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Front Surface Mirror for Projection Systems
This specification defines the quality and performance criteria for a thin film front surface mirror coated product on glass substrates for use in rear projection TV systems.
2.0 Reference Documents
The following documents form a part of this specification to the extent specified herein:
Constant Temperature Humidity Test
Scotch Tape Adhesion Test
Salt Spray (Fog) Test
Cheesecloth Rub Durability
3.0 Performance/Operating Characteristics Required
3.1 Physical Characteristics:
3.1.2 Flatness: Flatness of the mirror is defined in the table below.
|Nominal Thickness||Normal Tolerance Range|
|3mm||2.92 – 3.10mm|
|5mm||4.80 – 5.00mm|
3.2 Optical Performance:
Spectral reflectance performance of the front surface mirror coating at a 45° angle shall meet the following values:
|Wavelength||Minimum % Reflectance|
3.2.2 Optical drawlines:
This optical effect is inherently connected to the surface flatness of the glass and will ALWAYS be visible in nowadays high resolution projection system.
One can only reduce its visibility by setting parameters like number of mirrors, thickness of all mirrors involved, beam angle in the optical paths, polarization, size of the mirror, which is connected to the possibility to orient the drawlines to make them least visible. Only optically polished glasses don’t show this effect. However, they are not available for such applications.
3.3 Environmental Durability Characteristics:
Adhesion: The coating shall show no damage after 3M Scotch Brand No.600 tape (or equivalent) is pressed firmly against the front surface mirror coating surface and removed quickly by a snap of the wrist.
Abrasion Resistance: The coating shall show no damage after a 200-rub test with a cheesecloth pad approximately ⅜” (9.525mm) diameter by ½” (12.7mm) thick. The bearing force shall be one pound ±¼ pound (0.454 kilograms ± 0.114 kilograms).
Humidity Resistance: The coating optical performance (section 3.2) shall not deteriorate after exposure to 24-hour humidity test of 49° C @ 95% relative humidity.
Corrosion Resistance (Salt Fog): The coating optical performance (section 3.2) shall not deteriorate after exposure to a 24-hour salt fog test (5% NaCI by weight) at 35°C.
3.4 Dimensional Tolerances:
Clear Aperature: All surface area of the mirror except for a 10mm border around the entire perimeter of the fabricated part.
All fabricated parts are sized with tolerances specified by the customer’s drawing.
3.5 Surface Quality Characteristics:
|>5mm (0.200”)||None Allowed|
|Chip Depth||Quantity Allowed|
|>2.5mm (0.100”)||None Allowed|
Minimum Usable Area:
Fabricated parts will be inspected to a 100% usable surface area, minus a 10 mm border.
|Defect Category||Acceptance CriteriaQuantity of Defects per square foot (304.8 mm²)|
|Linear (size 100)Width of scratches: Scratches or other imperfections, which are long and narrow in nature and visible by reflection or by transmission. Defects are evaluated at the widest point.||> 0.10 mm width not allowed3 linear defects 0.05 -0.01mm width (0.002”- 0.004”) per square footSmaller defects are disregarded|
|Circular (size 120)Imperfections that are round in nature visible by transmission or by reflection. Diameter is mean diameter measured as (L + W) / 2)||10 circular defects diameter 0,25-0,50mm (0.010”- 0.019”) per square foot5 circular defects diameter 0.60- 1,20mm (0.024”- 0.047”) per square footIgnore circular defects <0.25mm (0.010”)|
Fractures: None allowed.
Glass Defects: For localized glass surface distortions, mirror acceptability will be based upon the visibility of the defect when viewed on the appropriate customized rear projection television.
5.0 Preparation for Delivery
Approved protective film is applied to the mirror’s front surface.
Distortion line: A distortion line is a ripple or wave induced in float glass due to localized contamination of raw materials used in the manufacturing of glass. Distortion lines can also result when there is physical contact with the glass while it is still molten. Distortion lines are more severe than drawlines and are not allowed.
Drawline in rawglass: A “glassdrawline” is a ripple or wave induced in float glass during the manufacturing process as the glass is being stretched to create the desired thickness. The condition is defined by the angle at which the distortion disappears when viewing at a zebra board in transmission.
Stain: A whitish defect in the mirror coating usually caused by clusters of microscopic pinholes.
Lightning Arcs: Lightning arc occurs during the coating process and is seen through transmission. The defect looks like lightning or snowflakes.
Standard Safety Seam: A light sanding of the edge of the fabricated mirror for removal of the sharp cutting edge.
Unterminated Fracture: An edge chip or fracture that does not have a distinct stopping location for its intrusion inward from the edge. Fine lines intruding into the part from the defect area usually distinguish this.
Usable area: The usable area is defined as the area of the fabricated part that meets the customer’s requirements.
The manufacturer reserves the right to make changes in processes, materials and packaging which do not affect the form, fit or function of the mirror in the inte