Silk printing training

One of the most popular ways to create beautiful designs, screen printing is a traditional, high-precision printing process used by many merchants and manufacturers around the world. Manual silk printing with a stencil is one of the earliest methods of printing, which has many applications even today. The basis of silk printing is based on silk net on a wooden or metal template or a frame made of wood or metal, which is sensitive to gelatin. The light is impregnated and washed off after exposure, and printing is done with paint on the objects.

In terms of price, silk work is very economical compared to other printing methods and can be done with minimal capital; Most of the jobs related to printing that exist today, start with a few hundred million tomans, but for silk printing, it is possible to set up a workshop with a small cost, and all the necessary materials can be found in all cities.

Different parts and process of silk printing

In the rest of this article, we will mention all the different parts of silk printing and how each one works and the process of using them

1.      Silk printing work page:

One of the most important characteristics of the working screen in the silk printing machine is the smoothness of the screen, the dimples or protrusions of the screen cause the printing process to not be done properly. The material of this plate is not different, but currently the plates are made of chipboard, MDF and iron plate, the thickness of the printing plates should be such that it does not change with pressure, and it should be noted that if color is spilled on the plate during the work, it will be faster. to be cleared.

In more professional work, the plates are made with small holes and a suction device is installed under the plate to make the work stick to the plate completely. The size of the pages depends on the type of printing, usually printers prefer to have a wide and large work page so as not to have a shortage in printing, and of course, many printing workshops use the work page as the desktop, which is economically useful at the beginning of the activity. ; But there are some problems: First, the color and scratches on the table will gradually cause the printing failure, so it is recommended that the work surface is separate from the normal table. The common sizes of the screen for silk printing are 30x40, 40x50, 50x60, and 60x70, of course, for long works, they make tables that can be used for fabric printing with a length of 100x300.

2.      Clip and hinge:

On the work surface in silk printing, clips and hinges play an important role, closing the wood frame on the work table is done by clips; Usually a few screws play the main role. The thickness of the screw is usually eight or ten screws, and the number of screws depends on the size of the wood, most of the molds can be closed with two screws.

The length of the screw should be enough to tighten the frame completely, of course, if we put a plate like a metal belt under the screw, so that it does not damage the effect of the pressure of the screw on the frame, and of course, it is better for the clamp to have height adjustment screws on the sides. To be able to print objects of different heights with one machine. But if the height adjustment is not needed, the clamp can be installed to the work surface without screws with a simple hinge.

3.      Work desk in silk printing:

In the specifications of the silk printing work table, the height of the table is important, the height of the table is directly related to the height of the printing work, the shortness of the table causes bending of the back and slowness of work, and the height of the table causes not reaching the hands and fatigue. The width and length of the table depends on the printing substrate, for example a long table is needed for a long wide job, but a long table is not needed for a CD printing series.

The silk printing work table should not have thin legs and should be strong and stable, not slip or vibrate, and the connection between the screen and the legs should be completely firm. The floor on which the table is placed must be completely smooth and clean; It is also necessary to clean the table and the floor.

4.      Silk printing format and its use:

The mold or frame in silk printing is made of wood or metal, mostly aluminum, it is important that the edges are not sharp and the frame is not complicated during use. The size of the width and length of the frame depends on the design and usually it should be at least five centimeters larger than the design on each side; On the other hand, the thickness of the mold also has a formula that depends on the width and length of the printing media, but in traditional workshops, 4x4-3x5 and less than 2x4 molds are usually used.

Tabbing is very important when creating a template; Sometimes they only nail the wood end to end and this causes the complexity of the mold over time. The mold should be half tongued, and if it is metal, it should be welded and seamless so that the color inside the can does not come out. If the silk screen printing mold is made of wood, it is better to make the wood completely dry and paint or oil it at least twice for better resistance to moisture. Mold cleaning is basic and important; Be sure to wash the mold completely after finishing the printing process so that there is no trace of paint, and if the wood of the mold is already saturated with oil, it is easier to clean it.

5.      stencil in silk printing:

The main piece in silk printing is the silk net, which has different numbers depending on the type of printing media and has a scientific table, but in the simple method, up to number 50 is used for fabric printing, and from 50 to 90 for normal work, and from 90 to 150 for delicate work and from 150 to 200 for very precise work like printing electronic circuits. The type of silk net is important, and the best net in Iran for silk printing is Swiss net, but due to the high price, Italian nets are usually used, and if the number of works is small or the printing is new, the Chinese net is the best practice net. The very small holes inside the net, which are for the color to pass through, must be cleaned with retarder or instant thinner during the printing process and after the printing is finished so that there is no trace of color in the holes.

How to stretch the net on the template is simple, but it requires a lot of practice, in professional workshops there is a special tool for stretching the net. But in a simple method, with a small black nail, a shoemaker's pattern or a staple is fixed on one side of the net on the mold, then it is completely stretched and gradually fixed on the mold at a 90-degree angle, and then again, the 90-degree angle and finally the last angle is very important. Because the stretching of the net is final in the last stage, so it should be stretched tighter to the extent that it cannot be swallowed by hand pressure, then it is glued on a nail or a staple. From the inside of the mold, we stick the net to the walls of the mold with a wide adhesive tape so that the color does not penetrate under the work; During silk printing, a sharp object should never hit the net, but if a tear is found in a point of the net, it can be repaired with wide glue, but it will not be used for printing.

6.      Squeegee spatula and how to use it:

For silk printing, we can use any device, but this method requires a spatula with a certain standard, each printing substrate requires a special spatula, fabric printing spatula differs from cardboard and nylon printing in terms of edge angle, but most Current workshops use rubber spatulas and rarely gelatin. The thickness of the spatula for silk printing should be enough to not bend easily, but it should not be dry and inflexible. This spatula should not have holes or cuts or holes for the paint to penetrate.

It should also be completely cleaned and washed during work and after finishing printing. There are spatulas used in silk printing both made in Iran and made in other countries. In works with a small width, the problem of the type of spatula is not much, but the more and wider the printing surface, the smoothness of the edge of the spatula will require more skill; The amount of pressure of the spatula on the net also depends on the type of design and the amount of color and thickness of the design lines.

7.      Drug appearing in silk printing:

Silk printing medicine consists of raw materials as follows

•    Gelatin 88 grams

•    Distilled water 538 grams

•    Ammoniaknh3 9 grams

•    Antifoam 8 grams

•    Kajelin (a type of glue) 88 grams

•    270 grams of water

•    20 grams Potassium bichromate Cr2O7K2

In large workshops, drugs are sprayed on printing media. A special gelatin, which is sensitized with several other substances, creates the base of the silk-screen sensitive varnish. This commercial medicine available in the market mostly contains two substances, bichromate and gelatin in the amount of one to ten, of course, the method and duration of mixing and preparing the medicine in the dark are among the mandatory items; The prepared medicine can be used for 24 hours if it is not exposed to light. After making this drug, with a spatula, the surface of the net should be uniformly smeared on both sides, and in order to draw the drug on the template, one side should be stretched vertically and the horizontal work should be completed on the back until uniformity is complete.

Some of the old masters, once this drug has been drawn and dried with a hair dryer or fan or in the open air, they dilute the drug with water and again apply a very thin layer on the template so that there is no possible hole empty of varnish. Iranian drugs are of good quality and most of the printers are satisfied with it, but in large workshops they mostly use foreign drugs, because after erasing, less traces of the design are left. grease, dust and any type of pollution, and after cleaning, the net should be protected from the above and kept in a place away from danger.

8.      Retarder for silk printing:

Retarder is used in silk printing as a kind of color relaxer, creating color adhesion to the media and for washing the net. Many traditional workshops use instant thinner instead of retarder, in normal prints this is not a problem, but in delicate works it is important to use retarder, for example, when using P.V.C paint or polyethylene paint, using retarder in loosening Color is essential.

9.      Cleaners in silk printing:

In silk printing, a cleaning solution should be used to remove and whiten the varnish from the net, but in many cases, they use Vitex or chlorine, which is harmful to the net in the long run. It is better to wash the screen-printing net with standard detergents to have a longer life and higher quality. There are several types of these cleaners: there is a powder type that mixes 100 grams in seven liters of water, and a liquid type that mixes one kilo in 50 liters of water. Maybe the price of Vitex seems reasonable, but considering the high price of the net, the use of these cleaners is recommended because it completely removes the varnish and maintains the resistance and quality of the net.

10.  Silk printing color:

The variety of colors in silk printing is very large, which include:

✔  Ordinary oil paint that is diluted with thinner or gasoline and is used for simple and ordinary work. Using retarder in oil paint makes the work stickier, but drying of this paint takes a long time or needs a dryer.

✔  Polyethylene paint, which is diluted with thinner and preferably with retarder, has average quality, dries faster and has average adhesion, which is better than oil paint.

✔  PVC paint that is diluted with retarder and has good quality and dries very quickly. Polyethylene and PVC paint have a color base that can be dyed with different colored inks and its variety is great.

✔  Pigment colors are used for silk printing on fabric and have base and color paste and have good quality for fabric printing.

✔  Salt water color is used to print cartons and cardboard.

✔  Plastic color is used in washable silk printing for fabric and is cheaper than other colors.

✔  High-baking paint is used for paint on porcelain flower paper and melamine flower. It has a high price and has its own leaves.

✔  Transfer color or decal that is printed on normal paper and then printed on the garment with heat and a hot press.

✔  Powder in different colors that is mixed with a special paste and dissolved in water and used for scratch printing

11.  Light table in silk printing:

A light table is used to print the design on the stencil and perform silk printing. In this table, several (usually two to five) moonlight lamps or special lamps are used. The greater the width and length of the table, the better, so that we don't have a problem in printing large designs. The height of the table from the surface of the lamp to the glass on the table is between 20 and 30 cm, and the exposure time is between 5 and 10 minutes depending on the distance, thickness of the design, ambient temperature and thickness.

When the design was placed on the glass of the light table and the stencil was placed on the design, the design was covered with a black cloth and a flat object was placed inside the mold on the cloth and with a weight like a four-liter water container, the design was completely attached to the glass of the light table. It sticks and after exposing the stencil, it is washed with half warm water without pressure, then it dries, and if it has a black design, it is necessary to apply some medicine in some places and expose it, then wash and dry it again. Of course, this stage of silk printing must be done in a darkroom, and this darkroom can be a warehouse where the entrance of light is closed with cloth or cardboard or any other device.

12.  Design conditions in silk printing:

The desired design can be printed on transparent talc or film or ordinary paper, but the transparency of the design is very important at the points where the light is going to pass through, and the blackness of the lines is even more important. In professional workshops, special films are used for printing, but in most traditional workshops, calque paper is used as design film; Of course, you can also use black paper cut in the shape of the desired design as a film. In new designs that use photos, landscapes, clothes and people, such as Photoshop, consistency is added to the photo and the photo has very small holes for color to pass through.

Of course, you should put a + sign on the four corners of the design so that it matches the + sign on the design by placing it on the template, and prevents the design from moving and moving unintentionally. Also, if it is going to be printed in multiple colors, first all the pages of the design must have these marks in the four corners in the same way, and a design and a stencil are needed for each color.

13.  Drying methods in silk printing:

One way to dry the printed design is to use clothesline and clothespins, or use a drying rack. Another way is to create a warm environment with a heater or hair dryer and any heat-generating device, but if you do not have the possibility to provide a drying environment, use fast-yielding paints such as PVC paint or polyethylene paint.

14.  Silk printing process:

After doing the mentioned things, we come to the most basic stage of silk printing, first we put the desired media on the screen of the machine, of course, we must know that if the number of jobs is large and the place of printing must be exactly at a specific point, it must be on the work table. Put templates so that all the media can be placed in one place. For example, when you want to print a CD, we stick a semi-circular shape to its diameters on the table that matches the design and the CD and does not move.

After placing the stencil on it, it should be a few millimeters away from the media to print the color inside the wood with the pressure of a spatula. Of course, during the silk printing operation, the net should always be cleaned, the table should not be colored, the net should not be colored, and the thickness of the net should be compatible with the desired media type. Also, after silk printing, if you need a stencil and a design on it for future times, it should only be cleaned with retarder and then washed and dried with water and placed in a suitable place. It takes a lot of practice to print thin letters and small letters and numbers using the silk method, and another important point is the cleanliness of the objects during printing, for example, if we clean the surface of Nylex with a gasoline cloth, it will print much better.

Application of silk printing

•    Nylex and nylon

•    CD-DVD

•    Phone book and due date

•    Wall Calendars

•    Leather

•    Cardboard

•    Mirror and glass

•    shoes and bag

•    Box of sweets

•    Various cardboard boxes

•    Art boards

•    Industrial signs

•    Notice boards

•    Promotional items such as watches and pens

•    Sack

•    Fabrics and types of clothing

Possible problems in silk printing:

✔  In silk printing, sometimes the color is continuously filled in the net, to solve the first problem, you need to mix the color more with the solvent and keep in mind that the net needs to be cleaned after several prints.

✔  It is possible that when washing the medicine after exposure, the medicine is cleared too much, the reason for this is that the exposure time is probably too short or the medicine ingredients are not mixed well, and it is also possible that the amount of the mixture is not appropriate and the distance between the lamp and the design be a lot.

✔  In silk printing, there are cases where the color does not spread well. To solve this problem, the smoothness of the edge of the spatula must be controlled and uniform pressure must be observed during printing.

✔  There may be a lot of color spread in silk printing, to solve it, it must first be cleaned under the net continuously, then the color should be thicker and the possibility of a mistake in installing the low number net should be checked, the upper net number has a smaller hole and the distance between the stencil and the screen also set

✔  The cleanliness of the glass of the light table is also very important in silk printing, because there are many defects in the printing due to the dirtiness of the glass.

✔  Also, the cleanliness of all the equipment used is necessary for printing, grease and dust and any kind of obstacle for printing will ruin the work.

✔  Using too little or too much solvent causes many problems as a result of silk printing, make sure that the color must be mixed with full solvent for a long time.

✔  After combining the drug with exposure materials, it must be in a dark environment, otherwise it will cause disruption in silk printing.