Offset printing is a type of printing that is done with the use of inks on a metallic plate, built by an aluminum alloy, the plate is moistened with ink in the spaces that are covered with a greasy material which rejects water and The rest of the plate gets wet to absorb the water and reject the excess ink, this is how everything that wants to print is passed with pressure to a rubber blanket where the image or photograph of the plate is received to transfer them to the medium that is desired .
Proceso de impresión offset
Offset printing is used regularly with the INKED technique where the figure or image is transferred from plates to a rubber blanket and then onto paper. The process of offset printing is a lithographic technique that is based on the repulsion of oil and water.
An offset printing figure is divided into the fundamental colors, an example would be a form with texts and images that use 4 colors, where sometimes only 2 colors or less are used and in others up to 6 different colors.
The form could be separated into the main CMYK printing colors (cyan, magenta, yellow and black), where 4 independent plates are made. When these four colors are printed one on top of the other, the figure is put back together and looks like the original figure.
This process happens fairly quickly and efficiently, and some prints can be made from a set of plates, which lends itself well to long runs in a short period of time.
Supplies for offset printing
There is a wide variety of offset printing supplies, including press ink, dampening systems, blankets, powders, and more. Here are a few:
Sheetfed offset printing presses would be nothing without ink. It is the main reason the press exists. Quality printing starts with good ink that works well on the press and in the pressroom, and printing ink is the biggest indicator of overall print quality.
Inks can come in many varieties beyond color, different finishes, different additives that can help them dry faster.
In traditional offset printing, there is a constant balance between ink and water. In the printing process, the figure goes through the special chemical properties of the printing plate itself. In some areas it is hydrophobic and in other areas it is hydrophilic. These two terms essentially mean that the plate will either attract or repel water. In areas that are hydrophobic, the plate will collect ink from the ink train. In areas where the plate is hydrophilic, the plate will collect water and repel ink.
The printing blanket has become an essential element of the offset printing method. It is an offset printing input that represents a smooth mat, which is wrapped around a cylinder inside the printing unit. This mat plays the role of a cushion that presses against the master and collects the figure, to transfer it to the sheet. That is, the printing blanket is the medium that transports the figure from the plate to the paper. These blankets are designed to be removed and replaced from time to time to repair wear and tear.
Offset printing powder offers several benefits in the printing process and is used by almost all manufacturers in the industry. The first and most important benefit is preventing ink drift. The powder is sprayed onto the sheets as they are stacked at the delivery end of the press, the thin layer of powder forming a micro barrier between the sheets to prevent ink from coming into contact. A second benefit of the powder is to reduce drying time due to an air gap between the individual sheets. This small space allows air to circulate through the stack of sheets and causes moisture to escape within the ink.
Digital and offset printing, differences
It uses liquid inks, metallic plates with a complex machinery of gears and rollers that transmits the ink to the paper.
Offset printing allows printing large and medium runs in a short time, with very good quality, with the use of “rotary” machines that have the ability to print “all colors”.
Emphasis is placed on rotary words and all colors, since they are the nature of lithography, or high-speed offset printing, in addition, offset printing machines are rotary, since their work is done by means of continuous rotation. and at high speed from a wide variety of rollers, such as newspaper printing machines.
There are two types of technologies for digital printing, inkjet (a special liquid ink other than offset) and toner (they are particles with pigments), the machines use electrical charges to place both the toner and the inkjet on the paper , for which metal plates are not necessary. Additionally, digital printing machines are generally lighter, more delicate and cheaper (with the exception of some high-end machines that can quite match offset machinery), they print directly from the computer to the machine, so both there is a considerable cost reduction.
How to save on offset printing costs
Sometimes, due to ignorance, we are incurring additional printing costs but by changing a small detail, the cost of printing catalogs or brochures can be reduced by 30%. Most printers do not provide this type of information, but here we give you some tricks to optimize each weight.
Tips and strategies to achieve much cheaper prints:
- Choose the appropriate and most efficient technology. Use digital printing for short or rush runs, but switch to offset printing to cut costs on much larger runs.
- Take advantage of the role. By optimizing their printing sizes so that they conform to the standards: DIN A7, DIN A6, DIN A5, DIN A4 and DIN A3 among others. All the waste on paper is money that will be lost, that’s not the idea!
- As far as possible, use dies or templates that the printing company has standardized (stickers, folders, displays, etc.). You will save fixed costs.
- Set the number of inks. It will always be more economical when printing in four-color, avoiding special or spot inks, which are more expensive for runs of less than 5,000.
- Choose the finishes that best suit your needs and especially your budget: varnished, laminated and laminated, among others.
- Avoid everything that cannot be automated, as it greatly increases the final cost.
- Group the projects. You will get better prices if you try to print everything at the same time: cards, catalogs, posters, flyers, posters.
- Request deliveries urgently only when essential.
Offset in graphic design
If you are new to this topic, it is worth taking a look at the following recommendations before starting a design, which is sure to save you a lot of headaches when sending your file to the printer.
Any file that goes to press has to be in CMYK mode. Thanks to the combination of these colors, all kinds of images and texts can be reflected on paper, although sometimes the images require more tones, this is possible thanks to the CMYK color combination.
When you are on the computer making the final finishes, you must confirm that all the images are in this format, if on the contrary they are in RGB, you could have an unpredictable result. Colors tend to fade a bit when converted from RGB to CMYK.
In the designs, the images must be at 300-360 DPI ((Dots Per Inch – DPI), and in the total size at which they will be printed. Although it seems obvious, it will not do any good to buy an image at 300 DPI that measures 10x15cm, if it is later stretched to a larger size, the unit of pixels is not multiplied when applied to an image, but these are enlarged in size to a limit that goes beyond what is correct, that is when an image is pixelated.
When the file has a background color, or an image that is received up to the cut line of the paper, it is essential to lengthen that background or image more or less 3 millimeters outside the cut line for a better result. This rule must always be fulfilled, no matter if it is a business card, a flyer or a 130-page magazine.
PDF format, the ideal
Today, printing companies prefer when the client sends them jobs in PDF files. A well-configured PDF model ensures that everything that has been done on the final art, is respected by the printer since it has all the information that a printer needs at the time of printing.
The same is not the case with bitmaps (JPEG or TIFF) so these files do not contain important information for the press. A JPEG could be printed in this format, but not before having explained in detail some issues such as what the size would be when cutting the file or also how many millimeters it should have bleed.
When we deliver a file in a PDF format it is advisable to put the sources. If the printing company receives other types of files, such as InDesign or Illustrator, Adobe programs allow you to create folders for printing with the option of “packing”, in which it will automatically include the fonts that have been used in the document.
If a Corel Draw file is delivered, the recommendation is to convert all texts to curves, making sure to attach the font when submitting the file to print. Not taking these recommendations into account may cause some other unpleasant surprise, additionally when common fonts such as Helvetica or Arial have been used, the version of the font may have differences with the font model that the printing press has installed on the computers.
It is recommended that all designers, before starting their professional career, carry out internships in the manipulation workshops of a printing press, that is where the meaning of all those requirements that are so much needed when making a print is found.
Advantages and disadvantages of offset printing
- It offers excellent photographic quality.
- It can be printed on all kinds of papers.
- Resists the use of special inks.
- Paper sizes can be larger than in digital printing.
- Allows you to print large runs with lower costs.
- For large runs, the offset printing model is much faster.
- Allows a faithful duplication of image detail.
- It is faster as there is less time to prepare the plates, compared to printing systems such as gravure or flexography.
Disadvantages of offset printing
- Inks may repaint if not allowed to dry long enough.
- There may be out-of-color inconsistencies during runs.
- The printed models have to be the same, therefore they cannot be modified.
- The start of the commissioning is expensive and highly complex.
- Depending on the type of varnish, it could pass through the sheet of paper.
- Work should not be used until 24 hours later.