Optical waveguides – Having particular optical characteristic modifying chemical...
Reexamination Certificate
2002-04-04
2004-07-06
Tucker, Philip (Department: 1712)
Optical waveguides
Having particular optical characteristic modifying chemical...
C523S404000, C525S524000, C528S027000, C528S028000, C528S033000
Reexamination Certificate
active
06760533
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an adhesive composition and an optical device constructed by bonding together optical parts with an optically transparent adhesive layer formed therefrom.
PRIOR ART
Bonding technologies used for the assembly of optical parts and optical elements used in optical fiber communication systems must have high reliability. For the assembly of optical parts, soldering, laser welding and organic adhesives such as acrylic and epoxy resins have been used. A refractive index control precision adhesive is disclosed by (i) JP-A 6-073358 and JP-A 6-073359 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), and an organic-inorganic adhesive prepared by a sold-gel method is described in (ii) Journal of Non-Crystalline Solids, vol. 80, pp. 557-563, 1986 and (iii) Intl. Congr. On Glass, pp. 429 to 436, 1986. An optical element assembled by using a sold-gel adhesive comprising an alkoxide and a metal salt is disclosed by (iv) Japanese Patent No. 1829914 (JP-A 62-297369) and a prism assembled by using an adhesive comprising a silicic acid salt and an alkoxide is disclosed by (v) Japanese Patent No. 2786996 (JP-A 7-5307). Further, an organic-inorganic composite adhesive is disclosed by (vi) USP 5991493.
(vii) JP-A 11-343474 discloses an adhesive composition comprising an epoxy resin, organoalkoxysilane and aluminum chelating compound. (viii) JP-A 9-243870 teaches that an optical part is sealed by an optically curable resin composition material which comprises a bisphenol type epoxy resin, novolak type epoxy resin, optically acid generating agent and epoxysilane as a coupling agent. Further, (ix) JP-A 2000-109780 discloses an ultraviolet curable adhesive composition for optical parts which comprises a bisphenol A type epoxy resin, alicyclic epoxy resin, optical cationic initiator and &ggr;-glycidoxypropyl trimethoxysilane.
However, the above bonding technologies and adhesives for optical parts have the following problems. The soldering and laser welding are unsatisfactory in terms of fixing position accuracy and need a laser light source and advanced technologies. The epoxy adhesive and acrylic adhesive (i) are inferior in heat resistance of 250° C. or more (soldering heat resistance) and moisture resistance. The adhesives comprising an alkoxide and a metal salt (ii to vii) have such a problem that an alcohol formed by a hydrolytic reaction or water formed by a dehydration reaction is gasified during curing by heating, whereby bubbles remain by bonding optical parts such as lenses, the adhesive becomes opaque, or sufficient adhesion cannot be obtained. The adhesives comprising an epoxy resin (viii, ix) are not satisfactory in terms of the heat resistance of the adhesive layers.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an adhesive composition which overcomes the above defects, has excellent moisture resistance and heat resistance, rarely generates bubbles during curing to eliminate such a defect as opaqueness caused by bubbles and can be used for the assembly and bonding of optical parts.
It is another object of the present invention to provide an optically transparent optical part which is bonded by the adhesive composition of the present invention.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by an adhesive composition for bonding together optical parts, comprising:
(A) an epoxysilane represented by the following chemical formula (1) or a hydrolysis/polycondensation product thereof:
R
n
SiX
4-n
(1)
wherein R is an organic group having an epoxy bond or organic group having no epoxy bond, X is a hydrolyzable group or atom, and n is 1 or 2, with the proviso that when n is 1, R is an organic group having an epoxy bond and when n is 2, at least one of R's is an organic group having an epoxy bond;
(B) a bisphenol type epoxy resin having a viscosity of 2,000 to 5,000 mPa·s;
(C) a novolak type epoxy resin;
(D) a curing agent which is an amine; and
(E) at least one of water and an alcohol, wherein the amounts of the above components (A), (B), (C) and (D) are 3 to 60 wt %, 5 to 90 wt %, 5 to 35 wt % and 3 to 30 wt % based on the total weight of the components (A), (B) and (C), respectively and the amount of the above component (E) is 0 to 0.75 time the total number of mols of the hydrolyzable groups or atoms contained in the component (A).
Secondly, the above object sand advantages of the present invention are attained by an optical device comprising at least two optically transparent optical parts and an optically transparent adhesive layer which is formed by curing the above adhesive composition of the present invention to bond together these optical parts, wherein
when the refractive indices of two adjacent optical parts are represented by n
1
and n
2
(n
1
≧n
2
), the above adhesive layer between the adjacent optical parts satisfies a refractive index n
3
represented by the following expression (1):
{square root over ((
n
1
·n
2
))}−(({square root over ((
n
1
·n
2
))}−
n
2
)/3)−0.05≦
n
3
≦{square root over ((
n
1
·n
2
))}+((
n
1
−{square root over ((
n
1
·n
2
))}/3)+0.05 (1)
THE PREFERRED EMBODIMENTS OF THE INVENTION
The adhesive composition used in the present invention comprises the components (A), (B), (C), (D) and (E). The component (A) is a component which strengthens bonding between the surface of an adherend and an adhesive and contributes to the improvement of moisture resistance. As shown by the above chemical formula (1), when n is 1, the compound used as the component (A) is a silane compound having one organic group with an epoxy bond and three hydrolyzable groups or atoms, or a hydrolysate or polycondensate thereof. When n is 2, a silane compound having one or two organic groups with an epoxy bond and two hydrolyzable groups or atoms or having one organic group with an epoxy bond and one organic group without an epoxy bond such as an alkyl group, aryl group or alkenyl group or a hydrolysis/polycondensation product thereof is used. An epoxysilane of the above chemical formula (1) in which n is 1, or a hydrolysis/polycondensation product thereof having excellent heat resistance and moisture resistance is obtained advantageously. Examples of the organic group having an epoxy bond include glycidoxypropyl group and 3,4-epoxycyclohexyl group. The glycidoxypropyl group and 3,4-epoxycyclohexyl group are preferably used because they are easily acquired. The hydrolyzable group is, for example, an alkoxyl group. Out of these, an alkoxyl group having 1 to 4 carbon atoms is preferred. The hydrolyzable atom is, for example, a halogen atom. Chlorine atom is preferred as the halogen atom. Preferred examples of the silane compound represented by the above chemical formula (1) include 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl triethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl triethoxysilane, 3-glycidoxypropylmethyl dimethoxysilane, 3-glycidoxypropylmethyl diethoxylsilane, di(3-glycidoxypropyl)diethoxysilane, di(3-glycidoxypropyl)dimethoxysilane and hydrolysis/polycondensation products thereof.
The component (A) may be a silane compound represented by the above chemical formula (1) or a hydrolysis/polycondensation product thereof. When the hydrolysis/polycondensation product is used, a reaction is preferably carried out while an alcohol and water by-produced by the reaction are distilled off to ensure that the adhesive composition should not contain water and the alcohol substantially. When the component (A) is a silane compound represented by the above chemical formula (1) and the amount thereof is too large, the viscosity of the obtained adhesive composition becomes too low, resulting in deteriorated coatability. Meanwhile, when the amount is too small, the effect of im
Ishimaru Takeshi
Nakamura Koichiro
Aylward D. E.
Nippon Sheet Glass Co. Ltd.
Tucker Philip
Wenderoth , Lind & Ponack, L.L.P.
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