Method for preparing chlorinated polyvinyl chloride

Abstract

The present disclosure provides a method for preparing chlorinated polyvinyl chloride by using a UV LED as a light source and changing its wavelength, which method has improved thermal stability while minimizing the reduction in reaction efficiency.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2020-0173572, filed with the Korean Intellectual Property Office on December 11, 2020, the disclosure of which is incorporated herein by reference in its entirety.

[0003] The present disclosure relates to a method for preparing chlorinated polyvinyl chloride using ultraviolet LEDs. Background Art

[0004] Chlorinated polyvinyl chloride has excellent heat resistance and is used in various fields such as pipes, films, and sheets. Chlorinated polyvinyl chloride is produced by reacting polyvinyl chloride with chlorine. However, in general, to react chlorine with polyvinyl chloride, chlorine radicals must be generated, and this reaction requires ultraviolet irradiation.

[0005] To date, the most commonly used ultraviolet irradiation method in the preparation of chlorinated polyvinyl chloride is the use of a mercury ultraviolet lamp. Mercury ultraviolet lamps are inexpensive, readily available, and widely used, but they have low energy efficiency and a short lifespan, so they need to be frequently replaced. In addition, mercury ultraviolet lamps emit ultraviolet light radially, and there is a problem that the ultraviolet light cannot sufficiently reach the reactants, resulting in a decrease in reaction efficiency.

[0006] Therefore, in recent years, research has been conducted to replace mercury UV lamps with UV LED lamps that have higher energy efficiency, lower power consumption, and a longer lifespan. However, the use of UV LED lamps has problems caused by the trade-off relationship between reaction efficiency and thermal stability. Specifically, when using a short wavelength with high energy, the reaction efficiency increases but the thermal stability decreases, and when using a long wavelength with low energy, the thermal stability increases but the reaction efficiency decreases.

[0007] Therefore, the present inventors made earnest efforts to solve the above problems, and as a result, it was confirmed that, as described below, the wavelength band of the UV LED lamp can be changed to a specific band during the chlorination reaction, thereby improving thermal stability while minimizing the decrease in reaction efficiency, and the present disclosure was completed. Summary of the Invention

[0008] Technical Problem

[0009] An object of the present disclosure is to provide a method for preparing chlorinated polyvinyl chloride, which improves thermal stability while minimizing the decrease in reaction efficiency by using a UV LED as a light source and changing its wavelength.

[0010] Technical Solution

[0011] According to the present disclosure, there is provided a method for preparing chlorinated polyvinyl chloride, the method comprising the following steps:

[0012] 1) Add a reactant containing polyvinyl chloride and chlorine to the reactor while irradiating ultraviolet light of a first wavelength; and

[0013] 2) Stir the reactant while irradiating ultraviolet light of a second wavelength,

[0014] wherein, the ultraviolet irradiation in steps 1 and 2 uses a UV LED disposed in the reactor as a light source, and

[0015] wherein, the value obtained by subtracting the first wavelength from the second wavelength is 10 nm or more and 50 nm or less.

[0016] Advantageous Effects

[0017] As described above, in the preparation of chlorinated polyvinyl chloride, by using a UV LED as a light source and changing its wavelength, the thermal stability can be improved while minimizing the reduction in reaction efficiency. Detailed Embodiments

[0018] The embodiments of the present disclosure can be best understood by referring to the following detailed description.

[0019] Polyvinyl chloride can react with chlorine to prepare chlorinated polyvinyl chloride, which has higher heat resistance than polyvinyl chloride and is thus used in various fields such as pipes, films, and sheets. To prepare such chlorinated polyvinyl chloride, chlorine radicals must be generated, and this reaction requires ultraviolet irradiation.

[0020] In the past, as a light source for irradiating ultraviolet light, a mercury UV lamp or the like was used, but there were problems such as low energy efficiency and short lifespan, so it needed to be frequently replaced. Therefore, the present disclosure uses a UV LED as a light source, but it is characterized in that the wavelengths irradiated between the chlorine addition step and the reaction step after chlorine addition are different from each other to minimize the problems caused by the trade-off between reaction efficiency and thermal stability.

[0021] Step 1 is a step of adding a reactant containing polyvinyl chloride and chlorine to the reactor while irradiating ultraviolet light of a first wavelength, and it is a step of preparing for the reaction of step 2 (which will be described later).

[0022] Meanwhile, in step 1 of adding the reactant, ultraviolet light of a first wavelength is irradiated. Specifically, the present disclosure uses a UV LED as a light source.

[0023] The UV LED is disposed in the reactor. One UV LED can be configured, or multiple UV LEDs can be configured as needed. Further, the arrangement position of the UV LED is not particularly limited as long as the ultraviolet light emitted by the UV LED can irradiate the position of the reactant in the reactor. Preferably, the UV LED is arranged above the reactor so that the ultraviolet light emitted by the UV LED can effectively irradiate the reactant.

[0024] Irradiating with a first wavelength of short wavelength having higher energy than the second wavelength irradiated in Step 2 described later can improve the reaction efficiency of the initial reaction. Preferably, the first wavelength can be from 300 nm to 400 nm, or from 350 nm to 390 nm. Most preferably, the first wavelength can be 365 nm or 385 nm.

[0025] There is no particular limitation on the reactor as long as it is a reactor for preparing chlorinated polyvinyl chloride. In addition, the reactor can be equipped with devices capable of adjusting the conditions required for the reaction of the reactants, such as a temperature control device, a pressure control device, etc. In addition, since polyvinyl chloride and chlorine usually react under stirring, a stirrer can be provided inside the reactor.

[0026] Among the reactants, it is preferred to introduce polyvinyl chloride into the reactor as an aqueous suspension, so it is preferred to arrange the stirrer at the lower end inside the reactor. A polyvinyl chloride aqueous suspension can be prepared by mixing and suspending polyvinyl chloride with water, and the polyvinyl chloride in the suspension can be adjusted to 1 to 90% by weight before use. Alternatively, the suspension can be prepared first and then added to the reactor, or polyvinyl chloride and water can be added to the reactor sequentially or together and then stirred.

[0027] In addition, chlorine in the reactants can be added to the reactor in a gaseous or liquid phase. At the same time, since the chlorine is consumed in the chlorination reaction described later, chlorine can be further supplied to the reactor during the chlorination reaction. This process can be adjusted by monitoring the degree of chlorination of polyvinyl chloride.

[0028] In addition, the amount of the added reactants can be appropriately adjusted considering the reactor size, etc.

[0029] Step 2 is a step of performing a chlorination reaction while irradiating ultraviolet rays of the second wavelength and stirring the reactants.

[0030] The temperature of the chlorination reaction is preferably 50 to 95 °C. When the temperature of the chlorination reaction is lower than 50 °C, the chlorination reaction cannot proceed sufficiently, while when the reaction temperature exceeds 95 °C, the polyvinyl chloride will deteriorate continuously and the physical properties may deteriorate. In addition, as the chlorination reaction proceeds, the temperature inside the reactor rises, so it is preferred to adjust the internal temperature of the reactor to maintain within the above range.

[0031] At the same time, for the chlorination reaction in Step 2, ultraviolet rays of the second wavelength are irradiated, and the ultraviolet LED is used as the light source in the same way as in Step 1 above. The details of the ultraviolet LED are the same as those described in Step 1 above.

[0032] As the second wavelength, a longer wavelength having lower energy than the first wavelength irradiated in Step 1 may be irradiated to improve thermal stability. Preferably, the second wavelength may be from 350 nm to 450 nm, or from 380 nm to 410 nm. More preferably, the second wavelength may be 385 nm, 395 nm or 405 nm, and most preferably, the second wavelength may be 405 nm.

[0033] At this time, in order to minimize the reduction in efficiency due to the trade-off between reaction efficiency and thermal stability and to improve thermal stability, the difference between the first wavelength and the second wavelength is limited to a specific range. Specifically, the value obtained by subtracting the first wavelength from the second wavelength may be 10 nm or more and 50 nm or less, or 20 nm or more and 40 nm or less.

[0034] When the value obtained by subtracting the first wavelength from the second wavelength is less than 10 nm, the reaction efficiency is poor and the improvement effect of physical properties is slight. In addition, if the first wavelength used is too short such that the value obtained by subtracting the first wavelength from the second wavelength exceeds 50 nm, the energy of the first wavelength is too high, which results in a decrease in physical properties. If the second wavelength used is too long such that the value obtained by subtracting the first wavelength from the second wavelength exceeds 50 nm, the energy of the second wavelength is too low, and the reaction time is greatly increased, resulting in disadvantages in terms of efficiency and economy. That is, when the value obtained by subtracting the first wavelength from the second wavelength is within the above range, the effects of improving reaction efficiency and thermal stability caused by the change in wavelength are both excellent.

[0035] Preferably, the light output of the light source is from 20 W to 160 W, and more preferably from 40 W to 100 W. At this time, the light output of the light source means the sum of the light outputs of a plurality of light sources when the number of light sources is plural.

[0036] The distance between the light source and the reactant may be appropriately adjusted in consideration of the light output and the ultraviolet intensity, and preferably, the distance is 10 cm or less.

[0037] Meanwhile, as the chlorination reaction proceeds through the above Step 2, chlorinated polyvinyl chloride is prepared, and the reaction time of the chlorination reaction may be adjusted by monitoring the degree of chlorination of the polyvinyl chloride. Preferably, the reaction time is adjusted until the chlorine content of the prepared chlorinated polyvinyl chloride becomes 62 to 69%, 64 to 68% or 66 to 67.5%. Meanwhile, the chlorination reaction may be terminated by terminating the UV irradiation via the light source.

[0038] In addition, the method of the present disclosure may further include dehydrating and / or drying the chlorinated polyvinyl chloride prepared by the chlorination reaction.

[0039] For ease of understanding of the present disclosure, the specific embodiments of the present disclosure will be described in more detail below. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure.

[0040] [Example]

[0041] Comparative Example 1

[0042] Polyvinyl chloride with a degree of polymerization of 1000 (average molecular chain length 1000; K value of 67) was mixed with deionized water to prepare a 20 wt% slurry, which was then charged into a 200 L reactor. After charging, degassing was carried out while stirring at a constant speed of 450 rpm until the internal pressure of the reactor reached more than -0.9 bar. If it was confirmed that the internal pressure of the reactor remained at -0.9 bar for more than 5 minutes after degassing, the reactor temperature was raised. When the reaction temperature reached 40 °C, chlorine gas was started to be added, and two UV lamps (200 W * 2, main wavelength: 365 nm, mercury lamp) were operated for the chlorination reaction. At this time, the reaction pressure was maintained at 2.0 bar, and the chlorination reaction was carried out at a reaction temperature of 70 °C.

[0043] When the added chlorine gas reached the target value, the chlorination reaction was terminated. After the reaction ended, the unreacted residual chlorine gas was removed with sufficient nitrogen, the obtained chlorinated polyvinyl chloride slurry was dehydrated, and then a slurry was prepared with deionized water. After neutralization with a neutralizing agent (sodium carbonate), dehydration and drying were carried out to prepare powdered chlorinated polyvinyl chloride.

[0044] Comparative Example 2

[0045] Chlorinated polyvinyl chloride was prepared in the same manner as in Comparative Example 1, except that UV LED lamps (5 W * 80, main wavelength: 365 nm) were operated after adding chlorine gas.

[0046] Comparative Example 3

[0047] Chlorinated polyvinyl chloride was prepared in the same manner as in Comparative Example 1, except that UV LED lamps (1 W * 80, main wavelength: 365 nm) were operated after adding chlorine gas.

[0048] Comparative Example 4

[0049] Chlorinated polyvinyl chloride was prepared in the same manner as in Comparative Example 1, except that UV LED lamps (1 W * 80, main wavelength: 385 nm) were operated after adding chlorine gas.

[0050] Comparative Example 5

[0051] Chlorinated polyvinyl chloride was prepared in the same manner as in Comparative Example 1, except that UV LED lamps (1 W * 80, main wavelength: 405 nm) were operated after adding chlorine gas.

[0052] Example 1

[0053] Chlorinated polyvinyl chloride was prepared in the same manner as in Comparative Example 1, except that after adding chlorine gas, a UV LED lamp (1W * 80, main wavelength: 365 nm) was operated. After the addition of chlorine gas was completed, a UV LED lamp (1W * 80, main wavelength: 405 nm) was operated and maintained until the reaction was completed.

[0054] Example 2

[0055] Chlorinated polyvinyl chloride was prepared in the same manner as in Comparative Example 1, except that after adding chlorine gas, a UV LED lamp (1W * 80, main wavelength: 365 nm) was operated. After the addition of chlorine gas was completed, a UV LED lamp (1W * 80, main wavelength: 405 nm) was operated and maintained until the reaction was completed.

[0056] Example 3

[0057] Chlorinated polyvinyl chloride was prepared in the same manner as in Comparative Example 1, except that after adding chlorine gas, a UV LED lamp (1W * 80, main wavelength: 385 nm) was operated. After the addition of chlorine gas was completed, a UV LED lamp (1W * 80, main wavelength: 405 nm) was operated and maintained until the reaction was completed.

[0058] [Experimental Example]

[0059] The physical properties of the above-prepared chlorinated polyvinyl chloride were evaluated by the following method, and the results are shown in Table 1 below.

[0060] (1) Processing coloration: The whiteness index (WI) and yellowness index (YI) were measured using a color difference meter.

[0061] (2) Thermal stability: Using a Mathis Oven, the oven temperature was set to 195 °C, and the sample was extruded at a speed of 23 mm / 10 min, and the time point when the color changed to black was measured.

[0062] (3) Vicat softening temperature: Measured according to KS M ISO 306:2015 under the conditions of a heating rate of 50 °C and a load of 50 N.

[0063] (4) Chlorine content: The CHNS element content was determined using an elemental analyzer.

[0064] [Table 1]

[0065]

[0066] Observing the results in Table 1, it can be confirmed that when using a 365 nm single-wavelength UV LED lamp with high energy (Comparative Example 2), it is advantageous that the reaction efficiency is improved due to high luminous efficiency (a characteristic of LEDs), but the problem is that the physical properties of the prepared chlorinated polyvinyl chloride deteriorate. On the contrary, when using a 405 nm single-wavelength UV LED lamp with relatively low energy (Comparative Example 5), the physical properties of the prepared chlorinated polyvinyl chloride are improved, but the problems are a decrease in reaction efficiency and an extension of the reaction time.

[0067] On the other hand, in the case of one embodiment of the present disclosure, in order to minimize the decrease in reaction efficiency and improve the physical properties of the prepared chlorinated polyvinyl chloride, ultraviolet rays of different wavelengths are irradiated from the addition of chlorine until the addition of chlorine is completed and after the addition of chlorine is completed until the reaction is completed. It was confirmed that during the addition of chlorine, the reaction efficiency was improved by using a short-wavelength UV LED lamp with relatively high energy, and the deterioration of physical properties was prevented by using a UV LED lamp with relatively low energy after the addition of chlorine until the reaction was completed.

Claims

1. A method for preparing chlorinated polyvinyl chloride, the method comprising the following steps: 1) Adding a reactant containing polyvinyl chloride and chlorine into a reactor, while irradiating ultraviolet light of a first wavelength; And 2) Stirring the reactant while irradiating ultraviolet light of a second wavelength, wherein, the ultraviolet irradiation in steps 1 and 2 uses ultraviolet LEDs arranged in the reactor as the light source, and wherein, the first wavelength is 300 nm to 400 nm, wherein, the second wavelength is 350 nm to 450 nm, and wherein, the value obtained by subtracting the first wavelength from the second wavelength is 10 nm or more and 50 nm or less.

2. The method for preparing chlorinated polyvinyl chloride according to claim 1, wherein: The first wavelength is 350 nm to 390 nm.

3. The method for preparing chlorinated polyvinyl chloride according to claim 1, wherein: The second wavelength is 380 nm to 410 nm.

4. The method for preparing chlorinated polyvinyl chloride according to claim 1, wherein: The value obtained by subtracting the first wavelength from the second wavelength is 20 nm or more and 40 nm or less.

5. The method for preparing chlorinated polyvinyl chloride according to claim 1, wherein: The light output of the light source is 20 W to 160 W.

6. The method for preparing chlorinated polyvinyl chloride according to claim 1, wherein: The light output of the light source is 40 W to 100 W.

7. The method for preparing chlorinated polyvinyl chloride according to claim 1, wherein: A plurality of the ultraviolet LEDs are arranged in the reactor.

8. The method for preparing chlorinated polyvinyl chloride according to claim 1, wherein: Step 2 is carried out until the chlorine content of the prepared chlorinated polyvinyl chloride is 62 to 69%.

9. The method for preparing chlorinated polyvinyl chloride according to claim 1, further comprising dehydrating and / or drying the prepared chlorinated polyvinyl chloride.

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