KR970002527B1 - Method for preparing a microencapsulated catalyst for storage stable heat curable organosiloxane compositions - Google Patents

Abstract

None.

Description

Method for preparing microencapsulation catalyst for organosiloxane composition capable of thermosetting storage stability

The present invention relates to an organosiloxane composition that is cured by catalysis. More particularly, the present invention relates to one-part organosiloxane compositions containing novel microencapsulated curing catalysts. The composition exhibits long term storage stability in ambient conditions but rapidly cures at high temperatures.

The organosiloxane composition is cured by various reactions. Some common curing means include: 1) free radical reactions initiated by the decomposition of photoinitiators or heat-induced decomposition of organic peroxides in the presence of ultraviolet light, and 2) two or more hydrolysis occurring under atmospheric conditions in the presence of moisture and suitable catalysts. It relates to the reaction of an organosilicon compound comprising a possible group with a hydroxyl-containing polyorganosiloxane.

One more useful class of polyorganosiloxane compositions is cured by reaction of silicon-bonded hydrogen atoms with silicon-bonded alkenyl radicals or hydroxyl groups. These reactions are promoted by the metals of the platinum group or compounds of these metals of the periodic table. The advantages of these compositions include, among other things, the rapid cure rate at high temperatures, the unproductive and thick formation of undesirable by-products that occur during the curing process of compositions containing organic peroxides or silanes having hydrolyzable groups such as acetoxy or methoxy. Difficulties in achieving complete cure of the moisture-curable organosiloxane composition used in the layer.

A composition cured by a hydrosilation reaction is a polydiorganosiloxane having at least two ethylenically unsaturated hydrocarbon radicals per molecule, an organohydrogen having at least two silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure the composition. It generally contains an amount of platinum- or rhodium-containing catalyst sufficient to promote curing of the siloxane and the composition.

Fillers and other additives may be included before or after curing for the purpose of changing the physical and / or chemical properties of the composition.

Organosiloxane compositions cured by platinum-catalyzed hydrosilylation reactions generally begin to cure at ambient temperature once the reactants are bonded, so the catalyst and organohydrogensiloxane reactants are usually stored in separate containers and when the composition is cured. Do not combine until you try to turn it on. Even if one or more known platinum catalyst inhibitors are added to the composition, they cannot be stored in a single container for more than several hours.

As one alternative to feeding the platinum-catalyzed curable organosiloxane composition into a two-vessel material, the method proposed in the prior art provides a catalyst or organo in a matrix of material that is solid under the conditions in which the curable composition is stored. Hydrogensiloxane is isolated and mixed with other components when attempting to cure the composition by distilling out stored reactants or catalyst.

Other one-part curable organosiloxane compositions containing microencapsulated reactants or catalysts are shown as prior art. Examples of these compositions are described in US Pat. No. 4,528,354, filed July 9, 1985 to McDougal and Dougherty. This patent document describes one-part peroxide curable silicone rubber compositions. The composition contains a microencapsulated liquid phase containing an organic peroxide on the outer surface of the thermosetting resin material which peroxide cannot penetrate.

When the curable composition containing the microcapsules is heated, the capsules are designed to rupture by a constant internal vapor pressure generated by the liquid in the capsules.

Since the release of the peroxide depends on the rupture rather than on the melting of the shell separating the other components of the organosiloxane composition from the peroxide, the thickness and composition of the shell are carefully controlled to ensure that the rupture of the capsule is sufficient to control the organosiloxane composition. It should occur within the temperature range of curing.

U.S. Patent No. 4,604,444 (August 5, 1986, Donnadieu) describes a storage stable polyorgano consisting of a microcapsule accelerator containing or generating moisture, polyhydroxylate and polyorganosiloxane, and multifunctional acyloxysilane. The siloxane composition is described. The capsule material may be released by heating and / or light irradiation. Suitable capsule materials include polystyrene, acrylonitrile-styrene copolymers and poly (methyl methacrylate).

This patent does not address the use of microcapsule materials in organosiloxane compositions curable by reactions other than the reaction of polyhydroxylated polyorganosiloxanes with acyloxysilanes.

US Pat. No. 4,461,854 (July 24, 1984) describes two-part curable organosiloxane compositions. One component contains silanol-terminated polyorganosiloxane and the second component contains a curing agent, a filler and an encapsulation catalyst. The catalyst is a specific group of carboxylic acid metal salt, wherein the metal is for example tin, lead or zirconium. The capsule material is preferably a salt of carboxylic acid that does not promote curing of the composition at room temperature. Encapsulation catalysts extend the bath-life of the curing composition.

U.S. Patent No. 4,293,677 (6 October 1981, Imai) describes an encapsulated organohydrogensiloxane using the most common microencapsulation techniques, in-situ polymerization and complex coacervation.

The in situ polymerization method illustrated in the second embodiment of the Imai patent specification is a polymerization of styrene in the presence of a dimethylsiloxane / methylhydrogensiloxane copolymer as an emulsion dispersion phase containing a liquid-dissolved polyvinyl alcohol and potassium persulfate in an aqueous phase. Is related.

A disadvantage of encapsulating the organohydrogensiloxane reactants presented by Imai et al. Is the relatively high amount of encapsulated polymer introduced into the composition. Many thermoplastic organic polymers suitable for use as capsules are incompatible with the reactants present in the curing composition. The presence of relatively large amounts of incompatible polymers degrades the physical, optical and form properties of the cured material.

One way to reduce the amount of incompatible encapsulated polymer introduced into the curing composition is to encapsulate the platinum-containing catalyst rather than the organohydrogensiloxane reactants set forth by Imai et al. One class of the most effective catalysts for cured organosiloxane compositions of the type described in the Imai patent is the use of liquid vinyl-containing organosilicon compounds such as sim-tetramethyldivinyldisiloxane and inorganic platinum compounds such as crawlroplatinic acid. Reaction product. Liquid dimethylvinylsiloxy terminated polydimethylsiloxane can be used to dilute this solution to the desired platinum content, typically 0.1 to 1% by weight. Alternatively, undiluted reaction products can be used as catalyst.

U.S. Patent 4,481,341 (Schlak et al., November 6, 1984) and Japanese Patent Application No. 49 / 134,786 (published December 25, 1974) are polyorganosiloxanes containing at least two ethylenically unsaturated hydrocarbon groups per molecule. A thermosetting organosiloxane composition consisting of a polyorganohydrogensiloxane containing at least two silicon-bonded hydrogen atoms per molecule and a platinum-containing catalyst dispersed in a finely divided solid matrix as a silicone resin or organic resin, and have. The concentration of catalyst is from 0.001 to 5% by weight of platinum metal.

The fine nutrient material in which the catalyst is dispersed is substantially insoluble in the polyorganosiloxane or polyorganohydrogensiloxane and softens or melts at a temperature of 70 to 250 ° C. An advantage of the composition set forth in the Schlak et al. Patent is the fact that the catalyst is isolated from the other components of the curing composition until the composition is sufficiently heated to melt the material in which the catalyst is dispersed. Since the organosiloxane compound present in the composition does not cure without the catalyst, the composition can be stored for a long time without curing or increasing viscosity. A disadvantage of the cured organosiloxane compositions presented by published Japanese patent applications and Schlak et al. Lies in the method of preparing the catalyst / resin composition. Solid blocks or sheets of resin containing a widely dispersed platinum composition are ground to a fine powder. Based on the randomness of the grinding process, there is a significant possibility that the particles will contain platinum catalyst on the surface. Even trace amounts of platinum appear to cause hasty curing of the organosiloxane type exemplified in this patent.

One method of avoiding the inherent disadvantages of the catalyst compositions set forth in Schlak et al. Is to isolate the fine powders or particles of the catalyst composition effectively from the reactive components of the curable organosiloxane composition and completely fine into the material impermeable to the catalyst. Is to encapsulate. The encapsulant softens or melts at the desired curing temperature of the composition. Various methods of preparing microencapsulated materials are known in the art.

US Patent No. 4,874,667 (patented on October 17, 1989 by Lee et al., Assigned to the same applicant as the present patent application) describes a one-part organosiloxane composition that is cured by platinum-catalyzed hydrosilylation reactions. have. Platinum catalysts are microencapsulated with one or two layers of thermoplastic organic polymers. The diameter of the microencapsulated catalyst particles is 100 microns or less.

Disadvantages of the manufacturing methods described in Lee et al. And related U.S. Pat.No. 4,766,176 (patented on Aug. 23, 1988) and U.S. Pat. It is a fact that the curable composition containing the microcapsules cannot produce microcapsules of a size small enough to be optically clear. Curable compositions containing these microcapsules are translucent or opaque.

US patent application Ser. No. 07 / 431,352 (filed Nov. 3, 1989, assigned to the applicant of the present application) relates to thermoset silicone compositions useful for use as release coatings. The composition comprises 1) an organosiloxane compound containing a large number of silicon-bonded hydroxyl groups and / or alkenyl radicals, 2) an organohydrogensiloxane containing at least two silicon-bonded hydrogen atoms per molecule, and 3) promoting curing of the composition. A sufficient amount of platinum group metal-containing catalyst and 4) a platinum catalyst inhibitor which is insufficient to inhibit the reaction at high temperature but sufficient to delay the curing reaction at room temperature. The composition typically takes the form of a coating bath. A continuous length of paper or other material to be coated was drawn from the feed roll, passed through the coating bath and first cured before winding onto the take-up roll.

The inventive component of the composition is invalid for extending the shelf life of the curing composition but when used in combination with a platinum inhibitor the effectiveness of the composition at room temperature without substantially extending the time required to cure the composition at typical curing temperatures of 70 to 120 ° C. It is a Beth period extender to extend the period.

Useful bath extenders are defined by the concept of Hansen partial solubility parameters for hydrogen bonding. This variable is at least 8.0 as the useful bath extender and is preferably in the range of 13 to 48. Preferred bath extenders are organic compounds containing one or more primary and secondary alcohol hydroxy groups, carboxylic acids, cyclic ethers and water. Primary and secondary alcohols are particularly preferred bath extenders. A bath duration of at least 168 hours is known for the combination of diethylfumarate as catalyst inhibitor and benzyl alcohol as bath extender.

We have modified the composition described in Application Serial No. 07 / 431,352 above by replacing the hydroxy-substituted ester bath extender of polymerizable ethylenically unsaturated acids. If the ester is polymerized continuously, the resulting composition results in a surprisingly long term storage stability increase over the compositions containing bath extenders described in the patent application. Examination of the composition by electron microscopy revealed a platinum metal catalyst in the form of an independent microcapsule having a diameter of 3 microns or less.

The present inventors have found that the method used to extend the shelf life of curable organosiloxane compositions containing platinum metal-containing catalysts in the presence of metal-containing catalysts complexed with ethylene or acetylenically unsaturated organic compounds. It is thought that it can be used in other one-part organosiloxane compositions in which is accelerated.

One object of the present invention is to provide a novel type of microencapsulated platinum group metal-containing curing catalyst that does not degrade the curing rate or optical transparency at high temperatures of the curable organosiloxane composition containing the catalyst.

A second object of the present invention is to provide a process for preparing microencapsulated catalysts containing other metal compounds and platinum group compounds of the curing catalyst effective for organosiloxane modifiers.

Another object is to provide an optically clear, one-part storage stable organosiloxane composition containing the microencapsulated curing catalyst of the present invention.

The present invention provides microencapsulated liquid or soluble hardening catalyst for one-part thermoset organosiloxane compositions. Compositions containing preferred platinum group metal catalysts are optically transparent as well as exhibiting long term storage stability as well as the absence of opaque additives. At least some of these microcapsules are less than 1 micron in diameter and substantially all are less than about 3 microns in diameter.

The microcapsule curing catalyst of the present invention provides for photoinitiation of at least one dissolved hydroxyl-containing ethylenically unsaturated compound in the presence of a liquid or dissolved curing catalyst for the photoinitiator, optical surfactant and organosiloxane composition for the polymerization of the compound. It is prepared by polymerization. The curing catalyst is in the form of a coordination compound with an ethylenic or acetylene unsaturated organic compound and the solvent for the polymerization reaction is a monovalent or polyhydric alcohol having at least two carbon atoms. If the curing catalyst is a compound of a platinum group metal, the coordinating agent preferably comprises at least one known ethylenic or acetylene-based unsaturated inhibitor for platinum-containing hydrosilylation reactions.

The present invention relates to a liquid or gum type curable polyorganosiloxane containing at least two groups selected from the first group of reactors which combine with the second group of reactors present in the curing agent during the curing of the composition; B. The concentration of the curing agent is sufficient to cure the composition in the presence of the curing catalyst and the sum of the average number of first group reactors per molecule of polyorganosiloxane (A) and the average number of second group reactors per molecule of curing agent (B) A curing agent for a composition selected from organosilicon compounds containing at least two second group reactors having 4 or more; And C. an improved catalyst wherein the catalyst is microencapsulated in a matrix or layer of a synthetic organic polymer derived from ethylenically unsaturated organic compounds, and composed of a microencapsulated liquid or dissolved curing catalyst in an amount sufficient to promote curing of the composition at high temperatures. One-part, storage stable, thermoset organosiloxane compositions are provided.

Improvements include (1) (a) hydroxyl-containing ethylenically unsaturated organic compounds, (b) an amount of photoinitiator sufficient to initiate polymerization of unsaturated organic compounds in the presence of ultraviolet light to form thermoplastic polymers, (c) The solvent of the solution is a monovalent or polyhydric alcohol and the metal is selected from the group consisting of platinum group metals and titanium, (i) ethylenic or acetylenically unsaturated organic compounds selected from the group consisting of (ii) carboxyl groups of carboxylic acids, Forming a first solution consisting of a curing catalyst in the form of a coordination complex of residues and metals, and (2) irradiating the first solution with an ultraviolet light sufficient to polymerize the hydroxyl-containing ethylenically unsaturated compound Phases of polymers formed from the compounds, most of the particles having a diameter of less than 1 micron and substantially no more than 3 microns in diameter. The presence of a microencapsulated curing catalyst in the form of a liquid composition consisting of forming the microencapsulated curing catalyst as dispersed particles in a second solution consisting of a pre-solvent.

A feature of preferred curable organosiloxane compositions containing microcapsule compounds of platinum group metals as curing catalysts is their optical transparency. Transparency is believed to be due to the low concentration of microcapsules and at least a substantial portion, typically at least 50% of the sub-micron diameter of the microcapsules, required to achieve rapid cure rates at high temperatures. Practically the microcapsules are never more than 3 microns in diameter.

The present invention also provides a method for producing a microencapsulated curing catalyst of this size range.

Since the catalyst is effectively isolated from the other components of the curing composition until the composition is heated to the softening or melting temperature of the thermoplastic polymer portion of the microcapsules, the composition is stable at room temperature for a long time, typically months or more, and the thermoplastic microcapsules It hardens rapidly at temperatures above its softening or melting point.

The present process for preparing microencapsulated curing catalysts is not limited but is particularly suitable for microencapsulated liquids or dissolved coordination compounds (hereinafter referred to as platinum-containing hydrosilylation catalysts) in platinum group metals. These compounds are effective as curing catalysts for organosiloxane compositions that are curable by reaction between hydroxyl groups and silicon-bonded hydrogen atoms or by hydrosilylation reactions.

The curable organosiloxane composition comprises at least one polyorganosiloxane containing two or more hydroxyl groups or unsaturated terminal hydrocarbon radicals per molecule as the first group of reactors and two or more silicone bonds as the second group of reactors. The polyorganosiloxane containing a hydrogen atom is comprised as a hardening | curing agent.

Other curing catalysts and promoters for organosiloxane compositions that can be microencapsulated by the process are, but are not limited to, coordination compounds of titanium with organic chelate reagents such as esters of acetoacetic acid.

Due to the large amounts of titanium and other catalysts typically required to obtain rapid cure of organosiloxane compositions at temperatures above about 70 ° C. relative to the concentration of platinum group metals necessary to obtain significant cure rates, the corresponding concentrations of the microcapsules in the composition are optical It may be above the threshold required for transparency. Thus curable compositions containing microcapsule catalysts other than platinum metal may not exhibit the optical properties of compositions containing these preferred catalysts.

The average diameter of the microcapsules prepared according to the method of the invention is 3 microns or less. The preferred diameter of at least some of the microcapsules is less than 1 micron.

Platinum-containing hydrosilylation catalysts and other types of curing catalysts and accelerators for curable organosiloxane compositions that can be microencapsulated in accordance with the process are suitable for the polymerization of hydroxyl-containing ethylenically unsaturated organic compounds encapsulating the curing catalyst. It should be in the form of a coordination complex that is miscible or dissolved with the monohydric or polyhydric alcohols used as the solvent. It is believed that the curing catalyst should not dissolve or degrade the encapsulated polymer. The curing catalyst should not have a high vapor pressure at a temperature of 25 to about 60 ° C. to avoid premature rupture of the microcapsules during storage. A particularly preferred class of curing catalysts is the coordination complex of titanium and platinum. The coordinating platinum compound is most preferably derived from halogen compounds of platinum group metals such as chloroplatinic acid. Chloroplatinic acid may be given initially in the anhydride form set forth by Speier of US Pat. No. 2,823,218 or as a commercially available hexahydrate. Platinum-containing hydrosilylation catalysts suitable for preparing the microencapsulation catalyst of the present invention include reaction products of chloroplatinic acid with aliphatic unsaturated organosilicon compounds such as sim-divinyltetramethyldisiloxane. These reaction products are presented by Willing in US Pat. No. 3,419,593. Other platinum-containing hydrosilylation catalysts that are believed to be useful in preparing the microcapsule catalysts of the present invention are described in U.S. Pat. And the compounds described in, and the like.

Platinum-containing hydrosilylation catalysts form ethylene or acetylene unsaturated silicones or coordination compounds with organic compounds. These compounds include organosiloxane compounds, such as tetramethyldivinylsiloxane, which are present as coordinating agents in preferred platinum-containing hydrosilylation catalysts, and many inhibitors used to retard catalytic activity at temperatures below about 50 ° C.

When the coordinating agent is a weak or intermediate catalyst inhibitor such as the above ethylenically unsaturated organosilicon compound, the composition for preparing the microencapsulated platinum-containing hydrosilylation catalyst is known to form coordination compounds with the platinum-containing hydrosilylation catalyst. At least one effective inhibitor. Suitable inhibitors include, but are not limited to, acetylene compounds, in particular alcohols such as 2-methyl-3-butyn-2-ol and 1-ethynyl-1-cyclohexanol (described in US Pat. Nos. 3,445,420 and 4,347,346). And esters of ethylenically unsaturated acids such as diethyl fumarate and bis (2-methoxyisopropyl) maleate (described in US Pat. Nos. 4,256,870, 4,476,166 and 4,562,096, etc.). The alcohol portion of these esters preferably has 1 to 4 carbon atoms.

Ethylene-based or acetylene-based unsaturated organic compounds containing one or more polar groups such as carbonyl or hydroxyl are particularly preferred coordination agents for platinum-containing hydrosilylation catalysts.

The concentrations of inhibitors necessary to prepare microencapsulated platinum-containing hydrosilylation catalysts that provide the desired long-term storage stability for certain curable organosiloxane compositions include, but are not limited to, the type and concentration of the catalyst, (A) and ( It depends on many variables such as the type and relative amount of the components referred to as B) and the presence of optional components.

For various uses, the amount of inhibitor should be sufficient to provide about 25 to 500 moles per mole of platinum group metal present in the curable composition. Using the preferred esters of maleic acid or fumaric acid as inhibitors, only about 25 moles of inhibitor per mole of platinum is sufficient to prepare the present microcapsule platinum containing hydrosilylation catalyst.

The microcapsule curing catalyst is prepared by photoinitiated polymerization of (a) a curing catalyst as a dissolved coordination complex and (b) at least one dissolved hydroxyl-containing ethylenically unsaturated organic compound in the presence of a monovalent or polyhydric alcohol as a solvent. .

Suitable solvents for the polymerization of hydroxyl-containing ethylenically unsaturated organic compounds are alcohols having one or two hydroxyl groups and 2 to 10 carbon atoms. Representative alcohols include, but are not limited to, ethanol, propanol isomers, butanol and nusanol as monohydric alcohols, and ethylene glycol and propylene glycol as dihydric alcohols.

Water and methanol are not suitable as solvents for the polymerization of hydroxyl-containing ethylenically unsaturated organic compounds. Polymerizations carried out in these solvents generally form gels which are not liquid dispersions of the desired microencapsulated curing catalyst. The gel may be mechanically ground but the particle size of the resulting microencapsulated curing catalyst is too large to produce an optically clear organosiloxane composition. Hydroxyl-containing ethylenically unsaturated organic compounds (hereinafter referred to as monomers) are a type of polymerisation in the presence of ultraviolet and photoinitiators to form polymers that are insoluble in the liquid polymerization medium. Preferred monomers include (a) vinyl esters of carboxylic acids, such as vinyl acetate, which are at least partially hydrolyzed after polymerization (b) hydroxyl-containing ethylenically unsaturated carboxylic acids (c) esters derived from these carboxylic acids and ( d) esters derived from ethylenically unsaturated carboxylic acids such as acrylic or methacrylic acid and substantially equivalent molar amounts of alcohol having at least two hydroxyl groups per molecule. Monomers selected from the group (d) are preferred and include, but are not limited to, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and the like.

Suitable monomers for use in the present invention may be present in a mixture containing two or more monomers or separately.

The inventors have found that the presence of hydroxyl groups on the monomers is essential for the preparation of the microencapsulated curing catalyst of the present invention.

The concentration of monomers in the polymerization reaction mixture is not critical. The monomer concentration is generally determined according to the desired viscosity of the final composition containing the microencapsulated curing catalyst as the dispersed phase. Generally from 1 to about 50% by weight monomer may be present based on the weight of the polymerization mixture. A monomer concentration of 1 to about 20 weight percent is preferred.

Any known photoinitiator can be used to initiate the polymerization of monomers in the presence of ultraviolet light. Useful photoinitiators include, but are not limited to, benzophenone, substituted benzophenone, benzyl, substituted benzyl, acetophenone, substituted acetophenone, and the like. Preferred photoinitiators include 2-ethoxy-2-methylacetophenone, 3-bromoacetophenone, 4-methylbenzophenone and photoinitiators available under the trade names Darocure (R) from Merck Company Inc. and Irgacure (R) from Ciba-Geugy. Etc.

The reaction mixture used to prepare the present microencapsulated curing catalyst optionally contains a surfactant that facilitates the polymerization of hydroxyl-substituted monomers and the formation of microcapsules.

Known anionic, cationic or nonionic surfactants can be used for this purpose as long as they are compatible with the polymerization mixture and do not interfere with the formation of microcapsules. Preferred surfactants are anionic surfactants under the Triton brand name of Rohm Haas Chemical Co.

The microencapsulated curing catalyst of the present invention irradiates a composition containing hydroxyl-containing monomers, a coordination curing catalyst, a photoinitiator and an optional surfactant to ultraviolet light for a time sufficient to polymerize monomers around the micelles of the coordination catalyst. It is formed by.

The product of the UV initiated polymerization is generally a low to mid viscosity liquid containing dispersed microcapsules, in which the curing catalyst is completely covered with the thermoplastic organic polymer layer. The catalyst composition may be diffused throughout the entire microcapsules and may be concentrated on one or more cores.

When it is necessary to prepare microcapsules containing two layers of organic polymers, which is one of the embodiments of the present invention, the product of the initial photopolymerization is combined with the dissolved photopolymerization monomer and the photoinitiator and then for a time sufficient to polymerize with the added monomer. Irradiate UV light. Alternatively, the polymerization can be initiated using other free radical generators such as organic peroxides or azo compounds that do not adversely affect the structure or activity of the microencapsulated curing catalyst.

The inventors have found that the second intermediate layer substantially increases the storage stability of some curable organosiloxane compositions containing the present microencapsulated curing catalyst. If the capsule curing catalyst is one of the preferred platinum-containing hydrosilylation catalysts and the microcapsules contain two layers of polymer, the catalyst inhibitor may be included in the monomer solution used in the second polymer layer.

The monomers used to form the second polymer layer on the microcapsules are not limited to the hydroxyl-containing ethylenically unsaturated compounds to be used in the initial polymerization reaction. Suitable monomers include all ethylenically unsaturated organic compounds and the like polymerized under conditions using a second polymer layer in the microcapsule catalyst.

Preferred monomers for use in forming the second polymer layer in the present microcapsule curing catalyst are, but are not limited to, esters of alcohols having 1 to about 4 carbon atoms and acrylic acid or methacrylic acid. An exemplary type of such ester is methylmethacrylate. Thermoplastic polymers that encapsulate the catalyst must be impermeable and insoluble in the catalyst to achieve long term storage stability. The polymer should also be insoluble in the curable organosiloxane of the present invention. Insolubility and impermeability are considered relative concepts. Just as a very limited amount of material diffuses through a impermeable layer in a given sufficient time, many solids are considered insoluble if dissolved in a very limited amount in the liquid.

As used herein, the concept of insoluble and impermeable is that the amount of capsules dissolved in the catalyst and / or the curable composition and the amount of catalyst that diffuses through the walls of the microcapsules during storage of the curable organosiloxane composition cures the composition. It is meant to be insufficient enough to cause it. In some cases, a slight increase in viscosity is observed during storage.

In order for the present microencapsulation catalyst to work effectively in the curable organosiloxane composition, the organic polymer encapsulating the catalyst must be melted at or slightly below the desired curing temperature of the organosiloxane composition.

The microcapsules are essentially spherical in appearance up to about 3 microns in diameter. In order for the curable composition containing this microcapsule to be reliably optically transparent, the diameter is preferably 3 microns or less.

The inventors have found that encapsulating all of the catalyst in a microcapsule comprising one layer of polymer when the metal part of the coordination curing catalyst exceeds 0.5% by weight of the monomers used to make the microcapsules. The metal portion of the coordination catalyst is preferably about 0.3% by weight or less of the monomer weight. Only some of the initial monomers appear to be used to form microcapsules. The remainder is polymerized to form a liquid carrier in which the microencapsulated curing catalyst is dispersed.

The use of a second polymer layer in the microcapsules reduces the likelihood that the curing catalyst is present on the surface of the microcapsules or in the liquid medium containing the microcapsules. If the second polymer layer is present in the microcapsules, the upper limit of the coordination catalyst that can bind to the monomers used to form the initial microcapsules substantially increases.

From the data of the illustrated examples, the cured compositions with long term storage stability can be prepared using concentrations of the catalyst corresponding to 1% by weight of the metal part of the catalyst based on the weight of the monomers used to prepare the initial microcapsules.

In addition to the microcapsule curing catalysts described previously herein, the curable organosiloxane composition of the present invention is a polyolefin containing a second group of reactors present in the curing agent and at least two first reactors that react during curing of the composition. Representatively an organosiloxane (hereinafter referred to as component (A)). The organic group bonded to the silicon atom of the polyorganosiloxane is a hydrocarbon radical or a substituted hydrocarbon radical whose substituent is at least one halogen atom, particularly preferably chlorine or fluorine.

In one type of curing composition preferred for use with platinum-containing hydrosilylation catalysts, the reactor present in component (A) is an ethylenically unsaturated hydrocarbon radical having 2 to 10 carbon atoms per molecule. Component (B) is a polyorganohydrogensiloxane having at least two silicon-bonded hydrogen atoms per molecule as the second group reactor.

To ensure acceptable levels of physical properties and adequate crosslinking, the sum of the average number of silicon-bonded hydrogen atoms per molecule of polyorganosiloxane and the average number of ethylenically unsaturated hydrocarbon radicals per molecule of polyorganosiloxane is at least four. .

Component (A) of the preferred curable composition may be a polyorganosiloxane curable by platinum-catalyzed hydrosilylation reactions. The viscosity of component (A) varies from a liquid to a high viscosity gum that can flow under pressure.

The silicon-bonded hydrocarbon or substituted hydrocarbon radicals that make up the organic groups bonded to silicon in component (A) contain 1 to 20 or more carbon atoms. Preferred these radicals are lower alkyl, phenyl, or perfluoroalkylethyl radicals such as 3,3,3-trifluoropropyl and the like. This preference is based on the availability of intermediates used to prepare component (A). Most preferably at least some of the repeating units of component (A) contain silicone-bonded methyl groups and the reactive ethylenically unsaturated hydrocarbon radicals of component (A) are unsaturated ends. Most preferred such groups are vinyl, allyl, 5-hexenyl and the like.

The reactor present in component (A) may be present at any position of the molecule. In an embodiment of the preferred component (A), these groups are at least at the terminal position of the molecule in the form of a dimethylvinylsiloxy, methylphenylvinylsiloxy or dimethyl-1-hexenyl group or the like.

When the curable composition is a liquid or paste material, the viscosity of component (A) is preferably 1 to 500 Pa · s. Polymers of this type are known and commercially available. In addition to the diorganosiloxane and terminal triorganosiloxane groups, component (A) contains one or more monoorganosiloxane units per molecule to form branches of the polymer molecule. These types of polymers are described in US Pat. No. 3,284,406 (November 8, 1966, Nelson). On the other hand, component (A) may be a semi-solid substance exhibiting a viscosity of 1000 Pa · s or more at 25 ° C., which is known as a gum in the art. Curable compositions containing polydiorganosiloxanes of this type are generally prepared by mixing the components under high shear using a roll rubber mill or dough-type mixer of two to three. .

It has been found that the microencapsulation catalysts of the present invention do not rupture or disintegrate under the conditions of the preparation of high hardness organosiloxane compositions. The catalyst can thus be mixed in this type of hardening composition according to conventional mixing methods.

In this preferred embodiment of the curable composition, component (A) is cured by hydrosilylation between its ethylenically unsaturated hydrocarbon radical and the silicon-bonded hydrogen atoms of the organohydrogensiloxane of component (B).

In typical compositions one or more polydiorganosiloxanes containing two ethylenically unsaturated hydrocarbon groups are combined with relatively low molecular weight liquid organohydrogensiloxanes containing on average at least three silicon-bonded hydrogen atoms per molecule. The residual organic group bonded to the silicon atom of component (B) is a hydrocarbon or substituted hydrocarbon radical as defined for the organic group of component (A).

Component (B) contains an average of 20 or more silicon atoms from at least 4 per molecule and has a viscosity of 10 Pa · s or more at 25 ° C. Component (B) has a repeating unit of formula HSiO _1.5, RHSiO and / or R ₂ HSiO _0.5 .

The molecules of this component also contain one or more monoorganosiloxanes, diorganosiloxanes, triorganosiloxy and SiO _4/2 units that do not contain silicon-bonded hydrogen atoms. In which R is a monovalent hydrocarbon radical selected from the group as defined above for the hydrocarbon radical of component (A).

On the other hand, component (B) can be a cyclic compound having at least 4 organohydrogensiloxane units of the formula RHSiO or a compound of the formula HR ₂ Si (HR ₂ SiO) aSiR ₂ H (a is at least 1).

Most preferably R is methyl and component (B) is a linear trimethylsiloxy terminated polymethylhydrogensiloxane or dimethylsiloxane / methylhydrogensiloxane copolymer having an average of 5-50 repeat units per molecule (30-100% is methyl Hydrogensiloxane unit). The molecular weights of components (A) and (B) and the number and distribution of silicon-bonded hydrogen atoms and ethylenically unsaturated hydrocarbon radicals in these components determine the position of crosslinks in the cured product and from elasto To mers and gels.

The concentration of crosslinks per unit volume is usually referred to as crosslink density and determines some of the physical properties of the cured elastomer, in particular firmness, tension, elongation, and the like. Specific combinations of polydiorganosiloxanes and curing agents to obtain a combination of desirable physical properties can be determined by routine experimentation in accordance with the teachings of the present invention.

The molar ratio of silicon-bonded hydrogen atoms to vinyl or other ethylenically unsaturated hydrocarbon radicals present in the preferred curable compositions of the present invention is an important factor in determining the properties of the cured elastomer.

Due to the difficulties often encountered in achieving complete bonds between all vinyl or other ethylenically unsaturated hydrocarbon radicals and all silicon-bonded hydrogen atoms present in the reaction mixture, there is a stoichiometric excess of any such species in the curable composition. It is preferable to contain. It has been found that the proportion of silicon-bonded hydrogen atoms of 1.0 to 1.6 per vinyl or other ethylenically unsaturated hydrocarbon radical represents the most desirable combination of properties.

Preferred proportions for the particular composition are determined, at least in part, by the average molecular weight of component (A) and the type of curing agent.

The second type of curable composition is one that cures in the presence of moisture. In this type of composition, component (A) is a silanol-containing polyorganosiloxane, most preferably a substantially linear polydiorganosiloxane, wherein the silanol group is located at the terminal of the molecule. Component (B), which is a curing agent, is an organosilicon compound, typically silane, having at least three silicon-bonded alkoxy groups having 1 to 4 carbon atoms. The curing catalyst for this type of hydrolyzable composition which can be microencapsulated in accordance with the present invention is a coordination compound of the chelate titanium compound described herein. As described earlier herein, due to the high concentration of titanium-containing catalysts required over preferred platinum-containing hydrosilylation catalysts, the curable compositions containing microencapsulated titanium catalysts may be optically opaque.

The hardness of the compositions of the present invention varies from flowing liquids to high hardness gums that can only flow under semisolid pastes and high shear.

In addition to the above components, the present composition may include, but is not limited to, other additives such as reinforcing and non-reinforcing fillers, treatment agents for these fillers, pigments, preparation aids, stabilizers and flame retardants. Some of these additives appear to be able to degrade the optical clarity of curable and cured organosiloxane compositions containing preferred platinum-containing hydrosilylation catalysts.

The amount of microencapsulated curing catalyst present in the curable composition of the present invention is generally not limited as long as there is an amount sufficient to promote the reaction between component (A) and component (B).

Because of the small particle size of the microencapsulated curing catalyst, it is possible to obtain a uniform curing composition using a catalyst concentration equivalent to 1 part by weight or less of the coordinating platinum group metal per million of the curable composition.

Through the following examples, specific examples of the curing catalyst of the microcapsules of the present invention, one-part storage stability curable organosiloxane composition containing the microencapsulated curing catalyst and a method of preparing these catalysts will be described in detail. The present embodiments in no way limit the scope of the invention as defined in the appended claims. Unless otherwise noted, all parts and percentages are by weight and all viscosity is measured at 25 ° C.

General Process (Examples 1-7)

A. Microencapsulation Process

1. Homopolymer layer

The composition used to prepare the microencapsulation catalyst contains the following components:

100 parts by weight of isopropane; 0 to 1 part surfactant (Triton X-100, purchased from Rohm Hass); 10 to 25 parts of 2-hydroxyethyl acrylate (HEA) or 2-hydroxyethyl methacrylate (HEMA); 0.1 to 0.2 parts of 2-hydroxy-2-methyl-1-phenylpropan-1-one; 0 to 2.5 parts of one of diethyl fumarate (DEF), bis (2-methoxyisopropylmaleate; MAL), 1-ethynyl-cyclohexanol (ETCH) as a platinum catalyst inhibitor; And 2,800 to 11,000 parts per million parts of platinum catalyst containing 4.2 weight percent platinum and 95.8 weight percent divinyltetramethyldisiloxane.

The composition was placed in a quartz tube equipped with a nitrogen injection and a mechanically operated stirrer. The contents of the tube were exposed to light for 1-2 hours at a distance of 1 to 2 inches from a 150 watt medium pressure mercury vapor lamp.

After the exposure time, the obtained liquid mixture was heated at a temperature of 45 ° C. under reduced pressure to remove isopropanol. Examination of the final product using an electron microscope revealed a double distribution of particle diameter consisting of a first portion in the range of 2 to 3 microns and a second portion of less than 1 micron.

2. Formation of Second Polymer Layer

The first part of the preparation is identical to that described for microcapsules containing a single layer of polymer. The resulting dispersion of microcapsules was placed in a quartz tube with the same photoinitiators and inhibitors, 2-hydroxyethylacrylate (HEA) or methylmethacrylate (MMA), used to prepare single layer microcapsules. The amount of these components is specified in the following examples. The required amount of isopropanol was added to compensate for the volume reduction during the manufacturing process. The resulting mixture was exposed to ultraviolet light to polymerize monomers to form a second polymer layer in the microcapsules. The added isopropanol was removed by heating under reduced pressure.

B. Evaluation of Microencapsulated Catalyst

The encapsulated platinum catalyst was prepared from 1) dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of about 400 Pa.s and 2) trimethylsiloxy-terminated copolymer containing an average of 3 dimethylsiloxane and 5 methylhydrogensiloxane units per molecule. Combined with a homogeneous mixture of. The concentration of microencapsulation catalyst in the curable composition was generally equivalent to 1 ppm of platinum, based on the total weight of the curable composition. The curable composition was a colorless transparent liquid. The pot-life of the curable composition can be assessed by measuring the time interval during flow when the composition is stored in a closed container at room temperature or 60 ° C.

The curing time of the composition was measured by placing 0.5 g of the composition in a glass bottle into an oven at 150 ° C. and observing the minimum time interval required for the liquid composition to be converted into an elastomer.

Example 1

In this example, (a) a composition containing the same components without irradiating UV rays to augment the microencapsulated catalyst composition of the invention and (b) monomers without an optional inhibitor and (c) a composition containing no monomers The storage stability of was compared. All compositions contained 100 parts of isopropyl alcohol and a catalyst concentration of 2800 ppm based on the monomer weight and 1 ppm by weight of the curable composition.

HEA = 2-hydroxyethyl acrylate

Irradiation time = exposure time to UV rays

Even if no platinum catalyst inhibitor is added, the storage stability of the curable composition is almost nine times higher than that observed for compositions containing the same components without the polymerization to form microencapsulation catalysts. The curing times of the two compositions are equivalent.

Example 2

This example reveals that ethanol can be used as a solvent for the preparation of microencapsulated platinum-containing hydrosilylation catalysts. Both compositions contained an amount of catalyst equivalent to 100 parts alcohol, 10 parts 2-hydroxyethylacrylate, 2800 ppm platinum based on the monomer weight and 1 ppm platinum based on the total weight of the curable composition. The light irradiation time was 70 minutes.

Example 3

This example demonstrates an improvement in the storage stability of the curable composition achieved when a conventional platinum catalyst inhibitor is present in the composition.

All compositions contain 100 parts of isopropane as a solvent for the polymerization, 10 parts of 2-hydroxyethylacrylate and 1 part of inhibitor as monomers.

The composition containing diethylfumarate (DEF) as an inhibitor also contains 1 part of anionic surfactant (Triton X-100).

DEF = diethyl fumarate

MAL = bis (2-methoxyisopropyl) maleate

ETCH = 1-ethynyl-1-cyclohexanol

* = Platinum content was 1200 ppm based on monomer.

** = platinum content was 2800 ppm based on monomer.

a = The composition did not harden at the end of this time interval.

Example 4

This example reveals the use of 2-hydroxyethyl methacrylate as a monomer to prepare the microencapsulation catalyst.

Each composition contains 10 parts of monomer, 2800 ppm of platinum in the monomer and 1 ppm of curable composition, and 1 part of diethylfumarate as catalyst inhibitor. The solvent for the light irradiation composition was isopropanol.

a = sample did not harden at the end of this time interval.

Example 5

This example reveals the presence of an upper limit of platinum concentration of about 5000 ppm (0.5% by weight) relative to monomers for storage stable curable compositions containing microcapsules of single layer polymer.

Each composition contains 1 part diethylfumarate as catalyst inhibitor and 10 parts 2-hydroxyethylacrylate as monomer and the curable composition contains 1 ppm platinum.

* = Based on monomer

** = monomer does not polymerize

If the metal portion concentration of the curing catalyst exceeds 0.5% of the monomer weight, it appears that not all of the catalyst is microencapsulated in the polymer layer. When the platinum concentration was 1% of the monomer weight, the pot period was worse than the control that did not polymerize to form the microencapsulation catalyst.

Example 6

This example illustrates the process for preparing a microencapsulated catalyst having two polymer layers and the improved storage stability achieved using this catalyst.

The microencapsulation catalyst was prepared according to step 1 or 2 of the general process described herein using 100 parts of isopropane, 10 parts of 2-hydroxyethylacrylate and 1 part of diethylfumarate in the initial polymerization mixture.

Ten parts of 2-hydroxyethylacrylate were further added for use in the second polymer layer.

The catalyst concentration in the initial polymerization reaction corresponds to 1 weight percent platinum based on the monomers and the catalyst concentration of the curable composition corresponds to 1 ppm platinum. One of the two compositions used as a control did not contain isopropanol and contained 10 parts 2-hydroxyethyl acrylate, 1 part diethylfumarate and 1 weight percent platinum and 1 ppm curable composition based on monomers. Contains the catalyst amount of the initial mixture corresponding to the concentration. The concentration of catalyst in the second comparative composition corresponds to 0.52 weight percent platinum based on the monomer and the curable composition contains 1 ppm platinum.

The initial composition contained 10 parts of 2-hydroxyethyl acrylate and 0.5 part of diethyl fumarate.

* = Comparative composition, contains 1% platinum based on monomer

** = Comparative composition, contains 0.5% platinum based on monomer

Example 7

In this example, the microencapsulation catalyst was prepared using 1-ethynyl-1-cyclohexanol as platinum catalyst inhibitor and methylmethacrylate instead of 2-hydroxyethylacrylate as monomer for the second polymerization step. The two-step polymerization preparation method is illustrated. The initiation polymerization mixture for all samples corresponds to 100 parts of isopropane, 10 parts of 2-hydroxyethyl acrylate, 1 part of 1-ethyl-1-cyclohexanol as platinum catalyst inhibitor and 0.48% by weight based on monomer It contains an amount of catalyst. No inhibitor was added in the second polymerization step. The irradiation time for all polymerizations was 100 minutes and all curable compositions contained 1 ppm of curing catalyst based on platinum.

* = The monomer for the second polymerization was 2-hydroxyethylacrylate.

** = The monomer for the second polymerization was methyl methacrylate.

a = sample was not cured at the end of time interval.

NE = Not rated.

All curable or curable compositions described in the first through seventh examples were optically clear.

Example 8

This example illustrates the performance of a titanium catalyst encapsulated in accordance with the present method.

The catalyst used was E.I. Chelate titanium compound (T1) of Tyzor (R) DC and non-chelate compound of Tyzor (R) available from DuPont de Nemours and Co. Chelate compound (T2) was prepared by combining 1 part of non-chelate compound and 2 parts of 2-hydroxyethylacrylate and leaving the resulting mixture at room temperature for about 1 hour.

0.18 parts of titanium compound (T1 or T2), 100 parts of isopropanol, 10 parts of 2-hydroxyethyl acrylate and 0.2 parts of 2-hydroxy-2-methyl-1-phenylpropan-1-one Both chelate titanium compounds were encapsulated by binding in a quartz tube equipped. The contents of the tube were exposed to light for about 70 minutes, 1 to 2 inches away from a 150 watt medium pressure mercury vapor lamp. After the exposure time had elapsed, the resulting solution was heated at a temperature of 45 ° C. under reduced pressure to remove isopropanol. As a result of electron microscopy, the diameter of the resulting microencapsulated catalyst particles was found to be 1 to 2 microns.

The amount of the encapsulation catalyst specified in the table below was combined with 100 parts of silanol-terminated polydimethylsiloxane containing an average of 80 units of dimethylsiloxane and 4 parts of n-propyl orthosilicate per molecule to prepare a curable composition.

The time required to form the resulting composition to cure at room temperature, 60 and 150 ° C. is shown in the table below.

a = part based on microcapsules

b = sample does not harden at the end of the time interval

NE = Not rated.

Claims (4)

(1) (a) a hydroxyl-containing ethylenically unsaturated organic compound, (b) an amount of photoinitiator sufficient to initiate polymerization of said compound in the presence of ultraviolet light to form a thermoplastic polymer, (c) (i) ethylene-based Or (ii) forming a first solution comprising a residue after removal of a hydrogen atom from a carboxyl group of a carboxylic acid or an acetylene-based unsaturated organic compound or the curing catalyst in the form of a coordination salt of a metal, wherein the solvent portion of the solution is 1 Is a valent or polyhydric alcohol and the metal is selected from the group consisting of platinum group metals and titanium; (2) irradiating the first solution with an ultraviolet ray in an amount sufficient to polymerize the hydroxyl-containing ethylenically unsaturated compound to disperse the particles as a dispersion of particles in a second solution composed of the polymer portion formed from the compound and the solvent. Forming an encapsulated curing catalyst, wherein a majority of the particles are less than 1 micron in diameter and no particles substantially exceed 3 microns in diameter; Method for producing a microencapsulated curing catalyst to produce an optically transparent curable organosiloxane composition, characterized in that consisting of. The method of claim 1, wherein the particles consist of a single polymer layer formed from the hydroxyl-containing organic compound and the catalyst and the maximum of the catalyst present in the first solution based on the weight of the hydroxyl-containing organic compound. The concentration corresponds to 0.5% by weight of the metal. The photoinitiator of claim 2, wherein (1) (a) consists of an amount of photoinitiator sufficient to initiate polymerization of said compound in the presence of at least one ethylenically unsaturated organic compound and (b) ultraviolet light to form a thermoplastic polymer. Combining the mixture with the second solution containing the particles, and (2) irradiating the second solution with an ultraviolet ray in an amount sufficient to polymerize the ethylenically unsaturated organic compound to form a polymer outer layer on the particles. And coating said particles with a second polymer layer. 4. The curing catalyst according to claim 3, wherein the curing catalyst is a coordination compound of a metal selected from the platinum group of the periodic table and the hydroxyl-containing organic compound is a hydrolyzed vinyl ester of a carboxylic acid, a hydroxyl-containing ethylenically unsaturated carboxylic acid. Selected from the group consisting of esters derived from ethylenically unsaturated carboxylic acids and esters derived from ethylenically unsaturated carboxylic acids and substantially equivalent molar amounts of alcohol containing at least two hydroxyl groups per molecule, said solvent Is a monohydric alcohol having 2 to 10 carbon atoms, wherein the hydroxyl-containing organic compound constitutes 1 to 50% of the weight of the first solution and the composition is optically transparent.