Abstract:
An apparatus for subjecting light sensitive materials to visible radiation is disclosed which minimizes the amount of heat generated. The apparatus includes a source of visible radiation including at least one microwave energy responsive sulfur bulb and applies microwave energy to the sulfur bulb to cause the sulfur bulb to emit visible light. The apparatus further includes a holder defining a surface for receiving light sensitive materials located relative to the microwave energy responsive sulfur bulb. A light diffusing assembly is disposed relative to the sulfur bulb and responsive to the visible light emitted by the sulfur bulb to illuminate light sensitive materials received by the holder with diffused uniform visible light.

Description:
FIELD OF THE INVENTION 
     The present invention relates to producing accelerated aging in light sensitive materials. 
     BACKGROUND OF THE INVENTION 
     Weathering units and fade units are used to generate accelerated aging or fading of light sensitive materials by exposing the light sensitive materials to incident radiation levels above the levels typically found in office or home environments. 
     Existing units rely on high intensity xenon discharge lamps to create levels of incident radiation that are 2 to 4 times as intense as the radiation from the sun. These systems typically employ lamps that require 6000-12000 watts of electrical power to operate. 
     Much of the energy given off by such lamps is in the form of heat. To accommodate the heat generated by these lamps, accelerated aging units require large amounts of cooling air to keep the light sensitive materials at ambient temperature. Alternatively, such units only operate above ambient temperatures. 
     Accelerated fade units also require complex mechanical systems to ensure all the light sensitive materials are subject to the same, total amount of incident radiation no matter where they are located on a sample plane. 
     Such systems cause difficulty in testing the accelerated aging of light sensitive materials where the predominant source of aging will be due to incident light radiation, as the results are confounded by the use of elevated temperatures during the aging tests. 
     Alternatively, these systems can operate at reduced light levels to maintain the ambient temperature conditions. This removes the difficulty of interpreting the accelerated aging data, but it requires a longer period of time to perform the test procedures due to the use of lower light levels. 
     U.S. Pat. No. 4,760,748, issued to Kataynagi, et al, on Aug. 2, 1988, discloses an accelerated fade system based on a central light source, whereby a sample plane carrying light sensitive material rotates around a central light source. Thermal deterioration of the light sensitive material is inhibited by a cold air guide which encloses a portion of the rotating sample plane. The Kataynagi et al structure permits a large amount of light sensitive material to be loaded on the sample plane at one time, but requires a rotating sample assembly and an auxiliary cooling system. 
     U.S. Pat. No. 5,206,518, issued to Fedor, et al., on Apr. 27, 1993, discloses an accelerated fade unit based on a bank of lamps having an appropriate barrier array with a multiple detector feedback system to achieve a uniform power distribution over the sample plane. The Fedor et al structure permits a large amount of sample material to be loaded on the sample plane at one time, and it does not require any movement of the sample plane to maintain uniformity of light exposure at the sample plane. Fedor et al suffer from certain limitations. They require multiple lamps to obtain spatial uniformity of the incident light. They also require a complex system of detectors and feedback circuitry to control the lamp outputs individually. Finally, they use cooling air at the sample plane for temperature control. 
     Commonly assigned U.S. Pat. No 5,734,115, issued to Camp, et. al. on Jun. 16, 1998, employ an integrating sphere to allow the light sensitive material to remain stationary during the test. Camp et. al. suffer from certain design limitations in that the amount of light sensitive material that can be accommodated by the accelerated fade unit is limited to approximately 20 square inches of material at one time. 
     Commonly-assigned U.S. Pat. No. 5,767,423, issued to Camp, et. al., on Dec. 4, 1996 discloses a cooled sample holder for use in an accelerated fade apparatus that eliminates the need for external air cooling. Camp et. al. suffers from certain limitations. The disclosed holders are only capable of handling several square inches of light sensitive materials at any one time. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide improved apparatus for the accelerated aging of light sensitive materials at high levels of incident radiation without suffering substantial heat problems. 
     It is a further object of the present invention to create high levels of incident radiation at only slightly elevated ambient temperatures. 
     It is another object of the present invention to operate at slightly elevated temperature without requiring additional cooling capabilities. 
     It is yet a further object of the present invention to permit for a large sample plane without requiring any complex mechanical subsystems. 
     A still further object of the present invention is to provide a uniform and stable source of incident radiation. 
     It is a further object of the present invention to provide for easy addition and removal of light sensitive materials from the apparatus. 
     These objects are achieved in an apparatus for subjecting light sensitive materials to visible radiation while minimizing the amount of heat generated, comprising: 
     (a) a source of visible radiation including at least one microwave energy responsive sulfur bulb; 
     (b) means for applying microwave energy to the microwave energy responsive sulfur bulb to cause such microwave energy responsive sulfur bulb to emit visible light; 
     (c) a holder defining a surface for receiving light sensitive materials located relative to the microwave energy responsive sulfur bulb; and 
     (d) a light diffusing assembly disposed relative to the microwave energy responsive sulfur bulb and responsive to the visible light emitted by the microwave energy responsive sulfur bulb to illuminate light sensitive materials received by the holder with diffused uniform visible light. 
     A microwave energy responsive sulfur bulb provides a stable visible light source which does not produce excessive quantities of heat. 
     It is a feature of the present invention that microwave energy responsive sulfur bulbs are commercially available. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side view of a fading apparatus in accordance with the present invention; 
     FIG. 2A is a schematic section view of the apparatus of FIG. 1, taken along the section line  2 — 2 , and showing the sample holder in an operative up position; 
     FIG. 2B is a section view of the apparatus of FIG. 1 taken along the section line  2 — 2  and showing the sample holder in a down-position and laterally translated to provide for loading/unloading of samples to be tested; 
     FIG. 3A is a schematic front view of the apparatus of FIG. 1 (with the waveguide removed) showing the sample holder in an up position; 
     FIG. 3B is a schematic front view of the apparatus of FIG. 1 (with the waveguide removed) and showing the sample holder in a down position; and 
     FIG. 4 is a top view of the sample holder shown in FIG.  1  and holding a plurality of samples to be tested. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning first to FIG. 1, there is shown a fading apparatus  10  for subjecting light sensitive materials to visible radiation while minimizing the amount of heat generated. As shown, there is provided a light diffusing assembly  30  disposed relative to a microwave energy responsive sulfur bulb light source  20  having a sulfur bulb  22 . The microwave energy responsive sulfur bulb light source  20  can be of a construction well known in the art. In operation, a microwave generator  70  under the control of a power supply  80  causes the production of microwave energy which illuminates the microwave energy responsive sulfur bulb  22  via a waveguide  72  to provide guided microwaves  74  to be directed at the bulb  22 . In turn, the microwave energy responsive sulfur bulb  22  produces visible light  26  which will illuminate light sensitive materials to cause their aging or fading. The light diffusing assembly  30  includes a light pipe  32  defining a cavity  33  for receiving light. This light is projected by an arcuate reflective portion  34 . The arcuate reflective portion  34  is fastened to the internal surface of the light pipe  32  in the cavity  33 . Also, a planar reflector  44  is fastened to an inside of an end surface  40  of the light pipe  32  in the cavity  33 . A parabolic reflector  24  is disposed relative to the microwave energy responsive sulfur bulb  22  along a parabolic surface  23  of the light source  20 . In operation, visible light produced by the microwave energy responsive sulfur bulb  22  is reflected off the parabolic reflector  24  into the cavity  33  via a transparent window  28 . 
     An arcuate diffusive portion  36  diffuses the light received from within the cavity  33  and directs diffused light  27  from the cavity  33  towards a sample holder  50  which is disposed outside the cavity  33  proximate the diffusive portion  36 . The diffusive portion  36  can be fastened to an internal surface of the light pipe  32  for transmitting diffused light through a light-transmissive wall of the light diffusing assembly  30 . Alternatively, as shown schematically in FIG. 2A, the diffusive portion  36  can extend through the wall of the cavity  33  to provide uniformly diffuse exposure of light sensitive samples positioned on the sample holder  50 . 
     The sample holder  50  is formed with a surface for receiving light sensitive samples (Samples  90   a - 90   d  in FIG. 1, and Samples  90   a - 90   j  in FIG.  4 ), and this surface is arcuately disposed in relation to the outside surface of the light pipe  32  in a position where diffuse light will pass from the light pipe  32  onto the light sensitive samples to be tested. 
     The sample holder  50  is supported by a mounting bracket  64  to which a piston rod  62  is attached. The piston rod  62  extends into a motion actuator  60  for vertical motion actuation  66  to provide an up position  50 U of the sample holder  50  for exposing samples in the fading apparatus  10 , as depicted in FIG.  1 . The motion actuator  60  includes means for laterally translating the actuator  60  and the sample holder  50  in a down position  50 D (See FIGS. 2B and 3B) in which samples can be readily removed from, or installed on the sample holder  50 . The means for lateral translation can include rollers, casters, or slides  68  which can be guided in a track on a support plate having a stop bracket  69  to provide accurate positioning of the sample holder  50  in the up position  50 U with respect to the light diffusing assembly  30 . 
     An input line  82  provides electrical input to a power supply  80  via a switch  84 , and an output line  86  provides electrical power to the microwave generator  70  for producing microwaves which are guided by the waveguide  72  towards the sulfur bulb  22  to provide light emission therefrom as light rays  26 . 
     FIG. 2A is an enlarged section view taken along the section line  2 — 2  of FIG. 1, and showing the sample holder in an up position  50 U for exposing a light sensitive sample  90   a  to diffuse light  27  which exits the cavity  33  through an arcuate diffusive portion  36  extending throughout a wall of the light pipe  32 . As depicted for illustrative purposes only, the arcuate reflective portion  36  can be equal portions of the light pipe  32 . The planar reflector  44  at the end surface  40  (See FIG. 1) is indicated. 
     The light pipe  32  can be constructed from a light transmissive plastic tube since the sulfur bulb light source  20  produces light efficiently and without significant heat generation. As indicated above, the arcuate diffusive portion  36  can be provided by fastening a diffusive member (not shown) to an inside surface of the light pipe  32 . In such construction of the diffusive portion, the portion of the wall of the light pipe  32  in contact with the diffusive member can be a transparent wall. 
     FIG. 2B indicates schematically how the sample holder  50  is lowered and laterally translated to a down position  50 D for removal and/or loading of samples. First, the vertical motion actuation  66 D proceeds by actuating the motion actuator  60  to retract the piston rod  62  to achieve the down position  50 D of the sample holder  50 . Then the horizontal motion  68 D is actuated (if that motion is automated), or alternatively, the motion actuator  60  and the sample holder  50  are manually translated via the rollers, casters, or slides  68  into the horizontal position  68 D. 
     FIGS. 3A and 3B are schematic front views of the fading apparatus  10 , shown with the waveguide  72  (See FIG. 1) removed. FIG. 3A depicts the sample holder  50  in the up position  50 U, with the motion actuator  60  resting against a stop bracket  69  to provide accurate positioning of the sample holder  50  with respect to the light diffusing assembly  30 . FIG. 3B shows the sample holder  50  in the down position  50 D which is achieved by a vertical motion  1 , followed by a horizontal motion  2 . Upon installing samples for testing, the motion actuator  60  (and the sample holder  50 ) is first translated laterally (horizontally) to the stop bracket  69 , followed by vertical motion actuation  66 U to achieve an up position  50 U of the sample holder  50 . 
     FIG. 4 is a schematic top view of the sample holder  50 . Numerous samples  90   a - 90   j  are mounted on the concave side of the arcuate sample holder  50 . The sample holder  50  is preferably constructed of a ferromagnetic material such as, for example, steel, vidrel or of alloys, such that the samples can be held in a position of contact with the arcuate surface of the sample holder  50  by magnets or by magnetic strips. This sample holder surface can be coated with a white, diffusely reflective layer (not shown). 
     The motion actuator  60  can be actuated to provide a vertical motion actuation  66  (U; D) by well-known pneumatic, hydraulic or electromagnetic (solenoid) means. The horizontal motion actuation, if automated, can employ the above means, or a motor-driven spindle transport means. 
     The sulfur bulb light source  20  is available commercially from Fusion Lighting of Rockville, Md. under the designation or model Solar 1000. Under application of microwave energy to the sulfur bulb  22 , the light produced by the bulb  22  has a spectral distribution approximating daylight minus the infrared and ultraviolet components of daylight. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
       1  vertical motion of sample holder 
       2  horizontal motion of sample holder 
       10  fading apparatus 
       20  sulfur bulb light source 
       23  parabolic surface 
       24  parabolic reflector 
       26  light rays 
       27  diffuse light 
       28  transparent window 
       30  light diffusing assembly 
       32  light pipe 
       33  cavity (of light pipe) 
       34  arcuate reflective portion 
       36  acruate diffusive portion 
       40  end surface 
       44  planar reflector 
       50  sample holder 
       50 (U;D) sample holder (Up or Down position) 
       60  motion actuator (for sample holder) 
       62  piston rod (Up or Down position) 
       64  mounting bracket 
       66 (U;D) vertical motion actuation (Up or Down position) 
       68 (U;D) horizontal motion actuators (preceding Up position, and following Down position) 
       69  stop bracket 
       70  microwave generator 
       72  waveguide 
       74  guided microwaves 
       80  power supply 
       82  input line 
       84  switch 
       86  output line 
       90  light sensitive samples (a-j) 
     CL center line