Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-06-25
2004-06-29
Aylward, David E (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C257S787000, C257S788000, C257S793000, C528S088000, C549S513000, C549S541000, C549S542000
Reexamination Certificate
active
06756453
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to alicyclic epoxy compounds and their preparation process, alicyclic epoxy resin composition, and encapsulant for light-emitting diode (LED).
Since epoxy compounds have many advantageous properties such as excellent heat resistance, adhesion, water resistance, mechanical strength and electrical properties, epoxy compounds are used in various fields of industries, for example as adhesive, coating material, engineering and construction material, and insulating material for electric and electronic parts.
These epoxy compounds comprise typically aromatic epoxy resins such as diglycidyl ethers of bisphenol A, diglycidyl ethers of bisphenol F, and phenol or cresol novolak type epoxy resins.
LED is used for a variety of commercial products such as display boards, light source for image reading, traffic signals, and large-size display units. In a luminous device comprising LED, the surroundings of the luminous element are generally encapsulated with a transparent resin, especially an epoxy compound because of high adhesiveness, etc., for the purposes of protection of the semiconductor and converging of light.
It is known, however, that the epoxy resins cured with an acid anhydride are subject to a change of quality originating in the acid anhydride used. These epoxy resins also involve the problems such as yellowing which occurs when the cured resin is kept exposed to the open air or to a light source generating ultraviolet rays. In recent years, remarkable progress has been made in the development of high-brightness blue LED (main luminescence at around 460 nm) and the development of LED having main luminescence in the ultraviolet region (e.g. 350-400 nm). Also, improvement in performance of blue LED in addition to the conventional red LED and green LED has enabled display of the three primary colors, and this blue LED is now offered to use for display units. There has further been proposed white LED designed to effect color mixing by combined use of a luminous element and a fluorescent substance, with part or whole of the short wavelength luminescence of the luminous element being converted to the long wavelength luminescence, and this white LED has already been offered to use for illumination, back-lighting and such.
Shortening of the light-emitting wavelength as mentioned above increases the light energy, which tends to cause early deterioration of the encapsulant for LED. For example, Japanese Patent Application Laid-Open (KOKAI) No. 8-148717 describes reduction of light intensity as a result of deterioration of the encapsulant by the heat or light generated from the blue LED. Further, in the case of white LED, as it is of a mixed color, it is feared that its color tone would be varied when the encapsulant has light absorption at a wavelength in the visible region. It is noticeable that the human sense of tonality is particularly sharp to white color. For example, Japanese Patent Application Laid-Open (KOKAI) No. 2000-315826 describes that the direction of measurement of LED could be a causative factor of color shading due to diffraction by the encapsulant and/or other reasons.
As a solution to the problems posed by the light of short wavelength such as mentioned above, Japanese Patent Application Laid-Open (KOKAI) No. 2001-19742 proposes a composition comprising a hydrogenated compound of an aromatic epoxy compound and a cationic curing catalyst. This composition is improved in toughness and coloration of its cured product and also excels in light resistance.
On the other hand, various proposals have been made on the attempt to produce alicyclic epoxy compounds by hydrogenating the aromatic rings of aromatic epoxy compounds.
U.S. Pat. No. 3,336,241 proposes a method in which an organic compound having at least one epoxy group and at least one carbon-carbon double bond is hydrogenated in the presence of a hydrogenation catalyst comprising rhodium or ruthenium carried on an inert carrier such as activated carbon. Japanese Patent Application Laid-Open (KOKAI) No. 11-217379 proposes use of a hydrogenation catalyst comprising rhodium or ruthenium carried on a carbonaceous carrier having a specific surface area in the range of 5 to 600 m
2
/g for improving activity or selectivity. Further, Japanese Patent Application Laid-Open (KOKAI) No. 11-199645 proposes an embodiment of an epoxy compound of low chlorine content, which is high in hydrogenation rate and small in loss of epoxy groups, in the above methods.
However, in the hydrogenation method using a noble metal catalyst, transmittance of the obtained alicyclic epoxy compound (encapsulant) in the short wavelength region decreases with the passage of time. Therefore, in case of LED having its main light-emitting wavelength in the short wavelength region, the radial luminous intensity of LED decreases with time caused by such an alicyclic epoxy compound. In case of white LED, there arises the problem that the white color tone is varied due to the distribution of transmittance in the visible light region, caused by the alicyclic epoxy compound.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances, and its object is to provide alicyclic epoxy compounds (encapsulant) which are small in change of reproducibility, uniformity and stability of hue and also capable of minimizing the decrease of radial luminous intensity of LED with time, and a process for producing such compounds.
To attain the above aim, in the first aspect of the present invention, there is provided alicyclic epoxy compounds obtained by selectively hydrogenating aromatic rings of aromatic epoxy compounds in the presence of a hydrogenation catalyst comprising a platinum group element, the concentration of the platinum group element in the product of alicyclic epoxy compound being not more than 2 ppm.
In the second aspect of the present invention, there is provided an alicyclic epoxy resin composition comprising alicyclic epoxy compound as main component, which alicyclic epoxy compound is obtained by selectively hydrogenating aromatic rings of aromatic epoxy compounds in the presence of a hydrogenation catalyst comprising a platinum group element, the concentration of the platinum group element in the alicyclic epoxy resin composition being not more than 2 ppm.
In the third aspect of the present invention, there is provided an encapsulant for light-emitting diode comprising the alicyclic epoxy resin composition as defined in the above second aspect.
In the fourth aspect of the present invention, there is provided a process for producing an alicyclic epoxy compound which comprises selectively hydrogenating aromatic ring of an aromatic epoxy compound in the presence of a hydrogenation catalyst, and bringing the obtained alicyclic epoxy compound into contact with an adsorbent to remove the platinum group element in said alicyclic epoxy compound.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is explained as follows.
The aromatic epoxy compounds used in the present invention are the aromatic compounds having two or more epoxy groups in the molecule and include various types such as glycidyl ethers, glycidyl esters and glycidylamines.
Typical examples of the said aromatic compounds are epoxy compounds represented by the formula (I) produced from bisphenol A or bisphenol F and epichlorohydrin, and polyglycidyl ethers of phenol or cresol novolak type resins represented by the formula (II).
wherein R
1
is a hydrogen atom or a methyl group; n is an integer of 0 to 40; and Ep represents the following chemical formula.
It is also possible to use various aromatic epoxy compounds obtained from phenolic compounds with a valence of 2 or more and epichlorohydrin. Examples of such aromatic epoxy compounds are hydroquinone diglycidyl ether, resorcin diglycidyl ethers, biphenol diglycidyl ether, and 3,3′,5,5′-tetramethylbiphenol diglycidyl ether.
In the compounds mentioned above, bisphenol A type epoxy compounds represented by the formula (I) and polyglycidyl ethers
Honda Masayuki
Murai Kouya
Nishi Mineo
Aylward David E
Mitsubishi Chemical Corporation
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