WO2002072368A2

WO2002072368A2 - Graphics-displaying sheet

Info

Publication number: WO2002072368A2
Application number: PCT/US2002/005550
Authority: WO
Inventors: Yasuyuki Takeda
Original assignee: 3M Innovative Properties Company
Priority date: 2001-03-08
Filing date: 2002-02-20
Publication date: 2002-09-19
Also published as: JP2002278490A; AU2002244136A1; WO2002072368A3

Abstract

A graphics-displaying sheet that uses a glittering prismatic sheet, can easily form a fine and clear graphics even with ink jet printing using aqueous inks, and significantly improves the water-resistance of the printed graphics. A graphics-displaying sheet comprising a glittering prismatic sheet which is a light-transmitting prismatic sheet and includes triangular pyramid-shaped prisms arranged on the sheet surface such that they glitter when light is incident thereon, and a graphics which contains a coloring material and to which the light glittering property is imparted with the function of the prismatic sheet.

Description

GRAPHICS-DISPLAYING SHEET

Field of the Invention

The present invention relates to a graphics-displaying sheet comprising a glittering prismatic sheet with light transmission, a coloring material-receptive layer adhered to the back surface of the glittering prismatic sheet, and a support adhered to the coloring material-receptive layer, in which a coloring material (e.g. a printing ink or a toner) received on the coloring material-receptive layer forms graphics.

With the graphics-displaying sheet of the present invention, the graphics can be seen through the glittering prismatic sheet, and the graphics having the glittering properties (glittering graphics) can be displayed. Such a graphics-displaying sheet can be used as a part of a signboard, a sign and the like, which displays advertisements, information, etc. outdoors.

Background of the Invention

Hitherto, graphics having a metallic appearance imparted with a metallic material are known as graphics having a glittering appearance formed with coloring materials such as printing inks.

For example, JP-A-2000-52639 discloses an ink jet-recording medium comprising a transparent or translucent substrate film, a metal deposition layer formed on the back surface of the substrate film and an ink-receptive layer formed on the surface of the substrate film. The surface of the ink-receptive layer of this recording medium is printed with ink jet printing to allow the inks received on the surface of the receptive layer to form the graphics comprising the received inks. Usually, the ink-receptive layer comprises a water-soluble or water-absorptive resin such as polyvinyl alcohol, ethylcellulose, methylcellulose, carboxymethylcellulose, polyethylene glycol, polyethyleneoxide, polyacrylate, maleic acid resin, etc., or their mixtures. Since the ink-receptive layer has relatively high transparency, an observer can see both the reflected light on the metal deposition layer and that on the printed graphics. Thus, the metallic graphics can be formed on the metallic background.

JP-A-8-207424 discloses an ink jet-recording medium comprising a printing ink- receptive layer containing an adhesive and a metal deposition film which is cut and divided in fragments. The adhesive functions as a binder which disperse and binds the divided metal deposition film. The metal deposition film is prepared by depositing a metal such as aluminum on the surface of a paper sheet or a polymer film. The surface of the ink-receptive layer of this recording medium is printed with ink jet printing so that the ink is received on the surface of the ink receptive layer to form the graphics comprising the received ink. In general, the printing inks have high transparency. Thus, such a recording medium can form the metallic graphics on the metallic background.

JP-A-2000- 17208 discloses that an ink jetting ink itself contains a glittering powder comprising irregular form flat particles of a metal deposition film. Also, this patent publication discloses an ink comprising microcapsules including the glittering metallic powder, which are dispersed in a medium.

When the metallic materials are used as the recording media, it is difficult to increase the glittering of the graphics while maintaining the color tones of the graphics and the background. For example, in the case of the use of a metal with a silver gloss, when the glittering of the graphics is increased, the graphics as a whole tends to become grayish.

In particular, at parts where white or pale colored inks are concentrated, the clearness (resolution) tends to decrease, and such graphics represents a peculiar appearance. Although the graphics having such an appearance may be preferred in a relatively large number of applications, such recording media are not suitable for applications which require bright color tones. When the above-described glittering inks are used, the glittering of the graphics can be increased. However, the color tone of the graphics themselves is modulated more or less. Thus, such inks are not suitable when the bright color tone is required.

The applicant proposed the use of a glittering prismatic sheet for the production of glittering graphics. Such a glittering prismatic sheet is disclosed in the earlier patent applications of the applicant, for example, U.S. Patent Nos. 5,948,488, 5,763,049, 5,814,355 and 5,840,405, etc.

The glittering prismatic sheet means a prismatic sheet having an array of triangular pyramid-shaped prisms provided on its surface so that the prisms glitter when light is incident on the prismatic surface. The glittering of the sheet is achieved by the presence of discrete glittering points which blink on and off in accordance with the change of an observation angle or the incident angle of the light. When the sheet is seen brightly with glittering, about 10 to 50 glittering points are observed per one square centimeter, while the points other than the glittering points are not seen with glittering. As shown in Fig. 1, such a glittering prismatic sheet is defined with three sets of intersecting parallel grooves A, B and C (11, 12, 13), and has an array of cube-corners as the triangular pyramid-shaped prisms (14) provided on the surface of the sheet. The prisms are arranged such that each prism is connected with the adjacent prism at one side of the bottom triangle through the groove. In one of the three sets of grooves, an angle formed by the side faces (21) of a pair the adjacent prisms (that is, a dihedral angle ; see Fig. 2) preferably differs between an angle formed by a pair of the prisms which are adjacent each other through one groove and other angle formed by other pair of the prisms which are adjacent each other through other groove in the same set. In addition, the prisms may be arranged such that the base planes (25) of the prisms are not parallel with each other, when the glittering prism sheet is laid flat. Preferably, the dihedral angles α are vary in essentially all the grooves such that the optical axes of the light beams which pass through the apexes (22) of the triangular pyramid-shaped prisms are randomly tilted throughout the array of the prisms as shown in Fig. 2. Here, Fig. 2 shows a vertical cross sectional view of the prismatic sheet of Fig. 1 along the line X-X'.

Such a glittering prismatic sheet well glitters under the observable conditions in the daylight. Such a glittering function can increase the visibility of the sheet and highlights the presence of the article having the sheet.

To form the glittering graphics using the above-described glittering prismatic sheet, usually, the method disclosed in JP-A-2000-509164 is employed. In this method, a non-glittering prismatic sheet having an array of triangular pyramid-shaped prisms which are regularly arranged to have the non-glittering properties is provided, and then a heat- transfer toner is printed on the prismatic surface by transferring while the non-glittering prisms are being deformed by heating under pressure so that the prismatic sheet can exhibit the glittering properties. In general, the body part on which the pyramid-shaped prisms are arranged, the prisms, or both the body parts and the prisms are made opaque by the addition of fillers, opaque colorants, flakes, etc.

When the glittering prismatic sheet is effectively used, the glittering of the graphics can be easily improved while maintaining the color tones of the graphics and also the background.

Summary of the Invention

When the graphic is formed on the prismatic surface of the glittering prismatic sheet as described above, it is difficult for the ink jet-printing to form a fine and clear graphics. In particular, the use of aqueous inks is very difficult, since a thermoplastic polymer, which is contained in the prisms of the glittering prismatic sheet so that they are easily heated, pressed and processed, has low hydrophilicity and thus low aqueous ink- fixing properties. When the graphic is printed on the outermost layer of the sheet, the durability, in particular, water-resistance of the printed graphics cannot be improved. Therefore, the glittering prismatic sheet having the graphics printed on the prismatic surface as such cannot be used as a graphics-displaying sheet to be used outdoors. Therefore, one object of the present invention is to provide an improved graphics- displaying sheet which comprises a glittering prismatic sheet and can easily increase the glittering of the graphics while maintaining the color tones of the graphics and the background. In particular, the object of the present invention is to provide a graphics- displaying sheet which effectively uses a glittering prismatic sheet, can easily form the fine and clear graphics even with ink jet printing using aqueous inks, and significantly improves the water-resistance of the printed graphics.

To solve the above problems, the present invention provides a graphics-displaying sheet comprising:

(a) a glittering prismatic sheet which is a light-transmitting prismatic sheet having a surface and a back surface and includes an array of triangular pyramid-shaped prisms on said surface, said prisms being arranged such that they glitter property when light is incident thereon, and

(b) a graphics which contains a coloring material and to which the light glittering property is imparted with the function of said prismatic sheet, wherein said displaying sheet further comprises

(c) a coloring material-receptive layer having a surface and a back surface, the surface of which is adhered to the back surface of said prismatic sheet, and

(d) a support having a surface and a back surface, the surface of which is adhered to said coloring material-receptive layer, characterized in that said prismatic sheet and said coloring material-receptive layer are closely adhered through a light-transmitting adhesive layer, said coloring material received on said coloring material-receptive layer forms said graphics, and said graphics can be seen through said prismatic sheet.

Brief Description of the Drawings Fig. 1 is a plan view of one example of the prismatic sheet used in the present invention.

Fig. 2 is a cross section of the prismatic sheet of Fig. 1 along the line X-X'. Fig. 3 is a schematic cross section of one examples of the graphics-displaying sheet of the present invention.

Detailed Description of the Invention

In the graphics-displaying sheet of the present invention, the glittering prismatic sheet is adhered to the surface of the coloring material-receptive layer. The coloring material-receptive layer contains printing inks or toners, which are received by the receptive layer as the coloring materials, and the inks or toners received form the graphics.

Thus, the graphics can be seen through the prismatic sheet. Accordingly, the glittering of the graphics can be very easily increased while maintaining the color tones of the graphics and the background. Furthermore, the attractive graphics with good decorativeness can be formed with the conventional printing methods. The prismatic sheet and the coloring material-receptive layer are adhered each other through the light-transmitting adhesive layer. Thus, the graphics can be observed in good conditions through the prismatic sheet. When the sheet is seen with glittering, a plurality of glittering points are seen, while the graphics provided on the back surface of the prismatic sheet can be seen through the prismatic sheet in the areas of the sheet other than the glittering points. If the prismatic sheet and the coloring material-receptive sheet are not closely adhered, gaps, that is, an air layer or bubbles may be present at the interface between them. The air layer at the interface reflects light which is incident on the prismatic surface of the prismatic sheet and reaches the interface of the air layer so that the amount of light reaching the coloring material-receptive sheet decreases. Thus, the definition of the graphics observed through the prismatic sheet decreases and therefore the visibility of the graphics deteriorates. Furthermore, the bubbles are observed as glittering points on the graphics in the areas where the graphics should be observed in the absence of the bubbles, and recognized like the defects of the image. Therefore, the adhesion between the prismatic sheet and the coloring magerial-receptive layer should be improved so that neither the air layer nor the bubbles are present between them. The adhesion between them can be improved with the use of a light-transmitting adhesive layer. The coloring material-receptive layer is closely adhered to the support in addition to the prismatic sheet. The support is necessary to protect the back surface of the coloring material-receptive layer. Also, the prismatic sheet may function to protect the surface of the coloring material-receptive layer. When these three layers, that is, the prismatic sheet, the coloring material-receptive layer and the support are closely adhered each other, it is possible to prevent the penetration of water in the form of vapor in the coloring material- receptive layer though the interfaces between the layers, and thus the water resistance of the printed graphics can be effectively improved.

Accordingly, the present invention can provide a graphics-displaying sheet particularly suitable for the applications wherein the bright color tone is required, and the sheet is used outdoors.

In one preferred embodiment of the present invention, there is provided the graphics-displaying sheet having the structure of Fig. 3. In the graphics-displaying sheet of Fig. 3, the parts below the prismatic sheet usually consist of the printing medium having the support (31), the primer layer (31) which is fixedly provided on the surface of the support and the coloring material-receptive layer (33) (hereinafter sometimes referred to as

"receptive layer") which is fixedly provided on the surface of the primer layer, and the graphics (34) formed with the printing inks or toners received on the receptive layer of the printing medium. The prismatic sheet part consists of the glittering prismatic sheet (36) having the triangular pyramid-shaped prisms which are aπanged to glitter (hereinafter sometimes referred to as "prismatic sheet") and the transparent adhesive layer (35) which is fixedly provided on the back surface of the prismatic sheet. The graphic is formed by applying a printing means on the surface of the receptive layer so that the coloring materials (printing inks or toners) are received by the receptive layer. After the formation of the graphics, the prismatic sheet is fixed to the surface of the receptive layer using the adhesive layer to complete the graphics-displaying sheet shown in Fig. 3. The adhesive layer is usually a layer comprising a self-adherent polymer, which will be explained in detail below.

In the embodiment of Fig. 3, the prismatic sheet (36) and the coloring material- receptive layer (33) carrying the graphics (34) are adhered through the adhesive layer (35), and the coloring material-receptive layer (33) and the support (31) are adhered through the primer layer (32). Therefore, the graphic-displaying sheet can advantageously improve the above-described effects (e.g. visibility, water-resistance, etc.).

An additional adhesive layer (not shown) may be formed on the back surface of the support (31 ) to fix the graphic-displaying sheet to the surface of a material.

In another preferred embodiment, the receptive layer is fixed to the back surface of the prismatic layer through the adhesive layer, and then the graphic is formed on the back surface of the receptive layer with the printing means. In this case, the coloring materials are retained on the back surface or the printed areas of the receptive layer, and the graphics must be seen in some cases through the receptive layer from the surface side of the receptive layer (which is adhered to the prismatic layer). In such a case, the transparency of the receptive layer should be made high. For example, the receptive layer contains no inorganic fine powder, which is added to impart the ink-absorbability, or contains such fine powder in an amount such that the transparency of the receptive layer is not impaired. The details of such fine powder will be explained in detail below. In the above embodiment, the adhesive layer may contain a priming polymer so that it functions also as a primer layer for the receptive layer. For example, when the receptive layer is made of a coating film of a paint containing an ink-fixing polymer which will be explained below, the primer layer is fixed to the back surface of the prismatic sheet and then the paint is applied to form the receptive layer. After the formation of the graphics, the support is adhered to the back surface of the receptive layer to complete the graphics-displaying sheet. To adhere the receptive layer and the support, preferably the adhesive layer containing a self-adherent polymer is interposed between them.

When both the support and the receptive layer have high transparency and the light is incident on the sheet from the back surface side of the support, light which passes through the graphics (the inks or toners) is retroreflected on the glittering prismatic sheet and observed together with the light reflected on the graphics. In such a case, the graphics having the retroreflectivity in addition to the glittering properties can be obtained.

The graphic is formed using conventional printing inks or toners by a conventional method such as electrostatic printing, silk-screen printing, gravure printing, offset printing, ink jet printing, etc.

The coloring material-receptive layer comprises a polymer which can fix the printing inks or toners (fixing polymer). As the fixing polymers, those used in the field of printing media may be used. Preferably, ionically modified polymers, which will be explained below, and thermoplastic resins are used.

For example, when the graphic is formed with the ink jet printing using the aqueous inks, the ionically modified polymer is preferably used as the fixing polymer. The ionically modified polymer is particularly suitable for the increase of the water resistance of the graphics printed with the aqueous inks. When the displaying sheet having the graphics printed with the aqueous inks according to the present invention is used outdoors for a long time, its edges are preferably sealed. For example, the edge sealing is carried out by adhering an adhesive tape with bridging the peripheral edges of the sheet and the surface of the material after fixing the displaying sheet on the material. In the case of the displaying sheet of the present invention, the prisms present on the surface of the sheet form a roughened surface with the size such that the adhesion of the adhesive tape is difficult. When the adhesive tape cannot be closely adhered, gaps are left between the adhesive tape and the sheet edges and thus the displaying sheet cannot be sufficiently sealed for the protection of the graphics. In the case of the sealing with a resin coating film, the grooves between the prisms are buried with the resin so that the glittering is lost at the sealed parts and the appearance becomes less attractive. The water resistance of the aqueous ink-printed graphics can be effectively improved when the prismatic sheet and the support are used as the protective layers and they are both closely adhered to the receptive layer. However, when the receptive layer has low hydrophilicity and thus low ink-fixing properties, the graphic-displaying sheet cannot be used outdoors for a long time in the absence of edge seals. The receptive layer containing the ionically modified polymer can increase the water-resistance of the graphics with avoiding the use of such edge seals.

When the ionically modified polymer is used, it is not necessary for the receptive layer (ink-receptive layer) to contain inorganic fine powder such as inorganic oxides, which are usually required to impart the ink- absorbability to the receptive layer. When the receptive layer may have low transparency, or when the receptive layer is colored white or other color to form the background for the graphics, it may contain the inorganic oxide in a suitable amount.

The ionically modified polymer may be a cationically modified polyurethane, a cationically modified polyester, etc. The receptive layer containing the ionically modified polymer is advantageous to increase the water-resistance of the images printed with ink jet printing. Examples of the ionically modified polymer include PATERACOL^® IJ-170 (a paint containing a cationically modified polyurethane and inorganic fine powder) and PATERACOL^® IJ-21 (a paint containing a cationically modified polyurethane and no inorganic fine powder) both available from DAINIPPON INK AND CHEMICALS, INC., and so on. Here, the inorganic fine powder is used to increase the porosity of the receptive layer so that the ink-absorbability increases. When the aqueous inks are used, the receptive layer may contain a water-soluble salt (e.g. a salt of an organic or inorganic acid) as a coagulant. The coagulant quickly coagulates the coloring component such as a pigment on the surface of the receptive layer when the aqueous ink is applied on the printing surface of the receptive layer, and thus improves the quick-drying properties. When the receptive layer contains the coagulant and the ionically modified polymer, the water-resistance of the graphics formed of the ink- image fixed on the printing surface of the receptive layer through the synergistic effect of the coagulation function described above and the binding function of the polymer.

The coagulation function of the water-soluble salt can be effectively increased through the ionization. Thus, the ink to be applied to the receptive layer is preferably an ink containing water, that is, an aqueous ink. The salt being "water-soluble" means that the salt reacts with water and can generate an ionic chemical species. Herein, the solubility of the salt is usually from 0.001 to 100 g in terms of an amount of the salt dissolved in 100 g of water at 20°C.

Preferably, the salt may be a polyvalent metal salt of an organic or inorganic acid, since such a salt has a relatively high coagulation function and a good effect on the increase of the quick-drying property and the water-resistance of the fixed ink-image at the same time. As the ion of the polyvalent metal, one or more of the ions of metals such as aluminum, titanium, zirconium, zinc, magnesium, calcium, iron, copper, tin, cobalt, etc. Preferred examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, etc. Preferred examples of the inorganic salt include aluminum sulfate, etc.

The amount of the coagulant contained in the receptive layer is usually from 1 to 70 wt. parts, preferably from 3 to 50 wt. parts, per 100 wt. parts of the ink-fixing polymer. When the amount of the coagulant is too low, the ink-fixing property decreases so that the water-resistance or color-developing properties may deteriorate. When the amount of the coagulant is too high, the ink-image may smudge.

The receptive layer may optionally contain an inorganic fine powder to increase the porosity of the receptive layer, as descried above. As the inorganic fine powder, calcium carbonate, calcined clay, silica (including amorphous silica), diatomaceous earth, talc, titanium oxide, barium sulfate, and the like may be used. The particle size of the fine powder is usually from 0.3 to 10 μm, preferably from 0.8 to 5 μm.

Furthermore, the receptive layer may contain other additives such as a heat stabilizer, a UN absorber, a dispersant, an antistatic agent, an antioxidant, etc.

The coloring material-receptive layer as the ink-receptive layer is formed, for example, by applying a liquid containing the coagulant and the fixing polymer and drying it. In this case, a medium is preferably water or alcohol. As an application means, a conventional coater such as a bar coater, a knife coater, a roll coater, a die coater, etc. may be used.

When the image is formed by the electrostatic printing method, the toner-receptive layer (the coloring material-receptive layer) preferably contains a thermoplastic resin as a fixing polymer so that the toners can be thermally transfeπed and fixed on the printing surface of the layer. Such a thermoplastic resin is a resin which can be molten at a temperature for thermally transferring and fixing the toners, and may preferably be the same resin as the binder of the toners. As the thermoplastic resin, a vinyl chloride polymer (including a copolymer such as a vinyl chloride-vinyl acetate copolymer), an acrylic polymer, a saturated polyester, etc. are preferably used.

The toner-receptive layer may be formed by applying a paint containing a toner- fixing polymer and drying it. In this case, a medium is preferably water or alcohol. As an application means, a conventional coater such as a bar coater, a knife coater, a roll coater, a die coater, etc. may be used. As described above, when the transparency of the coloring material-receptive layer is increased, the haze (turbidity) of the receptive layer, which is measured with a color meter, is preferably 30 % or less, more preferably 20 % or less. The light transmittance is usually at least 85 %, preferably at least 90 %. Here, the light transmittance is a total light transmittance measured with a spectrophotometer or a color meter which functions also as a photometer at a wavelength of 550 nm.

The thickness of the receptive layer is preferably from 5 to 200 μm, more preferably from 10 to 100 μm. When the receptive layer is too thin, it has the low ink- absorbing ability when the ink is used, and thus the color development of the image may deteriorate. When the receptive layer is too thick, the surface area of the edges becomes too large so that the water resistance may deteriorate.

As described above, the receptive layer is preferably fixed to the surface of the support through the primer layer to increase the adhesion of the receptive layer to the support. A primer layer may be used as the adhesive layer to adhere the prismatic layer and the receptive layer.

The prismatic layer has a surface as a prismatic surface on which an array of the glittering prisms are arranged, and a body part having a back surface to which the receptive layer is adhered, as described in detail below. The body part comprises the sheet part (23) when the prismatic sheet is produced by a method which will be explained in detail below, and the back surface of the sheet part is adhered to the receptive layer.

When the receptive layer is formed by the application of the liquid on the body part, the sheet part (23) or the support, preferably the primer layer is formed on the body part, the sheet part (23) or the support, and then the paint for the receptive layer is applied. In connection with the primer layer, a term "substrate" is used to include the body part, the sheet part and the support of the prismatic sheet.

For example, the primer layer is fixedly provided on the primer-providing surface of the substrate (i.e. the surface of the support, the back surface (24) of the body part, or the back surface of the sheet part), and then the paint for the receptive layer is applied to form the receptive layer.

The primer layer usually contains a priming polymer, and such a polymer is selected so that it has an affinity with the substrate and the receptive layer. For example, when the receptive layer contains the ionically modified polyester or polyurethane, and the substrate is a polymer sheet comprising an acrylic polymer, the priming polymer is preferably an aminoethylated polymer. Thereby, the water resistance of the image recorded with the aqueous inks can be increased, and at the same time, the adhesion between the receptive layer and the substrate is improved, and thus the outdoor durability of the sheet can be significantly increased.

The aminoethylated polymer is a polymer in which a primary amino group (-NH₂) is introduced using ethylene imine. In general, the introduction of the primary amine through the ring opening addition of ethylene imine is called "aminoethylation". Thus, in the present specification, the polymer having the primary amino group, which is introduced by the aminoethylation, is named an aminoethylated polymer or resin.

When the receptive layer contains the ionically modified polyester or polyurethane, and the substrate is (i) a polymer sheet containing a vinyl chloride polymer or (ii) a polymer sheet containing a polyester, the priming polymer is preferably a saturated polyester for the same reason as described above. Such a primer is preferably used to increase the adhesion of the primer layer and the receptive layer particularly when the polyester of the substrate is a phthalate polyester having repeating units derived from phthalic acid and/or naphthalic acid, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), an ethylene terephthalate copolymer comprising ethylene teraphthalate units and other comonomer units (co-PET), an ethylene naphthalate copolymer comprising ethylene naphthalate units and other comonomer units (co-PEN), etc. The saturated polyester is preferably a linear polyester, and particularly preferably a polyester having a Tg higher than 50°C. The saturated polyester may be crosslinked with a crosslinking agent such as an isocyanate compound, insofar as the effects of the present invention are not impaired. The priming polymer may be a polymer blend (mixture). For example, a primer layer comprising a blend of a urethane elastomer and other polymer is formed to increase the adhesion between the substrate and the coloring material-receptive layer containing the ionically modified polyurethane. The urethane elastomer is an elastomer of polyurethane prepared by polymerizing a starting material containing a polyol and a diisocyanate. The thickness of the primer layer is usually from 0.1 to 30 μm, preferably from 0.5 to 10 μm.

To increase the transparency of the primer layer, the haze (turbidity) of the primer layer, which is measured with a color meter, is preferably 30 % or less, more preferably 20 % or less. The light transmittance of the primer layer is usually at least 85 %, preferably at least 90 %.

The primer layer may be formed by applying a liquid containing the priming polymer and solidifying (curing or drying) it. As an application means, a conventional coater such as a bar coater, a knife coater, a roll coater, a die coater, etc. may be used.

The support is usually a sheet (or a film) made of a polymer. When the graphic is formed by ink jet printing, a porous film can be used.

As the polymer of the support, polyester, an acrylic polymer, a vinyl chloride polymer, olefin copolymers (e.g. ethylene-acrylic acid copolymers, ionomers, etc.), polyurethane, etc. may be used. The above-described phthalate polyester is preferable from the viewpoint of good weather resistance and the increase of the water resistance of the graphics.

The thickness of the substrate made of the polymer sheet is usually from 10 to 500 μm, preferably from 20 to 300 μm. The substrate may be opaque, when the graphics on the receptive layer are observed from the surface of the prismatic sheet. The substrate should allow light to transmit, when the graphic is observed also from the substrate side (the back surface of the substrate), or when the displaying sheet is illuminated from the back surface of the substrate and the graphic is observed from the surface of the prismatic surface at night. In the latter case, the sheet, which is prepared from the above polymer is usually used so that the sheet allows light to transmit. Alternatively, an optical film such as a light- transmitting non-glittering prismatic film (e.g. a retroreflective sheet or a glittering- increasing prismatic film), a polarization film, etc. may be used as the substrate. The light transmittance of the support is usually at least 85 %, preferably at least

90 %, when the graphic is observed from the back surface of the support. When the graphic is observed from the surface of the prismatic sheet using the illumination from the back surface of the support, the haze of the support, which is measured with a color meter, is usually from 35 to 60 %, preferably from 40 to 55 %. The support may be a porous film or sheet having permeable micropores

(hereinafter refeπed to as "porous film"). Such a porous film can quickly absorbs the solvent (dispersing medium) such as water in the inks applied, and increase the quick drying properties. The porous film is usually a fibrous sheet such as a paper sheet, a non- woven fabric, a woven fabric, etc, or a resin film having porosity, although any porous sheet which achieves the above effects may be used. For example, expanded porous resin films such as an expanded porous resin film of PPG Industries, Inc. (Teslin^® resin film) are preferable.

The permeability of the support is usually from 10 to 3,000 sec/ 100 ml, preferably from 50 to 2,500 sec/ 100 ml, particularly preferably from 100 to 2,000 sec/100 ml, in terms of a Gurley permeability. Herein, the Gurley permeability is a value measured with a Gurley permeability tester according to JIS P-8117-1980, and expressed by a time (seconds) necessary to allow 100 ml of the air to pass through a sample. The porosity of the porous film (that is, the total volume of the pores in the whole volume of the film) is usually from 10 to 90 vol. %, preferalby from 20 to 80 vol. %.

The diameter of the pores measured on the cross section vertical to the wall thickness direction of the film (that is, in the horizontal direction of the expanded film) is usually from 0.01 to 3 μm, preferably from 0.02 to 2 μm, more preferably from 0.03 to 1 μm.

Examples of the material of the porous film include polyolefins such as polyethylene, polypropylene, polymethylpentene-1, etc., polyvinyl chloride, polystyrene, styrene-butadiene-acrylonitrile copolymers, polyamide, poymethyl methacrylate, polyesters, and the like. They maybe used as a mixture of two or more.

The porous film may optionally contain inorganic fine powder. Examples of the inorganic fine powder include calcium carbonate, alumina, calcined clay, silica (including amorphous silica), diatomaceous earth, talc, titanium oxide, barium sulfate, and the like. The particle size of the fine powder is usually from 0.3 to 10 μm, preferably from 0.8 to 5 μm. In addition, the porous film may contain other additives such as a heat stabilizer, a

UN absorber, a dispersant, an antistatic agent, an antioxidant, an oil (e.g. mineral oil, etc.), and so on.

The thickness of the support comprising the porous film is usually from 30 to 500 μm, preferably from 50 to 300 μm. When the thickness is too small the quick-drying property may deteriorate. When the thickness is too large, the handling of the displaying sheet as the recording medium in the printing process may become troublesome.

Preferably, the surfaces of the support and the micropores are hydrophilically treated with a surfactant. The surfactant may be any of anionic, cationic, amphoteric and nonionic surfactants. The anionic surfactants include carboxylate salt type, sulfonate salt type and phosphate salt type ones, the cationic surfactants include amine salt type and quaternary ammonium type ones, the amphoteric surfactants include betaine type and sulfobetaine type ones, and the nonionic surfactants include polyoxyalkylene type ones (e.g. polyethylene glycol, etc.), sorbitane type and sorbitol type ones.

When the hydrophilic treatment is carried out by the application and drying of a liquid containing the surfactant, a medium is preferably water or alcohol such as ethanol. The concentration of the surfactant in the liquid is usually from 1 to 30 wt. %, preferably from 5 to 25 wt. %. As an application means, a conventional coater such as a bar coater, a knife coater, a roll coater, a die coater, etc. may be used.

When the prismatic sheet is adhered to the receptive layer after the formation of the graphics on the receptive layer on the support, a transparent adhesive layer containing a self-adherent polymer is used.

The self-adherent polymer used in the present invention is a polymer which is tacky at room temperature (about 25°C), and has a property to impart pressure-sensitive adhesiveness to the adhesive comprising the polymer itself.

For example, the self-adherent polymer is an acrylic polymer. The self-adherent polymer consists of one polymer or a mixture of two or more acrylic polymers. The self- adherent polymer may be prepared by polymerizing a monomer mixture containing a specific starting monomer or monomers. The polymerization method may be a conventional method such as solution polymerization, bulk polymerization, emulsion polymerization, etc. Such an acrylic polymer may be prepared by polymerizing a monomer mixture containing (A) an alkyl acrylate with 4 to 8 carbon atoms in the alkyl group and (B) a (meth)acrylic monomer having a carboxyl group in the molecule. In addition, other (meth)acrylic monomer or a monomer having an unsaturated double bond (e.g. a vinyl bond), which is copolymerizable with the monomers (A) and (B), may be copolymerized. As the monomer (A), acrylates such as n-butyl acrylate, isobutyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, and the like are preferable. As the monomer (B), (meth)acrylic acid may be used. Examples of the other (meth)acrylic monomer include phenoxyethyl acrylate, phenoxypropyl acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxymefhyl (meth)acrylate, hydroxy-3 -phenoxypropyl acrylate, glycidyl (meth)acrylate, acryloylbenzophenone, etc. The total amount of the recurring units derived from the components (A) and (B) in the whole tackifying polymer is usually from 40 to 90 wt. %, preferably from 45 to 85 wt. %.

The self-adherent polymer is usually crosslinked. For example, the self-adherent polymer is crosslinked through the reaction of the polymer and a crosslinking agent. The kind of the crosslinking agent is not limited. As the crosslinking agent, a compound, which reacts with the carboxyl group of the self-adherent polymer or an optional crosslinkable group such as a hydroxyl group to crosslink the self-adherent polymer, is selected. Preferably, the crosslinking agent is an isocyanate compound causing no yellowing or a bisamide crosslinking agent. They can increase the transparency of the adhesive layer and effectively prevent the yellowing.

The isocyanate compound may be a compound synthesized from a starting material containing at least one diisocyanate selected from the group consisting of isophorone diisocyanate, diphenylmethane diisocyanate (MDI), hydrogenated MDI (diphenylmethane diisocyanate) and 1,6-hexanediol diisocyanate. For example, (a) compounds prepared by reacting a triol (e.g. 1,1,1-trimethylolpropane, etc.) with the above diisocyanate to form urethane, or (b) compounds having a biuret structure or an isocyanurate structure, which are obtained by the reaction of the above diisocyanates, may be used. To control the NCO equivalence, a crosslinking agent prepared by reacting the above compound and a diol such as polycaprolactonediol, etc. As the bisamide crosslinking agent, bisaziridine derivatives of dibasic acids such as isophthaloyl bis(2-methylaziridine) may be used. The bisamide crosslinking agent is particularly preferable since it can react with the self-adherent polymer having the carboxyl group at a relatively low temperature and easily achieves the sufficient crosslinking degree.

The amount of the crosslinking agent is usually from 0.1 to 5 wt. parts per 100 wt. parts of the self-adherent polymer. The adhesive layer may contain elastic microspheres or a crystalline polymer insofar as the effects of the present invention are not deteriorated. Furthermore, the adhesive layer with repeelability may be used.

The adhesive layer should be designed so that it has a refractive index in the specific range as a whole. When the refractive index is too high, the amount of the light reflected at the interface between the receptive layer and the adhesive layer unnecessarily increases so that the proportion of light reaching the graphics in the light incident in the graphics-displaying sheet decreases. When the refractive index is too low, the amount of light reflected at the interface between the receptive layer and the adhesive layer among the light reflected by the graphics unnecessarily increases. In either case, the definition of the graphics decreases. From such a viewpoint, the refractive index of the adhesive layer is usually from 1.4 to 1.9, preferably from 1.45 to 1.8.

The light transmittance of the adhesive layer is usually at least 70 %, preferably at least 80 %. When the light transmittance of the adhesive layer is too low, the definition of the graphics may decrease. The thickness of the adhesive layer is not limited insofar as the effects of the present invention can be achieved. The thickness is usually from 5 to 200 μm, preferably from 10 to 100 μm.

The adhesive layer containing the same self-adherent polymer as described above is used, when the support is adhered to the receptive layer after the formation of the graphics on the receptive layer which has been fixed to the back surface of the prismatic sheet. The glittering prismatic sheet comprises an array of triangular pyramid-shaped prisms on its surface, as described above. Such a prismatic sheet has the structure shown in Figs. 1 and 2 like the known prismatic sheets.

The glittering prismatic sheet may be produced by the method disclosed in the above-described patent publications of the applicant. However, the glittering prismatic sheet used in the present invention should have high transparency. Thus, the body part on which the prisms are formed (including the sheet part) and the prisms should not be made opaque.

The glittering prismatic sheet may be produced using a mold having an array of triangular pyramid-shaped dents corresponding to the negative of each cube-corner, which is designed so that an aπay of cube-corners are fixed to the surface of the sheet part with a specific arrangement. A paint containing a polymerizable monomer is poured on the mold to fill the dents and form a coating film on the mold and then the paint is cured (polymerized) with laminating the substrate which forms the sheet part on the coated paint. After the completion of the curing, the mold is removed. The cube-corners made of the cured film and the land part are integrally molded and fixed to the sheet part. Thereby, the glittering prismatic sheet can be obtained.

The triangular pyramid-shaped prisms are usually cube-corners. The dihedral angle α formed with the side faces of a pair of the adjacent cube-corners is different from the dihedral angle between another pair of the prisms adjacent to the above pair. Like this, the slopes of the side faces of the cube-corners are preferably irregular so that the dihedral angles of all the pairs of the cube-corners are substantially different. Preferably, the dihedral angles of substantially all the pairs of the cube-comers are in the range between 35 and 115 degrees, and the average dihedral angle is in the range between 35 and 115 degrees.

A distance from the back surface of the sheet part (that is, the back surface of the prismatic sheet) to the apex of the cube-comer, namely the height, varies with the cube- comers. The height of the cube-comer is usually from 10 to 600 μm. The difference of the heights of the adjacent cube-comers is usually from 1 to 100 μm, preferably from 3 to 60 μm.

The polymerizable monomer used to form the cube-corners may be a (mefh)acrylate monomer such as methyl methacrylate, or a mixture of the (mefh)acrylate monomer and other monomer (e.g. a vinyl monomer, an epoxy compound, etc.). The paint comprising the polymerizable monomer may contain various additives such as a polymerization initiator, a UN absorber, a light stabilizer, a free-radical scavenger, an antioxidant, an anti-blocking agent, a peeling agent, a lubricant, etc. A filler may be added to the paint insofar as the transparency of the cube-comers is not impaired. Examples of the filler include inorganic oxides such as silica, titania, zirconia, alumina, etc. They may be used in the form of a colloid or transparent beads. The colloid of the inorganic oxide can increase the hardness and scratch-resistance of the cube-comers, or increase the refractive index of the cube-comers and thus increase the glittering. The beads of the inorganic oxide can increase the abrasion-resistance of the cube-comers.

The sheet part is preferably made of a polymer to avoid the decrease of the transparency of the prismatic sheet. Examples of the polymer used to form the sheet part include polyester, acrylic polymers, vinyl chloride polymers, olefin copolymers (e.g. ethylene-acrylic acid copolymers, ionomers, etc.), polyurethane, etc. The thickness of the sheet part is usually from 20 μm to 1.3 mm. The light transmittance of the sheet part is usually at least 80 %, preferably at least 85 %, more preferably at least 90 %. When the light transmittance is too low, the definition of the graphics may deteriorate.

The light transmittance of the prismatic sheet as a whole is at least 80 %, preferably at least 90 %, more preferably at least 95 %, when it is measured with light being incident from the surface of the prismatic sheet (prismatic surface). When this light transmittance is too low, the amount of light which reaches the graphics decreases so that the definition of the graphics may deteriorate. Also the light transmittance of the prismatic sheet is usually at least 50 %, preferably at least 55 %, more preferably at least 60 % when it is measured with light being incident from the back surface of the prismatic sheet. When this light transmittance is too low, the amount of light reflected on the graphics to be observed decreases so that the definition of the graphics may deteriorate.

The triangular pyramid-shaped prism is not limited to the cube-comer and may be of any other triangular pyramid shape.

Examples Example 1

As a support, a white PET film having a thickness of 50 μm (KRISPER^® K 1211 manufactured by TOYOBO Co., Ltd.) was used. On the surface of the support, BYRON^®

24 SS (comprising a saturated linear polyester; manufactured by TOYOBO) was applied and dried at 100°C for 2 minutes to form a primer layer having a thickness of 3 μm. On the primer layer PATERACOL^® IJ-21 (manufactured by DAINIPON INK &

CHEMICALS, INC.) was applied and dried at 150°C for 2 minutes to form a coloring material-receptive layer having a thickness of 22 μm.

On the surface of the coloring material-receptive layer, a multicolor image was printed with an aqueous ink jet system to form a graphics. A printer used was Novajet^® III (manufactured by Encad). The printing direction was a single direction, the number of passes was 4, and the ink jetting rate was 5,000 Hz. The inks used were aqueous pigment inks of 3M (855 Series; Yellow, Magenta, Cyan and Black).

Then, onto the printed surface of the receptive layer, a glittering prismatic sheet

(White High Gloss Sparkle Film No. 6560 manufactured by 3M) was adhered with an adhesive layer comprising a self-adherent acrylic polymer having a refractive index of

1.47. Thus, the graphics-displaying sheet of this Example was completed. The light transmittance of this glittering prismatic sheet, that is, the total light transmittance measured with a color meter having the function of a photometer, was 101 % with light being incident from the surface of the prismatic sheet, and 66 % with light being incident from the back surface of the prismatic sheet. The graphics-displaying sheet of this Example was adhered to the surface of a signboard for advertisement with the prismatic surface facing outward using an adhesive containing a self-adherent polymer. Then, the displaying sheet was observed from the side of the prismatic surface under the sun. As a result, a plurality of glittering points were observed, while the graphics provided on the back surface of the prismatic sheet was clearly seen through the prismatic sheet in the areas other than the glittering points. No defects due to bubbling were observed. When the displaying sheet was observed with varying the observation angle, the glittering points moved and the graphics could be clearly seen in the areas which previously had the glittering points.

The signboard was placed outdoors for two months and exposed to winds and rains under the atmospheric conditions to evaluate the durability such as water resistance of the graphics. As a result, the change of the appearance such as the flowing of inks, decrease of glittering properties, generation of the defects in the image, etc. were not observed. Thus, the durability of the graphics was judged "excellent".

Example 2

The graphics-displaying sheet of this Example was produced in the same manner as in Example 1 except that a transparent PET film having a thickness of 50 μm (E 5101 manufactured by TOYOBO Co., Ltd.) was used as a support.

Then, the graphics-displaying sheet of this Example was observed under the sun in the same manner as in Example 1. As a result, a plurality of glittering points were observed, while the graphics provided on the back surface of the prismatic sheet was clearly seen through the prismatic sheet in the areas other than the glittering points. The durability of the graphics was also evaluated in the same manner as in Example 1. The durability of the graphics was judged "excellent".

When the graphics-displaying sheet of this Example was observed from the back surface side of the support (transparent PET film) under the sun, the clearly glittering points were observed. Furthermore, when the displaying sheet was observed with illuminating it from the back surface side of the support at night, the retroreflective graphics were observed.

Claims

We Claim:

1. A graphics-displaying sheet comprising

(a) a glittering prismatic sheet which is a light-transmitting prismatic sheet having a surface and a back surface and includes an array of triangular pyramid-shaped prisms on said surface, said prisms being arranged such that they glitter when light is incident thereon, and

2. The graphics-displaying sheet according to claim 1, wherein said coloring material-receptive layer comprises an ionically modified polymer, and said coloring material is an aqueous ink.

3. The graphics-displaying sheet according to claim 1, wherein said support and said coloring material-receptive layer are closely adhered through a primer layer, and said coloring material is received by said coloring material-receptive layer with the application of printing on the surface of said coloring material-receptive layer.

4. The graphics-displaying sheet according to claim 3, wherein said coloring material-receptive layer comprises an ionically modified polyurethane, said support comprises a polyester or a vinyl chloride polymer, and said primer comprises a saturated polyester.