Offset printing is WJPC‘s primary printing method, and it is also the most professional and comprehensive solution for mass printing in the world. You may have never understood the process and details of it, so we will select the parts that are most relevant to your project and explain them to you concisely and clearly:
Making Plates: A Modern Offset Printing Process
Today, most large printers use CTP (Computer to Plate) direct plate making machines to produce their printing plates. Compared to traditional technology, CTP plate making reproduces the details of the print better and reduces dirty spots. It produces thicker and more vibrant ink colors, accurate registration, and requires very little overprint paper.
After the imposition in pre-press is complete, your design will be split into four separate files for each color of ink: cyan, magenta, yellow and black (CMYK). Each file is then laser engraved onto 4 thin metal printing plates inside the plate maker and then installed into the press.
The reason for this is that each printing sheet requires 4 printing plates for each color of ink printed. These thin metal plates are flexible and strong enough to be wound tightly around the rotating cylinders inside the press and to make thousands of repetitive prints.
For color printing, the ability to register CTP plates quickly and accurately after they are loaded on the press is an important factor affecting the quality and efficiency of printing. Therefore, we are equipped with a corresponding cross-line register, which can be used for precise registration with a high-definition camera.
What’s more, it also has the function of adjustment, which can correct the deviation of crosses produced by plate making and drying in advance on the CTP plate, thus reducing the waste of overprinted paper, ink and your turnaround time.
Parent Sheet and Parent Plate
The parent sheet is a pre-cut large sheet of paper. Our different offset printing presses can print paper sizes ranging from a minimum of 360 x 210mm to a maximum of 1035 x 702mm, while digital presses only accept fixed sizes of 750 x 530mm.
The diverse size settings of the parent sheet allow you to get the most cost effective option for your printing project. Generally, we have the flexibility to choose the right parent sheet size for printing based on the number of cards you have. For example, 55 cards of 63 x 88mm would use a 740 x 412mm parent sheet, 78 Tarot cards of 70 x 120mm would use a 750 x 874mm parent sheet, etc.
A parent plate is the initial printing plate needed for a deck of cards, box or booklet. Once your deck size and number of cards exceed our our maximum parent sheet’s size (1035 x 702mm), you must increase the use of the parent sheet, and accordingly the number of parent plates will increase. Even if you have just a few extra cards, or even 1 card, you may not be able to avoid the increase in the number of parent plates.
To facilitate your understanding, let’s take a 63 x 88mm playing card as an example:
- 55 cards or less, with different front design and same back design, only 2 parent plates are needed;
- 55 cards or less, with different front and different back designs, still 2 parent plates are required;
- 55~110 cards, with different front designs and the same back design, 3 parent plates are needed;
- 55~110 cards, with different front and different back designs, requiring 4 parent plates;
- And so on.
You can click on “Custom Size of Deck” to learn more about the optimal number of cards for different cardstock size options, so that to make the most cost effective choice. Of course, if this cost-effectiveness will seriously affect the operability or playability of your deck, we recommend that you do not reduce the number of cards easily.
For the printer, we will carry out basic cleaning each time after the last use and before the next use. Then, regular deep cleaning and maintenance is performed to ensure that the printer is always in good condition. The cleaning steps include: removing all plates, cleaning all cylinders, rollers and fountains, and clearing setting data. All this will ensure a clean and tidy print run every time.
2. Install the plates
Since the plates are removed during cleaning, we need to re-clamp the 4 CMYK plates to the cylinders inside the press each time, when we have a new print. The cost and time involved in these installations made small runs of offset printing very expensive.
3. Calibrate the printer
Our press operators use professional calibration software to adjust the press for color gradations, curves, density, accuracy, and to calculate the thickness and coating of the paper, so that the ink will land on the paper correctly.
During the adjustment process, we will run the press at a low speed to allow sufficient time to check the registration and color of the initial printing plates. Once the calibration is complete, we will increase the speed and begin full production.
Most of the design works need to be printed on both sides. For example, when the printer has printed all the front side of the cards, it needs to turn over and print the back side, this action is called flipping in printing. According to the different print content and flip direction, we mainly take the following two flip way:
This means that at least two parent plates are needed for one plate for the front side and one plate for the back side. After printing one side, another CTP plate is replaced for the other side. Our cards are usually printed in this way, so a deck with a double-sided design will have at least two parent plates.
This means that the front and back contents are on the same CTP plate, and after one side is printed, the paper is flipped horizontally (left and right) and the other side is printed. At this time, the CTP plate and calibration parameters of the press do not need to be replaced and adjusted.
After printing, we will cut the paper by the vertical mid-gauge line and get 2 same stacks of prints. This is the way we generally use for our booklets (except folding booklets), so a booklet with double-sided content has at least 1 parent plate.
As we have mentioned many times, most of full printing use 4 color inks of CMYK that are mixed to produce millions of colors. These inks will flow from the fountains (the containers that holds the ink) down onto the plate, then onto the rubber blanket, and finally onto the paper.
In the fountain, you can find its structure is more complex, containing many movable rollers, cylinders and a reservoir. Here is a description of their roles in order:
1. Fountain Solution
Fountain solution (the blue part in the picture above) is a container of water-based liquid. Through water rollers, the liquid can flow onto the plate and repel the ink to achieve the desired blank print area.
2. Plate Cylinder
Four made CMYK plates will be wound on the plate cylinder. By rotating them, water and ink will flow from the water rollers and ink rollers respectively and will be distributed on the plates.
3. Offset Cylinder
A rubber blanket is wrapped around the surface of the offset cylinder to receive the ink from the printing plate. Then, by rotating the offset cylinder, the ink is transferred to the parent sheet finally.
4. Impression Cylinder
The impression cylinder is located at the bottom, and by moving the two small rollers to the left and right, it assists in passing the sheet to receive the ink and apply some pressure to it.
All rollers and cylinders rotate and apply pressure in an even, controlled manner to create consistent ink coverage across the plate.
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