Ink Mileage
Ink mileage is usually defined as the number of copies produced with a kilogram of ink, or more commonly quoted in the newspaper industry as the kgs of ink required to print a thousand impressions on paper.
. Estimating ink mileage has always been a difficult task. This is because there are several interesting factors that control the amount of ink required to achieve the final ink density. The factors that most influence the ink requirements are as follows:
1) Strength of the ink
2) Substrate
3) Print Density Control
4) Ink and Water Balance
5) Print coverage
Strength of the ink
The key factor here is the level of pigment in the final ink formulation which determines how much ink is required to achieve density. The pigment is the ingredient in the ink that either absorbs or reflects light. When ink is printed on paper, what we are trying to do is to change the light reflection off of the paper so that the reader perceives color. The pigment type has certain characteristics to achieve this. We cannot change this property, but we can put more pigment into an ink so that the ink films are reduced, but there are limitations to this.
Ink manufacturers look at the strength of an ink or level of pigmentation. The strength is a critical factor in determining the ink film weight requirements or thickness on the final print. In this the smoothness and absorbency of paper is also taken into account. Typically coated stock will be printed by a stronger ink, as the absorbency of paper will be very low. And a thin film of ink will be required to achieve required density. There is a limit to increase the strength of the ink, as a too strong ink will result in a very thin film of ink for the required density. This may lead to poor coverage of image on the plate which in turn leads to plate wearing, besides other problems like poor ink transfer and poor ink water balance.
On uncoated stock, apart from achieving the required density, one has to cover the paper surface; broadly speaking paper surface has peaks and valleys. Here on one hand we have to fill the valleys with ink and cover the peaks also. Covering the peaks is important other wise we will have pinholes visible in the print So on uncoated stock we print with a thicker film of ink.
Substrate
The substrate on which the ink is printed on can also be a major factor in determining ink mileage. Many people would think that this would not be a major factor. To understand this better, we have to look at the surface characteristics of the stock and how the ink is applied to this surface.
Paper is made of fibers that are pressed together to form the paper. The surface is not smooth, and depending on the uniformity, will change the level of ink required to achieve the final print density. An uncoated paper is printed by the offset process, which means the ink dries mainly by absorption of the ink ,in the paper. So, the level of ink required can change with the paper’s physical characteristics, (smoothness, absorption, etc.). If coated paper is used, the drying is mainly by oxidation and partly by absorption in the coating. So here also condition of the surface i.e., .smoothness will be a factor apart from acidity of paper.
Print Density Control
Print Density is measured with a Densitometer. The Densitometer is an instrument that measures the amount of light reflected off of the surface. As explained earlier, the pigment level in the ink determines how it will absorb or reflect light. In order to do this on press the operator cannot change the level of pigmentation; they can only increase or decrease the film thickness of ink to achieve a density change. The density function of a Densitometer is based on what is referred to as a logarithmic function. The level of ink required to achieve this also follows this same logarithmic response. This means that as the density is increased, it will require progressively larger amounts of ink to affect a change in density. For example, an increase in print density of 20% (from 1.0 to 1.2) requires an ink film weight increase of 58%. This film weight percentage increase is over double the percentage of the print density change.
Ink and Water Balance
The setting of the proper ink and water balance has always been a key part of the process of Lithography. As the levels of ink and water are increased on press, ink mileage can be inadvertently affected. The degree of emulsification of ink and water will also determine the thickness of ink film.
Print coverage
The final factor to be discussed is probably the most critical factor in determining ink mileage. This is the coverage of area printed on a sheet of newsprint. The coverage will be determined by the print designer.. Color ink coverage can be dramatically changed in the design or layout of the page..
Dear friends whether you are printing, Packaging or newspaper or leaflet or anything by offset, the above basic factors will be the same.
. Estimating ink mileage has always been a difficult task. This is because there are several interesting factors that control the amount of ink required to achieve the final ink density. The factors that most influence the ink requirements are as follows:
1) Strength of the ink
2) Substrate
3) Print Density Control
4) Ink and Water Balance
5) Print coverage
Strength of the ink
The key factor here is the level of pigment in the final ink formulation which determines how much ink is required to achieve density. The pigment is the ingredient in the ink that either absorbs or reflects light. When ink is printed on paper, what we are trying to do is to change the light reflection off of the paper so that the reader perceives color. The pigment type has certain characteristics to achieve this. We cannot change this property, but we can put more pigment into an ink so that the ink films are reduced, but there are limitations to this.
Ink manufacturers look at the strength of an ink or level of pigmentation. The strength is a critical factor in determining the ink film weight requirements or thickness on the final print. In this the smoothness and absorbency of paper is also taken into account. Typically coated stock will be printed by a stronger ink, as the absorbency of paper will be very low. And a thin film of ink will be required to achieve required density. There is a limit to increase the strength of the ink, as a too strong ink will result in a very thin film of ink for the required density. This may lead to poor coverage of image on the plate which in turn leads to plate wearing, besides other problems like poor ink transfer and poor ink water balance.
On uncoated stock, apart from achieving the required density, one has to cover the paper surface; broadly speaking paper surface has peaks and valleys. Here on one hand we have to fill the valleys with ink and cover the peaks also. Covering the peaks is important other wise we will have pinholes visible in the print So on uncoated stock we print with a thicker film of ink.
Substrate
The substrate on which the ink is printed on can also be a major factor in determining ink mileage. Many people would think that this would not be a major factor. To understand this better, we have to look at the surface characteristics of the stock and how the ink is applied to this surface.
Paper is made of fibers that are pressed together to form the paper. The surface is not smooth, and depending on the uniformity, will change the level of ink required to achieve the final print density. An uncoated paper is printed by the offset process, which means the ink dries mainly by absorption of the ink ,in the paper. So, the level of ink required can change with the paper’s physical characteristics, (smoothness, absorption, etc.). If coated paper is used, the drying is mainly by oxidation and partly by absorption in the coating. So here also condition of the surface i.e., .smoothness will be a factor apart from acidity of paper.
Print Density Control
Print Density is measured with a Densitometer. The Densitometer is an instrument that measures the amount of light reflected off of the surface. As explained earlier, the pigment level in the ink determines how it will absorb or reflect light. In order to do this on press the operator cannot change the level of pigmentation; they can only increase or decrease the film thickness of ink to achieve a density change. The density function of a Densitometer is based on what is referred to as a logarithmic function. The level of ink required to achieve this also follows this same logarithmic response. This means that as the density is increased, it will require progressively larger amounts of ink to affect a change in density. For example, an increase in print density of 20% (from 1.0 to 1.2) requires an ink film weight increase of 58%. This film weight percentage increase is over double the percentage of the print density change.
Ink and Water Balance
The setting of the proper ink and water balance has always been a key part of the process of Lithography. As the levels of ink and water are increased on press, ink mileage can be inadvertently affected. The degree of emulsification of ink and water will also determine the thickness of ink film.
Print coverage
The final factor to be discussed is probably the most critical factor in determining ink mileage. This is the coverage of area printed on a sheet of newsprint. The coverage will be determined by the print designer.. Color ink coverage can be dramatically changed in the design or layout of the page..
Dear friends whether you are printing, Packaging or newspaper or leaflet or anything by offset, the above basic factors will be the same.
Our ultra-violet offset printing preserves inks and specialty finishes instantly, resulting in sharp and vibrant printing plus additional flexibility with exclusive substrates and coatings. Offset Inks are compounded specially for use on offset presses. Contact Us: +91 9911005177
ReplyDelete