JP7242211B2 - Method for evaluating transparency of transparent polymeric materials - Google Patents

Description

The present invention relates to a method for evaluating the transparency of transparent polymeric materials.

Molded bodies of transparent polymer materials are used for various purposes. As a method for quantitatively evaluating the transparency of a transparent polymer material, a method using haze (JIS K7136), which is the ratio of diffusely transmitted light to all light transmitted light, is widely known (see, for example, Patent Document 1). . Haze is also referred to as cloudiness, and it has been believed that the smaller the value, the more transparent, and the higher the transparency.
However, depending on the type of material, haze has a low correlation with visual evaluation of transparency, and has a problem of low practicality in transparency evaluation.
As a method for solving this problem, the present inventor measured the tristimulus values of the XYZ color system by measuring the colors of a colorimetric specimen consisting of a transparent flat test piece, and obtained the opacity from the values. proposed a method of evaluating transparency based on its opacity (Patent Document 2).

Japanese Patent Application Laid-Open No. 2006-190508 JP 2015-121480 A

However, even in the transparency evaluation method described in Patent Document 2, the correlation with visual evaluation of transparency was not necessarily sufficient.
An object of the present invention is to provide a method for evaluating the transparency of a transparent polymeric material, which has a high correlation with visual evaluation of the transparency and is highly practical.

The present invention includes the following aspects.
A method for evaluating the transparency of a transparent polymeric material according to one aspect of the present invention comprises evaluating the transparency of a colorimetric test specimen made of a flat plate-shaped test piece of a transparent polymeric material by measuring the transparency using a spectrophotometer. A method for evaluating the transparency of a transparent polymer material,
In a state where the sample surface opening of the spectrophotometer is shielded from light using a dark box, the color inside the dark box is measured according to JIS Z8722 under the geometric condition b in JIS Z8722 using the spectrophotometer to obtain an XYZ color system. a first step of determining tristimulus values X ₀ , Y ₀ , Z ₀ ;
a second step of substituting Y _{0 and Z 0 out of the tristimulus values X 0 , Y 0} and Z ₀ into the following equation (1) to determine the background whiteness WI ₀ ;
The normal to the surface of the colorimetric specimen is arranged toward the sample surface opening, and the colorimetric specimen and the sample surface opening are shielded from light using the dark box, and the same as the first step. a third step of obtaining tristimulus values X ₁ , Y ₁ , and Z ₁ of the XYZ color system by measuring the colorimetric specimen under conditions;
a fourth step of substituting Y ₁ and Z 1 out of _{the tristimulus values X 1 , Y 1 and Z 1 into the following} equation (2) to determine the whiteness WI ₁ of the colorimetric specimen;
a fifth step of evaluating the transparency of the colorimetric specimen based on the value of the whiteness _WIA determined by the following formula (3);
In the third step, the method for evaluating the transparency of a transparent polymeric material, wherein the dark box is placed over the colorimetric specimen and the sample surface opening so as to form a space between the colorimetric specimen and the specimen. .
WI ₀ =3.388×Z ₀ −3×Y ₀ (1)
WI ₁ =3.388×Z ₁ −3×Y ₁ (2)
WI _A =WI ₁ -WI ₀ (3)

The method for evaluating the transparency of a transparent polymer material of the present invention has a high correlation with visual evaluation of transparency, and is highly practical.

1 is a graph plotting the results of visual transparency evaluation on the horizontal axis and the whiteness WI _A , haze and opacity on the vertical axis for Test Examples IV in which liquid paraffin was applied on both sides. 1 is a graph plotting the results of visual transparency evaluation on the horizontal axis and the whiteness _WIA on the vertical axis for Test Examples IV in which silicone oil was applied to both surfaces.

The method for evaluating the transparency of a transparent polymeric material according to the present invention is a method of evaluating the transparency of a colorimetric test specimen made of a flat plate-shaped specimen of a transparent polymeric material using a spectrophotometer.
The transparent polymer contained in the transparent polymer material to which the present invention is applied includes, for example, polypropylene, polyethylene, ethylene/α-olefin copolymer, ethylene/vinyl acetate copolymer, ethylene/acrylic copolymer, polychlorinated vinyl, polyvinylidene chloride, polystyrene, styrene-acrylic copolymer, acrylic resin, ABS resin, polyester, polycarbonate, polyamide, triacetyl cellulose and the like. Among these, crystalline polymers (eg, polypropylene, polyethylene, etc.) are preferable, and polypropylene is more preferable, since the effects of the present invention are exhibited more remarkably.
The transparent polymeric material may contain a coloring agent such as a bluing agent or carbon black as long as the transparency is not impaired.
Furthermore, the transparent polymer material may contain various additives such as crystal nucleating agents, antioxidants, light stabilizers, and lubricants, if necessary.
A transparent polymer material is a material having a total light transmittance of 50% or more as measured according to JIS K7361-1. It is difficult to apply the present invention to opaque polymeric materials with a total light transmittance of less than 50%.

One aspect of the method for evaluating the transparency of a transparent polymer material according to the present invention will be described below.
The method for evaluating the transparency of a transparent polymeric material according to this aspect includes the following first step, second step, third step, fourth step, and fifth step.
The first step and the second step are steps for determining the background whiteness WI ₀ when measuring the color of the transparent polymeric material. The third and fourth steps are steps for determining the whiteness index WI ₁ of the transparent polymeric material. The fifth step is a step of evaluating transparency.

The first step is to obtain the tristimulus values X ₀ , Y ₀ , and Z ₀ of the XYZ color system by measuring the color inside the dark box while the sample surface opening is shielded from light using the dark box. . That is, in the first step, the inside of the dark box is subjected to colorimetry without a colorimetric specimen consisting of a flat plate-shaped test piece of a transparent polymeric material, and the tristimulus values X ₀ , Y ₀ , and Z ₀ are obtained.

The sample surface aperture is an opening for allowing the illuminant emitted inside the spectrophotometer to exit the spectrophotometer and allowing the light reflected by the sample or the like to enter the spectrophotometer. It's about. In other words, the aperture includes an illuminant exit opening and an entrance opening for reflected light from the sample or the like. The sample plane aperture is preferably formed in the center of a disc attached to the upper surface of the spectrophotometer.
A more preferable opening diameter of the sample surface opening is in the range of 5 mmφ or more and 50 mmφ or less. For example, the opening diameter of the sample surface opening is preferably 30 mmφ, and if the specimen is smaller than 30 mm, it is preferably 10 mmφ. The diameter of the lens that emits the illuminant is adjusted to the sample surface aperture.

The dark box used in this embodiment is not particularly limited as long as it prevents outside light from entering. As the structure of the dark box, for example, one having a cylindrical portion and a top plate portion integrally formed with the cylindrical portion can be mentioned. Moreover, it is preferable that at least the entire inner surface of the dark box used in this embodiment is blackened to suppress light reflectivity. As the light reflectivity in the dark box is suppressed, the occurrence of stray light in the dark box can be suppressed, so that the accuracy of the transparency evaluation of the transparent polymer material is increased.
Moreover, the dark box preferably has tristimulus values X ₀ , Y ₀ , and Z ₀ measured in the second step, which will be described later, each of which is 0.3 or less. By using a dark box in which each of the tristimulus values X ₀ , Y ₀ , and Z ₀ is 0.3 or less, transparency can be obtained with higher accuracy even for colorimetric specimens made of flat test pieces with high transparency. can be evaluated.
In the dark box used in this embodiment, the inner diameter of the cylindrical portion is the same as the outer diameter of the disk in which the sample surface opening is formed. Therefore, when the sample surface opening is covered with a dark box, the vicinity of the opening of the cylindrical portion can be fitted to the outer peripheral surface of the disk. Therefore, when the sample surface opening is covered with a dark box, it is possible to form a structure that further prevents external light from entering the sample surface opening.
The top plate of the dark box is provided at a position where it does not come into contact with the sample surface opening and the colorimetric specimen when the sample surface opening is covered with the dark box.
Also, the dark box may be provided with black felt, for example, on its inner surface side. If black felt or the like is provided on the inner surface side of the dark box, it may be possible to further suppress the light reflectivity.

Colorimetry is performed according to JIS Z8722 using a spectrophotometer. The field of view for measurement is 2° or 10°, preferably 2°. The geometric condition of irradiation and light reception during measurement shall be the geometric condition b described in 5.3.1 of JIS Z8722. Although the illuminant of the spectrophotometer is not limited, it is preferable to use the standard illuminant or auxiliary illuminant specified in JIS Z 8720, and standard illuminant D65 or auxiliary illuminant C is preferable.

A spectrophotometric method using a spectrophotometer is a method of measuring a spectral reflectance coefficient or a spectral transmittance coefficient to obtain tristimulus values X, Y, and Z defined in JIS Z8722. The spectrophotometer may be a first-class spectrophotometer described in JIS Z8722-4, or a second-class spectrophotometer.
The measurement of the spectral reflectance coefficient in the spectrophotometric method may be method a or method b described in 5.3.3 of JIS Z 8722.

In the second step, out of the tristimulus values X ₀ , Y ₀ , and Z ₀ obtained in the first step, Y ₀ and Z ₀ are substituted into the following equation (1) to obtain the background whiteness WI ₀ It is a process to find Formula (1) and formula (2) described later are Taube's formula (WI=3.388Z-3Y) described in ASTM E313, and are formulas for obtaining whiteness WI.
WI ₀ =3.388×Z ₀ −3×Y ₀ (1)
The background whiteness WI ₀ is the whiteness in the dark box measured when the dark box is placed over the sample plane opening and shielded from light. This background whiteness WI ₀ is the whiteness of the background when colorimetrically measuring the colorimetric specimen in the third step described later.
The derivation of WI ₀ may be computer assisted. For example, formula (1) may be stored in a computer, the tristimulus values Y ₀ and Z ₀ obtained in the first step may be input to the computer, and WI ₀ may be obtained by calculating formula (1). The computer may be a computer attached to the spectrophotometer used for colorimetry, or may be a computer separate from the computer attached to the spectrophotometer.

After the second step, it is preferable to have a step of applying transparent oil to the surface of the colorimetric test piece made of a flat plate-like transparent polymer material to obtain a colorimetric test piece.
As for the shape of the test piece, a plate-like, sheet-like or film-like shape is preferable because the color can be easily measured with a commercially available spectrophotometer.
Specimens are made by molding a transparent polymeric material. The molding method may be any of various molding methods such as injection molding, extrusion molding, compression molding, and vacuum molding. The thickness of the test piece is preferably 0.01 to 5 mm, more preferably 0.01 to 1 mm, even more preferably 0.01 to 0.5 mm. Here, the thickness of the test piece is the average value of the thicknesses at 10 arbitrary locations.

Here, the transparent oil is an oil that is visually recognized as transparent, and is preferably 6% or less when haze is measured in accordance with JIS K 7136 in a cell with an optical path length of 6 mm. More preferably 1% or less, still more preferably 0.6% or less. The lower limit of haze is usually 0% or more.
Examples of transparent oils include organic compound oils such as saturated aliphatic hydrocarbon oils and unsaturated aliphatic hydrocarbon oils, and organic silicon compound oils such as silicone oils. In addition, the application classification includes lubricating oil, edible oil, fuel oil, industrial oil, cosmetic oil, pharmaceutical oil, and the like. As the transparent oil used in the present invention, it suffices if it can be applied so as to smooth the surface of the transparent polymer material, and there are no particular restrictions on the component classification or application classification, but the test piece is a polyolefin such as polypropylene or polyethylene. In some cases, an organic compound-based oil is preferable, and liquid paraffin, which is an aliphatic saturated hydrocarbon oil, is more preferable because the test piece has a refractive index close to that of the test piece and is less affected by reflection and scattering at the interface with the test piece.
The method for applying the transparent oil is not particularly limited, and examples thereof include a method using a brush, a method using a coater, and a method using a spray. Alternatively, the transparent oil may be applied to the test piece by immersing the test piece in the transparent oil.

An oil film made of the transparent oil is formed on at least one of the surface (surface on the sample surface opening side) and the back surface (surface on the side opposite to the sample surface opening) of the colorimetric specimen in this aspect. there is The thickness of the oil film is not particularly limited, and can be in the range of 20 to 80 μm, for example.
When the thickness of the oil film is at least the lower limit of the above range, the thickness of the oil film tends to be uniform in the surface direction, and the following effects due to the provision of the oil film can be more reliably obtained. When the value is equal to or less than the upper limit of the above range, the oil is less likely to drip from the colorimetric specimen and the operability is excellent.
The thickness (t) of the oil film is calculated from the volume (V) of oil used for application and the application area (A) as t=V/A.
In this aspect, when at least one of the front surface and the back surface of the test piece is provided with an oil film, fine unevenness on the surface of the test piece prevents the measurement from being affected by reflecting or scattering light. effect is obtained. From the viewpoint of enhancing this effect, it is preferable to provide an oil film on both surfaces of the test piece.

In the third step, the normal to the surface of the colorimetric specimen is arranged to face the sample surface opening, and the colorimetric specimen and the sample surface opening are shielded from light using the dark box. This is a step of measuring the colors of the colorimetric specimen under the same conditions as in the first step to obtain tristimulus values X ₁ , Y ₁ and Z ₁ of the XYZ color system.
When the normal of the surface of the specimen for colorimetry is directed to the sample surface opening, the surface faces the sample surface opening, resulting in excellent measurement accuracy.
There may or may not be a space (gap) between the surface of the colorimetric specimen and the sample plane aperture of the spectrophotometer. The colorimetric specimen is arranged so as to be in contact with the sample surface opening from the viewpoint that the colorimetric specimen can be stably placed and the surface of the colorimetric specimen can easily face the sample surface opening. preferably.
When the sample plane aperture of the spectrophotometer is provided on the top surface of the spectrophotometer, in order to place the colorimetric specimen so that it is in contact with the sample plane aperture provided on the top surface of the spectrophotometer, the sample plane A sample for colorimetry should be placed on the opening.
The dark box used in the third step is the same as the dark box used in the first step. In this step, a dark box is placed over the colorimetric specimen and the opening of the sample surface so that a space is formed between the colorimetric specimen and the dark box.

In the third step, the spectrophotometer to be used, the angle of field of view, the geometrical conditions of illumination and light reception, the type of illuminant, and the method of measuring the spectral reflectance coefficient are the same as in the first step, and the colorimetric specimen is measured. Measure color.
In this step, a dark box is placed over the colorimetric specimen and the sample surface opening to shield the colorimetric specimen and the sample surface opening from light, and the colorimetric specimen is placed in a state in which outside light is prevented from entering the dark box. Measure color. By eliminating the influence of external light, it is possible to improve the measurement accuracy of colorimetry.

In the fourth step, among the tristimulus values X ₁ , Y ₁ , and Z ₁ obtained in the third step, Y ₁ and Z ₁ are substituted into the following formula (2), and the colorimetric specimen This is the step for obtaining the whiteness WI _{of 1} .
WI ₁ =3.388×Z ₁ −3×Y ₁ (2)
The whiteness of the colorimetric specimen WI ₁ is the whiteness of the colorimetric specimen placed in the dark box.
WI ₁ , like WI ₀ , can be derived using a computer.

The fifth step is a step of evaluating the transparency of the colorimetric specimen based on the whiteness _WIA value obtained from the following formula (3). That is, the transparency of the transparent polymeric material is evaluated according to the magnitude of the _WIA value. Specifically, the smaller the whiteness index _WIA , the higher the transparency of the transparent polymeric material.
WI _A =WI ₁ -WI ₀ (3)

As a result of investigation by the present inventors, it was found that the transparency evaluation result of this embodiment based on the whiteness _WIA has a high correlation with the visual transparency evaluation result. Therefore, the transparency evaluation method of this embodiment is highly practical.
The reason why the transparency evaluation result according to this embodiment has a high correlation with the visual transparency evaluation result is considered to be as follows.
That is, in this embodiment, the tristimulus values X ₁ , Y ₁ , and Z ₁ are measured with a dark box placed over the colorimetric specimen, and the whiteness WI ₁ is obtained. The dark box does not touch the surface of the specimen for colorimetry opposite to the opening side of the specimen (hereinafter referred to as the “back surface”), and there is a space between the dark box and the specimen for colorimetry. is formed. In this case, since the back surface of the colorimetric specimen is in contact with the air, the colorimetric light incident on the colorimetric specimen is reflected by the back surface of the colorimetric specimen. The state in which light is reflected on the back surface of the specimen for colorimetry is similar to the state in which the transparency is visually evaluated.
Further, in this embodiment, the whiteness WI of the colorimetric specimen is subtracted from the whiteness WI _{of 1} in the dark box without the colorimetric specimen to obtain the whiteness WI _A. Transparency is evaluated based on the value of _A. This allows the transparency to be evaluated without background effects. By eliminating the influence of the background, even when measuring the transparency of a highly transparent specimen, the transparency can be evaluated stably with high accuracy.
From the above, it is considered that the transparency evaluation method of this embodiment has a high correlation with the visual transparency evaluation result.
When the transparency evaluation method of this embodiment is applied to the quality inspection of transparent polymer material products, the transparency inspection becomes stricter, so that higher quality transparent polymer materials can be provided to users.

For this embodiment, haze, which is a general index for evaluation of transparency, is mainly a transparency measurement under transmission conditions, and the measurement under reflection conditions is not sufficiently reflected. Therefore, it is presumed that the haze value of the transparent polymeric material has a low correlation with the visual evaluation result of transparency.
In addition, the opacity described in Patent Document 2 is obtained by bringing a black glass plate into close contact with the back surface of the liquid paraffin-applied molding. In this case, liquid paraffin loses the difference in refractive index with air at the interface between the back surface of the molded body and the black glass plate, and light is not reflected on the back surface of the molded body. This state is different from the state when visually evaluating the transparency. Therefore, it is presumed that the opacity value described in Patent Document 2 does not necessarily have a high correlation with the visual evaluation result of transparency.

Hereinafter, the present invention will be described in more detail by showing test examples. However, the present invention is not limited to the following test examples.
The transparent polymeric materials used in the examples below are as follows.
Material a: A material obtained by dry-blending 80% by mass of PS320M manufactured by SunAllomer Co., Ltd. and 20% by mass of Engage 8480 manufactured by The Dow Chemical Company.
Material b: CS356M manufactured by SunAllomer Co., Ltd.
Material c: A material obtained by dry-blending 95% by mass of PL500A manufactured by SunAllomer Co., Ltd. and 5% by mass of transparent nucleating agent masterbatch PP-RM-SKZ H8020 manufactured by Dainichiseika Kogyo Co., Ltd.

(Test example I)
Using a 40 mmφ single-layer sheet molding machine (manufactured by Tanabe Plastics Machine Co., Ltd.), the material a was sheet-molded under the following conditions to obtain a sheet with a thickness of 300 μm.
The clearance between the cast roll and the touch roll was set to 300 μm.
Extruder cylinder temperature: C1 was set at 200°C, and C2 to C5 were set at 220°C.
T-die temperature: 230°C.
T-die lip opening: 1 mm.
Roll temperature: 60°C.
Air gap: 100 mm.
Sheet take-up speed: 1.1 m/min. and

(Test example II)
A sheet having a thickness of 300 μm was obtained in the same manner as in Test Example I except that material a was changed to material b.

(Test example III)
Using a 25 mmφ three-layer three-layer film/sheet molding machine (manufactured by Thermo Plastics Industry Co., Ltd.), the material c was sheet-molded under the following conditions to obtain a sheet with a thickness of 350 μm.
The clearance between the cast roll and the touch roll was set to 350 μm.
Extruder cylinder temperature: 230°C.
T-die temperature: 270°C.
T-die lip opening: 1 mm.
Roll temperature: 30°C.
Air gap: 100 mm.
Sheet take-up speed: 2.2-2.3 m/min. and

(Test example IV)
A sheet with a thickness of 350 μm was obtained in the same manner as in Test Example III except that the T-die temperature was changed to 230° C. and the lip opening of the T-die was changed to 0.8 mm.

(Test example V)
A sheet having a thickness of 350 μm was obtained in the same manner as in Test Example III except that the cylinder temperature was changed to 215° C., the T-die temperature to 250° C., and the lip opening of the T-die to 0.8 mm.

<Evaluation>
Each obtained sheet was visually evaluated for transparency, and whiteness WI _A , haze and opacity were measured by the following methods. The measurement results and evaluation results are shown in Table 1 and FIG.

[Evaluation of transparency by visual inspection]
A flat test piece of 4 cm square was cut out from the sheet, and about 75 μl of transparent oil was applied to each side using a brush to obtain a test piece. Liquid paraffin (first grade reagent manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) and silicone oil (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.) were used as transparent oils. This test sample was placed on a black mat placed on a desk, visually observed, and the transparency was evaluated in 5 grades. The higher the numerical value, the higher the transparency.
As the black mat, one with XYZ color system tristimulus values (X, Y, Z)=(1.2, 1.2, 1.4) was used.

[Measurement of background whiteness WI ₀ ]
A spectrophotometer (SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd., 2° field of view, lens aperture 30 mmφ) is covered with a dark box so that external light does not enter the sample surface aperture (aperture diameter 30 mmφ). bottom. Here, as the dark box, a zero calibration box manufactured by Nippon Denshoku Industries Co., Ltd., XYZ color system tristimulus values (X, Y, Z) = (0.16, 0.16, 0.21) is used. bottom. This dark box has a cylindrical portion and a top plate portion, and forms a space between the colorimetric test body and the colorimetric test body when it is placed over the sample surface opening and the colorimetric test body, which will be described later.
Then, in a state where the opening of the sample surface is shielded from light using the dark box, the color inside the dark box is measured using the spectrophotometer to obtain the tristimulus values X ₀ , Y ₀ , and Z ₀ of the XYZ color system. asked. At that time, according to JIS Z8722, the color was measured with the geometric condition b in JIS Z8722 and the auxiliary illuminant C specified in JIS Z8720.
Then, the background whiteness WI ₀ was determined by the following formula (1).
WI ₀ =3.388×Z ₀ −3×Y ₀ (1)

[Measurement of Whiteness WI _A ]
About 40 .mu.l of transparent oil was applied to each side of a 4 cm square flat test piece cut from the sheet in a central area of 35 mm.phi. As the transparent oil, liquid paraffin (first grade reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and silicone oil (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.) were used.
The specimen for colorimetry was placed so as to be in contact with the sample surface opening of the spectrophotometer, and a dark box was placed to cover the specimen for colorimetry and the sample surface opening to shield from light. The spectrophotometer and dark box used at this time are the same as those used when the background whiteness WI ₀ was measured.
The tristimulus values X ₁ , Y ₁ , Z ₁ of the XYZ color system were obtained by measuring the colors of the colorimetric specimen under the same conditions as when the background whiteness WI ₀ was measured.
Next, the whiteness WI ₁ of the colorimetric test sample was determined by the following formula (2).
WI ₁ =3.388×Z ₁ −3×Y ₁ (2)
Next, the whiteness WI _A was obtained from the following formula (3).
WI _A =WI ₁ -WI ₀ (3)
In addition, using a transparent glass plate (microscope glass manufactured by Matsunami Glass Industry Co., Ltd. (thickness 0.12 to 0.17 mm)), the WI _A of the transparent glass plate and the range of 35 mmφ in the center of both sides of the transparent glass plate Approximately 40 µl of liquid paraffin or silicone oil was applied to each side of the test piece using a brush, and the _WIA was found to be 0.0% in both cases. was confirmed.

[Haze measurement]
About 40 μl of transparent oil was applied to each side of a plate-shaped test piece cut out from the sheet into a 4 cm square with a brush in a range of 35 mmφ in the center of both sides to obtain a test piece. Liquid paraffin (first grade reagent manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was used as the transparent oil. The haze of this test piece was measured according to JIS K7136 using a haze measuring device (Model HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd.). CIE standard illuminant D65 was used as the illuminant for the haze measuring device. In addition, pure water, liquid paraffin (Fuji Film Wako Pure Chemical Industries, Ltd. first grade reagent), silicone oil (Shin-Etsu Chemical Co., Ltd. KF-96-50CS) was added to a glass cell with an optical path length of 6 mm (Murakami Color Research Co., Ltd.). The haze values measured by placing them in a laboratory) were 0.0%, 0.4% and 0.8%, respectively.

[Measurement of opacity described in Patent Document 2]
Liquid paraffin (first-class reagent manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was applied to both sides of a flat test piece cut out from the sheet into 4 cm squares using a brush, and sandwiched between a pair of cover glasses to obtain a test piece. Using a spectrophotometer (SE-2000, manufactured by Nippon Denshoku Industries Co., Ltd., 2° field of view, lens diameter 30 mmφ), the color of this test sample was measured according to geometric condition b, auxiliary illuminant C, and method b in accordance with JIS Z8722. , tristimulus values X, Y, and Z of the XYZ color system were determined. Then, the opacity was obtained from the following formula (4).
Opacity = Y + 0.3018Z - 3.831X (4)

1 and 2 show graphs in which the abscissa indicates the visual transparency evaluation results, and the ordinate indicates the whiteness WI _A , opacity and haze. As transparent oil, FIG. 1 shows liquid paraffin (first grade reagent manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and FIG. 2 shows the results using silicone oil (KF-96-50CS manufactured by Shin-Etsu Chemical Co., Ltd.). .
As shown in FIGS. 1 and 2, the whiteness _WIA had a high correlation with the visual transparency evaluation results. On the other hand, the haze could not be correctly evaluated in the region 1 to 2 in the visual evaluation of transparency. In addition, regarding the opacity, no difference could be evaluated in the range of 2 to 5 in visual transparency evaluation. From this, it was shown that the transparency evaluation method of the present invention, which evaluates transparency from the whiteness _WIA value, is highly practical for evaluating transparency.

Claims (2)

A method for evaluating the transparency of a transparent polymer material, comprising: evaluating the transparency of a colorimetric test specimen made of a flat plate-shaped test piece of the transparent polymer material by measuring the transparency using a spectrophotometer;
In a state where the sample surface opening of the spectrophotometer is shielded from light using a dark box, the color inside the dark box is measured according to JIS Z8722 under the geometric condition b in JIS Z8722 using the spectrophotometer to obtain an XYZ color system. a first step of determining tristimulus values X ₀ , Y ₀ , Z ₀ ;
a second step of substituting Y _{0 and Z 0 out of the tristimulus values X 0 , Y 0} and Z ₀ into the following equation (1) to determine the background whiteness WI ₀ ;
A coating step of applying a transparent oil to at least one of the front surface and the back surface of the flat test piece to obtain the colorimetric test body in which the oil film made of the oil is exposed;
The normal to the surface of the colorimetric specimen is arranged toward the sample surface opening, and the colorimetric specimen and the sample surface opening are shielded from light using the dark box, and the same as the first step. a third step of obtaining tristimulus values X ₁ , Y ₁ , and Z ₁ of the XYZ color system by measuring the colorimetric specimen under conditions;
a fourth step of substituting Y ₁ and Z 1 out of _{the tristimulus values X 1 , Y 1 and Z 1 into the following} equation (2) to determine the whiteness WI ₁ of the colorimetric specimen;
a fifth step of evaluating the transparency of the colorimetric specimen based on the value of the whiteness _WIA determined by the following formula (3);
In the third step, the method for evaluating the transparency of a transparent polymeric material, wherein the dark box is placed over the colorimetric specimen and the sample surface opening so as to form a space between the colorimetric specimen and the specimen. .
WI ₀ =3.388×Z ₀ −3×Y ₀ (1)
WI ₁ =3.388×Z ₁ −3×Y ₁ (2)
WI _A =WI ₁ -WI ₀ (3) 2. The method for evaluating the transparency of a transparent polymeric material according to claim 1, wherein the oil film has a thickness of 20 to 80 μm.

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