AS-Film>

about AS-Film

article about AS-Film from German magazine "Modell" 11/99

Comparison of properties of cover-films for model-aeroplanes

Dimensions, series and types what is strain reliev? Deformation of wings

AS-Film is a laminating decor film inside a "thermal window low heat bonding cover film". Its two shrinkable series "LS" and "LLS-T" only differ from each other in the shrinking power ("Expander power"); shrinkage of the surface near 40% ore more depending of condition. With AS-Film parts can be bonded and shrunk on (covered). AS-Film enables the covering of parts which are difficult or otherwise impossible to cover, (points on the uselage, round parts, hemispherical parts, spherical wings which are split many times etc.) by high powered hot adhesiver. For decors AS-Film can be ironed at low sealing temperature on and removed by re-warming. AS-Film is an Adhesive Sealable Film, which is a physiologically recognised as safe and which can, on request, be shrinkable; hence the name AS-Film. Only peelable if re-warmed Its current properties can be summed up as follows:

AS-Film is not affected by climate, does not absorb humidity, melts on wood and achieves a long-lasting stable flexible bonding which lasts years on wood and many plastics incl. epoxy resin. Later formation of bubbles or folds in the cover can be ruled out; extra work (ironing, using the hot air dryer) etc. is avoided! AS-Film can be removed from wood without leaving residual matter. Repairs become easier. Prior coating (primary coat) to bond the glue to the ironing layer are not needed. In-built elastic layers lessen any further tearing; it is useful as a controlled surface joint. AS-Film is shrinkable from all sides; it shows this on the edges and spherical wings. Folds are removed by shrinking power!
AS-Film Series "LS" shows a very quick thermal reaction, requires little heat, is a soft adaptable flexible film which can be slightly stretched with very light shrinking power for covering less stable static parts; e.g. rip-fin wings. The light shrinking power avoids the distortion of (stable-light) wood constructions (rip-fin wings). Curved or bent wings or wings with plastic foam-filled wood can be covered without problems. The absolutely successful Universal method!
AS-FilmSeries "LLS" has other properties such as: Very low shrinking tension, lower dart drop, lowest weigth e.g.) than type LS-T, special manufactured for ultra light plane-constructions! Available only transparent lucent coloured.
AS-Film Series "LS-O Tape" is the self-adhesive type of the "LS"-series and differs from them only in the other glue with a very high adhesive strenght. The film is removable without destroying the surface of the wood! Adhesive on nearly all surfaces, e.g. glass!
AS-Film optic properties: "O" is for Opaque is a film which covers well. The grain of the wood is covered. Nothing shows through. The high pigment content increases the weight only slightly! "T" is for transparent. Light colours are intentionally hazy so that you can see the model at a great height.
Dimensions, application of the series, types and weight of the films

AS-Film is available on a roll in width of 623 mm (241/2") in the "LS" and "LLS" series.
The Reasons for two series: A) Strain relief, also called residual shrinkage, occurs when a film is heated to an elevated temperature. The resulting shrinkage of the film is merely a relaxation of strains included during the manufacturing of the film or processing of the film. Once these strains are relieved at a specific temperature, there should be no further shrinkage due to strain relief as long as that temperature is not reached. The greatest value is evident after one hour and sealed after 2 weeks!
B) Shrinking tension at the same time of strain relief is depending of the thickness of the iron layer. For fully filled wings, a higher thickness with higher mechanical resistance is preferred, and for finrip-wings, a film with the lowest weight. Shrinking tension is a power similar to expander power.
Type "LS": a film with a lower shrinking power for fin rip wings. Distortion of stable constructed wings is hardly to be expected. The thinner "thermal window" - lighter thorough melting requires more time and care. Available types:
- Type "LS-O" opaque WHITE and opaque COLOURED: with restricted shrinking power - weight approx. 95 g/m² Type
- "LS-T" transparent and translucent hazy coloured. The measured remaining shrinking strength is less than type LS-O; high performance, the aerodynamics is hardly changed and secures best performances! Ideal for lightly constructed static stable fin-rip wing parts without a risk of a twisted frame e. g. for high performance regulator. Weight approx.49 g/m²
- "LLS-T" transparent and translucent hazy coloured. Similar type LS-T; developed for extreme light fin-rip wings with additional lower shrinking strength than type LS-T. Never a risk of twisted wings of and highest performances! Ideal for very lightly constructed planes wing parts e.g. for high performance regulator. Weight approx.42 g/m²
- "LS-O Tape": Film for wooden sheeted, foam filled wings! Or other applications e.g. the covering of nearly every surface. Weight approx.112 g/m².

Strain reliev:

Strain reliev (also called residual shrinkage) occurs when a plastic film is heated to an elevated temperature. The resulting shrinkage of the film is merely a relaxation of strains included during the manufacturing of the film or processing of the film. Once these strains are relieved at a specific temperature, there should be no further shrinkage due to strain reliev as long as that temperature is not reached. The 1/2 til 3/4 of reliev is done within one hour, the rest 2-4 weeks - depending of thickeness and kind of polymer - later.
Strain reliev is a inevitable property of all plastic films, based on the movement in the new position after the last higher heat treatment of the (polymer) molecules chains; each chain has few 100.000 atomes!
Some typical curves of shrinkage due to strain relief are shown in Fig. 3 and 4 for two types of a bi-axially oriented polyester films; other polymers are similar! Controlled shrinkage levels are provided for those industries on the manufacturing or use of the product. For example: 50% shrinkage in machine direction and transverse direction of the film = volume near 25 % of the surface (space) of film only 100°C of special shrinking films is used as an aid in manufacturing some products.

Fig. 3
Shrinkage vs. temperatureMYLAR A, 23痠

Fig. 4
Shrinkage vs. temperatureMYLAR A, 190痠

Deformation of wings - shrinking strength

Strenght of shrinking (shrinking tension): The other inevitable main property is the strength (also called shrinking tension) in according of dtrain reliev depending of the thickness and the kind of the polymer (chemical of the polymer). It is a power similar a expander-power; a delayed spring-power.
For full filled wings and and normal static stabil finrip wings is prefered the low shrinking strength of serial LS;
for extreme static light built finrip-wings is prefered the serial LLS with a reduced shrinking tension.
There is no chance (cure) to influence by any kind of processing or converting this natural chemical law of the polymer; the only solution (cure) is the chemical and at this reason are few seriales manufactured!

Manufacture and name of film	Gap on curved area (frontside)	Gap on oposite of curved area (backside)	Addition	Balance against frame	Colour of films
non covered finrip frame	+ 4 mm	+ 1,5 mm	5,50 mm	0,00	without film
SOLARFILM	+ 4 mm	+ 10 mm	14,00 mm	8,50 mm	Orange
ORACOVER LIGHT	+ 4 mm	+ 5 mm	9,00 mm	3,50 mm	Yellow luzent
AS-Film type LS-O	+ 3 mm	+ 6 mm	9,00 mm	3,50 mm	Yellow amber
AS-Film type LS-T	+ 3 mm	+ 2 mm	5,00 mm	0,00	Blue dark
AS-Film type LLS-T	Shrinking strength (also called shrinking tension) -25% than LS-T

Small differences on the curved gap are the result of the curves of the wing because measuring was taken not all on the same position. The test was done in spring time year 2001.