Organic compounds -- part of the class 532-570 series – Organic compounds – Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
2001-02-23
2003-08-12
Ford, John M. (Department: 1624)
Organic compounds -- part of the class 532-570 series
Organic compounds
Four or more ring nitrogens in the bicyclo ring system
Reexamination Certificate
active
06605718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for reducing organic solvents remaining in tris-(2,3-epoxypropyl)-isocyanurate crystals, by removing the organic solvents remaining in said crystals while evaporating a volatile component from the surface of the crystals, particularly by e.g. machine pulverization in a gas stream.
2. Discussion of Background
In view of an increasing demand in recent years for the properties required for a solder resist material, such as adhesion, electrical insulating properties, soldering heat resistance and solvent resistance, a solder resist ink composition is presently used which is a combination of a photosensitive prepolymer and a thermosetting resin. Namely, it is designed to satisfy the above required properties by forming a solder resist pattern by the photosensitive prepolymer, followed by thermosetting. Further, demands have been increasing for high densification of printed circuit boards along with a trend for light weight and miniaturization of electronic appliances in recent years, for low scumming during formation of solder resist patterns for surface mounting of parts and for precision in embedding between circuits. Accordingly, as the thermosetting resin to be incorporated to the solder resist ink, a fine particulate solid epoxy having high solvent resistance is desired.
As a solid epoxy to satisfy the above required properties, tris-(2,3-epoxypropyl)-isocyanurate may be mentioned. Tris-(2,3-epoxypropyl)-isocyanurate has three asymmetric carbon atoms, and crystals made of an equimolar mixture of (2R,2′R,2″R)-tris-(2,3-epoxypropyl)-isocyanurate and (2S,2′S,2″S)-tris-(2,3-epoxypropyl)-isocyanurate, wherein all of the three asymmetric carbon atoms are optically isotropic, are commonly called &bgr;-form crystals and known to give crystals having a high melting point of a level of about 150° C. This is attributable to the fact that a pair of these two types of enantiomers form a molecular lattice having six firm hydrogen bonds and thus form a crystal lattice. On the other hand, crystals made of a mixture of (2R,2R,2S)-tris-(2,3-epoxypropyl)-isocyanurate and (2S,2S,2R)-tris-(2,3-epoxypropyl)-isocyanurate, wherein one of the three asymmetric carbon atoms is different in the optical anisotropy, are commonly called &agr;-form crystals, and they do not have the above crystal structure and accordingly present only a low melting point of a level of about 100° C. The &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate crystals not only have a high melting point but also have an extremely low solubility in various solvents. Accordingly, when they are used as a crosslinking agent for different types of compounds or for reactive polymers in the form of a one pack type reactive mixture, the reaction will not proceed during storage, until they are forcibly cured. Such &bgr;-form crystals have been used for applications to electric and electronic materials, for example, as a solder resist ink composition of photocuring/thermosetting combined type.
The liquid epoxy composition is likely to undergo an increase in viscosity during storage, since a part of the epoxy compound dissolves in the solvent, and entanglement with the photosensitive prepolymer is likely to result, whereby elution tends to be poor during washing off of the non-exposed portion. JP-B-7-17737 discloses use of &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate as a hardly soluble epoxy compound. &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate fine particles which have a high melting point and which are hardly soluble, are in a state enclosed by a photosensitive prepolymer, whereby they will not reduce the solubility of the photosensitive prepolymer at the non-exposed portion. Further, they are hardly soluble in an organic solvent, whereby the exposed portion is hardly eroded by a developer, whereby there will be no deterioration in the sensitivity. Further, the storage stability of the solder resist ink composition is excellent.
As a method for separating &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate and &agr;-form tris-(2,3-epoxypropyl)-isocyanurate from tris-(2,3-epoxypropyl)-isocyanurate, a separation method has been available wherein a solvent which dissolves &agr;-form tris-(2,3-epoxypropyl)-isocyanurate relatively well and which hardly dissolves &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate, for example, an alcohol such as methanol, is employed. For example, Journal of Thermal Analysis, vol.36 (1990) p.1819 discloses separation by means of a methanol solvent. Further, Plaste und Kautschuk 23 Jahrgang Heft 4/1975 discloses a method wherein firstly a methanol solvent is used for separating &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate, and then the &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate is purified by chloroform. Further, Kobunshi Ronbunshu (polymer report collection), vol.47, No.3 (1990) p.169, discloses a method wherein synthesized tris-(2,3-epoxypropyl)-isocyanurate is put into methanol, followed by heating and stirring, whereupon the non-dissolved content is collected by filtration, and the obtained non-dissolved substance is re-crystallized from methyl ethyl ketone to obtain &bgr;-form tris-(2,3-epoxypropyl)-isocyanurate crystals.
Many of &bgr;-form tris-(2,3-epoxypropyl)-isocyanurates obtained by such separation methods, hardly undergo crystal growth, and many of them have a small particle size, whereby the filtration operation in the filtration step tends to be very difficult. Accordingly, it is undesirable that the crystals obtained by recrystallization are too fine.
Further, by a single separation operation by the foregoing separation method, &bgr;-form tris-(2,3epoxypropyl)-isocyanurate crystals tend to contain the solvent for recrystallization, chlorine-containing impurities or other impurities. Accordingly, it will be necessary to remove them by further carrying out recrystallization or by melting the crystals once.
Particularly, if the remaining organic solvent is not adequately removed, when the tris-(2,3-epoxypropyl)-isocyanurate is used for e.g. a solder resist material, holes formed by evaporation of the solvent are likely to form on the surface of a printed circuit board, and original properties of the resist material can not be adequately obtained. Further, there may be a problem in an application in which surface smoothness is required. Further, in a case where the remaining organic solvent is a halogenated hydrocarbon, it is not suitable for applications to electronic materials. Further, in a case where the remaining organic solvent is a protic organic solvent, storage stability of a composition may be impaired by proton in some cases.
JP-B-48-24039 discloses a process wherein a chlorohydrin ester of isocyanuric acid obtained by reacting cyanuric acid with epichlorohydrin, is dehydrochlorinated with an alkali, the alkali metal chloride thereby formed is separated, and the obtained epichlorohydrin solution of tris-(2,3-epoxypropyl)-isocyanurate is concentrated to a tris-(2,3-epoxypropyl)-isocyanurate concentration of from 50 to 60%, and then the solution is cooled to from 20 to 25° C. to obtain tris-(2,3-epoxypropyl)-isocyanurate crystals in an yield of 27% based on cyanuric acid. However, the crystals are obtained by crystallization from the epichlorohydrin solution, whereby a large amount of epichlorohydrin, etc. are contained in the interior of the crystals. Further, epichlorohydrin is composed of a hydrolyzable chlorine which is not only hazardous to human bodies but also hazardous to applications to electronic materials, and should be contained as little as possible. However, epichlorohydrin remaining in the crystals can be removed only by heating the crystals to at least the melting point to melt the crystals once. Such a method makes the production step more complicated, and costs much, whereby it is not practical industrially.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method to make the amount of organic solvents remaining in tris-(2,3-epoxyp
Gunji Yasuhiro
Hidaka Motohiko
Ikeda Hisao
Ford John M.
McKenzie Thomas
Nissan Chemical Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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