Alkaline earth metal carbonate, resin composition, optical film, and method for producing alkaline earth metal carbonate

Abstract

This alkaline-earth metal carbonate contains an aragonite-type carbonate having a composition represented by CaxSr1-xCO3 (0.1≤x≤0.5).

Description

[Technical Field]

[0001] The present invention relates to an alkaline earth metal carbonate, a resin composition, an optical film, and a method for producing an alkaline earth metal carbonate. [Background technology]

[0002] In recent years, strontium carbonate and calcium carbonate, which have controllable optical properties such as birefringence, have been attracting attention as inorganic fillers for optical films such as retardation films. Strontium carbonate has a non-polymorphic crystal system, making it easy to produce acicular particles but with a low birefringence. On the other hand, calcium carbonate has a high birefringence but is prone to becoming calcite during the carbonation reaction, which reduces the proportion of acicular aragonite.

[0003] The birefringence of strontium carbonate is an inherent value, and depending on the type of optical film, a large amount of addition is required to control the phase difference, which affects dispersibility (requires a large amount of surface treatment agent) and optical properties (increased haze). Calcium carbonate has a birefringence 1.3 times that of strontium carbonate, but because it tends to become spherical calcite during the carbonation reaction of calcium hydroxide, it does not form the desired needle shape that is easy to orient, making it difficult to apply to optical applications.

[0004] Highly dispersible aragonite-type calcium carbonate has been proposed (see, for example, Patent Document 1). Also, a method for producing precipitated calcium carbonate with a total aragonite content of more than 60% has been proposed (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-43809 [Patent Document 2] Special Publication No. 2013-527105 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an alkaline earth metal carbonate, a resin composition, an optical film, and a method for producing the alkaline earth metal carbonate, which are capable of controlling the optical properties such as birefringence of an optical resin. [Means for solving the problem]

[0007] As a result of extensive research to achieve the above object, the present inventors have found a specific composition containing Ca and Sr, specifically Ca x Sr 1-x The inventors have discovered that aragonite-type carbonates with a composition expressed as CO3 (0.1≦x<0.5) are alkaline earth metal carbonates that can control the optical properties such as birefringence of optical resins, and have completed the present invention.

[0008] That is, the present invention provides Ca x Sr 1-x It is an alkaline earth metal carbonate containing aragonite-type carbonate with a composition expressed as CO3 (0.1≦x<0.5).

[0009] The present invention also provides a resin composition comprising a resin and the alkaline earth metal carbonate described above.

[0010] Furthermore, the present invention provides an optical film comprising a resin composition containing a resin and the alkaline earth metal carbonate described above.

[0011] Furthermore, the present invention relates to a method for producing the aforementioned alkaline earth metal carbonate, which comprises adding a strontium compound and an organic acid to a slurry of a calcium compound, and then blowing in a carbon dioxide-containing gas. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an alkaline earth metal carbonate capable of controlling optical properties such as birefringence of an optical resin, an optical film, and a method for producing the alkaline earth metal carbonate. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a transmission electron microscope photograph of the CaxSr1-xCO3 fine powder obtained in Example 1. [Figure 2] X-ray diffraction diagrams of alkaline earth metal carbonates. [Figure 3] FIG. 2 is a diagram showing the relationship between the composition of alkaline earth metal carbonate and the in-plane retardation. [Figure 4] FIG. 1 is a diagram showing the relationship between the composition of alkaline earth metal carbonates and ΔV. DETAILED DESCRIPTION OF THE INVENTION

[0014] The alkaline earth metal carbonate of the present invention is Ca x Sr 1-x It contains an aragonite-type carbonate having a composition represented by the formula CO3 (0.1≦x<0.5). As long as it contains a carbonate of this composition, it may contain alkaline earth metal carbonates of other compositions. For example, Ba x Sr 1-x Examples of compositions include CO3.

[0015] Below, Ca x Sr 1-x We will explain about aragonite-type carbonates with the composition CO3 (0.1≦x<0.5). x Sr 1-x If x in CO3 is less than 0.1, the amount of particles with an aspect ratio of less than 2.0 will be large, and if it is 0.5 or more, the amount of heterophase CaCO3 (calcite) will be large. In either case, the object of the present invention cannot be achieved. The preferred range of x is 0.15≦x≦0.4, and the more preferred range is 0.2≦x≦0.335. The presence of Ca in carbonates can be confirmed by energy dispersive X-ray spectroscopy (EDS).

[0016] The BET specific surface area of ​​aragonite-type carbonates is 60m 2 / g. The BET specific surface area is preferably greater than 60 m 2 If the specific surface area is less than 100 nm, the particle size may be larger than 100 nm. 2 / g or more is more preferable.

[0017] The aragonite-type carbonate in the present invention preferably has a major axis of 100 nm or less. Furthermore, the major axis is more preferably within the range of 10 to 100 nm, and most preferably within the range of 10 to 60 nm. If the major axis is less than 10 nm, the particles are too small and prone to aggregation, resulting in poor dispersibility. On the other hand, if the major axis exceeds 100 nm, the particles are too large and prone to poor transparency when mixed with a resin.

[0018] Here, the major axis can be measured by visual inspection or automatic image processing of a transmission electron microscope (TEM) photograph of the alkaline earth metal carbonate particles. The major axis can be measured as the length in the longitudinal direction (the length of the long side) when the carbonate particle is considered as a rectangle. The minor axis can be measured as the length in the lateral direction (the length of the short side) when the carbonate particle is considered as a rectangle. Specifically, the rectangle that circumscribes the carbonate particle in the image and has the smallest area is calculated, and the major axis and minor axis are determined from the lengths of the long and short sides of the calculated rectangle.

[0019] The "major axis / minor axis" of the particle is defined as the aspect ratio. The aspect ratio of the aragonite-type carbonate is preferably 2.0 or more. Furthermore, it is more preferably in the range of 2.0 to 4.0, and most preferably in the range of 2.0 to 3.0. If the aspect ratio is less than 2.0, it becomes difficult to effectively control birefringence. On the other hand, if the aspect ratio exceeds 4.0, the particles become too elongated and easily break, which can lead to a deterioration in particle size distribution.

[0020] Particles having the above-described major axis and aspect ratio preferably have a major axis variation coefficient of 0.5 or less. The major axis variation coefficient is expressed as the ratio of the standard deviation of the major axis to the average major axis value, and can be calculated using the following mathematical formula (1):

[0021]

number

[0022] In the above formula (1), r is the average major axis length, n is the number of particles whose major axis is measured, and r i represents the major axis of the i-th measured particle. The value of n is defined as 100 or more, and a large value of n is preferable, more preferably 200 or more. If the value of n is less than 100, the dispersion of the particles cannot be accurately reflected. When the coefficient of variation is expressed as a percentage, the value of the above formula (1) can be multiplied by 100. For example, a coefficient of variation of 0.5 or less can be expressed as a coefficient of variation of 50% or less.

[0023] The coefficient of variation of the major axis is preferably small, specifically, preferably 0.5 or less, more preferably 0.4 or less. If the coefficient of variation of the major axis exceeds 0.5, the proportion of particles having a major axis longer than the average value increases, which may result in a decrease in light transmittance.

[0024] The coefficient of variation can be measured, for example, by observing well-dispersed carbonate particles under a transmission electron microscope, capturing the particle photographs with a scanner and saving them as image files, and then measuring and aggregating the information in these saved image files for each particle using image analysis particle size distribution measurement software "Mac-View" Ver. 3 manufactured by Mountech Co., Ltd.

[0025] In the alkaline earth metal carbonate of the present invention, the aragonite-type carbonate preferably accounts for at least 90% by mass. If 90% by mass or more of the aragonite-type carbonate is present, for example, an effect of reducing the birefringence of an optical film in which carbonate particles are dispersed can be obtained. The aragonite-type carbonate is more preferably 95% by mass or more. The content of the aragonite-type carbonate can be confirmed, for example, by XRD analysis.

[0026] (Method for producing alkaline earth metal carbonate) The alkaline earth metal carbonate of the present invention can be produced, for example, by the following method using a slurry of a calcium compound. Examples of calcium compounds include quicklime. Quicklime slurry can be prepared, for example, by suspending quicklime powder in water, but is not limited to this. The quicklime concentration in the quicklime slurry is preferably in the range of 2.6 to 12.6 g / L, more preferably in the range of 2.6 to 8.6 g / L. If the concentration is too high, contact between particles is promoted, which tends to increase the particle size and lead to the formation of spherical CaCO3 (calcite) as a heterogeneous phase. Any calcium compound that releases calcium ions in water can be used, including carbonates, sulfates, nitrates, oxides, chlorides, and hydroxides.

[0027] Before or after the start of the reaction, a strontium compound and an organic acid are added, and the reaction is carried out in the presence of strontium ions and the organic acid. The strontium compound may be any compound that releases strontium ions in water, and its carbonate, sulfate, nitrate, oxide, chloride, hydroxide, etc. may be used.

[0028] The coexistence of strontium ions inhibits the formation of calcite and increases the content of aragonite-type carbonates. The amount of calcium compound added relative to the strontium compound is 0.96 mol or less, preferably 0.50 mol or less, per mol of strontium hydroxide octahydrate in the raw material. For example, when calcium oxide is used, the amount is 2.3% by mass or more and 20.3% by mass or less, preferably 2.3% by mass or more and 10.6% by mass or less, relative to strontium hydroxide octahydrate.

[0029] On the other hand, the organic acid is preferably an organic acid having two or more carboxyl groups or hydroxyl groups, such as a dicarboxylic acid or a hydroxycarboxylic acid. Specifically, citric acid, tartaric acid, phthalic acid, etc. can be used, with tartaric acid being particularly preferred.

[0030] The amount of organic acid added is preferably 18.7% by mass or more, more preferably 18.7% by mass or more and less than 91.6% by mass of calcium oxide in the raw material. The ratio of the strontium compound to the organic acid (strontium compound:organic acid) is preferably 96.3:3.7 to 97.9:2.1 by mass. By setting the ratio of the organic acid to the strontium compound to 96.3:3.7 or less, the formation of calcite can be effectively suppressed. By setting the ratio to 97.2:2.8, aragonite with excellent dispersibility and other properties can be produced.

[0031] The method for producing the alkaline earth metal carbonate of the present invention will now be described in detail. The alkaline earth metal carbonate of the present invention can be produced, for example, by a method comprising a reaction step of reacting an alkaline earth metal hydroxide, a strontium compound, and carbon dioxide in the presence of an organic acid to produce alkaline earth metal carbonate particles, an aging step of growing the alkaline earth metal carbonate particles into needle-like shapes, a surface treatment step of treating the alkaline earth metal carbonate particles with a surfactant, and a drying step of drying the alkaline earth metal carbonate particles.

[0032] (Reaction step) In the reaction step, a raw material liquid containing an organic acid, an alkaline earth metal hydroxide, and a strontium compound is preferably stirred while a carbon dioxide-containing gas is introduced into the raw material liquid to carbonate the alkaline earth metal hydroxide and the strontium compound, thereby producing alkaline earth metal carbonate particles. The reaction may be started after all materials are mixed at once, or may be carried out in multiple stages while materials are added. The carbon dioxide-containing gas may contain an inert gas such as oxygen or nitrogen, as long as the carbon dioxide content is 50% or more.

[0033] By controlling the supply rate of carbon dioxide-containing gas to a low level in the early stages of the reaction, the formation of aragonite seed crystals can be promoted. After sufficient aragonite seed crystals have formed, the gas injection rate can be increased (for example, to about 3.75 L / min), which promotes the reaction. Furthermore, the formation of large crystals can be suppressed.

[0034] The raw material liquid can be an aqueous solution in which an alkaline earth metal hydroxide and a strontium compound are dissolved, or it can be an aqueous suspension in which an alkaline earth metal hydroxide and a strontium compound are dispersed. The concentration of the alkaline earth metal hydroxide in the raw material liquid is not particularly limited, but is usually in the range of 1% by mass to 20% by mass, preferably 2% by mass to 18% by mass, and more preferably 3% by mass to 15% by mass.

[0035] The organic acid is a carboxylic acid having a hydroxyl group that adheres to the generated alkaline earth metal carbonate particles and inhibits the crystal growth of the alkaline earth metal carbonate particles. The organic acid is preferably an organic acid having two carboxyl groups and a total of 3 to 6 carboxyl groups and hydroxyl groups. A dicarboxylic acid or anhydride thereof containing one or more hydroxyl groups in the molecule is more preferred. The organic acid may be a monomer that serves as a raw material for the optical resin to which the alkaline earth metal carbonate fine powder is added. The content of the organic acid in the raw material solution is generally in the range of 0.1 to 20 parts by mass, preferably 1 to 10 parts by mass, per 100 parts by mass of alkaline earth metal hydroxide.

[0036] The temperature of the raw material liquid is preferably within a range of 5° C. to 60° C. The flow rate of carbon dioxide gas introduced into the raw material liquid is generally within a range of 0.5 mL / min to 200 mL / min, preferably 0.5 mL / min to 100 mL / min, per 1 g of alkaline earth metal hydroxide.

[0037] The particle shape of the alkaline earth metal carbonate particles produced in the reaction step is not particularly limited and may be either granular or acicular. The particle shape and size of the alkaline earth metal carbonate particles can be adjusted by conditions such as the liquid temperature of the raw material liquid, the concentration of the alkaline earth metal hydroxide and monomer in the raw material liquid, and the flow rate of the carbon dioxide-containing gas introduced into the raw material liquid. If the alkaline earth metal carbonate particles produced in the reaction step are acicular, the subsequent aging step may be omitted. The completion of the reaction is monitored by pH, and is terminated when the pH reaches approximately 7.0.

[0038] (ripening process) In the aging step, the aqueous suspension of alkaline earth metal carbonate particles obtained in the reaction step is preferably heated and aged at a temperature in the range of 75°C to 115°C, thereby growing the alkaline earth metal carbonate particles into needle-like particles. If the heating temperature is less than 75°C, crystal growth in the major axis of the alkaline earth metal carbonate particles tends to be insufficient, resulting in a low average aspect ratio. On the other hand, if the heating temperature exceeds 115°C, crystal growth in the minor axis of the alkaline earth metal carbonate particles tends to be accelerated, resulting in a low aspect ratio.

[0039] The heating temperature is preferably in the range of 80°C to 110°C, particularly preferably in the range of 85°C to 105°C. Heat aging is preferably carried out with stirring. The heating time is not particularly limited, but is usually in the range of 1 hour to 100 hours, preferably in the range of 5 hours to 50 hours, particularly preferably in the range of 10 hours to 30 hours.

[0040] (Surface treatment process) In the surface treatment step, a surfactant is preferably added to the slurry of acicular alkaline earth metal carbonate particles obtained in the aging step to treat the surfaces of the alkaline earth metal carbonate particles, thereby obtaining an aqueous slurry of highly dispersible acicular alkaline earth metal carbonate particles. After adding the surfactant to the slurry, the slurry is preferably stirred to make the surfactant concentration uniform, and then a shear force is applied to the slurry. By applying a shear force to break down the agglomerates of the alkaline earth metal carbonate particles, the surfaces of the alkaline earth metal carbonate particles (primary particles) can be uniformly treated with the surfactant.

[0041] The surfactant may be, for example, polyoxyethylene styrenated phenyl ether phosphate, etc. The amount of surfactant added to the slurry is generally in the range of 1 to 40 parts by mass, preferably 3 to 30 parts by mass, per 100 parts by mass of alkaline earth metal carbonate particles in the slurry.

[0042] (drying process) In the drying step, the aqueous slurry of highly dispersible acicular alkaline earth metal carbonate particles obtained in the surface treatment step is dried to obtain alkaline earth metal carbonate. The drying step can be carried out by a known drying method using a dryer such as a spray dryer or a drum dryer.

[0043] In this way, Ca x Sr 1-x It is possible to obtain alkaline earth metal carbonates containing aragonite-type carbonates with a composition represented by CO3 (0.1≦x<0.5). 2 / g, a major axis of 100 nm or less, an aspect ratio of 2.0 or more, and a coefficient of variation of the major axis of 0.5 or less can be suitably obtained. Specifically, the particles are acicular particles with a minor axis of about 5 to 30 nm (average 20 nm) and a major axis of 100 nm or less, specifically about 10 to 80 nm (average 60 nm), and do not contain particles of 1 μm or more. In addition, the aragonite content is as high as 95% by weight, and there is almost no aggregation of aragonite particles.

[0044] The alkaline earth metal carbonate of the present invention can be used as a filler for paper, ink, paint, etc., an additive for plastics, adhesives, films, etc., or a carrier for foods, medicines, etc.

[0045] In particular, the alkaline earth metal carbonate of the present invention can be mixed with a resin to form a resin composition, which can be suitably used as an optical film by forming a film from the resin composition. The optical film will now be described.

[0046] The resin is not particularly limited as long as it is a resin used in ordinary optical films, and various resins can be selected depending on the purpose. Examples of such resins include polymethyl methacrylate resin, polycarbonate resin, cycloolefin resin (including cyclic olefin copolymer), and polyester resin. Furthermore, one or more types selected from the group consisting of cellulose esters such as triacetyl cellulose, polystyrene, styrene-acrylonitrile copolymer, polyfumaric acid diester, polyarylate, polyethersulfone, polyolefins such as polycyclic olefin, maleimide copolymers, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, and polyurethane can also be used.

[0047] The content of alkaline earth metal carbonate in the entire resin composition is preferably within the range of 0.1 to 50% by mass. If the content of alkaline earth metal carbonate is less than 0.1% by mass, the birefringence control effect of the alkaline earth metal carbonate will be too small. Conversely, if the content of alkaline earth metal carbonate exceeds 50% by mass, the ratio of alkaline earth metal carbonate to the resin will be too high, resulting in poor transparency of the formed film. The content of alkaline earth metal carbonate in the entire resin composition is more preferably within the range of 0.5 to 40% by mass, particularly preferably 1 to 35% by mass. It is even more preferably within the range of 5 to 20% by mass.

[0048] The resin composition can be prepared by mixing the above-mentioned resin with an alkaline earth metal carbonate. The mixing of the alkaline earth metal carbonate and the resin can be carried out by a known method such as a method using an ultrasonic homogenizer, a stirring blade, or a liquid jet mill.

[0049] Alternatively, an optical film may be formed by preparing a dope solution by mixing a resin composition with an appropriate solvent. The solvent is not particularly limited and can be appropriately selected depending on the properties of the resin. Preferred examples of the solvent include organic solvents, such as alcohols (ethanol, 1-propanol, 2-propanol, 1-butanol, ethylene glycol), methylene chloride, N-methylpyrrolidone (NMP), tetrahydrofuran (THF), methyl ethyl ketone (MEK), ethyl acetate, cyclohexane, and toluene. Of these, methylene chloride is particularly preferred among organic solvents. The resins can be used alone or in combination.

[0050] The ratio of resin to solvent is preferably within a range of 1:10 to 10:1 by mass. The dope solution can be prepared by mixing the resin and the solvent to form a resin mixed solution and then adding an alkaline earth metal carbonate to the resin mixed solution. Alternatively, the alkaline earth metal carbonate and the solvent can be mixed to form a carbonate mixed solution, and then the resin can be added and mixed. Furthermore, the above-mentioned resin mixed solution and carbonate mixed solution can be prepared separately and then mixed to form the dope solution. The alkaline earth metal carbonate, resin, and solvent can be mixed by a known method such as a method using an ultrasonic homogenizer, a stirring blade, or a liquid jet mill.

[0051] The resin composition or dope solution can be formed into a film by a known method to form an optical film. Examples of the film formation method include known film formation methods such as melt extrusion film formation and solution casting film formation. The melt extrusion film formation method is a method in which a resin composition is heated and melted to form a melt, which is then cast into a film on a support and cooled to solidify. The solution casting film formation method is a method in which a dope solution is cast onto a support and the solvent is evaporated to form a film.

[0052] Depending on the type of resin, convection may occur in the resin solution during film formation, resulting in the formation of a Benard cell structure. When the Benard cell structure is formed, alkaline earth metal carbonates aggregate, reducing the transparency of the optical film. This aggregation also reduces the birefringence-adjusting effect of the alkaline earth metal carbonates. Therefore, it is preferable to add a surface modifier to the resin composition or dope solution to improve wettability with the support and suppress the formation of Benard cells. When polycarbonate is used as the resin, Benard cells are likely to form, so adding a surface modifier has a significant effect on improving transparency, etc. Examples of surface modifiers include vinyl surfactants, fluorine-based surfactants, and silicone oils.

[0053] The formed film can be stretched appropriately depending on the application. Examples of the stretching method include uniaxial stretching and biaxial stretching. Biaxial stretching can be sequential or simultaneous stretching. Stretching can be performed using a known stretching device such as a tenter.

[0054] The optical film obtained in this manner contains fine, highly dispersed alkaline earth metal carbonates, and therefore has excellent transparency. Moreover, by adjusting the content of alkaline earth metal carbonates relative to the entire optical film, the birefringence of the optical film itself can be adjusted. Since alkaline earth metal carbonates themselves exhibit negative birefringence, the birefringence of the optical film can be adjusted depending on the intended use of the optical film.

[0055] For example, by adding an alkaline earth metal compound fine powder to a resin exhibiting positive intrinsic birefringence, such as polycarbonate or polycyclic olefin, the intrinsic birefringence of the resin can be offset to produce an optical film with birefringence close to zero. Examples of such optical films include protective films. Protective films include not only ordinary protective films laminated on the surface of a polarizing plate, but also polarizer protective films laminated directly on the surface of a polarizer to protect the polarizer.

[0056] Alternatively, an optical film having positive birefringence may be obtained by adding a small amount of alkaline earth metal carbonate to a resin exhibiting positive birefringence, such as polycarbonate or polycyclic olefin. Furthermore, an optical film having negative birefringence may be obtained by adding a large amount of alkaline earth metal carbonate to these resins exhibiting positive birefringence. Here, "birefringence" refers to the value of the in-plane birefringence (ΔNxy) described above. An example of an optical film exhibiting such positive or negative in-plane birefringence is a retardation film. Examples of retardation films include a quarter-wave plate and a half-wave plate.

[0057] Conversely, by using a resin that exhibits negative birefringence or a resin with low birefringence, such as polymethyl methacrylate or polystyrene, an optical film that exhibits negative birefringence can be obtained. Examples of such optical films include retardation films. Examples of retardation films include quarter-wave plates and half-wave plates.

[0058] Examples of optical films include retardation films and protective films, as well as anti-reflection films, anti-glare films, brightness-enhancing films, prism films, and viewing angle-improving films.

[0059] The haze of the optical film can be 10% or less, preferably 5% or less, and more preferably 1% or less. It is also possible to intentionally increase the haze depending on the application of the optical film. For example, the haze can be increased by adding light-scattering fine particles such as glass beads to the resin composition to form an antiglare film. The light transmittance of the optical film can be 85% or more, preferably 88% or more, and more preferably 90% or more.

[0060] The optical film as described above can also be laminated with other optical films to form an optical laminate. Examples of other optical films include a polarizing film (also called a polarizer) and a substrate film. Examples of the optical laminate include a polarizing plate in which a protective film as the optical film of the present invention and a polarizing film are laminated, an elliptical polarizing plate in which a retardation film as the optical film of the present invention and a polarizing film are laminated, and a retardation plate in which a retardation film as the optical film of the present invention and a substrate film are laminated.

[0061] The optical film of the present invention can be used in image display devices. Examples of image display devices include liquid crystal display devices (LCDs) and organic electroluminescence display devices. Applications of image display devices include televisions, computer monitors, mobile phones, smartphones, personal digital assistants (PDAs), and other portable information terminals. [Example]

[0062] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0063] <Alkaline earth metal carbonates (Ca x Sr 1-x CO3) production (a) Reaction step A solution was prepared by adding 7.08 g of DL-tartaric acid as a crystal growth inhibitor to 3 L of pure water at a temperature of 10°C and stirring. 7.73 g of calcium oxide was added to the resulting aqueous solution, and after stirring for 30 minutes, 329.40 g of strontium hydroxide octahydrate was added to prepare an aqueous suspension containing calcium ions and strontium ions. While maintaining the resulting aqueous suspension at 10°C and continuing to stir, carbon dioxide gas was blown into the aqueous suspension at a flow rate of 0.5 L / min. x Sr 1-x After that, stirring was continued for another 30 minutes, and the Ca x Sr 1-x An aqueous suspension of CO3 microparticles was obtained.

[0064] (b) Aging process The Ca obtained in (a) above x Sr 1-x The aqueous CO3 particle suspension was heated at 85°C for 12 hours while being stirred using a stirring blade rotating at a peripheral speed of 2.5 m / sec. x Sr 1-x The CO3 particles were grown into needle-like particles. After that, they were allowed to cool to room temperature. x Sr 1-x An aqueous slurry of CO3 particulates was prepared.

[0065] (c) Surface treatment process The Ca obtained in (b) above x Sr 1-x An aqueous slurry of CO3 particles (solid concentration: 6 mass%) was added to the solution containing polyoxyethylene styrenated phenyl ether phosphate ester (Ca x Sr 1-x CO3 (30 parts by mass per 100 parts by mass) was added and dissolved, and then the mixture was stirred for 5 minutes using a stirrer. After that, a dispersion treatment was carried out by applying shear force using Clearmix (manufactured by M Technique Co., Ltd.).

[0066] (d) Drying process (spray dryer) Highly dispersible needle-shaped Ca obtained in (c) above x Sr 1-x The aqueous slurry of CO3 microparticles was sprayed using a spray dryer set at an inlet temperature of 220°C and an outlet temperature of 110°C. x Sr 1-x CO3 fine powder was obtained. x Sr 1-x The CO3 fine powder was observed using a transmission electron microscope (TEM). x Sr 1-x The TEM photograph of CO3 fine powder is shown in Figure 1. x Sr 1-x The CO3 fine powder was confirmed to be a fine powder of acicular particles. Image analysis of SEM photographs revealed that the average major axis of the acicular particles was 75.83 nm and the aspect ratio was 2.5.

[0067] Ca in Example 1 x Sr 1-x The value of x in CO3 was 0.1. The carbonates of Examples 2 and 3 and Comparative Example 1 were produced by changing the conditions so that the value of x was 0.2, 0.335, and 0.0. The carbonates of Examples 2 and 3 and Comparative Examples 1 and 2 were produced through the same reaction step, aging step, and surface treatment step as described above, except that the amounts of calcium oxide and strontium hydroxide octahydrate used as raw materials were changed appropriately.

[0068] The crystal structure of the obtained particles was determined by XRD analysis. x Sr 1-x It can be seen that CO3 is a single aragonite phase. Also, a peak shift due to solid solution can be confirmed from Figure 2(b). The presence of Ca was confirmed by EDS. On the other hand, the Ca prepared at x = 0.5 x Sr 1-x In CO3, calcite was formed as a complex phase in addition to the aragonite phase. The resulting carbonates were observed for their phase, specific surface area, and shape, and the major and minor diameters of the particles were determined. x Sr 1-x The values ​​of x in CO3 are summarized in the table below.

[0069] [Table 1]

[0070] As shown in the above table, the carbonates of Examples 1 to 3 all have a specific surface area of ​​60 m 2 / g or more, a long diameter of 100 nm or less, an aspect ratio of 2.0 or more, and a coefficient of variation of 0.5 or less. Thus, the carbonates of the examples have a large specific surface area, but also a large long diameter. Furthermore, it can be seen from the TEM photograph (Figure 1) that aggregation is suppressed in the carbonates of the examples. When x=0.5, the calcite phase is generated in addition to the aragonite phase, and the specific surface area is 60 m 2It is estimated that it is not possible to obtain more than 10 ...

[0071] The table below summarizes the lattice constants and lattice volumes of the carbonates of the examples and comparative examples, along with their compositions.

[0072] [Table 2]

[0073] As shown in the above table, the carbonates of Examples 1 to 3 all have an a-axis length of 6.021 Å or less, a b-axis length of 5.036 Å or less, a c-axis length of 8.488 Å or less, and a lattice volume of 257.38 Å. 3 It meets the following criteria.

[0074] Optical films were produced and their physical properties were examined using the carbonates of Examples 1 to 3 and Comparative Example 1. Polymethyl methacrylate resin (PMMA), polycarbonate resin (PC), and cycloolefin resin (COP) were used as resins, and predetermined amounts of carbonates were blended, and each was produced by the following method.

[0075] <Polymethyl methacrylate (PMMA) film> (1) 6 g of polymethyl methacrylate (hereinafter referred to as "PMMA") was added to 25 g of methylene chloride and stirred for 3 hours to prepare a PMMA-methylene chloride solution. Next, 0.6 g of the carbonate of Example 1 was added to 10 g of methylene chloride, and the mixture was dispersed for 3 minutes using an ultrasonic homogenizer. The mixture was then filtered through a membrane filter with a pore size of 1 μm to prepare a carbonate dispersion. The PMMA-methylene chloride dispersion and the carbonate dispersion were mixed and dispersed for 5 minutes using an ultrasonic homogenizer. x Sr 1-x The CO3-added dope solution was obtained.

[0076] (2) PMMA film deposition method Ca x Sr 1-xThe CO3-doped dope solution was applied to a PET film at a wet thickness of 13 mils using a Baker applicator. The resulting film was dried at 40°C for 2 minutes, 60°C for 15 minutes, and 85°C for 30 minutes. The PMMA film was peeled off from the PET film to obtain a PMMA film. The PMMA film was then uniaxially stretched at 2.0 times its original length at 100°C using a stretching apparatus (Imoto Manufacturing Co., Ltd., IMC-1A8D) to obtain a PMMA stretched film.

[0077] <Polycarbonate (PC) film> A PC film was produced using polycarbonate (hereinafter referred to as "PC") as the resin under the same conditions as for the PMMA film.

[0078] <Cycloolefin polymer (COP) film> A cycloolefin polymer (COP) film was produced under the same conditions as for the PMMA film, using COP as the resin.

[0079] The physical properties of the optical film obtained from the resin composition containing carbonate were examined as follows. In-plane retardation: Measured using KOBRA-WR manufactured by Oji Scientific Instruments Co., Ltd., and shown as a value converted into Re@40 μm thickness. Total light transmittance: Measured using a Haze Meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd. Haze: Measured using a Haze Meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd.

[0080] The following table summarizes the physical properties of the optical films using the carbonates of Examples 1 to 3 and Comparative Example 1. The content (mass %) in the table indicates the content of the carbonate relative to the total weight of the resin.

[0081] [Table 3]

[0082] [Table 4]

[0083] [Table 5]

[0084] [Table 6]

[0085] For reference, an optical film was produced using only the resin without adding any carbonate, and the physical properties were similarly examined. The results are summarized below.

[0086] [Table 7]

[0087] Furthermore, Ca 0.05 Sr 0.95 PMMA films were prepared in the same manner as above using CO3, and their properties, along with the carbonate content, are summarized in the table below.

[0088] [Table 8]

[0089] Ca with x less than 0.1 x Sr 1-x The physical properties of the optical film using CO3 are inferior to those of the film using carbonate (x=0.1) in Example 1. The same is true for optical films using other resins. x Sr 1-x As long as CO3 (0.1≦x<0.5) is used, an optical film having desired physical properties can be obtained regardless of the type of resin.

[0090] Figure 3 shows the effect of the carbonate composition on the in-plane retardation of a PMMA film and a COP film. In both cases, the retardation is significantly controlled by adding the alkaline earth metal carbonate of the present invention. This is presumably due to the generation of strain within the carbonate crystals.

[0091] Here, two types of blended carbonates containing CaCO3 and SrCO3 were used to prepare PMMA films in the same manner as described above, and the in-plane retardation was examined. The proportion of CaCO3 in each blended carbonate was 0.2 mass% or 0.335 mass%, and the added amount was 15 mass%. 0.2 Sr 0.8 CO3 or Ca 0.335 Sr 0.675 Compared with the case where CO3 was added, the substitution carbonate (Ca x Sr 1-x It was confirmed that the retardation reduction effect of CO3 (0.1≦x<0.5) was 1.5 times or more that of the blend system.

[0092] Figure 4 shows the effect of the alkaline earth metal carbonate composition on ΔV. ΔV represents the difference between the experimental value of the lattice volume V calculated from the lattice constant measured by XRD and the literature value (experimental value - literature value), and was calculated. Ca x Sr 1-x Figure 4 shows that aragonite-type carbonates with a composition expressed as CO3 (0.1≦x<0.5) have the effect of changing the lattice distortion that affects the refractive index within a certain Ca substitution range.

Claims

1. Ca ｘ Sr １－ｘ CO ３ An alkaline earth metal carbonate containing an aragonite-type carbonate having a composition represented by (0.15≦x≦0.4), The aragonite-type carbonate is an alkaline earth metal carbonate characterized in that it is in the form of particles having a BET specific surface area of ​​more than 60 m 2 / g, a major axis of 100 nm or less, an aspect ratio of 2.0 or more, and a coefficient of variation of the major axis of 0.5 or less.

2. 2. The alkaline earth metal carbonate according to claim 1, wherein the content of the aragonite-type carbonate is 90% by mass or more.

3. A resin composition comprising a resin and an alkaline earth metal carbonate according to claim 1 or 2.

4. An optical film comprising a resin composition containing a resin and the alkaline earth metal carbonate according to claim 1 or 2.

5. An optical film as described in Claim 4, characterized in that the resin is at least one selected from polymethyl methacrylate resin, polycarbonate resin, cycloolefin resin, and polyester resin.

6. A method for producing the alkaline earth metal carbonate according to claim 1 or 2, comprising: A method for producing alkaline earth metal carbonates, comprising adding a calcium compound and a strontium compound to an aqueous solution of an organic acid having two or more carboxyl or hydroxyl groups to form a slurry, and then blowing in a carbon dioxide-containing gas.

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