WO2019189144A1

WO2019189144A1 - Flakes, method for producing same, and paint

Info

Publication number: WO2019189144A1
Application number: PCT/JP2019/012802
Authority: WO
Inventors: 謙一原井
Original assignee: 日本ゼオン株式会社
Priority date: 2018-03-27
Filing date: 2019-03-26
Publication date: 2019-10-03
Also published as: TWI840350B; TW202003603A; JP7327382B2; JPWO2019189144A1

Abstract

To provide flakes of which the reflected color is clearly visible in both a frontal direction and an inclined direction of a layer containing the flakes. (Solution) Flakes containing crushed pieces of a layer of a resin having cholesteric regularity, the layer of resin containing alignment defects in which the cholesteric regularity is impaired, and the haze of the layer of resin being 10-60%.

Description

Flakes, method for producing the same, and paint

The present invention relates to flakes, a method for producing the same, and a paint.

In the security ink field, special pigments are sometimes used to prevent counterfeiting. As one type of such a special pigment, one using a resin having cholesteric regularity (hereinafter sometimes referred to as “cholesteric resin” as appropriate) is known (see Patent Document 1).

JP 2007-141117 A

The present inventor paid attention to 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 reflection color of the flakes visually recognized by observing the optical layer varies depending on the observation angle. Here, the observation angle of a certain layer represents an angle formed by the observation direction with respect to the thickness direction of the layer. Thus, for example, the reflected color observed in the front direction of the optical layer (observation angle is 0 °) and the inclination direction of the optical layer (observation angle is greater than 0 ° and less than 90 °). The observed reflected color is often different. Therefore, it is conceivable to use flakes containing a cholesteric resin as a special pigment by utilizing the unique property that the reflection color varies depending on the observation angle.

By the way, various printed materials such as certificate papers, securities, banknotes, cards, and the like are printed as security inks containing special pigments. The environment for viewing these printed materials may be a bright environment or a dark environment. Furthermore, the illumination in the environment described above may include illumination with a wide light distribution angle and illumination with a narrow light distribution angle. As described above, there are various environments to which the security ink containing the special pigment is applied. Therefore, the special pigment is required to have a clearly visible reflected color under various lighting environments.

However, it was difficult for the conventional flakes containing cholesteric resin to clearly see the reflected color in both the front direction and the tilt direction. In particular, even in an environment where the reflected color can be clearly recognized by observation in the front direction, the reflected color cannot often be clearly recognized in the inclined direction.

The present invention has been made in view of the above-mentioned problems, and includes flakes in which the reflected color can be clearly visually recognized in both the front direction and the tilt direction of the layer containing the flakes, and a method for producing the flakes. The object is to provide a paint.

The present inventor has intensively studied to solve the above problems. As a result, the present inventor found that flakes containing pulverized pieces of a cholesteric resin layer having a predetermined range of haze due to light scattering caused by orientation defects can solve the above-mentioned problems, and completed the present invention. It was. That is, the present invention includes the following.

[1] A crushed piece of a resin layer having cholesteric regularity,
The resin layer includes orientation defects in which cholesteric regularity is impaired,
The flakes having a haze of the resin layer of 10% to 60%.
[2] The flake according to [1], wherein the flake has one or more reflection bands including a visible range.
[3] The flake according to [2], wherein a bandwidth per one reflection band is 100 nm or more.
[4] The flake according to any one of [1] to [3], wherein an average particle size of the flake is 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 a step of 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 visually recognized in both the front direction and the inclination direction of the layer containing the flakes and 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 an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing an example of an optical layer containing flakes according to an 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 present 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 implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

In the following description, the front direction of a certain layer represents a direction parallel to the thickness direction of the certain layer unless otherwise specified. In addition, the inclination direction of a certain layer represents a direction that is neither parallel nor perpendicular to the thickness direction of a certain layer unless otherwise specified.

[1. Flakes structure]
The flakes according to one embodiment of the present invention include crushed pieces of a layer of cholesteric resin. The 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 a certain plane, but the direction of the molecular axis is slightly shifted in the next plane that overlaps it, and the angle is further shifted in the next plane. In this way, the structure is such that the molecular axes in the planes are displaced (twisted) as they sequentially pass through the overlapping planes. That is, when the molecules inside a certain resin layer have cholesteric regularity, the molecules are aligned so that the molecular axis is in a certain direction on a certain first plane inside the layer. In the next second plane inside the layer that overlaps the first plane, the direction of the molecular axis deviates slightly from the direction of the molecular axis in the first plane. In the next third plane that further overlaps the second plane, the direction of the molecular axis deviates further from the direction of the molecular axis in the second plane. In this way, in the planes arranged in an overlapping manner, the angles of the molecular axes in the planes are sequentially shifted (twisted). 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 an alignment defect 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 from the surrounding molecules. For this reason, such orientation defects generally cause optical phenomena such as refraction, reflection, and diffraction. Therefore, the cholesteric resin containing orientation defects has a scattering property that scatters light.

The layer of cholesteric resin 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. It is. When the haze of the cholesteric resin layer is not less than the lower limit of the above range, the visibility of the reflected color of the flakes can be improved in both the front direction and the tilt direction of the optical layer containing the flakes. Further, when the haze of the cholesteric resin layer is not more than the upper limit of the above range, the degree of blue shift can be increased, so that the difference in reflected color according to the observation 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 alignment treatment conditions included in the method of manufacturing the cholesteric resin layer; a method of adjusting the thickness of the cholesteric resin layer; Specifically, the lower the alignment temperature during the alignment treatment, the easier it is for alignment defects to occur, so haze can be increased. In addition, the thicker the cholesteric resin, the easier it is for alignment defects to occur, so 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 embodiment can be adopted.

The layer of cholesteric resin usually has a circularly polarized light separation function. That is, the cholesteric resin layer can function as a circularly polarized light separation film having a property of transmitting one circularly polarized light of right circularly polarized light and left circularly polarized light and reflecting part or all of the other circularly polarized light. Reflection in the cholesteric resin layer 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 in this way may be referred to as “reflection band”. By adjusting this reflection band, the flakes can reflect circularly polarized light of a color corresponding to the reflection band. Therefore, the reflection color of the flakes can be adjusted by adjusting the reflection band.

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 plane normal direction until the angle of the molecular axis in the helical structure gradually shifts as it advances along the plane and then returns to the original molecular axis direction again. By changing the pitch of the helical structure, the wavelength at which the circularly polarized light separating function is exhibited can be changed.

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 of the cholesteric resin layer are parallel, the helical structure The pitch p of the circularly polarized light and the wavelength λ of the circularly polarized light to be reflected usually have the relationship of the formula (X) and the formula (Y).

Formula (X): λ _c = n × p × cos θ
Formula (Y): n _o × p × cos θ ≦ λ ≦ n _e × p × cos θ

In formula (X) and formula (Y), lambda _c is the center wavelength of the reflection band (hereinafter sometimes referred to as "reflection center wavelength".) Represent, n _o denotes the refractive index along the short axis of the liquid crystal compound , n _e represents the refractive index of the long axis direction of the liquid crystal compounds, n represents an _{(n e + n o) /} 2, p represents the pitch of the helical structure, theta is a normal angle of incidence (the plane of the light Angle).

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

Further, as can be seen from the above formulas (X) and (Y), the reflection band varies depending on the incident angle of light. Therefore, a phenomenon called a blue shift in which the reflection band shifts to the lower wavelength side as the incident angle increases usually occurs in the cholesteric resin layer.

Examples of the cholesteric resin layer include (i) a cholesteric resin layer in which the pitch of the helical structure is changed stepwise, and (ii) a continuous change in the pitch of the helical structure. Examples thereof include a cholesteric resin layer.

(I) The cholesteric resin layer in which the pitch of the helical structure 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 previously preparing a plurality of cholesteric resin layers having different helical structure pitches, and then fixing each layer via an adhesive or an adhesive. Alternatively, the lamination may be performed by forming a layer of a cholesteric resin and then sequentially forming another cholesteric resin layer.

(Ii) The cholesteric resin layer in which the pitch of the spiral structure is continuously changed includes, for example, one or more active energy ray irradiation treatments and / or heating treatments for the liquid crystal composition layer. After performing the broadening treatment, the liquid crystal composition layer can be cured. According to the band broadening process, since the pitch of the spiral structure can be continuously changed in the thickness direction, the reflection band of the cholesteric resin layer can be expanded, and is therefore called a band broadening process.

The layer of cholesteric resin may be a single-layer structure composed of only one layer, or may be 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 having a narrow reflection band and high color purity, it is preferable to use a cholesteric resin layer having a refractive index anisotropy Δn of 0.2 or less. In the case of producing flakes having a reflection band in a mixed color, multiple colors, or in the entire visible range, a layer of cholesteric resin having a large refractive index anisotropy Δn of 0.2 or more is preferable. However, the refractive index anisotropy Δn of the cholesteric resin layer is 0.05 or more from the viewpoint of facilitating the adjustment of the haze of the cholesteric resin layer according to the thickness by reducing the thickness necessary for ensuring the reflectance. 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 to the visible range. It can be used as long as the performance is not adversely affected. Here, the refractive index anisotropy Δn can be measured by the Senarmon 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 include the above-mentioned pulverized pieces of the cholesteric resin layer, the flakes usually include a cholesteric resin layer. In the following description, the layer of cholesteric resin before being pulverized may be referred to as a “cholesteric raw fabric layer”, and the layer of cholesteric resin after pulverization included in the flakes may be appropriately referred to as a “cholesteric pulverized layer”.

Since the cholesteric ground layer is included, the flakes usually have a single or different multiple reflection bands. Especially, it is preferable that a flake has one or more reflection bands including a visible region. Specifically, the visible range usually refers to a wavelength range of 400 nm to 800 nm. Further, the phrase “the reflection band includes the visible range” means that the reflection band includes at least a part of the visible range. Further, the specific wavelength range of the reflection band is a wavelength range corresponding to the half-value width of the reflection peak in the reflection spectrum measured using a spectroscope (for example, JASCO Corporation “V570”) (that is, intensity) Is a wavelength range in which the peak intensity is 50% or more of the peak intensity). The above measurement is usually performed under measurement conditions with a light incident angle of 5 ° and a detection angle of 0 °. Thus, flakes having a reflection band in the visible range can visually recognize the reflected light of the flakes with the naked eye. Therefore, such flakes can be applied to a wide range of uses.

When flakes have a reflection band in the visible range, the number of reflection bands in the visible range may be 1 or 2 or more. For example, flakes having only one reflection band with a narrow bandwidth in the visible range can obtain reflected light of a single color (for example, red, green, blue, etc.) corresponding to the reflection band. Further, for example, flakes having only one reflection band having a wide bandwidth in the visible range so as to cover the entire visible range 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 range can obtain mixed color reflected light corresponding to each of the reflection bands.

The bandwidth per one reflection band is preferably 100 nm or more, preferably 200 nm or more, and particularly preferably 400 nm or more. In particular, the flakes more preferably have a reflection band having the above bandwidth in the visible range. Thereby, it is possible to increase the amount of reflected light per flake, and it is possible to obtain a paint with more excellent 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 obtained by measuring the reflection spectrum using a spectroscope (for example, JASCO Corporation “V570”). More specifically, the half-value width of the reflection peak in the measured reflection spectrum can be used as the bandwidth value of the reflection band. The above measurement is usually performed under measurement conditions with a light incident angle of 5 ° and a detection angle of 0 °.

As described above, a blue shift usually occurs in a cholesteric pulverized layer containing a cholesteric resin. Therefore, when observing flakes, different reflection colors are usually visually recognized according to the observation angle. In general, the color visually recognized when the observation angle is small is changed to a color having a shorter wavelength as the observation angle is increased. For example, when green is visually recognized when the observation angle is small, blue is visually recognized as the observation angle increases. However, in the case of flakes having reflection bands in the blue region and the infrared region, it is possible to cause a color change called a red shift opposite to the blue shift. In such a red shift, for example, when the observation angle is small, blue is visually recognized, but as the observation angle increases, red is visually recognized.

The flakes may further include an optional layer in combination with the cholesteric pulverized layer. For example, when a flake is produced by pulverizing a multilayer film containing a combination of a cholesteric raw fabric layer and an arbitrary layer, the flake may include a cholesteric pulverized layer and an optional layer.

Flakes usually have a flake shape because they contain crushed pieces obtained by pulverizing a cholesteric raw fabric layer. When flakes having such a flake shape are 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 due to the shearing force during coating. Tends to be oriented.

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 preferably 500 μm or less, more preferably 100 μm or less from the viewpoint of improving the coating property of the paint. It is.
The average particle size of the flakes can be measured by the method described in the examples.

[2. Flakes manufacturing method]
The flakes according to this embodiment can be usually produced by a production method including a step of forming a cholesteric raw fabric layer; and a step of pulverizing the cholesteric raw fabric layer.

In the step of forming the cholesteric raw fabric layer, for example, a cholesteric liquid crystal composition layer is provided on a suitable support for forming the cholesteric raw fabric layer, and the layer is cured to obtain a cholesteric raw fabric layer. For convenience, the material referred to as a “liquid crystal composition” includes not only a mixture of two or more substances but also a material composed of a single substance. The cholesteric liquid crystal composition refers to a composition that can exhibit a liquid crystal phase (cholesteric liquid crystal phase) having cholesteric regularity 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 further containing an optional component as necessary 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 the polymerizable liquid crystal compound in a state exhibiting cholesteric regularity, the layer of the cholesteric liquid crystal composition can be cured to obtain a layer of a non-liquid crystalline cholesteric resin cured while exhibiting the cholesteric regularity. it can. As the cholesteric liquid crystal composition, for example, those described in International Publication No. 2016/002765 can be used.

As the support, any member having a flat support surface capable of supporting the cholesteric liquid crystal composition layer can be used. As such a support, a resin film is usually used. Further, the support surface of the support may be subjected to a treatment for imparting an alignment regulating force in order to promote the alignment of the liquid crystal compound in the cholesteric liquid crystal composition layer. Here, the alignment regulating force of a certain surface means the property of the surface capable of aligning the liquid crystal compound in the cholesteric liquid crystal composition. Examples of the treatment for imparting the alignment regulating force to the support surface include rubbing treatment, alignment film formation treatment, stretching treatment, ion beam alignment treatment, and the like.

Usually, a layer of the cholesteric liquid crystal composition is provided by coating the cholesteric liquid crystal composition on the support surface of the support. The layer thickness of the cholesteric liquid crystal composition can be set according to the thickness of the target cholesteric raw fabric layer. The thickness of the cholesteric liquid crystal composition layer is preferably set according to the haze of the cholesteric raw fabric layer. In general, the thicker the cholesteric liquid crystal composition layer is, the thicker the cholesteric raw fabric layer is obtained. And the haze of a cholesteric original fabric layer can be raised, so that a cholesteric original fabric layer is thick. Accordingly, 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 support surface.

The coating method of the cholesteric liquid crystal composition is arbitrary. 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 cholesteric liquid crystal composition, if necessary, the layer of cholesteric liquid crystal composition may be subjected to an alignment treatment. The alignment treatment is usually performed by heating a 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 becomes a state exhibiting cholesteric regularity.

The alignment temperature can be arbitrarily set within the 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. Generally, the haze of a cholesteric original fabric layer can be raised, so that orientation temperature is low. Therefore, the haze of the cholesteric original fabric layer can be adjusted by adjusting the orientation temperature. The specific alignment temperature is adjusted according to the composition of the cholesteric liquid crystal composition, and is set, for example, within a range of 50 ° C. to 150 ° C. so as to obtain a desired haze.

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

However, the alignment of the liquid crystal compound contained in the cholesteric liquid crystal composition may be immediately achieved by application of the cholesteric liquid crystal composition. Therefore, the alignment treatment is not necessarily performed on the layer of the cholesteric liquid crystal composition.

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

Further, after aligning the liquid crystal compound, the layer of the cholesteric liquid crystal composition may be subjected to a broadening treatment before the layer of the cholesteric liquid crystal composition is cured. Such a broadening process can be performed, for example, by a combination of one or more active energy ray irradiation processes and a heating process. The irradiation treatment in the broadening treatment can be performed, for example, by irradiating light with a wavelength of 200 nm to 500 nm for 0.01 second 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 . 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, 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 broadening process, it is possible to obtain a wide reflection band by continuously changing the pitch of the helical structure greatly.

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

The step of coating and curing the cholesteric liquid crystal composition is not limited to once, and the coating and curing may be repeated a plurality of times. Thereby, a thick cholesteric resin layer containing two or more layers is obtained.

In the case of producing a cholesteric raw fabric layer by the method described above, the twist direction in the cholesteric regularity can be appropriately selected depending on the structure of the chiral agent to be used. For example, when the twist is set to the right direction, a cholesteric liquid crystal composition containing a chiral agent that imparts dextrorotation is used. When the twist direction is set to the left direction, a cholesteric containing a chiral agent that imparts levorotation is used. A liquid crystal composition is used.

The thickness of the cholesteric raw fabric layer is preferably 0.1 μm or more, and more preferably 1 μm or more, in order to obtain sufficient reflectance. Moreover, when obtaining transparency of a cholesteric original fabric layer, it is preferable that it is 20 micrometers or less, and it is more preferable that it is 10 micrometers or less.

According to the above process, a cholesteric raw fabric layer is usually obtained on the support. Then, you may perform the process of peeling a support body before the process of grind | pulverizing a cholesteric original fabric layer as needed. The peeling method is arbitrary, and for example, the method described in JP-A-2015-27743 may be used.

After preparing the cholesteric raw fabric layer, a step of pulverizing the cholesteric raw fabric layer is performed. By pulverizing the cholesteric original fabric layer, flakes containing a cholesteric pulverized layer as a pulverized piece of the cholesteric original fabric layer are obtained. The grinding method is arbitrary. Examples of the crusher include a hammer crusher, a cutter mill, a hammer mill, a bead mill, a vibration mill, a meteor ball mill, a sand mill, a ball mill, a roll mill, a three-roll mill, a jet mill, a high-speed rotary crusher, a fine crusher and a crusher. Examples thereof include a particle sizer and a nano jet mizer.

The above-described flake production method may further include an optional step. Examples of the optional step include a step of classifying flakes.

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

Normally, the paint contains a dispersion medium in combination with flakes. In this coating material, the flakes are usually dispersed in the dispersion medium. For example, an inorganic solvent such as water may be used as the dispersion medium, but an organic solvent is usually used. Examples of the organic solvent 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, a ketone compound is preferable in consideration of environmental load. Moreover, a dispersion medium may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

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 with respect to 100 parts by weight of the flakes. The amount is not more than parts by weight, particularly preferably not more than 600 parts by weight. By making the amount of the dispersion medium within the above range, the coating property of the paint can be improved.

Further, the paint may contain a binder for binding flakes after the dispersion medium is dried. As the binder, a polymer is usually used. Examples of the polymer include polyester polymers, acrylic polymers, polystyrene polymers, polyamide polymers, polyurethane polymers, polyolefin polymers, polycarbonate polymers, polyvinyl polymers, and the like. A binder may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

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 with respect to 100 parts by weight of the flakes. Parts or less, particularly preferably 600 parts by weight or less. By making the amount of the binder within the above range, the coating property of the paint can be improved. Further, the flakes can be stably bound after the dispersion medium is dried.

Further, the coating material may contain a monomer of the polymer instead of the polymer as the binder or in combination with the polymer. In this case, an optical layer containing flakes and a binder can be produced by coating the paint on an appropriate member and drying the polymer to polymerize the monomer. Furthermore, it is preferable that the coating material containing a monomer further contains a polymerization initiator.

The paint may contain any component other than the flakes, the dispersion medium, and the binder. Examples of optional components include antioxidants, ultraviolet absorbers, light stabilizers, and bluing agents. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

[4. How to use and effect of flakes]
The said flake is normally used for manufacture of the optical layer containing the said flake. Such an optical layer can be manufactured by applying a coating material to an appropriate member and curing the coating layer formed by coating. Curing of the paint layer can be achieved by, for example, drying the paint layer or polymerizing monomers contained in the paint layer.

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

As described above, the present inventors infer that the mechanism for achieving high visibility in both the front direction and the tilt direction 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 including flakes 100 according to an embodiment of the present invention.
Consider an example of an optical layer 10 that includes flakes 100 and a binder 200 as shown in FIGS. In the example shown here, the flake 100 is oriented parallel to the layer plane of the optical layer 10, and therefore the layer plane of the cholesteric pulverized layer 110 included in the flake 100 and the layer plane of the optical layer 10 are parallel. ing. The cholesteric pulverized layer 110 is obtained by pulverizing the cholesteric raw fabric layer (not shown) having the above-mentioned specific range of haze, and includes orientation defects 120. When light enters such flakes 100, circularly polarized light in the 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 the flake 100 usually varies depending on the incident angle of light. Therefore, as shown in FIG. 1, the flake 100 tends to receive the light A1 in the front direction with a small incident angle with a relatively large amount of light. On the other hand, as shown in FIG. 2, the flake 100 tends to receive the light A2 in the tilt direction with a large incident angle with a relatively small amount of light. 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 tilt direction of the optical layer 10. Therefore, when the conventional flakes are used, it is difficult to visually recognize the reflected color of the flakes viewed from the tilt direction.

On the other hand, when the flake 100 includes the alignment defect 120 as in the present embodiment, the alignment defect 120 causes light scattering as shown in FIG. Therefore, a part of the light A1 incident in the front direction is changed in the traveling direction by the action of scattering and exits in the tilt direction after reflection. 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 improved. Therefore, in both the front direction and the inclination direction of the optical layer 10, the observer can clearly see the reflected color.

Although FIG. 3 shows an example in which the light scattered by the alignment defect 120 is reflected by the flake 100 including the alignment defect 120, the light scattered by the alignment defect 120 is flake 100 including the alignment defect 120. It may be reflected by another flake (not shown). 3 shows an example in which the traveling direction of the light A1 is changed before being reflected by the flake 100 due to scattering by the alignment defect 120. However, as circularly polarized light after being reflected by the flake 100, FIG. The traveling direction of the light A <b> 1 may be changed by scattering at the alignment defect 120.

Furthermore, even when the layer plane of the cholesteric pulverized layer 110 included in the flake 100 is not parallel to the layer plane of the optical layer 10, it is considered that the effect can be obtained by the same mechanism as described above. In other words, the scattering action can suppress variations in the amount of light depending on the traveling direction of the light, so that the observer can clearly see the reflected color regardless of the observation angle.

In the optical layer, the flakes are generally oriented in a certain direction as a whole. Therefore, the layer plane of the cholesteric pulverized layer contained in the flake is 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, and therefore the layer plane of the cholesteric grinding layer is often also parallel to the layer plane of the optical layer. Thus, when the flakes are oriented in a certain direction as a whole, an observer who observes the optical layer can visually recognize the reflected flake color uniformly as the whole optical layer.

In addition, since the reflection color on the flakes can be changed by the influence of blue shift, the reflection color visually observed by observing the optical layer containing the flakes can usually be changed according to the observation angle with respect to the optical layer. In general, compared to the front direction in which the observation angle formed with respect to the thickness direction of the optical layer is 0 °, the reflected color closer to blue tends to be visually recognized in the inclined direction where the observation angle is larger.

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

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

Further, for example, the authenticity may be determined using the circularly polarized light separation function of the cholesteric pulverized layer included in the flakes. The flakes usually reflect only one of right circular polarization and left circular polarization. Therefore, different images are visually recognized when the optical layer including flakes is observed using the right circularly polarizing plate and when observed using the left circularly polarizing plate. Therefore, if the image observed using the right circularly polarizing plate is different from the image observed using the left circularly polarizing plate, the article on which the optical layer is formed is authentic. Can be judged.

There is no limitation on the object as an object for forming the optical layer as described above, and a wide variety 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; and rubber products such as tires. It is not limited to. The optical layer may be formed in a predetermined planar shape such as a design, a number, a symbol, or an identifier (such as a bar coat) in order to impart designability or information.

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 implemented with any modifications without departing from the scope of the claims of the present invention and its equivalent scope.
In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Evaluation methods]
[Measurement method of haze]
One side of the flat glass plate was subjected to corona treatment. Moreover, the corona treatment was given to the surface of the cholesteric original fabric layer manufactured by the Example or the comparative example. The corona-treated surface of the glass plate and the corona-treated surface of the cholesteric raw fabric layer were brought into contact, pressed at a temperature of 40 ° C. and a pressure of 5 MPa, and bonded together. Thereafter, the support was peeled off to obtain a sample having a layer configuration 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.).

[Method for measuring average particle size of flakes]
The average particle size of the flakes was measured by the following method. First, using several sieves having different openings, the ratio of flakes passing through the sieve having the openings was measured. The particle size distribution of the flakes was expressed as an integrated weight percentage from the size of the openings and the ratio of the flakes passing through the sieve having the openings. In this particle size distribution, a particle size having an integrated value of 50% by weight was adopted as the average particle size.

[Method of measuring wavelength range and bandwidth of reflection band]
Using the sample prepared in the above [Method for measuring haze], the reflection spectrum of the cholesteric raw fabric layer was measured using a spectroscope (JASCO Corporation "V570"). The measurement was performed under the measurement conditions of a light incident angle of 5 ° and a detection angle of 0 °. In the measured reflection spectrum, a reflection peak having 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 determined as a reflection band. In addition, the half-width value of the reflection peak was determined as the bandwidth value of the reflection band.

[Evaluation method of flake reflection color]
The optical layers produced in the examples or comparative examples were visually observed. This observation was performed under (1) illumination of a white fluorescent lamp and (2) under a room lamp of an automobile. Furthermore, the above observation was performed in (i) the front direction of the optical layer and (ii) the tilt direction of the optical layer. The evaluation was performed based on the following criteria according to the reflected color of the observed flakes.
“A”: A clear and vivid reflected color could be recognized.
“B”: Although not clear, the reflected color itself could be recognized.
“C”: The reflected color was barely recognized.
“D”: The reflected color could not be recognized.

[Evaluation method of color change]
The optical layer produced in the example or the comparative example was visually observed under illumination of a white fluorescent lamp. This visual observation was initially performed (i) in the front direction of the optical layer, and thereafter with a larger observation angle (ii) in the tilt direction of the optical layer. Thus, evaluation was performed based on the following criteria according to the color change (blue shift) of the reflected color that occurs when the observation direction is changed from the front direction of the optical layer to the tilt direction.
“A”: It was recognized that the reflected color changed sharply and clearly as the observation angle increased.
“B”: It was recognized that the reflected color changed clearly but not suddenly as the observation angle increased.
“C”: It was barely recognized that the reflected color was changed by increasing the observation angle.
“D”: Even when the observation angle was large, the change in the reflected color was slow, and the color change could not be recognized.

[Example 1]
(1-1. Production of cholesteric liquid crystal composition)
25.5 parts of a compound having a refractive index anisotropy Δn 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 Corporation) ) 2.3 parts, 1.2 parts of a polymerization initiator (“Irgacure OXE02” manufactured by Ciba Specialty Chemicals), 0.04 part of a surfactant (“Futergent 209F” manufactured by Neos), and cyclopentanone 60 as a solvent The cholesteric liquid crystal composition was prepared by mixing the parts.

As the compound represented by the formula (X1), a compound produced according to the method described in Japanese Patent No. 5365519 was used. Moreover, what was manufactured according to the method described in the patent 4054392 was used for the compound represented by said Formula (Y1).

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

The liquid crystal composition layer was subjected to an alignment treatment by heating at 80 ° C. for 5 minutes. Thereafter, the liquid crystal composition layer is subjected to a broadening treatment including a UV irradiation treatment for irradiating weak ultraviolet rays of 20.7 mJ / cm ² and a subsequent heating treatment for heating at 100 ° C. for 1 minute. did. Thereafter, the liquid crystal composition layer was cured by irradiating with 800 mJ / cm ² of ultraviolet rays. As a result, a cholesteric original fabric layer as a circularly polarized light separating 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. Manufacture of flakes)
The cholesteric raw fabric layer was peeled off from the support by blowing a water stream. The cholesteric raw fabric layer was pulverized using a counter jet mill to obtain flakes as a scale-like filler having an average particle diameter of 20 μm.

(1-4. Production of paint)
20 parts by weight of the flakes described above, 80 parts by weight of urethane acrylate UV curable resin (“Unidic 17-806” manufactured by Dainippon Ink & Chemicals, Inc.), and UV polymerization initiator (“Irgacure” manufactured by Ciba Specialty Chemicals) 187 ") 2 parts by weight was dispersed in toluene to produce a paint having a solids concentration of 20% by weight.

(1-5. Production of optical layer)
The above-mentioned paint is applied to a 100 μm-thick resin film made of norbornene-based resin (“ZEONOR FILM ZF14-100” manufactured by ZEON Corporation) using an applicator, dried, and further at 100 ° C. for 2 minutes. Heated to form a coating. Thereafter, this coating film was irradiated with ultraviolet rays of 50 mW / cm ² × 1 second using an ultraviolet irradiator (“UVC321AM1” manufactured by USHIO INC.) To cure the coating film, and 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 in the same manner as in Example 1, except that the wire bar count was changed to # 8. In Example 2, the obtained cholesteric raw fabric layer had a thickness of 3.7 μm and had two reflection bands. One reflection band had a bandwidth of 100 nm in a wavelength range of 400 nm to 500 nm. The other reflection band had a bandwidth of 100 nm in the wavelength range of 550 nm to 650 nm.

[Example 3]
The optical layer was manufactured and evaluated in the same manner as in Example 1 except that the wire bar count 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 a wavelength range of 450 nm to 650 nm.

[Example 4]
The optical layer was manufactured and evaluated in the same manner as in Example 2 except that the 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]
The optical layer was produced and evaluated in the same manner as in Example 2 except that the temperature of the alignment treatment was changed to 130 ° C. In Comparative Example 1, the obtained cholesteric raw fabric layer had a thickness of 3.6 μm and had two reflection bands. One reflection band had a bandwidth of 100 nm in a wavelength range of 400 nm to 500 nm. The other reflection band had a bandwidth of 100 nm in the wavelength range of 550 nm to 650 nm.

[Comparative Example 2]
The optical layer was produced and evaluated by the same operation as in Example 1 except that the rubbing treatment on the surface opposite to the surface of the support that was opposite to the easy adhesion treatment surface was not performed. The liquid crystal compound contained in the cholesteric raw fabric layer obtained in Comparative Example 2 was not aligned as a whole layer, but was aligned for each small segment. Therefore, the cholesteric raw fabric layer obtained in Comparative Example 2 was a set of the above-mentioned segments, and the entire layer did not have cholesteric regularity, and a large number of orientation defects were generated. Moreover, this cholesteric raw fabric layer did not show a clear reflection band and was clouded as a whole.

[result]
The results of the examples and comparative examples are shown in Table 1 below.

DESCRIPTION OF SYMBOLS 10 Optical layer 100 Flakes 110 Cholesteric ground layer 120 Orientation defect 200 Binder

Claims

Including crushed pieces of a resin layer having cholesteric regularity,
The resin layer includes orientation defects in which cholesteric regularity is impaired,
The flakes having a haze of the resin layer of 10% to 60%.
The flake according to claim 1, wherein the flake has one or more reflection bands including a visible range.
The flakes according to claim 2, wherein the bandwidth per reflection band is 100 nm or more.
The flakes according to any one of claims 1 to 3, wherein an average particle size of the flakes is 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 a step of pulverizing the resin layer.
A paint comprising the flakes according to any one of claims 1 to 4 and a dispersion medium.