JPS6147852B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polyester synthetic resin by terminating the reaction when the resin exhibits conductivity such that the molecular weight falls within a specific range. Conventionally, when determining the end point of a reaction of a synthetic resin, such as polyester, samples were taken from the reaction solution at regular intervals, weighed, diluted with a solvent as needed, and then treated with a solution such as potassium hydroxide at a certain concentration. The acid value was measured by neutralization titration using an alkaline solution, and the viscosity was measured at the same time. However, with this method, it is clearly impossible to obtain samples continuously, and it is difficult to obtain a resin with a uniform reaction rate, which requires a considerable amount of time to obtain results. This is a fatal flaw when attempting to automate the reaction process, ie, in either continuous production method or batch production method. The present inventors have improved this shortcoming by measuring the reaction rate in the synthesis of condensation resins, especially polyesters, continuously, automatically, and in a short time, controlling the reaction, and determining the end point of the reaction. We have found a method to do this and have completed the present invention. That is, in the present invention, the electrode of a conductivity meter is inserted into the polyester raw material solution, the reaction is allowed to proceed, and the conductivity of the reaction solution is measured, and the point at which the conductivity of the resulting resin is such that the molecular weight is 300 to 7000 is shown. The present invention provides a method for producing a polyester-based synthetic resin, characterized in that the reaction is terminated at In the present invention, as the concentration of carboxyl groups or hydroxyl groups in the reaction solution of polyester decreases as esterification progresses, the concentration of ions generated from functional groups in the reaction solution decreases, and at the same time, the viscosity increases, so that the conductivity of the reaction solution decreases. It is based on the fact that there is a certain relationship between the conductivity and the reaction rate depending on the conditions. This relationship mainly changes depending on the reaction conditions, especially the type of monomer, the charging ratio, the reaction temperature, the frequency of the interelectrode current, and may also change depending on the reaction vessel, but under certain specific conditions Once the relationship is determined below, the reaction rate can be automatically determined from then on, allowing abnormal reactions to be discovered, reaction control, and the end point to be determined. The polyester synthetic resin used in the present invention is saturated or unsaturated polyester. In addition, the conductivity meter used in the present invention has an electrode that is not corroded by the reaction liquid and is heat resistant.
Moreover, it is desirable to have a device that can sufficiently measure minute changes in the conductivity of the reaction solution. Since the conductivity of this conductivity meter changes depending on temperature, it is desirable that the conductivity meter has a temperature compensation circuit. These instruments have no moving parts or pores, and can be measured simply by passing an electric current between the electrodes, so there are almost no problems that occur with process viscometers, such as obstructions caused by minute solids, disturbances caused by air bubbles, and corrosivity, making them extremely easy to use. Suitable for actual manufacturing process. Incidentally, the current between the electrodes of the conductivity meter may be direct current or alternating current, but preferably alternating current, and the frequency is 100 to 10,000 Hz, preferably 1,000 to 5,000 Hz to avoid polarization of the liquid. According to the method of the present invention, the molecular weight of the resin is 300~
The reaction is terminated when the conductivity reaches 7000, but the end point of the reaction can be measured by the conductivity, and the end point can be accurately determined by an electric pulse, and the value can be determined in advance. By setting the temperature in advance, it becomes possible to automatically and continuously produce a resin having a specific molecular weight. In the present invention, the relationship between the molecular weight and electrical conductivity of the resin varies depending on the resin, and also varies widely depending on the reaction components and the molar ratio of the reaction components, so it cannot be generalized, but for example, when a saturated polyester is When obtained by reacting with an acid, the molecular weight of polyester is 1000-5000 and the conductivity is approximately 0.05-0.01μ.
〓/cm, and when unsaturated polyester is obtained by an equimolar reaction of acid and alcohol, the conductivity is approximately 0.08 to 0.02μ when the molecular weight of the polyester is 1000 to 2000.
It will be about 〓/cm. Next, the present invention will be further explained by examples. Example 1 1708 g (27.5 moles) of ethylene glycol and 3914 g (26.8 moles) of adipic acid were placed in a glass flask with a capacity of 5, and esterification was carried out at 215°C. At that time, a sensor made primarily of stainless steel with a fixed cell constant was inserted into the reaction solution, and a current with a frequency of 5,000 Hz was applied to measure the conductivity as the reaction progressed. At the same time, the molecular weight, acid value, and viscosity of the resin were also measured. The results are shown in the table below.

[Table] Next, the reaction was carried out in the same manner as above, and the reaction was stopped when the electrical conductivity of the reaction solution showed 0.013μ〓/cm. The molecular weight, acid value, and viscosity of the resin at that time were measured. This operation was performed a total of 5 times. The following table shows the molecular weight, acid value, and viscosity of the resin produced each time.

[Table] As is clear from the results in the above table, if the reaction is terminated when the electrical conductivity shows a specific value, a resin having a substantially constant molecular weight can be obtained. Example 2 Maleic anhydride 1150g (11.7mol), phthalic anhydride 3500g (23.6mol), propylene glycol
1350g (17.7 moles) and ethylene glycol
1100 g (17.7 mol) was placed in a stainless steel reaction vessel and an esterification reaction was carried out at 215°C. The following steps were carried out in the same manner as in Example 1. The sensor used had a cylindrical shape with a diameter of about 30 mm and had a sensing part with a length of about 60 mm at the tip and an insertion length of about 2 m from below the flange of the reactor.

[Table] Next, the reaction was carried out in the same manner as above, and the reaction was stopped when the electrical conductivity of the reaction solution showed 0.026μ〓/cm, and the molecular weight, acid value, and viscosity of the resin at that time were measured. This operation was performed a total of 5 times. The following table shows the molecular weight, acid value, and viscosity of the resin produced each time.

[Table] As is clear from the results in the table above, the conductivity is 0.026.
If the reaction is stopped at the point where μ〓/cm is reached, the molecular weight will be approximately
1860 resin can be obtained with good reproducibility.

Claims (1)

[Claims] 1 Insert the electrode of a conductivity meter into the polyester raw material solution, proceed with the reaction, measure the conductivity of the reaction solution, and end the reaction when the conductivity shows that the molecular weight of the produced resin is 300 to 7000. 1. A method for producing a polyester synthetic resin.