Screen Printing

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Screen Printing:

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A printing process that uses a squeegee to force ink through a porous fabric covered by a stencil that blocks the nonimage areas. The ink pressed through the open image areas produces the images on a substrate.

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Squeegee:

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A rubber or plastic blade used to force ink through the open areas of a screen-printing stencil.

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Durometer:

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A measure if a rubber squeegee blade’s hardness.

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Thinners:

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Solvents added to the ink to change the viscosity of the ink.

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Viscosity:

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the state of being thick, sticky, and semifluid in consistency, due to internal friction.

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Retarders:

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Solvents added to ink to thin the viscosity and slow the drying time.

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Washup Solvents:

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Solvents used to dissolve ink from a screen.

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Filament:

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A single thread.

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Mesh Count:

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The number of threads (or strands) per linear inch in a fabric.

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Sawtoothing:

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A distortion in a design contours that causes a notched effect.

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Weft Threads:

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Threads that run horizontally, at a 90º angle to the warp threads.

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Warp Threads:

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Threads that run vertically at a 90º angle to the warp threads.

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Percent Open Area:

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Percentage of area per square inch in a fabric through which ink can pass.

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Cell Size:

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The distance across individual open areas between adjacent threads.

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Cell Distortion:

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The result of stretching fabric openings unequally in two directions.

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Percent Stretch:

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A technique for measuring screen tension that entails taking very accurate measurements before and during tensioning.

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Tensiometer:

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An instrument that measures screen fabric.

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Burned Edges:

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An imperfection in a water- or lacquer- soluble stencil in which solvents collects in an improperly cut area of the stencil and melts (burns) the edge.

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Mesh-bringing Capability:

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The ability of a stencil to bridge diagonally across an individual fabric cell.

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Pinholes:

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Imperfections on a photographic negative or stencil caused by dust and other airborne contaminants.

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Advantages of Screen Printing:

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• Images can printed on a wide variety of substrates

• The production process is relatively easy

• Costs are low compared to other printing processes

• Images can be printed glitterm flock, and other decorative finishes

• The ink film is very resilient due to the thickness of the ink deposit

because the film is up to 100 times as thick as in other printing processes.

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Disadvantages of Screen Printing:

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• Rate of production is slow

• Ink mileage is poor

• Details and fine-line images may be difficult to print

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Squared-edge:

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Flat surfaces and general-purpose printing

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Squared-edge with rounded corners:

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Provides extra-heavy ink deposits on flat substrates and is used when a light color will be used on a dark substrate.

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Rounded-edge:

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Used primarily in textile printing where an extra-heavy ink film is required.

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Single-sided beveled edge:

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Used for printing on glass.

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Double-sided beveled edge with flat tip:

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Used for printing on ceramics.

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Double-sided beveled edge with point:

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Used for printing on cylindrical objects such as bottles and containers.

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Neoprene squeegee blades:

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least durable and require frequent sharpening.

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Plastic squeegee blades:

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frequently used and provide good durability and easy sharpening.

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Polyurethane squeegee blades:

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Maximum durability, but prove to be difficult to sharpen

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Blades can be sharpened by either...

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cutting or grinding.

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Dull squeegee blades can be assoicated with these problems:

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• Bubbles in the ink film

• Poor edge definition in print

• Loss of detail

• Spread images

• Poor ink mileage

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The viscosity of thinned ink should resemble...

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pancake syrup, or 40-weight motor oil at room temp

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Conduction:

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Occurs when heat is generated within an object by contact with a heat source.

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Convection:

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Uses warm air to transfer heat to the object.

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Radiation:

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Occurs when heat is generated within an object through exposure to radiation.

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The screen frame serves several important functions. A frame:

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• Provides a means of attaching fabric at the proper tension

• Provides rigidity and dimensional stability

• Resists mechanical stress and warpage

• Resists chemcial action ans corrosion

•Provides a means for register

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Wood Frames:

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Popular for general screen printing applications.

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Metal Alloy Frames:

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Provides greater rigidity and dimensional stability than than wood frames and are essential in commercial screen printing

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What kind of frame is not susceptible to chemical attack from water, have poor

resistance to acids and soda solutions.

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Metal Alloy Frames

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What kind if frame is usually constructed with screws, corrugated fasteners, dowels, splines, or nails

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Wood Frames

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the nonimage area should be _____ the size of the image area.

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Twice

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An ideal frame size is ______ times the image area

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Four

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The mesh count per linear inch is estimated by

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multiplying the mesh number by 10

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Monofilament fabrics are specified by

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actual thread count

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Fabric strength is directly related to

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thread diameter.

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Specified by X, XX, or XXX

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Multifilament

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Specified by either the actual thread diameter is given, expressed in thousandths of an inch, or a letter rating is given. S = Small, T = Medium, and HD = Heavy Duty.

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Monofilament

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Weave patterns determines

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how the vertical and horizontal threads are woven into the fabric.

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Plain or Taffeta Weave:

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General-purpose weave used in most situations requiring good strength and sharp detail.

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Gauze Weave:

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Strong, generally selected for extremely long runs.The squeegee must move parallel to the double threads. Can’t produce fine details due to double threads.

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Twill Weave:

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Twill causes uneveness in ink film thickness and poor edge definition, resulting in a more pronounced sawtooth effect. Not capable of producing fine details.

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Natural fabrics are always

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multifilament

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Synthetic fabrics are:

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either multifilament or monofilament

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Metal mesh are always monofilament

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monofilament

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The most common fabrics used are

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synthetic and metal fabrics.

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Silk:

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Natural fabric. Good durability and dimensional stability, cant be used with certain chemicals.

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Polyester:

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Has wide applications in almost all the areas of screen printing and can be used with any stencil.

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Nylon:

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Has relatively good dimensional stability if used in a climate controlled environment. Adapts well when printing on rough-textured or uneven

substances. Its flexibilty makes it suitable for printing on concave or convex surfaces.

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Metal Mesh:

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Typically stainless steel, but also can be bronze, copper, or brass. Used for printing with heated inks on plastic or when the excellent dimensional stability is required. Durable but fragile, any kinks or deformities usually replacement.

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Metalized Polyester:

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A hybrid monofilament fabric with a nickel-plated coating.

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Stapling:

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Least desirable means for attaching and tensioning fabric.

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Cord and Groove:

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Popular in small screen applications where

printing requirements are not critical. A cotton or plastic cord is forced into a groove in the frame. As the cord moves down the groove, the fabric is stretched across the frame. A groove depth one and one half times the cord diameter is

recommended.

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Mechanical Clamping:

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Mechanical clamps arre available on many aluminum frames. The fabric is clamped in position on all four sides. Screws are rhen turned, forcing the movable clamps outward and resulting in fabric tension. With mechanical clamping, the fabric may be tenioned to exact specifications

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Adhesive Bonding:

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To attach fabric to a frame with adhesive, a stretching machine is necessary. These machines may be mechanical or pneumatic. With a stretching machine, fabric may be tensioned to exact specifications without cell distortion.

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Measuring Fabric Tension:

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Screen tension, or tightness, can be accurately measures using a tensiometer.

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Proper tension ensures the screen will create an_______ image on the substrate.

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quality

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What treatment alters the adhesion characteristics of the fabric and allows for better bonding between the stencil and fabric

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Chemical treatment

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What treatment changes the physical properties of the fabric to enhance the bond between stencil and fabric.

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Mechanical Treatment