Tracing paper is paper made to have low opacity, allowing light to pass through. Originally developed for architects and design engineers to create drawings which could be copied precisely using the diazo copy process, it found many other uses; the description evolved to include transparent paper. The original use for drawing and tracing was largely superseded by technologies which do not require diazo copying or manual copying (by tracing) of drawings.
The transparency of the paper is achieved by careful selection of the raw materials and the process used to create transparency. Cellulose fibre forms the basis of the paper, usually from wood species but also from cotton fibre. This material has a refractive index close to 1, which makes the material translucent to normal light[dubious ]. However, in the papermaking process, the spaces between the fibres provide interfaces for the light to be refracted, therefore creating a paper with relatively high opacity. Often, paper contains other filler materials to enhance opacity and print quality. For tracing or translucent paper it is necessary to remove any material which obstructs the transmission of light.
There are three main processes to manufacture this type of paper, as follows:-
- Through mechanical ‘refining’ of the cellulose fibre to create a fibre which is highly fibrillated and gelatinous, so that in forming the sheet of paper, virtually all air is excluded from the internal structure of the paper. This method produces a very translucent and even looking paper over a range of grammages from 42 to over 200 gsm.
- By making a ‘normal’ sheet of paper and then filling the spaces between the fibres with a material that has the same refractive index as the cellulose. This was a common process adopted in the USA. The product was frequently called Vellum, although this terminology can refer to a wider range of special papers. Due to the relatively high cost, this method of manufacture has largely disappeared.
- As with 2, by making a normal sheet of paper, which is followed by immersing uncut and unloaded paper of good quality in sulfuric acid for a few seconds. The acid converts some of the cellulose into amyloid form having a gelatinous and impermeable character. When the treated paper is thoroughly washed and dried, the resultant product is much stronger than the original paper. Tracing paper is resistant to oil, grease and to a large extent impervious to water and gas.
Tracing paper is named as such for its ability for an artist to trace an image onto it. When tracing paper is placed onto a picture, the picture is easily viewable through the tracing paper. Thus, it becomes easy for the artist to find edges in the picture and trace the image onto the tracing paper. Pure cellulose fiber is translucent, and it is the air trapped between fibers, that makes paper opaque and looks white. If the fibers are refined and beaten until all the air is taken out, then the resulting sheet will be translucent. Translucent papers are dense and contain up to 10% moisture at 50% humidity. This type of paper is roughly 25% lighter than regular paper.
Tracing paper may be uncoated or coated. Natural tracing paper for laser printing is usually uncoated.
- Traditional printing methods: letterpress, planographic / offset, silk-screen printing...
- Laser and inkjet printing
- Processing: varnishing, laminating, punching, embossing, folding, scoring
- Drawing: ink, Indian ink, graphite, pencils
- Photographic and cinema lighting: diffusion filter for light sources to produce aesthetic effect
- Offset printing:
- Print multicolored files on a multicolored machine – this helps to avoid registration problems.
- Packaging has to be removed immediately before printing.
- Paper stacks should be fanned out.
- Printing sheets should preferably be finished long grain.
- Translucent paper is printable with all popular as well as very fine screen widths.
- The use of frequency adjusted screen processes is also possible (FM-screening).
- The fountain solution pH has to be controlled (pH greater than 5.5).
- Only oxidative drying or UV-curing inks should be used.
- Addition of drying material should be avoided.
- Do not dry with hot air or infrared-heater, flatness problems may occur.
- Use powder spraying sparingly.
- Do not allow the stack after printing to be too high, thus allowing air to circulate to aid drying.
- Transparent papers require longer drying times, this has to be considered.
- Further processing can be done once the printing colors are completely dry.
- Inkjet printing:
- Line and script printing shows good results.
- Ink absorption is limited due to the high density of the transparent papers.
- Longer drying times have to be considered.
- Recommend a test-print.
- Laser printing:
- Transparent paper offers a fine closed surface that provides a high image quality.
- Due to high processing temperatures the paper may show some shrinkage or stretching effects.
- Therefore it is essential to test the run ability of the paper with the precise printing conditions.
- Transparent papers require a very high degree of mechanical treatment of the fiber.
- Thus it is sensitive to temperature and moisture fluctuations.
- The transparent paper should be stored in its original packing for 24 hours in the printing room.
- Ideal climate conditions for the transparent paper are 18 - 23°C at 45 – 55 %RH air humidity.
- Printed and unprinted transparent paper should be protected from moisture during storage.
- Marketing inlays
- Flyer, coversheets, dividers, prestige printings, business cards, greeting cards, invitations, playcards and posters, origami
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