Film curl evaluation method, film curl evaluation device, and polyvinyl alcohol film

Abstract

The invention relates to a thin film curling technology, and discloses a thin film curling evaluation method, a thin film curling evaluation device and a polyvinyl alcohol thin film. The curl evaluation method comprises the following steps: soaking a film sample in a test solvent, and determining a curl time coefficient A, a curl direction coefficient B and a curl swelling rate coefficient C of the film sample in the test solvent; the curling coefficient omega of the thin film in the test solvent is calculated through the curling time coefficient A, the curling direction coefficient B and the curling swelling rate coefficient C, and the curling degree of the thin film is evaluated through the curling coefficient omega. According to the evaluation method, the curling degree of the film is quantified by using the curling coefficient, evaluation is more objective and accurate, the processing technology can be guided, the curling degree of the film can be reduced, and flaws such as wrinkles, creases and bubbles of subsequent products can be reduced.

Description

Technical Field

[0001] The invention relates to a film curling technology, and in particular to a film curling evaluation method, a film curling evaluation device and a polyvinyl alcohol film. Background Art

[0002] The production of advanced functional polymer films is an important part of modern flat panel displays. Many types of film materials have slight differences in composition and structure on the front and back sides due to the asymmetric processing of the two sides such as cast film processing. In many cases, the film is straight when it is just produced, but under certain temperature and humidity conditions, the two sides of the film have different abilities to absorb water molecules, resulting in different expansion rates on both sides of the film, which is reflected in the macroscopic view that the film curls during storage, transportation, and processing.

[0003] The polyvinyl alcohol (PVA) optical base film used in polarizer processing is a typical example of the above situation. Due to the difference in the structure of the front and back sides caused by the asymmetric processing of the two sides, it curled during the swelling process, seriously affecting the structural uniformity and processing stability of the iodine dyeing process, and causing wrinkles, creases, bubbles and other product defects in the subsequent processing of winding and laminating. In addition, the curling and stretching of the currently produced PVA film in water is unstable, especially the film in any area of ​​the film has inconsistent changes in size in water in different directions, and it is impossible to judge the degree of film curling.

[0004] Therefore, it is necessary to reduce the degree of film curling through process improvement, and how to measure and evaluate the film curling is also an important issue. Therefore, it is particularly urgent to provide a curling device that can evaluate the curling of PVA films. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems in the prior art that it is difficult to measure and evaluate the degree of film curling and that film curling affects subsequent processing, and to provide a film curling evaluation method, a film curling evaluation device and a polyvinyl alcohol film. The evaluation method uses a curl coefficient to quantify the degree of film curling, and the evaluation is more objective and accurate, which is beneficial to guiding the processing technology, reducing the degree of film curling, and reducing the occurrence of wrinkles, creases, bubbles and other defects in subsequent products.

[0006] In order to achieve the above object, the first aspect of the present invention provides a film curling evaluation method, the method comprising:

[0007] Immersing the film sample in a test solvent, and measuring the curling time coefficient A, curling direction coefficient B and curling swelling rate coefficient C of the film sample in the test solvent;

[0008] The curling coefficient ω of the film in the test solvent is calculated by the curling time coefficient A, the curling direction coefficient B and the curling swelling rate coefficient C, and the curling degree of the film is evaluated by the curling coefficient ω.

[0009] Preferably, the curl coefficient ω is calculated by the following formula (I):

[0010] ω=a*A+b*B+c*C;

[0011] Wherein, a is the curling time specific gravity, b is the curling direction specific gravity, and c is the curling swelling rate specific gravity; when the film sample is immersed in the test solvent, if curling occurs, a and b are both 1, and if no curling occurs, a and b are both 0. If the length and / or width of the film sample changes, c is 1, and if the length and width of the film do not change, c is 0.

[0012] Preferably, the process of determining the curling time coefficient A comprises: determining the time T0 when the film sample starts curling after being immersed in the test solvent and the total time T when the film sample is immersed in the test solvent, and calculating the curling time coefficient A by the following formula (II);

[0013] A=(T-T0) / T formula (II).

[0014] Preferably, the process of determining the curling direction coefficient B comprises: determining the curling direction index r of the film sample immersed in the test solvent, the initial area S of the film sample and the area S1 of the film sample after being immersed in the test solvent, and calculating the curling direction coefficient B by the following formula (III);

[0015] B=|r|*(S-S1) / S Formula (III),

[0016] Among them, if the curling direction is the TD direction, the value of r is +1, if the curling direction is the MD direction, the value of r is -1, and if there is no curling, the value of r is 0.

[0017] Preferably, the process of determining the curl swelling coefficient C includes: determining the initial length L of the film sample and the length L1 of the film sample after being immersed in the test solvent, and calculating the curl swelling coefficient C by the following formula (IV);

[0018] C=L1 / L formula (IV).

[0019] Preferably, the test solvent is water, the immersion temperature is 24-28° C., and the immersion time is 120-180 s.

[0020] Preferably, the process of evaluating the curl degree of the film includes: selecting a film with a curl coefficient ω satisfying 0<ω<5.1; more preferably 0.5<ω<5.1, and further preferably 0.6<ω<2.1.

[0021] A second aspect of the present invention provides a film curling evaluation device for performing the film curling evaluation method as described above, the device comprising a box for loading a test solvent, a supporting plate located in the box, and a temperature control unit for controlling the temperature of the test solvent in the box, wherein the supporting plate is liftably connected to the inner wall of the box.

[0022] Preferably, a surface of the supporting plate in contact with the film is provided with a grid for measuring the size of the film, and the grid has scale lines of various specifications.

[0023] Preferably, the temperature control unit includes a temperature control component located in the box body, a temperature display screen located on the box body, and a switch for controlling the working state of the temperature control component.

[0024] Preferably, an openable and closable cover is provided on the top of the box body, and a blade detachably connected to the cover is provided on the inner side of the cover.

[0025] A third aspect of the present invention provides the use of the above-mentioned film curling evaluation method and the above-mentioned film curling evaluation device in film processing.

[0026] Preferably, the film is a polyvinyl alcohol film.

[0027] A fourth aspect of the present invention provides a polyvinyl alcohol film, which is obtained by rolling up a polyvinyl alcohol film under the condition of controlling the traction coefficient α, and then screening using the film curling evaluation method as described above, wherein the curling coefficient ω of the polyvinyl alcohol film is 0<ω<5.1; the traction coefficient α is calculated by the following formula (V);

[0028] α=N*D formula (V),

[0029] Wherein, N is the winding tension of the film, and D is the specific speed of the roller group.

[0030] Preferably, the curl coefficient ω of the polyvinyl alcohol film is 0.5<ω<5.1, and more preferably 0.6<ω<2.1;

[0031] The traction coefficient α is controlled to be 0.9<α<16.2, more preferably 4.9<α<14, and further preferably 10<α<13.1.

[0032] Through the above technical solution, the beneficial effects of the present invention are:

[0033] The film curling evaluation method provided by the present invention is based on the curling time coefficient A, the curling direction coefficient B and the curling swelling rate coefficient C of the sample immersed in the test solvent, and quantifies the curling degree of the film in the form of the curling coefficient ω, taking into account the curling direction, the curling time and the curling swelling rate, so that the evaluation is more objective and accurate; the curling coefficient ω can be used to guide the selection of the film to reduce the curling degree of the film, which is beneficial to reduce the subsequent defects such as wrinkles, creases, bubbles, etc. in the product, and shows certain application potential in the field of film performance improvement; it is particularly suitable for the evaluation of polyvinyl alcohol film, and the polyvinyl alcohol film obtained by winding by controlling the traction coefficient α is evaluated by adopting this method, and the polyvinyl alcohol film with the curling coefficient ω within the limited range is selected, which will not curl in the later use, and the stability of the downstream polyvinyl alcohol film and iodine complex and the film tensile performance are improved.

[0034] The film curling evaluation device provided by the present invention has a simple structure and is easy to operate, so that the film does not deform or wrinkle during evaluation and measurement, and the device occupies a small indoor space. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of a specific embodiment of the film curling evaluation device of the present invention;

[0036] Figure 2 It is a measure of the different degrees of curling of the film in Test Example 1.

[0037] Description of Reference Numerals

[0038] 1 box 2 temperature display

[0039] 3 switches 4 grids

[0040] 5 scale line 6 support plate

[0041] 7 blades DETAILED DESCRIPTION

[0042] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0043] First of all, it should be noted that in the following description, some directional words, such as "inside", "outside", "upper", "lower", etc., are involved in order to clearly explain the technical solution of the present invention. Based on the box 1, "inside" refers to the inner cavity of the box 1, "outside" refers to the outer side of the box 1, "upper" refers to the position where the top of the box 1 is located, and "lower" refers to the position where the bottom of the box 1 is located. The terms are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0044] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "fixation" and "connection" should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] A first aspect of the present invention provides a method for evaluating film curling, the method comprising:

[0046] Immersing the film sample in a test solvent, and measuring the curling time coefficient A, curling direction coefficient B and curling swelling rate coefficient C of the film sample in the test solvent;

[0047] The curling coefficient ω of the film in the test solvent is calculated by the curling time coefficient A, the curling direction coefficient B and the curling swelling rate coefficient C, and the curling degree of the film is evaluated by the curling coefficient ω.

[0048] The inventors of the present invention discovered during the research and development process that by immersing a film sample in a test solvent to measure its curling time coefficient A, curling direction coefficient B and curling swelling rate coefficient C, and calculating the curling coefficient ω through these three coefficients, the curling degree of the film is quantified in the form of the curling coefficient ω, making the evaluation more objective and accurate.

[0049] The curl coefficient ω obtained by the film curling evaluation method of the present invention can be used to screen the film after winding to reduce the curling degree of the film, which is conducive to reducing the defects such as wrinkles, creases, bubbles, etc. in subsequent products, and shows certain application potential in the field of film performance improvement. Taking polyvinyl alcohol film as an example, the traction coefficient α of the polyvinyl alcohol film when winding is controlled to meet: 0.9<α=N*D<14, preferably 4.9<α<13.1, and most preferably 7.9<α<13.1, wherein N represents the winding tension, and D is the roller group speed. After evaluation by the film curling evaluation method provided by the present invention, the curl coefficient ω in water is selected to meet: 0<ω<5.1, preferably 0.5<ω<5.1, and most preferably 0.6<ω<5.1. The polyvinyl alcohol film can make the polyvinyl alcohol film no longer curl, and improve the stability of the downstream polyvinyl alcohol film and iodine complex and the film tensile performance.

[0050] According to the present invention, preferably, the curl coefficient ω is calculated by the following formula (I):

[0051] ω=a*A+b*B+c*C;

[0052] Among them, a is the curling time specific gravity, b is the curling direction specific gravity, and c is the curling swelling ratio specific gravity. The values ​​of a, b, and c are determined according to whether the film sample curls when immersed in the test solvent. If curling occurs, a=1, if not, a=0; if curling occurs, regardless of whether the film curls in the length direction or the width direction, b=1, if not, b=0; the curling swelling ratio specific gravity c is determined by whether the film length and width change before and after immersion in the test solvent. If the film length and / or width change, c=1, if the film length and width do not change, c=0.

[0053] According to the present invention, the curling time coefficient A reflects the relationship between the time when the film sample is immersed in the test solvent and the total time without curling. Preferably, the process of determining the curling time coefficient A includes: determining the time T0 when the film sample starts to curl after being immersed in the test solvent and the total time T when the film sample is immersed in the test solvent, and calculating the curling time coefficient A by the following formula (II);

[0054] A=(T-T0) / T formula (II).

[0055] According to the present invention, the curling direction coefficient B reflects the change in curling direction and curling area of ​​the film sample immersed in the test solvent. Preferably, the process of measuring the curling direction coefficient B includes: measuring the curling direction index r of the film sample immersed in the test solvent, the initial area S of the film sample and the area S1 of the film sample after being immersed in the test solvent, and calculating the curling direction coefficient B by the following formula (III);

[0056] B=|r|*(S-S1) / S Formula (III),

[0057] Among them, if the curling direction is the TD direction, r is +1, if the curling direction is the MD direction, r is -1, and if there is no curling, r is 0. The TD direction refers to the width direction of the film sample, and the MD direction refers to the length direction of the film sample.

[0058] According to the present invention, the curling swelling coefficient C reflects the relationship between the curling length and the original length of the film sample immersed in the test solvent. Preferably, the process of determining the curling swelling coefficient C includes: determining the initial length L of the film sample and the length L1 of the film sample after being immersed in the test solvent, and calculating the curling swelling coefficient C by the following formula (IV);

[0059] C=L1 / L formula (IV).

[0060] According to the present invention, the selection of the test solvent and the soaking conditions can be selected according to the properties of the film. When the film is a polyvinyl alcohol film, preferably, the test solvent is water, the soaking temperature is 24-28°C, specifically 24°C, 25°C, 26°C, 27°C, 28°C, or any value between the two values; the soaking time is 120-180s, specifically 120s, 130s, 140s, 150s, 160s, 170s, 180s, or any value between the two values.

[0061] According to the present invention, preferably, the process of evaluating the curling degree of the film includes: selecting a film with a curl coefficient ω satisfying 0<ω<5.1 for use or downstream processing; more preferably 0.5<ω<5.1, and further preferably 0.6<ω<2.1. For example, selecting a polyvinyl alcohol film with a curl coefficient ω within a limited range for iodine dyeing can improve the stability of the polyvinyl alcohol film and iodine complex and the tensile properties of the film.

[0062] The second aspect of the present invention provides a film curling evaluation device for performing the film curling evaluation method as described above, see Figure 1 The device includes a box 1 for loading a test solvent, a supporting plate 6 located in the box 1, and a temperature control unit for controlling the temperature of the test solvent in the box 1. The supporting plate 6 is connected to the inner wall of the box 1 in a liftable manner; the surface of the supporting plate 6 in contact with the film is provided with a grid 4 for measuring the size of the film, and the grid 4 has scale lines 5 of various specifications.

[0063] The film curling evaluation device is used to perform the film curling evaluation method as described above, and the specific process is: adding the test solvent into the box 1, raising the supporting plate 6 above the liquid surface and placing the film sample in the grid 4 on the supporting plate 6, and measuring the initial size of the film sample using the scale line 5; using the temperature control unit to control the test solvent in the box 1 to a set temperature, slowly lowering the supporting plate 6 below the liquid surface, and after the entire film sample is immersed in the test solvent of the set temperature, the test is started, and the curling direction of the film, the time when curling starts, the swelling rate of immersion, the area after immersion, etc. are recorded in real time to obtain the curling time coefficient A, the curling direction coefficient B and the curling swelling rate coefficient C, and then the curling coefficient ω of the film in the test solvent is calculated.

[0064] The initial area of ​​the film and the area after immersion can be measured or calculated by matching the grid 4 and the scale lines 5. Furthermore, the scale lines 5 of various specifications on the grid 4 can be used for cutting and measuring films of different sizes. The support plate 6 can be connected to the bottom of the box body 1 through a telescopic rod in the height direction, and the telescopic rod in the height direction can also be connected to the side wall of the box body 1 through a connecting rod. The length of the telescopic rod can be adjusted manually or electrically.

[0065] In the present invention, the temperature control unit can use any element that can heat up or cool down the test solvent to control the temperature of the test solvent within a desired range. Preferably, the temperature control unit includes a temperature control element located in the box 1, a temperature display screen 2 located on the box 1, and a switch 3 for controlling the working state of the temperature control element; after the switch 3 is turned on, the desired temperature can be set through the temperature display screen 2, the cooling or heating function can be selected, and the set temperature and the real-time temperature can be observed. The temperature control element can use a conventional heating element or a cooling element.

[0066] In the present invention, the box body 1 can be open, or can be provided with a detachable or openable top cover. Preferably, the top of the box body 1 is provided with an openable cover plate, and a blade 7 detachably connected to the cover plate is provided inside the cover plate, and the blade 7 can be used to cut the film, or the blade 7 can be used to cut the film by turning over the cover plate of the box body 1.

[0067] A third aspect of the present invention provides the use of the above-mentioned film curling evaluation method and the above-mentioned film curling evaluation device in film processing.

[0068] In the present invention, the film can be any rollable film. Preferably, the film is a polyvinyl alcohol film.

[0069] A fourth aspect of the present invention provides a polyvinyl alcohol film, which is obtained by rolling up a polyvinyl alcohol film under the condition of controlling the traction coefficient α, and then screening using the film curling evaluation method as described above, wherein the curling coefficient ω of the polyvinyl alcohol film is 0<ω<5.1; the traction coefficient α is calculated by the following formula (V);

[0070] α=N*D formula (V),

[0071] Wherein, N is the winding tension of the film, and D is the specific speed of the roller group.

[0072] In the present invention, winding tension refers to the tension exerted on the roller during the entire winding process. Both the winding tension and the roller group speed ratio can be adjusted and set by the equipment according to the process; illustratively, PVA drying and film forming equipment is used for winding, and the corresponding winding tension and roller group speed ratio are set.

[0073] The polyvinyl alcohol film can be obtained by the following process: a plasticizer and a polyvinyl alcohol resin with a saponification degree of 95-100% are dissolved in a solution to form a 25-35% by weight polyvinyl alcohol casting solution, which is then filtered using a filter, and then a gear pump and a die coater are used to cast the polyvinyl alcohol casting solution onto a casting drum, which is then dried at high temperature to form a polyvinyl alcohol polymer film, which is then peeled off from the casting drum, and subjected to an oven heat treatment to obtain a polyvinyl alcohol film.

[0074] According to the present invention, preferably, the curl coefficient ω of the polyvinyl alcohol film is 0.5<ω<5.1, more preferably 0.6<ω<2.1; the traction coefficient α is controlled to be 0.9<α<16.2, more preferably 4.9<α<14, and more preferably 10<α<13.1. Under this preferred embodiment, the polyvinyl alcohol film can no longer curl, and the stability of the downstream polyvinyl alcohol film and iodine complex and the film tensile properties are improved.

[0075] According to a particularly preferred embodiment of the present invention, a film curling evaluation device includes a box 1 for loading a test solvent, a supporting plate 6 located in the box 1, and a temperature control unit for controlling the temperature of the test solvent in the box 1, wherein the supporting plate 6 is connected to the bottom of the box 1 in a liftable manner; a surface of the supporting plate 6 in contact with the film is provided with a grid 4 for measuring the size of the film, and the grid 4 has scale lines 5 of various specifications; the temperature control unit includes a temperature control component located in the box 1, a temperature display screen 2 located on the box 1, and a switch 3 for controlling the working state of the temperature control component, and an openable and closable cover is provided on the top of the box 1, and a blade 7 detachably connected to the cover is provided on the inner side of the cover.

[0076] The process of obtaining a polyvinyl alcohol film by screening through a film curling evaluation method includes: rolling up a polyvinyl alcohol film under the condition of controlling a traction coefficient α (the traction coefficient α is controlled to be 0.9<α<16.2, more preferably 4.9<α<14, and further preferably 10<α<13.1) to obtain a film to be tested, using the above-mentioned film curling evaluation device, adding a test solvent into a box 1, raising a supporting plate 6 above the liquid surface and placing a film sample in a grid 4 on the supporting plate 6, using a blade 7 to cut the film by turning over the cover of the water tank 1, combining with the scale line 5 to obtain a suitable film sample and measure the initial size of the film sample; turning on the switch 3, setting the required temperature to 24-28°C through the temperature display screen 2, selecting a cooling or heating function, and observing the set temperature and the real-time temperature, so that the temperature of the test solvent in the box 1 is 24-28°C;

[0077] The supporting plate 6 is slowly lowered below the liquid surface. After the entire film sample is immersed in the test solvent, the test is started. The immersion time of the film sample in the test solvent is controlled to be 120-180s.

[0078] The time T0 when the film sample starts to curl after being immersed in the test solvent and the total time T when the film sample is immersed in the test solvent are recorded in real time, and the curling time coefficient A is calculated by the following formula (II);

[0079] A=(T-T0) / Tformula (II);

[0080] The curling direction index r of the film sample immersed in the test solvent, the initial area S of the film sample and the area S1 of the film sample after being immersed in the test solvent are measured, and the curling direction coefficient B is calculated by the following formula (III);

[0081] B=|r|*(S-S1) / S Formula (III),

[0082] Among them, if the curling direction is the TD direction, r is +1, if the curling direction is the MD direction, r is -1, and if there is no curling, r is 0;

[0083] The initial length L of the film sample and the length L1 of the film sample after being immersed in the test solvent are measured, and the curling swelling coefficient C is calculated by the following formula (IV);

[0084] C = L1 / L formula (IV);

[0085] The curl coefficient ω is calculated by the following formula (I):

[0086] ω=a*A+b*B+c*C;

[0087] Among them, a is the curling time specific gravity, b is the curling direction specific gravity, and c is the curling swelling ratio specific gravity;

[0088] Based on the obtained curl coefficient ω, a polyvinyl alcohol film having a curl coefficient ω within a limited range is selected;

[0089] The curl coefficient ω is limited to a range of 0<ω<5.1, more preferably 0.5<ω<5.1, and further preferably 0.6<ω<2.1.

[0090] The present invention will be described in detail below through examples.

[0091] In the following examples, wet tensile elongation at break is measured by an elongation at break tester, and the measurement method refers to the international standard ISO 1184-1983 "Determination of tensile properties of plastic films", and the light transmittance and haze are measured by a haze meter, and the measurement method refers to the national standard GB / T 2410-2008 "Determination of light transmittance and haze of transparent plastics"; unless otherwise specified, the raw materials or reagents used are conventional commercially available products.

[0092] Example 1

[0093] The structure of the film curling evaluation device is shown in Figure 1 , including a box 1 for loading a test solvent, a supporting plate 6 located in the box 1, and a temperature control unit for controlling the temperature of the test solvent in the box 1, the supporting plate 6 being connected to the bottom of the box 1 in a liftable manner; a grid 4 for measuring the size of the film is provided on the surface of the supporting plate 6 in contact with the film, and the grid 4 has scale lines 5 of various specifications; the temperature control unit includes a temperature control component located in the box 1, a temperature display screen 2 located on the box 1, and a switch 3 for controlling the working state of the temperature control component, and an openable and closable cover is provided on the top of the box 1, and a blade 7 detachably connected to the cover is provided on the inner side of the cover.

[0094] A plasticizer and a polyvinyl alcohol resin having a saponification degree of 99.9% are dissolved in a solution to form a 30 wt% polyvinyl alcohol casting solution, which is then filtered using a filter, and then the polyvinyl alcohol casting solution is cast onto a casting drum using a gear pump and a die coater, and then dried at high temperature to form a polyvinyl alcohol polymer film, and then the polyvinyl alcohol polymer film is peeled off from the casting drum, and after heat treatment in an oven, it is rolled up under the condition of controlling the traction coefficient α=10.1 to obtain a polyvinyl alcohol film; the traction coefficient α is calculated by the following formula (V);

[0095] α=N*D formula (V),

[0096] Wherein, N is the winding tension of the film, and D is the specific speed of the roller group, as shown in Table 2 for details.

[0097] The curl evaluation device for the film is used to evaluate the curl of the prepared polyvinyl alcohol film to obtain the curl coefficient ω: water is added to the box 1, the supporting plate 6 is raised above the liquid level and the film sample is placed in the grid 4 on the supporting plate 6, the cover of the water tank 1 is turned over and the film is cut with a blade 7, and a suitable film sample is obtained in combination with the scale line 5 and the initial size of the film sample is measured, as shown in Table 1; the switch 3 is turned on, the required temperature is set to 26°C through the temperature display screen 2, the cooling or heating function is selected, and the set temperature and the real-time temperature are observed, so that the temperature of the water in the box 1 is 26°C;

[0098] The supporting plate 6 is slowly lowered below the liquid surface, and the entire film sample is immersed in water, and then the test is started. The immersion time of the film sample in water is controlled to be 150s;

[0099] The time T0 when the film sample starts to curl after being immersed in water and the total time T when the film sample is immersed in water are recorded and measured in real time, and the curling time coefficient A is calculated by the following formula (II), as shown in Table 1;

[0100] A=(T-T0) / Tformula (II);

[0101] The curling direction index r of the film sample immersed in water, the initial area S of the film sample and the area S1 of the film sample after being immersed in water are measured, and the curling direction coefficient B is calculated by the following formula (III), as shown in Table 1;

[0102] B=|r|*(S-S1) / S Formula (III),

[0103] Among them, if the curling direction is the TD direction, r is +1, if the curling direction is the MD direction, r is -1, and if there is no curling, r is 0;

[0104] The initial length L of the film sample and the length L1 of the film sample after being immersed in water were measured, and the curling swelling coefficient C was calculated by the following formula (IV), as shown in Table 1;

[0105] C = L1 / L formula (IV);

[0106] The curl coefficient ω is calculated by the following formula (I), as shown in Table 2:

[0107] ω=a*A+b*B+c*C;

[0108] Among them, a is the curling time specific gravity, b is the curling direction specific gravity, and c is the curling swelling rate specific gravity. The specific values ​​are shown in Table 2.

[0109] Based on the obtained curl factor ω, a film having a curl factor ω within a limited range is selected.

[0110] The wet tensile elongation at break, light transmittance and haze of the polyvinyl alcohol film obtained in Example 1 were measured. The results are shown in Table 2.

[0111] Example 2

[0112] The film curling evaluation device in Example 1 is used, and the film curling evaluation is performed and the film process is improved according to the method of Example 1. The difference is that different batches of polyvinyl alcohol resins are used to prepare the polyvinyl alcohol film, and the traction coefficient α is controlled to be 8.1. The temperature display screen 2 sets the required temperature to 24°C, so that the temperature of the water in the box 1 is 24°C, and the immersion time of the film sample in water is controlled to be 180s.

[0113] The parameters involved in Example 2 and the data obtained from the test are specifically shown in Tables 1 and 2.

[0114] The wet tensile elongation at break, light transmittance and haze of the polyvinyl alcohol film obtained in Example 2 were measured. The results are shown in Table 2.

[0115] Example 3

[0116] The film curling evaluation device in Example 1 was used, and the film curling evaluation was performed and the film process was improved according to the method in Example 1, except that different batches of polyvinyl alcohol-based resins were used to prepare the polyvinyl alcohol film, and the traction coefficient α was controlled to be 12.0, the temperature display screen 2 was set to the required temperature of 28°C, so that the temperature of the water in the box 1 was 28°C, and the immersion time of the film sample in water was controlled to be 120s.

[0117] The parameters involved in Example 3 and the data obtained from the test are specifically shown in Tables 1 and 2.

[0118] The wet tensile elongation at break, light transmittance and haze of the polyvinyl alcohol film obtained in Example 3 were measured. The results are shown in Table 2.

[0119] Example 4

[0120] Polyvinyl alcohol films were prepared using different batches of polyvinyl alcohol resins according to the method in Example 1, and the traction coefficient α was controlled to be 10.9; the obtained polyvinyl alcohol films were subjected to curling evaluation to obtain the curling coefficient ω: the initial size of the film sample was measured, as shown in Table 1, and the film sample was immersed in water at a temperature of 26° C. for 150 s; the time T0 when the film sample started to curl after being immersed in water and the total time T when the film sample was immersed in water were recorded in real time, and the curling time coefficient A was calculated by the following formula (II), as shown in Table 1;

[0121] A=(T-T0) / Tformula (II);

[0122] The curling direction index r of the film sample immersed in water, the initial area S of the film sample and the area S1 of the film sample after being immersed in water are measured, and the curling direction coefficient B is calculated by the following formula (III), as shown in Table 1;

[0123] B=|r|*(S-S1) / S Formula (III),

[0124] Among them, if the curling direction is the TD direction, r is +1, if the curling direction is the MD direction, r is -1, and if there is no curling, r is 0;

[0125] The initial length L of the film sample and the length L1 of the film sample after being immersed in water were measured, and the curling swelling coefficient C was calculated by the following formula (IV), as shown in Table 1;

[0126] C = L1 / L formula (IV);

[0127] The curl coefficient ω is calculated by the following formula (I), as shown in Table 2:

[0128] ω=a*A+b*B+c*C;

[0129] Among them, a is the curling time specific gravity, b is the curling direction specific gravity, and c is the curling swelling rate specific gravity. The specific values ​​are shown in Table 2.

[0130] Based on the obtained curl factor ω, a film having a curl factor ω within a limited range is selected.

[0131] The wet tensile elongation at break, light transmittance and haze of the polyvinyl alcohol film obtained in Example 4 were measured. The results are shown in Table 2.

[0132] Table 1

[0133] serial number Example 1 Example 2 Example 3 Example 4 Initial length L, cm 8 10 15 12 Initial width, cm 3 3 3 3 <![CDATA[T0,s]]> 149 90 40 1 T,s 150 150 150 150 Curl time coefficient A 0.01 0.40 0.73 0.99 r 1 1 1 1 S 24 30 45 54 S1 12.5 22 15 6 Curl direction coefficient B 0.48 0.27 0.67 0.88 L1 10.5 12.3 17.2 14.8 Curl swelling coefficient C 1.31 1.23 1.15 1.23

[0134] Table 2

[0135] serial number Example 1 Example 2 Example 3 Example 4 a 1 1 1 1 b 1 1 1 1 c 1 1 1 1 Curl coefficient ω 1.8 1.9 2.5 3.1 N 10 9 12 10 D 1.01 0.9 1 1.09 Traction coefficient α 10.1 8.1 12.0 10.9 Wet tensile elongation at break, % 683 620 586 644 Light transmittance, % 91.91 91.77 91.52 91.86 Haze, % 0.03 0.08 0.16 0.04

[0136] Example 5-Example 10

[0137] The film curl evaluation device in Example 1 was used to prepare the film and perform curl evaluation according to the method in Example 1, except that the curl coefficient ω and traction coefficient α of the polyvinyl alcohol film, the parameters involved and the test data are specifically shown in Tables 3 and 4.

[0138] The wet tensile elongation at break, light transmittance and haze of the polyvinyl alcohol films obtained in Examples 5 to 10 were measured. The results are shown in Table 4.

[0139] Table 3

[0140] serial number Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Initial length L, cm 8 10 15 12 10 10 Initial width, cm 3 3 3 3 3 3 <![CDATA[T0,s]]> 150 25.5 150 82.5 1 1 T,s 150 150 150 150 150 150 Curl time coefficient A 0 0.83 0 0.45 0.99 0.99 r 0 1 0 1 1 1 S 24 30 45 36 30 30 S1 1 25 1 9 11 1 Curl direction coefficient B 0 0.17 0 0.75 0.63 0.97 L1 10.7 13 17.8 15.6 12.9 13.2 Curl swelling coefficient C 1.34 1.3 1.19 1.3 1.29 1.32

[0141] Table 4

[0142] serial number Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 a 0 1 0 1 1 1 b 0 1 0 1 1 1 c 1 1 1 1 1 1 Curl coefficient ω 1.34 2.29 1.19 2.5 2.91 3.28 N 0.98 1.08 0.99 1.15 1.095 1.125 D 5 13 1 14 15 16 Traction coefficient α 4.9 14.0 1.0 16.1 16.4 18.0 Wet tensile elongation at break, % 638 609 622 613 537 542 Light transmittance, % 91.42 90.89 91.09 91.14 90.43 90.26 Haze, % 0.55 0.62 0.44 0.49 1.12 1.03

[0143] It can be seen from the data in Table 2 and Table 4 that by controlling the traction coefficient α when preparing the film and then using the film curling evaluation method provided by the present invention to obtain the curling coefficient ω of the film in water, the curling degree of the film can be quantified. By selecting a film with a curling coefficient ω within a specific range, the elongation at break of the wet film is significantly improved, the transmittance can be increased from 90.26% to 91.91%, and the haze can be reduced from 1.12% to 0.03%.

[0144] Test Example 1

[0145] The polyvinyl alcohol films in Example 1 and Example 9 were taken out after being immersed in water and observed, and the results were compared with those in Example 1 and Example 9. Figure 2 The curl degree was graded according to the different curl degree measurement standards shown in Table 5.

[0146] Table 5

[0147] serial number Initial length Curl degree grading Example 1 8 Unrolled Example 2 10 slight Example 3 15 slight Example 4 12 slight Example 5 8 Unrolled Example 6 10 slight Example 7 15 Unrolled Example 8 12 serious Example 9 10 More serious Example 10 10 More serious

[0148] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A film curling evaluation method, characterized in that: The method includes: Immersing the film sample in a test solvent, and measuring the curling time coefficient A, curling direction coefficient B and curling swelling rate coefficient C of the film sample in the test solvent; The curling coefficient ω of the film in the test solvent is calculated by the curling time coefficient A, the curling direction coefficient B and the curling swelling rate coefficient C, and the curling degree of the film is evaluated by the curling coefficient ω.

2. The film curling evaluation method according to claim 1, characterized in that: The curl coefficient ω is calculated by the following formula (I): ω=a*A+b*B+c*C; Wherein, a is the curling time specific gravity, b is the curling direction specific gravity, and c is the curling swelling rate specific gravity; when the film sample is immersed in the test solvent, if curling occurs, a and b are both 1, and if no curling occurs, a and b are both 0. If the length and / or width of the film sample changes, c is 1, and if the length and width of the film do not change, c is 0.

3. The film curling evaluation method according to claim 1, characterized in that: The process of determining the curling time coefficient A includes: determining the time T0 when the film sample starts curling after being immersed in the test solvent and the total time T when the film sample is immersed in the test solvent, and calculating the curling time coefficient A by the following formula (II); A=(T-T0) / T formula (II).

4. The film curling evaluation method according to claim 1, characterized in that: The process of determining the curling direction coefficient B includes: determining the curling direction index r of the film sample immersed in the test solvent, the initial area S of the film sample, and the area S1 of the film sample after being immersed in the test solvent, and calculating the curling direction coefficient B by the following formula (III); B=|r|*(S-S1) / S Formula (III), Among them, if the curling direction is the TD direction, the value of r is +1, if the curling direction is the MD direction, the value of r is -1, and if there is no curling, the value of r is 0.

5. The film curling evaluation method according to claim 1, characterized in that: The process of determining the curling swelling coefficient C includes: determining the initial length L of the film sample and the length L1 of the film sample after being immersed in the test solvent, and calculating the curling swelling coefficient C by the following formula (IV); C=L1 / L formula (IV).

6. The film curling evaluation method according to any one of claims 1 to 5, characterized in that: The test solvent is water, the immersion temperature is 24-28°C, and the immersion time is 120-180s; Preferably, the process of evaluating the curl degree of the film includes: selecting a film with a curl coefficient ω satisfying 0<ω<5.1; more preferably 0.5<ω<5.1, and further preferably 0.6<ω<2.

1.

7. A film curling evaluation device, characterized in that: The device is used for carrying out the film curling evaluation method as described in any one of claims 1 to 6, comprising a box (1) for loading a test solvent, a supporting plate (6) located in the box (1), and a temperature control unit for controlling the temperature of the test solvent in the box (1), wherein the supporting plate (6) is connected to the inner wall of the box (1) in a liftable manner; a grid (4) for measuring the size of the film is provided on the surface of the supporting plate (6) in contact with the film, and the grid (4) has scale lines (5) of various specifications.

8. The film curling evaluation device according to claim 7, characterized in that: The temperature control unit comprises a temperature control component located in the box (1), a temperature display screen (2) located on the box (1), and a switch (3) for controlling the working state of the temperature control component; Preferably, the top of the box body (1) is provided with an openable and closable cover plate, and a blade (7) detachably connected to the cover plate is provided on the inner side of the cover plate.

9. Use of the film curling evaluation method according to any one of claims 1 to 6, or the film curling evaluation device according to claim 7 or 8 in film processing; Preferably, the film is a polyvinyl alcohol film.

10. A polyvinyl alcohol film, characterized in that: The polyvinyl alcohol film is obtained by rolling up a polyvinyl alcohol film under a condition of controlling a traction coefficient α, and then screening using the film curling evaluation method according to any one of claims 1 to 6, wherein the curling coefficient ω of the polyvinyl alcohol film is 0<ω<5.1; The traction coefficient α is calculated by the following formula (V): α=N*D formula (V), Wherein, N is the winding tension of the film, and D is the specific speed of the roller group; Preferably, the curl coefficient ω of the polyvinyl alcohol film is 0.5<ω<5.1, and more preferably 0.6<ω<2.1; The traction coefficient α is controlled to be 0.9<α<16.2, more preferably 4.9<α<14, and further preferably 10<α<13.1.

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