1.5 The use of Finishes Flashcards
What is the substrate?
the material on to which the prink ink is applied, such as paper or boards
What items use screen printing?
posters, display boards and textile t-shirts
Why does screen printing have minimal set-up costs?
due to the basic screens and printing inks
How does screen printing work?
The substrate to be printed sits on the screen print machine base and the upper section secures the screen. The image to be printed is created on a screen (or a stencil), which is a mesh held by a frame. The screen has open areas for the ink to pass through. A different screen is required for each colour. This can increase the time taken to produce the print as well as the overall production cost per item. The screen is placed over the substrate on the machine bed. The pigmented printing ink is placed on the screen. A squeegee (a flexible polymer blade, held in a rigid handle) is then used to force the ink to flow through the mesh onto the substrate. Once ach colour is complete, the ink dries or cures to complete the print.
Does screen printing print one or multiple colours at a time?
One colour
Which printing processes uses a four-colour process?
flexography
offset lithography
digital printing
What are the four colours that are used in the four-colour process of printing?
cyan
magenta
yellow
black
How do you ensure an accurate and non-blurry print in flexographic printing?
The colours must line up precisely with each other. If one colour is slightly out of position, the printed image will appear blurred. In colour printing, a registration system is used to ensure the final image is consistent and of high quality.
How does the registration system work with flexographic printing?
The registration mark is a set of precision marks on the final substrate, outside the print area, which is used as a quality control (QC) check to ensure all four colours have printed in the correct place. These registration marks are often seen at the side of printed newspapers as a bar of CMYK colours.
Where can you find the registration marks from flexographic printing?
the sides of newspapers
What is the least expensive printing process and why?
Flexographic printing is the least expensive of the printing processes due to the simple operation and use of fast-drying water-based inks.
When is flexographic printing used?
newspapers
comics
catalogues
folding packaging cartons
labels
carrier bags
wallpaper
What type of print runs does flexographic printing use and why?
As flexographic printing uses rolls of substrate rather than sheets, this allows large continuous print runs to be completed with ease.
What is the process of flexographic printing?
- it uses flexible printing plates wrapped around rotating cylinders on a web press.
- Water-based or UV curable ink is fed from the first ink roller to the anilox roller.
- The anilox roller makes the ink a uniform thickness and transfers the ink to the plate cylinder.
- The substrate moves between the plate cylinder and the impression cylinder.
- The impression cylinder applies pressure to the plate cylinder to transfer the image on to the substrate.
- The web, which by now has been printed, is fed into the overhead dryer so that the ink is dry before it goes to the next print unit.
What are the advantages of flexographic printing?
High print speed
Ideally suitable for long runs
Prints on a wide variety of substrate materials, both porous and non-porous.
Low cost of equipment and consumables
Low maintenance
What are the disadvantages of flexographic printing?
The cost of the printing plates is relatively high, but they last for millions of print runs.
Takes a large amount of substrate to set up the job, excess material may be wasted.
Time consuming to change for any alterations to the print content.
What kinds of printing processes is offset lithographic printing suitable for?
one colour (single roller)
five colours (CMYK plus can additional metallic colour on a five-roller machine)
ten-feature machine (CMYK, metallic, varnishing, spot varnishing and duplex on a ten-roller machine)
What length of print runs does offset lithographic printing use?
medium and long print runs
What products are printed using offset lithographic printing?
books
business forms and documentation
magazines
posters
packaging
What principle is offset lithographic printing based on and how does this work?
Lithographic printing is based on the principle that oil and water do not mix. Lithographic plates are chemically treated to make the image area oleophilic (absorbs oils easily) and therefore receptive to oil-based printing inks. The non-image area is treated to be hydrophilic (absorbs water easily).
What is the process of offset lithographic printing?
- During printing, fountain (dampening) solution, which consists primarily of water, applied in a thin layer to the printing plate cylinder and is attracted to the hydrophilic non-image areas of the printing plate.
- Ink is then applied to the plate and is attracted to the oleophilic image areas.
- Since ink and water essentially do not mix, the fountain solution prevents ink from entering the non-image areas of the plate.
- Printing substrate is either sheet-fed or web roll-fed into the printing machinery.
- Printing plates are produced by a computer to plate (CTP) process via a laser which etches the image onto the plate. The plates are then attached to the machine and dampened by a damping roller.
- The ink is applied to the printing plate. The plate cylinder rotates onto a blanket roller which becomes coated with ink. As the substrate is fed through, the image on the blanket is transferred to the substrate to produce the printed product.
What are the advantages of lithographic printing?
Consistently high image quality
Suited to higher volume print runs of 1000 or more
Quick and easy production of printing plates
Long life of printing plates because they only come into contact with the printing blanket, which is softer and less abrasive than the substrate.
What are the disadvantages of lithographic printing?
Expensive setup and running cost for small quantities
Only suitable for porous substrate materials
Why is digital printing so popular?
its speed and efficiency
What types of images do digital printers produce?
full colour, highly detailed print runs with the option of different designs on each page, both front and reverse sides.
How do digital printers apply ink?
Similar to laser printers, where the ink sits on top of the paper and is allowed to dry or be laminated.
What are some products that are printed using digital printers?
promotional materials such as business flyers and business cards
Why is the use of digital printing ideal for mass customisation?
Due to the fast drying inks similar to those used in flexography
Why are polymers described as self-finishing?
They can be pigmented during the manufacture process to give colour and there require no additional secondary finishing process.
What are the 3 types of finishes that you can apply to polymers?
- adding colour in the moulding process
- acrylic spray finished
- overmouldings
How can you add colour to the polymer in the moulding process?
Pigments are tiny particles, which are added to the polymer to create a particular colour. The pigment can be added to the polymer during the manufacturing process or they can be added during the manufacture of the polymer stock form.
What are some examples of smart pigments?
Thermochromic (change colour at specific temperatures)
Phosphorescent (glow in the dark)
Why are acrylic spray paints used on polymers?
enhance aesthetics and improve product function
it can also protect against the effects of UV light and weathering
Why are acrylic spray paints appropriate to use on polymers?
It is fast-drying, water soluble paint that becomes water resistant when dry.
In what industry are acrylic spray paints used a lot for mass customisation?
Car manufacturers as it allows the customers to choose their preferred colours for the different components of the car.
What is overmoulding?
it is moulding a second polymer over specific parts of a product.
Why is overmoulding used?
It is primarily used to provide areas of grip or texture or to highlight different colours for different component parts on products.
What is an example of a product that has overmouldings?
A toothbrush made from PP would have a TPE overmoulding to provide an area of grip on the handle.
What are the two ways of producing an overmoulding?
- Use two injection moulding moulds
- Twin shot injection moulding
Using two injection moulding moulds is one way of producing an overmould. How does it work?
One mould is made for the product, for example toothbrush body, and one mould is for the grip areas. The toothbrush body is injection moulded and then the product is placed into a second mould and the grip is injection moulded onto the body.
Twin shot injection moulding is one way of producing an overmoulding. How does it work?
This process uses an injection moulding machine with a mould designed to produce the product in one cycle. The mould has two separate component cavities and can be rotated through 180 degrees so that they line up with the twin injection points.
First, the moulded part, for example the toothbrush body, is created in the first mould cavity. The mould then opens slightly and rotates 180 degrees to secondary position. The mould closes again and the second injection applies the overmould, for example the grip on the toothbrush body.
What are the 2 lamination methods in relation to papers and boards?
1 lamination via encapsulation
2 lamination via surface coating
What is lamination via encapsulation with papers and boards?
This is carried out via a desk top laminator and the sheet of paper is encapsulated by a polymer pouch or film roll. The paper is fed through the desk top laminator and heat sealed, leaving a polymer sheet cover on both sides of the paper, along with a border around the paper edges. The laminating polymer is usually a mix of PET and ethylene-vinyl acetate (EVA).
