JP7476566B2 - Powder manufacturing method - Google Patents

Description

The present invention relates to a method for producing powder.

As a pigment for ink, a powder consisting of thin film flakes formed from a thin film formed of metal, resin, or the like is sometimes used.
A method is known for producing resin thin film flakes, in which a release layer is formed on a base film, a resin thin film is formed on the release layer, cracks are formed in the resin thin film, and then the base film is bent at an acute angle to cause the resin thin film to peel off as thin film flakes (see Patent Document 1).
Also known is a method in which a thin resin film is formed on a base film, a member having an uneven shape is pressed against the thin resin film to form cracks in the thin resin film, and a fluid is sprayed onto the cracked thin resin film to cause the thin resin film to peel off (see Patent Document 2).

Japanese Patent Publication No. 07-080248 International Publication No. 2019/189246

The ink is used in printing such as screen printing, gravure printing, intaglio printing, offset printing, etc. It is preferable that the powder contained in the ink has a sharper peak in its particle size distribution in order to improve the texture of the printed matter.
In order for the powder to have a sharp peak in its particle size distribution, it is preferable that the shapes of the thin film flakes contained in the powder are as uniform as possible.
In addition, in order to confirm the authenticity of a printed matter, the powder contained in the ink used in the printed matter may be observed, for example, under a microscope. In this case, if it can be confirmed that the shapes of the thin film flakes contained in the powder are uniform, the authenticity of the printed matter can be easily determined, and the security performance of the printed matter can be improved.
Therefore, it is preferable that the thin film flakes contained in the powder have as uniform a shape as possible.
However, when powder consisting of thin film flakes was produced using conventional technology, the thin film would peel off from the base film without being divided along the cracks, and as a result, the powder consisting of thin film flakes would sometimes contain a significant amount of thin film flakes with shapes other than the regular shape that follows the cracks.
Therefore, a manufacturing method is required that can produce powder with a high proportion of thin film flakes that have a consistent shape along the cracks.

Means for Solving the Problems The present inventors conducted extensive research to find a solution to the above problems, and as a result discovered that the above problems could be solved by forming a predetermined crack in a multilayer film, thereby completing the present invention.
That is, the present invention provides the following.

[1] A step (1) of forming a crack in a multilayer film including a base layer and a thin film arranged on the outermost side, the crack dividing the thin film into small pieces of the same shape when viewed from the thickness direction of the thin film, the crack reaching a position deeper than the surface of the base layer on the thin film side;
and (2) peeling the thin film flakes from the base layer of the multilayer film in which the cracks are formed to obtain a powder containing the thin film flakes.
[2] The method for producing a powder according to [1], wherein the major axis of the small particles is 150 μm or less.
[3] The method for producing a powder according to [1] or [2], wherein in the step (1), a member having an uneven shape is pressed against the thin film side of the multilayer film to form the cracks.
[4] The method for producing a powder according to [3], wherein the pressing is performed in a state where the multilayer film is supported by a support member having a surface hardness of D40 or more.
[5] The method for producing a powder according to [4], wherein the pressure applied to the member having the concave-convex shape is 0.5 MPa or more.
[6] The method for producing a powder according to any one of [1] to [5], wherein the step (2) includes a step (2a) of spraying a fluid onto the multilayer film in which the cracks have been formed.
[7] The method for producing a powder according to any one of [1] to [6], wherein the thickness of the base layer is 12 μm or more and 250 μm or less.
[8] The method for producing a powder according to any one of [1] to [7], wherein in the step (1), the cracks are formed so that the shape of the small pieces is a triangle, a rectangle, or a hexagon when viewed from the thickness direction of the thin film.

The present invention provides a manufacturing method that can produce powder with a high proportion of thin film pieces that have a consistent shape along the cracks.

FIG. 1 is a cross-sectional view showing an example of a multilayer film used in step (1) according to one embodiment. FIG. 2 is a schematic plan view of a surface on the thin film side of a multilayer film in which a crack has been formed, as viewed from the thickness direction of the multilayer film according to one embodiment. FIG. 3 is a cross-sectional view showing a schematic cross section taken along line III-III of FIG. FIG. 4 is a schematic plan view of the thin film side surface of a multilayer film in accordance with one embodiment, in which cracks are formed, viewed from the thickness direction of the multilayer film. FIG. 5 is a cross-sectional view showing a schematic cross section taken along line VV of FIG. FIG. 6 is a perspective view that illustrates an example of a member having a concave-convex shape that can be used in the powder manufacturing method of one embodiment. FIG. 7 is a perspective view that shows a schematic diagram of the member having the concave and convex shape shown in FIG. FIG. 8 is a plan view showing a schematic development of the member shown in FIG. 7 cut along line X1-X1. FIG. 9 is a partial cross-sectional view taken along line Y1-Y1 in FIG. FIG. 10 is a perspective view that illustrates an example of a member having an uneven shape that can be used in the powder manufacturing method of one embodiment. FIG. 11 is a perspective view that illustrates the member having the uneven shape illustrated in FIG. FIG. 12 is a plan view showing a schematic development of the member shown in FIG. 11 cut along line X2-X2. FIG. 13 is a partial cross-sectional view taken along line Y2-Y2 in FIG.

The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be modified and implemented as desired without departing from the scope of the claims of the present invention and their equivalents.

In the following description, a "long" film refers to a film that is 5 times or more longer than its width, preferably 10 times or more longer, specifically a film that is long enough to be wound into a roll for storage or transportation. There is no particular upper limit to the length of the film, and it can be, for example, 100,000 times or less than its width.

In the following description, the term "(meth)acrylic" includes "acrylic," "methacrylic," and combinations thereof.

In the following description, unless otherwise specified, the directions of elements as "parallel" and "perpendicular" may include an error within a range that does not impair the effect of the present invention, for example, within a range of ±3°, ±2°, or ±1°.

[1. Overview of powder manufacturing method]
The method for producing powder according to one embodiment of the present invention includes the steps of: forming a crack in a multilayer film including a base layer and a thin film arranged on the outermost side, the crack dividing the thin film into small pieces of the same shape when viewed in the thickness direction and reaching a position deeper than the surface of the thin film side of the base layer; and peeling the small pieces of the thin film from the base layer of the multilayer film in which the crack is formed to obtain a powder containing the small pieces of the thin film. This allows the production of a powder containing a high proportion of thin film pieces having a uniform shape along the crack.

[2. Step (1)]
In step (1), a multilayer film including a base layer and a thin film disposed on the outermost side is provided with cracks that divide the thin film into small pieces of the same shape when viewed in the thickness direction, and the cracks divide the base layer and the thin film. Cracks are formed that reach deeper than the surface of the thin film side of the material layer.

[2.1. Multilayer film]
The multilayer film used in step (1) includes a base layer and a thin film. The thin film is disposed on the outermost side of the multilayer film. Here, "disposed on the outermost side" means that the thin film is disposed on the outermost side in the thickness direction of the multilayer film. Therefore, the surface of the thin film is exposed on one side of the multilayer film. The multilayer film may have any layer between the thin film and the base layer.
The multi-layer film is preferably long in order to efficiently form cracks.
1 is a cross-sectional view showing an example of a multilayer film used in step (1) according to one embodiment. As shown in FIG. 1, the multilayer film 10 includes a base layer 12 and a thin film 11 provided directly on the base layer 12.

(Base layer)
The base layer is preferably long in order to efficiently form a thin film.
Examples of materials for forming the base layer include, but are not limited to, resins containing polymers, paper, and metals, with resins containing polymers being preferred because of their excellent flexibility and mechanical strength.
Examples of polymers contained in the resin capable of forming the base layer include cellulose-based polymers (e.g., triacetyl cellulose); polymers containing an alicyclic structure (e.g., cycloolefin polymer); polyesters (e.g., polyethylene terephthalate); acrylic polymers (e.g., poly(meth)acrylic acid, poly(meth)acrylic acid ester, polyacrylonitrile); and polycarbonates. The resin capable of forming the base layer may contain one type of polymer alone or a combination of two or more types. The polymer may be a homopolymer or a copolymer. The resin may contain any additive in addition to the polymer.

Examples of polymers containing an alicyclic structure include (1) norbornene-based polymers, (2) monocyclic olefin polymers, (3) cyclic conjugated diene polymers, (4) vinyl alicyclic hydrocarbon polymers, and hydrogenated versions of these. Among these, norbornene-based polymers and hydrogenated versions of these are preferred from the viewpoints of transparency and moldability.

Examples of norbornene-based polymers include ring-opening polymers of monomers having a norbornene structure and their hydrogenated products; addition polymers of monomers having a norbornene structure and their hydrogenated products. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of a monomer having a norbornene structure and any monomer that can be copolymerized therewith. Examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of a monomer having a norbornene structure and any monomer that can be copolymerized therewith. Examples of these polymers include the polymers disclosed in, for example, JP 2002-321302 A.

Specific examples of suitable norbornene-based polymers and their hydrogenated products include "ZEONOR" manufactured by Zeon Corporation; "ARTON" manufactured by JSR Corporation; and "TOPAS" manufactured by TOPAS ADVANCED POLYMERS.

The thickness of the substrate layer is preferably 12 μm or more, more preferably 25 μm or more, even more preferably 50 μm or more, and is preferably 250 μm or less, more preferably 200 μm or less, even more preferably 188 μm or less. When the thickness of the substrate layer is equal to or greater than the lower limit, the mechanical strength of the substrate layer can be made superior. When the thickness of the substrate layer is equal to or less than the upper limit, the flexibility of the substrate layer can be improved, making handling during manufacturing easier.

The substrate layer may have a single layer structure or a multilayer structure.

When the base layer has a multi-layer structure, it is preferable that each layer included in the base layer has a peel strength sufficient to prevent the layers from peeling off from each other in steps (1) and (2).
The substrate layer preferably has a single layer structure.

The surface of the substrate layer may be subjected to a treatment such as rubbing treatment or corona treatment.
The substrate layer may be an unstretched layer, that is, an unoriented layer, or a stretched layer.

The multilayer film may be a film consisting of only the base layer and the thin film, or may have any layer in addition to the base layer and the thin film. For example, when a liquid crystal composition is used as the composition for forming the thin film, the multilayer film may have an alignment film between the base layer and the thin film from the viewpoint of favorably aligning the liquid crystal composition. The alignment film may be formed from a resin containing a polymer such as polyimide, polyvinyl alcohol, polyester, polyarylate, polyamideimide, polyetherimide, or polyamide. In addition, one type of these polymers may be used alone, or two or more types may be used in combination in any ratio. The alignment film may be produced by applying a solution containing the polymer, drying it, and performing a rubbing treatment.

(Thin Film)
The thin film may have either a single-layer structure or a multilayer structure. The thin film may be either a conductor or a dielectric. The thin film may be either an inorganic film or an organic film. Examples of the thin film include metal films such as aluminum and silver; dielectric multilayer films formed of dielectric materials such as titanium oxide, silicon oxide, niobium oxide, tantalum oxide, and magnesium fluoride; and resin films.
Examples of resin materials for forming the resin film include photocurable liquid crystal compositions, acrylic resins, polystyrene, polyesters, polyamides, polyvinyl chloride, polyvinyl acetate, cellulose-based polymers (e.g., triacetyl cellulose), polycarbonates, polyurethanes, polyolefins, alicyclic structure-containing polymers, epoxy resins, melamine resins, phenolic resins, and combinations thereof. The polymers that can be contained in the resin material may be homopolymers or copolymers. In addition to the polymer, the resin material may contain any additives such as a curing agent and an antioxidant.

The thickness of the thin film can be set appropriately depending on the material of the thin film and the purpose of use of the powder, but from the viewpoint of ensuring the reflectivity of the thin film, it is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1 μm or more, and preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less. By setting the thickness of the thin film to the above upper limit or less, the obtained powder can be suitably used in inks corresponding to printing layers of various thicknesses.

The thin film may be, for example, a film made of a cured product obtained by curing a photocurable liquid crystal composition as a resin-containing composition. That is, the resin that forms the thin film may be, for example, a cured product of a photocurable liquid crystal composition. Here, 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 made of a single substance.

As the thin film, for example, a cholesteric resin layer may be used. A cholesteric resin layer refers to a resin layer having cholesteric regularity. The cholesteric regularity of a resin layer having cholesteric regularity is a structure in which the molecular axes are aligned in a certain direction on one plane, but the direction of the molecular axes is shifted at a slight angle on the next plane that overlaps it, and the angle is further shifted on the next plane, and so on, such that the angle of the molecular axes in the plane shifts (twists) as the molecules pass through the overlapping and arranged planes one after another. That is, when the molecules in the layer have cholesteric regularity, the molecules are aligned in the resin layer in a manner that forms a layer of many molecules. In a certain layer A of such a layer of many molecules, the molecules are aligned so that the molecular axes are in a certain direction, and in the adjacent layer B, the molecules are aligned in a direction shifted at an angle from the direction in layer A, and in the further adjacent layer C, the molecules are aligned in a direction further shifted at an angle from the direction in layer B. In this way, in a layer of many molecules, the angles of the molecular axes are continuously shifted, forming a structure in which the molecules are twisted. A structure in which the directions of the molecular axes are twisted in this way becomes an optically chiral structure.

Cholesteric resin layers usually have the function of separating circularly polarized light. In other words, they have the property of transmitting one of right-handed and left-handed circularly polarized light and reflecting part or all of the other circularly polarized light. Furthermore, the cholesteric resin layer reflects circularly polarized light while maintaining its chirality.

When a cholesteric resin layer such as that described above is used as the thin film, the manufacturing method of this embodiment can produce a powder consisting of small pieces of resin film that utilize the circularly polarized light separation function, and in which a large proportion of thin film pieces have a uniform shape.

The thin film can be formed by any method depending on the material of the thin film. For example, the thin film can be formed by a deposition method, a sputtering method, a coating method, etc. Examples of coating methods include die coating, curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, and gap coating.

2.2. Crack formation
(crack)
The cracks formed in step (1) divide the thin film included in the multilayer film into small pieces of the same shape when viewed from the thickness direction. The cracks are formed so as to reach a position deeper than the surface of the thin film side of the base layer. The cracks are also formed so as to reach a position deeper than the surface of the thin film side of the base layer over the entire surface of the multilayer film.

The shape of the flakes as viewed in the thickness direction of the thin film is not particularly limited, and examples include polygons such as triangles, squares, and hexagons, crosses, and circles, with triangles, squares, or hexagons being preferred.

The major axis of the flakes as viewed in the thickness direction of the thin film is preferably 250 μm or less, more preferably 200 μm or less, even more preferably 175 μm or less, and even more preferably 150 μm or less, from the viewpoint of preventing clogging of the printing plate with ink, and is usually greater than 0 μm, preferably 10 μm or more, from the viewpoint of improving the visibility of the printing layer formed by the ink. Here, the major axis refers to the longest distance between multiple parallel lines when multiple parallel lines are drawn tangent to the outline of the flakes.

An example of the cracks formed in step (1) will be described below.
Fig. 2 is a schematic plan view of a surface of a thin film side of a multilayer film having a crack formed therein according to one embodiment, as viewed from the thickness direction of the multilayer film. Fig. 3 is a schematic cross-sectional view of the III-III cut surface of Fig. 1.

As shown in Figure 2, lattice-shaped cracks 100C are formed in the multilayer film 100. The cracks 100C are composed of a number of linear notches 100C1 that extend downward to the right at an angle of θ1 with respect to the width direction WD of the multilayer film 100, and a number of linear notches 100C2 that extend upward to the right at an angle of θ2. Here, if the angle in the clockwise direction with respect to the width direction WD of the multilayer film 100 in Figure 2 is positive and the angle in the counterclockwise direction is negative, then θ1 is 45° and θ2 is -45°.

In this embodiment, the spacing P11 between adjacent indentations 100C1 is approximately the same as the spacing P12 between adjacent indentations 100C2. Here, approximately the same means that P12 is 90% or more and 110% or less of P11. The lattice-shaped crack 100C, which has such multiple indentations 100C1 and multiple indentations 100C2, divides the thin film arranged on the outermost side of the multilayer film 100 into multiple small pieces 101 that are approximately square. The multiple small pieces 101 have sides with lengths corresponding to the spacing P11 and the spacing P12, and in this embodiment, the length of one side of the multiple small pieces 101 is P11.

As shown in FIG. 3, the multilayer film 100 comprises a base layer 120 and a thin film 110 formed directly on the base layer 120. The depth 100Cd of the crack 100C is the distance from the surface 110U of the multilayer film 100 on the thin film 110 side to the tip 100Ct of the crack 100C. The depth 100Cd of the crack 100C is greater than the thickness 110T of the thin film 110. Therefore, the tip 100Ct of the crack 100C reaches a position deeper than the surface 120U of the base layer 120 on the thin film 110 side.

Figure 4 is a schematic plan view of the thin film side of a multilayer film in which a crack has been formed according to another embodiment, viewed from the thickness direction of the multilayer film. Figure 5 is a schematic cross-sectional view showing the V-V cut surface of Figure 4.

As shown in Fig. 4, honeycomb-shaped cracks 200C are formed in the multilayer film 200. The honeycomb-shaped cracks 200C divide the thin film disposed on the outermost side of the multilayer film 200 into a plurality of small pieces 201 each having a substantially regular hexagonal shape.
5, the multilayer film 200 includes a base layer 220 and a thin film 210 formed directly on the base layer 220. In this embodiment, too, the tip 200Ct of the crack 200C reaches a position deeper than the surface 220U of the base layer 220 on the thin film 210 side.

In another embodiment, continuous triangular cracks may be formed in the multilayer film when viewed in the thickness direction of the multilayer film.

(Method of forming cracks)
The cracks can be formed, for example, by pressing a member having an uneven shape against the thin film side of the multilayer film. More specifically, in a state where the multilayer film is supported by a support member, the multilayer film is sandwiched between the support member and the member having an uneven shape, and the member having an uneven shape is pressed against the multilayer film to form the cracks.

As a member having an uneven shape, a member having convex portions on its surface that correspond to the shape of the cracks as viewed from the thickness direction of the multilayer film can be used. For example, if the shape of the cracks as viewed from the thickness direction of the multilayer film is lattice-shaped, a member having convex portions in a lattice shape on its surface can be used. Also, if the shape of the cracks as viewed from the thickness direction of the multilayer film is honeycomb-shaped, a member having convex portions in a honeycomb shape on its surface can be used.

In addition, multiple members may be used as the member having an uneven shape. For example, a member having a convex portion on its surface corresponding to one part of the crack and a member having a convex portion on its surface corresponding to another part of the crack may be used. For example, if the crack is lattice-shaped and divides the thin film into squares when viewed in the thickness direction, the crack may be formed by pressing a first member having an uneven shape and having convex portions on its surface corresponding to the indentations in one direction that make up the crack, and a second member having an uneven shape and having convex portions on its surface corresponding to the indentations in another direction that make up the crack, against the multilayer film.

The same member having an uneven shape may also be pressed against the multilayer film multiple times in different positions to form cracks.

The unevenly shaped member may be cylindrical, forming continuous cracks in the multilayer film.

As the member having a concave-convex shape, a material that has a strength that does not break even when the multilayer film is pressed and can form a concave-convex structure can be used. Examples of such materials include carbon steel and stainless steel. In addition, the member having a concave-convex shape may have a multilayer coating of one or more layers on the surface for the purpose of increasing corrosion resistance, strength, thermal conductivity, etc. Examples of such coatings include, but are not limited to, plating films of nickel, nickel phosphorus, silicon, copper, etc., and coatings formed by ceramic spraying. The member having a concave-convex shape may be equipped with heating means using, for example, a heater, a heat medium, dielectric heating, induction heating, etc., a static eliminator for static electricity countermeasures, an earth, etc.

A member having a concave-convex shape can be manufactured by any conventional method. For example, a member such as a cylindrical metal roll can be cut using a cutting tool such as a diamond bit, or processed using a laser processing device to form a member having a desired concave-convex shape.

The pressure when pressing the member having an uneven shape against the thin film side of the multilayer film is preferably 0.5 MPa or more, more preferably 1 MPa or more, even more preferably 5 MPa or more, and preferably 100 MPa or less, more preferably 75 MPa or less. By setting the pressure at or above the lower limit, it is possible to form cracks of sufficient depth in the multilayer film, and by setting the pressure at or below the upper limit, it is possible to suppress damage to the multilayer film. When a member having one or more kinds of uneven shapes is pressed against the multilayer film multiple times to form cracks in the multilayer film, the multiple pressings may be the same or different. Preferably, the multiple pressings are performed at the same pressure.

The support member usually has a support surface that supports the surface opposite to the thin film that the multilayer film contains. The hardness of the support surface that supports the surface of the multilayer film is preferably D40 or more, more preferably D60 or more, even more preferably D70 or more, and preferably D99 or less, more preferably D97 or less, even more preferably D95 or less. Here, the hardness is a value measured using a durometer (type D) in accordance with JIS K-6253. By setting the hardness of the support surface of the support member within the above range, cracks of an appropriate depth can be easily formed in the multilayer film. As the support member, a material having a strength that does not break even when the multilayer film is pressed by a member having an uneven shape can be used. Examples of materials for the surface of the support member include rubber and resin.

The shape of the support member can be any shape (e.g., roll shape, flat plate shape) depending on, for example, the method of transporting the multilayer film and the method of pressing the member having an uneven shape against the multilayer film. Since cracks can be continuously formed in the multilayer film by using a long multilayer film, the support member is preferably in a roll shape.

Below, we will explain an example of a member with a concave-convex shape and the process (1) using the member.

Figure 6 is a perspective view showing an example of a member having a concave-convex shape that can be used in the powder manufacturing method of this embodiment. Figure 7 is a perspective view showing the member having the concave-convex shape shown in Figure 6. Figure 8 is a plan view showing the member of Figure 7 cut along line X1-X1 and developed. Figure 9 is a partial cross-sectional view taken along line Y1-Y1 in Figure 8. Figure 10 is a perspective view showing an example of a member having a concave-convex shape that can be used in the powder manufacturing method of this embodiment. Figure 11 is a perspective view showing the member having the concave-convex shape shown in Figure 10. Figure 12 is a plan view showing the member of Figure 11 cut along line X2-X2 and developed. Figure 13 is a partial cross-sectional view taken along line Y2-Y2 in Figure 12.

6, the member 1110 having a concave-convex shape is arranged so as to contact the surface of the multilayer film 10 on the thin film 11 side, and presses the multilayer film 10. Also, as shown in FIG. 10, the member 1115 having a concave-convex shape is arranged so as to contact the surface of the multilayer film 10 on the thin film 11 side, and presses the multilayer film 10. The order of pressing the multilayer film 10 by the member 1110 having a concave-convex shape and pressing the multilayer film 10 by the member 1115 having a concave-convex shape is not particularly limited. For example, the multilayer film 10 may be pressed by the member 1110 having a concave-convex shape and then pressed by the member 1115 having a concave-convex shape, or the multilayer film 10 may be pressed by the member 1115 having a concave-convex shape and then pressed by the member 1110 having a concave-convex shape.

The outer surface (surface that comes into contact with the multilayer film 10) of the member 1110 having an uneven shape is provided with unevenness as shown in FIG. 6. The outer surface of the member 1115 having an uneven shape is also provided with unevenness as shown in FIG. 10. The members 1110 and 1115 having an uneven shape are cylindrical as shown in FIG. 6 and FIG. 10, and can rotate on the multilayer film 10.

The support member 1120 disposed on the surface of the multilayer film 10 facing the base layer 12 is a member that sandwiches and presses the multilayer film 10 together with the member 1110 having an uneven shape.
The support member 1125 arranged on the surface of the multilayer film 10 on the side of the base layer 12 is a member that, together with the member 1115 having an uneven shape, sandwiches and presses the multilayer film 10. The support members 1120 and 1125 are each cylindrical, and can rotate and move on the lower side of the multilayer film 10.

Among the surfaces of the multilayer film 10, the surface (top surface in the figure) that comes into contact with the members 1110 and 1115 having an uneven shape is the surface on which the thin film 11 is formed. When the multilayer film 10 is sandwiched between the member 1110 having an uneven shape and the support member 1120, the convex portion 1110T of the member 1110 having an uneven shape comes into contact with the thin film 11. By pressing the multilayer film 10 while it is sandwiched between the member 1110 having an uneven shape and the support member 1120, the convex portion 1110T of the member 1110 having an uneven shape penetrates into the thin film 11 and the base layer 12, and the notch 100C1 that constitutes the crack 100C is formed. Furthermore, when the multilayer film 10 is sandwiched between the member 1115 having an uneven shape and the support member 1125, the convex portion 1115T of the member 1115 having an uneven shape comes into contact with the thin film 11. By pressing the multilayer film 10 between the member 1115 having a concave-convex shape and the support member 1125, the convex portion 1115T of the member 1115 having a concave-convex shape penetrates into the thin film 11 and the base layer 12, forming the indentation 100C2 that constitutes the crack 100C. In this way, the multilayer film 10 with the crack 100C formed therein is obtained (see Figures 2 and 3).

The outer surface of the member 1110 having a concave-convex shape is formed with a concave-convex shape. As shown in FIG. 8, the concave-convex shape is a shape in which convex portions 1110T and concave portions 1110D extending in a direction inclined by an angle θx with respect to the direction indicated by L1 are alternately and repeatedly formed in a direction perpendicular to the formation direction of the convex portions 1110T. θx is not particularly limited and can be, for example, 45°. As shown in FIG. 8, the concave-convex shape of the member 1110 having a concave-convex shape is a shape of straight lines slanting downward to the right when viewed from above the paper. The distance between two adjacent convex portions 1110T (the distance Q1 between the convex portions 1110T1 and 1110T2 shown in FIG. 9) can be set appropriately. In FIG. 7 and FIG. 8, the ends 1111 and 1112 are the ends of the member 1110 having a concave-convex shape.

As shown in FIG. 9, the convex portion 1110T may have a mountain shape with an acute apex 1110t in cross section. In FIG. 9, θ11 is the angle of the apex of the convex portion. Although it is preferable that θ11 is small, it may be, for example, 10° or more, 20° or more, or 30° or more, and may be, for example, 90° or less, 80° or less, 70° or less, or 60° or less. The apex shape of the convex portion 1110T may be rounded or chamfered as long as it is possible to form cracks in the thin film and the base layer.

The outer surface of the member 1115 having a concave-convex shape is formed with a concave-convex shape. As shown in FIG. 12, the concave-convex shape is a shape in which convex portions 1115T and concave portions 1115D extending in a direction inclined by an angle θy with respect to the direction indicated by L2 are alternately and repeatedly formed in a direction perpendicular to the formation direction of the convex portions 1115T. θy is not particularly limited and can be, for example, 45°. As shown in FIG. 12, the concave-convex shape of the member 1115 having a concave-convex shape is a shape of straight lines sloping upward to the right when viewed from above the paper. The distance between two adjacent convex portions 1115T (the distance Q2 between the convex portions 1115T1 and 1115T2 shown in FIG. 13) can be set appropriately. In FIG. 11 and FIG. 12, the ends 1116 and 1117 are the ends of the member 1115 having a concave-convex shape.

As shown in Fig. 13, the convex portion 1115T may have a mountain shape having an acute apex 1115t in a cross-sectional view. In Fig. 13, θ12 is the angle of the apex of the convex portion 1115T. Although it is preferable that θ12 is small, it may be, for example, 10° or more, 20° or more, or 30° or more, and may be, for example, 90° or less, 80° or less, 70° or less, or 60° or less. The apex shape of the convex portion 1115T may be a rounded shape or a chamfered shape as long as it is possible to form a crack in the thin film and the base layer.
By carrying out step (1), a crack is formed in the multilayer film (for example, a crack 100C or a crack 200C is formed in the multilayer film 10 as shown in Figs. 3 and 5). The multilayer film with the crack formed therein (for example, the multilayer film 100, 200) is subjected to step (2).

The shape of the crack reflects the shape of the convex portion of the member having the uneven shape. For example, when a member 1110 having an uneven shape with the unfolded shape shown in FIG. 8 is arranged so that the L1 direction in FIG. 8 is parallel to the longitudinal direction of the multilayer film and pressed, a notch can be formed in a diagonal direction to the longitudinal direction of the multilayer film 10. Next, when a member 1115 having an uneven shape with the unfolded shape shown in FIG. 12 is arranged so that the L2 direction in FIG. 12 is parallel to the longitudinal direction of the multilayer film and pressed, a lattice-shaped crack 100C as shown in FIG. 2 can be formed. In FIG. 2, the linear notch 100C1 slanting downward to the right reflects the shape of the convex portion of the member 1110 having the uneven shape, and the linear notch 100C2 slanting upward to the right reflects the shape of the convex portion of the member 1115 having the uneven shape.

[3. Step (2)]
In step (2), the thin film flakes are peeled off from the substrate layer of the multilayer film in which cracks have been formed, to obtain a powder containing the thin film flakes.

The method for peeling off the thin film fragments from the base layer is not particularly limited, and examples thereof include: (1) a method of sliding a cracked multilayer film on a blade to peel off the fragments; (2) a method of spraying a fluid such as water or air onto a cracked multilayer film to peel off the fragments; (3) a method of immersing a cracked multilayer film in a solvent (e.g., water) that does not easily dissolve a thin film (e.g., a cholesteric resin layer) but dissolves the base layer or a layer present between the thin film and the base layer (e.g., an orientation film formed of polyvinyl alcohol) to peel off the thin film fragments from the base layer; (4) a method of bonding the thin film side of a cracked multilayer film to a transfer base film using a water-soluble adhesive, and then peeling off the base layer from the multilayer film to peel off the thin film fragments from the base layer; and combinations thereof.
In the above method (4), a laminate having a layer structure of (substrate film for transfer)/(layer of water-soluble adhesive)/(thin film with cracks formed therein) is usually obtained. By removing the layer of water-soluble adhesive from the laminate by immersing the laminate in water at an appropriate temperature, a powder containing small pieces of the thin film can be obtained.

If the multilayer film in which cracks have formed is long, the above peeling process can be carried out continuously to efficiently produce powder.

For example, step (2) may include step (2a) of spraying a fluid onto the cracked multilayer film.
In step (2a), the fluid is sprayed onto the cracked side (i.e., the thin film side) of the multilayer film in which the crack is formed. A known fluid ejection device can be used as the spraying device. The pressure of the fluid ejected from the fluid ejection device can be appropriately adjusted according to the density of the fluid, the peel strength between the base layer and the thin film, etc. The ejection pressure is not particularly limited, but is preferably 5 MPa or more, more preferably 10 MPa or more, and is preferably 50 MPa or less, more preferably 35 MPa or less.

Step (2) may include a step (2b) of passing the thin film pieces through a sieve after peeling the thin film pieces.
For example, after the step (2a) of spraying a fluid onto the multilayer film in which cracks have been formed, the small pieces peeled off from the base layer may be passed through a filter having a predetermined mesh size.
Step (2) may also include a step (2c) of recovering the thin film pieces after peeling them off.
For example, after the step (2a) of spraying a fluid onto the multilayer film in which cracks have been formed, the small pieces peeled off from the base layer may be guided together with the fluid into a recovery passage, and the small pieces may be recovered by a recovery device to obtain a powder that is an aggregate of the small pieces. As the recovery device, for example, a cyclone-type separator and various filters may be used.

4. Powder Characteristics
The powder obtained by the manufacturing method of this embodiment has a high proportion of thin film flakes having a uniform shape along the cracks. The proportion can be evaluated, for example, by the following method.
The powder is dispersed in water at 10% by weight. The aqueous dispersion is dropped onto a preparation, and the water is evaporated to allow the powder (thin film flakes) to adhere to the preparation. The portion of the preparation to which the thin film flakes are adhered is observed under a microscope. Within a 1 mm square area, the number (A) of thin film flakes of a fixed shape and the number (B) of thin film flakes of an irregular shape are counted, and the percentage X of the number (B) to the number (A) is calculated according to the following formula: X = B/A x 100 (%)
The smaller the percentage X, the higher the proportion of thin film flakes that have a consistent shape along the crack.

The powder has a percentage X of preferably 5% or less, more preferably 4% or less, even more preferably 3% or less, and preferably 0%, but may be 0% or more or 1% or more.

[5. Uses of Powder]
The powder produced by the production method of this embodiment has a high proportion of thin film flakes with a fixed shape along the cracks. Therefore, it is possible to obtain a printed matter with a good texture by using an ink containing the powder. In addition, it is possible to easily determine the authenticity of a printed matter using an ink containing the powder. Therefore, the powder can be suitably used as an ink material.

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and may be modified as desired without departing from the scope of the claims of the present invention and the scope of equivalents thereto.

In the following explanation, the percentages and parts are by weight unless otherwise specified. Furthermore, the operations described below were carried out at room temperature and pressure unless otherwise specified.

[evaluation]
(Evaluation of crack condition)
The cross section of the multilayer film of each example in which a crack was introduced was observed with a scanning electron microscope to evaluate whether the crack reached a position deeper than the surface of the base layer of the multilayer film. The observation was performed on a cross section of an arbitrary position of the multilayer film with a length of 500 μm in the plane direction. When the crack reached a position deeper than the surface of the base layer of the multilayer film in the observation range, it was deemed that the crack reached a position deeper than the surface of the base layer of the multilayer film over the entire surface of the multilayer film. When some cracks did not reach a position deeper than the surface of the base layer of the multilayer film in the observation range, or when all cracks did not reach a position deeper than the surface of the base layer of the multilayer film, it was deemed that the crack did not reach a position deeper than the surface of the base layer of the multilayer film.

(Evaluation of shape consistency of powder (thin film piece))
The powder (thin film flakes) obtained in each example was made into a 10 wt% aqueous dispersion. The aqueous dispersion was then dropped onto a preparation, and the water was evaporated to allow the thin film flakes to adhere to the preparation. The portion of the preparation to which the thin film flakes had adhered was observed under an optical microscope. Within a 1 mm square area, the number (A) of regular thin film flakes and the number (B) of irregular thin film flakes corresponding to the irregularities of the member having an irregular shape in each example were counted, and the percentage X of the number (B) to the number (A) was calculated according to the following formula: X=B/A×100(%)
The smaller the percentage X, the higher the proportion of thin film flakes that have a consistent shape along the crack, i.e., the higher the conformity.
The shape consistency of the thin film pieces was evaluated according to the following criteria.
"Good": X≦5%
"Defective": 5% < X or A = 0

[Example 1]
(1-1. Preparation of Photocurable Liquid Crystal Composition)
A photocurable liquid crystal composition was prepared by mixing 18.1 parts of a photopolymerizable liquid crystal compound "Paliocolor LC242" manufactured by BASF, 1.3 parts of "LC756" manufactured by BASF as a chiral agent, 0.6 parts of "Irgacure OXEO2" manufactured by Ciba Japan as a photopolymerization initiator, 0.02 parts of "Ftergent 209F" manufactured by Neos as a surfactant, and 80 parts of cyclopentanone.

(1-2. Production of long multilayer films)
A long cycloolefin polymer (COP) film (ZF16-100 manufactured by Zeon Corporation; thickness 100 μm) was prepared as the substrate film. This substrate film was attached to the unwinding section of a film transport device, and the following operations were carried out while transporting the substrate film in the longitudinal direction. First, a rubbing treatment was carried out in the longitudinal direction parallel to the transport direction. Next, the liquid crystal composition prepared in (1-1) was applied to the rubbed surface using a die coater. As a result, a film of the liquid crystal composition in an uncured state was formed on one side of the substrate film.

The obtained liquid crystal composition film was subjected to an alignment treatment at 100° C. for 5 minutes, and then the liquid crystal composition film was irradiated with 800 mJ/cm ² ultraviolet light under a nitrogen atmosphere to completely harden the liquid crystal composition film. This resulted in a multilayer film having a 3.5 μm thick resin thin film on one side of a long substrate film. The multilayer film had a layer structure of (substrate film as substrate layer)/(resin thin film). The resin thin film had the function of a cholesteric resin layer.

(1-3. Manufacturing of a member (roll) having a concave-convex shape)
A metal roll made of stainless steel and having a surface that was electroless nickel plated (NiP plated) was prepared. The plated surface of the roll was cut with a diamond tool (vertex angle 60°) to obtain roll A and roll B having a plurality of protrusions.
In roll A, the multiple protrusions were formed so that the protrusions extended in a direction that formed an angle of 45° upward to the right with respect to a straight line on the circumferential surface of the roll that was parallel to the roll axis, so that the pitch of the protrusions was 50 μm, and so that the angle of the apexes of the protrusions was 60° in a cross section perpendicular to the direction in which the protrusions extended.
In roll B, a plurality of protrusions were formed so that the protrusions extended in a direction that formed an angle of 45° upward to the left with respect to a straight line on the circumferential surface of the roll that was parallel to the roll axis, the pitch of the protrusions was 50 μm, and further the angle of the apexes of the protrusions was 60° in a cross section perpendicular to the direction in which the protrusions extended.

(1-4. Step (1): Crack Formation Step)
The roll A produced in (1-3) was pressed (press pressure 10 MPa) from the resin thin film side of the multilayer film produced in (1-2), and then the roll B was pressed (press pressure 10 MPa) to form cracks in the multilayer film. At that time, the side opposite to the resin thin film of the multilayer film (substrate film side, backup roll side) was supported by a backup roll. The backup roll used was a roll with a surface hardness of D70. Here, the hardness is a value measured by a durometer (type D) according to JIS K-6253. The same applies below. As a result, the resin thin film of the multilayer film was divided into square pieces (long diameter 70 μm) with one side of 50 μm when viewed from the thickness direction of the resin thin film.

The state of cracks in the multilayer film after it was pressed against rolls A and B was evaluated using the method described above. As a result, it was found that cracks had formed on the entire surface of the multilayer film, extending to a position deeper than the surface of the base film that the multilayer film has.

(1-5. Step (2): Powder manufacturing step)
Next, water was sprayed onto the cracked multilayer film from the resin thin film side at a discharge pressure of 60 MPa to peel off small pieces of the resin thin film from the base film.

Next, the peeled pieces of the thin resin film were passed through a sieve with a nominal mesh size of 53 μm, and the pieces that fell through the sieve were collected using a filter collector (all-polypropylene filter manufactured by 3M) to obtain a powder containing small pieces of the thin resin film. The shape consistency of the obtained powder was evaluated using the method described above. The results are shown in the table below.

[Example 2]
(2-1 to 2-2)
A long triacetyl cellulose film (Konica Minolta's "KC6UY"; thickness 60 μm) was used as the base film. Except for the above, a multilayer film was produced in the same manner as in (1-1) to (1-2) of Example 1.

(2-3. Manufacturing of a member (roll) having a concave-convex shape)
A metal roll similar to that in (1-3) of Example 1 was prepared, and the plated surface of the roll was cut with a diamond turning tool (vertex angle 60°) to obtain a roll C having a plurality of protrusions.
In roll C, multiple protrusions were formed so that the protrusions extended in a direction that formed an angle of 45° upward to the left with respect to a straight line on the roll circumferential surface that was parallel to the roll axis, and the pitch of the protrusions was 100 μm.

(2-4. Step (1): Crack Formation Step)
Instead of roll B, roll C was used.
The pressing pressure of roll A and roll C was each set to 8 MPa.
A roll with a surface hardness of D90 was used as the backup roll.
Except for the above, the same operation as in (1-4) of Example 1 was carried out to form cracks in the multilayer film. As a result, the resin thin film of the multilayer film was divided into rectangular pieces (long diameter 112 μm) measuring 50 μm × 100 μm when viewed from the thickness direction of the resin thin film.

The state of cracks in the multilayer film after it was pressed against rolls A and C was evaluated using the method described above. As a result, it was found that cracks had formed on the entire surface of the multilayer film, extending to a position deeper than the surface of the base film that the multilayer film has.

(2-5. Step (2): Powder manufacturing step)
The mesh size of the sieve through which the peeled resin thin film pieces were passed was changed from a nominal mesh size of 53 μm to a nominal mesh size of 106 μm. Except for the above, a powder was obtained in the same manner as in (1-5) of Example 1, and the obtained powder was evaluated. The results are shown in the table below.

[Example 3]
(3-1 to 3-2)
As the multilayer film, a polyethylene terephthalate (PET) film ("VMPET1519" manufactured by Toray Advanced Film Co., Ltd.) on which aluminum was vapor-deposited to a thickness of 12 μm was prepared. The multilayer film had a layer structure of (aluminum film as thin film)/(PET film as base layer).

(3-3. Manufacturing of a member (roll) having a concave-convex shape)
A metal roll was prepared similar to that in (1-3) of Example 1. Depressions were formed on the plated surface of the roll by an ultrashort pulse laser (dimple processing), to obtain Roll D.
Roll D has continuous hexagonal protrusions with a major axis of 50 μm and a side of 25 μm.

(3-4. Step (1): Crack Formation Step)
Instead of roll A, roll D was used.
- The multilayer film was not pressed by roll B.
The pressing pressure of roll D was set to 12 MPa.
A roll with a surface hardness of D88 was used as the backup roll.
Except for the above, the same procedure as in (1-4) of Example 1 was followed to form cracks in the multilayer film, thereby dividing the aluminum film of the multilayer film into small hexagonal pieces with a major axis of 50 μm and a side length of 25 μm when viewed in the thickness direction of the film.

The state of cracks in the multilayer film after it was pressed against Roll D was evaluated using the method described above. As a result, it was found that cracks had formed on the entire surface of the multilayer film, extending deeper than the surface of the base film that the multilayer film had.

(3-5. Step (2): Powder manufacturing step)
A powder was obtained and evaluated in the same manner as in (1-5) of Example 1. The results are shown in the table below.

[Comparative Example 1]
The backup roll was changed to a roll made of stainless steel covered with silicone rubber having a hardness of D20.
The pressing pressure of roll A and roll B was set to 70 MPa.
Except for the above, the same procedure as in Example 1 was carried out to obtain a powder, and the obtained powder was evaluated. The results are shown in the table below.
The state of cracks in the multilayer film after being pressed by roll A and roll B was evaluated by the above-mentioned method. As a result, in the observation range, there were no cracks that reached a position deeper than the surface of the base film of the multilayer film.

In the table below, the abbreviations have the following meanings.
"Cholesteric resin layer": A layer of a cured liquid crystal composition "Al film": A deposited aluminum film "COP": Cycloolefin polymer film "TAC": Triacetyl cellulose film "PET": Polyethylene terephthalate film

From the above results, the manufacturing method of Comparative Example 1, which does not form cracks that reach deeper than the surface of the thin film side of the base layer, results in poor shape conformity of the resulting powder. On the other hand, the manufacturing method of the Example, which forms cracks that reach deeper than the surface of the thin film side of the base layer, results in good shape conformity of the resulting powder.
The above results show that the powder production method of the present invention makes it possible to produce powder containing a high proportion of thin flakes having the desired shape.

10 Multilayer film 11 Thin film 12 Base layer 100 Multilayer film 100C Crack 100C1 Indentation 100C2 Indentation 100Cd Depth 100Ct Tip 101 Small piece 110 Thin film 110T Thickness 110U Surface 120 Base layer 120U Surface 200 Multilayer film 200C Crack 200Ct Tip 201 Small piece 210 Thin film 220 Base layer 220U Surface 1110 Member having uneven shape 1110T Convex portion 1110T1 Convex portion 1110T2 Convex portion 1110t Apex 1110D Concave portion 1111 End portion 1112 End portion 1115 Member having uneven shape 1115T Convex portion 1115T1 convex portion 1115T2 convex portion 1115t apex 1115D concave portion 1116 end portion 1117 end portion 1120 support member 1125 support member

Claims (7)

A step (1) of forming a crack in a multilayer film including a base layer and a thin film disposed on the outermost side, the crack dividing the thin film into small pieces of the same shape as viewed in the thickness direction of the thin film, the crack reaching a position deeper than the surface of the base layer on the thin film side;
and (2) peeling off the thin film fragments from the base layer of the multilayer film in which the cracks are formed to obtain a powder containing the thin film fragments,
The step (2) includes a step (2a) of spraying a fluid onto the multilayer film in which the cracks have been formed from the thin film side,
The method for producing powder, wherein the thin film is a cholesteric resin layer obtained by curing a photocurable liquid crystal composition. The method for producing powder according to claim 1, wherein the major axis of the small particles is 150 μm or less. The method for producing powder according to claim 1 or 2, wherein in step (1), a member having an uneven shape is pressed against the thin film side of the multilayer film to form the cracks. The method for producing powder according to claim 3, wherein the pressing is performed while the multilayer film is supported by a support member having a surface hardness of D40 or more. The method for producing powder according to claim 4, wherein the pressure applied to the member having the uneven shape is 0.5 MPa or more. The method for producing powder according to any one of claims 1 to 5, wherein the thickness of the base layer is 12 μm or more and 250 μm or less. The method for producing powder according to any one of claims 1 to 6, wherein in step (1), the cracks are formed so that the shape of the small pieces is a triangle, a rectangle, or a hexagon when viewed in the thickness direction of the thin film.

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