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CAD/CAM Vinyls

Choosing The Right Vinyl

Face Films

Vinyls can generally be manufactured in one of two ways, i.e. by calendering or by casting.

Calendering

The molten resin is squeezed between a series of rollers to produce a film of vinyl. Due to the mechanical method of manufacture, the PVC has a built in memory and will attempt to return to its original form, which in turn may lead to film shrinkage.

PVC in its 'natural' form is a rigid material, so additives known as plasticisers have been added to soften the film and make it usable. Other additives have to be included to stabilise against the effects of heat and UV and to add colour, etc.

There are two different types of plasticisers currently used which sub-divide the calendered vinyls into distinct groups. Monomeric and Polymeric. Both types of calendered films perform slightly different in one direction than the other, i.e. in machine direction and cross machine direction.

Monomeric PVCs

In this case the plasticisers used are short-chain, which means that they do not bind into the film particularly efficiently and have a tendency to migrate out of the film itself, leaving the film brittle. These films are generally 80-100 micron thick and are prone to shrinkage. They are also quite stiff and hard on blade wear.

Generally they have an expected outdoor life of 3 years for black and white and 2 years for colours. They are available in a range of matt and gloss finishes and are economically priced.

They are suitable for most internal applications and selective short term external applications. They are barely conformable over contours and are recommended for flat-sided applications only.

Polymeric PVCs

These are sometimes also known as stabilised films or extended life films. The plasticisers used are long-chain, which allows them to bind into the film more efficiently, reducing the migratory effect. These films are generally 60-80 microns thick and are far less prone to shrinkage than the monomeric range, typically 50% less.

They feel softer and generally have an outdoor life expectancy of 7 years for black and white, 5 years for colours and 3 years for metallic colours. Available mainly in gloss finish, although translucents and some matt finishes are available. They are suitable for most external applications, but conformability over complex contours is still somewhat limited.

Casting

The liquefied resin is coated onto a highly polished substrate, such as casting paper to produce a thin film of vinyl. Due to the lack of mechanical force being used, cast films do not have the same memory as calendered vinyls and the resulting shrinkage is minimal, typically 50% less than polymeric films. These films are generally 50-60 micron thick and have a very soft handle.

Generally they have an expected outdoor life of 10 years for black and white, 7 years for colours and 5 years for metallic colours.

Available in mainly a high gloss finish, these films are the ultimate in terms of conformability over contours such as rivets, corrugations, etc.

Due to the film construction, these vinyls can be cut and weeded in finer detail than the calendered films. Generally all the ingredients used in the production of cast vinyls are of the best quality and so the performance in terms of temperature ranges, colour fastness, etc. is better than the calendered films. Cast films perform equally well in both directions, i.e. in machine and cross machine direction.

Adhesives

In the signage market, manufacturers generally standardise on acrylic adhesives for external, permanent applications and the adhesives are formulated to be compatible with the life expectancy of the face film being used.

Guide For The Correct Usage Of Self-Adhesive Materials

Storage

Rolls should be stored on end, to avoid pressure marking. Extremes in temperature and humidity should be avoided. High temperatures can lead to adhesive bleed, causing problems with the sprocketed material in particular, whilst humidity may cause problems with the backing papers, such as curl, etc. All self-adhesive vinyls should be allowed 24 hours to acclimatise to workshop temperatures and humidity levels, before usage.

An ideal storage condition, recommended by most manufacturers, is 15°C - 25°C and at 50% relative humidity. Avoid storing in direct sunlight or near heaters. Keep the rolls off the floor, as dampness from the floor may be absorbed into the backing paper.

Cutting

Ensure the depth/pressure setting of the plotter blade is correct for the vinyl being used. Not cutting deep enough will create difficulties in weeding the waste matrix. Whereas cutting too deeply into the siliconised backing paper, may cause delamination of the paper onto the adhesive side of the vinyl when removing the cut lettering from the backing paper. It is always recommended to test cut the vinyl, by producing some lettering in the same size as the finished work.

Cutting the vinyl, then leaving for some time before the weeding process, may lead to difficulties in weeding the waste and removing the lettering. These problems are caused by the adhesive flowing back and are especially noticeable in warmer conditions. Cold conditions may cause the face of the film to harden and become brittle. This in turn can cause the blade to skid across the surface and cause the film to break when weeding. We would recommend using a new blade in cold conditions and to allow the film to acclimatise to room temperature.

Weeding

Weeding in the process and the name given to the removal of the waste matrix, prior to the transfer of the cut lettering. Tweezers and scalpels are the most common tools used for weeding. To begin the process, start at one corner and work across the image in short diagonal movements, usually in a right to left direction.

Transfer Of The Pre-Spaced Image

After the waste matrix is weeded away, the cut lettering has to be transferred accurately from the backing paper to the finished substrate, using application tapes to achieve this successfully. As a general rule, matt finished vinyls require a higher tack application tape than a gloss vinyl, and smaller images require a higher tack tape than larger ones.

Apply the application tape smoothly to the weeded image, avoiding wrinkles and bubbles wherever possible. Squeegee the application tape down using a plastic applicator. Start from the centre and work outwards - follow a pattern similar to the 'Union Jack'.

Turn the vinyl over, so that the application tape is facing down on the bench and the backing paper is facing upwards. Remove the backing paper, starting at one corner and peeling back diagonally at an angle of 180°.

Removal Of Existing Vinyl Lettering

To remove old lettering, use a heat source, i.e. a hair dryer or heat gun, to soften the vinyl, then strip the vinyl slowly off the substrate. This tends to leave a residue of adhesive on the substrate. Using adhesive remover, spray the adhesive residue and let it penetrate for 30-60 seconds. Use a squeegee to remove as much of the adhesive as possible. Spray adhesive remover onto a rag or paper towel and wipe the area clean. Finally clean the entire area with water and detergent then degrease as detailed below. Use Rapid Remover adhesive remover.

Can be used on most surfaces, but avoid use on latex printed surfaces, styrofoam or styrene surfaces.

Always test the area first.

Preparation Of The Substrate

The substrate must be free from grease, dirt and foreign matter before application. The safest and easiest way to clean and degrease the surface is to use Rapid Prep, a non-toxic, degreasing agent that removes most waxes and silicones. This will thoroughly degrease the surface in preparation for the application of the vinyl graphic.

Application Of The Pre-Spaced Image

There are two basic methods of applying self-adhesive vinyls, depending on the size/complexity of the image and difficulty of the substrate. In all cases, ensure that the sign is applied above the minimum recommended application temperature, i.e. most good self-adhesive vinyl manufacturers recommend the range of 15°C - 25°C as the ideal temperature for the application of self-adhesive vinyls.

Dry Application - used in the majority of cases.

Top Hinge Method

Before commencing, establish exactly where the sign is to be located, then tape the sign into position using small pieces of masking tape. Use 2" masking tape to create a hinge - half the masking tape on top of the sign and the other half on the application surface. Squeegee the masking tape hinge firmly into position.

To apply, lift the sign away from the surface and fold back on the hinge. Peel off about 6" of the backing paper then lower the sign, keeping the adhesive away from the application surface. Starting at the top in the centre, squeegee down and outwards towards each edge in turn. Remove another 6" of backing paper and keep repeating the process, using overlapping strokes, until the sign is completely applied (for large pre-spaced signs, do as above, but slit between each letter, so that every letter can be applied individually). Now carefully remove the application tape, diagonally at 180°.

Air bubbles can be removed by puncturing the bubble with a pin, then squeegee the trapped air towards and out of the puncture. Finally re-squeegee the sign, paying particular attention to the top and leading edges. If the sign is long and narrow, the same procedure can be adopted with the hinge on the edge of the sign, instead of the top.

Wet Application - used to apply large or multi-coloured images to difficult substrates, i.e. convex or concave curvatures. Also recommended for application onto glass surfaces.

One of the secrets of good long term application is to have optimum contact of the adhesive to the surface. Any gaps between the adhesive and the surface will inevitably, through time, lead to adhesive failure.

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