JPH0257570B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of blending various additives into a resin produced through a polymerization step, a devolatilization step, and a granulation step. In general, various additives are added to resins to improve the performance of the resin or to impart new performance to the resin, such as stabilizers such as heat stabilizers, antioxidants, and ultraviolet absorbers, and to improve moldability. Lubricants, plasticizers, antistatic agents, colorants, etc. depending on the purpose.
Addition of flame retardants and the like is being carried out. These various additives are blended in the resin manufacturing process, or blended in a blending process provided separately from the manufacturing process. When blending additives with resin, in a method of blending additives with resin in a blending process separate from the manufacturing process, it is possible to mix the additives with the resin, heat melt, knead, and granulate it. This results in increased costs, increased heat history, and decomposition loss of additives, deterioration, and deterioration of the resin. On the other hand, when adding additives during the resin manufacturing process, the resin is already in a molten state, so there is no need to heat and melt the resin, making it possible to save significant costs. It is advantageous that additives that can be blended are blended as much as possible during the manufacturing process. However, conventionally, when blending additives in the resin manufacturing process, the additives are blended during the preparation of raw material monomers, the polymerization process, or the devolatilization process. If the resin has a viscosity, there will be a volatilization loss of the additive during the devolatilization process, and the concentration of the additive contained in the resin will fluctuate due to changes in the devolatilization conditions, causing problems such as the additive concentration becoming unstable. be. In particular, when blending additives in the process before the devolatilization process, which is carried out under high-temperature conditions, if the additives used have relatively poor thermal stability, they may decompose or change color due to thermal history. Therefore, it is preferable to mix the additives in a process as close to the granulation process as possible. In addition, there is a method of adding powdered additives to the molten resin after the devolatilization process, in which the powdered additives are dissolved in a solvent and added in liquid form, but the total volatile content in the resulting product increases. However, it may pose a food hygiene problem, and such a blending method is virtually impossible. In addition, the blending method in which powdered additives are added to the molten resin after the devolatilization process is as follows:
This is undesirable because it is difficult to achieve a uniform mixing degree of the molten resin and the powdered additive, and in addition, since the process after the devolatilization process is a line for transferring the molten resin, pressure higher than atmospheric pressure is generated. For some time now, it has been technically difficult to continuously and stably supply powdered additives in fixed amounts. In view of this, the present inventors have worked diligently to find a method for blending powdered additives that has less volatilization loss and is less subject to thermal history when blending additives in the resin manufacturing process. As a result of repeated research, we found that powdered additives are liquefied in advance and continuously mixed into the molten resin extracted from the devolatilization process in the resin manufacturing process, and then mixed in a mixer. The present invention was achieved by discovering that it can be easily and uniformly mixed into a molten resin and also solve the problems of the conventional methods as described above. The resin manufacturing process to which the present invention is applied is not particularly limited depending on whether it is a bulk polymerization method, solution polymerization method, emulsion polymerization method, suspension polymerization method, etc. Any continuous resin production process that includes at least a polymerization step, a devolatilization step, and a granulation step may be used. As resins manufactured in such a manufacturing process, there are various thermoplastic resins such as polyolefin-based, polystyrene-based, polyvinyl-based, polyamide-based, and the like. The present invention is preferably applied to a polystyrene resin manufacturing process using continuous bulk polymerization. In addition, additives that can be incorporated in the present invention include, for example, organic stabilizers such as phosphite, heat stabilizers such as inorganic stabilizers such as calcium and tin, antioxidants such as phenol type and sulfide type, benzophenone type, UV absorbers such as phenyl salicylate, lubricants such as fatty acid, fatty acid amide, ester, and metallolithic agents, other plasticizers, antistatic agents,
Examples include, but are not limited to, colorants, flame retardants, and the like. Additives that are powder solid at room temperature are melted by heating at a temperature 5 to 30° C. higher than the melting point of the additive to make a liquid, and then mixed into the molten resin. The heating and melting conditions for this powdered additive are preferably such that the heating temperature and heating time are as low or short as possible so as to suppress deterioration and discoloration caused by heating the additive as much as possible. This powdered additive is taken out in fixed quantities by a screw feeder installed at the bottom of the hopper, and supplied to a heated melting tank via a supply pipe, and then continuously delivered in fixed quantities from the bottom of the heated melting tank with a metering pump. It is preferable to take it out and mix it into the molten resin,
At this time, it is desirable to cool the supply pipe from the outside to condense and solidify the molten additive gas, thereby preventing the additive gas from flowing back toward the screw feeder or hopper. When mixing the additive that has been heated and melted into a liquid state into the molten resin, only one type of additive may be mixed.
Also, a plurality of types may be mixed. When mixing multiple types of additives into the molten resin, separate mixing lines may be provided for each additive, but
Multiple types of additives may be mixed in a mixer that mixes them in advance and then mixed into the molten resin;
The additives may be mixed in advance and mixed into the molten resin by quantitatively supplying a plurality of types of additives to a heating melting tank. The additives mixed into the molten resin are uniformly mixed by a mixer provided after the devolatilization step. The mixer for mixing the molten resin and additives may be either a screw mixer using mechanical shearing force or a static mixer used as a static mixer. The molten resin and additives are uniformly mixed by passing through the mixer described above and then transferred to the granulation process. An example of the method of the present invention will be explained below based on the flow sheet shown in the attached drawings. In the drawing, reference numeral 1 is a resin polymerization step, and the resin produced continuously or intermittently in this polymerization step 1 is produced in line 2. The polymer is then transferred to a devolatilization step 3, where volatile components such as unreacted monomers and the solvent used in the polymerization step 1 are removed. On the other hand, the powdered additive supplied from the line 4 enters the hopper 5, and the screw feeder 6 provided at the bottom of the hopper 5 feeds into the supply pipe 7.
A fixed amount is supplied to the heating melting tank 8. The supply pipe 7 is composed of a water-cooled jacket cooling pipe,
The additive vaporized in the heating melting tank 8 is cooled and condensed. As a result, the vaporized additive flows back toward the screw feeder 6, and transportation troubles of the screw feeder 6 can be prevented. The liquid additive melted and liquefied in the heated melting tank 8 is extracted from the lower part by a metering pump 9, mixed with the molten resin extracted from the devolatilization step 3, and uniformly and The mixture is completely mixed and transferred to the granulation process 11.
In step 1, it is granulated into chip strands or spherical pellets. The method of the present invention will be explained below based on Examples. [Example] Styrene 95-85% by weight and synthetic rubber 5-15% by weight
and are continuously polymerized in bulk using a stirring polymerization tank,
When manufacturing rubber-modified polystyrene, for the purpose of improving the thermal deterioration characteristics of rubber-modified polystyrene,
An additive (2,6-di-t-butyl-p-cresol; MP70°C), which is a white powder at room temperature, was blended as follows to achieve a target blending ratio of 0.45% by weight. That is, the above-mentioned additives are supplied from the screw feeder at the bottom of the hopper through a supply pipe cooled by a water-cooled jacket to a heated melting tank in an air atmosphere, and are heated within a range of 90 to 110°C in this heated melting tank. After being heated and melted, it is continuously mixed into the degassing process exit line of the rubber modified polystyrene manufacturing line using a metering pump, and then passed through a mixer in the granulation process, where it is stranded from the mold into a water tank. Resin pellets were obtained by extrusion and cutting. In order to check the degree of mixing of the additives, the resin pellets were randomly sampled five times every 10 minutes, and the concentration after addition was measured. The results are shown in Table 1. As is clear from Table 1, the coefficient of change with respect to the target value is small and almost constant, indicating that the ingredients are uniformly blended. In addition, as long as the supply pipe was water-cooled, no fluctuation was observed in the amount of powder supplied, and no problems were observed in long-term continuous operation. However, as a result of discontinuing water cooling of the supply pipe, 1~2
As time passed, the power load on the screw feeder fluctuated, and the amount of powder supplied was observed to fluctuate. At this time, as a result of investigating the inside of the supply pipe, it was found that a considerable amount of needle-like crystals of the additive had adhered, making long-term continuous operation difficult unless the supply pipe was water-cooled. [Comparative Example] In the above example, the additive was mixed at the polymerization step (stirring polymerization tank) before the degassing step of the rubber-modified polystyrene production line, and the additive blending ratio was
Rubber-modified polystyrene pellets were obtained in the same manner as in the example except that the mixture was continuously blended at a concentration of 0.35% by weight. In order to confirm the degree of mixing of additives, sampling was carried out in the same manner as in the examples, and the additive concentrations were measured. Table 1 shows the results. As is clear from Table 1, the resin contained only an average of 547 ppm compared to the target value of 3500 ppm. This means that only 15.6% of the target value remains, and the remaining 84.4% is thought to have been volatilized during the degassing process. Moreover, the reason why the change coefficient with respect to the target value is large compared to the example and the concentration fluctuation is large is that the amount of volatilization differs due to pressure fluctuation in the degassing step.

[Table] Standard deviation
(Note) Coefficient of change (CV) =

Claims (1)

[Claims] 1 Powder taken out from the bottom of the hopper by a screw feeder when continuously blending powdered additives for modification into the resin that is continuously produced through the polymerization process, devolatilization process, and granulation process. The granular additive is supplied to a heating melting tank via a cooled supply pipe, the powder additive is liquefied in advance in this heating melting tank, and this liquefied additive is extracted from the above devolatilization process. A method for blending powdered additives, which comprises continuously introducing a fixed amount of molten resin into a transfer line, mixing it in a mixer, and transferring it to a granulation process.