CN112858084B - A method for evaluating the quality of PVA optical films - Google Patents

Abstract

The invention discloses a method for evaluating the quality of a PVA optical film. The binding state of PVA in the film, and then evaluate the quality of PVA optical film. The method of the invention has simple operation and reliable results.

Description

A method for evaluating the quality of PVA optical films

technical field

The invention belongs to the field of polarizers, and in particular relates to a method for evaluating the quality of a PVA optical film.

Background technique

Apple's iPhone 12 series this year is equipped with OLED screens, which have higher color contrast and near-perfect color accuracy than LCD screens, which are almost indistinguishable to the naked eye. The core components of display panels contain polarizers, and polyvinyl alcohol (PVA) optical films are key materials for producing polarizers.

The formed PVA optical film is pre-swollen, washed with water, dyed with iodine, uniaxially stretched, and cured with boric acid to form a polarizing film, and then a protective film is attached on both sides to obtain a polarizing film. The production process of PVA optical film is as follows: PVA, plasticizer (usually glycerin) and additives are added to water to prepare a certain concentration of PVA stock solution, which is defoamed and homogenized by an extruder and casted to form a film. The indicators for directly evaluating the quality of PVA optical films include stretch ratio, tensile strength, light transmittance, haze, etc. However, these quality indicators can only reflect the performance of PVA film in one aspect, but cannot reflect the microstructure of PVA optical film. The quality of produced polarizers is not completely related to these indicators, especially the uniformity of dyeing after stretching. At present, the front-end PVA optical film is divided into high-quality products, mid-end products, low-end products and inferior products according to the performance of downstream production polarizers. . Therefore, it is of great significance to find a convenient method for evaluating PVA optical films.

The plasticizer used today is usually glycerol. The better the combination of glycerin and PVA in the film, the more uniform the distribution of glycerol in the film, the better the plasticizing effect of the PVA film, the higher the downstream stretching multiple, The better the dyeing uniformity, the better the quality of the polarizing film made. Glycerol will be completely washed out by swelling water before downstream dyeing, and glycerol in PVA molecules will be gradually replaced by water molecules during swelling and washing process. According to the research of the present invention, it is found that the dissolution rate of glycerin in the swelling process and the swelling time will show a certain correlation. The relationship between the dissolution rate of glycerin from the PVA film and the swelling time can determine the combination of glycerol and PVA in the film condition to assess product quality.

SUMMARY OF THE INVENTION

Based on the shortcomings of the above-mentioned prior art, the present invention provides a method for evaluating the quality of the PVA optical film, in order to realize timely, accurate and convenient measurement of the quality of the PVA optical film.

The present invention adopts the following technical solutions for realizing the purpose of the invention:

A method for evaluating the quality of PVA optical film, which is characterized by: swelling the PVA optical film, and judging the relationship between the plasticizer and the PVA in the film by the relationship between the dissolution rate of the plasticizer in the PVA optical film and the swelling time. Combined condition, and then evaluate the quality of PVA optical film.

Further, the plasticizer is glycerin. The method specifically includes the following steps:

Step 1. After equilibrating several PVA optical films of equal quality under constant temperature and humidity, put them into water for swelling, and set the swelling time as t _i , i=0, 1, 2, 3..., where t ₀ =0s;

Step 2. After the swelling is over, take out the film and absorb the moisture on the surface of the film, then add it to the water, heat to fully dissolve the film, and then test the plasticizer glycerin concentration in the solution according to GB/T 13216.6-91, so as to obtain swelling. The residual glycerin mass m _i in the film after moistening time t _i , and the mass of dissolved glycerin in the film at time t _i+1 is calculated as the percentage of the initial glycerin mass in the film W _i+1 : W _i+1 =(m ₀ -m _i+1 )/m ₀ ;

Step 3. According to the result of Step 2, calculate the dissolution rate v _i+1 of glycerol in the film at time t _i +1:

v _i+1 =(W _i+1 -W _i )/(t _i+1 -t _i )

Step 4. According to the result of step 3, take the swelling time t _i+1 as the abscissa and the logarithm lnv _i+1 of the dissolution rate v _i+ 1 as the ordinate, draw the glycerol dissolution rate-swelling time relationship curve and Linear fitting was carried out, and the combination of plasticizer and PVA in the film was ^judged according to the linear determination coefficient R2 of the fitted curve, and then the quality of the PVA optical film was evaluated.

Further, the larger the coefficient of linear determination, the better the combination of the plasticizer and the PVA in the film, and the better the quality of the PVA optical film.

Further, set 15s≤t _i+ 1≤60s.

Further: if R ² ≥0.990, the PVA optical film to be evaluated is a superior product; if 0.855≤R ² <0.990, the PVA optical film to be evaluated is a mid-end product; if 0.75≤R ² <0.855, it is to be evaluated The PVA optical film is a low-end product; if R ² <0.75, the PVA optical film to be evaluated is an inferior product.

Further, in step 1, the equilibrium constant temperature and humidity conditions are 25±0.5° C., 55±1 RH%, and the equilibrium time is 6-24h.

Further, in step 1, the temperature of the water used for swelling is 30±0.5°C.

Compared with the prior art, the beneficial effects of the present invention are embodied in:

The invention utilizes the relationship between the dissolution rate of the plasticizer (glycerol) and the swelling time to judge the bonding state of the plasticizer and the PVA in the film, and then evaluate the quality of the PVA optical film. Film production section to improve production efficiency.

Description of drawings

Fig. 1 is the relation curve of glycerol dissolution rate and swelling time of superior product I in Example 1;

Figure 2 is the relationship curve of the glycerol dissolution rate and swelling time (within 15-60s) of the superior product I in Example 1 and its linear fitting curve.

Detailed ways

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and provides detailed implementation modes and specific operation processes, but the protection scope of the present invention is not limited to the following implementations example.

The following examples are without special instructions, and the raw materials and reagents used are all commercially available conventional materials without special treatment.

Example 1

In order to verify the reliability of the method of the present invention, several PVA optical films of different qualities (superior grade I, superior grade II, superior grade III, mid-end grade I, mid-end grade II, mid-end grade III, low-end grade grade Product I, low-end product II, inferior product I, inferior product II), respectively, carry out quality assessment according to the method of the present invention, and the specific steps are as follows:

Step 1. Cut a number of film samples with a mass of 5.0g to be evaluated, put them in an environment with a temperature of 25°C and a humidity of 55RH% for 12 hours, and then put them into 30°C water for different times of swelling. The swelling time is t _i (i=0, 1, 2, 3...) are 0s, 5s, 10s, 15s, 20s, 25s, 30s, 40s, 50s, 60s, 70s, 90s, 100s, 120s, 150s, 200s, 250s , 300s.

Step 2. After the swelling is completed, take out the film and absorb the moisture on the surface of the film, then add it to distilled water, heat to 80°C to fully dissolve the film, and then test the plasticizer glycerin concentration in the solution according to GB/T 13216.6-91 , so as to obtain the residual glycerin mass m _i in the film after the swelling time t _i , and calculate the percentage of the mass of glycerol dissolved in the film at the time of swelling t _i+1 to the initial mass of glycerin in the film W _i+1 :W _{i+ 1} =(m ₀ -m _i+1 )/m ₀ . Each swelling time was tested three times, the relative standard deviation was less than or equal to 0.5%, and the average value was taken.

Step 3. According to the result of Step 2, calculate the dissolution rate v _i+1 of glycerin in the film at time t _i+1 . The result of the superior product I is shown in Figure 1:

v _i+1 =(W _i+1 -W _i )/(t _i+1 -t _i )

When the film is immersed in water, glycerol will dissolve from the film. It can be seen from Figure 1 that the dissolution rate of glycerol decreases with the increase of swelling time, and it is basically zero after 150s, and the glycerin in the film has been completely dissolved after 150s. In the initial stage (within 15s), the dissolution rate of glycerol is very fast. The glycerol dissolved in this stage is mainly the glycerol that is not bound to PVA in the membrane and the part that is weakly bound to PVA; At 60s, the dissolution rate decreased greatly, and then the dissolution rate of glycerol was very low until it was 0, because there was very little glycerol in the film after 60s. In 15-60s, the dissolution rate of glycerin gradually decreased with the increase of swelling time, and the dissolved glycerin at this stage is the part that is closely bound to PVA. Therefore, the dissolution rate of glycerol within 15-60s of swelling time can be studied As a standard for judging the binding status of glycerol and PVA in the membrane.

Step 4. The better the combination of glycerol and PVA, the more uniform the distribution of glycerol in PVA, and the decay of glycerol dissolution rate and the swelling time show a certain correlation with the extension of swelling time. Taking the swelling time t _i+1 (within 15 to 60s) as the abscissa and the logarithm lnv _i+1 of the dissolution rate v _i+ 1 as the ordinate, draw the glycerol dissolution rate-swelling time relationship curve and perform a linear simulation. Combined, Figure 2 is the correlation curve of superior grade I. The linear determination coefficient R2 of each sample is shown in Table ¹ .

Table 1

The higher the coefficient of linear determination R ² , the higher the linear correlation of the curve, the gradual decrease of the dissolution rate with the decrease of the glycerin content in the film, the more uniform the distribution of glycerol in the film, and the better the combination of glycerol and PVA. It can be seen that the curve of the superior grade film sample has the highest linear correlation, followed by the mid-end grade, and the inferior grade is the smallest. Therefore, the linear correlation coefficient of the fitted curve can be used as the basis to judge the combination of plasticizer and PVA in the film, and then evaluate the quality of PVA optical film. The evaluation rules are shown in Table 2:

Table 2

PVA film quality Linear coefficient of determination Premium product R²≥0.990 mid-range If 0.855≤R²&lt;0.990 low end 0.75≤R²&lt;0.855 inferior product R²<0.75

Example 2

Take two samples of unknown quality and evaluate them as follows:

Step 1. Cut a number of film samples with a mass of 5.0g to be evaluated, put them in an environment with a temperature of 25°C and a humidity of 55RH% for 12 hours, and then put them into 30°C water for different times of swelling. The swelling time is t _i (i=0, 1, 2, 3...) are 0s, 15s, 20s, 25s, 30s, 40s, 50s, 60s, respectively.

Step 2. After the swelling is completed, take out the film and absorb the moisture on the surface of the film, then add it to distilled water, heat to 80°C to fully dissolve the film, and then test the plasticizer glycerin concentration in the solution according to GB/T 13216.6-91 , so as to obtain the residual glycerin mass m _i in the film after the swelling time t _i , and calculate the mass of dissolved glycerol in the film when the swelling time t _i+1 accounts for the percentage of the initial glycerin mass in the film W _i+1 (unit is % ): Wi ₊₁ =(m ₀ -m _i+1 )/m ₀ . Each swelling time was tested three times, the relative standard deviation was less than or equal to 0.5%, and the average value was taken.

Step 3. According to the result of Step 2, calculate the dissolution rate v _i+1 of glycerol in the film at time t _i +1 (unit is %/s):

v _i+1 =(W _i+1 -W _i )/(t _i+1 -t _i )

Step 4. Take the swelling time t _i+1 (within 15 to 60s) as the abscissa and the logarithm lnv _i+1 of the dissolution rate v _i+ 1 as the ordinate, draw the glycerol dissolution rate-swelling time relationship curve and Perform a linear fit. The linear correlation coefficients R ² of the two samples are 0.870 and 0.815, respectively. According to Table 2, the two samples are evaluated as middle-end products and low-end products, respectively. The feedback results from the downstream are consistent with the evaluation results of this example, which further confirms the present invention. program reliability.

The above descriptions are only exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (5)

1. a method for evaluating the quality of PVA optical film, it is characterized in that: PVA optical film is swelled, by the relationship of the dissolution rate of plasticizer in PVA optical film and swelling time, it is judged that in the plasticizer and the film The combination of PVA, and then evaluate the quality of the PVA optical film; the specific steps include the following: Step 1. After equilibrating several PVA optical films of equal quality under constant temperature and humidity, put them into water for swelling, and set the swelling time as t _i , i=0, 1, 2, 3..., where t ₀ =0s; Step 2. After the swelling is over, take out the film and absorb the moisture on the surface of the film, then add it to the water, heat to fully dissolve the film, and then test the plasticizer glycerin concentration in the solution according to GB/T 13216.6-91, so as to obtain swelling. The residual glycerin mass m _i in the film after moistening time t _i , and the mass of dissolved glycerol in the film at time t _{i +1} is calculated as a percentage of the initial glycerin mass in the film W _{i +1} : Wi ₊₁ = ( m ₀ - m _{i +1} )/ m ₀ ; Step 3. According to the result of Step 2, calculate the dissolution rate v _{i +1} of glycerol in the film at time t _i +1: v _{i +1} = ( W _{i +1} -W _i )/( t _{i +1 -} t _i ) Step 4. According to the result of step 3, take the swelling time t _{i +1} as the abscissa and the logarithm ln v _{i +1} of the dissolution rate v _i +1 as the ordinate, draw the glycerol dissolution rate-swelling time relationship curve And perform linear fitting, according to the linear determination coefficient R ² of the fitting curve to judge the combination of plasticizer and PVA in the film, and then evaluate the quality of PVA optical film; the larger the linear determination coefficient, the better the combination of plasticizer and PVA in the film. The better the condition, the better the quality of the PVA optical film. 2 . The method for evaluating the quality of a PVA optical film according to claim 1 , wherein: 15s≦ t _{i +1} ≦60s is set. 3 . 3. The method for evaluating the quality of a PVA optical film according to claim 1, wherein: if R ² ≥ 0.990, the PVA optical film to be evaluated is a superior product; if 0.855≤R ² <0.990, the PVA optical film to be evaluated is The PVA optical film is evaluated as a mid-end product; if 0.75≤R ² <0.855, the PVA optical film to be evaluated is a low-end product; if R ² <0.75, the PVA optical film to be evaluated is an inferior product. 4. The method for evaluating the quality of a PVA optical film according to claim 1, wherein in step 1, the balanced constant temperature and humidity conditions are 25±0.5° C., 55±1 RH%, and the balanced The time is 6-24h. 5 . The method for evaluating the quality of PVA optical film according to claim 1 , wherein in step 1, the temperature of the water used for swelling is 30±0.5° C. 6 .

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