Acrylic resin production FAQ solution summary

Introduction to Acrylic Resin Production

1. Production mechanism and process of acrylic resin

The production of acrylic resin involves free radical polymerization mechanism, formulation and process design, control of raw materials for synthesis (acrylic acid monomer, solvent, initiator, auxiliary agent, etc.), production equipment and process conditions, measurement and instruments, production operation, central control, Quality inspection, packaging and other links.

The chemical synthesis reaction principle of acrylic resin is free radical polymerization of monomers, including chain initiation, chain growth, and chain termination. The reaction mechanism is relatively complicated.

It is worth emphasizing that the reaction of acrylic resin is an exothermic reaction (slight heating is required in the early and late stage of the reaction, and the reaction itself can basically maintain the synthesis of polymers by controlling the reaction itself during the middle process of the reaction), while the reaction of alkyd resin is an endothermic reaction (requires continuous The dehydration reaction can only be carried out by heating and increasing the temperature). 

2. Introduction to common problems in acrylic resin production

If we can objectively and correctly recognize many influencing factors in the production of acrylic resin in advance, and deal with the existing problems and hidden dangers in a timely and correct manner, we can effectively avoid mistakes or losses in production, and ensure qualified products and continuous and stable production.

For example, there are some abnormal phenomena in production, such as high or low solid content or viscosity of acrylic resin, strong odor, low monomer conversion rate, etc., by taking effective measures to adjust, the unqualified products can be turned into qualified products. This type of phenomenon is reversible.

Another example is that the acrylic resin has a darker hue, such as a yellowish phase or a reddish phase. The appearance of the resin product is whitish, milky, and muddy. The resin has poor fluidity, gel, and colloidal particles. This kind of situation is an irreversible abnormal phenomenon, which is difficult to deal with, and even impossible to save. Try to avoid and eliminate the occurrence of this problem. For such finished products, pay special attention not to flow into downstream customers, otherwise the consequences will become more serious.

Control of Raw Materials Link in Acrylic Resin Production

1. Introduction to the main raw materials of acrylic resin

Acrylic resin raw materials, especially the monomers, need to be carefully tested batch by batch before feeding into the factory. It is better to use products from large manufacturers, and avoid frequent replacement of raw material manufacturers. of. If there are some problems with the raw materials and you are in a hurry to produce, you need to do a pre-production test carefully to ensure that the production is qualified. Raw materials are the most critical link and must be taken care of.

1.1. Types and requirements of initiators

Initiator is one of the most critical factors affecting free radical polymerization. It is mainly divided into high, medium and low temperature initiators. High temperature initiators are DCP and di-tert-butyl peroxide; medium temperature initiators are TBPB; low temperature initiators are BPO, AIBN, etc. Among them, the most commonly used initiators are introduced as follows:

1.1.1, BPO (dibenzoyl peroxide)

It is an initiator with more significant impact and lower cost at present. When using it, you need to pay attention to the following aspects:

A. It is better to choose products with a content of 70-75%, and the active oxygen and chlorine content are up to the standard, and the safety is relatively high.

BPO with a content of >98% has a risk of explosion when used, so it needs to be used with caution. At the same time, it needs to be flexibly adjusted in actual production according to the BPO content marked in the formula. Otherwise, the formula introduced by our company will have high or low viscosity. low phenomenon.

The use of unqualified BPO is likely to cause the appearance of the produced acrylic resin to be muddy, milky, and low in conversion rate, and these unqualified resins are difficult to reform.

B. If BPO is stored for too long (such as more than 6 months), the moisture and active oxygen in the product will decrease, and the resin produced with this initiator will often turn yellow in color and fail to meet the water-white and transparent appearance requirements. Therefore, it is better to buy BPO and use it now, and store and use it correctly according to the requirements. For example, BPO products need to be sealed immediately after use to avoid moisture volatilization, otherwise the viscosity of the produced resin will become low.

C. BPO, which is relatively cheap in the market, can not be completely dissolved with xylene or toluene, which makes it difficult to add the initiator. For example, when the pipeline is blocked during the addition, it cannot be used in actual production. There are also significant security risks.

D. The best moisture content of BPO is 25%. Most formulations or experiments are based on this data. High or low moisture content will result in low or high viscosity of the resin produced. If the production and profit conditions permit, choose Aksu's BPO to produce a resin with better transparency and compatibility.

1.1.2 Medium temperature initiator TBPB (tert-butyl peroxybenzoate)

The liquid initiator has good solubility and compatibility. In the formula that uses toluene or xylene as the reflux system, TBPB/BPO composite initiator is mostly used. The heat release during the reaction is easy to control, and the stability and safety are relatively simple. BPO system It is much better, especially effective in the production of high-solid and low-viscosity resins. The disadvantage is that it is difficult to produce water-white and transparent resins, and the color will become yellower as the amount increases. If TBPB is left for too long or some domestically produced inferior quality TBPB, the light yellow or deep yellow resin that may be produced cannot be changed, so be careful when using it.

However, foreign di-tert-amyl peroxide and di-tert-butyl peroxide can produce water-white and transparent resin, and the viscosity of the resin is much lower than that of domestic TBPB. The disadvantage is that the cost is too high. The decomposition speed is too slow, and it is mostly used in high-temperature production formula systems.

1.1.3 High temperature initiator DCP

It is mostly used in high-temperature formulation systems. It is more suitable for the production of high-viscosity resins, resins with high styrene content, and resins in heat-conducting oil high-temperature heating process systems. The appearance of crystalline solids is mostly imported products, and it is easy to dissolve in benzene solvents and monomers. , good usability and safety, high monomer conversion rate, the disadvantage is that it needs a longer reaction time or a higher reaction temperature to effectively avoid the initiator residue.

Special reminder, the production must follow the formula process requirements, if the reaction time required by the process is arbitrarily shortened and the post-reaction temperature is lowered, because the initiator residue will cause the aging resistance and other properties of the customer's coating film to decline rapidly, and the durability of the product cannot be guaranteed. , which is fatal for industrial paint.

Initiators need to be stored in ventilated, cool, low-temperature, and low-light warehouses. They need to be handled with care and supervised by special personnel. Take as much as you need in the workshop, and cannot be placed in a corner of the workshop at will, or placed in a corner of the workshop, or exposed to high temperature or sunlight or are prone to collisions. Easy-to-touch places, etc.

1.2 Introduction to (meth)acrylate monomers

1.2.1 Due to the higher activity of acrylic acid monomers (containing unsaturated double bonds)

It is not suitable for storage at high temperature, such as butyl acrylate BA, styrene ST, methacrylic acid MAA, etc., the storage time is longer at high temperature or under sunlight exposure, the double bonds of monomers are easy to self-polymerize, and slightly small Particles (liquids have opalescence), flocs, severe monomers will gel and solidify. If the above-mentioned acrylic monomers that have been polymerized in a small amount are used, the appearance of the produced acrylic resin will be poor, opalescent or whitish, and contain a small amount of white soft particles, which are easy to block the mesh and are extremely difficult to filter. Whitening, opacity, grainy spots on the layout, etc. When encountering such customer complaints, most of them end up with compensation from the resin manufacturer. Such problems are extremely serious.

Precautionary measures: Acrylic acid monomer should be stored in cold storage, and its temperature should be controlled at about 15 ℃. At present, most manufacturers do not have cold storage conditions. At this time, the following points should be noted:

①Acrylic acid monomer storage tank should not be too large, and the primary storage should not be too much.

②Single storage tanks should be equipped with canopies, and cooling water should be passed through in summer. The lower the water temperature, the better.

④Acrylic acid monomers should be checked for each batch before feeding to see if there is any polymerization of the monomers.

⑤ Commonly used acrylic acid or methacrylic acid usually crystallizes in winter or when the temperature is low, so it cannot be added for use. Therefore, it should be slowly melted in the warm storage before feeding, and the temperature of the warm storage should not be higher than 35 ℃. Because the above two acrylic acid monomers are easy to gel at high temperature, which affects the quality of the resin produced by the polymerization reaction, so boiling water or hot steam must not be used when compounding the materials.

⑥ When raw material manufacturers supply acrylic acid monomers, in order to prevent polymerization during storage or illegal storage, polymerization inhibitors are generally added. Resin manufacturers buy it and use it directly. If you really want to store and add a polymerization inhibitor, be careful not to add a high-temperature polymerization inhibitor such as hydroquinone, which will easily make the color of the resin darker, and at the same time affect the polymerization reaction speed and affect the transformation. The rate increases the viscosity of the resin (a part of the initiator is reacted during the reaction), that is to say, the formula must be adjusted accordingly to ensure that the resin index remains unchanged.

1.2.2 Preliminary judgment and test method of monomer polymer content

The first is visual inspection to see if the appearance of the monomer is transparent; the second is to check whether the viscosity of the monomer is normal, whether there is any thickening, whether there are small particles or flocs, and the more precise method is to use the methanol method to test. If the above abnormal situation is found, feed feeding should be prohibited, and effective measures should be taken to ensure that the raw materials are qualified. If slight opalescence is observed, it is necessary to make a small test to see whether the synthetic resin is transparent, and then decide whether to feed.

1.3 Solvent for acrylic resin

Commonly used solvents for acrylic resin synthesis are solvents such as toluene, xylene, butyl acetate, mesitylene, CAC, PMA, BCS, butanol, petroleum solvent isomerization grade product grade, less purity and odor, and relatively high content of water and other components. Low. In particular, the narrower the flow range of solvents such as toluene and xylene commonly used as reflux solvents, the better.

The solvent is the carrier of the polymerization reaction of the acrylic resin solution. If the color of the solvent is yellow or the content is unqualified, it is difficult to ensure the production of qualified resin, so feeding is not allowed. It is very important to ensure that the solvent is qualified.

If the water content of the solvent is too high, after adding the solvent, before the mixed monomers are added dropwise for reaction, there should be enough time to dehydrate the solvent under reflux stirring until the water is completely removed. After adding all the solvents in the late stage of the reaction, the process requires reflux for 30 minutes. This process cannot be ignored. First, ensure that all the water in the system is brought out through reflux, and second, ensure that there are very few residual monomers/initiators in the system, so as not to cause strong resin odor. , The emergence of problems such as poor paint durability.

1.4 Brief introduction of functional monomers or additives

When the synthesis of acrylic resin uses functional monomers, additives, special resin modification, etc., it must be strictly controlled such as glycidyl tertiary 12) The quality of raw materials such as chlorinated polypropylene is guaranteed to be qualified. Otherwise, it will affect the technical indicators and quality of the appearance, color and conversion rate of the resin. The use of a new raw material requires careful small-scale tests and application tests to avoid the risk of unknown side effects of new materials, which are mainly reflected in resin synthesis or coating application, and the consequences of damage or loss are often extremely serious.

1.5配料过程中的原料控制

配料之前首先需要校准物料磅秤准确无误，大批量配料精度控制在0.1公斤范畴以内，小批量物料如引发剂、丙烯酸等配料精度控制在0.05公斤范畴以内；

投料时如发现有的丙烯酸单体(包括苯乙烯等)颜色深、发黄、水分、有铁锈等异物，则不应投料，否则生产出的树脂颜色易变深或发黄，也有可能有乳光或胶粒。此时，应进行生产前小样试验，以确保树脂外观、细度、颜色等指标合格。上述情况在大生产中最易发生,需要引起高度重视。

丙烯酸聚合反应中水分处理，即使在溶剂合格的情况下,也需要保证溶剂在回流搅拌30 min后，允许滴加丙烯酸混合单体，其目的是确保溶剂中不能含有水，同时也为确保溶剂的蒸气能充满整个反应釜中，防止树脂氧化和氧的阻聚作用，确保合成树脂颜色水白透明及自由基聚合反应的顺利进行。

丙烯酸单体滴加工艺要求及预防措施：

滴加工艺控制好坏对于树脂质量和生产安全有大大的影响。

反应滴加混合单体之所以强调要均匀、中等速度，就是为了使反应均匀，物料热交换好。因此滴加混合单体需要有很好的滴加速度要求,一般固体分在50%,均在2.5-3 h滴加完；一般固体分在60%，均在3.0-3.5 h滴加完；高固体分(70%)应在4.5～6 h滴加完为宜。这是大量生产积累的经验数据，更好不要找各种理由肆意变化单体滴加时间。

由于工艺操作不当,造成滴加混合单体时，釜内有冲料情况发生，是由于丙烯酸树脂生产反应是溶液聚合反应,该反应是一种放热反应。冲料有二种情况，其一、如果不严格按照操作规程的滴加时间和速度来控制，如滴加混合单体的速度过快，又加上反应釜夹套中导热油给的热量过大，则会造成反应液急剧升温，反应热过多、过大、过快，如果来不及冷却，就势必会造成急剧涨锅冲料现象发生。此时应采取紧急措施：立即关闭导热油, 开大量降温水进行急剧降温，迅速停止搅拌，停止滴加混合单体，此时操作者一定要注意人身安全，千万不能烫着，注意防止可燃物引起火灾发生。

其二、就是有时滴加混合单体时温度偏低,当滴加速度过快,升温过猛,釜内物料积累到一定程度时,反应剧烈,释放热量骤然增加,此时根本来不及正常散热、冷却。此时也应该采取上述应急措施,直到不冲料再开搅拌,关闭降温水,缓慢升温,缓慢滴加混合单体,直至正常为止。出现上述两种情况,一定要措施得当，否则会引起严重后果。

丙烯酸树脂生产设备与工艺的控制

丙烯酸树脂生产是一个庞大、复杂的系统工程,绝不可顾此失彼,要确保所有技术指标全部合格。生产中需要按照上面所述众多因素一一把关。首先应该进一步查找的就是使用的原材料,这些排除后,下一步就应查找设备、操作、中控、检测、过滤等各个环节。

1、设备设计的合理性要求：

反应釜在丙烯酸树脂生产设计

要保证有足够的冷凝器面积，一般情况下，10 m3反应釜应配冷凝面积应大于40 M2，3M3反应釜应配冷凝面积应大于25 M2，否则冷凝效果不好，造成原料消耗大，固体分偏高，转化率不准，收率低，反应不完全。

反应釜冷却盘管或夹套面积设计极为重要。降温水的温度和流量也会影响降温效果，如满足不了降温要求，会造成跑料、收率低、反应不完全，因此，需要保证降温效果要好,保证树脂的聚合反应顺利正常进行。

反应釜加热方式设计对于合成稳定比较重要。一般采用蒸汽加热、100-170℃的热媒加热方式等比较好，若加热热媒温度极高如与合成醇酸或聚酯采用统一热媒管道（温度约270-290℃），通常在进入丙烯酸树脂车间或反应釜前，设置一个热交换器，把高温介质转换为适合反应温度的介质，这是比较好选择。否则，常规工艺下树脂配方及工艺都要随之调整，以适应既定设备与工艺的需要，即使如此，树脂产品质量与稳定性也会受到不同程度的影响。

反应釜、分水器、冷凝器、单体储罐、管路等凡主体反应设备系统,需要是良好不锈钢材质,绝不能用碳钢设备,否则会严重影响丙烯酸树脂的外观、颜色等,一旦因上述原因出现树脂颜色深,是无法处理的。所以挽救树脂生产中出现种种异常情况是有前提和条件的,并非一切异常情况都能在事后解决。

2、一釜生产多品种,洗锅不干净

也会造成树脂发浑、发乳。当热塑性和热固性两种丙烯酸树脂混合生产时,由于树脂分子量差异过大,树脂的结构不同,相容性差,加上洗釜不干净,不有效(包括管路,过滤器等),往往由于树脂混溶性不好,造成树脂出现发乳、发浑现象,出现这种情况,树脂无法挽救。热固性和热塑性丙烯酸树脂需要分开生产,做到专釜专用。

3、有时生产出的树脂有轻微发乳、发浑现象

要通过小试抽样进行检查，如果发现树脂中含有水珠，则应该是工艺操作过程中脱水未净造成，需要耐心仔细地将树脂重新进行脱水,观察苯水分离器脱水情况，直至将水脱净为止，此时树脂可以达到水白透明。所以,生产投料前需要严格检查原材料、单体是否合格,溶剂中不能含有水,如果合成树脂后发现含水量较大,就很难处理,特别是高黏度树脂,甚至无法挽救。

4、丙烯酸树脂合成过程中，中控指标粘度、固含、酸价、转化率等变化与调整。

4.1中控时发现树脂黏度、转化率不合格(偏低时),应仔细地检查原因：

是否反应时间不够、反应过程中回流效果不好、引发剂加量不够或未加。如果未配错料,则应按规定补加引发剂,继续保温进行反应,按时再取样进行测试,一般正常情况,固体含量、黏度都应该有所增加。可According to上述指标增加情况,再适当补加引发剂,直至树脂指标合格为止。如果通过补加引发剂继续保持反应,树脂黏度和固化剂仍无变化,则应该认为是配料所致(配料错误),即垫底溶剂加的多,或者单体加的少,此时单独正确处理方式,就是应按所测黏度及固含量,通过计算将多余溶剂脱出,直至树脂技术指标合格为止,这种情况可挽救树脂,使树脂最终指标达到合格。

4.2中控时发现树脂的黏度和固体分偏高

If the above-mentioned equipment, condenser, cooling water, etc. are all normal, there will be two possibilities. One is that the amount of acid is too large, which can be locked by measuring the acid value of the resin, otherwise there is a problem with the ingredients; The amount of solvent is more, but the amount of solvent added is less. At this time, the solvent should be added according to the resin index detected by the central control, and the viscosity and solid content of the resin should be adjusted until it is qualified. If it is handled properly, the resin with unqualified indicators can be adjusted to be qualified.

4.3 During the central control, it was found that the resin index was unqualified

Using the above-mentioned troubleshooting method, if there are no problems with ingredients, raw materials, and operating processes, you should look for errors in the central control inspection (that is, inaccurate detection, problems with thermometers, balances, etc.), and you need to re-test , and should be reviewed in order to obtain correct test data and determine the true technical indicators of the resin.

4.4 If the acid value of the resin is found to be high or low (other technical indicators are qualified)

The general situation is that the amount of acid fed is not accurate enough. If there is still room for adjustment in the solid content or viscosity of the resin, the acid value can be adjusted by properly adjusting the solvent. If there is no room for adjustment, one pot of new one can be produced (acid value or other index adjusted data), and the two pots of resin are mixed together, and the control is qualified. At this time, resin viscosity, solid content or other technical indicators should also be taken into account.

5 Filtration and packaging requirements for acrylic resin

After the resin is filled into barrels, it is found that there are abnormalities such as impurities, dark appearance, or water droplets, etc. At this time, it is necessary to find out the reason. There may be three reasons for the problem of particles or other impurities: the filter bag is broken during resin press filtration, or the filter bag fineness is unqualified, then the resin should be re-filtered at this time; the packaging barrel is not clean; the packaging barrel is filled with water or the original packaging of the recycling barrel Other chemicals are not washed off effectively.

Responses:

During resin press filtration, samples should be taken frequently, visually check whether the resin is clear and transparent, and use a scraper Fineness Meter to check whether the fineness is qualified. Before packaging, the quality of the packaging barrel must be strictly checked, especially the recycling barrel. If it is unqualified, it must not be used.

Qualified packaging barrels should be placed in warehouses to prevent water or sand from entering.

Qualified resin can only be packaged after cooling down, and the lid of the barrel should not be tightened immediately, otherwise the vat is easily deformed during transportation when it is hot.

The appearance requirements of the packaging barrels: the lids of the large and small barrels are tightened, and the tops need to be covered with iron sheets or plastic covers; the exterior paint is clean and free of stolen goods, and there are no random marks; the labels are clear and tidy.