Adhesion Properties

Lens bond has been successfully used to bond materials other than optical glass. Listed below are some of these materials.

Aluminum, Copper, Stainless Steel, Quartz, Phenolics, Lithium Fluoride, Lexsan, Polystyrene, Gelatin Filters, KDP Crystals, ADP Crystals, Plexiglas, Nylon, Ceramics, Polarizing Sheet.

NOTE: When bonding elements to metal fixtures , stronger bonds are achieved when the metal surfaces are "roughed" with fine steel wool or emery paper.

Lens Bond has also been successful in bonding optics coated with:

Zinc Sulfide, Silicon Monoxide, Aluminum, Silver, Magnesium Fluoride, Titanium Oxide, Gold.

NOTE: The few materials we know of that Lens Bond will not bond are: PTFE, and PVC

Solvent and
Thermal Resistance

1. Cured Lens Bond is a cross linked Vinyl Copolymer which accounts for its extreme resistance to solvents and temperature extremes.

Glass slides cemented with Lens Bond optical cements were immersed in the following solvents and solvent combinations without any ill effects:

*All tests were done at 20�C unless otherwise stated

Methylene Chloride
TX-100
Methyl Ethyl Ketone
Acetone
N,N Dimethylformamide
Cyclohexanone
Diethylene Triamine
Pyridine
H₂SO₄ (concentrated and diluted in solvents)
NaOH
Benzene
Ethyl Acetate
Helix 101 Solvent at 70�C
Tri-Toyl Phosphate at 70�C
Chlorobenzene, Bromobenzene
Xylene
Methanol
Tetrahydrofuran (THF)
Dimethylsulfoxide (DMSO)
Ether

2. Acid resistance of slides bonded with Lens Bond optical cement.

3. The thicker the layer of Lens Bond the more resistance it will show to thermal extremes. When applied in a thick layer, Lens Bond will act as a buffer when bonding elements with different coefficients of expansion.

1. Doublets cemented with Lens Bond were slowly taken up to 700�F to test coatings. They were held at this temperature for 20 minutes and slowly returned to room temperature. After this cycle, it was observed that there was no decementing or deterioration of the cement.
2. A complex 5 piece prism and lens assembly was slowly taken down to -120�F and then up to +400�F. No thermal shock or stress was observed.
3. Sapphire bonded to 7052 glass was subjected to 20 cycles liquid nitrogen and then back to room temperature. The cement that was used was UV-74.

Laser Applications

Although our information is limited, we have found that Lens Bond Cements can be used in lasers, depending on the strength of the beam.

Laser                                     Cement Film
25 watt continuous wave(CO2)................no effect
5 megawatt/cm2 pulsed 20 Nanosecond(6900A)..burned
109 watts/cm2 Subnanosecond pulse
   (1.06 micron mm YAG).....................no effect
15 watts/cm2 Continuous wave (YAG)..........no effect
6 watts/0.1mm Diameter beam (Argon, ion)....no effect

Diode Pump
*150w CW-Diode Pump Module..................no effect
*200w CW-Diode Pump Module..................no effect
*2400w CW-Diode Pump Module.................no effect
*5kw Peak 808 nm Diode Pump Module..........no effect
Thanks to Laser Diode Array, Inc. for Laser Diode 
Information

Environmental Testing

Thermal Shock Test:

The object of this test is to determine the ability of a cemented component to withstand abrupt temperature changes between the limits of +40�C and -40�C. The upper temperature was achieved with a normal laboratory oven. The lower temperature was achieved with a cooling mixture of acetone/solid carbon dioxide.

The specimen was placed in a polyethylene bag on removal from the oven(before immersion) to eliminate any solvent reaction.

A doublet of 1/4" Pilkington Plate 1" square was used.

A specimen was subjected to three cycles, and examined after each. The cycles were as follows:

a.
+40�C for 2h-> -40�C or 1/2 h->+40�C for 2h-> room temperature

b.
+40�C for 2h-> -40�C for 2 h->+40�C for 2h-> room temperature

c.
+40�C for 2h-> -40�C for 2 h->+40�C for 2h-> room temperature

Lens Bond withstood the temperature cycling with no adverse effects.

Mechanical Shock Test:

The object of this test is to determine the ability of cemented components to withstand sudden shocks as may be experienced in weapons applications. The specimen was composed of cylinders of glass 1" high and 1 inch diameter bonded with Lens Bond onto flats of dimensions 1-1/4" x 1-1/4". The specimen was clamped to a trolley surface and subjected to a 1/2 sinewave pulse having peak acceleration of 100g for a duration of 1 microsecond. The specimen survived this test without discernable damage.

Vibration Tests:

The object of this test was to ascertain the ability of cemented components to withstand vibrations as such that might be met in service conditions. The specimen was identical with that used for mechanical shock treating. It was clamped to a vibration rig and vibrated both in the plane of the cement layer and perpendicular to it. The peak acceleration was 10g over the range of 10-300 c/s and 8g from 300-500 c/s. The rate of sweep was approximately 7 c/m. No deterioration was found in the sample after testing. The specimen was checked for resonance. None was found.

In order to simulate heavier stresses on the cement layer, the specimen was again subjected to vibration over the range given above, after attaching a collar of 1 lb lead weighing around the cylindrical element of each flat. No damage was found in the specimen.

Creep Test:

The object of this test was to ascertain the creep or relative movement of two components of a doublet over an extended period. One component of the specimen was clamped rigidly and a load of 1 lb applied to the other. Measurements were made at regular intervals. The plotted results are given below:  

Creep Test Results

Transmission Studies

of Lens Bond Optical Cements (.0001" film thickness) Not including J-91

Transmission Studies

of Lens Bond Optical Cements J-91

Common Problems Encountered in Bonding Elements

Overview:

1. The most common problem reported to us is failure of the cement to cure within the specified time. This problem is caused usually by one of the following problems:

1. Wrong catalyst ratio: the instructions are misread or misapplied concerning the proper catalyst:cement ratio. Follow carefully the instructions under "Preparation of Cement".
2. Improper mixing of catalyst and cement. Because of the high viscosity of the cement, casual mixing is not sufficient. Follow instructions carefully using the Schlieren Technique outlined under "Preparation of Cement".
3. Curing temperature is too low: The specified cure times refer to a room temperature of 72�F and an oven temperature of 160�F. Although a drop of 5�F in the oven is not critical, such a drop at room temperature can resulting the cure taking from 50% to 100% longer.
4. Overloading the oven: Unless the oven has ample force air circulation, a large number of trays, doublets, and holding devices will lower the oven temperature for a surprisingly long time.
5. Large elements: Cure speeds noted on instructions were achieved with lenses approximately 3/4" to one inch diameter. When bonding elements of larger diameters, or extremely thick lenses, extra time must be given to allow heat to reach inner bonded surfaces.

2. Reticulation near outside edge of curing. If the chamfer has ample cement remaining in it after curing, reticulation is likely caused by microscopic air bubbles entrained while mixing the catalyst. There are 4 possible solutions:

1. Mix the catalyst with the cement more carefully to avoid entertainment of air, or de-gas the cement after mixing (25" mercury vacuum for about one minute).
2. Allow the cemented doublet to remain at room temperature for one to two hours making sure that the cement interface is in a concave upward position. After this hold period place in oven to complete cure.
3. When working with elements that do not have a chamfer, the technician should not remove excess cement from outer perimeter before full curing. When Lens Bond cures it contracts and needs this excess cement to draw in between the elements.
4. Mismatched surfaces: Because of Lens Bond contraction factor, it is not a good filler. Surfaces of the elements to be bonded should match with at least 4 or 5 rings.

3. Stress cracking seperation, lack of bond strength and curing. When a cylinder is cemented within a cylinder(for example a metallic or glass sleeve cemented around a lens) it is not unusual for the bond to break on curing. As Lens Bond cures it contracts slightly. This contraction causes an evenly distributed inward pull on the outer cylinder. The cylinder will not accommodate the contraction and the bond separates. To prevent this separation, one of the following steps can be taken:

1. Reduce to a minimum the tolerance between the two members. Although the percentage of contraction of the cement remains the same, the overall physical change in thickness of the cement layer will be extremely small.
2. Design the outer cylinder with a slit. This slit will allow the cylinder to accommodate the contraction and will close as the cure will achieve.
3. Use Lens Bond Type RD3-74. This cement remains slightly elastic after curing.

Thin lenses and lenses with extremely short radii are susceptible to stress cracking, separation and distortion. This problem can be eliminated by using RD3-74.

4. Separation of lenses can occur because of the following factors:

1. Improper cleaning: If denatured alcohol is used as a final cleaner, care should be taken that the denaturants and not oily and will completely evaporate. We emphasize that acetone is the best final cleaner.
2. Clean lenses should be placed on dry towels or unprinted paper. Ink from newsprint will interfere with Lens Bond adhesion properties.
3. Improper cement layer: With normal pressure and correct procedure for working air bubbles out, layer thickness is usually about .005 to .0001". Excessive pressure will force out too much cement, causing separation, reticulation, or low resistance to thermal shock.