HK1110280B - Printing method on curved surface and curved surface body printed by that method - Google Patents

Description

Method for printing on curved surface and curved printed body obtained by the method

Technical Field

The present invention relates to a method for printing with good accuracy on a printed object having a curved surface, and a curved printed object obtained by the method.

Background

In the past, as a method of performing various printing on a curved surface of a printing object having a curved surface, particularly a curved surface long in the longitudinal direction, a printing method using an elastic blanket has been known. That is, in the conventional blanket printing method, ink is applied to a printing original plate of an intaglio plate made of steel or plastic, excess ink on the convex portion is removed by a spatula, the surface of a soft curved elastic blanket is pressed against the printing original plate, the ink remaining in the concave portion of the printing original plate conductor is copied, and the elastic blanket is brought into contact with the curved surface of the object to be printed, thereby completing printing.

However, in this case, the printing original plate has been conventionally made of steel or plastic, and since the excess ink on the convex portion is removed after the ink is applied, it is necessary to make the concave portion have a sufficient depth in order to reliably retain the ink on the concave portion and to sufficiently transfer the ink to the elastic blanket, which causes a reduction in printing accuracy.

When printing is performed using the elastic blanket, if the unevenness of the printing original plate is large, the surface of the elastic blanket is greatly deformed, and printing cannot be performed with good accuracy. Further, since the plate is an intaglio plate, it is necessary to make the recess have a sufficient depth in order to reliably maintain the ink amount. However, since the elastic blanket is deformed greatly when the depth is deep and the ink at the bottom is transferred to the elastic blanket, the elastic blanket itself must be made soft enough to conform to the change of the unevenness, and the conditions are further deteriorated.

On the other hand, if the printing original plate is a relief plate, the ink may be applied only to the convex portions thereof, or the convex portions may be formed by the ink itself so that the amount of the concave-convex portions is smaller. Therefore, the elastic blanket itself may be made of a slightly hard material, and the surface of the elastic blanket may be deformed little because the unevenness may be small, and the amount of ink may be finely adjusted, so that printing may be performed with good precision. For curved surface printing using a relief plate and an elastic blanket, various techniques have been developed as described in, for example, japanese unexamined patent publication No. h 2-239972.

As described above, in the past, when printing on a printing object having a curved surface, particularly a curved surface that is long in the longitudinal direction, printing was performed using a combination of a curved printing blanket and an intaglio printing original plate, and therefore, printing accuracy was low and it was difficult to perform multicolor color printing. In particular, when the gravure plate is used, the amount of ink is large, and thus there is a disadvantage that printing accuracy such as fine dots is extremely poor.

Further, the shape and properties of the elastic blanket are almost set in accordance with an empirical thinking in setting of a shape having good flexibility conforming to a curved surface to be printed, setting of a material and a surface state which meet requirements for retention and separation of printing ink, and setting of conditions such as enabling printing with desired fidelity as a result, and the like, and the setting thereof takes much time and labor.

In particular, when forming a pattern on a curved printing surface having a long shape, for example, an automobile interior part, a so-called fluid printing method is used as a printing method, for example, in which a printing ink is applied to a water-soluble film and floated on the surface of an aqueous solution in a transfer tank to be transferred to the curved printing surface 10. In addition, there is a method of providing a film or a laminate having a pattern formed in advance by bonding or welding in the molding of a curved body.

However, the former is a large-scale device such as a transfer tank, which is expensive and has poor pattern accuracy. In the latter case, the process is complicated, and the pattern does not necessarily correspond to a curved surface.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method of printing on a curved surface capable of performing curved surface printing on a curved surface body having a long shape or a plurality of curved surface bodies arranged side by side in an advantageous manner for mass production and at a low cost with good printing accuracy, and a printed curved surface body obtained by the method.

As the method of printing to a curved surface of the present invention,

(1) comprising: applying printing ink on the convex part of the flat relief printing original plate with the height h of the convex part of the relief printing original plate being 3-50 μm; a step of pressing a rubber or rubber-like cylindrical elastic blanket having a curved surface of a predetermined shape set with respect to a curved surface of a curved surface body to be printed, against a relief printing original plate attached at a fixed position and coated with the printing ink, and copying the printing ink onto the curved surface of the predetermined shape; a step of moving a roller-shaped elastic blanket having the predetermined-shaped curved surface to which printing ink is transferred to contact the curved surface of the curved body to be printed, and printing the curved surface of the curved body to be printed, the curved surface having a uniform convex curvature radius Rn at least at each position in the width direction along the major axis direction thereof, the roller-shaped elastic blanket having a main axis cross section of the predetermined-shaped curved surface with respect to the convex curvature radius Rn, the main axis cross section being composed of two main curved surfaces and an end curved surface connecting smoothly the intersection of the two main curved surfaces, the two main curved surfaces having curvature radii R1 and R2 constituting the predetermined-shaped curved surface with respect to the curvature radius R of the main axis cross section of the convex curved surface of the curved body to be printed, the curvature radii R1 and R2 being 1 to 3 times the curvature radius R of the main axis cross section, and the printing ink being printed on the curved body to be printed, the value of the intersection of the distance L between the two centers of the radii of curvature R1 and R2 is 0.05 to 0.15 times the radius of curvature R of the main axis cross section, and the end curved surface has a radius of curvature equal to the radius of curvature of the curved surface body to be printed.

(2) In the above (1), the material of the roller-shaped elastic blanket is silicone rubber, and the hardness thereof is 5 to 40 as represented by JIS A-grade,

(3) in the above (1) or (2), the viscosity of the printing ink is 15 to 250PaS,

(4) the printing ink of the above (1) or (2), which has a viscosity 1/1.5 to 1/3 times the viscosity of a usual offset printing ink as a practical measure,

(5) in the above (1) or (2), the surface roughness of the roller-shaped elastic blanket is Hmax 0.5 to 2 μm,

(6) in the above (1) or (2), the image of the convex portion of the flat plate-shaped original relief printing plate on which the printing ink is applied is reduced or enlarged based on a ratio of an orthogonal projection of the curved surface of the curved body to be printed on the original relief printing plate to an actual length of the curved surface,

(7) in the above (1) or (2), the curved printing object is a curved printing object having a shape elongated in the longitudinal direction, or a printed matter in which a plurality of curved printing objects are arranged in the longitudinal direction.

In addition, as the curved printing surface body of the invention,

(8) surface printing is performed by the method for flexographic printing according to (1) to (7) above,

(9) in the above item (8), the curved printed object is an automobile part,

(10) in the above (8), the curved printed body is a steering wheel or an interior or exterior member of an automobile,

(11) in the above item (8), the curved printed object is an exterior member of an electronic device,

(12) in the above (8), the curved printed body is an exterior member of a cellular phone,

(13) in the above (8), the curved printed object is a decoration,

(14) in the above (8), the curved printed body is a spectacle frame in a decorative article.

According to the method of printing on a curved surface of the present invention, it is possible to print on a curved surface to be printed, particularly a curved surface of a curved surface to be printed having a shape relatively long in the longitudinal direction, with good accuracy, and to provide a curved surface to be printed obtained by the method at a low price.

Drawings

Fig. 1 is a drawing showing a relationship between the hardness (JIS a level) of a cylindrical elastic blanket 2 (silicone rubber) used in the present invention and printing accuracy.

Fig. 2 is a diagram showing the test results of the relationship between the height of the projection (C is the depth of the recess) and the printing accuracy of the printing original plate 3 of the present invention.

Fig. 3 is a drawing showing the relationship between the main radius of curvature r of the elastic blanket of the present invention and the offset distance X of the center thereof.

Fig. 4 is a schematic view showing a schematic shape of a curved-surface-body-to-be-printed sample 1 in example 1 of the present invention.

Fig. 5 shows the print object patterns applied to the relief printing original plate 3 in embodiment 1 of the present invention, (a) is a pattern parallel to the axial direction, and (b) is a pattern perpendicular to the axial direction.

Fig. 6 is an explanatory diagram showing the shape of the curved surface test piece 1 to be printed used in example 2.

Fig. 7 is a perspective reference view schematically showing the roller-shaped elastic blanket 2 in the present embodiment 2.

Fig. 8 is a diagram schematically showing a relationship between the main radius R of curvature of the cylindrical elastic blanket 2 and the center offset distance X, which corresponds to the main radius R of curvature of the curved body to be printed 10.

Detailed Description

The present invention is characterized in that the specification for producing the cylinder-shaped elastic blanket 2 to be intuitively and empirically determined in the past can be determined more easily, and that curved surface printing with high printing accuracy can be realized at high efficiency and low cost by combining an appropriate combination of the cylinder-shaped elastic blanket 2 obtained in accordance with the determined specification with a special relief printing original plate 3 having an extremely low difference in height of convex portions and further with a characteristic low-viscosity (thin) printing ink. Further, it is possible to provide a curved printed body 10 obtained more efficiently and at a lower cost by the curved surface printing method, particularly a steering wheel, an interior and exterior member, and the like of an automobile.

That is, the optimum specifications of the cylindrical elastic blanket 2 and the relief printing original plate 3 are particularly determined as follows.

(1) An elastic blanket shape corresponding to the shape of the curved body to be printed 10, particularly the curved shape of the curved body having a shape elongated in the longitudinal direction, an elastic blanket material (particularly hardness and elastic modulus),

(2) the surface characteristics (ink spreading property, separation property) of the elastic blanket for efficiently transferring the printing ink on the relief printing original plate 3 to the surface of the elastic blanket and efficiently printing the ink on the curved body 10 to be printed,

(3) the height and accuracy of the projections of the relief printing original plate 3 are set.

As the material of the roller-shaped elastic blanket 2, silicone rubber is mainly used. The surface properties of the cylindrical elastic blanket 2 are required to include ink absorbability to allow ink to be transferred from the relief printing original plate 3 to the surface of the elastic blanket, ability to absorb a solvent in the ink to increase the viscosity of the ink, separability to allow the ink to be completely transferred to the surface of the curved object to be printed 10, and ability to prevent the ink from remaining on the surface of the elastic blanket after printing on the curved object to be printed 10.

These properties are closely related to the performance of the printing ink used, but in terms of the cylindrical elastic blanket 2, the properties are determined by the surface free energy of the elastic blanket surface itself, and are largely influenced by the material of the elastic blanket and the form, particularly the surface roughness, of the elastic blanket surface.

That is, the adsorption property when the ink is transferred from the relief printing original plate 3 to the surface of the elastic blanket is opposite to the separability when the ink is completely transferred to the curved surface body to be printed 10 and the property for preventing the ink from remaining on the surface of the elastic blanket after printing on the curved surface to be printed, and it is difficult to change the properties depending on the blanket material itself in a short time in the printing process. Further, when the height difference of the curved body to be printed 10 is large, the deformation of the surface of the elastic blanket is of course large and more complicated.

The present inventors found through experiments that in the combination of the step (a) of transferring ink from the relief printing original plate 3 to the curved elastic blanket 2 (deformation of the surface of the elastic blanket from a curved surface to a flat surface), the step (B) of moving the elastic blanket to the position of the curved body to be printed 10 (deformation of the surface of the elastic blanket from a flat surface to a curved surface), and the step (C) of pressing the elastic blanket against the curved body to be printed 10 to perform curved printing (deformation of the surface of the elastic blanket from a positive curved surface to a negative curved surface), the ink retentivity of the surface of the curved elastic blanket can be changed within a certain roughness range to correspond to the above-described opposite properties in the actual working process of the cylindrical elastic blanket 2 of the present invention.

As a result of the comparative test described later, it was found that the surface roughness of the elastic blanket was not good when it was too fine or too coarse, and that the holding property was good but the separation property was poor when it was fine, and that the holding property was poor but the separation property was good when it was too coarse. Particularly, the holding property and the separation property are sufficiently good in the range of 0.5 to 2 μm, and the surface roughness of the printing curved elastic blanket of the present invention is preferably 0.5 to 2 μm.

The material of the cylinder-shaped elastic blanket 2 is preferably a silicone rubber which can balance the adsorption property when the ink is transferred from the relief printing original plate 3 to the surface of the elastic blanket, the separation property when the ink is completely transferred to the curved surface to be printed, and the property for preventing the ink from remaining on the surface of the elastic blanket after the printing is performed on the curved surface to be printed. Further, although the hardness of the silicone rubber to be practically used is usually 20 to 90, it is found from the results of the multiple tests that the material hardness (JIS class a) of the roller elastic blanket 2 is preferably about 3 to 40 and the deformation amount can be considered, and more preferably about 3 to 20, which is soft.

Fig. 1 is a drawing showing a relationship between hardness (JIS a grade) of a roll-shaped elastic blanket 2 (silicone rubber) and printing accuracy.

In the figure, a is a test result when the cylinder-shaped elastic blanket 2 (silicone rubber) of the present invention is used, and C is a test result when conventional letterpress printing is performed. As can be seen from the figure, the material hardness (JIS A grade) of the roller-shaped elastic blanket 2 is preferably about 3 to 20.

As described above, the surface shape of the roller-shaped elastic blanket 2 is changed in each of the steps of (a) transferring ink from the relief printing original plate to the curved elastic blanket (deformation of the surface of the elastic blanket from a curved surface to a flat surface), (B) moving the elastic blanket to the position of the curved body to be printed 10 (deformation of the surface of the elastic blanket from a flat surface to a curved surface), and (C) pressing the elastic blanket against the curved body to be printed 10 to perform curved printing (deformation of the surface of the elastic blanket from the curved surface of the roller-shaped elastic blanket 2 to the curved surface of the curved body to be printed 10). Therefore, the image transfer accuracy in the first step a is extremely important. The present invention is characterized in that the height of the convex part coated with ink on the relief printing original plate is as low as possible, so as to improve the image transfer precision and further improve the printing precision.

That is, the present invention is characterized by combining a cylinder-shaped elastic blanket 2 having appropriate hardness, a relief printing original plate having an extremely low projection height, and a printing ink having appropriate viscosity. This makes it possible to perform multicolor printing by curved surface printing while maintaining printing accuracy.

In this case, the flat plate-shaped relief printing original plate is made of an aluminum alloy plate, and the convex portion thereof is formed of a photosensitive agent.

The height of the convex part is 0.1 to 50 μm, preferably 0.1 to 25 μm, more preferably 0.1 to 15 μm, and it is important that the height is sufficient for transferring the ink to the roller elastic blanket 2.

In general, in the elastic blanket printing, an intaglio plate is used as the original plate. In general knowledge, the recessed portions of the gravure printing plate are formed by a photo-sensitive/etching method, and the depth thereof is at least about several tens of the thickness of the photosensitive agent coating. Further, since the ink remaining in the concave portion is transferred to the elastic blanket by scraping the ink from the convex portion of the intaglio plate master, the deep concave portion having a deep depth as the concave portion causes curved surface printing having a changed surface shape, and the ink transfer accuracy and thus the printing accuracy are poor.

In contrast, in the aspect of the present invention in which the ink applied to the convex portion of the relief printing original plate 3 having an extremely low height is transferred, by using the relief printing original plate 3 having the convex portion, the height h of the convex portion is 0.1 to 50 μm, preferably 0.1 to 25 μm, and more preferably 0.1 to 15 μm, it is possible to obtain a good printing accuracy even on the cylindrical elastic blanket 2.

Fig. 2 is a diagram showing a test result of a relationship between a height h of a projection (C is a depth of a recess) of the relief printing original plate 3 and printing accuracy.

As is clear from the figure, the peak of printing accuracy is present in a certain range of the height h of the convex portion or the depth of the concave portion, and in the case (A) of the present invention, the peak of printing accuracy is present in the height h of the convex portion of 0.1 to 50 μm and exceeds the peak of the conventional intaglio printing original plate (C), and is higher than the accuracy of the conventional relief printing (B) in the height h of 3 to 25 μm, and more preferably, in the height h of 0.1 to 15 μm.

If the height is 0.1 μm or less, the degree of freedom in the printing step becomes extremely low, which is not desirable.

The printing ink used is naturally selected to have a property of being adsorbed to the cylindrical elastic blanket 2 and absorbing solvent components in the ink to increase the viscosity of the ink, and a separability of being completely transferable, and to satisfy a property that the ink does not remain on the surface of the elastic blanket 2 after printing on the curved printing object 10, but in the present invention, it is very important to further select an ink that can be adapted to the extremely low height of the convex portion of the relief printing original plate 3. In practice, the choice is made taking into account the balance of these properties.

The applicant has found the following through a plurality of basic experiments and physical experiments.

As a result of many practical tests, the viscosity of the printing ink is preferably in the range of 5 to 500PaS (at 25 ℃). Further, when the height h of the convex portion of the relief printing original plate 3 is 0.1 to 15 μm, the viscosity must be 5 to 250PaS (at 25 ℃).

In the present invention, if the viscosity is less than 5PaS, dirt other than the image is generated on the relief printing original plate 3, which is not desirable.

On the other hand, if the viscosity is higher than 250PaS, the rubber is less likely to spread on the surface of the elastic blanket 2 for flexographic printing, that is, the adhesion to the surface of the elastic blanket 2 is deteriorated. In addition, when the height of the projection is 15 μm or less, sufficient printing accuracy cannot be ensured if the viscosity is 500PaS (at 25 ℃) or more.

In addition, as a practical measure of the viscosity of the printing ink of the present invention, the above condition can be satisfied when the viscosity is about 1 to 1/5 times as high as that of the offset printing ink used under the same condition in the ordinary offset lithography.

In order to perform curved surface printing with good precision, it is necessary to sufficiently conform the surface of the elastic blanket 2 to the curved surface of the curved surface body to be printed 10. For this purpose, the radial thickness of the elastic part of the cylindrical elastic blanket 2, in this case silicone rubber, must be such as to be able to conform sufficiently to the thickness T required for the relief of the curved surface. In the case of using silicone rubber, since the poisson's ratio is extremely large, the lateral deformation thereof with respect to the pressing direction is large, and therefore, the radial thickness T must be within a range capable of sufficiently absorbing the lateral deformation. As a result of the physical test, it is found that, in the case of a silicone rubber having a material hardness (JIS class a) of about 3 to 40, particularly a soft silicone rubber having a preferable material hardness of about 3 to 20, the radial thickness T of the cylindrical elastic (silicone rubber) blanket 2 needs to be at least 2 times or more the maximum difference in height H between irregularities on the curved surface 10 to be printed. If the value is less than this value, the curved surface cannot be sufficiently fitted.

It is also found that when the thickness T is 8 times or more of H, the contact state between the convex top surface of the curved body to be printed 10 and the outer peripheral surface of the cylindrical elastic blanket 2 is close to the contact state between the flat surface and the flat surface, and therefore, a phenomenon of non-printing occurs due to the presence of a small amount of air bubbles on the printing surface of the convex top surface portion.

Therefore, the radial thickness T of the roller-shaped elastic (silicone rubber) blanket 2 of the present invention is preferably 2H. ltoreq. T.ltoreq.8H at least with respect to the maximum difference H in height between the concavities and convexities on the curved surface body 10 to be printed.

In the case where the curved surface of the curved object to be printed 10 has a shape in which the amount of unevenness is small or a shape in which unevenness is smoothly changed at relatively long pitches, or in the case where a printed image to be printed is not an image requiring high accuracy, an elastic blanket using the outer periphery of a right cylinder as it is may be used as the cylindrical elastic blanket 2. The curved surface body to be printed 10, which gently changes in the longitudinal direction, may be configured to have a conical shape or a shape similar to a conical shape within the range of the thickness T.

When the cylindrical or conical roller blanket 2 is used and curved surface printing is required to be performed with higher accuracy, the outer peripheral surface of the cylindrical blanket 2 is stretched or compressed on the curved surface of the curved printing object 10 when printing is performed by the flat relief printing original plate 3, and therefore, the printing accuracy is lowered. Therefore, in this case, it is preferable to set an image corresponding to a portion which is stretched or compressed on the plate-shaped relief printing original plate 3 with respect to the final image on the curved body 10 to be printed as an image which is compressed or stretched in advance.

Basically, the curved surface of the curved surface body 10 to be printed is reduced or enlarged based on the ratio of the orthographic projection of the curved surface on the relief printing original plate 3 to the actual length of the curved surface.

When the outer peripheral shape of the cylindrical elastic blanket 2 is set to a curved surface specification corresponding to the curved surface of the curved surface body 10 to be printed, the following setting is required.

That is, the pressing contact between the outer peripheral shape of the cylindrical elastic blanket 2 and the curved surface of the curved surface body to be printed 10 is basically corrected by a plurality of experiments based on the HertzStress theory when the outer peripheral surface of the cylinder is in pressing contact with the curved surface, and a relatively simple specification setting method is derived.

In the present invention, a curved surface having a large curvature radius is targeted for a gentle curved surface, and a curved surface portion having a small curvature radius is locally present, and the curved surface body 10 to be printed may be processed as described below, that is, a curved surface printing method using the cylindrical elastic blanket 2 as a main printing method of the present invention, and a sheet blanket curved surface printing method may be combined with the curved surface portion having a small local curvature radius.

The shape of the elastic blanket 2 is mainly composed of 3 elements with respect to a cross-sectional curvature radius R in a cross section perpendicular to the long axis direction of the curved object to be printed 10.

That is, a curved surface portion formed by two major radii of curvature R of the elastic blanket, which can be obtained from fig. 3, corresponding to the cross-sectional radius of curvature R, and a portion rounded by an arc rt (an apex angle of about 25 °) inscribed in a top portion to which the curved surface portion is joined.

The shape of the elastic blanket 2 in the longitudinal direction may be set such that the outer peripheral shape in the longitudinal direction is set with reference to a longitudinal direction bus R1 connecting outermost convex portions of a cross section perpendicular to the longitudinal direction of the curved printing object 10, and with reference to the major curvature radius R01, R02, R03.

Even in this case, it is necessary to set the radial thickness T of the cylindrical elastic (silicone rubber) blanket 2 to 2H. ltoreq. T.ltoreq.8H at least with respect to the maximum difference H in height between the irregularities on the curved surface 10 to be printed, as described above.

The main radii of curvature r01, r02, r03. However, the length of the arc formed by the major radius of curvature is set so as to be suitable for printing a maximum of half a circumference on the curved object to be printed 10 having the cross-sectional radius of curvature R.

As a result of a plurality of tests, it was found that when the roller-shaped elastic blanket 2 is used, the major curvature radius R0 is preferably (1 to 3), more preferably (1 to 2), times the cross-sectional curvature radius R of the curved surface to be printed.

Fig. 3 is a diagram showing a relationship between a major radius of curvature r of a cross section of two curved surfaces which are identical and which constitute the elastic blanket 2 and an optimum distance X for moving the center thereof to the inside where the curved surfaces intersect each other. Fig. 8 schematically shows the relationship between the main radius R of curvature of the cylindrical elastic blanket 2 corresponding to the radius R of curvature of the cross section of the curved body to be printed 10 and the distance X of movement of the center thereof.

The moving distance X of the center can be selected from fig. 3.

When the major radius of curvature R0 is set to be large relative to the cross-sectional radius of curvature R of the same curved object to be printed 10, the distance X of movement of the center must be increased substantially in proportion to the major radius of curvature R0. In addition, when the cross-sectional curvature radius R of the curved surface object to be printed 10 is small, the moving distance X of the center needs to take a large value.

When the values of X and r0 are selected, the ratio k is preferably set to a value of X/r0 within a range of (0.05 to 0.15).

When the radial protrusion height difference H in the longitudinal direction is large, it is preferable to subtract an amount corresponding to an expansion amount Δ X in the tangential direction with respect to the roll-shaped elastic blanket 2 in the press-in direction, which is generated based on a value obtained by multiplying a difference Δ H of press-in amounts corresponding to the protrusion height difference H in the longitudinal direction by the poisson's ratio, from the above X.

When the curved surface object to be printed 10 is maximally pressed into the elastic blanket 2, the non-contact portion of the outer peripheral surface of the elastic blanket 2 adjacent to the press-fitting portion is distorted and deformed by the press-fitting depth (convex portion height difference H). Therefore, it is important to determine the relative position of the printing surface of the curved surface object to be printed 10 and the cylindrical elastic blanket 2 at the position where they start to contact each other, taking the distortion amount into consideration.

When the curved surface object to be printed 10 is configured to have different radii of curvature R1, R2.. cndot.in the longitudinal direction, the major radii of curvature R01, R02.. cndot.for the curved surfaces of the cylindrical elastic blanket 2 with respect to the major radii of curvature R1, r2... cndot.in the outer peripheral shape along the longitudinal direction may be set by the same method as the above-described setting of the major radii of curvature R with respect to the radii of curvature R.

[ example 1]

Fig. 4 is a schematic view showing a schematic shape of a curved-surface-body-to-be-printed sample 1 in example 1 of the present invention.

In the figure, 1 is a curved surface object to be printed, B is the width of the object, B₁Is the width (1), B of the sample₂Is the width (2) of the sample, B₃The width (3) of the test piece at the maximum convex part of the curved surface printing test piece, B₄Is the width (4) of the sample up to the maximum convex part, H is the height difference of the maximum convex part, R₁The radius of curvature of the maximum convex portion, and t is the thickness of the sample.

Fig. 5 shows the print object pattern formed on the relief printing original plate 3 in embodiment 1 of the present invention, (a) is a pattern parallel to the axial direction, and (b) is a pattern perpendicular to the axial direction.

Printing a curved surface body sample 1:

shape: referring to the materials in FIG. 1: polypropylene (Black)

L₂：200mm，B：100mm，R₁：60mm，H：15mm

(L₁：100，B₁：50，B₂：50，B₃：30，B₄：60，B₅: 10, t: 2 (unit: mm)

Roller-shaped elastic blanket 2:

right cylinder drum Dxd (shaft diameter) xL₀＝120mm×40mm×220mm

Silicone rubber hardness (JIS A grade) 15

Surface roughness 1.5s

Using ink:

UV type ink (color: silver viscosity: about 20PaS)

Relief printing original plate 3:

height of projection of photosensitive material of aluminum relief printing original plate is 5 μm

0.1mm parallel line continuous pattern (pitch 0.15 equal interval)

(a) A pattern parallel to the axial direction, (b) a pattern perpendicular to the axial direction

A printing machine:

horizontal moving type 3-level cylinder blanket printing machine (SHUHO 3 type)

A printing test was performed in the order of (a) a pattern parallel to the axial direction and (B) a pattern perpendicular to the axial direction, which are two kinds of continuous patterns of parallel lines of 0.1mm formed on an aluminum relief printing original plate, by aligning the longitudinal direction L of the printing curved body sample 1 with the axial direction of the cylinder-shaped elastic blanket 2, and (C) a step of smoothly rotating and contacting the cylinder-shaped elastic blanket 2 on the original plate, (B) a step of moving the elastic blanket 2 to the position of the printing curved body 10, and a step of smoothly pressing and contacting the elastic blanket 2 on the printing curved body 10 to perform curved surface printing.

When the pattern is a pattern (a) parallel to the axial direction, the pitch is increased by about several percent at the printing start side ends b and c, and the pitch error gradually decreases toward the convex portions, so that good printing accuracy is maintained at the convex portions. The printing accuracy at the printing end e on the printing end side is as good as that of the raised portion due to the presence of the non-printing width B5 (5 mm in this case).

When the line printing of example 1 was performed on the longitudinal ends a and d of the curved surface body sample 1 to be printed, the printing accuracy was hardly deteriorated.

On the other hand, when the pattern is the pattern (b) perpendicular to the axial direction, a printing error is clearly observed at the end edge portion in the longitudinal direction of the curved surface printing sample. However, if the error is within 5mm from the end and the maximum height difference of the projection is about 15mm, the problem can be solved by avoiding printing at 5mm from the end or correcting the plate pitch in advance. On the printing start side and the printing end side, almost no printing error was observed. Therefore, in the case of a simple straight pattern, it is preferable to print a pattern in which the length of the lines is in the direction perpendicular to the long axis direction, that is, in the direction perpendicular to the axial direction of the cylindrical elastic blanket 2.

When the axis of the radius of curvature of the convex portion of the curved surface printing sample is aligned with the direction perpendicular to the axial direction of the cylindrical elastic blanket 2, it is necessary to make the number of convex portions following the axis of the cylindrical elastic blanket 2 at most 2, and to make the radius of curvature of the convex portions large and the height difference as small as possible.

In the case where the height difference of the convex portions is large and the case where two convex portions exist, the outer peripheral shape of the cylindrical elastic blanket 2 can be corrected, but the distance between the two convex portions needs to be a certain range or more so that the long-axis direction correction shapes of the portions corresponding to the convex portions of the cylindrical elastic blanket 2 do not interfere with each other.

That is, in order to correct the outer peripheral shape of the cylindrical elastic blanket 2 in the longitudinal direction, it is necessary to determine the major radius of curvature R1 and the eccentric distance X of the cylindrical elastic blanket 2 in the longitudinal direction from R1 of the printing curved body as described above, and to make the outer peripheral surface formed by the major radius of curvature R1 in the longitudinal direction and the height corresponding to the height difference H of the convex portion of the printing curved body 10 slightly distant from each other by setting at least the intersection point of the two as an interference limit.

[ example 2]

FIG. 6 is an explanatory view showing the shape of a curved surface-printed sample 1 used in example 2, wherein (a) is a perspective reference view, (b) is a cross-sectional reference view taken along the line A-A', (c) is a cross-sectional reference view taken at the maximum convex portion, and (d) is H₁Partial end view reference drawing, (e) is H₂Partial end faces are referenced.

Fig. 7 is a perspective reference view schematically showing the shape of the roller-shaped elastic blanket 2 in the present embodiment 2. (a) The polarity of the unevenness of the roller-shaped elastic blanket 2 is the same as the polarity of the shape of the curved surface-printed sample 1, and (b) the polarity is opposite to the polarity of the shape of the curved surface-printed sample.

The specifications in this example 2 are as follows.

Printed curved surface sample 1: (refer to FIG. 1)

L×B×H₃×R₁＝110×55×15×110

(L₁：40，L₂：70，R₂：45，R₃：75，R₄：35，H：10，H₁：10，H₂: 5 (unit: mm)

Materials: polypropylene material

Roller-shaped elastic blanket 2:

drum D × D (axial diameter) × L120 mm × 40mm × 220mm in a substantially cylindrical shape

(a)r1：132(k＝0.12)，r2：54(k＝0.14)，

r3：90(0.14)，r4：42(k＝0.14)，

l 1: 80, l 2: 140 (unit: mm)

(b)r’₁：110(k＝0.05)，r’₂：45(k＝0.05)，

r’₃：75(k＝0.05)，r’₄：35(k＝0.05)，

l’₁：80，l’₂: 140 (unit: mm)

Material silicon rubber

Hardness (JIS A grade) 15

Surface roughness 2 μm

Using ink UV type ink (color: brass)

Relief printing original plate 3:

height of projection of photosensitive material of aluminum relief printing original plate is 5 μm

Continuous wood grain pattern

A printing machine:

horizontal moving type 3 level blanket printing machine (SHUHO 3 type)

The results of printing using the two types of cylindrical elastic blankets 2 (a) and (b) in example 2 were compared with those of printing using a substantially cylindrical elastic blanket. The conditions are the same except that the shape of the cylindrical elastic blanket 2 is different.

The results of printing were visually observed, and when printing was performed using the basic cylindrical elastic blanket, the amount of expansion of the wood grain pattern near the maximum convex portion was large and the pattern was irregular, compared to the case where the cylinder-shaped elastic blanket 2 (a) and (b) in example 2 was used, although slight expansion was observed at the same portion, it was considered to be good within the range allowed by the product specification. As for the printing accuracy in the longitudinal direction, the expansion and the contraction hardly occur and the printing accuracy is good as compared with the case of using the substantially cylindrical elastic blanket.

Possibility of industrial utilization

The present invention has been described in the embodiments with respect to curved surface printing having a relatively simple radius of curvature, but the present invention is not limited to a single curved surface as long as it is a curved surface, and can be applied to printing of a complex curved surface.

Description of the reference numerals

1 a test piece of a curved body to be printed, 2 a roller-shaped elastic blanket, 3 a relief printing original plate, 10 a curved body to be printed, 21 curved surfaces of two main curvature radii R1 of the elastic blanket, 22 a top-rounded portion in which the two curved surfaces of R1 are joined, 23 a base portion of the elastic blanket, R a curvature radius of a cross section perpendicular to a long axis direction of the curved body to be printed, R1 a curvature radius of a length-direction generatrix connecting outermost convex portions of the cross section perpendicular to the long axis direction of the curved body to be printed, R a curvature radius of the elastic blanket corresponding to a curvature radius R of a cross section perpendicular to the long axis direction of the curved body to be printed, R1 a curvature radius of the elastic blanket corresponding to a curvature radius R1 of a length-direction generatrix of the curved body to be printed, R01, R02, R03. R01, R02, R03.. cndot.. cndot.r of the elastic blanket corresponding to the radii of curvature R01, R02, and R03.. cndot.r of the longitudinal generatrix of the curved surface body to be printed, the center offset (eccentricity) of X R1, the total width of the test piece of the curved surface body to be printed B, B₁Width of the sample (1), B₂Width of the sample (2), B₃To the width (3), B of the sample at the maximum protrusion₄To the maximum convex part width (4), H the height difference of the maximum convex part of the printed curved surface body sample, t the sample thickness, and the top angle at the part where the top of the two curved surfaces of r1 are connected by theta.

Claims (14)

1. A method of printing on a curved surface, comprising: a step of applying a printing ink to the convex portions of a flat relief printing original plate having a convex portion height of 3 to 50 [ mu ] m; a step of pressing a rubber or rubber-like cylindrical elastic blanket having a curved surface of a predetermined shape set with respect to a curved surface of a curved surface body to be printed, against a relief printing original plate attached at a fixed position and coated with the printing ink, and copying the printing ink onto the curved surface of the predetermined shape; moving the roller-shaped elastic blanket having the curved surface of the predetermined shape to which the printing ink is transferred, so as to be in contact with the curved surface of the curved surface body to be printed, and performing printing on the curved surface body;

the curved surface of the curved surface body to be printed has a uniform convex curvature radius Rn at each position in the width direction at least along the long axis direction, the main shaft section of the roller-shaped elastic blanket with respect to the predetermined curved surface having the convex curvature radius Rn is composed of two main curved surfaces and an end curved surface that smoothly connects the intersection of the two main curved surfaces, the two main curved surfaces have curvature radiuses R1 and R2 which form a curved surface of a predetermined shape relative to the curvature radius R of the main axis cross section of the convex curved surface of the curved object to be printed, the curvature radiuses R1 and R2 are 1 to 3 times the curvature radius R of the main shaft section, and the value of intersection of the distance L between the two centers of the curvature radiuses R1 and R2 is 0.05 to 0.15 times the curvature radius R of the main shaft section, and the end curved surface has a radius of curvature equal to that of the curved surface object to be printed.

2. The method of printing on a curved surface according to claim 1, wherein the material of the cylindrical elastic blanket is silicone rubber, and the hardness thereof is 5 to 40 as expressed in JIS a scale.

3. The method of printing on a curved surface according to claim 1 or 2, wherein the viscosity of the printing ink is 15 to 250 PaS.

4. The method of printing on a curved surface according to claim 1 or 2, wherein the printing ink has a viscosity 1/1.5 to 1/3 times the viscosity of a normal offset printing ink as a practical measure.

5. The method of printing on curved surfaces as claimed in claim 1 or 2, wherein the surface roughness of the cylindrical elastic blanket is Hmax 0.5 to 2 μm.

6. The method for printing on a curved surface according to claim 1 or 2, wherein the image of the plate convex portion of the flat plate-shaped original relief printing plate on which the printing ink is applied is reduced or enlarged based on a ratio of an orthogonal projection of the curved surface of the curved body to be printed on the original relief printing plate to an actual length of the curved surface.

7. The method of printing on a curved surface according to claim 1 or 2, wherein the curved surface to be printed is a curved surface to be printed having a shape elongated in a longitudinal direction, or a printed matter in which a plurality of curved surface to be printed are arranged in the longitudinal direction.

8. A curved surface body to be printed, which is obtained by performing surface printing by the method for curved surface printing according to any one of claims 1 to 7.

9. The curved printing surface of claim 8, wherein said curved printing surface is an automotive part.

10. The curved printed surface body according to claim 8, wherein said curved printed surface body is a steering wheel or an interior or exterior member of an automobile.

11. The curved printed surface body of claim 8, wherein said curved printed surface body is an exterior component of an electronic device.

12. The curved printing surface body according to claim 8, wherein said curved printing surface body is an exterior component of a mobile phone.

13. The curved printed surface of claim 8, wherein said curved printed surface is a decorative element.

14. The curved printed surface of claim 8, wherein said curved printed surface is a spectacle frame in a decorative article.