METHOD FOR PRODUCING A DECORATIVE SHEET

TECHNICAL FIELD

The present disclosure relates to a decorative sheet to be applied to a substrate using a vacuum-pressure molding method or an injection molding method, a structure including a decorative sheet, and a production method for a decorative sheet.

BACKGROUND

A known method of decorating the surfaces of a three-dimensional substrate such as the interior and exterior of an automobile is a method of attaching a decorative sheet or a film to the surface of the substrate. A representative method for attaching a decorative sheet is an in-mold injection molding method. In this method, a decorative sheet in which a decorative layer or the like is formed on a base sheet is set in a mold for injection molding directly or after being preformed, and a molded article with a three-dimensional shape is injection-molded, while the decorative sheet is simultaneously attached integrally to the molded article to achieve decoration.

A vacuum-pressure molding method is also known as a method for attaching a decorative sheet to a substrate. In a vacuum-pressure molding method, a decorative sheet is attached to a substrate molded in advance using a pressure difference while stretching the decorative sheet with respect to the substrate at room temperature or in a heated atmosphere. Since the decorative sheet is attached to the substrate surface of the part in an operation separate from the formation of the substrate, a decorative sheet can be attached to substrates of various shapes with a single vacuum-pressure molding device. In addition, with the vacuum-pressure molding method, a sheet can be attached with good conformity to the three-dimensional shape of the substrate surface, and continuous coating, that is, roll coating, from the front to the back near the end of the substrate, which is difficult with an in-mold injection molding method, also becomes possible. In this way, with the vacuum-pressure molding method, a decorative sheet can be attached with excellent coatability to three-dimensional substrates with various complex shapes.

JP 2009-035588A describes "an adhesive film including a substrate and an adhesive layer on the substrate, wherein the adhesive layer includes: (A) a carboxyl group- containing (meth)acrylic polymer having a glass transition temperature (Tg) of not higher than 25°C, a ratio of a number of repeating units containing carboxyl groups to a total number of repeating units of the polymer being from 4.0 to 25%; and (B) an amino group- containing (meth)acrylic polymer having a glass transition temperature (Tg) of not less than 75°C, a ratio of a number of repeating units containing amino groups to a total number of repeating units of the polymer being from 3.5 to 15%; and a compounding ratio of component (A) and component (B) is from 62:38 to 75:25 in terms of weight ratio."

SUMMARY OF THE INVENTION

The decorative layer of a decorative sheet is typically formed using a printing technique such as gravure printing, inkjet printing, offset printing, or screen printing.

Since these printing techniques express an image by means of the density of dots of ink, that is, ink dots, minute concavities and convexities caused by differences in the thickness of the printed ink material arise on the printing surface, and the height and density of the concavities and convexities also differ depending on the expressed color. Gravure printing is simpler than other printing techniques and is therefore widely used in the formation of decorative layers, but there is a tendency for the concavities and convexities formed on the printing surface to become relatively large.

The present inventors discovered that, when attaching a decorative sheet to a substrate while deforming the decorative sheet, in particular, while stretching the decorative sheet, using a vacuum -pressure molding method or an injection molding method, small concavities and convexities present on the printing surface may propagate to the decorative sheet surface, and the surface quality such as the image clarity or glossiness, for example, of the decorative sheet may be lost. This phenomenon had not been confirmed when attaching a decorative sheet to a flat substrate without deforming the decorative sheet.

The present disclosure provides a decorative sheet capable of yielding high surface quality when attached to a substrate by a vacuum-pressure molding method or an injection molding method. The present disclosure also provides a structure including such a decorative sheet and a production method for such a decorative sheet.

One embodiment of the present disclosure provides a decorative sheet to be attached to a substrate by a vacuum-pressure molding method or an injection molding method, the decorative sheet including: a decorative layer including a printing surface having concavities and convexities; and a smoothing resin layer disposed on the printing surface of the decorative layer or above the decorative layer; wherein a surface of the smoothing resin layer is smoother than the printing surface.

Another embodiment of the present disclosure provides a structure including a substrate and the decorative sheet applied to a surface of the substrate.

Yet another embodiment of the present disclosure provides a method for producing a decorative sheet to be attached to a substrate by a vacuum-pressure molding method or an injection molding method, the production method including: forming a decorative layer including a printing surface having concavities and convexities; and forming a smoothing resin layer on the printing surface of the decorative layer or above the decorative layer and forming a surface of the smoothing resin layer to be smoother than the printing surface.

With the present disclosure, by disposing the smoothing resin layer on the printing surface having concavities and convexities of the decorative layer or above the decorative layer and using the smoothing resin layer to impart the decorative sheet with a surface that is smoother than the printing surface, high surface quality such as image clarity or glossiness, for example, can be achieved even when the decorative sheet is attached to a substrate by a vacuum-pressure molding method or an injection molding method.

Note that the above descriptions are not to be interpreted as a disclosure of all embodiments of the present invention or all of the advantages related to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view of a decorative sheet according to one embodiment.

FIG. 2 is a schematic cross-sectional view of a decorative sheet according to another embodiment.

FIG. 3 is a photograph of the decorative sheet of Example 1 attached to a curved surface by a vacuum-pressure molding method, wherein the portion enclosed by the ellipse indicates the glare of an indoor fluorescent lamp.

FIG. 4 is a photograph of the decorative sheet of Comparative Example 1 attached to a curved surface by a vacuum-pressure molding method, wherein the portion enclosed by the ellipse indicates the glare of an indoor fluorescent lamp. DESCRIPTION OF PREFERRED EMBODIMENTS A more detailed description will be given hereinafter with the objective of illustrating representative embodiments of the present invention, but the present invention is not limited to these embodiments.

In the present disclosure, a "sheet" is a flexible laminate and also encompasses a thin laminate called a "film".

In the present disclosure, the "storage modulus (E')" refers to the storage modulus at a specified temperature when the viscoelasticity is measured in a stretched mode at a heating rate of 5.0°C/min and a frequency of 10 Hz in the temperature range from -40°C to 200°C.

In the present disclosure, "transparent" means that the total light transmittance in the wavelength range of 400 to 700 nm is not less than approximately 60%, not less than approximately 80%, or not less than approximately 90%. The total light transmittance can be determined in accordance with JIS K 7361-1 : 1997 (ISO 13468-1 : 1996).

In the present disclosure, "(meth)acryl" refers to acryl or methacryl, and

"(meth)acrylate" refers to acrylate or methacrylate.

In the present disclosure, a "vacuum-pressure molding method" refers to a molding method including: preparing a sheet and an article having a three-dimensional shape; disposing the sheet and the article inside a vacuum chamber including a heating device therein, the sheet dividing the internal space of the vacuum chamber into two, and the article being disposed in one of the divided internal spaces; heating the sheet with the heating device; setting both the internal space in which the article is disposed and the internal space on the opposite side to a reduced-pressure atmosphere; and bringing the article and the sheet into contact with one another while setting the internal space in which the article is disposed to a reduced-pressure atmosphere and setting the internal space on the opposite side to an increased-pressure atmosphere or a normal pressure atmosphere. This method is also called a "Three-dimensional Overlay Method"

("TOM").

The decorative sheet according to one embodiment of the present disclosure is attached to a substrate by a vacuum-pressure molding method or an injection molding method and includes: a decorative layer including a printing surface having concavities and convexities; and a smoothing resin layer disposed on the printing surface of the decorative layer or above the decorative layer; wherein the surface of the smoothing resin layer is smoother than the printing surface. FIG. 1 illustrates a cross-sectional view of a decorative sheet 10 according to one embodiment of the present disclosure. The decorative sheet 10 includes a decorative layer 12 including a printing surface 122 having concavities and convexities; and a smoothing resin layer 14 disposed on the printing 122 of the decorative layer 12; wherein the surface 142 of the smoothing resin layer 14 is smoother than the printing surface 122 of the decorative layer 12.

The decorative sheet may further include additional layers such as a support layer, an adhesive layer, a surface layer, a design layer other than a decorative layer, a junction layer, or a release liner as optional components but the number, type, disposition, and the like of the decorative layers are not particularly limited. In FIG. 1, the decorative sheet 10 is illustrated as a sheet further including, as optional components, a support layer 16, an adhesive layer 18 for attaching the decorative sheet to a substrate, a transparent surface layer 22 which contributes to the protection of the surface of the decorative sheet, and a junction layer 24 for joining together the layers constituting the decorative sheet (the surface layer 22 and the smoothing resin layer 14 in FIG. 1).

The decorative layer is typically formed using a printing technique such as gravure printing, inkjet printing, offset printing, or screen printing and includes a printing surface having concavities and convexities. The decorative layer may be formed by monochromatic printing or multicolor printing. The decorative layer may be continuous or discontinuous. In one embodiment, the decorative layer is formed by a collection of individual dots and is discontinuous.

In one embodiment, the printing surface of the decorative layer is a gravure printing surface. Gravure printing yields high image quality and excellent productivity, but the concavities and convexities on the printing surface tend to become large. With the present disclosure, the aforementioned advantages of gravure printing can be achieved while mitigating the effects of the concavities and convexities of the printing surface on the surface quality of the decorative sheet after molding.

The shape of the ink dots forming the printing surface of the decorative layer is not particularly limited, but the height may be, for example, not less than approximately 0.1 μιτι, not less than approximately 0.2 μιτι, or not less than approximately 0.3 μιη and not greater than approximately 5 μιτι, not greater than approximately 3 μιτι, or not greater than approximately 1 μιη. The density of the ink dots depends on the cell density or the number of lines per inch of the printing plate that is used. For example, the number of lines may be not fewer than approximately 18, not fewer than approximately 50, or not fewer than approximately 100 and not greater than approximately 500, not greater than approximately 300, or not greater than approximately 200. Printing is typically repeated multiple times to form complex colors, patterns, or the like. When printing is repeated multiple times, plates with different numbers of lines may be used each time.

In some embodiments, the surface roughness Rzl of the printing surface of the decorative layer is not less than approximately 0.2 μπι, not less than approximately 0.5 μπι, or not less than approximately 0.8 μιη and not greater than approximately 5 μπι, not greater than approximately 4 μηι, or not greater than approximately 3 μιη. The concavities and convexities on the printing surface having a surface roughness Rzl in the range described above are very fine, but when a decorative sheet that does not include a smoothing resin layer is attached to a substrate by a vacuum-pressure molding method or an injection molding method, the concavities and convexities propagate to the decorative sheet surface and diminish the surface quality. The surface roughness in the present disclosure is the maximum height roughness measured in accordance with JIS B 0601 :2001.

The decorative layer may contain an adhesive. A decorative layer containing an adhesive can be joined with the other layers constituting the decorative sheet without an intermediate junction layer. Solvent type, emulsion type, pressure-sensitive type, heat- sensitive type, thermosetting type, or UV-curing type adhesives such as commonly used acrylic, polyolefin, polyurethane, polyester, or rubber adhesives may be used as an adhesive. The adhesive may be incorporated into the decorative layer using a printing technique such as gravure printing, inkjet printing, offset printing, or screen printing.

In one embodiment, the adhesive is a heat-sensitive type adhesive and contains at least one thermoplastic resin selected from the group consisting of vinyl chloride/vinyl acetate copolymers, polyurethanes, polyesters, (meth)acrylic resins, and phenoxy resins. In the present disclosure, a "phenoxy resin" refers to a thermoplastic polyhydroxy polyether which is synthesized using a bisphenol and epichlorohydrin, and this also includes substances containing a minute amount of epoxy groups derived from epichlorohydrin in the molecule (for example, at a terminal). For example, the epoxy equivalent of a phenoxy resin is higher than that of an ordinary epoxy resin and is, for example, not less than 5000, not less than 7000, or not less than 10000.

The smoothing resin layer is disposed on the printing surface of the decorative layer or above the decorative layer and has a surface which is smoother than the printing surface of the decorative layer. In the present disclosure, "disclosed on" means that the smoothing resin layer is disposed in contact with the printing surface of the decorative layer, and "disposed above" means that the smoothing resin layer is disposed at a distance from the decorative layer on the surface side from the perspective of the decorative layer.

The smoothing resin layer suppresses the propagation of the concavities and convexities on the printing surface of the decorative layer to the decorative sheet surface during vacuum-pressure molding or injection molding. Although not restricted to any particular theory, when a decorative sheet is deformed and attached to a substrate, the stretching of the decorative sheet may become nonuniform within the plane, and this is particularly prominent in locations where the stress applied to the decorative sheet is large at the time of attachment, such as locations where the radius of curvature of the substrate surface is large. In addition, in locations where the density of ink dots is high (dark color), the decorative sheet tends to be difficult to stretch due to fusion or the like between ink dots, whereas in locations where the density of ink dots is low (light color), the decorative sheet tends to stretch easily and become thin. In portions where the decorative sheet has become thin, the concavities and convexities on the printing surface of the decorative layer propagate more easily to the decorative sheet surface, and the surface quality of the decorative sheet is diminished in these portions. The smoothing resin layer of the present disclosure is thought to suppress the propagation of the concavities and convexities on the printing surface of the decorative layer to the decorative sheet surface by flowing while maintaining a moderate internal stress so that the printing surface of the decorative layer spreads out uniformly within the lane and so that the concavities and convexities on the printing surface are absorbed when the decorative sheet is deformed, in particular, when the decorative sheet is stretched.

The smoothing resin layer may completely cover the printing surface of the decorative layer or may cover a portion of the printing surface of the decorative layer while not covering other portions. For example, at least some of the gaps between the ink dots on the printing surface of the decorative layer may be filled with the smoothing resin layer. In one embodiment, the smoothing resin layer is located inside the decorative sheet, and the surface of the smoothing resin layer is not exposed.

Various resins may be used as a smoothing resin layer, for example, acrylic resins including polymethyl methacrylate (PMMA) and (meth)acrylic copolymers, polyolefins such as polyurethane (PU), polyvinyl chloride (PVD), polycarbonate (PC), acrylonitrile- butadiene-styrene copolymers (ABS), polyethylene (PE), and polypropylene (PP), polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), copolymers such as ethylene-acrylic acid copolymers (EAA), ethyl ene-ethyl acrylate copolymers, and ethyl ene-vinyl acetate copolymers (EVA), or combinations thereof. By using a resin layer containing a polyurethane or acrylic resin as a smoothing resin layer, the propagation of the concavities and convexities on the printing surface of the decorative layer can be effectively suppressed. It is more advantageous for the decorative layer to contain a polyurethane.

In one embodiment, the surface roughness Rz2 of the smoothing resin layer is lower than the surface roughness Rzl of the printing surface of the decorative layer. In some embodiments, the surface roughness Rz2 of the smoothing resin layer is not less than approximately 0.05 μπι, not less than approximately 0.1 μπι, or not less than approximately 0.15 μιη and not greater than approximately 1.0 μπι, not greater than approximately 0.5 μπι, or not greater than approximately 0.3 μιη. By setting the surface roughness Rz2 of the smoothing resin layer to within the range described above, the surface quality of the decorative sheet after molding can be increased.

In some embodiments, the surface roughness Rz2 of the smoothing resin layer is not greater than approximately 0.95 times, not greater than approximately 0.8 times, or not greater than approximately 0.6 times the surface roughness Rzl of the printing surface of the decorative layer. By setting the surface roughness Rz2 of the smoothing resin layer to within the range described above, the surface quality of the decorative sheet after molding can be increased.

In some embodiments, the smoothing resin layer is a coating layer produced by applying a resin solvent prepared by mixing a resin and a solvent to the printing surface. The resin solvent having fluidity can fill the concavities and convexities on the printing surface, and therefore a smoother surface can be formed in comparison to the surface roughness of the printing surface. Coating methods include methods such as gravure printing, screen printing, and casting, and the viscosity of the resin solvent can be selected appropriately in accordance with the type of the coating method.

In some embodiments, the storage modulus of the smoothing resin layer is not less than approximately 1.0 x 10 ⁶ Pa, not less than approximately 1.5 x 10 ⁶ Pa, or not less than approximately 2.0 x 10 ⁶ Pa and not greater than approximately 1.5 x 10 ⁸ Pa or not greater than approximately 1.3 x 10 ⁸ Pa within a temperature range from 100°C to 150°C when measured under stretched mode conditions at a frequency of 10 Hz. By setting the storage modulus of the smoothing resin layer to within the range described above, the smoothing resin layer maintains a moderate internal stress during molding due to the presence of the smoothing resin layer which fills the concavities and convexities of the printing surface, and the printing surface of the decorative layer is stretched uniformly within the plane. As a result, the surface roughness of the decorative layer can be made even smaller, and the smoothness can be increased.

In some embodiments, the thickness of the smoothing resin layer after the coating and drying is not less than approximately 2 times, not less than approximately 5 times, or not less than approximately 10 times and not greater than approximately 200 times, not greater than approximately 150 times, or not greater than approximately 100 times the surface roughness Rzl of the printing surface of the decorative layer. By setting the thickness of the smoothing resin layer to within the range described above, the surface quality of the decorative sheet after molding can be increased. The thickness of the smoothing resin layer in the present disclosure refers to the thickness at the thickest part of the smoothing resin layer.

In some embodiments, the thickness of the smoothing resin layer is not less than approximately 3 μπι, not less than approximately 5 μπι, or not less than approximately 10 μπι and not greater than approximately 100 μπι, not greater than approximately 75 μπι, or not greater than approximately 50 μπι. By setting the thickness of the smoothing resin layer to within the range described above, the surface quality of the decorative sheet after molding can be increased.

Various resins may be used as a support layer, which is an optional component, for example, acrylic resins including polymethyl methacrylate (PMMA) and

(meth)acrylic copolymers, polyolefins such as polyurethane (PU), polyvinyl chloride (PVC), polycarbonate (PC), acrylonitrile-butadiene-styrene copolymers (ABS), polyethylene (PE), and polypropylene (PP), polyesters such as polyethylene

terephthalate (PET) and polyethylene naphthalate (PEN), copolymers such as ethylene- acrylic acid copolymers (EAA), ethyl ene-ethyl acrylate copolymers, and ethylene-vinyl acetate copolymers (EVA), or combinations thereof. From the perspective, of strength, impact resistance, or the like, polyurethane, polyvinyl chloride, polyethylene terephthalate, acrylonitrile-butadiene-styrene copolymers, and polycarbonate can be advantageously used as a support layer. The support layer is a support for the decorative layer or the like and may also function as a protective layer for imparting uniform stretching at the time of molding and more effectively protecting the structure from external puncture, impact, or the like. In one embodiment, the support layer has adhesiveness. In this embodiment, the decorative sheet can be attached to an article without requiring the adhesive layer described below. The adhesive support layer can be formed from the same material as that of the adhesive layer described below.

The thickness of the support layer varies, but from the perspective of providing the functions described above to the decorative sheet without adversely affecting the moldability of the decorative sheet, the thickness is typically not less than approximately 2 μπι, not less than approximately 5 μπι, or not less than approximately 10 μιη and not greater than approximately 100 μπι, not greater than approximately 75 μπι, or not greater than

approximately 50 μιη. The thickness of the support layer when the support layer is not flat refers to the thickness of the thinnest portion of the support layer.

In some embodiments, the storage modulus of the support layer is not less than approximately 1.0 x 10 ⁶ Pa, not less than approximately 1.5 x 10 ⁶ Pa, or not less than approximately 2.0 x 10 ⁶ Pa and not greater than approximately 1.5 x 10 ⁸ Pa or not greater than approximately 1.3 x 10 ⁸ Pa within a temperature range from 100°C to

150°C when measured under stretched mode conditions at a frequency of 10 Hz. When the storage modulus of the support layer is within the range described above, the strength and elongation at high temperatures required for vacuum-pressure molding or injection molding can be provided to the decorative sheet.

The support layer may be a single layer or may have a multilayer structure. When the support layer has a multilayer structure, the storage modulus of the support layer refers to one value observed for the entire multilayer structure as a composite of the storage moduli of each individual layer.

The decorative sheet may further include an adhesive layer for attaching the decorative sheet to the substrate. Solvent type, emulsion type, pressure-sensitive type, heat-sensitive type, thermosetting type, or UV-curing type adhesives such as commonly used acrylic, poly olefin, polyurethane, polyester, or rubber adhesives may be used as the adhesive layer, and acrylic adhesives and thermosetting polyurethane adhesives are advantageously used. A layer in which a thermoplastic polyurethane is formed into a film shape by molding, extrusion, stretching or the like may also be used as the adhesive layer.

The thickness of the adhesive layer is typically not less than approximately 5 μπι, not less than approximately 10 μπι, or not less than approximately 20 μπι and not greater than approximately 200 μπι, not greater than approximately 100 μπι, or not greater than approximately 80 μπι. The adhesive layer may be protected using an optional suitable release liner. Examples of representative release liners include liners made from paper (for example, craft paper) or polymer materials (for example, polyolefms such as polyethylene or polypropylene, polyesters such as ethylene vinyl acetate, polyurethane, or polyethylene terephthalate). The release liner may be coated with a release agent such as a silicon-containing material or a fluorocarbon- containing material as necessary.

The thickness of the release liner is typically not less than approximately 5 μπι, not less than approximately 15 μπι, or not less than approximately 25 μιη and not greater than approximately 300 μπι, not greater than approximately 200 μπι, or not greater than approximately 150 μιη.

Various resins may be used as a surface layer, which is an optional component, for example, acrylic resins including polymethyl methacrylate (PMMA) and (meth)acrylic copolymers, polyolefms such as polyurethane (PU), fluorine resins such as ethylene- tetrafluoroethylene copolymers (ETFE), polyvinylidene fluoride (PVDF), and methyl methacrylate-vinylidene fluoride copolymers (PMMA/PVDF), polyolefms such as polyvinyl chloride (PVD), polycarbonate (PC), polyethylene (PE), and polypropylene (PP), polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), copolymers such as ethylene-acrylic acid copolymers (EAA) and ionomers thereof, ethyl ene-ethyl acrylate copolymers, and ethylene-vinyl acetate copolymers (EVA), or combinations thereof.

Acrylic resins, polyurethane, fluorine resins, and polyvinyl chloride are preferable due to their excellent weather resistance, and acrylic resins and polyurethane are more preferable due to their excellent scratch resistance and small environmental burden when burned or buried as waste.

The surface layer may contain an isosorbide-based polycarbonate. A surface layer containing an isosorbide-based polycarbonate can be formed by applying a solution obtained by dissolving an isosorbide-based polycarbonate in a solvent to a substrate by means of casting and then drying the solution. A surface layer formed in this way has excellent flatness and can further enhance the surface quality of the decorative sheet.

The surface layer may also have a multilayer structure. For example, the surface layer may be a laminate of films formed from the resins described above or may be a multilayer coating of the resins described above.

The thickness of the surface layer varies but is typically not less than

approximately 1 μπι, not less than approximately 5 μπι, or not less than approximately 10 μηι and not greater than approximately 150 μιτι, not greater than approximately 100 μιη, or not greater than approximately 80 μιη. When the decorative sheet is applied to a substrate with a complex shape, it is advantageous for the surface layer to be thinner from the perspective of shape conformity, and the thickness is preferably not greater than approximately 100 μιη or not greater than approximately 80 μιτι, for example. On the other hand, when imparting the structure with high light resistance and/or weather resistance, it is advantageous for the surface layer to be thicker, and the thickness is preferably not less than approximately 5 μιη or not less than approximately 10 μηι, for example.

The surface layer may also contain, as necessary, a UV absorber such as benzotriazole or Tinuvin (trade name) 400 (available from BASF), a hindered amine light stabilizer (HALS) such as Tinuvin (trade name) 292 (available from BASF), or the like. By using a UV absorber, a hindered amine light stabilizer, or the like, the discoloration, fading, deterioration, or the like of colorants contained in the decorative layer or the like, in particular, organic pigments with relatively high sensitivity to light such as UV rays, can be effectively prevented. The surface layer may contain a gloss imparting agent or the like and may also include an additional bar code layer.

The surface layer is typically transparent. In some embodiments, the total light transmittance of the surface layer is not less than approximately 85% or not less than approximately 90% in a wavelength range from 400 to 700 nm. To provide the target external appearance, the surface layer may be completely or partially translucent and may be partially opaque.

A junction layer may be used to join the layers described above. Solvent type, emulsion type, pressure-sensitive type, heat-sensitive type, thermosetting type, or UV- curing type adhesives such as commonly used acrylic, polyolefin, polyurethane, polyester, or rubber adhesives may be used as a junction layer. The thickness of the junction layer is typically not less than approximately 0.05 μιτι, not less than

approximately 0.5 μιτι, or not less than approximately 5 μιη and not greater than approximately 100 μηι, not greater than approximately 50 μιτι, or not greater than approximately 20 μιη.

The decorative sheet may include a design layer other than the decorative layer.

Examples of design layers include a color layer of a painted color, a metallic color, or the like, a relief (relief pattern) layer, or a brilliant layer. The design layer may have a multilayer structure and may include the junction layer described above between layers. Examples of color layers that may be used include layers in which a pigment such as inorganic pigment such as titanium oxide, carbon black, chrome yellow, yellow iron oxide, red oxide, or red iron oxide, an organic pigment such as a phthalocyanine pigment such as phthalocyanine blue or phthalocyanine green, an azo lake pigment, an indigo pigment, a perinone pigment, a perylene pigment, a quinophthalone pigment, a dioxazine pigment, or a quinacridone pigment such as quinacridone red, an aluminum radiant material such as aluminum flakes, evaporated aluminum flakes, metal oxide-coated aluminum flakes, or colored aluminum flakes, or a pearl radiant material such as flake-like mica and synthetic mica coated with a metal material such as titanium oxide or iron oxide is dispersed in a binder resin such as an acrylic resin or polyurethane.

An example of a relief layer that may be used is a thermoplastic resin film having an irregular shape on the surface due to embossing, scratching, laser processing dry etching, or heat pressing, for example, in accordance with a known method. The relief layer can also be formed by applying a thermosetting or radiation curable resin such as a curable acrylic resin to a release film having an irregular shape, curing the resin by heating or radiation, and then removing the release film. The thermoplastic resin, the

thermosetting resin, and the radiation curable resin used in the relief layer are not particularly limited, but fluorine-based resins, polyester resins such as PET or PEN, acrylic resins, polyethylenes, polypropylenes, thermoplastic elastomers, polycarbonates, polyamides, ABS resins, acrylonitrile-styrene resins, polystyrenes, vinyl chlorides, polyurethanes, and the like may be used.

The thickness of the color layer and the relief layer may vary and is typically not less than approximately 5 μπι, not less than approximately 10 μπι, or not less than approximately 20 μπι and not greater than approximately 500 μπι, not greater than approximately 300 μπι, or not greater than approximately 200 μπι.

A thin film in which a metal such as aluminum, nickel, gold, platinum, chromium, iron, copper, tin, indium, silver, titanium, lead, zinc, or germanium or an alloy or compound thereof is formed on another layer of the decorative sheet by vacuum deposition, sputtering, ion plating, plating, or the like may be used as a brilliant layer. The brilliant layer has high glossiness and is therefore suitably used for a chrome plating replacement film or the like. In this case, the thickness of the metal layer may be not less than approximately 5 nm, not less than approximately 10 nm, or not less than approximately 20 nm and not greater than approximately 10 μπι, not greater than approximately 5 μπι, or not greater than approximately 2 μπι. The brilliant layer may be incorporated into the support layer. FIG. 2 illustrates a cross-sectional view of a decorative sheet 10 according to another embodiment of the present disclosure. In the decorative sheet 10 of FIG. 2, a support layer 16 is a laminate of a first support layer 162, a brilliant layer 26, and a second support layer 164. The first support layer 162 and the second support layer 164 include a relief surface formed by embossing or the like on the inside thereof, and the image of the decorative sheet changes visually due to the brilliant layer 26 provided on the relief surface.

Such a support layer 16 can be formed, for example, by forming the first support layer 162 including a relief surface by pressing a mold having an emboss pattern while heating as necessary into a flat layer formed from the material constituting the first support layer 162, forming the brilliant layer 26 by depositing a thin metal film thereon, and applying a composition containing the material constituting the second support layer 164 thereon and then drying or curing the composition.

The pattern or design of the relief layer may be regular or irregular and is not particularly limited, and examples thereof include a parallel line pattern, a woody texture, a sandy texture, a rocky texture, a fabric texture, a satin texture, a leather drawing pattern, a matte texture, a hair line pattern, a spinning pattern, characters, symbols, geometrical figures, or the like. When the relief surface is formed by grooves, the width of the grooves is typically in the range of not less than approximately 5 μπι or not less than

approximately 10 μπι and not greater than approximately 1 mm or not greater than approximately 100 μπι.

The depth of the relief pattern is defined as the elevation difference from the top of a convex shape to the base of a continuous concave shape. The depth of the relief surface may be uniform or may have various values over the entire relief surface. The depth of the relief surface is typically in the range of not less than approximately 5 μπι or not less than approximately 10 μπι and not greater than approximately 100 μπι or not greater than approximately 50 μπι.

The surface layer, the support layer, the adhesive layer, and/or the junction layer may include colorants such as the same inorganic pigments, organic pigments, aluminum radiant materials, or pear radiant materials as those described above for the design layer.

The method for producing a decorative sheet according to one embodiment includes: forming a decorative layer including a printing surface having concavities and convexities; and forming a smoothing resin layer on the printing surface of the decorative layer or above the decorative layer and forming the surface of the smoothing resin layer to be smoother than the printing surface. The formation of the decorative layer and the smoothing resin layer is as described above.

Layers formed into a film shape by extrusion, stretching, or the like, for example, may be used for other layers as well, and these layers may be laminated with or without using junction layers. Each layer may also be formed by coating another layer or a liner with a resin composition by means of knife coating, bar coating, blade coating, doctor coating, roll coating, cast coating, or the like and drying or curing the resin composition by heating as necessary.

For example, the decorative sheet can be formed by forming each layer on a liner such as a

PET film with a release-treated surface and then laminating these layers. Alternatively, each layer may be sequentially laminated on a single liner by repeating the coating step and the curing step as necessary. The decorative sheet may also be formed by extruding the material of each layer into multiple layers.

The thickness of the decorative sheet is typically not less than approximately 25 μπι, not less than approximately 50 μπι, or not less than approximately 100 μπι and not greater than approximately 2 mm, not greater than approximately 1 mm, or not greater than approximately 500 μπι. By setting the thickness of the decorative sheet to within the range described above, it is possible to make the decorative sheet sufficiently conform to even a substrate having a complex surface and to provide a structure having an excellent external appearance.

To evaluate the image clarity of the surface of the decorative sheet, it is more suitable to use an index called the undulated surface roughness Wz in which the surface state is captured by undulations in the surface rather than the surface roughness Rz of the decorative sheet surface. For example, the undulated surface roughness Wza of the decorative sheet prior to molding is typically not less than approximately 0.1 μπι, not less than approximately 0.3 μπι, or not less than approximately 0.5 μπι and not greater than approximately 5 μπι, not greater than approximately 3 μπι, or not greater than

approximately 1 μπι. In some embodiments, the propagation of the concavities and convexities on the printing surface of the decorative layer to the decorative sheet surface is suppressed, and thus the undulated surface roughness Wzb of the decorative sheet after molding is substantially the same as the undulated surface roughness Wza prior to molding, or is smaller because the decorative sheet surface is additionally smoothened by deformation during molding, and is not greater than approximately 1.2 times, not greater than approximately 1 time, or not greater than approximately 0.8 times the roughness, for example. The scratch resistance of the decorative sheet can be evaluated by the pencil hardness in accordance with JIS K5600-5-4: 1999. In the decorative sheet of one embodiment, the pencil hardness is not less than 2B when the decorative sheet is fixed to the top of a glass sheet while the adhesive layer is oriented toward the surface of the glass sheet and the surface layer is scratched at a rate of 600 mm/min. The pencil hardness may be not less than 6B, not less than 5B, not less than 4B, or not less than 3B.

The maximum area elongation of the decorative sheet after molding is typically not less than approximately 50%, not less than approximately 100%, or not less than

approximately 200% and not greater than approximately 1000%), not greater than

approximately 500%, or not greater than approximately 300%. The area elongation is defined as follows: area elongation (%) = (B-A)/A (A: area of a certain portion of the decorative sheet prior to molding; B: area of a certain portion corresponding to A of the decorative sheet after molding). For example, when the area of a certain portion of the decorative sheet is 100 cm ² prior to molding and that portion becomes 250 cm ² on the surface of the article after molding, the area elongation is 150%. The maximum area elongation refers to the value at the location of the highest area elongation of the decorative sheet over the entire surface of the molded article. When a flat film is attached to an article with a three-dimensional shape by means of a vacuum-pressure molding method, the area elongation greatly differs depending on the location; for example, the portion in which the film initially touches the article is stretched minimally, and thus the area elongation is approximately 0%, whereas the film is greatly stretched at the ends where it is attached, and thus the area elongation increases to 200%> or greater. Since the quality of molding is determined by whether problems such as

nonconformity to the article or the splitting of the film in a portion where the film is stretched to the greatest degree, the area elongation of the portion stretched to the greatest degree, that is, the maximum area elongation serves as the essential index for the quality of the molded article rather than the average area elongation of the entire molded article. The maximum area elongation can be confirmed, for example, by printing 1 mm squares over the entire surface of the decorative sheet prior to molding and then measuring the change in area after molding or measuring the thickness of the decorative sheet before and after molding.

One embodiment of the present disclosure provides a structure including a substrate and a decorative sheet applied to a surface of the substrate. The substrate may be made from various materials such as polypropylene, polycarbonate, acrylonitrile- butadiene-styrene copolymers, or mixtures or blends thereof, and materials having various planes and three-dimensional shapes can be used. By applying the decorative sheet to the substrate by a vacuum-pressure molding method or an injection molding method, a structure in which the decorative sheet and the substrate are formed integrally can be formed. Vacuum-pressure molding and injection molding can be performed with known methods.

The decorative sheet of the present disclosure can be used for the decoration of automobile parts, household electric appliances, railroad cars, construction materials, or the like. In particular, the decorative sheet can be advantageously used for the decoration of the interior and exterior of an automobile, household electric appliances, or the like having high glossiness or a minute pattern.

EXAMPLES

In the following examples, specific embodiments of the present disclosure will be illustrated, but the present invention is not limited to these examples. Parts and percentages all refer to mass unless clearly stated otherwise.

The reagents, raw materials, or the like used in these examples are shown in Table 1 below.

Table 1

Example 1

(1) A D-6260 polyurethane solution was applied to a G2 PET film and dried for 5 minutes at 80°C and then for 5 more minutes at 100°C to form a polyurethane layer with a thickness of 25 μπι.

(2) Using an embossing cylinder having a hairline-pattern design, the shape of a hairline pattern was transferred to the surface of the polyurethane layer formed in (1) at a cylinder temperature of 190°C.

(3) Tin was deposited onto the embossed surface of the polyurethane layer under the following conditions (OD value: 1.1-1.2).

Device: vacuum deposition device EX-400 (available from ULVAC, Inc., Chigasaki- shi, Kanagawa, Japan)

Target metal deposition energy source: electron beam

Thickness of tin deposition layer: 430 Angstrom

Tin deposition layer forming rate: 5 Angstrom/sec

(4) A D-6260 polyurethane solution was applied to the embossed surface of the polyurethane layer and dried under the same conditions as in (1) to fill the concavities and convexities of the embossed surface of the polyurethane layer.

(5) Acrylic adhesive layer

An acrylic adhesive solution obtained by mixing 50 parts by mass of

SK1506BHE, 17 parts by mass of YM-5, and 33 parts by mass of methyl isobutyl ketone (MIBK) was applied to a G2 PET film subjected to release treatment, and this was dried for 5 minutes at 80°C and then for 5 more minutes at 120°C to form an acrylic adhesive layer with a thickness of 40 μπι.

(6) The acrylic adhesive layer formed in (5) was heat-laminated at 50°C on the embossed surface of the polyurethane layer in which the concavities and convexities were filled in (4).

(7) A decorative layer was formed by sequentially gravure-printing a

polyurethane adhesive containing a phenoxy resin with 1 plate, ink with 5 plates, and then a polyurethane adhesive containing a phenoxy resin with 1 plate on the G2 PET film. A D-6260 polyurethane solution was applied thereon in a coated amount such that the dried thickness on a flat surface would be 10 μπι, and this was dried under the same conditions as in (1) to form a smoothing resin layer.

(8) After the G2 PET film on the polyurethane layer of the laminate formed in (6) was removed, the decorative layer coated with polyurethane in (7) and the polyurethane layer were heat-laminated at 120°C so that the decorative layer and the polyurethane layer were in contact.

(9) The G2 PET film on the decorative layer was removed, and a S014G acrylic film was heat-laminated at 120°C onto the decorative layer as a surface member to obtain the decorative sheet of Example 1.

Comparative Example 1

(1) A D-6260 polyurethane solution was applied to a G2 PET film and dried for 5 minutes at 80°C and then for 5 more minutes at 100°C to form a polyurethane layer with a thickness of 25 μπι.

(2) Using an embossing cylinder having a hairline-pattern design, the shape of a hairline pattern was transferred to the surface of the polyurethane layer formed in (1) at a cylinder temperature of 190°C.

(3) Tin was deposited onto the embossed surface of the polyurethane layer under the following conditions (OD value: 1.1-1.2).

Device: vacuum deposition device EX-400 (available from ULVAC)

Energy source for depositing target metal: electron beam

Thickness of tin deposition layer: 430 Angstrom

Tin deposition layer forming rate: 5 Angstrom/sec (4) A D-6260 polyurethane solution was applied to the embossed surface of the polyurethane layer and dried under the same conditions as in (1) to fill the concavities and convexities of the embossed surface of the polyurethane layer.

(5) Acrylic adhesive layer

An acrylic adhesive solution obtained by mixing 50 parts by mass of

SK1506BHE, 17 parts by mass of YM-5, and 33 parts by mass of methyl isobutyl ketone (MIBK) was applied to a G2 PET film subjected to release treatment, and this was dried for 5 minutes at 80°C and then for 5 more minutes at 120°C to form an acrylic adhesive layer with a thickness of 40 μπι.

(6) The acrylic adhesive layer formed in (5) was heat-laminated at 50°C on the embossed surface of the polyurethane layer in which the concavities and convexities were filled in (4).

(7) A decorative layer was formed by sequentially gravure-printing an adhesive with 1 plate, ink with 5 plates, and then an adhesive with 1 plate on the G2 PET film.

(8) After the G2 PET film on the polyurethane layer of the laminate formed in (6) was removed, the decorative layer of (7) and the polyurethane layer were heat-laminated at 120°C such that the decorative layer and the polyurethane layer were in contact.

(9) The G2 PET film on the decorative layer was removed, and a S014G acrylic film was heat-laminated at 120°C onto the decorative layer as a surface member to obtain the decorative sheet of Comparative Example 1.

Surface roughness measurements of the decorative layer and the smoothing resin layer

Using a Mitutoyo SURFTEST SV-3100 surface roughness measuring device

(Mitutoyo Co., Ltd., Kawasaki-shi, Kanagawa, Japan), a D-6260 polyurethane solution was applied to the decorative layer formed in (7) of Example 1 such that the dried thickness on the smooth surface was 10 μπι, and the surface roughness Rz (μπι) before and after coating was measured. The surface roughness prior to coating corresponds to the surface roughness Rzl of the printing surface of the decorative layer, and the surface roughness after coating corresponds to the surface roughness Rz2 of the smoothing resin layer. The results are shown in Table 2. Note that the coating direction with respect to the sheet is defined as the Machine Direction (MD), while the direction orthogonal to this direction is defined as the Cross

Direction (CD), and the surface roughness was measured in each of these directions. The rate of improvement in Table 2 is (Rzl-Rz2)/Rzl (%). Table 2

Cutoff value: 0.25 mm, evaluation measurement length: 1.25 mm

Viscoelasticity properties of the smoothing resin layer

The viscoelasticity properties of the smoothing resin layer were measured in accordance with the following procedure. A D-6260 polyurethane solution was applied to a G2 PET film and dried for 5 minutes at 80°C and then for 5 more minutes at 100°C to form a polyurethane layer with a thickness of 25 μπι as a smoothing resin layer. When measurements were taken in a stretched mode at a heating rate of 5.0°C/min and a frequency of 10 Hz in the temperature range from -40°C to 200°C using an ARES dynamic viscosity measuring device (available from TA Instruments, Shinagawa-ku, Tokyo, Japan), the viscoelasticity property was 8.55 x 10 ⁷ Pa at 100°C and 6.79 x 10 ⁶ Pa at 150°C, and the storage modulus in the temperature range from 100°C to 150°C in the stretched mode was within the range from 1 x 10 ⁶ Pa to 1.5 x 10 ⁸ Pa.

Vacuum molding

Using a double-sided vacuum molding device (available from Fu-se Vacuum Forming, Habikino-shi, Osaka, Japan), the decorative sheets of Example 1 and

Comparative Example 1 were attached at 145 °C by vacuum-pressure molding to plastic substrates (flat sheet and semi -cylindrical shape).

Image clarity

The states of glare of an indoor fluorescent lamp on the decorative sheet surface were compared. The results are shown in photographs in FIG. 3 (Example 1) and FIG. 4

(Comparative Example 1). In these figures, the glare of the fluorescent lamp can be seen in the portions enclosed by ellipses. In the decorative sheet of Example 1, the glare of the fluorescent lamp is clear, and the decorative sheet surface is smooth. In the decorative sheet of

Comparative Example 1, the glare of the fluorescent lamp is unclear, and the light is reflected in a particulate manner in the vicinity thereof, and therefore it is inferred that concavities and convexities are formed on the surface of the decorative sheet. Surface roughness measurement of the decorative sheet

As an index for obj ectively evaluating the image clarity of the decorative sheet surface, the undulated surface roughnesses Wza and Wzb before and after vacuum-pressure molding were measured in each of the MD and CD directions for the decorative sheets of Example 1 and Comparative Example 1. The results are shown in Table 3 together with the visual image clarity. In addition, the values of the surface roughness Ra before and after vacuum-pressure molding, which were measured together with the undulated surface roughness Wz, are shown in Table 4. The undulated rate of improvement in Table 3 is (Wza- Wzb)/Wza (%), and the planar rate of improvement in Table 4 is (Raa-Rab)/Raa (%).

Table 3

λί: 2.5 mm, c: 250 μπι

Table 4

Cutoff value: 0.25 mm, evaluation measurement length: 1.25 mm

In the decorative sheet of Comparative Example 1, the surface roughness increases after molding, and in particular when stretched and attached to a curved surface. This suggests that in Comparative Example 1 , in which no smoothing resin layer is present, the surface roughness of the decorative sheet increases due to a combination of the propagation of the concavities and convexities on the printing surface of the decorative layer to the decorative sheet surface during molding, the stretching and thinning of the decorative sheet during molding.