Screen printing basics

 

Basics screen printing.

 

Main components of the screen printing.

 

Stencil. In screen printing form is - stencil, which is a, which is stretched mesh. Emulsion is applied to the grid. Superimposed on the positive photographic emulsion (imagesetter). With copy setting, and ultraviolet light source will illuminate the emulsion. Those areas emulsion which came light harden, and where not hit washed. During the printing process through portions free of the grid is forced emulsion paint with a product resulting in a printed image.

Squeegee - is a device that is a rubber spatula with which the ink is forced through the mesh stencil.

Forrakel - is a device that consists of a metal spatula with which paint returns to start printing.

 

Theory of screen printing.

 

Basic conditions for ensuring quality printing.

 

1. To ensure contact between the emulsion layer side and a printed surface of the printing product along the whole length of the squeegee.

To ensure this condition corresponds to the following parameters. Squeegee pressure force. The magnitude of this force must be sufficient to ensure good contact between the grid and the photographic emulsion of substrates through contact. Strength is considered by the doctor blade 1 cm, however, the greater the length of the doctor blade, the greater the force to be exerted to ensure good contact. The higher squeegee pressure, the better the contact, but the higher the wear of the doctor blade and mesh. When excessive pressure of the doctor blade can deflect much that affects the reduction of the angle and the increase in printing ink metering. Many printers mistakenly believe that the harder you press, the better squeezed paint.

For optimum contact on the contact line with the printed surface of the squeegee pressure force should be 10-15% more power, which is enough for contact with the table.

2. Ensure uniform dosing paint. Punching through the desired volume of ink in the printing screen during the printing process (moving squeegee) over the entire area.

Printed angle (the angle between the plane of the squeegee and colorful mesh). Changing this angle changes the amount of ink is pressed through the mesh. The smaller the print angle the greater the amount of paint you can push through the mesh. For very small print angle arises from an overdose of paint which can print swim LUBE GO. With a large, filling the contrary will not be enough dense. At an angle greater than 90 ° count ink squeezes through the screen theoretically zero. The optimum is considered to yield an angle of 75 °.

Print speed. You must try to keep the maximum print speed to ensure performance of the printed area. The rate affects the viscosity. The higher the viscosity, the lower the print speed and high probability of ascent squeegee on the paint. So you need to install more squeegee pressure.

3. Ensure separation sieve paint immediately after the passage of the squeegee.

Printed gap (distance between the screen and printed materials). Changing this distance varies breakout force nets printed material. The more the printing gap, the smaller the angle of separation, and the more effort coming off the grid from the paint. But, by increasing the printing gap, and also decreases printing angle.

Separation angle (the angle between the grid and the printed materials for the squeegee). Changing this angle varies breakout force nets printed material. The smaller the angle of separation, the greater the force that pulls the mesh from paint. At an angle of 180 ° to tear off force is zero. In addition to coming off the corner of the effort depends on the tension force on the grid frame. Therefore, the more stretched grid, the greater the force at the same angles of separation.

Separation zone (distance between the line of contact with the screen and squeegee line of separation from the grid printed material). The size of the separation depends on the magnitude of force to tear off. The more the printing gap, the smaller the angle of separation, and the more effort coming off the grid from the paint, and therefore the separation zone will be reduced, which reduces the risk of blurred print LUBE BACK.

Power grid separation. The magnitude of this force must be sufficient to ensure a fast break after passing the grid squeegee. As above mentioned, the separating force depends on the effort of a tension grid. The more tension force, the greater the separating force at large angles of separation, then you can install less printing gap.

4. Provide uniform irrigation paint.

Return the paint is done by forrakelya (with his hand print function performs a squeegee). Do forrakelya also like squeegee angle exists between the screen and colorful plane. The value of this angle depends on how many push forrakel paint strainer when it returns to the initial position.

Forrakeli are 2x types: Spatulas, (up to 90 degrees), they are designed for viscous printing inks and paints pressed more in the sieve and scoops. These doctor blades have an angle greater than 90 degrees, and intended for liquid (low viscosity), such as UV inks, UV lacquer. When applying paint spatulas as they would be transported to the starting position.

Irrigation should be adjusted so that a uniform layer of paint covers the printed image surface, but it did not proceed to the print side. If the paint does not cover the printed image, it may not occur propechatka or uneven layer on the print. When the flow of ink on the printed surface (ink liquid) of its lubrication occurs usually forward.

5. Avoid smearing ink when printing.

When you print images through to printing screen squeegee vertical force is applied (to ensure contact between the printed surface and mesh flap substrate) and the horizontal force to move the squeegee. When moving the squeegee friction force between the doctor blade and the grid as well as any screen tends to stretch the image in the grid under influence of the force is displaced in the direction of motion of the squeegee. After the squeegee printing stroke makes it removable with force, which leads to the disappearance of the friction force and the grid returns to its original position. Thus there is a colorful blur edge. The more viscous paint, the higher the pressure on the squeegee, weaker stretch mesh and greater coefficient of expansion of the grid, the greater the blurring.

To reduce blur:

necessary to increase the tension of the printing screen,

need to reduce the pressure of the squeegee,

if possible to reduce the viscosity of the paint.

 

Types of screen printing.

 

Плоская печать.

 

1. Original condition.

a. Stencil raised.

b. Paint thrown over printing screen (in the image grid is paint).

c. Product is installed for printing.

2. Lowering the stencil and squeegee.

a. The stencil is lowered to the product.

b. The squeegee is lowered before contact with the workpiece.

c. Mesh stencil comes into contact with the workpiece.

3. Move squeegee, forcing paint on the product.

a. Raquel moved to the end of the image.

b. Paint using a doctor blade is brought into contact with the workpiece.

c. Squeegee cleaned off excess paint from the grid.

4. Raising a squeegee and stencil.

a. Raquel rises from the grid.

b. Stencil rises from the product.

5. Lowering forrakelya.

a. Forrakel lowered until contact with the mesh.

6. Moving forrakelya to start image.

a. Forrakel moved to the top of the image.

b. The paint is applied evenly on the exposed areas of the grid, filling them.

c. Printing over.

As a result, we can see how using the squeegee occurs forcing paint through the mesh on a flat product.

Disadvantages:

impossibility of printing on a curved surface.

low-speed printing compared to offset printing.

a large amount of paint.

Advantages:

the ability to print very large sizes at low cost.

high coverage of the paint layer.

possibility of a very high ink layer.

opportunity reusable stencil fotomulsiyu be rinsed and re-acquire a new image.

низкие затраты на производство трафарета.

Sealable timber - this way you can print on virtually any product having a flat shape. Textile products (T-shirts, sweatshirts, jackets, coats, spec. Clothes dryer). Sheet material (paper, cardboard, self-adhesive, folders, business cards, envelopes, letterheads, posters, boxes, plastic sheet - signs, light boxes, sheet metal - Signs, signs, panels, sheet glass - stained glass windows, light boxes, furniture doors, laminated chipboard - furniture doors, banner fabric - flags, banners, posters).

 

Circular seal.

 

The basic principle of the circular printing is a printing process that the product to roll across the stencil, and a squeegee pushes ink on it.

1. Original condition.

a. Stencil raised.

b. Paint thrown over printing screen (in the image grid is paint).

c. Product is installed for printing.

2. Lowering the stencil and squeegee.

a. The stencil is lowered to the product.

b. The squeegee is lowered before contact with the workpiece.

c. Mesh stencil comes into contact with the workpiece.

3. Move squeegee, forcing paint on the product.

a. Product roll stencil.

b. Paint using a doctor blade is brought into contact with the workpiece.

c. Mesh stencil comes into contact with the workpiece.

d. Squeegee cleaned off excess paint from the grid.

4. Raising a squeegee and stencil.

a. Raquel rises from the grid.

b. Stencil rises from the product.

5. Lowering forrakelya.

a. Forrakel lowered until contact with the mesh.

6. Moving forrakelya to start image.

a. Forrakel moved to the top of the image.

b. The paint is applied evenly on the exposed areas of the grid, filling them.

c. Printing over.

Disadvantages:

unable to print on products with large taper (3-4 degrees).

a large amount of paint.

can not print mug from handle to handle.

Advantages:

high coverage.

large field printing compared with pad printing.

possibility of a very high ink layer.

opportunity reusable stencil fotomulsiyu be rinsed and re-acquire a new image.

low production costs stencil.

Sealable timber - this method can print virtually any article having a cylindrical shape with a small taper. For the product must be sufficiently rigid. Tableware (cups, glasses, cups, bottles, ashtrays, flasks). Packaging (cans, bottles, tubes, pipes and cardboard, etc.).

 

Criteria for marriage in silkscreen and eliminating its causes.

 

Type of marriage

Reason

Elimination

Lubrication circuit, swimming vyvorotki

Large gap, liquid paint

Reduce the gap or thickened paint

Small gap thick paint

Increase the gap or dilute the paint

Small printed angle (large dosage paint)

Enlarge printed angle

Small angle of surge forrakelya (paint is pressed down)

  • Increase the angle of surge forrakelya
  • Change knife to scoop forrakelya

Poor fixing the printed form

  • Secure form
  • Call technician

Poor fixing items on the machine. (The product adheres to the frame)

  • Check mechanical fixation products
  • Necessary to tighten screws and nuts
  • Refresh fixing adhesive
  • Clean the vacuum holes
  • Cover the open vacuum holes

Rough texture of the printing products

  • Check the thickness of the emulsion with the print side. If a small layer stencil remake
  • Strongly thickened paint
  • Enlarge squeegee pressure
  • Enlarge printed angle

Availability differences surface seams on the product

  • Drown seams
  • Printed in two installation
  • Refer to the technologist

Saw circuit, tearing the thin lines or not printed

Paint has dried up due to a break in the press

Cloth to wipe the frame with hand printed with solvent and wipe dry with a clean dry cloth

Paint dries on the slow printing

  • Cloth to wipe the frame with hand printed with solvent and wipe dry with a clean dry cloth
  • Increase the speed of printing

The paint dries quickly in the frame

  • Cloth to wipe the frame with hand printed with solvent and wipe dry with a clean dry cloth
  • Add a moderator in thick glory diluent

Stencil overexposed or poorly washed

Remake stencil

Mismatch number sieve

Remake stencil finer sieve

Wrong angle screen printing thin parallel lines

Alter the stencil on a screen with an angle of 14 degrees

Static splashing paint

Electrical charge printing material (plastics, synthetics, glass org, etc.)

  • Add antistatic additive in paint. Process antistatic surface printed wallpaper and stencil
  • Thicken the paint
  • Ground the machine body
  • Increase the indoor humidity to 60%
  • Change the paint on the other analog

Dual image with 2 runs

Printing occurs both from himself and for himself

Only print in one direction

Bad stretch mesh

Redo frame higher-tension screen

Big difference in pressure in runs

Control of constant pressure when printing

Uneven paint layer banding

Bad edge of the doctor blade

Change the blade or grind it

Skewed frame along the line of contact squeegee

Aadjust the frame

Printed on the table to be garbage (glue, tape, thread, etc.)

Clear printing table

Squeegee for stretch yarn dye

Point configured to start printing ink tuber, not stack lowering squeegee mound in paint

Ampio angolo di stampa (piccolo vernice dosaggio)

Ridurre l'angolo di stampa

Uneven pounce paint (Irrigation)

  • Paint touch up the edges with a print area, or add fresh
  • Adjust the pressure forrakelya

Bad knife edge forrakelya

Change forrakelya knife or grind it

The presence of ghosting on the frame

Alter the stencil on clean sieve

Voids image

Paint has dried up due to a break in the press

Cloth to wipe the frame with hand printed with solvent and wipe dry with a clean dry cloth

Paint dries on the slow printing

  • Cloth to wipe the frame with hand printed with solvent and wipe dry with a clean dry cloth
  • Increase the speed of printing

The paint dries quickly in the frame

  • Cloth to wipe the frame with hand printed with solvent and wipe dry with a clean dry cloth
  • Add a moderator in thick glory diluent

Stencil overexposed or poorly washed

Remake stencil

Insufficient squeegee pressure

Enlarge squeegee pressure

Distorting the squeegee blade

Reinstall the blade, check its tightness or change to a new

Curved surface of the printed products

Change squeegee on a less rigid

Curved surface printed wallpaper

Consult a technician

Mechanical misalignment squeegee

Unscrew the screws skew

Skewed frame along the line of contact squeegee

Adjust the frame

On the printed side of the stencil debris from falling

  • Cloth to wipe the frame with hand printed with solvent and wipe dry with a clean dry cloth
  • Do not print dirty objects with dust and debris, wipe them free of dust and debris before printing
  • Do not cut the paper on which leaves a bad knife Mohr. Clear paper from Mohri
  • Follow the thread on textiles and remove them before printing.

Stencil overexposed or poorly washed

Remake stencil

Mismatch number sieve thickness lines

Alter the stencil on a smaller sieve

Wrong angle screen printing thin parallel lines

Alter the stencil on a screen with an angle of 14 degrees

Poor coverage of paint 

Mismatch number sieve

Alter the stencil on the larger sieve

Small thickness of the emulsion with the printed side

Check the thickness of the emulsion with the print side. If a small layer stencil remake

Low opacity of paint

Change the paint on a hiding

The high absorbency material (paint falls after drying)

  • Change the paint on the UF Or oil-based
  • Make the most of thick paint
  • Reduce drying time

Large printing angle (small dosage paint)

Reduce printing angle

Very high pressure on the squeegee

Reduce pressure on the squeegee

Fingerprints

Dirty hands

  • Wash hands and monitor their purity
  • Work with the assistant principle printer prints, and assistant is responsible for product

Vesicular on the print

Paint properties

Add fluidity improver (defoamer)

Poor irrigation (pounce)

Reduce the angle of irrigation

liquid paint

Thicken the paint

Dust on the print 

Dirty room

Keep clean and wet cleaning facilities

Big drying time

Reduce drying time

Low humidity in the room

Increase the humidity up to 60%

Peretiskivaetsya typos in the foot and scratched

Insufficient drying time

Increase the sushkido complete drying

Many of the moderator in the paint

Increase the drying time, the next time you print, reduce the number of moderator

Wrong additives in paint

Increase the sushkido completely dry, draw high-IR drying if possible. Later observe instruktsiyupo paint

Improper drying

Follow the instructions on the paint

Poor ventilation products during drying

Create a forced ventilation

Bad paint properties

Change the type of paint or vendor

Cracking paint 

Много растворителя или замедлителя

Knead a new batch of paint in the correct proportions

Wrong additives in paint

Follow vendor recommendations

The paint does not match the printed material

Change the paint or supplier

Paint does not stick to the product

Not matching dye printing material

Change the paint or supplier

Not the right supplements, and whether the proportion of additives

Reprint order to properly prepare the paint

Not added a hardener or catalyst

Reprint order to properly prepare the paint

Surface ill-prepared for printing (degrease, activated)

Properly prepare the surface for printing

Improper drying

Follow vendor recommendations

The drying temperature (the room) is lower than 18 degrees

Increase the temperature of drying

 

Choosing mesh for screen printing.

 

Basic parameters of mesh for screen printing.

 

1. Fiber mesh material.

Silk fiber. Now almost never used because filaments had a bad weave structure and low stability. But thanks to the first use of this material in the production of silk screen stencil comes the word.

Capron. This material has a high elasticity and low stability. Used when printing on uneven surfaces and cylinders.

Polyamide monofilament. This material has a high stability after the tension on the sieve frame. By stability is meant maintaining a constant tension in the sieve during its operation. In 80% of all work performed, he finds application.

Metallized fiber. Suitable for printing on materials with increased electrification. This material has good stability, and high discharge static electricity.

Stainless steel. Metal mesh have very high stability and low stretch factor. These properties are indispensable for printing circuit boards and precision scales. High wear resistance of the material is used for printing on glass and ceramics. Also, the grid have a high electro-static discharge.

2. Types weave mesh.

Simple weave (PW). This weaving weft weaves through each warp yarn. Based on the read coil filament arranged along the sieve.

Twill weave (TW). This weaving weft weaves through two warp threads.

Calendering sieve. To reduce the consumption of paints and reduce paint layer ( UF paint, gold- paint, etc.) sieve calendered. Calendering is a process of passing the grid between two shafts, one of which is heated. Due to this top under the influence of temperature filaments are flattened in the zone of inflection. This leads to a reduction in the thickness of the screen H, and ultimately to reduce the flow of paint. Calendering sieve may be unilateral or bilateral. When unilateral calendering paint consumption is reduced to 25 %, while 50% bilateral. Calendering disadvantages include reduced strength and reduced screen exposed surface area.

3. Number screen mesh.

Numbered (№ grid) means the number of threads per 1 cm or 1 inch.

The mesh number of 120 with a number means that in 1 cm interwoven yarns 120. The higher the mesh number, the finer the cell it is. When printing a rough image that require high coverage or ink film thickness should be used lower numbers sieves. Principle is as follows: the lower the number the grid, the lower the resolution of the stencil and thicker layer of paint, which means more consumption of paint. The main criterion for choosing a grid of numbers is the required thickness of the paint layer and the minimum thickness of the printed lines (resolution). If the thickness of the line is close in size to the diameter of the thread, these elements may simply not be possible already during copying.

Raster points in the manufacturing process can get on the thread and in the end did not turn out, other raster point contrary can get between the threads and just be washed away in the process of developing the stencil with water. Thin line can be blocked thread and printing have discontinuities as a dotted line, problems can occur with acute angles, generally push the paint through a small hole is almost impossible, because contact area with emulsion paint more than the printed materials.

The thicker the layer of paint is needed, the larger the grid should be applied. At the same time we must not forget that in the presence of printed motives subtle elements, the use of large nets can lead to distortion or complete absence of these elements when printing (insufficient resolution stencil). In such cases it is necessary to find a compromise between the film thickness and the resolution of the stencil. In some cases it is advisable to make a stencil on the two single color with different mesh numbers. One stencil with low numbers we obtain high coverage, and the other with a high number of high-resolution grid.

4. Series printing screens.

At one and the same issue of the grid can be different diameter thread. There classification grids by series: S - particularly light, T - easy, TH - average, H-heavy.

The difference between the series is the difference in diameter of the filament, the heavier series, the greater the diameter of the filament. Heavy series have greater run length, but less dense layer of colorful. This leads to a lower opacity prints.

5. Color printing screen.

Mesh is available in two types: undyed (white) and colored (golden yellow, orange).

Colored grid is recommended when copying very fine lines, and bitmaps. When you hit the light flux on the grid most of it passes through it, a very small part is reflected, as well as a significant portion of dissipated. Scattered light flux promotes lateral illumination of fine details, which can then bad promos. Painted mesh absorb light incident on the thread, and prevent the dispersion of the luminous flux which stops shining on photographic emulsion, similar to the Red Lantern, which is not shining on the photo paper. When applying colored nets should be noted that the exposure emulsion increases as the value of the useful luminous flux decreases due to the neutralization of the scattered parts of it.

 

Screen printing inks.

 

Composition screen printing inks.

 

1. Colorants. Colorants are pigments or dyes. Dyes soluble dye in a medium (solvent). In the dyeing process, they penetrate into the material and form a more or less strong bond with the fibers. Pigments are insoluble. In the ink, they are in a binder (varnish, nitrocellulose, etc.) and the properties of the paint binder is more dependent than that of the pigment. Communication with coloring materials provides a binder. Colorants typically - organic substances. Pigments largely - fine mineral dispersion, although they may be both organic and inorganic. The incorporation of pigments in paints is the main method of controlling the properties of decorative coatings - color and opacity (opacity). Opacifying pigment in the pigmented material if its refractive index above the refractive index of the binder. The greater the difference in refractive index of the pigment and binder, the more coverage of the pigmented material. In addition, important form of the pigment particles, such as leaf shape of the particles of pigment gives more coverage than a needle or spherical.

2. Binder. Problem binder glue colorant to the surface of the printed product. Depend on the properties of the binder: paint adhesion with the printed material, methods of drying, light fastness, the height of the paint layer, gloss, abrasion resistance. The basis of the binder usually is the resin with a solvent which is responsible for the consistency of the ink until it dries.

3. Additives. To improve the properties of the ink, there are various additives. Listed below are the main types of them. The producers may be other specialized supplements.

Solvents - reduce the viscosity of the paint.

Inhibitors - reduce the viscosity of the paint and its rate of drying.

Flow improvers - improve spreading paint on the print, reduce the formation of fine bubbles.

Thickeners - make the paint more viscous and thick.

Antistatic - improve the electrical conductivity of the paint, reduce the accumulation of static electricity, reduce static spatter.

Hardeners and catalysts - improve paint adhesion to difficult materials.

Matting agent - makes the paint more opaque.

Pigments - color additives that increase the aperture ratio (saturation) colors. Incorrect use of additives can worsen the properties of the paint. Therefore always strictly follow the manufacturer's recommendations paint.

 

Basic parameters of paint.

 

1. Type of binder. Depend on the type of binder printing, maintenance and paint adhesion properties.

2. Method of drying (natural drying, IR (infrared radiation), UV (ultraviolet radiation). Depends from the drying process drying speed and adhesion to a printing material.

3. Degree of opacity (transparent, translucent, polukroyuschaya, the coating, the coating super). Degree of opacity shows how tightly the paint layer can close the dark color of the printing material. If you print a transparent paint to black, the color of the paint will not be seen. If the paint polukroyuschaya, the paint color is dirty because of the color of the illuminated substrate. Super opaque paints can maximize tightly black.

4. Height paint (low, medium, high). Height paint indicates how thick the paint layer remains after it is completely dry (relief print).

5. Gloss Level (paint super matte, matte, velvety matte, glossy, super glossy). Gloss paint shows how much ink layer can reflect or scatter light.

 

Varieties stencil paints.

 

In screen printing uses four basic types of paints: plastisol, solvent, water and ultra-violet. They differ binder and drying method. Thus all kinds of colors, there are many different series. Between a series of different adhesive properties to various materials, elasticity, gloss, hiding power, non-slip, etc.

 

 

Plastisol

Solvent

Ultraviolet

Water

Printing materials

Textiles (cotton, nylon), transfer.

Paper, plastic bags, glass, metal, textiles.

Graphic printing (paper, plastic bags).

Textiles (cotton), paper.

Drying method

Polymerization. when it reaches 130-170°C*, (IR).

Evaporation of the solvent under natural drying, IR or R

The polymerization upon exposure to UV radiation.

La polimerizzazione per esposizione a radiazioni UV.
3-5 minutes 150-180°C.

Height

high

lowest

medium - high

average

Elasticity

high

low - medium

lowest

average

Plus

  • Dries in the grid (you can leave long-term).
  • High opacity.
  • High penetration.
  • Can print on a large variety of materials.
  • Quick-drying.
  • High-gloss.
  • Soft to the touch.
  • Withstands dry cleaning and ironing.
  • Availability etching series.
  • Environmentally friendly.
  • Can print on raw crude.

Minus

  • Rubber touch.
  • Unable to print on materials can not withstand high temperatures.
  • A limited number of print materials.
  • Requires long drying.
  • Drying the grid, adding retarder increases drying time.
  • Bad opacity (translucent).
  • Not all materials possible to achieve good adhesion.
  • High price.
  • Dries in the grid.
  • Requires prolonged drying at a high temperature.
  • Necessary to apply specialized emulsion.

Used additives

  • Plasticizer.
  • Increase elasticity.
  • Decreasing drying time.
  • Special Effects (Vzduvashka, 3D, etc.).
  • Thinner.
  • Retarder.
  • Catalyst (hardener).**
  • Thickener.
  • Flow improver (foam absorber).
  • АAntistatic.
  • Matting parpshok.
  • Thinner.
  • Catalyst (hardener).**
  • Thickener.
  • Flow improver (foam absorber).
  • Improver depth curing.

 

 

IR - Infrared.

R - convection drying.

UV - Ultraviolet drying.

* – The drying temperature depends on a series of paint.

** – Used in two component series.

 

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