JPS6153364B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing chloroprene rubber by recovering a chloroprene polymer from a chloroprene polymer latex, and more specifically, a method for producing chloroprene rubber by recovering a chloroprene polymer from a chloroprene polymer latex. This invention relates to a method for producing chloroprene rubber with excellent physical properties by removing chloroprene rubber. One of the steps for producing chloroprene rubber is the step of separating and recovering a chloroprene polymer from a chloroprene polymer latex to obtain a dried chloroprene polymer, so-called chloroprene rubber. This process consists of a coagulation step in which the polymer is separated from the chloroprene polymer latex as a coagulated material containing volatile substances such as water (hereinafter referred to as coagulated material), and a rubber-like polymer is obtained by removing volatile substances from the coagulated material. It can be roughly divided into the drying process of separating and taking out. These steps are extremely important steps in determining the quality of chloroprene rubber. Generally speaking, there are two methods for drying rubber-like polymers: mechanical means and heat treatment. It is a drying method that accelerates the evaporative removal of volatile substances by dehydration and mass heat by mechanical squeezing action, replenishment of latent heat of evaporation by external heating, and surface renewal effect by screw flight of the material to be dried. This is a method to obtain dry rubber by removing volatile substances such as water from the coagulated product, and the latter method, for example, has a greater degree of freedom in the shape of the coagulated product than the conventionally used hot air drying method.
It has many advantages such as excellent energy efficiency and running costs. Drying the chloroprene polymer using an extruder has many advantages in terms of energy efficiency and running costs, but the dried chloroprene rubber obtained by this method has poor quality and
In particular, this often causes a serious problem of deteriorating the physically important physical properties of raw rubber, such as stability during storage or processing stability. In addition, this drying method has a narrow operating range under normal operating conditions, and if operating conditions are set to improve the storage stability and processing stability mentioned above, the drying ability will significantly decrease and the content of volatile substances in the product will decrease. This tends to increase costs and reduce the quality of the resulting product. As a result of research on improving the drying method of chloroprene polymer using an extruder, the present inventor found that the stability during storage of raw rubber obtained by adding an alkali metal carbonate to a coagulated product of chloroprene polymer and drying it; The present invention was completed based on the knowledge that processing stability can be greatly improved. According to the present invention, when a coagulum of chloroprene polymer containing volatile substances obtained from a chloroprene polymer latex is removed with a screw type extruder and dried, 100 parts by weight of the chloroprene polymer is added. Provided is a method for producing chloroprene rubber, characterized in that 0.01 to 10 parts by weight of an alkali metal carbonate is added to the rubber. In the present invention, the chloroprene polymer is a polymer obtained by polymerizing chloroprene (2-chloro-1,3-butadiene) alone or with a monomer that can be copolymerized with chloroprene. The body is a compound containing at least one vinyl group in the molecule, and preferable examples include vinyl compounds such as styrene, methyl methacrylate, and acrylonitrile, 1,3-butadiene, isoprene, and 2,3-butadiene. Examples include conjugated dienes such as dichloro-1,3-butadiene. A chloroprene polymer latex is an emulsified dispersion of a chloroprene polymer obtained by emulsion polymerization, and most of the unreacted monomers are usually removed by steam stripping or the like. Further, a coagulated material containing a volatile substance can be obtained from a chloroprene polymer latex by a known method such as a freezing method or a salting-out method. As a freezing method, a method is used in which the latex is brought into contact with a part of a rotating roll that has been cooled to a temperature below the solidification temperature, the latex is frozen and solidified on the surface of the roll, and this solidified material is continuously peeled off. In addition, as a salting-out method, the latex is brought into contact with a compound capable of salting out and coagulating the latex, such as strong acid salts of alkali metals, alkaline earth metals, or aluminum, to destroy the emulsification of the latex and coagulate the polymer. A method of obtaining a coagulated product is used, and a tank equipped with a stirrer or a screw type extruder is used as the device. Other methods for obtaining a coagulated product include treatment with alcohol or ketones, treatment with strong acids, and heat treatment with steam, hot water, etc. Further, it is possible to obtain a coagulated product by subjecting a solution polymer or a bulk polymer to steam treatment, alcohol or ketone treatment. The volatile substances contained in the coagulum are usually mainly water, and contain small amounts of organic substances such as volatile monomers, volatile polymerization aids, and various volatile additives, and the content of these substances varies greatly depending on the processing method. However, excluding the surface adhesion, it is about 3 to 70%. Further, the coagulated product may be washed with warm water, alcohol, or ketones, or fillers, adjuvants, softeners, etc. may be added, if necessary. In the present invention, drying does not only mean completely removing volatile substances, but also substantially removing volatile substances so that the content of volatile substances in the dried product is reduced to several percent, preferably 1% or less. It also includes removal. The screw type extruder used in the present invention has a main structure of a screw and a barrel, and is equipped with mechanisms for raw material feed, drainage, washing, compression dehydration, exhaust, and removal of dried products as necessary. Functionally, it has functions for raw material feed, compression dehydration, drainage, evaporative removal of volatile substances, and removal of dry matter, and as necessary, to promote washing, addition of additives, and evaporative removal of volatile substances. It may be added with functions such as a heating or depressurizing device, a die for molding the dried product, etc. The screw flights of these extruders do not necessarily have to be continuous, and elements for mixing or pressurization may be incorporated as necessary. The number of axes of the screw is not particularly limited, but usually a single-shaft or two-shaft type is preferably used. or,
It is not necessarily necessary for one unit to have all the functions, and it may be achieved by combining multiple functions, and if necessary, one unit can also be combined with salting-out coagulation, which is one of the solidification methods in the previous process. The method of doing so is also fine.
In this case, the latex and salting-out agent are fed continuously to coagulate, and most of the water containing water-soluble substances is dehydrated by compression and removed from the system through the drain, and the coagulated product is directly transported to the drying area for drying. This is an extruder with the function of performing this process, and it can be advantageously operated continuously without the need to take out the coagulated material during the process. In this case, an extruder having a twin-screw self-cleaning type screw can be particularly advantageously used in order to prevent functional deterioration due to cohesiveness and stickiness of the coagulated material due to wrapping around the screw. Preferred examples of the alkali metal carbonate that can be used in the present invention include sodium carbonate and potassium carbonate. As alkali metal salts, low molecular weight carboxylic acid salts such as sodium formate and sodium acetate also have the effects seen in the present invention, but these salts have odor and corrosive properties due to decomposition products during the drying process. These problems often occur, and the vulcanization behavior of the obtained chloroprene rubber is often affected. Alkali metal carbonates pose no particular problems in these respects and can be preferably used. The amount of the alkali metal carbonate added is 0.01 to 10 parts by weight, preferably 0.03 to 5 parts by weight, per 100 parts by weight of the chloroprene polymer. If the amount added is less than 0.01 part by weight, the effects seen in the present invention will be small. On the other hand, if the amount added is more than 10 parts by weight, the increase in effect will be small, but on the other hand, the additive will become non-uniformly dispersed, and the purity of the product will be reduced, resulting in a substantial deterioration of quality. The alkali metal carbonate may be added in any form: solid (powder), dispersion, or solution.
It can be added to the chloroprene polymer latex or coagulum, or directly into the drying area of the extruder, but it is usually effective to add it after the extruder's decompressing area. . In the present invention, the stability of raw rubber during storage means:
It means that there is no change in quality during storage in a manufacturing factory, warehouse, etc., or during transportation by vehicle, ship, etc. Specific examples include an increase in the Mooney viscosity of raw rubber, coloring, discoloration, etc. Products with poor stability during storage (raw rubber) are difficult to store, and their quality deteriorates due to long-term storage, transportation, storage in summer, storage in high-temperature places such as the bottom of ships, and the product value decreases. Otherwise, large-scale cooling equipment is required to maintain quality, and storage costs are high. For these reasons, the stability of raw rubber during storage has become an important control point for this industry. The compound according to the invention, i.e. the chloroprene rubber obtained by drying in an extruder without the addition of an alkali metal carbonate, has poor stability during storage, e.g.
When stored at 70℃ for 12 days, the Mooney viscosity (ML ₁₊₄
100℃) can rise by more than 50 points. However, when dried by the method of the present invention, the Mooney viscosity of the chloroprene rubber obtained increases by 20 points or less, and there is little discoloration, and the stability during storage can be greatly improved. In addition, in the present invention, the processability of chloroprene rubber refers to the processability of chloroprene rubber containing a vulcanizing agent and a vulcanization accelerator.
When compounding ingredients such as fillers, reinforcing agents, softeners, etc. as necessary to make an unvulcanized compound (hereinafter referred to as a compound), or during or after storage of the compound, re-kneading, etc. In terms of stability during vulcanization and stability during vulcanization, if the stability of the compound is poor, the viscosity of the compound will increase, making kneading difficult, and vulcanization will be uneven during vulcanization, resulting in poor vulcanization. It will reduce the quality of the sulfur product or, in extreme cases, eliminate the commercial value of the product. Processing stability should be evaluated by actual processing operations, but since processing itself is diverse and diverse, it is often evaluated using scorch time as a general evaluation method. The compound of chloroprene rubber obtained by drying in an extruder without adding the compound according to the present invention has a t5 value, which is a typical value for the scorch time (Mooney viscosity is _5% lower than the lowest value using an S rotor using a Mooney viscometer). The total time required from the start of preheating until the point rises is short, which tends to cause problems in terms of processing stability. In order to improve processing stability, reducing the amount of vulcanization accelerator improves the stability to some extent and increases the _t5 value, but it also delays vulcanization itself, making vulcanization difficult and having a large impact on the physical properties of the vulcanized material. It becomes a trend. However, the _t5 value of the chloroprene rubber obtained by drying according to the present invention becomes long, and furthermore, it has excellent processing stability in that it can be processed without delaying the vulcanization rate during vulcanization. Examples are shown below to explain the present invention in more detail. In the following, all parts and percentages are expressed on a weight basis. Example 1 (1) 95 parts of chloroprene, 2,3-dichloro-1.
5 parts of 3-butadiene, 124 parts of water, 3 parts of disproportionated rosin acid, 0.22 parts of normal dodecyl mercaptan
1 part, 0.6 parts of sodium salt of a condensate of naphthalene sulfonic acid and formaldehyde, and 0.7 parts of sodium hydroxide are emulsified, and potassium persulfate is 0.5 parts.
%, sodium anthraquinone beta sulfonate was polymerized at 40°C using a mixed aqueous solution of 0.05% as a catalyst, and when the polymerization rate reached 60%, 0.4 part of parathalybutyl-catechol was added to stop the polymerization, and then steam-stripped. Unreacted monomers were removed by a ripping method to obtain a chloroprene polymer latex. (2) After adjusting the pH of the latex to 7.0, it is frozen and solidified in a rotating drum type freezer, then thawed by pouring hot water at a temperature of 30℃, and a part of the water is separated through a squeeze dehydrator. and the average volatile content is 32%
(110°C x 1 hr) to obtain a coagulated product. (3) The above coagulated material was put into a recovery device consisting of two extruders, and additives were added to obtain the chloroprene polymer shown in Table 1. The volatile content of this chloroprene polymer was 0.5% or less. This equipment has the main shafts of the first and second stage extruders.
It has a 90 degree angle, and the first stage extruder has a rotating cutter, which is arranged so that the shredded coagulum can be fed into the feed port of the second stage extruder by falling naturally. . The first stage extruder is mainly used for compressing and dewatering, and is equipped with a pressurizing mechanism and a drainage mechanism. The second stage extruder is mainly used for drying, and the extruder is turned toward the tip (in the extrusion direction) to reduce the clearance between the screw and the housing. It is a single-screw extruder with a structure in which the diameter gradually decreases towards the end, and the average screw diameter is 90mm. Behind the feed port (on the opposite side of the extrusion port) there is a drain port, feed port and extrusion port. An addition port equipped with two plunger pumps is installed in the middle of the extrusion port, and a rotary cutter is installed at the extrusion port to cut the chloroprene polymer into a length of approximately 5 mm, and to remove volatile substances from the atmosphere. We used a substance that was designed to be released at The second stage extruder was operated under the following conditions. Screw rotation speed 105 to 120 rpm Pressure at tip 90 to 98 Kg/cm ² (gauge pressure) Diameter and number of holes at extrusion port 3 x 24 (4) The above dried rubber was placed in a gear oven at a temperature of 70℃.
It was stored for 12 days, and the color change and Mooney viscosity before and after storage were measured. Table 1 shows the degree of discoloration and increase in Mooney viscosity due to storage. Note that Mooney viscosity was measured in accordance with JIS K6300. Rotor L type Preheating 1 minute Rotor operating time 4 minutes Test temperature 100°C In Table 1, test numbers 1 and 6 indicate comparative examples. Comparative examples of test numbers 1 and 6 changed color to blackish brown due to storage and the increase in Mooney viscosity exceeded 50, whereas test number 2 according to the present invention
In samples 5 to 5, no such changes were observed except for test number 2, which changed color to light brown, and there was little increase in Mooney viscosity. As can be seen from these results, the samples according to the present invention have excellent raw rubber stability.

【table】

[Table] The number of parts of additive per part.
Example 2 (1) 100 parts of chloroprene, 2,3-dichloro 1.
A chloroprene polymer latex was prepared according to Example 1 except that 3-butadiene was used as 0 parts,
After adjusting the pH to 7, salting out coagulation was performed using an extruder to obtain a rope-shaped coagulated product with a volatile content of 18.6%. This extruder has two screws with a diameter of approximately 55 mm L/D approximately 2.4 mm, and is equipped with a feed port, a drain port, and an extrusion port with 24 holes with a diameter of 4 mm at the tip. 25/h with 0.5% _CaCl2 as coagulant
The aqueous solution was fed to the chloroprene polymer latex at approximately the same speed, and the screw was rotated at 60 rpm for continuous coagulation. (2) The above solidified product was dried by passing it through an extruder equipped with a vacuum bend twice. At this time, the additives shown in Table 2 were mixed with the coagulated material discharged from the extrusion port in the first extrusion, and then passed through the second extrusion to obtain a chloroprene polymer. The volatile content of these chloroprene polymers is
It was less than 0.5%. This extruder has a diameter of approximately 29mmL/D approximately 17mm (length approximately
This is an extruder with two meshing screws (490 mm) rotating in the same direction, with a nozzle-shaped extrusion port with a diameter of 18 mm at the tip, and an inverted pitch screw for pressurization at a position approximately 390 mm from the tip, and approximately 300 mm from the tip. The exhaust port connected to the vacuum pump is at the returned position, and the opening is approximately 55mm at the returned position about 450mm from the tip.
mm x 40mm feed port, two drain ports with a diameter of about 12mm facing downward at a position about 465mm back from the tip, and a heating jacket (separated into two rows of threads at the front and back) on the outside of the housing. The equipment and operating conditions are as follows. Screw rotation speed: 1st time: 250 pm, 2nd time: 200 rpm Jacket temperature: 60°C hot water flows in the tip direction, no water flows in the rear direction Vacuum degree: 270 to 180 mmHg (3) Measure the increase in Mooney viscosity according to Example 1 and table -2. (4) The scorch time _t5 values were measured according to JIS K6300 and are shown in Table 2. Blending recipe 100 parts of chloroprene polymer Phenylalphanaphthylamine 1 MgO 4 ZnO 5 2-mercaptoimidazoline 0.35 Measurement conditions Rotor S type Preheating time 1 minute Test temperature 121℃ (5) The physical properties of the vulcanizate were measured according to JIS K6301 and are shown in the table below. −
Shown in 2. Mixing recipe Same as above (4) Vulcanization conditions 121°C x 25 minutes Test number 7 in Table 2 shows a comparative example. As is clear from these results, the rubber according to the present invention has excellent storage stability and processing stability of raw rubber, and does not delay vulcanization or deteriorate the vulcanized physical properties.

[Table] When sodium acetate was added in place of Na ₂ CO ₃ in Test No. 9 of Example 2, the product that passed once through an extruder with a vacuum bend had a strong odor of acetic acid. The vacuum pump exhaust gas had a similar odor. No such odor was felt in the products according to the present invention. Example 3 (1) Attach a stainless steel pipe with an inner diameter of 1.2 mm to the exhaust port of the extruder with a vacuum bend used in Example 2 so that the tip is approximately 15 mm away from the screw surface, and remove the other end from the system. I put it out. (2) The chloroprene polymer latex produced according to Example 2 and a 2% Al ₂ (SO ₄ ) ₃ aqueous solution were fed to the feed port of the extruder in (1) at approximately constant speed, and the exhaust port A 10% Na ₂ CO ₃ aqueous solvent is added to the coagulated material in the extruder through a stainless steel pipe attached to a
Less than 0.5% chloroprene polymer was obtained. still,
Separated water produced by coagulation and squeezing was discharged from the system through a drain port. The operating conditions of the extruder are as follows. ●Screw rotation speed: 150 rpm ●Jacket temperature: 60 on the jacket toward the tip
℃, hot water at 75℃ was passed through the jacket in the rear direction. ●Vacuum degree: 20 mmHg (3) The increase in Mooney viscosity of the obtained chloroprene polymer when stored at 70°C for 12 days according to Example 1 was measured and shown in Table 3.

【table】

Claims (1)

[Claims] 1. When removing volatile substances from a coagulated product of a chloroprene polymer containing volatile substances obtained from a chloroprene polymer latex using a screw type extruder and drying it, 0.01 to 10 parts by weight per 100 parts by weight of the chloroprene polymer A method for producing chloroprene rubber, which comprises adding parts by weight of an alkali metal carbonate.