Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2002-09-23
2004-11-16
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S150000, C522S152000, C522S162000, C522S164000, C522S173000, C522S176000, C522S180000, C522S182000, C428S3550RA, C428S3550CN, C428S3550EN, C428S3550EP, C427S207100, C427S162000, C427S164000, C427S165000
Reexamination Certificate
active
06818680
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to adhesive or coating compositions for use with glass and/or metal materials. In particular, the invention is directed to compositions in which multifunctional thiols are used as adhesion promoters and/or primers to enhance the adhesion of photo or electron beam curable polymers, coatings, adhesives or sealants to gold and other precious metals, and alloys thereof.
BACKGROUND OF THE INVENTION
Adhesives are useful in optical communications for quickly joining elements. In such optical communication applications it is frequently desirable to join together two materials (substrates) having either similar or different coefficients of thermal expansion. When similar materials are joined together, the adhesive is selected to have a coefficient of thermal expansion similar to that of both materials. However, when materials having different coefficients of thermal expansion are used to make a device or element, the selection of an adhesive becomes more difficult. For example, when a device or element is made by joining an optical grating mounted on ultra low expansion (“ULE”) glass to an optical prism made from a glass that has coefficient of thermal expansion different from that of the grating. This combination of grating and prism is frequently called a “grism”. In such an exemplary device it is imperative that the line spacing of the optical grating not change with temperature. For this to be accomplished the adhesive must allow for expansion and contraction of the prism with temperature and must not appreciably transfer excessive force to the grating. In addition, since the adhesive is in the optical light path, it must be transparent at the operating wavelength of the device, for example, at operating wavelengths of 1550 or 1300 nm. Consequently, the adhesive should also be minimally absorbing and minimally scattering (optically clear) at the operating wavelengths. The adhesive should also match as nearly as possible the refractive index of the materials used to make the device. For instance, in the above grism the adhesive should match as closely as possible the refractive index of the prism in order to avoid excessive refraction of the light signal entering or exiting the prism. In the case of the exemplary prism with a refractive index in the range of 1.51 to 1.54 and operating at 1550 nm, the ideal adhesive should have a refractive index in this range.
It is also desirable that the manufacturing of optical devices be as inexpensive as possible. In the early stages of the telecommunications industry devices made of two or more elements were typically made by manually aligning and fusing the elements. Since that time advances have been made through the use of photocurable adhesives. While manual alignment may still occur, the bonding process using adhesives is much simpler than the old fusion process which involves heating the elements to be joined to a temperature at which the material of which they are made is sufficiently soft and flowable so as to join together to form a bond. By using photocurable adhesives the need for such heating and the working of hot materials can be avoided. For example, bringing the grating and prism together with the adhesive in between, optically aligning them, and then curing the adhesive in place by the use of actinic radiation to form the exemplary grism. For example, the curing can be accomplished by shining UV and/or visible light through the prism. The photocure is fast, allowing for perfect alignment, does not involve the use of solvents, does not require the need to heat the adhesive to effect the cure, and does not the require the use of a heating step to joining the grating to the prism—a step which might adversely effect the delicate line structure of the optical grating.
In some applications, optical devices are made from optical elements which themselves are made of different materials. For example, one element may be made of glass and the other made of metal. In such applications precious metals are frequently used because they are resistant to corrosion, rusting and other deleterious effects which may occur during use. When a device is made from one element made of a precious metal and another made of glass, the adhesive must bond to the surface of both the glass and the metal. Further, in order to provide the durability necessary for actual use, the adhesive must maintain its bond to both through accelerated aging cycles commonly used in the industry. For example, accelerated aging under conditions 85° C. and 85% relative humidity (“RH”) for a minimum of 500 hours, and ideally up to 2000 hours. In addition, the adhesive must maintain its integrity through multiple temperature cycles, typically cycling between −40° C. to +85° C.
Formulating adhesives or coatings that have a high degree of adhesion to metals, and especially precious metals, is very difficult. The adhesive requirements enumerated precious metal surfaces to other surfaces such as glass. Further, low T
g
materials generally do not hold up well under conditions of 85° C. and 85% RH.
U.S. Pat. No. 4,497,890 to Herlbert claims a process for improving adhesion of polymeric photoresists to the precious metal gold. Various adhesion promoters were applied as primers to a gold metalized semiconductor substrate. The primers were claimed to enhance the adhesion of a polymeric photoresist to the gold surface during the development process. These adhesion promoters are not sufficient to enable the maintenance of adhesion to long term exposure (i.e. >500 hours) of 85° C. and 85% RH conditions. This is most likely because they were only designed to hold up to the photolithographic development process. The photolithography development process involves an exposure to acidic or basic, aqueous or solvent-based developing solutions. The exposure to the developing solutions is usually quite brief, ranging from a few seconds to several minutes, and is normally done at ambient temperature (approximately 18 to 25° C.) or slightly above ambient temperatures. Exposure to 85° C. and 85% RH for >500 hours is a much more aggressive condition.
Japanese Patent JP 10182779 to K. Murakami and T. Isonaka, assigned to Dainippon Ink and Chemicals Inc., discloses UV curable polyurethane-poly(meth)acrylate compositions as adhesives for optical disks with improved adhesion to gold or silicon nitride. These compositions however, contain urethane acrylates with polyester backbones that are susceptible to hydrolysis in the 85° C./85% RH accelerated aging tests, and hence are not suitable for optical communication use.
C. G. Khan Malek, and S. S. Das,
J. Vac. Science Technology B
(1998) 16(6); Pages 3543-2546, describe the enhancement of adhesion of a polymethylmethacrylate (PMMA) layer to gold by either using a novalac resist layer or an amino silane primer. This process involves several heating steps, under nitrogen, up to 180° C. and for times up to one hour. Heating at these temperatures is detrimental to many optical communications devices in which adhesives and/or coatings may be used.
Japanese patents JP 59-204676 and JP 59-189178, assigned to Mitsubishi Rayon Co., describe photosensitive adhesives comprising brominated epoxy resin with high refractive index useful for optical devices. However, while these brominated materials bond well to glass, they do not have a low T
g
value nor do they have the requisite thermal stability need for telecommunications applications.
M. Manning,
Adv. Sci. Technology
(1999), 17: pages 681-688 and pages 689-696; British Patent GB 2 289 472; and Japanese Patent JP 0303 1309 describe photocurable adhesives of various compositions for use with optical components. However, such materials, when cured, have high T
g
values and a re unsuitable for optical communications devices where low T
g
, materials are required.
The art describes thiols and other sulfur compounds reacting with and bonding to gold metal. However, most of these references involve the formation of what are called self-assembled monolaye
Corning Incorporated
Douglas Walter M.
McClendon Sanza L.
Seidleck James J.
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