Get to know the types of printing ink

Printing inks are divided based on the type of printing machine and printing method, in some cases this division is based on the drying method (IR-UV offset inks). Therefore, we are trying to introduce a summary of the types of constructions of printing inks that you can see in the figure below (due to the approximate obsolescence of embossed printing in the figure below) and provide brief explanations about each one.

How is embossing ink?

In this method, the compound is spread and prepared by prayer rollers and then it is transferred to the surface of the form (stereotype) by means of a rubber roller. When the paper is placed between the cliche and the printing cylinder, the ink smeared on the cliche surface is transferred to the paper surface. Care should only be taken in the compound formulation to use materials that can be easily spread on the surface of the mold or spread form or the form uniformly. This printing method is made and presented in the following forms due to the structure of the machines and the form and speed of the printing machine and the number of composite feeding rolls:

Tigel car compound

In this machine, the prayer rolls are limited and few. Therefore, the printing ink must have a low but short concentration, a low concentration so that it is easily transferred to the surface of the form and short, so that it does not spread around the form and does not fall.

Composite sheet cylinder

In this method, the number of prayer rolls and the spreading power of the compound have increased compared to the Tighel machine, and the surface of the form has become larger. Also, the printing ink is formulated in such a way that it has good drying properties while maintaining proper fluidity and concentration.

Roll-embossed compound

This printing machine has a suitable and large ink distribution system, the form has changed from a flat to a cylinder, and the printing cylinder has also become a cylinder.
This method is used to print high circulation newspapers and textbooks. Because in this method the speed of the machine is high and the printed work must be prepared and packaged quickly and then quickly bound and sent to the market for distribution, therefore the compound used in this method must be of low concentration, high fluidity and greater penetration power. and the type of roll paper used is absorbent or without chemical coating.

Since the ink is printed and transferred to the printed surface in this printing method without intermediaries and directly, therefore, compared to the offset printing method, a small percentage of pigment is used in the composite building.

Letterpress ink

Letterpress inks are designed for printing on raised surfaces such as gravure and electrotypes. These compounds usually have moderate adhesion and viscosity. Printing houses are more familiar with letterpress inks that dry by oxidation. These compounds are in the form of a paste and mostly contain pigments and drying particles that are based on oil. They may also contain various resins and compounds to give them properties such as gloss, resistance, deformation and abrasion, etc. to give

There are letterpress inks that dry by absorption and penetration like newspaper printing inks, or dry by evaporation like heating inks, or dry by settling like Moisture-Sed inks. It is done on the printed surface by the embossed surface on the form.

The surface by which printing is done is more prominent than the non-printing surface. In the relief printing, the rotary printing form and the paper are also placed around the cylinder. A layer of ink with a fixed thickness is transferred to the form, then by contacting and pressing the form on the paper or printing surface, a part of the ink is transferred to it and printing is done.

Letterpress printing ink

There is no pigment restriction to prevent spreading against the wetting solution for laterest compounds, as laterest does not require a wetting mechanism. Any type of pigment that is used for letterpress can also be used for letterpress.

Letterpress inks are stronger than letterpress inks, but not as strong as offset inks.

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How is offset printing compound?

Offset printing technology is based on the conflict between oil and water. Due to their high concentration, they are known as paste inks, which must vary according to the printing machine.
For sheet offset compounding, the concentration is equal to 550 to 500 poise, and for roll compounding, the ratio of the type of machine and the slope of the compound source is between 90 and 180 poise and varies. Due to the frequency of the use of composite offset printing A number of features of this compound are briefly explained.

Offset (lithographic) inks are formulated to print on flat surfaces, from printing plates that have neither raised nor pitted image surfaces. Offset (lithography) is the only printing process in which chemicals and pharmaceuticals play the main role.

In offset systems, the ink must be transferred from the zinc onto the cylinder rubber (blanket) and then onto the paper. During this transition; Its thickness decreases, so the compound must have high coloring power. This coloring power is provided by the pigment, so the greater the amount of pigment in the ink, the greater the coloring power of the final layer of the ink that is transferred on the paper, and it must also have a fluid property, so there must be some fluid in the ink to Pigments move in it.

This liquid should be made of polished oily materials and none of the composite components (pigment or fluid) should be mixed with the pool solution. This is one of the most important features of composite offset. This property causes when the ink is transferred on the zinc to stick to the dry printed areas and not penetrate to the non-printed areas.

The offset printing ink must have a high color concentration and must not be mixed with water. Increasing the ambient temperature and mixing the compound due to the rotation of the rollers of the offset printing machine reduces the concentration of the compound. The higher the adhesive properties of the compound, the higher the splitting resistance and the more difficult it is to divide by rolling. Offset printing inks are also called paste inks. Increasing the temperature decreases the concentration and viscosity, but stirring decreases the concentration and increases the viscosity.

In printing, four compound colors are used (yellow, magenta, cyan, black). For the correct transfer of colors, the first compound must have the highest adhesion and the last one must have the lowest adhesion. The ink maker must be aware of the printing turn of each color in order to be able to grade their adhesion or to obtain the best efficiency and quality of color transfer.

The ink is wet when it is in the offset press, and when it is transferred and printed, it should be dry as a thin layer.

The ink must be semi-solid when the print and paper are stacked on top of each other so that it does not transfer to the back of the next page. If this situation occurs, it is called backstabbing.

Emulsion control

In order to reach a balance in water and compound, it is necessary to control the degree of emulsification of the compound with water. In order to achieve this state in the printing process, so that all the properties of composite offset printing remain unchanged, it is necessary to consider and control the necessary mechanism for both the physical and chemical states of the composite formula.
Therefore, the water absorbed by the compound should not be affected by the chemical effects of water on the one hand and the viscosity of the compound on the other hand, and this issue must be investigated in the compound formulation and special attention should be paid to it.
The wide range of printing conditions requires compounds with very different physical properties compared to conventional printing methods. For example, concentration and viscosity can vary between 2 and 30 pascals according to the speed of the printing machine and the type of printing method.
Compounds with low viscosity can cause emulsification of the compound practically at high speeds. This happens if there is no chemical effect between the water and the ink, as a result, the two liquids of water with all its extra substances and the printing ink at high speed come close to each other in terms of viscosity due to emulsification.
The proper degree of emulsion is necessary to remove excess water from the image areas, but its excess amount causes the border between the image and non-image areas to disappear, that is, the non-image areas also acquire color and create a background.

compound prayer

To achieve Offset It seems necessary to have regular and frequent prayer trains; Because a very fine membrane of ink is needed for the image areas on the form, which is prepared and delivered to the printed form by means of prayer rollers of this layer of ink. During this process, the rolling train system encounters a series of limitations in the printing compound formulation, including the escape of compound solvents in the distance between the compound power source and the printed form.
On the other hand, it is necessary to comply with the conditions of the Salaya rolling system in the middle of metal and rubber rolling, so that both the transfer of the printing compound takes place in a natural way and the transfer heat on the wide surface of the rolls is minimized.

Solvent application and suitable materials

It is necessary not to use a solvent in the composite building that causes corrosion on the composite rubber rolls or absorbs non-rubber rolls, causing them to swell. Also, the chemicals used in the composite building should not cause corrosion in the metal rolls. The viscosity of the compound and its concentration should be such that it maintains the required concentration state for printing on the wide surface of the salaya rolls and the quality of the compound remains stable and constant.

Chemical activity

If the printing ink and the offset penetrating water do not have any effect on each other, then the emulsification process becomes difficult or cannot be done. If the printing composite materials have active groups, for example, in pigments and vegetable oils, then they can create a chemical relationship between water absorption and self-creation, so with changes in these factors, the amount of water absorption by Compound controlled.

compound cortex

The amount of layer or printed film in offset inks is much less than other types of printing . This is because the forms prepared by chemography have a small capacity to place and remove the compound, on the other hand, the amount of compound removed by the form or plate must be divided between the rubber and the form and then transferred to the printing surface. . Therefore, the order of transfer of the layer composed of prayer rolls to the printed form and from the printed form to the rubber and from the rubber to the printed surface is based on experimental calculation. It can be assumed that the amount of transitional composite layer will be equal to 1-3 microns.

Composite transfer

In the offset printing method, the printing ink is transferred to the printing form that has been in contact with water after being coated and spread on the spreading and leveling rolling train, then it is immediately transferred to the rubber and transferred from the rubber to the printing surface. In this process, water determines the image and non-image areas.

Drying mechanism in offset printing

The drying of the printing ink is done by classical methods. Due to the fact that the printed layer is very thin and small and there is a small amount of water absorption in the printed layer, so it is very difficult to check the degree of drying exactly for each type of ink.

An ink that is called a thermal ink, the factor of its stabilization and drying on the printed surface is done by the exit of the solvent and its evaporation from the printed layer and the absorption of a part of it to the printed surface, or an ink that dries by oxidation and polymerization. The drying mechanism of printing ink on the printing surface is done in five ways:

  • by absorption on the printed surface (penetration method)
  • Through oxidation and polymerization
  • By quick sitting method
  • By thermal method
  • through radiation (IR and UV)

How is dry offset printing ink?

Dry offset is also known as letterpress printing. The means of printing these types of inks consists of a cliché cylinder, which is usually embossed (such as letterpress) and has a rubber cylinder that directly contains plastic containers in a metal piston that exactly plays the roll of the printing cylinder, and the color is spread and prepared directly. It is transferred through the rubber to the printing surface, which is usually round.

The printing ink is transferred to the salaya rollers by a compound tank (paste compound), then the cliche or form cylinder is dipped in the compound and the ink is transferred to the rubber and from there it is immediately transferred to the containers to be printed. This type of compound must be dried quickly so that the containers can be supplied in bulk bags for packaging dairy products.

The method of drying the compound depends on the material of the plastic container and its size. After printing, the containers are passed through a path that is exposed to ultraviolet (IR) and infrared (UV) radiation. As a result, the compound dries immediately. In some cases, after printing, the container is exposed to hot air, which is usually carried out by a heat channel. Today, UV rays also play an important role in drying these tea pieces. Therefore, the desired compound formula should be made and prepared based on UV drying.

In this type of compounds, solvents with a boiling point of 200 degrees Celsius are used, which dry completely at a temperature between 80-100 degrees Celsius after printing. Due to the fact that these containers are made of plastic and are affected by heat and their appearance changes, care should be taken in the way of printing and its temperature.

If the containers to be printed are made of PP and PE, it is necessary to discharge their static charge by heat or by any possible means so that printing on these surfaces can be done without problems. Because these types of compounds are dried by IR rays or the heat of hot air. Pigments should be selected according to the composition maker’s opinion. Leakage resistance on plastic, the method and extent of drying play an important role in preparing and formulating these types of compounds.

How is flexo printing ink?

The name of flexographic printing has been changed and derived from aniline printing, and because it is used for printing flexible surfaces used in food packaging (such as various types of synthetic films), it has taken the name of flexography.

The basis of this printing method is based on the fact that a printing ink tank inside which an engraved metal roller (anilox) is rotating, measures the ink and delivers it to a rubber roller that is in direct contact with the rubber cliche. to give Relying on a special cylinder called the printing cylinder, this cliché transfers the color transferred on it to the printing surface that is passing in the form of a roll.

Of course, the arrangement of rubber rolling with anilox can be reversed and shifted; That is, instead of anilox rolling rubber, it is rotating in the tank.

This printing method is used for printing on cement bags (kraft paper) and types of absorbent and non-absorbent papers, aluminum foils, PP and PE cellophane and other types of synthetic and hybrid papers, and depending on the type of printing ink, ray printing is also used. It can be used as a drying method after printing here; Such as IR thermal method and UV method which is used after the printing unit.

In this method, for printing on tapes, polyethylene and polypropylene films, loading and unloading of the static charge must be done before printing; Because the presence of static charge and its accumulation on polyethylene and polypropylene films prevents the ink from settling, therefore, before the printing stage, a “Kerna” unit, which includes an electric discharge capacitor, is installed and prepares the film for printing. . Without this loading process, the ink is easily removed from this type of film after printing.

Flexography is a method of rotary letterpress printing, which uses flexible rubber plates and fluid inks on almost any type of printing surface, using fast-drying Flexo Inks. Flexo inks are used in printing flooring and wall paper, cellophane and various thin plastic sheets, metal foils, etc.

Inks that are used in flexography or gravure printing are liquid and therefore often called liquid inks. Flexo inks include pigments, soluble inks, along with a carrier fluid to carry the inks.

Flexo compounds are either alcohol based or water based. Alcohol base compounds are more common and are dried by evaporation. Water-based compounds are less expensive and dry by evaporation or absorption.

How is heliogravure printing ink?

Heliogravure printing is a simplified flexographic method. If, instead of anilox, a printed cylinder is engraved or engraved on the cylinder by the form or image gravure method, by moving this engraved cylinder inside the composite tank and placing a steel blade that can remove the excess paint from the engraved cylinder. And immediately with the help of a printing cylinder and the passage of paper or any type of flexible film, the image is transferred to the printing surface.

In this method of printing, by means of chemography, the form or image or any printed matter is transferred onto a cylinder that has already been subjected to copper plating and sensitized. After the image is transferred on the copper plated cylinder, hot plating is done to give the cylinder wear resistance, so by placing a steel blade and removing the excess paint, the image is transferred very well on the desired surface.

Gravure or heliogravure printing on all flexible surfaces, including kraft paper, glossy and coated paper, and all kinds of synthetic films such as; Cellophane (in different types) is made of PVC, PE, PP and PVDC.

Gravure compounds are quick-drying fluid compounds that must have sufficient concentration and viscosity to pass through the engraved holes in the cylinder and not blind them.

These compounds are generally dried by evaporating the solvent inside the compound with or without heat. These compounds must be free of hard particles that can scratch the cylinder or zinc. A wide variety of solvents are used in the gravure compound, depending on the carrier substrate.

These compounds are volatile and can cause fire if not stored properly. Solvent correction is used in the printing machines of publications to erase the pollution caused by the evaporation of solvents. Water based compounds are designed to eliminate both fire hazards and solvent contamination.

What is the composition of screen printing?

Silk screen printing is done based on the transfer of the printing compound from the open areas of the net, the image areas of which are open, but the non-image areas of which are completely closed by chemical substances.

Screen printing as individual sheets or as a roll for printing Fabric, plastic printing (in different types) or PVC surfaces are used.

Screen printing inks are mostly drying oils, although other inks can also be used. These inks have a thick color concentration, they are made in any color, and they use a suitable carrier fluid for the material to be printed. All inks should be thick and oily to print clearly and always with low resistance.

The viscosity of silk printing compound is medium, that is, its state is a paste between flexo and lithography or letterpress inks.

How are special can printing inks?

Two-piece metal cans of soft drinks are the most used nowadays, so that, for example, only in 1992, one hundred and fifty billion cans were consumed in the world. Inside these cans, there must be a coating of a special food varnish, and the drink’s specifications and its introduction must be printed on them.
These cans, which are produced on an average of 0.100 pieces per minute (in a production line, have two parts, the door and the body, so they are called two-piece cans. The printing of this type of can is done in the form of a roll. This means that the cans continuously rotate around a conveyor cylinder. Each of these cans is placed on a metal piston the size of the inside diameter of the can, which plays the role of the printing cylinder (only for each unit) and the stereotypes arc around a large cylinder that plays the role of the form cylinder. Can be built in several colors. The composition is transferred from the composite source to the surface of the stereotypes by means of prayer rollers and continues with the speed of the printing process.

The composition of these types of cans is usually chosen by dissolving the appropriate resin and solvent that can sit well on the metal, which requires the addition of suitable additives to prevent abrasion, slippage, resistance on the metal and non-welding.
Usually, the solvents that are chosen have a high boiling point of 200-300 degrees Celsius, and the resins are usually based on reactive polyesters and alkyds. Care must be taken in choosing the pigment to give high light resistance, good heat resistance, gloss and transparency to the print.

How are compounds without solvents?

Two new composite systems have been developed to remove air pollution from the composite:

Catalytic compounds: These compounds are used for web printing, they contain two liquid polymers such as melamine and formaldehyde, which form a solid global connection in the presence of an acid. A type of ink salt is mixed with the mixture to prevent them from joining together on the printing machine and at normal temperatures. When the web paper goes into the dryer, the salt ink is broken down and the polymer cross-linking becomes a dry, solid, thermoset resin. These compounds and hybrid systems contain small amounts of inert solvent. which are used in offset web and in spaces where air quality adjustment is difficult.

How are UV compounds?

Considering the environmental pollution and the harmfulness of chemical solvents that are used in the formulation of printing inks. UV compounds use different solutions to reduce the release of chemicals in the environment. It does not dry normally and it only dries with ultraviolet light and does not release any solvent in the environment and does not harm the printer.

The components of the UV compound are:

Pigment : You can usually use routine pigments in the market.

Prepolymer : It is the main resin that has the main properties of the compound such as: It determines adhesion, drying time, glossiness, compatibility, etc., and it has almost high viscosity.

Tekpar : This resin usually has a lower viscosity than the prepolymer and is used to adjust the viscosity and improve side properties such as wetting, etc. In fact, Takpar is like a solvent in ordinary compounds.

Photoinitiator : This material is sensitive to UV light, and as soon as UV light is exposed, it starts releasing radicals, and the bonding reaction is carried out by prepolymer and monolayer until the composite dries. If this substance is not present in the ink, the ink will not dry even when exposed to ultraviolet light.

Additives : To improve properties composed of additives such as: Aligners, wetting agents, waxes, etc. are used as needed.

In many industries today, colors have found their real place in the packaging industry. Colors have a special beauty and unconsciously draw the eye towards them, and this unique feature has caused all kinds of colors to be used in the printing industry of paper products, and cardboard, which is the best of all packaging products, from This rule is not an exception.

In addition to beauty, colors also convey feelings, yellow, orange, and red are considered warm colors, and seeing them conveys a feeling of warmth. The cold blue color conveys the feeling of coldness. By printing these colors on the packaging of heat-generating and cooling products, it leaves its effects on the buyer’s mind without any explanation. All these things have caused the composite manufacturing industry to open a new world on the packaging industry and create a tremendous transformation in it.

To achieve optimal results in printing, it is very important to use the right ink or inks. In order to achieve this goal, the ink producer should produce ink by studying information such as the type of printing process, the type of printing machine, the type of paper, the type of dryer, the type of finish, the type of coating or the application of printed items, etc.

When new paper is to be used, the composite source must also be revised. An ink that works well with one type of paper may perform poorly with another.

Despite printers’ wishes, there is no ink that works well with all types of paper. The ink manufacturer designs it to work best with a particular type of paper, which may not work as well with another type of paper. Sometimes printers blame the paper when the ink does not perform well on the paper they want.

What are the stages of compound making?

Printing inks must face new conditions in terms of performance, so it is necessary to make a lot of control in their production. Compounds have three main components. Pigments, liquid medium or solvent and resin. Pigments are suspended in a liquid medium during a grinding process.

These pigments may have an organic or inorganic source. Mineral pigments including zinc oxide (white), lead sulfate and lead chromate and lead oxide, which mix to create yellow, orange and red colors, iron oxide (yellow, red and brown) or black carbon pigments which color They make black. Also, pigments are made by precipitating a solution on a neutral salt such as sodium sulfate.

In addition, stabilizing and enhancing compounds are also added to the ink, and according to the final application and the type of printing in particular, other compounds are also added to it by the ink manufacturer.

The ink carrier or solvent transports the color pigments from the inking system of the printing machine to the desired points on the paper. Of course, this solvent must be compatible with the printing method used. For example, offset printing requires an ink that is resistant to water and is not emulsified in the printing machine and is hydrophobic.

Flexo inks, which make up more than 80% of the printing on cardboard, must be very thin and work with fast penetration to be easily absorbed by the paper. The carriers of these types of compounds are often made from linseed oil or synthetically based materials. Resins are also responsible for sticking pigments on cellulose fibers in the absence of solvents, and until the printed paper is not exposed to solvents again, there is a colored film on the paper and it is resistant to wear.

Machine printing inks exhibit properties known as user characteristics.

Which elements are used to make printing inks?

Liquid elements or carrier fluids and solvents : causes the pigments to spread evenly and also causes them to stick to the printed surface.

Solid elements or pigments : provide the coloring power of the compound.

Other various elements (driers and composite bodies) : cause the composite to dry faster.

Offset printing was done as a result of the development of indirect relief printing or letterpress. In fact, the word “offset” means indirect and sublime.

The invention of offset printing is attributed to two inventors, one American named Ira Rubel and the other German living in America named Gassiar Man. Around 1904, both inventors investigated and tested this idea that can be done with indirect printing lithography forms.

It is said that Rubel, who was a small printer with pre-lithographic printing equipment, one day, for some reason, faced a problem with print quality when printing banknotes. To solve this problem, he uses softer rubber for printing. In the meantime, the operator who was responsible for feeding the banknote paper into the machine did not insert the paper into the machine once every few printing rounds.

This action causes that when there is no paper, the ink is first transferred to the rubber and then to the back of the next paper. When Rubel examined one of these waste prints, he was surprised to find that the quality of the waste print on the back of the work was much better than the print on the work. This was an important discovery and the beginning of offset printing.

From then on, Rubel chose to research and develop the offset printing method. Of course, he abandoned the name of indirect “offset printing” with lithography forms, and this new method, which is offset today, is more for the purpose of, and compared to, the printing method using lithography forms. The use of these types of forms was popular before the discovery of the ruble and was known as stone printing.

Emergence of lithography forms : At the beginning of the emergence of lithography forms, printing was done with limestone stones, which are also known as Solnhofen stones. It is said that an Austrian dramatist and theater actor named Alius Zennefelder (1834-1771) wrote his laundry list on a Zolenhofen limestone and sent it to his mother due to lack of access to paper. In the meantime, he discovers that this limestone does not absorb pen ink when it is covered with hand grease.

Zane Felder, who was constantly looking for a way to cheaply reproduce musical notes that had many fans at the time, invented a new method of printing or stone printing, which later became known as stone printing.

Zane Felder had discovered that for printing with limestone, it is enough to be composed of oily material and the stone is kept continuously moist.

The first automatic cylinder printing machine was built in France around 1815, and then the Nicol printing machine, followed by the George Sickle printing machine in 1852, was built in Vienna, the capital of Austria.

This device required three operators; One person to rotate the main wheel, one person to feed the paper and one person to take the paper.

This printing machine used flat stone forms, which had a lot of weight. Zeneh Felder found a new solution to replace the slate, which was to carve the stone into a cylinder and attach metal pieces to its two sides. , used it as a cylindrical form.

Of course, the real success of offset printing came when copper plates with a photosensitive surface were invented as a form. In any case, it is clear that the idea of preparing a form that can be closed on a cylinder is from Felder.

Information transfer method : Information transfer is done indirectly in offset printing. This means that the information is transferred to another surface (rubber cylinder) before it is transferred to the paper or desired surface, and then transferred from it to the paper (printing cylinder).

Therefore, in offset printing, there is an intermediary between the plate (plate cylinder) and the printing surface (printing cylinder) called the rubber cylinder.

For this reason, this method of offset printing is called (indirect printing) because of the name of the rubber cylinder, which is covered with a rubber cover around this cylinder. This rubber plate wears out during printing and should be replaced once in a while.

Although in other printing methods it is also possible to use intermediate rubber for printing, but they are not called offset printing, but when we talk about offset printing, it means using a flat form that has the property of accepting the ink in the places that have the image. And it has information.

These types of forms are also called plate lithography and the printing method in which information is transferred using these types of forms is called offset printing.

In offset printing, the information bearing points and non-printing points of the used form are on the same level. For this reason, this method is also called smooth.

Before aluminum was used, these plates were made of copper and zinc (zinc) alloy; For this reason, they were also called zinc.

The surface of the plate is covered with a special material that interacts with it as a result of shining light or creating special heat for imaging. As a result, at the points where it is necessary to transfer the composite, the property of absorbing the composite is found. Offset printing is divided into two types: normal offset printing and dry offset printing. Each of these two types of printing has its own plate.

Offset printing machine : The structure of an offset printing machine is different depending on whether the used paper is roll or sheet.

Because the number of sheet printing machines is more compared to roll printing machines. Here we examine the sheet printing machine.

It shows the different and major parts of a printing machine, which includes three parts :

  • The feeding unit (apparatus) that carries out the process of transferring paper into the machine.
  • A printing unit that includes humidity and inking and pressure supply.
  • The delivery unit, which collects the printed papers on another and is ready for transfer.

Technical and economic factors, and the quality that customers expect from printed media, have made many settings and production steps of printing machines to be done automatically today.

Normal offset plates: Normal offset plates are the most common plates in the offset printing method that is used today. In these plates, the property of water and oil not dissolving in each other is used. Normal offset plates have two areas on the surface.

  • The area that carries information and images, which has the property of absorbing oil-based compounds and repelling water.
  • The non-carrying area of information and image that has the property of absorbing water.

At the beginning of printing, the plate is dipped in water; As a result, the points that carry the image repel water and the rest of the points get a very thin layer of water. Then, by transferring the ink onto the plate, only the areas prepared for the transfer of the ink image are absorbed, and as a result, the plate is ready for printing.

This method is repeated in every printing cycle and the amount of water (moisture) and ink transferred to the printed surface is replaced by the ink and humidification system.

Dry offset plates : In this type of offset printing, water is not used to separate the image and non-image points of the form. Rather, the property of the material that covers the surface of the plate is such that only the image points of the plate absorb the special ink for this type of printing.

One of the advantages of this printing method is that it is possible to print not only on paper but also on materials that do not absorb water, such as PVC.

It is noteworthy that the printing equipment required to use this type of plates is different from normal offset plates.

Intermediate cylinder rubber in offset printing : The transfer of ink from the form to the printed surface is done indirectly by a cylinder that is surrounded by a special rubber.

The elasticity of rubber and its ability to absorb ink and water are of particular importance for printing quality works, and the flexibility of rubber makes it possible to compensate for the slight difference in the surface of the plate with the thickness of the paper and not to damage the relevant components.

Cylinder rubber is one of the consumables of printing and usually it should be changed from time to time depending on the type of work, paper and its material.

Printing unit : The printing unit is a part of the printing machine that transfers the ink onto the printing surface, and because of its appearance, it is also called the printing tower.

An offset printing unit or printing tower consists of three main parts:

  • Compounding unit
  • Humidifying unit
  • Printing unit (pressure supply)

Each printing unit can transfer one color. Therefore, for example, if the printed work has two colors, you should either use a machine with two printing towers, or print one color once and print the second color in the next step by adding the second color.

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