JP6682423B2 - Method for measuring plasticizer content - Google Patents

Description

  The present invention relates to a method for measuring the content of a plasticizer contained in a polyvinyl alcohol film. The present invention also relates to a method for producing a polyvinyl alcohol film using the above measuring method.

  Polyvinyl alcohol films are used for various purposes because they have excellent properties such as mechanical properties, transparency, oxygen barrier properties, cryogenic electrical insulation properties and oil resistance. Further, it is also used as a raw film of a polarizing film used for a polarizing plate of a liquid crystal display.

  Examples of the method for producing a polyvinyl alcohol film include a method for forming a film by drying a film forming stock solution containing polyvinyl alcohol and water. At this time, a plasticizer is added to the film-forming stock solution for the purpose of imparting flexibility to the obtained film.

  The content of the plasticizer in the polyvinyl alcohol film is one of the important control items in the manufacturing process in order to obtain a film of constant quality. Therefore, there is a demand for a method capable of measuring the content of the plasticizer rapidly and accurately.

  In Patent Document 1, a calibration curve or an equation showing the relationship between the amount of plasticizer in the plasticized resin film and the refractive index of this plasticized resin film is prepared, and the refractive index of the plasticized resin film to be quantified is prepared. A method for quantifying a plasticizer in a plasticized resin film is described, which comprises measuring and quantifying the amount of the plasticizer in the plasticized resin film based on the calibration curve or the formula. According to this quantification method, the amount of the plasticizer in the plasticized resin film can be easily and accurately quantified. However, the accuracy of the measurement was not yet sufficient.

JP-A-6-273327

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a method capable of quickly and accurately measuring the content of a plasticizer.

  The above-mentioned problem is a method for measuring the content of a plasticizer contained in a film containing polyvinyl alcohol and a plasticizer; immersing the film in a solvent that does not dissolve the polyvinyl alcohol and dissolves the plasticizer. , An extraction step of extracting a plasticizer contained in the film to obtain an extract, a dry mass measurement step of measuring the mass after drying the film after being immersed in the solvent, and a refractive index of the extract Based on the calibration curve prepared in advance, a concentration calculating step of calculating the concentration of the plasticizer contained in the extract from the refractive index, the mass of the extract, the concentration of the plasticizer, and the dry mass. A solution is provided by providing a measuring method characterized by comprising a content rate calculating step of calculating a content rate of a plasticizer contained in the film.

  At this time, it is preferable to further include, before the concentration calculating step, a separation step of passing the extraction liquid obtained in the extraction step through a solid phase extraction column to obtain a separation liquid. It is also preferred that the plasticizer is a polyhydric alcohol.

  The above-mentioned problem is a method for producing a film using a film-forming stock solution in which a polyvinyl alcohol and a plasticizer are dissolved in a solvent, and based on the content of the plasticizer measured by the above method, the film-forming stock solution. It is also solved by providing a method of manufacturing a film, characterized by increasing or decreasing the amount of plasticizer therein.

  According to the measuring method of the present invention, the content of the plasticizer can be measured quickly and accurately. When this measuring method is used, the content of the plasticizer can be adjusted quickly and accurately in the production of the film, so that the quality of the film can be stabilized.

3 is a diagram in which the refractive index is plotted against the glycerin concentration in Example 1. FIG.

  The present invention relates to a method for measuring the content of a plasticizer contained in a film containing polyvinyl alcohol (hereinafter sometimes abbreviated as PVA) and a plasticizer. The measurement method of the present invention comprises an extraction step, a dry mass measurement step, a concentration calculation step, and a content rate calculation step. Hereinafter, each step will be described.

(Extraction process)
The extraction step is a step of immersing a film containing PVA and a plasticizer in a solvent to extract the plasticizer contained in the film to obtain an extract.

  The solvent in which the film is dipped needs to be a solvent that does not dissolve PVA and can dissolve the plasticizer. Water is suitable as such a solvent. A small amount of components other than water, such as an alkali metal salt such as sodium chloride and an alcohol such as methanol, can be added to the solvent. The content of components other than water is preferably 50% by mass or less, and more preferably 20% by mass or less.

  When the film is immersed, if the temperature of the solvent is too high, PVA may be dissolved. From this viewpoint, the temperature of the solvent is preferably 60 ° C or lower, more preferably 30 ° C or lower. The temperature of the solvent is usually 0 ° C or higher, preferably 10 ° C or higher. If the immersion time is too long, PVA may dissolve. The immersion time is set in relation to the temperature of the solvent, but is preferably 30 seconds to 30 minutes. The amount of the solvent is usually 500 to 10000 parts by mass with respect to 100 parts by mass of the film.

  As a method of extracting the plasticizer from the film, for example, a method of cutting the film into an appropriate size, placing the film and the solvent in a sealed container, immersing the film in the solvent, and shaking the container, etc. Can be mentioned. Moreover, the method using a Soxhlet extractor is also mentioned.

  In the measurement method of the present invention, from the viewpoint of increasing the measurement accuracy, the extract obtained in the above “extraction step” is passed through a solid phase extraction column to obtain a separated solution before the “concentration calculation step” described below. It is preferable to further include a “separation step”. When the film is immersed in a solvent, a small amount of PVA having a low degree of polymerization may be dissolved. In addition, a small amount of additives such as surfactants may be extracted. These substances can be removed by passing the extract through the solid phase extraction column. Examples of the packing material for the solid phase extraction column include styrene resin, methacrylate resin, silica gel, and alumina. Among them, a styrene resin is preferable, and a crosslinked polystyrene resin is more preferable, from the viewpoint that the purity of the filler is high and the influence of trace metals is small.

(Dry mass measurement process)
The dry mass measurement step is a step in which the film after being immersed in a solvent is dried, and then the mass of the film (hereinafter, also referred to as a dry mass) is measured. The method for drying the film is not particularly limited, and heat drying, vacuum drying or the like can be adopted. When the film is dried by heating, the heating temperature is preferably 100 to 180 ° C. The heating time is set in relation to the heating temperature, but is usually 1 to 60 minutes.

(Concentration calculation process)
In the concentration calculation step, first, the refractive index of the extract is measured. The method for measuring the refractive index is not particularly limited, and examples thereof include a method using an Abbe refractometer. Then, the concentration of the plasticizer contained in the extract is obtained based on the calibration curve prepared in advance.

  As a method of creating a calibration curve, prepare several standard solutions with defined plasticizer concentrations, measure the refractive index of the standard solutions, then plot the relationship between concentration and refractive index There is a method of obtaining a straight line or a curve by performing regression analysis on.

(Content rate calculation process)
The content calculation step includes the concentration of the plasticizer contained in the extract calculated in the "concentration calculation step", the dry mass of the film measured in the "dry mass measurement step" and the mass of the extract contained in the film. This is a step of calculating the content rate of the plasticizer to be used. Specifically, the mass of the extractant is multiplied by the concentration of the plasticizer contained in the extract to obtain the mass of the plasticizer contained in the extract. Then, the content of the plasticizer with respect to the amount of PVA in the film can be obtained by dividing the mass of the plasticizer contained in the extract by the dry mass.

  Here, the mass of the extract can be directly weighed, but can be determined from the mass of the solvent used in the extraction step, the mass of the film used for the measurement, and the dry mass. In this case, the difference between the mass of the film used for the measurement and the dry mass corresponds to the content of the plasticizer contained in the film. The mass of the extraction liquid is obtained by adding the mass of the solvent used in the extraction step to this difference.

  The film used for measurement is not particularly limited as long as it is a film containing PVA and a plasticizer. Moreover, the method for producing the film is not particularly limited. The PVA and film will be described below.

(PVA)
Examples of PVA used in the production of the film include unmodified PVA obtained by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester, and modified polyvinyl ester obtained by copolymerizing a vinyl ester and a comonomer. The modified PVA obtained may be mentioned. The type of vinyl ester is not particularly limited, but vinyl acetate is preferable from the viewpoint of ease of production of PVA, availability, cost, and the like. The catalyst used for saponification is, for example, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide, an alkali catalyst such as sodium methylate, or an acid catalyst such as a mineral acid.

  The polymerization method of the vinyl ester may be any of batch polymerization, semi-batch polymerization, continuous polymerization, semi-continuous polymerization, etc., and the polymerization method may be a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, or the like. Known methods can be applied. The polymerization initiator used when subjecting the vinyl ester to the polymerization reaction may be selected from known polymerization initiators such as azo-based initiators, peroxide-based initiators and redox-based initiators depending on the polymerization method. it can.

  The degree of polymerization of PVA is preferably 500 to 5000. When the degree of polymerization of PVA is less than 500, the mechanical strength of the obtained film is insufficient and breakage easily occurs. The degree of polymerization is more preferably 700 or more. On the other hand, when the degree of polymerization of PVA exceeds 5000, the production efficiency at the time of producing a film may decrease. The degree of polymerization is more preferably 4000 or less. The degree of polymerization of PVA is a value measured according to the description of JIS K6726-1994.

  From the viewpoint of durability of the obtained film, the saponification degree of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, and further preferably 99 mol% or more. The saponification degree of PVA is a value measured according to the description of JIS K6726-1994.

  Examples of the plasticizer contained in the film used in the measuring method of the present invention include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, polyhydric alcohols such as trimethylolpropane, and the like. Aliphatic polyhydric alcohols having 2 to 8 carbon atoms are preferable. These plasticizers may be used alone or in combination of two or more. Among these, glycerin is more preferable from the viewpoint of improving the stretchability and the viewpoint of being inexpensive and easily available.

  The amount of the plasticizer used is preferably 1 to 20 parts by mass, more preferably 3 to 17 parts by mass, and further preferably 5 to 15 parts by mass with respect to 100 parts by mass of PVA. When the content is 1 part by mass or more, the stretchability of the film is further improved. On the other hand, when the content is 20 parts by mass or less, it is possible to prevent the film from becoming too flexible and the handleability being deteriorated.

  In addition, in the production of the film, in addition to the above plasticizer, a surfactant, an antioxidant, an ultraviolet absorber, a lubricant, a pH adjuster, a filler, a colorant, an antiseptic, a fungicide, etc. may be added, if necessary. It can be appropriately blended. The proportion of the total of PVA and the plasticizer in the film is preferably 90% by mass or more, more preferably 95% by mass or more, and 99% by mass or more, based on the dry mass of the film. More preferable.

(Film manufacturing method)
The method for producing the film is not particularly limited, and usually includes a method using a stock solution for film formation in which PVA and a plasticizer are dissolved in a solvent.

  Examples of the solvent used for the preparation of the film-forming stock solution include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and triethylene glycol. Methylolpropane, ethylenediamine, diethylenetriamine and the like can be mentioned, and one or more of these can be used. Among them, water is preferable from the viewpoints of low environmental load and recoverability.

  The volatile content rate of the film-forming stock solution (content ratio of volatile components such as solvents removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc., but is 50 to 95. It is preferably mass%. Since the volatile matter content of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, and filtration and defoaming are smoothly performed when preparing the film-forming stock solution, and there are few foreign matters and defects. Will be easier to manufacture. On the other hand, when the volatile content of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and the industrial PVA film can be easily manufactured.

  Examples of the film forming method for forming a film using the above-mentioned stock solution for forming a film include a casting film forming method, a wet film forming method, and a gel film forming method. These film forming methods may be used alone or in combination of two or more. The film can be dried or heat-treated as required. Among them, the casting film-forming method in which the film is produced by casting the stock solution for film formation and then drying it is preferable from the viewpoint of obtaining a film having a uniform film thickness and width.

  A preferred embodiment of the present invention is a method for producing a film using a film-forming stock solution in which polyvinyl alcohol and a plasticizer are dissolved in a solvent, based on the content of the plasticizer measured by the measuring method of the present invention. , To increase or decrease the amount of plasticizer in the stock solution for film formation.

  In the production of a film, in order to obtain a film having a certain quality, a method is adopted in which the produced film is extracted and analyzed, and the analysis result is fed back to the production process. As the analysis method at this time, the measuring method of the present invention can be preferably used.

  As an example of the method for producing a film using the measuring method of the present invention, the measuring method of the present invention is programmed in an arithmetic unit such as a computer, and the content of the plasticizer with respect to the amount of PVA is calculated by the arithmetic unit. , A method of feeding back to the manufacturing process. The specific method is as follows. First, data indicating the relationship between the plasticizer concentration and the refractive index is stored in advance in the arithmetic unit. Then, during the production of the film, a sampling inspection is performed at a predetermined timing, and the mass of the solvent used in the extraction step, the measured refractive index, the mass of the film used for the measurement, and the dry mass are input to the arithmetic unit. Determine the content of plasticizer contained in the film. Then, the amount of the plasticizer charged in the stock solution is increased or decreased based on the obtained content rate. At this time, the control device can automatically control the increase or decrease in the amount of the plasticizer used based on the content rate output by the arithmetic device.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples below.

(Creation of calibration curve)
An aqueous solution having a glycerin concentration of 0, 1500, 3000, and 4500 ppm was prepared, the refractive index of each aqueous solution was measured, and the obtained refractive index was plotted against the glycerin concentration. The results are shown in FIG. For the measurement of the refractive index, a refractometer "ABBEMAT550" manufactured by Anton Pearl Japan Co., Ltd. was used. The measurement temperature was 23 ° C. The measuring device and the measuring temperature in the (III) concentration calculating step described later are the same as above.

Example 1
(Production of film)
100.00 parts by mass of PVA having a viscosity average degree of polymerization of 2,400 (saponification degree of 99.9 mol%), 9.00 parts by mass of glycerin as a plasticizer, 0.20 parts by mass of sodium polyoxyethylene lauryl ether sulfate as a surfactant, and A stock solution for film formation (volatile content: 90% by mass) was prepared. The stock solution for film formation was cast on a metal drum at 80 ° C. and dried until the volatile content (water content) of the stock solution for film formation was 5% by mass. By doing so, a long unheated film having a thickness of 30 μm, a length of 1.5 m and a width of 30 cm was obtained. Then, this unheat-treated film was heat-treated at 120 ° C. for 5 minutes to obtain a film 1. When the content of the plasticizer in the film 1 is calculated from the charged amount of the plasticizer, the film 1 contains 9.00 parts by mass of the plasticizer per 100 parts by mass of PVA.

(Measurement of content of plasticizer in film)
The plasticizer content is obtained by performing the following (I) extraction step, (II) dry mass measurement step, (III) concentration calculation step, and (IV) content rate calculation step on the obtained film 1. It was Moreover, the variation of the measurement data was evaluated.

(I) Extraction Step After the film 1 was cut into a size of 4 cm × 20 cm, the mass of the film 1 was measured. The mass at this time is W ₁ . Next, ultrapure water having a mass 30 times the mass (W ₁ ) of the film 1 was put into a screw tube to keep the liquid temperature at 25 ° C., and the film 1 was put and the lid was closed. The mass of ultrapure water placed in the screw tube is W ₂ . Then, the plasticizer contained in the film 1 was extracted by shaking the screw tube for 3 minutes at 25 ° C. Then, the film 1 was taken out from the screw tube to obtain an extract.

(II) Dry mass measurement step The film 1 taken out from the screw tube was heated and dried at 150 ° C. for 30 minutes to obtain the dry film 1, and the dry mass (W ₃ ) was measured.

(III) Concentration Calculation Step The refractive index of the extract obtained in the above (I) extraction step was measured. Then, the concentration (C ₁ ) of the plasticizer contained in the extract was calculated using the calibration curve prepared in advance.

(IV) Content calculation step (I) The mass (W ₄ ) of the extract obtained in the extraction step was determined by the following formula (1).
Mass of extract (W ₄ )
= Mass of ultra-pure water _(W 2) + _(Film 1 mass _{(W 1)} - dry weight _(W 3)) ₍₁₎

Then, the mass (W ₄ ) of the extract obtained by the formula (1), the dry mass (W ₃ ) obtained in the dry mass measurement step (II), and the concentration (C) of the plasticizer obtained in the concentration calculation step (III) ₁ ) was used to calculate the content (parts by mass) of the plasticizer contained in the film according to the following formulas (2) and (3).

Mass of plasticizer contained in the extract (W ₅ )
= Extract of mass concentration of _{(W 4)} × plasticizer _(C 1) ₍₂₎
Content of plasticizer with respect to the amount of PVA (parts by mass)
= (Mass of the plasticizer contained in the extract _(W 5) / dry weight _{(W 3)) × 100 (} 3)

  As a result, the plasticizer content was calculated to be 9.23% by mass. It took 40 minutes for the plasticizer content to be calculated in the (IV) content calculation step after the (I) extraction step, (II) dry mass measurement step, (III) concentration calculation step. . Table 1 shows the results.

(Evaluation of variations in measurement data)
According to the above method, the content of the plasticizer in Film 1 was measured 10 times, and the arithmetic mean and standard deviation were obtained. Then, the standard deviation was divided by the arithmetic mean to determine the coefficient of variation, which was used as an index of the variation in the measured data. The results are shown in Table 1.

Example 2
The content of the plasticizer was determined by the method described in Example 1 except that the following (V) separation step was added before the (III) concentration calculation step, and the variation in the measurement data was evaluated. The results are shown in Table 1.

(V) Separation step (I) 0.5 mL of the extract obtained in the extraction step was sampled, passed through a solid phase extraction column at a flow rate of 2 minutes / mL, and the passed solution was received by a 6 ml screw tube, The separated liquid was used as an extract in the (III) concentration calculation step and the (IV) content calculation step. The solid phase extraction column is "SOLA WAX" manufactured by Thermo Fisher Scientific (filler: surface-modified styrenedivinylbenzene particles). In the (IV) separation step, a column was used, which was repeatedly washed with 1 mL of ultrapure water 10 times or more and dried at room temperature for 12 hours or more in a desiccator containing a desiccant.

  As a result, the content of the plasticizer was calculated to be 9.05 parts by mass. (I) Extraction step, (II) Dry mass measurement step, (V) Separation step, (III) Concentration calculation step, (IV) Content rate calculation step The time required until the plasticizer content rate is calculated Was 45 minutes. Table 1 shows the results.

Example 3
In the production of the film, the film 2 was produced in the same manner as in Example 1 except that the amount of glycerin as the plasticizer was changed to 11.00 parts by mass. Then, in the same manner as in Example 1, the content of the plasticizer in the film 2 was determined and the variation in the measurement data was evaluated. The results are shown in Table 1.

Example 4
In the production of the film, PVA film 2 was produced in the same manner as in Example 1 except that the amount of glycerin as the plasticizer was changed to 11.00 parts by mass. Then, in the same manner as in Example 2, the content rate of the plasticizer contained in the film 2 was obtained and the variation in the measurement data was evaluated. The results are shown in Table 1.

Example 5
In the production of the film, the film 3 was produced in the same manner as in Example 1 except that the amount of glycerin as the plasticizer was changed to 13.00 parts by mass. Then, in the same manner as in Example 1, the content rate of the plasticizer contained in the film 3 was obtained, and the variation in the measurement data was evaluated. The results are shown in Table 1.

Example 6
In the production of the film, the film 3 was produced in the same manner as in Example 1 except that the amount of glycerin as the plasticizer was changed to 13.00 parts by mass. Then, in the same manner as in Example 2, the content rate of the plasticizer contained in the film 3 was obtained, and the variation in the measurement data was evaluated. The results are shown in Table 1.

Comparative Example 1
In the production of the film, a PVA film was produced in the same manner as in Example 1 except that the amount of glycerin which was the plasticizer was changed to 11.00 parts by mass to obtain film 2. And the content rate of the plasticizer was calculated | required by performing the following (i) Soxhlet extraction process, (ii) drying process, and (iii) gas chromatography measurement process with respect to the obtained film 2. Moreover, the variation of the measurement data was evaluated in the same manner as in Example 1.

(I) Soxhlet extraction step After the film 2 was cut into a size of 20 cm × 20 cm, it was further cut into a size of about 0.1 × 5 cm. Soxhlet extraction was performed on the cut film 2 with a methanol solvent for 2 hours to obtain an extract. The mass of the extract obtained at this time was defined as W ₆ .

(Ii) Drying Step After the above (i) Soxhlet extraction step, the finely cut film 2 was taken out from the Soxhlet extractor and dried by heating at 150 ° C. for 30 minutes, and then the mass of the dried film 2 was measured. The dry mass at this time was defined as W ₇ .

(Iii) Gas Chromatography Measurement Step A methanol solution to which naphthalene was added as an internal standard and an extract obtained by Soxhlet extraction were mixed in the same mass. Using this solution as a measurement liquid for gas chromatography, the concentration of the plasticizer in the solution was determined by gas chromatography. Then, the content (parts by mass) of the plasticizer with respect to the amount of PVA was obtained by the following formulas (4) and (5).

Mass of plasticizer contained in Soxhlet extract (W ₈ )
= Soxhlet extract of mass _{(W 6)} × Concentration of the plasticizer contained in the Soxhlet extract _(C 2) ₍₄₎
Content of plasticizer with respect to the amount of PVA (parts by mass)
= (Mass of the plasticizer contained in the Soxhlet extract _(W 8) / dry weight _{(W 7)) × 100 (} 5)

The concentration (C ₂ ) in the above formula (4) is a value obtained by a gas chromatography device.

  As a result, the content of the plasticizer was calculated to be 10.90 parts by mass. The time required until the content of the plasticizer was calculated in the (iii) gas chromatography measurement step after the (i) Soxhlet extraction step, (ii) drying step was 150 minutes. Table 1 shows the results.

  As is clear from the above examples, according to the measurement / quantification method of the present invention, the content of the plasticizer in the PVA film can be accurately measured in a short time.

Claims (4)

A method for measuring the content of a plasticizer contained in a film containing polyvinyl alcohol and a plasticizer;
An extraction step of obtaining an extract by extracting the plasticizer contained in the film by immersing the film in a solvent that does not dissolve the polyvinyl alcohol and dissolves the plasticizer,
A dry mass measurement step of measuring the mass after drying the film after being immersed in the solvent,
Measuring the refractive index of the extract, based on a calibration curve created in advance, a concentration calculation step of calculating the concentration of the plasticizer contained in the extract from the refractive index,
A measuring method comprising a content rate calculating step of calculating the content rate of the plasticizer contained in the film from the mass of the extract, the concentration of the plasticizer, and the dry mass.   The measuring method according to claim 1, further comprising a separation step of passing the extract obtained in the extraction step through a solid-phase extraction column to obtain a separated solution before the concentration calculation step.   The measuring method according to claim 1 or 2, wherein the plasticizer is a polyhydric alcohol.   A method for producing a film using a film-forming stock solution in which a polyvinyl alcohol and a plasticizer are dissolved in a solvent, based on the content of the plasticizer measured by the method according to claim 1. A method for producing a film, which comprises increasing or decreasing the amount of a plasticizer in the stock solution for film formation.

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