Graphic Overlay Processing

Determining the best printing process involves tradeoffs. Melrose can help you select the best printing option by providing pricing using alternative processes, and identifying the non-cost tradeoff’s applicable to your part’s artwork under different printing options

Digitally and Screen Printed Overlays

Determining the best printing process involves tradeoffs. Melrose can help you select the best printing option by providing pricing using alternative processes, and identifying the non-cost tradeoff’s applicable to your part’s artwork under different printing options

Color Matching involves several issues.

• Setting a Standard: A color reference must be defined. The Pantone Matching System (PMS) is the most commonly used system for specifying a color standard. The pantone "swatch book" is readily available, can be inexpensively purchased and contains more than 1000 colors. A less common color system is the Federal Standard 595a.
• Pantone & Fed Std 595a Limitations: These color systems have two limitations. 1) If the swatch book is not new, colors may have faded, and may not be comparable to a new book, 2) The pantone system was developed for 1st surface printing of lithographic inks on white coated paper. Because inks used are screen printed on the second surface of a transparent material, or the material printed on is not a totally opaque white, a color shift is introduced by the transparent material on which the ink is printed.
• Melrose Matches the Desired Color and Creates A Color Chip using the process and substrate material to be used in production. The preciseness of the match to a PMS color will be influenced by: 1) the substrate on which the color is printed, 2) the material through which the ink is viewed (if any), 3) the inks used, 4) characteristics of the full color process printing method (e.g., CMYK) employed to approximate a pms color match, )
• Comparing production parts to the standard: Once the customer has signed off on Melrose’s color match, color must be controlLED in production. In process control is achieved in one of two ways.
  • Visual comparison in a controlLED light booth. Under most circumstances, a careful visual comparison of the color chip and the production part is sufficient to assure good color control. It is essential that this color check be done in a in a light booth that ensures a controlLED lighting environment (typically fluorescent lighting). However full daylight, variable daylight, incandescent can also be used for illumination in the light booth if those environments more closely duplicate the environment in which the part will be used.
  • Instrumentation Comparison: Color difference in numerical terms can be determined using a spectrophotometer. Melrose uses a Minolta spectrophotometer to take numerical readings of color in the 3-D CIELAB color space. The spectrophotometer reads lightness, and chromaticity, reflecting those parameters as numerical values of L*, a*, b*. By comparing the 3D coordinates of a color chip to a production part the color difference can be determined. For more details on the CIELAB color space see this link: Colorimetry_photonics.pdf.

Die-cutting (Digital and Tooled): Overlays, labels, and membrane switch layers (e.g., spacers, static layers, backside adhesives) thinner than .020” are generally die-cut using steel rule dies, digital cutting methods or class 1 die-sets. Thicker parts are usually cut using digital routing, laser cutting, or water jet cutting technologies.

• Cutting Tolerances:
  • +-.015” to be the standard tolerance for general steel rule die-cutting.
  • Tolerances of +-.010” can be held for cutouts and perimeters if required.
  • Center to center tolerances of +-.005” are readily achievable for holes.
  • Tighter tolerances can be held with class 1 die-sets and with digital cutting methods.

• Digital vs Tooled Cutting Tradeoffs: For orders with limited amounts of cutting, and where the likelihood of reorders is low, digital cutting may be the best alternative.
  • Digital cutting methods 1) require no tooling investment, 2) have a quicker production set-up time than cutting with steel rule die’s or class 1 hard tools, 3) do not incur a lead time delay while the tool is being built.
  • Cycle times are shorter using steel rule dies or class 1 hard tools.

Overlay Embossing & Hydro forming:

• Graphic overlays can be embossed using a male/female die set. Features are typically raised .010” if embossed.
• Embossing is generally done to accentuate the key area of a graphic overlay or membrane switch. Key embossing can either be rim (perimeter) or pillow (pad).
• Embossing may also be done to raise LED’s above the surface of an overlay, or to provide a decorative effect to a logo, or copy. Braille can also be embossed.
• Hydro forming is an alternative to embossing that involves more costly tooling, setup and cycle times. However features heights up to three times the material thickness can be achieved if hydro formed (e.g., pillow or rim emboss heights of .021” for a .007” overlay are possible)

Embossing Overlays

Embossing Tooling

Graphic Overlays with LCD Windows: Graphic overlays are commonly provided with clear windows for viewing LCD’s.

• Overlays with LCD windows are produced using gloss, hard coated, scratch resistant polyester or polycarbonate.
• Colors and window tints (if any) are 2nd surface printed (viewed through the plastic).
• The 1st surface (top surface) is usually selectively textured using special inks in the areas where the LCD is not.
• The LCD windows can be specified with alternative gloss levels (for glare attenuation), or with a window tint. With selection of appropriate overlay background colors (generally dark colors).
• The adhesive or spacer is selectively applied to the back of the overlay so as not to obscure the LCD viewing area, and to avoid the accumulation of debris.

Graphic Overlays with LED Windows:

• Graphic overlays can be produced with small clear round windows for viewing LED’s (light emitting diodes)
• These windows can be flush with the overlay surface or embossed to facilitate the LED’s being raised above the overlay surface (illumination is visible at a more acute angle than if flush mounted)
• As with LCD windows, LED windows can be tinted, or dead fronted.
• Adhesive is excluded from the LED window to facilitate optimal light transmission, and avoid the accumulation of debris.