What Is Acrylic Fabrication?

Acrylic rubber (hereinafter referred to as ACM) is an elastomer obtained by copolymerizing acrylate as the main monomer. Its main chain is a saturated carbon chain and its side group is a polar ester group. Due to its special structure, it has many excellent characteristics, such as: heat resistance, aging resistance, oil resistance, ozone resistance, UV resistance, etc., its mechanical properties and processing properties are better than fluoro rubber and silicone rubber, and its heat resistance, aging resistance and oil resistance Better than nitrile rubber. ACM is widely used in various high-temperature and oil-resistant environments, and has become a sealing material that has been developed and promoted in the automotive industry in recent years, especially for automotive high-temperature oil seals, crankshafts, valve stems, cylinder pads, hydraulic oil pipes, etc. Domestic demand is almost entirely dependent on imports.

Acrylic rubber

Acrylic rubber (hereinafter referred to as ACM)

The comonomers of ACM can be divided into three types of monomers: main monomers, low temperature oil resistant monomers and vulcanization point monomers.

Master cell

Main monomer, commonly used main monomers are

2.1 ACM synthesis methods, there are three common methods for ACM synthesis:

Solution method

This method uses ethylene-acrylate in the presence of BF3 and a halogenated hydrocarbon as a solvent to form an ethylene-acrylate copolymer. At present, DuPont of the United States and Sumitomo Chemical of Japan mostly use high-temperature and high-pressure solution polymerization methods.

Suspension polymerization

Ethylene-acrylate-vinyl acetate was synthesized by the suspension polymerization method, which is currently used less frequently.

Emulsion polymerization

This method is currently the main method for producing ACM, mainly because the process equipment is simple and easy to implement; on the other hand, ACM is currently mainly used for high temperature and oil resistant sealing products. It does not require excessive low temperature flexure performance. If low temperature oil resistance is desired, you can It is achieved by intramolecular plasticization of low-temperature oil-resistant monomers. In the emulsion polymerization method to synthesize ACM system, the emulsion system and the amount will affect the stability, final conversion rate, molecular weight distribution, raw rubber processing performance and even the physical properties of the vulcanizate during the polymerization process. Therefore, many additives such as emulsifiers, Initiators, molecular weight regulators and coagulants. Generally use anionic or anionic and non-ionic composite emulsifiers such as sodium dodecyl sulfonate; oil-soluble initiator cumene hydrogen peroxide, water-soluble initiator persulfate, hydrogen peroxide and tert-butyl hydrogen peroxide Etc .; use tert-dodecyl mercaptan or alkyl disulfide xanthate as molecular weight regulator. The polymerization temperature is generally 50 to 100 ° C. The heat of polymerization can be removed by refluxing or gradually adding monomers to control the polymerization rate and reduce the amount of heat generated per unit time. To separate polymers from water by emulsion polymerization requires a salting-out process, so salting-out agents need to be added. Generally, salts such as NaCl and CaCl2 are used, and acids such as HCl and H2SO2 can also be used. CaCl2 is often used as a salting-out agent in industry. When salting out, sodium polyacrylate and polyvinyl alcohol can be used as protective agents to prevent the rubber particles from sticking together. After salting out, the emulsifier can be washed out of the gum with sodium hydroxide solution to make the raw rubber easy to vulcanize. In addition, the drying method of the emulsion polymerization method ACM, different companies will choose different methods, such as the American Cytec company, Japan's Rui Weng company using extrusion drying process, Japan's East Asia Paint Company is a drying product.

2.2 ACM processing

ACM processing is mainly to select the appropriate curing monomer and some additives to improve and maintain the excellent performance of ACM. In addition to the vulcanization point monomers described above, the selection of the vulcanization system is very important. Because different vulcanization point monomers are used in the synthesis of ACM, different vulcanization systems are required for cross-linking. An appropriate vulcanization system is a prerequisite to ensure that the rubber is fully vulcanized. At present, most of the ACMs sold in the domestic market are active chlorine products and few epoxy products. Activated chlorine products can eliminate secondary vulcanization. The key lies in the choice of curing system and conditions. The most commonly used curing systems for active chlorine ACM are:

Soap / sulfur combined vulcanization system

The technical characteristics of this system are good process performance, fast vulcanization speed, and good storage stability of the rubber; however, the thermal aging of the rubber is slightly worse, and the compression set is larger. Common soaps include sodium stearate and stearic acid. Potassium and sodium oleate.

N, N 'curing system

-Di (cinnamylidene-1,6-hexanediamine) vulcanization system. The vulcanizate used in this system has good heat aging performance and small compression set, but the process performance is slightly worse, and sometimes there will be sticking phenomenon. The storage period is short, the degree of vulcanization is not high, and secondary vulcanization is generally required.

TCY vulcanization system

(1,3,5-trimercapto-2,4,6-m-triazine) vulcanization system. This system has a fast vulcanization speed and can eliminate the two-stage vulcanization. The vulcanizate has good thermal aging properties, small compression set and small process performance However, it is relatively corrosive to the mold, the storage time of the mixed rubber is short, and it is easy to scorch.

Each of the three vulcanization systems has its advantages, and should be selected according to the actual application.

There should also be processing reinforcements, accelerators, cross-linking agents, antioxidants, scorch retarders, lubricants and plasticizers in the vulcanization system. These additives have a great impact on ACM performance. Processing reinforcement, ACM should not use acidic reinforcing fillers, such as: fumed silica, channel carbon black, etc., must use neutral or alkaline alkaline reinforcing agent.

Commonly used carbon blacks are: high wear-resistant carbon black, quick-extrusion carbon black, semi-reinforced carbon black and spray carbon black. Light-colored products can use neutral or alkaline precipitation methods such as silica, sericin, calcium carbonate, talc, and diatomaceous earth as fillers. Among them, the reinforcing effect of silica is the most ideal. When using white carbon black, it is necessary to pay attention to the significant differences in the properties of colloidal particles caused by its pH and different microstructures. A silane coupling agent can be added to improve the bonding strength of the interface when appropriate.

Accelerators , generally carbamate accelerators can be used;

As the cross-linking agent, polyamine, organic carboxylic acid ammonium salt, dithioformate, quaternary ammonium salt / urea system are generally used.

Anti-aging agent , you can choose different anti-aging agent according to ACM temperature resistance requirements. Anti-aging agent suitable for ACM requires not to be volatile at high temperature and difficult to be extracted in oil. Japan and the United States have developed antioxidants suitable for ACM, such as Naugard445 in the United States and Nocrac630F in Japan. At present, there is a lack of special antioxidants suitable for the use of ACM in China, especially the antioxidants which are mainly adapted to the use of ACM under high temperature conditions. According to reports, the domestic Sichuan Suining Qinglong Acrylic Rubber Factory has developed a special anti-aging agent TK100 suitable for use by ACM under high temperature conditions, with an adaptation temperature of 150-200 ° C. In addition, you can also choose commonly used p-phenylenediamine antioxidants such as 4010NA, 4020 and so on. As an anti-scorch agent, N-cyclohexyl thiotitanium imide (CTP) is most commonly used. Fatty acids, paraffin, silicone oil, and low-molecular-weight polyethylene are used as lubricants. In order to increase the abrasion resistance of rubber compounds, graphite powder, molybdenum disulfide, and carbon fiber can be added as lubricating fillers.

Plasticizers are usually high-boiling esters. In order to highlight or improve the performance of ACM, in recent years, modification of ACM, or the use of ACM to modify other elastomers has become one of the research hotspots in processing applications. There are:

Acrylate thermoplastic elastomer

(AC-TPE), which uses flexible acrylate segments as the elastic phase for the synthesis of thermoplastic elastomers. At present, the plasticization of thermoset ACM has become a hotspot for development, and AC-TPE has become an important variety of high temperature and oil resistance for automobiles. 5].

Blending modification between different types of ACM

ACM is divided into standard type (brittleness temperature -12 ° C), cold resistance type (-24 ° C), and ultra cold resistance type (-35 ° C) according to its cold resistance. Different types of ACM have different physical properties on the one hand due to their main chain structure differences; on the other hand, due to similar polarities, they have good compatibility and co-vulcanizability. Standard type ACM has good heat resistance, oil resistance and physical properties, but poor low temperature resistance performance, while ultra cold resistance type has good low temperature resistance performance, but poor oil resistance and poor physical properties of rubber. The overall performance of these two types of ACM blend compounds is improved. Therefore, for applications that require heat, oil and low temperature resistance, such as oil cooling pipes for automobiles, different types of ACM blend compounds have good comprehensive properties. Can meet its requirements.

ACM / NBR blending modification

ACM and NBR are both heat-resistant and oil-resistant rubbers. Through blending and modification, the strength and processing properties of ACM compounds can be improved, and costs can be reduced. Due to the different vulcanization mechanisms, types and amounts of vulcanizing agents of these two rubbers, the main difficulty in blending rubber is that vulcanization is not synchronized. The vulcanization speed of NBR is significantly faster than that of ACM, which causes the accelerator in the ACM phase to migrate to the NBR phase. A lot of research has been done on this and many patent reports have been published.

ACM / silicone blend modification

Silicone rubber has excellent high and low temperature resistance, but poor oil resistance. It is blended with "cold, crisp and hot" ACM.

Acrylic rubber

It can obviously improve the heat resistance and cold resistance of ACM, and achieve a balance between high, low and oil resistance. It is worth noting that ACM is a strong polar rubber and silicone rubber is a weak polar rubber. Therefore, we must find ways to solve the problems of poor compatibility and slow vulcanization speed of the blended rubber. For example, Japan Synthetic Rubber Co., Ltd. Blend modification to conduct research on compatibility and co-vulcanization, and develop an ideal blend rubber (QA). The vulcanizing agent used in the blend is 1,4-bis-tert-butyl cumene peroxide, and the co-vulcanizing agent is N. , N-m-phenylenemaleimide. The blended rubber shows good comprehensive properties of oil resistance and high and low temperature resistance. It is a modified ACM product with the best performance / price ratio. It has as many as 12 kinds of parts applicable in automobile manufacturing.

ACM / chloroether rubber blend

ACM / chloroether rubber (ECO) blend. ECO and ACM have similar structures and good compatibility, and the two rubber cross-linking groups are active chlorine, and the vulcanization system is the same. After blending, it will not cause the physical properties of the rubber to decline, and the heat resistance of ECO is no less than ACM has good strong tensile properties and cold resistance. ACM / ECO blending can improve the cold resistance, water resistance, elasticity and tensile strength of ACM compounds. The vulcanization system uses zinc oxide, magnesium oxide and 2-hydroxyimidazoline.

ACM / FKM blending

FKM has excellent high temperature and oil resistance, and can be used at 250 ° C for a long time, but the engine oil resistance is not as good as ACM, and the cost is much higher than ACM. ACM / FCK blending can overcome their respective shortcomings. The use of fluorine rubber and ACM high temperature rubber for vulcanization research at home and abroad can significantly improve the processing performance of fluororubber and reduce its production cost, resulting in new heat and oil resistant materials.