Pretreatment method and system for PVA raw material special for optical film and application

Abstract

The invention relates to the technical field of optical film processing, in particular to a pretreatment method and system for a PVA raw material special for an optical film and application. Enabling water vapor to be in contact with the PVA raw material, so that the PVA raw material is in a bubbling state; wherein in the direction from the PVA raw material inlet to the PVA raw material outlet, the bubbling height of the PVA raw material is gradually reduced. According to the method, the PVA raw material is bubbled by using the water vapor, so that the PVA raw material can be rapidly and fully swelled, the subsequent melting is rapid and more uniform, almost no PVA colloidal particles appear, and the product quality of a formed film is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of optical film processing, and particularly relates to a pretreatment method, system and application of a special PVA raw material for optical films. Background Art

[0002] Currently, to prepare a PVA optical film, the melting of PVA must be completed first. For the special PVA for preparing PVA optical films, not only a high degree of polymerization is required, but also the degree of alcoholysis is close to 99.9%. This determines that the special PVA is difficult to melt. The traditional method uses a melting process of high-temperature boiling and high-speed stirring. The characteristic is that the temperature needs to be quickly raised to the melting temperature after feeding, but the boiling and stirring for melting PVA takes 3 - 4 hours or longer. Not only is the melting time too long, consuming a large amount of steam, but also the process is difficult to control. Some factories use the method of soaking and swelling with cold water or hot water before melting, but PVA rubber particles often still appear in the melt, directly affecting the product quality of the subsequent film formation. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problems existing in the prior art when preparing special PVA for optical films, such as long boiling time during raw material pretreatment, large consumption of steam, difficult process control, and still many PVA rubber particles remaining after melting. A pretreatment method, system and application of a special PVA raw material for optical films are provided. By bubbling the PVA raw material with steam, the PVA raw material can be quickly and fully swollen. During subsequent melting, it is fast and more uniform, and almost no PVA rubber particles appear, ensuring the product quality of the film formation.

[0004] To achieve the above purpose, the first aspect of the present invention provides a pretreatment method of a special PVA raw material for optical films, including the following steps: contacting steam with the PVA raw material to make the PVA raw material in a bubbling state;

[0005] Wherein, along the direction from the PVA raw material inlet to the outlet, the bubbling height of the PVA raw material decreases.

[0006] The second aspect of the present invention provides a pretreatment system of a special PVA raw material for optical films. The system includes: a PVA chamber (1), a steam chamber (2), and a perforated plate (3); wherein, the PVA chamber (1) is located above the steam chamber (2), and a perforated plate (3) is arranged between the PVA chamber (1) and the steam chamber (2);

[0007] Wherein, along the direction from the PVA raw material inlet to the outlet, the number of openings of the perforated plate decreases in sequence, and at the same time, the perforated plate inclines downward along the direction from the PVA raw material inlet to the outlet.

[0008] The third aspect of the present invention provides an application of the pretreatment method described in the first aspect or the system described in the second aspect of the present invention in the preparation of an optical PVA film.

[0009] Through the above technical solutions, the pretreatment method, system and application of the PVA raw material special for the optical film provided by the present invention obtain the following beneficial effects:

[0010] (1) By using water vapor to bubble the PVA raw material, the PVA raw material can be quickly and fully swollen, and during subsequent melting, it is fast and more uniform, with almost no PVA colloidal particles appearing, ensuring the product quality of the film formation.

[0011] (2) The method does not require the use of a large amount of liquid water for swelling. When the PVA after melting treatment is subsequently boiled, it only needs to be stirred for 0.5 - 1 hour to meet the usage requirements.

[0012] (3) In the method, along the direction from the PVA raw material inlet to the outlet, the number of openings of the porous plate decreases in sequence. At the same time, the porous plate inclines downward along the direction from the PVA raw material inlet to the outlet, ensuring that the bubbling height of the PVA raw material decreases, further enabling the PVA raw material to move quickly, avoiding accumulation, and ensuring sufficient swelling. Description of the Drawings

[0013] Figure 1 is a schematic diagram of the implementation process of the special PVA pretreatment method.

[0014] Description of the Reference Numerals

[0015] 1. PVA chamber; 2. Water vapor chamber; 3. Porous plate; 4. Discharge outlet; 5. Water vapor outlet; 6. Drainage outlet; 7. Water vapor inlet; 8. PVA feed inlet Detailed Embodiments

[0016] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and 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.

[0017] In the present invention, unless otherwise stated, the orientation terms such as "upper, lower, left, right" generally refer to "upper, lower, left, right" in the PVA chamber.

[0018] The first aspect of the present invention provides a pretreatment method for a PVA raw material special for an optical film, including the following steps: bringing water vapor into contact with the PVA raw material so that the PVA raw material is in a bubbling state;

[0019] Among them, along the direction from the PVA raw material inlet to the outlet, the bubbling height of the PVA raw material decreases.

[0020] In the present invention, the inventor has found through research that by using water vapor to bubble the PVA raw material, the PVA raw material can be rapidly and fully swollen, and subsequent melting is fast. It only needs to be stirred for 0.5 - 1 hour to meet the usage requirements, and almost no or only a very small amount of PVA rubber particles appear, ensuring the product quality of the film formation.

[0021] Further research has found that along the direction from the PVA raw material inlet to the outlet, controlling the decreasing of the bubbling height of the PVA raw material can enable the PVA raw material to rapidly move towards the outlet, avoid accumulation, and at the same time control the water content of the swollen PVA to be appropriate, which is beneficial to the subsequent process utilization.

[0022] According to the present invention, along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material ≥ 1% per centimeter.

[0023] In the present invention, along the direction from the PVA raw material inlet to the outlet, when the decreasing rate of the bubbling height of the PVA raw material meets the above range, it can ensure that the PVA raw material rapidly moves towards the outlet, avoid raw material accumulation, and further ensure more sufficient swelling.

[0024] Furthermore, along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is 2 - 3% per centimeter.

[0025] According to the present invention, the conditions of the contact include: the contact temperature is 110 - 135 °C.

[0026] According to the present invention, the contact time is 10 - 50 min.

[0027] According to the present invention, the contact pressure is 1.5 bar - 3 bar.

[0028] In the present invention, when the contact temperature and contact pressure meet the above range, it can enable the formation of condensed small droplets when water vapor contacts the PVA raw material, further infiltrate into the PVA raw material particles, and conduct sufficient swelling. Furthermore, when the contact time meets the above range, it can further ensure the sufficiency of swelling.

[0029] Furthermore, the conditions of the contact include: the contact temperature is 110 - 120 °C; the contact time is 20 - 40 min; the contact pressure is 1.5 bar - 2 bar.

[0030] According to the present invention, the water vapor contacting the PVA raw material forms condensed droplets to swell the PVA raw material, and the swollen PVA is obtained.

[0031] According to the present invention, the swollen PVA is 130-150% of the weight of the PVA raw material.

[0032] In the present invention, when the weight of the swollen PVA meets the above limitation, the water content of the swollen PVA can be detected by weight gain, and then it can be determined whether the swollen PVA is sufficiently swollen. In the present invention, if the weight of the swollen PVA meets the above limited range, it proves that the swelling is sufficient.

[0033] Further, the swollen PVA is 140-145% of the weight of the PVA raw material.

[0034] According to the present invention, the degree of polymerization of the PVA raw material is 2000-4000, and the degree of alcoholysis is DA, where 97 mol% ≤ DA < 100 mol%.

[0035] In the present invention, when the degree of polymerization and the degree of alcoholysis of the PVA raw material meet the above ranges, optical special films can be better prepared to ensure the quality of the optical films.

[0036] Further, the degree of polymerization of the PVA raw material is 3000-4000, and the degree of alcoholysis is 99 mol%-99.9 mol%.

[0037] According to the present invention, the particle size of the PVA raw material is 0.5-0.8 cm.

[0038] In the present invention, through the research of the inventor, it is found that when the particle size of the PVA raw material is less than 0.5 cm, it will cause the raw materials to accumulate and agglomerate, block the equipment, and affect the swelling effect. When the particle size of the PVA raw material is greater than 0.8 cm, the droplets condensed from water vapor cannot be completely wetted, resulting in insufficient swelling.

[0039] Further, the particle size of the PVA raw material is 0.6-0.8 cm

[0040] According to the present invention, the flow rate of the water vapor is 35-50 m 3 / h, and the feeding rate of the PVA raw material is 70-100 kg / h.

[0041] In the present invention, when the flow rate of the water vapor and the feeding rate of the PVA raw material meet the above ranges, they complement each other and can jointly promote the swelling of the PVA raw material, further ensuring the smooth progress of melting.

[0042] Further, the flow rate of the water vapor is 40-45 m 3 / h, and the feeding rate of the PVA raw material is 80-90 kg / h.

[0043] According to the present invention, the stacking thickness of the PVA raw material is 15-25 cm.

[0044] In the present invention, the stacked thickness of the PVA raw material meets the above requirements, which can avoid extrusion of the PVA raw material and at the same time ensure that the PVA raw material is in a bubbling state, avoiding insufficient bubbling caused by too high thickness or process uncontrollability caused by too low thickness.

[0045] Further, the stacked thickness of the PVA raw material is 15 - 20 cm.

[0046] In the present invention, after the PVA raw material is pretreated, the swollen PVA is obtained. The swollen PVA is melted under stirring at 120 - 140 °C, 0.4 - 0.6 MPa and a high speed of 100 - 150 rpm, and the usage requirements can be met in 20 - 30 min.

[0047] In the second aspect of the present invention, a pretreatment system for a PVA raw material special for an optical film is provided. The system includes: a PVA chamber (1), a water vapor chamber (2), and a porous plate (3); wherein, the PVA chamber (1) is located above the water vapor chamber (2), and a porous plate (3) is arranged between the PVA chamber (1) and the water vapor chamber (2);

[0048] Among them, along the direction from the PVA raw material inlet to the outlet, the aperture ratio of the porous plate decreases successively. At the same time, the porous plate inclines downward along the direction from the PVA raw material inlet to the outlet.

[0049] According to the present invention, the PVA chamber (1) is provided with a discharge outlet (4) for discharging the pretreated PVA raw material.

[0050] According to the present invention, the top of the PVA chamber (1) is provided with a water vapor outlet (5) for discharging water vapor.

[0051] In the present invention, the discharged water vapor can be recycled after preheating.

[0052] According to the present invention, the bottom of the water vapor chamber (2) is provided with a drainage outlet (6) for discharging the formed condensate droplets.

[0053] According to the present invention, the water vapor chamber (2) is provided with a water vapor inlet (7).

[0054] According to the present invention, the PVA chamber 1 is provided with a PVA feed inlet for introducing the PVA raw material into the PVA chamber 1.

[0055] According to the present invention, along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the number of holes in the porous plate is ≥ 5% per square meter, preferably 5 - 10% per square meter.

[0056] According to the present invention, the inclination angle of the porous plate is 3-8°, preferably 5-8°.

[0057] Combined with Figure 1 , a specific application method of the pretreatment method according to the present invention in the system is provided, including: introducing water vapor into the water vapor chamber (2), and the water vapor enters the PVA chamber (1) through the porous plate (3) at a flow rate of 35-50 m 3 / h to contact and bubble with the PVA raw material with a particle size of 0.5-0.8 cm. Along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is ≥1% per centimeter;

[0058] Under the contact conditions of a contact temperature of 110-135 °C, a contact time of 10-50 min, and a contact pressure of 1.5 bar-3 bar, the water vapor contacting the PVA raw material forms condensate droplets to swell the PVA raw material, obtaining the swollen PVA, which is discharged through the discharge outlet (4) in the PVA chamber (1), and the remaining water vapor that has not been condensed into droplets is discharged through the water vapor outlet (5) at the top of the PVA chamber (1) and preheated and then introduced into the water vapor chamber (2) for recycling;

[0059] Among them, the stacking thickness of the PVA raw material in the PVA chamber (1) is 15-20 cm, the feeding amount of the PVA raw material is 70-100 kg / h, and the swollen PVA is 130-150% of the weight of the PVA raw material;

[0060] Along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the number of holes in the porous plate is 5-10% per square meter, and the inclination angle of the porous plate is 3-8°, preferably 5-8°.

[0061] The third aspect of the present invention provides an application of the pretreatment method according to the first aspect of the present invention or the system according to the second aspect in the preparation of an optical PVA film.

[0062] The present invention will be described in detail below through examples.

[0063] Cut a test piece with a length * width = 10 cm * 3 cm from the optical film product, fix both ends of the length direction of the test piece to the stretching fixture, swell it in water at 40 °C for 5 min, and stretch it along the length direction at a stretching speed of 10 cm / min until it breaks. The force at the break is the tensile strength, and the ratio of the length at the break to the initial length is the stretching ratio.

[0064] Among them, the preparation method of the optical film is as follows: 100 parts by weight of swollen PVA, 8 parts by weight of starch, 15 parts by weight of glycerol, 0.1 part by weight of sodium dodecylbenzenesulfonate, and 0.005 part by weight of 2,6-di-tert-butyl-p-cresol are mixed evenly at 130 °C, 0.5 MPa and a stirring speed of 130 rpm to obtain a film-forming stock solution, and the film-forming stock solution is extruded onto a casting roller by a die head to obtain an optical film.

[0065] The number of PVA particles is measured by visually counting after randomly sampling 100 g of PVA solution at room temperature;

[0066] Unless otherwise specified, in the following examples and comparative examples, the degree of polymerization of the PVA raw material is 3500 and the degree of alcoholysis is 99.9 mol%.

[0067] Example 1

[0068] Steam is introduced into the steam chamber (2), and the steam enters the PVA chamber (1) through the porous plate (3) at a flow rate of 40 m 3 / h to contact and bubble with the PVA raw material with a particle size of 0.6 - 0.8 cm. Along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is 2.5% per centimeter;

[0069] The steam in contact with the PVA raw material under the contact conditions of a contact temperature of 110 °C, a contact time of 30 min, and a contact pressure of 1.5 bar forms condensate droplets to swell the PVA raw material, and the swollen PVA is discharged through the discharge outlet (4) in the PVA chamber (1). The steam that is not condensed into droplets is discharged through the steam outlet (5) at the top of the PVA chamber (1) and is preheated and then introduced into the steam chamber (2) for recycling;

[0070] Among them, the stacking thickness of the PVA raw material in the PVA chamber (1) is 15 - 20 cm, the feeding amount of the PVA raw material is 85 kg / h, the swollen PVA is 140% of the weight of the PVA raw material, along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the number of openings of the porous plate is 8% per square meter, and the inclination angle of the porous plate is 5°.

[0071] The swollen PVA is melted under stirring at 130 °C, 0.5 MPa and a speed of 130 rpm, and the usage requirements can be met in 25 min. No PVA particles are found in the melt, and the tensile strength and tensile ratio results of the prepared optical film are shown in Table 1.

[0072] Example 2

[0073] According to the method of Example 1, the difference is that the contact temperature is 120 °C, the contact pressure is 1.7 bar, and the contact time is 20 min.

[0074] The water vapor flow rate is 50 m 3 / h, the PVA feed rate is 100 kg / h, and the thickness of the PVA chamber material layer is controlled at 20 - 25 cm. The swollen PVA is 130% of the weight of the PVA raw material. Along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is 2% per centimeter.

[0075] The swollen PVA is melted under stirring at 130 °C, 0.5 MPa and a rotation speed of 130 rpm. The usage requirements can be met in 30 min. No PVA colloidal particles are found in the melt. The tensile strength and elongation at break of the prepared optical film are shown in Table 1.

[0076] Example 3

[0077] According to the method of Example 1, the difference is that the contact temperature is 130 °C, the contact pressure is 2 bar, and the contact time is 50 min.

[0078] The water vapor flow rate is 35 m 3 / h, the PVA feed rate is 70 kg / h, and the thickness of the PVA chamber material layer is controlled at 15 - 20 cm. The swollen PVA is 130% of the weight of the PVA raw material. Along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is 1% per centimeter.

[0079] The swollen PVA is melted under stirring at 130 °C, 0.5 MPa and a rotation speed of 130 rpm. The usage requirements can be met in 30 min. A very small amount of PVA colloidal particles are found in the melt. The tensile strength and elongation at break of the prepared optical film are shown in Table 1.

[0080] Example 4

[0081] According to the method of Example 1, the difference is that the contact temperature is 120 °C, and the thickness of the PVA chamber material layer is controlled at 20 - 25 cm. The swollen PVA is 140% of the weight of the PVA raw material. Along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is 3% per centimeter.

[0082] The swollen PVA is melted under stirring at 130 °C, 0.5 MPa and a rotation speed of 130 rpm. The usage requirements can be met in 30 min. A very small amount of PVA colloidal particles are found in the melt. The tensile strength and elongation at break of the prepared optical film are shown in Table 1.

[0083] Example 5

[0084] According to the method of Example 1, the difference is that along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the number of openings of the porous plate is 3% per square meter, and the inclination angle of the porous plate is 8°, so that along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is 4% per centimeter.

[0085] Example 6

[0086] According to the method of Example 1, the difference is that the flow rate of water vapor is 30 m 3 / h. The swollen PVA is 120% of the weight of the PVA raw material.

[0087] Example 7

[0088] According to the method of Example 1, the difference is that the contact pressure is 3.5 bar.

[0089] Comparative Example 1

[0090] After the PVA raw material is first swollen with water, where water:PVA raw material = 1:2, and then melted at 130 °C, 0.5 MPa and high-speed stirring. After melting for 3 h, there are still many PVA rubber particles. The tensile strength and tensile ratio of the prepared optical film are weak. The results are shown in Table 1.

[0091] Comparative Example 2

[0092] The PVA raw material is directly melted at 130 °C, 0.5 MPa and 130 rpm stirring. After melting for 4 h, there are still many PVA rubber particles. The tensile strength and tensile ratio of the prepared optical film are weak. The results are shown in Table 1.

[0093] Comparative Example 3

[0094] According to the method of Example 1, the difference is that the decreasing rate of the number of openings of the porous plate is 8% per square meter, and the inclination angle of the porous plate is 0°, that is, it is not inclined. It is found that the swollen PVA accumulates at the discharge port, causing equipment blockage and unable to carry out the subsequent process.

[0095] Table 1

[0096]

[0097]

[0098] It can be seen from the results in Table 1 that Examples 1-7 of the special PVA pretreated by the present invention all have a short melting time, no PVA rubber particles or very few PVA rubber particles in the melt, the prepared optical film has excellent tensile strength and tensile ratio, the tensile strength is not less than 60 MPa, and the tensile ratio is not less than 520%.

[0099] Among them, Examples 1 and 4 that meet the most preferred embodiment of the present invention significantly obtain more excellent effects. Among them, there are no PVA colloidal particles in the solution of Example 1, and the number of colloidal particles in Example 4 is only 1, which does not affect the use. The prepared optical film has excellent mechanical properties, with a tensile strength of not less than 69 MPa and a tensile ratio of not less than 670%.

[0100] 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 pretreatment method for a PVA raw material special for optical films, characterized in that, water vapor is brought into contact with the PVA raw material, such that the PVA raw material is in a bubbling state; wherein, along the direction from the PVA raw material inlet to the outlet, the bubbling height of the PVA raw material decreases.

2. The pretreatment method according to claim 1, wherein, along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the bubbling height of the PVA raw material is ≥1% per centimeter, preferably 2-3% per centimeter.

3. The pretreatment method according to claim 1 or 2, wherein, the conditions of the contact include: the contact temperature is 110-135 °C, preferably 110-120 °C; preferably, the contact time is 10-50 min, preferably 20-40 min; preferably, the contact pressure is 1.5 bar - 3 bar, preferably 1.5 bar - 2 bar.

4. The pretreatment method according to any one of claims 1-3, wherein, the water vapor in contact with the PVA raw material forms condensate droplets to swell the PVA raw material, obtaining the swollen PVA; preferably, the swollen PVA is 130-150% of the weight of the PVA raw material, preferably 140-145%.

5. The pretreatment method according to any one of claims 1-4, wherein, the degree of polymerization of the PVA raw material is 2000-4000, preferably 3000-4000; preferably, the degree of alcoholysis of the PVA raw material is DA, wherein 97 mol% ≤ DA < 100 mol%, preferably 99 mol% - 99.9 mol%.

6. The pretreatment method according to any one of claims 1-5, wherein, the particle size of the PVA raw material is 0.5-0.8 cm, preferably 0.6-0.8 cm.

7. The pretreatment method according to any one of claims 1-6, wherein, The flow rate of the water vapor is 35 - 50 m 3 / h, preferably 40 - 45 m 3 / h; Preferably, the feeding amount of the PVA raw material is 70-100 kg / h, preferably 80-90 m 3 / h; preferably, the stacking thickness of the PVA raw material is 15-25 cm.

8. A pretreatment system for a PVA raw material special for optical films, characterized in that, the system includes: a PVA chamber 1, a water vapor chamber 2, a perforated plate 3; wherein, the PVA chamber 1 is located above the water vapor chamber 2, and a perforated plate 3 is arranged between the PVA chamber 1 and the water vapor chamber 2; wherein, along the direction from the PVA raw material inlet to the outlet, the number of openings of the perforated plate decreases in sequence. At the same time, the perforated plate slopes downward along the direction from the PVA raw material inlet to the outlet.

9. The system according to claim 8, wherein, the PVA chamber 1 is provided with a discharge outlet 4 for discharging the pretreated PVA raw material; preferably, the top of the PVA chamber 1 is provided with a water vapor outlet 5 for discharging the water vapor; preferably, the bottom of the water vapor chamber 2 is provided with a drainage outlet 6 for discharging the formed condensate droplets; preferably, the water vapor chamber 2 is provided with a water vapor inlet 7; preferably, the PVA chamber 1 is provided with a PVA feed inlet for introducing the PVA raw material into the PVA chamber 1; Preferably, along the direction from the PVA raw material inlet to the outlet, the decreasing rate of the number of holes in the porous plate is ≥5% per square meter, preferably 5-10% per square meter; Preferably, the inclination angle of the porous plate is 3-8°, preferably 5-8°.

10. Use of the pretreatment method according to any one of claims 1-7 or the system according to claim 8 or 9 in the preparation of an optical PVA film.

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