Print Quality Assurance Practical -...

Print Quality Assurance Practical ‘M’ Scheme Syllabus

Prepared by S. Uthanu Mallayan, Lecturer A.Paramasivam, Lecturer (SS) Department of Printing Technology Arasan Ganesan Polytechnic College, Sivakasi

PRINT QUALITY ASSURANCE PRACTICAL

PREFACE This book covers all the topics in a clear and organized format for the Third year

Diploma in Printing Technology students as prescribed by the Directorate of Technical Education, Chennai, Tamilnadu. It is confidently believed that this book furnishes the students the necessary study material. The topics covered were neatly illustrated for better understanding of the students.

The book’s step-by-step lessons in large, eye pleasing calligraphy make it suitable for both direct one-to-one tutoring and regular classroom use. The book is prepared in normal everyday English and is free from professional jargon characteristic of so many reading instruction books.

All of the lesson pages were carefully designed to eliminate distraction and to focus the pupil’s full attention on the work at hand.

S. Uthanu Mallayan, Lecturer / Print. Tech. A.Paramasivama, Lecturer (SS)/Print. Tech

Arasan Ganesan Polytechnic College Sivakasi.

CONTENTS

List of Exercises Page No.

1. Standardization of plate exposure using step wedge. 1

2. Testing of GSM for the paper/board sample. 3

3. Testing of paper grain direction for the paper sample. 5

4. Measuring solid print density using process colour control bar. 7

5. Determining the trapping tendency of the given print samples. 9

6. Determining the print contrast and tonal value of the given sample. 11

7. Measuring Gray Balance using colour control strip. 13

8. Determining CIE Lab values of the given print samples. 15

9. Finding the pH/Conductivity of the dampening solution. 17

10. Testing of Ink using draw down test method.. 19

AGPC, SIVAKASI PRINT QUALITY ASSURANCE PRACTICAL

1

EX. NO: 1 STANDARDIZATION OF PLATE EXPOSURE USING STEP WEDGE Aim: To standardization the plate exposure using step wedge. Apparatus and materials required: PS Plate, Step wedge, Plate Exposing Machine, Developer and finisher. What is Step Wedge? • The Stouffer 21-Step Transparent Guide is heralded around the world as "the platemaker's choice". • It serves as a gauge to evaluate the variables encountered in the exposure and processing of lithographic plates and photographic materials by contact. • If indicates the direction and magnitude of exposure or processing adjustments necessary to achieve the desired results. • It is also used with contact positives, silk screen, printed circuit boards, and most other photographic applications for judging results, determining speed and contrast for emulsions, and hardness of coatings. • Stouffer has a wide range of transmission step wedges that are used in the various industries requiring photosensitive quality control devices. • Several sizes and formats are offered to meet most needs. This listing covers the most widely used step wedges:

Part Number Steps Density Increment

F-Stop Equiv. Dmax Size T1015 10 .15 1/2 1.40 1/2 x3 3/4" T2115 21 .15 1/2 3.05 1/2 x 5" T3110 31 .10 1/3 3.05 3/4 x 8" T4105 41 .05 1/6 2.05 1" x 9 1/2" T4110 41 .10 1/3 4.05 1" x 9 1/2" T5100 5 1.00 N/A 4.00 2" x 4"


2

Procedure: • Set your contact printer or vacuum frame to make several trial exposures on separate pieces of film, with each exposure for a different length of time. • Make three exposures: one determined by past experience or the exposure normally used in daily production, one for less, and then one for more. It may be necessary to repeat this testing procedure using different exposure times. • Process the test negative for the time and temperature recommended by the film manufacturer. It is important to keep processing consistent. • Examine the step tablet/wedge image on each of the negatives. Select as the best the negative in which step 7(on a 21 step wedge) is developed to a dense black, with step 8 only slightly dense. Step 7 will be the aim point for normal copy. • There are many different ways for exposing plates. There are an abundance of different exposure systems and processing techniques. The one constant is the step tablet/wedge. Use the step tablet/wedge as a benchmark for all exposures to achieve accuracy and repeatability. • To find the exposure factor to hold more or less on the Stouffer 21 Step Platemaker Sensitivity guide, follow the chart below. To Change Exposure 1 Step 2 Steps 3 Steps 4 Steps To Increase Exposure 1.41x 2.00x 2.82x 4.00x To Decrease Exposure .71 .50 .35 .25 Conclusion: Thus we have learnt to standardize the plate exposure using Step Wedge.


3

EX. 2 TESTING OF GSM FOR THE PAPER/BOARD SAMPLE

Aim. To test of GSM for the paper/board sample. Apparatus and materials required: Paper Sample, Scale, Cutter or Round cutter. What is GSM? • Paper is measured in GSM. This stands for ‘Grams per Square Meter’ and means exactly that ie how many grams a single sheet of paper weighs measuring 1m x 1m. • If you weight a sheet of paper that is 1 metre x 1 metre in size, the weight of that sheet in grams is the GSM value of that paper type. • GSM stands for Grammes per Square Metre - and is how the quality of paper is measured. • The term GSM refers to the substance weight of paper, relating to an area of paper that remains constant, irrespective of sheet size, expressed as grams per square metre.

Testing Procedure:

1) Quadrant Scale Operating Procedure:

• Quadrant scale is used to measure the basis weight (GSM) of paper & other sheet materials by weighing a small test sample with given dimension. • Scales are calibrated to precision weights. This accuracy Is maintained as long as the pendulum returns its original form & is kept free from corrosion, distortion or other causes. • Unpack the machine and put on the flat surface, make the machine Initially zero by using black knob in the left bottom of the machine.


4

• Above figure shows the quadrant scale and template size 20 * 25 cm2 . • Cut a sample using template 20 * 25 cm2 and put on the basket , the machine indicates the gsm of the paper .

2) Precision Balance Testing Procedure

• The GSM tests are more or less the same even if the product is different. • It exist different GSM cutters depending on the material we want to cut. • Apart from that the method consists in cutting a circle of material from 10 to 100 cm² to check its weigh. • Two tools are used : a GSM cutter (also called “round cutter”) and a weighing scale. • GSM Round Cutter is utilized for circular cutting of samples with 100 sq. cm size with speed and accuracy. • The tester showed accurate GSM of the paper

Conclusion: We learnt about to test the paper GSM for the paper sample.


5

Ex. No. 3 - TESTING OF PAPER GRAIN DIRECTION FOR THE PAPER SAMPLE Aim: The aim is to Test the paper grain direction for the given paper sample. Apparatus and materials required: Paper or board sample, Scale, Cutter, Sponge, Water, Weight (50grams to 500grams) and Procircle. Procedure: In book repair it is very important to determine paper grain and to work with it. Grain must always run parallel to the spine, otherwise the paper will wrinkle, buckle, and curl because water in the adhesives causes paper to expand and contract at different rates in different directions. To check for paper grain apply one of these following tests: TESTING OF PAPER GRAIN DIRECTION FOR THE PAPER SAMPLE 1. The Droop Test

• Place a sheet of paper at the edge of the table and observe the degree to which it droops over the edge • It will droop more if the paper grain runs parallel to table edge.

2. Wet Test • Slightly wet one side of the paper with a mister or damp sponge • The paper will curl in the direction of the grain • Once the paper has dried it will be relaxed and easy to work with


6

3. Resistance Test • Turn a piece of paper back onto itself and feel the degree of resistance against your hand • Do this in both directions • With the grain – slight resistance • Against the grain – strong resistance

4. Tear Test • Use a piece of newspaper and tear it in one direction • Tear it in the other direction • With the grain the tear will be clean • Against the grain the tear will be ragged

Conclusion: We have learned to test the paper grain direction for the paper sample.


7

Ex. No. 4 – MEASURING SOLID PRINT DENSITY USING PROCESS COLOR CONTROL BAR Aim: The aim is to measure solid print density using process color control bar. Apparatus and Materials required: Spectrodensitometer, Printed Sample and Color control bar. Density measurement:

• Densitometers display their readings for the ink density D as a logarithmic number. • It is the logarithmic ratio of the absorbed light for a “reference white” to that obtained from the measured ink film. • In practice, the ink density reading is mostly referred to as the “density”. The ink density value is calculated using the following formula: D = Log 1/β The reflectance factor β is calculated as follows:

• where LeP is the light reflectance of the printing ink and LeW the light reflectance of the reference white. • The reflectance factor β gives the ratio between the light reflectance from a measuring sample (printing ink) and from a “white” (reference value). Testing Procedure: • Select the mode Density in Spectro-densitometer. • Measure the paper whiteness in non image area.


8

• Then, Select the sample density on the spectrodensitometer. • Set the Spectro Eye (Hole) on the required color (like Cyan, Magenta, Yellow, Black and Spot colors). • Take the reading form other solid patches of colors. (Min 4 batches to Max 8 batches). • In comparing two printed sheets, density readings should be within .05 units, when measured on a densitometer, for meaningful print quality assessment. • Calculate average for the Solid ink density for each color.

Conclusion: Thus we have learnt to measure solid print density on a process color control bar.


9

EX. NO. 5 - DETERMINING THE TRAPPING TENDENCY OF THE GIVEN PRINT SAMPLES Aim: To determine the trapping tendency of given print samples. Apparatus and materials required: Reflection Densitometer, Colour control bar and Printed sample Trapping Measurement: Trap is a measure of the ability of a wet ink film printed on the paper to accept the next ink printed on top of it. Preucil’s formula is used to measure trap. % Trap = Density of overprint – Density of 1st ink x 100 Density of 2nd ink

• Trap affects the colour values of the secondary colours. Poor trap leads to colour shift in the secondary colours. • The ink tack, viscosity, ink film thickness and the impression pressure, normally affects trap. • Trap plays a major role in defining the colour gamut of a press. • When there is a colour shift in the secondary colours due to bad trap, it means the colour gamut of a press is moving away from the ISO specified colour gamut. • So before using a new ink in the press, it is essential to find how good the trap is.

Procedure: • Select the mode Trapping in Spectro-densitometer. • Measure the paper whiteness in non image area. • Then, measure the density of 1st Color using the spectrodensitometer.


10

• Measure the solid over print ink density using the reflection densitometer on the colour control bar to know the ink densities of the respective over print colours namely Yellow, Magenta, Cyan and Black colours. • Then select the density of 2nd color. • Then use the formula to calculate the trapping percentage. Conclusion: Thus we have learnt how to measure and calculate the trapping tendency of given print samples.


11

Ex. No. 6 - DETERMINING THE PRINT CONTRAST AND TONAL VALUE OF THE GIVEN SAMPLE Aim: To determine the print contrast and tonal value of given sample. Apparatus and materials required: Reflection Densitometer, Colour control bar and Printed sample. What is Print Contrast?

• Print contrast is a measure of the ability of the printing process to hold shadow detail. • A density measurement is taken of the three-quarter tone patch and of a solid patch. • Print contrast is expressed as the percentage ratio of the difference in density between the two patches and the solid ink. • A value above 30% is generally considered acceptable. Measure Print Contrast • The relative print contrast is also calculated from the readings of the solid ink density DS and the screen ink density DT. • The DT value here is best measured in the three-quarter tone.

The formula for calculating the Print contrast is Print Contrast =

Ds - Dt

Ds

Ds = Density of Solid Dt = Density of Tint


12

We need to measure the density of a solid patch and the tint patch (30%), and then apply the measured value in the formula and we can find the print contrast.

Procedure: • Select the mode Contrast in Spectro-densitometer. • Measure the paper whiteness in non image area. • Then, measure the density of soild Color using the spectrodensitometer. • Measure the solid print ink density using the reflection densitometer on the colour control bar to know the ink densities of the respective halftone (tint ) colours namely Yellow, Magenta, Cyan and Black colours. • Then measure the density of halftone color (40% or 80%). • Then use the formula to calculate the print contrast percentage. Conclusion: Thus we have learnt how to measure the print contrast and tonal value of the given sample.


13

EX. NO. 7 - MEASURING GRAY BALANCE USING COLOUR CONTROL STRIP Aim: To measure Gray Balance using colour control strip. Apparatus and materials required: Reflection Densitometer, Colour control bar and Printed sample. What is Gray Balance? • Balance patches consisting of the three color halftones at about 50% dot are used to visually check color balance. • Given correct solid density and a normal dot gain approximately 15% the CMY halftone field gives a neutral gray. • This corresponds in line to the black halftone patch on its left. • In solid patches, the superimposition of cyan, magenta and yellow must result in an approximately neutral black. • For purposes of comparison, a black solid field is printed next to the overprint field. • Colour balance patches are also used for the automatic gray balance control of cyan, magenta and yellow.

Measure Gray Balance • The relative gray balalance is also calculated from the readings of the solid ink density of CMY DCMY and the Balck ink density DK. The formula for calculating the Gray Balance is

Gray Balance % = DK – DCM

DK

DCMY = Density of CMY Combination DK = Density of Black


14

Procedure: • Select the mode Density in Spectro-densitometer. • Measure the paper whiteness in non image area. • Then, measure the density of superimposition of CMY Color using the spectrodensitometer. • Then measure the density of Black color. • Then use the formula to calculate the Gray Balance percentage. Conclusion: Thus we have learnt how to measure Gray Balance using colour control strip.


15

EX. NO. 8 - DETERMINING CIE LAB VALUES OF THE GIVEN PRINT SAMPLES Aim: To determining CIE Lab values of the given print samples. Apparatus and materials required: Reflection Densitometer, Colour control bar and Printed sample. What is CIE Lab? • CIELab is the color space that ICC Profiles and CMMs often use as an intermediary space when converting colors. • So a monitor to printer match translates colors from the monitor's space (RGB) into Lab and then into the printer's color space • The values used by CIE are called L*, a* and b* and the color measurement method is called CIELAB.

� L* represents the difference between light (where L*=100) and dark (where L*=0). � a* represents the difference between green (-a*) and red (+a*), and � b* represents the difference between yellow (+b*) and blue (-b*).

Measure ∆E: • Color difference can be defined as the numerical comparison of a sample's color to

the standard.

• It indicates the differences in absolute color coordinates and is referred to as Delta (∆).


16

• These formulas calculate the difference between two colors to identify inconsistencies and help users control the color of their products more effectively.

∆E between 0 and 1 In general, this deviation cannot be perceived. ∆E between 1 and 2 Very small deviation; only perceivable by an experienced eye. ∆E between 2 and 3.5 Medium deviation; perceivable even by an unexperienced eye. ∆E between 3.5 and 5 Large deviation ∆E exceeding 5 Massive deviation Procedure: • Select the mode CIE Lab in Spectro-densitometer. • Measure the paper whiteness in non image area. • Then, measure the CIE lab value for the reference color using the spectrodensitometer. • Then measure the CIE lab value for the actual color. • Then use the formula to calculate the∆E . Conclusion: Thus we have learnt how to determine CIE Lab values of the given print samples.


17

Ex. No. 9 - FINDING THE PH/CONDUCTIVITY OF THE DAMPENING SOLUTION

Aim: To finding the pH/Conductivity of the dampening solution. Apparatus and materials required: Conductivity meter, pH meter, cleaning cloth and sample solutions. Principle: The pH value of a solution is based on H+ ion concentration. In general for offset printing the pH value of 4.5 to 5.5 has to be maintained. Principle of pH Meter • pH meter basically works on the fact that interface of two liquids produces a electric potential which can be measured. • In other words when a liquid inside an enclosure made of glass is placed inside a solution other than that liquid, there exists an electrochemical potential between the two liquids.

2) Conductivity of a Dampening Solution: • Conductivity unit = µS/cm • Conductivity describes how electricity is conducted through a liquid; impurities in the dampening solution allow conductivity to increase. • In water or any solution the degree of conductivity is determined by the amount of minerals and other ions present.


18

• Conductivity is measured on a linear scale, which is represented by the inverse of resistance. The units of measure are micromhos.

• When considering fountain solutions, most conductivities fall in the 1000 to 3000 micromhos range. Procedure: The pH meter is set right with power connection. The electrode is washed out with distilled water and set in position. A sample of standard buffer solution is taken in 250ml. beaker. The electrode dipped in it. The pH meter is calculated to the standard value at pH of the buffer solution. The electrode is taken out, washed with distilled water. The standard buffer solution taken in the beaker is transferred to the bottle. The beaker is washed with water. The given sample solution A is taken in the beaker. The electrode is dipped in to solution. The reading in the pH meter will give the pH value of solution “A”. The procedure is repeated for B, C sample solutions. The readings are tabulated. The same procedure is repeated for conductivity of dampening solution. Result: pH Conductivity (µS/Cm) Tape water sample A = Mineral water sample B= Fountain Solution Mixed sample C= Conclusion: We have learned to Finding the pH/Conductivity of the dampening solution..


19

EX. NO. 10 - TESTING OF INK USING DRAW DOWN TEST METHOD Aim: To test of Ink using draw down test method.. Apparatus and materials required: Offset Ink, knife, Testing sheet and waste cloth Draw Down Test Procedure: • A means of evaluating the color mixing of a printing ink by depositing a layer of the mixed ink on the surface of a substrate using a smooth-edged knife.

• Drawdown is one of three basic tests used to determine the accuracy of color matching and mixing processes, the compatibility of the various inks combined, the performance of the ink on the substrate, and the drying characteristics of the ink. • Drawdowns allow easy evaluation of wettability, opacity, color match, gloss, tack strength, drying weight, dye uniformity, degree of pigment dispersion, and other attributes. • A drawdown is a sample spread of ink that your print provider presses onto a paper. • For offset printed jobs the drawdown is the best way to see exactly how the ink will look on a given paper. • There are machines that will create the drawdown, but many shops still just hand roll the ink onto the paper. • The drawdown is the only truly effective way of seeing how ink will look on a given stock of paper. A drawdown just shows a single ink on a sheet.


20

• But, perhaps you are ordering a large run, and the paper or ink you are using is a concern. In those instances you might want to ask for a draw-down. Conclusion: Thus we learnt about test of Ink using draw down test method.

Print Quality Assurance Practical -...

Documents

Transcript of Print Quality Assurance Practical -...