JP7327382B2 - Flakes, method for producing the same, and paint - Google Patents

Description

The present invention relates to flakes and methods for their production, and coatings.

In the field of security inks, special pigments are sometimes used for the purpose of preventing counterfeiting. As one type of such special pigments, there is known one that uses a resin having cholesteric regularity (hereinafter sometimes referred to as "cholesteric resin" as appropriate) (see Patent Document 1).

JP 2007-141117 A

The present inventor focused on flakes containing a cholesteric resin as the special pigment. When the security ink containing the flakes is printed to form an optical layer containing the flakes, the reflected color of the flakes visually recognized by observing the optical layer usually differs depending on the observation angle. Here, the observation angle of a certain layer represents the angle formed by the observation direction with respect to the thickness direction of the layer. Therefore, for example, in the reflected color observed in the front direction of the optical layer (the direction in which the observation angle is 0°) and in the tilted direction of the optical layer (the direction in which the observation angle is greater than 0° and less than 90°) It is often different from the observed reflected color. Therefore, it is conceivable to use flakes containing a cholesteric resin as a special pigment by utilizing the unique property that the reflected color varies depending on the viewing angle.

By the way, there are various types of printed materials printed with security ink containing special pigments, such as certificate stamps, securities, banknotes, and cards. Moreover, the environment in which these printed materials are viewed can be either a bright environment or a dark environment. Furthermore, the illumination in the above environment may include illumination with a wide light distribution angle and illumination with a narrow light distribution angle. As described above, the environments in which security inks containing special pigments are applied are diverse. Therefore, the above-mentioned special pigments are required to have a clearly visible reflected color under various lighting environments.

However, with conventional flakes containing a cholesteric resin, it was difficult to clearly see the reflected color both in the front direction and in the oblique direction. In particular, even in an environment in which the reflected color can be clearly seen when observed in the front direction, the reflected color cannot be clearly seen in many cases when viewed in an oblique direction.

The present invention has been invented in view of the above problems, and includes a flake that can clearly see the reflected color in both the front direction and the inclined direction of the layer containing the flake, and a method for producing the flake; and the flake. Intended to provide paint.

The inventor of the present invention has made intensive studies to solve the above problems. As a result, the present inventor found that flakes containing crushed pieces of a cholesteric resin layer having a haze within a predetermined range due to light scattering properties caused by orientation defects can solve the above problems, and completed the present invention. Ta. That is, the present invention includes the following.

[1] containing crushed pieces of a resin layer having cholesteric regularity,
The layer of the resin contains orientation defects that impair the cholesteric regularity,
The flakes, wherein the resin layer has a haze of 10% or more and 60% or less.
[2] The flake according to [1], wherein the flake has one or more reflection bands including the visible range.
[3] The flakes according to [2], wherein the bandwidth per reflection band is 100 nm or more.
[4] The flakes according to any one of [1] to [3], wherein the flakes have an average particle size of 1 μm or more and 500 μm or less.
[5] A method for producing flakes according to any one of [1] to [4],
forming a layer of resin having cholesteric regularity;
and pulverizing the resin layer.
[6] A paint comprising the flakes according to any one of [1] to [4] and a dispersion medium.

According to the present invention, it is possible to provide flakes in which the reflected color can be clearly seen both in the front direction and the inclined direction of the layer containing the flakes, a method for producing the flakes, and a paint containing the flakes.

FIG. 1 is a cross-sectional view schematically showing an example of an optical layer containing flakes according to one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of an optical layer containing flakes according to one embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing an example of an optical layer containing flakes according to an embodiment of the invention.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be arbitrarily modified without departing from the scope of the claims of the present invention and equivalents thereof.

In the following description, the front direction of a layer means a direction parallel to the thickness direction of the layer unless otherwise specified. Further, unless otherwise specified, the tilt direction of a certain layer means a direction neither parallel nor perpendicular to the thickness direction of a certain layer.

[1. Flake structure]
Flakes according to one embodiment of the present invention comprise crushed pieces of a layer of cholesteric resin. A cholesteric resin refers to a resin having cholesteric regularity, as described above.

Cholesteric regularity means that the molecular axes are aligned in a certain direction on one plane, but the directions of the molecular axes on the next plane that overlaps with it are slightly shifted at an angle, and the angle is further shifted on the next plane. In this structure, the angle of the molecular axis in the plane shifts (twists) as it passes through the planes arranged in an overlapping manner. That is, when the molecules inside a certain resin layer have cholesteric regularity, the molecules are arranged such that the molecular axes are oriented in a certain direction on a certain first plane inside the layer. In the next second plane within the layer, which overlaps the first plane, the direction of the molecular axis is slightly angularly offset from the direction of the molecular axis in the first plane. In the next third plane, which further overlaps the second plane, the direction of the molecular axis is angularly offset from the direction of the molecular axis in the second plane. In this way, the angles of the molecular axes in the planes that are arranged to overlap each other gradually shift (twist). Such a structure in which the direction of the molecular axis is twisted is usually a helical structure and an optically chiral structure.

As the cholesteric resin layer, in this embodiment, a layer containing orientation defects is used. An orientation defect refers to a portion where the cholesteric regularity of the cholesteric resin is impaired. In such orientation defects, the molecules are usually oriented in a different direction than the surrounding molecules. Therefore, such orientation defects generally cause optical phenomena such as refraction, reflection, and diffraction. Therefore, a cholesteric resin containing orientation defects has a scattering property of scattering light.

The cholesteric resin layer has a specific range of haze due to scattering properties due to orientation defects. The specific haze range of the cholesteric resin layer is usually 10% or more, preferably 15% or more, more preferably 20% or more, and usually 60% or less, preferably 55% or less, more preferably 50% or less. is. When the haze of the cholesteric resin layer is at least the lower limit of the above range, the visibility of the reflected color of the flakes can be improved both in the front direction and the tilt direction of the optical layer containing the flakes. Further, when the haze of the cholesteric resin layer is equal to or less than the upper limit of the above range, the degree of blue shift can be increased, so that the difference in reflected color depending on the viewing angle of the optical layer containing flakes can be increased.

The haze of the cholesteric resin layer can be adjusted by, for example, a method of adjusting the orientation treatment conditions included in the method of producing the cholesteric resin layer; a method of adjusting the thickness of the cholesteric resin layer; Specifically, the lower the orientation temperature in the orientation treatment, the more easily orientation defects occur, so the haze can be increased. In addition, the thicker the cholesteric resin, the more easily orientation defects occur, so the haze can be increased.

The haze of the cholesteric resin layer can be measured with a haze meter using the cholesteric resin layer before pulverization. As a specific measuring method, the method described in the examples can be adopted.

A layer of cholesteric resin usually has a function of separating circularly polarized light. In other words, the cholesteric resin layer can function as a circularly polarized light separating film having a property of transmitting one of right-handed circularly polarized light and left-handed circularly polarized light and reflecting part or all of the other circularly polarized light. Reflection at a layer of cholesteric resin reflects circularly polarized light while maintaining its chirality. In the following description, the wavelength range in which the circularly polarized light separation function is exhibited is sometimes referred to as a "reflection band". By adjusting the reflection band, the flakes can reflect circularly polarized light of a color corresponding to the reflection band. Therefore, by adjusting the reflection band, it is possible to adjust the reflection color of the flakes.

The specific wavelength that exhibits the circularly polarized light separation function generally depends on the pitch of the helical structure in the cholesteric resin layer. The pitch of the helical structure is the distance in the direction of the normal to the plane, in which the angle gradually deviates as the direction of the molecular axis advances in the plane in the helical structure and returns to the original direction of the molecular axis. By changing the size of the pitch of this helical structure, it is possible to change the wavelength at which the circularly polarized light splitting function is exhibited.

For example, in a cholesteric resin layer formed using a liquid crystal compound, when the helical axis representing the rotation axis when the molecular axis is twisted in the helical structure and the normal line of the cholesteric resin layer are parallel, the helical structure The pitch p and the wavelength λ of the reflected circularly polarized light usually have the relationship of the formulas (X) and (Y).

Formula (X): λ _c =n×p×cos θ
Formula (Y): no _x p x cos θ ≤ λ ≤ n _e x p x cos θ

In formulas (X) and (Y), _λc represents the center wavelength of the reflection band (hereinafter sometimes referred to as “reflection center wavelength”), and _no represents the refractive index of the liquid crystal compound in the minor axis direction. , _ne represents the refractive index of the liquid crystal compound in the long axis direction, n represents (n _e +n _o )/2, p represents the pitch of the helical structure, and θ represents the incident angle of light (normal to the plane angle).

Therefore, the reflection central wavelength λ _c depends on the pitch p of the polymer helical structure in the layer of cholesteric resin. By changing the pitch p of this helical structure, the reflection band can be changed. Therefore, it is preferable to set the pitch p of the helical structure according to the wavelength of the circularly polarized light to be reflected by the cholesteric resin layer. As a method for adjusting the pitch p, for example, the method described in Japanese Patent Application Laid-Open No. 2009-300662 can be used. Specific examples include adjusting the type of chiral agent and adjusting the amount of the chiral agent in the cholesteric liquid crystal composition.

Also, as can be seen from the above equations (X) and (Y), the reflection band changes according to the incident angle of light. Therefore, in a cholesteric resin layer, a phenomenon called blue shift occurs, in which the reflection band shifts to the lower wavelength side as the incident angle increases.

As the cholesteric resin layer, for example, (i) a cholesteric resin layer in which the size of the pitch of the helical structure is changed stepwise, and (ii) a layer of the cholesteric resin in which the size of the pitch of the helical structure is changed continuously. layers of cholesteric resin, and the like.

(i) A cholesteric resin layer having a helical structure whose pitch is changed stepwise can be obtained, for example, by laminating a plurality of cholesteric resin layers having different helical structure pitches. Lamination can be performed by preparing a plurality of cholesteric resin layers having different helical structure pitches in advance, and then fixing each layer with a pressure-sensitive adhesive or an adhesive. Alternatively, lamination can be performed by forming a layer of cholesteric resin on top of which another layer of cholesteric resin is sequentially formed.

(ii) The cholesteric resin layer in which the pitch size of the helical structure is continuously changed includes, for example, one or more active energy ray irradiation treatments and/or heating treatments on the liquid crystal composition layer. It can be obtained by curing the layer of the liquid crystal composition after performing the band broadening treatment. According to the above-described band-broadening treatment, the pitch of the helical structure can be changed continuously in the thickness direction, so that the reflection band of the cholesteric resin layer can be expanded.

The layer of the cholesteric resin may be a layer having a single layer structure consisting of only one layer, or a layer having a multilayer structure including two or more layers. The number of layers contained in the cholesteric resin layer is preferably 1 to 100 layers, more preferably 1 to 20 layers, from the viewpoint of ease of production.

The refractive index anisotropy Δn of the cholesteric resin layer can be appropriately selected according to the reflection band of the flakes to be produced. For example, when producing flakes with a narrow reflection band and high color purity, it is preferable to use a layer of a cholesteric resin having a refractive index anisotropy Δn of 0.2 or less. In addition, in the case of producing flakes having a reflection band in the entire visible range, a layer of a cholesteric resin having a large refractive index anisotropy Δn of 0.2 or more is preferable. However, from the viewpoint of facilitating adjustment of the haze of the cholesteric resin layer according to the thickness by reducing the thickness necessary to ensure the reflectance, the refractive index anisotropy Δn of the cholesteric resin layer is 0.05 or more. is preferred. When the refractive index anisotropy Δn is 0.30 or more, the absorption edge on the long wavelength side of the ultraviolet absorption spectrum may extend into the visible region. can be used as long as it does not adversely affect performance. Here, the refractive index anisotropy Δn can be measured by the Senarmont method. The upper limit of the refractive index anisotropy Δn can be, for example, 0.25 or less.

Since the flakes according to this embodiment contain crushed pieces of the layer of cholesteric resin described above, the flakes usually contain a layer of cholesteric resin. In the following description, the layer of cholesteric resin before pulverization may be referred to as "cholesteric material layer" and the layer of cholesteric resin after pulverization included in the flakes may be referred to as "cholesteric pulverized layer".

Since they contain a cholesteric grind layer, the flakes typically have a single or different reflection bands. Among others, the flakes preferably have one or more reflection bands including the visible range. Specifically, the visible range usually means a wavelength range of 400 nm or more and 800 nm or less. Moreover, the expression that the reflection band includes the visible range means that the reflection band includes at least part of the visible range. Furthermore, the specific wavelength range of the reflection band is the wavelength range corresponding to the half width of the reflection peak in the reflection spectrum measured using a spectroscope (eg, JASCO Corporation "V570") (i.e., the intensity is 50% or more of the peak intensity). The above measurement is normally performed under the measurement conditions of a light incident angle of 5° and a detection angle of 0°. With the flakes having a reflection band in the visible range, the reflected light of the flakes can be visually recognized with the naked eye. Therefore, such flakes can be applied to a wide range of uses.

When the flake has reflection bands in the visible region, the number of reflection bands in the visible region may be one, or two or more. For example, a flake having only one narrow reflection band in the visible region can obtain a monochromatic (eg, red, green, blue, etc.) reflected light corresponding to the reflection band. Also, for example, a flake that has only one reflection band in the visible region that is wide enough to cover the entire visible region can obtain mixed-color (usually silver) reflected light corresponding to the reflection band. Further, for example, flakes having two or more reflection bands in the visible region can obtain mixed reflected light of colors corresponding to each of those reflection bands.

The bandwidth per reflection band is preferably greater than or equal to 100 nm, preferably greater than or equal to 200 nm, particularly preferably greater than or equal to 400 nm. In particular, the flakes more preferably have a reflection band with said bandwidth in the visible range. As a result, it is possible to increase the amount of reflected light per individual flake, and to obtain a paint that is more excellent in design and visibility. The upper limit of the bandwidth per reflection band can be 300 nm or less.

The bandwidth of the reflection band can be calculated based on the reflection spectrum measured using a spectrometer (eg, JASCO Corporation "V570"). More specifically, the value of the half width of the reflection peak in the measured reflection spectrum can be used as the value of the bandwidth of the reflection band. The above measurement is normally performed under the measurement conditions of a light incident angle of 5° and a detection angle of 0°.

As mentioned above, a cholesteric grinding layer containing a cholesteric resin typically undergoes a blue shift. Therefore, when flakes are observed, different reflected colors are usually visually recognized depending on the observation angle. In general, colors that are visually recognized when the viewing angle is small change to colors with shorter wavelengths as the viewing angle increases. For example, if green is visible when the viewing angle is small, blue is visible as the viewing angle increases. However, flakes with reflection bands in the blue and infrared regions can produce a color change called red shift, which is the opposite of blue shift. In such a red shift, for example, when the viewing angle is small, the blue color is visually recognized, but as the viewing angle increases, the red color is visually recognized.

The flakes may contain further optional layers in combination with the cholesteric comminuted layer. For example, when a multilayer film comprising a combination of a cholesteric raw layer and optional layers is ground to produce flakes, the flakes may include the cholesteric ground layer and optional layers.

Since the flakes contain pulverized pieces obtained by pulverizing the cholesteric raw fabric layer, they usually have a flaky shape. In the case of flakes having such a flake shape, when a layer is obtained by applying a paint containing the flakes, the layer plane of the layer and the layer plane of the cholesteric pulverized layer are parallel to each other due to the shear force during coating. tend to be oriented so that

The average particle diameter of the flakes is preferably 1 μm or more from the viewpoint of improving the visibility of the reflected color of the flakes, and is preferably 500 μm or less, more preferably 100 μm or less from the viewpoint of improving the coatability of the paint. is.
The average particle size of flakes can be measured by the method described in the Examples.

[2. Method for producing flakes]
The flakes according to the present embodiment can usually be produced by a production method including a step of forming a cholesteric raw layer; and a step of pulverizing the cholesteric raw layer.

In the step of forming the cholesteric master layer, for example, a layer of the cholesteric liquid crystal composition is provided on a suitable support for forming the cholesteric master layer, and the layer is cured to obtain the cholesteric master layer. For convenience, the material referred to as "liquid crystal composition" encompasses materials consisting of a single substance as well as mixtures of two or more substances. In addition, the cholesteric liquid crystal composition is a composition in which the liquid crystal compound exhibits a liquid crystal phase having cholesteric regularity (cholesteric liquid crystal phase) when the liquid crystal compound contained in the liquid crystal composition is aligned. .

As the cholesteric liquid crystal composition, a liquid crystal composition containing a liquid crystal compound and, if necessary, optional components can be used. As the liquid crystal compound, a liquid crystal compound that is a polymer compound and a polymerizable liquid crystal compound can be used. In order to obtain high thermal stability, it is preferable to use a polymerizable liquid crystal compound. By polymerizing a polymerizable liquid crystal compound in a state exhibiting cholesteric regularity, a layer of a cholesteric liquid crystal composition is cured to obtain a layer of a non-liquid crystal cholesteric resin cured while exhibiting cholesteric regularity. can. As the cholesteric liquid crystal composition, for example, one described in International Publication No. 2016/002765 can be used.

As the support, generally any member having a flat support surface capable of supporting the layer of the cholesteric liquid crystal composition can be used. A resin film is usually used as such a support. In addition, the support surface of the support may be subjected to a treatment for imparting alignment control force in order to promote the alignment of the liquid crystal compound in the layer of the cholesteric liquid crystal composition. Here, the alignment regulating force of a certain surface refers to the property of that surface that can align the liquid crystal compound in the cholesteric liquid crystal composition. Examples of the treatment for imparting an orientation regulating force to the supporting surface include rubbing treatment, orientation film forming treatment, stretching treatment, and ion beam orientation treatment.

A layer of the cholesteric liquid crystal composition is usually provided by coating the cholesteric liquid crystal composition on the supporting surface of the support. The thickness of the layer of the cholesteric liquid crystal composition can be set according to the desired thickness of the cholesteric raw fabric layer. Moreover, the thickness of the layer of the cholesteric liquid crystal composition is preferably set according to the haze of the cholesteric raw fabric layer. In general, the thicker the layer of the cholesteric liquid crystal composition, the thicker the cholesteric stock layer. Further, the thicker the cholesteric raw layer, the higher the haze of the cholesteric raw layer. Therefore, the haze of the cholesteric raw fabric layer can be adjusted by adjusting the thickness of the cholesteric liquid crystal composition layer formed on the supporting surface.

Any method may be used to apply the cholesteric liquid crystal composition. Examples of coating methods include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, and die coating. method, gap coating method, and dipping method.

After providing the layer of the cholesteric liquid crystal composition, the layer of the cholesteric liquid crystal composition may be subjected to alignment treatment, if necessary. Alignment treatment is usually performed by heating the layer of the cholesteric liquid crystal composition to a predetermined alignment temperature. By performing such an alignment treatment, the liquid crystal compound contained in the cholesteric liquid crystal composition is aligned and exhibits cholesteric regularity.

The alignment temperature can be arbitrarily set within a range in which the alignment of the liquid crystal compound proceeds. However, the orientation temperature is preferably set according to the haze of the cholesteric raw fabric layer. In general, the lower the orientation temperature, the higher the haze of the cholesteric raw fabric layer. Therefore, the haze of the cholesteric raw fabric layer can be adjusted by adjusting the orientation temperature. A specific alignment temperature is adjusted according to the composition of the cholesteric liquid crystal composition, and is set, for example, within the range of 50° C. to 150° C. so that a desired value of haze is obtained.

In the alignment treatment, the layer of the cholesteric liquid crystal composition is usually heated to the above alignment temperature for a predetermined time. The treatment time at this time can be arbitrarily set within a range in which the alignment of the liquid crystal compound proceeds, and can be, for example, 0.5 to 10 minutes.

However, the orientation of the liquid crystal compound contained in the cholesteric liquid crystal composition may be achieved immediately by coating the cholesteric liquid crystal composition. Therefore, the alignment treatment does not necessarily have to be applied to the layer of the cholesteric liquid crystal composition.

After orienting the liquid crystal compound, the layer of the cholesteric liquid crystal composition is cured to obtain a cholesteric raw fabric layer. In this step, a polymerizable component such as a polymerizable liquid crystal compound contained in the cholesteric liquid crystal composition is usually polymerized to cure the layer of the cholesteric liquid crystal composition. As the polymerization method, a method suitable for the properties of the components contained in the cholesteric liquid crystal composition can be selected. Examples of the polymerization method include a method of irradiating an active energy ray and a thermal polymerization method. Among them, the method of irradiating with active energy rays is preferable because the polymerization reaction can proceed at room temperature. Here, the active energy rays to be irradiated may include light such as visible rays, ultraviolet rays, and infrared rays, and arbitrary energy rays such as electron beams. When the layer of the cholesteric liquid crystal composition is cured by irradiation with active energy rays, the intensity of the irradiated active energy rays can be, for example, 50 mJ/cm ² to 10,000 mJ/cm ² .

After aligning the liquid crystal compound and before curing the layer of the cholesteric liquid crystal composition, the layer of the cholesteric liquid crystal composition may be subjected to a band broadening treatment. Such a band widening treatment can be performed, for example, by a combination of one or more active energy ray irradiation treatments and heating treatments. The irradiation treatment in the band broadening treatment can be performed, for example, by irradiating light with a wavelength of 200 nm to 500 nm for 0.01 seconds to 3 minutes. At this time, the energy of the irradiated light can be, for example, 0.01 mJ/cm ² to 50 mJ/cm ² . In addition, the heat treatment can be performed, for example, by heating to a temperature of preferably 40° C. or higher, more preferably 50° C. or higher, preferably 200° C. or lower, and more preferably 140° C. or lower. The heating time at this time is preferably 1 second or longer, more preferably 5 seconds or longer, and usually 3 minutes or shorter, preferably 120 seconds or shorter. By performing such a band-broadening process, the pitch of the helical structure can be greatly changed to obtain a wide reflection band.

The irradiation with the active energy ray may be performed in the air, or part or all of the process may be performed in an oxygen concentration-controlled atmosphere (for example, under a nitrogen atmosphere).

The process of coating and curing the cholesteric liquid crystal composition is not limited to one time, and the coating and curing may be repeated multiple times. This results in a thick cholesteric resin layer comprising two or more layers.

When the cholesteric raw fabric layer is produced by the method described above, the twist direction in the cholesteric regularity can be appropriately selected depending on the structure of the chiral agent used. For example, when the twist is in the right direction, a cholesteric liquid crystal composition containing a chiral agent that imparts dextrorotatory properties is used, and when the twist direction is in the left direction, a cholesteric liquid crystal composition containing a chiral agent that imparts levorotatory properties is used. A liquid crystal composition is used.

The thickness of the cholesteric raw fabric layer is preferably 0.1 μm or more, more preferably 1 μm or more, in order to obtain sufficient reflectance. In order to obtain the transparency of the cholesteric raw fabric layer, the thickness is preferably 20 μm or less, more preferably 10 μm or less.

According to the above process, a cholesteric raw fabric layer is usually obtained on the support. Therefore, before the step of pulverizing the cholesteric raw fabric layer, a step of peeling off the support may be performed, if necessary. Any peeling method may be used, and for example, the method described in JP-A-2015-27743 may be used.

After preparing the cholesteric material layer, a step of pulverizing the cholesteric material layer is performed. By pulverizing the cholesteric raw layer, flakes containing the cholesteric pulverized layer are obtained as pulverized pieces of the cholesteric raw layer. Any pulverization method may be used. Examples of pulverizing equipment include hammer crushers, cutter mills, hammer mills, bead mills, vibration mills, meteor ball mills, sand mills, ball mills, roll mills, three-roll mills, jet mills, high-speed rotary pulverizers, fine pulverizers and pulverizers. Examples include a grain sizer, a nano-jetmizer, and the like.

The flake manufacturing method described above may further include an optional step. The optional step includes, for example, a step of classifying flakes.

[3. paint]
The flakes described above can be used, for example, as pigments for paints. Such paint is a fluid material containing flakes as described above. Here, the fluid state includes not only a low-viscosity liquid state but also a high-viscosity gel state. A specific viscosity of the paint can be appropriately adjusted depending on the use of the paint. One type or two or more types of flakes may be included in the paint.

The paint typically includes a carrier medium in combination with the flakes. In this paint, the flakes are usually dispersed in the dispersion medium. As the dispersion medium, for example, an inorganic solvent such as water may be used, but an organic solvent is usually used. Examples of organic solvents include organic solvents such as ketone compounds, alkyl halide compounds, amide compounds, sulfoxide compounds, heterocyclic compounds, hydrocarbon compounds, ester compounds, and ether compounds. Among these, ketone compounds are preferred in consideration of the load on the environment. In addition, one type of dispersion medium may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The amount of the dispersion medium is preferably 40 parts by weight or more, more preferably 60 parts by weight or more, particularly preferably 80 parts by weight or more, preferably 1000 parts by weight or less, more preferably 800 parts by weight, based on 100 parts by weight of the flakes. It is not more than 600 parts by weight, particularly preferably not more than 600 parts by weight. By setting the amount of the dispersion medium within the above range, the coatability of the paint can be improved.

The paint may also contain a binder for binding the flakes after the dispersion medium has dried. A polymer is usually used as the binder. Examples of the polymer include polyester-based polymer, acrylic-based polymer, polystyrene-based polymer, polyamide-based polymer, polyurethane-based polymer, polyolefin-based polymer, polycarbonate-based polymer, and polyvinyl-based polymer. One binder may be used alone, or two or more binders may be used in combination at any ratio.

The amount of the binder is preferably 20 parts by weight or more, more preferably 40 parts by weight or more, particularly preferably 60 parts by weight or more, preferably 1000 parts by weight or less, more preferably 800 parts by weight, based on 100 parts by weight of the flakes. parts or less, particularly preferably 600 parts by weight or less. By setting the amount of the binder within the above range, the coatability of the paint can be improved. Also, the flakes can be stably bound after the dispersion medium is dried.

The paint may also contain a monomer of the polymer instead of or in combination with the polymer as a binder. In this case, an optical layer containing flakes and a binder can be produced by coating a suitable member with the coating material, drying it, and then polymerizing the monomers. Furthermore, it is preferable that the paint containing the monomer further contains a polymerization initiator.

The paint may contain optional ingredients in addition to the flakes, carrier medium and binder. Optional components include, for example, antioxidants, ultraviolet absorbers, light stabilizers, bluing agents, and the like. Moreover, these may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.

[4. How to use flakes and effects]
Said flakes are commonly used for the production of optical layers containing said flakes. Such an optical layer can be manufactured by coating a suitable member with a coating material and curing the coating layer formed by coating. Curing of the paint layer can be accomplished, for example, by drying the paint layer or polymerizing the monomers contained in the paint layer.

The optical layer includes the flakes described above. Therefore, when the optical layer is irradiated with light, the flakes reflect the circularly polarized light in the reflection band corresponding to the circularly polarized light separating function of the cholesteric resin. Therefore, the observer can visually recognize the reflected color corresponding to the wavelength of the reflected circularly polarized light as described above. In particular, when using the flakes according to the above-described embodiments, the observer can clearly see the reflected color in both the front direction and the tilt direction of the optical layer.

The present inventor presumes that the mechanism for achieving high visibility in both the front direction and the tilt direction as described above is as follows. However, the mechanism described below does not limit the technical scope of the present invention.

1 to 3 are cross-sectional views schematically showing an example of an optical layer 10 containing flakes 100 according to an embodiment of the invention.
Consider an example optical layer 10 comprising flakes 100 and a binder 200, as shown in FIGS. In the example shown here, the flakes 100 are oriented parallel to the layer plane of the optical layer 10, so that the layer plane of the cholesteric comminuted layer 110 that the flakes 100 comprise and the layer plane of the optical layer 10 are parallel. ing. Also, this cholesteric pulverized layer 110 is obtained by pulverizing a cholesteric raw fabric layer (not shown) having a haze within the specific range described above, and includes orientation defects 120 . When light is incident on such flakes 100 , circularly polarized light in a reflection band corresponding to the circularly polarized light separation function of the cholesteric resin is reflected by the cholesteric pulverized layer 110 .

As shown in FIGS. 1 and 2, the amount of light received by flakes 100 typically varies with the angle of incidence of the light. Therefore, as shown in FIG. 1, the flakes 100 tend to receive a relatively large amount of frontal light A1 having a small incident angle. On the other hand, as shown in FIG. 2, the flakes 100 tend to receive a relatively small amount of light A2 in the oblique direction with a large incident angle. Therefore, if there is no alignment defect 120, a large amount of light is reflected in the front direction of the optical layer 10, but a small amount of light is reflected in the inclined direction of the optical layer 10. FIG. Therefore, when conventional flakes were used, it was difficult to visually recognize the reflected color of the flakes when viewed from an inclined direction.

On the other hand, if the flake 100 contains the orientation defect 120 as in the present embodiment, the orientation defect 120 causes light scattering as shown in FIG. Therefore, part of the light A1 incident in the front direction is changed in the direction of travel by the action of scattering and exits in the oblique direction after being reflected. Therefore, since the amount of light that can be seen by the observer in the tilt direction can be increased, the visibility of the reflected color in the tilt direction can be enhanced. Therefore, the observer can clearly see the reflected color in both the front direction and the tilt direction of the optical layer 10 .

FIG. 3 shows an example in which the light scattered by the orientation defect 120 is reflected by the flake 100 including the orientation defect 120. The light scattered by the orientation defect 120 is reflected by the flake 100 including the orientation defect 120. It can also be reflected by another flake (not shown). In addition, FIG. 3 shows an example in which the traveling direction of the light A1 is changed before being reflected by the flakes 100 due to scattering at the orientation defect 120, but after being reflected by the flakes 100 It is also possible that the light A1 is redirected due to scattering at the orientation defect 120 .

Furthermore, even if the layer plane of the cholesteric pulverized layer 110 included in the flakes 100 is not parallel to the layer plane of the optical layer 10, it is believed that the same mechanism as described above will provide the same effect. That is, the effect of scattering makes it possible to suppress variations in the amount of light depending on the direction in which the light travels, so that the observer can clearly see the reflected color regardless of the viewing angle.

In the optical layer, generally the flakes are generally oriented in one direction. Therefore, the layer planes of the cholesteric pulverized layers contained in the flakes are also usually oriented in a certain direction as a whole. In many cases, the flakes are oriented parallel to the layer plane of the optical layer, so the layer plane of the cholesteric comminuted layer is also often parallel to the layer plane of the optical layer. When the flakes are oriented in a certain direction as a whole in this way, an observer who observes the optical layer can visually recognize the uniform reflected color of the flakes as a whole of the optical layer.

In addition, since the reflected color of flakes can change due to the effect of blue shift, the reflected color visually recognized by observing an optical layer containing the flakes can usually change according to the viewing angle with respect to the optical layer. In general, a reflected color closer to blue tends to be visually recognized in the oblique direction with a larger observation angle than in the front direction where the observation angle with respect to the thickness direction of the optical layer is 0°.

[5. Application]
The flakes and paints described above can be used, for example, as security products to prevent counterfeiting.

For example, the optical layer formed using the flakes or paint changes the visible reflected color depending on the viewing angle, as described above. Therefore, when an optical layer is formed on an article by a method such as printing, if the optical layer is observed and the color of the pigment changes depending on the viewing angle, the article can be determined to be genuine.

Further, for example, the authenticity may be determined using the circularly polarized light separation function of the cholesteric pulverized layer included in the flakes. Flakes typically reflect only one of right-handed and left-handed circularly polarized light. Therefore, different images are visually recognized in the optical layer containing the flakes when observed using the right-handed circularly polarizing plate and when observed using the left-handed circularly polarizing plate. Therefore, if the image observed using the right-handed circularly polarizing plate is different from the image observed using the left-handed circularly polarizing plate, it can be said that the article having the optical layer formed thereon is genuine. I can judge.

The object on which the optical layer as described above is to be formed is not limited, and a wide range of articles can be adopted. Examples of objects include cloth products such as clothing; leather products such as bags and shoes; metal products such as screws; paper products such as price tags; is not limited to In addition, the optical layer may be formed in a predetermined planar shape such as a design, number, symbol, identifier (bar coat, etc.) in order to provide design or information.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the embodiments described below, and can be arbitrarily modified without departing from the scope of the claims of the present invention and their equivalents.
In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. In addition, unless otherwise specified, the operations described below were performed under normal temperature and pressure conditions.

[Evaluation method]
[Method for measuring haze]
One side of the flat glass plate was subjected to corona treatment. In addition, the surface of the cholesteric raw fabric layer produced in Examples or Comparative Examples was subjected to corona treatment. The corona-treated surface of the glass plate and the corona-treated surface of the cholesteric raw layer were brought into contact with each other and pressed together at a temperature of 40° C. and a pressure of 5 MPa. After that, the support was peeled off to obtain a sample having a layer structure of "glass plate/cholesteric raw fabric layer". Using this sample, the haze of the cholesteric raw fabric layer was measured with a haze meter (“NDH-5000” manufactured by Nippon Denshoku Co., Ltd.).

[Measurement method of average particle size of flakes]
The average particle size of flakes was measured by the following method. First, several sieves with different mesh openings were used, and the ratio of flakes passing through the sieves having the mesh openings was measured. Then, the particle size distribution of the flakes was expressed as an integrated weight percentage based on the size of the opening and the ratio of the flakes passing through the sieve having the opening. In this particle size distribution, the particle size at which the integrated value of the weight is 50% was adopted as the average particle size.

[Method of measuring wavelength range and bandwidth of reflection band]
Using the sample prepared in [Method for Measuring Haze], the reflectance spectrum of the cholesteric raw fabric layer was measured using a spectroscope ("V570" by JASCO Corporation). The above measurements were performed under the conditions of a light incident angle of 5° and a detection angle of 0°. In the measured reflection spectrum, a reflection peak with a reflectance of 30% or more was specified as a reflection peak indicating a reflection band. A wavelength range corresponding to the half width of this reflection peak was obtained as a reflection band. Also, the value of the half width of the reflection peak was obtained as the value of the bandwidth of the reflection band.

[Method for evaluating reflected color of flakes]
The optical layers produced in Examples or Comparative Examples were visually observed. This observation was performed (1) under the illumination of a white fluorescent lamp and (2) under the room lamp of an automobile. Further, the observations were made in (i) the front direction of the optical layer and (ii) the tilt direction of the optical layer. Evaluation was performed according to the following criteria according to the observed reflected color of the flakes.
"A": A clear and bright reflected color was recognized.
"B": Although not clear, the reflected color itself could be recognized.
"C": The reflected color was barely recognized.
"D": Reflected color could not be recognized.

[Method for evaluating color change]
The optical layers produced in Examples or Comparative Examples were visually observed under the illumination of a white fluorescent lamp. This visual observation was first performed in (i) the front direction of the optical layer, then increased the viewing angle and (ii) was performed in the oblique direction of the optical layer. Evaluation was performed according to the following criteria according to the color change (blue shift) of the reflected color that occurs when the viewing direction is changed from the front direction of the optical layer to the oblique direction.
"A": It could be recognized that the reflected color changed sharply and clearly as the observation angle increased.
"B": It could be recognized that the reflected color changed clearly, though not abruptly, as the observation angle increased.
"C": It was barely recognizable that the reflected color changed as the observation angle increased.
"D": Even if the viewing angle is large, the change in the reflected color is gradual, and the color change cannot be recognized.

[Example 1]
(1-1. Production of cholesteric liquid crystal composition)
25.5 parts of a compound having a refractive index anisotropy Δn of 0.24 represented by the following formula (X1), 11 parts of a polymerizable liquid crystal compound represented by the following formula (Y1), a chiral agent ("LC756" manufactured by BASF) ) 2.3 parts, polymerization initiator ("Irgacure OXE02" manufactured by Ciba Specialty Chemicals) 1.2 parts, surfactant ("Ftergent 209F" manufactured by Neos) 0.04 parts, and cyclopentanone 60 as a solvent The parts were mixed to prepare a cholesteric liquid crystal composition.

The compound represented by the formula (X1) was prepared according to the method described in Japanese Patent No. 5365519 and used. Moreover, the compound represented by the above formula (Y1) was produced according to the method described in Japanese Patent No. 4,054,392.

(1-2. Production of circularly polarized light separating film)
As a support, a polyester film (“Cosmoshine A4100” manufactured by Toyobo Co., Ltd., thickness 100 μm) having an easy-adhesion-treated surface on one side was prepared. A rubbing treatment was applied to the surface of the support opposite to the easy-adhesion treatment surface. Thereafter, a cholesteric liquid crystal composition was applied to the rubbed surface using a #12 wire bar to form a liquid crystal composition layer.

The layer of the liquid crystal composition was subjected to alignment treatment by heating at 80° C. for 5 minutes. Thereafter, the liquid crystal composition layer was subjected to a UV irradiation treatment of irradiating weak ultraviolet rays of 20.7 mJ/cm ² followed by a heating treatment of heating at 100° C. for 1 minute to broaden the band. did. Thereafter, the liquid crystal composition layer was cured by irradiating ultraviolet rays of 800 mJ/cm ² . As a result, a cholesteric raw fabric layer as a circularly polarized light separation film having a thickness of 5.2 μm and a reflection band with a bandwidth of 250 nm in the wavelength range of 450 nm to 700 nm was obtained on the support. The haze of this cholesteric raw fabric layer was measured by the measurement method described above.

(1-3. Production of flakes)
The cholesteric raw fabric layer was peeled off from the support by spraying with a stream of water. This cholesteric raw fabric layer was pulverized using a counter jet mill to obtain flakes as scale-like filler having an average particle size of 20 μm.

(1-4. Production of paint)
20 parts by weight of the flakes, 80 parts by weight of a urethane acrylate UV-curable resin ("Unidic 17-806" manufactured by Dainippon Ink and Chemicals), and an ultraviolet polymerization initiator ("Irgacure" manufactured by Ciba Specialty Chemicals) 187") was dispersed in toluene to prepare a paint having a solid content concentration of 20% by weight.

(1-5. Production of optical layer)
The above paint is applied using an applicator onto a 100 μm thick resin film (“Zeonor Film ZF14-100” manufactured by Nippon Zeon Co., Ltd.) formed of norbornene resin, dried, and further at 100 ° C. for 2 minutes. It was heated to form a coating film. After that, the coating film is irradiated with UV rays of 50 mW/cm ² × 1 second using an ultraviolet irradiator (“UVC321AM1” manufactured by Ushio Inc.) to cure the coating film, thereby forming an optical layer having a thickness of 50 μm. got When the obtained optical layer was observed, the color tone of the optical layer changed according to the observation angle.
The optical layer thus obtained was evaluated according to the evaluation method described above.

[Example 2]
The optical layer was manufactured and evaluated by the same operation as in Example 1, except that the number of the wire bar was changed to #8. In Example 2, the obtained cholesteric raw fabric layer had a thickness of 3.7 μm and two reflection bands. One reflection band had a bandwidth of 100 nm in the wavelength range of 400 nm to 500 nm. The other reflection band had a bandwidth of 100 nm in the wavelength range from 550 nm to 650 nm.

[Example 3]
An optical layer was manufactured and evaluated by the same operation as in Example 1, except that the number of the wire bar was changed to #18. In Example 3, the obtained cholesteric raw fabric layer had a thickness of 8.6 μm and had a reflection band with a bandwidth of 200 nm in the wavelength range of 450 nm to 650 nm.

[Example 4]
The optical layer was manufactured and evaluated by the same operation as in Example 2, except that the band-broadening treatment was not performed. The cholesteric raw fabric layer obtained in Example 4 had a reflection band with a bandwidth of 150 nm in the wavelength range of 500 nm to 650 nm.

[Comparative Example 1]
An optical layer was produced and evaluated by the same operation as in Example 2, except that the orientation treatment temperature was changed to 130°C. In Comparative Example 1, the obtained cholesteric raw fabric layer had a thickness of 3.6 μm and two reflection bands. One reflection band had a bandwidth of 100 nm in the wavelength range of 400 nm to 500 nm. The other reflection band had a bandwidth of 100 nm in the wavelength range from 550 nm to 650 nm.

[Comparative Example 2]
An optical layer was produced and evaluated in the same manner as in Example 1, except that the surface opposite to the easy-adhesion-treated surface of the support was not rubbed. The liquid crystal compound contained in the cholesteric raw fabric layer obtained in Comparative Example 2 was not oriented as a whole layer, but was oriented in small segments. Therefore, the cholesteric raw fabric layer obtained in Comparative Example 2 was a set of the above segments, and the layer as a whole did not have cholesteric regularity and had many orientation defects. Moreover, this cholesteric raw fabric layer did not show a clear reflection band, and was cloudy as a whole.

[result]
The results of the above Examples and Comparative Examples are shown in Table 1 below.

REFERENCE SIGNS LIST 10 optical layer 100 flakes 110 cholesteric pulverized layer 120 orientation defects 200 binder

Claims (6)

comprising crushed pieces of a layer of resin having cholesteric regularity;
The layer of the resin contains orientation defects that impair the cholesteric regularity,
The flakes, wherein the resin layer has a haze of 10% or more and 60% or less. 2. The flake of claim 1, wherein the flake has one or more reflection bands that include the visible range. 3. The flakes of claim 2, wherein the bandwidth per reflection band is 100 nm or greater. The flakes according to any one of claims 1 to 3, wherein the flakes have an average particle size of 1 µm or more and 500 µm or less. A method for producing flakes according to any one of claims 1 to 4,
forming a layer of resin having cholesteric regularity;
and pulverizing the resin layer. A paint comprising the flakes according to any one of claims 1 to 4 and a dispersion medium.

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