HK1110279B - Method of printing curved surface and curved surface body printed by using same - 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

Conventionally, a blanket printing method is known as a method for performing various kinds of printing on a curved surface, particularly a single curved surface, of a material to be printed having a curved surface. 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 at the convex portion is removed by a bamboo-sheet-shaped squeegee, the surface of a soft curved 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 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 the excess ink on the convex portion is scraped off after the ink is applied, so that the concave portion must have a sufficient depth to reliably hold the ink on the concave portion and to enable sufficient copying onto the blanket, which also causes deterioration of printing accuracy.

When printing is performed by the blanket printing method, if the unevenness of the printing original plate is large, the deformation of the blanket surface becomes large, and printing cannot be performed with good accuracy. In addition, particularly when the plate is an intaglio plate, it is necessary to make the intaglio plate have a sufficient depth in order to reliably maintain the amount of ink. However, since the blanket is deformed greatly when the depth is deep and the ink at the bottom is transferred to the blanket, the blanket itself must be made soft enough to conform to the change of the unevenness, and the condition is further deteriorated.

On the other hand, if the printing original plate is a relief plate, 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 and convex portions is smaller. Therefore, the blanket itself may be made of a slightly hard material, and since the unevenness may be small, the deformation of the blanket surface is small, and the amount of ink can be finely adjusted, so that high-precision printing can be performed.

Various techniques have been developed in the past for flexographic printing using the relief plate and the blanket. For example, Japanese patent No. 2961153 (Japanese patent application No. 01-059697) was filed by the present inventors. However, in this system, a demand has been made for printing with higher accuracy, and the present inventors have made many experimental studies to obtain an invention capable of setting appropriate conditions for various specifications to satisfy such a demand. That is, the present invention is basically an improved patent of the patent.

Further, as for the relief printing original plate, an aluminum plate used in offset printing may also be utilized. The aluminum plate is formed by attaching a photosensitive agent to the surface, and is suitable for multicolor printing because of its high precision and extremely small unevenness, i.e., the order of micrometers. Even in the case of color separation printing, the accuracy is high, and thus the color separation printing is widely used. It goes without saying that in this case, any plate other than the aluminum plate may be used as long as it has small unevenness, high accuracy, and is capable of adhering ink.

As described above, in the past, when printing on a printing object having a curved surface, particularly a single curved surface, printing was performed with 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 of fine dots or the like is extremely poor.

Further, the shape and properties of the blanket are almost set in accordance with empirical erroneous 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 satisfying requirements for retention and separation of printing ink, and setting of conditions such as enabling printing with good fidelity as a result, and the setting takes much time and effort.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method capable of easily setting conditions for curved surface printing on a material to be printed having a curved surface R under conditions with better printing accuracy, and a curved surface body printed with better fidelity by the method.

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

(1) comprising: applying a printing ink to the plate convex portion of a flat plate-shaped relief printing original plate having a convex portion height of 0.1 to less than 3 μm; a step of copying the printing ink onto a predetermined curved surface of a printed object by pressing a rubber or rubber-like elastic blanket having a predetermined curved surface formed in the same polarity direction with respect to a convex curved surface or a concave curved surface of the printed object and set to the convex curved surface or the concave curved surface of the printed object onto a relief printing original plate attached to a fixed position and to which the printing ink is applied; a step of moving an elastic blanket having the curved surface of the predetermined shape, on which the printing ink is transferred, to contact the curved surface of the object to be printed, and printing the object,

further, the main axis cross section of the predetermined curved surface is composed of two main curved surfaces having curvature radii R1 and R2 constituting the predetermined curved surface with respect to a curvature radius R of the main axis cross section of the curved surface of the object to be printed, the curvature radii R1 and R2 are 4 to 8 times the curvature radius R, and a distance L between two centers of the curvature radii R1 and R2 is a value of intersection, which is 2 to 4 times the curvature radius R, and an end curved surface smoothly connecting an intersection of the two main curved surfaces, and the end curved surface has a curvature radius equal to the curvature radius of the object to be printed,

(2) in the above (1), the viscosity of the printing ink is 5 to 250PaS,

(3) in the above (1), the printing ink has a viscosity of 1 to 1/5 times that of a usual offset printing ink as a practical measure,

(4) in the above (1), the surface roughness of the elastic blanket is 0.5 to 2 μm in Hmax.

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

(5) surface printing is performed by any one of the methods (1) to (4) for flexographic printing,

(6) in the above (5), the curved printing surface is an automobile part,

(7) in the above (5), the curved printed body is a steering wheel or an interior or exterior member of an automobile,

(8) in the above (5), the curved printed object is a casing of a cellular phone or a household appliance,

(9) in the above item (5), the curved printed object is a sporting good,

(10) in the above (5), the curved printed object is a decoration,

(11) in the above item (5), the curved printed object is a spectacle frame in a decorative article.

According to the method for printing on a curved surface of the present invention, printing can be performed on a curved surface with good accuracy, and a curved surface body to be printed obtained by the method can be provided at a low price.

Drawings

Fig. 1 is a diagram schematically illustrating a blanket shape corresponding to a cross-sectional curvature radius R of a curved surface to be printed, (a) shows a main cross section of the curved surface to be printed, and (b) shows a cross-sectional shape of the corresponding blanket.

Fig. 2 is a diagram showing an example of the relationship between the main radii of curvature R1 and R2 and the center offset amount X according to the present invention.

Fig. 3 shows the results of comparative tests on the surface roughness of the flexographic printing blanket of the present invention and the adhesion of printing ink.

Fig. 4 shows the results of an experiment concerning the relationship between the height of the convex portion (C is the depth of the concave portion) and the printing accuracy of the printing original plate of the present invention.

Fig. 5 shows the results of the test with respect to the relationship between the blanket hardness H and the printing accuracy.

Description of the reference numerals

1: curved surface object to be printed 2: the blanket 221: curved surface 222 of main radius of curvature R1 of blanket: curved surface 21 of main radius of curvature R1 of blanket: the portion 23 where the joining portion of the curved surfaces of the curvature radii R1, R2 is rounded: blanket base portion R: cross-sectional radius of curvature R1, R2: main radius of curvature R0 of blanket: radius of curvature X of the portion where the joining portion is rounded: center offset amount (eccentricity) θ of R1 and R2: angle of contact part

Detailed Description

The present invention is characterized in that the specification for producing a blanket for flexographic printing which has been determined intuitively and empirically in the past can be determined more easily and simply, and moreover, by combining an appropriate blanket for flexographic printing produced in the determined specification with a special relief printing original plate, flexographic printing can be performed with high printing accuracy, and a curved printing body, particularly a steering wheel, an interior and exterior member, and the like of an automobile, which can be obtained at a low cost by the flexographic printing method can be provided.

That is, the optimum specifications of the flexographic printing blanket and the relief printing original plate are specified in the following manner.

(1) A blanket shape corresponding to the shape of the printed matter, particularly, an arc shape having a curvature radius R, a blanket material (particularly, hardness and elastic modulus),

(2) the surface characteristics (ink adhesion and separation) of a blanket which can transfer printing ink on a master plate to a blanket surface efficiently and print the ink on a printed object efficiently,

(3) the height of the projection of the printing original plate is set with proper precision.

The blanket for flexographic printing mainly uses silicone rubber. The surface properties required for the blanket for flexographic printing include ink adsorption property for transferring ink from the relief printing plate to the blanket surface, property for absorbing a solvent in ink to increase the viscosity of ink, separability for transferring the ink completely to the curved surface to be printed, and property for preventing the ink from remaining on the blanket surface after printing on the curved surface to be printed.

These properties are closely related to the performance of the printing ink used, but in terms of the blanket for flexographic printing, are determined by the surface free energy of the blanket surface itself, and are influenced by the material of the blanket and the form of the blanket surface, particularly by the surface roughness to a large extent.

That is, the adsorption property of ink transferred from the relief printing original plate to the surface of the blanket is opposite to the separability of ink completely transferred to the curved surface to be printed and the property of ink not remaining on the surface of the blanket after printing on the curved surface to be printed, and it is difficult to change the properties of the blanket material itself in a short time in the printing process.

The inventors of the present invention have found through a number of experiments that the ink retention of the curved blanket surface can be changed within a certain roughness range to correspond to the above-described opposite properties in the combination of the actual working process of the curved printing blanket of the present invention, that is, the process (a) of copying the ink from the relief plate original plate to the curved blanket (deformation of the blanket surface from the curved surface to the flat surface), the process (B) of moving the blanket to the position of the object to be printed (deformation of the blanket surface from the flat surface to the curved surface), and the process (C) of performing curved printing by pressing the blanket against the object to be printed (deformation of the blanket surface from the positive curved surface to the negative curved surface).

As is clear from the results of the comparative test described later, the surface roughness of the blanket had problems both when it was too thin and when it was too thick, the retention property was good but the separation property was problematic when it was thin, and when it was too thick, the retention property was reduced but the separation property was good. 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 blanket of the present invention is preferably 0.5 to 2 μm.

In order to realize a high-precision curved surface printing, it is necessary to prepare a curved surface blanket for printing having an appropriate blanket shape with respect to a curved surface body to be printed. As described above, in setting the specification conditions of the blanket, setting is performed almost always in accordance with empirical thinking, and setting takes much time and labor. In addition, the present invention proposes a setting method capable of relatively easily setting the shape of the blanket corresponding to the shape of the object to be printed, particularly, the circular arc shape having the curvature radius R.

Basically, the method is based on the Hertz Stress theory when two curved surfaces are in pressure contact, and is corrected according to multiple experiments, so that a relatively simple specification setting mode is derived.

Fig. 1 is a diagram schematically illustrating a blanket shape corresponding to a cross-sectional curvature radius R of a curved surface to be printed, (a) shows a main cross section of the curved surface to be printed, and (b) shows a cross-sectional shape of the corresponding blanket.

In the figure, 1 is a curved body to be printed, 2 is a blanket, 21 is a portion where a joining portion of the curved R1 and R2 surfaces is rounded, 221 is a curved surface having a main curvature radius R1, 222 is a curved surface having a main curvature radius R2, 23 is a blanket base portion, R is a cross-sectional curvature radius of the curved surface to be printed, R1 and R2 are two main curvature radii of the blanket, R0 is a curvature radius of the portion where the joining portion is rounded, X is a center offset amount (eccentricity amount) of the R1 and R2, and θ is an angle of a joint portion in example 4.

The shape of the blanket 2 is mainly composed of 3 elements with respect to the cross-sectional curvature radius R.

Namely: curved surface portions 221, 222 formed of two main radii of curvature R1, R2 in the shape of the blanket 2 with the sectional radius of curvature R as a parameter; a portion 21 rounded by an inscribed partial arc (about 25 °) having a curvature radius R0 inscribed in the joining portion of the curved surface; and a blanket base portion 23 for keeping the blanket 2 elastic and mounting the blanket.

The two main radii of curvature R1 and R2 are designed to be offset by a distance X toward the inside where their centers intersect with each other. The main radii of curvature R1 and R2 are set so that the maximum half-circumference portion of the curved surface 1 to be printed having the cross-sectional radius of curvature R can be sufficiently printed. It is found that the major radii of curvature R1 and R2 are preferably (4 to 8), more preferably (6 to 8), times the radius of curvature R of the cross-section of the curved surface 1 to be printed. Less than 4 times, the printing accuracy is deteriorated, and 8 times or more, the shape of the blanket itself is also large, which is disadvantageous in terms of design and cost.

The offset distance X of the center is preferably within a range of (1 to 2) times the radius of curvature R of the cross section of the curved surface 1 to be printed. The relationship between the main radii of curvature R1 and R2 and the center offset amount X is determined by a constant ratio k of X/R1 and R2. The ratio k is preferably about 0.5.

Fig. 2 is a diagram showing an example of the relationship between the main radii of curvature R1 and R2 and the center offset amount X.

As can be seen, it is preferable to use a proportional relationship in which the main radii of curvature R1 and R2 have a certain ratio to the center offset X.

When the blanket 2 is pressed to a printing length corresponding to the position of the maximum semi-circumference (90 ° from the apex) of the curved surface to be printed, the angle β between the major curvature radius surfaces 221 and 222 of the blanket 2 and the tangent line at the semi-circumference (90 ° from the apex) of the curved surface to be printed 1 is set to (60 ° ± 10 °), which makes the deflection δ of the major curvature radius surface of the blanket due to the pressing relatively stable.

The material of the blanket 2 for flexographic printing is preferably a silicone rubber which satisfies the aforementioned properties of adherence to allow the ink to be transferred from the relief printing plate onto the surface of the blanket 2, releasability to allow the ink to be completely transferred onto the curved surface 1 to be printed, and resistance to the ink remaining on the surface of the blanket 2 after printing on the curved surface 1 to be printed, and these properties are relatively balanced.

Further, while the hardness of the silicone rubber which is generally used in practice is about 20 to 90 as the material hardness (JIS a grade), it is preferable that the material hardness of the flexographic printing blanket 2 is about 3 to 30(JIS a grade) as a result of a plurality of tests and can satisfy the deformation amount, and more preferably about 3 to 20 which is soft.

As described above, the surface shape of the blanket 2 for flexographic printing changes in each of the steps (a) of copying ink from the relief printing original plate onto the curved blanket 2 (deformation of the surface of the blanket 2 from a curved surface to a flat surface), (B) of moving the blanket 2 to a position of the object 1 to be printed (deformation of the surface of the blanket 2 from a flat surface to a curved surface), and (C) of pressing the blanket 2 against the object 1 to be printed to perform flexographic printing (deformation of the surface of the blanket 2 from a positive curved surface to a negative curved surface).

Therefore, the image transfer accuracy in the first step a is extremely important.

The present invention is characterized in that the proper height of the convex part coated with ink on the relief printing original plate can be made as low as possible, so as to improve the image copying precision and further improve the printing precision.

In general, in blanket printing, an intaglio plate is used as the master. In general knowledge, the recessed portions of the gravure printing original plate are formed by a photo-sensitive/etching method, and the depth of the recessed portions 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 blanket by scraping the ink from the convex portion of the intaglio plate master, curved surface printing in which the surface shape changes occurs as the concave portion having a large depth, the ink transfer accuracy is poor, and the printing accuracy is poor.

On the other hand, a relief printing original plate having a low height has good printing accuracy and is suitable for flexographic printing.

Recently, the accuracy of making the convex portions of the relief printing original plate has been improved, the height of the convex portions can be made lower, not only is the ink viscosity reduced and the ink film thickness made thin, but also the use of a small amount of printing ink having a higher density is made possible due to the lower height of the convex portions, and the printing accuracy has been remarkably improved.

In the present invention, a flat relief printing original plate having a height of the convex portion of 0.1 to 50 μm is used, and the height of the convex portion may be 20 to 50 μm within a range where high printing accuracy is not required, but may be about 0.1 to 25 μm in a case where high curved surface printing accuracy is required, and particularly about 0.1 to 3 μm in a case where high accuracy is required.

Further, as the height of the convex portion is lower, the ink film thickness can be made thinner, and the printing accuracy is remarkably improved.

Generally, a flat plate-shaped relief printing original plate is made of an aluminum alloy plate and convex portions are formed from a photosensitive agent.

The practical numerical target of the projection height in the present invention is 1/2 to 1/3 of the thickness of the photosensitive agent in the relief printing original plate.

It is of course important to have a sufficient height to enable the ink to be copied onto the flexographic printing blanket 2.

By using a relief printing original plate having a convex portion with a height of about 1/2 to 1/3 of the thickness of a photosensitive agent on the relief printing original plate, good printing accuracy can be obtained on the flexographic printing blanket 2.

In the present invention, which is characterized in that the height of the convex portion of the relief printing original plate is low as described above, the properties of the printing ink, particularly its viscosity, are extremely important in order to maintain the printing accuracy.

As a result of many practical tests, it has been found that the viscosity of the printing ink is preferably in the range of 5 to 500PaS (at 25 ℃) under the condition that the production accuracy of the convex portion of the relief printing original plate is improved and the convex portion can be formed at a lower height as described above. Further, when the height of the convex portion of the relief printing original plate is 0.1 to 25 μm, it is preferably 15 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, which is not desirable.

Further, if the viscosity is higher than 500PaS, the adhesion to the surface of the silicone rubber blanket for flexographic printing is less likely to occur, that is, the adhesion to the surface of the blanket is deteriorated. In addition, when the height of the projection is 0.1 μm or less, sufficient printing accuracy cannot be ensured regardless of the thickness of the printing ink.

The practical measure of the viscosity of the printing ink of the present invention is that the viscosity is about 1 to 1/5 times as high as that of the printing ink for offset printing used under the same conditions in the usual offset printing, and the above conditions are substantially satisfied.

According to the above embodiment, since the curved surface printing with high accuracy can be easily realized, various articles can be printed as the curved surface body to be printed.

The printing method is suitable for printing curved printing surfaces of automobile parts, particularly automobile internal and external parts, automobile steering wheels, mobile phone shells, household appliance shells, heads and shafts of golf clubs used as sports goods, fishing rods, various rackets, helmets and the like.

Further, since the printing accuracy is good, it is possible to print various accessories, particularly eyeglass frames.

Examples

[ example 1]

The curved surface of the test piece is printed:

DxL 30mm phi x 100mm polypropylene cylinder

Peripheral 180-degree surface printing

Blanket for flexographic printing:

r1, 2 XL 1 (bottom width). times.top R90 mm. times.105 mm. times.15 mm

Silicone rubber hardness (JIS A grade) 15

Surface roughness a (0.1 to 0.3 μm), b (0.5 to 2 μm),

c(2.5～3.5μm)，d(5～10μm)，e(10～30μm)

using ink:

UV type ink

Relief plate original plate:

height of the photosensitive agent projection of aluminum relief printing plate precursor of 1 μm

Standard grid pattern printer with line width 0.5 + -0.02 mm and grid spacing 5 + -0.3 mm:

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

A blanket 2 for flexographic printing having different surface roughness was produced, blanket printing was performed on a test piece to be flexographic printed in the above-mentioned steps a to C, and the state of ink remaining on the original plate in the step a, the state of ink transferred to the blanket cover 2 in the step B, the state of printing on the surface of the test piece to be flexographic printing 1 and the state of ink remaining on the blanket surface in the step C were observed with a microscope (magnification × 50), respectively.

Fig. 3 shows the results of comparative tests on the surface roughness of the flexographic printing blanket 2 of the present invention and the adhesion of printing ink.

From the test results, it is understood that the surface roughness of the blanket 2 has a considerable influence on the adhesion of the ink. That is, the surface roughness of the blanket 2 is not appropriate whether it is too fine or too coarse, and a moderate roughness range exists. Particularly, if the thickness is too large, the ink may not be sufficiently transferred from the relief printing plate precursor in the step a, which is undesirable.

Fig. 4 shows the test results of the test on the relationship between the height of the convex portion of the printing original plate (C is the depth of the concave portion) and the printing accuracy. The X axis in the figure indicates a height ratio when the normal projection height (t1) of the conventional relief printing original plate is 1.

In the case (a) of the present invention, the printing accuracy peaks at a height of about 1/2 to 1/3 of the height (t1) of the conventional relief printing original plate, and it is found that a good printing accuracy of about 2 times the accuracy of the intaglio printing original plate (C) can be obtained.

[ example 2]

The curved surface of the test piece is printed:

DxL 30mm phi x 100mm polypropylene cylinder

Peripheral 180-degree surface printing

Blanket for flexographic printing:

r1, 2 XL 1 (bottom width). times.top R90 mm. times.105 mm. times.15 mm

Material silicon rubber

Hardness (JIS A grade) 5, 15, 30, 40, 50, 60

Surface roughness of 0.5-2 μm

Using ink: UV type ink

Relief plate original plate:

height of the photosensitive agent projection of aluminum relief printing plate precursor of 1 μm

Standard grid pattern printer with line width 0.5 + -0.02 mm and grid spacing 5 + -0.3 mm:

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

Only the hardness of the silicone rubber was changed, and the other conditions were not changed, and the printing accuracy was compared.

Fig. 5 shows the results of the test with respect to the relationship between the blanket hardness H and the printing accuracy.

Usually, the silicone rubber has a hardness (JIS A grade) of about 10 to 90, but according to the test results, the hardness of the flexographic printing blanket 2 is preferably about 3 to 30, more preferably about 3 to 20. If the hardness is higher than 40, the printing accuracy is extremely lowered. On the other hand, if the amount is 3 or less, the printing process becomes unstable.

In addition, it is found through experiments that the hardness of the blanket 2 should be changed according to the size of the curvature radius of the object to be printed, and for the case of a large curvature radius, the hardness of the blanket 2 is preferably low.

[ example 3]

The curved surface of the test piece is printed:

dxd 400mm phi x 30mm phi polypropylene ring-shaped piece

Face of annular piece axially divided into two parts (d peripheral 180 degree face) printing x 2 times (two faces)

Blanket for flexographic printing:

r1, 2 XL 1 Xtop R X D90 mm X105 mm X15 mm X400 mm

Material silicon rubber

Hardness (JIS A grade) 15

Surface roughness of 0.5-2 μm

Using ink: UV type printing ink (color: dark brown)

Relief plate original plate:

height of the photosensitive agent projection of aluminum relief printing plate precursor is 0.2 μm

Printing waveform non-continuous style with two-color fluorescent dye

As a result of the 2 nd printing performed by two times of solid printing on the upper and lower surfaces of the endless member, it was found that some printing misalignment occurred on the printing engagement surface, particularly on the inner diameter side of the endless member, but good printing was achieved on the entire surface as a whole within the allowable range as a commercial product.

[ example 4]

A curved surface to be printed was used in which a semi-cylindrical curved surface was formed by cutting a cylindrical portion having a diameter of 30mm Φ × 100mm in example 1 at an arc angle, the semi-cylindrical curved surface was formed at the center of a flat surface to be printed (100mm × 100mm), the flat portion was printed by a flat blanket method, and then the curved surface portion was overlapped by the blanket in example 1 to perform printing. The angles θ between the flat printed surface and the tangent line at the junction of the curved semi-cylindrical surface and the flat surface are 90 °, 105 °, 120 °, and 135 °, respectively, as the test piece of the printed object. Other conditions were the same as in example 1.

As a result of printing, a large dispersion in printing accuracy occurs at the contact point between the flat surface to be printed and the curved semi-cylindrical surface, and a sample having θ of 90 ° undesirably generates an unprinted portion at the corner. A sample with θ of 105 ° or more can be normally printed even at a corner, and the shape of the contact point between the flat printed surface and the curved surface body is preferably 105 ° or more, more preferably 120 ° or more. Even if θ is 90 °, the occurrence of unprinted portions can be avoided by providing an appropriate R-plane at the contact corner. In this case, the radius of curvature R of the R-face is preferably larger than the deflection R of the blanket at the corner.

Possibility of industrial utilization

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

Claims (11)

1. A method of printing on a curved surface, comprising: applying a printing ink to the plate convex portion of a flat plate-shaped relief printing original plate having a convex portion height of 0.1 μm or more and less than 3 μm; a step of copying the printing ink onto a predetermined curved surface of a printed object by pressing a rubber or rubber-like elastic blanket having a predetermined curved surface formed in the same polarity direction with respect to a convex curved surface or a concave curved surface of the printed object and set to the convex curved surface or the concave curved surface of the printed object onto a relief printing original plate attached to a fixed position and to which the printing ink is applied; a step of moving an elastic blanket having the curved surface of the predetermined shape, on which the printing ink is transferred, to contact the curved surface of the object to be printed, and printing the object,

the main axis cross section of the predetermined curved surface is composed of two main curved surfaces and end curved surfaces connecting the intersection of the two main curved surfaces smoothly, the two main curved surfaces have curvature radii R1 and R2 for forming the predetermined curved surface relative to the curvature radius R of the main axis cross section of the curved surface of the object, the curvature radii R1 and R2 are 4 to 8 times of the curvature radius R, the distance L between the two centers of the curvature radii R1 and R2 is a value of intersection, and is 2 to 4 times of the curvature radius R, and the end curved surfaces have the same curvature radius as the curvature radius of the object.

2. The method of printing on curved surfaces as claimed in claim 1, wherein the viscosity of said printing ink is from 5 to 250 PaS.

3. The method of printing on curved surfaces as claimed in claim 1, wherein said printing ink has a viscosity of 1 to 1/5 times the viscosity of a conventional offset ink as a practical measure.

4. A method of flexographic printing as claimed in claim 1, wherein said elastomeric blanket has a surface roughness Hmax of 0.5 to 2 μm.

5. A curved surface body to be printed, which is obtained by surface printing by the method of curved surface printing according to any one of claims 1 to 4.

6. The curved printing surface of claim 5, wherein said curved printing surface is an automotive part.

7. The curved printing surface body of claim 5, wherein said curved printing surface body is a steering wheel or an interior or exterior member of an automobile.

8. The curved printing surface of claim 5, wherein said curved printing surface is a housing of a mobile phone or a household appliance.

9. The printed dough body of claim 5 wherein said printed dough body is a sporting good.

10. The curved printing surface of claim 5, wherein said curved printing surface is a decorative element.

11. The curved printed object of claim 5, wherein said curved printed object is a spectacle frame in a decorative article.