Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
2000-06-14
2002-07-16
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S015000, C522S024000, C522S025000, C522S129000, C522S146000, C522S170000, C522S181000
Reexamination Certificate
active
06420450
ABSTRACT:
The invention relates to cationically hardening polymer masses, which can be stored in a stable manner for a duration of several months as single-component masses and which can be hardened by means of two different hardening mechanisms, a light-initiated and a heat-initiated hardening mechanism.
The invention relates in particular to those cationically hardening masses which can be hardened in a short time at low temperatures, but which at the same time have a satisfactory storage stability, and which can be used for the adhesion, casting, sealing and coating of substrates.
Finally, the invention relates to a process for preparing cationically hardened polymer masses from the cationically hardening masses according to the invention.
The light-initiated cationic polymerization of masses for adhesion, casting and sealing has been known for a long time. The hardened masses are characterized by a high degree of cohesion and an excellent adhesion capacity to a plurality of substrates. The wide range of application of the radiation-hardening masses is restricted, however, by the fact that in those cases of application in which the fluid masses can run or move into shadowed zones, hardening does not take place in the shadowed areas which are inaccessible to radiation. A considerable number of attempts has therefore been made to provide the cationic masses with a second hardening mechanism which will ensure a reliable hardening even in the shadowed areas.
In this way, cationically hardening epoxy masses are described in EP-A-0 688 804, which comprise the following constituents:
(1) Cationically polymerizable monomers containing epoxy groups;
(2) Lewis or Brønsted acids and/or compounds, which produce these acids under the action of light, and
(3) at least one of the further constituents: flexibilizing agents, retardants, radically polymerizable monomers, accelerators and/or modifiers such as dyes, pigments, fillers, reinforcement agents, thixotropic agents, initiators, stabilizers, inhibitors and bonding agents.
These known masses are extremely reactive, so that in the form of a single-component mixture, i.e. in the simultaneous presence of the constituents (1) to (3), they harden extremely rapidly in the presence of daylight and at room temperature and would have no storage stability. The constituents of these known masses must therefore be divided into at least two components in a defined manner and must be stored in this multi-component form. Only immediately before they are used in accordance with their purpose should the two or more components be mixed together and exposed to light and/or heat, after which they harden extremely rapidly. A special feature of these known masses is that one of the two components, which does not yet contain all the constituents, can be activated by radiation with light of a wavelength of from 280 to 650 nm and in this activated form can be stored in a stable manner for a duration of up to 90 days, as a result of which rapid hardening of the masses takes place even in the shadowed areas after the two or possibly more components have been combined.
A disadvantage of these known masses is the considerable outlay in terms of apparatus for a two- or multiple-component mixing unit required therefor as well as the greater outlay in terms of logistics for the separate storage of two or more components.
Cationically polymerizable masses are known from EP-A-0 508 046, which are completely exposed to light in a storage vessel and thus activated before their application. A disadvantage of this is that the volume of the mass respectively exposed in each case cannot be removed completely from the storage vessel and that the walls of the vessel build up at a greater or lesser rate of increase as a result of material hardening. A continuous manner of operation is not possible in this case.
Further hardening methods known from the field of adhesion, for example anaerobic hardening, moisture hardening, aerobic hardening, hardening by way of primers or activators, are not suitable for cationic polymerization. In the majority of publications which relate to the cationic hardening of polymer masses in areas inaccessible to light (shadowed zones), reaction mechanisms which are based on a heat-initiated hardening are therefore described.
DE-A-197 05 027 and 196 38 630 describe thermal initiators for cationic polymerization based upon thiolanium salts, which require long hardening times at a high temperature, however, for example 16 hours at 130° C. or 6 hours at 140° C. or 3 hours at 150° C. In addition, the poor availability and the high price of thiolanium salts are disadvantageous.
DE-A-30 07 684 and 28 53 886 disclose thermosettable compositions which, in addition to cationically polymerizable material and diaryliodonium salt, contain a copper chelate, optionally together with a reduction agent, or organic acids or anhydrides for cationic thermosetting. In this case, too, the long hardening time and the poor storage stability of the masses described are disadvantageous, as well as the toxicity of the copper compounds used, the blue-green colour, the poor solubility and the autocatalytic effect of the said copper compounds with respect to the light-induced decomposition of polymers.
Masses are known from EP-A-0 146 501 which contain aromatic iodosyl salts and metallic salts and/or peroxides as co-catalysts. The disadvantages of these masses are the high hardening temperatures, poor availability of the aromatic iodosyl salts and the toxicity of the metallic salts used.
Finally, cationically polymerizable masses based upon diaryliodonium salts are known from GB-A-2 070 616, which acquire a thermal hardening mechanism by way of dibenzyl compounds or oligomeric silyl ethers. The disadvantages of these masses are the high hardening temperatures of 140 or 160° C. as well as an only incomplete reaction of the cationically polymerizable groups.
Cationically hardening epoxy masses are known from U.S. Pat. No. 4,374,751, which consist of
(1) an at least difunctional cationically polymerizable epoxy compound;
(2) a photo-initiator for the cationic hardening based upon diaryliodonium salts;
(3) a peroxide compound which releases radicals when heated, and
(4) optionally adjuvants and additives, such as for example fillers, dyes, pigments and agents for setting the viscosity.
These known masses can be stored in a stable manner under normal conditions and harden relatively slowly only after thermal activation at temperatures above 100° C., preferably at 150° C. (within 3.5 hours at 150° C. according to Example 1).
The object of the invention is to propose novel cationically hardenable masses which can be stored and handled in a stable manner as single-component masses for a duration of several months, and which can be completely hardened rapidly and at low temperatures which light-induced and/or heat-induced and can be hardened under gentle conditions even in shadowed zones inaccessible to radiation without a special outlay in terms of apparatus. In particular, the masses should be suitable for the adhesion of heat-sensitive electronic components during the assembly of printed-circuit boards (surface-mounted devices).
This object is attained according to the invention by the cationically hardening mass of claim
1
; said mass consisting of:
(A) from 5 to 90 parts by mass of at least one difunctional cationically polymerizable compound;
(B) from 0.01 to 5 parts by mass of a photo-initiator for the cationic hardening based upon diaryliodonium salts;
(C) from 0.1 to 70 parts by mass of at least one compound containing an hydroxyl group and having a molar mass of from 150 to 10,000 g/mol and hydroxy-equivalent masses of from 50 to 5,000 g/mol;
(D) from 0.01 to 10 parts by mass of a compound releasing radicals when heated and having a half-life of one hour at a temperature of less than 100° C.;
(E) from 0.001 to 10 parts by mass of a photo-initiator forming radicals or of a photo-sensitizing agent for diaryliodonium salts, and
(F) from 0 to 60 parts by mass of modifiers, selected from at
Dengler Dietmar
Stumbeck Michael
Berman Susan W.
Delo Industrieklebstoffe GmbH & Co. KG
Hayes & Soloway P.C.
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