GB1598579A - (meth)acrylic resin plastisol or organosol dispersions - Google Patents

Description

(54) (METH)ACRYLIC RESIN PLASTISOL OR ORGANOSOL DISPERSIONS (71) We, E.I. DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America located at Wilmington, State of Delaware, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to nonaqueous (meth)acrylic resin dispersions and particularly to (meth)acrylic resin plastisols and organosols. This invention also relates to (meth)acrylic resin dispersions containing photopolymerizable ethylenically unsaturated compounds.

Furthermore, this invention also relates to the preparation of (meth)methyl methacrylate polymer powders.

Certain polymeric resin dispersions referred to as plastisols are fluid mixtures, ranging in viscosity from pourable liquids to heavy pastes, obtained by dispersing polymeric resin particles in nonvolatile, nonaqueous liquid plasticizers, i.e. materials which are compatible with the polymer or resin and increase its workability and flexibility but are not solvents for the polymeric resin under ordinary conditions of storage. When the plastisol has been formed into a desired shape, e.g. by molding or coating, it can be heated to coalesce the polymeric resin particles and the nonvolatile liquid constitutent, thereby forming a homogeneous mass. Volatile diluents can be added to plastisol dispersions to modify their viscosity and to achieve handling characteristics in coating or other forming operaions.

When the dispersion contains no more than 10% volatile diluent, it is still regarded as a plastisol; when the volatile diluent content exceeds 10%, however, the dispersion is regarded as an "organosol", H.A. Sarvetnick, "Plastisols and Organosols", Van Nostrand Reinhold Company, New York (1972), page 201.

Theoretically, by appropriate choice of ingredients, any polymeric resin can be made into a plastisol. In practice, however, both the commercial use and the technical literature have focused almost exclusively on the use of polyvinyl chloride in forming plastisols, to the extent that "plastisol" is cross-referenced to "polyvinyl chloride" in Chemical Abstracts and in many textbooks plastisols are described as suspensions of polyvinyl chloride resin.

This pre-eminence of polyvinyl chloride in the practical and technical plastisol art results from the fact that many polymers with otherwise highly useful and desirable characteristics can be dispersed in suitable plasticizers only with great difficulty to give dispersions that have impractically high initial viscosities or very short storage life or both. Among these other desirable materials are various polymers and copolymers of methyl methacrylate, which are attractive for a wide variety of uses because of their clarity, toughness, durability, availability, relatively low cost, and ease of forming into desired final products by a number of methods. Despite their many desirable attributes, these polymers and copolymers have found no practical application in the plastisol and organosol arts because it has not been known heretofore how to prepare compositions with suitably low and stable viscosities.

Polyvinyl chloride plastisols are known wherein the polyvinyl chloride is copolymerized with other monomers, including acrylic monomers, that constitute a minority ( < 35% by weight) of the polymer composition. In U.S. Patent 2,618,621 there are disclosed polyvinyl chloride plastisols wherein part of the plasticizer content is replaced with an acrylic monomer, which is then conventionally thermally polymerized at the temperature encountered in the step of coalescing the polyvinylchloride resin. French Patent 73.06503 discloses plastisols prepared from a variety of polymers, primarily of the styrene family, with the requirements that the polymers be multiple phase and that they be dispersed in polar plasticizers.

It has now been found possible to prepare plastisols based on (meth)acrylic polymers that are amenable to a variety of forming techniques with all of the economic, ecological, health and safety advantages attendant on solvent-free operation. The (meth)acrylic resin compositions may be either plastisols or organosols, depending on the amount of volatile diluent included, if any.

It has also now been found that plastisols and organosols with very acceptable rheological properties can be prepared from methyl methacrylate have polymer and copolymer powders that have been (a) made by stepwise emulsion polymerization in aqueous media in the absence of emulsifiers and surfactants and in such a manner that most of the monomer added at each step is consumed before the addition of the succeeding portion, and (b) isolated by evaporation of the latex at a temperature that is at least 30"C., preferably 40-50"C., below the glass transition temperature of the polymer. Particularly advantageous is the use of a stepwise polymerization procedure that entails the presence of "seed" polymer in the aqueous emulsion.

Emulsion polymerization, including stepwise and "seed" polymerization, of methyl methacrylate homo-polymers and copolymers in aqueous media with the help of emulsifiers and surfactants is known. It is also known to use emulsifiers and surfactants when making polyvinyl chloride powders for use in plastisols. In the known plastisol art, based on polyvinyl chloride, it is common practice to dry the polymer powder at a temperature sufficiently high to produce a thin surface skin of fused resin, i.e. at a temperature higher than the glass transition temperature of the polymer, e.g. C.E. Schildknecht, "Polymer Processes", High Polymers, Volume X, Interscience Publishers, Inc., New York (1956), page 558. A two-stage drying procedure for polyvinyl chloride is known, wherein 88-97% of the water is removed in a first step at a temperature higher than the glass transition temperature of the polymer and the remaining water is removed in a second step simultaneously with grinding at a temperature below the glass transition temperature. In contrast to, and simplification of, these prior art practices, the improved process of the present invention omits emulsifiers and surfactants previously thought to be required and accomplishes the drying in a single step at a temperature substantially below the glass transition temperature of the methyl methacrylate homo-polymer or co-polymer.

In accordance with this invention, thermally coalescible (meth)acrylic resin plastisol or organosol dispersions are prepared which comprise particles of a single-phase, surfactantfree, (meth)acrylic homo-polymer or random copolymer, containing at least 60% by weight of (meth)acrylic units, the homo-polymer or copolymer being dispersed in a surfactant-free medium that comprises a compatible liquid plasticizer that is nonvolatile at room temperature and is not a monomer that has the same chemical structure as a monomer of the homo-polymer or copolymer.

Also in accordance with this invention, in an emulsion polymerization process for the preparation of methyl methacrylate homo-polymers and copolymers containing at least 60% by weight of methyl methacrylate units, which comprises (a) adding stepwise in two or more steps with vigorous mixing in water at least one monomer which is methyl methacrylate, together with a polymerization initiator and chain transfer agent whereby at least most of the monomer added in any given step is consumed before the addition of the next succeeding portion, and (b) isolating the resulting polymer; the stepwise addition in step (a) occurring in the absence of any emulsifier and surfactant, and the isolation step (b) occurring at a temperature that is at least 300C. below the glass transition temperature of the polymer product.

The polymers suitable for use as the resin component in the dispersions of this invention are the single-phase polymers and copolymers of acrylic and methacrylic acids and their esters, i.e. polymers in which only one phase is present in the polymer particles, as evidenced by the fact that films cast from solutions of the polymers are clear. The polymers may be homo-polymers of a given acrylic monomer or they may be copolymers made from two or more acrylic monomers. Also suitable are copolymers made by copolyermizing one or more(meth)acrylic monomers with one or more other ethylenically unsaturated monomers, e.g. vinyl cloride, styrene and the vinyl pyridines, so long as (meth)acrylic units comprise, at least 60%, preferably 80%, by weight of the composition of the final polymer.

Representative materials are the homopolymers and the two- and three-component copolymers of ethyl acrylate, methyl methacrylate, and methacrylic acid. A number of suitable combinations are illustrated in the examples hereinafter. Particularly preferred materials are the methyl methacrylate/methacrylic acid copolymers in the ratios, by weight, of 80/20 to 99/1 and more preferably 90/10 to 98/2.

The polymers may be prepared by any of the methods familiar to polymer chemists, e.g. by emulsion, suspension, or seed polymerization. Several useful techniques are illustrated in the examples that follow. The method of making the polymer will, as recognized have an effect on such characteristics as the inherent viscosity of the polymer and the size of the polymer particles produced. The inherent viscosity iinh) (dt/g) of the polymer is not a critical factor, but for convenient practical operation will preferably be in the range 0.1-1.5 and more preferably 0.2-1.2. When polymer viscosity is high, the composition will be more difficult to coalesce; when polymer viscosity is low, the form stability of the final coalesced product may be affected adversely. Particle size, expressed as mean diameter of the particles, is likewise not critical, but for convenient practical operation will preferably be in the range 0.1-20 m and more preferably 0.5-10 llm. The desirable particle size in a given instance will be governed in part by the characteristics sought in the final product and by the forming procedures to be employed. Particles having a mean diameter < 0.1 llm have a large available surface area making them susceptible to rapid gelation with consequent short storage life, and requiring large amounts of plasticizer that result in low solids/liquid ratios that are inefficient and undesirable for practical operations. Very large particles may limit the minimum thickness of coatings that can be made from dispersions containing them, and may also require fusion or coalescence times that are unattractively long and/or severe. Particle sizes in the desired range in a given instance may be obtained either directly, by choice of an appropriate polymerization procedure, or by grinding or milling large particles to produce smaller ones, in equipment and by techniques known in the art.

To improve the rheology of the dispersions, it may be desirable to pretreat the polymer particles, for example, by exposure to ammonia, as described more fully in the examples hereinafter. The polymer particles must be surfactant-free.

To make the dispersions of this invention, the polymer particles will be dispersed in a medium that comprises a plasticizer for the polymer particles, that is, a surfactant-free compatible liquid that is nonvolatile at room temperature and is not a solvent for the polymer under ordinary storage conditions, but that is capable of interacting physically with the polymer in such a way as to reduce the mutual attractive forces between polymer chains, thereby increasing the workability and flexibility of the polymer. The plasticizer is not a monomer that has the same chemical structure as a monomer of the homo-polymer or copolymer. The plasticizer, which can be non-polymerizable, can be chosen from a large number of substances known to be plasticizers for polymers, e.g. phosphates, phthalates, sebacates, ricinoleates and adipates. Plasticizers are discussed in Sarvetnick, "Plastisols and Organosols", Van Nostrand Reinhold Company, New York, New York (1972), Chapter 3, pp. 33-59. Representative materials include: triallyl, tributyl and tricresyl phosphates; dibutyl, dicapryl, and dioctyl phthalates; and others shown in the examples hereinafter.

Plasticizers that contain ether groups are operable, but generally are not preferred because they appear to have an adverse effect on viscosity stability and shelf life of the polymer dispersions.

In a preferred process of the invention "plastisol-grade" powders of methyl methacrylate polymers, i.e. polymer powders having molecular weights of 20,000 to 325,000, or more with inherent viscosities in the range set forth above and average particles sizes in the ranges set forth above but more preferably 0.3 to 1.0 llm are produced. The methyl methacrylate polymers comprise at least 60% by weight of methyl methacrylate units, more preferably 80% by weight of such units. Acrylic and methacrylic acid and the lower alkyl esters thereof can be used with the methyl methacrylate. Also suitable and preferred are other monomers having lateral carboxylic, sulfonic, or phosphoric acid groups, especially such unsaturated carboxyl-containing monomers as cinnamic, crotonic, sorbic, itaconic, propiolic, maleic and fumaric acids and, where possible, their corresponding half-esters and anhydrides. The selection of monomeric components, and their relative proportions in copolymers, will be determined by such factors as (a) the properties desired in the final product that is to be made from the plastisol or organosol, (b) cost, (c) availability, (d) the ease with which they can be handled in the various process steps to be used, and (e) their compatibility with the plasticizers and other constituents intended to be used.

The preferred emulsion polymerization procedure can be carried out with known apparatus and techniques following basically the principles known to those skilled in the art, i.e. vigorous mixing of monomer, polymerization initiator, and chain transfer agent in water, preferably with the exclusion of oxygen. However, according to the invention, the polymerization step is carried out stepwise by the addition of successive portions of monomer in such manner that most, and preferably substantially all, of the monomer added at a given step is consumed before the addition of the next succeeding portion. Essentially complete consumption of monomer is indicated by the sudden appearance of foam on the surface of the reaction mixture and by cessation of the exothermic reaction. Preferably, but not necessarily, the polymerization is carried out at a ratio of about 17 parts by weight of. monomer to about 83 parts by volume of water. In the stepwise procedure, there should be at least two, and preferably five, separate portions of monomer, i.e. at least one and preferably four successive additions. Preferably, but not necessarily, the portions are of equal amount. When the stepwise procedure is used to make copolymers, each portion will preferably, but not necessarily, contain the comonomers in the same ratio; this ratio will be the ratio desired in the final copolymer product.

The polymerization initiator will be chosen from those known in the art as suitable for the monomers being used, and will be employed in the amounts known in the art. Since a large excess of initiator in the early stages may result in undesirably low molecular weights, it will generally be preferable to have only part of the total required initiator in the starting mixture, and to add the remainder portionwise as part of each successive addition of monomer. Likewise, the chain transfer agent will be selected from those known in the art as suitable for the monomers being used, and will be used in the amounts known in the art. A preferred group of chain transfer agents are alkyl mercaptans of at least 10 carbon atoms and particularly preferred is dodecyl mercaptan.

It is particularly preferred that the stepwise polymerization process be a "seed" polymerization process, wherein particles of previously prepared polymer are included in the starting mixture to serve as loci for the growth of new polymer particles. Such "seed" polymer should be included only in the first step and not in the successive additions. The amount of seed to be used may be in the range 0.5-10%, with an optimum at about 2%, by weight of the total amount of final polymer expected to be produced. The seed polymer may have the same composition as that of the final polymer to be made, or it may have a diffent composition provided that it is derived from related monomeric species, e.g. a methyl methacrylate homopolymer can be used as seed for the production of methyl methacrylate/methacrylic acid copolymer. The requirements to be met are that the monomer must be able to dissolve in the seed and the resultant copolymers must be compatible. It is also generally preferred that the seed polymer used be a "first generation" polymer, i.e., it should not itself be the product of a previous seed polymerization. Seeded polymerizations generally give bimodal distributions of particle size that lead to the most desirable plastisol rheology.

When the emulsion polymerization of methyl methacrylate polymers is carried out in stepwise fashion in the manner just described, it has been found that it is not only possible, but, in fact, suprisingly desirable to omit the emulsifiers or surfactants that have been considered essential in the prior art. As will be seen in greater detail in the examples hereinafter, although polymerization can be conducted with apparent success in aqueous media containing emulsifiers and surfactants, the resulting polymer powders do not disperse as readily in plasticizers as do polymer powders made without emulsifiers and surfactants, and the resulting plastisols are frequently difficult to filter and to coat.

Consequently it is also a feature of the process of the invention that the emulsion polymerization is conducted without the heretofore conventional emulsifiers and surfactants.

Upon completion of polymerization, according to the invention, the polymer is isolated directly, i.e. without filtration, by evaporation of the latex. This step can be carried out at room temperature, but is advantageously and preferably conducted at elevated temperature, provided that the temperature is at least 300C., and preferably is 40-50"C., below the glass transition temperature of the polymer. The rate of evaporation can be accelerated by stirring the latex as it dries, and by carrying out the evaporation, with or without stirring, in the presence of a moving stream of gas, especially an inert gas, e.g. nitrogen. Spray-drying is a particularly convenient and effective technique for isolating the polymer powder.

The polymer particles produced according to the process of this invention can be used to make thermally coalescible plastisols and organosols by dispersing them in a medium that comprises a plasticizer as described above for the polymer particles, that is, a surfactant-free compatible liquid that is nonvolatle at room temperature and is not a solvent for the polymer under ordinary storage conditions, but that is capable of interacting physically with the polymer in such a way as to reduce the mutual attractive forces between polymer chains, thereby increasing the workability and flexibility of the polymer.

The dispersing medium may also contain a volatile component, preferably one that is a solvent or swelling agent for the (meth)acrylic homo-polymer or copolymer component of the dispersion. Incorporation of a volatile component provides an additional means of controlling the viscosity of the dispersion and may frequently facilitate the forming operation, e.g. coating, and improve the rheology of the dispersion. Representative materials are methyl chloroform, chloroform, methylene chloride, and others shown in the examples. Following known practice, dispersions wherein the volatile component comprises up to 10% by weight of the total weight of the dispersion are classified as plastisols, whereas dispersions wherein the volatile component comprises more than 10% by weight of the total weight of the dispersion are classified as organosols.

The loading factor or amount of polymer solids in the liquid dispersing medium will be governed by practical factors relating to operating convenience. For coatability, ease of stirring, and the like, a practical upper limit for the solids/nonvolatile liquid (including photopolymerizable moreover when present) plasticizer ratio is 60/40, and more preferred is about 50/50, for the plastisol dispersions. This consideration is less important for the organosol dispersions, where solids/nonvolatile liquid plasticizer ratios of 80/20 and even 90/10 are feasible, inasmuch as any desired amount of volatile component can be incorporated to give a workable viscosity and then removed by evaporation by heating in the course of arriving at the desired temperature for fusing or coalescing the dispersion. The lower limit depends on properties desired in the final product, generally at least 20/80.

For the photosensitive dispersions, elements and processes that are a particularly preferred embodiment of this invention, the liquid portion of the dispersion will contain or may be nonvolatile photopolymerizable, ethylenically unsaturated compound together with any required or desired photoinitiator component(s), chain transfer agents, hydrogen donors, dyes and other conventional additives, all selected from the many materials known for their respective purposes in the photopolymer art and not forming, per se, a part of the present invention. A wide variety of suitable materials for use as photopolymerizable monomers, photoinitiators, and the other components just mentioned is disclosed in a number of patents dealing with the photopolymer art, conveniently, for example, in U.S.

Patent 3,784,378. Among the preferred photopolymerizable monomers are a number of polyfunctional acrylic and methacrylic monomers, such as tetraethylene glycol diacrylate and dimethacrylate, hexamethylene glycol diacrylate and dimethacrylate, polyethylene oxide diacrylate and dimethacrylate, polyethoxy trimethylolpropane triacrylate, trimethylolpropane triacrylate and trimethacrylate, tetramethylene glycol dimethacrylate, and decamethylene glycol dimethacrylate. Monomers that contain ether groups are operable, but ether-free monomers are preferred for viscosity stability of the plastisol. When a photopolymerizable (meth)acrylic monomer is used, it should not be a monomer of any of the already-polymerized component, i.e. the polymer resin that is dispersed in the liquid component, in order to insure against excessive plasticization and consequent gelation at storage temperatures. Thus, for example, a methyl methacrylate/methacrylic acid polymer can be dispersed in a liquid that contains trimethylolpropane trimethacrylate as one component for the liquid portion but not methyl methacrylate or methacrylic acid. It is important that any photopolymerizable monomer that may be included in the dispersion shall also contain a thermal polymerization inhibitor in an amount adequate to prevent premature polymerization of the monomer in response to the heat that may be encountered in stirring and especially in the coalescence step, thereby insuring that polymerization of the monomer occurs only as a consequence of photoexposure of the completed photosensitive element. The commercially available polymerization-grade monomers conventionaly contain thermal polymerization inhibitors in an amount adequate for this purpose.

It is recognized that nonvolatile plasticizer and photopolymerizable monomeric component can conceivably share plasticizing characteristics for the homo-polymer or copolymer component. In the event a suitable photopolymerizable monomeric compound is present which effectively provides plasticizing action then the monomeric component would comprise at least 10% by weight based on the weight of solid homo-polymer or copolymer particles, the weight percentages being common to both the plasticizer and monomeric component.

Preferably the thermally coalescible (meth)acrylic plastisol or organosol dispersion comprises particles having a mean diameter in the range of 0.1 to 20 Fm of a solid, single-phase, surfactant-free, (meth)acrylic homo-polymer or randem copolymer, contain ing at least 80% by weight of (meth)acrylic units and having an inherent viscosity in the range of 0.1 to 1.5, dispersed in a surfactant-free liquid medium that comprises (a) a compatible liquid plasticizer that is nonvolatile at room temperature and is not a monomer that has the same chemical structure as a monomer of the homo-polymer or copolymer, (b) a nonvolatile photopolymerizable ethylenically unsaturated monomer compound which is not a monomer that has the same chemical structure as a monomer of the homo-polymer or copolymer, and (c) at least one photoinitiator, the solid homo-polymer or copolymer particles being present in an amount of 40 to 90% by weight based on the weight of the solid particles and plasticizer, the plasticizer being present of the solid particles and plasticizer, and the photopolymerizable ethylenically unsaturated monomeric compound being present in an amount of 10 to 60% by weight based on the weight of the solid particles and plasticizer, and the photopolymerizable ethylenically unsaturated monomeric compound being present in an amount of 10 to 90% by weight based on the weight of the solid particles.

The photosensitive plastisols and organosols of the invention may be formed into articles by any of the forming procedures ordinarily used, e.g. by coating, extrusion, molding and dipping. In the preferred embodiment of photosensitive elements, the dispersions of the invention may be cast or extruded to form self-supporting elements, or they may be cast or coated on transparent or nontransparent substrates, e.g. glass, metal sheets and plates, and plastic sheets and films, to form supported photosensitive elements. A number of suitable substrates are disclosed in the examples hereinafter and in the aforementioned U.S. Patent 3,784,378, and are otherwise well known to those familiar with the general art of photosensitive elements. The particular substrates used and the particular structure of photosensitive elements or other objects formed from the dispersions of the invention are not part of the invention.

(Meth)acrylic homo-polymers and copolymers can be dispersed in a variety of compatible liquid media to form fluid plastisols having solids/liquid ratios of 50/50 or greater. Diluents can be added to these dispersions to give organosols that may have substantially higher ratios of solids to liquid, and, for both plastisols and organosols, there may be incorporated a variety of photopolymerizable monomers to permit the formation of photoimageable coatings and the like, useful for a variety of applications, such as relief and planographic printing plates, and photoresists; The preferred process of the present invention provides an improved route to highly desirable methyl methacrylate polymers that are suitable for use in plastisols and organosols for a variety of purposes. The improved process offers wide latitude in choice of starting materials, operating procedures and properties of polymer produced, all with economies of time and effort over prior art methods. Plastisols and organosols based on methyl methacrylate polymers have utility in a broad spectrum of uses, notably those where their clarity and toughness can be used to advantage.

The invention will be illustrated by the examples that follow, wherein parts and percentages are by weight unless otherwise noted. Data on the inherent viscosity of polymers (flint) (de/g) refer to the inherent viscosities of solutions of 0.25 g polymer in 50 ml solvent, either chloroform of 50/50 (by volume) chloroform/methanol, measured at 250C. with a No. 50 Cannon-Fenske viscometer. Particle size values are mean particle diameters determined by inspection of photomicrographs or electron micrographs. Dispersion viscosities, reported in centipoises (cp.), were measured with a Brookfield RVT viscometer with a No. 5 spindle. All monomers used in the examples, either to make the polymers or to serve as photopolymerizable monomers in photosensitive compositions, were commercially available polymerization-grade monomers containing conventional amounts of polymerization inhibitors. Dyes are identified, in some instances, by C.I. name and number as given in "Colour Index", Third Edition, The Society of Dyers and Colourists, Bradford, Yorkshire, England (1971). Values for glass transition temperature (tug) were determined in known manner by differential scanning calorimetry. Performance of photosensitive elements were measured in part by exposing them through a conventional graphic arts resolution guide, i.e. a series of transparent parallel lines of known width in a nontransparent background, and a series of transparent converging lines separated by nontransparent spacing areas of known width, then removing the unpolym methylene chloride, 1,2-dichloroethane, trichloroethylene and 1,2,3-trichloropropane. It was swollen but insoluble in methyl chloroform, perchloroethylene and carbon tetrachloride. It was insoluble and not swollen in hexane.

A plastisol was prepared by mixing equal parts by weight of the powder, prepared as just described, with dibutyl phthalate. The resultant soft translucent paste was spread at 1 mm thickness on glass and coalesced by heating for five minutes at 1200C. to give a clear, dry, soft, pliable film.

Example 2 One part of polymer powder prepared as in Example 1 was mixed with 0.6 part of a commercially available polyoxyethylated long chain alcohol, 0.2 part of a commercially available polyoxyethylene sorbitan monolaurate, and 0.2 part of methylene-bis-(4 cyclohexylisocyanate). The resultant white paste was spread on glass at 1 mm thickness and heated for 5 minutes at 1200C. It coalesced to give a clear, soft film that swelled 12.5% by volume when immersed in 5% aqueous sodium carbonate. The product was suitable for use as a binder for silver halide photographic systems. This example illustrates a crosslinkable formulation.

Examples 3-5 These examples illustrate useful upper limits for loading factor for acrylic resin plastisols, and they also show that, for a given polymer and plasticizer, relatively small changes in the solids/liquid ratio can have a rather large effect on plastisol rheology. In addition, these examples illustrate a decrease in viscosity upon aging that has been found to be characteristic of plastisols made from methyl methacrylate/methacrylic acid (90/10) copolymers. For the dispersions of these examples, a polymer like that of Example 1 was mixed with dibutyl phthalate by conventional high-speed sand-milling procedures. All formulations also contained 0.2% benzotriazole and 0.07% C. I. Solvent Red 109 (C. I. No.

13900/45170). Good filterability was achieved by adding a small amount of methyl chloroform, which was subsequently removed by evacuation after filtration to give substantially solvent-free plastisols. The viscosity of the dispersions was determined at high and low shear by varying the rotational velocity of a No. 5 spindle in a Brookfield RVT viscometer, with the results shown in Table 1. Viscosities were determined for the freshly prepared plastisols and again after aging at room temperature (1 day for Example 3; 3 days for Example 4). The plastisol of Example 5 was very shear-sensitive and set to firm paste at room temperature when stirred rapidly. The plastisols of Examples 3 and 4 were dilatant at high shear and thixotropic at low shear. They were cast and coalesced as described for preceding examples to give clear, pliable films.

TABLE 1 Example 3 4 5 Sol./liq. 58/42 59/41 60/40 Visc., cps. Initial Aged Initial Aged Initial at 50 rpm 6,000 2576 --- - 20 rpm 7,780 2040 16,200 2,000 10 rpm 11,600 2720 20,240 2,400 5 rpm 17,600 3760 30,240 3,440 40,000 1 rpm --- -- 105,000 9,600 Example 6 A methyl methacrylate/methacrylic acid (90/10) copolymer (Tiinh = 0.12) was made by conventional suspension polymerization in aqueous polymethacrylic acid as the suspending agent. The resultant spherical particles were about 100-120 Fm in diameter. The polymer was dry-milled in a ball mill with an equal volume of flint pebbles having a diameter of 12.5 mm for four days. The resultant product was an impalpable powder of 2-20 ,um particle size. The powder was soluble at room temperature in methylene chloride, chloroform, 1,2-dichloroethane, trichloroethylene, 1,1,2-trichloroethane and 1,2,3trichloropropane. It was partly soluble, swollen and agglomerated in methyl chloroform, insoluble but swollen in perchloroethylene and carbon tetrachloride, and insoluble but not swollen in hexane.

An 11.1 g sample of the powder was added to a blend of 8.75 g trimethylolpropane triacrylat, 4.00 g di-2-ethylhexyl phthalate, 1.00 g 2-o-chlorophenyl-4,5-(mmethoxyphenyl)-imidazolyl dimer, 0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0125 g Michler's ketone and 0.0375 g C.I. Solvent Red 109 (C.I. No. 13900/45170). This mixture was stirred for 15 minutes at room temperature to give a fluid plastisol with a Brookfield No. 5 viscosity of 8700 cps. It was spread on 25 iim thick polyethylene terephthalate film with a doctor knife set at 0.1 mm and heated for five minutes at 1200C. The plastisol coalesced to a smooth, clear, continuous film having a thickness of 0.05 mm when cooled.

The film was laminated at 100"C. to a copper-foil-coated phenolic circuit board and exposed through a graphic arts resolution guide a previously described for one minute to radiation from a commercially available pulsed xenon source. The polyethylene terephthalate support was then removed, and the exposed coating was developed by extracting with a solution of 10 g of the monobutyl ether of ethylene glycol plus 1 g of borax in 90 g of water.

The exposed areas had good image retention. Isolated lines having a width of 100 ,um were reproduced, and there was no line plugging at resolutions of 75-100 llm. The board could be clearly and sharply etched with commercial ferric chloride etchant solutions, and stripped with methylene chloride.

The plastisol had good stability; viscosity was 16,000 cps. after standing for one day at room temperature. By contrast, a similar plastisol made with a polyether-based plasticizer, triethylene glycol diacetate, instead of the di-2-ethylhexyl phthalate,had an initial visosity of 13,700 cps. and this increased to > 800,000 cps. after one day at room temperature.

When the unground 100-125 Fm suspension polymer was used to make a similar plastisol, the product could be not spread to a uniform film, even at a knife clearance of 0.15 mm, and thicker coatings could not be uniformly coalesced, even after 20 minutes at 1200C.

Example 7 A commercially available 75-125 ,um suspension-polymerized poly(methyl methacrylate) homopolymer (flint = 0.2) was pebble-milled as described in Example 6 to give 2-20 ,um particles, which were used to make a sand-milled plastisol (solids/liquid = 45/55) with the ingredients described in Example 6, except that the di-2-ethylhexyl phthalate was replaced by tricresyl phosphate/dibutyl phthalate (1/1). An equal volume of 20-30 mesh (-0.55-0.85 mm) sand was added to a premix of the ingredients and the mixture was stirred at 0 C. for 30 minutes with a disc stirrer running at a peripheral speed of 300 m/min. It was then pressure-filtered through a 200-mesh (74 Fm) screen and debubbled by evacuation. The resultant plastisol had a viscosity of 6000 cps. It was spread, coalesced, laminated and exposed as described in Example 6. It was developed for 15 seconds in a spray of methyl chloroform at room temperature. A sharp, clean image was retained. The image was etched and stripped as described in Example 6.

When a conventional, commercially available poly(methyl methacrylate) latex polymer of particle size < 0.1 Fm was isolated by drying at room temperature and comminuted by ball-milling, flowable plastisols could be prepared only at solids/liquid ratios between about 27/73. This demonstrates that acrylic powders of such small particle size are not suitable for the preparation of useful plastisols.

Example 8 To a solution of 0.4 g ammonium persulfate in 200 g water was added 23.4 ml of a solution of 4.0 g of dodecyl mercaptan in 100 g of methyl methacrylate. The suspension was blanketed with nitrogen, stirred vigorously, and heated at 80-85"C. At 30-minute intervals, there was added 20 ml of the methyl methacrylate/dodecyl mercaptan mixture plus 112 ml of a solution of 0.2 g ammonium persulfate in 450 g of water. Thirty minutes after the fourth addition, the reaction was terminated by admitting air and cooling to room temperature.

The product was strained through nainsook fabric and held as a seed latex.

To a solution of 0.4 g of ammonium persulfate in 364 g of water was added 36.2 g of the seed latex described above, 32 ml of a solution of 4.0 g dodecyl mercaptan, and 2.0 g of methacrylic acid in 98 g of methyl methacrylate. The suspension was blanketed with nitrogen, stirred vigorously, and heated at 80-85"C. At 30-minute intervals, there was added 20 ml of the dodecyl mercaptan/methyl methacrylate/methacrylic acid solution plus 25 ml of a solution of 0.2 g of ammonium persulfate in 100 g of water. Thirty minutes after the fourth addition, the reaction was terminated and the resultant latex was strained through glass wool and evaporated at 55-660C. or 60-70"C. under a stream of nitrogen with stirring. The copolymer powder so produced was methyl methacrylate/methacrylic acid (-99/1), Tg = 103 C.

The residue was ground in a mortar and passed through a 40-mesh (~0.38 mm) sieve to give an impalpable powder [inh = 0.15 in methylene chloride/methanol (90/10)] with a glass transition temperature of 1200C. by differential scanning calorimetry. It was soluble in methyl chloroform, swollen but not dissolved by carbon tetrachloride. The residue was used to make an organosol by the procedure of Example 7 in a formulation that comprised 11.1 g of the binder powder, 8.75 g of trimethylolpropane triacrylate, 2.0 g tricresyl phosphate, 1.0 g bis (2-o-chlorophenyl-4,5-diphenylimidazole, 0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C.I. Solvent Red 109, 0.0825 g Michler's ketone and 5 ml chloroform diluent. After sand-milling for 30 minutes at OOC., the mixture was held for 20 hours at 50C., then filtered through nylon flannel at 0 C. to give a nonthixotropic dispersion that was stable at 5"C. and that could be coated, fused, laminated, exposed, developed and stripped like the product of Example 7.

Example 9 To a solution of 0.4 g ammonium persulfate in 400 g of water was added 28.6 ml of a solution of 20 g methacrylic acid plus 1.07 g dodecyl mercaptan in 80 g of methyl methacrylate. The suspension was stirred vigorously under nitrogen and heated at 80-850C.

At 30-minute intervals, there was added 20 ml of the methyl methacrylate/methacrylic acid/dodecyl mercaptan solution plus 25 ml of a solution of 0.2 g ammonium persulfate in 100 ml water. Thirty minutes after the fourth such addition, the reaction was terminated by admitting air and cooling to room temperature. The latex was dried at 55-660C. under a stream of nitrogen with stirring, and the residual powder was ground in a mortar, passed through a 40-mesh (-Q.38 mm) screen and held for 20 hours in an atmosphere of ammonia.

The powder was soluble in the monobutyl ether of ethylene glycol. It was insoluble in methyl chloroform, carbon tetrachloride, chloroform, methylene chloride and perchloroethylene. It was used to make an organosol as described in Example 8.

Example 10 Ground methyl methacrylate/methacrylic acid (90/10) binder powder prepared as described in Example 6 was used to make a plastisol by the procedure of Example 7, using 12.1 g of binder powder, 7.75 g of trimethylolpropane trimethacrylate, 2.0 g tricresyl phosphate, 2.0 g dibutyl phthalate, 1.0 g bis(2-o-chlorophenyl-4,5-diphenyl) imidazole, 0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C.I. Solvent Red 109, and 0.0125 g Michler's ketone. The plastisol was filtered through a 100-mesh (147 ecum) screen and debubbled under vacuum. Viscosity was 28,400 cps. initially and 39,800 cps. After stirring for one day at room temperature. The plastisol was coated on 0.025 mm thick polyethylene terephthalate film under a 0.1 mm clearance knife at 1 m/min. and then passed through a 3.6 m drying oven at 1050C. The 0.05 mm product was clear, smooth and dry. It was used to prepare printed circuit boards by the procedures of Examples 6 and 7.

Examples 11-23 Plastisols were made according to the procedure of Example 6 using the ground methyl methacrylate/methacrylic acid (90/10) powder of Example 6 in a formulation that comprised 44.4% binder powder, 35% monomer, 4% triethylene glycol diacetate, 12% tricresyl phosphate 4% 2-o-chlorophenyl-4,5-(m-methoxyphenyl) imidazolyl dimer, 0.2% leuco crystal violet, 0.2% benzotriazole, and 0.15% C.I. Solvent Red 109. Viscosities and stability varied as shown in Table 2. In general, lower initial viscosities and better stabilties were obtained for monomers that did not contain polyoxyethylene moieties, and for methacrylate as compared with acrylate monomers.

TABLE 2 Viscosity, cps.

Example Monomer Initial After 4 hrs. After 1 day 11 Trimethylolpropane triacrylate 34,000 112,000 > 800,000 12 Trimethylolpropane trimethacrylate 6,200 10,440 35,000 13 Hexamethylene glycol diacrylate 3,400 27,000 Partly set up 14 Hexamethylene glycol dimethacrylate 1,800 15,550 Partly set up 15 Decamethylene glycol dimethacrylate 10,800 72,000 Set up 16 Trimethylene glycol dimethacrylate 13,400 268,000 > 800,000 17 Triethylene glycol diacrylate 15,200 Set up --18 Triethylene glycol dimethacrylate 8,800 Set up --19 Polyethylene glycol diacrylate 16,200 107,000 --20 Polyethylene glycol dimethacrylate 11,700 165,200 Set up 21 Pentaerythritol triacrylate 32,400 118,000 458,000 22 Ethoxylated trimethylolpropane 23,400 Set up --triacrylate 23 Bis(6-methacryloxyhexyl) adipate 17,600 126,000 Set up Example 24 To a solution of 0.4 g ammonium persulfate in 50 g of water was added 20 ml of a solution of 1.09 g dodecyl mercaptan plus 11 g methacrylic acid in 100 g methyl methacrylate. The suspension was stirred vigorously under nitrogen and heated at 80-90"C. At intervals of 10, 15, 25 and 60 minutes there was added 25 ml of the dodecyl mercaptan/methacrylic acid/methyl methacrylate solution plus 112 ml of a solution of 0.20 g ammonium persulfate in 450 g of water. After a further 90 minutes at 88-900C., the latex was vacuum-filtered through fine filter paper, the residual filter cake was twice resuspended in water and refiltered. The final filter cake was air-dried and ground in a mortar to give an impalpable powder of acid number 63 and Tlinb = 0.24 in acetone. The powder was swollen by and partly dissolved in methylene chloride. The powder was used to prepare an organosol by the procedure of Example 7, using 11.1 g of the powder, 8.75 g trimethylolpropane trimethacrylate, 2.0 g tricresyl phosphate, 2.0 g di-2-ethylhexyl phthalate, 1.0 g bis(2-ochlorophenyl-4,5-diphenyl)imidazole, 0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C.I. Solvent Red 109, 0.0125 g Michler's ketone, and 1.5 ml of methylene chloride diluent. The product was pressure-filtered through a 100-mesh (149 iim) screen and evacuated to give a soft, thixotropic plastisol. The plastisol was coated at a thickness of 2.5 mm on polyethylene terephthalate film having a thickness of 0.125 mm and heated for 5 minutes at 1200C. It coalesced to a hard, dry coating that was suitable for use as a photoimageable printing plate.

In contrast, plastisols made from similar powders that were similarly prepared except that as little as 7 x 10-5 g of sodium lauryl sulfate was incorporated in the polymerization medium were lumpy and difficult to disperse and filter.

Example 25 To a solution of 0.6 g ammonium persulfate in 500 g of water was added 19 ml of a solution of 11 g methacrylic acid plus 1.1 g dodecyl mercaptan in 100 g methyl methacrylate.

The suspension was stirred vigorously under nitrogen and heated at 80-85"C. After 12 minutes, when the initial exotherm had subsided, the remainder of the methacrylic acid/dodecyl mercaptan/methyl methacrylate solution was added dropwise over a period of 8 hours. After further heating and stirring for 30 minutes, the resultant latex was evaporated under nitrogen with stirring at 56-650C. The residual powder weighed 100 g and comprised agglomerates of 0.3 Fm spheres. It was comminuted in a mortar, held for 24 hours at room temperature over concentrated aqueous ammonium hydroxide and then dried for 24 hours at room temperature over sodium hydroxide pellets. Weight gain was 1.6%, i.e., 70% of the theoretical amount for complete conversion of all -COOH groups to -COONH4 groups. Predrying of the ammonia-treated powder was found to be necessary for the preparation of plastisols with best filterability and lowest ultimate viscosity. It was also found that, in general, such predrying should be carried out for a period at least as long as was the previous NH40H treatment.

The powder so prepared was used to make an organosol as described in Example 8, with the added precaution that the mixture was protected from ambient humidity by blanketing with dry nitrogen during the 0 C. milling step. This precaution served to improve filterability and reduce ultimate viscosity. After pressure-filtering through nylone flannel, the organosol had a viscosity of 200 cps. (Brookfield, No. 5 spindle, 100 rpm). It was then held under oil-pump vacuum at room temperature. After 20 minutes, the bubbles and diluent had been removed, and the final vacuum was 2 mm Hg. The residual plastisol was dilatant, with Brookfield No. 5 viscosities of 1176 cps. at 100 rpm and 832 cps. at 50 rpm. It was again pressure-filtered through nylon flannel and then coated at a thickness of 0.05 mm on 0.025 mm thich polyethylene terephthalate film and coalesced by passage at 3.6 m/min. through a 3.6 m tunnel at 100"C. The resultant 0.05 mm thick coating was smooth and uniform. The film could be laminated, imaged, developed, etched and stripped as described in Example 6. The plastisol was stable for many months at room temperature without significant increase in viscosity, yet it could be readily coalesced when heated to 100-1200C.

Example 26 A seeded latex polymerization was carried out essentially as described in Example 8, except that the monomer mixture comprised a solution of 25 g ethyl acrylate plus 10 g methacrylic acid in 65 g methyl methacrylate. The resultant latex was dried under nitrogen with stirring at room temperature, mortared, passed through a 40-mesh (~0.38 mm) sieve and held for 18 hours over concentrated aqueous ammonium hydroxide. The powder had a glass transition temperature of 74"C. It was used to prepare an organosol as described in Example 8. The organosol could be coated, coalesced, laminated, imaged, developed and etched as described in Example 6.

Example 27 A solution of 0.2 g ammonium persulfate in 100 g water was stirred under nitrogen and to it was added 29 ml of a solution of 5 g methacrylic acid plus 2 g dodecyl mercaptan in 95 g methyl methacrylate. The suspension was held at 80-90"C. for 30 minutes then at 30-minute intervals there was added 20 ml of the methacrylic acid/dodecyl mercaptan/methyl methacrylate solution plus 80 ml of a solution of 0.1 g ammonim persulfate in 320 ml of water. Thirty minutes after the last addition, the latex was evaporated under nitrogen with stirring at 650C. The resultant solid was mortared, passed through a 40-mesh (~0.38 mm) sieve, held one day over concentrated ammonium hydroxide, then one day over sodium hydroxide pellets.

A mixture of 87.5 g trimethylolpropane trimethacrylate, 20.0 g tricresyl phosphate, 10.0 g bis (2-o-chlorophenyl-4,5-diphenyl) imidazole, 0.5 g leuco crystal violet, 0.5 g benzotriazole, 0.375 g C.I. Solvent Red 109, and 0.125 g Michler's ketone was stirred for about 16 hours at room temperature, then milled for 30 minutes at OOC. under nitrogen with 100 ml of 20-30 mesh (-0.55-0.85 mm) sand, and pressure-filtered through nylon flannel. An 11.9 g sample of this premix was stirred at 0 C. and 11.1 g of the polymer powder was added portionwise. The resultant soft paste was held for 20 hours at room temperature. It became a flowable dispersion with a Brookfield No. 5 viscosity of 15,440 cps. at 20 rpm. An equal volume of 20-30 mesh (-0.55-0.85 mm) sand was added, and the suspension was milled for 30 minutes at OOC. under nitrogen. It was then pressure-filtered through a 325-mesh (44 vim) screen. The filtrate had a Brookfield No. 5 viscosity of 18,200 cps. and remained uncoalesced for many days at room temperature. It was coated, coalesced at 1200C., imaged, developed, etched and stripped as described in Examples 6 and 7.

Example 28 To a solution of 0.2 g ammonium persulfate in 100 g water was added 29 ml of a solution of 5 g methacrylic acid and 2 g dodecyl mercaptan in 95 g methyl methacrylate. The suspension was blanketed with nitrogen. stirred and heated under reflux at 80-90"C. At 30-minute intervals, there was added 20 ml of the methyl methacrylate/methacrylic acid/dodecyl mercaptan solution plus 80 ml of a solution of 0.1 g ammonium persulfate in 320 ml water. Thirty minutes after the fourth such addition, the reaction was terminated by opening to air and cooling to room temperature. A portion of the resultant milky latex was evaporated to dryness. The residue comprised 99% of the theoretical yield for complete polymerization.

A second polymerization was carried out as just described except that the initial charge comprised 0.2 g ammonium persulfate, 79.6 g water, and 20.4 g of the latex of the first polymerization to provide 4 g of polymer seed, i.e., 4% of the weight of the methyl methacrylate/methacrylic acid/dodecyl mercaptan used in the second polymerization.

After the second polymerization was complete, the latex was evaporated to dryness under nitrogen with stirring in a 55"C. water bath. The residue weighed 104 g (98% yield).

It was ground in a mortar and passed through a 3.2 mm mesh sieve. A 33.5 g portion was loaded into a column and anhydrous ammonia gas was passed slowly through the bed of powder for 30 minutes. Weight gain was 2.1%, vs. a theoretical maximum of 1.2% for complete conversion of the available -COOH groups to -COONH4, the excess probably being attributable to adsorption.

A solution of 48 g tricresyl phosphate, 16.0 g benzophenone, 0.8 g Michler's ketone, 0.8 g bis(2-0-chlorophenyl-4,5-diphenyl)imidazole, 0.8 g benzotriazole, 0.4 g tris(4diethylamino-o-tolyl)methane, 0.2 g leuco crystal violet, and 0.28 g C.I. Basic Blue 7 (C.I.

No. 42595) in 120 g trimethylolpropane triacrylate that contained 500 ppm hydroquinone was prepared by stirring for about 16 hours at room temperature. To 11.7 g of this solution there was added portionwise with stirring 12.5 g of the ammonia-treated binder powder.

The suspension was cooled in an ice bath and blanketed with nitrogen, and 20 ml of 20-30 mesh (-0.55-0.85 mm) sand was addedportionwise with disc-stirring at 300 m/min. peripheral speed. After stirring for one hour, the plastisol was separated from the sand by filtration through nylon flannel and was found to have a Brookfield No. 5 viscosity of 820 cps. at 20 rpm initially, 1400 cps. after standing 24 hours at room temperature, and 2460 cps. after further stirring after 24 hours at room temperature. It was used to make photoimaging circuit board resists in the manner described in preceding examples.

Substantially similar results were obtained when the amount of seed polymer was varied between 1% and 5% of the amount of the plastisol-forming powder. Beyond those limits, diluent-free plastisols were much more difficult to filter.

Example 29 A methyl methacrylate/methacrylic acid (90/10) copolymer (inh = 0.12) was made by conventional suspension polymerization in water using poly(methacrylic acid) as the suspending agent. The resultant spherical particles were about 100-125 ijm in diameter. The polymer was dry-milled in a ball mill with an equal volume of flint pebbles having a diameter of -12.5 mm for four days. The product was an impalpable powder of 2-20 ,um particle size. The polymer powder was soluble at room temperature in methylene chloride, chloroform, 1 ,2-dichloroethane, 1,1,2-trichloroethane, and trichloroethylene. It was insoluble but swollen in methyl chloroform, perchloroethylene, and carbon tetrachloride. It was insoluble and not swollen in hexane.

An 11.1 g sample of the polymer powder was added to a prefiltered mixture of 1 g triethylene glycol diacetate, 3 g tricresyl phosphate, 8.75 g hexamethylene glycol dimethacrylate, 1 g bis[2-o-chlorophenyl-4,5-bis(m-methoxyphenyl)]imidazole, 0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C.I. Solvent Red 109 (C.I. No.

13900/45170), and 0.0125 g Michler's ketone. When the plastisol was held at room temperature with intermittent stirring, its viscosity (Brookfield, No. 5) was 864 cps. initially, 1652 cps. after one hour, and 42,240 cps. after one day. By comparison, a control sample of the same composition that was held at room temperature without stirring had a viscosity of 15,550 cps. after four hours, and after one day had set up to a nonfluid gel with a 0.5-cm. thick layer of fluid plastisol on the surface.

Example 30 A solution of 31 g of ethyl acrylate plus 8 g of methacrylic acid in 61 g of methyl methacrylate was added to a solution of 0.6g ammonium persulfate in 500 g water. The suspension was blanketed with nitrogen and stirred vigorously for two hours at 80-850C.

The resultant latex was strained through nainsook fabric and held as "seed polymer latex".

A suspension of 30 g of the seed polymer latex in a solution of 0.6 g ammonium persulfate in 400 g water was blanketed with nitrogen, stirred vigorously, and heated to 400C. To this was added a solution of 7.75 g ethyl acrylate, 2 g methacrylic acid and 0.975 g dodecyl mercaptan in 15.25 g methyl methacrylate. Three more such additions were made at one-hour intervals. Thirty minutes after the final addition, the latex was strained through nainsook fabric and held at room temperature for 10 days. It was then reheated to 40"C. under nitrogen and stirred and to it was added 5 g methacrylic acid, 0.1 g sodium bisulfite, and a solution of 0.1 g ammonium persulfate in 200 g water. After one hour at 400C., the latex was evaporated under nitrogen with stirring at 25-40"C. for two days. The residual solid was ground in a mortar, passed through a 40-mesh (-0.38 mm) screen, and held for 20 hours over concentrated aqueous ammonium hydroxide. Microscopic examination indicated a particle size of 0.5-0.9 Fm.

An 11.1 g sample of the binder powder prepared as just described was added to a mixture of 8.75 g trimethylolpropane trimethacrylate, 2 g tricresyl phosphate, 1 g bis(2-ochlorophenyl-4,5-diphenyl)imidazole, 0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C.I. Solvent Red 109, 0.0125 g Michler's ketone, and 7.5 ml carbon tetrachloride.

An equal volume of 20-30 mesh (-0.55-0.85 mm) sand was added and the mixture was milled for 30 minutes at 0 C. with a disc impeller running at a peripheral speed of 300 mlmin. The resultant organosol remained fluid when held for one day at 5"C., but set up to a firm gel in two hours at room temperature.

Example 31 A methyl methacrylate/methacrylic acid (93/7) copolymer powder was prepared by procedures like those of Example 26, using 93 g methyl methacrylate, 7 g methacrylic acid and 2 g dodecyl mercaptan. The powder was isolated from the latex by drying at 55-660C., ground in a mortar, held for 24 hours over concentrated aqueous ammonium hydroxide, then held for 24 hours over sodium hydroxide pellets.

A mixture of 29 g trimethylolpropane triacrylate, 4.3 g dioctyl phthalate, 4.3 g triethylene glycol diacetate, 4.3 g tricresyl phosphate, 4 g bis(2-o-chlorophenyl-4,5-diphenyl)imidazole, 0.2 g benzotriazole 1 g Michler's ketone, 0.3 g tris?4-diethylamino-o-tolyi)-methane, 0.11 g leuco crystal vio Initial 300 cps.

After 15 min. 344 cps.

After 30 min. 520 cps.

After 1 hour 1052 cps.

After 2.5 hours 3560 cps.

After 5 hours 86,400 cps.

After 6 hours 380,000 cps.

Example 32 To a solution of 0.4 g ammonium persulfate in 50 ml water was added 20 ml of a solution of 1.1 g dodecyl mercaptan plus 11 g methacrylic acid in 100 g methyl methacrylate. The suspension was stirred vigorously under nitrogen and heated to 80-99"C. Further additions of 25 ml of the methyl methacrylate/methacrylic acid/dodecyl mercaptan solution and of 112 ml of a solution of 0.2 g ammonium persulfate in 450 ml of water were made at intervals of 10, 21, 14 and 45 minutes. After a further 90 minutes at 80-99"C., the latex was strained through nainsook fabric and evaporated at 65-950C. for 2.75 hours in air. The residue amounted to 93% of the theoretical yield, and had these properties: acid number = 63.7; T = 1300C., tlinh = 0.37. It was ground in a mortar to an impalpable powder that was stored for about 20 hours in a closed container over aqueous ammonium hydroxide.

An organosol was prepared by mixing 11.1 g of the powder prepared as just described, 8.75 g trimethylol-propane trimethacrylate, 2.0 g tricresyl phosphate, 1.0 g bis(2-ochlorophenyl-4,5-diphenyl)imidazole, 0.05 g leuco crystal violet, 0.05 g benzotriazole, 0.0375 g C.I. Solvent Red 109, 0.0125 g Michler's ketone, 6 ml methylene chloride and 23 ml of 20-30 mesh (-0.55-0.85 mm) sand, and milling for 30 minutes at OOC. with a disc impeller running at a peripheral speed of 1000 ft./min. (-300 m/min.). The organosol was then filtered through a 200-mesh (0.074 mm) screen, coated at 0.004" (0.1 mm) clearance on 0.001"-thick (0.025 mm) polyethylene terephthalate film, and heated for 5 minutes at 1200C. to give a film that was nontacky and resistant to cold flow. The organosol was still fluid after storage for 20 hours at room temperature open to the air.

In contrast, a similar polymerization wherein 0.00007 g sodium lauryl sulfate was incorporated in the reaction medium gave a plastisol that was difficult to disperse and spread. When 0.5 g sodium lauryl sulfate was used, the plastisols were even more difficult to disperse and could not be filtered.

Example 33 A mixture of 61.0 g methyl methacrylate, 31.0 g ethyl acrylate, 8.0 g methacrylic acid and 0.6 g ammonium persulfate in 500 ml water was heated for two hours at 80-85"C. in a one-step preparation of terpolymer of methyl methacrylate/ethyl acrylate/methacrylic acid in the approximate ratios of 61/31/8. The reaction mixture was cooled, strained through nainsook fabric, and held as "seed latex 1".

To a solution of 0.4 g ammonium persulfate in 370 ml water was added 30 ml of "seed latex 1" prepared as just described (equal to 5 g of seed polymer) and 20 ml of a mixture of methyl methacrylate/ethyl acrylate/methacrylic acid monomers in weight ratio 61/31/8. The suspension was stirred vigorously under nitrogen and heated to 80-85"C. At 30-minute intervals there was added 25 ml of a solution of 0.2 g ammonium persulfate in 100 ml water and 20 ml of the 61/31/8 monomer mixture. Thirty minutes after the fourth addition, the reaction mixture was cooled to room temperature, strained through nainsook fabric, and held as "seed latex 2".

To a solution of 0.4 g ammonium persulfate in 380 ml water there was added 11.8 g of "seed latex 2" (equals 2.5 g of seed polymer) and 26.5 ml of a mixture of methyl methacrylate/ethyl acrylate/methacrylic acid monomers in weight ratio 65/25/10. The suspension was stirred vigorously under nitrogen and heated at 80-880C. At 30 minute intervals, there was added 25 ml of a solution of 0.2 g ammonium persulfate in 100 ml water and 20 ml of the 65/25/10 monomer mixture. Thirty minutes after the fourth such addition, the reaction was terminated, and the reaction mixture was cooled, strained through glass wool, and evaporated at room temperature for 5 days under nitrogen with stirring to give 102 g (97% of theoretical yield) of terpolymer powder with Tg = 740C. The powder was ground in a mortar, passed through a 40-mesh (~0.38 mm) screen, stored for 20 hours in a closed container over aqueous ammonium hydroxide, and was readily made ito plastisols and organosols.

A similar copolymer that was isolated by drying the latex at 1000C. coagulated to a hard lump that could not be comminuted. A similar copolymer that was isolated by drying the latex at 55-60"C. coalesced and was very difficult to comminute and gave plastisols that were difficult to mill and filter. Thus, while it is possible to isolate plastisol-grade powders at temperatures as high as 14"C. below the glass transition temperature, it is preferable to carry out the isolation at a temperature at least 30"C. below the glass transition temperature of the polymer.

Example 34 A solution of 0.4 g ammonium persulfate in 200 g of water was stirred vigorously under nitrogen. To this was added 23 ml of a solution of 4.0 g dodecyl mercaptan in 100 g methyl methacrylate and the suspension was heated to 80-85"C. At intervals of 30 minutes, there was further added 20 ml of the dodecyl mercaptan/methyl methacrylate solution and 112 g of a solution of 0.2 g ammonium persulfate in 400 g water. Thirty minutes after the fourth such addition, the reaction was terminated by admitting air and cooling to room temperature. The latex was dried for 20 hours at 60-70"C. under a stream of nitrogen with stirring and the resultant methyl methacrylate homopolymer powder (T5 = 99"C.) was ground in a mortar and passed through a 40-mesh (-0.38 mm) screen. It was used to make an organosol that comprised 13.75 g of the polymer powder, 8.75 g trimethylolpropane triacrylate, 2.125 g triethylene glycol diacetate, 0.08 g Michler's ketone, 0.165 g benzophenone, 0.025 g benzotriazole, 0.11 g C.I. Solvent Red 109, and 10 ml carbon tetrachloride. The organosol was passed through a 200-mesh (0.074 mm) screen, then coated, coalesced, laminated, imaged, developed and stripped as described in Example 6.

Example 35 A solution of 0.4 g ammonium persulfate in 400 g water was stirred vigorously under nitrogen. To it was added 27 ml of a solution of 10 g methacrylic acid plus 0.92 g dodecyl mercaptan in 90 g methyl methacrylate and the suspension was heated to 80-850C. At intervals of 30 minutes, there was added 20 ml of the methyl methacrylate/methacrylic acid/dodecyl mercaptan solution plus 25 g of a solution of 0.2 g ammonium persulfate in 100 g water. Thirty minutes after the fourth such addition, the reaction was terminated by admitting air and cooling to room temperature. The latex was dried for 20 hours at 55-66"C. under a stream of nitrogen with stirring. After storage in a closed container for 20 hours over aqueous ammonium hydroxide, the resulting powder (Tg -130"C.) was used to make an organosol in the same formulation as that of Example 32 except that the diluent was 5 ml of methyl chloroform in place of 6 ml of methylene chloride. The fluid, stable organosol was coated at a thickness of 0.0015" (-0.038 mm) on 0.001"-thick (0.025 mm) polyethylene terephthalate film and passed at 12 ft./min. (3.6 m/min.) through a 12-foot (3.6 m) drying oven maintained at 208"F. (--98"C.). The resultant coalesced coating was smooth, dry and tough. It was laminated, imaged, developed, etched and stripped as previously described.

Substantially similar results were obtained when similar stepwise polymerizations were carried out with intervals between monomer additions of 60, 45, 15 and 10 minutes. When the polymerization was carried out in one step, with all ingredients present from the start, the resulting organosols could not be filtered through 100-mesh (0.149 mm) screens, even after aging for two days at room temperature. When similar polymer was made with two 50 ml additions of the methyl methacrylate/methacrylic acid/dodecyl mercaptan solution, filterability of the resultant organosols was not as good as with the preferred procedure of four additions of 25 ml portions.

When a similarly prepared latex was dried at 83-88"C., it partially coagulated and was very difficult to grind and disperse. Since the polymer had T5 = -130"C., it is thus demonstrated that such latices should be dried at a temperature at least 300C., and preferably 40-50"C., below the glass transition temperature of the polymer. Lower temperatures are operable, but require correspondingly longer drying times.

Similarly, a methyl methacrylate/methacrylic acid (95/5) copolymer, with a glass transition temperature of 113"C. was isolated from the latex as a friable powder by drying at 70"C., but it coalesced when dried at 1000C.

Example 36 To a solution of 0.4 g ammonium persulfate in 400 g water was added 27.29 ml of a solution of 1.02 g dodecyl mercaptan, 5 g ethyl acrylate and 10 g methacrylic acid in 85 g methyl methacrylate. The suspension was stirred vigorously under nitrogen and heated for thirty minutes at 80-85"C. At 30-minute intervals, there was added 25 ml of a solution of 0.2 g ammonium persulfate in 100 g water and 20 ml of the dodecyl mercaptan/ethyl acrylate/methacrylic acid/methyl methacrylate solution. Thirty minutes after the fourth such addition, the reactor was opened to air and cooled to room temperature. The latex was evaporated at 55-660C. for 20 hours under nitrogen with stirring to yield a terpolymer powder (Tg = 115"C.) of methyl methacrylate/ethyl acrylate/methacrylic acid (85/5/10). The powder was ground in a mortar, passed through a 40-mesh (-0.38 mm) sieve, treated with ammonia as previously described, and used to make an organosol in the formulation given in Example 35, which was milled, filtered, coated, coalesced, laminated, imaged, developed, etched and stripped as previously described.

Example 37 Polymer Preparation: A methyl methacrylate/methacrylic acid (98/2) copolymer powder was prepared by procedures substantially like those of Example 32, using 98 g methyl methacrylate, 2.0 g methacrylic acid and 2.0 g dodecyl mercaptan. The polymer powder was isolated by drying at 630C., then it was held for 19 hours over concentrated aqueous ammonium hydroxide and dried for 21 hours over sodium hydroxide pellets. Weight gain indicated that 0.5% NH3 was combined. Examination in the electron microscope indicated a particle size of 0.2-0.4 ,um. The powder (T5 = 122"C.) was partly soluble at room temperature in methyl chloroform, and was swollen but insoluble in perchloroethylene.

Liquid Premix: A mixture of 29.0 g trimethylolpropane triacrylate, 4.3 g dioctyl phthalate, 4.3 g triethyleneglycol diacetate, 4.3 g tricresyl phosphate, 4.0 g bis(2-o chlorophenylA,5-diphenyl)imidazole, 0.2 g benzotriazole, 1.0 g Michler's ketone, 0.3 g tris-(4-diethylamino-o-tolyl)methane, 0.11 g leuco crystal violet, 0.03 g C.I. Basic Blue 7 (C.I. No. 42595) and 31.8 g methyl chloroform was stirred for 18 hours at room temperature, then pressure-filtered through nylon flannel.

Preparation of Organosol: A mixture of 19.95 g of the above liquid premix, 13.0 g of the above binder powder, and 25 ml of 20-30 mesh (--0.55-0.85 mm) sand was milled for 30 minutes at OOC. under nitrogen, then pressure-filtered at OOC. The organosol had a viscosity at 0 C. of 10,320 cps. initially, 3600 cps. after 5 hours at 5"C., and 4600 cps. after 22 hours at 5"C. When held at room temperature, viscosity was 36,800 cps. after one hour and > 800,000 cps. after two hours. The organosol was used for the preparation of photoresists as described in preceding examples.

When similar polymer powders were isolated by drying at 100"C., they coalesced to hard lumps that could not easily be ground. Since this polymer had T5 -122"C., it is demonstrated that it is preferable to carry out the polymer isolation step at a temperature at least 30"C. below the Tg of the polymer.

Example 38 To a solution of 0.4 g ammonium persulfate in 100 g water there was added 21 ml of a solution of 1.76 g dodecyl mercaptan in 88 g methyl methacrylate. The suspension was stirred vigorously under nitrogen and heated to 80-900C. After 21 minutes at 80-900C., there was added 25 ml of the dodecyl mercaptan/methyl methacrylate solution plus 112 ml of a solution of 0.2 g ammonium persulfate in 450 ml water. Two further such additions were made at 15-minute intervals. After a further 15 minutes, a final addition was made of 112 ml of the 0.04% aqueous ammonium persulfate plus a solution of 0.44 g dodecyl mercaptan plus 2.2 g methacrylic acid in 19.8 g methyl methacrylate. These ingredients and amounts were designed to give methyl methacrylate/methacrylic acid (98/2) particles, each comprising a core of poly(methyl methacrylate) and a skin of poly(methyl methacrylate/ methacrylic acid) (90/10).

After a further 15 minutes at 81-830C., the latex was evaporated at 55-670C. The solid residue weighed 108.6 g (96% yield). It was ground in a mortar, held one day over concentrated aqueous ammonium hydroxide, then dried for one day over sodium hydroxide pellets. Weight gain was 0.37%.

The powder (T = --122"C.) was used to make an organosol had a viscosity at OOC. of 400 cps. initially and t000 cps. after 5 hours at 5"C., and 720-2068 cps. after 24 hours at 50C. It was coated and used for photoresists in the manner previously described.

Example 39 To a solution of 0.55 g ammonium persulfate in 436 g water was added 94 ml of a solution of 11 g methacrylic acid plus 1.1 g dodecyl mercaptan in 100 g methyl methacrylate. The suspension was blanketed with nitrogen, stirred vigorously, and heated at 80-930C. for 31 minutes. Then there was added a further 25 ml of the methyl methacrylate/methacrylic acid/dodecyl mercaptan solution plus a solution of 0.05 g ammonium persulfate in 112 ml water. After a further 10 minutes at 85"C., the latex was dried with stirring under nitrogen at 59-66"C. The residue weighted 109.8 g (97.4% yield). It was ground in a mortar, held for 3 days over concentrated aqueous ammonium hydroxide, then held for 4 days over sodium hydroxide pellets. The powder (Tg = -130"C.) was used to make stable, low-viscosity plastisols in formulations like the organosol formulation of Example 32 but omitting the methylene chloride diluent. This example illustrates that good plastisol-forming powders can be prepared in a simple two-step polymerization procedure, provided that the second (or last) step entails the addition of 10-30%, preferably about 20%, of the total monomer charge after the initial reaction has subsided.

Example 40 To a solution of 0.2 g ammonium persulfate in 67 ml water was added 20 ml of a monomer mixture comprising 100 g methyl methacrylate, 11 g methacrylic acid and 2.2 g dodecyl mercaptan. The suspension was stirred under nitrogen and heated to 80-890C. for 22 minutes, then at 10-minute intervals there were made four additions, each comprising 25 ml of the monomer mixture as described and 83 ml of a solution of 0.1 g ammonium persulfate in 333 ml water. After a final 10 minutes at 80-890C., the reaction was terminated, the mixture cooled to room temperature, and the latex than dried under nitrogen with stirring at 69-70"C. The residue weighed 110.5 g (98% yield). It was ground in a mortar and held for one day over concentrated aqueous ammonium hydroxide, then for one day over sodium hydroxide pellets. The treated powder (T = --130"C.) was used to make stable, low-viscosity plastisols like those of Example 39. This example illustrates that polymerizations can be carried out without coagulation at monomer/water ratios as high as 23 parts (by volume) monomer to 77 parts (by weight) water.

Claims (33)

In copending Application No. 11186/78 (Specification No. 1598578) we describe and claim a thermally coalescible nonaqueous resin plastisol or organosol dispersion of essentially homogeneous particles of a homo-polymer or random copolymer resin in a medium that comprises a liquid that is nonvolatile at room temperature and is compatible with the resin, wherein the dispersion resin comprises an organic polyelectrolyte that contains at least 1% by weight of ionizable monomer or comonomer. In copending Application No. 11188/78 (Specification No. 1598580) we describe and claim a thermally coalescible (meth)acrylic resin plastisol or organosol dispersion which comprises particles of a single-phase, finely divided (meth)acrylic homo-polymer or random copolymer containing at least 50% by weight of (meth)acrylic units, dispersed in a medium that comprises (a) a compatible liquid that is nonvolatile at room temperature, has no substantial solvent activity for the homo-polymer or copolymer at room temperature, and is not a monomer that has the same chemical structure as a monomer of the homo-polymer or copolymer, and (b) up to 40% by volume of the total volume of the dispersion of a liquid that is volatile at room temperature and has substantial solvent or swelling action on the homo-polymer or copolymer at room temperature. WHAT WE CLAIM IS:

1. A thermally coalescible resin plastisol or organosol dispersion comprising particles having a mean diameter of at least 0.1 Fm of a single-phase, surfactant-free, (meth)acrylic homo-polymer or random copolymer, containing at least 60% by weight of (meth)acrylic units, dispersed in a surfactant-free medium that comprises a compatible liquid plasticizer that is nonvolatile at room temperature and is not a monomer that has the same chemical structure as a monomer of the homo-polymer or copolymer.

2. A dispersion according to claim 1 wherein the (meth)acrylic homo-polymer or copolymer contains at least 80% by weight of (meth)acrylic units.

3. A dispersion according to claim 1 or 2 wherein the particles are of a homo-polymer or copolymer of acrylic or methacrylic acid or of esters of said acids.

4. A dispersion according to any one of the preceding claims wherein the mean diameter of the particles is from 0.1 to 20 llm.

5. A dispersion according to any one of the preceding claims wherein the plasticizer is present in an amount of 40 to 60% by weight of the (meth)acrylic homo-polymer or copolymer and plasticizer.

6. A dispersion according to any one of the preceding claims wherein there is present in the liquid phase a volatile component in an amount greater than 10% by weight based on the total dispersion weight.

7. A dispersion according to claim 6 wherein the volatile component is a solvent for the (meth)acrylic homopolymer or copolymer component.

8. A dispersion according to claim 6 wherein the volatile component is a swelling agent for the (meth)acrylic homopolymer or copolymer component.

9. A dispersion according to any one of claims 1 to 5 wherein the ratio of (meth)acrylic homopolymer or copolymer to nonvolatile liquid plasticizer component is 90:10 to 10:90.

10. A dispersion according to any one of the preceding claims which in addition contains a nonvolatile photopolymerisable ethylenically unsaturated monomeric compound which is not a monomer that has the same chemical structure as a monomer of the homopolymer or copolymer and at least one photoinitiator.

11. A dispersion according to claim 10 wherein the monomeric compound is a polyfunctional acrylic or methacrylic compound.

12. A dispersion according to claim 11 wherein the monomeric compound is selected from trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene glycol diacrylate and ethoxylated trimethylolpropane triacrylate.

13. A dispersion according to claim 10 wherein the photopolymerisable monomeric compound is a compatible liquid plasticizer.

14. A dispersion according to claim 1 substantially as described with reference to any one of Examples 3 to 5 and 33.

15. A dispersion according to claim 10 substantially as described with reference to any one of Examples 6 to 8, 10 to 24, 26, 29, 31, 32, 34 to 36 and 38 to 40.

16. A photopolymerisable element which comprises a support bearing a coalesced layer of a dispersion as claimed in any one of claims 10 to 13 and 15.

17. An emulsion polymerisation process for the preparation of methyl methacrylate homopolymers and copolymers containing at least 60% by weight of methyl methacrylate units and suitable for use in a dispersion as claimed in any one of the preceding claims, which process comprises (a) adding stepwise in two or more steps with vigorous mixing in water and in the absence of any emulsifier and surfactant at least one monomer which is methyl methacrylate, together with a polymerisation initiator and chain transfer agent whereby at least most of the monomer added in any given step is consumed before the addition of the next succeeding portion, and (b) isolating the resulting polymer at a temperature that is at least 30"C below the glass transition temperature of the polymer product.

18. A process according to claim 17 wherein methyl methacrylate homopolymers and copolymers containing at least 80% by weight of methyl methacrylate are prepared.

19. A process according to claim 17 or 18 wherein a methyl methacrylate copolymer containing at least 1% by weight of methacrylic acid units is prepared.

20. A process according to any one of claims 17 to 19 wherein the chain transfer agent is an alkyl mercaptan wherein the alkyl group is of at least 10 carbon atoms.

21. A process according to claim 20 wherein the alkyl group of the chain transfer agent is of 12 carbon atoms.

22. A process according to any one of claims 17 to 21 wherein substantially all the monomer added in any given step is completely consumed before more monomer is added in the next succeeding step.

23. A process according to any one of claims 17 to 22 wherein the isolation step (b) occurs at a temperature that is at least 40 to 50"C below the glass transition temperature of the polymer product.

24. A process according to any one of claims 17 to 23 wherein methyl methacrylate homo-polymers and copolymers having molecular weights in the range of 20,000 to greater than 325,000 inherent viscosities in the range of 0.1 to 1.5, and average particle sizes in the range of 0.1 to 20 llm are prepared.

25. A methyl methacrylate homo-polymer or copolymer when prepared by a process as claimed in any one of claims 17 to 24.

26. A process for the preparation of a plastisol or organosol dispersion which comprises dispersing a methyl methacrylate homo-polymer or copolymer as claimed in claim 25 in a surfactant-free medium that comprises a compatible liquid plasticizer that is nonvolatile at room temperature and is not a monomer that has the same chemical structure as a monomer of the homo-polymer or copolymer.

27. A process according to claim 26 wherein the liquid phase of the dispersion contains a volatile component in an amount of 5 to 40% by volume.

28. A process according to claim 27 wherein the volatile component is a solvent for the methyl methacrylate homo-polymer or copolymer.

29. A process according to claim 27 wherein the volatile component is a swelling agent for the methyl methacrylate homo-polymer or copolymer.

30. A process according to claim 26 wherein the dispersing medium contains a photopolymerisable ethylenically unsaturated monomeric compound and at least one photoinitiator.

31. A process according to claim 30 wherein the monomeric compound is a polyfunctional acrylic or methacrylic compound.

32. A process according to claim 31 wherein the monomeric compound is selected from trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene glycol diacrylate, and ethoxylated trimethylolpropane triacrylate.

33. A process according to any one of claims 30 to 32 wherein the photopolymerisable monomeric compound is a compatible liquid plasticizer.