GB2049712A - Method of Preparing Resin - Google Patents

Abstract

Method of preparing a resin by free radical polymerizing a mixture of hard segment hydrophobic enhancing monomer, optional soft segment hydrophobic enhancing monomer and hydrophilic enhancing organic acid where said method is characterized by the steps of (1) charging a reactor with water and a portion of the initiator and (2) slowly substantially simultaneously adding thereto said monomers and the remainder of the initiator. The important feature of the invention relies upon a relative excess of the initiator in a combination with an elevated temperature (75-95 DEG C) in order to enable the polymerization system substantially free of added emulsifier to be used. The advantage of the invention is the preparation of a particulate resin without the usual attendant, residual coating of emulsifier thereon.

Description

SPECIFICATION Method of Preparing Resin Field of Invention This invention relates to a method of preparing a particulate resin, water reducible resin composition and a coating prepared therefrom. The invention particularly relates to a method of preparing a particulate resin suitable for a water reducible composition by polymerizing balanced mixture of a major portion of hydrophobic enhancing monomers and a minor portion of hydrophilic enhancing monomers under conditions which will enable an essentially emulsion agent-free latex polymerization system and generally enable the preparation of a high solids latex. Similarly, the method can be used to prepare such resin for use in a solvent-based composition.

Background Art Water reducible, or water dilutable, resin compositions can be prepared by the aqueous emulsion polymerization of a manipulated and balanced monomer mixture containing a major portion of hydrophobic enhancing monomers and a minor portion of hydrophilic enhancing monomers. A singular primary advantage of such resins is their departure from a primary dependence upon organic solvents for producing coatings therefrom, thereby enabling coating preparations for various substrates with a much reduced heretofore inherent potential toxicity, flammability and environmental pollution.

It should be appreciated that such aqueous emulsion polymerizations could conveniently be conducted with the aid of typical emulsifiers to suspend or emulsify the monomers and polymers resulting therefrom, following which the polymers could simply be coagulated by the addition of a coagulant such as aluminum sulfate. An inherent disadvantage in such a polymerization and emulsion system for a water reducible resin is that a water-deposit coating thereof on the resin carries with it the water-sensitive emulsifier products. Thus, when the coalesced coating is dried, thereby becoming essentially water-insoluble, the hydrophilic emulsifier products remain to attract water to the coating and promote its degradation.

A second advantage of water dilutable (reducible) resins is that such a resin can be isolated from its latex by spray drying. In such a process, the resin is recovered in powder form directly from its latex without the typical necessity of coagulating, filtering and grinding before packaging. Conventional emulsion promoting surfactants used in conventional resin preparation by latex technique generally leave water soluble residue on the spray dried resin with very poor water resistance.

Therefore, it is an object of this invention to provide a resin formed by aqueous emulsion polymerization which can conveniently be dispersed or dissolved in an aqueous medium to form a suitable coating composition and a coating resulting therefrom without the disadvantage of containing hydrophilic surfactant residue.

Disclosure and Practice of Invention According to this invention, a method of preparing a resin, suitable for a water reducible (dilutable) composition, having a Ring and Ball softening point in the range of about 1 000C to about 3000 C, comprises free radical polymerizing, in an aqueous medium having a pH in the range of about 2 to about 7, and essentially without additional emulsifiers, a mixture which comprises, based on 100 weight percent of initiator and monomers (A) about 0.1 to about 2, preferably about 0.8 to about 1.5, weight percent of at least one free radical polymerization initiator, (B) about 60 to about 95, preferably about 70 to about 85, weight percent of at least one hard segment hydrophobic enhancing monomer selected from styrene, a-methylstyrene, acrylonitrile, vinyl toluene, methyl methacrylate, vinyl chloride and vinylidene chloride, (C) about 0 to about 35, preferably about 1 5 to about 25, weight percent of at least one soft segment hydrophobic enhancing monomer selected from at least one acrylate selected from methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, isodecyl methacrylate, butyl methacrylate, isobutyl methacrylate, hydroxy ethylacrylate, hydroxy ethylmethacrylate or at least one vinyl ether selected from ethyl, butyl, octyl, decyl and cetyl vinyl ether and/or at least one diene selected from 1 ,3-butadiene, isoprene and 2,3-dimethyl butadiene, provided that said dienes of monomer part (C) and said monomer part (B) vinyl chloride and vinylidene chloride are not mixed together and copolymerized, and (D) about 0.25 to 5.0, preferably about 1 to about 3, weight percent of at least one hydrophilic enhancing organic acid selected from acrylic, methacrylic, fumaric, itaconic and maleic acid; wherein said method is characterized by the sequential steps of (1) charging a reactor vessel with about 50 to about 200 parts by weight water and about 40 to about 60 percent of said initiator and, with such reactor contents adjusted to a temperature in a range of about 750C to about 950C, (2) slowly, substantially simultaneously, adding thereto 100 parts by weight of said monomers (B, C and D), the remainder of said initiator, and a minimal amount of water as a vehicle for said initiator, and allowing the reaction at a temperature in a range of about 750C to about 950C.

Preferred free radical initiators are water soluble persulfates, peroxides and hydroperoxides such as, for example, those selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, sodium valerate, hydrogen peroxide and various hydroperoxides such as cumene hydroperoxide, tertiary butyl hydroperoxide and diisopropyl benzene hydroperoxide.

In the practice of this invention, a resin according to the prescribed method is produced which is suitable for a water reducible (dilutable) composition having a Ring and Ball softening point in the range of about 1 000C. to about 3000C.

It is important to appreciate that the advantageous method of this invention enables the preparation of a resin essentially without additional emulsifiers, through the combination of the utilization of both (1) an elevated preparatory and reaction temperature and, in combination therewith, (2) a slow, preferably essentially continuous, addition of an excessive amount of free radical initiator.

Thus, little or no emulsification agents are added or used and preferably none of such agents in order to minimize eventual surface coatings on the resultant recovered resin.

A particular feature of this invention is that a resin is prepared without a surfactant coating from a higher solids latex (55-60 weight percent solids) having a larger particle size and generally a higher softening point (50C-100C).

In the practice of this invention the preferable hard segment hydrophobic enhanced monomer is selected from at least one of styrene, methyl styrene, acrylonitrile and vinyl toluene.

Preferred soft segment hydrophobic enhancing monomers for this invention are selected from at least one of methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxy ethylacrylate, hydroxy ethyl methacrylate, or a vinyl ether selected from methyl vinyl ether, butyl vinyl ether or 2ethylhexyl vinyl ether and/or at least one diene selected from 1 3-butadiene or isoprene.

The preferred hydrophilic enhancing organic acid for the resin of this invention are at least one of acrylic, methacrylic, or maleic acid.

In the preparation of the resin of this invention it is required that a major portion of the monomers are required to form a hard segment of a hydrophobic nature and that a substantial minor portion of the monomers form a relatively soft segment which is hydrophobic in nature. Indeed, only a very minor amount of hydrophilic organic acid is required or allowed in order to provide only a minimal amount of carboxylation of the resin itself.

In the preparation of the resin it is required that the aqueous medium have a pH in the range of about 2 to about 7. The pH can simply be adjusted with an inorganic base such as sodium hydroxide, potassium hydroxide and ammonium hydroxide. The polymerization itself containing the bifunctional emulsion-promoting monomer can be conducted by conventional means such as adequate stirring, general reactor and reaction control, usually at a temperature in the range of about 750C to about 950C.

Although the major thrust and importance of the invention is the method of polymerization to enhance both the emulsion, and attainment af a high solids latex, it should be understood that minimal amounts of additional and somewhat conventional emulsifiers can be used. If such additional emulsifiers are used in order to maintain the usefulness of this invention, it is desired and required that they amount to a maximum of about 25% by weight of the hereinbefore described bifunctional emulsion promoting monomer utilized in this invention. The resin can then be recovered, preferably by spray drying, although conventional methods can also be used, such as coagulation, evaporation and extrusion to yield a hard, particulate resin.

It is of a particular advantage of this invention that a water reducible (or dilutable) resin is prepared which is particularly useful for providing coatings which are essentially emulsifier-free.

In this regard, a suitable water reducible composition can comprise an admixture or solution of 100 parts by weight of the resin with about 50 to about 100 parts of coalescing, preferably water soluble, solvent for the resin and about 5 to about 70 parts by weight of at least one resin-compatible plasticizer.

Various coalescing solvents can be used, representative of which are ethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol diethyl ether, diethylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl propyl ketone and diacetone alcohol. Representative of various resins compatible plasticizers are those generally characterized by having a melting point of about-400C. to about 250C., a boiling point of at least about 950C and a solubility parameter of about 8 to about 1 6.

From the water reducible composition is provided a suitable coating composition by mixing and reacting therewith a sufficient amount of a volatile amine foliowed by mixing water therewith to form a relatively stable dispersion or solution of said composition having a pH in the range of about 8 to about 14. Various amines can be used, representative of which are primary, secondary and tertiary amines having a melting point in the range of about -400C to about 250C and a boiling point in the range of about 500C to about 1 500C.

From the coating composition is then prepared a substantially water insoluble coating on a substrate, said coating having a thickness in the range of about 1 to about 40, preferably about 1 to about 5 mils, by simply applying the coating composition to the substrate surface and drying the applied coating to remove the said water, amine and coalescing solvent. The so-called solubility parameter characteristic of the coalescing solvent can be conveniently found and described in The Encyclopedia of Polymer Science and Technology, vol. 3, p. 854 ( 1975), John Wiley 8 Sons., Inc.

The practice of this invention is further illustrated by reference to the following examples which are intended to be representative rather than restrictive of the scope of the invention. Unless otherwise indicated, all parts and percentages are by weight.

Example I Various resins suitable for preparing water reducible compositions were prepared by the following method and labeled herein as Experiments 1-7.

A reactor was charged with water and heated to 750C. During heat-up the reactor was alternately evacuated and purged with N2 several times to exclude oxygen from the system. When the internal temperature of the reactor lined out at 750C., a water solution of about 50 percent of a suitable free radical generating initiator to be used was added. Then the hydrophilic/hydrophobic comonomer blend containing acidic monomer and the remaining half of the initiator was slowly, simultaneously added to the reactor at such a rate to take approximately 4-5 hours. The reactor was kept at 750C. during the polymerization and for 2 additional hours after all of the monomers were added. The latex was then cooled and discharged from the reactor.The resulting latex was then coagulated and dried to form a particulate resin having a Ring and Ball softening point within a range of about 1 000C to about 3000C. The Ring and Ball softening point is of the type determinable by ASTM Method E28-58T.

In this example, various monomer mixtures were used which are summarized in the following Table 1. The column 1-7 represent Experiments 1-7 with their corresponding amounts of monomers in parts by weight. All polymerized with ease up to 50% solids.

Table 1 Resin Compositions Monomers 1 2 3 4 5 6 7 A. Hard segment 36 71 71 71 67 75 80 Styrene 35 - - - - - - B. Soft segment 2-ethylhexylacrylate - - - - - 20 1 7 Butyl acrylate 26 26 26 27 30 - - C.Hydrophilic enhancing Acrylic acid - - 2 2 2 - Methacrylic acid 3 3 1 - 1 5 3 Table 2 Organic Solution Viscosities and Film Properties Resins from Table 1 1 2 3 4 5 6 7 Viscosity, 33-1/3% in 240 225 380 115 205 525 400 toluene Film properties B T T T T T T (Tough/Brittle) *Water sensitivity Fair OK OK OK OK OK OK *Films, 1-2 mils dry, were cast on glass and air dried 4 days then oven dried 2 hours at 1 200F. The films were water spotted and a watch glass was taped over the water spot to prevent evaporation. The films were rated after 24 hours.

Table 3 Emulsion Properties Resin from Table 1: 1 30 2 30 3 30 4 30 5 30 6 30 7 30 water 56 56 56 56 56 56 56 triethylamine 1 1 1 1 1 1 1 dimethylethanolamine 1 1 1 1 1 1 1 Defoamer (B) 2 2 2 2 2 2 2 Butyl cellosolve 8 8 8 8 8 8 8 MIBK 3 3 3 3 3 3 3 Alkaryl polyether1 1 1 1 1 1 1 1 Total 102 102 102 102 102 102 012 Viscosity, cps 530 25 65 23 50 28 22 Film properties All were tough and mar resistant 'Obtained as Triton CF-10 (Rohm and Haas Co.) For the preparation of the resins of Table 3, the isolated resin was wet with water. To the wet resin was added the mixture of amines, defoamer, solvents and nonionic surfactant. The resin was then dissolved in the presence of water to form a white emulsion which was stable to settling. This emulsion can be used to prepare paints and coatings.

Tables 4, 5 and 6 show formulations prepared from Example 7 of Table 1. The resin prepared (#7) was used as 100% solids to prepare a solvent type paint and the latex was used to prepare a water reducible type paint. The paints were compared to a standard solvent type paint where no carboxylation was present. Resin #7 could also have been used to prepare water reducible type paints following the procedures given in Table Ill. Tables 4, 5 and 6 show that the properties of the carboxylated resin in paint formulations are equivalent and equal to the solvent paint.

Table 4 (White Enamels) Grind ControlA Solvent B Emulsion C S/acrylate (80/20)1 28 Resin 7 (100%) 28 28 Resin 7 (45% latex) - 215 Titanium dioxide 231 231 231 Water - 60 Ammonium hydroxide - 3 Triethylamine - 5 Defoamer (A) - 3 Defoamer (B) - 5 Diethylene glycol - 70 monobutyl ether Aromatic solvent - 15 Alkyl, aryl ether - - 4 Rule 66 Solvent2 142 142 Let Down S/acrylate(80/20) 148 - Resin 7(100%) 148 148 Resin 7 (45% latex) - 215 Butyl benzyl phthalate 18 18 18 China wood oil 9 9 9 Water - 80 Rule 66 Solvent2 342 342 Water thickener (4%) - 70 Titanium chelate - 2 Triethylamine - 1 Defoamer (B) - 1 Total 918 918 1007 Pigment Volume Percent 22.5 22.5 21.1 Gloss Initial 90 90 81 Observations (1 0=maximum rating, O=failure) Weatherometer, 1000 hr Fading 8 8 8 Checking 6 6 6 Appearance 6 6 6 Noncarboxyiated styrene/acrylate resin of similar composition to Resin 7 2Mineral Spirits, 36 KB 45 Aromatic solvent 8 Diethylene glycol monobutyl ether acetate 47 100 Table 5 Blue Tint Flat Masonry Paints Control A Solvent B Emulsion C Rule 66 Solvent 300 300 - Butyl benzyl phthalate 47 47 Styrene resin (mp 100 C.) 47 47 S/acrylate (80/20) 94 - - Resin No. 7 (100%) 94 94 Resin No. 7 (45% latex) - 209 Dimethylethanolamine - 10 Alkylaryl polyether - 3 3 Titanium dioxide 141 141 141 Blue coloring 1.8 1.8 1.8 Calcium carbonate 236 236 236 Mica 68 68 68 Diatomaceous silica 63.5 63.5 63.5 Thickener 5 5 Soya Lecithin 4 4 Water - 100 Let Down Rule 66 Solvent 106 106 Butyl benzyl phthalate - 47 Styrene resin (mp 1000C) - 47 Defoamer (A) - 8 Aromatic solvent - 25 Diethylene glycol mono-butyl - 50 ether Water - 48 Cellulosic water thickener - 100 (2%) Titanium chelate - 3 Defoamer (B) - 2 Total 1113.3 1113.3 1162.3 Pigment volume percent 53 53 53 Observations, Resin Weatherometer, 1000 hr Fading 5 3 4 Checking 9 10 10 Appearance 5 4 5 Table 6 White, Flat Masonry Paints ControlA SolventB Emulsion C S/acrylate (80/20) 80 - Resin No. 7 (100%) 80 80 Resin No. 7 (45% latex) - 178 Butylbenzyl phthalate 40 40 Styrene resin (mp 1000C) 40 40 - Rule 66 Solvent 300 300 Dimethylethanolamine - 12 Alkylaryl polyether - - 3 Water - 205 Titanium dioxide 225 225 225 Talc 202 202 202 Diatomaceous silica 75 75 75 Thickener 5 5 Let Down Diethylene glycol mono-butyl - 90 ether Butyl benzyl phthalate - 40 Styrene resin (mp 100 C) - 40 Defoamer (A) - 8 Aromatic solvent - 25 Rule 66 Solvent 142 142 Table 6 (cont).

White, Flat Masonry Paints ControlA Solvent B Emulsion C Cellulosic water thickener - 100 (2%) Titanium chelate - 2 Defoamer (B) 2 2 Total 1109 1109 1207 Pigment volume percent 53 53 53 Observations, Resin Weatherometer, 1000 hrs Fading 6 6 6 Checking 10 10 10 Appearance 6 6 6 While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

Claims (8)

Claims

1. A method of preparing a resin having a softening point in the range of about 1 000C which comprises free radical polymerizing in an aqueous medium having a pH in the range of about 2 to about 7, a mixture which comprises, based on 100 weight percent of initiator and monomers (A) about 0.1 to about 2 weight percent of at least one free radical polymerization initiator, (B) about 60 to about 95 weight percent of at least one hard segment hydrophobic enhancing monomer selected from styrene, a-methylstyrene, acrylonitrile, vinyl toluene, methyl methacrylate, vinyl chloride and vinylidene chloride, (C) about 0 to about 35 weight percent of at least one soft segment hydrophobic enhancing monomer selected from at least one acrylate selected from methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, isodecyl methacrylate, butyl methacrylate, isobutyl methacrylate, hydroxy ethylacrylate hydroxy ethyl methylacrylate, or at least one vinyl ether selected from ethyl, butyl, octyl, decyl and cetyl vinyl ether and/or at least one diene selected from 1,3butadiene, isoprene and 2,3-dimethyl butadiene, provided that said dienes of monomer part (C) and said monomer part (B) vinyl chloride and vinylidene chloride are not mixed together and copolymerized, and (D) about 0.25 to 5.0 weight percent of at least one hydrophilic enhancing organic acid selected from acrylic, methacrylic, fumaric, itaconic and maleic acid; wherein said method is characterized by the sequential steps of (1) charging a reactor vessel with about 50 to about 200 parts by weight water and about 40 to about 60 percent of said initiator and, with such reactor contents adjusted to a temperature in a range of about 750C. to about 950 C., (2) slowly, substantially simultaneously, adding thereto 100 parts by weight of said monomers (B, C and D), the remainder of said initiator, and a minimal amount of water as a vehicle for said initiator, and allowing the reaction to proceed at a temperature in a range of about 750C. to about 950C.

2. The method of claim 1 where said hard segment hydrophobic enhancing monomer is selected from at least one of styrene, a-methylstyrene, acrylonitrile and vinyl toluene, where said soft segment hydrophobic enhancing monomer is selected from at least one of methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxy ethylacrylate, hydroxy ethyl methacrylate, or a vinyl ether selected from methyl vinyl ether, butyl vinyl ether or 2-ethylhexyl vinyl ether and/or at least one diene selected from 1,3-butadiene or isoprene and where said hydrophilic enhancing organic acid is selected from at least one of acrylic, methacrylic or maleic acid.

3. The method of claims 1 or 2 where said free radical initiator is selected from at least one of water soluble persulfates selected from ammonium, sodium, and potassium salts: sodium valerate and hydrogen peroxide.

4. The method of claim 1 where the resulting latex prior to resin recovery contains about 55 to about 60 weight percent solids.

5. The method of claim 1 which comprises free radical polymerizing in an aqueous medium having a pH in the range of about 2 to about 7, a mixture which comprises, based on 100 weight percent of initiator and monomers, (A) about 0.8 to about 1.5 weight percent of at least one free radical polymerization initiator selected from water soluble persulfates, peroxides and hydroperoxides, (B) about 70 to about 85 weight percent of at least one hard segment hydrophobic enhancing monomer selected from at least one of styrene, a-methylstyrene, acrylonitrile and vinyl toluene, (C) about 1 5 to about 25 weight percent of at least one soft segment hydrophobic enhancing monomer selected from at least one of methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxy ethylacrylate, hydroxy methylacrylate, vinyl ether selected from methyl vinyl ether, butyl vinyl ether or 2-ethylhexyl vinyl ether and/or at least one diene selected from 1 ,3-butadiene or isoprene, and (D) about 1 to about 3 weight percent of at least one hydrophilic enhancing organic acid selected from acrylic, methacrylic, fumaric, itaconic and maleic acid.

6. The method of claim 5 wherein said free radical initiator is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, sodium valerate, hydrogen peroxide, tertiary butyl hydroperoxide and diisopropyl benzene hydroperoxide.

7. A method as claimed in claim 1, substantially as described in the foregoing Examples section in respect of any of Experiments 1-7.

8. A resin prepared by a method as claimed in any of claims 1-7.