CN110903415A

CN110903415A - Purification method of PVA (polyvinyl alcohol) raw material for optical film

Info

Publication number: CN110903415A
Application number: CN201911047682.0A
Authority: CN
Inventors: 李永江; 何志群; 吕惠霞; 胡腊梅; 吴刚
Original assignee: Chongqing Vico Technology Co Ltd; China Petroleum and Chemical Corp; Sinopec Chongqing Chuanwei Chemical Co Ltd
Current assignee: Chongqing Vico Technology Co Ltd; China Petroleum and Chemical Corp; Sinopec Chongqing Chuanwei Chemical Co Ltd
Priority date: 2019-10-30
Filing date: 2019-10-30
Publication date: 2020-03-24
Anticipated expiration: 2039-10-30
Also published as: CN110903415B

Abstract

The invention relates to the technical field of polyvinyl alcohol purification, and particularly discloses a method for purifying a PVA (polyvinyl alcohol) raw material for an optical film, which comprises the following steps: step (1): pretreatment of PVA raw material: putting the PVA raw material into a pretreatment container, heating and stirring; step (2): washing of PVA raw material: stirring and washing the pretreated PVA raw material; and (3): discharging: discharging the washed PVA raw material from the washing device, and feeding the PVA raw material into a material bin for later use after dehydration. The invention solves the problems of large PVA loss and high content of volatile impurities in the finished product in the existing PVA purification method.

Description

Purification method of PVA (polyvinyl alcohol) raw material for optical film

Technical Field

The invention relates to the technical field of polyvinyl alcohol purification, in particular to a method for purifying a PVA (polyvinyl alcohol) raw material for an optical film.

Background

Polyvinyl alcohol (PVA) is a colorless, nontoxic, noncorrosive, biodegradable water-soluble organic high polymer, an optical film made of the PVA as a raw material is a core functional material for manufacturing the polarizer, the PVA optical film is dyed with iodine or dichroic dyes of dichroic pigments or dichroic dyes, oriented and coated with upper and lower films to manufacture the polarizer which has a polarization effect on light, and the polarizer is a basic constituent element of a Liquid Crystal Display (LCD).

The PVA for optical films is required to have a high material demand, and it is required that the PVA has a polymerization degree of 1700 or more, a saponification degree of 98 mol% or more, and a volatile impurity content as low as possible. However, due to the limitations of the processing technology, the content of sodium acetate in such PVA raw materials in the market is generally higher, about 7000ppm, and the content of organic volatile components is also higher, and 2-3% by mass of methanol cannot meet the quality requirements of PVA raw materials for optical films, so that the PVA raw materials are usually required to be purified.

At present, in order to reduce the content of sodium acetate, the commonly adopted purification method is a water-soluble alcohol method: the PVA is fully dissolved in water, the sodium acetate in the PVA is also dissolved in the water, the solution is poured into a proper amount of ethanol solution to be separated out, and the PVA with less sodium acetate content is obtained by stirring, filtering, drying and crushing. However, by adopting the method, not only the PVA loss is large, but also the ethanol (methanol) consumption is large, so that the processing cost is increased, the ethanol (methanol) is difficult to remove in the later period, the content of volatile impurities in the finished product is increased, and the product quality cannot be ensured.

Disclosure of Invention

The invention aims to provide a method for purifying a PVA raw material for an optical film, which aims to solve the problems of high PVA loss and high content of volatile impurities in a finished product due to difficult removal of ethyl (methyl) alcohol in the existing PVA purification method.

In order to achieve the purpose, the technical scheme of the invention is as follows: a method for purifying PVA raw material for optical film comprises the following steps:

step (1): pretreatment of PVA raw material: putting the PVA raw material into a pretreatment container, heating and stirring;

step (2): washing of PVA raw material: stirring and washing the pretreated PVA raw material;

and (3): discharging: discharging the washed PVA raw material from the washing device, and feeding the PVA raw material into a material bin for later use after dehydration.

The principle and the beneficial effects of the technical scheme are as follows: among this technical scheme, before carrying out purification washing to the PVA raw materials, the pretreatment process to the PVA raw materials has been increased, usually in order to detach volatile impurity such as ethyl (methyl) alcohol in the finished product, mostly adopt after the raw materials preparation, refined in-process in later stage is got rid of again, the effect that later stage was got rid of is the decisive factor that influences finished product quality, and this technical scheme is through arranging the PVA raw materials in the pretreatment container in, the PVA raw materials in the stirred vessel when heating up the container, with the volatile component in the detached raw materials, then get rid of volatile material such as methyl alcohol in advance at the preparation front end, just guaranteed the quality of product at the front end, in time get rid of the effect not good, also have the room of remedy, can guarantee the quality of product to the greatest extent. Wherein, the intensification process can increase the temperature in the container to accelerate the volatile speed of volatile component in the raw materials, can improve the discharge rate of volatile component after volatilizing in the PVA raw materials through the stirring simultaneously, reach the purpose that volatile impurity was got rid of to raw materials washing front end. In addition, in the process of purifying the PVA raw material, the sodium acetate can be washed into water by adopting a stirring and water washing mode, the aim of reducing the content of the sodium acetate in the PVA raw material is fulfilled, meanwhile, the PVA raw material can be ensured to be only swelled and insoluble, and the problem of large PVA raw material loss in the traditional treatment method is avoided. And the process of pouring methanol solution to separate out sodium acetate is not involved in the process, additional volatile impurities are not introduced, and the problem that the volatile components in the finished product exceed the standard is avoided.

Further, in the step (1), the temperature raising operation is to introduce heated gas into the bottom of the pretreatment container.

The heating treatment of the pretreatment container is realized by introducing heated gas, so that the temperature of the pretreatment container and the PVA raw material can be increased to accelerate the volatilization of volatile components; on the other hand, the heated gas has low density and floating property, and after the hot gas is introduced to the bottom of the container, the floating liquidity of the hot gas can drive volatile components which can be emitted to float upwards along with the hot gas, and the volatile components are discharged out of the pretreatment container.

Further, in the step (1), the heating temperature of the gas is 38-42 ℃.

In the technical scheme, the heating temperature of the gas is set to be 38-42 ℃, so that the heat damage to the PVA raw material due to overhigh temperature can be avoided while the volatilization of volatile components is accelerated.

Further, in the step (2), the temperature of the washing water is 38-42 ℃.

In the technical scheme, in the washing process, the temperature of the washing water is set to 38-42 ℃, so that the dissolution of sodium acetate is accelerated, and the PVA raw material can be ensured to be only swelled and undissolved, so that the loss of the PVA raw material is reduced.

Further, in the step (2), the stirring and water washing time is 50-70 min.

In the technical scheme, the washing time is too short, PVA is not fully swelled, and the washing effect is not good; and the washing effect is not greatly influenced by the time for increasing the washing time from the washing to the later stage, but the washing efficiency is reduced, and the stirring and washing time is determined to be 50-70 min by comprehensive consideration.

Furthermore, in the step (2), the number of times of stirring and water washing is more than or equal to 2.

The washing of a single time, micromolecular substance and other impurities in the polyvinyl alcohol can not be thoroughly removed, and the washing effect can be increased through washing for many times.

Further, in the step (2), the mass ratio of PVA to water in the stirring and washing process is 1: 5-40.

In the technical scheme, the material-liquid ratio of the raw materials to water in the stirring and water washing process is determined to be 1: 5-40, if too little water is added, the washing effect is poor, and if too much water is added, the washing cost is increased.

Furthermore, the grain diameter of the PVA raw material is 0.3mm-7.0mm, and the purity of the PVA raw material is more than 95 percent.

The particle size and purity of the PVA raw material are limited, and the quality of the purified PVA raw material can be ensured from the source, so that the PVA raw material can be used for preparing optical films.

Further, in the step (3), the dehydrated PVA raw material is fed into the silo under the inert gas atmosphere.

In the process of conveying the dehydrated polyvinyl alcohol to the storage bin, the inert gas plays a role in protection and isolation, so that the polyvinyl alcohol material can be prevented from contacting oxygen and other impurities, and the cleanness and no pollution of the polyvinyl alcohol material during pipeline transportation are ensured.

Further, the inert gas is nitrogen.

Two nitrogen atoms in the nitrogen form a nitrogen-nitrogen triple bond with very large bond energy, so the nitrogen has very stable chemical properties and is not easy to react with other substances; in addition, the nitrogen is widely distributed in the atmosphere, is nontoxic and harmless, and cannot directly cause damage to human bodies.

Detailed Description

Examples 1 to 11 are examples of the present invention, comparative examples 1 to 5 are comparative examples of the present invention, in which the gas temperature is represented by the heating temperature of the gas introduced during the pretreatment, the washing liquid ratio is represented by the mass ratio of the PVA raw material to the washing water during the agitation washing, the nitrogen atmosphere is whether or not the dehydration of the polyvinyl alcohol is carried out under the nitrogen atmosphere in the course of feeding the polyvinyl alcohol into the silo, "√ denotes that the dehydration is carried out under the nitrogen atmosphere," × "denotes that the dehydration is not carried out under the nitrogen atmosphere, and the addition amounts of the respective raw materials and the operation conditions in each of the examples and comparative examples are shown in table 1.

The method for purifying a PVA raw material for an optical film of the present invention is described in detail by taking example 1 as an example, and comprises the following steps:

step (1): pretreatment of PVA raw material: putting a PVA raw material with the particle size of 1mm and the purity of 96% into a pretreatment container, wherein the pretreatment container is a wide-mouth bottle, introducing gas with the temperature of 40 ℃ to the bottom of the wide-mouth bottle, and stirring the PVA raw material;

step (2): washing of PVA raw material: stirring and washing the pretreated PVA raw material for 2 times, wherein the material-liquid ratio during stirring and washing is 1:5, the temperature of washing water (deionized water) is 38 ℃, and the stirring and washing time is 50 min;

and (3): discharging: discharging the washed PVA raw material from the washing device, conveying the PVA raw material into a material bin for later use after dehydration, and conveying the dehydrated PVA raw material into the material bin under the nitrogen atmosphere.

The polyvinyl alcohol was washed in accordance with the above examples and comparative examples, and the content of sodium acetate, the content of volatile matter (methanol), and the loss rate of the washed PVA in the PVA raw material after washing were measured, and the results are shown in table 2.

TABLE 2

As can be seen from Table 2, the PVA prepared in the examples 1 to 11 of the present invention has a sodium acetate content of 1000ppm or less, a PVA loss of 3.2% or less, a methanol content of 0.39% or less, a significant reduction in impurities compared with the non-purified PVA, and a very low loss rate. In comparative examples 1 to 5, the PVA methanol content obtained without or without the pretreatment process is obviously higher; comparative examples 4 and 5, which were washed only once, showed a decrease in the amount of PVA lost, but the sodium acetate content was close to 2000 ppm. In the technical scheme, the content of the sodium acetate is obviously related to the washing times and the washing material-liquid ratio, and certain relevance exists within the set washing temperature and washing time range. The washing times are increased, the ratio of the washing materials to the washing liquid is reduced, the washing temperature is increased, the washing time is prolonged, the washing of sodium acetate and the washing of methanol are facilitated, but the loss rate of PVA is increased. All factors are comprehensively considered, a PVA pretreatment process is adopted, and the content of sodium acetate and methanol in the PVA raw material can be effectively reduced by properly controlling the washing times, the washing material-liquid ratio, the washing temperature and the washing time in the washing process.

The foregoing is merely an example of the present invention and common general knowledge in the art of designing and/or characterizing particular aspects and/or features is not described in any greater detail herein. It should be noted that, for those skilled in the art, without departing from the technical solution of the present invention, several variations and modifications can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicability of the patent. The scope of the claims of the present application shall be determined by the contents of the claims, and the description of the embodiments and the like in the specification shall be used to explain the contents of the claims.

Claims

1. A method for purifying a PVA raw material for an optical film is characterized by comprising the following steps:

2. The method of claim 1, wherein the step of purifying the PVA starting material for the optical film comprises: in the step (1), the temperature raising operation is to introduce heated gas into the bottom of the pretreatment container.

3. The method of claim 2, wherein the step of purifying the PVA starting material for the optical film comprises: in the step (1), the heating temperature of the gas is 38-42 ℃.

4. The method of claim 3, wherein the PVA starting material for optical films comprises: in the step (2), the temperature of the washing water is 38-42 ℃.

5. The method of claim 4, wherein the PVA starting material for optical films comprises: in the step (2), the stirring and water washing time is 50-70 min.

6. The method of claim 5, wherein the PVA starting material for optical films comprises: in the step (2), the number of times of stirring and water washing is more than or equal to 2.

7. The method of claim 6, wherein the PVA starting material for optical films comprises: in the step (2), the mass ratio of PVA to water in the stirring and washing process is 1: 5-40.

8. The method of claim 7, wherein the PVA starting material for optical films comprises: the grain diameter of the PVA raw material is 0.3mm-7.0mm, and the purity of the PVA raw material is more than 95%.

9. The method of claim 8, wherein the step of purifying the PVA starting material for optical films comprises: in the step (3), the dehydrated PVA raw material is fed into a storage bin under the inert gas atmosphere.

10. The method of claim 9, wherein the step of purifying the PVA starting material for optical films comprises: the inert gas is nitrogen.