JP7287387B2 - Strontium carbonate particles, optical film and image display device - Google Patents

Description

The present invention relates to strontium carbonate particles, an optical film containing strontium carbonate particles, and an image display device containing the optical film.

For example, optical films for controlling the phase difference of light are used in various devices such as liquid crystal display devices. Attempts have been made to control the retardation (in-plane retardation) and birefringence (in-plane birefringence) of the optical film in order to adjust the properties of the optical film. Patent Documents 1 to 5 disclose adjustment of birefringence by incorporating microparticles of strontium carbonate into an optical material made of polymer resin.

Japanese Patent Application Laid-Open No. 2004-35347 Japanese Patent Application Laid-Open No. 2005-156863 Japanese Patent Application Laid-Open No. 2007-140011 Japanese Patent Application Laid-Open No. 2008-15118 Japanese Patent Application Laid-Open No. 2008-156479

Patent Documents 1 to 5 describe that birefringence is adjusted by including fine particles of strontium carbonate in an optical material made of a polymer resin. There is still room for improvement in raising it.

The strontium carbonate particles according to one aspect have an average major axis within the range of 10 to 100 nm and a crystallite size of 15 nm or more in the c-axis direction.

According to a preferred aspect, the average major axis is in the range of 20 to 70 nm, and the crystallite diameter in the c-axis direction is 20 nm or more.

According to a preferred aspect, the ratio of the average major diameter to the crystallite diameter is 2.5 or less.

According to one preferred embodiment, the strontium carbonate particles have a surfactant attached to their surface.

According to one preferred aspect, the surfactant has a phenyl group.

According to one preferred embodiment, the surfactant is a polyoxyethylene styrenated phenyl ether phosphate.

A resin composition according to one aspect includes the strontium carbonate particles described above and a resin containing the strontium carbonate particles.

According to a preferred aspect, the content of the strontium carbonate particles with respect to the entire resin composition is within the range of 0.1 to 50% by mass.

According to a preferred aspect, the content of the strontium carbonate particles with respect to the entire resin composition is within the range of 1 to 35% by mass.

According to a preferred embodiment, the resin is polycarbonate, polymethyl methacrylate, cellulose ester, polystyrene, styrene acrylonitrile copolymer, polyfumaric acid diester, polyarylate, polyether sulfone, polyolefin, maleimide copolymer, polyethylene terephthalate, One or more selected from the group consisting of polyethylene naphthalate, polyimide, polyamide, and polyurethane.

According to a preferred aspect, the resin is polyimide.

A resin composition according to one aspect includes the above strontium carbonate particles and a polyimide precursor.

A strontium carbonate-containing polyimide film according to one aspect is obtained from the above resin composition.

An optical film according to one aspect includes the above resin composition or the above strontium carbonate-containing polyimide film.

An image display device according to one aspect includes the optical film described above.

According to the above aspect, it is possible to provide strontium carbonate with high retardation, an optical film containing the strontium carbonate, and an image display device.

The inventors of the present application have found that by paying attention to the crystallite size of the strontium carbonate particles, it is possible to enhance the manifestation of the phase difference inherent to the strontium carbonate particles. Specifically, the inventors discovered that increasing the crystallite diameter in the c-axis direction of the strontium carbonate particles allowed the phase difference of transmitted light to be expressed more effectively.

More specifically, the strontium carbonate particles according to this embodiment have an average major axis within the range of 10 to 100 nm and a crystallite size of 15 nm or more in the c-axis direction. Preferably, the average length of the strontium carbonate particles is in the range of 20 to 70 nm, and the crystallite size in the c-axis direction is 20 nm or more. The ratio of the average length to the crystallite size in the c-axis direction (average length/crystallite size) is 2.5 or less, preferably 2.0 or less, and more preferably 1.5 or less. Here, when the crystallite diameter in the c-axis direction is less than 15 nm, the inherent retardation of strontium carbonate is reduced. Further, if the crystallite diameter in the c-axis direction is 15 nm or more and the ratio of the average length to the crystallite diameter in the c-axis direction exceeds 2.5, the haze will be deteriorated.

Here, the average length can be measured by visual observation or image processing of scanning electron microscope (SEM) photographs of the strontium carbonate particles. The major diameter of the strontium carbonate particles can be measured, for example, as the length in the longitudinal direction (long side length) when the strontium carbonate particles are assumed to be rectangular. The short diameter of the strontium carbonate particles can be measured as the length in the short side direction (the length of the short side) when the strontium carbonate particles are assumed to be rectangular.

Specifically, in the image, a rectangle that circumscribes the strontium carbonate particles and has the smallest area is calculated, and the long and short sides of the rectangle are obtained from the lengths of the long and short sides. Further, "average" means an average value obtained by measuring a number (N number) of strontium carbonate particles that are statistically reliable. The number (N number) is usually 300 or more, preferably 500 or more, more preferably 1000 or more.

Also, the average aspect ratio of the strontium carbonate particles is not particularly limited, but may be, for example, within the range of 1.0 to 10.0. More preferably, the average aspect ratio of the strontium carbonate particles is in the range of 2.0-5.0.

Here, the aspect ratio means "major axis/minor axis" of particles. Moreover, the average aspect ratio means the average value of the aspect ratios. That is, the average aspect ratio is calculated by measuring the aspect ratios of a plurality of particles and averaging the aspect ratios obtained from the plurality of particles. The number of particles (N number) for calculating the average value is as described above. Also, the content of the strontium carbonate particles with respect to the entire resin composition may be within the range of 0.1 to 50% by mass. Further, it is more preferable that the content of the strontium carbonate particles with respect to the entire resin composition is within the range of 1 to 35% by mass. Here, when the content of strontium carbonate particles is 35% by mass or less with respect to the entire resin composition, a haze of 2% or less can be satisfied, and the content of strontium carbonate particles with respect to the entire resin composition is 50% by mass or less. In the range of , a haze of 5% or less can be satisfied.

A surfactant is preferably attached to the strontium carbonate particles described above. This can improve the dispersibility of the strontium carbonate particles in the resin composition or in the solvent before being mixed in the resin composition.

Although not particularly limited, it is preferably a surfactant in which a hydrophilic group and a hydrophobic group are bonded together and a hydrophilic group and a group forming an anion in water are bonded together. The group forming an anion is preferably a carboxylic acid group (--CO ₂ H), a sulfate group (--OSO ₃ H) or a phosphoric acid group (--OPO ₃ H ₂ ). Hydrogen atoms of these acid groups may be substituted with alkali metals such as sodium and potassium, or with ammonium. The hydrophilic group is preferably an oxyalkylene group having 1 to 4 carbon atoms. The hydrophobic group is preferably an alkyl group having 3 to 30 carbon atoms, a phenyl group or an alkylphenyl group having 7 to 30 carbon atoms. The surfactant whose anion-forming group is a carboxylic acid group is preferably a compound represented by the following formula (I).

In formula (I), R1 means an alkyl group having 3 to 30 carbon atoms, a phenyl group or an alkylphenyl group having 7 to 30 carbon atoms, and L1 has 1 carbon atom. 4, M1 means hydrogen, alkali metal or ammonium, and k means a number in the range 2-10. Preferably, R1 is an alkyl or alkylphenyl group having 10 to 18 carbon atoms. L1 is preferably an ethylene group. The surfactant whose anion-forming group is a sulfate group is preferably a compound represented by the following formula (II).

In formula (II), R2 means an alkyl group having 3 to 30 carbon atoms, a phenyl group or an alkylphenyl group having 7 to 30 carbon atoms, and L2 has 1 carbon atom. 4, M2 means hydrogen, alkali metal or ammonium, and m means a number in the range 2-10. Preferably, R2 is an alkyl or alkylphenyl group having 12 to 18 carbon atoms. The surfactant whose anion-forming group is a phosphate group is preferably a compound represented by the following formula (III).

In formula (III), R3 means an alkyl group having 3 to 30 carbon atoms, a phenyl group or an alkylphenyl group having 7 to 30 carbon atoms, and L3 has 1 carbon atom. M3 and M4 each independently represent hydrogen, alkali metal or ammonium, and n represents a number ranging from 2 to 10. Preferably, R3 is an alkyl or alkylphenyl group having in the range of 12 to 18 carbon atoms.

Among the above surfactants, the surfactant preferably has a phenyl group. More preferably, the surfactant is a polyoxyethylene styrenated phenyl ether phosphate represented by the following chemical formula.

A surfactant having a phenyl group has high heat resistance. Therefore, the strontium carbonate particles coated with a surfactant having a phenyl group can maintain high dispersibility during the formation of an optical film (resin composition) at high temperatures. In addition, since the blocking or scattering of transmitted light by the strontium carbonate particles is reduced, the transparency of the optical film (resin composition) can be ensured. As an optical film, the haze is 3% or less, preferably 2% or less, more preferably 1% or less.

A method for producing granular particles of strontium carbonate includes, for example, introducing carbon dioxide gas into an aqueous solution or suspension of strontium hydroxide while stirring the aqueous solution or suspension to carbonate the strontium hydroxide. and a reaction step of generating strontium carbonate. The concentration of the aqueous solution or suspension of strontium hydroxide is generally in the range of 1-20% by weight, preferably in the range of 2-15% by weight, more preferably in the range of 3-8% by weight. The amount of carbon dioxide gas introduced is generally in the range of 0.5 to 200 mL/min, preferably in the range of 0.5 to 100 mL/min, relative to 1 g of strontium hydroxide in an aqueous solution or suspension of strontium hydroxide. More preferably, it is in the range of 1-50 mL/min. When strontium hydroxide is carbonated, it is preferable to dissolve a carboxylic acid having a hydroxyl group in an aqueous solution or aqueous suspension of strontium hydroxide as a particle growth inhibitor for strontium carbonate particles to be produced. The crystal growth inhibitor is preferably an organic acid having 2 carboxyl groups and 3 to 6 hydroxyl groups in total. Preferred examples of crystal growth inhibitors include tartaric acid, malic acid and tartronic acid. As the crystal growth inhibitor, an organic acid having two carboxyl groups and a hydroxyl group and having a total of at least three groups can be used. From the viewpoint of enhancing dispersibility while remaining fine, dicarboxylic acids containing one or more hydroxyl groups in the molecule or anhydrides thereof are more preferable, and DL-tartaric acid is particularly preferable. The amount of the crystal growth inhibitor used is generally in the range of 0.1 to 20 parts by weight, preferably in the range of 1 to 10 parts by weight, per 100 parts by weight of strontium hydroxide. Other examples of crystal growth inhibitors include citric acid and gluconic acid.

The aging step is a step of aging the aqueous slurry containing the spherical strontium carbonate microparticles obtained in the reaction step while stirring at a predetermined temperature for a predetermined period of time to grow needle-like strontium carbonate microparticles. The aging process can be performed in warm water. The aging temperature is in the range of 75-115°C, preferably in the range of 80-110°C, particularly preferably in the range of 85-105°C. When the aging temperature is lower than 75°C, crystal growth of the spherical strontium carbonate fine particles tends to be insufficient and the average aspect ratio tends to be too low. Aspect ratio tends to be low. The aging time is not particularly limited, but it is usually in the range of 1 to 100 hours, preferably in the range of 5 to 50 hours, and particularly preferably in the range of 10 to 30 hours. This makes it possible to grow the crystallite size of the strontium carbonate particles to be produced and to reduce the variation. Stirring is usually performed at a Reynolds number of 10,000 or more, preferably 50,000 or more, more preferably 100,000 or more, as determined by the following formula. Thereafter, the mixture is allowed to cool to room temperature to produce an aqueous slurry of fine strontium carbonate particles.
R (Reynolds number) = ^d2 x n x ρ/μ
d: blade diameter [m], n: rotation speed [1/sec], ρ: liquid density [kg/m ³ ], μ: viscosity coefficient [kg/(m·sec)]

The solvent for the surface treatment is not particularly limited, but as a method of treating the surface of the strontium carbonate particles using the above surfactant, the surfactant and strontium carbonate particles are brought into contact with each other in the above aqueous suspension. After drying, a method of drying the strontium carbonate particles can be used.

The dispersion used in the surface treatment step can be an aqueous slurry after the aging step when the aging step is performed. The surface treatment step can be performed by adding a surfactant to the dispersion while applying a shearing force. The content of strontium carbonate particles in the aqueous slurry is preferably in the range of 1 to 30% by mass. The amount of surfactant added to the aqueous slurry is generally in the range of 1 to 60% by mass, preferably in the range of 10 to 50% by mass, and in the range of 20 to 40% by mass. is more preferred. The shearing force can be applied using a known stirring device such as a stirring blade mixer, homomixer, magnetic stirrer, air stirrer, ultrasonic homogenizer, clearmix, filmix, wet jet mill, and the like.

The drying process can be carried out by a known drying method using a heat dryer such as a spray dryer, drum dryer, disk dryer, or the like.

The above strontium carbonate particles are highly dispersible in resins such as organic solvents. The strontium carbonate particles can be dispersed in the resin (organic solvent) as primary particles or similar fine particles by putting the particles into the resin and subjecting them to a normal dispersing treatment such as stirring or ultrasonic treatment. The type of organic solvent is not particularly limited, and can be appropriately selected and used according to the properties of the resin. Examples of organic solvents in which the strontium carbonate particles can be suitably dispersed include alcohols (eg, ethanol, 1-propanol, 2-propanol, 1-butanol, ethylene glycol), methylene chloride, N-methyl-2- Pyrrolidone, gamma-butyllactone, dimethylacetamide and tetrahydrofuran may be mentioned. These organic solvents may be used singly (one type), or may be used in combination.

Also, an optical film according to one embodiment includes a resin and strontium carbonate particles dispersed in the resin. As the strontium carbonate particles dispersed in the resin, those described above are used.

The resins that make up the optical film are polycarbonate, polymethyl methacrylate, cellulose ester, polystyrene, styrene acrylonitrile copolymer, polyfumaric acid diester, polyarylate, polyether sulfone, polyolefin, maleimide copolymer, polyethylene terephthalate, and polyethylene naphthalate. , polyimide, polyamide, and polyurethane.

Preferably, the resin constituting the optical film is polyimide. Polyimide is known to have excellent heat resistance due to its chemical structure. It is also known that polyimide has excellent bending resistance due to the ordered structure of its molecular chains. However, polyimide, which is also excellent in bending resistance, optically produces birefringence. Here, by dispersing the strontium carbonate particles described above in polyimide, it is possible to control the birefringence of the entire optical film due to the phase difference inherent to strontium carbonate. This makes it possible to provide an optical film which is excellent in heat resistance and bending resistance and whose birefringence is appropriately controlled. The dimensional shrinkage rate of the polyimide film is 250 ° C. or higher and 400 ° C. or lower when the temperature is monotonically increased from 25 ° C./min to 10 ° C./min. 0.05% or more, preferably 0.08% or more.
Dimensional shrinkage rate (%) = [{(Dimensions at 25°C) - (Dimensions after temperature rise)]/(Dimensions at 25°C)] x 100

（式中、Ｘ₁，は芳香族環または脂環構造を有する４価の基であり、Ｙは芳香族環または脂環構造を有する２価の基であり、Ｒ，Ｒ２はそれぞれ独立に水素、炭素数１～６のアルキル基、または炭素数３～９のアルキルシリル基である。）The polyimide composition according to the above embodiment contains a polyimide precursor (A1) and fine particles (B) having optical anisotropy. The polyimide precursor (A1) contains, for example, at least one repeating unit represented by the following chemical formula.

(Wherein, X ₁ is a tetravalent group having an aromatic ring or alicyclic structure, Y is a divalent group having an aromatic ring or alicyclic structure, R and R are each independently hydrogen , an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms.)

However, the polyimide precursor (A1) may be a partially imidized polyamic acid or the like containing repeating units of an imide structure in which imidization has partially progressed.

（式中、Ｘ₂は芳香族環または脂環構造を有する４価の基であり、Ｙ２は芳香族環または脂環構造を有する２価の基である。）The polyimide composition contains polyimide (A2) and strontium carbonate particles (B) having optical anisotropy. Polyimide (A2) contains, for example, at least one repeating unit represented by the following chemical formula.

(Wherein, _X2 is a tetravalent group having an aromatic ring or alicyclic structure, and Y2 is a divalent group having an aromatic ring or alicyclic structure.)

The polyimide precursor (A1) used in the polyimide precursor composition and the polyimide (A2) used in the polyimide composition are described in detail below.

<Polyimide precursor (A1)>
The polyimide precursor (A1) contains, for example, at least one repeating unit represented by [Chem. 6] above.

Although not particularly limited, since the resulting polyimide composition has excellent heat resistance, X ₁ in the above [Chemical 6] is a tetravalent group having an aromatic ring, Y is an aromatic ring It is preferably a divalent group having Further, since the polyimide composition obtained is excellent in heat resistance and at the same time excellent in transparency, X ₁ is a tetravalent group having an alicyclic structure, and Y is a divalent group having an aromatic ring. preferable. Further, since the polyimide composition obtained is excellent in heat resistance and at the same time excellent in dimensional stability, X is a tetravalent group having an aromatic ring, and Y is a divalent group having an alicyclic structure. preferable.

Properties of the resulting polyimide composition, for example, from the viewpoint of transparency, mechanical properties, or heat resistance, X ₁ is a tetravalent group having an alicyclic structure, Y is a divalent group having an alicyclic structure The content of the repeating unit represented by the above [Chemical 6], which is a group, is preferably 50 mol% or less, more preferably 30 mol% or less or less than 30 mol%, more preferably It is preferably 10 mol % or less.

In one embodiment, the polyimide precursor (A1), X ₁ is a tetravalent group having an aromatic ring, Y is a divalent group having an aromatic ring [Chemical 6] repeating unit The total content of one or more of the total repeating units is preferably 50 mol% or more, more preferably 70 mol% or more, more preferably 80 mol% or more, and still more preferably 90 mol% or more, Particularly preferably, it is 100 mol %. In this embodiment, particularly when a highly transparent polyimide composition is desired, the polyimide precursor (A1) preferably contains a fluorine atom. That is, in the polyimide precursor (A1), X ₁ is a tetravalent group having an aromatic ring containing a fluorine atom and / or the repeating unit of the above [Chemical 6] and / or Y is an aromatic ring containing a fluorine atom It is preferable that one or more repeating units of the above [Chem. 6], which is a divalent group having

In one embodiment, the polyimide precursor (A1), X ₁ is a tetravalent group having an alicyclic structure, Y is a divalent group having an aromatic ring [Chemical 6] repeating unit The total content of one or more of the total repeating units is preferably 50% or more, more preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, especially Preferably, it is 100 mol %.

In one embodiment, the polyimide precursor (A1), X ₁ is a tetravalent group having an aromatic ring, Y is a divalent group having an alicyclic structure [Chemical 6] repeating unit The total content of one or more of the total repeating units is preferably 50 mol% or more, more preferably 70 mol% or more, more preferably 80 mol% or more, and still more preferably 90 mol% or more, Particularly preferably, it is 100 mol %.

As the tetravalent group having an aromatic ring for X ₁ , a tetravalent group having an aromatic ring having 6 to 40 carbon atoms is preferable.

（式中、Ｚ₁は直接結合、または、下記の２価の基:

のいずれかである。ただし、式中のＺ₂は、２価の有機基である。）Examples of the tetravalent group having an aromatic ring include the following.

(Wherein, Z ₁ is a direct bond or the following divalent group:

is either However, Z ₂ in the formula is a divalent organic group. )

Specific examples of Z ₂ include aliphatic hydrocarbon groups having 2 to 24 carbon atoms and aromatic hydrocarbon groups having 6 to 24 carbon atoms.

As the tetravalent group having an aromatic ring, the following groups are particularly preferable because they can achieve both high heat resistance and high transparency of the resulting polyimide composition.

（式中、Ｚ₁は直接結合、または、ヘキサフルオロイソプロピリデン結合である。）

(Wherein, Z ₁ is a direct bond or a hexafluoroisopropylidene bond.)

Here, Z ₁ is more preferably a direct bond because the obtained polyimide composition can achieve both high heat resistance, high transparency, and a low coefficient of linear thermal expansion.

_Examples of the tetracarboxylic acid component that gives the repeating unit of [Chem. , 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid, pyromellitic acid, 3,3′,4,4′-benzophenone Tetracarboxylic acid, 3,3',4,4'-biphenyltetracarboxylic acid, 2,3,3',4'-biphenyltetracarboxylic acid, 4,4'-oxydiphthalic acid, bis(3,4-dicarboxy phenyl)sulfone, m-ter-phenyl-3,4,3',4'-tetracarboxylic acid, p-ter-phenyl-3,4,3',4'-tetracarboxylic acid, biscarboxyphenyldimethylsilane, Bisdicarboxyphenoxydiphenyl sulfide, sulfonyldiphthalic acid, and their derivatives such as tetracarboxylic dianhydrides, tetracarboxylic acid silyl esters, tetracarboxylic acid esters and tetracarboxylic acid chlorides. Examples of the tetracarboxylic acid component that gives the repeating unit of [Chem. 6], wherein X ₁ is a tetravalent group having an aromatic ring containing a fluorine atom, include phenyl)hexafluoropropane and its derivatives such as tetracarboxylic dianhydride, tetracarboxylic acid silyl ester, tetracarboxylic acid ester and tetracarboxylic acid chloride. The tetracarboxylic acid component may be used alone or in combination of multiple types.

The tetravalent group having an alicyclic structure for X ₁ is preferably a tetravalent group having an alicyclic structure having 4 to 40 carbon atoms, and at least one aliphatic 4- to 12-membered ring, more preferably an aliphatic More preferably it has a 4-membered ring or an aliphatic 6-membered ring.

Furthermore, as the tetravalent group having an alicyclic structure of X ₁ , since it is possible to achieve both heat resistance and transparency, it has at least one aliphatic 6-membered ring in the chemical structure and has an aromatic ring. preferably not. X ₁ (tetravalent group having an alicyclic structure) may have a plurality of 6-membered rings, and the plurality of 6-membered rings may be composed of two or more common carbon atoms. In addition, the 6-membered ring may be a bridged ring type in which carbon atoms (inside the 6-membered ring) constituting the ring are bonded to form a further ring.

X ₁ (tetravalent group having an alicyclic structure) has a 6-membered ring structure with high symmetry, which enables dense packing of polymer chains and enhances the solvent resistance, heat resistance, and mechanical strength of polyimide. It is preferable because it is excellent in Furthermore, in X ₁ (a tetravalent group having an alicyclic structure), a plurality of 6-membered rings are composed of two or more common carbon atoms, and the 6-membered ring is a ring-constituting carbon atom It is more preferable for the polyimides to bond together to form a ring, since it is easy to achieve good heat resistance, solvent resistance and low coefficient of linear expansion of the polyimide.

（式中、Ｒ₃₁～Ｒ₃₆は、それぞれ独立に直接結合、または、２価の有機基である。Ｒ₄₁～Ｒ₄₇は、それぞれ独立に式：－ＣＨ₂－、－ＣＨ＝ＣＨ－、－ＣＨ₂ＣＨ₂－、－Ｏ－、－Ｓ－で表される基よりなる群から選択される１種を示す。）Preferred tetravalent groups having an aliphatic 4-membered ring or an aliphatic 6-membered ring include the following.

₍ In the formula, R ₃₁ to R ₃₆ are each independently a direct bond or _a divalent _organic group. It represents one selected from the group consisting of groups represented by -CH ₂ CH ₂ -, -O- and -S-.)

R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R ₃₅ and R ₃₆ are specifically a direct bond, an aliphatic hydrocarbon group having 1 to 6 carbon atoms, or an oxygen atom (-O-) , a sulfur atom (--S--), a carbonyl bond, an ester bond, and an amide bond.

As the tetravalent group having an alicyclic structure, the following groups are particularly preferable because the obtained polyimide can have both high heat resistance, high transparency, and a low coefficient of linear thermal expansion.

Examples of the tetracarboxylic acid component that gives the repeating unit of [ _Chem . phenoxybisphthalic acid, cyclohexane-1,2,4,5-tetracarboxylic acid, [1,1'-bi(cyclohexane)]-3,3',4,4'-tetracarboxylic acid, [1,1' -bi(cyclohexane)]-2,3,3′,4′-tetracarboxylic acid, [1,1′-bi(cyclohexane)]-2,2′,3,3′-tetracarboxylic acid, 4,4 '-methylenebis(cyclohexane-1,2-dicarboxylic acid), 4,4'-(propane-2,2-diyl)bis(cyclohexane-1,2-dicarboxylic acid), 4,4'-oxybis(cyclohexane-1 ,2-dicarboxylic acid), 4,4′-thiobis(cyclohexane-1,2-dicarboxylic acid), 4,4′-sulfonylbis(cyclohexane-1,2-dicarboxylic acid), 4,4′-(dimethylsilane diyl)bis(cyclohexane-1,2-dicarboxylic acid), 4,4′-(tetrafluorofuropane-2,2-diyl)bis(cyclohexane-1,2-dicarboxylic acid), octahydropentalene-1, 3,4,6-tetracarboxylic acid, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid, 6-(carboxymethyl)bicyclo[2.2.1]heptane-2 , 3,5-tricarboxylic acid, bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid, bicyclo[2.2.2]oct-5-ene-2,3,7, 8-tetracarboxylic acid, tricyclo[4.2.2.02,5]decane-3,4,7,8-tetracarboxylic acid, tricyclo[4.2.2.02,5]dec-7-ene- 3,4,9,10-tetracarboxylic acid, 9-oxatricyclo[4.2.1.02,5]nonane-3,4,7,8-tetracarboxylic acid, norbornane-2-spiro-α- Cyclopentanone-α'-spiro-2',-norbornane 5,5'',6,6''-tetracarboxylic acid (4arH,8acH)-decahydro-1t,4t:5c,8c-dimethanonaphthalene-2c ,3c,6c,7c-tetracarboxylic acid, (4arH,8acH)-decahydro-1t,4t:5c,8c-dimethanonaphthalene-2c,3c,6c,7c-tetracarboxylic acid and these tetracarboxylic acid di Derivatives such as anhydrides, tetracarboxylic acid silyl esters, tetracarboxylic acid esters, and tetracarboxylic acid chlorides are included. The tetracarboxylic acid component may be used alone or in combination of multiple types.

The divalent group having an aromatic ring for Y ₁ preferably has 6 to 40 carbon atoms, more preferably a divalent group having 6 to 20 carbon atoms and having an aromatic ring.

（式中、Ｗ₁は直接結合、または、２価の有機基であり、ｎ１１～ｎ１３は、それぞれ独立に０～４の整数を表し、Ｒ₅₁、Ｒ₅₂、Ｒ₅₃は、それぞれ独立に炭素数１～６のアルキル基、ハロゲン基、水酸基、カルボキシル基、またはトリフルオロメチル基である。）Examples of the divalent group having an aromatic ring include the following.

(wherein W ₁ is a direct bond or a divalent organic group, n11 to n13 each independently represent an integer of 0 to 4, R ₅₁ , R ₅₂ and R ₅₃ each independently represent a carbon an alkyl group, a halogen group, a hydroxyl group, a carboxyl group, or a trifluoromethyl group of numbers 1 to 6.)

（式Ｒ₆₁～Ｒ₆₈は、それぞれ独立に上記式で表される２価の基のいずれかを表す。）Specific examples of W ₁ include a divalent group represented by Chemical Formula 14 below and a divalent group represented by Chemical Formula 15 below.

(Formulas R ₆₁ to R ₆₈ each independently represent any of the divalent groups represented by the above formulas.)

Here, since the resulting polyimide can have both high heat resistance, high transparency, and a low linear thermal expansion coefficient, W ₁ is a direct bond or a formula: -NHCO-, -CONH-, -COO-, -OCO- One selected from the group consisting of groups represented by is particularly preferred. In addition, W ₁ is one selected from the group consisting of R ₆₁ to R ₆₈ being a direct bond or a group represented by the formula: -NHCO-, -CONH-, -COO-, -OCO-. Any one of the divalent groups represented by [Chemical 14] of is also particularly preferred.

_Examples of the diamine component that gives the repeating unit of [Chem. Minobiphenyl, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, m-tolidine, 4,4'-diaminobenzanilide, 3,4'-diaminobenzanilide , N,N'-bis(4-aminophenyl)terephthalamide, N,N'-p-phenylenebis(p-aminobenzamide), 4-aminophenoxy-4-diaminobenzoate, bis(4-aminophenyl)terephthalate , biphenyl-4,4′-dicarboxylic acid bis(4-aminophenyl) ester, p-phenylene bis(p-aminobenzoate), bis(4-aminophenyl)-[1,1′-biphenyl]-4,4 '-dicarboxylate, [1,1'-biphenyl]-4,4'-diylbis(4-aminobenzoate), 4,4'-oxydianiline, 3,4'-oxydianiline, 3,3' -oxydianiline, p-methylenebis(phenylenediamine), 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy) Benzene, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, bis(4-aminophenyl)sulfone, 3,3′-bis(trifluoromethyl)benzidine, 3,3′-bis((aminophenoxy)phenyl) propane, 2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, bis(4-(4-aminophenoxy)diphenyl)sulfone, bis(4-(3-aminophenoxy)diphenyl)sulfone, Octafluorobenzidine, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-difluoro-4,4'-diaminobiphenyl, 2 ,4-bis(4-aminoanilino)-6-amino-1,3,5-triazine, 2,4-bis(4-aminoanilino)-6-methylamino-1,3,5-triazine, 2,4- bis(4-aminoanilino)-6-ethylamino-1,3,5-triazine and 2,4-bis(4-aminoanilino)-6-anilino-1,3,5-triazine. _Examples of the diamine component that gives the repeating unit of the above [Chem. ,3′-bis(trifluoromethyl)penzidine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, 2,2 '-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. A diamine component may be used individually and can also be used in combination of multiple types.

The divalent group having an alicyclic structure for Y ₁ is preferably a divalent group having an alicyclic structure having 4 to 40 carbon atoms, and at least one aliphatic 4- to 12-membered ring, more preferably an aliphatic It is more preferred to have a 6-membered ring.

（式中、Ｖ₁，Ｖ₂は、それぞれ独立に直接結合、または、２価の有機基であり、ｎ２１～ｍ２６は、それぞれ独立に０～４の整数を表し、Ｒ₈₁～Ｒ₈₆は、それぞれ独立に炭素数１～６のアルキル基、ハロゲン基、水酸基、カルボキシル基、またはトリフルオロメチル基であり、Ｒ₉₁、Ｒ₉₂、Ｒ₉₃は、それぞれ独立に式:－ＣＨ₂－、－ＣＨ＝ＣＨ－、－ＣＨ₂ＣＨ₂－、－Ｏ－、－Ｓ－で表される基よりなる群から選択される１種である。）Examples of divalent groups having an alicyclic structure include the following.

(Wherein, V ₁ and V ₂ are each independently a direct bond or a divalent organic group, n21 to m26 each independently represent an integer of 0 to 4, and R ₈₁ to R ₈₆ are each independently an alkyl group having 1 to 6 carbon atoms, _{a halogen} group, a hydroxyl group, a _carboxyl group or a trifluoromethyl _group ; =CH-, -CH ₂ CH ₂ -, -O-, and -S-.)

Specific examples of V ₁ and V ₂ include divalent groups represented by the above [Chem. 14].

As the divalent group having an alicyclic structure, the following groups are particularly preferable because they can achieve both high heat resistance and a low coefficient of linear thermal expansion of the resulting polyimide.

Among the divalent groups having an alicyclic structure, the following are preferred.

_Examples of the diamine component that gives the repeating unit of [Chem. ,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-phlopylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-phthylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, 1,2-diaminocyclohexane, 1,3-diamino Cyclobutane, 1,4-bis(aminomethyl)cyclohexane, 1,3-bis(aminomethyl)cyclohexane, diaminobicycloheptane, diaminomethylbicycloheptane, diaminooxybicycloheptane, diaminomethyloxybicycloheptane, isophorone diamine , diaminotricyclodecane, diaminomethyltricyclodecane, bis(aminocyclohexyl)methane, bis(aminocyclohexyl)isopropylidene, 6,6′-bis(3-aminophenoxy)-3,3,3′,3 '-Tetramethyl-1,1'-spirobiindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane. A diamine component may be used individually and can also be used in combination of multiple types.

The polyimide precursor (A1) containing at least one type of repeating unit represented by [Chemical 6] above may contain other repeating units other than the repeating unit represented by [Chemical 6].

The tetracarboxylic acid component and diamine component that give other repeating units are not particularly limited, and other known aliphatic tetracarboxylic acids and known aliphatic diamines can be used. Other tetracarboxylic acid components may also be used singly or in combination. Other diamine components may also be used singly or in combination.

The content of other repeating units other than the repeating unit represented by [Chemical Formula 6] is preferably 30 mol% or less or less than 30 mol%, more preferably 20 mol% or less, relative to all repeating units, More preferably, it is 10 mol % or less.

In [Formula 6] of the polyimide precursor (A1), R ₁ and R ₂ are either C 3-9 alkylsilyl groups. When R ₁ and R ₂ are hydrogen, polyimide tends to be easier to produce.

For R ₁ and R ₂ , the type of functional group and the introduction rate of the functional group can be changed according to the manufacturing method described below.

The polyimide precursor (A1) (a polyimide precursor containing at least one type of repeating unit represented by [Chem. 6]) has a chemical structure represented by R ₁ and R ₂ ,
1) Polyamic acid (R ₁ and R ₂ are hydrogen),
2) polyamic acid ester (at least part of R ₁ and R ₂ are alkyl groups),
3) 4) polyamic acid silyl ester (at least a portion of R ₁ and R ₂ are alkylsilyl groups),
can be classified into Then, the polyimide precursor (A1) can be easily produced by the following production methods for each of these classifications. However, the method for producing the polyimide precursor (A1) is not limited to the following production method.

1) Polyamic acid The polyimide precursor (A1) contains a tetracarboxylic dianhydride as a tetracarboxylic acid component and a diamine component in a solvent in approximately equimolar amounts, preferably the molar ratio of the diamine component to the tetracarboxylic acid component [diamine Mole number of component/mol number of tetracarboxylic acid component] is preferably 0.90 to 1.10, more preferably 0.95 to 1.05, for example, imidation at a relatively low temperature of 1200 ° C. or less can be suitably obtained as a polyimide precursor solution composition by reacting while suppressing

More specifically, but not limited to, diamine is dissolved in an organic solvent or water, tetracarboxylic dianhydride is gradually added to this solution while stirring, and the temperature is adjusted to 0 to 120° C., preferably 5 A polyimide precursor can be obtained by holding at a temperature in the range of ~80°C for 1 to 72 hours. When the reaction is carried out at 800° C. or higher, the molecular weight fluctuates depending on the temperature history during polymerization, and imidization proceeds due to heat, so there is a possibility that the polyimide precursor cannot be stably produced. The order of addition of the diamine and the tetracarboxylic dianhydride in the above production method is preferable because the molecular weight of the polyimide precursor tends to increase. It is also possible to reverse the order of addition of the diamine and the tetracarboxylic dianhydride in the production method described above, which is preferable because the precipitates are reduced. When water is used as a solvent, imidazoles such as 1,2-dimethylimidazole, or bases such as triethylamine, with respect to the carboxyl groups of the polyamic acid (polyimide precursor) to be generated, preferably 0.8 equivalents or more. is preferably added in an amount of

2) Polyamic Acid Ester A tetracarboxylic acid dianhydride is reacted with any alcohol to obtain a diester dicarboxylic acid, which is then reacted with a chlorinating reagent (thionyl chloride, oxalyl chloride, etc.) to obtain a diester dicarboxylic acid chloride. The diester dicarboxylic acid chloride and diamine are stirred at −20 to 120° C., preferably −5 to 80° C. for 1 to 72 hours to obtain a polyimide precursor. When the reaction is carried out at 800° C. or higher, the molecular weight fluctuates depending on the temperature history during polymerization, and imidization proceeds due to heat, so there is a possibility that the polyimide precursor cannot be stably produced. A polyimide precursor can also be easily obtained by subjecting a diester dicarboxylic acid and a diamine to dehydration condensation using a phosphorus-based condensing agent, a carbodiimide condensing agent, or the like.

Since the polyimide precursor obtained by this method is stable, it can be purified by reprecipitation by adding a solvent such as water or alcohol.

3) Polyamic acid silyl ester (indirect method)
A diamine and a silylating agent are reacted in advance to obtain a silylated diamine. If necessary, the silylated diamine is purified by distillation or the like. Then, the silylated diamine is dissolved in the dehydrated solvent, and the tetracarboxylic dianhydride is gradually added while stirring, and the temperature is maintained at 0 to 120°C, preferably 5 to 80°C. Stirring for ~72 hours gives the polyimide precursor. When the reaction is carried out at 800° C. or higher, the molecular weight fluctuates depending on the temperature history during polymerization, and imidization proceeds due to heat, so there is a possibility that the polyimide precursor cannot be stably produced.

4) Polyamic acid silyl ester (direct method)
The polyamic acid solution obtained by the above method 1) and the silylating agent are mixed and stirred at 0 to 120° C., preferably 5 to 80° C. for 1 to 72 hours to obtain a polyimide precursor. . When the reaction is carried out at 800° C. or higher, the molecular weight fluctuates depending on the temperature history during polymerization, and imidization proceeds due to heat, so there is a possibility that the polyimide precursor cannot be stably produced.

Using a chlorine-free silylating agent as the silylating agent used in the above methods 3) and 4) eliminates the need to purify the silylated polyamic acid or the resulting polyimide. Therefore, it is preferable. Silylating agents containing no chlorine atoms include N,0-bis(trimethylsilyl)trifluoroacetamide, N,0-bis(trimethylsilyl)acetamide and hexamethyldisilazane. N,0-bis(trimethylsilyl)acetamide and hexamethyldisilazane are particularly preferred because they do not contain fluorine atoms and are low in cost.

In the silylation reaction of diamine in method 3), an amine-based catalyst such as pyridine, piperidine, and triethylamine can be used to promote the reaction. This catalyst can be used as it is as a polymerization catalyst for the polyimide precursor.

The solvent (C) used in preparing the polyimide precursor (A1) is water or, for example, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl -2-Imidazolidinone, dimethyl sulfoxide and other aprotic solvents are preferred, and any kind of solvent can be used without problems as long as the raw material monomer component and the polyimide precursor to be formed dissolve, so the structure is not limited to Solvents include water, amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, γ-butyrolactone, γ-valerolactone, δvalerolactone, γ-cabrolactone, ε-cabrolactone, α -Cyclic ester solvents such as methyl-γ-butyrolactone, carbonate solvents such as ethylene carbonate and propylene carbonate, glycol solvents such as triethylene glycol, m-cresol, p-cresol, 3-chlorophenol, 4-chloro Phenolic solvents such as phenol, acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, dimethylsulfoxide and the like are preferably employed. In addition, other common organic solvents, namely phenol, o-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, tetrahydrofuran. , dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone, methyl ethyl ketone, acetone, phthalol, ethanol, xylene, toluene, chlorobenzene, terpene, mineral spirits, petroleum naphtha Solvents and the like can also be used. In addition, a solvent can also be used in combination of multiple types.

The logarithmic viscosity of the polyimide precursor (A1) is not particularly limited. It is preferably 3 dL/g or more, particularly preferably 0.4 dL/g or more. When the logarithmic viscosity is 0.2 dL/g or more, the molecular weight of the polyimide precursor is high, and the obtained polyimide is excellent in mechanical strength and heat resistance.

<Polyimide (A2)>
The polyimide (A2) is not particularly limited, but is obtained from the polyimide precursor (A1) and contains, for example, at least one repeating unit represented by [Chem. 7].

The above [Chem. 7] corresponds to the above [Chem. 6], where X ₁ corresponds to X ₂ and Y ₁ corresponds to Y ₂ . X ₂ and Y ₂ in the above [Chem. 7] include the same as X ₁ and Y ₁ in the above [Chem. 6], and preferable ones are also the same.

Although it is not particularly limited, since it has excellent heat resistance, X ₂ in the chemical formula (7) of the polyimide (A2) is a tetravalent group having an aromatic ring, and Y ₂ is 2 having an aromatic ring. It is preferably a valent group. Moreover, it is preferable that X ₂ is a tetravalent group having an alicyclic structure and Y ₂ is a divalent group having an aromatic ring, in order to obtain excellent heat resistance and transparency. Moreover, it is preferable that X ₂ is a tetravalent group having an aromatic ring and Y ₂ is a divalent group having an alicyclic structure, because of excellent heat resistance and dimensional stability.

In order to obtain a polyimide composition having a small retardation in the thickness direction and in-plane direction and excellent properties such as transparency, mechanical properties, or heat resistance, the polyimide (A2) preferably contains fluorine atoms. polyimide obtained from an aromatic tetracarboxylic acid component and an aromatic diamine, or a polyimide obtained from an alicyclic tetracarboxylic acid component and an aromatic diamine, or an aromatic tetracarboxylic acid component and an alicyclic A polyimide obtained from a diamine is preferred. The tetracarboxylic acid component includes tetracarboxylic acid and tetracarboxylic acid derivatives such as tetracarboxylic acid dianhydride, tetracarboxylic acid silyl ester, tetracarboxylic acid ester, and tetracarboxylic acid chloride.

Properties of the polyimide composition, for example, from the viewpoint of transparency, mechanical properties, or heat resistance, X ₂ is a tetravalent group having an alicyclic structure, Y ₂ is a divalent group having an alicyclic structure The content of the repeating unit represented by the above [Chemical 7] is preferably 50 mol% or less, more preferably 30 mol% or less or less than 30 mol%, more preferably 10 mol % or less.

In one embodiment, the polyimide (A2) is a repeating unit of the above [Chemical 7], wherein X ₂ is a tetravalent group having an aromatic ring, and Y ₂ is a divalent group having an aromatic ring. The total content of one or more of the repeating units is preferably 50 mol% or more, more preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly Preferably, it is 100 mol %. In this embodiment, especially when high transparency is required, the polyimide (A2) preferably contains fluorine atoms. That is, in the polyimide (A2), X ₂ is a tetravalent group having an aromatic ring containing a fluorine atom and / or the repeating unit of the above [Chemical 7] and / or Y ₂ is an aromatic ring containing a fluorine atom It preferably contains one or more of the repeating units of [Chem. 7], which is a divalent group having

In one embodiment, in the polyimide (A2), X ₂ is a tetravalent group having an alicyclic structure, and Y ₂ is a divalent group having an aromatic ring. The total content of one or more of the repeating units is preferably 50 mol% or more, more preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly Preferably, it is 100 mol %.

In one embodiment, in the polyimide (A2), X ₂ is a tetravalent group having an aromatic ring, and Y ₂ is a divalent group having an alicyclic structure. The total content of one or more of the repeating units is preferably 50 mol% or more, more preferably 70 mol% or more, more preferably 80 mol% or more, still more preferably 90 mol% or more, particularly Preferably, it is 100 mol %.

The polyimide (A2) containing at least one type of repeating unit represented by [Chem. 7] can contain one or more types of other repeating units other than the repeating unit represented by [Chem. 7].

The content of other repeating units other than the repeating unit represented by [Chemical 7] is preferably 30 mol% or less or less than 30 mol%, more preferably 20 mol% or less, based on the total repeating units. More preferably, it is 10 mol % or less.

The polyimide (A2) can be produced by imidizing the polyimide precursor (A1) (that is, subjecting the polyimide precursor (A1) to a dehydration ring closure reaction. The imidization method is not particularly limited, and a known A method of thermal imidization or chemical imidization can be suitably applied.

In the above-mentioned optical film made of a resin containing strontium carbonate particles, the average length of the strontium carbonate particles is as small as 10 to 100 nm, and a surfactant is attached to the surface of the strontium carbonate particles. The dispersibility of the strontium carbonate particles is increased. Thereby, the haze of the optical film can be reduced.

For example, an optical film having a haze of 1% or less and a positive out-of-plane birefringence can be provided. It is also possible to provide an optical film having a haze of 1% or less and an out-of-plane birefringence of zero. Furthermore, it is possible to provide an optical film having a haze of 1% or less and a negative out-of-plane birefringence.

Moreover, such an optical film can be suitably applied to an image display device.

EXAMPLES The present invention will be specifically described below based on examples, but these are not intended to limit the object of the present invention.

1. Example 1
(1) Production of strontium carbonate fine particles (a) Reaction step

DL-tartaric acid (special grade reagent, purity: 99% or more) was added to 3 L of pure water at a water temperature of 10° C. and dissolved in the aqueous suspension by stirring. 366 g of strontium hydroxide octahydrate (guaranteed reagent, purity: 96% or higher) was added and mixed to prepare an aqueous strontium hydroxide suspension with a concentration of 5.6% by mass. While maintaining this strontium hydroxide aqueous suspension at 10° C. and continuing to stir, carbon dioxide gas was added to the aqueous suspension at a flow rate of 0.5 L/min (flow rate of 22 mL/min for 1 g of strontium hydroxide). ) until the pH of the aqueous suspension reaches 7 to generate strontium carbonate particles. After that, stirring was continued for an additional 30 minutes to obtain an aqueous suspension of strontium carbonate particles.

(b) Aging step The obtained strontium carbonate particle aqueous suspension was heated at a temperature of 95°C for 12 hours while stirring at a peripheral speed of 2.5 m/sec to grow needle-like strontium carbonate particles. . Thereafter, the mixture was allowed to cool to room temperature to produce an aqueous slurry of fine strontium carbonate particles.

(2) Production of Highly Dispersible Strontium Carbonate Particles (a) Surface Treatment Step An aqueous slurry (solid concentration: 6% by mass) of the strontium carbonate particles prepared above was added with polyoxyethylene styrene phenyl ether phosphate as a surfactant. The ester was added and dissolved and stirred with a stirrer for 5 minutes. Then, a shearing force was applied with CLEARMIX to carry out dispersion treatment. As a result, an aqueous slurry of highly dispersible strontium carbonate particles was obtained.

(b) Drying step (drum dryer)
The aqueous slurry after stirring and mixing was sprayed on a rotary drum dryer heated to 110 to 120° C. to obtain highly dispersible strontium carbonate fine powder. As a result of observing the obtained highly dispersible strontium carbonate fine powder with an electron microscope, it was confirmed that it was a fine powder of acicular particles. Image analysis of the results of electron microscopic observation revealed that the average length of the strontium carbonate particles was 35 nm.

(3) Measurement of crystallite diameter The crystallite diameter in the c-axis direction of the strontium carbonate fine particles obtained above was measured. Using a RINT-TTR III type wide-angle X-ray diffractometer manufactured by Rigaku Co., Ltd., the X-ray diffraction pattern was measured under the following conditions. The crystallite diameter in the c-axis direction was calculated by Scherrer's formula using the half width of . The results of crystallite size measurements are shown in Table 1 below.
(conditions)
X-ray source; CuKα ray Tube voltage - tube current; 50kV-300mA
Step width; 0.04deg
Measurement speed; 2 sec/step
Slit system; Divergence - Reception - Scattering
0.5deg-0.15mm-0.5deg
diffraction line curved crystal monochromator

(Method for preparing _SrCO3- added dope solution)
To 25 g of N-methyl-2-pyrrolidone (hereinafter, "NMP"), 6 g of soluble polyimide (hereinafter, "PI") was added and stirred for 6 hours to prepare a PI-NMP solution. Next, 1.2 g of the strontium carbonate fine powder described above was added to 10 g of NMP, placed in an ultrasonic bath for 30 seconds, and filtered without pressure through a membrane filter with a pore size of 1 μm to prepare Dispersion 1. The PI-NMP solution and Dispersion Liquid 1 were mixed and dispersed by an ultrasonic homogenizer to obtain SrCO ₃ -added dope liquid A-1.

(Polyimide film deposition method)
The SrCO ₃ -added dope solution A-1 was applied to a glass plate with a wet film thickness of 11 mil using a Baker applicator. This was dried in an inert oven by raising the temperature from 30° C. at a rate of 3° C./min under a nitrogen atmosphere and maintaining the temperature at 350° C. for 10 minutes. The PI film was peeled off from the glass plate to obtain PI film A-1.

(Transmittance and haze measurement)
Visible light transmittance and haze of PI film A-1 were measured using a spectrophotometer (manufactured by JASCO Corporation).

(Evaluation of retardation of film)
The thickness of the PI film A-1 was measured with a micrometer. After that, the out-of-plane retardation expression (ΔP) of the PI film was measured using a phase measuring device (KOBRA-WR manufactured by Oji Scientific Instruments Co., Ltd.).

Specifically, the out-of-plane retardation (retardation in the thickness direction; retardation in the thickness direction) Rth of the PI film was measured. The above-mentioned phase measurement apparatus measures the in-plane retardation (retardation) R0 measured by light incident on the measurement object (PI film) perpendicularly, and the phase difference (retardation) measured by light incident on the measurement object at the incident angle θ The out-of-plane retardation Rth is calculated from the retardation Rθ, the thickness d (input value) of the object to be measured, and the average refractive index N _avr (input value) of the object to be measured. The incident angle θ is 40° and the wavelength of light is 547.4 nm.

The average refractive index N _avr means an average value of refractive indices in three mutually orthogonal directions, and is defined by "N _{avr =} (Nx + Ny + Nz)/3". Here, Nx, Ny, and Nz mean the refractive indices of the object to be measured in the X-axis direction, Y-axis direction, and Z-axis direction, respectively. In this specification, the X-axis direction is the direction of the slow axis. The Y-axis direction is the direction of the fast axis. The Z-axis direction is the thickness direction of the object to be measured.

Generally, the out-of-plane retardation Rth is defined by the following formula: Rth=(Nx+Ny)/2−Nz)×d. Here, "d" means the thickness of the object to be measured. An out-of-plane birefringence value ΔP was calculated from the measured out-of-plane retardation value Rth. The out-of-plane birefringence value ΔP is calculated by the following formula: ΔP=Rth/d. Note that the thickness d of the object to be measured can be measured with a micrometer.

2. Example 2
A PI film A-2 was produced in the same manner as in Example 1, except that the temperature during aging was changed to 80° C. in the aging process for producing strontium carbonate fine particles, and retardation expression was evaluated. Evaluation results are shown in Table 1.

3. Example 3
A PI film A-3 was produced in the same manner as in Example 1, except that the heating treatment during aging was changed to 24 hours in the aging process for producing strontium carbonate fine particles, and the retardation expression was evaluated. Evaluation results are shown in Table 1.

4. Comparative example 1
A PI film B-1 was produced in the same manner as in Example 1, except that the film was allowed to stand without stirring during aging in the aging process for producing strontium carbonate microparticles, and the retardation expression property was evaluated. The evaluation results are shown in Table 1 below.

5. Comparative example 2
A PI film C-1 was produced in the same manner as in Example 1, except that the aging step was omitted in the production of strontium carbonate microparticles, and retardation expression was evaluated. The evaluation results are shown in Table 1 below.

6. Comparative example 3
A PI film D-1 was produced in the same manner as in Example 1 except that strontium carbonate was not added during polyimide film formation, and retardation expression was evaluated. The evaluation results are shown in Table 1 below.

7. Reference Example In the surface treatment step, a PI film E-1 was prepared in the same manner as in Example 1 except that stearic acid was used as a surfactant, and a spectrophotometer (manufactured by JASCO Corporation) was used. Visible light transmittance and haze measurements were performed on PI film E-1. The evaluation results are shown in Table 1 below.

8. Comparative example 4
PI film F-1 was prepared in the same manner as in Example 1, except that DL-tartaric acid was not added in the reaction step for producing strontium carbonate fine particles, the reaction temperature was set to 40° C., and the aging step was omitted. It was prepared and evaluated for phase difference expression. Evaluation results are shown in Table 1.

Referring to Table 1, the crystallite size in the c-axis direction of the strontium carbonate particles of Examples 1, 2 and 3 is larger than the crystallite size in the c-axis direction of the strontium carbonate particles of Comparative Example 1. Furthermore, the crystallite size in the c-axis direction of the strontium carbonate particles of Comparative Example 1 is larger than the crystallite size in the c-axis direction of the strontium carbonate particles of Comparative Example 2.
In Comparative Example 1, since the crystallite diameter of strontium carbonate is as small as 12 nm, the intrinsic retardation property of strontium carbonate is small, and the Rth value is 2.3 times or more as compared with Example 2. .

Comparative Example 3 does not contain strontium carbonate particles. Therefore, the polyimide film (optical film) of Comparative Example 3 exhibits the out-of-plane retardation Rth and the out-of-plane birefringence value ΔP of the polyimide resin alone.

Strontium carbonate particles are known to have a "negative" retardation property. Therefore, the out-of-plane retardation Rth and the out-of-plane birefringence value ΔP of the polyimide films of Example 1 and Comparative Examples 1 and 2 are smaller than those of Comparative Example 3 due to the development of the negative retardation of the strontium carbonate particles. .

Referring to Table 1, it can be seen that the out-of-plane retardation Rth and the out-of-plane birefringence value ΔP of the polyimide film decrease as the crystallite size in the c-axis direction of the strontium carbonate particles increases. It is considered that this is because the larger the crystallite diameter in the c-axis direction of the strontium carbonate particles, the easier it is for the strontium carbonate particles to develop a phase difference specific to them.

From the viewpoint of sufficiently expressing the out-of-plane birefringence value unique to strontium carbonate particles, considering based on Table 1, the crystallite size in the c-axis direction of strontium carbonate particles having an average major axis within the range of 10 to 100 nm is It can be seen that the thickness is preferably 15 nm or more, preferably 20 nm or more. When the crystallite diameter is 15 nm or less or 40 times or less than the c-axis lattice constant (0.513 nm), the crystallinity of the particles is low, and the original birefringence of strontium carbonate is difficult to develop. Therefore, the crystallite diameter is preferably 20 nm or more.

Further, when comparing Example 1 and Reference Example, it can be seen that the haze of the optical film is higher when the phenyl-based surfactant is used than when stearic acid is used as the surfactant. This is probably because the phenyl-based surfactant has higher dispersibility of the strontium carbonate particles.

In Comparative Example 4, the average major axis of strontium carbonate is as large as 200 nm. Therefore, it can be seen that the optical film of Comparative Example 4 has a high haze. It is considered that this is because light scattering increases when the particle diameter exceeds 100 nm.

Although the present invention has been described in detail using the above embodiments and examples, it should be apparent to those skilled in the art that the present invention is not limited to the embodiments and examples described herein. is. The present invention can be implemented with modifications and variations without departing from the spirit and scope of the invention defined by the claims. Accordingly, the descriptions herein are for illustrative purposes only and are not meant to be limiting of the present invention.

Claims (14)

having an average length within the range of 20 to 70 nm and a crystallite diameter of 15 nm or more in the c-axis direction,
Strontium carbonate particles with surfactant attached to the surface . 2. The strontium carbonate particles according to claim 1, wherein the crystallite size in the c-axis direction is 20 nm or more. 3. The strontium carbonate particles according to claim 1, wherein the ratio of said average length to said crystallite diameter is 2.5 or less. The strontium carbonate particles according to any one of claims 1 to 3, wherein the surfactant has a phenyl group. The strontium carbonate particles according to any one of claims 1 to 4 , wherein the surfactant is polyoxyethylene styrenated phenyl ether phosphate. Strontium carbonate particles according to any one of claims 1 to 5 ;
and a resin containing the strontium carbonate particles. 7. The resin composition according to claim 6 , wherein the content of said strontium carbonate particles with respect to said entire resin composition is within the range of 0.1 to 50% by mass. The resin composition according to claim 7 , wherein the content is within the range of 1 to 35% by mass. The resin is polycarbonate, polymethyl methacrylate, cellulose ester, polystyrene, styrene acrylonitrile copolymer, polyfumarate diester, polyarylate, polyether sulfone, polyolefin, maleimide copolymer, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide. and polyurethane, the resin composition according to any one of claims 6 to 8 . 10. The resin composition according to any one of Claims 6 to 9 , wherein the resin is polyimide. A resin composition comprising the strontium carbonate particles according to any one of claims 1 to 5 and a polyimide precursor. A strontium carbonate-containing polyimide film obtained from the resin composition according to claim 10 or 11 . An optical film comprising the resin composition according to any one of claims 6 to 11 or the strontium carbonate-containing polyimide film according to claim 12 . An image display device comprising the optical film according to claim 13 .