Bimodal particle size distribution latex and preparation method thereof

Abstract

The present invention provides a method for preparing a latex with a bimodal particle size distribution. In the first step of the method, a small-particle-size latex is prepared. In the second step, a monomer is fed once to increase the monomer concentration, thereby solving the problem of a long reaction time of conventional seed emulsion polymerization. By controlling the addition method of the emulsifier in the second step, the latex particle size is formed into a regular bimodal distribution in situ, and the size and ratio are adjustable, flexible and controllable. The prepared bimodal particle size distribution latex can be used as a raw material for preparing ABS resin.

Description

Technical Field

[0001] The invention belongs to the field of latex preparation, and in particular relates to a latex with bimodal particle size distribution and a preparation method thereof. Background Art

[0002] ABS resin is an acrylonitrile-butadiene-styrene terpolymer, which has the characteristics of high gloss and easy processing of polystyrene, high toughness and impact resistance of polybutadiene, and chemical resistance and weather resistance of polyacrylonitrile. It is widely used in all aspects of life and industry such as electronic appliances, automobiles, and building materials. The current global annual consumption is nearly 10 million tons. ABS resin is essentially a rubber-toughened polystyrene series resin, which is a mixture of polybutadiene rubber and SAN (styrene-acrylonitrile copolymer) resin. The former provides impact resistance as a dispersed phase, and the latter provides strength as a continuous phase matrix. Due to the high polarity of acrylonitrile monomer, the solubility parameters between polybutadiene rubber and SAN resin containing acrylonitrile structural units are different, the interfacial tension is large, and the compatibility is poor. Direct physical blending will result in macroscopic phase separation. Therefore, the usual method for preparing ABS resin is to prepare PBL (polybutadiene latex) with a particle size of about 300nm through emulsion polymerization, and then further carry out core-shell emulsion polymerization (sometimes also called seed emulsion polymerization) of PBL with styrene and acrylonitrile monomers. A grafted SAN shell layer with a thickness of tens of nanometers is attached to the surface of the polybutadiene latex particles by chemical bonding. The high-rubber powder obtained after condensation and drying is then blended with the separately prepared SAN resin, solving the problem of compatibility between the two phases.

[0003] With the further development of ABS polymerization technology, bimodal or multimodal particle size ABS resins have emerged, that is, the resin contains two or more polybutadiene rubbers with different particle size distributions (the particle size is a statistical average value, and there is a distribution. Unless otherwise specified, the particle size mentioned below is the average particle size). Those skilled in the art know that particles of different particle sizes can often have a synergistic toughening effect in the matrix, and have better impact resistance than ABS resins with a single particle size distribution.

[0004] Patent document CN103910946A discloses a method for preparing bimodal ABS, wherein PBL with a particle size of 0.1 μm is prepared by emulsion polymerization, and then polymer agglomeration is performed to prepare latex with a particle size of 0.3 μm, and then two latexes with different particle sizes are grafted separately, coagulated and dried, and then blended with SAN resin. This bimodal ABS resin has many steps to prepare, and needs to be grafted and coagulated separately.

[0005] A more common method is to mix latexes with different particle size distributions first, and then carry out graft polymerization and coagulation drying. CN103044842A discloses that 100nm particle size styrene butadiene latex and 300nm particle size polybutadiene latex are mixed and then grafted. CN102199253A discloses that latex with a particle size of about 300nm and ultra-large particle size latex with particle sizes of 450nm, 650nm and 720nm are mixed and grafted. US5008331A discloses that a series of latexes with average particle sizes of 250nm, 170nm, 110nm and 330nm are prepared by emulsion polymerization, and then selectively mixed in pairs and grafted as raw materials for further grafting. TW201229141A discloses that a small particle size latex is first synthesized, the particle size is enlarged by acetic acid agglomeration, and then mixed with a small particle size PBL to obtain a bimodal or multimodal PBL.

[0006] It can be seen that the raw material bimodal PBL of bimodal ABS is mostly obtained by mixing separately prepared small-particle latex of 60-110nm and large-particle latex of 270-320nm. There is also a large-particle latex of 280-300nm and a small amount of super-large particle latex of 450-750nm. Generally, the larger the latex particle size, the higher the solid content during polymerization, the more stringent the reaction conditions, and the greater the difficulty of the polymerization process. The emulsion polymerization reaction conditions of small-particle latex are mild, but the ABS resin prepared by PBL with too small particle size is poor in toughness, so it cannot be used alone, but as one of the raw materials of bimodal or multimodal distribution ABS resin. Super-large particle size polybutadiene latex is basically impossible to be directly prepared by a one-step process, and most of them are amplified by chemical agglomeration, polymer agglomeration, etc. The agglomeration process is to first briefly and locally demulsify the small-particle latex. In theory, stable large-particle particles can be obtained after aggregation. However, the process is not stable, which makes the process complicated and the conditions harsh. It is easy to cause a large amount of demulsification and the formation of agglomerates. In addition, there are problems such as difficulty in controlling the particle size after agglomeration and poor batch stability.

[0007] The most mature polybutadiene latex polymerization is a one-step process for preparing particles with a diameter of 280-300nm. The early latex polymerization cycle of about 300nm particle size was as long as 80 hours. With the advancement of technology, it can now be controlled within about 30 hours. Compared with the early emulsion polymerization and small particle size latex polymerization, its overall reaction temperature is also higher to increase the reaction rate, but after the conversion rate reaches 90%, the gel content of the rubber at high temperature rises suddenly, or even gets out of control. Therefore, when the conversion rate reaches between 90-93%, a rapid terminator will be added, but it also causes a waste of monomer raw materials and an increase in raw material costs and waste gas emission costs, and limits the further growth of particle size. In addition, the one-step emulsion polymerization is limited by process and production efficiency considerations. The particle size is generally fixed between 280-300nm, and it is difficult to prepare latex particles with a particle size of 330-400nm, which limits the particle size distribution range of the large particle size peak of bimodal ABS.

[0008] Seed emulsion polymerization is a two-step polymerization process, first preparing small-particle latex, and then using a small amount of small-particle latex as seeds to carry out further emulsion polymerization to enlarge the particle size. People familiar with this technical field know that the biggest feature of seed emulsion polymerization compared to one-step polymerization is that the particle size and gel content are controllable, the process conditions are mild, and latex with narrow particle size distribution can be obtained. In the case of the unchanged amount of polymerization monomers in the second step, the particle size can be adjusted by simply changing the amount of seeds, and polybutadiene latex with a particle size exceeding 400nm can be prepared. CN1535297A discloses preparing latexes with an average particle size of 112nm, 158nm, 191nm, 216nm, 285nm, 350nm, and 415nm respectively by seed emulsion polymerization, and then selecting two or more of them to mix, and then carrying out bimodal or multimodal graft polymerization to adjust the resin performance of later production. However, in the second step polymerization of traditional seed emulsion polymerization, in order to avoid the generation of new latex particles, the monomer and emulsifier are added continuously or semi-continuously, i.e., "starvation feeding method", so that the monomer polymerization speed is close to the feeding speed, so as to suppress the generation of new micelles and latex particles, and allow the monomer to polymerize only on the seed. This monomer continuous or semi-continuous feeding method keeps the monomer concentration in the reactor at a very low level, and the diffusion rate controls the overall reaction speed, which essentially determines the slowness of the seed emulsion polymerization speed. In patent document US5071946A, only the second step polymerization time is as long as 90-100 hours, and the larger the particle size, the longer the required time, and because the time is too long, butadiene monomer produces dimer through DA addition reaction, which is difficult to further carry out free radical polymerization, resulting in the loss of raw materials, and the dimer smells big at the same time, which is considered to be one of the reasons for the large odor of ABS resin finished product.

[0009] Patent document CN107075039A discloses that when the one-step polymerization conversion rate reaches between 60% and 85%, a bimodal distribution latex can be prepared in situ by adding an appropriate amount of monomers and a special emulsifier with a CMC less than 10 mg / L. However, the small particle size of this latex is 60-70 nm according to transmission electron microscopy observation and statistics, and the number is only between 2-4%. The relationship between the volume V and radius R of a sphere is Under the condition of the same density, the mass (volume) of the small-size latex particles of 2-4% is almost negligible compared with the mass (volume) of the latex particles of 300nm particle size, and the volume (weight) particle size will still be a unimodal distribution. In fact, the latex particle size is polydisperse, and the particle size is a statistical average. The conventional unimodal 300nm particle size latex particles also contain a certain number of small-size latex particles. Therefore, the latex particle size distribution disclosed in CN107075039A is not bimodal in the true sense. In addition, people familiar with this technical field know that bimodal ABS should be prepared by feeding large and small particle size latex according to the mass ratio, and the mass ratio is usually prepared between 8:2 and 5:5. The mechanical properties of ABS resin prepared with the latex disclosed in CN107075039A have not been improved, but have decreased when the quantity contains 4%.

[0010] In summary, bimodal PBL is generally prepared by a one-step process or a two-step process such as seed polymerization, where large and small particle sizes of latex are prepared separately, and then mixed, grafted, and blended to prepare ABS resin. The process of the small particle size part of the bimodal is simple, but there are various problems in the polymerization of the large particle size part. For example, although the one-step method is the current mainstream PBL production process, it is difficult to prepare a large particle size latex due to the limitation of particle size growth. The seed method can prepare a large particle size latex, but it is limited by the reaction time and the production efficiency is extremely low. It is almost not adopted by ABS polymerization manufacturers and its development is almost stagnant.

[0011] Therefore, there is a need in the art for a method for preparing a latex with a high efficiency and bimodal particle size distribution. Summary of the invention

[0012] The purpose of the present invention is to provide a method for preparing a latex with a bimodal particle size distribution. In the first step of the method of the present invention, a small-particle latex is prepared. In the second step, a monomer is fed once to increase the monomer concentration, thereby solving the problem of a long reaction time of conventional seed emulsion polymerization. At the same time, the emulsifier is added in the second step to form a regular bimodal particle size distribution in situ, and the size and ratio are adjustable, flexible and controllable. The prepared latex with a bimodal particle size distribution can be used as a raw material for preparing ABS resin.

[0013] Specifically, the present invention provides a method for preparing a latex with a bimodal particle size distribution, the method comprising:

[0014] (1) providing seed latex;

[0015] (2) Particle size enlargement polymerization: subjecting the reaction raw material mixture comprising the seed latex and monomers described in step (1) to polymerization reaction, wherein an emulsifier is added during the period when the monomer conversion rate reaches 20-45%.

[0016] In one or more embodiments, the monomers of the polymer contained in the seed latex in step (1) include butadiene, and the monomers in the reaction raw material mixture in step (2) include butadiene.

[0017] In one or more embodiments, based on 100 parts by weight of the monomers contained in the reaction raw material mixture, in step (2), the amount of the emulsifier added during the period when the monomer conversion rate reaches 20-45% is 1-4 parts by weight.

[0018] In one or more embodiments, in step (2), an emulsifier is added during the period when the monomer conversion rate reaches 50-60%; preferably, the amount of emulsifier added during the period when the monomer conversion rate reaches 50-60% does not exceed 4 parts by weight based on 100 parts by weight of the monomer contained in the reaction raw material mixture.

[0019] In one or more embodiments, the polymerization reaction described in step (2) includes: heating the reaction raw material mixture to 45-70°C, adding an initiator, and reacting for 5-10 hours; then heating to 65-80°C, reacting for 5-15 hours, during which time an initiator is optionally added; and finally heating to 80-90°C, aging for 2-4 hours, during which time an initiator is optionally added to complete the reaction.

[0020] In one or more embodiments, in step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of initiator added after the temperature is raised to 45-70°C is preferably 0.05-1 part by weight, the amount of initiator optionally added during the reaction when the temperature is raised to 65-80°C is preferably not more than 1 part by weight, and the amount of initiator optionally added during the reaction when the temperature is raised to 80-90°C is preferably not more than 1 part by weight; preferably, the initiator is a persulfate, a peroxide compound or a redox system, preferably a persulfate; preferably, the temperature is raised to 65-80°C when the reaction at 45-70°C reaches a conversion rate of 45-55%; preferably, the temperature is raised to 80-90°C when the reaction at 65-80°C reaches a conversion rate of 70-85%; preferably, the reaction is stopped when the reaction at 80-90°C reaches a conversion rate of 90-97%.

[0021] In one or more embodiments, in step (2), no additional monomer is added during the polymerization reaction.

[0022] In one or more embodiments, the polymer contained in the seed latex in step (1) is obtained by polymerizing one or more monomers selected from butadiene, isoprene and butyl acrylate, preferably by polymerizing butadiene.

[0023] In one or more embodiments, the average particle size of the seed latex in step (1) is 50-130 nm, such as 100-130 nm.

[0024] In one or more embodiments, in step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the content of the seed latex in the reaction raw material mixture on a dry weight basis is 1-15 parts by weight.

[0025] In one or more embodiments, the monomer in the reaction raw material mixture in step (2) is selected from one or more of butadiene, isoprene and butyl acrylate, preferably butadiene.

[0026] In one or more embodiments, the additional emulsifier added in step (2) comprises one or more of rosin acid salts, fatty acid salts and sulfonates thereof, alkylaryl sulfonates and sulfonated alkyl esters, preferably comprises disproportionated rosin acid salts.

[0027] In one or more embodiments, in step (2), the reaction raw material mixture comprises seed latex, water, electrolyte, emulsifier, chain transfer agent and monomer; based on 100 parts by weight of the monomer contained in the reaction raw material mixture, the content of water in the reaction raw material mixture is preferably 50-180 parts by weight, the content of electrolyte is preferably 0.1-5 parts by weight, the content of emulsifier is preferably 0.2-4 parts by weight, and the content of chain transfer agent is preferably 0.1-1 parts by weight; preferably, the electrolyte in the reaction raw material mixture is selected from sodium chloride, potassium chloride, sodium carbonate, One or more of potassium carbonate, sodium bicarbonate, potassium bicarbonate; preferably, the emulsifier in the reaction raw material mixture includes one or more of rosin acid salts, fatty acid salts and sulfonates thereof, alkyl aryl sulfonates and sulfonated alkyl esters, preferably comprises disproportionated rosin acid salts, more preferably disproportionated rosin acid salts; preferably, the chain transfer agent in the reaction raw material mixture is a normal or tert-alkyl mercaptan with a carbon chain length of 10-16, preferably tert-dodecyl mercaptan; preferably, the initiator in the reaction raw material mixture is a persulfate, a peroxide compound or a redox system, preferably a persulfate.

[0028] In one or more embodiments, in step (2), the emulsifier added during the period when the monomer conversion rate reaches 20-45% includes disproportionated rosin acid salt, preferably includes disproportionated rosin acid salt and an emulsifier whose critical micelle concentration in the polymerization reaction system of step (2) is less than that of disproportionated rosin acid salt; the emulsifier whose critical micelle concentration in the polymerization reaction system of step (2) is less than that of disproportionated rosin acid salt is preferably a fatty acid salt; preferably, in the emulsifier added during the period when the monomer conversion rate reaches 20-40%, the mass ratio of disproportionated rosin acid salt to the emulsifier whose critical micelle concentration in the polymerization reaction system of step (2) is preferably ≥2:1, more preferably ≥3:1, for example, 3:1 to 20:1.

[0029] In one or more embodiments, in step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of emulsifier added during the period when the monomer conversion rate reaches 20-45% is 1-2 parts by weight.

[0030] In one or more embodiments, in step (2), an emulsifier is added during the period when the monomer conversion rate reaches 50-60%; preferably, the emulsifier added during the period when the monomer conversion rate reaches 50-60% comprises disproportionated rosin acid salt, preferably disproportionated rosin acid salt; preferably, the amount of the emulsifier added during the period when the monomer conversion rate reaches 50-60% is not more than 1 part by weight, based on 100 parts by weight of the monomer contained in the reaction raw material mixture.

[0031] In one or more embodiments, the reaction raw material mixture in step (2) comprises seed latex, water, electrolyte, emulsifier, chain transfer agent and monomer, and based on 100 parts by weight of the monomer contained in the reaction raw material mixture, the content of seed latex in the reaction raw material mixture on a dry weight basis is 2-8 parts by weight, the content of water is 50-100 parts by weight, the content of electrolyte is 0.2-1 part by weight, the content of emulsifier is 0.2-1 part by weight, and the content of chain transfer agent is 0.1-1 part by weight.

[0032] In one or more embodiments, the polymerization reaction in step (2) comprises: heating the reaction raw material mixture to 45-70°C, adding an initiator, and reacting for 5-10 hours; then heating the mixture to 65-80°C, reacting for 5-15 hours, during which time an initiator is optionally added; and finally heating the mixture to 80-90°C, aging for 2-4 hours, during which time an initiator is optionally added to complete the reaction, wherein, based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of initiator added after heating to 45-70°C is 0.1-0.5 parts by weight, the amount of initiator optionally added during the reaction when the temperature is raised to 65-80°C is no more than 0.2 parts by weight, and the amount of initiator optionally added during the reaction when the temperature is raised to 80-90°C is no more than 0.2 parts by weight.

[0033] In one or more embodiments, the seed latex is prepared by the following method: mixing water, emulsifier, electrolyte, chain transfer agent and monomer to obtain a seed latex raw material mixture, heating the mixture to 35-65°C, adding an initiator, and reacting for 10-20 hours, during which an emulsifier is optionally added; then heating the mixture to 65-85°C, reacting for 5-10 hours, during which an initiator is optionally added to complete the reaction.

[0034] In one or more embodiments, the method of preparing a bimodal particle size distribution latex of the present invention comprises:

[0035] (1) preparing seed latex: mixing water, emulsifier, electrolyte, chain transfer agent and monomer to obtain seed latex raw material mixture, heating to 35-65° C., adding initiator, reacting for 10-20 hours, during which emulsifier is optionally added; then heating to 65-85° C., reacting for 5-10 hours, during which initiator is optionally added, to complete the reaction;

[0036] (2) Particle size enlargement polymerization: subjecting the reaction raw material mixture comprising the seed latex and monomers described in step (1) to polymerization reaction, wherein an emulsifier is added during the period when the monomer conversion rate reaches 20-45%.

[0037] In one or more embodiments, the monomer in the seed latex raw material mixture is selected from one or more of butadiene, isoprene and butyl acrylate, preferably butadiene.

[0038] In one or more embodiments, the average particle size of the seed latex is 50-130 nm, such as 100-130 nm.

[0039] In one or more embodiments, based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, the water content in the seed latex raw material mixture is 50-180 parts by weight, the electrolyte content is 0.05-3 parts by weight, the emulsifier content is 1-8 parts by weight, and the chain transfer agent content is 0.1-1 part by weight.

[0040] In one or more embodiments, based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, when preparing the seed latex, the amount of initiator added after heating to 35-65°C is 0.05-1 part by weight, and the amount of initiator optionally added during the reaction when the temperature is raised to 65-85°C does not exceed 1 part by weight.

[0041] In one or more embodiments, the electrolyte in the seed latex raw material mixture is selected from one or more of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

[0042] In one or more embodiments, the emulsifier in the seed latex raw material mixture comprises one or more of rosin acid salts, fatty acid salts and sulfonates thereof, alkylaryl sulfonates, and sulfonated alkyl esters, preferably disproportionated rosin acid salts.

[0043] In one or more embodiments, the chain transfer agent in the seed latex raw material mixture is a normal or tertiary alkyl mercaptan having a carbon chain length of 10-16, preferably tert-dodecyl mercaptan.

[0044] In one or more embodiments, the initiator added during the preparation of the seed latex is a persulfate, a peroxy compound or a redox system, preferably a persulfate.

[0045] In one or more embodiments, the emulsifier optionally added during the reaction at 35-65° C. in the process of preparing the seed latex comprises one or more of rosin acid salts, fatty acid salts and sulfonates thereof, alkylaryl sulfonates and sulfonated alkyl esters, preferably disproportionated rosin acid salts.

[0046] In one or more embodiments, when preparing the seed latex, the reaction is carried out at 35-65° C. until the conversion rate reaches 60-75%, and then the temperature is raised to 65-85° C.

[0047] In one or more embodiments, when preparing the seed latex, the reaction is stopped at 65-85° C. when the conversion rate reaches 90-97%.

[0048] In one or more embodiments, no additional monomer is added during the reaction to prepare the seed latex.

[0049] In one or more embodiments, the emulsifier in the seed latex raw material mixture includes one or more of rosin salts, fatty acid salts and sulfonates thereof, alkylaryl sulfonates and sulfonated alkyl esters, preferably includes disproportionated rosin salts; preferably, in the seed latex raw material mixture, the mass of disproportionated rosin salt accounts for more than 60% of the total mass of the emulsifier, for example, more than 75%.

[0050] In one or more embodiments, the emulsifier optionally added during the reaction at a temperature of 35-65° C. in the process of preparing the seed latex is disproportionated rosin acid salt.

[0051] In one or more embodiments, based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, the amount of emulsifier optionally added during the reaction at 35-65°C during the preparation of the seed latex does not exceed 4 parts by weight, and preferably does not exceed 2 parts by weight.

[0052] In one or more embodiments, based on 100 parts by weight of the monomer contained in the seed latex raw material mixture, the water content in the seed latex raw material mixture is 100-150 parts by weight, the electrolyte content is 0.1-1 part by weight, the emulsifier content is 1-4 parts by weight, and the chain transfer agent content is 0.1-1 part by weight.

[0053] In one or more embodiments, based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, when preparing the seed latex, the amount of initiator added after heating to 35-65°C is 0.1-0.5 parts by weight, and the amount of initiator optionally added during the reaction when the temperature is raised to 65-85°C does not exceed 0.2 parts by weight.

[0054] The present invention also provides a latex with bimodal particle size distribution prepared by the method described in any embodiment of the present invention.

[0055] In one or more embodiments, in the bimodal particle size distribution latex, the average particle size of the large particle size latex particles is 280-400 nm.

[0056] In one or more embodiments, in the bimodal particle size distribution latex, the average particle size of the small particle size latex particles is 90-170 nm.

[0057] In one or more embodiments, in the bimodal particle size distribution latex, the mass ratio of large particle size latex particles to small particle size latex particles is 3:1 to 1:1.5.

[0058] In one or more embodiments, in the bimodal particle size distribution latex, the area ratio of the large particle size peak to the small particle size peak is 7:3 to 3:7.

[0059] The present invention also provides the use of the latex with bimodal particle size distribution described in any embodiment of the present invention in the preparation of ABS resin or high-rubber powder.

[0060] The present invention also provides a high-rubber powder, which is prepared by core-shell emulsion polymerization of the latex with bimodal particle size distribution described in any embodiment of the present invention and a monomer composition containing styrene and acrylonitrile.

[0061] The present invention also provides an ABS resin obtained by blending the high-rubber powder described in any embodiment of the present invention with a resin composition containing a styrene-acrylonitrile copolymer. DETAILED DESCRIPTION

[0062] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0063] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0064] Herein, “comprising”, “including”, “containing” and similar terms cover the meanings of “consisting essentially of” and “consisting of”, for example, when “A comprises B and C” is disclosed herein, “A consists of B and C” should be deemed to be disclosed herein.

[0065] Herein, "optionally including" and similar terms cover the meanings of "including" and "not including". Herein, "optionally adding" and similar terms cover the meanings of "adding" and "not adding". When this document discloses "the amount of A optionally added does not exceed a", "no additional A" and "the amount of A added is greater than 0 and less than or equal to a" should be considered to have been disclosed herein. It can be understood that, herein, "the amount of A added does not exceed a" means that the amount of A added is greater than 0 and less than or equal to a.

[0066] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​(including integers and fractions) within the range. In this article, unless otherwise specified, numerical ranges and percentage ranges include endpoint values.

[0067] Herein, unless otherwise specified, percentage refers to mass percentage, ratio refers to mass ratio, and part refers to mass part.

[0068] Herein, when describing embodiments or examples, it should be understood that they are not used to limit the present invention to these embodiments or examples. On the contrary, all substitutes, improvements and equivalents of the methods and materials described in the present invention can be included in the scope limited by the claims.

[0069] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0070] Conventional butadiene emulsion polymerization, whether one-step or two-step, is basically to obtain a stable, monodisperse latex. Conventional bimodal latex is obtained by mixing latexes of different particle sizes. These latexes are all unimodal before mixing, especially those prepared by the seed method.

[0071] In the second step of traditional seed polymerization, the monomer and emulsifier concentrations are kept at a low level, so that no new latex particles are generated, and only the seeds put in react to increase the particle size. The resulting particle size distribution is relatively narrow, that is, the degree of monodispersion is higher, and larger latex particles can be prepared than the one-step method. However, the biggest drawback of the seed method is that the polymerization time is twice or even three times that of the one-step method, and the production efficiency is very low, resulting in the stagnation of research on seed emulsion polymerization of butadiene.

[0072] Compared with the traditional seed method, the preparation method of the present invention takes the opposite approach. In the second step, the monomer is directly added into the small-particle latex prepared in the first step at one time, that is, no monomer is added during the reaction. At the same time, by controlling the addition method of the emulsifier, the particle size of the latex is regularized into a bimodal distribution, and the large-particle size part in the bimodal distribution can be larger than the latex prepared by the one-step method.

[0073] It is understood that, herein, the particle size of latex (e.g., the particle size of PBL) refers to the particle size (diameter) of polymer particles in latex, specifically refers to the average particle size of polymer particles. Generally, if the particle size-volume fraction distribution curve or the particle size-mass fraction distribution curve of polymer particles has a plurality of relatively significant peaks, it is considered that the particle size of polymer particles is multimodal. When the particle size of polymer particles is multimodal, the polymer particles have a plurality of particle size values ​​corresponding to the number of peaks, and each particle size value is the average particle size of polymer particles corresponding to the corresponding peaks, for example, when the particle size of polymer particles is bimodal, the polymer particles have large and small particle size values, which are the average particle size of polymer particles (large particle size latex particles) corresponding to the large particle size peak (large particle size portion in the bimodal) and the average particle size of polymer particles (small particle size latex particles) corresponding to the small particle size peak (small particle size portion in the bimodal).

[0074] The preparation method of the particle size bimodal distribution latex of the present invention comprises the following steps:

[0075] (1) providing seed latex;

[0076] (2) Particle size enlargement polymerization: Using the seed latex in step (1) as a seed, emulsion polymerization is carried out.

[0077] The seed latex in step (1) can be a seed latex prepared by a conventional emulsion polymerization method in the art or a seed latex prepared by the method provided by the present invention. Herein, the seed latex refers to an emulsion containing polymer particles with a relatively small particle size (e.g., a particle size of 50-130 nm), the polymer particles in the emulsion serve as cores (seeds), and a shell layer is grafted on the surface in the subsequent core-shell emulsion polymerization.

[0078] In some embodiments, the seed latex is prepared by the following method:

[0079] Preparing a raw material mixture: mixing water, an emulsifier, an electrolyte, a chain transfer agent and a monomer to obtain a seed latex raw material mixture;

[0080] First step reaction: after heating to 35-65°C, add initiator and react for 10-20 hours, during which time emulsifier may be added;

[0081] The second step reaction: heating to 65-85°C and reacting for 5-10 hours, during which time an initiator is optionally added to complete the reaction, thereby obtaining a seed latex with a particle size of 50-130 nm.

[0082] In some embodiments, the particle size of the seed latex is 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, or within a range of any two of these particle size values, such as 100-130 nm.

[0083] The water suitable for use in the present invention may be deionized water.

[0084] The monomers suitable for the present invention are one or more of butadiene, isoprene, butyl acrylate, etc. Butyl acrylate includes n-butyl acrylate and isobutyl acrylate. In some embodiments, the monomer of the polymer contained in the seed latex includes butadiene, that is, the polymer contained in the seed latex is obtained by polymerization of monomers including butadiene. In some embodiments, the polymer contained in the seed latex is obtained by polymerization of butadiene, that is, the monomer used to prepare the seed latex is butadiene. When preparing the seed latex, the monomer is put into the reaction system at one time (that is, no monomer is added during the polymerization reaction).

[0085] The initiator suitable for the present invention is a persulfate, a peroxy compound or a redox system. Persulfate can be potassium persulfate, sodium persulfate, ammonium persulfate, etc. Peroxy compounds can be hydrogen peroxide, azo peroxy compounds (such as azobisisobutyronitrile), etc. The redox system includes a main initiator, a reducing agent, a co-reducing agent and a chelating agent. The main initiator can be a persulfate, a peroxy compound, etc., or it can be oil-soluble isopropyl hydroperoxide, diisopropylbenzene peroxide, tert-butyl hydroperoxide, benzoyl peroxide and mixtures thereof. The reducing agent can be one or more of mercaptan, ferrous salt (such as ferrous sulfate), and bisulfite, preferably ferrous sulfate. The co-reducing agent can be one or more of dextrose, sodium ascorbate, fructose, and bleaching block. The chelating agent can be one or more of ethylenediamine diacetate and pyrophosphate. In some embodiments, the initiator used to prepare the seed latex is a persulfate, such as potassium persulfate, sodium persulfate, and ammonium persulfate. In some embodiments, the initiator used to prepare the seed latex is potassium persulfate.

[0086] Emulsifiers suitable for the present invention include one or more of rosin salts, fatty acid salts and sulfonates thereof, alkyl aryl sulfonates, and sulfonated alkyl esters. The cation of the salt emulsifier can be potassium ions and sodium ions, preferably potassium ions. Herein, rosin salts include disproportionated rosin salts (i.e., disproportionated rosin salts) and undisproportionated rosin salts. Examples of alkyl aryl sulfonates include, but are not limited to, dodecyl sulfonates. In the present invention, the emulsifier preferably comprises disproportionated rosin salts (e.g., disproportionated rosin acid potassium). In some embodiments, the emulsifier used in the present invention includes disproportionated rosin salts and optionally one or more selected from fatty acid salts and sulfonates thereof, alkyl aryl sulfonates, and sulfonated alkyl esters. In the present invention, the amount of disproportionated rosin salt can account for more than 60% of the total mass of the emulsifier, for example, more than 66%, more than 70%, or more than 75%.

[0087] The emulsifier in the seed latex raw material mixture may include disproportionated rosin acid salt and one or more selected from fatty acid salts and sulfonates thereof, alkyl aryl sulfonates and sulfonated alkyl esters. In some embodiments, the emulsifier in the seed latex raw material mixture includes disproportionated rosin acid salt and one or two selected from fatty acid salts and dodecyl sulfonates. Among the emulsifiers used in preparing the seed latex, the mass ratio of disproportionated rosin acid salt and the emulsifier other than disproportionated rosin acid salt may be ≥2:1, preferably ≥3:1, for example, 3:1 to 20:1. In some embodiments, the emulsifier in the seed latex raw material mixture includes disproportionated rosin acid salt, fatty acid salt and dodecyl sulfonate. Among them, the mass ratio of disproportionated rosin acid salt, fatty acid salt and dodecyl sulfonate may be (10-20):(1-5):1, for example (15±2):(3±1):1.

[0088] In some embodiments, the emulsifier optionally added in the first step of preparing the seed latex is disproportionated rosin acid salt.

[0089] The electrolyte suitable for the present invention is one or more of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate. In some embodiments, the electrolyte used in the present invention is selected from one or more of potassium carbonate, sodium bicarbonate, and potassium bicarbonate. In some embodiments, the electrolyte used to prepare the seed emulsion is potassium carbonate.

[0090] The chain transfer agent suitable for the present invention can be selected from carbon tetrachloride, dithioisocyanate, ethylene glycol, dithiazole sulfide and normal or tertiary alkyl mercaptan with a carbon chain length of 10 to 16. In some embodiments, the chain transfer agent used in the present invention is a normal or tertiary alkyl mercaptan with a carbon chain length of 10 to 16, preferably tert-dodecyl mercaptan.

[0091] Based on the amount of monomers contained in the seed latex raw material mixture as 100 parts by weight, in the seed latex raw material mixture, the content of water is 50-180 parts by weight, the content of electrolyte is 0.05-3 parts by weight, the content of emulsifier is 1-8 parts by weight, and the content of chain transfer agent is 0.1-1 parts by weight. In some embodiments, based on the amount of monomers contained in the seed latex raw material mixture as 100 parts by weight, in the seed latex raw material mixture, the content of water is 50 parts by weight, 60 parts by weight, 70 parts by weight, 80 parts by weight, 90 parts by weight, 100 parts by weight, 110 parts by weight, 115 parts by weight, 120 parts by weight, 130 parts by weight, 140 parts by weight, 150 parts by weight, 160 parts by weight, 170 parts by weight, 180 parts by weight, or in the range of any two of these content values, for example, 100-150 parts by weight. In some embodiments, based on the amount of monomers contained in the seed latex raw material mixture as 100 parts by weight, the content of electrolyte in the seed latex raw material mixture is 0.05 parts by weight, 0.1 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, or in the range of any two of these content values, for example, 0.1-1 parts by weight. In some embodiments, based on the amount of monomers contained in the seed latex raw material mixture as 100 parts by weight, the content of emulsifier in the seed latex raw material mixture is 1 part by weight, 1.5 parts by weight, 1.8 parts by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, or in the range of any two of these content values, for example, 1-4 parts by weight. In some embodiments, based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, the content of the chain transfer agent in the seed latex raw material mixture is 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 part by weight or within a range composed of any two of these content values.

[0092] Based on the amount of monomers contained in the seed latex raw material mixture as 100 parts by weight, the amount of initiator added in the first step reaction when preparing the seed latex is 0.05-1 parts by weight, and the amount of initiator optionally added during the second step reaction does not exceed 1 part by weight. In some embodiments, based on the amount of monomers contained in the seed latex raw material mixture as 100 parts by weight, the amount of initiator added in the first step reaction when preparing the seed latex is 0.05 parts by weight, 0.1 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 1 part by weight, or in the range of any two of these amounts, for example, 0.1-0.5 parts by weight. In some embodiments, based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, the amount of initiator optionally added during the second step reaction when preparing the seed latex is no more than 0.5 parts by weight, no more than 0.2 parts by weight, no more than 0.1 parts by weight, not less than 0.01 parts by weight, not less than 0.02 parts by weight, 0.05 parts by weight, or within the range of any two of these amounts, for example, 0.02-0.1 parts by weight.

[0093] Based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, the amount of emulsifier optionally added in the first step reaction of preparing the seed latex shall not exceed 4 parts by weight, for example, not more than 2 parts by weight, not more than 1 part by weight, not less than 0.1 parts by weight, not less than 0.2 parts by weight, not less than 0.5 parts by weight, 0.9 parts by weight or within the range of any two of these amounts, for example, 0.2-2 parts by weight.

[0094] In some embodiments, in the first step of preparing the seed latex, the seed latex raw material mixture is heated to 55-65° C., such as 58±2° C., and the reaction time is 10-15 hours, such as 12±1 hours.

[0095] In the first step of the reaction for preparing the seed latex, the emulsifier may be optionally added in batches, for example, in the 8th hour and the 11th hour respectively.

[0096] In some embodiments, in the second step of preparing the seed latex, the reaction system is heated to 70-80° C., such as 73° C.±2° C., and the reaction time is 5-10 hours.

[0097] In the second step of particle size enlargement polymerization, the present invention adopts a one-time feeding mode of monomers to increase the monomer concentration, thereby greatly shortening the polymerization time and overcoming the major defect of low production efficiency of traditional seed emulsion polymerization. For traditional seed emulsion polymerization, if the monomers are fed once in the second step, a large number of new latex particles will inevitably be generated during the polymerization process, and the particle size distribution will be chaotic. The present invention does not pursue the result that the latex prepared by the traditional seed emulsion polymerization method presents a single, narrow particle size distribution, but by controlling the timing, amount and type of the additional emulsifier, the particle size is formed in situ. Regular bimodal distribution, and the size and ratio are adjustable, flexible and controllable. In addition, in the method of the present invention, due to the presence of seeds in the second step, the large particle size of the latex finally generated can reach 280-400nm, which has a larger adjustable range than the 280-300nm latex of the traditional one-step method, providing more options for subsequent ABS resin performance adjustment.

[0098] In the present invention, the particle size enlargement polymerization comprises: subjecting a particle size enlargement polymerization reaction raw material mixture (hereinafter referred to as the reaction raw material mixture) comprising monomers and the seed latex described herein to polymerization reaction, wherein an emulsifier is added during the period when the monomer conversion rate reaches 20-45%.

[0099] The present invention has found that by adding monomers at once during the particle size enlargement polymerization process (i.e., no additional monomers are added during the polymerization reaction), and adding an emulsifier during the period when the monomer conversion rate reaches 20-45%, the particle size can be formed into a regular bimodal distribution in situ, thereby obtaining a latex with a bimodal particle size distribution. In the present invention, based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of the emulsifier added during the period when the monomer conversion rate reaches 20-45% is preferably 1-4 parts by weight, for example 1-2 parts by weight.

[0100] It is understood that, in the present invention, the addition of emulsifier during the period when the monomer conversion rate reaches 20-45% is the first addition of emulsifier, and no emulsifier is added before the monomer conversion rate reaches 20%.

[0101] In the particle size enlargement polymerization of the present invention, an emulsifier can be optionally added during the period when the monomer conversion rate reaches 50-60%. In the present invention, the addition of an emulsifier when the monomer conversion rate reaches 50-60% is not necessary for forming a bimodal particle size distribution latex with a desired particle size, but it is beneficial to improve the overall stability and quality of the latex. When the emulsifier is added during the period when the monomer conversion rate reaches 50-60%, the amount of the added emulsifier is preferably not more than 4 parts by weight, such as 1-4 parts by weight or 1-2 parts by weight, based on 100 parts by weight of the monomer contained in the reaction raw material mixture.

[0102] In some embodiments, the particle size enlargement polymerization comprises the following three steps:

[0103] The first step of reaction: after heating the reaction raw material mixture to 45-70°C, add the initiator and react for 5-10 hours;

[0104] Step 2: heating to 65-80°C and reacting for 5-15 hours, during which time an initiator may be optionally added;

[0105] The third step reaction: heating to 80-90°C and aging for 2-4 hours, during which time initiator is optionally added to complete the reaction.

[0106] In the present invention, the reaction raw material mixture generally includes seed latex, water, electrolyte, emulsifier, chain transfer agent and monomer.

[0107] The types of electrolytes, emulsifiers, chain transfer agents, monomers, and initiators suitable for particle size enlargement polymerization are as described in any of the above embodiments, and the electrolytes, emulsifiers, chain transfer agents, monomers, and initiators used to prepare the seed latex can be used.

[0108] In some embodiments, the electrolyte used in the particle size enlargement polymerization is selected from one or more of potassium carbonate, sodium bicarbonate and potassium bicarbonate.

[0109] The emulsifier used in the particle size enlargement polymerization preferably includes a disproportionate rosin acid salt (such as potassium disproportionate rosin acid salt), which has suitable stability and critical micelle concentration (CMC value) to prevent the reaction rate from being too high and out of control, and is conducive to obtaining a latex with a bimodal particle size distribution.

[0110] In some embodiments, the emulsifier in the reaction raw material mixture includes disproportionated rosin acid salt, and its amount can account for more than 60% of the total mass of the emulsifier in the reaction raw material mixture, such as more than 66%, more than 70%, more than 75%, more than 80%, or more than 90%. In some embodiments, the emulsifier in the reaction raw material mixture is disproportionated rosin acid salt.

[0111] In the particle size enlargement polymerization, the added emulsifier may optionally include a small amount of an emulsifier (e.g., fatty acid salt) whose CMC value in the reaction system of the particle size enlargement polymerization is less than that of the disproportionated rosin acid salt, in addition to the disproportionated rosin acid salt, to further promote the formation of small-size latex particles. When the added emulsifier includes the disproportionated rosin acid salt and the emulsifier whose CMC value in the reaction system of the particle size enlargement polymerization is less than that of the disproportionated rosin acid salt, the mass ratio of the disproportionated rosin acid salt to the emulsifier whose CMC value in the reaction system of the particle size enlargement polymerization is preferably ≥2:1, more preferably ≥3:1, for example, 3:1-20:1, for example, 3.2:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 15:1.

[0112] In some embodiments, the emulsifier added during the period when the monomer conversion rate reaches 20-45% in the particle size enlargement polymerization includes disproportionated rosin acid salt and an emulsifier having a CMC value less than that of disproportionated rosin acid salt in the reaction system of the particle size enlargement polymerization.

[0113] In some embodiments, the emulsifier added during the particle size enlargement polymerization when the monomer conversion rate reaches 50-60% is disproportionated rosin acid salt.

[0114] Taking the amount of monomers contained in the reaction raw material mixture as 100 parts by weight, the content of seed latex in the reaction raw material mixture on a dry weight basis is 1-15 parts by weight, the content of water is 50-180 parts by weight, the content of electrolyte is 0.1-5 parts by weight, the content of emulsifier is 0.2-4 parts by weight, and the content of chain transfer agent is 0.1-1 parts by weight. The solid content of seed latex suitable for the present invention is usually 35-50%, such as 38-48%, 40±2%. Taking the amount of monomers contained in the reaction raw material mixture as 100 parts by weight, the content of seed latex in the reaction raw material mixture on a dry weight basis can be 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 10 parts by weight, 15 parts by weight, or within the range of any two of these content values, such as 2-8 parts by weight. Based on the amount of monomers contained in the reaction raw material mixture as 100 parts by weight, the content of water in the reaction raw material mixture can be 50 parts by weight, 60 parts by weight, 70 parts by weight, 75 parts by weight, 80 parts by weight, 90 parts by weight, 100 parts by weight, 120 parts by weight, 150 parts by weight, 180 parts by weight, or in the range of any two of these content values, for example, 50-100 parts by weight. Based on the amount of monomers contained in the reaction raw material mixture as 100 parts by weight, the content of electrolyte in the reaction raw material mixture can be 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.8 parts by weight, 1 part by weight, 2 parts by weight, 5 parts by weight, or in the range of any two of these content values, for example, 0.2-1 parts by weight. Based on the amount of monomers contained in the reaction raw material mixture as 100 parts by weight, the content of the emulsifier in the reaction raw material mixture can be 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.8 parts by weight, 1 part by weight, 2 parts by weight, 4 parts by weight, or in the range of any two of these content values, for example, 0.2-1 parts by weight. Based on the amount of monomers contained in the reaction raw material mixture as 100 parts by weight, the content of the chain transfer agent in the reaction raw material mixture can be 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.8 parts by weight, 1 part by weight, or in the range of any two of these content values.

[0115] Based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of initiator added in the first step of the particle size enlargement polymerization reaction is 0.05-1 parts by weight, the amount of initiator optionally added in the second step of the particle size enlargement polymerization reaction does not exceed 1 part by weight, and the amount of initiator optionally added in the third step of the particle size enlargement polymerization reaction does not exceed 1 part by weight. In some embodiments, based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of initiator added in the first step of the particle size enlargement polymerization reaction is 0.05 parts by weight, 0.1 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 1 part by weight, or in the range of any two of these amounts, for example, 0.1-0.5 parts by weight. In some embodiments, based on 100 parts by weight of the monomers contained in the reaction raw material mixture, in the second step of the particle size enlargement polymerization, the amount of the initiator optionally added does not exceed 0.5 parts by weight, for example, not more than 0.2 parts by weight, not more than 0.1 parts by weight, not less than 0.01 parts by weight, not less than 0.02 parts by weight, 0.05 parts by weight, or in the range of any two of these amounts. In some embodiments, based on 100 parts by weight of the monomers contained in the reaction raw material mixture, in the third step of the particle size enlargement polymerization, the amount of the initiator optionally added does not exceed 0.5 parts by weight, for example, not more than 0.2 parts by weight, not more than 0.1 parts by weight, not less than 0.01 parts by weight, not less than 0.02 parts by weight, 0.05 parts by weight, or in the range of any two of these amounts.

[0116] In some embodiments, in the particle size enlargement polymerization, based on 100 parts by weight of the monomer, the amount of emulsifier added during the period when the monomer conversion rate reaches 20-45% is 1 part by weight, 1.05 parts by weight, 1.2 parts by weight, 1.4 parts by weight, 1.8 parts by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight or within the range of any two of these amounts, for example, 1-2 parts by weight.

[0117] In some embodiments, in the particle size enlargement polymerization, the amount of emulsifier optionally added during the period when the monomer conversion rate reaches 50-60% is no more than 2 parts by weight, no more than 1 part by weight, no less than 0.1 parts by weight, no less than 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.8 parts by weight, or within the range of any two of these amounts, based on 100 parts by weight of the monomer used. In some embodiments, the preparation method of the latex with bimodal particle size distribution of the present invention includes a first step of seed latex preparation and a second step of particle size enlargement polymerization. The first step is to prepare a small particle size PBL with a particle size of 50-130nm, and the reaction time is 10-25 hours. In the second step, a small amount of the small particle size PBL prepared in the first step is taken as a seed, and emulsion polymerization is carried out to prepare a PBL with a bimodal particle size distribution, and the reaction time is 20-30 hours. In the method of the present invention, the small-particle PBL obtained in the first step of polymerization can provide 15-20 batches of raw materials for the second step of polymerization, which is equivalent to an average polymerization period of 20.5-31.66 hours.

[0118] In the present invention, the seed latex preparation and particle size enlargement polymerization are usually carried out under the protection of an inert gas (such as nitrogen).

[0119] In some embodiments, the method for preparing the bimodal particle size distribution latex of the present invention comprises:

[0120] (1) Preparation of seed latex: 50-180 parts of deionized water, 1-8 parts of emulsifier, 0.05-3 parts of electrolyte and 0.1-1 parts of chain transfer agent are added to a reactor, the reactor is replaced with nitrogen three times, and after vacuuming, 100 parts of butadiene monomer is added, the temperature is raised to 35-65°C, 0.05-1 parts of initiator are added, and the reaction is carried out for 10-20 hours, wherein the emulsifier can be added in batches. After the reaction at 35-65°C is completed, the temperature is raised to 65-85°C, 0-1 parts of initiator are added, and the reaction is continued for 5-10 hours until the polymerization conversion rate reaches 90-97%, and the temperature is lowered to room temperature, and the reaction is stopped to prepare small-particle PBL with an average particle size of 50-130nm;

[0121] (2) Particle size enlargement polymerization: 1-15 parts (dry basis, i.e., dry weight of PBL) of small particle size 50-130 nm prepared in step (1), 50-180 parts of deionized water, 0.1-5 parts of electrolyte, 0.2-4 parts of emulsifier and 0.1-1 parts of chain transfer agent are added into a reactor. The reactor is replaced with nitrogen three times and evacuated. Then, 100 parts of butadiene monomer is added. After heating to 45-70°C, 0.05-1 parts of initiator are added and the reaction is carried out for 5-10 hours until the conversion rate reaches 50±5%. Then, the temperature is raised to 65-80°C, 0-1 parts of initiator are added and the reaction is carried out for 5-15 hours. Finally, the temperature is raised to 80-90°C, 0-1 parts of initiator are added and the reaction is carried out for 2-4 hours until the polymerization conversion rate reaches 90-97%, thus completing the reaction. When the conversion rate reaches 20-45%, 1-4 parts of emulsifier are added. Optionally, when the conversion rate reaches 50-60%, 0-4 parts of emulsifier are added. The particle size distribution of the PBL prepared in this way is bimodal, with large and small particle sizes of 280-400nm and 90-170nm respectively, and the mass ratio of large and small particle sizes of latex particles is 3:1 to 1:1.5.

[0122] The present invention includes a particle size bimodal distribution latex prepared by the method described in the text. In the particle size bimodal distribution latex, the average particle size of large particle size latex particles is 280-400nm, the average particle size of small particle size latex particles is 90-170nm, and the mass ratio of large particle size latex particles to small particle size latex particles is 3:1 to 1:1.5. In the double peaks of the particle size-volume fraction distribution curve of the latex of the particle size bimodal distribution latex, the area ratio of the large particle size peak to the small particle size peak is 7:3 to 3:7.

[0123] Only latex with a particle size of 280-300nm can be prepared by the traditional one-step method, and it is difficult to prepare latex with a larger particle size. Therefore, the present invention includes a latex with a bimodal particle size distribution, wherein the average particle size of large particle size latex particles is >300nm to ≤400nm, and the average particle size of small particle size latex particles is 90-170nm. Preferably, in the latex with a bimodal particle size distribution, the mass ratio of large particle size latex particles to small particle size latex particles is 3:1 to 1:1.5. Preferably, in the bimodal particle size distribution curve of the latex particles of the bimodal particle size distribution latex, the area ratio of the large particle size peak to the small particle size peak is 7:3 to 3:7.

[0124] The bimodal particle size distribution latex of the present invention is suitable for preparing ABS resin and high-rubber powder. Therefore, the present invention includes a high-rubber powder, which is prepared by core-shell emulsion polymerization of the bimodal particle size distribution latex of the present invention and a monomer composition containing styrene and acrylonitrile. The present invention also includes an ABS resin, which includes the high-rubber powder of the present invention and a resin composition containing a styrene-acrylonitrile copolymer, or is obtained by blending the high-rubber powder of the present invention with a resin composition containing a styrene-acrylonitrile copolymer. The method for preparing high-rubber powder by core-shell emulsion polymerization and the method for preparing ABS resin by blending can be conventional in the art.

[0125] The present invention has the following advantages:

[0126] 1. The important innovation of the present invention is that it bypasses the continuous or semi-continuous feeding method adopted by traditional seed emulsion polymerization to obtain latex particles with single-peak particle size distribution. By changing the monomer feeding method to a one-time feeding method, the time required for seed emulsion polymerization is greatly shortened, the production efficiency is improved, and the shortcomings of fewer polymerization sites and low concentration caused by the continuous feeding method adopted in traditional seed polymerization to inhibit the generation of new latex particles are avoided, thus overcoming the major defect of low production efficiency of traditional seed emulsion polymerization.

[0127] 2. In traditional seed emulsion polymerization, the one-time feeding of monomers will lead to a chaotic particle size distribution and no use value. Another important innovation of the present invention is that in the second step of seed emulsion polymerization, the type, total amount, proportion and addition time of the composite emulsifier are adjusted to regulate the particle size and distribution, so that the latex particle size is bimodal. This method of controlling the particle size and proportion of secondary particles instead of inhibiting the formation of secondary particles can maintain a high monomer concentration in the kettle, with multiple polymerization sites, and greatly improve the reaction rate.

[0128] 3. The present invention can prepare in situ a bimodal particle size distribution latex in the second step, and the particle size and distribution are controllable. In the second step polymerization of the present invention, there are 50-120nm particle size seeds, and a latex with a large particle size range of 280-400nm can be obtained, which is larger than the common 280-300nm particle size range of latex prepared by the one-step method, and has a larger adjustable range between 280-300nm than the bimodal latex prepared by the mixing method, providing more options for improving and balancing the toughness and optical properties of the resin. . Traditional bimodal distribution latex is prepared by a one-step method or a seed polymerization method, and then mixed with large and small particle size latex, and the particle size of the large particle size latex is often limited to 280-300nm. The emulsion polymerization of the present invention can be controlled by process to obtain a large particle size latex with a particle size of 280-400nm, which broadens the types of large particle size rubbers of bimodal ABS resins and enriches the methods for optimizing resin properties.

[0129] In order to better understand the present invention, the present invention will be described in the form of specific examples below. The present invention is a two-step process. The following examples are divided into two steps. The first step is "seed latex preparation", and the second step is to use the seeds as raw materials to carry out "particle size enlargement polymerization". It should be pointed out that the examples provided are only for the purpose of illustrating the present invention, and the scope of the present invention is not limited thereto. The methods, equipment and materials used in the examples are conventional methods, equipment and materials in the art, unless otherwise specified. The raw material compounds in the preparation examples can all be purchased through commercial channels. The feeding portions mentioned in the examples are all mass portions. The particle size mentioned in the examples is measured by the Litesizer particle size analyzer of Anton Paar Company. If not specified, it is defaulted to the weight (volume) average particle size.

[0130] Example 1

[0131] Seed latex preparation

[0132] 115 parts of deionized water, 0.3 parts of potassium carbonate, 0.3 parts of tert-dodecyl mercaptan, 0.3 parts of fatty acid potassium, 0.1 parts of sodium dodecylbenzene sulfonate and 1.5 parts of disproportionate potassium rosin acid were added to the reactor. After the reactor was replaced with nitrogen three times, it was evacuated and 100 parts of butadiene were added. The temperature was raised to 58°C, 0.25 parts of potassium persulfate were added, and the reaction was continued for 12 hours. Among them, 0.5 parts and 0.4 parts of disproportionate potassium rosin acid were added in the 8th and 11th hours, respectively. After 12 hours, the temperature was raised to 73°C, 0.05 parts of potassium persulfate were added, and the reaction was continued for about 7 hours. When the total reaction time was about 22 hours, the conversion rate reached 96%, the temperature was lowered, the reaction was stopped, and the particle size was 110nm.

[0133] Particle size enlargement polymerization

[0134] After adding 4.0 parts (dry basis) of the seed latex prepared above to the reactor, 75 parts of deionized water, 0.3 parts of dodecyl mercaptan, 0.5 parts of disproportionate potassium rosin acid and 0.5 parts of sodium bicarbonate are added in sequence. After the reactor is replaced with nitrogen three times, it is evacuated and 100 parts of butadiene are added. The temperature is raised to 70°C, 0.25 parts of potassium persulfate are added, and the reaction is continued until the conversion rate reaches 50%. The temperature is raised to 75°C and the reaction is continued for 8 hours. Among them, 0.2 parts of fatty acid potassium and 1.2 parts of disproportionate potassium rosin acid are added when the conversion rate reaches 25%, 0.4 parts of disproportionate potassium rosin acid are added when the conversion rate reaches 50%, and 0.05 parts of potassium persulfate are added when the temperature is raised to 75°C. Finally, the temperature is raised to 80°C, 0.05 parts of potassium persulfate are added, and the reaction is stopped when the conversion rate reaches 96%, and the temperature is lowered to room temperature. The total reaction time is about 27 hours. The obtained latex weight (volume) particle size showed a bimodal distribution, wherein the large particle size peak area was 54%, the average particle size was 345 nm, and the small particle size peak area was 46%, the average particle size was 151 nm.

[0135] Example 2

[0136] Seed latex preparation

[0137] The experimental conditions are the same as those in Example 1.

[0138] Particle size enlargement polymerization

[0139] The difference from Example 1 is that the 0.2 parts of fatty acid potassium and 1.2 parts of disproportionated rosin acid potassium added when the conversion rate reaches 25% are changed to be added when the conversion rate reaches 35%; other conditions remain unchanged. The obtained latex weight (volume) particle size is bimodal distribution, wherein the large particle size peak area is 60%, the average particle size is 345nm, the small particle size peak area is 40%, the average particle size is 132nm, and the total reaction time is about 27.5 hours.

[0140] Example 3

[0141] Seed latex preparation

[0142] The experimental conditions are the same as those in Example 1.

[0143] Particle size enlargement polymerization

[0144] The difference from Example 1 is that the number of seed latex parts added is changed to 3.0 parts, and the 0.2 parts of fatty acid potassium and 1.2 parts of disproportionate rosin acid potassium added when the conversion rate reaches 25% are changed to be added when the conversion rate reaches 30%; other conditions remain unchanged. The obtained latex weight (volume) particle size is bimodal distribution, wherein the large particle size peak area is 53%, the average particle size is 353nm, the small particle size peak area is 47%, the average particle size is 155nm, and the total reaction time is about 27 hours.

[0145] Example 4

[0146] Seed latex preparation

[0147] The experimental conditions are the same as those in Example 1.

[0148] Particle size enlargement polymerization

[0149] The difference from Example 1 is that 0.2 parts of fatty acid potassium and 1.2 parts of disproportionated rosin potassium are added when the conversion rate reaches 25% instead of 0.3 parts of fatty acid potassium and 1.5 parts of disproportionated rosin potassium; other conditions remain unchanged. The obtained latex weight (volume) particle size is bimodal distribution, wherein the large particle size peak area is 43%, the average particle size is 337nm, the small particle size peak area is 57%, the average particle size is 169nm, and the total reaction time is about 25.5 hours.

[0150] Example 5

[0151] Seed latex preparation

[0152] The experimental conditions are the same as those in Example 1.

[0153] Particle size enlargement polymerization

[0154] The difference from Example 1 is that 0.25 parts of fatty acid potassium and 0.8 parts of disproportionated rosin potassium are added when the conversion rate reaches 40%, instead of adding 0.25 parts of fatty acid potassium and 0.8 parts of disproportionated rosin potassium when the conversion rate reaches 25%; other conditions remain unchanged. The obtained latex weight (volume) particle size is bimodal distribution, wherein the large particle size peak area is 60%, the average particle size is 367nm, the small particle size peak area is 40%, the average particle size is 112nm, and the total reaction time is about 28 hours.

[0155] Example 6

[0156] Seed latex preparation

[0157] The experimental conditions are the same as those in Example 1.

[0158] Particle size enlargement polymerization

[0159] The difference from Example 1 is that when the conversion rate reaches 25%, 0.2 parts of fatty acid potassium and 1.2 parts of disproportionated rosin potassium are added instead of 0.1 parts of fatty acid potassium and 1.1 parts of disproportionated rosin potassium; other conditions remain unchanged. The obtained latex weight (volume) particle size is bimodal distribution, wherein the large particle size peak area is 61%, the average particle size is 349nm, the small particle size peak area is 39%, the average particle size is 132nm, and the total reaction time is about 27.5 hours.

[0160] Example 7

[0161] Seed latex preparation

[0162] The experimental conditions are the same as those in Example 1.

[0163] Particle size enlargement polymerization

[0164] The difference from Example 1 is that the 0.5 part of sodium bicarbonate added at the initial feeding is replaced by 0.5 part of potassium bicarbonate and 0.15 part of potassium carbonate; other conditions remain unchanged. The obtained latex weight (volume) particle size is bimodal distribution, wherein the large particle size peak area is 46%, the average particle size is 342nm, the small particle size peak area is 54%, the average particle size is 137nm, and the total reaction time is about 26.5 hours.

[0165] Example 8

[0166] Seed latex preparation

[0167] The experimental conditions are the same as those in Example 1.

[0168] Particle size enlargement polymerization

[0169] The difference from Example 1 is that the number of seed latex parts added is adjusted to 5.0 parts; other conditions remain unchanged. The obtained latex weight (volume) particle size is bimodal distribution, wherein the large particle size peak area is 50%, the average particle size is 368nm, the small particle size peak area is 50%, the average particle size is 170nm, and the total reaction time is about 27 hours.

[0170] Example 9

[0171] Seed latex preparation

[0172] 100 parts of deionized water, 0.4 parts of potassium carbonate, 0.3 parts of tert-dodecyl mercaptan, 0.4 parts of fatty acid potassium, 0.1 parts of sodium dodecylbenzene sulfonate and 1.3 parts of disproportionate potassium rosin acid were added to the reactor. After the reactor was replaced with nitrogen three times, it was evacuated and 100 parts of butadiene were added. The temperature was raised to 58°C, 0.25 parts of potassium persulfate were added, and the reaction was continued for 12 hours. In the 8th and 11th hours, 0.5 parts and 0.4 parts of disproportionate potassium rosin acid were added respectively. After 12 hours, the temperature was raised to 73°C, 0.05 parts of potassium persulfate were added, and the reaction was continued for about 4 hours. When the conversion rate reached 96%, the temperature was lowered and the reaction was stopped. The particle size was 130nm.

[0173] Particle size enlargement polymerization

[0174] Except that the seed latex was replaced with a seed latex with a particle size of 130 nm, other conditions were unchanged compared with Example 1. The obtained latex weight (volume) particle size showed a bimodal distribution, wherein the large particle size peak area was 56%, the average particle size was 379 nm, the small particle size peak area was 44%, the average particle size was 142 nm, and the total reaction time was about 27.5 hours.

[0175] Comparative Example 1

[0176] Seed latex preparation

[0177] The experimental conditions are the same as those in Example 1.

[0178] Particle size enlargement polymerization

[0179] The difference from Example 1 is that the 0.2 parts of fatty acid potassium and 1.2 parts of disproportionated rosin acid potassium added when the conversion rate reaches 25% are added at the beginning of the reaction; other conditions remain unchanged. The obtained latex weight (volume) particle size is widely distributed, the hydrated particle size is 290nm, and the PDI is 24%. At this time, the average particle size loses its meaning under the overly wide distribution.

[0180] Comparative Example 2

[0181] Seed latex preparation

[0182] The experimental conditions are the same as those in Example 1.

[0183] Particle size enlargement polymerization

[0184] The difference from Example 1 is that the 0.2 parts of fatty acid potassium and 1.2 parts of disproportionated rosin acid potassium added when the conversion rate reaches 25% are changed to be added when the conversion rate reaches 55%; other conditions remain unchanged. Demulsification is serious during the reaction, so the obtained latex has unqualified performance and cannot be used.

[0185] Comparative Example 3

[0186] Seed latex preparation

[0187] The experimental conditions are the same as those in Example 1.

[0188] Particle size enlargement polymerization

[0189] The difference from Example 1 is that 1.4 parts of fatty acid potassium are added instead of 0.2 parts of fatty acid potassium and 1.2 parts of disproportionated rosin acid potassium when the conversion rate reaches 25%; other conditions remain unchanged. During the reaction, after a large amount of fatty acid potassium is added, the polymerization rate increases suddenly and the emulsion breaks seriously, so the obtained latex has unqualified performance and cannot be used.

[0190] Comparative Example 4

[0191] Seed latex preparation

[0192] The experimental conditions are the same as those in Example 1.

[0193] Seed polymerization

[0194] The conventional continuous feeding method is adopted, and monomers and emulsifiers are continuously fed, and the emulsifier concentration is maintained below CMC. After adding 4.0 parts (dry basis) of the seed latex prepared above to the reactor, 75 parts of deionized water, 0.3 parts of dodecyl mercaptan, 0.5 parts of disproportionate potassium rosin acid and 0.5 parts of sodium bicarbonate are added in sequence. After the reactor is replaced with nitrogen three times, it is evacuated, heated to 70°C, and 0.25 parts of potassium persulfate are added. 100 parts of butadiene monomer, 0.2 parts of fatty acid potassium, and 2.1 parts of disproportionate potassium rosin acid emulsifier are fed separately and continuously, and the emulsifier feeding rate is maintained below CMC, and the monomer continuous feeding time is the same as the emulsifier feeding time. When the reaction reaches a conversion rate of 50%, the temperature is raised to 75°C, and the reaction is reacted until the conversion rate reaches 80%. Finally, the temperature is raised to 80°C, 0.05 parts of potassium persulfate are added, and when the reaction reaches a conversion rate of 95%, the reaction is stopped and cooled to room temperature. The obtained latex had a unimodal distribution of weight (volume) particle size, an average particle size of 378 nm, and a total reaction time of 79 hours.

[0195] Some experimental conditions and results of Examples 1-9 and Comparative Examples 1-4 are shown in Table 1. In Table 1, the large particle size peak and the small particle size peak refer to the double peaks of the latex particle size (diameter)-volume fraction distribution curve.

[0196] Table 1: Partial experimental conditions and results of Examples 1-9 and Comparative Examples 1-4

[0197]

[0198]

Claims

1. A method for preparing a latex having a bimodal particle size distribution, characterized in that: The method comprises: (1) providing seed latex; (2) Particle size enlargement polymerization: subjecting the reaction raw material mixture comprising the seed latex and the monomer described in step (1) to polymerization reaction, wherein an emulsifier is added during the period when the monomer conversion rate reaches 20-45%; The monomers of the polymer contained in the seed latex in step (1) include butadiene, and the monomers in the reaction raw material mixture in step (2) include butadiene; The reaction raw material mixture in step (2) comprises seed latex, water, electrolyte, emulsifier, chain transfer agent and monomer; Based on 100 parts by weight of the monomers contained in the reaction raw material mixture, in step (2), the amount of the emulsifier added during the period when the monomer conversion rate reaches 20-45% is 1-4 parts by weight; In step (2), no monomer is added during the polymerization reaction; The emulsifier in the reaction raw material mixture includes disproportionated rosin salt, and the amount of disproportionated rosin salt accounts for more than 60% of the total mass of the emulsifier in the reaction raw material mixture; In step (2), the emulsifier added during the period when the monomer conversion rate reaches 20-45% includes a disproportionate rosin acid salt in a mass ratio of ≥2:1 and an emulsifier having a critical micelle concentration less than that of the disproportionate rosin acid salt in the polymerization reaction system of step (2).

2. The method according to claim 1, characterized in that The method has one or more of the following features: In step (2), when the monomer conversion rate reaches 50-60%, additional emulsifier is added; The polymerization reaction in step (2) comprises: heating the reaction raw material mixture to 45-70° C., adding an initiator, and reacting for 5-10 hours; then heating the mixture to 65-80° C., reacting for 5-15 hours, during which time an initiator is optionally added; and finally heating the mixture to 80-90° C., aging for 2-4 hours, during which time an initiator is optionally added to complete the reaction; The polymer contained in the seed latex in step (1) is obtained by polymerization of one or more monomers selected from butadiene, isoprene and butyl acrylate; The average particle size of the seed latex in step (1) is 50-130 nm; In step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the content of the seed latex in the reaction raw material mixture on a dry weight basis is 1-15 parts by weight; The monomers in the reaction raw material mixture in step (2) are selected from one or more of butadiene, isoprene and butyl acrylate; Based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the content of water in the reaction raw material mixture is 50-180 parts by weight, the content of electrolyte is 0.1-5 parts by weight, the content of emulsifier is 0.2-4 parts by weight, and the content of chain transfer agent is 0.1-1 part by weight.

3. The method according to claim 2, characterized in that In step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of the emulsifier added during the period when the monomer conversion rate reaches 50-60% does not exceed 4 parts by weight.

4. The method according to claim 2, characterized in that In step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of the initiator added after heating to 45-70° C. is 0.05-1 part by weight.

5. The method according to claim 2, characterized in that In step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of initiator optionally added during the reaction when the temperature is raised to 65-80° C. does not exceed 1 part by weight.

6. The method according to claim 2, characterized in that In step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of initiator optionally added during the reaction when the temperature is raised to 80-90° C. does not exceed 1 part by weight.

7. The method according to claim 2, characterized in that In step (2), the initiator is a peroxide compound or a redox system.

8. The method according to claim 7, characterized in that In step (2), the initiator is persulfate.

9. The method according to claim 2, characterized in that Step (2) has one or more of the following characteristics: React at 45-70°C until the conversion rate reaches 45-55%, and then heat to 65-80°C; React at 65-80°C until the conversion rate reaches 70-85%, and then heat to 80-90°C; The reaction was continued at 80-90°C until the conversion rate reached 90-97%, and then the reaction was stopped.

10. The method according to claim 2, characterized in that In step (1), the polymer contained in the seed latex is obtained by polymerization of butadiene.

11. The method according to claim 2, characterized in that In step (1), the average particle size of the seed latex is 100-130 nm.

12. The method according to claim 2, characterized in that In step (2), the electrolyte in the reaction raw material mixture is selected from one or more of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

13. The method according to claim 2, characterized in that In step (2), the emulsifier in the reaction raw material mixture is disproportionated rosin acid salt.

14. The method according to claim 2, characterized in that In step (2), the chain transfer agent in the reaction raw material mixture is a normal or tertiary alkyl mercaptan with a carbon chain length of 10-16.

15. The method according to claim 14, characterized in that In step (2), the chain transfer agent in the reaction raw material mixture is tert-dodecyl mercaptan.

16. The method according to claim 1, wherein: The method has one or more of the following features: The emulsifier having a critical micelle concentration less than that of disproportionate rosin salt in the polymerization reaction system of step (2) is a fatty acid salt; In step (2), in the emulsifier added during the period when the monomer conversion rate reaches 20-45%, the mass ratio of the disproportionated rosin salt to the emulsifier having a critical micelle concentration less than the disproportionated rosin salt in the polymerization reaction system of step (2) is ≥3:1; In step (2), based on 100 parts by weight of the monomer contained in the reaction raw material mixture, the amount of the emulsifier added during the period when the monomer conversion rate reaches 20-45% is 1-2 parts by weight; In step (2), when the monomer conversion rate reaches 50-60%, additional emulsifier is added; The reaction raw material mixture in step (2) comprises seed latex, water, electrolyte, emulsifier, chain transfer agent and monomer, and based on 100 parts by weight of the monomer contained in the reaction raw material mixture, the content of seed latex in the reaction raw material mixture on a dry weight basis is 2-8 parts by weight, the content of water is 50-100 parts by weight, the content of electrolyte is 0.2-1 parts by weight, the content of emulsifier is 0.2-1 parts by weight, and the content of chain transfer agent is 0.1-1 parts by weight; The polymerization reaction described in step (2) comprises: heating the reaction raw material mixture to 45-70°C, adding an initiator, and reacting for 5-10 hours; then heating the mixture to 65-80°C, reacting for 5-15 hours, during which time an initiator is optionally added; and finally heating the mixture to 80-90°C, aging for 2-4 hours, during which time an initiator is optionally added to complete the reaction, wherein, based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of initiator added after heating to 45-70°C is 0.1-0.5 parts by weight, the amount of initiator optionally added during the reaction when the temperature is raised to 65-80°C is no more than 0.2 parts by weight, and the amount of initiator optionally added during the reaction when the temperature is raised to 80-90°C is no more than 0.2 parts by weight.

17. The method according to claim 16, characterized in that In step (2), in the emulsifier added during the period when the monomer conversion rate reaches 20-45%, the mass ratio of disproportionated rosin salt to the emulsifier whose critical micelle concentration in the polymerization reaction system of step (2) is less than that of disproportionated rosin salt is 3:1 to 20:

1.

18. The method according to claim 16, characterized in that In step (2), the emulsifier added during the period when the monomer conversion rate reaches 50-60% includes disproportionated rosin acid salt.

19. The method according to claim 18, characterized in that In step (2), the emulsifier added during the period when the monomer conversion rate reaches 50-60% is disproportionated rosin acid salt.

20. The method of claim 16, wherein: In step (2), based on 100 parts by weight of the monomers contained in the reaction raw material mixture, the amount of the emulsifier added during the period when the monomer conversion rate reaches 50-60% is no more than 1 part by weight.

21. The method according to any one of claims 1 to 20, characterized in that The seed latex is prepared by the following method: mixing water, emulsifier, electrolyte, chain transfer agent and monomer to obtain a seed latex raw material mixture, heating the mixture to 35-65° C., adding an initiator, reacting for 10-20 hours, during which an emulsifier is optionally added; then heating the mixture to 65-85° C., reacting for 5-10 hours, during which an initiator is optionally added, to complete the reaction.

22. The method according to claim 21, characterized in that The method has one or more of the following features: The monomer in the seed latex raw material mixture is butadiene; Based on 100 parts by weight of the monomer contained in the seed latex raw material mixture, the seed latex raw material mixture contains 50-180 parts by weight of water, 0.05-3 parts by weight of electrolyte, 1-8 parts by weight of emulsifier, and 0.1-1 parts by weight of chain transfer agent; Based on 100 parts by weight of the monomer contained in the seed latex raw material mixture, when preparing the seed latex, the amount of the initiator added after heating to 35-65° C. is 0.05-1 part by weight, and the amount of the initiator optionally added during the reaction when the temperature is raised to 65-85° C. does not exceed 1 part by weight; The electrolyte in the seed latex raw material mixture is selected from one or more of sodium chloride, potassium chloride, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate; The emulsifier in the seed latex raw material mixture comprises one or more of rosin acid salts, fatty acid salts and sulfonates thereof, alkylaryl sulfonates and sulfonated alkyl esters; The chain transfer agent in the seed latex raw material mixture is a normal or tertiary alkyl mercaptan with a carbon chain length of 10-16; The initiator added in the process of preparing the seed latex is a peroxide compound or a redox system; The emulsifier optionally added during the reaction at a temperature of 35-65° C. in the process of preparing the seed latex comprises one or more of rosin acid salts, fatty acid salts and sulfonates thereof, alkylaryl sulfonates and sulfonated alkyl esters; When preparing the seed latex, react at 35-65°C until the conversion rate reaches 60-75% and then heat to 65-85°C; When preparing the seed latex, the reaction is carried out at 65-85° C. until the conversion rate reaches 90-97%, and then the reaction is stopped; No additional monomers are added during the reaction process of preparing the seed latex.

23. The method of claim 22, wherein: The emulsifier in the seed latex raw material mixture comprises disproportionated rosin acid salt.

24. The method of claim 22, wherein: The chain transfer agent in the seed latex raw material mixture is tert-dodecyl mercaptan.

25. The method of claim 22, wherein: The initiator added in the process of preparing the seed latex is persulfate.

26. The method of claim 22, wherein: The emulsifier optionally added during the reaction at a temperature of 35-65° C. in the preparation of the seed latex comprises disproportionated rosin acid salt.

27. The method of claim 21, wherein: The method has one or more of the following features: In the process of preparing the seed latex, the emulsifier optionally added during the reaction at a temperature of 35-65°C is disproportionate rosin acid salt; Based on 100 parts by weight of the monomer contained in the seed latex raw material mixture, the amount of the emulsifier optionally added during the reaction at 35-65° C. during the preparation of the seed latex does not exceed 4 parts by weight; Based on 100 parts by weight of the monomer contained in the seed latex raw material mixture, the seed latex raw material mixture contains 100-150 parts by weight of water, 0.1-1 parts by weight of electrolyte, 1-4 parts by weight of emulsifier, and 0.1-1 parts by weight of chain transfer agent; Based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, when preparing the seed latex, the amount of initiator added after heating to 35-65°C is 0.1-0.5 parts by weight, and the amount of initiator optionally added during the reaction when the temperature is raised to 65-85°C does not exceed 0.2 parts by weight.

28. The method of claim 27, wherein: In the seed latex raw material mixture, the mass of disproportionated rosin acid salt accounts for more than 60% of the total mass of the emulsifier.

29. The method of claim 28, wherein: In the seed latex raw material mixture, the mass of disproportionated rosin acid salt accounts for more than 75% of the total mass of the emulsifier.

30. The method of claim 27, wherein: Based on 100 parts by weight of the monomers contained in the seed latex raw material mixture, the amount of the emulsifier optionally added during the reaction at 35-65° C. during the preparation of the seed latex does not exceed 2 parts by weight.

31. A latex with bimodal particle size distribution prepared by the method according to any one of claims 1 to 30.

32. The bimodal particle size distribution latex of claim 31, wherein: The bimodal particle size distribution latex has one or more of the following characteristics: In the latex with bimodal particle size distribution, the average particle size of the large particle size latex particles is 280-400nm; In the bimodal particle size distribution latex, the average particle size of the small particle size latex particles is 90-170nm; In the bimodal particle size distribution latex, the mass ratio of large particle size latex particles to small particle size latex particles is 3:1 to 1:1.5; In the bimodal particle size distribution latex, the area ratio of the large particle size peak to the small particle size peak is 7:3 to 3:

7.

33. Use of the latex with bimodal particle size distribution according to claim 31 or 32 in the preparation of ABS resin.

34. A high-rubber powder prepared by core-shell emulsion polymerization of the latex with bimodal particle size distribution according to claim 31 or 32 and a monomer composition comprising styrene and acrylonitrile.

35. An ABS resin obtained by blending the high-rubber powder according to claim 34 with a resin composition comprising a styrene-acrylonitrile copolymer.

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