Screen Printing

Screen Printing and Defects and Their Remedies

When you put a paste of Color, then the color comes through the fine holes of the design and comes on the fabric. In this printing, a color can be printed from one screen in the same way as the color printing. For every color design, 
There are many runs needed in this.
 In manual screen printing, the fabric is piled well on the printing panel and it is taken care that there is no fall on the cloth. 

Therefore, by pulling this cloth properly, fix it with the help of pins and Put the screen on the cloth and put a color paste. Spread the paste on top of the screen with the help of Squeegee, which spreads well on the screen, so that the color can be seen from the hood of the screen. Check it out.

making a screen for printing

Screen printing is a form of stencil printing. This printing has a frame for printing which is covered with silk, metal, nylon, or polyester cloth. The screen is prepared like this. On the screen, a photographic film is coated with a design based on trace paper. Design made on the screen is made of very fine holes. 


Screen printing



Machine screen printing

This kind of printing can also be done by machine, which is called flat band printing. Textile with such a machine is constantly printing. With the help of a cloth conveyor belt, the printing keeps on moving forward. In the law, the screen is one after the other, which is above the belt. 

The time of printing stops the belt so that the cloth comes in a steady-state, the screen comes on top of the screen and after printing, the screen is up like the above and the cloth moves further. The next screen is placed on another screen. This process keeps running on the fabric (which is printed from the first screen). 

In this method, the colors are brought to the screen with the help of Pump and the skiing process comes from mechanical squeezing.
Two types of suites are used. A conventional squeegee moves forward and backward on the screen with the help of a motor, and there is a squire like the other roller bar which keeps roll on the screen.

Printing in flatbed 6 Maybe at a meter/minute speed. Fig - The flat-screen printing process is shown in

Vertical Duplex Screen Printing Machine
 


This new vertical duplex screen printing machine has been developed by the firm Franz Zimmer. The screens are used vertically at twin pairs, which clamp together over the cloth at the moment of printing. They register the prints exactly at the same place on the back and face of the cloth. 

This is insured by the method of packing the screen. The machine provides a new technique for the whole range of textiles, particularly very wide and thick materials such as drills, blankets, toweling, etc. It is possible to print on both sides with ease and economy. 

Depending upon the type of dye used, the fabric after printing and dyeing is passed through either a steamer or a polymerize to fix the dye the fabric. The fabric is then washed on a soaper and dried. The details regarding steamer, polymerizer and 
soaper are mentioned earlier in the Chapter n Machinery Used in Dyeing.

Screen Printing Defects and Their Remedies

The defects that occur in screen printing is not as many as those which occur in roller printing because being a hand.

printing process, the defects which arise in a machine due to say,. doctor blade roller engraving, are absent in screen printing. Other defects and the remedies thereof are as under  

Uneven Prints :

These occur if the printing table is not level or if the edge of the rubber squeegee is uneven. The remedy lies in using a perfectly lovely table and sharpening the edge of the squeegee.

The badly bleached cloth also gives rise to uneven prints due to uneven absorption of color; the remedy is to use a well-bleached cloth.

Lighter Prints

These arise il the openings of the screen get clogged particularly by pigment colors which dry up too soon; the remedy lies in washing the screen immediately after use because it is difficult to dean the opening once the synthetic resin ( binder ) is set

Lighter prints are also caused it the colour paste is too thick; the paste produces a weak impression because it is too solid to be absorbed freely. The remedy is to thin down the pasta, The foam produced in the paste also causes Lighter prints; the remedy lies in adding anti-foaming agents like pine oil, turpentine or cyclohexane to the paste.

Specks of Dark Color:

These appear as minute specks on the cloth due to faulty color mixing; the remedy is to mix the ingredients properly.

Small specks on the unprinted portions of the cloth appear due to Pinholes on the screen or due to negligence of the screen maker. The remedy is to check the pinholes and cover them with lacquer.

Light and Dark Prints:

These appear on the selvages steaming in the Star Ager is not uniform; uneven prints. appear one to batch-wise steaming on batch rollers. The remedy applies pressure on the squeegee evenly ensure proper steaming and avoid too much loading on the roller

Once the cloth is badly printed, it is difficult to rectify the defect; therefore, great care has to be taken to prevent the faults and to rectify the same immediately so that The number of rejects is kept to the minimum. 

 

Advantages of Screen Printing:

1. The method is simple to operate and does oat require elaborate and expansive equipment.

2. The method enables new patterns to be produced quickly and without a large initial expense since the screens can be produced cheaply.

3. The method is useful for printing knitted rayon fabrics which cannot be manipulated satisfactorily on the roller printing machine.

5. The method is economical in production and manually less exacting than block printing.

6. Blotch designs can be printed by this method which cannot be printed by block or roller printing: further, it is possible to produce larger repeats than those in roller printing.

7.  As many as 16 colors can be printed in one pattern by this method. In roller printing, even though it is possible to do this, it is difficult in practice to use more than 6 rollers.

8.  Prints obtained by this method are more intense, more bright and possess natural bloom as corn pared with those obtained by roller printing method; further, by using fine- mesh screens, sharp line effects including vertical lines can be produced by this method which is difficult it to produce with roller printing.

 

Disadvantages of Screen Printing

1.  For high production, a large number of tables have to be used requiring huge space with incidental overheads; in roller printing, tale space required Is very much less.

2. Delicate shading and gradation of colour are difficult to obtain by this method and the joint marks at the repeals are often perceptible.

3. Fine mesh screens used for sharp line effect: often get choked rendering the screen redundant. 

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