Patent Description:
Hitherto, sheet-like wallpapers having good designs have been used on buildings' internal walls and ceilings.

These wallpapers are typically formed of noninflammable base paper or noninflammable non-woven fabric from the viewpoints of an adhesive property on wall surfaces, noninflammability, and fireproofness. Further, these wallpapers have scratch-resistant, stainproof resin layers on the surfaces.

The resin layers are formed of polyvinyl chloride-based resins containing plasticizers mainly formed of ester oils. Furthermore, it has been widely known to further add foaming agents to the resin layers to foam the resin layers and impart flexibility to the resin layers, or to emboss the resin layers to impart stereoscopic decorations to the resin layers.

In recent years, attempts have been made to print desired images on the resin layers by inkjet methods and apply the resin layers to the wallpapers. However, there is a problem that the polyvinyl chloride-based resins contained in the resin layers have a significantly poor ink absorbability due mainly to the materials' properties.

Hence, there is proposed an embossed wallpaper producing method of additionally providing an ink receiving layer as the upper layer of the resin layer formed of a vinyl chloride resin, to promote permeation and fixing of an ink (see, e.g., PTL <NUM>).

As inks used for printing images, oil-based inks have been used. Advantages of the oil-based inks include a high image density attributable to solubility/dispersibility of coloring materials at high densities, a good water resistance, and a good anti-clogging property in head nozzles of inkjet apparatuses. Particularly, in recent years, excellent light resistance and ozone resistance of the oil-based inks have brought the oil-based inks to be widely used on wallpapers for large-sized POP arts, advertisements, and displays.

For example, there is proposed a semi-gloss oil-based inkjet print sheet formed of a support and an overlying oil-based ink receiving layer mainly formed of a vinyl chloride-acrylic resin copolymer having a glass transition temperature prescribed within a desired range (see, e.g., PTL <NUM>). Additionally, <CIT> might be cited as prior art.

The present invention has an object to provide a method for coating inks, where the method can provide an image with a high image density and an excellent chromogenic property when printing the image on a target such as a wallpaper with a plurality of kinds of inks having a good ink droplet spreadability on the target.

According to one aspect of the present invention, a method for coating inks of the present invention is a method for coating a plurality of kinds of inks on a target by an inkjet method individually. The target includes a base and a gel layer provided on the base and containing a vinyl chloride resin and a plasticizer. The plurality of kinds of inks are oil-based inks and include an ink x and an ink y that is to be discharged after the ink x is discharged. An interpenetration ratio Pxy of the ink y to the ink x is <NUM>% or greater but <NUM>% or less. The oil-based inks comprise an oil constituent comprising at least one of adipic acid esters and octanoic acid esters. The Hansen solubility parameter polarity term (δP) of the oil constituent is <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less.

The present invention can provide a method for coating inks, where the method can provide an image with a high image density and an excellent chromogenic property when printing the image on a target such as a wallpaper with a plurality of kinds of inks having a good ink droplet spreadability on the target.

A method for coating inks of the present invention is a method for coating a plurality of kinds of inks on a target by an inkjet method individually. The target includes a base and a gel layer provided on the base and containing a vinyl chloride resin and a plasticizer. The plurality of kinds of inks are oil-based inks and include an ink x and an ink y that is to be discharged after the ink x is discharged. An interpenetration ratio Pxy of the ink y to the ink x is <NUM>% or greater but <NUM>% or less. The oil-based inks comprise an oil constituent comprising at least one of adipic acid esters and octanoic acid esters. The Hansen solubility parameter polarity term (δP) of the oil constituent is <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less. The method further includes other steps as needed.

The method for coating inks of the present invention is based on the following finding. When oil-based inks are used in existing methods for producing embossed wallpapers, there is a problem that oil-based inks, most of which are non-volatile, have an extremely poor permeation/absorption property on the ink receiving layers. The method for coating inks of the present invention is also based on the following finding. Existing semi-gloss oil-based inkjet print sheets additionally need a step of forming an ink receiving layer to make the process complicated.

A method for producing a wallpaper of the present invention is the method for coating inks of the present invention where the target is a wallpaper. The method preferably includes a heating step and an embossing step and further includes other steps as needed.

The target includes a base and a gel layer provided on the base and containing a vinyl chloride resin and a plasticizer, and further includes other layers as needed.

As a characteristic of the target, it is preferable that when a free induction decay curve obtained by measuring the target by a pulse NMR method is decomposed to <NUM> curves attributed to a hard component and a soft component, the ratio of the hard component be in a range of <NUM>% or greater but <NUM>% or less. Further, it is preferable that a spin-spin relaxation time obtained by measuring the soft component by a Hahn echo method be <NUM> or longer but <NUM> or shorter.

When the ratio of the hard component and the spin-spin relaxation time of the soft component are in the ranges described above, liquid droplets of an ink landing on the target can satisfy both of a good wetting/spreading property and a good absorption property and can form an image having a good image density with slight ink bleed. A good image density means that beading can be suppressed.

It is preferable that the target have a good affinity with the oil-based inks and have a state of being capable of quickly absorbing the inks into the inside of the target. This performance is influenced by the fluidic state (molecular mobility) of the plasticizer contained in the gel layer of the target. When the spin-spin relaxation time, measured by the Hahn echo method, of the soft component obtained by the pulse NMR method is longer than <NUM> during printing on the target, the oil-based inks have a poorer wetting/spreading property and tend to form an image having a low image density and a poor solid coverage.

The reason for this result is considered as follows. An increased molecular mobility of the plasticizer in the gel promotes absorption of the landed inks into the gel, but in turn inhibits wetting/spreading of the ink in the horizontal direction. When the relaxation time is shorter than <NUM>, absorption of the landed inks into the target is significantly poor. This makes <NUM> colors likely to bleed (color bleed). In an extreme case, adjoining inks coalesce and attract each other to be repelled, and tend to make the image density extremely poor. The reason for this result is considered as follows. The molecular flow of, for example, the plasticizer is insufficient, to make the landed ink component stop at the surface of the target for long.

The spin-spin relaxation time, measured by the Hahn echo method, of the soft component obtained by measuring the target by the pulse NMR method is adjusted by controlling the state of the gel formed of the vinyl chloride resin and the plasticizer constituting the target. Specifically, it is possible to control the spin-spin relaxation time by varying the heating temperature or the heating time during formation of the gel layer on the base, or by varying the temperature of the target when the oil-based inks contact on the target during inkjet printing.

In the present invention, the pulse NMR measurement of the target can be performed in the manner described below, for example.

With MINISPEC MQ series for pulse NMR available from Bruker Corporation, a high-frequency magnetic field is applied in the form of pulses to the target put in an NMR tube, to tip the magnetization vector. The mobility of the molecules constituting the target is evaluated based on the time (=relaxation time) taken until the x and y components of the magnetization vector disappear.

For being used for the measurement, the target is weighed out in <NUM> in an NMR tube having a diameter of <NUM> and heated for <NUM> minutes in a preheater adjusted to the same heating temperature as in printing. Note that a sample would undergo a significant gel state change and come to have completely different properties if the sample once became higher than the set temperature and then became the predetermined temperature through cooling even though these temperatures are the same heating temperatures. Hence, it is indispensable to start heating the sample after adjusting the preheater to the predetermined temperature.

By exponential approximation with ORIGIN <NUM> (available from Origin Lab Corporation), a spin-spin relaxation time (t2) is calculated from a decay curve obtained by the Hahn echo method in the pulse NMR measurement. The spin-spin relaxation time is known to be shorter as the molecular mobility is lower and longer as the molecular mobility is higher.

The decay curve obtained by the Hahn echo method in the pulse NMR measurement is a superimposition of relaxation curves attributed to <NUM> components, namely the hard component having a low molecular mobility and the soft component having a high molecular mobility.

By bi-exponential approximation with ORIGIN <NUM> (available from Origin Lab Corporation), the obtained echo signal is decomposed to <NUM> relaxation curves attributed to the <NUM> components. In this way, spin-spin relaxation times (tH, tS) of the respective components can be calculated.

<FIG> plots <NUM> relaxation curves including an example of the decay curve, and the relaxation curves of the hard component and the soft component obtained by decomposing the decay curve.

The hard component having a low molecular mobility is typically a component attributable to a hard material, and the soft component having a high molecular mobility is attributable to a soft material.

The spin-spin relaxation time is known to be shorter as the molecular mobility is lower and longer as the molecular mobility is higher.

Hence, it can be said that of the <NUM> relaxation curves resulting from the decomposition, the relaxation curve having a shorter spin-spin relaxation time represents the hard component, and the relaxation curve having a longer spin-spin relaxation time represents the soft component.

The target is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably a wallpaper.

The base is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the base include plastic film, synthetic paper formed of synthetic fiber, and sheet of non-woven fabric. Among these bases, a base having water resistance is preferable. When the target is a wallpaper, it is preferable that the base have a mechanical strength and heat resistance suitable as the base of the wallpaper.

The base used for the wallpaper is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the base include paper such as natural paper and synthetic paper, plastic film, non-woven fabric, fabric, wood, and metallic thin film.

Examples of the plastic film include: polyester film; polypropylene film; polyethylene film; plastic film of, e.g., nylon, vinylon, and acrylic; and products obtained by pasting these films together.

The plastic film is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably uniaxially or biaxially stretched in terms of strength.

The non-woven fabric is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the non-woven fabric include non-woven fabric obtained by scattering polyethylene fibers in a sheet-like form and bonding the fibers by thermocompression bonding into a sheet shape.

The gel layer contains a vinyl chloride resin and a plasticizer, and further contains a foaming agent, a filler, a dispersant, a defoaming agent, an antiblocking agent, a thickener, and other components as needed.

The vinyl chloride resin is a general-purpose resin excellent in physical or chemical properties, and less expensive than other resins.

Examples of the vinyl chloride resin include soft vinyl chloride resins, semi-hard vinyl chloride resins, and hard vinyl chloride resins. One of these vinyl chloride resins may be used alone or two or more of these vinyl chloride resins may be used in combination.

The content of the vinyl chloride resin is preferably <NUM>% by mass or greater but <NUM>% by mass or less and more preferably <NUM>% by mass or greater but <NUM>% by mass or less of the total amount of the gel layer.

The plasticizer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the plasticizer include: phthalic acid ester-based plasticizers such as dinonyl phthalate (DNP), dioctyl phthalate (DOP, with HSP δP of <NUM> MPa<NUM>/<NUM>), didecyl phthalate (DDP), diisodecyl phthalate (DIDP, with HSP δP of <NUM> MPa<NUM>/<NUM>), diisononyl phthalate (diisononyl phthalate, DINP), ditridecyl phthalate (DTDP), and n-hexyl-n-decyl phthalate (NHDP); phosphoric acid ester-based plasticizers such as tri-<NUM>-ethylhexyl phosphate (TOP); adipic acid ester-based plasticizers such as didecyl adipate (DDA) and diisodecyl adipate (DIDA); trimellitic acid ester-based plasticizers such as trioctyl trimellitate (TOTM) and tri-n-octyl-n-decyl trimellitate (nonyl DTM); polyester-based plasticizers; epoxy-based plasticizers; sebacic acid ester-based plasticizers; azelaic acid ester-based plasticizers; citric acid ester-based plasticizers; glycolic acid-based plasticizers; ricinoleic acid-based plasticizers; maleic acid ester-based plasticizers; fumaric acid ester-based plasticizers; pyromellitic acid ester-based plasticizers; and itaconic acid ester-based plasticizers. One of these plasticizers may be used alone or two or more of these plasticizers may be used in combination.

It is possible to introduce the plasticizer into the gel layer by making the plasticizer coexist with the vinyl chloride resin during coating, so the plasticizer may be capsulated in the gel layer during gelation. In this way, the target having a high affinity with the oil-based inks can be produced.

The Hansen solubility parameter (HSP) polarity term (δP) of the plasticizer is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less and more preferably <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less.

The Hansen solubility parameter polarity term (δP) can be calculated with software such as a product named: HSPIP.

The content of the plasticizer is preferably <NUM> parts by mass or greater but <NUM> parts by mass or less relative to <NUM> parts by mass of the vinyl chloride resin. When the content of the plasticizer is <NUM> parts by mass or greater but <NUM> parts by mass or less, a gel layer in which the vinyl chloride resin is swelled and solvated by the plasticizer can be obtained.

The foaming agent is not particularly limited, may be appropriately selected depending on the intended purpose, and is preferably a foaming agent commonly used for wallpapers.

Examples of the foaming agents include inorganic foaming agents, organic foaming agents, and microcapsule foaming agents. One of these foaming agents may be used alone or two or more of these foaming agents may be used in combination.

Examples of the organic foaming agents include azodicarboxylic acid amide (ADCA), azobis isobutylnitrile (AIBN), p,p'-oxybisbenzenesulfonyl hydrazide (OBSH), and dinitrosopentamethylene tetramine (DPT).

Examples of the inorganic defoaming agents include inorganic carbonates such as sodium hydrogen carbonate.

Examples of the filler include aluminum hydroxide, magnesium hydroxide, barium hydroxide, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, ferrous hydroxide, basic zinc carbonate, basic lead carbonate, silica sand, clay, talc, silicas, titanium dioxide, and magnesium silicate. Among these fillers, calcium carbonate, magnesium carbonate, aluminum hydroxide, and magnesium hydroxide are preferable.

The plurality of kinds of inks are oil-based inks, include an ink x and an ink y that is to be discharged after the ink x is discharged, and further include other inks as needed.

The oil-based inks preferably contain an oil constituent (solvent) and a colorant, and more preferably contain a dispersant, a binder resin, and other components as needed.

The oil constituent (solvent) comprises at least one of adipic acid esters and octanoic acid esters, and otherwise is not particularly limited, may be appropriately selected depending on the intended purpose, and preferably contains an ester oil as the main component. When the ester oil is the main component of the oil constituent, an image having a good image quality can be formed by performing printing in a heating condition on a gel layer containing a plasticizer, even without a special ink receiving layer for inkjet inks. This has been impossible with existing techniques.

Examples of the oil constituent (solvent) include: phthalic acid esters such as dibutyl phthalate, dicapryl phthalate, diisodecyl phthalate, dioctyl phthalate (DOP), diisononyl phthalate, dioctyl phthalate, butyl-<NUM>-ethylhexyl phthalate, and di-<NUM>-ethylhexyl phthalate; adipic acid esters such as dioctyl adipate (diethylhexyl adipate: DOA, with HSP δP of <NUM> MPa<NUM>/<NUM>) and diisononyl adipate (DINA); sebacic acid esters such as dibutyl sebacate, dioctyl sebacate, and diisononyl sebacate; azelaic acid esters such as dibutyl azelate, dioctyl azelate, and diisononyl azelate; lauric acid esters such as methyl laurate, ethyl laurate, and isobutyl laurate; myristic acid esters such as isopropyl myristate, isocetyl myristate, and octyldodecyl myristate; palmitic acid esters such as isopropyl palmitate and octyl palmitate; octanoic acid esters such as cetyl octanoate, octyl octanoate (ethylhexyl ethylhexanoate: OOE), and isononyl octanoate; and isononylic acid esters such as ethylhexyl isononanoate and isononyl isononanoate. One of these oil constituents may be used alone or two or more of these oil constituents may be used in combination.

Among these oil constituents, adipic acid esters such as dioctyl adipate and diisononyl adipate and octanoic acid esters such as octyl octanoate are preferable.

The Hansen solubility parameter polarity term (δP) of the oil constituent (solvent) is <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less and more preferably <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less.

The content of the oil constituent (solvent) is preferably <NUM>% by mass or greater and more preferably <NUM>% by mass or greater but <NUM>% by mass or less of the total amount of the inks. When the content of the oil constituent is <NUM>% by mass or greater, image qualities can be improved.

The colorant is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the colorant include: pigments such as carbon black, azo-based pigments, phthalocyanine-based pigments, nitroso-based pigments, nitro-based pigments, built dye-based pigments, mordant dye-based pigments, basic dye-based pigments, acid dye-based pigments, and natural dye-based pigments: and oil colors such as diazo dyes and anthraquinone-based dyes. One of these colorants may be used alone or two or more of these colorants may be used in combination. Among these colorants, pigments are preferable.

The content of the colorant is preferably <NUM>% by mass or greater but <NUM>% by mass or less and more preferably <NUM>% by mass or greater but <NUM>% by mass or less of the total amount of the inks. When the content of the colorant is <NUM>% by mass or greater but <NUM>% by mass or less, image qualities can be improved.

It is preferable that the oil-based inks have a heating loss of less than <NUM>% by mass when left to stand at <NUM> degrees C for <NUM> hour, from the viewpoints that the inks will not undergo property changes by volatilization and can be printed stably and provide good image qualities by an inkjet method.

The plurality of kinds of inks include the ink x and the ink y that is to be discharged after the ink x is discharged. An interpenetration ratio Pxy of the ink y to the ink x is <NUM>% or greater but <NUM>% or less, preferably <NUM>% or greater but <NUM>% or less, and more preferably <NUM>% or greater but <NUM>% or less. When the interpenetration ratio Pxy is <NUM>% or greater, the ink x and the ink y do not overlap with each other much, so the colors of the images formed of these inks can have intensities in suitable absorption wavelength ranges, leading to improvement of image qualities. When the interpenetration ratio Pxy is <NUM>% or less, the ink y is prevented from spreading too widely on a fixed image of the ink x and from spreading on the surface of a fixed image other than a fixed image of an ink intended to be overlapped by the ink y in printing in actual use, resulting in suppression of saturation degradation due to mixing of an unintended color, leading to improvement of image qualities. When the interpenetration ratio Pxy is <NUM>% or greater but <NUM>% or less, liquid droplets of the inks can spread well, the chromogenic property of secondary colors can be good, and an image having good image qualities can be formed. Even when the target is a wallpaper, so long as the interpenetration ratio Pxy is <NUM>% or greater but <NUM>% or less, an image printed on the wallpaper can keep good image qualities even if the wallpaper is heated and embossed after printing.

The interpenetration ratio Pxy will be described in detail with reference to <FIG> and <FIG>.

<FIG> are exemplary views illustrating a case where a blue image is formed with a cyan ink and a magenta ink. A liquid droplet of a cyan ink <NUM>, defined as the ink x, is applied on the target (<FIG>). The cyan ink <NUM> is absorbed into and fixed on a target <NUM> (<FIG>). When the surface becomes smooth, a liquid droplet of a magenta ink <NUM>, defined as the ink y, is then applied on an edge of the position to which the cyan ink <NUM> is applied (<FIG>). Here, the liquid droplet of the magenta ink <NUM> is about to spread onto the fixed image of the cyan ink <NUM> on the target <NUM> (<FIG>). Therefore, the liquid droplet of the magenta ink gradually overlaps the fixed image of the cyan ink (<FIG>), to form a blue image (<FIG>).

The interpenetration ratio Pxy is a value ((Ay/Ax)×<NUM>) obtained by dividing an area Ay by an area Ax and expressing the result in percentage, where the area Ax is the area of the fixed image of the cyan ink, of which liquid droplet is fixed first, and the area Ay is the area of the overlapping portion between the fixed images of the liquid droplets of the cyan ink and the magenta ink.

An example of the interpenetration ratio Pxy is presented above using the cyan ink and the magenta ink. This relationship can be established for all secondary color formation patterns. In all combinations of the ink x and the ink y selectable from the plurality of kinds of inks, the interpenetration ratio Pxy is preferably <NUM>% or greater but <NUM>% or less, more preferably <NUM>% or greater but <NUM>% or less, and particularly preferably <NUM>% or greater but <NUM>% or less.

Examples of the combinations of the inks include a case of printing an image of a cyan ink on a fixed image of a magenta ink or a yellow ink; a case of printing an image of a yellow ink on a fixed image of a magenta ink or a cyan ink; and a case of printing an image of a magenta ink on a fixed image of a yellow ink or a cyan ink.

It is preferable that the ink x and the ink y each be any one selected from a cyan ink, a magenta ink, and a yellow ink, and that the ink x and the ink y be different colors.

The dispersant can adjust the surface tension of the inks. This makes it possible to improve permeability of the inks into the target.

The dispersant is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the dispersant include polyamide, polyurethane, polyester, polyurea, epoxy resins, polycarbonate, urea resins, melamine resins, phenol resins, polysaccharides, gelatin, gum Arabic, dextran, casein, proteins, natural rubbers, carboxypolymethylene, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, cellulose, ethyl cellulose, methyl cellulose, nitro cellulose, hydroxyethyl cellulose, cellulose acetate, polyethylene, polystyrene, polymers or copolymers of (meth)acrylic acid, polymers or copolymers of (meth)acrylic acid esters, (meth)acrylic acid-(meth)acrylic acid ester copolymers, styrene-(meth)acrylic acid copolymers, styrene-maleic acid copolymers, sodium alginate, fatty acids, paraffin, beeswax, privet, hydrogenated beef tallow, carnauba wax, albumin, and copolymers of these dispersants. One of these dispersants may be used alone or two or more of these dispersants may be used in combination. Among these dispersants, nitrogen atom-containing resin-based dispersants such as polyamide are preferable.

As the dispersant, a commercially available product may be used. Examples of the commercially available product include a product named: SOLSPERSE <NUM> and a product named: SOLSPERSE <NUM> (both available from Lubrizol Japan Limited). One of these commercially available products may be used alone or two or more of these commercially available products may be used in combination.

The content of the dispersant is preferably <NUM>% by mass or greater but <NUM>% by mass or less and more preferably <NUM>% by mass or greater but <NUM>% by mass or less of the total amount of the inks. When the content of the dispersant is <NUM>% by mass or greater but <NUM>% by mass or less, the dispersant can prevent aggregation of the dispersed colorant, a representative example of which is a pigment, and can improve dispersion stability.

The difference between the Hansen solubility parameter (HSP) polarity term (δP) of the plasticizer in the gel layer of the target and the Hansen solubility parameter (HSP) polarity term (δP) of at least one solvent in the inks is preferably <NUM> MPa<NUM>/<NUM> or less and more preferably <NUM> MPa<NUM>/<NUM> or less. When the difference is <NUM> MPa<NUM>/<NUM> or less, the wetting/spreading property of the inks on the target can be improved.

When an image is formed with <NUM> or more inks containing the solvent, in order to prevent a poor image quality, there is a need to not only impart a good wetting/spreading property to the inks on the base but also impart a wetting/spreading property to the liquid droplets of one of the inks on the fixed surface of the liquid droplets of any other of the inks. As described above, a wetting/spreading property between the base and the inks for obtaining good image qualities can be obtained with the use of the oil-based inks containing the oil constituent (solvent), which is similar to the plasticizer in the base. In order for the liquid droplets of one of the inks to have a wetting/spreading property on the fixed surface of the liquid droplets of any other of the inks, there is a need to select the kind of the colorant to be blended and the content ratios of the dispersant and solvent to be blended, in a manner that the inks concerned have a high affinity with each other. For example, when the pigment in one of the inks has a relatively low hydrophobicity and a relatively high hydrophilicity, a measure to increase the content of the dispersant to control the wetting/spreading property is taken. The measure to be taken is determined based on the relationship among the kind of the pigment, the combination of the dispersant and the solvent, and the other ink.

A method for coating inks of the present invention will be described below.

<FIG> is a schematic view illustrating an example of an inkjet-type ink coating apparatus used in the method for coating inks of the present invention. As illustrated in <FIG>, a target <NUM> including a gel layer on a base is preheated by a preheat drum <NUM>, and then conveyed to the inkjet discharging unit <NUM> while being heated at a constant temperature by a heating drum <NUM>. Here, liquid droplets of an ink discharged by the inkjet discharging unit <NUM> land on the target <NUM>. In this way, a desired image can be formed.

The target is obtained by forming a gel layer containing a vinyl chloride resin and a plasticizer on a base.

A method for coating the gel layer on the base is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the method include coating methods such as a knife coating method, a nozzle coating method, a die coating method, a lip coating method, a comma coating method, a gravure coating method, a rotary screen coating method, and a reverse roll coating method.

The step of producing the target may be added as a previous step before the ink coating step.

The vinyl chloride resin gelates by heating treatment after the coating, and can form a gel layer containing the plasticizer.

The temperature for gelation is preferably <NUM> degrees C or higher but <NUM> degrees C or lower. When the temperature is <NUM> degrees C or lower, it is possible to suppress generation of a plurality of grooves in the surface along with advancement of the gelation, leading to promotion of absorbability of the inks into the gel layer and improvement of image qualities. When the temperature is <NUM> degrees C or higher, it is possible to promote the gelation, suppress a printed image from being blurred, and obtain a desired image density.

A method for producing a wallpaper in the case where the target is a wallpaper will be described below.

The method for producing a wallpaper is the method for coating inks of the present invention where the target is a wallpaper. The method preferably includes a heating step and an embossing step and further includes other steps as needed.

As the case may be, the method for producing a wallpaper may include a heating step of heating a gel layer containing a foaming agent to foam the foaming agent, or may not include a heating step for foaming when a gel layer does not contain a foaming agent.

As the ink coating method, the same method as the method for coating inks of the present invention may be used.

The heating step is a step of heating a gel layer containing a foaming agent to foam the foaming agent.

The heating temperature is preferably <NUM> degrees C or higher but <NUM> degrees C or lower.

The embossing step is a step of forming a bossed-recessed pattern in the foamed gel layer of the target.

For the bossed-recessed pattern, well-known methods typically used for imparting bosses and recesses to, for example, wallpapers and decorative plates, such as embossing processing, chemical embossing processing, rotary screening processing, or flexographic printing may be selectively used.

The embossing step may employ a method of imparting bosses and recesses by processing with an embossing plate, chemical embossing processing, rotary screening, or flexographic printing.

The embossing step may employ any of a method of performing embossing with a cooling roller after heating, and a method of performing embossing in one step by hot roller embossing.

The embossing depth by the embossing processing is preferably <NUM> or greater but <NUM> or less. When the embossing depth is <NUM> or greater, a stereoscopic effect can be produced. When the embossing depth is <NUM> or less, abrasion resistance on the surface can be improved.

These steps may be performed individually batch-wise, but may also be performed serially.

In the present invention, other steps that may be typically employed in a wallpaper producing process may be appropriately selected as needed. Examples of the other steps include coating treatment for imparting scratch resistance.

Particularly, in the present invention, it is possible to prevent stickiness and improve a design property by providing a transparent protective layer by the coating treatment.

The transparent protective layer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the transparent protective layer include urethane-based resins, acrylic-based resins such as polymethyl methacrylate, and fluorine-based resins such as polyvinyl fluoride resins, polyvinylidene fluoride resins, and polyethylene fluoride resins.

As needed, the other steps may be employed both before and after each of the steps of coating the inks.

An image forming set of the present invention is an image forming set including a target and a plurality of kinds of inks to be coated on the target by an inkjet method individually. The target includes a base and a gel layer provided on the base and containing a vinyl chloride resin and a plasticizer. The plurality of kinds of inks are oil-based inks and include an ink x and an ink y that is to be discharged after the ink x is discharged. An interpenetration ratio Pxy of the ink y to the ink x is <NUM>% or greater but <NUM>% or less. The oil-based inks comprise an oil constituent comprising at least one of adipic acid esters and octanoic acid esters. The Hansen solubility parameter polarity term (δP) of the oil constituent is <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less.

As the target, the same as the target in the method for coating inks of the present invention or the method for producing a wallpaper of the present invention may be used.

As the plurality of kinds of inks, the same as the plurality of kinds of inks in the method for coating inks of the present invention may be used.

An image forming system of the present invention includes a target, a plurality of kinds of inks, and an image forming apparatus configured to coat the plurality of kinds of inks on the target by an inkjet method individually. The target includes a base and a gel layer provided on the base and containing a vinyl chloride resin and a plasticizer. The plurality of kinds of inks are oil-based inks and include an ink x and an ink y that is to be discharged after the ink x is discharged. An interpenetration ratio Pxy of the ink y to the ink x is <NUM>% or greater but <NUM>% or less. The oil-based inks comprise an oil constituent comprising at least one of adipic acid esters and octanoic acid esters. The Hansen solubility parameter polarity term (δP) of the oil constituent is <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less.

An ink set of the present invention is an ink set including an ink x and an ink y to be coated on a target by an inkjet method. The target includes a base and a gel layer provided on the base and containing a vinyl chloride resin and a plasticizer. The ink x and the ink y are oil-based inks. An interpenetration ratio Pxy of the ink y to the ink x is <NUM>% or greater but <NUM>% or less. The oil-based inks comprise an oil constituent comprising at least one of adipic acid esters and octanoic acid esters. The Hansen solubility parameter polarity term (δP) of the oil constituent is <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less.

As the target, the same as the target in the method for coating inks of the present invention may be used.

As the ink x and the ink y, the same as the plurality of kinds of inks in the method for coating inks of the present invention may be used.

The present invention will be more specifically described below by way of Examples. However, the present invention should not be construed as being limited to these Examples.

Dioctyl phthalate as a plasticizer (available from Tokyo Chemical Industry Co. ) (<NUM> parts by mass) and a Ba/Zn-based stabilizer for vinyl chloride as a stabilizer (available from Tokyo Chemical Industry Co. ) (<NUM> parts by mass) were added together, stirred well, and mixed. To the resultant, an emulsion-polymerized polyvinyl chloride resin (product name: PSL-<NUM>, available from Kaneka Corporation) (<NUM> parts by mass), azodicarboxylic amide as a defoaming agent (available from Tokyo Chemical Industry Co. ) (<NUM> parts by mass), calcium carbonate (<NUM> parts by mass), and titanium dioxide (<NUM> parts by mass) were added, to obtain a mixture liquid. With a coater, the obtained mixture liquid was coated on a sheet having a mass of <NUM>/m<NUM> (product name: ECOCOAT IJ80, available from Sakurai Co. ) in a coating amount of <NUM>/m<NUM>, and left to stand in an oven at a heating temperature of <NUM> degrees C for a heating time of <NUM> seconds, to bring the polyvinyl chloride sol into a pre-gel state, to obtain a target (wallpaper) <NUM>.

A target (wallpaper) <NUM> was obtained in the same manner as in Target production example <NUM>, except that the composition of Target production example <NUM> was changed to the composition presented in Table <NUM> below.

Product names and supplier names of the components presented in Table <NUM> are as follows.

The targets <NUM> and <NUM> were measured by heating-temperature-varied pulse NMR according to the measuring method described below.

With MINISPEC MQ series for pulse NMR available from Bruker Corporation, the targets <NUM> and <NUM> were measured according to (<NUM>) to (<NUM>) below to obtain the ratio of a hard component and a spin-spin relaxation time of a soft component by a Hahn echo method. The ratio of the hard component, and the spin-spin relaxation time of the soft component at each heating temperature are presented in Table <NUM> below.

For being used for the measurement, the target was weighed out in <NUM> in an NMR tube having a diameter of <NUM> and heated for <NUM> minutes in a preheater adjusted to the same heating temperature as in printing. Note that a sample would undergo a significant gel state change and come to have completely different properties if the sample once became higher than the set temperature and then became the predetermined temperature through cooling even though these temperatures are the same heating temperatures. Hence, it was indispensable to start heating the sample after adjusting the preheater to the predetermined temperature.

By exponential approximation with ORIGIN <NUM> (available from Origin Lab Corporation), a spin-spin relaxation time (t2) was calculated from a decay curve obtained by the Hahn echo method in the pulse NMR measurement.

The decay curve obtained by the Hahn echo method in the pulse NMR measurement was a superimposition of relaxation curves attributed to <NUM> components, namely the hard component having a low molecular mobility and the soft component having a high molecular mobility.

By bi-exponential approximation with ORIGIN <NUM> (available from Origin Lab Corporation), the obtained echo signal was decomposed to <NUM> relaxation curves attributed to the <NUM> components. In this way, spin-spin relaxation times (tH, tS) of the respective components were calculated.

A pigment blue <NUM>:<NUM> as a pigment (PB15:<NUM>, available from Toyo Color Co. ) (<NUM> parts by mass), diisononyl adipate as a solvent (oil constituent) (available from Tokyo Chemical Industry Co. ) (<NUM> parts by mass), SOLSPERSE <NUM> as a dispersant (available from Lubrizol Japan Limited) (<NUM> parts by mass) were added together as a mixture, which was subjected to dispersion by mixing with a bead mill disperser, to obtain an ink 1C.

An ink 2C to an ink 10C, an ink <NUM> to an ink <NUM>, and an ink 1Y to an ink 10Y were obtained in the same manner as in Ink preparation example <NUM>, except that the composition of Ink preparation example <NUM> was changed to the compositions presented in Table <NUM> below.

The targets and inks obtained were combined as presented in Tables <NUM> to <NUM> below, and "interpenetration ratio Pxy" and "image density" were evaluated in the manners described below. The same evaluations were also performed for a case where the targets <NUM> and <NUM> were heated at <NUM> degrees C after the coating step and continuously processed with an embossing roll having a matte pattern. The results are presented in Tables <NUM> to <NUM> below.

The inks were combined in a manner to form a secondary color as presented in Tables <NUM> to <NUM> below. Liquid droplets of the inks in each of the ink combinations were dropped onto each target according to the measuring method described above, and the interpenetration ratio Pxy was obtained in the manner described below.

The targets <NUM> and <NUM> were secured to a hot plate with a heat-resistant double-face tape (product name: KAPTON No. <NUM>, available from Teraoka Seisakusho Co. ) and heated with the hot plate set to <NUM> degrees C such that the surface temperature of each target became <NUM> degrees C. Next, an inkjet printer (apparatus name: IPSIO GX5500, available from Ricoh Company, Ltd. ) filled with each of the inks was remodeled such that the hot plate was introduced into the ink printing portion of the inkjet printer. With the obtained image forming apparatus, a <NUM> by <NUM> color patch of a secondary color, which was blue, green, or red, was printed at <NUM> dpi in an image printing order presented in Tables <NUM> to <NUM> below (i.e., the ink x first and the ink y next), to obtain a solid image. In the obtained solid image, the image densities of the single colors constituting the secondary color (blue = C and M, green = C and Y, and red = M and Y) were measured with a reflective/color spectrophotometric densitometer (available from X-Rite Inc. The "image density" of cyan (C), magenta (M), or yellow (Y) was evaluated according to the evaluation criteria described below. The lower value of the image densities in the image formed with each ink combination was used for the evaluation. The grade B or higher is the pass level. A high image density means that it was possible to suppress beading.

Claim 1:
A method for coating inks, the method comprising
coating a plurality of kinds of inks on a target by an inkjet method individually,
wherein the target comprises a base and a gel layer that is provided on the base and comprises a vinyl chloride resin and a plasticizer,
wherein the plurality of kinds of inks are oil-based inks and comprise an ink x and an ink y that is to be discharged after the ink x is discharged,
wherein an interpenetration ratio Pxy of the ink y to the ink x is <NUM>% or greater but <NUM>% or less,
wherein the oil-based inks comprise an oil constituent comprising at least one of adipic acid esters and octanoic acid esters, and
wherein the Hansen solubility parameter polarity term (δP) of the oil constituent is <NUM> MPa<NUM>/<NUM> or greater but <NUM> MPa<NUM>/<NUM> or less.