Casting resin compositions for sealing opto-electronic components

Casting resin compositions for sealing opto-electronic components on the basis of quick-setting casting resin compounds, consisting of at least one epoxy compound with a cycloaliphatic base with at least two oxiran rings in the molecule, at least one carbonic acid anhydride, a zinc octoate, a low-molecular polyol and/or a low-molecular acid ester and, optionally, an organic phosphorus compound and customary brighteners and light-scattering material in powder form and pigments. Especially suitable is a zinc octoate with a zinc content of 21 to 22% by weight. The compounds are used for covering and coating light-emitting diodes, photo transistors, photo diodes and light-emitting diode displays and as light guides for opto-electronic couplers.

BACKGROUND OF THE INVENTION 
The invention relates to transparent casting resin compositions for sealing 
opto-electronic components on the basis of acid anhydride-hardenable epoxy 
compounds with at least two oxiran rings in the molecule, together with 
organo-metallic compounds, low-molecular polyols and/or low-molecular acid 
esters and, optionally, with organic phosphorus compounds, optical 
brighteners, pigments and light-scattering materials in powder form. 
It is known to use, for covering or coating opto-electronic components, 
light-permeable, acid anhydride-hardenable epoxy casting resin compounds 
of the bisphenol-A type (German Offenlegungsschrift No. 589 264 =U.S. Pat. 
No. 3,544,827). 
One disadvantage of epoxy casting resin compounds based on bisphenol-A/acid 
anhydride, which harden fast through the use of known accelerators such as 
tertiary amines, imidazoles or borofluoride complexes, is their poor 
thermal aging stability. The materials used heretofore become discolored 
in extended storage at temperatures above 80.degree. C., through yellow to 
brown, whereby their light transmittancy decreases considerably. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the invention to prepare transparent or 
transparently colored, optionally light-scattering casting resin coverings 
or casting resin coatings for opto-electronic components, which do not 
become discolored up to at least 120.degree. C. when heat-aged for more 
than 2,000 hours, are system-compatible and adhere well. 
In addition, it should be possible to take the components covered or coated 
with the casting resin compounds according to the invention out of the 
mold at a hardening temperature of 150.degree. C. in less than 5 minutes. 
The molded material generated on and around the opto-electronic components 
should protect the functional parts of the components against mechanical 
damage, moisture, corrosive gases and other environment effects. Further, 
the molded material should be resistant to electroplating baths such as 
tin-plating baths. 
According to the invention, the above objects are achieved with a casting 
resin composition comprising: 
(a) at least one epoxy compound of the cycloaliphatic type; 
(b) at least one carbonic acid anhydride; 
(c) a zinc octoate; 
(d) a low-molecular polyol and/or low-molecular acid ester; and, 
(e) optionally, an organic phosphorus compound. 
The casting resin composition according to the invention sets in a few 
minutes as a molded material without voids, without striations and with an 
optically perfect surface. 
The casting resin compositions according to the invention, whether 
colorless or transparently colored, can be prepared from preliminary 
mixtures which are unaffected by storage, namely, the preliminary mixture 
(A) consisting of a cycloaliphatic epoxy resin, a low-molecular polyol, 
optionally together with an optical brightener; the preliminary mixture 
(B) consisting of a carbonic acid anhydride and a low-molecular acid 
ester; and the preliminary mixture (C) consisting of zinc octoate, an 
organic phosphorus compound and a low-molecular acid ester, optionally 
together with pigments. To produce light-scattering casting resin coatings 
according to the invention, a further storage-stable preliminary mixture 
(D) consisting of a cycloaliphatic epoxy resin and a light-scattering 
material in powder form is admixed to the casting resin composition. This 
division into storage-stable, flowable preliminary mixtures allows the 
casting resin compositions to be prepared and processed in a mechanized or 
automated manner. 
The molded cast-resin material produced for covering or coating may have 
different shapes. For example, it may be lens-shaped, cyclindrical, planar 
or prismatic. 
Epoxies suitable for preparing the casting resin compositions according to 
the invention are, for example, 3,4-epoxycyclohexylmethyl-(3,4-epoxy) 
cyclohexane carboxylate, 2-(3,4-epoxy) cyclohexyl-5,5-spiro(3,4-epoxy) 
cyclohexane-m-dioxane and mixtures of those compounds. 
Suitable carbonic acid anhydrides are, for example, tetrahydrophthalic acid 
anhydride, methylhexahydrophthalic acid anhydride or succinic acid 
anhydride. Hexahydrophthalic acid anhydride has been found to be 
particularly well suited. Mixtures of the cited acid anhydrides can also 
be employed. 
As a reaction accelerator, a zinc octoate consisting of zinc and a 
2-ethylhexane acid residue in a mol ratio of 1:2, corresponding to a zinc 
content of approximately 18% by weight, is suitable. A zinc octoate with a 
zinc content in the range of from about 21 to 22% by weight has been found 
to be particularly advantageous. With the same weight content of 
accelerator, the mold release time at a hardening temperature of 
150.degree. C. can be reduced to less than 3 minutes even with a very 
small amount of casting resin composition (less than 0.1 g). Zinc octoate 
is preferably utilized together with an organic phosphorus compound in 
solution. As a solvent, compounds are suitable which, on the one hand, 
completely solve zinc octoate and any phosphite used and, on the other 
hand, form a chemical compound with the resin or hardener component during 
the hardening by at least one reactive group via an addition reaction, in 
order to prevent later migration of the solvent in the molded casting 
resin material. 
Suitable solvents are, for example, low-molecular polyols and low-molecular 
acid carbonic-acid esters and their mixtures. As particularly well suited 
have been found trimethylol propane or 3-methylpentanediol-1,5 and 
hexahydrophthalic acid monoethyl ester. 
Suitable organic phosphorus compounds are, for example, 
diphenyldecylphosphite, triphenylphosphite and didecylphenylphosphite. 
Diphenyldecylphosphite has been found to be especially suitable. These 
compounds act as antioxidation agents and as reaction accelerators and 
lower the initial viscosity of the casting resin composition. 
As an optical brightener, the commercially available Waxoline Violet.RTM. 
is suited. 
Suitable light-scattering materials in powder form are silicic acids 
produced by flame hydrolysis from silicon tetrachloride in an 
oxygen-hydrogen flame, commercially available as Aerosil.RTM., as well as 
synthetically prepared, micronized porous silicic acid, commercially 
available as Syloid.RTM., and barium sulfate, boron nitride, calcium 
carbonate and calcium fluoride. 
For coloring the casting resin compounds according to the invention, 
commerically available Orasol dyes.RTM. (for example, Orasol scarlet GLN, 
Orasol yellow 3 GLG), Waxoline dyes.RTM. (for example, Waxoline red O), 
Mikrolite dyes.RTM. (for example, Mikrolith green GT) and pigment colors 
(chromium oxide, color paste DW 04) can be used. 
The casting resin compositions according to the invention are liquid at 
room temperature. At room temperature, they have a long use span. They can 
be dosed easily, which greatly facilitates processing them by means of 
multiple dosing devices. A great advantage is the fast release from the 
mold of the molded materials made from the casting resin composition 
according to the invention, which reduces the mold use time considerably. 
The casting resin compounds can be used for covering or coating 
opto-electronic components such as light-emitting diodes, photo diodes, 
photo transistors and for sealing light-emitting diode displays and as 
light guide resins for opto-electronic couplers.

DETAILED DESCRIPTION OF THE INVENTION 
The invention will be explained in further detail by the following 
examples. 
EXAMPLE 1 
Transparent casting resin composition 
Preparation of the preliminary mixture A: 
94 parts by weight 3,4-epoxycyclohexylmethyl-(3,4-epoxy) cyclohexane 
carboxylate are mixed homogeneously at room temperature with 0.00014 parts 
by weight Waxoline Violet A and 6 parts by weight 3-methylpentanediol-1,5. 
Preparation of preliminary mixture B: 
88 parts by weight hexahydrophthalic acid anhydride are mixed homogeneously 
at 60.degree. to 70.degree. C. with 12 parts by weight hexahydrophthalic 
acid monoethylester. 
Preparation of preliminary mixture C: 
7 parts by weight diphenyldecyl phosphite and 6 parts by weight zinc 
octoate are mixed at room temperature with 13 parts by weight of the 
hexahydrophthalic acid monoethyl ester melted at 40.degree. to 50.degree. 
C. 
Preparation of the casting resin composition from the preliminary mixtures 
A, B and C: 
100 parts by weight of preliminary mixture A are mixed homogeneously at 
room temperature with 100 parts by weight of the preliminary mixture B and 
18 parts by weight of the preliminary mixture C. 
EXAMPLE 2 
Transparent Casting Resin Composition (without phosphite) 
Preparation of preliminary mixture A: 
94 parts by weight 3,4-epoxycyclohexylmethyl-(3,4-epoxy) cyclohexane 
carboxylate are homogeneously mixed at room temperature with 0.00015 parts 
by weight Waxoline Violet A and 6 parts by weight 3-methylpentanediol-1,5. 
Preparation of preliminary mixture B: 
88 parts by weight hexahydrophthalic acid anhydride are mixed homogeneously 
with 12 parts by weight hexahydrophthalic acid monoethyl ester. 
Preparation of the casting resin composition of the preliminary mixtures A, 
B and zinc octoate: 
6 parts by weight zinc octoate are stirred at room temperature into 100 
parts by weight of preliminary mixture B and then 100 parts by weight of 
the preliminary mixture A are admixed. 
EXAMPLE 3 
Red-Colored, Light-Scattering Casting Resin Composition 
Preparation of the preliminary mixture A: 
94 parts by weight 3,4-epoxycyclohexylmethyl-(3,4-epoxy) cyclohexane 
carboxylate are mixed homogeneously at room temperature with 0.00015 parts 
by weight Waxoline Violet A and 6 parts by weight 3-methylpentanediol-1,5. 
Preparation of the preliminary mixture B: 
88 parts by weight hexahydrophthalic acid anhydride are mixed with 12 parts 
by weight hexahydrophthalic acid monoethyl ester at 60.degree. to 
70.degree. C. 
Preparation of preliminary mixture C: 
7 parts by weight diphenyldecyl phosphite and 6 parts by weight zinc 
octoate are mixed at room temperature with 13 parts by weight of the 
hexahydrophthalic acid ethyl ester melted at 40.degree. to 50.degree. C. 
To 18 parts by weight of this mixture are admixed 0.04 parts by weight 
Waxoline red O. 
Preparation of preliminary mixture D: 
1.3 parts by weight calcium fluoride are made into a paste with 0.5 parts 
by weight 
3,4-epoxicyclohexylmethyl-(3,4-epoxicyclohexylmethyl-(3,4-epoxi)cyclohexan 
e carboxylate. 
Preparation of the casting resin composition from the preliminary mixtures 
A, B, C and D: 
100 parts by weight of the preliminary mixture A are homogeneously mixed at 
room temperature with 100 parts by weight of the preliminary mixture B, 18 
parts by weight of the preliminary mixture C and 1.8 parts by weight of 
the preliminary mixture D. 
EXAMPLE 4 
Transparent Casting Resin Composition 
Preparation of preliminary mixture A: 
100 parts by weight of a mixture of 50 parts by weight 3,4- 
epoxycyclohexylmethyl-(3,4-epoxy)cyclohexane carboxylate and 50 parts by 
weight 2-(3,4-epoxy)cyclohexyl-5,5-spiro(3,4-epoxy) cyclohexane-m-dioxane 
are mixed at room temperature with 0.00015 parts by weight Waxoline Violet 
A. 
Preparation of preliminary mixture B: 
A mixture of 43 parts by weight hexahydrophthalic acid anhydride and 47 
parts by weight methylhexahydrophthalic acid anhydride is homogeneously 
mixed with 12 parts by weight hexahydrophthalic acid monoethyl ester. 
Preparation of preliminary mixture C: 
7 parts by weight diphenyldecyl phosphite and 5 parts by weight zinc 
octoate are mixed at room temperature with 13 parts by weight of the 
hexahydrophthalic acid monoethyl ester melted at 40.degree. to 50.degree. 
C. 
Preparation of the casting resin composition from the preliminary mixtures 
A, B and C: 
100 parts by weight of the preliminary mixture A are mixed homogeneously at 
room temperature with 102 parts by weight of the preliminary mixture B and 
18 parts by weight of the preliminary mixture C.