Any way you look at it, Pad Printing is an unlikely imaging process. It borrows a unique amalgamation of features from gravure, screenprinting and rubber stamp printing, yet its most frequent industrial decorating competitor is none of these processes. Instead, Pad Printing most often encroaches on jobs once dominated by Hot Stamping. Even the process itself is somewhat befuddling. If the ink is so attracted by the silicone pad that it leaves the recessed areas of the printing plate, why does it abandon the pad so completely upon touching the substrate? Unlikely as it may be however, this process is finding increasing favour in a host of commercial and industrial applications. Why?

It is adaptable to a variety of shapes and contours on parts with a variation in the surface, yet fine detail and precise copy can be achieved. Four color process is obtained with exact registration. Pad printing is ideal for decorating toys, plastic housewares, and injection molded components. This technology also lends itself to marking electronic components such as resistors, canisters, and connectors. Any part, plastic, ceramic, or metal can be production marked by this process. The equipment can be semi or fully automated, yet remains a low capital expenditure technology.

Features of Pad Printing:

Following are the unique features of the Pad Printing process.

Can print on convex, concave, curved, recessed and discontinuous surfaces allowing product designers a substantially broader range of shapes and designs.
Pad printing is able to print shapes and surface structures well outside the capabilities of Screen Printing and Hot Stamping opening up a way to decorate a whole new range of products.
Allows wet-on-wet multicolour printing (without intermediate drying) on non-absorbent surfaces - therefore much reduced down time.
Is capable of 90 degree wraparound on three-dimensional objects.
Offers better edge definition and higher resolution than most other printing systems therefore offering a method of decorating high quality high priced items.
Is a relatively inexpensive printing system particularly for multi-colour and process colour printing which means reduced capital outlay.
The many advantages of Pad Printing:

Variety of substrates - Almost any material including glass, ceramic, metal can be printed with suitable inks.
Ability to print fine details - Resolution is far better than that of screen printing in fact up to 120 lines / Cm (300 lines per inch)
High resistance of printing inks - Depending on ink type used extremely high resistance against mechanical abrasion or chemicals can be achieved.
Easy handling and little maintenance - Compared to other printing processes pad printing is easy to learn
Multi-colour printing: wet on wet - Possibility to apply multiple prints without intermediate drying
Short tooling-up times - Plates and inks can be exchanged within a few minutes
Low set up cost - Plates can be produced in-house
Relatively low space requirement - Compared to other printing machines pad printing equipment is space efficient
Low drying cost - In the most simple case air drying at room temperature is sufficient.
Integration into complex systems, inline production and assembly lines - For years now there has been a successful combination of pad printing systems with injection moulding equipment or assembly lines.
Limitations of Pad Printing:

Size of motive - Motive sizes are limited by plate, pad and efficiency of the pad printing machine. The diameters of the largest efficiently printed motives are currently approx. 30 cm.
Layer thickness of ink film - The pad process uses plates up to a depth of approx. 20-25µm (at the most 35µm). Thus conventional inks will result in printed ink films of approx. 7µm. This layer thickness can be increased correspondingly by multi-layer printing. Rough particles (e.g. glitter pigments) are difficult to print in an efficient manner
Printing speed - Even substrates can be printed a lot faster with other printing processes.
What does the process require?

Artwork i.e. the image that is to be printed. Because Pad Printing is often used for its ability to print very fine detail Artwork can be quite specialised.
A film positive, which is produced from the artwork.
A printing plate, which is either a "plastic" or steel printing plate, referred to as a cliché. Onto this cliché we have etched an image (from the film positive) into the surface. So the image is said to be in relief rather than in profile as in letterpress printing.
A Pad Printing machine to facilitate the inking and doctoring of the image, the pick up of the image from the cliché and the put down of the image onto the item being printed.
A Tampon or Pad, which is moulded from silicone rubber.
Specialist Pad printing ink.

source: http://www.packmark.com.au

Screenprinting, silkscreening, or serigraphy is a printmaking technique that creates a sharp-edged image using a stencil. A screenprint or serigraph is an image created using this technique.

It began as an industrial technology, and was adopted by American graphic artists in the early 1900s. It is currently popular both in fine arts and in commercial printing, where it is commonly used to print images on T-shirts, hats, CDs, DVDs, ceramics, glass, polyethylene, polypropylene, paper, metals, and wood. The Printer's National Environmental Assistance Center says "Screen printing is arguably the most versatile of all printing processes."^[1] Since rudimentary screen-printing materials are so affordable and readily available, it has been used frequently in underground settings and subcultures, and the non-professional look of such DIY culture screen prints has become a significant cultural aesthetic seen on movie posters, record album covers, flyers, shirts, commercial fonts in advertising, and elsewhere.

Graphic screenprinting is widely used today to create many mass or large batch produced graphics, such as posters or display stands. Full color prints can be created by printing in CMYK (cyan, magenta, yellow and black). Screenprinting is often preferred over other processes such as dye sublimation or inkjet printing because of its low cost and ability to print on many types of media.

Printing Teqnique

A screen is made of a piece of porous, finely woven fabric (originally silk, but typically made of polyester since the 1940s) stretched over a frame of aluminum or wood. Areas of the screen are blocked off with a non-permeable material to form a stencil, which is a positive of the image to be printed; that is, the open spaces are where the ink will appear.

The screen is placed atop a substrate such as papyrus or fabric. Ink is placed on top of the screen, and a fill bar (also known as a floodbar) is used to fill the mesh openings with ink. The operator begins with the fill bar at the rear of the screen and behind a reservoir of ink. The operator lifts the screen to prevent contact with the substrate and then using a slight amount of downward force pulls the fill bar to the front of the screen. This effectively fills the mesh openings with ink and moves the ink reservoir to the front of the screen. The operator then uses a squeegee (rubber blade) to move the mesh down to the substrate and pushes the squeegee to the rear of the screen. The ink that is in the mesh opening is transferred by capillary action to the substrate in a controlled and prescribed amount, i.e. the wet ink deposit is equal to the thickness of the stencil. As the squeegee moves toward the rear of the screen the tension of the mesh pulls the mesh up away from the substrate leaving the ink upon the substrate surface.

There are three types of screen printing presses. The 'flat-bed' (probably the most widely used), 'cylinder', and 'rotary'.^[1]

Textile items are printed in multi-color designs using a wet on wet technique, while graphic items are allowed to dry between colors that are then printed with another screen and often in a different color.

The screen can be re-used after cleaning. However if the design is no longer needed, then the screen can be "reclaimed", that is cleared of all emulsion and used again. The reclaiming process involves removing the ink from the screen then spraying on stencil remover to remove all emulsion. Stencil removers come in the form of liquids, gels, or powders. The powdered types have to be mixed with water before use, and so can be considered to belong to the liquid category. After applying the stencil remover the emulsion must be washed out using a pressure washer.

Most screens are ready for recoating at this stage, but sometimes screens will have to undergo a further step in the reclaiming process called dehazing. This additional step removes haze or "ghost images" left behind in the screen once the emulsion has been removed. Ghost images tend to faintly outline the open areas of previous stencils, hence the name. They are the result of ink residue trapped in the mesh, often in the knuckles of the mesh, those points where threads overlap. ^[2]

While the public thinks of garments in conjunction with screen printing, the technique is used on tens of thousands of items, decals, clock and watch faces, and many more products.

source:  http://en.wikipedia.org/wiki/Screen-printing

Laser engraving is the practice of using lasers to engrave or mark an object (it is also sometimes incorrectly described as etching, which involves the use of acid or a similar chemical). The technique can be very technical and complex, and often a computer system is used to drive the movements of the laser head. Despite this complexity, very precise and clean engravings can be achieved at a high rate. The technique does not involve tool bits which contact the engraving surface and wear out. This is considered an advantage over alternative engraving technologies where bit heads have to be replaced regularly.

The impact of laser engraving has been more pronounced for specially-designed "laserable" materials. These include polymer and novel metal alloys.

In situations where physical alteration of a surface by engraving is undesirable, an alternative such as "marking" is available. This is a generic term that covers a broad spectrum of surfacing techniques, including printing and hot-branding. In many instances, laser engraving machines are able to do marking that would have been done by other processes.

Laser engraving machines

A laser engraving machine can be thought of as three main parts: a laser, a controller, and a surface. The laser is like a pencil - the beam emitted from it allows the controller to trace patterns onto the surface. The controller (usually a computer) controls the direction, intensity, speed of movement, and spread of the laser beam aimed at the surface. The surface is picked to match what the laser can act on.

There are three main genres of engraving machines: The most common is the X-Y table where, usually, the workpiece (surface) is stationary and the laser moves around in X and Y directions drawing vectors. Sometimes the laser is stationary and the workpiece moves. Sometimes the workpiece moves in the Y axis and the laser in the X axis. A second genre is for cylindrical workpieces (or flat workpieces mounted around a cylinder) where the laser effectively traverses a fine helix and on/off laser pulsing produces the desired image on a raster basis. In the third method, both the laser and workpiece are stationary and galvo mirrors move the laser beam over the workpiece surface. Laser engravers using this technology can work in either raster or vector mode.

The point where the laser (the terms "laser" and "laser beam" may be used interchangeably) touches the surface should be on the focal plane of the laser's optical system, and is usually synonymous with its focal point. This point is typically small, perhaps less than a fraction of a millimeter (depending on the optical wavelength). Only the area inside this focal point is significantly affected when the laser beam passes over the surface. The energy delivered by the laser changes the surface of the material under the focal point. It may heat up the surface and subsequently vaporize the material, or perhaps the material may fracture (known as "glass" or "glass up") and flake off the surface. This is how material is removed from the surface to create an engraving.

If the surface material is vaporized during laser engraving, ventilation through the use of blowers or a vacuum pump are almost always required to remove the noxious fumes and smoke arising from this process, and for removal of debris on the surface to allow the laser to continue engraving.

A laser can remove material very efficiently because the laser beam can be designed to deliver energy to the surface in a manner which converts a high percentage of the light energy into heat. The beam is highly focused and collimated - in most non-reflective materials like wood, plastics and enamel surfaces, the conversion of light energy to heat is more than {x%} efficient {example reference needed}. However, because of this efficiency, the equipment used in laser engraving may heat up rather quickly. Elaborate cooling systems are required for the laser. Alternatively, the laser beam may be pulsed to decrease the amount of excessive heating.

Different patterns can be engraved by programming the controller to traverse a particular path for the laser beam over time. The trace of the laser beam is carefully regulated to achieve a consistent removal depth of material. For example, criss-crossed paths are avoided to ensure that each etched surface is exposed to the laser only once, so the same amount of material is removed. The speed at which the beam moves across the material is also considered in creating engraving patterns. Changing the intensity and spread of the beam allows more flexibility in the design. For example, by changing the proportion of time (known as "duty-cycle") the laser is turned on during each pulse, the power delivered to the engraving surface can be controlled appropriately for the material.

Since the position of the laser is known exactly by the controller, it is not necessary to add barriers to the surface to prevent the laser from deviating from the prescribed engraving pattern. As a result, no resistive mask is needed in laser engraving. This is primarily why this technique is different from older engraving methods.

A good example of where laser engraving technology has been adopted into the industry norm is the production line. In this particular setup, the laser beam is directed towards a rotating or vibrating mirror. The mirror moves in a manner which may trace out numbers and letters onto the surface being marked. This is particularly useful for printing dates, expiry codes, and lot numbering of products travelling along a production line. Laser engraving has allowed materials made of plastic and glass to be marked "on the move". The location where the marking takes place is called a "marking laser station", an entity often found in packaging and bottling plants. Older, slower technologies such as hot-stamping and pad printing have largely been phased out and replaced with laser engraving.

Mirrors on both X and Y carriages allow exact positioning.

For more precise and visually decorative engravings, a laser table is used. A laser table (or "X-Y table") is a sophisticated setup of equipment used to guide the laser beam more precisely. The laser is usually fixed permanently to the side of the table and emits light towards a pair of movable mirrors so that every point of the table surface can be swept by the laser. At the point of engraving, the laser beam is focused through a lens at the engraving surface, allowing very precise and intricate patterns to be traced out.

A typical setup of a laser table involves the fixed laser emitting light parallel to one axis of the table aimed at a mirror mounted on the end of an adjustable rail. The beam reflects off the mirror angled at 45 degrees so that the laser travels a path exactly along the length of the rail. This beam is then reflected by another mirror mounted to a movable trolley which directs the beam perpendicular to the original axis. In this scheme, two degrees of freedom (one vertical, and one horizontal) for etching can be represented.

In other laser engraving devices such as flat table or drum engraving, the laser beam is controlled to direct most of its energy a fixed penetration depth into the material to be engraved. In this manner, only a particular depth of material is removed when the engraving takes place. A simple machined stick or angle-iron can be used as a tool to help trained technologists adjust the engraver to achieve the required focusing. This setup is preferred for surfaces which do not vary in height appreciably.

For surfaces that vary in height, more elaborate focusing mechanisms have been developed. Some are known as dynamic auto focus systems. They adjust the lasering parameters in real time to adapt to the changes to the material as it is being etched. Typically, the height and depth of the surface is monitored with devices tracking changes to ultrasound, infrared, or visible light aimed at the engraving surface. These devices, known as pilot beams or pilot lasers (if a laser is used) help guide the adjustments made to the lens of the laser in determining the optimal spot to focus on the surface and remove material effectively.

"X-Y" laser engraving machines may operate in vector and raster mode.

Vector engraving follows the line and curve of the pattern to be engraved, much like a pen-based plotter draws by constructing line segments from a description of the outlines of a pattern. Much early engraving of signs and plaques (laser or otherwise) used pre-stored font outlines so that letters, numbers or even logos could be scaled to size and reproduced with exactly defined strokes. Unfortunately, "fill" areas were problematic, as cross-hatching patterns and dot-fills sometimes exhibited moiré effects or uber-patterns caused by the imprecise calculation of dot spacings. Moreover, rotations of a font or dynamic scaling often were beyond the capabilities of the font-rendering device. The introduction of the PostScript page-description language now allows much greater flexibility-- now virtually anything that can be described in vectors by PostScript-enabled software like CorelDRAW or Adobe Illustrator can be outlined, filled with suitable patterns, and laser-engraved.

Raster engraving traces the laser across the surface in a back-and-forth slowly-advancing linear pattern that will remind one of the printhead on an inkjet or similar printer. The pattern is usually optimized by the controller/computer so that areas to either side of the pattern which aren't to be engraved are ignored and the trace across the material is thus shortened for better efficiency. The amount of advance of each line is normally less than the actual dot-size of the laser; the engraved lines overlap just slightly to create a continuity of engravure. As is true of all rasterized devices, curves and diagonals can sometimes suffer if the length or position of the raster lines varies even slightly in relation to the adjacent raster scan; therefore exact positioning and repeatability are critically important to the design of the machine. The advantage of rasterizing is the near effortless "fill" it produces. Most images to be engraved are bold letters or have large continuously-engraved areas, and these are well-rasterized. Photos are rasterized (as in printing), with dots larger than that of the laser's spot, and these also are best engraved as a raster image. Almost any page-layout software can be used to feed a raster driver for an X-Y or drum laser engraver. While traditional sign and plaque engraving tended to favor the solid strokes of vectors out of necessity, modern shops tend to run their laser engravers mostly in raster mode, reserving vector for a traditional outline "look" or for speedily marking out lines or "hatches" where a plate is to be cut.

source: http://en.wikipedia.org/wiki/Laser_engraving

Most people think of screen printing as a flat printing process because the substrates are usually flat and decorated in a horizontal position. Screen printing is also associated with piece-decorating applications, in which individual sheets of substrate are printed one by one, usually on semi- and three-quarter-automatic flatbed presses that require manual loading and/or unloading.

When screen printing is used as a piece-printing process with manual material handling, screen shops sacrifice productivity. Businesses that invest in automatic, multicolor, inline flatbed systems regain some of this productivity by eliminating manual handling from all or most of the sequence. Yet throughput continues to be limited because every sheet of substrate still must pause at each printing station to receive the image.

The good news is that you don't have to sacrifice the benefits of screen printing to overcome the limitations of flatbed printing technology. For many applications requiring efficient, high-volume, high-quality printing, rotary screen printing may be the answer.

What is rotary screen printing?

Rotary screen printing is so named because it uses a cylindrical screen that rotates in a fixed position rather than a flat screen that is raised and lowered over the same print location. Rotary presses place the squeegee within the screen. These machines are designed for roll-to-roll (web) printing on flexible materials ranging from narrow web films to wide-format roll textiles.

In rotary printing, the web travels at a consistent speed between the screen and a steel or rubber impression roller immediately below the screen. (The impression roller serves the same function as the press bed on a flatbed press.) As the web passes through the rotary unit, the screen spins at a rate that identically matches the speed of substrate movement.

The squeegee on a rotary press is in a fixed position with its edge making contact with the inside surface of the screen precisely at the point where the screen, substrate, and impression roller come together (Figure 1). Ink is automatically fed into the center of the screen and collects in a wedge-shaped "well" formed by the leading side of the squeegee and the screen's interior surface. The motion of the screen causes this bead of ink to roll, which forces ink into stencil openings, essentially flooding the screen without requiring a floodbar. The squeegee then shears the ink as the stencil and substrate come into contact, allowing the ink to transfer cleanly to the material.

In short, rotary printing is a continuous, stepless image-transfer method. The geometry of the screen and the position of the squeegee within the screen combine to provide both the screen-flooding and image-transfer functions in a single smooth operation that repeats with every revolution of the screen.

source: