.5 Shape Large Letters can be rectangular or square within the permitted dimensions and can be laid out (address and indicia) in landscape or portrait format. 5.6 Polywrap Outer • The film must be intact, undamaged and must not be punctured or torn • Perforations are not acceptable • The film must be sufficiently strong enough to tolerate handling without tearing or splitting at the seals • The film must be >15 microns thick when measured at any point on the Large Letter other than the seal • Any overprinted text must adhere to the film and must not break up or wear during processing • There must only be a single layer of film covering the delivery address block 6.0 Print Contrast • Required print contrast ratio for addresses printed on envelopes >50% • Required print contrast ratio for addresses printed on window inserts >55% • Required minimum reflective difference >30% • Required minimum background reflectance >35% • Inverse printing i.e. negative contrast is not permitted (i.e. Delivery address block lighter than background) 7.0 Sealing This section is divided into the paper and polymer/ polwrap requirements as they are different 7.1 Paper Paper envelopes must be sealed securely on the back, front and edges. A tolerance of 35mm x 25mm is permitted on the opening flap. Regardless of whether the opening flap is placed on the front or reverse of the item (the front being where the
For polymer envelopes or polywrapped large letters – where the polymer is transparent only the largest insert must be visible to the front of the large letter and the lateral movement is <20mm. There is no requirement for the content to be referenced to the bottom left corner, customers just need to ensure that there is no more than 20mm along the long edges and no more than 20mm along the short edges. 5.0 Material – Construction 5.1 Paper Envelopes • Must be paper based and no perforations are permitted • Envelope paper weight = 70gsm minimum • Single piece (folded and sealed) = 100gsm minimum • Large letter sized postcards = 200gsm minimum 5.2 Polymer envelopes and polywrap • Must be made of polymer film e.g. polyethylene • Materials produced from polymer fibres that are randomly distributed and non-directional (laid as web) and bonded together by heat and pressure are acceptable e.g. Tyvek 5.3 Material – General Absorbency: (paper based envelopes): 15-35 gsm of water in 1 minute (BS EN 20535 – Paper and board. (Determination of water absorptiveness) Glue: Any adhesives used in the production of envelopes must not leak onto the open surface of the envelope and must be dry when the mail is presented. In no instance should mail pieces be stuck together. When polymer envelopes are used, the glue must be stronger than the polymer and must not produce protruding mounds on the mail item. Opacity: >85% (BS ISO 2471 – Paper and board. Determination of opacity (paper backing) Porosity: <700ml/minute (BS 6538-2-Air permeance of paper and board) Rigidity/Stiffness: The acceptable rigidity/stiffness is >8N.mm. There is no upper limit on mail piece
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