JPS6333290B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a biaxially stretched polyester film for capacitors. More specifically, the present invention relates to a biaxially stretched polyester film for capacitors that has both excellent workability and electrical properties. Nowadays, as capacitors are becoming smaller, polyethylene terephthalate biaxially stretched film is thinner and has a uniform thickness, and has better voltage resistance than the conventionally used impregnated paper. Therefore, demand is gradually increasing to replace impregnated paper. Producing thin films from polyethylene terephthalate requires fairly sophisticated film-forming technology, but in recent years, along with advances in film-forming methods, ultra-thin films of up to 2.5 μm in thickness have appeared. However, as the film becomes thinner, various problems arise regarding the workability and electrical properties of the film when handling it. There are two types of plastic film capacitors: evaporated capacitors and foil-wound capacitors, both of which have similar characteristics required for the film. First, it is essential that the film has good workability, ie, good slipperiness of the film, in manufacturing processes such as roll winding and element winding. This workability can be approximately represented by the coefficient of friction, but according to our knowledge, a material whose static friction coefficient and dynamic friction coefficient are approximately equal is preferably used. Further, this polyester film is slit and used as strips, but if the workability during slitting is poor, the slit portions may bulge, impairing the uniformity of the thickness of the capacitor film. Therefore, good workability during slitting is one of the important requirements for a capacitor film. On the other hand, representative electrical properties required for a capacitor film include withstand voltage properties and a property called "CR value", which is the product of capacitance and electrical resistance at room temperature and high temperature. Furthermore, it is desired that the capacitor has a long life, that is, it has excellent life characteristics. In order to improve the slipperiness of the film, which is one of the characteristics that such a film for capacitors should possess, it is sufficient to provide irregularities on the surface of the film by some method, and for this purpose, fine particles that are inert to the polyester are present in the raw polyester. It is known that this is a good thing. There are two main methods for making these inert fine particles exist. One of them is kaolin by a method called addition method.
Silica, talc, calcium carbonate, calcium phosphate, etc. are added to the polyester reaction system, during molding, etc., either as they are or after being made into fine particles. These methods of adding inert inorganic particles to polyester can control the particle size and amount of fine particles, so the reproducibility of the results is good, but unnecessary coarse particles are often mixed in. In order to remove these coarse particles, a classification operation is necessarily required, and if necessary, a crushing operation is required as a pretreatment thereof, which makes the operation complicated. Moreover, even if such an operation is performed, the contamination of coarse particles is still unavoidable. The presence of coarse particles or secondary particles due to aggregation is particularly fatal for capacitor films, and has an adverse effect on withstand voltage characteristics and other electrical properties. Another method that is compared to the addition method is the precipitation method, in which a catalyst such as a calcium or lithium compound used in the transesterification reaction is added to the polyester production reaction system in the presence or absence of a phosphorus compound using fine inert particles. It is precipitated as In this case, it goes without saying that calcium or lithium compounds may be added after the transesterification reaction to form fine inert particles, and the same method also applies to cases where the esterification reaction is performed. When attempting to improve the slipperiness using the precipitated inert fine particles, it becomes difficult to control the slipperiness because the precipitated particle diameter and particle amount generally tend to change. Furthermore, it has the disadvantage that it generally has poor slipperiness compared to the addition method, and that it no longer provides the original slipperiness when recycled. However, since the precipitation method is simple to operate and can be carried out industrially, it has great utility if it can overcome these drawbacks and produce a polyester film with excellent electrical properties. The present inventors have made extensive studies in view of the above circumstances, and have arrived at the present invention. That is, the present invention is a polyester film containing inert fine particles precipitated by reacting a trialkyl phosphite and a trialkyl phosphate to a calcium compound soluble in the reaction system in a polyester production reaction system. The active fine particles contain calcium element and phosphorus element with a molar ratio of phosphorus element to calcium element of 0.7~
2.5, the solution haze of the polyester film is within the range obtained by connecting the coordinate points A, B, C, and D shown in the table below with straight lines, and the polyester film is crystallized. degree is 45
This relates to a biaxially oriented polyester film for capacitors that has a polyester film of ~55%.

[Table] (A, B, C, and D in the above table are points on the coordinate axis with H ⁵⁵⁰ on the horizontal axis and H ⁴⁵⁰ /H ⁶⁷⁰ on the vertical axis.
H ⁴⁵⁰ , H ⁵⁵⁰ and H ⁶⁷⁰ are 450nm and 550nm respectively
and solution haze (%) measured with light at a wavelength of 670 nm by the method defined in the following description. ) The present invention will be explained in more detail below. The polyester film of the present invention is produced by melting a polymer mainly composed of polyethylene terephthalate, such as a polyethylene terephthalate homopolymer, a copolymer containing at least 80 mol% of ethylene terephthalate units, or a block copolymer, and
Although it is obtained by stretching, one of the features of the present invention is the inert fine particles in the polyester film. That is, the main component of the inert fine particles in the film of the present invention is the precipitated particles precipitated in the polyester manufacturing reaction system, and furthermore, the inert fine particles contain calcium and phosphorus elements, and the phosphorus element is smaller than the calcium element. It is essential that the molar ratio of these precipitated particles be from 0.7 to 2.5, and that the solution haze of the polyester film containing these precipitated particles be within a certain range. If the molar ratio of the phosphorus element to the calcium element in the inert fine particles is less than 0.7, the precipitated particles will be easily destroyed by stretching and will no longer provide the original slipperiness when recycled. Also, the molar ratio is 2.5
If it exceeds this amount, a large amount of phosphorus compound will inevitably be present in the polymer, which will slow down the polymerization rate during polyester production, resulting in a significant industrial disadvantage. In the present invention, it is preferable that the inert fine particles do not substantially contain other metal elements such as lithium, zinc, manganese, magnesium, barium elements, etc. This is because if precipitated particles are formed in the coexistence of metal elements other than calcium, the form of the precipitated particles often changes, making it impossible to obtain stable inert fine particles. The amount of metal elements other than calcium in the precipitated inert fine particles is preferably 0.1 times or less, preferably 0.05 times or less, relative to calcium element. Next, in the present invention, the solution haze of a polyester film containing this specific inert fine particle that is not destroyed even by stretching is expressed on a coordinate axis with H ⁵⁵⁰ on the horizontal axis and H ⁴⁵⁰ /H ⁶⁷⁰ on the vertical axis. It must be within the range obtained by connecting points A, B, C, and D shown below (Figure 1).

[Table] Here, H ⁴⁵⁰ , H ⁵⁵⁰ , and H ⁶⁷⁰ are solution hazes measured by the methods shown below. Add 2.7 g of polyester to 20 ml of a 4/6 (weight ratio) mixed solution of tetrachloroethane/phenol,
After heating and dissolving at ℃ for 1 hour, the solution was cooled, a portion of the solution was collected in a 10 mm thick cell made of quartz glass, and measured using an integrating sphere haze meter. In this case, change the wavelength of the light source to 450, 550 and 670n.
The solution haze when measured at a wavelength of m is
^H450 , ^H550 and ^H670 (%). That is, even if the polyester film contains precipitated inert fine particles, if the solution haze of the polyester film is outside the above-mentioned range, some defects will occur when the polyester film is used as a capacitor film. That is, the measurement results of solution haze are shown in Figure 1.
If it is located below the AB line, a large number of coarse particles due to aggregation will exist in the polyester film, resulting in poor film slipperiness and poor voltage resistance characteristics. Furthermore, even when located to the right of the BC line, there are still many coarse particles due to aggregation, giving the same result. On the other hand, if it is located above the CD line, the particle size of the precipitated inert fine particles is too small and the sliding properties are insufficient. It is also one of the electrical characteristics
CR value is also not good. Furthermore, if the inert particles are located to the left of the DA line, there are too few inert particles and the slipperiness of the film deteriorates. In this way, the present inventors have demonstrated for the first time that when the solution haze of a polyester film containing inert fine particles containing specific amounts of calcium and phosphorus elements is within a certain range, it satisfies the requirements for a film for a condenser. In order to manufacture this film, we discovered that it has excellent slip properties, the coefficient of static friction and the coefficient of dynamic friction are almost equal, the slip property hardly decreases even when recycled and used, and that it has excellent electrical properties. The raw material polyester can be manufactured, for example, by the following method. That is, by adding one or more calcium compounds before or during the transesterification reaction, and then adding a plurality of phosphorus compounds consisting of a trivalent phosphorus compound and a pentavalent phosphorus compound to the reaction system before starting the polycondensation reaction. Obtainable. Of course, even within the scope of this method, the molar ratio of the phosphorus compound to the calcium compound, the molar ratio of the pentavalent phosphorus compound to the trivalent phosphorus compound, the timing of addition of the phosphorus compound, and polymerization conditions such as temperature elevation and pressure reduction, etc. Since the shape of the precipitated particles differs depending on the conditions, conditions suitable for the present invention must be selected from among these combinations. Among these methods, particularly preferred methods are as follows. That is, first, about 0.05 to 0.3 mol% of the total acid component of the polyester raw material as a transesterification catalyst,
Preferably, 0.08 to 0.14 mol% of the calcium compound is used to carry out the transesterification reaction. The calcium compound that can be used at this time may be any calcium compound as long as it is soluble in the reaction system, such as calcium salts of aliphatic carboxylic acids such as acetic acid, propionic acid, and butyric acid, benzoic acid, and p-methylbenzoic acid. Examples include calcium salts of aromatic carboxylic acids such as, calcium compounds such as calcium glycolates such as ethylene glycol and propylene glycol, and inorganic compounds such as calcium hydride. Among these, calcium acetate is particularly preferably used. Next, two types of trivalent and pentavalent phosphorus compounds are added to this reaction mixture in which the transesterification reaction has been substantially completed. In this case, the trivalent phosphorus compounds include, for example, phosphorous acid, trimethyl phosphite,
Mention may be made of triethyl phosphite, tributyl phosphite, dimethyl phosphite, diethyl phosphite, monobutyl phosphite, dibutyl phosphite, etc., while examples of pentavalent phosphorus compounds include trialkyl phosphate, particularly trimethyl phosphite, triethyl phosphite, etc. Mention may be made of phosphate or tributyl phosphate. In this case, the molar ratio of the pentavalent phosphorus compound to the trivalent phosphorus compound is 1 to 20, preferably 2 to 10.
The total amount of these phosphorus compounds is preferably 1 to 3 times the mole of the calcium compound previously used as the transesterification catalyst. If the molar ratio of the pentavalent phosphorus compound to the trivalent phosphorus compound is less than 1, the resulting polymer tends to become dark, or black foreign matter is likely to be generated during polymer production, making it difficult to perform stable operations; If it exceeds the amount, the amount of precipitated particles will be small and the effect of imparting slipperiness will likely be insufficient. Furthermore, if the molar ratio of the total amount of phosphorus compounds to calcium compounds is less than 1, the molar ratio of phosphorus elements to calcium elements in the precipitated particles will be less than 0.7, resulting in particles that are easily destroyed by stretching. When it exceeds 3, the polymerization rate during polymer production becomes extremely slow, which is industrially disadvantageous. In addition, when a metal element other than calcium is present when adding a phosphorus compound, for example, when adding a calcium compound after carrying out a transesterification reaction using lithium, zinc, manganese, magnesium, barium compounds, etc., or when adding a calcium compound with these metal compounds. When the transesterification reaction is carried out in the presence of a calcium compound, the solution haze of the resulting polymer is often unstable, and polyester films often outside the range shown in FIG. 1 are obtained. Furthermore, in this case, if the inert fine particles contain metal elements other than calcium element beyond the permissible limit, the particles are generally unsuitable for use in the present invention. The timing of adding the phosphorus compound is when the liquid temperature of the polyester oligomer is 225 to 250℃, preferably
Preferably, the temperature is 230-240°C. In the present invention, a capacitor film is produced using such a specific polyester, but another important component of the present invention is that such a film must be a biaxially oriented polyester film with a crystallinity of 45 to 55%. . That is, the film of the present invention can be obtained by melt-extruding a raw material polyester into an unstretched film by a conventional method, biaxially stretching it, and heat-setting it. However, by adjusting these conditions, the film crystals obtained can be Adjust the degree of oxidation to 45-55%. Specifically, the stretching temperature is 80 to 120℃, the stretching ratio is 2.5 to 4.5 times in both length and width, and the heat setting temperature is 150 to 250.
℃ and heat setting time are selected from the range of 1.5 to 8 seconds. Among these, the heat setting conditions are particularly related to the crystallinity of the obtained film, and the higher the heat setting temperature and the longer the heat setting time, the higher the crystallinity. This value cannot be determined unconditionally as it depends on the size and structure of the heat treatment chamber, the thickness of the film, etc., but for example, if the heat setting temperature is set at 210 to 230℃,
By setting the heat setting time to 2 to 7 seconds, the crystallinity of the resulting film can be approximately 48 to 53%. Keeping other conditions constant, only the heat fixing temperature is set to 160
If the temperature is lowered to ~180°C, a film with a crystallinity of 38 to 42% will be obtained. Only when the crystallinity of the film obtained by this method is in the range of 45 to 55%, preferably 47 to 53%, it is possible to maintain good workability in slitting, etc., and the CR value at high temperatures can be maintained. can prevent a decline in If the crystallinity of the film is less than 45%, the workability during slitting will be poor;
%, the CR value at high temperatures will drop significantly. Also, as a film for capacitors, it is usually 3~
Preferably, the thickness is about 12μ. In addition to the inert fine particles precipitated in the reaction system as described above, the film of the present invention contains additive particles such as kaolin, talc, and silica, and other additives within the range that does not impair the properties of the film. I can't help it. As detailed above, the present invention provides a polyester film in which the main component of the inert material particles is precipitated particles in which the molar ratio of phosphorus element to calcium element in the precipitated particles is within a specific range, and This relates to a biaxially oriented polyester film for capacitors that is characterized by solution haze and crystallinity within a certain range, and only when all of these conditions are met at the same time will various workability during film handling be achieved. It has been discovered that it is possible to obtain a polyester film for capacitor dielectrics that satisfies all of various electrical properties at the same time, and its industrial value is great. The present invention will be explained in more detail below with reference to Examples and Comparative Examples. In the examples and comparative examples, "parts" indicate "parts by weight." The measurement method used is shown below. Solution haze: Measured using an integrating sphere haze meter (SR type, manufactured by Nippon Seimitsu Kogaku Co., Ltd.) according to the method defined in the specification. Precipitated particle composition: First, the precipitated particles are separated. That is, 1.0 g of 0-chlorophenol was added to 100 g of polyester film, heated at 120°C for 3 hours, and then heated using a Beckman ultracentrifuge L3-50.
The particles obtained by centrifugation at 30,000 rpm for 40 minutes are vacuum dried at 100°C. When the particles are measured using a scanning differential calorimeter, if a melting peak corresponding to the polymer is observed, the particles are 0-
After adding chlorphenol and heating and cooling, perform centrifugation again. When the melting peak is no longer observed, the particles are defined as precipitated particles. Normally, two centrifugation operations are sufficient. According to this operation, all the inert material particles in the polyester film are determined, but if additive particles are included as inert material particles, the amount of precipitated particles can be determined by subtracting the amount, which is known in advance. Next, the calcium and phosphorus elements in the precipitated particles are determined. Calcium element: After incinerating the precipitated particle sample at 100°C for 2 hours, dissolve it in a hydrochloric acid solution and quantify by atomic absorption method. Phosphorus element: After wet ashing the precipitated particle sample in the presence of sulfuric acid and perchloric acid, color was developed with ammonium molybdate in an acidic solution of sulfuric acid, and 845n
The absorbance of m is measured and quantified using a calibration curve prepared in advance. Sliding property: The slipping property of the film is represented by the coefficient of friction, which was measured in accordance with ASTM D-1894 using a method modified so that it can be measured using a tape-shaped sample. The measurements were carried out in an atmosphere with a temperature of 21±2℃ and a humidity of 65±5%.The size of the sample used was 15mm in width.
mm, length 150mm, and the pulling speed is 20mm/min
And so. The coefficients of static and kinetic friction are μ _S and μ _D, respectively.
It was shown in Workability during slitting: The degree of swelling of the slit portion when polyester film was slit was divided into three ranks by observing with an electron microscope. A: There is almost no bulge and the shape of the roll is good, and C: the bulge is large (0.3μ or more).
B is the one that swells at the end when rolled, and is in the middle of the two. Measurement of withstand voltage: Using a 100KV AC withstand voltage tester (OEL-72034 manufactured by Toyo Seiki), the voltage was increased and the voltage at which the film broke and a short circuit occurred was read. Measurement of CR value: The test film was kept at a predetermined temperature for 1 hour and then measured. The capacitance C was measured using General Radio's "RLC DigiBridge" at 1KHz and 0.3Vrms, and the electrical resistance R was measured at 100 VDC using a super megohmmeter made by Yokogawa Hyuretsu Card Co., Ltd.
The measured value was read 1 minute after the application of . The product of both [Ω·F] is the CR value. Life characteristics: A foil-wound capacitor element with a capacitance of 0.1 μF was created by laminating and winding the test film with 6μ thick aluminum foil.A DC voltage of 300V was applied across the device, and the temperature was increased to 85℃ as an accelerated test. Capacitor element after 1000 hours in an atmosphere
The survival rate of elements that functioned as capacitors without shorting out of 100 was shown. Crystallinity: The crystallinity is calculated using the density method (June 1963).
(200 pages, published by Coronasha Polyester Fiber Co., Ltd., written by Mio Yokouchi and Itaru Nakamura). That is, the degree of crystallinity is expressed as Xc = d _k (d - d _a )/d (d _k - d _a ) x 100 (%). where d _a : Amorphous density 1.331 g/cm ² d _k : Crystalline density 1.455 g/cm ² d : Sample density Example 1 (Production of polyester) 100 parts of dimethyl terephthalate, 70 parts of ethylene glycol, 0.11 part of calcium acetate monohydrate was placed in a reactor and heated to raise the temperature, and methanol was distilled off to carry out the transesterification reaction. It took about 4 hours after the start of the reaction to reach 230°C, and the transesterification reaction was substantially completed. finished. Triethyl phosphite is then added to this reaction mixture.
A solution obtained by uniformly dissolving 0.062 part of triethyl phosphate and 0.27 part of triethyl phosphate in ethylene glycol was added, and then 0.04 part of antimony trioxide was added, and the temperature was raised to 236°C over 10 minutes. From this point on, the pressure in the system was gradually reduced, and 80 minutes after adding antimony trioxide, the temperature in the system was 265℃ and the pressure was 300mmHg, and then the temperature and pressure were gradually increased and the pressure was reduced to 285℃ and 1mmHg or less. . After 4 hours, the pressure in the system was returned to normal, and the polymer was discharged and made into chips. (Manufacture of polyester film) Next, the polymer was extruded into a sheet form from an extruder at 290°C, rapidly cooled to form an amorphous sheet, and then
Stretched to 3.5 times in the longitudinal and transverse directions at ℃, and stretched to 3.5 times at 200℃.
Heat treatment was performed for seconds to obtain a 6μ film. The crystallinity of this film was 47%. Table 1 shows the results of measuring the static friction coefficient, dynamic friction coefficient, workability during slitting, CR value and life characteristics at room temperature (25°C) and high temperature (125°C) for this film. (Measurement of Precipitated Particles) The amount of precipitated particles obtained from the film by centrifugation was 0.22% by weight based on the polyester film. The amounts of calcium element and phosphorus element in the precipitated particles were 6.3 and 6.4% by weight, respectively, based on the precipitated particles, and the molar ratio of phosphorus element to calcium element was 1.3. Next, when the solution haze of the film containing the precipitated particles was measured, H ⁴⁴⁰ = 35.9%, H ⁵⁵⁰ = 26.0.
%, H ⁶⁷⁰ = 17.2%. Therefore, H ⁴⁴⁰ / H ⁶⁷⁰ is
It becomes 2.09. Example 2 A test was conducted using the end portion of the film obtained during the film forming operation in Example 1 as a recycled product. That is, the ends of the film obtained in Example 1 were melted again and pelletized, and the chips of Example 1 and this recycled product were mixed at a ratio of 3:1. After measuring the precipitated particles on this mixed chip in the same manner as in Example 1, it was formed into a film in the same manner as in Example 1 to obtain a polyethylene terephthalate film having a thickness of 6 μm and a crystallinity of 50%. Table 1 shows the measurement results for this film. Comparative Example 1 In Example 1, the amount of triethyl phosphite and triethyl phosphate added was 0.025 parts and
0.26 part, and the temperature at the end of the transesterification reaction was 238
A polyester was produced in the same manner as in Example 1, except that the temperature was adjusted to 10.degree. C. and polymerization was started immediately after adding the phosphorus compound and antimony trioxide. Next, using the obtained polymer, a film having a thickness of 6 μm and a crystallinity of 47% was obtained in the same manner as in Example 1. Table 1 shows the measurement results for this film. Note that the molar ratio of phosphorus element to calcium element in the precipitated particles in the film was 1.4,
The H ⁵⁵⁰ = 6.0% and H ⁴⁵⁰ /H ⁶⁷⁰ = 2.80, which were outside the range shown in Figure 1. Comparative Example 2 After carrying out the transesterification reaction under the same conditions as in Example 1, 0.25 parts of silica with an average particle size of 2.5μ, 0.04 parts of phosphoric acid and 0.04 parts of antimony trioxide were added and polymerized according to a conventional method to form a polymer. I got it. Next, by using the polymer and changing the heat treatment conditions, a 6 μm thick film with a crystallinity of 35% was obtained. Table 1 shows the measurement results for this film. Comparative Example 3 A polymer was obtained in the same manner as in Example 1, except that after carrying out the transesterification reaction under the same conditions as in Example 1, only 0.04 part of antimony trioxide was added. Next, using this polymer, a polyester film having a thickness of 6 μm and a crystallinity of 47% was obtained in the same manner as in Example 1. The measurement results for this film are
Shown in the table. In addition, a large number of precipitated particles were observed in the film, and when the solution haze was measured, H ⁵⁵⁰ = 34.3
%, H ⁴⁵⁰ /H ⁶⁷⁰ =2.01, which was within the range shown in FIG. 1, but the precipitated particles did not contain phosphorus element. Comparative Example 4 After carrying out the transesterification reaction under the same conditions as in Example 1, 0.3 parts of calcium acetate hydrate, 0.15 parts of triethyl phosphite, and 0.5 parts of triethyl phosphate were added, and then antimony trioxide was added.
A polyester was obtained in the same manner as in Example 1 except that 0.04 part was added. Next, using this polymer, a polyester film having a thickness of 6 μm and a crystallinity of 47% was obtained in the same manner as in Example 1. The measurement results for this film are
Shown in the table. The measurement result of the solution haze of this film is located to the right of the BC line shown in Figure 1, and there are many coarse particles exceeding about 4μ due to agglomeration in this film, and the withstand voltage characteristics are is getting worse. Comparative Example 5 A polyester was obtained in the same manner as in Comparative Example 4, except that only 0.1 part of triethyl phosphite was used as the phosphorus compound. Next, using this polymer, a film with a thickness of 6 μm was obtained in the same manner as in Example 1. However, by changing the heat treatment conditions at this time, the crystallinity of the resulting film was reduced to 43
%. Table 1 shows the measurement results for this film. The measurement result of the solution haze of this film is located below the AB line shown in Figure 1, and there are many coarse particles exceeding about 4μ in the film, which deteriorates the withstand voltage characteristics. ing. Also,
The ratio between the coefficient of static friction and the coefficient of dynamic friction was large, and the workability during slitting was insufficient, making it unsatisfactory as a film for capacitors. As is clear from the Examples and Comparative Examples, the polyester film of the present invention, which contains precipitated particles of a specific composition and has a solution haze and crystallinity within a specific range, has various characteristics that should be possessed as a capacitor dielectric film. Moreover, the method of the present invention can be easily carried out industrially, and therefore has great utility value.

【table】 [Brief explanation of the drawing]

FIG. 1 is a graph showing the preferred solution haze range of the polyester film of the present invention.

Claims (1)

[Scope of Claims] 1. A polyester film containing inert fine particles precipitated by causing trialkyl phosphite and trialkyl phosphate to act on a calcium compound soluble in the reaction system for polyester production, , the inert fine particles are
The polyester film contains calcium element and phosphorus element in a molar ratio of 0.7 to 2.5, and the solution haze of the polyester film is such that the coordinate points A, B, C, and D shown in the table below are connected to each other by a straight line. A biaxially stretched polyester film for a capacitor, which is within the range obtained by binding the polyester film with a degree of crystallinity of 45 to 55%. [Table] (A, B, C, and D in the above table are points on the coordinate axis with H ⁵⁵⁰ on the horizontal axis and H ⁴⁵⁰ /H ⁶⁷⁰ on the vertical axis.
H ⁴⁵⁰ , H ⁵⁵⁰ and H ⁶⁷⁰ are 450nm and 550nm respectively
and solution haze (%) measured by the method defined in the specification using light at a wavelength of 670 nm.