Water-containing polyvinyl alcohol resin particle, preparation method thereof, polyvinyl alcohol optical film and application thereof

Abstract

The invention relates to the field of polyvinyl alcohol materials, and discloses a water-containing polyvinyl alcohol resin particle, a preparation method thereof, a polyvinyl alcohol optical film and application thereof. The water-containing polyvinyl alcohol resin particles comprise polyvinyl alcohol and water; the surface water content of the water-containing polyvinyl alcohol resin particles is 1.3 wt%-2.2 wt%. The surface water content of the water-containing polyvinyl alcohol resin particles ensures that the finally prepared polyvinyl alcohol optical film has good haze and few defects.

Description

Technical Field

[0001] The present invention relates to the field of polyvinyl alcohol materials, and particularly relates to a water-containing polyvinyl alcohol resin particle, a preparation method thereof, a polyvinyl alcohol optical film and an application thereof. Background Art

[0002] Polyvinyl alcohol (PVA) is a water-soluble polymer with excellent film-forming properties. The PVA film has high transparency and good gloss, and has good affinity with iodine, dyes, etc. After being stretched, the PVA film dyed with iodine or dye is highly oriented, and the iodine ions attached to the PVA also have a directionality, and the formed iodine ion oriented long chain can absorb light in a specific direction, making the film have a polarizing function. However, sodium acetate impurities are inevitably contained in the production process of polyvinyl alcohol resin, usually less than 1.5%. These impurities will seriously affect the stability of PVA film preparation and the optical properties of the PVA film, and will also cause the PVA film to turn yellow. The sodium acetate impurity in the PVA resin for optical film is usually required to be below 500 ppm, and more preferably below 300 ppm. Usually, most of the sodium acetate in PVA is removed by washing with water.

[0003] However, in actual production, the PVA optical film prepared from the water-containing PVA particles obtained after washing with water has problems such as poor haze and many film surface defects. Summary of the Invention

[0004] The object of the present invention is to overcome the problems of poor haze and defects in the polyvinyl alcohol optical film prepared from the existing water-containing polyvinyl alcohol resin particles, and to provide a water-containing polyvinyl alcohol resin particle, a preparation method thereof, a polyvinyl alcohol optical film and an application thereof; finally, the obtained polyvinyl alcohol optical film has good haze and few defects.

[0005] To achieve the above object, in the first aspect of the present invention, a water-containing polyvinyl alcohol resin particle is provided, wherein the water-containing polyvinyl alcohol resin particle comprises polyvinyl alcohol and water;

[0006] Among them, the surface water content of the water-containing polyvinyl alcohol resin particle is 1.3 wt% - 2.2 wt%.

[0007] In the second aspect of the present invention, a preparation method of a water-containing polyvinyl alcohol resin particle is provided, wherein the preparation method comprises the following steps:

[0008] (1) Washing and purifying the polyvinyl alcohol resin particles;

[0009] (2) Centrifugally dehydrating the washed and purified polyvinyl alcohol resin particles;

[0010] (3) Blowing the dehydrated polyvinyl alcohol resin to obtain the water-containing polyvinyl alcohol resin particle.

[0011] The third aspect of the present invention provides an aqueous polyvinyl alcohol resin particle prepared by the aforementioned preparation method.

[0012] The fourth aspect of the present invention provides a polyvinyl alcohol optical film, which is obtained by casting a solution of the aforementioned aqueous polyvinyl alcohol resin particles.

[0013] The fifth aspect of the present invention provides an application of the aforementioned polyvinyl alcohol optical film in the field of polarization.

[0014] By the above technical solutions, the present invention has obtained the following beneficial effects:

[0015] (1) The surface water content of the aqueous polyvinyl alcohol resin particles ensures that the aqueous polyvinyl alcohol resin particles with the same average water content have excellent solubility and fluidity during processing.

[0016] (2) In the preparation method of the aqueous polyvinyl alcohol resin particles, specific water washing conditions can affect the initial average water content of the polyvinyl alcohol resin particles, then centrifugal dehydration is used to adjust its average water content, and then blowing is used to adjust its surface water content. All of the above ensure that the prepared aqueous polyvinyl alcohol resin particles have good solubility, are not prone to agglomeration during processing, and have good fluidity.

[0017] (3) The polyvinyl alcohol optical film is prepared by casting a solution containing aqueous polyvinyl alcohol resin particles. The specific aqueous polyvinyl alcohol resin particles may not be easily agglomerated to form gels, and the prepared polyvinyl alcohol optical film has good haze and few defects. Detailed Embodiments

[0018] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0019] The first aspect of the present invention provides an aqueous polyvinyl alcohol resin particle, wherein the aqueous polyvinyl alcohol resin particle contains polyvinyl alcohol and water;

[0020] Among them, the surface water content of the aqueous polyvinyl alcohol resin particle is 1.3 wt% - 2.2 wt%.

[0021] The surface water content in the present invention is the mass concentration of the water on the surface of the aqueous polyvinyl alcohol resin particle in the total mass of the aqueous polyvinyl alcohol resin particle.

[0022] In the present invention, the inventors unexpectedly found that the surface water content of the water-containing polyvinyl alcohol resin particles can ensure that the finally prepared polyvinyl alcohol optical film has good haze and few defects. It is speculated that the reason may be that the water-containing polyvinyl alcohol resin particles have excellent solubility and fluidity during processing and are not prone to agglomeration.

[0023] When the surface water content is less than this range, the water-containing polyvinyl alcohol resin particles are prone to skin formation, resulting in poor resin dissolution when preparing the solution, and the finally prepared polyvinyl alcohol optical film is uneven and prone to defects. When the surface water content is greater than this range, the water-containing polyvinyl alcohol resin particles are prone to agglomeration and block the pipeline during transportation, resulting in poor feeding and affecting the stability of production. At the same time, the agglomerated polyvinyl alcohol resin particles are not easily soluble in water and are prone to form micelles or gels in the polyvinyl alcohol resin solution, and the finally prepared polyvinyl alcohol optical film has poor haze and defects.

[0024] Furthermore, the surface water content of the water-containing polyvinyl alcohol resin particles is 1.5 wt% - 2 wt%.

[0025] According to the present invention, the average water content of the water-containing polyvinyl alcohol resin particles is 20 wt% - 50 wt%.

[0026] In the present invention, when the water-containing polyvinyl alcohol resin particles meet the above average water content range, it can make the water-containing polyvinyl alcohol resin particles more likely to have an appropriate surface water content. During processing, it may further improve the solubility and fluidity of the water-containing polyvinyl alcohol resin particles, and finally prepare a polyvinyl alcohol optical film with good haze and few defects.

[0027] Furthermore, the average water content of the water-containing polyvinyl alcohol resin particles is 30 wt% - 45 wt%.

[0028] According to the present invention, the degree of polymerization of the polyvinyl alcohol is 2000 - 4000.

[0029] According to the present invention, the degree of alcoholysis of the polyvinyl alcohol is 97 mol% - 100 mol%.

[0030] In the present invention, when the degree of polymerization and the degree of alcoholysis of the polyvinyl alcohol meet the above ranges, the solubility and fluidity of the water-containing polyvinyl alcohol resin particles are further improved.

[0031] Furthermore, the degree of polymerization of the polyvinyl alcohol is 2200 - 3500.

[0032] Furthermore, the degree of alcoholysis of the polyvinyl alcohol is 99 mol% - 99.9 mol%.

[0033] According to the present invention, the swelling degree of the polyvinyl alcohol is 120 wt% - 200 wt%, preferably 125 wt% - 150 wt%.

[0034] A second aspect of the present invention provides a method for preparing aqueous polyvinyl alcohol resin particles, wherein the preparation method comprises the following steps:

[0035] (1) washing and purifying polyvinyl alcohol;

[0036] (2) centrifugally dehydrating the polyvinyl alcohol after washing and purification;

[0037] (3) Purging the dehydrated polyvinyl alcohol to obtain the water-containing polyvinyl alcohol resin particles.

[0038] In the present invention, specific water washing conditions can affect the initial average moisture content of the polyvinyl alcohol resin particles. The average moisture content of the hydrous polyvinyl alcohol resin particles is controlled by centrifugal dehydration, and a large amount of water is driven to the surface of the particles. Then, the surface water content is controlled within a suitable range by blowing. As a result, the polyvinyl alcohol optical film prepared using the hydrous polyvinyl alcohol resin particles has good haze and few defects. The possible reason is that the hydrous polyvinyl alcohol resin particles have good solubility and good fluidity during processing.

[0039] In the present invention, the purging location is a common location in the art, including a pipeline, an intermediate storage tank, an intermediate silo, etc., preferably an intermediate silo.

[0040] The definition of polyvinyl alcohol in the present invention is the same as above and will not be repeated here.

[0041] According to the present invention, during water washing and purification, the weight ratio of the water to the polyvinyl alcohol is 5-200:1.

[0042] In the present invention, when the weight ratio of water to polyvinyl alcohol satisfies the above range, an excellent water washing effect can be obtained and the initial average water content of the water-containing polyvinyl alcohol resin particles can be controlled.

[0043] Furthermore, during water washing and purification, the weight ratio of the water: the polyvinyl alcohol is 10-50:1.

[0044] According to the present invention, the water washing conditions include: the water washing temperature is 10-40°C; the water washing time is 40-300min.

[0045] In the present invention, when the water washing temperature and time meet the above ranges, the water washing can be more sufficient, and the obtained water-containing polyvinyl alcohol resin particles have a specific initial average moisture content.

[0046] Furthermore, the water washing conditions include: the water washing temperature is 15-35°C; and the water washing time is 60-150min.

[0047] According to the present invention, the centrifugation method is continuous conveyor centrifugation, and the conditions include: the centrifugation speed is 1000 - 3500 rpm.

[0048] In the present invention, when the above centrifugation range is satisfied, water-containing polyvinyl alcohol resin particles with appropriate average water content can be obtained, which may enable the water-containing polyvinyl alcohol resin particles to have excellent solubility and fluidity during processing, not easily agglomerate, and finally the prepared polyvinyl alcohol optical film has good haze and few defects.

[0049] During centrifugation, if the centrifugation speed is too low, the separation effect will be poor, and the average water content of the prepared water-containing polyvinyl alcohol resin particles is high and easy to agglomerate; if the centrifugation speed is too high, it is easy to cause large equipment vibration and poor operation safety.

[0050] Furthermore, the centrifugation conditions include: the centrifugation speed is 1500 - 3000 rpm.

[0051] After centrifugation, take polyvinyl alcohol to measure its water content. When the average water content satisfies 20wt% - 50wt%, the centrifugation is completed.

[0052] Specific test method: Take 1 g of water-containing polyvinyl alcohol resin particles, and record the mass as m 1 , and treat it with an infrared rapid moisture meter at 180 °C for 15 min to measure the mass m 2 , and the average water content of the water-containing polyvinyl alcohol resin particles is: (m 1 - m 2 ) / m 1 ×100%.

[0053] According to the present invention, the purging gas is selected from at least one of protective gas, compressed air, and instrument air, preferably selected from at least one of nitrogen, compressed air, and instrument air.

[0054] According to the present invention, the purging conditions include: the purging temperature is 15 - 60 °C; the purging time is 5 - 48 h.

[0055] In the present invention, when the above purging range is satisfied, water-containing polyvinyl alcohol resin particles with appropriate surface water content can be obtained, further enabling the finally prepared polyvinyl alcohol optical film to have good haze and few defects. The possible reason is that during processing, the solubility and fluidity of the water-containing polyvinyl alcohol resin particles are improved.

[0056] Furthermore, the purging conditions include: the purging temperature is 20 - 40 °C; the purging time is 5 - 24 h.

[0057] According to the present invention, the gas flow rate is 20 - 300 m 3 / h.

[0058] In the present invention, when the above flow rate range is satisfied, it is possible to further make the obtained water-containing polyvinyl alcohol resin particles have a suitable surface water content.

[0059] Furthermore, the flow rate of the gas is 30 - 150 m 3 / h.

[0060] The third aspect of the present invention provides water-containing polyvinyl alcohol resin particles prepared by the aforementioned preparation method.

[0061] The fourth aspect of the present invention provides a polyvinyl alcohol optical film, wherein the polyvinyl alcohol optical film is obtained by casting from a solution of the aforementioned water-containing polyvinyl alcohol resin particles.

[0062] According to the present invention, the haze of the polyvinyl alcohol optical film is ≤ 1.5%, preferably ≤ 1%.

[0063] In the present invention, the casting method is a common casting method in the art. A particularly preferred embodiment is: water, a surfactant, a processing aid, and water-containing polyvinyl alcohol resin particles are formulated into a polyvinyl alcohol solution with a certain concentration in a dissolving device, and then cast into a film.

[0064] There is no particular limitation on the dissolving device for polyvinyl alcohol. The reaction kettle can be controlled to carry out dissolution at a pressure of more than 0.1 MPa and a temperature of 120 - 150 °C, or the water-containing polyvinyl alcohol resin particles can be continuously fed into a twin-screw extruder for dissolution, and the temperature of the twin-screw extruder is controlled to be 60 - 180 °C, and the rotation speed is 50 - 300 r / min.

[0065] According to the present invention, the solution of the water-containing polyvinyl alcohol resin particles contains water, a surfactant, a processing aid, and water-containing polyvinyl alcohol resin particles.

[0066] In the present invention, after the water-containing polyvinyl alcohol resin particles are configured into a solution, the water in the water-containing polyvinyl alcohol resin particles is fused with the water added later, and they are not distinguished and are collectively referred to as water. In the solution of the water-containing polyvinyl alcohol resin particles, "water" and "water-containing polyvinyl alcohol resin particles" will exist in the form of "water" and "polyvinyl alcohol".

[0067] In the present invention, when the surface water content in the water-containing polyvinyl alcohol resin particles is different, the dissolution behaviors are different. Even when preparing solutions of water-containing polyvinyl alcohol resin particles with the same content of polyvinyl alcohol, the performances during the film-forming process of polyvinyl alcohol are also different. Therefore, the contents of the components in the solution of the water-containing polyvinyl alcohol resin particles are not limited and are conventional contents in the art. In a particularly preferred embodiment, based on the solution of the water-containing polyvinyl alcohol resin particles, the water content is 66.33 wt%, the content of the surfactant is 0.07 wt%, the content of the processing aid is 3.6 wt%, and the content of polyvinyl alcohol is 30 wt%.

[0068] According to the present invention, the surfactant is a common surfactant in the art, and the surfactant is selected from nonionic surfactants and / or anionic surfactants, preferably nonionic surfactants and anionic surfactants.

[0069] In the present invention, the nonionic surfactant is selected from at least one of alkyl ether type surfactants, alkyl amine type surfactants, and alkyl amide type surfactants, and the anionic surfactant is selected from alkyl sulfates and / or alkyl sulfate esters.

[0070] According to the present invention, the processing aid is a common processing aid in the art, and the processing aid is selected from polyhydric alcohols, preferably selected from at least one of ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane.

[0071] The fifth aspect of the present invention provides an application of the aforementioned polyvinyl alcohol optical film in the field of polarization.

[0072] The present invention will be described in detail below through examples.

[0073] (1) Surface water content of water-containing polyvinyl alcohol resin particles

[0074] Take 5 g of water-containing polyvinyl alcohol resin particles, and record the mass as m 0 , spread it flat on a filter paper with a diameter of 12.5 cm, then cover it with another same filter paper (the mass of the two filter papers is pre-weighed as v 0 ), and then place it between two glass plates to make the filter paper fully contact with the water-containing polyvinyl alcohol resin particles. After standing for 5 minutes, separate the filter paper and the PVA particles, and weigh the mass of the two filter papers as v 1 , then the surface water content of the water-containing polyvinyl alcohol resin particles is: (v 1 - v 0 ) / m 0 × 100%.

[0075] (2) Average moisture content of water-containing polyvinyl alcohol resin particles

[0076] Take 1 g of water-containing polyvinyl alcohol resin particles, and record the mass as m 1 , and treat them with an infrared rapid moisture analyzer at 180 °C for 15 min to measure the mass m 2 . The average moisture content of the water-containing polyvinyl alcohol resin particles is: (m 1 - m 2 ) / m 1 ×100%.

[0077] (3) Pipeline transportation fluidity within 24 h

[0078] The number of blockages in the pipeline from the silo to the dissolution device during continuous operation within 24 h. The pipeline length is 10 m; the specific method is: the number of blockages in the pipeline. When the number of blockages is 0, it is recorded as "good"; when blockages occur occasionally, it is recorded as "the number of blockages ≤ 1 time"; when blockages occur frequently, it is recorded as "the number of blockages ≥ 3 times"; when there is no fluidity and it cannot be used, it is recorded as "the number of blockages ≥ 8 times".

[0079] (4) Haze of the polyvinyl alcohol optical film

[0080] Cut out 3 film pieces of 50 mm × 50 mm from the prepared polyvinyl alcohol optical film and measure them with a haze meter, and take the average value of the 3 samples.

[0081] (5) Defects of the polyvinyl alcohol optical film

[0082] Irradiate strong light behind the polyvinyl alcohol optical film, and visually observe the defects of the polyvinyl alcohol optical film through a polarizer. The specific method is: record the number of bright dots. When the number is 0, it is recorded as "none"; when the number is 1 per m 2 it is recorded as "few"; when the number is 2 - 5 per m 2 it is recorded as "many"; when the number > 5 per m 2 it is recorded as "very many".

[0083] The degree of polymerization of polyvinyl alcohol - 1 is 2500, the degree of alcoholysis is 99.5 mol%, and the swelling degree is 135 wt%;

[0084] The degree of polymerization of polyvinyl alcohol - 2 is 1700, the degree of alcoholysis is 96 mol%, and the swelling degree is 150 wt%;

[0085] The surfactants are lauric acid diethanolamide and sodium dodecyl sulfonate; the processing aid is glycerol;

[0086] All are commercially available.

[0087] Example 1

[0088] (1) At 20 °C, 1 kg of polyvinyl alcohol - 1 was washed with 20 kg of water for 80 min, and the weight ratio of the water to the polyvinyl alcohol - 1 was 20:1; it was continuously conveyed to a centrifuge and centrifuged at 2000 rpm, and after centrifugation, it was sent to an intermediate silo. At 25 °C, 50 m 3 / h of nitrogen was introduced for purging for 8 h to obtain water - containing polyvinyl alcohol resin particles A1;

[0089] (2) 1667 g of water - containing polyvinyl alcohol resin particles A1 were continuously conveyed to a reaction kettle through a pipeline. At the same time, 1544 g of water, 0.4 g of diethanolamide laurate, 2 g of sodium dodecyl sulfate, and 120 g of glycerol were added. It was dissolved and formulated into a solution at 0.4 Mpa and 130 °C, and a polyvinyl alcohol optical film N1 was obtained by casting.

[0090] Based on the total weight of the solution of water - containing polyvinyl alcohol resin particles, the water content was 66.33 wt%, the surfactant content was 0.07 wt%, the processing aid content was 3.6 wt%, and the polyvinyl alcohol content was 30 wt%.

[0091] Example 2

[0092] (1) At 20 °C, 1000 g of polyvinyl alcohol - 1 was washed with 20 kg of water for 100 min, and the weight ratio of the water to the polyvinyl alcohol - 1 was 20:1; it was continuously conveyed to a centrifuge and centrifuged at 2500 rpm, and after centrifugation, it was sent to an intermediate silo. At 20 °C, 100 m 3 / h of nitrogen was introduced for purging for 15 h to obtain water - containing polyvinyl alcohol resin particles A2;

[0093] (2) 1818 g of water - containing polyvinyl alcohol resin particles A2 were continuously conveyed to a twin - screw extruder through a pipeline. At the same time, 1392 g of water, 0.4 g of diethanolamide laurate, 2 g of sodium dodecyl sulfate, and 120 g of glycerol were added. The rotational speed of the twin - screw extruder was 250 r / min. At 180 °C, it was dissolved to prepare a solution, and a polyvinyl alcohol optical film N2 was obtained by casting.

[0094] Based on the total weight of the solution of water - containing polyvinyl alcohol resin particles, the water content was 66.33 wt%, the surfactant content was 0.07 wt%, the processing aid content was 3.6 wt%, and the polyvinyl alcohol content was 30 wt%.

[0095] Example 3

[0096] (1) At 30°C, 1000 g of polyvinyl alcohol-1 was washed with 20 kg of water for 120 min, and the weight ratio of the water to the polyvinyl alcohol-1 was 20:1; continuously conveyed to a centrifuge and centrifuged at 2500 rpm; after centrifugation, it was fed into an intermediate bin, and at 20°C, 100 m 3 / h of nitrogen was introduced and purged for 8 h to obtain water-containing polyvinyl alcohol resin particles A3;

[0097] (2) Step (2) was carried out in the same manner as in Example 2 to obtain a polyvinyl alcohol optical film N3.

[0098] Example 4

[0099] (1) Step (1) was carried out in the same manner as in Example 1, except that "polyvinyl alcohol-2" was used to replace "polyvinyl alcohol-1" to obtain water-containing polyvinyl alcohol resin particles A4;

[0100] (2) Step (2) was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol optical film N4.

[0101] Example 5

[0102] (1) Step (1) was carried out in the same manner as in Example 1, except that "centrifuged at 1200 rpm" was used to replace "centrifuged at 2000 rpm" to obtain water-containing polyvinyl alcohol resin particles A5;

[0103] (2) Step (2) was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol optical film N5.

[0104] Example 6

[0105] (1) Step (1) was carried out in the same manner as in Example 1, except that "centrifuged at 800 rpm" was used to replace "centrifuged at 2000 rpm" to obtain water-containing polyvinyl alcohol resin particles A6;

[0106] (2) Step (2) was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol optical film N6.

[0107] Example 7

[0108] (1) Step (1) was carried out in the same manner as in Example 1, except that "introducing 25 m 3 / h of nitrogen" was used to replace "introducing 50 m 3 / h of nitrogen" to obtain water-containing polyvinyl alcohol resin particles A7;

[0109] (2) Step (2) was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol optical film N7.

[0110] Example 8

[0111] (1) Step (1) is carried out in the same manner as in Example 1, except that "introducing nitrogen purge at 5 m 3 / h for 3 h" is used to replace "introducing nitrogen purge at 50 m 3 / h for 8 h", and water-containing polyvinyl alcohol resin particles A8 are obtained;

[0112] (2) Step (2) is carried out in the same manner as in Example 1, and polyvinyl alcohol optical film N8 is obtained.

[0113] Example 9

[0114] (1) Step (1) is carried out in the same manner as in Example 1, except that "at 50 °C, introducing nitrogen purge at 50 m 3 / h for 8 h" is used to replace "at 25 °C, introducing nitrogen purge at 50 m 3 / h for 8 h", and water-containing polyvinyl alcohol resin particles A9 are obtained;

[0115] (2) Step (2) is carried out in the same manner as in Example 1, and polyvinyl alcohol optical film N9 is obtained.

[0116] Example 10

[0117] (1) Step (1) is carried out in the same manner as in Example 1, except that "at 70 °C, introducing nitrogen purge at 50 m 3 / h for 8 h" is used to replace "at 25 °C, introducing nitrogen purge at 50 m 3 / h for 8 h", and water-containing polyvinyl alcohol resin particles A10 are obtained;

[0118] (2) Step (2) is carried out in the same manner as in Example 1, and polyvinyl alcohol optical film N10 is obtained.

[0119] Example 11

[0120] (1) Step (1) is carried out in the same manner as in Example 2, except that "at 18 °C, washing 1000 g of polyvinyl alcohol-1 with 20 kg of water for 30 min" is used to replace "at 20 °C, washing 1000 g of polyvinyl alcohol-1 with 20 kg of water for 100 min", and water-containing polyvinyl alcohol resin particles A11 are obtained;

[0121] (2) Step (2) is carried out in the same manner as in Example 1, and polyvinyl alcohol optical film N11 is obtained.

[0122] Example 12

[0123] (1) At 15°C, 1000 g of polyvinyl alcohol-2 was washed with 20 kg of water for 30 min, and the weight ratio of the water to the polyvinyl alcohol-2 was 20:1; it was continuously conveyed to a centrifuge and centrifuged at 1200 rpm, and after centrifugation, it was sent to an intermediate silo. At 70°C, 15 m 3 / h of nitrogen was introduced and purged for 2 h to obtain water-containing polyvinyl alcohol resin particles A12;

[0124] (2) Step (2) was carried out in the same manner as in Example 2 to obtain a polyvinyl alcohol optical film N12.

[0125] Comparative Example 1

[0126] (1) Step (1) was carried out in the same manner as in Example 1, except that instead of washing and purifying, the polyvinyl alcohol resin particles D1 were directly dissolved;

[0127] (2) Step (2) was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol optical film ND1.

[0128] Comparative Example 2

[0129] (1) Step (1) was carried out in the same manner as in Example 1, except that "filtration" was used to replace "continuously conveyed to a centrifuge and centrifuged at 2000 rpm, and after centrifugation, it was sent to an intermediate silo" to obtain water-containing polyvinyl alcohol resin particles D2;

[0130] (2) In step (2), after the water-containing polyvinyl alcohol resin particles D2 were sent to the silo, they agglomerated and could not be continuously conveyed to the dissolving device, and a polyvinyl alcohol optical film ND2 could not be obtained.

[0131] Comparative Example 3

[0132] (1) Step (1) was carried out in the same manner as in Example 1, except that no purging was carried out to obtain water-containing polyvinyl alcohol resin particles D3;

[0133] (2) Step (2) was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol optical film ND3.

[0134] The performance of the prepared water-containing polyvinyl alcohol resin particles was detected as shown in Table 1.

[0135] Table 1

[0136]

[0137]

[0138] "-" indicates that it could not be measured.

[0139] The performance of the prepared polyvinyl alcohol optical film was detected as shown in Table 2.

[0140] Table 2

[0141]

[0142] In Example 1, a reaction kettle was used to prepare the solution, and in Example 2, a twin-screw extruder was used to prepare the solution. The content of polyvinyl alcohol in the solution was 30 wt%.

[0143] From the comparison between Examples 1-12 and Comparative Examples 1-3, it can be seen that specific water washing conditions will affect the initial average water content rate of polyvinyl alcohol resin particles. Then, centrifugal dehydration adjusted its water content rate, and then purging adjusted its surface water content. The surface water content of the water-containing polyvinyl alcohol resin particles enables the water-containing polyvinyl alcohol resin particles to have excellent solubility and fluidity during processing, and the prepared polyvinyl alcohol optical film has good haze and few defects.

[0144] From the comparison between Example 1, Example 5 and Example 6, it can be seen that a specific centrifugal speed can obtain water-containing polyvinyl alcohol resin particles with a specific average water content rate. If the centrifugal rotation speed is too low, the separation effect will be poor, and the average water content rate of the prepared water-containing polyvinyl alcohol resin particles will be high, and they are prone to agglomeration.

[0145] From the comparison between Example 1, Example 7 and Example 8, it can be seen that a specific gas flow rate and purging time can enable the prepared water-containing polyvinyl alcohol resin particles to have a suitable surface water content, improving the solubility and fluidity of the water-containing polyvinyl alcohol resin particles during processing, and finally preparing a polyvinyl alcohol optical film with good haze and few defects.

[0146] From the comparison between Example 1 and Example 10, it can be seen that a specific purging temperature can obtain water-containing polyvinyl alcohol resin particles with a suitable surface water content. From the comparison between Example 1 and Example 11, it can be seen that specific water washing conditions will affect the initial average water content rate of polyvinyl alcohol resin particles.

[0147] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A kind of aqueous polyvinyl alcohol resin particles, It is characterized in that The aqueous polyvinyl alcohol resin particles contain polyvinyl alcohol and water; Wherein, the surface water content of the aqueous polyvinyl alcohol resin particles is 1.3wt%-2.2wt%.

2. The aqueous polyvinyl alcohol resin particles according to claim 1, in, The surface water content of the aqueous polyvinyl alcohol resin particles is 1.5wt%-2wt%; Preferably, the average water content of the aqueous polyvinyl alcohol resin particles is 20wt%-50wt%, preferably 30wt%-45wt%.

3. The aqueous polyvinyl alcohol resin particles according to claim 1 or 2, in, The degree of polymerization of the polyvinyl alcohol is 2000-4000, preferably 2200-3500; Preferably, the alcoholysis degree of the polyvinyl alcohol is 97 mol%-100 mol%, preferably 99 mol%-99.9 mol%; Preferably, the degree of swelling of the polyvinyl alcohol is 120wt%-200wt%, preferably 125wt%-150wt%.

4. A method for preparing aqueous polyvinyl alcohol resin particles, It is characterized in that The preparation method comprises the following steps: (1) washing and purifying polyvinyl alcohol; (2) centrifugally dehydrating the polyvinyl alcohol after washing and purification; (3) Purging the dehydrated polyvinyl alcohol to obtain the water-containing polyvinyl alcohol resin particles.

5. The preparation method according to claim 4, in, In step (1), the degree of polymerization of the polyvinyl alcohol is 2000-4000, preferably 2200-3500; Preferably, the alcoholysis degree of the polyvinyl alcohol is 97 mol%-100 mol%, preferably 99 mol%-99.9 mol%; Preferably, during water washing and purification, the weight ratio of the water to the polyvinyl alcohol is 5-200:1, preferably 10-50:1; Preferably, the water washing conditions include: the water washing temperature is 10-40°C, preferably 15-35°C; the water washing time is 40-300min, preferably 60-150min; Preferably, in step (2), the centrifugation method is continuous conveying centrifugation; Preferably, the centrifugal conditions include: the centrifugal rotation speed is 1000-3500 rpm, preferably 1500-3000 rpm.

6. The preparation method according to claim 4 or 5, in, The purging gas is selected from at least one of protective gas, compressed air and instrument air, preferably selected from at least one of nitrogen, compressed air and instrument air; Preferably, the purging conditions include: the purging temperature is 15-60°C, preferably 20-40°C; the purging time is 5-48h, preferably 5-24h; Preferably, the flow rate of the gas is 20 - 300 m 3 / h, preferably 30 - 150 m 3 / h.

7. Aqueous polyvinyl alcohol resin particles prepared by the preparation method according to any one of claims 4 to 6.

8. A polyvinyl alcohol optical film, It is characterized in that The polyvinyl alcohol optical film is obtained by casting a solution containing the aqueous polyvinyl alcohol resin particles according to any one of claims 1 to 3 and 7; Preferably, the haze of the polyvinyl alcohol optical film is ≤1.5%, preferably ≤1%.

9. The polyvinyl alcohol optical film according to claim 8, wherein, the solution of the water-containing polyvinyl alcohol resin particles comprises water, a surfactant, a processing aid and water-containing polyvinyl alcohol resin particles; Preferably, the surfactant is selected from nonionic surfactants and / or anionic surfactants, preferably a nonionic surfactant and anionic surfactant; Preferably, the processing aid is selected from polyhydric alcohols, preferably at least one selected from ethylene glycol, glycerol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and trimethylolpropane.

10. Application of the polyvinyl alcohol optical film according to claim 8 or 9 in the field of polarization.

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