Printing Processes Flashcards
Process of Offset Lithography Printing
- The printing plate has the image to be printed, in relief, on its surface (the image stands out slightly from the printing plate surface).
- The printing plate is kept dampened. Ink is applied to the plate but it is repelled from the dampened surfaces which are the non-image areas.
- As the printing cylinder rotates the ink is transferred to the rubber blanket cylinder.
- The ink, now on the rubber blanket cylinder, is pressed onto the paper or card as it is pulled through the machine. (The paper is trapped between the blanket cylinder and the impression cylinder - these pull the paper through the machine)
What makes the ink attractive to the dark areas?
With some modern lithography printing machines the image is put onto the printing plate by shining ultra violet light through a negative (similar to a photograph negative). The plate is coated with a chemical which allows the ink (made from oil) to attach to the image area.
What material is usually printed in with Offset Lithography Printing
Usually used for paper and thin card.
This is known as CMYK printing. Why is black K and not B?
Black is K and not B, because it is the ‘Key’ colour for creating images, as Black is able to add depth, as well as tone into images. This means without the black, images would not look/seem right. Also, B needs to be used for other colours such as Brown or Blue.
What are the lines in the corners used for Offset Lithography Printing?
These crosses, are to make sure that the sheets and plates are all aligned with each other.
What are there blocks of colour underneath the image of something that has been printed using Offset Lithography
There are blocks of colour under the image to show the colours used in making the image.
What is the circle with a cross in used for in Offset Lithography Printing?
The circle with a cross is used for lining up everything in the right order.
A typical offset lithography press used in commercial printing may have 6 sections. This has four sections for the CMYK colour separations. What might the other two be used for?
The other two sections could be used for applying special colours, such as gold, silver, bronze, as well as white ink too. Other things like fluorescent colours and special inks can be put in these final 5th and 6th sections too.
This printing process is known as Offset printing. What does this mean in relation to the way the image is printed onto the paper?
Offset printing is when the ink is tranferred onto the plate cylinder, and then put onto the blanket cylinder with water, and is then rolled onto the paper afterwards. This is why it gets the name of ‘offset’ because the ink isn’t directly applies to the paper.
How cost effective is Offset Lithography for 50 A4 Posters?
This won’t be very cost effective because it is a very long and costly process, which takes time to set up, and this wouldn’t be made the most of if it was only printed 50 times, and could be done cheaper using a different process
How cost effective is Offset Lithography for 5000 A4 Posters?
This would be a lot more cost effective because here, you would be making the most of the amount of setup that is needed, and therefore making the process of printing 5000 things a lot better and higher quality than just using a cheaper method of printing.
Computer monitors do not always display CMYK colours very accurately, as they use an RGB system to generate the colour reporduction. What is the difference between RGB and CMYK?
The difference between RGB and CMYK is that in the RGB system, you have the colours Red, Green, and Blue are used, while in the CMYK system, you have the colours Cyan, Magenta, Yellow, and Black. The reason why these different systems are used between monitors and printed images are because it is to do with the way that we see light. In a monitor, the light is being projected from the screen, while in a print, the colour that you want needs to get reflected by light for you to be able to see it. This is why when you preview a print on a computer, the colours will look slightly different to when it is in real life.
The school commendation card gets re-printed from time to time in batches of around 2000. The costs for reprinting are much less than the original batch we had printed. Why would this be?
The costs of reprinting will be far less because you will already have manufactured the necessary plates that are shaped and made in the right way for what you want to print, which is the main initial cost that makes it more expensive, but these can be re-used again, so now you will only need to pay for the setup of the machine, as well as the ink being used.
Offset Lithography Advantages and Disadvantages
Advantages:
- It is versatile: the print media can be any type of paper you want and can be printed on any flat surface.
- Long-term usability: the plates life is extended due to the print media not coming into contact with them.
- Has great flexibility: rollers and rubber plates are flexible, which means offset lithography can be used on any media with rough surfaces as well.
Disadvantages:
- It is not cost-effective: because of the time and costs required to set up, offset printing is not cost effective when it comes to smaller amounts. Usually, it is only used when needing very large volumes of print.
- Not environmentally friendly: by using traditional offset printing methods, the only option is to print in bulk, this means there can be more waste leftover.
Where is Offset Lithography used most
Offset Lithography is most often used for rough-surfaced media such as wood and canvas. However, due to it being so versatile, it can also be used for other packaging material, including paper.
