申请人：Revertex Ltd.
公开号：US03989661A1
公开（公告）日：1976-11-02
The average particle size of latices of polymers prepared by aqueous emulsion polymerization of ethylenically unsaturated and/or diolefinic monomers is increased markedly by admixture therewith of polyethoxylated surfactants having an HLB Value of 16-19.5 which are based on either long chain alkyl amines and/or esters of aliphatic polyols and fatty acids. This invention relates to a process for enlarging or agglomerating, i.e. coarsening irreversibly, the particles contained in a polymer dispersion. In particular, the invention is concerned with polymer dispersions obtained by emulsion polymerization of ethylenically unsaturated or polyunsaturated monomers. Preferred polymer dispersions (latex polymers) for which the method of the invention can best be used are the water immiscible emulsion homopolymers and copolymers of C.sub.4.sub.-6 conjugated diolefins such as butadiene, isoprene, chloroprene, 2,3-dimethyl-butadiene and 2-methyl-butadiene. Suitable comonomers include ethylenically unsaturated compounds such as vinyl aromatic compounds (styrene, 2-methylstyrene, vinyl toluene, divinyl benzene, and chlorinated styrenes), vinylidene chloride, vinyl pyrrolidone, acrylic nitriles (acrylonitrile, methacrylonitrile), lower alkyl esters of acrylic acids (ethyl acrylate, methylmethacrylate and butylacrylate), carboxylic acid amides and copolymerizable .alpha.-.beta.-unsaturated carboxylic acids, (acrylic, methacrylic, itaconic, maleic and fumaric acids) and the lower alkyl monoesters of polymerizable dicarboxylic acids (monomethyl itaconate). In the preparation of polymer dispersions by emulsion polymerization of ethylenically unsaturated or polyunsaturated monomers, it is often advantageous to make the dispersions with particles of small diameter, typically in the range of 0.05 to 0.25 .mu.. in order to benefit from the high rates of conversion of monomer to polymer obtainable when the particle size is small. However, in many technological applications, fine particled polymer dispersions suffer from certain drawbacks, such as a low tolerance towards fillers, pigments, vulcanizing ingredients and the like, as well as from instability towards agitation, shearing forces and other mechanical influences. Further drawbacks may be found in the rheological properties of fine particled dispersions, notably high viscosity at low shear rates or at high concentration. In order to overcome the disadvantages of fineparticled dispersions, various processes have been proposed for agglomerating the particles. Some of these processes are purely physical, involving the expenditure of energy, some are chemical and some are a combination of physical and chemical processes. Many of these processes can not be applied to latex polymers derived from mixtures of monomers of which at least one provides hydrophilic groups in the polymer, e.g. carboxylated latices, or can not be applied to such latex polymers in such a way as to provide reproducible results. Among chemical agglomerating agents, it has been proposed to employ polyethoxylated compounds of the formula ##EQU1## where R is an organic hydrophobic group A is a hydrogen atom or an R(CH.sub.2 CH.sub.2 O).sub.m H group B is a hydrogen atom or an (CH.sub.2 CH.sub.2 O).sub.p H group n, m and p are each 23 to 455 and the weight ratio of R to ethylene oxide chains is from 1:3 to 2:1. The preferred chemical agglomerating agents of the above formula are obtained by reacting polyoxyethylene glycol with the reaction product of a polyhydric phenol and epichlorohydrin. It has also been indicated that in order to agglomerate a synthetic rubber containing carboxy groups, it is necessary that the latex should have a content of free emulsifier of from 0.1 to 3.5% with reference to latex solids, and that from 10 to 55% of the carboxylic groups contained in the synthetic rubber should be neutralized. The amount of emulsifier may be increased to 4.0% and up to 70% of the carboxyl groups may be neutralized if the pH during polymerization is maintained in the range from 1.5 to 3.6. It is believed that these critical conditions are necessary with certain disclosed agglomerating agents and that such carboxylated latices can not be agglomerated or reproducibly agglomerated with certain other previously proposed chemical agglomerating agents or physical agglomerating processes. We have now discovered a class of polyethoxylated compounds which are useful for agglomerating both carboxylated and non-carboxylated polymers over a wide range of conditions and which do not require critical conditions as to free emulsifier content and neutralization of carboxyl groups, if present. The surfactants having this effect belong to the class of non-ionic polyethoxylated high and/or substituted long chain fatty acid esters and higher hydrocarbyl amines. In particular the polyethoxylated fatty acid esters are those of aliphatic (including cycloaliphatic) polyols. Examples of suitable esterifying polyols are glycerol, sorbitol, pentaerithritol, alkylene glycols, di-alkylene glycols, trimethylol propane, mannitol, glucose and sucrose. The preferred fatty acid esters are the readily and economically available glycerides contained in or derived from naturally occurring oils and fats. Typical compounds useful for carrying out the present invention include the following: 1. Polyethoxylated completely esterified polyols, such as glycerol, alkylene glycols, pentaerithritol, sorbitol, mannitol and trimethylol propane, in which at least one of the esterifying long chain fatty acids contains a substituent group on its hydrophobic long chain capable of reacting with ethylene oxide to append a poly(ethylene oxide) chain, e.g. amino or hydroxy groups. Ricinoleic and 12-hydroxy stearic acids are examples of such substituted fatty acids and suitable surfactant compounds of this type are represented by polyethoxylated castor oil or polyethoxylated hydrogenated castor oil; 2. Polyethoxylated partial fatty acid esters of polyols, such as glycerol, sorbitol, ethylene glycol, di-ethylene glycol and trimethylol propane, in which one or more of the esterifying long chain fatty acids may contain ethoxylatable substituent groups as described immediately above; and 3. Polyethoxylated long chain alkyl amines (including aralkyl amines), optionally containing one or more ethoxylatable substituent groups on the alkyl chain. In the case of both the fatty acid components of the esters and the alkyl amines described above it is preferred that the hydrophobic portions thereof be from about 12 to about 22 carbon atoms in length and preferably from about 14 to 20 carbon atoms. The polyethoxylated surfactants of this invention are further characterized by having: 1. An HLB number in the range of from 16 to 19.5. A definition of the term "HLB number" is given in articles by W. C. Griffin in Journal Soc. Cosmetic Chemists, Volume 1, p.311 (1949) and Volume 5, p.249 (1957). For the purpose of this invention, the HLB number may be calculated from the expression ##EQU2## where H is the molecular weight of the hydrophilic portion of the polyethoxylated surfactant and M is the total molecular weight of the surfactant. In the case of polyethoxylated fatty acid esters of polyols, H may be represented with sufficient accuracy by the molecular weight of the polyoxyethylene chains plus the molecular weight of the polyol. In the case of the polyethoxylated amines, H may be represented by the molecular weight of the polyoxyethylene chains only; and 2. A molecular weight in the range of from 1800 to 25,000 and preferably in the range of from 2500 to 20,000. The polymer dispersions capable of being coarsened or agglomerated by the present process are those stabilized predominantly by surfactants and/or by the presence in the polymer of hydrophilic comonomers, examples of which are .alpha.,.beta.-ethylenically unsaturated mono- di- or polycarboxylic acids, di- or poly-carboxylic acid partial alkyl esters, carboxylic acid amides, carboxylic acid monoesters of diols or polyols, carboxylic esters of amino-alcohols and vinyl pyrrolidone. Surfactant dispersion stabilizers are well known to those skilled in the art of emulsion polymerization. Typical examples are the higher alkyl esters of sulphosuccinic acid, the C.sub.8 to C.sub.20 hydrocarbyl sulphates or sulphonates and the polyethoxylated alkanols, alkylated phenols, alkanoic acids or acid amides and their sulphated, sulphonated or phosphated derivatives. It is a further prerequisite of the present process that the surfaces of the dispersed polymer particles are incompletely covered by any stabilizing surfactants. This may be determined by soap titration according to Nouben-Weyl "Methoden der organischen Chemie" Vol. 14/1, p.370, and will usually be found to be the case if the surface tension of the polymer dispersion is higher than 50 dynes/cm. and preferably higher than 55 dynes/cm. For irreversible coalescence of fine particles to coarser ones to take place, it is furthermore necessary that the polymer constituting the major volume proportion of the dispersed polymer particles, e.g. in a dispersion of mixed polymers, should have a glass transition temperature (Tg) below and preferably more than 20.degree.C. below the temperature at which the coalescence is induced. Fortunately, many polymers, e.g. those containing a high proportion of butadiene and/or isoprene and/or acrylic acid esters of higher alkanols have a glass transition temperature well below 0.degree.C. Thus, irreversible coalescence can frequently be readily achieved at ambient temperature when employing the present process. Based on the foregoing, the present invention broadly provides a process for enlarging the particle size of a polymer dispersion, wherein the polymer dispersion is mixed with a surfactant which is a non-ionic polyethoxylated high and/or substituted fatty acid ester or higher hydrocarbyl amine. In particular, the surfactant should have an HLB number (as hereinbefore defined) of from 16 to 19.5 and a molecular weight of from 1800 to 25,000, while the polymer should be stabilized either by groups derived from hydrophilic monomers or by a stabilizing surfactant present in an amount which is not sufficient completely to cover the surfaces of the dispersed particles. Finally, the enlarging process should take place at a temperature above the glass transition temperature of the polymer constituent constituting the major volume proportion of the dispersed polymer. In order to carry the present process into effect, the polyethoxylated surfactant is preferably first dissolved in a suitable solvent for the surfactant, ordinarily in water or a water-containing mixture, and is then mixed with the polymer dispersion to be treated. The surfactant solution may be added to the polymer dispersion or vice versa. The quantity of surfactant employed may vary from 0.01 to 5 parts dry per 100 parts of polymer contained in the dispersion. Preferably the quantity is in the range of 0.02 to 1.0 part of surfactant per 100 parts of polymer. The polyethoxylated surfactants used in the present process, especially those having molecular weights in excess of 3000 and HLB numbers higher than 17 may, when added to the fine particled polymer dispersion, frequently cause the formation of macroscopic coagulum. Several methods are envisaged to minimize or obviate the danger of such coagulum formation and these are as follows: 1. The addition of a stabilizing surfactant of the type normally employed in the process of emulsion polymerization and mentioned previously in that context to either the dispersion or the solution of the coarsening surfactant before or during the mixing of the two. Suitable stabilizing surfactants include non-ionic surfactants, e.g. polyethoxylated C.sub.12 -C.sub.20 alcohols, alkylated phenols, amides and aminos with HLB numbers lower than 17 and preferably lower than 16 and with molecular weights lower than 1500 and preferably lower than 1200. Examples of other suitable stabilizing surfactants are the sulphates, sulphonates, phosphates and sulphosuccinates previously mentioned. 2. Adjustment of the pH value of the polymer dispersion and/or coarsening agent solution to a higher or lower value by the addition of bases or acids which have preferably been diluted with water. In one preferred embodiment of the present process, applicable to dispersions of carboxylated polymers, the pH of the dispersion is first raised to a value greater than will ensure the ionization of at least 50% of the carboxyl groups, by means of a base, which is preferably a volatile base, such as ammonia or an organic amine. The coarsening agent is then added, but does not cause any major alteration of the average particle size until the pH is lowered by the volatilization of the base or by chemical means. Examples of chemical means of lowering the pH of the mixture are the reaction of ammonia with formaldehyde or the addition of an acidic reagent like carbon dioxide, an organic or mineral acid, an acid salt or a substance capable of forming an acid such as an ester, acid amide, anhydride or halide. 3. In a further preferred embodiment of the present process, by the stepwise coarsening of the polymer dispersion. The stepwise coarsening may be achieved in several different ways. For example: a. By the sequential addition to the polymer dispersion of coarsening polyethoxylated surfactants as hereinbefore defined of increasing HLB numbers and molecular weight in two or more steps. In each step, single surfactants or blends of surfactants of the appropriate HLB numbers and molecular weights may be employed. b. By the addition to the polymer dispersion of a mixture of one or more coarsening surfactants with one or more stabilizing surfactants followed in one or more steps by the addition of coarsening surfactant containing lower amounts of stabilizing surfactant or none at all. The last step is preferably carried out with no admixture of a stabilizing surfactant using a coarsening surfactant having an HLB value greater than 17.5 and a molecular weight in excess of 4000. c. By the addition of the polymer dispersion to a solution of one or more coarsening surfactants optionally containing also one or more stabilizing surfactants and/or a pH adjusting base or acid. In the second or any subsequent step, a solution of coarsening surfactant is added to the pre-coarsened dispersion of the first step, preferably in the manner described under 3a. It will be readily understood that suitable combinations of methods 1, 2 and 3a to 3c may be also employed. When carrying out the present process it is furthermore envisaged that the polymer dispersions to be coarsened may be mixtures of two or more separate polymer dispersions. As previously mentioned, in this case only the polymer or polymers constituting the major proportion contained in the mixture need possess a glass transition temperature below the temperature at which the process is performed. It is also envisaged that one or more component dispersions present in a mixed polymer dispersion may have a larger average particle size than the fine particled dispersion to be coarsened. In fact it has been found that the presence of usually minor proportions of coarser particled dispersions may exert a beneficial regulating effect on the particle size distribution of the final coarsened material. This effect may be described as "seeding" or "nucleating" in as far as the coarser particles present act as seeds or nuclei for at least a proportion of the newly formed coarsened particles. The particle size distribution in the final product is influenced by both the amount and the particle size distribution of the seed dispersion employed. The regulation of particle size distribution in the final product may also be achieved by mixing a suitable "seed" dispersion with the solution of polyethoxylated surfactant, whether added by the stepwise method described above or not. The seed dispersion need not have a high surface tension nor a low glass transition temperature. The present process may also be carried out by treating a fine particled polymer dispersion with the aforementioned coarsening agent in the presence of one or more of inert inorganic or organic fillers, pigments, vulcanizing agents, plasticizers, electrolytes, pH buffers, antifoaming agents, chelating agents and other ingredients customarily employed by those skilled in the art of compounding polymer dispersions. The coarsened dispersions obtained by the present process may at any later stage be mixed with such further ingredients as their technological application will require. Examples of such ingredients are dispersants, surfactant stabilizers, acids, bases, plasticizers, vulcanizing ingredients and so on as is customary in the art of using such dispersions. The coarsened dispersions, with or without the addition of further, e.g. stabilizing, ingredients, may be concentrated by evaporation, creaming, centrifuging or similar means well known to those skilled in the art. The following Examples in which all parts are parts by weight illustrate the invention and the manner in which it is to be performed.
通过
水乳液聚合制备的聚合物乳胶的平均粒径可以通过与具有HLB值为16-19.5的聚乙氧基化表面活性剂混合明显增加，该表面活性剂基于长链烷基胺和/或
脂肪酸的脂肪族多元醇酯。本发明涉及一种扩大或聚集聚合物分散体中的颗粒，即不可逆地变粗的过程。特别是，本发明涉及通过
乙烯不饱和或多不饱和单体的乳液聚合获得的聚合物分散体。最适合使用本发明方法的优选聚合物分散体（乳液聚合物）是C.sub.4.sub.-6共轭二烯的
水不相容乳液均聚物和共聚物，例如
丁二烯、
异戊二烯、
氯丁二烯、2,3-二甲基-
丁二烯和2-甲基-
丁二烯。适当的共聚单体包括
乙烯不饱和化合物，例如
乙烯基芳香化合物（
苯乙烯、
2-甲基苯乙烯、
乙烯基甲苯、
二乙烯基苯和
氯化
苯乙烯）、
乙烯基氯、
乙烯吡咯烷、
丙烯腈（
丙烯腈、
甲基丙烯腈）、
丙烯酸酯的低烷基酯（乙基
丙烯酸酯、
甲基丙烯酸甲酯和丁基
丙烯酸酯）、
羧酸酰胺和可共聚的α-β-不饱和
羧酸（
丙烯酸、
甲基丙烯酸、
己二酸、
马来酸和
富马酸）和可聚合的二
羧酸酯的低烷基单酯（单甲基
己二酸酯）。在通过
乙烯不饱和或多不饱和单体的乳液聚合制备聚合物分散体时，通常有利于制备粒径小的颗粒分散体，通常在0.05至0.25μm的范围内，以从小粒径获得高单体转化率为聚合物。然而，在许多技术应用中，细小颗粒的聚合物分散体存在某些缺点，例如对填充剂、
颜料、
硫化剂和类似物质的低耐受性，以及对搅拌、剪切力和其他机械影响的不稳定性。细小颗粒分散体的进一步缺点可能在于其流变特性，特别是在低剪切速率或高浓度下的高粘度。为了克服细小颗粒分散体的缺点，已提出了各种聚集颗粒的方法。其中一些方法是纯物理过程，涉及能量消耗，一些是
化学的，一些是物理和
化学过程的组合。许多这些过程不能应用于由至少一种在聚合物中提供亲
水基团的单体混合物制得的乳液聚合物，例如羧化乳液，或不能以可重复的方式应用于这种乳液聚合物。在
化学聚集剂中，已提出使用公式##EQU1##的聚乙氧化合物，其中R是有机疏
水基团，A是氢原子或R（CH.sub.2 CH.sub.2 O）.sub.m H基团，B是氢原子或（CH.sub.2 CH.sub.2 O）.sub.p H基团，n、m和p分别为23至455，R与
乙烯氧化物链的重量比为1:3至2:1。上述公式的优选
化学聚集剂是通过将聚氧
乙烯醇与多羟基
酚和
环氧氯丙烷的反应产物反应获得的。还指出，为了使含有羧基的合成橡胶聚集，需要保证乳液中游离
乳化剂的含量相对于乳液固体为0.1至3.5％，并且合成橡胶中含有的
羧酸基的10％至55％应该被中和。如果在聚合过程中维持pH在1.5至3.6的范围内，则可以将
乳化剂的含量增加到4.0％，并且可以中和70％的羧基，据信这些临界条件对于某些披露的聚集剂是必要的，而这样的羧化乳液不能使用某些其他先前提出的
化学聚集剂或物理聚集过程进行聚集或可重复地聚集。我们现在发现了一类聚乙氧基化化合物，它们对于在广泛的条件下聚集羧化和非羧化聚合物都是有用的，并且如果存在，则不需要关于游离
乳化剂含量和羧基中和的临界条件。具有这种效果的表面活性剂属于非离子聚乙氧基化高和/或取代
脂肪酸酯和较高的烃基
胺类。特别是，聚乙氧基化
脂肪酸酯是脂肪族（包括环脂族）多元醇的酯化物。适当的酯化多元醇的例子包括
甘油、
山梨醇、戊糖、烷基二醇、二烷基二醇、三甲基
丙烷、
甘露醇、
葡萄糖和
蔗糖。优选的
脂肪酸酯是从天然油脂中提取或得到的容易和经济的
甘油酯。用于执行本发明的典型化合物包括以下化合物：1.聚乙氧化完全酯化的多元醇，例如
甘油、烷基二醇、戊糖、
山梨醇、
甘露醇和三甲基
丙烷，其中至少一个酯化长链
脂肪酸含有其疏
水长链上的取代基团，其能够与
乙烯氧化物反应以附加聚（
乙烯氧化物）链，例如
氨基或羟基。
蓖麻油酸和
12-羟基硬脂酸是这种取代
脂肪酸的例子，而适当的此类表面活性剂化合物由聚乙氧化
蓖麻油或聚乙
氧化氢化
蓖麻油表示；2.多元醇的聚乙氧化部分
脂肪酸酯，例如
甘油、
山梨醇、
乙二醇、
二乙二醇和三甲基
丙烷，其中一个或多个酯化长链
脂肪酸可以含有上述可乙氧化取代基团；和3.聚乙氧化长链烷基胺（包括芳基烷基胺），其上的烷基链上可以有一个或多个可乙氧化取代基团。在上述酯和烷基胺的
脂肪酸组分的情况下，优选的是其疏
水部分的碳链长度为约12至22个碳原子，优选为14至20个碳原子。本发明的聚乙氧基表面活性剂还具有以下特征：1.在16至19.5的HLB数范围内。关于术语“HLB数”的定义，请参见W.C. Griffin在Journal Soc. Cosmetic Chemists，Volume 1，p.311（1949）和Volume 5，p.249（1957）中的文章。为了本发明的目的，HLB数可以从表达式##EQU2##计算，其中H是聚乙氧基表面活性剂的亲
水部分的分子量，M是表面活性剂的总分子量。在酯化多元醇的
脂肪酸成分的情况下，H可以由聚氧
乙烯链的分子量加上多元醇的分子量来足够准确地表示。在聚乙氧化胺的情况下，H仅可以由聚氧
乙烯链的分子量来表示；和2.分子量在1800至25,000之间，优选在2500至20,000之间。能够被本过程聚集或聚集的聚合物分散体是由表面活性剂和/或由聚合物中的亲
水共聚单体衍生的基团稳定的那些，例如α，β-
乙烯不饱和的单、双或多
羧酸，部分
羧酸酯，
羧酸酰胺，二元醇或多元醇的
羧酸单酯，
氨基醇的
羧酸酯和
乙烯吡咯烷。表面活性剂分散稳定剂对于乳液聚合的技术领域的熟练者是众所周知的。典型的例子是
硫酸酯化酰丙
氨酸的高级烷基酯，C.sub.8至C.sub.20烃基
硫酸盐或
磺酸盐，以及聚乙氧化的烷醇，烷基化
苯酚，烷基酸或酸酰胺及其磺化，磺化或
磷化衍
生物。本过程的另一个先决条件是分散的聚合物颗粒的表面不完全被任何稳定表面活性剂覆盖。这可以通过Nouben-Weyl“Methoden der organischen Chemie”Vol. 14/1，p.370根据肥皂滴定法确定，并且通常情况下会发现，如果聚合物分散体的表面张力高于50 dynes/cm，并且最好高于55 dynes/cm，则情况是如此。为了使细小颗粒不可逆地聚合成较粗的颗粒，还需要构成分散聚合物颗粒的主体积比例的聚合物，例如在混合聚合物的分散体中，其
玻璃化转变温度（Tg）低于并且最好比诱导聚合的温度低20℃以上。幸运的是，许多聚合物，例如含有高比例的
丁二烯和/或
异戊二烯和/或高级烷基醇的
丙烯酸酯，其
玻璃化转变温度远低于0℃。因此，当采用本过程时，通常可以在常温下轻松地实现不可逆聚合。基于上述，本发明广泛提供一种扩大聚合物分散体颗粒大小的过程，其中将聚合物分散体与表面活性剂混合，该表面活性剂是非离子聚乙氧基化高和/或取代
脂肪酸酯或较高的烃基胺。特别是，表面活性剂的HLB数（如前所述）应为16至19.5，分子量应为1800至25,000，而聚合物应通过来自亲
水单体的基团或存在于聚合物中的稳定表面活性剂稳定。该扩大过程应在分散聚合物的
玻璃化转变温度以上的温度下进行。为了实施本过程，最好首先将聚乙氧基化表面活性剂溶解在适当的溶剂中，通常为
水或含
水混合物中，然后将其与要处理的聚合物分散体混合。可以将表面活性剂溶液添加到聚合物分散体中，反之亦然。使用的表面活性剂量可以从每100份分散体中所含的聚合物干重0.01至5份干重变化。最好的量在每100份聚合物中为0.02至1.0份表面活性剂。在本过程中使用的聚乙氧基表面活性剂，特别是具有分子量大于3000和HLB数高于17的表面活性剂，当添加到细小颗粒的聚合物分散体中时，通常会导致宏观凝块的形成。有几种方法可用于最小化或消除这种凝块形成的危险，这些方法如下：1.向分散体或粗化表面活性剂溶液中添加通常在乳液聚合过程中使用的类型的稳定表面活性剂，如前面在该上下文中提到的。适当的稳定表面活性剂包括非离子表面活性剂，例如聚乙氧化C.sub.12-C.sub.20醇，烷基化
苯酚，酰胺和
氨基，其HLB数低于17且最好低于16，并且其分子量低于1500且最好低于1200。其他适当的稳定表面活性剂的例子是前面提到的
硫酸盐，
磺酸盐，
磷酸盐和
硫代
琥珀酸盐。2.通过添加碱或酸来调整聚合物分散体和/或粗化剂溶液的pH值，这些碱或酸最好已被稀释在
水中。在本发明的一种优选实施方式中，适用于羧化聚合物的分散体，首先通过碱（最好是挥发性碱，例如
氨或有机胺）将分散体的pH值提高到保证至少50％的
羧酸基离子化的值以上。然后添加粗化剂，但在
