Multilayer structures and interfaces
Multilayer and Interface codes are not used where no polymer is present, or when it is present only in minute amounts (e.g. as an additive to concrete).
Codes from the Multilayer Structure section are applied to objects that consist of two or more solid layers fixed together with a substantial degree of contact at their surfaces, forming a coextending or concentric structure – such as films, sheets, tubes, coatings and coated articles, microcapsules, encapsulated articles, laminates, balls.
For structures that are basically planar (e.g. films, tubes), the number of layers is found by counting from one side of the structure through to the other. For concentric objects (where one layer substantially surrounds another, such as a golf ball) the number of layers is found by counting from the middle layer to the surface.
Multilayer codes are not necessarily applied to insert/outsert moulded articles – it depends on the shape of the object being produced and whether the individual sections form a coextending/concentric structure or not.
For instance: a rubber seal formed around the edge of a window pane by outsert injection moulding should not be indexed as a Multilayer Structure because it does not consist of layers.
But a golf ball formed by insert injection moulding of an outer layer around a core can be coded as a Multilayer Structure because it clearly consists of a series of concentric layers.
When applying codes from the Multilayer Structure section you must also apply Interface codes, but the converse is not necessarily true. Where some feature of the interface is important, it is possible to apply Interface codes to a polymer which has an interface with some other material, but which cannot be regarded as a straightforward multilayered structure because of its shape. This would typically be for adhesives, or for the use of an additive or surface treatment to improve the adhesion between a moulded polymer and an insert.
A polymer interface with a liquid, vacuum or gas (including air) is no interface at all – you should index Polymeric exterior if the polymer is part of a Multilayer structure, but not if it is just a single layer.
A polymer interface with a material that is coded as an Additive is not indexed. For instance: for coating a polymer onto glass fibre to form a prepreg, do not index Glass fabric interface. For coating a metal substrate with a silane adhesion improver and then with a polymeric coat, you should index Metal interface, not Other interface.
Polymer interfaces with solids may be broken down into three types:
1) Non-permanent interfaces e.g. between a moulded polymer and the mould that it has just been made in. There is little or no adhesion between these two surfaces, and together the polymer and the mould cannot be regarded as a single object, but as two discrete objects that happen to be in close contact with each other. These interfaces are not indexed. The polymer surface may be indexed as a Polymeric exterior if the moulded item is itself a Multilayer structure.
2) Semi-permanent interfaces e.g. a perspex window with a layer of paper laminated onto it to protect the surface during transportation, which is removed when the window is installed. Although the paper does not form part of the window in its final state, the Paper interface may be indexed since the paper and the perspex adhere to each other to form a single laminate structure, which is itself an important stage in the processing of the window. When applying Multilayer codes you should index the number of layers both with and without the paper.
Pertinent to semi-permanent interfaces are the Application codes Q7205
Release coatings (a polymeric coating which, while staying attached
to its substrate, allows another material to be removed from it), and Q7227
Strippable coatings (a polymeric coating which may itself be removed
from its substrate).
When dealing with polymers which are not coatings the code B5334 Strippability
may be used to indicate a strippable polymer or a polymer interface with a strippable
material.
3) Permanent interfaces e.g. a polymeric paint. Obviously these are indexed.
When indexing a polymer interface with a heterogeneous material you may mix and match codes. For instance: for a polymeric coating on a substrate consisting of metal particles bound together with a polymer you should index Polymer interface and Metal interface.
When a polymer is used to bind discrete particles together to form a single heterogeneous mass, the interface with those particles should not be coded. For instance: for a magnet made from ferrite particles plus a polymer binder, you should not code Other interface.