TWI470013B - A method for producing a polyvinyl alcohol film - Google Patents

Description

Method for producing polyvinyl alcohol film

The present invention relates to a method of producing a polyvinyl alcohol film, and more particularly to a method of producing a polyvinyl alcohol film for use as an optical film.

The polarizer converts the natural light that is generally not polarized into a polarized light. LCD liquid crystal displays use this kind of polarized light, coupled with the twisting characteristics of liquid crystal molecules, to control the passage of light. With the wide application of liquid crystal displays, the market demand for polarizers has also risen with the rise of water. The polarizer mainly uses a polyvinyl alcohol (PVA) polymer film as a polarizing substrate, so the quality of the polyvinyl alcohol film directly affects the use effect of the polarizer.

Polyvinyl alcohol is a water-soluble high molecular polymer which is widely used. After the polyvinyl alcohol resin is dissolved in water to form a solution, it has good film forming properties. Therefore, the polyvinyl alcohol film is often produced by a solution method in the industry. The solubility of polyvinyl alcohol resin in water is affected by the degree of saponification, polymerization degree, and dissolution temperature. When the polyvinyl alcohol resin is dissolved in a T-die coater (T-DIE) to form a film, the solution state The polyvinyl alcohol resin is prone to gel formation, clogging the filter, and forming defects on the film, affecting the optical quality of the film.

The source of the gel comes from the incomplete dissolution process of the heating, which causes the resin to be completely dissolved, or the conveying pipeline has a dead angle, accumulates into a colloid and flows out for a long time, or the surface of the pipeline and equipment is easily dehydrated, resulting in The fluidity of the solution contacting the tube wall deteriorates, causing retention and formation of a colloid, and occasionally falling off following the solution out.

On the one hand, the gel causes the filter to be easily blocked, which shortens the continuous operation time of the process, reduces the utilization rate of the machine, and reduces the production capacity. On the other hand, defects in the surface of the polyvinyl alcohol film, such as gels, die-lines, affecting the quality of the film surface, or uneven film thickness are caused. In the process of making a polarizer, the polyvinyl alcohol film usually undergoes a process of stretching and laminating. If the polyvinyl alcohol film has too many defects, the film may be easily broken during the stretching process, and the film may be stuck when it is attached. Poor production, affecting product yield and productivity. In recent years, high definition and image quality requirements for liquid crystal displays have increased. Therefore, if there are too many defects in the polarizing film, the liquid crystal panel is liable to have problems such as chromatic aberration, bright spots, and dark spots, and the yield of the product is lowered.

The gel or the mold line on the polyvinyl alcohol film is caused by the gel in the solution. When the gel in the solution passes through the filter, most of the hard gel will be blocked by the filter and cannot penetrate. Shorten the filter life, a small part of the soft gel (sol-gel) will still deform through the filter, and coated into a film through a T-die coater, the defect formed on the film surface is "condensation gum". If the gel in the solution is coated by a T-die coater, it is stuck at the exit of the film lip (DIE-LIP) of the T-die coater, and the solution will always be interfered by the gel when it passes. The relative position on the film continues to create defects in the "mold line".

Japanese Patent Publication No. 2002-144406 discloses a method for producing a polyvinyl alcohol film by adjusting the roughness inside the coater line to reduce the occurrence of gelation of polyvinyl alcohol before film formation. However, in the industrial continuous process for producing a polyvinyl alcohol film, the polyvinyl alcohol resin is dissolved until it is coated into a film, and it is subjected to multiple filtration or placed in a standing device, which is disclosed in the prior art. It is still unavoidable that the polyvinyl alcohol solution gels before entering the T-die coater to adhere or clog the filter, and the filter is stopped due to excessive pressure difference.

Therefore, there is still a need for a method for preventing the formation of a gel of polyvinyl alcohol before coating into a film, prolonging the running time of the continuous process, and improving the film quality and uniformity of the polyvinyl alcohol film.

To achieve the above and other objects, the present invention provides a method of making a polyvinyl alcohol film, including steps of dissolving, filtering, and coating. The method of the invention is a device for dissolving, filtering and coating forming steps, and a conveying pipeline connecting the dissolving, filtering, and coating forming equipment, and applying a heat insulating device to the surface in contact with the atmosphere to make the device Maintain a uniform temperature with the surface of the pipeline to prevent gel formation. The heat retaining device can be insulated by a heating wire or a jacket for heating the liquid inside, and the polyvinyl alcohol solution is subjected to a heat insulating condition of 80 to 140 ° C from the dissolution to the coating forming step. The method of the invention utilizes an external heat preservation device to coat equipment for performing steps of dissolving, filtering and coating forming, and a conveying pipeline connecting the dissolving, filtering, and coating forming equipment, and the heat insulating device can be metal electric The hot wire is insulated by heating the metal wire, or the heat insulating jacket containing the heating liquid is heated to achieve the heat preservation effect, so that the polyvinyl alcohol maintains a uniform heat preservation state from self-dissolving to coating forming. In order to avoid the temperature loss of the equipment device or the pipeline surface, the gel is formed, which affects the quality and uniformity of the surface of the coated film.

On the other hand, the method of the present invention can prevent the polyvinyl alcohol from forming a gel before film formation by heating and heat-insulating means, and it is not easy to cause gel adhesion or clogging the filter to stop the operation of the line for a long time. Helps to extend the running time of a single drive in the overall process.

The embodiments of the present invention are described by way of specific examples, and those skilled in the art can readily understand the advantages and functions of the present invention from the disclosure. The present invention may be embodied or applied by other different embodiments, and the various details of the present invention may be variously modified and changed without departing from the spirit and scope of the invention.

The method for producing a polyvinyl alcohol film of the present invention is a device for coating, dissolving, filtering and coating forming a device by using an external heat insulating device, and a transfer line connecting the dissolving, filtering, and coating forming equipment to produce polyvinyl alcohol. In the process of the film, the polyvinyl alcohol is maintained in a uniform heating and holding state from the time of dissolution to the time of coating and molding, and the polyvinyl alcohol is prevented from forming a gel to block the filter. In general, the production of a polyvinyl alcohol film requires steps such as dissolution, filtration, and coating. The polyvinyl alcohol resin, the plasticizer, the solvent, and optionally the added component are heated and dissolved in the dissolution tank to form a homogeneous dissolved substance, filtered through a filter, and then coated and formed by a mold, and dried to form a polyvinyl alcohol film. The polyvinyl alcohol-based resin used in the method of the present invention is obtained by polymerizing a vinyl ester-based resin monomer to obtain a polyvinyl ester-based resin and then performing a saponification reaction. Examples of such a polyvinyl ester monomer include, but are not limited to, ethylene formate. A vinyl ester polymer such as ester, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate or vinyl octanoate, preferably vinyl acetate.

Further, an olefin compound such as ethylene, propylene, butylene or the like or an acrylate derivative such as acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate or the like and the above vinyl ester A copolymer formed by copolymerization of a monomer may also be used.

In general, the polyvinyl alcohol-based resin used in the method of the present invention has a degree of saponification of 90% or more, preferably 99% or more. Generally, the degree of polymerization of the polyvinyl alcohol resin used for forming the film is from 800 to 10,000, and the degree of polymerization is higher than 1200, which has better processing characteristics, and if it is higher than 10,000, it is disadvantageous for the dissolution process. The polyvinyl alcohol resin may be water as a solvent, and the solvent is added in an amount of about 10 to 40 parts by weight, preferably 20 to 30 parts by weight, based on 100 parts by weight of the polyvinyl alcohol resin.

Polyvinyl alcohol-based films are usually added with a plasticizer to facilitate film formation. Common plasticizers are mainly polyols, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, glycerol. Etc., preferably ethylene glycol and glycerol. The amount of the polyol to be added is from 3 to 30 parts by weight, preferably from 7 to 20 parts by weight, based on the polyvinyl alcohol resin.

In the method of the present invention, the dissolving tank, the filter, the coating machine and the conveying pipeline connected from the dissolving tank to the coating machine are all covered with a heat insulating device, and the heat insulating device can be a metal electric heating wire or an internal device. A liquid jacket, such as oil or water, maintains uniform heating of the dissolution tank, filter, coater, and line connecting the dissolution tank to the coater by heating the metal wire or the liquid in the jacket. The state of insulation, especially equipment and pipeline surfaces, avoids the loss of surface temperature of the equipment or pipeline, causing the polyvinyl alcohol in the solution to stay in the gel, sticking or clogging the filter, resulting in the process not being able to continue. On the other hand, if the heating temperature is too high, a part of the solution may be dehydrated or gelled to form a coke-yellow or black gel, which is also disadvantageous for improving the quality and uniformity of the surface of the film to be formed by coating. The heating wire is a metal wire, and the main material is a resistance wire of an alloy of two or more elements of nickel, chromium, copper or nickel, chromium or copper. The oil contained in the thermal insulation jacket has the characteristics of low air pressure, low viscosity, high specific heat, high conductivity, and operating temperature higher than 200 ° C, so that the equipment and the pipeline maintain a uniform heating state. In the method of the present invention, the polyvinyl alcohol is subjected to heating and heat preservation conditions of 80 to 140 ° C from the time of dissolution to the coating and forming, preferably under the heating and holding condition of 90 to 130 ° C, and more preferably It is carried out under heating and holding conditions of 100 to 120 °C.

In one embodiment, the method for producing a polyvinyl alcohol film of the present invention sequentially comprises the steps of dissolving, filtering, conveying, filtering, and coating forming, wherein the dissolving tank, the filter, the coating machine, and the connecting self-dissolving tank are The surface of the conveying pipeline of the coating machine is covered with a heat preservation device, so that the equipment and the pipeline maintain a uniform heating state. In this specific example, a polyvinyl alcohol resin is used as a raw material, and after heating and dissolving in a dissolution tank to form a homogeneous solution, it is first filtered using a filter, transported through a gear pump and a pipeline, and filtered again. After that, it is applied to a T-die coater for coating and forming, and after drying, a polyvinyl alcohol film is formed. In the method of the invention, the surface of the dissolving tank, the filter coating machine and the conveying pipeline are covered with a heat insulating device, and the device can be a heating wire or a heat insulating jacket, the electric heating wire is a metal wire contained therein, and the heat insulating jacket is inside. Packing water or oil, using a water bath or oil bath to heat and keep warm, the temperature of the heat preservation device and the outlet temperature of the dissolution tank are controlled in the range of 80 to 140 ° C, preferably controlled in the range of 90 ° C to 130 ° C, which will help Reduce gel formation and slow down filter differential pressure (the inlet pressure of the solution flowing into the filter is defined as P1, the outlet pressure of the solution flowing out of the filter is defined as P2, differential pressure (△P) = P1-P2), and the filtration is extended. The use time of the device and the single operation time of the process improve the quality of the polyvinyl alcohol film, and are particularly suitable for manufacturing a polarizing material such as an optical film of a polarizing plate or polarized glasses.

Example Comparative Example 1

100 parts by weight of a polyvinyl alcohol resin (saponification degree: 99.9 mol% or more, degree of polymerization 2400), 10 parts by weight of glycerin, and 250 parts by weight of water are added to a dissolution tank, and heated in a dissolution tank at 130 ° C. Dissolved to form a homogeneous solution. The homogeneous solution is filtered through a filter, transported through a gear pump and a pipeline, and after being filtered again, it is applied to a T-die coater for coating and drying, and a polyvinyl alcohol film is obtained after drying. There is no heat preservation device on the surface of the equipment and the pipeline, and the temperature of the solution at the outlet of the dissolution tank is controlled at 130 ° C to obtain a polyvinyl alcohol film control sample 1. The filter pressure difference (ΔP) between the gear pump and the T-die coater after 96 hours of operation was recorded (the inlet pressure of the solution flowing into the filter was defined as P1, and the outlet pressure of the solution flowing out of the filter was defined as P2, The pressure difference (ΔP)=P1-P2), the frequency of the mold line and the gel on the film surface of the polyvinyl alcohol film control sample was observed, and the overall process running time was calculated, and the results are shown in Table 1.

Comparative Example 2

The procedure of Comparative Example 1 was repeated, and the temperature of the solution at the outlet of the dissolution tank was controlled at 90 ° C to obtain a polyvinyl alcohol film control sample 2. The filter pressure difference (ΔP) between the gear pump and the T-die coater after 96 hours of operation was recorded, and the frequency of the mold line and the gelation on the film surface of the polyvinyl alcohol film control sample was observed. The overall process run time, and the results are listed in Table 1.

Example 1

100 parts by weight of a polyvinyl alcohol resin (saponification degree: 99.9 mol% or more, degree of polymerization 2400), 10 parts by weight of glycerin, and 250 parts by weight of water are added to a dissolution tank, and heated in a dissolution tank at 130 ° C. Dissolved to form a homogeneous solution. The homogeneous solution is filtered through a filter, transported through a gear pump and a pipeline, and after being filtered again, it is applied to a T-die coater for coating and drying, and a polyvinyl alcohol film is obtained after drying. The equipment including the dissolving tank, the filter and the coating machine, and the surface of the conveying pipeline connected from the dissolving tank to the coating machine are covered with electric heating lines, and the heating and holding of the metal wire is heated, and the temperature of the solution at the outlet of the dissolving tank is controlled. At 110 ° C, the temperature of the heating wire was controlled at 110 ° C to obtain a polyvinyl alcohol film sample 1. Record the filter pressure difference (ΔP) between the gear pump and the T-die coater after 96 hours of operation, observe the appearance of the mold line and the gel on the film surface of the polyvinyl alcohol film sample, and calculate the overall process. Run time, and the results are listed in Table 1.

Example 2

Repeat the steps of the first embodiment, including the dissolving tank, the filter and the coating machine, and the surface of the conveying pipeline connected from the dissolving tank to the coating machine, and changing the surface of the conveying jacket to cover the heat insulating jacket, and heat and heat the water bath to dissolve the tank. The temperature of the outlet solution was controlled at 85 ° C, and the temperature of the insulation jacket was controlled at 85 ° C to obtain a polyvinyl alcohol film sample 2. Record the filter pressure difference (ΔP) between the gear pump and the T-die coater after 96 hours of operation, observe the appearance of the mold line and the gel on the film surface of the polyvinyl alcohol film sample, and calculate the overall process. Run time, and the results are listed in Table 1.

Example 3

The procedure of Example 2 was repeated, and 100 parts by weight of a polyvinyl alcohol resin (saponification degree: 99.5 mol% or more, degree of polymerization 1700), 10 parts by weight of glycerin, and 250 parts by weight of water were added to the dissolution tank. The temperature of the solution at the outlet of the dissolution tank was controlled at 130 ° C, and the temperature of the insulation jacket was controlled at 130 ° C to obtain a polyvinyl alcohol film sample 3. Record the filter pressure difference (ΔP) between the gear pump and the T-die coater after 96 hours of operation, observe the appearance of the mold line and the gel on the film surface of the polyvinyl alcohol film sample, and calculate the overall process. Run time, and the results are listed in Table 1.

Example 4

The composition of Example 2 was repeated by adding a component of 100 parts by weight of a polyvinyl alcohol resin (saponification degree: 99.9 mol% or more, polymerization degree: 4000), 12 parts by weight of glycerin, and 250 parts by weight of water to a dissolution tank, and The oil bath was heated and kept warm, the temperature of the solution at the outlet of the dissolution tank was controlled at 110 ° C, and the temperature of the insulation jacket was controlled at 110 ° C to obtain a polyvinyl alcohol film sample 4. Record the filter pressure difference (ΔP) between the gear pump and the T-die coater after 96 hours of operation, observe the appearance of the mold line and the gel on the film surface of the polyvinyl alcohol film sample, and calculate the overall process. Run time, and the results are listed in Table 1.

According to the above results, the frequency of the mold line and the gel on the film surface of the formed polyvinyl alcohol film is relatively high without the heat preservation, and the filter pressure difference is 90 at the outlet temperature after 96 hours of new operation. At °C, it has risen to 38 kg / cm ^ 2 and needs to stop production. The pressure difference at the outlet temperature of 130 ° C also reaches 15 kg / cm ^ 2, resulting in a continuous operation time of more than 8 days. In contrast, in the method of the present invention, the pressure difference of the filter rises slowly, and the process can be continuously operated for more than 40 days, which helps to extend the running time of the single process of the whole process, and the frequency of the gel on the film surface is only 0.3. / square meter, no mold line will appear, which will help improve the quality of the film surface.

The above-described embodiments are merely illustrative of the principles of the invention and its effects, and are not intended to limit the invention. Modifications and variations of the above-described embodiments can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be as set forth in the scope of the claims described below.

Claims (12)

A method for producing a polyvinyl alcohol film, which comprises a dissolving, filtering, and coating forming step in sequence, which uses an external heat insulating device to make the polyvinyl alcohol from 80 to 140 in the steps from self-dissolution to coating forming. The heating and holding conditions of °C were carried out, wherein the polyvinyl alcohol film was used as an optical film. A method for producing a polyvinyl alcohol film according to the first aspect of the invention, wherein the heating and holding is carried out at a temperature of from 90 to 130 °C. The method for producing a polyvinyl alcohol film according to claim 1, wherein the heat insulating device is a metal heating wire. The method for producing a polyvinyl alcohol film according to the first aspect of the invention, wherein the heat insulating device is an insulating jacket for holding a liquid inside. The method for producing a polyvinyl alcohol film according to the first aspect of the invention, wherein the heat retaining device is coated with a device for dissolving and filtering. A method of producing a polyvinyl alcohol film according to the first aspect of the invention, wherein the heat retaining device is coated with a line for connecting a dissolution, filtration, and coating molding apparatus. The method for producing a polyvinyl alcohol film according to the third aspect of the invention, wherein the metal heating wire is selected from the group consisting of nickel, chromium, copper or an electric resistance wire of two or more alloys of nickel, chromium and copper. The method for producing a polyvinyl alcohol film according to claim 4, wherein the heat insulating jacket is filled with liquid system water or oil. The method for producing a polyvinyl alcohol film according to claim 8 wherein the oil contained in the heat insulating jacket has a boiling point higher than 200 °C. The method for producing a polyvinyl alcohol film according to claim 1, wherein the step of transporting and filtering is sequentially performed between the filtering and coating forming steps. A method of producing a polyvinyl alcohol film according to claim 10, wherein the dissolving step is carried out in a dissolution tank having an outlet temperature of between 80 and 140 °C. A method of producing a polyvinyl alcohol film according to the first aspect of the invention, wherein the coating forming step is carried out using a gear pump and a T-die coater.