BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a curable resin composition. The present invention particularly relates to a curable resin composition including ITO particles. The present invention also relates to a cured product obtained using the curable resin composition, and a diffractive optical element. The present invention further relates to a method for producing the curable resin composition.

2. Description of the Related Art

By using a diffractive optical element, it is possible to obtain a lens which has a shorter focal length as the wavelength is longer, and exhibits chromatic aberration opposite to that of a refractive lens in the related art. Unlike the refractive lens requiring a plurality of lenses for correcting chromatic aberration, chromatic aberration can be corrected by changing the period of a diffraction structure of a lens, therefore a more compact and high-performance lens unit can be designed by using the diffractive optical element.

In a multilayer diffractive optical element having a structure in which diffractive optical elements formed of two different materials are in contact with each other on lattice planes thereof, by forming one diffractive optical element with a material having a relatively high refractive index and high Abbe number, and forming the other diffractive optical element with a material having a relatively low refractive index and low Abbe number, it is possible to suppress the occurrence of flare in the lens, and the like, and sufficiently utilize a chromatic aberration reducing effect. In this case, in a case where the two diffractive optical elements have optical characteristics in which the difference in refractive index between the two diffractive optical elements is larger at a longer wavelength, the chromatic aberration reducing effect can be obtained in a wide wavelength range.

In recent years, in order to obtain, as described above, the chromatic aberration reducing effect in a wide wavelength range, it has been proposed to add indium tin oxide (ITO) particles to a curable resin composition which is used as a material for producing a low Abbe number diffractive optical element in the multilayer diffractive optical element. For example, JP2006-220689A discloses, as a curable resin composition for producing a diffractive optical element, a curable resin composition in which ITO fine particles are dispersed in a resin containing a photopolymerization initiator, a dispersant, and a mixture of two or more acryloyl groups, methacryloyl groups, or vinyl groups, or unsaturated ethylene groups thereof.

On the other hand, JP2008-308593A discloses, as a coating composition including a metal oxide, which has good dispersibility and temporal stability, and is excellent in transparency and coating film resistance in a case of being formed into a coating film, a composition including a dispersion resin. The dispersion resin includes an ethylenically unsaturated double bond, and includes at least one polar group selected from —COOM, —SO3M, —PO(OM)2(M represents a hydrogen atom, a quaternary amine, or an alkali metal), —OH, —NRn(R represents a hydrocarbon group and n represents an integer of 2 or 3), and a sulfobetaine group.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a curable resin composition suitable for producing a diffractive optical element. More specifically, an object of the present invention is to provide a curable resin composition including ITO particles, which provides a transparent cured product, hardly causes bubbles to be mixed in a case of applying the curable resin composition to a mold so as to form a lattice-shaped cured product, and also has a good peeled surface shape from the mold after curing.

In the process of study for achieving the above object, the present inventors have attempted to produce an optical element using the curable resin composition described in JP2006-220689A or JP2008-308593A, and in any case, it has been found that, in a case of applying the curable resin composition to a mold so as to form a diffractive optical element having a diffraction grating shape, a gap (bubble) is mixed in a corner of a level difference. As a result of studies by the present inventors, the reason is considered that any of the curable resin composition has a high viscosity. As a result of further repeated studies, the present inventors have attempted to control the viscosity by a structure of a dispersant to be added in addition to a monomer and ITO fine particles, thereby leading to the achievement of the above object.

That is, the present invention provides the following <1> to <20>.<1> A curable resin composition comprising:a bifunctional or more (meth)acrylate compound;indium tin oxide particles; andan acidic polymer,in which the acidic polymer has a moiety including a carboxyl group at a polymer skeleton of a (meth)acrylate compound and at any one of terminals of the polymer skeleton of a (meth)acrylate compound, andan acid value of the acidic polymer is 2.0 mgKOH/g or more and less than 100 mgKOH/g.<2> The curable resin composition according to <1>,in which the moiety of the acidic polymer includes the following partial structure.

<3> The curable resin composition according to <1> or <2>,

in which the acidic polymer is represented by Formula (1),
(R1—S—L2)n—L1—(L3—A—R2)m(1)in Formula (1), R1represents a substituent including at least one carboxyl group, A represents a polymer skeleton of a (meth)acrylate compound, R2represents a hydrogen atom or a substituent not including a carboxyl group, L1represents a single bond or a (m+n)-valent linking group, L2and L3each independently represent a single bond or a divalent linking group, m represents an integer of 1 to 8, and n represents an integer of 1 to 9, in which m+n satisfies 2 to 6, each of n R1and L2may be the same as or different from each other, and each of m R2, A, L3may be the same as or different from each other.<4> The curable resin composition according to any one of <1> to <3>, in which a weight-average molecular weight of the acidic polymer is 1,000 to 20,000.<5> The curable resin composition according to any one of <1> to <4>,in which a content of the acidic polymer is 5% by mass to 50% by mass with respect to a total mass of the indium tin oxide particles.<6> The curable resin composition according to any one of <1> to <5>,in which a content of the indium tin oxide particles is 10% by mass to 60% by mass with respect to a total mass of the curable resin composition.<7> The curable resin composition according to any one of <1> to <6>,in which a particle size of the indium tin oxide particle is 5 nm to 50 nm.<8> The curable resin composition according to any one of <1> to <7>, further comprising:a photopolymerization initiator.<9> A method for producing the curable resin composition according to any one of <1> to <8>, the method comprising:a step of preparing a dispersion liquid in which the indium tin oxide particles are dispersed in a solvent having a constituent (δp) 0 to 6 MPa(1/2), the constituent being a polarity term in an SP value;a step of obtaining a mixed solution by mixing the dispersion liquid with the bifunctional or more (meth)acrylate compound and the acidic polymer; anda step of distilling off the solvent from the mixed solution.<10> The producing method according to <9>,in which the solvent is selected from the group consisting of toluene, xylene, and hexane.<11> The producing method according to <9>,in which the solvent is toluene.<12> The producing method according to any one of <9> to <11>,in which the indium tin oxide particles in the dispersion liquid are surface-modified with a monocarboxylic acid having 6 to 20 carbon atoms.<13> The producing method according to <12>,in which the monocarboxylic acid is oleic acid.<14> The producing method according to any one of <9> to <13>, further comprising:a step of further mixing a photopolymerization initiator to a mixture obtained after the distillation.<15> A cured product of the curable resin composition according to any one of <1> to <8>,in which a refractive index at a wavelength of 587.56 nm is 1.40 to 1.57, and an Abbe number is 15 to 25.<16> A diffractive optical element comprising:the cured product according to <15>,in which the diffractive optical element includes a surface having a diffraction grating shape and formed of the cured product.<17> A multilayer diffractive optical element comprising:a first diffractive optical element; anda second diffractive optical element,in which the first diffractive optical element is the diffractive optical element according to <16>, andthe surface of the first diffractive optical element, which has a diffraction grating shape, and a surface of the second diffractive optical element, which has a diffraction grating shape, face each other.<18> The multilayer diffractive optical element according to <17>, in which a refractive index of the second diffractive optical element at a wavelength of 587.56 nm is 1.55 to 1.70, and is larger than a refractive index of the first diffractive optical element at the wavelength of 587.56 nm, andan Abbe number of the second diffractive optical element is 35 to 60.<19> The multilayer diffractive optical element according to <17> or <18>,in which the surface of the first diffractive optical element, which has a diffraction grating shape, and the surface of the second diffractive optical element, which has a diffraction grating shape, are in contact with each other.<20> The multilayer diffractive optical element according to any one of <17> to <19>, further comprising:a transparent substrate,in which the first diffractive optical element, the second diffractive optical element,and the transparent substrate are arranged in this order.

According to the present invention, a curable resin composition suitable for producing a diffractive optical element is provided. The curable resin composition according to an aspect of the present invention provides a transparent cured product, hardly causes bubbles to be mixed in a case of applying the curable resin composition to a mold so as to form a lattice-shaped cured product, and also has a good peeled surface shape from the mold after curing.

