JPS5991103A - Recovery of thermoplastic resin - Google Patents

Abstract

PURPOSE:To recover efficiently a thermoplastic resin having a sharp particle size distribution and a practically spherical particle form from a thermoplastic resin emulsion by adding a coagulant, etc., in a specified two-step process. CONSTITUTION:In step 1, a coagulant (e.g., sulfuric acid) and/or a coagulation aid (e.g., polyethylene oxide) are added to a thermoplastic resin emulsion to bring the emulsion into the state of an incomplete coagulation (the pH of the slurry being preferably about 3-7). In step 2, a coagulant (optionally, together with a coagulation aid) is added and the mixture is treated at a temperature which is about 10 deg.C above that 1 in step (preferably, at a pH of about 2-7) to recover the thermoplastic resin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering a thermoplastic resin, and more particularly to a method for recovering a thermoplastic resin by adding a coagulant to a thermoplastic resin emulsion.

Conventionally, when recovering resin from a thermoplastic resin emulsion produced by an emulsion polymerization method, coagulation is generally performed using a coagulant such as hydrochloric acid.

Examples of this method include adding a thermoplastic resin emulsion to an aqueous solution containing a coagulant and coagulating and recovering the resin, or adding a solution containing a coagulant to a thermoplastic resin emulsion to coagulate the resin.・Methods of collection are in place.

However, resin powder recovered by conventional coagulation methods cannot be obtained with uniform particle diameters, has a considerable amount of fine particles and coarse particles, and has unstable particle shapes. This causes various problems such as:

(1) If there are many fine particles in the powder, the fine particle powder will flow out or scatter during separation and recovery of the resin from the thermoplastic resin latex and during drying, resulting in loss of resin, deterioration of the working environment due to dust generation, and dust. may pose a risk of injury.

(2) Fine particles and coarse particles in the powder cause clogging in each device during the separation and drying process, resulting in decreased productivity and energy consumption.

(3) If the light particles are amorphous, the powder is transferred to a hopper,
When stored in a bag, etc., the powder may block together, making it impossible to easily remove the powder from the hopper, etc.
This poses a major problem when handling powder.

A possible solution to the problems in (1), (2), and (3) above is to improve equipment, but such improvements have limits and require a considerable amount of cost.

An object of the present invention is to provide a method for recovering a thermoplastic resin that eliminates the drawbacks of the prior art and can obtain powder having a particle size distribution as narrow as possible and a particle shape close to circular.

In order to achieve the above object, the present inventors have conducted intensive research and found that by coagulating thermoplastic resin latex under specific conditions in two or more steps, the particle shape is close to spherical, and coarse particles and fine particles can be obtained. The present invention was achieved by discovering that a resin powder with an extremely small amount can be obtained.

That is, the present invention provides a method for recovering a thermoplastic resin from a thermoplastic resin emulsion, in which the coagulant is added in two or more steps, and the coagulant and/or coagulation aid are added in the first step. death.

The second and subsequent steps are characterized by adding a coagulant, or a coagulant and a coagulation aid, and raising the temperature of the liquid higher than in the first step.

In the present invention, the above two or more steps are usually carried out using a coagulation tank twice or more, but are not limited to this. For example, the process is divided into two or more chambers, and each chamber is provided with stirring means. It may also be a cylindrical container with a It is also possible to use a so-called batch method in which one coagulation tank is used and the second and subsequent steps are performed after the first step is completed.

As the thermoplastic resin emulsion in the present invention, known ones can be used. As the thermoplastic resin, conjugated diene rubber, conjugated diene copolymer (for example, polybutadiene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer), or ethylene-
In the presence of a propylene copolymer, one or two of unsaturated nitrile monomers, aromatic vinyl monomers, (meth)acrylic acid ester monomers, or monomers copolymerizable with these monomers, etc. Graft copolymers obtained by polymerizing the above, such as ABS resin, ethylene-propylene rubber-modified styrene-acrylonitrile resin, methyl methacrylate-butadiene-styrene resin (MBS resin), high impact polystyrene resin (HIPS resin), etc. Suitably used.

In particular, a resin having a rubber content of 45% by weight or more is effective because it can improve blocking properties.

The method of the present invention is effective for improving the powder properties of these rubber-modified thermoplastic resins, but in addition to these polymers, it can also be used for ethylene vinyl acetate copolymer (EVA), vinyl chloride copolymer, and styrene-acrylonitrile copolymer. Application to emulsions of thermoplastic resins such as polymers, styrene polymers, high styrene-butadiene copolymers is also possible.

In the present invention, typically two or more coagulation tanks are used, and one selected from a coagulant and a coagulation aid is added to the first coagulation tank.
The resin powder which is the object of the present invention can be obtained by adding a coagulant alone or a coagulant and a coagulation aid in the second or subsequent coagulation baths.

Examples of the coagulant used in the present invention include inorganic acids such as hydrochloric acid and sulfuric acid, inorganic salts such as calcium chloride and magnesium sulfate, organic acids such as formic acid and acetic acid, and organic acid salts such as aluminum acetate. Among these, inorganic acids are more preferred. Coagulation aids include polyethylene oxide, polyvinyl alcohol, amines, imides,
Examples include water-soluble polymer compounds such as amides. When these coagulants and coagulation aids are used in the first coagulation tank and the second coagulation tank and subsequent coagulation tanks, one type or two or more types can be used. The amount of coagulant and coagulation aid to be used cannot be determined in part depending on the type of thermoplastic resin latex, but it can be determined as appropriate based on the pH value of the slurry in the coagulation tank, the coagulation state, and the particle state of the powder. It will be done. If the amount of coagulant and coagulation aid used is too large, the water washability will deteriorate, resulting in a longer washing time and the need for a large amount of washing water, which is not economical.On the other hand, if the amount is too small, the thermoplastic resin The emulsion is not completely solidified, and an uncondensed portion is present in the slurry, which causes a decrease in resin recovery rate and troubles during operation in the separation and drying steps.

The type of coagulant and coagulation aid used in the present invention is generally appropriately determined depending on the type of soap contained in the thermoplastic resin emulsion. In general, rosin acid soaps, fatty acid soaps, etc. can be sufficiently coagulated with ordinary coagulants and coagulation aids, but phosphate ester soaps,
For sulfate ester soaps, sulfonate soaps, cationic soaps, etc., it is suitable to use coagulants and coagulation aids mainly composed of organic acid salts, inorganic acid salts, water-soluble polymer compounds, and the like.

The coagulation tank used in each step of the present invention may be one equipped with a suitable stirrer, and examples of the stirrer include propeller blades, flat plate blades, spiral band stirrers, and homogenizers with high-speed shearing force. An example is a stirrer. However, the thermoplastic resin emulsion, coagulant, and coagulation aid can be added separately, or they can be mixed in advance in a premix tank, line mixer, etc.
It is also possible to introduce the first solidified sVC thereafter.

The slurry in the first coagulation tank is preferably in an incomplete coagulation state where the stability of the emulsion is partially destroyed and coagulation is not completed.For this purpose, the pH of the slurry is suitably in the range of 3 to 7, and more preferably. is 3-6. The above-mentioned incompletely solidified state is when more than 50% of the emulsion is solidified,
It is also preferable that the coagulation is not completed, and when the slurry is filtered through Toyo Roshi %131 (JIS P3801 Type 3), 50 or more polymers remain on the filter paper, and the filtrate is cloudy. Condition is appropriate. On the other hand, the temperature of the slurry is lower than the temperature of the slurry in the second and subsequent coagulation tanks, preferably a temperature lower than the temperature of the slurry by 10° C. or less. p of the slurry in the first coagulation tank
When H is less than 3, the particle shape of the resulting resin powder tends to be amorphous, while when pH exceeds 7, fine particles tend to be formed. Furthermore, when the temperature of the slurry in the first coagulation tank exceeds the temperature of the slurry in the second and subsequent coagulation tanks, powder with a wide particle size distribution is likely to be produced.

In the second and subsequent coagulation tanks, it is necessary to complete the coagulation of the slurry, and for this purpose, when the coagulant used is mainly an acidic coagulant such as an organic acid or an inorganic acid, the second and subsequent coagulation tanks must be It is preferable that the pH of the slurry is in the range of 1 to 3. On the other hand, when the slurry is mainly composed of an inorganic acid salt or an organic acid salt, or when a coagulation aid is used, the pH of the slurry is preferably in the range of 2 to 7. Observe the complete state of coagulation and check the force
It is desirable to determine the amounts of the coagulant and coagulation aid as appropriate.

The temperature of the slurry in the coagulation tank is usually 0 to 100°C, (9) preferably room temperature to 100°C. The appropriate temperature of the slurry in the second and subsequent coagulation tanks changes depending on the type of thermoplastic resin emulsion, so the temperature can be determined from the force by observing the characteristics and coagulation state of the powder. If the temperature is too high, the powder particles will aggregate too much and coarse particles will be produced, and if the temperature is too low, the powder particles will become fine particles and coagulation will not be completed, which is not desirable.

As described above, according to the method of the present invention, it is possible to continuously collect thermoplastic resin powder with uniform particle size with high efficiency, and the obtained resin powder has almost spherical particle shape. Since the diameter distribution is narrow and the angle of repose is small, blocking occurs<<, resulting in a powder that is very easy to handle in industrial production.

Next, examples of the present invention will be shown, and parts and percentages in the examples are parts by weight and weight %, respectively. In addition, the blocking properties, particle size distribution angle of repose, and particle shape in the Examples were measured by the following methods.

(1) Blocking property evaluation Put 3m9 of resin powder into a cylindrical mold with a diameter of 4C1ll,
(10) Next, a load is applied for 15 seconds at room temperature, and the minimum load G (kg) that allows a resin molded product to be obtained is determined.

If this value is large, blocking is less likely to occur.

(2) Particle size distribution measurement method Conditions Shaker: Rotortub type sieve shaker Shaking time: 220 minutes Sieve: Standard sieve (JIS-28801) Sample
:50q Find the remaining flA(l) on each sieve.

A: Remaining amount on each sieve after shaking This test allows you to know the size distribution of the particles that make up the powder.

(3) Angle of repose measurement method Angle of repose measuring device AN- manufactured by Showa Engineering Co., Ltd.
Type 1 was used, and the measurement method was carried out in accordance with the measurement method (11) for the AN-1 type. If the angle of repose is small, the powder will easily crumble, and when taking out the powder stored in the popper bag,
It has a property that makes it difficult to cause powder bridges, making it easier to remove powder and preventing blocking.

(4) Microscope Observation Using an optical microscope, the shapes of the resin particles in the solidified slurry and the particles in the powder were examined.

The magnification is 200x.

Example 1 As a thermoplastic resin emulsion, an emulsion of MBS resin having a solid content concentration of 30 cm was used, which was obtained by graft copolymerizing 45 parts of a styrene-butadiene rubber-like copolymer with 35 parts of styrene and 20 parts of methyl methacrylate. The MBS resin emulsion and sulfuric acid were continuously fed into the first coagulation tank equipped with a stirrer using separate pumps.
A slurry of H4,0 was produced. Note that the amount of sulfuric acid supplied is such that 7)H of the slurry is 4. I adjusted the IA so that it was OK.

Next, this slurry is introduced into the second coagulation tank and further into the second coagulation tank (
12) Continuously supply sulfuric acid to the 2 coagulation tank, and adjust the pH of the slurry to 2.
．． It was controlled once in 5. The temperature of each coagulation tank was maintained at outside air temperature in the first coagulation tank and at 85°C in the second coagulation tank.

Next, the resin component was separated from the slurry in the second coagulation tank using a centrifuge, and further washed with water, dehydrated, and dried to obtain resin powder.

Comparative Example 1 Example 1 except that the total amount of sulfuric acid in Example 1 was adjusted to 7) H2.5 by continuously supplying it in the first coagulation tank, and sulfuric acid was not supplied to the second coagulation tank. Resin powder was obtained in a similar manner (conventional method).

The specific results of the particle size distribution, angle of repose, blocking property, etc. of the resin powders obtained in Example 1 and Comparative Example 1 are shown in Table 1, and micrographs (X
200) are shown in FIGS. 1 and 2, FIG. 1 is for Example 1, and FIG. 2 is for Comparative Example 1.

The following margins (13) (14) (15) From the results in Table 1, regarding the particle size distribution, the powder of Example 1 is coarser than the powder recovered by the conventional coagulation method of Comparative Example 1. It can be seen that there are very few particles and fine particles, and that the particles are uniform.

Furthermore, the powder of Example 1 has a smaller angle of repose than Comparative Example IK, indicating that it is easier to flow, and also has a larger blocking resistance value, indicating that blocking is less likely to occur. Furthermore, from the micrograph, the powder of Example 1 (Fig. 1)
It can be seen that the powder of Comparative Example 1 (FIG. 2) has an irregular particle shape, whereas the powder of Comparative Example 1 has a spherical shape.

Example 2 In the method of Example 1, the pH of the slurry in the first coagulation tank was set to 3. A resin powder was obtained by pressing in the same manner as in Example 1, except that the amount of sulfuric acid supplied was controlled so that the result was OK.

Table 1 shows the particle size distribution and angle of repose blocking property of the resin powder.

Example 3 Resin powder was obtained in the same manner as in Example 1 except that the amount of sulfuric acid supplied was controlled so that the pH of the slurry in the first coagulation tank was 7.016). Ta.

Table 1 shows the measurement results of the particle size distribution, angle of repose, and blocking property of the resin powder.

Example 4 Here, an experimental example of the combination of coagulation aids is shown. In the method of Example 1, sulfuric acid and 7.5% by weight of polyethylene oxide (molecular weight 430 x 480 x 10') and the first
A resin powder was obtained in the same manner as in Example 1 except that the pH of the slurry in the coagulation tank was adjusted to 6.0. The measurement results of the particle size distribution, angle of repose, and blocking property of the resin powder were
Show it on the table.

Example 5 In the method of Example 1, only the polyethylene oxide of Example 4 was continuously added as a coagulation aid to the first coagulation tank at a ratio of 0.09 parts by weight per 100 parts by weight of the resin in the slurry. A resin powder was obtained in the same manner as in Example 1, except that the slurry was charged into the first coagulation tank and the pH of the slurry in the first coagulation tank was set to 7.0.

Particle size distribution, angle of repose, and blocking resistance of the resin powder (17
) The results of the sex measurements are shown in Table 1.

Example 6 Styrene 4 was obtained by graft polymerizing a mixture of styrene and acrylonitrile to polybutadiene as a thermoplastic resin.
A resin powder was obtained in the same manner as in Example 1, except that a thermoplastic resin emulsion containing 5% acrylonitrile, 17% acrylonitrile, and 38% butadiene and having a solid content concentration of 30% was used.

Table 1 shows the particle size distribution, angle of repose, and blocking resistance of the resin powder.

Comparative Example 2 The same thermoplastic resin emulsion used in Example 6 was continuously supplied to the first coagulation tank by a pump, and the total amount of sulfuric acid used in the first coagulation tank and the second coagulation tank of Example 6 was A resin powder was obtained in the same manner as in Example 1, except that sulfuric acid was continuously supplied to the first coagulation tank by a pump and sulfuric acid was not introduced into the second coagulation tank.

Note that the pH of the first coagulation tank was adjusted to 2.5. Table 1 shows the particle size distribution, angle of repose, and blocking resistance of the resin powder obtained in the second coagulation tank.

(1B)

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are 2a! of Examples 1 and 2, respectively. This is a micrograph (200x magnification) of a cross section of powder obtained in a solid bath. Agent Patent Attorney Takenaga Kawakita (19) Figure 1 Figure 2 Procedural amendment (method) % formula % 1. Indication of the case 1982 Patent Application No. 200359 2. Title of the invention Recovery of thermoplastic resin Method 3, Relationship with the case of the person making the amendment Patent applicant 4, agent Address: 11-8 Nihonbashi Kayabacho-Chome, Chuo-ku, Tokyo 103
(Shipping date: February 22, 1982) 6. Subject of amendment: Full text of application and specification. 7. Details of the amendments are as shown in the attached sheet. (No changes to the engravings and contents of the application and specification).

Claims (3)

[Claims] (1) In a method for recovering a thermoplastic resin from a thermoplastic resin emulsion, coagulants are added in two or more steps, the coagulant and/or coagulation aid is added in the first step, and the A method for recovering a thermoplastic resin, which comprises adding a coagulant or a coagulant and a coagulation aid in the second and subsequent steps, and increasing the temperature of the liquid even in the first step. (2) The method for recovering a thermoplastic resin according to claim 1, wherein in the first stage step, the pH of the liquid after adding the coagulant and/or coagulation aid is 3 to 7. (3) In the first stage step, after adding the coagulant and/or coagulation aid, the liquid becomes more than 50% of the resin emulsion and 1. The method for recovering thermoplastic resin according to claim 1, wherein the thermoplastic resin is in an incompletely solidified state in which solidification has not been completed.